JPH108291A - Cation electrodeposition coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form electrodeposition coating films having excellent chipping resistance on the outside plate parts of a material to be coated which has an intricate structure by making it possible to form the electrodeposition coating films having desired film thicknesses on the respective parts of the surfaces of the material to be coated. SOLUTION: This cation electrodeposition coating method forms the electrodeposition coating films by subjecting the material to be coated which has the intricate structure to electrodeposition coating of a cation electrodeposition coating material [1] capable of forming the coating films having the excellent chipping resistance. The material to be coated is so heated that the ultimate max. temp. on the surfaces of the material to be coated of the parts not attaining the desired film thicknesses attains 40 to 80 deg.C and that the max. temp. of the ultimate max. temp. on the surfaces of the material to be coated of the parts having the desired film thicknesses attains the temp. higher by 20 to 70 deg.C than the min. temp. of the ultimate max. temp. on the surfaces of the material to be coated of the parts not attaining the desired film thicknesses. The material to be coated is thereafter electrodeposition coated with a cation electrodeposition coating material [2] consisting essentially of a cation electrodepositable epoxy resin, by which the electrodeposition coating films by the cation electrodeposition coating material [2] are formed in the parts not attaining the desired film thicknesses. These coating films are then baked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cationic electrodeposition coating method, and more particularly, to a method for applying a cationic electrodeposition coating twice on a subject having a complicated structure such as an automobile body under specific conditions. Thereby, an electrodeposition coating film having excellent chipping resistance can be formed on a general portion of the object to be coated, and an electrodeposition coating film having a desired film thickness can be formed on each portion of the surface of the object to be coated. The present invention relates to a cation electrodeposition coating method capable of reducing the difference in the electrodeposition coating film thickness of portions.

[0002]

2. Description of the Related Art Cathodic electrodeposition coating is a method in which an object to be coated is used as a cathode and a voltage is applied between the object to be coated and a counter electrode in an electrodeposition bath. This is a method of forming a film, in which a coating film having excellent smoothness is obtained by heat flow in a baking process.

However, when the object to be coated has a complicated structure, for example, in the case of an automobile body having a bag-like structure, a film having a thickness sufficient to have a necessary anticorrosive property up to the inside of the bag-like structure. It was difficult to form an electrodeposition coating. For example, it is conceivable to increase the applied voltage in order to form a sufficient film thickness up to the inside of the bag-shaped structure.However, when the applied voltage is increased, the thickness of the electrodeposition coating film on the body outer plate becomes unnecessarily large. However, there is a problem in that the amount of paint used is too large, and the appearance of the coating film is reduced.

Accordingly, the applicant of the present invention has disclosed in Japanese Patent Laid-Open No. 7-41994.
In the publication, a cationic electrodeposition coating material (A) containing a hydroxyl group-containing cationic electrodeposition vinyl copolymer as a main component is applied to an object having a complicated structure,
After baking at a temperature lower than the above, a cationic electrodeposition coating method characterized by applying and baking a cationic electrodeposition paint (B) containing a cationic electrodeposition epoxy resin as a main component was proposed.

[0005] The above method can form an electrodeposition coating film having considerably good weather resistance and corrosion resistance. The difference in electrodeposition coating thickness between parts that do not require throwing power, such as parts, is still quite large, and further improves the corrosion resistance of parts that are difficult to paint if the turning properties are extremely poor, such as inside the bag structure, etc. When this is necessary, there is a problem that this method cannot sufficiently cope with the problem. Further, there is a problem that the chipping resistance is not sufficient in a part where chipping resistance is required, such as a body outer plate portion.

Therefore, the present inventors can increase the thickness of the electrodeposition coating film in a portion where it is difficult to apply the coating if the turning property is extremely poor, such as inside the bag structure portion. The difference in the thickness of the electrodeposited coating between parts where painting is difficult if the throwing power is extremely poor and parts that do not require throwing power such as the body outer plate can be made smaller than conventional methods, and Intensive research is needed to obtain a cationic electrodeposition coating method that can form an electrodeposition coating film with excellent chipping resistance in areas where chipping performance is required, and can also form an electrodeposition coating film with excellent corrosion resistance in difficult-to-paint areas. Done.
As a result, a cationic electrodeposition paint capable of forming an electrodeposition coating film having excellent chipping resistance was used as the first electrodeposition paint,
The temperature conditions for the heating performed after the first electrodeposition coating are set such that the surface temperature of a part where the coating is difficult if the throwing power is not good and a surface temperature of a part where the throwing power is not required are fixed. After that, it was found that the above object can be achieved by performing the second electrodeposition coating, and the present invention was completed.

[0007]

That is, the present invention provides an electrodeposition coating of a cationic electrodeposition coating [1] capable of forming a coating film having excellent chipping resistance on an object having a complicated structure.
After forming the part having the target film thickness and the part not reaching the target film thickness of the electrodeposition coating film thickness, the ultimate temperature of the surface of the object to be coated of the part not reaching the target film thickness is 40 to 80 ° C., and The coating is performed such that the maximum temperature of the maximum temperature of the surface of the substrate having the target film thickness is 20 to 70 ° C. higher than the minimum temperature of the maximum temperature of the surface of the substrate not reaching the target film thickness. After heating the coated material, a cationic electrodeposition paint [2] containing a cationic electrodeposition epoxy resin as a main component is electrodeposited, and a portion not reaching the target film thickness is electrodeposited with the cationic electrodeposition paint [2]. An object of the present invention is to provide a cationic electrodeposition coating method characterized by forming and baking a coating film.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, an object having a complicated structure is likely to have a partial difference in the coating film thickness formed by one electrodeposition coating. It is an object to be coated having a structural part that requires "throwing power". As the object to be coated, for example, an object having electric conductivity for electrodeposition coating and having a bag structure or a tubular structure, such as an automobile body, an automobile part having a complicated structure, a metal tube, Examples thereof include a box of electric equipment. As the material of the object to be coated, a metal can be used, but a material made of a rust-proofed steel plate is preferable from the viewpoint of rust prevention. Examples of the steel sheet include hot-dip galvanized steel sheet, electro-galvanized steel sheet, electro-zinc-iron double-layered steel sheet, organic composite coated steel sheet, and the like, and base materials such as these steel sheets and cold-rolled steel sheets. After the surface is cleaned by the method described above, a surface treatment such as a phosphate chemical treatment or a chromate treatment is performed.

Hereinafter, the cationic electrodeposition paint and the cationic electrodeposition coating method used in the present invention will be described.

