JP2004298838A - Method for forming multi-layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving cleanability of an intermediate coat in a three-coat one-bake coating method as shown in Fig. <P>SOLUTION: The method for forming multi-layer coating films by successively applying a water-base intermediate coat (1), a water-base base coat and a clear coat (3), wet on wet, on a base material formed with an electrodeposition coating film and simultaneously baking and curing the obtained multi-layer coating films, in which the water-base intermediate coat (1) contains, as a part a diluting medium, a hydrophilic organic solvent having a boiling point ≥80 to ≤250°C in 2 to 10wt% of the total weight of the coating material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

除去性は塗膜の除去面積［％］で表す。
＊１： プロピレングリコール３ｗｔ％とプロピレングリコールメチルエーテル２ｗｔ％。
＊２： 原料からの持ち込みの有機溶剤量。
【００７７】
上記実施例と比較例の比較から明らかなように、親水性有機溶剤を特定量含む水性中塗り塗料を用いた塗膜は、乾燥後でも除去性が優れている。特に、３分間の除去剤に浸漬したものおよび２分間超音波洗浄後の除去性は、親水性有機溶剤を特定量配合していない比較例１のものと比べて、非常に優れている。
【００７８】
複層塗膜の形成例
リン酸亜鉛処理したダル鋼板に、パワートップＵ−５０（日本ペイント社製カチオン電着塗料、商品名）を、乾燥塗膜が２０μｍとなるように電着塗装し、１６０℃で３０分間の加熱硬化後冷却して、鋼板基板を準備した。
【００７９】
得られた基板に、上記実施例１の水性中塗り塗料をエアースプレー塗装にて２０μｍ塗装し、８０℃で５分プレヒートを行った後、アクアレックスＡＲ−２０００シルバーメタリック（日本ペイント社製水性メタリックベース塗料、商品名）をエアースプレー塗装にて１０μｍ塗装し、８０℃で３分プレヒートを行った。更に、その塗板にクリヤー塗料として、マックフロー Ｏ−１８００Ｗ−２クリヤー（日本ペイント社製酸エポキシ硬化型クリヤー塗料、商品名）をエアースプレー塗装にて３５μｍ塗装した後、１４０℃で３０分間の加熱硬化を行い、試験片を得た。
【００８０】
加熱硬化後に得られた複層塗膜は、仕上がり外観に優れ良好なものであった。
【００８１】
水性ベース塗料とクリヤー塗料の希釈条件は次のとおりであった。
・水性ベース塗料
シンナー：イオン交換水
４５秒／ＮＯ．４フォードカップ／２０℃
・クリヤー塗料
シンナー：ＥＥＰ（エトキシエチルプロピオネート）／Ｓ−１５０（エクソン社製芳香族系炭化水素溶剤、商品名）＝１／１（重量比）の混合溶剤
３０秒／ＮＯ．４フォードカップ／２０℃
【００８２】
上記塗装実験から明らかなように、水性中塗り塗料に親水性有機溶剤を特定量配合したものを用いても、塗装性能に全く変化が無く、良好な塗膜がえられる。
【図面の簡単な説明】
【図１】本発明の塗膜形成工程を示す工程図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a multi-layer coating film, and more particularly to a method for forming a multi-layer coating film in which an aqueous intermediate coating, an aqueous base coating, and a clear coating are applied in a wet-on-wet manner and then baked and cured at a time.
[0002]
[Prior art]
A plurality of coating films having various functions are formed on the surface of a base material of an automobile or the like to protect the base material and give a beautiful appearance. However, in recent years, from the viewpoint of global environmental problems and resource saving, the use of water-based paints in which part or all of the organic solvent used in the paints is replaced with water has been widely adopted. At the same time, instead of baking and curing multiple layers of coatings one by one, paint without curing multiple layers, so-called wet-on-wet painting and baking at once after forming several layers Curing methods are also being adopted.
[0003]
Under such circumstances, among the currently proposed coating methods, an intermediate coating, a base coating, and a clear coating are applied in a wet-on-wet manner after the electrodeposition coating film is cured as shown in FIG. Three-coat one-bake coating (also called three-wet-on coating), in which an uncured coating film is baked and cured at one time, is considered to be the most feasible method.
[0004]
Also in this three-coat one-bake coating method, the water-based paint is progressing, and a water-based paint for the base paint and the intermediate paint has been proposed. One of the problems to be noticed when actually making the water-based paint is low washability of the water-based paint. The coating film forming component used in the paint is basically composed mainly of a polymer and inherently exhibits high solubility in an organic solvent. Therefore, when an organic solvent-based paint is used, the paint adhered to the coating gun or the non-painted portion used for spray coating can be easily cleaned by using an organic solvent, and the detergency is of little importance. Did not.
