JP2013067790A - Electrodeposition coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodeposition coating composition which can form a hardened electrodeposition coating film that has excellent corrosion resistance.SOLUTION: The electrodeposition coating composition comprises an aminated resin (A), a hardener (B) and zinc phosphate (C), wherein the zinc phosphate (C) has an average particle diameter D(a diameter at 50% in volume distribution) of ≤3 μm, and the zinc phosphate (C) is contained in a state dispersed with a cationic dispersing agent.

Description

  The present invention relates to an electrodeposition coating composition capable of forming a cured electrodeposition coating film having excellent corrosion resistance.

  Electrodeposition coating can be applied to the details even if the workpiece has a complicated shape, and can be applied automatically and continuously, especially in large and complex shapes such as automobile bodies. It has been widely put into practical use as an undercoating method for articles to be coated. Cationic electrodeposition coating is widely used as such electrodeposition coating. Cationic electrodeposition coating is a coating method performed by immersing an object to be coated as a cathode in a cationic electrodeposition coating composition and applying a voltage.

  Before the cationic electrodeposition coating, the article to be coated is often subjected to a chemical conversion treatment such as a zinc phosphate chemical conversion treatment. By performing this chemical conversion treatment, corrosion resistance and adhesion can be improved. However, since the chemical conversion composition used in the zinc phosphate chemical conversion treatment has a high metal ion concentration and is very reactive, it is not preferable from the viewpoints of economy and workability, such as costly wastewater treatment. Further, in the chemical conversion treatment using the zinc phosphate-based chemical conversion treatment composition, water-insoluble salts are generated along with the metal surface treatment, and are deposited as precipitates in the chemical conversion treatment tank. Such precipitates are generally called sludge, and the generation of costs associated with the removal and disposal of sludge is regarded as a problem. In addition, in the surface treatment with the zinc phosphate-based chemical conversion treatment composition, it is necessary to prepare the surface in advance, and there is a problem in production efficiency that the surface treatment process becomes complicated and long.

  In place of such a zinc phosphate-based chemical conversion treatment composition, methods using a zirconium-based chemical conversion treatment composition are being studied. However, the chemical conversion treatment film formed using such a zirconium-based chemical conversion treatment composition may have a problem in that the amount of deposited film varies depending on the site (shape) of the substrate that is the object to be coated. It was. Generally, a chemical conversion treatment film formed using a zirconium-based chemical conversion treatment composition has a film deposition amount of 1/10 compared to a chemical conversion treatment film formed using a zinc phosphate-based chemical conversion treatment composition. Less to the extent. For this reason, there is a problem that the amount of deposited film is extremely reduced at a portion where the amount of deposited film is generally reduced in electrodeposition coating, resulting in poor corrosion resistance. Therefore, when chemical conversion treatment is performed using a zirconium-based chemical conversion treatment composition, a means for ensuring corrosion resistance with the electrodeposition coating composition is required even in a portion where the amount of chemical conversion coating film deposition is reduced. However, in the conventional electrodeposition coating composition, although it is possible to develop sufficient corrosion resistance by electrodeposition coating on a material whose coating is pretreated such as zinc phosphate, When the pre-treatment (such as chemical conversion treatment) of the product is insufficient, there is a problem that it is difficult to ensure corrosion resistance.

JP-A-8-12905 (Patent Document 1) contains P ₂ O _{5 in a} range of _{4 to} 22 mol%, ZnO 25 to 65 mol%, and SiO _{2 in} a range of 13 to 71 mol%. It shows a diffraction peak, has a median diameter of 1.0 to 3.0 μm by a laser particle size distribution measurement method, has an oil absorption of 40 to 65 ml / 100 g by the JISK5101 method, and has a bulk specific gravity of 0.3 by the Ishiyama specific volume test method. -0.5 g / ml, and the pH of the aqueous suspension at 25 ° C. is in the range of 5.5 to 9.0. Is described. On the other hand, the said component contained in patent document 1 and the component contained in the electrodeposition coating material composition of this invention differ in a structure.

JP-A-8-12905

  An object of the present invention is to provide an electrodeposition coating composition capable of forming a cured electrodeposition coating film having excellent corrosion resistance and coating film appearance.

The present invention
An electrodeposition coating composition comprising an aminated resin (A), a curing agent (B) and zinc phosphate (C),
This zinc phosphate (C) has an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less, and this zinc phosphate (C) is dispersed with a cationic dispersant in the electrodeposition coating composition. Included in the state,
An electrodeposition coating composition is provided, which solves the above problems.

The zinc phosphate (C) has an average particle diameter D ₅₀ (volume 50% diameter) of 1 μm or less, and the electrodeposition coating composition further includes a pigment selected from the group consisting of titanium dioxide, carbon black, and kaolin. This pigment (D) is contained in the electrodeposition coating composition in a state dispersed with a cationic dispersant, and the average particle diameter D ₅₀ (volume 50% diameter) of this pigment (D) is contained. Is more preferably 3 μm or less.

  More preferably, the cation dispersant used for the dispersion of zinc phosphate (C) is an aminosilane compound.

  Moreover, it is more preferable that content of the said zinc phosphate (C) contained in an electrodeposition coating material composition is 0.01-10 mass%.

  The zinc phosphate (C) is more preferably zinc phosphate obtained by a solid-liquid reaction in which phosphoric acid is added and reacted in a state in which a zinc compound and a cationic dispersant are dispersed.

  More preferably, the electrodeposition coating composition further contains aminotetrazole (E).

In the electrodeposition coating composition of the present invention, a cured product obtained by containing zinc phosphate (C) having an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less dispersed in a cationic dispersant. The excellent effect of improving the corrosion resistance of the electrodeposition coating film and improving the throwing power of the electrodeposition coating composition is obtained. The zinc phosphate (C) contained in the electrodeposition coating composition of the present invention is in a fine particle state in which the average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less and is dispersed in a cationic dispersant. Therefore, in the electrodeposition coating composition, it plays the same role as the neutralizing acid with respect to the film-forming resin component present in the emulsion state. Therefore, the storage stability of the electrodeposition coating composition is not impaired. In addition, this zinc phosphate (C) is subjected to zinc ions and phosphate ions from the state dispersed with a cation dispersant as the interfacial pH rises on the object to be coated with the application of voltage. Dissociate into. The zinc ions promote the precipitation of the film-forming resin component. Further, the effect of phosphate ions makes it possible to obtain excellent throwing power. Further, the zinc ions deposit on the object to be coated due to the catalytic effect of zinc. The crosslink density of the resin can be increased. Thus, there is an advantage that a cured electrodeposition coating film excellent in corrosion resistance is formed.
Since the electrodeposition coating composition of the present invention can form a cured electrodeposition coating film excellent in corrosion resistance, it can be suitably used in the electrodeposition coating of an article subjected to zirconium chemical conversion treatment.

It is a perspective view which shows an example of the box used when evaluating throwing power. It is sectional drawing which shows typically the evaluation method of throwing power.

