JP4429199B2 - Multi-layer coating film forming method and paint used therefor - Google Patents

Description

  The present invention relates to a method for forming a multilayer coating film capable of imparting weather resistance and scratch resistance to a plastic substrate with high work efficiency, and a paint usable in the method.

  For example, synthetic resin molded products made from polymethyl methacrylate resin, polymethacrylimide resin, polycarbonate resin, polyethylene terephthalate resin, polybutylene phthalate resin, polystyrene resin, AS resin, ABS resin, polyolefin resin, etc. are lightweight and impact resistant. In addition to being excellent in performance, it is also excellent in transparency. For example, it is increasingly used as a plastic material for automobiles in headlamps, sunroofs, glazings, instrument covers and the like. However, it cannot be said that these synthetic resin molded products generally have sufficient performance in terms of weather resistance. For example, when used outdoors as a plastic material for automobile exteriors, the weather resistance is improved. It was sought to do. In addition, these synthetic resin molded products are not sufficient in terms of scratch resistance on the surface, so the surface is easily damaged by contact with other hard objects, friction, scratches, etc. There are also disadvantages in that the quality of the product is significantly reduced and the product becomes unusable in a short period of time. Therefore, as a means for imparting weather resistance and scratch resistance to a synthetic resin molded article, it is usually performed to form a coating film that can improve scratch resistance and weather resistance by applying a paint on the surface thereof. .

Conventionally, a method for forming a coating film is roughly divided into i) a method in which a paint is applied and then cured by baking at a high temperature, and ii) after application of the paint, irradiation with active energy rays such as ultraviolet rays. And a method of curing by this. In the case of using a plastic as a base material, in the method i), depending on the type of the base material, the base material may be deformed by being exposed to a high temperature during baking, and the method ii) is more suitable. The method ii) is desirable and useful because it is advantageous in terms of economy and work efficiency.
In order to improve the scratch resistance and weather resistance, as a technique for forming a coating film by the method of ii), that is, a method of curing by irradiating with active energy rays such as ultraviolet rays, there are three in the molecule so far. Identify poly (meth) acrylates having the above (meth) acryloyl groups, urethane poly (meth) acrylates having 6 or more (meth) acryloyl groups in the molecule, UV absorbers, light stabilizers and photopolymerization initiators There has been reported a method (see Patent Document 1) in which a coating film (one-coat coating film) is formed from an ultraviolet curable liquid composition containing a certain amount and then cured by irradiation with active energy rays.
JP-A-9-286809

  In recent years, attempts have been made to replace glass with plastic materials as vehicles become lighter, and for example, replacement of glass such as doors, front, and rear, sunroofs, and the like has been considered. Such coatings for glass substitute plastics are required to have higher weather resistance and scratch resistance than coatings for conventional general applications. Specifically, for example, in a headlamp which is a conventional application, with regard to weather resistance, when a weather resistance test according to the weather resistance evaluation described later in the examples is performed, the coating film abnormality (cracking) is reduced to about 30 cycles. , Exfoliation, luster, etc.) are not recognized, and the scratch resistance is such that the haze value is about 20 or less when the scratch resistance evaluation described later in the examples is performed. It was able to be used without problems with the level performance. On the other hand, as a coating film in the glass substitute plastic application, it is a level at which coating film abnormality (crack, peeling, glossiness, etc.) is not recognized up to 50 cycles or more in the above test, and the scratch resistance is about The haze value needs to be 10 or less.

  However, the conventionally known coating film using an active energy ray-curable coating material has not been able to achieve a higher level as described above with respect to weather resistance and scratch resistance. In other words, in a one-coat coating film using a conventional active energy ray-curable coating material, a coating film abnormality (cracking, peeling, glossing, etc.) does not occur up to about 50 cycles in the above test by containing a large amount of UV absorber. Although it is possible to improve the weather resistance to the level, this level is the limit, and in this case, by containing a large amount of the UV absorber, the degree of crosslinking of the coating film is lowered, and the scratch resistance is reduced. The haze value becomes 30 or more. On the other hand, regarding the scratch resistance, the haze value can be reduced to 10 or less in the prior art by increasing the glass transition temperature and the crosslinking density of the coating film by appropriately setting the monomer composition constituting the resin in the paint. In this case, however, problems such as the occurrence of cracks in the coating film are likely to occur, and the weather resistance is reduced.

  More specifically, with regard to weather resistance, it has been known that, in order to obtain good weather resistance, a large amount of an ultraviolet absorber may be contained in the paint. Contains UV absorber. Thereby, even when used outdoors, the ultraviolet absorber absorbs ultraviolet rays contained in sunlight, and the effect that the coating film and the substrate itself are not easily deteriorated by ultraviolet rays can be obtained. On the other hand, when the coating film is formed, the active energy ray irradiated for curing is absorbed, and as a result, the amount of active energy that acts on curing. Decreases and becomes a factor that inhibits the curing of the coating film (particularly, the coating film on the side in contact with the substrate). Thus, when the curing in the coating film (particularly the coating film on the side in contact with the base material) is inhibited and insufficient, cohesive failure occurs with the passage of time, resulting in a decrease in adhesion to the base material. The film does not function as a coating film, and the weather resistance as well as the scratch resistance are greatly impaired. That is, in the case of curing with active energy rays, it has been impossible to obtain sufficient weather resistance by increasing the amount of the ultraviolet absorber as in the prior art.

  Further, in the paint disclosed in Patent Document 1, in order to improve the scratch resistance, it has been devised to introduce a large amount of (meth) acryloyl groups to increase the crosslinking density, but in general, if there are many photocurable groups Another problem is that rapid volume shrinkage tends to occur during curing, and there is a tendency for scratches and cracks to occur in the coating film, and the adhesion to the substrate deteriorates, resulting in a decrease in weather resistance. Will occur. Further, as described above, the presence of the ultraviolet absorber makes the curing insufficient, and when the (meth) acryloyl group introduced in a large amount remains without being consumed, the remaining (meth) acryloyl group is outdoors. There is also a concern that when it is used in the environment, it is deteriorated by ultraviolet rays contained in sunlight, which may deteriorate the weather resistance.

As described above, it is difficult to solve the contradiction phenomenon between weather resistance and scratch resistance with the conventional technology, and it is impossible to achieve both weather resistance and scratch resistance.
Therefore, the problem to be solved by the present invention is a method for forming a multilayer coating film capable of forming a coating film excellent in weather resistance and scratch resistance with work efficiency by curing with active energy rays, and can be used in the method. To provide paint.

