U.S. patent application number 09/811887 was filed with the patent office on 2001-10-04 for magnetic recording media.
Invention is credited to Heilmann, Peter, Hoffmann, Erich, Hubner, Werner, Jachow, Harald, Jakusch, Helmut, Koch, Volker, Kohl, Albert, Lehner, August, Lehnert, Rudi, Lenz, Werner, Ohlinger, Manfred, Schneider, Norbert, Veitch, Ronald John.
Application Number | 20010026880 09/811887 |
Document ID | / |
Family ID | 7757901 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026880 |
Kind Code |
A1 |
Lehner, August ; et
al. |
October 4, 2001 |
Magnetic recording media
Abstract
Tape-like magnetic recording media having a nonmagnetic
substrate and at least one layer applied to the substrate having
incorporated into at least one of these layers, an inorganic
needle-shaped pigment which serves as a supporting pigment and has
a ratio of the average length to the average diameter of the
pigment of at least 3, and the mean modulus of elasticity of the
layers is not less than 15 Gpa in the longitudinal direction of the
tape-like recording media.
Inventors: |
Lehner, August;
(Rodersheim-Gronau, DE) ; Jakusch, Helmut;
(Frankenthal, DE) ; Koch, Volker; (Battenberg,
DE) ; Ohlinger, Manfred; (Frankenthal, DE) ;
Kohl, Albert; (Laumersheim, DE) ; Lenz, Werner;
(Bad Durkheim, DE) ; Schneider, Norbert; (Altrip,
DE) ; Heilmann, Peter; (Bad Durkheim, DE) ;
Hubner, Werner; (Frankenthal, DE) ; Hoffmann,
Erich; (Heidelberg, DE) ; Veitch, Ronald John;
(Maxdorf, DE) ; Lehnert, Rudi; (Ludwigshafen,
DE) ; Jachow, Harald; (Worms, DE) |
Correspondence
Address: |
KEIL & WEINKAUF
1101 Connecticut Avenue, N.W.
Washington
DC
20036
US
|
Family ID: |
7757901 |
Appl. No.: |
09/811887 |
Filed: |
March 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09811887 |
Mar 19, 2001 |
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08913808 |
Mar 17, 1998 |
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6231963 |
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08913808 |
Mar 17, 1998 |
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PCT/EP96/01155 |
Mar 18, 1996 |
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Current U.S.
Class: |
428/846 ;
G9B/5.271; G9B/5.284; G9B/5.286 |
Current CPC
Class: |
Y10T 428/257 20150115;
G11B 5/733 20130101; G11B 5/708 20130101; Y10S 428/90 20130101;
Y10T 428/256 20150115 |
Class at
Publication: |
428/694.0BN |
International
Class: |
G11B 005/708 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 1995 |
DE |
P19511239.3 |
Claims
We claim:
1. A tape-like, magnetic recording medium 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 from 3:1 to 15:1, 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.
2. A tape-like, magnetic recording medium I as claimed in claim 1,
having a modulus of elasticity in the longitudinal direction of the
tape-like recording medium I of not less than 20 GPa.
3. A recording medium I as claimed in claim 1 or 2, comprising a) a
nonmagnetic substrate III and b) a layer IV suitable for magnetic
information storage.
4. A recording medium I as claimed in any of claims 1 to 3,
comprising a layer V which contains a binder and the supporting
pigment II.
5. A recording medium I as claimed in any of claims 1 to 4, wherein
the nonmagnetic substrate III contains the supporting pigment
II.
6. A recording medium I as claimed in any of claims 1 to 5, wherein
the layer IV suitable for magnetic information storage contains the
supporting pigment II.
7. A recording medium I as claimed in claim 3, wherein a layer V is
arranged between the nonmagnetic substrate III and the layer IV
suitable for magnetic information storage.
8. A recording medium I as claimed in claim 3, wherein the
nonmagnetic substrate III is arranged between a layer V and the
layer IV suitable for magnetic information storage.
