JPH09125287A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method excellent in the performance such as the resistance of an electrodeposition paint to powder coating film, the resistance to washing water marking and the smoothness, corrosion resistance, weatherability, etc. of the electrodeposition coating film interface. SOLUTION: A material to be coated is coated with a thermosetting powder paint obtained by blending the low condensate of a tetraalkoxysilane, then the powder coating film is baked in the first stage to form an uncured coating film, the uncured part is coated with a thermosetting epoxy resin-base cationic electro-deposition paint, and second-stage baking is then conducted to cure the powder coating film and electrodeposition coating film at the same time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel coating method.

[0002]

2. Description of the Related Art Conventionally, powder coating has attracted attention as a coating excellent in prevention of pollution and protection of the global environment because it hardly contains volatile components such as organic solvents.
However, the coating method is such that the back surface of the article to be coated, the corner
It has a drawback that it is difficult to coat the portion or the slit portion, and it is difficult to coat an object having a complicated shape.

As a method for preventing such a defect, Japanese Patent Application Laid-Open No. 51-2746 proposes an undercoat coating method in which an uncoated portion is electrodeposited after powder coating on an object to be coated.

However, in this method, the electrodeposition bath paint and the washing water carried out after the electrodeposition coating adhere to the surface of the powder coating film, which remains in the form of polka dots on the surface of the powder coating film, and the coating film. Defects such as dents in the powder coating when baked, water marks such as tingling, and coating defects on the surface such as appearance, adhesion, and coloring when the top coating is applied. There is.

Further, since the electrodeposition coating used in this method is an anionic electrodeposition coating, there is still a drawback that the anticorrosion property is poor.

[0006]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, in the conventional method, a low-condensation product of tetraalkoxysilane was blended as a powder coating material. Using thermosetting powder coating
And by using a thermosetting epoxy resin-based cationic electrodeposition coating as the electrodeposition coating, it was found that it is a method capable of forming a coating film excellent in finished appearance, anticorrosion property, etc.,
The present invention has been completed.

That is, according to the present invention, a thermosetting powder coating material containing a low-condensation product of tetraalkoxysilane is applied to an object to be coated, and then the powder coating film is baked in the first stage to be uncured. After the coating film is formed, a thermosetting epoxy resin-based cationic electrodeposition coating is applied to the uncoated portion of the powder to form a coating film, and then the second step baking is performed to perform powder coating and electrode coating. The present invention relates to a coating method characterized by simultaneously curing an applied coating film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The article to be used in the present invention is a conductive article which can be powder-coated and electrodeposition-coated. As the article to be coated, the article to be coated conventionally used for these coatings can be used without particular limitation, and specifically, aluminum, alumite, iron or steel, zinc, tin, chromium, aluminum or the like on the surface of steel can be used. Examples include a wide range of metals such as plated steel sheets and those whose surfaces are subjected to chemical conversion treatment with chromic acid, phosphoric acid, or the like.

As the thermosetting powder coating material used in the present invention, an epoxy resin or polyester resin as a base resin and a crosslinking agent mixed therein can be used. The epoxy resin has an epoxy equivalent of about 200 to 5
000, an average molecular weight of about 1,000 to 80,000, and a softening temperature of about 60 to 150 ° C. can be used as a powder resin. Specifically, as trade names, for example, Epicort 1004, same left 1002, same left 1007 (above, Yuka Shell Epoxy Co., Ltd.), Araldite GY-6084, same left 60
97 (manufactured by Ciba Geigy), DER-662, same as left 6
64, same as 667 (manufactured by Dow Chemical Co.), bisphenol-epichlorohydrin type epoxy resin, EPPN
-201, same as 202, EOCN-1020, same as 10
Novolak type epoxy resins such as 2S (all manufactured by Nippon Kayaku Co., Ltd.), vinyl polymers (eg, glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, etc.) Radical homopolymers of epoxy group-containing unsaturated monomers and, if necessary, (meth) acryl such as methyl (meth) acrylate, ethyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. Alkyl or cycloalkyl esters of acids, unsaturated monomers containing hydroxyl groups such as hydroxyethyl (meth) acrylate, aromatic compounds such as styrene, and other unsaturated compounds such as nitrile compounds such as (meth) acrylonitrile Radical copolymers with monomers, etc.) and the like. Among these, bisphenol-epichlorohydrin type epoxy resins and novolac type epoxy resins are preferably used since they are excellent in corrosion resistance and the like.