  The present inventor has intensively studied to solve the above problems. As a result, two layers of a base coating film and a clear coating film are formed by active energy rays, and each coating film is different so that sufficient weather resistance can be exhibited by the base coating film and scratch resistance can be expressed by the clear coating film. Inspired to play a role. In other words, as an undercoat paint for forming a base coating film, it has excellent adhesion to a plastic substrate, and the formed coating film exhibits good weather resistance even when exposed to sunlight during outdoor use. With regard to its curability, it is considered that it should be cured to such an extent that the weather resistance is not impaired even with a small amount of active energy rays. On the other hand, as a clear paint for forming a clear coating film, it has high scratch resistance. In order to obtain the above, it is considered that a paint that emphasizes only the curability by a generally known active energy ray should be selected. Based on this idea, as a result of various studies on the undercoat paint that can satisfy the above-described properties, (meth) acrylic resin (A) having a double bond group in the side chain, polyfunctional (meth) acrylate (B) If it is a paint which has an ultraviolet absorber (C) having a (meth) acryloyl group and a photopolymerization initiator (D) as essential components, it has excellent adhesion to a plastic substrate and exhibits good weather resistance. It has been found that sufficient curability can be exhibited by active energy rays. Then, it is confirmed that the above-mentioned problems can be solved all at once by forming a clear coating layer with a known active energy ray-curable clear coating layer on the base coating layer formed with the coating material. The present invention has been completed.

That is, the method for forming a multi-layer coating film according to the present invention comprises forming a base coating film with an undercoat paint that is cured by active energy rays on a plastic substrate, and then clearing the base coating film with active energy rays. In the multi-layer coating film forming method for forming a clear coating film, a (meth) acrylic resin (A) having a double bond group in the side chain, a polyfunctional (meth) acrylate (B), ( The ultraviolet absorber (C) having a (meth) acryloyl group and the photopolymerization initiator (D) are essential components , and the (meth) acrylic resin (A) has a weight average molecular weight of 5,000 to 50,000. A double bond group is added to the side chain of the resin so as to have a double bond group equivalent of 600 to 2400, and the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) The form fraction is (A) / (B) = 10/90 to 50/50 (mass ratio), and the total solid content of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) It is characterized by using a coating material in which the ultraviolet absorber (C) is 5 to 15 parts by mass and the photopolymerization initiator (D) is 3 to 10 parts by mass in a solid content ratio with respect to 100 parts by mass .
The paint according to the present invention is an undercoat paint for a plastic substrate that is cured by active energy rays, and includes a (meth) acrylic resin (A) having a double bond group in the side chain, and a polyfunctional (meth) acrylate (B). , An ultraviolet absorber (C) having a (meth) acryloyl group and a photopolymerization initiator (D) as essential components , and the (meth) acrylic resin (A) has a weight average molecular weight of 5,000 to 50, A double bond group is added to the side chain of 000 resin so as to have a double bond group equivalent of 600 to 2400, and the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) The solid content ratio of (A) / (B) = 10/90 to 50/50 (mass ratio), and the total solid of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) For 100 parts by weight A solids fraction, the ultraviolet absorber (C) is 5 to 15 parts by weight, the photopolymerization initiator (D) is 3 to 10 parts by weight, and wherein.

  According to the present invention, it is possible to provide a multi-layer coating film forming method capable of forming a coating film excellent in weather resistance and scratch resistance with work efficiency by curing with an active energy ray, and a paint usable in the method. it can.

Hereinafter, the multilayer coating film forming method according to the present invention and the paint that can be used in the method will be described in detail. However, the scope of the present invention is not limited to these descriptions, and the present invention is not limited to the following examples. Changes can be made as appropriate without departing from the spirit of the invention.
Hereinafter, the paint (undercoat paint) that can be used in the multilayer coating film forming method according to the present invention will be described first, and then the multilayer coating film forming method according to the present invention will be described in detail.
〔paint〕
The paint according to the present invention is an undercoat paint for a plastic substrate that is cured by active energy rays, and includes a (meth) acrylic resin (A) having a double bond group in the side chain, and a polyfunctional (meth) acrylate (B). The ultraviolet absorber (C) having a (meth) acryloyl group and the photopolymerization initiator (D) are essential components.

Although the production method of the (meth) acrylic resin (A) having a double bond group in the side chain is not limited, for example, a (meth) acrylic resin having no double bond group in the side chain ( Hereinafter, it is obtained by adding an organic substance having a double bond group (hereinafter also referred to as “organic substance a2”) to “(meth) acrylic resin a1”. In the present specification, acrylic acid and / or methacrylic acid are collectively referred to as “(meth) acrylic acid”.
The (meth) acrylic resin a1 is not particularly limited, and can be obtained by (co) polymerizing a commonly used (meth) acrylic monomer and, if necessary, a monomer component composed of another ethylenically unsaturated monomer. (Co) polymers that can be used.

  Examples of the (meth) acrylic monomer include (meth) acrylic acid and esterified products thereof (for example, methyl ester, ethyl ester, propyl ester, n-butyl ester, i-butyl ester, t-butyl ester, 2-ethylhexyl ester, lauryl ester, phenyl ester, benzyl ester, isobornyl ester, 2-hydroxyethyl ester, 2-hydroxypropyl ester, 2-hydroxybutyl ester, 4-hydroxybutyl ester, (β-methyl) glycidyl ester Amides containing amide groups such as acrylamide, methacrylamide, N, N-dimethylacrylamide, N, N-dimethylmethacrylamide, N, N-dibutylmethacrylamide, etc. Chromatography; and the like are; (meth) ring-opening adduct of caprolactone of 2-hydroxyethyl acrylate.

Examples of the other ethylenically unsaturated monomers include styrene, α-methylstyrene, itaconic acid, maleic acid, and vinyl acetate.
The (meth) acrylic resin a1 can be obtained by (co) polymerizing the above-mentioned arbitrary monomer components by a known method. In order to add the organic substance a2 to the (meth) acrylic resin a1. The (meth) acrylic resin a1 needs to have functional groups such as hydroxyl group, carboxyl group, glycidyl group, isocyanate group, etc., and monomers having these functional groups are appropriately used as monomer components. It is important to choose. For example, when the hydroxyl group is given to the (meth) acrylic resin a1, a hydroxyl group-containing monomer such as 2-hydroxyethyl ester of (meth) acrylic acid or a ring-opening adduct of these with caprolactone may be selected. When the meth) acrylic resin a1 has a carboxyl group, a carboxyl group-containing monomer such as (meth) acrylic acid or itaconic acid may be selected. When the methacrylic resin a1 has a glycidyl group, (meth) A glycidyl group-containing monomer such as glycidyl ester of acrylic acid may be selected.

