JP2002294141A - Cationic electrodeposition coating material composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cationic electrodeposition coating material composition having excellent low-temperature curability and durability. SOLUTION: This cationic electrodeposition coating material composition comprises (1) an amine-modified epoxy resin, (2) a blocked isocyanate curing agent obtained by blocking an aromatic polyisocyanate with at least a lactam based blocking agent, and (3) a curing accelerator containing a copper catalyst and at least one kind selected from the group consisting of a zinc catalyst and a tin catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cationic electrodeposition coating composition.

[0002]

2. Description of the Related Art In order to protect a metal material from corrosion and maintain its beauty during use, its surface is generally coated. Since the cationic electrodeposition coating can be applied continuously, it is widely used as an undercoating method for an object to be coated, such as an automobile body, which is large and requires high corrosion resistance.

[0003] Cationic electrodeposition coating is generally performed by dispersing a binder component containing a cationic resin and a curing agent in an aqueous medium containing a neutralizing agent such as an organic acid. Is immersed as a cathode, and a voltage is applied. When a voltage is applied between the electrodes during the coating process, an electrodeposition coating film is deposited on the surface of the cathode (object to be coated) by an electrochemical reaction. Since the electrodeposited coating film thus formed contains a curing agent together with the cationic resin, after completion of the electrodeposition coating, the coating film is cured by baking the coating film to form a desired cured coating film. Is done.

As the cationic resin used for the cationic electrodeposition coating, an amine-modified epoxy resin is used from the viewpoint of corrosion resistance.

[0005] In recent years, from the viewpoint of energy saving, cationic electrodeposition paints capable of baking electrodeposition coating films at low temperatures have become mainstream (for example, USP5902871, USP585165, USP6001900).

[0006] However, the lower the baking temperature, the lower the degree of curing of the coating film and the lower the corrosion resistance.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cationic electrodeposition coating composition which can be sufficiently cured at a low temperature and has excellent corrosion resistance.

[0008]

The present invention provides (1) an amine-modified epoxy resin, (2) a blocked isocyanate curing agent obtained by blocking an aromatic polyisocyanate with at least a lactam blocking agent, and (3) a copper catalyst. The present invention relates to a cationic electrodeposition coating composition comprising a curing accelerator comprising at least one selected from the group consisting of a zinc catalyst and a tin catalyst.

The cationic electrodeposition coating composition of the present invention comprises at least an amine-modified epoxy resin, a curing agent, and a curing accelerator.

The amine-modified epoxy resin is typically
The epoxy resin is prepared by opening all the epoxy groups of an epoxy resin with an amine or opening some epoxy groups with another active hydrogen compound and opening the remaining epoxy groups with an amine.

The epoxy resin generally has a molecular weight of 600 to 8000,
Preferably, those having 700 to 6000, epoxy equivalent of 300 to 4000, preferably 350 to 3000 are used. Typically, it is a polyphenol polyglycidyl ether type epoxy resin using a polyphenol such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, and cresol novolak.

It is preferable to use an oxazolidone ring-containing epoxy resin. Such an oxazolidone ring-containing epoxy resin, for example, reversibly blocks some isocyanate groups of aromatic diisocyanates such as tolylene diisocyanate with monoalcohols (eg, methanol and the like) and further reduces some isocyanate groups. Irreversibly blocked with a hydroxyl group-containing compound (e.g., ethylene glycol mono-2-ethylhexyl ether, etc.), and the remaining isocyanate group is dihydroxy compound such as bisphenol A alkylene oxide (e.g., bisphenol A-propylene oxide adduct). It is obtained by blocking to obtain a modified asymmetric bisurethane, and reacting the modified asymmetric bisurethane with a diepoxide (for example, an epoxy resin obtained from bisphenol A and epichlorin).

More specifically, an epoxy resin having an oxazolidone ring as described in the formula (1) of JP-A-5-306327, No. 0004, or a method described in Japanese Patent Application No. 10-305294, No. 0012-0047. The oxazolidone ring-containing epoxy resin produced by the above.

