JP6343518B2 - Method for forming pearl-like thermal barrier multilayer coating film and thermal barrier multilayer coating film obtained therefrom - Google Patents

Description

  The present invention relates to a method for forming a pearl-like heat-insulating multilayer coating film, particularly a pearl-like heat-insulating multilayer coating film for an automobile, and a heat-insulating multilayer coating film obtained therefrom.

  In recent years, a pearl tone coating color containing a so-called glitter pigment, which changes in color depending on the viewing angle, has been preferred as a paint for automobile bodies. This makes it possible to make an object appear three-dimensional.

  Examples of glitter pigments used in such paint color design include interference-type mica pigments. This interference-based mica pigment is a coating of metal oxide on mica flakes or alumina flakes, and causes interference of light at the coating part, so it brings about a pearl-based color development due to the color change due to interference in addition to the sparkle feeling of the flake pigment .

  As shown in FIG. 1, the method for forming such a pearl-like multi-layer coating film is generally such that an electrodeposition coating film 2 is formed on a substrate 1 and an intermediate coating film 3 is formed thereon. Furthermore, the color base coating film 4, the glitter coating film 5 containing the glitter coating described above, and the clear coating film 6 are formed thereon. In the formation of a multilayer coating film composed of such an electrodeposition coating film, an intermediate coating film, a color base coating film and a clear coating film, there is a coating method in which the intermediate coating film 3 is not formed because of saving resources or omitting processes It has been proposed (for example, Patent Document 1 below).

  However, if a low-hiding color base coating is applied directly on the cured electrodeposition coating without forming an intermediate coating, the ultraviolet rays contained in the sun will not be sufficiently shielded by the color base coating. It has been reported that the ultraviolet rays of sunlight reach the coating film, thereby causing photodegradation of the electrodeposition coating film and peeling off the entire multilayer coating film.

  On the other hand, since an automobile body is likely to be exposed to sunlight and cause a temperature rise, it may be desired to apply a heat-shielding paint to reduce the temperature rise in the car, and a black heat-shielding paint is prepared. As a method, a method is known in which a color pigment having a high infrared wavelength region reflectance is mixed by a subtractive color mixing method (Patent Document 2 or the like). In addition, Patent Document 3 proposes that each layer of an automobile coating film be a thermal barrier coating film based on the concept of so-called subtractive color mixture that produces low-brightness colors with yellow, red and blue pigments having high reflectance in the infrared wavelength region. Has been. However, in Patent Documents 2 and 3, there is no study on a colored coating film having a lightness of L25 value 60 to 80, and neither a saturation nor a colored coating film having a C value of 60 or more is studied. .

JP 2012-25905 A JP 2009-286862 A JP 2000-212475 A

  The present invention relates to a method for forming a colored pearl-like multilayer coating film for forming an electrodeposition coating film, a colored intermediate coating film, a glitter coating film and a clear coating film on an automobile body. Provided is a method for forming a multilayer coating film in which light transmittance is specified and brightness is controlled by subtractive color mixing. Furthermore, the present invention provides a method for forming a multilayer coating film from which a colored pearl-tone multilayer coating film with high saturation can be obtained. In the present specification, the “colored intermediate coating film” refers to a coating film in which the color base coating film and the intermediate coating film are integrated in an embodiment in which the above-described intermediate coating film is not formed.

That is, the present invention includes a step (1) of forming a cured electrodeposition coating film by electrodeposition-coating and baking a substrate, and a coloring agent containing a titanium dioxide pigment and a coloring pigment on the obtained cured electrodeposition coating film. Step (2) of applying and baking a paint to form a cured colored intermediate coating film, and applying a glittering paint containing an interference glittering pigment on the resulting cured colored intermediate coating film to obtain glitter Step (3) for forming a coating film, step (4) for forming a clear coating film by applying a clear coating onto the resulting glittering coating film, and the brightness obtained in the above steps (3) and (4) (5) to form a multilayer coating film by baking a protective coating film and a clear coating film
A method for forming a pearl-like heat-insulating multilayer coating film comprising:
The cured colored intermediate coating film has a light transmittance of 0.1% or less in a wavelength region of 300 to 420 nm, does not contain carbon black, and has an L25 value of 60 or more by subtractive color mixing of the colored pigment. Adjusted to less than 80,
The colored pigment is a colored pigment having an infrared reflectance of 30% or more in a wavelength region of 780 to 2500 nm, and is selected from the group consisting of a blue pigment, a red pigment, a green pigment, and a yellow pigment. Using two or more kinds of coloring pigments,
Using titanium dioxide having a primary average particle diameter of 200 to 1000 nm as the titanium dioxide pigment,
Provided is a method for forming a pearl-like heat-insulating multilayer coating film in which the infrared reflectance of the multilayer coating film is 60% or more.