9. A recording medium I as claimed in any of claims 1 to 8, wherein
the layer IV suitable for magnetic information storage contains a
binder and finely divided ferromagnetic pigments.
10. A recording medium I as claimed in any of claims 1 to 8,
wherein the layer IV suitable for magnetic information storage
essentially comprises a ferromagnetic metal or ferromagnetic
alloy.
11. A recording medium I as claimed in any of claims 1 to 10,
containing a ferromagnetic pigment as supporting pigment II.
12. A recording medium I as claimed in claim 11, containing
ferromagnetic metal or alloy pigments as supporting pigment II.
13. A recording medium I as claimed in claim 11, containing
ferromagnetic metal oxide pigments as supporting pigment II.
14. A recording medium I as claimed in claim 13, containing
.gamma.-Fe.sub.2O.sub.3 pigments, Co-containing
.gamma.-Fe.sub.2O.sub.3 pigments, .gamma.-Fe.sub.3O.sub.4 pigments
or CrO.sub.2 pigments as supporting pigment II.
15. A recording medium I as claimed in claim 13, containing, as
supporting pigment II, needle-shaped chromium-containing pigments
of the formula VI Cr.sup.aO.sub.x.n H.sub.2O VI where a is the
average valency of the chromium with 3.0<a.ltoreq.3.25, x is the
oxygen equivalents determined by the valency of the chromium and n
is the water content with 0<n<(4-a)/2, having a ratio of the
average length of the needles to the average diameter of the
needles of from 3:1 to 10:1.
16. A recording medium I as claimed in claim 15, wherein the
pigments VI consist of a) 50% by weight of a core and b) 50% by
weight of a shell and the atomic ratios of Cr(IV) to Cr(III) in the
core and in the shell are identical.
17. A recording medium I as claimed in claim 15, wherein the
pigments VI consist of a) 50% by weight of a core and b) 50% by
weight of a shell and the atomic ratio of Cr(IV) to Cr(III) in the
shell is greater than that in the core.
18. A recording medium I as claimed in claim 15, wherein the
pigments VI consist of a) 50% by weight of a core and b) 50% by
weight of a shell and the atomic ratio of Cr(IV) to Cr(III) in the
core is greater than that in the shell.
19. A recording medium I as claimed in any of claims 1 to 10,
containing a nonferromagnetic pigment as supporting pigment II.
20. A recording medium I as claimed in claim 19, containing FeOOH
or .alpha.-Fe.sub.2O.sub.3 as supporting pigment II.
21. A recording medium I as claimed in claim 19, containing, as
supporting pigment II, a pigment of the formula VII
Cr.sub.2O.sub.3.n H.sub.2O VII where n is from 0 to 0.5, having a
ratio of the average length of the needles to the average diameter
of the needles of from 3:1 to 10:1.
22. A recording medium I as claimed in any of claims 14 to 18 and
21, containing a) a nonmagnetic substrate III and, arranged
thereon, b) a layer V which contains a binder and a
chromium-containing needle-shaped metal oxide having a ratio of the
average length to the average diameter of the pigment of at least 7
and an orientation ratio of at least 4 and, arranged thereon, c) a
layer IV suitable for information storage and containing a binder
and ferromagnetic metallic pigments, the modulus of elasticity in
the longitudinal direction of the tape-like recording medium I
being greater than 30 GPa.
23. A pigment VI or VII suitable as a supporting pigment and
according to the definition in claims 15 to 18, 21 and 22.
24. A supporting pigment as claimed in claim 23, having an average
needle length of from 100 to 400 nm.
25. A process for the preparation of the pigments VI and VII as
claimed in claims 23 and 24, wherein pigments of the formula VIII
CrO.sub.x VIII where x is 1.8.ltoreq.x.ltoreq.2.2, a) are heated at
from 400 to 500.degree. C. or b) are reacted under hydrothermal
conditions at from 110 to 250.degree. C. with a reducing agent and
then heated at from 200 to 400.degree. C.
