JPS624473A - Formation of coated film - Google Patents

Abstract

PURPOSE:To obtain a composite coated film having excellent resistance to chipping, etc. by coating an electrodeposition paint on a steel material, an org. solvent type paint forming a coated film having specified performance on the coated surface thereof and further a thermosetting liquid finish paint forming a coated film having specific performance thereon. CONSTITUTION:This invention relates to a method for forming the composite coated film on the steel material, more particularly an antomotive body, etc. in which the electrodeposition paint is coated on the steel material and the org. solvent type paint forming the coated film having >=150% tensile break strength elongation and >=20kg/cm<2> press at break is coated on the coated surface thereof. The thermosetting liquid finish paint forming the coated film having <=40% tensile break strength elongation and >=300kg/cm<2> stress at break is coated thereon. Such composite coated film has excellent finish appearance, water resistance, weatherability, etc. and improves the resistance to chipping, corrosion resistance and physical performance in particular.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides improvements in chip resistance, corrosion resistance, physical performance, etc., which can be applied to steel materials, particularly automobile bodies, with coating systems including electrodeposition coatings and liquid top coatings. The present invention relates to a method of forming a composite coating film.

In the automotive industry, emphasis is being placed on the durability of paint films, particularly the decline in corrosion resistance of paint films due to impact peeling and the progression of corrosion on 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 down 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. When the rock salt particles and pebbles thrown up by the wheels collide with the paint surface of the vehicle, the impact often causes the paint film to be partially peeled off from the vehicle body, resulting in so-called "chipping." As a result of this phenomenon, the metal surface of the impact area on the outer surface of the car body is exposed, which quickly rusts and corrosion progresses.Normally, peeling of the paint film due to chipping is most common at the bottom of the car body and the 9 parts around the suspension. It is known that localized corrosion can become noticeable in about six months to a year.

In order to prevent this chipping and the progression of corrosion caused by it, various studies have been carried out on chemical oxidation treatments, electrodeposition paints, and liquid top coats on the surface of the metal base of the outer 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.

Regarding electrodeposition paints and liquid topcoat paints, various studies have been conducted on the resins and i! It has not been discovered until now.

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 liquid top coat coating, and have achieved chipping resistance without reducing weather resistance, chemical resistance, etc. , conducted extensive research with the aim of providing a method for forming composite coatings with improved corrosion resistance, physical performance, etc. As a result, after applying the electrodeposited paint and prior to applying the liquid top coat,
To achieve the above objective by forming in advance a specific coating film that has a high elongation rate of tensile strength at break and also having toughness, and by using a paint that forms a tough and hard coating film as a liquid paint. find out what you can do,
The company succeeded in forming a coating film with significantly improved chipping resistance, corrosion resistance, and physical performance.

Therefore, according to the present invention, an electrodeposited paint is applied to a steel material, and then an organic material capable of forming a coating film having a tensile strength elongation at break of 150% or more and a stress at break of 20 kg/ff1 or more is applied to the coated surface. After applying a solvent-based paint, the tensile strength elongation at break is 40% or less and the stress at break is 300%.
Provided is a method for forming a coating film, which comprises forming a coating film having a coating film having a ratio of 9/cff1 or more on the surface of the substrate, and applying a thermosetting liquid topcoat paint obtained by obtaining 2.

A feature of the present invention is that in the process of sequentially applying electrodeposition paint and liquid top coat to steel materials, ) is 150% or more and the stress at break is 20 kg/d or more. Applying an organic solvent-based paint (hereinafter referred to as "barrier coat") to the surface of the electrodeposited film; (2) As a liquid top coat, one that can form a coating film with an elongation rate of 40% or less and a stress at break of 300 kg/d is used.

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 top coat film. It consists of a coating film with physical properties that allow it to be dispersed as much as possible without causing any problems. Specifically, we are developing a coating film (with a high elongation rate and excellent elasticity).
A barrier coat film is provided as an intermediate layer to make it easier for the paint film to absorb impact energy, and the top coat has the toughness and impact energy to prevent scratches and cracks even when rock salt particles collide with it. It forms a coating film that has a specific elongation rate and stress at break that are adjusted to a hardness that facilitates dispersion. As a result, even if rock salt particles etc. collide with the coated surface, the composite coating film formed by the method of the present invention disperses the collision energy in the coating surface layer. Since the energy is small and absorbed within the barrier coating film provided in the intermediate layer,
The coating film does not peel off due to impact, almost no cracks or scratches are observed, and almost no steel surface is exposed. Furthermore, if the chipping resistance of the coating film is improved in this way, any problems such as corrosion and rusting of steel materials will naturally be resolved, and in addition, the corrosion resistance of the composite coating film itself formed by the method of the present invention will also be improved. Significant improvement compared to one without a barrier coat.

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

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

Steel material: The steel material on which a coating film can be formed by the method of the present invention is subject to any restrictions as long as it is a conductive material and has a metal surface that can be coated by electrodeposition. do not have.

