JPS6242771A - Painting method for steel products - Google Patents

Abstract

PURPOSE:To obtain a coated film having excellent chipping resistance, etc., by coating an electrodeposition paint compounded with a pigment at a high concn. on steel products and applying an aq. barrier coat to form the coated film having a glass transition temp. within a specific range thereon then applying an intermediate coat and finish coat thereon. CONSTITUTION:The electrodeposition paint compounded with the pigment at a high concn. is coated on the steel products, then the aq. barrier coat having 0--75 deg.C static glass transition temp. of the formed coated film is applied on the coated surface. The intermediate coat and finish coat are thereafter applied thereon. As a result, the composite coated film which has the excellent chipping resistance and physical performance and is improved in the corrosion resistance at the end faces, sharp angle parts, etc., of the steel products is formed without deteriorating the finish appearance, weatherability and chemical resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a coating method for steel materials, which forms a coating film with excellent chipping resistance, anticorrosion properties on acute corners and end faces, and physical performance on steel materials, such as steel plate parts of automobile bodies. Regarding.

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 type of straight road, rock salt particles and pebbles thrown up by the wheels collide with the paint surface on the outside of the car.
The impact often causes the impact peeling phenomenon in which the paint film partially peels off from the car body (steel plate), so-called ``chipping.'' This phenomenon exposes the metal surface of the impact area on the outside of the car body, and it is quickly removed. Rust develops on the surface and corrosion progresses. Paint peeling due to chipping usually occurs on the bottom of the car body and around the suspension, but it also occurs on the hood and roof, and localized corrosion becomes noticeable after about 6 months to 1 year. It is known that

In order to prevent this threading and the progress of corrosion of steel materials caused by it, various studies have been conducted regarding chemical conversion treatments on the surface of the external metal base of the vehicle body, as well as electrocoating paints, intermediate paints, 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, various studies have been conducted on the resin and/or pigment contained in electrodeposition paints and topcoats, but so far no one has been found that has a sufficient adhesion improvement effect to withstand chipping. A trench.

Furthermore, an inorganic foil-like pigment such as sericite or talc powder is contained in the intermediate coating, thereby achieving mitigation and/or dispersion of the impact force caused by shear in the intermediate coating layer due to the inorganic foil-like pigment, or It has also been proposed that the damage to the electrocoated paint film be prevented by using a scratch-free electrocoated paint film to ensure that the rust prevention function is maintained, but the impact force applied to the outer surface of the car body is not constant. In some cases, the impact force is quite large, and with these methods, 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 stopped at the intermediate coating layer, There is a disadvantage that all the coatings including the electrodeposited coating are affected by the impact, and the entire coating is peeled off from the surface of the metal substrate, and as a result, the affected area quickly rusts and corrosion progresses.

Furthermore, steel sheet products, such as automobile bodies, often have sharp corners and end surfaces (hereinafter referred to as "end surfaces, etc.") of the steel sheet (for example, Facia, Fenter, door knobs, panel 7-doors, etc.). /#Flannel roof, panel trunk lid, sides, lower end, back surface of the body, etc.) This part has a sharp shape unlike other flat parts. Therefore, the applied paint melts and flows during heating and curing at end surfaces, etc., and the coating film becomes thinner than on flat areas.
In particular, it was unavoidable that the coating film at acute corners would be extremely thin. As a result, it has been found that the corrosion resistance of the end faces, including the sharp corners, is significantly inferior to that of the flat parts, and rust tends to occur easily from the end faces, etc., and improvements in this respect are strongly desired.

Therefore, the present inventors solved the above-mentioned defects in the composite coating system consisting of electrodeposition coating, intermediate coating, and top coating, without deteriorating the finished appearance, weather resistance, chemical resistance, etc.
We have conducted extensive research into a method for forming composite coatings that have excellent chipping resistance and physical performance, as well as improved corrosion protection for steel edges. As a result, an electrodeposition paint containing a high concentration of pigment is applied, and a water-based barrier coat is applied to the electrodeposition coating surface to form a coating film having a glass transition temperature within a specific range prior to the intermediate coating. By,
It was possible to achieve the above objectives and to form a coating film with significantly improved chipping resistance, physical performance, and corrosion resistance of end surfaces, etc.

However, according to the present invention, an electrodeposition paint containing a high concentration of pigment is applied to the preparation, and then a coating film having a static glass transition temperature of 0 to -75°C is formed on the coated surface. A method for painting steel materials is provided, which comprises applying a barrier coat and then applying an intermediate coat and a top coat.

Although the term "barrier coat" is not commonly used,
In the present invention, a water-based paint having the above-mentioned physical property 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."