Cationic electrodeposition coating [1] In the method of the present invention, as the cationic electrodeposition coating [1], any cationic electrodeposition coating capable of forming a coating film having excellent chipping resistance can be used without any particular limitation. . As the cationic electrodeposition coating [1], for example, (1) a cationic water-dispersible resin is blended with a urethane elastomer having a blocked isocyanate group and a molecular weight of 1,000 to 10,000 and a curing agent. Cationic electrodeposition coating composition (see JP-A-55-52359), (2) Cationic electrodeposition coating composition containing amine-epoxy resin adduct and urethane resin adduct (JP-A-63-895)
No. 78) and (3) JP-A-7-150079.
JP-A No. 195/1995, the solubility parameter value (SP value) obtained by reacting an organic polyisocyanate (a), a polymer polyol (b) and a diol having a tertiary amino group (c) is 9.5. A resin component comprising 1 to 30% by weight of a high molecular weight polyurethane resin (A) having a number average molecular weight of at least 15,000 and 70 to 99% by weight of an epoxy resin-based cationic electrodeposition resin (B) And the like.

Among them, the cationic electrodeposition paint (3) (hereinafter sometimes abbreviated as “CED (3)”) is particularly excellent in chipping resistance and rust resistance and is preferred. is there. The CED (3) will be described below.

The high molecular weight polyurethane resin (A) in the CED (3) has a number average molecular weight of at least 15,000.
It is as large as 0 and the solubility parameter value (SP value) is 9.5.
When it is in the range of from 12.0 to 12.0, the compatibility with the epoxy-based cationic electrodeposition resin (B) is improved, and the effects of improving the chipping resistance and rust prevention of the coating film are enhanced. Further, a diol having a tertiary amino group as an essential component (c)
To introduce a tertiary amino group into the main chain using
Imparts cationic electrodeposition to high molecular weight polyurethane resin,
The electrodeposition bath is stabilized and the electrodeposition efficiency is increased.

The high molecular weight polyurethane resin (A) is
Organic polyisocyanate (a), polymer polyol (b), diol having tertiary amino group (c), polymerization terminator (d) if necessary, and chain extender (e) if necessary
Is obtained by reacting

The organic polyisocyanate (a) is a compound having two or more free isocyanate groups in one molecule and includes, for example, aromatic diisocyanates (tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p- Phenylene diisocyanate, naphthalene diisocyanate, etc.);
Aliphatic diisocyanates (hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate, etc.); alicyclic diisocyanates having 5 to 18 carbon atoms (1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate) (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI) and the like; Aliphatic diisocyanates having a ring (xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI), etc.); modified products of these diisocyanates ( Ethanedide, carbodiimide, uretdione, uretimine, buret and / or isocyanurate modified products), etc. These can be used alone or in combination of two or more types. Among these, HDI and IPDI are preferable. , MDI, hydrogenated MD
I and TMXDI.

The high molecular polyol (b) has two or more hydroxyl groups in one molecule, and has a number average molecular weight of 500
It is preferably from 5,000 to 5,000, particularly preferably from 1,000 to 4,000. Specific examples include the following.

Polyether polyols, for example, those obtained by polymerizing or copolymerizing alkylene oxides (ethylene oxide, propylene oxide, butylene oxide, etc.) and / or heterocyclic ethers (tetrahydrofuran, etc.), more specifically polyethylene glycol, Polypropylene glycol, polyethylene-propylene (block or random) ether glycol, polyethylene-tetramethylene ether glycol (block or random), polytetramethylene ether glycol,
Polyhexamethylene ether glycol and the like.

Polyester polyols such as aliphatic dicarboxylic acids (succinic acid, adipic acid, sebacic acid, glutaric acid, azelaic acid, etc.) and / or aromatic dicarboxylic acids (isophthalic acid, terephthalic acid, etc.) and low molecular weight glycols (ethylene glycol) ,Propylene glycol,
1,4-butanediol, 1,6-hexanediol,
3-methyl-1,5-pentanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-dihydroxymethylcyclohexane, etc.), specifically, Are polyethylene adipate diol, polybutylene adipate diol, polyhexamethylene adipate diol, polyneopentyl adipate diol, polyethylene / butylene adipate diol, polyneopentylene / hexamethylene adipate diol, poly-3-methylpentylene adipate diol, polybutylene Isophthalate diol and the like.

Polylactone polyols such as polycaprolactone diol or triol, poly-3-methylvalerolactone diol and the like.

Polycarbonate polyols such as polyhexamethylene carbonate diol.

Polyolefin polyols such as polybutadiene glycol, polyisoprene glycol or hydrides thereof.

These components (b) are used alone or as a mixture of two or more.

Preferred among the above-mentioned examples are at least one selected from and a mixture with at least one of the following.

Diol having a tertiary amino group (c)
Is a compound having one or more tertiary amino groups and two hydroxyl groups in one molecule, for introducing a cationic hydrophilic group for imparting cationic electrodeposition property to the polyurethane resin (A). And a specific example thereof is N
-Methyldiethanolamine, N-butyldiethanolamine, N-oleyldiethanolamine, N-cyclohexyldiethanolamine, N-methyldiisopropanolamine, N-cyclohexyldiisopropanolamine, N, N-dihydroxyethylaniline, N, N
-Dihydroxyethyltoluidine, N, N-dihydroxypropylnaphthylamine, and oxyalkylenated alkanolamines obtained by adding a small amount of an alkylene oxide such as ethylene oxide or propylene oxide to these alkanolamines. Preferred among these are N-methyldiethanolamine, N-butyldiethanolamine and N-oleyldiethanolamine.

The amount of the diol (c) having a tertiary amino group is such that the nitrogen atom based on the tertiary amino group is 0.1 to 5% by weight, preferably 0.2 to 5% by weight in the polyurethane resin (A).
The amount is 2% by weight. If the amount is less than 0.1% by weight, it is difficult to obtain a stable dispersion for cationic electrodeposition, and if the amount exceeds 5% by weight, the hydrophilicity of the polymer becomes high, so that the water resistance when formed into a coating film may decrease.

The high molecular weight polyurethane resin (A) can be obtained by reacting the above-mentioned components (a), (b) and (c). If necessary, the following polymerization terminator (d) and / or chain extender It is also possible to use (e) together.

The polymerization terminator (d) can be used to adjust the molecular weight of the component (A) within the above range, and is a compound having at least one active hydrogen capable of reacting with an isocyanate group in one molecule. is there. Specifically, for example, low molecular weight monoalcohols (methanol, ethanol, isopropanol, butanol, cyclohexanol, etc.); monovalent alkyl monoamines (mono- and di-ethylamine, mono- and di-butylamine, etc.); Alkanol monoamines having a secondary amino group (such as mono- and di-ethanolamine) are exemplified.

The amount of the polymerization terminator (d) is such that the number average molecular weight of the high molecular weight polyurethane resin (A) is at least 15.0.
00, preferably at least 20,000, that is, an amount that blocks less than 0.13 mmol / g, preferably less than 0.10 mmol / g, of the isocyanate groups of the isocyanate-terminated prepolymer that is the precursor of (A). . 0.13 mmol / g of isocyanate group blocked by polymerization terminator (d)
If it exceeds 300, it becomes difficult to increase the molecular weight, and the chipping resistance of the cationic electrodeposition coating film decreases.

