KR20050016955A - Cathodic electrocoating composition containing morpholine dione blocked polyisocyanate crosslinking agent - Google Patents

Abstract

The present invention relates to an improved aqueous negative electrode electrocoating composition having a binder of an epoxy-amine addition product and a polyisocyanate crosslinking agent, wherein the use of a polyisocyanate crosslinking agent having at least one crosslinkable morpholine dione group per molecule is improved. . 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 a polyisocyanate crosslinker blocked with morpholine dione {CATHODIC ELECTROCOATING COMPOSITION CONTAINING MORPHOLINE DIONE BLOCKED POLYISOCYANATE 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. 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 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. In addition, there is a need to find new crosslinking agents which can be produced simply and inexpensively on a commercial scale and have the above characteristics.

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, wherein the baking upon curing An improvement is the use of blocked polyisocyanate crosslinkers with on average one or more isocyanate groups blocked with morpholine dione compounds to reduce removal losses. Standard blocking agents are also preferably used to provide a highly crosslinked final film network.

Methods of cathodic 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.

The advantage of the electrocoating compositions of the invention formulated with the novel morpholine dione crosslinkers is to reduce the loss of volatiles and baking removal resulting from the film upon curing after electrodeposition, ie weight loss. In addition, the electrocoating composition has a lower curing temperature and better edge corrosion resistance compared to electrocoating compositions containing conventional alcohol blocked polyisocyanate crosslinkers.

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, etc. .

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 the novel blocked polyisocyanate crosslinker.

The novel blocked polyisocyanate crosslinkers used in the coating compositions of the present invention are organic polyisocyanates that have been at least partially pre-reacted with a blocking agent that does not contribute substantially to weight loss when the film is heated and cured. In addition, the crosslinking agent of the present invention is preferably completely blocked or capped with the desired blocking agent so that substantially no free isocyanate groups remain, so that the resulting blocked or capped isocyanate is stable to active hydrogen at room temperature but is active at the desired elevated temperature. React with hydrogen.

The polyisocyanate used to form the crosslinking agent is an organic polyisocyanate. These may be any suitable aliphatic, cycloaliphatic or aromatic polyisocyanates or derivatives thereof. Higher polyisocyanates such as triisocyanate can also be used, but diisocyanates are generally preferred. Examples of suitable aliphatic diisocyanates are straight-chain aliphatic diisocyanates such as 1,4-tetramethylene diisocyanate and 1,6-hexamethylene diisocyanate. In addition, an alicyclic diisocyanate can also be used. Examples thereof include isophorone diisocyanate and 4,4'-methylene-bis- (cyclohexyl isocyanate). Examples of aromatic diisocyanates are p-phenylene diisocyanate, methylene diphenyl diisocyanate, polymerizable methylene diphenyl diisocyanate and 2,4- or 2,6-toluene diisocyanate and the like. Suitable isocyanate derivatives include 4,4'-methylene dianiline diisocyanate or derivatives thereof in which methylene groups have been replaced by heteroatoms such as NCH ₃ , S, O, C (CH ₃ ) ₂ . Examples of some higher polyisocyanates such as triisocyanate include methylene triphenyl triisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanate and the like. In addition to the polyisocyanates listed above, other higher polyisocyanates such as isocyanate prepolymers can also be used. They are formed from organic polyisocyanates and polyols. Any of the above polyisocyanates can be used together with the polyol. Polyols, such as trimethylol alkanes, such as trimethylol propane or ethane, can be used. Polymerizable polyols, such as polycaprolactone diol and triol, can also be used. However, aromatic diisocyanates such as methylene diphenyl diisocyanate are usually most preferred.