Examples include materials such as iron, copper, aluminum, tin, zinc, etc., alloys containing these metals, and plating or vapor deposition products of these metals and alloys, and specifically, products made using these materials. passenger cars, trucks,
This includes vehicle bodies, parts, electrical products, building materials, etc. for motorcycles and other vehicles. 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 the electrodeposition paint for coating the steel material, any known cationic or anionic electrodeposition paint can be used.

First, cationic electrodeposition paints include cathodically deposited thermosetting electrodeposition paints made by using a resin with a basic amine group as a paste and neutralizing it with acid to make it water-soluble (water-dispersed). , this is painted using the steel material (object to be coated) as a cathode.

Examples of resins with basic amine groups include: ■ Bisphenol-type epoxy resins, acrylic resins containing epoxy groups (or glycytyl groups), dalicidyl ethers of alkylene glycols, epoxidized polybutatsuenes, and epoxidized products of novolac phenol resins containing epoxy groups. Addition of amine to epoxy group (oxirane ring) of resin;■
Unsaturated compounds with basic amino groups (for example) N, N-
Polymerization using tertiary amine group-containing glycols (e.g., N-methylsoethanolamine)
Reaction of a glycol component with a polyincyanate compound in which the glycol component is one component of the glycol; ■Introduction of an amine group into the resin by the reaction of an acid anhydride with a soamine to form an iminoamine; Generally, the base number obtained is about 2.
Resins ranging from 0 to about 200 are suitable.

Examples of amines that can be used in the reaction (2) above include aliphatic, alicyclic, or aromatic-aliphatic primary amines, secondary amines, and 6th-class amine salts. In addition, instead of such amines, a product obtained by adding a secondary sulfide salt or a 6th class phosphine salt to the epoxy group-containing resin described in (1) above can also be used as a vehicle component of a cationic electrodeposition paint. .

Examples of neutralizing agents for neutralizing the resin having basic amine groups and making it water-soluble (water-dispersed) include:
Acetic acid, hydroxyl acetic acid, blowonic acid, butyric acid, lactic acid,
Organic acids such as glycine; 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). be.

In addition, as a crosslinking agent that can be added to make a cationic electrodeposited coating film heat-curable, a blocked polyisocyanate compound is generally used. When heated (usually at about 140° C. or higher), the blocking agent dissociates, the incyanate group is regenerated, and the inocyanate group undergoes 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, and is cured. moreover,
Cationic electrodeposition paints contain pigments (coloring pigments, extender pigments,
Rust-preventing pigments, etc. The blending amount of the pigment is preferably 9150 parts by weight or less per 100 parts by weight of the resin solid content), a hydrophilic solvent, water, additives, etc. are blended as necessary, and the solid content concentration is about 5 to about 40%. It is diluted with deionized water or the like so as to give a weight percent, and the pH is adjusted within the range of 5.5 to 8.0.

Cationic electrodeposition coating using the cationic electrodeposition paint prepared in this way can usually be carried out under the conditions of a bath temperature of 15 to 65°C and a load voltage of 100 to 400℃, using the object to be coated as a cathode. . The film thickness of the electrodeposition coating is not particularly limited, but is generally preferably in the range of 10 to 40 μm based on the cured coating film. In addition, the baking hardening temperature of the coating film is generally 100~
A range of 200'C is suitable.

On the other hand, anionic electrodeposition paints are anodic electrodeposition paints that are made by using a resin containing carboxyl groups as a paste and neutralizing it with a basic compound to make it water-soluble (water dispersion). (The object to be coated) is used as an anode.

Examples of resins with carboxyl groups include: ■ Maleated oil resin obtained by adding maleic anhydride to drying oil (linseed oil, dehydrated castor oil, tung oil, etc.); ■ Polybutatsuene (
Maleated polybutadiene obtained by adding maleic anhydride to 1,2-type, 1,4-type, etc.); ■Resin obtained by adding maleic anhydride to unsaturated fatty acid ester of epoxy resin; ■High molecular weight Polyhydric alcohol (molecular weight approx. 1
,000 or more, and is obtained by adding polybasic acids (trimellitic anhydride, maleated fatty acids, maleated oils, etc.) to polybasic acids (including partial esters of epoxy resins and styrene/allyl alcohol copolymers, etc.) Resin; ■ Carboxyl group-containing polyester resin (including those modified with fatty acids); ■ Carboxyl group-containing acrylic resin; Formed using the reaction product of a polymerizable unsaturated monomer containing a glycytyl group or hydroxyl group and an unsaturated fatty acid. Resins obtained by adding maleic anhydride etc. to a polymer or copolymer obtained by adding maleic anhydride, etc., and the carboxyl group content is generally in the range of about 30 to about 200, based on the acid value. There is. Examples of neutralizing agents (basic compounds) that can be used to neutralize the carboxyl groups in these carboxyl group-containing resins and make the resins water-soluble (water-dispersed) include monoethanolamine, soethanol Narkanolamines such as amines and trimethylaminoethanol; alkylamines such as soethylamine and triethylamine; and inorganic alkalis such as potassium hydroxide and sodium hydroxide can be used. The amount of these neutralizing agents used is approximately 0.1 to approximately 1.0 times the theoretical neutralization equivalent to the acid value of the resin (preferably (14 to 0.8
A range of 2 times equivalents) is appropriate.