The characteristics of the present invention are that in the process of sequentially applying electrodeposition paint, intermediate coat paint, and top coat paint to steel materials, the electrodeposition paint contains a high concentration of pigment, and the static glass transition temperature is within a specific range. A water-based barrier coat that can form a coating film with 1! This is where the surface to be painted is pre-painted.

The pigment content in conventional electrodeposition paints is 100% resin solids.
Parts by weight, practically up to 35 parts by weight at most.
If more than this amount is added, the smoothness of the coating film and the sharpness of the overcoat will deteriorate, so adding more than the above amount is rarely practiced. On the other hand, the present inventors investigated the possibility of forming a thick electrodeposited coating on the end surfaces of steel materials to improve corrosion resistance, and found that when applied with an electrodeposition paint containing a high concentration of pigment, It has been found that a thick coating film is also formed on the end surfaces, etc., and there is a tendency for the corrosion resistance of the end surfaces to be improved, not just on the flat portions.

However, if you apply an electrodeposition paint containing a high concentration of pigment,
It was observed that the smoothness and sharpness of the finished coating film decreased.

Therefore, the present inventors continued to conduct research in order to further improve the corrosion resistance of the end surfaces, etc., as well as improve the smoothness and sharpness of the finished coating film. They succeeded in eliminating all of these defects by applying a barrier coat with specific physical properties to the surface of the electrodeposited coating. When the barrier coat that forms a coating film having such physical properties according to the present invention is applied to the surface of the electrodeposited coating film containing a large amount of pigment that is poor in smoothness, finish clarity, etc., the via coat is applied to the edge portions, etc. Moreover, it also impregnates even the minute irregularities on the surface of the electrodeposited film, reducing the suction of the intermediate paint, improving the smoothness of the resulting paint film, the sharpness of the topcoat, and the corrosion protection of edges, etc. It is presumed that this will improve the performance of

Then, a water-based barrier coating film with a static glass transition temperature adjusted to 0 to -75°C (more preferably, the tensile strength elongation rate of the coating film at -20°C as described below) is used. (adjusted to 200 to 1000% at a speed of 20 coats/min) is more flexible than the intermediate coating film for the purpose of improving chipping resistance, and the barrier coating film has such physical properties. Even if a strong impact force is applied to the surface of the intermediate coat-top coat system formed by the collision of rocks salt, pebbles, etc., most or all of the impact energy will be absorbed within the barrier coat film. It has been found that the damage does not spread to the underlying electrodeposited coating, and that both the top coat and intermediate coat are hardly physically damaged.

Tip 9: The barrier coating film layer exhibits a buffering effect against external impact forces, and the chipping resistance is significantly improved;
It was possible to prevent rusting and corrosion of steel materials due to chipping, and also eliminate deterioration of the top coat due to collisions with rock salt, pebbles, etc.

If the chipping resistance of the paint film is improved in this way, problems such as corrosion and rusting of steel will naturally be resolved, and in addition, the corrosion resistance of the paint film itself formed by the method of the present invention will also be improved through the barrier coating. Significant improvement compared to those without.

Furthermore, the coating film formed according to the present invention has excellent properties such as finished appearance, weather resistance, and chemical resistance.

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

Steel material: There are no restrictions on the type of steel material on which a coating film can be formed by the method of the present invention, as long as it is a conductive material and has a metal surface that can be coated by electrodeposition. .

Examples include materials such as iron, copper, aluminum, tin, zinc, etc., alloys containing these metals, and plating or vapor deposition products of these metals and alloys, and specifically, products made using these materials. passenger cars, trucks,
This includes vehicle bodies such as safari cars and motorcycles, parts, electrical products, and building materials. It is preferable that the steel material is previously subjected to a chemical conversion treatment with a phosphate or chromate prior to being coated with an electrodeposition paint.

Electrodeposition paints: Electrodeposition paints for coating the steel materials mentioned above are cationic and anionic paints that are known in themselves, except that they contain a higher concentration of pigment than the commonly used electrodeposition paints. Any type of electrodeposition paint can be used.

First, cationic electrodeposition paints include cathodically deposited thermosetting electrodeposition paints that are based on resins with basic amine groups and are neutralized with acid to make them water-soluble (water-dispersed). , this is painted using the steel material (object to be coated) as a cathode.

