JP2006111857A - Clear coating composition, forming process of multilayer coating film and decorative molded item - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear coating composition which suppresses corrosion reactions by blending a corrosion inhibitor in the clear layer on a silver plating layer to prevent the contact of corrosive materials such as chloride ion and the like and the silver plating layer and exhibits beautiful silver-plating design for a long period of time and to provide a decorative molded item containing a sliver plating. <P>SOLUTION: This clear coating composition is used to form a sliver plating layer-containing a multilayer coating film obtained by forming a base coating film, a silver plating layer and a clear coating film sequentially on a plastic substrate. The clear coating composition is a two-pack type polyurethane coating comprising a main agent containing an acrylic polyol and a curing agent containing a polyisocyanate compound. The equivalent ratio (NCO/OH) between OH group in the acrylic polyol and NCO group in the polyisocyanate compound is 0.8/1-1.2/1. The clear coating composition contains 1.0-13.0 pts. wt. (in terms of solid content) of a corrosion inhibitor against 100 pts. wt. of the total of the acrylic polyol and the inhibitor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a clear coating composition, a method for forming a multilayer coating film, and a decorative molded product.

Decorative molded products with a silver-plated layer on a plastic material have a metal-like appearance, so automobile interior parts such as meter clusters, center clusters, and center consoles, wheel caps, bumper moldings, foil garnishes, It can be used for exterior parts of automobiles such as grill radiators, back panels, door mirror covers, door handles, etc., applications other than automobile parts such as air conditioner housings, mobile phones, notebook computers and cosmetic containers.

However, the decorative multi-layer coating film including the silver plating layer loses its original design value due to discoloration of the silver plating layer or turbidity due to long-term aging during coating performance evaluation such as salt spray test. Have the problem of

As a method for improving such a problem, Patent Document 1 describes a method for manufacturing a plated product including a step of artificially removing a trace amount of impurities present on a metal surface. However, this method is not efficient because the number of steps increases, and the effect is not sufficient.

Patent Document 2 discloses a plating product that prevents the deterioration of designability by preventing the corrosion from spreading to the entire metal plating when the metal is corroded by intentionally forming micro cracks in the metal plating layer. Are listed. However, since such a method is not essentially a method for preventing metal corrosion itself, the effect is limited, and a beautiful appearance cannot be maintained for a sufficiently long period of time.

Patent Document 3 describes a method of suppressing metal corrosion by suppressing the penetration of moisture into the metal plating layer by providing a coating layer made of a specific silicon acrylic resin. However, it is desired to further improve the effect and prevent corrosion at a higher level.

JP 2002-256454 A JP 2002-256455 A JP 2003-155580 A

The present invention contains a rust preventive agent in the clear layer on the silver plating layer, prevents corrosion reaction by corrosive substances such as chloride ions and the silver plating surface layer, suppresses the corrosion reaction, and expresses a beautiful silver plating design for a long time It is an object of the present invention to provide a decorative molded product including a clear coating composition and a silver plating layer.

The present invention is a clear coating composition used in the formation of a multilayer coating film comprising a silver plating layer formed by sequentially forming a base coating layer, a silver plating layer, and a clear coating layer on a plastic substrate. A two-component polyurethane paint comprising a main agent containing an acrylic polyol and a curing agent containing a polyisocyanate compound, and an equivalent ratio of an OH group in the acrylic polyol and an NCO group in the polyisocyanate compound ( (NCO / OH) is 0.8 / 1 to 1.2 / 1, and the content of the rust inhibitor is 1.0 to 13.0 parts (solid content) with respect to 100 parts by mass of the acrylic polyol and the rust inhibitor. (Clear coating composition) characterized in that it is contained at a ratio of (mass conversion).
The main agent is an acrylic polyol, a non-aqueous dispersion resin and the following general formula (1);

(Wherein R ¹ represents a methyl group, a methoxy group or an ethoxy group, and R ² and R ³ are the same or different and represent a methoxy group or an ethoxy group) It may be.
The rust inhibitor is preferably a fatty acid amide compound.

The present invention relates to a method for forming a multi-layer coating film comprising a silver plating layer formed by sequentially forming a base coating layer, a silver plating layer, and a clear coating layer on a plastic substrate. Is also a method for forming a multilayer coating film characterized by being formed by the above-mentioned clear coating composition.

