JP4746500B2 - Method for forming multilayer film for plastic material and its coated product - Google Patents

Description

  The present invention relates to a method for coating a plastic material and a coated product thereof. Specifically, the present invention relates to a method for forming a multilayer film on the surface of a plastic material for automobiles and a coated product thereof.

In recent years, 3 wet-on-wet coating has been studied with the aim of shortening the coating process and saving energy. Three-wet-on-wet coating is a coating in which the three-layer coating film is formed by coating each of the three types of coatings in sequence without baking and curing, and then the three-layer coating film is baked and cured simultaneously. Is the method. For example, Patent Document 1 proposes 3-wet-on-wet coating using an aqueous primer paint, a colored paint, and a clear paint.
However, even when a technique such as that described in Patent Document 1 is used, when a plastic material used in a bumper or a molding for an automobile is overcoated with a base paint or a clear paint, the plastic material for an automobile (hereinafter referred to as a plastic material) The top coating used for the “plastic material” is sometimes different from the coating used for the metal material for automobiles (hereinafter sometimes simply referred to as “metal material”). In the present situation, there are the following problems, and it has not been possible to completely shorten the painting process and save energy.

In other words, in automobile paints, metal material paints and plastic material paints are manufactured separately because they use different paints as described above, and also for the coating process of metal materials and plastic materials, Since painting is done on separate lines, when the automobile is finally made by combining them, the coating color of each material may be different, and it takes a lot of time to adjust the color of the metal material and plastic material It is a problem that you have to spend time and effort.
Different paints are used for metal materials and plastic materials because metal materials are excellent in heat resistance, and in order to ensure sufficient curability, paints that are thermally cured at relatively high temperatures are used. On the other hand, since plastic materials are vulnerable to heat, paints that can exhibit the film performance required for the materials by baking and curing in a temperature range where thermal deformation does not occur are used.

Therefore, conventionally, development has been attempted on a technique that can cause sufficient curing at a low temperature such that the plastic material is not deformed even when a paint used for a metal material is used. For example, Patent Document 2 discloses a two-coat one-bake coating film forming method that cures at room temperature or a temperature of about 100 ° C. or less. Specifically, the technology of Patent Document 2 uses a paint mainly composed of a hydroxyl group-containing resin and a polyisocyanate compound as a top coat, and uses a hydroxyl group-containing resin as a resin component of the base coat. In the layer, the hydroxyl group-containing resin and the polyisocyanate compound react to cure, and in the base coat layer, the hydroxyl group contained in the base coat layer reacts with the polyisocyanate compound penetrating from the top coat layer to cure. Is.
JP-A-10-29671 JP 61-161179 A

However, the technique of Patent Document 2 is a technique that can be applied only when the base paint is a solvent-type paint (indicated as “organic liquid paint” in Patent Document 2), and is an aqueous base with high water absorption. In the case of a paint, there is a problem that water resistance is inferior because it cannot be cured sufficiently. In addition, if a large amount of moisture is present in the base layer, the moisture reacts with the polyisocyanate compound that has permeated from the clear layer, and the base coating is further insufficiently cured.
In recent years, in consideration of environmental protection, a shift from solvent-based paints to water-based paints is required. Therefore, there is a need for a technique that can solve the above-described problems and can be applied to water-based base paints.

  Therefore, the problem to be solved by the present invention is that the migration amount of the polyisocyanate compound from the clear layer to the base layer can be increased as compared with the conventional film, which is required for the clear layer such as solvent resistance and weather resistance. A multilayer film for plastic materials for automobiles that can be used as it is for plastic materials for automobiles as it is by increasing the curability of the water-based paint while maintaining performance. It is to provide a forming method.

  In order to solve the above-mentioned problems, the present inventors have conducted various experiments and used a high-solid clear paint having a large non-volatile content as a clear paint. The main components of the high-solid clear paint are a hydroxyl group-containing resin and a polyisocyanate compound. If the non-volatile content of the two-layer coating consisting of the primer paint and the base paint is adjusted before applying the high solid clear paint, the base of the high solid clear layer Even if the amount of polyisocyanate compound transferred to the layer is increased and a water-based coating is used, not only can a multilayer film be given sufficient water resistance, but also a film required for a clear layer such as solvent resistance and weather resistance. It is also possible to increase the curability of the base paint while maintaining performance, and as a result, it is possible to achieve bake hardening at a lower temperature than before. The aqueous base coating composition used in automotive metallic material, found that can be used in automotive plastic material as it is, the present invention has been completed.

That is, the method of painting the automotive plastic material of the present invention is as follows.
A water-based primer coating, a water-based base coating used for metal materials for automobiles, and a high solid clear coating are sequentially applied to the surface of the plastic material for automobiles to form a three-layer coating film. A method of painting a plastic material for automobiles that is simultaneously baked and cured at a temperature of ~ 100 ° C,
The high solid clear coating is mainly composed of a hydroxyl group-containing resin and a polyisocyanate compound,
The hydroxyl group-containing resin has a weight average molecular weight of 3500 to 10000, a hydroxyl value of 80 to 180 KOH mg / g, and a content ratio of primary and secondary hydroxyl groups based on the hydroxyl value (primary hydroxyl group / 2 Grade hydroxyl group) 10/90 to 80/20,
The polyisocyanate compound has an average number of isocyanate groups per molecule of 2.5 to 3.4, and
While the equivalent ratio (NCO / OH) of the isocyanate group in the polyisocyanate compound and the hydroxyl group in the hydroxyl group-containing resin is 1.0 to 3.0,
The non-volatile content of the two-layer coating film composed of the water-based primer paint and the water-based base paint when the high solid clear paint is applied is 75% by weight or more.
It is characterized by that.

  According to the present invention, the amount of the polyisocyanate compound transferred from the clear layer to the base layer is increased more than before, and the film performance required for the clear layer, such as solvent resistance and weather resistance, is maintained while maintaining the water-based base coating composition. Since it is possible to enhance the curability, it becomes possible to sufficiently cure the water-based base paint used in automobile metal materials at a low temperature of 100 ° C. or less, so that the plastic material is not deformed. Further, the water resistance of the multilayer film is not lowered. In addition, as a result of being able to apply the water-based paint used in metal materials to plastic materials as it is, it is possible to prevent situations where the colors of metal materials and plastic materials differ when an automobile is assembled. It is not necessary to separately manufacture the base paint of each plastic material, and the number of manufacturing steps can be reduced, and further resource saving and energy saving can be achieved. In addition, the time and labor required for the conventional color adjustment are not required.

The plastic material coating method of the present invention includes a coating film forming step and a baking step. Hereinafter, this coating method will be described in detail.
[Coating film forming process]
The coating film forming process is a process in which a water-based primer coating, a water-based base coating and a high solid clear coating are applied in this order on the surface of the plastic material to form three coating films including each coating on the surface of the plastic material. is there.
First, the plastic material, water-based primer coating, water-based base coating, and high solid clear coating used in the coating film forming process will be described in detail.

The plastic material used in the present invention is not particularly limited. For example, polyolefin such as polyethylene and polypropylene, polystyrene, ABS, vinyl chloride, polycarbonate, polyacetal, polyester, polyamide, polyurethane, PPO, polymethyl methacrylate, epoxy resin, phenol Examples thereof include resins and melamine resins.
The water-based primer paint used in the present invention is a paint that is directly applied to the surface of a plastic material prior to overcoating the water-based base paint and the high solid clear paint. The water-based primer coating contains a primer resin and water as main components, and appropriately contains pigments and the like. The primer resin is used to improve the water resistance and solvent resistance of the cured coating film by bringing a cured coating film and a plastic material, which will be described later, into close contact with each other, and is an aqueous primer in the form of an emulsion and / or water-soluble resin composition. Included in paint.

  In the emulsion, the primer resin is dispersed in an aqueous medium in the form of particles, and the particle surface is stabilized by an emulsifier, a surfactant, a dispersant, or the like. As the emulsion, for example, an acrylic resin emulsion using an acrylic resin as a primer resin, or a polyester resin emulsion, a polyurethane resin emulsion, a polyolefin resin emulsion, an epoxy resin emulsion, an amino resin, each using the same resin as a primer resin. A resin emulsion etc. are mentioned, You may use together 1 type, or 2 or more types. Furthermore, if necessary, those containing modified resins may be included, which is effective in improving various performances. Among these, when the emulsion is at least one selected from an acrylic resin emulsion, a polyurethane resin emulsion, and a polyolefin resin emulsion, the adhesion between the cured coating film obtained by curing the primer coating film and the plastic material is further improved. Therefore, it is preferable.

  The water-soluble resin composition has a polar functional group such as a carboxyl group, a hydroxyl group, an amino group, and an ether group, and includes a water-soluble resin that can be dissolved in an aqueous medium due to its hydrophilic property as a primer resin. It is a thing. Examples of the primer resin used in the water-soluble resin composition include water-soluble resins having, as a basic structure, an acrylic resin, a polyester resin, a polyurethane resin, an amino resin, a vinyl resin, a fiber resin, and the like. Or you may use 2 or more types together. Above all, when the primer resin contained in the water-soluble resin composition is a water-soluble resin having, as a basic structure, at least one selected from an acrylic resin, a polyester resin, a polyurethane resin, and an amino resin, adhesion to a plastic material is improved. It is preferable because it can be further improved.

  The blending ratio of the emulsion and the water-soluble resin composition contained in the water-based primer paint is not particularly limited. However, when the water-based primer paint is thermoplastic, if the emulsion is used as a main component, water evaporates quickly, so that it can be dried. This is preferable because it is easy to mix and is less likely to mix with the aqueous base paint to be repainted, and the coating film performance such as appearance, adhesion and water resistance is easily developed. On the other hand, when the water-based primer coating is thermosetting, coating properties such as adhesion and water resistance can be imparted without necessarily using an emulsion as a main component. Further, an emulsion may be used in combination, or only a water-soluble resin and a curing agent may be used. However, when the water-based primer coating is thermosetting, the baking temperature and time are important after recoating the water-based base coating and the high solid clear coating. In other words, the baking conditions necessary for the water-based primer paint to be sufficiently cured must be set. However, if it is excessively baked, the primer paint film, the water-based base paint film, and the high solid clear paint film are hardened. Since they are different, the appearance and adhesion may be reduced.

The emulsion or water-soluble resin composition contained in the aqueous primer coating may be a thermosetting resin composition containing a curing agent such as an amino resin, a polyisocyanate compound, an oxazoline compound, a polycarbodiimide compound, or a hydrazine compound.
The mixing ratio of water in the aqueous primer coating is preferably 50 to 90% by weight, more preferably 60 to 80% by weight, based on the entire aqueous primer coating. When the mixing ratio of water is less than 50% by weight, the viscosity of the coating is increased, and the storage stability and the coating workability are lowered. On the other hand, when the blending ratio of water exceeds 90% by weight, the ratio of the nonvolatile content in the aqueous primer coating is decreased, the coating efficiency is deteriorated, and appearance abnormalities such as sagging and armpits are liable to occur. The water-based primer paint may further contain an organic solvent, and the blending ratio is usually 40% by weight or less with respect to the water contained in the water-based primer paint.

  Examples of the organic solvent include aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane, and octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclopentane; ethyl acetate , Esters such as n-butyl acetate, isobutyl acetate and amyl acetate; ethers such as n-butyl ether and isobutyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; methanol, ethanol, isopropanol and n-butanol , 2-butanol, n-propylene glycol, isopropylene glycol and other alcohols; ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate Cellosolves such as: carbitols such as diethylene glycol monoethyl ether; propylene glycol alkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether; dioxane, N-methylpyrrolidone, dimethylformamide, diacetone alcohol, etc. Other solvents may be mentioned.

Examples of pigments contained in the aqueous primer coating include inorganic pigments such as carbon black, titanium oxide, iron oxide, chromium oxide, and bitumen; organic compounds such as azo, anthraquinone, perylene, quinacridone, indigo, and phthalocyanine A pigment etc. are mentioned, Only 1 type may be used or 2 or more types may be used together.
The water-based primer paint can contain a known auxiliary compounding agent as necessary. Examples of the auxiliary compounding agent include conductivity imparting agents such as conductive carbon, conductive filler, and metal powder; inorganic fillers; organic modifiers; stabilizers; plasticizers; In particular, if the water-based primer paint contains a conductivity-imparting agent, conductivity is imparted regardless of the water content of the coating film obtained from the water-based primer paint, and the water-based base paint and / or the high solid clear paint is used. This is preferable because it can be easily applied by electrostatic coating.

The water-based base paint used in the present invention is used to form a water-based base paint film by coating the primer paint film on the primer paint film as it is without baking and curing the primer paint film formed by applying the water-based primer paint. This paint is used prior to the high solid clear paint.
The water-based base paint is the same as the water-based base paint used for automobile metal materials. Therefore, it is no longer necessary to manufacture water-based paints separately for automotive metal materials and plastic materials, which can reduce the number of manufacturing steps, save resources and save energy, and automotive metal materials can also be made of plastic materials. There is no difference in color, so you can save the trouble of adjusting the color.

  Examples of the water base paint resin contained in the water base paint include acrylic resin, polyester resin, polyurethane resin, epoxy resin, amino resin, vinyl resin, and fiber resin. More than one species may be used in combination. The aqueous base paint resin is usually blended in the paint in the form of an emulsion and / or a water-soluble resin composition. The aqueous base paint may further contain a curing agent. In particular, despite the fact that it is often used as a water-based base paint for metal materials, an acrylic resin system that has not been used as a water-based base paint for plastic materials because it could not be cured sufficiently at low temperatures. The main melamine curable aqueous base paint is suitably used as the aqueous base paint according to the present invention.

  The aqueous base paint usually contains a metallic pigment or an aqueous base pigment. Examples of metallic pigments include aluminum flakes, copper bronze flakes, mica-like iron oxides, mica flakes, mica-like iron oxides coated with metal oxides, mica flakes coated with metal oxides, and the like. Or you may use 2 or more types together. Examples of the aqueous base pigment include inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate, and carbon black; And organic pigments such as quinacridone violet and the like, and only one type or two or more types may be used in combination.

The water-based base paint can contain a known auxiliary compounding agent as necessary. As an auxiliary | assistant compounding agent, an inorganic filler, an organic modifier, a stabilizer, a plasticizer, an additive etc. are mentioned, for example.
The high solid clear coating material used in the present invention is coated on the aqueous base coating film as it is without baking and curing the aqueous base coating film, that is, the top of the three-layer coating film. It is a paint used to form a layer (uppermost layer), and imparts excellent physical properties such as weather resistance and solvent resistance to the cured coating film.
The high solid clear coating is mainly composed of a hydroxyl group-containing resin and a polyisocyanate compound.

The hydroxyl group-containing resin can be obtained by polymerizing a monomer component comprising a hydroxyl group-containing unsaturated monomer by a known method, or is selected from other acid group-containing unsaturated monomers and other unsaturated monomers. It can also be obtained by polymerizing in combination with a monomer component comprising an unsaturated monomer.
The hydroxyl group-containing unsaturated monomer is not particularly limited. For example, as the primary hydroxyl group-containing unsaturated monomer, hydroxyethyl acrylate, hydroxyethyl methacrylate, Plaxel FM1 (ε-caprolactone-modified hydroxyethyl methacrylate, manufactured by Daicel Chemical Industries). Polyethylene glycol monoacrylate or monomethacrylate, polypropylene glycol monoacrylate or monomethacrylate, and the like, and secondary hydroxyl group-containing unsaturated monomers include hydroxypropyl methacrylate and hydroxybutyl acrylate.

The acid group-containing unsaturated monomer is not particularly limited, and examples thereof include carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, and maleic acid.
The other unsaturated monomer is not particularly limited, and examples thereof include acrylic monomers or acrylic monomers having an ester group such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, and lauryl of acrylic acid or methacrylic acid; vinyl alcohol and acetic acid. , Vinyl alcohol ester monomers with carboxylic acids such as propionic acid; unsaturated hydrocarbon monomers such as styrene, α-methylstyrene, vinyl naphthalene, butadiene, and isoprene; nitrile monomers such as acrylonitrile and methacrylonitrile Monomers; Examples include acrylamide monomers such as acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, and diacetoneacrylamide.

The hydroxyl group-containing resin has a weight average molecular weight of 3500 to 10,000, preferably 5,000 to 9000. If it is less than 3500, the film performance required for the clear layer such as solvent resistance, weather resistance, and appearance cannot be exhibited. If it exceeds 10,000, the viscosity of the paint becomes high, and in such a high viscosity state, the coating operation becomes difficult. The appearance of the coating film will be deteriorated. Although it is possible to reduce the proportion of non-volatile components in the paint using a volatile organic solvent, in that case, there arises a problem of environmental pollution by the organic solvent.
The hydroxyl value of the hydroxyl group-containing resin is 80 to 180 KOHmg / g, preferably 120 to 150 KOHmg / g. If it is less than 80 KOHmg / g, the crosslink density of the clear layer becomes insufficient, and the solvent resistance and weather resistance of the multilayer film are lowered. If it exceeds 180 KOHmg / g, a large amount of polyisocyanate compound is required.

  Further, the hydroxyl group in the hydroxyl group-containing resin contains primary and secondary hydroxyl groups, and the content ratio (primary hydroxyl group / secondary hydroxyl group) is 10/90 to 80/20 based on the hydroxyl value, preferably Is 30 / 70-50 / 50. Here, the primary hydroxyl group has a high reactivity with the polyisocyanate compound and has a characteristic that the transition from the clear layer to the base layer hardly occurs. The secondary hydroxyl group has a low reactivity with the polyisocyanate compound, and from the clear layer. There is a characteristic that the transition to the base layer easily occurs. Therefore, when the content ratio of the primary hydroxyl group is less than 10/90, the transition is easy, but the curing in the clear layer becomes insufficient, and the solvent resistance and weather resistance of the multilayer film are lowered, and when it exceeds 80/20. Curing in the clear layer is sufficient but difficult to migrate, and the water resistance of the multilayer film is lowered.

Moreover, it is preferable that the acid value of hydroxyl-containing resin is 1-20 KOHmg / g. More preferably, it is 2-15 KOHmg / g. If it is less than 1 KOHmg / g, curing with the clear paint may be insufficient, and if it exceeds 20 KOHmg / g, the curing speed of the clear paint becomes too fast, and the polyisocyanate compound migrates from the clear layer to the base layer. May become insufficient, and the water resistance of the multilayer film may be reduced.
The hydroxyl group-containing resin preferably has a glass transition temperature (Tg) of −10 ° C. to 50 ° C. When the temperature is lower than -10 ° C, the stain resistance and scratch resistance of the coating film may be deteriorated, and the adhesiveness may remain. When it exceeds 50 ° C., the flex resistance may be deteriorated, and cracks may be generated in the coating film.

As the polyisocyanate compound, an aliphatic or alicyclic polyisocyanate compound is preferably used.
The aliphatic or alicyclic polyisocyanate compound is not particularly limited, and examples thereof include hexamethylene diisocyanate, isophorone diisocyanate, and methylenebiscyclohexyl isocyanate, and isocyanurate compounds and uretdione compounds derived therefrom. , Urethane compounds, allophanate compounds, burette compounds, and adducts with trimethylolpropane.
The average number of isocyanate groups per molecule of the polyisocyanate compound is 2.5 to 3.4, and preferably 2.6 to 3.2. If it is less than 2.5, the crosslink density of the clear layer becomes insufficient, and the solvent resistance and weather resistance of the multilayer film are lowered. If it exceeds 3.4, the polyisocyanate compound hardly migrates from the clear layer to the base layer. Thus, the water resistance of the multilayer film is lowered.

Furthermore, the equivalent ratio (NCO / OH) between the isocyanate group in the polyisocyanate compound and the hydroxyl group in the hydroxyl group-containing resin is 1.0 to 3.0, preferably 1.2 to 2.8. . If it is less than 1.0, the migration of the polyisocyanate compound from the clear layer to the base layer is difficult to occur, the water resistance of the multilayer film is reduced, and if it exceeds 3.0, the crosslinking density of the clear layer becomes insufficient, The solvent resistance and weather resistance of the multilayer film are reduced.
The clear coating material can contain a known auxiliary compounding agent, if necessary. As an auxiliary | assistant compounding agent, an organic modifier, a stabilizer, an additive etc. are mentioned, for example.
Next, the operation of the coating film forming process will be described in detail.

When the coating film forming process is further subdivided, it is divided into an aqueous primer coating film forming process, an aqueous base coating film forming process, and a clear coating film forming process.
First, the water-based primer coating film forming step is a step of preparing a plastic material and applying a water-based primer coating to the surface to form a primer coating film. Prior to applying the water-based primer paint, the plastic material may be washed and degreased if necessary. The water-based primer coating can be applied by a technique such as spray coating, brush coating, roll coating, or flow coating. The coating amount (dry film thickness) of the aqueous primer coating is not particularly limited, but is preferably 5 to 20 μm because adhesion, water resistance, solvent resistance, and the like are improved.

In the aqueous primer coating film forming step, the obtained primer coating film is left without being baked and cured, and in the next aqueous base coating film forming process, the aqueous base coating material is applied over the primer coating film.
Next, in the water-based base coating film forming step, the water-based base coating film is formed on the surface of the primer coating film by repeatedly applying the water-based base coating on the primer coating film obtained in the water-based primer coating film forming step. It is a process.
In order to improve the finished appearance and obtain excellent cosmetics, the water-based base coating is usually applied over the surface of the primer coating film using air spray or airless spray.

In addition, when applying a water-based base coating repeatedly by electrostatic spraying, it is preferable that a conductive material is blended in the water-based primer coating because conductivity can be reliably imparted by the primer coating film. The coating amount (dry film thickness) of the aqueous base paint is not particularly limited, but it is preferably 10 to 30 μm because the polyisocyanate compound is easily impregnated and the solvent resistance is improved.
In the aqueous base coating film forming step, the obtained aqueous base coating film and the primer coating film obtained in the aqueous primer coating forming process are left without being baked and cured. Then, in the next clear coating film forming step, the clear coating is applied over the aqueous base coating film.

The non-volatile content of the two-layer coating film composed of the water-based primer paint and the water-based base paint is 75% by weight or more when a clear paint described later is applied. If it is less than 75% by weight, the polyisocyanate compound that migrates from the clear layer to the aqueous base layer in the baking process described later causes a reaction with water in the volatile component. This is because the curing is hindered and the appearance of the clear layer is poor.
The method for adjusting the non-volatile content is not particularly limited, and examples thereof include a method of drying for 1 to 20 minutes at room temperature or under hot air conditions. If such a drying treatment is performed after forming the primer coating film and / or after forming the water-based base coating film, the smoothness of the primer coating film is ensured and foam removal is promoted. In addition, it can ensure the smoothness of the water-based paint coating film, promote foam removal, and can be oriented when metallic pigments are used, and it can be cured on the surface of plastic materials. This is preferable because the finished appearance of the coating film can be improved.

The non-volatile content of the two-layer coating film composed of the aqueous primer paint and the aqueous base paint is calculated as follows.
First, the weight (g) of the material is measured using a polypropylene material (the measured value at this time is A). Next, a primer paint is applied and dried at 80 ° C. for 10 minutes. Further, after applying the base paint and drying at 80 ° C. for each required time, the weight (g) of the material and the two-layer coating film is measured (the measured value at this time is B). Finally, it is dried at 95 ° C. for 3 hours, and the weight (g) of the material and the two-layer coating film is measured (the measured value at this time is C).
The above measured values A, B, and C are substituted into the following equation, and the obtained value is defined as the nonvolatile content of the two-layer coating film composed of the aqueous primer coating and the aqueous base coating.

(Non-volatile content of two-layer coating consisting of water-based primer paint and water-based base paint)
= (CA) / (BA) × 100

Finally, the clear paint forming process is a process in which the clear paint is applied repeatedly on the surface of the aqueous base paint film obtained in the aqueous base paint film forming process to form a clear paint film on the aqueous base paint film. is there.
Clear paints are usually applied over the surface of water-based paint coatings using air spray or airless spray, but can also be applied using electrostatic sprays, further reducing energy costs and environmental pollution. Can be prevented. The coating amount (dry film thickness) of the clear coating is not particularly limited, but is preferably 15 to 40 μm because the finished appearance, water resistance, solvent resistance, weather resistance and the like are improved.

The high solid clear paint preferably has a non-volatile content of 50 to 60% by weight at the time of painting. If it is less than 50% by weight, the amount of the solvent increases as a result, which is unfavorable for the environment, and there is a possibility that the advantages of using a high solid clear paint may not be utilized. If it exceeds 60% by weight, the paint becomes highly viscous. The painting work may be difficult.
As described above, the surface of the plastic material is coated with the water-based primer paint, the water-based base paint and the high solid clear paint in this order to form three paint films including the respective paint components on the surface of the plastic material. The following baking process is performed.
In selecting the water-based primer paint, the water-based base paint, and the high solid clear paint, it is necessary to select a paint that can be sufficiently cured and dried in the baking process. If the drying is insufficient and water or solvent remains in the cured coating film, performances such as weather resistance, water resistance and solvent resistance are likely to deteriorate in the cured coating film.

[Baking process]
In the baking process, the primer paint film, the water-based base paint film and the high solid clear paint film formed in the above-mentioned paint film forming process are simultaneously baked to form a primer paint cured film, water-based on the surface of the plastic material. This is a step of forming a cured coating film comprising three layers of a base coating cured coating and a high solid clear coating curing coating. In this specification, temperature / time means the time that the surface of the plastic material actually keeps the target temperature, more specifically, the time until the target temperature is reached should be considered. It means the temperature and time when the temperature is maintained after reaching the target temperature.

The baking temperature is 70 to 100 ° C. If the baking temperature is within the above range, there is no risk of deformation of the plastic material, and sufficient curing can be realized in a short time. More preferably, it is 80-90 degreeC.
The baking time is usually 10 to 60 minutes, preferably 15 to 50 minutes, and more preferably 20 to 40 minutes. When the baking time is less than 10 minutes, the coating film is not sufficiently cured, and in the cured coating film, performance such as weather resistance, water resistance and solvent resistance is lowered. On the other hand, if the baking time exceeds 60 minutes, it will be hardened too much and the adhesion in the recoating will be reduced, the total time of the coating process will be prolonged, and the energy cost will be increased.

  Examples of the heating apparatus used for simultaneously baking the paint coating film include a drying furnace using a heating source such as hot air, electricity, gas, and infrared, and a drying furnace using two or more of these heating sources in combination. Is preferable because drying time is shortened.

Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. Parts and% mean parts by weight and% by weight. Moreover, all the numerical values regarding the compounding quantity of each substance in a table | surface mean a weight part.
[Production Example 1] Production of water-based primer paint As described below, a dispersion resin and a dispersion paste were produced in order, and a water-based primer paint was produced using them.
<Manufacture of dispersion resin>
137 parts of propylene glycol monomethyl ether was charged into a reactor equipped with a stirring blade, thermometer, dripping device, temperature control device, nitrogen gas inlet and cooling tube, and the temperature was raised to 120 ° C. with stirring while introducing nitrogen gas did. Next, a mixture comprising 29.0 parts of 2-hydroxyethyl methacrylate, 23.0 parts of methacrylic acid, 86.6 parts of isobutyl methacrylate and 110.7 parts of n-butyl acrylate, and t-butylperoxy-2-ethylhexa A solution obtained by dissolving 2.5 parts of narate in 20 parts of propylene glycol monomethyl ether was dropped into the reactor over 3 hours.

After completion of the dropwise addition, the mixture was aged for 1 hour, and further 0.25 part of t-butylperoxy-2-ethylhexanate was dissolved in 10 parts of propylene glycol monomethyl ether, and the resulting solution was placed in the reactor over 1 hour. It was dripped.
This was aged for 2 hours while maintaining at 120 ° C., then cooled to 70 ° C., 23.8 parts of dimethylaminoethanol was added thereto, and the mixture was stirred for 30 minutes. Next, 417 parts of ion-exchanged water was slowly dropped while maintaining the temperature at 70 ° C., and then cooled to obtain a water-soluble acrylic resin.
The non-volatile content was adjusted to 30% using ion-exchanged water. The obtained water-soluble acrylic resin had a pH of 8.2 and a weight average molecular weight of 42,000.

<Manufacture of dispersion paste>
In a container equipped with a stirrer, 100 parts of the water-soluble acrylic resin obtained in <Manufacture of dispersion resin> (non-volatile content 30%), 20 parts of carbon black EC600JD (manufactured by Akzo Nobel), titanium oxide Taipure R-960 (manufactured by DuPont) ) 112 parts, 3 parts of Surfinol GA (produced by Air Products) and 95 parts of ion-exchanged water were added, stirred for 30 minutes, premixed, dispersed using a sand glider mill, and PWC (in the non-volatile content) A dispersion paste having a pigment weight fraction of 80% and a non-volatile content of 50% was prepared.
<Manufacture of water-based primer paint>
In a container, 1000 parts of the dispersion paste prepared in <Manufacture of dispersion paste> is charged, and 294 parts of Neoletz R972 (urethane dispersion, manufactured by Avisia, 34% non-volatile content) and Super Clon EN-432 (chlorinated polypropylene emulsion) while stirring. , Nippon Paper Chemicals, non-volatile content 30%) 400 parts, Epiletz 6006W (epoxy emulsion, Japan Epoxy Resin, non-volatile content 70%) 114 parts in order, Nopco 8034L (San Nopco, active ingredient 100%) 4 parts and After adding 800 parts of ion-exchanged water, the pH was adjusted to 8.0 using dimethylaminoethanol.

To this was added primal ASE-60 (manufactured by Nippon Acrylic Chemical Co., Ltd., nonvolatile content 28%) pregelled with dimethylaminoethanol so that the viscosity would be 30 seconds at 20 ° C. in a No. 4 Ford cup. An aqueous primer having a non-volatile content of 30.1% and a pH of 8.1 was prepared.
[Production Example 2] Production of water-based base paint As described below, a core-shell emulsion and a water-soluble acrylic resin as a dispersion resin were produced, and an aqueous base paint was produced using these.
<Manufacture of core-shell emulsion>
In a reactor equipped with a stirring blade, a thermometer, a dripping device, a temperature control device, a nitrogen gas inlet and a cooling pipe, 450 parts of ion-exchanged water and 3.6 parts of HS-10 (Daiichi Kogyo Seiyaku Co., Ltd.) were added. The temperature was raised to 80 ° C. with stirring while introducing nitrogen gas. Next, as a core part, a mixture comprising 75.6 parts of methyl methacrylate, 21.6 parts of n-butyl acrylate, 5.4 parts of 2-hydroxyethyl methacrylate, 5.4 parts of ethylene glycol dimethacrylate, and ammonium persulfate 1. Using a solution obtained by dissolving 08 parts in 54 parts of ion-exchanged water, the mixture and the solution were simultaneously dropped into the reactor over 180 minutes. After completion of dropping, the mixture was aged for 60 minutes.

Next, a mixture comprising 36.0 parts of methyl methacrylate, 5.5 parts of methacrylic acid and 30.5 parts of n-butyl acrylate as a shell part, and a solution obtained by dissolving 0.72 parts of ammonium persulfate in 36 parts of ion-exchanged water, The mixture and the solution were simultaneously dropped into the reaction apparatus over 60 minutes.
After ripening for 60 minutes after completion of the dropping, a solution prepared by dissolving 0.18 part of ammonium persulfate in 9 parts of ion-exchanged water was further dropped into the reactor over 5 minutes. After completion of dropping, the mixture was aged for 60 minutes and cooled to obtain a core-shell emulsion having a nonvolatile content of 23%.
<Manufacture of dispersion resin>
137 parts of propylene glycol monomethyl ether was charged into a reactor equipped with a stirring blade, thermometer, dripping device, temperature control device, nitrogen gas inlet and cooling tube, and the temperature was raised to 120 ° C. with stirring while introducing nitrogen gas did.

Next, a mixture comprising 29.0 parts of 2-hydroxyethyl methacrylate, 23.0 parts of methacrylic acid, 86.6 parts of isobutyl methacrylate and 110.7 parts of n-butyl acrylate, and t-butylperoxy-2-ethylhexa A solution obtained by dissolving 2.5 parts of narate in 20 parts of propylene glycol monomethyl ether was dropped into the reactor over 3 hours.
After completion of the dropwise addition, the mixture was aged for 1 hour, and a solution prepared by dissolving 0.25 part of t-butylperoxy-2-ethylhexanate in 10 parts of propylene glycol monomethyl ether was dropped into the reaction apparatus over 1 hour. Thereafter, the mixture was aged for 2 hours while maintaining 120 ° C, cooled to 70 ° C, added with 23.8 parts of dimethylaminoethanol, and stirred for 30 minutes.

After stirring for 30 minutes, 417 parts of ion-exchanged water was slowly dropped while maintaining the temperature at 70 ° C., and this was cooled to obtain a water-soluble acrylic resin.
The non-volatile content was adjusted to 30% using ion-exchanged water. The obtained water-soluble acrylic resin had a pH of 8.2 and a weight average molecular weight of 42,000.
<Manufacture of water-based paint>
66.7 parts of the water-soluble acrylic resin prepared in <Manufacture of dispersion resin>, 27.3 parts of aluminum paste WJE7640 (manufactured by Toyo Aluminum Co., Ltd.) and 0.7 part of Surfynol 440 (manufactured by Air Products) are put into a container. The aluminum was dispersed with sufficient stirring.

Next, under stirring, 217 parts of the core-shell emulsion prepared in <Manufacture of core-shell emulsion> were added, and the pH was adjusted to 8.5 using dimethylaminoethanol.
After pH adjustment, urethane dispersion R-9603 (manufactured by Avicia) and methylated melamine cymel 325 (manufactured by Mitsui Cytec) were sequentially added, and further 20 parts of 2-ethylhexyl glycol, 3.3 parts of Surfinol 440, BYK341 ( Big Chemie Japan Co., Ltd.) 1.0 parts, BYK025 (Big Chemie Japan Co., Ltd.) was added and stirred. The pH was adjusted to 8.5 again using dimethylaminoethanol, and 210 parts of ion-exchanged water was added and nonvolatile. The minutes were adjusted to 20%. Thereafter, Primal ASE-60 (manufactured by Nippon Acrylic Chemical Co., Ltd.) was diluted with ion-exchanged water to a non-volatile content of 20%, pregelled with dimethylaminoethanol, and the viscosity was 20 in a No4 Ford cup. An aqueous base paint having a non-volatile content of 25% and a pH of 8.5 was prepared by adjusting the temperature to 45 seconds.

[Production Example 3] Production of high solid clear coating material A hydroxyl group-containing resin and a polyisocyanate compound were produced as follows, and a high solid clear coating material was produced using them.
<Production of hydroxyl group-containing resin>
According to the formulation shown in Table 1, acrylic resins AC-1 to AC-13, which are hydroxyl group-containing resins, were obtained. Note that the non-volatile content of the hydroxyl group-containing resin is not simply the non-volatile content of the monomer alone, but 70% by weight of Kayaester O, which is a polymerization initiator, reacts with the monomer to become a non-volatile content. That is, specifically, the ratio of the total amount of the monomer and 70% by weight of the amount of Kayaester O used was calculated based on the weight of the nonvolatile content.

  Furthermore, as described above, Kayaester O reacts with the monomer to constitute a part of the hydroxyl group-containing resin, but the hydroxyl group and acid group resulting from Kayaester O have an effect on the properties of the hydroxyl group-containing resin. Because it is small, it was ignored in the calculation.

Specific production examples are shown below.
-Manufacture of AC-1-
A reactor equipped with a stirring blade, thermometer, dripping device, temperature control device, nitrogen gas inlet and cooling tube was charged with 140 parts of butyl acetate as a solvent, and the temperature was raised to 125 ° C. with stirring while introducing nitrogen gas. did. Next, as monomers, 2-hydroxyethyl methacrylate 58.5 parts, 2-hydroxypropyl methacrylate 97.2 parts, styrene 45 parts, t-butyl methacrylate 112.9 parts, n-butyl acrylate 133.2 parts, methacrylic acid A reaction apparatus comprising 3.5 parts of a mixture and 45 parts of Kayaester O (t-butylperoxy-2-ethylhexanate, manufactured by Kayaku Akzo Co., Ltd.) dissolved in 90 parts of butyl acetate as a polymerization initiator. It was dripped in over 3 hours.

After completion of the dropwise addition, the mixture was aged for 1 hour, and 0.9 parts of polymerization initiator Kayaester O (t-butylperoxy-2-ethylhexanate) was dissolved in 10 parts of butyl acetate, and the reaction was continued for 1 hour. It was dripped in. Thereafter, the mixture was aged for 2 hours while being kept at 125 ° C. and cooled to complete the reaction.
The resulting acrylic resin had a weight average molecular weight of 7000 and a nonvolatile content of 65%.
-Manufacture of AC-2 to 13-
AC-2 to 13 were produced by the same method as the production of AC-1. After the polymerization, the nonvolatile content was adjusted to 65% using butyl acetate.
For AC-12, the viscosity increased when the nonvolatile content was 65%, so the nonvolatile content was adjusted to 60%.

<Production of polyisocyanate compound>
Polyisocyanate compounds NCO-1 to 5 were obtained by the formulation shown in Table 2.

Specific production examples are shown below.
-Manufacture of NCO-1-
The container was charged with 16.65 parts Takenate D178N (manufactured by Mitsui Takeda Chemical Co., Ltd.) and 83.35 parts Desmodur N3600 (manufactured by Sumika Bayer Urethane Co., Ltd.) while stirring well to obtain NCO-1.
―Manufacture of NCO-2 ~ 5―
NCO-2 to 5 were produced in the same manner as NCO-1. Note that Sumijour N3300 used in NCO- 5 is a curing agent manufactured by Sumitomo Bayer Urethane Co., Ltd.

<Manufacture of high solid clear paint>
High solid clear paints CL-1 to 21 were obtained according to the formulations shown in Tables 3 and 4.

Specific production examples are shown below.
-Manufacture of CL-1-
Charge 54.64 parts of AC-1 prepared in <Manufacture of hydroxyl group-containing resin> into a container and thoroughly stir it. 0.26 parts, 0.36 parts of a 1% dibutyltin dilaurate (DBTDL) butyl acetate solution, 0.39 parts of Tinuvin 292 (manufactured by Ciba Specialty Chemicals Co., Ltd.), Tinuvin 384-2 (Ciba Specialty) (Manufactured by Chemicals Co., Ltd.) 0.78 parts, 13.45 parts of butyl acetate, and 3.37 parts of methyl ethyl ketone (MEK) were sequentially charged into a container and stirred uniformly to form a clear coating main ingredient. The nonvolatile content of the main agent was 50%.

In another container, 25.02 parts of the polyisocyanate compound NCO-1 prepared in <Manufacture of polyisocyanate compound>, 8.70 parts of carbitol acetate, and 11.57 parts of MEK were sequentially charged and stirred uniformly. It was set as the hardening | curing agent for the coating-material base materials for coating. The non-volatile content of the curing agent was 55%.
Next, 73.51 parts of the above main agent and 45.29 parts of the curing agent were mixed to obtain a high solid clear paint CL-1. At this time, the non-volatile content of the high solid clear paint was 52%.
-Manufacture of CL-2 to 21-
CL-2 to 21 were produced by the same method as CL-1.

[Examples 1 to 19 and Comparative Examples 1 to 13]
As described below, coated plates A1 to 19 corresponding to Examples 1 to 19 and coated plates B1 to 13 corresponding to Comparative Examples 1 to 13 were produced and subjected to the tests described later. In the following, the water-based primer paint, water-based base paint, and high solid clear paint used for the preparation of each coated plate are shown in Tables 5 and 6 for Examples 1 to 19 and Tables 7 and 8 for Comparative Examples 1 to 13, respectively. It is shown.

<Example 1>
A water-based primer coating was spray-coated on a polypropylene material (TSOP-6, manufactured by Nippon Polypro) washed with isopropyl alcohol so as to have a dry film thickness of 10 μm. After the application of the aqueous primer coating, it was dried at 80 ° C. for 10 minutes. Next, after allowing to cool to room temperature, the aqueous base paint was spray-coated to a dry film thickness of 15 μm, left at room temperature for 2 minutes, and then dried at 80 ° C. for 10 minutes. Next, after allowing to cool to room temperature, the high solid clear paint was spray-coated to a dry film thickness of 25 μm and left at room temperature for 5 minutes. Next, a final coated plate A1 that was baked at 90 ° C. for 20 minutes and cured and dried was obtained.

<Examples 2 to 15>
Final coated plates A2 to 15 were obtained by the same method as in Example 1.
<Example 16>
A final coated plate A16 was obtained in the same manner as in Example 1 except that the drying temperature and time of the aqueous base coating material were changed from “10 minutes at 80 ° C.” to “5 minutes at 80 ° C.”.
<Example 17>
A final coated plate A17 was obtained in the same manner as in Example 1 except that the drying temperature and time of the water-based base coating material were changed from “10 minutes at 80 ° C.” to “20 minutes at 80 ° C.”.

<Example 18>
The drying temperature and time of the water-based base paint was changed from “10 minutes at 80 ° C.” to “5 minutes at 80 ° C.” and formed by the water-based primer paint, water-based base paint and high solid clear paint. The final coating plate A18 was prepared in the same manner as in Example 1 except that the temperature and time for simultaneous baking and curing of the three-layer coating film were changed from “20 minutes at 90 ° C.” to “20 minutes at 75 ° C.”. Obtained.
<Example 19>
Three layers formed by changing the drying temperature and time of the water-based base paint from “10 minutes at 80 ° C.” to “5 minutes at 80 ° C.” and the water-based primer paint, water-based base paint and high solid clear paint The final coated plate A19 was obtained in the same manner as in Example 1 except that the temperature and time for simultaneous baking and curing of the coating film were changed from “20 minutes at 90 ° C.” to “20 minutes at 100 ° C.”. .

<Comparative Examples 1-10>
Final coating plates B1 to B10 were obtained by the same method as in Example 1.
<Comparative Example 11>
A final coated plate B11 was obtained in the same manner as in Example 1, except that the drying temperature and time of the aqueous base coating material were changed from “80 ° C. for 10 minutes” to “80 ° C. for 2 minutes”.
<Comparative Example 12>
Changed the temperature and time for simultaneous baking and curing of three-layer coatings formed with water-based primer paint, water-based base paint, and high solid clear paint from "90 ° C for 20 minutes" to "60 ° C for 60 minutes" Except for the points described above, a final coated plate B12 was obtained in the same manner as in Example 1.

<Comparative Example 13>
Changed the temperature and time for simultaneous baking and curing of three-layer coatings formed with water-based primer paint, water-based base paint, and high solid clear paint from "90 ° C for 20 minutes" to "110 ° C for 20 minutes" Except for the points described above, a final coated plate B13 was obtained in the same manner as in Example 1.
The final coated plates A1 to A19 and B1 to B13 prepared in Examples 1 to 19 and Comparative Examples 1 to 13 were left for 1 day, and then the physical properties of the cured coating films were evaluated by the following test methods. The results are shown in Tables 5 to 8 together with the types of water-based primer paint, water-based base paint, and high solid clear paint used in the preparation of each coated plate. In Tables 5 to 8, “hydroxyl value” is the hydroxyl value of the hydroxyl group-containing resin, and “primary hydroxyl group / secondary hydroxyl group” is the content ratio of the primary hydroxyl group and the secondary hydroxyl group contained in the hydroxyl group in the hydroxyl group-containing resin. (Based on hydroxyl value), “average number of NCO groups” is the average number of isocyanate groups per molecule of the polyisocyanate compound, “NCO / OH” is the equivalent ratio of isocyanate groups in the polyisocyanate compound and hydroxyl groups in the hydroxyl group-containing resin, Means each.

〔Test method〕
<Initial adhesion>
The final coated plate was subjected to a cross-cut tape peeling test of JIS K5600.
The case where there was no peeling at all was marked as ◯, and the case where even a slight peeling was observed was marked as x.
<Water resistance>
The final coated plate is immersed in warm water of 40 ° C. for 240 hours, and then dried at room temperature for one day. The blister (swelling of the coating film due to water penetration) is visually evaluated based on ASTM D714, and a cross-cut tape peeling test of JIS K5600 is performed. It was.

A case where no abnormality was observed in the appearance compared to before the test and no peeling occurred was evaluated as ◯, and a case where an abnormality in the appearance was observed or even a slight peeling was observed as x.
<Solvent resistance>
Apply a load of 500 g with gauze containing xylene to the final coated plate, and perform an 8 reciprocating rubbing test with a Gakushin friction tester (manufactured by Suga Test Instruments) to check for abnormalities such as stickiness, wrinkles, blisters, peelings, etc. Evaluated.
A case where no abnormality was observed was marked with ◯, and a case where even a slight abnormality was observed was marked with ×.
<Appearance>
About the final coating board, the degree of the mixed layer of the interface of a base layer and a clear layer was evaluated visually.

The case where the degree of the mixed layer was low was marked with ◯, and the case where the mixed layer was high was marked with X.
<Weather resistance>
The final coated plate was subjected to an exposure test outdoors to evaluate the presence or absence of abnormalities such as gloss change, color difference change, adhesion, cracking and blistering.
Furthermore, as an accelerated weather resistance test, the same evaluation as the above-described exposure test was performed using a sunshine carbon weather meter (SWOM, manufactured by Suga Test Instruments) and a xenon weather meter (xenon, manufactured by Suga Test Instruments).
When the gloss retention rate is 85% or more in comparison with the initial gloss, the color difference (ΔE) is 3 or less, peeling is not observed in the adhesion evaluation, and no other abnormal appearance such as cracks or blisters is observed. ○ A case where even one item did not satisfy the above conditions was marked as x.

<VOC>
Calculate the amount of non-volatile content when the viscosity of the high solid clear paint is adjusted to 25 seconds with Ford Cup # 4, ○ if the non-volatile content is 50% by weight or more, less than 50% by weight X.
Here, in the solvent-type paint, the weight (g) of the volatile organic solvent contained in the paint 1L is referred to as “VOC”, and the VOC can be calculated from the ratio of the non-volatile content contained in the paint. Specifically, in accordance with ASTM D3960, the following formula is used.

VOC = 1000 × (paint specific gravity value) × (1-paint non-volatile content / 100)

The paint specific gravity value in the above equation is a value measured according to JIS K5600.

Therefore, the smaller the non-volatile content, the larger the value of VOC (requires a large amount of organic solvent), which is not preferable from the viewpoint of environmental conservation.
[Evaluation]
(1) Examples 1 to 19 according to the present invention satisfy the standards in all tests, and it is proved that an extremely excellent multilayer film can be formed on a plastic material by using the present invention.
(2) None of the comparative examples satisfy the criteria in any of the tests. Specifically, it is as described below.

In Comparative Examples 1 and 2, the hydroxyl value of the hydroxyl group-containing resin that is one of the main components of the clear paint is not in the range of 80 to 180 KOHmg / g. Therefore, the comparative example 1 which is less than 80 KOHmg / g is inferior in solvent resistance and a weather resistance, and the comparative example 2 which exceeds 180 KOHmg / g is inferior in an external appearance.
In Comparative Examples 3 and 4, the content ratio of primary and secondary hydroxyl groups contained in the hydroxyl group-containing resin (primary hydroxyl group / secondary hydroxyl group) is within the range of 10/90 to 80/20 (based on hydroxyl value). It is not. Therefore, Comparative Example 3 in which the proportion of primary hydroxyl groups exceeds 80/20 is inferior in water resistance, and Comparative Example 4 in which the ratio is less than 10/90 is inferior in solvent resistance and weather resistance.

In Comparative Examples 5 and 6, the average number of isocyanate groups per molecule of the polyisocyanate compound which is one of the main components of the clear coating is not in the range of 2.5 to 3.4. Therefore, the comparative example 5 which is less than 2.5 is inferior in solvent resistance and a weather resistance, and the comparative example 6 which exceeds 3.4 is inferior in water resistance.
In Comparative Examples 7 and 8, the equivalent ratio (NCO / OH) between the isocyanate group in the polyisocyanate compound and the hydroxyl group in the hydroxyl group-containing resin is not in the range of 1.0 to 3.0. Therefore, the comparative example 7 which is less than 1.0 is inferior in water resistance, and the comparative example 8 which exceeds 3.0 is inferior in solvent resistance, a weather resistance, and an external appearance.

In Comparative Examples 9 and 10, the hydroxyl group-containing resin does not have a weight average molecular weight in the range of 3500 to 10,000. Therefore, 1 0 000 cases compared exceeds 9, it can be seen that the high viscosity, in order to the other embodiments and comparative examples the same viscosity, and it is necessary to reduce the non-volatile content. Comparative Example 10, which is less than 3500, is inferior in water resistance and appearance.
Comparative Example 11 is inferior in water resistance and appearance because the non-volatile content of the two-layer coating composed of the aqueous primer coating and the aqueous base coating is 65%.
In Comparative Examples 12 and 13, the baking temperature when simultaneously baking and curing the three-layer coating film is not in the range of 70 to 100 ° C. Therefore, Comparative Example 12 having a temperature of less than 70 ° C. is inferior in initial adhesion, water resistance, solvent resistance, and weather resistance, and Comparative Example 13 having a temperature exceeding 100 ° C. causes deformation of the plastic material, resulting in an appearance. Inferior.

  The method for forming a multilayer film for a plastic material according to the present invention, for example, caused a thermal deformation of the material at a high temperature and was insufficiently cured at a low temperature, and used a base paint for a metal material that was not conventionally used. It can be suitably used for forming a multilayer film on the surface of a plastic material, and there is a possibility that a wide variety of multilayer films can be applied to a plastic material.

Claims (4)

A water-based primer coating, a water-based base coating used for metal materials for automobiles, and a high solid clear coating are sequentially applied to the surface of the plastic material for automobiles to form a three-layer coating film. A method of painting a plastic material for automobiles that is simultaneously baked and cured at a temperature of ~ 100 ° C,
The high solid clear coating is mainly composed of a hydroxyl group-containing resin and a polyisocyanate compound,
The hydroxyl group-containing resin has a weight average molecular weight of 3500 to 10000, a hydroxyl value of 80 to 180 KOH mg / g, and a content ratio of primary and secondary hydroxyl groups based on the hydroxyl value (primary hydroxyl group / 2 Grade hydroxyl group) 10/90 to 80/20,
The polyisocyanate compound has an average number of isocyanate groups per molecule of 2.5 to 3.4, and
While the equivalent ratio (NCO / OH) of the isocyanate group in the polyisocyanate compound and the hydroxyl group in the hydroxyl group-containing resin is 1.0 to 3.0,
The non-volatile content of the two-layer coating film composed of the water-based primer paint and the water-based base paint when the high solid clear paint is applied is 75% by weight or more.
A method of painting a plastic material for automobiles.   The method for coating an automotive plastic material according to claim 1, wherein the acid value of the hydroxyl group-containing resin is 1 to 20 KOHmg / g.   The method for coating an automotive plastic material according to claim 1 or 2, wherein a non-volatile content of the high solid clear coating is 50 to 60% by weight.   The plastic material for motor vehicles painted by the method in any one of Claim 1 to 3.