Magnetic recording medium

A magnetic recording medium is disclosed which comprises a non-magnetic support having provided thereon a magnetic recording layer and a backing layer on the opposite surface thereof, wherein said magnetic recording layer contains a fatty acid, said backing layer contains a cellulose resin, and said non-magnetic support has a Young's modulus of 7.times.10.sup.10 to 1.times.10.sup.13 dyn/cm.sup.2.

FIELD OF THE INVENTION 
The present invention relates to a magnetic recording medium provided with 
a backing layer which the improves jitter characteristics of the magnetic 
recording medium. 
BACKGROUND OF THE INVENTION 
With the increased usage of compact video tape recorders (hereinafter 
"VTR"), it has been required that various characteristics of video tapes 
be improved. One of these characteristics is jitter. Jitter occurs as a 
result of the fluctuation of the time axis when a magnetic head 
mechanically scans a magnetic recording tape. Jitter deteriorates image 
quality on a TV monitor and color blur or unevenness occurs. The jitter 
results from uneven rotation of the video head, elongation or shrinkage of 
vide tapes, change of tape running speed, etc., where a VTR having a 
rotation type head is used. Prevention of jitter has been sought by 
improving the mechanics of the VTR, but such has not been sufficient. 
Extensive researches on materials to be used for magnetic recording layers, 
supports and backing layers have been made in order to improve the jitter 
characteristics of a magnetic recording tape, and as the result, it has 
been found in the present invention that a particular combination of (1) 
lubricants in a magnetic recording layer, (2) binders in a backing layer, 
and (3) a Young's modulus of a non-magnetic support, remarkably improve 
the jitter characteristic. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a magnetic recording 
medium having improved jitter characteristics. 
The object of the present invention has been met by providing a magnetic 
recording medium comprising: a non-magnetic support having provided 
thereon a magnetic recording layer and a backing layer on the opposite 
surface thereof, wherein said magnetic recording layer contains a fatty 
acid, said backing layer containing a cellulose resin and said support has 
a Young's modulus of 7.times.10.sup.10 to 1.times.10.sup.13 dyn/cm.sup.2. 
DETAILED DESCRIPTION OF THE INVENTION 
The cellulose resins used in this invention can include a cellulose 
derivative such as cellulose acetate butyrate, cellulose diacetate, 
cellulose triacetate, cellulose propionate, cellulose acetate propionate 
or nitrocellulose and the mixtures thereof as described in, for example, 
U.S. Pat. No. 4,135,016. The cellulose resins can be used in an amount of 
1 to 100 parts by weight, preferably 3 to 50 parts by weight and more 
preferably 5 to 25 parts by weight per 100 parts by weight of the magnetic 
substance. 
The fatty acid used in this invention can include caprylic acid, capric 
acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic 
acid, oleic acid, elaidic acid, linolic acid, linolenic acid, stearolic 
acid and the like as described in, for example, U.S. Pat. Nos. 4,135,016, 
4,411,960 and 4,171,406. Of these, lauric acid, palmitic acid, stearic 
acid, myristic acid and oleic acid are preferred. However, fatty acids 
should not be limited thereto and isomerized fatty acids and the mixture 
thereof can also be used. Fatty acids having 10 to 22 carbon atoms are 
easily available and have preferred characteristics. The amount of a fatty 
acid is preferably 0.01 to 10 and is more preferably 0.1 to 5 parts by 
weight per 100 parts by weight of ferromagnetic particles. 
Any conventional plastic supports such as polyethylene terephthalate, 
polyethylene naphthalate, polyamide, polyimide, triacetyl cellulose and 
other supports as described in, for example, U.S. Pat. No. 4,135,016 can 
be used in the present invention. Preferred plastic support includes 
polyethylene terephthalate. A metal thin film can be used, if desired. The 
above-mentioned plastic supports can be provided on their furface with a 
layer of aluminum, copper, nickel or zinc which is deposited by vacuum 
evaporation. 
