WO1994011449A1

WO1994011449A1 - Composition comprising a polycarbonate-modified epoxide resin for electrodeposition on metal substrates

Info

Publication number: WO1994011449A1
Application number: PCT/US1993/010933
Authority: WO
Inventors: Gregory G. Menovcik; Jeffrey S. Depue
Original assignee: Basf Corporation
Priority date: 1992-11-16
Filing date: 1993-11-11
Publication date: 1994-05-26

Abstract

The present invention is directed to an electrocoating composition and process for preparation thereof. The electrocoating composition comprises a polycarbonate modified epoxy resin comprising the reaction product of i) a polyepoxide compound; ii) a polycarbonate diol; iii) optionally a compound having a functional group capable of reacting with component (i); and iv) an amine having at least one primary or one secondary amino group.

Description

COMPOSITION COMPRISING A POLYCARBONATE-MODIFIED EPOXIDE RESIN FOR ELECTRODEPOSITION ON METAL SUBSTRATES

FIELD OF THE INVENTION

The present invention is directed to an electrodeposition coating composition and a process for preparation thereof. The coating composition comprises a polycarbonate modified epoxy resin, and more specifically isan aliphatic, cycloaliphatic, aromatic, or araliphatic polycarbonate diol modified epoxy resin. BACKGROUND OF THE INVENTION

Cathodic electrodeposition as a coating application method for metallic substrates is well known and described for example in U.S. Pat. Nos. 4,575,523; 4,661,541; 4,780,524 and 4,920,162. The electrocoating composition comprises the principal resin, a crosslinker, a grind resin, pigments and other additives such as solvents, control agents, fillers and the like.

Typically, a principal resin is prepared by adducting an epoxy resin with an amine. An aqueous electrodeposition coating bath is prepared by mixing the principal resin with a crosslinking agent and salting it with acid and deionized water to form a dispersion, mixing the dispersion with a pigment paste and optionally with other additives like solvents, antifoam and the like.

U.S. Pat. No. 4,104,147 discloses a principal resin for an electrocoating composition comprising a polyepoxide, a secondary amine and a polyester polyol. Despite some improvements of the properties of the resulting films, the impact resistance as well as the corrosion resistance of these films were not sufficient for all applications.

It is therefore an object of the present invention to provide a process for preparing an electrocoating composition comprising a modified principle resin which forms films with improved impact resistance and corrosion resistance. Another object of the present invention is to provide stable aqueous electrocoating compositions containing such modified principal resins. Another object is substrates electrocoated with these aqueous electrocoating compositions. SUMMARY OF THE INVENTION

The objects of the present invention can be achieved by utilizing as a principal resin in a cationic electrodeposition coating composition a principal resin comprising a polycarbonate modified epoxy resin comprising the reaction product of i) a polyepoxide compound; ii) a polycarbonate diol that is the reaction product of a diol and a carbonate diester; iii) optionally a compound having a functional group capable of reacting with compound (i) ; and iv) an amine having at least one primary or one secondary a ino group;

This modified epoxy resin is salted with an acid and dispersed in an aqueous composition along with a cross-linker, an optional pigment paste comprising a grind resin and a pigment, and optional additives selected from the group consisting of organic solvents, catalysts, wetting agents, conditioning agents, thickeners, rheology control agents, antioxidants, surfactants, leveling agents and mixtures thereof to form an electrodeposition coating composition.

DETAILED DESCRIPTION OF THE INVENTION

Electrodeposition coating compositions according to the invention can be prepared by A) mixing the polycarbonate modified epoxy resin with a cross¬ linker, a pigment paste comprising a pigment with a grind resin and an additive selected from the group consisting of organic solvents, catalysts, wetting agents, conditioning agents, thickeners, rheology control agents, antioxidants, surfactants, leveling agents and mixtures thereof

B) salting with an acid and

C) dispersing in deionized water.

In a modified process, the pigment paste and/or the additive is added after the dispersing step (C) . In step (A) , the principal resin is used in an amount of from about 85 to about 50 %, by weight, preferably from about 80 to about 70% by weight, based on the total weight of the electrocoating composition. Polyepoxide compounds (i) are known in the art and described for example in U.S. Pat. Nos. 4,104,147; 4,575,523; 4,661,541 and 4,780,524.