As the cross-linking agent for the epoxy resin, conventionally known ones can be used without particular limitation as long as they can cross-link and harden the epoxy groups of the epoxy resin. Specifically, for example, (anhydrous) polycarboxylic acid compound (adipic acid, dodecanedioic acid, (anhydrous) trimellitic acid, (anhydrous) succinic acid, etc.), phenol resin, dicyandiamide, organic acid dihydrazide (adipic acid) Dihydrazide, sebacic acid dihydrazide, etc.), cationic polymerization catalyst of aromatic sulfonium salt (benzyl-4-hydroxyphenylmethylsulfonium hexafluoroantimonate, benzyl-4-methoxyphenylmethylsulfonium hexafluoroantimonate, 4-acetoxy) Phenyldimethylsulfonium hexafluoroantimonate, etc.) and the like.

As the polyester resin, a hydroxyl group and /
Or carboxyl group-containing polyester resin can be used,
Carboxyl equivalent and / or hydroxyl equivalent is about 200-5
000, an average molecular weight of about 500 to 50,000, and a softening temperature of about 60 to 150 ° C. can be used as a powder resin. The polyester resin is mainly an esterified product of polybasic acid (or methyl ester) and polyhydric alcohol, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydro (anhydrous) phthalic acid, hexahydro (anhydrous). Aromatic or alicyclic dicarboxylic acid compounds such as phthalic acid, dimethyl isophthalate, and dimethyl terephthalate, and, if necessary, other polycarboxylic acids such as adipic acid, sebacic acid, (anhydrous) maleic acid, (anhydrous) trimellitic acid, etc. Polyphenolic compounds such as ethylene glycol, propylene glycol, nepentyl glycol, butanediol and 1,6-hexanediol having carboxyl groups and / or hydroxyl groups in polybasic acids such as acid compounds The product obtained by the esterification reaction can be used.

As the crosslinking agent for polyester, when the polyester resin has a carboxyl group, triglycidyl isocyanurate, polyepoxide (the above-mentioned bisphenol (A, F, B) to epichlorohydrin type epoxy resin, novolac epoxy resin, Vinyl polymers and the like). When the polyester resin has a hydroxyl group, block polyisocyanate (ε-caprolactam diisocyanate or the like), β-hydroxyalkylamide, tetramethoxymethylglycoluril and the like can be mentioned.

The blending ratio of the base resin and the cross-linking agent is usually preferably in the range of about 95/5 to 60/40 by weight. However, when the cationic polymerization catalyst of the aromatic sulfonium salt is used, 99.99 / 0.01 to 90 /
A range of 10 weight ratio is sufficient.

Among the powder coatings, those in which polyepoxide is used as a cross-linking agent in the polyester base resin are excellent in weather resistance of coating film, electrodeposition coating composition, water trace resistance to washing water, adhesion to electrodeposition coating film and the like. .

The low-condensation product of tetraalkoxysilane to be added to the powder coating is obtained by hydrolyzing and condensing a tetraalkoxysilane compound with a catalyst such as an acid (hydrochloric acid, sulfuric acid) and / or a base (amine) and water. Condensation degree about 2-10
0, preferably about 2 to 10 is good. If the degree of condensation is less than 2, the water resistance to electrodeposition paint and washing water will deteriorate,
On the other hand, when it exceeds 100, the smoothness of the powder coating film (including the interface portion) is deteriorated, and the interlayer adhesion and the like are deteriorated, which is not preferable. As the alkoxyl group, a methyl group and an ethyl group are particularly preferable. Examples of the silane low condensate include methyl silicate 51, ethyl silicate 40, ethyl silicate 48 (these are Corcort Co., trade name, degree of condensation about 4 to 6). In addition, the low-condensation product is a tri- or bifunctional alkoxysilane such as trialkoxyalkylsilane, trialkoxyphenylsilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and aminopropyltrimethoxysilane. It can be modified with compounds.

