IE43283B1 - Process for the manufacture of plastics dispersions - Google Patents

Abstract

Aqueous polymer dispersions which are suitable for the preparation of paints having high wet adhesion are prepared by copolymerisation in an aqueous medium of a curing component and a plasticising component, and of acrylic acid, methacrylic acid, acrylamide and/or methacrylamide. The copolymerisation is additionally carried out in the presence of a compound of the formula in which X is -O-, -O-CH2- or , and R and R' are hydrogen or methyl, or the acetoacetic ester of hydroxypropyl acrylate or methacrylate.

Description

This invention relates to a process for the manufacture of plastics dispersions which are suitable for making dispersion paints having good wet adhesion, i.e. when wetted after drying.

The problem of the wet adhesion, i.e. the adhesion of dried paints on wetting of dispersion paints on smooth non-absorbent surfaces has long restricted the use of such dispersion paints. Dispersion paints having a low pigment content, which dry on the substrate with formation of a glossy or slightly dull film, have a poor adhesion to smooth non-absorbent surfaces when the paints are rewetted after drying. The wet adhesion is especially unsatisfactory with fresh paints which have not undergone ageing.

Dispersion paints of low pigment content are chosen when a washable coat of paint is desired. Owing to the high binder content of the paint a non-porous washable film is formed. Dispersion paints drying with formation of a glossy or slightly dull film also have a pigment content of less than 40% by volume, generally from about 10 to 25%. They also contain about 3 to 15% of organic solvents to improve the gloss and flow, to prolong the working time and for improving film consolidation, for example water-miscible polyhydric alcohols having up to 6 carbon atoms, especially ethylene and propylene glycols, or the monoftethyl to monobutyl ethers thereof. To improve the film consolidation, - 3 there are used solvents having a restricted solubility in water, such as the mono-glycol esters of carboxylic acids and more especially esters of carboxylic acids with monoalkyl ethers of glycols or oligoglycols. Butyl diglycol acetate is one of the most widely used representatives of this group. The combination of a low pigment content and a relatively high solvent content has a very detrimental effect on the wet adhesion of the coats of dispersion paints.

With poor wet adhesion, paints formulated to give washable coats do not have this property when applied to smooth non-absorbent surfaces, for example old coats of alkyd or oil paint. In moist rooms, such as kitchens, bath rooms, or industrial premises, where condensation may form, the new coat may detach itself from the substrate if the wet adhesion is not sufficient. Moreover, poor wet adhesion complicates painting. When, for example, the lower and upper parts of a wall or a wall and ceiling are to be painted in different colours, the first to be painted may be soiled accidentally with the second paint. In principle, the second paint could be wiped off with a wet cloth, but with poor wet adhesion the first paint may then be damaged or even removed simultaneously.

Many attempts have therefore been made to modify plastics dispersion in such a manner that the dispersion paints made therewith have the desired wet adhesion. In British Patent Specification No. 1,138,960, it has been proposed to prepare plastics dispersions by polymerizing suitable monomers in aqueous emulsion using as comonomers 0.2 to 15% by weight, calculated on the total amount of the monomers, of compounds carrying oxirane groups and then to react the copolymer at room temperature with ammonia or an amine. Suitable oxirane compounds are especially glycidyl esters of acrylic and methacrylic acids and allyl glycidyl ethers and vinyl glycidyl ethers.

Dispersion paints prepared with plastics dispersions of this type have quite good wet adhesion, but for many applications the wet adhesion is still not entirely sufficient.

The present invention is based on the observation that aqueous dispersions which are suitable for making paints having an excellent wet adhesion on non-absorbent or only slightly absorbent surfaces, can be obtained by copolymerizing in an aqueous system the following monomers: (A) from 20 to 79.4% by weight, preferably 40 to 60% by weight, based on the total monomers, of one or more hardening monomers selected from methyl methacrylate, styrene and vinyl toluene; (B) from 20 to 79.4% by weight, preferably 40 to 60% by weight, based on the total monomers, of one or more plasticizing monomers selected from acrylic acid esters in which the alcohol radical is a linear or branched alkyl radical having from 2 to 8 carbon atoms, and conjugated dienes having from 4 to 8 carbon atoms which may be substituted by halogen atoms; (C) from 0.1 to 5% by weight, preferably 1 to 3% by weight, of acrylic acid, methacrylic acid, acrylamide or methacrylamide; and (D) from 0.5 to 10% by weight, preferably 1 to 5% by weight, of an acetoacetic acid ester of the formula II II R R' CH3 C CH2 C — X C—C H, in which X is -0— — CH. — 0—CH2 — CH2—0— c — or -0—ch2 — ch2 ch2— 0—C0 - 5 H is H or CHg and R' is H or CHg.

