JPH1017788A - Metal painting composition of active energy ray curing type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metal painting composition of active energy ray curing type that has high adhesivity to metals and excellent chemical resistance, and forms a cured film of high hardness. SOLUTION: This metal painting composition of active energy ray curing type comprises a reactive resin (A) which is obtained by continuous polymerization of 30wt.% or more of (meth)acrylate having one or more number of hydroxyl group and 70wt.% of a monomer having an ethylenic unsaturated group at 150-350 deg.C to form a copolymer (a) having a number-average molecular weight of 1,000-10,000, and by esterification of the hydroxyl group of the copolymer (a) with a monomer having one or more ethylenic unsaturated groups and one carboxylic group; and a reactive diluent composed of one or more kinds of ultraviolet-curing monomers (B) and a photo-initiator (C) both of which are compounded with the reactive resin (A). If for the polymerization, a continuous high-temperature polymerization is adopted, a copolymer of relatively high molecular weight and low viscosity is obtained, thus enabling decrease of curing contraction of the composition and improvement of adhesivity of the cured film to the base material. A preferable reactive diluent is a monomer of high polarity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition for a metal which is cured by irradiation with an active energy ray such as an electron beam or an ultraviolet ray. Also, the present invention relates to an active energy ray-curable metal coating composition which is excellent in chemical resistance and forms a hardened film having high hardness. The composition of the present invention is used for coating metal cans and metal plates, and is particularly suitable as a coating composition for metal cans in which deep drawing is performed after coating. still,
In the present specification, acrylate and / or methacrylate will be referred to as (meth) acrylate, and acrylic acid and / or methacrylic acid will be referred to as (meth) acrylic acid.

[0002]

2. Description of the Related Art In recent years, organic solvents used in various industries, etc.,
Air pollution on a global scale due to the release of detergents and the like into the atmosphere has progressed, and there is a concern about the effects on living organisms. For this reason, in the metal coating composition, high solidification,
Studies are being made to remove the solvent. In order to solve these problems, coating compositions for metals that are cured by irradiation with active energy rays are known. For example, oligoester (meth) acrylates such as polyester acrylate, epoxy acrylate and urethane acrylate and a reactive diluent There is something consisting of The number average molecular weight of these oligoester (meth) acrylates is usually about 500 to 1,000 in order to reduce the viscosity of the composition to such an extent that it can be applied relatively easily.

[0003]

However, in a conventional active energy ray-curable metal coating composition, it is difficult to obtain a cured film having high adhesion (adhesion) to a metal substrate. Therefore, physical properties such as bending property of the cured film were insufficient. The cause of such low adhesion is compared with a composition using a solvent-dried resin or a composition using a thermosetting resin, which cures while gradually relaxing strain by thermal drying or thermosetting. On the other hand, the active energy ray-curable composition has a short curing time, so that stress strain caused by volume shrinkage at the time of curing is easily accumulated in the cured film. In addition, some of the conventional active energy ray-curable metal coating compositions have insufficient cured film bending properties.

[0004] As a method of improving the adhesion between the active energy ray-curable composition and the substrate, a non-reactive substance such as an acrylic polymer, polyester, or petroleum resin is used to reduce the volume shrinkage upon curing. A method of mixing and dissolving in a composition for use is known. However, the composition containing such a non-reactive substance, the active energy ray curability of the composition and the solvent resistance of the cured product, the chemical resistance, etc. are reduced as compared with the case where no non-reactive substance is contained. There's a problem. Further, since many of these non-reactive substances have low solubility in the composition, the selection range is limited, and the dissolving operation is often difficult. Further, it is not preferable because the coating aptitude decreases because the viscosity of the composition increases. In addition, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 3-49027 discloses a process adhesiveness and curability which can be cured by an active energy ray and comprises a predetermined oligoester (meth) acrylate, a predetermined epoxy mono (meth) acrylate and a polymer capable of these. And the like. However, this composition also did not have sufficient performance especially in terms of coating suitability and solvent resistance, chemical resistance and hardness of the cured film.

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating composition for an active energy ray-curable metal which forms a cured film having high adhesion to metals, excellent solvent resistance and chemical resistance, high hardness and excellent bending properties. To provide things.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, a composition obtained by blending a reactive diluent with a reactive resin obtained by a specific method is effective. I found something. That is, the coating composition for an active energy ray-curable metal according to claim 1 is 30% by weight or more of one or more (meth) acrylates having one or more hydroxyl groups and one other than the (meth) acrylate. And a copolymer having a number average molecular weight of 1,000 to 10,000 by continuously polymerizing at least 70% by weight of at least one kind of a monomer having an ethylenically unsaturated group at a copolymerization temperature of 150 to 350 ° C. (A), and then a reactive resin (A) obtained by subjecting a monomer having at least one ethylenically unsaturated group and one carboxyl group to an esterification reaction with respect to a hydroxyl group in the copolymer. And a reactive diluent (B) composed of at least one UV-curable monomer and a photoinitiator (C).

