GB1574721A

GB1574721A - Process for preparing aqueous copolymer emulsions

Info

Publication number: GB1574721A
Application number: GB8468/76A
Authority: GB
Original assignee: Canadian Industries Ltd
Current assignee: PPG Architectural Coatings Canada Inc
Priority date: 1976-03-03
Filing date: 1976-03-03
Publication date: 1980-09-10
Also published as: MX144637A; NO770723L; ES456487A1; JPS6059241B2; NZ183430A; IT1076178B; NL7702223A; JPS52107085A; DE2709308C2; DE2709308A1; FI770675A7; SE7702192L; BE851969A; BR7701289A; AU503408B2; FR2342992A1; FR2342992B1; AU2274577A

Description

(54) PROCESS FOR PREPARING AQUEOUS COPOLYMER EMULSIONS (71) We, CANADIAN INDUSTRIES LIMITED, a Corporation of Canada, of 630 Dorchester Blvd. West, Montreal, H3C2R4, Quebec, Canada, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an improved process for the aqueous polymerization of a p-ethylenically unsaturated monomers whereby latices are obtained which, when formulated into coatings, give films having improved resistance to water. The resulting coatings may be used in a wide variety of applications, examples of which include automotive finishes, trade sales paints and general industrial use applications, such as coil coatings, metal decorating formulations, interior can coatings, and resins for electrostatographic and electrofax duplicating processes.

The development of a wide range of products based on the use of anionic surfactant stabilized addition polymers is well established. In many coating formulations there is a need for very good resistance to moisture and water environments. Products based on conventional anionic emulsion technology have been found to lack satisfactory resistance to moisture and water environments in certain critical end applications. This has been identified as being due to the presence of water soluble "groups", additives, and/ or reaction by-products.

According to the present invention, there is provided a novel process whereby alkali metal and alkaline earth metal ions in the latex preparation step are replaced by ammonium or amine ions to result in surprisingly moisture and water environment resistant coatings.

The source of the offensive ions arises mainly from three classes of substances used in emulsion polymerization: (a) the catalyst, (b) the buffer system to keep the pH in the desired range and (c) the surfactant system used in emulsion stabilization. Some classical examples are sodium persulphate, peroxides and ferrous ions/or sodium hyposulphite as catalysts, sodium carbonate or bicarbonate as buffers, and sodium lauryl sulphate as surfactant.

It should be emphasized that the use of the amine salt forms of catalysts and surface active agents in aqueous emulsion polymerization is known. However, unlike the processes of the prior art, the process of the present invention uses exclusively the amine and ammonium ions, purposely avoiding the use of the offensive alkali metal and alkaline earth metal ions, such as sodium ions. in order to obtain an improved end product. This is contrary to established techniques which are currently recommended commercially and described in all the literature. wherein the basic raw materials recommended for such polymerization processes introduce these offensive ions in one or more of the above mentioned three basic ingredients.

Previous attempts have been made to remove all ions from the latex other than hydrogen and hydroxyl ions by dialysis or ion exchange techniques to give very high resistivity and thus to get water resistant coatings. These processes are relatively comples and involve treating the entire volume of the finished product. which certainly makes the processes time consuming and costly. This extreme step has been found not to be necessary for most end uses.

It is also theoretically possible to specifically ion-exchange out the alkali metal and alkaline earth metal ions in a latex and subsequently replace the hydrogen ions with amine ions.

However. in addition to the above mentioned drawbacks, this process will result in a latex having a very low pH at one stage of the process which could destabilize the emulsion.

Further, in some of the disclosures hereinafter, the use of ion-exchange techniques to make certain amine forms of specific surfactants is described. this is only because the particular surfactants were only currently available commercially in the highly undesirable sodium ion form and/or contain high levels of undesirable salts arising from the manufacture of the surfactant. In any event, the ion-exchange process used in these examples requires the processing of only a small fraction of the polymerization ingredients and presents no stability problems.

Finally, there have been proposed previously methods of surfactant-free polymerization which produce stable aqueous dispersions for coating compositions. Howver, such methods have failed to recognize that the absence of substantially any alkali metal or alkaline earth metal ions in the polymerization system results in aqueous copolymer dispersions which when formulated into coatings have increased resistance to water.

Thus, the present invention provides an improved process for the preparation of an aqueous emulsion of a copolymr which comprises polymerizing in aqueous medium, in the presence of a water-soluble surface-active agent and a water-soluble initiator for the polymerisation, both of which are ionisable salts, from 99.5 to 30 parts by weight of at least one monomer selected from the group consisting of styrene, methyl styrene, acrylonitrile, alkyl acrylates, alkyl methacrylates, alkyl fumarates, alkyl maleates, wherein the alkyl radical contains from 1 to 12 carbon atoms, vinyl esters of organic and inorganic acids, vinyl pyridine, butadiene and ethylene, from 0 to 30 parts by weight of an alkyl ether of methylol acrylamide or methylol methacrylamide, in which the alkyl group contains from 1 to 4 carbon atoms, from 0 to 25 parts by weight of an hydroxyl group-containing monomer, from 0 to 15 parts by weight of an epoxide group-containing monomer, from 0 to 15 parts by weight of an amine group-containing monomer and from 0 to 15 parts by weight of a carboxyl group-containing monomer, with the total parts by weight of monomers being 100, the improvement comprising introducing both the said surface-active agent and the said initiator in the form of an amine salt or an ammonium salt and carrying out the polymerization in the absence of alkali metal and alkaline earth metal ions.

