NO802786L - IRRIGATION SOLUTION OR DISPERSION OF A STYRENE / MALEIC ACID ANHYDRID COPOLYMER, PROCEDURE FOR ITS PREPARATION AND ITS USE - Google Patents

Description

The invention relates to an aqueous solution or dispersion of a styrene/maleic anhydride copolymer, a method for its preparation and its use.

The preparation of copolymers of maleic anhydride with vinyl compounds such as styrene has been known for a long time (cf. e.g. Ind. Eng. Chem 41 (1949), p. 1509).

These copolymers dissolve under the addition of alkali in water,

since their action as a pigment dispersant, protective colloid, thickener or glue requires salt formation.

Furthermore, copolymers of styrene and maleic anhydride are known which have a styrene/maleic anhydride molar ratio of 1:1 to 4:1, an average molecular weight of 400 to 100,000 and a melting point of 80 to 300°C (cf. US patent 34 44 151 ). These copolymers are reacted with amines to nitrogen-containing copolymers which are approximately insoluble in water or aqueous, alkaline media, they are used as emulsifiers in the emulsion polymerization of vinyl monomers.

Furthermore, it is known that in the production of starch-based adhesives, styrene/maleic anhydride copolymers are used, whose styrene/maleic anhydride molar ratio amounts to 1:1 to 3:1 and whose molecular weight varies between 1,600 and 50,000 (cf. US patent 39 39 108). These copolymers are usually prepared by solution polymerization in an aromatic hydrocarbon in the presence of a radical generator as a catalyst at a temperature from 75 to 300°C. After adding ammonia or alkali hydroxide, they can be dissolved under heating in water until a pH value of 8 to 11 is reached.

The object of the invention is to provide an aqueous solution or dispersion of a maleic anhydride copolymer which does not show an alkaline reaction and which is suitable as an emulsifier solution or dispersion for plastic dispersions.

The invention now relates to an aqueous solution or dispersion of a hydrolyzed copolymer of styrene and maleic anhydride with a styrene/maleic anhydride molar ratio of greater than 1:1 and a molecular weight (number average) of more than 400 and the solution or dispersion is characterized by the molar ratio being in the range from 1.5:1

to 6:1, the molecular weight is 500 to 80,000, 1 to 60% of the carboxyl group of the copolymer is neutralized and the pH value of the solution or dispersion is less than 7.

Furthermore, the invention relates to a method for producing an aqueous solution or dispersion of a hydrolyzed copolymer of styrene and maleic anhydride, which has a styrene/maleic anhydride molar ratio of greater than 1:1 and a molecular weight (number average) of more than 400 upon hydrolysis of a styrene/maleic anhydride copolymer and partial neutralization with an inorganic neutralizing agent, the method being characterized by a copolymer

with a styrene/maleic anhydride molar ratio of from 1.5:1 to 6:1 and a molecular weight of from 500 to 80,000 is heated in the presence of water and in the presence of so much ammonia or an alkali hydroxide or an alkaline earth hydroxide or zinc oxide to a temperature of from 75 to 250°C that 1 to 60% of the copolymer's carboxyl groups are neutralized.

Finally, the invention also relates to the use of the above-mentioned solution or dispersion as a stabilizer solution or dispersion for aqueous dispersions and in the dispersion polymerization of vinyl compounds.

The styrene/maleic anhydride copolymer used according to the invention has a molecular weight (number average) from 500 to 80,000, preferably from 800 to 30,000. The styrene/maleic anhydride molar ratio amounts to 1.5:1 to 6:1, preferably 1.6: 1 to 4:1.

