GB2217721A - Aqueous coating composition and process for the production thereof - Google Patents

Description

Aqueous coating composition and process for the production thereof 2217721

This invention relates to an aqueous coating composition which comprises incorporating an aqueous aminoplast resin into an aqueous resin obtained by rendering aqueous with an organic amine, etc., a copolymer comprised of hydroxyl-group-containing alkyl(meth)acrylate, di(meth)acrylate of glycol or polyoxyalkylene glycol, a, monoethylenically unsaturated carboxylic acid and a vinyl monomer copolymerizable therewith, a process for the production of the aqueous coating composition and an aqueous coating. Especially, it relates to an aqueous coating composition which is excellent in water resistance and gloss and in which its solvent content is reduced, a process for the production thereof and an aqueous coating.

n' The outer surfaces of beverage cans containing soft drinks, etc., and food cans containing food are covered with coatings which prevent corrosion of can materials, enhanceaesthetic goods value and can withstand the heat treatment in food sterilization treatment. In these conventional coatings, organic-solvent-containing solutions of epoxy/amino type resin, acryl/amino type resin, polyester/amino type resin, etc., are coated by a roll coater and the coatings are baked hard in a gas oven. However, these coatings cause volatilization of a large amount of solvents at the baking time, give rise to air pollution, and further, are undesirable from the viewpoint of resource saving. Accordingly, it has been desired to develop aqueous coatings which can solve these problems.

Known aqueous coatings are classified to two types of water-dispersible and water-soluble ones. Many of the water dispersible type are usually synthesized by emulsion polymerization method using a surfactant and therefore, have defect that the surfactant used remains in a formed coating C) - 2 - and lowers water resistance. On the other hand, there is a process which comprises synthesizing acid-content (carboxyl group)-containing resins in an organic solvent instead of using any surfactant, and neutralizing the resins with a volatile base to render them dispersible or water soluble materials. However, these aqueous coatings require an acid content of not less than 20 of acid value in a basic resin structure, and have defect that they are inferior in water resistance, alkali resistance, etc., i.e., they lack the basic coating properties.

Further, avoidance of the above-mentioned defects has led to a proposal of an aqueous coating in which the content of a,$-monoethylenically unsaturated carboxylic acid is reduced to 3 to 10 % by.using monoacrylic ester of glycol such as mono(meth)acrylates of polyethylene glycol (Japanese Patent Publication No. 1735/1977).

This aqueous coating has advantages that water -resistance is improved and that it is excellent in alkali resistance and antirust strength. However, it has defect of being inferior in coating properties, such as softening of a coated film, occurence of blisters, decrease of gloss, etc., which are caused by severe heat treatment with boiling water, retort at 117 t to 125 t, etc., used in food sterilization treatment of beverage cans, food cans, etc.

Further, the outer surfaces of beverage cans and food cans have to be coated with coatings having excellent gloss in order to enhance aesthetic goods value. However, the above coating has not reached such a level as would meet the requirement.

The conventional aqueous coatings contain not less than 10 % by weight of an organic solvent for storage stability of the coatings and improvement of leveling property in formation of the coatings. Accordingly, they are insufficient in terms of air pollution and resource saving with regard to solvent volatilization at the baking time.

Summary of the invention:

It is an object of this invention to provide an 11 L 11 1 1.

1 aqueous coating composition which can give a coating excellent in water resistance and antirust, a process for the production thereof and such an aqueous coating.

It is another object of this invention to provide an aqueous coating composition which can give a coating having water resistance and withstandability against heat treatment atthe time of food sterilization treatment of beverage cans and food cans, a process for the production thereof and such an aqueous coating.

It is yet another object of this invention to provide an aqueous coating composition which can give a coating-so excellent in gloss as to increase aesthetic goods value, a process for the production thereof and such an aqueous coating.

Further, it is still another object of this invention to provide an aqueous coating composition which can give a coating so excellent in gloss as to increase aesthetic goods value, a process for the production thereof and such an aqueous coating.

Further, it is still another object of this invention to provide an aqueous coating composition which has a small organic solvent content, a process for the production thereof and such an aqueous coating.