The process of this invention may be carried out according to conventional emulsion polymerization techniques; the following steps are generally practised. To a reactor vessel are added water, one or more surfactants in water-soluble amine or ammonium salt form and one or more water soluble amines or ammonium hydroxide. The vessel is heated to and maintained at temperatures in the range of from 30"C to 95"C, depending on the catalyst system employed. while a pre-emulsified mixture of monomers with further surfactant, at least one polymerization initiator and water is added. Further additions of the pre-emulsified feed are made over a period of four to six hours. When monomers containing co-reactive functional groups are included. separate feeds of each monomer are employed in order to prevent premature cross-linking. Further, after the addition of the first monomer is completed, some water-soluble amine or ammonium hydroxide is added to neutralize substantially the functional group and to give the dispersion a minimum pH of 5. The addition also helps to inhibit the functional groups from reacting.

Any water-soluble amine or ammonium salt forms of surface active agents which are known conventionally to give stable aqueous emulsions can be employed in the process of this invention. Other salt forms of stable aqueous emulsions can be employed in the process of this invention. Other salt forms of the surface active agents may be more readily available commercially, in which case these surface active agents may be treated with an ion-exchange resin and neutralized with an appropriate amine. Amines such as ammonia and water-soluble primary, secondary and tertiary aliphatic and aromatic amines have been successfully employed for such treatment.

The quantity of the water-soluble amine salt surfactant used in the process of this invention is the same quantity as for other salt forms suggested for use in aqueous emulsion polymerization processes. with the only guideline being that the minimum quantity which will give stability to the latex should be used.

The buffer system and polymerization initiators are also chosen to be in the form of water-soluble amine salts or the free amine (to regulate pH) in order to avoid the use of alkali metal and alkaline earth metal ions. Polymerization initiators as opposed to sodium persulphate. Suitable buffers include ammonium hydroxide or the free amine itself. A number of such agents are available commercially and they may be employed in the process of this invention.

As mentioned earlier the process of this invention may be used to produce latices for a variety of end uses. The polymerization ingredients are readily varied according to the desired utility. When the latices are formulated into paints a small quantity of alkali metal or alkaline earth metal ions may be included as part of the millbase. This quantity is so small that the ions do not exert a decisive influence on the adhesion of the paint. In any event, the majority of harmful alkali metal or alkaline earth metal ions arise from the latex as opposed to the millbase. The present invention thus seeks to overcome this problem by avoiding the use of or removing such harmful ions from the latex during its preparation.

Thus to produce a latex for use in an automotive coating formulation, the improved process of this invention comprises polymerizing from 93 to 30 parts by weight of styrene and methyl methacrylate, from 0 to 50 parts by weight of butyl acrylate, from 5 to 15 parts by weight of hydroxyethyl methacrylate or hydroxypropyl methacrylate and from 2 to 5 parts by weight of methacrylic acid. To produce latices for metallic paint formulation, the process comprises polymerizing 10 parts by weight of styrene, 42 parts by weight of methyl methacrylate, 40 parts by weight of butyl acrylate, 5 parts by weight of hydroxypropyl methacrylate or hydroxyethyl methacrylate and 3 parts by eight of methacrylic acid. To produce latices for solid colour formulations, the process comprises polymerizing 42 parts by weight of styrene, 10 parts by weight of methyl methacrylate, 40 parts by weight of butyl acrylate, 5 parts by weight of hydroxypropyl methacrylate or hydroxyethyl methacrylate and 3 parts by weight of methacrylic acid. The resulting copolymers have reduced viscosities in therange of 0.25 to 0.8 dl/g. measured in ethylene dichloride/ethanol (95/5) at 0.5 g. copolymer per 100 ml. solvent.

The latex copolymers prepared according to the process of the present invention may be used in automotive paint formulations which include melamine-formaldehyde resins. Suitable resins of this type include conventional alkylated melamine-formaldehyde resins designed for water-based coatings having a ratio of -CH2 OR groups to -CH20H groups, where R is lower alkyl, of at least 5:1. The latter resins can be prepared by known techniques in which a lower alcohol such as methanol, ethanol, butanol, isobutanol, propanol, or isopropanl is reacted with a melamine-formaldehyde resin to provide pendant hydroxyl groups. Examples of commercially available resins of this type are "Cymel" 300, "Cymel" 301. "Cymel" 303 ("Cymel" is a trade mark), "Uformite" MM-83 (trade mark) and "Resimene" 740 (trade mark). In fact, any conventional alkylated, e.g. butylated, melamine-formaldehyde resin may be used provided it meets the requirements of aqueous solubility. compatibility or dispersibility in the final system. Usually the resin will comprise from 8 to 30 parts by weight per 100 parts by weight of the paint formulation.

There may also be included in such automotive paint formulations a dissolved compatible copolymer present in the range from about 0 to about 45 parts by weight per 100 parts by weight of the formulations. The copolymer will usually be acrylic in nature and preferably has a reduced viscosity RV of from about 0.15 to about 0.50 dl/g. measured in ethylene dichloride/ethanol (95/5) at 0.5 g. copolymer per 100 ml. solvent.

The term''compatible" when used in relation to this dissolved copolymer indicates that the dissolved copolymer must be compatible with the latex copolymer and the melamineformaldehyde resin both in the liquid composition and when baked out as a finish. In the liquid phase. compatibility means that the stability of the system is such that no phase separation occurs while in the baked finish. the pigmented baked film should not suffer loss of gloss.