26. The use of pigments VI and VII as claimed in claims 23 and 24
for modifying the mechanical properties of the polymeric
materials.
27. The use as claimed in claim 26 for an isotropic modification of
the mechanical properties of polymeric materials.
28. A method for modifying the mechanical properties of polymeric
materials, wherein pigments VI or VII are incorporated into melts
or solutions of polymeric materials or melts or solutions of
compounds from which polymeric materials can be prepared, and the
mixture is then cured or allowed to solidify.
29. A method as claimed in claim 28, anisotropic modification of
the mechanical properties of polymeric materials being effected,
wherein the pigments are rheologically oriented and the materials
are cured or allowed to solidify.
30. A method as claimed in claim 29, wherein the pigments VI are
oriented in an external magnetic field and the materials are cured
or allowed to solidify.
31. A polymeric material obtainable as claimed in any of claims 28
to 30.
32. A magnetic recording medium produced with the use of a
polymeric material as claimed in claim 31.
33. A recording medium I as claimed in any of claims 15 to 18,
containing pigments VI, oriented in an external magnetic field.
Description
[0001] The present invention relates to magnetic recording media
stabilized by a supporting pigment.
[0002] 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
.mu.m, the magnetic layer thickness relevant for the write and read
operation being about 1 .mu.m, and the tape speed in modern
high-speed drives may be in the region of a few meters per
second.
[0003] 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.
[0004] 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.
[0005] In EP-A 0 520 155, the elasticity range of modern magnetic
layers having small thicknesses of less than or equal to 1 .mu.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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] Suitable supporting pigments are ferromagnetic and
nonferromagnetic inorganic needle-shaped pigments II.
[0013] Suitable ferromagnetic pigments II are metallic pigments,
such as Fe, Co, Ni and alloys of these elements, and oxidic
pigments, such as .gamma.-Fe.sub.2O.sub.3, Co-containing
.gamma.-Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, preferably
chromium-containing oxidic pigments, such as CrO.sub.2, and in
particular those of the formula VI
Cr.sup.HO.sub.x.n H.sub.2O VI
[0014] where
[0015] a is the average valency of the chromium with
3.0<a.ltoreq.3.25, preferably 3.0<a.ltoreq.3.1,
[0016] x is the oxygen equivalents determined by the valency of the
chromium and
[0017] n is the water content with 0<n<(4-a)/2.
[0018] 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.
[0019] Suitable nonferromagnetic pigments II are preferably oxidic
pigments, such as FeOOH, .alpha.-Fe.sub.2O.sub.3 and in particular
chromium-containing pigments of the formula VII
Cr.sub.2O.sub.3.n H.sub.2O VII
[0020] where
[0021] n is from 0 to 0.5.
[0022] The pigments VI and VII are obtainable by heating the
pigments of the formula VIII
CrO.sub.x VIII
[0023] where
[0024] x is 1.8.ltoreq.x.ltoreq.2.2,
[0025] at from 400 to 500.degree. C., preferably from 440 to
480.degree. C., particularly advantageously from 450 to 470.degree.
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.
[0026] 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.degree. C. with reaction times of from 0.5 to 10, in
particular from 0.5 to 5, hours.
[0027] The pigments VI and VII can also be obtained by first
reacting a pigment VIII under hydrothermal conditions at from 110
to 250.degree. C., preferably from 160 to 230.degree. C., in
particular from 190 to 210.degree. 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.
[0028] 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.
[0029] According to the invention, the reaction products are then
heated at from 100 to 500.degree. C., preferably from 200 to
400.degree. 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.
[0030] The reaction products 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.degree. C. with reaction times of from 0.5 to 10, in
particular from 0.5 to 5, hours.
[0031] The pigments VI and VII 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. 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.degree. C. with
reaction times of from 0.5 to 10, in particular from 0.5 to 5,
hours.
