MXPA97010245A - Compositions of catodicas electrorrecubrication that contain an antidepress agent - Google Patents

Abstract

An improved aqueous electrocoating composition is disclosed, which contains an antidepressant agent which is a reaction product of polyoxyalkylene diamine and isocyanate alkoxy alkoxy silane, which is hydrolyzed and has an average molecular weight number of about 2000-5000; Electrodeposits that are formed have a significant reduction in the depressions and are finished smooth and uniform

Description

BACKGROUND OF THE INVENTION This invention relates generally to a cathodic electrocoat composition and in particular to a cathodic electrorecovery composition containing an anti-depression agent, which significantly reduces depressions and improves the performance of the cathodic electrocoat composition. smoothness of an electrodeposited film of the composition. The coating of electrically conductive substrates by an electrodeposition process, also called an electrocoating process, is a well-known and important industrial process. The electrodeposition of primers to automotive substrates is widely used in the automotive industry. In this process, an automotive article, such as an automotive body or an autopart, is immersed in a bath of a coating composition of an aqueous emulsion of a polymer that forms a film and acts as an 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 counter electrode is the anode. Resin compositions used in the bath of a common cathodic electrodeposition process are also well known in the art. These resins are usually made from polyepoxide resins to which the chain has been extended and an adduct is then formed to include amine groups in the resin. The amine groups are normally introduced by REF: 26322 means of 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 emulsion in water which is usually referred to as a main emulsion. The main emulsion is combined with a pigment paste, 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 deposited on the article that is electrorecoverable is a function of the characteristics of the bath, the operating characteristics of the tank, the time of immersion and the like. The like coated article is removed from the bath after a set period of time and rinsed with deionized water. The coating on the article is solidified or normally cured in an oven at a temperature sufficient to produce a crosslinked finish on the article. The cathodic electrocoat compositions, the resin compositions, the electrodeposition baths and the cathodic electrodeposition processes are described in the North American patent of Jarabek et al, No. 3,922,253, issued November 25, 1975; the American patent of Wismer et al, No. 4,419,467, issued December 6, 1983; Belanger, US Pat. No. 4,137,140, issued January 30, 1979 and Wismer et al. US Patent No. 4,468,307 issued August 25, 1984.

A continuing problem with the cathodic electrocoat compositions has been the presence of depressions in the solidified or cured finish. An additive or agent for the electrocoating compositions is needed, so that smooth, smooth and uniform depressions are formed in the electrodeposition and curing. Chung et al, U.S. Patent 5,356,960 issued October 18, 1994, shows an antidepressant additive that forms a smooth, uniform, and free depression. However, when this additive is used in an electrocoating composition that is subjected to cooking in an indirect gas oven, after application to a metal substrate, such as a car or truck body, this anti-depression additive migrates very easily to the surface of the electrocoating composition during firing and any primers or primer compositions applied on a surface containing Polymeric melamine crosslinking agents adhere poorly to the electrocoating composition and hence, any failure of the addition of any surface coating applied on the primer is readily apparent. An antidepressant additive which does not migrate to the surface of the electrocoating composition during cooking is needed and should not adversely affect other properties such as the deposition power of the electrocoating bath, the curing of the deposited coating or the film properties of the electrodecoating composition. finished result.

BRIEF DESCRIPTION OF THE INVENTION An improved aqueous cathodic electrocoat composition is disclosed, having a binder of an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent; wherein the improvement consists of the use of an antidepressant agent which is a finished reaction product in polyoxyalkylene diamine silane and an alkyl alkoxy silane isocyanate which is hydrolyzed and the antidepressant agent has a number average molecular weight ratio of about 2000 -5000 determined by Gel Permeation Chromatography (GPC) when using polystyrene as the standard.