Furthermore, as a crosslinking agent for making the resin thermosetting, low molecular weight melamine resins such as hexakismethoxymethylmelamine, ethoxylated methylmelamine, and ethoxylated methylmelamine can be used as necessary.

Furthermore, anionic electrodeposition paints contain pigments (coloring pigments, extender pigments, anti-rust pigments, etc.).
0 parts by weight to 50 parts by weight or less of Shira)
, hydrophilic solvent, water, additives, etc. are added as necessary.
The solid content concentration can be adjusted to about 5 to about 40% by weight using deionized water or the like, 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, under conditions of a bath temperature of 15 to 35° C. and a load voltage of 100 to 350 V, using the object to be coated as an anode. The coating film thickness is not particularly limited, but it is usually preferably in the range of 10 to 40 μm based on the cured coating film.

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

A barrier coat is a paint that is applied on the electrodeposition coating as an intermediate buffer layer that absorbs impact energy, and includes:
In the present invention, in particular, an organic solvent-based paint is used that forms a coating film having physical properties such as an elongation rate of 150% or more and a stress at break of 20 kg/d or more.

Paints for barrier coating are mainly composed of a vehicle component and an organic solvent.A tackifier and pigments other than anticorrosion pigments (for example, color pigments 11 extender pigments, etc.) may be added as necessary. This coating composition uses an organic solvent as a solvent or a dispersion medium. .

The vehicle component that can be used in the barrier coat is preferably a thermoplastic or thermosetting resin that has excellent adhesion to the electrodeposition coating film and the intermediate coating film described below, and has an elongation rate and stress at break within the above range. Specifically, the following can be exemplified.

■ Vinyl acetate-ethylene copolymer: about 5 to about 70% by weight of vinyl acetate, preferably 15 to 50% by weight
% by weight and about 95 to about 60% by weight of ethylene, preferably 8
Includes vinyl acetate-ethylene copolymers obtained by copolymerizing 5 to 50% by weight of vinyl acetate and ethylene in a conventional manner, and whose number average molecular weight is about 5000 to about 500,000.
It is preferable that it is in the range of .

■ 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. A linear thermoplastic polyester resin substantially free of branched structures obtained by polycondensation reaction is included. Examples of the dibasic acid include succinic acid, glutaric acid, adipic acid,
Pimelic acid, corkic acid, azelaic acid, brassic acid,
It is preferable to use aliphatic saturated dibasic acids having 4 to 34 carbon atoms such as tabsic acid, and in combination with these dibasic acids, aromatic or alicyclic dibasic acids such as phthalic anhydride, Tetrahydrophthalic anhydride, hexahydrophthalic anhydride, etc. can also be used in combination. On the other hand, dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1.4-
7' ethylene glycol, 1,6-hexanesool, 1
．． Linear aliphatic alcohols such as 5-pentanesol and propylene glycol are particularly preferably used, and if necessary, 2,3-propylene glycol, neopentyl glycol, 1,2-butylene dalicol, etc. are also used. can.

The lIJ ester resin generally preferably has a number average molecular weight in the range of about 10,000 to about 100,000, and suitably has a glass transition temperature of 10°C or less.

■ A thermoplastic polyurethane distomer is obtained by extending the chain length of the Sool compound by 2 to 50 times by reacting a Sool compound with a molecular weight in the range of about 500 to about 4,000 with a sool compound having a hydroxyl group at the two side terminals and a soisocyanate compound. This includes resins that can be used. Examples of the sool compound include, for example, the OH deuterated ester of a 92-basic acid and a dihydric alcohol as described in (1) above; polyprogylene gellicol; Addition polymerization of oxides; copolymers of ethylene oxide and propylene oxide; -diethylene glycol, polytetramethylene glycol, etc.; examples of the soisocyanate compounds include tolylene diinocyanate, sophenylmethane soisocyanate, etc. , hexamethylene diisocyanate, xylylene diisocyanate, lysone diisocyanate, trimethylhexamethylene diisocyanate), 4, 4'-methylenebis(cyclohexyl isocyanate), 1.3
-(Incyanatomethyl)cyclohexane, inphorone diisocyanate, trimethylhexamethylene isocyanate, etc. are preferably used.

■ Polybutadiene-containing crosslinked curable resin composition Polybutazene or acrylonitrile having a number average molecular weight in the range of about 10,000 to about 1.000.000, into which a functional group selected from niamin group, hydroxyl group and carboxyl group is introduced at both ends. a butatsuene-acrylonitrile copolymer having a content of about 1 to about 50% by weight and a number average molecular weight of about 10,000 to about 1,000,000; an epoxy resin, a urethane resin, a polyester resin and a crosslinking agent; A crosslinked curable resin composition comprising a mixture with at least one resin selected from melamine resins is included.