The chain extender (e) is a compound having two or more active hydrogens capable of reacting with an isocyanate group in one molecule, and does not contain the components (b) and (c) and has a molecular weight of 5
It is a low molecular weight compound of less than 00.

The chain extender (e) includes water, low molecular weight polyols and polyamines.

Examples of the low-molecular polyol include low-molecular glycols listed as the raw materials for the polyester polyols, low-molecular-weight adducts of alkylene oxide with the glycol (number-average molecular weight of less than 500); low-molecular-weight adducts of bisphenol with alkylene oxide (number-average molecular weight). Molecular weight of less than 500); trihydric alcohols (glycerin, trimethylolethane, trimethylolpropane, etc.), low molar addition products of alkylene oxides of the trihydric alcohols (number average molecular weight of 50)
0); and mixtures of two or more of these. When a trihydric alcohol is used as the chain extender (e) together with the polymer polyol (b) and the diol having a tertiary amino group (c), the average of the total amount of these components (b) and (c) The number of hydroxyl groups is preferably 2.05 or less. If it exceeds 2.05, the product tends to gel.

Examples of the polyamine include aliphatic polyamines (ethylenediamine, N-hydroxyethylethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine); alicyclic polyamines (4,4'-diaminodicyclohexylmethane, 1,4
-Diaminocyclohexane, isophoronediamine, etc.);
Aliphatic polyamine having an aromatic ring (xylylenediamine, tetramethylxylylenediamine, etc.); aromatic polyamine (4,4'-diaminodiphenylmethane, tolylenediamine, phenylenediamine, etc.); hydrazines (hydrazine, carbodihydrazide, adipine) Acid dihydrazide, sebacic acid dihydrazide, phthalic acid dihydrazide, etc.); and mixtures of two or more thereof.

The amount of the chain extender (e) is usually 5 to 50 mol%, preferably 10 to 30 mol%, based on the organic polyisocyanate (a).

The method for producing the high molecular weight polyurethane resin (A) by reacting the above components (a), (b), (c), (d) if necessary, and (e) if necessary is not particularly limited. For example, the following method can be mentioned.

Organic solvents containing no active hydrogen group in the molecule (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, N-
Methylpyrrolidone, toluene, xylene and their two
), Or in the absence of a solvent, the organic polyisocyanate (a), the polymer polyol (b), the diol having a tertiary amino group (c), and the polymerization terminator (d). Urethane conversion by one-shot method.

The organic polyisocyanate (a), the polymer polyol (b), and the diol (c) having a tertiary amino group in the presence or absence of the organic solvent containing no active hydrogen group in the molecule. ) To form a urethane polymer having a terminal NCO group, chain elongation with a chain extender (e), and then adding a polymerization terminator (d) to complete the reaction.

A method in which a urethane prepolymer containing a terminal NCO group is obtained in the same manner as described above, and then a chain extender (e) and a polymerization terminator (d) are added at once to complete chain extension and complete the reaction. The organic polyisocyanate (a) in the presence or absence of the organic solvent containing no active hydrogen group in the molecule.
And a high molecular polyol (b) to form a urethane prepolymer having a terminal NCO group, and a chain extending agent (e) after extending the chain with a diol (c) having a tertiary amino group and a chain extender (e). To complete the reaction.

Here, the isocyanate (NCO) of (a)
The equivalent ratio of the group (b) + (c) to the active hydrogen group is usually in the range of 1.1 to 2.0, preferably 1.2 to 1.8. The polyurethane formation reaction is usually 2
The reaction is carried out at a temperature of 0 to 150 ° C, preferably 50 to 120 ° C (when a chain extension reaction is carried out with a polyamine, the reaction is usually carried out at a temperature of 80 ° C or lower, preferably 0 to 70 ° C). In order to promote the reaction, an amine-based or tin-based catalyst used in a usual urethane-forming reaction may be used.

The polyurethane resin (A) has an SP value in the range of 9.5 to 12.0, particularly preferably 9.5 to 11.5, and has a number average molecular weight of at least 1.
5,000, preferably 20,000 to 200,000
Must be within the range.

The SP value is determined by the solubility parameter (Solubility).
Parameter) value, which can be calculated by calculation using the Fedors method. Calculation by the Fedors method is based on Polymer Engineering an
d Science, 14, (2), 147 (1974). S
If the P value is less than 9.5, the compatibility with the epoxy resin is poor,
The rust prevention of the electrodeposition coating film is reduced. When the SP value exceeds 12.0, the effect of improving the chipping resistance of the electrodeposition coating film is lost.

The SP value of the component (A) is represented by the square root of the relaxation of the cohesive energy density of each component of the polyurethane (the relaxation of the molecular cohesion energy / the sum of the molecular volumes). Generally, the cohesive energy density is higher than the molecular polyol (b). Therefore, S
The SP value can be controlled by increasing the use amount of the component (a) constituting the component (A) to increase the P value, and by increasing the use amount of the component (b) to decrease the SP value.

The component (A) has a number average molecular weight of 15,
If it is smaller than 000, the chipping resistance of the cationic electrodeposition coating film is undesirably reduced.

The component (A) comprises, as a main skeleton, a urethanization reaction product of the component (a) and the component (b), and further introduces a cation-forming group by the component (c). The molecular weight and the like are controlled by the components (d) and (e) that may be used. Therefore, since the component (A) has a cation-forming group, it is electrodeposited together with the following component (B) during electrodeposition coating, and hardly dissociates during heat curing of the coating film. The component (A) can participate in a cross-linking reaction of a coating film by introducing a primary hydroxyl group to a molecular terminal using, for example, alkanolamine as the component (d).

Epoxy resin cationic electrodeposition resin (B)
Has a cationic group and a crosslinkable functional group (for example, a primary hydroxyl group) in principle, and is used in combination with the component (A). Specifically, it is a cationic resin having an amino group, which has been conventionally used in the field of cationic electrodeposition paints, and is an epoxy-based cationic resin having excellent compatibility with the high-molecular-weight polyurethane resin (A) and excellent rust prevention. Electrodeposition resin is mentioned. This resin is a water-soluble or water-dispersed product neutralized with a neutralizing agent such as hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, propionic acid, lactic acid, etc., for example, (1) polyepoxide and primary monoamine Adducts with primary, secondary, or mixed primary and secondary polyamines (see, eg, US Pat. No. 3,984,299);
(2) an adduct of a polyepoxide compound with an amine having a secondary amino group and a ketiminated primary amino group (see, for example, US Pat. No. 4,017,438);
(3) A reaction product obtained by etherification of a polyepoxide compound with a ketiminated hydroxy compound having a primary amino group (for example, see JP-A-59-43013) can be used.

The polyepoxide compound used for producing the resin (B) is a compound having two or more epoxy groups per molecule, and is generally at least 200, preferably 400 to 4,000, more preferably 800 to 4,000. , 0
Those having a number average molecular weight in the range of 00 are suitable, and those obtained by reacting a polyphenol compound with epichlorohydrin are particularly preferable.

