JPH0454505B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a coating film with improved chipping resistance, corrosion resistance, interlayer adhesion, coating surface finish, etc., obtained by a composite coating system consisting of electrodeposition coating and powder top coating. 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, so they are 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 finish, and improvements in these properties are desired. For example, with regard to chipping resistance, in the automobile industry, emphasis is being placed on the durability of coating films, particularly the reduction in corrosion resistance of coating films due to impact peeling and the progress of corrosion of steel materials. In particular, in cold regions of Europe and America, gravel mixed with a large amount of relatively coarsely crushed rock salt is often laid to prevent road surfaces from freezing during the winter, and vehicles driving on these types of roads are often covered with gravel mixed with large amounts of rock salt. Rock salt particles and pebbles thrown up by the wheels collide with the paint surface, and the impact often causes the paint film to peel off locally from the car body, a so-called "chipping" phenomenon. As a result of this phenomenon, the metal surface of the impacted portion of the outer panel of the vehicle body is exposed, and rust immediately develops and corrosion progresses. Paint peeling due to chipping usually occurs on the bottom of the car body and around the suspension, but it can also occur on the hood and roof, about 6 months to 1 year.
It is known that localized corrosion becomes quite noticeable over the years. In order to prevent this chipping and the progression 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 car 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 such chemical conversion treatments cannot sufficiently improve the adhesion of coatings on impact areas. Have difficulty. Also,
Various studies have been conducted on the resins and/or pigments used in electrocoating paints and powder topcoating paints, 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 the coating film 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. corrosion resistance,
We have conducted extensive research with the aim of providing a method for forming composite coatings with improved interlayer adhesion and coating surface smoothness. As a result, after applying the electrodeposited paint and prior to applying the powder paint, we preformed a specific coating film with a high elongation of tensile strength at break and toughness on the surface of the electrodeposited paint. In addition, by using a powder coating that forms a tough and hard coating, the above objectives can be achieved, and the above objectives can be achieved, such as chipping resistance, corrosion resistance, interlayer adhesion, and coating surface smoothness. We succeeded in forming a coating film with significantly improved properties. According to the present invention, the electrodeposited paint is applied to the steel material, and the tensile strength elongation at break is 150.
% or more and a stress at break of 20 Kg/cm ² or more, and then apply an organic solvent-based paint that can form a film with a tensile strength elongation of 40% or less and a stress at break of 300 Kg/cm ² A coating film forming method is provided which is characterized by applying a thermosetting powder topcoat paint that can form the coating film as described above. A feature of the present invention is that in the process of sequentially applying electrodeposition paint and powder paint to steel materials, the tensile strength elongation rate (hereinafter sometimes abbreviated as "elongation rate") is Organic solvent-based paint (hereinafter referred to as "barrier coat") that can form a coating film with a stress of 150% or more and a stress at break of 20Kg/cm2 or ^more .
) on the surface of the electrodeposited coating, and use a powder coating that can form a coating with an elongation rate of 40% or less and a stress at break of 300 kg/cm ² or more. There is a particular thing. The basic structure of the coating film for improving chipping resistance in the present invention is that an intermediate buffer layer is provided within the coating film to absorb collision energy caused by rock salt particles, etc., and the collision energy is concentrated on the surface layer of the coating film. A powder coating film with physical properties that allows it to be dispersed as much as possible without causing any damage. Specifically, a coating film with a high elongation rate and excellent flexibility (elasticity) (barrier coat coating film) is provided as an intermediate layer to make it easier for the coating film to absorb impact energy, and the surface layer is coated with rock salt particles. A coating film with a specific elongation rate and stress at break that has been adjusted to have toughness that prevents scratches and cracks from occurring even when objects collide with it, and a hardness that easily disperses impact energy. As a result, the composite coating film formed by the method of the present invention is
Even when rock salt particles collide with the painted surface, the collision energy is dispersed in the surface layer of the paint film, so the collision energy received per unit area of the paint film is reduced, and the impact energy is distributed within the barrier coating film provided as an intermediate layer. Because it is absorbed, the paint film does not peel off due to impact, and there are almost no cracks or scratches.
Almost no steel surface is exposed. 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 improve. It is significantly improved compared to the one that does not involve . Furthermore, the material 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 conductive and has a metal surface that can be coated by electrodeposition. I don't accept it. Examples include materials such as iron, copper, aluminum, tin, zinc, etc., alloys containing these metals, and plated or vapor-deposited products of these metals and alloys, and specifically, materials made using these materials. This includes car bodies and parts for passenger cars, trucks, safari cars, motorcycles, 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 paint: As an electrodeposition paint for coating the above steel materials,
Both cationic and anionic electrocoating paints known per se can be used. First, cationic electrodeposition paints include cathodically deposited thermosetting electrodeposition paints that are based on resins with basic amino 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 amino groups include bisphenol-type epoxy resins, acrylic resins containing epoxy groups (or glycidyl groups), glycidyl ethers of alkylene glycols, epoxidized polybutadiene, and epoxidized products of borax phenol resins containing epoxy groups. Addition of amines to epoxy groups (oxirane rings) of resins; unsaturated compounds with basic amino groups (e.g., N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl acrylate, N-vinylpyrazole, etc.) Polymerization used as polymer; 3rd
Reaction of a glycol component containing a polyisocyanate compound with a glycol containing a grade amino group (for example, N-methyldiethanolamine) as one component of the glycol; reaction of an amino group to the resin by a reaction to generate iminoamine by reaction with an acid anhydride and a diamine. The base number obtained by introduction; etc. is generally about 20.
