JP2003231860A - Ultraviolet light-curing type coating composition and its utilization - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultraviolet light-curing type composition containing a pigment, for coating a can or bottle for housing beverage, etc., made from a metal, plastic or plastic film-coated metal, and also a cationically polymerizable and ultraviolet light-curing type composition excellent in curing property even under a high environmental humidity on irradiating the ultraviolet light to the composition. <P>SOLUTION: This ultraviolet light-curing type composition contains (A) a pigment, (B) a cationically polymerizable substance having an alicyclic epoxy group containing (b1) a cationically polymerizable substance having ≥2 alicyclic epoxy groups as an essential components, (C) a compound having oxetane group, (D) a compound containing ≥2 hydroxyl groups and (E) a cationically polymerizable photo-initiator, and the ratios of the number of the alicyclic epoxy groups, the number of the oxetane groups and the number of the hydroxyl groups are; (the number of the alicyclic epoxy groups)/(the number of the oxetane group)=0.5-2.5 and (the number of the alicyclic epoxy groups + the number of the oxetane groups)/(the number of the hydroxyl groups)=3.5-9.0. <P>COPYRIGHT: (C)2003,JPO

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 that is cured by irradiation with ultraviolet rays. Mainly when a base coat and a white pigment are blended, a white base coat and when aluminum is blended as a pigment,
Used as a silver coat. More specifically, the present invention relates to an ultraviolet-curable coating composition that is suitably used as a coating agent for metals, plastics, and plastic film-coated metals. The present invention relates to an ultraviolet-curable coating composition suitable as a base coat or a silver coat for beverage cans and food cans (hereinafter referred to as beverage cans) containing beverages or foods.

[0002]

2. Description of the Related Art The outer surface of a beverage can or a food can containing a beverage or food (hereinafter referred to as a beverage can, etc.) is coated with a coating film in order to prevent corrosion of the can base material and enhance aesthetic commercial value. . This coating film is required to have resistance to a heat treatment process during food sterilization.

Conventionally, these coating films are roll-coated with organic solvent type paints such as epoxy / amino resin, acrylic / amino resin, polyester / amino resin, etc.
It has been formed by 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 are unlikely to cause air pollution and do not require a special recovery device have been proposed.

However, even in this water-based paint, 200
Since a high temperature of ℃ or more and a baking time in minutes are required, improvement is desired in terms of energy cost, productivity, and space of equipment. It is preferable to use the ultraviolet curable composition from the viewpoints of being less likely to pollute the atmosphere, saving energy, saving resources, and saving space.

As a composition which is cross-linked and cured in a short time by irradiation with ultraviolet rays, there are a radical polymerization type and a cationic polymerization type. As the radical polymerization type, compounds having an unsaturated double bond such as a composition having a (meth) acryloyl group, an unsaturated polyester composition and a polyene-thiol composition are known. As the cationic polymerization type, a composition having an epoxy group, a composition having an oxetane group, a composition having a vinyl ether group and the like are known, and each is used together with a suitable polymerization initiator.

Among the ultraviolet curable compositions, a composition containing a compound having an unsaturated double bond, such as a radically polymerizable composition, has the advantages that the curing is fast and the coating film hardness after curing is high. On the other hand, distortion easily occurs due to the curing reaction,
As a result, the adhesiveness to the base material tends to be insufficient. On the other hand, the cationically polymerizable composition has an advantage that distortion is less likely to occur due to the curing reaction and that the adhesiveness with the substrate is good, but has a disadvantage that the curing is slow and the coating film hardness after curing is low. .

Due to these characteristics, when the pigment is not contained, the radically polymerizable composition is often used in applications where curability and coating film hardness are high, and strong adhesion to the substrate is strongly required. In many applications, cationically polymerizable compositions are used.

On the other hand, when the pigment is contained, it is difficult to sufficiently cure the coating film with ultraviolet rays because the pigment absorbs the ultraviolet rays or reflects the ultraviolet rays to prevent the ultraviolet rays from reaching the inside of the coating film. Therefore, when a pigment is contained, a radically polymerizable composition excellent in curability is often used, but it is difficult to apply it to applications where strong adhesion is strongly required. When adhesion is important, a cationically polymerizable composition is used, but since it is difficult to ensure curability, in this case the pigment concentration is kept low and the coating film is sufficiently UV cured.