Plasticizing monomers (B) are, for example ethyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate and 2 - ethylhexyl acrylate and butadiene, isoprene and chloroprene.

Suitable monomers (D) are, for example vinyl acetoacetate, allyl acetoacetate and acetoacetic acid esters of ¢5hydroxyethyl acrylate and methacrylate and hydroxypropylacrylate and methacrylate. Allyl acetoacetate is preferred, since it yields the best results.

For dispersions prepared in an acid pH range, it is often advantageous for improving their storage life and for facilitating the preparation of paints, to adjust the pH to from 7.5 to 10 with ammonia or suitable amines, for example water-soluble tertiary amines.

Plastics dispersions are extremely complex systems.

The preparation of the high-quality dispersions according to the present invention requires knowledge and experience of the field of the emulsion polymerization for details of the process which are not described herein. A disregard of known principles of emulsion affect important properties such as the water resistance, of the dispersion films or the films of the coats of paint. For this reason the conventional content of up to 3%, preferably of up to 2% of ionic emulsifiers in the dispersions or of up to 6%, preferably of up to 4% of non-ionic emulsifiers should not be exceeded substantially.

Suitable non-ionic emulsifiers are, for example, alkyl polyglycol ethers such as the ethoxylation products of lauryl, oleyl or stearyl alcohol or of mixtures such as coconut fatty alcohol; alkyl phenol polyglycol ethers such as the ethoxylation products of octyl- or nonyl-phenol, diisopropyl-phenol, triisopropyl-phenol or di- or tri-tert.butylphenol; or ethoxylation products of polypropylene oxide.

As ionic emulsifiers, there can be used anionic emul283 - 6 sifiers, for example alkali metal or ammonium salts of alkyl, aryl or alkylaryl sulfonates, sulfates, phosphates, phosphonates, or compounds having different anionic end groups, oligo- or polyethylene oxide units possibly being contained between the hydrocarbon radical and the anionic group. Typical representatives are sodium lauryl sulfate, sodium octyl-phenol glycol ether sulfate, sodium dodecyl benzene sulfonate, sodium lauryl diglycol sulfate,ammonium tri-tert.butyl -phenol penta- or octa-glycol sulfate.

As protective colloids there may be used natural substances such as gum arabic, starch, alginates or modified natural substances such as methyl, ethyl, hydroxyalkyl, or carboxymethyl cellulose, or synthetic substances, for example polyvinyl alcohol, polyvinyl pyrrolidone, or mixtures of such substances. Modified cellulose derivatives and synthetic colloids are preferred.

These protective colloids can only be employed to a limited degree if the described monomer systems are used, as is known to one skilled in the art. The quantities used are frequently low, that is in the range from 0.001 to 1% and the tolerance and the kind of addition must be examined in each case. When the use of protective colloids is required, the principles, for example disclosed in German Auslegeschrift No. 1,570,312, may be applied.

To initiate and continue polymerization, oil-soluble and/or preferably water-soluble radical forming agents or redox systems are used, for example hydrogen peroxide, potassium or ammonium peroxydisulfate, dibenzoyl peroxide, lauryl, peroxide, di - tert.butyl peroxide, bisazodiisobutyronitril$, either singly or together with reducing components, for example sodium bisulfite, Rongalite ( Trade Mark) glucose, ascorbic acid, and other compounds having a reducing action.

The special advantage of the dispersions prepared according to the present invention resides in the fact that they - 7 are not only suitable for the manufacture of gloss dispersion paints having a good wet adhesion on non-absorbent surfaces, but that they also have a high resistance to saponification.

The following Examples and Comparative Examples, illustrate the invention. The words Tylose and Calgon are registered Trade Marks.

EXAMPLE 1 A monomer emulsion was prepared having the following composition: 310 parts by weight water, parts by weight sodium salt of lauryl alcohol diglycol ether sulfate, parts by weight methacrylic acid, parts by weight acrylic acid, 300 parts by weight n-butyl acrylate, 300 parts by weight styrene, and 12 parts by weight allyl acetoacetate.

The components were stirred in a rapid stirrer until a stable emulsion was obtained.

A mixture consisting of 303 parts by weight water parts by weight sodium salt of lauryl alcohol diglycol ether sulfate and parts by weight of the monomer emulsion. was heated in a 2 liter three-necked flask placed in a heating bath and equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer and a solution of 0.45 parts by weight ammonium peroxydisulfate in 15 parts by weight water was added. Thereafter the residual monomer emulsion was added and polymerization was carried to completion. The total time of addition was 2 hours, and the polymerization temperature and the temperature during the second heating period were in the range from 81 to 83°C. When the monomer addition was complete 0.15 parts by weight ammonium - 8 peroxydisulfate in 5 parts by weight water were added, heating was continued for 60 minutes and the reaction mixture was cooled.

