JP2012140516A - Ultraviolet-curing coating composition and method of coating ultraviolet-cured coating film again - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultraviolet-curing coating composition that is excellent in adhesiveness to a plastic material and the like and forms a coated film excellent in re-coating properties when coating the coating composition again, and to provide a method of coating an ultraviolet-cured coating film again.SOLUTION: The ultraviolet-curing coating composition comprises: 10-50 mass% of an ultraviolet-curing oligomer (A); 1-20 mass% of an unsaturated double bond-containing compound (B); 1-30 mass% of an acrylic resin (C); 0.01-2 mass% of a photopolymerization initiator (D); and 20-70 mass% of an organic solvent (E).

Description

  The present invention relates to an ultraviolet curable coating composition and a method for repainting an ultraviolet curable coating film. More specifically, the present invention relates to an ultraviolet curable coating composition having good adhesion to plastic materials such as home appliances and automobile interior parts, and having good recoatability when repainted, and a method for repainting the same.

In recent years, ultraviolet curable coatings (hereinafter also referred to as UV curable coatings) that chemically change in response to light energy of ultraviolet rays (UV) are energy-saving because they do not require a heating and drying furnace, and have an excellent CO ₂ reduction effect. Demand is increasing as a compatible paint. Moreover, since UV coating is cured and dried by UV irradiation, it has an advantage that the drying time is short and the process can be shortened. Therefore, UV paints are widely used for building materials, plastic materials such as acrylonitrile-butadiene-styrene resin, polycarbonate resin, polyethylene terephthalate resin, and various paints have been developed for that purpose (see, for example, Patent Documents 1 to 3). .

  However, although the UV coating film has a high crosslink density and has a tough coating film, the adhesion of the coating film is poor when repainting, etc., and the recoatability is inferior. was there. In addition, when the base coat and top coat are continuously applied with UV paint, the reactive groups remain after the base coat is applied (semi-cured) in order to improve the interlayer adhesion between the base coat and the top coat. Attempts have been made to cure by applying a top coating and curing (see, for example, Patent Documents 4 and 5). However, it was difficult to repaint after the UV coating film was completely cured due to poor adhesion. Therefore, by improving the recoating property, it has become possible to repair with UV paint, so that resources can be effectively used without being disposed of.

Japanese Patent Laid-Open No. 7-100433 JP 2001-146559 A JP 2010-167762 A JP 2005-205258 A JP 2005-307133 A

  An object of the present invention is to provide an ultraviolet curable coating composition that has good adhesion to a plastic material or the like and that forms a coating film with good recoatability when repainted, and a method for repainting an ultraviolet curable coating film. That is.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the above-described problems can be achieved by the following configurations, and have reached the present invention.

In accordance with the present invention,
(A) 10-50 mass% of ultraviolet curable oligomer,
(B) 1-20% by mass of unsaturated double bond-containing compound,
(C) Acrylic resin 1-30% by mass,
(D) 0.01-2% by mass of a photopolymerization initiator,
(E) 20-70 mass% of organic solvents,
An ultraviolet curable coating composition comprising:

  Further, according to the present invention, the ultraviolet curable coating composition is characterized in that the ultraviolet curable coating composition is applied, and the ultraviolet curable coating composition is further repainted on the surface of the ultraviolet cured coating film and then cured by ultraviolet radiation. A repainting method is provided.

  The present invention relates to an ultraviolet curable coating composition that adjusts the cross-linking density of a coating film by blending an acrylic resin with an ultraviolet curable binder resin, and forms a recoatable coating film with good adhesion and its re-application. It became possible to provide a painting method.

  The ultraviolet curable coating composition of the present invention will be specifically described.

The ultraviolet curable coating composition of the present invention comprises:
(A) 10-50 mass% of ultraviolet curable oligomer,
(B) 1-20% by mass of unsaturated double bond-containing compound,
(C) Acrylic resin 1-30% by mass,
(D) 0.01-2% by mass of a photopolymerization initiator,
(E) 20-70 mass% of organic solvents,
Each component will be described.

(A) Ultraviolet curable oligomer (A) An ultraviolet curable oligomer is an oligomer having the property of being cured by ultraviolet irradiation, for example, a urethane oligomer, epoxy oligomer, polyester oligomer, polyether having a (meth) acryloyl group. Examples include oligomers and unsaturated polyester resins. It is essential that the content of the ultraviolet curable oligomer is 10 to 50% by mass, preferably 10 to 20% by weight. When it is less than 10% by mass, the coating film is not sufficiently cured, and when it exceeds 50% by mass, the coating film has high hardness but poor adhesion to the material.

