EP1516009A1

EP1516009A1 - (meth)acrylic esters of polyalkoxylated trimethylolpropane

Info

Publication number: EP1516009A1
Application number: EP03732556A
Authority: EP
Inventors: Andreas Popp; Thomas Daniel; Jürgen Schröder; Thomas Jaworek; Rüdiger Funk; Reinhold Schwalm; Matthias Weismantel; Ulrich Riegel
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2002-06-11
Filing date: 2003-06-10
Publication date: 2005-03-23
Also published as: PL374428A1; CN1659211A; CN100349957C; BR0311501A; US7259212B2; WO2003104302A1; US20060020078A1; MXPA04011457A; AU2003238490A1; JP2005532432A; CA2487031A1

Abstract

The invention relates to novel (meth)acrylic esters of polyalkoxylated trimethylolpropane of formula (I), wherein EO represents O-CH2-CH2-,PO represents independently from each other O-CH2-CH(CH3)- or O-CH(CH3)-CH2-,n1, n2, n3 represent independently from each other 4,5 or 6, n1 + n2 + n3 is 14, 15 or 16,m1, m2, m3 represent independently from each other 1,2 or 3, m1 + m2 + m3 is 4, 5 or 6, R1, R2, R3 represent independently from each other H or CH3. The invention also relates to a simplified method for producing said esters and the use of the thus obtained reaction mixture.

Description

(Meth) acrylic ester of polyalkoxylated trimethylolpropane

description

The present invention relates to new (meth) acrylic esters of polyalkoxylated trimethylolpropane, a simplified process for the preparation of these esters and use of the reaction mixtures thus obtainable.

Swellable hydrogel-forming polymers, so-called superabsorbents (Super Absorbing Polymers, SAP), are known from the prior art. These are networks of flexible hydrophilic polymers, which can be both ionic and nonionic in nature. These are able to absorb and bind aqueous liquids with the formation of a hydrogel and are therefore preferred for the production of tampons, diapers, sanitary napkins, incontinence articles, training underwear for children, shoe insoles and other hygiene articles in the absorption of body fluids. Superabsorbents are also used in other areas of technology in which liquids, in particular water or aqueous solutions, are absorbed. These areas are, for example, storage, packaging, transport (packaging material for water-sensitive articles such as flower transport, shock protection); Food sector (transport of fish, fresh meat; absorption of water, blood in fresh fish AFI meat packaging); Medicine (wound plasters, water-absorbent material for burn dressings or for other wetting wounds), cosmetics (carrier material for pharmaceutical chemicals and medicines, rheumatic plasters, ultrasound gel, cooling gel, cosmetic thickener, sun protection); Thickeners for oil / water or water / oil emulsions; Textiles (gloves, sports clothing, moisture regulation in textiles, shoe inserts); chemical process industry. Applications (catalyst for organic reactions, immobilization of large functional molecules (enzymes), adhesive for agglomerations, heat storage, filtration aids, hydrophilic component in polymer laminates, dispersants, plasticizers); Construction and construction, installation (powder injection molding, clay-based plasters, vibration-inhibiting medium, tools for tunnel excavations in water-rich subsoil, cable sheathing); Water treatment, waste treatment, water separation (de-icing agents, reusable sandbags); Cleaning; Agricultural industry (irrigation, retention of melt water and dew precipitation, composting additive, protection of the forests from fungal / insect attack, delayed release of active substances in plants); in fire protection (flying sparks) (covering houses or covering house walls with SAP Gel, since the water has a very high heat capacity, flaming can be prevented; spraying SAP Gel on fires such as forest fires); Coextrusion agents in thermoplastic polymers (hydrophilization of multilayer films); Production of foils and thermoplastic moldings which can absorb water (eg foils that store rainwater and condensation for agriculture); Films containing SAP for keeping fruit and vegetables fresh, which can be packed in moist films; the SAP stores water released from the fruit and vegetables without the formation of condensation drops and partially releases the water back to the fruit and vegetables, so that neither rotting nor withering occurs; SAP polystyrene coextrudates, for example for food packaging such as meat, fish, poultry, fruit and vegetables); Carrier substance in active ingredient formulations (pharmaceuticals, crop protection). In the hygiene articles, the superabsorbers are usually located in the so-called absorbent core, which includes fibers (cellulose fibers), which, as a kind of liquid reservoir, temporarily store the spontaneously applied amounts of liquid and good drainage of body fluids in the absorbent core to ensure superabsorbent.

The current trend in diaper construction is to produce thinner constructions with a reduced cellulose fiber content and an increased hydrogel content. With the trend towards ever thinner diaper constructions, the requirement profile for the water-swellable hydrophilic polymers has changed significantly over the years. While the very high swelling capacity was initially the focus at the beginning of the development of highly absorbent hydrogels, it was later shown that the ability of the superabsorbent to transfer and distribute liquids is also of crucial importance. It has been shown that conventional superabsorbents on the

Swell the surface strongly when wetted with liquid, so that the liquid transport into the interior of the particle is very difficult or completely prevented. This peculiarity of the superabsorbent is also referred to as "gel blocking". Due to the higher load of the hygiene article (polymer per unit area), the polymer in the swollen state must not form a barrier layer for subsequent liquid. If the product has good transport properties, optimal utilization of the entire hygiene article can be guaranteed. The gel blocking phenomenon is thus prevented, which in extreme cases leads to the leakage of the liquid, the so-called leakage of the hygiene article. Fluid transfer and distribution is therefore critical in the initial absorption of body fluids.

Hydrogels, for example, have good transport properties and, when swollen, have a high gel strength. Gels with only low gel strength can be deformed under an applied pressure (body pressure), clog pores in the superabsorbent / cellulose fiber absorbent body and thereby prevent further fluid absorption. Increased gel strength is generally achieved through higher crosslinking, which, however, reduces the retention of the product. Surface post-crosslinking is an elegant method of increasing gel strength. In this process, dried superabsorbers with an average crosslinking density are subjected to additional crosslinking. Through the After surface crosslinking, the crosslink density increases in the shell of the superabsorbent particles, which increases the absorption under pressure to a higher level. While the absorption capacity in the superabsorbent shell decreases, the core of the superabsorbent particles has an improved absorption capacity compared to the shell due to the presence of movable polymer chains, so that the shell structure ensures improved liquid transmission without the effect of gel blocking occurring. It is entirely desirable that the total capacity of the superabsorbent is not used spontaneously, but with a time delay. Since the hygiene article is usually exposed to urine several times, the absorption capacity of the superabsorbent does not need to be exhausted after the first disposition.

Hydrophilic, highly swellable hydrogels are in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose or starch ethers, crosslinked carboxymethyl cellulose, partially crosslinked polyalkylene oxide or natural products swellable in aqueous liquids, such as guar derivatives. Such hydrogels are used as aqueous solution-absorbing products for the production of diapers, tampons, sanitary napkins and other types of hygiene, but also as water-retaining agents in agricultural horticulture.

To improve the application properties, e.g. Rewet in the diaper and AUL, hydrophilic, highly swellable hydrogels are generally surface or gel cross-linked. This postcrosslinking is known per se to the person skilled in the art and is preferably carried out in the aqueous gel phase or as surface postcrosslinking of the ground and sieved polymer particles.

EP 238050 discloses, as possible internal crosslinking agents for superabsorbents, addition products of ethylene oxide and / or propylene oxide onto trimethylolpropane esterified two or three times with acrylic acid or methacrylic acid.

Commercially available, for example, from Sartomer (Exton, PA, USA) under the specified trade names trimethylolpropane triacrylate (SR 351), three times ethoxylated trimethylolpropane triacrylate (SR 454), three times twice ethoxylated trimethylolpropane triacrylate (SR 499), three times triple ethoxylated trimethylolate SR3 ), three times five times ethoxylated trimethylolpropane triacrylate (SR 9035) and a total of 20 times ethoxylated trimethylolpropane triacrylate (SR 415). Propoxylated trimethylolpropane triacrylates are available under the trade names SR 492 (three times 1 PO per TMP) and CD 501 (three times 2 PO per TMP). WO 93/21237 discloses (meth) acrylates of alkoxylated polyvalent C ₂ -C ₁₀ hydrocarbons as crosslinking agents. Trimethyl propane crosslinkers corresponding to SR 351, SR 454, SR 502, SR 9035 and SR 415 were used. These networkers have 0, 3, 9, 15 or 20 EO units per TMP. According to WO 93/212373, 2 to 7 EO units per TMP are advantageous, in particular 3 times 4 to 6 EO units per TMP.

A disadvantage of these compounds is that complex cleaning operations are required for at least partial separation of starting materials and by-products - the crosslinking agents used in the document mentioned have an acrylic acid content of less than 0.1% by weight.

Ethoxylated trimethylolpropane tri (meth) acrylates are mentioned repeatedly in the patent literature as internal crosslinking agents, only the TMP derivatives commercially available from Sartomer being used, e.g. in WO 98/47951 trimethylolpropane triethoxylate triacrylate, in WO 01/41818 Sartomer # 9035 as so-called highly ethoxylated trimethylol propane triacrylate (HeTMPTA) and in WO 01/56625 SR 9035 and SR-492.

The production of such higher (meth) acrylic acid esters by acid-catalyzed esterification of (meth) acrylic acid with the corresponding alcohols in the presence of an inhibitor / inhibitor system and, if appropriate, a solvent, such as e.g. Benzene, toluene, cyclohexane is generally known.

Since, as is well known, the formation of the ester from (meth) acrylic acid and alcohol is based on an equilibrium reaction, in order to achieve economic conversions, a starting material is generally used in excess and / or the esterification water formed and / or the target ester are removed from the equilibrium.

Therefore, in the preparation of the higher (meth) acrylic acid esters, the water of reaction is generally removed and an excess of (meth) acrylic acid is usually used.

US 4 187383 describes an esterification process of (meth) acrylic acid with organic polyols at a reaction temperature of 20 to 80 ° C. with an equivalent excess of 2 to 3: 1.

A disadvantage of this process is that the reaction times are up to 35 hours due to the low reaction temperature and the excess acid in the reaction mixture is removed by neutralization with subsequent phase separation. WO 2001/14438 (Derwent Abstract No. 2001-191644 / 19) and WO 2001/10920 (Chemical Abstracts 134: 163502) describe processes for the esterification of (meth) acrylic acid with polyalkylene glycol monoalkyl ether in a ratio of 3: 1 - 50: 1 in Ge - presence of acids and polymerization inhibitors and, after deactivation of the acid catalyst, copolymerization of the residue from (meth) acrylic acid ester and (meth) acrylic acid at pH 1, 5 - 3.5, and its use as a cement additive.

A disadvantage of these processes is that it is limited to polyalkylene glycol monoalkyl ether, that the catalyst has to be deactivated and that such copolymers cannot be used as crosslinking agents for hydrogels, since they only have one functionality.

The object was to provide further compounds which can be used as radical crosslinkers for polymers, in particular for superabsorbers, and to simplify the production process for substances which can be used as radical crosslinkers for superabsorbers.

The object is achieved by providing an ester F of the formula

with EO means O-CH2-CH2-,

PO independently of one another means O-CH2-CH (CH3) - or O-CH (CH3) -CH2-,

n1, n2, n3 independently of one another are 4, 5 or 6,

n1 + n2 + n3 is 14, 15 or 16,

m1, m2, m3 independently mean 1, 2 or 3, m1 + m2 + m3 is 4, 5 or 6,

R1, R2, R3 independently of one another denote H or CH3.

The EO or PO units are installed in such a way that polyethers and no peroxides are formed.

Esters F with the above meanings are preferred, n1 + n2 + n3 being 15.

Esters F with the above meanings are particularly preferred, where n1 = n2 = n3 = 5.

Also preferred are esters F with the above meanings, where m1 + m2 + m3 is 5.

Also particularly preferred are esters F with the above meanings, where m1 = m2 = 2 and m3 = 1.

Esters F in which R1, R2 and R3 are identical are very particularly preferred, in particular when R1, R2 and R3 are H.

The further object is achieved by a process for the preparation of an ester F of alkoxylated trimethylolpropane with (meth) acrylic acid, comprising the steps

a) reaction of alkoxylated trimethylolpropane with (meth) acrylic acid in the presence of at least one esterification catalyst C and at least one polymerization inhibitor D and, if appropriate, a solvent E which forms an azeotrope with water to form an ester F, b) optionally removing at least part of the in a ) water formed from the reaction mixture, where b) can take place during and / or after a), f) optionally neutralizing the reaction mixture, h) if a solvent E was used, optionally removing this solvent by distillation and / or i) stripping with a gas inert to the reaction conditions.

Here is preferably

the molar excess (meth) acrylic acid to alkoxylated trimethylolpropane is 3.15: 1 and The optionally neutralized (meth) acrylic acid contained in the reaction mixture obtained after the last step essentially remains in the reaction mixture.

In the present invention, (meth) acrylic acid is understood to mean methacrylic acid, acrylic acid or mixtures of methacrylic acid and acrylic acid. Acrylic acid is preferred.

If the ester F is required in its pure form, it can be purified by known separation processes.

The molar excess of (meth) acrylic acid to alkoxylated trimethylolpropane is at least 3.15: 1, preferably at least 3.3: 1, particularly preferably at least 3.75: 1, very particularly preferably at least 4.5: 1 and in particular at least 7, 5: 1.

In a preferred embodiment, (meth) acrylic acid is used in an excess of, for example, greater than 15: 1, preferably greater than 30: 1, particularly preferably greater than 60: 1, very particularly preferably greater than 150: 1, in particular greater than 225: 1 and especially larger than 300: 1 used.

The esterification products obtainable in this way can be used as radical crosslinkers in hydrogels essentially without further purification, especially without substantial removal of the excess of (meth) acrylic acid and the content of esterification catalyst C.

