JP5478992B2 - Multi-layer coating formation method - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film exhibiting interference metal toning and a multilayer coating film formed by the method.

  In recent years, in the field of automobile painting, coating films having high design properties have been developed. For example, an interference coating using an interference pigment such as an interference mica pigment has been developed and provided. Specifically, a multilayer coating film (commonly known as a white mica coating film) in which an interference coating film containing an interference mica pigment is formed on a white color base coating film is well known as a coating film that gives a high-class feeling. ing. However, even these coating films are not new to consumers already, and new coating films with further design properties are required in this field.

  The interference of light by the coherent mica pigment is caused by the incident light being reflected by the pigment surface or the metal oxide layer formed on the pigment surface, thereby changing the phase and wavelength of the light. In particular, it is known that the interference property is drastically improved by making the base coating film of a coating film containing an interference mica pigment (hereinafter referred to as mica coating film) black. This is considered to be due to the fact that light that has passed through the mica coating film is absorbed by the black base coating film, and unnecessary reflection of light is suppressed. That is, when a white undercoat is used, the interference light expressed by the mica coat cannot be recognized due to the reflection of the undercoat. The color of the undercoat can usually be defined by measuring the lightness (L * value), and the L * value indicates that the lightness decreases as the value decreases, that is, the color becomes black. , The brightness increases as the L * value increases, that is, the white color is obtained. Therefore, when the interference pigment is used, the interference color is emphasized as the L * value of the base coating film is lower. The L * value of the undercoat at that time is 0.1-10.

  Further, as a coating film that gives high designability, a metallic coating film containing a metallic luster material such as aluminum powder is also very well known. The metallic coating can exhibit metallic toning due to the metallic glitter material, and the hue and brightness change depending on the viewing angle, giving the coating a superior design such as flip-flop properties. You can also. However, the metallic coating film containing a metallic luster material has a glare feeling in addition to a metallic feeling.

  In metallic coatings, it is possible to apply interference mica pigments to give interference to metallic coatings, but the color of metallic coatings that can exhibit interference is dark metal toning (black, dark green) Color, dark blue, dark red, dark gray, etc.). For example, even when an interference pigment is applied to a metallic coating film having a high lightness (L * value) such as a silver metallic color, since the reflection produced by a bright pigment such as an aluminum pigment is strong, the interference effect produced by the interference pigment is reduced. I can't save it. The reason for this is that, as described above, a coating film with high lightness (L * value) reflects incident light easily and the interference effect is extremely reduced.

  Special interference pigments other than interference mica pigments are also known, and coated silica flakes are an example. Patent Document 1 discloses a light-interfering coating film-forming paint containing silica flakes coated with titanium oxide or iron oxide. Specifically, in claim 1 of Patent Document 1, “Dense color coating film formation” is disclosed. A light-interfering coating film containing 0.1 to 2 parts by weight of silica flakes coated with paint (A), titanium oxide or iron oxide per 100 parts by weight of resin solids and having a base concealing film thickness of 40 μm or more A method for forming a multilayer coating film characterized by coating the forming paint (B) and the clear paint forming clear paint (C) is disclosed. The coated silica flakes used in Patent Document 1 are coated with titanium oxide or iron oxide, and show that the silica flakes and titanium oxide or iron oxide each have a special interference property that is different from the case where they are individually added to the paint. Features. In the optical interference coating film including silica flakes coated with titanium oxide or iron oxide disclosed in Patent Document 1, incident light is reflected light reflected on the coating layer made of titanium oxide or iron oxide, and the coating layer Is separated into reflected light that is warped on the silica flakes, and interference occurs between the two. On the other hand, when silica flakes are not coated with titanium oxide or iron oxide, that is, when silica flakes and titanium oxides or iron oxides are blended alone in the paint, incident light is emitted on silica flakes and on titanium oxide or iron oxides. Each of them is diffusely reflected and scattered, and the scattered light is generated. Therefore, both exhibit completely different interference colors.

  Patent Document 1 discloses a dark color coating film-forming coating material as a base coating film for the light interference coating film comprising the light interference coating film-forming coating material (B) for the purpose of remarkably improving the light interference property. Disclosed is the use of a dark color coating comprising (A). Specifically, the dark paint film-forming paint (A) contains color pigments such as carbon black and phthalocyanine blue, and the formed paint film has an L * value of 3 to 25 and exhibits almost black (patent) (See the example in document 1). Thus, even when using an interference pigment such as coated silica flakes, as described above, as in the case of using the interference mica pigment, by making the color of the base coating film dark, The optical coherence is remarkably improved. Thus, it was a conventional means in the field to make the base coating film dark color such as black for the purpose of improving the interference.

  Furthermore, the light-interfering coating film-forming paint (B) used in Patent Document 1 is a coated silica flake (the lengthwise dimension of scaly silica is 15 to 20 μm, and the thickness is 0.5 to 1 μm. The thickness of titanium oxide or iron oxide covering the surface is 4 to 50 nm), and it is a dark paint containing a color pigment such as carbon black. Therefore, the multilayer coating film disclosed in Patent Document 1 is almost black. This can also be seen from the fact that the L * value of the multilayer coating film obtained in the example of Patent Document 1 is 3 or 12.

  Patent Document 2 discloses the use of coated silica flakes as an interference pigment, as in Patent Document 1. Specifically, in claim 1 of Patent Document 2, “an interference clear coat containing an interference pigment on the color base coating layer after forming a color base coating layer having an L value of 65 to 100 on the substrate. A pearly luster coating film forming method for forming a matte top clear coat layer further comprising a matting agent thereon is disclosed, and as the interference pigment, a metal oxide-coated silica flake pigment, a mica pigment is disclosed. (Preferably pearl mica pigment), metal oxide-coated alumina flake pigment, metal oxide-coated glass flake pigment, titanium flake pigment, and hologram pigment are disclosed. However, the paint containing the interference pigment disclosed in Patent Document 2 is a clear paint having transparency, and the color base paint film has an L * value of 65 to 100 (approximately White). Further, Patent Document 2 is characterized in that a matte top clear coat layer containing a matting agent is formed on the interference clear coat layer. For this reason, the multilayer coating film disclosed in Patent Document 2 has a unique pearly luster (light incident direction) that is completely different from conventional white mica coating films and white pearl mica coating films including black base coating films. The design feature has a design in which a hue change boundary portion between a highlight portion that is perpendicular to the shade portion and a shade portion that is oblique to the light incident direction appears to change gently.

  Similarly, Patent Document 3 discloses a method for forming a pearly luster coating film, and more specifically, in claim 1, “After forming a color base coating film layer on a substrate, A pearly luster coating film forming method is disclosed in which an interference clear coat layer containing an interference pigment is formed thereon, and a matte top clear coat layer containing achromatic colored resin fine particles as a matting agent is further formed thereon. Yes. In Patent Document 3, as in Patent Document 2, as an interference pigment, mica pigment (preferably pearl mica pigment), metal oxide-coated alumina flake pigment, metal oxide-coated silica flake pigment, metal oxide-coated glass flake. Disclosed is a flake pigment comprising a pigment, a titanium flake pigment, a hologram pigment, and a cholesteric liquid crystal polymer. However, the paint containing the interference pigment disclosed in Patent Document 3 is a clear paint having transparency as in Patent Document 2, and in order to form a pearly luster, the color base paint L * The value is 65 to 100, and it is necessary to exhibit almost white color. Also in Patent Document 3, a design property having a unique pearly luster (a hue change boundary between a highlight portion perpendicular to the light incident direction and a shade portion oblique to the light incident direction. A matte top clear coat layer is required to provide a design where the part appears to slowly change with achromatic coloration (achromatic coloring pearl luster). Furthermore, the invention disclosed in Patent Document 3 is characterized in that the matte top clear coat layer contains achromatic colored resin fine particles. For this reason, the multi-layer coating film disclosed in Patent Document 3 is also different from conventional white pearl mica coating films by using a matte top clear coat layer as in Patent Document 2. A pearly luster having a design property can be provided.

  In Patent Document 4, an interference mica pigment whose surface is coated with titanium dioxide, a silica flake pigment coated with a metal oxide, a hologram pigment, a glass flake pigment coated with a metal oxide, and a metal are plated as an interference pigment. A bright clear paint comprising at least one scaly bright pigment selected from glass flake pigments as an essential component is disclosed. Specifically, claim 1 of Patent Document 4 states that “the surface is further coated with titanium dioxide on a coating film obtained by applying a base coat paint (A) containing a scaly glitter pigment on a substrate. One or more scaly glitter pigments selected from coated interference mica pigments, silica flake pigments coated with metal oxides, hologram pigments, glass flake pigments coated with metal oxides, and glass flake pigments plated with metal A method for forming a multilayer coating film, comprising: coating a bright clear coating (B) comprising 0.01 to 20 parts by weight with respect to 100 parts by weight of a vehicle solid content in the coating, to obtain a multilayer coating film Is disclosed. Note that the bright clear paint (B) disclosed in Patent Document 4 is a colorless or colored transparent paint similar to the interference clear paint described in Patent Documents 2 and 3. Therefore, the multilayer coating film disclosed in Patent Document 4 requires a base coating film containing a pigment as the base. In the invention disclosed in Patent Document 4, the base coat paint for forming the base coating film, that is, the base coat paint (A) contains a scaly glitter pigment, and further, if necessary, a colored pigment or an extender pigment, etc. Containing pigments. According to the invention disclosed in Patent Document 4, by coating the paints (A) and (B) containing the glitter pigment in a double layer, the multilayer coating film excellent in glitter feeling from the highlight portion to the shade portion. Can be formed, and excellent design properties can be provided.

