MXPA99007652A - Cathodic electrocoating compositions containing an anticrater agent - Google Patents

Abstract

Se describe una composición mejorada de electrorrecubrimiento acuoso que contiene un agente antiformación de cráteres el cual es un producto de reacción de la polioxialquilendiamina y el glicidoxialquilalcoxisilano, el cual es hidrolizado y tiene un peso molecular promedio en número de aproximadamente 700-5,000;se forman acabados electrodepositados que tienen una reducción significativa en los cráteres y son acabados lisos y uniformes.

Description

COMPOSITIONS OF CATHODIC ELECTRORRECUBRICATION CONTAINING AN AGENT AGAINST THE FORMATION OF CRATTERS BACKGROUND OF THE INVENTION This invention is directed to a cathodic electrocoat composition and in particular to a cathodic electrocoat composition containing an anti-cratering agent which significantly reduces craters and provides the smoothness or smoothness of an electrodeposited film of the composition. The coating of electroconductive substrates by an electrodeposition process, also called an electrocoating process, is a well known and important industrial process. The electrodeposition of the preachers to automobile substrates is widely used in the automotive industry. In this process, a conductive article, such as an automobile body or a car part, is immersed in a bath of a coating composition of an aqueous emulsion of the film-forming polymer and acts as a REF .: 30794 electrode in the electrodeposition process. An electric current is passed between the article and a counter electrode in electrical contact with the aqueous emulsion, until a desired coating is deposited on the article. In a cathodic electrorecovery process, the article to be coated is the cathode and the opposite electrode is the anode. Resin compositions used in the bath of a typical cathodic electrodeposition process are also well known in the art. These resins are typically made from polyepoxide resins that have been chain extended and then an adduct or addition complex is formed to include amine groups in the resin. The amine groups are typically introduced through the reaction of the resin with an amine compound. These resins are mixed with a crosslinking agent and then neutralized with an acid to form an aqueous emulsion which is usually referred to as a main emulsion. The main emulsion is combined with a paste of pigment, coalescing solvents, water, and other additives to form the electrocoating bath. The electrocoating bath is placed in an insulated tank containing the anode. The article to be coated is the cathode and is passed through the tank containing the electrodeposition bath. The thickness of the coating that is deposited on the article that is electrocoated, is a function of the characteristics of the bath, the electrical operation characteristics of the tank, the immersion time, and the like. The resulting coating article is removed from the bath after a set period of time and is rinsed with deionized water. The coating on the article is typically cured in an oven at sufficient temperature to produce a crosslinked finish on the article. Cationic electrocoat compositions, resin compositions, coating baths and cathodic electrodeposition processes are described in Jarabek et al., US Patent No. US 3,922,253 issued November 25, 1975; Wismer et al., US Patent No. US 4,419,467 issued December 6, 1983; Belanger, US Patent No. US 4,137,140 issued January 30, 1979 and Wismer et al., US Patent No. US 4,468,307 issued August 25, 1984. A constant problem with the cathode electrodecoating compositions has been the presence of craters in the finished cured. An additive or agent is necessary for electrocoating compositions, so that crater-free, smooth and uniform finishes are formed in electrodeposition and cure. Chung et al., US Patent 5,356,960 issued October 18, 1994, shows an anti-crater additive that forms a crater-free finish, smooth and uniform. However, when this additive is used in an electrocoating composition that is baked in an indirect gas furnace after application to a metal substrate such as a car or truck body, this anti-crater additive migrates very rapidly to the surface of the gas. the electrocoating composition during baking. Any sizing compositions applied on such a surface, containing polymeric melamine crosslinking agents, adhere poorly to the electrocoating composition and therefore, failure by adhesion of any top coat applied on the squeegee is readily apparent. An anti-crater additive is needed which will not migrate towards the surface of the electrocoating composition deposited during baking, and should not adversely affect other properties such as the hiding power of the electrocoating bath, the curing of the deposited coating or the film properties of the finish. resulting.

BRIEF DESCRIPTION OF THE INVENTION An improved, aqueous cathodic electrocoating composition having a binder of an epoxy-amine adduct and a block polyisocyanate cross-linking agent; wherein the improvement is the use of an anti-cratering agent which is a silane-terminated reaction product of the polyoxyalkylene diamine and a glykoxy-alkyl-alkoxy-silane which is hydrolyzed and the anti-crater agent has a of average molecular weight of approximately 700-5,000 determined by Gel Permeation Chromatography (GPC) using polystyrene as the standard.

