Magnetic recording disk loaded in a cartridge with a specified liner

A magnetic recording disk is disclosed which comprises a flexible magnetic disk comprising a nonmagnetic support having thereon a magnetic layer comprising ferromagnetic powders and binders which is rotatably loaded in a cartridge having a liner formed with a nonwoven fabric on the inside of the cartridge, wherein said liner comprises (A) two layers of a layer of the magnetic layer side comprising a nonwoven fabric of a mixed yarn of rayon fibers and polyester fibers formed on the side which contacts with the magnetic layer, and a layer of the cartridge side comprising a nonwoven fabric of acrylic fibers formed on the side which contacts with the cartridge; or (B) three layers of two layers comprising a nonwoven fabric of a mixed yarn of rayon fibers and polyester fibers, and an inter layer comprising acrylic fibers formed between the two layers.

FIELD OF THE INVENTION 
The present invention relates to a magnetic recording disk comprising a 
disk cartridge case (hereinafter referred to as "cartridge case") having a 
liner on the inside comprising a nonwoven fabric and a flexible magnetic 
disk rotatably loaded in the cartridge case. Specifically, the present 
invention relates to a magnetic recording disk having a liner, which is 
less susceptible to mold. 
BACKGROUND OF THE INVENTION 
A magnetic recording disk comprises mainly a cartridge case (i.e., 
cartridge or jacket) having a magnetic head-inserting gate and a hole for 
rotation-driving, a flexible magnetic recording disk rotatably loaded in 
the cartridge case and a liner provided on the inside of the above 
cartridge case. 
A liner of a conventional magnetic recording disk comprises a nonwoven 
fabric made of a mixed yarn of a rayon fiber and a polypropylene fiber, a 
polyethylene terephthalate fiber, a mixed yarn of an acrylic fiber and a 
polyester fiber, or a mixed yarn of an acrylic fiber and a rayon fiber. 
The liner is fixed on the inside of the cartridge case, for example, by 
heat fusion and an adhesive. 
In general, the flexible magnetic disk has on one side or both sides of a 
nonmagnetic support of polyester film or the like, a magnetic layer formed 
by coating on the support a magnetic coating solution prepared by 
dispersing and mixing a binder, a dispersant, a lubricant and an abrasive 
in an organic solvent, or by directly depositing a ferromagnetic metal by 
vacuum deposition. Further, the discoid magnetic recording medium 
comprises mainly a cartridge case having a magnetic head-inserting gate 
and a hole for rotation-driving and has a liner for supporting the 
magnetic recording medium. 
Binders for a magnetic recording medium include synthetic resins such as a 
copolymer of vinyl chloride, vinyl acetate and vinyl alcohol, a 
polyurethane resin, a polyester resin, a cellulose derivative, a synthetic 
rubber type resin, an epoxy resin, an isocyanate type resin, and an 
acrylic type resin. 
Further, the above magnetic layer may contain various additives such as a 
dispersant, a lubricant and an antistatic agent. These additives are 
usually various organic compounds such as, for example, fatty acids and 
their derivatives (fatty acid esters, fatty acid metal salts and fatty 
acid amides), aliphatic ethers, aliphatic alcohols, and aliphatic ketones 
as well as compounds having a saturated or unsaturated hydrocarbon group. 
The materials for the liner are natural and synthetic fibers such as 
cellulose, rayon, polypropylene, polyethylene terephthalate, polyacrylic 
ester, and nylon. Mixed and impregnated into these fibers are each of a 
dispersant, a smoothing agent and an antistatic agent in an amount of each 
component of from 0.1 to 0.5% by weight. The above mixed solution is known 
as an oil solutions such as polyoxyethylene, glycol fatty acid ester and 
sodium alkylsulfuric acid ester. A nonwoven fabric is formed from the 
fibers singly or in combination, and the nonwoven fabric thus prepared is 
used in a single layer or a multilayer. 
However, the compounds present in the binder and various additives 
contained in the magnetic layer are the nutritive sources for molds. 
These substances help molds to grow on the surface of the medium in the 
high humidity. These molds are deposited on the surface of the disk and 
are liable to create problems such as a dropout. 
It is proposed in JP-A-61-241212 and JP-A-2-49217 (the term "JP-A" as used 
herein refers to a "published unexamined Japanese patent application") to 
add an antimold agent to a magnetic layer to prevent mold from growing on 
the magnetic recording disk. JP-A-62-252582, JP-A-62-281176, 
JP-A-61-258075 and JP-A-63-157876 propose improving the material of a 
liner. However, these techniques are insufficient to prevent molds in the 
high humidity. Further, there are no countermeasures, for example, for a 
running durability in the high humidity where ferromagnetic powder, as 
discussed below, is used for a high density recording. 
To increase the recording density of the recording medium, the recording 
capacity must be increased from 1M to 4M and further to 10M. In order to 
attain an increase in recording capacity, ferromagnetic metal powders 
consisting mainly of Fe, Ni and Co and tabular hexagonal ferrite powders 
such as barium ferrite have been investigated as ferromagnetic powders 
used for the recording medium. 
