JP2002153806A - Method for forming coating film, and multilayer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a multilayer coating film having excellent finished appearance and excellent also in physical properties such as chipping resistance is formed when the top of a substrate is successively coated with an intermediate coating film and a final coating film by a wet-on-wet process. SOLUTION: In the method for forming a coating film in which an intermediate coating film, a base coating film and a clear coating film are successively formed on a substrate by a wet-on-wet process, each of an intermediate coating material for forming the intermediate coating film and a base coating material for forming the base coating film contains an amido-containing acrylic resin and a curing agent, and the curing agent contained in the intermediate coating material comprises an aliphatic isocyanate type active methylene blocked isocyanate having >3 functional groups on the average.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a laminated coating film formed on an automobile body or the like, and more specifically, to form an intermediate coating film, a base coating film and a clear coating film sequentially on a wet basis. The present invention relates to a method for forming a coating film by a so-called three-coat one-bake method and a laminated coating film obtained by the method.

[0002]

2. Description of the Related Art A laminated coating film for automobiles is divided into a method of baking and curing each time each coating film is formed, and a method of simultaneously curing a plurality of laminated coating films. For example, forming a base coating film and a clear coating film by two coats and one bake is a commonly used method.
As disclosed in Japanese Patent No. 4489, a coating forming method of sequentially forming a color base coating, a metallic base coating and a clear coating in order to enhance the design property of the top coating, and simultaneously baking and curing the same has already been proposed. I have.

[0003] Further, the step of curing only the intermediate coating film is omitted, the intermediate coating film and the top coating film are applied by wet-on-wet, and two or three layers of the coating film are simultaneously baked and cured. As a method of forming a film, a baking / drying furnace for intermediate coating can be omitted, and a great effect can be expected from economical and environmental aspects, but it has not been realized due to many problems.

However, when the conventional intermediate coating is applied to a method of forming a two-layer or three-layer coating by wet-on-wet by omitting the above-described step of curing only the intermediate coating, a conventional method is applied. In addition, problems such as inversion and inversion occur, and the appearance as a laminated coating film is not established. In particular, when an automobile body or the like having a large number of irregularities is entirely coated by wet-on-wet, the conventional intermediate coating material cannot be used because appearance defects such as abrasion and conformity occur depending on parts.

[0005] Furthermore, the intermediate coating film is usually formed on the electrodeposition coating film. Regarding the rough surface of the electrodeposition coating film, only the intermediate coating film is once cured and then the top coating paint is applied. In the conventional method of coating, the undercoat concealing property is high and does not affect the finished appearance, but the above-mentioned step of curing only the intermediate coating film is omitted, and the two- or three-layer coating film is wet-on-wet. In the method of forming a coating film, there is also a problem that the underlying layer concealing property is low, and a smooth skin (yuzu skin) due to the rough surface of the electrodeposited coating film is developed.

In the conventional process of forming a laminated coating film, the intermediate coating film is baked once only with the intermediate coating film, and further baked after forming the top coating film. However, in the above-described method of forming a coating film on a wet basis, the intermediate coating film is baked only once, so that the physical properties of the coating film cannot be sufficiently exhibited. In some cases, peeling of the coating film occurred from the film or the surface of the steel sheet, and defects such as rust occurred.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method comprising:
When the intermediate coating film and the top coating film are sequentially coated by wet-on-wet, controlling the adaptation and reversal at the interface between the respective coating layers, improving the concealment property of the base against the electrodeposition coating film,
An object of the present invention is to provide a method for forming a laminated coating film having excellent finished appearance and excellent coating film properties such as chipping resistance.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for forming a coating film on a substrate, in which an intermediate coating film, a base coating film and a clear coating film are sequentially formed on a substrate in a wet-on-wet manner. The intermediate coating for forming a coating film and the base coating for forming the base coating film contain an amide group-containing acrylic resin and a curing agent, and the curing agent contained in the intermediate coating material is an aliphatic isocyanate. The aliphatic methylene block isocyanate of the present invention is a coating film forming method wherein the aliphatic methylene block isocyanate has an average number of functional groups greater than 3. .

Further, the present invention is a laminated coating film formed by the above-mentioned coating film forming method. Hereinafter, the present invention will be described in more detail.

