JPS61242668A - Coating method for steel products - Google Patents

Abstract

PURPOSE:To improve pitting resistance, corrosion resistance, etc., of coated film by coating aqueous barrier coat having a static glass transfer point at a specified temp. on the electrodeposition coating surface applied to a steel product, then coating intermediate coat and top coat thereon. CONSTITUTION:After treating previously a steel product with chemical conversion treatment using phosphate or chromate, it is further subjected to electrodeposition coating using a cationic or anionic electrodeposition paint. Then, an aq. compsn. consisting primarily of a water-soluble vehicle and water capable of forming coated film having 0--75 deg.C static glass transition point contg., if necessary, a tackifier and an org. solvent, is prepd. An aq. barrier coat is formed on the electrodeposition coated steel product by coating with the aq. compsn. Then, intermediate coat and top coat are applied thereto. Suitable intermediate coat is alkyd resin having <30% oil length, etc., and suitable top coat is aminoacryl resin, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method for forming a coating film with excellent chipping resistance, corrosion resistance, and physical performance on steel materials, particularly automobile bodies.

In the automobile industry, emphasis is being placed on the durability of paint films, especially the problem of reduced corrosion resistance of paint films due to impact peeling and progress of corrosion of steel materials. In particular, in cold regions of Europe and the United States, gravel mixed with a large amount of relatively coarsely crushed rock salt is often laid to prevent road surfaces from freezing in the winter.
When a car runs on this road, rock salt particles and pebbles thrown up by the wheels collide with the painted surface of the car.
The impact often causes the paint film to peel off locally from the car body, a so-called "chipping" phenomenon. As a result of this phenomenon, the metal surface of the impact area on the outer surface of the vehicle body is exposed, and rusting occurs quickly and corrosion progresses.

Usually, peeling off of the paint film due to chipping occurs mostly on the bottom of the car body and around the legs, but it is known that it also occurs on the hood and roof, and localized corrosion becomes quite noticeable after about six months to a year.

In order to prevent this chipping and the progression of corrosion caused by it, various studies have been made on chemical conversion treatments on the surface of the external metal base of the car body, as well as electrodeposition paints, intermediate coats, and top coats.

For example, in chemical conversion treatments, the use of iron phosphate coatings and zinc phosphate coatings with different crystal forms has been considered, but it is difficult to sufficiently improve the adhesion of coatings on impact areas with such chemical conversion treatments. be. In addition, electrodeposition paint and O
- Various studies have been made regarding the resin and/or pigment contained in the top coating, but so far no one has been found that has a sufficient adhesion improvement effect to withstand chipping.

It has also been proposed to include sericite or talcum powder, which are inorganic foil-like pigments, in the intermediate coating composition, and this reduces the impact force caused by shearing in the intermediate coating film layer due to the inorganic foil-like pigment. and/or to achieve dispersion or to cause delamination locally only within the intermediate coat layer or at the interface between the electrocoated paint film and the intermediate coat film, thus preventing damage to the fixing paint film. The aim was to ensure that this scratch-free electrodeposited paint film maintains its anti-rust function, but the impact force applied to the outside surface of the car body is not constant and can be large at times, so these In this method, if an impact force that exceeds the mitigation and dispersion ability due to shear in the intermediate coating layer is applied, the impact force cannot be fully absorbed at the intermediate coating layer, and the affected area may include the electrodeposited coating. All coatings have the disadvantage that the coating as a whole peels off from the surface of the metal substrate, and as a result, the affected area quickly rusts and corrosion progresses.

Therefore, in order to improve the above-mentioned problems, the present inventors aimed to achieve a finish that is at least equivalent in appearance to that obtained with a steel plate coating system consisting of a normal electrodeposition paint, an intermediate coat paint, and a top coat paint, and has chipping resistance. The present invention has been completed as a result of extensive research aimed at providing a coating method for forming a coating film with excellent physical properties and corrosion resistance.

That is, according to the present invention, the steel material is coated with electrodeposition paint,
Then, the static glass transition of the coating film formed on the coating surface 'IIA a
Provided is a method for coating steel materials, characterized in that after applying a water-poured barrier coat having a temperature of 0 to -75°C, an intermediate coat and a top coat are sequentially applied.

Although the term "barrier coat" is not commonly used,
In the present invention, a water-based paint having the above characteristic values and capable of forming a coating film that achieves the object of the present invention is referred to as a "water-based barrier coat."

A feature of the present invention is that in the process of sequentially applying electrodeposition paint, intermediate coat paint, and top coat paint to steel materials, after applying the electrodeposition paint,
Prior to applying the intermediate paint, a water-based barrier coat having specific physical properties is applied in advance to the electrodeposited surface. As a result, chipping resistance, corrosion resistance,
It has been found that it is possible to form a coating film with significantly superior physical properties.