The term dissolved" or soluble indicates that the copolymer is dissolved or soluble (giving clear or slightly hazy solutions) in one or more mixtures of water and water-miscible organic solvents. usually the solvents in which it is prepared and which meet pollution regulations for compositions and level.

The process of this invention may also be used to produce latices for trade sales paints. The main monomer for such a process is vinyl acetate copolymerized with one or more monomers selected from the following group and in the following amounts: from 0 to 60 parts by weight of alkyl acrylates such as dibutyl or dioctyl fumarate. dibutyl or dioctvl maleate. butyl acrylate. ethyl hexvl acrylate. the vinyl ester of "Versatic" and ("Versatic" is a Registered Trade Mark) vinyl caproate, vinyl propionate or ethylene. from 0 to 10 parts b weight of an alkyl ether of methylol acrylamide or methylol methac rvlamide. in which the alkyl group contains from 1 to 4 carbon atoms. from 0 to 10 parts by weight of an hydroxyalkyl acrylate or an hydroxyalkyl methacrylate, from 0 to 5 parts by weight of glycidyl methacrylate. from 0 to 5 parts bv weight of acrylic or crotonic acid. and from 0 to 5 parts by weight of dimethylamino-ethylmethacrylate or vinyl pyridine.

The total parts by weight of monomers comprises 100 with the vinyl acetate constituting the remaining portion.

The above copolvmer latices will have glass transition temperatures (Tg) in the range of from about 5 C. to about 30"C. and minimum film forming temperatures in the range of from about 0 C. to about 75"C. The lattices may be formulated into interior and exterior paint formulations according to conventional procedures.

For the preparation of a trade sales acrylic latex via the process of this invention. the following monomers are suitably employed in the polymerization process in amounts within the designated ranges.

Monomer Parts by weight Methyl methacrylate 30-50 Styrene 10-50 Ethyl acrylate 30-70 Butyl acrylate 20-50 2-Ethylhexyl acrylate 20-50 Acrylic acid 0-15 Methacrylic acid 0-15 Dimethylaminoethylmethacrylate 0-5 Glycidyl methacrylate 0-5 Hydroxypropyl methacrylate 0-10 Isobutoxymethylacrylamide 0-10 These copolymer latices have Tg's in the range of from about 0 to 100C. and minimun film forming temperatures in the range of from about 0 C. to about 25"C.

The above latices may be formulated into interior and exterior paint formulations according to conventional procedures also. For the interior paints the pigment volume concentration may range from about 45-65% and the pH from 8.5-9.0. The white exterior paint generally has a pigment volume concentration of 40-50% and a pH of 8.5-9.0. The tint base exterior paint usually has a pigment volume concentration of 30-40% and a similar pH range.

In the same trade sales paints field, when the main copolymers comprise styrene and butadiene monomers, they are preferably polymerized in the weight ratio of 60:40, and the resulting latex has a pH in the range of 7.0-8.5. When the main copolymers comprise vinyl chloride and acrylic monomers, they are preferably polymerized in the weight ratio of about 40:60, and the latex has a pH of 7.0. Copolymers of vinyl chloride and ethylene monomers preferably comprise a weight ratio of about 70:30 of each monomer respectively, and the resulting latex has a pH of 7.0. In each process, the functional monomers, such as acrylic acid, methacrylic acid, dimethylaminoethylmethacrylate and glycidyl methacrylate are also present in the same parts by weight ranges previously described for the acrylic paint formulations.

The process of the present invention has also proved advantageous in the production of latex copolymers for general industrial use such as in coil-coatings, metal decorating formulations and interior can coating formulations. The copolymers are thermosetting and comprise acrylic-type monomers including one or more monomers containing reactive groups such as acid, hydroxyl and substituted amide. The latices may optionally then be combined with from 0 to 30 parts by weight of a water-soluble or water-dispersible crosslinking agent such as melamine-formaldehyde, urea-formaldehyde, epoxy and phenolic resins. The latex copolymers can be dried to form powders which can then be used as electrostatographic toner resins. coatings, adhesives and moulding compounds. Preferred polymerization ingredients and amounts for preparing such latex copolymers are as follows:from 0 to 30 parts by weight of at least one monomer selected from alkyl ethers of methylolacrylamide and methylolmethacrylamide in which the alkyl groups contain from 1 to 4 carbon atoms. from 0 to 25 parts by weight of at least one hydroxyl group containing monomer, from 2 to 15 parts by weight of at least one carboxyl group containing monomer, from 0 to 40 parts by weight of at least one hard monomer selected from methyl methacrylate and styrene. and from 40 to 80 parts by weight of at least one soft monomer selected from butyl acrylate and ethyl acrylate.

The resulting latices are neutralized with water soluble amines or ammonia to get adequate application characteristics, to pH's of 6 to 9. In addition the formulations may contain water soluble organic solvents such as the alcohols, ketones and glycol ethers at levels of from 0 to 30% by weight of the volatile components.

The invention is illustrated by the following Examples which are not to be regarded as limiting the invention in any way. All parts, percentages and ratios are by weight unless otherwise indicated.

EXAMPLE I 1- AUTOMOTIVE FORMULATION In this example. a comparison was made of two latices having identical formulations with the exception that one contained sodium ions and the other contained ammonium ions.

Each latex was formulated with an aminoplast resin into paints and the paints were tested for water resistance.

PREPARATION OF LATICES Latex No. 1 Latex No. 2 Parts Parts Components By weight By weight Water 230 230 Surfactant Solution A (see below) 210 Surfactant Solution B (see below) - 210 The above ingredients were combined in a vessel and heated to 80-850C. and held at this temperature during the addition of the following ingredients.

Latex No. 1 Latex No. 2 Parts Parts Components By weight By weight Water 15 15 Sodium persulphate - 1.5 Ammonium persulphate 1.5 Monomer mixture (see below) 2.5 25 Sodium carbonate - 1.5 The mixture was held at 80-850C. for a further 1/4 to 1/2 hour. Subsequently additions of pre-emulsified feeds 1 and 2 as outlined below were carried out over 5 hours.

PREPARATION OF MONOMER MIXTURE Latex No. 1 Latex No. 2 Parts Parts Feed 1 By weight By weight Methyl methacrylate 630 630 Styrene 102 102 Butyl acrylate 203 203 Methacrylic acid 38 38 Octanethiol 3.8 3.8 Dimethylaminoethanol 4.0 Dibenzyl adipate 150 150 Surfactant Solution A 580 Surfactant Solution B - 580 Water 474 474 Ammonium persulphate 1.5 Sodium persulphate - 1.5 Sodium carbonate - 1.5 Feed 2 Methyl methacrylate 157 157 Styrene 25 25 Butyl acrylate 51 51 Hydroxypropyl methacrylate 66 66 Octanethiol 1.2 Surfactant Solution A 210 Surfactant Solution B - 210 Ammonium persulphate 0.8 Sodium persulphate - 0.8 The mixture was then held at 8-85 C, for a further one hour. The resulting latices had the following properties: Total solids = 45% Reduced viscosity = 0.32 dl/g pH = 5.0 PREPARATION OF SURFACTANT SOLUTIONS Surfactant Solution B "Aerosol" A-196 (Trade Mark) 12 g "Siponate" DS-10 (Trade Mark) 24 g Water 2406 g Total 2442 g The above ingredients were mixed in the quantities shown.

Surfactant Solution A The above Surfactant Solution B was treated with 1000 grams of "Dowex" 50 W X 8 (Trade Mark) (acidic form) ion exchange resin beads to remove the sodium ions. The beads were filteed off and the solution was titrated with sufficient dimethylaminoethanol to give it a pH of 8, thereby forming the amine salt of the surfactant blend. As an added control to ensure complete removal of sodium ions from the surfactant solution, the acid number must be a minimim of 146 and generally should be in the range of from 146 to 152. The use of pH alone as a control is not adequate. Acid number may be defined as the number of milligrams of potassium hydroxide needed to neutralize 1.0 gm. sample.

Evaluation of Water Sensitivity as indicated by the Cleveland Condensing Humidity Cabinet Test (QCT) carried out at 1500F.

QCT 1500F. Bake 30' at 300"F.

Latex White Clear No. 1 Initial Gloss (20"Head) 84-86 88-92 Gloss after 24 hours on QCT 79-81 89-90 Whitening - None Blistering etc. very slight very very slight No. 2 Initial Gloss (200 Head) 74-76 76-82 Gloss after 24 hrs. on QCT 45-52 38-43 Whitening - significant Blistering. etc. significant significant EXAMPLE 2-TRADE SALES PAINT In this example. a comparison was made of sodium salt surfactant containing latices vs ammonium salt surfactant and dimethylethanolamine salt surfactant containing latices. The latices were formulated into exterior flat finishes and applied to a smooth, glossy, grey alkyd surface. aged 3 days. Following overnight humidity exposure (QCT), the films were crossscribed using a comb template and taped using No. 610 high adhesion tape. The tape was then removed and loss of adhesion was noted.

Preparation of Latex A latex copolymer having a fixed composition of methyl methacrylate/butyl acrylate/acrylic acid/glycidyl methacrylate in the respective weight ratio of 44:53:2:1 was prepared using the sodium salt surfactant (0.8% based on the weight of copolymer) and sodium persulphate as a polymerization initiator. With the amine form of surfactant, ammonium persulphate was employed. In non-ionically stabilized systems. 4.3% surfactant based on the weight of copolymer was required to obtain adequate emulsion stability.

Latex No. 1 (Anionic/nonionic stabilized latex using sodium cations) Composition Parts by weight Water 450 "Triton" X 200 (Trade Mark) 10 "Triton" X 405 (Trade Mark) 6 "Alcolac" DV 720 (Trade Mark) 10 Na2S208 2 The first four ingredients were combined and heated to 75 C. at which point the sodium persulphate was added.

The following ingredients were then added over a period of 1 1/2 hours, the mixture being held at 75 C.

Methyl methacrylate 350 Butyl acrylate 422 Acrylic acid 16 Glycidyl methacrylate 8 Water 400 "Triton" X 405 20 The mixture was maintained at 750C. and the follwing were added during the last 1/3 of the time of the above feed.

Na2S208 1.0 "Triton" X 405 4 Water 40 The mixture was held at 75 C. for a further 1/2 hour and then cooled to rz-t. anu ule following addition was made.

Na2S208 1 "Triton" X 405 4 Water 10 The mixture was cooled to 25 C. and the following ingredients were added: NR4OH 16 Water 10 The resulting latex had a T.S. = 45% pH = 8.5% Latex No. 2 (Amine form of surfactant) Composition Parts by weight Surfactant solution (see below) 115 Water @ 335 (NH4)2S2Os 0.8 NH40H 1.0 The above ingredients were combined and heated to 820 C.