The main blocking agent used to form the crosslinking agent of the present invention is one which does not substantially contribute to weight loss, that is, baking removal loss, when the film is heated and cured. More specifically, the blocking agent used herein is a morpholine dione blocking agent containing at least one crosslinkable morpholine dione blocking group. Upon heating, morpholine dione blocking groups are thought to participate in the crosslinking reaction by reacting with amine groups, ie crosslinkable functional groups, on the film forming epoxy-amine resin, instead of leaving the film, becoming a permanent part of the final film network. This reaction involves a ring opening reaction and therefore is carried out at relatively low temperatures and does not emit 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. This type of curing mechanism can also allow the electrocoating composition of the invention to cure at much lower temperatures than conventional electrocoating compositions, which can provide significant energy savings for auto assembly plants.

A variety of hydroxy functional morpholine dione monomers can be used to introduce such crosslinkable morpholine dione blocking groups into polyisocyanate molecules. These blocking agents can be any hydroxy functional morpholine dione monomer having one or more reactive hydroxyl groups and one or more morpholine dione groups per molecule. Preference is given to N- or 4-substituted hydroxy alkyl morpholine dione monomers having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms in the alkyl group. These monomers are prepared simply, efficiently and inexpensively by reacting a dialkyl oxalate, such as diethyl oxalate, with a suitable polyvalent secondary amine, such as dialkanolamine, having two or more reactive hydroxyl groups per molecule. This reaction is preferably carried out in a polar solvent at low temperature, for example 0 ° C. to 5 ° C. The obtained compound is then purified according to its properties by appropriate techniques to remove alcohol formed during the reaction and traces of unreacted starting material. Useful secondary amines that can be used to form hydroxy functional morpholine dione monomers are usually those having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, among the alkanolamines, such as alkanol groups, Among these, diethanolamine is most preferred. Examples of dialkyl oxalate esters are those having from about 1 to 15 carbon atoms, preferably 1 or 2 carbon atoms in the alkyl group, of which diethyl oxalate is most preferred.

One preferred class of hydroxy functional morpholine dione monomers that can be used as blocking agents in the present invention is represented by the following formula (1).

Wherein R is selected from the group consisting of lower alkanols having up to 8 carbon atoms, preferably up to 4 carbon atoms in alkanols, preferably alkanol groups, of which hydroxyethyl is the most desirable.

US Patent No. 4,118,422 to Klein, issued October 3, 1978, and other US Pat. No. 2,723,247 to Harrington, issued November 8, 1955, to other hydroxy functional morpholine dione monomers that may be used ( Both are incorporated herein by reference).

The blocked polyisocyanates of the present invention can be completely blocked (ie, 100% or as close as possible to 100%) with the hydroxy functional morpholine dione monomer without substantially remaining unreacted isocyanate groups. . However, in the present invention, a mixture of blocking agents is usually preferred. Accordingly, the reaction conditions are preferably selected such that 90 to 0 mol% of polyisocyanate groups can react with conventional isocyanate blocking agents by reacting 10 to 100 mol% of polyisocyanate groups to convert them into morpholine dione groups. Examples of conventional blocking agents are ether alcohols, alkyl alcohols, oximes, amides or any compounds having active hydrogens, of which low molecular weight ethers or alkyl alcohols which do not contribute substantially to weight loss upon curing are preferred. Low molecular weight means that the number average molecular weight of the other blocking agent is preferably less than about 162. In the present invention, an additional blocking agent may be used to heat at least some isocyanate groups to release blocking and react with any remaining active hydrogen groups present in the resin system. During heating, these blocking agents separate to provide reactive isocyanates and cause further crosslinking with the epoxy-amine addition product.