As described above, it is difficult to achieve both curability and adhesion in an ultraviolet curable composition containing a pigment.
It was difficult to apply to a base material that requires particularly high adhesion. Applications requiring high adhesion performance, for example, when applying a cationically polymerizable coating composition containing a pigment to the outer surface of a cylindrical body of a beverage can, bottle, etc., high-speed coating is currently underway to improve production efficiency. In addition, it is required that the rapid curing property in the vicinity of the coating film surface is excellent and the rapid curing property inside the coating film is excellent.

That is, the body portion of a beverage can, bottle, etc. is irradiated with ultraviolet rays after applying the coating composition, and after about 10 seconds, the can or bottle is conveyed to the next processing step. In this transportation process, the cured coating films may come into contact with each other or the coating film may come into contact with transportation equipment. Therefore, immediately after the ultraviolet curing, specifically, after about 10 seconds, it is necessary that the vicinity of the surface of the coating film be rapidly cured to a hardness that can withstand the conveying process. Further, it is required that the coating film further cures by about 30 seconds after the irradiation with ultraviolet rays, and the interior also be sufficiently cured.

JP-A-2001-31905 discloses that the number of epoxy groups of a cationically polymerizable substance having an alicyclic epoxy group and the hydroxyl group of a compound having a hydroxyl group are improved in order to improve the curability of the cationically polymerizable composition immediately after irradiation with ultraviolet rays. The ratio of the numbers is (the number of epoxy groups) / (the number of hydroxyl groups) = 1.0 to 2.
It is described that the value is 0. JP 2001-3190A
The ultraviolet curable composition described in 5 has an effect of improving curability immediately after irradiation with ultraviolet rays. However, when the environmental humidity at the time of ultraviolet irradiation is high, a coating film having sufficient hardness cannot be obtained immediately after irradiation (after about 10 seconds). This is because water in the environment easily causes inhibition of cationic polymerization.

[0012]

The object of the present invention is to form a coating by applying and curing it on the surface of metal, plastic, plastic film-coated metal cans, bottles, etc. for containing beverages, foods, etc. An object of the present invention is to provide a cation-polymerizable UV-curable coating composition which is excellent in curability even when the environmental humidity at the time of UV irradiation is high, which is an ultraviolet-curable coating composition containing the pigment of (1).

Specifically, an object of the present invention is to coat a cationic polymerization type composition on a plastic, a plastic film and a metal so as to have a film thickness of about 5 μ after curing, and an environment of relative humidity = 60% or more. UV irradiation under about 10
It is an object of the present invention to provide an ultraviolet-curable coating composition capable of forming a coating film, which has a pencil hardness of HB or more after 30 seconds and a pencil hardness of H or more after about 30 seconds after ultraviolet irradiation.

[0014]

[Means for Solving the Problems] That is, the first invention is a cycloaliphatic epoxy containing as an essential component a pigment (A) and a cationically polymerizable substance (b1) having two or more cycloaliphatic epoxy groups. Containing a cationically polymerizable substance having a group (B), a compound having an oxetane group (C), a compound having at least two hydroxyl groups (D) and a cationically polymerizable photoinitiator (E), the number of alicyclic epoxy groups And the ratio of the number of oxetane groups to the number of hydroxyl groups is (the number of alicyclic epoxy groups) / (the number of oxetane groups) = 0.5 to 2.5 and (the number of alicyclic epoxy groups + the number of oxetane groups) / (the number of hydroxyl groups) = 3.5 It is an ultraviolet-curable coating composition, characterized in that

A second invention is the ultraviolet-curable coating composition according to the first invention, wherein the pigment (A) is a white pigment or an aluminum pigment, and the third invention is an oxetane. The compound (C) having a group is the ultraviolet-curable coating composition according to the first or second invention, which is characterized in that it does not have a hydroxyl group, and the fourth invention is a compound (C) having an oxetane group. 1) to 3) are compounds having two or more oxetane groups
The ultraviolet-curable coating composition according to any one of the inventions.