Unless otherwise mentioned, crosslinking in this document means radical crosslinking (gel crosslinking, internal crosslinking, crosslinking of linear or weakly crosslinked polymer). This crosslinking can take place via free-radical or cationic polymerization mechanisms or other mechanisms, for example Michael addition, transesterification or transesterification mechanisms, preferably by free-radical polymerization.

Aqueous liquid-absorbent hydrogel-forming polymers are preferably those with an absorption of distilled water of at least their own weight, preferably 10 times their own weight, this absorption is preferably also achieved under a pressure of 0.7 psi.

Alkoxylated trimethylolpropane which can be used according to the invention have the structure as in formula II given, where EO, PO, n1, n2, n3, m1, m2, m3 have the meaning given for the esters.

The reaction of trimethylolpropane with an alkylene oxide is known per se to the person skilled in the art. Possible implementation forms can be found in Houben-Weyl, Methods of Organic Chemistry, 4th edition, 1979, Thieme Verlag Stuttgart, ed. Heinz Kropf, Volume 6/1 a, Part 1, pages 373 to 385.

For the preparation of compounds of formula II e.g. first reacted the trimethylolpropane with EO and then reacted with PO.

This can e.g. happen in which about 77 g of trimethylolpropane with 0.5 g of KOH, 45% in water is placed in an autoclave and dewatered together at 80 ° C. and reduced pressure (about 20 mbar). Then the appropriate amount of propylene oxide is added at 120 to 130 ° C. and allowed to react at this temperature under increased pressure. The reaction is complete when no change in pressure is observed. The mixture is then stirred at 120 ° C. for a further 30 min. The corresponding amount of ethyl oxide is then metered in at 145 to 155 ° C. over a prolonged period at elevated pressure and is also allowed to react. After purging with inert gas and cooling to 60 ° C., the catalyst is separated off by adding sodium pyrophosphate and subsequent filtration.

No particular demands are placed on the viscosity of the polyalcohols which can be used according to the invention, except that they should be able to be pumped without problems at a temperature of up to approximately 80 ° C., they should preferably have a viscosity below 1000 mPas, preferably below 800 mPas and very particularly preferably below 500 mPas.

Esterification catalysts C which can be used according to the invention are sulfuric acid, aryl or alkylsulfonic acids or mixtures thereof. Examples of arylsulfonic acids are benzenesulfonic acid, para-toluenesulfonic acid or dodecylbenzenesulfonic acid, examples of alkylsulfonic acids are methanesulfonic acid, ethanesulfonic acid or trifluoromethanesulfonic acid. sulfonic acid. Strongly acidic ion exchangers or zeolites can also be used as esterification catalysts. Sulfuric acid and ion exchangers are preferred.

Polymerization inhibitors D which can be used according to the invention are, for example, phenols such as alkylphenols, for example o-, m- or p-cresol (methylphenol), 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethyl- phenol, 2,6-di-tert-butyl-4-methylphenol, 2-tert-butylphenol, 4-tert-butylphenol, 2,4-di-tert-butylphenol, 2-methyl-4-tert.- Butylphenol, 4-tert-butyl-2,6-dimethylphenol, or 2,2'-methylene-bis- (6-tert-butyl-4-methylphenol), 4,4'-oxydiphenyl, 3,4-methylenedioxydiphenol (Sesamol), 3,4-dimethylphenol, hydroquinone, pyrocatechol (1, 2-dihydroxybenzene), 2- (1'-

Methylcyclohex-1'-yl) -4,6-dimethylphenol, 2- or 4- (1'-phenyl-eth-1 ^, -yl) -phenol, 2-tert-butyl-6-methylphenol, 2,4,6 -Tris-tert-butylphenol, 2,6-di-tert-butylphenol, 2,4-di-tert-butylphenol, 4-tert-butylphenol, nonylphenol [11066-49-2], octylphenol [140-66 -9], 2,6-dimethylphenol, bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol S, 3,3 \ 5,5'-tetrabromobisphenol A, 2,6-di-tert-butyl-p-cresol , Koresin® from BASF AG, 3,5-di-tert-butyl-4-hydroxybenzoic acid methyl ester, 4-tert-butylpyrocatechol, 2-hydroxybenzyl alcohol, 2-methoxy-4-methylphenol, 2,3,6-trimethylphenol, 2,4 , 5-trimethylphenol, 2,4,6-trimethylphenol, 2-isopropylphenol, 4-isopropylphenol, 6-isopropyl-m-cresol, n-octadecyl-beta (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1, 1, 3-tris- (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1, 3,5-trimethyl-2,4,6-tris- (3,5-di- tert-butyl-4-hydroxybenzyl) benzene, 1,3,5, -Tris- (3,5-di-tert-butyI-4-hydroxybenzyl) isocyanurate, 1, 3,5 ₎ -Tris- (3,5- di-tert-butyl-4-hydroxyphenyl ) - propionyloxyethyl isocyanurate, 1,3,5-tris (2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate or pentaerythritol tetrakis [beta (3,5, -di-tert -butyI-4-hydroxyphenyl) propionate], 2,6-di-te / τ.-butyl-4-dimethylaminomethyl-phenol, 6-se / c.-butyl-2,4-dinitrophenol, Irganox® 565, 1141 , 1192, 1222 and 1425 from Ciba Specialty Chemicals, 3- (3 ', 5 ^l -di-tert-butyl-4 ^, -hydroxyphenyl) propionic acid octadecyl ester, 3- (3', 5'-di-tert-butyl- 4'-hydroxyphenyl) propionic acid hexadecyl ester, 3- (3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionic acid octyl ester, 3-thia-1 _l 5-pentanediol-bis - [(3', 5 ^, - di-tert-butyl-4 ^l - hydroxyphenyl) propionate], 4,8-dioxa-1, 11 -undecandiol-bis - ^[(3, 5'-di-te-.-butyl-4'-hydroxyphenyl) propionate], 4,8-dioxa-1, 11-undecanediol-bis - [(3 ^, -fe / τ.-butyl-4 ^, -hydroxy-5'-methylphenyl) propionate], l .θ-nonanediol-bis- ^ S'.δ'-di-fetϊ. butyW--hydroxyphenyl) propionate], 1 _l 7-heptanediamine-bis [3- ^(3, ^{5-di-fert.-butyl-4} ^l - hydroxyphenyl) propionamide] , 1, 1 met handiamin-bis [3- (3 ', 5'-di-butyl-4'-hydroxyphenyl ferf.-) propionamide], 3- (3', ^5'-di-te /.-butyl-4'-hydroxyphenyl) propionic acid hydrazide, 3- (3 ', 5'-dimethyl-4'-hydroxyphenyl) propionic acid hydrazide, bis (3-fe / f.-butyl-5-ethyl-2-hydroxy-phen-1-yl) methane, bis (3,5-di --- ert.-butyl-4-hydroxy-phen-1-yl) methane, bis [3- (1'-methylcyclohex-1'-yl) -5-methyl-2-hydroxy- phen-1 -yl] methane, bis (3-ferf.-butyl-2-hydroxy-5-methyl-phen-1 -yl) methane, 1, 1-bis (5-finished-butyl-4-hydroxy- 2-methyl-phen-1-yl) ethane, bis (5-fe /.-Butyl- 4-hydroxy-2-methyl-phen-1-yl) sulfide, bis (3-te / t-butyl-2-hydroxy-5-methyl-phen-1-yl) sulfide, 1, 1-bis (3, 4-dimethyl-2-hydroxy-phen-1-yl) -2-methylpropane, 1,1-bis (5-te / t-butyl-3-methyl-2-hydroxy-phen-1-yl) -butane, 1, 3,5-tris [1 '- (3 ", 5" -di-fert.-butyl-4 "-hydroxyphen-1" -yl) -meth-1' -yl ^ Aδ-trimethylbenzene, 1 , 1, 4-tris ⁽⁵ th ^{/.-butyl-4-hydroxy-2'-methyl-phen-1'-yl)} butane, aminophenols, for example para-aminophenol, nitrosophenols, such as para-nitrosophenol , p-nitroso-o-cresol, alkoxyphenols, for example 2-methoxyphenoi (guaiacol, pyrocatechol monomethyl ether), 2-ethoxyphenol, 2-isopropoxyphenol, 4-methoxyphenol (hydroquinone monomethyl ether), mono- or di-tert-butyl-4-methoxyphenol, 3,5-di-tert-butyl-4-hydroxyanisole, 3-hydroxy-4-methoxybenzyl alcohol, 2,5-dimethoxy-4-hydroxybenzyl alcohol (Syringa alcohol), 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy- 3-ethoxybenzaldehyde (ethylvanillin), 3-hydroxy-4-methoxybenzaldehyde (isovanillin), 1 - (4-hydroxy-3-methoxyphenyl) e thanon (acetovanillon), eugenol, dihydroeugenol, isoeugenol, tocopherols, such as, for example, alpha, beta, gamma, delta and epsilon tocopherol, tocol, alpha tocopherol hydroquinone, and 2,3-dihydro-2,2-dimethyl 7-hydroxybenzofuran (2,2-dimethyl-7-hydroxycoumaran), quinones and hydroquinones such as hydroquinone or hydroquinone monomethyl ether, 2,5-di-fe-t-butylhydroquinone, 2-methyl-p-hydroquinone, 2,3-dimethylhydroquinone, trimethylhydroquinone , 4-methyl pyrocatechol, tert-butyl hydroquinone, 3-methyl pyrocatechol, benzoquinone, 2-methyl p-hydroquinone, 2,3-dimethyl hydroquinone, trimethyl hydroquinone, 3-methyl pyrocatechol, 4-

Methyl catechol, tert-butylhydroquinone, 4-ethoxyphenol, 4-butoxyphenol, hydroquinone monobenzyl ether, p-phenoxyphenol, 2-methylhydroquinone, 2,5-di-tert-butylhydroquinone, tetramethyl-p-benzoquinone, diethyl-1, 4-cyclohexanedione -2,5- dicarboxylate, phenyl-p-benzoquinone, 2,5-dimethyl-3-benzyl-p-benzoquinone, 2- isopropyl-5-methyl-p-benzoquinone (thymoquinone), 2,6-diisopropyl-p- benzoquinone, 2,5-dimethyl-3-hydroxy-p-benzoquinone, 2,5-dihydroxy-p-benzoquinone, embelin, tetra-hydroxy-p-benzoquinone, 2,5-dimethoxy-1, 4-benzoquinone, 2- Amino-5-methyl-p-benzoquinone, 2,5-bisphenylamino-1, 4-benzoquinone, 5,8-dihydroxy-1, 4-naphthoquinone, 2-anilino-1, 4, naphthoquinone, anthraquinone, N, N- Dimethylindoaniline, N, N-diphenyl-p-benzoquinone diimine, 1, 4-benzoquinone dioxime, Coerulignon, S.S'-di-tert-butyl-δ.δ ¹ - dimethyldiphenoquinone, p-rosolic acid (aurine), 2,6-di tert-butyl-4-benzylidene-benzoquinone, 2,5-di-tert-amylhydroquinone, N-oxyls such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 4-oxo 2,2,6,6-t etramethyl-piperidine-N-oxyl ₁ 4-acetoxy-2,2,6,6-tetramethyl-piperidine-N-oxyl, 2,2,6,6-tetramethyl-piperidine-N-oxyl, 4,4 ', 4 "- Tris (2,2 ₎ 6,6-tetramethyl-piperidine-N-oxyl) phosphite, 3-oxo-2,2,5,5-tetramethyl-pyrrolidine-N-oxyl, 1-oxyl ^^. E .ö-tetramethyl ^ -methoxypiperidine, 1 -oxyl-2,2,6,6-tetramethyl-4-trimethylsilyloxypiperidine, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-2-ethylhexanoate, 1 - Oxyl-2,2,6,6-tetramethylpiperidin-4-yl stearate, 1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl-benzoate, 1-oxyl-2,2,6,6- tetramethylpiperidin-4-yl- (4-tert-butyl) benzoate, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) succinate, bis (1-oxyl- 2,2 ₎ 6,6-tetramethylpiperidin-4-yl) adipate, 1,10-decanedioic acid bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) ester, bis (1-oxyl -2,2,6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) phthalate, bis (1-oxyl-2,2 , 6,6-tetramethylpiperidin-4-yl) isophthalate, bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) terephthalate, bis (1-oxyl-2,2,6,6 tetramethylpiperidin-4-yl) hexahydroterephthalate, N, N'- bis (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) adipinamide, N- (1-oxyI-2,2,6 , 6-tetramethylpiperidin-4-yl) caprolactam, N- (1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl) dodecylsuccinimide, 2,4,6-tris [N-butyl-N - (1-oxyl-2,2 ₎ 6,6-tetramethylpiperidin-4-yl] triazine, N, N'-bis (1 -oxyl ^ .θ.e-tetramethylpiperidine ^ -y -N.N'-bis- formyl-l, 6-diaminohexane, 4,4 ^, -ethylenebis (1-oxyl-2,2,6,6-tetramethyipiperazin-3-one) aromatic amines such as phenylenediamines, NN-diphenylamine, N-nitrosodiphenylamine, nitroso diethylaniline, N.N'-dialkyl-para-phenylenediamine, the alkyl radicals being the same I or can be different and each independently consist of 1 to 4 carbon atoms and can be straight-chain or branched, for example N, N'-di- / so-butyl-p-phenylenediamine, N.N'-di-feo-propyl- p-phenylenediamine, Irganox 5057 from Ciba Specialty Chemicals, N, N'-di- / so-butyl-p-phenylenediamine, N, N'-di- / so-propyl-p-phenylenediamine, p-phenylenediamine, N-phenyl -p-phenylenediamine, N, N'- diphenyl-p-phenylenediamine, N-isopropyl-N-phenyl-p-phenylenediamine, N, N'Di-sec-butyl-p-phenylenediamine (Kerobit® BPD from BASF AG), N-phenyl-N'-isopropyl-p-phenylenediamine (Vulkanox® 4010 from Bayer AG), N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, N-phenyl-2-naphthylamine, imoinodibenzyl, N.N'-diphenylbenzidine, N-phenyltetraaniline, acridone, 3-hydroxydiphenylamine, 4-hydroxydiphenylamine, hydroxylamines such as NN-diethylhydroxylamine, urea derivatives such as urea or thiourea, phosphorus-containing compounds such as triphenylphosphine, triphenylphosphite, hypophite acid or triethyl phosphite, sulfur-containing compounds such as diphenyl sulfide, phenothiazine or metal salts, such as copper, manganese, cerium, nickel, chromium

-chloride, -dithiocarbamate, -sulfate, -salicylate or -acetate or mixtures thereof. The phenols and quinones mentioned are preferred, and hydroquinone, hydroquinone monomethyl ether, 2-tert-butyl-4-methylphenol, 6-tert-butyl-2,4-dimethyl-phenol, 2,6-di-tert are particularly preferred .-Butyl-4-methylphenol, 2,4-di-tert-butylphenol, triphenylphosphite, hypophosphorous acid, CuCl ₂ and guaiacol, hydroquinone and hydroquinone monomethyl ether are very particularly preferred.

