KR20050016956A - Cathodic electrocoating composition containing a morpholine dione crosslinking agent - Google Patents

Abstract

The present invention relates to an improved aqueous negative electrode electrocoating composition having a binder and a crosslinking agent of an epoxy-amine addition product, with the improvement of using a crosslinking agent having at least one, preferably a plurality of, morpholine dione groups per molecule. . When cured by heating, an electrodeposited finish is formed which reduces the release of volatiles and the weight loss of the film.

Description

Cathodic electrocoating composition containing morpholine dione crosslinking agent {CATHODIC ELECTROCOATING COMPOSITION CONTAINING A MORPHOLINE DIONE CROSSLINKING AGENT}

The present invention relates to negative electrode electrocoating compositions, in particular negative electrode electrocoating compositions containing morpholine dione crosslinkers which significantly reduce the release and baking removal losses of volatiles from the coating film upon curing.

Coating of a conductive substrate by an electrodeposition process, also referred to as an electrocoating process, is a known important industrial process. Electrodeposition of primers to metal automotive substrates is widely used in the automotive industry. In this method, conductive articles such as automobile bodies or automobile parts are immersed in an electrolytic cell of a coating composition of an aqueous emulsion of a polymer forming a film, and the article acts as an electrode during the electrodeposition process. Current is flowed between the counter electrode in electrical contact with the article and the coating composition until a coating of desired thickness is deposited on the article. In the cathode electrocoating process, the article to be coated is the cathode and the counter electrode is the anode.

Film-forming resin compositions used in electrolytic baths of conventional cathode electrodeposition processes are also known in the art. Such resins are usually made from polyepoxide resins with extended chains, and addition products are formed to include amine groups in the resin. The amine group is usually introduced through the reaction of an amine compound and a resin. This resin is blended with a crosslinking agent, which is usually polyisocyanate, and then neutralized with acid to form an aqueous emulsion, commonly referred to as the main emulsion.

The main emulsion combines with other additives such as pigment paste, flocculant solvent, water, and catalyst to form an electrocoating bath. The electrocoating bath is located in an insulated tank containing a positive electrode. The article to be coated is a cathode and passes through a tank containing an electrodeposition tank. The thickness of the coating deposited on the electrocoated article is a function of the electrolyzer characteristics, the electrical operating characteristics of the tank, the immersion time, and the like.

The coated article obtained is taken out of the electrolytic cell and washed with deionized water. The coating on the article is usually cured in an oven to a temperature sufficient to form a crosslinked finish on the article. The presence of the catalyst enhances the crosslinking of the finish. Cathode electrocoating compositions, resin compositions, coating baths and cathode electrodeposition processes are described in US Pat. No. 3,922,253 to Jarabek et al., Issued November 25, 1975; US Patent No. 4,419,467 to Wismer et al., Issued December 6, 1983; US Patent No. 4,137,140 to Bellanger, issued January 30, 1979; And US Pat. No. 4,468,307 to Wismer et al., Issued August 25, 1984.

One disadvantage of conventional electrocoating compositions containing polyisocyanate crosslinkers is that the highly reactive isocyanate groups of the curing agent must be blocked, such as alcohols, to prevent premature gelation of the electrocoating composition. However, blocked polyisocyanates require a high temperature to release blocking and start the curing reaction. In addition, this curing mechanism releases a significant amount of volatile blocking agent upon curing and generates a weight loss of the unwanted film, also known as bake removal loss, which necessitates the purification of the exhaust air exhausted from the oven, which is undesirable in the resin solids. Contribute to loss. In addition, the volatile blocking agents released upon curing may adversely affect various coating properties, for example to produce a rough film surface.

United States Patent No. 4,615,779 to McCollum et al., Issued October 7, 1986, suggests the use of low molecular weight alcohol blocking agents to reduce weight loss when the film is cured by heating. However, such blocking agents can create undesirable film defects. U.S. Patent No. 5,431,791, issued July 11, 1995, still provides desirable urethane crosslinks in place of blocked polyisocyanates, but suffers from loss of baking removal and other problems associated with the use of blocked polyisocyanate curing agents. The use of a curing agent having a plurality of cyclic carbonate groups is described, which can be avoided. However, cyclic carbonates are often difficult to incorporate into the main emulsion.

Accordingly, there remains a need for new crosslinkers for negative electrode electrocoating compositions that reduce volatile release and bake removal losses while maintaining the desired coating properties.

Summary of the Invention

The present invention relates to an improved aqueous negative electrode electrocoating composition having an organic or inorganic acid which is a film forming binder of an epoxy-amine addition product, a crosslinking agent for an epoxy-amine addition product, and a neutralizer for an epoxy-amine addition product. An improvement is the use of a crosslinking agent having on average two or more morpholine dione groups per molecule which can react with the amine groups of the addition product. Additional crosslinking agents are also preferably used to provide a highly crosslinked final film network.

The present invention is based on the discovery that the crosslinking reaction of morpholine dione and amine groups occurs at relatively low temperatures and does not release volatile byproducts. Thus, it has finally been found that significantly reduces the bake removal loss upon curing and significantly avoids the problems associated with the use of blocked polyisocyanate curing agents.

Methods of cathode electrocoating conductive substrates using any of the above compositions and conductive articles coated with any of the above compositions also form part of the present invention.

