JP2005170958A - Cationic electrodeposition paint composition and cationic electrodeposition coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cationic electrodeposition paint composition which can acquire both a cold-setting property and a long-term stability. <P>SOLUTION: The cationic electrodeposition paint composition contains a cationic polymer which is a substrate resin and a blocked isocyanate which is a hardener and has isocyanate groups blocked by a blocking agent. The blocked isocyanate contains at least three blocked isocyanate groups, at least one of which is sequestered by an alcohol compound having an active hydrogen reactive with the isocyanate group and at least two tertiary nitrogens. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cationic electrodeposition coating composition and a cationic electrodeposition coating method, and more particularly to a cationic electrodeposition coating composition and a cationic electrodeposition coating method that can be baked at a low temperature in a short time.

  Conventionally, in the field of electrodeposition coatings for automobiles, a method in which a cation-modified epoxy resin is used as a cell, a coacervation product having a blocked isocyanate as a core is electrodeposited on an electrode, and then heated to cross-link both of them. It has come to be used for. In this case, baking (crosslinking) is usually performed at a relatively high temperature of about 180 ° C. After the electrodeposition coating is formed by this baking, the intermediate coating layer and the top coating layer are usually formed at about 140 ° C.

  However, in recent years, in order to reduce energy costs, cationic electrodeposition paints are required to be baked at low temperature in a short time, and the drying temperature of the intermediate coating layer and the top coating layer formed on the electrodeposition coating film There has been a demand for a cationic electrodeposition coating material that can form an electrodeposition coating film that can be crosslinked at 140 ° C. of the same level. If the electrodeposition coating can be baked at about 140 ° C., which is the same as the drying temperature of the intermediate coating layer and the top coating layer, energy can be reduced and the process can be shortened, and a significant cost reduction can be achieved.

In order to reduce the crosslinking temperature of the modified epoxy resin, which is a base resin, in response to such demands, it is possible to use oximes, active methylene-containing compounds, phenols, etc. that dissociate in a low temperature range as blocking agents. It has been proposed (Patent Document 1, Patent Document 2, etc.). However, when such a blocking agent that dissociates in a low temperature range is used, problems such as a decrease in long-term stability as a paint have been pointed out.
JP-A-7-233239 JP-A-10-120947

  The present invention solves such problems of the prior art, and an object of the present invention is to provide a cationic electrodeposition coating composition capable of achieving both low-temperature curability and long-term stability, and cationic electrodeposition using the same. It is to provide a painting method.

  The cationic electrodeposition coating composition of the present invention is a cationic electrodeposition coating composition containing a cationic polymer as a base resin and a blocked isocyanate having an isocyanate group blocked by a blocking agent, wherein the block The deisocyanate contains three or more isocyanate groups, and at least one of the three or more isocyanate groups includes one active hydrogen having reactivity with the isocyanate group and two or more tertiary nitrogens. It is blocked by an alcohol compound having

  As described above, in the present invention, since the blocked isocyanate contains three or more isocyanate groups, the crosslinking effect is enhanced. In addition, since at least one isocyanate group among the three or more isocyanate groups is blocked by an alcohol compound having one active hydrogen having reactivity with the isocyanate group and two or more tertiary nitrogens, The dissociation temperature is lowered.

  As an electrodeposition coating composition, while maintaining long-term storage stability, the electrodeposition coating can be cross-linked at 140 ° C, which is the same level as the drying temperature of the intermediate coating layer and the top coating layer, resulting in significant rationalization in terms of energy Is possible.

  As described above, in the cationic electrodeposition coating composition of the present invention, the blocked isocyanate contains three or more isocyanate groups. Examples of the isocyanate compound constituting the blocked isocyanate include urethane prepolymers in which aromatic diisocyanates, araliphatic diisocyanates and the like are adducted with trihydric or higher polyhydric alcohols.

  Examples of the trihydric or higher polyhydric alcohol include trifunctional polyols such as glycerin and trimethylolpropane, and tetrafunctional polyols such as diglycerin and pentaerythritol. Examples of these trifunctional polyols and tetrafunctional polyols include: What added alkylene oxides, such as ethylene oxide, a propylene oxide, a butylene oxide, can also be used. Trifunctional polyols, tetrafunctional polyols, and adducts of these alkylene oxides can be used in admixture of two or more.

  Examples of the aromatic diisocyanate include 2,6-tolylene isocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, and 4,4′-diphenyldimethylmethane diisocyanate. 4,4′-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate and the like.

  Examples of the araliphatic diisocyanate include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, α, α, α, α-tetramethylxylylene diisocyanate, and the like.

