JP2021172688A - Coating composition - Google Patents

Abstract

To provide a coating composition containing inorganic fine particles and having high recoat adhesion.SOLUTION: The present invention discloses a coating composition containing a hydroxyl group-containing resin, a curing agent, and inorganic fine particles. Applying and curing the coating composition forms a film, which has a surface free energy higher than that of the film formed by curing the coating composition, from which only the inorganic fine particles have been removed.SELECTED DRAWING: None

Description

The present invention relates to a coating composition, particularly a coating composition in which the surface free energy of a cured coating film is controlled.

Inorganic fine particles such as nanosilica particles are blended in the coating composition to improve the performance of the coating film and the coating film. Japanese Unexamined Patent Publication No. 2009-62548 (Patent Document 1) discloses a coating composition containing inorganic fine particles such as a film-forming resin and silica, in which the surface tension of the inorganic particles is controlled.

The coating composition of Patent Document 1 is a coating film obtained by treating inorganic particles with a so-called coupling agent to reduce the surface tension so that the surface tension has a relationship of film without inorganic particles> film with inorganic particles. It has improved scratch resistance. However, although the coating composition of Patent Document 1 can provide a coating film having good scratch resistance, the wettability of the coating film surface is lowered, and the so-called recoat adhesion is greatly lowered. Recoat adhesion means that when a coating film defect is present, the defective portion is polished or not polished and covered with another coating film to repair the coating film defect, and the adhesion with the coating film that comes above is used. When the property is good, the recoat adhesion (or recoat property) is said to be good.

In technologies such as automobile painting, recoating is often performed, and recoat adhesion is particularly necessary for the performance of topcoat paints.

JP-A-2009-62548

An object of the present invention is to provide a coating composition having high recoat adhesion in a coating system containing inorganic fine particles.

That is, the present invention provides the following aspects:
[1]
A coating composition containing a hydroxyl group-containing resin, a curing agent, and inorganic fine particles.
A coating composition characterized in that the surface free energy of a film coated and cured with the coating composition is higher than the surface free energy of a film coated and cured by removing only inorganic fine particles from the coating composition.
[2]
[1] The difference obtained by subtracting (the surface free energy of the film cured by excluding only the inorganic fine particles) from (the surface free energy of the film cured by blending the inorganic fine particles) is 0 to 0.5. Paint composition.
[3]
The coating composition according to [1], wherein the inorganic fine particles have an average particle diameter of 2 to 500 nm.
[4]
The inorganic fine particles are selected from the group consisting of silica, alumina, alumina silicate alkali, borosilicate glass, quartz, nepheline syenite, zircon, baddeluite, eudialite and mixtures thereof. 1] The coating composition according to the above.
[5]
The coating composition according to [4], wherein the silica is selected from crystalline silica, amorphous silica, molten silica, precipitated silica and a mixture thereof.
[6]
The coating composition according to [1], wherein the inorganic fine particles are contained in the coating composition in an amount of 0.01 to 10% by weight based on the solid content.
[7]
The coating composition according to [1], wherein at least one of an aminoplast resin and an isocyanate resin is selected as the curing agent.
[8]
The coating composition according to [1], wherein the coating composition is blended in one pack.
[9]
The paint composition according to [1], wherein the paint composition is blended in two packs.

In the present invention, the performance of the film cured by the surface free energy is controlled, and the recoat adhesion is good as (the surface free energy of the film containing the inorganic fine particles) <(the surface free energy of the film containing the inorganic fine particles). At the same time, the scratch resistance was also ensured. Therefore, since the coating composition of the present invention has high recoat adhesion, it is effective as a coating composition for forming the coating film of the uppermost layer, and therefore, the clear coating film is usually present in the uppermost layer in many cases. Therefore, it is effective as a clear coating composition. The coating composition of the present invention also has high adhesion to high-pressure car washing.

The surface free energy of the cured coating can often be controlled by a surface conditioner. By blending the surface conditioner into the coating composition, the surface free energy of the cured coating film can be easily adjusted, so that the surface free energy can be easily controlled and the invention is not difficult to carry out.

<Paint composition>
Hydroxy Group-Containing Resin The coating composition of the present invention contains a hydroxyl group-containing resin, a curing agent, and inorganic fine particles. The hydroxyl group-containing resin is not particularly limited as long as it is a polymer containing a hydroxyl group, and examples thereof include a hydroxyl group-containing acrylic resin, a hydroxyl group-containing polyester resin, a hydroxyl group-containing alkyd resin, and a hydroxyl group-containing silicone resin. A hydroxyl group-containing acrylic resin or a hydroxyl group-containing polyester resin, which is easy to use, is preferable.

Hydroxyl group-containing acrylic resin Examples of the hydroxyl group-containing acrylic resin suitable for the present invention include those obtained by copolymerizing a hydroxyl group-containing ethylenically unsaturated monomer and another ethylenically unsaturated monomer. The hydroxyl group-containing acrylic resin according to the present invention preferably has a number average molecular weight (Mn) of 1000 to 10000, and more preferably 1100 to 8000. If the number average molecular weight is less than the lower limit, the coating workability and the multi-layerability with the clear coating film tend to decrease, while if the number average molecular weight exceeds the upper limit, the non-volatile content at the time of coating tends to decrease and the workability tends to deteriorate. .. Further, it is particularly preferable that the number average molecular weight of the hydroxyl group-containing acrylic resin is in the range of 1200 to 7000 from the viewpoint of the appearance of the coating film. The hydroxyl value of the hydroxyl group-containing acrylic resin according to the present invention is preferably 50 to 280 mgKOH / g, and more preferably 70 to 260 mgKOH / g. If the hydroxyl value exceeds the upper limit, the water resistance tends to decrease when the coating film is formed, while if it is less than the lower limit, the curability of the coating film tends to decrease. Further, the acid value of the hydroxyl group-containing acrylic resin according to the present invention is preferably 0 to 32 mgKOH / g, more preferably 2 to 20 mgKOH / g. If the acid value exceeds the upper limit, the water resistance tends to decrease when the coating film is formed, while if it is less than the lower limit, the curability of the coating film tends to decrease.