Commonly useful alkyl alcohol blocking agents are aliphatic, cycloaliphatic or aromatic alkyl monoalcohols having 1 to 20 carbon atoms, preferably up to 12 carbon atoms in the alkyl group, for example methanol, ethanol, n-propanol, butanol, 2-ethyl hexanol, cyclohexanol, cyclooctanol, phenol, pyridinol, thiophenol and cresol. Commonly usable ether alcohols include ethylene glycol mono alkyl ethers having alkyl groups of 1 to 10 carbon atoms, diethylene glycol mono alkyl ethers, propylene glycol mono alkyl ethers or dipropylene glycol mono alkyl ethers such as diethylene glycol mono butyl ether, Ethylene glycol butyl ether, diethylene glycol mono methyl ether, ethylene glycol methyl ether, dipropylene glycol mono methyl ether, dipropylene glycol mono butyl ether, propylene glycol mono butyl ether, propylene glycol mono methyl ether. Representative oximes are methyl ethyl ketone oxime, methyl isobutyl ketone oxime, methyl isoamyl ketone oxime, methyl n-amyl ketone oxime, cyclohexanone oxime, diisobutyl ketone oxime. Representative amides that can be used as blocking agents are caprolactam, methylacetamide, succinimide, acetanilide. One preferred mixture of blocking agents is 4 (2-hydroxyethyl) morpholine-2,3-dione and diethylene glycol mono methyl ether.

Thus, the resulting polyisocyanate curing agent provides a useful amount of crosslinkable morpholine dione groups that do not contribute to weight loss when the film is cured by heating. Most preferably, blocked isocyanates are partially blocked with conventional blocking agents and have reactive morpholine dione groups.

One preferred class of morpholine dione compounds useful as crosslinking agents in the present invention are morpholine dione polyisocyanate oligomers represented by the following formula (2).

Wherein R represents an aromatic, cycloaliphatic or aliphatic hydrocarbon radical, preferably aromatic methylene diphenyl radical, R ₁ is a conventional polyisocyanate blocking agent such as aliphatic monoalcohol, ether alcohol or R ₂ , R ₂ Is a morpholine dione radical represented by the following formula (3).

In the above formula, R ₃ is an alkyl group having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms; n is a positive integer of 1 to 4, preferably 1.

The blocked polyisocyanate crosslinkers can be prepared in several different approaches as will be appreciated by those skilled in the art. A preferred method for preparing such compounds is to sequentially react selected polyisocyanates with hydroxy functional morpholine dione monomers and optionally, but with additional preferred blocking agents. This reaction is preferably carried out at elevated temperature in the presence of an inert solvent such as methyl isobutyl ketone and a suitable catalyst such as dibutyl tin dilaurate until the infrared is shown to react all the isocyanates.

Representative catalysts that can be used in the formation process are conventional tin catalysts, of which dibutyl tin dilaurate is preferred.

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. Polar solvents such as ethanol, butanol and the like can also be used to reduce the viscosity of the reaction mixture.

In addition, the number average molecular weight of the blocked polyisocyanate of 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.

As noted above, these compounds are preferably stable to active hydrogen at room temperature, as required for anionic electrocoated crosslinkers, and much lower baking temperatures, preferably 275 ° to 325 ° F., than blocked standard polyisocyanates. Activation (ie ring opening) upon curing at 135 ° C. to 162.5 ° C.). By comparison, polyisocyanate crosslinkers blocked with standard ether alcohols are currently baked at 330 ° F. (165.5 ° C.) or higher to release isocyanate blocking and initiate the curing reaction.

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

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

Optionally, the coating composition may further contain additional crosslinking agents together 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 crosslinking agents can also 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 as listed above. One preferred mixture of blocking agents is methanol, ethanol and diethylene glycol monobutyl ether. Upon heating, these blocking agents separate 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 amperes 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, at least some of the curing reactions are ring-opening reactions that involve the decomposition of the amines of morpholine dione and do 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, the hydroxy groups formed during the reaction can be further reacted with a crosslinking agent or, if present, the free isocyanate groups on the further crosslinking agent to produce a highly crosslinked network.