[0032] As is generally known, the supporting pigments II, VI and
VII may contain further chemical elements or compounds. According
to the invention, the needle-shaped pigments II, VI and VII have a
ratio of the average length of the needles to the average diameter
of the needles of from 3:1 to 15:1, preferably from 5:1 to 10:1,
and a length of from 50 to 400 nm, preferably from 90 to 300 nm, in
particular from 100 to 200 nm. The specific surface area according
to DIN 66132 of the pigments VI and VII should be from 30 to 150,
preferably from 50 to 100, m.sup.2/g. According to the invention,
the saturation magnetization of the pigments VI is from 0.1 to 65,
preferably from 0.1 to 40, in particular from 0.1 to 22,
nTm.sup.3/g and the residual induction is from 0.05 to 24,
preferably from 0.05 to 12, in particular from 0.05 to 5,
nTm.sup.3/g.
[0033] The pigments II, preferably VI and VII, are suitable for, in
particular, anisotropic strengthening of polymeric materials. Such
polymeric materials may advantageously be used for coating
surfaces, for example films, or three-dimensional bodies, such as
cylinders, for example wires.
[0034] For the production of polymeric materials or layers
strengthened in this manner, pigments II, in particular VI or VII,
are incorporated, according to the invention, into melts or
solutions of polymeric materials or melts or solutions of compounds
from which polymeric materials can be prepared, and the mixtures
are then cured or allowed to solidify.
[0035] For the anisotropic strengthening of polymeric materials, as
can be particularly advantageously used in the novel magnetic
recording media I, the supporting pigments II, in particular VI or
VII, can be oriented before the curing or solidification of the
polymeric materials.
[0036] In the case of nonferromagnetic supporting pigments, this
orientation can be achieved, for example, by rheological measures,
such as pouring the mixture through a narrow gap. In the case of
ferromagnetic supporting pigments II, in particular VI, orientation
can advantageously be effected by means of an external magnetic
field.
[0037] In particularly advantageous magnetic recording media in
which a layer V containing a ferromagnetic supporting pigment II is
present between a substrate III and a layer IV suitable for
information storage, the orientation ratio in the layer V should be
at least 2.5 and that in the layer IV at least 4.0. The orientation
ratio is understood as meaning the quotient of the residual
induction of the tape-like magnetic recording medium in the running
direction and the residual induction of the magnetic recording
medium perpendicular to this direction. The orientation of the
pigments II, preferably VI and VII, can be determined by ultrathin
sections. For this purpose, ultrathin sections having a thickness
of from 0.1 to 0.2 .mu.m are viewed by means of a transmission
electron microscope at not less than 20,000 times magnification. In
a measuring field about 20 .mu.m wide, from 50 to 100 needle-shaped
pigments per ultrathin section are randomly selected and the
average diameter in the longitudinal direction of the tape
(d.sub.L) and in the transverse direction (d.sub.T) is
determined.
[0038] Where
d.sub.L.gtoreq.2.multidot.d.sub.T,
[0039] the pigments are considered to be oriented predominantly in
the longitudinal direction of the tape.
[0040] Tape-like magnetic recording media I are known to contain a
nonmagnetic substrate III and at least one layer (magnetic layer)
IV suitable for the magnetic information storage.
[0041] The novel magnetic recording media I may contain the
supporting pigments II described in the nonmagnetic substrate III,
in at least one of the layers IV suitable for information storage
or in at least one layer V. The layer V may be arranged between the
substrate III and a magnetic layer IV or on that side of the
substrate III which faces away from a magnetic layer IV.
[0042] Nonmagnetic substrates III which may be used are the
conventional rigid or flexible substrates, in particular films of
linear polyesters, such as polyethylene terephthalate, which
generally have thicknesses of from 4 to 200 .mu.m, in particular
from 6 to 36 .mu.m.
[0043] The magnetic layer IV of the novel magnetic recording media
I may be based on either vapor-deposited or sputtered, metallic
thin films which essentially contain ferromagnetic elements, such
as Fe, Co and Ni or their alloys, or on ferromagnetic pigments.