A particularly useful class of polyepoxides are the glycidyl polyethers of polyhydric phenols like glycidyl polyethers of bisphenol A having epoxide equivalent weights of from about 450 to about 2,000, more typically from about 800 to about 1,600, and preferably about 800 to about 1,500. Typical preferred commercial formulations of diglycidyl ether starting materials are sold under the trade names "EPON^® 828" and "EPON^® 1001" (Shell Chemical Co., Division of Shell Oil Company, 50 West 50th Street, New York, N.Y.), Araldite^® GY 2600 (CibaGeigy, Division of Ciba Corporation, Fair Lawn, N.J.), or DER™ 632 (Dow Chemical Co., Midland, Mich.). Suitable polycarbonate diols (ii) are known and described for example in U.S. Pat. No. 4,024,113. They are formed by the reaction of a diol such as p,p'-dihydroxy-2,2- diphenyl-propane or hexanediol, and a carbonate diester such as diethyl carbonate, in the presence of a catalyst such as tetrabutyl titanate. The polycarbonate diol can be an aliphatic polycarbonate diol such as those derived from aliphatic diols like hexanediol, 1,2 propanediol; a cycloaliphatic polycarbonate diol such as those derived from cycloaliphatic diols like 1,4- cyclohexanedimethanol (CHDM) ; or an aromatic polycarbonate diol such as those derived from aromatic diols like catechol, hydroquinone, and bisphenol A. Included also are composite polycarbonate diols such as aliphatic and cycloaliphatic polycarbonate diols that are terminated with aromatic diols such as bisphenol A. The polycarbonate diols have a number average molecular weight of from about 400 to about 3,000, preferably from about 800 to about 2000.

Preferred are aliphatic polycarbonate diols and aliphatic polycarbonate diols terminated with bisphenols. Optional compounds (iii) having a functional group capable of reacting with compound (i) may be used like polyols, fatty acids and monoepoxides. Preferred are polyols as described in U.S. Pat. No. 4,104,147. Suitable polyols are polyalkylene ether polyols and polyester polyols including hydroxyl-containing lactone polyesters.

Examples for polyalkylene ether polyols are polyoxytetramethylene glycols, polyoxyethylene glycol, polyoxygropylene glycol. Examples for polyester polyols are reaction products of polyesterification of organic polycarboxylic acids or anhydrides thereof with organic polyols containing primary hydroxyl groups.

The diols which are usually employed in making the polyester include alkylene glycol, such as ethylene glycol and butylene glycol, neopentyl glycol and other glycols such as cyclohexanedimethanol.

The acid component of the polyester consists primarily of onomeric carboxylic acids or anhydrides having 2 to 18 carbon atoms per molecule. Among the acids which are useful are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, adipic acid, azelaic tetrachlorophthalic acid and the like. Where acids are referred to above, it is understood that the anhydrides of those acids which form anhydrides can be used in place of the acid.

Besides polyester polyols formed from polybasic acids of polyols, lactone polyesters can also be employed. These products are formed from the reaction of a lactone such as epsilon-caprolactone with a polyol which is described in U.S. Pat. No. 3,169,945.

The polyether polyols and polyester polyols have number average molecular weights of from about 800 to about 3,000, preferably from about 900 to about 2,000.

Examples of amines (iv) with at least one primary or secondary amine group include aliphatic diamines and triamines, aliphatic alcohol amines, alkylene diamines, alkanol amines and N-alkyl substituted forms thereof. Especially preferred are the aliphatic diamines and alcohol amines having 1 to 10 carbons in the aliphatic group. Examples for diamines are ethylene diamine, 1,2- propylene diamine, 1,3-propylene diamine, 1,2-butylene diamine, 1,3-butylene diamine, 1,4-butylene diamine, 1,5-pentylene diamine, 1,6-hexylene diamine, 1,4-diaminocyclohexane, methyl- aminopropylamine, N,N-dimethylaminopropylamine and the like. Examples for aminoalcohols are ethanolamine, diethanolamine and N-methylethanolamine.

Preferred examples are N,N-dimethylaminopropyl amine, ethanolamine, diethanolamine and N-methylethanolamine. The reaction of component (i) with (ii) and optional

(iii) is accomplished by mixing the polycarbonate diol and optionally the compound (iii) with the polyepoxide (i) in an organic solvent, such as toluene, methyl isobutyl ketone xylene, etc. , and reacting these products at a sufficient temperature for a sufficient amount of time in a conventional reactor in the presence of a catalyst like a tertiary amine or a phospine derivative to form a chain extended polyepoxide.