As the polyphenol compound used for forming the polyepoxide compound, for example, bis (4-
(Hydroxyphenyl) -2,2-propane, 4,4′-
Dihydroxybenzophenone, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-
tert-butylphenyl) -2,2-propane, bis (2
-Hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-hydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2
2-ethane, 4,4'-dihydroxyphenyl sulfone, phenol novolak, cresol novolak and the like.

The polyepoxide compound may be partially reacted with a polyol (polyether polyol, polyester polyol, etc.), a polyamidoamine, a polycarboxylic acid, a polyisocyanate compound, and the like. Further, ε-caprolactone, It may be obtained by graft polymerization of an acrylic monomer or the like.

Examples of the cationizing agent for introducing a cationic group into the polyepoxide compound include the following amino compounds.

Primary alkanolamines such as monoethanolamine, monopropanolamine and monobutanolamine.

Secondary alkanolamines such as N-methylethanolamine, N-ethylethanolamine, diethanolamine, di-n (or iso) -propanolamine and dibutanolamine.

The above primary alkanolamine and α, β
Adducts with unsaturated carbonyl compounds (secondary alkanolamines): for example, monoethanolamine and N, N
An adduct with dimethylaminopropylacrylamide,
Adducts of monoethanolamine and hydroxyethyl (meth) acrylate, adducts of monoethanolamine and hydroxypropyl (meth) acrylate, adducts of monoethanolamine and hydroxybutyl (meth) acrylate, and the like.

The hydroxyl group which is a crosslinkable functional group of the resin (B) includes, for example, alkanolamine in the above-mentioned cationizing agent, ring-opened product of caprolactone which may be introduced into the epoxide compound, polyol and the like. A primary hydroxyl group introduced from an epoxy resin; a secondary hydroxyl group in an epoxy resin; and the like. Of these, primary hydroxyl groups introduced by alkanolamines are preferred because of their excellent crosslinking curing reactivity.

The content of the hydroxyl group in the resin (B) is from 20 to 50,000 in terms of the hydroxyl equivalent from the viewpoint of the crosslinking and curing reactivity.
00, particularly preferably in the range of 100 to 1,000, more preferably 200 to 1,000. The content of the cationic group is preferably at least the minimum necessary for stably dispersing the resin (B). The content of the cationic group is generally 3 to 2 in terms of mgKOH / g resin, that is, an amine value.
00, particularly preferably in the range of 10 to 100.

The amount of the high molecular weight polyurethane resin (A) in the CED (3) is such that the resin (A): resin (B) = 3 with respect to the epoxy-based cationic electrodeposition resin (B).
The solid content weight ratio is in the range of 0:70 to 1:99, and preferably, resin (A): resin (B) = 5: 95 to 20: 8.
The solid content weight ratio is 0. When the compounding amount of the high molecular weight polyurethane resin (A) is as follows: resin (A): resin (B) = 1: 99
If the weight ratio is less than the solid content ratio, the effect of improving the chipping resistance is not sufficient. On the other hand, the resin (A): resin (B)
If the solid content ratio is more than 30:70, the bath stability of the electrodeposition bath becomes poor, and sediment is formed at the bottom of the electrodeposition bath. Further, it is not preferable because the rust prevention property is reduced and the coating cost is increased.

The resin (A) and the resin (B) are acetic acid,
Neutralized with an acid such as propionic acid, lactic acid, or hydroxyacetic acid to impart water dispersibility.

The CED (3) may contain a crosslinking agent such as a blocked polyisocyanate compound blocked with an alcohol, a phenol, a tertiary hydroxyamine or an oxime, or a melamine resin, if necessary. .

In the cationic electrodeposition paint [1] such as the above-mentioned CED (3), in addition to the resin component and the crosslinking agent, if necessary, usual additives such as a coloring pigment such as titanium white, Carbon black, red iron, graphite, etc .: extender pigments, for example, silica, clay, mica, calcium carbonate, talc, etc .; rust preventive pigments, for example, chromium pigments such as strontium chromate, zinc chromate, lead silicate, lead chromate, hydroxide Lead pigments such as lead; a pigment dispersing resin, an anti-cissing agent, an aqueous solvent, a curing catalyst, and the like can be included. The pigment is preferably blended as a pigment paste usually dispersed in a pigment dispersing resin.

The cationic electrodeposition paint [1] may further contain, if necessary, a conductive powder such as conductive carbon (eg, graphite) or a metallic powder. The coating film formed by the coating material [1]
At 20 ° C. and 20 V, it preferably has a volume specific electric resistance (film thickness 25 μm) in the range of 1 × 10 ⁷ to 10 ¹³ Ω · cm, so that the first electrodeposition coating film and the second electrodeposition coating The formation of a coating film at the boundary with the film can be performed better.

The above cationic electrodeposition paint [1] is appropriately diluted with deionized water to have a solid content of about 5 to 25% by weight,
Can be adjusted to fall within the range of 5.5 to 8. Coating of cationic electrodeposition coating [1] As a method and an apparatus for performing electrodeposition coating on an object to be coated using the above-mentioned cationic electrodeposition coating [1], there are known per se known methods used in cationic electrodeposition coating. The method and apparatus can be used. In this case, it is preferable to use a coating object as a cathode and a stainless steel # 316 plate, a ferrite metal plate or the like as an anode. Electrodeposition conditions that can be used are not particularly limited, but generally,
Bath temperature: 15 to 35 ° C (preferably 20 to 30 ° C), voltage: 100 to 400 V (preferably 200 to 300 V)
V), current density: 0.01 to 3 A / dm ² , energization time: 30
It is desirable that the electrodeposition is performed in a stirring state with a pole area ratio (A / C) of 6/1 to 1/6, a distance between the poles of 10 to 100 cm, and a period of 10 seconds to 10 minutes.

The first electrodeposition coating using the above-mentioned cationic electrodeposition coating material [1] on the object having the above-mentioned complicated structure gives the target film thickness, which is a general part such as an automobile body outer panel. When an electrodeposited coating film having a desired film thickness is formed on a portion where the film can be easily formed (hereinafter abbreviated as “electrodeposition-easy portion”), the throwing power of the inner plate portion of the bag structure of the automobile body is good. Unless it is difficult to apply the coating (hereinafter simply referred to as “electrodeposition difficulties”), the portion may be thinner than the target film thickness or may not have a coating film formed at all.

In the method of the present invention, the film thickness of the electrodeposited film of the cationic electrodeposition paint [1] in the electrodeposited portion is appropriately selected according to the intended performance such as the desired chipping resistance and rust prevention. 10 to 70 μm, preferably 10 to 30 μm, more preferably 10 to 20 μm.
Preferably, m.