Examples of resins with basic amine groups include: bisphenol-type epoxy resins, acrylic resins containing epoxy groups (or glycidyl groups), cricidyl ethers of alkylene glycols, epoxidized polybutadiene, and epoxidized products of novolak phenol resins. Addition of amine to the epoxy group (oxirane ring) of the epoxy group-containing resin; ■
Unsaturated compounds with basic amino groups (e.g. N, N-
Polymerization using dimethylaminoethyl methacrylate, N,N-dinybruaminoethyl acrylate, N-vinylpyrazole, etc.) as a monomer ■Glycol containing a tertiary amino group (e.g., N-methyljetanolamine)
The base number obtained by the reaction of a glycol component with a polyisocyanate compound as one component of the glycol; ■Introduction of amide 7 groups into the resin by the reaction of an acid anhydride and a diamine to form an iminoamine; etc. 2
Resins in the range of 0 to about 200 are suitable.

Examples of amines that can be used in the reaction (2) above include aliphatic, alicyclic, or aromatic-aliphatic primary amines, secondary amines, and tertiary amine salts. Furthermore, in place of the amine, at least one selected from secondary sulfide salts, 5th class phosphine salts, etc. can be added to the epoxy resin described in (1) above and used as a cationic electrodeposition paint.

Examples of neutralizing agents for neutralizing the resin having basic amine groups and making it water-soluble (water-dispersed) 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 amount of the neutralizing agent added to the above resin is suitably within the range of about 0.1 to about 0.4 times the neutralization equivalent based on the base number of the resin (generally in the range of about 20 to about 200). It is.

In addition, as a crosslinking agent added to make a cationic electrodeposited coating film heat-curable, a blocked polyisocyanate compound is generally used.
When the formed coating film is heated (usually at about 140°C or higher), the blocking agent dissociates and the isocyanate groups are regenerated, and the isocyanate groups are regenerated and combined with various hydrogen-containing functional groups such as hydroxyl groups that may exist in the above-mentioned cationic resins. It undergoes a crosslinking reaction and hardens.

On the other hand, anionic electrodeposition paints are mainly composed of carbo electrodeposition paints and are applied using the above-mentioned fAi<object to be coated) as an anode.

Examples of resins with carboxyl groups include: ■ Maleated oil resin obtained by adding maleic anhydride to drying oil (linseed oil, dehydrated castor oil, tung oil, etc.); ■ Polybutadiene (
Maleated polybutadiene obtained by adding maleic anhydride to 1,2-type, 1,4-type, etc.); ■Resin obtained by adding maleic anhydride to unsaturated fatty acid ester of epoxy resin; ■High molecular weight Polyhydric alcohol (molecular weight approx. 1
000 or higher, and includes S-component esters of epoxy resins and styrene/ax & IJ alcohol copolymers), polybasic acids (trimellitic anhydride, maleated fatty acids, maleated oils, etc.) are added to them. ■ Carboxyl group-containing polyester resin (including those modified with fatty acids); ■ Carboxyl group-containing acrylic resin; ■ Reaction product between a polymerizable unsaturated monomer containing a glycidyl group or a hydroxyl group and an unsaturated fatty acid. Resins obtained by adding maleic anhydride etc. to a polymer or copolymer formed by using a polymer; and the like, and the carboxyl group content is generally about 60 to about 200 based on the acid value.
Those within the range are suitable.

Examples of neutralizing agents that can be used to neutralize the carboxyl groups in these carboxyl group-containing resins and make the resins water-soluble (water-dispersed) include monoethanolamine, jetanolamine, dimethyl alkanolamines such as amines ethanol; diethylamines;
Alkylamines such as triethylamine; inorganic alkalis such as potassium hydroxide and sodium hydroxide can be used. The amount of these neutralizing agents to be used is suitably within the range of about 0.1 to about 1.0 times t (preferably 0.4 to a8 times equivalent) of the theoretical neutralization equivalent to the acid value of the resin. .

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

One feature of the present invention is that the temperature of the pigment in the electrodeposition paint is set to a higher concentration than the usual concentration (up to 55 parts by weight per 100 parts by weight of resin solid content). Specifically, the pigment content of the electrodeposition paint used in the present invention is 40 to 150 parts by weight, preferably 55 to 100 parts by weight, and more preferably 60 to 85 parts by weight per 100 parts by weight of resin solid content. can be within the range of

If the content of the pigment is small, as described above, sufficient improvement in the corrosion resistance of the end surfaces of the steel material cannot be expected.