Resins in the range of ~200 are suitable. Examples of amines that can be used in the above reaction include aliphatic, alicyclic, or aromatic-aliphatic primary amines, secondary amines, and tertiary amine salts. Furthermore, in place of such amines, secondary sulfide salts or tertiary phosphine salts added to the above-mentioned epoxy group-containing resins can also be used as vehicle components of cationic electrodeposition paints in the present invention. Examples of neutralizing agents for neutralizing the resin having basic amino 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. Acid: Inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid can be used. The amount of the neutralizing agent to be blended with the resin is suitably in 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). In addition, as a crosslinking agent to make a cationic electrodeposited coating film heat-curable, a blocked polyisocyanate compound is generally used. (usually above about 140°C), the blocking agent dissociates and
The isocyanate group is regenerated and cured by a crosslinking reaction with an active hydrogen-containing functional group such as a hydroxyl group that may be present in the above-mentioned cationic resin. Furthermore, cationic electrodeposition paints include pigments (coloring pigments, extender pigments, anti-rust pigments, etc. The amount of pigment blended is preferably 150 parts by weight or less per 100 parts by weight of resin solid content),
Mix hydrophilic solvents, water, additives, etc. as necessary, dilute with deionized water etc. so that the solid content concentration is about 5 to about 40% by weight, and adjust the pH within the range of 5.5 to 8.0. do. Cationic electrodeposition coating using the cationic electrodeposition paint thus prepared can usually be carried out under the conditions of a bath temperature of 15 to 35°C and a load voltage of 100 to 400V, with the object to be coated serving as a cathode. The thickness of the electrodeposition coating film is not particularly limited, but is generally preferably in the range of 10 to 40 μm based on the cured coating film. Also,
The baking hardening temperature of the coating film is generally suitable within the range of 100 to 200°C. On the other hand, anionic electrodeposition paints are anodic electrodeposition paints that are mainly based on resins having carboxyl groups and are neutralized with basic compounds to make them water-soluble (water-dispersed). (The object to be coated) is used as an anode. Examples of resins with carboxyl groups include maleated oil resins obtained by adding maleic anhydride to drying oils (linseed oil, dehydrated castor oil, tung oil, etc.); polybutadiene (1,2-type, 1,4-type); Maleated polybutadiene obtained by adding maleic anhydride to unsaturated fatty acid ester of epoxy resin; Resin obtained by adding maleic anhydride to unsaturated fatty acid ester of epoxy resin: High molecular weight polyhydric alcohol (molecular weight
1000 or more, including partial esters of epoxy resins and styrene/allylic alcohol copolymers) and polybasic acids (trimellitic anhydride,
(maleated fatty acids, maleated oils, etc.); carboxyl group-containing polyester resins (including those modified with fatty acids); carboxyl group-containing acrylic resins; polymerizable unsaturated monomers containing glycidyl groups or hydroxyl groups. Examples include resins obtained by adding maleic anhydride to polymers or copolymers formed using reaction products with unsaturated fatty acids, and the carboxyl group content is generally determined based on the acid value. Approximately 30 to approx.
Something in the 200 range is suitable. Neutralizing agents (basic compounds) that can be used to neutralize the carxyl groups in these carboxyl group-containing resins and make the resins water-soluble (water-dispersed) include:
For example, alkanolamines such as monoethanolamine, diethanolamine, and dimethylaminomethanol; alkylamines such as diethylamine and triethylamine; and inorganic alkalis such as potassium hydroxide and sodium hydroxide can be used. The amount of these neutralizing agents to be used is suitably in the range of about 0.1 to about 1.0 times the theoretical neutralization equivalent (preferably 0.4 to 0.8 times equivalent) with respect to the acid value of the resin. In addition, in order to make the above resin thermosetting, the crosslinking agent is hexakismethoxymethylmelamine,
Low molecular weight melamine resins such as butoxylated methyl melamine, ethoxylated methyl melamine, etc. can be used if desired. Furthermore, anionic electrodeposition paints include pigments (coloring pigments, extender pigments, anti-rust pigments, etc. The amount of pigment blended can be 150 parts by weight or less per 100 parts by weight of resin solid content), hydrophilic solvents, Water, additives, etc. can be mixed as necessary, the solid content concentration can be adjusted to about 5 to about 40% by weight with deionized water, etc., and the pH can be maintained in the range of 7 to 9 for anionic electrodeposition coating. . Anion electrodeposition coating can be carried out according to a conventional method, for example, at a bath temperature of 15-35°C and a load voltage of 100-35°C.
It can be carried out under the condition of 350V with the object to be coated as the anode. The coating film thickness is not particularly limited, but it is usually preferably in the range of 10 to 40 μm based on the cured coating film. In principle, anionic electrodeposited coatings are cured by heating to a temperature in the range of 100 to 200°C, preferably 140 to 200°C, but if an air-drying resin modified with unsaturated fatty acids is used, it can be dried at room temperature. You can also do so. Barrier coat: Barrier coat is a paint that is applied on the surface of the electrodeposited film as an intermediate buffer layer that absorbs the impact energy present in rock salt particles, etc. In the present invention, especially, the barrier coat is a paint with an elongation rate of 150% or more. and the stress at break is 20
Use an organic solvent-based paint that forms a coating film with physical properties of Kg/cm ² or more. Paints for barrier coatings have a vehicle component and an organic solvent as their main components, and if necessary, pigments other than tackifiers and anticorrosion pigments (e.g.