[0007] The active energy ray-curable metal coating composition according to claim 2 is the composition according to claim 11, wherein at least one of the monomers having one ethylenically unsaturated group is selected from the group consisting of: Styrene or alkylstyrene, and the copolymerization ratio of the styrene or the alkylstyrene in the copolymer is 20 to 60% by weight.

[0008] Further, the active energy ray-curable metal coating composition according to claim 3 is the composition according to claim 1 or 2, wherein the glass transition temperature of the copolymer is 30 ° C.
~ 120 ° C.

The active energy ray-curable metal coating composition of the present invention comprises a (meth) acrylate having at least one hydroxyl group as a copolymer (a) serving as a skeleton of the reactive resin (A) [hereinafter, referred to as “methacrylate”]. "Hydroxy group-containing (meth) acrylate"
That. And one or more monomers having one ethylenically unsaturated group other than the (meth) acrylate (hereinafter referred to as
It is referred to as "ethylenically unsaturated monomer". ) Is used.

As the "hydroxyl group-containing (meth) acrylate", various ones can be used. For example, hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl (meth) acrylate Epoxides and (meth) acryls such as mono- or poly (meth) acrylates of polyhydric alcohols such as pentaerythritol tri (meth) acrylate and glycerin mono (meth) acrylate, and adducts of cyclohexene oxide and (meth) acrylic acid Adducts with acids are mentioned.

As the "ethylenically unsaturated monomer", various ones other than the above-mentioned hydroxyl group-containing (meth) acrylate can be used. For example, styrene, alkylstyrene, acrylonitrile, methacrylonitrile, vinyl acetate and vinyl acetate can be used. (Meth) acrylate and the like. (Meta)
Specific examples of the acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth)
Acrylate, isobutyl (meth) acrylate, 2-
Examples include ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, and isobornyl (meth) acrylate.

In the present invention, the copolymer (a) has a hydroxyl group-containing (meth) content of 30% by weight or more based on the total amount of the hydroxyl group-containing (meth) acrylate and the ethylenically unsaturated monomer.
Acrylate must be copolymerized, and 4
The content is preferably set to 0 to 80% by weight. This is because when the copolymerization ratio of the hydroxyl group-containing (meth) acrylate is less than 30% by weight, the resulting reactive resin has a monomer having one or more ethylenically unsaturated groups and one carboxyl group described later. The amount of the ethylenically unsaturated group introduced in the esterification reaction with the monomer becomes insufficient, whereby the active energy ray curability of the reactive resin and the hardness, solvent resistance, chemical resistance and chemical resistance of the cured product are reduced. This is because the abrasion and the like become insufficient.

It is preferable that at least one of the above-mentioned ethylenically unsaturated monomers is selected from styrene and alkylstyrene (hereinafter, referred to as “styrenic monomer”), and that the copolymer contains The copolymerization ratio of the styrenic monomer is 20 to 60% by weight (preferably 40
~ 55% by weight). This is achieved by copolymerizing 20% by weight or more of a styrenic monomer.
This is because the glass transition temperature (Tg) of the reactive resin after curing rises, so that a tough cured film can be obtained and the gloss of the cured film becomes good. However, if the copolymerization ratio of the styrenic monomer exceeds 60% by weight, the cured film becomes too hard, and physical properties such as bendability tend to decrease. Therefore, the upper limit of the copolymerization ratio is 60% by weight. And As the “styrenic monomer”, styrene, α-
Methyl styrene, α-ethyl styrene, β-methyl styrene, 3-methyl styrene, 4-methyl styrene, etc.
One or more compounds selected from the compounds represented by the structural formulas shown in Chemical Formula 1 below can be used. Among them, it is particularly preferable to use styrene.

[0014]

Embedded image (However, R ₁ , R ₂ , R ₃ , and R ₄ are each H or an alkyl group having 1 to 6 carbon atoms)

Further, it is preferable to select the type of the monomer and the copolymerization ratio so that the copolymer (a) has a glass transition temperature (Tg) in the range of 30 ° C. to 120 ° C.
More preferably, the temperature is in the range of 50C to 100C. This is because if the Tg is less than 30 ° C., the cured film of the composition of the present invention containing the reactive resin obtained in the subsequent esterification reaction has insufficient hardness. On the other hand, if the Tg exceeds 120 ° C., it takes a long time to relax the stress strain generated during curing of the composition, so that the adhesion between the cured film and the metal substrate is reduced, and the cured film is too hard. Therefore, physical properties such as bending property may be reduced.