It is necessary that the support has a Young's modulus of 7.times.10.sup.10 
to 1.times.10.sup.-- dyn/cm.sup.2, preferably 8.times.10.sup.10 to 
8.times.10.sup.11 dyn/cm.sup.2, in the main direction. The term "main 
direction" referred to herein indicates the direction in which recording 
is carried out by the magnetic recording system. For example, it is 
necessary for various tapes for audio recording (3.8 mm width Phillips 
type compact cassette, 1/4 inch open reel, 1/4 inch endless cartridge) to 
have a Young's modulus of 7.times.10.sup.10 to 1.times.10.sup.13 
dyn/cm.sup.2, preferably 8.times.10.sup.10 to 8.times.10.sup.11 
dyn/cm.sup.2 in the machine (longitudinal) direction. It is necessary for 
video tapes of 2 inches width for broadcasting to have a Young's modulus 
of 7.times.10.sup.10 to 1.times.10.sup.13 dyn/cm.sup.2, preferably 
8.times.10.sup.10 to 8.times.10.sup.11 dyn/cm.sup.2 in the transverse 
direction because video signals are recorded in the tape width direction 
(transversal direction) by a four head system. Yet it is more preferably 
for those tapes to have a Young's modulus of 7.times.10.sup.10 to 
1.times.10.sup.13 dyn/cm.sup.2, preferably 8.times.10.sup.10 to 
8.times.10.sup.11 dyn/cm.sup.2 in the machine direction because audio 
signals are recorded in the machine direction. 
It is necessary for video tapes of 1 inch for broadcasting, compact video 
tapes of 1/2 inch (VHS system, Beta format system, and the like), and 
Umafic video tape of 3/4 inch to have a Young's modulus of 
7.times.10.sup.10 to 1.times.10.sup.13 dyn/cm.sup.2, preferably 
8.times.10.sup.10 to 8.times.10.sup.11 in the machine direction because 
both of video signals and audio signals are actually recorded in the 
machine direction. 
A method for preparing a magnetic coating composition used in this 
invention is disclosed in detail in Japanese Patent Publication No. 
26890/81. 
Ferromagnetic fine particles used in this invention include 
.gamma.-Fe.sub.2 O.sub.3, Co-containing .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 
O.sub.4, Co-containing Fe.sub.3 O.sub.4, Bertholide compound of 
.gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 (FeOx, 1,33&lt;x&lt;1.50), 
Bertholide compound of Co-containing .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 
O.sub.4 (FeOx, 1.33&lt;x&lt;1.50), CrO.sub.2, Co-Ni-P alloy, Co-Ni-Fe alloy, 
Co-Ni-Fe-B alloy, Fe-Ni-Zn alloy, Fe-Mn-Zn alloy, Fe-Co-Ni-P alloy, Ni-Co 
alloy, plate-shape barium ferrite and those conventionally used 
ferromagnetic particles. Specific examples are disclosed in Japanese 
Patent Publication No. 26890/81. 
Thermoplastic resins which can be used in the magnetic recording layer 
include those having a softening point of not higher than 150.degree. C., 
a number average molecular weight of 10,000 to 200,000, and a 
polymerization degree of about 200 to 2,000, e.g., a copolymer of vinyl 
chloride and vinyl acetate, a copolymer of vinyl chloride and vinylidene 
chloride, a copolymer of vinyl chloride and acrylonitrile, a copolymer of 
acrylte and acrylonitrile, a copolymer of acrylate and vinylidene 
chloride, a copolymer of acrylate and styrene, a copolymer of methacrylate 
and acrylonitrile, a copolymer of methacrylate and vinylidene chloride, a 
copolymer of methacrylate and styrene, urethane elastomer, polyvinyl 
fluoride, a copolyer of vinylidene chloride and acrylonitrile, a copolymer 
of butadiene and acrylonitrile, a polyamide resin, polyvinyl butyral, a 
cellulose derivative (cellulose acetate butyrate, cellulose diacetate, 
cellulose triacetate, cellulose propionate, nitrocellulose and the like), 
a copolymer of chlorovinyl ether and acrylate, an amino resin, various 
synthetic rubber type thermoplastic resin and the mixture thereof as 
described in U.S. Pat. No. 4,135,016. Of these, a copolymer of vinyl 
chloride and vinyl acetate, a copolymer of vinyl chloride and vinylidene 
chloride, a urethane elastomer and a cellulose derivative are preferred. 
