Magnetic recording medium

A magnetic recording medium is disclosed which comprises a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic metal particles and a binder, wherein the ferromagnetic metal particles have a specific surface area of 30 m.sup.2 /g or more, and a saturation magnetization of 120 emu/g or more and have been surface-treated with an organic compound. Also, a magnetic recording medium is disclosed which comprises a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic particles and a binder, wherein the ferromagnetic particles have been surface-treated with an organic compound and the binder has essentially no functional groups which adsorb onto ferromagnetic metal particles.

FIELD OF THE INVENTION 
The present invention relates to a magnetic recording medium, and more 
particularly it relates to an inproved magnetic recording medium using 
ferromagnetic metal particles. 
BACKGROUND OF THE INVENTION 
Commonly used iron oxide type fine particles and ferromagnetic metal 
particles which are used for improving a magnetic recording density and a 
reproduced output because of their high saturation magnetization and high 
coercive force have been investigated as ferromagnetic particles. 
The dispersibility of ferromagnetic particles has continuously been 
improved in order to improve the characteristics of a magnetic recording 
medium, particularly the electromagnetic properties such as the 
sensitivities of S/N ratio. However, ferromagnetic metal particles have 
problems in that the particles readily aggregate because of their high 
magnetization. Thus, a coating composition having the particles well 
dispersed therein cannot be obtained. As a result, a smooth magnetic layer 
having a good surface property cannot be obtained. 
Additionally, ferromagnetic metal particlas are easily oxidized and are 
unstable in air. A magnetic tape (a metal tape) prepared using 
ferromagnetic metal particles thus has a tendency that the magnetization 
is reduced (demagnetization) particulary when the tape is exposed to high 
humidity. 
It is necessary that the particle size of the ferromagnetic metal particles 
is minimized and that the saturation magnetization (.sigma.s) is increased 
in order to improve the sensitivity and S/N of a magnetic recording medium 
(or a magnetic metal tape) using ferromagnetic metal particles. 
However, as the particle size is minimized and as saturation magnetization 
is increased, the dispersibility and stability of the magnetic 
characteristics deteriorates. 
Various methods for providing ferromagnetic particles with a surface 
treatment have been proposed in order to improve the dispersibility of the 
ferromagnetic particles and to improve the demagnetization of the 
ferromagnetic metal particles are described, for example, in U.S. Pat. 
Nos. 3,700,499, 3,284,358, 4,420,330 and 4,369,076. 
One of the methods which is commonly employed is forming an oxide layer on 
the surface of the ferromagnetic metal particles. However, this does not 
provide satisfactory results. Further, a chemical treatment and a method 
for chemically connecting organic compounds such as a complex and a 
coupling agent on the surface of the ferromagnetic metal particles have 
also been proposed. 
Of the proposals, the method for chemically connecting organic compounds on 
the surface of the particles is the most efficient because the caking 
phenomenon hardly occurs among the particles at the time of treatment and 
the treating agent does not separate from the surface of particles. 
Further, the dispersibility of particles is greatly improved at the time 
of mixing a binder in the coating composition. However, the surface 
property of a magnetic layer which is coated and dried is not greatly 
improved and on the contrary, it often happens that the surface property 
thereof is worse than that of a magnetic layer comprising particles which 
have not been subjected to surface treatment. 
The above problem is more serious as the amount of an organic compound 
which connects on the surface of particles increases. 
A certain amount of an organic compound is necessary in order to prevent 
ferromagnetic metal particles from demagnetization. But this method is not 
satisfactory because of the above described problem. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a magnetic recording 
medium having excellent electromagnetic properties. 
A second object of the present invention is to provide a magnetic recording 
medium using ferromagnetic metal particles which are stable and have low 
demagnetization. 
A third object of the present invention is to provide a method for 
preparing a magnetic recording medium which comprises easily dispersing 
ferromagnetic metal particles with a binder. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to (1) a magnetic recording medium comprising 
a non-magnetic support having provided thereon a magnetic layer consisting 
mainly of ferromagnetic metal particles and a binder, wherein the 
ferromagnetic metal particles have specific surface area of 30 m.sup.2 /g 
or more and a saturation magnetization of 120 emu/g or more, and wherein 
the particles have been subjected to surface treatment with an organic 
compound, and it relates to (2) a magnetic recording medium comprising a 
non-magnetic support having provided thereon a magnetic layer consisting 
mainly of ferromagnetic particles and a binder, wherein the ferromagnetic 
particles have been subjected to surface treatment with an organic 
compound, and wherein the binder has substantially no functional groups 
which adsorb the ferromagnetic particles. 
The surface treatment in the present invention comprises a method for 
treating with a fatty acid, a metal salt of a fatty acid, a complex, a 
coupling agent, an isocyanic acid compound, an isocyanate, an oligomer 
having various functional groups and an organic compound having a reactive 
group or functional group which easily coats the surface of the 
ferromagnetic metal particles and a method for coating a polymer layer on 
the surface of the ferromagnetic metal particles by reacting a 
polymerizable monomer thereon. The amount of an organic compound used for 
coating is 0.2 wt% or more, preferably 0.5 wt% or more, and 20 wt% or 
less, preferably 10 wt% or less. 
