GB1580919A

GB1580919A - Baking finishes comprising acrylate and epoxy resins

Info

Publication number: GB1580919A
Application number: GB32720/77A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1976-08-05
Filing date: 1977-08-04
Publication date: 1980-12-10
Also published as: FR2360647A1; NL186180C; CH631478A5; IT1085666B; FR2360647B1; NL7708707A

Abstract

The low-solvent baking finishes contain an acrylate resin, an epoxy resin and a mixture of organic solvents. The acrylate resin is a copolymer containing 10 to 35% by weight of alpha ,ss-olefinically unsaturated carboxylic acids as copolymerised units, and having a K value (according to Fikentscher) of below 15 and an acid number of between 70 and 250 mg KOH/g. The epoxy resin contains at least two oxiran groups per molecule. The mixture of organic solvents contains 20 to 80% by weight of a solvent or solvent mixture having a boiling point between 100 and 280 DEG C and a dielectric constant between 2 and 4.99 and 80 to 20% by weight of a solvent or solvent mixture having a boiling point between 80 and 200 DEG C and a dielectric constant between 5 and 27. The baking finishes of the invention are suitable for example for producing coatings for domestic appliances and automotive base coatings.

Description

(54) BAKING FINISHES COMPRISING ACRYLATE AND EPOXY RESINS (71) We, BASF AKTIENGESELLSCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, 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: The present invention relates to baking finishes which comprise an acrylate resin, an epoxy resin and solvent, with or without pigment, catalyst and other conventional auxiliaries.

Baking finishes which contain mixtures of an acidic acrylate resin and an epoxy resin as the binder, together with pigment and solvent and with or without catalyst, were disclosed long ago and are described, for example, in U.S. Patent 3,301,801, British Patent 943,217, U.S.

Patent 3,196,120, French Patent 1,250,867, French Patent 1,315,679 and French Patent 1,352,572.

Such baking finishes give coatings having good mechanical properties and good resistance to chemicals. They are therefore used for, for example, finishes on appliances.

A disadvantage of baking finishes based on such compositions is, however, that they can only be processed if the finish contains a relatively high proportion of volatile organic solvents, and hence they cause substantial pollution of the environment.

The present invention seeks to provide baking finishes which contain an acrylate resin, an epoxy resin and solvent, with or without pigment and catalyst, which can be processed, e.g. sprayed, with substantially smaller proportions of organic solvent without thereby adversely influencing other processing characteristics or resulting in a poorer level of properties of the baked coatings than those of the corresponding prior art.

According to the present invention, there is provided a composition for use as a baking finish, which comprises (A) an acrylate resin, (B) an epoxy resin and (C) a mixture of organic solvents, in which the acrylate resin (A) is a copolymer which contains from 10 to 35% by weight of copolymerized a, ss-olefinically unsaturated carboxylic acid units, has a K value (measured by the Fikentscher method) of less than 15 and has an acid number of from 70 to 250 mg of KOH/g, the epoxy resin (B) contains at least 2 oxirane groups per molecule, and the mixture of organic solvents (C) is a mixture comprising from 20 to 80% by weight of a solvent having a boiling point of from 100 to 2800C and a dielectric constant of from 2 to 4.99 and from 80 to 20% by weight of a solvent having a boiling point of from 80 to 2000C and a dielectric constant of from 5 to 27, the weight ratio of the components (A):(B) being from 9:1 to 6:4 and the weight ratio of the components (A+B):(C) being from 7:3 to 5:5.

Preferred baking finishes of the above type are those in which the acrylate resin (A) is a copolymer of from 12 to 25% by weight of acrylic acid and/or methacrylic acid, from 5 to 70% by weight of one or more esters of acrylic acid and/or methacrylic acid with monoalkanols of 1 to 8 carbon atoms, from 5 to 40% or 5 to 70% by weight of styrene and from 0 to 20% by weight of one or more alkanediol monoesters of acrylic acid and/or methacrylic acid. Particularly preferred baking finishes are those in which the acrylate resin (A) has a mean molecular weight Mn of from 1500 to 3000 and an inhomogeneity (Mw/Mn), measured by gel permeation chromatography, of from 1.5 to 2.0.

