JP2002018349A - Multilayer coating film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of giving a multilayer electrodeposition and an aqueous intermediate coating film for a car body or the like having an excellent finishing property, sticking property and chipping resistance at low cost. SOLUTION: The multilayer coating film forming method includes the following processes. A step (1): a process for forming the electrodeposition coating film on a metal made material to be coated such as the car body having a bag structure by applying a cation electrodeposition coating material composition. A step (2): a process for washing the material to be coated having the electrodeposition coating film with water to remove the excessively sticking cation electro-deposition coating material composition, finally washing the resultant electrodeposition coating film with pure water at 30-70 deg.C and removing water retained in a gap and bubbles contained in the coating film. A step (3): a process for forming the intermediate coating film on the material to be coated having the electrodeposition coating film obtained in the above described process by applying the water based intermediate coating material composition containing a (blocked) polyisocyanate as a cross-linking agent. A step 4: a process for hardening the coating films simultaneously by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film, and more particularly to a method for forming a coating film obtained by coating a cationic electrodeposition coating composition and an aqueous intermediate coating composition. Feeling, etc.), and the adhesion and chipping resistance of both coating films.

[0002]

2. Description of the Related Art After coating a cationic electrodeposition coating composition using a (blocked) polyisocyanate compound as a cross-linking agent on an outer panel of an automobile or the like, a preheating is carried out, and an aqueous solution containing a polyester resin and an amino resin is applied. Conventionally, a method of applying an intermediate coating composition and then heating and simultaneously curing the two coating films to form a multi-layer coating film has been known, as disclosed in JP-A-6-17294 and JP-A-6-41788.
And JP-A-11-216422, for example.

[0003] In this step, after the cationic electrodeposition coating composition is applied, washing is carried out to remove excess paint, but the water temperature is not particularly limited, and the water temperature is in the range of 0 ° C or more and less than 40 ° C. Thereafter, preheating was performed in a temperature range of 40 ° C. to 100 ° C. for 1 minute to 10 minutes to apply the aqueous intermediate coating composition.

However, in the preheating process since the recent cost reduction of automobile bodies, cost reductions such as equipment costs for dryers, running costs, space in lines, and maintenance of equipment have been required. Cost reduction has been demanded while maintaining performance such as chipping resistance.

[0005]

Means for Solving the Problems Therefore, the present inventors have
(Blocked) A cationic electrodeposition coating composition using a polyisocyanate compound as a cross-linking agent is applied, and the coating surface is cured without curing the coating film in an aqueous solution using a block polyisocyanate compound as a cross-linking agent. In applying the coating composition and then heating to simultaneously cure the two coatings to form a multi-layer coating, 30 to 70 times in the final washing with water after the cationic electrodeposition coating composition is applied. By washing with water at a temperature of ° C., the above problems were solved, and it was found that a multilayer coating film having excellent finishability and adhesion, and further having chipping resistance and the like could be formed, and to solve the present invention. Reached.

That is, the present invention provides the following steps: Step (1): a step of applying a cationic electrodeposition coating composition to a metal substrate having a bag structure such as an automobile body to form an electrodeposition coating film. Step (2); Next, the object having the electrodeposition coating film obtained above is washed with water to remove the excessively adhered cationic electrodeposition coating composition, and the obtained electrodeposition coating film is subjected to 30 to 30 minutes. A step of performing final washing with pure water at 70 ° C. to remove water accumulated in the voids and bubbles contained in the coating film; step (3); and a coating having the electrodeposition coating film obtained in the above step. A step of applying an aqueous intermediate coating composition containing a (blocked) polyisocyanate compound as a cross-linking agent to the coating material to form an intermediate coating film, step (4); Heating and curing, and a method for forming a multilayer coating film, comprising: .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a multilayer coating film composed of a cationic electrodeposition coating composition and an aqueous intermediate coating film composition, which has excellent finish, adhesion and chipping resistance at low cost. For details on the method of forming the multilayer coating film,
After forming the cationic electrodeposition coating film, it is characterized by using pure water having a final washing temperature of 30 to 70 ° C. Hereinafter, the steps (1) to (4), the cationic electrodeposition coating composition, and the aqueous intermediate coating composition in the present invention will be described.

The article to be coated used in the step (1) may be an article having a complicated structure such as an automobile body, an automobile part, or a bag. Examples of the material of the object to be coated include metals, and rust-proof steel plates are preferable from the viewpoint of rust prevention. Steel sheets include hot-dip galvanized steel sheets, electro-galvanized steel sheets, electro-zinc-iron bilayer coated steel sheets, organic composite coated steel sheets, etc., and base materials such as these steel sheets and cold-rolled steel sheets, if necessary, by alkali degreasing. After the surface is cleaned, a surface treatment such as a phosphoric acid conversion treatment or a chromate treatment may be performed.

