JPS6261679A - Method for painting steel material - Google Patents

Abstract

PURPOSE:To enhance chipping property and interlayer adhesiveness, in a composite painting system consisting of electrodeposition painting and powder top coat painting, by applying aqueous barrier coat capable of forming a film having a specific range of static glass transition temp. after electrodeposition painting. CONSTITUTION:Aqueous barrier coat is a coating composition applied to the surface of an electrodeposition film and an aqueous composition containing water as a main solvent or a main despersing medium and forming a film with static glass transition temp. of 0--75 deg.C is used. For example, an aqueous vehicle of a modified polyolefin resin, a styrene/butadiene copolymer or a butadi ene resin and water are contained as main components and, if necessary, a viscosity imparting agent, an org. solvent and various pigments are appropriately added thereto. This aqueous composition is applied to the coated surface of a steel material after electrodeposition painting prior to the painting of thermo setting powder top coat paint to form a high performance composite film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a composite coating system that is obtained by a composite coating system consisting of an electrodeposition coating and a powder topcoat coating and has improved chipping resistance, corrosion resistance, interlayer adhesion, coating surface finish, etc. Concerning a method of forming a film.

Electrodeposition paints and powder paints used in composite coating systems consisting of electrodeposition paints and top coats contain almost no organic solvents and have excellent coating efficiency, making them effective in preventing pollution and conserving resources. Recently, coating systems using both of these paints are being adopted. However, the coating film formed by this coating system does not have sufficient properties such as chipping resistance, corrosion resistance, interlayer adhesion, and coating surface smoothness, and improvements in these properties are desired.

For example, when looking at chipping resistance, how is it used in the automotive industry? ! During the durability of a single film, attention is being paid to the problem of deterioration of the corrosion resistance of the paint film due to impact peeling and the progress of corrosion of steel materials.In particular, in cold regions of Europe and America, winter motorway road surfaces are In order to prevent freezing, gravel mixed with a large amount of relatively coarsely crushed rock salt is often laid down, and cars driving on this type of road are exposed to rock salt particles and pebbles thrown up by the wheels on the outside of the road. Impact peeling development, in which the paint film is partially peeled off entirely from the car body due to the collision with the paint film surface, often causes so-called 9 chipping.This phenomenon causes damage to the car body outer surface. The metal surface of the striking part is exposed and quickly rusts and corrosion progresses.9 Normally, peeling of the paint film due to chipping is most common on the bottom of the car body and around the suspension, but it can also occur on the hood and roof and will last for about 6 months to 1 year. It is known that localized corrosion becomes more noticeable over the years.

In order to prevent this chipping and the progress of corrosion caused by it, various studies have been conducted on chemical conversion treatments, electrodeposition paints, and powder topcoats on the surface of the metal base of the outer panel of the vehicle body. 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. It is. Also,
Various studies have been conducted on the resins and/or pigments used in electrodeposition paints and powder topcoats, but no paints have been found that have sufficient adhesion-improving effects to withstand chipping.

Therefore, the present inventors have solved the above-mentioned defects in composite coating films obtained by a composite coating system consisting of electrodeposition coating and powder coating, and have achieved chipping resistance without reducing weather resistance, chemical resistance, etc. We have conducted extensive research with the aim of providing a method for forming composite coatings with improved corrosion resistance, interlayer adhesion, coating surface smoothness, etc. As a result, after applying the electrodeposited paint and prior to applying the powder topcoat, a coating film with a static glass transition temperature in the range of 0 to -75°C was formed on the surface of the electrodeposited paint. The above objectives can be achieved by applying a water-based barrier coat that can be applied in advance, creating a coating film with significantly improved chipping resistance, corrosion resistance, glabellar adhesion, and painted surface smoothness. It was successfully formed.

That is, according to the present invention, the steel material is coated with electrodeposition paint,
A method for coating a steel plate, comprising applying a water-based barrier coat capable of forming a coating film having a static glass transition temperature of 0 to 75°C on the coated surface, and then applying a thermosetting powder top coat. is provided.

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 and powder topcoat to steel materials, after applying the electrodeposition paint and before applying the powder topcoat, A water-based barrier coat that forms the M film is applied in advance to the surface of the electrodeposited film. As a result, we were able to form a composite coating film with outstanding chipping resistance, corrosion resistance, physical performance, and coating surface smoothness.

That is, the composite coating film formed by the method of the present invention is
The intermediate barrier coat film is flexible and has unique viscoelastic properties, so even if a strong impact force is applied to the surface of the top coat film from rock salt, pebbles, etc., most of the impact energy will be absorbed. Most or all of it is absorbed into the barrier coat film and does not spread to the underlying electrodeposited film, and the top coat is also virtually free from physical damage such as cracking and peeling. . In other words, the above-mentioned barrier coating film layer exhibits a buffering effect against external impact forces, significantly improving chipping resistance, and preventing rusting and corrosion of the steel plate due to chipping.
Deterioration of the topcoat film caused by collisions with pebbles and other objects was also eliminated.

