GB2102430A

GB2102430A - Resinous compositions curable through a transesterification curing mechanism

Info

Publication number: GB2102430A
Application number: GB08212566A
Authority: GB
Inventors: Joseph Theodore Valko
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1981-07-29
Filing date: 1982-04-30
Publication date: 1983-02-02
Also published as: IT8222002A0; FR2510590B1; CA1189995A; IT1159067B; GB2102430B; MX160805A; DE3224864A1; NL8201224A; ES511416A0; DE3224864C2; ES8307934A1; FR2510590A1

Abstract

Coating aqueous of organic solvent-based compositions comprise a polymeric polyol with a polyester crosslinking agent having at least two substituted ester groups per molecule. The substituents are selected from the class consisting of beta-alkoxyester groups, beta-ester groups, beta-amido groups, gamma-hydroxy groups, gamma-ester groups and delta- hydroxy groups. The polymeric polyol is preferably an epoxy resin and it may contain cationic group for use in electrodeposition processes. The compositions, when applied to a substrate and cured in the presence of a transesterification catalyst, give solvent-resistant coatings.

Description

SPECIFICATION Resinous compositions curable through a transesterification curing mechanism The present invention relates to heat-curable resinous coating compositions and to the use of these coating compositions in cationic electrodeposition. More particularly, the present invention relates to resinous coating compositions which cure through a transesterification reaction.

U.S. Patent 3,937,679 discloses cationic heat-curable resinous coating compositions such as hydroxyl group-containing polymers in combination with aminoplast resin curing agents. These compositions can be used in an electrodeposition process where they coat out on the cathode, and when cured, produce coatings with excellent properties. Coating compositions using aminoplast cure best in an acidic environment. However, the deposit on the cathode is basic and high curing temperatures must be used to overcome the unfavourable curing environment.

U.S. Patent 4,101,486 is similar to U.S. 3,937,679 in that it discloses cationic electrodeposition of hydroxyl group-containing polymers; however, the curing agent is a blocked isocyanate. Coating compositions using blocked isocyanates cure very well at relatively low temperatures in a basic environment and are today widely used in industrial cationic electrodeposition. Examples of cationic electrodepositable compositions which are used industrially are those described in U.S. Patents 4,031,050 and 4,190,567 and DE-OS 2,752,255. Although used extensiveiy throughout the electrodeposition industry, blocked isocyanate-containing compositions are undesirable from the point of view of the isocyanate, some of which are undesirable to handle.

European Patent Application 0012463 discloses thermosetting resinous coating compositions which cure through a transesterification reaction. The resinous binder of the coating composition comprises a hydroxyl-containing polymer and a crosslinking agent which is a polyester containing two or more beta-hydroxyester groups per molecule. The coating composition can be made cationic and used for electrodeposition.

It is known in the art that esters containing beta-hydroxyalkyl groups transesterify very quickly.

See, for example, J. Prakt. Chew. 312 (1970), 660--668. However, European Patent Application 0012463 discloses that polyesters which do not contain beta-hydroxyester groups but rather simple ester groups such as methyl esters or butyl esters do not transesterify as readily and are too sluggish to effect sufficient crosslinking at acceptable conditions.

Surprisingly, it has been found that coating compositions comprising hydroxyl group-containing polymers and a polyester crosslinking agent which do not contain beta-hydroxyester groups can be cured quite effectively.

It is an object of the invention to provide heat-curable coating compositions which can be cured quite effectively forming solvent-resistant coatings.

In accordance with this invention, a coating composition which is heat curable to give a solventresistant coating is provided. The coating composition comprises as the resinous binder: (A) a polymeric polyol; (B) a polyester crosslinking agent having at least two substituted ester groups per molecule, and (C) a transesterification catalyst.

The substituents to the ester group are selected from the class consisting of beta-alkoxyester groups, beta-ester groups, beta-amido groups, gamma-hydroxy groups, gamma-ester groups and delta-hydroxy groups.

The coating compositions can be made cationic in character such as by using a polymeric polyol which contains cationic salt groups, the resinous binder dispersed in water and the aqueous dispersion used in a method of cationic electrodeposition.

The polymeric polyol component of the coating compositions can be selected from a wide variety of hydroxyl group-containing polymers such as alkyd resins, polyester resins, hydroxyl group-containing acrylic polymers, hydroxyl group-containing epoxy resins and hydroxyl group-containing resins which are derived from epoxy resins such as polyepoxide-amine adducts.

The molecular weights of the polymeric polyols can vary over a wide range depending upon their type and on whether the coating composition is organic solvent based or aqueous based and also on the desired performance characteristics of the coating. Polyester, epoxy and aikyd resins can have molecular weights as low as about 500 and as high as about 10,000, preferably the molecular weights are usually in the range of about 1,000 to 5,000; the molecular weights being on a weight average basis relative to polystyrene, as determined by gel permeation chromatography. Acrylic polymers, on the other hand, can have molecular weights as high as about 100,000, and usually will be in the range of about 5,000 to 50,000 on a weight average basis relative to polystyrene, as determined by gel permeation chromatography.

The hydroxyl content of the polymeric polyol should be sufficient such that when the polyol is in combination with the curing agent, the composition will cure to a solvent-resistant coating. Generally, the hydroxyl number of the polymeric polyol will be at least about 1 70 and preferably will be in the range of about 1 80 to 300, based on resin solids.

A preferred class of polymeric polyols are hydroxyl group-containing epoxy resins or resins which are derived from epoxy resins such as polyepoxide-amine adducts which are particularly preferred. The epoxy resins which can be used in the practice of the invention are polyepoxides, that is, polymers having a 1,2-epoxy equivalency greater than 1, preferably about 2 or more. Preferred are polyepoxides which are difunctional with regard to epoxy. The preferred polyepoxides are polyglycidyl ethers of cyclic polyols. Particularly preferred are polyglycidyl ethers of polyphenols such as bisphenol A. Examples of polyepoxides are given in U.S. Patent 4,260,71 6, column 3, line 20, to column 4, line 30.

Besides the epoxy resins disclosed above, other epoxy-containing polymers which can be used are acrylic polymers which contain epoxy groups. These polymers are formed by polymerizing an unsaturated epoxy group-containing monomer such as glycidyl acrylate or methacrylate with one or more other polymerizable ethylenically unsaturated monomers. Examples of these polymers are described in U.S. Patent 4,001,156, column 3, line 59, to column 5, line 60.

Besides the hydroxyl group-containing epoxy resins disclosed above, hydroxyl group-containing polymers derived from epoxy resins such as polyepoxide-amine adducts can also be used. Examples of amines are ammonia, primary, secondary and tertiary amines and mixtures thereof. The reaction product of the poly-epoxide and the amine can be at least partially neutralized with an acid to form a polymeric product containing amine salt and/or quaternary ammonium salt groups. Reaction conditions of polyepoxides with amines, examples of various amines and at least partial neutralization with acid are disclosed in U.S. Patent 4,260,720, column 5, line 20, to column 7, line 4.

Also, various polyepoxide-amine adducts are described in European Patent Application 0012463.

With regard to the amount of organic amine and polyepoxide which are reacted with one another, the relative amounts depend upon the extent of cationic salt group formation desired and this in turn will depend upon the molecular weight of the polymer. The extent of cationic salt group formation and the molecular weight of the reaction product should be selected such that when the cationic polymer is mixed with aqueous medium, a stable dispersion will form. A stable dispersion is one which does not settle or is one which is easily dispersible if some sedimentation occurs. In addition, the dispersion should be of sufficient cationic character that the dispersed resin particles will migrate towards the cathode when an electrical potential is impressed between an anode and a cathode immersed in aqueous dispersion.

Also, the molecular weight, structure and extent of cationic salt group formation should be controlled such that the dispersed resin will have the required flow to form a film on the substrate; in the case of electrodeposition, to form a film on the cathode. The film should be insensitive to moisture to the extent that it will not redissolve in the electrodeposition bath or be rinsed away from the coated surface after removal from the bath.