In the method of the present invention, after the electrodeposition coating of the above-mentioned cationic electrodeposition coating material [1], washing with water is carried out if necessary.
Heating is performed, and this heating condition is important. First, it is necessary that the maximum temperature reached on the surface of the electrodeposition difficult part be 40 to 80 ° C, preferably 50 to 70 ° C. When the maximum temperature of the surface of the electrodeposition difficult part is less than 40 ° C., the first electrodeposition coating and the second electrodeposition coating are performed when the second electrodeposition coating with the cationic electrodeposition coating [2] is performed. It becomes easy to mix with the film, the finish is reduced, and a coating film having sufficient coating performance such as chipping property and anticorrosion property cannot be obtained. On the other hand, if the maximum temperature reached on the surface of the electrodeposition difficult part exceeds 80 ° C., the first electrodeposition coating film formed on the electrodeposition difficult part and not reaching the target film thickness also melts and becomes a dense film. Therefore, even on the coating film which has not reached the target film thickness in the electrodeposition difficult part, a portion where the electrodeposition coating film is not formed by the second electrodeposition coating is likely to occur.

Further, in the above heating, the maximum temperature at the surface of the electrodeposited portion and the maximum temperature at the surface of the electrodeposited portion may vary depending on the heating method. It is necessary that the maximum temperature of the highest temperature of the surface of the portion is 20 to 70 ° C. higher than the minimum temperature of the highest temperature of the surface of the difficult-to-electrode portion. If this temperature difference is smaller than 20 ° C., the difference in the coating state between the coating in the portion easy to electrodeposit by heating and the coating in the portion difficult to electrodeposit becomes small, and the second electrodeposition coating due to the temperature difference There is no difference in the ease of formation. On the other hand, when the temperature difference is 70
When the temperature is higher than ℃, the temperature variation in each place of the electrodeposited portion becomes large, and the degree of drying of the coating in the electrodeposited portion becomes different from place to place, which causes a decrease in the smoothness of the coated surface. There's a problem.

In the method of the present invention, when the object to be coated is an automobile body, the heating is preferably carried out usually for 3 to 7 minutes. If the heating time is short, it is likely that the maximum temperature of the electrodeposition difficult part does not reach 40 ° C., and if the heating time is long, the maximum temperature of the maximum temperature of the surface of the electrodeposition easy part and the electrodeposition The temperature difference between the highest temperature reached on the surface of the difficult part and the minimum temperature tends to be smaller than 20 ° C.

In the above heating, the maximum temperature at any point on the surface of the electrodepositable portion is substantially higher than the maximum temperature at any point on the surface of the electrodeposition difficult portion. Is preferable.

In the method of the present invention, after the above-mentioned heating, the object to be coated is usually cooled, and then, as a second electrodeposition coating, a cationic electrodeposition coating [2] is electrodeposited.

Cationic electrodeposition paint [2] Examples of the cationic electrodeposition paint [2] include an electrodeposition paint containing a cationic electrodeposition epoxy resin as a main component from the viewpoint of corrosion resistance. By using a cationic electrodeposition paint that forms a film having a different function from the cationic electrodeposition paint [1] as the cationic electrodeposition paint [2], a coating film having a different function is formed at a portion of the object to be coated. It is possible to

As the cationic electrodeposition epoxy resin in the above-mentioned electrodeposition coating composition containing a cationic electrodeposition epoxy resin as a main component (hereinafter sometimes abbreviated as “EP-CED”), the cationic electrodeposition coating resin [1] C as an example
An epoxy resin-based cationic electrodeposition resin as the component (B) in the ED (3) can be mentioned.

The above cationic electrodepositable epoxy resin is neutralized with an acid such as acetic acid, propionic acid, lactic acid, or hydroxyacetic acid to give water dispersibility.

In the EP-CED, a crosslinking agent may be mixed with the cationic electrodepositable epoxy resin as required. Examples of the cross-linking agent include the block polyisocyanate compounds and melamine resins mentioned as the cross-linking agent which may be contained in the CED (3) as needed.

Further, a self-crosslinking type amine-added epoxy resin which can be cured without using the above-mentioned crosslinking agent can be used. For example, a resin obtained by introducing a β-hydroxyalkyl carbamate group into a polyepoxy substance can be used. (See, for example, JP-A-59-155470); a resin that can be cured by a transesterification reaction (see, for example, JP-A-55-80436); a resin in which a blocked isocyanate group is introduced into a base resin; You can also.

The cationic electrodeposition coating material [2] such as EP-CED may be further used as necessary, if necessary, with the usual additives, for example, pigments, incorporated in the cationic electrodeposition coating material [1]. , A pigment dispersing resin, an anti-cissing agent, an organic solvent, a curing catalyst, and the like.

In the case where the above-mentioned cationic electrodeposition coating material [2] is strongly required to have an edge-corrosion-proof property, it is preferable to improve the edge-coating property by incorporating gelling fine particles.

As the gelled fine particles, conventionally known fine particles can be used without particular limitation as long as they are fine particle polymers gelled by a cross-linking reaction in the particles. For example, acrylic gels containing an alkoxysilyl group and a cationic group can be used. Copolymers dispersed in water and cross-linked in particles (Japanese Patent Application No. 62-54)
No. 141); internally crosslinked gelled fine particles having an alkoxysilyl group, a hydroxyl group and a cationic group (Japanese Patent Laid-Open No.
-Interlinked gelled fine particles having an alkoxysilyl group, a urethane bond, a hydroxyl group and a cationic group (see JP-A-3-62860).

Further, as the above-mentioned gelled fine particles, in particular, cationic electrodepositable gelled fine particles obtained by dispersing a hydrolyzable alkoxysilyl group-containing epoxy resin amine adduct in water and cross-linking within the particles are preferable. Can be suitably used.

The particle size of the gelled fine particles is generally 0.5 μm
Hereinafter, it can be in the range of preferably 0.01 to 0.3 μm, more preferably 0.05 to 0.2 μm.
The particle size can be adjusted by adjusting the amount of the cationic group in the epoxy resin amine adduct containing a hydrolyzable alkoxysilane group, thereby easily obtaining a particle size within a desired range. Can be.

When the above gelled fine particles are blended in the cationic electrodeposition paint [2], the blending amount is 3 to the total resin solid content (total of the cationically electrodepositable epoxy resin and the gelled fine particles). Suitably, it is from 50 to 50% by weight, preferably from 7 to 35% by weight. The cationic electrodeposition coating [2] thus obtained is appropriately diluted with deionized water to have a solid content of about 3 to 25% by weight, preferably 5 to 20% by weight, p.
It is appropriate to adjust H so that it is in the range of about 5.5-8.

[0077] As coating the second electrodeposition coating of the cationic electrodeposition paint [2], the cationic electrodeposition paint [2] painting cation electrodeposition to a coating object to the first electrodeposited coating is formed . By this electrodeposition coating, the coating of the cationic electrodeposition coating [2] is applied to at least the coating object having a complicated structure in which the coating of the cationic electrodeposition coating [1] has already been formed in the electrodeposition-easy part. It is formed in the difficult-to-wear part. At this time, a coating film of the cationic electrodeposition paint [2] may be formed on a part of the electrodeposition-easy part.