That is, a water-based barrier coating film whose static glass transition temperature was adjusted to 0 to -75°C (furthermore, as described later, the tensile strength elongation rate of the coating film at -20°C was adjusted to a tensile rate of 20 m5) (adjusted to 200 to 1000% per minute) is more flexible than the intermediate coating film for the purpose of improving chipping resistance, and is coated with a barrier coating film that has such physical properties. Even if a strong impact force is applied to the surface of the intermediate coating film and top coating film system formed by collisions with rock salt, pebbles, etc., most or all of the impact energy will be absorbed within the barrier coating film and the It has been found that the damage does not extend to the underlying electrodeposited coating, and that both the top coat and intermediate coat are hardly physically damaged. Toru 1 The above barrier coat coating layer exhibits a buffering effect against external impact forces, significantly improving chipping resistance, and preventing rusting of steel materials due to chipping.
It was possible to prevent the occurrence of corrosion, and also eliminate the deterioration of the top coat due to collisions with rock salt, pebbles, etc.

The coating method of the present invention will be explained in more detail below.

Steel material: The steel material to be coated by the method of the present invention is not limited in any way as long as it is a conductive material to be coated and has a metal surface that can be coated by electrodeposition. Examples include materials such as iron, copper, aluminum, tin, zinc, alloys containing these metals, and plated or vapor-deposited products of these metals and alloys. Specifically, passenger cars made using these materials, This includes vehicle bodies and parts for trucks, safari cars, motorcycles, electrical products, and building materials. Before the steel material is coated with electrodeposition paint,
It is advisable to pre-treat it with phosphate or chromate.

Electrodeposition paint: The electrodeposition paint for coating the above-mentioned steel material can be either a known cation type or anion type.

First, cationic electrodeposition paints include cathodically deposited thermosetting electrodeposition paints that are based on resins with basic amine groups and are neutralized with acid and made water-soluble (water-dispersed). This is painted using the steel material (object to be coated) as a cathode. Resins with basic amine groups, such as bisphenol-type epoxy resins, acrylic resins containing epoxy groups (or glycidyl groups), glycidyl ethers of alkylene glycols,
Addition of amines to the epoxy groups of epoxy group-containing resins such as epoxidized polybutadiene and epoxidized products of novolac phenol resin; Polymerization using glycols containing tertiary amine groups (N-vinylpyrazole, N-diethylaminoethyl acrylate, etc.) as monomers;
-Methylgetanolamine) as one component of the glycol with a glycol component polyisocyanate compound: ■Introduction of an amino group into the resin by generating iminoamine by reaction with an acid anhydride and a diamine; etc. The amines that can be used in the reaction (2) above include basic amines such as aliphatic, alicyclic, or aromatic-alicyclic primary amines, secondary amines, tertiary amine salts, and quaternary amines. For example, secondary ammonium salts can be used, and secondary sulfide salts and tertiary phosphine salts can also be used.

Examples of neutralizing agents for neutralizing and water-solubilizing (water-dispersing) the resin having a basic amino group include organic acids such as acetic acid, hydroxyl acetic acid, propionic acid, butyric acid, lactic acid, and glycine; Inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid can be used. The appropriate amount of the neutralizing agent is within the range of neutralization equivalent of about 0.1 to 0.4 based on the base number (about 20 to 200) of the resin.

In addition, blocked polyisocyanate compounds are generally used as crosslinking agents for cationic electrodeposition paints.
When the coating film is heated (approximately 140° C. or higher), the blocking agent dissociates, the incyanate group is regenerated, and crosslinks with the hydroxyl group in the cationic resin as described above, resulting in curing. moreover,
Cationic electrodeposition paints contain pigments (coloring pigments, extender pigments,
Rust-preventing pigments, etc. The blending amount of the pigment can be less than 40 parts by weight per 100 parts by weight of the resin solid content), a hydrophilic solvent, water, additives, etc. are blended as necessary, and the solid content concentration is about 5 to 40% by weight. Dilute with deionized water or the like so that the pH is adjusted to within the range of 5.5 to 8.0. Cationic electrodeposition coating using the cationic electrodeposition paint prepared in this way is usually carried out at a bath temperature of 15 to 35°C and a load of 'cj
t, pressure 100-4. It can be carried out under OOV conditions with the object to be coated as a cathode.

The thickness of the electrodeposition coating film is not particularly limited, but is preferably in the range of 10 to 40 μm, even for a cured coating film. The baking hardening temperature of the coating film is generally suitable within the range of 100 to 200°C.