It is a coating composition that uses an organic solvent as a solvent or dispersion medium, which is appropriately blended with color pigments, extender pigments, etc.), ultraviolet absorbers, light stabilizers, antioxidants, etc. The vehicle component that can be used in the barrier coat is a thermoplastic (or thermosetting) material that has excellent adhesion to the electrodeposition coating film and the powder topcoat film described below, and is capable of forming a coating film having the above characteristic values. Any resin may be used, and specific examples include, but are not limited to, the following. Vinyl acetate-ethylene copolymer: about 5 to about 70% by weight vinyl acetate, preferably 15% by weight
Vinyl acetate-ethylene copolymers obtained by copolymerizing ~50% by weight with about 95 to 30% by weight, preferably 85 to 50% by weight of ethylene, are included, and the number average Preferably, the molecular weight ranges from about 5,000 to about 500,000. Linear saturated polyester resin: A saturated dibasic acid having two carboxyl groups in one molecule and containing no polymerizable unsaturated bonds and a dihydric alcohol containing no polymerizable unsaturated bonds are combined in a normal manner. Included are linear thermoplastic polyester resins substantially free of branched structures obtained by polycondensation reaction. As the dibasic acid, for example, an aliphatic saturated dibasic acid having 4 to 34 carbon atoms, such as succinic acid, glutaric acid, adipic acid, pimelic acid, corkic acid, azelaic acid, brassylic acid, and tabmic acid, is used. Preferably, aromatic or aliphatic dibasic acids such as phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc. can also be used in combination with these dibasic acids. On the other hand, examples of dihydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,6-hexanediol, 1,5-
Linear aliphatic alcohols such as pentanediol and propylene glycol are particularly preferably used, and if necessary, 2,3-propylene glycol, neopentyl glycol,
1,2-butylene glycol and the like can also be used. The polyester resin generally has a molecular weight of about 10,000 to about
It is preferable to have a number average molecular weight in the range of 100,000, and suitably have a glass transition temperature of 10°C or less. Thermoplastic polyurethane elastomer: has hydroxyl groups at both ends and has a molecular weight of approximately 500 to approximately
It includes resins obtained by reacting a diol compound in the range of 4,000 with an isocyanate compound to extend the chain length of the diol compound by 2 to 50 times. Examples of the diol compound include OH-terminated esters of dibasic acids and dihydric alcohols as described above; addition polymerization of propylene oxide to polypropylene glycol, triols (e.g., glycerin, hexanetriol, trimethylolpropane, etc.); , a copolymer of ethylene oxide and propylene oxide; examples include polyethylene glycol, polytetramethylene glycol, etc. On the other hand, examples of the diisocyanate compound include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate. , lysine diisocyanate, trimethylhexamethylene diisocyanate, 4,
4'-methylenebis(cyclohexyl isocyanate), 1,3-(isocyanatomethyl)cyclohexane, isophorone diisocyanate, trimethylhexamethylene diisocyanate, and the like are preferably used. Polybutadiene-containing crosslinked curable resin composition: The content of polybutadiene or acrylonitrile having a number average molecular weight in the range of about 10,000 to about 1,000,000, in which functional groups selected from amine groups, hydroxyl groups, and carboxyl groups are introduced at both ends, is about 1 to about 1.
50% by weight and a number average molecular weight of about 10,000 to about
butadiene-acrylonitrile copolymer in the range of 1,000,000 and an epoxy resin as a crosslinking agent,
A crosslinked curable composition comprising a mixed system with at least one resin selected from urethane resin, polyester resin, and melamine resin is included.
The mixing ratio of the polybutadiene or butadiene-acrylonitrile copolymer and the crosslinking agent in the mixed system is not strictly limited, but generally the latter is about 10 to about 60 parts by weight per 100 parts by weight of the former. It is suitable for use within the range of The mixed system undergoes a crosslinking reaction and is cured at room temperature or by heating, depending on the type of crosslinking agent. Therefore, when preparing a barrier coat using the above composition, the molecular weight of the polybutadiene or its copolymer, the type and amount of the crosslinking agent, etc. are selected appropriately to form a barrier coat coating having the above characteristic values. A film can be easily formed. Thermosetting polyester resin composition: As exemplified above, an acid component mainly composed of a resin group dibasic acid, a linear dihydric alcohol as exemplified above, and a small amount of trihydric or tetrahydric alcohol (for example, glycerin) The chain length of a polyester having a relatively low molecular weight (molecular weight: about 500 to about 10,000) obtained by esterification with an alcohol component consisting of , trimethylolethane, pentaerythritol, etc.), and a diisocyanate compound as exemplified above. The mixture includes a urethane-modified polyester resin which has been reacted and has a length of 2 to 50 times, and a blocked polyisocyanate compound as a crosslinking agent. The urethane-modified polyester resin generally has a hydroxyl value of about 20.