  The film thickness of the cured colored intermediate coating film is preferably 25 μm or more.

  The present invention also provides a multilayer coating film obtained by the above-described method for forming a pearl-like thermal barrier multilayer coating film.

  In the present invention, by limiting the light transmittance of the colored intermediate coating film, it becomes difficult for ultraviolet rays of sunlight to reach the electrodeposition coating film, and peeling of the multilayer coating film due to photodegradation of the electrodeposition coating film It almost never happens.

  Further, since the colored intermediate coating film of the present invention controls the brightness and hue by subtractive color mixing without using carbon black, the heat shielding effect is high, and the final multilayer using this intermediate coating film The infrared reflectance of the coating film is excellent and exceeds 60%.

It is a figure which shows the conventional multilayer coating film typically.

  The method for forming a multilayer coating film according to the present invention includes a step (1) of electrodepositing and baking an automobile body to form a cured electrodeposition coating film, and a titanium dioxide pigment and coloring on the obtained cured electrodeposition coating film. Step (2) of forming a cured colored intermediate coating film by applying and baking a colored intermediate coating composition containing a pigment, and a glittering coating composition containing an interference bright pigment on the resulting cured colored intermediate coating film Step (3) for forming a glittering coating film by applying a coating, Step (4) for forming a clear coating film by applying a clear coating on the resulting glittering coating film, Steps (3) and (4) 5) including the step (5) of baking the glittering coating film and the clear coating film obtained in (5) to form a multilayer coating film. The steps will be described in order.

Process (1)
The first step of the present invention is a step of forming a cured electrodeposition coating film by electrodeposition-coating and baking an automobile body.

In the multilayer coating film forming method of the present invention, examples of the automobile body include automobile body substrates made of steel sheets such as cold-rolled steel sheet and hot-dip galvanized steel sheet, and other metals. Further, it may contain a foam or the like.

  Examples of the steel plate and other metals include iron, copper, aluminum, tin, and zinc, and alloys containing these metals. Examples of the automobile body include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are preferably subjected to chemical conversion treatment with a phosphate, chromate, zirconium compound or the like and then washed with water.

Electrodeposition coating The automobile body is electrodeposited and baked to form a cured electrodeposition coating. The electrodeposition coating may be either cationic electrodeposition coating or anion electrodeposition coating, but cationic electrodeposition coating is usually used. The cationic electrodeposition paint used for the electrodeposition coating of the present invention is not particularly limited, and known ones can be used. The cationic electrodeposition paint contains a cationic base resin, a curing agent and a pigment.

  Although it does not specifically limit as a cationic base resin, For example, it describes in the amine-modified epoxy resin type | system | group described in Japanese Patent Publication No.54-4978, Japanese Patent Publication No.56-34186, etc., Japanese Patent Publication No.55-115476, etc. Amine-modified polyurethane polyol resin system, amine-modified polybutadiene resin system described in JP-B-62-61077, JP-A-63-86766, etc., JP-A-63-139909, JP-B-1-60516 Examples include amine-modified acrylic resin systems described in JP-A No. 6-128351, sulfonium group-containing resin systems described in JP-A-6-128351, and the like. In addition to those described in the above references, phosphonium group-containing resin systems and the like can also be used. Among the above cationic base resins, it is particularly preferable to use an amine-modified epoxy resin system.

  Examples of the curing agent include, but are not limited to, amino resins and block polyisocyanate compounds.

  In this invention, the film thickness after baking hardening of an electrodeposition coating film becomes like this. Preferably it is 5-40 micrometers, More preferably, you may be 10-25 micrometers. If the film thickness is less than 5 μm, the corrosion resistance may be insufficient. On the other hand, even if it exceeds 40 μm, the corrosion resistance is not further improved. In the present invention, the electrodeposition coating film for obtaining the cured electrodeposition coating film can be baked under general conditions. For example, it can carry out at 130-180 degreeC for 10 to 60 minutes.

Process (2)
Step (2) is a step of applying a colored intermediate coating containing a titanium dioxide pigment and a colored pigment onto the cured electrodeposition coating obtained in step (1) and baking it to form a cured colored intermediate coating. It is.

In the method for forming a multi-layer coating film of the present invention, in step (2), a colored intermediate coating composition containing a titanium dioxide pigment and a coloring pigment is formed on the cured electrodeposition coating film obtained in step (1). It is applied to form a colored intermediate coating film.

  The cured colored intermediate coating film needs to have an L25 value of 60 or more and less than 80. By setting the lightness of the cured colored intermediate coating film within the above range, a multi-layer coating film with intermediate lightness can be obtained. The L25 value can be measured by a commercially available colorimeter, and can be determined by, for example, the L25 value of CM512m-3 (spectral colorimeter manufactured by Konica Minolta).