In short, the surface treatment referred to in the present invention means 
that various organic compounds which will be illustrated hereinafter are 
made to coat the surface of the ferromagnetic metal particles by a 
chemical reaction or similar reaction force. Therefore, even though the 
ferromagnetic metal particles which have been subjected to a surface 
treatment are washed by an organic solvent having strong dissolving power 
such as methyl ethyl ketone or tetrahydrofuran, the organic compound 
coated on the surface of particles are hardly removed therefrom. If any, 
only 20% or less of the organic compound coated on the surface are removed 
therefrom. 
Many methods of surface treatment have been proposed and known. 
Surface tretment using a coupling agent is disclosed in Japanese Patent 
Application (OPI) Nos. 111829/1982, 60535/1982, 104594/1976, 109498/1976, 
125539/1980 and 111829/1982 (the term "OPI" as used herein means a 
"published unexamined Japanese Patent Application"). Surface treatment 
using a chrome complex is disclosed in Japanese Patent Application (OPI) 
No. 72498/1977. Surface treatment using metal alkolate and metal alkoxide 
is disclosed in Japanese Patent Application (OPI) Nos. 13548/1982, 
120704/1983, 63601/1982 and 50599/1977, and U.S. Pat. No. 4,330,600. 
Surface treatment using an isocyanate compound is disclosed in Japanese 
Patent Publication Nos. 4122/1975 and 115506/1975, and U.S. Pat. No. 
3,964,939. 
Surface treatment using a fatty acid and a metal salt of a fatty acid is 
disclosed in Japanese Patent Application Nos. 143521/1981, 4199/1974, 
116114/1978, Japanese Patent Publication Nos. 20116/1968, Japanese Patent 
Application (OPI) Nos. 97738/1974, 13906/1978 and 8798/1978. 
Surface treatment of coating the surface of particles with a polymer is 
disclosed in Japanese Patent Application (OPI) Nos. 102606/1976, 
134752/1979, 134753/1979, 15280/1980 and 15281/1980, and U.S. Pat. No. 
4,073,977. 
Surface treatment using the other organic compounds is disclosed in 
Japanese Patent Publication Nos. 19056/1982, 342/1982, 4470/1969, Japanese 
Patent Application (OPI) Nos. 62904/1981, 62905/1981, 62906/1981, 
119696/1979, 152067/1983, 142949/1983, 155703/1983, 186907/1983 and 
205929/1983. 
A binder used together with the ferromagnetic metal particles in the 
present invention is a conventionally known thermoplastic resin, a 
thermosetting resin or a mixture thereof. Specific examples include a 
cellulose type resin, a copolymer of polyvinyl chloride type, a 
polyurethane type resin, which can be hardened by an isocyanate compound, 
a butadiene type resin, a copolymer of acryle type and an epoxy type 
resin. these binders can be used alone or in combination and additives can 
be added thereto. The binder can be used in an amount of 10 to 50, 
preferably 15 to 35, and more preferably 20 to 30, parts by weight based 
on 100 parts by weight of the ferromagnetic metal particles. 
The binder used in the present invention is preferably a non-polar polymer 
or an oligomer which does not have any functional group which easily 
adsorbs onto the surface of the ferromagnetic metal particles, or which 
has a functional group in such a slight amount that the functional group 
does not essentially adsorb onto the surface of the particles. The amount 
of the functional group is preferably 0.03 wt% or less based on the total 
amount of the binder. Specific examples of the functional group is a 
hydroxy group, a carboxyl group, a sulfonic acid group, a phosphoric 
group, etc. 
The binder which does not adsorb on the surface of the ferromagnetic 
particles is a thermosetting resin, a thermoplastic resin, a reactive type 
resin or a mixture thereof which is generally used for a magnetic 
recording medium. Specific examples include a copolymer of vinyl chloride 
and vinyl acetate, an acrylic type resin, an epoxy type resin, a polyamide 
resin, a butadiene type resin, a urethane elastomer and a curable 
isocyanate resin. The degree of polymrization is preferably 100 to 10,000. 
The above described binders can be used alone or in combination. 
When a binder having a functional group is used in combination, the total 
amount of the functional group is preferably 0.03 wt% or less based on the 
total amount of the binder. 
Ferromagnetic particles used in the present invention include 
.gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, CrO.sub.2, Co-FeOx (x=1.33 to 
1.50), and Ba-ferrite particles as described, e.g., in U.S. Pat. Nos. 
4,305,921, 4,251,504 and 3,046,158. 
In the present invention, ferromagnetic metal particles are the most 
preferred. The methods for preparing ferromagnetic metal particles are 
illustrated as follows. 