Typically, the reaction temperature will be from about 85°C to about 160°C, more typically from about 110° to about 150'C, preferably from about 120^CC to about 140^βC. Typically the reaction time is from about 120 minutes to about 300 minutes, more typically from about 160 minutes to about 260 minutes, preferably from about 180 minutes to about 240 minutes.

The molar ratio of the polyepoxide (i) to the sum of components (ii) and (iii) is from about 3.5:1 to about 2.0:1, preferably from about 2.5:1 to about 2.0:1. The chain extended polyepoxide has additional epoxide groups which are reacted with component (iv) to form terminal amine groups.

These provide the cationic sites which largely contribute to the ready dispersibility of the principal resin in the aqueous acidic medium in the electrocoating composition.

The reaction conditions are known and typically, the reaction temperature will be from about 20°C to about 95°C, more typically from about 25°C to about 80°C, and preferably from about 55°C to about 75°C. The reaction time is typically from about five minutes to about 60 minutes, more typically from about ten minutes to about 40 minutes and preferably from about 25 minutes to about 30 minutes.

The epoxide groups of the chain extended polyepoxide from components (i) , (ii) and optional (iii) are partly or completely capped by the amine. Preferred all epoxy groups are fully lapped by the amine (iv) .

The preferred crosslinker used in the practice of this invention is an organic polyisocyanate and, in particular, a blocked polyisocyanate. The organic polyisocyanate and the blocking agents used in the practice of this invention are typical of those used in the art, e.g., U.S. Pat. No. 4,182,831 the disclosure of which is incorporated by reference. Useful blocked polyisocyanates are those which are stable in the dispersion systems at ordinary room temperature and which react with the resinous product of this invention at elevated temperatures.

In the preparation of the blocked organic polyisocyanates, any suitable organic polyisocyanate can be used. Representative examples are the aliphatic compounds such as trimethylene, tetramethylene, pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene and 1,3-butylene diisocyanates; the aromatic compounds such as m-phenylene, p- phenylene, ,4'-diphenyl, and 1,4-napthalene diisocyanates; the aliphatic aromatic compounds such as 4,4•-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof, 4,4'-toluidine, and 1,4-xylylene diisocyanates; the triisocyanates such as triphenyl methane -4,4' ,4"-triisocyanate, 1,3,5-triisocyanate benzene and 2,4,6-triisocyanate toluene and the tetraisocyanates such as 4,4'-diphenyl-di ethyl methane-2,2' , 5,5'tetraisocyanate; the polymerized polyisocyanates such as tolylene diisocyanate dimers and timers, polymethylenepolyphenylene polyisocyanates having NCO functionalities of 2 to 3, and the like. In addition, the organic polyisocyanate can be a prepolymer derived from a polyol such as glycols, e.g., ethylene glycol and propylene glycol, as well as other polyols such as glycerol, trimethylolpropane, hexanetriol, pentaerythritol, and the like as well as monoethers, such as diethylene glycol, tripropylene glycol and the like and polyethers, i.e., alkylene oxide condensates of the above. Among the alkylene oxides that may be condensed with these polyols to form polyethers are ethylene oxide, propylene oxide, butylene oxide, styrene oxide and the like. These are generally called hydroxyl-terminated polyethers and can be linear or branched. Especially useful polyether polyols are those derived from reacting polyols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,4- butylene glycol, 1,3-butylene glycol, 1,6-hexanediol, and their mixtures; glycerol trimethylolethane, trimethylolpropane, 1,2,6- hexanetriol, pentaerythritol, dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol, methyl glycosides, sucrose and the like with alkylene oxides such as ethylene oxide, propylene oxide, their mixtures, and the like. Preferred polyisocyanates include the reaction product of toluene diisocyanate and trimethylolpropane, the reaction product of 4,4'-diphenylene methane diisocyanate and trimethylolpropane, and 4,4'-diphenylene methane diisocyanate with glycerol; additionally, the isocyanurate of hexamethylene diisocyanate.

Any suitable aliphatic, cycloaliphatic, aromatic, alkyl monoalcohol and phenolic compound can be used as a blocking agent in the practice of the present invention, such as lower aliphatic alcohols, such as methyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5- trimethylhexanol, decyl and lauryl alcohols, and the like; the aromatic-alkyl alcohols, such as phenylcarbinol , methylphenylcarbinol, ethyl glycol monoethyl ether, ethyl glycol monobutyl ether and the like; the phenolic compounds such as phenol itself, substituted phenols in which the substituents do not adversely affect the coating operations. Examples include cresol, nitrophenol, chlorophenol and t-butyl phenol.