(A-1) Oligomer having (meth) acryloyl group Examples of the oligomer having (meth) acryloyl group include urethane (meth) acrylate, epoxy (meth) acrylate, polyester (meth) acrylate, and polyether (meth) acrylate. Can be mentioned.

  The mass average molecular weight of these oligomers may vary depending on the type of the oligomer, but is generally about 300 to 30,000, preferably 500 to 10,000. The oligomer having the (meth) acryloyl group preferably has at least 2 to 8, preferably 2 to 6, (meth) acryloyl groups in one molecule.

(A-1-1) Urethane (meth) acrylate oligomer The urethane (meth) acrylate oligomer as an oligomer used in the present invention includes, for example, (1) an organic diisocyanate compound, (2) an organic polyol compound, and (3 ) Hydroxyalkyl (meth) acrylate is mixed in an existing ratio such that the NCO / OH ratio is, for example, 0.8 to 1.0, preferably 0.9 to 1.0. Can be manufactured. An oligomer having a large number of hydroxyl groups can be obtained by using excessive hydroxyl groups or using a large amount of hydroxyalkyl (meth) acrylate.

  Specifically, (1) an organic diisocyanate compound and (2) an organic polyol compound or the like are reacted in the presence of a urethanization catalyst such as dibutyltin laurate to obtain an isocyanate-terminated polyurethane prepolymer. Subsequently, the urethane (meth) acrylate oligomer can be produced by reacting (3) hydroxyalkyl (meth) acrylate until almost the free isocyanate group is reacted. The ratio of (2) organic polyol compound and (3) hydroxyalkyl (meth) acrylate is, for example, about 0.1 to 0.5 mol for the former with respect to 1 mol of the latter.

  Examples of (1) organic diisocyanate compounds used in the above reaction include 1,2-diisocyanatoethane, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, hexamethylene diisocyanate, and lysine. Diisocyanate, trimethylhexamethylene diisocyanate, tetramethylene diisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, bis (4-isocyanatocyclohexyl) methane, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 1, 3-bis (isocyanatomethyl) cyclohexane, 1,3-bis (isocyanatoethyl) cyclohexane, 1,3-bis (isocyanatomethyl) benzene , It can be used 1,3-bis (isocyanato-1-methylethyl) benzene and the like. These organic diisocyanate compounds can be used alone or as a mixture of two or more thereof.

  The organic polyol compound (2) used in the above reaction preferably includes, as the organic diol compound, for example, alkyl diol, polyether diol, polyester diol and the like.

Examples of the alkyl diol include ethylene glycol, 1,3-propanediol, propylene glycol, 2,3-butanediol, 1,4-butanediol, 2-ethylbutane-1,4-diol, and 1,5-pentane. Diol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,4-cyclohexanediol, 1,4-dimethylolcyclohexane, 4,8-dihydroxy Typical examples include tricyclo [5.2.1.0 ^2,6 ] decane, 2,2-bis (4-hydroxycyclohexyl) propane and the like.

  The polyether diol as the organic diol compound can be synthesized, for example, by polymerization of aldehyde, alkylene oxide, glycol or the like by a known method. For example, polyether diol can be obtained by addition polymerization of formaldehyde, ethylene oxide, propylene oxide, tetramethylene oxide, epichlorohydrin or the like to alkyl diol under appropriate conditions.

  Examples of the polyester diol as the organic diol compound include esterification reaction products obtained by reacting saturated or unsaturated dicarboxylic acids and / or their acid anhydrides with excess alkyl diols, and alkyl diols. An esterification reaction product obtained by polymerizing hydroxycarboxylic acid and / or lactone which is an intramolecular ester thereof and / or lactide which is an intermolecular ester can be used. These organic polyol compounds can be used alone or in combination of two or more thereof.

  As said (3) hydroxyalkyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, etc. can be mentioned.

  In addition, the urethane (meth) acrylate oligomer as an oligomer used in the present invention is a compound having a (meth) acryloyl group and a hydroxyl group in one molecule and an organic diisocyanate compound, and the NCO / OH ratio is, for example, Even if it reacts in the ratio of 0.9-1.0 in presence of urethanization catalysts, such as dibutyltin dilaurate, it can manufacture.

