JPH09125286A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method by which the performances such as the smoothness, corrosion resistance and weatherability of a powder- electrodeposition coating film interface are improved. SOLUTION: A material to be coated is coated with a thermosetting epoxy polyester resin powder paint, the powder coating film is baked in the first stage to form an uncured coating film, then the part not coated with the powder paint is coated with a thermosetting polyester-modified epoxy resin cationic electrodeposition paint to form a coating film, and then second-stage baking is 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, since the electrodeposition coating used in this method is an anionic electrodeposition coating, it has a drawback that it has poor corrosion resistance.

In recent years, cationic electrodeposition coatings of amine-added epoxy resins have been widely used as the electrodeposition coatings by substituting them with anionic electrodeposition coatings because of their excellent corrosion resistance.

In the above-mentioned publication, in the method of using a cationic electrocoating instead of the anionic electrocoating as the electrocoating, for example, the one using epoxy powder coating as the powder coating has poor weather resistance. Therefore, there is a drawback that the adhesion with the topcoat is poor, and in the case where polyester powder coating is used as the powder coating, the fluidity of both coatings at the interface between the powder coating and the electrodeposition coating is poor. There are disadvantages that the appearance of the coating film at the boundary is poor and the adhesion between the powder coating film and the electrodeposition coating film is poor.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that by combining a specific powder coating and electrodeposition coating in a conventional method, The inventors have found that it is a method capable of improving the smoothness, corrosion resistance, adhesion, weather resistance and the like of the boundary portion, and completed the present invention.

That is, according to the present invention, a thermosetting epoxy polyester resin powder coating material is applied to an object to be coated, and then the powder coating film is baked in the first step to form an uncured coating film.
A thermosetting polyester-modified epoxy resin cationic electrodeposition coating is applied to the uncoated portion of the powder to form a coating, and then a second stage baking is performed to simultaneously form the powder coating and the electrodeposition coating. The present invention relates to a coating method characterized by curing.

[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.

The thermosetting powder coating used in the present invention uses a polyester polycarboxylic acid resin as a base resin and a mixed resin prepared by mixing an epoxy resin as a cross-linking agent with this as a curable base resin. Is particularly preferable.

The polyester polycarboxylic acid resin has an acid value (mg of KOH / g of resin 1) of about 10 to 10.
0, preferably about 20-80, average molecular weight about 500-5
A powder resin having a softening temperature of about 0000 and about 60 to 150 ° C. can be used. When the acid value is less than about 10, the curability is lowered and the performances such as corrosion resistance and weather resistance are deteriorated, while when it exceeds about 100, the water resistance and weather resistance of the coating film are unfavorably deteriorated. If the average molecular weight is less than about 500, the water resistance and processability of the coating film will deteriorate, while if it exceeds about 50,000, the smoothness of the coating film will decrease, which is not preferable. Softening point is about 60
If the temperature falls below ℃, the blocking resistance of the paint will decrease, while
If it exceeds about 150 ° C., the smoothness of the coating film is deteriorated, which is not preferable.

The polyester polycarboxylic acid resin is mainly an esterified product of polybasic acid (or methyl ester) and polyhydric alcohol, and is, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydro (anhydrous) phthalate. Acid, hexahydro (anhydrous) phthalic acid, dimethyl isophthalate,
Aromatic or alicyclic dicarboxylic acid compounds such as dimethyl terephthalate and, if necessary, adipic acid, sebacic acid,
Polybasic acids such as other polycarboxylic acid compounds such as (anhydrous) maleic acid and (anhydrous) trimellitic acid are added to ethylene glycol, propylene glycol, nepentyl glyco-
It is possible to use those obtained by subjecting a polyol compound such as diol, butanediol and 1,6-hexanediol to an esterification reaction so as to have a carboxyl group.