In the method of the present invention, the electrodeposition coating composition used for the electrodeposition coating can be used without any particular limitation as long as it is an electrodeposition coating composition. Select and use.

The above cationic electrodeposition coating composition includes:
For example, an electrodeposition coating composition containing a vinyl copolymer as a main component or a cationic electrodeposition coating composition containing an epoxy resin as a main component can be used.

For example, in a cationic electrodeposition coating composition containing a vinyl copolymer as a main component, a conventionally known vinyl copolymer can be used, for example, an amino group-containing monomer and a hydroxyl group-containing monomer, and Those obtained by copolymerizing with other vinyl monomers are mentioned.

The amino group-containing monomer is preferably an amino group-containing acrylic monomer, for example, aminoethyl (meth) acrylate, N-tert-butylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate N, N-diethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N N, N-dimethylaminobutyl (meth) acrylate and other aminoalkyl acrylates or methacrylates; N, N-
Dimethylaminoethyl (meth) acrylamide, N, N
-Diethylaminoethyl (meth) acrylamide, N,
N-dipropylaminoethyl (meth) acrylamide,
Examples include aminoalkylacrylamides such as N, N-dimethylaminopropyl (meth) acrylamide or methacrylamides. These can be used alone or 2
It can be used in combination of more than one species. Such an amino group-containing monomer is suitably used in a range of 3 to 20% by weight, preferably 5 to 18% by weight of the total amount of the monomers.

As the hydroxyl group-containing monomer, for example, C ₁ -C ₈ hydroxyalkyl esters of acrylic acid or methacrylic acid such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate can be preferably used.

The other vinyl monomers mentioned above include:
There is no particular limitation as long as it is a monomer copolymerizable with an amino group-containing monomer or a hydroxyl group-containing monomer. For example, methyl (meth) acrylate, ethyl (meth) acrylate,
n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, etc. C ₁ -C ₂₄ alkyl or cycloalkyl esters of acrylic or methacrylic acid; styrene, vinyltoluene, α
-Methylstyrene, vinyl propionate, vinyl acetate,
(Meth) acrylonitrile, vinyl propionate,
Vinyl monomers such as (meth) acrylamide, N, N-diethyl (meth) acrylamide, and veova monomer (shell chemical products) can be mentioned, and they can be used alone or in combination of two or more. These monomers can be appropriately selected according to the properties of the intended electrodeposition paint and the required performance of the coating film formed thereby. The production of a copolymer comprising the above monomers can be carried out by a conventionally known method, and is generally carried out according to a solution polymerization method.

In addition, as an electrodeposition coating composition containing a vinyl copolymer as a main component, a copolymer containing a glycidyl group-containing monomer and a hydroxyl group-containing monomer and another vinyl monomer copolymerizable therewith and not reacting with a glycidyl group is used. A polymer obtained by adding an amine to a polymer may also be used.

Examples of the glycidyl group-containing monomer include glycidyl (meth) acrylate, vinylcyclohexene monoepoxide, N-glycidyl acrylamide, allyl glycidyl ether and the like. Such a glycidyl group-containing monomer is used in an amount of 5 to 5 of the total monomer amount.
It is suitably used in an amount of 0% by weight, preferably 10 to 40% by weight. As the hydroxyl group-containing monomer and other vinyl monomers copolymerizable therewith and not reacting with the glycidyl group, those described above can be used similarly. The production of a copolymer comprising such monomers can also be carried out by a conventionally known method.

The addition reaction of the glycidyl group-containing copolymer obtained as described above with an amine can be carried out in accordance with a conventionally known method. A method of reacting at a temperature of 120 ° C. for about 1 to 20 hours is exemplified. Examples of the amine used include alkylamines such as propylamine, butylamine, dimethylamine, diethylamine and di-n-propylamine; alkanolamines such as diethanolamine, diisopropanolamine and N-methylethanolamine; piperidine, morpholine, N-methylpiperazine and the like. Usually, the amount of the amine used is suitably in the range of about 0.1 to 1 mol per mol of glycidyl group.