A range of ~100 is suitable. Also,
The blocked polyisocyanate compound can be a diisocyanate compound as exemplified above to which a blocking agent (active hydrogen compound) containing a hydroxyl group such as methanol, phenol, or catechol is added. The composition is heated at a temperature above the dissociation temperature of the blocking agent of the blocked polyisocyanate compound, usually about
When heated to a temperature of 100° C. or higher, the blocking agent dissociates and the diisocyanate compound is regenerated, undergoes a crosslinking reaction with the urethane-modified polyester resin, and is cured. The elongation rate and stress at break of the cured film can be adjusted as desired by adjusting the chain length of the polyester resin, the hydroxyl group content (ie, hydroxyl value), the amount of the bronc polyisocyanate compound, and the like. Styrene-butadiene copolymer: 1-80% by weight of styrene, preferably 10-40% by weight and 99-20% by weight of butadiene, preferably 90% by weight
A copolymer obtained by copolymerizing styrene and butadiene with ~60% by weight; or a copolymer obtained by copolymerizing styrene and butadiene with about 1 to about 20% by weight based on the total amount of styrene and butadiene. These copolymers generally have number average molecular weights ranging from about 10,000 to about 500,000. Polybutadiene: A resin whose main component is cis-1,4-polybutadiene, which may further contain trans-1,4-bonds, vinyl bonds, etc., and whose number average molecular weight is in the range of about 10,000 to about 500,000. That is suitable. Acrylonitrile-butadiene copolymer: A copolymer obtained by copolymerizing 10 to 55% by weight, preferably 10 to 40% by weight, of acrylonitrile and 90 to 45% by weight, preferably 90 to 60% by weight of butadiene. Yes, and if necessary, a third
Ingredients include styrene, acrylic acid, methacrylic acid, and vinylpyridine, based on the total amount of acrylonitrile and butadiene.
These copolymers can preferably have number average molecular weights ranging from about 10,000 to about 500,000, including copolymers copolymerized from 0.5 to 35% by weight to improve adhesion. Butyl rubber: A copolymer of isobutylene and a small amount (usually 1 to 10% by weight, based on the weight of the copolymer) of isoprene, having a number average molecular weight of about 10,000 to about
Something in the range of 500,000 is preferred. Acrylic resin: Mainly composed of acrylic ester and/or methacrylic ester, and optionally containing functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, and/or other polymers. It includes those obtained by polymerizing a vinyl monomer component consisting of a sexually unsaturated monomer. Examples of the acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate,
iso-butyl acrylate, 3-pentyl acrylate, hexyl acrylate, 2-heptyl acrylate, octyl acrylate, 2-
Octyl acrylate, nonyl acrylate,
Particularly preferred are _C1-18 alkyl esters of acrylic acid such as lauryl acrylate, 2-ethylhexyl acrylate, 2-ethylbutyl acrylate, and methacrylic esters such as pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate. _C5-18 alkyl esters of methacrylic acid such as , lauryl methacrylate, stearyl methacrylate are particularly preferred. The static glass transition temperature of the homopolymers derived from these acrylic esters and methacrylic esters exemplified here is 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 resins, which typically have a molecular weight of about 5,000 to
It can have a number average molecular weight in the range of about 1,000,000. Furthermore, in addition to those exemplified above, chloropropylene rubber, chlorosulfonated polyethylene, reaction products of alkyl dihalides (e.g., ethylene dichloride, ethylene dichloride formal, propylene dichloride, etc.) and sodium polysulfide, Silicon rubber (e.g. dimethyl silicone rubber,
methyl phenyl silicon rubber, methyl vinyl silicon rubber, fluorinated alkyl methyl silicon rubber, cyanoalkyl silicon rubber, etc.), ethylene-propylene rubber, propylene oxide rubber, and epoxy resin-polyamide compositions. Vehicle components of the barrier coat used in the present invention include one or more selected from those exemplified above. Among these, it is particularly preferable to use those selected from the above . . However, it should be understood that even organic solvent-based resins not exemplified above may be used as long as they provide a coating film having the above performance and characteristic values. The vehicle component is dissolved or dispersed in an organic solvent and applied to the electrodeposited surface. The organic solvent for dissolving or dispersing the vehicle component is not particularly limited, and any organic solvent generally known for paints can be used, such as aromatic hydrocarbons such as benzene, toluene, and xylene; hexane; Aliphatic hydrocarbon solvents such as , heptane and octane; chlorinated hydrocarbon solvents such as trichlorethylene, perchlorethylene, dichloroethylene and dichloroethane can be used. In addition, as an organic solvent, the above organic solvents may be used, such as diisopropylbenzene, tetralin, decalin, o-dichlorobenzene, trichlorobenzene, benzyl alcohol, diisobutyl ketone, isophorone, cellosolve acetate, carbitol acetate, dimethyl phthalate, etc. It is preferable to use an organic solvent with a boiling point of 150° C. or higher and an affinity for the powder topcoat (hereinafter sometimes abbreviated as "affinity solvent") such as . This is because after applying a barrier coat made by dissolving or dispersing the vehicle component in an organic solvent containing an affinity solvent, the powder topcoat can be applied immediately to the wet wax without baking the paint film. When baked after coating, the affinity solvent remaining in the barrier coat film evaporates and reaches the powder top coat film, which promotes the heat-melting fluidity of the powder resin particles and improves the finish. This is because the smoothness of the painted surface can be significantly improved. The content of the affinity solvent in the organic solvent in the barrier coat is not particularly limited, but is preferably in the range of 5 to 50% by weight.
