Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2002-01-24
2003-12-30
Woodward, Ana (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S474700, C428S474900, C428S475500, C428S475800, C428S476300, C525S066000
Reexamination Certificate
active
06670047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a stretched gas-barring polyamide film having flexibility, impact resistance and pinhole resistance, which can be boiled or retorted.
2. Description of the Prior Art
As gas-barring packaging materials, there have been used multi-layer films by using a polyvinylidene chloride (PVDC), an ethylene-vinyl alcohol copolymer (EVOH) or a polyamide as a gas barrier layer. Among the polyamides, a metaxylylene group-containing polyamide obtained by polycondensing a metaxylylenediamine with an &agr;,&ohgr;-aliphatic dicarboxylic acid having 6 to 12 carbon atoms, loses gas-barring property less and recovers gas-barring property more than those of other gas-barring resins when it is subjected to the boiling or the retorting. In particular, the polymetaxylyleneadipamide (hereinafter often referred to as nylon MXD6) using an adipic acid as the &agr;,&ohgr;-alphatic dicarboxylic acid having 6 to 12 carbon atoms, is now finding spreading applications in the field of packaging by utilizing the above-mentioned features.
When not stretched, the nylon MXD6 has such defects as small impact resistance and low flexibility. When stretched, the nylon MXD6 exhibits impact resistance and flexibility which are improved to some extent. With the nylon MXD6 alone, however, the improvement is not satisfactory and a further improvement is desired. There have been proposed a method of adding a polyolefin to the nylon MXD6 (Japanese Unexamined Patent Publication (Kokai) No. 77373/1993), a method of adding a modified polyolefin (Japanese Patent Nos. 3021854 and 3021851), a method of adding ionomers (Japanese Unexamined Patent Publications (Kokai) Nos. 193081/1993, 117198/1995 and 276591/1995), and a method of adding a polyamide elastomer (Japanese Unexamined Patent Publications (Kokai) Nos. 224844/1996 and 165427/1995) without, however, accomplishing impact resistance and flexibility to a satisfactory degree.
SUMMARY OF THE INVENTION
The present inventors have conducted study in an effort to improve the impact resistance of a metaxylylene group-containing polyamide film by blending it with various resins, have discovered the fact that the gas-barring property, flexibility and impact resistance can be greatly improved yet maintaining a practically acceptable level of transparency by blending the xylylene group-containing polyamide with a modified product of an ethylene-ethyl acrylate copolymer resin, and have arrived at the present invention.
According to the present invention, there is provided a stretched polyamide film obtained by melt-kneading and extruding a mixed resin (Z) containing a polyamide resin (X) and a modified resin (Y) into a film followed by biaxial stretching, wherein:
the polyamide resin (X) is obtained by polycondensing a diamine component containing not less than 70 mol % of a metaxylylenediamine with a dicarboxylic acid component containing not less than 70 mol % of an &agr;,&ohgr;-aliphatic dicarboxylic acid having 6 to 12 carbon atoms;
the modified resin (Y) is obtained by graft-modifying an ethylene-ethyl acrylate copolymer resin with a maleic anhydride; and
the mixed resin (Z) contains from 80 to 99% by weight of the polyamide and from 20 to 1% by weight of the modified resin.
According to the present invention, further, there is provided a multi-layer stretched polyamide film obtained by biaxially stretching the multi-layer film that is obtained by melting and simultaneously extruding the mixed resin (Z), an adhesive resin and a thermoplastic resin (excluding the polyamide resin (X) and the resin (Y), the same holds hereinafter).
DETAILED DESCRIPTION OF THE INVENTION
[Polyamide Resin (X)]
A polyamide resin (X) used in the present invention is obtained by polycondensing a diamine component containing not less than 70 mol % of a metaxylylene diamine with a dicarboxylic acid component containing not less than 70 mol % of an &agr;,&ohgr;-aliphatic dicarboxylic acid having 6 to 12 carbon atoms.
According to the present invention, there is obtained a stretched film maintaining a predetermined gas-barring property by using the diamine component containing not less than 70 mol % of a metaxylylenediamine. The diamine component may contain any other diamine as far as it contains the metaxylylenediamine in an amount of not less than 70 mol %. Examples of the other diamine include paraxylylenediamine, orthoxylylenediamine, bisaminomethylcyclohexane, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, orthophenylenediamine, metaphenylenediamine and paraphenylenediamine. These other diamines can be used in a single kind or in a combination of two or more kinds together with the metaxylylenediamine.
Use of the dicarboxylic acid component containing not less than 70 mol % of the &agr;,&ohgr;-aliphatic dicarboxylic acid having 6 to 12 carbon atoms enables the polyamide resin to exhibit practicable properties. Representative examples of the &agr;,&ohgr;-aliphatic dicarboxylic acid having 6 to 12 carbon atoms include adipic acid and sebacic acid to which only, however, the invention is in no way limited. These dicarboxylic acids can be used in one kind or being mixed together in two or more kinds. The dicarboxylic acid component may contain any other dicarboxylic acid as far as it contains the above &agr;,&ohgr;-aliphatic dicarboxylic acid in an amount of not less than 70 mol %. Though not being limited thereto only, the other dicarboxylic acids will be aromatic dicarboxylic acids such as isophthalic acid and terephthalic acid. These other dicarboxylic acids, too, can be used in one kind or in a combination of two or more kinds together with the above-mentioned &agr;,&ohgr;-aliphatic dicarboxylic acid.
The above-mentioned polyamide resin (X) may have a molecular weight large enough for forming a film. From the standpoint of gas-barring property, further, the nylon MXD6 using the adipic acid as the dicarboxylic acid component is particularly suited as the polyamide resin
[Modified Resin (Y)]
A modified resin (Y) used in combination with the above-mentioned polyamide resin (X) is obtained by graft-modifying an ethylene-ethyl acrylate copolymer resin with a maleic anhydride.
It is desired that the ratio of the ethylene copolymerization (ethylene content) in the ethylene-ethyl acrylate copolymer resin that is to be graft-modified, is in a range of from 5 to 50 mol %.
Further, the ethylene-ethyl acrylate copolymer resin should be graft-modified with a maleic anhydride. When the unmodified ethylene-ethyl acrylate copolymer resin is used or when an unsaturated carboxylic anhydride other than the maleic anhydride is used as a modifier, the flexibility is not improved and the transparency becomes worse. In order to maintain a sufficient degree of flexibility and transparency, further, it is desired that the maleic anhydride is used in an amount of from 1 to 30% by weight per the ethylene-ethyl acrylate copolymer.
[Mixed Resin (Z)]
In the present invention, a mixed resin (Z) of the above-mentioned polyamide resin (X) and the modified resin (Y), contains the polyamide resin (X) in an amount of from 80 to 99% by weight and, particularly, from 90 to 97.5% by weight and contains the modified resin (Y) in an amount of from 1 to 20% by weight and, particularly, from 2.5 to 10% by weight. Namely, a favorable impact resistance is maintained by using the polyamide resin (X) in an amount that lies in the above-mentioned range, and a favorable gas-barring property and transparency are maintained by using the modified resin (Y) in an amount that lies in the above-mentioned range.
The mixed resin (Z) according to the present invention may further be blended with other resins and known additives so far as it contains the polyamide resin (X) and the modified resin (Y) in amounts lying within the above-mentioned ranges. In order to further improve the flexibility and impact resistance of the film, the mixed resin (z) may be further blend
Nanba Hiroyuki
Yamamoto Koji
Mitsubishi Gas Chemical Co. Inc.
Sherman & Shalloway
Woodward Ana
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