The hydroxyl value of the cationic electrodepositable vinyl copolymer obtained as described above is not particularly limited, but is usually 30 to 200 mgKOH / g, preferably 5 to 200 mgKOH / g.
A range from 0 to 150 mg KOH / g is suitable. If the hydroxyl value is less than 30 mgKOH / g, the curability of the obtained coating film tends to be poor, and if it exceeds 200 mgKOH / g, the weather resistance and corrosion resistance tend to be poor. The molecular weight of the cationic electrodepositable vinyl copolymer is usually about 5,000 to 1
00,000, preferably 10,000-50,000
Is appropriate.

The above cationic electrodepositable vinyl copolymer is neutralized by an organic acid such as acetic acid, propionic acid, lactic acid, or hydroxyacetic acid, and can be imparted with water dispersibility. The cationic electrodepositable vinyl copolymer may be mixed with a crosslinking agent such as a (blocked) polyisocyanate compound or a melamine resin, if necessary.

Each of the (blocked) polyisocyanate compounds is an addition reaction product of the polyisocyanate compound and an isocyanate blocking agent (eg, an alcohol compound, an oxime compound, a tertiary hydroxyamine compound, a phenol compound, etc.). Examples of the polyisocyanate compound include aromatic and alicyclic compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, bis (isocyanatomethyl) cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and isophorone diisocyanate. Formula or aliphatic polyisocyanate compounds and excess amounts of these polyisocyanate compounds may be added to ethylene glycol or propylene glycol. Lumpur, trimethylolpropane,
Examples of the compound include a terminal isocyanate-containing compound obtained by reacting a low-molecular-weight active hydrogen-containing compound such as hexanetriol or castor oil.

Further, in the cationic electrodeposition coating composition containing the vinyl copolymer as a main component, a small amount of a conventionally known amine-added epoxy resin as another resin for electrodeposition may be used in combination with the anticorrosive property. desirable.

The epoxy resin in the cationic electrodeposition coating composition containing an epoxy resin as a main component includes an amine-added epoxy resin, and the amine-added epoxy resin is usually used in the electrodeposition coating composition. Polyamine resins, such as (i) adducts of polyepoxide compounds with primary mono- and polyamines, secondary mono- and polyamines, or mixed primary and secondary polyamines (eg, US Pat. No. 3,984,299); ii) adducts of polyepoxide compounds with ketiminated secondary mono- and polyamines having primary amino groups (eg, US Pat. No. 4,017,438); (iii) polyepoxide compounds and ketiminated 1 Reaction product obtained by etherification with a hydroxy compound having a secondary amino group (for example, JP-A-59-43013) ), And the like.

The polyepoxide compound used in the production of the polyamine resin is a compound having two or more epoxy groups in one molecule, and is generally at least 200, preferably 400 to 4,000, more preferably 800.
Those having a number average molecular weight in the range of 2,000 to 2,000 are suitable, and those obtained by the reaction of a polyphenol compound with epichlorohydrin are particularly preferred. Examples of the polyphenol compound that can be used for forming the polyepoxide compound include bis (4-hydroxyphenyl) -2,2-propane, 4,4'-dihydroxybenzophenone, and bis (4-hydroxyphenyl) -1,1.
-Ethane, bis (4-hydroxyphenyl) -1,1-
Isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxynabutyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane, 4,4'-dihydroxydiphenylsulfone, phenol novolak, cresol novolak and the like.

The polyepoxide compound may be a compound partially reacted with a polyol, polyether polyol, polyester polyol, polyacidamine, polycarboxylic acid, polyisocyanate compound, etc. Further, ε-caprolactone, acrylic monomer, etc. May be obtained by graft polymerization.

The above amine-added epoxy resin is neutralized with an acid such as acetic acid, propionic acid, lactic acid, or hydroxyacetic acid, so that the epoxy resin has a water dispersing ability. A crosslinking agent may be mixed with the amine-added epoxy resin as necessary. Examples of the cross-linking agent include (blocked) polyisocyanate compounds, melamine resins, and the like mentioned as a cross-linking agent that can be mixed with the cationic electrodeposition coating composition containing a vinyl copolymer as a main component, if necessary. be able to.

The (blocked) polyisocyanate compound used as a curing agent in the present invention is a compound obtained by blocking an aliphatic and / or alicyclic polyisocyanate compound with a blocking agent. When the polyisocyanate compound is a non-aliphatic and / or alicyclic polyisocyanate compound, for example, an aromatic polyisocyanate compound, it is not preferable because the weather resistance of the coating film is deteriorated. Examples of the aliphatic and / or alicyclic polyisocyanate compound include aliphatic or alicyclic diisocyanate compounds such as isophorone diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, and methylene diisocyanate, and dimers and dimers thereof. And isocyanate-terminated compounds obtained by reacting an excess of these isocyanate compounds with a low molecular active hydrogen-containing compound such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol, or castor oil.

