JPH0662889B2 - Two-piece can coating composition and method for producing painted two-piece can - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coating composition useful for coating the outer surface of a two-piece can and a method for producing a coated two-piece can using the coating composition.

(Prior Art) Conventionally, a thermosetting coating composition and a radiation curable coating composition have been used for coating the outer surface of a two-piece can.

(Problems to be solved by the invention) Conventionally, a thermosetting coating composition used as a coating for the outer surface of a two-piece can requires a high temperature of 200 ° C. or higher and a baking time in minutes for its curing. There are problems in terms of productivity, energy efficiency and equipment efficiency. In order to solve such problems, a radiation curable paint was considered as a paint for the outer surface of a two-piece can, but such a radiation curable paint has a high paint price and causes a large stress during curing of the coating film. Therefore, there is a problem that adhesion to metal and processing performance are inferior to those of thermosetting paints.

(Means for Solving Problems) As a result of earnest research to solve the above-mentioned drawbacks of the prior art, the present inventors have added a thermosetting resin to a conventional radiation curable coating composition. As a result, they have found that the above-mentioned drawbacks of the prior art are solved, and completed the present invention.

That is, the present invention provides a two-piece can outer surface coating composition obtained by adding and mixing a thermosetting resin to a radiation curable coating composition containing 5% by weight or more of a trifunctional or higher functional radiation curable resin, and A method for producing a coated two-piece can, characterized in that the coating composition is applied to the outer surface of the two-piece can, radiation-cured, and simultaneously heat-cured by the heat required for heat-curing the paint on the inner surface of the can.

Explaining the present invention in detail, the radiation-curable resin composition itself used in the present invention, which firstly characterizes the present invention, is a known material, and the radiation-curable resin and, if necessary, a sensitizer. And other optional components. Typical of the radiation curable resin, a relatively low molecular weight polyester resin having a radically polymerizable unsaturated double bond in its molecular structure, a polyether resin, an acrylic resin, an epoxy resin, a urethane resin, an alkyd resin,
It includes oligomers or prepolymers such as acrylates and methacrylates of polyfunctional compounds such as polyhydric alcohols, and addition-polymerizable compounds such as styrene, methylstyrene, divinylbenzene, acrylic acid (or methacrylic acid) ester, etc. These are contained alone or as a mixture. Further, as the radiation curable resin of other examples, cationic polymerization type of vinyl ethers and epoxy resins can be used in the same manner as the above radical polymerization type. These cationic polymerization types use, for example, a radiation-sensitive catalyst, which is an aryldiazonium salt of a halogenide, to generate a Lewis acid by irradiation, and produce vinyl-2-ethylhexyl ether, vinyl decyl ether, vinyl allyl ether, etc. Vinyl ethers or their compounds, 1,2-epoxycyclohexane, 1,2-epoxy-4- (epoxyethyl)
Cyclohexane, dicyclopentadiene oxide,
Epoxy resins such as sorbitol polyglycidyl ether and 2,2'-bis [P- (2,3-epoxy) phenyl] propane or mixtures thereof are subjected to cationic polymerization. In the present invention, as these radiation curable resins, it is desirable to use triacrylate, trimethacrylate, trifunctional or higher functional polyacrylates such as sorbitol glycidyl ether, polymethacrylates or polyepoxides in an amount of about 5 to 100% by weight,
When the content of such a polyacrylate is 5% by weight or less, the cross-linking of the coating film becomes insufficient and a coating film having a sufficient surface hardness cannot be formed. As the radiation curable resin as described above, it is preferable to use one having an average molecular weight of about 5,000 or less.

Further, a sensitizer required when using ultraviolet rays as radiation is a compound that generates a free radical by the energy of ultraviolet rays, such as carbonyl compounds such as benzoin, benzophenone or their esters, and organic peroxides such as benzoyl peroxide. There are oxides, azo compounds such as azobisisobutyronitrile, and sulfur compounds such as diphenyldisulfide. In the case of cationic polymerization type, 2,
What is represented by the aryldiazonium salt of a complex halogenide such as 5-diethoxy-4- (P-tolylthio) benzenediazonium hexafluorophosphate is used.

The second feature of the present invention is to add a thermosetting resin to the radiation curable resin composition as described above, and as such a thermosetting resin, a conventionally known phenolic resin, epoxy resin Examples thereof include amino resins, epoxy / phenolic resins, epoxy / polyamide resins, epoxy / ester resins, alkyd resins, acrylic resins and the like. Such a thermosetting resin is, of course, another additive,
For example, a crosslinking agent, which may optionally include a solvent,
It is preferable to add 10 to 100 parts by weight to 100 parts by weight of the radiation curable resin composition. When the addition amount exceeds the upper limit of the above range, the radiation curability of the radiation curable coating composition of the present invention becomes insufficient, and when it exceeds the lower limit of the above range, adhesion to metal, workability, resistance to It is not preferable because the processability and cost merit are insufficient.

The radiation-curable resin composition of the present invention can be obtained by simply mixing the above-mentioned essential components, but if necessary, various additives such as colorants, crosslinking agents, waxes, silicones, etc. As a matter of course, conventionally known additives can be optionally included.

