JP2005517781A - Aminic acid zwitterionic additive for cathodic electrodeposition composition - Google Patents

Abstract

The invention comprises a cathode comprising a binder of a polyisocyanate cross-linking agent blocked with (a) a resin for forming a cathode electroweldable film and (b) a non-hazardous non-air-contaminating compound such as an alkoxyalkanol or alkyl alcohol An improved aqueous cathodic electrodeposition composition comprising an electroweldable composition and a method for electrowelding of the composition, wherein the improvement is a reaction product of an amine acid and an alkyl glycidyl ether To 0.1% to 5.0% by weight of a water-miscible amic acid zwitterionic additive based on the weight of

Description

  The present invention relates to an electrodeposition composition having improved cure using a blocked isocyanate crosslinker blocked with a non-hazardous non-air polluting compound.

  Coating conductive substrates by electrowelding (also referred to as electrodeposition) is well known and is an important industrial process particularly used in the manufacture of automobiles and trucks. In the electrowelding of the primer, an article such as an automobile body or a truck body or parts thereof is immersed in an electrodeposition water bath of an electrodeposition composition containing an aqueous emulsion of a film-forming polymer. The article to be electrodeposited functions as an electrode that creates a current that passes between the article in contact with the aqueous emulsion and the counter electrode until a coating having the desired thickness is deposited on the article. In the cathodic electrodeposition method, the article to be coated is a cathode and the counter electrode is an anode. The article to be coated is immersed and passed through the bath for a period of time (time in the bath controls the thickness of the deposited film), after which the coated article is removed from the bath, rinsed with water, Baking produces a primer coating on the article.

  An aqueous emulsion of a film-forming polymer used in the cathodic electrodeposition method is also well known. The film-forming polymer is a polyepoxide that is chain-extended and formed into an adduct having an amine group, and the adduct is later neutralized with an acid and blended with a crosslinker such as a block polyisocyanate crosslinker. The electrodeposition water bath includes a film-forming polymer, a blocking cross-linking agent, a pigment paste or pigment dispersion, a flocculating solvent and other additives.

  It would be highly desirable to use a blocked isocyanate crosslinker with a non-hazardous, non-air-contaminant blocking agent that does not need to be recovered and recycled in some manner. Although such barriers are known, it is necessary to raise the baking temperature for the deposited electrodeposition composition during curing in order to remove these known barriers and thus activate the isocyanate crosslinking agent. And Although raising the bake temperature for small metal parts that are electrodeposited is fine, raising the bake temperature for car bodies and truck bodies presents a major problem. This is because such increases cause a significant increase in energy consumption and manufacturing costs. Use of blocking agents for isocyanate crosslinkers that are non-hazardous, non-air-contaminating, and that also allow car bodies and truck bodies to be baked at standard temperatures typically used in automobile and truck manufacturing processes Would be desirable.

U.S. Pat. No. 4,419,467

  The present invention comprises (a) a cathode electroweldable film-forming resin and (b) a polyisocyanate crosslinker binder blocked with a non-hazardous, non-air-contaminating compound such as an alkoxyalkanol or alkyl alcohol, An improved aqueous cathodic electrodeposition composition and method for electrodeposition of the composition, wherein the improvement is a reaction product of an amine acid and an alkyl glycidyl ether based on the weight of the binder. . Relates to compositions and methods comprising the use of 1-5.0% by weight of a water miscible amic acid zwitterionic additive.

  A typical automobile body or truck body is manufactured from sheet steel or a plastic or composite substrate. When steel is used, the steel is first treated with an inorganic rust inhibitor compound such as zinc phosphate or iron phosphate, after which the primer coating is generally applied by electrowelding. Plastic substrates and composite substrates can also be electrodeposited with a primer as long as the substrate is first made conductive. Typically, the electrodeposition primer consists of an epoxy-modified resin that is cross-linked with polyisocyanate and is deposited by a cathodic electrowelding method. Optionally, a second primer may be deposited on the electro-welded primer, usually by spraying, to provide a better appearance and / or improved adhesion of the basecoat or monocoat to the primer. Is possible. A monocoat of a pigmented paint composition can then be deposited later, but a preferred paint composition includes a pigmented base coat with a clear top coat deposited thereon. Usually, each paint is cured by baking at a high temperature after being applied. It is generally known that a clear topcoat can be applied over a basecoat and that both paints can be cured together at elevated temperatures.