The blocking agent is one which blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is stable at room temperature and is about 100 to 20.
When heated to 0 ° C, preferably 120 to 150 ° C, it is desirable that the blocking agent be dissociated to regenerate free isocyanate groups.

As such a blocking agent, for example,
Lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenol compounds such as phenol, para-t-butylphenol and cresol; fats such as n-butanol and 2-ethylhexanol Aromatic alcohols such as phenylcarbinol and methylphenylcarbinol; ether alcohol compounds such as ethylene glycol monobutyl ether;

The amount of the blocking agent is preferably 1: 1 to 1: 1.3 with respect to the NCO group of the isocyanate. If the ratio exceeds 1.3, the blocking agent remains to lower the corrosion resistance of the coating film, and if the ratio is less than 1.0, NCO groups remain to impair the stability of the coating composition, which is not preferable.

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 material can be used. (For example, JP-A-59-155470); a resin which can be cured by a transesterification reaction (for example, JP-A-55-80436);
Resins into which isocyanate groups have been introduced can also be used.

The above-mentioned coating composition which can be used as the cationic electrodeposition coating composition may optionally contain additives, for example,
Color pigments such as carbon black, titanium white, red iron oxide; extender pigments such as clay, talc, calcium carbonate; strontium chromate, lead chromate, lead silicate;
Aluminum tripolyphosphate, zinc tripolyphosphate, zinc white,
Rust-preventive pigments such as inorganic bismuth and organic acid bismuth; as other additives, for example, surfactants; surface modifiers for painted surfaces (acrylic resin, fluororesin, silicon resin, etc.); curing catalysts (for example, tin, Salts of metals such as zinc, lead and bismuth); gelled fine particles, polymeric polyurethane resins and other additives; and organic solvents.

The neutralization and dispersion of the base resin with water are usually carried out by adding an aliphatic carboxylic acid such as glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, tartaric acid, malic acid, or the like. It is carried out by neutralizing with a water-soluble organic acid such as hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, acetic acid and formic acid, followed by dispersing in water.
Use of formic acid as a neutralizing agent is preferable because of excellent throwing power. It is also possible to use as a clear paint without blending pigments.

The above-mentioned cationic electrodeposition coating composition is appropriately diluted with pure water and adjusted so that the solid content concentration is about 5 to 25% by weight and the pH is within the range of 5.5 to 8. As a method and an apparatus for performing electrodeposition coating on an object to be coated using the cationic electrodeposition coating composition, known methods and apparatuses conventionally used in electrodeposition coating can be used.

At this time, the conditions for electrodeposition coating are not particularly limited, but generally, the bath temperature is 15 to 35 ° C. (preferably 20 to 30 ° C.), and the voltage: 100 to 400 V (preferably 200 to 300 V), energization time: 30 seconds to 10
Min, pole area ratio (A / C) 8/1 to 1/8, distance between poles 10
It is desirable to perform electrodeposition coating in a stirring state of up to 200 cm.

The thickness of the electrodeposition coating film of the cationic electrodeposition coating composition may be appropriately selected according to the desired performance.
It is good to be in the range of 10 to 70 μm, preferably 15 to 40 μm. As the electrodeposition coating composition, by using a cationic electrodeposition coating composition containing a vinyl copolymer as a main component, a coating film having good weather resistance can be generally obtained, and a cationic resin containing an epoxy resin as a main component can be obtained. By using the electrodeposition coating composition, a coating film having good corrosion resistance can be obtained.

In the step (2), the cationic electrodeposition coating composition is coated on the surface of the coating with ultrafiltration solution, RO permeated water, industrial water, pure water, etc., in order to remove the excessively adhered cationic electrodeposition coating composition. Rinse thoroughly with water two or more times so that no objects remain. This water washing equipment can be performed by dipping water washing in which the body is immersed, or spray water washing. The present invention is characterized in that the final rinsing temperature in this multiple rinsing is 30 to 70C, preferably 40 to 60C. As a method of heating, it is possible to use residual heat of a paint circulation pump, a drying facility, and the like, and it is possible to cope with the cost at a low cost.

Here, if the washing temperature is lower than 30 ° C., moisture generated in the bubbles formed during the first electrodeposition coating or gas holes in the coating film remains, and the fusion ability of the formed film is reduced. As a result, a coating film having a sufficient finish cannot be obtained. On the other hand, when the temperature of the rinsing water exceeds 70 ° C., the surface of the electrodeposition coating film is partially cured, which affects the coating film formation of the intermediate coating film to be applied next, and the finish is reduced. Such a trouble occurs.

