Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer or spacer insulating structure
Reexamination Certificate
2001-12-05
2004-08-31
Killiman, Leszek B (Department: 1773)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer or spacer insulating structure
C428S212000, C428S473500, C428S474400, C428S690000, C428S900000, C427S128000, C427S129000, C427S130000, C427S131000
Reexamination Certificate
active
06783889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polyester films having superior quality, in particular, having significantly improved dimensional stability and surface properties compared to conventional polyester films.
2. Description of the Related Art
Polyester films have been widely used due to their superior thermal properties, dimensional stability, mechanical properties, and controllability of surface conditions, and in particular, it has been well known that polyester films have been useful as a base film for forming magnetic tapes or the like. In recent years, higher density recording has been required for magnetic tapes for achieving the trend towards the reduction in material weight, miniaturization, and longer recording time. In order to fulfill the requirements for this higher density recording, it is effective to shorten the recording wavelength, that is, to compress the recording signals.
However, when recording signals are compressed, various properties, such as heat dimensional stability in environments in which the tapes are used, finer surface projections, and reduction in the number of coarse projections, are required for the base film.
First, when recording signals are compressed, there has been a problem in that recording track deviation is likely to occur due to heat generated when the magnetic tape runs or due to heat distortion of the magnetic tape which occurs during storage. Accordingly, improved characteristics, such as heat dimensional stability and storage stability in environments in which the tapes are used, have been increasingly required.
In addition, in the case of a magnetic tape having a deposited magnetic layer, a significant decrease in thickness of the magnetic layer is very effective to compress the recording signals for obtaining improved electromagnetic conversion characteristics; however, in accordance with the decrease in thickness of the film, the surface conditions of the base film have an increased influence on the surface conditions of the magnetic tape. Accordingly, reduction in height of surface projections, formation of smoother surfaces, and accurate control of the surface roughness of the base tape are increasingly required.
In addition, it also becomes more important to suppress the degradation of film flatness caused by heat in a step of coating or depositing a magnetic layer and to suppress the degradation of film quality caused by precipitation of oligomers.
Furthermore, concomitant with the trend toward the compression of recording signals, the sensitivity of a recording head which reads the recording signals must be improved, and hence, in place of conventional heads, highly sensitive magnetic resistance (MR) heads must be used. However, the MR heads have inferior abrasion resistance compared to the conventional heads. In addition, since the distance between the head and the magnetic tape is being decreased significantly in order to reduce the gap loss, the problem of coarse projections damaging the magnetic head becomes more serious, and hence, a reduction in coarse projections has been increasingly demanded.
That is, development of a film having a surface which can satisfy the requirements of dimensional stability, surface smoothness, and reduction in coarse projections has been desired.
As a base film which can meet the dimensional stability requirement described above, aramid films have been used in view of their strength and dimensional stability. Even though the aramid films have cost and productivity disadvantages, that is, even though the aramid films are expensive and are not molded by melting extrusion as a conventional poly(ethylene terephthalate) resin is, the aramid films have been used since there has been no alternative material.
Through intensive research, as a technique for improving the dimensional stability of a biaxially oriented polyester film having high productivity, a biaxially oriented polyester film (for example, Japanese Unexamined Patent Application Publication No. 12-141475) formed of poly(ethylene terephthalate) and poly(ether imide) has been developed.
However, since the biaxially oriented polyester film described above has melt viscosity or the like which is considerably different from that of the conventional polyester represented by poly(ethylene terephthalate), when a conventional film-forming method is used, voids are easily formed around particles added to the polyester described above. In addition to that, due to poor dispersibility or the like between two different polymers, coarse projections may be formed, and hence, there has been a problem in that it is difficult to accurately control the surface conditions which are preferably used for a high-density magnetic recording medium.
In addition, as a method for obtaining high surface quality, there may be mentioned, for example, a method for forming a laminated polyester film (for example, Japanese Unexamined Patent Application Publication No. 7-272249) containing particles for forming surface projections or a method for coating a non-continuous film (Japanese Unexamined Patent Application Publication No. 3-208639) containing fine particles. However, among the requirements which will be further demanded for polyester films due to the inferior heat resistance thereof, there may be still problems in that wrinkles are generated or oligomers are precipitated due to heat applied in a deposition step.
Concerning the above-mentioned biaxially oriented polyester film composed of a poly(ethylene terephthalate) and poly(ether imide), a method for obtaining the surface conditions which are preferably used for high-density magnetic recording medium has not been known at all. In the case in which the method described above for improving the surface quality is applied to this film, there have been various problems, such as coating mottle caused by difference in wettability of the polymer surfaces or by difference in affinity between a coating solution and the polymer; an inferior lamination state caused by difference in melt viscosity between the two polymers; and the formation of coarse projections described above. For the film composed of polyester and poly(ether imide), a method (for example, Japanese Unexamined Patent Application Publication No. 12-355631) for reducing coarse projections (H2) having a height of 0.5 &mgr;m or more has been known; however, the level of control of the surface conditions by the method described above is far from that which can be satisfactory applied to future high-density magnetic recording media.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a polyester film which has superior dimensional stability and a superior property of restraining the precipitation of oligomers (hereinafter referred to as “oligomer-restraining property) and which also has a reduced number of coarse projections formed by voids around particles, coarse dispersed materials, degraded materials, contaminants, and the like. In particular, when the polyester film described above is used as a base film for a magnetic recording medium, track deviation or dropouts are unlikely to occur, and superior running durability, electromagnetic conversion characteristics, deposition stability, and the like can be obtained, whereby the polyester film of the present invention can be preferably used as a base film for a high-density magnetic recording tape.
The object of the present invention is achieved by a film formed of a polyester resin and a thermoplastic resin other than a polyester resin, in which the number H1 of coarse projections having a height of 0.28 &mgr;m or more per 100 cm
2
of at least one surface of the polyester film and the number H2 of coarse projections having a height of 0.56 &mgr;m or more per 100 cm
2
of said at least one surface of the polyester film satisfy the equations, 0≦H1≦100 and 0≦H2≦10.
In addition, the film described above can be formed of a laminated polyester film having at least two layers composed of a laminated portion (B lay
Eto Kenichi
Kubota Akira
Nakamori Yukari
Tsunekawa Tetsuya
Killiman Leszek B
Kubovcik & Kubovcik
Toray Industries Inc.
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