Hydroquinone monomethyl ether, hydroquinone and alkylphenols, optionally in combination with tripehnyl phosphite and / or hypophosphorous acid, are particularly preferred. Α-Tocopherol (vitamin E), β-tocopherol, y-tocopherol, or δ-tocopherol are very particularly preferred, optionally in combination with triphenyl phosphite and / or hypophosphorous acid.

To further support the stabilization, an oxygen-containing gas, preferably air or a mixture of air and nitrogen (lean air) can be present.

Among the stabilizers listed, preferred are those that are aerobic, i.e. those that require the presence of oxygen to develop their full inhibitory effect.

Solvents E which can be used according to the invention are, in particular, those which are suitable for azeotropic removal of the water of reaction, if desired, in particular aliphatic, cycloaliphatic and aromatic hydrocarbons or mixtures thereof.

Preferably n-pentane, n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene or xylene are used. Cyclohexane, methylcyclohexane and toluene are particularly preferred.

For the esterification, the preparation and / or processing methods of polyhydric alcohols known to the person skilled in the art can be used, for example those mentioned at the beginning or those described in DE-A 19941 136, DE-A 3843843, DE-A 3843 854, DE-A 19937911, DE -A 19929258, EP-A 331 845, EP 554651 or US 4 187 383.

In general, the esterification can be carried out as follows:

The esterification apparatus consists of a stirred reactor, preferably a reactor with a circulation evaporator and an attached distillation unit with a condenser and phase separation vessel.

The reactor can be, for example, a reactor with double-wall heating and / or internal heating coils. A reactor with an external heat exchanger and natural or forced circulation, that is to say using a pump, particularly preferably natural circulation, in which the recycle stream is brought about without mechanical aids, is preferably used. Of course, the reaction can also be carried out in several reaction zones, for example a reactor cascade consisting of two to four, preferably two to three, reactors.

Suitable circulation evaporators are known to the person skilled in the art and are described, for example, in R. Billet, Verdampfertechnik, HTB-Verlag, Bibliographisches Institut Mannheim, 1965, 53. Examples of circulation evaporators are tube bundle heat exchangers, plate heat exchangers, etc.

Of course, several heat exchangers can also be present in the circulation.

The distillation unit is of a type known per se. This can be a simple distillation, which may be equipped with a splash guard, or a rectification column. In principle, all common internals come into consideration as column internals, for example trays, packings and / or fillings. Of the trays, bubble trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred; of the fillings, those with rings, spirals, saddle bodies or braids are preferred.

As a rule, 5 to 20 theoretical floors are sufficient.

The condenser and the separation vessel are of conventional construction.

(Meth) acrylic acid and alkoxylated trimethylolpropane are generally used in the esterification a) in a molar excess as indicated above. The excess used can be up to approximately 3000: 1, if desired.

The above-mentioned esterification catalysts C are suitable.

They are generally used in an amount of 0.1-5% by weight, based on the esterification mixture, preferably 0.5-5%, more preferably 1-4% and very particularly preferably 2-4% by weight.

If necessary, the esterification catalyst can be removed from the reaction mixture using an ion exchanger. The ion exchanger can be added directly to the reaction mixture and then filtered off, or the reaction mixture can be passed over an ion exchange bed. The esterification catalyst is preferably left in the reaction mixture. However, if the catalyst is an ion exchanger, this is preferably removed, for example by filtration.

This oxygen-containing gas is preferably metered into the bottom region of a column and / or into a circulation evaporator and / or passed through the reaction mixture and / or over it.

The polymerization inhibitor (mixture) D (as mentioned above) is used in a total amount of 0.01-1% by weight, based on the esterification mixture, preferably 0.02-0.8, particularly preferably 0.05-0.5% %.

The polymerization inhibitor (mixture) D can be used, for example, as an aqueous solution or as a solution in a starting material or product.

b) The water of reaction formed during the reaction can be distilled off during or after the esterification a), this process being able to be supported by a solvent which forms an azeotrope with water.

The solvents listed above are suitable as solvent E for azeotropic removal of the water of reaction, if desired.

It is preferred to carry out the esterification in the presence of a solvent.

The amount of solvent used is 10-200% by weight, preferably 20-100% by weight, particularly preferably 30-100% by weight, based on the sum of alkoxylated trimethylolpropane and (meth) acrylic acid.

However, it is also conceivable to carry it out without entrainer, e.g. is described in DE-A1 3843854, column 2, line 18 to column 4, line 45, but in contrast to this with the stabilizers mentioned above.

If the water contained in the reaction mixture is not removed using an azeotroping solvent, it is possible to remove it by stripping with an inert gas, preferably an oxygen-containing gas, particularly preferably with air or lean air, for example as in DE-A 3843 843 described. The reaction temperature of the esterification a) is generally 40-160 ° C., preferably 60-140 ° C. and particularly preferably 80-120 ° C. The temperature can remain the same or rise in the course of the reaction, but is preferably raised in the course of the reaction. In this case the final temperature of the esterification is 5 - 30 ° C higher than the initial temperature. The temperature of the esterification can be determined and regulated by varying the solvent concentration in the reaction mixture, as described in DE-A 19941 136 and the German application with the file number 100 63 175.4.

If a solvent is used, it can be distilled off from the reaction mixture via the distillation unit attached to the reactor.

The distillate can either be removed or, after condensation, fed into a phase separator. The aqueous phase obtained in this way is generally discharged, the organic phase can be fed as reflux into the distillation unit and / or be passed directly into the reaction zone and / or into a circulation evaporator, as in the German patent application with the file number 100 63 175.4 described.

When used as reflux, the organic phase, as described in DE-A 19941 136, can be used to control the temperature in the esterification.

The esterification a) can be carried out without pressure, but also under overpressure or underpressure, preferably under normal pressure.

The reaction time is generally 2 to 20 hours, preferably 4 to 15 hours and particularly preferably 7 to 12 hours.

The order of addition of the individual reaction components is not essential according to the invention. All components can be initially mixed and then heated, or one or more components cannot be initially or only partially and only added after the heating.

The composition of the (meth) acrylic acid which can be used is not restricted and can have, for example, the following components:

(Meth) acrylic acid 90 - 99.9% by weight

Acetic acid 0.05 - 3% by weight

Propionic acid 0.01 - 1% by weight

Diacrylic acid 0.01 - 5% by weight Water 0.05 - 5% by weight carbonyl-containing 0.01 - 0.3% by weight inhibitors 0.01 - 0.1% by weight maleic acid (anhydride) 0.001 - 0.5% by weight

The crude (meth) acrylic acid used is generally stabilized with 200-600 ppm phenothiazine or other stabilizers in amounts which enable comparable stabilization. The term carbonyl-containing includes acetone and lower aldehydes, e.g. Formaldehyde, acetaldehyde, crotonaldehyde, acrolein, 2- and 3-furfural and benazaldehyde, understood.

Crude (meth) acrylic acid is understood here to mean the (meth) acrylic acid-containing mixture which occurs after absorption of the reaction gases of the propane / propene / acrolein or isobutane / isobutene / methacrolein oxidation in an absorption medium and subsequent separation of the absorption medium or that is obtained by fractional condensation of the reaction gases.

Of course, pure (meth) acrylic acid can also be used, for example with the following purity:

(Meth) acrylic acid 99.7 - 99.99% by weight

Acetic acid 50 - 1000 ppm by weight

Propionic acid 10 - 500 ppm by weight

Diacrylic acid 10 - 500 ppm by weight

Water 50 - 1000 ppm by weight

Carbonyl-containing 1 - 500 ppm by weight

Inhibitors 1 - 300 ppm by weight

Maleic acid (anhydride) 1 - 200 ppm by weight

The pure (meth) acrylic acid used is generally stabilized with 100-300 ppm hydroquinone monomethyl ether or other storage stabilizers in amounts which enable comparable stabilization.

Pure or pre-cleaned (meth) acrylic acid is generally understood to mean (meth) acrylic acid, the purity of which is at least 99.5% by weight and which is essentially free of the aldehydic, other carbonyl-containing and high-boiling components.

The distilled off aqueous phase of the condensate, if any, separated off via the attached column, which can generally contain 0.1-10% by weight (meth) acrylic acid, is separated off and discharged. Can be beneficial the (meth) acrylic acid contained therein with an extractant, preferably the solvent optionally used in the esterification, for example with cyclohexane, at a temperature between 10 and 40 ° C. and a ratio of aqueous phase to extractant of 1: 5-30, preferably 1:10 - 20, extracted and returned to the esterification.

To further support the circulation, an inert gas, preferably an oxygen-containing gas, particularly preferably air or a mixture of air and nitrogen (lean air) can be passed into the circulation, through or over the reaction mixture, for example in amounts of 0.1-1. preferably 0.2-0.8 and particularly preferably 0.3-0.7 m ³ / m ³ h, based on the volume of the reaction mixture.

The course of the esterification a) can be followed by tracking the amount of water discharged and / or the decrease in the carboxylic acid concentration in the reactor.

The reaction can be ended, for example, as soon as 90% of the theoretically expected amount of water has been discharged through the solvent, preferably at least 95% and particularly preferably at least 98%.

The end of the reaction can be determined, for example, by essentially no further water of reaction being removed via the entrainer. ; If (methacrylic) acid is discharged together with the water of reaction, its proportion can be determined, for example, by back-titrating an aliquot of the aqueous phase.

Removal of the reaction water can be dispensed with, for example, if the (methacrylic) acid is used in a high stoichiometric excess, for example of at least 4.5: 1, preferably at least 7.5: 1 and very particularly preferably at least 15: 1. In this case, a substantial part of the amount of water formed remains in the reaction mixture. During or after the reaction, only the proportion of water which is determined by the volatility at the temperature applied is removed from the reaction mixture and, in addition, no measures are taken to separate off the water of reaction formed. For example, at least 10% by weight of the water of reaction formed can remain in the reaction mixture, preferably at least 20% by weight, particularly preferably at least 30% by weight, very particularly preferably at least 40 and in particular at least 50% by weight. c) After the esterification has ended, the reactor mixture can be cooled in a customary manner to a temperature of 10 to 30 ° C. and, if appropriate, by adding solvent, which can be the same as or different from the solvent which may be used for the azeotropic removal of water any target ester concentration can be set.

In a further embodiment, the reaction can be stopped with a suitable diluent G and to a concentration of, for example, 10-90% by weight, preferably 20-80%, particularly preferably 20 to 60%, very particularly preferably 30 to 50% and in particular diluted approx. 40%, for example to reduce the viscosity.

It is important that an essentially homogeneous solution is formed after dilution.

This is preferably done only relatively shortly before use in the preparation of the hydrogel, for example not more than 24 hours beforehand, preferably not more than 20, particularly preferably not more than 12, very particularly preferably not more than 6 and in particular not more than 3 hours in advance.

The diluent G is selected from the group consisting of water, a mixture of water with one or more water-soluble organic solvents or a mixture of water with one or more single or multi-functional alcohols, e.g. Methanol and glycerin. The alcohols preferably carry 1, 2 or 3 hydroxyl groups and preferably have between 1 and 10, in particular up to 4, carbon atoms. Primary and secondary alcohols are preferred.

Preferred alcohols are methanol, ethanol, isopropanol, ethylene glycol, glycerin, 1,2-propanediol or 1,3-propanediol.

d) If necessary, the reaction mixture can be decolorized, for example by treatment with activated carbon or metal oxides, e.g. Aluminum oxide, silicon oxide, magnesium oxide, zirconium oxide, boron oxide or mixtures thereof, in amounts of, for example, 0.1-50% by weight, preferably 0.5 to 25% by weight, particularly preferably 1-10% by weight, at temperatures of, for example, 10 to 100 ° C, preferably 20 to 80 ° C and particularly preferably 30 to 60 ° C.

This can be done by adding the powdery or granular decolorizing agent to the reaction mixture and subsequent filtration or by passing the reaction mixture take place over a bed of the decolorizing agent in the form of any suitable moldings.

The reaction mixture can be decolorized at any point in the workup process, for example at the stage of the crude reaction mixture or after prewashing, neutralization, washing or solvent removal, if appropriate.

The reaction mixture can also be subjected to a prewash e) and / or a neutralization f) and / or a postwash g), preferably only a neutralization f). If necessary, neutralization f) and prewash e) can also be interchanged in the order.

The (meth) acrylic acid and / or catalyst C contained in the aqueous phase of the washes e) and g) and / or neutralization f) can be at least partially recovered by acidification and extraction with a solvent and used again.

