Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2001-03-16
2003-08-19
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S409000, C428S480000, C428S690000, C428S690000
Reexamination Certificate
active
06607822
ABSTRACT:
The invention relates to a single-layer or multilayer biaxially oriented film support for magnetic recording media which is predominantly composed of crystallizable polyester. The film is distinguished by the fact that, after coating, it has a low laser defect rate and is therefore very suitable for high-quality magnetic recording media. The invention furthermore relates to a process for the production of the film.
BACKGROUND OF THE INVENTION
Owing to their superior properties, such as tensile strength, their ultimate tensile strength, their modulus of elasticity, their transparency, their chemical and thermal stability and the like, biaxially oriented films of polyester, in particular of polyethylene terephthalate, polyethylene naphthalate or polycyclohexanedimethanol terephthalate, are used in large amounts in numerous industrial areas, and also as film supports for magnetic recording media, such as, for example, for audio, video and computer tapes and floppy disks, thermal printing tapes, etc.
For the various fields of use, the polyester films must meet specific requirements, which are usually achieved with the aid of the raw material formulations or by means of specific process engineering during the film production.
Thus, for example in the case of film supports for magnetic tapes, in addition to uniform and good sliding behavior and high abrasion resistance, particularly high requirements are set with respect to the homogeneity of the surface and the static behavior, because undesired protuberances on the surface of the support films, electrostatic errors and high static charge build-up within the magnetic layer applied to this surface lead to information losses and so-called laser defects which reduce the quality of the tape and limit the potential uses of the information medium. Overcoming or reducing the effect of, said electrostatic errors and high electrostatic charge build-up on the surface by incorporating inorganic and/or organic inert particles having a defined particle size distribution forms part of the prior art. Examples of such inert particles, which may be used alone or in combination, are CaCO
3
, TiO
2
, Al
2
O
3
, ZrO
2
, BaSO
4
, calcium phosphate, kaolin, SiO
2
or natural and synthetic silicates.
To improve their infinity to the polymer matrix and hence to improve the quality, i.e. the properties of the moldings produced using these inert particles, these inert particles are subjected to a surface treatment, depending on their chemical composition.
A description of the possibilities of surface modification of carbonate fillers with the aim of influencing the interactions at in particular the CaCO
3
/polymer interfaces is given in Plaste und Kautschuk [Plastics and Rubber], 37th year, Part 8/1990, page 269 et seq.
U.S. Pat. No. 3,227,675 describes the treatment of clays (kaolins) with organosilicon compounds for better incorporation into a polymer matrix.
DE-A-35 34 143 describes monodisperse SiO
2
particles which are preferably intended for chromatographic purposes and whose functional groups present on the surface have been reacted with organotrialkoxysilanes without the existing properties of the particles being adversely affected.
A process for the modification of synthetic silicate fillers with sulfur-containing organosilicon compounds for improving their incorporation into vulcanizable rubber blends is described in EP-A-0 177 674.
U.S. Pat. No. 4,567,030 likewise describes monodisperse mixed oxide particles which can be used as fillers and whose surfaces may have been modified for improving the resistance to moisture and the “dispersibility in a resin”, i.e. for reducing the agglomerate formation with an aminopropyltrimethoxysilane or silanes which contain ethylenically unsaturated groups. In EP-A-0 236 945, it is pointed out that, for reducing agglomerate formation during polymerization, the monodisperse mixed oxide particles are expediently subjected to a treatment with a silane, titanium or aluminum coupling reagent.
None of these publications describes methods which makes it possible to reduce the laser defect rate, which very greatly influences the quality of the coated magnetic tape.
Laser defects are coating errors. They are thin, round to oval areas in a magnetic layer or, in the advanced stage, even round or oval holes in the magnetic layer (transparent areas). In the case of laser defects, the polyester film is completely or partly exposed. The edge of the magnetic layer is highly fissured, which indicates a process similar to local tearing away of the magnetic layer. The defect has a diameter of between 0.2 and 0.8 mm. During the actual coating of the magnetic tape, some of the laser defects are not yet fully developed. The errors are fully displayed when the magnetic tape is cut into so-called “pancakes”. The laser defects are detected by means of a laser scanner. A 100% check is performed. On detection of a laser defect, the entire pancake is rejected in each case. It would be of great advantage for the magnetic tape coating industry to use a film support which, after coating, leads to few or, better still, even no laser defects at all. Usually, the rejection rate owing to laser defects is between 3 and 5%.
It was therefore the object of the present invention to provide an at least single-layer, biaxially oriented film support for magnetic recording media having a total thickness of from 1 &mgr;m to 40 &mgr;m, which essentially comprises polyester and which is distinguished by the fact that the laser defect rate is less than 2%, in particular less than 1%.
SUMMARY OF THE INVENTION
The object is achieved by an at least single-layer polyester film of the generic type stated at the outset and having a thickness of from 1 &mgr;m to 40 &mgr;m, wherein the film has, over the total roll length and roll width and after it has been made up into customer rolls, an electrostatic charge build-up which is in the range from −80 kV/m to +80 kV/m, in particular form −70 kV/m to +70 kV/m and preferably from −60 kV/m to +60 kV/m, in combination with a contact pressure at the roll cutters which is in the range from 300 N/m to 350 N/m, in particular from 310 N/m to 340 N/m.
DETAILED DESCRIPTION OF THE INVENTION
If the contact pressure of the roll cutters is >350 N/m, electrostatic errors (static marks) occur to a greater extent and lead to a higher laser defect rate.
If the contact pressure at the roll cutters is <300 N/m, the quality of the film in the roll is substantially adversely affected, which leads to considerable problems during further processing.
More than surprising is the fact that a film support for magnetic recording media which, after making up into customer rolls, has an electrostatic charge build-up of from −80 kV/m to +80 kV/m, in particular from −70 kV/m to +70 kV/m, preferably from −60 kV/m to +60 kV/m over the total roll length and roll width and was wound into customer rolls with a contact pressure at the roll cutters which is in the range from 300 N/m to 350 N/m, in particular from 310 N/m to 340 N/m, has a laser defect rate of ≦2% and in particular ≦1%.
In an attempt to reduce the laser defect rate, the person skilled in the art would have first improved the internal purity of the polyester raw material and investigated the production plant for contamination by foreign substances (oil, lubricants, oligomers, etc.). Furthermore, the person skilled in the art would have then reduced the production and make-up speeds in order thus to achieve a possible reduction in the laser defect rate.
It was therefore more than surprising for the person skilled in the art that an at least single-layer film support for magnetic recording media can be produced, with said electrostatic charge build-ups in combination with said contact pressure at the roll cutters, at high speeds of up to 400 m/min in an outstanding quality with a laser defect rate of ≦2%, in particular ≦1%.
The outstanding values for the electrostatics in combination with said contact p
Crass Guenther
Mueller Harald
Murschall Ursula
Stopp Andreas
Mitsubishi Polyester Film GmbH
ProPat L.L.C.
Resan Stevan A.
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