The hydroxyl group-containing acrylic resin according to the present invention can be obtained by copolymerizing a hydroxyl group-containing ethylenically unsaturated monomer with another ethylenically unsaturated monomer. Based on the total amount of ethylenically unsaturated monomers used for production, 5 to 60% by mass (more preferably 8 to 50% by mass) of hydroxyl group-containing ethylenically unsaturated monomers and 95% of other ethylenically unsaturated monomers. It is preferably about 40% by mass (more preferably 92 to 50% by mass). If the content of the hydroxyl group-containing ethylenically unsaturated monomer is lower than the lower limit, the production stability tends to decrease, while if it exceeds the upper limit, the water resistance of the coating film tends to decrease.

Specific examples of the hydroxyl group-containing ethylenically unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, allyl alcohol, methacryl alcohol, and the like. These and lactones (β-propiolaclone, dimethylpropiolactone, butyl lactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprilolactone, crotolactone, δ-valerolactone, δ-caprolactone, etc. ) And the like. Further, from the viewpoint of further improving the scratch resistance of the obtained coating film, those having a structure represented by _{"-(CH 2) n-" are used as at least a part of the hydroxyl group-containing ethylenically unsaturated monomer.} Of these, it is particularly preferable to use an adduct of 4-hydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate and ε-caprolactone. It should be noted that such a hydroxyl group-containing ethylenically unsaturated monomer may be used alone or in combination of two or more.

The other ethylenically unsaturated monomer is not particularly limited, but first, an ethylenically unsaturated monomer having a carboxyl group can be mentioned. As an example, a (meth) acrylic acid derivative (for example, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, acrylic acid dimer, α-hydro-ω- ((1)) obtained by adding ε-caprolactone to acrylic acid. -Oxo-2-propenyl) oxy) poly (oxy (1-oxo-1,6-hexanediyl)); and unsaturated dibasic acids, their half esters, half amides and half thioesters (eg, maleic acid, etc.) Fumaric acid, itaconic acid, its half ester, half amide, half thioester, etc.) can be mentioned. Further, examples of ethylenically unsaturated monomers other than those having a carboxyl group include (meth) acrylate ester monomers (for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl acrylate). , T-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl methacrylate, phenyl acrylate, isobornyl (meth) acrylate, cyclohexyl methacrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, dihydro Dicyclopentadienyl (meth) acrylate, etc.), polymerizable aromatic compounds (eg, styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.), polymerizable nitriles (eg, acrylonitrile) , Methacrylonitrile, etc.), α-olefin (eg, ethylene, propylene, etc.), vinyl ester (eg, vinyl acetate, vinyl propionate, etc.), diene (eg, butadiene, isoprene, etc.), if necessary, isocyanate group-containing monomer, etc. Can be mentioned. It should be noted that such other ethylenically unsaturated monomers may be used alone or in combination of two or more.

A hydroxyl group-containing acrylic resin suitable for the present invention can be obtained by copolymerizing the above-mentioned hydroxyl group-containing ethylenically unsaturated monomer with another ethylenically unsaturated monomer, but the polymerization method is not particularly limited and the solution radical is not particularly limited. Ordinary methods described in publicly known documents such as polymerization can be used. For example, a method of stirring a suitable radical polymerization initiator and a monomer mixed solution while dropping them into a suitable solvent at a polymerization temperature of 60 to 160 ° C. for 2 to 10 hours can be mentioned. The radical polymerization initiator that can be used here is not particularly limited as long as it is usually used for polymerization, and is an azo compound (for example, dimethyl-2,2'-azobisisobutyrate) or a peroxide (for example, dimethyl-2,2'-azobisisobutyrate). t-Butylperoxy-2-ethylhexanoate) and the like. The amount of such initiator is generally 0.1 to 10% by weight, preferably 0.5 to 8% by weight, based on the total amount of unsaturated monomers. 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 (for example, propylene glycol monomethyl ether acetate and xylene). In addition, mercaptans such as lauryl mercaptan and chain transfer agents such as α-methylstyrene dimer can be used as needed to regulate the molecular weight.

Hydroxyl group-containing polyester resin Examples of the hydroxyl group-containing polyester resin suitable for the present invention include those obtained by polycondensation of a polyhydric carboxylic acid and / or an acid anhydride and a polyhydric alcohol, and can be used as a low molecular weight polyhydric alcohol. A polymer obtained by adding a lactone compound can also be used. The hydroxyl group-containing polyester resin according to the present invention preferably has a number average molecular weight (Mn) of 1000 to 4500. If the number average molecular weight is less than the lower limit, sufficient curing tends not to be obtained, while if it exceeds the upper limit, smoothness becomes insufficient and a good appearance cannot be obtained, and at the same time, the viscosity at the time of coating becomes too high. There is a tendency. The hydroxyl value of the hydroxyl group-containing polyester resin according to the present invention is preferably 70 to 300 mgKOH / g. When the hydroxyl value exceeds the upper limit, the elasticity tends to decrease and the chipping resistance tends to be poor, while when it is less than the lower limit, the curability tends to be poor. Further, the acid value of the hydroxyl group-containing polyester resin according to the present invention is preferably 5 to 20 mgKOH / g. When the acid value exceeds the upper limit, the water resistance tends to decrease, while when the acid value is less than the lower limit, the curability of the coating film tends to decrease.