According to the invention, the styrene/maleic anhydride copolymer is heated in the presence of water and in the presence of an inorganic neutralizing agent at a temperature from 75 to 250°C, preferably 85 to 180°C and hydrolyzed. The resulting free carboxyl groups of the copolymer are thereby neutralized to 1 to 60%, preferably 6 to 50%. In this alkaline treatment of the copolymer, its concentration is 5 to 50% by weight, preferably 10 to 30% by weight

(referred to total amount of water and copolymer). Depending on the concentration and composition of the copolymer as well as the

temperature used, the treatment lasts 5 minutes to 5 hours, preferably 10 to 200 minutes. A high amount of styrene in the copolymer, a high copolymer concentration and a low treatment temperature generally require an increased treatment time,

by varying the specified parameters, the treatment time can therefore be changed. Work under inert gas, e.g. nitrogen is recommended.

The styrene/maleic anhydride copolymer optionally also contains one or more additional monomers in an amount of up to 20 mol-% (referred to the total monomer amount) polymerized. Suitable are olefinically unsaturated compounds such as vinyl ester, vinyl ether, acrylic acid ester and unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, vinylsulfonic acid and N-methacryloylamino-propanesulfonic acid.

Ammonium hydroxide or an alkali hydroxide, e.g. lithium hydroxide, sodium hydroxide and potassium hydroxide or an alkaline earth hydroxide, e.g. magnesium hydroxide and calcium hydroxide, as well as zinc oxide. Instead of a single neutralizing agent, a mixture of several neutralizing agents can also be used. The amounts of neutralizing agent used are to be chosen so that the desired degree of neutralization is obtained, it lies in the range from 0.02 to 1.2 base equivalent, preferably 0.12 to 1 base equivalent (referred to a mole of maleic anhydride in the copolymer) . Depending on the neutralizing agent plus type and amount, a copolymer solution or dispersion is obtained, for the preparation of a solution a higher amount of neutralizing agent is used than for the preparation of a dispersion.

For the preparation of an acidic solution of a hydrolyser t styrene/maleic anhydride copolymer, it pays to carry out the alkaline treatment in the presence of an emulsifier, preferably an anionic emulsifier. Alkaline salts or ammonium salts of alkylsulfonic acids, arylsulfonic acids or alkylarylsulfonic acids and the corresponding sulfuric acids, phosphoric acids or phosphonic acids are particularly suitable as emulsifiers, the compounds mentioned possibly having oxyethylene units between the possible hydrocarbon residue, preferably up to 18 carbon atoms and an anionic group , the oxyethylated compounds preferably contain 5 to 30 ethylene oxide units. Examples of suitable emulsifiers are sodium lauryl sulfate, sodium octylphenol glycol ether sulfate, sodium dodecyl benzene sulfonate, sodium lauryl diglycol sulfate as well as the ammonium salts of oxytylated and sulfated tri-t-butylphenol, t-butylphenol and nonylphenol.

The emulsifier is used in an amount from 3 to 100% by weight, preferably 5 to 25% by weight (referred to the styrene/maleic anhydride copolymer).

The copolymer dispersion according to the invention is also transferred in a solution, since after the addition of an emulsifier of the above-mentioned type, it is heated to a temperature within the range of the above-mentioned treatment temperature.

The aqueous solution or dispersion of a hydrolyzed copolymer according to the invention of styrene and maleic anhydride shows an acidic reaction. Its pH value is less than 7 and preferably less than 6, particularly advantageous is a solution or dispersion with a pH value of from 2.0 to 5.7. The copolymer content of the solution or dispersion is in the range from 5 to 50% by weight, preferably 10 to 30% by weight. The viscosity of the solution or dispersion is 20 to 20,000 mPa•s, preferably 50 to 3,000 mPa•s (measured according to Epprecht).

The copolymer solution or dispersion according to the invention is used as an emulsifier, dispersant, adhesive, adhesive, thickener, flocculant and hydrophobic agent and in the textile, coating, adhesive and paper sectors as a coating and binding agent. On materials such as wood, paper, ceramics, metal or plastic, the dissolved or dispersed copolymer is applied after application of the solution or dispersion by removal of water or by electrochemical separation.