Specific examples of those resins are disclosed in Japanese Patent 
Publication No. 26890/81. The amount of the thermoplastic resins which can 
be used is 1 to 100 parts by weight, preferbly 3 to 60 parts by weight and 
more preferably 5 to 30 parts by weight per 100 parts by weight of the 
magnetic substance. 
The molecular weight of curing agents used for a magnetic recording layer 
is not higher than 200,000, preferably 50 to 10,000, in the state of the 
coating composition, and becomes infinite by the reaction, such as a 
condensation reaction or addition reaction, after coating and drying the 
coating layer. Of resins useful for the curing agents, those that do not 
soften nor melt until the resins are heat-decomposed are preferred. 
Specifically, those resins include a phenol resin, an epoxy resin, a 
curable polyurethane resin, a urea resin, a melamine resin, an alkyd 
resin, a silicone resin, an acryl type reactive resin, a mixture of a high 
molecular polyester resin and an isocyanate prepolymer, a mixture of a 
copolymer of methacrylate and a diisocyanate prepolymer, a mixture of 
polyester polyol and polyisocyanate, a urea formaldehyde resin, a mixture 
of a low molecular glycol/high molecular diol/triphenyl methane 
triisocyante, a polyamine resin and a mixture thereof. Of these, 
polyisocyanate based resins are preferred. Preferably, the curing agent is 
used in an amount of 1 to 50 parts by weight per 100 parts by weight of 
the magnetic substance. 
The typical examples of resins for the curing agents are disclosed in 
Japanese Patent Publication No. 26890/81. 
Lubricants which can be used in this invention include silicone oil, carbon 
black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acid 
esters composed of a monobasic fatty acid having 12 to 16 carbon atoms and 
monohydric alcohol having 3 to 12 carbon atoms and a fatty acid esters 
consisting of a monobasic fatty acid having not less than 17 carbon atoms 
and a monohydric alcohol having 21 to 23 carbon atoms inclusive of the 
number of carbon atoms of the fatty acid. These lubricants can be added in 
an amount of 0.2 to 20, preferably 0.5 to 10, parts by weight per 100 
parts by weight of the binder. Details thereof are disclosed in Japanese 
Patent Publication No. 26890/81. 
Abrasive which can be used in this invention include those commonly used 
such as fused alumina, silicone carbide, chrome oxide, corundum, 
artificial corundum, diamond, artificial diamond, garnet, and emery (main 
component, corundum and magnetite). The average particle diameter is 0.05 
to 5.mu. and is preferably 0.1 to 2.mu.. These abrasives can be added in 
an amount of 7 to 20, preferably 10 to 15, parts by weight per 100 parts 
by weight of the binder. Details thereof are disclosed in Japanese Patent 
Publication No. 26890/81. 
Nonionic surfactants such as alkylene oxides, glycerols and glycidols; 
cationic surfactants such as higher alkyl amines, quaternary ammonium 
salts, heterocyclic compounds (e.g., pyridine), phosphoniums or 
sulfoniums; anionic surfactants having an acid group such as carboxylic 
acid, sulfonic acid, phosphoric acid, sulfate or phosphate; and amphotric 
surfactants such as amino acids, amino sulfonic acids, sulfates or 
phosphates of aminoalcohols can be used in this invention. 
These surfactants can be used alone or in combination. The amount of the 
surfactants is 0.1 to 5 parts by weight per 100 parts by weight of the 
magnetic substance. These surfactants can be used as an antistatic agent. 
