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Magnetic recording media
| Details |
Inventors: Ryoke, Katsumi; Takahashi, Masatoshi; Hashimoto, Akihiro;
Assignee: Fuji Photo Film Co., Ltd. (Kanagawa, JP)
Primary Examiner: Thibodeau; Paul J.
Assistant Examiner:
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
A magnetic recording medium having excellent running properties and excellent durability is disclosed, which comprises a non-magnetic support having thereon a magnetic layer comprising a ferromagnetic powder and carbon black, said carbon black being a mixture which contains high structure furnace carbon black and acetylene black in the weight ratio of the former to the latter of from 95:5 to 45:55, and said high structure furnace carbon black having properties satisfying the general equations (I) or (II) below: 0<X.ltoreq.120, Y.gtoreq.0.625X+75 (I) X>120, Y.ltoreq.0.01125X.sup.2 -2.005X+229 (II) wherein Y is the amount of DBP oil absorbed (Ml/100 grams) by said high structure carbon furnace black, X is the specific surface area (m.sup.2 /gram) of said high structure carbon furnace black, and Y.gtoreq.120, wherein W is the amount of DBP oil adsorbed (ml/100 grams) by said actylene black, Z is the specific surface area (m.sup.2 /gram) of said acetylene black, and W.gtoreq.120. |
|
DETAILED DESCRIPTION OF THE INVENTION In the present invention, the amount of DBP oil absorbed is the amount in m.
lambda.
of DBP required to form a stiff past on milling with 100 grams of carbon black.
Furthermore, this amount is measured in accordance with the method set forth for testing carbon black for use in rubber in JIS K-6221-1982.
The specific surface area of the high structure furnace carbon black is measured using an electron Carbon Black Binran (Carbon Black Handbook), edited by Carbon Black Association, 3rd edition, pp.
176-179 (1973), and H.
K.
Livingston, Journal of Colloid Science, Vol.
4, p.
450 (1949).
The method comprises taking a picture of a dispersion of carbon black using a transmission type electron microscope, for example, with magnification of 20,000, enlarging the picture 5 times large (i.
e.
, magnification of 100,000) and examining distribution of the particle size of the carbon black using a particle size analyzer (e.
g.
, produced by Carl Zeiss Co.
), and an average particle size (d.
sub.
A) and the specific surface area (S.
sub.
EM) are calculated from the following equations .
rho.
d.
sub.
A =.
SIGMA.
n.
sub.
i d.
sub.
i.
sup.
3 /.
SIGMA.
n.
sub.
i d.
sub.
i.
sup.
2 S.
sub.
EM =6/.
rho.
.
multidot.
d.
sub.
A wherein n.
sub.
i is the number of particles having a particle size (d.
sub.
i) and .
rho.
is the specific gravity of carbon black, i.
e.
, 1.
86.
The magnetic recording medium of this invention, by using carbon black of the specified composition as indicated above in a specified proportion, provides a magnetic layer which is tough and which has a low coefficient of friction.
That is to say, the compatibility of the carbon black and a binding agent is improved by including a high structure furnace carbon black.
This improvement results in a tougher magnetic layer which has a higher S/N ratio.
Furthermore, the magnetic layer surface has the appropriate roughness due to the acetylene black, thus lowering the coefficient of friction (.
mu.
value) of the magnetic layer surface with respect to the parts of the running system
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