Ferromagnetic metal powders are suitable for a high density recording 
medium because of their excellent magnetic properties such as coercive 
force and saturation magnetization. The tabular hexagonal ferrite powders 
are advantageous because of the easiness in utilizing a vertical 
magnetization component of the magnetic layer due to an axis of easy 
magnetization existing in the direction vertical to the plate of the 
grains thereof. In combination with the above properties, the recording 
density can be further increased by using the ferromagnetic metal powders 
having a specific surface area of 30 m.sup.2 /g or more and a crystallite 
size of 300 .ANG. or less measured by an X-ray diffraction method and the 
tabular hexagonal ferrite powders having a specific surface area of 25 
m.sup.2 or more, a tabular ratio (tabular diameter/tabular thickness) of 2 
to 6 and a grain length as small as 0.02 to 1.0 .mu.m. 
Usually, a liner comprising a nonwoven fabric, which is provided on the 
inside wall of a jacket (i.e., cartridge) for the purpose of cleaning and 
protecting the surface of a magnetic layer, protects the magnetic layer 
without scratching the surface thereof or increasing torque at whatever 
condition the magnetic recording disk is used. However, where 
ferromagnetic metal powders and tabular hexagonal ferrite powders each 
having a small grain size are used as described above in order to increase 
recording density of a magnetic recording disk, the magnetic layer 
sometimes is rubbed and scratched by the liner present between a jacket 
(i.e., a cartridge or a jacket) and the flexible magnetic disk. Further, 
where these powders are used in high humidity, torque sometimes is 
increased which prevents the disk from smoothly rotating. 
The above problems cannot be sufficiently solved merely by incorporating 
abrasive particles and fatty acid esters into the magnetic layer, which 
have previously been carried out in order to improve the durability of the 
magnetic recording disk. 
Further, with respect to the scratching of the magnetic layer, there are 
proposed primarily means for mechanically strengthening the layer quality 
of a magnetic layer, such as the method of improving the binder used for a 
magnetic layer as disclosed, for example, in JP-A-3-102618, JP-A-3-44818 
and JP-A-3-63927; and the method of improving layer quality of a magnetic 
layer as disclosed in JP-A-3-309913, JP-A-3-150720 and JP-A-3-259466. 
These methods have been effective to some extent. 
Furthermore, in order to increase the function of a liner, there are 
proposed the method of using a nonwoven fabric made of a mixed yarn of a 
polyester fiber and an acrylic fiber, or a mixed yarn of a polyester fiber 
and a rayon fiber as disclosed, for example, in JP-A-1-171176, 
JP-A-61-208685 and JP-A-1-199371; and the method of impregnating various 
lubricants into a liner as disclosed in JP-A-61-120386 and JP-A-61-120387. 
Also, the method of providing a roughness on the surface of a liner is 
proposed as disclosed in JP-A-U-62-29678 and JP-A-U-62-22774 (the term 
"JP-A-U" as used herein refers to a "published unexamined Japanese utility 
model application"). 
A reduction in dust released by the liner itself and an excellent cleaning 
property (dust collecting) are required by the liner for reliability. 
Further, with respect to running durability, the liner must not scratch 
the surface of the magnetic layer of a magnetic recording disk and must 
not cause an increase in torque nor dropout in the high humidity. However, 
conventional liner materials cannot necessarily provide the best 
properties. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to improve the storage stability 
of a magnetic recording disk in the high humidity by preventing the 
generating of molds. 
A second object of the present invention is to prevent the deterioration of 
magnetic layer durability, which is liable to take place, for example, 
when ferromagnetic metal fine powders and hexagonal ferrite fine powders 
are used for high density recording. 
Through various investigations, the present inventors have found that the 
prevention of the generation of molds can be achieved by using a nonwoven 
fabric liner made of an acrylic fiber and by improving (using a polyester 
fiber) the material of the liner on the side that contacts the magnetic 
disk. Further, the prevention of the deterioration of the magnetic layer 
durability can be achieved by using a mixed yarn of a rayon fiber and a 
polyester fiber for the liner on the magnetic layer side. 
More particularly, the present invention provides a magnetic recording disk 
which comprises a flexible magnetic disk comprising a nonmagnetic support 
having thereon a magnetic layer comprising ferromagnetic powders and 
binders which is rotatably loaded in a cartridge having a liner formed 
with a nonwoven fabric on the inside of the cartridge, wherein said liner 
comprises (A) two layers of a layer of the magnetic layer side comprising 
a nonwoven fabric of a mixed yarn of rayon fibers and polyester fibers 
formed on the side which contacts with the magnetic layer, and a layer of 
the cartridge side comprising a nonwoven fabric of acrylic fibers formed 
on the side which contacts with the cartridge; or (B) three layers of two 
layers comprising a nonwoven fabric of a mixed yarn of rayon fibers and 
polyester fibers, and an inter layer comprising acrylic fibers formed 
between the two layers. 
Further, in order to improve the running durability, preferably a fatty 
acid ester can be further added to the magnetic layer in an amount of 3 to 
20 parts by weight per 100 parts by weight of a magnetic powder and an 
abrasive having a Moh's hardness of 6 or more can be further added to the 
magnetic layer in an amount of to 20 parts by weight per 100 parts by 
weight of a binder.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be explained below in detail. 