In the electrodeposition coating of the cationic electrodeposition coating [2], since a coating film having a large film resistance is formed in the electrodeposition-easy portion, current hardly flows in the electrodeposition-easy portion.
Since the current flows intensively in the electrodeposition difficult part, the coating film of the electrodeposition paint [2] can be formed on the electrodeposition difficult part, and the electrodeposition coating film of the target film thickness is also formed on the electrodeposition difficult part comprehensively. Can be formed, and an electrodeposition coating film can be formed on an unpainted portion such as an edge portion where the substrate is exposed by the heat flow.

The method and apparatus for performing electrodeposition coating using the cationic electrodeposition coating [2] may be the same as those used for coating the cationic electrodeposition coating [1]. Among them, about the energization time,
Although not particularly limited, usually, the time required for coating the cationic electrodeposition paint [1] is 1/4 to 1/4.
Even if it is 1/1, the electrodeposition coating film of the cationic electrodeposition coating material [1] can be sufficiently formed on the portion not reaching the target film thickness of the object to be coated.

In general, a method of applying an electrodeposition coating by completely immersing an object to be coated in an electrodeposition bath is used. The second electrodeposition coating can be performed by so-called “semi-immersion electrodeposition method” in which the electrodeposition is performed by immersion in the electrodeposition.

As described above, a coating film of the electrodeposition paint [1] and the electrodeposition paint [2] is formed on the object to be coated, and baking is performed under the condition that both of these are hardened, so that the object to be coated is An electrodeposited cured coating film can be formed. The baking condition is a condition in which the temperature is usually maintained at 120 to 180 ° C. for 10 to 30 minutes.

As described above, the general portion (the first electrodeposition) of the object having a complicated structure is performed by the two electrodeposition coatings using the cationic electrodeposition coating [1] and the cationic electrodeposition coating [2]. In the part where the target film thickness is formed by coating), a coating film having excellent chipping resistance by the cationic electrodeposition coating [1] is mainly formed, and the inside of the bag structure portion of the object having a complicated structure is formed. For complex structures such as the inner plate part and the inside of a cylinder (where the target film thickness is not formed by the first electrodeposition coating), the cationic electrodeposition coating [1] A coating film of the coating [2] is formed, or a coating film of the cationic electrodeposition coating [2] is formed without a coating of the cationic electrodeposition coating [1], thereby obtaining a coating having a desired film thickness.

As described above, the coating film formed on the object to be coated can be changed depending on the part of the object to be coated, so that a coating film having excellent chipping resistance can be formed on the general portion of the object to be coated, and a complicated film can be formed. An electrodeposition coating film having excellent corrosion resistance and, if necessary, exhibiting other functions can be formed on such a structural portion. For example, as the cationic electrodeposition coating [2], a mixture containing gelling fine particles can be used to sufficiently cover the edge portion of the object to be coated. In addition, it can be a combination of coating films having various functions according to the purpose.

On the electrodeposition coating film formed as described above, an intermediate coating and / or a top coating can be applied as needed to finish.

[0085]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited thereto. "Parts" in each example indicates parts by weight, and "%" indicates% by weight.

Production Example 1 Production of High Molecular Weight Polyurethane Resin (A) (A-1): Polyethylene-propylene (block) ether glycol [Sanixdiol PL-21
00 (number average molecular weight 2,477); manufactured by Sanyo Chemical Industries, Ltd.] 479.2 parts, neopentyl glycol 39.7
4 parts, 158.3 parts of hexamethylene diisocyanate and 75 parts of methyl isobutyl ketone were charged into a reaction vessel,
After the inside of the reaction system was replaced with nitrogen gas, 110 ° C. while stirring.
The reaction product was cooled to 60 ° C., 23.78 parts of N-methyldiethanolamine and 225 parts of methyl isobutyl ketone were added, and the mixture was further reacted at 90 ° C. for 4 hours to obtain a residual NCO group content of 1.30. % Urethane prepolymer solution was synthesized. After cooling the urethane prepolymer solution to 40 ° C., 22.9 parts of isophoronediamine,
A mixture of 2.44 parts of monoethanolamine, 355 parts of methyl isobutyl ketone and 70 parts of isopropanol was added thereto, and the mixture was reacted for 1 hour. A chain elongation reaction was carried out until the remaining NCO groups disappeared. 3
A pale yellow solution of 5,000 high molecular weight polyurethane resin (A-1) was obtained. The amine value of the resin (A-1) is 15.
The resin content was 4 mgKOH / g resin (0.39% as nitrogen atom content based on tertiary amino groups). The SP value calculated by the Fedors method was 9.7. Production Example 2 Production of Epoxy Cationic Electrodepositable Resin (B) (B-1): Obtained by reacting bisphenol A with epichlorohydrin in a flask equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser. Number average molecular weight 3
70, 518 parts of an epoxy resin having an epoxy equivalent of 185 were charged, and 57 parts of bisphenol A and 0.2 part of dimethylbenzylamine were added.
The reaction was continued until Then, ε-caprolactone 21
3 parts and 0.03 part of tetrabutoxy titanium were added, and 17 parts were added.
The temperature was raised to 0 ° C., sampling was performed over time while maintaining this temperature, the amount of unreacted ε-caprolactone was traced by infrared absorption spectrum measurement, and when the reaction rate reached 98% or more, 148 parts of bisphenol A was added. 0.4 parts of dimethylbenzylamine was further added, and the epoxy equivalent was 9 at 130 ° C.
The reaction was allowed to reach 36. Next, 257.4 parts of methyl isobutyl ketone, 25.6 parts of diethylamine, and 68.3 parts of diethanolamine were added, and the mixture was reacted at 80 ° C. for 2 hours. The mixture was diluted with 143.4 parts of methyl ethyl ketone to obtain an epoxy-polyamine resin having a resin solid content of 72%. A solution of (B-1) was obtained. The amine value of this resin was 54.5 mg KOH / g resin, and the primary hydroxyl equivalent was 500.

Production Example 3 Production of Gelled Fine Particles In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser and a nitrogen gas injection port, Epon 8 was injected under nitrogen gas injection.
28EL (Note 1) 1,045 parts, bisphenol A17
1 part and 52.2 parts of diethanolamine
The mixture was heated to 0 ° C and the epoxy equivalent (Note 2) was changed to the theoretical value (31
The reaction was continued until 7) was reached. Thereafter, the mixture was cooled to 80 ° C., and 221 parts of KBE-903 (Note 3) and 157.5 parts of diethanolamine were added, and the mixture was reacted until the tertiary amine value (Note 4) reached the theoretical value (102). Thereafter, the mixture was diluted with 706 parts of ethylene glycol monobutyl ether to obtain an ethylene glycol monobutyl ether solution having a 70% solid content of an epoxy resin amine adduct containing a hydrolyzable alkoxysilane group having a number average molecular weight of about 1,650.