A second invention of the present invention is a method for producing a coated two-piece can by using the coating composition of the first invention of the present invention as described above. For example, the radiation curable coating composition can be prepared to have an appropriate viscosity ( For example, after adjusting to about 50 to 2,000 cps), preferably using a roll coater, about 1 to 1 on the outer surface of the two-piece can.
It is applied to a thickness of 12 μm (dry thickness), and radiation, for example, ultraviolet rays, is output from an ultraviolet ray generation source such as a high pressure mercury lamp or a medium to low pressure mercury lamp at 50 to 300 w / cm, preferably 80 to 120 w / cm,
By irradiating with ultraviolet rays for 2 to 0.1 seconds, preferably 2 to 1 seconds, it is possible to handle the can in the can manufacturing process up to the predetermined performance, that is, coating with the thermosetting paint on the inner surface of the can and heating process. On the other hand, a coating film having sufficient performance is formed. Next, the processing conditions for heat-curing the inner coating, such as
5 seconds to 10 minutes at 150-300 ℃, preferably 3 at 200-220 ℃
Under the curing condition of ˜4 minutes, the coating film on the outer surface, which has been cured by the above-mentioned ultraviolet rays, is completely cured together with the curing of the inner surface paint, and the coated two-piece can of the present invention is obtained.

(Operation / Effect) According to the present invention as described above, the radiation-curable coating composition of the present invention, which is low in cost, is used for coating the outer surface of the can with simple equipment and in a relatively short period of time with relatively little energy. A coating film having a predetermined performance can be easily formed, and then the energy applied during curing of the coating film on the inner surface of the can can be simultaneously utilized to achieve complete curing of the coating film on the outer surface of the can. Since a curable resin is added, the drawbacks of conventional radiation curable coating materials, such as adhesion to metal and workability of a coating can, have been solved. Therefore, by using the radiation-curable coating composition of the present invention for the outer surface coating of a two-piece can, the problems of energy waste, adhesion to metal, processability and cost, which are problems of the prior art, are sufficient. It is possible to form a strong and tough coating film on the outer surface of a two-piece can, and when a multifunctional oligomer or monomer is used as a radiation curable resin, the pencil hardness is 4H to 5H or more, which is excellent. A hard coating film can be formed with excellent chemical resistance, water resistance, impact resistance, surface smoothness, and adhesion. In the above description, the case where ultraviolet rays are used as the radiation has been described, but the same effect can be obtained by using electron beams or other active energy rays instead of ultraviolet rays. Next, the present invention will be described more specifically with reference to examples. In addition, in the text, "%" or "%" is based on weight.

Example 1 Epoxy acrylate oligomer (average mwt 1,000 to 1,500) 40 parts Trifunctional acrylate monomer 20 parts Bifunctional acrylate monomer 20 parts Monofunctional acrylate monomer 10 parts 1-hydroxycyclohexyl phenyl ketone 3 parts 2-hydroxy-2- Methyl-1-phenylpropane-
1-on 3 parts Radiation curable resin paint prepared by mixing the above components, polyethylene wax 3 parts, silicone 2 parts, epoxy resin
25 parts, 10 parts of benzoguanamine melamine resin and 20 parts of an organic solvent (xylol, acetic acid butyl ester, n-butanol) are added and mixed to obtain the radiation curable coating composition of the present invention. 6 dm ^{2 of} this paint on the outer surface of a two-piece can
Roll coating is applied to a coating amount of 0 ± 10 mg, and the coating is cured by passing it under a high pressure mercury lamp. Then, the two-piece can was heat-treated at 200 ° C. for 3 minutes in an oven to obtain a completely cured coating film having the performance shown in Table 1. The physical properties of this coating film are shown in Table 1.

Example 2 Epoxy acrylate oligomer (average mwt 1,000 to 1,500) 30 parts Trifunctional acrylate monomer 40 parts Bifunctional acrylate monomer 20 parts 1-hydroxycyclohexyl phenyl ketone 3 parts 2-hydroxy-2-methyl-1-phenylpropane-
1-on 3 parts Radiation curable resin paint prepared by mixing the above components, polyethylene wax 3 parts, silicone 1 part, epoxy resin
30 parts, 12 parts of phenol resin, and 20 parts of organic solvent are added and mixed to obtain the radiation curable coating composition of the present invention. By performing the same operation as in Example 1 on this paint, the first
As shown in the table, a coating film having the same performance as in Example 1 was obtained. Table 1 Example 1 Example 2 Pencil hardness 5H 5H Tape adhesion 100/100 100/100 Impact resistance Abnormal pear Abnormal pear Solvent resistance Abnormal pear Abnormal pliability Good Good Process resistance Abnormal pear Abnormal pear Pencil hardness: Hardness of coating film in scratch test by Mitsubishi Uni-Pencil Tape adhesion: 1mm interval goggles tape peeling test Impact resistance: DuPont type impact resistance tester used, load 500g,
Punch diameter 1/2 inch, drop height 30 cm Solvent resistance: Film judgment when the film is rubbed 50 times with methyl etorketone-impregnated flannel Lubricity: Using dynamic friction coefficient measuring machine Process resistance: 100 ° C boiling water 30 Coating film judgment such as whitening, softening, peeling of coating film after treatment for minutes

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuo Takezawa 2-1607-3 Nisshin-cho, Omiya-shi, Saitama (2-203) (72) Inventor Akira Kuboshima 2-2-21 Nihonmatsu, Sagamihara-shi, Kanagawa (72) Inventor Kenichi Uematsu 2-2-17-3 Nihonmatsu, Sagamihara City, Kanagawa Prefecture (56) Reference JP-A-47-42974 (JP, A)

Claims (2)

[Claims] 1. A two-piece can outer coating composition comprising a radiation-curable coating composition containing 5% by weight or more of a trifunctional or higher-functional radiation-curable resin and a thermosetting resin added thereto. 2. A coating composition obtained by adding and mixing a thermosetting resin to a radiation curable coating composition containing 5% by weight or more of a trifunctional or higher functional radiation curable resin is applied to the outer surface of a two-piece can. A method for producing a painted two-piece can, which comprises radiation-curing and heat-curing at the same time by the heat required for heat-curing the paint on the inside of the can.