  The urethane (meth) acrylate oligomer as an oligomer used in the present invention is preferably at least one of a urethane (meth) acrylate oligomer or an aliphatic urethane (meth) acrylate oligomer having an alicyclic structure, particularly preferably an alicyclic structure. It is useful from the surface of the weather resistance and reactivity of a coating film that it is a urethane (meth) acrylate oligomer which has.

(A-1-2) Polyester (meth) acrylate oligomer The polyester (meth) acrylate as an oligomer used in the present invention is produced, for example, by a reaction between a polyester polyol having a hydroxyl group at the terminal and an unsaturated carboxylic acid. be able to. Such a polyester polyol can be typically produced by esterifying a saturated or unsaturated dicarboxylic acid or an acid anhydride thereof with an excess amount of an alkylene diol. Typical examples of the dicarboxylic acid used include oxalic acid, succinic acid, adipic acid, phthalic acid, maleic acid and the like. Examples of alkylene diols that can be used include ethylene glycol, propylene glycol, butane diol, pentane diol, and the like. Here, as unsaturated carboxylic acid, acrylic acid, methacrylic acid, etc. can be mentioned as a typical thing, for example.

(A-1-3) Epoxy (meth) acrylate oligomer The epoxy (meth) acrylate oligomer as an oligomer used in the present invention includes, for example, an epoxy compound and an unsaturated carboxylic acid as described above as an epoxy group 1. A carboxyl group equivalent per equivalent is used, for example, at a ratio of 0.5 to 1.5, and is produced by an acid ring-opening addition reaction to an ordinary epoxy group. As an epoxy compound used here, bisphenol A type epoxy, phenolic novolak type epoxy, etc. can be mentioned suitably, for example.

(A-1-4) Polyether (meth) acrylate oligomer The polyether (meth) acrylate as an oligomer used in the present invention is, for example, a polyether polyol such as polyethylene glycol or polypropylene glycol, and the above-mentioned unsaturated. It can be produced by reaction with a carboxylic acid.

(A-2) Unsaturated polyester resin On the other hand, in the present invention, the unsaturated polyester resin used as the component (A) is, for example, a reaction between an organic polyol compound and an unsaturated carboxylic acid by a known method, Further, if necessary, it can be produced by reacting a saturated polycarboxylic acid. Typical examples of the organic polyol to be used include ethylene glycol, propylene glycol, triethylene glycol, trimethylolpropane, glycerin, bisphenol A, and the like. Moreover, as unsaturated polycarboxylic acid to be used, (anhydrous) maleic acid, (anhydrous) fumaric acid, (anhydrous) itaconic acid etc. can be mentioned as a typical thing, for example.

  As these (A) components, you may use together the said (meth) acryloyl group containing oligomer and unsaturated polyester resin.

  The UV curable oligomer used in the present invention is preferably a urethane acrylate oligomer from the viewpoints of coating film properties, coating film weather resistance, and the like. Furthermore, even a urethane acrylate oligomer is particularly preferably a bifunctional or higher polyfunctional urethane acrylate oligomer.

<Bifunctional urethane acrylate oligomer>
The bifunctional urethane acrylate oligomer can be obtained by reacting an isocyanate compound obtained by reacting a polyether polyol with a linear aliphatic or alicyclic diisocyanate and an acrylate monomer having a hydroxyl group.

  Examples of the polyether polyol include polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide random copolymer, etc. Among them, those having a number average molecular weight of 400 or more are desirable.

  Examples of the linear aliphatic diisocyanate include hexamethylene diisocyanate. Examples of the alicyclic diisocyanate include isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, and hydrogenated methylene diphenyl diisocyanate.

  Examples of the acrylate monomer having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl acrylate, and polyethylene glycol monoacrylate.

<Multifunctional urethane acrylate oligomer>
The polyfunctional urethane acrylate oligomer is a reaction product of an isocyanate compound obtained by reacting a polyol and diisocyanate and an acrylate monomer having a hydroxyl group.

  Examples of the polyol include polyester polyol, polyether polyol, and polycarbonate polyol.

  The manufacturing method of a polyester polyol is not specifically limited, A well-known manufacturing method can be employ | adopted. For example, the diol and dicarboxylic acid or dicarboxylic acid chloride may be subjected to a polycondensation reaction, or the diol or dicarboxylic acid may be esterified and subjected to an ester exchange reaction.

  Dicarboxylic acids include adipic acid, succinic acid, glutaric acid, pimelic acid, sebacic acid, azelaic acid, maleic acid, terephthalic acid, isophthalic acid, phthalic acid, etc., and diols include ethylene glycol, 1,4-butanediol, 1 , 6-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, tripropylene glycol, tetrapropylene glycol and the like are used.