  The electrodeposition coating composition of the present invention contains an aminated resin (A), a curing agent (B), and zinc phosphate (C). Hereinafter, each component will be described.

Aminated resin (A)
The electrodeposition coating composition of the present invention contains an aminated resin (A). This aminated resin (A) is a coating film forming resin constituting an electrodeposition coating film. As the aminated resin (A), a cation-modified epoxy resin obtained by modifying an oxirane ring in the resin skeleton with an organic amine compound is preferable. In general, a cation-modified epoxy resin is produced by ring-opening an oxirane ring in a starting material resin molecule by a reaction with a primary amine, a secondary amine, a tertiary amine, and / or an amine such as an acid salt thereof. A typical example of the starting material resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, and epichlorohydrin. Examples of other starting material resins include oxazolidone ring-containing epoxy resins described in JP-A-5-306327 and known. These epoxy resins can be prepared by reacting a diisocyanate compound or a bisurethane compound obtained by blocking an NCO group of a diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

  The above starting raw material resin can be used by extending the chain length with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before the oxirane ring-opening reaction with amines.

  Similarly, before the oxirane ring-opening reaction with amines, 2-ethylhexanol, nonylphenol, ethylene glycol is used for some oxirane rings for the purpose of adjusting molecular weight or amine equivalent and improving heat flow. Monohydroxy compounds such as mono-2-ethylhexyl ether, ethylene glycol mono n-butyl ether, and propylene glycol mono-2-ethylhexyl ether can also be added and used.

  Examples of amines that can be used for opening an oxirane ring and introducing an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine , N, N-dimethylbenzylamine, primary amines such as N, N-dimethylethanolamine, secondary amines or tertiary amines and / or their acid salts. Further, ketimine block primary amino group-containing secondary amine such as aminoethylethanolamine methyl isobutyl ketimine, diethylenetriamine diketimine can also be used. These amines must be reacted with at least an equivalent amount relative to the oxirane ring in order to open all the oxirane rings.

  The number average molecular weight of the aminated resin (A) is preferably 1,000 to 5,000. When the number average molecular weight is less than 1,000, physical properties such as solvent resistance and corrosion resistance of the obtained cured electrodeposition coating film may be inferior. On the other hand, when the number average molecular weight exceeds 5,000, it is difficult to adjust the viscosity of the aminated resin, which may cause problems in synthesis, and the obtained aminated resin (A) may be emulsified and dispersed. There is a risk of poor handling. The number average molecular weight of the aminated resin (A) is more preferably in the range of 1,600 to 3,200.

  In addition, in this specification, a number average molecular weight is a number average molecular weight of polystyrene conversion measured by gel permeation chromatography (GPC).

  The amine value (mg / g resin solid content in terms of KOH) of the aminated resin (A) is preferably within the range of 30 to 100 mgKOH / g. When the amine value of the aminated resin (A) is less than 30 mgKOH / g, the emulsion dispersion stability of the aminated resin (A) in the electrodeposition coating composition may be inferior. On the other hand, when the amine value exceeds 100 mgKOH / g, excessive amino groups remain in the cured electrodeposition coating film, and the water resistance of the coating film may be lowered. The amine value of the aminated resin (A) is more preferably in the range of 40 to 80 mgKOH / g.

  The hydroxyl value (mg / g resin solid content in terms of KOH) of the aminated resin (A) is preferably in the range of 50 to 350 mgKOH / g. When the hydroxyl value is less than 50 mgKOH / g, curing failure may occur in the cured electrodeposition coating film. On the other hand, when the hydroxyl value exceeds 350 mgKOH / g, excessive hydroxyl groups remain in the cured electrodeposition coating film, which may reduce the water resistance of the coating film. The hydroxyl value of the aminated resin (A) is more preferably in the range of 100 to 300 mgKOH / g.

  In the electrodeposition coating composition of the present invention, an aminated resin having a number average molecular weight of 1,000 to 5,000, an amine value of 30 to 100 mgKOH / g, and a hydroxyl value of 50 to 350 mgKOH / g By using (A), there is an advantage that excellent corrosion resistance can be imparted to the article to be coated.

  The aminated resin (A) may contain an amino group-containing acrylic resin, an amino group-containing polyester resin, or the like as necessary.

Curing agent (B)
The electrodeposition coating composition of the present invention contains a curing agent (B). As a hardening | curing agent (B), the component which can harden amination resin (A) can be arbitrarily used in the heating (baking) process after electrodeposition coating. As the curing agent (B), a blocked isocyanate curing agent is preferably used from the viewpoint of stability and coating performance. As the curing agent, organic curing agents such as melamine resin and phenol resin, silane coupling agents, metal curing agents and the like can also be used.

  The blocked isocyanate curing agent can be prepared by blocking polyisocyanate with a sealing agent. Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimers), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate, isophorone diisocyanate, and fats such as 4,4′-methylenebis (cyclohexyl isocyanate). Aromatic diisocyanates such as cyclic polyisocyanate, 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate and the like can be mentioned.

  Examples of sealants include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, methylphenyl carbinol; ethylene glycol mono Cellosolves such as hexyl ether and ethylene glycol mono 2-ethylhexyl ether; Polyether type terminal diols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol phenol; ethylene glycol, propylene glycol, 1,4-butanediol, etc. Polyester type terminal polyols obtained from diols of the above and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid and sebacic acid; para-t-butyl Phenols such as enol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam are preferably used. .

  The blocking ratio of the blocked isocyanate curing agent is preferably 100%. Thereby, there exists an advantage that the storage stability of an electrodeposition coating composition becomes favorable.

Zinc phosphate (C)
The electrodeposition coating composition of the present invention contains zinc phosphate (C). In the present invention, the zinc phosphate (C) has an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less, and the zinc phosphate (C) is cationically dispersed in the electrodeposition coating composition. It is contained in the state disperse | distributed with the agent.

The electrodeposition coating composition of the present invention is obtained by containing zinc phosphate (C) having an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less dispersed in a cationic dispersant. The excellent effect of improving the corrosion resistance of the cured electrodeposition coating film and improving the throwing power of the electrodeposition coating composition is obtained. The zinc phosphate (C) contained in the electrodeposition coating composition of the present invention is in a fine particle state in which the average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less and is dispersed in a cationic dispersant. Therefore, in the electrodeposition coating composition, it plays the same role as the neutralizing acid with respect to the film-forming resin component present in the emulsion state. Therefore, the storage stability of the electrodeposition coating composition is not impaired. In addition, this zinc phosphate (C) is subjected to zinc ions and phosphate ions from the state dispersed with a cation dispersant as the interfacial pH rises on the object to be coated with the application of voltage. Dissociate into. This zinc ion accelerates the deposition of the film-forming resin component, and it can obtain excellent throwing power due to the effect of phosphate ions, and further, the resin deposited on the object to be coated due to the catalytic effect of zinc. The crosslinking density of can be increased. Thus, there is an advantage that a cured electrodeposition coating film excellent in corrosion resistance is formed.