The hydroxyl group-containing polyester resin according to the present invention can be obtained by polycondensing a polyvalent carboxylic acid and / or an acid anhydride with a polyhydric alcohol, and the compounding ratio in this polycondensation is a hydroxyl group and a carboxylic acid group. And / or the molar ratio of the acid anhydride group is preferably 1.105-2. If the hydroxyl group is less than the lower limit, the number average molecular weight (Mn) becomes too large, so that the crosslink density is lowered and sufficient curability cannot be obtained. On the other hand, if the hydroxyl group exceeds the upper limit, the water resistance tends to be lowered.

The polyvalent carboxylic acid and / or acid anhydride is not particularly limited, and for example, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, Methyltetrahydrophthalic acid, methyltetrahydrohydrophthalic acid, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipine Examples thereof include acids, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenyl succinic acid, dodecenyl succinic anhydride and the like. It should be noted that such a polyvalent carboxylic acid and / or an acid anhydride may be used alone or in combination of two or more.

The polyhydric alcohol is not particularly limited, and for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, and 1,3-butane. Diol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2, 2-Dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, Examples thereof include trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol and the like. It should be noted that such a polyhydric alcohol may be used alone or in combination of two or more.

Further, when obtaining a hydroxyl group-containing polyester resin suitable for the present invention, monocarboxylic acid, hydroxycarboxylic acid, and lactone are used as reaction components other than the polyvalent carboxylic acid and / or acid anhydride and the polyhydric alcohol component. It may contain a kind and the like. Such lactones can be ring-opened and added to the polyester chain of polyvalent carboxylic acid and polyhydric alcohol to form a graft chain. For example, β-propiolaclone, dimethylpropiolactone, butyllactone, etc. Examples thereof include γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone is most preferable.

Further, the polyhydric alcohol used when obtaining a polymer obtained by adding a lactone compound to a low molecular weight polyhydric alcohol is not particularly limited, and for example, one having at least three hydroxyl groups in one molecule is preferable. , Trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, ditrimethylolpropane, pentaerythritol, dipentaerythritol, glycerin and the like. The lactone compound is not particularly limited as long as it is a lactone compound capable of causing a ring-opening addition reaction with the small molecule polyhydric alcohol compound. Since the ring-opening addition reaction is likely to occur, the lactone compound preferably has 4 to 7 carbon atoms, for example, ε-caprolactone, γ-caprolactone, γ-valerolactone, δ-valerolactone, γ-butyrolactone and the like. Can be mentioned. This may be used alone or in combination of two or more. Among these, ε-caprolactone and δ-valerolactone are more preferable, and ε-caprolactone is further preferable from the viewpoint of reactivity and the like.

The hydroxyl group-containing resin is generally present in the coating composition in an amount of 20 to 90% by weight, preferably 40 to 80% by weight, based on the total solid content weight of the coating composition.

Curing agent Examples of the curing agent include aminoplast resin and isocyanate resin, and the aminoplast resin and the isocyanate resin may be used alone or in combination. Aminoplast resins include formaldehyde condensates of nitrogen-containing compounds such as urea, thiourea, melamine, and benzoguanamine, and lower alkyl ethers (alkyl groups having 1 to 4 carbon atoms) of the condensates. Examples of the isocyanate resin include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), and a mixture thereof (TDI), diphenylmethane-4,4'. -Diisocyanate (4,4'-MDI), diphenylmethane-2,4'-diisocyanate (2,4'-MDI), and mixtures thereof (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3'-Dimethyl-4,4'-biphenylenediocyanate (TODI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated HDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydride xylylene diisocyanate (HXDI) and the like can be mentioned. Further, multimers and mixtures such as these burettes and nurates can be used. The isocyanate resin can also be used as a block body. The blocked isocyanate resin is not particularly limited as long as it is a blocked isocyanate resin used as a curing agent for paints. Blocked isocyanate is an isocyanate resin blocked with a blocking agent. Typical isocyanate resins include aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), and trimethylhexamethylene diisocyanate, 1,3-cyclopentane diisocyanate, and 1,4-cyclohexane. Diisocyanate, aliphatic cyclic isocyanate such as 1,2-cyclohexane diisocyanate, aromatic isocyanate such as xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, isophorone diisocyanate (isophorone diisocyanate) IPDI), alicyclic isocyanates such as norbornandiisocyanate methyl, multimers and mixtures such as burettes and nurates thereof can be used.

Blocking agents that block the isocyanate resin include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylcarbinol; ethylene. Cellosolves such as glycol monohexyl ether and ethylene glycol mono2-ethylhexyl ether; polyether-type both-terminal diols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol phenol; ethylene glycol, propylene glycol and 1,4-butane. Polyester-type double-ended polyols obtained from diols such as diols and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; dimethyl ketooxime , Methyl ethyl keto oxime, methyl isobutyl keto oxime, methyl amilketo oxime, cyclohexanone oxime and other oximes; and lactams typified by ε-caprolactam and γ-butyrolactam are preferably used.

The curing agent is generally present in an amount of up to 50 weight percent. Both% by weight are based on the total solid weight of the coating composition.

Inorganic Fine Particles The coating composition of the present invention contains inorganic fine particles. Examples of the inorganic fine particles are not particularly limited, but are a group consisting of silica, alumina, alumina alkali silicate, borosilicate glass, quartz, nepheline syenite, zircon, baddeluite, eudialite and a mixture thereof. Is selected from. As silica, crystalline silica, amorphous silica, fused silica, precipitated silica or a mixture thereof is used. These inorganic fine particles have an average particle size of 2 to 500 nm. If the average particle size is smaller than 2 nm, the stability is lost, and if it is larger than 500 nm, the scratch resistance and the finished appearance are deteriorated. The average particle size of the inorganic fine particles is preferably 5 to 200 nm, more preferably 5 to 100 nm. The particle size can be determined according to any method known in the art, for example by a conventional particle size analyzer. For example, if the average particle size is greater than 1 micron, laser scattering techniques can be used, and for average particle sizes less than 1 micron, TEM can be used.

The inorganic fine particles are contained in the coating composition of the present invention in an amount of 0.01 to 10% by weight based on the solid content thereof. If the amount of the inorganic fine particles is less than 0.01% by weight, the advantage of blending the inorganic fine particles cannot be obtained, and if it exceeds 10% by weight, a defect is given to the paint or the coating film. The blending amount of the inorganic fine particles is preferably 0.1 to 5% by weight, more preferably 1 to 5% by weight.

（上記計算式中、γ_１２は物質１と物質２との間の界面張力を表し、γ_ｉは物質ｉの表面張力を表し、γ_ｉ ^ｄはγ_ｉの分散成分を表し、γ_ｉ ^ｐは極性成分を表す。） Surface free energy In the coating composition of the present invention, the surface free energy of the cured coating film needs to be higher than the surface free energy of the cured coating film excluding the inorganic fine particles. The surface free energy corresponds to the surface tension in a liquid, and is the energy of the molecule of the solid surface itself. The unit is the surface tension (mN / m), and the surface free energy (mJ / m ² ). However, both values are considered to be equal. The difference in surface free energy is not particularly limited, but (surface free energy of the coating film cured by blending inorganic fine particles)-(surface free energy of the coating film cured by excluding the inorganic fine particles) It is preferably about 0 to 0.5, preferably about 0.1 to 0.4. In the present invention, the "surface free energy" was calculated by calculating the contact angle between water and methylene iodide on the coated surface according to the following formula.
Measurement method (SOUHENG WU, J. Poly.Sci., PARTC.34 19 (1971))

(In the above formula, gamma ₁₂ represents the interfacial tension between the material 1 and material 2, gamma _i represents the surface tension of the substance _i, γ i ^d represents the dispersion component of the γ _i, γ _i ^p is Represents a polar component.)

The surface free energy of the cured film formed of the coating composition of the present invention can be controlled by the components blended in the coating composition, but it is not always possible to control by blending the components. In the coating composition of the present invention, the surface free energy can be relatively adjusted by blending the surface conditioner. Therefore, in the examples of the present invention, the surface free energy was adjusted by changing the type of the surface conditioner. It is not limited to controlling the amount and type of surface conditioner. Specifically, the surface free energy can be controlled by the type of inorganic fine particles, the type of hydroxyl group-containing resin of the paint to be blended, and the like.

As the name suggests, surface conditioners are additives that act as defoamers, leveling agents, and anti-armpit agents by controlling surface tension. There are fluorine-based materials. The above surface conditioners can be used alone or in combination of two or more as appropriate.

The present invention is characterized in that the surface free energy of the cured film containing the inorganic fine particles is higher than the surface free energy of the cured film obtained by removing only the inorganic fine particles, and the function required of the surface conditioner is the surface of the cured film. It is to orient to increase the surface free energy. In order to orient the surface, the solubility parameter of the surface conditioner needs to be lower than that of the resin or additive constituting the cured film. The chemical structure of a surface conditioner having a function of increasing the surface free energy is not particularly limited, but in general, many polyester-based and silicone-based agents have the function. Commercially available surface conditioners include, for example, BYK series (silicone type, acrylic type) manufactured by Big Chemie, Tego series (silicone type, acrylic type) manufactured by Evonic, and Polyflow series (acrylic type) manufactured by Kyoeisha Chemical Co., Ltd. DYNOADD series (polyester type) manufactured by DYNEA, silicone-based surface conditioner manufactured by Toray Dow Corning, and the like can be mentioned.

The surface tension of the surface conditioner is preferably 26 mN / m or more, more preferably 28 to 30 mN / m. The surface tension was measured by the platinum ring method using a dynometer (manufactured by Big Gardner, Germany).

Other Ingredients The coating composition of the present invention contains a solvent, particularly an organic solvent, in order to reduce the viscosity of the coating material during coating. Organic solvents include, for example, alcohols, ketones, aromatic hydrocarbons, glycol ethers, esters or mixtures thereof. In solvent-based paints, the organic solvent is generally present in an amount of 5-80% by weight, especially 30-50% by weight, based on the total weight of the paint composition. The coating composition may be a water-based water-based paint, in which case the solvent comprises a water / co-solvent mixture.

The liquid composition of the present invention contains additives (eg, plasticizers, antioxidants, light stabilizers, UV absorbers, viscosity control agents, organic co-solvents, surfactants and catalysts) that are added to the coating composition in a general amount. ) Can be included. All such additives known in the art can be used without compatibility issues.

The coating composition of the present invention may be a coating material in one pack (package) depending on the intended use, or may be blended in two packs (package) divided into a coating material and a curing agent. When coating the coating composition of the present invention, from the viewpoint of the influence of the content of the organic solvent on the environment, the Ford Cup No. 1 at 20 ° C. It is preferably a solvent-based coating composition or a water-based coating composition in which the solid content of the coating composition is 50% by mass or more when diluted with 4 to a viscosity of 20 to 50 seconds.

The coating compositions of the present invention are coated by any conventional method (eg, brushing, dipping, flow coating, roll coating, conventional and electrostatic spraying). Spray technology is most often used. Typically, the thickness of the film for liquid coating can be in the range of 10-70 μm, preferably 30-60 μm.

The coating composition of the present invention is usually used as a clear coating material for forming the uppermost layer of a coating film, specifically, a clear coating film. Usually, in the painting of automobiles and other articles, a coating called an undercoat, a coating containing a colorant called an intermediate coating or a base coating, and a coating called a clear coating that gives depth to a shade are performed. To form a multi-layer coating. When the coating composition of the present invention is used as a clear coating material used for the uppermost layer, the recoat adhesion performance, which is the effect of the coating composition of the present invention, can be exhibited.

As already mentioned, when painting a paint, paint film defects are inevitably generated due to the presence of dust and dirt, defects caused by the paint during painting, defects caused by the coating machine, and the like. When a coating film defect occurs, there are various repair methods depending on the state of the coating film defect and when it was formed. Generally, after polishing the defective portion, the polished portion is polished. The intermediate coating and the clear coating are performed again so as to cover the surface. Of course, there are various repair methods, such as a method that does not polish, and a method that only clear paint is applied without painting from the middle coat, but whichever method is used, the top layer that has already been formed Another coating film is formed by coating another coating film on the coating film (specifically, a clear coating film). Since the coating composition of the present invention has excellent recoating adhesion, it has excellent adhesion to another coating film formed when repairing a coating film defect, and thus has excellent recoating property (multi-layer coating film repair). Gender) is excellent.

Hereinafter, a general method for forming a multi-layer coating film will be briefly described, but the method is not limited thereto.

<Multi-layer coating film forming method>
The method for forming a multi-layer coating film is to apply the above-mentioned base coating composition on a base material to form a base coating film layer, and then apply a clear coating composition on the base coating film to form a clear coating film layer. It is formed to form a multi-layer coating film including a base coating film layer and a clear coating film layer on the base material. Further, in the present invention, the above-mentioned base coating composition can be suitably used as a water-based brilliant coating material for automobiles (automobile bodies, parts, etc.).

The base material is not particularly limited, and metals such as iron, aluminum, magnesium, copper, tin, zinc or alloys thereof and molded products thereof; inorganic materials such as glass, cement and concrete; polyethylene resin, Resins such as polypropylene resin, ethylene-vinyl acetate resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, polyester resin, polystyrene resin, ABS resin, various plastic materials such as FRP, and their plastic materials. Molded products or foams; natural or synthetic materials such as wood and fiber materials (paper, cloth, etc.) can be mentioned. The base material preferably has a curved surface, such as an automobile body and parts (automobile body, door, etc.) such as a passenger car, a truck, a motorcycle, and a bus. Specific examples of the plastic molded product include automobile parts such as spoilers, bumpers, mirror covers, grills, and doorknobs. Further, these plastic molded products are preferably those washed with trichloroethane by steam or with a neutral detergent. Further, a primer coating may be applied to enable electrostatic coating.

In the method for forming a multi-layer coating film, when the base material is an automobile body or its parts, the conductive base material is previously degreased or chemical-treated (chemical conversion treatment with phosphate, chromate, etc.). After that, it is preferable to apply a base coating such as electrodeposition coating or intermediate coating to the base material.

Electrodeposition coating is performed for the purpose of forming an electrodeposition coating on a conductive base material such as a steel plate to impart rust resistance, and forming such an electrodeposition coating can be performed. The electrodeposition coating composition that can be produced is not particularly limited, and both a cationic electrodeposition coating composition and an anion type electrodeposition coating composition that are well known to those skilled in the art can be used and have rust resistance. From the viewpoint, the cationic electrodeposition coating composition is preferable, and among them, the epoxy-based cationic electrodeposition coating composition is particularly preferable.

In the present invention, when the base material is an automobile body or a steel plate, degreasing, washing with water, forming a chemical conversion film, washing with water, washing with pure water, and pretreatment until drying can be performed by a conventionally known method before forming an electrodeposition coating film. preferable. As the electrodeposition coating film forming method, an appropriate method may be arbitrarily selected from the conventionally known methods, and the electrodeposition coating film forming conditions, the baking curing conditions, the electrodeposition coating film thickness and the like are also based. It may be appropriately determined according to the material, the type of electrodeposition coating composition to be used, and the like.

In the intermediate coating, an intermediate coating layer is formed on the base material or electrodeposition coating, and the performance such as base hiding property, chipping resistance, and adhesion to the top coating (clear coating) layer is achieved. It is done for the purpose of improvement. In addition, the intermediate coating film layer also functions as a base for smoothing the final multi-layer coating film and forming a coating film having a good appearance, and further, between the electrodeposition coating film layer and the top coating film layer. It is required to be a binder for the coating film and to have weather resistance against deterioration of the coating film due to ultraviolet rays and water reaching through the surface of the coating film. The intermediate coating composition capable of forming the intermediate coating layer is not particularly limited, and in addition to solvent-based coatings well known to those skilled in the art, water-based coatings, powder coatings, high-solid coatings, etc. Also applicable, specifically, epoxy ester / melamine resin, alkyd / melamine resin or oil-free polyester / melamine resin paint, acrylic resin and / or polyester resin combined with amino resin and / or isocyanate hardener. It can be appropriately selected and used from conventionally known intermediate coating paints such as intermediate coating paints.

As for the method for forming the intermediate coating film layer, an appropriate method may be arbitrarily selected from the conventionally known methods. Further, in the present invention, a so-called combination of a gray-based intermediate coating composition containing carbon black and titanium dioxide as main pigments, set gray matching the lightness and hue with the topcoat coating layer, and various coloring pigments. A color intermediate coating composition can be used. These color intermediate coating composition can develop a composite color of the intermediate coating layer and the top coating layer, and can further enhance the design. Further, a flat pigment such as aluminum powder or mica powder may be added to these intermediate coating compositions. Further, the intermediate coating composition may contain additives which can be usually added to the coating material, such as a surface conditioner, an antioxidant, an antifoaming agent and the like. The dry film thickness of the intermediate coating film layer is preferably 10 to 100 μm, more preferably 20 to 40 μm.

In the multi-layer coating film of the present invention, a clear coating film composition is preferably applied onto an intermediate coating film formed on a base material to form a clear coating film layer.

The present invention will be described in more detail by way of examples. In the examples, parts and% are based on weight (mass) unless otherwise specified. The present invention should not be construed as being limited to these examples.

Production Example 1 Production of hydroxyl group-containing acrylic resin To a reaction vessel equipped with a thermometer, a stirring blade, a nitrogen introduction tube, a cooling condenser and a dropping funnel, 448 parts of propylene glycol monomethyl ether acetate was added and heated to 120 ° C. under a nitrogen atmosphere. .. In the container, 100 parts of propylene glycol monomethyl ether acetate, 105 parts of tert-butylperoxy2-ethylhexanoate, and 200 parts of styrene, 67 parts of acrylic acid-n-butyl, and methacrylic acid as a monomer combination using a dropping funnel. A monomer mixed solution consisting of 100 parts of alkyl acid, 270 parts of isobolonyl methacrylate, 360 parts of -4-hydroxybutyl acrylate and 3 parts of methacrylic acid was added dropwise at a constant velocity over 3 hours. Then, the mixture was kept at 120 ° C. for 0.5 hours, and 10 parts of tert-butylperoxy2-ethylhexanoate dissolved in 50 parts of propylene glycol monomethyl ether acetate was added dropwise at a constant rate in 30 minutes as a post-drop solution. Further, heating was continued at 120 ° C. for 1 hour.

As a result, the calculated Tg was 5.3 ° C., the solid content acid value was 2 mgKOH / g, the hydroxyl value was 140 mgKOH / g, the number average molecular weight (Mn) was 4600, and the weight average molecular weight (Mw) was 11300 in terms of standard polystyrene obtained by using GPC. An acrylic resin A having a resin solid content of 62.5% was obtained. As the alkyl methacrylate, Acryester SL (manufactured by Mitsubishi Rayon Co., Ltd.) having a mixing ratio (mass basis) of lauryl methacrylate / tridecylic methacrylate of 4/6 was used.

Example 1
Preparation of Clear Paint Composition a1 In a 1 L metal container, add 60.0 parts of the hydroxyl group-containing acrylic resin of Production Example 1 in terms of resin solid content, and dismodule N-3300 (isocyanurate compound manufactured by Sumika Cobestrourethane). 40.0 parts of solid content, DYNOADD F-1 (surface conditioner manufactured by DYNEA AS: surface tension 28.6 mN / m), 1 part of solid content, NANOBYK-3652 (inorganic fine particles manufactured by Big Chemie: particle size 40 nm) 2.0 parts, chinubin 384 (ultraviolet absorber manufactured by Ciba Geigy) 2.0 parts, chinubin 123 (light stabilizer manufactured by Ciba Geigy) 1.0 part, methylamyl ketone 57.0 parts and DBE (manufactured by Shoei Chemical Co., Ltd.) 22.0 parts were sequentially added and sufficiently stirred with a disper to obtain a two-component clear coating composition a1.

Preparation of Clear Paint Composition a2 In a 1 L metal container, 60.0 parts of the hydroxyl group-containing acrylic resin of Production Example 1 in terms of resin solid content and Dismodule N-3300 (isocyanurate compound manufactured by Sumika Cobestro Urethane Co., Ltd.) were placed. 40.0 parts of solid content, 1 part of DYNOADD F-1 (surface conditioner manufactured by DYNEA AS: surface tension 28.6 mN / m), 2.0 parts of tinubin 384 (ultraviolet absorber manufactured by Ciba Geigy) , Tinubin 123 (light stabilizer manufactured by Ciba Geigy Co., Ltd.), 57.0 parts of methylamylketone and 22.0 parts of DBE (manufactured by Shoei Chemical Co., Ltd.) were added in sequence, and the mixture was sufficiently stirred with a disper to form a two-component type. A clear paint composition a2 was obtained.

Creation of coating film A1 (coating film using clear paint a1)
Japan Paint Automotive Coatings Co., Ltd.'s cationic electrodeposition paint "Power Top U-50" (trade name) was applied to a phosphoric acid-treated steel plate so that the dry film thickness was 25 μm, and the test plate was heat-cured. Paint Automotive Coatings water-based paint "Aqualex AR-800" (trade name) is applied so that the dry film thickness is 20 μm, and then Nippon Paint Automotive Coatings water-based paint "Aqualex AR-2000" (Product name) A black color was applied so that the dry film thickness was 10 μm, and the mixture was dried at 80 ° C. for 5 minutes. The clear coating composition a1 was applied wet-on-wet to a dry film thickness of 40 μm and baked and dried at 140 ° C. for 30 minutes to prepare a test coating plate A1.

Creation of coating film A2 (coating film using clear paint a2)
Japan Paint Automotive Coatings Co., Ltd.'s cationic electrodeposition paint "Power Top U-50" (trade name) was applied to a phosphoric acid-treated steel plate so that the dry film thickness was 25 μm, and the test plate was heat-cured. Paint Automotive Coatings water-based paint "Aqualex AR-800" (trade name) is applied so that the dry film thickness is 20 μm, and then Nippon Paint Automotive Coatings water-based paint "Aqualex AR-2000" (Product name) A black color was applied so that the dry film thickness was 10 μm, and the mixture was dried at 80 ° C. for 5 minutes. The clear coating composition a2 was applied wet-on-wet to a dry film thickness of 40 μm and baked and dried at 140 ° C. for 30 minutes to prepare a test coating plate A-2.

Examples 2-3 and Comparative Examples 1-3
As the inorganic fine particles and the surface conditioner, the two-component clear coating compositions b1 to f2 were used in the same manner as in Example 1 except that those shown in the following table (Table 1) were used in the amounts shown in the table. After preparation, coating films B1 to F2 were further prepared.

表１中、無機微粒子と表面調整剤は以下の通りである：
ＮＡＮＯＢＹＫ−３６５２：ビックケミー・ジャパン社製無機微粒子：粒径４０ｎｍ。
ＳＯ−Ｃ４：アドマテックス社製無機微粒子：粒径１，０００ｎｍ。
ＤＹＮＯＡＤＤ Ｆ−１：ＤＹＮＥＡ ＡＳ社製表面調整剤（ポリエステル系）、表面張力２８．６ｍＮ／ｍ。
ＤＯＷ ＣＯＲＮＩＮＧ ＴＯＲＡＹ Ｌ−７６０４：東レ・ダウコーニング社製表面調整剤（シリコーン系）、表面張力２８．５ｍＮ／ｍ。
ＤＯＷ ＣＯＲＮＩＮＧ ＴＯＲＡＹ ８６３７：東レ・ダウコーニング社製表面調整剤（シリコーン系）、表面張力２５．０ｍＮ／ｍ。
ＢＹＫ−３３７：ビックケミー・ジャパン社製表面調整剤（シリコーン系）、表面張力２３．３ｍＮ／ｍ。
ＢＹＫ−３０６：ビックケミー・ジャパン社製表面調整剤（シリコーン系）、表面張力２３．４ｍＮ／ｍ。

In Table 1, the inorganic fine particles and surface conditioners are as follows:
NANOBYK-3652: Inorganic fine particles manufactured by Big Chemie Japan Co., Ltd .: Particle size 40 nm.
SO-C4: Inorganic fine particles manufactured by Admatex: particle size 1,000 nm.
DYNOADD F-1: Surface conditioner (polyester type) manufactured by DYNEA AS, surface tension 28.6 mN / m.
DOWN CORNING TORAY L-7604: Toray Dow Corning surface conditioner (silicone type), surface tension 28.5 mN / m.
DOWN CORNING TORAY 8637: Toray Dow Corning surface conditioner (silicone type), surface tension 25.0 mN / m.
BYK-337: Surface conditioner (silicone type) manufactured by Big Chemie Japan, surface tension 23.3 mN / m.
BYK-306: Surface conditioner (silicone type) manufactured by Big Chemie Japan, surface tension 23.4 mN / m.

<Method of measuring surface tension of surface conditioner>
It was measured by the platinum ring method using a dynometer (manufactured by Big Gardner, Germany).

The following evaluations were carried out using the clear coating compositions prepared in the above Examples and Comparative Examples. The evaluation results are shown in the following tables (Tables 2 and 3).

<Measurement method of surface free energy>
The surface free energy was calculated by calculating the contact angle between water and methylene iodide on the coating film surface according to the following formula. Table 2 shows the surface free energies of the coating films A1 to F2 and the Δ surface free energy (the formed coating film 1 minus 2; for example, the coating film A1-coating film A2).
Measurement method (SOUHENG WU, J. Poly.Sci., PARTC.34 19 (1971))

<Scratch property>
The scratch resistance (scratch resistance) of the obtained coating film (coating film A1, coating film B1, coating film C1, coating film D1, coating film E1 and coating film F1) was evaluated by Daiei Kagaku Seiki Seisakusho Co., Ltd. A metal columnar jig with a diameter of 16 mm, which is horizontal to the surface of the object whose tip is worn, is attached to the flat surface wear tester, and felt and wear paper (281Q manufactured by 3M, WETORDRY PRODUCTION POLISHING PAPER) are attached to the tip of the jig. 9 μGRADE) is fixed in the order of the tip of the jig, felt, and worn paper, and a load is applied so that a total load of 900 g is applied to the surface of the worn paper fixed to the jig, with a stroke length of 10 cm and 40 per minute. The surface of the coating film obtained at the reciprocating speed was worn 10 times.