  The novel cathodic electrodeposition composition of the present invention comprises an acid neutralized polyepoxyamine adduct resin for forming a cathodic electroweldable film of 30 to 70 wt. Contains 70 to 30% by weight of a blocked polyisocyanate blocked with an agent. The electrodeposition composition of the present invention contains 0.1 to 5.0% by weight of a water-miscible amic acid zwitterionic additive based on the weight of the binder, which is a reaction product of an amino acid and an alkyl glycidyl ether. By introducing, the composition has the advantage of curing at conventional baking temperatures of 125-175 ° C. Preferably 0.5-2.0% by weight of water miscible amic acid zwitterionic additive is introduced into the composition, based on the weight of the binder.

  The amic acid zwitterion has the following formula:

In the formula, R is an aromatic group or an aliphatic group, and R ¹ is an aliphatic group having 1 to 25 carbon atoms. The amic acid zwitterionic additive is a reaction product of an amic acid and an equimolar amount of alkyl glycidyl ether.

Typically, the amic acid has the formula HOOC-R-NH _{2 where} R is an aliphatic or aromatic group. Typical amine acids that can be used are paraaminobenzoic acid, glycine, alanine and valine.

  The alkyl glycidyl ether has the following formula:

R ¹ is preferably an aliphatic group having 1 to 25 carbon atoms and an epoxy equivalent of 200 to 500. A preferred type of alkyl glycidyl ether has an equivalent weight of 300-325. One typical useful alkyl glycidyl ether is "Araldite" (R) DY025 from Ciba Specialty Chemicals.

  The aminic acid zwitterionic additive dissolves the amine acid in a solvent such as 2-butoxyethanol, then blends the dissolved acid with the alkyl glycidyl ether, and then blends the blended composition at 80-120 ° C. Prepared by reacting for 5 to 2.0 hours to form an additive. Any conventional solvent can be used as long as the ingredients and the resulting amic acid zwitterionic additive are dissolved.

  Typically, polyepoxyamine adduct emulsions are used in cathodic electrodeposition compositions. The adduct is neutralized with an acid to form a water-soluble or water-dispersible product and blended with a crosslinker. Generally, a metal catalyst such as dibutyltin oxide is added to the electrodeposition composition.

  Useful polyepoxyamine adducts are generally disclosed in US Patent Publication (Patent Document 1). This patent is incorporated herein by reference.

  Typical epoxy resins used to form the adduct have an epoxy equivalent weight of about 100 to 2,000. Typically useful epoxy resins are “Epon” ® 828, “Epon” ® 1001 and “Epon” having epoxy equivalents of 188, 500 and 650, respectively. It is an epoxy resin of diglycidyl ether such as (registered trademark) 1002F and bisphenol A. Other epoxy resins that can be used are aliphatic epoxy resins such as neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. is there. These epoxy resins can be chain extended with polyphenols such as bisphenol A, hydrogenated bisphenol A, ethoxylated bisphenol A and cyclohexanediol, or other cyclic or alicyclic polyols.

  Amines such as primary amines, secondary amines and tertiary amines, monoamines, polyamines and hydroxyamines can all be used to form the cationic groups of the adduct. Typically, ethylenediamine, diethylenetriamine, piperidine, ethanolamine, methylethanolamine and diethanolamine are used. Diketimine, which is a reaction product of diethylenetriamine and methyl isobutyl ketone, can also be used.

  Typical acids that can be used to neutralize the polyepoxyamine adduct are organic acids such as lactic acid, acetic acid, carbonic acid and formic acid, and other acids such as phosphoric acid, sulfamic acid and sulfonic acid.

  Isocyanate crosslinking agents used include aliphatic, cycloaliphatic and aromatic polyisocyanates such as hexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluene diisocyanate, methylene diphenyl diisocyanate, polymeric methylene diphenyl diisocyanate and isocyanurate of hexamethylene diisocyanate. This is well known in the art.