The pH was adjusted to 9.5 by means of 15 ml of 25% ΝΗ^; the solids content was about 50%.

EXAMPLE 2 (comparison) The procedure described in Example 1 was repeated with the exception that allyl acetoacetate was omitted from the polymerization.

EXAMPLE 3 A monomer emulsion was prepared from 310 parts by weight water parts by weight ammonium - tri - tertiary butyl phenol polyglycol ether sulfate having about 8 ethylene oxide units parts by weight methacrylic acid parts by weight acrylic acid 300 parts by weight 2 - ethylhexyl acrylate 300 parts by weight methyl methacrylate and 18 parts by weight allyl acetoacetate, by stirring rapidly, until a stable emulsion was obtained.

In an apparatus as described in Example 1 a mixture consisting of 306 parts by weight water parts by weight ammonium - tri - tertiary butyl phenol polyglycol ether sulfate having about 8 ethylene oxide units and parts by weight monomer emulsion was heated to 81°C and a solution of 0.45 parts by weight ammonium peroxydisulfate in 15 parts by weight water was added. The residual monomer emulsion was metered in and - 9 polymerization was carried to completion. The total time of addition was 2 hours and the polymerization temperature and the temperature during the second heating period were in the range from 81 to 83°C. When the addition of monomers was complete, 0.15 parts by weight ammonium peroxydisulfate in 5 parts by weight water was added, heating was continued for 1 hour and the reaction mixture was cooled. The pH was adjusted to 9.3 by means of 15 ml of 25% NHg. The solids content was about 50%.

EXAMPLE 4 (comparison) The procedure described in Example 3 was repeated with the exception that allyl acetoacetate was omitted from the polymerization.

EXAMPLE 5 A monomer emulsion was prepared from 380 parts by weight water parts by weight ammonium - tri - tertiary butyl phenol polyglycol ether sulfate having about 8 ethylene oxide units parts by weight methacrylic acid parts by weight acrylic acid 12 parts by weight acrylamide 450 parts by weight ethyl acrylate 150 parts by weight vinyl toluene 18 parts by weight allyl acetoacetate by stirring rapidly, until a stable emulsion was obtained.

In an apparatus as described in Example 1 a mixture consisting of 390 parts by weight water parts by weight ammonium - tri - tertiary butyl phenol polyglycol ether sulfate having about 8 ethylene oxide units 283 - 10 3 parts by weight nonyl phenol polyglycol ether having about 30 ethylene oxide units and parts by weight monomer emulsion was heated to 81°C and a solution of 0.45 parts by weight ammonium peroxydisulfate in 15 parts by weight water was added. The residual monomer emulsion was then metered in and polymerization was carried to completion. The total time of addition was 2 hours, and the polymerization temperature and the temperature during the second heating period were in the range from 81 to 83°C. When the addition of monomers was complete 0.15 parts by weight of ammonium peroxydisulfate in 5 parts by weight of water was added, heating was continued for 60 minutes and the reaction mixture was cooled. The pH was adjusted to 9.5 by means of 15 ml of NHg/25%.

The solids content was about 45%.

EXAMPLE 6 (comparison) The procedure described in Example 5 was repeated with the exception that allyl acetoacetate was omitted from the polymerization.

EXAMPLE 7 In a 16 liter autoclave provided with an impeller stirrer there was introduced a liquor consisting of 3090 g of demineralized water 80.5 g of sodium dodecylbenzene sulfonate 15 g of potassium persulfate and g of NaOH (solid) The liquor and the whole apparatus were flushed with nitrogen. The following steps were also performed under a protective gas atmosphere.

Prom a second vessel a mixture consisting of - 11 1200 g of butadiene 1560 g of styrene g of allyl acetoacetate was introduced by pumping into the autoclave.

The stirrer was set in motion (about 300 r.p.m.) and heating was started. The mixture was polymerized for 2-1/2 hours at 70°C (the internal pressure was about 10 bars) and a solution consisting of g of sodium dodecylbenzene sulfonate in 750 g of demineralized water was added by pumping.

After another 2 hours of polymerization at 70°C a solution of g of potassium persulfate in 250 g of demineralized water was added and a mixture consisting of 180 g of styrene and g of acrylic acid was metered in the course of about 15 minutes.

The post-reaction time was 3 hours (also at 70°C). Thereafter the vessel was cooled, ventilated and the product was filtered.