For prewashing or afterwashing e) or g), the reaction mixture is washed in a washing apparatus with a washing liquid, for example water or a 5-30% by weight, preferably 5-20, particularly preferably 5-15% by weight sodium chloride. , Potassium chloride, ammonium chloride, sodium sulfate or ammonium sulfate solution, preferably water or saline, treated.

The quantitative ratio of reaction mixture: washing liquid is generally 1: 0.1-1, preferably 1: 0.2-0.8, particularly preferably 1: 0.3-0.7.

The washing or neutralization can be carried out, for example, in a stirred tank or in other conventional equipment, e.g. in a column or mixer-settler apparatus.

In terms of process technology, all extraction and washing processes and apparatuses known per se can be used for washing or neutralization in the process according to the invention, for example those described in Ullmann's Encyclopedia of Industrial Chemistry, 6th ed, 1999 Electronic Release, chapter: Liquid - Liquid Extraction - Apparatus , are described. For example, these can be single- or multi-stage, preferably single-stage extractions, as well as those in cocurrent or countercurrent mode, preferably countercurrent mode. Sieve plate or packed or packed columns, stirred tanks or mixer-settlers, and pulsed columns or those with rotating internals are preferably used.

The prewash e) is preferably used when metal salts, preferably copper or copper salts, are used as inhibitors (with).

Rinsing g) can be advantageous for removing base or salt traces from the reaction mixture neutralized in f).

For neutralization f), the optionally prewashed reaction mixture, which may still contain small amounts of catalyst and the main amount of excess (meth) acrylic acid, can be mixed with a 5-25, preferably 5-20, particularly preferably 5-15% by weight aqueous solution of a Base, such as, for example, alkali or alkaline earth metal oxides, hydroxides, carbonates or hydrogen carbonates, preferably sodium hydroxide solution, potassium hydroxide solution, sodium hydrogen carbonate, sodium carbonate, potassium hydrogen carbonate, calcium hydroxide, lime milk, ammonia, ammonia water or potassium carbonate, which may contain 5-15% by weight Saline, potassium chloride, ammonium chloride or ammonium sulfate can be added, particularly preferably with sodium hydroxide solution or sodium hydroxide solution, neutralized. The degree of neutralization is preferably 5 to 60 mol%, preferably 10 to 40 mol%, particularly preferably 20 to 30 mol%, based on the monomers containing acid groups. This neutralization can take place before and / or during the polymerization, preferably before the polymerization.

The base is added in such a way that the temperature in the apparatus does not rise above 60 ° C., is preferably between 20 and 35 ° C. and the pH is 4-13. The heat of neutralization is preferably dissipated by cooling the container with the aid of internal cooling coils or via double-wall cooling.

The ratio of the reaction mixture to the neutralizing liquid is generally 1: 0.1-1, preferably 1: 0.2-0.8, particularly preferably 1: 0.3-0.7.

The statements made above apply to the apparatus.

h) If a solvent is present in the reaction mixture, this can essentially be removed by distillation. Optionally contained solvent is preferred after washing and / or neutralization from the reaction mixture removed, if desired, this can also be done before washing or neutralization.

For this purpose, an amount of storage stabilizer, preferably hydroquinone monomethyl ether, is added to the reaction mixture such that after removal of the solvent 100-500, preferably 200-500 and particularly preferably 200-400 ppm thereof are contained in the target ester (residue).

The main amount of solvent is removed by distillation, for example, in a stirred tank with double-wall heating and / or internal heating coils under reduced pressure, for example at 20-700 mbar, preferably 30-500 and particularly preferably 50-150 mbar and a temperature of 40-80 ° C. ,

Of course, the distillation can also be carried out in a falling film or thin film evaporator. For this purpose, the reaction mixture is passed through the apparatus, preferably several times in a circuit, under reduced pressure, for example at 20-700 mbar, preferably 30-500 and particularly preferably 50-150 mbar and a temperature of 40-80 ° C.

An inert gas, preferably an oxygen-containing gas, particularly preferably air or a mixture of air and nitrogen (lean air) can advantageously be introduced into the distillation apparatus, for example 0.1-1, preferably 0.2-0.8 and particularly preferably 0, 3 - 0.7 m ³ / m ³ h, based on the volume of the reaction mixture.

The residual solvent content in the residue after the distillation is generally less than 5% by weight, preferably 0.5-5% and particularly preferably 1 to 3% by weight.

The separated solvent is condensed and preferably reused.

If necessary, solvent stripping i) can be carried out in addition to or instead of the distillation.

For this purpose, the target ester, which still contains small amounts of solvent, is heated to 50-90 ° C., preferably 80-90 ° C., and the remaining amounts of solvent are removed with a suitable gas in a suitable apparatus. A vacuum can also be applied to assist.

Suitable apparatuses are, for example, columns of a type known per se, which have the usual internals, for example trays, beds or oriented packings, preferably beds. In principle, all common conditions, such as floors, packings and / or fillers. Bell bottoms, sieve bottoms, valve bottoms, Thormann bottoms and / or dual flow bottoms are preferred of the bottoms, of the fillings are those with rings, spirals, saddle bodies, Raschig, Intos or Pall rings, Barrel or Intalox saddles, Top-Pak etc. or braids, preferred.

A falling film, thin film or wiped film evaporator, such as e.g. a Luwa, Rotafiim or Sambay evaporator, which can be equipped, for example, with a demister as a splash guard.

Suitable gases are gases which are inert under the stripping conditions, preferably oxygen-containing gases, particularly preferably air or mixtures of air and nitrogen (lean air) or water vapor, in particular those which are heated to 50 to 100.degree.

The amount of stripping gas is, for example, 5-20, particularly preferably 10-20 and very particularly preferably 10 to 15 m ³ / m ³ h, based on the volume of the reaction mixture.

If necessary, the ester can be subjected to filtration j) at any stage of the work-up process, preferably after washing / neutralization and, if appropriate, solvent removal, in order to remove traces of salts and any decolorizing agent present.

In a conceivable embodiment, the esterification a) of alkoxylated trimethylolpropane with the (methacrylic) acid is carried out in a molar excess of at least 15: 1 as mentioned above in the presence of at least one esterification catalyst C and at least one polymerization inhibitor D without one using water Azeotropically forming solvent carried out.

In a preferred embodiment, the (methacrylic) acid used in excess is essentially not separated, i.e. only the proportion of (methacrylic acid is removed from the reaction mixture, which is determined by the volatility at the temperature applied, and in addition no measures are taken to separate the carboxylic acid, such as, for example, distillative, rectifying, extractive, such as, for example, washing, absorptive , such as passing over activated carbon or via ion exchanger, and / or chemical steps, such as trapping the carboxylic acid with epoxides.

The (methacrylic) acid contained in the reaction mixture is preferably not more than 75% by weight, particularly preferably not more than 50% by weight, very particularly preferably not more than 25% by weight, in particular not more than 10% by weight and especially not more than 5% by weight, separated from the reaction mixture, based on the (methacrylic) acid present in the reaction mixture after the end of the reaction. In a particularly preferred embodiment, step b) can be dispensed with, so that only the proportion of water of reaction and (methacrylic) acid which is determined by the volatility at the temperature applied is removed from the reaction mixture. This can preferably be prevented by essentially complete condensation.

Furthermore, the esterification catalyst C used essentially remains in the reaction mixture.

The reaction mixture obtainable in this way preferably has an acid number in accordance with. DIN EN 3682 from at least 25 mg KOH / g reaction mixture, particularly preferably from 25 to 80 and very particularly preferably from 25 to 50 mg KOH / g.

Prewashing or afterwashing e) or g) is preferably dispensed with, only one filtration step j) can be useful.

The reaction mixture can then be diluted in step c)

In this case, it is preferably converted to the hydrogel within 6 hours, particularly preferably within 3 hours. It can preferably be neutralized in step f).

The sequence of steps c), j) and f) is arbitrary.

The invention also relates to a mixture of substances

at least one ester F, obtainable by one of the esterification processes described above,

(Methacrylic) acid and diluent G.

May be included as further components

Esterification catalyst C in protonated or unprotonated form,

Polymerization inhibitor D and optionally solvent E, if such was used in the esterification. The mixture of substances can optionally be neutralized and have a pH, as listed under f) above.

When the mixture of substances is neutralized, at least part of the (methacrylic) acid is converted into its water-soluble alkali metal, alkaline earth metal or ammonium salts.

Preferred mixture contains

Ester F in the mixture of substances 0.1 to 40% by weight, particularly preferably 0.5 to 20, very particularly preferably 1 to 10, in particular 2 to 5 and especially 2 to 4

Wt .-%,

Monomer M 0.5-99.9% by weight, particularly preferably 0.5-50% by weight, very particularly preferably 1-25, in particular 2-15 and especially 3 to 5% by weight, esterification catalyst C 0-10% by weight, particularly preferably 0.02 - 5, very particularly preferably 0.05 - 2.5% by weight and in particular 0.1 - 1% by weight,

Polymerization inhibitor D 0-5% by weight, particularly preferably 0.01-1.0, very particularly preferably 0.02-0.75, in particular 0.05-0.5 and especially 0.075-0.25% by weight, solvent E0 10% by weight, particularly preferably 0-5% by weight, very particularly preferably 0.05-1.5% by weight and in particular 0.1-0.5% by weight, with the

Provided that the total is always 100% by weight and, if necessary, diluent G ad 100% by weight.

The reaction mixtures and mixtures of substances according to the invention obtainable by the above process can be used

as a radical crosslinker for water-absorbing hydrogels, as a starting material for the production of polymer dispersions, as a starting material for the production of polyacrylates (except hydrogels), - as a coating raw material or as a cement additive.

Those mixtures according to the invention which have a water solubility (at 25 ° C. in distilled water) of at least 0.5% by weight, preferably at least 1% by weight, more preferably at least 2% by weight, are particularly suitable for use as radical crosslinkers of water-absorbing hydrogels. %, even more preferably at least 5% by weight, particularly preferably at least 10% by weight, very particularly preferably at least 20% by weight and in particular at least 30% by weight. k) The reaction mixture from the esterification, including its work-up steps, as far as they are carried out, for example the reaction mixture from f), or, if f) is omitted, from b), or, if b) is dispensed with, the reaction mixture from a ), can optionally be mixed with additional monoethylenically unsaturated compounds N which do not carry any acid groups but can be copolymerized with the hydrophilic monomers M, then can be polymerized in the presence of at least one radical initiator K and optionally at least one graft base L to prepare water-absorbing hydrogels ,

Can be beneficial

I) the reaction mixture from k) is post-crosslinked.

Hydrophilic monomers M suitable for producing k) these hydrophilic, highly swellable hydrogels are, for example, polymerizable acids, such as acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, vinylsulfonic acid, vinylphosphonic acid, maleic acid including their anhydride, fumaric acid, Itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, allylsulfonic acid, sulfoethyl acrylate, sulfomethacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloxypropyisulfonic acid, 2-hydroxy-3-methacryl-oxypropylsulfonic acid, allylphosphonic acid, 2-hydroxylsulfonic acid, 2-hydroxylsulfonic acid, 2-hydroxylsulfonic acid, 2-hydroxylsulfonic acid, 2-hydroxyphosphonic acid, Acrylamido-2-methylpropanephosphonic acid and their amides, hydroxyalkyl esters and esters and amides containing amino groups or ammonium groups. The monomers can be used alone or as a mixture with one another. Furthermore, water-soluble N-vinylamides or diallyidimethylammonium chloride. Preferred hydrophilic monomers are compounds of the formula V.

wherein

R ^{3 is} hydrogen, methyl or ethyl,

R ^{4 is} the group -COOR ⁶ , a sulfonyl group or phosphonyl group, a phosphonyl group esterified with a (CC ₄ ) alkyl alcohol or a group of the formula VI

R ^{5 is} hydrogen, methyl, ethyl or a carboxyl group, R ^{6 is} hydrogen, amino or hydroxy- (C ₁ -C ₄ ) -alkyl and R ^{7 is} a sulfonyl group, a phosphonyl group or a carboxyl group.

Examples of (CrC) alkyl alcohol are methanol, ethanol, n-propanol or n-butanol.

Particularly preferred hydrophilic monomers are acrylic acid and methacrylic acid, especially acrylic acid.

To optimize properties, it can be useful to use additional monoethylenically unsaturated compounds N which do not carry any acid groups but are copolymerizable with the monomers bearing acid groups. These include, for example, the amides and nitriles of monoethylenically unsaturated carboxylic acid, e.g. B. acrylamide, methacrylamide and N-vinylformamide, N-vinyl acetamide, N-methyl-vinyl acetamide, acrylonitrile and methacrylonitrile. Other suitable compounds are, for example, vinyl esters of saturated C to C carboxylic acids, such as vinyl formate, vinyl acetate or vinyl propionate, alkyl vinyl ethers with at least 2 C atoms in the alkyl group, such as, for. B. ethyl vinyl ether or butyl vinyl ether, esters of monoethylenically unsaturated C ₃ - to C ₆ -carboxylic acids, for. B. esters of monohydric C ^ to C ₁₈ alcohols and acrylic acid, methacrylic acid or maleic acid, half-ester of maleic acid, for. B. Maieinsäuremono-methyl ester, N-vinyl lactams such as N-vinyl pyrrolidone or N-vinyl caprolactam, acrylic acid and methacrylic acid esters of alkoxylated monohydric, saturated alcohols, for. B. of alcohols with 10 to 25 carbon atoms which have been reacted with 2 to 200 moles of ethylene oxide and / or propylene oxide per mole of alcohol, and monoacrylic acid esters and monomethacrylic acid esters of polyethylene glycol or polypropylene glycol, the molar masses (M _n ) the polyalkylene glycols can be, for example, up to 2000. Other suitable monomers are styrene and alkyl-substituted styrenes such as ethylstyrene or tert-butylstyrene.