The number average molecular weight of the copolymer (a) is 1,0
Must be from 00 to 10,000, preferably 1,
000-5,000. Number average molecular weight of 10,000
If it exceeds 0, the reactivity in the esterification reaction between one or more ethylenically unsaturated groups and a monomer having one carboxyl group, which will be described later, is poor, and as a result, ethylenically unsaturated The introduction ratio of the group may be reduced, or it may be difficult to separate the product from the basic aqueous solution or water in a post-treatment after the esterification reaction. Further, if the number average molecular weight exceeds 10,000, the viscosity of the obtained reactive resin becomes extremely high. Therefore, many reactive diluents are blended in order to make the metal coating composition have a coatable viscosity. It will be. If the mixing ratio of the reactive diluent is high, the composition may exhibit skin irritation, and the adhesion between the cured film and the metal substrate tends to decrease, which is not preferable. On the other hand, if the number average molecular weight of the copolymer is less than 1,000, the composition comprising the obtained reactive resin will have a large curing shrinkage, and the adhesion between the cured film and the metal substrate will be reduced.

In the present invention, the "polydispersity (Mw / Mn)" which is a ratio of the weight average molecular weight (Mw) of the copolymer to the number average molecular weight (Mn) is 2.5 or less (for example, , 1.0 to 2.5), and more preferably 2.0 or less (e.g., 1.0 to 2.0). This is because a copolymer having a polydispersity of 2.5 or less has excellent reactivity in an esterification reaction described later. Further, when the number average molecular weights are about the same, the closer the polydispersity is to 1, the lower the viscosity of the obtained reactive resin tends to be. Accordingly, a composition having a viscosity that can be applied using a reactive resin having a higher number average molecular weight can be obtained, which is preferable in improving the adhesion between the cured film and the metal substrate. In the present invention, the number average molecular weight and the weight average molecular weight are values obtained by using tetrahydrofuran as a solvent and converting the molecular weight measured by GPC into polystyrene.

The copolymer used in the present invention is obtained by continuously polymerizing a hydroxyl group-containing (meth) acrylate and an ethylenically unsaturated monomer at a high temperature of 150 to 350 ° C. According to this high-temperature continuous polymerization method, it is not necessary to use a thermal polymerization initiator, or even when a thermal polymerization initiator is used, a copolymer having a desired molecular weight can be obtained with a small amount of use, so that radicals are generated by heat or light. A highly pure copolymer containing almost no impurities generating seeds is obtained. Therefore, the esterification reaction between the copolymer described below and the monomer having one or more ethylenically unsaturated groups and one carboxyl group can be stably performed, and the finally obtained reactivity can be improved. The resin and the metal coating composition comprising the reactive resin are excellent in storage stability, and the cured film of the composition is excellent in weather resistance. In addition, a copolymer having a lower polydispersity and therefore a lower viscosity than those obtained by conventional solution polymerization can be easily obtained, which is preferable.

The high temperature continuous polymerization method is disclosed in
Nos. 02171, 59-6207 and 60-215
007 or the like may be used. For example, a pressurizable reactor is filled with a solvent, and after a predetermined temperature is set under pressure, a monomer comprising a hydroxyl group-containing (meth) acrylate, an ethylenically unsaturated monomer, and, if necessary, a polymerization solvent is used. There is a method in which the body mixture is supplied to the reactor at a constant supply rate, and an amount of the reaction solution corresponding to the supply amount of the monomer mixture is withdrawn. When a reaction solvent is used, the solvent to be charged into the reactor at the start of the reaction and the reaction solvent to be mixed with the monomer mixture may be the same or different.

The solvent or the polymerization solvent is not particularly limited as long as it can dissolve the produced copolymer. For example, alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol and tripropylene glycol, toluene and Aromatic hydrocarbons such as xylene, ethyl acetate, butyl acetate,
Examples thereof include acetates such as cellosolve acetate, methyl propylene glycol acetate, carbitol acetate and ethyl carbitol acetate, and ketones such as acetone and methyl ethyl ketone. When an alcohol is used as a polymerization solvent, if the next esterification reaction is carried out in a state where the alcohol remains in the reaction solution after the production of the copolymer, the active energy as the reactive resin and the reactive diluent can be obtained. It is also possible to simultaneously produce a line-curable monomer. The mixing ratio of the polymerization solvent is preferably 200 parts by weight or less based on 100 parts by weight of the monomer mixture.

The monomer mixture may be mixed with a thermal polymerization initiator, if necessary. The type of the thermal polymerization initiator is not particularly limited, and examples thereof include an azonitrile-based initiator and a peroxide-based initiator. As the azonitrile initiator, 2,2′-azobisisobutyronitrile,
2,2'-azobis (2-methylbutyronitrile) and 2,2'-
Azobis (2,4-dimethylvaleronitrile) and the like. Further, as the peroxide-based initiator, hydrogen peroxide,
Di-t-butyl peroxide and benzoyl peroxide. Of these, it is preferable to use an azonitrile initiator because of easy handling. When the thermal polymerization initiator is blended with the monomer mixture, the amount is 0.001 to 5 parts by weight per 100 parts by weight of the monomer mixture.
It is preferably in parts by weight.