[0010]Intermediate coating  In the coating film forming method of the present invention, the formation of the intermediate coating film
An intermediate coating is used. The intermediate coating contains an amide group.
It contains an acrylic resin and a curing agent. Change
Contains various organic and inorganic coloring pigments and extenders.
Can have. In the present invention, the film-forming tree
Amide group-containing acrylic resin contained as fat has polarity
Since it contains an amide group, it has a viscosity control effect.
Each time when painted by 3 coats 1 bake method
Familiarity and inversion at the interface between coating layers can be controlled
You. It also contributes to improvement of 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 non-volatile content at the time of coating will be too low, and the workability will be worse. In the present specification, the molecular weight is determined by a GPC method using a styrene polymer as a standard.

[0012] 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 2 to 30 mgKOH / g, and more preferably 3 to 25 mgKOH / g.
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.

The amide group-containing acrylic resin can be obtained by radically polymerizing 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 examples thereof include a hydroxyl group-containing ethylenically unsaturated monomer. 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 may 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, di-butyl 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.

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 include acrylic resins, polyester resins, alkyd resins,
Epoxy resins, urethane resins and the like can be mentioned as preferable ones, and one kind or two or more kinds can be used in combination.

In the above film-forming resin component, the weight ratio of the solid content of the amide group-containing acrylic resin to the other film-forming resin is preferably 30/70 to 100/0, more preferably 50/70. / 50 to 100/0.
When the amide group-containing acrylic resin falls below the lower limit, sag is suppressed and the appearance is reduced.

In the present invention, the curing agent contained in the intermediate coating composition comprises an aliphatic isocyanate-based active methylene block isocyanate. The active methylene block isocyanate is excellent in low-temperature curability as compared with other block isocyanates using an oxime-based or alcohol-based compound as a blocking agent. Moreover, it is excellent in baking yellowing and weather resistance when a coating film is formed.

In the present invention, the aliphatic methylene-based active methylene block isocyanate has an average number of functional groups of more than 3. By using an isocyanate having an average number of functional groups greater than 3, the reactivity and curability are high and a tough network structure is formed, so that the strength of the coating film obtained can be increased. If it is 3 or less, the reactivity and curability, particularly low-temperature curability, are poor. Preferably, the average number of functional groups is 5-7.

The active methylene block isocyanate of the aliphatic isocyanate series is an active methylene block type excellent in low-temperature curability and has an average number of functional groups of more than 3, so that the low-temperature curability is greatly improved. For example, curing can be performed even at a temperature of about 90 ° C. Therefore, when the intermediate coating, the base coating, and the clear coating are applied by wet-on-wet and three layers are baked at a time, the curing of the intermediate coating starts before the curing of the base coating and the clear coating. As a result, it is possible to improve the base material concealing property with respect to the electrodeposition coating film.

Furthermore, the softness of the aliphatic isocyanate-based block isocyanate imparts flexibility to the coating film obtained, and the isocyanate extends the crosslinking point to contribute to the flexibility of the coating film obtained. As a result, chipping resistance is improved. Further, the aliphatic isocyanate-based block isocyanate has a structure in which the isocyanate functional group is directed outward in the molecule, as compared with other block isocyanates such as aromatic isocyanate and alicyclic isocyanate. Also, since the functional group is located at the tip of the long chain and there is little steric hindrance, it is highly reactive.

The active methylene block isocyanate based on aliphatic isocyanate is obtained by adding an active methylene compound as a blocking agent to an aliphatic isocyanate based polyisocyanate. In the coating film, the blocking agent is dissociated by heating to generate an isocyanate group, which reacts with the functional group in the coating film-forming resin and cures. Examples of the aliphatic isocyanate-based polyisocyanate include, for example, trimer diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and a polymer of a diisocyanate having 2 to 12 carbon atoms such as trimethylhexamethylene diisocyanate. it can. Among them, a polymer of hexamethylene diisocyanate (HMDI) is preferred. The active methylene compound is not particularly limited as long as it has an active methylene group, and examples thereof include methyl acetoacetate and dimethyl malonate.