[0044] For the production of such layers, the pigments can, if
required, be dispersed with fillers in a manner known per se in a
solution comprising a solvent, binder and further additives, such
as lubricant and dispersant, and can be applied to a nonmagnetic
substrate. After the orientation of the ferromagnetic pigments in a
strong magnetic field, the further processing can be carried out in
the usual manner, for example by removing the solvent and, if
required, curing the binder with subsequent calendering.
[0045] Suitable magnetic pigments are the conventional oxidic
pigments, such as .gamma.-Fe.sub.2O.sub.3, Fe.sub.3O.sub.4 and
CrO.sub.2, or metallic pigments, such as Fe, Co and Ni. As is
generally known, these pigments may contain further chemical
elements or compounds.
[0046] As usual, the solvents used may be water, ethers, such as
tetrahydrofuran or dioxane, ketones, such as methyl ethyl ketone or
cyclohexanone, esters, such as ethyl acetate, or hydrocarbons, such
as alkanes or aromatics, or mixtures of these solvents.
[0047] Suitable binders are known to be polyacrylates,
polymethacrylates, polyacrylamide, vinyl polymers, such as
polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl
propionate or polyacrylonitrile, cellulose-containing binders, such
as cellulose esters, in particular cellulose nitrates, cellulose
acetate, cellulose triacetate, cellulose acetopropionate or
cellulose acetobutyrate, phenoxy resins, epoxy resins or,
preferably, polyurethanes and block polymers or copolymers of these
compounds. Suitable polyurethanes are described, for example, in
DE-B 11 06 959, DE-B 27 53 694, DE-A 32 26 995, DE-A 32 27 163 and
DE-A 32 27 164. Polyurethanes may be used as the sole binders or,
preferably, with other polymers, such as polyvinyl formals, phenoxy
resins, PVC or PVC copolymers.
[0048] The abrasion resistance and the modulus of elasticity of the
polyurethanes and polyurethane mixtures can be further increased by
crosslinking these components with polyfunctional isocyanates, in
particular those having more than 2 isocyanate groups. Such
crosslinking agents can advantageously be obtained by an addition
reaction of bifunctional isocyanates, such as toluylene
diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate
of the formula 1
[0049] with polyhydric alcohols or by biuret or isocyanurate
formation. Suitable crosslinking agents are in particular an adduct
of toluylene diisocyanate with trimethylolpropane and diethylene
glycol. The amount of crosslinking agent required in relation to
the amount of polyurethane used for achieving optimum performance
characteristics can readily be determined in a few simple
preliminary experiments.
[0050] Lubricants usually used are carboxylic acids of 10 to 20
carbon atoms, in particular stearic acid and palmitic acid,
derivatives of carboxylic acids, such as their salts, esters and
amides, or fluorinated hydrocarbons.
[0051] Cationic, nonionic or, preferably, anionic surfactants, such
as carboxylates, sulfonates, phosphonates or phosphates of
hydrocarbons, in particular alkyl or aryl compounds, may be used in
the usual manner as dispersants.
[0052] Suitable fillers are known to be inorganic and organic
pigments, eg. alumina, silica, carbon black, polyethylene and
polypropylene.
[0053] In the production of magnetic recording media I, a plurality
of magnetic layers IV, at least one of which contains a supporting
pigment II, or a plurality of layers V, at least one of which
contains a supporting pigment II, can be applied to the substrate
III.
EXAMPLES
Preparation of a CrO.sub.2 Pigment
Example 1
[0054] 554 g of CrO.sub.3 were dispersed in 159 g of water in the
course of 10 minutes. 70 g of potassium antimonyl tartrate (PAT)
were slowly added to the mixture at 40-60.degree. C. and stirring
was carried out for 5 minutes at 60.degree. C. 170 g of
Cr.sub.2O.sub.3 were then added at 20-30.degree. C. in the course
of 3 minutes with stirring.
[0055] Homogenization was then carried out for 15 minutes with
thorough stirring, the temperature increasing to 80.degree. C.