Also, amines can be used as blocking agent like dibutylamine. A preferred blocking agent is monopropyl ether of ethylene glycol. Additional blocking agents include tertiary hydroxyl amines, such as diethylethanola ine and oximes, such as methylethyl ketoxime, acetone oxime and cyclohexanone oxime, and caprolactam. A preferred oxime is methyl-n-amyl ketoxime. The blocked polyisocyanates are formed by reacting sufficient quantities of blocking agent with sufficient quantities of organic polyisocyanate under reaction conditions conventional in this art such that no free isocyanate groups are present when the reaction has run its course. Sufficient quantities of blocked polyisocyanate are incorporated into the electrodepositable coating compositions of this invention such that the deposited coating will be completely cured upon baking and there will be no free isocyanate groups remaining. Typically, from about 90 to about 10 by weight, based of the total amount of electrocoating compositions of blocked polyisocyanate is used, more typically from about 70 to about 30% by weight, preferably from about 60% to about 40% by weight, based on the total weight of the electrocoating composition.

The pigment paste comprising a grind resin and a pigment is known in the art and described for example in U.S. Pat. Nos. 4,445,257; 4,530,945; 4,540,725 and 4,920,162. Suitable grind resins are epoxy resin-amine adducts like an adduct of a polyglycidyl ether of a polyhydric phenol with at least one amine with at least one primary amino group.

The pigments are well known in the art and are described for example in U.S. Pat. No. 4,780,524. Suitable examples are iron oxides, lead oxides, strontium chromate, carbon black, titanium dioxide, talc, barium sulphite, barium yellow, cadmium red, chromic green, lead silicate, and the like.

The pigment paste is usually used in an amount from about 5 to about 20% by weight, based on the total weight of electrocoating composition, preferably from about 7 to about 15% by weight.

Suitable additives are selected from the group consisting of organic solvents, catalysts, wetting agents, conditioning agents, thickeners, rheology control agents, antioxidants, surfactants, leveling agents, and mixtures thereof.

Examples of suitable solvents include ethylene glycol monoethyl ether, ethylene glycol monobutylether ethylene glycol monohexylether diethylene glycol monobutylether, xylene, ethanol, isopropanol, isobutanol, n-butanol, methylisobutylketone and the like.

These solvents could be used in an amount of about 1% by weight to 15% by weight, preferably about 2 to 6% by weight of the total weight of the electrocoating composition.

All other additives could be used in effective amounts.

In step (B) an acid is used for salting the amino groups of the principle resin and the grind resin. Useful acids include for example acetic acid, lactic acid, formic acid and phosphoric acid. Sufficient acid is used to have a pH of the electrocoating composition of step (C) of from about 4 to about 7, more typically from about 5 to about 6.8, and preferably from about 6 to about 6.5.

In step (C) the salted mixture of (A) is dispersed in deionized water to form a stable aqueous dispersion.

The concentration of components of steps (A) and (B) in water is from about 10% by weight to about 60% by weight, typically from about 20% by weight to about 60% by weight, and preferably from about 30% by weight to about 60% by weight, based on the total weight of the electrocoating composition.

The electrodeposition process typically takes place in an electrically insulated tank containing an electrically conductive anode which is attached to a direct current source. The size of the tank will depend on the size of the article to be coated. Typically the tank is constructed of stainless steel or mild steel lined with a dielectric coating such as epoxy impregnated fiberglass or polyepoxide. The electrodepositable cathodic resinous coating compositions of this invention are typically used to coat articles such as automobile or truck bodies. The typical size of an electrodeposition bath tank used for this purpose is about 60,000 gallons to about 120,000 gallons capacity.