This invention provides an aqueous coating composition comprised of an aqueous resin obtained by neutralizing with a volatile base,a copolymer comprised of (a) 5 to 65 % by weight of hydroxyalkylacrylate or methacrylate in which the alkyl group has a carbon number of 1 to 5, - (b) 5 to 50 % by weight of diacrylate or dimethacrylate of alkylene glycol or polyoxyalkylene glycol, (c) 2 to 20 % by weight of a,-monoethylenically unsaturated carboxylic acid, and (d) 20 to 88 % by weight of a vinyl monomer copolyverizable with the above compounds (a), (b) and (c), and an aqueous amine formaldehyde condensate.

1 4 Moreover, this invention provides a process for the production of an aqueous coating composition which comprises copolymerizing the above components (a), (b), (c) and (d) in an organic solvent in the pre.5ence of a polymerization initiator to convert these components to a precrosslinked ungelled copolymer, neutralizing said copolymer by addition of a volatile base to obtain an aqueous resin, then mixing said aqueous resin with an aqueous amine formaldehede condensate, and thererafter, distilling the organic solvent off.

Furthermore, this invention provides an aqueous coating comprised of the above aqueous resin and aqueous amine formaldehyde condensate.

Detailed description of the invention

The composition of this invention is described more in detail hereinbelow.

Examples coming under the component (a), i.e., C,-Cs hydroxyalkylacrylate or methacrylate of this invention, are hydroxymethylacrylate, hydroxyethylacrylate, hydroxypropylacrylate, hydroxyamylacrylate, hydroxybutylacrylate and methacrylates corresponding thereto. Preferably used are hydroxymethylacrylate, hydroxyethylacrylate and methacrylates corresponding thereto.

The component (b),i.e.,' diacrylate or dimethacrylate of alkylene glycol or polyoxyalkylene glycol, is represented by the following general formula.

R, R2 R3 1 1 1 CH2=C-C-O-(CH2-CH-0),,-C-C=CH2 h 11 0 0 wherein R,, R2 and R3 represent H or CH3 and n represents an integer of from 1 to 50f preferably from 1 to 8.

More specifically, those represented by the above formula in which n is 1 to 8 are preferable,, i.e., ethylene glycol diacrylate,- diethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, tetrapropylene glycol diacrylate, pentaethylene glycol diacrylate, pentapropylene glycol 1 1 diacrylate, hexaethlene glycol diacrylate, hexapropylene glycol diacrylate and methacrylates corresponding thereto.

Examples of the component (c), i.e., a,fl-monoethylenically unsaturated carboxylic acid, are acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc., and especially, preferable are acrylic acid and methacrylic acid.

Examples of the component (d), i.e., vinyl monomer copolymerizable with the above components (a) to (c), are alkylesters of acrylic acid or methacrylic acid such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, ethyl methacrylate, butyl methacrylate, stearyl methacrylate and cyclohexyl metahcrylate, aromatic vinyl compounds such as styrene, vinyl toluene and a-methylstyrene, vinyl acetate, vinyl ethyl ether, etc.

The content of the component (a) in the copolymer resin is 5 to 65 % by weight, preferably 5 to 20 % by weight. If the content of the component (a) is smaller than the above lower limit, the number of crosslinkage points is not sufficient. As a result, the water resistance of the resultant coating is made inferior, and the coating atability is made insufficient since the number of hydrophilic groups is small. On the other hand, if the content of the component (a) is larger than the above upper limit, too large a number of crosslinkage points results in inferior flexibility of the resultant coating.

The component (b) is used in an amount of 5 to 50 % by weight, of the copolymer resin. If the amount is less than the above lower limit, the precrosslinkage effect can not rather be obtained, and the improvement of water resistance is poor. If the amount is more than the above upper limit, the flexibility is made inferior. The above range is one in which the improvement of water resistance and the flexibility can be well balanced.

The content of the component (c) in the copolymer resin is 2 to 20 % by weight, preferably 5 to 15 % by weight. As far as the coating composition is rendered aqueous, the - 6 Smaller the content is, the better the water resistance is. This purpose can be achieved if the content is not less than the above lower limit. However, if the content exceeds the above upper limit, the water resistance is made insufficient. Further, incorporation of the component (d) in the range from 20 to 88 % by weight in the copolymer makes it poss'ible to adjust the coating hardness and flexibility of the composition.