[0005]
However, since the water-based paint is originally a polymer material having low solubility in water forcibly dispersed in an aqueous medium, when the aqueous medium volatilizes, only the polymer component having low solubility in the aqueous medium remains. Will be. The portion where only the polymer component remains, which is considered to be the stain adhered to the unpainted portion, cannot be dissolved or removed even by using an aqueous medium. Therefore, when a water-based paint is used, it is necessary to take its washing property into consideration.
[0006]
Patent Document 1 listed below recognizes the problems associated with the water-based paint, and proposes a method of cleaning and removing the water-based paint attached to the coating line. I have. Although this method is often effective, it has been found that it is not necessarily effective in all aqueous coating systems.
[0007]
The paint that can be made water-based by the coating method shown in FIG. 1 is only the base paint, and the water-based coating of the intermediate coating has been proposed in the patent literature (for example, Patent Literature 2). There is a difficult problem.
[0008]
After applying the aqueous intermediate coating, a slight drying step, for example, a preheating step, is applied to the aqueous base coating, but the intermediate coating is slowly dried, and the aqueous base coating layer formed thereon is formed. It is necessary to make the surface hydrophobic so as not to cause a mixed layer. That is, it is necessary to select a material whose hydrophobicity is rapidly increased. However, as a result, on the contrary, once the paint has adhered, the washing property using the aqueous medium is greatly deteriorated in washability. Even with the cleaning described in Patent Literature 1, it may not always be possible to perform sufficient cleaning.
[0009]
[Patent Document 1]
JP 2000-290544 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 4-284881
[Problems to be solved by the invention]
An object of the present invention is to provide a method for improving the washability of an intermediate coating in a three-coat one-bake coating method as shown in FIG.
[0011]
[Means for Solving the Problems]
That is, in the present invention, an aqueous intermediate coating material (1), an aqueous base coating material (2), and a clear coating material (3) are sequentially applied on a substrate on which an electrodeposition coating film is formed by wet-on-wet. In the method for forming a multilayer coating film, in which the multilayer coating film is simultaneously baked and cured, the aqueous intermediate coating composition (1) comprises, as a part of a dilution medium, a hydrophilic organic solvent having a boiling point of 80 ° C. or more and less than 250 ° C. Provided is a method for forming a multi-layer coating film, which is contained in an amount of 2 to 10% by weight based on the total weight of the coating composition.
[0012]
By blending the above-mentioned hydrophilic organic solvent in the aqueous intermediate coating composition, the aqueous intermediate coating composition exhibits high detergency, particularly high cleaning properties for a commonly used cleaning agent for aqueous coating compositions. Therefore, when used in a three-coat one-bake waterborne intermediate coating material in which low detergency is a problem, detergency is improved, and problems encountered during implementation can be greatly improved.
[0013]
The hydrophilic organic solvent has the general formula R ¹ —OH
(Wherein, R ¹ represents a linear or branched alkyl group having 3 to 8 carbon atoms).
[0014]
Wherein the hydrophilic organic solvent, the general formula ^HO- (R 2 _-O) n -H
(Wherein, R ² represents a linear or branched alkyl group having 2 to 8 carbon atoms, and n represents an integer of 1 to 6).
[0015]
Further, the hydrophilic organic solvent has a general formula of R ³ O— (R ⁴ —O) _m —R ⁵
(Wherein, R ⁴ represents a linear or branched alkyl group having 1 to 8 carbon atoms, and R ³ and R ⁵ each represent hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms. (Where R ³ and R ⁵ are not both hydrogen), and m represents an integer of 1 to 6).
[0016]
The hydrophilic organic solvent may be a combination of two or more of the above hydrophilic organic solvents.
[0017]
Preferred examples of the hydrophilic organic solvent include isopropyl alcohol, propylene glycol, propylene glycol monomethyl ether, and the like.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Aqueous intermediate coating In the coating film forming method of the present invention, the intermediate coating is used for concealing base defects and ensuring surface smoothness (appearance improvement) after top coating. The aqueous intermediate coating composition contains various organic and inorganic coloring pigments, extender pigments, a film-forming resin, a curing agent, and the like.
[0019]
Examples of the coloring pigment used in the aqueous intermediate coating material include, for example, organic azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxazine pigments, Quinacridone pigments, isoindolinone pigments, metal complex pigments, etc., inorganic graphite, yellow iron oxide, red iron oxide, carbon black, titanium dioxide, etc., and extender pigments such as calcium carbonate, barium sulfate, clay, talc, etc. Is used. For example, those described in the above base paint are used. Further, flat pigments such as aluminum powder and graphite powder may be added.
[0020]
As a standard, a gray intermediate paint containing carbon black and titanium dioxide as main pigments is used. Further, a so-called color intermediate coating which is a combination of set gray and various color pigments may be used.