However, they can also be used for other purposes, e.g., for improving the 
dispersing property, the magnetic characteristics and the lubricity and as 
a coating aid. 
The magnetic recording layer can be prepared by dissolving a coating 
composition in an organic solvent and coating it on a non-magnetic support 
at a dry thickness of 0.1 to 20.mu., preferably 1 to 15.mu. and more 
preferably 2 to 10.mu.. 
Magnetic particles, the above-mentioned binders, dispersing agents, 
lubricants, abrasives, antistatic agents and solvents are mixed and 
kneaded to prepare a magetic coating composition. 
The magnetic particles and other components can be put into a mixing and 
kneading device at the same time or in sequence. For example, there is a 
method in which magnetic particles are first added into a solvent 
containing a dispersing agent and mixed and kneaded for a predetermined 
period of time, and then the rest of the components are added and mixed 
and kneaded to prepare a magnetic coating composition. 
Various mixing-kneading devices are used to mix, knead and disperse. For 
example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, 
trommel, a sand grinder, Szegvari attritor, a high speed impeller 
dispersing device, a high speed stone mill, a high speed impact mill, a 
disper, a kneader, a high speed mixer, a homogenizer and an ultrasonic 
dispersing device. 
The art of mixing, kneading and dispersing is disclosed in T. C. Patton: 
Paint Flow and Pigment Disperion (1964, John Wiley & Sons Co., Ltd.). It 
is also described in U.S. Pat. Nos. 2,581,414 and 2,855,156. 
The method for providing a magnetic recording layer on a support includes 
air doctor coating, blade coating, air knife coating, squeeze coating, 
impregnating coating, reverse roll coating, transfer roll coating, gravure 
coating, kiss coating, cast coating and spray coating and other coating 
methods. Those methods are described in detail in Coating Engineering on 
pages 253 to 277 by Asakura Shoten (Mar. 20, 1971). 
Organic solvents which can be used for coating include ketones such as 
acetone, methyl ethyl ketone, methyl isobutyl ketone or cyclohexanone; 
alcohols such as methanol, ethanol, propanol or butanol; esters such as 
methyl acetate, ethyl acetate, butyl acetate, ethyl lactate or monoethyl 
ether of glycol acetate; glycol ethers such as ether, glycol dimethyl 
ether, glycol monoethyl ether or dioxane; tars (aromatoc hydrocarbon) such 
as benzene, toluene or xylene; chlorinated hydrocarbons such as methylene 
chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene 
chlorohydrin or dichlorobenzene as described in, for example, U.S. Pat. 
No. 4,135,016. Of these, methyl ethyl ketone, methyl isobutyl ketone, 
cyclohexanone, butanol, butyl acetate, toluene and xylene are preferred. 
The solvents can be used in an amount of 100 to 1,000 parts by weight, 
preferably 150 to 750 parts by weight and more preferably 200 to 500 parts 
by weight per 100 parts by weight of the magnetic substance. 
The magnetic recording layer coated on a support by the above mentioned 
manner is, if desired, subjected to magnetic orientation to orientate the 
magnetic particles therein and is dried. If desired, the magnetic 
recording layer is subjected to a surface smoothing treatment and slit to 
a predetermined shape to prepare the magnetic recording medium of this 
invention. 
A magnetic orientation field can be applied with either an alternate or 
direct current of about 500 to 2,000 gauss. The drying temperature is 
about 50.degree. to 100.degree. C. and the period for drying is about 3 to 
10 minutes. 
Carbon black and graphite can be mixed into the backing layer to provide 
antistatic properties. The amount of carbon black and/or graphite is 0.1 
to 10 parts by weight, preferably 0.5 to 5 parts by weight and more 
preferably 1 to 3 parts by weight per 100 parts by weight of the binder. 