The copolymer of this invention can be obtained in the form of a precrosslinked ungelled copolymer by copolymerizing the above components (a) to (d) in an organic solvent by the use of peroxide or azo compound as a catalyst. Examples of the peroxide include benzoyl peroxide, acetyl peroxide, succinic acid peroxide, m-toluQryl peroxide, t-butyl peroxy-2ethylhexanoate, t-butyl peroxyisobutylate, 1-1-bis(tbutylperoxy)3,3,5trimethyl cyclohexane, lauroyl peroxide, etc. Examples of the azo compound include 2.2'azobisisobutylonitrile, dimethyl-2,2'- azobisisobutylate, 2,2'azobis-2,4-dimethylbaleronitrile, 4,4'-azobis-4- cyanovaleric acid, 1,1'-azobiscyclohexane carbonitrile, etc.

The synthesis of the copolymer without gellation can be carried out at a temperature of 90 to 120 V in a comparatively low polymerization solid content of not more than 50 % by weight, preferably 30 to 45 % by weight. The resulting copolymer solution scarecely exhibits ultraviolet ray absorption as compared with those before the polymerization. This fact also shows that the charged monomers have been entirely copolymerized under the above conditions, and it is surprising that the precrosslinkage without gellation is possible.

The_copolymer comprised of the above four components is rendered aqueous by the use of a volatile base such as ammonia or organic amine. Examples of the organic amine include monoethanol amine, dimethyl amine, diethyl amine, triethyl amine, triethanol amine, diethyl ethanol amine, dimethylethanol amine, diethylethanol amine, etc.

After the copolymer is rendered aqueous or after an C.

4 1 i 1 aqueous aminoplast resin is incorporated, the organic solvent in the solution is distilled off at reduced pressure of about to about 200 torr at a temperature in the range from 40 to t to give a water-soluble or water-dispersible resin solution. V For this reason, in view of the distilling-off at a post-step, it is preferable to use, in the synthesis, an organic solvent haying a boiling point of not higher than 180 t. When consideration is given to temperatures at the synthesis time and solubility of the copolymer in an organic solvent, it is desirable to use a solvent having a boiling point in the range from 75 to 180 t; Examples of such a solvent are alcohol- type solvents such as isopropyl alcohol, n-butanol, isobutyl alcohol, n- amyl alcohol, isoamyl alcohol, etc., and an ether-type solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobuthyl ether.

As the aqueous amine formaldehyde condensate in this invention, used alone or in combination are alkyletherified melamine resin, alkyletherified urea resin, alkyletherified guanamine resin, alkyletherified resin of diguanamine in which two triazine rings are bonded to its phenylene nucleus, and alkyletherified glycol resin, alkyletherified guanamine resine. Completely etherified hexamethoxymelamine is preferably used.

The aqueous resin which the aqueous-rendering treatment has rendered water-soluble or water-dispersible is converted to a coating by mixing it with an aqueous aminoplast resin and optionally adding 0.1 to 1.0 part by weight, based on 100 parts by weight of resin solid content, of an amineblocked acid catalyst as a curing agent such as p-toluene benzene sulfonic acid, dodecylbenzene sulfonic acid, dinonyl naphthalene disulfonic acid. It is also possible to incorporate thereinto a watersoluble resin and/or waterdispersible resin generally used as a resin for an aqueous coating resin. Examples of such a resin are water-soluble polyester resin, maleic acid-added fatty acid, water-soluble 1 1 or water-dispersible epoxy resin. polyol such as bisphenol-A propylene oxide adduct, ethylene oxide adduct, etc., and the like.

Similarly, it is also possible to add a levelling agent, antifoaming agent and/or lubricating agent.' Further, when a pigment paste is prepared by mixing and kneading a pi gment with the aforesaid copolymer resin solution from which the solvent is removed, the pigment paste can be also converted to a coating in a similar way to that mentioned above.

The aqueous coating composition of this inventn can be applied by known means such as roll coat, spray, brush, etc.