DESCRIPTION D: CARVING OF THE INVENTION The new anti-crater or anti-crater agent is easily incorporated into the electrocoating composition by dispersing it with a non-ionic surfactant in water and then adding it to an aqueous electrocoating composition, since it is compatible with the other components of the composition . The anti-crater agent remains stable in the composition and electrocoating bath for extended periods of time under conventional bath operating conditions, since it is not reactive with the other constituents in the composition. The anti-crater agent significantly reduces and frequently eliminates craters in electrodeposited coatings, and forms smooth and uniform finishes that do not migrate to the surface when baking the finish. Also, the additive does not adversely affect other properties of the electrocoating bath or the finishes of the electrocoating composition. In addition, the cratering antiforming agent can be used as an agent for the control of rheology to improve the protection of the edges of an electrodeposited finish. The anti-crater additive is used in an electrocoating composition, in an amount sufficient to significantly reduce or eliminate cratering in the electrodeposited finish. In general, the antro-tracer agent is used in the electrocoating composition at a level of at least 0.5% by weight, based on the total weight of the binder solids in the electrocoating composition and is preferably used at a level of approximately 0.5-10% by weight. More preferably, about 1-5% by weight of the anti-crater agent is used. The binder of the electrocoating composition is typically a mixture of an epoxyamine adduct and a block polyisocyanate crosslinking agent. The anti-cratering agent is prepared by reacting a polyoxyalkylene diamine with the glycidoxy-alkyl-alkoxy-silane in a molar ratio of 1: 2 to form a cratering antiforming agent having terminal silane groups. These constituents are reacted at a temperature of about 50 to 130 ° C for about 1 to 5 hours until there is no residual epoxy present, and subsequently it is hydrolyzed. The anti-crater agent has a number average molecular weight of about 700-5,000. The polyoxyalkylene diamine used to form the anti-crater agent has 2-4 carbon atoms in the alkylene group and is preferably the polyoxypropylene diamine having an average number-average molecular weight. of about 230-3,000, preferably 1,500-2,500 such as Jeffamine D-2000® having a number average molecular weight of 2000, available from Huntsman Corporation. Another polyoxyalkylene diamine that can be used is polyoxyethylene diamine having a similar molecular weight. Typically useful glycoxyalkylalkoxysilanes have the formula wherein R is methyl, ethyl, or a mixture of methyl and ethyl and n is 1-3. Typical silanes are gamma-glycidoxypropyl trimethoxysilane, gamma-glycidoxyethyl trimethoxysilane, gamma-glycidoxymethyl trimethoxysilane, gamma-glycidoxymethyl triethoxysilane, gamma-glycidoxyethyl triethoxysilane, gamma-glycidoxypropyltriethoxysilane. The gamma-glycidoxypropyltrimethoxysilane is preferred to form a high quality cratering antiforming agent. The anti-cratering agent can be added to the electrocoating composition almost at any time. This can be added to the main emulsion, or the anti-crater agent is mixed in the bath with a non-ionic surfactant and an acid such as lactic acid, and dispersed in water until the hydrolysis of the silane group to silanol groups is complete, and then added to the electrocoating composition as indicated above. The anti-crater agent after the complete hydrolysis has the following structural formula: OH OH HH (OH) 3-Si- (CEZ) nO-CH-CH-CHi-N- (ORa) mN-CH2-CH-CH2-0- (CH2) "-Si- (OH) 3 where n is 1 -3 and m is 5-40 and R is an alkyl group having 2-4 carbon atoms. The most main emulsions used in an electrocoating composition comprise an aqueous emulsion of a binder of an epoxyamine adduct mixed with a crosslinking agent which has been neutralized with an acid to form a water soluble product. The anti-crater agent is potentially usable with a variety of different cathodic electrocoating resins, but the preferred resin is the typical epoxy-amine adduct of the prior art. These resins are generally described in U.S. Patent No. 4,419,467 which is incorporated by reference herein. Typical acids used to neutralize the epoxy-amine adduct to form the water-dispersible cationic groups are lactic acid, acetic acid, formic acid, sulfamic acid, alkanol phonic acids, such as methanesulphonic acid and the like. Preferred crosslinkers for the above resins are also well known in the prior art. These isocyanates are aliphatic, cycloaliphatic and aromatic isocyanates such as hexamethylene diisocyanate, cyclohexanmethylene diisocyanate, toluene diisocyanate, methylenediphenyl diisocyanate and the like. These isocyanates are pre-reacted with a blocking agent such as oximes, alcohols, or caprolactams which block the isocyanate functional group, for example, the cross-linking functional group. After heating, the blocking agents are separated, whereby a reactive isocyanate group is provided and cross-linking occurs. Isocyanate and blocking crosslinking agents are well known in the prior art and are also described in the aforementioned US Patent No. 4, 19, 467. The cathodic binder of the epoxy-amine adduct and the blocked isocyanate are the resinous ingredients major in the electrocoating composition and are usually present in amounts of about 30 to 50% by weight solids of the composition. To form an electrocoating bath, the solids are generally reduced with an aqueous medium. In addition to the binder resin described above, the electrocoating composition usually contains pigment which is incorporated into the composition in the form of a pigment paste. The pigment paste is prepared by grinding or dispersing a pigment in a grinding vehicle and optional ingredients, such as wetting agents, surfactants, and defoamers. Any of the pigment grinding vehicles that are well known in the art can be used, or the anti-crater agent of this invention can be used. After grinding, the particle size of the pigment should be as small as practical, in general, the particle size is about 6 to 8 using a Hegman milling calibrator. The pigments which are used in this invention include titanium dioxide, basic lead silicate, strontium chromate, carbon black, iron oxide, clay and the like. Pigments with high surface areas and oil absorbencies should be used judiciously, because these can have an undesirable effect on the coalescence and electrodeposited coating flow.