The reaction temperature of the high-temperature continuous polymerization in the present invention is in the range of 150 to 350 ° C. This is because if the reaction temperature is lower than 150 ° C., the molecular weight of the obtained copolymer may be too large or the reaction rate may be slow. This is because coloring may be observed in the reaction solution due to generation of, a later-described esterification reaction may become unstable, and the obtained reactive resin may become unstable. The pressure during the reaction is
It depends on the reaction temperature and the boiling point of the monomer mixture and the solvent used and does not affect the reaction, but any pressure may be used as long as the reaction temperature can be maintained. The residence time of the monomer mixture is preferably 2 to 60 minutes. When the residence time is less than 2 minutes, the amount of unreacted monomer increases, and the copolymer yield may decrease. On the other hand, when the residence time exceeds 60 minutes, the productivity is poor. Sometimes it becomes.

The reactive resin which is the component (A) of the composition of the present invention comprises one or more ethylenically unsaturated groups relative to the hydroxyl groups in the copolymer (a) obtained as described above. And a monomer having one carboxyl group (hereinafter referred to as "carboxyl group-containing unsaturated monomer").

Examples of the unsaturated monomer having a carboxyl group include oligomers of dimer or more by Michael addition of acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, acrylic acid or methacrylic acid, and ω-carboxypolycaprolactone monomer. (Meth) acrylate, monohydroxyethyl phthalate (meth) acrylate and monohydroxyethyl succinate (meth) acrylate are exemplified. Among them, (meth) acrylic acid is preferable because the obtained reactive resin has excellent reactivity since the content of ethylenically unsaturated groups in the obtained reactive resin is high.

The reaction ratio of the carboxyl group-containing unsaturated monomer to the hydroxyl group in the copolymer is preferably 0.5 to 2.0 mol per 1 mol of all the hydroxyl groups in the copolymer. Most preferably, it is about mol. If this ratio is less than 0.5 mol, the esterification reaction rate will be reduced, and side reactions such as Michael addition of hydroxyl groups in the reactive resin to the double bond of the carboxyl group-containing unsaturated monomer will occur. Occurs, the viscosity of the reaction solution increases, the neutralization separation in the post-treatment becomes difficult, or the reactivity of the resin becomes poor because the ratio of ethylenically unsaturated groups in the obtained reactive resin becomes low. It may be. On the other hand, when it exceeds 2.0 mol, the amount of unreacted carboxyl group-containing unsaturated monomer increases only, which is not economical, and in addition, post-treatment after the reaction may be complicated.

The esterification reaction between the copolymer and the carboxyl group-containing unsaturated monomer may be carried out according to a conventionally known method. For example, there is a method in which the copolymer and the carboxyl group-containing unsaturated monomer are heated and stirred in the presence of a catalyst. In this case, since the reaction is a dehydration reaction, it is preferable to carry out the reaction by distilling water out of the reaction system. For this purpose, benzene, toluene, xylene, ethyl acetate, butyl acetate and / or methyl isobutyl ketone are used. It is preferable to carry out the reaction using a solvent that is not completely mixed with water, while distilling off water produced in the reaction by azeotropic distillation outside the reaction system. The amount of the solvent used in this case is preferably such that the solid content concentration of the obtained reactive resin is 20 to 80% by weight. As a catalyst for the esterification reaction, an acidic catalyst such as sulfuric acid, methanesulfonic acid or p-toluenesulfonic acid is used. The preferred amount of the catalyst is 0.1 to 5% by weight based on the reaction solution. The reaction temperature may be appropriately determined depending on the boiling point of the solvent to be used and the like, but it is generally preferable to carry out the reaction at 60 to 140 ° C. In this reaction, in order to stably perform the reaction, it is preferable to add a polymerization inhibitor such as hydroquinone or hydroquinone monomethyl ether, or to blow in molecular oxygen. When a polymerization inhibitor is used, it is preferably used in a range of 10 wtppm to 2% by weight based on the reaction solution.

After completion of the esterification reaction, the reaction solution is preferably mixed with a basic aqueous solution such as an aqueous sodium hydroxide solution in order to remove the used acidic catalyst from the reaction solution. The desired reactive resin can be obtained by separating the aqueous phase from this mixture and further distilling off the solvent in the oil phase under reduced pressure.

The reactive diluent, which is the component (B) of the composition of the present invention, is an active energy ray-curable monomer compounded for the purpose of adjusting the viscosity of the composition and the like. Various kinds of so-called "" can be used. Here, in the metal coating composition of the present invention, it is preferable to use a highly polar active energy ray-curable monomer. This is because the metal as the target substrate of the composition of the present invention has a high surface energy, so that a composition containing a highly polar reactive diluent is blended with the cured film and the metal substrate of the composition. This is because the effect of improving the adhesiveness of is obtained. Such highly polar active energy ray-curable monomers include (meth) acrylates having one or more hydroxyl groups in one molecule, (meth) acrylates having one or more carboxyl groups in one molecule, and others. And an active energy ray-curable monomer having a high polarity. Of these, only one kind may be used, or two or more kinds may be used in combination.