On the other hand, anionic electrodeposition paints are anodic electrodeposition paints that are mainly based on resins having carboxyl groups and are neutralized with basic compounds and made water-soluble (water-dispersed).
The above steel material (:4 coating) is used as an anode for painting.

Resins with carboxyl groups include: ■ Maleated oil resins obtained by adding maleic anhydride to drying oils (linseed oil, dehydrated castor oil, tung oil, etc.); ■ Polybutadiene (1, 2 type, 1.4 type);
■ Maleated polybutadiene with maleic anhydride added to the unsaturated fatty acid ester of epoxy resin; ■ High molecular weight polyhydric alcohol (with a molecular weight of about 1 ooo or more, partial ester of epoxy resin and Resins obtained by adding polybasic acids (trimellitic anhydride, maleated fatty acids, maleated oils, etc.) to polyester resins (including styrene/allylic alcohol copolymers, etc.); Acrylic resin containing a carboxyl group: ■A polymer or copolymer formed using a reaction product of a polymerizable unsaturated monomer containing a glycidyl group or a hydroxyl group and an unsaturated fatty acid containing maleic anhydride. Examples include resins to which acids have been added, and those having a carboxyl group content in the range of about 30 to 200 based on the acid value are generally suitable. Then, the carboxyl groups in these carboxyl group-containing resins are neutralized, and the above resins are dissolved in water (
Examples of neutralizing agents for dispersion include alkanolamines such as monoethanolamine, jetanolamine, and dimethylamineethanol; alkylamines such as diethylamine and triethylamine; and inorganic alkalis such as potassium hydroxide and sodium hydroxide. etc. can be used. The appropriate amount of these neutralizing agents to be used is within the range of approximately 0.1 to 1.0 times the theoretical neutralization equivalent (or 0.4 to 0.8 times equivalent) relative to the acid value of the resin. be.

Furthermore, as a crosslinking agent for the above resin, a low molecular weight melamine resin such as hexakismethoxymethylmelamine, butoxylated methylmelamine, or ethoxylated methylmelamine can be used as required.

Furthermore, anionic electrodeposition paints contain pigments (coloring pigments, extender pigments, anti-rust pigments, etc.).
0 parts by weight),
Add a hydrophilic solvent, water, additives, etc. as necessary, adjust the solid content concentration to about 5 to 40% by weight with deionized water, maintain the pH in the range of 7 to 9, and use it for anionic electrodeposition coating. be able to. Anion electrodeposition coating can be carried out according to a conventional method, for example, at a bath temperature of 15 to 35°C and a load voltage of 10
The coating can be carried out under the conditions of 0 to 350 square meters, using the object to be coated as an anode. The coating film thickness is not particularly limited, but it is usually preferably in the range of 10 to 40 μm based on the cured coating film.

In principle, anionic electrodeposition coatings are cured by heating to a temperature in the range of 100 to 200°C, preferably 140 to 200°C, but if an air-drying resin modified with unsaturated fatty acids is used, it can be dried at room temperature. You can also do it.

The aqueous barrier coat is a coating composition to be applied to the above-mentioned electrodeposition coating surface, and in the present invention, it is particularly preferable that water is used as the main solvent and the static glass transition temperature of the formed coating is 0 to -75°C. Alternatively, an aqueous composition as a dispersion medium is used.

The composition has an aqueous vehicle and water as main components, and can further contain a viscosity imparting agent, an organic solvent, a coloring pigment, an extender pigment, an anticorrosive pigment, etc., as necessary.

As the aqueous vehicle, thermoplastic resins which have excellent adhesion to the electrodeposited coating film described above and the intermediate coating film described below, and which have a static glass transfer temperature within the range of the static glass transition temperature described above, are suitable. These include:

■Modified polyolefin resin: For example, propylene-ethylene copolymer (in molar ratio, 4
0 to 80: 60 to 20 is preferred) and 1 to 50 parts by weight, preferably 10 to 20 parts by weight of chlorinated polyolefin (for example, polypropylene with a chlorination rate of about 1 to 60% by weight) (both of which are based on the copolymer). (per 100 parts by weight); or the above propylene-ethylene copolymer 10
0 parts by weight of simalic acid or maleic anhydride.
Examples include graft polymers in which 1 to 50 parts by weight, preferably 0.3 to 20 parts by weight, are graft-polymerized.

The number average molecular weight of these copolymers, chlorinated polyolefins and graft polymers generally ranges from about 5,000 to about 30.
Preferably, it is in the range of 0000.