The proportion of the low-condensation product of tetraalkoxysilane is about 0.5 to 20 parts by weight, preferably about 1 to 15 parts by weight per 100 parts by weight of the above-mentioned base resin and crosslinking agent.
A range of parts by weight is preferred. If the blending ratio is less than about 0.5 parts by weight, the water resistance to electrodeposition coating and washing water will be reduced, while if it exceeds about 20 parts by weight, the blocking resistance and coating smoothness of the coating will be reduced. Not preferable.

In addition to the above-mentioned components, the powder coating composition may include, for example, a coloring pigment, a filler, a fluidity adjusting agent, an antiblocking agent, an ultraviolet absorber, an ultraviolet stabilizer, a surface adjusting agent, an anti-armpitting agent, and an oxidizing agent. Other compounds such as an inhibitor, a charge control agent, a curing accelerator, and other resins can be compounded as necessary.
As the powder coating material, one that has passed through about 150 mesh can be preferably used.

The powder coating is manufactured by a conventionally known method,
For example, after blending the base resin, the cross-linking agent, the tetraalkoxysilane low condensate and, if necessary, other blends, dry blending, and then melt blending,
It can be manufactured by cooling, coarsely pulverizing, finely pulverizing and filtering.

The powder coating can be performed by an electrostatic powder coating method known per se, for example, a corona charging type or a friction charging type. In the portion other than the boundary portion (continuous coating film), the powder coating film thickness is usually about 20 to 100 μm, preferably about 30 to 60 μm.

The first-stage baking of the powder coating material is a condition that the coating powder is fused and flows to form a coating film and is reflowed by the second-stage baking (to an extent that it is not cured or not completely cured).
Is baked in. The conditions for the first-stage baking are the first
0.8 g of powder obtained by pulverizing the powder coating after step baking to 200 microns or less has an average diameter of 13 mm and a height of 4 mm.
When 30 Kg / mm ² pressure-molded to have a cylindrical shape, the spread length when heated at the second stage baking is 10% or more, preferably 20%, of the original average diameter.
It can be baked under the condition that the size is increased by 170%. The baking conditions differ depending on the type of powder coating,
For example, at about 100 to 140 ° C, about 1 to 10 minutes,
At about 150 to 170 ° C., it is considered to be about 30 seconds to 5 minutes. First stage baking is 10% spread under the above conditions
If it is less than the above range, the secondary flow of the powder coating film is insufficient, so that there is a drawback that the anticorrosion property, the smoothness and the like at the boundary are deteriorated. As the thermosetting electrodeposition coating used in the present invention, any conventionally known coating can be used as long as it is a cationic electrodeposition coating containing an epoxy resin as a base resin.
Examples of the electrodeposition paint include amine-added epoxy resins and amine-added polyester-modified epoxy resins as base resins, which are blended or added with a crosslinking agent of block polyisocyanate to neutralize and disperse in water. You can use what you have done. Among these, the electrodeposition coating composition using the amine-added polyester-modified epoxy resin as the base resin has the effect that the weather resistance of the electrodeposition coating film itself, the smoothness at the interface portion of the coating film, the anticorrosion property, the weather resistance, the adhesion property, etc. There is.

An electrodeposition coating composition using the amine-added polyester-modified epoxy resin as a base resin is disclosed in JP-A-2-9.
Those described in Japanese Patent No. 1169 can be preferably used. Amino group-containing polyester modified epoxy resin derivative obtained by further adding a polyphenol compound and an amino group-containing compound to an addition reaction product of a hydroxyl group-containing epoxy resin having an epoxy equivalent of 200 to 400 and a cyclic ester compound (polyester) It is possible to use a composition obtained by mixing or adding a block polyisocyanate crosslinking agent to a coating resin composition containing as a main component, protonating with a neutralizing agent (acid) and dissolving or dispersing in water.