The proportion of the pigment to binder, by weight is also important and should preferably be less than 0.5: 1, more preferably less than 0.4: 1, and usually from about 0.2 to 0.4: 1. It has been found that the higher weight proportions of pigment to binder adversely affect coalescence and flow. The coating compositions of the invention may contain optional ingredients, such as wetting agents, surfactants, defoamers, and the like. Examples of surfactants and wetting agents include alkylimidazolines such as those available from Ciba-Geigy Industrial Chemicals as "Amine C", acetylenic alcohols available from Air Products and Chemicals as "Surfynol 104". These optional ingredients, when present, constitute from about 0.1 to 20 weight percent of the binding solids of the composition. Optionally, plasticizers can be used to promote the flow. Examples of useful plasticizers are water-immiscible, high-boiling materials, such as ethylene or propylene oxide adducts of nonylphenols or bisphenol A. Plasticizers are usually used at levels of about 0.1 to 15 weight percent of the resin solids. The electrocoating composition of this invention is an aqueous dispersion. The term "dispersion" as used within the context of this invention is believed to be a two-phase aqueous, translucent or opaque resinous binder system in which the binder is in the dispersed phase and the water is the continuous phase. The average particle size diameter of the binder phase is about 0.1 to 10 microns, preferably less than 5 microns.The concentrations of the binder in the aqueous medium are generally not critical, but ordinarily the largest portion of the aqueous dispersion is water The aqueous dispersion usually contains from about 3 to 50 percent, preferably from 5 to 40 percent by weight of binder solids.The aqueous binder concentrates which are to be further diluted with water, when added to an electrocoating bath, they generally have a range of binding solids of 10 to 30 weight percent.

The following example illustrates the invention. All parts and percentages are on a weight basis, unless otherwise indicated.

EXAMPLE Preparation of Antriatrater Agent The antrotransetting agent was prepared by loading 996.5 parts of Jeffamine D2000® (polyoxypropylene diamine having a number-average molecular weight of 2000 and an amine equivalent of 996.5) and 236 parts of gamma-glycidoxypropyl trimethoxysilane. The reaction mixture was heated to about 59 ° C until the epoxy equivalent weight was greater than 40,000.

The resulting adduct was then dispersed by the combination of 35 parts of acetic acid and 4,900 parts of deionized water and agitated until there was complete hydrolysis of the silane groups to silanol groups. The resulting adduct solution had a non-volatile content of 20%.

Preparation of Extended Chain Polyepoxide Solution The following ingredients were loaded into a suitable reaction vessel: 1478 parts of Epon 828® (diglycidyl ether epoxy resin of bisphenol A having an epoxide equivalent weight of 188; (427 parts of bisphenol A; 533 parts of bisphenol To ethoxylate having a hydroxyl equivalent weight of 247 (Synfac 8009®) and 121 parts of xylene, the resulting reaction mixture was heated to 160 ° C under nitrogen atmosphere and maintained at room temperature for 1 hour. portions of dimethyl ilbenzylamine and the mixture was maintained at 147 ° C until an epoxy equivalent weight of 1050 was obtained. The reaction mixture was cooled to 98 ° C and 168 parts of diketimine (reaction product of diethylenetriamine and methyl isobutylcetone having a non-volatile content of 72.27%) and 143 parts of methanolamine The resulting mixture was kept at 120 ° C for 1 hour and then 727 parts of methyl isobutyl ketone were added. The resulting sine had a non-volatile content of 75%.