As the epoxy resin, a liquid or solid epoxy resin having an average of about 2 or more, preferably about 2 to 500 epoxy groups in one molecule can be used. Specifically, as the trade name, for example, Epicote 812, same left 815, same left 828, same left 820, same left 834, same left 1001, same left 1002, same left 1004, same left 1007.
(Above, manufactured by Yuka Shell Epoxy Co., Ltd.), Araldite 502, same left 6005, same left GY-6084, same left 6
097, same left GT7004 (manufactured by Ciba-Geigy), D
ER-662, same as left 664, same as left 667 (manufactured by Dow Chemical Co.), bisphenol-epichlorohydrin type epoxy resin, EPPN-201, same as left 202, EOCN
-1020, same as 102S (above, manufactured by Nippon Kayaku Co., Ltd.), novolac type epoxy resin, vinyl polymer (eg, glycidyl (meth) acrylate, 3,4-).
Radical homopolymers of epoxy group-containing unsaturated monomers such as epoxycyclohexylmethyl (meth) acrylate,
And, if necessary, for example, methyl (meth) acryl-
Alkyl or cycloalkyl esters of (meth) acrylic acid such as ethyl ester, ethyl (meth) acrylate, cyclohexyl (meth) acrylate, etc., hydroxyl group-containing unsaturated monomers such as hydroxyethyl (meth) acrylate, Aromatic compounds such as styrene, radical copolymers with other unsaturated monomers such as nitrile compounds such as (meth) acrylonitrile), and the like. Among these, bisphenol (A, F, B) to epichlorohydrin type epoxy resin and novolac type epoxy resin are preferably used because they have excellent corrosion resistance and the like.

The blending ratio of the above-mentioned polyester polycarboxylic acid resin and epoxy resin is usually about 95/5 to 50 /
A range of 50 weight ratio, preferably about 90/10 to 60/40 weight ratio is suitable.

In addition to the above-mentioned components, the powder coating material 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 100 mesh can be preferably used.

The powder coating can be carried out by a known electrostatic powder coating method, for example, a corona charging type, a friction charging type or the like. 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 re-flowed by the second-stage baking (unhardened or not completely hardened).
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 electrocoating paint used in the present invention, any paint known in the art can be used as long as it is a paint containing a polyester-modified epoxy resin as a base resin. As the electrodeposition paint, those described in JP-A-2-91169 can be preferably used. Epoxy equivalent is 20
A main component is an 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 0-400 hydroxyl group-containing epoxy resin and a cyclic ester compound (polyester). It is possible to use a coating resin composition prepared by blending or adding a block polyisocyanate cross-linking agent, which is protonated with a neutralizing agent (acid) and dissolved or dispersed 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 400. Those in the range of 1000, preferably about 450 to 700 are preferred. Particularly useful epoxy resins include bisphenol (A,
Polyglycidyl ethers of polyphenols such as F, B)
Tell etc. are included. Specific examples of the epoxy resin include, for example, bis (4-hydroxyphenyl) -2,2
-Propane, bis (4-hydroxyphenyl) -1,1
Ethane, bis (4-hydroxyphenyl) -methane,
4,4'-dihydroxydiphenyl sulfone; polyphenol glycidyl ethers such as phenol novolac and cresol novolac and polymers thereof.

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

As the polyphenol compound, for example,
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 compounds (react with an epoxy group to form an amino group) and tertiary compounds.
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, polyamine β-hydroxycarbamic acid ester and 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 in which the amino group is protonated 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 electrodeposition coating method may be 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. The energizing condition is that the electrodeposition coating film thickness is about 10-40 microns,
It is desirable to carry out in the range of preferably about 15 to 30 microns. Further, after electrodeposition coating, it is preferable to wash with ultrafiltration filtrate, ultrafiltrate or the like.

The electrodeposition coating film is baked under the baking conditions that can cure 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.

If necessary, the surface of the coating film formed by the present invention may be coated with a paint such as an intermediate coating composition and a top coating composition.

[0027]

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 epoxy polyester resin-based thermosetting powder coating was tilted on half of a 00 (mm) dull steel plate with an electrostatic powder coating machine (manufactured by Gema Co.) so as to be 0 to 100 microns (0 microns near the center) Painted Then, the first stage baking was performed at 90 ° C. for 15 minutes to form a powder uncured coating film. Next, the powder coated plate was electrodeposited with the following cationic electrodeposition coating so that the dry coating film would be about 20 microns, washed with ultrafiltration filtration liquid, and then second-stage baked at 170 ° C for 30 minutes. Then, a powder coating film and an electrodeposition coating film were formed.