Typically the article to be coated is connected to the direct current electric circuit so that the conductive object acts as the cathode. When the article is then immersed in the coating bath, flow of electrons from the cathode to the anode, that is, conventional current flow from the anode to the cathode, results in the particles of the dispersed cationic electrodepositable resin composition being deposited on the surfaces of the article. The particles of the dispersed resin composition are positively charged and are therefore attracted to the negative cathodic surface of the object to be coated. The thickness of coating deposited upon the object during its residence in the electric cathodic coating bath is a function of the cathodic electrodepositable resin composition, the voltage across the article, the current flux, the pH of the coating bath, the conductivity, and the residence time. Sufficient voltage is applied to the coated article for a sufficient time to obtain a coating of sufficient thickness. Typically the voltage applied across the coated article is about 50 volts to about 500 volts, more typically about 200 to about 350 volts, and preferably about 225 volts to about 300 volts. The current density is typically from about 0.5 amperes per sq. ft. to about 30 amperes per sq. ft. , more typically from about one ampere per sq. ft. to about 25 amperes per sq. ft., and preferably from about one empere per sq. ft. The article to be coated typically remains in the coating bath for a sufficient period of time to produce a coating or film of sufficient thickness having sufficient resistance to corrosion and flexibility. The residence time or holding time is typically from about 1 minute to about 2 1/2 minutes, and preferably about 2 minutes. The conductivity of the coating bath will be sufficient to produce a coated film of sufficient thickness. The desirable coatings have sufficient thicknesses to provide resistance to corrosion while having adequate flexibility. Typically, the film thicknesses of the coated objects of this invention will be from about 0.4 mils to about 1.8 mils, more typically from about 0.6 mils to about 1.6 mils, and preferably from about 0.6 mils to about 1.0 mils.

The temperature of the coating bath is maintained, typically by cooling, at a temperature less than about 90^βF. When the desired thickness of the coating has been produced, the coated object is removed from the electrodeposition bath and cured. Typically, the electrodeposited coatings are cured in a conventional convection oven at a sufficient temperature for a sufficient length of time to cause the cross-linking composition to cross-link the resin. In the case of a blocked polyisocyanate, this would be a sufficient time and temperature to unblock the blocked polyisocyanates and allow for cross-linking of the electrodepositable resin compositions. Typically, the coated articles will be baked at a temperature of from about 85°C to about 280°C, more typically from about 110"C to about 115°C, and preferably from about 120^βC to about 160°C. The coated articles will be baked for a time period of from about ten minutes to about 40 minutes, more typically from about ten minutes to about 35 minutes, and preferably from about 15 minutes to about 30 minutes. It is contemplated that the coated articles of the present invention may also be cured by using radiation, vapor curing, contact with heat transfer fluids and equivalent methods. Typically, the coated articles of this invention will comprise conductive substrates such as metal, including steel, aluminum, copper, etc. ; however, any conductive substrate having a conductivity similar to the aforementioned metals may be used. The articles to be coated may comprise any shape so long as all surfaces can be wetted by the electrodeposition bath. The characteristics of the article to be coated, which have an effect on the coating, include the shape of the article, the capacity of the surfaces to be wetted by the coating solution, and the degree of shielding from the anode. Shielding is defined as the degree of interference with the electromotive field produced between the cathode and the anode, thereby preventing coating composition from being deposited in those shielded areas. A measure of the ability of the coating bath to coat remote areas of the object is throwpower. Throwpower is a function of the electrical configuration of the anode and cathode as well as the conductivity of the electrodeposition bath.

The invention provides stable aqueous electrocoating dispersions. The coating of the coated article exhibit good appearance, hiding, gloss, film thickness, impact resistance and corrosion resistance.

EXAMPLE 1 -Preparation of blocked isocyanurate used as a flexible crosslinker.

Desmodur^® N-3300 (BASF Corporation, Parsippany, New Jersey) and methyl isobutylketon (MIBK) are charged to a clean, dry reaction vessel. At ambient temperature the first addition of dibutylamine (DBA) is charged. The amount of DBA is 90% on an equivalent basis relative to NCO groups as shown in Figure 1.

The addition rate is adjusted such that the temperature remains below a specified level during the resulting exotherm.

Typically, the reaction temperature will be from about 50"C to about 70°C and preferably between 55"C to about 65^βC. Heating and or cooling is carried out to maintain temperatures at this level until all the amine has reacted, this is determined with an NCO titration according to ASTM D2572-92. Thirty minutes after all the amine (from the first addition) has been added a sample is taken and titrated for NCO content. The theoretical Wt./Eq. NCO for the 90% blocked isocyanurate is 3856g. eq. on 5 solution. Once the theoretical value is obtained the second DBA addition is made at a rate similar to the first addition. The amount of DBA added on the second addition leaves the crosslinker with 96% of the NCO groups blocked. If the first charge of DBA exceeded 90% blocking (determined by NCO titration

10 than the second charge must be adjusted accordingly. This assures that after all the amine has reacted, only 96% of the NCO groups of the crosslinker are blocked. The temperature is maintained as described another 30 minutes following the second addition of DBA. After the thirty minutes the crosslinker is

15 titrated again to confirm the NCO content. The value should be

9891 g./eq. on solution. When the reaction is complete, n- butanol is charged in a 2:1 excess of equivalents relative to the NCO groups remaining. Completion of the reaction is determined by infrared spectroscopy. 20

eq.