One of the characteristics of the present invention is that a layer of an 
acrylic fiber is used for a liner provided in a cartridge case (i.e., a 
cartridge or a jacket) of a magnetic recording disk. 
In a conventional liner consisting of, for example, a rayon/polyester mixed 
yarn, molds grow when the magnetic recording disk using such liner is 
stored, for example, in the high humidity of 23.degree. C. and 95% RH, and 
the molds are transferred on the surface of a magnetic layer of a magnetic 
disk (a medium) as foreign matter (i.e., dust), which causes dropout. On 
the contrary, where a liner comprising an acrylic fiber is used for a 
magnetic recording disk, no molds grow during storage even in the high 
humidity as mentioned above. 
The reason thereof is not clear but it is assumed that an acrylic acid 
monomer remaining in the acrylic fiber may contribute to the effect. 
The direct contact of the acrylic fiber with the magnetic layer of the 
magnetic disk is liable to shave and scratch the surface of the magnetic 
layer because the acrylic fiber is very hard. Therefore, in the present 
invention, the liner structure having the acrylic fiber layer does not 
directly contact the magnetic layer. The mixed yarn made of a rayon fiber 
and a polyester fiber both of which have no possibility of scratching the 
surface of the magnetic layer is used for the liner layer contacting with 
the magnetic layer. 
The attached drawings are enlarged cross-sectional drawings showing 
examples of the liner used in the present invention. FIG. 1 shows the 
liner comprising Layer 1 of a rayon/polyester mixed yarn and Layer 2 of an 
acrylic fiber. Layer 1 of the rayon/polyester mixed yarn is disposed in 
the cartridge case so that it contacts with the magnetic layer. FIG. 2 is 
an enlarged cross-sectional drawing showing another example of the liner 
used in the present invention. In this embodiment, the acrylic fiber Layer 
2 is interposed between the rayon/polyester mixed yarn Layers 1 and 3, and 
the rayon/polyester mixed yarn Layer 1 is disposed on the side where it 
contacts the magnetic layer. 
The thickness of the liner used in the present invention is preferably 100 
to 400 .mu.m and more preferably 160 to 290 .mu.m, in which the thickness 
of the acrylic fiber layer may be preferably from about 10 to 390 .mu.m 
and more preferably from 50 to 190 .mu.m. 
Even in such a two-layer structure or three-layer structure (a sandwich 
structure) in which the rayon/polyester mixed yarn layer is disposed on 
the side where it contacts with the magnetic layer (a medium), an antimold 
effect due to the acrylic fiber can be observed, and no molds grow on the 
magnetic recording disk even in the high humidity. Further, the magnetic 
layer is prevented from being scratched and thereby the running durability 
is improved because the relatively soft nonwoven fabric is disposed on the 
side where it contacts with the magnetic layer. 
In the present invention, the incorporation of a fatty acid ester and an 
abrasive having a Moh's hardness of 6 or more into the magnetic layer can 
further improve the running property of the magnetic disk as was described 
above. The amount of fatty acid ester contained in the magnetic layer is 
preferably 3 to 20 parts by weight, more preferably 5 to 15 parts by 
weight, per 100 parts by weight of a ferromagnetic powder. 
Too little amount of fatty acid contained in the magnetic layer makes the 
magnetic layer more susceptible to shaving in the high humidity. On the 
contrary, too much fatty acid plasticizes the binder to lower the layer 
quality, which deteriorates durability and increases torque in the high 
humidity. 
Fatty acid esters prepared by condensing fatty acids having preferably 6 to 
22 carbon atoms, more preferably 12 to 22 carbon atoms, with fatty 
alcohols having preferably 4 to 22 carbon atoms, more preferably 4 to 18 
carbon atoms, can be used to lower the dynamic friction coefficient 
between a flexible magnetic disk and the liner and to stabilize running. 
Too few carbon atoms in the above fatty acid ester sometimes makes the 
fatty acid ester more volatile and deteriorates the running property after 
storing over a long period of time. Too many carbon atoms in the fatty 
acid increases the viscosity thereof and deteriorates the running 
property, especially at a low temperature. 
As long as the number of carbon atoms in the fatty acid ester falls within 
the above range, any fatty acid ester can be selected regardless of 
branching or linearity of the fatty acids and alcohols, the isomeric 
structure such as cis and trans, the number and branching position of 
alcohols, provided that the melting point is preferably 30.degree. C. or 
less in order to provide the magnetic layer with a lubricating property 
under usual conditions. 
As described above, too few carbon atoms in the fatty acid ester makes the 
fatty acid ester more volatile at a relatively high temperature. Exposure 
to high temperature for a long time creates the portion where an amount of 
fatty acid ester is partially reduced, and, therefore, the objects of the 
present invention cannot be sufficiently achieved. 
On the contrary, too many carbon atoms increases the viscosity of the fatty 
acid ester, which causes sticking of the liner on the surface of the 
magnetic layer, which increases torque. 