Pigments that can be added to the above electrodeposition paint include coloring pigments, extender pigments, antirust pigments, etc. that are known per se, and are not particularly limited. Examples include zinc white, antimony white, basic lead sulfate, and basic lead carbonate. , titanium white, lithopone, lead silicate, zircon oxide, carbon black, graphite, black iron oxide, aniline black, suboxide steel, cadmium red, chromium oxide (
- Million, Red Garla, Pigment Red, Pigmento (Iolette, Pigment Orange, Basic Lead Chromate, Yellow Lead, Ochre, Cadmium Yellow, Strontium Chromate, Titanium Yellow, Resurge, Pigment Yellow, Pigment Green, Zinc Edge, Chrome Green, Chromium oxide, phthalocyanine green, ultramarine, dark blue, phthalocyanine blue, pigment blue, cobalt purple, pigment violet, zinc powder, zinc oxide, red lead, lead cyanamide, calcium leadate, zinc yellow, silicon carbide, aluminum powder, asbestin , alumina, clay, keisoshi,
Slaked lime, stone base, Merck, barium carbonate, precipitated calcium carbonate, calcium carbonate, precipitated barium sulfate 1. Examples include halide, bentonite, white carbon, and glass beads. These can be used alone or in combination of two or more.

Furthermore, these electrodeposition paints can be blended with hydrophilic solvents, water, additives, etc. as necessary, and diluted with deionized water etc. so that the solid content concentration is about 5 to about 40% by weight. The pH is adjusted within the range of 5.5 to aO for the cationic type and 7 to 9 for the anionic type. The electrodeposition paint using the electrodeposition paint prepared in this way is usually used at a bath temperature of 15 to 6
Under the conditions of 5 DEG C. and a load voltage of 100 to 400 V, the object to be coated can be used as a cathode in cationic electrodeposition, and as an IS4 pole in anionic electrodeposition. The thickness of the electrodeposition coating is not particularly limited, but is generally preferably within the range of 10 to 40 microns based on the cured coating. Further, the baking hardening temperature of the coating film is generally suitable within the range of 100 to 200°C.

In principle, anionic electrodeposition coatings are cured by heating, but if an air-drying resin modified with an unsaturated fatty acid is used, they can also be dried at room temperature.

Water-based barrier coat: The water-based barrier coat is a coating composition to be applied to the electrodeposited surface, and in the present invention, the static glass transition temperature of the formed coating is 0 to -75°C. Aqueous compositions having water as the main solvent or dispersion medium are used.

The composition is preferably a thermoplastic resin which has an aqueous vehicle and water as main components, has excellent properties, and has a static glass transition temperature within the above range, and specifically includes the following.

■Modified polyolefin resin: Example EVA, progylene-ethylene copolymer (mole 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
6 parts of 0M simaleic acid or maleic anhydride α1
Examples include graft polymers obtained by graft polymerization of ~50 parts by weight, preferably α3 to 2,01 parts by weight. The number average molecular weight of these copolymers, chlorinated polyolefins and graft polymers generally ranges from about 5000 to about! lo, o
o[lo is preferably within the range.

When 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. Further, the number average molecular weight of the copolymer is about 10,000 to about 1.00.
It is preferably within the range of 0.000.

(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 volume, preferably 10 to 4%
A 0% by weight copolymer is prepared by adding functional monomers such as acrylic acid and methacrylic acid to acrylonitrile and butadiene as necessary, and adding 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 about 10.00
A range of 0 to about 1.000.000 is suitable.

■Polybutene: Mainly inbutylene, mixed with normal butylene as necessary, polybutene obtained by low-temperature polymerization is heated to 50-70℃ in the presence of an emulsifier, water is added, and stirred uniformly and thoroughly. obtained by The number average molecular weight of the resin is preferably within the range of about 1000 to about 5oooooo.

■Acrylic resin] The main component is acrylic acid ester and (or) methacrylic acid ester, and if necessary, polymerization of functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, etc. It can be obtained by emulsion polymerizing a vinyl monomer component obtained by mixing a sexually unsaturated monomer to form an aqueous dispersion, or by performing solution polymerization and converting it into an aqueous solution or aqueous dispersion. Examples of the acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate, 1so-butyl acrylate, 6-pentyl acrylate (V-), hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, 2-octyl acrylate, Particularly suitable are nonyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-ethylbutyl acrylate, and examples of methacrylic acid esters include pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, tethyl methacrylate, and lauryl methacrylate. , stearyl methacrylate and the like are particularly preferred. 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 as monomers for forming the acrylic resin. The acrylic resin has a number average molecular weight of about 500.
Preferably, it is in the range of 0 to 1,000,000.

■In addition to these, natural rubber latex, methyl methacrylate-butadiene copolymer emulsion: <, y
Telichloroprene emulsions, polyvinylidene chloride emulsions, and the like can also be used as aqueous vehicles.