The mixing ratio of the polybutadiene or butadiene-acrylonitrile copolymer and the crosslinking agent in the core mixture is not strictly limited, but generally the latter is mixed in an amount of about 10 to about 60 parts by weight per 100 parts by weight of the former. Suitable for use within a range. The above mixture 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 resin composition, a barrier coat film having the above characteristic values can be obtained by appropriately selecting the molecular weight of polybutadiene or its copolymer, the type and amount of the crosslinking agent, etc. Easy to form.

■ Thermosetting polyester resin composition; an acid component mainly composed of aliphatic dibasic acids such as those exemplified in (■) above, linear dihydric alcohols such as those exemplified in (■) above, and a small amount of trihydric or tetrahydric alcohol ( For example, the chain length of a polyester having a relatively low molecular weight (molecular weight: about 500 to about 10,000) obtained by esterification with glycerin, trimethylolethane, or pentaerythritol caranal alcohol component can be changed to a twin cyanate as exemplified in (1) above. Included are those consisting of a mixture of a urethane-modified polyester resin and a blocked polyisocyanate compound, which are reacted with a compound and extended 2 to 50 times.The urethane-modified polyester resin generally has a hydroxyl value of about 20 to about 100. A block polyisocyanate compound is one obtained by adding a blocking agent (active hydrogen compound) containing a hydroxyl group such as methanol, phenol, or catechol to a twin cyanate compound as exemplified in (1) above. The composition may be heated at a temperature above the dissociation temperature of the blocking agent of the blocked polyisocyanate compound (usually about 100°C).
When heated to above), the twin cyanate compound is regenerated and undergoes a crosslinking reaction with the urethane-modified polyester resin, resulting in curing. The elongation rate and stress at break of the cured film can be adjusted as desired by adjusting the composition, chain length, hydroxyl group content (ie, hydroxyl value) of the polyester resin, the amount of the block polyisocyanate compound, etc.

■ Styrene-butatsuene copolymer: Styrene 1-8
0% by weight, preferably 10-40% by weight and butatsuene 9
A copolymer obtained by copolymerization with 9 to 20% by weight, preferably 90 to 60% by weight; still styrene and butadiene, and about 1 to about 20% by weight based on the total amount of styrene and butadiene, such as vinylvirison. Examples include copolymers obtained by copolymerization.

These copolymers generally contain from about 10,000 to about so
Preferably, it has a number average molecular weight in the range of o, o o o.

Noboributatsuene: A resin whose main component is cis-1,4-,y-butaduene, and may also contain trans-1,4-bonds and vinyl bonding strength, and its number average molecular weight is approximately 10,0.
Suitably, the range is from 0.00 to about soo, ooo.

■ Acrylotrile-butadiene copolymer: 10-55% by weight of acrylonitrile, preferably 10-40% by weight and 90-45% by weight of butatsuene, preferably 90-8% by weight.
It is a copolymer obtained by copolymerization of 0% by weight, and if necessary, styrene, acrylic acid, methacrylic acid, vinylvirison, etc. as a third component is added at 0.5% by weight based on the total amount of acrylonitrile and butadiene.
Also included are copolymers with improved adhesion by copolymerizing up to 35% by weight. These copolymers are preferably 10,0
It can have a number average molecular weight in the range of 00 to soo, ooo.

■ Butyl rubber: A copolymer of inbutylene and a small amount (usually 1 to 10% by weight, based on the weight of the copolymer) of isoprene, with a number average molecular weight of about 10,000 to about so o, o o.
Preferably, it is within the range of o.

[Phase] The main component is an acrylic resin diacrylic acid ester and/or a methacrylic acid ester, and if necessary, a functional monomer such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, etc. and (t8 or) Other polymerizable unsaturated monomers include those obtained by polymerizing the nil monomer component. Examples of the acrylic esters include ethyl acrylate, propyl acrylate, n-butyl acrylate, 18o-butyl acrylate), 3-
01 to 1 of acrylic acids such as pentyl acrylate, hexyl acrylate, 2-hebutyl acrylate, octyl acrylate, 2-octyl acrylate, nonyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, and 2-ethylbutyl acrylate. Alkyl esters are particularly preferred; examples of methacrylic esters include R-termethacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate,
01 of methacrylic acids such as decyl methacrylate, lauryl methacrylate, and stearyl methacrylate. ~1
．． Alkyl esters are particularly preferred. The static glass transition temperature of the homopolymers derived from these acrylic esters and methacrylic esters exemplified here is 0°C, and one or more acrylic acids selected from these monomers Esters and methacrylic esters are suitable as monomers for forming the acrylic resin. The acrylic resin usually has 5.
000~1.000. It can have a number average molecular weight in the range OOO.