The fifth aspect of the invention is to cure the ultraviolet ray according to any one of the first to fourth aspects, which is characterized by coating at least one kind of substrate selected from metals, plastics, and plastic film-coated metals. A sixth invention is the ultraviolet-curable coating composition according to the fifth invention, wherein the base material is a can or a bottle.

Further, a seventh invention is an article to be coated which comprises a base material coated with the ultraviolet-curable coating composition according to any one of the first to fourth inventions.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The pigment (A) used in the present invention will be described. The ultraviolet curable coating composition of the present invention is mainly used as a base coat for the outer surface of a beverage can. By blending an aluminum pigment, it is used as a silver base coat, and by blending a white pigment, it is used as a white base coat.

As the aluminum pigment, aluminum powder can be mentioned, and an aluminum paste obtained by making a paste with mineral spirit or solvent naphtha is preferably used. The content of the aluminum pigment is such that the aluminum pigment and the cationic polymerizable substance having an alicyclic epoxy group (B1) containing two or more cationic polymerizable substances (b1) having an alicyclic epoxy group described later as essential components ), A compound (C) having an oxetane group, a compound (D) having two or more hydroxyl groups, and a cationically polymerizable photoinitiator (E) in a total of 100% by weight, preferably 1 to 50% by weight. . More preferably, it is 5 to 30% by weight.

Examples of the white pigment include titanium oxide, zinc oxide, zinc sulfide and the like. The content ratio of the white pigment is a white pigment and a cationic polymerizable substance having an alicyclic epoxy group (B1) containing as an essential component a cationic polymerizable substance (b1) having two or more alicyclic epoxy groups described below. ), A compound (C) having an oxetane group, a compound (D) having two or more hydroxyl groups, and a cationically polymerizable photoinitiator (E) in total of 100% by weight, preferably 10% by weight or more. This is because if it is less than 10% by weight, the coloring power is poor.

The cationically polymerizable substance (B) having an alicyclic epoxy group containing as an essential component a cationically polymerizable substance (b1) having two or more alicyclic epoxy groups will be described. As the cationically polymerizable substance (b1) having two or more alicyclic epoxy groups, those containing at least two cyclopentane oxides in its molecular structure, and at least two cyclohexane oxides in its molecular structure At least one containing, or cyclopentane oxide and cyclohexane oxide
Those contained in the molecular structure one by one can be mentioned, and they can be used alone or in combination as the case requires.
Examples of the cationically polymerizable substance (b1) having two or more alicyclic epoxy groups include those shown below.

[0022]

[Chemical 1]

[0023]

[Chemical 2]

[0024]

[Chemical 3]

Specifically, UVR-6110, UVR-
6199 (above UCC), Celoxide 2083,
There are Celoxide 2085, Epolide GT-302, Epolide GT-303, Epolide GT-401, Epolide GT-402 (all manufactured by Daicel Chemical Industries, Ltd.) and the like.

As the cationically polymerizable substance having an alicyclic epoxy group (B), a cationically polymerizable substance having one alicyclic epoxy group may be used in combination. However, when the cationically polymerizable substance having two or more alicyclic epoxy groups (b1) = 100 parts by weight, the cationically polymerizable substance having one alicyclic epoxy group = 40 parts by weight or less Is preferred. If the monofunctional component exceeds 40 parts by weight, the cured coating film tends to become brittle. 1
Examples of the cationically polymerizable substance having one alicyclic epoxy group include those shown below.

[0027]

[Chemical 4]

Specifically, CHXO and celoxide 30
00, Celoxide 2000, ETHB, HD-300
(These are manufactured by Daicel Chemical Co., Ltd.).

Next, the compound (C) having an oxetane group will be described. As the compound (C) having an oxetane group, a compound having no hydroxyl group is preferable. An oxetane compound having no hydroxyl group is preferable because its ultraviolet curability is less likely to decrease due to environmental humidity. As the compound (C) having an oxetane group, a compound having two or more oxetane groups is preferable. This is because a compound having two or more oxetane groups is easier to obtain a coating film with high hardness.