The following ingredients were added to this mixture over a period of 2 hours, the temperature being maintained at 820 C.

Methyl methacrylate 350 Butyl acrylate 422 Acrylic acid 16 Glycidyl methacrylate 8 Surfactant Solution 430 NH4OH 4 (NH4)2S208 0.8 After the above addition was completed, the mixture was held at 820C. for a further 1/2 hour, it was cooled and the following were added: NH40H 16 Water 10 Surfactant Solution "Siponate" DS-10 (Trade Mark) 42 "Aerosol" A-196 (Trade Mark) 21 Water 4277 Total 4340 A solution of the above ingredients was prepared and treated with 1500 grams of "Dowex" 50 W X 8 (acidic form) ion exchange resin beads to remove the sodium ions. The beads were filtered off and the solution was titrated with sufficient ammonia to give a pH of 8, thereby forming the ammonium salt of the surfactant blend. As before the acid number was measured and found to be in the range of 146 to 152.

Latex No. 3 (Dimethylethanolamine form ofsurfactant) A latex identical to Latex No. 2 was prepared except that dimethylaminoethanolamine replaced the ammonia and ammonium hydroxide on a 1:1 molar basis.

Latex No. 4 A latex similar to Latex No. 2 was prepared except that the surfactant solution was not treated with an ion exchange resin and the ammonium hydroxide and ammonium persulfate were replaced with sodium carbonate and sodium persulfate on a 1:1 molar basis.

Paint Formulation Mill base Deionized water 76.2 Tetrapotassium pyrophosphate 1.7 "Tamol" 731 (Trade Mark) (25So) Wetting Agent 3.5 Rutile TiO2 154.5 Calcium carbonate 87.0 Magnesium silicate 46.7 Total: 369.6 The above mixture was ground on a cowles blade and the following premix was added thereto.

Ethylene glycol 14.0 Hexylene glycol 7.0 Hydroxyethyl cellulose thickener 2.0 Antifoam "Nopco" WHT (Trade Mark) 3.5 Deionized water 38.9 Total: 65.4 Grand Total: 435.0 To this mill base was added 302 parts of each of four latices (at 46.5% solids) and each paint was tested for Wet Adhesion with the results as follows: Wet Adhesion Description Results Latex No. 3 Ionexchanged, Dimethylethanolamine Topcoat did salt not lose adhesion Latex No. 1 Anionic/Nonionic, sodium salt Topcoat suffered severe loss of adhesion Latex No. 4 Sodium salt Topcoat lost adhesion Latex No. 2 Iionexchanged, NH4 salt Topcoat did not lose adhesion The above results indicate that the presence of sodium ions causes weak adhesion.

EXAMPLE 3 Preparation of Typ-ical Automotive Acrylic Copolymer Lates Methyl methacry late / styrene / butylacrylate / hydroxy-propylmethacrylate/ methac-rylic acid copolymer in the respectiveweight ratio of 42/10/40/5/3 Preparation of Sur-factant Solution "Aerosol" A-196 12 parts "Siponae" DS-10 24 parts Water 2406 parts Total 2442 parts The above ingredients were mixed and then treated with 1000 grams "Dowex" 50 W X 8 (acidic form) ion exchange resin beads to remove the sodium ions. The beads were filtered off and the solution was titrated with sufficient dimethylaminoethanol to give it a pH of 8, thereby forming the amine salt of the surfactant blend.

Preparation of Latex An aqueous charge of 230 parts of water and 210 parts of the above surfactant solution was prepared and heated to 800C. An addition of 15 parts of water and 1.5 parts of ammonium persulphate was made and the whole was held at 800 C. for 30 minutes.

An emulsion (1) of the following ingredients was prepared and added to the above over 3 1/2 to 3 3/4 hours.

Parts Methyl methacrylate 477 Styrene 114 Butyl acrylate 454 Methacrylic acid 38 1-Octanethiol 4.8 Surfactant solution 580 Water 474 Ammonium persulphate 1.5 A further emulsion (2) of the following ingredients was prepared and immediately added to the above emulsion (1) over 1 1/4 to 1 1/2 hours.

Methyl methacrylate 119 Styrene 28 Butyl acrylate 114 Hydroxypropyl methacrylate (99% distilled grade) 74 1-Octanethiol 1.5 Surfactant solution 210 Ammonium persulphate 0.8 After the additions were completed, the mixture was held for a further one hour at 80"C., then cooled to 250C. and filtered through a 10,u bag. The resulting latex had a T.S. = 45%, RV = 0.33 dl/g.

The following are typical compositions for automotive waterborne enamels using the latices produced by the process of the present invention as described above.

Colour -- Medium Blue Metallic Enamel Parts by wt.

45% by weight total solids 65.2 acrylic copolymer latex 30% by weight triethanolamine 0.71 50% by weight aluminium millbase 2.08 Blue millbase 2.81 "Cymel" 301 3.7 40% by weight total solids dissolved acrylic copolymer 14.8 Deionized water 4.1 Butyl "Cellosolve" 5.1 But 1.89 parts by weight of dimethylaminoethanol were added. While the temperature was maintained at 70-900C., 29.89 parts of warm deionized water were added very slowly. The whole was stirred for 1/2 hour and cooled. The resulting solution copolymer had a total solids content of 39.5% by weight and a Cardner-Holt Viscosity equal to Zs-Z6.