The epoxy resin has an average of at least about 0.5 hydroxyl groups per molecule, preferably about 0.8 or more and less than 2, and an epoxy equivalent of about 200 to 400, preferably about 230 to 350, and a molecular weight of about 400 to 1000. And preferably in the range of about 450-700. Particularly useful epoxy resins include bisphenol (A,
Polyglycidyl ethers of polyphenols such as F, B)
Ter is included. Specific examples of the epoxy resin include:
For example, bis (4-hydroxyphenyl) -2,2-propane, bis (4-hydroxyphenyl) -1,1ethane, bis (4-hydroxyphenyl) -methane, 4,4
′ -Dihydroxydiphenyl sulfone; polyphenol glycidyl ethers such as phenol novolak and cresol novolac, and polymers thereof.

Examples of the cyclic ester compound include δ-valerolactone, ε-caprolactone, ζ-enalactone, η-caprylolactone, γ-valerolactone, ε-enalactone, ζ-caprylolactone and the like.

Examples of the polyphenol compound include:
Bis (4-hydroxyphenyl) -2,2-propane,
Bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane,
4,4'-dihydroxybenzophenone, bis (4-hydroxy-3-t-butylphenyl) -2,2-propane, bis (hydroxynaphthyl) methane, 1,5-dihydroxynaphthalene and the like can be mentioned.

As the amino group-containing compound, aliphatic, alicyclic or aromatic-aliphatic primary or secondary (reacts with an epoxy group to form an amino group) and tertiary
Examples thereof include tertiary aminomonoisocyanate obtained by reacting a primary amino alcohol with a diisocyanate (which can react with a hydroxyl group of an epoxy resin to introduce an amino group into the epoxy resin).

The average molecular weight of the amino group-containing polyester modified epoxy resin derivative is preferably in the range of about 1,000 to 7,000.

The amino group-containing polyester-modified epoxy resin derivative is a compound containing two or more crosslinkable groups in one molecule, for example, block polyisocyanate, β-hydroxycarbamic acid ester of malonamine, malonic acid ester. Those containing a cross-linking agent such as a derivative, a methylolated melamine, a methylolated urea, a polyepoxy compound, and an α, β-unsaturated double bond compound are used. A part of the crosslinkable groups of the crosslinker may be bonded to the amino group-containing polyester-modified epoxy resin derivative. The mixing ratio of the amino group-containing polyester modified epoxy resin derivative and the crosslinking agent is preferably in the range of about 90/10 to 60/40 weight ratio.

The amino group-containing polyester-modified epoxy resin derivative uses a resin component obtained by protonating the amino group with a water-soluble organic acid such as formic acid, acetic acid, lactic acid, etc. to make it water-soluble. A pigment, an organic solvent, a curing catalyst, a surfactant, and the like can be added to the electrodeposition coating material, if necessary.

The cationic electrodeposition coating method can be carried out by a conventionally known method. For example, it can be carried out by using the above electrodeposition coating as an electrodeposition bath, using the object to be coated as a cathode, and using a material (such as a carbon plate) which does not elute metal as an anode, and conducting electricity. It is desirable that the electric current is applied in such a manner that the thickness of the electrodeposition coating film is about 10 to 40 μm, preferably about 15 to 30 μm. Further, after electrodeposition coating, it is preferable to wash with ultrafiltration filtrate, ultrafiltrate or the like.

Baking of the electrodeposition coating film is carried out under the baking conditions capable of curing the electrodeposition coating film and the powder coating film. The baking depends on the type of electrodeposition coating and powder coating, but usually about 1
In the range of 40 to 180 ° C., it can be performed in the range of about 20 to 40 minutes.

On the coating film formed according to the present invention, a coating material such as an intermediate coating material and a top coating material can be applied.