[0014] The epoxy resin may be modified with a suitable resin such as a polyester polyol, a polyether polyol, and a monofunctional alkylphenol. Examples of the resin used for this modification include polycaprolactone diol and ethylene oxide addition polymer.

The epoxy resin can be chain-extended by utilizing the reaction between an epoxy group and a diol or dicarboxylic acid. Examples of diols are ethylene glycol, 1,
Alkylene diols such as 2-propylene glycol, 1,3-propanediol, 1,4-butanediol and 1,6-hexanediol; alicyclic diols such as 1,2-cyclohexanediol and 1,4-cyclohexanediol; Examples thereof include aromatic diols such as bisphenol A, bisphenol F, resorcinol, and hydroquinone. Succinate Examples of dicarboxylic acids, adipic acid, azelaic acid, dodecanedioic acid, dimer acid, C ₁₈ ~
Long chain aliphatic dicarboxylic acids of C _20, terminal carboxyl group modified butadiene - aliphatic dicarboxylic acids such as acrylonitrile copolymer, or phthalic acid, isophthalic acid, and aromatic dicarboxylic acids such as terephthalic acid.

The amine used to open the epoxy group as described above is generally a primary amine, a secondary amine,
Secondary amine. Examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, ketimine of aminoethylethanolamine. And secondary amines in which primary amines are blocked, such as diethylenetriamine diketimine. The amines may be used in combination of two or more.

When an amine having two or more active hydrogens is reacted, the amine functions as a chain extender of the epoxy resin, and makes the epoxy resin have a high molecular weight. These amines which react with the epoxy groups are preferably used in approximately equivalent amounts to the epoxy groups of the epoxy resin.

The number average molecular weight of the amine-modified epoxy resin by GPC analysis is preferably from 600 to 8,000. When the number average molecular weight is less than 600, the film-forming property is insufficient, and when it exceeds 8,000, it is difficult to disperse the binder component in an aqueous medium.

The amino group equivalent of the amine-modified epoxy resin is 20 to 250 milligram equivalent (me
q) Use the one of the degree. Preferably it is 40-200.

The curing agent is a component that cures the coating of the electrodeposition coating composition by crosslinking the cationic resin. In the present invention, a blocked polyisocyanate is used as a curing agent. The blocked polyisocyanate is a polyisocyanate in which the isocyanate group of the polyisocyanate is protected by a blocking agent.

The polyisocyanate which can be used for preparing the blocked polyisocyanate curing agent is 4,4'-
Diphenylmethane diisocyanate, m- or p-xylylene diisocyanate or mixtures thereof, 2,
4- or 2,6-tolylene diisocyanate, of the following formula (I):

Embedded image (Where n is an integer of 1 to 6) or a mixture thereof (aliphatic-aromatic compound), m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 1,5-naphthalene Diisocyanate, 1,4-naphthalenediisocyanate,
Aroma such as 4,4′-toluidine diisocyanate, 1,4-xylene diisocyanate (aromatic compound), dianisidine diisocyanate, 4,4-diphenyl ether diisocyanate, chlorodiphenyl diisocyanate or a mixture thereof (nuclear substituted aromatic compound) And group III polyisocyanate compounds.

In the present invention, among the above-mentioned isocyanates, an aromatic polyisocyanate compound, particularly an aliphatic-aromatic aromatic polyisocyanate compound, is preferred, and 4,4'-diphenylmethane diisocyanate is particularly preferably used. The polyisocyanate may be a polymerized polyisocyanate such as a dimer or trimer.

The blocking agent used for preparing the blocked polyisocyanate curing agent refers to a low molecular weight compound which is temporarily reacted with an isocyanate group in the polyisocyanate in order to prevent the isocyanate from reacting in a room temperature environment. Generally, the blocking agent is released from the isocyanate group under heating.

In the present invention, at least a lactam blocking agent is used as the blocking agent. Examples of the lactam blocking agent include ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam.