The active methylene block isocyanate of the aliphatic isocyanate type has no self-crosslinking property unlike the amino resin. Therefore, even when a resin having a high hydroxyl value is used as a film-forming resin, a large amount is blended. be able to. The ratio of the number of moles of hydroxyl groups of the film-forming resin to the number of moles of isocyanate groups of the curing agent is 0.7 / 1 to 1 /
It is preferably 1. However, in the present invention, in addition to the above-mentioned aliphatic isocyanate-based active methylene block isocyanate, an oxime-based or alcohol-based block isocyanate or an amino resin may be used in combination. In the intermediate coating, a catalyst can be used to dissociate the blocking agent.

The amount of the curing agent is 20 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. Outside the above range, the curability is insufficient.

When the aliphatic methylene block isocyanate active methylene block isocyanate and another curing agent are used in combination, 50% of the methylene block isocyanate of aliphatic isocyanate is used in the total weight of the curing agent.
It is preferable to mix it by weight percent or more. If it is less than 50% by weight, the low-temperature curability may be poor, and a coating film having good appearance and physical properties cannot be obtained.

Examples of the color pigment to be incorporated in the intermediate coating used in the present invention include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, and benzimitazolone pigments. Pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and the like. , Carbon black, titanium dioxide and the like. As the extender, calcium carbonate, barium sulfate, clay, talc and the like are used. Further, flat pigments such as aluminum powder and mica powder may be added.

As a standard, a gray pigment having carbon black and titanium dioxide as main pigments is used.
Further, a combination of a hue with the top coat and a combination of various coloring pigments can also be used.

Further, a viscosity control agent can be added to the above intermediate coating material in order to prevent adaptation to the top coating film and ensure coating workability. As the viscosity control agent, those which generally show thixotropic properties can be contained, for example, swelling dispersions of fatty acid amides, amide-based fatty acids, and polyamide-based ones such as long-chain polyaminoamide phosphates,
Polyethylene-based materials such as colloidal swelling dispersion of polyethylene oxide, organic acid smectite clay, organic bentonite-based materials such as montmorillonite, aluminum silicate,
Examples of the viscosity control agent include inorganic pigments such as barium sulfate, flat pigments exhibiting viscosity depending on the shape of the pigment, and crosslinked or non-crosslinked resin particles.

The total solid content of the intermediate coating used in the present invention at the time of coating is 30 to 80% by weight, preferably 3 to 80% by weight.
5 to 65% by weight. Outside this range, the paint stability decreases. On the other hand, if the ratio exceeds the upper limit, the viscosity is too high, and the appearance of the coating film deteriorates. If the ratio is lower than the lower limit, the viscosity is too low, and poor appearance such as adaptation or unevenness occurs.

The intermediate coating composition used in the present invention may contain, in addition to the above components, additives usually added to the coating composition, for example, a surface conditioner, an antioxidant and an antifoaming agent. These amounts are within the range known to those skilled in the art.

The method for producing the coating composition used in the present invention is not particularly limited, including those described below, and those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll. All known methods can be used.

[0035]Base coating  In the coating film forming method of the present invention, the base coating film is
-It constitutes the top coat together with the coating. This
The base coat is formed from a base paint. For base paint
Is a film-forming resin, curing agent, coloring pigment, if necessary
Bright pigments and the like are included.

In the present invention, the base paint for forming the base coating film contains an amide group-containing acrylic resin and a curing agent. When the base coating is composed of two or more layers such as a color base coating and a metallic base coating, at least the lowermost layer of the base coating contains an amide group-containing acrylic resin and a curing agent. There is a need. In the present invention, it is preferable that all base coating films contain an amide group-containing acrylic resin and a curing agent. Examples of the amide group-containing acrylic resin include the amide group-containing acrylic resins described in the description of the intermediate coating film.

In the above base paint, the solid content weight ratio of the amide group-containing acrylic resin and the other film-forming resin is preferably 30/70 to 90/10, more preferably 50/50 to 80/90. / 20. If the amide group-containing acrylic resin is below the lower limit, sagging is suppressed and the appearance is reduced, and if it exceeds the upper limit, the film forming property is deteriorated.

Preferred examples of the curing agent used in the base paint include amino resins, block isocyanates, epoxy compounds, aziridine compounds, carbodiimide compounds, oxazoline compounds, and the like, and mixtures thereof can be used. Amino resin is particularly preferably used in view of various properties and cost of the obtained coating film.