Among the oxetane compounds having no hydroxyl group, compounds having one oxetane group include hexyl oxetane, oxetane methacrylate, 3-ethyl-3-phenoxymethyl oxetane, allyl oxetane, 3-ethyl-3- (2- Among ethylhexyloxymethyl) oxetane and oxetane compounds having no hydroxyl group, compounds having two or more oxetane groups include
Examples thereof include carbonate bisoxetane, adipate bisoxetane, xylylene bisoxetane, terephthalate bisoxetane, cyclohexanedicarboxylic acid bisoxetane, and bis (3-ethyl-3-oxetanylmethyl) ether. These may be used alone or as a mixture, if necessary.

Next, the compound (D) having two or more hydroxyl groups will be described. Whether the compound having a hydroxyl group is incorporated into the cationic polymerization of the compound (B) having an alicyclic epoxy group and the compound (C) having an oxetane group or only accelerating the cationic polymerization is not known in detail. is there. However, by using the compound (D) having two or more hydroxyl groups in combination, it is possible to obtain a coating film having good processability, probably because the molecular weight becomes large as a result of irradiation with ultraviolet rays.

As the compound (D) having two or more hydroxyl groups, ethylene glycol, propylene glycol,
1,3-butylene glycol, 1,4-butanediol, butenediol, butynediol, 1,4-cyclohexanedimethanol, 2,2,4-trimethylpentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol , Neopentyl glycol, triethylene glycol, pentanediol,
Dihydric or higher alcohols such as trimethylpentanediol, polyethylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, dipantaerythritol, and diglycerin can be used. Furthermore, these can be used alone or in combination as required.

As the cationically polymerizable photoinitiator (E),
Aryl diazonium salt (for example, P- manufactured by Asahi Denka Co., Ltd.
33), an aryl iodonium salt (for example, F manufactured by 3M Company)
C-509, 2074 manufactured by Rhone-Poulin, arylsulfonium salt (Cyracure UVI-6974, UVI-6970, UVI-6 manufactured by Union Carbide).
990, UVI-6950, Asahi Denka Kogyo SP-15
0, SP-170, San-Aid SI-made by Sanshin Chemical Industry Co., Ltd.
110L, SI-180L, SI-100L, CI-2855 manufactured by Nippon Soda Co., Ltd., arene-ion complex (CG-24-61 manufactured by Ciba-Geigy), and the like.

The cationically polymerizable photoinitiator (E) comprises a cationically polymerizable substance (B) having an alicyclic epoxy group, a compound (C) having an oxetane group and a compound (D) having two or more hydroxyl groups. 1 to 10 for 100 parts by weight in total
It is desirable that the compounding amount be within the range of parts by weight. If it is less than 1 part by weight, the irradiation time of ultraviolet rays required for curing becomes long and the productivity becomes poor. If it exceeds 10 parts by weight, the cured coating film tends to become brittle.

The coating composition of the present invention may further contain a photosensitizer. In this case, the photosensitizer is preferably one having a hydrogen abstracting action, and one having a characteristic absorption in a long wavelength region of ultraviolet rays, for example, a long wavelength region of 300 nm or more is suitable. For example, ITX, QTX, CPTX, D from KAYACURE series (manufactured by Nippon Kayaku Co., Ltd.)
ETX-S, ADEKA OPTOMER SP-100 (manufactured by Asahi Denka Co., Ltd.) and the like can be mentioned.

In the coating composition of the present invention, the ratio of the number of alicyclic epoxy groups to the number of oxetane groups to the number of hydroxyl groups is (number of alicyclic epoxy groups) / (number of oxetane groups) = 0.5 to 2.5, and It is extremely important that the number of cyclic epoxy groups + the number of oxetane groups / (the number of hydroxyl groups) = 3.5 to 9.0.
That is, by setting the number of each functional group to a specific ratio as described above, the environmental humidity at the time of ultraviolet irradiation is, for example, relative humidity = 6.
Even if it is as high as 0% or more, a cationically polymerizable ultraviolet-curable coating composition having excellent curability can be obtained.