Preparation of the Crosslinking Resin Solution A solution of polyisocyanate crosslinking resin, blocked with alcohol, was prepared by charging 317.14 parts of PAPI 2027® (methylenediphenyl diisocyanate), 47.98 parts of methyl isobutyl ketone and 0.064 parts of dibutyltin dilaurate in a suitable reaction vessel and heated at 37 ° C under a nitrogen atmosphere. A mixture of 323.10 parts of diethylene glycol monobutyl ether and 13.04 parts of trimethylolpropane was slowly charged into the reaction vessel while maintaining the reaction mixture below 93 ° C for an additional hour until essentially all the isocyanate had reacted, as indicated by the infrared scan of the reaction mixture. 2.30 parts of butanol and 167.37 parts of methyl isobutyl ketone were added. The resulting resin solution had a non-volatile content of 75%.

Preparation of the Quaternization Agent The quaternizing agent was prepared by the addition of 87 parts of dimethylethanolamine to 320 parts of toluene diisocyanate hemien casked with ethylhexanol, in the reaction vessel at room temperature. An exothermic reaction occurred and the reaction mixture was stirred for an additional hour at 80 ° C. Then 118 parts of an aqueous lactic acid solution (75% non-volatile content) were added followed by the addition of 39 parts of 2-butoxyethanol. The reaction mixture was maintained for about 1 hour at 65 ° C with constant stirring to form the quaternizing agent.

Preparation of Pigment Grinding Vehicle The pigment grinding vehicle was prepared by loading 710 parts of Epon 829® (diglycidyl ether of bisphenol A having an epoxide equivalent weight of 193-203) and 290 parts of bisphenol A in a suitable vessel under a nitrogen atmosphere and heated to 150-160 ° C to initiate an exothermic reaction. The exothermic reaction was continued for approximately one hour at 150-160 ° C. The reaction mixture was then cooled to 120 ° C and 496 parts of the hemolyzed-toluene diisocyanate were added with 2-ethylhexanol. The temperature of the reaction mixture was maintained at 110-120 ° C for one hour, followed by the addition of 1095 parts of 2-butoxyethanol, the reaction mixture was then cooled to 85-90 ° C and then 71 parts of deionized water was added followed by the addition of 496 parts of quaternizing agent (prepared above) . The temperature of the reaction mixture was maintained at 85-90 ° C until an acid value of about 1 was obtained.

I. Preparation of Emulsion Parts in Weight Extended Chain Polyepoxide Solution (prepared above) 1255.31 Crosslinking resin solution (prepared above) 805.85 Surfactant "13.62 Lactic acid 27.24 Deionized water 1897.9S Total 4000.00 1Surfactant - 120 parts of Amine® C from Ciba Geigy, 120 parts of acetylenic alcohol available as Surfynol® 104 from AirProducts and Chemicals, Inc., 120 parts of 1-butoxyethanol, 221 parts of deionized water and 19 parts of glacial acetic acid.

The extended chain polyepoxide solution, the crosslinking resin solution, the surfactant and the lactic acid were mixed perfectly. The deionized water was then added under agitation. The content of non-volatile materials in emulsion was adjusted to 36% with the necessary amount of deionized water. The emulsion was kept under stirring until the methyl isobutyl ketone had evaporated.

II. Preparation of Pigment Paste Parts in Weight Pigment Grinding Vehicle (prepared above) 812 Deionized water 1660 Pigment of titanium dioxide 1068 Pigment of aluminum silicate 212 Pigment of lead silicate 92 Pigment of carbon black 32 Oxide of dibutyl zinc 124 Total 4000.00 The above ingredients were mixed until a homogeneous mixture was formed in a suitable mixing vessel. They were then dispersed by loading the mixture into a sand mill and then crushing until a Hegman reading of seven or greater was obtained.