(1) A method which comprises heat-decomposing an organic acid salt of the 
ferromagnetic metal particles and reducing it with a reducing gas as 
described, e.g., in U.S. Pat. Nos. 3,186,829 and 3,190,748. 
(2) A method of reducing acicular oxyhydroxides, metal containing 
oxyhydroxides or acicular iron oxide obtained from the oxyhydroxides 
(method of reducing iron oxide) as described, e.g., in U.S. Pat. Nos. 
3,598,568, 3,634,036, 3,607,219 and 3,607,220. 
(3) A method of evaporating ferromagnetic metal in an inactive gas under a 
low pressure (low vacuum evaporation method) as described, e.g., in U.S. 
Pat. No. 4,197,347. 
(4) A method of heat-decomposing a metal carbonyl compound as described, 
e.g., in U.S. Pat. Nos. 2,983,997 and 3,172,776. 
(5) A method which comprises electrodepositing ferromagnetic metal 
particles using a mercury cathode and separating them from mercury as 
described, e.g., in U.S. Pat. Nos. 3,198,777 and 3,156,650. 
(6) A method of reducing metal salts which form ferromagnetic particles in 
an aqueous solution with a reducing substance such as a boron hydride 
compound, a hypophosphite or a hydrazine as descrobed, e.g., in U.S. Pat. 
Nos. 3,607,218, 3,756,866 and 3,206,338. 
In the present invention, ferromagnetic metal particles prepared in 
accordance with the above-described methods (2), (3) and (6) are easy to 
use and particularly particles prepared in accordance with method (2) are 
the most preferred in view of low cost and high quality. Upon preparing 
ferromagnetic metal particles of the present invention, it is preferred 
that an oxide layer is coated on the surface of particles according to the 
methods described in Japanese Patent Application (OPI) Nos. 67798/77, 
140221/78 and 16601/81 to improve the chemical stability of the metal 
particles. 
Ferromagnetic metal particles are composed of pure iron or an alloy such as 
Fe, Fe--Ni, Fe--Ni--Co and can further contain non-magnetic or 
non-metallic elements such as B, C, N, Al, Si, P, S, Ti, Cr, Mn, Cu or Zn 
in a slight amount, e.g., 0.01 to 10 wt%, preferably 0.05 to 5 wt% based 
on the total composition. In order to realize the present invention the 
most effectively, specific surface area of ferromagnetic metal particles 
is 30 m.sup.2 /g or more and preferably 40 m.sup.2 /g or more. 
Necessary saturation magnetization of ferromagnetic metal particles in 120 
emu/g or more, preferably 125 emu/g or more. the residual magnetization 
(Br) or a magnetic layer can be increased using magnetic particles having 
high saturation magnetization, whereby a magnetic recording medium having 
high video sensitivity can be obtained. 
The above described ferromagnetic metal particles are mixed and kneaded 
with a binder to prepare a magnetic coating composition. 
The binder is used in an amount of 8 to 25 parts by weight, preferably 15 
to 25 parts by weight based on 100 parts by weight of the ferromagnetic 
metal particles. 
The method of preparing a magnetic recording medium by mixing and kneading 
ferromagnetic metal particles which are subjected to surface treatment as 
described above, and by coating the thus prepared magnetic coating 
composition on the non-magnetic support is a generally known method. 
A magnetic coating composition mainly contains ferromagnetic metal 
particles, a binder and a solvent for coating and further can contain a 
dispersing agent, a lubricating agent, an abrasive agent and an antistatic 
agent as additives. 
The dispersing agents (wetting agents for pigment) are a fatty acid having 
12 to 18 carbon atoms (R.sub.1 COOH, where R.sub.1 is an alkyl or an 
alkenyl group having 11 to 17 carbon atoms) such as caprylic acid, capric 
acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, 
elaidic acid, linolic acid, linolenic acid or stearol acid; metal soap 
consisting of alkali metal (e.g., Li, Na, K and the like) or alkaline 
earth metal (Mg, Ca, Ba) of the fatty acid; a fluorine-containing ester of 
the fatty acid; an amide of the fatty acid; polyalkylene oxide alkyl 
phosphate; lecithin; trialkyl polyolefin oxyquaternary ammonium salt 
(alkyl group having 1 to 5 carbon atoms, olefin such as ethylene, 
propylene and the like). In addition to the above, higher alcohols having 
12 or more of carbon atoms and sulfates can be also used. These dispersing 
agents can be used in an amount of 0.5 to 20 parts, preferably 0.5 to 2 
parts, by weight based on 100 parts by weight of the binders. 
The antistatic agents used in the present invention are electroconductive 
fine particles such as carbon black or carbon black graft polymer; natural 
surface active agents such as saponin; nonionic surface active agents such 
as alkylene oxide type agent, a glycerine type agent or glycidol type 
agent; cationic surface active agents such as higher alkyl amines, 
quaternary ammonium salts, pyridine and other heterocyclic compounds, 
phosphonium or sulfonium; anionic surface active agents such as carboxylic 
acid, a sulfonic acid, a phosphoric acid or a compound having an acid 
group of sulfate or phosphate; and amphoteric surface active agents such 
as amino acid, amino sulphonic acids or a sulfate or a phosphate of 
aminoalcohol. 