Specifically, (number of alicyclic epoxy groups) /
When (Oxetane group number) is less than 0.5, relative humidity = 6
The pencil hardness of the coating film does not reach HB after UV irradiation for about 10 seconds in an environment of 0% or more. On the other hand, (number of alicyclic epoxy groups)
If / (number of oxetane groups) is more than 2.5, the pencil hardness of the coating film does not reach H after UV irradiation for about 30 seconds in an environment of relative humidity = 60% or more. When (the number of alicyclic epoxy groups + the number of oxetane groups) / (the number of hydroxyl groups) is less than 3.5, after irradiation with ultraviolet rays for about 30 seconds under an environment of relative humidity = 60% or more,
The pencil hardness of the coating film does not reach H. On the other hand, when (the number of alicyclic epoxy groups + the number of oxetane groups) / (the number of hydroxyl groups) is larger than 9.0, the pencil hardness of the coating film becomes HB after the ultraviolet irradiation for about 10 seconds in the environment where the relative humidity is 60% or more. Not reach

The number of alicyclic epoxy groups in the present invention is the number of all alicyclic epoxy groups in the coating composition,
When a compound having one alicyclic epoxy group is used, this is also included in the number of alicyclic epoxy groups. Similarly, the number of oxetane groups and the number of hydroxyl groups are also the total number of functional groups in the coating composition.

The UV-curable coating composition of the present invention is preferably applied (painted / cured) to metals, plastics, and plastic-coated metals, but can also be applied to substrates such as paper, wood, and glass. Examples of the metal include steel and aluminum. As the plastic, polyethylene, polypropylene, polyethylene terephthalate, nylon, vinyl chloride, vinylidene chloride, polycarbonate or the like is used. Plastic film coated metal means polyethylene, polypropylene, polyethylene terephthalate, metal plate such as steel or aluminum,
It is a laminate of plastic films such as nylon, vinyl chloride, vinylidene chloride, and polycarbonate.

The metal, plastic, plastic-coated metal is preferably a can or bottle. The UV-curable coating composition of the present invention may be applied (painted / cured) to a plate-shaped substrate and then formed into a can or bottle, or may be applied to a can-shaped or bottle-shaped substrate in advance. 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 is with or without a bottom and a lid.
Regardless of piece or piece, it means a shape having a cylindrical curved surface. These cans or bottles are mainly used as containers for storing food and drink such as soft drinks, coffee drinks, alcoholic drinks, black tea and oolong tea.

The UV-curable coating composition of the present invention can be 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. It

The light source for photo-curing the ultraviolet-curable coating composition of the present invention usually has a wavelength of 200 to 50.
A light source containing light in the range of 0 nm, for example, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a metal halide lamp, a gallium lamp, a xenon lamp, a carbon arc lamp or the like can be used. or,
Heat from infrared rays, far infrared rays, hot air, high frequency heating, etc. may be used in combination with these light sources.

The UV-curable coating composition of the present invention contains, if necessary, other conventional components such as organic or inorganic pigments, extender pigments, dyes, resins, organic solvents and dispersion aids, as long as the purpose is not impaired. , A leveling agent, an anti-crater agent, a surfactant, an antifoaming agent, a slipping agent, an ultraviolet absorber, a reactive or non-reactive diluent, and the like can be added to the coating composition. Examples of the resin include epoxy, polyester, acrylic and urethane. As a reactive diluent,
Examples thereof include lactone compounds.

[0044]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited thereto. In the examples, "part" means "part by weight" and "%" means "% by weight". The materials used are as follows.

Example 1 3,4-epoxycyclohexylmethyl-
3,4-epoxycyclohexanecarboxylate 4
6.23%, bis (3-ethyl-3-oxetanylmethyl) ether 24.43%, propylene glycol
After 34% was dissolved and mixed, 20% of aluminum paste (solid content = 70%, compounding solvent = mineral spirit) was added and sufficiently stirred, and then Cyracure UVI-699
0 (manufactured by UCC, cationically polymerizable photoinitiator) 5% was added, and the mixture was thoroughly stirred again to obtain a silver base coat which is the ultraviolet curable coating composition of the present invention.