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 oligomer 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 4 (2-hydroxyethyl) morpholine-2,3-dione monomer

125 g of diethyl oxalate and 80 g of n-butanol were charged to a suitable reaction vessel and heated to 22 ° C. under a blanket of nitrogen to prepare 4 (2-hydroxyethyl) morpholine-2,3-dione. A mixture of 89.9 g of diethanolamine and 72 g of n-butanol was slowly charged into the reaction vessel while maintaining the reaction mixture below 50 ° C. After stirring for 30 minutes, the reaction mixture was refluxed for 1 hour and left at room temperature for 16 hours. The product was collected by filtration, and the solid was washed twice with diethyl ether and dried under nitrogen to give 100 g of white crystals having a melting point of 83.3 ° C to 84.4 ° C (yield 73.4%). IR (Nujol mull) 1759 (ester carbonyl), 1684 (amide carbonyl) cm ⁻¹ . 1 H NMR (500 MHz, Acetone-d ₆ ) δ 4.592 (about triplet, 2H, J = 5.0 Hz, ring CH ₂ 0), 3.903 (about triplet, 2H, J = 5.0 Hz, ring CH ₂ N), 3.767 (t, 2H, J = 5.5 Hz, CH ₂ 0H), 3.597 (t, 2H, J = 5.5 Hz, chain CH ₂ N). ¹³ C NMR (500 MHz, D ₂ 0) δ 158.514 (ester C = O), 155.338 (amide C = O), 67.036 (ring CH ₂ 0), 60.399 (CH ₂ 0H), 51.034 (ring CH ₂ N) , 47.600 (chain CH ₂ N).

Example 2

Preparation of 4 (2-hydroxyethyl) morpholine-2,3-dione monomer at low temperature and high yield

4 (2-hydroxyethyl) morpholine-2,3-dione was prepared at a low temperature in the following manner. A 22 L five-necked round bottom flask equipped with a reflux condenser, nitrogen foamer, addition funnel, thermocouple and mechanical stirrer was charged with 3,000 g (20.53 mol) of diethyl oxalate and 2,000 ml of isopropyl alcohol. The solution was cooled to 0-5 [deg.] C. using an ice cold bath of ice and methanol. A solution of 2,160 g (20.53 mol) of diethanolamine dissolved in 2,000 ml of isopropyl alcohol was added via an addition funnel over a period of 5-6 hours. The reaction was exothermic. After the addition was completed, the mixture was left at room temperature overnight. The product was recovered by filtration. After air drying, 2,923 g of white crystals having the same characteristics as those of the compound prepared in Example 1 were obtained (yield 89.5%).

Example 3

Preparation of Polyisocyanate Resin Blocked with 4 (2-hydroxyethyl) morpholine-2,3-dione and diethylene glycol monobutyl ether

338 parts of Mondur® MR (methylene diphenyl diisocyanate, manufactured by Bayer Corp.), 113 parts of methyl isobutyl ketone and 0.07 parts of dibutyl tin dilaurate were charged into a suitable reaction vessel and dried A new blocked polyisocyanate crosslinked resin solution was prepared by heating to 37 ° C. under a nitrogen blanket. 269 parts of diethylene glycol monobutyl ether were slowly charged into the reaction vessel while maintaining the reaction mixture below 93 ° C. Thereafter, 142 parts of 4 (2-hydroxyethyl) morpholine-2,3-dione (prepared in Example 1) were charged into the reaction vessel and the reaction temperature was maintained below 93 ° C. The resulting mixture was maintained at 110 ° C. until infrared scanning showed that all of the isocyanates reacted. 5 parts butanol and 133 parts methyl isobutyl ketone were added to the reaction mixture. The obtained resin solution had 75% of content of a nonvolatile substance.

Example 4

Preparation of conventional crosslinked resin solution

317.14 parts of Mondur® MR (methylene diphenyl diisocyanate, manufactured by Bayer), 105.71 parts of methyl isobutyl ketone and 0.06 parts of dibutyl tin dilaurate were charged into a suitable reaction vessel and heated to 37 ° C. under a blanket of nitrogen. A double alcohol blocked polyisocyanate crosslinked resin solution was prepared. While maintaining the reaction mixture below 93 ° C., a mixture of 189.20 parts of diethylene glycol monomethyl ether and 13.24 parts of trimethylolpropane 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 3.17 parts of butanol and 64.33 parts of methyl isobutyl ketone were added. The obtained resin solution had 75% of content of a nonvolatile substance.