The above electroconductive fine particles are used in an amount of 0.2 to 
20 parts, preferably 0.2 to 10 parts, by weight based on 100 parts by 
weight of the binder. The above surface active agents are used in an 
amount of 0 to 10 parts, preferably 0 to 5 parts, by weight based on 100 
parts of the binder. 
Various fatty acids and fatty acid esters are added in order to improve the 
running property and to reduce the friction coefficient of a magnetic 
layer to guide parts, a head cylinder and cassette parts of VTR, an audio 
deck and the like. A solid lubricating agent of inorganic particles such 
as silicone oil (e.g., polysiloxane), graphite, molybdenum disulfide, 
plastic fine particles such as polyethylene or polytetrafluoro ethylene 
and fluorocarbons; an abrasive agent such as alumina, silicon carbide, 
chrome oxide (Cr.sub.2 O.sub.3), corundum or diamond; ketones such as 
methyl ethyl ketone or cyclohexanone, alcohols, esters such as ethyl 
acetate or butyl acetate, aromatic solvents such as benzene, toluene or 
xylene and chlorinated hydrocarbon type solvents such as carbon 
tetrachloride or chloroform can be further added, if desired. 
Non-magnetic supports include a synthetic resin such as polyester, vinyl 
type polymer or cellulose type derivative, non-magnetic metal and a paper, 
which are used in a form of a film, a tape or a sheet. 
It is effective that a backing layer is provided on the back surface of the 
support opposite to the magnetic layer for the purpose of improving the 
running properties and durability. When ferromagnetic metal particles are 
used as magnetic particles, the thickness of the magnetic recording medium 
tends to be reduced. Therefore, provision of the backing layer is 
particularly effective when ferromagnetic metal particles are used. The 
backing layer has a thickness of 0.1 to 2.0 .mu.m, preferably 0.3 to 1.0 
.mu.m, and comprises a binder and fine particles. Fine particles mainly 
contain inorganic particles such as carbon black, graphite, calcium 
carbonate, alumina, titanium oxide, SiC, SiO.sub.2, chromium oxide, boron 
nitride, MgO or CoO. Among these, carbon black is the most preferred 
because it works as an antistatic agent for running tapes. Chromium oxide, 
calcium carbonate, SiO.sub.2 and titanium oxide can be mixed together with 
carbon black. The fine particles are used in an amount of 0.5 to 1.5 times 
as much as the binder. 
The magnetic layer provided on the support is subjected to magnetic 
orientation to improve magnetic properties such as S/N and the like before 
it is dried and it is subjected to smoothing treatment such as calendering 
after it is dried as described in U.S. Pat. Nos. 2,688,567 and 2,998,325. 
It is effective that the magnetic layer is abraded with a grinding stone or 
is subjected to sliding treatment using a blade to eliminate sticked 
substance or a bump which is present on the surface of the magnetic 
recording medium and is the cause of drop-out or noise. The above surface 
treatment is very effective for the magnetic recording medium using 
ferromagnetic metal particles used for high density recording, because 
slight defects on the surface properties are very serious for that medium. 
The above described additives, supports and the method for preparing the 
magnetic recording medium are disclosed in U.S. Pat. No. 4,135,016. 
The feature of the present invention is that a non-polar binder is used ass 
a binder. When ferromagnetic metal particles which are subjected to 
surface treatment using an organic compound are used, the conventionally 
used binder used for a magnetic recording medium deteriorates the 
dispersibility of the treated particles more than that of the untreated 
particles, whereby a smooth magnetic layer cannot be obtained. 
In the present invention it has been found that the relationship between 
the ferromagnetic metal particles treated with an organic compound and the 
binder depends upon the amount of the polar functional group of the binder 
in a molecule and that as the amount of the functional group decreases and 
reaches, in some cases, zero, better results can be obtained. It is not 
clear why the large amount of the functional group in the binder is not 
preferable, but it is considered that as the site where the functional 
group of a binder is to adsorb is occupied by an organic compound, the 
excessive large amount of the functional group of the binder interacts 
with each other, whereby a stable coating composition and a homogeneously 
smooth magnetic layer cannot be obtained. 
In accordance with the present invention, ferromagnetic particles can 
easily be dispersed, the period of time for dispersion can be shortened 
and the dispersing device can have a reduced task. Even under the same 
dispersing condition as that of a conventional prior art, a coating 
composition having better dispersibility can be obtained. 
Magnetic particles hardly agglomerate with the passage of time after being 
dispersed, and therefore, the pot life of the coating composition can be 
improved. 
It is considered that the above advantages are obtained because an organic 
compound which is coated on the surface of the ferromagnetic particles 
prevents the magnetic particles from their interaction and agglomeration. 
