CA2123377A1

CA2123377A1 - Polymer powder

Info

Publication number: CA2123377A1
Application number: CA002123377A
Authority: CA
Inventors: Wilhelm F. Beckerle; Manfred Schwartz; Bernhard Dotzauer; Maximilian Angel
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1993-05-21
Filing date: 1994-05-11
Publication date: 1994-11-22
Also published as: DE4317036A1; ATE151083T1; DE59402279D1; EP0630920B1; ES2099506T3; DK0630920T3; EP0630920A1

Abstract

Abstract of the Disclosure: Polymer powders comprise a polymer essentially composed of a predominant amount of methyl methacrylate and an .alpha.,.beta.-monoethylenically un-saturated carboxylic acid and are used as additives for cement-containing mineral building materials having binding properties.

Description

`- 2123377 O.Z. 0050/44058 Polymer powder The present invention relates to polymer powders whose polymer, in polymerized form, i8 composed of from 60 to 85% by weight of methyl methacrylate (monomer a), from 15 to 25% by weight of at least one ~ mono-ethylenically unsaturated carboxylic acid of 3 to 6 carbon atoms (monomer b) and from 0 to 15% by weight of other copolymerizable monomer~
(monomer c), with the proviso that the composition of the monomer~ a, b and c is chosen 80 that, according to the Fox relationship for a polymer composed of these monomers, a glass transition tempera-ture of from 70 to 150C results and the K value of the polymer, determined ~or the fully acidic form of the polymer in dimethylformamide at 23C
and at a polymer content of 0.1% by weight, is from 45 to 100 .
The present invention furthsrmore relatez to processes for the preparation of these polymer powders and their use, in dry or aqueous form, as additives for cement-containing mineral building materials ha~ing binding properties.
Mineral building materials having binding proper-ties include formulations which contain, as essential component~, min~ral binders, such a~ cement, lime or gypsum, and sands, gravels or crushed rocks Derving as additive~, or other fillers, for example pigments, and natural or sy~thetic fibers, and which, after mixing with water, ~olidify and harden (set) in the air and in some ca~es also under water.
In many cases, it i~ now desirable on the one hand for the mineral building material having binding properties and mixed in ready-to-use form to exhibit advantageou~ flow behavior, ie. a high flow limit (the flow limit is defin0d as the shear stress above which an . . - ~ : , , ~ ~
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': ~ : ~ ' , ' 21233~7 2 - o.Z. 0050/44058 engineering makerial behave3 like a liquid, ie. flows, whereas it behaves like a solid, ie. does not flow, under the action of 3hear ~tresses below the flow limit), and, under the action of shear ~tresses above the flow limit, very low flow resistance and a very low dynamic viscosity ~ and, on the other hand, for the set mineral building - material having binding properties to posisessi high ~ internal ~trength (flexural tensile strength and compres-,~ sive strength) and good adhesion to the substrate.
Mortars for repair purposes are an example of such requirement~. They should have a viscosity ~uitable for proce~sing when in the ready-to-use mixed ~tate but should not run off, ie. ~hould exhibit ~tability, im-mediately after application to the generally vertical repair site~ under the shear stre~s of their own weight.
Moreover, they should, in the set state, adhere well to the substrate to be improved and en~ure high mechanical ,~ 8 trength.
- Adheeive mortar~ for mounting ceramic tile~
con~titute a further example of the abovementioned requirements.
It is now generally known that the properties of "~ mineral building material~ having binding properties can `~ be modified by adding agueous polymer disper~ions (in aqueous or dried form). As a rule, however, this i~
accompanied by an increase in the time required for said mineral building material to reach its strength suitable for uEe.
It i~ an object of the present invention to j30 provide polymer powders which, when added (in dry or 'agueou~ form) to cement-containing mineral building -, ~ materials ha~ing binding propertie~, in a freshly mixed ~tate, impart advantageous flow behavior to ~aid building materials without sub~tantially in$1uencing the ~etting time before the strength suitable for ueie ii reached, and which at the same time improves the mechanical strength and the adhesion to the iubstrate.