Example 5

Preparation of Chain Extended Polyepoxide Emulsions with Polyisocyanates containing 4 (2-hydroxyethyl) morpholine-2,3-dione

Epon® 828 (epoxy resin of diglycidyl ether of bisphenol A of epoxy equivalent 188, manufactured by Shell) 512 parts, 302 parts of bisphenol A, ethoxylated bisphenol A of hydroxyl equivalent 247 380 parts of Sinpak® 8009, manufactured by Milliken, 89 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., 852 parts of a polyisocyanate resin (prepared in Example 3) containing 4 (2-hydroxyethyl) morpholine-2,3-dione were added. At 107 ° C., 290 parts of diketamine (the reaction product of methyl isobutyl ketone and diethylenetriamine with a content of nonvolatile material of 73%) and 59 parts of methylethanolamine were added. The resulting mixture was left at 120 ° C. for 1 hour and dispersed in an aqueous medium of 1,250 parts of deionized water and 70 parts of methanesulfonic acid (70% methanesulfonic acid in deionized water). It was further diluted with 800 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 6

Polyepoxide Emulsion Chain Extended with Conventional Crosslinking Resin Solutions

EPON® 828 (epoxy resin of diglycidyl ether of bisphenol A of epoxy equivalent 188, manufactured by Shell Corporation) 520 parts, bisphenol A 151 parts, ethoxylated bisphenol A of hydroxyl equivalent 247 (new pack (registered trademark)) 8009, manufactured by Milliken Co., Ltd., 44 parts of xylene and 1 part of dimethylbenzylamine were charged into a suitable reaction vessel. The reaction mixture obtained was heated to 160 ° C. under a blanket of nitrogen and held 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., 797 parts of a conventional crosslinked resin (prepared in Example 4) were added. At 107 ° C., 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 an aqueous medium of 1,335 parts of deionized water and 61 parts of lactic acid (88% lactic 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 7

Preparation of Quaternization Agent

A quaternizing agent was prepared by adding 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. 118 parts of an aqueous solution of lactic acid (content of nonvolatile material 75%) was added followed by 39 parts of 2-butoxyethanol. The reaction mixture was stirred constantly at 65 ° C. for about 1 hour to form a quaternizing agent.

Example 8

Preparation of Pigment Grinding Developer

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 reaction. The pigment pulverizing developer was prepared by initiating. The exothermic reaction lasted for about 1 hour at 150 ° C to 160 ° C. The reaction mixture was then cooled to 120 ° C. and 496 parts of toluene diisocyanate semi-capped with 2-ethyl hexanol were added. The temperature of the reaction mixture was maintained at 110 ° C. to 120 ° C. for 1 hour, and 1,095 parts of 2-butoxyethanol were added, then the reaction mixture was cooled to 85 ° C. to 90 ° C., 71 parts of deionized water was added, and then a quaternizing agent was added. 496 parts (prepared above) were added. The temperature of the reaction mixture was maintained at 85 ° C to 90 ° C until the acid value became about 1.

Example 9

Preparation of Pigment Paste

Parts by weight Pigment Grinding Developer (Prepared in Example 8) 597.29 Deionized water 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 and then dispersed by filling the mixture with an Ager mill and grinding until it passed the Hegman test.

Example 10

Manufacture of Electro Coating Bath

Parts by weight Coating bath Ⅰ Coating bath Ⅱ Emulsion (prepared in Example 5) 1503.08 - Emulsion (prepared in Example 6) - 1503.08 Deionized water 2013.49 2013.49 Pigment Paste (Prepared in Example 9) 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.

The above components were mixed to prepare a cathode electrocoating bath. Thereafter, each electrolytic cell was ultrafiltration. The phosphate treated cold rolled steel sheet was electrocoated in each coating bath at 180 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. Each plate was then baked as shown below to check for proper curing and bake removal losses.