For the purpose of further increasing the effects of the present invention, 
it is effective to subject the liner to an embossing finish to form a 
roughness on the surface thereof. That is, the roughness formed on the 
surface of the liner with the embossing finish decreases the contact area 
with the magnetic layer to decrease the friction coefficient with the 
liner in the high humidity. Therefore, the increase in torque is 
suppressed, and the magnetic layer also is less liable to scratch. 
Several methods of providing this embossing finish are available. In the 
calender rolling method, a nonwoven fabric can be passed through between 
an embossing roll having a roughness on the surface thereof and a 
smoothing roll, which are heated, to provide a roughness on the surface of 
the nonwoven fabric. An embossing pattern can be changed by changing the 
pattern of the roughness provided on the surface of the embossing roll. In 
addition, the hot blast method and supersonic method are available. 
The thickness of the liner in the magnetic recording disk of the present 
invention is preferably 100 to 400 .mu.m, more preferably 120 to 300 
.mu.m. The thickness of the liner is defined by the average of the values 
measured at five points in the lateral direction by the compression 
elasticity tester based on JIS-L-1085 with the load of 6 g/cm.sup.2 and 20 
g/cm.sup.2 and the area of 5 cm.sup.2. 
A mixed yarn of a rayon fiber and a polyester fiber is used for the 
material of the nonwoven fabric used for the liner provided on the inside 
surface of the cartridge of the magnetic recording disk of the present 
invention because it has a soft surface at least on the side where it 
contacts with the magnetic layer and is less liable to scratch the 
magnetic layer, as described above. 
Because of the large moisture absorption rate thereof, a rayon fiber 
expands in the high humidity to increase the area contacting with the 
magnetic layer, which in turn results in not only increasing torque but 
also scratching the magnetic layer. Accordingly, in the nonwoven fabric 
used for the liner of the magnetic recording disk of the present 
invention, the rayon fiber is not used alone but is mixed with a polyester 
fiber having a low moisture absorption rate, wherein the rayon fiber is 
mixed in the ratio of preferably 30% by weight or more, more preferably 
45% by weight or more in the mixed yarn of the rayon fiber and polyester 
fiber. 
A polyester fiber is used as the fiber mixed with the rayon fiber because 
the polyester fiber has very low moisture absorption rate. Additionally, 
an acrylic fiber, a nylon fiber and a polypropylene fiber may be mixed 
according to necessity. 
The above rayon fiber used in the present invention is a viscose rayon 
fiber, a cupro-ammonium rayon fiber or an acetate rayon fiber. The rayon 
fiber (staple) preferably has a tensile strength of about 2.0 to 4.0 g/D, 
an extension percentage of about 12 to 28%, an extension elastic modulus 
(in 3% extension) of about 50 to 85%, an initial Young's modulus of about 
400 to 950 kg/mm.sup.2, and a specific gravity of about 1.50 to 1.52. 
The polyester fiber used in the present invention is preferably a 
polyethylene terephthalate fiber prepared by polycondensation of 
terephthalic acid or dimethyl terephthalate and ethylene glycol. The 
polyester fiber (staple) preferably has a tensile strength of about 4.5 to 
6.8 g/D, an extension percentage of about 20 to 50%, an extension elastic 
modulus (in 3% extension) of about 90 to 99%, an initial Young's modulus 
of about 310 to 870 kg/mm.sup.2, and a specific gravity of about 1.37 to 
1.39. 
The acrylic fiber used in a single layer in the present invention 
preferably has a tensile strength of about 2.5 to 5.0 g/D, an extension 
percentage of about 25 to 50%, an initial Young's modulus of about 260 to 
650 kg/mm.sup.2, and a specific gravity of about 1.14 to 1.17. 
The mixed ratio of the rayon fiber and the polyester fiber is preferably 
30/70 to 95/5, more preferably 45/55 to 90/10. The preferred mixed ratio 
depends on the composition of a magnetic layer. 
The materials for the disk cartridge used in the present invention are 
mainly a vinyl chloride resin for 8 inch and 5.25 inch flexible magnetic 
disks and an ABS resin and a polystyrene resin for a 3.5 inch flexible 
disk based on JIS-X-6223 and JIX-X-6224. 
In the present invention, a fatty acid ester and an abrasive, as described 
below, having a Moh's hardness of 6 or higher are preferably added to the 
magnetic layer. They can improve the running durability in combination 
with the above mentioned prevention of mold growth. 
Examples of fatty acid esters used in the present invention include butyl 
caprylate, ethyl laurate, butyl laurate, octyl laurate, ethyl myristate, 
butyl myristate, octyl myristate, ethyl palmitate, butyl palmitate, ethyl 
stearate, butyl stearate, octyl stearate, amyl stearate, anhydrosorbitan 
monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, 
hexadecyl stearate, oleyl oleate, and lauryl alcohol. Of these, butyl 
myristate, butyl stearate, ethyl stearate, amyl stearate, hexadecyl 
stearate, and oleyl oleate are preferred. 
The ferromagnetic powders used for the magnetic recording disk of the 
present invention include .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, 
FeO.sub.x (x=1.33 to 1.5), CrO.sub.2, Co-containing Fe.sub.2 O.sub.3, 
Co-containing FeO.sub.x (x = 1.33 to 1.5), ferromagnetic metal powders, 
and tabular hexagonal ferrite powders. 
Particularly, use of ferromagnetic metal powders having a small grain size 
and barium ferrite ferromagnetic powders, which are suitable for high 
density recording, can effectively produce the advantages in the magnetic 
recording disk. However, where the ferromagnetic powders are the 
ferromagnetic metal powders and barium ferrite ferromagnetic powders each 
having the above small grain sizes, the magnetic layer is liable to be 
scratched by the liner especially in the high humidity. In the magnetic 
recording disk of the present invention, however, such problem has been 
reduced. 
Where the ferromagnetic powders are the ferromagnetic metal powders, the 
specific surface area thereof is preferably 30 to 60 m.sup.2 /g and the 
crystallite size measured by the X-ray diffraction method is 100 to 300 
.ANG.. 
Too small a specific surface area of the magnetic powders cannot 
sufficiently meet the requirements of high density recording, while too 
large a specific surface area prevents the magnetic powders from 
sufficiently dispersing and does not enable the smooth magnetic layer 
surface to be formed, which also unfavorably makes it impossible to meet 
the requirements of high density recording. 
The tabular hexagonal ferrite powders used in the present invention have a 
specific surface area of 20 to 50 m.sup.2 /g, a tabular ratio (tabular 
diameter/tabular thickness) of 2 to 6 and a grain length of 0.02 to 1.0 
.mu.m. 
For the same reasons as in the ferromagnetic metal powders, either too 
large or too small grain size thereof makes it difficult to record at a 
high density. 
The above ferromagnetic metal powders should contain Fe. Examples thereof 
include the metal elements or alloys mainly composed of Fe, Fe-Co, Fe-Ni 
and Fe-Ni-Co. 
In order t provide the magnetic recording disk of the present invention 
with a high density recording property, while the grain size of the 
ferromagnetic powders has to be small as described above, the saturation 
magnetization thereof is generally 110 emu/g or more, preferably 120 emu/g 
or more; the coercive force thereof is generally 800 Oe or more, 
preferably 900 Oe or more; and the axis ratio thereof is preferably 5 or 
more. 
In order to further improve the characteristics, the nonmetallic elements 
such as B, C, Al, Si and P sometimes may be contained in the composition 
of the ferromagnetic powders. Usually, an oxide layer is formed on the 
surface of the above ferromagnetic metal powders for chemical 
stabilization. 
Tabular hexagonal ferrite is a ferromagnetic powder which is tabular and 
has an axis of easy magnetization in the direction vertical to the plate 
thereof. Examples of the tabular hexagonal ferrite include barium ferrite, 
strontium ferrite, lead ferrite, calcium ferrite, and the 
cobalt-substituted compounds thereof. Of these, the cobalt-substituted 
compound of barium ferrite and the cobalt-substituted compound of 
strontium ferrite are preferred. If necessary, elements such as In, Zn, 
Ge, Nb and V may be added in order to improve the characteristics. 
In order to provide the magnetic recording disk of the present invention 
with a high density recording property, while the grain size of the above 
tabular hexagonal ferrite powders has to be small as described above, the 
saturation magnetization thereof is generally 50 emu/g or more, preferably 
53 emu/g or more. The coercive force thereof is generally 500 Oe or more, 
preferably 600 Oe or more. 
The binders used for the above magnetic layer of the flexible magnetic disk 
include thermoplastic resins, thermosetting resins, reaction type resins, 
and mixtures thereof. Examples of them include, for example, a vinyl 
chloride-vinyl acetate copolymer, other vinyl chloride type resins, an 
acrylic acid ester type copolymer, a methacrylic acid ester type 
copolymer, a urethane elastomer, a cellulose derivative, and an 
epoxypolyamid resin. Various polyisocyanates are used as a hardener. 
The above binders are used preferably in the amount of 5 to 300 parts by 
weight per 100 parts by weight of the ferromagnetic metal powders. 
Further, a suitable amount of a polar functional group such as a carboxylic 
acid group, a sulfonic acid group, a hydroxy group, an amino group and an 
epoxy group is preferably introduced into molecules of the binder in order 
to increase the dispersing property thereof. 
Compounds having various functions, such as an abrasive, a dispersant and 
an antistatic agent are usually added to the above magnetic layer. 
In the present invention, the abrasive having a Moh's hardness of 6 or more 
is preferably used. Examples of the abrasive include, for example, fused 
alumina, silicon carbide, chromium oxide, corundum, artificial corundum, 
diamond, artificial diamond, garnet, and emery (the main components: 
corundum and magnetite). These abrasives (i.e., abrasive agents) have a 
Moh's hardness of 6 or more and an average particle size preferably of 0.3 
to 1.0 .mu.m, more preferably 0.4 to 0.8 .mu.m. 
These abrasives are used in the amount of generally 5 parts by weight or 
more, preferably 5 to 20 parts by weight and more preferably 5 to 15 parts 
by weight, per 100 parts by weight of the ferromagnetic powder. An amount 
less than the above cannot provide sufficient durability and too much 
decreases the filled amount of the magnetic powders, which in turn results 
in an insufficient output. 