Regarding anticorrosion properties, as will be described later, when an anticorrosion pigment was included in the barrier coating film, the anticorrosion properties were significantly improved compared to the case where the anticorrosion pigments were blended into the electrodeposition paint.

Furthermore, the coating film formed according to the present invention has coating surface smoothness,
It also has excellent properties such as 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. Passenger cars, trucks,
The products include car bodies, parts, electrical products, building materials, etc. for motorcycles and other cars. 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 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 amino groups and are neutralized with acid and made water-soluble (water-dispersed). This is done by using the steel material (object to be coated) as a cathode. Examples of resins with basic amino groups include ■bisphenol-type epoxy resins, acrylic resins containing epoxy groups (or glycidyl groups), glycidyl ethers of alkylene glycols,
Addition of amines to epoxy groups (oxirane rings) of epoxy group-containing resins such as epoxidized polybutadiene and epoxidized products of novolak phenol resin; (pyrazole, N-diethylaminoethyl acrylate, etc.) as a monomer;
Reaction of a polyisocyanate compound with a glycol component containing (methyljetanolamine) as one component of the glycol; ■Introduction of amino groups into the resin by generating iminoamine by reaction with acid anhydride and diamine; etc. Obtained by K, Examples of amines that can be used in the reaction (2) above include aliphatic, alicyclic, or aromatic-alicyclic primary amines, secondary amines, and tertiary amine salts. Further, in place of the amine, a secondary sulfide salt, an f4 tertiary phosphine salt, or the like can be used to form an onium salt.

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 isocyanate groups are regenerated, and the resin undergoes a crosslinking reaction with the hydroxyl groups in the cationic resin as described above and is cured.

On the other hand, Anionya electrodeposition paint is an anodic deposition type electrodeposition paint mainly based on a resin having a carboxyl group, which is neutralized with a basic compound and made water-soluble (water-dispersed).
The above steel material (subject to be coated) is used as an anode for coating.

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);
■ Maleic acid 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 1000 or more, partial ester of epoxy resin) Resin obtained by adding polybasic rR (anhydrous trimellitic acid, maleated fatty acid, maleated oil, etc.) to a polyester resin containing 0 carboxyl groups (including fatty acid-modified ); ■ Carboxyl group-containing acrylic resin; ■ Polymer or copolymer formed using the reaction product of a polymerizable unsaturated monomer containing a glycidyl group or a hydroxyl group and an unsaturated fatty acid Km hydrated maleic acid and the like, and those having a carboxyl group content in the range of about 30 to 200 based on the acid value are generally suitable. As a neutralizing agent for neutralizing the carboxyl groups in these carboxyl group-containing resins and making the resin water soluble (dispersed), for example, alkanolamines such as monoethanolamine, jetanolamine, dimethylaminoethanol, etc. ; Alkylamines such as diethylamine and triethylamine; and inorganic alkalis such as potassium hydroxide and sodium hydroxide. The amount of these neutralizing agents used is approximately 0.1 to 1.0 times the theoretical neutralization trade name to the acid value of the resin! (preferably 0.4 to 0.8 times per 4i) is suitable.

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, these electrodeposition paints contain pigments (coloring pigments, extender pigments, anti-#f pigments, etc.).
01i), a hydrophilic solvent, water, additives, etc. are blended as necessary, and the solid content concentration is adjusted to about 5 to 40% by weight with deionized water, etc. do. Then, the pH can be maintained in the range of 5.5 for cationic type to 7 to 9 for &01 anionic type and used for electrodeposition coating. 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 100 to 400°C.
Under the conditions of V, the object to be coated is a cathode for cationic reeds and lli for 1 anionic type! It can be implemented as another. The coating film thickness is not particularly limited, but is usually 10% based on the cured coating film.
It is preferable to set it as the range of -40micro.

As a general rule, the electrodeposition coating film is heated at 100 to 200°C, preferably 1
It can be cured by heating in the range of 40 to 200°C,
When an air-drying unsaturated fatty acid-modified resin is used in the anionic electrodeposition coating, it can also be dried at room temperature.

Water-based barrier coat: The water-based barrier coat is a coating composition for coating on 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 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 that have excellent adhesion to the electrodeposited coating film and the top coating film described below and have a static glass transition temperature within the above range are preferred, and specific examples include the following: .

@Modified polyolefin resin: For example, chlorinated polyolefin (e.g., polypropylene with a chlorination rate of about 1 to 60 wt. ), preferably 10 to 20 parts by weight (both per 100 parts by weight of the copolymer); or maleic acid per 100 parts by weight of the above propylene-ethylene copolymer. Examples include graft polymers obtained by raft polymerization of 0.1 to 50 parts by weight, preferably 0.3 to 20 parts by weight, of maleic anhydride. It is generally preferred that the number average molecular weight of these copolymers, chlorinated polyolefins and graft a polymers range from about 5,000 to about 300,000.