  The isocyanate crosslinking agent reacts with the blocking agent to prevent the crosslinking action from occurring in the electrodeposition bath when the composition is electrowelded. When the coating is cured during baking, the isocyanate is not blocked and the resulting coating or finish is crosslinked. The blocking agents used are non-hazardous non-air-contaminating agents such as alkoxyalkanols, for example alkoxypropanols such as 2-methoxypropanol, 2-butoxypropanol and 2-propoxypropanol. Alkyl alcohols having 1 to 3 carbon atoms in an alkyl group such as methanol, ethanol, propanol, and isopropanol can also be used.

  Without the amic acid zwitterionic composition, the above crosslinker could not be used under conventional baking temperatures of 125-175 ° C. This is because these blocking agents will not be non-blocking at these temperatures.

  The metal catalyst is present in the cathodic electrodeposition composition in an amount of 0.1 to 2.0% by weight, based on the weight of the binder. Typically useful catalysts are dibutyltin oxide, dibutyltin dilaurate and alkyltin diacetylacetonate.

  The pigment is introduced into the cathodic electrodeposition composition by forming a pigment paste, and the pigment paste is cathodic electrodeposition composition such as cathodic polyepoxyamine adduct and blocking cross-linking agent, aggregating solvent, water and other additives. Later blended with other ingredients. The pigment paste is prepared by pulverizing a pigment in a pigment dispersant or dispersing the pigment in the pigment dispersant. Optionally, other ingredients such as wetting agents, surfactants and defoamers are added. Grinding continues until a Hegman grinding gauge reading of about 6-8 is reached. The pigment paste or dispersant is generally used in an amount of 1 to 15% by weight, based on the weight of the binder of the electrodeposition composition.

  Typical pigments used in the cathodic electrodeposition composition include titanium dioxide, carbon black, iron oxide and clay. Pigments with high surface area and oil absorption should be used with caution as they can have undesirable effects on the fusion and flow of the electro-deposited coating.

  The cathode electrodeposition composition of the present invention can contain any raw material such as a wetting agent, a surfactant and a defoaming agent. Examples of surfactants and wetting agents include alkyl imidazoles and acetylenic alcohols. When these optional ingredients are present, they comprise 0.1-2.0% by weight of the binder solids of the composition.

  Optionally, a plasticizer can be used to facilitate flow. Examples of useful plasticizers are high boiling water immiscible materials such as ethylene oxide adducts or propylene oxide adducts of bisphenol A nonylphenol. The plasticizer is usually used at a level of 0.1 to 15% by weight, based on the binder solids.

  The electrodeposition composition is an aqueous dispersion. The term “dispersion” as used within this context is considered to be a two-phase translucent or opaque aqueous resinous binder system in which the binder is in the dispersed phase and water is in the continuous phase. The average particle size diameter of the binder phase is about 0.1 to 10 micrometers, preferably less than 5 micrometers. The concentration of the binder in the aqueous medium is not critical and 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. The concentration of the composition shipped to the manufacturing site is diluted with water to provide an electrodeposition bath having a binder solids content in the range of 10-30% by weight.

  In addition to water, the aqueous medium of the cathodic electrodeposition composition contains a coalescing solvent. Useful coalescing solvents include hydrocarbons, alcohols, polyols and ketones. Preferred flocculating solvents include ethylene glycol monobutyl ether and monohexyl ether and propylene glycol phenyl ether. The amount of flocculating solvent is not unduly critical and is generally between 0.1 and 15% by weight, preferably 0.5 to 5% by weight, based on the total weight of the binder solids of the composition.

  The conditions for electro-deposition of the new composition are similar to those typically used in cathodic electro-deposition processes. The applied voltage is typically between 50 and 500 volts, and the current density is between 0.5 and 15 amperes / square foot, which tends to decrease during electrodeposition as the insulating film is formed. is there. Typically, the composition is cured by baking at an elevated temperature of 125-175 ° C. for about 5-30 minutes.

  The following examples illustrate the invention. Unless otherwise indicated, all parts and percentages are on a weight basis.

