Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-05-09
2003-12-23
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S036600, C428S036700, C428S036910, C428S515000, C428S517000, C428S519000, C428S520000, C525S191000, C525S207000, C525S214000, C525S217000, C525S221000, C525S222000, C525S232000, C525S238000, C525S239000, C525S240000, C525S241000
Reexamination Certificate
active
06667083
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multilayer injection blow molded container having excellent gas-barrier properties, good interlayer adhesion and excellent thermal stability.
DESCRIPTION OF THE RELATED ART
Since ethylene-vinyl alcohol copolymers (hereinafter, referred to as EVOH) are excellent in transparency, barrier properties against oxygen, carbon dioxide and nitrogen and oil resistance, and also excellent in melt-molding properties, they are used as wrapping materials for foods, medicaments and the like while making the best use of these properties. In recent years, in order to make up for gas-barrier properties at higher humidity, impact resistance and the like, EVOH are frequently used while being laminated with other thermoplastic resin excellent in moisture-proof property and impact resistance. Also, in the field of hollow containers, a constitution is favored that contains a resin such as polyethylene, polypropylene, polyethylene terephthalate (PET), etc. in inner and outer layers and EVOH in an intermediate layer.
Containers of thermoplastic polyesters, typically PET, are used in many fields, since they are excellent in various properties including transparency, mechanical properties, flavor-barrier properties and the like, low in possibility of elution of residual monomers and harmful additives upon molding, and excellent in hygienic quality and safety. On the other hand, since polypropylene is inactive to blood, small in thermal shrinkage and is low in priced, polypropylene containers are attracting attention in medicament use and food use wherein contents are filled while hot, or so-called hot-filled.
Concerning the polypropylene containers, Japanese Patent Laid Open No. 139228/1980 discloses a technique for improving adhesion strength between a polypropylene layer and an EVOH layer by adding an adhesive resin made of a maleic anhydride-modified polypropylene or the like to the polypropylene layer. It has been known that, in this case, an alkali metal such as sodium, etc. contained in EVOH is effective for obtaining sufficient adhesion strength because it exhibits a catalytic effect.
SUMMARY OF THE INVENTION
An object of the invention is to provide a multilayer injection blow molded container that has excellent gas-barrier properties, has good interlayer adhesion, has excellent thermal stability and is low in production cost.
The above object can be attained by a multilayer injection blow molded container comprising a layer of an ethylene-vinyl alcohol copolymer (A) having an ethylene content of 5 to 60% by mol and a degree of saponification of 85% or more and a layer of a resin composition (B), characterized in that the resin composition (B) comprises 1 to 40% by weight of a thermoplastic resin (b1) having at least one functional group selected from the group consisting of boron-containing groups that are convertible to a boronic acid group in the presence of water and a boronic acid group (hereinafter, referred to as a boron-containing functional group), and 60 to 99% by weight of polypropylene (b2).
The invention also encompasses a process for producing a multilayer injection blow molded container, characterized by multilayer injection blow molding an ethylene-vinyl alcohol copolymer (A) having an ethylene content of 5 to 60% by mol and a degree of saponification of 85% or more and a resin composition (B) comprising 1 to 40% by weight of a thermoplastic resin (b1) having a boron-containing functional group and 60 to 99% by weight of polypropylene (b2), and subsequently stretch blow molding them.
DETAILED DESCRIPTION
The invention will be described below in detail.
It is necessary that the ethylene content in EVOH (A) used in the invention is 5 to 60% by mol. The ethylene content is suitably 15% by mol or more, and more suitably 25% by mol or more. In addition, the ethylene content is suitably 55% by mol or less, and more suitably 50% by mol or less. When the ethylene content is less than 5% by mol, the melt-molding properties are inferior. On the other hand, when it exceeds 60% by mol, the gas-barrier properties are insufficient.
It is necessary that the degree of saponification of EVOH (A) is 85% or more, suitably 90% or more, and most suitably 99% or more. When the degree of saponification is less than 85%, the gas-barrier properties and the thermal stability are insufficient.
EVOH (A) can be produced, for example, by a known process in which ethylene and a vinyl ester are copolymerized, followed by saponification. The vinyl ester includes vinyl acetate as a typical one, and vinyl esters of other aliphatic acids such as vinyl propionate, vinyl pivalate, etc. can also be used. In this case, a vinylsilane compound may be used as a component for copolymerization. Examples of the vinylsilane compound includes, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(&bgr;-methoxy-ethoxy)silane, &ggr;-methacryloxypropyl-methoxysilane, etc. Among them, vinyltrimethoxysilane and vinyltriethoxysilane are preferably used. The content of the vinylsilane compound is preferably within a range of 0.0002 to 0.2% by mol. In addition, other polymerizable monomers, for example, &agr;-olefins such as propylene, 1-butene, etc.; unsaturated carboxylic acids or esters thereof such as (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, etc.; vinylpyrrolidone compounds such as N-vinylpyrrolidone, etc.; can also be used as a component for copolymerization, so far as it does not adversely affect the object of the invention.
The alkali metal salt content in EVOH (A) is preferably 100 ppm or less, more preferably 70 ppm or less, and most preferably 50 ppm or less, converted to an alkali metal element. Japanese Patent Laid-Open No. 139228/1980 discloses a technique for improving adhesion strength between polypropylene layer and an EVOH layer by adding an adhesive resin made of maleic anhydride-modified polypropylene or the like to the polypropylene layer. It is described that, in this case, an alkali metal such as sodium, etc. contained in EVOH exhibits a catalytic effect, and therefore, the addition of an alkali metal salt is effective for obtaining sufficient adhesion strength. In the invention, it has been discovered that the sufficient adhesion strength between the polypropylene layer and the EVOH layer is maintained by using a thermoplastic resin (b1) having a boron-containing functional group even when the amount of the alkali metal salt is low. When the amount of the alkali metal is within the above-described range, phenomena such as occurrence of fish eye, streak, etc., lowering of tint and the like, attributed to cross-linking reaction between EVOHs during melting by heat, can be avoided. Particularly, the thermal stability of EVOH at or above 240° C. is improved.
Methods for adjusting the content of alkali metal salt in EVOH (A) within the above-described range are not particularly limited; since EVOH after saponification usually contains an alkali metal salt as a saponification catalyst residue, a method is preferred in which EVOH after saponification is washed to remove the alkali metal salt in accordance with a known method, and then, a prescribed amount of an alkali metal salt is added again. Methods for washing EVOH after saponification include a method in which chipped EVOH is added to a large amount of water, followed by stirring, a method in which shower water is sprayed, a method in which continuous washing is effected using a tower type washing apparatus, and so on. Methods for adding the alkali metal salt in EVOH include a method in which EVOH is soaked in a solution of an alkali metal salt, a method in which EVOH is melted and blended with an alkali metal salt, a method in which EVOH is dissolved in an appropriate solvent and mixed with an alkali metal salt, and so on.
When EVOH (A) is soaked in a solution of an alkali metal salt, the concentration of the alkali metal salt in the solution is not particularly limited. Although solvents for the solution are not limited, an aqueous solution is preferred for reasons concerning handl
Hayashi Nahoto
Ikeda Kaoru
Kawai Hiroshi
Lambert William Scott
Tai Shinji
Kuraray Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pyon Harold
Simone Catherine A.
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