The electrocoating composition of the present invention is an aqueous composition in which the solids content of main emulsions such as negative electrode film forming binders, additives, pigment dispersant resins, pigments and the like is preferably about 5 to 50% by weight, and usually contains an organic flocculant solvent.

The film forming binders of the main emulsions used to form the negative electrode electrocoating compositions of the present invention are epoxy-amine addition products and novel morpholine dione group containing crosslinkers. Epoxy-amine addition products are usually formed from epoxy resins which are chain-extended and react with amines to form addition products with amine groups and then neutralized with acid. The epoxy-amine addition product is usually blended with the crosslinking resin, neutralized with acid and then converted to water to form an aqueous emulsion called main emulsion. Other components such as pigments in the form of pigment pastes, flocculant solvents, anti-cratering agents, softeners, antifoams, wetting agents, and catalysts for forming commercially available electrocoating compositions are then added to the main emulsion. Typical aqueous cathode electrocoating compositions include U.S. Patent Nos. 5,070,149 and 3,922,253 to DeBroy et al., Issued Dec. 3, 1991; 4,419,467; 4,137,140 and 4,468,307.

An advantage of the inventive electrocoating compositions formulated with the novel morpholine dione crosslinkers is to reduce the release and baking removal losses of volatiles resulting from the film upon curing after electrodeposition, and the associated weight loss. In addition, the electrocoating composition has a lower curing temperature, better edge corrosion resistance, and smoother appearance compared to the electrocoating composition containing only the alcohol-blocked polyisocyanate crosslinker.

The epoxy-amine addition product of the novel composition is preferably formed of an epoxy resin that reacts with the amine after the chain is extended. The obtained epoxy-amine addition product has a reactive hydroxyl group, an epoxy group, and an amine group.

The epoxy resin used in the epoxy-amine addition product is a polyepoxy-hydroxy-ether resin having an epoxy equivalent of about 150 to 2,000.

Epoxy equivalent is the weight in grams of resin containing 1 gram equivalent of epoxy.

Such epoxy resins may be any epoxy-hydroxy containing polymer having at least two, 1,2-epoxy (ie, terminal) equivalents per molecule, ie, polyepoxides having, on average, at least two epoxy groups per molecule. Preference is given to polyglycidyl ethers of cyclic polyols. Polyglycidyl ethers of polyhydric phenols such as bisphenol A are particularly preferred. Such polyepoxides can be prepared by etherifying polyhydric phenols with epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkali. Examples of polyhydric phenols include 2,2-bis- (4-hydroxyphenyl) ethane, 2-methyl-1,1-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4-hydroxy -3-tert-butylphenyl) propane, 1,1-bis- (4-hydroxyphenol) ethane, bis- (2-hydroxynaphthyl) methane, 1,5-dihydroxy-3-naphthalene and the like have.

In addition to the polyhydric phenols, other cyclic polyols can be used to prepare polyglycidyl ethers of cyclic polyol derivatives. Examples of other cyclic polyols are alicyclic polyols, in particular 1,2-bis- (hydroxymethyl) cyclohexane, 1,3-bis- (hydroxymethyl) cyclohexane, 1,2-cyclohexane diol, 1, Alicyclic polyols such as 4-cyclohexane diol and hydrogenated bisphenol A.

The epoxy resin can, for example, be chain extended with any of the above polyhydric phenols. Preferred chain extenders are bisphenol A and ethoxylated bisphenol A and are preferably combinations of these phenols. In addition, polyepoxides can be chain extended with polyether or polyester polyols that improve flow and cohesiveness. Representative useful chain extenders include polyols, such as polycaprolactone diols, such as the Tone® 200 series manufactured by Union Carbide / Dow Corporation and ethoxylated bisphenol A, such as Milliken Chemical SYNFAC® 8009 manufactured by Milliken Chemical Company.

Examples of polyether polyols and chain extension conditions are disclosed in US Pat. No. 4,468,307. Examples of chain extending polyester polyols are disclosed in US Pat. No. 4,148,772 to Marchetti et al. Issued April 10, 1979.

Representative catalysts used in the formation of the polyepoxy hydroxy ether resins are tertiary amines such as dimethylbenzylamine and organometallic complexes such as ethyl or other alkyl triphenyl phosphonium iodide.

Ketamine and / or secondary amines and / or primary amines may be used for capping, ie, reacted with the epoxy end groups of the resin to form the epoxy-amine addition product. Ketamine, a potential primary amine, is formed by reacting a ketone with a primary amine. Water formed during the reaction is removed, for example, by azeotropic distillation. Useful ketones include dialkyl, diaryl and alkylaryl ketones having 3 to 13 carbon atoms. Specific examples of ketones used to form the ketimine include acetone, methyl ethyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, methyl aryl ketone, ethyl isoamyl ketone, ethyl amyl ketone, aceto Phenone and benzophenone. Suitable diamines are ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 4,9-dioxododecane and 1,12-dodecanediamine and the like. One commonly useful ketimine is diketamine, a ketimine of diethylene triamine and methyl isobutyl ketone.

Common useful primary and secondary amines that can be used to form the epoxy-amine addition product include methylamine, ethylamine, propylamine, butylamine, isobutylamine, benzylamine, and the like; And dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine and the like. Ethanolamine, propanolamine and the like; And alkanol amines such as methylethanolamine, ethyl ethanolamine, phenylethanolamine and diethanolamine. Other amines that can be used are described in US Pat. No. 4,419,467, incorporated herein by reference.

