Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1999-06-22
2002-03-19
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S475500, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06358619
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aromatic polyamide film, particularly an aromatic polyamide film suitably used as a base film of a magnetic recording medium, which is free from the wrinkling and weaving caused at the time of film winding and excellent in the abrasion resistance of the film surface. The present invention also relates to a magnetic recording medium using it.
BACKGROUND ARTS
In recent years, with the progress of digital recording technology and the increased use of the technology in the external memories of computers, the demand for films suitable for thinner, higher density recordable and more highly durable magnetic recording media is intensively growing.
Aromatic polyamide films are stiffer, hence can be thinner than polyester films of polyethylene terephthalate, polyethylene naphthalate, etc. conventionally used as base films of magnetic recording media, and are suitable for large capacity magnetic recording media.
However, since aromatic polyamide films are used as thinner films for smaller devices which can effectively use such excellent properties, the wrinkling of the film roll more adversely affects the productivity and the quality of the obtained product than before. Furthermore, when a very thin magnetic layer is formed by coating or a magnetic layer is formed by vapor deposition directly on a film for achieving a higher output, the base film becomes smoother on the surface and is likely to be wrinkled, for degrading the film smoothness and the electromagnetic conversion properties due to the wrinkling.
Aromatic films improved in the wrinkling caused at the time of film winding or in temporally caused wrinkling are disclosed in Japanese Patent Laid-Open (Kokai) Nos. Hei3-119512, Hei3-114830, Hei8-230124, etc. in which the ratio of the diameter of inactive particles to the thickness of the laminate, Young's modulus, moisture absorption and winding hardness are specified in respective ranges.
However, the aromatic polyamide films improved in wrinkling by forming projections on the film surface by containing inactive particles as described above have still the following problems to be solved, under the very severe conditions required for speed-up of processing in recent years.
Firstly, since particles different in nature from aromatic polyamides such as inorganic particles or organic particles made of a crosslinked polymer are added to an aromatic polyamide, the strong inter-molecular force of the aromatic polyamide lowers the affinity between the particles and the aromatic polyamide constituting the film. As a result, the particles are likely to fall off and the film surface is likely to be abraded, to lower the abrasion resistance of the film surface, being likely to cause wrinkling.
Secondly, in the solution casting process used for forming films from aromatic polyamides, inactive particles small in inter-particle repulsion are likely to cohere. As a result, large projections are formed on the film surface, being likely to degrade the electromagnetic conversion properties or to cause dropouts when the film is used as a magnetic recording medium.
Thirdly, aromatic polyamide films are often driven to run on guide rolls and guide pins during processing or when used as final products, and since the inorganic particles and particles made of a crosslinked polymer are very hard, it can happen that guides are abraded on the surfaces, and that the produced dust is deposited on the guides and films. Especially if the guides are plastic, the repeated running or high speed running of the films is likely to cause the deposition.
As a method other than the above methods of using inactive particles, Japanese Patent Laid-Open (Kokal) No. Hei7-44857 disc loses a method of letting an aromatic polyamide contain a different aromatic polyamide lower in solubility than it, and causing the mixture to be separated in phase at the time of film formation, to form projections on the film surface.
However, an aromatic polyamide, especially a para-oriented polyamide is not excellent in solubility, and if an aromatic polyamide poor in solubility is blended with it, it is actually difficult to mix them perfectly though the polymer solution looks perfectly dissolved.
The inventors formed films from such polymer solutions for examination, and found that though fine projections also existed, there were many 150 nm or higher large projections, and that the film surfaces were rough with craters, etc. Furthermore, it can happen that if an aromatic polyamide with low solubility is precipitated in the beginning of film formation process, the film is devitrified or becomes a fragile film low in elongation. On the other hand, it was also found that if an aromatic polyamide with a structure very close to that of the main aromatic polyamide, i.e., having a solubility almost equal to that of the main aromatic polyamide is blended, few projections are formed probably because the added aromatic polyamide is perfectly mixed with the main aromatic polyamide. Therefore, it is difficult to uniformly form fine projections according to the technique disclosed in the patent gazette.
Japanese Patent Laid-Open (Kokai) No. Hei4-8763 discloses a method of adding a polyether sulfone before completion of aromatic polyamide polymerization for production of an aromatic polyamide-polyether sulfone composition, but it does not state at all the properties of the molded article (film, etc.), particularly what surface is designed and intended to be obtained.
On the other hand, Japanese Patent Laid-Open No. Hei3-237135 discloses a heat resistant film made from an aromatic polyamide and a soluble resin with the amount of the soluble resin kept at 10 wt % to 95 wt %, but it is intended to improve chemical properties and economy, without describing or suggesting any technical idea on the formation of a fine surface. Furthermore, since a soluble resin is contained more compared to an aromatic polyamide, the high mechanical properties, especially high Young's modulus peculiar to the aromatic polyamide are lost. For example, the highest Young's modulus achieved in the examples of the patent gazette is as low as 6.2GPa (Example2). Similar techniques are also disclosed in Japanese Patent Laid-Open (Kokai) Nos. Hei3-286680, Hei3-227290, Hei4-117433 and Hei4-27110, etc., but the achievements are also similar.
As polyimide films, laminated films in which a layer containing 0.01 wt % to 10 wt % of an aromatic polysulfone based polymer contained in a polyimide is laminated on one side of a film mainly made of a polyimide are disclosed in Japanese Patent Laid-Open (Kokai) Nos. Sho59-122547 and Sho62-68746, etc. However, a polyimide belongs to a technical field different from that of a polyamide since it is greatly different from a polyamide in production method and the properties of the film formed from it. For example, while a polyimide is produced by polymerization under mild conditions in an organic solvent, a polyamide is produced by polymerization under severe conditions that sulfuric acid is used as solvent or hydrogen chloride is produced during polymerization. Furthermore, since the polymer solution used for film formation contains said hydrogen chloride or its neutralization product, it is difficult to control the film surface. Moreover, if the neutralization product remains in the film, it can cause dropouts in the magnetic recording medium produced from it, and if the neutralization product is removed suddenly, the film becomes irregular in thickness. Under this technical extent, the patent gazette does not describe or suggest at all the technical idea of improving the wrinkling and weaving caused at the time of film winding.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an aromatic polyamide film free from the wrinkling and weaving caused at the time of film winding and excellent in the abrasion resistance of the film surface because of high affinity of a contained different polymer to an aromatic polyamide, by separating the aromatic polyamide and the
Horiuchi Mitsuhiro
Sueoka Masanori
Tsukuda Akimitsu
Kiliman Leszek
Morrison & Foerster / LLP
Toray Industries Inc.
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