The effects are particularly increased when ferromagnetic metal particles 
having high saturation magnetization (.sigma.s) and having large specific 
surface area are used. It is expected that as the saturation magnetization 
increases, the specific surface area becomes larger, the particle size 
becomes smaller, the sensitivity increases more and S/N increases higher. 
But in the prior art, that expectation is not realized. That is, in 
actuality, as the saturation magnetization and specific surface area 
become higher, the particles disperse with more difficulty. Even if the 
particles are once dispersed, they easily agglomerate. Therefore a smooth 
surface of a magnetic layer can hardly be obtained. Thus, the output 
cannot be improved as expected, noise is high and high S/N cannot be 
obtained. 
The difference between the prior art and the present invention becomes 
remarkable when the saturation magnetization is 120 emu/g or more and 
specific surface area is 30 m.sup.2 /g or more, and in the present 
invention a magnetic recording medium having excellent electromagnetic 
properties can be obtained. 
In accordance with the present invention, as particles can easily be 
dispersed, the dispersion step is very simple, since the period of time of 
dispersion can be shortened and the number of dispersing devices to be 
used can be reduced. 
And also in accordance with the present invention, the viscosity of the 
coating composition can be decreased, thereby reducing the amount of 
solvent to be employed. Therefore, the drying step becomes very simple. In 
short, in the present invention, manufacturing the cost can be reduced, 
because the steps are simple. 
In the present invention, as the magnetic orientation of the particles is 
good, the squareness ratio is high and the electromagnetic properties can 
be improved. 
Stability, which is an important factor for the ferromagnetic metal 
particles, can be improved in the present invention. Particles which are 
allowed to stand in air proceed to be oxidized with difficulty because an 
organic compound is coated on the surface of the particles. Additionally, 
even after the particles are mixed and kneaded with a binder, 
deterioration of the magnetic characteristics (demagnetization) caused by 
oxygen and moisture in air hardly occurs.

The present invention will be illustrated in more detail by the following 
non-limiting examples and comparative examples. In examples and 
comparative examples, all parts are by weight. 
Samples prepared in the following examples and comparative examples were 
measured in the following manner: 
Magnetic characteristics of particles and magnetic tapes were measured by a 
vibration sample magnetometer, "VSM-III type", a trademark, manufactured 
by Toei Kogyo Co.) in 10 kOe magnetic field (Hm); 
The video characteristic is shown by a reproduced output of each magnetic 
tape at 4 MHz which is measured by means of a VHS type VTR (trademark: 
"NV-8800" manufactured by Matsushita Electric Co., Ltd.) of which the 
recording and reproducing head is replaced by a sendust alloy head. A 
standard magnetic tape is a VHS type magnetic tape "T-120 E", manufactured 
by Fuji Photo Film Co., Ltd.; 
The S/N ratio is a ratio of output to noise level measured at 3.0 MHz of 
reproduced amplified modulated signals after recording carrier signals at 
4 MHz; 
Demagnetization was calculated in the following formula by measuring the 
residual magnetic flux density Br at 2 kOe magnetic field (Hm) by means of 
the above described vibration sample magnetometer "VSN-III type"; 
EQU (1-Br'/Br).times.100 
Br' is the residual magnetic flux density of a magnetic tape which was 
allowed to stand at 60.degree. C. and 90% RH for 7 days. 
EXAMPLES 1 AND 2 AND COMATIVE EXAMPLES 1 TO 4 
Fe--Ni alloy particles "A to D" (Ni content: about 5%) having the following 
saturation magnetization (.sigma.s) and specific surface area which is 
measured by BET method using N.sub.2 gas ("Quantasorb", Quantachrome Co., 
Ltd.) as shown in Table 1 were dipped in a toluene solution of 25 wt% 
lauryl acetoaluminum diisopropionate, stirred, allowed to stand for 10 
hours, filtered and dried to obtain surface treated particles having about 
0.5 wt% of the aluminum compound coated on the surface of the particles 
per magnetic particle based on the weight of the ferromagnetic particles. 
The surface treated particles were washed with toluene and the amount of 
aluminum compound dissolved into the toluene was 5% or less per total 
amount of the aluminum compound coated on the magnetic particles. 
TABLE 1 
______________________________________ 
Ferromagnetic Saturation Specific 
Metal Particles 
Magnetization 
Surface Area S 
(Fe--Ni) (emu/g) (m.sup.2 /g) 
______________________________________ 
A 110 45 
B 115 43 
C 123 45 
D 130 46 
______________________________________ 
For comparison, Fe--Ni alloy particles were treated in the same manner as 
above except that the toluene solution did not contain the aluminum 
compound. 
______________________________________ 
Ferromagnetic Metal Particles 
300 parts 
(Fe--Ni alloy) 
Copolymer of Vinyl Chloride 
30 parts 
and Vinyl Acetate (87/13 by 
weight) ("VYHH", trademark, 
manufactured by Union Carbide Co.) 
