JP2016188332A - Clear coating composition for automobile body, method for forming multiple layered coated film for automobile body and multiple layered coated film for automobile body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a clear coating composition for an automobile body, having weather resistance and higher transmission coefficient of visible light in a clear coating film than conventional ones, a method for forming a multiple layered coated film for an automobile body and a multiple layered coated film for an automobile body.SOLUTION: The clear coating composition for an automobile body is provided which contains a binder component (a), an organic ultraviolet absorber (b), a hindered amine-based light stabilizer (c) and fine particle titanium oxide (d), and in which average particle diameter of a primary particle of the fine particle titanium oxide (d) is 10 nm to 50 nm and PWC of the fine particle titanium oxide (d) to a solid component of the binder component (a) is 0.025 pts.mass to 0.050 pts.mass.SELECTED DRAWING: None

Description

  The present invention relates to a clear coating composition for an automobile body, a method for forming a multilayer coating film for an automobile body using the clear coating composition for an automobile body, and a multilayer coating film for an automobile body obtained by this forming method.

A coating film is usually formed on an automobile body from the viewpoint of imparting various functions such as aesthetics and weather resistance.
In particular, from the viewpoint of weather resistance, a clear coating composition containing a benzophenone or benzotriazole organic ultraviolet absorber is generally used as the clear coating composition having an ultraviolet absorbing function. A clear coating composition containing an organic ultraviolet absorber has an excellent ability to absorb ultraviolet rays, but the organic ultraviolet absorber itself may deteriorate and discolor with the absorption of ultraviolet rays. In addition, when used over a long period of time, the organic ultraviolet absorber may come out on the surface of the coating film due to bleed-out, so the concentration of the organic ultraviolet absorber in the coating film over time There is a concern about performance deterioration such as weather resistance.

  On the other hand, examples of inorganic ultraviolet absorbers include fine particles of metal oxides such as zinc oxide, titanium oxide, and cerium oxide. These inorganic ultraviolet absorbers themselves do not oxidize and discolor, and do not bleed out to the coating surface. However, if a predetermined weather resistance is obtained only with an inorganic ultraviolet absorber, the transparency of the clear coating film is lowered, and as a result, the aesthetic appearance of the automobile body may be impaired.

  Therefore, in Patent Document 1, surface-treated fine particles obtained by surface-treating an inorganic ultraviolet absorbent having an average primary particle diameter of 10 to 50 nm with an amino group-containing alkoxysilane are dispersed using an acid group-containing dispersant. A clear coating composition containing a dispersion and a binder component is disclosed. Moreover, titanium oxide, zinc oxide, and cerium oxide are illustrated as an inorganic ultraviolet absorber which has a specific average particle diameter, The content of the said surface treatment microparticles | fine-particles is 0.5-10 with respect to 100 mass parts of binder components. It is described that it is a mass part.

JP 2012-121933 A

The clear coating film formed by using the clear coating composition described in Patent Document 1 includes only surface-treated fine particles obtained by subjecting an inorganic ultraviolet absorber having a specific average particle diameter to a specific surface treatment as an ultraviolet absorber. Is used. Therefore, even if the surface-treated fine particles are well dispersed in the clear coating film, in order for the clear coating film to have a predetermined weather resistance, the content of the surface-treated fine particles is 100 parts by mass of the binder component. On the other hand, it is necessary to add a little more with 0.5-10 mass parts. As a result, the clear coating film obtained has a predetermined weather resistance to ultraviolet rays, but the transmittance for visible light cannot be denied.
On the other hand, the multilayer coating film for an automobile body has an important role in producing the beauty of the automobile body. And the higher the visible light transmittance in the clear coating film that is the uppermost film of this multilayer coating film, the more vividly expressed hue, saturation, brightness, glitter, etc. by the multilayer coating film below the clear coating film Is done.

An object of the present invention is to provide a clear coating composition for an automobile body that has a weather resistance equal to or higher than that of the conventional one and has a higher visible light transmittance in the clear coating than in the past.
Another object of the present invention is to provide a multilayer coating film for an automobile body that has a weather resistance equal to or higher than that of the conventional one, has a higher visible light transmittance in the clear coating film, and is excellent in aesthetics. It is providing the formation method and the multilayer coating film for motor vehicle bodies.

  In particular, in the clear coating composition used for coating for automobile bodies, the present inventors have added a small amount of fine particle titanium oxide having an average primary particle size of 10 to 50 nm, thereby providing an ultraviolet absorber and a hindered amine system. The amount of light stabilizer added can be reduced compared to conventional products, and the resulting multilayer coating for automobile bodies has weather resistance equivalent to or better than that of conventional coatings. The inventors have found that the rate is high and have arrived at the present invention. That is, the present invention is as follows.

[1] A clear coating composition for an automobile body containing a binder component (a), an organic ultraviolet absorber (b), a hindered amine light stabilizer (c), and fine particle titanium oxide (d), wherein the fine particle oxidation The average particle diameter of the primary particles of titanium (d) is 10 nm or more and 50 nm or less, and the PWC of the fine particle titanium oxide (d) is 0.025 parts by mass or more with respect to the solid content of the binder component (a). The clear coating composition for an automobile body is 0.050 part by mass or less.
[2] The PWC of the organic ultraviolet absorber (b) is 1 part by mass or more and 3 parts by mass or less with respect to the solid content of the binder component (a), and the solid content of the binder component (a) The clear coating composition for an automobile body according to [1], wherein the hindered amine light stabilizer (c) has a PWC of 0.5 parts by mass or more and 1.5 parts by mass or less.
[3] A method for forming a multilayer coating film for an automobile body, wherein a base coating film is formed on a base material on which a base coating film has been formed, and further a clear coating film is formed thereon. A clear coating composition for an automobile body to be formed contains a binder component (a), an organic ultraviolet absorber (b), a hindered amine light stabilizer (c) and fine particle titanium oxide (d), and the fine particle titanium oxide (d ) Primary particles have an average particle size of 10 nm or more and 50 nm or less, and the fine particle titanium oxide (d) has a PWC of 0.025 parts by mass or more and 0.0. The formation method of the multilayer coating film for motor vehicle bodies which is 050 mass parts or less.
[4] The PWC of the organic ultraviolet absorber (b) is 1 part by mass or more and 3 parts by mass or less with respect to the solid content of the binder component (a), and the solid content of the binder component (a) And the PWC of the said hindered amine light stabilizer (c) is 0.5 mass part or more and 1.5 mass parts or less, The formation method of the multilayer coating film for motor vehicle bodies as described in [3].
[5] A multilayer coating film for automobile bodies, comprising a base coating film and a clear coating film, formed by the method according to [3] or [4].

  According to the present invention, there is provided a clear coating composition capable of obtaining a clear coating film having a higher visible light transmittance and superior aesthetics as compared with the prior art, and for an automobile body using the clear coating film. It is possible to provide a clear coating composition capable of obtaining excellent weather resistance even in a multilayer coating film.

It is sectional drawing which shows an example of the structure of the multilayer coating film of this invention.

[Clear coating composition for automobile bodies]
The clear paint composition for an automobile body of the present invention comprises a clear paint for an automobile body containing a binder component (a), an organic ultraviolet absorber (b), a hindered amine light stabilizer (c), and particulate titanium oxide (d). In the composition, the fine particle titanium oxide (d) has an average primary particle diameter of 10 nm or more and 100 nm or less, and the fine particle titanium oxide (d) with respect to the solid content of the binder component (a). The content ratio (hereinafter referred to as PWC) is 0.025 parts by mass or more and 0.050 parts by mass or less. Here, the content ratio (PWC) of the fine particle titanium oxide (d) with respect to the binder component (a) is (particulate titanium oxide (d) / (binder component (a) + fine particle oxidation) in terms of parts by mass. Titanium (d)).

Here, the fine particle titanium oxide (d) has an average primary particle diameter of 10 nm or more and 100 nm or less, and the content of fine particle titanium oxide (d) with respect to the solid content of the binder component (a) (PWC). ) Is 0.025 parts by mass or more and 0.050 parts by mass or less, the added amount of the organic ultraviolet absorber and the hindered amine light stabilizer is reduced as compared with the conventional, and the clear coating film obtained is visible. Even if the light transmittance is increased to a practical level, the multilayer coating film for an automobile body using the clear coating film has a weather resistance equal to or higher than that of the conventional coating film.
The average particle diameter of primary particles of fine particle titanium oxide (d) is preferably 10 nm or more and 50 nm or less, more preferably 40 nm or more and 50 nm, from the viewpoint of visible light transmittance and glossiness of the clear coating film. It is as follows.

In the clear coating composition for an automobile body of the present invention, the fine particle titanium oxide (d) has an average primary particle diameter of 10 nm or more and 100 nm or less, and is based on the solid content of the binder component (a). The content ratio (PWC) of fine particle titanium oxide (d) is 0.025 parts by mass or more and 0.050 parts by mass or less. The content (PWC) of the organic ultraviolet absorber (b) is preferably 1 part by weight or more and 3 parts by weight or less with respect to the solid content of the binder component (a), and the viewpoint of the color difference of the clear coating film More preferably, it is 2 parts by mass or more and 3 parts by mass or less.
Moreover, the PWC of the hindered amine light stabilizer (c) contained in the clear coating composition for an automobile body is preferably 0.5 parts by mass or more and 1.5 parts by mass relative to the solid content of the binder component (a). From the viewpoint of the color difference of the clear coating film, more preferably 1 part by mass or more and 1.5 parts by mass or less.
Here, the content (PWC) of the organic ultraviolet absorber (b) with respect to the binder component (a) is expressed in terms of parts by mass (organic ultraviolet absorber (b) / (binder component (a ) + Organic ultraviolet absorber (b)) The content ratio (PWC) of the hindered amine light stabilizer (c) relative to the binder component (a) is (hindered amine) in terms of parts by mass. System light stabilizer (c) / (binder component (a) + hindered amine light stabilizer (c)).

  In the clear coating film obtained by using the clear coating composition for an automobile body of the present invention, the “fine particle titanium oxide” used in the present invention has an average primary particle diameter of 10 nm or more and 50 nm or less. Compared with titanium oxide having a large diameter, the dispersibility in the clear paint and the clear coating film is high. Therefore, even if a small amount of “fine particle titanium oxide” is added compared to the conventional inorganic UV absorber, the weather resistance of the clear coating film is equal to or higher than that of the conventional coating film, and the clear coating film is visible. It is presumed that the light transmittance is higher than the conventional one. Furthermore, since “fine particle titanium oxide” has better dispersibility with respect to organic components than conventional titanium oxide having a large particle size, in the present invention, “ultraviolet absorber” and “ It is considered that the dispersibility is good also for the “hindered amine light stabilizer”. Therefore, even if any "ultraviolet absorber" and "hindered amine light stabilizer" used in the present invention are combined with "fine particle titanium oxide" used in the present invention, the weather resistance of the clear coating film is equal to or higher than that of the conventional coating film. In addition, it is presumed that the visible light transmittance of the clear coating film is higher than the conventional one.

The clear coating composition for automobile bodies can take various forms such as a solvent type, an aqueous type, and a powder type. As the solvent-based paint or water-based paint, a one-component paint may be used, or a two-component paint such as a two-component urethane resin paint may be used.
In addition, the clear coating composition for automobile bodies used in the method for forming a multilayer coating film for automobile bodies, which will be described later, is a Ford Cup No. 20 at 20 ° C. from the viewpoint of the effect of PWC of an organic solvent on the environment. 4 is a solvent-type clear coating composition or a water-based clear coating composition, or a powder-type clear, in which the solid content of the clear coating composition when diluted to a viscosity of 20 to 50 seconds is 50% by mass or more A coating composition is preferred.

<Binder component (a)>
As the binder component, for example, at least one thermosetting resin selected from an acrylic resin, a polyester resin, a fluororesin, an epoxy resin, a polyurethane resin, a polyether resin, and a modified resin thereof, and cured as necessary. The thing containing an agent etc. can be used. As the curing agent, for example, an amino resin and / or a blocked isocyanate compound, an amine curing agent, a polyamide curing agent, a polyvalent carboxylic acid, or the like is used.

  When the vehicle body clear coating composition is a solvent-based clear coating composition, preferred examples include acrylic resin and / or polyester resin, amino resin and / or isocyanate from the viewpoint of transparency or acid etching resistance. Examples thereof include an acrylic resin and / or a polyester resin having a combination or a carboxylic acid / epoxy curing system.

  Further, when the clear coating composition for an automobile body is an aqueous clear coating composition, for example, the film-forming resin contained in the above-mentioned examples of the solvent-type clear coating composition is neutralized with a base. And water-containing resins. This neutralization can be carried out by adding tertiary amines such as dimethylethanolamine and triethylamine before or after polymerization.

<Organic UV absorber (b)>
Examples of the organic ultraviolet absorber (b) include benzotriazole ultraviolet absorbers, liquid ultraviolet absorbers, triazine ultraviolet absorbers, benzophenone ultraviolet absorbers, and benzoate ultraviolet absorbers.
Examples of the benzotriazole ultraviolet absorber include trade names “TINUVIN P”, “TINUVIN P FL”, “TINUVIN 234”, “TINUVIN 326”, “TINUVIN FL”, “TINUVIN 329”, “TINUVIN 329F”, “ TINUVIN 900 "(all the above-mentioned products are manufactured by BASF), trade name" ADK STAB LA-29 "(IUPAC name: 2-2H-benzotriazol-2-yl) -4- (1,1,3 , 3-tetramethylbutyl) phenol), trade names “Adekastab LA-31”, “Adekastab LA-31RG”, “Adekastab LA-31G” (both IUPAC name: 2,2′-methylenebis [6- (2H -Benzotriazol-2-yl) -4- (1,1,3 -Tetramethylbutyl) phenol]), trade name "ADK STAB LA-32" (IUPAC name: 2- (2H-benzotriazol-2-yl) -p-cresol), trade names "ADK STAB LA-36", "ADK STAB LA-36RG "(both IUPAC name: 2- (5-chloro-2H-benzotriazol-2-yl) -6-tert-butyl-4-methylphenol) (all the products in the latter stage are ADEKA Corporation) For example). Here, “TINUVIN” is a registered trademark of BASF Corporation. The same applies hereinafter. “ADEKA STAB” is a registered trademark of ADEKA Corporation. The same applies hereinafter.
Examples of the liquid ultraviolet absorber include trade names “TINUVIN 213” and “TINUVIN 571” (both manufactured by BASF).
Examples of the triazine-based ultraviolet absorber include a trade name “TINUVIN 1577ED” (manufactured by BASF), a trade name “ADK STAB LA-46” (IUPAC name: 2- (4,6-diphenyl-1,3,5-triazine). -2-yl) -5- [2- (2-ethylhexanoyloxy) ethoxy] phenol), trade name “ADEKA STAB LA-F70” (IUPAC name: 2,4,6-tris (2-hydroxy-4-) (Hexyloxy-3-methylphenyl) -1,3,5-triazine) (all of the subsequent products are manufactured by ADEKA Corporation).
Examples of the benzophenone-based ultraviolet absorber include trade names “CHIMASSORB 81”, “CHIMASSORB 81 FL” (both manufactured by BASF), trade name “Adekastab 1413” (IUPAC name: [2-hydroxy-4- (octyloxy) ) Phenyl] (phenyl) methanone) (manufactured by ADEKA Corporation). Here, “CHIMASSORB” is a registered trademark of BASF Corporation. The same applies hereinafter.
Examples of the benzoate-based ultraviolet absorber include trade name “TINUVIN 120” (manufactured by BASF).

<Hindered amine light stabilizer (c)>
As the hindered amine light stabilizer (c), a hindered amine light stabilizer (c) is used as a light stabilizer in order to improve weather resistance. Examples of the hindered amine light stabilizer include trade names “CHIMASSORB 2020 FDL”, “CHIMASSORB 944 FDL”, “TINUVIN 622 SF”, “TINUVIN 144”, “TINUVIN 292”, “TINUVIN PA144”, “TINUVIN 765”. "TINUVIN 770 DF", "TINUVIN 111 FDL", "TINUVIN 783 FDL", and "TINUVIN 791 FB" (all manufactured by BASF).

<Fine particle titanium oxide (d)>
The fine particle titanium oxide (d) refers to titanium oxide particles having an average primary particle diameter of 10 nm or more and 50 nm or less.
As the fine particle titanium oxide (d), trade names “MT-100S”, “MT-100T”, “MT-100TV”, “MT-100Z”, “MT-100F”, “MT-150W”, “MT-” 100AQ "," MT-100SA "," MT-100HD "," MT-100SAS "," MT-500SAS "," MT-500B "," MT-500H "," MT-500SA "," MT-500HD " , “SMT-100SAS”, “SMT-500SAS”, “MT-600B”, “MT-600SA”, “MT-700HD” (all manufactured by Teika Corporation), trade names “TTO-51”, “TTO” -55 "(all manufactured by Ishihara Sangyo Co., Ltd.), trade names" STR-60 "," STR-100 "(all manufactured by Sakai Chemical Industry Co., Ltd.), etc. These may be used in combination of at least one or more kinds. Further, “MT-700HD” (manufactured by Teika Co., Ltd.) is preferable from the viewpoint of dispersibility of fine particle titanium oxide in the clear coating composition for automobile body.

[Measurement method of average particle diameter of primary particles of fine particle titanium oxide]
The average particle diameter of the primary particles of fine particle titanium oxide described above is a number average value obtained by measuring the long diameters of 50 fine particle titanium oxides using a transmission electron microscope (TEM) photograph and averaging them. In the examples described later, the same measurement was performed.

<Other additives>
If necessary, the clear coating composition for an automobile body is a color pigment, an extender pigment, a modifier, a leveling agent, a dispersion, as long as the transparency is not impaired or the design of the base is not disturbed. Additives such as agents and antifoaming agents can be blended.
Furthermore, it is preferable that a viscosity control agent is added to the clear coating composition for an automobile body in order to ensure coating workability. As the viscosity control agent, those generally showing thixotropy can be used. For example, a conventionally well-known thing can be used as such a thing. Moreover, a curing catalyst, a surface conditioner, etc. can be included if necessary.

[Method for forming multilayer coating film for automobile body]
The method for forming a multilayer coating film for an automobile body according to the present invention comprises forming a base coating film on a base material on which a base coating film is formed, and further forming a clear coating film thereon. A clear coating composition for an automobile body for forming a clear coating film comprising a binder component (a), an ultraviolet absorber (b), a hindered amine light stabilizer (c), and a fine particle titanium oxide (d The average particle diameter of primary particles of the fine particle titanium oxide (d) is 10 nm or more and 50 nm or less, and the PWC of the fine particle titanium oxide (d) is based on the solid content of the binder component (a). 0.025 parts by mass or more and 0.050 parts by mass or less.
Furthermore, in the method for forming a multilayer coating film for an automobile body of the present invention, the PWC of the organic ultraviolet absorber (b) is 1 part by mass or more and 3 parts by mass with respect to the solid content of the binder component (a). Preferably, the PWC of the hindered amine light stabilizer (c) is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to the solid content of the binder component (a). Is preferred.
Since the “clear coating composition for automobile bodies forming a clear coating film” is the same as the above-mentioned “clear coating composition for automobile bodies”, each component and its specific examples are described here. Is omitted.

<Coating material>
In the method for forming a multilayer coating film for an automobile body according to the present invention, the object to be coated is obtained by subjecting a conductive base material (for example, an automobile body and its parts) to a degreasing treatment or a chemical conversion treatment (such as phosphate or zirconium salt) in advance. After applying chemical conversion treatment, etc., it is applied with base coating such as electrodeposition coating and intermediate coating.

  Electrodeposition coating is performed for the purpose of imparting rust prevention by forming an electrodeposition coating film on a conductive object such as a steel plate. The electrodeposition coating composition capable of forming such an electrodeposition coating film is not particularly limited, and cationic electrodeposition coating compositions and anionic electrodeposition coating compositions well known to those skilled in the art are included. Either can be used. From the viewpoint of rust prevention, a cationic electrodeposition coating composition is preferable, and an epoxy cationic electrodeposition coating composition is particularly preferable.

  In the present invention, when the object to be coated is an automobile body, it is preferable to perform pretreatments such as degreasing, water washing, chemical conversion film formation, water washing, pure water washing and drying by a conventionally known method before electrodeposition coating film formation. . As the electrodeposition coating film forming method, an appropriate method may be arbitrarily selected from conventionally known methods. In addition, the electrodeposition coating film forming conditions, the baking curing conditions, the thickness of the electrodeposition coating film, and the like can be appropriately determined according to the type of the object to be coated and the type of the electrodeposition coating composition to be used. .

  The purpose of intermediate coating is to form an intermediate coating film on the electrodeposition coating film formed as necessary, and to improve performance such as base concealment, chipping resistance, and adhesion to the top coating film. As done. The intermediate coating film also functions as a base for making the final multilayer coating film smooth and having a good appearance. The intermediate coating film further serves as a binder between the electrodeposition coating film and the top coating film, and can improve the weather resistance against deterioration of the coating film due to ultraviolet rays, water, etc. that reach through the coating film surface.

  The intermediate coating composition that can form an intermediate coating film is not particularly limited, and includes solvent-based coatings well known to those skilled in the art, water-based coatings, powder coatings, and high solid coatings. Can be used. Specifically, conventionally known alkyd / melamine resins or oil-free polyester / melamine resin coatings, intermediate coating compositions combining acrylic resins and / or polyester resins with amino resins and / or isocyanate curing agents, etc. It can be used by appropriately selecting from the intermediate coating composition.

  As a method for forming the intermediate coating film, an appropriate method can be arbitrarily selected from conventionally known methods. Further, in the present invention, a gray-based intermediate coating composition containing carbon black and titanium dioxide as main pigments, a so-called color that combines set gray and various colored pigments that match the brightness and hue of the top coating film. An intermediate coating composition can be used. These color intermediate coating compositions exhibit a composite color of the intermediate coating film and the top coating film, and can further enhance the design. Further, flat pigments such as aluminum powder and mica powder may be added to these intermediate coating compositions. Further, the intermediate coating composition may contain additives that can be usually added to the coating, for example, a surface conditioner, an antioxidant, an antifoaming agent, and the like. The dry film thickness of the intermediate coating film is preferably 20 to 100 μm, more preferably 30 to 50 μm.

  The intermediate coating film can be used in an uncured state after being coated on an object or an electrodeposition coating film, or can be used in a cured state. In the case of curing the intermediate coating film, a cured film having a high degree of crosslinking can be obtained by setting the curing temperature to 100 to 180 ° C, preferably 120 to 160 ° C. By setting the curing temperature within the above range, it is possible to prevent the curing from becoming insufficient and the coating film from becoming hard and brittle. The curing time varies depending on the curing temperature, but 10 to 30 minutes at 120 to 160 ° C. is appropriate.

<Method for forming base coating and clear coating>
In the method for forming a multilayer coating film for an automobile body of the present invention, a base coating composition, the above-described clear coating composition for an automobile body (hereinafter referred to as “clear coating composition”) is formed on a substrate on which a base coating film is formed. It is preferable to form the coating film by a two-coat one-bake method in which coating is sequentially performed wet-on-wet and these coating films are simultaneously cured. Further, the present invention can also be applied to a 2-coat 2-bake coating method in which the base coating composition is applied and cured on a base material on which a base coating film has been formed, and then the clear coating composition is applied and cured.

  The base coating composition may be applied by, for example, a multi-stage coating by air electrostatic spray coating, preferably a two-stage coating, or an air coating for improving the design of an automobile body. It must be a coating method that combines electrostatic spray coating with a rotary atomizing electrostatic coating machine called “μμ (micro) bell”, “μ (micro) bell” or “metabell”. preferable.

  The dry film thickness of the base coating film formed by application of the base coating composition varies depending on the desired application, but in many cases, the lower limit is preferably 5 μm and the upper limit is 30 μm. By making the impression film thickness of a base coating film into the said range, it is suppressed that the foundation | substrate cannot be concealed and a film | membrane cut | disconnection generate | occur | produces and troubles, such as a flow, arise at the time of coating.

  In the case of forming a multilayer coating film by the above-mentioned two-coat one-bake, after applying the base coating composition, the process proceeds to the step of applying the clear coating composition without heating and curing. In this case, if necessary, before applying the clear coating composition, a solvent such as moisture by heating at a temperature lower than the temperature used in the heat curing (baking) treatment, for example, at 40 to 100 ° C. for 1 to 10 minutes. You may perform the preheating process which volatilizes.

  As the coating method of the clear coating composition, as with the base coating composition, a method of coating with the above-described rotary atomizing electrostatic coating machine is preferable. In general, the dry film thickness of the clear coating film formed from the clear coating composition is preferably 20 μm at the lower limit and 70 μm at the upper limit. If it is less than 20 μm, there is a possibility that the concavity and convexity of the foundation is insufficiently concealed. If it exceeds 70 μm, there is a risk that problems such as cracking or sagging may occur during painting. The lower limit is more preferably 25 μm, and the upper limit is more preferably 60 μm.

  In the 2-coat 1-bake method, after the base coating composition and the clear coating composition are applied, these uncured coating films are cured. The curing temperature is preferably a lower limit of 100 ° C. and an upper limit of 180 ° C. If it is less than 100 ° C, curing may be insufficient. If it exceeds 180 ° C, the coating film may become hard and brittle. The lower limit is more preferably 120 ° C. and the upper limit is more preferably 160 ° C. in that a cured coating film having a high degree of crosslinking can be obtained. Although hardening time changes with hardening temperature, in the case of 120-160 degreeC, 10-30 minutes are preferable.

  When a multilayer coating film is formed by two coats and two bake, after the base coating composition is applied, it is cured by heating at, for example, 120 to 160 ° C. for 10 to 30 minutes. After coating in the same manner as described above, it is preferable to cure by heating at 120 to 160 ° C. for 10 to 30 minutes, for example.

  The film thickness of the multilayer coating film formed by the multilayer coating film forming method of the present invention is preferably a lower limit of 30 μm and an upper limit of 300 μm. By making the film thickness of a multilayer coating film into the said range, the fall of the intensity | strength of film | membrane itself is suppressed and the fall of film physical properties, such as a weather resistance, is prevented. From the viewpoint of film physical properties of the composite coating film, the lower limit is more preferably 50 μm, and the upper limit is more preferably 250 μm.

[Base paint composition]
The base coating composition used in the method for forming a multilayer coating film for an automobile body of the present invention may be either a curable coating composition or a dry coating composition, and a film-forming component and a coloring component. And / or a bright material.

  Examples of the film-forming component include resin components such as acrylic resin, polyester resin, epoxy resin, and urethane resin. When the base coating is a curable coating, a combination of the above resin components having a curing functional group and a curing agent such as an amino resin corresponding to these functional groups or, if necessary, a blocked isocyanate resin Can be illustrated.

  Examples of the coloring component include inorganic coloring pigments such as titanium dioxide, carbon black, iron oxide, yellow iron oxide, phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo Organic coloring pigments such as yellow, indanthrone blue, dibromanthanthrone red, perylene red, azo red, anthraquinone red, quinacridone red, 1: 2 chromium complex black, 1: 2 chromium complex yellow, 1: 2 cobalt complex yellow, etc. These dyes can be exemplified.

  Examples of the bright material include, for example, the aluminum powder, alumina powder, glass powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, metal-coated mica powder, titanium dioxide-coated mica powder, and titanium dioxide coating. Glass powder etc. can be illustrated.

  Although it does not specifically limit as content of the coloring component of a base coating material, and a luster material, From a design viewpoint, it is preferable that it is 1-60 mass% with respect to the resin solid content in a coating material. Here, the resin solid content in the paint according to the present invention refers to the solid content weight of the film-forming component. In addition, it is preferable that the base coating material used for the highly designable coating-film formation method for motor vehicle bodies of this invention contains the said brilliant material from a design viewpoint.

  The base paint can further contain resin particles. By including the resin particles, it is possible to control the viscosity of the coating film at the time of coating and after coating, for example, it is possible to suppress the familiarity and inversion between the layers of the top coating film on the base coating film. The resin particles are not particularly limited, and can be obtained, for example, by polymerizing an ethylenically unsaturated monomer in an organic medium in the presence of a polyester resin or alkyd resin having a soluble part and an insoluble part in an organic solvent. Examples thereof include acrylic resin particles called NAD particles, and acrylic resin particles obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of a surfactant in an aqueous medium. These resin particles may be crosslinked resin particles or non-crosslinked resin particles. The average particle diameter of the resin particles is preferably 20 to 500 nm from the viewpoint of storage stability. As PWC of the resin particle in a base coating material, it is 1-20 mass% normally with respect to the resin solid content in a coating material.

  The base paint may contain extender pigments, curing catalysts, surface conditioners, ultraviolet absorbers, light stabilizers, and those well known by those skilled in the art, as necessary. In addition, it does not specifically limit as a form of a base coating material, Any of a solvent type, a water dispersion type, or a water-soluble type may be sufficient.

[Multi-layer coating for automobile bodies]
The multilayer coating film for automobile bodies of the present invention includes a base coating film and a clear coating film formed by the above-described method for forming a multilayer coating film for automobile bodies.
In FIG. 1, an example of the structure of the multilayer coating film for motor vehicle bodies of this invention is shown.
As shown in FIG. 1, the multilayer coating film for an automobile body of the present invention has the above-described electrodeposition coating film 12, intermediate coating film 14, base coating film 16 and clear coating film 18 on the surface of a base material 10. Sequentially formed.
In addition, since it mentioned above about the coating material and coating composition for forming each coating film, and the formation method of each coating film, description here is abbreviate | omitted.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these. In the following examples, “part” and “%” are based on mass unless otherwise specified.

[Production Example 1]
A fine particle titanium oxide dispersion was prepared with the ingredients shown in Table 1.

* 1: Trade name “Solfit” (registered trademark) (alcohol solvent, manufactured by Kuraray Co., Ltd.), IUPAC name: 3-methoxy-3-methyl-1-butanol (CAS: 56539-66-3)
* 2: Trade name “MT-700HD” (manufactured by Teika Co., Ltd., average particle diameter of primary particles: 50 nm)
* 3: Product name “ACR-421” (manufactured by Nippon Paint Co., Ltd., solid content: 50 mass%)

[Production Example 2]
The pre-clear coating composition before addition of the organic ultraviolet absorber and the hindered amine light stabilizer was prepared with the ingredients shown in Table 2.
In the present specification, hereinafter, the content ratio (also referred to as “PWC”) of each component is described using “part by mass” with respect to the solid content of the binder component.

* 4: Clear paint; trade name “MAC 0-1820” (manufactured by Nippon Paint Co., Ltd., carboxylic acid / epoxy curable solvent-based paint, binder component; acid half ester-containing acrylic resin, epoxy / hydroxyl group-containing acrylic resin, low molecular weight (Oligomer, solid content: 54% by mass)
* 5: Trade name “Solvesso 150” (manufactured by TonenGeneral Sekiyu KK, aromatic hydrocarbon solvent, “Solvesso” is a registered trademark of TonenGeneral Sekiyu KK)

<Example 1-a>
The “pre-clear coating composition” containing 0.025 parts by mass of fine titanium oxide content (also referred to as “PWC”) with respect to the solid content of the binder component in the clear coating shown in Table 2 The organic UV absorber PWC is added in an amount of 1 part by mass and the hindered amine light stabilizer PWC is added in an amount of 0.5 part by mass. A “composition” was prepared.
<Example 1-b>
“Pre-clear coating composition” containing 0.050 part by mass of fine particle titanium oxide PWC with respect to the solid content of the binder component in the clear coating shown in Table 2 absorbs organic ultraviolet rays with respect to the solid content of the binder component. The agent was added so that the PWC of the agent was 1 part by mass and the PWC of the hindered amine light stabilizer was 0.5 part by mass, and the mixture was stirred with a stirrer for 30 minutes to prepare a “clear coating composition”.

<Reference Example 1>
In Example 1-a, except that PWC of an organic ultraviolet absorber and a hindered amine light stabilizer is not added in a double amount of Example 1-a, but does not contain fine particle titanium oxide in Example 1-a. In accordance with this, a clear coating composition was prepared.

<Reference Example 2>
A clear coating composition was prepared according to Example 1-a, except that fine particle titanium oxide in Example 1-a was not included.

<Comparative Example 1>
In Example 1-a, a clear coating composition was prepared according to Example 1-a, except that the PWC of fine particle titanium oxide was 5 parts by mass with respect to the solid content of the binder component.

[Creation of clear coating for test]
Each clear coating composition obtained in Examples 1-a and 1-b, Reference Examples 1 and 2, and Comparative Example 1 was applied by air spray on a tin plate so that the dry film thickness was 30 μm. Heat cured for 30 minutes. Then, the cured coating film was peeled off from the tinplate, and each test coating film having a width of 1 cm, a length of 30 cm, and a film thickness of 30 μm was prepared. Each of the prepared test coating films was subjected to the following evaluation test. The results obtained are shown in Table 3.

[UV transmittance and visible light transmittance]
Using a Hitachi spectrophotometer U-3000 (trade name, manufactured by Hitachi High-Technologies Corporation), the transmittance of the test coating film and the reference coating film from a wavelength of 500 nm to 300 nm was measured. The transmittance (%) of each wavelength was determined by correcting the transmittance of the test coating film with the transmittance of the reference coating film according to the following formula.
Table 3 shows the transmittance (%) at a wavelength of 300 to 400 nm as the ultraviolet transmittance and the transmittance (%) at a wavelength of 400 to 700 nm as the visible light transmittance among the transmittance (%) determined by the above formula. It was.
In Table 3, components with different blending amounts in the clear coating composition are clearly shown and evaluation results are shown.

* 2, * 4, * 5: Since they are the same as described above, description here is omitted.
* 6: “UVA” is an abbreviation for ultraviolet absorbers, and “HALS” is an abbreviation for hindered amine light stabilizers. The trade name “TINUVIN 900” (manufactured by BASF) was used as the ultraviolet absorber, and the trade name “TINUVIN 144” (manufactured by BASF) was used as the hindered amine light stabilizer.

  As shown in Table 3, by adding a small amount of fine particle titanium oxide as compared with the conventional one, the transmittance of visible light is maintained while maintaining the ultraviolet transmittance even when the addition amount of the ultraviolet absorber and the hindered amine light stabilizer is reduced. It was found that can be kept high.

<Example 2>
[Formation of multi-layer coating film]
A dull steel plate (length 300 mm, width 100 mm and thickness 0.8 mm) is degreased using a trade name “Surf Clear EC92” (manufactured by Nippon Paint Co., Ltd.), and then a zinc phosphate treating agent (trade name) After chemical conversion treatment using "Surffine GL1 / Surfdyne SD6350" (manufactured by Nippon Paint Co., Ltd.), a cationic electrodeposition paint (trade name "Powernics PN 1010E", manufactured by Nippon Paint Co., Ltd.) Electrodeposition coating was performed so that the thickness was 25 μm. Next, after baking at 160 ° C. for 30 minutes, as an intermediate coating material, a polyester / melamine gray intermediate coating material (trade name “Orga P-30-8005”, manufactured by Nippon Paint Co., Ltd.) is used as ethyl acetate / solvesso 100 / butyl. Diglycol acetate = 1/1/1 (mass ratio), Ford Cup No. 4 was adjusted so that the viscosity was 30 seconds, and the intermediate coating was performed using a rotary electrostatic coating machine, and baked and dried at 140 ° C. for 30 minutes. The intermediate coating film with an average dry film thickness of 30 μm Formed.

Further, a base paint (trade name “SPM-350 # 5A #”, manufactured by Nippon Paint Co., Ltd.) was spray-coated on the intermediate coating film so that the average dry film thickness was 15 μm. The coating was performed using an electrostatic coating machine (“AutoREA”, manufactured by ABB Industry) at an atomization pressure of 2.0 kg / cm ² . The booth atmosphere during painting was maintained at a temperature of 25 ° C. and a humidity of 75%. After setting for 60 seconds, set for 3 minutes after painting, preheat at 80 ° C. for 5 minutes, and then wet-on-wet the clear coating composition of the ingredients shown in Table 4 to a dry film thickness of 35 μm. This was spray-coated, set at room temperature for 7 minutes, and baked at a temperature of 140 ° C. for 30 minutes to form a multilayer coating film by 2 coats 1 bake (2C1B).
Here, the clear composition used for the multilayer coating film of Example 2 is the same as the clear coating composition of Example 1.

<Examples 3-7, Comparative Examples 2-11>
A multilayer according to Example 2 except that the organic ultraviolet absorber, hindered amine light stabilizer and fine particle titanium oxide in the clear coating composition of Example 1 were replaced with the compositions shown in Tables 4 and 5. A coating film was formed.

<Example 8>
Fine titanium oxide (trade name “MT-700HD”, manufactured by Teika Co., Ltd., primary particle average particle diameter: 50 nm) in the clear coating composition used in Example 1 was converted to fine titanium oxide (trade name “MT”). The multilayer coating film shown in Table 4 was formed in accordance with Example 2 except that it was changed to “−100S”, manufactured by Teika Co., Ltd., and the average particle diameter of primary particles: 15 nm.

<Example 9>
Fine titanium oxide (trade name “MT-700HD”, manufactured by Teika Co., Ltd., primary particle average particle diameter: 50 nm) in the clear coating composition used in Example 1 was converted to fine titanium oxide (trade name “MT”). A multilayer coating film shown in Table 4 was formed in accordance with Example 2 except that it was changed to “-500 SA”, manufactured by Teika Co., Ltd., and the average particle diameter of primary particles: 35 nm.

〔Evaluation method〕
<Xenon method>
In accordance with the xenon lamp method of JIS K5600-7-7, a super-xenon weather meter SX2-75 (manufactured by Suga Test Instruments Co., Ltd.) is attached with a test piece (hereinafter referred to as “test piece”) on which a multilayer coating film is formed. Then, accelerated exposure was performed for 2000 hours at an illuminance of 180 W / m ² using simulated sunlight.
(Glossy)
After accelerated exposure, the 60 ° gloss value of the surface of the test piece was measured using a surface gloss system defined in JIS Z 8741 (Specular Glossiness—Measurement Method) and ASTM D 523. The 60 ° gloss value was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). The passing score was “80 or more”.
(Color difference)
After the accelerated exposure, the color difference of the test piece was evaluated by measuring the L value with CR400 (manufactured by Konica Minolta) and the magnitude of the absolute value | ΔL | of the change with respect to the L value before the test. The smaller the color difference, the better.

<DPW method>
The test piece was used as an accelerated weather resistance test QUV (product name “Dupanel Control Weather Meter (FDP)” manufactured by Suga Test Instruments Co., Ltd.), and the light irradiation was simulated sunlight at an illuminance of 180 W / m ² at 70 ° C. 8 hours, 4 hours at 50 ° C. condensation, 12 hours in total for one cycle, this is repeated for 250 hours. )
(Break)
Visual evaluation was performed. When the continuity of the coated surface was broken into cracks and cracks, it was judged as “break”. The numerical value of “crack” is a result of evaluating the time (hour) at which crack occurred, and the higher this value, the higher the weather resistance.
(Glossy)
After accelerated exposure, the 60 ° gloss value of the surface of the test piece was measured using a surface gloss system defined in JIS Z 8741 (Specular Glossiness—Measurement Method) and ASTM D 523. The 60 ° gloss value was measured using a gloss meter (micro-TRI-gloss, manufactured by BYK-Gardner). The passing score was “80 or more”.

* 4, * 5, * 6: Since they are the same as described above, description here is omitted.
* 7: Trade name “MT-700HD” (manufactured by Teika Co., Ltd., average particle diameter of primary particles: 50 nm)

  * 4, * 5, * 6, * 7: Since they are the same as described above, description thereof is omitted here.

  As shown in Tables 4 and 5, it was found that the multilayer coating films obtained by the examples had higher weather resistance than the comparative examples in any of the accelerated weathering test methods of the Xenon method and the DPW method. . It was also found that by adding a small amount of fine particle titanium oxide, even if the addition amount of the ultraviolet absorber and the hindered amine light stabilizer is reduced, the weather resistance is sufficiently obtained.

  The method for forming a multilayer coating film for an automobile body using the clear coating composition for an automobile body according to the present invention is particularly applicable to the coating of automobile bodies and parts, and provides a multilayer coating film having excellent weather resistance. can do.

  10 substrate, 12 electrodeposition coating, 14 intermediate coating, 16 base coating, 18 clear coating.

Claims (5)

A clear coating composition for an automobile body containing a binder component (a), an organic ultraviolet absorber (b), a hindered amine light stabilizer (c) and fine particle titanium oxide (d),
The average particle diameter of primary particles of the fine particle titanium oxide (d) is 10 nm or more and 50 nm or less,
A clear coating composition for automobile bodies, wherein the PWC of the fine particle titanium oxide (d) is 0.025 parts by mass or more and 0.050 parts by mass or less with respect to the solid content of the binder component (a). PWC of the organic ultraviolet absorber (b) is 1 part by mass or more and 3 parts by mass or less with respect to the solid content of the binder component (a),
2. The automobile body according to claim 1, wherein the PWC of the hindered amine light stabilizer (c) is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to the solid content of the binder component (a). Clear paint composition. A method for forming a multilayer coating film for an automobile body, wherein a base coating film is formed on a substrate on which a base coating film is formed, and further a clear coating film is formed thereon,
A clear coating composition for an automobile body that forms a clear coating film includes a binder component (a), an organic ultraviolet absorber (b), a hindered amine light stabilizer (c), and fine particle titanium oxide (d),
The average particle diameter of primary particles of the fine particle titanium oxide (d) is 10 nm or more and 50 nm or less,
The multilayer coating film for automobile bodies, wherein the fine particle titanium oxide (d) has a PWC of 0.025 parts by mass or more and 0.050 parts by mass or less based on the solid content of the binder component (a). Forming method. PWC of the organic ultraviolet absorber (b) is 1 part by mass or more and 3 parts by mass or less with respect to the solid content of the binder component (a),
The automobile body according to claim 3, wherein a PWC of the hindered amine light stabilizer (c) is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to the solid content of the binder component (a). A method for forming a multilayer coating film.   The multilayer coating film for motor vehicle bodies containing the base coating film and the clear coating film formed by the method of Claim 3 or 4.