The coating film formed by the water-based barrier coat has a static glass transition temperature (Ty) of 0 to -75°C, preferably -30°C.
It is important that the Tg is within the range of ~-60°C, particularly preferably -30 ~ -60°C, particularly preferably -40 ~ -55°C, and if the Tg is higher than 0°C, the chipping resistance of the final composite coating will decrease. However, the corrosion resistance, corrosion resistance, physical performance, etc. were not improved;
If the temperature is lower than 75°C, the water resistance, adhesion, etc. of the final composite coating 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 a barrier coating by themselves, but if the static glass transition temperature is outside the above range, the glass transition temperature may be within the acceptable 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, stone mW resin (coumarone resin), ester gum, epoxy-modified polybutadiene, low molecular weight aliphatic epoxy resin, and low molecular weight aliphatic bisphenol. Type II I xy resin, polyoxy 7 tetramethylene glycol, vinyl acetate modified, f+
) Emulsified dispersions of ethylene and the like can be mentioned, and the blending amount of these is 91% per 100 parts by weight of the above aqueous vehicle (solid content).
It is preferably within the range of 50 parts by weight (as solid content). In addition, to improve the finish of water-based barrier coats,
For aqueous barrier coatings, organic solvents with good affinity or solubility with the aqueous vehicle, such as benzene,
Toluene, xylene-blown aromatic hydrocarbons, hexane,
Aliphatic hydrocarbons such as heptane, octane, and decane; chlorinated hydrocarbons such as nitrichloroethylene, dichloroethylene, dichloroethane, dichloroethane, and dichlorobenzene; ketone solvents such as methyl ethyl keto/, and diacet alcohol; ethanol, prononol,
It is also possible to add alcohol-based solvents such as butamele; cellosolve-based solvents such as methyl cellosolve, butyl cellosolve, and selonlube acetate.

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

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

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 inhibiting or preventing corrosion of metals. It is clearly distinguished from extender pigments, and includes, for example, lead pigments, chromate pigments, metal powder pigments, etc. Among these, the anticorrosive pigments that can be blended into the barrier coat by the method of the present invention are not particularly limited.

However, pigments with a composition that elutes components with an anticorrosive function when in contact with water are suitable, especially anticorrosive pigments whose water extract has an electrical conductivity of 1 mm/α or higher, especially 600 μ/1 or higher. It is preferable to use

In addition, the measurement of the "electrical conductivity" of the aqueous extract of the anticorrosive pigment is as follows:
Mix 80 parts by weight of deionized water with an electrical conductivity of 1 μg/cm or less and 20 parts by weight of anticorrosion pigment, and leave 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 water extract has the above-mentioned conductivity include zinc chromate! 1570μυ/cIn), strontium chromate (976μ′rJ/α), barium chromate (735μo/crIL), calcium chromate (8000aυ/crn), basic lead chromate (111μH/cWL), basic lead sulfate (118ti
u/cx), calcium phosphate (332 μh/cII
L), zinc molybdate (363 μU/cm),
Calcium molybdate (256 μv/CTrL), aluminum phosphomolybdate (182 μv/cm
), barium metaborate (1540 μU/α), and ammonium metavanadate (7450 μU/crn) (the ones in parentheses can be used in combination with the electrical conductivity of the aqueous extract or higher. Among these, particularly preferred are Anticorrosion pigments selected from zinc chromate, strontium chromate, barium chromate, and calcium chromate may also be used.The amount of these anticorrosion pigments is generally 1 to 150 parts by weight per 100 parts by weight of the aqueous vehicle (solid content).
Parts by weight, preferably within the range of 2 to 50 parts by weight. In order to fully demonstrate the anticorrosive function of the anticorrosive pigments blended into the water-based barrier coat, the water absorption rate of the electrodeposited coating is adjusted within the range of 13 to 20% by weight, particularly 0.5 to 5% by weight. It is preferable to keep it.

Here, the "water absorption rate" of an electrodeposition coating is determined by applying the electrodeposition coating to a cured film thickness of 20μ (cold-blooded area 5×5α), baking it under conditions according to its components, and then isolated 5
The weight of the coating film immediately after being immersed in warm water at 0℃ for 48 hours and after drying it at 105℃ for 1 hour was measured, and these results were calculated using the following formula. be.

By adjusting the water absorption rate of the electrodeposited coating in this way,
The water-extracted components of the anti-corrosion pigment, which are extracted by water from the aqueous barrier coating film containing the anti-corrosion pigment that has been overcoated on the surface of the paint film, easily permeate into the electrocoated film.

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.

In the present invention, regarding the formed coating film of the barrier coat,
It is essential that the static glass transition temperature is within the above range, but furthermore, the tensile strength elongation rate of the coating film itself at a tensile rate of 20 degrees/min in a V atmosphere of -20°C, If the content is adjusted within the range of 200 to 1000%, 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 calorimeter (Model Daini Seikosha GDsc-10), and the "tensile breaking strength elongation rate" ” was carried out using a universal tensile tester with a constant temperature bath (Shimadzu Rakusakusho Autograph = S, -D type), and the length of the sample was 20 mm.
m, the tensile speed is a value measured at 20 m5+/min. The samples used for these measurements were coated on a tin plate to a thickness of 25 μm with the barrier coat added to the coating film, baked at 120°C for 30 minutes, and then isolated using the mercury amalgam method. be.

