Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
1999-01-19
2001-06-12
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S036600, C428S036700, C428S412000, C428S423700, C428S475200, C428S480000, C428S910000, C528S354000, C528S361000, C528S425000
Reexamination Certificate
active
06245437
ABSTRACT:
TECHNICAL FIELD
The present invention relates to composite gas barrier films, and more particularly to composite films which comprise in combination a thermoplastic resin film such as a polyolefin film, and a polyglycolic acid film, and by which the oxygen gas barrier property and/or carbon dioxide gas barrier property of the thermoplastic resin film is markedly improved. The composite gas barrier films according to the present invention are particularly suitable for various kinds of packaging materials.
BACKGROUND ART
Various kinds of resin-made packaging materials have heretofore been used for resin-made packaging various food or goods. Such resin-made packaging materials include those making use of, for example, films of thermoplastic resins such as polyolefin, polyester, polystyrene and polyvinyl chloride. Since these resin-made packaging materials are generally insufficient in gas barrier properties such as oxygen gas barrier property and carbon dioxide gas barrier property, however, they are unsatisfactory for applications to especially food packaging materials (packaging materials for meat, fishes and shellfishes, dairy products, pickles, miso, confectionery, tea•coffee, noodles, rice, etc.), toiletry packaging materials, drug packaging materials, etc. In order to improve the gas barrier properties of such resin-made packaging materials, there have thus been developed composite films in which a gas barrier film composed of an ethylene vinyl alcohol copolymer (EVOH) or polyamide is combined therewith.
However, the films formed of EVOH or polyamide are impaired in gas barrier properties to a great extent under high-temperature and high-humidity conditions. Therefore, the conventional composite films containing these films have been insufficient for packaging materials for food and goods which require a treatment under high-temperature and high-humidity conditions, such as retorting, food and goods which particularly require a long-term storage, and the like.
In recent years, biodegradable polymers, for example, polylactic acid, polysuccinates, polycaprolactone, etc. have attracted attention as plastic materials which scarcely impose burden on the environment. Packaging material making use of these biodegradable polymers are also going to be developed. However, films of these biodegradable polymers are insufficient in gas barrier properties such as oxygen gas barrier property and carbon dioxide gas barrier property. When these films are combined with the conventional EVOH or polyamide film to improve their gas barrier properties, a problem of increasing burden on the environment has arisen.
Recently, the present inventors succeeded in producing films having excellent gas barrier properties from polyglycolic acid. However, only a single layer of the polyglycolic acid film is not always sufficient in, for example, heat sealability, moisture resistance, mechanical strength, profitability, etc.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a composite gas barrier film suitable for use as a packaging material for food and goods which require a treatment under high-temperature and high-humidity conditions, such as retorting, food and goods which require a long-term storage, and the like.
Another object of the present invention is to provide a composite film far excellent in oxygen gas barrier property and carbon dioxide gas barrier property.
A further object of the present invention is to provide a composite gas barrier film which scarcely imposes burden on the environment.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that a polyglycolic acid film is combined with a thermoplastic resin film, whereby a composite film, by which the oxygen gas barrier property and/or carbon dioxide gas barrier property of the thermoplastic resin film is markedly improved, is obtained.
When in the conventional composite gas barrier film having a layer structure of, for example, polyolefin/gas barrier resin/polyolefin, a polyglycolic acid film is used in place of the film of the gas barrier resin such as EVOH or polyamide, a composite film having sufficient properties for a packaging material for food and goods which require a treatment under high-temperature and high-humidity conditions, and food and goods which require a long-term storage can be obtained. When the film of the gas barrier resin such as EVOH or polyamide is used in combination with the polyglycolic acid film, a composite film markedly improved in not only oxygen gas barrier property but also carbon dioxide gas barrier property can be obtained.
When a film of a biodegradable polymer such as polylactic acid, polysuccinate or polycaprolactone is combined with the polyglycolic acid film, a composite film excellent in gas barrier properties and profitability can be obtained without impairing biodegradability (decomposability in soil).
The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a composite gas barrier film having a layer structure that a thermoplastic resin film is laminated on at least one side of a film formed from polyglycolic acid containing at least 60 wt. % of a repeating unit represented by the following formula (1):
The thermoplastic resin film may preferably be a film formed from a thermoplastic resin selected from the group consisting of polyolefin, polyester, polystyrene, polyvinyl chloride, polycarbonate, polyamide, polyurethane, ethylene.vinyl alcohol copolymer, polyvinylidene chloride, polylactic acid, polysuccinate and polycaprolactone. In the composite gas barrier film according to the present invention, at least one of the oxygen gas transmission rate and carbon dioxide gas transmission rate of the composite film as determined at 23° C. and 80% relative humidity (RH) may be reduced to at most a half of that of the thermoplastic resin film to be combined.
The thickness of the polyglycolic acid film may be generally 1 &mgr;m to 2 mm, and the thickness of the composite gas barrier film may be generally 2 &mgr;m to 3 mm. In the composite gas barrier film according to the present invention, an adhesive layer may be optionally provided to improve interlayer adhesion.
BEST MODE FOR CARRYING OUT THE INVENTION
Layer Structure of Composite Gas Barrier Film
The composite gas barrier films according to the present invention are multi-layer films comprising at least one thermoplastic resin film (hereinafter may be referred to as “base film”) and a polyglycolic acid film. As needed, an adhesive layer may be provided between the individual layers. The total thickness of the composite gas barrier film is generally 2 &mgr;m to 3 mm, preferably 5 &mgr;m to 2 mm, more preferably 10 &mgr;m to 1 mm. If this thickness is smaller than 2 &mgr;m, such a composite film is difficult to produce, and so results in increase in its production cost. It is hence not preferable to produce such a composite film from the viewpoints of productivity and profitability. If the thickness exceeds 3 mm, it is difficult to subject such a composite film to secondary processing for using it as a packaging material, and the cost of the packaging material becomes increased. It is hence not preferable to produce such a composite film from the viewpoints of productivity and profitability.
The basic layer structures of the composite gas barrier films according to the present invention are as follows. However, these layer structures are indicated with optional adhesive layer(s) omitted. The polyglycolic acid is abbreviated as PGA.
(1) Thermoplastic resin/PGA;
(2) Thermoplastic resin 1/PGA/Thermoplastic resin 1; and
(3) Thermoplastic resin 1/PGA/Thermoplastic resin 2.
In the composite gas barrier films according to the present invention, various thermoplastic resin films of the same or different kind may be additionally laminated according to properties required so far as any one of the above-described b
Hoshino Mitsuru
Kawakami Yukichika
Kouyama Toshitaka
Sato Nobuo
Shiiki Zenya
Chen Vivian
Dinsmore & Shohl LLP
Kureha Kagaku Kogyo K.K.
LandOfFree
Gas-barrier composite film does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gas-barrier composite film, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas-barrier composite film will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522463