Further, the total organic solvent content in the barrier coat is generally suitably in the range of 15 to 95% by weight. Therefore, in the present invention, it is effective to apply the powder topcoat directly onto the undried wet barrier coat surface containing an compatible solvent in order to finish the coated surface with excellent smoothness. The coating film formed by the barrier coat, which is basically composed of the vehicle component described above and the organic solvent described above, has an elongation rate (+20℃, tensile speed 20mm/min) of 150.
% or more, preferably 180 to 1500%, more preferably 200 to 850%, and the stress at break (+20°C, tensile speed 20 mm/min) is 20 Kg/cm ² or more,
Preferably 30-700Kg/cm ² , more preferably 40
It is important to have characteristic values in the range ~500 Kg/ ^cm2 . This is because if the elongation rate is less than 150%, the impact energy during chipping cannot be absorbed sufficiently, and on the other hand, the stress at break is 20Kg/cm ²
This is because if the size is smaller, the barrier coating film is more likely to be damaged by impact from pebbles during chipping, and the electrodeposited film is more likely to peel off due to impact. In addition, the values of the elongation rate and stress at break of the barrier coating film in this specification are measured at +20°C for a sample with a length of 20 mm using a universal tensile tester with a constant temperature bath (Shimadzu Autograph S-D model). These are the values when measured at a tensile speed of 20 mm/min at After baking at 120°C for 30 minutes, it was isolated using the mercury amalgam method. In the present invention, if the vehicle component has an elongation rate and a stress at break within the above range, it can be used by itself as a barrier coat, but even if it deviates from the above range or has a stress at break. When it is desired to finely adjust the elongation rate and/or the stress at break, a viscosity imparting agent can be added as necessary. The viscosity imparting agent is a resin having good compatibility with the vehicle component, for example,
Examples include rosin, petroleum resin (chroman resin), ester gum, low molecular weight aliphatic epoxy resin, low molecular weight aliphatic bisphenol type epoxy resin, polyoxytetramethylene glycol, etc. The amount of these compounds is 100 parts by weight of the vehicle component above. The preferred range is 1 to 50 parts by weight. In addition, the barrier coat according to the present invention may further include coloring pigments other than anticorrosion pigments (e.g., titanium white, carbon blank, etc.), extender pigments (e.g., asbestos, talc, clay, etc.),
plasticizers (e.g. dioctyl phthalate, tricresyl phosphate, dibutyl sebacate, 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. As a result, if the hiding power of the top coat is low, it is 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,
2,2',4,4'-tetrahydrobenzophenone,
2-hydroxy-4-methoxybenzophenone,
2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-do Desyloxybenzophenone, 2-hydroxy-4-
Methoxy-5-sulfobenzophenone, 5-chloro-2-hydroxybenzophenone, 2,2'-
Dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2-hydroxy-4-(2-hydroxy-3-methylacryloxy) Benzophenone UV absorbers such as propoxybenzophenone; 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole;
2-[2'-hydroxy-3',5'-di-(1,1-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(2'-hydroxy-3',5'-di-tert
-butylphenyl)benzotriazole, 2-
(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-(2'- hydroxy-3′,
5'-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-
di-isoamyl phenyl)benzotriazole,
Benzotriazole UV absorbers such as 2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole; phenyl salicylate, 4-
Salicylic acid ester UV absorbers such as tert-butylphenyl salicylate and p-octyl phenyl salicylate; ethyl-2-cyano-3,
Diphenylacrylate UV absorbers such as 3'-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate; hydroxy-5-methoxy-acetophenone, 2-hydroxy-naphthophenone, 2-ethoxy Ethyl-p-methoxycinnamate, nickel-bisoctylphenyl sulfide, [2,
2'-thiobis(4-tert-octylphenolate)]
Examples of commercially available benzotriazole-based UV absorbers include Tinuvin 900 and Tinuvin 328 (CIBA-
Geigy), benzophenone UV absorbers include Uvinul 400 (BASF), and oxalic acid anilide UV absorbers include Sando 3206 (Sandbore). The blending amount of these ultraviolet absorbers is preferably in the range of 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. Examples of light stabilizers include 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-pentamethyl-4-piperidinyl) sebacate, bis-(2,2,6,6
-tetramethyl-4-piperidyl) sebacate,
His(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-traazine-2,4-diyl 4-
(2,2,6,6-tetramethylpiperidyl)hexamethylene-4,4-(2,2,6,6-tetramethylpiperidyl)imine], 1-[2-3-
(3,5di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]-4-[3-(3,
Examples of antioxidants include 5-di-tert-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine and the like; 3-
methyl-6-tert-butylphenol), 2,2'-
Methylenebis-(4-methyl-6-tert-butylphenol), 4,4'-methylenebis-(2,6-
di-tert-butylphenol), 1,3,5-trimethyl-2,4,6-tris-(3,5-di-
tert-butyl-4-hydroxybenzyl)benzene, tris-(2-methyl-4-hydroxy-5
-t-butylphenyl)-butane, pentaerythritol-tetrakis-(3-laurylthiopropionate), dilaurylthiodipropionate,
Distearylthiodiprobionate, dimyristylthiodipropionate, triethylene glycol-bis-3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)-propionate,
1,6-hexanediol-bis-3-(3,5
-di-tert-butyl-4-hydroxyphenyl)
-propionate, 2,4-bis-(n-octylthio)-6-(4-fluoroxy-3,5-di-
tert-butylanilino)-1,3,5-triazine, pentaerythrityl-tetrakis-[3-
(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate], 2,2-thio-diethylene-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) ) - propionate],
octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,
2,2-thiobis-(4-methyl-6-tert-butylphenol), N,N'-hexamethylene-bis-(3,5-di-tert-butyl-4-hydroxycinnamamide), etc. It will be done. These are preferably used in combination with the ultraviolet absorber, and the amount of the light stabilizer is 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, per 100 parts by weight of the barrier coating resin.
