JP2001031905A - Uv curable coating composition and its usage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the rapid curing characteristics in the vicinity of the film surface of a coating compsn. by having the coating compsn. comprise an aluminum pigment, an alicyclic epoxy group-contg. cationically polymerizable material, a hydroxyl group- contg. compd. and a cationic photoinitiator, and by specifying the ratio of the epoxy group number to the hydroxyl group number. SOLUTION: (A) 1-50 wt.% of an aluminum pigment, (B) a cationically polymerizable material having an alicyclic epoxy group, (C) a compd. having a hydroxyl group and (D) a cationic photoinitiator in an amt. of 1-10 pts.wt. based on 100 pts.wt. of the sum of compds. B and C are blended to form a UV curable coating compsn., wherein the ratio of the epoxy group number of compd. B to the hydroxyl group number of compd. C is regulated to be in the range of 1.0-2.0. A coating film is obtd. from this coating compsn., wherein the surface of the coating film shows a pencil hardness of HB or more at the point 10 sec after the UV irradiation, when the coating compsn. is applied to a substrate such as a metal, a plastic or a plastic film-coated metal and is cured by irradiating a light beam comprising a wavelength of 200500 nm emitted from a light source to form the film having a thickness of about 5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition containing a pigment which is cured by irradiation with ultraviolet rays.
The present invention relates to an ultraviolet-curable coating composition suitably used as a coating agent for metals, plastics, and plastic film-coated metals.

[0002]

2. Description of the Related Art The outer surface of a beverage can or food can (hereinafter referred to as a beverage can or the like) containing a beverage or food is coated with a coating film in order to prevent corrosion of the can base material and enhance aesthetic commercial value. However, such a paint is required to have resistance to a heat treatment step during food sterilization. Conventionally, these coating films have been formed by applying an organic solvent type paint such as an epoxy / amino resin, an acrylic / amino resin, or a polyester / amino resin with a roll coat and baking and curing. However, since these paints volatilize a large amount of solvent at the time of baking, a special recovery device is required to prevent air pollution. Therefore, recently, various water-based paints that hardly cause air pollution and do not require a special recovery device have been proposed. However, even in this water-based paint,
Since a high temperature of 200 ° C. or more and a baking time in units of minutes are required, improvements are desired in terms of energy cost and productivity, as well as the space of equipment.

[0003] The use of an ultraviolet-curable resin composition is preferred in terms of energy saving, resource saving, and space saving, which are less likely to pollute the atmosphere. There are radically polymerizable and cationically polymerizable resin compositions that can be cross-linked and cured in a short time by irradiation with ultraviolet rays. The radically polymerizable resin compositions include (meth) acryloyl group-containing resin compositions and unsaturated polyester resin compositions. A compound having an unsaturated double bond such as a polyene-thiol resin composition, and an epoxy resin composition as a cationic polymerization type are known, and each is used together with a suitable polymerization initiator. These resin compositions are used for coating agents, printing inks, adhesives and the like. However, a composition containing a compound having an unsaturated double bond, such as a radical polymerizable composition, among the ultraviolet curable resin compositions was not suitable for a paint containing an aluminum pigment. This is because aluminum acts as a polymerization catalyst for the compound having an unsaturated double bond, and the viscosity of the coating material increases with time, which causes a problem in storage stability.

On the other hand, the cationically polymerizable composition has good storage stability even in an aluminum pigment-containing system, but because of its slow curing, it is difficult to obtain sufficient curing performance in view of high-speed coating. When a coating composition containing a pigment is applied to a cylindrical body such as a can or a bottle, it is required that the coating composition be excellent in quick-curing properties near the surface of the coating film and be excellent in fast-curing properties inside the coating film. That is, after applying the coating composition, the body portion of the can or bottle is irradiated with ultraviolet rays, and after about 10 seconds, the can or bottle is transported to the next processing step.
In this transporting process, the cured coatings come into contact with each other, or the coatings come into contact with transporting equipment. Therefore, immediately after ultraviolet curing, it is necessary to rapidly cure the vicinity of the surface of the coating film to a hardness that can withstand the transport process.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a surface of a metal, plastic or plastic film-coated metal can or bottle for accommodating beverages and foods. It is intended to provide an ultraviolet-curable coating composition containing an aluminum pigment for coating these, which is excellent in quick-curing properties near the surface of the coating film. I do. Specifically, when the film thickness after curing is applied to about 5 μm, an ultraviolet-curable coating composition capable of forming a coating film having a coating surface hardness of HB or more in pencil hardness by 10 seconds after irradiation with ultraviolet light. The purpose is to provide things.

