Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Patent
1995-06-02
1997-10-07
Le, H. Thi
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
428328, 428330, 428331, 428332, 428480, 524601, 524847, B32B 516
Patent
active
056745893
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to PENBB compositions, a process for preparing the poly(ethylene naphthalate bibenzoate (hereinafter "PENBB") compositions, and biaxially oriented PENBB films obtained from the compositions. More particularly, the present invention relates to PENBB compositions of excellent particle dispersion in PENBB and other properties, and films obtained from such compositions.
Polyester films, especially biaxially stretched polyester films such as polyethylene terephthalate (PET) films have good physical, chemical and thermal properties and are widely used as fibers, films and other molded articles. It is, however, desirable to improve some of these properties to provide still more useful film products, such as magnetic recording media and the like.
A film property which is generally desired in the production of these films and in handling of the produced films is good slipperiness between the films themselves or between the film and other bate material. Poor slipperiness of film in the production process or post-treatment such as coating and layer deposition or in handling of the product itself may lead to bad defects such as wrinkles or even the tendency to break and reduced commercial value of the products.
For improving slipping properties of film, a general practice is to add fine particles into polyester to provide proper roughness to the film surface.
As the fine particles used for such purpose, the particles of inorganic compounds inert to polyesters such as talc, kaolin, silica, calcium carbonate, titanium dioxide, graphite, carbon black and the like have been employed. However, with these inorganic particles, which are usually obtained by crushing natural minerals or by synthesis, it is difficult to avoid the presence of some amount of coarse particles or agglomerates of particles.
If coarse particles are contained in polyester or dispersion of particles is poor, the filters used in the extrusion step tend to clog or the film may even break in production. Also, defects such as fish-eyes would be present in the film, giving rise to the problems such as drop-outs in magnetic tapes or reduced dielectric strength in capacitors, etc.
Particularly in the field of magnetic tapes, requests for the reduction of size, longer play times and higher image quality are rising. For the attainment thereof, it is necessary to make the roughness on the film surface more uniform and finer. Especially in order to increase playing time it is necessary to further decrease the film thickness, which in turn requires the mechanical strength, especially the stiffness (modulus) of the film to be improved.
To increase uniformity, it has been proposed to remove coarse particles from the inert inorganic particles by crushing and classifying the particles before use. For example, a method is known in which a powder obtained by crushing a mineral starting material or a powder obtained from a synthesis. The crushing treatment and classifying treatment may be either dry or wet. This method however, although capable of removing coarse particles to a certain extent, was still unsatisfactory.
Various types of silica particles differing in average diameter are commercially available. However, when films were made by incorporating such silica particles in polyester, the produced films would fail to meet said strict property requirements.
Generally, the finely divided particles having a relatively high surface activity such as silica particles tend to form agglomerate particles and are difficult to disperse thoroughly in the copolyester monomers or polymer. Also, agglomeration of particles accelerates in the course of preparation of polyester after the addition of the fine particles and, as a result, the coarse agglomerate particles are formed in the polyester, which make the film surface roughness non-uniform, resulting in a reduced commercial value of the film. Especially in the case that such film is used as support for high quality magnetic tapes such as deposited tapes or metal tapes,
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Bennett Cynthia
Choe E-Won
Flint John Anthony
Kuhmann Bodo
Hanf Scott E.
Hoechst Celanese Corp.
Le H. Thi
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