The aqueous coating composition of this invention has water resistance capable of withstanding the heat treatment carried out at the time of sterilizing cans to be used for food and beverage. It also forms a coated film having excellent gloss increasing the aesthetic value of can material and has excellent coating stability and flow coating capability even when the organic solvent content is not more than 5 % based on the entirety of coating composition.

The following Examples illustrate this invention in detail In the Examples, "parC stands for "part by weight" and stands for "% by weight".

Qbcamples) Preparation Example A1 Preparation Example of an acryl resin solution:

parts of n-butanol was charged to a 4-neck flask having a thermometer, stirrer, reflux condenser, dropping funnel and nitrogen gas flowing tube, and, with stirring and with keeping the temperature at 100 IC while a nitrogen gas was being introduced, added dropwise over 3 hours from the dropping funnel was a mixture of 15 parts of 2-hydroxyethyl acrylate, 20 parts of tetraethylene glycol diacrylate, 2 parts of acrylic acid, 63 parts of ethyl acrylate and 2 parts of benzoyl peroxide. Then, the reaction was continued for 2 hours by keeping the temperature at 100 t and thereafter 0.3 pdrt of 1 I.

9 henzoyl peroxide was added to continue_the reaction for 1 hour.

The resulting product was cooled to not higher than 40 t and 3 parts of triethyl amine and 200 parts of water were added to give a clear viscous resin solution having 60 % of a solid content and 10 jof residual nbutanol.

Preparation Examples A2 - A6 Synthesis was carried out according to the procedure of Preparation Example A1 by changing the solvent composition which was to be precharged into a flask, the vinyl monomer composition to be added dropwise, the catalyst amount, the catalyst amount to be additionally added and the reaction temperature as shown in Table 1, and further, the synthesized product was neutralized with an organic amine of which the amount was changed as shown in Table 1.

According to the procedure of Preparation Example Al, water was added to distil off the synthesis solvent together with the water under reduced pressure at 80 t to give a clear viscous resin solution having 60 % of solid content and 10 t of residual n-butanol.

Preparation Example B1 Preparation Example of pigment-dispersed paste:

parts of an acryl resin solution Al, 40 parts of rutile-type titanium white and 10 parts of water were mixed, and the mixture was dispersed by an attritor to give a pigment dispersed paste.

Preparation Example B2 parts of an acryl resin solution A2, 40 parts of rutile-type titanium white and 10 parts of water were mixed, and the mixture was dispersed by an attritor to give a pigment dispersed paste.

Example 1

47 parts of an acryl resin solution of Preparation Example Al, 12 parts of hexamethoxy melamine (product of Mitsui Toatsu Chemical Co., Ltd: named as SIMEL 303; the same is used in Examples hereinafter), 0.4 part of amine-blocked ptoluene sulfonic acid (product of Kusumoto Chemical Co., .Ltd:

named as NACURE 250OX; the same is used in Examples hereinafter) and 40.6 parts of water were mixed to convert them to a coating.

Examples 2 - 8 Example 1 was repeated except that the acryl resin solution and aqueous aminoplast resin were changed as shown in Table 2, and the mixture was converted to a coating.

Example 9

6.3 parts of an acryl resin solution of Preparation Example Al. 62.5 parts of a pigment-dispersed paste of Preparation Example Bl, 6.3 parts of hexamethoxy melamine, 0.2 parts of amine-blocked p-toluene sulfonic acid and 24.7 parts of water were mixed to convert them to a coating.

Example 10

6.3 parts of an acryl resin solution of Preparation Example A2, 62.5 parts of a pigment-dispersed paste of Preparation Example B2, 6.3 parts of hexamethoxy melamine, 0.2 part of amine-blocked p-toluene sulfonic acid and 24.7 parts of water were mixed to convert them to a coating.

Comparative Examples 1 - 2 The following are Comparative Examples 1 and 2 with regard to a coating consisting of a known aqueous acryl resin and an aqueous aminoplast resin- and a white coating in which a pigment-dispersed past6 is dispersed.

Comparative Example 1 parts of butyl cellosolve was charged into a four-neck flask, and with stirring and with keeping the temperature at 115!C while a nitrogen gas was being introduced, added dropwise over 3 hours from a dropping funnel a mixture of 20 parts of acrylic acid, 50 parts of ethyl acrylate. 25 parts of methyl methacrylate, 5 parts of hydroxyethyl acrylate and 1 part of benzoyl peroxide.

Then. by keeping the temperature at 115 t for 2 hours, the reaction was continued, and thereafter 0.1 part of benzoyl peroxide was added to continue the reacction for 1 hour. The reaction product was cooled to 70 'C and diluted with 60 parts of isopropyl alcohol, and further, the mixture was 1 ( t 1 C - 11 diluted with 25 parts of triethyl amine and 30 Parts of water to give an acryl resin solution. - 42.9 parts of hexamethoxy melamine, 1.9 parts of amine-blocked p-toluene sulfonic acid and 164 parts of water were mixed with the above acryl resin solution to gonvert them to a coating.

Comparative Example 2 parts of an acryl resin solution obtained in Comparative Example 1, 40 parts of rutile-type titanium white and 5 parts of water were mixed, and dispersed by an attritor. Then, mixed further therewith were 12.5 parts of an acryl resin solution obtained in same, 10 parts of hexamethoxy melamine, 0.4 part of amine-blocked p-toluene sulfonic acid and 37.1 parts of water to convert the mixture to a coating.

Comparative Example 3 33 parts of butylcellosolve was charged into a fourneck flask similar to one described in Preparation Example Al, and, with stirring and with keeping the temperature at 120 t, there was added dropwise from a dropping funnel over 2 hours a mixture of 5 parts of acrylic acid, 15 parts of 2hydroxyethylmethacrylate, 15 parts of polypropyleneglycol monomethacrylate, 40 parts of styrene, 24 parts of butylacrylate and 0.8 part of benzoyl peroxide. Thereafter, the reaction was continued at 120 t for 3 hours, and 0.2 part of benzoyl peroxide was added to continue the reaction for 1 hour. Then the reaction was stopped. The reaction product was cooled to 70 % diluted with 33 parts of isopropyl alcohol, and further diluted with 10 parts of triethylamine and 24 parts of water to give an acryl resin solution.

By the use of the above acryl resin solution, Example 1 was repeated to give a clear-type coating.

Comparative Example 4 By the use of an acryl resin of Comparative Example 3 and a titanium pigment-dispersed paste prepared in the same way as in Preparation Example B1, a white-color coating was obtained by repeating the procedure of Example 9.

With regard to each of coatings obtained in Exanples 1 12 - 1 to 10 and Comparative Examples 1 to 4, a coating test, test of coated film property after coated and baked, and test of flow coating property were carried out. The results are shown in Table 3.

Method of each of the above tests is as follows.

Coating Test - Test on coating stability:

Each of the coatings was stored at room temperature for 2 months, and then the state of gellation and separation of resin was observed.

Test on organic solvent content in coating:

Each of the coatings was diluted with methyl-ethyl ketone, and the content was directly determined by gas chromatography.

Test of coated film property Each of the coatings was coated on an electroplated tin plate having a thickness of 0.23 mm was coated by roll coat such that the thickness of a dried coated film had a thickness of 7 gm, and the coated plate was baked in a gas oven at an ambient temperature of 190 t for 10 minutes to make a baking-finish panel.

Test on water resistance:

A coated panel was.imifiersed in water and heattraeted at 100 t for 30 minutes, and then the whitened state of a coated film was evaluated.

Test by pencil hardness:

Evaluation was made according to pencil hardness test method on the basis of JIS No.K 5400 standard.

Test on intimate adhesion property:

A coated surface was cut crosswise at the intervals of 2 mm in 11- lines along both lengh and breadth such that the cut reached the substrate. Then an adhesive tape was applied over to the surface and detached therefrom to determine the proportion of peeling of cross-cut sections.

Test on impact strength:

By the use of a du Pont impact tester, a pin was brought into contact with a sample and a load of 500 g was 1 1:

1 R 13 dropped thereon. Impact resistance was evaluated by a height at which no crack was caused on a coated film.

Gloss: mirror reflectivity was measured at measUrment angle of 60. With regard to clear-type coating, the measurement was made after it was coated on a baked coated film of a white coating of Example 9 on a plate. Antirust property: Cross-cut was given to a coated film surface of a plate as deep as it reached the plate, salt water was sprayed thereover, and the plate was left to stand for 72 hours. Cut portions were peeled off with an adhesive tape, and evaluation was made in terms of peeled area. Coating proerty test Flow: Immediately after a sample was coated by a roll coater, the coated sample was baked in an oven, and the flow state of coating was-evaluated.

1 MONOMER COMP. Hydroxyethyl acrylate Hydroxyethyl methacrylate Hydroxypropyl methacrylate Diethyleneglycol diacrylate Tetraethylene diacrylate Polyethyleneglycol dimethacrylate Acryl acid Methacryl acid Ethylacrylate Methylmethacrylate Styrene SOLVENT n-Butanol Ethyleneglycol monoethylether n-Amylalcohol CATALYST Peroxybenzoyl (additional) Azoisobutylo nitrile (additional) Reaction temp. r' AMINE Triethylamine Dimethylethanol amine 14 - Table 1 Preparation Example of Acryl Resin Solution A1 A2 A3 A4 As A6 part part part part part part c is 20 10 3 5 62 75 2.2 2.2 4.4 (0.2) (0.2) (0.4) 100 95 3 7.5 12 is 18 32 60 2.2 (0.2) 10 5 2.2 2.2 (0.2) (0.2) 120 95 12 21 5.5 : Newfrontier 250Z produced by Daiichi Kogyo Seiyaku Co., Ltd.

1 3 1; Z5 I- 1 1 9 - is Table 2 Examples of Coating Conversion EX.1 Ex.2 EX.3 Ex.4 EX.5 Ex.6 EX.7 EX.8 part part part part part part part part Prep.Ex.Al Prep.Ex.A2 Prep.Ex.A3 Prep. Ebc. A4 Prep.Ex.A5 Prep.Ex.A6 CYMEL303 NACURE 250OX Water 47 40 47 40 47 47 47 12 16 12 16 12 12 12 47 12 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 40.6 40.6 40.6 43.6 40.6 40.6 40.6 40.6 CYMEL303: hexamethoxymelamine (produced by Mitsui Toatsu Chemicals,Inc.) NACURE 250OX: amine blocked p-toluene sufonic acid (Kusumoto kasei Co., Ltd.) Tabel 3 Test Results Example

1 2 3 4 -5 6 7 8 910 COATING TEST Coating stability A A --A A A A A A A A 75 Organic solvent content % 5 4 5 4 5 5 5 5 5 5 TEST OF COATED FILM PROPERTY Water resistace loot B B B B B B B B B B 120t C B C B C C c c c c Pencil hardness 4H SH 5H 6H 5H 6H 6H 6H 5H 5H Adhesion property D D D D D D D D D D Impact strength cm 40 30 40 30 30 25 30 25 30 30 Gloss 99 98 98 98 99 99 99 99 95 95 Antirust property % 3 2 2 2 3 3 3 3 3 3 COATABILITY Flow A A A A A A A A A A Tabel 3 Test Results (continued) Comparative Example 1 2 3 4 COATING TEST Coating stability A A A A Organic solvent content % 21 14 TEST OF COATED FILM PROPERTY R1 14 Water resistace loot l 1 2 2 120t 1 1 1 1 Pencil hardness 2H 2H 4H 4H Adhesion property D D D D Impact strength cm, 40 30 30 30 Gloss 93 90 94 92 Antirust property % 80 80 4 5 COATABILITY Flow A 3 A 3 Note:

A; Excellent B; Acceptable C; Nearly acceptable D; No peeling 1; Dissolved in water 3; No good due to flow patterns Z 2: All whitenina ( 'I i v

Claims (18)

1. An aqueous coating composition comIprising:

(1) an aqueous resin obtainable by neutral-izing,.with a volatile base, a copolymer comprising units derived f rom:

(a) 5 to 65% by weight of at least one hydroxyalkylacrylate or methacrylate in which the alkyl group has 1 to 5 carbon atoms, (b) 5 tc, 50% by weight of at least one diacrylate or dimethacrylate of an alkylene glycol or at least one polyoxyalkylene glycol, (c) 2 tc 20% by weight of at least one cy.13-monoethylenically unsaturated carboxylic acid, and (d) 20 to 88% by weight of at least one vinyl monomer copolymerizable with components (a), (b) and (c); and (2) an aqueous amine formaldehyde condensate.

2. An aqueous coating composition according to claim 1 wherein the copolymer comprises 5 to 20% by weight of component (a), 7 to 25% by weight of component (b), 5 to 15% by weight of component (c) and 40 to 83% by weight of component (d).

3. An aqueous coating composition according to claim 1 or 2 wherein the alkyl group of component (a) is a methyl, ethyl, propyl, butyl or amyl group, or a mixture thereof.

4. _ An aqueous coating composition according to any one of claims 1 to 3 wherein component (b) is at least one compound of formula R, R2 R3 CH2 cC-C-O- (CH2 -6H-0). -C-C=CH2 11 11 0 0 wherein R,, R. and R 3 each independently represents -15 i f 18 hydrogen or a methyl group and n represents an integer of from 1 to 50.

5. An aqueous coating composition acCording to claim 4 wherein n represents an integer of from 1 to 8.-

6. An aqueous coating composition according to any one of claims 1 to 5 wherein component (c) is acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid or itaconic acid, or a mixture thereof.

7. An aqueous coating composition according.to any one of claims 1 to 6 wherein component (d) is an alkyl ester of acrylic acid or methacrylic acid, styrene, vinyl toluene, a-methyl.styrene, vinyl acetate or vinylethyl ether, or a mixture thereof.

8. An aqueous coating composition according to claim 7 wherein the alkyl ester is an ethyl, butyl, 2-ethylhexyl or cyclohexyl ester, or a mixture thereof.

9. An aqueous coating composition according to any one of claims 1 to 8 wherein the volatile base is ammonia, monoethanolamine, dimethylamine, diethylamine, triethylamine, friethanolamine, dimethylethanolamine or diethylethanolamine, or a mixture thereof.

10. An aqueous coating composition according to any one of claims 1 to 9 Wherein the aqueous amine formaldehyde condensate is an alkyletherified melamine resin, an alkyletherified urea resin, an alkyletherified guanamine resin, an alkyletherified resin of diguanamine in which 2 triazine rings are bonded to the phenylene nucleus or an alkyletherified glycol resin, or a mixture thereof.

11. An aqueous coating composition according to any one of claims 1 to 10 which further comprises at least one of a curing agent, a water-soluble resin, a water-dispersible resin, a levelling agent, an antifoamer, a lubricant or a pigment.

12. An aqueous coating composition according to claim 1 substantially as described in any one of Examples 1 1 1 1 to 10.

13. A process for the preparation of an aqueous coating composition which comprises copolymerizi-ng components (a) to (d) as defined irl any one of claims 1 to 8 -in an organic solvent in the presence of a polymerization initiator to produce a precrosslinked ungelled copolymer, neutralizing said copolymer with a volatile base to obtain an aqueous resin, adding an aqueous amine formaldehyde condensate to said aqueous resin and distilling off the organic solvent.

14. A process according to claim 13 wherein the copolymerization is carried out at a temperature of from 90 to 120'C and the polymerization solids content is not more than 50% by weight.

15. A process according to claim 13 or 14 wherein the organic solvent is distilled off under reduced pressure at a temperature of from 40 to 800C.

16. A process according to any one of claims 13 to 15 wherein the polymerization initiator is a peroxide or azo compound.

17. A process according to any one of claims 12 to 15 wherein the organic solven has a boiling point of from 75 to 1800C.

18. A process for coating an article which comprises applying to the article an aqueous coating composition as defined in any one of claims I to 12.

published 1989 atThe Patent Offloe. State House. W71 High Holborn. London WCiR 4'_"P_ Further copies msybe Obtained from The Patent Office. Was Branch, St Mary CrV, Or-OW41Wn, Ke= BR5 3RD. Printed by Multiplex techniques ltd, St MW7 Cray, Kent, Son. 1/87