Specifically, examples of the (meth) acrylate having one or more hydroxyl groups in one molecule include the following. Hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate 2-hydroxy-3-butoxypropyl (meth) acrylate and 2-hydroxy-3-phenoxypropyl (meth) acrylate Glycidyl ethers such as (meth) acrylate of alkylene glycol diglycidyl ether, bisphenol A type epoxy (meth) acrylate and bisphenol F type epoxy (meth) acrylate, 2-hydroxy-3- (o-methylphenoxy) propyl (meth) acrylate (Cyclohexene oxide) mono (meth) acrylate Ethylene glycol mono or di (meth) acrylate, methoxyethylene glycol monomer Mono or di (meth) glycols, such as mono (meth) acrylate, mono or di (meth) acrylate of diethylene glycol, mono or di (meth) acrylate of tetraethylene glycol, mono or di (meth) acrylate of tripropylene glycol Acrylate Mono-, di- or tri- (meth) acrylate of pentaerythritol, mono-, di- or tri- (meth) acrylate of trimethylolpropane, or a (meth) acrylic acid ester of alkylene oxide thereof isocyanuric acid ethylene oxide-modified di ( Meta)
Acrylate

Specific examples of (meth) acrylates having one or more carboxyl groups in one molecule include ω-
Carboxy-polycaprolactone mono (meth) acrylate; 2-hydroxy (meth) acrylates such as monohydroxyethyl (meth) acrylate phthalate, monohydroxyethyl (meth) acrylate succinate, and monohydroxyethyl (meth) acrylate tetrahydrophthalate Dibasic acid adduct of acrylic acid; dimer of acrylic acid.

In addition, active energy ray-curable monomers having high polarity include N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, N, N-
Dimethylaminoethyl (meth) acrylate, N, N-
Dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, phosphoric acid mono-, di- or tri (meth) acrylate, tetrahydrofurfuryl (meth) acrylate and the like.

Incidentally, as the reactive diluent (B) of the present invention, it is also possible to use active energy ray-curable monomers other than those described above. Examples of such an active energy ray-curable monomer include phenol alkylene oxide-modified (meth) acrylate, nonylphenol alkylene oxide-modified (meth) acrylate, 2-ethylhexyl carbitol (meth) acrylate; and bisphenol A ethylene oxide-modified diacrylate. (Meth) acrylate; isocyanuric acid ethylene oxide-modified di- or tri (meth) acrylate; trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropanetetra ( (Meth) acrylates such as polyols or alkylene oxide (meth) acrylates thereof; isobornyl (meth) acrylates and the like. Rukoto can.

In the composition of the present invention, when the total of the reactive resin (A) and the reactive diluent (B) is 100% by weight, 30 to 90% by weight of the reactive resin (A), It is preferable to mix the diluent (B) at a ratio of 10 to 70% by weight, more preferably at a ratio of 40 to 80% by weight of the reactive resin (A) and 20 to 60% by weight of the reactive diluent (B). preferable. This is because if the proportion of the reactive resin is less than 30%, the effect of suppressing the curing shrinkage of the composition becomes insufficient, and therefore, the adhesion of the cured film to the substrate is reduced. On the other hand, when the ratio of the reactive diluent is less than 10%, the viscosity of the composition becomes too high and coating suitability is lowered, and the crosslink density of the cured film is insufficient and the solvent resistance and chemical resistance are insufficient. May decrease.

Further, in addition to the above essential components, the composition of the present invention may further comprise, if necessary, an inorganic filler such as barium sulfate, silicon oxide, talc, clay and calcium carbonate, phthalocyanine blue, phthalocyanine green, Dyes or pigments such as titanium oxide and carbon black, viscosity modifiers, treating agents, UV blocking agents, various additives such as adhesion promoters and leveling agents, and hydroquinone, hydroquinone monomethyl ether, phenothiazine and N-nitrosophenylhydroxyl A polymerization inhibitor such as an amine aluminum salt may be added. These components are:
It is preferable that the total amount of the above essential components is 100 parts by weight or less so that the total amount is 100 parts by weight or less. When a polymerization inhibitor is compounded, the compounding ratio in the composition is preferably 10 wtppm to 2% by weight.