Powder coating: Fine Deck M8860 (manufactured by Dainippon Ink and Co., Inc., trade name, acid value 35, powder) 70
0 g, Epicort 1002 (produced by Yuka Shell Epoxy Co., Ltd., trade name, epoxy equivalent 550 to 700, average about 2)
300 g of individual epoxy groups and 400 g of titanium white are dry blended with a Henschel mixer, then melt-mixed and dispersed with a Buscon Kneader, cooled, coarsely pulverized and finely pulverized, and then filtered with 150 mesh. Manufactured.

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.

Spreading 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). Next, the formula [{(average diameter of the molded product after baking mm-average diameter of the pressed product of the initial powder coating before baking 13 mm) / average diameter of the pressed product of the initial powder coating 13 mm} × 100] (hereinafter, the same meaning is given), and the spread average diameter elongation ratio of the powder coating film was calculated. The result was 100% (average diameter 26 mm), which was good.

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.

Interlayer adhesion between powder coating film and electrodeposition coating film: 50 pieces of 2 mm square Gobang eyes were made with a cutter and cellophane tape was adhered to the surface thereof, and the squares when strongly separated The degree of peeling was evaluated (hereinafter, the same meaning is given). As a result, there was no peeling and it was good.

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.

Accelerated weathering resistance: After a 400-hour test with a sunshine weatherometer, the coating film was evaluated (hereinafter, the same meaning is given). As a result, discoloration,
There were no defects such as luster, and it 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), which was good.

Coating smoothness: Good on both the powder-coated part, the electrodeposition-coated part and its interface.

Interlayer adhesion with powder coating and electrodeposition coating: Good with no peeling.

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

Accelerated weather resistance: Good with no defects such as discoloration and glossiness.

Comparative Example 1 A test was conducted in the same manner as in Example 1 except that the baking temperature of the powder coating material was 170 ° C. As a result, the spread of the powder coating film in the first-stage baking was 2 and the average diameter elongation was 2
% (Average diameter 13.3 mm) was poor. Regarding the smoothness of the coating film, the smoothness of the powder-coated portion and the electrodeposition-coated portion were good, but the interface was uneven and inferior. Regarding the salt spray resistance, the powder coating part and the electrodeposition coating part were good, but rust was generated at the interface, which was extremely bad. The interlayer adhesion between the powder coating film and the electrodeposition coating film was good without peeling. The accelerated weather resistance was good with no defects such as discoloration and glossiness.

Comparative Example 2 In Example 1, as the powder coating material, an epoxy resin type thermosetting powder coating material (Kansai Paint Co., Ltd., EVACLAD No. 3250 gray, bisphenol type epoxy resin /
A coating film was formed in the same manner as in Example 1 except that adipic acid dihydrazide curing system) was used. As a result, the spread of the powder coating film in the first baking was 100% and the average diameter elongation rate was 100.
% (Average diameter 26 mm) was good. The smoothness of the powder-coated part and the electrodeposition-coated part were good, but the interface was poor. 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.
The interlayer adhesion between the powder coating film and the electrodeposition coating film was poor because more than half of the crevices peeled off. Accelerated weathering resistance was poor due to discoloration and gloss on the powder coating.

[0044]

INDUSTRIAL APPLICABILITY The coating method of the present invention improves the interlaminar adhesion and wettability of a coating film formed by using polyester as a constituent of powder coatings and electrodeposition coatings, and furthermore, the electrodeposition coating film. Since the powder coating film and the electrodeposition coating film flow at the same time when baking is carried out, a remarkable effect such as excellent smoothness, corrosion resistance and weather resistance is exhibited.

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

Claims (4)

[Claims] 1. A thermosetting epoxy polyester resin powder coating material is applied to an object to be coated, and then the powder coating film is baked in the first step to form an uncured coating film. A part is coated with a thermosetting polyester-modified epoxy resin cationic electrodeposition coating to form a coating film, and then second step baking is performed to simultaneously cure the powder coating film and the electrodeposition coating film. How to paint. 2. A coating method, wherein the powder coating material contains a polyester polycarboxylic acid resin as a base resin and an epoxy resin as a cross-linking agent. 3. A coating method wherein the electrodeposition coating composition contains a caprolactone-modified epoxy resin as a base resin. 4. The first-stage baking is carried out so that 0.8 g of powder obtained by pulverizing the powder-coated film subjected to the first-stage baking to a size of 200 μm or less is made into 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.