The following dispersant, lubricant and antistatic agent may be impregnated 
and adsorbed on the surfaces of the ferromagnetic powders in a solvent for 
the respective purposes prior to dispersing them. 
Examples of the dispersants which can be used for the magnetic layer 
include fatty acids having 10 to 22 carbon atoms (R.sub.1 COOH, in which 
R.sub.1 is an alkyl group having 9 to 21 carbon atoms), such as caprylic 
acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic 
acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and 
stearolic acid; alkali metal (Li, Na and K) salts and alkali earth metal 
(Mg, Ca and Ba) salts of the above fatty acids; metallic soaps comprising 
Cu and Pb; and lecithin. 
Additionally, higher alcohols having 4 or more carbon atoms (e.g., butanol, 
octyl alcohol, myristyl alcohol, and stearyl alcohol) and sulfuric acid 
ester thereof and phosphoric acid ester thereof can also be used. 
These dispersants are used in the range of 0.005 to 20 parts by weight per 
100 parts by weight of a binder. These dispersants may be deposited 
beforehand on the surfaces of the magnetic fine powders and non-magnetic 
fine powders or may be added in the middle of dispersing. 
Examples of the antistatic agents used for the magnetic layer include 
electroconductive powders such as graphite, carbon black, and a carbon 
black-grafted polymer; natural surfactants such as saponin; nonionic 
surfactants such as an alkylene oxide type, a glycerine type, a glycidol 
type, a polyhydric alcohol type, a polyhydric alcohol ester type, and an 
alkylphenol EO adduct; cationic surfactants such as higher alkylamines, 
cyclic amines, hydantoin derivatives, amidoamines, esteramides, quaternary 
ammonium salts, pyridine and other heterocyclic compounds, phosphoniums, 
and sulfoniums; anionic surfactants having an acid group such as a 
carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a 
sulfuric acid ester group, and a phosphoric acid ester group; amphoteric 
surfactants such as amino acids, aminosulfonic acids, sulfuric acid esters 
or phosphoric acid esters of aminoalcohols, and alkylbetains. 
In the present invention, the fatty acid ester is preferably added to the 
magnetic layer. Additionally, one of the following compounds may be used 
in combination with the fatty acid ester as a lubricant: silicon oil, 
graphite, molybdenum disulfide, boron nitride, fluorinated graphite, 
fluorinated alcohol, polyolefin (polyethylene wax), polyglycol 
(polyethylene oxide wax), alkylphosphoric acid ester, and tungsten 
disulfide. However, fatty acid, fatty acid amide and an ether compound 
increases torque at a high temperature, and, therefore, they should be 
carefully used. 
In the present invention, the above flexible magnetic disk comprises a 
magnetic layer provided on a nonmagnetic support. 
The supports used for the flexible magnetic disk are films and plates of 
various plastics and plastics compositions including polyester such as 
polyethylene terephthalate and polyethylene 2,6-naphthalate, polyolefin 
resins such as polypropylene, cellulose derivatives such as cellulose 
triacetate and cellulose diacetate, vinyl type resins such as polyvinyl 
chloride, a polycarbonate resin, a polyamide resin, a polyimide resin, a 
polyamidoimide resin, a polysulfone resin, and a polyethersulfone resin. 
These nonmagnetic supports may be formed in advance to the prescribed 
shapes, or may be formed to the prescribed shapes, for example, by cutting 
after coating a magnetic layer and a back layer described below. These 
nonmagnetic supports may be subjected to various pretreatments such as a 
corona discharge treatment, a plasma treatment, an undercoating treatment, 
a heat treatment, a metal evaporation deposition treatment, and an alkali 
treatment. 
The above components, to which an organic solvent is added, are dispersed 
and mixed to prepare a magnetic coating solution, followed by coating the 
solution on the support and drying, whereby a magnetic layer is provided 
on the nonmagnetic support. 
Examples of the organic solvents used for preparing the magnetic coating 
solution include ketones such as acetone, methyl ethyl ketone, methyl 
isobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran; alcohols 
such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl 
alcohol, and methyl cyclohexanol; esters such as methyl acetate, ethyl 
acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl 
lactate, and glycol acetate, monoethyl ether; glycol ethers such as ether, 
glycol dimethyl ether, glycol monoethyl ether, and dioxane; aromatic 
hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, and 
styrene; chlorinated hydrocarbons such as methylene chloride, ethylene 
chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and 
dicholobenzene; N,N-dimethylformaldehyde; and hexane. 
Mixing is carried out by placing the magnetic powder and the above 
respective components into a mixer either together or separately in 
sequence. For example, the magnetic powder can be added to a solvent 
containing a dispersant and mixing is continued for a prescribed time to 
prepare a magnetic coating solution. 
Various mixers can be used for the purpose of mixing the magnetic coating 
solution. Examples thereof are a two-rod roll mill, a three-rod roll mill, 
a ball mill, a pebble mill, a Trommel mill, a sand grinder, a Szegvari 
attriter, a high speed impeller disperser, a high speed stone mill, a 
disper, a kneader, a high speed mixer, a homogenizer, and a supersonic 
disperser. 