  The organic substance a2 may be a bifunctional organic substance having both a group capable of reacting with the functional group of the (meth) acrylic resin a1 and a double bond group, and the (meth) acrylic resin a1 has. What is necessary is just to select suitably according to a functional group. For example, when the (meth) acrylic resin a1 has a hydroxyl group, an organic substance having an isocyanate group and a double bond group (for example, 2-isocyanatoethyl (meth) acrylate or n isocyanate groups) An adduct obtained by adding (n-1) equivalent of a compound having at least one double bond group and one or more hydroxyl groups in the molecule; specifically, isophorone diisocyanate and 2-hydroxy When the (meth) acrylic resin a1 has a carboxyl group, the equimolar reaction product with ethyl acrylate or the equimolar reaction product of hexamethylene diisocyanate and 2-hydroxypropyl acrylate may be selected. If you select an organic substance with a glycidyl group and a double bond group (for example, glycidyl ester of (meth) acrylic acid) In addition, when the (meth) acrylic resin a1 has a glycidyl group, an organic substance having any of a carboxyl group, a sulfonic acid group, a phosphoric acid group and the like and a double bond group (for example, (meth) acrylic acid, itacon) An adduct obtained by adding hydroxylpropyl acrylate, 2-hydroxyethyl (meth) acrylate, or the like to an acid, an acid anhydride, or the like may be selected.

The (meth) acrylic resin (A) having a double bond group in the side chain has a double bond group equivalent to 600-2400 in the side chain of the resin having a weight average molecular weight of 5,000 to 50,000. It is preferable that they are added. In other words, the weight average molecular weight of the (meth) acrylic resin a1 is 5,000 to 50,000, and the double bond group equivalent of the (meth) acrylic resin (A) having a double bond group in the side chain is 600. It is preferably ˜2400.
The (meth) acrylic resin a1 preferably has a weight average molecular weight of 5,000 to 50,000, more preferably 7,000 to 45,000. When the weight average molecular weight of the (meth) acrylic resin a1 is less than 5,000, the cohesive force of the coating film may be low and the adhesion may be insufficient even if the crosslink density is slightly increased. If it exceeds, the viscosity of the paint will increase, and it will be necessary to reduce the viscosity with a large amount of diluent. As a result, the solid content at the time of coating will become extremely low and dripping will occur, or the molecular weight will be too high. There is a possibility that the smoothness of the above cannot be obtained.

The (meth) acrylic resin (A) having a double bond group in the side chain preferably has a double bond group equivalent of 600 to 2400, more preferably 800 to 1800. If the double bond group equivalent of the (meth) acrylic resin (A) is less than 600, gelation tends to occur during the addition reaction for introducing the double bond group. The crosslink density of the film is lowered, the cohesive force is insufficient, and the adhesion with the substrate may be lowered.
The polyfunctional (meth) acrylate (B) is not particularly limited as long as it is a bifunctional or higher functional acrylate. Specifically, as the bifunctional acrylate, for example, a diol compound having a double bond group and an isocyanate group (for example, an equimolar reaction product of a diol compound and 2-isocyanatoethyl (meth) acrylate), A dicarboxylic acid compound having a double bond group and a glycidyl group (for example, an aliphatic dibasic acid such as maleic acid or adipic acid, an aromatic dibasic acid such as phthalic acid or terephthalic acid, and glycidyl (meth) acrylate) And the like. Examples of the trifunctional or higher functional acrylate include esterified products of a compound having three or more hydroxyl groups in the molecule and (meth) acrylic acid (for example, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, A reaction product of methylolpropane, ditrimethylolpropane, ditrimethylolethane and the like with (meth) acrylic acid), urethane acrylate (a compound having three or more hydroxyl groups in the molecule, 2-isocyanatoethyl (meth) acrylate) Equivalent reaction product, etc.).

  The solid content ratio of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) is preferably (A) / (B) = 10/90 to 50/50 (mass ratio). . If the (meth) acrylic resin (A) is more than the above range (if the polyfunctional (meth) acrylate (B) is too much less than the above range), the crosslinking density of the resulting coating film is lowered and the cohesive force is insufficient. Thus, the adhesion with the substrate may be reduced. On the other hand, when the (meth) acrylic resin (A) is less than the above range (when the polyfunctional (meth) acrylate (B) is too much than the above range), the polyfunctional (meth) acrylate (B) is cross-linked. Although the degree is increased, the amount of (meth) acrylic resin (A) is small, and as a result, the cohesive force is insufficient, and the adhesion to the substrate may be reduced. More preferably, the (meth) acrylic resin (A) should be 20 to 40% by mass with respect to the total solid content of (A) and (B), and the polyfunctional (meth) acrylate (B) It is good that it is 60-85 mass% with respect to the total solid of (A) and (B).

The (meth) acryloyl group-containing ultraviolet absorber (C) is not particularly limited as long as it is a compound having a (meth) acryloyl group and having an ultraviolet absorbing ability. Examples thereof include those having a (meth) acryloyl group among known ultraviolet absorbers and those obtained by reacting a known ultraviolet absorber with a (meth) acryloyl group-containing compound. Specific examples include 2- (2′-hydroxy-5′-methacryloxyphenyl) -2H-benzotriazole, 2- (4-benzoyl-3-hydroxyphenoxy) ethyl methacrylate, and the like.
The content of the (meth) acryloyl group-containing ultraviolet absorber (C) is 5 to 5 in terms of solid content with respect to 100 parts by mass of the total solid content of the acrylic resin (A) and the polyfunctional (meth) acrylate (B). It is preferably 15 parts by mass. More preferably, it is 7-13 mass parts. If it is less than 5 parts by mass, the weather resistance may be insufficient. On the other hand, if it exceeds 15 parts by mass, curing by active energy rays is significantly inhibited, and weather resistance and adhesion to a substrate are reduced. There is a fear.