The step (3) is a step of further applying the aqueous intermediate coating composition to the coating having the cationic electrodeposition coating film obtained in the above step to form a coating film. The aqueous intermediate coating composition used here is described below. The aqueous intermediate coating composition used in the present invention is an aqueous coating composition containing a (blocked) polyisocyanate compound as a curing agent, and specifically, a crosslinking reaction with an isocyanate group such as a hydroxyl group. A base resin having a hydrophilic group such as a carboxyl group useful for making the resin water-soluble or water-dispersible, and a (blocked) polyisocyanate compound, and mixing and dispersing these in water. Water-based coating composition.

The base resin is a resin having a functional group capable of undergoing a cross-linking reaction with an isocyanate group such as a hydroxyl group and a hydrophilic group such as a carboxyl group in an amount necessary for making the resin water-soluble or water-dispersible. And a polyester resin having a hydroxyl group and a carboxyl group.

The polyester resin can be produced by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction, and has a number average molecular weight of 1,000 to 50,000.
00, especially 2,000 to 20,000, with a hydroxyl value of 20
~ 200 mgKOH / g, especially 50-150 mgKOH
/ G, acid value is 1-100 mgKOH / g, especially 10-7
0 mgKOH / g is preferred.

The polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, Examples thereof include hexahydrophthalic acid, heptic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and anhydrides thereof. Polyhydric alcohols are compounds having two or more hydroxyl groups in one molecule, such as ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, hexanediol, and the like.
Diethylene glycol, dipropylene glycol, neopentyl glycol, hydrogenated bisphenol A, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane and pentaerythritol
And so on.

The introduction of the hydroxyl group into the polyester resin is carried out by adding glycerin, trimethylolpropane and trimethylol as polyhydric alcohol components in the production of the polyester resin.
The reaction can be carried out by using a trivalent or more alcohol such as luethane or pentaerythritol in combination with a divalent alcohol. The carboxyl group can be introduced by subjecting a part of the hydroxyl group of the obtained polyester resin having a hydroxyl group to a half esterification reaction of the above polybasic acid. (Blocked) polyisocyanate
The cross-linking compound is a cross-linking agent for the base resin, and the block polyisocyanate compound described as the cross-linking agent in the electrodeposition coating composition can be used similarly.

In the aqueous intermediate coating composition, the composition ratio of the base resin and the (blocked) polyisocyanate compound is not particularly limited, but the base resin is 40% based on the total solid weight of these two components. ~ 90% by weight, especially 50
~ 80% by weight, and the amount of the block polyisocyanate compound is 6%.
It is preferably in the range of 0 to 10% by weight, especially 50 to 20% by weight.

The aqueous intermediate coating composition contains, in addition to the base resin and the (blocked) polyisocyanate compound, a curing catalyst, an extender pigment, a coloring pigment, and a surface conditioner for accelerating a crosslinking reaction by these two components. Can be contained.

As the curing catalyst, the metal compounds described as the curing catalyst in the electrodeposition coating composition can be used in order to promote the crosslinking reaction, and tin octoate, dibutyltin dilaurate, manganese, cobalt, A curing catalyst such as lead, bismuth stannate, lead stannate, or zirconium octoate can be blended. The amount is usually
It is suitable that the total amount of the solid content of the base resin and the (blocked) polyisocyanate compound is in the range of 0.1 to 10 parts by weight per 100 parts by weight. In the aqueous intermediate coating composition, the composition of the resin can be adjusted in order to improve the hardening speed of the coating film and the finish, and the composition of the base resin and the (blocked) polyisocyanate compound can be appropriately selected. Can be easily achieved.

Specifically, the polyester resin as the base resin is obtained, for example, by reacting a lactone and / or a lactam with a polyester resin obtained by reacting a divalent or higher polyhydric alcohol with a divalent or higher polycarboxylic acid. A polyester resin having a hydroxyl group introduced into a terminal of a side chain; a hydroxyl group-containing resin selected from a polyester resin, a polyether resin, a polycarbonate resin and a polyurethane; Polyester resins having a hydroxyl group and a carboxyl group obtained by half-esterifying an acid anhydride with a hydroxyl group of a product obtained by reacting a divalent or higher polycarboxylic acid are suitable. Further, as the block polyisocyanate compound (B-2), a multimer of an aliphatic polyisocyanate, an adduct of the multimer,
Adducts of aliphatic polyisocyanates are suitable.