[0032]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 Thickness 0.8 × length 300 × width 1 after zinc phosphate conversion treatment
The following powder coating material was applied to the half of a 00 (mm) dull steel plate with an electrostatic powder coating machine at an inclination of 0 to 100 microns (0 micron near the center). Then, the first stage baking was performed at 90 ° C. for 15 minutes to form a powder uncured coating film. Next, the powder coated board was dried with the following cationic electrodeposition paint (Kansai Paint Co., Ltd., trade name, amine-added epoxy resin / block polyisocyanate curing type electrodeposition paint) about 20 times.
Cationic electrodeposition coating is performed to make the size of the micron, and the product is washed with ultrafiltration filtration liquid with water, and then at 30 ° C at 30 ° C.
Second step baking was performed for a minute to form a powder coating film and an electrodeposition coating film.

Powder coating: Epicort 1004 (trade name, made by Yuka Shell Epoxy Co., Ltd., trade name, bisphenol A to epichlorohydrin type epoxy resin) 994 g, adipic acid dihydrazide 6 g, ethyl silicate 40 (corco-coat)
(Product name, alkoxysilane low condensate) 100
g, and a titanium white pigment (200 g) were dry-blended, melt-kneaded and dispersed by a bus kneader, and then cooled, coarsely pulverized, finely pulverized, and 150-mesh filtered.

Cationic electrodeposition paint: A flask was charged with 518 g of an epoxy resin having a number average molecular weight of 370 and an epoxy equivalent of 185 obtained by the reaction of bisphenol A and epichlorohydrin, and 57 g of bisphenol A and 0.2 g of dimethylbenzylamine were charged. In addition, the reaction was carried out at 120 ° C. until the epoxy equivalent reached 250, and then 213 g of ε-caprolactone and 0.03 of tetrabutoxytitanium.
g was added and the temperature was raised to 170 ° C., and while maintaining this temperature,
After reacting until absorption disappeared by infrared absorption spectrum analysis of caprolactone, bisphenol A148
g and 0.4 G of dimethylbenzylamine are further added to 130
The reaction was carried out at 0 ° C. until the epoxy equivalent was 936. Then, 257.4 g of methyl isobutyl ketone, 25.5 g of dimethylamine, and 68.3 g of diethanolamine were added and reacted at 80 ° C. for 2 hours, then diluted with 143.4 g of ethylene glycol monomethyl ether to obtain a resin solid content of 72% by weight,
An amino group-containing polyester-modified epoxy resin derivative solution having an amine value of 54.5 was produced. Then, methyl ethyl ketoximeprok isophorone diisocyanate was added to the resin derivative solution so that the block isocyanate group was equivalent to the total amount of the primary hydroxyl group and primary amino group of the resin. Next, the solid content of 1 obtained above is 1
1 g of polypropylene glycol and 0.00 g of acetic acid.
96 g and 1 g of lead acetate were added, and deionized water was gradually added while heating at 60 ° C. to disperse water to obtain an emulsion. Next, 100 g of resin solid content of the emulsion
Against basic lead silicate 3g, titanium white 13g, Kure-3
g, dibutyltin oxide 2 g and Neugen 142B
(Daiichi Kogyo Seiyaku Co., Ltd., trade name, nonionic surfactant) 1 part by weight of which was dispersed in a ball mill to 10 μm, was mixed with a pigment paste, and the resin solid content was 15% by weight. Was diluted and manufactured.

Spread of the powder coating film in the first-stage baking Average diameter elongation ratio: 2 for the powder coating film subjected to the first-stage baking
It is crushed to less than 00 micron and 0.8g of the powder is made into a cylindrical shape with an average diameter of 13mm and a height of 4mm.
/ Mm ² Press-molded product placed on aluminum plate No. 2
The spread length was measured when heating was performed by step baking (170 ° C. for 30 minutes). Then, the formula [{(average diameter of the molded product after baking mm-diameter of pressed product of the initial powder coating before baking 13 mm) / diameter of pressed product of the initial powder coating 13 mm} × 100] (Hereinafter, it has the same meaning.) The spread average diameter elongation of the powder coating film was calculated. The result was 100% (average diameter 26 mm), which was good.

Appearance of coating film: The coated plate after washing with water in the second-step baking for forming the above coating film was laid down, and the coated plate was baked so that the washing water remained on the powder coating film. Represents the meaning). The coating film surface was good, with no blemishes, swelling, or deformation.