■ Furthermore, in addition to those exemplified in the above ■ ~ [phase], chloroprene rubber, chlorsulfone (41') ethylene, alkyl sobalides (e.g., ethylene dichloride, ethylene formal dichloride, propylene dichloride, etc.) and polysulfide silicon rubber (e.g. trimethyl silicone rubber, methyl phenyl silicon rubber, methyl vinyl silicon rubber, fluorinated alkyl methyl silicon rubber, cyanoalkyl silicon combnat), ethylene-propylene rubber,
Examples include propylene oxide rubber and epoxy resin-polyamide compositions.

Vehicle components used in the present invention include one or more selected from those exemplified in (■) to @ above, among which it is particularly preferable to use those selected from (3) to (3) and (◎) above. Particularly preferred. 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 may be any solvent capable of dissolving or dispersing the vehicle component selected from hydrocarbons (aliphatic, aromatic, alicyclic, etc.), alcohols, esters, ketones, ethers, etc. can be used.

The coating film formed by a barrier coat basically composed of the vehicle component and the organic solvent described above has an elongation rate (+2
0°C, tensile speed 20 min/min) is tSO 1 or more, preferably 180 to 1500%, more preferably 2oo to 85
0%, and the stress at break (+20℃, tensile speed 20M@/min) is 2okg/ff1 or more, preferably 30 to TOO bag/d1, more preferably 40 to 500
It is important to have characteristic values in the range kg/cr/l. This is because when the elongation rate becomes as small as 150 cm, the impact energy during chipping cannot be absorbed sufficiently. On the other hand, when the stress at break becomes as low as 20 klP/ci, the barrier 3 is damaged by the impact of pebbles during chipping. - This is because the electrodeposition coating film is easily damaged and the electrodeposition coating film is susceptible to impact peeling.

In addition, the values of the elongation rate and stress at break of the barrier coating film in this specification are +20 The values are measured at a tensile rate of 20 dew/min at After baking at 120°C for 30 minutes, it was isolated by 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 in barrieramicoat, but if it deviates from the above range or within the range. Even if there is a viscosity imparting agent, it is possible to add a viscosity imparting agent if necessary, such as when it is desired to finely adjust the elongation rate and/or the stress at break. As the viscosity imparting agent, a resin having good compatibility with the vehicle, such as rosin,
Petroleum resin (coumarone resin), ester gum, low molecular weight aliphatic epoxy resin, low molecular weight aliphatic bisphenol type epoxy resin, polyoxytetramethylene glycol, etc.
A range of 91 to 50 parts by weight is preferred. Also,
The barrier coat according to the present invention may further contain color pigments (e.g., titanium white, carbon black, etc.), extender pigments (e.g., asbestos, talc, clay, etc.), plasticizers (e.g., dioctyl phthalate, tricresyl, etc.). phosphate, diptyl sebacate, etc.), anti-sagging agents (for example, aluminum stearate, silica gel, etc.) can also be blended in appropriate amounts that are 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 can absorb the ultraviolet rays that pass through the top coat and prevent the barrier coating itself and the surface of the electrodeposition coating from deteriorating over time due to ultraviolet rays. .

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 one may be used as long as it does not lose its effectiveness. For example, benzophenone, 2,4-dihydroxybenzophenone, 2.2
', 4.4'-tetrahydroxybenzophenone, 2-
Hydroxy-4-methoxybenzophenone, 2,2'-
dihydroxy-4,4'-dimethoxybenzophenone,
2.2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2
-Hydroxy-4-dobutyloxybenzophenone, 2-
Hydroxy-4-methoxygosulfobenzophenone, S-chloro-2-hydroxybenzophenone, 2,
2'-dihydroxy-4,4'-dimethoxy-5-sulfobenzophenone, 2-hydroxy-4-methoxy-
2'-carboxybenzophenone, 2-hydroxy-4
Benzophenone UV absorbers such as -(2-hydroxy-3-methylacryloxy)propoxybenzophenone; 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-[2'-hydroxy-37
,5'-di(l,t-dimethylbenzyl)phenyl)
-2H-hensotriazole, 2-(2'-hydroxy-3/,5/-di-tert-butylphenyl)penztriazole, 2-(2'-hydroxy-3'-tt
trt-butyl-5'-methylphenyl)penztriazole, 2-(2'-hydroxy-3',5'-di-t
grt-amylphenyl)benzotriazole, 2-(
2'-Hydroxy-3'.