[0045]

Examples 2 to 6 and Comparative Examples 1 to 9 A silver base coat which is an ultraviolet curable coating composition of the present invention was prepared in the same manner as in Example 1 except that the formulations shown in Tables 1 and 2 were applied. Obtained.

[0046]

Example 7 3,4-epoxycyclohexylmethyl-
3,4-epoxycyclohexanecarboxylate 4
0.07%, bis (3-ethyl-3-oxetanylmethyl) ether 21.17%, propylene glycol 3.
After 76% was dissolved and mixed, 30% of titanium oxide was added and sufficiently stirred, and dispersed by a sand mill. After that, 5% of Syracure UVI-6990 (manufactured by UCC, cationically polymerizable photoinitiator) was added, and the mixture was thoroughly stirred again to obtain a white base coat which is the ultraviolet curable coating composition of the present invention.

[0047]

Examples 8 to 12 and Comparative Examples 10 to 18 A white base coat which is the ultraviolet curable coating composition of the present invention was prepared in the same manner as in Example 7 except that the formulations shown in Table 3 and Table 4 were applied. Obtained.

The ultraviolet-curable coating compositions of Examples 1 to 12 and Comparative Examples 1 to 18 were coated on a tin-free steel plate laminated with a polyethylene terephthalate film so that the coating amount was 60 mg / dm ^2. However, under two environments with different relative humidity (humidity 40% and 60%),
Each was irradiated with ultraviolet rays to obtain a test sample plate. In addition, the silver base coat is a D bulb (2
40 W / cm) and a white base coat using a V valve (240 W / cm) manufactured by Fusion Co., Ltd., and a conveyor speed of 40 m / min. Ultraviolet irradiation was performed by passing it at a speed of. The following tests were carried out and evaluated for each sample plate.

1. Pencil hardness According to JIS K5400, Mitsubishi pencil "Uni" at room temperature
Indicates the maximum hardness at which the coating does not peel off. Under each environment, measure the pencil hardness after 10 seconds and 30 seconds after UV irradiation. The results of the silver base coat are shown in Table-5, and the results of the white base coat are shown in Table-6.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

[Table 5]

[0055]

[Table 6]

[0056]

EFFECTS OF THE INVENTION The coating composition of the present invention is excellent in the surface curability of the coating film immediately after the irradiation and also in the internal curability even when the environmental humidity at the time of the irradiation of ultraviolet rays is high. It is suitable for coating the outer surface of metal cans, plastic bottles, and plastic film-coated metal cans, and is particularly suitable as a base coat paint.

Claims (7)

[Claims] 1. A pigment (A), a cationically polymerizable substance (B) having an alicyclic epoxy group, which contains a cationically polymerizable substance (b1) having two or more alicyclic epoxy groups as an essential component, and oxetane. Containing a compound (C) having a group, a compound (D) having two or more hydroxyl groups and a cationically polymerizable photoinitiator (E), the ratio of the number of alicyclic epoxy groups, the number of oxetane groups and the number of hydroxyl groups is ( Number of cyclic epoxy groups) /
(Number of oxetane groups) = 0.5 to 2.5 and (number of alicyclic epoxy groups + number of oxetane groups) / (number of hydroxyl groups) = 3.5 to
An ultraviolet-curable coating composition characterized in that it is 9.0. 2. The ultraviolet-curable coating composition according to claim 1, wherein the pigment (A) is a white pigment or an aluminum pigment. 3. A compound (C) having an oxetane group,
The ultraviolet-curable coating composition according to claim 1 or 2, which has no hydroxyl group. 4. A compound (C) having an oxetane group,
The ultraviolet-curable coating composition according to any one of claims 1 to 3, which is a compound having two or more oxetane groups. 5. The ultraviolet-curable coating composition according to claim 1, which is coated with at least one substrate selected from metals, plastics, and plastic film-coated metals. 6. The ultraviolet-curable coating composition according to claim 5, wherein the base material is a can or a bottle. 7. An article to be coated, which is obtained by coating a substrate with the ultraviolet-curable coating composition according to any one of claims 1 to 4.