(Example 1)
Preparation of chain-extended polyepoxide aqueous emulsion 453 parts “Epon” ® 828 (epoxy resin of diglycidyl ether of bisphenol A having an epoxy equivalent of 188), 130 parts bisphenol A, 163 parts “Synfac” ® 8009 (ethoxylated bisphenol A having a hydroxyl equivalent weight of 248), 39 parts of xylene and 0.9 parts of dimethylbenzylamine were charged to the reaction vessel. The resulting reaction mixture was heated to 160 ° C. under a nitrogen seal and held at this temperature for 1 hour. 1.5 parts dimethylbenzylamine was added and the mixture was held at 147 ° C. until an epoxy equivalent of 1121 was reached. 647 parts of a blocked isocyanate crosslinker solution (2-methoxypropanol block “Mondur” ® MR, polymeric methylene diphenyl diisocyanate from Bayer with a solids content of 75%) was added. When the reaction mixture temperature cooled to 107 ° C., 49 parts diketimine (reaction product of diethylenetriamine and methylisobutylketone at 72.7% solids) and 43 parts methylethanolamine were added. The resulting mixture was held at 120 ° C. for 1 hour. In an aqueous solution containing 60 parts 70% methanesulfonic acid, 21 parts surfactant mixture (120 parts alkylimidazoline, 120 parts acetylenic alcohol and 120 parts butoxyethanol) and 2008 parts deionized water. The resin solution was emulsified. The resulting emulsion was stripped to remove the organic solvent. The emulsion had a solids content of 38%.

(Preparation of dent prevention additive)
A dent prevention additive was prepared by charging the following ingredients into a suitable reaction vessel. 2322 parts of “Jeffamine” ® D-2000 (polyoxypropylenediamine with 1000 amine equivalents from Huntsman Company) and 188 parts of “Epon” (registered) Trademark) 828 (epoxy resin of diglycidyl ether of bisphenol A having an epoxy equivalent of 188) was added under a nitrogen atmosphere and heated to 90 ° C., then 859 parts by weight in 345 parts by weight of 2-butoxyethanol. A solution of “Epon” ® 1001 (epoxy resin of diglycidyl ether of bisphenol A having an epoxy equivalent weight of 500) was added. The resulting reaction mixture was dispersed by combining 68 parts acetic acid and 5354 parts by weight deionized water.

(Preparation of amic acid zwitterionic additive)
108 parts of para-aminobenzoic acid were dissolved in 354 parts of 2-butoxyethanol at 115 ° C. The temperature was cooled to 93 ° C. and 246 parts “Araldite” DY025 (an alkyl glycidyl ether having an epoxy equivalent weight of about 312) was slowly added to keep the temperature between 93-104 ° C. The resulting mixture was held at 100 ° C. until the combined amine and epoxy equivalents were equal to 898. The resulting resin was emulsified in 300 parts of deionized water and the resin had a solids content of 35%.

(Preparation of conventional quarterning agent)
A quartering agent was prepared by adding 87 parts dimethylethanolamine to 320 parts 2-ethylhexanol semi-encapsulated toluene diisocyanate at room temperature in a reaction vessel. An exothermic reaction occurred and the reaction mixture was stirred at 80 ° C. for 1 hour. Thereafter, 118 parts of a lactic acid aqueous solution (nonvolatile content: 75%) was added, followed by 39 parts of 2-butoxyethanol. With constant agitation, the reaction mixture was held at 65 ° C. for about 1 hour to produce the quartering agent.

(Preparation of pigment grinding vehicle)
710 parts "Epon" (R) 829 (epoxy resin of diglycidyl ether of bisphenol A having an epoxy equivalent weight of 190-203) and 210 parts of bisphenol A are charged into a suitable reaction vessel under a nitrogen seal. Thus, a pigment grinding vehicle was prepared and heated to 150 to 160 ° C. to initiate an exothermic reaction. The exothermic reaction was continued for about 1 hour at the above temperature. The reaction mixture was then cooled to 120 ° C. and 496 parts 2-ethylhexanol semi-encapsulated toluene diisocyanate was added. The temperature of the reaction mixture is held at 110-120 ° C. for 1 hour, after which 1095 parts 2-butoxyethanol are added, after which the reaction mixture is cooled to 85-90 ° C. and 71 parts deionized water is added. Thereafter, 496 parts of the quartering agent prepared above were added. The temperature of the reaction mixture was held at 85-90 ° C. until an acid number of about 1 was obtained.

(Preparation of pigment paste)
A pigment paste was prepared by putting the following raw materials into a suitable mixing container.

