JP2002179988A - Water-based coating material composition and method for forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based coating material composition which can obtain excellent finish external appearance having high brilliance and showing a sufficient feeling of luster and, simultaneously, can secure good coating performance even when the pigment weight concentration(PWC) of a luster pigment based on the solid content of the coating material is set at not less than 12 wt.%, furthermore not less than 15 wt.%, and a method for forming a coating film. SOLUTION: The water-based coating material composition has an amide group-containing acrylic resin and an aluminum pigment, and contains the above aluminum pigment in an amount of 15-50 wt.% as the pigment weight concentration(PWC) based on the solid content of the above water-based coating material and, out of the above aluminum pigment, an aluminum pigment having an average particle diameter of 17-60 μm in an amount of 0.1-50 wt.% as the pigment weight concentration(PWC) based on the solid content of the above water-based coating material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aqueous base coating composition, and more particularly to an aqueous base coating composition containing a large particle size aluminum pigment and an amide group-containing acrylic resin.
In addition, the present invention relates to a method for forming a coating film using the aqueous base coating composition.

[0002]

2. Description of the Related Art Usually, an electrodeposition coating film is formed as an undercoating on an automobile body or parts, and then an intermediate coating film, a base coating film and, if necessary, a clear coating film are sequentially formed.
Among these, as a method for forming the base coating film and the clear coating film, from the viewpoint of cost and labor reduction, the base coating material is applied to the base material, and then the clear coating material is applied without heating and curing the base coating material. A so-called two-coat one-bake method of simultaneously heating and curing the obtained base coating film and clear coating film is desired.

[0003] On the other hand, a base paint is sometimes made of a metallic base paint by adding a brilliant pigment such as aluminum flake. As the metallic base paint, the pigment weight concentration (PWC) of the brilliant pigment with respect to the solid content of the paint is increased, and further, by using a brilliant material having a large particle diameter capable of contributing to the improvement of the design, a beautiful luster is obtained in the coating film. Improvements in design properties, such as giving a brilliant feeling, have been expected.

Conventionally, when the PWC of a glittering pigment in a metallic base coating material is as high as 12% by weight or more, the finish of the coating film is remarkably reduced, such as blackening without gloss, and the surface of the base coating film Phenomenon such as clogging of glittering pigments occurs and the surface lacks smoothness, so it is necessary to bake once after applying the clear paint and then apply and bake the clear paint again. Finished appearance, cost, labor, etc. There was no suitable thing from the point of view. The above-mentioned disadvantages have been increased when a glitter pigment having a large particle size is used. As described above, conventionally, it has been difficult to design a metallic base paint containing a glittering pigment at a high PWC, and which can be used in a two-coat one-bake method.

[0005]

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a pigment weight concentration (P
Provided is a base coating composition and a method for forming a coating film which can obtain an excellent finished appearance having high brightness and sufficient luster even when WC) is increased, and which can secure good coating film performance. It is in.

[0006]

Means for Solving the Problems The present inventors have found that a conventional coating film made of a metallic base paint having a high PWC brilliant material has flake-like brilliant material particles caught on the surface of the coating film. When the smoothness of the coating film surface was impaired and the coating film was not glossy and turned black, when an aluminum pigment having a relatively large particle size was contained in a specific amount, an amide group-containing acrylic resin was compounded. When the base paint is used, the paint viscosity at the time of painting is kept low, the aluminum particles are oriented almost parallel to the paint film surface and are densely contained in the base paint film, and the head is caught on the base paint film surface. As a result, it was found that even when the two-coat one-bake method was used, it was possible to obtain an excellent finished appearance having a sufficient glitter, and completed the present invention.

The present invention is an aqueous base coating composition having an amide group-containing acrylic resin and an aluminum pigment, wherein the aluminum pigment has a pigment weight concentration (PWC) of 20 based on the solid content of the aqueous base coating composition.
Aluminum pigment having an average particle size of 17 to 60 μm among the aluminum pigments is 0.1 to 50 as a pigment weight concentration (PWC) based on the solid content of the aqueous base coating composition. It is an aqueous base coating composition characterized by containing by weight.

According to the present invention, there is also provided a step (I) of forming an uncured base coating film by applying the above-mentioned aqueous base coating composition on a substrate, and forming a clear coating material on the base coating film. Coating to form an uncured clear coating film (I
I) and a step of simultaneously heating and curing the uncured base coating film and clear coating film to obtain a laminated coating film (II)
This is a method for forming a coating film comprising I). The present invention further provides a substrate having a coating film formed by the above-described coating film forming method. Hereinafter, the present invention will be described in detail.