DETAILED DESCRIPTION OF THE INVENTION The novel antidepressant agent is easily incorporated into the electrocoating composition by dispersing it with a nonionic surfactant in water and then adding it to an aqueous electrocoating composition, since it is compatible with the other coatings of the composition. The antidepressant agent remains stable in the composition and in the electrocoating bath for extended periods of time under the conditions of conventional bath operations, since it is not reactive with the other constituents in the composition. The antidepressant agent significantly reduces and frequently eliminates depressions in the electrodeposited coatings and forms smooth and uniform finishes that do not migrate to the surface in the firing of the finish. Also, the additive does not adversely affect other properties of the electrocoating bath or finishes of the electrocoating composition. In addition, the antidepressant agent can be used as a rheology control agent to improve edge protection of an electrodeposited finish. The antidepressant additive is used in an electrocoating composition in an amount sufficient to significantly reduce or eliminate the formation of depressions in the electrodeposited finish. In general, the antidepressant 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 preferably used at a level of approximately 0.5-10% by weight. More preferably, about 1-5% by weight of the antidepressant agent is used. The binder of the electrocoating composition is usually a mixture of an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent. The antidepressant agent is prepared by reacting a polyoxyalkylene diamine with isocyanate alkyl alkoxy silane in a molar ratio of 1 2 to form an antidepressant agent having terminal silane groups. These constituents are reacted at a temperature of about 70 ° C to 130 ° C for about one to five hours, until there is no longer residual isocyanate present and subsequently hydrolysed. The antidepressant agent has an average molecular weight number of about 2000-5000. The polyoxyalkylene diamine used to form the antidepressant agent has 2-4 carbon atoms in the alkylene group and preferably consists of polyoxypropylene diamine having an average molecular weight number of about 230-3000, preferably 1500-2500, such as Jeffamine D- 2000®, which has an average molecular weight number of about 2000, available from "Texaco Chemical Company". Another polyoxyalkylene diamine that can be used is polyoxyethylene diamine having a similar molecular weight. The isocyanate alkyl alkoxysilanes normally useful have the formula O = C = N (CH 2) n Si (OR) 3, wherein R is methyl, ethyl or a mixture of methyl and ethyl and n is 1-3. Typical silanes are isocyanate propyl trimethoxy silane, isocyanate ethyl trimethoxy silane, isocyanate methyl trimethoxy silane, isocyanate methyl triethoxy silane, isocyanate ethyl triethoxy silane, isocyanate propyl triethoxy silane. The isocyanate propyl triethoxy silane is preferred to form a high quality antidepressant agent. The antidepressant agent can be added to the electrocoating composition at almost any time. It can be added to the main emulsion or the bath, the antidepressant agent is combined with a nonionic surfactant and an acid such as lactic acid and dispersed in water until the hydrolysis of the silane group to silanol groups is consumed and then added to the electrocoating composition as indicated above. The antidepressant agent after the complete hydrolysis has the following structural formula: wherein n is 1-3 and m is 5-40 and R1 is an alkyl group having 2-4 carbon atoms. Most of the main emulsions used in an electrocoating composition comprise an aqueous emulsion of a binder of an epoxy-amine adduct combined with a crosslinking agent which has been neutralized with an acid to form a water-soluble product. The antidepressant agent is potentially usable with a variety of different cathodic electrocoat resins, but the preferred resin is the epoxy-amine adduct typical of the prior art. These resins are generally described in U.S. Patent No. 4,419,467, which is incorporated by reference. Typical acids used to neutralize the epoxy-amine adduct to form water-dispersible cationic groups are lactic acid, acetic acid, formic acid, sulfamic acid, alkanesulfonic acids, such as methanesulfonic acid and the like. Preferred crosslinking agents for the above resins are also well known in the prior art. These are aliphatic, cycloaliphatic and aromatic isocyanates, such as hexamethylene diisocyanate, cyclohexamethylene diisocyanate, toluene diisocyanate, methylene diphenyl diisocyanate and the like. These isocyanates are pre-reacted with a blocking agent, such as oximes, alcohols or caprolactams, which block the isocyanate functionality, that is, the crosslinking functionality. After heating the blocking agents are separated, to thereby provide a reactive isocyanate group and crosslinking occurs. Isocyanate crosslinking agents and blocking agents are well known in the prior art and are described in the aforementioned U.S. Patent No. 4,419,467.