3 parts by weight, and the antioxidant is suitably in the range of 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight. Furthermore, it is also an important factor that the coating film formed by the above-mentioned barrier coat has excellent adhesion to the electrodeposition coating film and the powder top coating film described below, and the adhesion to each coating film is also important. It is desirable that the weight is at least 25 Kg/cm ² or more. Here, the adhesion force is the energy (Kg/cm ^{2 )} required to stick the attachment to the electrodeposited barrier coated surface or the intermediate coated surface and peel it off using a tensile strength measuring device. It is. That is, after each paint is applied under specified conditions and cured, an epoxy resin-based two-component adhesive is attached to the Veria coated surface and the top coated surface with a circular attachment with a diameter of 5 mm. Then, the power required to peel the attachment in the vertical direction from each coating film (Kg/ cm ² ). The above-mentioned characteristic values of the barrier coating film are mainly adjusted by selecting the type and composition of the vehicle component, but also by adding viscosity-imparting agents, adding pigments (excluding anti-corrosion pigments), etc. It is possible. In the present invention, the barrier coat can be applied either after the electrodeposited coating is cured by heating or in an uncured state, preferably after being cured in advance. The coating method is not particularly limited, and for example, spray coating, brush coating, dipping coating, electrostatic coating, etc. can be used, and the coating film thickness is 1 to 20 μm, particularly 5 to 20 μm, depending on the coating film formed.
It is preferable to set it to 10μ. When applying the powder topcoat to the barrier coat coating surface, the barrier coat may be baked in advance, but it is preferable to apply the powder topcoat in a wet-on-wet manner without baking. The baking temperature of the barrier coat is generally suitable in the range of 80 to 180°C, particularly 80 to 140°C. Powder topcoat paint: As the topcoat paint applied to the barrier coated surface, a powder paint that imparts cosmetic properties to the coated object is used. Therefore, the finished appearance (image clarity,
Thermosetting properties that can form coatings with excellent properties such as smoothness, gloss, etc.), weather resistance (glossy retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, and hardening properties. It is preferable to use powder coatings, in particular, for example, amino-acrylic resin systems, acid-glycidyl functional acrylic resin systems, amino-polyester resin systems, isocyanate-polyester resin systems, isocyanate-acrylic resin systems, etc. Examples include thermosetting powder coatings that serve as vehicle components. As a finishing method using these powder topcoats, for example, a solid color powder topcoat containing colored pigments or a metallic powder topcoat containing metallic pigments is applied to the surface of the viacoat coating, and the coating is heated and cured. 1 coat 1
Solid color or metallic finish by baking method: Applying a liquid solid color or metallic paint made by blending a colored pigment or metallic pigment to the solid color or metallic powder paint or liquid paint used above on the barrier coat coating surface, Solid color or metallic finishes using a two-coat, two-bake method or a two-coat, one-bake method in which a powder top clear paint containing little or no color pigment is applied and baked after heat curing (or without heat curing). can be given. First, regarding the above, after baking the barrier coat film, or preferably by applying the barrier coat containing the above-mentioned affinity solvent and without baking, apply a solid color or metallic powder topcoat of about 30 to 150 microns, preferably is 40~100μ,
More preferably, it is coated to a film thickness of 45 to 90 μm (based on the coating film after baking, the same applies hereinafter), and 120 to 210 μm thick.
It is convenient to bake at temperatures between 130 and 180 °C, especially between 130 and 180 °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, Yuzu skin,
It is possible to prevent the occurrence of tangerine skin (tangerine skin), and it is possible to finish the painted surface with excellent smoothness. For this, apply a barrier coat, and then apply solid color or metallic liquid paint or powder paint to a film thickness of 10 to 150μ after baking it or without baking it, and then bake it (baking temperature 80 to 170℃). Alternatively, it is preferable to apply the powder clear paint to a film thickness of 20 to 150 μm without baking, and then heat it to 120 to 210° C. and bake it. The total thickness of the solid color or metallic coating and the clear coating can be 20μ or more, preferably 40 to 300μ, more preferably 50 to 200μ. Examples of the liquid paint include solution-type paints, dispersion-type paints using an organic solvent as a vehicle component such as an amino-acrylic resin system, an amino-alkyd resin system, an amino-polyester resin system, and/or water as a solvent or dispersion medium; Examples include non-aqueous dispersion type and high solids type paints. This liquid paint contains the same ultraviolet absorbers, light stabilizers, antioxidants, coloring pigments, metallic pigments, and affinity solvents as listed above as substances that can be added or blended into the barrier coat. It is preferable to add or blend the like, since weather resistance, smoothness, etc. will be improved. In addition, after curing, the top coat film (including liquid paint film) has an elongation rate of 40% or less, preferably 5 to 5%.