The aqueous base coating composition of the present invention has an amide group-containing acrylic resin and an aluminum pigment. The amide group-containing acrylic resin is included as a film-forming resin, but by being mixed with the aqueous base coating composition, the coating fluidity at the time of coating is increased, and the sharpness at the time of coating is further increased. Due to the synergistic effect of viscosity increase and volume shrinkage, the aluminum particles are oriented almost parallel to the base material surface and are densely contained in the base coating film and do not cue on the base coating surface. Even with the method, an excellent finished appearance having a sufficient glitter can be obtained.
Further, since the amide group-containing acrylic resin contains a polar amide group, the viscosity control effect is exhibited,
Also in the two-coat one-bake method, the adaptation and inversion at the interface between the base coating film and the clear coating film are controlled, so that a coating film having excellent gloss can be obtained and also contribute to improvement in chipping resistance.

The amide group-containing acrylic resin preferably has a number average molecular weight of 5,000 to 30,000,
More preferably, it is 7000 to 25000. 5000
If it is smaller, workability and curability are not sufficient, and 3000
If it exceeds 0, the viscosity at the time of coating increases, and the workability deteriorates. In the present specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.

[0011] The amide group-containing acrylic resin is 20 to
It preferably has a hydroxyl value of 180, more preferably 30 to 160. If it exceeds the upper limit, the water resistance of the coating film will decrease, and if it falls below the lower limit, the curability of the coating film will decrease. Further, it preferably has an acid value of 5 to 80 mgKOH / g, more preferably 10 to 60 mgKOH / g. When the amount exceeds the upper limit, the water resistance of the coating film is reduced. When the amount is less than the lower limit, the curability of the coating film is reduced, which may cause aggregation in the aqueous coating medium.

The amide group-containing acrylic resin can be obtained by radical polymerization of an amide group-containing ethylenically unsaturated monomer and another ethylenically unsaturated monomer. The mixing ratio in this radical polymerization is
The amide group-containing ethylenically unsaturated monomer is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and the like, based on the total amount of the ethylenically unsaturated monomer used for producing the amide group-containing acrylic resin. Is preferably 99 to 80% by weight, more preferably 98 to 85% by weight. When the content of the amide group-containing ethylenically unsaturated monomer is less than 1% by weight, the viscosity controllability and chipping resistance decrease. If it exceeds 20% by weight, the water resistance of the resulting coating film will be reduced.

Examples of the amide group-containing ethylenically unsaturated monomer include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dioctyl (meth) acrylamide, N-monobutyl (meth) acrylamide, N-monooctyl (meth) acrylamide and the like can be mentioned. Preferred amide group-containing ethylenically unsaturated monomers are acrylamide, methacrylamide, N-monobutylacrylamide and N-monobutylmethacrylamide.

The above-mentioned other ethylenically unsaturated monomers are not particularly limited, but firstly, a hydroxyl group-containing ethylenically unsaturated monomer is exemplified. Specifically, 2-hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate,
Examples include hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, allyl alcohol and methacryl alcohol, and adducts of 2-hydroxyethyl (meth) acrylate with ε-caprolactone. Among them, it is preferable to use a long-chain hydroxyl group-containing monomer as the hydroxyl group-containing monomer from the viewpoint of improving chipping resistance. Examples include 4-hydroxybutyl (meth) acrylate, adducts of 2-hydroxyethyl (meth) acrylate and ε-caprolactone, and the like.

Next, there can be mentioned ethylenically unsaturated monomers having a carboxyl group. Examples thereof include (meth) acrylic acid derivatives (for example, acrylic acid,
Α-hydro-ω-((1-oxo-2-propenyl) oxy) poly (oxy (1-oxo) obtained by adding ε-caprolactone to methacrylic acid, crotonic acid, isocrotonic acid, acrylic acid dimer and acrylic acid And unsaturated dibasic acids, their half esters, half amides and half thioesters (eg, maleic acid, fumaric acid, itaconic acid, their half esters, half amides and half thioesters) ).

Further, examples other than the above monomers include:
(Meth) acrylate ester monomers (eg, methyl (meth) acrylate, ethyl (meth) acrylate,
n-butyl (meth) acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butyl cyclohexyl (meth) acrylate, Cyclopentadienyl (meth) acrylate and dihydrodicyclopentadienyl (meth) acrylate, and the like, polymerizable aromatic compounds (such as styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, and vinylnaphthalene) ), Polymerizable nitriles (eg, acrylonitrile and methacrylonitrile), α-olefins (eg, ethylene and propylene), vinyl esters (eg, vinyl acetate and Vinyl dipropionate), and a diene (such as butadiene and isoprene). Such other ethylenically unsaturated monomers can be used alone or in combination of two or more.

An amide group-containing acrylic resin can be obtained by radical copolymerization of each of the above ethylenically unsaturated monomers. As the polymerization method, an ordinary method described in known literature such as solution radical polymerization can be used. For example, a method in which an appropriate radical polymerization initiator and a monomer mixed solution are added dropwise to an appropriate solvent over a period of 2 to 10 hours at a polymerization temperature of 60 to 160 ° C. and agitated while stirring. The radical polymerization initiator that can be used here is not particularly limited as long as it is usually used at the time of polymerization, and examples thereof include an azo compound and a peroxide. The solvent that can be used here is not particularly limited as long as it does not adversely affect the reaction, and examples thereof include alcohols, ketones, and hydrocarbon solvents. Further, to control the molecular weight, mercaptans such as lauryl mercaptan and α
-A chain transfer agent such as methylstyrene dimer and the like may be used if necessary.

The amide group-containing acrylic resin is used in an amount of 2 per 100 parts by weight of the solid content of the aqueous base coating composition of the present invention.
It is preferable to contain 0 to 80 parts by weight. When the amount is less than 20 parts by weight, gloss is insufficient, and the appearance such as a decrease in lightness is liable to be caused. In addition, the physical properties of the coating film may be inferior. Performance may be reduced. Preferably, it is 25 to 70 parts by weight.

In the present invention, the film-forming resin may include other film-forming resins other than the amide group-containing acrylic resin. Such other film-forming resins are not particularly limited, and preferred examples include acrylic resins, polyester resins, alkyd resins, epoxy resins, and urethane resins. Can be used in combination.

With respect to the total of 100 parts by weight of the solid content of the amide group-containing acrylic resin and the other film-forming resin, the other film-forming resin has a solid content ratio of 50 parts by weight or less. Preferably, it is 30 parts by weight or less. Exceeding these lower limits may prevent sagging and reduce the appearance.

The aqueous base coating composition of the present invention has an aluminum pigment. The aluminum pigment is not particularly limited, and examples thereof include flat pigments such as aluminum flakes, which may be colored, and one or more of these may be used. The total amount of the above-mentioned aluminum pigment is defined as the weight concentration of pigment (P) with respect to the solid content of the aqueous base coating composition of the present invention.
WC) by 15 to 50% by weight. If the ratio exceeds the upper limit, the viscosity is too high to deteriorate the appearance of the coating film and the stability of the coating material. If the ratio is below the lower limit, the glitter will be insufficient, and the original purpose of the design will not be obtained. Preferably, it is 20 to 50% by weight.

In the present invention, a large particle size aluminum pigment having an average particle size of 17 to 60 μm is used as all or a part of the aluminum pigment. By using the aluminum pigment having the large particle size, a high glossiness is exhibited and a finished appearance excellent in design can be obtained. The large-diameter aluminum pigment preferably has a thickness of 0.1 to 5 μm. As the aluminum pigment having a large particle size, a commercially available product can be used. For example, 91-0562, 762ONS, 94-058 as an aluminum paste can be used.
3, 97-0534, 97-0647, 99-060
5, TCR2020, TCR2060, TCR301
0, TCR3030 (all manufactured by Toyo Aluminum Co., Ltd.) and the like. The average particle size of the aluminum pigment having the large particle size is preferably 20 to 50 μm, and more preferably 25 to 45 μm.

The aluminum pigment having a large particle diameter having an average particle diameter of 17 to 60 μm has a pigment weight concentration (PWC) of 0.1 based on the solid content of the aqueous base coating composition of the present invention.
1 to 50% by weight. If it is less than 0.1% by weight,
When the content exceeds 50% by weight, the coating film performance such as adhesion deteriorates and the appearance is poor. Preferably, 1-3
0% by weight.

As the aluminum pigment used in the aqueous base coating composition of the present invention, a small particle size aluminum pigment having an average particle size of less than 17 μm may be used in combination with the above large particle size aluminum pigment. By blending such an aluminum pigment, it is possible to finely adjust the coating color design so as to obtain the desired glitter. As the aluminum pigment having the small particle size, for example, a commercially available product can be used. For example, 60-600, 65-388, 5656NS, 56
58NS (all manufactured by Toyo Aluminum Co., Ltd.) and the like. The average particle size of the small particle size aluminum pigment is preferably 4 to less than 16 μm. The compounding amount of the aluminum pigment having a small particle diameter is such that the PWC of the aluminum pigment having a large particle diameter satisfies the above-mentioned conditions and the total amount of the aluminum pigment having the large particle diameter is 15 to 50% by weight.

The aqueous base coating composition of the present invention usually comprises
It contains a curing agent. Preferred examples of the curing agent include an amino resin, a blocked isocyanate resin, an epoxy compound, an aziridine compound, a carbodiimide compound, and an oxazoline compound, and a mixture thereof can be used. An amino resin and / or a blocked isocyanate resin are particularly preferably used in view of various properties and cost of the obtained coating film.

The content of the curing agent is 15 to 100% by weight based on the total solid content of the film-forming resin including the amide group-containing acrylic resin and other film-forming resins. If the content is less than 15% by weight, the curability becomes insufficient and
If it exceeds 00% by weight, the cured film becomes too hard and brittle.

The amino resin is not particularly limited, and a methylated melamine resin, a butylated melamine resin, or a mixed melamine resin of methyl and butyl can be used. For example, “Symel-303” and “Symel 254” commercially available from Mitsui Chemicals, Inc.
"Symel Series"; and "Uban 226",
"Uban series" such as "Uban 20N60";"Sumimarseries" commercially available from Sumitomo Chemical Co., Ltd .;

The content of the amino resin is preferably 15 to 100% by weight, more preferably 20 to 100% by weight, based on the solid content of the amide group-containing acrylic resin and the film-forming resin. It is. Content is 15% by weight
If it is less than 100%, the curability will be insufficient, and if it exceeds 100% by weight, the cured film will be too hard and brittle.

Further, the blocked isocyanate resin is obtained by adding a blocking agent having active hydrogen to polyisocyanate, and the heating dissociates the blocking agent to generate an isocyanate group. One that reacts with a functional group and cures.

The above-mentioned blocked isocyanate resin is not particularly limited, and typical polyisocyanates include:
Aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate;
Cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, aliphatic cyclic isocyanate such as 1,2-cyclohexane diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, aromatic isocyanate such as 2,6-tolylene diisocyanate, Alicyclic isocyanates such as isophorone diisocyanate and norbornane diisocyanate methyl,
Multimers and mixtures of these nurate compounds can be used.

Examples of the blocking agent include aliphatic, aromatic or heterocyclic compounds such as halogenated hydrocarbons, methanol, ethanol, n-propanol, isopropanol, furfuryl alcohol, alkyl-substituted furfuryl alcohol and benzyl alcohol. Oximes such as alcohol, methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime and cyclohexane oxime, and caprolactam and the like can be mentioned. Preferred among these are oximes,
Alcohols. Further, a catalyst for dissociating the blocking agent can be used.

The amount of the above blocked isocyanate is as follows:
It is preferably from 20 to 100% by weight, more preferably from 40 to 100% by weight, based on the solid content of the amide group-containing acrylic resin and the film-forming resin.
Outside the above range, curing is insufficient.

The pigments that can be used in the aqueous base coating composition of the present invention can include other glittering pigments in combination with the above-mentioned aluminum pigments. For example, interference mica powder, colored mica powder, white mica Colorless colored flat pigments such as powder and graphite; flake pigments; and uncolored or colored metallic glitters such as metals and alloys such as aluminum oxide, copper, zinc, iron, nickel and tin.

The glitter pigment other than the above-mentioned aluminum pigments is not particularly limited in its shape and may be colored. For example, the pigment may have an average particle diameter (D ₅₀ ) of 2 to ₅₀ μm.
It is preferable that the thickness is 0.1 to 5 μm.
Those having an average particle size of 10 to 35 μm are excellent in glitter and are more preferably used. As the glitter pigment used in the aqueous base coating composition of the present invention, in combination with the above-described aluminum pigment having a large particle diameter, or in combination with the aluminum pigment having a large particle diameter and the aluminum pigment having a small particle diameter described above. In addition, a brilliant pigment having an average particle size of more than 60 μm, for example, a material containing glass flake or the like may be used. The glitter pigment other than the above-mentioned aluminum pigment has a total amount of 15 to 15 as a pigment weight concentration (PWC) with respect to the solid content of the aqueous base coating composition of the present invention.
It is preferable to mix so as to be 50% by weight.

The aqueous base coating composition of the present invention may contain a pigment other than the glitter pigment in combination with the above-mentioned aluminum pigment. Such pigments are not particularly limited, and include, for example, azochelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments And organic coloring pigments such as perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments; inorganic coloring such as graphite, yellow iron oxide, chromium oxide, red iron oxide, carbon black, titanium dioxide, etc. Pigments and the like. Furthermore, calcium carbonate, barium sulfate, magnesium silicate, clay,
An extender pigment such as talc or calcined kaolin may be used in combination.
These may be used alone or in combination of two or more.

The pigment concentration (PWC) in the aqueous base coating composition of the present invention, including the above-mentioned aluminum flakes, other brilliant pigments and all other pigments, is generally from 0.1 to 0.1.
It is 50% by weight, preferably 0.5 to 40% by weight, more preferably 1 to 30% by weight. 50% by weight
If it exceeds, the appearance of the coating film is deteriorated. The mixing ratio of the aluminum pigment / the other glittering pigment is 100/0 by weight.
５０50/50 is preferred. If the amount of the other brilliant pigments, especially the flat pigments such as mica powder, exceeds the above upper limit, the finished appearance may be inferior, such as excessive brilliancy.

The aqueous base coating composition of the present invention may contain additives in addition to the above components. The additive is not particularly limited, and examples thereof include a viscosity control agent in order to ensure coating workability. The viscosity control agent is not particularly limited, but those generally exhibiting thixotropic properties can be used.For example, crosslinkable or non-crosslinkable polymer fine particles, swelling dispersion of fatty acid amide, amide-based fatty acid, long-chain polyamino acid Polyamides such as amide phosphates; polyethylenes such as colloidal swelling dispersions of polyethylene oxide; organic bentonites such as organic acid smectite clay and montmorillonite; inorganics such as aluminum silicate and barium sulfate Pigment; flat pigments which exhibit viscosity depending on the shape of the pigment; As the above-mentioned additive, in addition to the above-mentioned viscosity control agent, an additive which is usually added to a paint, for example, a surface conditioner, an antioxidant, an antifoaming agent, etc. may be blended. The amounts used are those commonly used by those skilled in the art.

The total solid content of the aqueous base coating composition of the present invention is preferably from 10 to 70% by weight. If the amount is less than 10% by weight, the viscosity is too low, causing poor appearance such as conformity and unevenness. If the amount is more than 70% by weight, the viscosity may be too high and the appearance of the coating film may be deteriorated. Preferably, 15
６０60% by weight.

The method for producing the aqueous base coating composition of the present invention is not particularly limited. For example, a method known to those skilled in the art, such as dispersing a compound such as a pigment using a pigment dispersing resin or the like as desired, may be used. can do.

In the method for forming a coating film of the present invention, a step (I) of applying the above-mentioned aqueous base coating composition on a substrate to form an uncured base coating film; Applying a clear coating to form an uncured clear coating (II), and simultaneously heating and curing the uncured base coating and the clear coating to obtain a laminated coating (III) ).

The substrate in the step (I) is not particularly limited, and includes, for example, metals, plastics, foams and the like. Among them, metals, particularly castings, are advantageously used. Paintable metal products are particularly preferably used. The metal product is not particularly limited, and examples thereof include simple metals such as iron, copper, aluminum, tin, and zinc, and alloys and castings containing the simple metals. Specifically, the vehicle body and parts of automobiles such as passenger cars, trucks, motorcycles, and buses are exemplified.
It is particularly preferable that the metal product has been subjected to a chemical conversion treatment with a phosphate, a chromate or the like in advance.

On the base material, an electrodeposition coating film may be formed on the steel sheet subjected to the chemical conversion treatment for the purpose of imparting corrosion resistance and rust prevention. As the electrodeposition paint for forming the above electrodeposition coating film, a cationic or anion type electrodeposition coating material can be used, but a cationic type electrodeposition coating material is preferable because it gives a laminated coating film having excellent anticorrosion properties.

On the base material, an intermediate coating film may be further formed on the electrodeposition coating film. When the intermediate coating film is formed, defects of the base are concealed, the surface smoothness after the top coating is secured and the appearance is improved, and the coating film properties such as impact resistance and chipping resistance are imparted. It becomes easier. The intermediate coating composition for forming the intermediate coating film is not particularly limited, but usually includes a pigment, a resin for forming a coating film, and a curing agent.

The pigment used in the intermediate coating composition is not particularly limited, and for example, the organic and inorganic pigments and extenders described as usable in the above-mentioned aqueous base coating composition can be used. . As the intermediate coating, a gray-based melamine-curable or isocyanate-curable paint containing carbon black and titanium dioxide as main pigments is generally used. The above-mentioned intermediate paint can be a so-called color intermediate paint in which lightness, hue and the like are combined with the top coat color.

The clear paint used in the above step (II) is not particularly limited, and examples thereof include those comprising a film-forming resin, a curing agent and other additives. The film-forming resin is not particularly limited, for example, acrylic resin, polyester resin, epoxy resin,
Urethane resins and the like, which are amino resins and / or
Alternatively, it is used in combination with a curing agent such as a blocked isocyanate resin. It is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system, from the viewpoint of transparency or acid etching resistance.

In the method for forming a coating film of the present invention, the clear coating composition is obtained by applying the aqueous base coating composition described above,
Since the coating is performed in an uncured state, it is preferable to contain the viscosity control agent described for the above-mentioned aqueous base coating composition in order to prevent adaptation, inversion, and sagging between layers. The addition amount of the viscosity control agent is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the resin solid content of the clear coating. When the amount is less than 0.01 part by weight, the viscosity control effect cannot be obtained, and there is a possibility that a problem such as sagging may be caused.
If the amount exceeds 0 parts by weight, the appearance tends to decrease. More preferably, it is 0.02 to 8 parts by weight, still more preferably 0.03 to 6 parts by weight.

The solid content in the clear coating is preferably 30 to 80% by weight, more preferably 40 to 80% by weight.
The solid content at the time of coating is preferably 25 to 75% by weight, and more preferably 30 to 70% by weight.

The coating form of the clear coating may be any of water-soluble, water-dispersible or water-based emulsion-based, organic solvent-based, non-aqueous dispersion-type, and powder-type.
If necessary, a curing catalyst, a surface conditioner and the like can be used. The method for preparing the electrodeposition coating, the intermediate coating, and the clear coating is not particularly limited, and for example, a conventionally known method can be used.

The method for applying the intermediate coating, the aqueous base coating composition, and the clear coating is not particularly limited, and for example, a method known to those skilled in the art can be used. Such a method includes, for example, an air electrostatic spray commonly referred to as a “react gun”; a rotary atomization commonly referred to as a “micro-micro (μμ) bell”, a “micro (μ) bell”, a “metabell” and the like. It can be performed by using a type electrostatic coating machine or the like. Preferably, a method using a rotary atomization type electrostatic coating machine or the like is used.

When the aqueous base coating composition is applied to an automobile body or the like, a multi-stage coating by air electrostatic spraying, preferably 2
It is preferable to perform painting on a stage or by a painting method in which an air electrostatic spray is combined with the above-mentioned rotary atomizing electrostatic painting machine.

The dry film thickness of each of the above coating films varies depending on the intended use, but they are respectively an intermediate coating film of 5 to 45 μm, a base coating film of 5 to 35 μm, and a clear coating film of 10 to 80 μm.
Exceeding these upper limits may result in poor image clarity or inconveniences such as unevenness and flow during coating. Below the lower limit, the unevenness of the base may not be concealed and the film may break.

The above-mentioned intermediate coating film is applied at a temperature of 100 to 180 ° C., preferably 1 to 100 ° C. before the application of the aqueous base coating composition.
Bake and cure at 20-160 ° C. The curing time varies depending on the curing temperature.
Minutes are appropriate. Before performing the baking hardening, the intermediate coating film is allowed to stand at room temperature for a certain period of time,
Water may be evaporated and the coating film may be dried in advance. In the method for forming a coating film of the present invention, a so-called two-coat one-bake method in which a clear coating material is applied on the base coating film by a wet-on-wet method and then baked and cured at a time without curing the base coating film. Is what you do. Before applying the clear coating after applying the aqueous base coating composition, it is allowed to stand at room temperature for a certain period of time, or can be subjected to the preheating step, and a cured coating film having a high degree of crosslinking can be obtained by performing this step. .

The baking and curing after the application of the clear paint in the above step (III) can be usually carried out at 100 to 180 ° C., whereby a cured coating film having a high crosslinking density can be obtained. If the temperature is lower than 100 ° C., the curing is not sufficient, and if it exceeds 180 ° C., the coating film becomes hard and brittle. Preferably, it is 120 to 160 ° C. The curing time varies depending on the curing temperature, but is suitably from 120 to 160 ° C. for 10 to 60 minutes.

The total thickness of the intermediate coating film, the base coating film and the clear coating film thus obtained is usually 3
0 to 300 μm. If it exceeds 300 μm, the physical properties of the film such as a thermal cycle decrease, and if it is less than 30 μm, the strength of the film itself decreases. Preferably, 50 to 250 μm
It is.

Since the aqueous base coating composition of the present invention contains the above-mentioned amide group-containing acrylic resin, the average particle size is 17%.
When a specific amount of the above-mentioned aluminum pigment having a thickness of ６０60 μm is contained and a two-coat one-bake method is used, an excellent finished appearance having sufficient glitter and surface smoothness can be obtained.
Although the mechanism for achieving such effects is not clear in detail, it is considered as follows.

That is, conventionally, when the PWC of the brilliant pigment in a metallic base paint is high, it becomes black without gloss and lacks smoothness of the surface, and the finish of the coating film is remarkably reduced. It was necessary to apply and bake at least twice. This phenomenon is caused by the fact that flake-like glittering pigment particles are oriented in the base coating film at an angle without being parallel to the base material surface and cue on the surface of the base coating film. It is estimated that The above-mentioned state of cueing is particularly remarkable when a bright pigment having a large particle diameter is included, but from the viewpoint of design, a glitter pigment uses a larger particle diameter than a small pigment. Is preferred.

On the other hand, since the aqueous base paint composition of the present invention contains the amide group-containing acrylic resin, the paint viscosity at the time of coating is lower than that of the conventional paint, and the fluidity is higher. Due to the synergistic effect of a sharp increase in viscosity and volume shrinkage, the glitter pigment is oriented almost parallel to the substrate surface in the base coating and is densely packed. It is considered that an excellent finished appearance having sufficient glitter, design properties and smoothness of the coating film surface is obtained without forming a cue on the film surface. Further, since the amide group-containing acrylic resin has a high hydrogen bonding force and a high volumetric shrinkage, the aqueous base coating composition of the present invention has a low post-coating moisture even if the viscosity at the time of coating is low as described above. As a result, the viscosity rises sharply due to the volatilization of Newtonian-like behavior, so that the interface with the clear coating film is easily controlled and mixing is avoided,
It is presumed to contribute to a high glossy and excellent appearance.

According to the method for forming a coating film of the present invention, a coating film having a high glitter and an excellent finished appearance can be obtained by the simple method as described above. The aqueous base coating composition and coating film forming method of the present invention exhibiting such advantageous effects can be suitably used particularly for metallic base coating of automobile bodies and parts by a two-coat one-bake method. The use can be extended to a paint color design in which a brilliant material of a concentration is blended.

[0059]

The present invention will now be described in detail with reference to specific examples.
However, the present invention is limited by the following examples.
Not something. Parts and% mean parts by weight and weight%, respectively.
To taste.Production example Production of film-forming resin  Nitrogen inlet tube, stirrer, temperature controller, dropping funnel and cooling
Propylene glycol ethyl is added to a 2 L reaction vessel equipped with a tube.
And 450 parts of ether.
Was. Next, 100 parts of acrylamide was
Dissolved in 200 parts of methyl ether
50 parts, 2-ethylhexyl methacrylate 200 parts,
313 parts of n-butyl acrylate, methacrylic acid 77
Part, hydroxyl group-containing polymerizable monomer (Placcel FM-1,
260 parts and t-butyl peroxy-
By mixing 8 parts of 2-hexanoate,
Solutions were prepared separately. This monomer solution is stirred into a reaction vessel.
After dripping over 3 hours with stirring, continue stirring for 30 minutes
And t-butylperoxy-2-hexanoate 5
And 50 parts of propylene glycol methyl ether
After dropping the mixture over 15 minutes, continue stirring for 1 hour
And a resin solid content of 59%, a number average molecular weight of 13,000, and water
Acrylic resin with acid value 60 and acid value 50mgKOH / g
I got 500 parts of this acrylic resin was mixed with a resin solid content of 7
Remove the solvent until the concentration becomes 5%, and add dimethylethanolamine 2
3.4 parts and 925 parts of ion-exchanged water were added, and the resin solid content was increased.
Obtained a 22% water-soluble acrylic resin.

[0060]Examples 1-3, Comparative Examples 1-2  (Production of water-based coating composition)
273 parts of acrylic resin and aluminum pigment
Large particle size aluminum pigment (TCR301)
0, average particle size 31.2 μm, average thickness 2.7 μm, Toyo
Aluminum) and small particle size aluminum pigments (Al
Paste 60-600, average particle size 15.0 μm, flat thickness
0.2μm, Toyo Aluminum Co., Ltd.)
Weight concentration (PWC) based on the solid content of the pigment composition
And add the amount shown in Table 1 (% by weight)
Melamine resin (cymel 202, solid content 80
(% By weight, manufactured by Mitsui Cytec Co., Ltd.) and uniformly dispersed
By doing so, a silver metallic base paint was obtained.

(Coating film forming method) A 30 cm × 40 cm, 0.8 mm thick dull steel plate was treated with zinc phosphate, and then a cationic electrodeposition paint (Powertop V-6, manufactured by Nippon Paint Co., Ltd.) was dried to a thickness of 20 μm. And cured by heating at 160 ° C. for 30 minutes.
Gray, manufactured by Nippon Paint Co., Ltd.) to a dry film thickness of 40 μm, left at room temperature for about 3 minutes, and then dried at 140 ° C. for 30 minutes.
The coating was heated and cured for 1 minute to obtain an object to be coated. The metallic base paint obtained above was applied to the base material using an internally applied metabell so as to have a dry film thickness of 15 μm.
V, the number of revolutions was 25,000 rpm, the shaving air pressure was 3.5 kg / cm ² , and the discharge rate was 120 cc / min. There was a 1.5 minute interval between the two applications. After setting for 3 minutes after the second application, preheating was performed at 80 ° C. for 3 minutes. next,
On one half of the aqueous base coated plate obtained above, a high solid clear coating material (Macflow O-1330, manufactured by Nippon Paint Co., Ltd.) was applied using a micro-micro bell so as to have a dry film thickness of 45 μm. 90kV, rotation speed 30,000rpm, shaving air pressure 1.5kg
/ Cm 2 and a discharge rate of 280 cc / min., One stage coating and setting for 7 minutes. Next, the obtained coated plate was baked in a dryer at 140 ° C. for 30 minutes to obtain a laminated coating film.

(Evaluation) The obtained laminated coating film was evaluated as follows. Table 1 shows the results. 1. Appearance The appearance of the laminated coating film was evaluated by SW (short wave) value of wave scan (manufactured by Big Chemie). The smaller the value, the better the appearance was obtained. 2. Front Lightness The front lightness was evaluated by measuring the L value using Minolta CR-300 (manufactured by Minolta). The higher the L value, the higher the front brightness. 3. Flip-flop property The reflection intensity (L value) of the laminated coating film obtained in the above 2 is
Using a variable angle colorimeter (512m-3, manufactured by Minolta),
The measurement was performed at 25 degrees and 75 degrees, and the flip-flop property (F / F value) was obtained by the following equation. The higher the F / F value, the higher the flip-flop property. F / F value = (measured intensity at 25 degrees) ÷ (measured intensity at 75 degrees)

[0063]

[Table 1]

From Table 1, it can be seen that in Comparative Example 1 in which no large-particle-size aluminum pigment was used, the flip-flop property was low, and it was desirable to finish the silver metallic paint white, but it turned black and poor in design.
In Comparative Example 2 in which WC exceeds the upper limit of 15 to 50% by weight,
When the SW value of the wave scan is regarded as a pass value of less than 10, the coating film appearance is inferior, but both PWCs of the large particle size aluminum pigment and the all aluminum pigment are within the scope of the present invention. Showed that the coating film appearance, the L value, and the flip-flop property were all good and exhibited excellent design properties.

[0065]

Since the aqueous base coating composition of the present invention has the above-described constitution, the pigment weight concentration (PWC) of the aluminum pigment with respect to the solid content of the aqueous base coating composition is determined by the two-coat one-bake method. Even when the content is 15 to 50% by weight, an excellent finished appearance in which the brightness is high, a sufficient glitter is exhibited, and the coating film surface is smooth can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C09D 5/29 C09D 5/29 F term (Reference) 4D075 AE12 BB26Z CA04 CA33 CA38 CA48 CB04 CB13 DA06 DA25 DB02 DB05 DB06 DB07 DB08 DB31 DC12 DC13 EA06 EA07 EA10 EA43 EB12 EB14 EB19 EB20 EB22 EB32 EB33 EB35 EB36 EB38 EB45 EB57 EC10 EC11 EC53 4J038 CG171 HA066 KA08 KA20 MA08 MA10 NA01 PA13 PA19 PB07 PC02 PC08

Claims (5)

[Claims] 1. An aqueous base coating composition having an amide group-containing acrylic resin and an aluminum pigment, wherein the aluminum pigment has a pigment weight concentration (PWC) based on the solid content of the aqueous base coating composition of 15 to 50% by weight. % Of the aluminum pigment having an average particle diameter of 17 to 60 μm is contained in an amount of 0.1 to 50% by weight as a pigment weight concentration (PWC) with respect to the solid content of the aqueous base coating composition. Water-based coating composition, characterized in that: 2. The aqueous base paint according to claim 1, wherein the aluminum pigment having an average particle size of 17 to 60 μm is contained in an amount of 1 to 30% by weight as a pigment weight concentration (PWC) based on the solid content of the aqueous base paint composition. Composition. 3. The aqueous base coating composition according to claim 1, wherein the average particle size is 20 to 50 μm. 4. A step (I) of applying the aqueous base coating composition according to claim 1, 2 or 3 onto a substrate to form an uncured base coating film, Applying a clear paint to form an uncured clear coating film (II), and simultaneously heating and curing the uncured base coating film and the clear coating film to obtain a laminated coating film (III) ). 5. A substrate having a coating film formed by the coating film forming method according to claim 4.