It was finally discovered that the amine group reacts with the morpholine dione crosslinking agent employed in the present invention.

The negative electrode binder of the electrocoating composition contains about 20 to 80% by weight of the epoxy-amine addition product and thus 80 to 20% of morpholine dione crosslinker.

As noted above, the coating compositions of the present invention comprise, on average, novel curing agents having at least one, preferably at least two, morpholine dione groups per molecule. As will be appreciated by those skilled in the art, when only one morpholine dione group is present, the crosslinking agent may include, but is not limited to, one or more other crosslinkable groups, including but not limited to melamine groups or isocyanate groups (blocked or unblocked). It can contain and harden a film. During curing, it is believed that morpholine dione groups, ie, crosslinkable functional groups and amine functional groups in the electrocoating resin, react to form a crosslinked network during curing. The reaction of morpholine dione groups with amine functional groups involves ring opening reactions and therefore occurs at relatively low temperatures and does not release volatile byproducts. Thus, this type of curing mechanism reduces baking removal loss and does not contribute to weight loss when the film is heated to cure. It has also been found that this curing mechanism is stable to active hydrogen at room temperature but only reacts with active hydrogen at only slightly elevated temperatures such as 275 ° F. to 325 ° F. (135 ° C. to 162.5 ° C.).

More specifically, the novel morpholine dione compounds used in the present invention are formed of an epoxy resin that reacts with an amine to provide an addition product with an amine group, which subsequently reacts with the oxalate to convert to an morpholine dione group. Let's do it.

The epoxy resin used for the preparation of the morpholine dione compound is a polyepoxy resin having an epoxy equivalent of about 150 to 2,000, and any epoxy resin listed above for the epoxy-amine addition product may be used for the morpholine dione crosslinking agent.

As noted above, such epoxy resins may be any epoxy-hydroxy containing polymer having at least two, 1,2-epoxy equivalents per molecule, ie, polyepoxides having, on average, at least two epoxy groups per molecule. Preference is given to polyglycidyl ethers of cyclic polyols. Polyglycidyl ethers of polyhydric phenols such as bisphenol A are particularly preferred. Such polyepoxides can be prepared by etherifying polyhydric phenols with epihalohydrin or dihalohydrin such as epichlorohydrin or dichlorohydrin in the presence of alkali. Examples of polyhydric phenols include 2,2-bis- (4-hydroxyphenyl) ethane, 2-methyl-1,1-bis- (4-hydroxyphenyl) propane, 2,2-bis- (4-hydroxy -3-tert-butylphenyl) propane, 1,1-bis- (4-hydroxyphenol) ethane, bis- (2-hydroxynaphthyl) methane, 1,5-dihydroxy-3-naphthalene and the like have.

In addition to the polyhydric phenols, other cyclic polyols can be used to prepare polyglycidyl ethers of cyclic polyol derivatives. Examples of other cyclic polyols are alicyclic polyols, in particular 1,2-bis- (hydroxymethyl) cyclohexane, 1,3-bis- (hydroxymethyl) cyclohexane, 1,2-cyclohexane diol, 1, Alicyclic polyols such as 4-cyclohexane diol and hydrogenated bisphenol A.

It is also possible to use acrylic polymers or oligomers containing oligomeric polyepoxides or polymerizable polyepoxides such as glycidyl methacrylate or epoxy terminated polyglycidyl ethers. Monomers commonly used in the production of acrylic polymers are styrene, methyl methacrylate, butyl acrylate, butyl methacrylate, ethyl hexyl methacrylate, glycidyl acrylate and glycidyl methacrylate and the like. However, the acrylic polymer should not contain any hydroxy functional monomers such as hydroxy alkyl acrylates and methacrylates since the hydroxyl alcohol groups may interfere with the formation reaction of the morpholine dione group. Other polyepoxide resins, such as epoxy novolacs, in particular epoxy cresols and epoxy phenol novolacs, may also be used in the present invention to form main emulsions. Epoxy novolac is usually prepared by reacting epichlorohydrin with a novolak resin, which is usually formed by the reaction of orthocresol or phenol with formaldehyde. As any polyepoxide, the epoxy novolac can react with alkyl amines and dialkyl oxalates to form morpholine dione crosslinkers.

The amine used for the preparation of morpholine dione is preferably a primary amine. Primary amines form amino alcohol groups thereon which can react with the epoxy groups of the resin to form morpholine dione structures. Useful primary amines include any of those listed above used to form epoxy-amine addition products. Particular preference is given to alkyl amines having 1 to 15 carbon atoms in the alkyl group. Most preferred are steric hindrance primary amines such as t-butyl amine. Hindered amines prevent dimerization of the epoxide and aid in the desired epoxy ring opening reaction.

The resulting addition product can then be reacted with any conventional oxalate ester to form a closed ring and form a crosslinkable morpholine dione group thereon. Alcohols formed during the reaction are removed, for example, by azeotropic distillation. Oxalates useful for forming morpholine dione compounds include dialkyl oxalates having 1 to 15 carbon atoms in the alkyl group, of which diethyl oxalate is most preferred.

The number average molecular weight of the morpholine dione compound used in the present invention is preferably less than about 2,000, more preferably less than about 1,500 in order to achieve high fluidity and high smoothness of the film. The preferable range of a number average molecular weight is 400-1,200. All molecular weights disclosed herein are determined by gel permeation chromatography using polystyrene standards. These compounds are activated (ie, ring-opened) during the amine decomposition reaction, preferably at much lower baking temperatures than the blocked standard polyisocyanates, preferably from 275 ° F. to 325 ° F. (135 ° C. to 162.5 ° C.). As a comparison, blocked standard polyisocyanates are currently baked at 330 ° F. (165.5 ° C.) or higher to release isocyanate blocking and begin the curing reaction.

One preferred class of morpholine dione compounds useful as crosslinking agents in the present invention are the reaction products of aromatic polyepoxy-hydroxy-ether resins such as polyglycidyl ethers of bisphenol A with alkyl amines and dialkyl oxalates. Examples of compounds useful within this class are those represented by the following formula (1).

In said formula, R is independently a C1-C10, Preferably it is a C2-C6 alkyl group, n is 0 or a positive integer of 1-4.

Another preferred class of morpholine dione compounds useful in the present invention are the reaction products of epoxy novolac resins such as epoxy phenol novolacs with alkyl amines and dialkyl oxalates. Examples of compounds useful within this class are those represented by the following formula (2).

In said formula, R is independently a C1-C8, Preferably it is a C2-C6 alkyl group, n is 0 or a positive integer of 1-4.

The novel morpholine dione compounds used in coating compositions can be prepared in any of several different approaches. The preferred method for preparing the morpholine dione compound from the epoxy resin is to slowly charge the epoxy resin into the reaction vessel containing the primary amine, and the reaction temperature is -10 ° C to 100 ° C until all the epoxy groups are reacted by infrared scanning. Preferably, it is a stepwise process maintained at 10 ° C to 40 ° C. The molar ratio of epoxy groups to amine groups in this reaction is preferably 1: 1 to 1:10, more preferably 1: 1, but there are variations from this range for various reasons as will be appreciated by those skilled in the art. The reaction is preferably carried out in the presence of a polar solvent such as ethanol to reduce the viscosity in the reaction vessel. Excess amine is preferably removed before the addition of the dialkyl oxalate. The reaction vessel is then charged normally with dialkyl oxalate and a suitable catalyst, such as 4-dimethylaminopyridine, until the epoxy-amino groups are all closed rings by infrared scanning to show that they have been converted to morpholine dione groups. Maintain at reflux temperature. The molar ratio of amine groups to oxalate groups in this reaction is preferably 0.8: 1 to 1: 0.8, more preferably 1: 1. The alcohol formed in this reaction is removed, for example, by azeotropic distillation.

Representative catalysts used in the formation process are tertiary amines, most particularly 4-dimethylaminopyridine.

Representative solvents that can be used in the formation process include ketones such as methyl amyl ketone, methyl isobutyl ketone and methyl ethyl ketone, aromatic hydrocarbons such as toluene and xylene, propylene carbonate, alkylene carbonates such as n-methyl pyrrolidone Carbonates, ethers, esters, acetates and any mixtures thereof, but polar solvents such as ethanol are usually preferred.

As noted above, the reaction conditions are preferably selected such that they can be converted to morpholine dione groups by reacting the epoxy groups to 100% or as close to 100% as possible without substantially remaining unreacted epoxy groups in the molecule.

The resulting morpholine dione compound can be used in the coating composition of the present invention with varying amounts of about 10 to 60%, preferably about 15 to 40%, relative to the total weight of the binder. Most preferably, about 20-30% by weight of this morpholine dione compound is included in the binder.

In addition to the morpholine dione compounds derived from epoxy resins as described above, other morpholine dione compounds may be used in the present invention as will be appreciated by those skilled in the art.

Optionally, the present coating composition may further contain additional crosslinking agents, preferably with morpholine dione crosslinking agents. The additional crosslinking agent may comprise 0 to 99% of the total weight of the crosslinking component used in the present coating composition. Additional crosslinkers can be used to react with any remaining active hydrogen groups present in the resin system. Examples of further crosslinking agents can include any conventionally known blocked polyisocyanate crosslinking agent. These are aliphatic, cycloaliphatic and aromatic isocyanates such as hexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluene diisocyanate, methylene diphenyl diisocyanate and the like. Aromatic diisocyanates such as methylene diphenyl diisocyanate are preferred. These isocyanates are preliminarily reacted with a blocking agent such as oxime, alcohol or caprolactam to block the isocyanate functional groups. One preferred mixture of blocking agents is methanol, ethanol and diethylene glycol monobutyl ether. Upon heating, the blocking agent separates to provide reactive isocyanate groups and cause further crosslinking with the epoxy-amine addition product. Isocyanate crosslinkers and blocking agents are known in the art and are disclosed in US Pat. No. 4,419,467 to Marchetti et al., Incorporated herein by reference and issued April 10, 1979. Melamine crosslinkers can also be used.