[0021]
The film-forming resin used for the intermediate coating is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, an alkyd resin, and a fluorine-based resin. As the curing agent, an amino resin and / or a blocked polyisocyanate compound is used. From the viewpoint of pigment dispersibility or workability, a combination of an alkyd resin and / or a polyester resin with an amino resin is preferable. These preferred solid contents in the coating material are in the range of 30 to 70% by weight at the time of production and 10 to 50% by weight at the time of application. The dry film thickness of the coating film formed by coating is preferably 10 to 30 μm.
[0022]
The aqueous intermediate paint may be, in particular, an aqueous intermediate paint containing a resin emulsion and a curing agent. The resin emulsion preferably has a glass transition temperature of −50 to 20 ° C., an acid value of 2 to 60 mg KOH / g and a hydroxyl value of 10 to 120 mg KOH / g. The curing agent in the case of the aqueous intermediate coating composition may be at least one selected from the group consisting of a melamine resin, an isocyanate resin, an oxazoline compound and a carbodiimide compound.
[0023]
The resin emulsion may be a copolymer emulsion, and can be obtained by emulsion polymerization of an acid group-containing polymerizable monomer, a hydroxyl group-containing monomer, a crosslinkable monomer, and another polymerizable monomer. Each monomer is known.
[0024]
In the copolymer resin emulsion of the present invention, the copolymer resin obtained from each of the monomer components has a glass transition temperature of −50 to 20 ° C., an acid value of 2 to 60 mg KOH / g, and a hydroxyl value of the resin of 10 to 120 mg KOH. / G is selected for the type and amount of each monomer component.
[0025]
The glass transition temperature (Tg) of the copolymer resin is in the range of −50 to 20 ° C. By setting the Tg of the resin in this range, when an aqueous intermediate coating containing a copolymer resin emulsion is used in a wet-on-wet method, the affinity and adhesion to the undercoat and the topcoat are improved, and the wet coating is improved. Good compatibility at the interface with both upper and lower coatings in the state, and no reversal occurs. In addition, appropriate flexibility of the finally obtained coating film is obtained, and chipping resistance is enhanced. As a result, a multilayer coating film having a very high appearance can be formed. If the Tg of the resin is lower than -50 ° C, the mechanical strength of the coating film is insufficient, and the chipping resistance is weak. On the other hand, if the Tg of the resin exceeds 20 ° C., the coating film is hard and brittle, and thus lacks impact resistance and weakens chipping resistance. Therefore, the Tg of the resin is preferably from -40 to 10C, more preferably from -30 to 0C.
[0026]
The acid value of the copolymer resin is 2 to 60 mgKOH / g. By setting the acid value of the resin in this range, storage stability, mechanical stability, stability against freezing and the like of the resin emulsion and the aqueous intermediate coating composition using the same are improved, and A sufficient curing reaction with a curing agent such as a melamine resin at the time of forming a coating film occurs sufficiently, and the strength, chipping resistance and water resistance of the coating film are improved. When the acid value of the resin is less than 2 mgKOH / g, the above-mentioned various stability is poor, and a curing reaction with a curing agent such as a melamine resin is not sufficiently performed, so that various strengths, chipping resistance and water resistance of the coating film are poor. On the other hand, when the acid value of the resin exceeds 60 mgKOH / g, the polymerization stability of the resin is deteriorated, the above-mentioned various stability is adversely deteriorated, and the water resistance of the obtained coating film is deteriorated. Therefore, the acid value of the resin is 2 to 60 mgKOH / g, preferably 5 to 50 mgKOH / g.
[0027]
The hydroxyl value of the copolymer resin is 10 to 120 mgKOH / g. By setting the hydroxyl value of the resin in this range, the resin has an appropriate hydrophilicity, and when used as a coating composition containing a resin emulsion, the workability and stability against freezing are increased, and a melamine resin or an isocyanate-based resin is used. The curing reactivity with the curing agent is also sufficient. When the hydroxyl value is less than 10 mgKOH / g, the curing reaction with the curing agent is insufficient, the mechanical properties of the coating film are weak, the chipping resistance is poor, and the water resistance and the solvent resistance are poor. On the other hand, when the hydroxyl value exceeds 120 mgKOH / g, on the contrary, the water resistance of the obtained coating film is reduced, or the compatibility with the curing agent is poor, and the coating film is distorted, and the curing reaction occurs unevenly. As a result, various strengths of the coating film, particularly, chipping resistance, solvent resistance and water resistance are inferior. Therefore, the hydroxyl value of the resin is 10 to 120 mgKOH / g, preferably 20 to 100 mgKOH / g.
[0028]
The weight average molecular weight of the copolymer resin emulsion is not particularly limited, but is generally about 50,000 to 1,000,000, for example, about 100,000 to 800,000.