In general, most of the cationic polymers useful in the practice of the invention will have average molecular weights within the range of about 500-100,000 and contain from about 0.01 to 10, preferably about 0.1 to 5.0, preferably from about 0.3 to 3.0 milliequivalents of cationic group per gram of resin solids. Obviously one must use the skill in the art to couple the molecular weight with the cationic group content to arrive at a satisfactory polymer. The polyglycidyl ethers will have molecular weights of about 500 to 10,000, preferably 1000 to 5,000. Acrylic polymers, on the other hand, will have molecular weights as high as 100,000, preferably 5,000 to 50,000.

Besides epoxy resins and resins derived from epoxy resins, other hydroxyl group-containing polymers such as alkyd resins, polyester resins and hydroxyl group-containing acrylic polymers can also be used in the practice of the invention. Examples of these polymers and their cationic electrodepositable derivatives are shown, for example, in British Patent 1,303,480 (hydroxyl groupcontaining acrylic polymers and polyesters) and British Patent 1,1 59,390 (hydroxyl group-containing acrylic polymers).

Besides the cationic polymers which are designed to form aqueous-based coating compositions which may be used in coating applications such as electrodeposition, it should also be appreciated that organic solvent-based coatings employing the above polymers without cationic salt groups can also be used. Formulating coating compositions with such polymers is well known in the art and need not be described in any further detail.

The crosslinking agent of the coating composition is a polyester containing at least two substituted ester groups per molecule and is substantially free of polyesters containing more than one beta-hydroxyester group per molecule. By substantially free is meant the beta-hydroxyester groups are present in amounts less than that sufficient to get a cured coating by themselves, i.e., a coating which can withstand 40 acetone double rubs as described infra. In general, the beta-hydroxyester groups will be present in amounts less than 5, preferably less than 2 percent by weight calculated as weight of beta-hydroxyester groups per total weight of crosslinker. Usually, the crosslinkers of the present invention are completely free of beta-hydroxyester groups.

The substituents to the ester group are selected from the class consisting of beta-alkoxyester groups, beta-ester groups, beta-amido groups, gamma-hydroxy groups, gamma-ester groups and delta-hydroxy groups. Examples of suitable crosslinking agents are those which contain at least two beta-alkoxyester groups per molecule such as those formed from reacting a polycarboxylic acid or its functional equivalent thereof with one or more 1,2-polyol monoethers. Examples of suitable polycarboxylic acids include dicarboxylic acids such as saturated aliphatic dicarboxylic acids, for example, adipic acid and azelaic acid; aromatic acids such as phthalic acid; ethylenically unsaturated dicarboxylic acids such as fumaric acid and itaconic acid.

Besides the acids themselves, functional equivalents of the acids such as anhydrides where they exist and lower alkyl (C1-C4) esters of the acids can be used. Examples include succinic an hydride, phthalic anhydride and maleic anhydride.

Polycarboxylic acids or their functional equivalents having a functionality greater than 2 can also be used. Examples include trimellitic anhydride and polycarboxylic acids formed from reacting a dicarboxylic acid with a stoichiometric deficiency of a polyol having a functionality of 3 or more, for example, reacting adipic acid with trimethylolpropane in a 3:1 molar ratio. The resulting product will have an acid functionality of about 3.

Examples of suitable 1,2-polyol monoethers are those of the structure:

where1, R2, R3, R4 and R5 are the same or different and include hydrogen, and the radicals alkyl, cycloalkyl, aryl, alkaryl containing from 1 to 1 8 carbon atoms, including substituted radicals in which the radicals and the substituents will not adversely affect the esterification reaction with the polycarboxylic acid or its functional equivalent thereof and will not adversely affect the transesterification curing reaction or the desirable properties of the coating composition. Examples of suitable substituents include chloro, alkoxy, carboxy, vinyl and when R1 and R3 form a closed hydrocarbon ring.Examples of suitable radicals for R1, R2, Ra and R4 include methyl, ethyl and chloromethyl. Examples of suitable radicals for RB include methyl, ethyl, propyl, butyl, isobutyl, cyclohexyl, phenyl, 2-ethoxyethyl and 2-methoxyethyl. Preferably, R1, R2, R3 and R4 are hydrogen or methyl and R5 is alkyl, cycloalkyl, aryl containing from 1 to 6 carbon atoms.

Specific examples of 1,2-glycol monoethers are 2-ethoxyethanol, 2-butoxyethanol, 2 phenoxyethanol, 2-ethoxypropanol and 2-butoxypropanol. Other examples are 2-methoxyethanol, 2 isopropoxyethanol, 2-(2-ethoxy-ethoxy)ethanol and 2-(2-methoxyethoxy)ethanol.

The crosslinking agent can be formed from reacting the polycarboxylic acid or its functional equivalent thereof with a 1,2-glycol monoether at an elevated temperature, usually reflux temperature, in the presence of an esterification catalyst such as an acid or a tin compound. Usually a solvent, for example, an azeotropic solvent such as toluene or xylene, is used. Reaction is continued with water being constantly removed until a low acid value, for example, 3 or less, is obtained.

Examples of other crosslinking agents are polyesters containing at least two beta-amido ester groups per molecule. Examples of suitable crosslinking agents are those which are formed from reacting a polycarboxylic acid or its functional equivalent thereof with one or more betahydroxyalkylamides to form the polyester containing at least two beta-alkoxy-amido groups per molecule.

Examples of suitable polycarboxylic acids are those mentioned above.

Examples of suitable beta-hydroxyalkylamides are those of the structure:

where R1 and R2 are hydrogen and R1, R2 and R3 are selected from the class consisting of alkyl, cycloalkyl, aryl, alkaryl containing from 1 to 1 8 carbon atoms, including substituted radicals in which the substituents will not adversely affect the esterification reaction with the polycarboxylic acid or its functional equivalent thereof and will not adversely affect the transesterification curing reaction or the desirable properties of the coating composition. Examples of suitable radicals include alkyl such as methyl, ethyl and isobutyl.

The beta-hydroxyalkylamides of the above structure can be formed by reacting a betahydroxyamine with an ester, anhydride, or other functional equivalent of an organic monocarboxylic acid. Examples of beta-hydroxyamines are hydroxyethylamine, beta-hydroxypropylamine and 2hydroxybutylamine. Examples of esters of organic monocarboxylic acids are alkyl esters of aliphatic monocarboxylic acids such as methyl, ethyl, hydroxyethyl and alkoxyethyl esters of acetic, propionic and isobutyric acids. The reaction conditions for forming the beta-hydroxyalkylamides are typical ammonialysis reaction conditions.

The crosslinking agent can be formed from reacting the polycarboxylic acid or its functional equivalent thereof with the beta-hydroxyalkylamide at an elevated temperature, usually reflux temperature, in the presence of a solvent, for example, an azeotropic solvent such as toluene or xylene.

Reaction is continued with water being constantly removed until a low acid value, for example, 7 or less, is obtained.

Examples of other crosslinking agents are polyesters containing at least two gamma and/or deltahydroxyester groups per molecule. Examples of suitable crosslinking agents are those which are formed from reacting a polycarboxylic acid or its functional equivalent thereof with one or more 1,3and/or 1,4-polyols.

Examples of suitable polycarboxylic acids are those mentioned above.

Examples of suitable 1,3-polyols and 1,4-polyols are those of the structure:

where R R R R R R R and R can be the same or different and include hydrogen, and the 1' 2' 3' 4' 5' 5' 7 B radicals alkyl, cycloalkyl, aryl, alkaryl, aralkyl containing from 1 to 1 8 carbon atoms, including substituted radicals in which the radicals and the substituents will not adversely affect the esterification reaction with the polycarboxylic acid or its functional equivalent thereof nor adversely affect the transesterification curing reaction or the desirable properties of the coating composition.

Examples of suitable substituents include chloro, hydroxy, alkoxy, carboxy and vinyl. Examples of suitable radicals include methyl, ethyl, propyl, phenyl and hydroxymethyl.

Specific examples of 1,3-polyols include 1,3-propanediol, trimethylolpropane, trimethylolethane and 1,3-butanediol.

Specific examples of 1,4-polyols include 1,4-butanediol and 2-butene-1,4-diol.