When an active hydrogen-containing blocking agent other than the lactam-based blocking agent is used together with the lactam-based blocking agent (hereinafter simply referred to as "active hydrogen-containing blocking agent"), the durability of the coating film is improved in addition to the low-temperature curability. It has been found that the properties can be further improved. When a curing agent blocked only with an active hydrogen-containing blocking agent is used, the corrosion resistance of the coating film is poor. As an active hydrogen-containing blocking agent,
For example, ethylene glycol monoalkyl ether-based blocking agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, ethylene glycol mono-2-ethylhexyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl Propylene glycol monoalkyl ether blocking agents such as ether; phenol blocking agents such as phenol, cresol, xylenol, chlorophenol and ethylphenol; active methylene blocking agents such as ethyl acetoacetate and acetylacetone; methanol, ethanol, propanol, butanol , Amyl alcohol, benzyl alcohol Alcohol-based blocking agents such as methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate and ethyl lactate; oxime-based blocking agents such as formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetylmonooxime, and cyclohexaneoxime; Mercaptan-based blocking agents such as butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based blocking agents such as acetate amide and benzamide; imide-based agents such as succinimide and maleic imide Blocking agents; imidazole-based blocking agents such as imidazole and 2-ethylimidazole; pyrazole-based blocking agents; and triazole-based blocking agents It can be mentioned. Preferred are ethylene glycol monoalkyl ether-based blocking agents and ethylene glycol mono-2-ethylhexyl ether.

The blocking agent used in the preparation of the blocked polyisocyanate is generally used in an equivalent amount to the isocyanate groups of the polyisocyanate.

The mixing ratio of the lactam blocking agent to the active hydrogen-containing blocking agent is preferably 2/8 to 1/0 in equivalent ratio. If the amount of the active hydrogen-containing blocking agent is too large,
The effect of improving corrosion resistance is reduced.

The amount of the curing agent is determined so that it reacts with the active hydrogen-containing functional groups such as primary, secondary and / or tertiary amino groups and hydroxyl groups in the cationic resin during curing to give a good cured coating film. Adjust. Generally expressed as a weight ratio of the amine-modified epoxy resin and the curing agent, 90/10 to 50/50, preferably 80/20 to 65 /
The range is 35.

The amino group equivalent is 20 to 250 milligram equivalents (meq), preferably 40 to 200 milligram equivalents, more preferably 50 to 150 milligram equivalents based on 100 g of the total weight of the amine-modified epoxy resin and the curing agent. If the amino group equivalent is too small, the dispersion stability of the binder component in an aqueous medium is reduced, and if it is too large, the throwing power of the coating composition is reduced. The amino group equivalent here is a value derived from an amine-modified epoxy resin. As the curing accelerator used in the cationic electrodeposition coating composition of the present invention, a combination of a copper catalyst and a zinc catalyst or a tin catalyst is used.

The copper catalyst is a compound capable of releasing copper ions in an aqueous medium, and examples thereof include copper acetate, copper acetylacetone, and copper formate.

The amount of the copper catalyst used is 200 to 2000 ppm, preferably 300 to 1500 ppm, based on the weight of the total coating composition in terms of copper. The copper conversion means a value obtained by dividing the mass of the copper catalyst compound when only copper is taken out by the total coating composition weight. Hereinafter, the same applies to tin conversion and zinc conversion. A plurality of catalysts may be used in combination, and in that case, the total used amount may be within the above range.

The zinc catalyst is a compound capable of releasing zinc ions in an aqueous medium, and examples thereof include zinc acetate, zinc lactate and zinc formate.

The tin catalyst includes a compound capable of releasing tin ions in an aqueous medium and a water-insoluble organotin compound. For example, a monoorganotin compound, a diorganotin compound (for example, dibutyltin oxide) and / or a triorganotin compound can be used, preferably a monoorganotin compound and / or a diorganotin compound,
More preferred are diorganotin compounds.

The amount of the zinc catalyst or the tin catalyst to be used relative to the copper catalyst is 1: 0.1 to 1:10, preferably 1: 1, in terms of the total weight of the weight of metal tin and the weight of zinc relative to the weight of copper.
0.2 to 1: 5. If it is less than 0.1, the corrosion resistance and curability decrease, and if it exceeds 10, the appearance of the coating film deteriorates.

The cationic electrodeposition coating composition of the present invention is obtained by dispersing the above-mentioned amine-modified epoxy resin, curing agent, curing accelerator and other components usually contained in the cationic electrodeposition coating composition in an aqueous medium. It is prepared by allowing The components may be dispersed by a usual method.

In the aqueous medium, various organic solvents may be used in addition to water to adjust the dissolution and viscosity of the resin.
Specific examples of organic solvents that can be used include, for example, hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n-butyl alcohol,
Isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene glycol), ethers (eg, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, propylene glycol monoethyl) Ether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether,
Diethylene glycol monobutyl ether), ketones (eg, methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate), and mixtures thereof. The use amount of these solvents is about 0.01 to 25% by weight, preferably 0.05 to 15% by weight, based on the whole paint. In addition, the organic solvent used at the time of preparation of a resin and a hardening agent may be used. In this case, after the resin or the curing agent is prepared, the resin or the curing agent may be used as it is without distilling off the organic solvent. In that case, the solid content weight ratio between the resin solution and the curing agent solution may be within the above range of the weight ratio.

The cationic electrodeposition coating composition of the present invention may contain, if necessary, components usually contained in the cationic electrodeposition coating composition, in addition to the above-mentioned components, in amounts usually used. Examples of such a component include a neutralizing agent, a pigment, a pigment-dispersed resin, a viscosity modifier, a surfactant, an antioxidant, and an ultraviolet absorber.

Pigments are generally included to impart color, hiding power, and corrosion resistance to the coating film. The electrodeposition coating composition of the present invention may contain a commonly used pigment. Examples of such pigments include coloring pigments such as titanium white, carbon black and red iron oxide, extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica, zinc phosphate, iron phosphate, Aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate,
Rust preventing pigments such as zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate are included.

When a pigment is used as a component of an electrodeposition coating composition, the pigment is generally dispersed in an aqueous medium at a high concentration in advance to form a paste. This is because the pigment is in powder form, and it is difficult to disperse the pigment in a single step in a low concentration uniform state used in the electrodeposition coating composition. Generally, such a paste is called a pigment dispersion paste.

The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersing resin in an aqueous medium. As the pigment dispersion resin, a cationic polymer such as a modified epoxy resin having a quaternary ammonium group, a tertiary sulfonium group, or an amino group, or a cationic or nonionic low molecular weight surfactant is generally used.

After mixing these components, the mixture is dispersed until the pigment has a predetermined uniform particle size to obtain a pigment-dispersed paste. A dispersing apparatus is usually used for dispersion. For example,
A ball mill, a sand grind mill, or the like is used. The particle size of the pigment contained in the pigment dispersion paste is usually 15 μm or less.

When the pigment-dispersed paste is mixed with the cationic electrodeposition coating composition, the amount of the pigment-dispersed paste is preferably not more than 50% by weight as a solid content in the cationic electrodeposition coating composition. .

The neutralizing agent is a component which binds to a cationic group contained in the cationic resin to form a salt and makes the cationic resin dispersible in an aqueous medium, and is an organic acid such as lactic acid or an inorganic acid. .

When electrodeposition coating is performed using the cationic electrodeposition coating composition of the present invention, the object to be coated is not particularly limited as long as it is conductive, and examples thereof include iron plates, steel plates, aluminum plates and the like. Those obtained by subjecting them to surface treatment, molded products thereof, and the like can be given.

The electrodeposition coating is usually carried out by applying a voltage of 50 to 450 V between the object to be coated as a cathode and the anode. If the applied voltage is less than 50 V, electrodeposition becomes insufficient, and if it exceeds 450 V, power consumption increases, which is uneconomical. When a voltage is applied within the above range using the composition of the present invention, a uniform film can be formed on the entire object without causing a sharp increase in the film thickness during the electrodeposition process.

When the above voltage is applied, the bath temperature of the cationic electrodeposition coating composition is usually preferably from 10 to 45 ° C.

The electrodeposition step includes (i) a step of immersing the object to be coated in the cationic electrodeposition coating composition, and (ii) a step of applying a voltage between the object and the anode by applying a voltage between the cathode and the anode. Is preferably formed. The time for applying the voltage varies depending on the electrodeposition conditions.
Can be 2-4 minutes.

After completion of the electrodeposition process, the electrodeposited film obtained as described above,
It is cured by baking for 10 to 30 minutes to obtain a cured coating film. The cationic electrodeposition coating composition of the present invention can be cured at a temperature as low as about 160 ° C., and even when cured at such a low temperature, the resulting coating film has high corrosion resistance.

The cationic electrodeposition coating composition of the present invention is used so that the thickness of the cured electrodeposition coating film is 10 to 30 μm. If it is less than 10 μm, the rust resistance is insufficient, and 30 μm
Exceeding this leads to waste of paint.

The substrate on which the coating film thus obtained is formed is further coated with a necessary intermediate coat and / or top coat according to the purpose. For example, in the case of a car outer panel, generally, after applying and baking a solvent-type, water-based or powder intermediate coating for imparting chipping resistance, a base coating is further applied and cured. A two-coat, one-bake coating method in which a clear paint is applied without coating, that is, a so-called wet-on-wet method, and then these films are simultaneously baked is applied.

[0051]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In the examples,
“Parts” and “%” are based on weight unless otherwise specified.

Synthesis of amine-modified epoxy resin 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2) was placed in a flask equipped with a stirrer, cooling tube, nitrogen inlet tube, thermometer and dropping funnel. 92 parts, methyl isobutyl ketone (MIBK) 95 parts and dibutyltin dilaurate 0.5
The department was charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction started at room temperature and was heated to 60 ° C. due to exotherm. Then, after continuing the reaction for 30 minutes, 57 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from a dropping funnel. Further, 42 parts of a 5 mol bisphenol A-propylene oxide adduct was added to the reaction mixture. The reaction was mainly performed at a temperature in the range of 60 to 65 ° C., and was continued until the absorption based on the isocyanate group disappeared in the measurement of the IR spectrum.

Thereafter, 1.0 part of benzyldimethylamine was added,
The reaction was carried out at 130 ° C. until the epoxy equivalent reached 410 parts.

Subsequently, 87 parts of bisphenol A was added to add 12 parts.
The reaction at 0 ° C. resulted in an epoxy equivalent of 1190. Thereafter, the reaction mixture was cooled and diethanolamine
11 parts, 24 parts of N-ethylethanolamine and 25 parts of a 79% by weight MIBK solution of a ketimine compound of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Then MIBK
To obtain an amine-modified epoxy resin (resin solid content: 80%).

The amino group equivalent of this amine-modified epoxy resin was 86 meq / 100 g (resin alone).

Synthesis of curing agent 1 4,4'-diphenylmethane diisocyanate (MDI) 1
250 parts and 266.4 parts of methyl isobutyl ketone were charged into a reaction vessel, heated to 80 ° C., and 2.5 parts of dibutyltin dilaurate was added. A solution obtained by dissolving 678 parts of ε-caprolactam in 696 parts of ethylene glycol mono-2-ethylhexyl ether (2-ethylhexyl cellosolve) was dropped into the above reaction vessel at 80 ° C over 2 hours. The temperature was increased to 100 ° C., and the mixture was heated for 4 hours, and it was confirmed that the absorption spectrum of the isocyanate group disappeared. Next, 387.1 parts of methyl isobutyl ketone was added to obtain a blocked polyisocyanate curing agent. Synthesis of Curing Agent 2 A blocked polyisocyanate curing agent was obtained in the same manner as in Synthesis 1 of the curing agent except that 1740 parts of ethylene glycol mono-2-ethylhexyl ether was used without using ε-caprolactam.

Synthesis of half-blocked isocyanate 222 parts of isophorone diisocyanate (IPDI) was placed in a reaction vessel and diluted with 39.1 parts of methyl isobutyl ketone.
0.2 parts of dibutyltin dilaurate was added, and the temperature was raised to 50 ° C.
Over 2 hours so as not to exceed. The reaction temperature was maintained at 50 ° C. for 1 hour with stirring to obtain a half-blocked isocyanate.