  There is no restriction | limiting in particular as a photoinitiator (D), What is generally used as a photoinitiator is mentioned. For example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, α-methylbenzoin, benzoin-n-butyl ether, 2-ethylanthraquinone, 2-t-butylanthraquinone, 1-chloroanthraquinone, 2- Amylanthraquinone, benzophenone, p-chlorobenzophenone, p-dimethylaminobenzophenone, benzophenone methyl ether, methylbenzophenone, 4,4-dichlorobenzophenone, 4,4-bisdiethylaminobenzophenone, diphenyl sulfide, tetramethylthiuram disulfide, 2,4- Dimethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4-diethylthioxanthone, 2-chloro Oxanthone, 2-isopropylthioxanthone, 2,2-dimethoxy-2-phenylacetophenone, α, α-dichloro-4-phenoxyacetone, pt-butyltrichloroacetophenone, pt-butyldichloroacetophenone, 2,2-di Ethoxyacetophenone, p-dimethylaminoacetophenone, hydroxycyclohexyl phenyl ketone, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2,2-dimethoxy-1,2-diphenylethane-1 -One, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 4- (2-acryloxy) oxyethoxy- Phenyl-2-hydro Si-2-propylketone, 4- (2-hydroxy) phenyl- (2-hydroxy-2-propyl) ketone, bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylphenylphosphine oxide, bis ( 2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide and the like. Among these, 2,4,6-trimethylbenzoyl is a compound having a maximum absorption wavelength in a long wavelength region of 350 nm or more from the viewpoint of curability in the presence of the (meth) acryloyl group-containing ultraviolet absorber (C). It is preferable to use a photopolymerization initiator such as diphenylphosphine oxide or bisacylphosphine oxide in combination with a hydrogen abstraction photopolymerization initiator such as benzophenone.

Content of a photoinitiator (D) is 3-10 mass parts as solid content with respect to 100 mass parts of total solid content of the said acrylic resin (A) and the said polyfunctional (meth) acrylate (B). It is preferable. More preferably, it is 4-8 mass parts. If it is less than 3 parts by mass, curing by active energy rays may be insufficient, and the weather resistance and adhesion to the substrate may be reduced. On the other hand, if it exceeds 10 parts by mass, an excessive photopolymerization initiator ( D) may remain, which may cause deterioration of weather resistance or cause discoloration of the coating film.
In addition to the essential components (A) to (D), the coating material according to the present invention includes an organic solvent, a light stabilizer, an antioxidant, an anti-yellowing agent, a blueing agent, and a pigment as necessary. , A leveling agent, an antifoaming agent, a thickening agent, an anti-settling agent, an antistatic agent, an antifogging agent and the like can be appropriately blended within a range not impairing the effects of the present invention.

The paint according to the present invention is an undercoat paint for plastic substrates. The plastic substrate to which the paint according to the present invention can be applied is not particularly limited. For example, polymethyl methacrylate resin, polymethacrylimide resin, polycarbonate resin, polyethylene terephthalate resin, polybutylene phthalate resin, polystyrene resin, AS resin, Examples include a base material formed by molding an ABS resin and the like, and among them, a base material formed by molding a polycarbonate resin is preferable in that it can exhibit excellent adhesion.
[Multi-layer coating method]
The method for forming a multilayer coating film according to the present invention comprises forming a base coating film on a plastic substrate with an undercoating paint curable with active energy rays, and using a clear coating composition curable on the base coating film with active energy rays. A clear coating film is formed.

In the method for forming a multilayer coating film according to the present invention, it is important to use the above-described paint according to the present invention as the undercoat paint.
In the method for forming a multilayer coating film according to the present invention, the clear coating is not particularly limited as long as it can be cured by active energy rays, and conventionally known active energy ray-curable clear coatings can be used. However, it is preferable to use a clear paint containing urethane acrylate, (meth) acrylate-modified colloidal silica, an ultraviolet absorber, a light stabilizer and a photopolymerization initiator as essential components (hereinafter, this clear paint is referred to as “preferred clear paint”). ) Is good.

  Examples of the urethane acrylate that can be used in the preferred clear coating include, for example, i) a compound having two or more isocyanate groups in the molecule, and one or more hydroxyl groups and one or more double bond groups in the molecule. A compound obtained by equivalent reaction with a compound having ii) a compound having two or more isocyanate groups in a molecule reacted with a condensate of a polyhydric alcohol and a monobasic acid and / or polybasic acid Later, a compound obtained by reacting a compound having one or more hydroxyl groups and one or more double bond groups in the molecule, iii) Polyhydric alcohol having two or more isocyanate groups in the molecule Examples thereof include compounds obtained by reacting a compound and then reacting a compound having one or more hydroxyl groups and one or more double bond groups in the molecule.

  In the above i) to iii), the compound having two or more isocyanate groups in the molecule is preferably other than the aromatic isocyanate compound. In the above i) to iii), examples of the compound having one or more hydroxyl groups and one or more double bond groups in the molecule include 2-hydroxy (meth) acrylate and 2-hydroxypropyl (meth). Examples of acrylate, 4-hydroxybutyl (meth) acrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, and other commercially available products include Plaxel F (M) A series (manufactured by Daicel Chemical Industries). In addition, in the above ii) to iii), as the polyhydric alcohol, for example, polyethylene glycol, polycarbonate diol, polytetramethylene glycol, trimethylolpropane, and the like, and commercially available products, Plaxeldiol series (manufactured by Daicel Chemical Industries), Examples include the plaque cell triol series (manufactured by Daicel Chemical Industries).

Examples of the (meth) acrylate-modified colloidal silica that can be used in a preferred clear coating include products obtained by a hydrolytic condensation reaction between colloidal silica and (meth) acrylic acid.
There is no restriction | limiting in particular as a ultraviolet absorber which can be used in a preferable clear coating material, The ultraviolet absorber generally used is mentioned. Specifically, for example, phenyl salicylate, 4-t-butylphenyl salicylate, 2,4-di-t-butylphenyl-3,5'-di-t-butyl-4'-hydroxylbenzoate, 4-t- Salicylate-based ultraviolet absorbers such as octylphenyl salicylate; 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 2-hydroxy-4-n-oct Xylbenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, 2,2'-dihydroxy-4 -Methoxybenzophenone, 2,2'-dihydride Xy-4,4'-dimethoxybenzophenone, 2,2 ', 4,4'-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2- Benzophenone ultraviolet absorbers such as hydroxy-4- (2-methacryloyloxyethoxy) benzophenone; 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- [2′-hydroxy-3 ′, 5 ′ -Bis (α, α-dimethylbenzyl) phenyl] benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t-butylphenyl) benzotriazole, 2- (2′-hydroxy-3′- t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydride) Xy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5'-di-t-amyl) benzotriazole, 2- (2 '-Hydroxy-5'-t-octylphenyl) benzotriazole, 2,2'-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2N-benzotriazol-2-yl) phenol And other commercially available products include benzophenone-based Seesorb 103 (manufactured by Cypro Kasei Co., Ltd.), benzotriazole-based tinuvin 1130 (manufactured by Ciba Specialty Chemicals), and the like. Among these, phenyl salicylate, 4-t-butylphenyl salicylate, 4-t-octylphenyl salicylate, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxy Benzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- [2′-hydroxy-3 ′, 5′-bis (α, α -Dimethylbenzyl) phenyl] benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3', 5 ' -Di-t-amyl) benzotriazole is preferred. In the preferred clear paint, the above-mentioned (meth) acryloyl group-containing ultraviolet absorber (C) can also be used as an essential component in the paint (undercoat paint) according to the present invention.