In making the modified polyolefin resin water-based, the propylene-ethylene copolymer can be made water-based by anionic, cationic or nonionic emulsion polymerization, which is known per se. The chlorinated polyolefin can be water-solubilized or water-dispersed by mixing, and the chlorinated polyolefin can be water-dispersed, for example, in the presence of an emulsifier.

■Styrene-butadiene copolymer: Styrene content is approximately 1 to 80% by weight, preferably 10% by weight.
An aqueous dispersion of the copolymer is obtained by copolymerizing styrene and butadiene in the presence of a polymerization modifier, catalyst, soap, and water. The polymerization temperature is preferably 100°C or less. Also,
The copolymer has a number average molecular weight of about 10,000 to about i,
It is clever that it is in the range of o o o, o o o.

(2) Butadiene resin: This is an aqueous dispersion composition obtained by polymerizing in (1) above without using styrene.

■Acrylonitrile-butadiene copolymer: acrylonitrile content is 1 to 50% by weight, preferably 10 to 4% by weight
A copolymer containing 0% by weight of acrylonitrile and butadiene, with the addition of a functional hexamer such as acrylic acid or methacrylic acid as necessary, and a polymerization catalyst, a molecular weight regulator,
It is obtained by emulsion polymerization in water in the presence of a surfactant or the like. The polymerization temperature is preferably 100°C or less. The number average molecular weight of the copolymer is approximately io, oo
A range of o to about 1.000.000 is suitable.

■Polybutene: Polybutene is mainly made of isobutylene, mixed with normal butylene if necessary, and is obtained by low-temperature polymerization. Heat the polybutene to 50-70℃ in the presence of an emulsifier, add water, and stir uniformly and thoroughly. obtained by. The number average molecular weight of the resin is preferably in the range of about 1,000 to about 500,000.

■Acrylic resin: The main component is acrylic ester and/or methacrylic ester, and if necessary, functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, and/or other polymerizable monomers. It can be obtained by emulsion polymerizing a vinyl monomer component obtained by mixing unsaturated monomers to form an aqueous dispersion, or by polymerizing a niobium solution and then converting it into an aqueous solution or aqueous dispersion. Examples of the above acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 3-pentyl acrylate, hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, -Octyl acrylate, nonyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-ethyl butyl acrylate, etc. are particularly suitable, and as the methacrylic acid ester, for example, pentyl methacrylate-1., hexyl methacrylate, 2-
Particularly preferred are ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate-1, stearyl methacrylate, and the like. The static glass transition temperatures of the homopolymers derived from these acrylic esters and methacrylic esters illustrated here are all 0°C or lower, and one or more acrylic monomers selected from these monomers are used. Acid esters and methacrylic esters are suitable monomers for forming the acrylic resin. Preferably, the acrylic resin has a number average molecular weight in the range of about 5000 to 1.000.000.

(2) In addition to these, natural rubber latex, methyl methacrylate-butadiene copolymer emulsion, polychloroprene emulsion, and polyvinylidene chloride emulsion can also be used as the aqueous vehicle.

The coating film formed by the water-based barrier coat has a static glass transition temperature (Tg) of 0 to -75°C, preferably -30°C.
It is important that the Tg is in the range of -60℃, especially in the range of -40 to -55℃.If the Tg is higher than 0℃, the chipping resistance, corrosion resistance, physical performance, etc. of the final coating film will improve. On the other hand, if the temperature is lower than -75°C, the water resistance, adhesion, etc. of the final coating film will deteriorate, which is not preferable.

In the present invention, if these aqueous vehicles themselves have a static glass transition temperature within the above range, they can be used as barrier coats by themselves, but even if the aqueous vehicle deviates from or is within the above range. When it is desired to finely adjust the static glass transition temperature, a viscosity imparting agent can be added as necessary. The viscosity imparting agent includes resins having good compatibility with the aqueous vehicle, such as rosin, petroleum resin (coumarone resin), ester gum, epoxy-modified polybutadiene, low molecular weight aliphatic epoxy resin, and low molecular weight aliphatic bisphenol type. Examples include emulsified dispersions of epoxy resins, polyoxytetramethylene glycol, vinyl acetate-modified polyethylene, etc., and the blending amount of these is 91 to 100 parts by weight of the above-mentioned aqueous vehicle (solid content).
A range of 50 parts by weight (as solids) is preferred. Also,
In order to improve the paint finish properties of the aqueous barrier coat, the aqueous barrier coat is coated with organic solvents that have good affinity or solubility with the aqueous vehicle, such as aromatic hydrocarbons such as benzene, toluene, and xylene, hexane, Aliphatic hydrocarbons such as heptane, octane, and decane; Chlorinated hydrocarbons such as trichlorethylene, perchloroethylene, dichloroethylene, dichloroethane, and dichlorobenzene; Ketone thread solvents such as methyl ethyl ketone and diacetalcohol; ethanol and glopanol It is also possible to add cellosolve-based solvents such as methyl cellosolve, methyl cellosolve, and selonlupus acetate.