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: A copolymer with a styrene content of about 1 to 80 F, preferably 10 to 40 F, in which styrene and butadiene are used as a polymerization modifier, catalyst, soap, and water. An aqueous dispersion of the copolymer can be obtained by copolymerizing in the presence of. 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
,000,000 is preferred.

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

■ Acrylonitrile-butadiene copolymer: The content of acrylonitrile is 1 to 50%, preferably 10%
A copolymer of ~40% by weight, which is made by adding functional monomers such as acrylic acid and methacrylic acid to acrylonitrile and butadiene as necessary, and then producing the mixture in water in the presence of a polymerization catalyst, a molecular weight regulator, a surfactant, etc. It is obtained by emulsion polymerization in . Polymerization temperature is 100℃
The following are preferred. The number average molecular weight of the copolymer is approximately io,
A range of ooo 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 about 1,000 to about 500,000. A range of OOO is preferred.

■ Acrylic resin Niacrylic acid ester and (or) methacrylic acid ester as the main component, and if necessary, functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, and (!) other polymers. 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, 3-pentyl acrylate, hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, 2-octyl acrylate, nonyl acrylate,
Lauryl acrylate, 2-ethylhexyl acrylate, 2-ethylbutyl acrylate, etc. are particularly suitable, and examples of methacrylic acid esters include pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, and stearyl methacrylate. etc. are particularly preferred. The static glass transition temperatures of the homopolymers derived from these acrylic esters and methacrylic esters exemplified here are all 0° C. or lower,
One or more acrylic esters and methacrylic esters selected from these monomers are suitable as monomers for forming the above-mentioned acrylic resin. The acrylic resin has a number average molecular weight of about 5000.
~1.000. Preferably, it is in the OOO range.

(2) In addition to these, natural rubber latex, methyl methacrylate-butadiene copolymer emulsion, polychloroprene emulsion, polyvinylidene chloride emulsion, etc. 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 θ to -75°C, preferably -3
It is important that the Tg is in the range of 0 to -60°C, particularly preferably -40 to -55°C; if Tg is higher than 0°C, the chipping resistance, corrosion resistance, physical performance, etc. of the final coating film will not be improved. 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 resin, polyoxytetramethylene glycol, vinyl acetate-modified polyethylene, etc., and the blending amount of these is υ1 to 5 per xooifi part of the above aqueous vehicle (solid content).
A range of 0.011 parts by weight (as solid content) is preferred.

In addition, in order to improve the paint finish properties of water-based barrier coats, organic solvents that have good affinity or solubility with the above-mentioned water-based vehicles, such as aromatic carbonized solvents such as benzene, toluene, and xylene, are used for water-based barrier coats. Aliphatic hydrocarbons such as hydrocarbons, hexane, heptane, octane, and decane; Chlorinated hydrocarbons such as nitrichloroethylene, perchlorethylene, dichloroethylene, dichloroethane, and dichlorobenzenato; ketones such as methyl ethyl ketone and diacet alcohol Solvent: Alcohol solvent such as ethanol, propatool, butanol; Methylceronlube,
It is also possible to add cellosolve solvents such as butyl cellosolve.

In particular, organic solvents such as diisopropylbenzene, tetralin, decalin, 0-dichlorobenzene, trichlorobenzene, benzyl alcohol, diisobutyl ketone, isophorone, cellosolve acetate, carpitol acetate, dimethyl phthalate, etc. with a boiling point of 150°C or higher are used. Moreover, organic solvents (hereinafter referred to as “
After applying a water-based barrier coat made by dissolving or dispersing a compatible solvent (sometimes abbreviated as "an affinity solvent"), and immediately applying a powder topcoat while the paint film is still wet without baking. When baked, the affinity solvent remaining in the barrier coating film evaporates and destroys the powder topcoat film, which promotes the heating and melting flow of the powder resin particles.
This is because the smoothness of the finished painted surface can be significantly improved. The amount of the organic solvent, including the affinity solvent, in the water-based barrier coat is not particularly limited, but it is preferably in the range of 1 to 5,011 percent of the total amount with water, and the vehicle component content in the mata barrier coat is generally VC1. ~
A range of 70 weights is suitable. Therefore, in the present invention, it is effective to directly apply the powder topcoat paint onto the wet barrier coat surface that is undried and contains an compatible solvent in order to finish the coated surface with excellent smoothness.

Furthermore, extender pigments, coloring pigments, anticorrosive 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, by incorporating anti-corrosion pigments into the aqueous barrier coat, electrodeposition is possible! l! It has been found that corrosion resistance can be significantly improved compared to when it is contained in one film.