  The light stabilizer that can be used in the preferred clear coating is not particularly limited, and examples thereof include phenyl-4-piperidinyl carbonate, bis- (2,2,6,6-tetramethyl-4-piperidinyl) sebacate, Bis- (N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis- (1,2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5 -Di-t-butyl-4-hydroxybenzyl) -2-n-butyl malonate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, 2,2,6,6-tetramethyl-4 Hindered amine light stabilizers such as piperidyl methacrylate; ethyl-2-cyano-3,3-diphenyl acrylate, 2-ethylhexyl-2-cyano-3,3′- Phenyl acrylate, butyl 2-cyano-3-methyl-3- (p-methoxyphenyl) cyanoacrylate-based light stabilizers such as acrylate, and the like. Among these, a hindered amine light stabilizer that can be expected to have a larger effect in a small amount is preferable.

There is no restriction | limiting in particular as a photoinitiator which can be used in a preferable clear coating material, The photoinitiator generally used is mentioned. Specifically, the same thing as the photoinitiator (D) mentioned above as an essential component in the coating material (undercoat coating material) concerning this invention is mentioned, for example.
The content ratio of each essential component in the preferred clear coating is not particularly limited, and may be appropriately set according to a conventionally known technique. In addition, preferable clear paints include organic solvents, antioxidants, anti-yellowing agents, bluing agents, pigments, leveling agents, antifoaming agents, thickeners, anti-settling agents, antistatic agents, if necessary. An antifogging agent and the like can be appropriately contained.

In the multilayer coating film forming method according to the present invention, the plastic substrate is the same as that described above as the plastic substrate to which the paint according to the present invention can be applied. In addition, the plastic substrate is subjected to a heat treatment (in advance) for the purpose of removing the strain at the time of forming the substrate before being subjected to the multilayer coating film forming method according to the present invention (that is, before applying the primer coating). Annealing is preferable.
Specifically, the method for forming a multilayer coating film according to the present invention includes, for example, applying a primer coating on a plastic substrate and irradiating an active energy ray to form the foundation coating, A clear coating is applied on top and irradiated with active energy rays to form a clear coating.

There are no particular limitations on the method of applying the undercoat paint and the clear paint, and for example, a known coating method such as spray coating, immersion coating, shower coating, roll coater coating, or rotating bell coating may be employed. In the case of spray coating or rotating bell coating, electrostatic coating may be used.
When the undercoat paint and / or the clear paint contains a solvent, it is desirable to remove the solvent after applying each paint and before irradiating the active energy ray. If the active energy rays are irradiated and cured while the solvent remains, the resulting base film or multi-layered film will be smudged, or the warm water resistance and weather resistance will be reduced. This is because it may be easily whitened.

  Although there is no restriction | limiting in particular as a method of removing a solvent after undercoat paint application and / or after clear paint application, For example, preheat etc. may be used. Preheating can be performed by an IR furnace, an electric furnace, a gas furnace, or the like. As conditions for performing preheating, it is preferable to hold the temperature of the base material (molded product) at 60 to 140 ° C. for 1 to 15 minutes. In addition, when removing a solvent, before irradiating an active energy ray, it is preferable to cool until the temperature of a base material (molded article) will be 50 degrees C or less. When irradiation with active energy rays is performed while the temperature of the base material (molded product) exceeds 50 ° C., the base material (molded product) is deformed as a result of further heat being applied by the irradiation of active energy rays. This is because there is a risk of it.

In the multilayer coating film forming method according to the present invention, the method of irradiating active energy rays is not particularly limited, and may be a normal method. For example, a method of irradiating ultraviolet rays using a high pressure mercury lamp, a metal halide lamp or the like as a light source can be mentioned. In the present invention, the active energy ray is not limited to ultraviolet rays, and may be, for example, a visible ray, an electron beam, or the like. When the ultraviolet ray is irradiated as the active energy ray, the integrated light amount is preferably 500 to 2000 mJ / cm ² , more preferably 1000 to 1500 mJ / cm ² for curing the base coating film. For curing, it is preferably 500 to 5000 mJ / cm ² .

In the multilayer coating film forming method according to the present invention, the film thickness (thickness after curing) of the base coating film is preferably 3 to 15 μm, and more preferably 4 to 10 μm. If the film thickness of the undercoating film is less than 3 μm, it tends to be affected by the inhibition of curing by oxygen, and the adhesion to the substrate and the weather resistance may be insufficient. On the other hand, if it exceeds 15 μm, the activity It becomes difficult for the energy rays to reach the side in contact with the base material, and the adhesion to the base material may be lowered, or cracks may easily occur.
In the multilayer coating film forming method according to the present invention, the thickness of the clear coating film (the film thickness after curing) is preferably 3 to 15 μm, and more preferably 5 to 10 μm. If the film thickness of the clear coating is less than 3 μm, it is likely to be affected by the inhibition of curing by oxygen, and the scratch resistance may be insufficient. Therefore, the cross-link density of the portion in contact with the base coating film is lowered, and there is a possibility that the weather resistance and interlayer adhesion with the base coating film may be lowered.

The multilayer coating film forming method according to the present invention can be performed, for example, as follows. Apply the undercoat so that the film thickness after curing is 3 to 15 μm on the base material (the synthetic resin molded product after molding is annealed by a general method if necessary and left to room temperature). Paint. Next, after preheating the coated substrate to remove the solvent, the substrate is cooled to 50 ° C. or lower. Next, using a lamp such as a high-pressure mercury lamp or a metal halide lamp, the height from the coating film to the lamp is set to 15 to 40 cm, and irradiation with ultraviolet rays of 500 to 2000 mJ / cm ² in the air or in a nitrogen atmosphere is performed. By doing so, the coating film is cured to form a base coating film. After forming the base coating film, the substrate is cooled to room temperature, and then the clear coating is applied so that the film thickness after curing is 3 to 15 μm. Next, after preheating to remove the solvent in the same manner as in the case of the undercoating film, it is cooled to 50 ° C. or lower, and thereafter, the ultraviolet ray having an ultraviolet light amount of 500 to 5000 mJ / cm ² is applied in the same manner as in the case of the undercoating film. Is applied to cure the coating film to form a multilayer coating film comprising a base coating film and a clear coating film.

  According to the method for forming a multilayer coating film according to the present invention, a multilayer coating film having excellent adhesion to a substrate and having both weather resistance and scratch resistance can be obtained.

Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. Hereinafter, unless otherwise specified, “part by mass” is simply referred to as “part”, and “mass%” is simply referred to as “%”.
The multilayer coating film obtained in the examples and the 1-coat coating film obtained in the comparative example were evaluated by the following methods.
<Abrasion resistance>
A 10 cm square test piece was prepared from the obtained base material with a multilayer coating film, and the amount of transmitted light of the coating film part of the test piece was measured using a turbidimeter (“NDH2000” manufactured by Nippon Denshoku Industries Co., Ltd.). After measuring (this value is set to Y0), and then subjecting the same portion to a taper wear test (load 500 g, 500 revolutions) based on JIS-K-5600-5-9, the transmitted light of the wear portion is It measured similarly (it makes this value Ym), and evaluated it on the following reference | standard as the value calculated | required by Ym-Y0 as a haze value.

○: Haze value is 10 or less Δ: Haze value is more than 10 and less than 20 ×: Haze value is 20 or more <Initial adhesion>
The resulting multi-layer coating film was cut at 2 mm intervals until reaching the base material in a grid pattern to create 100 cells, and a cellophane tape was pasted on it, and then the tape was peeled off at once. The peeled state of the film was observed with a magnifying glass (10 magnification) and evaluated according to the following criteria. Specifically, the interlayer adhesion was evaluated by observing the peeled state between the base coating and the clear coating, and the substrate adhesion was evaluated by observing the peeled state between the substrate and the base coating. .

○: No peeling is observed Δ: Slight peeling is observed along the grid-like cuts ×: One or more peelings are observed <Hot water resistant adhesion>
The obtained multilayer coating film is immersed in a constant temperature water bath at 40 ° C. for 500 hours, then pulled up, left to stand at room temperature for 1 hour, and then dried in the same manner as the initial adhesion evaluation method. The cellophane tape affixed to the film was peeled off at once, and the peeled state of the coating film was visually observed and evaluated according to the following criteria.

○: No peeling at all Δ: Slight peeling along the grid-like cuts is observed ×: One or more peelings are observed
The obtained multilayer coating film was subjected to the following weather resistance test using a die plastic metal weathero (manufactured by Dai Pla Wintes Co., Ltd.), and then the appearance of the coating film (presence of cracks, peeling, glossing) was visually observed. Observed and evaluated according to the following criteria. The weather resistance test includes L mode (90 mW / cm ² irradiation, black panel temperature 63.5 ° C.) 4 hours, R mode (90% RH, black panel temperature 70 ° C.) 4 hours, and D mode (95% RH, black The panel temperature was 30 ° C.) A total of 12 hours of 4 hours was defined as one cycle, and 50 cycles were performed. In each cycle, at the start of the D mode and the L mode, the surface of the coating film was sprayed with water for 15 seconds.

○: No crack or peeling is observed, and gloss is also negligible. Δ: Crack or peeling is not observed, but gloss is remarkable. ×: Crack or peeling is observed, and gloss is remarkable < Heat resistance>
The obtained multilayer coating film was left in an incubator at 80 ° C. for 720 hours, then taken out, and the cellophane tape attached to the cut coating film was peeled off at a stretch in the same manner as the initial adhesion evaluation method. The peeled state of the coating film was visually observed and evaluated according to the following criteria.
○: No separation is observed Δ: Slight separation is observed along the grid-like cuts ×: One or more cells are observed [Production Example 1]
(Acrylic resin polymerization)
200 g of propylene glycol monomethyl ether (hereinafter referred to as “PGM”) is placed in a 1 liter reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube, a dripping device, and a heating device with a thermostat, and is heated to 140 ° C. under a nitrogen atmosphere. Warmed up. Next, from 118 g of isobornyl methacrylate, 60 g of methyl methacrylate, 10 g of 2-ethylhexyl acrylate, 12 g of methacrylic acid and 160 g of PGM, from 6 g of t-butylperoxy-2-ethylhexanoate and 93 g of PGM as a polymerization initiator Initiator liquid A was added dropwise at a constant rate over 3 hours at the same time, and then held at 140 ° C. for 1 hour. Thereafter, an initiator liquid B consisting of 0.4 g of t-butylperoxy-2-ethylhexanoate and 16.8 g of PGM as a polymerization initiator was added dropwise at a constant rate over 1 hour, and a carboxyl group-containing acrylic resin was then added. A solution (a1) was obtained. When the weight average molecular weight of the carboxyl group-containing acrylic resin solution (a1) was measured by gel permeation chromatography (GPC), it was 20,000 in terms of polystyrene.

(Double bond introduced)
Next, a solution C composed of 1.5 g of tetrabutylammonium bromide, 0.2 g of hydroquinone and 3.3 g of PGM is added to the obtained carboxyl group-containing acrylic resin solution (a1), and the resin solution is bubbled into the resin solution while bubbling air. The temperature was set to 110 ° C., and a solution D consisting of 14 g of 4-hydroxy-butyl glycidyl ether acrylate and 35 g of PGM was added dropwise at a constant rate over 1 hour, and then aged at the same temperature for 5 hours. An acrylic resin solution (A1) having The solid content and double bond equivalent of the resulting acrylic resin solution (A1) are shown in Table 1.

[Production Example 2 and Production Example 3]
The same as the acrylic resin polymerization in Production Example 1 except that the amount of each raw material used in Production Example 1 was changed as shown in Table 1 (the values of the components shown in Table 1 are “g”). Carboxyl group-containing acrylic resin solutions (a1) and (a2) are obtained by the method described above, and an acrylic resin solution (A2) having a double bond group in the side chain by a method similar to the introduction of double bonds in Production Example 1; (A3) was obtained. Table 1 shows the solid contents and double bond equivalents of the obtained acrylic resin solutions (A2) and (A3). Moreover, the result of having measured the weight average molecular weight of carboxyl group-containing acrylic resin solution (a1) and (a2) similarly to manufacture example 1 is also shown in Table 1.