  The above ingredients were mixed until a homogeneous mixture was formed, then charged into a sand mill and ground until a Hegman reading of 7 or higher was obtained. The resulting pigment paste had a nonvolatile content of 50%.

  Electrodeposition baths I and II were prepared by combining and mixing the above ingredients. The pH of each bath was adjusted to 6.0-6.05. The bath solids were 20% and the bath pigment to binder ratio was 15-100. The temperature of each of the baths was maintained at about 33 ° C. during the electrodeposition process. Two sets of diphosphate-containing steel panels were electrodeposited separately in each bath at 200 volts to obtain a coating having a wet film thickness of 0.92 mil (23.3 microns) on each panel. The panel was baked at 166 ° C. for 17 minutes to produce a smooth film. The cured coating on each panel was tested by the methyl ethyl ketone double friction test, where the double friction for test purposes included a fabric soaked in methyl ethyl ketone rubbing the panel surface twice. Panels coated in bath I that did not contain the amic acid zwitterionic additive only withstood two double rubs. In contrast, panels coated in Bath II that contained the amic acid zwitterionic additive (invention) withstood 300 double rubs and showed a significant improvement in cure.

Claims (10)

(A) a cathode electroweldable film-forming resin and (b) a binder of a polyisocyanate crosslinking agent blocked with a non-hazardous non-air-contaminating compound, and a reaction product of an amine acid and an alkyl glycidyl ether. An aqueous cathode electrodeposition composition comprising 0.1 to 5.0% by weight of a water-miscible amic acid zwitterionic additive based on the weight of the binder.   The aqueous cathodic electrodeposition composition according to claim 1, wherein the non-hazardous non-air-contaminating compound is selected from the group consisting of alkoxyalkanols and alkyl alcohols. The amic acid zwitterionic additive comprises an amic acid of formula HOOC-R-NH ₂ and the following formula:

3. A reaction product of an alkyl glycidyl ether (wherein R is selected from the group consisting of an aliphatic group and an aromatic group, and R ¹ is an aliphatic group). The aqueous cathode electrodeposition composition described. The amic acid zwitterionic additive has the following formula

The aqueous cathode electrodeposition composition according to claim 2, wherein R is selected from the group consisting of an aliphatic group and an aromatic group, and R ¹ is an aliphatic group.   The aqueous cathodic electrodeposition composition according to claim 3, wherein the amino acid is composed of paraaminobenzoic acid, and the alkyl glycidyl ether has an epoxy equivalent of 200 to 500.   The aqueous cathodic electrodeposition composition according to claim 2, wherein the non-hazardous non-air-contaminating compound is alkoxypropanol.   3. The aqueous cathode electrodeposition composition according to claim 2, wherein the non-hazardous non-air polluting compound is an alkyl alcohol having 1 to 3 carbon atoms in the alkyl group.   The cathode electroweldable film-forming resin contains a polyepoxyamine adduct neutralized with an acid selected from the group consisting of formic acid, acetic acid, lactic acid, phosphoric acid, sulfamic acid, sulfonic acid and mixtures thereof. The aqueous cathode electrodeposition composition according to claim 2, wherein Based on the weight of the binder, wherein the binder comprises a polyepoxyamine adduct neutralized with an acid selected from the group consisting of formic acid, acetic acid, lactic acid, phosphoric acid, sulfamic acid, sulfonic acid and mixtures thereof. 30 to 70% by weight of the cathode electroweldable film-forming resin,
30 to 70, based on the weight of the binder, blocked with a non-hazardous, non-air-contaminating compound selected from the group consisting of alkoxy alkanols and alkyl alcohols having 1 to 3 carbon atoms in the alkyl group Weight percent polyisocyanate crosslinker,
The water-miscible amic acid zwitterionic additive comprises an amic acid of formula HOOC-R-NH ₂ and

(Wherein R is selected from the group consisting of aliphatic groups and aromatic groups, and R ¹ is an aliphatic group having ¹ to 25 carbon atoms). The aqueous cathode electrodeposition composition according to claim 1, wherein:   A method of cathodic electrodeposition onto a conductive object, comprising: (1) immersing the object in a bath of the electrodeposition composition according to claim 1; and (2) cathodic electrodepositing a film on the object. And (3) removing the coated object; and (4) baking the object at 125 to 175 ° C. to form a continuous film on the object.