The aqueous intermediate coating composition is obtained by uniformly mixing and dispersing the base resin and the (blocked) polyisocyanate compound in water, and adjusting the solid content concentration at the time of coating to 20 to 70% by weight. It is preferable to keep it.

The method of the present invention is to coat the electrodeposition coating composition as described above, wash it with water at 30 to 70 ° C. without curing, and then apply the aqueous intermediate coating composition. Then, the two coating films are simultaneously crosslinked, cured and dried by heating.

The aqueous intermediate coating composition is applied by electrostatic coating, airless spraying, air spraying, etc., and its film thickness is about 5 to 80 μm, particularly about 15 to 45 μm, based on the cured coating film. Are suitable. The heating temperature for crosslinking and curing both coating films of the electrodeposition coating composition and the aqueous intermediate coating composition is not lower than the dissociation temperature of the (blocked) polyisocyanate compound contained in the coating film. Usually, both coating films can be cross-linked, cured and dried by heating at 130 to 180 ° C. for 10 to 40 minutes.

According to the present invention, a top coat composition such as a solid color paint, a metallic paint and a clear paint is applied to a coating surface which is coated with a cationic electrodeposition paint composition and an aqueous intermediate paint composition and crosslinked and dried. In a known manner, a one-coat one-bake system (1C1B), a two-coat one-bake system (2C1B), and a two-coat two-bake system (2C2)
B) It can be applied by a three-coat one-bake method (3C1B) or the like.

Step (4), which is a step of simultaneously heating and curing these coating films, can be performed using an electric hot air dryer, a gas hot air dryer, or the like. The drying temperature is a temperature for curing both the electrodeposition coating film and the aqueous intermediate coating film, which is 110 ° C. to 20 ° C.
0 ° C., preferably 140 to 180 ° C., and the drying time is 10 minutes to 180 minutes, preferably 20 minutes to 40 minutes.

[0052]

According to the method for forming a multilayer coating film of the present invention, compared to installing, operating, and maintaining facilities such as a pre-heating process, space saving, facility saving, energy saving, process saving, finish, adhesion, A coating film having good chipping resistance can be obtained. The reason for this is that after the electrodeposition coating, the final washing with pure water of 30 to 70 ° C. is performed, so that the non-uniformly formed electrodeposition coating film is heated and heat flows and accumulates in the gas holes. Water and bubbles are eliminated and the coating surface becomes hydrophobic. From this, it is inferred that the aqueous intermediate coating becomes easy, and the finish, the adhesion, and the chipping resistance are good.

[0053]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited by this. Note that “parts” and “%” indicate “parts by weight” and “% by weight”.

Production example of cationic electrodeposition coating composition Epicoat 1002 (manufactured by Yuka Shell Epoxy Co., Ltd.)
1,260 parts of bisphenol A epoxy resin (trade name) are dissolved in 450 parts of butyl cellosolve, 132 parts of p-nonylphenol and 10 parts of N-methylethanolamine 10 are dissolved.
Five parts were added, the mixture was heated to 140 ° C., and reacted at the same temperature to obtain an amine-added epoxy resin (A) having a solid content of 77% and an amine value of 52. This amine-added epoxy resin (A)
30 parts of hexamethylene diisocyanate oxime-blocked product and 1.3 parts of polypropylene glycol (number average molecular weight 4000) were added to 130 parts, and then acetic acid 2.1 parts was added.
The resulting mixture is made water-soluble by adding an aqueous solution, and deionized water is gradually added to disperse the emulsion to obtain an emulsion (A) having a solid content of 32%. on the other hand,
4.7 parts of 75% amine type epoxy pigment dispersion resin
Neutralized with 0.16 parts of aqueous formic acid solution and then deionized water 2
2.2 parts were added, and JR-600E (Note 1) 16
Parts, 7 parts of purified clay, 0.3 parts of carbon black, 2.0 parts of bismuth hydroxide and 3 parts of dioctyltin oxide, and the mixture was dispersed in a ball mill for 40 hours to obtain a pigment paper having a solid content of 50%. Create a strike. Then, the solid content of 32%
After mixing 318.5 parts of the emulsion (A) and 70 parts of a pigment paste having a solid content of 50%, the mixture was diluted with deionized water to obtain a cationic electrodeposition coating composition having a solid content of 20%.