  As the polyether polyol, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide random copolymerization or the like is used.

  Examples of the polycarbonate diol include 1,4-butanediol, 1,6-hexanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, 2-ethyl-1,3-hexanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, polyoxyethylene glycol, and the like are used, and one kind or two kinds You may use the above together.

  As the diisocyanate, a linear or cyclic aliphatic diisocyanate is used. Typical examples include hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylylene diisocyanate, and the like.

  Examples of the acrylate monomer having a hydroxyl group include trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol triacrylate, and the like.

(B) Unsaturated double bond-containing compound The (B) unsaturated double bond-containing compound used in the present invention is a compound having a radical polymerizable carbon double bond in one molecule, and two in one molecule. There are monofunctional unsaturated monomers having one heavy bond and polyfunctional unsaturated monomers having two or more double bonds in one molecule. The content of the unsaturated double bond-containing compound is essential to be 1 to 20% by mass, preferably 2% to 20% by mass. When it is less than 1% by mass, the coating film is not sufficiently cured, and when it exceeds 20% by mass, the hardness of the coating film is increased, but the adhesion to the material is deteriorated.

(B-1) Monofunctional unsaturated monomer Examples of the monofunctional unsaturated monomer include:
Methyl acrylate, methyl methacrylate,
Ethyl acrylate, ethyl methacrylate,
Propyl acrylate, propyl methacrylate,
N-butyl acrylate, n-butyl methacrylate,
Iso-butyl acrylate, iso-butyl methacrylate,
Tert-butyl acrylate, tert-butyl methacrylate,
Hexyl acrylate, hexyl methacrylate,
Octyl acrylate, octyl methacrylate,
Lauryl acrylate, lauryl methacrylate,
2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,
Cyclohexyl acrylate, cyclohexyl methacrylate,
Stearyl acrylate, stearyl methacrylate,
Phenoxy polyethylene glycol acrylate, methoxy polyethylene glycol acrylate, 2-acryloyloxyethyl succinate, isostearyl acrylate,
Phenoxy polyethylene glycol methacrylate, methoxy polyethylene glycol methacrylate, stearyl methacrylate, 2-methacryloyloxyethyl succinate, isostearyl methacrylate and the like can be mentioned.

  Examples of the monomer include aromatic vinyl compounds such as styrene, vinyl toluene, methyl styrene, chloro styrene, and divinyl benzene; vinyl acetate, vinyl chloride, vinyl isobutyl ether, methyl vinyl ether, acrylonitrile, 2-ethylhexyl vinyl ether, and the like. Other vinyl compounds can be used.

  Furthermore, as the monomer, carboxyl group-containing monomers such as acrylic acid and methacrylic acid; hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; An adduct of an isocyanate compound such as butyl isocyanate or phenyl isocyanate and the above hydroxyl group-containing monomer; an adduct of phosphoric acid and the above hydroxyl group-containing monomer; a compound having a nitrogen-containing heterocyclic ring such as vinyl pyrrolidone or vinyl pyridine can be used. These monofunctional unsaturated monomers can be used alone or in combination of two or more.

(B-2) Polyfunctional unsaturated monomer As the polyfunctional unsaturated monomer, for example,
Diethylene glycol diacrylate, diethylene glycol dimethacrylate,
Polyethylene glycol diacrylate, polyethylene glycol dimethacrylate,
Neopentyl glycol diacrylate, neopentyl glycol dimethacrylate,
Propylene glycol diacrylate, propylene glycol dimethacrylate,
1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate,
1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate,
Neopentyl glycol diacrylate, neopentyl glycol dimethacrylate,
1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate,
Trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
Pentaerythritol triacrylate, pentaerythritol trimethacrylate,
Pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate,
Tricyclodecane dialcohol diacrylate, tricyclodecane dialcohol dimethacrylate,
Hydroxypivalate neopentyl glycol ester diol diacrylate, hydroxypivalate neopentyl glycol ester diol dimethacrylate,
Ethylene oxide modified bisphenol A diacrylate, ethylene oxide modified bisphenol A dimethacrylate,
Propylene oxide modified bisphenol A diacrylate, propylene oxide modified bisphenol A dimethacrylate,
Trimethylolpropane acrylate benzoate,
Pentaerythritol triacrylate, pentaerythritol trimethacrylate,
Pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate,
Dipentaerythritol hexaacrylate, dipentaerythritol hexamethacrylate,
Dipentaerythritol pentaacrylate, dipentaerythritol pentamethacrylate,
Glyceryl propoxy triacrylate, glyceryl propoxy trimethacrylate,
Tris-2-acryloxyethyl isocyanurate, tris-2-methacryloxyethyl isocyanurate,
Di-, tri- or tetravinyl compounds such as ditrimethylolpropane tetraacrylate and ditrimethylolpropane tetramethacrylate; products obtained by reacting an adduct of a polyhydric alcohol with ethylene oxide or propylene oxide with acrylic acid or / and methacrylic acid; A product obtained by reacting an adduct of alcohol and ε-caprolactone with acrylic acid or / and methacrylic acid; a phosphorus-containing polymerizable unsaturated monomer, and the like. These unsaturated monomers can be used alone or in combination of two or more.