Polyester Polyurethane 20 parts 
(butylene adipate/neopenyl 
glycol/diphenylmethane diiso- 
cyanate = 2/1/3 by mole; 
molecular weight: 48,000; 
OH groups are attached on both 
terminals of the molecule) 
.alpha.-alumina 15 parts 
(average particle size: 0.6 .mu.m) 
Butyl Acetate 500 parts 
Methyl Isobutyl Ketone 300 parts 
______________________________________ 
The above composition was mixed, kneaded and dispersed in a ball mill for 
about 10 hours, then a 75 wt% ethyl acetate solution of 25 parts of oleic 
acid, 5 parts of stearic acid, 6 parts of butyl stearate and 25 parts of 
triisocyanate compound ("Desmodur L-75", manufactured by Bayer Co., Ltd.) 
was added thereto and stirred with high speed for 1 hour to prepare a 
homogeneous magnetic coating composition. 
The coating composition was coated on a polyethylene terephthalate film 
(thickness: 12.5 .mu.m), which was subjected to magnetic orientation, 
dried and subjected to calendering treatment and slit to a desired width 
to prepare a magnetic tape. 
The characteristics of the tape thus obtained are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Magnetic Properties 
Maximum Video Degree 
Ferro- Saturation Output of 
magnetic 
Coercive 
Magnetic Flux 
Square- 
at S/N Demagne- 
Metal 
Force Hc 
Density Bm 
ness 4 MHz 
Ratio 
tization 
Particles 
(Oe) (G) Ratio 
(dB) 
(dB) 
(%) 
__________________________________________________________________________ 
Comparative 
A(0) 1510 2750 0.80 +7.5 
+6.5 
6.8 
Example 1 
Comparative 
B(0) 1500 2800 0.78 +8.0 
+6.5 
8.4 
Example 2 
Example 1 
C(0) 1480 2980 0.77 +9.0 
+7.8 
7.5 
Example 2 
D(0) 1500 2850 0.77 +10.0 
+8.5 
7.1 
Comparative 
C(x) 1500 3010 0.74 +8.0 
+6.0 
13.3 
Example 3 
Comparative 
D(x) 1510 2900 0.73 +8.0 
+6.0 
18.5 
Example 4 
__________________________________________________________________________ 
(0): Surface treated particles 
(x): Untreated particles 
It is apparent from Table 2 that magnetic particles which have high 
saturation magnetization (C and D) and are subjected to surface treatment 
(Examples 1 and 2) exhibited high squareness ratio and excellent 
electromagnetic properties. Magnetic particles which had high saturation 
and were not subjected to surface treatment (Comparative Examples 3 and 4) 
exhibited a low squareness ratio, and regarding the electromagnetic 
properties, the noise is high and S/N ratio is low, since dispersibility 
of the magnetic particles was poor. 
Untreated particles exhibited high demagnetization. 
EXAMPLES 3 TO 5 AND COMATIVE EXAMPLES 5 TO 8 
The same procedure as in Example 1 were repeated except using Fe--Ni 
ferromagnetic alloy particles E, F, C and G as shown in Table 3 to prepare 
a magnetic tape. The characteristics of the tape were measured in the same 
manner as above. The results are shown in Table 4. 
TABLE 3 
______________________________________ 
Ferromagnetic Saturation Specific 
Metal Particles 
Magnetization 
Surface Area S 
(Fe--Ni) (emu/g) (m.sup.2 /g) 
______________________________________ 
E 125 25 
F 127 32 
C 123 45 
G 125 56 
______________________________________ 
TABLE 4 
__________________________________________________________________________ 
Magnetic Properties 
Maximum Video Degree 
Ferro- Saturation Output of 
magnetic 
Coercive 
Magnetic Flux 
Square- 
at S/N Demagne- 
Metal 
Force Hc 
Density Bm 
ness 4 MHz 
Ratio 
tization 
Particles 
(Oe) (G) Ratio 
(dB) 
(dB) 
(%) 
__________________________________________________________________________ 
Comparative 
E(0) 1460 2880 0.80 +8.0 
+6.5 
4.3 
Example 5 
Example 3 
F(0) 1480 2900 0.80 +9.5 
+8.0 
6.7 
Example 4 
C(0) 1470 2930 0.78 +10.0 
+9.0 
7.3 
Example 5 
G(0) 1480 2850 0.78 +10.0 
+9.0 
6.6 
Comparative 
E(x) 1500 3050 0.75 +8.5 
+6.5 
8.8 
Example 6 
Comparative 
F(x) 1510 3000 0.75 +9.0 
+7.0 
16.2 
Example 7 
Comparative 
G(x) 1500 2960 0.73 +8.5 
+7.5 
17.0 
Example 8 
__________________________________________________________________________ 
(0): Surface treated particles 
(x): Untreated particles 
Even though the magnetic particles were subjected to surface treatment, 
excellent electromagnetic properties could not be obtained when the 
specific surface area of the particles was not high. 