The crosslinking agent can be formed from reacting the polycarboxylic acid or its functional equivalent thereof with the 1,3- and/or 1,4-polyol at an elevated temperature, usually reflux temperature, in the presence of an esterification catalyst such as an acid or a tin compound. Usually a solvent, for example, an azeotropic solvent such as toluene or xylene, is used. Reaction is continued with water being constantly removed until a low acid value, for example, 3 or less is obtained.

Examples of other crosslinking agents are polyesters containing at least two beta- and/or gamma-ester ester groups per molecule. Examples of suitable crosslinking agents are those which are formed from reacting: (a) a polycarboxylic acid or its functional equivalent with (b) a member selected from the class of: (i) 1,2-polyols or 1,2-epoxy compounds, (ii) 1,3-polyols, (c) a monocarboxylic acid.

Examples of suitable polycarboxylic acids are those mentioned above.

The crosslinking agent can be formed by reacting the polycarboxylic acid or its functional equivalent thereof with the 1 ,2-polyol, 1 ,2-epoxy compound, or a 1,3-polyol and the monocarboxylic acid in about a 1/2/1 equivalent ratio at an elevated temperature, usually reflux temperature, in the presence of an esterification catalyst such as an acid or a tin compound. Usually a solvent, for example, an azeotropic solvent such as toluene or xylene is used. Reaction is continued with water constantly being removed until a low acid value, for example, 7 or less, is obtained.

Examples of suitable 1,2-polyols and 1,3-polyols are those mentioned above. Examples of 1,2epoxy compounds are those of the structure:

where R, and R3 are the same or different and include hydrogen and the radicals alkyl, cycloalkyl, aryl, alkaryl containing from 1 to 1 8 carbon atoms, including substituted radicals in which the radicals or the substituents will not adversely affect the esterification reaction with the polycarboxylic acid or its functional equivalent thereof, nor adversely affect the transesterification curing reaction or the desirable properties of the coating composition. Examples of suitable substituents include chloro, hydroxy, alkoxy, carboxy, vinyl and when R1 and R3 form a closed hydrocarbon ring.Examples of suitable radicals include methyl, ethyl, hydroxymethyl, chloromethyl, carboxymethyl, phenyl, methoxy and phenoxy.

Specific examples of 1,2-epoxy compounds include ethylene oxide, propylene oxide, 1,2-epoxy butane, butadiene monoepoxide, glycidol, cyclohexane oxide and a glycidyl ester of a saturated aliphatic monocarboxylic acid containing from 9 to 12 carbon atoms, i.e. CARDURA E.

Examples of monocarboxylic acids are organic monocarboxylic acids having the following structure:

where R9 is a hydrocarbamyl radical containing from 1 to 1 8 carbon atoms. The preferred monocarboxylic acids contain from 1 to 8 carbon atoms and include acetic, propionic, isobutyric, benzoic and stearic acids.

The crosslinking agent can be formed from reacting the polycarboxylic acid or its functional equivalent with the 1,3-polyol and the monocarboxylic acid at elevated temperature, usually reflux temperature, in the presence of an esterification catalyst such as an acid or a tin compound. Usually a solvent such as toluene or xylene is used. Reaction is continued with water being constantly removed until a low acid value, for example, 7 or less, is obtained.

The third component in the coating compositions of the invention is a transesterification catalyst.

These catalysts are known in the art and include salts or complexes of metals such as lead, zinc, iron, tin and manganese. Suitable salts and complexes include 2-ethylhexonates (octoates), naphthanates and acetyl acetonates.

The relative amounts of the polymeric polyol and the crosslinking agent which are present in the coating composition can vary between fairly wide limits depending upon the reactivity of the components and the time and temperature of curing and the properties desired in the cured coating. In general, the polymeric polyol will be present in amounts of about 20 to 95 percent, preferably about 50 to 85 percent by weight, and the crosslinking agent in amounts of about 5 to 80, preferably 1 5 to 50 percent by weight; the percentages by weight being based on total weight of polymeric polyol and crosslinking agent, and being determined on a solids basis.

The catalyst is present in amounts of about 0.1 to 2.0, preferably about 0.2 to 1.0 percent by weight metal based on total weight (solids) of the polymeric polyol and the crosslinking agent.

The components of the coating composition can be mixed simultaneously or in any order that is convenient. If the components are a liquid and of sufficiently low viscosity, they can be mixed together neat to form the coating composition. Alternately, if the components are higher viscosity liquids or solids, the components can be mixed with a diluent to reduce the viscosity of the composition so that it may be suitable for coating applications.

By liquid diluent is meant a solvent or a non-solvent which is volatile and which is removed after the coating is applied and is needed to reduce viscosity sufficiently to enable forces available in simple coating techniques, that is, brushing and spraying, to spread the coating to controllable, desired, and uniform thickness. Also, diluents assist in substrate wetting, resinous component compatibility and coalescence or film formation. generally, when used, the diluent will be present in the composition in amounts of about 20 to 90, preferably 50 to 80 percent by weight based on total weight of the coating composition, although more diluent may be employed depending upon the particular coating application.

Examples of suitable liquid diluents for organic solvent-based coatings will depend somewhat on the particular system employed. In general, however, aromatic hydrocarbons such as toluene and xylene, ketones such as methyl ethyl ketone and methyl isobutyl ketone, alcohols such as isopropyl alcohol, normal butyl alcohol, monoalkyl ethers of glycols such as 2-alkoxyethanol, 2-alkoxypropanol and compatible mixtures of these solvents can be used.

Besides organic solvents, water can be used as a diluent either alone or in combination with water-miscible organic solvents. When water is used, the coating composition is usually modified such as by incorporating water-solubilizing groups such as the cationic groups mentioned above to provide for the necessary solubility in water. Besides the cationic groups mentioned above, other watersolubilizing groups such as non-ionic groups, for example, ethylene oxide groups, and anionic groups such as carboxylate salt groups may be introduced into the polymeric polyol or the polyester crosslinking agent to disperse or solubilize the coating composition in water.

The coating compositions of the invention may also optionally contains a pigment. Pigments may be of any conventional type, comprising, for example, iron oxides, lead oxides, strontium chromate, carbon black, coal dust, titanium dioxide, talc, barium sulfate, as well as colour pigments such as cadmium yellow, cadmium red, chromium yellow and metallic pigments such as aluminium flake.

The pigment content of the coating composition is usually expressed as the pigment-to-resin weight ratio. In the practice of the present invention, pigment-to-resin weight ratios can be as high as 2:1, and for most pigmented coatings, are usually within the range of about 0.05 to 1:1.

In addition to the above ingredients, various fillers, plasticizers, anti-oxidants, ultraviolet light absorbers, flow control agents, surfactants and other formulating additives can be employed if desired.

These materials are optional and generally constitute up to 30 percent by weight of the coating composition based on total solids.

The coating compositions of the invention can be applied by conventional methods including brushing, dipping, flow coating, spraying, and, for aqueous-based compositions containing ionic salt groups, by electrodeposition. Usually, they can be applied virtually over any substrate including wood, metal, glass, cloth, leather, plastic, foam and the like, as well as over various primers. For electroconductive substrates such as metals, the coatings can be applied by electrodeposition. In general, the coating thickness will vary somewhat depending upon the application desired. In general, coatings from about 0.1 to 10 mils can be applied and coatings from about 0.1 to 5 mils are usual.

When aqueous dispersions of the coating composition are employed for use in electrodeposition, the aqueous dispersion is placed in contact with an electrically conductive anode and an electrically conductive cathode. In the case of cationic electrodeposition, the surface to be coated is the cathode.

Following contact with the aqueous dispersion, an adherent film of the coating composition is deposited on the electrode being coated when a sufficient voltage is impressed between the electrodes. Conditions under which electrodeposition is carried out are known in the art. The applied voltage may be varied and can be, for example, as low as 1 volt or as high as several thousand volts, but is typically between 50 and 500 volts. Current density is usually between 1.0 ampere and 1 5 amperes per square foot and tends to decrease during electrodeposition indicating the formation of an insulating film.

After the coating has been applied, it is cured by heating at elevated temperatures such as at about 1 50 to 2050C for about 10 to 45 minutes to form solvent-resistant coatings. By solventresistant coatings is meant that the coating will be resistant to acetone, for example, by rubbing across the coating with an acetone-saturated cloth. Coatings which are not cured or poorly cured will not withstand the rubbing action with acetone and will be removed with less than 10 acetone double rubs.