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3 - O.Z. 0050/44058 We have found that this object is achieved by the polymer powders defined at the outset.
The ~ value i~ a relative visco~ity n~her which is determined similarly to DIN 53,726. It expre~es the flow rate of pure dimethylformamida (DMF) relative to the flow rate of DMF containing 0.1% by weight, based on the total weight, of polymer (in this ca3e in fully acidic form) and characterizes the average molecular weight of the polymer (cf. Cellulosechemie 13 (1932), 58-64, and Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 23, page~ 967-968). A high X value corresponds to a high average molecular weight.
According to Fox (T.G. Fox, Bull. Am. Phys. Soc.
(Ser. II) 1 (1956), 123), a good approximation for the glas~ transition temperature of copolymers i~
Xl X~ xn 2 -- + -- ~' ............. --Tg Tgl Tg2 Tg~
¦ where Xl, X2, .... , X~ are the mass fractions of ~he 20 monomer~ 1, 2, , n and Tgl, Tg2, , Tgn are the glass transition te~peratures of the particular poly~ers composed only of one of the monomers 1, 2, ... or n, in degrees Kelvin.
The gla~ transition temperature of these homo-polymers of the monomers a, b and c are known and arestated in, for example, J. Brandrup and E.~. Immergut, Polymer Handbook 1st ~d. J. Wiley, New York 1966 and 2nd Ed. J. Wiley, New York 1975. In particular, the glass transition temperature~ of the homopolymer~ of the i 30 monomers a and b appear in Ullmann's Encyclopedia of Industrial Chemistry, Verlag Chemie, Weinheim (1992), Vol. A21, Tab. 8, page 169. A gla~ transit~on tempera-ture of ~rom 90 to 130C is preferably calculated accord-ing to Fox or the monomer mixture~ to be polymerized according to the i~vention.
J. Appl. Polym. Sci. 11 (1970), 897-909 and 911-928 disclo~e~ a~ueous polymer di~persions which have been obtained by free radical amul~ion polymerization o~

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4 - O.Z. 0050/44058 monomer mixtures consisting of 80% by weight of methyl methacrylate and 20% by weight of methacrylic acid.
Since there is no mention of the presence of molecular - weight regulators, the R value of these emulsion polymers is from 40 to 60.
EP-A 262 326 and EP-A 332 067 relate to processes for the preparation of a redispersible polymer powder by drying a polymer di~per~ion containing a dispersed polymer having a dynamic freezing point T~ of from 60 to 150C and composed of from 20 to 60% by weight of acrylic and/or methacrylic acid and from 40 to 80% by weight of lower alkyl ester~ of acrylic and/or methacrylic acid or a mixture thereof with styrene and, if required, further comonomers, by special spray-drying methods. They recommend using the redispersed polymer powder for the production of coatings for drugs.
German Published Application DAS 1,669,903, BE-A 8 454 499, JP-A 54/43285, US-A 4 225 496, DE-A 32 20 384, DE-A 28 37 898, US-A 3 232 899 and JP-A 91/131 533 recommend aqucous polymer di~persions of emulsion poly-~ mero containing polymerized a,B-monoethylenically un-- saturated carboxylic acid~, a~ additives for cement-containing mineral building materials having binding -~ propertie~. However, owing to the fact that their glass transition t~parature is too low and/or their content of polymerized a,g-monoethylenically unsaturated carboxylic acids i~ too high or too low, ~hese emulsion polymers cannot completely satisfactorily achieve the object of this invention.
EP-A 537 411 reaommends the general use of polymer dispersion~ of polymers having a high Tg as additives for cement mortar. However, the property of a high glass transition temperature of the di~persed polymer is not sufficient for achieving the object of this invention.
DE-A 39 07 013 relates to aqueous polymer di~per-~ion~ whose emul~ion polymers aro compoeed of from 60 to ~'' ....
.
.'' ~' 2123~77 -~ - 5 - O.Z. 0050/44058 95~ by weight of methyl methacrylate, from 5 to 40% by weight of acrylic and/or methacrylic acid and, if required, other comonomers, with the proviso that their gla 8 tran~ition temperature i~ from 60 to 125C. These aqueou~ polymer disper~ions are recommended as binders for moldings. The range of from 5-103 to 5-106, prefer-ably from 2-105 to 2-106 is stated as the number average molecular weight of the emulsion polymers, and the preferred monomer composition i~ from 60 to 75% by weight of methyl methacrylate, from 5 to 30% by weight of methacrylic acid and from 0 to 10% by weight of acrylic acid.
According to the invention, acrylic and meth-acrylic acid are preferred a~ monomer~ b, the content of which i8 preferably from 20 to 25% by weight, based on the polymer. The total amount of the monomer~ b present in the polymer in polymerized form therefore preferably compri~es at least 50% by weight of at least one of these two monomers. The monomera b particularly advantageously 20 compri3e exclusively methacrylic acid.
Suitable monomers c are vinyl aromatic monomers, such a~ styrene or vinyltoluenes, nitrile~ of ~ mono-ethylenically unsaturated carboxylic acid~ of 3 to 6 carbon atom~, ester~, other than methyl methacrylate, of 25 ~,B-monoethylenically un~aturated carboxylic acid of 3 to 6 carbon atoms and alkanols of 1 to 12 carbon atom~, f unsub~tituted or substituted ~mides of ~,B-mono-ethylenically unsaturated carboxylic acid~ of 3 to 6 ~ carbon atoms, a~ well as monomers having a polar atruc-,` 30 ture, ~uch as acrylamidopropanesulfonic acid, vinyl-pyrrolidone, hydroxyethyl acrylate or quaternary vinyl-imidazole. The novel polymer pref~rably contains not more than 5% by weight of monomers c aa polymerized unit~
and i~ particularly advantageou~ly free of monomers c.
The novel polymer therefore particularly advan-tageously has the following compo~ition in polymerized form:

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.i 6 - O.Z. ~50/44058 from 70 to 85% by weight of methyl methacrylate and from 15 to 25% by weight of methacrylic acid.
The novel polymer powders can be prepared, for example, by polymerizing a monomer mixture of the corres-ponding composition in a conventional manner by themethod of free radical aqueous emulsion polymerization, ie. as a rule in the presence of dispersants and free radical polymerization initiators, and then drying the resulting aqueous polymer disper~ion. If the free radical aqueous emulsion polymerization is carried out in the absence of molecular weight regulator~, the resulting a~erage molecular weights with the use of conventional amounts of polymerization initiators, usually from 0.3 to 2% by weight, based on ths monomers to be polymerized, are customarily in the K value range according to the invention, which is preferably from 50 to 80. The poly~merization temperature i~ in general from room temperature to 100C, preferably from 60 to 90C.
Suitable free radical polymerization initiators are all tho~e which are capable of initiating a free radical aqueous ~mulsion polymerization in the ~tated t~mperature range. They may be both peroxide, for example alkali metal peroxydisulfates (in particular sodium psroxydi~ulfate), and azo co~pounds.
Suitable dispersant~ are both the protective colloids usually used for carrying out free radical aqueous emul~ion polymerizations and emulsi~ier~.
Examples of suitable protective colloids are polyvinyl alcohols, ~ellulose derivati~e~ and vinylpyrrolidon2-containing copolymer~. The agueous polymsr disper~ion~
are preferably prepared in the ab~ence of protectiv~ col-loids, ie. emulsifiers whose relati~e molecular weight~, in contrast to the protective colloids, are u~ually below 1,000 are preferably exclu~ively used as dispersants.
They are preferably anionic and/or nonionic. Convontion-al ~mulsifiers are, for example, ethoxylated mono-, di-and trialkylphenols (degree of ethoxylation: from 3 to .
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~ - 7 - O.Z. 0050/44058 50, alkyl radical: C4. to Cg), ethoxylated fatty alcohols (degree of ethoxylation: from 0 to 50, alkyl radical: C8 to C36) and alkali metal and ammonium salts of alkyl-sulfates (alkyl radical: C8 to Cl2), of sulfuric half-5 esters of ethoxylated alkylphenols (degree of ethoxyla-tion: from 3 to 50, alkyl radical: C~ to Cl5) and, par-ticularly preferably, ethoxylated alkanol~ (degree of ethoxylation: rom 0 to 30, alkyl radical: C10 to Cl~).
Based on the amount of monomers to be polymerized, 10 usually from 0.5 to 3% by weight are u~ed.
The emul~ion polymerization is preferably carried out in such a way that some of the dispersant~ (up to 10%
J by weight, ba~ed on the total amount thereof u~ed) and some of the polymerization initiator (up to 20% by 15 weight, ba~ed on the required total amount) are initially taken in the aqueou~ phase, the latter i~ heated to the polymerization temperature and the monomers to be poly-merized are then pre-emulaified in the aqueous pha~e while maintaining the polymerization temperature, and, 20 simultaneou~ly with this, an aqueoua ~olution of the remaining amount of polymerization initiator i8 continuou~ly added to the polymerization ~es~el (a~ a ~' rule in the cours~ of a few hours). After the end of the addition o monomer~ and initiator, the polymerization is usually continued for a further one to two hours while maintaining the polymerization temperature. Usually, the aqueou~ poly~er dieper~ion~ are produced with a solid~
content of from 10 to 30% by wsight. The conver~ion in the polymerization i8, a~ a rule, at lea~t 99.8~ by weight.
For example, the following methods can be used for converting the aqueou~ polymer disper~ions into , polymer powd~rs:
`` Spray drying of the aqueou~ polymer disper~io~ and freeze-drying of the aqueou~ polymer disperaion.
Anothar po~ible method for the preparation of the novel polymer powders comprioe~ polymerization of the .' ~
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8 - o.Z. 0050/44058 correRponding monomers by the free radical suspension polymerization method and sub~equent milling of the au~pension polymer.
Spray drying of the aqueous polymer di~persion proves particularly advantageou3, and conventional anticaking agentR and ~pray a~istants may be pre~ent.
However, it is particularly advantageous that the novel aqueous polymer disperuion~ are obtainable by the method of EP-A 262 326 or EP-A 332 067 even in the absence of spray assistantR, a~ polymers redispersible in an alka-line aqueous medium. The novel polymers can of couree contain, as polymerized units, monomsrs having acidic functions (for example the monomers b) in neutralized form ~for example with alkali metal hydroxide or ammonia or amines). The neutralization can be effected, for example, immediately before spray drying. Acidic mono-mers b and c can, however, al~o be used in the neutral-ized $orm for the polymerization.
It is particularly important that the novel polymer powder~ to be produced by the abovementioned preparation proces~ are redispersible in an alkaline aqueous medium.
Since the usual commercial form of mineral building materials having binding properties is the dry - 25 mixture thereof, which traditionally comprise~ the mineral binder and the additives, the novel powder form is of particular importance and permit~ the novel modifi-cation in the form of a commercial dry mixture which i8 immediately ready for u~e after mixing with water.
Xowever, the u~e form of the polymer-modified mineral building materials having binding propertiea can of course aleo be obtained by adding the novel polymer~
directly as aqueous polymer dispsrsion~ (thi~ may be both the aqueous starting polymer di~persion and the agueous di~persion of redi~persed polymer powder).
The novel polymer powder~ are particularly ~uitable a~ additive~ for aemsnt-containing minsral . . , :