  When the L25 value of the cured and colored intermediate coating film is 60 or more and less than 80, the transmitted light of the sun rays easily reaches the electrodeposition coating film, which may cause deterioration of the electrodeposition coating film. For this reason, in the present invention, the cured colored intermediate coating film is adjusted so that the light transmittance is 0.1% or less in a wavelength region of 300 nm to 420 nm. The light transmittance of the cured colored intermediate coating film is a wavelength of 300 to 420 nm using a spectrophotometer (U-3310 manufactured by Hitachi, Ltd.) for the single cured coating film formed by the colored intermediate coating composition used in step (2). The light transmittance is measured every 20 nm and calculated as the average value. When the light transmittance is larger than the upper limit of the above range, sunlight tends to transmit through the cured colored intermediate coating film, reach the cured electrodeposition coating film, and cause light deterioration. The light transmittance is basically controlled by a color pigment blended in the cured colored intermediate coating.

The cured colored intermediate coating film does not contain carbon black in the color pigment, and the brightness is adjusted by subtractive color mixing so that the L25 value is 60 or more and less than 80. Subtractive color mixing is a known method, and is a method for controlling brightness without using carbon black, which has a strong tendency to absorb heat, and is disclosed in JP-A Nos. 2000-212475 and 2009-286862. Are described in detail. The heat shielding effect of the multilayer coating film of the present invention can be improved by adjusting the brightness to 60 or more and less than 80 by subtractive color mixing of color pigments without using carbon black.

The color pigment to be used is a color pigment having an infrared reflectance of 30% or more in a wavelength range of 780 to 2500 nm, and is selected from a blue pigment, a red pigment, a green pigment, and a yellow pigment. (Hereinafter, such a colored pigment may be referred to as a “high-infrared reflective colored pigment”). Specific examples of the high-infrared reflective coloring pigment include Shannin Blue 5240KB, Fast Gen Super Red YE, Lionol Green 6YKPN, and Coco Pearl Yellow L-1100. The PWC of the high infrared reflective coloring pigment is preferably 0.1% to 30%, more preferably 0.15 to 25%. Here, PWC is the pigment mass concentration with respect to the solid content of all the binder components contained in the coating composition and the total amount of all the pigments. In addition, the infrared reflectance of the pigment in the wavelength region of 780 to 2500 nm has a PWC of 10 by mixing a resin component used in an aqueous base paint (for example, the glitter paint in the present invention) and a pigment paste in which the pigment is dispersed. For a single film obtained by coating and peeling this onto a polypropylene plate so that the dry film thickness becomes 10 μm ± 2, the light transmittance is measured every 20 nm at a wavelength of 780 to 2500 nm. The average value is calculated.

In order to obtain a multi-layer coating film with high saturation, it is preferable that the saturation of the cured colored intermediate coating film be high saturation, specifically, C value of 60 or more. For this reason, in the colored intermediate coating in the present invention, the high infrared reflective colored pigment is not only the high infrared reflective colored pigment that adjusts the brightness by the subtractive color mixture, but also the high infrared that increases the saturation of the cured colored intermediate coated film. It is preferable to contain a reflective coloring pigment. The high-infrared reflective color pigment that increases the saturation is included in the above-mentioned high-infrared reflection color pigment, and means a compound that is blended in a relatively large amount in order to impart saturation. Therefore, the high-infrared reflective color pigment that increases the saturation refers to a high-infrared reflective color pigment that makes the hue desired to be obtained as a cured colored intermediate coating film. For example, when it is desired to obtain a yellow-colored cured intermediate coating film, the yellow high-infrared reflective color pigment must be used in an amount larger than the amount used for subtractive color mixing, and if it is used more, the saturation is increased. It contributes to that. The high-infrared reflective coloring pigment that raises the saturation of the cured colored intermediate coating film is preferably 10% or more by PWC. Moreover, by containing 10% or more of the total amount of the PWC, the concealability of the cured colored intermediate coating film can be improved, and the light transmittance at a wavelength of 300 to 420 nm can be reduced to 0.1% or less. In addition, the high-infrared reflective coloring pigment for raising the saturation in the cured colored intermediate coating film corresponds to a PWC containing 3% or more alone, and preferably containing 5% or more alone as PWC. On the other hand, when the high-infrared reflective coloring pigment is less than 3% by itself as PWC, the cured colored intermediate coating film cannot have a high saturation with a C value of 60 or more. Similarly to the L25 value, the C value can be measured by a commercially available colorimeter, and can be determined by, for example, the C value of CM512m-3 (Spectrum Colorimeter manufactured by Konica Minolta).

In the high-infrared reflective color pigment, the color pigment other than the high-infrared reflective color pigment that makes the cured colored intermediate coating film have high saturation is one that adjusts the brightness of the cured colored intermediate coat to 60 or more and less than 80 by subtractive color mixing, The PWC is preferably 0.5% or less. If the PWC exceeds 0.5%, the lightness of the cured colored intermediate coating film may be too low to be 60 or more in the L value, and the saturation of the cured colored intermediate coating film may also be C value. In some cases, it cannot be over 60. In addition, when using 2 or more types of the said high-infrared reflective coloring pigment, these total amount should just be 0.5% or less as PWC.

In the present invention, the colored intermediate coating material may also contain a coloring pigment having an infrared reflectance of less than 30% in the wavelength region of 780 to 2500 nm. Specific examples of the color pigment include purple pigments such as dioxazine violet, red pigments such as perylene maroon and iron oxide red, Shannin green green pigments, mapico yellow and isoindoline yellow. And yellow pigments. However, carbon black cannot be contained as the coloring pigment. When the colored intermediate coating material used in the present invention includes a colored pigment having an infrared reflectance of less than 30% in the wavelength region of 780 to 2500 nm, the PWC in the colored intermediate coating material may be 0.2% or less. preferable. When the PWC exceeds 0.2%, the concealability of the cured colored intermediate coating film cannot be sufficiently achieved, and the infrared reflectance of the multilayer coating film of the invention may not be 60% or more.

As a high-infrared reflective color pigment other than the high-infrared reflective color pigment that makes the cured colored intermediate coating film high in saturation, a color pigment having an infrared reflectance of 30% or more in the wavelength region of 780 to 2500 nm, and the above-mentioned 780 When using in combination with a colored pigment having an infrared reflectance of less than 30% in the wavelength region of 2500 nm, the total amount of these colored pigments is preferably 0.5% or less in terms of PWC.

  As the titanium dioxide pigment contained in the colored intermediate coating, titanium dioxide whose primary particles have a volume average particle diameter of 200 to 1000 nm is used. When the volume average particle diameter of the primary particles of titanium dioxide to be used is less than 200 nm, it is difficult to obtain an infrared reflectance of 60% or more for the resulting multilayer coating film. The volume average particle diameter of primary particles of the titanium dioxide pigment is preferably 250 to 1000 nm. Examples of the titanium dioxide pigment used in the present invention include TITANIX JR-1000 (manufactured by Teika Co., Ltd., primary particle volume average particle size 800 nm), and Taipei CR-95 (Ishihara Sangyo Co., Ltd., primary particle volume average particle size 250 nm). It is done. In order to enhance the heat shielding effect of the resulting multilayer coating film, titanium dioxide having a primary particle volume average particle size of 200 to 1000 nm is preferably used in an amount of 20% or more as PWC, and more preferably 25% or more. preferable.

Binder Component The colored intermediate coating material contains a film-forming resin as a binder component in addition to the titanium dioxide pigment and the color pigment. Examples of the coating film-forming resin include acrylic resin, polyester resin, alkyd resin, and fluorine resin. The binder component contains a curing agent as necessary. Examples of the curing agent include amino resins and / or block polyisocyanate compounds. The solid content of the binder component contained in the colored intermediate coating is 30 to 70% by mass with respect to the entire coating composition when the coating composition is produced, and is within a range of 10 to 50% by mass when applied. .

  Furthermore, the colored intermediate coating material can contain other additives well known by those skilled in the art in addition to the colored pigment, the titanium dioxide pigment and the binder component. Examples of such additives include surface conditioners such as silicone and organic polymers, curing catalysts, ultraviolet absorbers, hindered amines, hindered phenols, viscosity control agents, and the like. These compounding amounts are within the range known to those skilled in the art. The coating form of the colored intermediate coating is not particularly limited, and specific examples include an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), and a non-aqueous dispersion type.

  In the above step (2), the method of applying the colored intermediate coating on the base material of the automobile body is not particularly limited, and multistage coating by air electrostatic spray coating, preferably two stages, is performed in order to improve the design. Paint or combine air electrostatic spray painting with a rotary atomization type electrostatic coating machine called "μμ (micro micro) bell", "μ (micro) bell" or "meta bell" Coating methods and the like.

  Although the coating film thickness of the colored intermediate coating material by the said application | coating method is fluctuate | varied with a use, it is not limited, For example, it is 25-50 micrometers in a dry film thickness. If it exceeds 50 μm, defects such as unevenness, flares, and sagging may occur during coating, and if it is less than 25 μm, the light transmittance increases and peeling occurs due to photodegradation of the electrodeposition coating film.

  The colored intermediate coating film obtained by the above step (2) is baked and cured after applying the colored intermediate coating. After application, the temperature and time for curing the colored intermediate coating film can be appropriately set according to the binder component contained in the colored intermediate coating composition, but it is usually 120 to 160 ° C. for 10 to 30 minutes. The colored intermediate coating material may be a water-based coating material.