Production example of cationic electrodeposition coating composition Epicoat 828EL (manufactured by Yuka Shell Epoxy Co., Ltd.)
260 g of ε-caprolactone and 0.03 g of tetrabutoxytitanium were added to 1400 parts of a trade name (bisphenol A type epoxy resin), the temperature was raised to 170 ° C., and the reaction was monitored over time while maintaining this temperature to monitor the reaction. When the reaction rate reached 98% or more, the temperature was lowered to 120 ° C. Next, 160 g of diethanolamine and 65 g of methyl isobutyl diketimine of diethylenetriamine were added, and reacted at 120 ° C. for 4 hours.
0 g was added to obtain an amine-added epoxy resin (B) having a solid content of 77% and an amine value of 52.

The above amine-added epoxy resin (B) 13
After adding 30 parts of an alcohol-blocked product of diphenylmethane-4-4'-diisocyanate (MDI) and 1.0 part of polypropylene glycol (number-average molecular weight 4000) to 0 parts, 2.1 parts of acetic acid was added thereto to dissolve in water. The emulsion is dispersed by gradually adding deionized water to obtain an emulsion (B) having a solid content of 32%.

On the other hand, 4.7 parts of a 75% amine-type epoxy pigment dispersion resin was neutralized with 0.16 parts of a 88% aqueous formic acid solution, 22.2 parts of deionized water was added, and JR-600 was further added.
E15 parts, Refined clay 7 parts, Carbon black 0.3
, 2.0 parts of bismuth hydroxide and 3 parts of dioctyltin oxide, and dispersed in a ball mill for 40 hours to prepare a pigment paste having a solid content of 50%. Then, 318.5 parts of the above-mentioned 32% solid content emulsion and 50% of this solid content
Was mixed with 70 parts of a pigment paste and diluted with deionized water to obtain a cationic electrodeposition coating composition having a solid content of 20%. (Note 1) JR-600E (manufactured by Teica Corporation, trade name,
Titanium white) Production example of aqueous intermediate coating composition 348 parts of neopentyl glycol, 150 parts of trimethylolpropane, 128 parts of adipic acid and 435 parts of phthalic anhydride were placed in a reaction vessel and reacted at 220 ° C. for 5 hours. Thereafter, 42 parts of trimellitic anhydride are added, and
Allowed to react for hours. Further, 88 parts of ε-caprolactone and 1 part of dodecylbenzenesulfonic acid were added to the reaction product, and reacted at 150 ° C. for 3 hours to obtain a number average molecular weight of about 50.
00, acid value 25mgKOH / g, hydroxyl value 110mgK
An OH / g polyester resin (1) was obtained. 1000 parts of the above-mentioned polyester resin (1) (the same hereinafter as solid content), 40 parts of dimethylaminoethanol (Note 2), 410 parts of an aliphatic hexafunctional block polyisocyanate compound (Note 3), 1400 parts of JR-806 (Note 4) and 20 parts of Carbon Black M-100 (Note 5) were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition.

Production Example of Aqueous Intermediate Coating Composition: 272 parts of neopentyl glycol, 136 parts of trimethylolpropane, 232 parts of adipic acid, 29 phthalic anhydride
6 parts and FLEXOREZ UD-320-100
(Note 6) 240 parts were placed in a reaction vessel and reacted at 220 ° C. for 5 hours. Then, 28 parts of trimellitic anhydride was added, and
The reaction was performed at 0 ° C. for 1 hour. Number average molecular weight about 4000, acid value 25 mg KOH / g, hydroxyl value 110 mg KOH / g
To obtain a polyester resin (2).

The above polyester resin (2) 1000
Part, dimethylaminoethanol 40 parts, aliphatic trifunctional block polyisocyanate compound 410 parts, JR-
8061400 parts and carbon black M-100
20 parts were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition. (Note 2) Dimethylaminoethanol: Nippon Emulsifier Co., Ltd., trade name, amino alcohol (Note 3) Aliphatic trifunctional block polyisocyanate compound: Hexamethylene diisocyanate 3 Compound obtained by blocking the monomer with methyl ethyl ketoxime. (* 4) JR-806: trade name, trade name, titanium white pigment (* 5) Carbon black M-100: trade name, trade name, manufactured by Mitsubishi Chemical Corporation -Bon Black (Note 6) FLEXOREZ UD-320-100: King Industry, trade name, polyurethane geo-
, A number average molecular weight of about 1000 to 1500 Examples and Comparative Examples Example 1 A bath temperature of 28 ° C. was set using the cationic electrodeposition coating composition obtained in Production Example 1 of the cationic electrodeposition coating composition, and Palbond was used. # 3020 (manufactured by Nippon Parker Rising, product name,
Cold rolled steel sheet (70 ×
(150 × 0.8 mm), and a coating test was performed in the following steps. Step (1): Electrodeposition was performed using the cationic electrodeposition coating composition to obtain an electrodeposition coating film having a thickness of 25 μm. Step (2): The cationic electrodeposition coating composition, which was excessively attached by the electrodeposition coating, was washed with water and then washed with pure water at 45 ° C. for 10 seconds. Step (3): Using the aqueous intermediate coating composition, a film thickness of 35 μm was obtained by spray coating. Step (4): The coating films obtained in the above steps (1) to (3) were baked at 170 ° C. for 20 minutes using an electric hot air drier to obtain an electrodeposition coating film and an intermediate coating film.