Even a decorative molded product including a silver plating layer, which is obtained by sequentially forming a base coating layer, a silver plating layer and a clear coating layer formed by the above-described corrosion-resistant clear coating on a plastic material. is there.
The decorative molded product preferably further has a primer layer between the plastic material and the base coating film layer.
The present invention is described in detail below.

The clear coating composition of the present invention is a clear coating composition containing a rust inhibitor. That is, by containing a rust inhibitor, discoloration of silver by corrosive substances such as chlorine ions is prevented. The rust inhibitor is preferably compatible with the main component of the two-component polyurethane paint. The use of the rust preventive as described above is preferable in that corrosion can be prevented while maintaining the transparency of the clear coating film.

Examples of the rust preventive agent include fatty acid amide compound rust preventive agents, benzothiazole rust preventive agents, and ketocarboxylic acid rust preventive agents. A fatty acid amide compound is particularly preferable in terms of particularly excellent compatibility with the main component of the two-component polyurethane paint.

Examples of the fatty acid amide compound include commercially available products such as Nopco Checks RA (trade name: manufactured by San Nopco).

The benzothiazole-based rust preventive is a compound having a benzothiazole skeleton containing succinic acid in the molecule. For example, 1- (benzothiazol-2-ylthio) succinic acid, (2-benzothiazol-2-yl- And thio) succinic acid di- (C12-C14 alkyl ammonium salt). Examples of commercially available benzothiazole-based rust preventives include Irga Core 252LD, Irga Core 153 (both trade names: Ciba Specialty Chemicals).

The ketocarboxylic acid rust inhibitor is a compound having a ketocarboxylic acid skeleton. Specifically, for example, an addition reaction product of 4-methyl-γ-oxo-benzenebutanoic acid and N-ethylmorpholine is known. Examples of commercially available products include Irga Core 1405 (trade name: Ciba Specialty Chemicals).

The said rust preventive agent is contained in the ratio of 1.0-13.0 mass parts (solid content mass conversion) with respect to the total amount of an acrylic polyol and a rust preventive agent. When the content of the rust inhibitor is less than 1.0 part by mass, the corrosion reaction cannot be sufficiently suppressed, and the discoloration cannot be sufficiently prevented. When the content of the rust inhibitor exceeds 13.0 parts by mass, the clear coating film is colored and the coating film adhesion is also lowered. The addition amount of the rust inhibitor is more preferably 2.0 to 10.0 parts by mass.

The clear coating composition of the present invention is a two-component polyurethane coating composed of a main agent containing an acrylic polyol and a curing agent containing a polyisocyanate compound. A two-component polyurethane paint comprising a main component containing an acrylic polyol and a curing agent containing a polyisocyanate compound has excellent properties in terms of water-resistant secondary adhesion, corrosion resistance, and the appearance of a decorative molded product. .

The acrylic polyol contained in the main agent for clear coating composition is not particularly limited as long as it is an acrylic resin containing a hydroxyl group, and may be modified.
The hydroxyl value of the acrylic polyol is preferably 35 to 85 mgKOH / g, more preferably 40 to 75 mgKOH / g. If it is less than 35 mg KOH / g, there may be insufficient crosslinking reaction points with the polyisocyanate curing agent, resulting in insufficient film physical properties. If it exceeds 85 mg KOH / g, there are too many crosslinking reaction points, In some cases, it becomes hard and brittle, and the moisture resistance and water resistance of the coating film are lowered due to excessive hydroxyl groups, which is not preferable.

The weight average molecular weight of the acrylic polyol is preferably in the range of 10,000 to 60,000, more preferably 10,000 to 40,000. If it is less than 10,000, the physical properties of the coating film tend to be lowered. If it exceeds 60000, the coating workability is lowered and the finished appearance tends to be lowered. In the present specification, the weight average molecular weight is a value measured by GPC (gel permeation chromatography) and calculated by a polystyrene conversion method, for example.

The acrylic polyol can be obtained by polymerizing a monomer composition comprising a hydroxyl group-containing radical polymerizable monomer and other radical polymerizable monomers used as necessary by a conventional method.

The hydroxyl group-containing radical polymerizable monomer is not particularly limited, and examples thereof include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypropyl (meth) acrylate, and 2-hydroxyethyl (meth) acrylate. Examples include ring-opened rings with ε-caprolactone (Placcel FA and FM series manufactured by Daicel Chemical Industries). These may be used alone or in combination of two or more.

The other radical polymerizable monomers are not particularly limited, and examples thereof include carboxylic acid group-containing monomers such as (meth) acrylic acid, maleic acid and itaconic acid, and epoxy group-containing monomers such as glycidyl (meth) acrylate, methyl (Meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, styrene, vinyltoluene, vinyl acetate, α-methylstyrene and the like. it can. These may be used alone or in combination of two or more.

An acrylic polyol can be obtained by polymerizing the monomer composition, and a conventionally known method for producing an acrylic resin can be used as a method for producing the acrylic polyol. That is, although a polymerization method such as solution polymerization, non-aqueous dispersion polymerization, and bulk polymerization can be used, the solution polymerization method is suitable from the viewpoint of ease of polymerization, molecular weight adjustment, and ease of use when forming a paint. .

A commercially available thing can also be used as said acrylic polyol. As a commercially available acrylic polyol, for example, Dianal LR-2586 (trade name, manufactured by Mitsubishi Rayon Co., Ltd .; hydroxyl value: 60 mgKOH / g, weight average molecular weight: 30,000, Tg: 40 ° C., acid value: 3 mgKOH / g) , Acryset 2050-55 (trade name, Nippon Shokubai Co., Ltd.), Hitaroid 3371 (trade name, manufactured by Hitachi Chemical Co., Ltd.) and the like.

The main agent is one constituent component of the two-component polyurethane paint and contains the acrylic polyol. The main agent may further contain, in addition to the acrylic polyol, a non-aqueous dispersion resin, an epoxy silane compound, a surface conditioner, a light stabilizer, an ultraviolet absorber, a curing catalyst, an antisettling agent, and the like.

The non-aqueous dispersion resin is a resin dispersed in an organic solvent, and is usually called NAD. The non-aqueous dispersion resin is not particularly limited, and any non-aqueous dispersion resin that can be used in the paint field, such as acrylic, acrylic polyol, and acrylic styrene, can be used.

The hydroxyl value of the non-aqueous dispersion resin is preferably 0 to 250 mgKOH / g, more preferably 100 to 190 mgKOH / g. When it exceeds 250 mgKOH / g, there are too many crosslinking reaction points, the coating film becomes hard and brittle, or the moisture resistance and water resistance of the coating film decrease due to excessive hydroxyl groups, which may be undesirable.

Examples of commercially available non-aqueous dispersion resins include Cetalux 1850SS-50 (manufactured by Akzo Nobel) and Hitaroid 6110 (manufactured by Hitachi Chemical Co., Ltd.).

When the main component in the clear coating composition of the present invention contains a non-aqueous dispersion resin, the solid content mass ratio of the non-aqueous dispersion resin and the acrylic polyol [(non-aqueous dispersion resin) / (acrylic polyol)]. Is preferably 5/95 to 25/75. If it is less than 5/95, adhesion to the silver plating layer and corrosion resistance may be reduced. If it exceeds 25/75, there is a risk that dust will occur. More preferably, it is 5/95 to 20/80.

As said epoxy silane, following General formula (1);

(Wherein R ¹ represents a methyl group, a methoxy group or an ethoxy group, and R ² and R ³ are the same or different and represent a methoxy group or an ethoxy group.)

The compound represented by these is preferable. The epoxysilane represented by the general formula (1) is a compound that acts as a coupling agent. Examples of the epoxy silane include 3-glycidoxypropyltrimethoxysilane (available from Shin-Etsu Chemical Co., Ltd. as KBM403), 3-glycidoxypropylmethyldiethoxysilane (commercially available as Shin-Etsu Chemical Co., Ltd. as KBE402), and 3-glycidide. And xylpropyltriethoxysilane (commercially available as KBE-403 from Shin-Etsu Chemical Co., Ltd.).

In the main agent in the clear coating composition for decorative molding of the present invention, the solid content mass ratio [(epoxysilane) / [(acrylic polyol) of the epoxysilane and the total amount of the acrylic polyol and the non-aqueous dispersion resin. ) + (Non-aqueous dispersion resin)]] is preferably 1.5 / 100 to 5.5 / 100. If it is less than 1.5 / 100, adhesion to the silver plating layer and corrosion resistance may be reduced. If it exceeds 5.5 / 100, it is disadvantageous from the viewpoint of economy. It is more preferable that it is 2.0 / 100-4.0 / 100.

When the solid content mass ratio of the acrylic polyol, epoxy silane, and non-aqueous dispersion resin is defined within the above-described range, the adhesion, corrosion resistance, silver precipitation, smoothness of the base coating layer, and the appearance of the laminated molded product are further improved. Can be improved.