  These organic polyisocyanate compounds can be used alone or in combination of two or more. Of these organic polyisocyanate compounds, aromatic isocyanates are preferred from the viewpoint of promoting curing at 140 ° C. or lower.

  Examples of the blocking agent that can be used in the present invention include lactam blocking agents such as ε-caprolactam, σ-valerolactam, γ-butyrolactam, and β-propiolactam. Among these lactam blocking agents, ε-caprolactam is preferably used from the viewpoint that it can be used for general purposes. In addition, when the low temperature dissociation type oxime type, active methylene type and phenol type are used, curing at 140 ° C. or lower is possible, but the long-term stability as a coating is lowered, which is not preferable.

  In the cationic electrodeposition coating composition of the present invention, at least one of the three or more isocyanate groups has one active hydrogen having reactivity with the isocyanate group and two or more tertiary nitrogens. Blocked by an alcohol compound. Here, as an alcohol compound having one active hydrogen having reactivity with an isocyanate group and two or more tertiary nitrogens, N-methyl-N- (N, N-dimethyl) represented by the following chemical formula 1 is used. Aminoethyl) aminoethanol), N-methyl-N- [N-methyl-N- (N, N-dimethylaminoethyl) -aminoethyl] -aminoethanol as shown in Chemical Formula 2, N-methyl-N as shown in Chemical Formula 3 -(N, N-dimethylaminoethyl) -aminoisopropanol, N-methyl-N- (N, N-dimethylaminopropyl) -aminoethanol represented by Chemical Formula 4, N-methyl-N- (N, N-dimethylaminopropyl) -aminoisopropanol, N-methyl-N- [N-methyl-N- (N, N-dimethylaminoethyl) -aminoethyl] -aminoisol Propanol and the like.

  Aminoalcohols having only one tertiary nitrogen in the molecule, such as N, N-dimethylethanolamine, N, N-dimethylpropanolamine, N, N-dimethylisopropanolamine, N, N-dimethylbutanolamine, N, Compared to the case where N-diethylethanolamine, 2- [2- (dimethylamino) ethoxy] ethanol, 2- (2- [2- (dimethylamino) ethoxy] ethoxy) ethanol or the like is introduced into the molecular skeleton, It has been found that curing is promoted even at 140 ° C. or lower when an alcohol compound having two or more tertiary nitrogen atoms in one molecule is introduced as in the invention.

  By introducing an alcohol compound having two or more tertiary nitrogens in one molecule, the electron density of the isocyanate group blocked by the caprolactam-based blocking agent increases, the reactivity increases, and the dissociation temperature decreases. Therefore, it is considered that low temperature dissociation can be realized.

  In the present invention, a known cationic resin can be used as the base resin constituting the cationic electrodeposition coating composition. Examples of the cationic resin include an amine-modified epoxy resin, an amine-modified polyurethane polyol resin, an amine-modified polybutadiene resin, and an amine-modified acrylic acid resin. These cationic resins can be obtained by adding a primary amine, a secondary amine, or a tertiary amine and an acid to a bisphenol-type epoxy resin and opening the epoxy ring. Also, starting from an epoxy resin having an oxazolidone ring in the chain obtained by reacting a bisurethane compound obtained by reacting a diisocyanate with a lower alkanol compound and a bisphenol type epoxy resin, an amine is added in the same manner. The resulting resin can also be used.

  In the present invention, an organic tin-based curing catalyst can be blended in order to promote the crosslinking reaction between the base resin and the blocked isocyanate. Examples of organotin curing catalysts include tin octoate, dibutyltin dilaurate, dioctyltin dineodecanate, dioctyltin dilaurate, manganese, cobalt, lead, bismuth stannate, lead stannate, zirconium octoate, zinc octoate, dibutyl Tin-bis-o-phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenylantimony dichloride, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate mercaptide, triethylenediamine, bismuth stearate, lead stearate Rate, dimethyltin dichloride and the like. The blending amount of the curing catalyst is usually in the range of 0.1 to 10 parts by weight per 100 parts by weight in total of the base resin and the blocked isocyanate.

  The reaction of the polyisocyanate compound and the blocking agent for preparing the blocked isocyanate can be performed by a known method, and the resulting blocked isocyanate has substantially no free isocyanate group.

  The constituent ratio of the base resin and blocked isocyanate in the cationic electrodeposition coating composition of the present invention is not particularly limited, but based on the total solid content weight of these two components, the base resin 40 to 90 % And blocked isocyanate is preferably in the range of 60 to 10%, particularly preferably in the range of 50 to 80% of the base resin and 50 to 20% of the blocked isocyanate.

  In the cationic electrodeposition coating composition of the present invention, the cationic group in the base resin is neutralized with an acidic compound such as acetic acid, formic acid, lactic acid and phosphoric acid, and then blocked isocyanate (a-2). In addition, the pH of the aqueous dispersion is preferably in the range of 3 to 9, particularly 5 to 7, and the resin solid content concentration is 5 to 5. A range of 30% by weight is suitable.

  The cationic electrodeposition coating composition of the present invention includes a metal hydroxide or oxide selected from aluminum, nickel, zinc, strontium, zirconium, molybdenum, tin, antimony, lanthanum, tungsten, bismuth, and the like, if necessary. Curing catalysts, extender pigments, color pigments, rust preventive pigments, anti-settling agents, and the like having rust preventive properties such as organic acid salts and inorganic acid salts can be appropriately blended.

  The start time of the cross-linking curing reaction of the coating film formed using the cationic electrodeposition coating composition of the present invention, that is, the time from the start of heating to the start of cross-linking curing is, for example, a polyisocyanate compound, a blocking agent, a curing catalyst. It can be easily adjusted by appropriately selecting the type and blending amount. Preferred onset times for the cross-linking cure reaction are from about 3 to about 20 minutes, with particularly preferred onset times ranging from about 5 to about 15 minutes.

  Application of the coating using the cationic electrodeposition coating composition of the present invention is carried out, for example, with the above-mentioned article as an anode and a carbon plate as a cathode, a bath temperature of 20 to 35 ° C., a voltage of 100 to 400 V, a current density of O.D. It can be performed in 01 to 5 A and energization time 1 to 10 minutes. In general, the coating film thickness is preferably about 10 to 40 μm after curing.

  The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the present specification, “%” and “part” represent “% by weight” and “part by weight”, respectively, unless otherwise specified.

<Preparation of base resin X>
465.0 parts of bisphenol A type epoxy resin (Epicoat 828, Japan Epoxy Resin Co., Ltd., epoxy equivalent = 186) was dissolved in 264 parts of MIBK (methyl isobutyl ketone), and a MIBK 70% solution of methyl isobutyl diketimine in diethylenetriamine 191. 4 parts and 150.3 parts of N-methylethanolamine were added and reacted at 120 ° C. for 1 hour to obtain a base resin X.

<Preparation of curing agent (blocked isocyanate)>
(Synthesis Example 1 ... Curing Agent 1)
500.0 parts of polymeric MDI (polymethylene polyphenyl polyisocyanate, PAPI-135, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%), 419.3 parts of MIBK, N-methyl-N- (N , N-dimethylaminoethyl) -aminoethanol was charged with 99.0 parts and reacted at 50 ° C. for 30 minutes with stirring. Next, 347.4 parts of ε-caprolactam and 2.4 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain a blocked isocyanate. The content of regenerated free isocyanate group in terms of solid content of the curing agent 1 was 12.84% (theoretical value).

(Synthesis Example 2 ... Curing Agent 2)
Polymeric MDI (PAPI-135, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%) 500.0 parts, MIBK 419.3 parts, N-methyl-N- (N, N-dimethylaminoethyl) -Aminoethanol (49.5 parts) was charged and reacted at 50 ° C for 30 minutes with stirring. Next, 385.8 parts of ε-caprolactam and 2.4 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain a blocked isocyanate. The recycled free isocyanate group content in terms of solid content of the curing agent 2 was 14.51% (theoretical value).

(Synthesis Example 3 ... Curing Agent 3)
500.0 parts of polymeric MDI (PAPI-20J, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%), 51.8 parts of 1,4-butanediol, 309.4 parts of MIBK, The reaction was performed at 65 ° C. for 60 minutes with stirring. Subsequently, 91.4 parts of N-methyl-N- (N, N-dimethylaminoethyl) -aminoethanol was added and reacted at 50 ° C. for 30 minutes with stirring. Next, 233.3 parts of ε-caprolactam and 2.6 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain a blocked isocyanate. The content of regenerated free isocyanate group in terms of solid content of the curing agent 3 was 8.68% (theoretical value).

(Synthesis Example 4 ... Curing Agent 4)
While stirring 500.0 parts of polymeric MDI (PAPI-20J, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%), 68.5 parts of N-methyldiethanolamine, and 309.4 parts of MIBK The reaction was performed at 65 ° C. for 60 minutes. Subsequently, 91.4 parts of N-methyl-N- (N, N-dimethylaminoethyl) -aminoethanol was added and reacted at 50 ° C. for 30 minutes with stirring. Next, 223.3 parts of ε-caprolactam and 2.6 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain a blocked isocyanate. The content of regenerated free isocyanate group in terms of solid content of the curing agent 4 was 8.51% (theoretical value).

