JP4273322B2 - Method for forming coating film on plastic substrate - Google Patents

Description

  The present invention relates to a method for forming a coating film on a plastic substrate.

  Conventionally, plastic substrates have been painted by spraying such as air spray or airless spray. However, in order to save energy and reduce the discharge of harmful substances into the environment, many electrostatic coatings with excellent coating efficiency are used. Has been adopted.

Since a plastic substrate generally has a high electric resistance value (usually about 10 ¹² to 10 ¹⁶ Ω / □), it is extremely difficult to directly apply a paint on the plastic surface by electrostatic coating. Therefore, electrostatic coating is usually performed after imparting conductivity to the plastic substrate itself or its surface.

  For example, in electrostatic coating of a paint on a plastic substrate, a conductive primer coating is applied in advance to impart conductivity to the substrate. As the conductive primer paint, a paint containing a resin component and a conductive filler is usually used.

  Conventionally, particles such as conductive carbon, metal, and conductive metal oxide have been used as the conductive filler. Moreover, as the particle shape of the conductive filler, a powdery, needle-like, fibrous or spherical one is usually used.

  When carbon powder or carbon fiber is used as the conductive filler, it is desirable that a conductive effect can be obtained with a relatively small amount because the specific gravity is low. There are problems such as affecting the color tone of the film.

  In addition, although metal powder and metal fibers have high conductivity, the particles need to contact each other in order to form a conductive path in the coating film. The whiteness and the stability of the paint may be impaired.

  In order to give good conductivity, needle-like or fibrous conductive fillers are advantageous, but they are scattered in the air when creating paints or recycling painted plastic substrates. It has a great influence on the human body.

  In addition, when a spherical conductive filler is used, there is a problem in that the amount used is also increased, and the stability of the paint is lowered and the cost is increased.

  On the other hand, conventionally, an undercoat paint containing a volatile conductive material is applied to the surface of a plastic substrate, and an overcoat paint is electrostatically applied to an undried undercoat film in which the volatile conductive material remains. Later, it became possible to realize shortening of the coating process and cost reduction by a coating method in which both coating films were heated and dried (see Patent Document 1). However, the primer coating containing a volatile conductive material has a problem in view of the recent progress of low VOC.

  In addition, a conductive coating composition containing a specific sulfonium salt compound that can impart electrostatic coating suitability to a plastic member and does not affect the hue of the upper layer when a multilayer coating film is formed has been proposed. However (see Patent Document 2), the sulfonium salt compound has an adverse effect on the environment when the coating film is baked or when the coated plastic product is recycled, and the whiteness of the coating film cannot be said to be sufficient.

Also, a coating film forming method for simultaneously baking these three-layer coating films after painting a colored paint, pearl paint and clear paint containing fine scaly mica coated with titanium white pigment and metal oxide on a plastic surface Is known (see Patent Document 3), but a colored coating film having a surface electrical resistance value of less than 10 ⁹ Ω / □ that can be electrostatically coated cannot be obtained with the above-mentioned colored paint. Moreover, it cannot be said that the brightness of the obtained multilayer coating film is sufficient.

  Furthermore, a water-based primer coating is applied to the surface of the plastic material to form a coating film. A colored coating is formed on the primer coating to form a colored coating, and a clear coating is applied to the colored coating. A coating method of a plastic material is known which is formed by forming a clear coating film and then baking the primer coating film, the colored coating film and the clear coating film simultaneously (see Patent Document 4). However, in this method, since the moisture content of the primer coating is usually as high as 50% by weight or more, moisture may remain in the coating film and water resistance may be lowered. It was not expensive.

JP 58-64164 A JP 2001-311047 A JP 2001-29873 A JP-A-10-296171

  The object of the present invention is to apply a water-based white primer coating to a plastic substrate, and then to apply a transparent colored coating and a clear coating by electrostatic coating, and to obtain a multi-layer coating film having high brightness and bright color tone. It is providing the coating-film formation method of a plastic substrate.

  In view of the current state of the prior art, the present inventor has intensively studied to develop a method for forming a coating film on a plastic substrate that can achieve the above object.

As a result, an aqueous white primer coating with a specific range of water content can be formed on a plastic substrate, which can form a coating film having a high whiteness of 80 or more in lightness (L ^* value). In addition, by adjusting the water content and surface electrical resistance value of the primer coating film within a specific range, a transparent colored coating and a clear coating can be applied thereon by electrostatic coating, and a multilayer coating film obtained thereby Has found that the lightness (N value) based on the Munsell color system has a bright color tone of 8.5 or more, and that the multilayer coating film has excellent coating performance such as adhesion and water resistance.

  As a result of further various studies based on the novel findings, the present inventor has completed the present invention.

  That is, the present invention relates to the following coating film forming method for a plastic substrate.

1. (1) A water content of 15 to 48% by weight can be obtained on a plastic base material with a brightness (L ^* value) of 80 or more based on the L ^* a ^* b ^* color system defined in JIS Z 8729. Painting the aqueous white primer paint (A)
(2) The above-mentioned coating film of the primer coating (A) is preheated so that the water content in the coating film is in the range of 1 to 10% by weight and the surface electrical resistance value of the coating film is 10 Adjusting to less than ⁹ Ω / □,
(3) A step of electrostatically coating the thermosetting transparent colored paint (B) on the adjusted coating film of the primer paint (A),
(4) A step of electrostatically applying a thermosetting clear coating (C) on the uncured coating of the colored coating (B), and then (5) the coatings (A), (B) and (C) And a step of obtaining a multilayer coating film having a lightness (N value) of 8.5 or more based on the Munsell color system defined in JIS Z 8721. A method for forming a coating film on a plastic substrate.

2. The coating film according to item 1, wherein the surface electrical resistance value of the coating film of the aqueous white primer coating (A) after the thermosetting transparent coloring coating (B) is applied in step (3) is less than 10 ⁹ Ω / □. Forming method.

  3. Item 2. The method for forming a coating film according to Item 1, wherein in the step (1), the plastic substrate is previously heated to 35 to 60 ° C.

  4). Item 2. The coating film forming method according to Item 1, wherein the aqueous primer white paint (A) is a paint containing a chlorinated polyolefin, a white pigment and water.

  5). Item 5. The coating film forming method according to Item 4, wherein the aqueous white primer paint (A) is a paint further containing a modified resin.

  6). The coated plastic article obtained by the coating-film formation method in any one of said claim | item 1 -5.

  According to the coating film forming method of the present invention, the following remarkable effects can be obtained.

  (1) Based on the high whiteness of the primer coating, it is possible to apply a thermosetting transparent colored coating and a thermosetting clear coating to the plastic substrate by electrostatic coating after applying an aqueous white primer coating. A multilayer coating film having a light color tone with a lightness (N value) of 8.5 or more based on the Munsell color system defined in JIS Z 8721 can be suitably formed. For example, a bright color tone of white pearl can be easily formed on a plastic substrate. Moreover, the obtained multilayer coating film is excellent also in coating film performance, such as adhesiveness and water resistance.

  (2) The coating efficiency of the water-based white primer coating (A) can be applied to both the thermosetting transparent colored coating (B) and the thermosetting clear coating (C) by electrostatic coating. Is good, energy saving, and does not discharge harmful substances into the environment. Moreover, energy saving can be achieved also by being able to form a multilayer coating film by one baking by a 3 coat 1 baking system.

  (3) By adjusting the water content in the coating film of the aqueous white primer paint (A), there is no occurrence of sagging or the like when the primer paint is applied, and the finish is excellent. Further, since the white primer paint is an aqueous type, it is suitable from the viewpoint of VOC reduction and the like.

  (4) Since there is no need to add a needle-shaped conductive filler harmful to the human body or a sulfonium salt compound that adversely affects the environment to the aqueous white primer paint (A), the coated plastic product is excellent in recyclability.

  Hereinafter, the coating film forming method of the present invention will be described in detail.

Plastic base material The plastic base material in the method of the present invention is not particularly limited. For example, various plastic members used for automobile outer plate parts such as bumpers, spoilers, grills, and fenders, and outer plate parts of home appliances. Etc.

  As a material for the plastic substrate, for example, polyolefin obtained by polymerizing at least one olefin having 2 to 10 carbon atoms such as ethylene, propylene, butylene, and hexene is particularly suitable, but is not limited thereto. A material such as polycarbonate, ABS resin, urethane resin, or nylon may be used. Further, these plastic substrates can be appropriately subjected to degreasing treatment, water washing treatment and the like in advance by a method known per se.

Water-based white primer paint (A)
The water-based white primer paint (A) is a paint that is directly applied to a plastic substrate and has a brightness (L ^* value) of 80 or more based on the L ^* a ^* b ^* color system defined in JIS Z 8729. It is a paint that can form a coating film with high whiteness.

In addition, the paint (A) needs to have a moisture content in the range of 15 to 48% by weight. When the water content is within this range, the water content in the coating film can be easily adjusted to a range of 1 to 10% by weight by preheating, such as the water content after this preheating. Therefore, the surface electric resistance value of the coating film can be adjusted to less than 10 ⁹ Ω / □, so that the thermosetting transparent colored paint (B) and the thermosetting clear paint (C) are applied on the coating film. It can be suitably applied by electrostatic coating. The paint (A) preferably has a moisture content in the range of 25 to 45% by weight.

  As the aqueous white primer coating (A), a coating containing chlorinated polyolefin, white pigment and water as essential components can be suitably used.

  The chlorinated polyolefin is a chlorinated polyolefin, and the base polyolefin is, for example, a radical homopolymer or copolymer of at least one olefin selected from ethylene, propylene, butene, methylbutene, isoprene and the like. And radical copolymers of the olefins with vinyl acetate, butadiene, acrylic esters, methacrylic esters and the like. The chlorinated polyolefin can generally have a weight average molecular weight in the range of about 30,000 to 200,000, preferably about 50,000 to 150,000, and the chlorination rate is about 50% by weight or less. Preferably, it is in the range of about 10 to 45% by weight, more preferably about 10 to 35% by weight.

  As the chlorinated polyolefin, chlorinated polyethylene, chlorinated polypropylene, chlorinated ethylene-propylene copolymer, chlorinated ethylene-vinyl acetate copolymer and the like are particularly suitable. Moreover, what graft-polymerized the polymerizable monomer to the chlorinated polyolefin can also be used.

  Examples of the polymerizable monomer to be graft-polymerized include (meth) acrylic acid alkyl ester, (meth) acrylic acid alkoxyalkyl ester, glycidyl (meth) acrylate, an adduct of glycidyl (meth) acrylate and monocarboxylic acid, and hydroxyalkyl. (Meth) acrylate, acrylic acid, methacrylic acid and the like can be mentioned.

  In order to impart water dispersibility to the chlorinated polyolefin, it is also possible to graft polymerize at least one hydrophilic monomer such as polymerizable unsaturated dicarboxylic acid or its anhydride to the chlorinated polyolefin by a known method. it can. A polymerizable unsaturated dicarboxylic acid or an anhydride thereof is a compound having one polymerizable unsaturated bond and two or more carboxyl groups or an anhydride group in one molecule. For example, maleic acid and an anhydride thereof , Itaconic acid and its anhydride, citraconic acid and its anhydride, and the like. The amount of these hydrophilic monomers used is preferably in the range of about 90 to 10% by weight, particularly about 80 to 30% by weight, based on the total amount with the chlorinated polyolefin.

  Graft polymerization of the above monomer to chlorinated polyolefin can be carried out by a method known per se. The amount of the polymerizable unsaturated dicarboxylic acid or its anhydride used is such that the saponification value of the resulting modified chlorinated polyolefin is within the range of about 10 to 60 mgKOH / g, particularly about 20 to 50 mgKOH / g. Is preferred.

  As described above, a chlorinated polyolefin graft-polymerized with a polymerizable unsaturated dicarboxylic acid or an anhydride thereof is partially or entirely amine-containing for the purpose of water-solubilization or water-dispersion. It is preferable to neutralize with a compound.

  Examples of the amine compound include tertiary amines such as triethylamine, tributylamine, dimethylethanolamine, and triethanolamine; secondary amines such as dimethylamine, dibutylamine, and diethanolamine; primary amines such as monoethanolamine. , One or more of these are used. A surfactant may be used in combination with these amine compounds for water-solubilization or water-dispersion.

  As the resin component of the aqueous white primer coating (A), it is necessary to use chlorinated polyolefin from the viewpoint of improving the adhesion of the coating film. The chlorinated polyolefin has flexibility and rigidity of the coating film. A modifying resin for adjusting or improving the film forming property can also be used in combination. As such a modified resin, for example, an acrylic resin, a polyester resin, a polyurethane resin, or the like can be used. In the case of using the modified resin in combination, the use ratio is usually suitably about 10 to 50 parts by weight with respect to 100 parts by weight of the chlorinated polyolefin.

  As the acrylic resin that is the modified resin, a hydroxyl group-containing acrylic resin can be suitably used. Moreover, it is preferable to have a carboxyl group for solubility in water or dispersibility, crosslinkability, and the like.

  The hydroxyl group-containing acrylic resin is obtained by polymerizing a hydroxyl group-containing monomer, a (meth) acrylic acid alkyl ester monomer, and other monomers as required by a known polymerization method such as a solution polymerization method. Can be obtained.

  The hydroxyl group-containing monomer is a compound having a hydroxyl group and a polymerizable unsaturated group, and examples thereof include (meth) acrylic acid such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and the like. Examples thereof include monoesterified products with alkylene glycols having 2 to 10 carbon atoms.

  Examples of (meth) acrylic acid alkyl ester monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. , (Meth) acrylic acid-2-ethylhexyl, (meth) acrylic acid lauryl, (meth) acrylic acid stearyl (meth) acrylic acid and monoesterified products of C1-20 monoalcohol, etc. it can.

  Other monomers include compounds having a polymerizable unsaturated bond other than hydroxyl group-containing monomers and (meth) acrylic acid alkyl ester monomers, such as (meth) acrylic acid and maleic acid. Carboxyl group-containing monomers of the above; epoxy group-containing monomers such as glycidyl (meth) acrylate; (meth) acrylamide, acrylonitrile, styrene, vinyl acetate, vinyl chloride and the like.

  The hydroxyl group-containing acrylic resin usually has a hydroxyl value of about 10 to 100 mgKOH / g, preferably about 50 to 90 mgKOH / g, and an acid value of about 10 to 100 mgKOH / g, preferably about 30 to 60 mgKOH / g. The number average molecular weight is about 2,000 to 100,000, preferably about 3,000 to 50,000.

  The polyester resin that is a modified resin can be usually obtained by an esterification reaction of a polybasic acid and a polyhydric alcohol. A polybasic acid is a compound (including an anhydride) having two or more carboxyl groups in one molecule, and a polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule. Those commonly used in the field can be used. Furthermore, it can be modified with a monobasic acid, a higher fatty acid, an oil component, or the like.

  The polyester resin can have a hydroxyl group, and the introduction can be performed by using a trihydric or higher alcohol together with a dihydric alcohol. Further, the polyester resin may have both a hydroxyl group and a carboxyl group, and generally has a weight average molecular weight in the range of about 1,000 to 100,000, preferably about 1,500 to 70,000. It is preferable.

  As the polyurethane resin that is a modified resin, a hydrophilic polyurethane resin that can be dissolved or dispersed in water can be particularly preferably used. Such a hydrophilic polyurethane resin is prepared by, for example, aliphatic and / or alicyclic diisocyanate, diol having a number average molecular weight of about 500 to 5,000, a low molecular weight polyhydroxyl compound and dimethylolalkanoic acid by a one-shot or multistage method. The urethane prepolymer obtained by the reaction can be obtained by elongation or emulsification after neutralization or while neutralizing, in particular, an average obtained by distilling off part or all of the organic solvent used in the production process An aqueous dispersion of a self-emulsifying polyurethane resin having a particle size of about 0.001 to 1 μm is preferable.

  Examples of commercially available polyurethane resins include “Takelac W610” (trade name, manufactured by Takeda Pharmaceutical Co., Ltd.), “Neolet's R960” (trade name, manufactured by Generalka Resin Co., Ltd.), and “Samprene UX-5100A” (Sanyo Kasei). Kogyo Co., Ltd., trade name) can also be used.

  Examples of the white pigment added to exhibit high whiteness include titanium oxide (rutile type titanium oxide, anatase type titanium oxide, etc.), lead white, zinc white, zinc sulfide, lithopone and the like. Of these, titanium oxide is preferred from the standpoint of chemical resistance and high whiteness. As the white pigment, rutile type titanium oxide having an average particle diameter of about 0.05 to 2.0 μm, particularly about 0.1 to 1.0 μm is most preferable.

  The amount of the white pigment is about 50 to 200 parts by weight, preferably about 70 to 180 parts by weight, based on 100 parts by weight of the solid content of the resin component including the chlorinated polyolefin and, if necessary, the modified resin. Is preferably used.

  The aqueous white primer coating is preferably used as a thermosetting coating by blending a crosslinking agent in order to improve the coating performance such as water resistance. Such crosslinking agents include hydrophilic polyisocyanate compounds having unreacted isocyanate groups, blocked polyisocyanate compounds in which the isocyanate groups of the polyisocyanate compounds are blocked with a blocking agent, melamine resins, epoxy resins, carbodiimide resins, oxazoline compounds, etc. Can be mentioned.

  Examples of hydrophilic polyisocyanate compounds having unreacted isocyanate groups include tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and metaxylylene diisocyanate (MXDI). Aromatic diisocyanates such as hexamethylene diisocyanate (HDI); Cycloaliphatic diisocyanates such as isophorone diisocyanate (IPDI) and hydrogenated MDI; Compounds in a form in which these diisocyanate compounds are made non-volatile and have low toxicity Polyisocyanates such as burettes, uretdiones, isocyanurates or adducts of these diisocyanate compounds; relatively low molecular urethane prepolymers; Things and may include those obtained by hydrophilizing.

  Hydrophilization of the polyisocyanate compound is achieved by, for example, introducing a hydrophilic group such as a carboxyl group, a sulfonic acid group or a tertiary amino group into the compound, and a neutralizing agent such as a hydroxycarboxylic acid such as dimethylolpropionic acid. It can be carried out by neutralization with ammonia, tertiary amine or the like. Also, for example, a polyisocyanate compound can be mixed and emulsified with a surfactant, and used as a so-called self-emulsifying type polyisocyanate compound.

  A commercial item can be used as a hydrophilic polyisocyanate compound. Examples of commercially available products include “Baihijoule 3100” (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., hydrophilic hexamethylene diisocyanurate).

  The blocked polyisocyanate compound is obtained by adding a blocking agent to the isocyanate group of the polyisocyanate compound to form a block.

  Examples of such blocking agents include lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenol compounds such as phenol, para-t-butylphenol and cresol; n -Aliphatic alcohols such as butanol and 2-ethylhexanol; Aromatic alkyl alcohols such as phenyl carbinol and methyl phenyl carbinol; Ether alcohol compounds such as ethylene glycol monobutyl ether.

  Since the polyisocyanate compound is blocked with the blocking agent and then generally hydrophobic, it can be blocked by, for example, dispersing in water using an appropriate emulsifier and / or protective colloid agent. .

  Specific examples of the melamine resin include a methylolated melamine resin obtained by reacting melamine with formaldehyde; a portion obtained by reacting a methylolated melamine resin with a monoalcohol having 1 to 10 carbon atoms, or a fully etherified melamine resin. Can be used. As these melamine resins, those having an imino group can also be used. These can be either hydrophobic or hydrophilic. In particular, a hydrophilic melamine resin having a low degree of condensation and a number average molecular weight of about 3,000 or less, particularly about 100 to 1,500, which is etherified with methanol is suitable. Examples of commercially available hydrophilic melamine resins include “Cymel 303” and “Cymel 325” (both are trade names, manufactured by Cytec Co., Ltd.).

  The epoxy resin is a resin having two or more epoxy groups in one molecule, and is effective for crosslinking and curing chlorinated polyolefin, acrylic resin, polyester resin, polyurethane resin and the like having a carboxyl group.

  Specific examples of the epoxy resin include a copolymer of an epoxy group-containing polymerizable monomer and a vinyl polymerizable monomer. Examples of the epoxy group-containing polymerizable monomer include glycidyl acrylate, glycidyl methacrylate, methyl glycidyl acrylate, and methyl glycidyl methacrylate. Examples of the vinyl polymerizable monomer other than the epoxy group-containing polymerizable monomer include (meth) acrylic acid alkyl ester, acrylonitrile, styrene, vinyl acetate, and vinyl chloride. The copolymerization reaction with these monomers can be carried out by a known method. The resulting polymer has an epoxy equivalent of about 20 to 2,800, particularly about 30 to 700, and a number average molecular weight of 3,000 to 100, About 000, especially within the range of about 4,000 to 50,000 is preferable.

  Furthermore, a glycidyl etherified epoxy resin of bisphenol, a hydrogenated product thereof, a glycidyl etherified epoxy resin of an aliphatic polyhydric alcohol, a glycidyl ester type epoxy resin, an alicyclic epoxy resin, or the like can also be used as a crosslinking agent. The molecular weight of these epoxy resins is preferably in the range of about 250 to 20,000, particularly about 300 to 5,000.

  A commercial item can be used as a carbodiimide resin of a crosslinking agent. As a commercial item, "Carbodilite E-01", "Carbodilite E-02" (all are the Nisshinbo Co., Ltd. make, brand name) etc. can be used, for example.

  The oxazoline compound is a hydrophilic compound having a carboxyl group and effective for crosslinking and curing chlorinated polyolefin, acrylic resin, polyester resin, polyurethane resin and the like. As the hydrophilic oxazoline compound, commercially available “Epocross WS-500” (trade name, manufactured by Nippon Shokubai Co., Ltd.) and the like can be used.

  The amount of these crosslinking agents is usually preferably in the range of about 0 to 50 parts by weight, particularly about 5 to 40 parts by weight per 100 parts by weight of the total solid content of the resin component containing chlorinated polyolefin.

  Since the water-based white primer paint (A) adjusts the moisture content of the coating film within a specific range, it ensures conductivity necessary for electrostatic coating of the paint to be applied on the paint film, Normally, it is not necessary to add a conductive filler that lowers the whiteness of the coating film, but a small amount of a conductive filler may be added as needed. Examples of the conductive filler include tin oxide, antimony-doped tin oxide (ATO), tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), phosphorus-doped tin oxide, zinc antimonate, indium-doped zinc oxide, and oxidation. Examples thereof include conductive metal oxide particles such as ruthenium, rhenium oxide, silver oxide, nickel oxide, and copper oxide.

  The aqueous white primer paint (A) is prepared by dissolving or dispersing the above-described components in water or an aqueous medium that is a mixture of water and an organic solvent by a method known per se. It can be prepared by setting the water content in the content to 15 to 48% by weight. As the aqueous medium, those used at the time of producing each component may be used as they are. In the aqueous medium, the amount of the organic solvent used is preferably as small as possible in order to reduce VOC.

  Examples of the organic solvent used in combination with water include ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as ethylene glycol monobutyl ether; isopropyl alcohol and n-butyl alcohol Alcohol solvents such as isobutyl alcohol; aliphatic hydrocarbon solvents such as n-heptane and n-hexane; aromatic hydrocarbon solvents such as toluene and xylene; other solvents such as N-methyl-pyrrolidone can do.

  The solid content of the aqueous white primer paint (A) is usually preferably about 10 to 80% by weight. Since the white primer paint is an aqueous type, it is suitable from the viewpoint of low VOC and the like.

The water-based white primer paint (A) is a paint that can form a coating film having a high whiteness of 80 or more as a lightness (L ^* value) based on the L ^* a ^* b ^* color system defined in JIS Z 8729. The brightness is a value measured as follows. That is, the paint (A) is obtained by spray-coating a plastic substrate so that the dry film thickness is about 30 to 40 μm, and then heating and drying at a temperature of about 80 to 120 ° C. for about 20 to 40 minutes. The lightness (L ^* value) of the coated film was measured using a color meter, for example, “Color Computer SM-7” manufactured by Suga Test Instruments Co., Ltd.

The lightness (L ^* value) of the coating film of the aqueous white primer paint (A) is preferably 85 or more.

Thermosetting transparent colored paint (B)
As the thermosetting transparent colored paint (B), any paint known per se can be used as the colored paint for the top coat. For example, an acrylic resin or a polyester resin having a crosslinkable functional group such as a carboxyl group or a hydroxyl group. Base resins such as alkyd resins, urethane resins and epoxy resins; cross-linking agents such as polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins and urea resins; and color pigments are dissolved or dispersed in water and / or organic solvents. What was made into a paint can be used conveniently.

  The transparent colored paint (B) is transparent so that the paint film of the lower aqueous white primer paint (A) can be observed through the paint film, as long as the transparency is not hindered. Additives such as pigment components and dyes other than colored pigments can be blended.

  Metallic pigments, mica pigments, extender pigments, and the like can be used as pigment components other than colored pigments. If metallic pigment is used as at least a part of the pigment component, it is possible to form a coating film with a dense metallic tone, and if a mica pigment is used, it forms a silky pearly transparent coating film. can do.

Thermosetting clear paint (C)
As the thermosetting clear paint (C), any paint known per se can be used as the paint for the top clear coat. For example, an acrylic resin, a polyester resin having a crosslinkable functional group such as a carboxyl group and a hydroxyl group, A base resin such as an alkyd resin, urethane resin, or epoxy resin and a cross-linking agent such as a polyisocyanate compound, a blocked polyisocyanate compound, a melamine resin, or a urea resin are dissolved or dispersed in water and / or an organic solvent to form a paint. What was done can be used conveniently.

  The clear paint (C) has transparency so that the paint film of the transparent colored paint (B) as a lower layer and further the paint film of the aqueous white primer paint (A) can be observed through the paint film. Accordingly, color pigments, metallic pigments, extender pigments, dyes, ultraviolet absorbers and the like can be appropriately contained to such an extent that transparency is not hindered.

Each process in a coating-film formation method The coating-film formation method of this invention includes the following process (1)-(5).

(1) A water content of 15 to 48% by weight can be obtained on a plastic base material with a brightness (L ^* value) of 80 or more based on the L ^* a ^* b ^* color system defined in JIS Z 8729. Painting the aqueous white primer paint (A)
(2) The above-mentioned coating film of the primer coating (A) is preheated so that the water content in the coating film is in the range of 1 to 10% by weight and the surface electrical resistance value of the coating film is 10 Adjusting to less than ⁹ Ω / □,
(3) A step of electrostatically coating the thermosetting transparent colored paint (B) on the adjusted coating film of the primer paint (A),
(4) A step of electrostatically applying a thermosetting clear paint (C) on the uncured coating film of the colored paint (B), and then (5) the paints (A), (B) and (C) A step of obtaining a multilayer coating film having a lightness (N value) of 8.5 or more based on the Munsell color system defined in JIS Z 8721.

  Step (1) can be performed by coating the specific aqueous white primer coating (A) on a plastic substrate by a known coating method. Examples of the coating method include air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, and the like. The coating film thickness is usually in the range of about 5 to 45 μm, preferably about 20 to 40 μm, as the dry film thickness.

In the step (2), the primer coating (A) obtained in the step (1) is preheated, and the water content in the coating is within a range of 1 to 10% by weight. And it is the process of adjusting the surface electrical resistance value of a coating film to less than 10 ⁹ Ω / □. In addition, before the preheating, settings may be appropriately performed.

For example, after setting for about 10 seconds to 120 minutes at room temperature, preheating at about 40 to 100 ° C. is performed for about 1 minute to 120 minutes, so that the water content in the coating film is reduced with respect to the total weight of the coating film. It is 1 to 10% by weight, preferably 1 to 8% by weight, more preferably 3 to 5% by weight. As a result, the surface electrical resistance value of the coating film is set to be less than 10 ⁹ Ω / □, preferably in the range of 10 ⁷ to 10 ⁸ Ω / □, and conductivity is imparted to the coating film. (C) can be electrostatically coated. At this time, the water content in the coating film is obtained by measuring the amount of water by the Karl Fischer method (JIS K 0068).

  As a preheating means for adjusting the water content of the coating film after the application of the aqueous white primer paint (A), a conventionally known drying means can be used, for example, air blow, (far) infrared heating, induction heating. Dielectric heating or the like can be used. Further, in the step (1), by heating the base material to about 35 to 60 ° C. in advance, it is possible to use means such as quickening the evaporation of moisture.

Here, when the water content in the coating film after the preheating is less than 1% by weight, the surface electric resistance value cannot be less than 10 ⁹ Ω / □, and electrostatic coating is applied on the coating film. It becomes difficult to apply. On the other hand, if the water content exceeds 10% by weight, the finish performance such as peeling and sagging and the coating film performance such as water resistance are deteriorated when applied to the vertical part of the substrate.

Step (3) is a step of electrostatically coating the thermosetting transparent colored paint (B) on the adjusted coating film of the primer paint (A). The coating film thickness can usually be in the range of about 5 to 30 μm, preferably about 10 to 20 μm, as the cured film thickness. After painting, settings may be made as appropriate. The surface electrical resistance value of the coating film of the aqueous white primer paint (A) after painting the colored paint (B) is also less than 10 ⁹ Ω / □. From the viewpoint of facilitating, it is preferable.

  Step (4) is a step of electrostatically coating the thermosetting clear coating (C) on the uncured coating film of the colored coating (B). The clear coating (C) is applied by electrostatic coating after applying the thermosetting transparent colored coating (B), preheating if necessary. The coating film thickness is usually in the range of about 10 to 40 μm, preferably about 20 to 35 μm, as the cured film thickness. After painting, settings may be made as appropriate.

  In step (5), the three-layer coating film composed of the paints (A), (B) and (C) is baked at the same time, and the lightness (N value) based on the Munsell color system defined in JIS Z 8721 is obtained. It is a step of obtaining a cured multilayer coating film having 8.5 or more. The baking conditions for the three-layer coating film are usually about 80 to 130 ° C. and preferably about 5 to 60 minutes.

  Thus, a multi-layer coating film having a light color tone (N value) based on the Munsell color system of 8.5 or more, more preferably 9.0 or more can be suitably formed by the 3-coat 1-bake method. it can.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. “Parts” and “%” in each example are based on weight.

Production Example 1 Production of Chlorinated Polyolefin for Water-Based Paint Chlorinated polypropylene (chlorine content 15%, maleic acid modification amount 2.0%, saponification value 30 mg KOH / g, weight average molecular weight 80,000) 500 parts, n-heptane 150 parts of N-methyl-pyrrolidone (50 ° C.), 12 parts of dimethylethanolamine and nonionic surfactant (trade name “Neugen EA-140”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) After 5 parts were charged and stirred at the same temperature for 1 hour, 2,000 parts of deionized water were gradually added and further stirred for 1 hour. Next, the pressure was reduced at a temperature of 70 ° C. to distill off a total of 600 parts of n-heptane and deionized water. 1 was obtained.

Manufacture example 2 Manufacture of chlorinated polyolefin for water-based paints Manufacture example using chlorinated polypropylene (chlorine content 35%, maleic acid modification amount 1.9%, saponification value 28 mgKOH / g, weight average molecular weight 60,000) In the same manner as in No. 1, polyolefin emulsion No. 24 having a solid content of 24% was used. 2 was obtained.

Production Example 3 Production of Acrylic Resin Solution for Water-Based Paint Into a reaction vessel equipped with a stirrer, thermometer, reflux condenser, etc., 40 parts of ethylene glycol monobutyl ether and 30 parts of isobutyl alcohol are heated and stirred to reach 100 ° C. Thereafter, a mixture of the following monomers and the like was dropped over 3 hours.

Styrene 10 parts Methyl methacrylate 38 parts n-butyl acrylate 25 parts 2-hydroxyethyl methacrylate 20 parts Acrylic acid 7 parts 2,2'-Azobisisobutyronitrile 1 part Isobutyl alcohol 5 parts.

  After completion of dropping, the mixture was kept at 100 ° C. for 30 minutes, and then an additional catalyst solution which was a mixture of 0.5 part of 2,2′-azobisisobutyronitrile and 10 parts of ethylene glycol monobutyl ether was required for 1 hour. It was dripped. The mixture was further stirred at 100 ° C. for 1 hour, cooled, added with 15 parts of isobutyl alcohol, added with 4 parts of N, N-dimethylaminoethanol at 75 ° C., and stirred for 30 minutes to have a solid content of 50%. Water-soluble hydroxyl group and carboxyl group-containing acrylic resin solution was obtained. The acrylic resin had a hydroxyl value of 86 mgKOH / g, an acid value of 54.5 mgKOH / g, and a number average molecular weight of 20,000.

Production Example 4 Production of Aqueous White Primer Paint Polyolefin Emulsion No. 1 obtained in Production Example 1 1 part 40 parts (solid content), water-soluble acrylic resin 15 parts (solid content) obtained in Production Example 3, urethane emulsion (trade name “Samprene UX-5100A”, Sanyo Chemical Industries, Ltd.) 30 parts ( Solid content), hydrophilic hexamethylene diisocyanurate (trade name “Baihijoru 3100”, manufactured by Sumika Bayer Urethane Co., Ltd.) 15 parts (solid content), rutile titanium oxide (trade name “JR-903”, Teika Co., Ltd.) 130 parts) was mixed and stirred thoroughly with a mixer. 1 was obtained. The paint had a moisture content of 45% and a solids content of 52%.

Production Examples 5-8 Production of Aqueous White Primer Paint In the same manner as in Production Example 4, the aqueous white primer paint no. 2-No. 5 was obtained.

  In Table 1, the compounding component of each primer coating material obtained by manufacture examples 4-8, moisture content, and solid content are shown.

表１における配合割合は、全て固形分の重量部を示す。また、各プライマー塗料の水分含有量及び固形分含量以外の残部は、実質的に有機溶媒である。

All blending ratios in Table 1 indicate parts by weight of solid content. Moreover, the remainder other than the water content and solid content of each primer coating is substantially an organic solvent.

  In Table 1, “Samprene UX-5100A”, “Baihijoule 3100”, “JR-903”, “Ketjen Black EC600J”, and “Dentor WK500” are as follows.

“Samprene UX-5100A”: trade name, manufactured by Sanyo Chemical Industries, Ltd., urethane emulsion,
“Baihijoule 3100”: trade name, manufactured by Sumika Bayer Urethane Co., Ltd., hydrophilic hexamethylene diisocyanurate,
“JR-903”: trade name, manufactured by Teica, rutile titanium oxide,
"Ketjen Black EC600J": trade name, manufactured by Lion Corporation, conductive carbon,
“Dentor WK500”: trade name, manufactured by Otsuka Chemical Co., Ltd., acicular titanium oxide surface-coated with tin oxide / antimony.

Example 1
Step 1: As a plastic substrate, black polypropylene was molded into a bumper shape and then degreased. 1 was applied by air spray so that the dry film thickness was 25 μm. The temperature of the substrate was 25 ° C.

Step 2: The coating film of Step 1 was allowed to stand at room temperature for 1 minute, and then preheated at 80 ° C. for 3 minutes. The water content of the coating film was 3%, and the surface electric resistance value was 1 × 10 ⁸ Ω / □.

  Step 3: The coating film having a water content of 3% obtained in Step 2 is coated with an aqueous thermosetting transparent colored paint (trade name “WBC-710 Mica Base”, manufactured by Kansai Paint Co., Ltd.). The coating was electrostatically coated to 15 μm and set at room temperature for 3 minutes.

  Step 4: Curing organic solvent acrylic resin / urethane resin thermosetting clear paint (trade name “SOFLEX # 520 Clear”, manufactured by Kansai Paint Co., Ltd.) on the uncured transparent colored coating film of Step 3. The film was electrostatically coated so as to have a film thickness of 25 μm, and was allowed to stand at room temperature for 5 minutes for setting.

  Step 5: The three-layer coating film obtained in Step 4 was baked by heating at 120 ° C. for 30 minutes. 1 was formed.

Examples 2-6
Compared with Example 1, except for changing the contents of Table 2 below, the multilayer coating film No. 2-No. 6 was formed.

実施例１〜６において、水性白色プライマー塗膜の予備加熱後の水分含有量、表面電気抵抗値Ｉ、透明着色塗料塗装後の該プライマー塗膜の表面電気抵抗値II及びＪＩＳ Ｚ ８７２９に規定されるＬ^*ａ^*ｂ^*表色系に基づくＬ^*値について、下記試験方法により、調べた。

In Examples 1 to 6, the water content after preheating of the aqueous white primer coating film, the surface electrical resistance value I, the surface electrical resistance value II of the primer coating film after coating with a transparent colored paint, and JIS Z 8729 are specified. The L ^* value based on the L ^* a ^* b ^* color system was examined by the following test method.

  Water content: An aqueous white primer coating was applied, and the water content (%) in the coating film after preheating was measured by the Karl Fischer method (JIS K 0068).

Surface electrical resistance value I: An aqueous white primer coating was applied, and the surface electrical resistance value of the coating film after preheating was measured with an electrical resistance measuring device (trade name “MODEL150” manufactured by TREK). If the measured value is less than 10 ⁹ Ω / □, the transparent colored paint can be electrostatically coated.

Surface electrical resistance value II: Aqueous white primer paint is applied, pre-heated, and then a transparent colored paint is applied. After 1 minute, the surface electrical resistance value of the primer coating is measured by an electrical resistance measuring instrument (manufactured by TREK, product Name “MODEL150”). If the electrical resistance value is less than 10 ⁹ Ω / □, the clear paint can be electrostatically coated.

L ^* value based on L ^* a ^* b ^* color system defined in JIS Z 8729: After drying the coating film of aqueous white primer paint at 120 ° C. for 20 minutes, a color measuring machine (manufactured by Suga Test Instruments Co., Ltd.) The L ^* value was measured using a trade name “Color Computer SM-7”).

  Table 3 shows the test results of the aqueous white primer coating films of Examples 1 to 6.

比較例１
工程１：プラスチック基材として、黒色のポリプロピレンをバンパー形状に成型加工したのち、脱脂処理したものを用い、これに水性白色プライマー塗料Ｎｏ．１を、乾燥膜厚で２５μｍになるようにエアスプレー塗装した。基材の温度は２５℃であった。

Comparative Example 1
Step 1: As a plastic substrate, black polypropylene was molded into a bumper shape and then degreased. 1 was applied by air spray so that the dry film thickness was 25 μm. The temperature of the substrate was 25 ° C.

Process 2: The coating film of the process 1 was left and set at room temperature for 10 seconds. The coating film had a moisture content of 22% and a surface electric resistance value of 1 × 10 ⁶ Ω / □.

  Step 3: The coating film having a moisture content of 22% obtained in Step 2 is coated with an aqueous thermosetting transparent colored paint (trade name “WBC-710 Mica Base”, manufactured by Kansai Paint Co., Ltd.). The coating was electrostatically coated to 15 μm and set at room temperature for 3 minutes.

  Step 4: Curing organic solvent acrylic resin / urethane resin thermosetting clear paint (trade name “SOFLEX # 520 Clear”, manufactured by Kansai Paint Co., Ltd.) on the uncured transparent colored coating film of Step 3. The film was electrostatically coated so as to have a film thickness of 25 μm, and was allowed to stand at room temperature for 5 minutes for setting.

  Step 5: The three-layer coating film obtained in Step 4 was baked by heating at 120 ° C. for 30 minutes. 7 was formed.

Comparative Examples 2-6
Compared with the comparative example 1, the multilayer coating film was formed in the same process except changing the content of the following Table 4.

比較例１〜６において、水性白色プライマー塗膜の予備加熱後の水分含有量、表面電気抵抗値Ｉ、透明着色塗料塗装後の該プライマー塗膜の表面電気抵抗値II及びＪＩＳ Ｚ ８７２９に規定されるＬ^*ａ^*ｂ^*表色系に基づくＬ^*値について、前記実施例の場合と同様にして、調べた。

In Comparative Examples 1 to 6, the water content after preheating of the aqueous white primer coating film, the surface electrical resistance value I, the surface electrical resistance value II of the primer coating film after coating with a transparent colored paint, and JIS Z 8729 are specified. The L ^* value based on the L ^* a ^* b ^* color system was examined in the same manner as in the above example.

In Comparative Example 3, the surface electrical resistance value I is 1 × 10 ¹⁰ Ω / □ and the resistance value is too high, so that the electrostatic coating of the thermosetting transparent colored paint in Step 3 cannot be performed. A multilayer coating film could not be formed.

  Table 5 shows the test results of the aqueous white primer coating films of Comparative Examples 1 to 6.

実施例１〜６及び比較例１〜２で得られた複層塗膜Ｎｏ．１〜Ｎｏ．８、並びに比較例４〜６で得られた複層塗膜Ｎｏ．９〜Ｎｏ．１１について、塗膜外観、ＪＩＳ Ｚ ８７２１に規定されるマンセル表色系に基づくＮ値、付着性及び耐水性の塗膜性能を、下記試験方法により調べた。

The multilayer coating film No. obtained in Examples 1-6 and Comparative Examples 1-2. 1-No. 8, and multilayer coating films No. 1 obtained in Comparative Examples 4-6. 9-No. No. 11, the coating film appearance, N value based on the Munsell color system defined in JIS Z 8721, adhesion and water-resistant coating film performance were examined by the following test methods.

  Appearance of coating film: In the vertical part of the base material, the presence or absence of abnormalities such as sagging, returning and swelling of the coating film was visually evaluated according to the following criteria.

  ◎ indicates that the above abnormality is not observed at all, ○ indicates that the above abnormality is hardly observed, △ indicates that at least one abnormality of sagging, return, and blistering is observed, × indicates sagging, returning, blistering It shows that the occurrence of abnormalities such as

  N value based on Munsell color system defined in JIS Z 8721: N value of Munsell chart was determined in a multi-layer coating film composed of three layers: an aqueous white primer coating film, a transparent coloring coating film and a clear coating film. 0 is black and 10 is pure white.

  Adhesiveness: In a multi-layer coating consisting of three layers: an aqueous white primer coating, a transparent coloring coating, and a clear coating, cut with a cutter to reach the substrate, and make 100 2mm wide gobangs. The pressure-sensitive adhesive tape was adhered to the surface, and the remaining number in 100 Gobanchi coatings after peeling off rapidly at 20 ° C. was examined and evaluated according to the following criteria.

  ○ indicates all adherence remains and has good adhesion, △ indicates adherence with 90 to 99 remaining, and × indicates less than 90 remaining and poor adhesion. , Respectively.

  Water resistance: A multi-layer coating consisting of three layers, an aqueous white primer coating, a transparent coloring coating, and a clear coating, is immersed in warm water at 40 ° C. for 240 hours, then cut with a cutter to reach the substrate, and 2 mm 100 gobangs having a width were made, and an adhesive tape was adhered to the surface, and the number of remaining in 100 gobain coatings after abrupt peeling at 20 ° C. was examined and evaluated according to the following criteria.

  ◎ means that all the gobangs remain and has excellent water resistance, and ○ means that 99 or 99.5 gobangs remain (one is a state of spotting (partially peeled off)) and the water resistance is substantially good. , Δ indicates that the remaining number of Gobanges is 90 to 98 and the water resistance is slightly poor, and × indicates that the remaining number of Gobanges is less than 90 and the water resistance is poor. .

  Table 6 shows the results of the performance test of the multilayer coating film.

Claims (6)

(1) A water content of 15 to 48% by weight can be obtained on a plastic base material with a brightness (L ^* value) of 80 or more based on the L ^* a ^* b ^* color system defined in JIS Z 8729. Painting the aqueous white primer paint (A)
(2) The above-mentioned coating film of the primer coating (A) is preheated so that the water content in the coating film is in the range of 1 to 10% by weight and the surface electrical resistance value of the coating film is 10 Adjusting to less than ⁹ Ω / □,
(3) A step of electrostatically coating the thermosetting transparent colored paint (B) on the adjusted coating film of the primer paint (A),
(4) A step of electrostatically applying a thermosetting clear coating (C) on the uncured coating of the colored coating (B), and then (5) the coatings (A), (B) and (C) And a step of obtaining a multilayer coating film having a lightness (N value) of 8.5 or more based on the Munsell color system defined in JIS Z 8721. A method for forming a coating film on a plastic substrate. The coating film according to claim 1, wherein the surface electrical resistance value of the coating film of the aqueous white primer coating (A) after the thermosetting transparent colored coating (B) is applied in step (3) is less than 10 ⁹ Ω / □. Forming method. The coating film forming method according to claim 1, wherein in step (1), the plastic substrate is heated to about 35 to 60 ° C. in advance. The coating film forming method according to claim 1, wherein the aqueous white primer coating (A) is a coating containing chlorinated polyolefin, a white pigment and water. The coating film forming method according to claim 4, wherein the aqueous white primer paint (A) is a paint further containing a modified resin. The coated plastic article obtained by the coating-film formation method in any one of Claims 1-5.