The cathodic binder of the epoxy-amine adduct and the blocked isocyanate are the main resinous ingredients 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 a 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 into 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 antidepressant 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 6-8, when using a Hegman grinding caliber. The pigments which can be 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 judiciously used because they may have an undesirable effect on the coalescence and flow of the electrodeposited coating. The weight ratio of pigment to binder 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 ratios 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 alkyl imidazoline 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% by weight of the binder solids of the composition. Optionally, plasticizers can be used to promote the flow. Examples of useful plasticizers are non-water-soluble high-boiling materials such as ethylene or propylene oxide adducts, diphenylphenols or bisphenol A. Plasticizers are usually used at levels of about 0.1 to 15% by weight of resin solids. The electrocoating composition of this invention is an aqueous dispersion. It is believed that the term "dispersion" as used within the context of this invention is a resinous, aqueous, translucent or opaque binder system of two kinds, in which the binder is in the dispersed phase and the water is the phase keep going. The diameter of the average particle size 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 not generally critical but ordinarily, the main or major portion of the aqueous dispersion consists of water. The aqueous dispersion usually contains from about 3 to 50%, preferably 5 to 40% by weight of solid binder. Aqueous binder concentrates which are to be further diluted with water when added to an electrocoating bath, generally have a binder solids range of 10 to 30% by weight. The following example illustrates the invention. All parts and percentages are on a weight basis, unless stated otherwise.

Example Preparation of an antidepressant agent The antidepressant agent is prepared by charging 999.7 parts of Jeffamine D-2000® (polyoxypropylene diamine having a molecular weight number of 2000) and 0.04 part of dibutyltin dilaurate in an appropriate reaction vessel and heat at 37 ° C under an atmosphere of anhydrous nitrogen. 205 parts of isocyanate propyltrimethoxy silane are slowly charged to the reaction vessel while maintaining the reaction mixture at a temperature of less than 82 ° C for an additional hour, until essentially all of the isocyanate was reduced, as indicated by the Infrared scan of the mixture. The adduct is then dispersed by mixing in an aqueous medium of 5288.33 deionized water, 58.73 parts of lactic acid and 1174.62 parts of ethoxylated phenol styrene (Synfac 8334®) and stirred for at least two hours for complete hydrolysis of the groups. silane to silanol groups. The solution of the resulting adduct has a non-volatile component content of 30%.

Preparation of the extended chain polyethyoxide solution The following ingredients are charged to an appropriate reaction vessel: 1478 parts of Epon 828® (diglycidyl ether epoxy resin of bisphenol A, having an epoxy equivalent weight of 188); 427 parts of bisphenol A; 533 parts of ethoxylated bisphenol A having an equivalent hydroxy weight of 247 (Synfac 8009®) and 121 parts of xylene. The resulting reaction mixture is heated to 160 ° C under a nitrogen atmosphere and maintained at room temperature for 1 hour. 5.1 parts of dimethyl benzyl amine are added and the mixture is maintained at 147 ° C until an epoxy equivalent weight of 1050 is obtained. The reaction mixture is cooled to a temperature of 98 ° C and 168 parts of diketimine are added ( reaction product of diethylenetriamine and methyl isobutyl ketone having a non-volatile component content of 72.27%) and 143 parts of methyl ethanol amine. The resulting mixture is maintained at 120 ° C for one hour and then 727 parts of methyl isobutyl ketone are added. The resulting resin solution had a non-volatile component content of 75%.

Preparation of the crosslinking resin solution A solution of polyisocyanate crosslinking resin blocked with alcohol is prepared by charging 317.14 parts of PAPI 2027® (methylene diphenyl diisocyanate), 47.98 parts of methyl isobutyl ketone and 0.064 parts of dibutyltin dilaurate to a suitable reaction vessel and heated to 37 ° C under a nitrogen atmosphere. A mixture of 323.10 parts of diethylene glycol monobutyl ether and 13.04 parts of trimethylolpropane are slowly charged to the reaction vessel, while maintaining the reaction mixture at a temperature lower than 93 ° C for an additional hour, until essentially all the Isocyanate reacted, as indicated by infrared scanning of the reaction mixture. 2.30 parts of butanol and 167.37 parts of methyl isobutyl ketone are added. The resulting resin solution had a non-volatile component content of 75%.