[0029]
The curing agent is not particularly limited as long as it causes a curing reaction with the copolymer resin and can be blended into the aqueous intermediate coating composition, and includes, for example, a melamine resin, an isocyanate resin, an oxazoline-based compound or a carbodiimide. And the like. One or more of these may be used in combination as appropriate.
[0030]
The melamine resin is not particularly limited, and those usually used as a curing agent can be used. For example, an alkyletherified melamine resin that is alkyletherified is preferable, and a melamine resin substituted with a methoxy group and / or a butoxy group is more preferable. Such melamine resins include Cymel 325, Cymel 327, Cymel 370, Mycoat 723; Cymel 202, Cymel 204, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 254, Cymel 266, Cymel 267 (all Mycoat 506 (trade name, manufactured by Mitsui Cytec), U-Van 20N60, U-van 20SE (all trade names, manufactured by Mitsui Chemicals), and the like. These may be used alone or in combination of two or more. Of these, Cymel 325, Cymel 327, and Mycoat 723 are more preferred.
[0031]
The isocyanate resin is obtained by blocking a diisocyanate compound with a suitable blocking agent.
[0032]
The oxazoline-based compound is preferably a compound having two or more 2-oxazoline groups.
[0033]
As the carbodiimide compound, those produced by various methods can be used. Basically, those obtained by synthesizing an isocyanate-terminated polycarbodiimide by a condensation reaction involving decarbonation of an organic diisocyanate can be used. Can be. More specifically, in the production of a polycarbodiimide compound, a polycarbodiimide compound having at least two isocyanate groups in one molecule and a polyol having a hydroxyl group at a molecular terminal are mixed with a molar amount of the isocyanate group of the polycarbodiimide compound. Are reacted at a ratio exceeding the molar amount of the hydroxyl group of the polyol, and the step of reacting the reaction product obtained in the above step with a hydrophilizing agent having an active hydrogen and a hydrophilic portion is performed. Modified carbodiimide compounds are preferred.
[0034]
The above-mentioned curing agent is a lower limit of 2% by weight, an upper limit of 50% by weight, preferably a lower limit of 4% by weight, an upper limit of 40% by weight, and more preferably a lower limit of 5% by weight based on the total amount of the solid content of the curing agent and the copolymer resin emulsion. %, The upper limit being 30% by weight. If it is less than 2% by weight, the water resistance of the resulting coating film tends to decrease. On the other hand, when the content exceeds 50% by weight, the chipping property of the obtained coating film tends to decrease.
[0035]
The method for producing the aqueous intermediate coating composition of the present invention is not particularly limited, and any method known to those skilled in the art can be used. The form of the aqueous intermediate coating composition of the present invention is not particularly limited as long as it is aqueous, and examples thereof include water-soluble, water-dispersible, and aqueous emulsion forms.
[0036]
In the present invention, a hydrophilic organic solvent having a boiling point of 80 ° C. or higher and lower than 250 ° C. is contained as a part of the aqueous dilution medium in an amount of 2 to 10% by weight based on the total weight of the coating composition. By blending such a hydrophilic organic solvent in the aqueous intermediate coating composition, the composition exhibits high detergency, particularly high detergency against an alkaline aqueous solution generally used as a detergent for aqueous coating compositions. Therefore, even when using the three-coat one-bake coating method of applying the aqueous intermediate coating, the aqueous base coating and the clear coating wet-on-wet, low detergency associated with the aqueous intermediate coating, that is, the aqueous base coating In order to prevent the mixed layer of the intermediate paint, the tendency of the washability of the intermediate coating material to decrease is improved, and the problems encountered during the operation are eliminated.
[0037]
As used herein, "hydrophilic organic solvent" means an organic solvent that dissolves in water at a temperature of 20 ° C without any limitation. In the present invention, the hydrophilic organic solvent has a boiling point of 80 ° C. or more and less than 250 ° C., particularly 80 to 170 ° C. If the boiling point is lower than 80 ° C., a large amount will be volatilized when the intermediate coating film is dried, and the performance due to the presence cannot be exhibited. A boiling point of 250 ° C. or more is not preferable because it remains in the coating film even during baking and curing.
[0038]
A hydrophilic organic solvent is used as part of the aqueous diluent medium. As a water-based paint, water forms the main component of the dilution medium. The weight ratio of water (ion-exchanged water) to the hydrophilic solvent (water / hydrophilic organic solvent) is from 40/1 to 5/1, preferably from 20/1 to 10/1. When it is lower than 40/1, it has disadvantages such as a decrease in the storage stability of the paint, and when it is more than 10/1, it exhibits defects such as an increase in the amount of the solvent (VOC) volatilized in the air.
[0039]
Specific examples of the hydrophilic organic solvent include alcohols, glycols, glycol ethers, and mixtures thereof. Examples of alcohols include those represented by the general formula R ¹ —OH
(In the formula, R ¹ represents a linear or branched alkyl group having 3 to 8 carbon atoms.) More specifically, propyl alcohol, isopropyl alcohol, butanol, pentanol and the like can be mentioned.