Coating smoothness: The smoothness of the coating smoothness was visually evaluated (hereinafter, the same meaning is given). The results were good both in the powder coating part, the electrodeposition coating part and the interface thereof.

Salt spray resistance: JIS K-5400 salt spray test The rust generation on the flat surface after 500 hours was visually evaluated (hereinafter, the same meaning is given). No rust was generated in any of the powder coating part, the electrodeposition coating part and the interface thereof, which was good.

Example 2 A test was conducted in the same manner as in Example 1 except that the baking temperature of the powder coating material was changed to 110 ° C.

The spread of the powder coating film in the first baking was 92% (average diameter 25 mm).

Appearance of coating film: The surface of the coating film was good with no tingling, swelling or deformation.

Coating smoothness: Good in both the powder coating part, the electrodeposition coating part and its interface.

Salt water spray resistance: No rust was generated in the powder coated portion, the electrodeposition coated portion, and the interface thereof, which was good.

Comparative Example 1 In Example 1, the first-stage baking temperature of the powder coating material was set to 170.
A coating film was formed in the same manner as in Example 1 except that the temperature was set to 0 ° C. and the powder coating film was cured. As a result, the spread of the powder coating film in the first-step baking was 1% in average diameter elongation (average diameter 13.
1 mm) was bad. The appearance of the coating film was good. The powder coating part and the electrodeposition coating part had good coating smoothness, but the interface was uneven and inferior. Although the salt spray resistance of the powder coating part and the electrodeposition coating part was good, rust was generated at the interface and it was extremely poor.

Comparative Example 2 In Example 1, ethyl silicate 4 was used as the powder coating material.
A powder coating material was produced in the same manner as in Example 1 except that 0 was not added. Then, using this, a coating film was formed in the same manner as in Example 1. As a result, the spread of the powder coating film in the first-stage baking was 100% (average diameter 2%).
6 mm) was good. The appearance of the coating film was not good, as it had tingling, swelling, and deformation. The powder coated part and the electrodeposition coated part had good smoothness, but their interfaces were slightly inferior. The powder coating part and the electrodeposition coating part were good, but rust was generated at the interface, which was bad.

[0047]

In the powder coating material used in the present invention, the uncured powder coating film formed by the first baking is a low-condensation component of tetraalkoxysilane which is a low-polarity component having poor compatibility on the surface. A coating film with a high content is formed. Therefore, the low-condensation component on the surface of the coating film is hydrolyzed by the electrodeposition coating composition and washing water to form silanol groups, and the surface of the coating film becomes hydrophilic. Since the coating film hydrophilized in this way has good wettability with the electrodeposition coating composition and washing water, it does not form polka dots and is uniformly present on the entire surface of the coating film. Further, since the low-condensation product undergoes a condensation reaction simultaneously with hydrolysis to become a polymer, the hydrophilic coating film obtained is not dissolved or swelled by the electrodeposition paint, washing water or the like, and defects such as water marks are eliminated.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Ogasawara 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. In Paint Co., Ltd. (72) Inventor Tadayoshi Tatsuno 4-17-1, Higashi-Hachiman, Hiratsuka City, Kanagawa Kansai Paint Co., Ltd.

Claims (2)

[Claims] 1. An uncured coating film is formed by applying a thermosetting powder coating composition containing a low-condensation product of tetraalkoxysilane to an object to be coated and then baking the powder coating film in the first step. After that, a thermosetting epoxy resin-based cationic electrodeposition coating composition is applied to the uncoated portion of the powder to form a coating film, followed by second baking to obtain a powder coating film and an electrodeposition coating film. A coating method characterized by curing simultaneously. 2. The first-stage baking is carried out by powdering 0.8 g of powder obtained by pulverizing the powder coating obtained by the first-stage baking to a size of 200 μm or less to obtain a cylindrical shape having an average diameter of 13 mm and a height of 4 mm. / Mm ² pressure molding, this is the second
A coating method, characterized in that baking is performed under conditions such that the spread length when heated by step baking becomes 10% or more larger than the original average diameter.