  Thus, in this field, various design properties are provided using various interference pigments or glitter pigments.

JP 2000-42487 A JP 2002-201421 A JP 2002-273334 A JP 2005-177642 A

  An object of this invention is to provide the multilayer coating film which has the outstanding designability which cannot be obtained with the conventional coating material and the coating method.

  As a result of intensive studies to solve the above problems, the present inventors have used a coating film having a specific brightness (L * value) as a base coating film without being bound by the prior art. It has been found that by forming an interference coating layer containing an interference pigment and a titanium dioxide pigment, an interference metal color matching which has not been conventionally obtained can be obtained, and the present invention has been completed. Accordingly, the present invention provides the following.

A method for forming a multilayer coating film comprising: forming a color base coating layer on a substrate; forming an interference base coating layer on the color base coating layer; and further forming a clear coating layer thereon. ,
In the color base coating layer, the concentration (PWC) of the pigment contained in the color base coating layer is 10 to 70% by mass, and the L * (25 ° C.) value is 67 to 83.
The interference base coating layer includes an interference pigment containing an interference silica flake pigment and a titanium dioxide pigment. In the interference base coating layer, the concentration of the interference pigment (PWC) is 3 to 15% by mass. And the concentration of the titanium dioxide pigment (PWC) is 0.1 to 0.6% by mass,
The L * (25 ° C.) value of the multilayer coating film is 70 to 100, the a * (25 ° C.) value is −1 to +5, and the b * (25 ° C.) value is −10 to −2. Presents an interfering metal toning,
A method for forming a multilayer coating film.

  In the above method for forming a multilayer coating film, it is preferable that the interference pigment further contains one or more scale-like transparent pigments selected from the group consisting of mica pigments, alumina flake pigments, and glass flake pigments.

  In the method for forming a multilayer coating film, the mass ratio of the coherent silica flake pigment to the scaly transparent pigment (the interfering silica flake pigment / the scaly transparent pigment) is 100/0 to 30/70. Preferably there is.

  In the method for forming a multilayer coating film, the mass ratio of the interfering silica flake pigment to the scaly transparent pigment (the interfering silica flake pigment / the scaly transparent pigment) is 95/5 to 40/60. Preferably there is.

  In the method for forming a multilayer coating film, in the color base coating layer, the concentration (PWC) of the pigment contained in the color base coating layer is 25 to 60% by mass, and the L * (25 ° C.) value is 70. It is preferable that it is -80.

  The present invention further relates to a multilayer coating film obtained by the above-described method for forming a multilayer coating film.

  In the said field, the coating film which has the outstanding design property is always calculated | required, and various coating films using an interference pigment are developed as described in the above-mentioned background art. However, it has been considered technically impossible to impart significant interference to a coating film with high brightness (L * value), such as a silver metallic coating film using a metallic luster material. Further, when using an interference pigment, it has been known that a high interference effect can be obtained by using a low brightness (low L * value) coating film as the base coating film. Since the color tone changes greatly depending on the thickness of the coating film contained, it has been judged that it is not suitable for a coating film for an automobile outer plate.

  However, in the present invention, a paint having a specific lightness is selected as the base base coating film, and a coating film obtained by combining an interference pigment and a titanium dioxide pigment is used in combination with the conventional paint and coating method. It is possible to provide a multilayer coating film that achieves both excellent design properties and excellent color variability.

  According to the present invention, a metallic glitter material is not used by forming an interference base coating layer containing an interference silica flake pigment and a titanium dioxide pigment on a color base coating layer having an L * value of 67 to 83. Both can give a metallic feeling. In the case of a metallic coating film containing a conventional metallic glitter material, an inorganic cold impression is given to the surroundings, and further, a glare feeling is emphasized, but in the case of the present invention, there is no soft conventional that suppresses the glare feeling. A metallic texture with a unique texture can be obtained. Furthermore, by forming an interference base coating layer containing an interference silica flake pigment and a titanium dioxide pigment on the color base coating layer, a unique interference that gradually changes gently from pink to green. Property can be imparted to the coating film. In particular, in the present invention, it is possible to provide a metallic feeling similar to that of a silver metallic coating film, and to provide a unique soft color such as frost. Therefore, the multi-layer coating film of the present invention can give the impression of soft wrapping around. Such designability is provided for the first time by the present invention, and cannot be obtained at all by conventional paints and coating methods.

FIG. 1 is a diagram schematically illustrating a method for measuring a lightness L * value and a chromaticity a * value and a b * value.

  The present invention relates to a multilayer coating film having excellent design characteristics that cannot be obtained by conventional coating materials and coating methods, and a method for producing the same.

  In the present invention, the color tone of the multilayer coating film is defined by lightness (L * value) and / or saturation (C * value). The lightness (L * value) and saturation (C * value) can be changed by, for example, “CM512m-3” (Minolta's variable angle color difference meter), X-Rite MA68II (X-Right's variable angle color difference meter), etc. It can be measured using an angular color difference meter.

  In the present invention, lightness (L * value) and saturation (C * value) can be determined in accordance with JIS Z8729. The lightness (L * value) and saturation (C * value) are indices used to represent the color of the object to be measured by the L * a * b * color system (CIE 1976). In this color system, lightness is indicated by an L * value and saturation is indicated by a C * value.

As described above, the lightness (L * value) 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.
Saturation (C * value) indicates that the color of the object to be measured increases as the value increases, and the color of the object to be measured decreases as the value decreases, that is, there is no color. Indicates that the color is close to an achromatic color.

In the L * a * b * color system (CIE 1976), the a * value and the b * value are referred to as a chromaticness index and are indices indicating chromaticity.
The a * value is based on 0. If the numerical value is negative (-), it means that the greenness of the measured substance increases. If the numerical value is positive (+), the redness of the measured substance is It means to increase.
The b * value is based on 0. When the numerical value is negative (−), it means that the blueness of the measured substance increases. When the numerical value is positive (+), the yellowness of the measured substance is It means to increase.
When both a * value and b * value are 0, it means an achromatic color.

  The saturation C * value is a value that can be determined from the chromaticity a * value and the b * value according to the following equation.

  The multilayer coating film of the present invention has a lightness L * value of 70 to 100, preferably 80 to 90, more preferably 83 to 88, and a chromaticity a * value of −1 to +5, preferably 0 to +4, more preferably. +1 to +3, and the chromaticity b * value is -10 to -2, preferably -8 to -4, more preferably -7 to -5. The above L * value and chromaticity a * value and b * value are all values at the highlight (25 °) (see FIG. 1). Even if any one of the L * value, the a * value, and the b * value deviates from the above range, it is not possible to provide the unique soft metal feeling and soft interference obtained by the present invention.

  The multilayer coating film of the present invention has a lightness L * (25 °) value of 70 to 100 even if it does not contain a metallic glitter such as aluminum, and has a high whiteness metal toning, that is, aluminum or the like. A bright metallic feeling close to that of a silver metallic coating film containing a metallic luster material can be provided. In the case of a metallic coating film containing a conventional metallic luster material, there is an inorganic cold impression, and further, the glare feeling is emphasized, but in the case of the present invention, the soft and gentle uniqueness that suppresses the glare feeling is unprecedented unique A metallic feeling with a flavor of. Therefore, according to this invention, the unique designability which cannot be obtained with the conventional metallic coating film can be provided.

  In the multilayer coating film of the present invention, the saturation C * value at highlight (25 °) is preferably 6.5 or more. A higher saturation C * value is preferable. When the saturation C * value is 6.5 or more, the color becomes vivid, and remarkable coherence can be exhibited in highlights. The saturation C * (25 °) value is more preferably in the range of 6.5 to 16.0. Further, when the saturation C * (25 °) value is less than 6.5, the coherence is not remarkable, and further, the color tone is lowered, and there is a possibility of exhibiting a color tone different from the metal color tone.

  Moreover, the multilayer coating film of this invention comprises remarkable interference nature in addition to a metal feeling as above-mentioned. That is, the multilayer coating film of the present invention exhibits interference metal toning, and according to the present invention, the coating film can be imparted with a unique interference property that gradually and gently changes from pink to green. . In particular, the multi-layer coating film of the present invention can provide a metallic feeling very similar to that of a conventional silver metallic coating film, and also provides a unique soft color that feels like frost. be able to. Therefore, in the present invention, it is possible to give a unique design property that wraps gently and softly. Such designability is provided for the first time by the present invention, and cannot be obtained at all by conventional paints and coating methods.

  In addition, the excellent designability obtained by the present invention can be achieved by using a color base coating layer having a hue that has not been applied due to the problem of color variability in the conventional 3-coat pearl for automobile outer panels. It can be done.

  In the present invention, a color base coating layer having a specific brightness is formed on a substrate, a specific interference base coating layer is formed on the color base coating layer, and a clear coating layer is further formed thereon. Thus, a multilayer coating film having the above-mentioned unique design properties can be formed. Conventionally, when forming a multi-layer coating film having high interference, a dark base coating film with low brightness is formed, and an interference coating layer is provided on the base coating film. It has been known that reflection is prevented and the interference due to the interference pigment is significantly expressed. Further, except for a special design coating film, an undercoating film with high brightness was not formed when the interference coating film layer was formed.