[0006]

That is, the first invention comprises an aluminum pigment (A), a cationic polymerizable substance having an alicyclic epoxy group (B), a compound having a hydroxyl group (C), and a cationic photoinitiator. (D), wherein the ratio of the number of epoxy groups in (B) to the number of hydroxyl groups in (C) is (number of epoxy groups) / (number of hydroxyl groups) = 1.0 to 2.0. It is a coating composition.

A second invention is the ultraviolet-curable coating composition according to claim 1, wherein (C) is a compound having two or more hydroxyl groups.

[0008] The third invention is characterized in that at least one selected from the group consisting of metal, plastic, and plastic film-coated metal is coated.
The UV-curable coating composition described in the above item.

A fourth aspect of the present invention is a coating obtained by coating a substrate with the ultraviolet-curable coating composition according to any one of the first and second aspects.

A fifth aspect of the present invention is a coating obtained by coating a substrate with the ultraviolet-curable coating composition according to any one of the first and second aspects.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The ultraviolet-curable coating composition of the present invention is made of metal, plastic, or the like for accommodating beverages and foods.
It is mainly used as a paint applied to the surface of a plastic film-coated metal can or bottle, and is particularly suitably used as a base coat, and is used as a silver base coat by blending an aluminum pigment. Examples of the aluminum pigment include aluminum powder, and an aluminum paste obtained by converting this into a paste with mineral spirit or solvent naphtha is preferably used. The aluminum pigment (A) preferably accounts for 1 to 50% by weight when (A) + (B) + (C) + (D) = 100% by weight. More preferably, it is 5 to 30% by weight.

The cationically polymerizable substance (B) having an alicyclic epoxy group contains at least one cyclohexane oxide in its molecular structure, and may be used alone or in combination as necessary. Can be done. Desirably, one or more compounds containing two or more cyclohexane oxides in the molecular structure are used. Examples of the cationic polymerizable substance (B) having an alicyclic epoxy group include those represented by the following formulas (1) to (17).

[0013]

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[0014]

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[0015]

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[0016]

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Specifically, CHXO, celloxide 30
00, Celoxide 2000, ETHB, HD-300
(Manufactured by Daicel Chemical Industries, Ltd.), UVR-6110, UVR
-6199 (all manufactured by UCC), Celloxide 208
3, Celoxide 2085, Eporide GT-302,
Epolide GT-303, Epolide GT-401, Epolide GT-402 (all manufactured by Daicel Chemical Industries, Ltd.) and the like can be used.

Examples of the compound (C) having a hydroxyl group include methyl alcohol, ethyl alcohol, n-propanol, isopropanol, n-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, 2-ethylbutanol, n-heptanol and 2-heptanol. , 2
-Ethylhexanol, 3,5,5-trimethylhexanol, n-nonyl alcohol, undecyl alcohol, n-dodecyl alcohol, trimethylnonyl alcohol, n-tetradecyl alcohol, heptadecyl alcohol, cyclohexanol, 2-methylcyclohexanol, Epoxidized tetrahydrobenzyl alcohol,
Lactone-modified epoxidized tetrahydrobenzyl alcohol, monohydric alcohol such as glycidol, 3-ethyl-3-hydroxymethyloxetane, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, butenediol, butyne Diol, 1,4-cyclohexanedimethanol, 2,
2,4-trimethylpentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, pentanediol, trimethylpentanediol, polyethylene glycol, glycerin, trimethylolethane, trimethylolpropane, penta 2 such as erythritol, dipantaerythritol, diglycerin, etc.
Although an alcohol having a valency or higher can be used, as the compound (C) having a hydroxyl group, the compound (C) having a hydroxyl group is more than the monofunctional one.
Compounds having at least two hydroxyl groups are more desirable. This is because having two or more hydroxyl groups tends to increase the molecular weight in the reaction with the epoxy group, thereby easily obtaining a coating film having good workability.