Cured coatings, on the other hand, will withstand 30 acetone double rubs, and preferably at least 100 acetone double rubs.

Illustrating the invention are the following examples which, however are not to be construed as limiting the invention to their details. All parts and percentages in the examples, as well as throughout the specification, are by weight unless otherwise indicated.

Example I The following example shows the preparation of a coating composition containing a crosslinking agent having three beta-alkoxyester groups per molecule. The crosslinking agent was formed by reacting trimellitic anhydride with 2-butoxyethanol in a 1:3 molar ratio. The crosslinking agent was then mixed with a polymeric polyol formed from condensing an epoxy resin (polyglycidyl ether of a polyphenol) with an amine. The mixture was dispersed in water with the aid of acid and combined with lead octoate catalyst. Steel panels were cathodically electrocoated in the dispersion and the coatings heated to make them solvent resistant. The details of the Example are shown below.

Crosslinking agent The crosslinking agent was prepared from the following mixture of ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Trimellitic 192 192.0 3.00 1.00 anhydride 2-butoxyethanol 365 354.0 3.09 3.09 Para-toluene- 1.4 1.4 sulfonic acid Xylene 40.0 The ingredients were charged to a reaction vessel under a nitrogen blanket. The mixture was heated to reflux until an acid value of 2.2 was obtained.

Polymeric polyol The polymeric polyol as described in European Patent Application 0,012,463 was formed from reacting a polyglycidyl ether of bisphenol A with diethanolamine in about a 3:1 equivalent ratio. The adduct was then chain extended with a mixture of a primary and a disecondary amine, namely, 3dimethylaminopropylamine, and the adduct of 1 ,6-hexamethylene diamine and the glycidyl ester of Versatic acid (CARDURA E).

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 829' 460.7 445.5 2.269 1.135 > (1.146) > (0.573) Bisphenol A 128.0 128.0 1.123 0.562 Xylene 30.0 Diethanolamine 38.0 38.0 0.362 0.362 2-butoxyethanol 307.2 - 3-dimethylaminopropylamine 18.4 18.4 0.361 0.180 1 ,6-hexamethylene-CARDURA E 122.4 122.4 0.36 0.18 adduct (1:2 molar ratio)2 Polyglycidyl ether of bisphenol A having an epoxide equivalent of 1 96 commercially available from Shell Chemical Company.

2 Adduct form by adding the glycidyl ester of Versatic acid dropwise to the 1 ,6-hexamethylene diamine at 600 C. At the completion of addition, the mixture was heated to 1 000C and held for two hours. The glycidyl ester of Versatic acid is commercially available from Shell Chemical Company as CARDURA E.

Aqueous dispersions An aqueous dispersion was prepared by mixing together the following ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Polymeric polyol 144.3 107.4 0.155 (amine) Crosslinking agent 44.5 39.9 Lead octoatel (catalyst) 2.70 2.05 Lactic acid 7.11 0.072 Deionized water 797.1 1 Lead octoate dissolved in a hydrocarbon solvent.

2 45 percent of the total theoretical neutralization.

Into a large stainless steel beaker was added the polymeric polyol, the crosslinking agent prepared as described above and the lead catalyst. The ingredients were blended until uniform. Lactic acid was added with agitation and the reaction mixture thinned with water to form the aqueous dispersion having a solids content of 14.8 percent (15 percent calculated). Both untreated and zinc phosphate pretreated steel panels were cathodically electrodeposited in the dispersion at about 90 1 20 volts for 90 seconds. The coated panels were baked at 1 800C for 30 minutes to form solventresistant coatings. The untreated steel panels withstood 100 acetone double rubs and the zinc phosphate pretreated panels withstood 45 acetone double rubs.The number of acetone double rubs are the number of rubs back and forth with an acetone-saturated cloth using normal hand pressure to remove the cured coating.

Example II The following example shows the preparation of a coating composition containing a crosslinking agent containing 6 beta-alkoxyester groups per molecule. The crosslinking agent was formed from reacting trimellitic anhydride with trimethylolpropane in a 3:1 molar ratio and esterifying with 6 moles of 2-butoxyethanol. The crosslinking agent was mixed with a polymeric polyol formed from condensing an epoxy resin (polyglycidyl ether of a polyphenol) with an amine as described below. The mixture was formulated into an organic solvent-based coating composition with and without lead octoate catalyst.

Steel panels were coated with the composition and the coated substrates heated to give cured coatings.

Polymeric polyol The polymeric polyol was formed by chain extending an epoxy resin with a polyester diol and reacting the chain-extended epoxy resin with a mixture of amines, namely, methylethanolamine and a diketimine derivative of diethyiene triamine.

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 828' 953.7 953.7 4.819 (epoxy) 2.41 PCP 02002 320.6 320.6 1.2 (OH) 0.6 Xylene 80.0 Bisphenol A 274.7 274.7 2.41 (OH) 1.205 Benzyldimethylamine 5.9 2-ethoxyethanol 31 7.9 Methylisobutyl diketimine of 85.7 61.9 0.232 (amine) 0.232 diethylene triamine3 N-methylethanolamine 69.5 69.5 0.926 (amine) 0.926 1 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 98 commercially available from the Shell Chemical Company.

2 Polycaprolactone diol having a molecular weight of about 545 commercially available from the Union Carbide Company.

3 Methylisobutyl ketone solvent.

The EPON 828, PCP 0200 and xylene were charged to a reaction vessel under a nitrogen blanket and heated to reflux and held for 30 minutes. The reaction mixture was cooled to 1 550C, followed by the addition of the bisphenol A. Benzyldimethylamine (1.9 grams) was added and the reaction mixture exothermed. It was cooled to 1300 C, followed by the addition of the remaining 4.0 grams of the benzyldimethylamine. The reaction mixture was held at about 1 300C for about 3 hours until the viscosity of the reaction mixture as a 50 percent resin solution in 2-ethoxyethanol was N+. The 2ethoxyethanol, methylisobutyl diketimine of diethylene triamine and methylethanolamine were added and the reaction mixture held at about 11 00C for about one hour, followed by cooling to room temperature.The reaction mixture had a solids content of about 80 percent by weight.

A coating composition was prepared by mixing 27.9 grams (23.2 grams solids) of the polymeric polyol and 12.3 grams (11.5 grams solids) of the crosslinking agent. The mixture was thinned with 6.1 grams of 2-ethoxyethanol to form a 75 percent solids coating composition. A portion of this coating composition was set aside; a second portion (21.2 grams) was mixed with 0.34 parts by weight (0.26 grams solids) of lead octoate. Both coating compositions were drawn down on untreated and zinc phosphate pretreated steel panels and the wet films cured at 3500F (1 770C) for 30 minutes.The coatings without the lead catalyst were removed by 23 acetone double rubs (on untreated steel panels) and 1 5 acetone double rubs (on zinc phosphate pretreated steel panels), whereas the coating with the catalyst withstood 175 acetone double rubs on both substrates.

Example Ill The following example shows the preparation of a coating composition containing a crosslinking agent having two beta-amido ester groups per molecule. The crosslinking agent was prepared by reacting N-(2-hydroxyethyl)-isobutyramide with a condensate ot trimethylolpropane and trimellitic anhydride. The crosslinking agent was mixed with a polymeric polyol made from condensing an epoxy resin (polyglycidyl ether of a polyphenol) with an amine. The mixture was formulated into a coating composition with lead octoate catalyst and the composition drawn down on steel panels to form coatings. The coatings were heated to give solvent-resistant coatings.