9 - O.Z. 0050/44058 building materialA having binding properties. The mineral binder on which ~aid building materialA are baAed preferably comprises at least 50%, based on its weight, of cement. The novel effect is particularly advan-tageously displayed when mineral binders compri~ingfrom 70 to 100% by weight of cement and from 0 to 30% by weight of gypsum are used. The u3e, according to the invention, in mineral building materials having binding properties and containing exclusively cement as the mineral binder proves very particularly advantageou~. The effect according to the invention is sub~tantially dependent on the type of cement. Depending on reguirement~, it is possible to use, for example, blast furnace cement, bituminou~ cement, Portland cament, hydrophobic Portland cement, fast-setting cement, expanding cement or high-alumina cement, the u~e of Portland cement proving particularly advantageou~.
The novel polymer powders are particularly suitabl~ a~ additives for mortar~ for carrying out repairs. Their dry composition i8, a~ a rule, a~
follows:
from 20 to 60% by weight of mineral binder (preferably exclu~ively cement), from 1 to 20 (preferably from 2 to 10) % by weight, based on the amount of the mineral binder, of novel polymer and from 0 to 5% by weight of co~ventional assi~tanta (for example antifoams), the remaining amount comprising sand, usually having a particle ~ize of from 0.05 to 3 mm.
The use for~ i~ obtainable tharefrom by adding water until the desired consistency is obtained. The latter u~ually corre~pond~ to the water/mineral binder (cement) weight ratio of from 0.3 to 0.6.
At the visco~ity suitable for processing, mortar~
for carrying out repairs which have been mixzd in thi3 way prove to be stable and, after setting, exhibit high "