30%, more preferably in the range of 5-20%,
Moreover, the stress at break is 300Kg/ ^cm2 or more, preferably
350-1000Kg/ ^cm2 , more preferably 450-900
It is important that it is in the range of Kg/cm ² . If the elongation rate of the coating film is greater than 40%, the coating film will be insufficient in terms of hardness and solvent resistance as a coating film for the exterior of a car body, and if the stress at break is less than 300 kg/cm ² , the chipping resistance will be poor. cannot expect sufficient improvement. The elongation rate and stress at break of the top coat film can be measured in the same manner as for the barrier coat film. As a method for adjusting the elongation rate and stress at break of the top coat formed using the above-mentioned top coat, for example, when using a top coat whose vehicle component is a polyester resin or an alkyd resin, the raw material component of the resin may be adjusted. A method of imparting hardness and toughness to a vehicle component by using a polybasic acid and an aromatic acid such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid or anhydride thereof; Vehicle When using a top coat consisting of an acrylic resin, examples include a method of selecting an acrylic resin having a high glass transition temperature. In addition, a resin with a relatively large molecular weight and a high content of crosslinkable functional groups is used as a vehicle component, and the amount and type of catalyst (internal or external catalyst) and/or type and amount of crosslinking agent (or curing agent) are used. By appropriately controlling the following, it is also possible to adjust physical properties such as the three-dimensional crosslinking density, elongation rate, and stress at break of the coating film formed using the vehicle component. However, in any case, the exact physical properties of the paint film formed by the top coat used can be determined by actually forming a paint film sample using a small amount of these paints, and measuring the elongation rate and stress at break using the method described above. This can be determined by measurement, and this makes it possible to select a paint that is compatible with the method of the invention. The performance of the coating film formed on steel by electrodeposition coating, barrier coating coating, and powder top coating according to the method of the present invention described above is particularly superior to that of the coating film formed by omitting the barrier coating coating. It is characterized by significantly improved finished appearance (for example, smoothness, gloss, sharpness, etc.), chipping resistance, corrosion resistance, interlayer adhesion, etc. Next, examples and comparative examples related to the present invention will be described. Sample preparation (1) Steel plate: Steel plate chemically treated with Bonderite #3030 (manufactured by Nihon Parkerizing Co., Ltd., zinc phosphate metal surface treatment agent) (size 300 x 90 x 0.8 mm) (2) Electrodeposition paint : (A) Cationic electrodeposition paint: Elekron #9200
(Manufactured by Kansai Paint Co., Ltd., epoxy polyamide cationic electrodeposition paint) (B) Anionic electrodeposition paint: Elekron #7200
(Manufactured by Kansai Paint Co., Ltd., polybutadiene-based anionic electrodeposition paint) (3) Barrier coat: (A) Vinyl acetate-ethylne copolymer (number average molecular weight: approximately 10,000, elongation rate: 700%, stress at break: 120Kg/cm ² ) of organic solvent [carbitol acetate/toluene = 10/90 (weight ratio)]
liquid. (B) Organic solvent of Vylon 30p (manufactured by Toyobo Co., Ltd., thermoplastic high molecular weight linear saturated polyester resin; elongation rate: 800%, stress at break: 40 Kg/cm ² , number average molecular weight approximately 18,000 to approximately 20,000) [Toluene/cellosolve acetate = 80/20 (weight ratio)] Liquid. (C) Elastolan E390 (Japan Elastolan Co., Ltd.)
Made of thermoplastic polyurethane elastomer;
Elongation rate of formed coating film: 500%, stress at break:
420Kg/cm ² ) of organic solvent [tetrahydrofuran/isophorone = 70/30 (weight ratio) liquid. (D) HYCAR CTBN1300×13 (Ube Industries, Ltd.)
Co., Ltd., carboxyl group-containing butadiene-acrylonitrile copolymer and Epicoat 828
(manufactured by Ciel Chemical Co., Ltd., epoxy resin) [using toluene/dimethyl phthalate = 70/30 (weight ratio) as the solvent]. (Rupture stress of formed coating film: 50Kg/cm ² , elongation rate: 400
%). (E) Thermosetting polyester resin composition Urethane-modified polyester resin (hydroxyl value: 80, molecular weight: approximately 6000), hexamethylene diisocyanate is blocked with phenol, and a blocked isocyanate compound is added (stress at break of formed coating film: approximately 300 Kg/cm ² , elongation rate: approximately 250%). .
