Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-05-18
2003-02-04
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S480000, C528S490000, C528S50200C, C528S50200C, C428S034100, C428S034700, C428S221000, C428S331000, C428S324000, C428S332000, C428S338000, C428S339000, C428S411100, C428S474400, C524S442000, C524S445000, C524S447000, C524S448000, C524S449000, C524S451000, C524S789000, C524S879000, C264S176100, C264S209100
Reexamination Certificate
active
06515099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polyamide resin shaped article excellent in clarity, appearance, gas barrier properties, mechanical properties, and moldability which are required in packaging materials for foods, beverages, medicines, electric parts, etc. The present invention further relates to a method for producing such a polyamide resin shaped article.
2. Description of the Prior Art
Polyamide resin has been widely used as the material for injection molding automotive parts, electric parts, electronic parts, etc., because of its excellent mechanical properties. Its application field extends to packaging materials for foods, beverages, medicines, electric parts, etc. Of various polyamide resins, a m-xylylene group-containing polyamide prepared by the polycondensation of m-xylylenediamine and an aliphatic dicarboxylic acid (hereinafter may be referred to as “MX nylon”), particularly polyamide MXD6 prepared from m-xylylenediamine and acidic acid is utilized as a gas-barrier material for manufacturing a shaped article such as film and bottle because of its low permeability against gaseous substance such as oxygen and carbon dioxide. Recently, there is an increasing demand for a gas-barrier package capable of storing foods, beverages, etc. for a long term without detracting their freshness. This in turn increases the demand for improvement of the gas-barrier properties much more.
As the method for improving the gas-barrier properties of polyamide resin, Japanese Patent Application Laid-Open Nos. 2-69562, 2-105856 and 2-305828 disclose to incorporate a layered silicate into a polyamide resin. The incorporation can be effected, for example, by melt-kneading the layered silicate and a polyamide in a known various types of extruders such as single or twin screw extruder and extruding the kneaded product, or by producing polyamide by melt polymerization in the presence of the layered silicate.
In the incorporation by the melt kneading, the whole part of polyamide which constitutes the final material for producing shaped article is melted and kneaded with the layered silicate in an extruder, extruded from the extruder, cooled for solidifying, and formed into pellets. The pellets thus prepared are made flowable again by heating in T-die extruder, injection molding machine, etc. to produce final shaped articles such as film. Therefore, the whole part of polyamide to constitute shaped articles is subject to heat history at least twice. As a result, as compared with the incorporation of the layered silicate during the production of polyamide by melt polymerization, the polyamide is cross-linked much more to result in the formation of a large amount of gel-like substances in the final shaped articles such as film, thereby spoiling the fine appearance of the shaped articles and causing frequent breaking and rupture during the production of the shaped articles such as film to reduce the industrial and commercial values.
Particularly, because of a higher melting point and a low heat stability in molten state as compared with nylon 6, the m-xylylene group-containing polyamide is liable to arise various problems such as deterioration in clarity and appearance, breaking during the shaping or molding process, etc. by the thermal decomposition and gel formation when subjected to heat history during the extrusion, etc. Since the lowering of the molecular weight by the thermal decomposition reduces the relative viscosity of the polyamide, films and sheets extruded from a T-die or circular die extruder are uneven in their thickness, and multi-layer preforms produced by injection molding has a core layer (center layer) with non-uniform section, thereby spoiling the appearance and reducing the barrier properties.
Generally, the layered silicate is finely and uniformly dispersed into nylon 6 by conducting the polycondensation for producing nylon 6 in the presence of the layered silicate. However, from the experience of the inventors, this method fails to produce a m-xylylene group-containing polyamide having a high molecular weight.
As described above, the attempt to disperse the layered silicate into the m-xylylene group-containing polyamide by the method conventionally applied to nylon 6, etc. arises technical problems which are inherent in the m-xylylene group-containing polyamide but not encountered in nylon 6, etc. However, the prior art has not ever considered such specific problems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polyamide resin shaped article comprising a m-xylylene group-containing polyamide resin, in which a layered silicate treated with an organic swelling agent are uniformly dispersed throughout the resin. Another object of the present invention is to provide a polyamide resin shaped article which is excellent in the properties required for packaging materials such as clarity, appearance, gas-barrier properties, mechanical strength and moldability and contains less gel-like substance. Still another object of the present invention is to provide a production method of a polyamide resin shaped article without lowering the molecular weight of the m-xylylene group-containing polyamide during the incorporating operation of the layered silicate.
As a result of extensive study in view of attaining the above objects, the inventors have found that the problems can be solved by preliminarily melt-kneading the m-xylylene group-containing polyamide resin and the layered silicate in a specific ratio under specific conditions to prepare a master batch, and melt-kneading the master batch with the m-xylylene group-containing polyamide resin in a specific ratio when producing the shaped articles.
Thus, the present invention provides a polyamide resin shaped article comprising (A) 92 to 99.7 mass % of a polyamide resin produced by polycondensation of a diamine component containing 70 mol % or more of m-xylylenediamine and a dicarboxylic acid component containing 70 mol % or more of a straight-chain, aliphatic &agr;, &ohgr;-dicarboxylic acid having 4 to 12 carbon atoms, and (B) 8 to 0.3 mass % of a silicate prepared by treating a layered silicate with an organic swelling agent with the proviso that the mass percentages are based on a sum of the polyamide resin A and the silicate B, wherein the polyamide resin shaped article is produced by preliminarily melt-kneading 70 to 95 mass % of the polyamide resin A and 30 to 5 mass % of the silicate B, on the basis of a sum of the polyamide resin A and the silicate B, to prepare a resin composition C; melt-kneading 3 to 40 mass % of the resin composition C and 97 to 60 mass % of the polyamide resin A, on the basis of a sum of the resin composition C and the polyamide resin A, at the time of producing the polyamide resin shaped article; and then shaping or molding the melt-kneaded product into the polyamide resin shaped article in which the silicate B is uniformly and finely dispersed throughout the polyamide resin A.
The present invention further provides a method for producing a polyamide resin shaped article comprising (A) 92 to 99.7 mass % of a polyamide resin produced by polycondensation of a diamine component containing 70 mol % or more of m-xylylenediamine and a dicarboxylic acid component containing 70 mol % or more of a straight-chain, aliphatic &agr;, &ohgr;-dicarboxylic acid having 4 to 12 carbon atoms, and (B) 8 to 0.3 mass % of a silicate prepared by treating a layered silicate with an organic swelling agent with the proviso that the mass percentages are based on a sum of the polyamide resin A and the silicate B, the method comprising: preliminarily melt-kneading 70 to 95 mass % of the polyamide resin A and 30 to 5 mass % of the silicate B, on the basis of a sum of the polyamide resin A and the silicate B, at 250 to 300° C. for a residence time of five minutes or shorter, thereby preparing a resin composition C; melt-kneading 3 to 40 mass % of the resin composition C and 97 to 60 mass % of the polyamide resin A, on the basis of a sum of the resin compositi
Maruo Kazunobu
Okada Satoshi
Sato Kazunobu
Yamamoto Koji
Antonelli Terry Stout & Kraus LLP
Hampton-Hightower P.
Mitsubishi Gas Chemical Company Inc.
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