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, no-ke coating, dip painting, electrostatic painting, etc. can be used, and the thickness of the applied coating is preferably 1 to 20 μm, particularly 5 to 10 μm, based on the formed coating film. .

When applying intermediate coating paint to the barrier coat coating surface,
Although it is preferable to bake the barrier coat in advance, it is also possible to apply the intermediate coating paint wet-on-wet without baking. Baking temperature is generally 8
A range of 0 to 200°C is suitable.

411■L: As the intermediate coating paint applied to the above-mentioned barrier coated surface, known intermediate coating paints with excellent adhesion, smoothness, sharpness, overpainting 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 preferably uses an unsaturated oil (or unsaturated fatty acid) as the modified oil, and the amine resin is an alkyl (preferably one having 1 to 5 carbon atoms) etherified melamine resin or urea resin. Benzoguanamine resin is suitable.

The blending ratio of these two resins is based on the solid weight: alkyd resin and/or oil-free polyester resin 6,
5-85%, especially 70-80%, amino resin 35-15
%, especially preferably 30 to 20%. moreover,
At least a portion of the above amino resin can be replaced with a polyisocyanate compound or a blocked polyisocyanate compound.

The form of the intermediate coating is most preferably an organic solution type, but it may also be a non-aqueous dispersion type, an inolide type, an aqueous solution type, an aqueous dispersion type, etc. using the above vehicle component. In the present invention, the hardness (pencil hardness) of the intermediate coating film is generally preferably in the range of 3B to 2H. Furthermore, extender pigments, coloring pigments, 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 to 10% based on the cured coating.
It is preferable to set it in the range of 50μ, and the curing temperature of the coating film varies depending on the vehicle component.
Preference is given to heating at a temperature in the range of 170°C, especially 120-150°C.

Top coat: The top coat applied to the intermediate coated surface imparts cosmetic properties to the object to be coated. Specifically, the finish appearance (sharpness, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, and curing properties. Dyes known per se which form excellent coatings such as, for example, amino-acrylic resins, amino-
Examples include paints whose vehicle main components include alkyd resins and amino-polyester resins. The form of these paints is not particularly limited, and any form such as an organic solution type, non-aqueous dispersion type, aqueous solution (aqueous dispersion) type, powder type, or high solid type can be used.

Drying or curing of the coating film is carried out by drying at room temperature, heating drying, irradiation with active energy rays, etc.

In the present invention, it is desirable that the paint film formed by these top coat paints 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 in which a metallic pigment and/or a colored pigment is blended into a paint whose main component is the vehicle described above, or a clear paint that does not contain any or almost any of these pigments. It may be of.

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 1 coat 1 beta method).

■ A method in which metallic paint or solid color paint is applied, heat cured, and then clear paint is applied and heat cured again (metallic or solid color finish using 2-coat, 2-bake method).

■ A method in which metallic paint or solid color paint is applied, followed by clear paint, and then both coatings are cured at the same time by heating (metallic or solid color finishing using a 2-coat, 1-bake method).

These top coatings are preferably applied by spray coating, electrostatic coating, or the like. In addition, the coating film thickness is based on the dry coating film, in the range of 25 to 40μ for the above (■), in the range of 10 to 30μ for metallic paints and solid color dyes, and the range of 25 to 50μ for clear paints in the above (■ and ■). are preferable. Heating conditions can be arbitrarily adopted depending on the vehicle components, but generally 80 to 170°C, especially 1
It is preferable to heat at 20 to 150°C for 10 to 40 minutes.

The "pencil hardness" of the above intermediate coat and top coat is determined by coating a test plate on a glass plate and curing it (cured film thickness: 30 μm).
Hold it in C, sharpen the tip of the thin end flat, and sharpen the corner of the pencil (
Hold the Mitsubishi drafting pencil "UNI" at a 45 degree angle and press it firmly against the painted surface, making sure not to break the tip, about 1 cm.
a (3 seconds/cIL), 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 coating, and top coating coating is superior to that of the coating film formed by omitting the barrier coating coating. The appearance (e.g., smoothness, gloss, sharpness, etc.), water resistance, weather resistance, etc. are at least the same, but the chipping resistance, corrosion resistance (particularly the corrosion resistance of the end face), and physical properties are significantly improved. It has the characteristic that

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

(1) Steel material: Steel plate chemically treated with Bonderitetona 3030 (manufactured by Japan/e-Car Rising Co., Ltd., zinc phosphate metal surface treatment agent) (size 300 x 90 x 0.8 cod) Bent 180 degrees around the center of the

(2+ t77i paint: (A) Cationic electrodeposition paint: Boryamide-modified epoxy resin/blocked inocyanate compound is used as a vehicle component, neutralized with acetic acid, and pigment (titanium) is added per 100 parts by weight (solid content) of the vehicle component. White: carbon black: clay = 30:1.5:3O (weight ratio)) 63 parts by weight, 2 parts by weight of organic lead, 3 parts by weight of organic tin, the non-volatile content is 20% by weight, A cationic electrodeposition paint with a pH of 6.5.