[0040]
Specific examples of glycols of general formula ^HO- (R 2 _-O) n -H
(Wherein, R ² represents a linear or branched alkyl group having 2 to 8 carbon atoms, and n represents an integer of 1 to 6). More specifically, examples include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, and tripropylene glycol.
[0041]
Examples of glycol ethers of the general formula _{^{R 3 O- (R 4 -O)}} m -R 5
(Wherein, R ⁴ represents a linear or branched alkyl group having 1 to 8 carbon atoms, and R ³ and R ⁵ each represent hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms. (Wherein, R ³ and R ⁵ are not both hydrogen), and m represents an integer of 1 to 6). More specifically, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol mono n-propyl ether, ethylene Glycol dimethyl ether, ethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, propylene glycol di-n-propyl ether are exemplified.
[0042]
Preferred examples of the hydrophilic organic solvent used in the present invention include isopropyl alcohol, propylene glycol, propylene glycol monomethyl ether and the like. Two or more hydrophilic organic solvents may be used in combination.
[0043]
Substrate The method of forming a multilayer coating film of the present invention can be advantageously used for various substrates, such as wood, metal, glass, cloth, plastic, foam and the like, particularly metal surfaces, and castings. However, it can be used particularly preferably for metal products that can be subjected to cationic electrodeposition coating.
[0044]
Examples of the metal product include iron, copper, aluminum, tin, zinc, and the like, and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. It is particularly preferable that these metals have been previously subjected to a chemical conversion treatment with a phosphate, a chromate or the like.
[0045]
Electrodeposited film An electrodeposited film is formed on a substrate by using a cationic electrodeposition paint. The cationic electrodeposition paint used in the present invention is not particularly limited, and a known one can be used. The cationic electrodeposition paint contains a cationic base resin and a curing agent.
[0046]
The cationic base resin is not particularly limited, and examples thereof include amine-modified epoxy resin systems described in JP-B-54-4978 and JP-B-56-34186, and those described in JP-B-55-115476. Amine-modified polyurethane polyol resin system, amine-modified polybutadiene resin system described in JP-B-62-61077, JP-A-63-86766, etc., JP-A-63-139909, JP-B-1-60516 And the like, and an amine-modified acrylic resin described in JP-A-6-128351 and a sulfonium group-containing resin described in JP-A-6-128351. In addition to those described in the above-mentioned references, resinous systems containing a phosphonium group can also be used. Among the above cationic base resins, it is particularly preferable to use an amine-modified epoxy resin system.
[0047]
Examples of the curing agent include, but are not limited to, an amino resin and a blocked polyisocyanate compound.
[0048]
In the present invention, the electrodeposition coating film is cured by heating. The heat curing of the electrodeposition coating film can be performed under general conditions. For example, the heat treatment may be performed at 160 to 200 ° C. for 20 to 40 minutes.
[0049]
In the method of the present invention, an intermediate coating, a base coating, and a clear coating are sequentially formed on the cured electrodeposition coating film on a wet-on-wet basis. The paint for forming each coating film will be described below, and the coating method will be described at the end.
[0050]
Aqueous base coating In the method for forming a multilayer coating of the present invention, an aqueous base coating is used to form a base coating. The aqueous base paint contains a coloring pigment, a film-forming resin, a curing agent, and the like.
[0051]
As the color pigment contained in the base paint, various organic and inorganic color pigments and extenders used in the intermediate paint can be effectively used.
[0052]
As the film-forming resin and curing agent of the base paint used in the method for forming a multilayer coating film of the present invention, for example, a film-forming resin such as an acrylic resin, a polyester resin, an alkyd resin, a fluorine-based resin, and an amino resin And / or a curing agent such as a blocked polyisocyanate compound is used. These preferred solid contents in the coating material are in the range of 30 to 70% by weight at the time of production and 10 to 50% by weight at the time of application. The dry film thickness of the coating film formed by coating is preferably 10 to 30 μm.
[0053]
In the present invention, the water-based base coating material may contain other additives, if desired. Such additives include, for example, surface conditioners such as silicones and organic polymers, UV absorbers, hindered amines, hindered phenols, and the like.
[0054]
The total pigment concentration (PWC) in the paint including all the pigments is 3 to 70%, preferably 4 to 65%, and more preferably 5 to 60%. If it exceeds the upper limit, the appearance of the coating film will be reduced.
[0055]
The aqueous base coating used in the present invention may generally be any of water-soluble, water-dispersible, and emulsion.
[0056]
Clear paint In the method for forming a multilayer paint film of the present invention, a clear paint is used for forming the clear paint film. This clear paint contains a film-forming resin, a curing agent, and the like. The film-forming resin is not particularly limited, and a film-forming resin such as an acrylic resin, a polyester resin, an epoxy resin, or a urethane resin can be used, and these are an amino resin and / or a block resin. Used in combination with a curing agent such as an isocyanate resin. From the viewpoint of transparency or acid etching resistance, a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system is exemplified.
[0057]
The solid content in the clear coating is 20 to 60% by weight, preferably 35 to 55% by weight. The solid content at the time of coating is 10 to 50% by weight, preferably 20 to 50% by weight.
[0058]
The clear paint is applied in an uncured state after the base paint is applied, so that the coating film is formed by a so-called wet-on-wet method. It is preferable to contain crosslinked resin particles. The content of the crosslinked resin particles is 0.01 to 10 parts by weight, preferably 0.02 to 8 parts by weight, more preferably 0.03 to 6 parts by weight, based on 100 parts by weight of the resin solid content of the clear coating composition. It is added in parts by weight. When the amount of the crosslinked resin particles exceeds 10 parts by weight, the appearance is deteriorated. When the amount is less than 0.1 parts by weight, the viscosity control effect cannot be obtained, which causes problems such as sagging.
[0059]
The form of the clear paint used in the present invention may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-aqueous dispersion type, and a powder type. Preparations and the like can be used.
[0060]
Method for Forming Multi-layer Coating Film Further, the method for forming the multi-layer coating film of the present invention will be described.
The method for forming a multilayer coating film of the present invention includes a step of forming an electrodeposition coating film by applying an electrodeposition coating material on an object to be coated, and the aqueous intermediate coating composition described above on the electrodeposition coating film. A step of applying an aqueous base coating on the intermediate coating by a wet-on-wet coating method, and a step of forming an aqueous base coating on the intermediate coating by wet-on coating. The method includes a step of forming a clear coating film by wet coating, and a step of heating and curing the coating film at once after forming all the coating films.
[0061]
The method of applying each paint is not particularly limited, and includes, for example, an air electrostatic spray so-called “react gun”, so-called “micro-micro bell (μμ bell)”, “micro bell (μ bell)”, “metallic” It can be performed by using a rotary atomizing electrostatic coating machine called "bell (metabell)" or the like. After applying the water-based paint, preheating is preferably performed. In particular, it is better to perform preheating after applying the intermediate coating and the base coating. The preheating condition may be a temperature from room temperature to 100 ° C. for 30 seconds to 15 minutes.
[0062]
When heat-curing in the final step, the temperature is 110 to 180 ° C, preferably 120 to 160 ° C, particularly 130 to 140 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. If the temperature is lower than 110 ° C, the curing tends to be insufficient. If the temperature exceeds 180 ° C, the resulting coating film may be hard and brittle. The time for heat curing can be appropriately set according to the above temperature. For example, when the temperature is 120 to 160 ° C, it is 10 to 60 minutes, and when it is 130 to 140 ° C, it is at least 10 minutes. . The dry film thickness of each coating film is 10 to 40 μm, preferably 15 to 30 μm for the intermediate coating film, 10 to 30 μm, preferably 12 to 18 μm for the base coating film, and 10 to 70 μm for the clear coating film. , Preferably 20 to 50 μm.
[0063]
【The invention's effect】
According to the present invention, by blending a specific hydrophilic organic solvent in the intermediate coating composition, the aqueous intermediate coating composition exhibits high detergency, particularly high cleaning properties for a commonly used aqueous coating liquid. . Therefore, when used for the three-coat / one-bake waterborne intermediate coating material in which low cleaning property is a problem, the cleaning property is improved, and the problems encountered during implementation can be greatly improved.
[0064]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In Examples, “parts” and “%” are based on weight unless otherwise specified.
[0065]
(Preparation of color pigment paste)
9.4 parts of a commercially available dispersant "Disperbyk 190" (a nonionic / anionic dispersant manufactured by BYK-Chemie), 36.8 parts of ion-exchanged water, 34.5 parts of rutile-type titanium dioxide, 34.4 parts of barium sulfate After preliminarily mixing 6 parts of talc and talc, a glass bead medium was added in a paint conditioner, and mixed and dispersed at room temperature until the particle size became 5 μm or less, to obtain a dispersant / color pigment dispersed paste.
[0066]
(Preparation of resin emulsion)
445 parts of water and 5 parts of Newcol 293 (manufactured by Nippon Emulsifier Co., Ltd.) are placed in a reaction vessel equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, a nitrogen inlet tube and the like for the production of an ordinary acrylic resin emulsion. The mixture was charged and heated to 75 ° C. with stirring. A mixture of the following monomer mixture (acid value of resin: 18, hydroxyl value: 85, Tg: -22 ° C), 240 parts of water and 30 parts of Newcol 293 (manufactured by Nippon Emulsifier Co., Ltd.) was emulsified using a homogenizer. Then, the monomer pre-emulsion was dropped into the reaction vessel over 3 hours while stirring. At the same time as the dropping of the monomer pre-emulsion, an aqueous solution in which 1 part of APS (ammonium persulfate) is dissolved as a polymerization initiator in 50 parts of water is evenly dropped into the reaction vessel until the dropping of the monomer pre-emulsion is completed. did. After the completion of the dropwise addition of the monomer pre-emulsion, the reaction was further continued at 80 ° C. for 1 hour, and then cooled. After cooling, an aqueous solution in which 2 parts of dimethylaminoethanol was dissolved in 20 parts of water was added to obtain an aqueous resin emulsion having a nonvolatile content of 40.6% by weight.
[0067]
(Monomer mixture composition)
Methyl methacrylate 45 parts Butyl acrylate 299 parts Styrene 50 parts 2-hydroxyethyl acrylate 92 parts Methacrylic acid 14 parts Ethylene glycol dimethacrylate 20 parts The resulting resin emulsion was adjusted to pH 7 using a 30% aqueous dimethylaminoethanol solution. .2.
[0068]
Examples 1 to 4 and Comparative Example 1
(Preparation of aqueous intermediate coating)
To 60.3 parts of the dispersant coloring pigment dispersion paste and 109.7 parts of the resin emulsion obtained as described above, 20.9 parts of Cymel 327 (Imino melamine resin, trade name, manufactured by Mitsui Cytec Co., Ltd.) as a curing agent was added. After mixing, 1.0 part of ADEKANOL UH-814N (urethane associative thickener, active ingredient 30%, manufactured by Asahi Denka Kogyo KK, trade name) was mixed and stirred to obtain an aqueous intermediate coating.
[0069]
The aqueous intermediate coating was diluted with an aqueous medium described in Table 1 below and used for coating. The solid content at the time of coating was all 50%.
[0070]
Example 1
A tin plate was coated with the aqueous coating composition of Example 1 in Table 1 using a bar coder so that the film thickness (in the uncured coating film) became about 50 μm, and dried with a hot air dryer set at 60 ° C. for 5 minutes. The coated test plate was immersed in a standing washing liquid at 20 ° C., and after 3 minutes, the removability of the coating film was confirmed. Further, the coated test plate was immersed in a cleaning solution at 20 ° C., immediately subjected to ultrasonic cleaning for 2 minutes, and the removability of the coating film was observed. Table 1 shows the results. In Table 1, the detergency indicates the area ratio of the coating film that could be washed and removed. For example, 100 [%] indicates that all of the coating film has been washed and removed, and 10 [%] indicates that most of the coating film remains on the tin plate.
[0071]
The cleaning liquid is a liquid obtained by adding N, N-dimethylethanolamine to a mixed liquid composed of 70% of deionized water and 30% of butyl cellosolve so that the pH becomes 10. Same in Examples and Comparative Examples.
[0072]
Example 2
The aqueous paint of Example 2 in Table 1 was applied to a tin plate with a bar coder so that the film thickness (in the uncured coating film) became about 50 μm, and dried for 5 minutes with a hot air dryer set at 60 ° C. The coated test plate was immersed in a standing washing liquid at 20 ° C. and immersed for 3 minutes to confirm the removability of the coating film. Further, the coated test plate was immersed in a cleaning solution at 20 ° C., immediately subjected to ultrasonic cleaning for 2 minutes, and the removability of the coating film was observed. Table 1 shows the results.
[0073]
Example 3
The aqueous paint of Example 3 in Table 1 was applied to a tin plate with a bar coder so that the film thickness (in the uncured coating film) was about 50 μm, and dried for 5 minutes with a hot air dryer set at 60 ° C. The coated test plate was immersed in a standing washing liquid at 20 ° C. and immersed for 3 minutes to confirm the removability of the coating film. Further, the coated test plate was immersed in a cleaning solution at 20 ° C., immediately subjected to ultrasonic cleaning for 2 minutes, and the removability of the coating film was observed. Table 1 shows the results.
[0074]
Example 4
The water-based paint of Example 4 in Table 1 was applied to a tin plate with a bar coder so that the film thickness (in the uncured coating film) became about 50 μm, and dried for 5 minutes with a hot air dryer set at 60 ° C. The coated test plate was immersed in a standing washing liquid at 20 ° C. and immersed for 3 minutes to confirm the removability of the coating film. Further, the coated test plate was immersed in a cleaning solution at 20 ° C., immediately subjected to ultrasonic cleaning for 2 minutes, and the removability of the coating film was observed. Table 1 shows the results.