Anticorrosion pigments that can be incorporated into water-based barrier coats are pigments that have the function of inhibiting or preventing corrosion of metals, and are also used as coloring pigments to add color to coatings and coating materials.
They are clearly distinguished from extender pigments, which are used to adjust the physical properties of paint, and include lead-based pigments, chromate-based pigments, metal powder pigments, etc. Among these, the method of the present invention can be applied to water-based barrier coatings. There are no particular restrictions on the anticorrosive pigments that can be blended, but pigments with a composition that elutes components with an anticorrosive function when they come into contact with water are suitable, and in particular pigments whose water extract has an electrical conductivity of 100 μy/cm or more, especially 300 μy/cm or more, are suitable. It is preferable to use an anticorrosion pigment having a value of /α or more.

In addition, the measurement of the "electrical conductivity" of the aqueous extract of the anticorrosive pigment is as follows:
After mixing 80 parts by weight of deionized water with an electrical conductivity of 1 μV/crn or less and 20 parts by weight of an anticorrosive pigment, and leaving the mixture at 30°C for 5 days (during which time, the mixture was stirred at a rate of 10 minutes/day), This is done by removing the supernatant liquid (aqueous extract) and measuring its electrical conductivity.

Examples of anticorrosive pigments whose aqueous extracts have the above-mentioned conductivity include zinc chrome (1570 μm Le/c!IL)
, strontium chromate (973 μV/cWL),
Barium chromate (736μy/cm), calcium chromate (soooμ?, r/an), monobasic chromic acid @ (111μV/α), basic lead sulfate (118μV/cm), calcium phosphate (332μU/crIL), Zinc molybdate (33311y-/b), calcium molybdate (25 (5μo/Crn), aluminum phosphomolybdate (182μV-/α), barium metaborate (1540μV/1), ammonium metavanadate (7450μV-/α) (The figure in parentheses is the electrical conductivity of the aqueous extract), and these can be used alone or in combination of two or more.Among these,
Particular preference is given to using anticorrosion pigments selected from zinc chromate, strontium chromate, barium chromate and calcium chromate. The amount of these anticorrosive pigments generally ranges from 1 to 150 parts by weight, preferably from 2 to 50 parts by weight, per 100 parts (solids) of the aqueous vehicle. In order to fully demonstrate the anti-corrosion function of the anti-corrosion pigments contained in the water-based barrier coat,
The water absorption rate of the above electrodeposited coating is 0.3 to 201i%, especially 1c0
．． It is preferable to adjust it to a range of 5 to 5 iit.

Here, the "water absorption rate" of the electrodeposition coating is determined by applying the electrodeposition coating to a cured film thickness of 20A (coating area 5 x 5cm).
After baking with Toji according to its composition, the coating film is isolated and immersed in hot water at 50°C for 48 hours, and the weight of the coating film immediately after being lifted and the coating film after drying it at 105°C for 1 hour. This is the value obtained by measuring each of these and incorporating these results into the following formula.

By adjusting the water absorption rate of the MJI coating within the above range, the water-extracted components of the anti-corrosion pigment extracted from the aqueous barrier coat film containing the anti-corrosion pigment coated on the surface of the electro-deposited coating film are It is presumed that it easily penetrates into the coating film and has a significant anode (or cathode) suppressing effect on the steel material surface, thereby protecting the steel material. The water absorption rate can be adjusted by adjusting the crosslinking density of the coating film,
This can be easily achieved by introducing hydrophilic groups, the amount of extender pigments, etc.

Therefore, according to this method of adjusting the water absorption rate, there is no particular need to incorporate an anticorrosion pigment into the electrodeposition paint, so that the storage stability of the core paint and the smoothness of the coating film can also 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, 1) the tensile strength elongation rate at break of the coating film itself is determined at a tensile rate of 20u+/in an atmosphere of -20°C.
If it is adjusted within the range of 200 to 1000 inches, especially 300 to 70 (liters), the chipping resistance, corrosion resistance, etc. of the composite 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 DSC-10 manufactured by Daini Seiko Kin), The "rate" is determined by using a universal tensile tester with constant mPa (Shimadzu Kosakusho Autograph S-D model) and measuring the length of the sample Fi2.
The value was measured at 0 m and a tensile speed of 20 Iu/min. The samples used for these measurements were coated with the barrier coat on a tin plate to a thickness of 25 μm based on the dry coating film formed, baked at 120°C for 30 minutes, and then isolated using the mercury amalgam method. This is what I did.

Additionally, the water-based barrier coat according to the present invention may further contain coloring pigments (e.g., titanium white, carbon black, etc.), extender pigments (e.g., asbestos, talc, etc.), as needed.
clay, etc.), plasticizers (e.g., dioctyl phthalate, tricresyl phosphate, dibutyl sepacate, etc.), anti-sagging agents (e.g., aluminum stearate,
Silica gel, etc.) can also be blended in an appropriate amount normally used.

Furthermore, in the present invention, it is more preferable that the barrier coat contains a resin deterioration inhibitor such as an ultraviolet absorber, a light stabilizer, and an antioxidant. If the hiding power of the top coat is lower than this K, it will be possible to absorb the ultraviolet rays that penetrate through the top coat and prevent the deterioration of the barrier coat itself and the surface of the electrodeposition coating over time due to ultraviolet rays. can.