EXAMPLE 4 Colour -- Light Blue Metallic Enamel Parts by weight 145% by weight total solids acrylic 42.79 copolymer latexa 30% by weight triethanolamine 0.4 Phthalocyanine Blue Millbaseb 1.17 Quindo Magenta Millbasec 0.09 Acid Resistant Aluminium 2.89 "Cymel" 301 6.21 Dissolved acrylic copolymerd 25.58 Butyl "Cellosolve" 4.78 Butanol 1.06 Water 13.16 80/20 Water/ butyl "Cellosolve" 1.88 Total: 100.00 a. Methyl methacrylate/ styrene/ butyl acrylate/ hydroxy propyl methacrylate/ methacrylic acid in the respective (% by weight) quantities 42/10/40/5/3 RV= 0.37 dl/g. b. A Cowles mix of phthalocyanine blue pigment (14 pts. by wet.), "Cymel" 301 (20 pts by wt.) deionized water (33 pts by wt.), butyl "Cellosolve" (33 pts. by wt.) and a trace amount of triethanolamine was prepared and passed twice through a sand mill. c. Same as for b. except Quindo Magenta pigment used in place of phthalocyanine blue pigment. d. Methyl methacrylate/butyl acrylate/hydroxypropyl methacrylate/acrylic acid in the respective (% by weight) quantities 20.5/61.6/15.4/2.5 RV=0.2 dl/g.

This enamel had a % by weight total solids = 37.2 (package solids) % by weight solvent = 20 No. 4 Ford Cup viscosity = 65 sec.

(package viscosity) The latex/ melamine-formaldehyde/ dissolved copolymer was combined in the respective parts by weight of 54/18/28.

The Cleveland Condensing Humidity Cabinet Test (QCT) was carried out on the Medium Blue metallic formulation and the off-white formulation of Example 3 and the Light Blue Metallic formulation of Example 4. These formulations showed no loss in gloss, blistering or whitening. whereas comparable systems using latices prepared using the sodium form of surfactants. sodium persulphate in place of ammonium persulphate and sodium carbonate in place of the dimethylethanolamine buffer suffered from blistering, loss of gloss and whitening.

In Table I there are listed formulations and RV' s for latex copolymers that were prepared according to the process of the present invention for the purpose of selecting an optimum composition for use in coating compositions of the type described in the previous examples.

TABLE I No. Copolymer Latex Copolymer/ Reduced Composition Dibenzyl Adipate Viscosity % by weight ratios Plasticizer ** RV MMA/S/BA/HPMA/MAA * dl/g 1 52/10/30/5/3 90/10 0.42 2 52/10/39/5/3 " 0.34 3 52/10/39/5/3 " 0.22 4 62/10/20/5/3 " 0.32 5 42/10/40/5/3 " 0.32 6 62/0/30/5/3 " 0.35 7 42/20/30/5/3 " 0.32 8 42/10/40/5/3 100/0 0.54 9 42/10/40/5/3 " 0.361 10 42/10/40/5/3 " 0.33 11 52/10/30/5/3 " 0.32 12 32/10/50/5/3 " 0.35 13 52/0/40/5/3 " 0.34 14 32/20/40/5/3 " 0.34 15 12/10/70*/5/3 " 0.246 *BMA in place of BA 16 35/10/47*/5/3 " 0.216 *EHMA in place of BA 17 32/30/39/5/3 " 0.322 18 42/10/40/5/3 " 0.347 19 62/10/20/5/3 " 0.347 20 72/10/10/5/3 " 0.358 21 52/ 10/39/5/3 " 0.405 22 72/10/10/5/3 90/10 0.318 23 40/10/40/5/5 100/0 0.382 24 35/10/40/5/10 " 0.365 25 35/10/35/10/10 " 0.377 26 35/10/40/10/5 " 0.365 27 10/42/40/5/3 " 0.406 28 0/52/49/5/3 " 0.348 29 0/62/30/5/3 " 0.382 30 10/52/30/5/3 100/0 0.35 31 10/40/40/5/5 " 0.37 32 10/35/40/5/10 " 0.375 33 10/35/35/10/10 " 0.342 34 10/35/40/10/5 " 0.357 35 22/10/60*/5/3 " 0.375 *EHMA in place of BA 36 46/10/36*/5/3 " 0.403 *EHA in place of BA 37 12/10/70*/5/3 " 0.33 38 35/10/47*/5/3 " 0.33 *EHMA in place of BA 39 57/10/25*/5/3 " 0.33 *EHA in place of BA *MMA = methyl methacrylate S = styrene BA = butylacrylate HPMA = hydroxypropyl methacrylate MAA = methacrylic acid BMA = butyl methacrylate EHMA = 2-ethylhexyl methacrylate EHA = 2-ethylhexyl acrylate ** preplasticized In the following Table II there are shown formulations of various latex copolymers prepared according to the process of this invention and dissolved or soluble copolymes which are suitable for formulating into coating compositions. Possible formulations using the copolymers are given. The melamine-formaldehyde resin in all cases is "Cymel" 301.