The gloss at an angle of 20 ° with respect to the coating film surface of the test site and the untested part is measured with a microtrigloss (gloss measuring device manufactured by Big Chemie), and the percentage of the quotient of the untested part with respect to the test part is the gloss by the wear test. Scratch resistance was evaluated as the retention rate. The results are shown in Table 3.
◎ (Very good scratch resistance): Gloss retention rate is 80% or more.
◯ (Good scratch resistance): Gloss retention rate is 70% or more and less than 80%.
Δ (generally good scratch resistance): Gloss retention rate is 60% or more and less than 70%.
× (weak scratch resistance): Gloss retention rate is less than 60%.

<Recoat adhesion>
Japan Paint Automotive Coatings Co., Ltd.'s cationic electrodeposition paint "Power Top U-50" (trade name) was applied to a phosphoric acid-treated steel plate so that the dry film thickness was 25 μm, and the test plate was heat-cured. Paint Automotive Coatings water-based paint "Aqualex AR-800" (trade name) is applied so that the dry film thickness is 20 μm, and then Nippon Paint Automotive Coatings water-based paint "Aqualex AR-2000" (Product name) A black color was applied so that the dry film thickness was 10 μm, and the mixture was dried at 80 ° C. for 5 minutes. The clear coating composition was applied wet-on-wet to a dry film thickness of 40 μm, and baked and dried at 150 ° C. for 60 minutes to prepare a first-coat coating film. Furthermore, on the obtained first coat coating film, a water-based paint "Aqualex AR-800" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. was applied so that the dry film thickness was 20 μm, and then Nippon Paint Automotive. A water-based paint "Aqualex AR-2000" (trade name) manufactured by Coatings Co., Ltd. was coated with a black color so that the dry film thickness was 10 μm, and dried at 80 ° C. for 5 minutes. On top of that, the clear paint composition (paint composition a1, paint composition b1, paint composition c1, paint composition d1, paint composition e1 and paint composition f1) is wet-on-wet to a dry film thickness of 40 μm. It was applied so as to be, baked and dried at 140 ° C. for 30 minutes to prepare a recoated coating film.

A 2 mm go board that reaches the substrate by holding the cutting edge of the cutter (NT cutter (trade name) S type, A type or its equivalent) at about 30 degrees with respect to the coating film surface of the obtained recoat coating film. An eye was formed, and an adhesive tape (cellotape manufactured by Nichiban Co., Ltd. (registered trademark)) was uniformly pressure-bonded on the eye with a fingertip so that no air bubbles remained. Immediately, he held one end of the adhesive tape and pulled it sharply perpendicular to the coated surface to peel off the adhesive tape from the test piece. At this time, [the number of peeled squares] / [the number of grids = 100] was visually measured, and the recoat adhesion was evaluated according to the following criteria. The results are shown in Table 3.
◯: 0/100
Δ: 1/100 to 25/100
X: 26/100 to 100/100

<High-pressure car wash adhesion>
At the boundary between the unpainted portion and the coating film of the obtained test piece (coating film A1, coating film B1, coating film C1, coating film D1, coating film E1 and coating film F1 used in the scratch resistance test). On the other hand, water at 23 ° C. was sprayed from a nozzle having a height of 100 mm to a diameter of 3 mm at a pressure of 80 kg / cm ² , and the state of the coating film was observed. Those with a mark were evaluated as Δ, and those with peeled coating film were evaluated as ×. The results are shown in Table 3.

As is clear from the above Examples and Comparative Examples, when the difference in surface free energy (coating film X1-X2) measured in Table 2 is positive, the recoat adhesion and high-pressure car wash are as seen in Examples 1 to 3. The adhesion is high, and the effect of the present invention can be seen. The scratch resistance is reduced in Example 3 because the particle size of the inorganic fine particles used in the paint c1 is as large as 1,000 nm. In the comparative examples, the difference in surface free energy is negative, the requirements of the present invention are not satisfied, and the recoat adhesion and the high-pressure car wash adhesion are deteriorated.

Claims (9)

A coating composition containing a hydroxyl group-containing resin, a curing agent, and inorganic fine particles.
A coating composition characterized in that the surface free energy of a film coated and cured with the coating composition is higher than the surface free energy of a film coated and cured by removing only inorganic fine particles from the coating composition. The difference according to claim 1, wherein the difference obtained by subtracting (the surface free energy of the film cured by removing only the inorganic fine particles) from (the surface free energy of the film cured by blending the inorganic fine particles) is 0 to 0.5. Paint composition. The coating composition according to claim 1, wherein the inorganic fine particles have an average particle diameter of 2 to 500 nm. The inorganic fine particles are selected from the group consisting of silica, alumina, alumina silicate alkali, borosilicate glass, quartz, nepheline syenite, zircon, baddeluite, eudialite and mixtures thereof. Item 3. The coating composition according to Item 1. The coating composition according to claim 4, wherein the silica is selected from crystalline silica, amorphous silica, molten silica, precipitated silica and a mixture thereof. The coating composition according to claim 1, wherein the inorganic fine particles are contained in the coating composition in an amount of 0.01 to 10% by weight based on the solid content. The coating composition according to claim 1, wherein at least one of an aminoplast resin and an isocyanate resin is selected as the curing agent. The coating composition according to claim 1, wherein the coating composition is blended in one pack. The coating composition according to claim 1, wherein the coating composition is blended in two packs.