  The unsaturated double bond-containing compound used in the present invention is preferably a polyfunctional unsaturated monomer, more preferably trimethylolpropane triacrylate or dipentaerythritol pentaacrylate.

(C) Acrylic resin The (C) acrylic resin used in the present invention can be produced by an ordinary solution polymerization method or suspension polymerization method. (C) As an acryl-type monomer which can be used for manufacture of an acrylic resin, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, sec- Butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, tridecyl acrylate, stearyl acrylate, cyclohexyl acrylate, benzyl acrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-methoxyethyl Acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, 2-phenoxyethyl acrylate, ethyl carbonate Bitol acrylate, allyl acrylate, glycidyl acrylate, dimethylaminoethyl acrylate, acrylic acid, sodium acrylate, trimethylolpropane acrylate, 1,4-butanediol diacrylate, 1,6-hexanediol acrylate, neopentyl glycol diacrylate, penta Acrylic acid and acrylic ester monomers such as erythritol triacrylate.

  Further, as methacrylic monomers that can be used for the production of acrylic resins, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, Cyclohexyl methacrylate, propyl methacrylate, benzyl methacrylate, isopropyl methacrylate, sec-butyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, allyl methacrylate, Tylene glycol methacrylate, triethylene glycol methacrylate, tetraethylene glycol methacrylate, 1,3-butylene glycol methacrylate, trimethylolpropane methacrylate, 2-ethoxyethyl methacrylate, 2-methoxyethyl methacrylate, dimethylaminoethylmethyl chloride salt methacrylate, methacrylic acid, Examples thereof include methacrylic acid and methacrylic acid ester monomers such as sodium methacrylate.

  In addition to the acrylic monomer components described above, as copolymerization components, vinyl monomers such as acrylamide, acrylonitrile, vinyl acetate, ethylene, propylene, isobutylene, butadiene, isoprene, chloroprene, glycidyl (meth) acrylate, methyl glycidyl (meta ) Epoxy group-containing ethylenically unsaturated monomers such as acrylate, allyl glycidyl ether, 3,4-epoxycyclohexylmethyl (meth) acrylate, carboxyl groups such as (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid Hydroxyl-containing ethylenically unsaturated monomers such as containing ethylenically unsaturated monomers, hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate can be used. These monomer components of the acrylic resin can be used alone or in combination of two or more. The acrylic resin (C) used in the present invention preferably has a Tg (glass transition temperature) of 50 to 100 ° C. When the Tg of the acrylic resin is less than 50 ° C., the coating film hardness tends to be insufficient, and when the Tg exceeds 100 ° C., the coating film tends to be too hard and the recoatability tends to decrease.

  The Tg of the acrylic resin is obtained by using a value calculated using the following FOX equation or by an actual measurement value by thermal analysis or the like.

<FOX type>
1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... + W _n / Tg _n
The above FOX formula shows the glass transition temperature of the homopolymer for each monomer constituting the copolymer composed of n types of monomer units as Tg ₁ , Tg ₂ ,..., Tg _n , respectively. (K) and the mass fraction of each monomer is W ₁ , W ₂ ,..., W _n (W ₁ + W ₂ +... + W _n = 1).

  A general UV paint uses only a reactive binder component, and the cross-linking density of the coating film is high and it is difficult to obtain a recoat property. However, in the ultraviolet curable paint composition of the present invention, 1 wt% to 30 wt% Preferably, by containing 5% to 25% by weight, a portion having a low crosslinking density can be dispersed and formed in the coating film, and the crosslinking density of the entire coating film is controlled to be low and the recoatability is enhanced. . Therefore, the shrinkage rate of the coating film during curing can be lowered, the residual stress of the coating film can be reduced, and problems due to deformations such as warping and bending of the coating object can be greatly reduced. When the content of the acrylic resin is less than 1% by mass, the recoatability is lowered, and when it exceeds 30% by mass, the coating film is not sufficiently cured, and sufficient coating film strength cannot be obtained.