I I I Preparing the Baths for Electrorrecovery I and I I Parts by weight Bathroom I Bathroom II Emulsion (prepared above) 1636 1569 Deionized water 1926 1913 Pigment paste (prepared above) 398 398 Antritrratter agent (prepared above) 40 120 Total 4000 4000 A cationic electrodecoating bath I and I I was prepared by mixing the above ingredients. Each bath was then ultrafiltered. Each bath was electrocoated at 250-270 volts to obtain 22.86 - 25.4 microns (0.9 - 1 thousandth of an inch). The ASPP blow crater test is used to test each bath. The crater resistance was rated according to the following rating scale of A-E: A - 0-10% defects B - 11-20% defects C - 21-40% defects D - 41-80% defects E - Greater than 80% defects The crater resistance rating for Baths I and II was A. An electrocoating bath identical to Bath I above was prepared, except that the anti-crater agent was replaced by a conventional anti-crater agent, which is Jeffamine's reaction product. ® 2000 and Epon® 1001, which are epoxy resins, and the crater resistance of this bath was tested as described above by using the ASPP blow-crater test. The crater resistance rating for this panel was E, which is substantially lower than the panels coated in Baths I and II, which contained the antracritic agent of the present invention. In order to measure the corrosion resistance of the edge, the blade knives (10 x 12 cm) were electrocoated in the I and II Baths at 250 volts and turned at 182 ° C (metal temperature) for 10 minutes. The blade knives were then exposed to saline dew for 7 days. The number of oxidation spots or mildew on each blade was counted by observing the blades under a microscope. The knives of Bath I had 100-120 spots of oxidation, while the blades of Bath II had 20-40 spots of oxidation, which shows that Bath II, which contained three times the amount of anti-crater agent, provided better protection against corrosion, on the edge.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. An improved cathodic electrocoating composition, comprising an aqueous carrier having dispersed therein a film-forming binder comprising an epoxy-amine adduct and a blocked polyisocyanate cross-linking agent; characterized by the improvement because it consists of a crater or anti-crater anti-cracking agent consisting of a polyoxyalkylene diamine and gamma-glycidoxy alkylalkoxysilane silane-terminated reaction product, which is hydrolyzed, and the cratering antiforming agent has a number-average molecular weight of approximately 700-5,000, determined by Gel Permeation Chromatography (GPC) using polystyrene as the standard; wherein the anti-crater agent is used in an amount sufficient to reduce the craters in a coating formed from the electrocoating composition.

2. The improved electrocoating composition according to claim 1, characterized in that the polyoxyalkylene diamine is a polyoxypropylendia having a weight average molecular weight of about 230-3,000.

3. The improved electrorecovery composition according to claim 1, characterized in that the glycidoxyalkylalkoxy silane is a gamma-glycidoxypropyl trimethoxysilane.

4. The improved electrocoating composition according to claim 1, characterized in that the polyoxyalkylene diamine is polyoxypropylene diamine having a weight average molecular weight of about 230-3,000 and the glycidoxyalkylalkoxy silane is gamma-glycidoxypropyl 1 trimethoxysilane.

5. The improved cathodic electrocoat composition according to claim 1, characterized in that the anti-cratering agent is present in an amount of about 0.5-10% by weight, based on the weight of the film-forming binder of the composition.

6. An anti-crater agent, characterized in that it has the structural formula: OH OH I H H | (OH) 3-Si- (CH 2) r-0-CH 2 -CH-CH 2 -N- (OR 1) m-N-CH 2 -CH-CH 2-0- (CHJ r-SÍ- (OH); wherein n is 1-3 and m is 5-40 and R1 is an alkyl group having 2-4 carbon atoms.

7. In a method for the preparation of a cathodic coating composition comprising the following steps in any functional order: (a) the preparation of an epoxy-amine adduct; (b) the preparation of a blocked polyisocyanate crosslinking agent; (c) mixing the epoxy-amine adduct with the blocked polyisocyanate crosslinking agent; (d) neutralization of the epoxy-amine adduct with an organic acid to form an emulsion; (e) mixing the emulsion with a pigment paste; and (f) adding an anti-crater agent to the electrocoating composition resulting from step (e), to improve the crater resistance of the coating after electrodeposition and cure of the coating; wherein the antricrater agent consists of a reaction product of polyoxyalkylene diamine and a glycidoxyalkylalkoxysilane, which is hydrolyzed, the anti-crater agent has a number average molecular weight of about 700-5,000, determined by Gel Permeation Chromatography (GPC) using polystyrene as the standard; wherein the anti-crater agent is used in an amount sufficient to reduce the craters in a coating formed from the electrocoating composition.

8. The method according to claim 7, characterized in that the polyoxyalkylene diamine is polyoxypropylene diamine having a weight average molecular weight of about 230-3,000.

9. The method according to claim 7, characterized in that the glycidoxyalkylalkoxy silane is gamma-glycidoxypropyl trimethoxysilane

10. The method according to claim 7, characterized in that the polyoxyalkylene diamine is polyoxyalkylene diamine having a weight average molecular weight of about 230-3,000 and the glycidoxyalkyl alkoxy silane is gamma, glycidoxypropyltrimethoxysilane.