Preparation of Pigment Dispersion Resin A reaction vessel was charged with a bisphenol A type epoxy resin having an epoxy equivalent of 188 (manufactured by Dow Chemical Company) 382.2.
In a nitrogen atmosphere, the mixture was reacted at 150 to 160 ° C. for 1 hour, cooled to 120 ° C., and then 209.8 parts by weight of a half-blocked isocyanate (methyl isobutyl ketone solution) was added. After reacting at 140 to 150 ° C for 1 hour, 205.0 parts by weight of ethylene glycol monobutyl ether was added, and the mixture was cooled to 60 to 65 ° C.

There, 408.0 parts by weight of 1- (2-hydroxyethylthio) -2-propanol, 144.0 parts of deionized water
Parts by weight, 134 parts by weight of dimethylolpropionic acid,
The tertiary sulfonium for pigment dispersion is obtained by reacting at 65 to 75 ° C. until the acid value becomes 1, introducing a tertiary sulfonium group into the epoxy resin, and adding 1595.2 parts by weight of deionized water to terminate the tertiary conversion. A base-containing epoxy resin was obtained (resin solid content 30%).

Preparation of Pigment Dispersion Paste The pigment dispersion resin 20 prepared above was placed in a sand grind mill.
0 parts, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, 18.0 parts of aluminum phosphomolybdate and ion-exchanged water were dispersed until the particle size became 10 μm or less to obtain a lead-free pigment dispersion paste (solid Min 60
%).

Preparation of cationic electrodeposition coating composition 1 Using the amine-modified epoxy resin, curing agent and pigment dispersion paste prepared above, a cationic electrodeposition coating composition 1 was produced as follows. First, the amine-modified epoxy resin and the curing agent 1 were mixed at a ratio of 75:25 (weight ratio).

Thereafter, ethylene glycol mono-2-ethylhexyl ether was added to a concentration of 3% based on the solid content. 26.4 parts of 50% lactic acid and 6.4 parts of copper acetate were added to 800 parts of the binder component. Further, ion-exchanged water was added to dilute the mixture slowly. The MIBK was removed under reduced pressure so that the solid content was 36.0%, to obtain a main emulsion.

1580.2 parts of the main emulsion and 385.2 parts of the pigment dispersion paste were added and mixed with 2025.2 parts of ion-exchanged water and 9.3 parts of dibutyltin oxide.
A 0.0% by weight cationic electrodeposition paint was prepared. The solid content weight ratio of the pigment content to the total resin content in the electrodeposition paint is 1 / 3.5
Met. The amount of copper ions to the total coating composition weight is 45
It corresponded to 0 ppm, and the amount of dibutyltin oxide based on the total resin solid content in the coating composition was 1.5% (1110 ppm in the coating composition in terms of tin).

Preparation of Cathodic Electrocoating Composition 2 The cationic electrocoating composition was prepared in the same manner as in Example 1 except that 6.8 parts of zinc acetate (zinc ion catalyst) and 25.7 parts of 50% lactic acid were used instead of copper acetate. The product 2 was obtained. The amount of zinc ions relative to the total coating composition weight was equivalent to 450 ppm.

Preparation of cationic electrodeposition coating composition 3 A cationic electrodeposition coating composition 3 was obtained in the same manner as the cationic electrodeposition coating composition 1 except that the curing agent 2 was used instead of the curing agent 1. The amount of copper ions based on the total coating composition weight is
It was equivalent to 450 ppm.

Preparation of cationic electrodeposition coating composition 4 Cationic electrodeposition coating composition 4 was prepared in the same manner as cationic electrodeposition coating composition 1 except that 12.8 parts of copper acetate and 6.8 parts of zinc acetate (zinc ion catalyst) were used as curing accelerators. A coating composition 4 was obtained. The amount of copper ions corresponded to 900 ppm and the amount of zinc ions corresponded to 450 ppm, based on the total coating composition weight.

Evaluation The curability and corrosion resistance of the cationic electrodeposition coating compositions 1-4 prepared as described above were evaluated.

(Curable) A cationic electrodeposition coating composition was placed on a tin plate whose weight had been measured in advance, and the dried coating film had a thickness of 20 μm.
Electrodeposition so that it becomes 150 ℃, 160 ℃, 170 ℃
It baked for 10 minutes at each temperature of ° C, 190 ° C, and 220 ° C.