25

2.49

30

FINAL CHARGE

DBTDL 0.2

45 n-BUTANOL 14.3 7.4 74.1 0.10

1000.0 799.1 EXAMPLE 2

A blocked isocyanate (polyurethane crosslinker) is prepared according to the following procedure. Slowly with stirring under a nitrogen atmosphere 291 parts of an 80/20 isomeric mixture of 2,4-/2,6-toluene diisocyanate, 0.08 parts of dibutyltindilaurate (DBTDL) and 180 parts of methyl isobutyl ketone (MIBK) were added to a reaction vessel capable for straight reflux. The reaction temperature was maintained from about 35°C to 55°C, preferably from about 38^βC to 42^βC. The reaction temperature was held at this temperature range from about 30 minutes to about 120 minutes, preferably from about 30 minutes to about 60 minutes. After this time period 75 parts of trimethylolpropane were charged to the reaction. The reaction proceeded from about 8 hours to about 11 hours, more preferably from about 9 hours to about 10 hours. After this hold period 175 parts of ethylene glycol monopropyl ether were charged to the reaction mixture and held at 121°C for 1.5 hours. After this time all of the isocyanate functional groups were reacted. The completion of the reaction is determined by first, the NCO titration and second, by the disappearance of the NCO groups in the infrared spectrum.

EXAMPLE 3

A blocked isocyanate crosslinker (polyurea) is prepared according to the following procedure. To a dry reactor, 483 parts of triisocyanurate hexamethylenediisocyanate and 193 parts of 2-hexanone are charged. To this reaction mixture is added 3907 parts dibutylamine slowly and with stirring under nitrogen atmosphere so that the temperature does not exceed 80°C. After all the amine has reacted (determined by NCO titration), 14 parts of n-butanol and 0.2 parts of dibutyl tin dilaurate are added. The reaction is held at 80^βC for 120 minutes for the completion of the reaction. The end of the reaction is when all the isocyanate functionality has reacted again which is determined through an NCO titration. EXAMPLE 4 - Main Vehicle Resin

To a clean dry reactor, 82.7 parts xylene are added. The mixing liquid is blanked with pure nitrogen and heated to 42 " C . To this mixture is added 1047.3 parts of Epon^® 828 (EEW = 188 - 200) diglycidyl ether of bisphenol A and 322.0 parts of bisphenol A. This mixture is heated to 130^βC and then charged 1.0 parts of triphenyl phosphine. After the addition of the triphenyl phosphine a slight exotherm should be noticed. This exotherm will drive the reaction temperature to about 150°C. The temperature is maintained at 145°C-150°C and the polymerization is followed by EEW (epoxy equivalent weight) titration. Every 30 minutes the reaction is sampled for EEW until the WPE (weight per epoxy) is equal to 490. The typical reaction time is three hours. Once the EEW reaches about

490,91.5 parts of dodecylphenol, 91.5 parts of a polycarbonate diol derived from bisphenol A and 1,6-hexane diol, 7.4 parts of xylene are charged and the reaction temperature is cooled to 130"C. At this temperature 2.7 parts of dimethyl benzylamine as a catalyst are charged and hold at 130°C until the WPE reaches 1050. The typical reaction time for this is three hours. Adjustment to the catalyst level may be necessary if the extension period deviates more than 30 minutes from the three hours. At the target EEW, 182.8 parts xyleene and 101.5 of butyl cellosolve are added followed by 102.7 parts of DEOA

(diethanolamine) . After the addition of the DEOA the reaction is cooled to 90^βC and hold for one hour. After the one hour hold 97.0 parts hexylcellosolve and 253.8 parts isobutyl alcohol is charged to the reaction over one hour period maintaining the temperature at 60^βC. After holding for one hour 34.9 part of dimethylamino propylamine (DMAPA) are charged with a solvent flush of 6.5 parts of xylene. The reaction is held at 60°C for three hours. After the three hour hold 81.8 parts of lactic acid 225.1 parts of Paraplex^® WP-1 plasticizer from Rohm and Haas Company, 5.6 parts of K-2000 surfactant from Air Products Chemicals Company and 6.5 parts of xylene are charged. Under agitation the reaction mixture is held at 60°C for 30 minutes. At the end of the 30 minute hold 574.6 parts of blocked isocyanate functional crosslinker prepared in accordance with example 3, 615.6 parts of the blocked isocyanate crosslinker prepared in accordance with example 1, 22.5 parts of xylene and 5.6 parts of Surfynol^® 104 BC surfactant from Air Products Chemicals Company is added to the reaction mixture. After this addition the reaction mixture is held at 60"C for 30 minutes. This material is then dispersed with the addition of 5.4 parts of lactic acid and 5962.5 parts of deionized water.