The average particle diameter D ₅₀ (volume 50% diameter) of zinc phosphate (C) is more preferably 1 μm or less. In the present invention, when the average particle diameter D ₅₀ (volume 50% diameter) of zinc phosphate (C) exceeds 3 μm, the coating appearance of the obtained cured electrodeposition coating film is lowered, and the corrosion resistance is also lowered. Become. The lower limit of the average particle diameter D ₅₀ of zinc phosphate (C) _(50% volume diameter) is not particularly limited, include aspects dispersion technique is in terms of, for example, 0.01μm or more at the present time.

The average particle diameter D ₅₀ (volume 50% diameter) is a particle diameter at which the cumulative curve is 50% when the cumulative curve is determined with the total volume of the particles as 100% based on the particle size distribution in the dispersion. is there. The average particle diameter D ₅₀ (volume 50% diameter) can be measured using a particle size measuring device such as a dynamic light scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., “Nanotrack UPA150”).

  The content of zinc phosphate (C) is preferably 0.01 to 10% by mass and more preferably 0.5 to 5% by mass with respect to 100 parts by mass of the electrodeposition coating composition. When the content of zinc phosphate (C) is less than 0.01% by mass, sufficient precipitation promoting effect cannot be obtained, and paintability such as throwing power may be insufficient. When the content of zinc phosphate (C) exceeds 10% by mass, the cohesive force is too strong, which may result in poor coating appearance.

  Examples of the cationic dispersant used for dispersion of zinc phosphate (C) include an aminosilane compound and a pigment dispersion resin having a cationic group.

Examples of the aminosilane compound include an aminosilane having at least one amino group in one molecule, and a hydrolysis condensate of aminosilane.
Specific examples of aminosilane having at least one amino group in one molecule include N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane. N- (2-aminoethyl) -3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- (1,3-dimethyl-butylidene ) Propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N- (vinylbenzyl) -2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride. “KBM-602”, “KBM-603”, “KBE-603”, “KBM-903”, “KBE-903”, “KBE-9103”, “KBM-603”, which are commercially available amino group-containing silane coupling agents "KBM-573", "KBP-90" (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), "XS1003" (trade names, manufactured by Chisso Corporation) and the like can be used. As the aminosilane compound, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and N- (2-aminoethyl) -3-aminopropyltriethoxysilane are preferable.

  An aminosilane hydrolyzed condensate can also be used as the aminosilane compound. When the aminosilane is subjected to a hydrolytic condensation reaction, it is preferable that the aminosilane is reacted under a condition that the aminosilane is more easily hydrolyzed and condensed. The conditions under which aminosilane is more easily hydrolyzed and condensable include, for example, reaction conditions in which a solvent is an alcohol, and reaction conditions by blending aminosilane that results in cocondensation rather than single condensation as described above. In addition, by carrying out the reaction under a condition where the aminosilane concentration is relatively high, a hydrolyzed condensate can be obtained under a condition of higher molecular weight and higher condensation rate. Specifically, it is preferable to condense the aminosilane concentration in the range of 5 mass% or more and 50 mass% or less. In addition, the aminosilane may be co-condensed with an alkoxysilane having no amino group such as epoxy silane “KBM-403” (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) as necessary.

  Examples of the pigment dispersion resin having a cationic group include a modified epoxy resin having at least one selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amine group. Examples of the epoxy resin that can be used for modification include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin. The pigment-dispersed resin having a cationic group is prepared by reacting a half-blocked blocked isocyanate curing agent with the above-described epoxy resin, and then various amines that can be used when introducing an amino group at the time of preparing the aminated resin (A). It can be prepared by reacting. In the above reaction, bisphenol A, bisphenol F and the like can be used together as necessary. It is more preferable to use a modified epoxy resin having a primary amine group as a pigment dispersion resin having a cationic group, which is used for dispersion of zinc phosphate (C).

The finely divided zinc phosphate used in the preparation of zinc phosphate (C) is obtained by dispersing zinc phosphate into fine particles by means of dispersion / stirring using a commonly used means such as a ball mill or a sand grind mill. Good. As another means of preparing particulate zinc phosphate, obtaining zinc phosphate in a particulate state by solid-liquid reaction in which zinc compound such as zinc oxide (solid state) is added and reacted. You can also. The zinc phosphate in a fine particle state obtained by this solid-liquid reaction has an advantage that a zinc phosphate having a spherical shape and a smaller average particle diameter D ₅₀ (volume 50% diameter) can be obtained. Therefore, there is an advantage that a dispersibility of zinc phosphate (C) in the electrodeposition coating composition is improved and a cured electrodeposition coating film having excellent coating film appearance and the like can be obtained.

Specific examples of the method for preparing zinc phosphate (C) that can be used in the present invention include, for example, the following three methods:
(1) By mixing zinc phosphate and the above aminosilane compound, and dispersing and stirring, the average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less and is in a state of being dispersed with a cationic dispersant. , A method of obtaining zinc phosphate (C),
(2) By mixing zinc phosphate and the above-mentioned pigment-dispersed resin having a cationic group, and dispersing and stirring, the average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less, and dispersed with a cationic dispersant. A method for obtaining zinc phosphate (C),
(3) The average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less by solid-liquid reaction in which zinc oxide is dispersed with the above-mentioned pigment-dispersed resin having a cationic group, and phosphoric acid is added to react with zinc oxide. A method for obtaining zinc phosphate (C), which is in a state dispersed with a cationic dispersant.
In the method (1) or (2), zinc phosphate (C) having a predetermined average particle diameter can be obtained by appropriately adjusting the conditions of dispersion and stirring.

In the electrodeposition coating composition of this invention, when the said zinc phosphate (C) is contained, there also exists an advantage that it becomes unnecessary to use an organotin hardening catalyst. Conventional electrodeposition coating compositions generally use an organic tin curing catalyst such as dibutyltin dilaurate or dioctyltin oxide as a curing catalyst. On the other hand, since these organotin compounds have recently been regarded as problematic in toxicity and are being studied for use restrictions, it is preferable that the electrodeposition coating composition of the present invention does not contain an organotin curing catalyst.
Here, the zinc phosphate (C) contained in the electrodeposition coating composition of the present invention contains zinc having a curing catalyst function. Therefore, when the said zinc phosphate (C) is contained, there exists an advantage that the usage-amount of an organic tin hardening catalyst can be reduced.

Pigment (D)
The electrodeposition coating composition of the present invention may contain a pigment usually used in an electrodeposition coating composition. Examples of pigments that can be used include commonly used inorganic pigments such as colored pigments such as titanium dioxide (titanium white), carbon black and bengara; such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay. Extender pigments; iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, and rust preventive pigments such as aluminum phosphomolybdate and aluminum zinc phosphomolybdate, Can be mentioned. When these pigments are contained in the electrodeposition coating composition, the amount of the pigment is preferably 1 to 30% by mass with respect to the resin solid content of the electrodeposition coating composition.