The single coating film of this electrodeposition paint had poor smoothness.

(B) Cationic electrodeposition paint 2 A paint in which the amount of pigment blended in (4) above was changed to 80 parts by weight.

(C) Cationic electric paint (for comparative example) 2 above (,
A paint in which the pigment content in 4) was changed to 20 parts by weight.

A single coating film of this electrodeposition paint had excellent smoothness.

(D) Anionic electrodeposition paint: Maleated polybutadiene/hexakismethoxymethylmelamine as the main 4J vehicle component, neutralized with monoethanolamine, and the above (A) per 100 parts by weight (solid content) of the vehicle component.
The non-volatile content is 12 by blending 65 parts by weight of pigment.
Anionic electrodeposition paint with weight% and pH of &l.

(E) Anionic electrodeposition paint 2 A paint in which the amount of pigment blended in the above (D) was changed to 78 parts by weight.

(3) Barrier coat (A): Propylene/ethylene copolymer (weight ratio: 7
0/30, number average molecular weight: approx. 200000) 100
Neutralized and aqueous dispersion of resin prepared by graft polymerization with 10 parts by weight of maleic acid (static glass transition temperature: 4 parts by weight)
Tensile strength elongation at 0°C and -20°C = 400%
).

(B) 2. A neutralized aqueous dispersion of a composition comprising 3 parts by weight of sizink chromate per 100 parts by weight of the graft resin of (4) above.

(C): An aqueous dispersion obtained by emulsion polymerization of a component consisting of 30% by weight of methi-2F and 70% by weight of butadiene according to a conventional method (static glass transition temperature: 48°C, -2% by weight)
Tensile breaking strength elongation rate at 0°C = 450 inches).

(D): Acrylonitrile 30% by weight, butadiene 67
An aqueous dispersion is obtained by emulsion polymerizing a composition consisting of three parts by weight and three parts by weight of acrylic acid according to a conventional method, and then adding strontium chromate (anticorrosion pigment) in parts by weight per part of the copolymer (1001i). Static glass transition temperature knee so'c.

Tensile strength elongation at -20°C = 500%).

(E>: emulsified aqueous dispersion of a copolymer consisting of isobutylene and normal butylene (static glass transition temperature: 55
℃, tensile strength elongation at -20℃ = 600 inches)
.

(F) 60% by weight of dinonyl acrylate, 20% by weight of 2-ethylhexyl acrylate, 1% by weight of methyl acrylate
An aqueous dispersion (static glass) prepared by blending 10 parts by weight of barium chromate (anticorrosion pigment) into an emulsion polymer composition consisting of 5 parts by weight of 5 parts by weight of hydroxyethyl acrylate and 5 parts by weight of hydroxyethyl acrylate. Transition temperature knee 48
℃, tensile strength elongation at -20℃: 370
%).

(G) An aqueous dispersion comprising the emulsion polymer of (F) 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-27-Lar (manufactured by Kansai Paint Co., Ltd., aminopolyester resin-based intermediate paint).

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

(B): Magikron Silver ([Nishi Paint Co., Ltd. Exhibition,
Aminoacrylic resin topcoat, 2-coat, 1-bake silver metallic paint, pencil hardness H (20°C)).

(C): Magikron Clear (manufactured by Kansai Paint Co., Ltd.,
Aminoacrylic resin topcoat, 2-coat, 1-bake clear paint, lead-nagi hardness H (zo'C)).

Using the above samples, electrodeposited paint, water-based barrier coat, intermediate coat and top coat 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 250V%, electricity applied for 180 seconds.

Anion electrodeposition coating conditions: Bath solid content concentration 12% by weight, bath temperature 30°C, pH 7.8, load voltage approximately 200F, TSO
Power on for seconds.

In any of the above cases, after electrodeposition coating, wash with water, air dry,
It was baked at 0° C. for 30 minutes to harden it.

The barrier coat is applied using an air spray machine, and the film thickness should be the same as the dry coating! Baked at t, t2oC for 30 minutes.