To a 2 liter flask were added 100 parts of the epoxy resin amine adduct containing a hydrolyzable alkoxysilyl group obtained above and 11 parts of 10% acetic acid, and the mixture was stirred at 30 ° C. for 5 minutes. The mixture was added dropwise over about 30 minutes with vigorous stirring, heated to 50 ° C., and stirred for about 3 hours. Thus, a milky white particle-crosslinked gelled fine particle dispersion (G) having a solid content of 20% was obtained, and the average particle size of the fine particles in ethylene glycol monobutyl ether was 0.15 μm.

(Note 1) Diglycidyl ether of bisphenol A having an epoxy equivalent of about 190 (manufactured by Yuka Shell Epoxy Co., Ltd.) (Note 2) Based on JIS-K-7236. However, amino groups are also included as epoxy groups.

(Note 3) γ-aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) (Note 4) After acetylation with acetic anhydride, titration with perchloric acid using crystal violet as an indicator.

Preparation of Cationic Electrodeposition Coating Preparation Example 1 24 parts (12 parts in solid content) of the high molecular weight polyurethane resin (A-1) solution obtained in Production Example 1, and the epoxy cationic electrodeposition property obtained in Production Example 2. 111 parts of resin (B-1) solution (80 parts in solid content) and methyl ethyl ketoxime blocked product of hexamethylene diisocyanate (2 in solid content)
0 parts), and 1 part of lead acetate and 1 part
After mixing 15 parts of 0% acetic acid aqueous solution and mixing uniformly,
While stirring, deionized water was added dropwise over about 15 minutes to obtain a clear emulsion for cationic electrodeposition paint having a solid content of about 35%. To this clear emulsion, 62.2 parts (28 parts in terms of solid content) of a pigment paste (P-1) shown in Table 1 below are added with stirring, and diluted with deionized water to obtain a solid content of about 20%.
% Of cationic electrodeposition paint (1) was obtained. The obtained cationic electrodeposition paint (1) is an electrodeposition paint capable of forming a coating film having excellent chipping resistance.

Preparation Example 2 HB3000 clear emulsion having a solid content of 32% (Kansai Paint Co., Ltd., resin emulsion for cationic electrodeposition paint,
The resin component is composed of a polyester-modified epoxy resin and a blocked diisocyanate compound. 687.5 parts of a 55% solid content pigment paste (P-2) 1 shown in Table 1
09 parts, stirred, diluted with deionized water and solid content 2
0% of the cationic electrodeposition paint (2) was obtained.

Preparation Example 3 HB3000 clear emulsion 625 having a solid content of 32%
To 109 parts of a pigment paste (P-2) having a solid content of 55% and 100 parts of a gelled fine particle dispersion (G) having a solid content of 20% obtained in Production Example 3 were stirred, and diluted with deionized water. Thus, a cationic electrodeposition paint (3) having a solid content of 20% was obtained.

[0094]

[Table 1]

Cathodic electrodeposition paint (1) having a solid content of 20%, obtained in Model Experiment Preparation Example 1 for throwing power (1)
, A reference plate is attached to a cylindrical stainless steel container having an inner diameter of 150 mm and a height of 350 mm and having a bottom.
A test in which an object to be coated having a size of 0.5 × 10.0 × 350 mm was arranged at a central position inside a stainless steel cylindrical tube having a length of 8 mm, an inner diameter of 16.0 mm and a length of 330 mm so as not to touch the stainless steel cylindrical tube. The instrument was installed as shown in FIG. 1 below.
The materials of the reference plate and the object to be coated in the above test apparatus are both zinc phosphate-treated cold-rolled steel plates. A stirrer chip that can be rotated by a magnetic stirrer is placed at the bottom of the stainless steel container.

Using the above test apparatus, the first electrodeposition coating and heating were performed under the conditions shown in Table 2 below, and then the solid content 20 obtained in Preparation Example 2 was used instead of the electrodeposition coating (1). % Of the cationic electrodeposition paint (2), and the second electrodeposition is performed using the same apparatus as described above except that the first electrodeposition is performed on the object to be coated. The test was performed under the conditions shown in Table 2. In Table 2, obtained by the first electrodeposition coating,
The thickness of the electrodeposition coating film on the reference plate, the throwing length of the electrodeposition coating material on the object to be coated (distance from the coating film forming end at the cylindrical entrance of the object to the point where no electrodeposition coating film is formed) ), And the total thickness of the electrodeposited coating film on the reference plate obtained by the second electrodeposition coating (the electrodeposition film thickness formed by the first electrodeposition coating and the second electrodeposition coating The total thickness of the electrodeposited film to be formed), the throwing length of the electrodeposition paint on the object to be coated after the second electrodeposition coating (the maximum length is 30 cm), and the first electrodeposition coating The thickness of the boundary between the electrodeposition coating film formed by the above and the electrodeposition coating film formed by the second electrodeposition coating (the thickness of the first electrodeposition coating film at the boundary portion) is described. Table 3 shows the total electrodeposition coating thickness (μm) with respect to the distance (cm) from the coating film forming end of the cylindrical entrance of the object to be coated on Experiment 3 to Experiment 3, Experiment 5 and Experiment 9. Is shown.

[0097]

[Table 2]

[0098]

[Table 3]

Example 1 The cationic electrodeposition coating [1] obtained in Preparation Example 1 was used as the cationic electrodeposition coating [1] for the first electrodeposition, and the cationic electrodeposition coating [2] for the second electrodeposition was used. ], Using the cationic electrodeposition coating material (3) obtained in Preparation Example 3, electrodeposition coating under the conditions shown in Table 4, and baking at 160 ° C. for 20 minutes to obtain an electrodeposition coating film. The following objects to be coated for the bag part paintability test were used as the objects to be coated. The electrode was immersed so that the distance between the object to be coated and the counter electrode during electrodeposition coating was 110 mm, and the surface with a hole of 8 mmφ faced the counter electrode. Of the four steel plates having no holes formed among the four steel plates arranged in parallel with each other to be coated, a portion corresponding to the inner surface of the box-shaped body is defined as an inner plate portion, and the holes forming the box-shaped body are formed. The portion of the steel plate closest to the counter electrode among the opened steel plates, which corresponds to the outer surface of the box-like body, is defined as an outer plate portion, and the thickness and heating conditions of the inner plate portion and the outer plate portion, and the inner plate portion and the outer plate Table 4 shows the total film thickness ratio of the outer plate and the chipping resistance of the obtained outer plate. The test method of chipping resistance is shown below. The thickness of the electrodeposited coating film in Table 4 is the thickness of the cured film. In the total coating film obtained in Example 1, the ratio of the total film thickness (the minimum total film thickness of the inner plate portion / the total film thickness of the outer plate portion) was 0.42, and the area where the throwing power was likely to be deteriorated Thus, a coating film having a sufficient thickness can be formed.