Magnetic particles having high specific surface area could further improve 
the electromagnetic properties, when they were subjected to surface 
treatment. As the specific surface area increased, the effect of the 
surface treatment increased more. Similarly, the demagnetization was 
improved when the particles were subjected to surface treatment and its 
effect increased more as the specific surface area increased. 
EXAMPLES 6 TO 8 AND COMATIVE EXAMPLES 9 AND 10 
Fe--Ni alloy particles (Ni content: 5%) having 50 m.sup.2 /g of specific 
surface area measure by the BET method were dipped in a toluene solution 
of 1 to 3 wt% lauryl acetoaluminum diisopropionate, allowed to stand for 
10 hours, filtered and dried to obtain surface treated particles having 
0.12 wt%, 0.24 wt%, 0.56 wt% and 1.2 wt% of the aluminum compound coated 
on the surface of the particles per magnetic particle based on the weight 
of the ferromagnetic particles. When the surface treated particles were 
washed with toluene, the amount of the aluminum compound dissolved into 
toluene was 5% or less per the aluminum compound coated on the magnetic 
particles. 
For comparison, magnetic particles treated only with toluene and having no 
organic compound on the surface of the particles (0 wt%) were prepared. 
______________________________________ 
Above-described Alloy Particles 
300 parts 
Copolymer of Vinyl Chloride and 
30 parts 
Vinyl Acetate (87/13 by weight) 
("VYHH" trademark, manufactured 
by Union Carbide Co.) 
Polyester Polyurethane 20 parts 
(butylene adipate/neopenyl 
glycol/diphenylmethane diiso- 
cyanate = 2/1/3 by mole; 
molecular weight of 48,000; 
OH group are attached on both 
terminals of the molecule 
Butyl Acetate 500 parts 
Methyl Isobutyl Ketone 300 parts 
.alpha.-alumina 15 parts 
(average particle size: 0.6 .mu.m) 
______________________________________ 
The above composition was mixed, kneaded and dispersed sufficiently in a 
ball mill for about 13 hours, then a 75 wt% ethyl acetate solution of 2.5 
parts of oleic acid, 5 parts of stearic acid, 6 parts of butyl stearate 
and 25 parts of triisocyanate compound ("Desmodur L-75", trademark, 
manufactured by Bayer A.G.) was added thereto and stirred homogeneously by 
a high speed shearing device for about 1 hour to prepare a magnetic 
coating composition. The thus obtained coating composition was coated on a 
polyethylene terephthalate film having a permeability of 15 .mu.Vz, which 
was subjected to magnetic orientation, dried and subjected to calendering 
treatment and slit to a predetermined width to prepare a magnetic tape. 
COMATIVE EXAMPLE 11 
The same procedure as in Example 7 were repeated except a copolymer of 
vinyl chloride, vinyl acetate and maleic anhydride (86/13/l; molecular 
weight: 25,000) was used instead of a copolymer of vinyl chloride and 
vinyl acetate ("VYHH", trademark, manufactured by Union Carbide Co.) as a 
binder. 
The resulting magnetic layer was not homogeneous and the squareness ratio 
and electromagnetic properties were not so improved. 
COMATIVE EXAMPLE 12 
The same procedures as in Comparative Example 11 were repeated except using 
alloy particles which had not been surface-treated with the same organic 
compound as that used in Comparative Example 10. A magnetic layer having 
much smoother surface than that prepared in Comparative Example 11 was 
obtained. The electromagnetic properties are relatively high, but the 
demagnetization was very high. 
EXAMPLE 9 
The same alloy particles as used in Example 6 were treated with dimethyl 
diethoxy silane in the same manner as in Example 6 to prepare 
surface-treated particles having 0.60 wt% of the organic compound coated 
on the surface of the particles, based on the weight of the ferromagnetic 
particles. A magnetic tape was prepared in the same manner as in Example 
6. 
The characteristics of four kinds of magnetic tapes are shown in Table 5. 
TABLE 5 
__________________________________________________________________________ 
Magnetic Properties 
Maximum Video Degree 
Amount of Saturation Output of 
Treating 
Coercive 
Magnetic Flux 
Square- 
at S/N Demagne- 
Compound 
Force Hc 
Density Bm 
ness 4 MHz 
Ratio 
tization 
(wt %) 
(Oe) (G) Ratio 
(dB) 
(dB) 
(%) 
__________________________________________________________________________ 
Example 6 
1.2 1510 2970 0.82 +10.4 
+8.7 
4 
Example 7 
0.56 1500 2850 0.80 +10.3 
+9.5 
6 
Example 8 
0.24 1510 2910 0.78 +8.0 
+7.2 
8 
Comparative 
0.12 1500 2800 0.73 +4.0 
+2.5 
13 
Example 9 
Comparative 
0 1500 2900 0.72 +3.3 
+0.8 
15 
Example 10 
Comparative 
0.56 1510 2820 0.73 +5.5 
+4.3 
5 
Example 11 
Comparative 
0 1500 2950 0.74 +7.8 
+6.8 
22 
Example 12 
Example 9 
0.60 1500 2850 0.78 +9.0 
+7.8 
4 
__________________________________________________________________________ 
(0): Surface treated particles 
(x): Untreated particles 
As the results in Table 5 demonstrate, the squareness ratio as well as the 
electromagnetic properties such as output, S/N ratio or demagnetization 
can be improved by surface treating the magnetic particles. 