[0056] After cooling to 30.degree. C., the mixture was heated to
320-350.degree. C. in an autoclave in the course of 3 hours and
kept at this temperature for 9 hours, the maximum pressure being
360 bar. The mixture was then cooled, the pressure in the autoclave
being let down at a temperature of the mixture of 200.degree.
C.
[0057] The product was then dried at 50.degree. C. and milled.
[0058] The properties are shown in Table 1.
Example 2a-g
[0059] 1000 g of the product from Example 1 were suspended at
25.degree. C. in a mixture of 780 g of oxalic acid in 1490 g of
water with stirring. The mixture was then kept in an autoclave for
96 hours at 210.degree. C. under the resulting autogenous pressure
of the mixture.
[0060] The product was then heated in air under the process
conditions stated in Table 2.
[0061] The properties are shown in Table 2.
Example 3
[0062] 100 g of the product from Example 1 were dispersed in 1000 g
of water and wet-milled. Thereafter, the mixture was filtered, the
filter cake was washed with water until the conductivity of the
wash water at 20.degree. C. was <50 .mu.S and the residue was
then dispersed in 1000 g of water.
[0063] A solution of 11 g of sodium sulfite in 50 g of water was
then added to the mixture and stirring was carried out for 30
minutes at from 20 to 28.degree. C.
[0064] The product was then filtered and the filter cake was washed
until the wash water had a conductivity at 20.degree. C. of <50
.mu.S.
[0065] The filter cake was dried at 50.degree. C. and granulated to
a pellet size of <1 mm.
[0066] The properties are shown in Table 1.
Example 4
[0067] 100 g of the product from Example 1 were dispersed in 1000 g
of water and wet-milled. Thereafter, the mixture was filtered, the
filter cake was washed with water until the conductivity of the
wash water at 20.degree. C. was <50 .mu.S and the residue was
then dispersed in 1000 g of water. The pH was then brought to 12
with 15% strength by weight sodium hydroxide solution and stirring
was carried out for 2 hours at 55.degree. C. and pH 12.
[0068] The product was then filtered and the filter cake was washed
until the wash water had a conductivity at 20.degree. C. of <50
.mu.S.
[0069] The filter cake was dried at 50.degree. C. and granulated to
a pellet size of <1 mm.
[0070] The properties are shown in Table 1.
Example 5
[0071] 100 g of the product from Example 1 were dispersed in 1000 g
of water and wet-milled. Thereafter, the mixture was filtered, the
filter cake was washed with water until the conductivity of the
wash water at 20.degree. C. was <50 .mu.S and the residue was
then dispersed in 1000 g of water.
[0072] The mixture was heated to 85.degree. C. with stirring and
blanketing with nitrogen, a solution of 20 g of sodium sulfite in
100 g of water was added at 85.degree. C. and stirring was carried
out for 2 hours at 85.degree. C.
[0073] The product was then filtered and the filter cake was washed
until the wash water had a conductivity at 20.degree. C. of <50
.mu.S.
[0074] The filter cake was dried at 50.degree. C. and granulated to
a pellet size of <1 mm.
[0075] The properties are shown in Table 1.
Example 6
[0076] 100 g of the product from Example 1 were dispersed in 1000 g
of water and wet-milled. Thereafter, the mixture was filtered and
the filter cake was washed with water until the conductivity of the
wash water at 20.degree. C. was <50 .mu.S, dried at 50.degree.
C. and granulated to a pellet size of <1 mm.
[0077] The product was heated in a rotary tubular furnace with a
residence time of 30 minutes at 460.degree. C. under air.
[0078] The properties are shown in Table 1.
Example 7
[0079] 100 g of the product from Example 6 were dispersed in 1000 g
of water and wet-milled. Thereafter, the mixture was filtered, the
filter cake was washed with water until the conductivity of the
wash water at 20.degree. C. was <50 .mu.S and the residue was
then dispersed in 1000 g of water.
[0080] The pH was then brought to 12 with 15% strength by weight
aqueous sodium hydroxide solution and stirring was carried out for
2 hours at 55.degree. C. and pH 12.
[0081] The product was then filtered off and the filter cake was
washed until the wash water had a conductivity at 20.degree. C. of
<50 .mu.S.
[0082] The filter cake was dried at 50.degree. C. and granulated to
a pellet size of <1 mm.
[0083] The properties are shown in Table 1.
[0084] Production of a Magnetic Recording Medium
Example 8
[0085] A first dispersion of 1000 parts by weight of chromium oxide
pigment according to Example 5, 75 parts by weight of a vinyl
polymer having polar anchor groups, 95 parts by weight of a
polyurethane having polar anchor groups, 25 parts by weight of
stearic acid, 180 parts by weight of tetrahydrofuran and 180 parts
by weight of dioxane was applied to a 14 .mu.m thick nonmagnetic
polyethylene terephthalate substrate in a layer thickness of 1.2
.mu.m. A second dispersion comprising 1000 parts by weight of a
ferromagnetic metal pigment having a coercive force of 133 kA/m and
a specific surface area of 52 m.sup.2/g, 80 parts by weight of
.alpha.-Al.sub.2O.sub.3 having a particle size of 0.2 .mu.m, 77
parts by weight of a vinyl polymer having polar anchor groups, 77
parts by weight of a polyurethane having polar anchor groups, 10
parts by weight of a phosphoric ester, 25 parts by weight of
stearic acid, 22.5 parts by weight of a polyisocyanate, 1837.5
parts by weight of tetrahydrofuran and 1837.5 parts by weight of
dioxane was applied to this layer in a layer thickness of 0.4
.mu.m, oriented by means of a magnetic orienting field, dried and
calendered.
[0086] A novel magnetic recording medium having very good magnetic
and mechanical properties was obtained.
Example 9
[0087] The procedure was as in Example 8, except that the first
dispersion contained 1000 parts by weight of chromium oxide pigment
according to Example 7 instead of 1000 parts by weight of chromium
oxide pigment according to Example 5.
[0088] A novel magnetic recording medium having excellent magnetic
and mechanical properties was obtained.
Example 10
[0089] The procedure was as in Example 8, except that the first
dispersion contained 1000 parts by weight of
.alpha.-Fe.sub.2O.sub.3 pigments having an average needle length of
125 nm and an average needle diameter of 25 nm, instead of the 1000
parts by weight of chromium oxide pigment.
[0090] A novel magnetic recording medium having good magnetic and
mechanical properties was obtained.
Comparative Example
[0091] The procedure was as in Example 8, except that the first
dispersion contained 1000 parts by weight of TiO.sub.2 pigment
having an average length of 60 nm and an average diameter of 30 nm,
instead of the 1000 parts by weight of chromium oxide pigment.
[0092] The layers of the magnetic recording medium had a modulus of
elasticity of 13 GPa.
1 TABLE 1 Ex. 1 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Length 130 130 130
130 130 130 [nm] Length/ 7 7 7 7 7 7 thickness SSA [m.sup.2/g] 73
73 73 73 64 64 Hc [kA/m] 15 15 16 15 0 0 .sigma..sub.r
[nTm.sup.3/g] 21 16 17 13 1 1 .sigma..sub.m 77 59 64 49 6 5
[nTm.sup.3/g]
[0093]
2TABLE 2 Exam- Hc .sigma..sub.r .sigma..sub.m ple Heating [kA/m]
[nTm.sup.3/g] [nTm.sup.3/g] SSA [m.sup.2/g] 2a unheated 0 0 1 76 2b
1 h/250.degree. C. 7 1 5 74.6 2c 1 h/300.degree. C. 17 3 14 73.6 2d
1 h/350.degree. C. 19 11 39 71.2 2e 1 h/400.degree. C. 10 7 33 71.5
2f 1 h/450.degree. C. 3.3 2 18 68.8 2g 1 h/500.degree. C. 6.2 <1
7 62.8
* * * * *