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", "Symel 254", which are commercially available from Mitsui Toatsu Co., Ltd.,
"Uban 22" commercially available from Mitsui Chemicals, Inc.
6 "," Uban 20N60 "," Sumimar series "marketed by Sumitomo Chemical Co., Ltd., and the like.

The content of the above-mentioned amino resin is 20 to the solid content of the amide group-containing acrylic resin and the film-forming resin.
The content is preferably from 100 to 100% by weight, more preferably from 30 to 100% by weight. If the content is less than 20% by weight, the curability becomes insufficient, and if it exceeds 100% by weight, the cured film becomes too hard and brittle.

The polyisocyanates used in preparing the block isocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate. Aliphatic isocyanates such as naphthalate; aliphatic cyclic isocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, and 1,2-cyclohexane diisocyanate; xylylene diisocyanate; , 4-tolylene diisocyanate, 2,6
-Aromatic isocyanates such as tolylene diisocyanate, alicyclic isocyanates such as isophorone diisocyanate and norbornane diisocyanate methyl, and multimers and mixtures thereof such as a nullate thereof can be used.

Examples of the blocking agent used in preparing the above block isocyanate include, in addition to the active methylene compounds mentioned in the description of the intermediate coating, halogenated hydrocarbons; methanol, ethanol, n-propanol Aliphatic, aromatic or heterocyclic alcohols such as isopropanol, furfuryl alcohol, alkyl-substituted furfuryl alcohol and benzyl alcohol; oximes such as methyl ethyl ketone oxime, methyl isobutyl ketone oxime, acetone oxime and cyclohexane oxime; and caprolactam And the like. Of these, oximes and active methylene compounds are preferred. Among them, those using an active methylene compound as a blocking agent are more preferable because of their excellent curability. Further, a catalyst for dissociating the blocking agent can be used.

The amount of the block isocyanate is as follows:
It is preferably 20 to 100% by weight based on 100% by weight of the total solid content of the film-forming resin in the paint, and 40 to 100% by weight.
More preferably, it is 100% by weight. Outside the above range, the curability is insufficient.

The content of the curing agent is preferably 20 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. More preferably, it is 30 to 100% by weight. Outside the above range, the curability is insufficient.

As the color pigment used in the base paint, for example, those described in the description of the intermediate paint described above can be contained. The glitter pigment optionally contained in the base paint is not particularly limited in its shape, and may be further colored. For example, the glitter pigment has an average particle size (D ₅₀ ) of 2 to ₅₀ μm and a thickness of It is preferable that the thickness is 0.1 to 5 μm. Those having an average particle size in the range of 10 to 35 μm are excellent in glitter and are more preferably used.

The pigment concentration (PW) of the bright pigment in the paint
C) is generally at most 20%. If it exceeds the upper limit, the appearance of the coating film deteriorates. Preferably, it is 0.01% to 18%, more preferably 0.1% to 15%.

The glitter pigments include aluminum,
Examples include non-colored or colored metal glitters such as metals or alloys such as copper, zinc, iron, nickel, tin and aluminum oxide, and mixtures thereof. Further, interference mica pigments, white mica pigments, graphite pigments, and other colored and colored flat pigments may be used in combination.

The total pigment concentration (PWC) in the paint, including the glitter pigment and all other pigments, is 0.1%.
To 50%, preferably 0.5% to 40%, more preferably 1.0% to 30%. If it exceeds the upper limit, the appearance of the coating film deteriorates.

Further, it is preferable to add a viscosity controlling agent to the base coating material in order to ensure the workability of coating, similarly to the intermediate coating material described above. The viscosity controlling agent is used for favorably forming a coating film without unevenness and sagging, and generally contains a material having thixotropic properties.
As such a material, for example, those described in the description of the intermediate coating material can be contained.

In the base paint used in the present invention, in addition to the above-mentioned components, additives usually added to the paint, such as a surface conditioner, a thickener, an antioxidant, an ultraviolet ray inhibitor and an antifoaming agent. May be blended. These amounts are within the range known to those skilled in the art.

The total solid content of the base paint used in the present invention at the time of coating is 10 to 60% by weight, preferably 1 to 60% by weight.
5 to 50% by weight. Exceeding the upper and lower limits lowers the paint stability. If it exceeds the upper limit, the viscosity is too high and the appearance of the coating film is reduced. If it is below the lower limit, the viscosity is too low and poor appearance such as familiarity and unevenness occurs.