(D) Photopolymerization initiator (D) The photopolymerization initiator used in the present invention is a compound that generates radicals by cleaving a bond in a molecule by ultraviolet irradiation or by extracting a hydrogen atom from another molecule. Can be mentioned. Examples of (D) photopolymerization initiators include alkylphenone photopolymerization initiators, acylphosphine oxide photopolymerization initiators, titanocene photopolymerization initiators, and oxime ester polymerization initiators. It is essential that the content of the photopolymerization initiator is 0.01 to 2% by mass, and preferably 0.1 to 2% by weight. If it is less than 0.01% by mass, the curing reaction due to photopolymerization does not proceed sufficiently, and if it exceeds 2% by mass, the photopolymerization initiator becomes excessive and the excess photopolymerization initiator causes yellowing. Adversely affect.

(D-1) Alkylphenone-based photopolymerization initiator Examples of the alkylphenone-based photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethane-1-one and 1-hydroxy-cyclohexyl-phenyl-ketone. 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-Hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one, 2-methyl-1- (4-methylthiophenyl) ) -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1,2- (dimethyl) Amino) -2-[(4-methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone and the like.

(D-2) Acylphosphine oxide photopolymerization initiator Examples of acylphosphine oxide photopolymerization initiators include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis (2,4,6-trimethyl). And benzoyl) -phenylphosphine oxide.

(D-3) Titanocene photopolymerization initiator As the titanocene photopolymerization initiator, for example, bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-) Pyrrol-1-yl) -phenyl) titanium and the like.

(D-4) Oxime ester polymerization initiator Examples of the oxime ester polymerization initiator include 1,2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)], ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (0-acetyloxime), oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxy Ethoxy] ethyl ester, 2- (2-hydroxyethoxy) ethyl ester and the like.

(D-5) Other photopolymerization initiators Further, hydrogen abstraction-type initiation of benzophenone, 2,4,6-trimethylbenzophenone, methyl benzoylbenzoate, 2,4-diethylthioxanthone, 2-ethylanthraquinone, camphorquinone, etc. An agent can also be used.

  These photoinitiators may be used individually by 1 type, and may use 2 or more types together. The photopolymerization initiator used in the present invention is preferably an alkylphenone photopolymerization initiator in terms of reactivity and the like, and more preferably 1-hydroxy-cyclohexyl-phenyl-ketone or 2-hydroxy-2-methyl-1- Phenyl-propan-1-one is particularly preferred.

(E) Organic solvent The ultraviolet curable coating composition of the present invention contains a normal (E) organic solvent as in the case of a general coating composition. As such an organic solvent, those having good compatibility with the binder component and the photopolymerization initiator are preferable, for example, ketones such as methyl ethyl ketone, methyl isobutyl ketone, isophorone, ethanol, 1-butanol, 2-propanol and the like. Alcohols, cellosolves, acetate esters, ethers, aromatic hydrocarbons and the like can be used alone or as a mixture thereof. Moreover, the compounding quantity is 20-70 mass% used as the quantity which gives the fluidity suitable for the coating method of a coating composition to a coating composition, Preferably it is 30-60 weight%.

  The ultraviolet curable coating composition of the present invention can contain ordinary additives as long as the properties of the obtained coating film are not impaired, in the same manner as general coating materials, in addition to the above components. Examples of such additives include ordinary dispersants, curing agents, curing catalysts, antioxidants, and leveling agents.

  Further, the ultraviolet curable coating composition of the present invention is basically clear, but can contain a pigment or a dye as a colorant to the extent that UV curing is not hindered. As the type, those used for ordinary paints and inks can be used.

<Coating method>
The ultraviolet curable coating composition of the present invention is coated by applying active energy rays (UV light, etc.) after being applied by air spray coating, airless spray coating, brush coating, roller brush coating, spatula coating or the like. A UV coating can be formed on top. As the active energy ray source, an ultraviolet ray source such as a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, a xenon lamp, an excimer laser, or a dye laser can be used. The irradiation amount is suitably in the range of 50 to 3000 mJ / cm ² . Therefore, since a heating furnace is not used for curing and drying, it can be applied to a resin base material having relatively low heat resistance, has a high surface hardness, and can be continuously mass-produced and increased in area. The active energy ray irradiation may be performed in an inert gas atmosphere such as nitrogen or argon gas depending on circumstances.