5'-tart-butylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroyac-3,5-diisoarξulfenyl)benzotriazole, 2-(2'
Benzotriazole UV absorbers such as -hydroxy-5'-tart-butylphenyl) benzotriazole; Phenyl salicylate; Salicylic acid ester UV absorbers such as 4-tert-butylphenyl salicylate and p-octyl phenyl salicylate; ethyl-
2-cyano-3,3/-diphenylacrylate, 2-
Ethylhexyl-2-7ano-3,3'-diphenyl-
Diphenylacrylate ultraviolet absorber such as acrylate; Hydroxy-5-methoxy-acetophenone, 2
-Hydroxy-naphthophenone, 2-ethoxyethyl-
p-methoxycinnamate, nickel-bisoctylphenyl sulfide, (2*2'-thiobis-(4-ta
rt-octylphenone)))-n-butylamine-nickel, oxalic acid anilide UV absorbers, etc. Commercially available benzotriazole UV absorbers include Tinuvin 900, Tinuvin 328, etc.
Pentupheno (CIEA-Gttigy), Pentupheno, Evinur 40 (BASF) as an oxalic acid anilide UV absorber, and Sajid 3206 (Sandbore) as an oxalic acid anilide UV absorber.

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

In addition, as a light stabilizer, for example, tetrakis (2e 2
# s t 6-tetramethyl-4-piperidyl)-
1,2,3,4-butanetetracarboxylate, 8-
Acetyl-3-dodecyl-7,7゜9.9-nato2methyl-1.3.8-triazaspiro(4t5)decane-2
,4-dione, bis-(1t 2 t 2 # s t
s-pentamethyl-4-piperidinyl) sebacate,
Bis-(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1@2# 214G t 6
-bentamethyl-4-piperidyl) sebacate, dimethyl-2-(4-hydroxy-2,2,6,6-titramethyl-1-piperidyl) ethanol condensate, ho! J (
s -(1,1,3,3-tetramethylbutyl)imino-1,3,5-)diazine-2,4-diyl-4-(2
12t s t s-tetramethylpiperidyl)hexamethylene-4,4-(2,2,6,6-tetramethylpiperidyl)imine), 1-(2-3-(3,5-di-t
art-butyl-4-hydroxyphenyl)-4-(a-(at5-di-tert)
-butyl-4-hydroxyphenyl)propionyloxy) -2$2t6.6-titramethylbiperidine, and examples of antioxidants include 4,4
/-thiobis-(3-methyl-6-tart-butyA/
7 z-nor), 2.2'-methylenebis-(4-methyl-6-tart-butylphenol), 4.4'-
Methylenebis-(2,6-tert-butylphenol), 1゜3,5-)listyl-2t 4t 6
-) Squirrel-(3°5-C jgrt-7'chill-4-
hydroxybenzyl)benzene, tris-(2-methyl-4-hydroxy-5-tert-butylneal)-butane, pentaerythritol-tetrakis-(3-laurylthioglobionate), dilaurylthiodipropionate, dilaurylthio Dipropionate, Similystylthiodipropionate, Triethylene glycol-bis-5-(3-tert-butyl-5-methyl-4-hydroxyphenyl)dipropionate, 1,6-hexanediol-bis-3-(3, 5-di-tert-butyl-4-hydroxyphenyl)-propionate, 2.
4-bis-(n-octylthio)-s-(4-hydroxy-3,5-di-tg-de-t-butylanilino)-1*3
*5-triazine, pe/taerythrityl-tetrakis-(3-(3,s-di-tert-butyl-4-hydroxyphenyl)-propionate), 2,2-thio-diethylenebis-(3-(3,5 -di-tart-butyl-4-hydroxyphenyl)-propionate], octadecyl-5-(3°5-di-tart-7'thi-4-
hydroxyphenyl)propionate, 2,2-thiobis-(4-methyl-6-tart-butylphenol)
,N.

Examples include N'hexamethylene bis-(3,5-di-tart-blue 4-hydroxynnamamide). It is preferable to use these in combination with the ultraviolet absorber, and the amount of the light stabilizer is α1 to 10 parts by weight, preferably 0.5 to 3 parts by weight, per 100 parts by weight of the resin for billier coating.
Suitable parts by weight of the antioxidant are 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight.

Furthermore, the coating film formed by the barrier coat is
It is also an important factor that the adhesive has excellent adhesion to the electrodeposition coating and the topcoat (sb) described later, and it is desirable that the adhesion to each coating be at least 25 kg/cI/I. Here, adhesion is the energy (kg/d) required to stick an attachment to a barrier coated surface applied to an electrodeposited surface or a surface coated with an additional top coat, and to peel off the attachment using a tensile strength measuring device. be.

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 5n. The power required to peel the attachment in the vertical direction from each coating film at 20° C. and at a rate of 50 strokes/min. (kP/d).

Adjustment of the above-mentioned characteristic values of the barrier coating film is mainly carried out by selecting the type and composition of the vehicle component, but it is also possible by adding a viscosity imparting agent, blending pigments, etc.

In the present invention, the barrier coat can be applied either after the electrodeposition coating has been cured by heating or in an uncured state, preferably after the electrodeposition coating has been cured in advance. The coating method is not particularly limited, and for example, spray coating, 71 coating, dipping coating, electrostatic coating, etc. can be used, and the coating film thickness is 1 to 20μ, especially 5 to 10μ, based on the formed coating. It is preferable to do so.

