JP2002361170A - Method for forming multilayer coating film excellent in stain resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which colors the surface of a base material and imparts stain resistance by using a powder coating. SOLUTION: After a colored coating film is formed on the surface of the base material by using an enamel powder coating composition, a clear coating film is formed by using a clear powder coating composition containing a silicate compound. When a hydroxy group is concerned in the curing system of the clear powder coating composition, an ethyl silicate compound the water tolerance value to acetone of which is 2 ml or below or a methyl alkyl silicate compound having methyl groups and 2-6C alkyl groups in a ratio of 50/50-98/2 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multi-layer coating film having excellent stain resistance and to a multi-layer coating film obtained by using the same, particularly to using a powder coating of an enamel type or a clear type. The present invention relates to a method for forming a multilayer coating film having excellent properties and a multilayer coating film obtained by using the method.

[0002]

2. Description of the Related Art It is well known that the addition of a silicate compound to a solvent-based paint can impart stain resistance to the resulting coating film. This is considered to be because the silicate compound is hydrolyzed after transferring to the surface, thereby enhancing the hydrophilicity of the surface. When this silicate compound is added to a so-called enamel type powder coating containing a pigment, the desired stain resistance may not be imparted in some cases. This is considered to be because the silicate compound was adsorbed on the pigment surface in the powder coating. In addition, the occurrence of problems during storage, such as blocking resistance, is considered to be due to the silicate compound having some interaction with the pigment.
Japanese Patent Application Laid-Open No. 2001-3006 discloses that a coating film without bubbles can be formed by adding a compound having a specific boiling point, melting point and SP value to a powder coating containing a silicate compound. However, the above-mentioned problems are not mentioned at all, and they have not been solved.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for coloring a substrate surface and imparting stain resistance using a powder coating.

[0004]

According to the present invention, there is provided a method for forming a multi-layer coating film having excellent stain resistance, comprising the steps of: forming a colored coating film on a substrate surface using an enamel powder coating composition; A clear coating film is formed using a clear powder coating composition containing a compound. Here, the enamel powder coating composition may not contain a silicate compound, and the content of the silicate compound in the clear powder coating composition is from 0.2 to 10% by weight based on the resin solid content. %. Further, after the formed colored coating film is baked, the clear coating film may be formed, or the formed colored coating film and the clear coating film may be baked simultaneously. Further, the curing system of the clear powder coating composition,
Wherein the silicate compound has a water tolerance value of 2 ml with respect to acetone.
The following ethyl silicate compounds or methyl alkyl silicate compounds having a methyl group and an alkyl group having 2 to 6 carbon atoms in a ratio of 50/50 to 98/2 may be used.
The multilayer coating film of the present invention is obtained by the above-mentioned forming method.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The method for forming a multilayer coating film of the present invention comprises:
A colored coating film is formed on the surface of a base material using an enamel powder coating composition, and then a clear coating film is formed using a clear powder coating composition containing a silicate compound.

[0006] The substrate is not particularly limited as long as it does not cause problems such as deformation due to baking after coating, and specifically, an iron plate, a steel plate, an aluminum plate or the like and a surface-treated one thereof. Can be mentioned.
Since the multi-layer coating film obtained by the formation method of the present invention is excellent in stain resistance, it is preferable to use a substrate which is installed in an easily contaminated state such as outdoors. Note that an undercoat film obtained from an undercoat paint such as a primer may be formed on the surface of the base material.

In the method for forming a multilayer coating film of the present invention, first, a colored coating film is formed on the surface of the above-mentioned substrate by using an enamel powder coating composition. The enamel powder coating composition used here is a commonly used pigment-containing enamel type powder coating composition, and does not particularly need to contain a silicate compound.

The above-mentioned enamel powder coating composition contains a binder resin, a curing agent and a pigment as essential components, and usually further contains other components such as additives as necessary. As the binder resin, a polyester resin, an epoxy resin, or an acrylic resin having a functional group capable of reacting with a curing agent is generally used. Further, these can be appropriately blended and used as a polyester / epoxy resin, an acryl / epoxy resin, or an acryl / polyester resin. Because a clear coating is formed on the colored coating as described below, except for the case where the colored coating and the clear coating are simultaneously baked, the binder resin contained in the enamel powder coating composition is It does not need to have high weather resistance and is not particularly limited.

The above polyester resin can be obtained by polycondensation using an acid component containing a polyhydric carboxylic acid as a main component and an alcohol component containing a polyhydric alcohol as a main component by a usual method. it can. The acid component is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid and anhydrides thereof, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, and the like. Anhydrides, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, saturated aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic bb acid and anhydrides thereof, γ-butyrolactone, ε-caprolactone, etc. Examples include lactones, aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid, and hydroxycarboxylic acids corresponding thereto.

The alcohol component is not particularly restricted but includes, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol and diethylene glycol. , Triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, 1,2-propanediol, neopentyl glycol, 1,2-butane Diol, 1,3-butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-
Aliphatic glycols having a side chain such as hexanediol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol, and 1,2-octadecanediol; trivalent such as trimethylolpropane, glycerin and pentaerythritol The above polyhydric alcohols and the like can be exemplified.

By controlling the types and amounts of the compounds contained in the acid component and the alcohol component, a polyester resin having a predetermined amount of a functional group capable of reacting with a curing agent can be obtained. In addition, when the acid component contains 50% by weight or more, preferably 80% by weight or more of isophthalic acid, a polyester resin having high weather resistance can be obtained.

The above acrylic resin can be obtained by blending an ethylenically unsaturated group-containing monomer and copolymerizing the same with a usual method. Examples of the ethylenically unsaturated group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl acrylate, Praxel FM and FA series (trade name, 2-hydroxyethyl Adduct of (meth) acrylate and polycaprolactone, manufactured by Daicel Chemical Industries, Ltd.)
Hydroxyl-containing monomers such as polyalkylene glycol mono (meth) acrylates, glycidyl acrylate,
Epoxy group-containing monomers such as glycidyl methacrylate and 2-methylglycidyl methacrylate; amino group-containing monomers such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate;
(Meth) acrylamide, N-methyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide,
Acrylamide monomers such as N-methylacrylamide, curing functional group-containing monomers such as carboxylic acid group-containing monomers such as (meth) acrylic acid, and acrylonitrile, vinyl acetate, methyl (meth) acrylate, and ethyl (meth) acrylate , N-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, styrene, vinyltoluene,
Other neutral monomers such as p-chlorostyrene can be exemplified. By appropriately blending these ethylenically unsaturated group-containing monomers, an acrylic resin having a predetermined amount of a functional group capable of reacting with a curing agent can be obtained.

Further, the epoxy resin is a compound having an epoxy group as a functional group capable of reacting with two or more curing agents in one molecule, for example, a glycidyl ester resin, bisphenol A and epichlorohydrin. Glycidyl ether type resins such as a condensation reaction product with phosphorus and a condensation reaction product of bisphenol F with epichlorohydrin,
Examples thereof include alicyclic epoxy resins, aliphatic epoxy resins, bromide-containing epoxy resins, phenol novolak epoxy resins, and cresol novolak epoxy resins.

On the other hand, the above-mentioned curing agent is usually used in powder coatings. When the functional group of the above-mentioned binder resin is a hydroxyl group, an aliphatic polycarboxylic acid, an aliphatic acid anhydride, an amino resin, Polyepoxy compounds, blocked isocyanate compounds, glycoluril curing agents and the like are used. When the functional group of the binder resin is a carboxyl group, examples of the curing agent include a polyepoxy compound, a polyhydroxy compound, and a β-hydroxyalkylamide compound. Further, when the functional group of the binder resin is an epoxy group, the curing agent may be an aliphatic polycarboxylic acid such as decanedicarboxylic acid or sebacic acid, a polycarboxylic acid anhydride, dicyandiamide, a blocked isocyanate compound, or an amine-based compound. Examples thereof include a curing agent, a polyamide-based curing agent, a phenol resin, imidazoles and imidazolines.
It is preferable that the binder resin and the curing agent contain functional groups involved in curing at a ratio that does not significantly deviate from a stoichiometrically equal ratio.

Further, as the above-mentioned pigment, those generally used can be used. Specifically, titanium dioxide, red iron oxide, yellow iron oxide, carbon black,
Color pigments such as phthalocyanine blue, phthalocyanine green, quinacridone pigments and azo pigments, metallic pigments, pearl pigments, metal powders and surface-treated ones, extenders such as talc, silica, calcium carbonate, and precipitated barium sulfate And the like.
The content of the pigment in the powder coating is not particularly limited as long as it can cover and color the surface of the base material. Generally, the content of the pigment is 30 to the total amount of the binder resin and the curing agent.
It is preferably from 100 to 100% by weight.

The other components such as additives include a surface conditioner, a curing catalyst, a plasticizer, an ultraviolet absorber,
Examples thereof include an antioxidant, an anti-bake agent, a charge control agent, and a fluidity-imparting agent. These are preferably contained in such an amount that they can exhibit their functions and do not cause any trouble when added.

The above-mentioned enamel powder coating composition is prepared by adding the above-mentioned various additives to the above-mentioned binder resin, curing agent and pigment, and mixing the mixture, at 60 to 150 ° C, preferably 80 to 130 ° C.
Is obtained by cooling and solidifying a melt obtained by melt-kneading in the range described above, and pulverizing to a desired particle size through coarse pulverization and fine pulverization steps. In addition, it is preferable that the fluidity imparting agent is added after the pulverization.

The volume average particle diameter of the above-mentioned enamel powder coating composition is preferably set to 5 to 50 μm by performing classification in order to adjust the particle size distribution by removing giant particles and fine particles. 5-40μ when used for thin film coating
m, especially when a thin and smooth coating film is to be obtained.
More preferably, it is set to 30 μm.

The formation of the colored coating film is carried out by applying the enamel powder coating composition to the surface of the substrate. The method of applying is not particularly limited, and a method well known by those skilled in the art such as an electrostatic coating method and a fluid immersion method can be used, but the electrostatic coating method is preferable from the viewpoint of coating efficiency. Examples of the charging method in the electrostatic coating method include a corona charging method and a friction charging method. These methods can be used in combination. The coating thickness of the colored coating film is not particularly limited as long as it can color and conceal the substrate surface. The coating film thickness may depend on the volume average particle diameter of the powder coating particles, but may be usually 20 to 200 μm.
After forming a colored coating film by this application, baking may or may not be performed. In the case of baking, curing conditions are set based on the types of the binder resin and the curing agent contained in the enamel powder coating composition. At that time, baking can be performed at a temperature at which curing does not completely proceed even when the colored coating film is melted, for example, 90 to 140 ° C. for 5 to 15 minutes.

In the method for forming a multilayer coating film of the present invention,
On the previously obtained colored coating film, a clear coating film is formed using a clear powder coating composition containing a silicate compound. Here, the colored coating film may or may not be baked.

As the silicate compound contained in the clear powder coating composition, tetraalkoxysilane having an alkoxy group having 1 to 8 carbon atoms and a condensate thereof, and an alkoxy group of these condensates are converted to alcohol Can be mentioned. Of these, preferred are condensates of tetramethoxysilane or tetraethoxysilane and those obtained by substituting the alkoxy groups of these two condensates with alcohols.

Specific examples of the tetraalkoxysilane having an alkoxy group having 1 to 8 carbon atoms include tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, tetrahexyloxysilane, tetraoctyloxysilane and the like. . The condensates of tetramethoxysilane and tetraethoxysilane listed as preferable ones are commercially available as MKC silicate series from Mitsubishi Chemical Corporation and ethyl silicate series from Colcoat Co., Ltd., respectively.

The above-mentioned tetraalkoxysilane condensate obtained by substituting an alkoxy group with an alcohol can be obtained by performing an exchange reaction using at least 1 mol of the above alcohol per 1 mol of the above condensate. . The amount of the above alcohol can be appropriately increased according to the number of target substituents. The exchange reaction is, for example, about 1
Preferably, the heating is performed up to 50 ° C. Further, in order to make the reaction proceed, it is preferable to reduce the pressure of the system and distill off the generated methanol or ethanol to the outside of the system. The reaction is terminated when a predetermined amount of substitution with alcohol has been performed. After completion of the reaction, the desired silicate compound can be obtained by performing separation and purification as required. The silicate compound thus obtained is generally a colorless to pale yellow oily substance. The determination of the replacement amount with the alcohol is performed by checking the amount of the produced methanol or ethanol or by using an analytical instrument.

As the alcohol used for the substitution of the alkoxy group, ethanol, propanol, butanol, hexanol, benzyl alcohol, 2-butoxyethanol, 3-methoxy-1-propanol, 2-ethylhexanol, octanol and the like can be used. it can. The alcohols may be used as a mixture of two or more.

The solvent does not have to be particularly used,
When used, it is preferably 10 times or less based on the total weight of the above condensate and alcohol. Specific examples of the solvent include, for example, aromatic hydrocarbons such as toluene, benzene and xylene, halogenated hydrocarbons such as dichloroethane, ethers such as THF and dioxane,
Examples include ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, dimethyl carbonate, and acetonitrile.

In the above exchange reaction, an acid or a base can be used as a catalyst, if necessary. Examples of the acid include a Bronsted acid such as hydrochloric acid, sulfuric acid, phosphoric acid, and sulfonic acid, and a Lewis acid such as an organic tin compound.
Examples of the base include triethylamine, dimethylbenzylamine, diazabicyclo [2.2.2] octane,
1,8-diazabicyclo [5.4.0] undecene-7
Such as tertiary amines can be used.

The content of the silicate compound in the clear powder coating composition is preferably 0.2 to 10% by weight based on the total resin solid content of the binder resin and the curing agent. If the amount is less than 0.2% by weight, a coating film excellent in stain resistance cannot be obtained. If the amount exceeds 10% by weight, the effect corresponding thereto cannot be recognized. There is a possibility that physical properties may be adversely affected. A more preferred range is 1 to 5% by weight.

On the other hand, as to other components such as a binder resin, a curing agent, and an additive contained in the clear powder coating composition, the contents described in the above enamel powder coating composition are applied as they are. You. The type of the binder resin and the curing agent is not particularly limited, but since the clear coating film obtained from the clear powder coating composition is located on the upper layer of the multilayer coating film, a binder resin having high weather resistance may be used. preferable. If the previously formed colored coating has not been baked yet, or has not been completely cured, use the same binder resin and curing agent used in the enamel powder coating composition. Is preferred. If they are different, cissing may occur between the colored coating and the clear coating.

In the case where the curing system of the clear powder coating composition involves a hydroxyl group, the silicate compound may be a condensate of tetraethoxysilane or an alkoxy group of the condensate having a carbon number Ethyl silicate compounds partially substituted with an alcohol having 3 to 8 and having a water tolerance value of 2 ml or less with respect to acetone or using a methyl group and an alkyl group having 2 to 6 carbon atoms in 50/50 to 98 It is preferable to use a methylalkyl silicate compound having a ratio of / 2.

When the curing system of the above clear powder coating composition proceeds with the involvement of hydroxyl groups, many hydroxyl groups are present in the system. For this reason, a side reaction between the silicate compound and the hydroxyl group is more likely to occur, and the silicate compound may not be able to exhibit its function due to the side reaction. This problem can be solved by using one of the silicate compounds having the above two characteristics. In addition, it is particularly preferable to use the above-mentioned methyl alkyl silicate compound from the viewpoint of reducing the water contact angle of the obtained coating film surface.

When the water tolerance value for the above acetone is 2
The ethyl silicate compound of not more than ml controls the compatibility and reactivity between the silicate compound and the component containing a large amount of hydroxyl groups so that the side reaction does not occur. The water tolerance value for acetone in this specification was determined using a 100 ml beaker as a container.
After adding 1 g of the silicate compound and dissolving by adding 10 ml of acetone, water was gradually dropped, and until the time when the No. 5 type character laid on the bottom of the beaker became invisible from the top of the beaker and became unreadable. This is the total amount of water added.

Usually, the compatibility is defined by the difference in SP value. However, since the silicate compound is completely dissolved in hexane used for determining the SP value, the SP value cannot be determined. However, in powder coatings containing many hydroxyl groups, S
It has been found that the above compatibility can be controlled by defining the tolerance value by adding water to the silicate compound instead of the P value. When the above water tolerance value exceeds 2 ml,
Compatibility with components containing a large amount of hydroxyl groups increases, and a side reaction occurs, so that the intended function cannot be exhibited. In order to satisfy the above-mentioned water tolerance value, the condensation degree is preferably 5 to 20. In addition, this condensation degree may be an average value.

On the other hand, with regard to reactivity, it is preferable to use a silicate compound in which the alkoxy group is an ethoxy group or a silicate compound in which this is partially substituted with an alcohol having 3 to 8 carbon atoms. In addition, this partial substitution means that half or less of the ethoxy groups are substituted. Examples of the alcohol having 3 to 8 carbon atoms include propanol, butanol, benzyl alcohol, 2-butoxyethanol, 3-methoxy-1-propanol,
Ethyl hexanol, octanol, trifluoroethanol, pentafluoropropanol and the like can be mentioned.

In the above-mentioned methylalkyl silicate compound, which is another silicate compound for preventing a side reaction between the silicate compound and the hydroxyl group, the methyl group and the alkyl group having 2 to 6 carbon atoms are based on the number, 50 /
It is present in a ratio of 50 to 98/2. By setting the ratio of the methyl group to the alkyl group having 2 to 6 carbon atoms in the above range, hydrophilicity by hydrolysis can be exhibited while avoiding a side reaction with a hydroxyl group. The above ratio is 50/5
If it is less than 0, hydrolysis does not easily progress, and if it exceeds 98/2, the reaction with the hydroxyl group in the binder resin progresses, and it is difficult to obtain good stain resistance. A preferred lower limit is 75/25, and a preferred upper limit is 96/4.
It is. The ratio between the methyl group and the alkyl group having 2 to 6 carbon atoms can be determined using a suitable analytical instrument, for example, a ¹ H-NMR spectrum.

The above methylalkyl silicate compound is
Obtained by various methods such as a reaction between a condensate of tetramethoxysilane and an aliphatic saturated alcohol having 2 to 6 carbon atoms, and a condensation polymerization of tetramethoxysilane with a tetraalkoxysilane having an alkyl group having 2 to 6 carbon atoms. be able to. It can also be obtained by mixing a condensate of tetramethoxysilane and a condensate of tetraalkoxysilane having 2 to 6 carbon atoms. Examples of the alkyl group having 2 to 6 carbon atoms other than the methyl group include an ethyl group, a propyl group, a butyl group, an amyl group, and a hexyl group. These may be branched. The alkyl group having 2 to 6 carbon atoms may be plural types, but it is preferable that the alkyl group is single in consideration of easiness of production. Considering the balance between avoiding side reactions with hydroxyl groups and expressing hydrophilicity by hydrolysis, preferred alkyl groups having 2 to 6 carbon atoms are ethyl groups,
They are a propyl group and a butyl group, and an ethyl group is particularly preferred. The reaction between the condensate of tetramethoxysilane and an aliphatic saturated alcohol having 2 to 6 carbon atoms is included in the above-described method of substituting the alkoxy group of the condensate of tetraalkoxysilane with an alcohol.

When a hydroxyl group is involved in the curing system, either the binder resin or the curing agent has a hydroxyl group as a main reactive group. Specific examples of such a binder resin include a hydroxyl group-containing acrylic resin or a polyester resin.
-Hydroxyalkylamide curing agents. Specific examples of the combination of the binder resin and the curing agent include a combination of a hydroxyl group-containing acrylic resin and a blocked isocyanate curing agent, a combination of a hydroxyl group-containing polyester resin and a blocked isocyanate curing agent, a carboxyl group-containing acrylic resin or a carboxyl group-containing polyester. A combination of a resin and a β-hydroxyalkylamide curing agent can be mentioned. The above-mentioned blocked isocyanate curing agent contains a uretdione compound. Among these, those having high versatility as an actual powder coating are combinations of a hydroxyl group-containing polyester resin and a blocked isocyanate curing agent, and a carboxyl group-containing polyester resin and a β-hydroxyalkylamide curing agent. It is also possible to use a plurality of these in combination. In these cases, the contents of the binder resin, the curing agent and the silicate compound in the powder coating composition are as described above.

The clear powder coating composition containing the above silicate compound basically does not contain a pigment, but a coloring material which can obtain a so-called turbid clear coating film or a clear coloring coating film. It may be contained.

The clear powder coating composition containing the above silicate compound can be obtained in the same manner as the above-mentioned enamel powder coating composition, and the volume average particle diameter is also described in the enamel powder coating composition. It is preferably within the range described above.

The clear powder coating composition containing the above silicate compound is applied on the previously obtained colored coating film in the same manner as the above enamel powder coating composition to form a clear coating film. You. The thickness of the clear coating film can be, for example, 20 to 200 μm so as to obtain smoothness.

In the method for forming a multilayer coating film according to the present invention, the clear coating film is finally baked. The curing conditions are set based on the types of the binder resin and the curing agent contained in the clear powder coating composition, but when the previous colored coating is not baked, the enamel powder coating composition It is necessary to consider the type of binder resin and curing agent contained in the resin. General curing conditions in the present invention are baking at 140 to 220 ° C. for 5 to 40 minutes. Thus, the multilayer coating film of the present invention is obtained.

[0041]

EXAMPLES Production Example 1 Alcohol-substituted ethyl acetate
5. Production of silicate compound In 595 g of ethyl silicate 40 (manufactured by Colcoat, a condensate having an average degree of condensation of tetraethoxysilane of 5), 283 g of 2-butoxyethanol and triethylamine 6.
5 g was added, and the mixture was heated and stirred at 90 ° C. for 1 hour, at 120 ° C. for 2 hours, and further at 140 ° C. for 3 hours while removing generated ethanol. After cooling, the remaining 2-butoxyethanol was removed under reduced pressure to obtain 662 g of an ethylsilicate compound substituted with 2-butoxyethanol. In addition,
The number of 2-butoxyethoxy groups in the ethyl silicate compound determined by ¹ H-NMR was 3. Also, in a 100 ml beaker, 1 g of the obtained ethyl silicate compound was dissolved in 10 ml of acetone, and when 1.07 ml of water was added, the No. 5 type printed on the bottom of the beaker became cloudy and could not be read. The tolerance value was determined to be 1.95 ml.

Production Example 2 Production of Methyl Ethyl Silicate 72.7 g of ethyl alcohol and triethylamine as aliphatic saturated alcohol were added to 829.5 g of MKC silicate 56 (manufactured by Mitsubishi Chemical Corporation, condensate of tetramethoxysilane, average degree of condensation: 10). 0 g, and at about 80 ° C.
Heated to reflux for an hour. Next, the mixture was heated and stirred while distilling the generated methanol out of the system. After cooling, the remaining methanol was distilled off under reduced pressure, and methyl ethyl silicate 79 was removed.
5 g were obtained. The ratio of methyl group to ethyl group determined from the ¹ H-NMR spectrum was 89.5 / 10.5.

Production Example 3 Hydroxyl-containing polyester resin
Powder coating composition containing blocked isocyanate curing agent
Production of product GV-545 (hydroxyl-containing polyester resin manufactured by Nippon Yupika Co., Ltd., hydroxyl value 33, acid value 2.5, number average molecular weight 50
00, weight average molecular weight 56100, glass transition point 56
C) 600 parts, B1530 (block isocyanate curing agent manufactured by Huls) 100 parts, 20 parts of ethyl silicate compound substituted with alcohol of Production Example 1 and 5 parts of benzoin as a surface conditioner were mixed by a Henschel mixer. The mixture is kneaded in a kneader while being heated to 100 to 110 ° C., cooled, pulverized and classified to obtain a volume average particle diameter of 35.
A μm powder coating composition was obtained.

Production Examples 4 to 7 Hydroxyl-containing polyester tree
Powder containing fat and a blocked isocyanate curing agent
Preparation of Powder Composition A powder coating composition having a volume average particle diameter of 35 μm was obtained in the same procedure as in Production Example 2 using the composition shown in Table 1.

Production Example 8 Polyester containing a carboxyl group
Resin and β-hydroxyalkylamide curing agent
Producing acrylic coating 7642 of the powder coating composition (Daicel UCB Co. carboxyl group-containing polyester resin, acid value 35, weight average molecular weight 7800, glass transition point 63 ° C.) 600 parts Primid XL552 (EMS-PRIMD Co. 1,1,
After mixing 30 parts of 8,8-tetra (2-hydroxyethyl) adipamide), 18 parts of the ethyl silicate compound substituted with the alcohol of Production Example 1 and 5 parts of benzoin as a surface conditioner with a Henschel mixer, 100 parts were mixed.
Kneading with a kneader while heating to ~ 110 ° C, and after cooling,
After pulverization and classification, a powder coating composition having a volume average particle diameter of 34 μm was obtained.

Production Examples 9 to 12 Carboxyl group-containing poly
Ester resin and β-hydroxyalkylamide curing agent
Production of a Powder Coating Composition Containing a Powder Coating Composition A powder coating composition having a volume average particle diameter of 35 μm was obtained in the same procedure as in Production Example 9 using the composition shown in Table 2.

<Evaluation of Blocking Resistance> Production Examples 3 to 14
The enamel powder coating composition and the clear powder coating composition obtained in the above were visually evaluated for blocking resistance at 35 ° C. × 1 week. Production Examples 4, 6, 9 and 1
It was confirmed that blocking occurred in the enamel powder coating composition containing a silicate compound and a pigment. No abnormalities were observed in other powder coating compositions.

[0048]

[Table 1]

[0049]

[Table 2]

Examples 1 to 10 Formation of Multi-Layer Coating Film First, a colored coating film was formed on a zinc phosphate-treated steel sheet using the enamel powder coating obtained in Production Example 7 or 12, and further produced in Production Example 3. A clear coating film was formed using the clear powder coating obtained in 5, 8, or 10, to obtain a multilayer coating film. Table 3 shows the types of the enamel powder coating and the clear powder coating used and the method of baking the colored coating and the clear coating. The coating was performed by electrostatic coating using a corona charging type coating gun so that the coating thickness per coating was about 60 μm, and the baking condition was 180 ° C. × 20 minutes.

<Evaluation of Coating Film> The gloss of the obtained multilayer coating film was measured. 90 or more passes. Further, the obtained multilayer coating film has a humidity of 85% or more and a temperature of 5% or more.
After standing for 24 hours in an environment maintained at 0 ° C., the surface water contact angle was measured using a CA-A type contact angle measuring device manufactured by Kyowa Interface Science Co., Ltd. When the angle is less than 60 degrees, the surface is sufficiently hydrophilized and has excellent stain resistance. Further, as Comparative Examples 1 to 4, the enamel powder coating compositions containing the silicate compounds of Production Examples 4, 6, 9, and 11, which had poor blocking resistance, were prepared under the same conditions as in Examples immediately after the production. A coating film was obtained, and the gloss and water contact angle were measured in the same manner as in the example. Table 3 shows the results.

[0052]

[Table 3]

[0053]

According to the method for forming a multilayer coating film of the present invention, coloring and imparting stain resistance to the surface of a substrate can be performed using a powder coating. This solves the problem of adsorption of the silicate compound to the pigment by performing the above-described coloring and imparting stain resistance using different coating films.

In the method for forming a multilayer coating film of the present invention, when the colored coating film and the clear coating film are separately baked, since the clear coating film is located on the upper layer, the powder for obtaining the lower colored coating film is obtained. Since the weather resistance of the binder resin contained in the paint is not an essential requirement, the binder resin can be selected based on a wide range of criteria such as enhancing the properties of other coating films.

Further, it is used for imparting the above-mentioned stain resistance.
If there are many hydroxyl groups in the clear powder coating containing the silicate compound and the silicate compound reacts with the hydroxyl group in the system and the function cannot be fully exhibited, ethyl silicate with a specific water tolerance value Compound,
Alternatively, by using a methylalkyl silicate compound having a specific ratio of a methyl group and an alkyl group having 2 to 6 carbon atoms, a side reaction with the above-mentioned hydroxyl group is controlled, and a multilayer coating film excellent in stain resistance is provided. Can be obtained.

The method for forming a multilayer coating film of the present invention is suitably used for vending machines, switchboards, gas tanks, construction machines, building exterior materials, etc., which are installed outdoors or are easily used outdoors. be able to.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C09D 183/04 C09D 183/04 201/00 201/00 (72) Inventor Tasaburo Ueno Ikeda Nakamachi, Neyagawa City, Osaka 19-17 Inside Nippon Paint Co., Ltd. (72) Inventor Satoshi Urano 19-17 Ikedanakamachi, Neyagawa City, Osaka Prefecture Inside Nippon Paint Co., Ltd. (72) Naoki Furuyama 19-17 Ikedananakacho, Neyagawa City, Osaka Prefecture F-term (reference) in Nippon Paint Co., Ltd. CG161 CG171 CG191 CH031 CH041 CH121 CH171 DA041 DB001 DB061 DB221 DB451 DD051 DD061 DD241 DG301 DL032 GA03 JA39 JA75 JB01 JB18 JB32 KA03 KA08 LA02 LA06 LA07 MA02 MA14 NA05 NA06 PA03 PA07 PA19 PC02 PC08

Claims (8)

[Claims] 1. A stain resistant film formed on a substrate surface by using an enamel powder coating composition and then forming a clear coating film using a clear powder coating composition containing a silicate compound. Method for forming a multilayer coating film with excellent properties. 2. The method according to claim 1, wherein said enamel powder coating composition does not contain a silicate compound. 3. The content of the silicate compound in the clear powder coating composition is 0.2 to 1 with respect to the resin solid content.
The method for forming a multilayer coating film having excellent stain resistance according to claim 1 or 2, which is 0% by weight. 4. The method according to claim 1, wherein the clear coating film is formed after baking the formed colored coating film.
The method for forming a multilayer coating film having excellent stain resistance according to one of the above. 5. The method for forming a multi-layer coating film having excellent stain resistance according to claim 1, wherein the formed colored coating film and the clear coating film are simultaneously baked. 6. The curing system of the clear powder coating composition proceeds with the participation of a hydroxyl group, and the silicate compound is an ethyl silicate compound having a water tolerance value of 2 ml or less with respect to acetone. The method for forming a multilayer coating film having excellent stain resistance according to any one of Items 1 to 5. 7. The curing system of the clear powder coating composition proceeds with the participation of a hydroxyl group, and the silicate compound comprises a methyl group and an alkyl group having 2 to 6 carbon atoms.
The method for forming a multilayer coating film excellent in stain resistance according to any one of claims 1 to 5, which is a methylalkylsilicate compound having a ratio of 0/50 to 98/2. 8. A multi-layer coating film obtained by the method according to claim 1.