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` - 21~3377 10 - O.Z. 0050/44058 adhesive, flexural and compres~ive strength.
EXAMPLES
1. Preparation of aqueous disper~ions Da to De Da: A mixture consisting of 220 g of water, OO5 g of a 28% strength by weight aqueous solution of the ~odium salt of a mixture of ~ulfuric half-e~ters of ethoxylated Cl,/C~4-fatty alcohols (having a degree of ethoxylation of 2.8) = emulsifier solution i and 20 g of feed I
was heated to 85C and, beginning at the Qame time and while maintaining the 85C, the remaining amount of feed I and Rimultaneou~ly feed II were added continuously in the cour~e of 2 hours. Stirring was then continued for a further hour at 85C.
Feed 1: 3 g of Yodium peroxydisulfate in 100 g of water;
Feed 2: 240 g of methyl methacrylate, 60 g of methacrylic acid, 15.6 g of amulsifier solution i and 391 g of water.
The R value of the reeulting emulsion polymer wa~
66.
- 25 Db: As for Da, but feed II contained an additional 2.4 g of mercaptoethanol (molecular weight regulator).
The R value of the ro~ulting emulsion polymer was 35.
Dc: AE for Da, but the monomer compo~ition was 70% by weight of methyl msthacrylate and 30% by weight of methacrylic acid. The ~ value of the resulting emulsion polymer was 62.
Dd: As for Da, but the monomer composition was 95% by welght of metffll methacrylate and 5% by weight of methacrylic acid. The R value of the re~ulting e~ul~ion polymer wa~ 580 De: As for Da, but the monomer composition was , , ~ , ` 21~3377 O.Z. 0050/44058 50% by weight of n-butyl acrylate, 30% by weight of methyl methacrylate and 20% by weight of methacrylic acid.
The R value of the re~ulting emulsion polymer was 63.
2. Preparation of a polymer powder Pa The aqueous polymer ~tarting di~per~ion Da was spray-dried in a conventional manner by the ~pray-drying method (inlet temperature: 130C, outlet temperature:
60C) in the absence of anticaking agents or spray assi~tant~ to give a finely divided polymer powder.
3. Testing the performance characteristics of cement mortar~ modified with the polymer di~per~ions Da to De and with the polymer powder Pa 40 g of Portland cement PZ 35 were dry-blended with 60 g of atandard ~and (DIN 1164 Part 7) and then stirred with use of water and the varioua polymer disper-sion~ ae tha poly~er powder at a polymer/cement weight ratio of 0.1, ~o-that ~tirred mortar~ having a standard ~tability re~ulted.
The mortar~ were then introduced into a pri~matic mold and compacted by ~ibration. The mortar pri~m~ were then ~tored in the mold for 28 dayn at 23C and 95%
relative humidity. Thereaftar, the pri~m~ were remoYed from the mold and their flexural ten~le ~trength and compres~ive ~trength were te~ted. The re~ults are shown in the Table below. A polymer-free mortar formulation ~uitable for proces~ing and havlng the same stability could not be prepared, and the Table thereforQ contain~
no values for poly~mer-free mortar formulation~.

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-- - 12 - O.Z. 0050/44058 . TABLE
; Polymer system Flexural tensile Co~pressive u~ed strength ~trength (N/mm2) (N/mm2) Da 15.55 57.6 Pa 15.95 60.4 : Db 3.78 20.1 Dc 4.49 29.4 Dd 7.70 42.0 De 6.81 41.5 The novel ~ystema Da and Pa have unexpected advantages over the comparativ- syatem~.

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Claims

1. A polymer powder whose polymer, in polymerized form, is composed of from 60 to 85% by weight of methyl methacrylate (monomer a), from 15 to 25% by weight of at least one .alpha.,.beta.-mono-ethylenically unsaturated carboxylic acid of 3 to 6 carbon atoms (monomer b) and from 0 to 15% by weight of other copolymerizable monomers (monomer c), with the proviso that the composition of the monomers a, b and c is chosen so that, according to the Fox relationship for a polymer composed of these monomers, a glass transition tempera-ture of from 70 to 150°C results and the K value of the polymer, determined for the fully acidic form of the polymer in dimethylformamide at 23°C
and at a polymer content of 0.1% by weight, is from 45 to 100 .

2. A polymer powder as claimed in claim 1, the polymer of which contains monomers b or c having acidic functions, in neutralized form.

3. A process for the preparation of a polymer powder as claimed in claim 1, wherein the monomers constituting the polymer are polymerized by the free radical aqueous emulsion polymerization method and the resulting aqueous polymer dispersion is dried.

4. A mineral building material having binding properties and based on a cement-containing mineral binder, containing a polymer powder as claimed in claim 1.

5. A method of using a polymer powder as claimed in claim 1 as an additive for mineral building materials having binding properties and based on cement-containing mineral binders.

6. A method of using an aqueous polymer dispersion containing a polymer composed of from 60 to 85% by weight of methyl methacrylate (monomer a), from 15 to 25% by weight of at least one .alpha.,.beta.-mono-ethylenically unsaturated carboxylic acid of 3 to 6 carbon atoms (monomer b) and from 0 to 15% by weight of other copolymerizable monomers (monomer c), with the proviso that the composition of the monomers a, b and c is chosen so that, according to the Fox relationship for a polymer composed of these monomers, a glass transition tempera-ture of from 70 to 150°C results and the K value of the polymer, determined for the fully acidic form of the polymer in dimethylformamide at 23°C
and at a polymer content of 0.1% by weight, is from 45 to 100, as an additive for mineral building materials having binding properties and based on cement-containing mineral binders.