Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1996-04-12
2001-05-15
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S331000, C428S480000, C428S327000, C428S910000
Reexamination Certificate
active
06231966
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an oriented polyester film. More particularly, the present invention relates to an oriented polyester film suitable for magnetic tapes, which has superior slipping property, resistance to scraping, scratch resistance, slitting property, winding property and the like. Most particularly, the present invention relates to an oriented polyester film comprising inactive particles and silica particles having a specific shape and a particle size distribution.
BACKGROUND OF THE INVENTION
A biaxially oriented polyester film represented by polyethylene terephthalate films has been widely used as a medium for magnetic recording, utilizing the superior physical and chemical properties. In such biaxially oriented polyester films, slipping property, resistance to scraping, scratch resistance, slitting property and winding property exert great influence on the suitability of the film production steps and processing steps, as well as the quality of the product.
For example, magnetic tapes obtained by applying a magnetic coating on the surface of biaxially oriented polyester films have been fed at faster speeds in recent years to bring down the costs, and the feeding speed is increased in the steps of coating, calendering, slitting, housing a magnetic tape into a cassette, and duplication for manufacture of soft copies, while creating various problems.
For example, when the feeding speed of the film is increased in the coating step, the film surfaces come into contact with a die used for the application of magnetic coating, as a result of which the surface is scraped and the scraped powder causes scratches in the magnetic layer, thus decreasing the yield of the product. An increased speed in the calendering step brings about the need for more frequent cleaning of the white powder adhered to a calendering roll, thus again decreasing the productivity.
Also, an increased speed at the slitting step causes insufficient winding of the film to decrease the yield of the product. In general, an improvement in winding property involves inclusion of larger particles to decrease the coefficient of friction between films. Thus, if such film is wound at a greater speed in the slitting step for the sake of an enhanced productivity, the film slips too much and causes disturbance in winding to the extent that, in an extreme case, the film winds around a slitter blade to lower the productivity.
When a tape is housed in a cassette at a high speed, the scraped powder and scratch occur to possibly cause drop outs (loss of information). Particularly in VTR use, a cheap metallic guide having an unfinished surface may be used as a guide post to be fixed in the cassette to lower the costs. The surface of such guide post is extremely rough and a magnetic tape which is produced according to the prior art wherein slipping property and resistance to scraping of the film have been improved but a back coating is not applied [for example, a method comprising addition of inorganic particles such as silicon oxide, titanium dioxide, calcium carbonate, talc, clay and sintered kaoline (e.g., Japanese Patent Unexamined Publication No. 54-57562) and a method comprising precipitating fine particles containing calcium, lithium or phosphorus in polymerization system (e.g., Japanese Patent Examined Publication No. 52-32914)] accompanies more drop outs due to the scraped powder and scratch experienced in this step.
To solve such problems, there has been proposed a method comprising adding alumina particles having a specific crystal form to decrease damages to the film (e.g., Japanese Patent Examined Publication No. 4-40375). This method provides sufficient improvement in scratch resistance, but when a polyester film containing said alumina particles is run under heating, the amount of the white powder adhering to the metallic pin increases. Therefore, for example, when the running speed of the film is increased in a calendering step in which the film is subject to heat histeresis, the amount of the white powder increases. In addition, the high hardness of alumina causes problems when used with a high pressure homogeneous dispersion machine or media dispersion type wet grinder for the preparation of alumina slurry, since it wears SUS which constitutes these apparatuses and SUS may be mixed in the slurry as a contaminant component. Along therewith, parts replacement frequency would become higher. In a polyester polymerization system including alumina fine particles, moreover, the products of degraded polyester, which are adhered to or deposited in a kettle, particularly at the vicinity of gas-liquid interface, are scraped by the alumina fine particles and contained in the polyester as bulky products.
Another method includes addition of spherical monodispersed silica obtained by removing alkali from sodium silicate or hydrolysis of alkoxysilane. This method shows a certain degree of improvement in scratch resistance under high film running speeds. However, the particles themselves tend to come off from the film and resistance to scraping of the film is degraded. The particles once fell are prone to form aggromerates, and the scraped matter including the aggromerates of the fallen particles gives damages to the magnetic surface, thus increasing the number of drop outs.
Faced with the need to increase feeding speed at the slitting step, the conventional problems such as chips from the film and build-up of the cut surfaces at slitting are desired to be solved, whereby to provide a film with less friction with a slitting blade and superior in continuous slitting.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the problems caused by the increased speed at a magnetic tape production step and a cassette housing step, and provide an oriented polyester film having high quality, which is superior in slipping property, slitting property, resistance to scraping, scratch resistance and winding property.
According to the present invention, there is provided a biaxially oriented polyester film comprising silica particles (A) having an average secondary particle size of 50-200 nm, an average primary particle size ratio (length/breadth) of 1.25-3.0, and a ratio of average primary particle size/standard deviation of primary particle size (d/&sgr;) of 0.5-5.0 in a proportion of 0.01-1% by weight, and inactive particles (B) having an average particle size of 300-1500 nm in a proportion of 0.01-1% by weight.
The more preferable embodiments of the present invention are the above-mentioned biaxially oriented polyester film wherein the silica particles (A) have a specific surface area of 30-80 m
2
/g; the film wherein the silica particles (A) contain chroline atom in a proportion of 10-500 ppm; the film wherein the inactive particle (B) is at least one kind from synthetic calcium carbonate particles and heat-resistant organic polymer particles; the film wherein the inactive particles (B) have an area proportion of not less than 60% relative to the circumscribed circle; the film wherein the inactive particles (B) have a particle dispersion of not more than 50%; the film wherein the inactive particles (B) comprise inactive particles (B1) having an average particle size of 300-650 nm in a proportion of 0.05-0.5% by weight and inactive particles (B2) having an average particle size of 750-1300 nm in a proportion of 0.01-0.25% by weight; the film wherein the difference in average particle size between the inactive particles (B2) and inactive particles (B1) is 200-600 nm; and the film having a limiting viscosity number (intrinsic viscosity) of 0.5-0.6.
In still other embodiments of the present invention, there are provided an oriented polyester film comprising silica particles (a) synthesized by flame hydrolysis of silicon tetrachloride, and having a specific surface area of 30-80 m
2
/g and an average particle size of 50-200 nm, in a proportion of not less than 0.01% by weight and less than 0.5% by weight, synthetic calcium carbonate particles (b) having an average
Matsumoto Haruo
Nishino Yasuhiro
Chen Vivian
Morrison & Foerster / LLP
Tarazano D. Lawrence
Toyo Boseki Kabushiki Kaisha
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