  Since the ultraviolet curable coating composition of the present invention contains an organic solvent, heat drying at a relatively low temperature and in a short time may be combined as preliminary drying before the ultraviolet curing.

<Coating material>
The objects to be coated with the ultraviolet curable coating composition of the present invention are mainly plastic materials, and the types thereof are acrylonitrile-styrene resin, acrylonitrile-butadiene-styrene resin (ABS), acrylic resin, polycarbonate resin ( PC), phenol resin, polyolefin (polypropylene, etc.), polystyrene, polyvinyl chloride, polyethylene terephthalate resin (PET), polybutylene terephthalate resin (PBT), polyphenylene oxide, polyamide resin, polymethyl methacrylate resin, polyallyl diglycol carbonate resin Or a complex thereof. Among them, any of ABS resin, PC resin, PET, polyolefin, or a composite thereof is preferable, and further, ABS resin, PC resin, and PC / ABS composite are preferable because of excellent adhesion.

  These plastic substrates may be subjected to surface treatment or the like for the purpose of improving adhesion.

  The UV curable coating composition of the present invention is applied to the surface of the object to be coated and once UV cured, and after a certain period of time, the same UV curable coating composition is repainted on the surface and peeled off even after UV curing. It is characterized by being in close contact (excellent recoatability). In that case, repainting can be further repeated up to three times (four-layer coating film). If repainting is performed more than 3 times, strain stress accumulates on the base material and deformation of the article to be coated is not preferable.

  Examples The present invention will be described in more detail with reference to examples, but these examples do not limit the scope of the present invention. In the examples, “parts” and “%” are based on mass unless otherwise specified.

(Examples 1-7 and Comparative Examples 1-6)
<Preparation of UV curable coating composition>
(A) Trifunctional urethane acrylate oligomer (trade name: BS550, manufactured by Arakawa Chemical Co., Ltd.) as an ultraviolet curable oligomer,
Hexafunctional urethane acrylate oligomer (trade name: BS575, manufactured by Arakawa Chemical)
2-3 functional epoxy acrylate oligomer (trade name: AQ-9, manufactured by Arakawa Chemical Co., Ltd.)
(B) Trimethylolpropane triacrylate (TMPTA, trifunctional monomer) as an unsaturated double bond-containing compound,
Dipentaerythritol pentaacrylate (DPEPA, pentafunctional monomer),
Octyl methacrylate (monofunctional monomer)
Phenoxypolyethylene glycol acrylate (PPEGA, monofunctional monomer),
(C) Acrylic resin A (styrene / methyl methacrylate, homemade, Tg = 90 ° C.) as an acrylic resin,
Acrylic resin B (styrene / butyl methacrylate, homemade, Tg = 55 ° C.)
Acrylic resin C (ethyl hexyl acrylate / butyl methacrylate, homemade, Tg = 30 ° C.)
(D) 1-hydroxy-cyclohexyl-phenyl-ketone (trade name: IC184, manufactured by Ciba Japan) as a photopolymerization initiator,
2-hydroxy-2-methyl-1-phenylpropan-1-one (trade name: DC1173, manufactured by Ciba Japan),
2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (trade name: DCTPO, manufactured by Ciba Japan)
(E) thinner composition as organic solvent (isobutyl alcohol 25%, butyl acetate 25%, ethyl acetate 20%, propylene glycol monomethyl ether 20%, ethylene glycol monobutyl ether 10%),
Polyester resin (trade name: Byron GK810, manufactured by Toyobo Co., Ltd., Tg = 46 ° C.)
HALS (hindered amine light stabilizer, trade name: Tinuvin 292, manufactured by Ciba Japan),
Using the formulation shown in Table 1, the components (A) to (E) were mixed, dispersed while stirring well, and the UV paints of Examples 1 to 7 and Comparative Examples 1 to 6 were prepared. It was. In addition, the liquid thing was described as solid content.

<Preparation of test plate>
Each ultraviolet curable coating composition was applied to an ABS plate and a polycarbonate (PC) plate so as to have a film thickness of 20 μm, and the ultraviolet ray was irradiated at about 400 mJ / cm ² (650 to 700 mW / cm ² ), and then the ultraviolet ray was cured and a test plate. Got. Each test and evaluation method were performed as follows.