When an ultraviolet ray is used as an active energy ray for curing the composition of the present invention, a photopolymerization initiator is added to the composition. When an electron beam is used as the active energy ray, it is not necessary to particularly incorporate a photopolymerization initiator. The photopolymerization initiator is not particularly limited. For example, benzoin such as benzoin, benzoin methyl ether, benzoin ethyl ether and benzoin isopropyl ether and its alkyl ether, acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2 2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxyacetophenone, 1-hydroxycyclohexylphenyl ketone and 2-methyl-1- [4- (methylthio)
Phenyl] -2-morpholino-propan-1-one and the like; anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone and 2-amylanthraquinone, and 2,4- Thioxanthones such as dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone and 2,4-diisopropylthioxanthone, ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal, benzophenones such as benzophenone, and xanthones. Can be The photoinitiator may be used alone or in combination with a benzoic acid-based or amine-based photopolymerization initiation accelerator. The photopolymerization initiator is preferably incorporated in the composition in an amount of 0.1 to 10% by weight.
As a method for irradiating the active energy ray for curing the composition of the present invention, a conventionally known method may be employed.

The metal substrate to which the composition of the present invention can be applied is a cut or coiled iron plate, a hot-rolled steel plate, a cold-rolled steel plate, an alloy-plated steel plate, an electro-galvanized steel plate, a hot-dip galvanized steel plate, or any of these. Which have been subjected to a chemical conversion treatment such as chromic acid or phosphoric acid treatment, an aluminum plate, a stainless steel plate, a tinplate and a tin-free steel plate. Further, a pretreatment or the like may be performed on the above-described metal base material as necessary. For example, when using a substrate that has already been subjected to a chemical conversion treatment in the manufacturing process as described above, it is possible to simply use a substrate that has been subjected to a washing treatment,
When a base material that has not been subjected to a chemical conversion treatment is used, a pretreatment according to the material may be performed. Further, as the steel sheet, a steel sheet having a surface coated with a primer may be used. By applying the primer to the surface of the steel sheet in this manner, the corrosion resistance of the steel sheet and the adhesion to the cured film of the coating composition can be improved. Various primers can be used, and examples thereof include an epoxy resin, a modified epoxy resin, a bisphenol resin, an epoxy acrylate, and a polyester.

As a method for applying the composition of the present invention to a metal substrate, a conventionally known method such as direct coating or printing may be used. Thereafter, the composition can be cured by irradiation with an active energy ray. When the composition is directly applied, a method such as curtain flow coating, roll coating, and spray coating may be used. When applying by printing, a normal printing method such as an offset method, a gravure offset method, and a gravure method can be used. The composition of the present invention may be formed into a desired shape after forming a cured film on a metal substrate in advance, or may be formed on a metal substrate that has been subjected to bending or extrusion in advance. The composition of the present invention may be applied and cured. The composition of the present invention can be used for cans such as two-piece cans or three-piece cans using the above-mentioned metal base material, or for precoated steel sheets for home appliance outer panels or tunnel interiors.

The active energy ray-curable metal coating composition of the present invention comprises a reactive resin (A) obtained from a relatively high-molecular-weight, low-viscosity copolymer (a) produced by a high-temperature continuous polymerization method. )including. Since the reactive resin (A) has a relatively high molecular weight, curing shrinkage of the composition is suppressed as compared with the prior art, so that the adhesion between the cured film and the metal substrate is excellent. In addition, since the reactive resin (A) has a relatively low viscosity despite having a relatively high molecular weight, a composition exhibiting good coating properties can be obtained. Furthermore, since sufficient adhesion can be obtained without using a non-reactive resin or the like, the composition is excellent in active energy ray curability and coating properties, and furthermore, the solvent resistance, chemical resistance and hardness of the cured film are also high. Excellent. Then, by blending a highly polar active energy ray-curable monomer as the reactive diluent (B), the adhesion to the metal substrate can be further improved.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to examples. In the following, parts and% are based on weight.

Reference Examples 1 to 7 A method for producing a reactive resin used in Examples of the present invention will be described. (1) Production of copolymer by high-temperature continuous polymerization method A 300 ml pressurized stirring tank type reactor equipped with an electric heater was filled with diethylene glycol monoethyl ether, the temperature was set to 250 ° C, and the pressure was gauged by a pressure controller. The pressure was maintained at 25-27 kg / cm ² . Then, while keeping the pressure of the reactor constant, the monomer mixture having the composition shown in Table 1 was supplied at a constant feed rate (23 g / min, residence time: 1).
(4 minutes), the mixture was continuously supplied from the raw material tank to the reactor, and a reactant corresponding to the supply amount of the monomer mixture was continuously extracted from the outlet. Immediately after the reaction starts, once the reaction temperature drops,
Although a rise in temperature due to the heat of polymerization was observed, the reaction temperature was maintained at 270 to 271 ° C. by controlling the heater.

One hour after the start of the supply of the monomer mixture having a stable temperature, the starting point of the withdrawal of the reaction solution as the raw material for the next esterification reaction was determined. Thereafter, the reaction was continued for 2 hours and 50 minutes, about 3900 g of the monomer mixture was supplied, and about 3900 g of the reaction solution was recovered. Thereafter, the reaction solution was introduced into a thin film evaporator to separate volatile components such as unreacted monomers to obtain about 3300 g of a copolymer concentrated solution. As a result of analysis by gas chromatography, no unreacted monomer was present in the concentrate. The number average molecular weight and the weight average molecular weight of this copolymer were determined by liquid chromatography using tetrahydrofuran as a solvent, and the polydispersity was calculated from this. The results are shown in Table 1 together with the hydroxyl group concentration of the copolymer.