These monomers not carrying acid groups can also be used in a mixture with other monomers, e.g. B. Mixtures of vinyl acetate and 2-hydroxyethyl acrylate in any ratio. These monomers not carrying acid groups are added to the reaction mixture in amounts between 0 and 50% by weight, preferably less than 20% by weight. The crosslinked (co) polymers preferably consist of monoethylenically unsaturated monomers bearing acid groups, which are optionally converted into their alkali metal or ammonium salts before or after the polymerization, and from 0 to 40% by weight, based on their total weight, of no monoethylenically unsaturated monomers bearing acid groups.

The production, testing and use of (meth) acrylic acid-containing (co) polymers, polyacrylic acids and superabsorbents has been described many times and is therefore well known, see e.g. "Modern Superabsorbent Polymer Technology", F.L. Buchholz and A.T. Graham, Wiley-VCH, 1998 or in Markus Frank "Superabsorbents" in Ullmann's Handbuch der Technische Chemie Volume 352003.

Preferred hydrogels are those obtained by crosslinking polymerization or copolymerization of acid-bearing monoethylenically unsaturated monomers M or their salts.

The available polymers are characterized by an improved saponification index (VSI).

In the process for postcrosslinking, the starting polymer is treated with a postcrosslinker and preferably postcrosslinked and dried during or after the treatment by increasing the temperature, the crosslinker preferably being contained in an inert solvent. Inert solvents are understood to mean those which, during the reaction, do not essentially react either with the starting polymer or with the postcrosslinker. Preferred solvents are those which more than 90%, preferably more than 95%, particularly preferably more than 99%, in particular more than 99.5%, do not react chemically with the starting polymer or postcrosslinker.

Preferred for post-crosslinking I) and drying m) is the temperature range between 30 and 250 ° C., in particular 50-200 ° C., the most preferred is

Range between 100 - 180 ° C. The surface post-crosslinking solution is preferably applied by spraying onto the polymer in suitable spray mixers. Following the spraying, the polymer powder is thermally dried, and the crosslinking reaction can take place both before and during the drying. It is preferred to spray on a solution of the crosslinking agent in reaction mixers or mixing and drying systems such as Lödige mixers, BEPEX mixers, NAUTA mixers, SHUGGI mixers or PROCESSALL. Fluidized bed dryers can also be used. Drying can take place in the mixer itself, by heating the jacket or by blowing in warm air. A downstream dryer such as a tray dryer, a rotary kiln or a heatable screw is also suitable. However, azeotropic distillation, for example, can also be used as the drying process. The preferred residence time at this temperature in the reaction mixer or dryer is less than 60 minutes, particularly preferably less than 30 minutes.

The above processes are preferred, the starting polymer being a polymeric acrylic acid or a polyacrylate, in particular a polymeric acrylic acid or a polyacrylate, which were obtained via free-radical polymerization and in which a polyfunctional ethylenically unsaturated radical crosslinker was used.

Processes in which the mixture of radical crosslinking agents, ie the ester F, and diluent G in a ratio of 0.1-20% by weight, in particular 0.5-10% by weight, based on the mass of the starting polymer, are preferred becomes.

Such processes are preferred in which the radical crosslinker is used in a dosage of 0.01-5.0% by weight, preferably 0.02-3.0% by weight, very particularly preferably 0.03-2.5% by weight, in particular 0.05-1.0 and especially 0.1-0.75% by weight based on the

Starting polymer is used.

The invention also relates to polymers produced by one of the abovementioned processes and their use in hygiene articles, packaging materials and in nonwovens, and to the use of an abovementioned mixture of substances for the production of crosslinked or heat-crosslinkable polymers, in particular in lacquers and paints.

The hydrophilic, highly swellable hydrogels to be used (starting polymer) are in particular polymers made from (co) polymerized hydrophilic monomers M,

Graft (co) polymers of one or more hydrophilic monomers M on a suitable graft base L, crosslinked cellulose or starch ethers or natural products swellable in aqueous liquids, such as guar derivatives. These hydrogels are known to the person skilled in the art and are described, for example, in US-4286082, DE-C-2706 135, US-4 340 706, DE-C-37 13 601, DE-C-2840 010, DE-A-4344548,

DE-A4020780, DE-A-4015085, DE-A-3917846, DE-A-3807289, DE-A-3533337, DE-A-3503458, DE-A-4244548, DE-A-4219607, DE-A- 4021847, DE-A-3831261, DE-A-3511086, DE-A-3118172, DE-A-3028043, DE-A-4418881, EP-A-0801483, EP-A-0455985, EP-A-0467073, EP-A-0312952, EP-A-0205874, EP-A-0499774, DE-A 2612846, DE-A-4020780 EP-A-0205674, US-5145906, EP-A-0530438, EP-A-0670073, US4057521, US-4062817, US-4525527, US-4295987, US-5011 892, US-4076 663 or US-4931 497. Highly swellable hydrogels from a manufacturing process as in WO 01/38402 are also particularly suitable and inorganic-organic hybrid highly swellable hydrogels as described in DE 198 54 575. The content of the aforementioned patent documents, in particular the hydrogels produced by the processes, are expressly part of the present disclosure.

Suitable graft bases L for hydrophilic hydrogels, which can be obtained by graft copolymerization of olefinically unsaturated acids, can be of natural or synthetic origin. Examples are starch, cellulose or cellulose derivatives and other polysaccharides and oligosaccharides, polyalkylene oxides, in particular polyethylene oxides and polypropylene oxides, and hydrophilic polyesters.

The water-absorbing polymer can be obtained by radical graft copolymerization of acrylic acid or acrylate onto a water-soluble polymer matrix. Suitable water-soluble polymer matrices are, for example, but not exclusively, alginates, polyvinyl alcohol and polysaccharides such as starch. A polyfunctional ethylenically unsaturated radical crosslinker is used in the graft copolymerization according to the invention.

The water-absorbing polymer can be an organic-inorganic hybrid polymer composed of a polymeric acrylic acid or a polyacrylate on the one hand and a silicate, aluminate or aluminosilicate on the other hand. In particular, polymeric acrylic acid or polyacrylate can be used, which were obtained via radical polymerization, and in which a multifunctional ethylenically unsaturated radical crosslinking agent was used and in the production process of which a water-soluble silicate or soluble aluminate or mixtures of the two was used.

Preferred hydrogels are, in particular, polyacrylates, polymethacrylates and those in

US-4931 497, US-5011 892 and US-5041 496 described graft polymers. Very particularly preferred hydrogels are the kneading polymers described in WO 01/38402 and the hybrid organic-inorganic hydrogels based on polyacrylates described in DE 19854575.

The substances prepared according to the invention and usable as radical crosslinkers in hydrogels can be used alone or in combination with other crosslinkers, for example internal or surface crosslinkers, for example the following: Suitable crosslinkers are, in particular, methylenebisacryl or methacrylamide, esters of unsaturated mono- or polycarboxylic acids of polyols, such as diacrylate or triacrylate, eg. B. butanediol or ethylene glycol diacrylate or methacrylate and trimethylolpropane triacrylate and allyl compounds such as allyl (meth) acrylate, triallyl cyanurate, maleinediallylester, polyallyl esters, tetraallyloxyethane, triallylamine, tetraallylethylenediamine, allylphosphate, for example phosphorus acid in phosphorus acid, such as phosphoric acid in phosphorus acid -0343427 are described. Suitable crosslinkers are pentaerythritol tri- and tetraallyl ether, polyethylene glycol diallyl ether, monoethylene glycol diallyl ether, glycerol di and triallyl ether, polyallyl ether based on sorbitol, and ethoxylated variants thereof. Other particularly preferred crosslinkers are

Polyethylene glycol diacrylates, ethoxylated derivatives of trimethylolpropane triacrylate e.g. Sartomer SR 9035, as well as ethoxylated derivatives of glycerol diacrylate and glycerol triacrylate. Mixtures of the above crosslinking agents can of course also be used. Hydrogels which are prepared as radical crosslinkers with an ester F prepared according to the invention are very particularly preferred.

The water-absorbing polymer is preferably a polymeric acrylic acid or a polyacrylate. This water-absorbing polymer can be prepared by a process known from the literature. Polymers which contain crosslinking comonomers are preferred (0.001-10 mol%), but very particularly preferred are polymers which have been obtained by free-radical polymerization and in which a polyfunctional ethylenically unsaturated radical crosslinker has been used.

The hydrophilic, highly swellable hydrogels can be produced by polymerization processes known per se. Polymerization in aqueous solution by the so-called gel polymerization method is preferred. As mentioned above, dilute, preferably aqueous, particularly preferably 15 to 50% by weight aqueous solutions of one or more hydrophilic monomers and, if appropriate, a suitable graft base L in the presence of a radical initiator are preferably used without mechanical mixing using the Trommsdorff-Norrish effect ( Makromol. Chem. 1, 169 (1947)), polymerized. The polymerization reaction can be carried out in the temperature range between 0 ° C. and 150 ° C., preferably between 10 ° C. and 100 ° C., both under normal pressure and under elevated or reduced pressure

Pressure. As usual, the polymerization can also be carried out in a protective gas atmosphere, preferably under nitrogen. To initiate the polymerization high-energy electromagnetic radiation or the usual chemical polymerization initiators K can be used, e.g. B. organic peroxides, such as benzoyl peroxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide, cumene hydroperoxide, azo compounds such as azodiisobutyronitrile and inorganic peroxy compounds such as (NH ₄ ) ₂ S ₂ O ₈ , K ₂ S ₂ O ₈ or H ₂ O ₂ .

If necessary, they can be used in combination with reducing agents such as e.g. Ascorbic acid, sodium hydrogen sulfite, and iron (II) sulfate or redox systems which contain an aliphatic and aromatic sulfinic acid, such as benzenesulfinic acid and toluenesulfinic acid or derivatives of these acids, such as, for example, as a reducing component. B. Mannich adducts of sulfinic acids, aldehydes and amino compounds, as described in DE-C-1 301 566, can be used. The quality properties of the polymers can be improved further by heating the polymer gels for several hours in the temperature range from 50 ° to 130 ° C., preferably from 70 ° to 100 ° C.

The gels obtained are neutralized to 0-100 mol%, preferably to 25-100 mol%, and particularly preferably to 50-85 mol%, based on the monomer used, it being possible to use the customary neutralizing agents, preferably alkali metal hydroxides, Alkali metal oxides or the corresponding alkali metal carbonates, but particularly preferably sodium hydroxide, sodium carbonate and sodium hydrogen carbonate.

The neutralization is usually achieved by mixing in the neutralizing agent as an aqueous solution or preferably also as a solid. For this purpose, the gel is mechanically crushed, e.g. using a meat grinder, and the neutralizing agent is sprayed, sprinkled or poured on, and then mixed thoroughly. For this purpose, the gel mass obtained can be mined several times for homogenization. The neutralized gel mass is then dried with a belt or roller dryer until the residual moisture content is preferably below 10% by weight, in particular below 5% by weight.

However, the polymerization itself can also be carried out by any of the other methods described in the literature. In particular, the neutralization of the acrylic acid can also be carried out before the polymerization, as described in step f) above. The polymerization can then be carried out continuously or batchwise in a belt reactor known to the person skilled in the art or in a kneading reactor. When the polymerization is carried out in a belt reactor, initiation by means of electromagnetic radiation, preferably by means of UV radiation, or alternatively initiation using a redox initiator system is particularly preferred. The combination of both initiation methods is also very particularly preferred: electromagnetic radiation and chemical redox initiator system simultaneously. n) The dried hydrogel can then be ground and sieved, with roller mills, pin mills or vibrating mills usually being used for grinding. The preferred particle size of the sieved hydrogel is preferably in the range 45-1000 μm, preferably 45-850 μm, particularly preferably 200-850 μm, and very particularly preferably 300-850 μm, and the range from 150 to 850 μm is also special preferred, very particularly the range 150 to 700 μm. These areas preferably contain 80% by weight of the particles, in particular 90% by weight of the particles. The size distribution can be determined using established laser methods.

The present invention furthermore relates to crosslinked hydrogels which contain at least one hydrophilic monomer M in polymerized form and are crosslinked with an ester F of alkoxylated trimethylolpropane with (methacrylic) acid. The ester can be prepared according to the invention or in a manner known in the prior art, preferably in a manner according to the invention.

Compounds as described above can be used as esters F.

The CRC value [g / g] of the hydrogel-forming polymers according to the invention can be measured by the methods given in the description and is preferably greater than 15, in particular 16, 18, 20, 22, 24 or higher, particularly preferably 25 in particular at 26, 27, 28, 29, particularly preferably at 30, 31, 32, 33, 34, 35, 36, 37 or higher.

The AUL 0.7 psi value [g / g] of the hydrogel-forming polymers according to the invention can be measured by the methods given in the description and is preferably greater than 8, in particular 9, 10, 11, 12, 13, 14 or higher, particularly preferably at 15, in particular at 16, 17, 18, 19 or higher, particularly preferably greater than 20, in particular 21, 22, 23, 24, 25, 26, 27, 28 or higher.

The AUL-0.5psi value [g / g] of the hydrogel-forming polymers according to the invention can be measured by the methods given in the description and is preferably greater than 8, in particular 9, 10, 11, 12, 13, 14 or higher, particularly preferably at 15, in particular at 16, 17, 18, 19 or higher, particularly preferably greater than 20, in particular 21, 22, 23, 24, 25, 26, 27, 28 or higher.

The saponification index VSI of the hydrogel-forming polymers according to the invention can be measured by the methods given in the description and is preferably less than 10, in particular 9.5, 9, or 8.5 or less, particularly preferably less than 8, in particular 7.5, 7, 6.5, 6, 5.5 or less, particularly preferably less than 5, in particular 4.4, 4 or less.