Example 2 and Comparative Examples 1 and 2 A coating test and a performance test were performed in the steps shown in Table 1. The results are also shown.

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[Table 1] (Note 7) Rinsing conditions: Rinsing was performed for 5 seconds at each temperature by rinsing with a spray nozzle. (Note 8) Finishing property: The surface roughness of the coated plate obtained through the steps shown in Table 1 and applied to the aqueous intermediate coating was determined by Surf Test 301.
(Manufactured by MITSUTOYO, trade name, surface roughness meter) to measure the Ra value. (Note 9) Specular gloss at 60 °: Spray coating of Neoamylac 6000 white (Kansai Paint Co., trade name, aminoalkyd topcoat) on the coated plate obtained through the process of Table 1 up to the aqueous intermediate coating. Paint 35μm 1
Bake at 40 ° C. for 20 minutes. JIS K-5
400 7.6 (1990), the degree of gloss of the coating film, the reflectivity when the incident angle and the light receiving angle are each 60 degrees are measured, and the gloss of the reference surface of the specular gloss is measured. Expressed as a percentage when the degree is set to 100. (Note 10) Chipping resistance: Sprayed with the same top coat Neo Neolac 6000 White (manufactured by Kansai Paint Co., trade name, amino alkyd top coat) as described above, on the coated plate obtained up to the aqueous intermediate coat obtained in the step of Table 2. 3 by painting
It was painted 5 μm and baked at 140 ° C. for 20 minutes. The coated plate was tested using a Gravelo stepping stone tester under the following conditions. Test conditions 1. Test equipment: QGR gravelometer (Q panel company product) Sprayed stone: No. 7 crushed stone 3. Amount of stone sprayed: 50 g 4. Air pressure to be blown: 3.92 mPa (4 kgf / cm ² ) Temperature during test: -20 ° C 6. Spraying angle on painted surface: 90 degrees Evaluation content ○: only scratches on top-coated surface △: scratch on top-coated surface and intermediate coating or electrodeposition coating or coating between materials X indicates that the material is almost completely scratched. (Note 11) Water-resistant secondary adhesiveness: In the same manner as described above, a topcoat paint is applied to the coated plate that has been applied to the aqueous intermediate coat obtained in the process of Table 1 in the same manner as above. Neo Amylac 6000 white (manufactured by Kansai Paint Co., Ltd., trade name, amino alkyd top coating) by spray coating 3
It was painted 5 μm and baked at 140 ° C. for 20 minutes. The coated plate is immersed in warm water of 40 ° C. for 240 hours and air-dried at room temperature for about 2 hours. After that, a 2 mm square cut is cut into squares, and cellotape (registered trademark) is peeled off to evaluate the remaining coating film.
The evaluation was performed based on the number of remaining pieces.

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 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yasuyuki Hirata 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa F-term in Kansai Paint Co., Ltd. 4D075 AE03 BB26Z BB65Y BB89X BB93Y CA04 CA13 CA48 CB04 DA23 DB02 DB05 DC12 DC13 EA06 EA07 EA13 EB14 EB19 EB22 EB32 EB33 EB35 EB37 EB38 EB39 EB45

Claims (1)

[Claims] 1. The following step (1): a step of applying a cationic electrodeposition coating composition to a metal substrate having a bag structure, such as an automobile body, to form an electrodeposition coating, and step (2). Next, the object having the electrodeposition coating film obtained above is washed with water to remove an excessively attached cationic electrodeposition coating composition, and the obtained electrodeposition coating film is purified water at 30 to 70 ° C. A final washing with water to remove water accumulated in the voids and bubbles contained in the coating film; Step (3); (Blocking) a step of applying an aqueous intermediate coating composition containing a polyisocyanate compound as a crosslinking agent to form an intermediate coating film, step (4); and simultaneously heating and curing these coating films. A method for forming a multilayer coating film, comprising: