Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-03-11
2004-01-06
Rice, Kenneth R. (Department: 3627)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
Reexamination Certificate
active
06673403
ABSTRACT:
TECHNICAL FIELD
The present invention relates to gas barrier multi-layer hollow containers, and more particularly to gas barrier multi-layer hollow containers which comprise in combination a layer of a thermoplastic resin such as polyolefin and a layer of polyglycolic acid, and by which the oxygen gas barrier property and/or carbon dioxide gas barrier property of the thermoplastic resin layer is markedly improved. The gas barrier multi-layer hollow containers according to the present invention are particularly suitable for use as various kinds of containers for drink, food, daily needs, gasoline and the like.
BACKGROUND ART
Various kinds of resin-made hollow containers have heretofore been used as containers for various goods such as drink, food, daily needs and gasoline. Specific examples thereof include hollow containers making use of a thermoplastic resin such as polyolefin, polyester, polystyrene or polyvinyl chloride. Since these hollow containers 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 containers for drink food, toiletry containers, etc. In order to improve the gas barrier properties of such resin-made hollow containers, there have thus been developed multi-layer hollow containers in which a gas barrier layer composed of an ethylene.vinyl alcohol copolymer (EVOH), polyamide or the like is combined with a layer of such a resin.
However, the layer formed of a gas barrier resin such as EVOH or polyamide is deteriorated in gas barrier properties to a great extent under high-temperature and high-humidity conditions. Therefore, the conventional multi-layer hollow containers containing these layers have been insufficient for hollow containers for goods which require a treating process under high-temperature and high-humidity conditions, such as retorting, goods which particularly require a long-term storage, and the like.
In recent years, biodegradable polymers, for example, polylactic acid, polysuccinate, polycaprolactone, etc., have attracted attention as plastic materials which scarcely impose burden on the environment. Hollow containers making use of these biodegradable polymers are also going to be developed. However, the hollow containers formed of these biodegradable polymers are insufficient in gas barrier properties such as oxygen gas barrier property and carbon dioxide gas barrier property. When layers of these biodegradable polymers are combined with the conventional gas barrier resin layers formed of EVOH, polyamide, etc. to improve their gas barrier properties, a problem of increasing burden on the environment has arisen.
The present inventors succeeded in producing hollow containers having excellent gas barrier properties from polyglycolic acid. However, the mere single layer of the polyglycolic acid is not always sufficient in, for example, moisture resistance, mechanical strength, profitability, etc.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a gas barrier multi-layer hollow container suitable for use as a container for goods which require a treating process under high-temperature and high-humidity conditions, such as retorting, goods which require a long-term storage, and the like.
Another object of the present invention is to provide a gas barrier multi-layer hollow container far excellent in oxygen gas barrier property and carbon dioxide gas barrier property.
A further object of the present invention is to provide a gas barrier multi-layer hollow container 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 when a polyglycolic acid layer is combined with a thermoplastic resin layer, a gas barrier multi-layer hollow container, by which the oxygen gas barrier property and/or carbon dioxide gas barrier property of the thermoplastic resin layer is markedly improved, is obtained.
When in the conventional gas barrier multi-layer hollow container having a container wall of the layer structure of, for example, polyolefin/gas barrier resin/polyolefin, a polyglycolic acid layer is provided in place of the gas barrier resin layer formed of EVOH, polyamide or the like, a gas barrier multi-layer hollow container having excellent oxygen gas barrier property and carbon dioxide gas barrier property and sufficient properties for a container for goods which require a treating process under high-temperature and high-humidity conditions, and goods which require a long-term storage can be obtained.
When a gas barrier resin layer formed of EVOH, polyamide or the like is used in combination with the polyglycolic acid layer, a gas barrier multi-layer hollow container markedly improved in not only oxygen gas barrier property but also carbon dioxide gas barrier property can be obtained. When a layer of a biodegradable polymer such as polylactic acid, polysuccinate or polycaprolactone is combined with the polyglycolic acid layer, a multi-layer hollow container 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 gas barrier multi-layer hollow container having a multi-layer wall structure that a thermoplastic resin layer is laminated on at least one side of a layer formed from polyglycolic acid containing at least 60 wt. % of a repeating unit represented by the following formula (1):
According to the present invention, there is also provided a process for producing a multi-layer hollow container, which comprises respectively heating and melting polyglycolic acid containing at least 60 wt. % of a repeating unit represented by the following formula (1):
at least one thermoplastic resin, and optionally an adhesive in extruders, causing the respective resins to flow into a die for forming a multi-layer parison to put them together, extruding the joined resins into a multi-layer tubular parison, holding the parison by a split mold before it is solidified, pinching one end of the parison, and at the same time blowing up the parison up to the mold wall by introducing air into the parison, and then cooling the blown parison, thereby molding the container.
According to the present invention, there is further provided a process for producing a multi-layer hollow container, which comprises co-injecting polyglycolic acid containing at least 60 wt. % of a repeating unit represented by the following formula (1):
at least one thermoplastic resin, and optionally an adhesive into a closed-end parison, blowing up the parison up to the wall of a mold by introducing air into the parison in the mold after solidifying the parison once, or in a supercooled state or at a temperature not higher than the melting point, Tm of the parison without solidifying it, while stretching the parison in a longitudinal direction or without stretching it, and cooling the blown parison, thereby molding the container.
The thermoplastic resin layer may preferably be a layer formed from a thermoplastic resin selected from the group consisting of polyolefin (including polyolefin obtained by using a metallocene catalyst), polyester, polystyrene, polyvinyl chloride, polycarbonate, polyamide, polyurethane, ethylene vinyl alcohol copolymers, polyvinylidene chloride, polylactic acid, polysuccinate and polycaprolactone.
In the gas barrier multi-layer hollow containers according to the present invention, at least one of the oxygen gas transmission rate and carbon dioxide gas transmission rate of the container wall thereof as determined at 23° C. and 80% relative humidity (RH) may be reduced to at most a half of that of the container wall of a hollow container formed of the thermoplastic resin alone.
The thickness of the polyglycolic acid layer may be general
Hoshino Mitsuru
Kawakami Yukichika
Kouyama Toshitaka
Sato Nobuo
Shiiki Zenya
Dinsmore & Shohl LLP
Kureha Kagaku Kogyo K.K.
Rice Kenneth R.
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