In the present invention, it is preferable that one or more pigments (D) selected from the group consisting of titanium dioxide, carbon black, and kaolin are included. The pigment (D) has an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less, and the pigment (D) is dispersed in the electrodeposition coating composition with a cationic dispersant. More preferably it is included. As the cationic dispersant, a pigment dispersion resin having a cationic group that can be used in the dispersion of zinc phosphate (C) can be used. However, since the aminosilane compound used for the dispersion of zinc phosphate (C) may aggregate when used as a dispersant for the pigment component (D), a pigment dispersion resin having a cationic group is used as the dispersant for the pigment (D). desirable.

  When a pigment is used as a component of an electrodeposition paint, generally, the pigment is dispersed in advance in an aqueous solvent at a high concentration to form a paste (pigment dispersion paste). This is because the pigment is in a powder form, and it is difficult to disperse it in a single step at a low concentration used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous solvent. As the pigment dispersion resin, a pigment dispersion resin having a cationic group such as the above-described modified epoxy resin having at least one selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amine group is used. Can do. As the aqueous solvent, ion-exchanged water or water containing a small amount of alcohol is used. In general, the pigment dispersion resin is used in an amount of 20 to 100 parts by mass with respect to 100 parts by mass of the pigment. After the pigment dispersion resin and the pigment are mixed, the pigment is dispersed using a normal dispersing device such as a ball mill or a sand grind mill until the pigment particle size in the mixture reaches a predetermined uniform particle size. A paste can be obtained. It is more preferable to disperse the pigment (D) until the average particle diameter D ₅₀ (volume 50% diameter) is 3 μm or less. The lower limit of the average particle diameter D ₅₀ (volume 50% diameter) of the pigment (D) is not particularly limited, but an embodiment in which the average particle diameter is ₅₀ μm or more from the viewpoint of the dispersion technique at the present time can be mentioned.

Aminotetrazole (E)
The electrodeposition coating composition of the present invention preferably further contains aminotetrazole (E). Aminotetrazole (E) effectively accelerates the crosslinking and curing reaction between the aminated resin (A) and the curing agent (B) contained in the electrodeposition coating composition, and improves the corrosion resistance of the resulting cured electrodeposition coating film. Can be made.

  When aminotetrazole (E) is used, the content of aminotetrazole (E) in the electrodeposition coating composition is preferably 0.01 to 5% by mass. When the content of aminotetrazole (E) exceeds 5% by mass, the coating stability may be lowered.

Other Additives The electrodeposition coating composition of the present invention is an organic coating such as ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethyl hexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Surfactants such as solvents, anti-drying agents, antifoaming agents, viscosity modifiers such as acrylic resin fine particles, anti-fogging agents, vanadium salts, copper, iron, manganese, magnesium, calcium, yttrium, lanthanum, cerium, neodymium, zirconium Ordinary paint additives such as inorganic rust preventives such as titanium salts may be added as necessary. In addition to these, known auxiliary complexing agents, buffering agents, smoothing agents, stress relaxation agents, brighteners, semi-brightening agents, plasticizers, antioxidants, and ultraviolet absorbers may be blended depending on the purpose. Good.

Other Film Forming Resin Components The electrodeposition coating composition of the present invention may contain other film forming resin components in addition to the aminated resin (A). Examples of other film forming resin components include acrylic resins, polyester resins, urethane resins, butadiene resins, xylene resins, and phenol resins. As another film forming resin component that can be contained in the electrodeposition coating composition, a xylene resin is preferable. Examples of the xylene resin include xylene resins having 2 to 10 aromatic rings. The other coating film-forming resin component can be contained up to 30% by mass in the coating film-forming resin component.

  In the present specification, the “resin solid content” means the solid mass of all solid contents of the coating film-forming resin contained in the electrodeposition coating composition. Specifically, it means the total amount of the solid content mass of the aminated resin (A), the curing agent (B), and other coating film-forming resin components as required, contained in the electrodeposition coating composition.

  The resin solid content of the electrodeposition coating composition is preferably 1 to 30% by mass. When the resin solid content of the electrodeposition coating composition is less than 1% by mass, the amount of electrodeposition coating film deposited decreases, and it may be difficult to ensure sufficient corrosion resistance. Moreover, when the resin solid content of the electrodeposition coating composition exceeds 30% by mass, the throwing power and the coating film appearance may be deteriorated.

Preparation of electrodeposition coating composition The electrodeposition coating composition of the present invention is prepared by dispersing an aminated resin (A), a curing agent (B), and a pigment dispersion paste as required in an aqueous solvent, and then phosphoric acid. It can be prepared by adding zinc (C) and, if necessary, pigment (D) and aminotetrazole (E) and mixing them.

  In the preparation of the electrodeposition coating composition, the dispersibility is improved by neutralizing the aminated resin (A) with a neutralizing acid. Organic acids such as formic acid, acetic acid and lactic acid are used as the neutralizing acid used for neutralization of the aminated resin (A). The amount of the neutralizing acid used is 10 to 30 mg equivalent (MEQ (A) with respect to 100 g of the resin solid content including the aminated resin (A), the curing agent (B) and the coating film forming resin as required. 10 to 30) is preferable. The lower limit is more preferably 15 mg equivalent (MEQ (A) 15), and the upper limit is more preferably 25 mg equivalent (MEQ (A) 25). If the amount of the neutralizing acid is less than 10 mg equivalent (MEQ (A) 10), the affinity for water is not sufficient and dispersion in water may be difficult. On the other hand, when the amount of the neutralizing acid exceeds 30 mg equivalent (MEQ (A) 30), the amount of electricity required for precipitation increases, the precipitation of the coating solid content decreases, and the throwing power may be inferior. There is.

  Here, MEQ (A) is an abbreviation for mg equivalent (acid), and is the mg equivalent of neutralizing agent (acid) per 100 g of the solid content of the paint. This MEQ (A) is prepared by accurately weighing about 10 g of an electrodeposition coating composition and dissolving it in about 50 ml of a solvent (THF), followed by potentiometric titration using a 1/10 N NaOH solution. The amount of acid contained in the product can be quantified and measured. The milligram equivalent (MEQ (A)) of the acid with respect to 100 g of the resin solid content of the electrodeposition coating composition can be adjusted by the amination of the aminated resin and the neutralized acid amount.

  The amount of the curing agent (B) is sufficient to react with active hydrogen-containing functional groups such as primary, secondary amino groups and hydroxyl groups in the aminated resin (A) during curing to give a good cured coating film. Amount is needed. A preferable amount of the curing agent (B) is 90/10 to 50 expressed in terms of a solid content mass ratio of the aminated resin (A) to the curing agent (B) (aminated resin (A) / curing agent (B)). / 50, more preferably in the range of 80/20 to 65/35. By adjusting the solid content ratio between the aminated resin (A) and the curing agent (B), the fluidity and curing speed of the coating film (deposition film) during film formation are improved, and the smoothness of the coating film (appearance of the coating film) ) Will improve.

  The electrodeposition coating composition is prepared by preparing a resin emulsion in which an aminated resin (A), a curing agent (B) and other coating film forming resin components as required are dispersed using a neutralizing acid, and phosphorus It can be prepared by separately preparing zinc acid (C) prepared by dispersing it using a cationic dispersant, adding these, and mixing them. When the pigment (D) is used, it may be dispersed together with a cationic dispersant during the preparation of the zinc phosphate (C) dispersion, or the rust preventive pigment (D) and / or the pigment may be separately dispersed. Good.

  The electrodeposition coating composition of the present invention preferably contains substantially no tin compound or lead compound. In the present specification, “the electrodeposition coating composition is substantially free of both a tin compound and a lead compound” means that the concentration of the lead compound contained in the electrodeposition coating composition does not exceed 50 ppm as a lead metal element, And it means that the concentration of the organic tin compound does not exceed 50 ppm as a tin metal element. The electrodeposition coating composition of the present invention contains zinc phosphate (C). Therefore, there is no need to use a rust inhibitor, a lead compound as a curing catalyst, or an organic tin compound. Thereby, the electrodeposition coating composition which does not contain any of a tin compound and a lead compound can be prepared.

Electrodeposition coating
Coatings Various coatings that can be energized can be used as coatings for applying the electrodeposition coating composition of the present invention. Examples of coatings that can be used include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy based plating. Examples of the coating material include steel plates, zinc-aluminum-magnesium alloy-plated steel plates, aluminum-plated steel plates, aluminum-silicon alloy-plated steel plates, and tin-based plated steel plates.

  In addition, before forming the electrodeposition coating film, foreign substances such as rust preventive oil and processing oil adhering to the object to be coated may be removed using an alkaline degreasing liquid and / or washing water, if necessary. .

Electrodeposition process Electrodeposition is usually carried out by applying a voltage of 50 to 450 V between the object to be coated as the cathode and the anode. If the applied voltage is less than 50V, electrodeposition may be insufficient, and if it exceeds 450V, the coating film may be destroyed and the appearance may be abnormal. At the time of electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

  The electrodeposition coating process is composed of a process of immersing an object to be coated in an electrodeposition paint composition, and a process of applying a voltage between the above-mentioned object to be coated as a cathode and an anode to deposit an electrodeposition film. Is done. Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 5 minutes.

  The film thickness of the electrodeposition coating film after baking is preferably 5 to 40 μm, more preferably 10 to 25 μm. If the film thickness is less than 5 μm, the corrosion resistance may be insufficient. On the other hand, if it exceeds 40 μm, it leads to waste of paint.

  The electrodeposition coating film obtained as described above is baked by baking it at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water. A cured cured electrodeposition coating is formed.

  The electrodeposition coating composition of the present invention can be suitably used for an object to be coated that has been subjected to a chemical conversion treatment using a zirconium-based chemical conversion treatment composition. More specifically, by using the electrodeposition coating composition of the present invention, it is possible to compensate for a variation in the amount of deposited film in the chemical conversion treatment using the zirconium-based chemical conversion treatment composition, and to impart sufficient corrosion resistance. be able to. The coating film formed using the electrodeposition coating composition of the present invention also has an advantage that a coating film having high coating film smoothness (coating film appearance) can be obtained.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1-1 Production of Aminated Resin (Resin A) 92 parts of methyl isobutyl ketone, 940 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company), 350 parts of bisphenol A, 95 parts of octylic acid, dimethyl 2 parts of benzylamine was added, the temperature in the reaction vessel was maintained at 120 ° C., and the reaction was continued until the epoxy equivalent reached 1170 g / eq, followed by cooling until the temperature in the reaction vessel reached 110 ° C. Then, a mixture of 82 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%), 26 parts of N-methylethanolamine and 60 parts of diethanolamine was added and reacted at 110 ° C. for 1 hour to give an aminated resin (cationic). Modified epoxy resin: Resin A) was obtained.
The number average molecular weight of this resin was 2,600, the amine value was 58 mgKOH / g (of which the amine value derived from the primary amine was 17 mgKOH / g), and the hydroxyl value was 240 mgKOH / g.

Production Example 1-2 Production of Aminated Resin (B) 92 parts of methyl isobutyl ketone, 940 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company), 350 parts of bisphenol A, 30 parts of octylic acid, dimethylbenzyl After adding 2 parts of amine and maintaining the temperature in the reaction vessel at 120 ° C. until the epoxy equivalent was 820 g / eq, the reaction vessel was cooled until the temperature in the reaction vessel was 110 ° C. Subsequently, 160 parts of diethanolamine was added and reacted at 110 ° C. for 1 hour to obtain an aminated resin (cation-modified epoxy resin: resin B).
The number average molecular weight of this resin was 2,600, the amine value was 58 mgKOH / g, and the hydroxyl value was 310 mgKOH / g.

Production Example 2-1 Production of Blocked Isocyanate Curing Agent (1) 1680 parts of hexamethylene diisocyanate (HDI) and 732 parts of methyl isobutyl ketone were charged into a reaction vessel and heated to 60 ° C. A solution obtained by dissolving 346 parts of trimethylolpropane in 1067 parts of MEK oxime was added dropwise at 60 ° C. over 2 hours. Further, after heating at 75 ° C. for 4 hours, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group had disappeared, and after standing to cool, 27 parts of methyl isobutyl ketone was added to cure the blocked isocyanate having a solid content of 78%. Agent (1) was obtained. The isocyanate group value was 252 mgKOH / g.

Production Example 2-2 Production of Blocked Isocyanate Curing Agent (2) 1340 parts of diphenylmethane diisocyanate and 277 parts of methyl isobutyl ketone were charged into a reaction vessel and heated to 80 ° C., and then 226 parts of ε-caprolactam was added to 944 parts of butyl cellosolve. What was dissolved in was dropped at 80 ° C. over 2 hours. Further, after heating at 100 ° C. for 4 hours, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group disappeared, and after standing to cool, 349 parts of methyl isobutyl ketone was added to obtain a blocked isocyanate curing agent (2). (Solid content 80%). The isocyanate group value was 251 mgKOH / g.

Production Example 3 Production of Pigment Dispersion Resin 385 parts of bisphenol A type epoxy resin, 120 parts of bisphenol A, 95 parts of octylic acid, 2-ethyl-4-methyl in a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe and a thermometer 1 part of imidazole 1% solution was charged, reacted at 160-170 ° C. for 1 hour under a nitrogen atmosphere, then cooled to 120 ° C., and then methyl isobutyl ketone solution of 2-ethylhexanolated half-blocked tolylene diisocyanate (solid content 95 %) 198 parts were added. After maintaining the reaction mixture at 120 to 130 ° C. for 1 hour, 157 parts of ethylene glycol mono n-butyl ether was added. And it cooled to 85-95 degreeC and made it uniform. Next, 277 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%) was added and stirred at 120 ° C. for 1 hour, and 13 parts of ethylene glycol mono-n-butyl ether was added to produce an aminated resin. Next, 18 parts of ion exchange water and 8 parts of formic acid were added, the aminated resin was mixed and stirred for 15 minutes, 200 parts of ion exchange water was mixed, and a pigment dispersion resin having a primary amine group (average molecular weight 2,200). ) Resin solution (resin solid content 25%).