The techniques regarding mixing and dispersing can be selected from the 
methods described in Flowing of Dye and Pigment Dispersion written by T. 
C. Patton. Two or more layers may be provided simultaneously by the 
simultaneous multilayer coating method. 
In the present invention, the dry thickness of the magnetic layer of the 
flexible magnetic disk is about 0.5 to 12 .mu.m. In the case of multilayer 
coating, the total thickness of the coated layers falls within the above 
range. This dry thickness depends on the applications, shape and 
specification of the magnetic recording medium. 
The magnetic layer thus-coated on the non-magnetic support is subjected to 
a treatment for orienting the magnetic powders in the layer according to 
necessity, and then the formed magnetic layer is dried. If desired, the 
magnetic recording medium is subjected to a surface smoothing treatment, 
and then is cut to a prescribed form, whereby the magnetic recording disk 
of the present invention is prepared. 
In the present invention, it has been found that the magnetic recording 
medium subjected particularly to the surface smoothing treatment for the 
magnetic layer can have a smooth surface and an excellent wear resistance. 
This surface smoothing treatment is carried out by a smoothing treatment 
before drying and by a calendering treatment after drying. 
EXAMPLES 
The present invention will be explained in detail with reference to the 
following nonlimiting examples and comparative examples. Unless otherwise 
indicated, amounts are in parts or % by weight. 
EXAMPLE 1 
The following components were mixed and kneaded with a kneader for two 
hours to obtain a uniform mixed dispersion. 
______________________________________ 
Amount 
Components (part by weight) 
______________________________________ 
Ferromagnetic Powder 100 
Co-substituted Ba ferrite (specific 
surface area: 35 m.sup.2 /g, grain length: 
0.06 .mu.m, tabular ratio: 5) 
Binder Resin 10 
Vinyl chloride copolymer having 
a polar group (--SO.sub.3 Na group: 
8 .times. 10.sup.-5 equivalent/g, number average 
molecular weight: 75,000) 
Abrasive Particles 7 
Al.sub.2 O.sub.3 (average particle size: 0.3 .mu.m) 
Carbon Black 
Ketjen Black EC (average particle size: 
5 
30 .mu.m, manufactured by Lion Akzo 
Co., Ltd.) 
Thermacs MT (average particle size: 280 .mu.m, 
2 
manufactured by Carcarb Co., Ltd.) 
Solvent 
Toluene 36 
Methyl ethyl ketone 36 
______________________________________ 
The following components were added to the mixed dispersion thus-obtained, 
and the mixture was further dispersed with a sand grinder at 2,000 rpm for 
2 hours. 
______________________________________ 
Amount 
Components (part by weight) 
______________________________________ 
Binder Resin 5 
Polyester polyurethane resin having 
a polar group (--SO.sub.3 Na group: 
1 .times. 10.sup.-4 equivalent/g, weight average 
molecular weight: 35,000) 
Solvent 
Toluene 250 
Methyl ethyl ketone 250 
______________________________________ 
Further added to this dispersion were 6 parts by weight of polyisocanate 
Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) and 6 parts by 
weight of tridecyl stearate as a fatty acid ester and were uniformly 
mixed, whereby the magnetic coating solution in which the ferromagnetic 
powders were uniformly dispersed was obtained. 
This magnetic coating solution was applied on both sides of a polyethylene 
terephthalate film of 300 mm width and 75 .mu.m thickness by gravure 
coating so that the dry thickness thereof was 2.5 .mu.m. After drying at 
100.degree. C., the coated support was subjected to a pressure pressing 
treatment with a calendering roll at about 100.degree. C., whereby the 
magnetic recording medium sample was obtained. Then, the magnetic 
recording medium was punched to 3.5 inches. 
The nonwoven fabric subjected to the embossing finish and having a 
thickness (which is measured with a pressure of 50 g/cm.sup.2) of about 
220 .mu.m (the thickness of an acrylic fiber layer: about 120 .mu.m), in 
which a mixed yarn layer of a rayon (viscose rayon) fiber and a polyester 
(polyethylene terephthalate) fiber (mixed ratio: 5:5) was disposed on the 
magnetic layer side and the acrylic fiber layer on the other side (shell 
side, i.e., cartridge side), was prepared. The above 3.5 inch flexible 
magnetic recording disk was loaded in the cartridge case provided therein 
with the above nonwoven fabric as the liner, whereby the magnetic 
recording disk sample was prepared. 
EXAMPLE 2 
The magnetic recording disk sample was prepared in the same manner as 
Example 1, except that the liner was replaced with one in which an acrylic 
fiber layer as an inter layer was interposed between the rayon/polyester 
mixed yarn layer, wherein the thickness of the rayon/polyester mixed yarn 
layer was 50 .mu.m and that of the inter layer of the acrylic fiber was 
120 .mu.m. 
EXAMPLE 3 
The magnetic recording disk sample was prepared in the same manner as 
Example 1, except that the mixed ratio of rayon/polyester of 5:5 was 
changed to 35:65. 
EXAMPLE 4 
The magnetic recording disk sample was prepared in the same manner as 
Example 1, except that in place of 6 parts by weight of tridecyl stearate, 
5 parts by weight of oleyl oleate was used. 
COMATIVE EXAMPLE 1 
The magnetic recording disk sample was prepared in the same manner as 
Example 1, except that the liner was of the constitution in which the 
acrylic fiber layer was disposed on the magnetic layer side and the 
rayon/polyester mixed yarn layer was disposed on the shell side. 
COMATIVE EXAMPLE 2 
The magnetic recording disk sample was prepared in the same manner as 
Example 2, except that the liner was of the constitution in which in place 
of the acrylic fiber for the inter layer, a polypropylene fiber was used 
for the inter layer. 
COMATIVE EXAMPLE 3 
The magnetic recording disk sample was prepared in the same manner as 
Example 1, except that the liner was of the constitution in which the 
rayon/polyester mixed yarn layer alone was provided. 
Each of the magnetic recording disk samples thus-prepared was loaded and 
driven in the 3.5 inch floppy disk drive PD211 (manufactured by Toshiba 
Co., Ltd.) to carry out a 24 hour thermocycle test in which the following 
thermocycle flow shown in Table 1 was one cycle, with the head positioned 
at the track 12. 
TABLE 
______________________________________ 
Thermocycle Flow 
##STR1## 
______________________________________ 
Running durability was evaluated for the magnetic recording disk samples 
after running them 15 million times at the above thermocycle condition. 
The generation of foreign matter on the surface of the magnetic layer was 
evaluated in the following manner: each of the magnetic recording disk 
samples was allowed to stand at 23.degree. C. and 90% RH for two weeks, 
and then it was stored at room temperature for three more days after the 
temperature thereof was back to room temperature. Then, the disk cartridge 
was opened and the surface of the magnetic layer of the flexible magnetic 
disk was observed with an optical microscope of 125 magnification to 
evaluate the generation of foreign matter. The evaluation results were 
classified as G and B, wherein G means no generation of foreign matter was 
observed and B means the generation of foreign matter was observed. 
Further, the outputs of all trucks were measured every 500,000 passes and 
the output which was lowered to 45% or lower of the initial level was 
regarded as dropout. 
The cartridge case of each of the above samples was opened after running 
1,500 passes, and the surface of the magnetic layer was visually observed 
to evaluate the surface of the magnetic layer. The evaluation results were 
classified as G and B, wherein G means no change was observed on the 
surface of the magnetic layer, B means many fine scratches were observed 
on the surface thereof, and M means a few fine scratches were observed on 
the surface thereof. 
The torque change due to humidity was measured with the 3.5 inch floppy 
disk drive PD211 (manufactured by Toshiba Co., Ltd.) similarly to the 
measurement of the running durability. A floppy disk was loaded in the 
floppy disk drive and was run with a head off at 23.degree. C. and 50% RH 
to measure the torque loaded on the motor. Next, the atmospheric condition 
was changed to 23.degree. C. and 80% RH and the torque loaded on the motor 
was measured as well, and the increase in the torque was obtained in terms 
of rate of increase. 
The results thus obtained are summarized in Table 2. 
TABLE 2 
______________________________________ 
Generation 
of 
Foreign Running Durability 
Test B*2 
Matter Dropout Test A*1 (%) 
______________________________________ 
Example 1 
G None G 13 
Example 2 
G None G 17 
Example 3 
G None G 14 
Example 4 
G None G 21 
Compara- 
G Occurrence after 
B 18 
tive running 950 .times. 10.sup.4 
Example 1 passes 
Compara- 
B Occurrence after 
M 15 
tive running 300 .times. 10.sup.4 
Example 2 passes 
Compara- 
B None G 17 
tive 
Example 3 
______________________________________ 
*1:Surface of the magnetic layer after running 1,500 passes. 
*2:Torque increase rate. 
As is apparent from the above results, the samples of the invention 
prepared in Examples 1 to 4 had no generation of foreign matter 
attributable to the growth of molds and the running durability thereof was 
stable while they showed the characteristics of less increase in the 
torque in the high humidity. 
On the other hand, in Comparative Example 1, in which the rayon/polyester 
mixed yarn layer and the acrylic fiber layer were reversed with respect to 
the magnetic layer compared with the liner layer structure of Example 1, 
foreign matter was not generated due to the growth of molds, but scratches 
were generated on the surface of the magnetic layer in measurement of the 
running durability; in Comparative Example 2, in which the acrylic fiber 
in the inter layer was replaced with the polypropylene fiber, foreign 
matter was generated due to the growth of molds and much dropout was 
caused due to dust originated from the polypropylene fiber; and in 
Comparative Example 3, in which no acrylic fiber was present, foreign 
matter was generated due to the growth of molds. 
The present invention, in which the nonwoven fabric made of a 
rayon/polyester mixed yarn layer in the liner provided in the magnetic 
recording disk is provided on the side where it contacts with the magnetic 
layer and the nonwoven fabric made of an acrylic fiber layer is provided 
on the other side, can prevent molds from growing in the high humidity and 
improve the running durability of the magnetic recording disk. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.