[0075]
Comparative Example 1
A tin plate was coated with the aqueous coating composition of Comparative Example 1 in Table 1 using a bar coder so that the film thickness (in the uncured coating film) became about 50 μm, and dried for 5 minutes with a hot air dryer set at 60 ° C. The coated test plate was immersed in a standing washing liquid at 20 ° C. and immersed for 3 minutes to confirm the removability of the coating film. Further, the coated test plate was immersed in a cleaning solution at 20 ° C., immediately subjected to ultrasonic cleaning for 2 minutes, and the removability of the coating film was observed. Table 1 shows the results.
[0076]
[Table 1]
Table 1

The removability is represented by the removal area [%] of the coating film.
* 1: 3% by weight of propylene glycol and 2% by weight of propylene glycol methyl ether.
* 2: The amount of organic solvent brought in from raw materials.
[0077]
As is clear from the comparison between the above Examples and Comparative Examples, a coating film using an aqueous intermediate coating containing a specific amount of a hydrophilic organic solvent has excellent removability even after drying. In particular, the removability after immersion in the remover for 3 minutes and the removability after ultrasonic cleaning for 2 minutes are much better than that of Comparative Example 1 in which a specific amount of the hydrophilic organic solvent is not blended.
[0078]
Example of forming a multi-layer coating film A power top U-50 (a cationic electrodeposition coating material manufactured by Nippon Paint Co., Ltd.) is electrodeposited on a dull steel plate treated with zinc phosphate such that the dry coating film has a thickness of 20 μm. After heating and curing at 160 ° C. for 30 minutes, cooling was performed to prepare a steel plate substrate.
[0079]
The obtained substrate was coated with the aqueous intermediate coating composition of Example 1 by air spray coating at a thickness of 20 μm, preheated at 80 ° C. for 5 minutes, and then Aqualex AR-2000 silver metallic (Nippon Paint Co., Ltd. aqueous metallic base). (Paint, trade name) was applied by air spray coating at 10 μm, and preheated at 80 ° C. for 3 minutes. Further, as a clear paint, Macflow O-1800W-2 clear (acid epoxy-curable clear paint, trade name, manufactured by Nippon Paint Co., Ltd., trade name) was applied to the coated plate by air spraying at 35 μm, and then heated at 140 ° C. for 30 minutes. Curing was performed to obtain a test piece.
[0080]
The multilayer coating film obtained after the heat curing was excellent in finished appearance and excellent.
[0081]
The dilution conditions of the aqueous base paint and the clear paint were as follows.
Aqueous base paint thinner: ion exchange water 45 seconds / NO. 4 Ford cup / 20 ℃
-Clear paint thinner: EEP (ethoxyethyl propionate) / S-150 (aromatic hydrocarbon solvent manufactured by Exxon, trade name) = 1/1 (weight ratio) mixed solvent 30 seconds / NO. 4 Ford cup / 20 ℃
[0082]
As is clear from the above-mentioned coating experiment, even when a specific amount of a hydrophilic organic solvent is blended with the aqueous intermediate coating, there is no change in coating performance, and a good coating film can be obtained.
[Brief description of the drawings]
FIG. 1 is a process chart showing a coating film forming process of the present invention.

Claims (5)

An aqueous intermediate coating (1), an aqueous base coating (2) and a clear coating (3) are sequentially applied on a substrate on which an electrodeposition coating film is formed by wet-on-wet, and the resulting multilayer coating film is obtained. In the method of forming a multilayer coating film simultaneously baking and curing,
The aqueous intermediate coating composition (1) contains a hydrophilic organic solvent having a boiling point of 80 ° C. or more and less than 250 ° C. as a part of a diluting medium in an amount of 2 to 10% by weight based on the total weight of the coating composition. A method for forming a multilayer coating film. The hydrophilic organic solvent has the general formula R ¹ —OH
(Wherein, R ¹ represents. A linear or branched alkyl group having 3 to 8 carbon atoms) forming the multilayer coating film according to claim 1, characterized in that the alcohol represented by Method. Wherein the hydrophilic organic solvent has the general formula ^HO- (R 2 _-O) n -H
Wherein R ² is a glycol represented by the formula: wherein R ² is a linear or branched alkyl group having 2 to 8 carbon atoms, and n is an integer of 1 to 6. 3. The method for forming a multilayer coating film according to item 1. The hydrophilic organic solvent has a general formula of R ³ O— (R ⁴ —O) _m —R ^5.
(Wherein, R ⁴ represents a linear or branched alkyl group having 1 to 8 carbon atoms, and R ³ and R ⁵ each represent hydrogen, a linear or branched alkyl group having 1 to 8 carbon atoms. Wherein R ³ and R ⁵ are not both hydrogen, and m represents an integer of 1 to 6). Item 4. The method for forming a multilayer coating film according to Item 1. The method for forming a multilayer coating film according to claim 1, wherein the hydrophilic organic solvent is a combination of two or more of the hydrophilic organic solvents described in claims 2 to 5.

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