Use toluene as a solvent. (F) Acrylic resin Copolymer of ethyl acrylate and hexyl acrylate with a small amount of acrylic acid and hydroxyethyl acrylate (number average molecular weight: approximately 25,000) in organic solvent [toluene benzyl alcohol = 70/30 (weight ratio)] liquid . (Stress at break of formed coating film: 100
Kg/cm ² , elongation rate: 600%). (G) Thermosetting polyester resin composition (for comparative example) Composition consisting of short oil polyester resin (oil length: 20%, hydroxyl value: 80, acid value: 10) and butanol-modified methylated melamine resin [organic solvent Toluene/benzyl alcohol = 70/30 (weight ratio) was used]. (Stress at break of formed coating film: 100Kg/cm ² , elongation rate:
100%). (H) Thermosetting polyester resin (for comparative example) A composition consisting of a short oily polyester resin (oil length: 20, hydroxyl value: 120, acid value: 15) and butanol-modified melamine resin (toluene is used as the solvent). (Stress at break of formed coating film: 15Kg/cm ² , elongation rate: 250%). (4) Top coating: (A) Powder top coating for solid color Acrylic copolymer (number average molecular weight :
Approximately 25,000) per 100 parts by weight, dodecanedioic acid
25 parts by weight of titanium white pigment, 30 parts by weight of titanium white pigment, and 1 part by weight of a coating surface conditioner (stress at break of formed coating film: 700 Kg/cm ² , elongation rate: 8%). (B) Clear powder topcoat 35 parts by weight of glycidyl methacrylate, 20 parts by weight of methyl methacrylate, 2 parts by weight of acrylic acid
- 15 parts by weight of ethylhexyl and styrene
Per 100 parts by weight of acrylic copolymer (number average molecular weight: approximately 35,000) consisting of 30 parts by weight,
30 parts by weight of dodecanedioic acid and 1 part of paint surface conditioner
Powder paint for clear finishing consisting of parts by weight (stress at break of formed coating film: 800Kg/cm ² ,
elongation rate 7%). (C) Acrylic resin-based organic solution-type metallic paint 75% by weight of a copolymer of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and hydroxyethyl methacrylate (number average molecular weight: approx. 30,000, hydroxyl value: 100) and butylated melamine. An organic solution-type metallic paint made by adding aluminum powder paste to a vehicle component consisting of 25% by weight of resin (stress at break of formed coating: 500 Kg/cm ² , elongation: 5%). Toluene/carbitol acetate as organic solvent≠
Use 70/30 (weight ratio). Examples and Comparative Examples Using the samples prepared above, steel materials were coated with electrodeposition paint, barrier coat, and top coat 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℃, PH6.5, load voltage approximately 250V,
Power on for 180 seconds. Anion electrodeposition coating conditions: Bath solid content concentration 12% by weight, bath temperature 30℃, PH7.8, load voltage approximately 200V,
Power on for 180 seconds. In any of the above cases, wash with water after electrodeposition coating,
Bake at 170℃ for 30 minutes. The coating thickness is 20μ based on the cured coating. The barrier coat is applied using an air spray machine.
Film thickness is 10μ based on dry coating. All top coats are sprayed using an electrostatic sprayer. For topcoating, "1C1B" is a coating system in which topcoat A is applied and then baked at 160℃ for 30 minutes, and "2C1B" is a coating system in which topcoat C and B are applied wet-on-wet and then baked at 160℃ for 30 minutes. This system hardens both coatings by baking for 30 minutes. 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 500ml Blow air pressure: Approximately 3Kg/cm ² Temperature during test: Approximately 20℃ Attach the test piece to the test piece holder and apply approximately 3Kg/cm2.
Approximately 400 ml of crushed stone was shot onto the test piece at a blowing air pressure of cm ² , and then 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, and the salt spray resistance was evaluated using a test piece.
A salt spray test was conducted for 840 hours according to JISZ2371, and then an adhesive cellophane tape was attached to the painted surface, and after rapid peeling, the presence or absence of rust from the impacted area, corrosion state, peeling of the paint film, etc. were observed. do. Coated surface condition ◎ (Good): Very few scratches due to impact are observed on a part of the top coat, and no peeling of the electrodeposited coating is observed. Δ (slightly poor): Many scratches due to impact were observed on the top coat, and peeling of the electrodeposition coating was also observed here and there. × (Poor): Most of the top coat has peeled off, and the electrodeposition coating on the impact area including the impact area and its surroundings has peeled off. Salt spray resistance ◎: No rust, corrosion, peeling of paint film, etc. observed. ○: Rust, corrosion, and paint peeling are slightly observed. Δ: Slightly more rust, corrosion, and peeling of the paint film are observed. ×: Significant rust, corrosion, and paint peeling occurred. (*2) Impact resistance: According to JIS K5400-1979, 6.133B method,
The test is carried out in an atmosphere of 0°C. weight 500
Drop a weight of g from a height of 50 cm to check for damage to the paint film. (*3) Adhesion: Make 100 goblets of 1 mm x 1 mm in size on the coating film according to JIS K5400-1979, 6.15,
Paste adhesive cellophane tape on the surface,
Evaluate the painted surface after rapid peeling. (*4) Water resistance: Evaluate the painted surface after immersing it in water at 40°C for 10 days. (*5) Visually observe the presence or absence of unevenness on the painted surface,
If there is almost no occurrence, it is considered "good".
"Somewhat inferior" or "inferior" depending on the degree of occurrence
shall be.

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Claims (1)

[Claims] 1 Electrodeposition paint is applied to steel material, and the coated surface has a tensile strength elongation rate of 150% or more and a stress at break.
An organic solvent-based paint that can form a film with a strength of 20 kg/cm2 or ^more is applied, and then the tensile strength and elongation at break are measured.
A coating film forming method characterized by applying a thermosetting powder topcoat paint capable of forming a coating film having a stress at break of 40% or less and a stress at break of 300 Kg/cm ² or more.