(Comparative Synthesis Example 1 ... Hardener a)
500.0 parts of polymeric MDI (PAPI-135, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%), 419.3 parts of MIBK, and 60.3 parts of N, N-dimethylethanolamine were charged. The reaction was carried out at 50 ° C. for 30 minutes with stirring. Next, 347.4 parts of ε-caprolactam and 2.4 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain blocked isocyanate, which was used as curing agent a. The recycled free isocyanate group content in terms of solid content of the cured a was 13.39% (theoretical value).

(Comparative Synthesis Example 2 ... Curing Agent b)
Polymeric MDI (PAPI-135, manufactured by Dow Polyurethane Japan Co., Ltd., NCO content 30%) 500.0 parts, MIBK 419.3 parts, N-methyl-N- (N, N-dimethylaminoethyl) -Aminoethanol was charged with 99.0 parts and reacted at 50 ° C for 30 minutes with stirring. Next, 267.1 parts of methyl ethyl ketoxime and 2.4 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain blocked isocyanate, which was used as curing agent b. The content of regenerated free isocyanate group in terms of solid content of the cured b was 14.4.03% (theoretical value).

(Comparative Synthesis Example 3 ... Curing Agent c)
600.0 parts of HMDI (hexamethylene diisocyanate) nurate (deyuranate TPA100, manufactured by Asahi Kasei Corporation, NCO content 25%), 419.3 parts of MIBK, and 60.3 parts of N, N-dimethylethanolamine The reaction was carried out at 50 ° C. for 30 minutes while charging and stirring. Next, 347.4 parts of ε-caprolactam and 2.4 parts of triethylamine were added and reacted at 65 ° C. for 2 hours to obtain a blocked isocyanate, which was used as a curing agent c. The content of regenerated free isocyanate group in terms of solid content of the cured c was 12.06% (theoretical value).

<Preparation of paint>
In the formulation shown in Table 1, the base resin X, the curing agent shown in each synthesis example and each comparative synthesis example, a catalyst (dioctyltin dineodecanate), a pigment (kaolin and titanium oxide), ethylene glycol monobutyl ether, Carbon black was added and mixed with stirring for 1 hour. Next, acetic acid was added, 100 parts by weight of diluting water was added and emulsified to prepare cationic electrodeposition paints of Examples 1 to 4 and Comparative Examples 1 to 3.

<Preparation of paint sample>
Using the thus obtained cationic electrodeposition paint, a zinc phosphate-treated steel sheet was electrodeposited and baked at 140 ° C. for 15 minutes to prepare a coated sample. The film thickness of the coating after baking was 20 ± 5 μm.

<Performance test>
Using the coating material and the coating sample obtained above, tests were conducted for storage stability, coating film appearance, coating film smoothness and gel fraction. The conditions of each test are as follows.

(Storage stability of paint)
The paint was stored at 40 ° C. for 3 months, and the stability of the paint was observed with the naked eye.

(Appearance and smoothness of paint film)
The coating film after baking was visually evaluated.

(Gel fraction)
The coating sample was immersed in acetone at room temperature for 24 hours, and the remaining amount (weight) of the coating film after drying was determined.

(result)
As a result of the above performance test, Examples 1 to 4 were all good test results, but Comparative Examples 1 and 3 had a low gel fraction of the coating film, and Comparative Example 2 was the storage stability of the paint. The sex was inferior.

The composition of the present invention can crosslink the electrodeposition layer at 140 ° C., which is the same level as the drying temperature of the intermediate coating layer and the top coating layer, while maintaining long-term storage stability, thereby greatly streamlining energy. Therefore, it can be used as a cationic electrodeposition coating composition and can be used in a cationic electrodeposition coating method.

Claims (5)

A cationic electrodeposition coating composition containing a cationic polymer as a base resin and a blocked isocyanate as a curing agent having an isocyanate group blocked by a blocking agent,
The blocked isocyanate contains three or more of the blocked isocyanate groups, and at least one of the three or more isocyanate groups includes one active hydrogen and two reactive groups having reactivity with the isocyanate group. A cationic electrodeposition coating composition, which is blocked with an alcohol compound having the above tertiary nitrogen.   The cationic electrodeposition coating composition according to claim 1, wherein the blocked isocyanate dissociates at 140 ° C. or lower.   The cationic electrodeposition coating composition according to claim 1, wherein the blocking agent is a caprolactam-based blocking agent.   The cationic electrodeposition coating composition according to any one of claims 1 to 3, comprising an aromatic organic polyisocyanate as the polyisocyanate component constituting the blocked isocyanate. A coating film is formed using an electrodeposition coating material containing the cationic electrodeposition coating composition according to any one of claims 1 to 4 with an article to be coated as an anode, and then the coating film is baked and cured. Cationic electrodeposition coating method.