Production Example 4-1 Production of Electrodeposition Paint Resin Emulsion (Em1) 350 g of aminated resin (resin A) obtained in Production Example 1 (in terms of solid content) and blocked isocyanate curing agent obtained in Production Example 2-1 (1 ) And the blocked isocyanate curing agent (2) obtained in Production Example 2-2, 75 g (in terms of solid content), respectively, and ethylene glycol mono-2-ethylhexyl ether to 15 g (3% relative to the total solid content) It added so that it might become. Next, formic acid is neutralized by adding 40% neutralization, ion-exchanged water is added to slowly dilute, and then methyl isobutyl ketone is removed under reduced pressure so that the solid content is 36%. An electrodeposition paint resin emulsion (Em1) was obtained.

Production Example 4-2 Production of Electrodeposition Paint Resin Emulsion (Em2) 400 g of aminated resin (resin A) obtained in Production Example 1 (in terms of solid content) and blocked isocyanate curing agent obtained in Production Example 2-1 (1 ) 100 g (converted to solid content) and ethylene glycol mono-2-ethylhexyl ether was added to 15 g (3% relative to the total solid content). Next, formic acid is neutralized by adding 40% neutralization, ion-exchanged water is added to slowly dilute, and then methyl isobutyl ketone is removed under reduced pressure so that the solid content is 36%. An electrodeposition paint resin emulsion (Em2) was obtained.

Production Example 4-3 Production of Electrodeposition Paint Resin Emulsion (Em3) 350 g (solid content) of the aminated resin (resin B) obtained in Production Example 2 and blocked isocyanate curing agent (1) obtained in Production Example 2-1. Each of the blocked isocyanate curing agents (2) obtained in Production Example 2-2 was mixed with 75 g (solid content), so that ethylene glycol mono-2-ethylhexyl ether was 3% (15 g) based on the solid content. Added. Next, formic acid is neutralized by adding 40% neutralization, ion-exchanged water is added to slowly dilute, and then methyl isobutyl ketone is removed under reduced pressure so that the solid content is 36%. An electrodeposition paint resin emulsion (Em3) was obtained.

Production Example 5-1 Production of zinc phosphate dispersed paste (1) (zinc phosphate fine particles 1)
30 g of aminosilane (KBM603) was added to 570 g of ion-exchanged water with stirring, and hydrolyzed at room temperature for 30 minutes. Next, 400 g of zinc phosphate (reagent) was added and stirred for 10 minutes. Thereafter, using a sand mill, the dispersion was prepared until the average particle diameter D ₅₀ (volume 50% diameter) became 0.6 μm at 40 ° C., and thus a zinc phosphate dispersion paste (1) (solid content 43%) was obtained. .
The average particle diameter D ₅₀ (volume 50% diameter) is measured using a laser Doppler type particle size analyzer (manufactured by Nikkiso Co., Ltd., “Microtrac UPA150”), and ion exchange is performed so that the signal level of the dispersion becomes appropriate. and diluted with water to measure the average particle diameter _{D 50} (volume 50% diameter).

Production Example 5-2 Production of zinc phosphate dispersed paste (2) (zinc phosphate fine particles 2)
A zinc phosphate dispersion paste (2) (2) (dispersed and prepared in the same manner as in Production Example 5-1, except that the average particle size D ₅₀ (50% volume diameter) was 1.5 μm. 43% solids) was obtained.

Production Example 5-3 Production of zinc phosphate dispersed paste (3) (zinc phosphate fine particles 3)
100 g of pigment-dispersed resin obtained in Production Example 3 (in terms of solid content) was added to 50 g of ion-exchanged water, and 290 g of zinc oxide (reagent) was further added, followed by stirring for 15 minutes. Then, it was dispersed at 40 ° C. using a sand mill. Next, 280 g of 75% phosphoric acid (reagent) was gradually added and dispersed while reacting to prepare a zinc phosphate dispersed paste (3) (solid content 55%, average particle diameter D ₅₀ (volume 50% diameter)). 4 μm).

Production Example 5-4 Production of Zinc Phosphate Dispersion Paste (4) (Zinc Phosphate Fine Particles 4)
Prepared by dispersing in the same manner as in Production Example 5-1, except that 30 g (in terms of solid content) of the pigment dispersion resin obtained in Production Example 3 was used instead of the aminosilane used in Production Example 5-1. A zinc phosphate dispersion paste (4) (average particle diameter D ₅₀ (volume 50% diameter) 3.5 μm) was obtained.

Production Example 5-5 Production of zinc phosphate dispersed paste (5) (zinc phosphate fine particles 5)
Instead of the aminosilane used in Production Example 5-1, 30 g (in terms of solid content) of the pigment dispersion resin obtained in Production Example 3 was used, and the dispersion solid content was 40%. It was prepared by dispersing in the same manner to obtain a zinc phosphate dispersion paste (5) (average particle diameter D ₅₀ (volume 50% diameter) 0.6 μm).

Production Example 6 Production of Pigment Dispersion Paste for Electrodeposition Paint Using a sand mill, based on the formulation shown in the following Table 1 containing the pigment dispersion resin obtained in Production Example 3, the resulting mixture was averaged at 40 ° C. Dispersion was carried out until the diameter D ₅₀ (volume 50% diameter) was 0.6 μm, and a pigment dispersion paste for electrodeposition paint (solid content 49%) was obtained.

Production Example 7 Production of Dispersion Paste Containing Pigment and Tin Curing Catalyst In the same manner as in Production Example 6 using a sand mill, it was obtained based on the formulation shown in Table 2 below containing the pigment-dispersed resin obtained in Production Example 3. The mixture was dispersed at 40 ° C. until the average particle diameter D ₅₀ (volume 50% diameter) was 0.6 μm, and prepared to obtain a dispersion paste (solid content 49%) containing a pigment and a tin curing catalyst. . The obtained dispersion paste containing a pigment and a tin curing catalyst was used in Comparative Example 3 and Reference Example 1.

Example 1
17 parts of electrodeposition paint resin emulsion (2) of Production Example 4-2 (described as “Resin Em (2)” in Table 3) containing ion-exchanged water, aminated resin and blocked isocyanate curing agent in a stainless steel container Then, 0.3 parts of the zinc phosphate dispersion paste (1) of Production Example 5-1 (described as “dispersion paste (1)” in Table 3) and the pigment dispersion paste of Production Example 6 were added and mixed, and then Aging was performed at 40 ° C. for 16 hours. In Table 3 below, the amount of 0.3 parts of the zinc phosphate dispersion paste (1) is the mass of the zinc phosphate, not the amount of the zinc phosphate dispersion paste. The amount of the pigment was added so that the total mass of titanium dioxide, carbon black and kaolin would be the amount shown in Table 3 below (2.7 parts).

  “MEQA” described in Table 3 below is the milligram equivalent (MEQ (A)) of acid to 100 g of resin solid content of the electrodeposition coating composition. The MEQ (A) was determined by accurately weighing 10 g of the electrodeposition coating composition and dissolving it in 50 ml of a solvent (THF), followed by potentiometric titration using a 1/10 N NaOH solution.