The polyisocyanate is not particularly limited as long as it is a compound having two or more isocyanate groups. For example, aromatic compounds such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate Aliphatic groups such as hexamethylene diisocyanate; alicyclic groups such as isophorone diisocyanate; monomers thereof and multimers such as burette type, nurate type and adduct type.

Commercially available products of the above polyisocyanates include Duranate 24A-90PX (NCO: 23.6%, trade name, manufactured by Asahi Kasei Co., Ltd.), Sumijour N-3200-90M (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.), Takenate D165N- 90X (trade name, manufactured by Mitsui Takeda Chemical Co., Ltd.), Sumijoule N-3300, Sumijoule N-3500 (both trade names, manufactured by Sumitomo Bayer Urethane Co., Ltd.), Duranate THA-100 (trade name, manufactured by Asahi Kasei) Can be mentioned.

In the clear coating composition, the equivalent ratio (NCO / OH) of the NCO group in the clear curing agent to the OH group in the clear acrylic polyol is 0.8 / 1 to 1.2 / 1. is there. If it is less than 0.8 / 1, the coating strength of the clear coating will be insufficient. If it exceeds 1.2 / 1, the adhesion becomes insufficient. The equivalent ratio (NCO / OH) is more preferably 0.9 / 1 to 1.1 / 1.

The method for forming a multilayer coating film according to the present invention is such that a base coating film layer, a silver plating layer, and a clear coating film layer are sequentially formed on a plastic substrate. That is, a base coating layer, a silver plating layer and a clear coating layer are formed on a plastic material of a molded product having a specific shape, such as an injection molded product made of a plastic material, a plate such as a film or a sheet, or a blow molded container A molded product having a coating film formed by the method for forming a multilayer coating film of the present invention, which is a sequential forming method, exhibits a metal-like appearance by a silver plating layer.

The base coating layer is formed using a base coating composition. The base paint composition is not particularly limited, and examples thereof include polyurethane resin paints, acrylic resin paints, silicone resin paints, epoxy resin paints, alkyd resin paints, aminoalkyd resin paints, and the like. . Among these, it is preferable to use a two-component curable polyurethane resin-based paint from the viewpoint of water-resistant secondary adhesion, corrosion resistance, appearance of a decorative molded product, and the like.

The two-component curable polyurethane resin coating used as the base coating composition comprises a main agent containing an acrylic polyol and a curing agent containing a polyisocyanate compound, as in the clear coating composition of the present invention. Is. The main component of the base coating composition may contain an organic modified polydimethylsiloxane or an epoxysilane compound in addition to the acrylic polyol.

The acrylic polyol contained in the base main agent is not particularly limited as long as it is an acrylic resin containing a hydroxyl group, and may be modified.
The hydroxyl value of the acrylic polyol contained in the base main agent is preferably 60 to 140 mgKOH / g, more preferably 70 to 100 mgKOH / g. If it is less than 60 mgKOH / g, the crosslinking reaction point with the polyisocyanate curing agent may be insufficient, and the physical properties of the coating film may be insufficient. If it exceeds 140 mgKOH / g, there are too many crosslinking reaction points. In some cases, it becomes hard and brittle, and the moisture resistance and water resistance of the coating film are lowered due to excessive hydroxyl groups, which is not preferable.

The weight average molecular weight of the acrylic polyol contained in the base main agent is preferably 10,000 to 70,000, more preferably 15,000 to 50,000. If it is less than 10,000, the physical properties of the coating film tend to be lowered. If it exceeds 70,000, the coating workability is lowered and the finished appearance tends to be lowered. In the present specification, the weight average molecular weight is a value measured by GPC (gel permeation chromatography) and calculated by a polystyrene conversion method, for example.

The acrylic polyol contained in the base main agent can be obtained by polymerizing a monomer composition comprising a hydroxyl group-containing radical polymerizable monomer and other radical polymerizable monomers used as necessary by a conventional method.

The hydroxyl group-containing radical polymerizable monomer and other radical polymerizable monomers are not particularly limited, and the monomers exemplified as being usable for the synthesis of acrylic polyols used in the main component of the clear coating composition are used. be able to. These may be used alone or in combination of two or more. The polymerization method can also be carried out in the same manner as the acrylic polyol used as the main ingredient of the clear coating composition.

An acrylic polyol can be obtained by polymerizing the monomer composition, and a conventionally known method for producing an acrylic resin can be used as a method for producing the acrylic polyol. That is, although a polymerization method such as solution polymerization, non-aqueous dispersion polymerization, and bulk polymerization can be used, the solution polymerization method is suitable from the viewpoint of ease of polymerization, molecular weight adjustment, and ease of use when forming a paint. .

The acrylic polyol may be an alkyd-modified acrylic polyol resin. The alkyd-modified acrylic polyol resin is obtained by polymerizing a polymerization reaction of the monomer in the presence of the alkyd resin.

As a commercial item of the said alkyd modified acrylic polyol resin, for example, ACRYDIC WZU-771, ACRIDIC LU-293 (all manufactured by Dainippon Ink and Chemicals), Tesroid 4220-50 (manufactured by Hitachi Chemical) Can be mentioned.

The organically modified polydimethylsiloxane that can be added to the base agent is a polydimethylsiloxane modified with an organic compound, and is a compound used as a high molecular weight surface conditioner. The organic-modified polydimethylsiloxane is not particularly limited, and examples thereof include polyester-modified acrylic group-containing polydimethylsiloxane and polyether-modified polydimethylsiloxane. These may be used alone or in combination of two or more.

The weight average molecular weight of the organically modified polydimethylsiloxane is preferably in the range of 10,000 to 50,000, more preferably 10,000 to 35,000. If it is less than 10,000, the physical properties of the coating film tend to be lowered. If it exceeds 70,000, the coating workability is lowered and the finished appearance tends to be lowered.

Examples of commercially available organic modified polydimethylsiloxanes include polyester-modified acrylic group-containing polydimethylsiloxanes such as BYK-371 and BYK-307 (both manufactured by Big Chemie Japan), polyether-modified polydimethylsiloxanes, and the like. be able to.

As the epoxy silane compound that can be added to the base main agent, the same compounds as those exemplified as the epoxy silane compound that can be used in the clear coating composition can be used.

When the organic modified polydimethylsiloxane is used in the base agent, the solid content mass ratio [organic modified polydimethylsiloxane / acrylic polyol] of the organic modified polydimethylsiloxane and the acrylic polyol is 0.02 / 100 to 0.20 / 100 is preferable. If it is less than 0.02 / 100, the silver depositability and the smoothness of the base coating layer may be lowered. If it exceeds 0.20 / 100, the adhesion, corrosion resistance, and water resistance between the base coating layer and the silver plating layer may be reduced. It is more preferable that it is 0.04 / 100-0.16 / 100.

When the epoxy silane is used in the base agent for the base, the solid content mass ratio [epoxy silane / acrylic polyol] between the epoxy silane and the acrylic polyol is 1.5 / 100 to 5.5 / 100. It is preferable that If it is less than 1.5 / 100, the adhesion between the base coating layer and the silver plating layer and the corrosion resistance may be reduced. If it exceeds 5.5 / 100, a rainbow may occur in the decorative molded product. It is more preferable that it is 2.0 / 100-5.0 / 100.

The base agent for base can be obtained by mixing and stirring the above components by known means. In addition, if necessary, pigments such as colored pigments, extender pigments and glittering materials; solvents such as butyl acetate, toluene, xylene, and methyl isobutyl ketone; ultraviolet absorbers, antioxidants, curing catalysts, and anti-settling agents You may add components, such as additives.

In the base coating composition, the equivalent ratio (NCO / OH) of the NCO group in the base curing agent and the OH group in the acrylic polyol is preferably 1.5 to 3.0. If it is less than 1.5, the adhesion between the base coating film layer and the silver plating layer and the corrosion resistance may be reduced, and a rainbow may be generated in the decorative molded product. If it exceeds 3.0, a rainbow may occur in the decorative molded product. The equivalent ratio (NCO / OH) is more preferably 1.5 to 2.5.

The base curing agent is preferably composed of a polyisocyanate compound. It does not specifically limit as said polyisocyanate compound, For example, the compound illustrated as what can be used in the clear coating composition mentioned above can be used.

When the base coating composition is a two-component polyurethane coating composition composed of a base main component and a base curing agent, the base coating layer is formed by mixing the two components immediately before use. Can be formed. Formation of the base coating film layer by the application of the base coating composition can be performed by an ordinary method such as spray coating. After coating, it is preferable to perform heat curing at 60 to 100 ° C. to obtain a coating film with a cured film thickness of 20 to 30 μm.

The formation method of the multilayer coating film of this invention forms a silver plating layer on the said base coating film layer. By forming a silver plating layer on the base coating layer, it is possible to form a silver plating layer with good silver precipitation and excellent appearance and adhesion.

In the plating coating process, 0.1 to 3% by mass of a stannic chloride (SnCl ₂ ) solution of 0.1 to 3% by mass is applied or immersed in the molded product on which the base coating layer after drying is formed, and tin is used as the base coating layer. It is preferable to have a process of adsorbing to the surface. By performing the above steps, the silver mirror adheres well. Subsequently, it is preferable that the surface of the molded product is washed with ion-exchanged water or distilled water to remove excess tin chloride that has not been adsorbed. This is preferable in that corrosion, discoloration, and the like of the plating layer of the silver mirror can be suppressed more favorably. Note that palladium (Pd) may be used instead of tin.

The formation method of a silver plating layer is not specifically limited, It can carry out by the electroless plating method called a silver mirror reaction. As the most general method, an ammoniacal silver nitrate ([Ag (NH ₃ ) ₂ ] ⁺ OH ⁻ ) called a Trens reagent and a reducing agent solution are applied so as to be mixed on the surface of the base coating layer. A method can be mentioned. The reducing agent is not particularly limited, and examples thereof include sugars such as glucose; organic compounds having an aldehyde group such as glyoxal; sodium nitrite and sodium thiosulfate.

In the method for forming a multilayer coating film of the present invention, a clear coating film layer is provided on the silver plating layer. This prevents deterioration of the silver plating layer, improves the corrosion resistance, and further improves the appearance of the laminated molded product. In the decorative molded product of the present invention, the clear coating layer is formed using the above-mentioned clear coating composition.

The clear coating composition is a mixture prepared by mixing the above-mentioned components immediately before use. The formation of the clear coating layer by the application of the clear coating composition can be performed by a usual method such as spray coating. After coating, it is preferable to carry out heat curing at 60 to 100 ° C. to obtain a coating film having a cured film thickness of 20 to 40 μm. There exists a possibility that corrosion resistance and an external appearance may deteriorate that a dry film thickness is less than 20 micrometers. When the dry film thickness exceeds 50 μm, it is not preferable in terms of sagging and peeling. The dry film thickness of the clear coating layer is more preferably 25 to 35 μm.

The plastic material to which the method for forming a multilayer coating film of the present invention is applied is not particularly limited. For example, ABS (acrylonitrile / butadiene / styrene copolymer), PC (polycarbonate) / ABS alloy, PP (polypropylene), olefin Examples thereof include a thermoplastic elastomer (TPO), PMMA (polymethyl methacrylate), and TPE (thermoplastic elastomer). These can be molded by a known molding method such as an injection molding method, an extrusion molding method, or a blow molding method.

The plastic material may have a primer layer between the base coating film layer and the material surface. By forming the primer layer, the adhesion between the base coating layer and the material surface can be improved. In particular, when using an olefin plastic material having poor adhesion such as polypropylene, it is preferable to have a primer layer.

The primer layer can be formed by applying a primer paint. As the primer paint, a chlorinated polypropylene primer paint is preferably used, and examples thereof include RB116 primer paint (manufactured by Nippon B Chemical Co., Ltd.).

A decorative molded product having a multilayer coating film formed by the above-described method for forming a multilayer coating film of the present invention is also a part of the present invention. The decorative molded product of the present invention includes, for example, automobile interior parts such as meter clusters, center clusters, and center consoles, automobiles such as wheel caps, bumper moldings, foil garnishes, grill radiators, back panels, door mirror covers, and door handles. It can be suitably used for applications other than automobile parts such as exterior parts, air conditioner housings, mobile phones, notebook computers, cosmetic containers and the like.

By using the clear coating composition of the present invention, it is possible to suppress the problem that the silver plating is discolored or white and turbid and deteriorates the design property, and a multilayer that can express a beautiful silver plating design for a long period of time. A coating film can be obtained.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail, this invention is not limited only to these Examples. In the examples, “part” means “part by mass” unless otherwise specified, and “%” means “% by mass” unless otherwise specified.

(Preparation of base solution for base)
An acrylic polyol was placed in a container equipped with a stirrer, and organically modified polydimethylsiloxane and epoxysilane were added while stirring, and finally butyl acetate was added and stirred for 30 minutes to obtain a base solution for base. In addition, the compounding quantity of each raw material was shown in Table 1. In Table 1, “Acridic WZU-771” is an acrylic polyol manufactured by Dainippon Ink & Chemicals, Inc., having an OH value of 84 mg KOH / g, a weight average molecular weight of 20000, a solid content of 50%, and an acid value of 5 mg KOH / g. It is a modified acrylic resin. “BYK-371” is a polyester-modified acrylic group-containing polydimethylsiloxane manufactured by Big Chemie Japan, and has a weight average molecular weight of 28000 and an OH value of 0 mgKOH / g. “KBM-403” is 3-glycidoxypropyltrimethoxysilane (epoxy equivalent 236) manufactured by Shin-Etsu Chemical Co., Ltd. Numerical values in Table 1 represent parts by mass.

Preparation of clear paint main agent liquid (Examples 1-4, Comparative Examples 1-4)
Acrylic polyol, rust inhibitor and butyl acetate are put into a container equipped with a stirrer, and a 90% by weight xylene solution of surface conditioner, sanol LS-292 and tinuvin 384 is added with stirring and stirred for 30 minutes. A base solution was obtained.
Acrylic polyol: Dianal LR-2586 / manufactured by Mitsubishi Rayon Co., Ltd .; hydroxyl value: 60 KOH mg / g, weight average molecular weight: 30,000, Tg: 40 ° C., acid value: 3 KOH mg / g
Surface conditioner: SH2000-100CS / manufactured by Toray Dow Corning Silicone.
Sanol LS-292: Light stabilizer made by Sankyo.
Tinuvin 384: UV absorber manufactured by Ciba Specialty Chemicals.

Preparation of clear coating liquid (Example 5)
Acrylic polyol, rust inhibitor and butyl acetate are put in a container equipped with a stirrer, and a 90% by mass xylene solution of epoxy silane, surface conditioner, Sanol LS-292, Tinuvin 384 is added with stirring, and finally non-aqueous The dispersion resin was added and stirred for 30 minutes to obtain a clear coating liquid.
Acrylic polyol: Dianal LR-2586 / manufactured by Mitsubishi Rayon Co., Ltd .; hydroxyl value: 60 KOH mg / g, weight average molecular weight: 30,000, Tg: 40 ° C., acid value: 3 KOH mg / g
Non-aqueous dispersion resin: Setarax 1850SS-50 / Akzo Nobel acrylic NAD. OHV: 169 mg KOH / g. NV: 50%.
Epoxysilane: KBM403 / manufactured by Shin-Etsu Chemical Co., Ltd. 3-Glycidoxypropyltrimethoxysilane. Epoxy equivalent: 236.
Surface conditioner: SH2000-100CS / manufactured by Toray Dow Corning Silicone.
Sanol LS-292: Light stabilizer made by Sankyo.
Tinuvin 384: UV absorber manufactured by Ciba Specialty Chemicals.

In Table 2, the curing agent solution for clear paint, the polyisocyanate compound is obtained by diluting Duranate 24A-90PX (trade name, manufactured by Asahi Kasei Co., Ltd .: NCO: 23.6%) with acetic acid butyl ester to NV = 70% by mass. .

(Creation of specimen)
Pretreatment of polypropylene substrate 70 × 100 × 3 mm polypropylene substrate was washed with isopropanol and dried, then chlorinated polypropylene primer diluted paint was spray coated to a dry film thickness of 7 μm and dried at 80 ° C. for 10 minutes. . In addition, the chlorinated polypropylene-type primer dilution paint used what diluted 100 parts of RB-116 (made by Nippon Bee Chemical) with the following dilution solvent A40 part. Diluent A is a solvent mixed at a ratio of 20 parts of toluene, 20 parts of xylene, and 60 parts of Ipsol (a hydrocarbon solvent manufactured by Marubeni Chemix Co., Ltd.) (100 parts in total).

Pretreatment of ABS substrate A 70 × 100 × 3 mm ABS substrate was washed with isopropanol and dried.

Formation of base layer On the polypropylene substrate or ABS substrate subjected to the above pretreatment, a two-component curable polyurethane base diluted paint is spray-coated to a dry film thickness of 25 μm and dried at 80 ° C. for 30 minutes. A test piece on which a base layer was formed was obtained. The two-component curable polyurethane-based diluted coating is composed of 248.98 parts of an acrylic polyol-based main agent solution, 248.98 parts of diluent solvent B (total of 497.96 parts), and 76.3 parts of a curing agent liquid A. A total of 574.26 parts was used. Diluent B is a solvent mixed at a ratio of 35 parts of butyl acetate, 10 parts of methyl isobutyl ketone, 33 parts of xylene, and 22 parts of ipsol (100 parts in total). The curing agent liquid A is a solution in which 75 parts of Sumijour N-3300, which is a commercially available polyisocyanate compound, and 25 parts of butyl acetate are mixed.

Formation of Silver Plating Layer A 0.2% hydrochloric acid solution of 0.2% tin (II) chloride was applied to the surface of the coating film on the test piece on which the base layer was formed, and then washed with water. By simultaneously applying a mixed aqueous solution of silver nitrate and excess ammonia and a glucose solution on the test piece after washing with water on the test piece, a uniform silver plating film of about 20 μm is formed, and the residue is removed by washing with water. A test piece having a silver plating layer formed on the base layer was obtained.

Formation of Clear Layer A paint base liquid and a curing agent liquid shown in Table 2 were mixed to obtain a clear paint. On the test piece on which the silver plating layer was formed, these clear paints were spray-coated so as to have a cured film thickness of 30 μm and cured at 80 ° C. for 20 minutes to obtain a test piece on which a clear layer was formed.
The obtained test piece was evaluated by the following evaluation method. The results are shown in Table 2.

(Evaluation methods)
After being immersed in a 5% aqueous solution of sodium chloride at 40 ° C. for 10 days and then taken out, washed with water and wiped off the surface water, the surface condition was visually observed.
○: Silver plating film is in good condition with no abnormalities such as discoloration, white turbidity, desorption, etc. ×: Abnormalities such as discoloration, white turbidity, desorption, etc. are observed in the silver plating film

The appearance of the test pieces of Examples and Comparative Examples was observed based on the following criteria by visual observation of the appearance of the coating film.
○: No appearance abnormality such as interference fringes and turbidity.
X: Appearance abnormalities such as interference fringes and turbidity are observed.

Adhesiveness: Secondary adhesion to hot water After immersion in hot water of 40 ° C. for 10 days, the surface water was wiped off and left at 25 ° C. for 1 hour. Thereafter, 100 squares of 2 mm square were put with a cutter knife, and a peel test was performed with an adhesive tape.
◯: No abnormality such as peeling or chipping of the cut part.
X: Abnormalities such as peeling and chipping of cut portions are observed.

From the results shown in Table 2, it was revealed that the multilayer coating film obtained using the clear coating composition of the present invention has properties excellent in corrosion resistance and adhesion.

Since the clear coating composition of the present invention has excellent design properties over a long period of time without discoloration or white turbidity even during long-term use, the meter cluster, center cluster, Automotive interior parts such as center consoles, wheel caps, bumper moldings, foil garnishes, grill radiators, back panels, door mirror covers, door handles and other automotive exterior parts, air conditioner housings, mobile phones, laptop computers, cosmetic containers, etc. It can be used for painting in applications other than automotive parts.

Claims (6)

A clear coating composition used in the formation of a multilayer coating film comprising a silver plating layer formed by sequentially forming a base coating layer, a silver plating layer, and a clear coating layer on a plastic substrate,
A two-component polyurethane paint comprising a main agent containing an acrylic polyol and a curing agent containing a polyisocyanate compound,
The equivalent ratio (NCO / OH) of OH groups in the acrylic polyol and NCO groups in the polyisocyanate compound is 0.8 / 1 to 1.2 / 1,
A clear coating composition comprising a rust inhibitor at a content of 1.0 to 13.0 parts (in terms of solid content) with respect to 100 parts by mass of acrylic polyol and rust inhibitor in total. The main agent is acrylic polyol, non-aqueous dispersion resin and the following general formula (1);

(Wherein R ¹ represents a methyl group, a methoxy group or an ethoxy group, and R ² and R ³ are the same or different and represent a methoxy group or an ethoxy group.)
The clear coating composition according to claim 1, comprising an epoxysilane represented by the formula: The clear coating composition according to claim 1 or 2, wherein the rust inhibitor is a fatty acid amide compound. A method for forming a multilayer coating film comprising a silver plating layer formed by sequentially forming a base coating layer, a silver plating layer, and a clear coating layer on a plastic substrate,
A method for forming a multilayer coating film, wherein the clear coating layer is formed by the clear coating composition according to claim 1, 2 or 3. Silver plating obtained by sequentially forming a base coating layer, a silver plating layer and a clear coating layer formed from the clear coating composition according to claim 1, 2 or 3 on a plastic material. Decorative molded product including layers. The decorative molded product according to claim 5, further comprising a primer layer between the plastic material and the base coating layer.