WO2021215172A1

WO2021215172A1 - Coating material composition

Info

Publication number: WO2021215172A1
Application number: PCT/JP2021/011757
Authority: WO
Inventors: 勝彦杉本; 智之石河; 琢也白石; みずほ富樫
Original assignee: 日本ペイント・オートモーティブコーティングス株式会社
Priority date: 2020-04-20
Filing date: 2021-03-22
Publication date: 2021-10-28
Also published as: JP2021172688A

Abstract

The purpose of the present invention is to provide a coating material composition containing inorganic fine particles and having high recoat adhesion. The present invention is a coating material composition containing a hydroxyl group-containing resin, a curing agent, and inorganic fine particles, wherein the surface free energy of a film which is coated with the coating material composition and cured is higher than the surface free energy of a film which is coated with the coating material composition excluding only the inorganic fine particles and cured.

Description

Paint composition

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.

The performance of paints and coating films has been improved by blending inorganic fine particles such as nanosilica particles with the paint composition. 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 and controlling the surface tension of the inorganic particles.

In the coating composition of Patent Document 1, the inorganic particles are treated with a so-called coupling agent to reduce the surface tension thereof. As a result, the surface tension becomes (film without inorganic particles)> (film with inorganic particles), and it is said that the scratch resistance of the coating film is improved. Therefore, the coating composition of Patent Document 1 seems to provide a coating film having good scratch resistance. However, when such a coating composition is used, the wettability of the coating film surface is lowered, and the so-called recoat adhesion is greatly lowered. Recoating is to repair a coating film defect by covering the defective portion with another coating film when a defect is present in the coating film, with or without polishing the defective portion. When the original coating film has excellent adhesion to a newly formed coating film at the time of recoating, it is said that the recoating adhesion (also referred to as recoating property) is good.

In automobile painting, recoating may be performed in no small measure. Therefore, recoat adhesion is particularly necessary as one of the performances of topcoat paints (for example, clear paints).

Japanese Unexamined Patent Publication No. 2009-62548

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

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 in which 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 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.
[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 an amount of 0.01 to 10% by weight based on the solid content in the coating composition.
[7]
The coating composition according to [1], wherein the curing agent is selected from at least one of an aminoplast resin and an isocyanate resin.
[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.

The present invention controls the performance of the cured film by surface free energy. Specifically, (the surface free energy of the film containing the inorganic fine particles) <(the surface free energy of the film containing the inorganic fine particles). As a result, the recoat adhesion is improved and the scratch resistance is also improved. Since the coating composition of the present invention has high recoat adhesion, it is useful as a coating composition for forming a coating film on the uppermost layer. Usually, a clear coating film is present on the uppermost layer. Therefore, the coating composition of the present invention is particularly useful as a clear coating composition. The coating composition of the present invention also has high adhesion to car washing at high pressure.

The surface free energy of the cured coating film can be controlled by, for example, a surface conditioner.

<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. Of these, a hydroxyl group-containing acrylic resin or a hydroxyl group-containing polyester resin is preferable because it is easy to design and synthesize.

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 number average molecular weight (Mn) of the hydroxyl group-containing acrylic resin is preferably 1000 to 10000, and more preferably 1100 to 8000. When the number average molecular weight is in the above range, the coating workability is improved, and the mixed layer with the base coating film (hereinafter, may be referred to as an intermediate coating film) is easily suppressed. Further, when the number average molecular weight is in the above range, the viscosity can be easily adjusted, so that a large amount of non-volatile components can be blended in the coating material. From the viewpoint of the appearance of the coating film, the number average molecular weight of the hydroxyl group-containing acrylic resin is particularly preferably 1200 to 7000. The hydroxyl value of the hydroxyl group-containing acrylic resin is preferably 50 to 280 mgKOH / g, more preferably 70 to 260 mgKOH / g. When the hydroxyl value is in the above range, the water resistance of the obtained coating film and the curability are likely to be improved. From the same viewpoint, the acid value of the hydroxyl group-containing acrylic resin is preferably 0 to 32 mgKOH / g, more preferably 2 to 20 mgKOH / g.

In the copolymerization of the hydroxyl group-containing ethylenically unsaturated monomer and other ethylenically unsaturated monomers, the blending ratio of each monomer is based on the total amount of the ethylenically unsaturated monomers, and the hydroxyl group-containing ethylenically unsaturated monomer is used. It is preferably 5 to 60% by mass (more preferably 8 to 50% by mass), and the other ethylenically unsaturated monomer is preferably 95 to 40% by mass (more preferably 92 to 50% by mass). When the content of the hydroxyl group-containing ethylenically unsaturated monomer is in the above range, the hydroxyl group-containing acrylic resin can be stably produced, and the water resistance of the obtained coating film can be easily improved.

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 additives such as. From the viewpoint of further improving the scratch resistance of the obtained coating film, it is possible to use one having a structure represented by _{"-(CH 2) n-" as at least a part of the hydroxyl group-containing ethylenically unsaturated monomer.} preferable. Of these, it is particularly preferable to use an adduct of 4-hydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate and ε-caprolactone. 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, and examples thereof include an ethylenically unsaturated monomer having a carboxyl group. 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)), etc.), and unsaturated dibasic acids, their half esters, half amides and half thioesters (eg, maleic acid). , Fumaric acid, itaconic acid, its half ester, half amide, half thioester, etc.). Examples of ethylenically unsaturated monomers other than those having a carboxyl group 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-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, dihydrodicyclo Pentazienyl (meth) acrylate, etc.); Polymerizable aromatic compounds (eg, styrene, α-methylstyrene, vinylketone, t-butylstyrene, parachlorostyrene, vinylnaphthalene, etc.); Lonitrile, etc.); α-olefin (eg, ethylene, propylene, etc.); Vinyl ester (eg, vinyl acetate, vinyl propionate, etc.); Diene (eg, butadiene, isoprene, etc.); be able to. It should be noted that such other ethylenically unsaturated monomers may be used alone or in combination of two or more.

By copolymerizing the above-mentioned hydroxyl group-containing ethylenically unsaturated monomer with another ethylenically unsaturated monomer, a hydroxyl group-containing acrylic resin suitable for the present invention can be obtained. The polymerization method is not particularly limited, and ordinary methods described in publicly known documents such as solution radical 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 over 2 to 10 hours at a polymerization temperature of 60 to 160 ° C. 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 0.1-10% by weight, preferably 0.5-8% 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.

A hydroxyl group-containing polyester resin Examples of the hydroxyl group-containing polyester resin suitable for the present invention include those obtained by polycondensing a polyvalent carboxylic acid and / or an acid anhydride and a polyhydric alcohol. A polymer obtained by adding a lactone compound to a low molecular weight polyhydric alcohol can also be used. The number average molecular weight (Mn) of the hydroxyl group-containing polyester resin is preferably 1000 to 4500. When the number average molecular weight is in the above range, sufficient curability can be easily obtained, and the smoothness of the obtained coating film is improved, so that a good appearance can be easily obtained. Further, it is easy to suppress an excessive increase in viscosity at the time of coating. The hydroxyl value of the hydroxyl group-containing polyester resin is preferably 70 to 300 mgKOH / g. When the hydroxyl value is in the above range, the decrease in elasticity is suppressed, the chipping resistance is likely to be improved, and the curability is also likely to be improved. The acid value of the hydroxyl group-containing polyester resin is preferably 5 to 20 mgKOH / g. When the acid value is in the above range, water resistance and curability are likely to be improved.

In the polycondensation of polyvalent carboxylic acid and / or acid anhydride and polyhydric alcohol, the compounding ratio of each component is 1.105 to 2 in terms of the molar ratio of hydroxyl group to carboxylic acid group and / or acid anhydride group. Is preferable. When the ratio of the hydroxyl groups is in the above range, it is suppressed that the number average molecular weight (Mn) of the obtained hydroxyl group-containing polyester resin becomes excessively large, and the decrease in the crosslink density is suppressed. Therefore, the curability is likely to be improved. Furthermore, the water resistance is likely to increase.

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 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, 1,3-butanediol, and the like. 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, trimethylol Butane, hexanetriol, pentaerythritol, dipentaerythritol and the like can be mentioned. It should be noted that such a polyhydric alcohol may be used alone or in combination of two or more.

When obtaining a hydroxyl group-containing polyester resin, monocarboxylic acid, hydroxycarboxylic acid, lactones and the like may be contained as reaction components other than the above-mentioned polyvalent carboxylic acid and / or acid anhydride and polyhydric alcohol component. Such lactones can be ring-opened and added to the polyester chain of a polyvalent carboxylic acid and a polyhydric alcohol to form a graft chain. Examples of lactones include β-propiolaclone, dimethylpropiolactone, butyllactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, and δ-. Caprolactone and the like can be mentioned, and ε-caprolactone is most preferable.

The hydroxyl group-containing polyester resin can be obtained by adding a lactone compound to a low molecular weight polyhydric alcohol. The low-molecular-weight polyhydric alcohol is not particularly limited, and for example, one having at least three hydroxyl groups in one molecule is preferable, and trimethylolpropane, trimethylolethane, 1,2,4-butanetriol, ditrimethylolpropane, and penta Examples thereof include erythritol, dipentaerythritol, and glycerin. 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 low molecular weight 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 a weight percent based on the total solid content weight of the coating composition, and is present in the coating composition in an amount of 20 to 90% by weight, preferably 40 to 80% by weight.

Curing agent Examples of the curing agent include aminoplast resin and isocyanate resin. The aminoplast resin and the isocyanate resin may be used alone or in combination. Examples of the aminoplast resin 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. Furthermore, 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 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.

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 , Oxims such as methyl ethyl keto oxime, methyl isobutyl keto oxime, methyl amilketo oxime, cyclohexanone oxime; 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. The weight% is based on the total solid content 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. At least one selected from. Examples of silica include crystalline silica, amorphous silica, fused silica, precipitated silica or a mixture thereof. These inorganic fine particles have an average particle size of 2 to 500 nm. When the average particle size is in the above range, dispersion stability, scratch resistance, and finished appearance are likely to be improved. 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. Specifically, laser scattering techniques can be used if the average particle size is greater than 1 micron, and TEM can be used for average particle sizes less than 1 micron.

Inorganic fine particles are contained in the coating composition of the present invention in an amount of, for example, 0.01 to 10% by weight based on the solid content thereof. When the content of the inorganic fine particles is in the above range, the advantage of blending the inorganic fine particles is fully exhibited, but the paint or the coating film is not damaged. The blending amount of the inorganic fine particles is preferably 0.1 to 5% by weight, more preferably 1 to 5% by weight.

Surface free energy The surface free energy of the cured coating film obtained by the coating composition of the present invention is higher than the surface free energy of the coating film cured except for the inorganic fine particles. The surface free energy corresponds to the surface tension of a liquid and is the energy of the molecules of the solid surface itself. The unit of surface tension is "mN / m" and the unit of surface free energy is "mJ / m ² ", but both values are considered to be equal. The difference between these surface free energies is not particularly limited. (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) is, for example, 0 to 0.5, and 0.1 to 0.1. It is about 0.4. In the present invention, the "surface free energy" is calculated according to the following formula by determining the contact angle of the mixed solution of water and methylene iodide on the coated surface.
The measuring method and calculation formula are based on the description of 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 by the coating composition of the present invention can be controlled by the components blended in the coating composition. Its ingredients are not limited. In the examples of the present invention, the surface free energy was adjusted by changing the type of the surface conditioner. This is because the surface free energy can be adjusted relatively easily. However, the surface free energy is not controlled only by the amount and type of surface conditioner. For example, the surface free energy can be controlled by the type of inorganic fine particles, the type of hydroxyl group-containing resin of the coating material to be blended, and the like.

As the name suggests, the surface conditioner controls the surface tension and works as an antifoaming agent, a leveling agent, and an armpit preventive agent. There are many types of surface conditioners, and examples thereof include acrylic, vinyl, silicone, and fluorine compounds. 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. The function required of the surface conditioner is to orient the surface of the cured film and 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 the surface conditioner is not particularly limited as long as it has a function of increasing the surface free energy. Examples of the surface conditioner include polyester-based and silicone-based compounds. 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.

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

Other Ingredients The coating composition of the present invention preferably 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 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 coating, in which case a mixture of water and an organic solvent is included as the solvent.

The coating 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. Upon painting, the coating composition may be diluted. The solid content of the coating composition is determined by Ford Cup No. 2 at 20 ° C. in consideration of the influence of the organic solvent on the environment. When diluted with 4 to a viscosity of 20 to 50 seconds, it is preferably 50% by mass or more.

The coating composition of the present invention is coated by any conventional method (eg, brushing, dipping, flow coating, roll coating, conventional and electrostatic spray). Spray technology is most often used. The thickness of the obtained dry coating film can be in the range of 10 to 70 μm, preferably 30 to 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 applied. This is done to form a multi-layer coating. When the coating composition of the present invention is used as a clear coating material forming the uppermost layer, the recoat adhesion, which is the effect of the coating composition of the present invention, is more likely to be exhibited.

As already mentioned, when painting paint, paint film defects inevitably occur due to the presence of dust and dirt, defects caused by paint during painting, defects caused by painting machines, etc. Various repair methods are examined depending on the state of the defect and the time of occurrence. Generally, after polishing the defective portion, intermediate coating and clear coating are performed again so as to cover the polished portion. Of course, there are various repair methods, such as a method without polishing and a method in which only clear painting is performed without painting from the intermediate coating. Regardless of which method is used, another coating film is formed by applying another coating film on the already formed top layer coating film (specifically, a clear coating film). The coating composition of the present invention is excellent in recoat adhesion (multi-layer coating film repairability) to another coating film formed at the time of repairing coating film defects.

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 a base coating composition on a base material to form a base coating film layer, and then apply the above clear coating composition on the base coating film to form a clear coating film layer. Form. As a result, a multi-layer coating film including a base coating film layer and a clear coating film layer is formed on the base material. Further, as the base coating composition, a water-based brilliant coating material for automobiles (automobile body, parts, etc.) can be preferably used.

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.

When forming a multi-layer coating film, if 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.). , 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 film on a conductive base material such as a steel plate to impart rust resistance. The electrodeposition coating composition capable of forming such an electrodeposition coating film is not particularly limited, and cationic electrodeposition coating compositions and anion-type electrodeposition coating compositions well known to those skilled in the art can be used. Both can be used. Of these, from the viewpoint of rust prevention, a cationic electrodeposition coating composition is preferable, and an epoxy-based cationic electrodeposition coating composition is particularly preferable.

When the base material is an automobile body or a steel plate, it is preferable to perform pretreatments such as degreasing, washing with water, forming a chemical conversion film, washing with water, washing with pure water, and drying by a conventionally known method before forming an electrodeposition coating film. As the electrodeposition coating film forming method, an appropriate method may be arbitrarily selected from conventionally known methods. The conditions for forming the electrodeposition coating film, the conditions for baking and curing, the thickness of the electrodeposition coating film, and the like may be appropriately determined according to the base material, the type of the 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 surface of the obtained multi-layer coating film and forming a coating film having a good appearance. The intermediate coating film layer further serves as a binder between the electrodeposition coating film layer and the top coating film layer. The intermediate coating film layer is required to have weather resistance against deterioration due to ultraviolet rays and water reaching through the top 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. Can also be applied. Specifically, epoxy ester / melamine resin, alkyd / melamine resin or oil-free polyester / melamine resin paint, intermediate coating paint combining acrylic resin and / or polyester resin with amino resin and / or isocyanate curing agent. Etc., can be appropriately selected and used from conventionally known intermediate coating paints.

Regarding the method for forming the intermediate coating film layer, an appropriate method may be arbitrarily selected from the conventionally known methods. A gray-based intermediate coating composition containing carbon black and titanium dioxide as the main pigments, a set gray that matches the brightness and hue with the topcoat coating layer, and a so-called color intermediate coating composition that combines various coloring pigments. Things 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.

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 velocity 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, 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) were placed. 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, methyl amylketone 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)
The phosphoric acid-treated steel sheet was coated with a cationic electrodeposition paint "Power Top U-50" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 25 μm. Then, the paint was cured by heating to obtain a test plate. This test plate was coated with a water-based paint "Aqualex AR-800" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 20 μm. Next, a water-based paint "Aqualex AR-2000" (trade name) manufactured by Nippon Paint Automotive 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 it, the clear coating composition a1 was applied wet-on-wet so that the dry film thickness was 40 μm. Subsequently, it was 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)
The phosphoric acid-treated steel sheet was coated with a cationic electrodeposition paint "Power Top U-50" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 25 μm. Then, the paint was cured by heating to obtain a test plate. This test plate was coated with a water-based paint "Aqualex AR-800" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 20 μm. Next, a water-based paint "Aqualex AR-2000" (trade name) manufactured by Nippon Paint Automotive 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 it, the clear coating composition a2 was applied wet-on-wet so that the dry film thickness was 40 μm. Subsequently, it was baked and dried at 140 ° C. for 30 minutes to prepare a test coating plate A-2.

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

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 evaluation was performed using the clear paint composition 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 determining the contact angle of the mixed solution of water and methylene iodide on the coating film surface and according to the above formula. Table 2 shows the surface free energies of the coating films A1 to F2 and the Δ surface free energy (1 to 2 of the formed coating film, for example, coating film A1-coating film A2).
The measuring method and calculation formula are based on the description of 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 flat surface wear tester was used. A metal cylindrical jig having a diameter of 16 mm, which is horizontal to the surface of an object whose jig tip is worn, was attached to this flat surface wear tester. Felt and wear paper (281Q manufactured by 3M, WETORDRY PRODUCTION POLISHING PAPER 9 μGRADE) were fixed to the tip of this jig in the order of the jig tip, felt, and wear paper. A load was applied to the surface of the worn paper fixed to the jig so that a load of 900 g was applied, and the surface of the coating film obtained at a speed of 40 reciprocations per minute with a stroke length of 10 cm was abraded 10 times.

The gloss at an angle of 20 ° with respect to the coating film surface of the tested part and the untested part was measured with a microtrigloss (gloss measuring device manufactured by Big Chemie). The scratch resistance was evaluated by using the percentage of the quotient of the untested part with respect to the tested part as the gloss retention rate by the wear test. 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%.
X (weak scratch resistance): Gloss retention rate is less than 60%.

<Recoat adhesion>
The phosphoric acid-treated steel sheet was coated with a cationic electrodeposition paint "Power Top U-50" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 25 μm. Then, the paint was cured by heating to obtain a test plate. The obtained test plate was coated with a water-based paint "Aqualex AR-800" (trade name) manufactured by Nippon Paint Automotive Coatings Co., Ltd. so that the dry film thickness was 20 μm. Next, a water-based paint "Aqualex AR-2000" (trade name) manufactured by Nippon Paint Automotive 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 it, the clear coating composition was applied wet-on-wet so that the dry film thickness was 40 μm. Subsequently, it was baked and dried at 150 ° C. for 60 minutes to prepare a first coat coating film. 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. Next, a water-based paint "Aqualex AR-2000" (trade name) manufactured by Nippon Paint Automotive 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 or paint composition f1) is wet-on-wet and has a dry film thickness. It was applied so as to be 40 μm. Subsequently, it was baked and dried at 140 ° C. for 30 minutes to prepare a recoated coating film.

Hold 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, and cut so that it reaches the substrate. Was put in to form a 2 mm square grid. An adhesive tape (cellotape manufactured by Nichiban Co., Ltd. (registered trademark)) was uniformly pressure-bonded on the adhesive tape with the fingertips 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 it off 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, from a height of 100 mm, water at 23 ° C. ^{was sprayed from a nozzle having a diameter of 3 mm at a pressure of 80 kg / cm 2} , and the state of the coating film was observed. Those with no change in the coating film were evaluated as ◯, those with a slight change in the coating film were evaluated as Δ, and those with the coating film peeled off were evaluated as x. 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.

According to the present invention, there is provided a coating composition containing inorganic fine particles and having high recoat adhesion.

The present application claims priority based on Japanese Patent Application No. 2020-074829 filed in Japan on April 20, 2020, the entire contents of which are incorporated herein by reference.

Claims

A coating composition containing a hydroxyl group-containing resin, a curing agent, and inorganic fine particles.
A coating composition in which 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 coating composition according to claim 1, wherein the inorganic fine particles are selected from the group consisting of silica, alumina, alumina silicate alkali, borosilicate glass, quartz, nepheline syenite, zircon, badelieuite, eugenic stone and a mixture thereof. thing.
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 an amount of 0.01 to 10% by weight with respect to the solid content in the coating composition.
The coating composition according to claim 1, wherein the curing agent is selected from at least one of an aminoplast resin and an isocyanate resin.
The paint composition according to claim 1, wherein the paint composition is blended in one pack.
The paint composition according to claim 1, wherein the paint composition is blended in two packs.