N-(2-hydroxyethyl )isobutyra m ide N-(2-hydroxyethyl)isobutyramide was prepared as follows: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Isobutyric acid 440.0 440.0 4.994 4.994 2-ethoxy ethanol 495.0 450.0 5.500 5.500 Xylene 80.0 Para-toluenesulfonic acid 2.0 2.0 Ethanolamine 305.0 305.0 5.000 5.000 The isobutyric acid, 2-ethoxyethanol, xylene and para-toluenesulfonic acid were charged to a reaction vessel under a nitrogen blanket and a Dean-Stark trap and heated to reflux. The reaction mixture was held at reflux temperature (1 650C) until an acid value of 3.4 was obtained (123 grams of aqueous phase collected).The reaction mixture was cooled to 100 C, the ethanolamine was added and refluxing was continued for 9 hours. At that point, the reaction mixture was sparged until 447 grams of distillate was obtained. The product formed a dark brown, wet crystalline mass on standing overnight. This was recrystallized from ethanol and toluene to obtain 231.8 grams (35.4 percent yield, which could be increased with subsequent crops) of off-white needle crystals, mp 54-570C.

Crosslinking agent Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Trimellitic anhydride 131.9 131.9 2.061 2.687 Trimethylolpropane 30.7 30.7 0.687 0.229 N-(2-hydroxyethyl)-isobutyramide 180.0 180.0 1.374 1.374 Xylene 80.0 The trimellitic anhydride, trimethylolpropane and the xylene were charged to a reaction vessel under a nitrogen blanket and a Dean-Stark trap and held at reflux for 30 minutes. The reaction mixture was then cooled to 100 C, the amino alcohol was added, and refluxing was continued until an acid value of 3.2 was obtained. The product was found to have a solids content of 81.7 percent.

Polymeric polyol The polymeric polyol was formed by chain extending an epoxy resin with a polyester diol and then reacting the chain-extended polyester with a mixture of amines, one of which included primary amine groups blocked with ketimine.

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 8281 1686.2 1686.2 8.674 (epoxy) 4.337 PCP 02002 588.4 588.4 2.160 (OH) 1.080 Xylene 144.0 Bisphenol A 494.5 494.5 4.337 (OH) 2.169 Benzyldimethylamine 10.6 2-ethoxyethanol 572.2 Methylisobutyldiketimine of 150.2 111.4 0.417 (amine) 0.417 diethylene triamine3 Monoethanolamine 125.1 125.1 1.668 (amine) 1.668 1 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 98 commercially available from Shell Chemical Company.

3 Solution in methylisobutyl ketone.

The EPON 828, PCP 0200 and xylene were charged to a reaction vessel and heated under a nitrogen blanket to reflux and held for 30 minutes. The reaction mixture was cooled to 1 55"C, followed by the addition of the bisphenol A. Benzyldimethylamine (3.4 grams) was added and the reaction mixture exothermed. The reaction mixture was cooled to 1 300 C, followed by the addition of the remaining benzyldimethylamine and the reaction mixture held at 1300C until it attained a reduced Gardner-Holdt viscosity (50 percent resin solids in 2-ethoxyethanol) of N+. The 2-ethoxyethanol, diketimine and monoethanolamine were then added and the reaction mixture held at 11000 for about one hour to complete the reaction.

To 34.78 parts by weight of the polymeric polyol reaction mixture prepared as described above were added 1 7.43 parts by weight of the crosslinking agent and 7.87 grams of 2-ethoxyethanol. The mixture was heated and stirred until homogeneous to form a coating composition. A portion of this mixture was put aside and the remaining portion (27.70 grams) was blended with 0.44 grams of lead octoate (0.33 grams solids). Both coating compositions were drawn down over untreated and zinc phosphate pretreated steel panels. The coated panels were then baked at 3500F (1770C) for 30 minutes. The coatings obtained from the compositions which contained no lead exhibited practically no acetone resistance (13-15 acetone double rubs).However, the coatings obtained from compositions containing the lead catalyst exhibited 75 acetone double rubs on the untreated steel and 60 acetone double rubs on the zinc phosphate pretreated steel panels.

Example IV The following example shows the preparation of a coating composition containing a crosslinking agent having two delta hydroxyester groups per molecule. The crosslinking agent is formed by reacting adipic acid with 1 ,4-butanediol in a 1:2 molar ratio. The crosslinking agent was mixed with a polymeric polyol formed from condensing an epoxy resin (polyglycidyl ether of a polyphenol) with an amine. The mixture was dissolved in organic solvent, lead octoate was added, and the solution drawn down on steel panels and the coated panels heated to give solvent-resistant coatings.The details of the Example are shown below: Crosslinking agent The crosslinking agent was prepared from the following mixture of ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Adipic acid 146.0 146.0 2.000 1.000 1,4-butanediol 180.0 180.0 4.000 2.000 Xylene 50.0 Para-toluenesulfonic acid 1.0 1.0 The ingredients were charged to a reaction vessel under a nitrogen blanket. The reaction mixture was heated to reflux until an acid value of 1.3 was obtained. During the reaction, 48.1 grams of aqueous layer was collected in a Dean-Stark trap.

Polymeric polyol The polymeric polyol was formed from reacting a polyglycidyl ether of bisphenol A with diethanolamine in about a 3:1 equivalent ratio. The adduct was then chain extended with a mixture of a primary and a disecondary amine, namely, 3-dimethylaminopropylamine, and the adduct of 1,6hexamethylene diamine and the glycidyl ester of Versatic acid (CARDURA E).

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 829' 921.0 890.6 4.537 2.268 Bisphenol A 255.8 255.8 > (2.293) 1.122 2.244 Xylene 30.0 2-ethoxyethanol 608.0 Diethanolamine 80.3 80.3 0.765 0.765 Dimethylaminopropylamine 38.0 38.0 0.744 0.372 1 ,6-hexamethylene diamine-glycidyl 252.9 244.5 0.745 0.372 ester of Versatic acid adduct (1:2) molar ratio)2 1 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 96 commercially available from the Shell Chemical Company.

2 Adduct formed by adding the glycidyl ester of Versatic acid dropwise to the 1 6-hexamethylene diamine at a temperature of 600 C. At the completion of addition, the mixture was heated to 1000C and held for two hours. The glycidyl ester of Versatic acid is commercially available from Shell Chemical Company as CARDURA E.

Organic solvent-based coating composition Weight Ingredient (in grams) Polymeric polyol 36.18 Crosslinking agent 11.04 Lead Octoate (75.9% solids in hydrocarbon solvent) 0.67 2-ethoxyethyl acetate 8.79 The ingredients were mixed together and heated in a 2-ounce glass jar to obtain a clear, yellow resin. The coating composition was drawn down on an untreated steel panel and on a zinc phosphate pretreated steel panel. The coated panels were cured for about 30 minutes at 1 800 C. The cured coatings exhibited a medium to high gloss and had a thickness of from about 1.6 to 2.2 mils. The coating on the untreated steel was removed after 125 acetone double rubs. The coated zinc phosphate pretreated steel panel withstood 1 32 acetone double rubs.

Example V The following example shows the preparation of a coating composition containing a crosslinking agent which is a gamma-hydroxy polyester formed by reacting adipic acid with trimethylolpropane in a 1:2 molar ratio. The crosslinking agent was mixed with a polymeric polyol formed from condensing a polyglycidyl ether of a polyphenol with an amine. The mixture was combined with lead octoate catalyst to form a coating composition. Steel panels were coated with the composition and the coated substrates heated to give solvent-resistant coatings. Also, the mixture was dispersed in water with the aid of acid and steel panels were cathodically electrocoated with the dispersion.The details of the Example are shown below: Crosslinking agent The crosslinking agent was prepared from the following mixture of ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Adipic acid 146.0 146.0 2.000 1.000 Trimethylolpropane 268.0 268.0 6.000 2.000 Xylene 40.0 Para-toluenesulfonic acid 1.0 1.0 The ingredients were charged to a reaction vessel under a nitrogen blanket and heated to reflux.

The reaction mixture was held at reflux temperature until an acid value of about 1.7 was obtained.

Polymeric polyol The polymeric polyol was formed from chain extending a polyglycidyl ether of bisphenol A with a polyester diol. The adduct was then reacted with a mixture of amines, namely, monoethanolamine and the methylisobutyl diketimine of ethylene triamine.

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 8281 953.7 953.7 4.819 (epoxy) 2.41 PCP 02002 320.6 320.6 1.2 (OH) 0.6 Xylene 80.0 Bisphenol A 274.7 274.7 2.41 (OH) 1.205 Benzyldimethylamine 5.9 2-ethoxyethanol 31 7.9 Methylisobutyl diketimine of 85.7 61.9 0.232 (amine) 0.232 diethylene triamine3 Monoethanolamine 69.5 69.5 0.926 (amine) 0.926 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 98 commercially available from Shell Chemical Company.