Examples 2 to 10 and Comparative Examples 1 to 3 Production of Electrodeposition Coating Composition Into a stainless steel container, the components listed in Table 3 were mixed in the amounts shown in Table 3, and then aged at 40 ° C. for 16 hours. In Table 3 below, the amounts of the zinc phosphate dispersion pastes (1) to (5) were added so that the mass of the zinc phosphate would be the amount in Table 3 below. Further, in Examples 2 to 10 and Comparative Examples 1 and 2, the amount of the pigment was added so that the total mass of titanium dioxide, carbon black, and kaolin was the amount shown in Table 3 below. In Comparative Example 3, the total mass of titanium dioxide, carbon black, kaolin and tin was added so as to be in the amount shown in Table 3 below.

  In Example 9, aminotetrazole (manufactured by Masuda Chemical Co., Ltd.) was added so as to have the amount shown in Table 3.

  In Example 10, calcium nitrite (manufactured by Nissan Chemical Industries, Ltd.) was added so as to have the amount shown in Table 3.

  In Comparative Example 2, an aqueous solution in which 10 parts by mass of zinc acetate dihydrate was previously dissolved in 90 parts by mass of ion-exchanged water was added so as to have the amount shown in Table 3 when converted to metal as zinc.

  In Comparative Example 3, instead of the pigment dispersion paste of Production Example 6, the dispersion paste containing the pigment and tin curing catalyst of Production Example 7 was used.

An electrodeposition-coated cold-rolled steel sheet (JIS G3141, SPCC-SD) using the electrodeposition paint compositions of Examples and Comparative Examples was immersed in Surf Cleaner EC90 (Nihon Paint Co., Ltd.) at 50 ° C. for 2 minutes, Degreased. Next, the zirconium chemical conversion treatment was performed by immersing in a zirconium chemical conversion solution containing 500 ppm of ZrF and adjusted to pH 4 with NaOH at 40 ° C. for 90 seconds.
Next, the steel sheet subjected to the zirconium chemical conversion treatment was immersed in the electrodeposition coating compositions obtained in the above examples and comparative examples, and the voltage (150 seconds after reaching the voltage of 180 V for 30 seconds) was listed in the table. (Second holding) was applied to deposit an uncured electrodeposition coating on the object. Subsequently, it heated at the baking temperature described in Table 3 for 15 minutes, and the cured electrodeposition coating film was formed. The following evaluation was performed using the obtained cured electrodeposition coating film.

Reference example 1
Reference Example 1 is a reference example in which zinc phosphate conversion treatment was performed before electrodeposition coating. The electrodeposition coating composition used in Reference Example 1 was mixed by adding the dispersion emulsion containing the resin emulsion (1) of Production Example 4-1 and the pigment of Production Example 7 and a tin curing catalyst in the blending amounts shown in Table 3. And then aged at 40 ° C. for 16 hours. The amount of the pigment was added so that the total mass of titanium dioxide, carbon black, kaolin and tin was the amount shown in Table 3 below.

In the electrodeposition coating reference example 1 using the reference example 1, the cold-rolled steel sheet (JIS G3141, SPCC-SD) was degreased by immersing it in a surf cleaner EC90 (manufactured by Nippon Paint Co., Ltd.) at 50 ° C. for 2 minutes. The surface is adjusted with Surf Fine GL-1 (manufactured by Nippon Paint Co., Ltd.), and then in SurfDyne SD-5000 (manufactured by Nippon Paint Co., Ltd., zinc phosphate chemical conversion treatment liquid) at 40 ° C. for 2 minutes. It was immersed and a zinc phosphate chemical conversion treatment was performed. Next, electrodeposition coating was performed in the same manner as in Example 1 using the electrodeposition coating composition obtained above.

  The following evaluation tests were conducted using the electrodeposition coating compositions and coated plates obtained in the above Examples, Comparative Examples and Reference Examples.

Cycle Corrosion Test (CCT)
The coating film of the resulting coated plate was cross-cut with a knife so as to reach the substrate, and JASO M609-91 “Automobile Material Corrosion Test Method” was performed 100 cycles. Thereafter, the occurrence of rust and blistering from the crosscut portion was observed to evaluate the corrosion resistance in accordance with the actual corrosive environment. The evaluation criteria are as follows.

Evaluation standard ◎: Maximum width of rust or swelling is less than 5mm from the cut part (both sides)
○: The maximum width of rust or swelling is 5 mm or more and less than 7.5 mm (both sides) from the cut part. No blister other than the cut part. ○ △: The maximum width of rust or swelling is 5 mm or more and less than 7.5 mm (both sides) from the cut part. There is also a blister other than the part Δ: The maximum width of rust or blister is 7.5mm or more and less than 10mm from the cut part
Δ: The maximum width of rust or swelling is 10 mm or more and less than 12.5 mm from the cut part (both sides)
X: The maximum width of rust or blisters is 12.5 mm or more from the cut part (both sides)

Salt water immersion test (SDT) test Cold rolled steel sheet (JIS G3141, SPCC-SD) was immersed in Surf Cleaner EC90 (Nihon Paint Co., Ltd.) at 50 ° C. for 2 minutes for degreasing treatment. Next, a steel sheet is immersed in the electrodeposition coating composition obtained in the examples or comparative examples, and a voltage is applied in the same manner as described above under the conditions described in the table, so that an uncured electrode is applied on the object to be coated. A coated film was deposited. Subsequently, it heated at the baking temperature described in Table 3 for 15 minutes, and the cured electrodeposition coating film was formed.
A linear wound was made with a knife so as to reach the substrate in the coating film of the electrodeposition coating plate after curing. After this coated plate was immersed in 5% saline at 480 ° C. for 480 hours, rust and blistering from a linear scratch were observed and evaluated. The evaluation criteria are as follows.

Evaluation standard ◎: No rust or blisters occurred ○: Maximum width of rust or blisters is less than 2.5 mm from the cut part (both sides) No blister ○ △: Maximum width of rust or blisters is less than 2.5 mm from the cut part ( Both sides) With blisters △: Maximum width of rust or blister is 2.5mm or more and less than 5mm from the cut part (both sides)
Δ: The maximum width of rust or blister is 5mm or more and less than 10mm from the cut part (both sides)
X: The maximum width of rust or blister is 10mm or more from the cut part (both sides)

Evaluation of Curability The coated film having the cured electrodeposition coating film obtained as described above was rubbed 10 times with gauze soaked with methyl isobutyl ketone, and the peeled state was visually evaluated based on the following evaluation criteria.