After measuring the weight of the obtained coated plate,
The mixture was refluxed for 6 hours in acetone and dried at 105 ° C for 20 minutes. After drying, the weight of the coated plate was measured. The gel fraction was determined by the following formula, and the curability was evaluated based on the following criteria. The results are shown in Table 1 below.

Gel fraction (%) = (W2−W0) / (W1−W0) × 100 (W0 is the weight of the tin plate, W1 is the weight of the coated plate after baking, and W2 is the weight of the coated plate after immersion in acetone. The results are ranked as follows and are shown in Table 1 below: ：: Gel fraction is 90% or more; ：: Gel fraction is 80% or more to less than 90%; Δ: Gel fraction is ×: The gel fraction is less than 70%.

(Corrosion resistance) A cold-rolled steel sheet (15 cm × 7 cm) obtained by treating the cationic electrodeposition coating composition with zinc phosphate was subjected to electrodeposition so that the thickness of the dried coating film became 20 μm. This is 150 ℃,
Baking was performed at each of 160 ° C, 170 ° C, 190 ° C, and 220 ° C for 10 minutes. The obtained cationic electrodeposition coating film was placed in a 5% saline solution at 55 ° C. for 240 minutes.
After immersion for a period of time, the coating film peeling widths on both sides of the long side of the steel sheet were measured, and the average value was calculated. The results are shown in Table 1 below. ◎: less than 3 mm; ○: 3 mm or more to 5 mm or less; ×: more than 5 mm.

[0072]

[Table 1]

Table 1 shows that the cationic electrodeposition coating compositions 1 and 4 are excellent in both low-temperature baking characteristics and corrosion resistance.

Further, when comparing the coating films baked at the same temperature of 160 ° C., coating composition 3 using a curing agent blocked only with 2-ethylhexyl cellosolve as a curing agent was used.
It can be seen that the coating compositions 1 and 2 using the curing agent blocked by using both 2-ethylhexyl cellosolve and caprolactam are much more excellent in corrosion resistance than those of the above.

When copper is not used as a curing accelerator,
Not only the corrosion resistance at the time of low-temperature curing is poor, but also the low-temperature curing property is poor.

[0076]

The cationic electrodeposition coating composition of the present invention has excellent low-temperature curability and corrosion resistance.

Continued on the front page (72) Inventor Mitsuo Yamada 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Nippon Paint Co., Ltd. (reference) 4J038 DB061 DB071 DB281 DB391 DG161 DG301 JA47 JC38 KA04 NA03 NA23 PA04 PB07 PC02

Claims (6)

[Claims] 1. A group consisting of (1) an amine-modified epoxy resin, (2) a blocked isocyanate curing agent obtained by blocking an aromatic polyisocyanate with at least a lactam blocking agent, and (3) a copper catalyst, a zinc catalyst and a tin catalyst. A cationic electrodeposition coating composition comprising at least one curing accelerator selected from the group consisting of: 2. The cationic electrodeposition coating composition according to claim 1, wherein the copper catalyst is copper acetate or copper acetylacetone. 3. The method according to claim 1, wherein the aromatic polyisocyanate is 4,4′-
Diphenylmethane diisocyanate, m- or p-xylylene diisocyanate or mixtures thereof, 2,
4- or 2,6-tolylene diisocyanate, dimer or trimer thereof, having the following formula (I): The cationic electrodeposition coating composition according to claim 1, wherein n is an integer of 1 to 6, or a mixture thereof. 4. The cationic electrodeposition coating composition according to claim 1, wherein the blocked isocyanate curing agent is blocked with a lactam-based blocking agent and an active hydrogen-containing blocking agent. 5. The cationic electrodeposition coating composition according to claim 4, wherein the mixing ratio of the lactam blocking agent / the active hydrogen-containing blocking agent is 2/8 to 1/0 in equivalent ratio. 6. The active hydrogen-containing blocking agent is an ethylene glycol monoalkyl ether-based blocking agent.
6. The cationic electrodeposition coating composition according to 4 or 5.