Use and use of the hydrogel-forming polymers according to the invention

The present invention further relates to the use of the above-mentioned hydrogel-forming polymers in hygiene articles, comprising

(P) an upper liquid-permeable cover (Q) a lower liquid-impermeable layer

(R) containing a core located between (P) and (Q)

10-100% by weight of the hydrogel-forming polymer according to the invention

0 to 90% by weight of hydrophilic fiber material, preferably 20 to 100% by weight of the hydrogel-forming polymer according to the invention, 0 to 80% by weight of hydrophilic fiber material more preferably 30 to 100% by weight of the hydrogel-forming polymer according to the invention, 0 70% by weight of hydrophilic fiber material even more preferably 40-100% by weight of the hydrogel-forming polymer according to the invention, 0-60% by weight of hydrophilic fiber material more preferably 50-100% by weight of the hydrogel-forming polymer according to the invention 50% by weight of hydrophilic fiber material, particularly preferably 60-100% by weight of the hydrogel-forming polymer according to the invention, 0-40% by weight of hydrophilic fiber material, particularly preferably 70-100% by weight of the hydrogel-forming polymer according to the invention, 0 - 30% by weight of hydrophilic fiber material extremely preferably 80-100% by weight of the hydrogel-forming polymer according to the invention, 0-20% by weight of hydrophilic fiber material most preferably 90-100% by weight of the hydrogel-f shaping polymer, 0-10% by weight of hydrophilic fiber material (S) optionally a tissue layer located immediately above and below the core (R) and (T) optionally a receiving layer located between (P) and (R).

The percentages are to be understood such that at 10-100% by weight, 11, 12, 13, 14, 15, 16, 17, 18, 19 to 100% by weight of the hydrogel-forming polymer according to the invention and all the intermediate% Data (for example 12.2%) are possible and correspondingly hydrophilic fiber material from 0 to 89, 88, 87, 86, 85, 83, 82, 81% by weight and percentages in between (for example 87.8%) are possible are. If there are other materials in the core, the percentages of polymer and fiber decrease accordingly. The analog applies to the preferred areas, such as for 81, 82, 83, 84, 85, 86, 87, 88, 89% by weight for the hydrogel-forming polymer according to the invention and correspondingly 19, 18, 17, 16, 15, 14, 13, 12, 11% by weight can be properly preferred -% of the fiber material is present. Thus, in the preferred range 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 to 100% by weight of hydrogel-forming polymer according to the invention, in the more preferred range 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 to 100 wt .-% hydrogel-forming polymer according to the invention, in the even more preferred range 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 to 100 wt % hydrogel-forming polymer according to the invention, in the more preferred range 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 to 100% by weight hydrogel-forming polymer according to the invention, in the particularly preferred range 60, 61, 62, 63, 64, 65, 66, 67, 68, 69 to 100% by weight of hydrogel-forming polymer according to the invention, in the particularly preferred range 70, 71, 71, 72, 73, 74, 75, 76, 77 , 78, 79 to 100% by weight of hydrogel-forming polymer according to the invention and in the most preferred range 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% by weight of hydrogel-forming according to the invention Polymer present.

Hygiene articles mean both incontinence pads and incontinence pants for adults and diapers for babies.

The liquid-permeable cover (P) is the layer that has direct skin contact. The material for this consists of conventional synthetic or semi-synthetic fibers or films of polyester, polyolefins, rayon or natural fibers such as cotton. In the case of non-woven materials, the fibers are generally to be connected using binders such as polyacrylates. Preferred materials are polyester, rayon and their blends, polyethylene and polypropylene. Examples of liquid-permeable layers are described in WO 99/57355 A1, EP 102 388 3 A2.

The liquid-impermeable layer (Q) usually consists of a film made of polyethylene or polypropylene.

In addition to the hydrogel-forming polymer according to the invention, the core (R) contains hydrophilic fiber material. Hydrophilic is understood to mean that aqueous liquids are quickly distributed over the fiber. The fiber material is usually cellulose, modified cellulose, rayon, polyester such as polyethylene terephthalate. Cellulose fibers such as cellulose are particularly preferred. The fibers generally have a diameter of 1 to 200 μm, preferably 10 to 100 μm. In addition, the fibers have a minimum length of 1 mm. The structure and shape of diapers is generally known and is described, for example, in WO 95/26 209 p. 66 line 34 to p. 69 line 11, DE 196 04 601 A1, EP-A-0 316 518 and EP-A-0 202 127. In general, diapers and other hygiene articles are also described in WO 00/65084, in particular on pages 6-15, WO 00/65348, in particular on pages 4 - 17, WO 00/35502, in particular pages 3-9, DE 19737434, WO 98/8439 described. Hygiene articles for feminine hygiene are described in the following references. The hydrogel-forming polymers absorbing aqueous liquids according to the invention can be used there. References for feminine hygiene: WO 95/24173: Absorption Articie for Controlling Odor, WO 91/11977: Body Fluid Odor Control, EP 389023: Absorbent Sanitary Articles, WO 94/25077: Odor Control Material, WO 97/01317: Absorbent Hygienic Articie, WO 99/18905, EP 8342 ^~ 97, US 5,762,644, US 5,895,381, WO 98/57609, WO 2000/065083, WO 2000/069485, WO 2000/069484, WO 2000/069481, US 6,123,693, EP 1104666, WO 2001/024755 , WO 2001/000115, EP 105373, WO 2001/041692, EP 1074233. Tampons are described in the following documents: WO 98/48753, WO 98/41179, WO 97/09022, WO

98/46182, WO 98/46181, WO 2001/043679, WO 2001/043680, WO 2000/061052, EP 1108408, WO 2001/033962, DE 200020662, WO 2001/001910, WO 2001/001908, WO 2001/001909, WO 2001/001906, WO 2001/001905, WO 2001/24729. Incontinence articles are described in the following writings: Disposable Absorbent Articie for Incontinent Individuais: EP 311344 Description pp. 3 - 9; Disposable Absorbent Articie: EP 850623; Absorbent Articie: WO 95/26207; Absorbent Articie: EP 894502; Dry Laid Fibrous Structure: EP 850 616; WO 98/22063; WO 97/49365; EP 903134; EP 887060; EP 887059; EP 887058; EP 887057; EP 887056; EP 931530; WO 99/25284; WO 98/48753. Feminine hygiene and incontinence articles are described in the following documents: Catamenial Device: WO 93/22998 Description pp. 26 - 33; Absorbent Members for Body Fluids: WO 95/26209 description pp. 36-69; Disposable Absorbent Articie: WO 98/20916 Description pp. 13 - 24; Improved Composite Absorbent Structures: EP 306262 Description pp. 3 - 14; Body Waste Absorbent Articie: WO 99/45973. These references and the references there are hereby expressly included in the disclosure of the invention.

The hydrogel-forming polymers according to the invention are outstandingly suitable as absorbents for water and aqueous liquids, so that they can advantageously be used as water-retaining agents in agricultural horticulture, as filtration aids and particularly as absorbent components in hygiene articles such as diapers, tampons or sanitary napkins.

Storage and fixation of the highly swellable hydrogels according to the invention In addition to the highly swellable hydrogels described above, the absorbent composition according to the present invention contains compositions which contain the highly swellable hydrogels or to which they are fixed. Any composition is suitable that can absorb the highly swellable hydrogels and that can also be integrated into the absorption layer. A large number of such compositions are already known and have been described in detail in the literature. A composition for incorporating the highly swellable hydrogels can e.g. B. be a fiber matrix, which consists of a cellulose fiber mixture (airlaid web, wet laid web) or synthetic polymer fibers (meltblown web, spunbonded web), or consists of a mixed fiber structure made of cellulose fibers and synthetic fibers. Possible fiber materials are described in detail in the following chapter. The process of an air-laid web is described, for example, in WO 98/28478. Furthermore, open-pore foams or the like can be used for the installation of highly swellable hydrogels.

Alternatively, such a composition can be created by fusing two individual layers, one or better a plurality of chambers being formed which contain the highly swellable hydrogels. Such a chamber system is described in detail in EP 0615736 A1 p. 7 line 26 ff.

In this case, at least one of the two layers should be permeable to water. The second layer can be either water permeable or water impermeable. Tissues or other fabrics, closed or open-cell foams, perforated films, elastomers or fabrics made of fiber material can be used as layer material. If the absorbent composition consists of a composition of layers, the layer material should have a pore structure whose pore dimensions are small enough to retain the highly swellable hydrogel particles. The above examples for the composition of the absorbent composition also include laminates of at least two layers, between which the highly swellable hydrogels are installed and fixed.

In general, there is the possibility of fixing hydrogel particles within the absorbent gore to improve the so-called dry and wet integrity. Dry and wet integrity means the ability to incorporate highly swellable hydrogels into the absorbent composition in such a way that they can withstand external forces both in the wet and in the dry state and there is no displacement or leakage of highly swellable polymer. The effects of force are to be understood above all as mechanical loads, such as those that occur in the course of movement when the hygiene article is worn, or the weight load under which the hygiene article is primarily exposed to incontinence. There are a variety of options for fixing ten, which are known to the expert. Examples such as fixation by heat treatment, addition of adhesives, thermoplastics, binder materials are listed in WO 95/26209 page 37 line 36 to page 41 line 14. Said passage is therefore part of this invention. Methods for increasing the wet strength can also be found in WO 2000/36216 A1.

Furthermore, the absorbent composition can consist of a carrier material, such as. B. consist of a polymer film on which the highly swellable hydrogel particles are fixed. The fixation can be done on one or both sides. The carrier material can be water-permeable or water-impermeable.

In the above compositions of the absorbent composition, the highly swellable hydrogels are used in a weight fraction of 10 to 100% by weight, preferably 20-100% by weight, more preferably 30-100% by weight, even more preferably 40-100% by weight, more preferably 50-100% by weight, particularly preferably 60-100% by weight, particularly preferably 70-100% by weight, extremely preferably 80-100% by weight and most preferably 90-100% by weight based on the total weight of the composition and the highly swellable hydrogels.

Fibrous materials of the absorbent composition

The structure of the present absorbent composition according to the invention is based on a variety of fiber materials which are used as fiber networks or matrices. Included in the present invention are both fibers of natural origin (modified or unmodified) and synthetic fibers.

Patent WO 95/26209 p. 28 line 9 to p. 36 line 8 gives a detailed overview of examples of fibers which can be used in the present invention. Said passage is therefore part of this invention.

Examples of cellulose fibers include those commonly used in absorption products such as fleece pulp and cotton-type pulp. The materials (softwood or hardwood), manufacturing processes such as chemical pulp, semi-chemical pulp, chemothermal mechanical pulp (CTMP) and bleaching processes are not particularly limited. For example, natural cellulose fibers such as cotton, flax, silk, wool, jute, ethyl cellulose and cellulose acetate are used.

Suitable synthetic fibers are made from polyvinyl chloride, polyvinyl fluoride, polytetrafluoroethylene, polyvinylidene chloride, polyacrylic compounds such as ORLON ^® , Polyvinyl acetate, polyethyl vinyl acetate, soluble or insoluble polyvinyl alcohol. Examples of synthetic fibers include thermoplastic polyolefin fibers such as polyethylene fibers (PULPEX ^®), polypropylene fibers and polyethylene-polypropylene bicomponent fibers, polyester fibers such as polyethylene terephthalate fibers (DAC RON ^® or KODEL ^®), copolyesters, Polyvinylaeetat, polyethylvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyacrylics , Polyamides, copolyamides, polystyrene and copolymers of the abovementioned polymers, and also two-component fibers made of polyethylene terephthalate-polyethylene-isophthalate copolymer, polyvinyl vinyl acetate, polypropylene, polyethylene / polyester, polypropylene / polyester, copolyester / polyester, polyamide fibers (nylon ), Polyurethane fibers, polystyrene fibers and polyacrylonitrile fibers. Polyolefin fibers, polyester fibers and their two-component fibers are preferred. Also preferred are thermally adhesive two-component fibers made of polyolefin of the shell-core type and side-by-side type because of their excellent dimensional stability after the liquid absorption.

The synthetic fibers mentioned are preferably used in combination with thermoplastic fibers. During heat treatment, the latter partly migrate into the matrix of the existing fiber material and thus represent connection points and renewed stiffening elements when cooling. In addition, the addition of thermoplastic fibers means an expansion of the existing pore dimensions after the heat treatment has taken place. In this way, it is possible to continuously increase the proportion of thermoplastic fibers towards the cover sheet by continuously metering in thermoplastic fibers during the formation of the absorption layer, which results in an equally continuous increase in pore sizes. Thermoplastic fibers can be formed from a large number of thermoplastic polymers which have a melting point of less than 190 ° C., preferably between 75 ° C. and 175 ° C. At these temperatures, no damage to the cellulose fibers is yet to be expected.

The lengths and diameters of the synthetic fibers described above are not particularly limited, and in general, any fiber with a length of 1 to 200 mm and a diameter of 0.1 to 100 denier (grams per 9,000 meters) can be preferably used. Preferred thermoplastic fibers have a length of 3 to 50 mm, particularly preferred a length of 6 to 12 mm. The preferred diameter of the thermoplastic fiber is between 1, 4 and 10 decitex, particularly preferably between 1, 7 and 3.3 decitex (grams per 10,000 meters). The shape is not particularly limited, and examples include fabric-like, narrow cylinder-like, cut / split yarn-like, staple fiber-like and continuous fiber-like. The fibers in the absorbent composition of the invention can be hydrophilic, hydrophobic, or a combination of both. According to the definition by Robert F. Gould in the publication "Contact Angle, Wettability and Adhesion", American Chemical Society (1964), a fiber is said to be hydrophilic if the contact angle between the liquid and the fiber (or its surface) is less than 90 ° or if the liquid tends to spread spontaneously on the same surface. As a rule, both processes are coexistent. Conversely, a fiber is said to be hydrophobic if a contact angle of greater than 90 ° is formed and no spreading is observed.

