Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-08-20
2001-05-22
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C522S025000, C522S031000, C428S035800, C428S413000
Reexamination Certificate
active
06235358
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a packing container and a container closure having a coating layer or a printing ink layer of an ultraviolet ray-curable resin on an outside surface, and more specifically, to a packaging container and a container closure having excellent curability, aesthetic beauty of an ultraviolet ray hardened coating, transferability of a container, heat-resistant treatability, retortability, and sanitary characteristics.
2. Prior Art
An ink or coating composition containing an ultraviolet-curable resin does not have a problem of the volatilization of a solvent in drying or baking. Furthermore, since a printed matter or a coated product does not need heating, these compositions are used in various applications or such a use have been investigated.
As examples of heretofore used ultraviolet ray-curable resin commpositions, a combination of an epoxy resin and a cationic ultraviolet ray polymerization initiator, a combination of urethane (meth)acrylate and an acrylate monomer, and an epoxy (meth)acrylate resin have been known.
Japanese technical Publication No. 7344/96 (Published on Jul. 3, 1996; Nippon Unicar Co.; developer: Eiji Ando and Kenichi Suzuki; Int.Cl. C09D163/00) describes a resin composition composed of an ultraviolet-curable resin composition comprising an aliphatic cyclic epoxy resin, a cationic polymerization initiator, and polydiorganosiloxane-polyoxyalkylene alternate block copolymer.
An ultraviolet-curable resin composition contains an photo-cationic-polymerizable epoxy-type monomer and an photo-cationic-polymerization initiator has an advantage of forming a cured coating by ultraviolet irradiation without the need of heating. However, the ultraviolet-cured coating to be formed has an insufficient degree of curing, and as a coating layer or a printing ink layer of a package container, it has an insufficient problem in transferability, heat-resistant treatability and retortability. In this packaging container, a smooth transferring operation of a container is essential in a production step and a filling step. If the degree of curing is low in the coating layer or in the printing ink layer or slidability is poor on the outer surface, the coating will be easily damaged by contact with another object or by collision with another object. Furthermore, to improve the preservability of the contents, hot filling, sterilization by pasteurizer and retort sterilization have been carried out, but known ultraviolet ray-curable resins which can withstand these heat treatments, especially retort sterilization operation, are very few.
The photo-cationic-curing catalysts are decomposed by ultraviolet rays and release Lews acid. This Lewis acid polymerizes an epoxy group, and for example, an aromatic iodonium salt, an aromatic sulfonium salt, an aromatic selenium salt and an aromatic diazonium salt are used. However, although these photo-cationic-curing catalysts have a satisfactory sensitivity to ultraviolet rays having a short wavelength of generally 280 nm or below, they do not have a sufficient sensitivity to ultraviolet rays having a long wavelength. They only can insufficiently satisfy a purpose of forming the coating layer or the printing ink layer of the containers by curing due to ultraviolet rays. The pigments contained in the coating layer or the printing ink layer absorb ultraviolet rays having a short wavelength, for example, titanium dioxide absorbs ultraviolet rays having a shorter wavelength than 380 nm.
Furthermore, the photo-cationic-curing catalysts have a problem of sanitary characteristics. Known photo-cationic-curing catalysts may have a toxicity, and an iodonium salt has a problem of irritability of a bodily part. Furthermore, antimonate has a problem because it is composed of a heavy metal salt.
Of course, these photo-cationic-curing catalysts may be used in combination with known sensitizers, but many of the sensitizers have a problem of toxicity. Such sensitizers might not show a sensitizing action on ultraviolet rays having a long wavelength. Furthermore, some sensitizer may have a strongly brown color and may color the cured coated film. Combinations of photo-cationic-curing catalysts showing satisfactory curing properties to ultraviolet rays on the long wavelength with sensitizers have not been known so much.
SUMMARY OF THE INVENTION
The present inventors have found that a combination of a photo-cationic-curing catalyst composed of a specified sulfonium salt with a thioxanthone-type sensitizer shows satisfactory curing properties to ultraviolet rays having a long wavelength without generating the above-mentioned defects even when a pigment of titanium dioxide is contained in a high optical concentration, a coating layer or a printing ink layer having excellent curability, aesthetic beauty, transferrability of a container, heat treatability, retortability, and sanitary characteristics can formed on a packaging container or a container closure.
It is an object of this invention to provide a packaging container and a container closure having an ultraviolet-curable coating layer or a printing ink layer having excellnet curability, aesthetic beauty, transferrability of a container, heat treatability. retortability, and sanitary characteristics, the above coating layer or the printing ink layer showing satisfactory curing properties on ultraviolet rays having a long wavelength.
According to this invention, there are provided a packaging container and a container closure having, on the outer surface, a coating layer of a resin composition which comprises
a cationic curable resin comprising an alcyclic epoxy resin.
a photo-cationic-curing catalyst comprising a compound of the following formula (1),
wherein each of R
1
and R
2
is an alkyl group, and they may be the same or different, and R
3
is a hydrogen atom or an alkyl group,
a sensitizer comprising a thioxanthone sensitizer, and
a pigment comprising titanium dioxide,
wherein;
the amount of said titanium dioxide is at least 0.3 mg, especially 0.4 to 0.9 mg, per 1 cm
2
of said coating layer,
the amount of said photo-cationic-curing catalyst is 1 to 20%, especially 1.5 to 10%, by weight with regard to said titanium dioxide, and
the amount of said sensitizer is 1.5 to 5%. especially 1.5 to 4% by weight with regards to said titanium dioxide.
1. The photo-cationic-curing catalysts include 2-naphthyl-1-ethoxycarbonylethylmethyl sulfonium.hexafluorophosphonate (catalyst 1), 2-naphthyl-1-methoxycarbonylethylmethyl sulfonium.hexafluorophosphonate (catalyst 2) and 2-naphthyl-1-ethoxycarbonylpropylmethyl sulfonium.hexafluorophosphonate (catalyst 3).
2. The above resin composition contains 1 to 20 parts by weight, especially 1.5 to 10 parts by weight, of the photo-cationic-curing catalyst, and 1.5 to 5 parts by weight, especially 1.5 to 4 parts by weight, of the thioxanthone-type sensitizer, per 100 parts by weight of titanium dioxide.
3. The above resin composition contains 30 to 250 parts by weight, especially 40 to 220 parts by weight, of tittanium dioxide, especially rutile-type titanium dioxide, per 100 parts by weight of the alicyclic epoxy resin.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION
The container of this invention may be any packaging container or any container closure formed from a metal, a plastic or a laminate thereof, such as a can or a closure composed of a metal material or a coated metal material, a bottle or a closure composed of a thermoplastic resin, or a pouch or a closure composed of a thermoplastic resin laminate or a thermoplastic resin-metal foil laminate.
In this invention, a specified sulfonium salt of the above formula (1) is selected as the photo-cationic-curing catalyst, and is combined with the thioxanthone-type sensitizer, the alicyclic epoxy resin and the titanium dioxide pigment to use the combination in forming the coating layer or the printing ink layer of the package or closure.
The sulfonium salt used in this invention is structurally characterized in that the aryl group bonded to a sulf
Goto Hiroaki
Sasaki Hiroshi
Dye Rena L.
Hon Sow-Fun
Sughrue Mion Zinn Macpeak & Seas, PLLC
Toyo Seikan Kaisha Ltd.
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