Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1999-05-24
2002-04-23
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S474700, C428S474900, C428S475500, C428S690000
Reexamination Certificate
active
06376093
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polyamide film (inclusive of sheet, hereinafter the same throughout this specification) having superior transparency, resistance to fatigue from flexing and slip characteristic, particularly such film superior in slip characteristic under high humidity. More particularly, the present invention relates to a polyamide laminate film superior in properties of a wrapping film for fresh food, processed food, pharmaceutical products, medical equipment, electronic parts and the like, such as gas barrier property and moisture-proof property, and showing superior transparency and handling property.
BACKGROUND OF THE INVENTION
Polyamide films have been conventionally used for a broad range of applications inclusive of wrapping purpose, because they are superior in mechanical properties (e.g., tenacity, flexing resistance and the lie), optical property, thermal property, gas barrier property and the like. On the other hand, conventional polyamide films are associated with problems in that they show high moisture absorption resulting from the property of the polyamide resin itself, which in practice results in lower slip characteristic and extremely degraded handling property due to an increased contact area by moisture absorption when in use in a highly humid environment.
To overcome such problems, a method for decreasing coefficient of friction between films or that between a film and a material in contact with the film has been studied. To be specific, inorganic fine particles inert to polyamide are contained in a polyamide film to decrease the coefficient of friction of the film surface, or a method comprising addition of an organic surface lubricant has been employed.
The above-mentioned conventional methods suffer from a problem in that greater amounts of inorganic fine particles added to minimize the coefficient of friction cause lower transparency of the polyamide resin film. The above-mentioned coefficient of friction and the transparency of the film are in an ambivalent relationship, and a polyamide resin film having both properties of fine slip characteristic and transparency has been unattainable. Particularly, a polyamide resin film satisfying the transparency and slip characteristic under high humidity has been unattainable.
From the practical view, the use of an organic surface lubricant lowers the surface energy of the film and enhances slip characteristic. However, adhesiveness in printing or Laminating on the film surface also becomes lower and the amount of the organic lubricant to be added cannot be increased in view of the practical aspect of the film.
In accordance with the varying food distribution systems and dietary habits in recent years, the food packaging style and mode have been strikingly changing, which in turn has created an increasing demand toward high quality wrapping films.
A degraded quality of a product, which is caused by temperature, moisture, oxygen, ultraviolet rays, microorganisms such as bacteria and mold, and the like during distribution and sales, leads to serious problems of loss of sales and insufficient food hygiene. Such degradation of quality has been conventionally supressed by adding an antioxidant, a preservative and the like directy to food. In view of increasing levels of strict regulation imposed on food additives for the protection of consumers, however, decease in the amount to be added or elimination of addition itself has been demanded. Under the circumstances, a demand has been rising toward a wrapping film having smaller vapor and moisture permeabilities and which does not degrade food value due to freezing, boiling treatment, retort treatment and the like.
To be specific, when wrapping fish meat, meat, shellfish and the like, oxidation and spoilage of protein, fats and oils and the like need to be inhibited but taste and freshness need to be retained. This requirement is met by cutting off air permeation by the use of a wrapping material having superior gas barrier property. In addition, gas barrier film used for wrapping food contributes to the retention of flavor of the content and inhibition of moisture permeation. As a result, dry food is not deteriorated by the absorption of moisture and water-containing food is not spoiled or solidified by the evaporation of moisture, thus enabling retention of fresh flavor present at the time of wrapping for an extended period of time.
For the above-mentioned reasons, it is considered extremely important that a wrapping film used for, for example, food made from boiled fish paste such as boiled fish sausage, dainty products such as butter and cheese, fermented soybean paste, tea, coffee, ham and sausage, instant food, confectionery such as castella and biscuit, and the like, should have gas barrier property and moisture-proof property. These properties are not required only of a film for wrapping food. They are significantly important for a film used for wrapping medical products that require handling in a sterilized state and electronic parts that require rust-proof property.
As a film having superior gas barrier property, there have been known, for example, a film wherein a metal foil such as an aluminum foil is laminated on a plastic film, and a film having a coating of vinylidene chloride or ethylene-vinyl alcohol copolymer. In addition, as a film utilizing an inorganic thin film, a laminate having a vapor deposition layer of silicon oxide, aluminum oxide and the like has been known.
In practice, a sealant layer may be formed by dry laminating on a printing layer or an adhesive. Alternatively, a sealant layer is formed by extrusion laminating to give a polyamide laminate film and this laminate film is used, for example, to prepare a bag. After packing the bag, the opening is heat sealed, whereby seasoning such as fermented soybean paste, soy sauce and the like, water-containing food such as soup, retort food and the like, pharmaceutical products and the like in package bags have been supplied to general consumers.
The above-mentioned conventional gas barrier films each have the following problems. A laminate having an aluminum foil as a gas barrier layer is superior in economic aspect and gas barrier property, but it is associated with a problem in that opacity thereof hides contents after wrapping and that it cannot be cooked in a microwave oven, since the film does not pass microwaves.
A film coated with vinylidene chloride or ethylene-vinyl alcohol copolymer has insufficient gas barrier property against water vapor, oxygen and the lie, and shows marked degradation of the property by a high temperature treatment. The film coated with vinylidene chloride generates chlorine gas on incineration, and may cause air pollution.
Thus, a resin film has been proposed that has an inorganic vapor deposition layer of silicon oxide, aluminum oxide and the like as a gas barrier layer. As the base film on which silicon oxide, aluminum oxide and the like can be vapor-deposited, a polyester film (PET) superior in dimensional stability has been conventionally used. It typically has a structure of a laminate of PET/vapor deposition layer/adhesive layer/PET/adhesive layer/unoriented polypropylene (CPP) and the like. Such laminate film has insufficient strength to stand a fall impact.
In the case of a laminate film of PET/vapor deposition layer/adhesive layer/oriented nylon (ONY)/adhesive layer/unoriented polypropylene (CPP) and the like, the property of nylon to shrink causes degradation of gas barrier property after boiling treatment and retort treatment
Therefore, Japanese Patent Unexamined Publication No. 276571/1995 proposes a laminate film using nylon having lower shrinkage percentage upon high temperature hot water treatment This film comprises more number of films to be laminated. Consequently, the film-forming step and process for transport and storage become complicated to make the film economically disadvantageous, and the greater film thickness makes the handling of the film difficult. Thus, the film is impractical.
Meanwh
Fujita Shinji
Iseki Kiyoshi
Iwanishi Masazumi
Komeda Shigeru
Morishige Chikao
Kenyon & Kenyon
Kiliman Leszek
Toyo Boseki Kabushiki Kaisha
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