[Production Example 4]
(Acrylic resin polymerization)
The acrylic of Production Example 1 except that the amount of each raw material used in the acrylic resin polymerization of Production Example 1 was changed as shown in Table 2 (values of each component shown in Table 2 are “g”). A hydroxyl group-containing acrylic resin solution (a4-1) having a solid content of 50% was obtained in the same manner as the resin polymerization. In Production Example 4, 2-hydroxyethyl acrylate was used instead of methacrylic acid in Production Example 1. The results of measuring the weight average molecular weight of the hydroxyl group-containing acrylic resin solution (a4-1) in the same manner as in Production Example 1 are shown in Table 2.

(Double bond introduced)
First, 222 g (1 mol) of isophorone diisocyanate, 0.2 g of dibutyltin laurate and 222 g of butyl acetate were charged into a reaction vessel equipped with a stirrer, an air introduction tube, a cooling tube, a dripping device, and a heating device with a thermostat. While maintaining the internal temperature at 60 ° C., a liquid mixture consisting of 116 g (1 mol) of 2-hydroxyethyl acrylate, 0.3 g of hydroquinone and 116 g of butyl acetate was added dropwise over 2 hours. . Thereafter, the mixture was aged at the same temperature for 1 hour to obtain a solution (a4-2) containing an adduct containing an acryloyl group and an isocyanate group at a concentration of 50%.

Next, 400 g of the solution (a4-1) and 0.2 g of hydroquinone as a polymerization inhibitor were charged into a reaction vessel equipped with a stirrer, an air introduction tube, a cooling tube, a dripping device, and a heating device with a thermostat, and the internal temperature After the temperature of 80 ° C., 318 g of the above solution (a4-2) was added dropwise over 1 hour while blowing air, and then stirring was continued until no absorption of isocyanate groups was observed by IR measurement. A resin solution (A4) was obtained. Table 2 shows the solid content and double bond equivalent of the resulting acrylic resin solution (A4).
[Production Example 5]
(Acrylic resin polymerization)
The acrylic of Production Example 1 except that the amount of each raw material used in the acrylic resin polymerization of Production Example 1 was changed as shown in Table 2 (values of each component shown in Table 2 are “g”). A hydroxyl group-containing acrylic resin solution (a5) having a solid content of 50% was obtained in the same manner as the resin polymerization. In Production Example 5, 2-hydroxyethyl acrylate was used instead of methacrylic acid in Production Example 1. The results of measuring the weight average molecular weight of the hydroxyl group-containing acrylic resin solution (a5) in the same manner as in Production Example 1 are shown in Table 2.

(Double bond introduced)
Next, 400 g of the above solution (a5), 0.2 g of dibutyltin laurate, and 0.2 g of hydroquinone as a polymerization inhibitor are placed in a reaction vessel equipped with a stirrer, an air introduction tube, a cooling tube, a dripping device, and a heating device with a thermostat. After maintaining the temperature at 80 ° C. and blowing air, a mixed solution of 17 g of acryloyl group-containing isocyanate (“Karenz AOI” manufactured by Showa Denko KK) and 17 g of butyl acetate was added for 1 hour. After that, stirring was continued until absorption of isocyanate groups was not observed by IR measurement to obtain an acrylic resin solution (A5). The solid content and double bond equivalent of the resulting acrylic resin solution (A5) are shown in Table 2.

[Production Example 6, Production Example 7]
Except that the amount of each raw material used in Production Example 4 was changed as shown in Table 2 (the value of each component shown in Table 2 is “g”), the same as in Production Example 4 (that is, The hydroxyl group-containing acrylic resin solutions (a6) and (a7) were obtained in the same manner as in the acrylic resin polymerization in Production Example 1, and further doubled in the side chain in the same manner as in the introduction of the double bond in Production Example 4. Acrylic resin solutions (A6) and (A7) having a linking group were obtained. Table 2 shows the solid contents and double bond equivalents of the resulting acrylic resin solutions (A6) and (a7). Further, the results of measuring the weight average molecular weight of the hydroxyl group-containing acrylic resin solutions (a6) and (a7) in the same manner as in Production Example 1 are also shown in Table 2.

[Examples 1 to 19]
(Manufacture of undercoat paint)
Each component shown in Tables 3 to 5 was mixed at a blending ratio shown in each table (values of each component shown in Tables 3 to 5 are “parts”) and sufficiently stirred to obtain an undercoat paint. . The details of each component used are as follows.
(Meth) acrylic resin (A): Any one of the acrylic resin solutions (A1) to (A7) obtained in Production Examples 1 to 7 Multifunctional (meth) acrylate (B): “Evecril” manufactured by Daicel UCB 1290 ", solid content 100%
(Meth) acryloyl group-containing ultraviolet absorber (C): “RUVA-93” manufactured by Otsuka Chemical Co., Ltd.
Photopolymerization initiator (D): Benzophenone / Ciba Specialty Chemicals “Irgacure 819” = 1/3 (mass ratio) mixture, solid content 100%
Light stabilizer: “Chinubin 123” manufactured by Ciba Specialty Chemicals, 100% solid content
PGM
(Manufacture of clear paint)
Urethane acrylate was produced as follows. First, 136 g (1 mol) of pentaerythritol as a polyhydric alcohol, 603 g (3.92 mol) of hexahydrophthalic anhydride (“Rikacid HH” manufactured by Shin Nippon Chemical Co., Ltd.) as a polyvalent carboxylic acid, and 80 mL of xylene in a 2 L 4-neck flask And purged with nitrogen, and reacted at 120 ° C. until absorption due to anhydride disappeared by IR analysis (about 6 hours). Then, 816 g (4 mol) of hydroxypivalate neopentyl glycol (Mitsubishi Gas Chemical Co., Ltd.) was added and maintained at 200 ° C. or higher under a nitrogen atmosphere (final temperature was 240 ° C.). The dehydration reaction was performed until it became 10 mg KOH or less (about 15 hours). Thereafter, xylene was removed under reduced pressure to obtain a polyester polyol. Next, 1302 g of the polyester polyol obtained, 746 g of isophorone diisocyanate, 2127 g of pentaerythritol triacrylate (“NK Ester A-TMM-3Lnew” manufactured by Shin-Nakamura Chemical Co., Ltd.), 2.087 g of hydroquinone monomethyl ether as a polymerization inhibitor, Mixing 2.087 g of t-butyl-4-methylphenol and 2.087 g of di-n-butyltin dilaurate, reaction at 85 to 90 ° C. until there is no absorption of NCO groups by infrared spectroscopic analysis (about 5 hours) I let you. After the reaction, 1289 g of n-butyl acetate was added to obtain urethane acrylate having a solid content of 80%.