[0042]

[Table 1]

The abbreviations of the monomers shown in Table 1 have the following meanings. HEMA; hydroxyethyl methacrylate HEA; hydroxyethyl acrylate St; styrene

(2) Introduction of Acryloyl Group by Esterification Reaction The copolymer 50 obtained in the above step was placed in a flask equipped with a stirrer, a cooling pipe and a water separator (Dean Stark trap).
0 g, hydroxyl group in each copolymer and equimolar amounts of acrylic acid, 600 g of toluene, 12 g of p-toluenesulfonic acid and 0.3 g of hydroquinone were charged, and the mixture was heated and stirred, refluxed with toluene, and reacted until water formation was not observed. Continued.
At this time, the conversion of the esterification reaction was determined from the weight of the water removed by the water separator. Table 1 shows the results. In each of the reference examples, an acryloyl group could be introduced at a high rate of 85% or more. After cooling,
200 g of a 10% aqueous NaOH solution was poured into the reaction solution,
Stirred for minutes. Thereafter, the reaction solution was transferred to a separating funnel, the aqueous layer was separated, and the catalyst and unreacted acrylic acid were removed from the reaction solution. The oil phase was transferred to a flask, and the solvent was distilled off under reduced pressure to obtain reactive resins A-1 to A-7. The obtained reactive resins A-1 to A-7 were heated at 100 ° C. for 6 hours and evaluated for heating stability. As a result, no change was observed in the resin, and the resin was excellent in heating stability.

Examples 1 to 7 Reactive diluents and photoinitiators were mixed with the reactive resins A-1 to A-7 obtained in Reference Examples 1 to 7 at the composition ratios shown in Table 2 by stirring. An active energy ray-curable metal coating composition was prepared. The substances used are as follows. M-305; pentaerythritol triacrylate (trade name "Aronix M-30" manufactured by Toagosei Co., Ltd.)
5 ") M-5700; 2-hydroxy-3-phenoxypropyl acrylate (trade name" Aronix M-5700 ", manufactured by Toagosei Co., Ltd.) Photoinitiator; benzyl dimethyl ketal (trade name," Irgacure 651 ", manufactured by Ciba Geigy Co., Ltd.) ")

Comparative Examples 1 to 3 Active energy ray-curable metal coating compositions were prepared in the same manner as in Examples 1 to 7, except that the compositions shown in Table 2 were used. The substances used are as follows. SP-1509; bisphenol A type epoxy acrylate, number average molecular weight 520, Tg 117 ° C (manufactured by Showa Polymer Co., Ltd., trade name "SP-1509") Non-reactive resin; acrylic polymer (manufactured by Mitsubishi Rayon Co., Ltd., trade name "Dia" NARL BR-60 ")

[0047]

[Table 2]

[Evaluation of Performance] The compositions prepared in Examples 1 to 7 and Comparative Examples 1 to 3 and their cured films were evaluated by the following methods. Table 3 shows the results.

(1) Solubility The ease of dissolution of each component when adjusting each composition was evaluated. The evaluation results are shown in Table 4 below based on the time required for heating a predetermined amount of the reactive resin, the reactive diluent and the non-reactive resin shown in Table 2 to 70 ° C., stirring with a three-one motor, and completely mixing and dissolving. Shown in stages. ：: Mixed dissolution in less than 30 minutes ○: Mixed dissolution in 30 minutes or more and less than 60 minutes △: Mixed dissolution in 60 minutes or more and less than 120 minutes ×: Not dissolved even in 120 minutes or more

(2) Coating Suitability A bar coater # 1 was prepared using a bonderite steel sheet PB-144 (manufactured by Nippon Test Panel Co., Ltd.) and an aluminum plate H-4000 (manufactured by Nippon Test Panel Co., Ltd.) as base materials.
Each composition was applied using 0, and the coating suitability at this time was visually evaluated according to the following three grades. ：: A smooth coating film is formed. Δ: 1-2 streaks are formed in the coating direction. X: 3 or more streaks are formed in the coating direction.

(3) Curability The coating was repeatedly passed under an ultraviolet lamp under the following conditions, and the number of passes until the tack disappeared from the surface was evaluated. UV irradiation conditions; Lamp: 80 W / cm condensing high-pressure mercury lamp Lamp height: 10 cm Conveyor speed: 10 m / min After the surface tack was eliminated in the above-mentioned curability test,
Further, the cured film passed under an ultraviolet lamp twice was evaluated in the following (4) to (8).

