Powder for lower layer of application type of layered magnetic recording medium and magnetic recording medium using the same
An underlayer powder for a coating-type double-layer magnetic recording medium is a powder composed of acicular nonmagnetic iron oxide particles whose average major axis length of the particles is 20-200 nm, and specific surface area calculated by BET method is 30-100 m 2 /g, which has a phosphorus content in the particulate powder of 0.1-5 wt %, and soluble phosphorus compound of not greater than 100 ppm based on P, and which preferably has a powder pH of less than 8, a soluble sodium content of not greater than 100 ppm based on Na and soluble sulfate of not greater than 100 ppm based on SO 4.
1 . A powder for an underlayer of a coating-type double-layer magnetic recording medium, which is a powder composed of acicular or nearly acicular nonmagnetic iron oxide particles, characterized in having:
average major axis length of the particles of 20-200 nm, and
specific surface area calculated by BET method of 30-100 m 2 /g, and containing:
0.1-5 wt % of phosphorus,
soluble phosphorus compound being not greater than 100 ppm based on P.
2 . An underlayer powder according to claim 1 , wherein:
powder pH is less than 8,
soluble sodium content is not greater than 100 ppm based on Na, and
soluble sulfate is not greater than 100 ppm based on SO 4 .
3 . An underlayer powder according to claim 1 , containing R (R representing at least one rare earth element including Y) at R/Fe expressed in atomic percent (at. %) of 0.1-10 at %.
4 . An underlayer powder according to claim 1 , containing 0.1-50 wt % of A1.
5 . An underlayer powder according to claim 1 , containing 0.1-50 wt % of Si.
6 . An underlayer powder according to claim 4 , wherein A1 and/or Si are concentrated on the particle surfaces.
7 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 1 is used as the nonmagnetic powder.
8 . An underlayer powder according to claim 2 , containing R (R representing at least one rare earth element including Y) at R/Fe expressed in atomic percent (at. %) of 0.1-10 at %.
9 . An underlayer powder according to claim 2 , containing 0.1-50 wt % of A1.
10 . An underlayer powder according to claim 3 , containing 0.1-50 wt % of A1.
11 . An underlayer powder according to claim 2 , containing 0.1-50 wt % of Si.
12 . An underlayer powder according to claim 3 , containing 0.1-50 wt % of Si.
13 . An underlayer powder according to claim 4 , containing 0.1-50 wt % of Si.
14 . An underlayer powder according to claim 5 , wherein A1 and/or Si are concentrated on the particle surfaces.
15 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 2 is used as the nonmagnetic powder.
16 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 3 is used as the nonmagnetic powder.
17 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 4 is used as the nonmagnetic powder.
18 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 5 is used as the nonmagnetic powder.
19 . A coating-type magnetic recording medium characterized in that in a coating-type magnetic recording medium of double-layer structure provided between a magnetic recording layer composed of magnetic powder dispersed in resin and a base film with a nonmagnetic layer (underlayer) composed of nonmagnetic powder dispersed in resin, an underlayer powder of claim 6 is used as the nonmagnetic powder.