Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2002-02-25
2004-05-11
Woodward, Ana L. (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S220000, C428S474400, C428S475500, C525S425000
Reexamination Certificate
active
06733853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin composition comprising a polyamide resin and a polyester resin, a shaped article and a packaging container made of the resin composition. More specifically, the present invention relates to a resin composition produced by melt-blending a specific polyamide resin containing a phosphorus compound and a polyester resin containing an antimony compound, the resin composition being improved in gas barrier properties insufficient in resin compositions containing only a polyester resin and being eliminated in the problem of a darkened appearance due to the blend of a polyamide resin that lies in conventional resin compositions. The present invention also relates to a shaped article and a packaging container made of such a resin composition.
2. Description of the Prior Art
A polyester resin represented by a polymer, such as poly(ethylene terephthalate), which is prepared using an aromatic dicarboxylic acid and an aliphatic diol as monomers (hereinafter referred to as “polyester resin”) has been now widely used as packaging materials such as films, sheets and hollow containers because of its excellency in clearness, mechanical properties, melt stability, solvent resistance, flavor retention, recycling ability, etc. In spite of such excellent properties, the application field of packaging containers made of a polyester resin is limited because the polyester resin is not always sufficient in gas barrier properties against oxygen, carbon dioxide, etc. Improvement of the gas barrier properties of polyester resin has been attempted by vapor depositing aluminum oxide or silicon oxide onto a shaped article or packaging container made of a polyester resin, or by coating or laminating a resin having gas barrier properties higher than that of a polyester resin onto a shaped article or packaging container made of a polyester resin. However, since a complicated product process is required and the recycling ability or mechanical properties are detracted, these methods have been used in limited fields.
As an alternative method for improving the gas barrier properties of polyester resin which is free from the above problems, cited is a melt blending of a thermoplastic resin having high gas barrier properties with a polyester resin. An ethylene-vinyl alcohol copolymer resin can be mentioned as an example for such a high gas barrier resin. However, the ethylene-vinyl alcohol copolymer resin is little compatible with a polyester resin because of its molecular structure to give a white cloudy resin composition when blended with a polyester resin, thereby spoiling the clearness that is one of the beneficial characteristics of a polyester resin. In addition, since the ethylene-vinyl alcohol copolymer resin is relatively high in crystallizability as compared with a polyester resin, the stretchability of polyester resin tends to be lowered, this making the resin blend inapplicable to the production of packaging containers such as biaxially stretched films and blown bottles because a stretching process is indispensable. Further, the ethylene-vinyl alcohol copolymer resin is susceptible to a rapid thermal degradation at an optimum processing temperature for a polyester resin. Thus, the blend of the ethylene-vinyl alcohol copolymer resin raises another problem of reducing the processing stability of polyester resin.
Gas barrier resins other than the ethylene-vinyl alcohol copolymer include polyamide resins represented by Nylon 6, Nylon 66, etc. Of the polyamide resins, poly(m-xylylene diadipamide) prepared by the polymerization of a diamine component mainly comprising m-xylylene diamine and a dicarboxylic acid component mainly comprising adipic acid is particularly excellent in the gas barrier properties. In addition to its high gas barrier properties as compared with those of other polyamide resins, poly(m-xylylene diadipamide) does not detract the processing stability of polyester resin because its glass transition temperature, melting point and crystallizability are close to those of a poly(ethylene terephthalate) which is a typical polyester resin being in extremely wide use. Therefore, poly(m-xylylene diadipamide) is quite suitable for improving the gas barrier properties of polyester resin. A commercially available poly(m-xylylene diadipamide), for example, MX Nylon (product name) of Mitsubishi Gas Chemical Company, Inc., contains a phosphorus compound in an amount of several hundred ppm in terms of phosphorus atom to prevent the coloring of the resin during the melt processing.
The production of polyester resin is generally carried out in the presence of a metal catalyst containing germanium atom or antimony atom to increase the polymerization rate of monomers. It has been known in the art that a shaped article made of a polyester resin that is produced using an antimony-bearing catalyst is slightly darkened because of the deposition of metallic antimony by the reduction of an antimony compound. Therefore, to avoid the decrease of the commercial value of shaped article, the darkening is prevented by limiting the use amount of the antimony compound. Even in the case of using a limited amount of the antimony compound, if a shaped article is produced by melt-kneading and molding a polyester resin blended with poly(m-xylylene diadipamide) to improve the gas barrier properties, the darkening of the shaped article is considerably enhanced, as compared with a shaped article from a polyester resin added with no poly(m-xylylene diadipamide), because of the deposition of metallic antimony promoted by a phosphorus compound in poly(m-xylylene diadipamide). Therefore, the commercial value is reduced much when the shaped article is used as packaging materials or packaging containers for foodstuffs, etc., where the appearance is of extreme importance.
In Japanese Patent Publication No. 4-54702, is proposed a hollow shaped article excellent in gas barrier properties which is made of a resin composition containing a thermoplastic polyester resin mainly constituted by ethylene terephthalate repeating units and a polyamide resin. This document merely proposes to improve the gas barrier properties by incorporating a polyamide resin, and is quite silent as to the problem addressed in the present invention, i.e., the prevention of darkening of shaped articles by the action of phosphorus atom in a polyamide resin. Japanese Patent Publication No.6-78094 proposes a method of producing a heat-resistant synthetic resin bottle from a poly(ethylene terephthalate) resin blended with a nylon mainly constituted by m-xylylene diamine and adipic acid. This document relates to the improvement of the production method of heat-resistant bottles, and there is nothing about the prevention of darkening of shaped articles by the action of phosphorus atom in a polyamide resin.
SUMMARY OF THE INVENTION
A first object of the present invention is to solve the above problems and provide a resin composition excellent in gas barrier properties and reduced in the darkening, which comprises a polyester resin prepared using an antimony compound as a catalyst and a specific polyamide resin containing a phosphorus compound.
Another object of the present invention is to provide a shaped article and a packaging container made of such a resin composition.
As a result of extensive study in view of solving the above problems, the inventors have found that the increase in the darkening of a resin composition comprising a polyester resin prepared using an antimony compound as a catalyst and a polyamide resin can be prevented by regulating a relationship between a concentration of phosphorus atom derived from a phosphorus compound in the polyamide resin and a blending amount of the polyamide resin within a limited range, thereby obtaining a polyester-based resin composition with improved gas barrier properties.
Thus, the present invention relates to a polyester-based resin composition comprising a melt blend (C) consisting of 3 to 40% by mass of a polyamide resin (A) whi
Nanba Hiroyuki
Takashima Masahiko
Yamamoto Koji
Antonelli Terry Stout & Kraus LLP
Mitsubishi Gas Chemical Company Inc.
Woodward Ana L.
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