The coating composition of the present invention has a ratio of the number of epoxy groups of the cationically polymerizable substance (B) having an alicyclic epoxy group to the number of hydroxyl groups of the compound (C) having a hydroxyl group, ie, (number of epoxy groups) / It is extremely important that (the number of hydroxyl groups) is 1.0 to 2.0. Although the reason is unknown, when the ratio of (the number of epoxy groups) / (the number of hydroxyl groups) is in the above range, a cured film whose surface hardness becomes HB or higher in pencil hardness by about 10 seconds after ultraviolet irradiation is obtained. Can be done. If this ratio is less than 1.0 or greater than 2.0, the required pencil hardness cannot be ensured.

As the cationic photoinitiator (D), an aryldiazonium salt (for example, P-3 manufactured by Asahi Denka Kogyo KK)
3), aryl iodonium salts (for example, FC manufactured by 3M)
-509, Rhone Poulin 2074), arylsulfonium salts (Union Carbide Silacure UVI-6974, UVI-6970, UVI-69)
90, UVI-6950, SP-15 manufactured by Asahi Denka Kogyo Co., Ltd.
0, SP-170, San-Aid SI- manufactured by Sanshin Chemical Industry Co., Ltd.
110L, SI-180L, SI-100L, CI-2855 manufactured by Nippon Soda Co., Ltd.) Allene-ion complex (CG-24-61 manufactured by Ciba Geigy) and the like. The cationic polymerization initiator (D) is used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total amount of the cationically polymerizable substance (B) having an alicyclic epoxy group and the compound (C) having a hydroxyl group. It is desirable to be blended. If it is less than 1%, the irradiation time of ultraviolet rays required for curing becomes long, and the productivity is poor. If it exceeds 10%, the cured coating film tends to be brittle.

The coating composition of the present invention may further contain a photosensitizer. In particular, a hydrogen abstraction type photo-enhancing agent is desirable, and those having characteristic absorption in a long wavelength region of ultraviolet light, for example, a long wavelength region of 300 nm or more are preferable. For example, from the KAYACURE series (Nippon Kayaku Co., Ltd.)
TX, QTX, CPTX, DETX-S, Adeka Optomer SP-100 (manufactured by Asahi Denka Kogyo KK) and the like.

The ultraviolet-curable coating composition of the present invention can be applied (painted / cured) to various substrates such as plastic, plastic-coated metal, paper, wood, glass and the like, and can be applied to plastic and plastic-coated metal (painting / curing). Curing). As the plastic, polyethylene, polypropylene, polyethylene terephthalate, nylon, vinyl chloride, vinylidene chloride, polycarbonate and the like are used. The plastic film-coated metal is obtained by laminating a metal plate such as steel or aluminum with a plastic film such as polyethylene, polypropylene, polyethylene terephthalate, nylon, vinyl chloride, vinylidene chloride, or polycarbonate. Preferably, the plastic or plastic-coated metal is a can or a bottle. The UV-curable coating composition of the present invention may be applied to a plate-shaped substrate (painting / curing) and then formed into a can or a bottle, or may be applied in advance to a can- or bottle-shaped substrate. Is also good. The plate shape may be a relatively short sheet shape, a relatively long roll shape, or a flat plate shape. In addition, the can shape refers to a shape having a cylindrical curved surface regardless of the presence or absence of a bottom and a lid, and irrespective of two pieces or three pieces. These cans or bottles are mainly soft drinks, coffee drinks,
It is used as a container for storing food and drink such as alcoholic beverages, black tea, and oolong tea.

The UV-curable coating composition of the present invention is applied by a method such as roll coating, gravure coating, gravure offset coating, curtain flow coating, reverse coating, screen printing, spray coating, and dip coating. You. The light source for photocuring the ultraviolet-curable coating composition of the present invention usually has a wavelength of 20.
A light source including light in the range of 0 to 500 nm, for example, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a gallium lamp,
Xenon lamps, carbon arc lamps and the like can be used. Further, these light sources may be used in combination with heat from infrared rays, far infrared rays, hot air, high-frequency heating, or the like.