The UV absorber that can be incorporated into the barrier coat absorbs UV energy, is compatible with the barrier coating resin or can be uniformly dispersed in the resin, and is easily decomposed at the baking temperature of the paint. Any type of compound may be used as long as it does not lose its effectiveness, such as benzophenone, 2,4-dihydroxybenzophenone,
212'14.4'-Tetrahydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2°2'-dihydroxy-4,4'-dimethoxybenzophenone, 2.2'-dihydroxy-4-methoxybenzophenone/, 2 -Hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dobyloxybenzophenone, 2-hydroxy-4-methquine-5-sulfobenzophenone, 5-chloro-2-hydroxybenzophenone, 2,2'-dihydroxy -4,4'-dimethoxy-5
-Sulfobenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2-hydroquine-4-(2-hydroxy-3-methylacryloxy)
Benzophenone UV absorbers such as propoxybenzophenone: 2-(2'-hydroxy-5'-methyl-phenyl)penztriazole, 2-[2'-hydroxy-31,5/-di(1,1-dimethylbenzyl) phenyl)-2H-benzotriazole, 2-(2'-hydroxy-3',5'-t6rt-butylphenyl)
benzo) IJ azole, 2-(2'-hydroxy-3
'-tert-butyl-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-
t6rt-amylphenyl)benzotriazole,
2-+)'-Hydroxy-3',5'-t6rt-butylphenyl)-5-chlorobenzotriazole, 2-(
2'-Hydroxy-3',5'-di-isoamylphenyl)benzotriol, 2-(2'-hydroquine-5
Benzotriazole UV absorbers such as '-t6rt-butylphenyl) benzotriazole; salicylic acid ester UV absorbers such as phenylsalicylate), 4-tert-butylphenyl salicylate, and p-octyl phenyl salicylate; ethyl-2 -cyano-3,
3'-diphenylacrylate, 2-ethylhexyl-
Diphenylacrylate UV absorbers such as 2-cyano-3゜3'-diphenyl-acrylate; hydroxy-5-methoxy-acetophenone, 2-hydroxy-naphthophenone, 2-ethoxyethyl-p-methoxycinnamate, nickel-bisoctyl Phenyl sulfide, (2,2'-thiobis-(4-t6rt-octylphenol)))-n-butylamine-nickel, oxalic acid anilide UV absorbers, etc., and commercially available benzotriazole-based Examples of ultraviolet absorbers include Tinuvin 900, Tinuvin 328, etc. (CI BA-Ge
Benzophenone UV absorbers include Ebinur 400 (BASF), and oxalic acid anilide UV absorbers include Sando 3206 (Sandbore).

The blending ratio of these ultraviolet absorbers is preferably 0.1 to 10 parts by weight, particularly 0.5 to 5 parts by weight, per 100 parts by weight of the barrier coating resin.

In addition, as a light stabilizer, for example, tetrakis (2,2,
6,6-tetramethyl-4-piperidyl)-1,2,3
, 4-butanetetracarboxylate, 8-acetyl-
3-dodecyl-7,7゜9.9-tetramethyl-1,3
,8-triazaspiro(4,5)decane-2,4-dione, bis-(1,2,2,6,6-bentamethyl-4-
piperidinyl) sebacate, bis-(2,2,6,6-
Tetramethyl-4-piperidyl) sebacate, bis(1
, 2,2,6,6-pentamethyl-4-piperidyl) sebacate, dimethyl-2-(4-hydroxy-2,2,
6,6-tetramethyl-1-piperidyl) ethanol condensate, poly[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-)cyazine-2,4-diyl-4 -(2,2,6,6-tetramethylbiveridyl)hexamethylene-4,4-(2,2,6,6-titramethylpiperidyl)imine: l, 1-(2-3-(3, 5-
t6rt-butyl-4-hydroxyphenyl)propionyloxyethyl)-4-(3-(3,5-dit)
Examples of antioxidants include ert-butyl-4-hydroxyphenyl)propionyloxy)-2,2゜6.6-tetramethylbiperidine, and examples of antioxidants include 4.4%
'-Thiobis-(3-methyl-6-tert-butylphenol), 2,2'-methylenebis-(4-methyl-
〇-tert-butylphenol), 4,4'-methylenebis-(2,6-sheet tcrt-butylphenol)
,1゜3.5-)Listyl-2,4,6-)Listyl-(3
゜5- Sheet Cr t-phthyl-4-hydroxybenzyl)benzene, tris-(2-methyl-4-hydroxy-5-t6rt-butylneal)-butane, pentaerythritol-tetrakis-(3-laurylthiopropionate) , dilauryl thiodipropionate, distearyl thiodiglopionate, simiristyl thiodipropionate, triethylene glycol-bis-3-(
3-tert-butyl-5-methyl-4-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-3-(3,5-di-tcrt-butyl-4-hydroxyphenyl)-propionate, 2,4-bis −
(n-octylthio)-6-(4-hydroxy-3,5
-rut6rt-butylanilino)-1,3,5-)+
77 Gin, Pentaerythrityl Tetragysu[:3-
(3,5-butyl-4-hydroxyphenyl)-propionate], 2,2-thio-diethylenebis-[3-(3,5-butyl-4-hydroxyphenyl)-propionate] , octadecyl-3-(3゜5-di-t6rt-butyl-4-
Hydroxyphenyl)propionate, 2,2-thiobis-(4-l thyl-6-tert-butylphenol), N.