Furthermore, extender pigments, coloring pigments, anticorrosion pigments, etc. may be added to the barrier coat.

The blending amount of these pigments is 100% of the aqueous vehicle (solid content).
A range of 1 to 150 parts by weight is preferred.

In particular, it has been found that by incorporating an anti-corrosion pigment into the aqueous barrier coat, it is possible to significantly improve the anti-corrosion properties compared to when the anti-corrosion pigment is included in the electrodeposition coating.

Anticorrosive pigments that can be added to water-based barrier coatings are pigments that have the function of suppressing or preventing corrosion of metals, and are simply used as coloring pigments for imparting color and for adjusting the physical properties of paint films. Extending pigments are clearly distinguished and include, for example, lead-based pigments, chromate-based pigments, metal powder pigments, etc., and there are no particular restrictions on the anticorrosive pigments that can be incorporated into the barrier coat by the method of the present invention. Pigments with a composition in which components having an anticorrosion function are eluted when in contact with water are suitable, and in particular, pigments whose water extract has an electrical conductivity of 100 μv/cm or more, especially 3 Q 011
It is preferable to use an anticorrosion pigment having a ratio of y/Cr of 11 or more.

In addition, the measurement of the "electrical conductivity" of the aqueous extract of the anticorrosive pigment is as follows:
Mix 80 parts of deionized water with an electrical conductivity of 1 mm/cm or less and 20 parts by weight of an anticorrosive pigment, and leave it at 30°C for 5 days (during this time, stir the mixture at a rate of 10 minutes/day). After that, the supernatant liquid (aqueous extract) is taken out and its electrical conductivity is measured.

Examples of anticorrosion pigments whose aqueous extracts have the above-mentioned conductivity include zinc chromate (1570μ/c7Il), strontium chromate (973μ/σ), barium chromate (736μU/crrL), and calcium chromate (soooμ/c/σ). cfrL), basic lead chromate (1
11μV/Cm), basic lead sulfate (118μC/Cm)
m), calcium phosphate (332μcr/crrt
), zinc molybdate (333μcr/cm),
Calcium molybdate (256 μU/crrL), aluminum phosphomolybdate (182 μA/cTL),
Examples include barium metaborate (1540 μv/cfrL) and ammonium metavanadate (7450 μV/cr/L) (the electrical conductivity of the water extract is shown in parentheses), each of which can be used alone or in combination of two or more. It can be used as Among these, it is particularly preferable to use an anticorrosive pigment selected from zinc chromate, strontium chromate, barium chromate, and calcium chromate. The amount of these anticorrosive pigments is generally in the range of 1-150 parts by weight, preferably 2-50 parts by weight per 100 parts by weight of the aqueous vehicle (solid content).
In order to fully demonstrate the anticorrosive function of the anticorrosion pigments contained in the water-based barrier coat, the water absorption rate of the electrodeposited coating is 0.
, 3 to 20% by weight, particularly preferably 0.5 to 5% by weight.

Here, the "water absorption rate" of the electrodeposition coating is determined by applying the electrodeposition coating to a cured film thickness of 20μ (coated area 5 x 5CTL), baking it under conditions according to its components, and then applying the coating to the coating layer. Isolate it and soak it in hot water at 50°C for 48 hours, measure the weight of the coating film immediately after pulling it up, and the weight of the coating film after drying it at 105°C for 1 hour, and calculate these results by incorporating them into the following formula. This is the value.

By adjusting the water absorption rate of the electrodeposited coating in this way,
The water-extracted component of the anti-corrosion pigment, which is extracted from the water-based barrier coating film containing the anti-corrosion pigment that has been overcoated on the coating surface, easily penetrates into the electrodeposited coating film and becomes the anode (or cathode) on the steel surface. ) It is presumed that the suppressing effect becomes noticeable and protects the steel material.

The water absorption rate can be easily adjusted by adjusting the crosslinking density of the coating film, introduction of hydrophilic groups, amount of extender pigment, etc.

Therefore, according to this method of adjusting the water absorption rate, there is no particular need to incorporate an anticorrosive pigment into the electrodeposition paint, and therefore the storage stability of the paint, the smoothness of the coating film, etc. can be improved.

In the present invention, regarding the formed coating film of the barrier coat,
Although it is essential that the static glass transition temperature is within the above range, the tensile strength elongation rate at break of the coating film itself is adjusted at a tensile speed of 20 m in an atmosphere of -20°C.
If the rate is adjusted within the range of 200 to 1000 units per minute, particularly 300 to 700%, the chipping resistance, corrosion resistance, etc. of the final coating film can be further improved.

The "static glass transition temperature" of the formed coating film of the aqueous barrier coat used in the present invention is a value measured with a differential scanning thermal helmet meter (Model DSC-10 manufactured by Daini Seikokin Co., Ltd.), and the "tensile breaking strength" The elongation rate was measured using a universal tensile testing machine with a constant temperature bath (Takasu Seisakusho Autograph S-D model), and the length of the sample was 20M.
1 tensile speed is a value measured at 20 strokes/min. The samples used for these measurements were coated on a Purigi board to a thickness of 25 μm including the barrier coat and the coating film.
After baking at 0°C for 30 minutes, it was isolated by the mercury amalgam method.

In the present invention, the aqueous barrier coat can be applied either after the electrodeposited coating is cured by heating or in an uncured state. The coating method is not particularly limited,
For example, spray painting, brush painting, dipping painting, electrostatic painting, etc. can be used, and the thickness of the coating film is preferably 1 to 20 µm, particularly 5 to 10 µm, including the formed coating film.

Before applying the intermediate paint to the barrier coat film surface, it is preferable to bake the barrier coat beforehand, but it is also possible to apply the intermediate paint by wet-on-wet without baking. Generally, a baking temperature range of 80 to 200°C is suitable.

Intermediate paint: As the intermediate paint applied to the barrier coated surface, known intermediate paints with excellent adhesion, smoothness, sharpness, overbake resistance, weather resistance, etc. can be used. . Specifically, an organic solution-type thermosetting intermediate coating material whose vehicle main components are a short oil or ultra-short oil alkyd resin with an oil length of 30% or less or an oil-free polyester resin and an amine resin can be mentioned. These alkyd resins and polyester resins have a hydroxyl value of 60 to 140 and an acid value of 5 to 20, and those that use unsaturated oil (or unsaturated fatty acid) as the modified oil are clever, and amino resins have Alkyl (preferably one with 1 to 5 carbon atoms)
Etherified melamine resin, urea resin, benzoguanamine resin, etc. are suitable. The blending ratio of these two resins should be 65-85%, especially 70-80% of alkyd resin and oil-free polyester resin, and 35-15% of amine resin, especially 30-2096%, based on solid weight. is preferred. Furthermore, it is possible to replace at least a portion of the amine resin with a polyincyanate compound or a blocked polyincyanate compound.

The form of the intermediate coating is most preferably an organic solution type, but it may also be a non-aqueous dispersion type, a high solid type, an aqueous solution type, an aqueous dispersion type, etc. using the above vehicle component. In the present invention, the hardness of the intermediate coating film (pencil hardness)
is generally preferably in the range of 3B to 2H. Furthermore, extender pigments, colorants, other paint additives, and the like can be added to the intermediate paint as necessary.

In the present invention, the intermediate coating can be applied to the surface of the barrier coat by the same method as the barrier coat, and the coating thickness is 10% based on the cured coating.
The curing temperature of the linear film varies depending on the vehicle component, and when curing by heating, the curing temperature is preferably 80 μm.
Heating at temperatures in the range from ~170°C, especially from 120 to 150°C is advantageous.

Top coat: The top coat applied to the intermediate coated surface imparts cosmetic properties to the object to be coated. Specifically, the finished appearance (
(image clarity, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance,
Known paints that form coating films with excellent curability can be used, such as paints whose vehicle main component is amino-acrylic resin, amino-alkyd resin, amino-polyester resin, etc. . The form of these paints is not particularly limited, and any form such as an organic solution type, non-aqueous dispersion type, aqueous (dispersion) liquid type, powder type, or high solid type can be used. Drying or curing of the paint film
This is carried out by drying at room temperature, drying by heating, irradiation with active energy rays, etc. In the present invention, the coating film formed by these top coats preferably has a pencil hardness usually within the range of 2B to 3H.

The top coating used in the present invention may be either an enamel paint containing a metallic pigment and/or a colored pigment in a paint whose main component is the vehicle described above, or a clear paint containing no or almost no pigments. It may be something.

Examples of methods for forming a top coat film using these paints include the following methods: ■Metallic paints containing metallic pigments and, if necessary, coloring pigments, or metallic paints containing colored pigments. A method of applying solid color paint and curing it by heating (metallic or solid color finish using one-coat bake method).

■Paint with metallic paint or solid color paint,
After heat curing, apply clear paint and heat harden again (metallic or solid color finish using 2 coats, 2 coats, 1 coat).

■Paint with metallic paint or solid color paint,
Subsequently, after applying a clear paint, both coatings are cured at the same time by heating (metallic or solid color finish using a 2-coat, 1-bake method).

These top coat paints are preferably applied by spray painting, electrostatic painting, etc. In addition, the coating film thickness is based on the dry coating film, and in the above (■), the coating film thickness is in the range of 25 to 40μ, in the above (■) and (■), the metallic paint and solid color paint are in the range of 10 to 30μ, and the clear paint is in the range of 25 to 50μ. are preferable. Heating conditions can be arbitrarily selected depending on the vehicle components, but it is generally preferable to heat at 80 to 170°C, particularly 120 to 150°C, for 10 to 40 minutes.

The "competitive hardness" of the above intermediate coating and top coating is determined by applying a test plate coated on a glass plate and cured (cured coating thickness 30μ).
Hold it at 0 degrees Celsius and hold a lead roast (Mitsubishi drafting pencil ``UNI''') with a flat tip and a sharp edge at a 45 degree angle.
About 1 hour while pressing firmly against the painted surface so that the thin film does not break.
cyn (3 seconds/c7Il), and the value is evaluated based on the hardness of the hardest pencil that leaves no trace of scratches caused by the pencil.

According to the method of the present invention described above, the performance of the coating film formed on steel by electrodeposition coating, barrier coating coating, intermediate coating, and top coating is superior to that of the coating film formed by omitting the barrier coating. The appearance (for example, smoothness, gloss, sharpness, etc.), water resistance, weather resistance, etc. are at least the same, but chipping resistance, corrosion resistance, physical properties, etc. are significantly improved.

Next, the present invention will be further explained by Examples and Comparative Examples.

(1) Steel material: Steel plate (size 3
00 x 90 x O, 8ms).

(2) Electrodeposition paint: (A) Cationic electrodeposition paint: Elekronna 9200
(Manufactured by Kansai Paint Co., Ltd., epoxy polyamide cationic electrodeposition paint, gray color). The water absorption rate of the cured coating is 4.2
% by weight, without anticorrosion pigments.

(B) Add basic lead chromate (anticorrosive pigment) to the cationic electrodeposition paint of (A) above at 2 parts per 100 parts by weight of resin solid content.
Parts by weight were blended. The water absorption rate of the cured coating is 4.2% by weight.

(C) Anionic electrodeposition paint: Nireclone +7200 (manufactured by Kansai Paint Co., Ltd., polybutadiene thread anionic electrodeposition paint, containing 91 parts by weight of strontium chromate per 100 parts by weight of resin solid content).

The water absorption rate of the cured coating film is 3.6% by weight.

(3) Barrier coat (A): Propylene/ethylene copolymer (weight ratio = 70
/30, number average molecular weight: approximately 200,000) Neutralized aqueous dispersion of a resin grafted with 10 parts by weight of simalic acid per 100 parts by weight (static glass transition temperature: 41°C,
Tensile strength elongation at -20°C: 400%).

(B) 2. A neutralized aqueous dispersion of a composition containing 3 parts by weight of zinc chromate per 100 parts by weight of the graft resin of (A) above.

(C): Aqueous dispersion obtained by emulsion polymerization of a component consisting of 30% by weight of styrene and 70% by weight of Yoshibutadiene (static glass transition temperature: 48°C, -20°C).
Tensile strength elongation at break = 450 inches).

(D): A composition consisting of 30% by weight of acrylonitrile, 6% by weight of Butashev, and 3% by weight of acrylic acid was subjected to emulsion polymerization according to a conventional method, and then strontium chromate (anticorrosion pigment) was added per 100 parts by weight of the copolymer. An aqueous dispersion (static glass transition temperature: 50° C., tensile strength elongation at -20° C.: 500%).

(E): Emulsified aqueous dispersion of a copolymer consisting of inbutylene and n-butylene (static glass transition temperature: 55°C
, tensile strength elongation at -20°C = 600%).

(F): 60% by weight of nonyl acrylate, 20% by weight of 2-ethylhexyl acrylate, 1% by weight of methyl acrylate
An aqueous dispersion (static glass) in which barium chromate (anticorrosion pigment) is mixed with an emulsion polymer of a composition consisting of 5 parts by weight and 5 parts by weight of hydroxyethyl acrylate and 1 part by weight of SilOM per 100 parts by weight of pattern coalescence. Transition temperature knee 48
℃, tensile strength elongation at -20℃: 370%)
.

(G): An aqueous dispersion comprising the emulsion polymer of (P) above.

(H): 60% by weight of hexadecyl acrylate, 20% by weight of 2-ethylhexyl acrylate, 15% by weight of methyl acrylate, and 5% by weight of hydroxyethyl acrylate.
An aqueous dispersion (static glass transition temperature: +4°C) obtained by emulsion polymerization of a composition consisting of % by weight.

(4) Intermediate paint Near Mirac N-2 Sealer (manufactured by Kansai Paint Co., Ltd., amine polyester resin intermediate paint).

(5) Top coat paint: (A) Near Miracle White (manufactured by Kansai Paint Co., Ltd.,
Amino-alkyd resin top coat paint, white paint for Coat 1 Beta, pencil hardness H (20°C)).

(B): Magikron Silver (manufactured by Kansai Paint Co., Ltd.,
Aminoacrylic resin thread topcoat paint, 2 coats] Baking silver metallic paint, pencil hardness H (20°C)).

(C): Magikron Clear (manufactured by Kansai Paint Co., Ltd.,
Aminoacrylic resin top coat, 2-coat, 1-bake clear paint, pencil hardness H (20°C).

(2) Examples and Comparative Examples Using the above samples, electrodeposition paint, barrier coat, intermediate coat paint, and top coat paint were applied to steel materials according to the steps shown in Table 1 below.

In Table 1, cationic electrodeposition coating conditions: bath solid content concentration 19% by weight, bath temperature 28° C., pH 6.5, load voltage approximately 250 V, electricity applied for 1 so second.

Anionic electrodeposition coating conditions: Bath solid content concentration 12% by weight, bath temperature 30°C, pH 7.8, load voltage approximately 200μ, energization for 180 seconds.

In any of the above cases, wash with water after electrodeposition coating. The coating film thickness is 20 μm even for the cured coating film.

The barrier coat was applied using an air spray machine, and the film thickness was 6 μm, including the dry coating.

Both the intermediate coating and the top coating were spray coated using an electrostatic coating machine, and the film thickness of the intermediate coating was 25 μm based on the cured coating.

1cIBJ is a coating system that can be baked at 140℃ for 30 minutes after applying the topcoat.
, r2clBJ is a system in which top coats B and C are applied wet-on-wet and then baked at 140° C. for 30 minutes to cure both coatings.

A coating film performance test was conducted using the coated plates coated in the above Examples and Comparative Examples. The results are shown in Table 2 below.

〔Test method〕

(*1) Chipping resistance: ■Test equipment: Q-G-R Gravelometer (product of Q Panel Company) ■Stone to be sprayed: Crushed stone with a diameter of approximately 15-20m/m ■Capacity of stone to be sprayed: Approx. 5001 ■Air pressure is about 4kg/cm2 ■Temperature during test: approx. 20℃ Place the test piece on the test piece holder and apply approximately 4kg/crIL
In the spraying step 2, approximately 500 ml of crushed stone was sprayed onto the test piece using air pressure, and the coated surface condition and salt spray resistance were evaluated. The condition of the painted surface was visually observed and evaluated using the following criteria.
Salt water spray resistance was determined by subjecting the test piece to a salt water spray test for 960 hours in accordance with JIS Z 2371=42-, then applying adhesive cellophane tape to the coated surface and rapidly peeling it off to determine whether rust developed from the impacted area. Observe the presence or absence of corrosion, corrosion, and peeling of the paint film.

■ Painted surface condition ◎ (Good) Only a few scratches due to impact are observed on a part of the second top coat, and no peeling of the electrodeposition coating is observed.

△ (slightly poor) There are many scratches on the second and intermediate coats due to impact, and there are also some peelings of the electrodeposition coating.

× (Poor): Most of the top coat and intermediate coat peeled off, and the electrodeposited film on the impact area including the impact area and its surroundings peeled off.

■Salt water spray resistance ◎No secondary rust, corrosion, or peeling of the paint film.

○: Rust, corrosion, and paint peeling are slightly observed.

△: Slightly more rust, corrosion, and peeling of the paint film were observed.

×: Significant rust, corrosion, and paint peeling occurred.

(*2) Impact resistance: Performed in an atmosphere at 0°C according to JIS K5400-1979 6.13.3B method. A weight weighing 500 g is dropped from a height of 50 cm to examine damage to the paint film.

(*3) Adhesion: In accordance with JIS K5400-1979 6.15, grooves are made on the coating film, an adhesive cellophane tape is attached to the surface, and the coated surface is evaluated after being abruptly peeled off.

(*4) Water resistance: The coated surface after being immersed in water at 40°C for 10 days is evaluated.

Claims (1)

[Claims] Electrodeposition paint is applied to the steel material, and then a water-based barrier coat whose static glass transition temperature is 0 to -75°C is applied to the coated surface, and then an intermediate coat and a top coat are applied. Characteristic steel painting method.