The solids content was about 42%. The quantity of coagulate was low.

EXAMPLE 8 The procedure described in Example 7 was repeated with the exception that the styrene was replaced by the same quantity (1740 g) of vinyl toluene.

EXAMPLE 9 The procedure described in Example 7 was repeated with the exception that half of the quantity of styrene (780 g in the second vessel and 90 g in the second addition) was replaced by vinyl toluene. - 12 EXAMPLE 10 (comparison) A dispersion was prepared in the manner described in Example 7 with the exception that the allyl acetoacetate was omitted and the amount of water was reduced by 90 g to 300° g.

To prepare dispersion paints having a high wet adhesion, the dispersions obtained according to the preceding Examples were blended with a pigment suspension. Pigment suspensions or pigment pastes of this type, which are suitable for making dispersion paints of low pigment content and especially gloss paints consist, for example, of titanium dioxide uniformly dispersed in water. They contain, in general, protective colloids such as cellulose derivatives, for example hydroxyethyl cellulose, and dispersing agents, for example salts of poly(meth)acrylic acid or sodium polyphosphate. Other conventional constituents of pigment suspensions are furthermore antimicrobic preserving agents, anti-foaming agents, pH stabilizers and fillers. Especially suitable titanium dioxide pigments are the rutile and anatase modifications. For the manufacture of gloss paints the average particle diameter of the pigment should be near the lower limit of the wave length of light, i.e. at about 0.4 to 0.2 micron. For making dull paints of low pigment content special large surface silicate pigments could be concomitantly used. Dull paints of high binder content yield paint coatings that are easy to clean. The pigment paste may, of course, also contain coloured pigments the desired shade is obtained by adding a shading dyestuff to the dispersion paint containing the white pigment.

The pigment suspension can be prepared in known manner, for example by dispersing the pigment in a dissolver, a ball mill or sand mill. For use in gloss paints, the pigment suspension should not contain noticeable amounts of pigment aggregates which would affect the gloss.

Auxiliaries such as plasticizers, cross-linking agents, - 13 buffer substances, thickening agents, thixotropic agents, rust preventing agents, alkyd resins, or drying oils may be added to the dispersion or the dispersion paint. Suitable plasticizers are not the solvents initially mentioned as film consolidation agents having only a temporary action, but compounds which reduce the film forming temperature and remain in the polymer for a longer period of time, for example dibutyl phthalate.

To test the wet adhesion dispersion paints were prepared as follows: Formulation I: (1) 41.0 parts by weight water .6 parts by weight of a 3% aqueous solution of Tylose II 20 0.4 part by weight Calgon N (solid) 3.0 parts by weight dispersing agent PA 30 1.0 parts by weight ammonia of 25% strength 2.0 parts by weight of preserving agent 3.0 parts by weight of anti-foaming agent 175 parts of titanium dioxide having a particle size of from 0.2 to 0.4 micron parts 1,2 - propylene glycol were dispersed and (2) 710.0 parts by weight of one of the dispersions of Examples 1 to 6 having a solids content of about 50% or 843 parts by weight of one of the dispersions of Examples 7 to 10 having a solids content of 42%, to which 2.0 parts by weight of ammonia of 25% were added lf the pH was not higher than about 7, were added. (3) A mixture of parts by weight butyl diglycol acetate, 27.0 parts by weight 1,2-propylene glycol - 14 was slowly added while stirring.

The liquid or soluble components indicated in (1), except 1,2-propylene glycol, were introduced into a vessel provided with a stirrer in the above order and the pigment was dissolved therein by means of a dissolver. 1,2-Propylene glycol was added thereafter. This pigment paste was prepared in a large amount so that for the blends with the dispersions to be tested equal conditions, for example as regards the pigment dispersion, were ensured.

Formulation XI: This differed from formulation I by a different composition of the mixture of solvent added to the finished paint (step 3 of the preparation of paint). A mixture of 36 parts by weight of 1,2-propylene glycol, 13.5 parts by L5 weight of butyl diglycol acetate and 20 parts by weight 2,2,4 - trimethylpentanediol - 1,3 - monoisobutyrate - 1 (Texanol) was added.

Formulation III: This also differed from the above formulations by a !0 different composition of the mixture of solvent added to the finished paint, i.e. a mixture of 51.1 parts by weight of 1,2-propylene glycol, 18.9 parts by weight of butyl diglycol acetate and 20 parts by weight of 2,2,4 - trimethylpentanediol - 1,3 - monoisobutyrate (Texanol) was added. :5 For the manufacture of the individual paints a corresponding proportion of the pigment paste was mixed, while slowly stirring, with the dispersions approximately one day old, whereupon the solvents (3) were added. After complete mixing, the paints were passed through a sieve.