3 Solution in methylisobutyl ketone.

The EPON 828, PCP 0200 and xylene were charged to a reaction vessel and heated under a nitrogen blanket to reflux and held for 30 minutes. The reaction mixture was cooled to 1 550C followed by addition of the bisphenol A. Benzyldimethylamine (1.9 grams) was added and the reaction mixture exothermed. The reaction mixture was cooled to 1 300C followed by the addition of the remaining benzyldimethylamine and the reaction mixture held at 1300C until it attained a reduced Gardner-Holdt viscosity (50 percent resin solids in 2-ethoxyethanol) of N+. The 2-ethoxyethanol, diketimine and monoethanolamine were then added and the reaction mixture held at 108--1 12 OC for about one hour to complete the reaction.

To 39.55 grams (31.64 grams solids) of the polymeric polyol prepared as described immediately above was added 17.07 grams (15.60 grams solids) of the crosslinking agent prepared as described above. To a 31.78 grams sample (26.5 grams solids) of the mixture was added 0.50 grams of the lead octoate solution as described in Example IV. The composition was drawn down with a drawbar over untreated and zinc phosphate pretreated steel panels and the panels heated to 3600 F ( 1 82 OC) for 30 minutes. The cured films were glossy with a textured surface. The coating over the untreated steel was removed after 1 50 acetone double rubs, whereas the coating over the zinc phosphate pretreated steel withstood 107 acetone double rubs.

When comparable coatings were made without the use of the lead catalyst, the cured coatings were removed by about 10 to 23 acetone double rubs.

Aqueous dispersion An aqueous dispersion was prepared by mixing together the following ingredients: Weight Solids (in (in Ingredients grams) grams) Equivalents Polymeric polyol 122.4 100.5 0.098 Crosslinking agent 52.4 49.5 Lead octoate (catalyst)' 2.75 2.09 Surfactant2 3.75 Lactic acid 3.49 0.034 Deionized water 829.1 Lead octoate in a hydrocarbon solvent.

2 Surfactant was prepared by blending 120 grams of alkyl imidazoline commercially available from Geigy Industrial Chemicals as GEIGY AMINE C, 120 parts by weight of an acetylenic alcohol commercially available from Air Products and Chemicals Inc. as SURFYNOL 104, 120 parts by weight of 2-butoxyethanol and 221 parts by weight of deionized water and 1 9 parts by weight of glacial acetic acid.

The polymeric polyol and the crosslinking agent were blended together with warming in a steel beaker. The lead octoate was blended in, followed by the addition of the lactic acid. The reaction mixture was then thinned with the deionized water to form a 1 4.6 percent by weight resin solids dispersion.

Untreated steel and zinc phosphate pretreated steel panels were cathodically electrocoated in the dispersion at 200 volts for 90 seconds. The coated substrates were then heated to 4000F (204 C for 30 minutes to form cured coatings. The coating on the untreated steel withstood 1 50 acetone double rubs, whereas the coating on the zinc phosphate pretreated steel withstood 1 40 acetone double rubs.

Example VI The following example was similar to Example V with the exception that the crosslinking agent was introduced into the resin cook.

Polymeric polyol containing crosslinking agent The polymeric polyol was prepared as generally described above in Example V with the exception that the crosslinking agent was cooked in. The charge for preparing the polymeric polyol was as follows: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 828 702.6 702.6 3.614(epoxy) 1.807 PCP 0200 244.0 244.0 0.90 (OH) 0.45 Xylene 60.0 Bisphenol A 206.1 206.1 1.808 (OH) 0.904 Benzyldimethylamine 4.8 Crosslinking agent' 652.9 616.3 2-butoxyethanol 373.4 Methylisobutyl diketimine of 59.7 46.5 0.1 74 (amine) 0.174 diethylene triamine Monoethanolamine 52.1 52.1 0.694 (amine) 0.694 Crosslinker was the adipic acid/trimethylolpropane condensate prepared as generally described in Example V.

The EPON 828, PCP 0200 and xylene were charged to a reaction vessel under a nitrogen blanket and heated to reflux and held for 30 minutes. The reaction mixture was cooled to 1550C and the bisphenol A added. The temperature dropped to 1280C and the reaction mixture was held for about 20 minutes at this temperature. Benzyldimethylamine (1.5 grams) was added and the reaction mixture exothermed with the temperature reaching 1700C. The reaction mixture was cooled to 1300C, followed by the addition of 3.3 grams of the benzyldimethylamine. The reaction mixture was held at a temperature of about 1 3000 until a Gardner-Holdt viscosity (50 percent resin solids in 2ethoxyethanol) of P was obtained.The cross-linking agent dissolved in the 2-butoxyethanol was then added, the reaction mixture temperature dropping to 850C. The reaction mixture was heated to 11000 and held for about one hour to complete the reaction. The reaction mixture had a solids content of 82.7 percent.

Aqueous dispersion The resinous reaction product prepared as described immediately above was dispersed in aqueous medium as follows: Weight Solids (in (in Ingredient grams) grams) Equivalents Polymeric polyol containing 965.0 800.0 0.521 (amine) cross-linking agent prepared as described immediately above Surfactant of Example V 20.0 Lactic acid 18.65 0.182 Deionized water 1282.1 The polymeric polyol and the surfactant were mixed together in a stainless steel beaker, followed by the addition with mixing of the lactic acid. The reaction mixture was then thinned with deionized water to form a 34.2 percent solids aqueous dispersion.

A cationic electrodeposition paint was prepared from the following mixture of ingredients: Weight Ingredient (in grams) Deionized water 1704.2 Lead acetate 6.9 Aqueous dispersion of polymeric polyol 1703.2 Pigment paste1 385.7 1 The pigment paste contained 32.9 percent by weight pigment, 13.2 percent by weight resinous vehicle and 1.1 percent by weight dibutyltin oxide. The pigment paste was prepared as generally described in Example Ill of U.S. 4,007,154.

The deionized water was charged to a mixing vessel followed by the addition of the lead acetate.

The polymeric polyol (34.2 percent solids was then stirred in, followed by the addition of the pigment paste with stirring. The final paint had a total solids content of 20 percent, a pH of 6.25, pigment-tobinder ratio of 0.2:1. After stirring for two days, the pH remained at 6.25 and the specific conductivity of the dispersion was 1250 measured at 770F (250 C). Zinc phosphate pretreated steel panels were cathodically electrocoated in the dispersion at 1 20 volts for 20 minutes at a bath temperature of 700 F (21 0 C). The coatings were cured at 3500 F (1 77 OC) for 30 minutes.The coatings were removed after 35 acetone double rubs and were evaluated for corrosion resistance which was determined by scribing the cured coated panel with an "X" and exposing the scribed panel to a salt spray fog in accordance with ASTM D-1 17 for 14 days. The panels were removed from the chamber, dried and the scribe mark taped with masking tape, the tape pulled off at a 450 angle and the creepage from the scribe mark measured. Creepage is the rusted, darkened area of the panel where the coating has lifted from the panel surface. The scribe creepage was 1/16 inch. When untreated steel panels were cathodically eiectrocoated in the bath at 80 volts for 2 minutes and the coatings cured and exposed for 14 days to salt spray corrosion as described above, the scribe creepage was 3/1 6 of an inch.

Example VII The following example shows the preparation of a coating composition containing the crosslinking agent of Example IV and the polymeric polyol of Example V. The coating composition was formulated with lead catalyst and steel panels were coated with the composition and the coated substrates heated to give solvent-resistant coatings. The specific coating formulation is shown below: Organic solvent-based coating composition Weight Solids Ingredient (in grams) (in grams) Polymeric polyol 11.64 9.67 Crosslinking agent 5.28 4.77 2-ethoxyethanol 7.15 Lead octoate 0.24 0.18 The ingredients were mixed and heated to form a homogeneous composition which was then drawn down on untreated and zinc phosphate pretreated steel panels.The coated panels were cured for 30 minutes at 4000F (204 C) to give cured coatings which withstood 150 acetone double rubs.

