Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-15
2002-08-06
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S398000, C524S513000, C523S505000, C523S506000, C428S034200, C428S035700, C428S481000
Reexamination Certificate
active
06429243
ABSTRACT:
TECHNICAL FIELD
The present invention relates to polyester resin compositions, and films, packaging materials, laminates and containers comprising the compositions. More specifically, the present invention relates to polyester resin compositions having excellent heatsealability, resistance to hydrogen peroxide, flavor-barrier properties, gas-barrier properties and mechanical properties such as elongation and strength, and also to films and the like comprising such compositions. The polyester resin compositions, films and the like of the present invention can, utilizing the above features, effectively be used for various uses, in particular as packaging materials for containers for beverages containing flavor ingredients.
BACKGROUND ART
The problem of the disposal of plastic containers having once been used has become a big social issue. Demand has therefore increased for paper containers, which can be incinerated or regenerated relatively simply and smoothly compared to plastic containers. This trend also holds for containers for beverages such as juices, and thus paper containers covered, on their inner surface, with resin films are generally used widely for containers for juices and the like. In this case, olefin resins are generally used as the resin films covering the inner surface of the paper containers. However, such paper containers covered on their inner surface with olefin resins will, when used for beverages containing flavor components, such as fruit juices, sometimes cause loss of flavor, change in taste and like problems.
Japanese Patent Application Laid-open No. 133638/1991 proposes, to solve the problems, covering the inner surface of paper containers with, instead of olefin resins, a polyester resin laminate comprising a layer of a modified polyethylene terephthalate containing about 5 to 20 mole % of a copolymerization component. This improvement is, due to the gas-barrier properties and flavor-barrier properties inherently possessed by polyester resin, successful in keeping good, to some extent, the level of the flavor and taste of the beverages or the like packed in the paper containers.
However, the covering layer comprising the above modified polyester resin laminate has several drawbacks as follows. That is, the covering layer tends, on sterilization by hydrogen peroxide, which treatment is widely adopted in the production process of paper containers, to swell, produce bubbles in the covering layer and partly delaminate from the paper base. These troubles markedly deteriorate the processability and process-runnability on the production of paper containers. Besides, the hydrogen, peroxide contained in the thus swollen covering layer comprising the polyester resin laminate migrates to the contents packed in the paper containers, which may lead to decreases in the quality and safety of the food contained.
Japanese Patent Application Laid-open No. 45883/1998 proposes use of a modified polyethylene terephthalate copolymerized with naphthalenedicarboxylic acid, in which the content of remaining metals has been suppressed to 10 millimoles % or below and the content of a phosphorus compound has been adjusted to 3 to 20 millimoles %, to improve the transparency and color tone of the copolyester. In this case, however, the features inherent in polyethylene terephthalate, such as resistance to hydrogen peroxide, are not sufficiently improved.
Under the above situation, the present inventors have studied to develop a polyester resin composition which can effectively be used for food containers and the like. That is, the present inventors have studied in order to provide a polyester resin composition which maintains at a good level the gas-barrier properties and flavor-barrier properties inherently possessed by polyester resins, does not cause, on sterilization with hydrogen peroxide, swelling, bubble generation, delamination from the base and like troubles, has excellent heatsealability, thereby being able to be bonded and laminated firmly and smoothly on bases such as paper, and is excellent in mechanical properties such as elongation in handleability.
As a result, the present inventors have found that a polyester resin composition having excellent gas-barrier and flavor-barrier properties, resistance to hydrogen peroxide, heatsealability and mechanical properties can be obtained by melt kneading under specific conditions a copolyester resin having specific contents of naphthalenedicarboxylic acid component and/or a specific diol component, which co-polyester resin has been mixed with an olefin polymer and a compatibility-improving agent in specific amounts. Japanese Patent Application Laid-open No. 302204/1997 was filed based on the above finding.
DISCLOSURE OF THE INVENTION
Based on the invention disclosed in the above Japanese Patent Application Laid-open No. 302204/1997, the present inventors have made a further study to achieve a better improvement technology.
As a result, the present inventors have found that the polyester resin composition of the invention of the above Japanese Patent Application Laid-open No. 302204/1997 is, when a specific amount of at least one metal compound selected from the group consisting of manganese compounds and cobalt compounds is incorporated therein, more improved in its resistance to hydrogen peroxide, while maintaining its excellent gas-barrier and flavor-barrier properties, heatsealability and mechanical properties. The resulting composition becomes markedly useful as molded articles such as film, packaging material for foods and like uses.
The present inventors have further found that another polyester resin composition having excellent resistance to hydrogen peroxide, as well as excellent gas-barrier and flavor-barrier properties, heatsealability and mechanical properties can be obtained by incorporation of both a manganese compound and a cobalt compound into the same copolyester resin containing a specific amount of naphthalenedicarboxylic acid as that used in the invention of the above Japanese Patent Application Laid-open No. 302204/1997.
The present inventors have still further found that, with the above two types of polyester resin compositions, incorporation of a specific amount of an alkali metal salt of an organic carboxylic acid and/or a phosphorus compound leads to further improvement of the resistance to hydrogen peroxide, thermal resistance and resistance to coloring, and completed the present invention based on these findings.
Thus, the present invention provides a polyester resin composition (hereinafter sometimes referred to as “polyester resin composition (A)”)
(i) which comprises:
(a) units from a diol consisting essentially of ethylene glycol units and units from a dicarboxylic acid consisting essentially of terephthalic acid, as essential components, and units from naphthalenedicarboxylic acid in an amount of 5 to 40 mole % based on the total moles of all structural units;
(b) at least one metal compound selected from the group consisting of cobalt compounds and manganese compounds;
(c) an olefin polymer; and
(d) a compatibility-improving agent;
(ii) said metal compound being contained in an amount based on the weight-of said polyester resin of 100 to 1,000 ppm and said olefin polymer and compatibility-improving agent being contained in such amounts as to satisfy the following formulas {circle around (1)} and {circle around (2)}:
10 (parts by weight)≦
X+Y
≦100 (parts by weight) {circle around (1)}
1
≦X/Y
≦90 {circle around (2)}
wherein X and Y represent, respectively, the content of the olefin polymer (parts by weight) based on 100 parts by weight of the polyester resin and that of the compatibility-improving agent on the same basis; and
(iii) which has been obtained by melt kneading in such a manner as to satisfy the following formula {circle around (3)}
E/F
≦1 {circle around (3)}
where E=&eegr;
1
(X+Y)/(&eegr;
2
X+&eegr;
3
Y)
F=100D
2
D
3
/D
1
(D
3
X+D
2
Y)
wherein X and Y are the same as defined for formula
Okamoto Chihiro
Taniguchi Shunro
Kuraray Co. Ltd.
Yoon Tae H.
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