The ultraviolet-curable resin composition of the present invention may contain other conventional components, if necessary, as long as the purpose is not impaired.
For example, organic or inorganic pigments, extenders, dyes, non-reactive resins, organic solvents, dispersing aids, leveling agents, anti-crater agents, surfactants, defoamers, slip agents, ultraviolet absorbers,
Paint additives such as reactive or non-reactive diluents can be included. Examples of the non-reactive resin include epoxy, polyester, acrylic, and urethane. Examples of the reactive diluent include oxetane compounds and lactone compounds having a 4-membered cyclic ether structure.

[0025]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples, “parts” represents “parts by weight” and “%” represents “% by weight”. The materials used are as follows. (A) Aluminum pigment: aluminum paste (solid content = 70%,
(Blended solvent = mineral spirit) (B) Cationic polymerizable substance having alicyclic epoxy group (Siracure UVR-6110, manufactured by UCC) (C) Compound having hydroxyl group: ethylene glycol, butenediol (D) Cationic photoinitiation Agent (Siracure UVI-699)
0, manufactured by UCC) After dissolving and mixing the above (B) and (C), add (A) and stir well, then add (D) and stir well again to obtain the ultraviolet curable coating composition of the present invention. I got something.

[0026]

Examples 1 to 6 UV-curable coating compositions were obtained according to the above-mentioned method according to the formulations shown in Table 1.

[0027]

Comparative Examples 1 to 9 Ultraviolet-curable coating compositions were obtained in the same manner as in the examples with the formulations shown in Table 2.

The UV-curable coating compositions of Examples 1 to 6 and Comparative Examples 1 to 9 were applied on a film of a material obtained by laminating a polyethylene terephthalate film on a tin-free steel plate so that the coating amount was 60 mg / dm 2. The sample was passed under a V valve (240 W / cm) manufactured by Fusion Co. at a conveyor speed of 40 m / min and irradiated with ultraviolet rays to obtain a test sample plate. The following test was performed on this sample plate and evaluated.

1. Adhesion In accordance with JIS K5400, it is indicated by the area where the coating film remains by a cellophane tape peeling test after the cut of the gobang. 2. Pencil hardness Based on JIS K5400, Mitsubishi pencil "Uni" at room temperature
The maximum hardness at which the coating does not peel off is indicated. Measure pencil hardness 5-10 seconds after UV irradiation. 3. Workability A water-based thermosetting type top coat is applied to the UV-cured test sample, and the heat-cured coated plate is measured with a DuPont impact tester using a 1/2 inch rod from the back side of the coating film surface.
A 00 g weight was dropped from a height of 50 cm, and cracks generated in the coating film were visually evaluated. ◎: No abnormalities 若干: Some cracks generated Δ: Some cracks generated ×: Cracks generated over the entire surface The evaluation results are shown in Table-3.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

According to the present invention, it has a sufficiently practical ultraviolet curability and coating film properties, and particularly, a plastic bottle,
When coating a metal can coated with a plastic film, a coating agent useful as a coating material for an ultraviolet-curable base coat can be provided.

Continued on the front page F term (reference) 4J038 DB261 DB262 DF021 DF022 FA011 FA012 GA01 GA02 GA03 GA06 HA066 JA14 JA19 JA20 JA21 JA22 JA26 JA27 JA69 JA70 JB16 JC17 JC38 KA03 KA08 NA23 PA17 PC02 PC08

Claims (5)

[Claims] 1. An epoxy resin comprising (B) an aluminum pigment (A), a cationically polymerizable substance (B) having an alicyclic epoxy group, a compound (C) having a hydroxyl group, and a cationic photoinitiator (D). An ultraviolet-curable coating composition, wherein the ratio of the number of groups to the number of hydroxyl groups in (C) is (number of epoxy groups) / (number of hydroxyl groups) = 1.0 to 2.0. 2. The ultraviolet-curable coating composition according to claim 1, wherein (C) is a compound having two or more hydroxyl groups. 3. The UV-curable coating composition according to claim 1, wherein the coating composition is coated with at least one selected from the group consisting of metal, plastic, and metal coated with a plastic film. 4. The ultraviolet-curable coating composition according to claim 3, wherein the metal, plastic, or metal coated with a plastic film is a can or a bottle. 5. A coating obtained by coating a substrate with the ultraviolet-curable coating composition according to any one of claims 1 and 2.