Coatings formulated without lead catalyst and baked at 4000F (204 C) for 30 minutes were removed by only 23 acetone double rubs on untreated steel and 1 6 acetone double rubs on zinc phosphate pretreated steel.

Example VIII The following example shows the preparation of a coating composition containing a crosslinking agent having three beta-ester ester groups per molecule. The crosslinking agent was formed by reacting trimellitic anhydride with ethylene glycol and isobutyric acid in a 1:3:3 molar ratio. The crosslinking agent was then mixed with a polymeric polyol formed from condensing an epoxy resin (polyglycidyl ether of a polyphenol) with an amine. The mixture was combined with lead octoate catalyst and dispersed in water with the aid of acid. Steel panels were cathodically electrocoated with the dispersion and the coatings heated to give solvent-resistant coatings. Also, the mixture was dissolved in organic solvent, the solution drawn down on steel panels and the coated panels heated to give solvent-resistant coatings.The details of the Example are shown below: Crosslinking agent The crosslinking agent was prepared from the following mixture of ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Trimellitic anhydride 192.0 192.0 3.000 1.000 Ethylene glycol 21 7.2 186.2 7.000 3.500 Isobutyric acid 264.3 264.3 3.000 3.000 Para-toluenesulfonic acid 1.4 1.4 Toluene 80.0 The above ingredients were charged to a reaction vessel under a nitrogen blanket and heated to reflux. Reflux was continued until an acid value of 4.1 was obtained. The hydroxyl value of the product was 2.9 (apart from the acid value), and the water content was 0.03 percent.

Polymeric polyol The polymeric polyol was formed from reacting a polyglycidyl ether of bisphenol A with diethanolamine in about a 3:1 equivalent ratio. The adduct was then chain extended with a mixture of a primary and a disecondary amine, namely, 3-dimethylaminopropylamine, and the adduct of 1,6hexamethvlene diamine and the qlycidyl ester of Versatic acid (CARDURA E).

Weight Solids (in (in Ingredient grams) grams) Equivalents Moles EPON 829' 921.0 890.6 4.537 2.268 > (2.293) > (1.147) Bisphenol A 255.8 255.8 2.244 1.122 Xylene 30.0 Diethanolamine 80.3 80.3 0.765 0.765 3-dimethylaminopropylamine 38.0 38.0 0.745 0.372 1,6-hexamethylene glycidyl ester 256.8 253.4 0.745 0.372 of Versatic acid adduct (1:2 molar ratio)2 2-butoxyethanol 614.2 1 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 93-203 commercially available from the Shell Chemical Company.

2 Adduct formed by adding the glycidyl ester of Versatic acid dropwise to the 1 ,6-hexamethylene diamine at a temperature of 60"C. At the completion of addition, the mixture was heated to 1000C and held for two hours. The glycidyl ester of Versatic acid is commercially available from Shell Chemical Company as CARDURA E.

Aqueous dispersion An aqueous dispersion of the polymeric polyol and the crosslinking agent prepared as described above was made as follows: Weight Solids (in (in Ingredient grams) grams) Equivalents Polymeric polyol 146.2 109.4 0.162 (amine) Crosslinking agent 52.7 40.7 Lead octoate solution 2.75 2.091 Lactic acid 7.48 0.0732 Deionized water 805.5 1 75.9% solids lead octoate dissolved in hydrocarbon solvent.

2 45 percent of the total theoretical neutralization.

The polymeric polyol, crosslinking agent and lead were charged to a stainless steel beaker and mixed together. The lactic acid was added and blended into the mixture, followed by thinning with the deionized water. The aqueous dispersion had a solids content of 14.3 percent.

Untreated and zinc phosphate pretreated steel panels were cathodically electrocoated in the dispersion at 100 volts for 90 seconds. The coatings were then cured at 1 80C for 30 minutes to form films having a thickness of about 0.7 to 0.9 mil. The untreated steel panels had from between 56 to 70 acetone double rubs and the zinc phosphate pretreated steel panels withstood between 38 to 65 acetone double rubs.

Organic solvent-based coating composition Weight Solids Ingredient (in grams) (in grams) Polymeric polyol 36.39 27.19 Crosslinking agent 18.12 13.46 2-ethoxyethanol 11.82 The above ingredients were charged to a 2-ounce glass jar and 25.19 grams were transferred (after heating and mixing to homogeneity) to a second 2-ounce glass jar. After transfer, 0.37 gram of lead octoate (75.9 percent solids in a hydrocarbon solvent) was added to form the coating composition.

The coating composition was drawn down on an untreated steel panel and on a zinc phosphate pretreated steel panel. The coated panels were cured for 30 minutes at 3500F (1 77 OC). The cured coating had a thickness of about 1.8-2.8 mils and withstood 1 50 acetone double rubs (untreated steel) and 1 75 acetone double rubs (zinc phosphate pretreated steel).

Coating compositions formulated without lead, applied and cured as described above were removed by only 25 acetone double rubs over untreated steel and 37 acetone double rubs over zinc phosphate pretreated steel.

Example IX The following example shows the preparation of a coating composition containing a crosslinking agent having three gamma-ester ester groups per molecule. The crosslinking agent was formed by reacting trimellitic anhydride with 1,3-propanediol and isobutyric acid in a 1:3:3 molar ratio: The crosslinking agent was mixed with a polymeric polyol as described in Example VIII, combined with lead octoate catalyst and dispersed in water with the aid of acid. Steel panels were cathodically electrocoated with the dispersion and the coating baked to give solvent-resistant coatings. Also, the mixture was dissolved in organic solvent, the solution drawn down on steel panels and the coated panels heated to give solvent-resistant coatings.

Crosslinking agent The crosslinking agent was prepared from the following mixture of ingredients: Weight Solids (in (in Ingredient grams) grams) Equivalents Moles Trimellitic anhydride 80.1 80.1 1.252 0.417 1,3-propanediol 100.0 95.3 2.628 1.314 Isobutyric acid 110.3 110.3 1.252 1.252 Para-toluenesulfonic acid 1.0 1.0 Toluene 50.0 The ingredients were charged to a reaction vessel and heated to reflux under a nitrogen blanket until an acid value of 6.3 was obtained.

Aqueous dispersion An aqueous dispersion of the crosslinking agent as described above and the polymeric polyol of Example VIII and lead catalyst was prepared as follows: Weight Solids (in (in Ingredient grams) grams) Equivalents Polymeric polyol of 146.2 109.4 0.162 (amine) Example VIII Crosslinking agent 68.1 40.7 Lead octoate 2.75 2.09 Lactic acid 7.48 0.073' Deionized water 790.1 1 45 percent of the total theoretical neutralization.

The polymeric polyol and the crosslinking agent were charged to a stainless steel beaker, followed by the addition of the lead octoate. The ingredients were blended together followed by the addition of the lactic acid. The blend was then thinned with deionized water to form a 14.4 percent solids dispersion.

Untreated and zinc phosphate pretreated steel panels were cathodically electrocoated in the dispersion at 100 volts for 90 seconds. The coated panels were baked for 30 minutes at 1800C to form coatings having a thickness of about 0.9-1.1 mil. The untreated steel panels withstood 39-41 acetone double rubs, whereas the coatings on the zinc phosphated panels withstood 16-21 acetone double rubs.

Organic solvent-based coating composition Weight Solids Ingredient (in grams) (in grams) Polymeric polyol 34.43 27.10 Crosslinking agent 22.36 13.35 The above ingredients were charged to a 2-ounce glass jar and warmed and mixed to uniformity.

The contents were transferred to a second 2-ounce glass jar and combined with 0.35 grams of lead octoate (75 percent solids) to form the coating composition.

The coating composition was drawn down on steel panels and cured at elevated temperature.