Coating material for bag coatability test : 70 × 15
8mmφ at a position that is 45mm from the bottom and symmetrical to the left and right of three of the four cold rolled zinc phosphate-treated steel sheets of 0x0.8mm thickness
A box-shaped structure of 70 x 150 x 60 mm, with four steel plates arranged in parallel at equal intervals, and the side and bottom surfaces are also shielded with zinc phosphate-treated cold-rolled steel plates, and the top surface is open It was created. In addition, it arrange | positioned so that the steel plate which does not perforate among the said four steel plates may form the outer surface of a structure. The obtained box-shaped structure is used for a bag part coatability test. This box-shaped structure is immersed to a depth of 90 mm at the time of electrodeposition coating, and the electrodeposition coating enters and exits only through an 8 mmφ hole.

Test method for chipping resistance : The obtained electrodeposition coated plate is further coated with a thermosetting intermediate coating material and a top coating material, and then subjected to the following test with respect to a heat-cured one.

Test equipment: QGR gravelometer (manufactured by Q panel company) Blowing stone: crushed stone having a diameter of about 15 to 20 mm Blowing stone volume: about 500 ml Blowing air pressure: about 4 kg / cm ² Temperature during the test: about 20 ° C. The test piece was attached to a test piece holding table, and about 500 ml of crushed stone was fired on the test piece at a blowing air pressure of about 4 kg / cm ² . The state of the coated surface is visually observed and evaluated according to the following criteria.

◎: Very little scratches due to impact were observed in part of the overcoat film, and no peeling of the electrodeposited film was observed.

：: scratches due to impact were observed in the top coat and the intermediate coat, and peeling of the electrodeposited coat was slightly observed.

Δ: Many scratches due to impact were observed in the top coat and the intermediate coat, and peeling of the electrodeposited coat was also considerably observed.

Examples 2 to 6 and Comparative Examples 1 to 3 In Example 1, the types of the cationic electrodeposition paints [1] and [2] used, the electrodeposition conditions and the heating conditions are shown in Table 4.
The procedure was the same as in Example 1, except that

As is apparent from Table 4, the total film thickness ratio of (the minimum total film thickness of the inner plate portion / the total film thickness of the outer plate portion) is the total film ratio of Comparative Examples 1 and 2 in all of Examples 1 to 6. The value is larger than the film thickness ratio, and the throwing power is good. In Comparative Example 3, the total film thickness ratio was almost the same as that of the example, but the chipping resistance was poor.

[0108]

[Table 4]

[0109]

According to the method of the present invention, the first time and the second time
When the second electrodeposition coating is performed, the second electrodeposition coating is selectively applied to a portion not reaching the target film thickness, such as a complicated structure part where the first electrodeposition coating film did not sufficiently cover. A coating film is formed. Since the heating of the portion which does not reach the target film thickness by the first electrodeposition coating is suppressed to the range of 40 to 80 ° C., the coating film having a sufficient film thickness is formed on this portion by the second electrodeposition coating. It can be formed, and the thickness of the boundary between the first electrodeposition coating film and the second electrodeposition coating film can be sufficiently ensured. Furthermore, in the electrodeposition easy part,
The first electrodeposition coating can form an electrodeposition coating film with excellent chipping resistance, and the second electrodeposition coating uses a cationic electrodeposition paint mainly composed of a cationic electrodeposition epoxy resin. In addition, an electrodeposition coating film having excellent corrosion resistance can be formed in a portion where electrodeposition is difficult.

Further, the first electrodeposition time is shortened,
By adjusting the electrodeposition time, the total electrodeposition coating film after the second electrodeposition coating in the portion reaching the target film thickness by the first electrodeposition coating and the portion not reaching the target film thickness in the first electrodeposition coating The difference in film thickness between parts can be reduced, so that the electrodeposition film thickness can be made uniform, the electrodeposition time can be shortened, and the amount of electrodeposition paint used can be reduced by preventing the formation of excessive film thickness. You can also.

[Brief description of the drawings]

FIG. 1 is a model diagram showing an installation state of a test device used in the “model experiment on throwing power”.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reference plate 2 ... Coating object 3 ... Stainless steel cylindrical tube 4 ... Stainless steel container 5 ... Cationic electrodeposition paint 6 ... Stirrer chip 7 ... Magnetic stirrer

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Satoru Matsubara 33-1, Kanzakicho, Amagasaki-shi, Hyogo Kansai Paint Co., Ltd.

Claims (7)

[Claims] 1. A cationic electrodeposition paint [1] capable of forming a coating film having excellent chipping resistance is electrodeposited on an object having a complicated structure, and the target thickness of the electrodeposition coating film is adjusted. After forming the portion having the target thickness and the portion having the target thickness, the maximum temperature of the surface of the object to be coated in the portion not reaching the target thickness is 40 to
80 ° C., and the maximum temperature of the maximum temperature of the surface of the substrate in the portion having the target film thickness is 20 to 70 ° C. from the minimum temperature of the maximum temperature of the surface of the substrate in the portion not reaching the target film thickness.
After the object to be coated is heated to a high temperature, a cationic electrodeposition paint [2] containing a cationic electrodepositable epoxy resin as a main component is electrodeposited, and the portion not reaching the target film thickness is subjected to cationic electrodeposition. A cationic electrodeposition coating method comprising forming and baking an electrodeposition coating film of a coating [2]. 2. The cationic electrodeposition coating [1] comprises an organic polyisocyanate (a), a polymer polyol (b) and a third
Having a solubility parameter value (SP value) of 9.5 to 12.0 obtained by reacting a diol (c) having a secondary amino group.
And a cation containing a resin component consisting of 1 to 30% by weight of a high molecular weight polyurethane resin (A) having a number average molecular weight of at least 15,000 and 70 to 99% by weight of an epoxy resin cationic electrodeposition resin (B). The electrodeposition coating method according to claim 1, wherein the electrodeposition coating is an electrodeposition coating. 3. The electrodeposition coating method according to claim 1, wherein the heating time of the object to be coated after coating the cationic electrodeposition paint [1] is 3 to 7 minutes. 4. The electrodeposition coating method according to claim 1, wherein the coating film of the cationic electrodeposition coating [1] has a maximum thickness of 10 to 20 μm. 5. The electrodeposition coating method according to claim 1, wherein the cationic electrodeposition coating [2] contains gelled fine particles. 6. The cationic electrodepositable gelled fine particles according to claim 5, wherein the gelled fine particles are obtained by dispersing an epoxy resin amine adduct containing a hydrolyzable alkoxysilyl group in water and crosslinking the particles. How to paint. 7. The article to be coated is a rust-proofed steel sheet.
The cationic electrodeposition coating method according to any one of items 6 to 6.