  Hereinafter, each coating composition used in the present invention will be described in detail. The method for forming a multilayer coating film according to the present invention particularly forms a color base coating composition capable of forming a color base coating film layer having a specific lightness and a specific interference base coating layer formed thereon. It is characterized in that it is used in combination with a coherent base coating composition that can be used.

Color Base Coating Composition The color base coating composition that can be used in the present invention is, for example, a color base coating composition containing a film-forming resin, a curing agent and a pigment, and having a specific brightness (specifically, 25 ° L * value: 67 to 83) is not particularly limited as long as it is a coating composition capable of forming a color base coating film layer.

  Examples of the pigment contained in the color base coating composition include organic and inorganic color pigments and extender pigments. Examples of organic coloring pigments include azo lake pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. Examples thereof include pigments, dioxazine pigments, quinacridone pigments, selenium pigments, isoindoline pigments, isoindolinone pigments, and metal complex pigments. Examples of inorganic coloring pigments include chrome yellow, zinc white, iron oxide, yellow iron oxide, bengara, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, and titanium oxide (for example, , Titanium dioxide) and the like. Examples of extender pigments include calcium carbonate, barium sulfate, calcined kaolin, magnesium silicate, clay, and talc. You may use the said pigment 1 type or in combination of 2 or more types.

  The pigment concentration (PWC) (pigment weight concentration) contained in the color base coating composition or the color base coating layer is 10 to 70% by mass, preferably 25 to 60% by mass.

  In this invention, the density | concentration (PWC) of the pigment contained in a color base coating composition or a color base coating film can be determined based on the following formula | equation.

  Pigment concentration (PWC) = (total mass of all pigments) / (total mass of all pigments and all resin solids) × 100 (mass%)

  When the pigment concentration (PWC) is less than 10% by mass, the background hiding property is not sufficiently ensured, and when the background hiding property is low, the hue of the background is transparent and the hue of the color base is not stable. Further, if the amount of transmitted ultraviolet rays increases and reaches the underlying electrodeposition coating film, peeling may occur. On the other hand, when the pigment concentration (PWC) exceeds 70% by mass, there is a risk of problems such as poor dispersibility and poor gloss, poor coating smoothness, and poor adhesion. Further, when the pigment concentration (PWC) is 10 to 70% by mass, a color base coating layer having a lightness L * value of 67 to 83, preferably 70 to 80, can be formed.

  In the present invention, the color base coating layer has an L * (25 °) value of 67 to 83, that is, low brightness as a color base for conventional white mica. Conventionally, when providing interference by using an interference coating layer, a black base coating with low brightness is provided, and an interference coating layer is provided thereon to reflect incident light by the base coating. Although it has been known that the color tone changes greatly depending on the thickness of the coating film containing the interference pigment, it has been considered unsuitable for a coating film for an automobile outer plate. However, in the present invention, a paint having a proper brightness as described above is selected as a base coating film, and a coating film in which an interference pigment and a titanium oxide pigment are combined is used in the conventional paint and coating method. It is possible to provide a multilayer coating film that achieves both excellent design properties that cannot be achieved and excellent color variability. Such an effect has been revealed for the first time by the present invention.

  The color base coating composition that can be used in the present invention contains a film-forming resin and a curing agent in addition to the pigment. Preferably, the color base coating composition used in the present invention is a melamine curable coating composition containing the pigment, polyester resin and melamine curing agent, and in particular, the pigment; number average molecular weight 1000 to 4500, hydroxyl value At least one selected from the group consisting of 70-220 mg KOH / g (solid content) and an acid value of 5-20 mg KOH / g (solid content) polyester resin; and methyl / butyl mixed alkyl etherified melamine resin and butyl etherified melamine resin A melamine curable coating composition containing a curing agent is preferred.

  As the above-mentioned polyester resin, it is preferable to use the same resin as the basic resin component that imparts the chipping resistance, base concealment, surface smoothness and the like, which are functions of the intermediate coating.

  The number average molecular weight of the polyester resin is 1000 to 4500. If the number average molecular weight is less than 1000, sufficient curing cannot be obtained. If the number average molecular weight exceeds 4500, smoothness becomes insufficient and a good appearance cannot be obtained. At the same time, the viscosity during coating becomes too high.

  The polyester resin has a hydroxyl value of 70 to 220 mgKOH / g (solid content). When the hydroxyl value is less than 70 mgKOH / g (solid content), the curability is poor, and when it exceeds 220 mgKOH / g (solid content), the elasticity is lowered and the chipping resistance is poor.

  The polyester resin has an acid value of 5 to 20 mg KOH / g (solid content). If the acid value is lower than 5 mgKOH / g (solid content), the curability becomes poor, and if it exceeds 20 mgKOH / g (solid content), the water resistance is retreated.

  The polyester resin can be produced by polycondensation of polyvalent carboxylic acid and / or acid anhydride and polyhydric alcohol as essential components. Examples of reaction components other than the essential components include monocarboxylic acid, hydroxycarboxylic acid, and lactone. Moreover, you may add drying oil, anti-drying oil, and those fatty acids in a reaction system.

  The content of the polyester resin in the color base coating composition is 20 to 70 mass%, preferably 30 to 50 mass%, based on the solid content of the coating. When the content is less than 20% by mass, the dispersion becomes poor and the glossiness is lowered. When the content exceeds 70% by mass, the concealability of the base becomes insufficient.

  As said hardening | curing agent, Preferably a melamine hardening | curing agent, More preferably, a methyl / butyl mixed alkyl etherified melamine resin is used effectively. The reason for this is that the curing agent component has a low degree of condensation and a slow reaction initiation rate, which increases the degree of flow during heating and improves surface smoothness, while at the same time self-condensation despite the slow reaction initiation rate. The rate is low and the coating film performance is excellent.

  However, if there is a possibility of baking at a low temperature, sufficient coating performance may not be obtained with the methyl / butyl mixed alkyl etherified melamine resin alone. In such a case, a butyl etherified melamine resin can be used in combination with the methyl / butyl mixed alkyl etherified melamine resin.

  Further, two or more kinds of the above curing agents may be appropriately mixed and used.

  The content of the curing agent in the color base coating composition is 10 to 40% by mass, preferably 15 to 35% by mass, based on the solid content of the coating. When the content is less than 10% by mass, the curability becomes insufficient, and when it exceeds 40% by mass, the formed coating film becomes hard and brittle.

  The color base coating composition that can be used in the present invention includes an organic solvent (for example, an aromatic hydrocarbon type, an aliphatic group) as necessary, in addition to the pigment, the film-forming resin, and the curing agent, which are essential components. Hydrocarbon-based, ester-based, alcohol-based solvents, etc.), thickeners (for example, crosslinked resin particles, organic bentonite, fatty acid polyamide, polyethylene wax, etc.), glittering materials (for example, aluminum foil, mica, tin foil, gold foil, metal) Titanium foil, nickel foil, etc.), acid catalyst, ultraviolet absorber, hindered amine light stabilizer, antioxidant, surface conditioner, leveling agent, pigment dispersant, plasticizer, antifoaming agent and the like may be appropriately blended.

Interfering Base Coating Composition In the present invention, the interfering base coating composition capable of forming an interference base coating layer is preferably an aqueous coating composition, including an interference pigment containing an interference silica flake pigment and a carbon dioxide. As the titanium pigment and the film-forming resin, an emulsion resin obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture is included.

  In the present invention, a color base coating layer having a specific brightness (that is, a color base coating layer having an L * value of 25 °: 67 to 83) is formed as a base coating, and an interference pigment and a titanium dioxide pigment are formed thereon. By forming an interfering base coating film layer containing, a metal color tone similar to a silver metallic coating film using a conventional metallic luster material can be imparted to the multilayer coating film. In addition, according to the present invention, metal toning can be achieved without using a metallic luster material, and further, remarkable interference can be imparted by this interference base coating layer. Such an interfering metal toning (L * value at 25 °: 70 to 100) is a design found for the first time by the present invention, and is completely different from a conventional metallic coating film using a metallic luster material. A unique design can be provided. Conventionally, it has been impossible to impart significant interference to a coating film having high brightness such as a silver metallic coating film. In addition, in order to impart interference to the coating film, it was essential that the base coating film be a dark or dark color such as black, but the color tone greatly changes depending on the thickness of the coating film containing the interference pigment. Therefore, it has been considered unsuitable as a coating for automobile outer panels. However, in the present invention, the interference pigment and the titanium oxide pigment are combined while using the color base coating film having the specific brightness described above, not the metallic coating film using the conventional metallic glitter material, without being bound by the prior art. By using these coating films together, it is possible to provide a multilayer coating film that achieves both excellent design characteristics and excellent color variability that cannot be obtained by conventional coating materials and coating methods.

  In the present invention, the interference base coating composition contains an interference silica flake pigment as an interference pigment, and further contains a titanium dioxide pigment. In the present invention, the interference silica flake pigment is an essential component as an interference pigment, and can impart significant interference to the coating film. Further, in this field, interference pigments such as mica are widely used as pigments that impart interference, but interference pigments are generally transparent pigments that are highly transparent, and usually white pigments such as titanium dioxide and the like. It was not used together. This is because when a white pigment such as titanium dioxide and an interference mica pigment are used in combination, the formed coating film becomes turbid and the interference property is remarkably reduced. Hereinafter, the interference pigment and the titanium dioxide pigment will be described in detail.

(Interference pigment)
As the interference pigment contained in the interference base coating composition and the interference base coating layer of the present invention, it is preferable to use a scaly interference pigment such as an interference silica flake pigment. The interference pigment that can be used in the present invention has, for example, an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm, preferably 10 to 35 μm, and a thickness of 0.1 to 5 μm, preferably 0.5. ~ 2 μm. In the present invention, the interference pigment may be colored.

  Examples of the interfering silica flake pigment include “Colorstream T20-01” (Merck's interference pink-green silica flake pigment) and Colorstream T20-02 ”(Merck's interference turquoise-red silica flake pigment). , Colorstream T20-03 "(Merck's interference green-red silica flake pigment) and Colorstream F20-00" (Merck's interference red-gold silica flake pigment) can be used. . The use of an interference silica flake pigment is particularly preferable because an effect such as large color change (strong dichroism) and strong interference can be obtained. In particular, "Colorstream T20-01" (Merck's interference pink-green silica flake pigment), Colorstream T20-02 "(Merck's interference turquoise-red silica flake pigment), Colorstream T20-03" (Merck) It is preferable to use an interference silica flake having dichroism such as “Interference Green-Red Silica Flake Pigment” manufactured by Co., Ltd. More preferably, it is used.

  Examples of the interference pigment include scaly transparent pigments other than the above-mentioned interference silica flake pigment. For example, mica pigment (for example, interference mica pigment is preferable), alumina flake pigment (for example, interference alumina flake is preferable). ) And glass flake pigments (for example, interference glass flakes are preferred).

  The scaly transparent pigment is preferably a mica pigment because of its high lightness and small color change, and particularly preferably an interference mica pigment.

  In the interference base coating composition or the interference base coating layer that can be used in the present invention, the interference pigment concentration (PWC) (pigment weight concentration) is 3 to 15% by mass, preferably 4 to 13% by mass. It is. If the concentration (PWC) of the interference pigment is less than 3% by mass, sufficient interference effect cannot be obtained, and the interference pigment may be mottled and uneven and easily become uneven. If it exceeds 50%, there is a risk of problems such as poor appearance and poor appearance such as rough skin.

  In the present invention, the concentration (PWC) of the interference pigment can be determined based on the following equation.

  Interference pigment concentration (PWC) = (total mass of all interference pigments) / (total mass of all pigments and all resin solids including interference pigments) × 100 (mass%)

  In the present invention, as the interference pigment, the interference silica flake pigment and a flaky transparent pigment other than the interference silica flake pigment may be used in combination. For example, when the interference silica flake pigment is used in combination with the other scale-like transparent pigment, the mass ratio of the interference silica flake pigment and the other scale-like transparent pigment (interference silica flake pigment / others The scale-like transparent pigment) is 100/0 to 30/70, preferably 95/5 to 40/60. When the mass ratio is within the above range, the interference effect of the silica flakes can be sufficiently extracted, and an effect that a design with high brightness can be obtained can be obtained. In the present invention, it is most preferable to use an interference silica flake pigment alone as the interference pigment, and the interference metal toning defined above can be successfully imparted to the multilayer coating film. In that case, the concentration (PWC) of the interfering silica flake pigment is preferably 4 to 13% by mass, more preferably 9 to 12% by mass.

(Titanium dioxide pigment)
The titanium dioxide pigment contained in the interference base coating composition and the interference base coating layer of the present invention is not particularly limited. For example, titanium white pigment “CR-97” (manufactured by Ishihara Sangyo Co., Ltd.), “CR- Commercial products such as “95” (manufactured by Ishihara Sangyo Co., Ltd.) and “D-918” (manufactured by Sakai Chemical Co., Ltd.) can be used. By blending titanium dioxide pigment into the interference base paint composition and using it together with the above-mentioned interference pigment in an optimum ratio, the hue fluctuation when the film thickness of the interference base paint fluctuates without impairing the design properties is achieved. The effect that it can suppress small is acquired.
In the prior art, when a white pigment such as titanium dioxide and the above-described transparent interference pigment are used in combination, the coating film becomes turbid and the interference is significantly reduced. The above-mentioned effect is an effect that has been clarified for the first time by the present invention, and contributes greatly to the provision of an excellent design that has not been achieved in the past.

  In the interference base coating composition or the interference base coating layer that can be used in the present invention, the titanium dioxide pigment concentration (PWC) (pigment weight concentration) is 0.1 to 0.6% by mass, preferably 0. .2 to 0.4% by mass. When the concentration (PWC) of the interference pigment is less than 0.1% by mass, the coloring effect of the titanium dioxide pigment is small, and the hue variation suppression effect when the film thickness of the interference base paint varies is small. If the amount exceeds 0.6% by mass, the coloring effect of the titanium dioxide pigment is too strong, and the coloring effect of the interference pigment is inhibited.

  In the present invention, the concentration of titanium dioxide pigment (PWC) can be determined based on the following equation.

  Titanium dioxide pigment concentration (PWC) = (mass of titanium dioxide pigment) / (total mass of all pigments including titanium dioxide pigment and all resin solids) × 100 (mass%)

(Coating film forming resin)
The interference base coating composition further includes an emulsion resin obtained by emulsion polymerization of an α, β-ethylenically unsaturated monomer mixture as a film-forming resin. The α, β-ethylenically unsaturated monomer mixture contains 65% by weight or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion. When it is less than 65% by weight, the appearance of the resulting coating film is deteriorated. Examples of the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester part include methyl (meth) acrylate and ethyl (meth) acrylate. In this specification, “(meth) acrylic acid ester” means both acrylic acid ester and methacrylic acid ester.

  The α, β-ethylenically unsaturated monomer mixture has an acid value of 3 to 50, preferably 7 to 40. When the acid value is less than 3, workability cannot be improved, and when it exceeds 50, the water resistance of the coating film is lowered. On the other hand, when the interference base coating composition needs to have curability, the α, β-ethylenically unsaturated monomer mixture has a hydroxyl value of 10 to 150, preferably 20 to 100. If it is less than 10, sufficient curability cannot be obtained, and if it exceeds 150, the water resistance of the coating film decreases. In addition, the glass transition temperature of the polymer obtained by copolymerizing the α, β-ethylenically unsaturated monomer mixture is between -20 and 80 ° C. from the viewpoint of the mechanical properties of the resulting coating film. preferable.

  The α, β-ethylenically unsaturated monomer mixture can have the acid value and the hydroxyl value by including therein an α, β-ethylenically unsaturated monomer having an acid group or a hydroxyl group.

  Examples of the α, β-ethylenically unsaturated monomer having an acid group include acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethylphthalic acid, 2-acryloyloxyethyl succinic acid, and ω-carboxy-polycaprolactone. Mono (meth) acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, Itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acryloyloxyethyl acid phosphate, 2-acrylamido-2-methylpropanesulfonic acid and the like can be mentioned. Among these, acrylic acid and methacrylic acid are preferable.

  On the other hand, as the α, β-ethylenically unsaturated monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, (meth) Mention may be made of adducts of hydroxyethyl acrylate and ε-caprolactone. Among these, preferred are hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and an adduct of hydroxyethyl (meth) acrylate and ε-caprolactone.

  Furthermore, the α, β-ethylenically unsaturated monomer mixture may further contain other α, β-ethylenically unsaturated monomers. Examples of the other α, β-ethylenically unsaturated monomers include (meth) acrylic acid esters having an ester part of 3 or more carbon atoms (for example, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (meth) T-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, di (meth) acrylate Cyclopentadienyl, (meth) acrylic acid dihydrodicyclopentadienyl, etc.), polymerizable amide compounds (for example, (meth) acrylamide, N-methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibu Chill (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide 2,4-dihydroxy-4'-vinylbenzophenone, N- (2-hydroxy Ethyl) acrylamide, N- (2-hydroxyethyl) methacrylamide, etc.), polymerizable aromatic compounds (for example, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.), polymerizable Nitriles (eg, acrylonitrile, methacrylonitrile, etc.), α-olefins (eg, ethylene, propylene, etc.), vinyl esters (eg, vinyl acetate, vinyl propionate, etc.), dienes (eg, butadiene, isoprene, etc.), polymerizable Aromatic compounds, Polymerizable nitriles, alpha-olefin, and vinyl esters, and dienes. These can be selected depending on the purpose, but (meth) acrylamide is preferably used when hydrophilicity is easily imparted.

  The α, β-ethylenically unsaturated monomer other than the (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion has a content in the α, β-ethylenically unsaturated monomer mixture. Must be set to less than 35% by weight.

  The emulsion resin contained in the interference base coating composition is obtained by emulsion polymerization of the α, β-ethylenically unsaturated monomer mixture. The emulsion polymerization carried out here can be carried out using a generally well-known method. Specifically, an emulsifier is dissolved in water or an aqueous medium containing an organic solvent such as alcohol as necessary, and the α, β-ethylenically unsaturated monomer mixture and the polymerization initiator are heated and stirred. This can be done by dripping. An α, β-ethylenically unsaturated monomer mixture emulsified in advance using an emulsifier and water may be similarly added dropwise.

  Suitable polymerization initiators include azo oily compounds (for example, azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile) and 2,2′-azobis (2,4 -Dimethylvaleronitrile) and the like, and aqueous compounds (for example, anionic 4,4'-azobis (4-cyanovaleric acid), 2,2-azobis (N- (2-carboxyethyl) -2-methylpropion) Amidine and cationic 2,2′-azobis (2-methylpropionamidine)); and redox oily peroxides (eg, benzoyl peroxide, parachlorobenzoyl peroxide, lauroyl peroxide and t-butyl perbenzoate) Etc.), and aqueous peroxides such as potassium persulfate and ammonium persulfate It is below.

  As the emulsifier, those commonly used by those skilled in the art can be used. However, reactive emulsifiers such as Antox MS-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminol JS-2 (manufactured by Sanyo Chemical Industries Ltd.) Adekaria soap NE-20 (Asahi Denka Co., Ltd.) and Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.) are particularly preferred.

  In order to adjust the molecular weight, a mercaptan such as lauryl mercaptan and a chain transfer agent such as α-methylstyrene dimer may be used as necessary.

  The reaction temperature is determined by the initiator, and for example, it is preferably 60 to 90 ° C. for an azo initiator and 30 to 70 ° C. for a redox system. In general, the reaction time is 1 to 8 hours. The amount of initiator relative to the total amount of α, β-ethylenically unsaturated monomer mixture is generally 0.1 to 5% by weight, preferably 0.2 to 2% by weight.

  The emulsion polymerization can be performed in multiple stages, for example, in two stages. That is, first, a part of the α, β-ethylenically unsaturated monomer mixture (α, β-ethylenically unsaturated monomer mixture 1) is emulsion-polymerized, and the α, β-ethylenically unsaturated monomer mixture is added thereto. The remainder (α, β-ethylenically unsaturated monomer mixture 2) is further added to carry out emulsion polymerization.

  Here, from the viewpoint of preventing the compatibility with the clear coating composition, the α, β-ethylenically unsaturated monomer mixture 1 preferably contains an α, β-ethylenically unsaturated monomer having an amide group. At this time, it is more preferable that the α, β-ethylenically unsaturated monomer mixture 2 does not contain an α, β-ethylenically unsaturated monomer having an amide group. Since the α, β-ethylenically unsaturated monomer mixture 1 and 2 together is the α, β-ethylenically unsaturated monomer mixture, the α, β-ethylenically unsaturated compound described above is used. The requirements for the monomer mixture will be met by the combined α, β-ethylenically unsaturated monomer mixture 1 and 2.

  The particle diameter of the emulsion resin thus obtained is preferably in the range of 0.01 to 1.0 μm. When the particle diameter is less than 0.01 μm, the effect of improving workability is small, and when it exceeds 1.0 μm, the appearance of the resulting coating film may be deteriorated. The particle size can be adjusted, for example, by adjusting the monomer composition and emulsion polymerization conditions.

  The emulsion resin can be used at a pH of 5 to 10 by neutralizing with a base as necessary. This is because the stability in this pH region is high. This neutralization is preferably carried out by adding a tertiary amine such as dimethylethanolamine or triethylamine to the system before or after emulsion polymerization.

  The interference base coating composition may further contain a curing agent. As a hardening | curing agent, what is generally used for the coating material can be used. Examples of such compounds include amino resins, blocked isocyanates, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and metal ions. An amino resin and / or a blocked isocyanate resin is generally used in view of various performances and costs of the obtained coating film.

  The amino resin as the curing agent is not particularly limited, and a water-soluble melamine resin or a water-insoluble melamine resin can be used. In addition, it is preferable on stability that the water tolerance of 3.0 or more is used among melamine resins. The water tolerance used here is for evaluating the degree of hydrophilicity, and the higher the value, the higher the hydrophilicity. The water tolerance value was measured by mixing 0.5 g of a sample in 10 ml of acetone and dispersing in a 100 ml beaker at 25 ° C., and gradually adding ion-exchanged water using a burette until the mixture became cloudy. The amount (ml) of ion exchange water required is measured, and this amount (ml) of ion exchange water is used as a water tolerance value.

  The above-mentioned blocked isocyanate can be obtained by adding a blocking agent having active hydrogen to a polyisocyanate such as trimethylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, etc. Examples include those that dissociate and generate isocyanate groups.

  When these hardening | curing agents are contained, it is preferable that the content is 20-100 weight part with respect to 100 weight part of resin solid content in an interference base coating composition. Outside the above range, curability is insufficient.

  The interference base coating composition may contain other film-forming resin as necessary. Other film-forming resins are not particularly limited, and film-forming resins such as acrylic resins, polyester resins, alkyd resins, epoxy resins, and urethane resins can be used.

  The other film-forming resin has a number average molecular weight of 3,000 to 50,000, preferably 6,000 to 30,000. If it is less than 3000, workability and curability are not sufficient, and if it exceeds 50000, the non-volatile content at the time of coating becomes too low, and workability is rather deteriorated.

  The coating film-forming resin preferably has an acid value of 10 to 100 mgKOH / g, more preferably 20 to 80 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the water dispersibility of the resin is reduced. Decreases. Further, it preferably has a hydroxyl value of 20 to 180 mgKOH / g, more preferably 30 to 160 mgKOH / g. When the upper limit is exceeded, the water resistance of the coating film decreases, and when the lower limit is exceeded, the curability of the coating film decreases.

  The blending ratio of the emulsion resin and the other film-forming resin in the interference base coating composition is 5 to 95% by weight, preferably 10 to 85% by weight of the emulsion resin, based on the total resin solid content. %, More preferably 20 to 70% by weight, and other film-forming resin is 95 to 5% by weight, preferably 90 to 15% by weight, and more preferably 80 to 30% by weight. When the proportion of the emulsion resin is less than 5% by weight, the workability is lowered, and when it is more than 95% by weight, the film forming property may be deteriorated.

  As said other film forming resin, it is preferable to use a water-soluble acrylic resin from a compatible point with emulsion resin. This water-soluble acrylic resin has an α, β-ethylenically unsaturated monomer having an acid group described in the above α, β-ethylenically unsaturated monomer mixture as an essential component, and other α, β-ethylenic monomers. It can be obtained by performing solution polymerization together with an unsaturated monomer. Here, the component used to obtain this water-soluble acrylic resin contains 65% by weight or more of (meth) acrylic acid ester having 1 or 2 carbon atoms in the ester portion. It is preferable from the point.

  The water-soluble acrylic resin is usually neutralized with a basic compound, for example, an organic amine such as monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, and dimethylethanolamine, and added to water. Although it is used after being dissolved, this neutralization may be performed on the water-soluble acrylic resin itself or at the time of producing an interference base coating composition described later.

  The interference base coating composition that can be used in the present invention emulsifies an α, β-ethylenically unsaturated monomer mixture as the above-mentioned essential components, ie, an interference pigment, a titanium dioxide pigment, and a film-forming resin. In addition to the emulsion resin obtained by polymerization, an organic solvent (for example, aromatic hydrocarbon type, aliphatic hydrocarbon type, ester type, alcohol type solvent, etc.), thickener (for example, cross-linked resin), if necessary. Particles, organic bentonite, fatty acid polyamide, polyethylene wax, etc.), organic color pigments (eg, azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments) , Indigo pigment, perinone pigment, perylene pigment, dioxane pigment, quinacridone pigment, isoindolinone Pigments, metal complex pigments, etc.), inorganic color pigments (eg, yellow lead, yellow iron oxide, bengara, carbon black, etc.), extenders (eg, calcium carbonate, barium sulfate, calcined kaolin, magnesium silicate, clay, talc) Etc.), glittering material (for example, aluminum foil, tin foil, gold foil, metal titanium foil, nickel foil, etc.), acid catalyst, ultraviolet absorber, hindered amine light stabilizer, antioxidant, surface conditioner, leveling agent, pigment dispersion You may mix | blend an agent, a plasticizer, an antifoamer, etc. suitably.

Clear coating composition The clear coating composition capable of forming a clear coating layer in the present invention is not particularly limited, and those containing a film-forming thermosetting resin and a curing agent can be used. . The form of the clear coating composition may be any of a solvent type, an aqueous type and a powder type.

  Preferred examples of the solvent-type clear coating composition include a combination of an acrylic resin and / or a polyester resin and an amino resin as a film-forming resin from the viewpoint of transparency or acid etching resistance, or a carboxylic acid / Examples thereof include solvent-type clear coating compositions containing an acrylic resin and / or a polyester resin having an epoxy curing system.

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

  On the other hand, as the powder-type clear coating composition, ordinary powder coatings such as thermoplastic and thermosetting powder coatings can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of thermosetting powder coatings include epoxy, acrylic and polyester powder-type clear coating compositions, etc., but acrylic powder-type clear coatings with good weather resistance. Compositions are particularly preferred.

  As a powder-type clear coating composition used in the present invention, there is no volatilized substance at the time of curing, a good appearance is obtained, and there is little yellowing, so an epoxy-containing acrylic resin / polyvalent carboxylic acid system powder A body-type clear coating composition is particularly preferred.

  Furthermore, it is preferable to add a viscosity control agent to the clear coating composition in order to ensure coating workability. As the viscosity control agent, those generally showing thixotropy can be used. Moreover, you may mix | blend a curing catalyst, a surface adjusting agent, etc. as needed.

Substrates The multi-layer coating film forming method of the present invention can be advantageously applied to various substrates such as metals, plastics, foams, etc., particularly metal surfaces and castings. It can be particularly suitably applied to products.

  Examples of the metal products include iron, copper, aluminum, magnesium, tin, zinc, and alloys containing these metals. Specific examples include automobile bodies such as passenger cars, trucks, motorcycles, buses, and parts thereof. These metal products are particularly preferably those which have been previously subjected to chemical conversion treatment with phosphate, chromate or the like.

  Moreover, an electrodeposition coating film and / or an intermediate coating film may be formed on the substrate used in the method for forming a multilayer coating film of the present invention after the chemical conversion treatment. As the electrodeposition paint for forming the electrodeposition coating film, both cationic type and anion type can be used, but the cationic type electrodeposition coating composition is preferable because it provides a laminated coating film excellent in anticorrosion.

  As the intermediate coating composition for forming the intermediate coating film, a gray melamine curing system or isocyanate curing system using carbon black and titanium dioxide as main pigments is used. Furthermore, the thing which combined the hue with top coat and the thing which combined various coloring pigments can also be used.

Multilayer coating film forming method The multilayer coating film forming method of the present invention comprises forming a color base coating layer on a base material, forming an interference base coating layer on the color base coating layer, and further thereon. Forming a clear coating layer. For example, the multi-layer coating film of the present invention is formed on the base material on which an undercoat film and / or an intermediate coat film such as an electrodeposition film is formed using, for example, an electrostatic coating machine. The paint composition, the interference base coating composition and the clear coating composition are applied in this order by wet-on-wet, and the color base coating film, the interference base coating film and the clear coating film are applied. Can be formed by a method (three-coat one-bake (3C1B) method) in which a multi-layer coating film consisting of three layers is obtained by heating and curing at the same time.

  When the above-described coating composition is applied to a substrate such as an automobile body in the present invention, an electrostatic coating machine may be used to improve workability and appearance. Examples of electrostatic coating machines include, for example, air electrostatic spray coating called “react gun” or the like, or “μμ (micro micro) bell”, “μ (micro) bell” or “metabell”. Rotating atomization type electrostatic coating machine. A coating film can be formed by multistage coating, preferably 2-3 stage coating, using the electrostatic coating machine. Moreover, a coating film can also be formed by the coating method etc. which combined the air electrostatic spray coating and the rotary atomization type electrostatic coating machine.

  In this invention, although the dry film thickness of a color base coating film layer changes with desired uses, it is 20-80 micrometers normally, Preferably it is 25-60 micrometers, More preferably, it is 30-50 micrometers. If the dry film thickness is less than 20 μm, the hiding power cannot be ensured and the hue of the groundwork is transparent, the hue is not stable, the shape of the groundwork cannot be sufficiently masked, and the skin and gloss are finished. There is a possibility of a problem, and if it exceeds 80 μm, there is a possibility of problems such as sagging on the vertical surface and occurrence of cracks.

  In the present invention, the dry film thickness of the coherent base coating layer varies depending on the desired application, but is usually 10 to 30 μm, preferably 12 to 20 μm, more preferably 13 to 18 μm, and most preferably 15 μm. When the dry film thickness is less than 10 μm, the interference base coating film is too transparent, and a sufficient interference coloring effect is not exhibited. There is a risk of problems such as instability of hue, and if it exceeds 30 μm, there is a risk of problems such as sagging on the vertical surface, occurrence of cracks, deterioration of gloss and skin.

  In the present invention, the dry film thickness of the clear coating layer varies depending on the desired application, but is usually 10 to 80 μm, preferably 20 to 60 μm. If the dry film thickness is less than 10 μm, there may be problems such as the unevenness of the foundation cannot be concealed, gloss and skin deterioration, and the protective function as a coating film cannot be fully exhibited. If it exceeds 80 μm, There is a risk of problems such as sagging.

  In the method for forming a multilayer coating film of the present invention, the clear coating layer is formed in order to smooth and protect the unevenness caused by the color base coating film and the interference base coating film. As a coating method of the clear coating composition, the above-described coating method using a rotary atomizing electrostatic coating machine such as μμ bell or μbell is preferable.

  You may perform operation which leaves the time interval called an interval (or setting) between each coating. By this interval, the organic solvent or water contained in the formed coating film can be sufficiently volatilized, and the appearance of the coating film is improved. The interval is, for example, 30 seconds to 15 minutes.

  Moreover, you may perform the heating operation called preheating during the said interval. By this preheating, the organic solvent or water contained in the formed coating film can be volatilized efficiently in a short time. This preheating heating does not actively cure the formed coating film. Therefore, preheating heating conditions are 40-100 degreeC, for example, for 1 to 10 minutes. Preheating may be performed using, for example, a warm air heater or an infrared heater.

  In a three-coat one-bake method in which a color base coating film, an interference base coating film, and a clear coating film that have been re-applied wet-on-wet are simultaneously heat-cured to obtain a multi-layer coating film consisting of three layers, the heat-curing temperature is 80 to 180 ° C., preferably 120 to 160 ° C. If it is less than 80 ° C., sufficient curing cannot be obtained, and if it exceeds 180 ° C., the coating film may become hard and brittle. The heat curing time varies depending on the temperature, but is usually 10 to 30 minutes at 120 to 180 ° C.

  In the multilayer coating film forming method of the present invention, the coating film may optionally be heat-cured after the coating composition is applied. For example, after forming a color base coating film using a color base coating composition, heat curing is performed under the above conditions to form a cured coating film, and an interference base coating film is formed thereon using the interference base coating composition. After that, the clear coating composition may be applied over the substrate by wet-on-wet and heat-cured under the above conditions (that is, 3 coat 2 (3C2B) baking method). By increasing the heat curing step, the number of steps increases, but there is an advantage that an excellent coating film appearance can be obtained.

  The dry film thickness of the multilayer coating film formed by the method of the present invention is 30 to 300 μm, preferably 50 to 250 μm. If it is less than 30 μm, the coating film strength is lowered, and if it exceeds 300 μm, the physical properties of the coating film such as a cooling cycle may be lowered.

  Conventionally, it has been impossible to impart significant interference to a coating film exhibiting a high-brightness metal toning, such as a silver metallic coating film containing a metallic glitter material, but the composite formed by the method of the present invention is not possible. As described above, even if the layer coating film does not contain a metallic luster material, the layer coating film can exhibit metallic toning, and can also provide remarkable interference. This is because, in the present invention, a color base coating layer having a specific brightness that has not been applied to pearl mica for automobile outer plates due to the problem of conventional color variability, and an interference pigment (particularly, an interference silica flake pigment). And an interfering base coating layer comprising a titanium dioxide pigment can be achieved. Further, conventionally, a combination of an interference pigment and a titanium dioxide pigment has not been used in a mica coating. Therefore, according to the present invention, it is possible to provide an excellent design property that is not found in the prior art, that is, an interference metal toning with high brightness.

  As described above, the multilayer coating film showing the coherent metal toning of the present invention has an L * value of 70 to 100, an a * value of −1 to +5, and −10 to −2 at highlight (25 °). In order for the multi-layer coating film of the present invention to exhibit a metallic color tone and to exhibit a remarkable interference property, the L * (25 °) value of the color base coating layer serving as a base coating film The concentration (PWC) of the titanium dioxide pigment contained in the interference base coating layer is an important factor. Therefore, in the present invention, in order to obtain a metal color tone exhibiting remarkable interference, the color base coating layer has an L * (25 °) value of 67 to 83, and is included in the interference base coating layer. It is necessary that the concentration (PWC) of the titanium dioxide pigment is 0.1 to 0.6% by mass.

  In addition, in order for the multilayer coating film of the present invention to exhibit a metal color tone having remarkable interference, it is necessary to consider “workability” when forming the multilayer coating film. Generally, when the workability at the time of forming the multilayer coating film is lowered, the coating film is uneven and the design property is remarkably lowered. The occurrence of unevenness mainly depends on the film thickness of the coating layer containing a solid such as an interference pigment. Therefore, in the present invention, the workability index (Total ΔE) is derived from the change in the thickness of the coherent base coating layer and the change in the L * value, a * value, and b * value of the multilayer coating film. It was.

  Specifically, the workability index (Total ΔE) can be derived as follows. As described above, the thickness of the coherent base coating film layer is most preferably 15 μm, and the actual film thickness variation during coating is predicted to be about ± 2 μm. Therefore, the L * value, a * value, and b * value of the multilayer coating film when the film thickness of the interference base coating film layer varies between 13 μm (= 15 μm−2 μm) and 17 μm (= 15 μm + 2 μm). From this change, an index of workability (Total ΔE) was derived.

  The lightness L * value, chromaticity a * value, and b * value are as shown in the schematic diagram of FIG. It can be measured by irradiating the coating film with light from an angle of 25 ° (highlight), 45 ° or 75 ° (shade) using a light source.

(When light is irradiated at an angle of 25 ° from the light source)
(1) The L * value, a * value, and b * value at 25 ° of the multilayer coating film when the thickness of the interference base coating film layer is 13 μm are measured.
(2) The L * value, a * value, and b * value at 25 ° of the multilayer coating film when the thickness of the interference base coating film layer is 17 μm are measured.
(3) L * value, a * value, and b * value change amounts ΔL (25 °), Δa (25 °), and Δb (25) associated with changes in the thickness of the coherent base coating layer (13 to 17 μm) °) using the following formulas.

      ΔL (25 °) = (L * value at 25 ° of the multilayer coating film when the thickness of the coherent base coating film layer is 13 μm) − (Compound when the film thickness of the interference coating film layer is 17 μm) L * value at 25 ° of layer coating)

      Δa (25 °) = (a * value at 25 ° of the multilayer coating film when the thickness of the coherent base coating layer is 13 μm) − (multiplication when the thickness of the interference coating layer is 17 μm) A * value at 25 ° of the layer coating)

      Δb (25 °) = (b * value at 25 ° of the multilayer coating film when the thickness of the coherent base coating layer is 13 μm) − (multiplication when the thickness of the interference coating layer is 17 μm) B * value at 25 ° of layer coating)

  (4) ΔE (25 °) is obtained from ΔL (25 °), Δa (25 °) and Δb (25 °) according to the following equation.

ΔE (25 °) = [(ΔL (25 °)) ² + (Δa (25 °)) ² + (Δb (25 °)) ² ] ^1/2

  Similarly, ΔE (45 °) and ΔE (75 °) are determined when light is emitted from the light source at angles of 45 ° and 75 °, respectively.

  The workability index (Total ΔE) is the sum of ΔE (25 °), ΔE (45 °), and ΔE (75 °), and can be obtained by calculation from the following equation.

      Total ΔE = ΔE (25 °) + ΔE (45 °) + ΔE (75 °)

  When the workability index (Total ΔE) is less than 3, the color change is small and stable, and when it is 3 or more, the color variation is large and unstable.

  In the present invention, the L * (25 °) value of the color base coating layer is 67 to 83, and the concentration of the titanium dioxide pigment in the interference base coating layer is 0.1 to 0.6% by mass, preferably 0, in terms of PWC. By setting the content to 2 to 0.4% by mass, the workability, that is, the color fluctuation stability index (Total ΔE) is less than 3.

  In the present invention, as described above, from the lightness L * (25 °) value, chromaticity a * (25 °) value, and b * (25 °) value of the multilayer coating film, the saturation C * (25 ° ) Value, that is, the coherence in the highlight can be evaluated. When the C * (25 °) value is 6.5 or more, the coherence is remarkable.

  In the present invention, by forming a color base coating film layer having a lightness L * (25 °) value of 67 to 83 as a base, a metallic feeling can be given without using a metallic luster material. The metallic paint film using a conventional metallic glitter material has an inorganic cold impression, and the glittering feeling is further emphasized. . Furthermore, by forming an interference base coating layer containing an interference pigment and a titanium dioxide pigment on the color base coating layer, a unique interference property that gradually changes gently from pink to green is applied. It can be applied to the membrane. In particular, in the present invention, as described above, by combining a color base coating layer having a specific brightness and a specific interference base coating layer, it is possible to provide a bright metallic coating similar to a silver metallic coating. In addition, it can produce a unique soft, fluffy, soft, soft color that feels like frost. Therefore, according to the multilayer coating film of the present invention, it is possible to give the design of the impression that it is softly wrapped. Such designability is provided for the first time by the present invention, and cannot be obtained at all by conventional paints and coating methods.

  EXAMPLES Hereinafter, although a specific Example is given and this invention is demonstrated in detail, this invention is not limited by a following example. In the following description, “part” means “part by weight”.

Production Example 1: Preparation of Color Base Coating Composition Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., hydroxyl value 80, acid value 8 mgKOH / g, number average molecular weight 1800, solid content 70% by mass) 48.8 parts, titanium white pigment 50 parts of “CR-97” (Ishihara Sangyo Co., Ltd.), 0.3 part of carbon black “MA-100” (Mitsubishi Carbon Co., Ltd.), cyanine blue “Shanin Blue 5240KB” (manufactured by Dainichi Seika Co., Ltd.) 1 part and 0.1 part of quinacridone red “Sinkasha Red Y-RT-759D” (manufactured by Ciba Geigy) are added and dispersed uniformly. Further, 24.4 parts of melamine resin “Uban 128” (manufactured by Mitsui Cytec) are added. In addition, a color base coating composition was obtained by uniformly dispersing.

Production Example 2: Preparation of Color Base Coating Composition Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., hydroxyl value 80, acid value 8 mgKOH / g, number average molecular weight 1800, solid content 70% by mass) 48.8 parts, titanium white pigment 50 parts of “CR-97” (Ishihara Sangyo Co., Ltd.), 0.4 part of carbon black “MA-100” (Mitsubishi Carbon Co., Ltd.), cyanine blue “Shanin Blue 5240KB” (manufactured by Dainichi Seika Co., Ltd.) 1 part and 0.1 part of quinacridone red “Sinkasha Red Y-RT-759D” (manufactured by Ciba Geigy) are added and dispersed uniformly. Further, 24.4 parts of melamine resin “Uban 128” (manufactured by Mitsui Cytec) are added. In addition, a color base coating composition was obtained by uniformly dispersing.

Production Example 3: Preparation of Color Base Coating Composition Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., hydroxyl value 80, acid value 8 mgKOH / g, number average molecular weight 1800, solid content 70% by mass) 48.8 parts, titanium white pigment 50 parts of “CR-97” (Ishihara Sangyo Co., Ltd.), 0.2 part of carbon black “MA-100” (Mitsubishi Carbon Co., Ltd.), cyanine blue “Shanin Blue 5240KB” (manufactured by Dainichi Seika Co., Ltd.) 1 part and 0.1 part of quinacridone red “Sinkasha Red Y-RT-759D” (manufactured by Ciba Geigy) are added and dispersed uniformly. Further, 24.4 parts of melamine resin “Uban 128” (manufactured by Mitsui Cytec) are added. In addition, a color base coating composition was obtained by uniformly dispersing.

Production Example 4: Preparation of Color Base Coating Composition Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., hydroxyl value 80, acid value 8 mgKOH / g, number average molecular weight 1800, solid content 70% by mass) 48.8 parts, titanium white pigment 50 parts of “CR-97” (Ishihara Sangyo Co., Ltd.), 0.5 parts of carbon black “MA-100” (Mitsubishi Carbon Co., Ltd.), cyanine blue “Shanin Blue 5240KB” (manufactured by Dainichi Seika Co., Ltd.) 1 part and 0.1 part of quinacridone red “Sinkasha Red Y-RT-759D” (manufactured by Ciba Geigy) are added and dispersed uniformly. Further, 24.4 parts of melamine resin “Uban 128” (manufactured by Mitsui Cytec) are added. In addition, a color base coating composition was obtained by uniformly dispersing.

Production Example 5: Preparation of Color Base Coating Composition Thermosetting polyester resin (manufactured by Nippon Paint Co., Ltd., hydroxyl value 80, acid value 8 mgKOH / g, number average molecular weight 1800, solid content 70% by mass) 48.8 parts, titanium white pigment 50 parts of “CR-97” (Ishihara Sangyo Co., Ltd.), 0.1 part of carbon black “MA-100” (Mitsubishi Carbon Co., Ltd.), cyanine blue “Shanin Blue 5240KB” (manufactured by Dainichi Seika Co., Ltd.) 1 part and 0.1 part of quinacridone red “Sinkasha Red Y-RT-759D” (manufactured by Ciba Geigy) are added and dispersed uniformly. Further, 24.4 parts of melamine resin “Uban 128” (manufactured by Mitsui Cytec) are added. In addition, a color base coating composition was obtained by uniformly dispersing.

Production Example 6: Preparation of interference base coating composition Acrylic emulsion manufactured by Nippon Paint Co., Ltd. (average particle size 150 nm, nonvolatile content 20%, solid content acid value 20 mgKOH / g, hydroxyl value 40 mgKOH / g) 236 parts, dimethylethanolamine 10 10 parts by mass aqueous solution, water-soluble acrylic resin manufactured by Nippon Paint Co., Ltd. (non-volatile content: 30.0%, solid content acid value: 40 mgKOH / g, hydroxyl value: 50 mgKOH / g), 31.9 parts, Primepole PX-1000 (Sanyo Chemical Industries) Bifunctional polyether polyol, number average molecular weight 400, hydroxyl value 278 mgKOH / g, primary / secondary hydroxyl value ratio = 63/37, non-volatile content 100%) 8.6 parts, Cymel 204 (Mitsui Cytec Co., Ltd. mixed alkyl) Melamine resin, non-volatile content 100%) 24.3 parts, lauryl acid phosphate 0.2 part, interference silica flake pigment “Colorstream T20-01” (manufactured by Merck & Co., Inc., interference pink-green silica flake pigment) 10 parts and titanium white pigment “CR-97” (Ishihara Sangyo Co., Ltd.) 0.3 A water-based interference base coating composition was prepared by adding parts and uniformly dispersing.

Production Example 7 Preparation of Interfering Base Coating Composition According to Production Example 6, 0.2 part of titanium white pigment “CR-97” (manufactured by Ishihara Sangyo Co., Ltd.) was used. An aqueous base coating composition was prepared.

Production Example 8: Preparation of interference base coating composition According to Production Example 6, 0.4 part of titanium white pigment “CR-97” (manufactured by Ishihara Sangyo Co., Ltd.) was used. An aqueous base coating composition was prepared.

Production Example 9 Preparation of Interfering Base Coating Composition According to Production Example 6, 5 parts of interference silica flake pigment “Colorstream T20-01” (Merck) and interference white mica pigment “Iriodin 103” (Merck) 5 Other than that, a water-based interference base coating composition was prepared in the same manner as in Production Example 6.

Production Example 10: Preparation of interference base coating composition According to Production Example 6, 0 parts of titanium white pigment "CR-97" (Ishihara Sangyo Co., Ltd.) was used, i.e. not used, otherwise A water-based interference base coating composition was prepared in the same manner as in Production Example 6.

Production Example 11 Preparation of Interfering Base Coating Composition According to Production Example 6, 1.0 part of titanium white pigment “CR-97” (manufactured by Ishihara Sangyo Co., Ltd.) was used. An aqueous base coating composition was prepared.

Production Example 12: Preparation of interference base coating composition According to Production Example 6, an interference white mica pigment "Iriodin 103" was used as the interference pigment instead of the interference silica flake pigment "Colorstream T20-01" (Merck). A water-based interference base coating composition was prepared in the same manner as in Production Example 6 except that only 10 parts (Merck) were used.

Example 1: Formation of a multilayer coating film 30 cm × 40 cm, a 0.8 mm thick dull steel sheet was treated with zinc phosphate, and then a cationic electrodeposition paint “Power Top V-6” (manufactured by Nippon Paint Co., Ltd.) was electrodeposited. The film was heat-cured at 170 ° C. for 20 minutes to form an electrodeposition coating film having a dry film thickness of 25 μm.
The color base coating composition prepared in Production Example 1 is diluted (22 seconds / # 4FC / 20 ° C./N-179 thinner), and externally applied so that the dry film thickness is 30 μm on the electrodeposition coating film. No. “Metabell” was used for two-stage coating at an applied voltage of −60 kV, a rotational speed of 25,000 rpm, a shaving air pressure of 1.5 kg / cm ² , and a discharge rate of 200 cc / min. Then, after setting for 7 minutes, it was baked and cured in a dryer at 140 ° C. for 30 minutes to form a cured color base coating film having a dry film thickness of 30 μm.
Diluting the coherent base coating composition prepared in Production Example 6 (45 seconds / # 4FC / ion exchange water) and applying the externally applied “Metabell” to a dry film thickness of 15 μm on the color base coating film. Was applied in two stages at an applied voltage of −60 kV, a rotational speed of 25000 rpm, a shaving air pressure of 1.5 kg / cm ² , and a discharge rate of 200 cc / min.
Then, after setting for 3 minutes, preheating was performed at 80 ° C. for 3 minutes.
Next, “Super Lac O-150 Clear” (acrylic melamine curable solvent clear coating composition manufactured by Nippon Paint Co., Ltd.) is wet-on-wet on an uncured interference base coating film to a dry film thickness of 35 μm. As described above, coating was performed using an “micro-microbell” at an applied voltage of −90 kV, a rotation speed of 30000 rpm, a shaving air pressure of 1.5 kg / cm ² , and a discharge rate of 280 cc / min. After setting for 7 minutes, baking curing was performed in a dryer at 140 ° C. for 30 minutes.

Examples 2 to 6 and Comparative Examples 1 to 5: Formation of multilayer coating film The multilayer coating of Examples 2 to 6 and Comparative Examples 1 to 5 was performed in the same manner as in Example 1 using the components shown in the following table. A membrane was formed according to Example 1.

  In the table, the L * (25 °) value of the color base coating layer was measured using “CM512m-3” (a variable angle color difference meter manufactured by Minolta).

  In addition, the lightness (L * value) and chromaticity (a * value and b * value) at 25 ° of the multilayer coating films of Examples 1 to 6 and Comparative Examples 1 to 5 were measured with a variable angle color difference meter “Minolta”. CM512m-3 "was measured, and the lightness L * (25 °) value and chroma C * (25 °) value of the multilayer coating film were determined in accordance with JIS Z8729.

  Moreover, the design property of the multilayer coating film of this invention was evaluated by C * (25 degree) value. The C * (25 °) value is an index indicating the coherence at the highlight. The results are shown in the table below.

Good evaluation criteria for designability (◯): C * (25 °) value = 6.5 or more Poor (×): C * (25 °) value = less than 6.5

  Furthermore, the thickness of the coherent base coating film layer included in the multilayer coating films of Examples 1 to 6 and Comparative Examples 1 to 5 was changed to ± 2 μm (that is, 13 μm and 17 μm). L * value, a * value, and b * value were measured at 25 °, 45 °, and 75 °, respectively, and fluctuation values of L * value, a * value, and b * value due to film thickness fluctuation (ΔL, Δa, and Δb) Were determined at 25 °, 45 ° and 75 °, respectively. From ΔL, Δa, and Δb at 25 °, 45 °, and 75 °, ΔE at 25 °, 45 °, and 75 ° is determined, respectively, and the sum total thereof is an index of workability (Total ΔE = ΔE (25 °) + ΔE (45 °) + ΔE (75 °)). The results are shown in the table below.

Good evaluation criteria for workability (○): Total ΔE = less than 3 Poor (×): Total ΔE = 3 or more

  In the table, the C * value, L * value, a * value and b * value at 25 ° of the multilayer coating film were measured using “CM512m-3” (a variable angle color difference meter manufactured by Minolta Co., Ltd.). Total ΔE was determined as described above.

  In the multilayer coating films of Examples 1 to 6 of the present invention, the L * value at 25 ° is 70 to 100, the a * value is −1 to +5, and the b * value is −10 to −2. It exhibits metallic toning and also has excellent interference properties. In addition, the multilayer coating films of Examples 1 to 6 of the present invention have a C * (25 °) value (interference in highlight) of 6.5 or more, have remarkable interference, and are further excellent. Further, it is possible to provide the coating film with a design property in which the interference color changes gradually and gently from pink to green. In the multilayer coating film of the present invention, as shown in the above table, the color base coating layer has an L * (25 °) value of 67 to 83, and the titanium dioxide pigment contained in the interference base coating layer. A density | concentration (PWC) is 0.1-0.6 mass%, and this can provide the said unique outstanding design property.

On the other hand, in Comparative Example 1, the coherent base coating layer does not contain a titanium dioxide pigment, so that workability is lowered and excellent color variability and designability cannot be provided.
In Comparative Example 2, the titanium dioxide pigment in the interference base coating layer has (PWC) of 1.0% by mass and deviates from the specified amount (0.1 to 0.6% by mass) of the present invention. , The design properties are significantly reduced.
In Comparative Example 3, the interference base coating layer contains only the conventional interference white mica pigment as the interference pigment, but no significant interference can be obtained with the conventional interference white mica pigment alone.
In Comparative Example 4, the L * (25 °) value of the color base coating film layer is 65, which deviates from the specified range 67 to 83 of the present invention, so that workability is reduced, and excellent color variability and design are achieved. Can't provide sex.
In Comparative Example 5, the L * (25 °) value of the color base coating layer is 85 and deviates from the specified range 67 to 83 of the present invention, so that the design properties are remarkably lowered.
Therefore, in the comparative example, the L * (25 °) value of the color base coating layer deviates from the specified range 67 to 83 of the present invention, or the titanium dioxide pigment contained in the interference base coating layer is (PWC). Even if it deviates from the specified amount (0.1 to 0.6% by mass) of the invention, the designability and / or workability is remarkably lowered, and excellent designability and color variability cannot be obtained.

  In the present invention, the application of a color base coating layer (L * (25 °) value: 67 to 83) having a specific brightness, which has not been applied in the conventional 3-coat pearl for automobile outer panels due to the problem of color variability, and the titanium dioxide pigment By combining with the coherent base coating film layer containing, it is possible to provide a multilayer coating film having excellent design properties and color variability that cannot be obtained by conventional coating materials and coating methods.

  In the multilayer coating film of the present invention, pink color is obtained by combining a color base coating layer having an L * value of 67 to 83 at 25 ° with an interference base coating layer containing an interference silica flake pigment and a titanium dioxide pigment. The coating film can be imparted with a unique interference property that gradually and gently changes from green to green. In particular, in the present invention, it is possible to provide a metallic feeling very similar to a silver metallic coating film, and also to provide a unique soft, soft, soft and soft color that feels like frost. Can do. Therefore, according to the multilayer coating film of the present invention, it is possible to give a design property that wraps softly and gently, which is very useful in a field where a high texture such as a luxury car is required.

Claims (6)

A method for forming a multilayer coating film comprising: forming a color base coating layer on a substrate; forming an interference base coating layer on the color base coating layer; and further forming a clear coating layer thereon. ,
In the color base coating layer, the concentration (PWC) of the pigment contained in the color base coating layer is 10 to 70% by mass, and the L * (25 °) value is 67 to 83.
The interference base coating layer includes an interference pigment containing an interference silica flake pigment and a titanium dioxide pigment. In the interference base coating layer, the concentration of the interference pigment (PWC) is 3 to 15% by mass. And the concentration of the titanium dioxide pigment (PWC) is 0.1 to 0.6% by mass,
The multilayer coating film has an L * (25 °) value of 70 to 100, an a * (25 °) value of −1 to +5, and a b * (25 °) value of −10 to −2. Presents an interfering metal toning,
A method for forming a multilayer coating film. The interference pigment is an interference silica flake pigment alone, or a combination of an interference silica flake pigment and a scaly transparent pigment other than the interference silica flake pigment, and the scaly transparent pigment is a mica pigment, an alumina flake pigment and The formation method of the multilayer coating film of Claim 1 which is 1 or more types selected from the group which consists of a glass flake pigment.   The mass ratio of the interfering silica flake pigment and the scaly transparent pigment other than the interfering silica flake pigment (the interfering silica flake pigment / the scaly transparent pigment) is 100/0 to 30/70. 2. A method for forming a multilayer coating film according to 2.   The mass ratio of the interference-like silica flake pigment to the scale-like transparent pigment other than the interference-like silica flake pigment (the interference-like silica flake pigment / the scale-like transparent pigment) is 95/5 to 40/60. 4. A method for forming a multilayer coating film according to 2 or 3.   In the color base coating layer, the concentration (PWC) of the pigment contained in the color base coating layer is 25 to 60% by mass, and the L * (25 °) value is 70 to 80. The formation method of the multilayer coating film of any one of Claims 1.   The multilayer coating film obtained by the formation method of the multilayer coating film of any one of Claims 1-5.

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