Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-07-07
2002-11-26
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S520000, C524S394000, C524S464000, C524S414000
Reexamination Certificate
active
06485842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin composition comprising an ethylene-vinyl alcohol copolymer (EVOH) and a multi-layered structure comprising the resin composition. The resin composition has extremely good adhesiveness, and its moldings have good appearances with few gels and fish eyes. When molded, the resin composition ensures good long-run workability and recyclability, and the recycled resin composition is yellowed little.
2. Description of the Related Art
EVOH is a useful polymer material having good oxygen barrier properties, oil resistance, antistatic properties and mechanical strength, and is widely used for various wrapping and packaging materials such as films, sheets, containers, etc. As being generally molded in melt into such moldings, EVOH is required to have good long-run workability in melt molding (that is, it can be molded in good moldings with neither fish eyes nor streaks even in long-run molding lines), and its moldings are required to have good appearances (that is, they have neither gels nor hard spots). Another important matter with EVOH recently discussed is its recyclability. Concretely, in case where wastes of EVOH moldings are recovered and again molded in melt through repeated heat history, they are required to have good recyclability (that is, the recovered EVOH wastes have good moldability) and the recycled EVOH moldings are required to be yellowed little.
For producing EVOH moldings with good mechanical strength, moisture resistance and heat-sealability, in general, EVOH is co-extruded together with a substrate of polyolefinic resin or the like to give multi-layered structures in which the EVOH layer and the substrate resin layer are bonded to each other via an adhesive layer therebetween. In those structures, therefore, EVOH is required to have high interlayer adhesiveness. For improving the interlayer adhesiveness of EVOH in such multi-layered structures, known is (1) a method of adding a minor component, especially an alkali metal, to EVOH. On the other hand, disclosed is (2) an EVOH composition containing from 0.0005 to 0.05% by weight (in terms of the metal) of a salt of a metal of Group 2 of the Periodic Table, from 0.002 to 0.2% by weight of an acid having pKa of at least 3.5 and a boiling point of not lower than 180° C., and from 0.01 to 0.2% by weight of an acid having pKa of at least 3.5 and a boiling point of not higher than 120° C., and having a specific melt viscosity (Japanese Patent Laid-Open No. 66262/1989). They say that the EVOH composition with such additives has improved long-run workability and its moldings have good appearances with neither gels nor fish eyes. Also disclosed is (3) an EVOH resin composition containing, relative to 100 parts by weight of EVOH therein, from 0.001 to 1 part by weight (in terms of the boron element) of a boron compound, at most 0.05 parts by weight of acetic acid, and from 0.001 to 0.05 parts by weight (in terms of the metal) of a metal acetate (EP 930339, corresponding to Japanese Patent Laid-Open No. 43571/1999). They say that the EVOH resin composition has good long-run workability in melt molding lines and gives moldings with good appearances and good interlayer adhesiveness. In Comparative Example 5 in the laid-open specification, demonstrated is a resin composition comprising 100 parts by weight of EVOH, 0.03 parts by weight (in terms of the boron element) of boric acid, 0.009 parts by weight of acetic acid and 0.08 parts by weight (in terms of sodium) of sodium acetate. They say that, though their interlayer adhesiveness is good, films of the resin composition have many streaks and fish eyes and their appearances are not good, and, in addition, the stretched films are uneven.
There is (4) still another related art disclosure of an EVOH resin composition capable of being molded in melt to give moldings with few fish eyes and having good adhesiveness (Japanese Patent Laid-Open No. 67898/1998). The EVOH resin composition contains from 100 to 5000 ppm, in terms of the free acid, of a hydroxycarboxylic acid and/or its salt, from 50 to 500 ppm, in terms of the metal, of an alkali metal salt, and from 20 to 200 ppm, in terms of the metal, of an alkaline earth metal salt.
In the related art disclosures (1) to (4), however, the interlayer adhesiveness of EVOH could not be improved to a satisfactory degree. Therefore, further improving EVOH resins to that effect is desired. In addition, heretofore, adhesive resins for nylons could not be used in multi-layered structures with EVOH, as their adhesiveness to EVOH is poor. Therefore, in case where EVOH is layered over substrates of polyolefinic resins and the like, it indispensably requires high-performance and expensive adhesive resins for its exclusive use. In that situation, the latitude in choosing the adhesive resins for EVOH is limited.
As in Comparative Example 5 in the related art disclosure (3), EVOH has good interlayer adhesiveness, but its films are still problematic in their appearances and stretchability. As in the related art disclosures discussed herein, it has heretofore been said that improving both the interlayer adhesiveness and the appearances of EVOH resin compositions and moldings is extremely difficult, and developing EVOH resin compositions and moldings having both good interlayer adhesiveness and good appearances is much desired in the art.
For recycling burrs and other wastes that will be inevitable in long-run molding lines for producing EVOH resin moldings, EVOH resin compositions and moldings are required to have not only good interlayer adhesiveness and good appearances but also good long-run workability and recyclability, and, in addition, the recycled compositions and moldings are required to be yellowed little.
To meet the requirements, desired is to provide an improved EVOH resin composition of which the advantages are that it has extremely good adhesiveness and its moldings have good appearances with few gels and fish eyes, and, when molded, it ensures good long-run workability and recyclability and the recycled resin composition is yellowed little. Also desired is to provide a multi-layered structure comprising the resin composition.
SUMMARY OF THE INVENTION
To attain the object as above, the present invention provides an EVOH resin composition containing from 500 to 2000 ppm, in terms of the metal, of an alkali metal salt (A) and from 0.05 to 4.5 &mgr;mols/g of a carboxylic acid (B), where the ratio of the content (&mgr;mol/g) of a carboxylic acid (b1) having a molecular weight of at least 75 and its salt to the total content (&mgr;mol/g) of the carboxylic acid (B) and its salt is at least 0.1.
In one preferred embodiment of the resin composition, the carboxylic acid (B) has pKa of at least 3.5. In another preferred embodiment thereof, the carboxylic acid (b1) having a molecular weight of at least 75 is a hydroxycarboxylic acid, more preferably a lactic acid.
In still another preferred embodiment, the content (&mgr;mol/g in terms of the metal) of the alkali metal salt (A) is from 10 to 100 times the content (&mgr;mol/g) of the carboxylic acid (B).
The invention also provides an EVOH resin composition containing from 500 to 2000 ppm, in terms of the metal, of an alkali metal salt (A), from 10 to 500 ppm of a carboxylic acid (b2) having a molecular weight of smaller than 75, and from 10 to 500 ppm, in terms of the phosphate radical, of a phosphate compound (C).
In one preferred embodiment of the resin composition, the content (&mgr;mol/g in terms of the metal) of the alkali metal salt (A) is from 3 to 20 times the content (&mgr;mol/g) of the carboxylic acid (b2) having a molecular weight of smaller than 75. In another preferred embodiment thereof, the carboxylic acid (b2) having a molecular weight of smaller than 75 is acetic acid.
Still another preferred embodiment of the resin composition contains from 50 to 2000 ppm of a boron compound (D). In this, preferably, the content (&mgr;mol/g, in terms of the boron element) of the boron compound (D) is from 2 to
Inomata Naokiyo
Shindome Hiroyuki
Kuraray Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tarazano D. Lawrence
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