N'-hexamethylenebis-(3,5-t6rt-
butyl-4-hydroxynnamamide) and the like. It is preferable to use these in combination with the ultraviolet absorber, and the amount of compounded ingredients is 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the resin for billier coating.
3 parts by weight, and 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight of the antioxidant.

Furthermore, the coating formed by the water-based barrier coat [
Another important factor is that it has excellent adhesion to the electrodeposition coating and the topcoat (described later), and the adhesion to each coating is at least 25 to 9/CI! It is desirable that the adhesive strength be at least L". Here, the adhesion force is determined by fixing the attachment to the barrier coated surface applied to the electrodeposited surface or to the top coated surface further coated, and then peeling off the attachment using a tensile strength measuring device. The energy required for (k
g/crrL. That is, after each paint is applied under predetermined conditions and cured, an epoxy resin two-component adhesive is attached to the barrier coated surface and the top coated surface with an attachment whose contact surface with the coated surface is circular with a diameter of 5u. The power required to peel the attachment in the vertical direction from each coating film at 20° C. at a tensile speed of 50 sa for 7 minutes using a Schottspa complete tensile strength measuring device (manufactured by Ichishima Seisakusho) was measured. (Measure yu/1ri.

The above-mentioned characteristic values of the barrier coating film are mainly controlled by selecting the type and composition of the vehicle component, but it is also possible by adding a viscosity-imparting agent, adjusting the pigment formulation, etc.

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 coating, dipping, dipping, electrostatic coating, etc. can be used, and the thickness of the coating film is preferably 1 to 20 microns, particularly 5 to 10 microns, depending on the coating film formed.

When applying a powder topcoat to a barrier coat coating surface, the barrier coat may be baked in advance, or the powder topcoat may be applied wet-on-wet without baking. The baking temperature of water-based barrier coats is generally 80 to 200℃, especially 80℃.
A range of ~160°C is suitable.

Powder topcoat: A powder coating that is applied to the barrier coated surface to give the coated object a cosmetic effect, and is suitable for the finished appearance (sharpness, smoothness, gloss, etc.), weather resistance (glossy retention, etc.) It is preferable to use a thermosetting powder coating that can form a coating with excellent properties such as hardness, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, and hardening properties. Examples include thermosetting powder coatings whose vehicle components are amino-acrylic resins, acid-glycidyl-functional acrylic resins, amino-polyester resins, isocyanate-polyester resins, and isocyanate-acrylic resins. It will be done.

Top coating finishing methods using these powder top coatings include, for example: ■ Applying solid color powder top coating containing colored pigments or metallic powder top coating containing metallic pigments to the barrier coat coating surface, and heating. A solid color or metallic finish using a 1-coat, 1-bake method of curing; ■ Add a colored pigment or metallic pigment to the solid color or metallic powder coating used in (■) above or the liquid coating described below on the barrier coat coating surface. A two-coat process in which a liquid solid color or metallic paint is applied, and then heated and cured (or without heat cured) and then a powder topcoat clear paint containing little or no colored pigment is applied and baked. Examples include solid color or metallic finishing using a two-bake method or a two-coat-one-bake method.

First, regarding (2) above, after baking the barrier coat film, or preferably applying a water-based barrier coat containing the above-mentioned affinity solvent, without baking, apply a solid color or metallic powder topcoat for about 30 to 30 minutes. 15
0 μ, preferably 40 to 100 μ, more preferably 4
Paint to a film thickness of 5 to 90μ (based on the coating film after baking, the same applies hereinafter), and heat at 120 to 210℃, especially 130 to 18℃.
It is convenient to bake at a temperature of 0°C. If an affinity solvent is contained in the barrier coating film and a powder topcoat is applied without baking, the affinity solvent improves the fluidity of the topcoat and eliminates minute irregularities (for example,
It is possible to prevent the occurrence of yuzu (citrus skin, tangerine skin), and it is possible to finish the painted surface with excellent smoothness.

Regarding ■, apply a barrier coat and then apply 10 to 150 microns of solid color or metallic liquid paint or powder paint after baking it or without baking it.
The powder clear paint is coated to a film thickness of
It is preferable to heat and bake at 120 to 210° C. after coating the film to a thickness of 150 μm. The total thickness of solid color or metallic coating and clear coating is 20μ
It is preferably in the range of 40 to 300μ, more preferably in the range of 50 to 200μ.