  A reaction vessel equipped with a stirrer was charged with 45 g of butyl acetate, 77 g of propylene glycol monomethyl ether, and 96 g of diacetone alcohol. While stirring, 87.5 g of the urethane acrylate (solid content 80%) obtained above, special acrylate (Toa Gosei) "Aronix M408", 30 g, benzophenone 3 g as a photopolymerization initiator, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide 2 g as a photopolymerization initiator, light stabilizer (Cinuvin 123 manufactured by Ciba Specialty Chemicals) )) 1 g, UV absorber (Shin Nakamura Chemical “UVA-1050T”, solid content 50%) 10 g, and methacrylate-modified colloidal silica (Korean Bee Chemical Co., Ltd. “FCS-016”, solid content 50%) 20 g In the order listed and charged And stirred in to give a clear coating.

(Formation of multilayer coating)
A transparent polycarbonate plate (Mitsubishi Engineering Plastics Co., Ltd., thickness: 3 mm) is annealed at 120 ° C. for 1 hour and then left to room temperature, and the substrate is shown in Tables 3-5. The undercoat paint obtained by blending was applied by air spray coating so that the film thickness after curing would be the values shown in Tables 3-5. Then, after evaporating the solvent by preheating at 60 ° C. for 10 minutes, using a 120 W / cm metal halide lamp, the substrate was coated with ultraviolet rays from a height of 25 cm in a parallel light type lamp house. A film was formed. The UV integrated light quantity at this time was 1000 mJ / cm ² when measured using UV-350 (manufactured by Oak Co.).

Next, the clear coating was applied on the base coating film by air spray coating so that the film thickness after curing was 5 μm. Then, after evaporating the solvent by preheating at 60 ° C. for 10 minutes, using a single 120 W / cm high-pressure mercury lamp, the substrate was irradiated with ultraviolet rays from a height of 25 cm in a parallel light type lamp house. A multilayer coating consisting of a coating and a clear coating was formed. The UV integrated light quantity at this time was 2000 mJ / cm ² when measured using UV-350 (manufactured by Oak Co.).

[Comparative Example 1]
(Manufacture of paint)
Each component shown in Table 6 was mixed at a blending ratio shown in Table 6 (the value of each component shown in Table 6 is “parts”) and sufficiently stirred to obtain a paint. Details of each component used are the same as in Tables 3 to 5.
(Formation of coating film)
A transparent polycarbonate plate (Mitsubishi Engineering Plastics Co., Ltd., thickness: 3 mm) is annealed at 120 ° C. for 1 hour, and then left to room temperature as a base material. The coating was performed by air spray coating so that the film thickness was a value shown in Table 6. Then, after evaporating the solvent by preheating at 60 ° C. for 10 minutes, one coat of 120 W / cm metal halide lamp was irradiated with ultraviolet rays from a height of 25 cm in a parallel light type lamp house. A coating film was formed. The UV integrated light quantity at this time was 1000 mJ / cm ² when measured using UV-350 (manufactured by Oak Co.).

[Comparative Example 2]
(Formation of coating film)
A transparent polycarbonate plate (Mitsubishi Engineering Plastics Co., Ltd., thickness: 3 mm) is annealed at 120 ° C. for 1 hour and then left to room temperature. A hard coat paint (“K2052” manufactured by Nippon Bee Chemical Co., Ltd.) was applied by air spray coating so that the film thickness after curing was a value shown in Table 6. Then, after evaporating the solvent by preheating at 60 ° C. for 10 minutes, one coat of 120 W / cm metal halide lamp was irradiated with ultraviolet rays from a height of 25 cm in a parallel light type lamp house. A coating film was formed. The UV integrated light quantity at this time was 1000 mJ / cm ² when measured using UV-350 (manufactured by Oak Co.).

  The multilayer coating film forming method according to the present invention is a method capable of imparting weather resistance and scratch resistance to a plastic substrate with high work efficiency. For example, plastic materials for automobile exteriors, sunroofs, window glass Further, it can be suitably applied to a molded product that is used in a state exposed to sunlight outdoors, such as a glass substitute plastic material used as a headlamp and the like, and whose surface is easily damaged. The coating material according to the present invention can be suitably used in the method for forming a multilayer coating film of the present invention.

Claims (3)

A method for forming a multi-layer coating film, comprising: forming a base coating film on a plastic substrate with an undercoat paint curable by active energy rays; and forming a clear coating film on the base coating film with a clear coating composition curable by active energy rays In
As the undercoat paint, a (meth) acrylic resin (A) having a double bond group in the side chain, a polyfunctional (meth) acrylate (B), an ultraviolet absorber (C) having a (meth) acryloyl group, and photopolymerization start The agent (D) is an essential component , and the (meth) acrylic resin (A) has a double bond group equivalent to 600 in the side chain of a resin having a weight average molecular weight of 5,000 to 50,000. To 2400, the solid content ratio of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) is (A) / (B) = 10 / 90-50 / 50 (mass ratio), and the ultraviolet absorber (C) is a solid content ratio with respect to 100 mass parts of the total solid content of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B). 5-15 parts by mass, photopolymerization open Agent (D) is 3 to 10 parts by weight, using a paint,
A method for forming a multilayer coating film. The method for forming a multilayer coating film according to claim 1, wherein a paint containing urethane acrylate, (meth) acrylate-modified colloidal silica, an ultraviolet absorber, a light stabilizer, and a photopolymerization initiator as essential components is used as the clear paint. An undercoat paint for a plastic substrate that is cured by an active energy ray, and has a (meth) acrylic resin (A), a polyfunctional (meth) acrylate (B), and a (meth) acryloyl group having a double bond group in the side chain. The ultraviolet absorber (C) and the photopolymerization initiator (D) are essential components , and the (meth) acrylic resin (A) has a side chain of a resin having a weight average molecular weight of 5,000 to 50,000. A double bond group is added so as to have a double bond group equivalent of 600 to 2400, and the solid content ratio of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B) is (A ) / (B) = 10/90 to 50/50 (mass ratio), and the solid content with respect to 100 parts by mass of the total solid content of the (meth) acrylic resin (A) and the polyfunctional (meth) acrylate (B). In proportion, said purple Linear absorption agent (C) is 5 to 15 parts by weight, the photopolymerization initiator (D) is 3 to 10 parts by weight, and wherein the paint.