Preparation of the Quaternary Function Agent The Quaternary Function Agent is prepared by adding 87 parts of dimethylethanolamine to 320 parts of toluene diisocyanate topped with ethylhexanol in the reaction vessel at room temperature. An exothermic reaction occurs and the reaction mixture is stirred for one hour at 80 ° C. Then 118 parts of aqueous lactic acid solution (75% nonvolatile content) are added followed by the addition of 39 parts of 2-butoxyethanol. The reaction mixture is maintained for about one hour at 65 ° C with constant stirring to form a quaternary agent.

Preparation of the pigment grinding vehicle The pigment grinding vehicle is prepared by loading 710 parts of Epon 829® (diglycidyl ether of bisphenol A having an epoxy equivalent weight of 193-203) and 290 parts of bisphenol A into a container of appropriate reaction under a hydrogen atmosphere and heated to 150-160 ° C to initiate an exothermic reaction. The exothermic reaction continues for about one hour at 150-160 ° C. Then the reaction mixture is cooled to 120 ° C and 496 parts of toluene diisocyanate topped with 2-ethylhexanol are added. The temperature of the reaction mixture is maintained at 110-120 ° C for one hour, followed by the addition of 1095 parts of 2-butoxyethanol, then the reaction mixture is cooled to 85-90 ° C and then 71 parts of deionized water are added followed by the addition of 496 parts of the quaternary function agent (prepared above) . The temperature of the reaction mixture is maintained at 85-90 ° C until an acid value of about 1 is obtained.

I. Preparation of the emulsion Parts by weight Extended chain polyepoxide solution (prepared 1255.31 above) Crosslinking resin solution (prepared 805.85 previously) Surfactant1 13.62 Lactic acid 27.24 Deionized water 1897.98 Total 4000.00 The extended chain polyepoxide solution, the crosslinking resin solution surfactant and the lactic acid are thoroughly mixed. Then the deionized water is added under agitation. The content of non-volatile components of the emulsion is adjusted to 36% with the necessary amount of deionized water. The emulsion is kept stirred until the methyl isobutyl ketone had evaporated.

Preparation of pigment paste Parts by weight Pigment grinding vehicle (prepared 812 above) Deionized water 1660 Titanium dioxide pigment 1068 Aluminum silicate pigment 212 Lead silicate pigment 92 Carbon black pigment 32 Dibutyl tin oxide pigment 124 Total 40,000 Surfactant-120 parts Amine®C from Ciba-Geigy, 120 parts acetylenic alcohol available as Surfynol ®104 from Air Products and Chemicals, Inc., 120 parts of 1-butoxyethanol, 221 parts of deionized water and 19 parts of glacial acetic acid . The above ingredients are mixed until a homogeneous mixture is formed in an appropriate mixing vessel. They are then dispersed by loading the mixture into a sand mill and then milling until a Hegman reading of 7 or higher is obtained.

III. Preparation of electrocoating baths I and II Parts by weight Bath I Bath II Emulsion (prepared above) 1636 1569 Deionised water 1926 1913 Pigment paste (prepared above) 398 398 Antidepressant agent (prepared 40 120 above) Total 4000 4000 A cationic electrocoating coating I and II is prepared by mixing the above ingredients. Then each bath is ultrafiltered. Each bath is electrocoated at 250-270 volts to obtain 22.86-25.4 microns (0.9-1.0 thousandths of an inch). The ASPP blown depression test is used to test each bath. The resistance to depression is classified according to the following nominal scale of A-E: A - 0-10% defects B - 11 -20% defects C - 21-40% defects D - 41-80% defects E - more than 80% defects The classification of the resistance to depression for both baths I and II was A. An electrocoating bath was prepared identically to bath I, above, except that the antidepressant agent was replaced with a conventional anti-depression agent, which is the reaction product of Jeffamine D-2000® and epoxy resin Epon® 1001 and the resistance to the depression of this bath was tested as was done previously when using the ASPP blowdown vacuum test. The resistance rating for this panel was E, which is substantially less than the panels coated in baths I and II which contained the antidepressant agent of this invention. In order to measure the corrosion resistance of the edge, blade blades (10 x 2cm) were coated from baths I and II at 250 volts and subjected to firing at 182 ° (metal temperature) for 10 minutes. Then the blades of the blades were exposed to a salt spray for 7 days. The number of spots or spots of oxide in each leaf was counted when visualizing the leaves under a microscope. The leaves of the bath I: had 100-120 points of oxide while the leaves of the bath II had 40-50 points of oxide, which shows that the bath II which contained twice the amount of the antidepressant agent, provided a better production against corrosion. It is noted that in relation to this date the best method known by 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. Claims 1. An improved cathodic electrorecovery composition, comprising an aqueous carrier having a film-forming binder dispersed therein, comprising an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent; the improvement is characterized in that it consists essentially of an antidepressant agent which essentially consists of a polyoxy alkylene diamine silane-terminated reaction product and an isocyanate alkyl alkoxy silane, which is hydrolyzate and the antidepressant agent has an average molecular weight number of about 2000-5000, determined by Gel Permeation Chromatography (GPC) when using polystyrene as the standard wherein the antidepressant agent is used in an amount sufficient to reduce the depressions in a coating formed from the electrocoating composition.
2. 2. The improved electrocoating composition according to claim 1, characterized in that the polyoxyalkylene diamine is a polyoxypropylene diamine having a weight average molecular weight of about 1500-2500.
3. 3. The improved electrocoating composition according to claim 1, characterized in that the isocyanate alkyl alkoxy silane is an isocyanate prapyl trimethoxy silane.
4. 4. The improved electrocoating composition according to claim 1, characterized in that the polyoxyalkylene diamine is polyoxopropylenediamine having a weight average molecular weight of about 1500-2500 and the isocyanate alkyl alkoxy silane is isocyanato propyl trimethoxysilane.
5. 5. The improved electrocoating composition according to claim 1 characterized in that the antidepressant 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. 6. An antidepressant agent, characterized in that it has the structural formula: n is 1-3 and m is 5-40 and R1 is an alkyl group having 2-4 carbon atoms.
7. 7. A method for the preparation of a cathodic electrorecovery composition, characterized in that it comprises the following steps in any feasible order: a) preparing an epoxy-amine adduct; b) preparing a blocked polyisocyanate crosslinking agent; c) combining the epoxy-amine adduct with the blocked polyisocyanate crosslinking agent: d) neutralizing the epoxy-amine adduct with an organic acid to form an emulsion; e) combining the emulsion with a pigment paste, and f) adding an anti-depression agent to the electrocoating composition to improve the depression resistance of the coating on electrodeposition, a coating cure, wherein the antidepressant agent consists essentially of a product of polyoxyalkylene diamine reaction and an alkoxysilane alkylisocyanate which is hydrolyzed and the antidepressant agent has an average molecular weight number of about 2000-5000 determined by gel permeation chromatography (GPC), when using polystyrene as the standard, wherein the The antidepressant agent is used in an amount sufficient to reduce the depressions in a coating formed from the composition of the electrocoating.
8. 8. The method according to claim 7, characterized in that the polyoxyalkylene diamine is polyoxypropylene diamine having a weight average molecular weight of about 1500-2500.
9. 9. The method according to claim 7, characterized in that the isocyanate alkyl alkoxysilane is isocyanato propyl trimethoxy silane.
10. 10. The method according to claim 7, characterized in that the polyoxy alkylene diamine is polyoxy alkylene diamine having a weight average molecular weight of about 1500 to 2500 and the isocyanate alkyl alkoxy silane is isocyanato propyl trimethoxy silane.