The solution or dispersion is excellently suited for stabilizing aqueous dispersions of natural or synthetic, inorganic or organic substances, e.g. cellulose, plastics, pigments and fillers. The copolymer solution or dispersion is further used in suspension or emulsion polymerization of vinyl compounds, especially vinyl esters and acrylic acid esters. The thus stabilized plastic dispersions show an increased stability against cutting forces and pigments. The time of addition of the stabilizer solution or dispersion is therefore of secondary importance, the addition can with the same result take place during the preparation of the dispersion to be stabilized or later.

The copolymer solution or dispersion according to the invention is used above all in the polymerization of vinyl compounds which are polymerized in an aqueous medium under acidic conditions. Particularly suitable monomers are olefinic unsaturated compounds of the formula

1 2 where R means a hydrogen atom or a methyl residue and R means (a) an alkylcarboxy residue with 2-18, preferably 2-12 carbon atoms, (b) an alkoxy acid residue with 1-4 carbon atoms, (c) a nitrile group, (d) a halogen atom, preferably a chlorine atom, (e) a carboxyl group or sulfo group, (f) an alkoxycarbonyl radical with 2-12, preferably 2-9 carbon atoms, (g) an aminocarbonyl radical, (h) a hydrogen atom, (i) a phenyl- residue or (k) a vinyl residue. Examples of such olefinic unsaturated compounds should be mentioned (a) vinyl esters of aliphatic carboxylic acids with 2-18, preferably 2-12 carbon atoms, e.g. vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl isononate, vinyl laurate and vinyl decanate as well as vinyl esters of a mixture of monocarboxylic acids with 9-11 carbon atoms, (b) vinyl ethers, e.g. vinyl methyl ether, vinyl ethyl ether and

vinyl n-butyl ether,

(c) acrylonitrile and methacrylonitrile,

(d) vinyl halides, e.g. vinyl chloride and allyl chloride,

(e) unsaturated monocarboxylic acids, e.g. acrylic acid, methacrylic acid and vinyl sulphonic acid, (f) acrylic acid esters or methacrylic acid esters of monovalent alkanols with 1-11, preferably 1-8 carbon atoms, e.g. methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate and 2-ethylhexyl methacrylate, (g) acrylic acid amides and methacrylic acid amides, e.g. acrylic acid amide, N-methylolacrylic acid amide, methacrylic acid amide and

N-methylol methacrylic acid amide,

(h) ethylene,

(i) styrene and methylstyrene or

(k) butadiene and isoprene.

Particularly suitable monomers are the vinyl esters (a), the vinyl ethers (b), the vinyl halides (d) and acrylic acid esters and methacrylic acid esters (f). The monomers are used individually or in a mixture with each other, monomer combinations are formed, for example, from an acrylic acid ester and a methacrylic acid ester,

an acrylic or methacrylic acid ester and a vinyl ester as well as a mixture of different vinyl esters, especially vinyl acetate and vinyl ester of a mixture of monocarboxylic acid with 9-11 carbon atoms, further of vinyl and ethylene as well as of vinyl acetate, ethylene and vinyl chloride.

The polymerization usually takes place in the presence of

a radical-forming initiator, preferably a peroxide compound or an aliphatic azo compound. The initiator is oil-soluble or preferably water-soluble, it is used in an amount of 0.05 to 2% by weight, preferably 0.1 to 1% by weight (referred to the total amount of monomer). Hydrogen peroxide, alkali or ammonium salts of persulfuric acid, peroxydisulfuric acid or peroxy-diphosphoric acid are particularly suitable, e.g. sodium persulfate, potassium peroxydisulfate and ammonium peroxydisulfate, further alkyl hydroperoxides such as t-butyl hydroperoxide, dialkyl peroxides such as di-t-butyl peroxide, diacyl peroxides such as diacetyl peroxide, dilauroyl peroxide and

dibenzoyl peroxide, as well as azodiisobutyric nitrile, azodicarbonamide and azo-Y/Y<1->bis(4-cyanvaleric acid). The initiator is optionally used together with a reducing agent, especially with an ammonium salt, alkali salt or alkaline earth salt of a reducing-acting sulphurous acid, preferably sulphites, bisulphites, pyrosulphites, dithionites, thiosulphates and formaldehyde sulphoxylates are suitable. The amount of the reducing agent amounts to 0.05 to 20% by weight, preferably 0.5 to 10% by weight (referred to styrene/maleic anhydride copolymer).