TABLE II Latex Copolymer Reduced Dissolved Acrylic Reduced Pigment Coating Composition Composition Viscosity Copolymer Composition Viscosity Latex Copolymer/MF/Dissolved % by weight ratios RV % by weight ratios RV Acrylic Copolymer MMA/S/BA/HPMA/MAA dl/g. MMA/BA/HPMA/AA dl/g. parts by weight ratios 42/10/40/5/3 0.33 20.5/61.6/15.4/2.5 0.2 Off-white &num; 62/5/12.5/2.5 light blue 59.5/16.7/23.8 metallic 56.6/20.8/22.6 52.7/12.5/34.8 50.1/16.7/33.1 47.7/20.8/31.5 32/30/30/5/3 0.683 50/30/15/5 0.15 Off-white &num; 81/12/7 (Off-white) light blue 47/10/30/10/3 0.44 20.5/61.5/15.4/2.5 0.2 metallic 73/12/15 (Off-white) 48/10/30/10/2 0.356 73/12/15 (Metallic) 32/25+30/10/3 0.33 57.5/12.5/30 (Metallic) 37/10/40/10/3 0.42 27/10/50/10/3 0.366 7/10/70/10/3* *BA substituted by BMA TABLE II (continued) Latex Copolymer Reduced Dissolved Acrylic Reduced Pigment Coating Composition Composition Viscosity Copolymer Composition Viscosity Latex Copolymer/MF/Dissolved %by weight ratios RV % by weight ratios RV Acrylic Copolymer MMA/S/BA/HPMA/MAA dl/g MMA/BA/HPMA/AA dl/g parts by weight ratios 32/30/30/5/3 0.383 20.5/61.6/15.4/2.5 0.2 Light Blue 54/18/28 metallic 47/10/30/10/3 0.44 48/10/30/10/3 0.356 32/25/30/10/3 0.33 37/10/40/10/3 0.42 27/10/50/10/3 0.366 7/10/70/10/3* *BA substituted by BMA 42/10/40/5/3 0.36 20.5/61.6/15.4/2.5 0.194 Light blue 52/18/30 metallic &num; 42/10/40/5/3 0.45 20.5/61.6/15.4/2.5 0.321 medium blue metallic 47/10/30/10/3 0.407 52/10/30/5/3 0.387 35/10/40/10/5 0.399 MMA = methyl methacrylate HPMA = hydroxypropyl methacryalte BMA = butyl methacrylate S = styrene MAA = methacrylic acid MF = melamine-formaldehyde BA = butyl acrylate AA = acrylic acid EXAMPLE 5 Formulation for Can Coatings Preparation of Latex (External crosslinking agent required) A surfactant solution of 0.4 % by weight of "Aerosol" A196 and "Siponate" DS-10 (1:2) in water was prepared and converted by ion exchange techniques to the amine form of the surfactants. A charge of 3.5% by weight of this surfactant solution in 27.2% by weight of water was prepared. The solution was heated to 800-850C and a charge of 0.07%by weight of (NH4)2S20s and 0.5% by weight of water was then added.

The following premix was prepared and added to the heated mixture over a period of 5 hours while the temperature was maintained at 80"-85"C.

Methyl methacrylate 8.3 Styrene 4.1 Butyl acrylate 25 Hydroxy propyl methacrylate 2.1 Methacrylic acid 2.1 Dimethylethanolamine 0.13 Surfactant solution (as prepared above) 13.4 (NH4)2S2O5 0.07 Water 13.53 The mixture was then held for a further one hour at a temperature of 80"-85"c.

The resulting latex was blended with 10% by weight of "Uformite" MM83 (Trade Mark for a melamineformaldehyde resin), reduced to application viscosity by use of a compatable solvent. The films when baked produce a high cure, durable can coating.

COMPARATIVE EXAMPLE Example 5 was repeated except that sodium carbonate and sodium persulfate replaced the dimethylethanolamine and ammonium persulphate on a 1:1 molar basis. In addition the surfactant solution was not converted by ion exchange techniques to the amine form of the surfactants.

EXAMPLE 6 Formulation For Can Coatings Preparation of Latex (Self-crosslinking) Copolymer: styrene/ methyl methacrylate/ethyl acrylate / isobutyoxymethyl acrylamide/methacrylic acid (10/20/55/10/5) Charge Parts Percent Water 1575 35.4 Surfactant Solution* 650 14.6 The above ingredients were heated to 80 -85 c and the following was added thereto.

(NH4)2S2O5 2.5 0.06 Premixes of Charges A and B were prepared and each was added simultaneously to the above mixture over a period of 2 hours.

Charge Parts Percent A. Styrene 81 1.8 Methyl methacrylate 162 3.6 Ethyl acrylate 446 10.0 Methacrylic acid 81 1.8 B. (MH4)2S208 1.5 0.04 Water 62 1.4 The following was then added: Charge Parts Percent Dimethylethanolamine 12 0.3 Premixes of Charges C and D were prepared and each was added simultaneously over a further 2 hour period.

Charge Parts Percent C. Styrene 81 1.8 Methyl methacrylate 162 3.6 Ethyl acrylate 446 10.0 Isobutyoxymethyl acrylamide 162 3.6 D. (NH4)2S20e 1.5 0.04 Water 62 1.4 The whole mixture was held at 800-850C. for a further 1 hour. The following substances were then added separately: Dimethylethanolamine 18.5 0.4 Butyl "Cellosolve" (trade mark) 450 10.1 Total 4456 100.0 The latex was cooled to 250C. and filtered. Durable films of high cure for use as can coatings were obtained.

*Surfactant Solution: A solution of 0.4% by weight of "Siponate" DS-10 in water was converted by ion exchange techniques to the amine form of the surfactant.

Beer Pasteurization Adhesion Test The latices of Examples 5, 6 and 7 were tested for adhesion as outlined below.

Panels of untreated aluminium (2" x 4" dimension) were coated with each of the latices to a thickness of 200 mg/4 square inches. The panels were baked for five minutes at 320"F.