When applying the top coat to the barrier coat coating surface, it is preferable to bake the barrier coat in advance, but it is also possible to apply the top coat wet-on-wet without baking. Baking temperature is generally 80-160'C.

A temperature range of 80 to 140°C is particularly suitable.

101 Application Above - Barrier Coat As the thermosetting liquid top coating paint to be applied to the coated surface, one that imparts cosmetic properties to the object to be coated is used. Specifically, the finished appearance (sharpness, smoothness, gloss, etc.), weather resistance (gloss retention, color retention, chalking resistance, etc.), chemical resistance, water resistance, moisture resistance, hardenability, etc. Any thermosetting liquid topcoat known per se that forms a coating film with excellent properties can be used. Examples include liquid topcoat paints. The form of these paints is not particularly limited, and any form such as an organic bath liquid type, a non-aqueous dispersion type, an aqueous (dispersion) liquid foam, and a high solid type can be used.

The top coating used in the present invention may be either an enamel paint in which a metallic pigment and/or a colored pigment is blended into a paint whose main component is the vehicle described above, or a clear paint that does not contain any or almost any of these pigments. It may be of.

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

■ A method of applying metallic paint or solid color paint, heating and hardening it, then applying clear paint and heating and hardening it again (metallic or solid color finish using 2-coat, 2-bake method).

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

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

The topcoat film formed on the barrier coat film surface according to the method of the present invention has an elongation rate of 40% after curing.
Below, preferably 5 to 30 inches, more preferably 5 to 2 inches
sb in the range of 0, and the stress at break is 300Kf/c
d or more, preferably 350 to 1000 KIi/cit,
More preferably, it is important that the elongation is in the range of 450 to 900 4/cIi.1 If the elongation rate is greater than 40%, it is generally not suitable for use as a coating film for car body exterior panels in terms of coating hardness and solvent resistance. It is insufficient, and the stress at break is 300Kp/cd.
If the thickness becomes smaller, sufficient improvement in chipping resistance cannot be expected.

The elongation rate and stress at break of the topcoat 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 vehicle components by using aromatic acids such as 7-thalic acid, inphthalic acid, terephthalic acid, trimellitic acid, or their anhydrides as polybasic acids. When using a top coating whose vehicle component is 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 a catalyst (
By appropriately controlling the amount and type of the internal or external catalyst and/or the type and amount of the crosslinking agent (or curing agent), the three-dimensional coating film formed using the vehicle component can be It is also possible to adjust physical properties such as crosslink density, ie elongation and stress at break.

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 sample of these paints, and measuring the elongation rate and stress at break using the method described above. From this information, it is possible to select a paint that is compatible with the method of the present invention.

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

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

1. Preparation of sample (1) Steel material: A steel plate (size 300 x 90 x cL 81 m) chemically treated with Bonderitetona 3030 (manufactured by Nippon Parkerizing °C Co., Ltd., zinc phosphate metal surface treatment agent).

(2) Coating paint: (a) Cationic electrodeposition paint: Elekronna 9200
(Manufactured by Kansai Paint Co., Ltd., epoxy polyamide cationic electrodeposition paint, gray color).

(3) Anionic electrodeposition paint: Elekronna 7200 (
Kansai Paint Co., Ltd., polybutadiene-based anionic electrodeposition paint).

(3) (i-barrier coat: (2) Vinyl acetate-ethylene copolymer (number average molecular weight:
Approximately 10:000, elongation rate: 700%, break point: 120%/a! )' organic solvent [toluene] bath solution.

(c) Pylon 300 (manufactured by Toyobo M Co., Ltd., thermoplastic high molecular weight linear saturation, 1? Reester resin; elongation rate 28
Organic solvent [toluene/
Methyl ethyl ketone (8/2))? ! [.

(0 Elastolan E390 (Nippon Elasto 221 Co., Ltd.), thermoplastic polyurethane elastomer; elongation rate: 5
Organic solvent (tetrahydrofuran) solution μ HYCARCT
BN 1300x13 (manufactured by Ube Industries, Ltd., carboxyl group-containing butadiene-acrylonitrile copolymer)
and Epicor) 828 (Shell Chemical Co., Ltd.,!!!,
Mixed system with epoxy resin (epoxy resin)
50 Ky/cry.

Elongation rate: 400 inches).

(6) Thermosetting polyester resin composition adipic acid, 1
．． Urethane-modified polyester resin (hydroxyl value: about 80, molecular weight: about 6) made by reacting hexamethylene diisocyanate with a low molecular weight polyester (molecular weight: about 800) consisting of 6-hexanediol and trimethylolpropane.
000) and a blocked incyanate compound obtained by blocking hexamethylene diisocyanate with phenol (the breaking point of the formed coating film is approximately 300 K).
f/d, elongation rate: approximately 250 inches).

(0 Acrylic resin ethyl acrylate and hexyl acrylate and a small amount of acrylic acid and hydroxyethyl acrylate copolymer (number average molecular weight: about 25,000) organic solvent (
toluene/xylene) solution (rupture of formed coating film)
100 K9/c! 1. Elongation rate: 600 inches).