Inorganic pigments such as magnesium silicate, calcium carbonate, aluminum 
silicate, barium sulfate or clay and organic particles such as 
benzoguanamine or polyethylene terephthalate can be added into the backing 
layer to adjust surface roughness of the coated layer to improve running 
properties and durability. The inorganic pigment and/or organic particles 
can be added in an amount of 10 to 300 parts by weight, preferably 15 to 
200 parts by weight and more preferably 50 to 150 parts by weight per 100 
parts by weight of the binder. 
The above-mentioned surfactants, abrasives and lubricants used for the 
magnetic recording layer can be used for the backing layer. 
Binders except cellulose resins and organic solvents can be used for the 
magnetic recording layer can be used for the backing layer in an amount of 
0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight and more 
preferably 1 to 3 parts by weight per 100 parts of the binder.

The techniques of preparing a coating composition for a magnetic recording 
layer and of coating the composition can also be used for preparing a 
coating composition for the backing layer and for coating the composition. 
This invention will be further explained in more detail by the following 
Examples. In those Examples, all parts are by weight. 
EXAMPLE 1 
Composition for the Magnetic Recording Layer 
Co-added .gamma.-Fe.sub.2 O.sub.3 (Particle size 0.35.mu., acicular ratio 
1:8, Coercive force 650 Oe): 300 parts 
Fatty acid (Oleic acid): 6 parts 
Copolymer of vinyl chloride and vinyl acetate (vinyl chloride:vinyl 
acetate=87:13, polymerization degree 420): 30 parts 
Polyester polyurethane (synthesized from butylene adipate and 4,4'-diphenyl 
methane diisocyanate, styrene equivalent molecular weight about 130,000): 
30 parts 
Cr.sub.2 O.sub.3 : 12 parts 
Butyl acetate: 600 parts 
The above composition was dispersed in a ball mill for 48 hours. To the 
dispersion, 40 parts of "Desmodule L-75" (solid content: 30 parts, 75 wt% 
ethyl acetate solution of an adduct of 1 mole of trimethylol propane and 3 
moles of toluylene diisocyanate) were added and dispersed for 30 min. 
Then, the dispersion was filtrated by a filter having an average pore size 
of 1.mu. to prepare a magnetic coating composition. 
A coating composition for the backing layer having the following 
composition was coated on a polyethylene terephthalate film (Young's 
modulus of 8.times.10.sup.10 dyn/cm.sup.2 in the machine direction) having 
a thickness of 14.mu.. Then the above magnetic coating composition was 
coated thereon by a doctor coating method. The magnetic layer was 
subjected to magnetic orientation in the machine direction and to a 
calendering treatment. Then, it was slit to a width of 1/2 inch to prepare 
a video tape for VHS (Sample No. 1). 
Composition of the Backing Layer 
Cellulose resin (nitrocellulose, H.1/2): 400 parts 
Desmodule L-75: 133 parts 
Carbon black (furnace black, particle size 60 m.mu.): 300 parts 
Methyl ethyl ketone: 2000 parts 
Methyl isobutyl ketone: 2000 parts 
The above composition without the curing agent for the backing layer was 
dispersed in a ball mill for 90 hours. To the dispersion, the curing agent 
was added, and after adjusting the viscosity of the mixture, it was 
filtrated by a filter having a pore size of 5.mu. and coated. 
The thickness of the magnetic recording layer was 5.mu. and that of the 
backing layer was 1.5.mu.. 
COMATIVE EXAMPLE 1 
The same procedrue as in Example 1 was repeated except that the following 
coating composition was used to prepare Sample Nos. 2 to 5. 
Sample No. 2 was prepared without a fatty acid in the magnetic recording 
layer. 
Sample No. 3 was prepared using liquid paraffin instead of a fatty acid. 
Sample No. 4 was prepared without a cellulose resin in the backing layer, 
using additionally "Desmodule L-75" in the same amount as the cellulose 
resin. 
Sample No. 5 was prepared using a copolymer of vinyl chloride and vinyl 
acetate used for the magnetic recording layer in Example 1 instead of a 
cellulose resin. 
COMATIVE EXAMPLE 2 
The same procedure as in Example 1 was repeated except that a polyethylene 
terephthalate support having a Young's modulus of 5.times.10.sup.10 
dyn/cm.sup.2 was used to prepare Sample No. 6. 
EXAMPLE 2 
The same procedrue as in Example 1 was repeated except that a polyethylene 
terephthalate support having a Young's modulus of 7.times.10.sup.10 
dyn/cm.sup.2 was used to prepare Sample No. 7. 
EXAMPLE 3 
The same procedure as in Example 1 was repeated except that a polyethylene 
terephthalate support (Young's modulus of 5.times.10.sup.10 dyn/cm.sup.2) 
which was vapor deposited with aluminum to have a Young's modulus of 
10.times.10.sup.10 dyn/cm.sup.2 in the machine direction was used to 
prepare Sample No. 8. 
EXAMPLE 4 
Sample Nos. 9 and 10 were prepared in the same manner as in Example 1 
except that the type of a fatty acid (oleic acid) in the mangetic 
recording layer and the type of a cellulose resin (nitrocellulose, H.1/2) 
in the backing layer were changed. 
______________________________________ 
Sample No. Fatty Acid Cellulose Resin 
______________________________________ 
No. 9 Stearic acid 
Acetyl butyl cellulose 
No.10 Lauric acid Acetyl propyl cellulose 
______________________________________ 
Video tapes of Samples Nos. 1 to 10 were mounted on a video cassette for 
VHS and the results of the evaluation of jitter are shown in the Table. 
It is clear from the Table that jitter can be improved in this invention 
where the following three conditions simultaneously are met, that is, (1) 
a fatty acid is included in the magnetic recording layer, (2) a cellulose 
resin is included in the backing layer and (3) the Young's modulus of the 
support is 7.times.10.sup.10 dyn/cm.sup.2. 
Regarding Sample No. 4, the coating composition for the backing layer was 
filtrated with difficulty and the final tape could not be prepared. 
TABLE 1 
__________________________________________________________________________ 
Fatty Acid Young's Modumuls of 
Sample 
in Magnetic 
Cellulose Resin in 
support: dyn/cm.sup.2 
Jitter 
No. Recording Layer 
Backing Layer 
(Machine Direction) 
Characteristics 
__________________________________________________________________________ 
Example 1 
1 Oleic Acid 
Nitrocellulose 
8 .times. 10.sup.10 
.circle. 
Comparative 
2 None " " XX 
Example 1 
Comparative 
3 None (liquid 
" " X 
Example 1 Paraffin) 
Comparative 
4 Oleic Acid 
None " Sample could not 
Example 1 be prepared 
Comparative 
5 " None (Copolymer 
" X 
Example 1 of Vinyl Chloride - 
Vinyl Acetate) 
Comparative 
6 " Nitrocellulose 
5 .times. 10.sup.10 
X 
Example 2 
Example 2 
7 " " 7 .times. 10.sup.10 
.circle. 
Example 3 
8 " " 10 .times. 10.sup.10 
.circleincircle. 
Example 4 
9 Stearic Acid 
Acetyl Butyl 
8 .times. 10.sup.10 
.circle. 
Cellulose 
Example 4 
10 Lauric Acid 
Acetyl Propyl 
" .circle. 
Cellulose 
__________________________________________________________________________ 
The evaluation method was as follows: 
A gray scale signal (gradation wave) was recorded on each tape sample which 
were counted on a VTR of a VHS system and the jitter amount (.mu.sec) was 
visually observed where the horizontal axis or reproduced images on a 
monitor television were enlarged 10 times. The jitter characteristics are 
shown by the following marks. 
.circleincircle. : less than 0.1 .mu.sec. 
.circle. : not less than 0.1 .mu.sec to less than 0.2 .mu.sec 
X: not less than 0.2.mu. to less than 0.3 .mu.sec 
XX: not less than 0.3 .mu.sec 
While the invention has been described in detail and with reference to 
specific embodiment 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.