Hydrophilic fiber material is preferably used. It is particularly preferred to use fiber material that is weakly hydrophilic on the body side and most hydrophilic in the region around the highly swellable hydrogels. In the manufacturing process, the use of layers of different hydrophilicity creates a gradient that channels the impinging liquid to the hydrogel, where the absorption ultimately takes place.

Suitable hydrophilic fibers for use in the absorbent composition according to the invention are, for example, cellulose fibers, modified cellulose fibers, rayon, polyester fibers such as, for. B. polyethylene terephthalate (DACRON ^® ), and hydrophilic nylon (HYDROFIL ^® ). Suitable hydrophilic fibers can also be obtained by hydrophilizing hydrophobic fibers, such as treating thermoplastic fibers obtained from polyolefins (such as polyethylene or polypropylene, polyamides, polystyrenes, polyurethanes, etc.) with surfactants or silica. However, cellulose fibers are preferred for reasons of cost and availability.

The highly swellable hydrogel particles are embedded in the fiber material described. This can be done in a variety of ways, e.g. B. builds up an absorption layer in the form of a matrix with the hydrogel material and the fibers, or by embedding highly swellable hydrogels in layers of fiber mixture, where they are ultimately fixed, whether by adhesive or lamination of the layers.

The liquid-absorbing and -distributing fiber matrix can consist of synthetic fiber or cellulose fiber or a mixture of synthetic fiber and cellulose fiber, the mixing ratio of (100 to 0) synthetic fiber: (0 to 100) cellulose fiber being able to vary. The cellulose fibers used can also be chemically stiffened to increase the dimensional stability of the hygiene article. The chemical stiffening of cellulose fibers can be achieved in different ways. On the one hand, fiber stiffening can be achieved by adding suitable coatings to the fiber material. Such additives include for example polyamide-epichlorohydrin coatings (Kymene ^® 557H, Hercoles, Inc. Wil- Remington Delaware, USA), polyacrylamide coatings (described in US Patent No. 3,556,932 or as a product of Parez ^® 631 NC trademark, American Cyanamid Co. , Stamford, CT, USA), melamine-formaldehyde coatings and polyethyleneimine coatings.

The chemical stiffening of cellulose fibers can also be carried out by chemical reaction. So z. B. the addition of suitable crosslinking substances bring about a crosslinking that takes place within the fiber. Suitable crosslinking substances are typical substances that are used to crosslink monomers. Included, but not limited to, are C ₂ -C ₈ dialdehydes, C ₂ -C ₈ monoaldehyde with acid functionality, and in particular C ₂ -C ₉ polycarboxylic acids. Specific substances from this series are, for example, glutaraldehyde, glyoxal, glyoxylic acid, formaldehyde and citric acid. These substances react with at least 2 hydroxyl groups within a single cellulose chain or between two adjacent cellulose chains within a single cellulose fiber. The crosslinking causes the fibers to be stiffened, which increases with this treatment

Get dimensional stability. In addition to their hydrophilic character, these fibers have uniform combinations of stiffening and elasticity. This physical property makes it possible to maintain the capillary structure even with simultaneous contact with liquid and compression forces and to prevent premature collapse.

Chemically crosslinked cellulose fibers are known and are described in WO 91/11162, U.S. Patent 3,224,926, U.S. Patent 3,440,135, U.S. U.S. Patent 3,932,209 Patent 4,035,147, U.S. U.S. Patent 4,822,453, U.S. U.S. Patent 4,888,093, U.S. U.S. Patent 4,898,642 and U.S. Patent 5,137,537. The chemical crosslinking stiffens the fiber material, which is ultimately reflected in the improved dimensional stability of the entire hygiene article. The individual layers are by methods known to those skilled in the art, such as. B. fused together by heat treatment, adding hot melt adhesives, latex binders, etc.

Manufacturing process of the absorbent composition

The absorbent composition is composed of compositions which contain highly swellable hydrogels and the highly swellable hydrogels which are present in or fixed to said compositions. Examples of processes with which an absorbent composition is obtained, which for example consist of a carrier material to which hydrogels which are highly swellable on one or both sides are fixed, are known and included by the invention, but not limited thereto.

Examples of processes with which an absorbent composition is obtained which consists, for example, of highly swellable hydrogels (c) embedded in a fiber material mixture of synthetic fibers (a) and cellulose fibers (b), the mixing ratio of (100 to 0) synthetic fibers : (0 to 100) cellulose fiber may vary include (1) a process in which (a), (b) and (c) are mixed simultaneously, (2) a process in which a mixture of (a) and ( b) is mixed into (c), (3) a process in which a mixture of (b) and (c) is mixed with (a), (4) a process in which a mixture of (a) and ( c) is mixed into (b), (5) a process in which (b) and (c) are mixed and (a) is metered in continuously, (6) a process in which (a) and (c) are mixed and (b) is metered in continuously, and (7) a process in which (b) and (c) are mixed separately into (a). Of these examples, methods (1) and (5) are preferred. The device used in this method is not particularly limited, and a conventional device known to those skilled in the art can be used.

The correspondingly produced absorbent composition can optionally be subjected to a heat treatment, so that an absorption layer with excellent dimensional stability in the moist state results. The heat treatment process is not particularly limited. Examples include heat treatment by supplying hot air or infrared radiation. The temperature during the heat treatment is in the range from 60 ° C. to 230 ° C., preferably between 100 ° C. and 200 ° C., particularly preferably between 100 ° C. and 180 ° C.

The duration of the heat treatment depends on the type of synthetic fiber, its quantity and the speed at which the hygiene article is manufactured. Generally, the duration of the heat treatment is between 0.5 seconds to 3 minutes, preferably 1 second to 1 minute.

The absorbent composition is generally provided, for example, with a liquid pervious top layer and a liquid impervious bottom layer. Leg cuffs and adhesive tapes are also attached, thus completing the hygiene article. The materials and types of the permeable top layer and impermeable bottom layer, as well as the leg cuffs and adhesive tapes are known to the person skilled in the art and are not particularly restricted. Examples of this can be found in WO 95/26 209.

The advantage of the present invention resides in the fact that the esters F which can be used as crosslinking agents do not have to be purified after their preparation, in particular that the (meth) acrylic acid, preferably acrylic acid, does not have to be separated off since these are generally a monomer for the preparation of the hydrogels represents.

Experimental part

Unless otherwise stated, the ppm and percentages used in this document relate to percentages by weight and ppm.

The method according to the invention is explained in more detail by the following example.

Examples

Manufacture of acrylic raw esters as superabsorbent crosslinkers

The preparation of the Superabsorbervemetzer carried out in the examples by esterification ^• tion of alkoxylated trimethylolpropane with acrylic acid wherein the removal of the water in an azeotropic distillation is carried out. Esterification catalyst in the examples is sulfuric acid. The reactants are presented together with a stabilizer mixture consisting of hydroquinone monomethyl ether, triphenyl phosphite and hypophosphorous acid in the examples in methylcyclohexane as an entrainer. The reaction mixture is then heated to about 98 ° C until the azeotropic distillation begins. During the azeotropic distillation, the temperature in the reaction mixture rises. The amount of water separated off is determined. The distillation is stopped when at least the theoretical amount of water has been removed.

The entrainer is then removed in a vacuum distillation. The product is cooled and used as a crosslinker in the production of superabsorbents.

The conversion and yield of the reaction are not exactly determined, since the water separated off in the esterification also contains acrylic acid and acrylic acid is also removed during the vacuum distillation of the entrainer. The crude ester also contains free acrylic acid, which is titrated together with the catalyst (acid number).

Unless otherwise stated, all quantities are parts by weight. Preparation of the ester

Acid numbers were acc. DIN EN 3682 determined.

Example 1 Preparation of the Alkoxylated Trimethylolpropane

77 g of trimethylolpropane are placed in an autoclave with 0.5 g of KOH, 45% in water and dewatered together at 80 ° C. and reduced pressure (approx. 20 mbar). Then 167 g of propylene oxide are added at 120 to 130 ° C. and allowed to react at this temperature under elevated pressure. The reaction is complete when no change in pressure is observed. The mixture is then stirred at about 120 ° C for 30 minutes. 379 g of ethylene oxide are then metered in at 145 to 155 ° C. over a prolonged period at elevated pressure and are also allowed to react. After purging with inert gas and cooling to 60 ° C., the catalyst is separated off by adding sodium pyrophosphate and subsequent filtration.

Example 2 Preparation of the acrylic acid ester

887 parts of approximately 5-fold propoxylated and 15-fold ethoxylated trimethylolpropane (according to Example 1) are esterified with 216 parts of acrylic acid and 5 parts of sulfuric acid in 345 parts of methylcyclohexane. 3 parts of hydroquinone monomethyl ether, 1 part of triphenyl phosphite and 1 part of hypophosphorous acid are added as auxiliaries. 44 parts of water are separated off before the entrainer is removed by vacuum distillation. The product is cleaned using K300 filters. The acid number is determined. The viscosity is adjusted by adding 96 parts of acrylic acid. The viscosity of the almost colorless product (iodine color number 0-1) is approx. 320 mPas.

Production of hydrogels

To determine the quality of the surface crosslinking, the dried hydrogel can be examined using the following test methods.

test methods

a) Centrifuge Retention Capacity (CRC Centrifuge Retention Capacity)

This method determines the free swellability of the hydrogel in the tea bag. To determine the CRC, 0.2000 * 0.0050 g of dried hydrogel (grain fraction 106 - 850 μm) are weighed into a 60 x 85 mm tea bag, which is then sealed. The tea bag is left in an excess of 0.9 for 30 minutes % By weight saline solution (at least 0.831 saline solution / 1 g polymer powder). The tea bag is then centrifuged at 250 g for 3 minutes. The amount of liquid is determined by weighing the centrifuged tea bag.

b) Absorption under pressure (AUL Absorbency Under Load) (0.7 psi)

The measuring cell for determining the AUL 0.7 psi is a plexiglass cylinder with an inner diameter of 60 mm and a height of 50 mm, which has a glued-on stainless steel sieve bottom with a mesh size of 36 μm on the underside. The measuring cell also includes a plastic plate with a diameter of 59 mm and a weight, which can be placed together with the plastic plate in the measuring cell. The weight of the plastic plate and the total weight are 1345 g. To carry out the determination of the AUL 0.7 psi, the weight of the empty plexiglass cylinder and the plastic plate is determined and noted as W ₀ . Then 0.900 ^* 0.005 g of hydrogel-forming polymer (particle size distribution 150 - 800 μm) are weighed into the plexiglass cylinder and distributed as evenly as possible on the stainless steel sieve plate. Then the plastic plate is carefully placed in the plexiglass cylinder and the entire unit is weighed; the weight is noted as W _a . Now the weight is placed on the plastic plate in the plexiglass cylinder. In the middle of the Petri dish with a diameter of 200 mm and a height of 30 mm, a ceramic filter plate with a diameter of 120 mm and a porosity of 0 is placed and 0.9% by weight sodium chloride solution is filled in so that the liquid surface with the filter plate surface closes without the surface of the filter plate being wetted. Then a round filter paper with a diameter of 90 mm and a pore size <20 μm (S&S 589 black tape from Schleicher & Schüll) is placed on the ceramic plate. The plexiglass cylinder containing the hydrogel-forming polymer is now placed with the plastic plate and weight on the filter paper and left there for 60 minutes. After this time, the complete unit is removed from the Petri dish from the filter paper and then the weight is removed from the Plexiglas cylinder. The plexiglass cylinder containing swollen hydrogel is weighed out together with the plastic plate and the weight is noted as W _b .

The absorption under pressure (AUL) is calculated as follows:

AUL 0.7 psi [g / g] = [W _b -W _a ] / [W _a -W ₀ ]

The AUL 0.5psi is measured analogously with lower pressure. c) The fraction extractable after 16 h (Extract. 16 h) was determined analogously as described in EP-A1 811 636, p. 13, lines 1 to 19.

d) Method for determining residual levels of crosslinking agents in hydrogels

To determine the content of unreacted residual crosslinking agent, this residual crosslinking agent is first extracted from the dried hydrogel by means of a double extraction. For this, 0.400 g of dry hydrogel and 40 g of 0.9% by weight saline solution are weighed into a closable and centrifugable ampoule. To do this, add 8 ml dichloromethane, close the ampoule and then shake for 60 min. The ampoule is then immediately centrifuged at 1500 rpm for 5 minutes, so that the organic phase is clearly separated from the aqueous phase.

50 μl of monoethylene glycol is weighed into a second ampoule, and about 5 - 6 ml of the dichloromethane extract is added, the weight of the extract is recorded to the nearest 0.001 g. The dichloromethane is then evaporated at 50-55 ° C. and the residue is taken up in 2 ml of a methanol / water mixture (50 parts by volume each) after cooling. It is shaken for 10 min and then filtered through a PTFE 0.45 μm filter.

The sample obtained in this way is separated by means of liquid phase chromatography and analyzed by mass spectrometry. The quantification is carried out against a dilution series of the same crosslinking agent used.

A Zorbax Eclipse XDB C-8 (150 x 4.6 mm - 5 μm) is used as the chromatography column and a Zorbax Eclipse XDB C-8 (12.5 x 4.6 mm - 5 μm) as the precolumn. A methanol / water mixture (75/25) is used as the eluent.

The gradient course is as follows:

Flow is 1 ml / min at 1600 psi pressure.

The injection volume is 20 μl.