The coating composition was allowed to stand for about 15 hours and then a 
magnetic layer was coated in the same manner as in Example 6. A magnetic 
tape having a coarse surface was obtained in the comparative examples. On 
the other hand, a magnetic having a homogenously smooth surface was 
obtained in the examples. More specifically, in Examples 6 to 9, the 
magnetic tape using the coating composition which was allowed to stand for 
15 hours exhibited nearly the same characteristics as that of the coating 
composition which was not allowed to stand for 15 hours. 
EXAMPLE 10 
.gamma.-Iron oxide having a specific surface area of 30 m.sup.2 /g was used 
instead of the ferromagnetic alloy particles used in Example 7. A 
homogeneously dispersed coating composition was obtained after dispersing 
for 13 hours in a ball mill. A magnetic layer having a smooth surface was 
obtained. Both the magnetic properties and electromagnetic properties were 
excellent. 
EXAMPLE 11 TO 17 
A copolymer of vinyl chloride, vinyl acetate and maleic acid was 
synthesized under the conditions that the mixing weight ratio of vinyl 
chloride and vinyl acetate was determined as 85:15 and that the weight 
ratio of maleic acid was that as shown in Table 6. 
The same procedures as in Example 6 were repeated except for using the 
magnetic particles as used in Example 7 and the above resin as a binder in 
the ratio of 100 g to 25 g, to prepare a magnetic tape. 
With each example, numbers of polar groups (calculated values) and gloss 
measured by a mirror gloss meter (angle of incidence and angle of 
reflection, 45.degree.) are shown in Table 6. 
TABLE 6 
______________________________________ 
Weight 
Ratio of Number of 
Gloss on 
Maleic Number Polar Group 
the Surface 
Acid to of COOH per g of of Coated 
be Used per 100 g Magnetic Layer 
Example 
(wt %) of Resin Particles 
(%) 
______________________________________ 
11 5.00 5.26 .times. 10.sup.22 
1.31 .times. 10.sup.20 
58 
12 1.25 1.32 .times. 10.sup.22 
3.3 .times. 10.sup.19 
60 
13 0.875 9.2 .times. 10.sup.21 
2.3 .times. 10.sup.19 
63 
14 0.625 6.6 .times. 10.sup.21 
1.65 .times. 10.sup.19 
77 
15 0.50 5.3 .times. 10.sup.21 
1.33 .times. 10.sup.19 
86 
16 0.375 3.9 .times. 10.sup.21 
9.75 .times. 10.sup.18 
94 
17 0.125 1.3 .times. 10.sup.21 
3.25 .times. 10.sup.18 
95 
______________________________________ 
It is clear from the results of gloss in Table 6 that resins having a 
functional group of 1.65.times.10.sup.19 or more per g of magnetic 
particles exhibited poor gloss and resins having a functional group of 
less than 1.65.times.10.sup.19 per g of magnetic particles exhibited high 
gloss. 
EXAMPLES 18 TO 27 
The same procedures as in Example 7 were repeated except mixing 25 parts of 
polyester polyurethane as used in Example 6 with a copolymer of vinyl 
chloride, vinyl acetate and maleic acid (85:15:5) as used in Exlample 12 
in an amount as shown in Table 7 and dispersing 100 parts of magnetic 
particles as used in Example 7 to prepare a magnetic tape. 
For each Example, the number of polar groups and gloss measured by a mirro 
gloss meter (angle of incidence and reflection: 45.degree.) are shown in 
Table 7. 
TABLE 7 
______________________________________ 
Number of 
Gloss on 
Polar Group 
the Surface 
per g of of Coated 
Polyester Resin Magnetic Layer 
Example Polyurethane 
(parts) Particles 
(%) 
______________________________________ 
18 25 0 6.25 .times. 10.sup.18 
108 
19 24 1 1.12 .times. 10.sup.19 
100 
20 23 2 1.62 .times. 10.sup.19 
98 
21 22 3 2.12 .times. 10.sup.19 
69 
22 21 4 2.62 .times. 10.sup.19 
63 
23 20 5 3.12 .times. 10.sup.19 
62 
24 15 10 5.62 .times. 10.sup.19 
61 
25 10 15 8.11 .times. 10.sup.19 
61 
26 5 20 1.06 .times. 10.sup.20 
60 
27 0 25 1.31 .times. 10.sup.20 
58 
______________________________________ 
It is apparent from Table 7 that samples having polar groups of 
2.12.times.10.sup.19 or more per g of magnetic particles exhibited poor 
gloss. 
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.