Examples of the liquid paint include amino-acrylic resin,
Examples include solution-type, dispersed-type, non-aqueous-dispersed, and high-solid type paints that use organic solvents and/or water as solvents or dispersion mediums, including avano-alkyd resins, amino-polyester resins, etc. as vehicle components. . This liquid paint contains the same ultraviolet absorbers, light stabilizers, antioxidants, coloring pigments, metallic pigments, and affinity solvents as listed above as things that can be added or blended into the barrier coat. Adding or blending these ingredients will improve weather resistance, smoothness, etc., making it a good choice.

The coating hardness of these powder top coatings is preferably 3B or more, particularly H to 9H, as determined by the pencil hardness test method.

The "pencil hardness" of the above topcoat film is determined by applying it to a glass plate and curing it (cured film thickness: 30μ).The test coated plate was kept at 20℃, and the tip of the paint was sharpened to make it flat. Hold a piece of lead foil (1 unit) at a 45 degree angle and press it firmly against the coated surface as hard as possible to prevent the thin film from breaking.
In) This is the value when the hardness is evaluated using the hardest ship's hardness that leaves no trace of scratches caused by lead IiK.

According to the method of the present invention described above, electrodeposition coating on materials - water-based barrier coating coating - W on powder! The performance of the coating film formed by L coating is particularly improved in terms of finished appearance (e.g., smoothness, gloss, sharpness, etc.), chipping resistance, corrosion resistance, It is characterized by a marked improvement in adhesive properties over a period of time.

Next, examples and comparative examples related to the present invention will be described.

■Preparation of samples (1) Steel plate: Steel plate chemically treated with Bonderite φ3030 (manufactured by Nihon Parkerizing Co., Ltd., zinc phosphate metal surface treatment agent) (size 300 x 90 x 0.8 Dragon) (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) 2 parts by weight of basic lead chromate (anticorrosion pigment) was added to the cationic electrodeposition paint of (A) per 100 parts by weight of resin solid content. The water absorption rate f′i of the hardened dragon film is 4.2% by weight.

(C) Anionic electrodeposition paint: Elekronna 7200
(Manufactured by Kansai Paint Co., Ltd., polybutadiene-based anionic electrodeposition paint, strontium chromate with a resin solid content of 10
1 per 011 parts! (parts included).

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

(3) Water-based barrier coat (A): Propylene/ethylene copolymer (weight ratio near
0/30. Number average molecular weight: approx. 200000) 100ii
Neutralized and aqueous dispersion of a resin graft-polymerized with 10 parts by weight of maleic acid (static glass transition temperature: 41
℃, tensile strength elongation at -20℃: 400 inches)
.

(B): Graft resin 1001 of the above (A)! 3 parts by weight of zinc chromate (anticorrosive pigment) and 2-(2'-hydroxy-3115/-di() as an ultraviolet absorber)
1 part by weight of IJ azole (1,1-dimethylbenzyl)phenyl)-2H-benzo), bis(1
,2,2,6,6-bentamethyl-4-piperidinyl)
Neutralization of a composition containing 0.5 parts by weight of Separate,
In the aqueous dispersion, 100 parts by weight of cellosolve acetate as an affinity solvent was further added together with water.

(C): Aqueous dispersion obtained by emulsion polymerization of a component consisting of 20 parts by weight of styrene and 70% by weight of butadiene (static glass transition temperature: 48°C, -2
Tensile strength elongation at 0°C: 450 inches).

(D): Acrylonitrile 30% by weight, Butashev 6
A composition consisting of 3 parts by weight of acrylic acid and 3 parts by weight of acrylic acid was subjected to emulsion polymerization according to a conventional method, and then 100 parts by weight of the copolymer, 6 parts by weight of strontium chromate (anticorrosion pigment), and 2 parts by weight of ultraviolet absorber were added. - 2 parts by weight of hydroxy-4-methoxybenzophenone, be/nuerythrityl-tetrakis (3-(3,
5-tert-phthyl-4-hydroxyphenyl)-
An aqueous dispersion containing 1 part by weight of propionate, and a total of 155 parts by weight of carpitol acetate as an affinity solvent with water (static glass transition temperature: 50°C)
, tensile strength elongation at -20°C: SOO)
.

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

(F) dinonyl acrylate) 600% by weight 2-ethylhexyl acrylate 20 parts by weight, methyl acrylate 1
5 parts by weight of barium chromate (anticorrosion pigment) per 100 parts by weight of the emulsion polymer of the composition consisting of 5 parts by weight and 5 parts by weight of hydroxyethyl acrylate, and the antioxidant and light used in (B) above. An aqueous dispersion containing a stabilizer and an affinity solvent in the same amounts as above (static glass transition temperature knee: 48°C, tensile strength elongation at -20°C: 370%).

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

(H): Hexadecyl acrylate 60 1% by weight, 2-
An aqueous dispersion (static glass transition temperature: +4°C) obtained by emulsion polymerization of a composition consisting of 201% by weight of ethylhexyl acrylate, 15% by weight of methyl acrylate, and 5% by weight of hydroxyethyl acrylate.