[0052]Clear coating  Clear paint is used to form the above clear coating film.
You. This clear paint is not particularly limited,
Uses those containing thermosetting resins and curing agents
You. The form of this clear coating is solvent type, aqueous type
And powder type.

Preferred examples of the solvent-type clear paint include a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin having a carboxylic acid / epoxy curing system, in terms of transparency or acid etching resistance. Resins and / or polyester resins.

Examples of the above-mentioned aqueous clear paint include a resin obtained by neutralizing a film-forming resin contained in the above-mentioned examples of the solvent-type clear paint with a base to form an aqueous solution. Things can be mentioned. This neutralization can be carried out before or after the polymerization by adding a tertiary amine such as dimethylethanolamine and triethylamine.

On the other hand, as the powder type clear coating material, an ordinary powder coating material such as a thermoplastic and thermosetting powder coating material can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of the thermosetting powder coating include epoxy-based, acrylic-based, and polyester-based powder clear coatings, and an acrylic-based powder clear coating having good weather resistance is particularly preferable.

As the powder type clear paint used in the present invention, there is no volatile matter at the time of curing, a good appearance is obtained, and there is little yellowing.
Powder coatings based on polycarboxylic acids are particularly preferred.

Further, it is preferable that a viscosity control agent is added to the clear coating material in order to ensure coating workability, similarly to the intermediate coating material described above. The viscosity controlling agent can generally contain one exhibiting thixotropic properties. As such a material, for example, those described in the description of the intermediate coating material can be contained. If necessary, a curing catalyst, a surface conditioner and the like can be included.

[0058]Base material  The coating film forming method of the present invention can be applied to various substrates, for example, metals,
Useful for plastics and plastics, especially on metal surfaces and castings.
Although it can be used for
And can be used particularly preferably.

The metal products include, for example, iron, copper,
Aluminum, tin, zinc, and the like, and alloys containing these metals are included. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. It is particularly preferable that these metals have been previously subjected to a chemical conversion treatment with a phosphate, a chromate or the like.

Further, the base material used in the method of forming a coating film of the present invention may have an electrodeposition coating film formed on a chemically treated steel sheet. As an electrodeposition paint for forming an electrodeposition coating film,
Cationic and anionic types can be used, but a cationic type electrodeposition coating composition is preferable because it gives a laminated coating film having excellent anticorrosion properties.

[0061]Coating method  In the coating film forming method of the present invention, an intermediate coating
Base coat and clear paint with base coat and base paint
-Apply a clear paint film sequentially with wet paint
To form.

When the intermediate coating is applied to an automobile body in the present invention, in order to enhance the appearance, it is necessary to apply a multi-stage coating by air electrostatic spray coating called "react gun" or the like, preferably two-stage coating. Alternatively, a coating method in which air electrostatic spray coating is combined with a rotary atomization type electrostatic coating machine commonly referred to as “μμ (micro micro) bell”, “μ (micro) bell” or “metabell”. Thus, a coating film can be formed.

In the present invention, the thickness of the dried coating film of the intermediate coating varies depending on the desired use.
0-60 μm is useful. If the upper limit is exceeded, the sharpness may deteriorate, or problems such as unevenness or flow may occur at the time of coating. If the lower limit is not reached, the substrate cannot be concealed and the film is cut.

In the method for forming a coating film of the present invention, a base coating material and a clear coating material are further applied on an uncured intermediate coating film by wet-on-wet to form a base coating film and a clear coating film.

The base paint used for forming the base coating film in the method of the present invention is the same as the above-mentioned intermediate paint.
For example, it can be applied by air electrostatic spray coating called "react gun" or by a rotary atomization type electrostatic coating machine such as μμ bell, μ bell, etc., and the dry film thickness of the coating film is set to 5-35 μm. And preferably from 7 to
25 μm. When the thickness of the base coating film is more than 35 μm, sharpness may be reduced or unevenness or flow may occur in the coating film. Both are not preferable because the film may be discontinuous).

In the method for forming a coating film of the present invention, the clear coating film applied after the formation of the above-mentioned base coating film smoothes out irregularities caused by the above-mentioned base coating film, and glints and the like which occur when a brilliant pigment is contained. Formed for protection. Specifically, as a coating method, it is preferable to form a coating film by using a rotary atomizing electrostatic coating machine such as a μμ bell or μ bell described above.

The dry film thickness of the clear coating film formed by the clear coating is generally preferably about 10 to 80 μm, more preferably about 20 to 60 μm. If the upper limit is exceeded, problems such as waking or sagging may occur during coating, and if the lower limit is not reached, unevenness of the base cannot be concealed.

The laminated coating film obtained as described above is simultaneously cured, that is, a coating film is formed by so-called three coats and one bake. In this case, the baking / drying furnace can be omitted, which is preferable in terms of economy and environment.

The curing temperature for curing the laminated coating film is 80
By setting the temperature to 180 ° C, preferably 120 ° C to 160 ° C, a cured coating film having a high degree of crosslinking can be obtained. When the amount exceeds the upper limit, the coating film becomes hard and brittle, and when the amount is less than the lower limit, curing is insufficient. The curing time varies depending on the curing temperature.
A temperature of 160 ° C. for 10 to 30 minutes is appropriate.

The thickness of the laminated coating film formed in the present invention is usually 30 to 300 μm, preferably 50 to 2 μm.
50 μm. If it exceeds the upper limit, the physical properties of the film such as a thermal cycle decrease, and if it falls below the lower limit, the strength of the film itself decreases.

[0071]

EXAMPLES The present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. In the following, “parts” means “parts by weight”.

[0072]Manufacturing example Production of amide group-containing acrylic resin 1  Nitrogen inlet tube, stirrer, temperature controller, dropping funnel and deca
Into a 1 L reaction vessel equipped with a cooling tube
Charge 80 parts of silene and 20 parts of butyl acetate, and adjust the temperature.
120 ° C. Next, 5 parts of styrene and methyl methacrylate
Rate 30 parts, 4-hydroxybutyl acrylate 1
1.5 parts, ethyl acrylate 38.3 parts, ethyl meta
Acrylate 7 parts, methacrylic acid 2.3 parts, acrylamide
5 parts and t-butyl peroxy-2 as a polymerization initiator
-Charge 2.5 parts of ethyl hexanoate into the dropping funnel
A monomer solution was prepared. Keep the inside of the reaction vessel at 120 ° C.
The monomer solution was added dropwise over 3 hours. After dripping
It was kept at 120 ° C. for another hour. Number average molecular weight 140
00, hydroxyl value 45 and acid value 15 mg KOH / g
Thus, an acrylic resin 1 having a hydroxyl group was obtained.

[0073]Manufacture of other film-forming resins  Nitrogen inlet tube, stirrer, temperature controller, dropping funnel and cooling
In a 1 L reaction vessel equipped with a tube, 80 parts of xylene and
The temperature was set to 120 ° C. by charging 20 parts of chill. Stille
5 parts, methyl methacrylate 30 parts, 2-hydroxy
10.4 parts of ethyl methacrylate, ethyl acrylate
44.4 parts, ethyl methacrylate 7 parts, methacrylic acid
2.3 parts and t-butylperoxy-2-hexanoe
Separately prepare a monomer solution by mixing 2 parts
Was. This monomer solution is stirred in a reaction vessel over 3 hours.
After the addition, stirring was continued for 1 hour. Number average molecular weight 2
1000, hydroxyl value 45 and acid value 15 mg KOH / g
Acrylic resin 2 was obtained.

[0074]Production of crosslinkable resin particles  Stirring heater, thermometer, nitrogen inlet pipe, cooling pipe and decane
Bishydroxyethyl tauri in a reaction vessel equipped with
213 parts by weight, neopentyl glycol 208 parts by weight
Parts, 296 parts by weight of phthalic anhydride, 376 parts of azelaic acid
And 30 parts by weight of xylene and heated to reflux temperature.
Warmed. Here, the water generated by the reaction is
Removed azeotropically. Reaction takes about 3 hours from the start of reflux
Raise the temperature in the system to 210
Stir until the acid value corresponding to the acid becomes 135 mgKOH / g.
The reaction was carried out while stirring and dehydrating.

After cooling the temperature in the reaction system to 140 ° C., 500 parts by weight of “Kajura E10” (trade name, glycidyl versatate) manufactured by Shell Co., Ltd. were added to 30 parts by weight.
Dropped over minutes. Then, after stirring for about 2 hours, the reaction was terminated. Thereby, the acid value of the resin solid content is 55 m
gKOH / g and hydroxyl value of 91 mgKOH / g
And a zwitterionic group-containing polyester resin having a number average molecular weight of 1250 was obtained. 10 parts by weight of the obtained amphoteric group-containing polyester resin, 140 parts by weight of deionized water, 1 part by weight of dimethylethanolamine, 50 parts by weight of styrene and 50 parts by weight of ethylene glycol dimethacrylate are vigorously stirred in a stainless steel beaker. Thereby, a monomer suspension was prepared. Also, an initiator aqueous solution was separately prepared by mixing 0.5 parts by weight of azobiscyanovaleric acid, 40 parts by weight of deionized water, and 0.32 parts by weight of dimethylethanolamine.

A reaction vessel equipped with a stirring and heating device, a thermometer, a nitrogen inlet tube and a cooling tube was charged with 5 parts by weight of a zwitterionic group-containing polyester resin, 280 parts by weight of deionized water and 0.5 part by weight of dimethylethanolamine. To 80 ° C. Here, the previously prepared monomer suspension 251
Parts by weight and 40.82 parts by weight of the aqueous initiator solution at the same time
After the reaction was continued for 60 minutes, the reaction was terminated to obtain a crosslinkable resin particle emulsion.

The average particle size of the crosslinked resin particle emulsion was 55 nm as measured by a dynamic light scattering method. Xylene was added to this crosslinkable resin particle emulsion, and azeotropic distillation was performed under reduced pressure to remove water and replace the medium with xylene. Thus, a xylene solution of crosslinkable resin particles having a resin solid content of 20% by weight, which can function as a structural viscosity imparting agent, was obtained.

[0078]Example 1 Intermediate paint 1  The amide group-containing acrylic resin 1 produced in the above production example was replaced with 6
3 parts, Taipaque CR-97 (Ishihara Sangyo Co., Ltd.
39.5 parts, MA-100 (Car made by Mitsubishi Carbon Corporation)
Bon pigment) 0.4 parts, ASP200 (Engelhard Company)
4.4 parts of scaly talc) and S-100 (Exxon Co., Ltd.)
22.8 parts of an aromatic hydrocarbon solvent)
Put in a stainless steel container and apply paint conditioner
Mix and disperse for 45 minutes at room temperature using a gray pigment paste
And

In addition to this, Duranate MFK-60X
37 parts by weight of HMDI-based active methylene block isocyanate (Asahi Kasei Kogyo Co., Ltd .; average number of functional groups: 6) was added, and the mixture was further stirred and mixed with a lab mixer for 30 minutes to obtain a gray intermediate coating material 1. In addition, the compounding amount (part) was shown by solid content.

[0080]Base paint 1  Alpaste 7160N (Toyo Aluminum Co., Ltd. aluminum
10 parts by weight of pigment paste, aluminum content 65%)
The amide group-containing acrylic resin 1 obtained in the above production example
42 parts, acrylic resin 2 28 parts, Uban 20N6
0 (butylated melamine resin manufactured by Mitsui Toatsu) 30 parts
And mixed homogeneously. Furthermore, the cross-linkability produced in the previous production example
By adding 10 parts of resin particles and further dispersing uniformly
A metallic base paint 1 was obtained. The blending amount (parts)
Expressed as solids.

[0081]Coating method  After zinc phosphate treatment, Power Top V-6 (Nippon Pay
Coat Co., Ltd.) with a dry film thickness of 20 μm.
And then baked at 160 ° C for 30 minutes
First apply the intermediate coating paint 1 on the coated plate in advance with ethyl acetate / ethyl acetate.
Diluted thinner consisting of luethoxypropanol = 6/4
For 19 seconds using a No. 4 Ford Cup and 2
(Measured at 0 ° C.) to a dry film thickness of 20 μm.
"Micro Bell" (rotary atomizing electrostatic coating machine)
Painted. After the application, take an interval of 5 minutes.
I went to the meeting.

Next, the above metallic base paint 1 was
Toluene / ethyl acetate / ethylethoxypropanol =
18 seconds using a 5/2/3 dilution thinner (N
o. Using a 3 Ford cup (measured at 20 ° C.), a two-stage coating with “Microbell” and “Metabell” was applied to a dry film thickness of 20 μm. There was a 1.5 minute interval between the two applications. After the second application, setting was performed for 8 minutes.

Next, MAC O-380 Clear (acid epoxy curing type solvent clear paint manufactured by Nippon Paint Co., Ltd.) was used.
One-stage coating was performed with a “microbell” so as to have a dry film thickness of 40 μm, and setting was performed for 7 minutes. Next, the obtained coated plate was baked in a dryer at 140 ° C. for 30 minutes.

The obtained coated plate was visually evaluated for the smooth skin and glossiness of the coating film according to the following evaluation criteria. <Smoothness judgment criteria> 5: No feeling of feeling 4; Slight feeling is slightly recognized 3; Feeling of feeling 2; Slightly feeling 1; Slight feeling 1; Poor feeling of feeling

<Criteria for determining glossiness> 5: Very glossy 4; Glossy 3; Glossy 2; Slightly glossy 1; No glossiness

[0086]Example 2, Comparative Example 1  In advance, paint components (shown in solid content) shown in Table 1
Intermediate paint, metallic base paint as in Example 1.
And clear paint to create a multilayer coating
Valued. Examples of base paint and clear paint
The same as 1 was used. In addition, with the intermediate paint of Example 2,
Is a curing agent, Duranate MFK-60X (Asahi Kagaku)
HMDI-based active methylene block isocyana manufactured by Seiko Kogyo
And functional group 6) and duranate ME20-B80
S (HMDI-based oxime block isocyanate manufactured by Asahi Kasei Corporation)
Anato) was used. In the intermediate coating of Comparative Example 1,
Uban 226 (butylated Mera manufactured by Mitsui Chemicals, Inc.)
Min resin). About the above Examples and Comparative Examples
Table 1 shows the evaluation results.

[0087]

[Table 1]

In Examples 1 and 2, when the intermediate coating film, the base coating film, and the clear coating film were sequentially formed on a wet-on-wet basis, the base layer concealing property from the electrodeposition coating film was good.
It was possible to obtain a laminated coating film having an excellent appearance in both skin and glossiness. On the other hand, in Comparative Example 1, the obtained coating film had poor skin and glossiness.

[0089]

According to the present invention, the viscosity control effect is exhibited by the amide group-containing acrylic resin contained as a film-forming resin in the intermediate coating composition, and each coating film when applied by a three-coat one-bake method. Familiarity and inversion at the interface between layers can be controlled. Furthermore, as the curing agent, one comprising an aliphatic isocyanate-based active methylene block isocyanate having excellent low-temperature curability allows the intermediate coating film to be cured before the base coating film and the clear coating film. Starting and securing a sufficient flow property, it is possible to make the base material concealing property against the rough surface of the electrodeposition coating film excellent. The multilayer coating film obtained by the coating film forming method of the present invention has excellent finished appearance and excellent coating physical properties, particularly chipping resistance and coating strength.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 5/00 C09D 5/00 D 175/04 175/04 (72) Inventor Hideaki Tsujioka Takahama-shi, Aichi 3-5-5 Nittacho Japan Paint Co., Ltd. (72) Inventor Yoshiko Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F term (reference) 4D075 AE06 CA04 DA25 DB01 DB02 DB05 DB06 DB07 DB31 DC12 DC13 EA43 EB22 EB33 EB35 EB36 EB38 EB39 EB52 EB55 EB56 4J038 DG191 DG301 GA03 GA09 MA14 NA01 NA11 PA07 PA19 PB07 PC02 PC03 PC08

Claims (3)

[Claims] 1. A coating film forming method for forming an intermediate coating film, a base coating film, and a clear coating film on a substrate in a wet-on-wet sequence, wherein said intermediate coating film is formed. And the base paint forming the base coating film contains an amide group-containing acrylic resin and a curing agent, and the curing agent contained in the intermediate coating is an aliphatic isocyanate-based active methylene block isocyanate. Wherein the aliphatic isocyanate-based active methylene block isocyanate has an average number of functional groups of 3
A method for forming a coating film, wherein 2. The coating film forming method according to claim 1, wherein the aliphatic methylene block isocyanate-based active methylene block isocyanate has an average number of functional groups of 5 to 7. 3. A laminated coating film formed by the method for forming a coating film according to claim 1.