To increase the polymerization rate, it is advantageous to use a solution or dispersion of a hydrolyzed styrene/maleic anhydride copolymer, the preparation of which is carried out in the presence of a sulphite. Suitable sulphites are neutral or acidic salts of sulfuric acid or pyrosulphuric acid, especially ammonium salts, alkali salts and alkaline earth salts. Sulfite is optionally used in an amount from 0.05 to 20% by weight, preferably 0.5 to 10% by weight

(referred to styrene/maleic anhydride copolymer).

In emulsion polymerization, the solution or dispersion of the hydrolyzed styrene/maleic anhydride is used in such an amount that the copolymer is present in an amount of from 0.1 to 10% by weight, preferably 0.5 to 5% by weight

(referred to the total amount of monomer). In suspension polymerization, 0.01 to 2% by weight, preferably 0.01 to 1% by weight, of comonomer (referred to the total amount of monomer) is sufficient. The polymerization takes place each time at a temperature from 25 to 90°C, preferably 40 to 75°C. Depending on the type and quantity of the participating monomers, the polymerization time is in the range from 2 to 8 hours, preferably 2.5 to 5 hours.

The resulting polymer dispersions are highly stable against shear forces and show very good pigment binding ability. They are therefore primarily used as binder dispersions in coating agents, especially dispersion paints and paper coating compounds. The paper treated in this way is distinguished by high pilling resistance and ironing water resistance.

The invention will be explained in more detail with the help of some examples to which the percentages each time refer

to weight.

Example 1

150 g of a copolymer of styrene and maleic anhydride (molar ratio 2:1), which has an average molecular weight

of 1700, is heated together with 790 g of water and 7.05 g of caustic soda in a stirrer with a reflux condenser for 2 hours at a temperature of 95-100°C and then cooled to room temperature. You get a clear solution with a pH value of 4.7 and a polymer content of 16.5%. The hydrolyzed copolymer's carboxyl groups are neutralized to 18%.

Example 2

a) Example 1 is repeated, however, instead of 7.05 g of caustic soda, 3.52 g of caustic soda is now used and instead of 790 g of water, 720 g of water. In addition, the reaction mixture is filtered after cooling to room temperature, thereby leaving a residue of 30.9 g (after drying). A dispersion with a pH value of 4.1 and a polymer content of 14.9% is obtained as filtrate. b) 8 g of the dispersion formed according to a) is heated together with 2 g of a 15% aqueous solution of sodium lauryl sulfate at 70°C, the copolymer dissolving. c) 8 g of the dispersion formed according to a) is heated together with 2 g of a 15% aqueous solution of the ammonium salt of a nonylphenol oxyethylated with 25 mol of ethylene oxide and then sulfated as an emulsifier at 80°C, the

copolymers dissolve.

Example 3

300 g of a copolymer of styrene and maleic anhydride (molar ratio 3:1) with an average molecular weight of

1900 is heated together with 1680 g of water and 29.3 g of caustic soda in a stirrer with a reflux condenser for 2 hours at a temperature of 96°C and then cooled to room temperature. A solution with a pH value of 6.8 and a polymer content of 16.7% is obtained. The carboxyl groups of the hydrolyzed copolymer

is neutralized to 50%.

Example 4

Heat in a mixing vessel with reflux condenser

150 g of a copolymer of styrene and maleic anhydride (molar ratio 3:1) with an average molecular weight of 1900 together with 790 g of water and 25 g of a 25% aqueous ammonia solution for 2 hours at a temperature of 100°C and then cooled to room temperature. A solution with a pH value of 6.8 and a polymer content of 16.1% is obtained. The hydrolyzed copolymer's carboxyl groups are neutralized to 50%.