Both the intermediate coat and the top coat were spray-painted using an electrostatic coating machine, and the film thickness was the same as that of the cured film.

For topcoat painting, "ICIB" is a coating system in which topcoat paint A is applied and then baked at 140℃ for 30 minutes.
CIB 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 harden both coats.

(2) Performance test results 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: ■ Tile device: Q-G-R Gravelometer (product of Q Panel Company) ■ Stone to be sprayed: Crushed stone with a diameter of approximately 15 to 2Q m/m ■ Capacity of stone to be sprayed: Approximately 500-■ Spraying with air pressure of approximately 4 kg/cd■ Temperature during test: Approximately 20℃ The test specimen was attached to a test specimen holder, and approximately 4 kg/d of crushed stone was tested with air pressure of approximately 500- After the pieces were fired, the condition of the coated surface and resistance to salt water spray were evaluated.

The condition of the painted surface was visually observed and evaluated using the following criteria. For salt spray resistance, test pieces were subjected to a salt spray test for 960 hours according to JIS Z2371. Then, adhesive cellophane tape was attached to the painted surface and it was rapidly peeled off. Rust, corrosion, paint peeling, etc. from the impact area after applying the coating ■ Paint surface condition ◎ (Good): There are very few scratches due to the impact on a part of the top coat, and it is not electrodeposited. No peeling of the paint film was observed.

Δ (fairly poor) Many scratches due to impact were observed on the second and intermediate coats, and peeling of the electrodeposited coating was also observed here and there.

× (Poor) Most of the second top coat and intermediate coat peeled off, and the T-adhesive paint film on the impact area including the impact area and its surrounding area peeled off.

■ Salt spray resistance ◎: Rust, corrosion, paint film scratches, etc. are not observed.

O: Rust, corrosion, and paint film scratches are slightly observed.

Δ: Slightly more rust, corrosion, and paint film scratches are observed.

×: Rust, spoilage, and paint film scratches were clearly observed.

(*2) Impact resistance: Performed in an atmosphere at 0°C according to JIS K5400-1979 6.1 & 3B method. Weight 500I
Drop a weight from a height of 501 to check for damage to the paint film.

(■: No abnormality at all.

X: Significant cracking and peeling occurred.

(*3) Adhesiveness: In accordance with JIS K5400-1979 6.15, gongs are made on the coating film, adhesive seronone tape is applied to the surface, and the surface is evaluated after rapid peeling.

◎: No peeling of the coating film was observed.

O: The paint film peeled off slightly.

(*4) Water resistance: Evaluate the coated surface after immersing it in water at 40°C for 10 days. No abnormalities were detected in either case.

(*5) Smoothness: Judging by visual inspection.

◎: Good smoothness.

○: Some unevenness is observed.

Δ: Many irregularities are observed.

(*6) Edge corrosion resistance: A salt spray test was conducted for 480 hours in the same manner as in (*1) above, and the condition of the coated surface at the edge of the steel plate was visually determined.

◎No double rust or corrosion is observed.

○: Very slight rust is observed.

X: Significant rust, corrosion, etc. occur.

(*7) Thread rust resistance: Cut the coating film in two diagonal lines with a cutter to reach the substrate, place it in a salt spray tester according to JIS Z 2371 for 48 hours, and then test the coated surface with deionized water. After cleaning the room, place it in a constant temperature toilet box (temperature 40±2℃, humidity 85℃).
The occurrence of yarn rust was investigated after the yarn was placed in a temperature of ±2% for 720 hours.

Record the average length and density of thread rust. 3 or less thread rust within 10 m length of the cut part. F 5 to 6 threads inside or outside. M 10 or more threads. D Evaluate as a total guideline.

In addition, the numbers in the upper row indicate the length of thread rust.

(*8) Scapping resistance: After soaking in hot water at 40°C for 120 hours and then drying at 20°C for 4 hours,
A coated board that had been chipped with 0F using a 4mm/piece (straight cutting also used) was subjected to [soaking in 5% saline (30'C) for 2 hours → leaving at -20℃ for 1 hour → exposing outdoors for 45 hours] for a week. This was repeated three times, and each cycle was counted as one cycle, and the state of the painted surface (particularly rust, blisters, etc.) after 30 cycles was examined.

◎: No rust or blisters observed.

O: Slight rust and blistering.

Δ: Rust, many 7 cracks occur.

×: Significant rust and blistering occurred.

Claims (1)

[Claims] Electrodeposition paint containing a high concentration of pigment is applied to the steel material, and then the static glass transition temperature of the film formed on the painted surface is 0 to -75.
A steel coating method characterized by applying an intermediate coat and a top coat after applying a water-based barrier coat at ℃.