(4) Powder topcoat: (A) Powder topcoat for solid color Acrylic paint consisting of 30 parts by weight of glycidyl methacrylate, 30i parts by weight of methyl methacrylate, 20 parts by weight of butyl acrylate and 20 parts by weight of styrene. Polymer (number average molecular weight: approx. 2
5.000 >25 dodecanoic acid per 100 parts by weight
A powder coating for solid color finishing, which contains a superposition part, 30 parts by weight of titanium white pigment, and 1 part by weight of a coating surface conditioner.

(B) Powder topcoat for clear acrylic copolymer (number average molecular weight: approximately 35 parts by weight) consisting of 35 parts by weight of glycidyl methacrylate, 20 parts by weight of methyl methacrylate, 15 parts by weight of 2-ethylhexyl acrylate, and 30 parts by weight of styrene. 000) Per 100 parts by weight, 30 parts of dodecanedioic acid and 11 parts of coating surface conditioner
Clear finishing powder paint containing t part.

(C) Acrylic resin-based organic solution-type metallic paint Copolymer consisting of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and hydroxyethyl methacrylate (number average molecular weight: approx. 30.000
, Hydroxyl value: 100) Adding aluminum uneven powder paste to a vehicle component consisting of a 75 weight range and 25% by weight of a butylated melamine resin [, Teoru organic solution-type metallic paint. Toluene/carbitol acetate as organic solvent = 70
/30 (weight ratio) is used.

Using the sample thickened in step (2) above, electrodeposition paint, barrier coat, and top coat paint were applied to a common material using the ingredients 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 12wt 1%, bath temperature 30°C, pH 7.8, load voltage approximately 200V, electricity applied for 180 seconds.

In any of the above cases, after electrodeposition coating, wash with water and heat at 170°C for 30 minutes.
Bake for 0 minutes. The coating thickness is 20μ based on the cured coating.

The barrier coat is applied using an air spray machine and has a film thickness of 8μ based on the dry coating.

All top coats are sprayed using an electrostatic sprayer.

In topcoat painting, rlcIBJ is a coating system in which topcoat paint A is applied and then baked at 160℃ for 30 minutes.
cIBJ is a system in which top coats C and B are applied wet-on-wet and then baked at 160°C for 30 minutes to cure 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: ■Test equipment: Q-G-R gravelometer (product of Q Panel Company) ■Stone to be sprayed: Crushed stone with a diameter of approximately 15 to 20 m/m■Capacity of stone to be sprayed: Approximately 500m ■ Spraying with air pressure of approximately 4 kg/cm ``■ Temperature during test: Approximately 20℃ Place the test specimen on the specimen holding table, and blowing approximately 4 ky/cm'' with air pressure of approximately 500 d of crushed stone was fired onto a test piece, and the coated surface condition and salt water spray resistance were evaluated. The condition of the painted surface was visually observed and evaluated using the following criteria.The salt spray resistance was determined by subjecting the test piece to a salt spray test for 720 hours according to JISZ 2371. ■Full condition ◎ (Good): There are very few scratches due to debt on a part of the topcoat, and there is no electrodeposition. No peeling of the paint film was observed.

Δ (slightly poor) There are many scratches on the second top coat due to impact, and peeling of the electrodeposited film is also observed here and there.

× (Poor) Most of the second top coat has peeled off, and the electrodeposition coating on the impact area including the impact area and its surroundings has peeled off.

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

○: @, slight corrosion and peeling of the paint film are observed.

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

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

(*2) Impact resistance: JIS K5400-1979 6.13.3B
The test is carried out in an atmosphere at 0°C in accordance with the law. weight 50
09 weight was dropped from a height of 50 crn to check the damage to the paint film.

◎: No cracks or peeling observed. Δ: Slight cracking, peeling, ×: Significant cracking and peeling occurred.

(*3) Adhesion: According to JIS K5400-1979 6.15 K, there are 10 goblets with a size of 1 ma x 1 wm on the coating film.
0 pieces were made, adhesive cellophane tape was attached to the surface, and after rapid peeling off, the remaining goblin coating was examined.

(*4) Water resistance: Evaluate the coated surface after immersing it in water at 40°C for 10 days. ◎
There is no abnormality.

(*5) Smoothness: Visually judge the painted surface ◎: Hardly any unevenness observed ○: Some unevenness observed Δ: Many unevenness observed (*6) Salt water resistance r! X-fogging property: Cross-cut scratches are made on the coating film with a knife to reach the substrate, and the coating is tested visually for 1680 hours using the same salt spray tester as above (*1), after which the condition of the coating surface is visually evaluated. did. Evaluation was based on (*1).

Continuation of the first truth

Claims (1)

[Claims] Electrodeposition paint is applied to the steel material, a water-based barrier coat capable of forming a film with a static glass transition temperature of 0 to -75°C is applied to the applied surface, and then a thermosetting powder topcoat is applied. A steel coating method characterized by: