Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1998-10-16
2001-10-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S520000, C427S327000
Reexamination Certificate
active
06306519
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a film or a laminated film of a vinylidene chloride copolymer, which is excellent in barrier properties, and a method for producing the same.
BACKGROUND ART
Coating films of vinylidene chloride copolymers are characterized by excellent barrier properties. Accordingly, films coated with the vinylidene chloride copolymers have been used for making it possible to store food packaged, with oxygen and water vapor cut off, for a long period of time without making the food therein moisturized or oxidized. Of films, some are excellent in barrier properties against oxygen or water vapor. However, films which can cut both oxygen and water vapor off at a high level are rare except for the vinylidene chloride copolymer films. The films coated with the vinylidene chloride copolymers have been widely used mainly as food packaging materials.
Methods for preparing the vinylidene chloride copolymer films are roughly divided into two methods. One is a method of preparing the films by melt extrusion (melt extrusion method), and the other is a method of coating films with aqueous dispersions of the vinylidene chloride copolymers or solutions of the vinylidene chloride copolymers in organic solvents (coating method).
In the case of the melt extrusion method, the polymers are orientated by drawing the vinylidene chloride copolymer films after extrusion, and the films excellent in barrier properties can be prepared. However, when polymers containing 88% or more of vinylidene chloride are intended to be extruded, thermal degradation takes place upon extrusion. Extrusion thereof is therefore practically difficult. In contrast, according to the coating method, even the polymers having a vinylidene chloride content as high as 88% or more can be formed into films, so that films excellent in barrier properties per unit thickness can be obtained. In particular, when solutions of vinylidene chloride copolymers dissolved in organic solvents are applied, coating films very thin in thickness and excellent in barrier properties are obtained because the solutions little contain additives impeding the barrier properties such as plasticizers and surfactants. As the method for preparing a coating film excellent in barrier properties by applying a solution of a vinylidene chloride copolymer dissolved in an organic solvent, for example, JP-B-63-24016 (the term “JP-B” as used herein means an “examined Japanese patent publication”) and JP-A-3-54244 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) disclose methods for preparing films excellent in barrier properties by dissolving vinylidene chloride polymers in specific organic solvents.
However, with recent high-level requirements for barrier properties in the market, films more excellent in barrier properties than the conventional films have now been demanded.
It is an object of the present invention to provide a film or a laminated film of a vinylidene chloride polymer more excellent in barrier properties than the conventional ones.
DISCLOSURE OF INVENTION
As a result of extensive investigation for solving the above-mentioned problems, the present inventors have obtained a surprising finding as described below. That is to say, the present inventors have discovered that application of a coating material obtained by dissolving a vinylidene chloride copolymer in an organic solvent, then cooling the resulting solution to nearly a temperature at which the solution is gelated, and allowing it to stand can provide a vinylidene chloride copolymer film or laminated film having a unique structure, in which although the density is scarcely different, the degree of orientation is high as compared with the films obtained by the prior art, and being excellent in barrier properties, thus completing the present invention.
That is, the present invention relates to a vinylidene chloride copolymer film having excellent barrier properties, which comprises 88% to 93% by weight of vinylidene chloride and 12% to 7% by weight of at least one monomer copolymerizable with vinylidene chloride and which has a ratio (Q/P) of 1.5 or more, wherein Q is the integrated intensity of the peak at 2&thgr;=38° and P is the integrated intensity of the peak at 2&thgr;=15°, each as determined by the wide angle X-ray reflection method.
Further, the present invention also relates to a laminated film having excellent barrier properties, comprising a base film and a vinylidene chloride copolymer layer which comprises 88% to 93% by weight of vinylidene chloride and 12% to 7% by weight of at least one monomer copolymerizable with vinylidene chloride and which has a ratio (I/J) of 1.4 or above, wherein I and J are the peak intensity and base line intensity at 2&thgr;=38°, respectively, and a half band width of the peak at 2&thgr;=38° of 3° or below, each as determined by the wide angle X-ray reflection method while the incident X-ray is introduced from the vinylidene chloride copolymer layer side.
The base film for use herein is at least one polymer selected from polyesters, polyamides, polyimides, polypropylene, polyethylene, polyvinyl alcohol, cellophane, polystyrene, polyvinyl chloride, ethylene-vinyl alcohol copolymers and polycarbonates.
Here, the diffraction angle 2&thgr;=15° corresponds to a (100) plane in terms of crystal structure, and 2&thgr;=38° corresponds to a (020) plane in terms of crystal structure. In the films or laminated films obtained by the conventional coating methods, polymers are little orientated, so that a peak is scarcely observed at 2&thgr;=38° according to the wide angle X-ray reflection method. However, interestingly, in the vinylidene chloride copolymer films or laminated films of the present invention, a (020) plane is orientated in parallel with a film surface, so that a great peak is observed at 2&thgr;=38°. In the case of vinylidene chloride copolymer films, therefore, the orientation can be specified by the ratio of the intensity of a peak at 2&thgr;=38° on the basis of the base line intensity at 2&thgr;=15°, of the diffraction peaks obtained by the wide angle X-ray reflection method. In the case of laminated films, the orientation can be specified by the ratio of the intensity of a peak at 2&thgr;=38° on the basis of the base line intensity obtained by the wide angle X-ray reflection method while the incident X-ray is introduced from the vinylidene chloride copolymer layer side.
In the vinylidene chloride copolymer film of the present invention, it is necessary that the ratio (Q/P) be 1.5 or more, wherein Q is the integrated intensity of the peak at 2&thgr;=38° and P is the integrated intensity of the peak at 2&thgr;=15°, each as determined by the wide angle X-ray reflection method. The ratio (Q/P) is preferably 2 or more. When the integrated intensity ratio is less than 1.5, sufficient barrier properties are not exhibited because of low degree of orientation.
Further, in the laminated films of the present invention, it is necessary that the ratio (I/J) be 1.4 or above, wherein I and J are the peak intensity and base line intensity at 2&thgr;=38°, respectively, and that the half band width of the peak at 2&thgr;=38° be 3° or below, each as determined by the wide angle X-ray reflection method while the incident X-ray is introduced from the vinylidene chloride copolymer layer side. The intensity ratio (I/J) is preferably 1.8 or above. When the intensity ratio is less than 1.4, sufficient barrier properties are not exhibited because of low degree of orientation.
Methods for producing the vinylidene chloride copolymer film or laminated film of the present invention include the following methods:
(1) A method of: applying a coating material prepared by putting, into an organic solvent, powder of a vinylidene chloride copolymer obtained by emulsion polymerization of 88% to 93% by weight of vinylidene chloride with 12% to 7% by weight of at least one copolymerizable monomer, dissolving it
Katoh Yukiko
Sakai Hideki
Asahi Kasei Kaisha
Birch & Stewart Kolasch & Birch, LLP
Tarazano D. Lawrence
Thibodeau Paul
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