The negative electrode binder and crosslinker (s) of the epoxy-amine addition product are the major resin components in the electrocoating composition and are usually present in amounts of about 30-50% by weight of the solids of the composition. The basic group (amine group) of the negative electrode binder is partially or completely neutralized with an acid to form a water soluble product. Representative acids used to neutralize the epoxy-amine addition product to form water dispersible cationic groups are lactic acid, acetic acid, formic acid, sulfamic acid, alkanesulfonic acids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and the like. Alkanesulfonic acid is usually preferred. The degree of neutralization depends on the nature of the binder used in each individual case. Typically, sufficient acid is added to provide an electrocoating composition with a pH of about 5.5 to 8.0. To form the electrocoating bath, the solids of the electrocoating composition are usually reduced to the desired electrolytic cell solids using an aqueous medium.

In addition to the binder resin component, the electrocoating composition usually contains a pigment incorporated into the composition in the form of a pigment paste. Pigment pastes are prepared by pulverizing the pigment or dispersing the pigment in the pulverizing developer with a curing catalyst and other optional ingredients such as crater inhibitors, wetting agents, surfactants and antifoaming agents. Any pigment grinding developer known in the art may be used. Usually, grinding is carried out using a conventional apparatus known in the art such as an Eiger mill, Dynomill or a sand mill. Grinding is usually carried out for about 2 to 3 hours until at least 7 or more is obtained in Hegman power.

The viscosity of the pigment dispersion before grinding or milling is important. B Brookfield viscosity, usually measured according to ASTM D-2196, is used. Although the desired viscosity may vary depending on the component selected, the viscosity is usually in the range of 8,000 centipoises to 1,500 centipoises (0.8 Pa.s to 1.5 Pa.s) to achieve pulverization upon grinding. Viscosity usually increases upon grinding and is easily adjusted by changing the amount of water present.

Examples of the pigment that can be used in the present invention include titanium dioxide, basic lead silicate, strontium chromate, carbon black, iron oxide and clay. Pigments with high surface area and oil absorption can adversely affect the cohesiveness and fluidity of the electrodeposition coating and should be used as appropriate.

In addition, the weight ratio of pigment to binder is important, which should preferably be less than 5: 1, more preferably less than 4: 1, usually about 2 to 4: 1. High weight ratios of pigment to binder have been found to adversely affect cohesiveness and flowability.

The electrocoating composition of the present invention may contain optional components such as wetting agents, surfactants, antifoaming agents, and the like. Examples of surfactants and wetting agents include alkyl imidazolines, such as those available from Ciba-Geigy Industrial Chemicals as Amine C®, Air Products and Chemicals, Inc. Acetylene alcohols available from Surfynol 104® from Products and Chemicals. When present, these optional components comprise about 0.1 to 20 weight percent of the binder solids of the composition.

Optionally, plasticizers can be used to enhance fluidity. Examples of useful plasticizers include ethylene oxide or propylene oxide addition products of high boiling water immiscible materials such as nonyl phenol or bisphenol A. The plasticizer is usually used at a concentration of about 0.1 to 15% by weight of the resin solids.

Curing catalysts such as tin are usually present in the composition. Examples are dibutyl tin dilaurate and dibutyl tin oxide. When used, the curing catalyst is usually present in an amount of about 0.05 to 2 weight percent tin based on the total weight of the resin solids.

The electrocoating composition of the invention is dispersed in an aqueous medium. The term "dispersion" as used herein is believed to be a two-phase translucent or opaque aqueous resin binder system in which the binder is located in the disperse phase and the water in the continuous phase. The average particle diameter of the binder phase is about 0.05 to 10 μm, preferably less than 0.2 μm. The concentration of the binder in the aqueous medium is usually not critical, but usually the main part of the aqueous dispersion is water. Aqueous dispersions usually contain about 3-50% by weight, preferably 5-40% by weight of binder solids. When added to an electrocoating bath, the aqueous binder concentrate, which is further diluted with water, usually has 10 to 30% by weight binder solids.

In addition to water, the aqueous medium of the negative electrode electrocoating composition contains a flocculating solvent. Useful flocculating solvents include hydrocarbons, alcohols, polyols and ketones. Preferred flocculating solvents include monobutyl and monohexyl ethers of ethylene glycol, and phenyl ethers of propylene glycol. The amount of flocculant solvent is not critical but is usually 0.1 to 15% by weight, preferably 0.5% by weight, based on the total weight of the aqueous medium.

The electrocoating composition of the present invention is used in a conventional cathode electrocoating method. The electrocoating tank contains two conductive electrodes, an anode which is part of the electrocoating tank and a cathode which is the substrate to be coated. The substrate may include conductive (eg, metal) objects, or yard care fixtures (eg, lawn mowers, snow plows, horticultural power tools, and the like, including but not limited to articles such as the automobile itself or automobile parts, and the like. Components), office furniture, home appliances, baby toys, and the like, and any OEM or industrial coating component, and the like. When sufficient voltage is applied between the two electrodes, an adhesive film adheres on the cathode. The applied voltage can vary depending on the type of coating, coating thickness, and required electrodeposition, and can be as low as 1 volt or as high as thousands of volts. Commonly used voltages are between 50 and 500 volts. Current densities are typically 0.5 to 5 amps per square foot (4.65 to 46.5 amps per square meter) and decrease in electrodeposition, indicating that an insulating film is attached. Immersion times should be sufficient to obtain a cured coating of about 0.5 to 1.5 mils (10 to 40 μm), preferably 0.8 to 1.2 mils (20 to 30 μm). Various substrates such as steel, phosphate treated steel, zinc steel, copper, aluminum, magnesium, and various plastics coated with conductive plating can be electrocoated with the composition of the present invention.

After the electrocoating is carried out, it is cured by baking for a time sufficient to cure the coating at elevated temperatures, such as 135 ° C. to 200 ° C., usually about 5 to 30 minutes.

In the present invention, the curing reaction is a ring-opening reaction that involves the decomposition of amines of morpholine dione and does not release volatile byproducts. The gaamine decomposition reaction of morpholine dione can be explained by the amide formation reaction, which still provides the desired amide crosslinking but avoids significant baking removal loss. Upon curing, hydroxyl groups, when present, can be further reacted with additional crosslinking agents to produce highly crosslinked networks.

The following examples illustrate the invention. All parts and percentages are by weight unless otherwise indicated. The molecular weights disclosed herein are all determined by GPC using polystyrene standards. Unless otherwise specified, all chemicals and reactants are used as obtained from Aldrich Chemical Co. (Milwaukee, WI).

The following morpholine dione crosslinked resin solution was prepared according to the conventional blocked polyisocyanate crosslinked resin solution, after which the main emulsion and electrocoating composition were prepared and the properties of the composition were compared.

Example 1

Preparation of morpholine dione crosslinked resin solution

About 2,537 parts of butylamine were charged to a suitable reaction vessel and kept at 0 ° C. under a blanket of nitrogen to prepare di-((4-butyl-2,3-dioxomorpholin-6-yl) -methyl) ether of bisphenol A. . A mixture of approximately 1,269 parts of epoxy resin of diglycidyl ether of bisphenol A, manufactured by Shell, having an equivalent weight of 188 and 805 parts of ethanol was slowly charged into the reaction vessel and the reaction temperature was decreased. Hold at 0 ° C. for 2 hours. The reaction temperature was gradually raised to 10 ° C. to 15 ° C. for 6 hours to finally 25 ° C., and maintained at 25 ° C. until all of the epoxy groups reacted by IR scanning. Excess butylamine and ethanol were removed using a rotary evaporator. About 805 parts of ethanol, 1.2 parts of 4-dimethylaminopyridine and 880 parts of diethyl oxalate were added to the reaction vessel, and the reaction mixture was refluxed under a blanket of nitrogen for 2 hours. Excess ethanol was distilled off through a Vigreux column under atmospheric pressure and the ethanol produced upon ring closure was removed by heating the reaction mixture to 160 ° C. with a vacuum pump. The resulting resin was a colorless solid that was brittle.

Example 2

Preparation of conventional crosslinked resin solution

About 336.86 parts of Mondur® MR (methylene diphenyl diisocyanate, manufactured by Bayer), 112.29 parts of methyl isobutyl ketone and 0.07 parts of dibutyl tin dilaurate are charged into a suitable reaction vessel and a nitrogen blanket Under heating to 82 ° C. to prepare an alcohol blocked polyisocyanate crosslinked resin mixed solution. While maintaining the reaction mixture below 93 ° C., about 229.68 parts of propylene glycol mono methyl ether was slowly charged into the reaction vessel. The reaction mixture was then kept at 110 ° C. until infrared scanning showed almost all of the isocyanates reacted. Then about 3.46 parts of butanol and 73.13 parts of methyl isobutyl ketone were added. The obtained resin solution had 75% of content of a nonvolatile substance.

Example 3

Preparation of Chain Extended Polyepoxide Main Emulsions with Di-((4-butyl-2,3-dioxomorpholin-6-yl) -methyl) ether of Bisphenol A and Conventional Crosslinkers

EPON® 828 (Epoxy resin of diglycidyl ether of bisphenol A of epoxy equivalent 188, manufactured by Shell) About 520 parts, 151 parts of bisphenol A, ethoxylated bisphenol A of hydroxyl equivalent 247 (New Pack (registered trademark) ) 8009, 190 parts of Milliken), 44 parts of xylene and 0.5 parts of dimethylbenzylamine were charged into a suitable reaction vessel. The resulting reaction mixture was heated to 160 ° C. under a blanket of nitrogen and maintained at this temperature for 1 hour. One part of dimethylbenzylamine was added and the mixture was kept at 147 ° C. until the epoxy equivalent was 1,050. After cooling the reaction mixture to 149 ° C., 996 parts of alcohol blocked polyisocyanate resin (prepared in Example 2) and di-((4-butyl-2,3-dioxomorpholine-6-) of bisphenol A resin 596 parts of 1) -methyl) ether (prepared in Example 1) were added. At 107 ° C., about 58 parts of diketamine (the reaction product of methyl isobutyl ketone and diethylenetriamine having a content of nonvolatile material of 73%) and 47 parts of methylethanolamine were added. The resulting mixture was left at 120 ° C. for 1 hour and dispersed in an aqueous medium of 1,500 parts of deionized water and 81 parts of methanesulfonic acid (70% methanesulfonic acid in deionized water). It was further diluted with 818 parts of deionized water. The emulsion was stirred until methyl isobutyl ketone evaporated. The emulsion obtained had a content of nonvolatile matters of 38%.

Example 4

Preparation of Chain Extended Polyepoxide Main Emulsions with Conventional Crosslinked Resin Solutions

EPON® 828 (Epoxy resin of diglycidyl ether of bisphenol A of epoxy equivalent 188, manufactured by Shell) About 520 parts, 151 parts of bisphenol A, ethoxylated bisphenol A of hydroxyl equivalent 247 (New Pack (registered trademark) 19009, 44 parts of xylene and 1 part of dimethylbenzylamine were charged into a suitable reaction vessel. The resulting reaction mixture was heated to 160 ° C. under a blanket of nitrogen and maintained at this temperature for 1 hour. 2 parts of dimethylbenzylamine were added and the mixture was kept at 147 ° C. until the epoxy equivalent became 1,050. After the reaction mixture was cooled to 149 ° C., about 797 parts of a conventional crosslinked resin (prepared in Example 2) were added. At 107 ° C., about 58 parts of diketamine (the reaction product of methyl isobutyl ketone and diethylenetriamine having a content of nonvolatile material of 73%) and 48 parts of methylethanolamine were added. The resulting mixture was left at 120 ° C. for 1 hour and dispersed in 1,335 parts of deionized water and about 81 parts of methanesulfonic acid (70% methanesulfonic acid in deionized water). It was further diluted with 825 parts of deionized water. The emulsion was stirred until methyl isobutyl ketone evaporated. The emulsion obtained had a content of nonvolatile matters of 38%.

Example 5

Preparation of Quaternization Agent

A quaternizing agent was prepared by adding about 87 parts of dimethylethanolamine to the reaction vessel at room temperature for 320 parts of toluene diisocyanate semi-capped with 2-ethyl hexanol. An exothermic reaction occurred and the reaction mixture was stirred at 80 ° C for 1 hour. About 118 parts of an aqueous solution of lactic acid (content of 75% of nonvolatile matter) was added, followed by 39 parts of 2-butoxyethanol. The reaction mixture was left to stir constantly at 65 ° C. for about 1 hour to form a quaternizing agent.

Example 6

Preparation of Pigment Grinding Developer

About 710 parts of EPON® 828 (diglycidyl ether of bisphenol A of Epoxy equivalent 188, manufactured by Shell) and 290 parts of bisphenol A were charged into a suitable reaction vessel under a nitrogen blanket, and heated to 150 ° C. to 160 ° C. to exothermic A pigment pulverizing developer was prepared by initiating the reaction. The exothermic reaction lasted for about 1 hour at 150 ° C to 160 ° C. The reaction mixture was then cooled to 120 ° C. and about 496 parts of toluene diisocyanate semi-capped with 2-ethyl hexanol was added. The temperature of the reaction mixture was maintained at 110 ° C. to 120 ° C. for 1 hour, and about 1,095 parts of 2-butoxyethanol was added, and then the reaction mixture was cooled to 85 ° C. to 90 ° C., and 71 parts of deionized water were added, followed by quaternary About 496 parts of the agent (prepared in Example 5) were added. The temperature of the reaction mixture was maintained at 85 ° C to 90 ° C until the acid value became about 1.

Example

Preparation of Pigment Paste

Parts by weight Pigment Grinding Developer (Prepared in Example 6) 597.29 Deionized water 1140.97 Titanium dioxide pigment 835.66 Aluminum silicate pigment 246.81 Carbon black pigment 15.27 Dibutyl Tin Oxide 164.00 Sum 3000.00

The components were mixed in a suitable mixing vessel until a homogeneous mixture was formed, then the mixture was filled with an Ager mill and ground by dispersion until it passed the Hegman test.

Example 8

Preparation of Electro Coating Bath I and II

Parts by weight Coating bath Ⅰ Coating bath Ⅱ According to the present invention According to the prior art Emulsion (prepared in Example 3) 1503.08 - Emulsion (prepared in Example 4) - 1503.08 Deionized water 2013.49 2013.49 Pigment Paste (Prepared in Example 7) 397.54 397.54 Conventional crater inhibitors ^* 85.89 85.89 Sum 4000.00 4000.00

Conventional crater inhibitors are reaction products of Jeffamine® D2000 from Huntsman and EPON® 1001 epoxy resin from Shell.

Cathode electrocoating baths I and II were prepared by mixing the above components. Thereafter, each coating bath was ultrafiltration. The phosphate treated cold rolled steel sheet was electrocoated in each coating bath at 240 to 280 volts to obtain a film having a thickness of 0.8 to 1.0 mils (20.32 to 25.4 μm) on each plate. The electrocoated panels were then baked at metal temperature 360 ° F. (182.2 ° C.) for 10 minutes. For solvent resistance testing, the electrocoated panels were baked instead for 10 minutes at a metal temperature of 330 ° F. (165.5 ° C.).

The prepared steel sheet was tested for solvent resistance by a standard rub test (20 rub with a cloth moistened with methyl ethyl ketone) and the bake removal loss was tested.

One method used to check for proper curing of an e-coat film at a particular baking temperature is to rub a cloth soaked in methyl ethyl ketone at least 20 times back and forth on the e-coat film. The degree of curing can be evaluated by examining the discoloration of the fabric and the matt appearance of the film surface. Matte appearance or discoloration of the fabric on the e-coat film indicates poor curing of the e-coat film.

In this example, the phosphate treated cold rolled steel sheet coated with coating bath I and baked at metal temperature of 330 ° F. (165.5 ° C.) for 10 minutes did not exhibit a matt appearance, indicating full cure. On the other hand, phosphated cold rolled steel sheets coated with coating bath II and baked at the same temperature showed a significant amount of matt appearance or incomplete hardening.

