JP2012050908A - Method of forming multi-layer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a multi-layer coating film exhibiting high brightness at both of a highlight position and a shade position, and having dense brilliant feeling.SOLUTION: This method of forming the multi-layer coating film includes a process for forming a base coating film containing an aluminum pigment (A) having an average particle diameter of 5-12 μm, a white-colored aluminum pigment (B) having an average particle diameter of 5-12 μm, and an alumina flake pigment coated with metal oxide (C) having an average particle diameter of 15-25 μm and having an interference color; and a process for forming a clear coating film. The multi-layer coating film has the brightness of the coating film at 15 degrees (L15 value) of 95 or more, the brightness of the coating film at 110 degrees (L110 value) of 43 or more, and a total pigment concentration (PWC) of the aluminum pigment (A), the white-colored aluminum pigment (B) and the alumina flake pigment coated with metal oxide (C) in the base coating film is 10-20 mass%, and a mass ratio (C)/((A)+(B)) of the alumina flake pigment coated with metal oxide (C) to the total of the aluminum pigment (A) and the white-colored aluminum pigment (B) is 1/20-10/4.

Description

  The present invention relates to a method for forming a multilayer coating film that can be applied to painting of an automobile body or the like and has high brightness at both a highlight position and a shade position and has a fine glitter feeling.

  A plurality of coating films having various roles are sequentially formed on the surface of an object such as an automobile body to protect the object to be coated and at the same time impart a beautiful appearance and an excellent design. As a method of forming a multilayer coating film, a method of forming an undercoating film such as an electrodeposition coating film on an object having excellent conductivity, and sequentially forming an intermediate coating film and an overcoating film thereon Is common. Among these coating films, the top coating film composed of a base coating film and a clear coating film particularly greatly affects the appearance and design of the coating film. In particular, in automobiles, the appearance and design of a top coating film comprising a base coating film and a clear coating film formed on a vehicle body are extremely important.

  In addition, recently, consumers tend to prefer a brilliant paint color rather than a so-called solid color. Furthermore, consumer preferences for coating films are diversifying, and a top coating film having a so-called intermediate hue such as purple or brown is being demanded. On the other hand, achromatic hues of white, gray and black are still popular among Japanese consumers. In these achromatic hues, those having a glittering feeling tend to be preferred.

  A bright metallic pigment coating such as an aluminum pigment is generally used for a metallic silver coating film having a bright feeling. In a general metallic silver coating film, a bright pigment appears to shine by reflecting a lot of light at a highlight position. On the other hand, in the shade position, the shadow caused by this glittering pigment is visible, and the coating appears dark and dark. This is because a bright pigment such as an aluminum pigment has a large average particle diameter and aspect ratio (average particle diameter / average thickness) in order to reflect a large amount of light.

  Examples of glitter pigments other than aluminum pigments include mica pigments. However, since the mica pigment has a smaller function of reflecting incident light than the aluminum pigment, the glitter feeling at the highlight position is weak and the metallic feeling is weak. Further, this mica pigment makes the color of the coating appear cloudy at the shade position, giving an impression of becoming clouded.

  As described above, in the metallic silver coating film, when the glittering feeling at the highlight position is expressed, the coating film has a problem that the coating film is darkened or darkened at the shade position. For this reason, it has been difficult to obtain a metallic coating film that has a bright feeling at a highlight position and is not accompanied by darkness or cloudiness even at a shade position, and has a high brightness and a refreshing feeling.

  JP-A-2002-275423 (Patent Document 1) describes a glittering paint composition containing a titanium dioxide-coated white colored aluminum flake pigment, an aluminum flake pigment not coated with titanium dioxide, and a vehicle. And it describes that the multilayer coating film formed with this glittering paint composition is excellent in the FF effect, the improvement of a glitter feeling, and white based on the combination using the said 2 types of aluminum flake pigment. On the other hand, in the present invention, three kinds of glitter pigments of an aluminum pigment (A), a white colored aluminum pigment (B), and a metal oxide-coated alumina flake pigment (C) having an interference color are used as essential components. This is different from the invention described in Patent Document 1. Further, Patent Document 1 aims to improve the FF (flip-flop) effect, that is, to form a coating film that looks bright at the highlight position and dark at the shade position. On the other hand, in this invention, it aims at providing the method of forming the metallic coating film which has high brightness in both a highlight position and a shade position, and patent document 1 and this invention have the target design. Different.

JP 2002-275423 A

  An object of the present invention is to provide a method for forming a multilayer coating film having high brightness at both a highlight position and a shade position and having a dense glitter feeling (glitter feeling).

The present invention
An aluminum pigment (A) having an average particle diameter of 5 to 12 μm; a white-colored aluminum pigment (B) having an average particle diameter of 5 to 12 μm; and a metal oxide having an interference color having an average particle diameter of 15 to 25 μm on the object to be coated A method for forming a multilayer coating film, comprising: forming a base coating film containing a coated alumina flake pigment (C); and further forming a clear coating film,
This multi-layer coating film has a ∠15 degree coating film brightness (L15 value) of 95 or more, a ∠110 degree coating film brightness (L110 value) of 43 or more,
The total pigment concentration (PWC) of the aluminum pigment (A), the white colored aluminum pigment (B) and the metal oxide-coated alumina flake pigment (C) in the base coating film is 10 to 20% by mass, and this metal The mass ratio (C) / ((A) + (B)) of the oxide-coated alumina flake pigment (C) and the total amount of the aluminum pigment (A) and the white colored aluminum pigment (B) is 1/20. 10/4,
The formation method of a multilayer coating film is provided, and the said subject is solved by this.

  The mass ratio (A) / (B) of the aluminum pigment (A) and the white colored aluminum pigment (B) is preferably 3/7 to 7/3.

  The white colored aluminum pigment (B) is a pigment in which aluminum flakes are coated with a color pigment containing titanium dioxide. The aluminum flakes have an average thickness in the range of 0.01 to 1 μm, and an aspect ratio (average The particle size / average thickness is preferably in the range of 50 to 1000.

  The present invention also provides a multilayer coating film obtained by the method for forming a multilayer coating film.

The multi-layer coating film obtained by the method of the present invention does not have a glittery metallic shine, but has a fine shine (shiny sensation) in which fine particles shine delicately in response to the incidence of light. is doing. This multi-layer coating film has higher brightness at both the highlight position and the shade position. This multi-layer coating film is a multi-layer coating film where a bright feeling is felt at the highlight position, and there is no darkness or cloudiness at the shade position, and a high brightness and a clear glitter feeling is felt. . The multi-layer coating film obtained by the present invention expresses a fine radiance in the part where the light is different, and it seems that a fine light with glittering glitters. This fine glitter can be visually recognized even at the shade position. As described above, the multilayer coating film of the present invention is a highly designable coating film in which a delicate glitter is visually recognized, and at the same time has high brightness at both the highlight position and the shade position, and at the shade position. It is a coating film with a clean and bright design that does not have a darkness or cloudiness.
There is an advantage that an excellent design can be imparted by applying the method for forming a multilayer coating film of the present invention to the coating of automobile bodies and parts.

It is a schematic explanatory drawing which shows the measurement position of the lightness (L *) in an Example and a comparative example. It is a graph which shows the value of the 15 degree coating film brightness (L15 value) and the 110 degree coating film brightness (L110 value) of the multilayer coating film obtained by the Example and the comparative example.

  The method for forming a multi-layer coating film of the present invention is a method of sequentially forming a base coating film and a clear coating film on an object to be coated on which an undercoat coating film and an intermediate coating film are formed. Hereinafter, the base coating composition used for forming the base coating film and the clear coating composition used for forming the clear coating film will be sequentially described.

Base coating composition In the method of the present invention, the base coating film comprises an aluminum pigment (A) having an average particle diameter of 5 to 12 μm; a white-colored aluminum pigment (B) having an average particle diameter of 5 to 12 μm; and an average particle diameter of 15 to 25 μm. Is formed by using a base coating composition comprising a metal oxide coated alumina flake pigment (C) having an interference color of In addition to the pigments (A) to (C), the base coating composition contains a film-forming resin, and optionally a curing agent and other components.

Aluminum pigment (A)
The base coating composition used in the method of the present invention contains an aluminum pigment (A). The aluminum pigment (A) used in the present invention is limited to those having an average particle diameter (D ₅₀ ) of 5 to 12 μm. The average particle size is more preferably 6 to 10 μm. When the average particle diameter of the aluminum pigment (A) exceeds 12 μm, the brightness at the highlight position becomes high. In addition, a multi-layer coating film having a fine glitter feeling (glitter feeling) cannot be obtained. When the average particle diameter of the aluminum pigment (A) is less than 5 μm, the glitter feeling at the highlight position is inferior.

  The aluminum pigment (A) preferably has an average thickness of 0.1 to 1 μm.

The average particle size of the aluminum pigment (A) is to measure particle size distribution by a laser diffraction method, showing a median value (D _50). The average thickness of the aluminum pigment (A) can be determined by observing and measuring the cross section of the aluminum pigment using, for example, a scanning electron microscope.

  The aluminum pigment (A) can be produced by a vapor deposition method or a pulverization method.

  As the aluminum pigment (A), an aluminum pigment coated with an organic film or an inorganic film may be used. Examples of organic coatings include monomeric or polymer (oligomer) fatty acids such as dimer acid, organic phosphates, phosphate ester compounds, organic phosphonic acid compounds (esters), aminosilane compounds, and organic silicate compounds such as silane coupling agents. Examples of inorganic coatings include borate, phosphate, phosphite, silicate, molybdate, vanadate, chromium oxide, zirconium oxide, and aluminum oxide. . However, the coating component constituting the white-colored aluminum pigment (B) below is not included in the organic coating or the inorganic coating described here. In the aluminum pigment coated with such an organic film or inorganic film, the surface of the metal pigment is stabilized by the coating. By using an aluminum pigment coated with such an organic film or inorganic film, there is an advantage that generation of hydrogen gas in the paint can be suppressed when the base paint composition is an aqueous base paint. .

  A commercially available pigment may be used as the aluminum pigment (A). Examples of commercially available pigments include aluminum pigment pastes “96-0635”, “97-0510”, “6390NS”, and “4690NS” manufactured by Toyo Aluminum.

  The concentration (PWC) of the aluminum pigment (A) is preferably 2 to 10% by mass and more preferably 3 to 7% by mass in the base coating composition (and the base coating film). When the density | concentration of an aluminum pigment (A) exceeds 10 mass%, there exists a possibility that the external appearance of the obtained multilayer coating film may be inferior. When the density | concentration of an aluminum pigment (A) is less than 2 mass%, there exists a possibility that the base concealability of the obtained multilayer coating film may be inferior. This density | concentration (PWC) represents the mass of the aluminum pigment (A) in percentage (mass%) with respect to the mass of the total solid of a base coating composition, and the density | concentration with respect to the total solid of a base coating film. It has the same meaning as (PWC). The total solid content of the base coating composition includes an aluminum pigment (A), a white colored aluminum pigment (B), a metal oxide-coated alumina flake pigment (C), and a resin solid content of the base coating composition. All other corresponding pigments and other components (solids) are included.

White colored aluminum pigment (B)
The base coating composition used in the method of the present invention contains a white colored aluminum pigment (B) in combination with the aluminum pigment (A). In the present specification, the term “white coloring” means a pigment whose white color has been visually recognized by attaching a white pigment to the surface of an aluminum pigment that usually has a metallic color.

The white colored aluminum pigment (B) used in the present invention is limited to those having an average particle diameter (D ₅₀ ) of 5 to 12 μm. The average particle size is more preferably 6 to 10 μm. When the average particle diameter of the white colored aluminum pigment (B) exceeds 12 μm, the degree of orientation increases, the brightness difference between the highlight position and the shade position increases, and the brightness at the shade position decreases. In addition, a multi-layer coating film having a fine glitter feeling (glitter feeling) cannot be obtained. When the average particle diameter of the white colored aluminum pigment (B) is less than 5 μm, the glitter feeling at the highlight position is inferior.

  The white colored aluminum pigment (B) can be produced by coating aluminum flakes with a white pigment such as titanium dioxide. The average thickness of the aluminum flakes constituting the white colored aluminum pigment (B) is preferably in the range of 0.01 to 1 μm, and more preferably in the range of 0.03 to 0.8 μm. When the average thickness is less than 0.01 μm, the aluminum flakes are pulverized in the process of producing the white colored aluminum pigment (B) and become finer, and the glittering feeling tends to decrease. On the other hand, if the average thickness is greater than 1 μm, the average thickness of the white colored aluminum pigment (B) may exceed 1 μm, and a coating film having the intended design may not be obtained.

  The aspect ratio (average particle size / average thickness) of the aluminum flakes is preferably in the range of 50 to 1000, more preferably in the range of 80 to 500. When the aspect ratio is less than 50, the glitter of the pigment tends to be insufficient, and when the aspect ratio is greater than 1000, the color tone of the pigment tends to change.

  The average particle size of the aluminum flakes is preferably in the range of 5 to 12 μm. When the average particle size is smaller than 5 μm, the glitter of the pigment tends to be insufficient. On the other hand, when the average particle diameter is larger than 12 μm, the average particle diameter of the white colored aluminum pigment (B) also exceeds 12 μm, and the brightness at the shade position is lowered. In addition, what was manufactured by the vapor deposition method or the grinding | pulverization method can be used as aluminum flakes.

The average particle size in the white colored aluminum pigment (B) is a median value (D ₅₀ ) measured by a particle size distribution by a laser diffraction method. The average thickness of the white colored aluminum pigment (B) can be determined by observing and measuring the cross section of the aluminum pigment using, for example, a scanning electron microscope. The average particle diameter and average thickness of the aluminum flakes constituting the white colored aluminum pigment (B) can be measured in the same manner.

The white colored aluminum pigment (B) can be obtained by coating the aluminum flakes with a white colored pigment. Examples of white pigments include colored pigments such as titanium dioxide. In particular, titanium dioxide is preferably used as the white pigment. The color pigment preferably has a primary particle size in the range of 0.01 to 0.1 μm, and more preferably in the range of 0.02 to 0.05 μm. When the primary particle diameter is less than 0.01 μm, the pigment tends to be difficult to disperse, and when the primary particle diameter exceeds 0.1 μm, it tends to be difficult to uniformly adhere to the aluminum flakes. The primary particle diameter of the colored pigment is a median value (D ₅₀ ) measured by a particle size distribution by a laser diffraction method.

  The content of the color pigment in the white colored aluminum pigment (B) is preferably in the range of 100 to 500 parts by mass, more preferably in the range of 200 to 400 parts by mass with respect to 100 parts by mass of the aluminum flakes. When the content of the color pigment is less than 100 parts by mass, there is a tendency that sufficient coloring cannot be obtained, and when the content of the color pigment exceeds 500 parts by mass, the color pigment may easily fall off.

  In the white colored aluminum pigment (B), the color pigment may adhere to the individual particle surfaces of the aluminum flakes in a state of partially covering the particle surface, but uniformly adhered to the entire particle surface. Is preferred. Furthermore, it is more preferable if the thickness of the color pigment layer on the particle surface is equivalent to one color pigment particle. By uniformly attaching the color pigment to the entire surface of the aluminum flake particles, the particles of the individual aluminum flakes can be colored efficiently and vividly, and the color pigment can be easily fixed to the surface of the metal pigment.

  The white colored aluminum pigment (B) is prepared by coating aluminum flakes with a colored pigment such as titanium dioxide. As a method for preparing the white colored aluminum pigment (B), there is a method in which aluminum flakes are mixed with a dispersion of colored pigments in a nonpolar solvent, and the colored pigments are adhered to the surface of the aluminum flakes. Here, it is preferable to form an inorganic acid group adsorption layer by previously adsorbing a compound containing an inorganic acid group on the surface of the aluminum flake. Further, it is preferable that the surface of the colored pigment is previously coated with an amino compound and / or a monobasic aromatic carboxylic acid.

  In the preparation of the white colored aluminum pigment (B), an inorganic acid group adsorption layer is provided in advance on the aluminum flakes, thereby increasing the active sites on the surface of the aluminum flakes and facilitating the adhesion of the colored pigments. Work to raise. Preferable inorganic acid groups include, for example, phosphoric acid, molybdic acid, tungstic acid, vanadic acid, and their condensates such as pyrophosphoric acid, polyphosphoric acid, polymolybdic acid, polytungstic acid, phosphomolybdic acid, and phosphotungsten. An acid etc. are mentioned.

  The method for adsorbing the inorganic acid group on the surface of the aluminum flake is not particularly limited. For example, an acid having an inorganic acid group or a compound such as an ammonium salt is mixed with water or an alcohol solvent, a glycol ether solvent, A solution dissolved in a hydrophilic solvent such as a ketone solvent is added to a mixture of an organic solvent and aluminum flakes, stirred or mixed or kneaded in a slurry state or a paste state, and inorganic acid groups are formed on the surface of the aluminum flakes. A reaction and adsorption method is preferred.

  The amount of the inorganic acid group adsorbed on the surface of the aluminum flakes is preferably in the range of 0.05 to 5 parts by mass with respect to 100 parts by mass of the aluminum flakes. When the amount of the inorganic acid group is less than 0.05 parts by mass, the color pigment tends to be insufficiently adhered to the surface of the aluminum flakes. When the amount of the inorganic acid group exceeds 5 parts by mass, the aluminum flakes Problems such as agglomeration may occur.

  By coating the surface of the color pigment with an amino compound and / or a monobasic aromatic carboxylic acid, the adhesion between the color pigment and the aluminum flakes can be enhanced by a heteroaggregation phenomenon in a nonpolar solvent. Examples of amino compounds include aliphatic diamines having 6 to 12 carbon atoms, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, and the like. Can be mentioned. Examples of the monobasic aromatic carboxylic acid include benzoic acid, aminobenzoic acid, aminohydroxybenzoic acid, naphthoic acid, aminonaphthoic acid, cinnamic acid, and aminocinnamic acid.

  The total content of the amino compound and / or the monobasic aromatic carboxylic acid in the white colored aluminum pigment (B) may be in the range of 0.2 to 100 parts by mass with respect to 100 parts by mass of the colored pigment. The range of 0.5 to 50 parts by mass is more preferable.

  The method for coating the surface of the color pigment with the amino compound and / or monobasic aromatic carboxylic acid is not particularly limited. For example, aliphatic carbonization having a boiling point in the range of 100 to 250 ° C. A method including a step of dissolving an amino compound and / or a monobasic aromatic carboxylic acid in a nonpolar solvent of hydrogen or aromatic hydrocarbon and dispersing a color pigment in the resulting solution is preferable.

  The white colored aluminum pigment (B) was prepared by, as necessary, adding a colored pigment coated with an amino compound and / or a monobasic aromatic carboxylic acid to an aluminum flake having an inorganic acid group adsorption layer as necessary. It is prepared by coating. Here, a method of mixing aluminum flakes with a dispersion of colored pigments in a nonpolar solvent and attaching the colored pigments to the surface of the aluminum flakes can be mentioned.

  As the nonpolar solvent, an aliphatic hydrocarbon, an aromatic hydrocarbon and a mixture thereof having a boiling point in the range of 100 to 250 ° C. are preferable. Specific examples of the nonpolar solvent include normal paraffin, isoparaffin, toluene, xylene, solvent naphtha, kerosene, mineral spirit, petroleum benzine and the like. If necessary, a small amount of an alcohol solvent or an ester solvent may be added to assist the dispersion of the color pigment. As a method for dispersing aluminum flakes and coloring pigments, a dispersion method using a grinding medium such as a ball mill, a bead mill, or a sand mill is preferable, but a dispersion method using stirring by a stirrer or a disper is also preferable.

  The white colored aluminum pigment (B) thus obtained has high brightness because the white colored pigment is uniformly attached to the individual particle surfaces of the aluminum flakes.

  The surface of the white colored aluminum pigment (B) thus obtained may be further covered with a film of the resin composition. The resin composition that can be used as the coating is preferably a resin composition containing a polymer synthesized from a polymerizable monomer by in-situ polymerization. Here, in-situ polymerization means polymerizing a polymerizable monomer such as an acrylic monomer in the process of producing the white colored aluminum pigment (B), specifically, coloring. The aluminum flakes with pigments are dispersed in a solvent to form a slurry. While adding a polymerizable monomer and stirring and mixing, a polymerization initiator is further added to cause a polymerization reaction, and a polymer is formed on the surface of the aluminum flakes. Is to be precipitated.

  The coating amount when the white colored aluminum pigment (B) is coated with the resin composition is preferably in the range of 30 to 300 parts by mass with respect to 100 parts by mass of the aluminum flakes contained in the white colored aluminum pigment (B). The range of 50 to 200 parts by mass is more preferable.

  The white colored aluminum pigment (B) preferably has an average thickness of 0.1 to 1 μm, and more preferably 0.15 to 0.8 μm. When the average thickness is less than 0.1 μm, the white-colored aluminum pigment (B) may be deformed or crushed during the production process of the coating composition using the white-colored aluminum pigment (B) to change the color tone. There is. If the average thickness exceeds 1 μm, the white-colored aluminum pigment (B) tends to protrude on the surface of the coating film, and a coating film having the intended design may not be obtained.

  A commercially available pigment may be used as the white colored aluminum pigment (B). Examples of commercially available pigments include white colored aluminum pigment pastes “97-4053WH”, “97-4057WH”, “97-4002WH”, and “98-4083WH” manufactured by Toyo Aluminum.

  The concentration (PWC) of the white colored aluminum pigment (B) in the base coating composition (and the base coating film) is preferably 2 to 10% by mass, and more preferably 3 to 7% by mass. When the concentration of the white colored aluminum pigment (B) exceeds 10% by mass, the appearance of the resulting multilayer coating film may be inferior. When the density | concentration of a white coloring aluminum pigment (B) is less than 2 mass%, there exists a possibility that the brightness in the shade position of the obtained multilayer coating film may fall. This concentration (PWC) represents the mass of the white colored aluminum pigment (B) in percentage (mass%) with respect to the mass of the total solid content of the base coating composition, and the total solid content of the base coating film. It has the same meaning as the concentration (PWC). The total solid content of the base coating composition includes an aluminum pigment (A), a white colored aluminum pigment (B), a metal oxide-coated alumina flake pigment (C), and a resin solid content of the base coating composition. All other corresponding pigments and other components (solids) are included.

  The mass ratio (A) / (B) of the aluminum pigment (A) and the white colored aluminum pigment (B) is preferably 3/7 to 7/3. By including the aluminum pigment (A) and the white-colored aluminum pigment (B) in the above mass ratio range, there is an advantage that the brightness at both the highlight position and the shade position can be set high and concealment can be imparted. is there.

Metal oxide coated alumina flake pigment (C)
The base coating composition used in the method of the present invention contains a metal oxide-coated alumina flake pigment (C). In this metal oxide-coated alumina flake pigment, natural or synthetic alumina flake (aluminum oxide: Al ₂ O ₃ ) is desirably uniformly coated with a metal oxide mainly composed of titanium dioxide (TiO ₂ ). Can be manufactured by. An interference color is developed by coating alumina flakes with a metal oxide mainly composed of titanium dioxide (TiO ₂ ).

In the present invention, the metal oxide-coated alumina flake pigment (C) is limited to those having an average particle diameter (D ₅₀ ) of 15 to 25 μm. The average particle size is more preferably 15 to 20 μm. When the average particle diameter is outside the above range, there is a possibility that a dense glitter feeling (glitter feeling) in the multilayer coating film cannot be achieved. In addition, the average particle diameter of the pigment in the present specification is a median value (D ₅₀ ) measured by a particle size distribution by a laser diffraction method.

  The thickness of the alumina flakes constituting the metal oxide-coated alumina flake pigment (C) is preferably 100 to 800 nm, more preferably 200 to 400 nm. If the thickness of the alumina flake is out of the above range, the color developability may be lowered. The alumina flakes are preferably synthetic alumina flakes. Synthetic alumina flakes have an advantage that more stable color development can be obtained because of high purity and a narrow average particle size distribution.

The metal oxide layer covering the alumina flakes contains titanium dioxide (TiO ₂ ). Since the refractive index of alumina flakes is 1.63 and the refractive index of titanium dioxide is 2.30, the refractive index is 0.5 or more between the alumina flakes as the substrate and the metal oxide layer as the coating layer. A difference in rate occurs, and thereby an interference color excellent in visibility appears. This metal oxide layer may contain a metal oxide other than titanium dioxide. Examples of such metal oxides include zirconium oxide (refractive index 2.40), iron oxide (refractive index 2.36), tin dioxide (refractive index 1.98), and zinc oxide (2.0). .

  The ratio of the metal oxide coating layer is preferably 10 to 50% by mass, more preferably 20 to 45% by mass, based on the total amount of the alumina flake (flake base material) and the coating layer. . Although the thickness of the said coating layer is not specifically limited, 50-500 nm is preferable.

  A commercially available product may be used as the metal oxide-coated alumina flake pigment (C). Specific examples of commercially available products of the metal oxide-coated alumina flake pigment (C) include trade names “Xiallic T60-10WNT”, “Xiallic T60-20WNT”, “Xiallic T60-21WNT”, “Xiallic T60-22WNT” manufactured by Merck & Co., Inc. ”,“ Xiallic T60-23WNT ”,“ Xiallic T60-24WNT ”,“ Xiallic T60-25WNT ”,“ Xiallic T61-10WNT ”, and the like.

  The concentration (PWC) of the metal oxide-coated alumina flake pigment (C) is preferably 1 to 10% by mass and more preferably 1 to 8% by mass in the base coating composition (and the base coating film). preferable. If the concentration of the metal oxide-coated alumina flake pigment (C) is less than 1% by mass, the fine glitter (glitter) may be reduced, and if it exceeds 10% by mass, the finished appearance may be reduced. is there. This concentration (PWC) represents the mass of the metal oxide-coated alumina flake pigment (C) as a percentage (mass%) with respect to the mass of the total solid content of the base coating composition. It has the same meaning as the concentration (PWC) based on the total solid content. The total solid content of the base coating composition includes an aluminum pigment (A), a white colored aluminum pigment (B), a metal oxide-coated alumina flake pigment (C), and a resin solid content of the base coating composition. All other corresponding pigments and other components (solids) are included.

  In the present invention, the mass ratio (C) / ((A) + (B)) of the metal oxide-coated alumina flake pigment (C) and the total amount of the aluminum pigment (A) and the white colored aluminum pigment (B) is , 1/20 to 10/4. When the mass ratio of the pigments (A) to (C) deviates from the above range, there is a fear that the expression of a dense glitter (glitter feeling) and high brightness at both the highlight position and the shade position cannot be achieved. is there.

  In the present invention, the total pigment concentration (PWC) of the aluminum pigment (A), the white colored aluminum pigment (B) and the metal oxide-coated alumina flake pigment (C) in the base coating film is 10 to 20% by mass. The total pigment concentration is preferably 10 to 15% by mass. When the total pigment concentration (PWC) of the pigments (A) to (C) is less than 10% by mass, the concealability of the resulting coating film is lowered. When the total pigment concentration (PWC) of the pigments (A) to (C) exceeds 20% by mass, the appearance of the resulting coating film is deteriorated.

  In the present invention, the specific aluminum pigment (A), the white-colored aluminum pigment (B), and the metal oxide-coated alumina flake pigment (C) are contained in the base coating composition in the base coating film. ), (B) and (C) in a total pigment concentration (PWC) of 10 to 15% by mass, and the metal oxide-coated alumina flake pigment (C), the aluminum pigment (A) and the white colored aluminum By including the mass ratio (C) / ((A) + (B)) to the total amount of the pigment (B) in an amount of 1/20 to 10/4, both in the highlight position and the shade position. A multi-layer coating film having high brightness and a dense glitter feeling (glitter feeling) will be obtained. Specifically, the multilayer coating film thus obtained is a coating film having a ∠15 degree coating film brightness (L15 value) of 95 or more and a ∠110 degree coating film brightness (L110 value) of 43 or more. Here, “brightness” means L *. L * is a parameter in the L * C * h color system, and can be determined according to JIS Z8729. In the L * C * h color system, L * represents lightness, C * represents saturation, and h represents hue angle. The lightness L * means that the whiteness of the substance to be measured increases as the numerical value increases, and the blackness of the substance to be measured increases as the numerical value decreases.

  In the present invention, by using the specific pigments (A) to (C) in a specific amount range, a glittering feeling is felt at the highlight position, and no darkness or cloudiness is felt even at the shade position. Thus, it is possible to prepare a multilayer coating film that has a high brightness and feels a clean radiance. The multi-layer coating film obtained by the present invention expresses a fine shine in the light-diffused portion, and the shimmering fine light appears to shine. This fine glitter can be visually recognized even at the shade position. As described above, the multilayer coating film of the present invention is a coating film in which the glitter feeling can be visually recognized, and at the same time has high brightness at both the highlight position and the shade position, and is accompanied by a dark feeling or a cloudiness feeling at the shade position. It is characterized by being a coating film with a clean and bright design.

  In the present invention, if necessary, in addition to the aluminum pigment (A), the white colored aluminum pigment (B) and the metal oxide-coated alumina flake pigment (C), other organic colored pigments, inorganic type You may mix | blend pigments, such as a coloring pigment and extender, with a base coating composition suitably.

  As the coloring pigment, an organic coloring pigment and an inorganic coloring pigment can be used. Examples of organic coloring pigments include azo pigments (for example, azo chelate pigments, insoluble azo pigments, condensed azo pigments), quinacridone pigments, benzimidazolone pigments, diketopyrrolopyrrole pigments, and isoindole. Examples thereof include linone pigments, perinone pigments, perylene pigments, dioxane pigments, quinophthalone pigments, dioxazine pigments, and metal complex organic pigments. These may be used individually by 1 type and may be used in combination of 2 or more type.

  Examples of inorganic coloring pigments include chrome lead, zinc white, cadmium red, molybdenum red, chromium yellow, chromium oxide, yellow iron oxide, and bengara. These may be used individually by 1 type and may be used in combination of 2 or more type.

  Examples of extender pigments include calcium carbonate, barium sulfate, clay, and talc. These may be used alone or in combination of two or more.

  However, when these other pigments are used, they are used in an amount that does not adversely affect the design exhibited by the aluminum pigment (A), the white colored aluminum pigment (B) and the metal oxide-coated alumina flake pigment (C) in the present invention. Subject to being.

  In the base coating composition, the concentration (PWC) of all pigments is 5 to 50% by mass, preferably 5 to 30% by mass. If it is less than 5% by mass, the base concealability in the case of a coating film may be reduced, and if it exceeds 50% by mass, the finished appearance may be reduced.

Coating film-forming resin and curing agent Examples of the coating film-forming resin contained in the base coating composition used for forming the base coating film formed by the method of the present invention include acrylic resins, polyester resins, and alkyds. Resins, epoxy resins, polyurethane resins, polyether resins and the like can be mentioned, and acrylic resins and polyester resins are particularly preferably used. These can be used in combination of two or more. In addition, the film-forming resin includes a curable type and a lacquer type, but a curable type is usually used. In the case of a curable type, it is used after being mixed with a curing agent (or crosslinking agent) such as an amino resin and / or a blocked isocyanate compound, an amine, a polyamide, or a polyvalent carboxylic acid, and heated or at room temperature. The curing reaction can proceed. It is also possible to use a film-forming resin of a type having no curability in combination with a type having curability.

Examples of the acrylic resin acrylic resin include a copolymer of an acrylic monomer, or a copolymer of an acrylic monomer and another ethylenically unsaturated monomer. Acrylic monomers that can be used for the copolymerization include methyl, ethyl, propyl, n-butyl, i-butyl, t-butyl, 2-ethylhexyl, lauryl, phenyl of acrylic acid, methacrylic acid, acrylic acid or methacrylic acid. , Benzyl, 2-hydroxyethyl, 2-hydroxypropyl esterified products, acrylic acid or 2-hydroxyethyl methacrylate caprolactone ring-opening adduct, acrylamide, methacrylamide and N-methylolacrylamide. Examples of other ethylenically unsaturated monomers copolymerizable with these include styrene, α-methylstyrene (or dimer), itaconic acid, maleic acid, vinyl acetate and the like. Moreover, it is preferable to make an acrylic resin into an aqueous emulsion by a method known to those skilled in the art, for example, according to the method disclosed in JP-A-2007-39615.

As the polyester resin polyester resin, saturated and polyester resins and unsaturated polyester resins. For example, condensate obtained a polybasic acid and a polyhydric alcohol heated condensation and the like. Examples of the polybasic acid include saturated polybasic acids and unsaturated polybasic acids. Examples of the saturated polybasic acid include phthalic anhydride, terephthalic acid, succinic acid, and the like. Examples of the acid include maleic acid, maleic anhydride, fumaric acid and the like. Examples of the polyhydric alcohol include dihydric alcohol and trihydric alcohol. Examples of the dihydric alcohol include ethylene glycol and diethylene glycol. Examples of the trihydric alcohol include glycerin and trimethylolpropane. Etc.

Alkyd resin Alkyd resin reacts with the above polybasic acids and polyhydric alcohols and other modifiers such as fats and oils and fats (soybean oil, linseed oil, coconut oil, stearic acid, etc.) and natural resins (rosin, amber, etc.). The alkyd resin obtained by making it use can be used.

Examples of the epoxy resin epoxy resin include resins obtained by reaction of bisphenol and epichlorohydrin. Examples of bisphenol include bisphenol A and F. Examples of the bisphenol type epoxy resin include Epicoat 828, Epicoat 1001, Epicoat 1004, Epicoat 1007, Epicoat 1009 (all manufactured by Shell Chemical Co., Ltd.), etc., and these can be chained using an appropriate chain extender. Extended ones can also be used.

Examples of the polyurethane resin include a resin having a urethane bond obtained from various polyol components such as acrylic, polyester, polyether, and polycarbonate and a polyisocyanate compound. Examples of the polyisocyanate compound include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), and mixtures thereof (TDI), diphenylmethane-4,4 ′. Diisocyanate (4,4′-MDI), diphenylmethane-2,4′-diisocyanate (2,4′-MDI), and mixtures thereof (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3 ′ -Dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated HDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydrogenated xylylene diene Isocyanate (HXDI) It can be mentioned.

Polyether resin Polyether resin is a polymer or copolymer having an ether bond, such as polyoxyethylene polyether, polyoxypropylene polyether, polyoxybutylene polyether, bisphenol A or bisphenol F. A polyether resin having at least two hydroxyl groups per molecule, such as a polyether derived from an aromatic polyhydroxy compound, or the polyether resin and succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, Examples thereof include a carboxyl group-containing polyether resin obtained by reacting a polyvalent carboxylic acid such as terephthalic acid or trimellitic acid or a reactive derivative such as an acid anhydride thereof.

  As a ratio of the coating film-forming resin and the curing agent, the coating film-forming resin is preferably 90 to 50% by mass and the curing agent is 10 to 50% by mass in terms of solid content. It is 85-60 mass%, and it is more preferable that a hardening | curing agent is 15-40 mass%. When the curing agent is less than 10% by mass (when the coating film-forming resin exceeds 90% by mass), crosslinking in the coating film may not be sufficient. On the other hand, when the curing agent exceeds 50% by mass (when the coating film-forming resin is less than 50% by mass), the storage stability of the coating composition is decreased and the curing rate is increased, so that the coating film appearance may be decreased. There is.

The base coating composition that can be used in the present invention, such as other components , includes, in addition to the above components, polyamide wax which is a lubricating dispersion of aliphatic amide and polyethylene which is a colloidal dispersion mainly composed of oxidized polyethylene. Anti-settling agent such as wax, curing catalyst, UV absorber, antioxidant, leveling agent, surface conditioner such as silicon and organic polymer, anti-sagging agent, thickener, antifoaming agent, lubricant, organic amide, cross-linking Resin particles and the like can be added as appropriate. These additives are generally blended at a ratio of 15 parts by mass or less with respect to 100 parts by mass (solid content basis) of the total amount of the film-forming resin and the curing agent, thereby improving the performance of the paint or coating film. Can be improved.

  The base coating composition of the present invention is provided in a form in which the above-mentioned constituents are usually dissolved or dispersed in a solvent. Any solvent can be used as long as it dissolves or disperses the film-forming resin and the curing agent, and an organic solvent and / or water can be used. Examples of the organic solvent include those usually used in the paint field. Examples thereof include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ether ketone, esters such as ethyl acetate, cellosolve acetate and butylcellosolve, alcohols and the like. From the viewpoint of the environment, it is preferable to use water when the use of an organic solvent is regulated. In this case, an appropriate amount of a hydrophilic organic solvent may be blended.

  In a particularly preferred embodiment, the base coating composition that can be used in the present invention is obtained by water-dispersing a film-forming resin containing an acrylic resin emulsion and a reaction product obtained by reacting an acrylic resin and a hydrophobic melamine resin. It may contain the hardening | curing agent containing the hydrophobic melamine resin water dispersion of 20-140 nm of particle sizes obtained by this, By this, the coating film which has the outstanding coloring property can be obtained. In addition, in the method for forming a multilayer coating film in automobile coating, when the above base coating composition is used as a water-based coating, a coating film having excellent recoat adhesion, chipping property, and water-resistant adhesion can be obtained. Accordingly, the above base coating composition can be suitably used as an aqueous base coating composition.

Clear coating composition In the method of the present invention, the clear coating film is formed using a clear coating composition. The clear coating composition that can be used in the method of the present invention is not particularly limited, and a clear coating composition generally used for top coating can be used, for example, acrylic resin, polyester resin, fluorine It is possible to use at least one thermosetting resin selected from resins, epoxy resins, polyurethane resins, polyether resins, modified resins thereof, and the like, and those containing the curing agent as necessary.

  If necessary, the clear coating composition is a colored pigment, an extender pigment, a modifier, an ultraviolet absorber, a leveling agent, as long as the transparency is not impaired or the design of the base is not hindered. Additives such as a dispersant and an antifoaming agent can be blended. Further, a clear coating composition containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in JP-B-8-19315 forms the above base coating layer in terms of acid rain countermeasures and the W / W method. When used, it is preferably used from the viewpoint of not disturbing the orientation of the glitter pigment and the color pigment. In addition, the clear coating composition 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.

  Preferred examples of the solvent-based clear coating composition include a combination of an acrylic resin and / or a polyester resin with an amino resin and / or an isocyanate, or a carboxylic acid / epoxy curing system from the viewpoint of transparency or acid etching resistance. Examples thereof include acrylic resins and / or polyester resins.

  Examples of the water-based clear coating composition include a resin obtained by neutralizing a film-forming resin contained in the solvent-based clear coating composition described above as an example of the solvent-type clear coating composition with a base to make it water-based. Things can be mentioned. This neutralization can be carried out by adding tertiary amines such as dimethylethanolamine and triethylamine before or after polymerization.

  Furthermore, it is preferable that a viscosity control agent is added to the clear coating composition 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.

  In addition, as a clear coating composition used in the above-mentioned multilayer coating film forming method, Ford Cup No. 20 at 20 ° C. is used from the viewpoint of the influence on the environment due to the content of the organic solvent. 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.

Multilayer coating film forming method The method of the present invention is a multilayer coating film forming method in which a base coating film and a clear coating film are sequentially formed on an object to be coated.

The object to be coated used in the method for forming a multilayer coating film of the present invention is not particularly limited, and metals such as iron, aluminum, magnesium, copper, tin, zinc or alloys thereof, and Molded articles; inorganic materials such as glass; polyethylene resins, polypropylene resins, ethylene-vinyl acetate copolymer resins, polyamide resins, acrylic resins, vinylidene chloride resins, polycarbonate resins, polyurethane resins, epoxy resins, polyester resins, polystyrene resins, Examples thereof include resins such as ABS resin, various plastic materials such as FRP, and molded products or foams thereof; natural or synthetic materials such as wood and fiber materials (paper, cloth, etc.). In order to effectively express the vivid design obtained by the present invention, the object to be coated has a curved surface, for example, a car body and parts (car body, door, etc.) such as a passenger car, a truck, a motorcycle, and a bus. It is preferable that it has. Specific examples of the plastic molded product include automobile parts such as a spoiler, a bumper, a mirror cover, a grill, and a door knob. Further, these plastic molded articles are preferably washed with a neutral detergent. Furthermore, primer coating for enabling electrostatic coating may be applied.

  In the method for forming a multilayer coating film according to the present invention, when the object to be coated is an automobile body or its parts, the conductive object to be coated is previously subjected to degreasing treatment or chemical conversion treatment (such as phosphate or zirconium salt). After the chemical conversion treatment, etc., it is preferable to apply a base coating such as electrodeposition coating or intermediate coating to the object to be coated.

  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 or a steel plate, pretreatment up to degreasing, water washing, chemical film formation, water washing, pure water washing and drying is performed by a conventionally known method before electrodeposition coating film formation. Is preferred. As the electrodeposition coating film forming method, an appropriate method may be arbitrarily selected from conventionally known methods. Further, the electrodeposition coating film forming conditions, the bake 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. .

  In the intermediate coating, an intermediate coating layer is formed on the electrodeposition coating formed as necessary to improve performance such as undercoating, chipping resistance, and adhesion to the top coating layer. It is done for the purpose. The intermediate coating layer also functions as a base for smoothing the final glittering multilayer coating film to obtain a coating film having a good appearance. The intermediate coating layer further serves as a binder between the electrodeposition coating layer and the top coating layer, and can improve the weather resistance against degradation of the coating due to ultraviolet rays, water, etc. that reach through the coating surface. it can.

  There are no particular limitations on the intermediate coating composition that can form the intermediate coating layer. In addition to solvent-based coatings well known to those skilled in the art, aqueous coatings, powder coatings, high solid coatings, etc. Can also 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 the method for forming the intermediate coating film layer, an appropriate method can be arbitrarily selected from conventionally known methods. Further, in the present invention, a gray-based intermediate coating composition comprising carbon black and titanium dioxide as main pigments, a combination of set gray and various colored pigments that match the lightness and hue of the top coat layer, so-called A color intermediate coating composition can be used. These color intermediate coating compositions can develop a composite color of the intermediate coating layer and the top coating layer, 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 layer is preferably 20 to 100 μm, more preferably 30 to 50 μm.

  The intermediate coating film layer 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. If the upper limit is exceeded, the coating film becomes hard and brittle, and if it is less than the lower limit, curing is not sufficient. The curing time varies depending on the curing temperature, but 10 to 30 minutes at 120 to 160 ° C. is appropriate.

Application of base coating composition and clear coating composition In the method of the present invention, the base coating composition and the clear coating composition are applied in this order on the above-mentioned object by wet-on-wet, and then these coating films are applied. It is preferable to form a coating film by a two-coat one-bake method in which 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 the object to be coated, 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. If it is less than 5 μm, the underlying layer cannot be concealed and there is a risk of film breakage. If it exceeds 30 μm, there is a risk of problems such as flow during painting.

  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, the underlying concavity and convexity may be insufficient. 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 lower 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-coat two-bake, after the base coating composition is applied, it is cured by heating, for example, at 120 to 160 ° C. for 10 to 30 minutes, and then the clear coating composition is used as described above. Similarly, after coating, for example, it is preferable to cure by heating at 120 to 160 ° C. for 10 to 30 minutes.

  The film thickness of the multilayer coating film formed by the method for forming a multilayer coating film of the present invention is preferably a lower limit of 30 μm and an upper limit of 300 μm. If it is less than 30 μm, the strength of the film itself may be reduced, and if it exceeds 300 μm, film physical properties such as a cooling / heating cycle may be reduced. The lower limit is more preferably 50 μm, and the upper limit is more preferably 250 μm.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on mass unless otherwise specified.

Production Example 1 Preparation of Acrylic Resin Emulsion (Em-1) 135.4 parts of ion exchange water, Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 1.1 The temperature was raised to 80 ° C. with mixing and stirring in a nitrogen stream. Next, 35.73 parts of methyl acrylate, 8.57 parts of butyl methacrylate, 5.7 parts of 2-hydroxyethyl methacrylate, 20 parts of styrene, 0.5 part of Aqualon HS-10, Adeka Soap NE-20 ( α- [1-[(allyloxy) methyl] -2-nonylphenoxy] ethyl) -ω-hydroxyoxyethylene (manufactured by Asahi Denka Co., Ltd., 80% aqueous solution) 0.5 part and ion-exchanged water 49.7 parts A first-stage ethylenically unsaturated monomer mixture and an initiator solution consisting of 0.21 part of ammonium persulfate and 8.6 parts of ion-exchanged water were dropped into the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour.

  Furthermore, 25.3 parts of butyl methacrylate, 2.4 parts of 2-hydroxyethyl methacrylate, 2.3 parts of methacrylic acid, 0.1 part of Aqualon HS-10 and 24.7 parts of ion-exchanged water were added to this reaction vessel. A second stage ethylenically unsaturated monomer mixture and an initiator solution consisting of 0.08 parts ammonium persulfate and 7.4 parts ion-exchanged water were added dropwise in parallel over 0.5 hours at 80 ° C. . After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Next, after cooling to 40 ° C. and filtering with a 400 mesh filter, 2.14 parts of ion-exchanged water and 0.24 part of dimethylaminoethanol were added to adjust the pH to 6.5, an average particle diameter of 80 nm, and a non-volatile content of 30%. An acrylic resin emulsion (Em-1) having a solid content acid value of 15 mgKOH / g and a hydroxyl value of 35 mgKOH / g was obtained.

Production Example 2: Preparation of water-soluble acrylic resin 23.89 parts of dipropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to a reaction vessel, and the mixture was heated to 105 ° C. with mixing and stirring in a nitrogen stream. Next, 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, 6.9 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl An initiator solution consisting of 1 part of peroxy 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours.

  Next, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of t-butylperoxy 2-ethylhexanoate was dropped into the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  Further, using a solvent removal apparatus, 16.11 parts of the solvent was distilled off at 110 ° C. under reduced pressure (70 torr), and then 204 parts of ion-exchanged water and 7.1 parts of dimethylethanolamine were added to obtain a water-soluble acrylic resin. It was. The obtained acrylic resin solution had a non-volatile content of 30%, a solid content acid value of 40 mgKOH / g, and a hydroxyl value of 50 mgKOH / g.

Production Example 3: Preparation of Hydrophobic Melamine Resin Water Dispersion (MFD-1 ) 50 parts of MFDG (methylpropylene diglycol, manufactured by Nippon Emulsifier Co., Ltd.) was added to the reaction vessel, and the temperature was raised to 130 ° C. while stirring in a nitrogen stream. Warm up. Next, an ethylenic polymer consisting of 14.77 parts of acrylic acid, 32.48 parts of 2-hydroxyethyl methacrylate, 47.75 parts of butyl acrylate, and 5 parts of MSD-100 (α-methylstyrene dimer, Mitsui Chemicals). A saturated monomer mixture and an initiator solution consisting of 13 parts of Kayaester O (tert-butyl peroctanoate, manufactured by Kayaku Akzo) and 10 parts of MFDG were dropped into the reaction vessel in parallel over 3 hours. After the completion of dropping, an initiator solution consisting of 0.5 parts of Kayaester O and 5 parts of MFDG was added dropwise over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 1 hour. Subsequently, it was cooled to 50 ° C. to obtain an acrylic resin (Ac1) having a nonvolatile content of 60%, a solid content acid value of 110 mgKOH / g, a hydroxyl value of 140 mgKOH / g, and a number average molecular weight (Mn) = 3000.

  178.5 parts of the obtained acrylic resin (Ac1) was mixed with 800 parts of Uban 20SB (fully butylated melamine resin, Nippon Cytec Co., Ltd., non-volatile content 75%, Sp = 9.6), and 4 at 80 ° C. Stir for hours. Thereafter, 18.3 parts of dimethylethanolamine was added and dispersed uniformly. After cooling to 40 ° C., 1003.2 parts of ion-exchanged water was added dropwise over 1 hour, whereby a hydrophobic melamine resin aqueous dispersion (MFD-1) was added. ) The particle size of the resin particles in this aqueous dispersion was 80 nm.

Example 1
Preparation of base coating composition 153.3 parts of the acrylic resin emulsion (Em-1) of Production Example 1 as a coating film-forming resin, 5 parts of a 10 mass% dimethylethanolamine aqueous solution, and 16 of the water-soluble acrylic resin of Production Example 2 7 parts, Prime Pol PX-1000 (manufactured by Sanyo Chemical Industries, Ltd., bifunctional polyether polyol, number average molecular weight 1000, hydroxyl value 278 mg KOH / g, water tolerance infinity), hydrophobic melamine resin water of Production Example 3 Dispersion (MFD-1) as 100 parts, and aluminum pigment (A) as an aluminum pigment paste “96-0635” (average particle size of 8 μm) manufactured by Toyo Aluminum Co., Ltd., 5 parts by mass,
As the white colored aluminum pigment (B), 5 parts of a white colored aluminum pigment paste “98-4083WH” (average particle diameter of 8 μm) manufactured by Toyo Aluminum Co., Ltd.
As a metal oxide-coated alumina flake pigment (C) having an interference color, 2 parts of “Xirallic T60-10WNT” (average particle diameter: 17 μm) manufactured by Merck & Co., Ltd.
Was formulated. Further, 30 parts of ethylene glycol monohexyl ether was mixed and stirred, adjusted to pH = 8.5 by adding 10% by mass aqueous dimethylaminoethanol solution, and uniformly dispersed to obtain an aqueous base coating composition. The resulting aqueous base coating composition has a coating viscosity of 20 ° C. The base coating composition was obtained by diluting by adding ion-exchanged water so that it would be 60 seconds in a 4 Ford cup.

Formation of multilayer coating Dull steel plate (length 300 mm, width 100 mm and thickness 0.8 mm) was subjected to chemical conversion treatment using a zinc phosphate treating agent ("Surfdyne SD2000", manufactured by Nippon Paint Co., Ltd.), and then cation An electrodeposition paint (“Powernics PN 310”, manufactured by Nippon Paint Co., Ltd.) was electrodeposited so that the dry film 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 (“Olga P-30”, manufactured by Nippon Paint Co., Ltd.) 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 A layer was formed.

Further, the base coating composition was spray-coated on the intermediate coating layer so that the average dry film thickness was 15 μm. The coating was performed using an electrostatic coating machine (“Auto REA”, 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 painting, set for 3 minutes, preheat at 80 ° C. for 5 minutes, and then wet-on-wet on top of the acrylic / melamine resin-based clear coating composition (acid epoxy curable acrylic resin-based clear coating composition, “Mac Flow O -1810 "(manufactured by Nippon Paint Co., Ltd.) was spray-coated to a dry film thickness of 35 μm, set at room temperature for 7 minutes, baked at 140 ° C. for 30 minutes, and then double-layered by 2 coats 1 bake (2C1B) A coating film was formed.

Examples 2-3 and Comparative Examples 1-3
A base coating composition was prepared in the same manner as in Example 1 except that the aluminum pigment (A), the white colored aluminum pigment (B), and the metal oxide-coated alumina flake pigment (C) were changed to those shown in Table 1. did. Next, a multilayer coating film was formed in the same manner as in Example 1 using the obtained base coating composition.

  The following evaluation was performed using the multilayer coating film obtained by the said Example and comparative example. The results are shown in the table below.

Measurement of Lightness (L *) of Multilayer Coating Film The lightness (L *) of the multilayer coating films obtained in Examples and Comparative Examples was measured as follows. The results are shown in the table below.

Lightness (L *)
The obtained multi-layer coating film was irradiated with a light source at an angle of 45 ° from the vertical position, and the L * value received at an angle of 15 ° from the position was measured as a multi-angle spectrophotometer “MA” manufactured by X-Rite. -68 II ". The lightness (L *) at a light receiving angle of 15 degrees was determined by calculating the average value of the measured values thus obtained. In the following table, it is indicated as “15L *”. Note that the position at the light receiving angle of 15 degrees corresponds to the highlight position.
Further, the L * value received at an angle of 110 degrees from the light source irradiation position was measured in the same manner as described above, and the lightness (L *) at the light receiving angle of 110 degrees was obtained. In the following table, it is shown as “110L *”. The position at the light receiving angle of 110 degrees corresponds to the shade position.
FIG. 1 is a schematic explanatory diagram showing measurement positions of the lightness (L *).

  The L * is a parameter in the L * C * h color system, and can be obtained according to JIS Z8729. This L * C * h color system is a color system defined by the International Lighting Commission, and is described in Section 4.2 of CIE Publication 15.2 (1986). In the L * C * h color system, L * represents lightness, C * represents saturation, and h represents hue angle. The lightness L * means that the whiteness of the substance to be measured increases as the numerical value increases, and the blackness increases as the numerical value decreases.

Visual evaluation of the multilayer coating film The multilayer coating film obtained was visually evaluated according to the following items.

Highlight brightness When the multilayer coating film was viewed at the highlight position, the brightness was visually evaluated according to the following criteria.
5: A coating film that is bright and does not feel any cloudiness.
4: A coating film that is bright and does not feel cloudy.
3: Although it is slightly inferior in brightness, it is a coating film in which no cloudiness is felt.
2: Although it is slightly inferior in brightness, it is a coating film in which no white turbidity is felt.
1: Brightness decreases and white turbidity appears.

The brightness when the shade lightness multilayer coating film was viewed at the shade position was visually evaluated according to the following criteria.
5: A coating film that is bright and does not feel any cloudiness.
4: A coating film that is bright and does not feel cloudy.
3: Although it is slightly inferior in brightness, it is a coating film in which no cloudiness is felt.
2: Although it is slightly inferior in brightness, it is a coating film in which no white turbidity is felt.
1: Brightness decreases and white turbidity appears.

The glitter feeling when the glittering multilayer coating film was viewed at the highlight position and shade position was visually evaluated according to the following criteria.
5: An excellent fine shine is felt in highlights and shades.
4: Feels fine shine with highlights and shades.
3: A fine glitter feeling is felt in the highlights, but a slight glitter feeling is lowered in the shade.
2: A fine radiance is felt in highlights, but a dense radiance is reduced in shades.
1: Dense shine is not felt in highlights and shades.

In the table above,
96-0635: Aluminum pigment paste (average particle size 8 μm) manufactured by Toyo Aluminum Co., Ltd.
93-0647: Aluminum pigment paste (average particle size 20 μm) manufactured by Toyo Aluminum Co., Ltd.
98-4038WH: White colored aluminum pigment paste (average particle size 8 μm, aspect ratio 97) manufactured by Toyo Aluminum Co., Ltd.
WH-2600: White colored aluminum pigment paste (average particle size 15 μm, aspect ratio 27) manufactured by Toyo Aluminum Co., Ltd.
Xirallic T60-10WNT: manufactured by Merck & Co., Inc., metal oxide-coated alumina flake pigment having an interference color (average particle diameter: 17 μm),
It is.

The multilayer coating films obtained in Examples 1 to 3 all had high highlight brightness and shade brightness. Moreover, it was a coating film in which a fine glitter feeling (shiny feeling) was felt.
Comparative Example 1 is an experimental example using a base coating composition containing no metal oxide-coated alumina flake pigment (C). The multi-layer coating film obtained in Comparative Example 1 was a coating film that had a bright shade, but did not feel a dense glitter (glitter). Also, the highlight brightness was low.
Comparative Example 2 is an experimental example using a base coating composition in which the average particle size of the aluminum pigment (A) exceeds 12 μm. The multilayer coating film obtained in Comparative Example 2 had low highlight brightness. This is presumably because the content of the aluminum pigment (A) is relatively less than other pigments due to the increase in the average particle size of the aluminum pigment (A). Moreover, it did not have a fine glitter feeling (glitter feeling), and a glaring reflected light was felt at the highlight position.
Comparative Example 3 is an experimental example using a base coating composition in which the average particle size of the white colored aluminum pigment (B) exceeds 12 μm. The multilayer coating film obtained in Comparative Example 3 had a slight brightness (glitter feeling) and a low brightness at the shade position.

  The graph which shows the value of the 15 degree coating film brightness (L15 value) and the 110 degree coating film brightness (L110 value) of the multilayer coating film obtained by the said Examples 1-3 and Comparative Examples 1-3 is FIG. As shown.

  The multilayer coating film obtained by the method of the present invention has a dense glitter feeling (shiny feeling) and is characterized by high brightness at both the highlight position and the shade position. This multi-layer coating film is a multi-layer coating film where a bright feeling is felt at the highlight position, and there is no darkness or cloudiness at the shade position, and a high brightness and a clear glitter feeling is felt. . The multi-layer coating film obtained by the present invention develops a fine glitter feeling in the light-diffused portion, and a fine glitter feeling appears to shine. This fine glitter can be visually recognized even at the shade position. As described above, the multilayer coating film of the present invention is a coating film in which the glitter feeling can be visually recognized, and at the same time has high brightness at both the highlight position and the shade position, and is accompanied by a dark feeling or a cloudiness feeling at the shade position. It is a coating film with a clean and bright design. There is an advantage that an excellent design can be imparted by applying the method for forming a multilayer coating film of the present invention to the coating of automobile bodies and parts.

Claims (4)

An aluminum pigment (A) having an average particle diameter of 5 to 12 μm; a white-colored aluminum pigment (B) having an average particle diameter of 5 to 12 μm; and a metal oxide having an interference color having an average particle diameter of 15 to 25 μm on the object to be coated A method for forming a multilayer coating film, comprising: forming a base coating film containing a coated alumina flake pigment (C); and further forming a clear coating film,
The multi-layer coating film has a ∠15 degree coating film brightness (L15 value) of 95 or more, a ∠110 degree coating film brightness (L110 value) of 43 or more,
The total pigment concentration (PWC) of the aluminum pigment (A), the white colored aluminum pigment (B) and the metal oxide-coated alumina flake pigment (C) in the base coating film is 10 to 20% by mass, and the metal The mass ratio (C) / ((A) + (B)) of the oxide-coated alumina flake pigment (C) and the total amount of the aluminum pigment (A) and the white colored aluminum pigment (B) is 1/20. 10/4,
A method for forming a multilayer coating film.   The formation method of the multilayer coating film of Claim 1 whose mass ratio (A) / (B) of the said aluminum pigment (A) and the said white coloring aluminum pigment (B) is 3/7-7/3.   The white colored aluminum pigment (B) is a pigment in which aluminum flakes are coated with a color pigment containing titanium dioxide, and the aluminum flakes have an average thickness in the range of 0.01 to 1 μm and an aspect ratio (average The method for forming a multilayer coating film according to claim 1 or 2, wherein the particle size / average thickness is in the range of 50 to 1,000.   The multilayer coating film obtained by the formation method of the multilayer coating film in any one of the said Claims 1-3.

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