Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-09-10
2002-07-16
Copenheaver, Blaine (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S213000, C428S215000, C428S480000, C428S473500, C428S910000, C525S432000
Reexamination Certificate
active
06420011
ABSTRACT:
The present invention relates to a polyester film greatly improved in quality, and a production process thereof. In more detail, the present invention relates to a polyester film excellent in thermal dimensional stability and clarity and good in productivity, suitable as a film for various industrial materials, for example, as a magnetic recording film, packaging film, heat-sensitive mimeograph stencil film, capacitor film, thermal transfer ribbon film, photographic or printing plate making film, or electric insulation film, and also relates to a production process thereof.
Plastic films can be produced continuously as large area films which cannot be produced with other materials, and because of their features in strength, durability, clarity, flexibility and surface properties, they are used in fields needing them in large quantities such as magnetic recording, agriculture, packaging and building materials. Among them, biaxially oriented polyester films are used in various fields because of their excellent mechanical properties, thermal properties, electric properties and chemicals resistance, and especially as base films for magnetic tapes, they are unrivaled by other films in usefulness. However, depending on applications, polyester films are insufficient in dimensional stability and thermostability, and are limited in application as films for various industrial materials. Especially for magnetic recording, films are thinned and processed to allow recording at higher densities for miniaturization and longer-time recording, and the base films are demanded to be higher in strength and further improved in form stability and dimensional stability in the service environment. However, no effective means has been found to meet these demands. Furthermore, though raising the glass transition temperature of the polyester is generally an effective means for enhancing thermal dimensional stability and thermostability, no effective means has been established to obtain a biaxially oriented polyester film with high quality and high glass transition temperature.
On the other hand, as the prior art for enhancing the strength of a biaxially oriented polyester film, the longitudinal re-stretching method is generally practiced, in which a biaxially stretched film is re-stretched in the machine direction, to be enhanced in the strength in the machine direction. Furthermore, to enhance the strength also in the transverse direction, the longitudinal re-stretching and lateral re-stretching method is proposed, in which the longitudinally re-stretched film is re-stretched in the transverse direction (e.g., U.S. Pat. No. 4,226,826, etc.). When the higher strength polyester film obtained according to such prior art is used as a large capacity high density magnetic recording tape, it has a problem that desired electromagnetic conversion properties cannot be obtained since errors occur at the time of recording and reproducing due to the shift of the recording track caused by stress elongation deformation or dimensional change under environmental conditions.
For blends consisting of polyethylene terephthalate (PET) and a polyether imide (PEI), it is disclosed that the glass transition temperature rises with the increase of the PEI content (e.g., U.S. Pat. No. 4,141,927, “Journal of Applied Polymer Science, 48, 935-937 (1993)”, “Macromolecule, 28, 2845-2851 (1995)”, “Polymer, 38, 4043-4048 (1997)”, etc.). However, these documents, patents and publications do not disclose a biaxially oriented high quality polyester film consisting of PET and a PEI, and do not describe at all the stretchability of the film, the film quality such as strength, thermal dimensional stability and clarify of the biaxially oriented polyester film, or the film properties for applications. Said U.S. Pat. No. 4,141,927 discloses a solution method or a melt method using a melt kneading apparatus for obtaining a compatible blend consisting of PET and a PEI. However, if the compatible blend prepared by using the solution method is cast into a sheet, the molecules of the solvent must be removed after film formation, and the film casting speed is low, making it difficult to form a film at a low cost. Furthermore, if a compatible blend is obtained by the melt method using a melt kneading apparatus such as Brabender or Banbury mixer, the polymers must be kneaded for a long time in a field of melt shearing, and this is unsuitable for industrial continuous film formation disadvantageously. Moreover, since the film made of a blend consisting of PET and a PEI produced by the conventional melt method contains many coarse particles mainly composed of a polyether imide, the film is often broken during biaxial stretching and the film surface has many coarse protrusions, not allowing use as a base film for high density magnetic recording disadvantageously. These problems are serious especially in the case of a biaxially oriented thin polyester film with a thickness of less than 10 &mgr;m and with higher strength, and a technological breakthrough for industrialization is desired.
Japanese Patent Laid-Open (Kokai) No. Hei7-228761 discloses a resin composition consisting of PET-polyethylene-2,6-napthalenedicarboxylic acid (PEN) copolymer (PET/N) and a PEI, and an injection-molded article made thereof. However, this invention relates to a partially compatible blend with more than one glass transition temperature, and is quite different from the present invention.
Japanese Patent Laid-Open (Kokai) No. Hei1-315465 discloses a composition consisting of a PET-PEI mixture (A) and ethylene-glycidyl methacrylate copolymer (B). However, this invention also relates to a non-compatible blend with more than one glass transition temperature, and is quite different from the present invention.
Japanese Patent Laid-Open (,Kokai) No. Hei10-204268 discloses a hollow molded article made of a resin composition consisting of PET and a PEI, but does not describe at all about a biaxially oriented polyester film. Of course, it does not describe at all about the method for obtaining a biaxially oriented high quality polyester film or the method for decreasing the coarse particles.
As described above, any biaxially oriented high quality polyester film composed of a compatible blend consisting of PET and a PEI with a single glass transition temperature has not been found and has not been industrialized.
SUMMARY OF THE INVENTION
A problem of the present invention is to provide a biaxially oriented high quality polyester film excellent in thermal dimensional stability, clarity and also in productivity, and a production process thereof. Another problem is to provide a biaxially oriented polyester film greatly improved in practical properties highly respected in various applications of the polyester film, such as the recording track shift in magnetic recording tape application, curling in magnetic recording card application, dimensional change during processing in printing plate making application, printing shift in ribbon application, thermostability in capacitor application, and perforation sensitivity and low temperature curling in heat-sensitive mimeograph stencil application.
The inventors studied intensively to solve the above problems. As a result, they found at first that a film with a single glass transition temperature and with a refractive index of 1.60 to 1.80 at least in either the machine direction or transverse direction, obtained by melt-extruding a polyester (A) mainly composed of ethylene terephthalate and a polyether imide (B) by a specific method for forming a film can provide a biaxially oriented high quality polyester film excellent in thermal dimensional stability and clarity and small in thickness variation. Then, they pursued to enhance the quality of the film, and found that the preferable production method disclosed in the present invention can provide a biaxially oriented high quality polyester film with high stiffness, less coarse protrusions on the surface and excellent productivity to allow various applications.
The present invention is a biaxially o
Higashioji Takuji
Hosokawa Hirofumi
Tsunekawa Tetsuya
Chevalier Alicia
Copenheaver Blaine
Toray Industries Inc.
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