(5) Thermosetting polyester resin composition Short wave polyester resin (oil length: 2i, hydroxyl value 280,
An organic solvent (toluene) of a composition consisting of acid value: 10) and 1-tanol-modified methylated melamine resin.
0chi).

(c) Thermosetting polyester resin Short wave polyester resin (oil length: 20, hydroxyl value: j2
An organic solvent (toluene) solution of a composition consisting of a melamine resin modified with 0.9 (valence: 15) and a butanol-modified melamine resin (rupture anaphora of formed membrane 11/c!/l, elongation rate: 250 inches).

(4) Top coating: (a) Acrylic resin-based color paint Copolymer consisting of isobutyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate and hydroxyethyl acrylate (number average molecular t: about 20,
000. Hydroxyl value: 120) A liquid paint for solid color finishing made of a vehicle component consisting of 75% by weight of glylated melamine resin, an organic solvent (toluene), and a titanium white pigment. 65
oh/crl, elongation rate = 10%).

(b) Acrylic resin-based metallic paint Copolymer consisting of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and hydroxyethyl methacrylate (number average molecular weight: approximately 30.OU
Organic m-liquid metallic paint made by adding aluminum powder paste to a vehicle component consisting of 75% by weight of O1 hydroxyl value: 110) and 25% by weight of butylated melamine resin (breakage of formed coating film 500 K9/cWt,
Elongation rate = 5 inches).

First acrylic resin-based clear paint Copolymer consisting of ethyl methacrylate, isobutyl methacrylate, styrene and hydroxyethyl acrylate (number average molecular weight: approx. 15.

00, hydroxyl value: 100) 70% by weight and butylated melamine (30% by weight). ).

the above! Using the sample prepared above, a barrier coat of electrodeposition paint and a top coat of paint were applied to the steel material 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°G, H6.5, load voltage approximately 250V,
Power on for 180 seconds.

Anion-wi coating conditions: Bath solid content l [12% by weight, bath temperature 30°C, 7) H7,8, load voltage approximately 200V, 1
Power on for 80 seconds.

In all of the above cases, wash with water after electrodeposition coating. 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.

The top coat was sprayed using an electrostatic coating machine.

In topcoat painting, ``ICIBJ is a coating system in which topcoat paint A is applied and then baked at 150℃ for 30 minutes.
201B" is a system in which top coats B and C are layered wet-on-wet, and then baked at 140° C. for 30 minutes to cure both coats.

A coating film performance test was conducted using the coated plates coated in the above Examples and Comparative Examples.
Shown in the table.

〔Test method〕

(*1) Chipping resistance: ■ Test equipment: Q-G-R Graperometer (product of Q.9nel company) ■ Stone to be sprayed: Crushed stone with a diameter of approximately 15 to 20 ML/m ■ Capacity of stone to be sprayed : Approximately 5001 Rt■ Spraying with air pressure of approximately 4Kg/d■ Temperature during test: Approximately 20℃ The test piece was attached to a test piece holding stand, and approximately 4Kf/cd of air pressure was applied to crush approximately 500-kg of crushed stone into the test piece. After firing, the coated surface condition and salt spray resistance were evaluated.

The condition of the painted surface was visually observed and evaluated using the following criteria. For salt spray resistance, test pieces were subjected to a salt spray test for 840 hours according to JIS Z2371, and then adhesive cellophane tape was attached to the painted surface and rapidly peeled off. Afterward, check for rust, corrosion, and peeling of the paint from the impacted area.

■ Coated surface condition ◎ (good): Only a few scratches due to impact are observed on a portion of the top coat, and no peeling of the electrodeposition coating is observed.

Δ (slightly poor): Many scratches due to impact were observed on the top coat, and peeling of the electrodeposited film 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 water spray resistance ◎:・Rust, corrosion, paint film scratches, etc. are not observed.

○: Rust, corrosion, and paint film... slight scratches are observed.

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

×: Significant rust, corrosion, and paint film scratches occurred.

(*2) Impact resistance: JIS f5400-1979 6. 13. 3B
The test is carried out in an atmosphere at 0°C in accordance with the law.

A weight weighing 500 g is dropped from a height of 50 cIN to examine damage to the paint film.

(*5) Adhesion: According to Its f5400-1979 6.15, 100 gopans of size 1a+X1m+ are made on the coating film.
Adhesive Serono Ntegu is applied to the surface, and the coated surface is evaluated after it is rapidly peeled off.

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

Claims (1)

[Claims] Electrodeposition paint is applied to steel material, and the coated surface has a tensile strength elongation rate of 150% or more and a stress at break of 20 kg/cm.
Apply an organic solvent-based paint capable of forming a coating film having a tensile strength at break of 40% or less and a stress at break of 300 kg/cm^2 or more. A method for forming a coating film characterized by applying a thermosetting liquid top coat.