(4) Adhesion A cross-cut was made on the obtained cured film with a cutter knife, a commercially available pressure-sensitive adhesive tape (manufactured by Nichiban Co., Ltd.) was pressed on the surface, and the cured film was peeled off. Was evaluated in the following four stages. ◎: No peeling ○: Slight peeling at the intersection of cuts △: Peeling along the intersections and lines of cuts ×: The entire surface with cellophane tape peeled off

(5) Pencil hardness Measured according to JIS K5400.

(6) Alkali resistance A 1% aqueous solution of sodium carbonate is spotted on the surface of the cured film with a dropper so as to have a diameter of 1 cm. After 6 hours, the aqueous solution of sodium carbonate was wiped off, and the state of the surface of the cured film was visually observed, and evaluated according to the following four grades. A: No abnormality. Even after 6 hours after the above solution was spotted on the same spot again, there was no abnormality in the cured film. ：: No abnormality △: Slight trace of marks left ×: Cured film whitens

(7) Acid resistance Evaluation was made in the same manner as in the above alkali resistance test, except that a 5% acetic acid aqueous solution was used instead of the 1% sodium carbonate aqueous solution.
The notation method of the evaluation result is the same as described above.

(8) Solvent resistance Using a cotton swab impregnated with acetone, a load of 500
g, the surface of the cured film obtained under the condition of one reciprocation per second was rubbed, and the number of times until an abnormality such as whitening or peeling of the cured film surface occurred was evaluated in the following four grades. ：: Abnormality of the cured film after 50 reciprocations or more ○: Abnormality of the cured film after 20 reciprocations and less than 50 reciprocations △: Abnormality of the cured film after 10 reciprocations and less than 20 reciprocations ×: Abnormality of the cured film after less than 10 reciprocations Furthermore, the bending property was evaluated using the test piece produced by the following method.

(9) Bendability Test piece preparation method: Each composition was applied to a thickness of 2 μm on a zinc-phosphated steel sheet having a thickness of 0.6 mm, and the surface was irradiated under the above-mentioned ultraviolet irradiation conditions. Was passed under the lamp until the tack disappeared, and then passed under the lamp two more times. Measuring method: Evaluated by a mandrel test using the diameter of the smallest circular rod that does not cause cracking, peeling, or the like on the cured film. That is, the smaller the numerical value, the better the bendability.

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[Table 3]

As shown in Table 3, according to the UV-curable metal coating compositions of Examples 1 to 7, a smooth coating film was obtained at the time of application, and the active energy ray curability was good. there were. Further, the cured films of these compositions exhibited excellent performance in each of the evaluation items (4) to (9). In addition, since these cured films have good adhesiveness and bendability, it is understood that they are also suitable for deep drawing. On the other hand, in Comparative Example 1 in which no reactive diluent was used, the coating suitability was low because the viscosity of the coating solution was too high.
Also, the performance of the cured film was inferior to those of Examples 1 to 7. In Comparative Example 2 using a composition comprising an epoxy acrylate and a reactive diluent, Example 1 was used.
7, the adhesiveness and the bending property of the cured film were extremely low. In Comparative Example 3 in which a non-reactive resin was blended with the composition of Comparative Example 2, although the adhesion was slightly improved, it did not reach Examples 1 to 7, and the bending property was insufficient, and the alkali resistance was high. And acid resistance decreased. Comparative Example 3
In this case, the viscosity of the coating solution increased due to the compounding of the resin, so that the coating suitability decreased. Furthermore, since the solubility of this resin is low, it takes a long time to mix the composition.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application.

[0061]

The composition of the present invention has good coatability and curability of active energy rays, and the cured film is excellent in adhesion to a metal substrate, solvent resistance, chemical resistance and hardness. .
Therefore, it is extremely useful as an active energy ray-curable metal coating composition.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08F 299/00 C08F 299/00

Claims (3)

[Claims] 1. One or more (meth) acrylates having one or more hydroxyl groups and 30% by weight or more, and one kind of a monomer other than the (meth) acrylate and having one ethylenically unsaturated group 70% by weight or less of the above
It is continuously polymerized at a copolymerization temperature of 0 ° C. to obtain a copolymer (a) having a number average molecular weight of 1,000 to 10,000, and then has one or more ethylenically unsaturated groups and one carboxyl group. A reactive resin (A) obtained by subjecting a monomer to an esterification reaction with a hydroxyl group in the copolymer, a reactive diluent (B) comprising at least one ultraviolet-curable monomer, An active energy ray-curable metal coating composition comprising an agent (C). 2. At least one kind of the monomer having one ethylenically unsaturated group is styrene or alkylstyrene, and the copolymerization ratio of the styrene or the alkylstyrene in the copolymer is 20 to The active energy ray-curable metal coating composition according to claim 1, which is 60% by weight. 3. The glass transition temperature of the copolymer is 30 ° C.
The active energy ray-curable metal coating composition according to claim 1, which has a temperature of from −120 ° C.