Evaluation criteria ○: No peeling ○ △: Slight peeling ×: With peeling

Evaluation of throwing power The throwing power was evaluated by a so-called four-sheet box method. That is, as shown in FIG. 1, the four steel sheets 11 to 14 subjected to the chemical conversion treatment are arranged in parallel in an upright state with an interval of 20 mm, and the lower and bottom surfaces of both sides are made of an insulating material such as cloth adhesive tape. A sealed box 10 was prepared. In addition, the steel plates 11 to 13 other than the steel plate 14 are provided with an 8 mmφ through hole 15 at the bottom. 4 liters of the electrodeposition coating composition obtained in the above examples and comparative examples was transferred to a vinyl chloride container to form a first electrodeposition bath. As shown in FIG. 2, the box 10 was immersed in an electrodeposition paint container 20 containing an electrodeposition paint 21 as an object to be coated. In this case, the paint 21 enters the box 10 only from each through hole 15.

  The electrodeposition coating composition 21 was stirred with a magnetic stirrer (not shown). And each steel plate 11-14 was electrically connected and the counter electrode 22 was arrange | positioned so that the distance with the nearest steel plate 11 might be set to 150 mm. Cathode electrodeposition coating was performed on the steel plates subjected to the zirconium chemical conversion treatment by applying a voltage with the steel plates 11 to 14 as cathodes and the counter electrode 22 as an anode. The coating was performed by increasing the voltage to a voltage at which the film thickness of the coating film formed on the A surface of the steel plate 11 reached 15 μm in 30 seconds from the start of application, and then maintaining the voltage for 150 seconds.

  Each steel sheet after painting is washed with water, baked at 170 ° C. for 25 minutes, and after air cooling, the film thickness of the coating film formed on the A surface of the steel sheet 11 closest to the counter electrode 22 and the farthest from the counter electrode 22 The film thickness of the coating film formed on the G surface of the steel plate 14 was measured, and the throwing power was evaluated by the ratio (G / A value) of film thickness (G surface) / film thickness (A surface).

Gas pin resistance evaluation GA steel sheet that has been subjected to zirconium chemical conversion treatment is immersed, and a voltage is applied under the conditions described in Table 3 (after reaching a voltage of 200 V for 30 seconds and holding for 150 seconds), on the object to be coated. An uncured electrodeposition coating was deposited. Subsequently, it heated for 15 minutes at the baking temperature described in the table | surface, and the cured electrodeposition coating film was formed. Evaluation was performed based on the following evaluation criteria using the obtained cured electrodeposition coating film.

Evaluation criteria ○: No gas pin generated △: Gas pin generated slightly ×: Gas pin generated on the entire surface

Appearance of cured electrodeposition coating film The presence or absence of abnormality in the appearance of the cured electrodeposition coating film was visually determined. The evaluation criteria were as follows.

Evaluation Criteria A: Very uniform coating appearance B: Uniform coating appearance B: Appears if there is some unevenness, but almost uniform coating as a whole Appearance △: Unevenness is visually recognized x: Appearance of the coating is clearly uneven

Stability of the electrodeposition coating composition In a state where the electrodeposition coating composition was left standing or stirred, the state of the coating composition was visually determined to evaluate the stability. The evaluation criteria were as follows.

Evaluation criteria ○: The electrodeposition coating composition is satisfactorily dispersed and stable in a standing state. ○ △: The pigment component is likely to settle and is not stable in the state where the electrodeposition coating composition is left standing, but is stirred again. Δ: It is necessary to continue stirring continuously in order to maintain the dispersion state of the electrodeposition coating composition. X: Dispersion even when the electrodeposition coating composition is continuously stirred. Does not stabilize

All of the electrodeposition coating compositions of the examples were excellent in paint stability, exhibited excellent corrosion resistance in the obtained cured electrodeposition coating film, and were excellent in throwing power and gas pin resistance. .
Comparative Example 1 is an experimental example in which the average particle diameter D ₅₀ (volume 50% diameter) of zinc phosphate contained in the zinc phosphate dispersion paste exceeds 3 μm. In this case, the obtained cured electrodeposition coating film was inferior in corrosion resistance, and also incurability and throwing power.
Comparative Example 2 is an experimental example containing zinc acetate instead of zinc phosphate. Also in this case, the obtained cured electrodeposition coating film was inferior in corrosion resistance, further inferior in gas pin resistance, and the coating film appearance of the obtained coating film was also inferior. In addition, the throwing power of this electrodeposition coating composition was significantly reduced.
Comparative Example 3 is an experimental example that does not contain zinc phosphate and uses dibutyltin oxide as a curing catalyst. Also in this case, the obtained cured electrodeposition coating film was inferior in corrosion resistance, further inferior in gas pin resistance, and in throwing power.
Reference Example 1 is an experimental example in which a chemical conversion treatment was performed using a zinc phosphate chemical conversion treatment solution. By comparison between the results of Reference Example 1 and the results of Examples 1 to 10, the electrodeposition coating composition of the example was prepared by applying the zinc phosphate chemical conversion treatment liquid even when the electrodeposition coating was performed after the zirconium chemical conversion treatment. It was confirmed that corrosion resistance and throwing power equivalent to or higher than those obtained by electrodeposition coating using a conventional electrodeposition coating composition after chemical conversion treatment were obtained.

In the electrodeposition coating composition of the present invention, a cured product obtained by containing zinc phosphate (C) having an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less dispersed in a cationic dispersant. The excellent effect of improving the corrosion resistance of the electrodeposition coating film and improving the throwing power of the electrodeposition coating composition is obtained. Since the electrodeposition coating composition of the present invention can form a cured electrodeposition coating film excellent in corrosion resistance, it can be suitably used in the electrodeposition coating of an article subjected to zirconium chemical conversion treatment.

10: Box 11-14: Chemical conversion treatment steel plate 15: Through hole 20: Electrodeposition coating container 21: Electrodeposition paint 22: Counter electrode

Claims (6)

An electrodeposition coating composition comprising an aminated resin (A), a curing agent (B) and zinc phosphate (C),
The zinc phosphate (C) has an average particle diameter D ₅₀ (volume 50% diameter) of 3 μm or less, and the zinc phosphate (C) is dispersed with a cationic dispersant in the electrodeposition coating composition. Included in the state,
Electrodeposition paint composition. The zinc phosphate (C) has an average particle diameter D ₅₀ (volume 50% diameter) of 1 μm or less, and the electrodeposition coating composition is further a pigment selected from the group consisting of titanium dioxide, carbon black, and kaolin In the electrodeposition coating composition, the pigment (D) is contained in a state dispersed with a cationic dispersant, and the pigment (D) has an average particle diameter D ₅₀ (volume 50% diameter). Is 3 μm or less,
The electrodeposition coating composition according to claim 1.   The electrodeposition coating composition according to claim 1 or 2, wherein the cationic dispersant used for dispersion of the zinc phosphate (C) is an aminosilane compound.   The electrodeposition coating composition according to any one of claims 1 to 3, wherein a content of the zinc phosphate (C) contained in the electrodeposition coating composition is 0.01 to 10% by mass.   The zinc phosphate (C) is zinc phosphate obtained by a solid-liquid reaction in which phosphoric acid is added and reacted in a state where a zinc compound and a cationic dispersant are dispersed. The electrodeposition coating composition as described.   The electrodeposition coating composition according to any one of claims 1 to 5, wherein the electrodeposition coating composition further contains aminotetrazole (E).

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