Particularly preferred acrylate resins (A) are those which have been manufactured from the monomers at temperatures of from 170 to 280"C and pressures of from 1.5 to 30 bars in the presence or absence of a free-radical initiator and/or an organic solvent.

Surprisingly, baking finishes according to the invention may be processed with very low solvent contents. They can be sprayed at total solids contents (including pigment etc.) of more than 70% by weight, preferably of from 75 to 85% by weight, can be used on vertical surfaces, exhibit good levelling and, after baking, give coatings which have good resistance to chemicals and solvents and provide good corrosion protection.

The following is to be noted in respect of the individual components on which the baking finishes are based. (A) The acrylate resin (A) comprises from 10 to 35% by weight of copolymerized a, ss-olefinically unsaturated carboxylic acid units, has a K value, measured by the method of Fikentscher (cf.

Cellulosechemie 13 (1932), 58), of less than 15 and has an acid number of from 70 to 250 mg of KOH/g. Examples of a, d- olefinically unsaturated carboxylic acids are dicarboxylic acids, e.g. maleic acid, fumaric acid and itaconic acid, and, preferably, monocarboxylic acids, e.g. acrylic acid and/or methacrylic acid, which are preferably present, as copolymerized units, in amounts of from 12 to 25% by weight.

One or more of the following comonomers can additionally be present as copolymerized units in the copolymer (A): a) Esters of acrylic acid and/or methacrylic acid with linear and/or branched monoalkanols of 1 to 8 carbon atoms, e.g. ethyl acrylate, n-, iso- and tert.-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate, preferably in amounts of from 5 to 70% by weight based on the copolymer (A), b) Vinyl-aromatics, e.g. styrene and/or vinyltoluene, preferably in amounts of from 5 to 40% by weight, based on copolymer (A), c) Optionally, in amounts up to 20% by weight, acrylic acid monoesters and/or methacrylic acid monoesters of alkanediols of 2 to 6 carbon atoms, which alkanediols may also contain one or more oxa groups, e.g.

hydroxypropyl acrylate, butanediol monoacrylate, hydroxyethyl methacrylate, diethylene glycol monoacrylate and monomethacrylate and triethylene glycol monoacrylate and monomethacrylate, and d) Optionally, in minor amounts, of up to 10% by weight, further copolymerizable monomers, e.g. acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, Nalkoxymethylacrylamide, N-alkoxymethylmethacrylamide, vinyl esters, e.g. vinyl acetate and vinyl propionate, dialkylmaleates and dialkylfumarates, monoalkylmaleates and monoalkylfumarates, acrolein and allyl alcohol.

Examples of particularly preferred acrylate resins (A) are copolymers of from 12 to 25% by weight of acrylic acid and/or methacrylic acid, from 10 to 40% by weight of ethyl acrylate, n-butyl acrylate and/or 2-ethylhexyl acrylate, from 0 to 30% by weight of t-butyl acrylate and from 10 to 40% or from 30 to 70% by weight of styrene.

The acrylate resin (A) to be employed is preferably manufactured as a solution polymer in a fairly high-boiling solvent, having a boiling range of from 100 to 2800C and a dielectric constant of from 2 to 5. The polymerization is advantageously carried out at the reflux temperature of the solvent, without a regulator.

The acrylate resin (A) to be employed can alternatively be manufactured as a solution polymer in a solvent having a boiling point of from 80 to 200 C and a dielectric constant of from 5 to 27. In some cases it is also advantageous to use a mixture of solvents from the stated groups of solvents.

However, the manufacture of the acrylate resin (A) by polymerization can also be carried out in other conventional solvents for finishes, in the presence or absence of a regulator.

The acrylate resin (A) can also be manufactured by bulk polymerization and be dissolved subsequently.

The acrylate resins (A) with K values of less than 15 have viscosities, measured on 60% strength solutions in Solvesso 100 from Esso (an aromatic hydrocarbon of boiling range from 155 to 168 C, containing more than 95% of aromatics (SOLVESSO is a Registered Trade Mark), n-butanol of from 10 to 30 poise, preferably from 50 to 25 poise, at 23 C. This corresponds to efflux times (beaker with a 6 mm orifice, at 230C) of from 70 to 200 seconds, preferably from 90 to 150 seconds.

It is however particularly preferred to manufacture the acrylate resins (A) by freeradical oligomerization at pressures of from 1.5 to 30 bars and temperatures of from 160 to 2800C, in substance, especially at temperatures of from 170 to 250 C, or in solution at from 160 to 2500C. The free-radical oligomerization is advantageously carried out in the absence of a regulator.

The oligomerization may, if desired, be carried out in the presence of free-radical initiators, such as peroxides and hydroperoxides, e.g. di-t-butyl peroxide, t-butyl perbenzoate, butyl hydroperoxide, pinane hydroperoxide and cumene hydroperoxide, and of organic solvents, such as aromatic hydrocarbons, e.g.

Solvesso 100, xylene, alcohols, e.g. n-propanol and n-butanol, ethylene glycol monoalkyl ethers, e.g. methylglycol, ethylglycol, butylglycol, alkyl glycol ether acetates, e.g.

methyl glycol acetate, ethyl glycol acetate and butyl glycol acetate, esters, e.g. butyl acetate, and/or ketones, e.g. methyl isobutyl ketone and methyl ethyl ketone.

The acrylate resins, preferably with molecular weights Mn of from 1500 to 3000, have, as 60% strength solutions in a 6:4 mixture of Solvesso 100 and n-butanol, efflux times (beaker with a 6 mm orifice/230C) of from 15 to 150 seconds, preferably 20 to 90 seconds; the inhomogeneity (Mw/Mn), measured by gel permeation chromatography, is from 1.5 to 2.0.

The determination of the inhomogeneity (Mw/Mn) by gel permeation chromatography is effected by the method indicated in the Journal of Applied Polymer Science, vol. 19 (1975), pages 629 to 631 or described at the 5th International Seminar held by Messrs.

Waters in London in 1968 and at the 6th International Seminar held by the same company in Miami Beach, Florida, in 1968.

Tetrahydrofuran is used as solvent, and crosslinked polystyrene gel (TSKG 3000 H8 and TSKG 4000 H8) as separation column.

Measurement is carried out at 230C. In each case, 0.2 ml of a 0.25% strength solution is injected. The flow rate is 0.8 ml/minute.

(B) Especially suitable epoxy resins with at least 2 oxirane groups per molecule are those having epoxide values of from 0.2 to 0.7 mole of epoxide/100 g of material. Examples of suitable components (B) are reaction products of epichlorohydrin and bisphenol A, epichlorohydrin and polyalcohols, e.g. trimethylolpropane or pentaerythritol, or epi chlorohydrin and aliphatic, cycloaliphatic or aromatic polycarboxylic acids. However, low molecular weight acrylate resins with oxirane side groups, e.g. glycidyl methacrylate homopolymers and copolymers, may also be used as epoxy resins (B).

The ratio of acrylate resin (A) to epoxy resin (B) may be varied within wide limits, but preferably the carboxyl/epoxide ratio is from 0.3:1 to 3:].

(C) Component C is a mixture of from 20 to 80% by weight of a solvent having a boiling point of from 100 to 2800C and a dielectric constant of from 2 to 4.99, and from 80 to 20% by weight of a solvent having a boiling point of from 80 to 2000C and a dielectric constant of from 5 to 27.

The following are suitable solvents having a boiling point of from 100 to 280 C and a dielectric constant of from 2 to 4.99: Solvesso 100, Solvesso 150 (an aromatic hydrocarbon from Esso, containing more than 95% of aromatics), Shellsol R (an aromatic hydrocarbon from Shell, containing more than 80% of aromatics (SHELLSOL is a Registered Trade Mark), toluene and xylene, as well as mixtures of these solvents.

Examples of suitable solvents having a boiling point of from 80 to 2000 C and a dielectric constant of from 5 to 27 are n-propanol, ipropanol, n-butanol, i-butanol, pentanol, amyl alcohol, 2,2-di-methylpropanol, hexanol, 2-ethylhexanol, cyclohexanol, ethylene glycol monomethyl ether (methylglycol), ethylene glycol monoethyl ether (ethylglycol), ethylene glycol monobutyl ether (butylglycol), diethylene glycol monomethyl ether (methyldiglycol), diethylene glycol monomethyl ether (ethyldiglycol), diethylene glycol monobutyl ether (butyldiglycol), propylene glycol monomethyl ether, ethylene glycol monoacetate, propylene glycol monoacetate, ethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, butyl acetate, diacetone-alcohol, 2ethylmercaptoethanol, methyl isobutyl ketone and mixtures of these solvents.

Solvent mixtures of from 30 to 70% by weight of hydrocarbons having a boiling range of from 150 to 2700C and containing more than 80% by weight of aromatics, and from 70 to 30% by weight of alcohols boiling at from 80 to 2000C which may or may not contain one or more glycol monoalkyl ethers and/or glycol monoalkyl ether acetates boiling at from 80 to 2000C are preferred.

Examples of pigments are the inorganic and organic pigments conventionally used in the surface coating industry, e.g. titanium dioxide, inorganic and organic coloured pigments, carbon black, talc, Aerosil (Registered Trade Mark) and rust-protection pigments.

Preferably, the solvents already described may be used to dilute the optionally pigmented compositions according to the invention to a spraying viscosity. However, it is also possible to use other conventional solvents for baking finishes, e.g. aromatics, alcohols, esters and ketones.

The resulting baking finishes, which are in general of low solvent content, can also, if desired, be crosslinked using conventional catalysts. Examples of such catalysts are tertiary amines, e.g. 1 ,2-di-methylimidazole and l-phenylimidazole, or quaternary ammonium salts, e.g. tetrabutylammonium iodide.

In addition, one or more auxiliaries conventionally used in the surface coatings industry, e.g. levelling agents, anti-crater agents, dispersants, e.g. silicone oils, and, for example, finely divided silica to act as a thixotropic agent, may be added to the baking finishes.

The baking finishes may be used, for example, for the manufacture of finishes for domestic equipment, and of automotive primers.

It is a particular advantage that the finishes can be applied, in layers from 40 to 50 liy thick, to vertical surfaces, even in the absence of thixotropic agents, without sagging.

The parts and percentages in the text which follows, and in the Example, are by weight.

Manufåcture of acrylate resin I 376 parts of aromatic hydrocarbon having a boiling range of from 155 to 1780C and containing more than 95% of aromatics (for example Solvesso 100) and 94 parts of ethylglycol acetate are introduced into a round flask and heated to the reflux temperature (-155"C). A mixture of 300 parts of 2ethylhexyl acrylate, 300 parts of styrene, 200 parts of t-butyi acrylate, 200 parts of methacrylic acid and 27 parts of t-butyl perbenzoate is added, under N2, in the course of 2 hours. 30 minutes after completion of the addition, a further 13 parts of t-butyl perbenzoate are added and the polymerization is continued for 1 hour at the reflux temperature. Solids content = 70.0%, K value (according to Fikentscher) = 13.5 (measured on a 3% strength solution in acetone).

The resin solution is diluted to 60% solids content with n-butanol.

Viscosity/23 C 17.2 poise Efflux time 120 seconds (beaker with 6 mm orifice/ 23"C) If the acrylate resin I is diluted with nbutanol to, respectively, 50 or 40% solids content, the following viscosities are obtained.

Solids content 50% by 40% by weight weight Viscosity/ 2.71 poise 1.25 poise 23"C Efflux time 62 seconds 21 seconds (beaker with 6 mm orifice/ 230C) Manufacture of the acrylate resin II 175 parts of an aromatic hydrocarbon having a boiling range of from 155 to 178 C and containing more than 95% of aromatics (for example Solvesso 100), are introduced into a round flask and heated to the reflux temperature (--1600C) under N2.A mixture of 210 parts of 2-ethylhexyl acrylate, 210 parts of styrene, 140 parts of t-butyl acrylate, 140 parts of methacrylic acid and 19 parts oft- butyl perbenzoate is then added in the course of 2 hours. 30 minutes after completion of the addition, a further 9 parts of t-butyl perbenzoate are added and the polymerization is continued for 1 hour. Solids content = 81.0%, K value (according to Fikentscher) = 13.2 (measured on a 3% strength solution in acetone).

The acrylate resin II is diluted with an aromatic hydrocarbon (boiling point 155 to 178"C, containing more than 95% of aromatics, for example Solvesso 100), n-butanol or mixtures of this aromatic hydrocarbon (= HC) and n-butanol, to a solids content of 65%. The following viscosities are found: Solvent to give 65% Viscosity solids content 100 parts of aromatic HC more than 800 p 62 parts of aromatic HC 104 p 38 parts of n-butanol 50 parts of aromatic HC 72 p 50 parts of n-butanol 38 parts of aromatic HC 53 p 62 parts of n-butanol If the acrylate resin II is diluted with an aromatic hydrocarbon (boiling range 155-1780C, for example Solvesso 100) to a solids content of 50%, the viscosity is 220 poise.

An acrylate resin III manufactured similarly to acrylate resin II gives a solids content of 82.0% and a K value (according to Fikentscher) of 14.8.

The acrylate resin III is diluted to 65% solids content with various polar solvents. The following viscosities are found: Diluent Viscosity n-Butanol 127 poise Ethyiglycol 121 poise i-Butanol 208 poise jButylglycol 288 poise iButyldiglycol 500 poise Ethylglycol acetate 796 poise Manufacture ofacrylate resin (A) IV 1.5 parts of an aromatic hydrocarbon having a boiling range of from 155 to 1780C and an aromatics content of more than 95% (e.g.

Solvesso 100) are heated to 2000C in a steel vessel heated with oil. The pressure in the vessel rises to about 1.6 bars. A monomer mix ture of 1.575 parts of styrene, 1.313 parts of ! 2-ethylhexyl acrylate and 0.613 parts of acrylic acid, to which 0.070 part of di-t-butyl peroxide has previously been added, is added under pressure to the boiling solvent in the course of 30 minutes. The pressure in the vessel rises to 7 bars. When all has been added, the resin is stirred under pressure at 200"C for another 30 minutes, whereupon the vessel is cooled to 1200C and vented and the resin is adjusted to a solids content of 60% with nbutanol.

Efflux time (beaker 31 seconds with 6 mm orifice/23 C) Acid number 135 mg of KOH/g (solid resin) Mean molecular weight 2300 Mn in toluene Inhomogeneity 1.78 (Mw/Mn) GPC Manufacture of acrylate resin (A) V 60 parts of styrene, 25 parts of 2ethylhexyl acrylate, 15 parts of acrylic acid and 2 parts of di-t-butyl peroxide are heated at 210"C and 24 bars for 10 minutes in a continuously operated autoclave. The reaction mixture is then forced through a static mixer for after-polymerization (about 15 minutes at 200"C). The unreacted monomers are subsequently distilled off at 2300C and atmospheric pressure. The resin is dissolved in a solvent mixture consisting of 6 parts of Solvesso 100 and 4 parts of n-butanol to give a 60% strength solution.

Efflux time (beaker Z 6 26 seconds with a 6 mm orifice/23 C) Acid number 113 mg of KOH/g (solid resin) Mean molecular weight 1800 Mn in toluene Inhomogeneity 1.86 (Mw/Mn) GPC EXAMPLE 1 124.0 parts of acrylate resin I (solids content = 60%), 26.4 parts of an epoxy resin based on bisphenol A/epichlorohydrin (epoxide value = 0.54), 140.0 parts of TiO2, 2.0 parts of tetrabutyl-ammonium iodide (a 10% strength solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of n-butanol and 6.0 parts of xylene are thoroughly dispersed for 30 minutes in a vibratory mill, for example a Red Devil (Registered Trade Mark).

The mixture is then diluted to spraying viscosity (60 seconds, measured according to DIN 53,211) with about 15 parts of a 1:1 solvent mixture of butylglycol and xylene.

Solids content = 74.0%.

The finish is sprayed onto sheet steel and is baked for 30 minutes at from 140 to 1900C.

Testing of the coating gives the following results: Coating thickness 50 /um Gloss at 600 (DIN 67,530) 95 Pendulum hardness (DIN 160 sec.

53,157) Erichsen value (DIN 53,156) 4.5 mm Resistance to wash liquors 7 cycles The resistance to wash liquors is determined by boiling a coated sheet for 8 hours in a 1% strength solution of a commercial detergent (e.g. OMO, Registered Trade Mark) and leaving it to lie in the cold solution overnight. This test is repeated until recognizable changes in the coating, e.g. a deterioration of the gloss, blistering or detachment from the sheet, are observable The baking finish of low solvent content can be applied, even without thixotropic agents, in a thickness of from 40 to 50 /um to vertical surfaces without sagging.

EXAMPLE 2 124.0 parts of acrylate resin I (solids content = 60%), 26.4 parts of an epoxy resin based on bisphenol A (epoxide value = 0.54), 140.0 parts of TiO2, 2.0 parts of tetrabutylammonium iodide (a 10% strength solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of nbutanol and 6.0 parts of xylene are thoroughly dispersed for 30 minutes in a vibratory ball mill, for example a Red Devil.

The mixture is then diluted to spraying viscosity (60 seconds, measured according to DIN 53,211) by means of about 15 parts of a 1:1 solvent mixture of butylglycol and xylene.

Solids content = 76.1%.

The finish is sprayed onto sheet steel and is baked for 30 minutes at 1500C.

Testing of the coating gives the following results: Coating thickness 64 lug Gloss at 600 (DIN 67,530) 92 Pendulum hardness (DIN 164 sec.

53,157) Erichsen value (DIN 53,156) 2.6 mm Resistance to wash liquors 8 cycles The resistance to wash liquors is determined by boiling a coated sheet for 8 hours in a 1% strength solution of a commercial detergent (e.g. OMO) and leaving it to lie in the cold solution overnight. This test is repeated until recognizable changes in the coating, e.g. a deterioration of the gloss, blistering or detachment from the sheet, are observable.

EXAMPLE 3 124.0 parts of acrylate resin II (solids content = 60%), 26.4 parts of an epoxy resin based on bisphenol A (epoxide value = 0.54), 140 parts of TiO2, 2.0 parts of tetrabutylammonium iodide (a 10% strength solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of n-butanol and 6.0 parts of xylene are thoroughly dispersed in a vibratory ball mill, for example a Red Devil.

The mixture is then diluted to spraying vis-- cosity (60 seconds, measured according to DIN 53,211) with about 15 parts of a 1:1 solvent mixture of butylglycol and xylene.

Solids content = 78.5%.

The finish is sprayed onto sheet steel and is baked for 30 minutes at 150 C.

Testing of the coating gives the following results: Coating thickness 62 lum Gloss at 600C (DIN 67,530) 96 Pendulum hardness (DIN 144 sec.

53,157) Erichsen value (DIN 53,156) 8.8 mm Resistance to wash liquors 7 cycles WHAT WE CLAIM IS: 1. A composition for use as a baking finish and comprising an acrylate resin (A) which is a copolymer containing from 10 to 35% by weight of copolymerized a, ss-olefinically unsaturated carboxylic acid units, the copolymer having a K value (measured by the Fikentscher method) of less than 15 and an acid number of from 70 to 250 mg of KOH/g, an epoxy resin (B) which contains at least 2 oxirane groups per molecule and an organic solvent mixture (C) comprising from 20 to 80% by weight of a solvent having a boiling point of from 100 to 2800C and a dielectric constant of from 2 to 4.99 and from 80 to 20% by weight of a solvent having a boiling point of from 80 to 2000C and a dielectric constant of from 5 to 27, the weight ratio of the components (A):(B) being from 9:1 to 6:4 and the weight ratio of the components (A+B):(C) being from 7:3 to 5:5.

2. A composition as claimed in Claim 1 in which the acrylate resin (A) is a copolymer of from 12 to 25% by weight of acrylic acid and/ or methacrylic acid, from 5 to 70% by weight of one or more esters of acrylic acid and/or methacrylic acid with monoalkanols of 1 to 8 carbon atoms, from 5 to 40% by weight of styrene and from 0 to 20% by weight of one or more alkanediol monoesters of acrylic acid and/ or methacrylic acid.

3. A composition as claimed in Claim 1 or Claim 2 in which the acrylate resin (A) is a copolymer of from 12 to 25% by weight of acrylic acid and/or methacrylic acid, from 10 to 40% by weight of at least one compound selected from ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, from 10 to 40% by weight of styrene and from 0 to 30% by weight of t-butyl acrylate.

4. A composition as claimed in any pre

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of n-butanol and 6.0 parts of xylene are thoroughly dispersed for 30 minutes in a vibratory mill, for example a Red Devil (Registered Trade Mark). The mixture is then diluted to spraying viscosity (60 seconds, measured according to DIN 53,211) with about 15 parts of a 1:1 solvent mixture of butylglycol and xylene. Solids content = 74.0%. The finish is sprayed onto sheet steel and is baked for 30 minutes at from 140 to 1900C. Testing of the coating gives the following results: Coating thickness 50 /um Gloss at 600 (DIN 67,530) 95 Pendulum hardness (DIN 160 sec. 53,157) Erichsen value (DIN 53,156) 4.5 mm Resistance to wash liquors 7 cycles The resistance to wash liquors is determined by boiling a coated sheet for 8 hours in a 1% strength solution of a commercial detergent (e.g. OMO, Registered Trade Mark) and leaving it to lie in the cold solution overnight. This test is repeated until recognizable changes in the coating, e.g. a deterioration of the gloss, blistering or detachment from the sheet, are observable The baking finish of low solvent content can be applied, even without thixotropic agents, in a thickness of from 40 to 50 /um to vertical surfaces without sagging. EXAMPLE 2 124.0 parts of acrylate resin I (solids content = 60%), 26.4 parts of an epoxy resin based on bisphenol A (epoxide value = 0.54), 140.0 parts of TiO2, 2.0 parts of tetrabutylammonium iodide (a 10% strength solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of nbutanol and 6.0 parts of xylene are thoroughly dispersed for 30 minutes in a vibratory ball mill, for example a Red Devil. The mixture is then diluted to spraying viscosity (60 seconds, measured according to DIN 53,211) by means of about 15 parts of a 1:1 solvent mixture of butylglycol and xylene. Solids content = 76.1%. The finish is sprayed onto sheet steel and is baked for 30 minutes at 1500C. Testing of the coating gives the following results: Coating thickness 64 lug Gloss at 600 (DIN 67,530) 92 Pendulum hardness (DIN 164 sec. 53,157) Erichsen value (DIN 53,156) 2.6 mm Resistance to wash liquors 8 cycles The resistance to wash liquors is determined by boiling a coated sheet for 8 hours in a 1% strength solution of a commercial detergent (e.g. OMO) and leaving it to lie in the cold solution overnight. This test is repeated until recognizable changes in the coating, e.g. a deterioration of the gloss, blistering or detachment from the sheet, are observable. EXAMPLE 3 124.0 parts of acrylate resin II (solids content = 60%), 26.4 parts of an epoxy resin based on bisphenol A (epoxide value = 0.54), 140 parts of TiO2, 2.0 parts of tetrabutylammonium iodide (a 10% strength solution in a 1:1 mixture of n-butanol and xylene), 6.0 parts of n-butanol and 6.0 parts of xylene are thoroughly dispersed in a vibratory ball mill, for example a Red Devil. The mixture is then diluted to spraying vis-- cosity (60 seconds, measured according to DIN 53,211) with about 15 parts of a 1:1 solvent mixture of butylglycol and xylene. Solids content = 78.5%. The finish is sprayed onto sheet steel and is baked for 30 minutes at 150 C. Testing of the coating gives the following results: Coating thickness 62 lum Gloss at 600C (DIN 67,530) 96 Pendulum hardness (DIN 144 sec. 53,157) Erichsen value (DIN 53,156) 8.8 mm Resistance to wash liquors 7 cycles WHAT WE CLAIM IS:

1. A composition for use as a baking finish and comprising an acrylate resin (A) which is a copolymer containing from 10 to 35% by weight of copolymerized a, ss-olefinically unsaturated carboxylic acid units, the copolymer having a K value (measured by the Fikentscher method) of less than 15 and an acid number of from 70 to 250 mg of KOH/g, an epoxy resin (B) which contains at least 2 oxirane groups per molecule and an organic solvent mixture (C) comprising from 20 to 80% by weight of a solvent having a boiling point of from 100 to 2800C and a dielectric constant of from 2 to 4.99 and from 80 to 20% by weight of a solvent having a boiling point of from 80 to 2000C and a dielectric constant of from 5 to 27, the weight ratio of the components (A):(B) being from 9:1 to 6:4 and the weight ratio of the components (A+B):(C) being from 7:3 to 5:5.

4. A composition as claimed in any pre

ceding Claim in which the organic solvent mixture (C) is a mixture of from 30 to 70% by weight of a hydrocarbon mixture having a boiling range of from 150 to 2700C and containing more than 80% by weight of aromatics with from 70 to 30% by weight of an alcohol mixture having a boiling point range of from 80 to 200 C, or a mixture of said alcohol mixture with at least one compound boiling at from 80 to 2000C and selected from glycol monoalkyl ethers and glycol monoalkyl acetates.

5 A composition as claimed in any preceding Claim in which the epoxy resin (B) has an epoxide value of from 0.2 to 0.7 mole of epoxide/100 g of material.

6. A composition as claimed in any preceding Claim in which the carboxyl/epoxide ratio of the acrylate resin (A) to the epoxy resin (B) is from 0.3:1 to 3:1.

7. A composition as claimed in any preceding Claim in which the acrylate resin (A) has a mean molecular weight Mn of from 1500 to 3000 and an inhomogeneity (Mw/Mn), measured by gel permeation chromatography, of from 1.5 to 2.0.

8. A composition as claimed in any preceding Claim in which the acrylate resin (A) is one which has been manufactured from the monomers at temperatures of from 170 to 280"C and pressures of from 1.5 to 30 bars in the presence or absence of a free-radical initiator and/or an organic solvent.

9. A composition as claimed in any preceding Claim and containing one or more pigments.

10. A composition as claimed in any preceding Claim and containing a catalyst effective to achieve crosslinking of the composition.

11. A composition as claimed in any preceding Claim having a solids content of more than 70% by weight.

12. A composition as claimed in Claim 11 having a solids content of from 75 to 85% by weight.

13. A composition as claimed in Claim 1 and substantially as described in any one of the Examples.

14. A method of coating a substrate wherein a composition as claimed in any preceding Claim is applied to the substrate and thereafter baked.

15. A method as claimed in Claim 14 wherein the composition having a solids content of more than 70% by weight is sprayed onto the substrate.

16. A method as claimed in Claim 14 or 15 wherein the composition is applied to a vertical surface.

17. Automotive parts and domestic equipment finished with a composition as claimed in any of Claims 1 to 13.