Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-12-18
2004-02-10
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C252S188280, C428S035100, C428S035500
Reexamination Certificate
active
06689437
ABSTRACT:
TECHNICAL FIELD
The present invention relates to oxygen-absorbing materials excellent in their oxygen-absorbing property and suitable for use in the form of powder, particles or film or for use as one component of a molded product such as a container. The present invention further relates to containers and molded products excellent in their gas barrier property that use the oxygen-absorbing materials therein. More specifically, the present invention relates to containers and molded products excellent in their gas barrier property and accordingly suitable for preserving food items/beverages or pharmaceutical drugs that are damaged by oxygen in terms of their taste, oxygen-sensitive substances and the like.
BACKGROUND ART
Thermoplastic polyester resin which includes polyethylene terephthalate as a major component has been used widely for packaging materials by being processed into various containers, films, sheets and the like, because of its superior dynamic properties, gas barrier property, chemical resistance, flavor-retaining property, hygienic properties and the like. However, even the thermoplastic polyester resin including the polyethylene terephthalate as a major component does not have absolutely perfect properties. Especially, the thermoplastic polyester resin is not suitable for containers of food items, beverages, cosmetics, pharmaceutical drugs and the like that are contents requiring a gas blocking property, since the thermoplastic polyester resin is particularly insufficient in a gas barrier property against oxygen. Accordingly, improvements have been made by blending the polyester resin including the polyethylene terephthalate as a major component with any gas barrier material having an excellent gas barrier property or layering them on each other to produce a laminate. However, the improvements are not appropriate for food items and beverages sensitive to oxygen. Moreover, National Patent Publication No. 2-500846 and Japanese Laying-Open No. 3-762 disclose techniques according to which molded products such as container, package and lid are produced by blending the polyester resin with MXD6 (condensation polymer of metaxylylene diamine and adipic acid) which is oxidizable polyamide resin and a Co compound which is oxidation catalyst, or by layering them on each other to produce a laminate. Although the techniques provide improvements to some degree, they are still inappropriate for food items, beverages, pharmaceutical drugs and cosmetics that are sensitive to oxygen.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an oxygen-absorbing material superior in its ability to preserve food items, beer, soft drinks, cosmetics, drugs or the like that are sensitive to oxygen for a long period of time without damage, which has not been achieved by any prior art, and to provide a molded product such as packaging container with the gas barrier property using the oxygen-absorbing material therein.
DISCLOSURE OF THE INVENTION
According to the present invention achieving the object above, a packaging container or molded product having the gas barrier property can contain a composition structured by blending a non-oxidizable thermoplastic resin with at least one type of oxidizable polymer having an oxygen-capturing function and a metal catalyst catalyzing oxidation of the oxidizable polymer or layering them on each other to form a laminate.
Here, the oxidizable resin refers to a resin oxidized through an oxidization reaction in the presence of oxygen. Specifically, the oxidizable resin has a structural unit including a methylene group bonded to an aromatic ring, the methylene group being further bonded to an element other than hydrogen and carbon, for example. Examples of the element other than hydrogen and carbon are N, O, S and the like preferably having a xylylene diamine structure.
It is particularly important that the content of the blended or layered oxidizable resin to form the container is at least 1 wt % with respect to structural components and that a polyamide resin is used containing a basic group such as amino group of 20 mmol/kg or less. Examples of the metal catalyst are compounds of Fe, Mn and Co that are transition metals of the first period. These metal catalysts can be included in advance in the oxidizable resin before being molded. The present invention is described below in more detail together with functions thereof
DETAILED DESCRIPTION
The inventors of the present invention have found that an amino group contained in the oxidizable resin has an influence on the oxygen-capturing function of the oxidizable resin which is subjected to an oxidation reaction by the metal catalyst. The inventors have accordingly found a resin with the gas barrier property excellent in the oxygen-capturing ability, by controlling the amount of such functional groups within an appropriate range. According to findings of the inventors, the amount of the basic group such as amino group included in the oxidizable resin is 20 mmol/kg or less, preferably 15 mmol/kg, and more preferably 10 mmol/kg or less, so that an excellent oxygen-capturing ability is achieved with the help of the metal catalyst such as Co.
The oxidizable resin used for the present invention is preferably a polyamide and more preferably a polyamide resin containing a metaxylylene group. A particularly preferable polymer contains, in a molecular chain, at least 70 mol % of a structural unit formed of metaxylylene diamine or mixed xylylene diamine including metaxylylene diamine and paraxylylene diamine of 80% or less with respect to the entire amount and &agr;, &ohgr; aliphatic dicarboxylic acid with the carbon number of 6-10. Examples of the polymer are homopolymers such as polymetaxylylene adipamide, polymetaxylylene sebacamide and polymetaxylylene superamide, copolymer of metaxylylene diamine/adipic acid/isophthalic acid, copolymer of metaxylylene/paraxylylene adipamide, copolymer of metaxylylene/paraxylylene piperamide, copolymer of metaxylylene/paraxylylene azelamide, and the like.
These polyamide resins containing the metaxylylene group are brittle in an amorphous state. Therefore, such resins are required to have a relative viscosity of preferably at least 1.5 and more preferably at least 2.0.
It is necessary that the amount of the amino group (AG) contained in the oxidizable polyamide is 20 mmol/kg or less. The amount of amino group can be adjusted by adding an excessive amount of dicarboxylic acid component to the diamine component in the process of polymerization, or by adding any sealing agent reacting with the amino group such as acid anhydride, monocarboxylic acid and the like when the polymerization process is completed, for example.
The amount of carboxyl end group contained in the polyamide resin is preferably at least 10 mmol/kg and more preferably at least 20 mmol/kg.
Preferably, the molar ratio of the carboxyl end group (CEG) and amino group (AG) contained in the polyamide resin, i.e., CEG/AG is at least 2, or at least 4, so that the oxygen capturing ability obtained by the metal catalyst such as Co can be enhanced.
According to the present invention, in addition to the oxidizable resin, a non-oxidizable thermoplastic resin is preferably used for forming a molded product such as container by blending or layering of them. Examples of the non-oxidizable thermoplastic resin are polyester resin, polyamide resin such as nylon 6 and nylon 66, polymer with a high nitrile content, copolymer of ethylene-vinyl alcohol, polycarbonate, polystyrene resin, and the like. The non-oxidizable thermoplastic polyester resin refers to a polyester usually containing at least 80 mol %, preferably at least 90 mol % of terephthalic acid in an acid component and containing at least 80 mol %, preferably at least 90 mol % of ethylene glycol in a glycol component. The remaining portion of the acid component includes for example isophthalic acid, diphenyl ether 4,4′-dicarboxylic acid, naphthalene 1,4- or 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane 1,10-dicarboxylic acid, or hexahydro
Gyobu Shoichi
Kodama Tetsuo
Kurahara Syunji
Matsuda Koichi
Mizuno Naoki
Nolan Sandra M.
Toyo Boseki Kabushiki Kaisha
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