Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2001-12-05
2004-04-27
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S035400, C428S035900, C428S036600, C428S036700, C428S325000, C428S331000, C428S451000
Reexamination Certificate
active
06727001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laminated film that has an excellent oxygen-permeability barrier at high humidity and firm bonding between the coated film and the resin substrate at high humidity. This invention further relates to a packaging material derived from such a laminated film.
2. Description of the Related Art
With regard to packaging materials for use with foods or medicines, the contents in such packaging materials tend to denature on exposure to oxygen gas which permeates the outside into the packaging material. Therefore, the contents cannot be stored over a long period of time. This has given impetus to the development of a film which is so resistant to gas permeation as to preclude gas entering from the outside.
As disclosed in “Polymer Engineering and Science”, Vol. 20, No. 22, pp. 1543-1546 (December, 1986), conventional gas barrier films have been formed from polyvinylidene chloride, polyacrylonitrile or polyvinyl alcohol. Recently, however, a serious problem has arisen in that polyvinylidene chloride and polyacrylonitrile are detrimental to the environment when the films formed from these polymers are disposed of. This is because polyvinylidene chloride has chlorine atoms attached to its molecular structure, and polyacrylonitrile has —CN groups attached to its molecular structure. On the other hand, polyvinyl alcohol has a superior gas permeation barrier at low humidity, but largely depends on humidity, resulting in a sharp decline in the gas permeation barrier at high humidity.
In Japanese Unexamined Patent Application Publications No. 10-296929 and No. 11-151786, barrier films against gas permeation have been proposed in which a lamella composed of inorganic particles is laminated on a water-soluble polymer film. Such a barrier film is sufficiently impermeable to gas since it is less dependent on humidity. However, it poses a problem in that the bonding between the coated film and the resin substrate becomes markedly poor at high humidity.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to provide a laminated film which has an excellent oxygen-permeability barrier even at high humidity and firm bonding between the coated film and the resin substrate even at high humidity. Another object of this invention is to provide a packaging material using such a laminated film.
The above objects of the present invention can be achieved by the provision of a laminated film comprising a resin substrate and a coated film laminated thereon, wherein the coated film comprises a montmorillonite containing a cation exchanger other than sodium ions and a water-soluble polymer.
More specifically, according to a first aspect of the present invention, a laminated film comprising a resin substrate and a coated film laminated thereon is provided, wherein the coated film comprises a montmorillonite and a water-soluble polymer, and the content of a potassium element in the coated film is in the range of 0.1% by weight to 5% by weight.
According to a second aspect of this invention, a laminated film comprising a resin substrate and a coated film laminated thereon is provided, wherein the coated film comprises a montmorillonite and a water-soluble polymer, and the content of a sodium element in the coated film is 0.6% by weight or less.
According to a third aspect of this invention, a laminated film comprising a resin substrate and a coated film laminated thereon is provided, wherein the coated film comprises a montmorillonite and a water-soluble polymer, and said water-soluble polymer comprises at least two water-soluble resins having different polymerization degrees.
According to a fourth aspect of this invention, a packaging material is provided comprising a laminated film described in one of the first to third aspects.
According to a fifth aspect of this invention, a packaging material is provided comprising a laminated film described in one of the first to third aspects and a supporting material disposed on the laminated film.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In general, montmorillonite has a configuration in which a tetrahedral structure-constituting layer and an octahedral structure-constituting layer are bonded to each other in a 2 to 1 ratio and in a plate-like formation. In the tetrahedral layer, Si
4+
is coordinated relative to O
2−
, and in the octahedral layer, Al
3+
, Mg
2+
, Fe
2+
, Fe
3+
, Li
+
and the like are coordinated relative to O
2−
and OH
−
. Montmorillonite is mineral clay which has a tendency to incorporate and absorb water between its crystalline plate-like layer units, is very thin and is formed as a single particulate plate from one such crystalline layer unit or those layer units overlaid on each other.
Moreover, montmorillonite has a water molecule-accompanying cation exchanger existing between the crystalline layers (this cation exchanger also being called an interlaminar cation exchanger). The cation exchanger usually includes Mg
2+
, Ca
2+
, Na
+
, K
+
and H
+
. Naturally occurring montmorillonite is broadly grouped into sodium ion-type montmorillonite (Na-montmorillonite), which is abundant in sodium ions as the cation exchanger, and calcium ion-type montmorillonite (Ca-montmorillonite), which is abundant in calcium ions as the cation exchanger.
Montmorillonite suitable for the present invention contains a cation exchanger other than sodium ions. The cation exchanger other than sodium ions, which can be used in this invention, is chosen from alkaline metal ions excluding sodium ions, alkaline earth metal ions, benzoruthenium ions, alkyldimethylammonium ions, quaternary alkylammonium ions such as aminosilanes made quaternary, and surface active agents capable of developing complex ions. The sodium ions contained in the montmorillonite can be replaced by such a cation exchanger. This replacement prevents the montmorillonite from swelling, so that the resulting laminated film yields a high oxygen-permeation barrier at high humidity and firm bonding between the coated film and the resin substrate at high humidity. Replacing the sodium ions with potassium ions is particularly preferred because the above effects can be further enhanced.
In the laminated film of the present invention, the potassium element content in the coated film is set within the range of 0.1% by weight to 5% by weight in order to improve the oxygen-permeation barrier and film-to-substrate bonding at high humidity. A content of 0.3% by weight to 1.2% by weight is more preferable.
The term “potassium element content in the coated film” used here refers to the potassium element content based on the total weight of all the components in the coated film containing montmorillonite and a water-soluble polymer.
In addition, in the laminated film of the present invention, the sodium element content in the coated film is set at 0.6% by weight or less in order to improve the oxygen-permeation barrier and the film-to-substrate bonding at high humidity. A content of 0.4% by weight or less is more preferable, and a content of 0.2% by weight or less is still more preferable.
For analytical examination of the above contents of elements, conventional atomic spectrometry and ICP may be used.
In the montmorillonite according to the present invention, the leaching of a cation exchanger other than sodium ions is preferably 40 or more (milliequivalent per 100 g of montmorillonite), and the leaching of potassium ions is preferably 10 or more (milliequivalent/100 g). A leaching of potassium of 40 or more (milliequivalent/100 g) is particularly preferable. When the leaching of a cation exchanger other than sodium ions is within the above specified range, a good oxygen-permeation barrier and film-to-substrate bonding can be obtained.
The term “leaching of a cation exchanger” used here represents the amount of a cation exchanger contained between the crystalline layers in the montmorillonite.
With further regard to the leaching of
Hirota Kusato
Hochi Motonori
Tanaka Shigeru
Kubovcik & Kubovcik
Nakarani D. S.
Toray Industries Inc.
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