Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1999-11-30
2002-04-09
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S475800, C428S690000, C428S690000, C428S900000, C427S129000, C427S393500
Reexamination Certificate
active
06368722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laminated film, and in particular, to a laminated film which is useful as industrial materials as well as magnetic material, and can be produced with high productivity, in which a resin layer having excellent heat resistance is directly provided on a thermoplastic resin film without employing any adhesive layer.
2. Description of the Related Art
Conventionally, thermoplastic films such as polyesters and polyolefins have been used for various industrial materials including magnetic recording materials, electric insulation materials, materials for capacitors, packaging materials, photographic and graphic materials and heat transfer materials. They are useful due to their transparency, mechanical characteristics and electric characteristics.
On the other hand, films represented by aromatic polyamides have such characteristics as high heat resistance, dimensional stability, mechanical strength and non-combustibility, and have been used for high density magnetic recording media and flexible printed substrates and the like. Also a laminate comprising a thermoplastic film coated (Japanese Unexamined Patent Publication No. 1-97638), or laminated (Japanese Unexamined Patent Publication No. 3-164244) with a heat resisting polymer layer are known.
The thermoplastic films have some thermal drawbacks since they soften or melt by heat, or burn easily, while films having high heat resistance such as aromatic polyamides have low productivity since they are usually produced by the solvent casting method. This makes these films very expensive, and their uses have been limited accordingly.
In order to compensate for these drawbacks, laminated films produced by laminating or coating have been proposed. However, such laminated films have been adhered by an adhesive layer at the interface, adding an adhesive composition to the heat resisting resin layer in order to improve adhesion, or by carrying out thermocompression bonding at a temperature of 200° C. or higher. However, the produced laminates had such problems as insufficient adhesion, inhibition of the functions originally possessed by the heat resisting resin due to the presence of the other components added to the heat resisting resin, or inhibition of flatness of the thermoplastic film caused by the inserted adhesive layer which was exposed to high temperature. When the thermoplastic film is subjected to crystalline orientation, the adhesion at the interface has been even worse. In addition to that, additional processing such as coating on the film or laminating allows adhesion of dust, or mixing of bubbles. Therefore, a product having a highly flat surface has been difficult to obtain.
According to the present invention, a laminated film can be made free from these defects. The product has high flatness and high adhesion between the thermoplastic film and the heat resisting resin-layer without substantially providing any adhesive layer between them.
SUMMARY OF THE INVENTION
The laminated film according to the present invention has a layer containing a heat resisting resin which is soluble in a dipolar aprotic solvent as a main component. It is laminated on at least one surface of a biaxially. oriented thermoplastic film. The biaxially oriented thermoplastic film and the heat resisting resin layer are directly adhered to each other.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The thermoplastic film in the laminated film according to the present invention is a film which can be melt-extruded and subjected to crystalline orientation by biaxial orientation. Examples thereof include polyester, polyolefin, polyamide, and polyphenyl sulphide films. Polyester films are particularly preferable due to their transparency, dimensional stability, mechanical characteristics, and adhesion to the heat resisting resin layer which is used for lamination according to the present invention. Preferable polyesters are not particularly limited; however, examples include polyethylene terephthalate, polyethylene naphthalate, polypropylene terephthalate, polybutylene terephthalate and polypropylene naphthalate and the like. Two or more kinds of these polyesters can be used in admixture. These can be copolymerized with another dicarboxylic acid component or diol component and used. However, in such a case, the crystallinity of the film after crystalline orientation is completed is preferably 25% or more, more preferably 30% or more, further preferably 35% or more. The upper limit of crystallinity is not particularly limited; however, it is usually difficult to obtain a polyester film having a crystallinity of 60% or higher. It can be a laminated film comprising two or more laminations including a surface layer and lower laminations. Examples include a laminated film having a lower lamination substantially free from particles and a surface layer containing particles. It can be a laminated film comprising a lower lamination containing crude particles and a surface layer containing finely divided particles. It can be a laminated film comprising a lower lamination containing fine bubbles and a surface layer that is substantially free from bubbles and the like. In those laminated films, the lower lamination and the surface layer can be made of the same kind of polymers or different kinds of polymers. When the crystallinity of the polymer is less than 25%, the resulting laminate tends to show insufficient dimensional stability and insufficient mechanical strength. When the above-mentioned polyesters are employed, the intrinsic viscosity thereof (measured in o-chlorophenol at 25° C.) is preferably 0.4-1.2 dl/g, more preferably 0.5-0.8 dl/g. The thermoplastic film according to the present invention is preferably subjected to biaxial orientation so that a heat resisting resin layer is provided on the film. The thermoplastic film is at least partially unstretched, meaning that its crystalline orientation has not yet been completed. It may be subsequently stretched in the longitudinal and lateral directions to around 2.5-5.0 times, and subjected to heat treatment to complete crystalline orientation, showing a biaxial orientation pattern by wide-angle X-ray diffraction. When the thermoplastic film is not biaxially oriented, the dimensional stability of the laminated film, particularly under high temperature and high humidity conditions, becomes insufficient, its mechanical strength becomes inferior and its flatness becomes worse.
The laminated film of the present invention has a form in which a heat resisting resin layer is the main component, and is soluble in a dipolar aprotic solvent. It is laminated on at least one surface of a biaxially oriented thermoplastic film base material.
Examples of the dipolar aprotic solvents include N-methyl-2-pyrolidone, dimethylformamide, dimethylacetoamide, dimethylsulphoxide and the like. According to the present invention, it is very important that the resin is dissolved in such a dipolar aprotic solvent, for the adhesion with the thermoplastic film. In the absence of such a solvent, the desired interfacial adhesion is not obtained.
The heat resisting resin is preferably a resin having a glass transition point of not less than about 170° C. and/or having no melting point or no decomposition point of not more than about 300° C. The heat resisting resin to be selected is not particularly limited, provided it satisfies the above-mentioned requirements. However, examples include aromatic polyamide type resins, aromatic polyimide type resins and precursors thereof, polyamideimide type resins, polyether sulphone type resins, polyether imide type resins, polybenzimidazole and precursors thereof, polybenzoxazole and precursors thereof, polybenzthiazole and precursors thereof, polysulphone type resins and the like. When a polyester film is used as a base material, aromatic polyamide type resins are preferable due to their interfacial adhesion as well as heat resisting characteristics and dimensional stability of the laminate, and recoverability by re-dissolution. A
Mimura Takashi
Takada Yasushi
Tanaka Hiroyuki
Tsukuda Akimitsu
Kiliman Leszek
Schnader Harrison Segal & Lewis LLP
Toray Industries Inc.
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