Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-03-17
2001-05-15
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S328000, C428S329000, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06231963
ABSTRACT:
In the case of modern magnetic recording media, there is constantly the desire for greater storage capacity and for faster access to the stored information. For the tape-like recording media, these requirements imply, in the first case, a continuous reduction in the tape thickness on the one hand and, on the other hand, a continuous decrease in the thickness of the magnetic layer, at least for the longitudinal recording method predominantly used in practice. In the second case, the result is a constantly increasing tape speed. For example, tape-like recording media having a high storage capacity now have a tape thickness of only 10 &mgr;m, the magnetic layer thickness relevant for the write and read operation being about 1 &mgr;m, and the tape speed in modern high-speed drives may be in the region of a few meters per second.
Particularly in start-stop operation, when it is intended to access preselected information packages, high accelerations may act on the magnetic recording medium in the longitudinal direction in some cases. Associated with this is a dynamic tensile load with short-term, high dynamic tensile stress values which act over the cross-section of the tape. This may even be sufficient to result in plastic deformation of the tape-like recording medium, which may lead to tearing under continuous stress with recurring load changes.
Polyester films, for example comprising polyethylene terephthalate, are usually used as substrate material for tape-like recording media. It is known that the modulus of elasticity of this material is from 4 to 8 GPa, corresponding to the exact conditions of the production process, and that the elastic limit is not more than about 0.5% elongation. These values are measured in the static tensile test on film samples which are cut in the machine direction of the film production machine and clamped in a suitable tensile tester. Thus, the substrate material itself can elastically absorb a maximum tensile stress which is not more than the product of these two characteristics, ie. 40 MPa.
In EP-A 0 520 155, the elasticity range of modern magnetic layers having small thicknesses of less than or equal to 1 &mgr;m was characterized by a minimum yield point of 30 MPa and by a minimum elongation at yield of 0.2%. The stated elastic limits for the substrate and the magnetic layer resulted in an elastic tensile stress of from 30 to 40 MPa with an elastic elongation of from 0.2 to 0.5% for the tape-like recording medium composed of said substrate and said layer.
Further publications on the subject of the elasticity of tape-like recording media are JP-A 57-078 630, JP-A 57-078 629 and JP-A 02-260 229. The inventive concept of the first two publications consists in establishing the ratio of the moduli of elasticity in the longitudinal and transverse directions at not more than 2.5 so that the magnetic recording properties are not impaired by deformation of the recording medium. JP-A 02-260 229 is concerned with improving the life of the magnetic layer and its running properties. In this context, a further magnetic layer as a lower layer between the nonmagnetic substrate and the actual recording layer is proposed as a solution, and the lower layer has a greater modulus of elasticity than the recording layer.
None of these publications permit the production of tape-like magnetic recording media having a satisfactorily high elastic tensile stress range and a satisfactorily high modulus of elasticity.
It is an object of the present invention to remedy the stated disadvantages and to provide a resilient tape-like magnetic recording medium for high tensile stresses varying as a function of time in high-speed tape drives.
We have found that this object is achieved by tape-like, magnetic recording media I comprising a nonmagnetic substrate III, at least one layer applied to this substrate, and, in at least one of these layers, an inorganic needle-shaped pigment II which is suitable as a supporting pigment and has a ratio of the average length to the average diameter of the pigment II of at least 3, wherein the mean modulus of elasticity of the stated layers is not less than 15 GPa in the longitudinal direction of the tape-like recording medium I.
We have also found novel chromium-containing inorganic needle-shaped pigments VI and VII suitable as supporting pigments, processes for their preparation and the use of the pigments for, in particular anisotropic strengthening of polymeric materials.
According to the invention, the modulus of elasticity is understood as meaning the modulus of elasticity in extension E, which is obtained as the ratio of the tensile stress to the longitudinal elongation and can readily be determined in a generally known manner.
Suitable supporting pigments are ferromagnetic and nonferromagnetic inorganic needle-shaped pigments II.
Suitable ferromagnetic pigments II are metallic pigments, such as Fe, Co, Ni and alloys of these elements, and oxidic pigments, such as &ggr;-Fe
2
O
3
, Co-containing &ggr;-Fe
2
O
3
, Fe
3
O
4
, preferably chromium-containing oxidic pigments, such as CrO
2
, and in particular those of the formula VI
Cr
a
O
x
.nH
2
O VI
where
a is the average valency of the chromium with 3.0<a≦3.25, preferably 3.0<a≦3.1,
x is the oxygen equivalents determined by the valency of the chromium and
n is the water content with 0<n<(4−a)/2.
According to the invention, the pigments VI may be composed of 50% by weight of a core and 50% by weight of a shell, it being possible for the atomic ratios of Cr(IV) to Cr(III) in the core and shell to be identical or different.
Suitable nonferromagnetic pigments II are preferably oxidic pigments, such as FeOOH, &agr;-Fe
2
O
3
and in particular chromium-containing pigments of the formula VII
Cr
2
O
3
.nH
2
O VII
where
n is from 0 to 0.5.
The pigments VI and VII are obtainable by heating the pigments of the formula VIII
CrO
x
VIII
where
x is 1.8≦x≦2.2,
at from 400 to 500° C., preferably from 440 to 480° C., particularly advantageously from 450 to 470° C., in a gas containing in particular molecular oxygen, such as air, resulting in reaction times of from 0.5 to 10, preferably from 0.5 to 2, hours, wherein the pigments VIII may be purified before the heating in a manner known per se, for example by washing with water.
Advantageously, the pigments VIII can be treated with organic or, preferably, inorganic compounds, such as mineral bases, advantageously alkali metal hydroxides, alkaline earth metal hydroxides and earth metal hydroxides, for example potassium hydroxide, calcium hydroxide, in particular sodium hydroxide, or their basic salts, for example carbonates or sulfites, in particular sodium sulfite, before the heating. A reaction in inorganic, in particular aqueous solution at a pH of from 7 to 14, in particular from 11 to 13, is advisable, with the exception of sulfites, for which a pH of from 7 to 9 is recommended, at from 10 to 90° C. with reaction times of from 0.5 to 10, in particular from 0.5 to 5, hours.
The pigments VI and VII can also be obtained by first reacting a pigment VIII under hydrothermal conditions at from 110 to 250° C., preferably from 160 to 230° C., in particular from 190 to 210° C., with a reducing agent at from 2 to 500, preferably from 100 to 300, in particular from 150 to 250 bar, in the course of from 10 to 500, preferably from 50 to 250, in particular from 80 to 120, hours. Suitable reducing agents are inorganic or, preferably, organic compounds, such as carboxylic acids, in particular oxalic acid.
The reaction products can be further processed in the reaction mixture or advantageously isolated from the suspension by known methods, such as filtration, and preferably purified, for example washed.
According to the invention, the reaction products are then heated at from 100 to 500° C., preferably from 200 to 400° C., in a gas containing in particular molecular oxygen, such as air, resulting in reaction times of from 0.5 to 10, preferably from 0.5 to 2, hours.
The reaction products can be treated with organ
Heilmann Peter
Hoffmann Erich
Hubner Werner
Jachow Harald
Jakusch Helmut
EMTEC Magnetics GmbH
Keil & Weinkauf
Resan Stevan A.
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