Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1999-08-12
2001-11-20
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S213000, C428S215000, C428S216000, C428S323000, C428S480000, C428S690000, C428S910000, C264S288400, C264S290200
Reexamination Certificate
active
06319587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to biaxially-oriented polyester films.
2. Description of the Related Art
Among known biaxially-oriented polyester films are biaxially-oriented laminated polyester films disclosed in, for example, Japanese Patent Application Laid-Open No. 2-77431. When conventional biaxially-oriented polyester films are used as magnetic recording media, they have improved output and traveling performance. High-density magnetic recording such as digital video recording, however, requires further increased output and higher reliability of magnetic recording media.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a biaxially-oriented polyester film having high output characteristics suitable for digital video recorders and high-density data recording.
A biaxially-oriented polyester film in accordance with the present invention includes at least two layers, at least one outermost layer comprising a polyester having a rigid amorphous content of about 10 to 55%, and the biaxally-oriented polyester film has a longitudinal Young's modulus of at least about 4.5 GPa.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The biaxially-oriented polyester film in accordance with the present invention has a multilayer configuration including at least two layers. The multilayer configuration is essential for satisfying the requirements for high-quality digital video recording and high density data recording. Single-layer films do not satisfy such requirements due to difficulty in optimization of the surface characteristics thereof, because the formation of the optimized surface in the single-layer configuration is not practical due to production costs. In the present invention, the multilayer configuration includes at least two layers. For example, the multilayer configuration may include three layers, e.g., A/B/A and A/B/C, and more layers.
At least one outermost layer (hereinafter referred to as the “A layer”) as a constituent of the biaxially-oriented polyester film in accordance with the present invention is preferably composed of polyethylene terephthalate (hereinafter referred to as PET) or polyethylene 2,6-naphthalenedicarboxylate (hereinafter referred to as PEN) in view of output characteristics. The A layer may contain any other polymer or may be composed of a copolymer thereof within the scope satisfying the advantages of the present invention. In addition, the A layer may contain proper amounts of additives, such as antioxidants, thermal stabilizers, and UV absorbents within the scope necessary for the advantages of the present invention.
Other layers as constituents of the biaxially-oriented polyester film in accordance with the present invention are preferably composed of polyesters. Examples of preferable polyesters include PET, polypropylene terephthalate (hereinafter referred to as PPT), PEN, and polypropylene 2,6-naphthalenedicarboxylate (hereinafter referred to as PPN). Among polyesters having propylene repeating units, 1,3-propylene glycol is preferably used as a monomer in view of output characteristics. The other layers may contain any other polymer or may be composed of a copolymer thereof within the scope necessary for the advantages of the present invention. In addition, the other layers may contain proper amounts of additives, such as antioxidants, thermal stabilizers, and UV absorbents within the scope necessary for the advantages of the present invention.
A crystalline polymer includes a crystalline phase and an amorphous phase. The amorphous phase is partially unfrozen above the glass transition temperature. The unfrozen phase is called a “mobile amorphous phase”, whereas the frozen phase is called a “rigid amorphous phase”. The rigid amorphous content is defined as the residual content when the crystalline content or crystallinity (%) and the mobile amorphous content are subtracted from the total 100%.
In the present invention, the polyester constituting the A layer has a rigid amorphous content of about 10 to 55% and preferably about 15 to 45%. The rigid amorphous phase having such a content contributes to increased film strength and improved size stability, resulting in improved output characteristics.
The biaxially-oriented polyester film in accordance with the present invention has a longitudinal Young's modulus of at least about 4.5 GPa and preferably about 5 to 10 GPa. Output characteristics are significantly improved by increasing the longitudinal Young's modulus.
When the A layer is primarily composed of PET, the glass transition temperature (Tg) of the A layer is in a range of preferably about 95 to 125° C. and more preferably about 100 to 120° C. In this case, the rigid amorphous content of the A layer is in a range of about 10 to 45% and more preferably about 15 to 45%.
When the A layer is primarily composed of PEN, the glass transition temperature of the A layer is in a range of preferably about 120 to 155° C. and more preferably about 125 to 150° C. in view of output characteristics. In this case, the rigid amorphous content of the A layer is preferably in a range of about 15 to 45%.
The outermost layers of the biaxially-oriented polyester film have a crystallinity in a range of preferably about 25 to 50% and more preferably about 30 to 45%, in view of output characteristics and abrasion resistance.
When the A layer is primarily composed of PET, it is preferable in view of output characteristics that the biaxially-oriented polyester film of the present invention satisfy the relationship of approximately Y
1
≦0.05X, wherein Y
1
is the thermal shrinkage (%) in the longitudinal direction at 80° C. after 30 minutes and X is the longitudinal Young's modulus (GPa).
When the A layer is primarily composed of PEN, it is preferable in view of output characteristics that the biaxially-oriented polyester film of the present invention satisfy the relationship of approximately Y
2
≦0.05X, wherein Y
2
is the thermal shrinkage (%) in the longitudinal direction at 100° C. after 30 minutes.
The A layer preferably contains inorganic or organic inert particles to improve output characteristics. The particle content is in a range of preferably about 0.05 to 3.0 percent by weight and more preferably about 0.1 to 2 percent by weight. The number of the surface projections on the A layer is controlled to be in a range of preferably about 3,000/mm
2
to 15,000,000/mm
2
and more preferably about 5,000/mm
2
to 12,000,0001/mm
2
, in order to maintain high levels of output characteristics. The average size of the particles is in a range of generally about 0.01 to 1.5 &mgr; and preferably about 0.02 to 1.0 &mgr;. The relative standard deviation of the particle sizes is in a range of preferably about 0.5 or less, more preferably about 0.3 or less, and most preferably about 0.2 or less. Any type of particles may be used without restriction in the present invention. Examples of preferable particles include aluminum silicate, calcium carbonate, alumina, silica, calcium phosphate, titanium oxide, and organic particles. Different types of particles may be used in combination.
In the biaxially-oriented polyester film of the present invention, layers other than the outermost layers also may contain particles. In this case, the average size of the particles is in a range of generally about 0.05 to 1.0 &mgr; and preferably about 0.1 to 0.8 &mgr;. The relative standard deviation of the particle sizes of said film is in a range of preferably about 0.5 or less, more preferably about 0.3 or less, and most preferably about 0.2 or less. The particle content of said film is in a range of preferably about 0.05 to 3.0 percent by weight, more preferably about 0.02 to 2 percent by weight, and most preferably about 0.05 to 1 percent by weight. Any type of particle may be used without restriction in the present invention. Examples of preferable particles in view of output characteristics include aluminum silicate, calcium carbonate, alumina, silica, calcium phosphate, titanium oxide, and organ
Nakajima Shozi
Nakamori Yukari
Okazaki Iwao
Chen Vivian
Schnader Harrison Segal & Lewis LLP
Toray Industries Inc.
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