EXAMPLE 5 -Preparation of the polyepoxy-polycarbonate grind resin. To a clean dry reactor 82.7 parts xylene are added.

The liquid is blanked with pure nitrogen and heated to 42^βC. To this solvent is added 1047.3 parts of Epon^® 828 (EEW =188 - 200) diglycidyl ether of bisphenol A and 322.0 parts of bisphenol A.

This mixture is heated to 130°C and 1.0 parts of triphenyl phosphine is charged. After the addition of the triphenyl phosphine a slight exotherm should be noticed. This exotherm will drive the reaction temperature to about 150°C and the polymerization is followed by EEW (epoxy equivalent weight) titration. Every 30 minutes the reaction is sampled for EEW until the WPE (weight per epoxy) is equal to 490. The typical reaction time is three hours. Adjustment to the catalyst level may be necessary if the extension period deviates more than 30 minutes from the three hours. At the target EEW, 182.8 parts xylene and 101.5 of butyl cellosolve are added, followed by 102.7 parts of DEOA (diethanolamine). After the addition of the DEOA the reaction is cooled to 90^βC and hold for one hour. After the one hour hold 97.0 parts hexylcellosolve and 253.8 parts isobutyl alcohol is charged to the reaction over one hour period maintaining the temperature at 60°C. After holding for one hour 34.9 parts of dimethylamino propylamine (DMAPA) are charged with a solvent flush of 6.5 parts of xylene. The reaction is held at 60"C for three hours. After the three hour hold 81.8 parts of lactic acid, 226.1 parts of Paraplex^® WP-1 plasticizer from Rohm and Haas Company, 5.6 parts of K-2000 surfactant from Air Products Chemicals Company and 6.5 parts of xylene is charged. Under agitation the reaction mixture is held at 60°C for 30 minutes. At the end of the 30 minute hold 574.6 parts of blocked isocyanate functional crosslinker prepared in accordance with example 3, 615.6 parts of the blocked isocyanate crosslinker prepared in accordance with example 1, 22.5 parts of xylene and 5.6 parts of Surfynol^® 104 BC surfactant from Air Products Chemicals Company is added to the reaction mixture. After this addition the reaction mixture is held at 60°C for 30 minutes. This material is then dispersed with the addition of 5.4 parts of lactic acid and 5962.5 parts of deionized water.

EXAMPLE 6 - Preparation of pigment dispersion resin.

To a clean dry reactor, 29.7 parts xylene are added. Under a nitrogen blanket 569.8 parts of Epon^® (EEW =188 - 200) diglycidyl ether of bisphenol A (DGEBA) and 118.8 parts of bisphenol A are added. This mixture is then heated to 118^βC. When the temperature of 118°C is reached, 0.43 parts of triphenyl phosphine is charged and a slight exotherm will be noticed. This exotherm will drive the temperature to about 150°C. This temperature is maintained from between 145°c to about 150°C. The polymerization is followed by EEW (epoxy equivalent weight) titration. The reaction is sampled every 30 minutes for EEW until the WPE (weight per epoxy) is equal to 340. The typical reaction time is from between 2 to 2.5 hours. Once the EEW of 340 is reached the reaction is cooled to 130^βC and 573.2 parts of butyl cellosolve is added. The reaction is then cooled to 48^βC where 160.4 parts of polyglycola ine (PGA) and 83.4 parts of 3-dimethylaminopropylamine (dmapa) is added in small aliquots over a 15 minutes period. After the PGA and

DMAPA is added, the reaction mixture is heated to 118^βC and held at this temperature for one hour. After the one hour hold is over, the reaction is cooled to 110"C and 109.2 parts of butyl cellosolve is added. The reaction mixture is then cooled until a temperature of 80°C is reached where 304.2 parts of p-nonyl glycidyl ether (NPGE) is added. After all of the NPGI is added, the reaction is heated to 90^βC and held for one hour. After the one hour hold is over, 99.0 parts of butyl cellosolve is added and the reaction mixture is cooled to room temperature. EXAMPLE 7 -Preparation of pigment paste for the electrocoat syste .