Example 5

a) 150 g of a copolymer of styrene and maleic anhydride (molar ratio 3:1) with an average molecular weight of

1900 is heated together with 720 g of water and 7.3 g of caustic soda in a stirrer with a reflux condenser for 3 hours at a temperature of 97°C and then cooled to room temperature. A dispersion with a pH value of 5.6 and a polymer content of 17.6% is obtained. The carboxyl groups of the hydrolyzed copolymer are neutralized to 25%. The average diameter of the dispersed polymer particles is 0.038 µm. b) 8 g of the dispersion formed according to a) is heated with 2 g of a 15% aqueous solution of sodium lauryl sulfate at 85°C, whereby the copolymer dissolves. c) 8 g of the dispersion formed according to a) is heated with 2 g of a 15% aqueous solution of the emulsifier from

example 2 c) to 90°C, whereby the copolymer dissolves.

Example. 6 to 8

Each time 150 g of a copolymer of styrene and maleic anhydride (molar ratio 3:1) with an average molecular weight of 1900 is heated together with each time 720 g of water and different amounts of lithium hydroxide in a stirrer with a reflux condenser of different lengths at a temperature of 97° C

and then cooled to room temperature. Details and

properties of the solution or dispersion obtained each time are shown in table 1.

Example 9

150 g of a copolymer of styrene and maleic anhydride (molar ratio 3:1) with an average molecular weight of

1900 is heated together with 1300 g of water, 7.3 g of caustic soda,

125 g of a 30% solution of the emulsifier from example 2 c) and 12 g of sodium pyrosulphite under a nitrogen overlay in a stirring vessel with a reflux condenser for 2 hours at a temperature of 96°C and then cooled to room temperature.

You get a solution with a pH value of 5.3 and a polymer content of 13.3%. The carboxyl groups of the hydrolyzed copolymer are neutralized to 25%.

For use in the polymerization of vinyl acetate, solutions are adjusted with water to a concentration of 7.8%.

Example 10

150 g of copolymer of styrene and maleic anhydride (molar ratio 2:1) with an average molecular weight of 1700 is heated together with 1300 g of water, 7.3 g of caustic soda, 125 g of a 30% aqueous solution of the emulsifier from example 2 c) and 12 g

sodium pyrosulphite under a blanket of nitrogen in a stirrer with a reflux condenser for 2 hours at a temperature of 96°C and then cooled to room temperature. A solution with a pH value of 4.3 and a polymer content of 13% is obtained.

The hydrolyzed copolymer's carboxyl groups are neutralized to 18.6%.

For use in the polymerization of vinyl acetate, the solution is adjusted with water to a concentration of 7.8%.

Application example 1

In a mixing vessel there are 510 g of water, 1.77 g of a 6% aqueous sodium alkylsulfonate solution (average chain length in the alkyl group: 12-14 carbon atoms) and 2 g of a 30% aqueous solution of the ammonium salt of one with 25 mol of ethylene oxide oxyethylated and then sulfated nonylphenol and flushed with nitrogen. After adding a solution of 2.25 g of ammonium persulphate in 20 g of water, the mixture is heated to a temperature of 50°C. While maintaining this temperature, 750 g of vinyl acetate and a solution of 0.39 g of sodium formaldehyde sulfoxylate in 50 g of water are added evenly to the mixture over the course of 3 hours, separated from each other. During the first hour, the same amount of the emulsifier combination is added again, during the following two hours, 100 g of the copolymer solution formed according to example 9 is added, as well as 1.87 g of the above-mentioned alkylsulfonate solution and 21.2 g of the above-mentioned 30% ammonium salt solution. The mixture is then mixed with a solution of 0.75 g of ammonium persulphate in 30 g of water and heated for 30 minutes at a temperature of 75°C and then cooled to room temperature.

A coagulate-free polyvinyl acetate dispersion is obtained which is adjusted with 3.2 g of 12.5% ammonia solution to a pH value of 6. The solids content of the dispersion amounts to 50.8%, and the polymer particles have an average diameter of 0.22 um. The dispersion is shear stable, because after 2 minutes of stirring with a high-speed stirrer (5000 rpm) no coagulate formation occurs and the average particle size of the polymer does not change.