Another major factor in evaluating an e-coat film is the bake removal loss upon baking. In order to measure the% loss of bake removal during baking, an e-coat film was deposited on the metal plate pre-weighed in the first step and the plate was heated at 105 ° C. for 3 hours to remove residual water, and finally the plate was removed. Baked at specific times and temperatures. The bake removal loss rate (%) of the e-coat film was measured by dividing the weight difference of the e-coat before and after baking by the initial weight.

For coating bath I, the% bake removal loss (%) for 10 minutes at metal temperature 360 ° F. (182.2 ° C.) was 8-9%. For coating bath II, for 10 minutes at metal temperature 360 ° F. (182.2 ° C.) Baking removal loss rate (%) was 12 to 13%.

The test results are summarized in Table 3 below.

result Coating bath I Coating bath II Solvent resistance for 10 minutes at 330 ° F (165.5 ° C) No wear (excellent hardening) Matte appearance (hardening) 10 minutes bake removal loss at 360 ° F (182.2 ° C) 8 to 9% 12 to 13%

The results show that coating bath I with morpholine dione crosslinker has better low temperature crosslinkability and less baking removal loss than coating bath II with conventional crosslinking agent.

Claims (20)

In an aqueous medium, (A) a crosslinkable resin having at least one acid neutralized amine group, and (B) a crosslinking agent for the resin having at least one morpholine dione group Cathode electrocoating composition comprising a. The negative electrode electrocoating composition according to claim 1, further comprising an auxiliary crosslinking agent capable of reacting with the amine group on the resin. The negative electrode electrocoating composition according to claim 1, wherein the crosslinking agent (B) has a plurality of morpholine dione groups. (1) immersing the conductive substrate in a coating composition comprising (A) a crosslinkable resin having at least one acid neutralized amine group, and (B) a crosslinking agent having at least one morpholine dione group, in an aqueous medium, (2) applying a current potential between the anode and the conductive substrate, and (3) removing the substrate from the coating composition Cathode electrical coating method comprising a. The method according to claim 4, wherein in step (1), (A) the crosslinkable resin contains a plurality of acid neutralized amine groups, and (B) the crosslinker contains a plurality of morpholine dione groups. An aqueous negative electrode electrocoating composition comprising an organic or inorganic acid which is a binder of an epoxy-amine addition product, a crosslinking agent, and a neutralizer for an epoxy-amine addition product, wherein the crosslinking agent has at least one morpholine dione group per molecule. The electrocoating composition according to claim 6, wherein the crosslinking agent has a plurality of morpholine dione groups per molecule. 8. The electrocoating composition of claim 7, wherein the morpholine dione crosslinker is a reaction product of a polyepoxide with an alkyl amine and a dialkyl oxalate. The electrocoating composition according to claim 8, wherein the morpholine dione crosslinking agent is represented by the following Chemical Formula 2. <Formula 2> In said formula, n is 0 or a positive integer of 1-4, R is a C1-C8 alkyl group. The electrocoating composition according to claim 8, wherein the morpholine dione crosslinking agent is represented by the following Chemical Formula 1. <Formula 1> In said formula, n is 0 or a positive integer of 1-4, R is a C1-C10 alkyl group. 8. The electrocoating composition of claim 7, further comprising an additional crosslinker selected from blocked polyisocyanates. 8. The electrocoating composition of claim 7, wherein the epoxy-amine addition product contains an amine selected from the group consisting of primary amines, secondary amines, ketimines, and mixtures thereof. 8. The electrocoating composition of claim 7, wherein the epoxy addition product comprises a polyepoxy-hydroxy-ether resin extended with dihydric phenol and reacted with an amine and neutralized with an organic or inorganic acid. A method comprising contacting a morpholine dione compound with a film forming amine compound to form a crosslinked film. A morpholine dione crosslinking agent represented by the following formula (2) and used as a crosslinking agent in a coating composition containing an amine compound (s) capable of reacting with a morpholine dione group. <Formula 2> In said formula, n is 0 or a positive integer of 1-4, R is a C1-C8 alkyl group. The morpholine dione crosslinking agent represented by following formula (1) and used as a crosslinking agent in the coating composition containing the amine compound (s) which can react with a morpholine dione group. <Formula 1> In said formula, n is 0 or a positive integer of 1-4, R is a C1-C10 alkyl group. (1) preparing an epoxy-amine addition product of an epoxy resin extended with dihydric phenol and reacted with an amine; (2) preparing a crosslinking agent for the epoxy-amine addition product; (3) blending the epoxy-amine addition product with the morpholine dione crosslinker; (4) neutralizing the epoxy-amine addition product with an organic or inorganic acid to form an emulsion; And (5) forming a pigment dispersion and blending it with the neutralized emulsion A process for preparing a negative electrode electrocoating composition comprising a morpholine dione crosslinking agent of an epoxy resin, comprising in any operable order, reacted with an alkyl amine followed by a dialkyl oxalate in step (2). A substrate coated with the dried and cured composition of claim 1. The coated substrate of claim 18, wherein the substrate is an OEM or industrial component. 20. The coated substrate of claim 19, wherein the substrate is an automobile body or automobile part.