A pigment paste composition was prepared according to the following formulation.

COMPONENT GRAMS (TOTAL) GRAMS (NV) PIGMENT BINDER

1. GRIND RESIN 428.04 143.40 143.20 EXAMPLE 5

2. PROPASOL^® BEP 12.20

1.60

21.68

TOTALS 1000.00 608.00 433.32 166.68

This formula is for 60% nonvolatiles (N.V.), however, the viscosity is adjusted to 83-84 KU with an additional 80.0 grams of water which is then ground on the vertical sand mill pigment/binder = 2.6/1.0 % NV = 61.0

1. BASF grind resin described in example 5 with 33.5% NV.

2. Propasol^® BEP Ashland Chemicals.

3. Latic acid 88.0% NV Mallinckrodt Corporation.

4. Carbon black (Raven^® 410) Columbian Chemicals Company Tulsa, OK 74102.

5. DBTO Fine ground (Fascat^® 4203) Di-n-butyl-oxo-stannane organotin compound from M&T chemicals Inc. New Jersey 07065.

6. Lead Silicate basic white, Eagle-Picher Industries, Inc. 7. Clay extender Glowmax^® JDF

8. iθ2 R-900 Titanium Dioxide from DuPont EXAMPLE 8 -Preparation of the electrocoat coating composition.

An electrodeposition coating composition was prepared according to the following formulation.

COMPONENT GRAMS fTOTALi GRAMS (NV.

EMULSION (35% NV) 435.43 152.40 EXAMPLE 4

PASTE (52% NV) 110.76 57.60 EXAMPLE 6

DI H₂0 453.80 TOTALS 1000.00 210.00

%NV - 21.0 P/B = 0.24

Claims

Claims :

1. A cationic electrodeposition coating composition comprising

A) a salted polycarbonate modified epoxy resin that is the reaction product of i) a polyepoxide compound; ii) a polycarbonate diol that is the reaction product of a diol and a carbonate diester; iii) optionally a compound having a functional group capable of reacting with compound (i) ; and iv) an amine having at least one primary or one secondary amino group; and

B) a cross-linker.

2. A coating composition according to claim 1, wherein a glycidyl polyether of a polyhydric phenol is used as component (i) .

3. A coating composition according to claims 1 or 2, wherein an aliphatic, cycloaliphatic, or aromatic polycarbonate diol is used as component (ii) .

4. A coating composition according to claims 1-3, wherein an aliphatic or cycloaliphatic carbonate diol, or an aliphatic or cycloaliphatic carbonate diol terminated with a bisphenol is used as component (ii) .

5. A coating composition according to claims 1-4, wherein the polycarbonate diol has an average molecular weight of 600 to 2000.

6. A coating composition according to claims 1-5, wherein a compound (iii) is used selected from the group consisting of polyols, fatty acids, monoepoxides, and mixtures thereof.

7. A coating composition according to claim 5, wherein a polyether diol, a polyester diol or mixtures thereof are used as components (iii) .

8. A coating composition according to claims 1-7, wherein component (iv) is selected from the group consisting of aliphatic diamines, aliphatic triamines, aliphatic alcohol amines and mixtures thereof.

9. A coating composition according to claims 1-8, wherein the molar ratio of component (ii) to component (i) is from about 10 to about 30:1.

10. A coating composition according to claims 1-9, wherein the electrodeposition coating composition comprises from about

10 to about 50% by weight of said polycarbonate modified epoxy resin.

11. An electrocoated with an electrocoating composition according to claims 1-10.

12. A process for preparing an electrocoating composition comprising the steps:

A) mixing a principal resin comprising a polycarbonate modified epoxy resin comprising the reaction product of i) a polyepoxide compound; ii) a polycarbonate diol that is the reaction product of a diol and a carbonate diester; iii) optionally a compound having a functional group capable of reacting with compound (i) ; and iv) an amine having at least one primary or one secondary amino group; with a cross-linker, an optional pigment paste comprising a grind resin and a pigment, and an optional additive selected from the group consisting of organic solvents, catalysts, wetting agents, conditioning agents, thickeners, rheology control agents, antioxidants, surfactants, leveling agents and mixtures thereof;

B) salting with an acid; and

C) dispersing in deionized water.