The test used to check for proper curing of the e-coat film at a particular baking temperature is to rub a cloth soaked with 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 decolorization of the fabric on the e-coat film indicated poor curing of the e-coat film.

The phosphate treated cold rolled steel sheet coated with coating bath I and baked at a metal temperature of 320 ° F. (160 ° C.) for 10 minutes did not exhibit a matt appearance. 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.

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. (182.22 ° C.) was 11%. For coating bath II, baking for 10 minutes at metal temperature 360 ° F. (182.22 ° C.) The removal loss rate (%) was 16%.

The test results are summarized in Table 3 below.

result Coating bath I Coating bath II Solvent resistance at 320 ° F (160 ° C) for 10 minutes No wear (excellent hardening) Matte appearance (hardening) 10 minutes bake removal loss at 360 ° F (182.22 ° C) 11% 16%

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 (15)

A binder of the epoxy-amine addition product, a blocked polyisocyanate crosslinker and an organic or inorganic acid that is a neutralizing agent for the epoxy-amine addition product, wherein the blocked polyisocyanate crosslinker is one blocked with a hydroxy functional morpholine dione blocking agent. An aqueous negative electrode electrocoating composition having the above isocyanate group. The electrocoating composition of claim 1, wherein the blocked polyisocyanate crosslinker is completely blocked with a morpholine dione blocking agent. The electrocoating composition of claim 1 wherein the blocked polyisocyanate is partially blocked with a morpholine dione blocking agent and the remaining isocyanate groups are blocked with conventional isocyanate blocking agents selected from the group consisting of saturated alkyl alcohols, ether alcohols, oximes and amides. . The electrocoating composition of claim 1 wherein the epoxy-amine addition product contains an amine selected from the group consisting of primary amines, secondary amines, ketimines, and mixtures thereof. The electrocoating composition of claim 1, wherein the morpholine dione blocking agent is N- (2-hydroxyethyl) morpholine-2,3-dione. The electrocoating composition of claim 1, wherein the morpholine dione blocking agent is represented by the following Chemical Formula 1. <Formula 1> In the above formula, R is selected from the group consisting of alkanols having 4 or less carbon atoms in the alkanol group. The electrocoating composition of claim 1 wherein the epoxy addition product comprises a polyepoxy hydroxy ether resin extended with dihydric phenol and reacted with an amine. A blocked polyisocyanate crosslinker wherein at least one isocyanate group is blocked with a hydroxy functional morpholine dione monomer and the remaining isocyanate group is blocked with any of morpholine dione blocking agents, ether alcohols or alkyl alcohols. The blocked polyisocyanate crosslinking agent of claim 8, represented by the following Chemical Formula 2. <Formula 2> Wherein R represents an aromatic, cycloaliphatic or aliphatic hydrocarbon radical, R ₁ is any of conventional polyisocyanate blocking agents such as aliphatic monoalcohols, ether alcohols or R ₂ , and R ₂ is represented by the formula Being a morpholine dione radical. <Formula 3> In the above formula, R ₃ is an alkyl group having 1 to 4 carbon atoms; n is a positive integer from 1 to 4. 10. The crosslinking agent of claim 9, wherein R is an aromatic radical and n is 1. The electrocoating composition of claim 1 further comprising 0 to 99% by weight of additional crosslinking agent relative to the total weight of the crosslinking component of the composition. (1) a coating comprising (a) a crosslinkable resin having an amine group neutralized with at least one acid in an aqueous medium, and (b) a crosslinking agent having at least one isocyanate group blocked with a hydroxy functional morpholine dione blocking agent Immersing the conductive substrate in the composition, (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. A substrate coated with the dried and cured composition of claim 1. The electrocoated substrate of claim 13, wherein the substrate is an OEM or industrial coating component. 15. The electrocoated substrate of claim 14, wherein the substrate is an automobile body or automobile part.