<Appearance of coating film>
The coating film appearance of the coated plate produced above was visually observed and evaluated as follows, based on the presence or absence of coating film defects such as wrinkles and wrinkles, the presence or absence of gloss or blur.
○… No abnormality △… Brightness and blurring are seen ×… Wrinkles and wrinkles are seen

<Coating hardness>
Using the coated plate prepared above, according to JIS K5600-5-4, the surface of the coating film was scratched using a Mitsubishi Hi-Uni pencil, and the hardness was evaluated as follows with the hardest pencil hardness at which the coating film was not damaged.
〇… HB or more △… B
× ... 2B or less

<Abrasion resistance>
Using the coating plate prepared above, the coating film surface after the rubbing test was repeated 20 times with steel wool (# 000) at room temperature was visually evaluated as follows.
〇… No abnormality △… Scratches ×… Many scratches, some peeled off

<Heat resistance>
Using the coated plate prepared above, the adhesiveness of the coating film was confirmed after heating at 80 ° C. for 120 hours. According to JIS K5600-5-6, a 2 mm wide gobang eye adhesion test was performed on the coating film surface of the test plate, and when the coating film surface was peeled off with cello tape (registered trademark), according to the number of gobang eyes that did not peel off The evaluation was as follows.
○ ... 100/100
Δ: 10-99 / 100
× ... 9/100 or less

<Moisture resistance>
The test piece was left in a constant temperature and humidity chamber of 98% RH or higher at 50 ° C. for 120 hours, and then a Gobang eye adhesion test of the coating film was performed in the same manner as the heat resistance test, and evaluated according to the following criteria.
○ ... 100/100
Δ: 10-99 / 100
× ... 9/100 or less

<Recoat / Adhesiveness>
The coated plate prepared above is allowed to stand at room temperature in a dark room for one week after the production, re-apply each ultraviolet paint from the coating film so as to have a film thickness of 20 μm, and perform ultraviolet irradiation under the same conditions as above, UV curing was performed. Thereafter, a gobang eye adhesion test of the coating film was performed and evaluated according to the following criteria.
○ ... 100/100
Δ: 10-99 / 100
× ... 9/100 or less

<Recoat / War>
About what used the ABS board, about the thing which repeated the repainting and ultraviolet curing to the 3rd time and performed 4 layer coating, the curvature (deflection) of the test board was confirmed and the following reference | standard evaluated.
◎… No abnormality ○… Slight deflection was generated △… Slight deflection was generated but there was no problem in actual use ×… Slack occurred and there was a problem in actual use XX… Large deflection occurred

  The ultraviolet curable coating composition of the present invention has good adhesion and is excellent in recoatability when repainted, so it can be used as a plastic material for home appliances, audio, personal computers, automobile interior parts, etc. .

Claims (8)

(A) 10-50 mass% of ultraviolet curable oligomer,
(B) 1-20% by mass of unsaturated double bond-containing compound,
(C) Acrylic resin 1-30% by mass,
(D) 0.01-2% by mass of a photopolymerization initiator,
(E) 20-70 mass% of organic solvents,
An ultraviolet curable coating composition comprising:   The ultraviolet curable coating composition according to claim 1, wherein the (A) ultraviolet curable oligomer is a polyfunctional urethane acrylate oligomer.   The ultraviolet curable coating composition according to claim 1 or 2, wherein the (B) unsaturated double bond-containing compound is a bifunctional or higher unsaturated monomer.   The ultraviolet curable coating composition according to any one of claims 1 to 3, wherein the glass transition temperature Tg of the (C) acrylic resin is 50 to 100 ° C.   The ultraviolet curable coating composition according to any one of claims 1 to 4, wherein the photopolymerization initiator (D) is an alkylphenone photopolymerization initiator.   The ultraviolet curable coating composition according to any one of claims 1 to 5 is applied, and the ultraviolet curable coating composition is further repainted on the surface of the ultraviolet-cured coating film, followed by ultraviolet curing. Re-painting method for UV-cured coatings.   The method for recoating an ultraviolet curable coating film according to claim 6, wherein the ultraviolet curable coating composition can be repainted up to three times.   The object to be coated with the ultraviolet curable coating composition is a plastic, and is selected from the group consisting of acrylonitrile-butadiene-styrene resin, polycarbonate resin, polyethylene terephthalate resin, polyolefin resin, and composites thereof. 8. A method for repainting an ultraviolet curable coating film according to item 7.