Typical analysis time is 14 minutes for the samples. The detection is carried out by mass spectrometry, for example in the range 800 - 1300 m / z (fill scan, positive). The device works with APCI (Atmospheric Pressure Chemical Ionization, positive ionization). For optimization, the capillary temperature is set to 180 ° C, the APCI vaporizer temperature to 450 ° C, source current to 5.0 μA, and the gas flow to 80 ml / min.

The individual settings must be made specifically for each networker. For this purpose, the characteristic peaks that are later relevant for the evaluation are determined using a suitable calibration solution of the crosslinking agent. As a rule, the main peak is selected.

The calculation of the residual crosslinker concentration is then as follows:

CONCp _r0 be = A _sample x CONCstd x VF / A _st d

CONCpro _b e: is the desired crosslinker concentration in the dry hydrogel in mg / kg

CONCs _td : is the desired crosslinker concentration in the calibration solution in mg / kg

Aprobe: is the peak area of the extract sample of the dried hydrogel

A _Std : is the peak area of the calibration solution

VF is the dilution factor:

VF = M _DCM X Msolv / (Mp _r ob _e XM _Ex t _rao t)

MDCM is a weight of dichloromethane for extraction

Mpro e is a sample of dry hydrogel

Msoivist weight of methanol-water mixture + monoethylene glycol

Mεxtract is a weight of dichloromethane extract

Calibration (several points, for example in the range 0 - 50 ppm) must be used to ensure that the determination is carried out in the linear range. e) saponification index VSI

The crushed gel is then processed in two different ways:

Refurbishment method 1:

The comminuted gel is homogeneously distributed in a thin layer on sheets with sieve trays and then dried in vacuo at 80 ^° C. for 24 h. This drying is very gentle on the product and is therefore the optimal standard of comparison.

The dried hydrogel is then milled and the 300-600 micron sieve fraction is isolated.

Refurbishment method 2:

The crushed gel is first annealed in a sealed plastic bag at 90 ⁹ C for 24 h. Then it is distributed homogeneously in a thin layer on sheets with sieve trays and dried in vacuo at 80 ^° C. for 24 h. This drying simulates the drying conditions that occur in typical production plants, which usually limit the drying performance and throughput due to the associated decrease in quality.

The dried hydrogel is ground and the sieve fraction of 300-600 microns is isolated.

The hydrogels obtained by the two work-up methods are characterized by determining the teabag capacity (CRC) and the content of extractables after 16 h and in terms of the content of unreacted residual crosslinking agent. In addition, the moisture content is determined and if this is over 1% by weight, it is taken into account mathematically when determining these properties. The moisture content is typically about 5% by weight.

The saponification index (VSI) of the crosslinking agent in the gel is then determined from the measured values, which is calculated as follows:

VSI = 0.5 x (CRC ₂ - CRCi) + 0.5 x (extractable ₂ - extractable _! )

The subscripts here indicate the processing method 1 or 2. The saponification index is therefore greater, the more the teabag capacity increases due to the drying process and the more the extractables increase. Both contributions are weighted equally.

In general, it is advantageous to use crosslinkers whose saponification index is as small as possible. The ideal networker has a VSI of zero. The use of such crosslinkers makes it possible to increase the performance of the operational dryer without sacrificing quality up to the technically achievable maximum. The reason for this is that the crosslinking set during the polymerization - and thus the properties of the end product - no longer changes due to hydrolysis during drying.

Example 3 Production of superabsorbent using the acrylic acid ester from Example 2 and other internal crosslinkers Example a

305 g of acrylic acid and 3204 g of a 37.3% by weight sodium acrylate solution are dissolved in 1465 g of distilled water in an acid-resistant plastic tub. For this purpose, 12.2 g of TMP-15EO triacrylate as a crosslinking agent as well as 0.61 g of V-50 (2,2'-azobisamidinopropane dihydrochloride) and 3.05 g of sodium persulfate as initiators are added. The initiators are advantageously pre-dissolved in part of the preparation water. The mixture is stirred well for a few minutes.

Then nitrogen gas is bubbled through the solution covered with plastic film in the tub for about 30 minutes in order to remove the oxygen and distribute the crosslinker homogeneously. Finally, 0.244 g of hydrogen peroxide dissolved in 5 g of water and 0.244 g of ascorbic acid dissolved in 5 g of water are added. The starting temperature at the start of the reaction should be 11 - 13 ^S C. The layer thickness of the reaction solution is approximately 6 cm. The reaction starts after a few minutes, the mixture is allowed to react adiabatically and the thermally insulated tub is left to stand for no longer than 30 minutes before the gel is worked up.

To work up the gel, the gel block is first broken into pieces and then crushed by a meat grinder with a 6 mm perforated disc.

The crushed gel is then processed in two different ways:.

Refurbishment method 1:

The comminuted gel is homogeneously distributed in a thin layer on sheets with sieve trays and then dried in vacuo at 80 ^° C. for 24 h. This drying is very gentle on the product and is therefore the optimal standard of comparison. The dried hydrogel is then milled and the 300-600 micron sieve fraction is isolated.

Refurbishment method 2:

The crushed gel is first annealed in a sealed plastic bag at 90 ⁹ C for 24 h. Then it is distributed homogeneously in a thin layer on sheets with sieve trays and dried in vacuo at 80 ^° C. for 24 h. This drying simulates the drying conditions that occur in typical production plants, which usually limit the drying performance and throughput due to the associated decrease in quality. The dried hydrogel is ground and the sieve fraction of 300-600 microns is isolated.

The following further examples are produced analogously to example a:

Tab. 1

The properties of these hydrogels are summarized in Tab. 2:

Extracting crosslinker Extracting crosslinker

E.g. CRC 1 CRC 2 VSI 16h 1 residual salary 1 16h 2 residual salary 2

[g / g] [wt%] [ppm] [g / g] [wt%] [ppm] a TMP-3EO 36.6 4.4 857 70.6 44.2 1302 36.9 b TMP- 15EO 29.7 2.8 51 43.1 12.6 20 11.6 c TMP-20EO 30.3 2.9 29 41, 1 13.1 14 10.5

TMP 5PO

29.7 2.7 18 38.7 11, 0 <10 8.7

15EO

Example 4a: Preparation of a superabsorbent using the acrylic acid ester from Example 2

388 g of deionized water, 173.5 g of acrylic acid, 2033.2 g of a 37.3% by weight sodium acrylate solution (100 mol% neutralized) and 5. Are placed in a Lödige ploughshare mixer type VT 5R-MK (5 l volume) , 90 g of the crosslinker trimethylolpropane-5 PO-15 EO-triacrylate prepared in Example 2 and inerted for 20 minutes while bubbling with nitrogen. Then start by adding (dilute aqueous solutions) of 2.112 g sodium persulfate, 0.045 g ascorbic acid and 0.126 g hydrogen peroxide at about 23 ° C. After the start, the temperature of the heating jacket is adjusted to the reaction temperature in the reactor by means of control. The crumbly gel ultimately obtained is then dried at 160 ° C. for about 3 hours in a forced-air drying cabinet. It is then ground and sieved to 300-850 micrometers. The hydrogel obtained is then postcrosslinked.

Example 4b: Carried out analogously to example 4a, only the amount of crosslinker used is increased to 12 g.

Example 5a (Comparative Example): The procedure is completely analogous to Example 4a, but the crosslinker trimethylolpropane-15 EO-5 PO triacrylate is used. The gel obtained is lumpy and must be minced with a meat grinder before drying.

Example 5b (comparative example): Carried out analogously to example 5a, only the amount of crosslinker used is increased to 12 g.

postcrosslinking:

The dry base polymer powder from Examples 4 + 5 is based on a solution of 0.10% by weight of ethylene glycol diglycidyl ether (Nagase, Japan), 3.43% by weight of water and 1.47% by weight of 1,2-propanediol polymer used - sprayed homogeneously with stirring.

The moist powder is then heated in a drying cabinet at 150 ° C. for 60 minutes. Then sieve again at 850 micrometers to remove agglomerates. The properties of this post-crosslinked polymer are determined.

The properties of the post-crosslinked polymers from Examples 4 and 5 and further variants are summarized in Table 3:

Only the crosslinking agent used in Examples 4a and 4b clearly leads to product properties which are typical of modern superabsorbents.

In addition, the crosslinker used in FIGS. 5a and 5b only leads to very tough and poorly processable gels, which are difficult to produce in the kneader.

Claims

claims

1. Ester F of formula I.

with EO means O-CH2-CH2-

PO independently of one another means O-CH2-CH (CH3) - or O- CH (CH3) -CH2-

n1, n2, n3 independently of one another are 4, 5 or 6,

n1 + n2 + n3 is 14, 15 or 16

m1, m2, m3 independently mean 1, 2 or 3,

m1 + m2 + m3 is 4, 5 or 6.

R1, R2, R3 independently of one another H or CH3.

2. Ester F according to claim 1, wherein n1 + n2 + n3 is 15.

3. Ester F according to one of claims 1 or 2, wherein n1 = n2 = n3 = 5.

4. Ester F according to any one of claims 1 to 3, wherein m1 + m2 + m3 is 5.

5. Ester F according to any one of claims 1 to 4, wherein m1 = m2 = 2 and m3 = 1.

6. Ester F according to any one of claims 1 to 5, wherein R1, R2 and R3 are identical, preferably H.

7. A process for the preparation of an ester F according to any one of claims 1 to 6 of alkoxylated trimethylolpropane of the formula II

where EO, PO, n1, n2, n3, m1, m2, m3 have the meaning as in one of claims 1 to 6, with (meth) acrylic acid, comprising the steps

a) reaction of alkoxylated trimethylolpropane with (meth) acrylic acid in the presence of at least one esterification catalyst C and at least one polymerization inhibitor D and optionally one with

Water forming an azeotrope with the formation of an ester F, b) optionally removing at least part of the water formed in a) from the reaction mixture, where b) can take place during and / or after a), f) optionally neutralizing the reaction mixture, h ) If a solvent E was used, remove it if necessary

Solvent by distillation and / or i) stripping with a gas which is inert under the reaction conditions.

8. The method according to claim 7, characterized in that

the molar excess (meth) acrylic acid to the alkoxylated trimethylolpropane is at least 3.15: 1 and - the optionally neutralized (meth) acrylic acid contained in the reaction mixture obtained after the last step essentially remains in the reaction mixture.

9. The method according to any one of claims 7 or 8, characterized in that the (meth) acrylic acid is separated from the reaction mixture obtained after the last step, containing ester F to not more than 75% by weight.

10. The method according to any one of claims 7 to 9, characterized in that the ester mixture containing reaction F obtained after the last step has an acid number acc. DIN EN 3682 of at least 25 mg KOH / g.

11. The method according to any one of claims 7 to 10, characterized in that the reaction mixture containing ester F obtained after the last step has a (meth) acrylic acid content of at least 0.5% by weight.

12. The method according to any one of claims 7 to 11, characterized in that in the reaction a) the molar ratio of (meth) acrylic acid to the alkoxylated trimethylolpropane is at least 15: 1.

13. A method of making a cross-linked hydrogel comprising the steps

k) polymerizing an ester F according to one of claims 1 to 6 with (meth) acrylic acid, with optionally additional monoethylenically unsaturated compounds N, and optionally with at least one further copolymerizable hydrophilic monomer M in the presence of at least one radical initiator K and optionally at least one graft base L

I) optionally post-crosslinking the reaction mixture obtained from k), m) drying the reaction mixture obtained from k) or I) and n) optionally grinding and / or sieving the mixture obtained from k), I) or m)

Reaction mixture.

14. A method for producing a crosslinked hydrogel, comprising steps a) to i) according to one of claims 7 to 12 and additionally

k) polymerizing the reaction mixture from one of steps a) to i), if it has been carried out, with optionally additional monoethylenically unsaturated compounds N, and optionally at least one further copolymerizable hydrophilic monomer M in the presence of at least one radical initiator K and optionally at least one graft base L, I) optionally post-crosslinking the reaction mixture obtained from k), m) drying the reaction mixture obtained from k) or I) and n) optionally grinding and / or sieving the reaction mixture obtained from k), I) or m).

15. Polymer obtainable by a process according to one of claims 13 or 14.

16. Crosslinked hydrogel containing at least one hydrophilic monomer M in polymerized form, crosslinked with an ester F according to one of claims 1 to 6.

17. Crosslinked hydrogel containing at least one hydrophilic monomer M in polymerized form, crosslinked with an ester F-containing reaction mixture, as can be obtained by a process of claims 7 to 11.

18. Use of a polymer according to any one of claims 15 to 17 in hygiene articles, packaging materials and in nonwovens.

19. Mixture of substances containing

0.1 to 40% by weight of at least one ester F according to one of the claims

1 to 5 and (meth) acrylic acid,

0.5 - 99.9% by weight of at least one hydrophilic monomer M, 0 - 10% by weight of at least one esterification catalyst C, 0 - 5% by weight of at least one polymerization inhibitor D and - 0 - 10% by weight of a solvent E, with the proviso that the sum is always 100% by weight.

20. A mixture of substances according to claim 19, additionally containing

- Diluent G ad 100% by weight.

21. Crosslinked hydrogel obtainable from a mixture of substances according to claim 19 or 20 I) optionally postcrosslinking of the reaction mixture obtained,

m) drying the reaction mixture obtained directly or obtained from I) and n) optionally grinding and / or sieving the reaction mixture obtained directly or obtained from I) or m).

22. Use of a reaction mixture obtainable according to one of claims 7 to 11 or a mixture of substances according to claim 19 or 20

as a radical crosslinker for water-absorbing hydrogels, - as a starting material for the production of polymer dispersions, as a starting material for the production of polyacrylates, as a raw material for coatings or as a cement additive.

23. Crosslinked hydrogel with a saponification index of less than 10, preferably less than 8.

24. Crosslinked hydrogel according to one of claims 15, 16, 17 or 21 with a saponification index less than 10, preferably less than 9.