Process (3)
The third step of the present invention is a step of forming a glittering coating film by applying a glittering paint containing an interference glittering pigment on the colored intermediate coating film obtained in the step (2).

Interfering bright pigment The interference bright pigment contained in the above-mentioned bright paint is usually used for pearl paint, and is selected from the group consisting of mica flakes, silica flakes, alumina flakes and glass flakes. The thing which the coating layer of the metal oxide was provided in the surface of the base material more than a kind can be mentioned. From the viewpoint of particle feeling, an alumina flake pigment whose surface is coated with a metal oxide such as TiO ₂ and their hydrates is preferable. The shape of the interfering bright pigment is not particularly limited. For example, if the pigment has a scaly shape, a volume cumulative particle diameter D50 of 2 to 50 μm and a thickness of 0.1 to 3 μm are suitable. ing.

  The volume cumulative particle diameter D50 is a volume cumulative average particle diameter. In the particle size distribution of the coherent bright pigment, the total volume of particles accumulated from the small particle diameter side to a certain particle diameter is the total particle diameter. When expressed as a percentage of the volume, this is the particle diameter when the value is 50%. Measured by dynamic light scattering method. More specifically, it can be measured with UPA-150 (a particle size distribution measuring device manufactured by Microtrac).

  The above-mentioned interference bright pigments are commercially available, SILALIC T60-10 WNT (interference alumina flake pigment manufactured by Merck Japan), Pearl Glaze SME 90-9 (Mika-based pearl pigment manufactured by Nippon Koken Co., Ltd.), Metashine MC1020RSJA1. (Nippon Sheet Glass Co., Ltd.) is preferably used.

Titanium dioxide pigment The glittering paint in the present invention preferably contains titanium dioxide having a primary average particle size of 200 to 1000 nm in order to improve the heat shielding effect of the resulting multilayer coating film. Specifically, the volume average particle diameter of the primary particles can be measured using UPA-150 (a particle size distribution measuring device manufactured by Microtrac).

  Titanium dioxide pigments having a primary average particle size of 200 to 1000 nm are commercially available, such as TITANIX JR-1000 (manufactured by Teika, primary average particle size 800 nm), Type CR-95 (manufactured by Ishihara Sangyo Co., Ltd., primary average particle size). 250 nm). Of course, it is not limited to these.

  When the glitter paint includes two kinds of the interference glitter pigment and the titanium dioxide pigment, the mass ratio of the interference glitter pigment and the titanium dioxide pigment is determined by the ratio of the interference glitter pigment / dioxide dioxide. The ratio of titanium pigment is 10/1 to 5/1, preferably 10/1 to 6/1. When the amount of the interfering bright pigment is larger than 10/1 at the above mass ratio, the finished appearance of the resulting coating film is deteriorated. When the amount of the interference bright pigment is smaller than 5/1, the glitter feeling is lost and the interference bright pigment is used. Design properties due to color development deteriorate.

  The interference glittering pigment contained in the glittering paint is 1 to 30% by mass in terms of the pigment mass concentration (PWC) based on the total content of all the resin components and all the pigments contained in the glittering paint composition. Preferably, the amount is 1 to 25% by mass. Moreover, 0.1-5 mass% is preferable in titanium dioxide contained in the said glittering coating material by PWC, and it is more preferable that it is 0.1-4 mass%. The total amount of the interfering bright pigment and the titanium dioxide pigment contained in the bright paint is preferably 1.1 to 35% by mass and more preferably 1.1 to 30% by mass in terms of PWC.

Binder Component The glitter paint of the present invention usually contains a film-forming resin as a binder component in addition to the interference glitter pigment and, if necessary, a titanium dioxide pigment. As the coating film-forming resin, the same one as described for the colored intermediate coating can be used. The solid content of the binder component contained in the glitter paint is 30 to 70% by mass with respect to the whole paint when the paint is manufactured, and is 10 to 50% by mass when applied. The curing agent is not particularly limited.

Other components In addition to the above-mentioned interference bright pigment, titanium dioxide pigment and binder component, a viscosity control agent can generally be added to the bright paint used in the present invention in order to ensure coating workability. . As the above viscosity control agent, those generally showing thixotropy can be used, for example, swelling dispersions of fatty acid amides, polyamides such as amide fatty acids, phosphates of long chain polyaminoamides, colloidal swelling of polyethylene oxide Polyethylene-based materials such as dispersions, organic bentonite-based materials such as organic acid smectite clay, montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, flat pigments that develop viscosity depending on the shape of the pigment, cross-linked or non-cross-linked Resin particles and the like.

  Further, the glittering paint can contain other additives as desired. Examples of such additives include surface conditioners such as silicone and organic polymers, curing catalysts, ultraviolet absorbers, hindered amines, hindered phenols, and the like. These compounding amounts are within the range known to those skilled in the art.

  If desired, the glitter paint can contain a glitter pigment other than the interference glitter pigment. The total amount of glitter pigments other than the interference glitter pigment and the interference glitter pigment contained in the glitter paint is preferably 1 to 50% by mass and 1 to 40% by mass in terms of PWC. More preferred. Examples of the bright pigment other than the interference bright pigment include aluminum flakes, colored aluminum flakes, glass flakes, hologram pigments, and liquid crystal polymer pigments.

If desired, the glitter paint can contain a color pigment. Examples of the color pigment include violet, blue, red, green, and yellow pigments. The heat shielding effect can be enhanced by using two or more kinds of color pigments whose brightness can be adjusted by subtractive color mixing as the color pigments. The PWC of the color pigment is preferably 0.1 to 30% by mass, and more preferably 0.1 to 20% by mass. Examples of extender pigments include talc, calcined kaolin, calcium carbonate, barium sulfate, and magnesium silicate. The PWC of the extender pigment is preferably 25 to 60% by mass, and more preferably 30 to 50% by mass.

  The form of the glittering paint is not particularly limited, and any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), and a non-aqueous dispersion type may be used.

  The glitter paint is prepared by mixing and dispersing the above-mentioned interference glitter pigment, other glitter pigment, titanium dioxide pigment, binder component, viscosity control agent and other components.

  In the method for forming a multilayer coating film of the present invention, the step (3) is to form a glittering coating film by applying a glittering paint on the colored intermediate coating film obtained in the step (2). . The glitter paint is formed in order to express a design such as a glitter feeling and a pearl interference color in the multilayer coating film obtained from the transmitted light and the reflected light from the colored intermediate coating film.

The coating method is the same as the coating method for the colored intermediate coating film in the step (2). The coating film thickness is preferably 10 to 30 μm in terms of dry film thickness.

Process (4)
In the method for forming a multilayer coating film of the present invention, in step (4), a clear coating is applied on the glitter coating obtained in step (3) to form a clear coating.

  The clear coating usually contains a film-forming resin and a curing agent. The coating film-forming resin and the curing agent used for the clear coating are not particularly limited, and those described above for the colored intermediate coating can be used. In addition, from the point of transparency or acid etching resistance of the coating film obtained, a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system is used. Can be mentioned. In the case of a urethane-based clear paint, either a one-component type or a two-component type may be used.

  Furthermore, the clear coating material may contain other additives as in the colored intermediate coating material. In particular, it is preferable to contain a viscosity control agent in order to prevent a mixed layer, inversion or sagging between the lower glitter coating film and the resulting clear coating film. The solid content of the viscosity control agent is 0.01 to 10 parts by weight, preferably 0.02 to 8 parts by weight, and 0.03 to 6 parts by weight with respect to 100 parts by weight of the resin solids contained in the clear paint. More preferred. When the solid content exceeds 10 parts by mass, the appearance is deteriorated. When the solids content is less than 0.01 parts by mass, the viscosity control effect cannot be obtained, which causes problems such as sagging.

  The coating form of the clear coating is not particularly limited, and is the same as the colored intermediate coating, organic solvent type, aqueous type (water-soluble, water-dispersible, emulsion), non-aqueous dispersion type, powder type, and slurry type. Etc.

  The solid content of the clear coating is not particularly limited, and is, for example, 20 to 60% by mass, preferably 35 to 55% by mass. Moreover, solid content at the time of application | coating is 10-50 mass%, Preferably it is 20-50 mass%.

  Examples of the coating method include those described for the colored intermediate coating. The coating film thickness of the clear coating by the above coating method is not limited because it varies depending on the application, but is, for example, 10 to 70 μm in dry film thickness.

Step (5)
In the step (5) of the present invention, after the clear coating film is formed, the glitter coating film and the clear coating film are simultaneously baked to form a multilayer coating film.

  The curing temperature and curing time can be appropriately set depending on the binder component contained in the glitter paint and clear paint, and are, for example, 120 to 160 ° C. and 10 to 30 minutes.

  The dry film thickness of the multilayer coating film formed by the multilayer coating film forming method of the present invention is 55 to 300 μm, and preferably 70 to 250 μm. If the dry film thickness of the multilayer coating film is less than 55 μm, the strength of the coating film itself may be reduced, and if the dry film thickness of the multilayer coating film exceeds 300 μm, film properties such as a cooling cycle are deteriorated.

  The multilayer coating film of the present invention is obtained by the multilayer coating film forming method. In the multi-layer coating film, the cured colored intermediate coating film has a light transmittance within a predetermined range, the photodegradation of the electrodeposition coating film is suppressed, and peeling of the coating film does not occur. In addition, the cured colored intermediate coating film does not use carbon black, and a color pigment having an infrared reflectance of 30% or more is adjusted by subtractive color mixing so that the brightness is adjusted to an L25 value of 60 or more and less than 80, and a carbon dioxide having a predetermined particle diameter. Since the titanium pigment is used, a heat-shielding effect is high, and a medium-light colored pearl-like coating film can be obtained. Furthermore, a high-saturation multilayer coating film can be obtained by using a predetermined amount of the high-infrared reflective color pigment.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Creating paints to use
Colored intermediate coating 1
Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., solid content acid value 8 mgKOH / g, hydroxyl value 80 mgKOH / g, number average molecular weight 1,800, solid content 70% by mass) Shani, which is a high-infrared reflective coloring pigment having 38.0 parts by mass of CR-95 (Ishihara Sangyo Co., Ltd., titanium dioxide pigment, primary average particle diameter 300 nm) described in the column of Coating Paint 1 and an infrared reflectance of 30% or more Blue pigment 5240KB (blue pigment commercially available from Dainichi Seika Co., Ltd.) 0.04 parts by mass, Lionol Green 6YKPN (green pigment commercially available from Toyo Ink) 0.2 parts by mass, Fast Gen Super Red YE (from DIC) 0.1 parts by weight of a commercially available red pigment) and 13.6 parts by weight of Sicotrans Yellow L-1100 (a yellow pigment commercially available from BASF) were added, By distributing, to obtain a colored intermediate coating 1. The film thickness was 30 μm. It was 75 when L25 value was measured by CM512m-3 (Konica Minolta Co., Ltd. spectrocolorimeter). When the chroma (C value) of the single coating film and the light transmittance at a wavelength of 300 to 420 nm were also measured, the C value was 68.7 and the light transmittance was 0%.

Colored intermediate coating 2-6
A colored intermediate coating composition was prepared in the same manner as the colored intermediate coating composition 1 except that the pigment combinations described in Table 1 were used in the amounts described in Table 1. In addition, the colored intermediate coating material 5 is an example in which carbon black (MA-100 manufactured by Mitsubishi Carbon Co., Ltd.) is added separately and is not based on subtractive color mixture. The L25 value of the coating film and the saturation (C value) and light transmittance of the single coating film were measured and listed in Table 1. The film thickness is also shown in Table 1.

Measurement of light transmittance:
The light transmittance was measured by coating with a colored intermediate coating to a film thickness of 25 μm, 30 μm, and 35 μm, and then peeled off to form a single coating of the coating. A spectrophotometer (U-3310 manufactured by Hitachi, Ltd.) ), The light transmittance is measured every 10 nm at a wavelength of 300 to 420 nm, and the average value is calculated. The results are listed in Table 1.

Glitter paint manufactured by Nippon Paint Co., Ltd. acrylic emulsion (volume average particle diameter of 150 nm, a nonvolatile content of 20%, acid value of solid content 20 mgKOH / g, hydroxyl value 40 mg KOH / g) 35.0 parts by weight, manufactured by Nippon Paint Co., Ltd. water-soluble acrylic resin (Non-volatile content is 30.0% by mass, solid content acid value is 40 mgKOH / g, hydroxyl value is 50 mgKOH / g) 15.0 parts by mass, Primepole PX-1000 (polyether polyol manufactured by Sanyo Chemical Industries, non-volatile content is 100% ) 5.0 parts by mass, polyester resin (polyester resin commercially available from Toyobo Co., Ltd., 71 mass% nonvolatile content), 20.0 mass parts, Cymel 204 (Mitsui Cytec Co., Ltd. mixed alkylated melamine resin, nonvolatile content 100%) 25.0 parts by mass, alumina flake T60-10 (alumina flake face available from Merck & Co., Inc.) ) 1.0 parts by mass, Irgacolor 2GLMA (titanium dioxide pigment commercially available from CIBA) and 1.0 part by weight CR-95 (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd., primary average particle size 300 nm). 1 part by mass was added to the container and dispersed with glass beads for 180 minutes to obtain a glittering paint 1 having a mass ratio of glittering pigment / titanium dioxide of 8/1.

Clear paint Macflow O-1820 clear (carboxylic acid / epoxy curable clear paint manufactured by Nippon Paint Co., Ltd.) was used.

Example 1
(1) Preparation of test plate Cationic electrodeposition paint “Power Top U-50” (Nippon Paint Co., Ltd.) on SPCC-SD steel plate (dull steel plate) of 0.8 cm thickness and 20 cm × 30 cm treated with zinc phosphate Manufactured) was subjected to electrodeposition coating so that the dry film thickness was 20 μm, and baked at 160 ° C. for 30 minutes to form a cured electrodeposition coating film. On the cured cationic electrodeposition coating film, the colored intermediate coating material 1 was spray-coated so as to have a dry film thickness of 30 μm and cured by heating at 140 ° C. for 30 minutes to obtain a cured colored intermediate coating film 1. Next, on the obtained cured colored intermediate coating film 1, the glitter paint was applied using a rotary atomizing electrostatic coating apparatus so as to have a dry film thickness of 15 μm to obtain a glitter paint film. Thereafter, preheating was performed at 80 ° C. for 4 minutes.

  Next, the clear coating film 1 was obtained by coating the clear coating film on the obtained glitter coating film using a rotary atomizing electrostatic coating apparatus so as to have a dry film thickness of 35 μm. Thereafter, the glittering coating film 1 and the clear coating film 1 were heat-cured at 140 ° C. for 20 minutes at a time to obtain a test plate having a multilayer coating film.

About the coating film appearance of the obtained test plate, the light transmittance at a wavelength of 300 to 420 nm, the design property (multilayer coating film), the infrared reflectance (multilayer coating film), the electrodeposition coating film and the intermediate coating film Was evaluated according to the following criteria. The results are shown in Table 2.

Design by coloring of interference bright pigment ○: Visible pearl-based color ×: Invisible pearl-based color

Infrared reflectance (%)
Infrared reflectance (780-2500 nm) was measured using a spectrophotometer U4100 manufactured by Hitachi High-Tech.

Peel test between electrodeposition coating and intermediate coating:
The test plate on which the multilayer coating film was formed by the above method was immersed in pure water at 80 ° C. for 10 days, and then subjected to a cello tape (registered trademark) peel test to evaluate the presence or absence of peeling.
○: no peeling ×: peeling

Examples 2, 3 and Comparative Examples 1-3
A test plate was prepared in the same manner as in Example 1 in place of the colored intermediate coating 1 in place of the colored intermediate coating described in Table 1 and evaluated in the same manner as in Example 1. Went. The results are shown in Table 2.

  As is clear from the above Examples and Comparative Examples, Examples 1 to 3 have good evaluations in all of the design properties, the infrared reflectance, and the peel test between the electrodeposition coating and the intermediate coating.

On the other hand, Comparative Example 1 is an example in which the primary average particle diameter of the titanium dioxide pigment is smaller than 200 nm, and the infrared reflectance is poor. In Comparative Example 2, carbon black was used instead of subtractive color mixing, and the infrared reflectance was very poor. In Comparative Example 3, since the light transmittance at a wavelength of 300 to 420 nm exceeded 0.1%, peeling occurred between the cured electrodeposition coating film and the cured colored intermediate coating film. The reason for this peeling is that the content of the colored pigment having an infrared reflectance of 30% or more in the wavelength range of 780 to 2500 nm is 0.1% or less, and the concealing property of the cured colored intermediate coating film is low. Conceivable. Furthermore, the intermediate coating film in Comparative Example 3 had a saturation of only 5 and could not be said to be highly saturated, and had an adverse effect on the saturation of the multilayer coating film.

  The present invention provides a method for forming a multi-layer coating film that can obtain a colored pearl-tone coating color having an excellent appearance in the coating of automobiles and the like, and has a heat shielding effect.

DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Electrodeposition coating film 3 ... Intermediate coating film 4 ... Colored base coating film 5 ... Glossy coating film 6 ... Clear coating film.

Claims (2)

Step (1) of forming a cured electrodeposition coating film by electrodeposition coating and baking of an automobile body, and applying and baking a colored intermediate coating containing a titanium dioxide pigment and a color pigment on the obtained cured electrodeposition coating film Step (2) of forming a cured colored intermediate coating film, and a step of forming a glittering coating film by applying a glittering paint containing an interference bright pigment on the resulting cured colored intermediate coating film (3) The step (4) of applying a clear coating onto the resulting glitter coating to form a clear coating, and the glitter coating and clear coating obtained in the steps (3) and (4). Step (5) of baking a film to form a multilayer coating film
A method for forming a pearl-like heat-insulating multilayer coating film comprising:
The cured colored intermediate coating film has a light transmittance of 0.1% or less in a wavelength region of 300 to 420 nm, does not contain carbon black as the colored pigment, and is L25 by subtractive color mixing of the colored pigment. The value is adjusted to 60 or more and less than 80,
The colored pigment is a colored pigment having an infrared reflectance of 30% or more in a wavelength region of 780 to 2500 nm, and is selected from the group consisting of a blue pigment, a red pigment, a green pigment, and a yellow pigment. Using two or more kinds of coloring pigments,
Using titanium dioxide having a volume average particle diameter of primary particles of 200 to 1000 nm as the titanium dioxide pigment,
A method for forming a pearl-like heat-insulating multilayer coating film for an automobile body, wherein the multilayer coating film has an infrared reflectance of 60% or more.   The method for forming a pearl-like heat-insulating multilayer coating film for an automobile body according to claim 1, wherein the thickness of the cured colored intermediate coating film is 25 µm or more.

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