The results are presented below: Curing Coating schedule thickness Acetone Panel 0minutes (in mils) resistance Untreated steel 350/30 1.9 9596 Zinc phosphate pretreated steel 350/30 3.2 84 Untreated steel 400/30 2.0 137-175 Zinc phosphate pretreated steel 400/30 2.8-3.3 > 175 Coating compositions formulated without lead, deposited and cured as described above had the following properties:: Curing Coating schedule thickness Acetone Panel 0minutes (in mils) resistance Untreated steel 350/30 1.7 30 Zinc phosphate pretreated steel 350/30 2.3 32 Untreated steel 400/30 2.2 89 Zinc phosphate pretreated steel 400/30 4.0-4.2 91 Example X The following example shows the preparation of a coating composition containing a crosslinking agent having three gamma-ester ester groups per molecule as described in Example IX. The crosslinking agent was mixed with a polymeric polyol as described below; the mixture dissolved in organic solvent and combined with lead octoate catalyst. The coating composition was drawn down on steel panels and heated to give solvent-resistant coatings.

Polymeric polyol The polymeric polyol was formed from chain extending a polyglycidyl ether of bisphenol A with a polyester diol. The adduct was then reacted with a mixture of amines, namely, monoethanolamines and the methylisobutyl diketimine of diethylene triamine.

Weight Solids (in Kin Ingredients grams) grams) Equivalents Moles EPON 8281 953.7 953.7 4.819 (epoxy) 2.41 PCP 02002 320.6 320.6 1.2 (OH) 0.6 Xylene 80.0 Bisphenol A 274.7 274.7 2.41 (OH) 1.205 Benzyldimethylamine 5.9 2-ethoxyethanol 317.9 Methylisobutyldiketimine of 85.7 61.9 0.232 (amine) 0.232 diethylene triamine3 Monoethanolamine 69.5 69.5 0.926 (amine) 0.926 Polyglycidyl ether of bisphenol A having an epoxide equivalent of about 1 98 commercially available from Shell Chemical Company.

3 Solution in methylisobutyl ketone.

The EPON 828, PCP 0200 and xylene were charged to a reaction vessel and heated under a nitrogen blanket to reflux and held for 30 minutes. The reaction mixture was cooled to 1 550C, followed by the addition of the bisphenol A. Benzyldimethylamine (1.9 grams) was added and the reaction mixture exothermed. The reaction mixture was cooled to 1 300C, followed by the addition of the remaining benzyldimethylamine and the reaction mixture held at 1300C until it attained a reduced Gardner-Holdt viscosity (50 percent resin solids in 2-ethoxyethanol) of N+. The 2-ethoxyethanol, diketimine and monoethanolamine were then added and the reaction mixture held at 108--1 120C for about one hour to complete the reaction.

To 24.23 grams (20.14 grams solids) of the polymeric polyol prepared as described immediately above was added 16.69 grams (9.96 grams solids) of the crosslinking agent prepared as described in Example IX and 5.6 grams of 2-ethoxyethanol. To a 20.01 gram sample (12.94 grams solids) of the mixture was added 0.23 grams of the lead octoate solution as described in Example VIII. The composition was drawn down with a draw bar over untreated and zinc phosphate pretreated steel panels and the panels heated to 3500F (1770C) for 30 minutes. The cured coatings over the untreated steel were 1.6 mils in thickness and withstood 1 50 acetone double rubs, whereas the coating over the zinc phosphate pretreated steel was 2.8 mils in thickness and withstood 75 acetone double rubs.

When comparable coatings were made without the use of the lead catalyst, the cured coating withstood only from about 13 to 25 acetone double rubs.

Claims

1. A heat-curable coating composition comprising a hydroxyl-containing polymer, a polyester curing agent and a transesterification catalyst, characterized in that the polyester crosslinking agent has at least two substituted ester groups per molecule in which the substituents are selected from the class consisting of: (A) beta-alkoxy groups, (B) beta-ester groups, (C) beta-amido groups, (D) gamma-hydroxy groups, (E) gamma-ester groups, (F) delta-hydroxy groups; including mixtures thereof.

2. The coating composition of claim 1 in which the hydroxyl-containing polymer also contains cationic groups and the coating composition is dispersed in an aqueous medium.

3. The coating composition of claim 1 or 2 in which the hydroxyl-containing polymer has a hydroxyl value within the range of 180 to 300.

4. The coating composition of claim 1,2 or 3 in which the substituents are beta-alkoxy groups.

5. The coating composition of claim 4 in which the polyester crosslinking agent is prepared from reacting a polycarboxylic acid or its functional equivalent thereof with one or more 1,2-polyol monoethers.

6. The composition of claim 5 in which the polycarboxylic acid or its functional equivalent thereof is selected from the class consisting of trimellitic anhydride, adipic acid, and phthalic anhydride.

7. The composition of claim 5 or 6 in which the 1,2-polyol monoether is an alkyl ether of ethylene or propylene glycol in which the alkyl group contains from 1 to 6 carbon atoms.

8. The composition of claim 1,2 or 3 in which the substituents are gamma and/or delta-hydroxy groups.

9. The composition of claim 8 in which the substituents are gamma-hydroxy groups.

10. The composition of claim 9 in which the crosslinking agent is formed from reacting a polycarboxylic acid or its functional equivalent thereof with a 1,3-polyol.

11. The composition of claim 10 in which the polycarboxylic acid or its functional equivalent thereof is selected from the class consisting of trimellitic anhydride, adipic acid and phthalic anhydride.

12. The composition of claim 10 or 11 in which the 1,3-polyol is selected from the class consisting of trimethylolethane, trimethylolpropane, 1 ,3-butanediol, 1 3-propanediol and mixtures thereof.

1 3. The composition of claim 8 in which the substituents are delta-hydroxy groups.

14. The composition of claim 1 3 in which the crosslinking agent is formed from reacting a polycarboxylic acid or its functional equivalent thereof with a 1,4-polyol.

1 5. The composition of claim 14 in which the 1,4-polyol is 1,4-butanediol.

1 6. The composition of claim 1, 2 or 3 in which the substituents are beta and/or gamma-ester groups.

1 7. The composition of claim 1 6 in which the substituents are beta-ester groups.

1 8. The composition of claim 1 7 in which the crosslinking agent is prepared from reacting: (A) a polycarboxylic acid or its functional equivalent thereof, (B) a 1,2-polyol or 1,2-epoxy compound, (C) a monocarboxylic acid.

1 9. The composition of claim 1 8 in which the 1,2-polyol is selected from the class consisting of ethylene glycol, propylene glycol, and 1,2-butanediol.

20. The composition of claim 1 8 in which the 1,2-epoxy compound is selected from the class consisting of 1,2-epoxy butane, the glycidyl ester of a saturated aliphatic monocarboxylic acid containing from 9 to 12 carbon atoms, ethylene oxide, propylene oxide and n-butyl glycidyl ether.

21. The composition of claim 1 6 in which the substituents are gamma-ester groups.

22. The composition of claim 21 in which the crosslinking agent is formed from reacting: (A) a polycarboxylic acid or its functional equivalent thereof, (B) a 1 ,3-polyol, (C) a monocarboxylic acid.

23. The composition of claim 22 in which the 1,3-polyol is selected from the class consisting of 1,3-propanediol, trimethylolpropane, trimethylolethane and 1,3-butanediol.

24. The composition of any of claims 1 8 to 23 in which the polycarboxylic acid or its functional equivalent thereof is selected from the class consisting of trimellitic anhydride, adipic acid and phthalic acid.

25. The composition of any of claims 1 8 to 24 in which the monocarboxylic acid is selected from the class consisting of isobutyric acid, acetic acid, propionic acid and benzoic acid.

26. The coating composition of claim 1,2 or 3 in which the substituents are beta-amido groups.

27. The composition of claim 26 in which the crosslinking agent is formed from reacting a polycarboxylic acid or its functional equivalent thereof with a betahydroxyalkylamide.

28. The composition of claim 27 in which the betahydroxyalkylamide is of the structure:

where R, and R2 are hydrogen and R1, R2 and R3 are selected from the class consisting of alkyl, cycloalkyl, aryl, alkaryl, including substituted radicals in which the substituents will not adversely affect the esterification reaction with the polycarboxylic acid or its functional equivalent thereof and will not adversely affect the transesterification curing reaction or the desirable properties of the coating composition.

29. The composition of claim 27 or 28 in which the polycarboxylic acid or its functional equivalent thereof is selected from the class consisting of trimellitic anhydride, phthalic anhydride, and adipic acid.

30. A composition as claimed in claim 1 substantially as hereinbefore described in any one of the Examples.