The paints were allowed to stand for one day and then spread onto glass plates and steel sheets onto which a pigmented glossy air-drying alkyd resin enamel had been sprayed and which had been kept after drying for 24 hours - 15 4328? at 100°C. A film applicator was used having a slit diameter of 200 microns. After a drying period of 24 hours the wet adhesion of the gloss paints was tested according to the two following methods: (1) Abrasion test The glass plates with the dried coating of dispersion paint were inserted in a mechanical abrasion device as described, for example, in German Offenlegungsschrift No. 2,262,956 and similar to the Gardner Washability and Abrasion Machine, but having a stroke length of approximately 1.20 m in a manner such that the applied films of dispersion paint were in a vertical position with respect to the direction of movement of the brush. Due to the long moving distance about 15 paints could be simultaneously tested in one run.

A brush with hog's bristles was used which, at the beginning of the test, had been wetted with distilled water. During the test the area on which the brush moved was also wetted with distilled water so that the brushed areas were permanently covered with a water film. With a poor wet adhesion the dispersion paint was brushed off the substrate after a few strokes of the brush and torn at the boundary between wetted and dry film. The better the wet adhesion the greater the number of strokes of the brush until the film is shifted aside. The dispersion paint has an optimum wet adhesion when in the wetted area the film is not damaged after 5,000 strokes of the brush one stroke including a backward and forward movement. (2) Condensation test A rectangular thermostat chamber was used one half of which was filled with water at 50°C and in the gas space of which above the water level was mounted a fan. The upper opening was covered with the steel sheets with the coated surface facing downwards so that the thermostat chamber was closed. The thermostat was kept in a room maintained at 23°C. 13283 - 16 Owing to the temperature difference, steam condensed on the lower surface of the sheets and acted on the coats of paint. After 15 minutes the sheets were removed and the coatings evaluated.

With an unsatisfactory wet adhesion, blisters formed between the film of wet dispersion paint and the alkyd resin lacquer and the film could be easily shifted aside. A film having a good wet adhesion was still free of blisters after a period of 6 hours and could not be shifted.

LO The test results are listed in The Table TABLE Summary of the test results : ’aint incorporating lispersion of !xample No. Formulation No. abrasion test, number of strokes of brush stability in condensation test 1 I >5000 > 6 hrs. 2* I 110 <15 min. 3 I >5000 > 6 hrs. II >5000 > 6 hrs. III >5000 > 6 hrs. 4* I 70 <15 min. 5 I >5000 > 6 hrs. 6* I 50 <15 min. 7 I >3000 > 4 hrs. 8 I >3000 > 4 hrs. 9 I >3000 > 4 hrs. 10* I 170 <15 min. * Comparative Examples.

Claims (7)

1. CLAIMS;1. A process for the preparation of an aqueous plastics dispersion which comprises copolymerizing in an aqueous system the following monomers: (A) from 20 to 79.4% by weight, based on the total monomers, of one or more hardening monomers selected from methyl methacrylate, styrene and vinyl toluene; (B) from 20 to 79.4% by weight, based on the total monomer, of one or more plasticizing monomers selected from acrylic acid esters in which the alcohol radical is a linear or branched alkyl radical having from 2 to 8 carbon atoms and conjugated dienes having from 4 to 8 carbon atoms which may be substituted by halogen atoms; (C) from 0.1 to 5% by weight of acrylic acid, methacrylic acid, acrylamide or methacrylamide; and (D) from 0.5 to 10% by weight of an acetoacetic acid ester of the formula 0 0 R R' ll il 11 CH 3 — C—CH 2 -C-X-C = C-H, in which R is H or CH^, R' is H or CH^, and X is -0-, -OCHp II —0 CH 2 CH 2 0—c — or II —0 — CH 2 -CH 2 — CH 2 — o— c —,

2. A process as claimed in claim 1, wherein component (A) is used in an amount of from 40 to 60% by weight. 13283 - 18

3. Λ process as claimed in claim 1 or claim 2, wherein component (B) is used in an amount of from 40 to 60% by weight.

4. A process as claimed in any one of claims 1 to 3, 5. Wherein component (D) is used in an amount of from 1 to 5% by weight.

5. A process as claimed in any one of claims 1 to 4, wherein component (D) is allyl acetoacetate.

6. A process as claimed in claim 1 carried out subLO stantially as described in any one of Examples 1, 3, 5 and 7. To 9 herein.

7. An aqueous plastics dispersion whenever obtained by a process as claimed in any one of claims 1 to 6,