Application example 2

Application example 1 is repeated, however, instead of the copolymer solution formed according to example 9, the copolymer solution formed according to example 10 is now used. The vinyl acetate dispersion formed each time is coagulant-free. The solids content of the dispersion amounts to 50.4% and the polymer particles have an average diameter of 0.18 um. The dispersion is shear stable (sample analogous to application example 1).

Comparative example 1

1620 g of the styrene/maleic anhydride copolymer used in example 3 is stirred in 8024 g of water with the addition of 316 g of caustic soda for 6 3/4 hours at a temperature of 80°C.

The suspension formed after cooling to room temperature is filtered, resulting in a solid residue of 47 g. The filtrate has a pH value of 10.0 and a polymer content of 18.7%. The carboxyl groups of the hydrolyzed copolymer are neutralized to 100%.

Comparative example 2

Example 4 is repeated, but the heating temperature is only 70°C. Thereby, only 50% of the styrene/maleic anhydride copolymer dissolves. The solution shows a pH value of 5.2.

Comparative example 3

Example 4 is repeated, however, the heating temperature is only 70°C and a double amount of ammonia solution is used. The formed solution shows a pH value of 9.3.

Comparative example 4

Application example 1 is repeated, replacing the copolymer solution formed according to example 9 with water. The polyvinyl acetate dispersion formed coagulates when tested for shear stability.

Comparative example 5

Application example 1 is repeated, with the copolymer solution formed according to example 9 being replaced with a correspondingly prepared solution of a styrene/maleic anhydride copolymer (molar ratio 1:1) with an average molecular weight of 1600, whose carboxyl groups have been neutralized to 12.3% after hydrolysis. The formed polyvinyl acetate dispersion coagulates when tested for so-called lime stability.

Claims (9)

1. Aqueous solution or dispersion of a hydrolyzed copolymer of styrene and maleic anhydride with a styrene/maleic anhydride molar ratio greater than 1:1 and a molecular weight (number average) of more than 400, characterized in that the copolymer has a molar ratio of 1.5: 1 to 6:1 and a molecular weight of 500 to 80,000, 1 to 60% of the copolymer's carboxyl groups are neutralized and the pH value of the solution or dispersion is less than 7. 2. Solution or dispersion according to claim 1, characterized in that the copolymer has a styrene/maleic anhydride molar ratio of 1.6:1 to 4:1. 3. Solution or dispersion according to claim 1, characterized in that the copolymer has a molecular weight from 800 to 30,000. 4. Solution or dispersion according to claim 1, characterized in that 6 to 50% of the copolymer's carboxyl groups are neutralized. 5. Process for preparing an aqueous solution or dispersion of a hydrolyzed copolymer of styrene/maleic anhydride having a styrene/maleic anhydride molar ratio of greater than 1:1 and a molecular weight (number average) of more than 400, by means of hydrolysis of a styrene/maleic anhydride copolymer and partial neutralization with an inorganic neutralizing agent, characterized in that a copolymer with a styrene/maleic anhydride molar ratio of 1.5:1 to 6:1 and a molecular weight of 500 to 80,000 is heated in the presence of water and in the presence of so much ammonia or an alkali hydroxide or an alkaline earth hydroxide or a zinc oxide at a temperature from 75 to 250°C, that 1 to 60% of the copolymer's carboxyl group is neutralized. 6. Method according to claim 5, characterized in that the copolymer is used in a concentration of from 5 to 50% by weight (referred to the total amount of copolymer and water). 7. Method according to claim 5, characterized in that the heating is carried out in the presence of an anionic emulsifier. 8. Use of the solution or dispersion according to claim 1 as a stabilizer solution or dispersion for aqueous dispersions. 9. Use of the solution or dispersion according to claim 1 as a stabilizer solution or dispersion in dispersion polymerization of vinyl compounds.