Each of the panels was then submerged in cooled beer in a sealed glass jar. The jars were then placed in a water bath and heated to 65"C. over 3/4 hour, and held at 65"C. for a further 1/2 hour. The panels were removed from the jars and washed quickly under cold water, dried and examined for blooming and whitening. A cross was cut in each panel with a sharp scalpel. The cross was covered with tape and the tape was pulled off and the panel was observed for loss of adhesion.

A good system will show slight whitening on examination but very rapid recovery within 30 seconds. A poor system will stay white for several minutes before it recovers. A system with excellent adhesion will not show any peeling when the tape is pulled off.

Coatings formulated from the latices of Examples 5 and 7 showed slight whitening on examination and very rapid recovery as well as excellent adhesion. A coating formulated from the latex of Example 6 stayed white for several minutes and showed peeling on removal of the tape.

Claims

WHAT WE CLAIM IS:

1. An improved process for the preparation of an aqueous emulsion of a copolymer which comprises polymerizing in acjueous medium, in the presnece of a water-soluble surface-active agent and a water-soluble initiator for the polymerisation, both of which are ionisable salts. from 99.5 to 30 parts by weight of at least one monomer selected'from styrene, a-methyl styrene. acrylonitrile. alkyl acrylates, alkyl methacrylates, alkyl fumarates, alkyl maleates, wherein the alkyl radical contains from 1 to 12 carbon atoms, vinyl esters of organic and inorganic acids. vinyl pyridine. butadiene and ethylene, from 0 to 30 parts by weight of an alkyl ether of methylol acrylamide or methylol methacrylamide, in which the alkyl group contains from 1 to 4 carbon atoms, from 0 to 25 parts by weight of an hydroxyl groupcontaining monomer. from 0 to 25 parts by weight of an hyeroxyl group-contraining monomer, from 0 to 15 parts by weight of an epoxide group-containing monomer, from 0 to 15 parts by weight of an amine group-containing monomer and from 0 to 15 parts by weight of a carboxyl group-containing monomer, with the total parts by weight of monomers being 100, the improvement comprising introducing both the said surface-active agent and the said initiator in the form of an amine salt or an ammonium salt and carrying out the polymerization in the absence of alkali metal and alkaline earth metal ions.

2. A process as claimed in Claim 1 wherein from 93 to 30 parts by weight of styrene and methyl methacrylate, from 0 to 50 parts by weight of butyl acryate, from 5 to 15 parts by weight of hydroxyethyl methacrylate or hyroxypropyl methacrylate, and from 2 to 5 parts by weight of methacrylic acid are polymerized.

3. A process as claimed in Claim 1 wherein 10 parts by weight of styrene, 42 parts by weight of methyl methacrylate, 40 parts by weight of butyl acrylate, 5 parts by weight of hydroxypropyl methacrylate or hydroxyethyl methacrylate and 3 parts by weight of methacrylic acid are polymerized.

4. A process as claimed in Claim 1 wherein 42 parts by weight of styrene, 10 parts by weight of methyl methacrylate, 40 parts by weight of butyl acrylate, 5 parts by weight of hydroxypropyl methacrylate or hydroxyethyl methacrylate and 3 parts by weight of methacrylic acid are polymerized.

5. A process as claimed in Claim 1 wherein from 10 to 60 parts by weight of at least one monomer selected from dibutyl fumarate, dibutyl maleate, dioctylfumarate, dioctyl maleate, butyl acrylate, 2-ethylhexylacrylate, ethylene the vinyl ester C9 l, tertiary carboxylic acids, vinyl caproate, vinyl propionate are polymerized with from 0 to 10 parts by weight of an alkyl ether of methylol acrylamide or an alkyl ether of methylol methacrylamide, in which the alkyl group contains from 1 to 4 carbon atoms, from 0 to 5 parts by weight of glycidyl methacrylate, from 0 to 5 parts by weight of vinyl pyridine or dimethylaminoethylmethacrylate, from 0 to 5 parts by weight of crotonic acid or acrylic acid, from 0 to 10 parts by weight of an hydroxyalkyl acrylate or an hydroxy alkyl methacrylate, the total parts by weight of monomer being 100, with the remaining parts by weight comprising vinyl acetate.

6. A process as claimed in Claim 1 wherein from 10 to 70 parts by weight of at least one monomer selected from methyl methacrylate, styrene ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are polymerized with from 0 to 10 parts by weight of isobutoxymethyl acrylamide, from 0 to 10 parts by weight of hydroxypropyl methacrylate, from 0 to 5 parts by weight of dimethylaminoethylmethacrylate, from 0 to 5 parts by weight of glycidyl methacrylate and from 0 to 15 parts by weight of acrylic acid or methacrylic acid, the total parts by weight of monomer being 100.

7. A process as claimed in Claim l wherein from 0 to 30 parts by weight of at least one monomer selected from alkyl ethers of methylolacrylamide and methylolmethacrylamide, in which the alkyl group contains from 1 to 4 carbon atoms, are polymerized with from 0 to 25 parts by weight of at least one hydroxyl group-containing monomer, from 2 to 15 parts by weight of at least one carboxyl group-containing monomer, from 0 to 40 parts by weight of at least one hard monomer selected from methyl methacrylate and styrene and from 40 to 80 parts by weight of at least one soft monomer selected from butyl acrylate and ethyl acrylate.

8. A process according to claim 1 substantially as hereinbefore described, with reference to the foregoing examples.