# US 5,705,268 A · Magnetic recording medium with magnetic powder in lower magnetic layer having protective image diameters > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,268 A - Document ID: US5705268A - Status: Granted - Kind: A - Application number: 08/579,405 - Filed: 1995-12-27 - Granted: 1998-01-06 - Earliest claimed: 1994-12-27 - Assignees: Kao Corporation - Inventors: Akira Ishikawa; Hidehiko Nakayama; Kazutaka Yamashita - Web page: https://patentgrep.com/patent/US5705268A ## CPC - G11B 5/714: characterised by the dimension of the magnetic particles - G11B 5/716: characterised by two or more magnetic layers - Y10S 428/90: Magnetic feature - Y10T 428/265: 1 mil or less - Y10T 428/2982: Particulate matter [e.g., sphere, flake, etc.] - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A magnetic recording medium comprising a nonmagnetic support having formed thereon a plurality of magnetic layers including a top magnetic layer and an intermediate magnetic layer adjacent to the top magnetic layer, wherein the intermediate magnetic layer contains soft magnetic powder, the soft magnetic powder having, in its projective image, an average longer diameter <L> and a standard deviation of the longer diameter .DELTA.L satisfying the relationship represented by formula (1), and an average shorter diameter <W> and a standard deviation of the shorter diameter .DELTA.W satisfying the relationship represented by formula (2): 0.05.ltoreq..DELTA.L/<L>.ltoreq.0.8 (1) 0.05.ltoreq..DELTA.W/<W>.ltoreq.0.8 (2) ## Claims ### Claim 1 A magnetic recording medium comprising a nonmagnetic support having formed thereon a plurality of magnetic layers including a top magnetic layer and a lower magnetic layer adjacent to the top magnetic layer, wherein the lower magnetic layer contains soft magnetic oxide powder or soft magnetic metal powder, said soft magnetic oxide powder and soft magnetic metal powder having, in its projective image, an average long diameter <L> and a standard deviation of the longer diameter .DELTA.L satisfying the relationship represented by formula (1), and an average shorter diameter <W> and a standard deviation of the shorter diameter .DELTA.W satisfying the relationship represented by formula (2): 0.05.ltoreq..DELTA.L/<L>.ltoreq.0.8 (1) 0.05.ltoreq..DELTA.W/<W>.ltoreq.0.8 (2) and the top magnetic layer contains ferromagnetic metal powder or hexagonal ferrite powder. ### Claim 2 (depends on 1) The magnetic recording medium according to claim 1, wherein the average <L> of the longer diameter L is about 0.01 to 0.2 .mu.m, the standard deviation .DELTA.L of the longer diameter L is about 0.003 to 0.2 .mu.m, the average <W> of the shorter diameter W is about 0.01 to 0.2 .mu.m, and the standard deviation .DELTA.W of the shorter diameter W is about 0.003 to 0.2 .mu.m. ### Claim 3 (depends on 1) The magnetic recording medium according to claim 1, wherein the saturation magnetization of the ferromagnetic metal powder ranges from 130 to 160 emu/g. ### Claim 4 (depends on 1) The magnetic recording medium according to claim 1, wherein the top magnetic layer has a thickness of 0.05 to 1.0 .mu.m, and said top magnetic layer is formed while the intermediate magnetic layer is wet. ### Claim 5 (depends on 1) The magnetic recording medium according to claim 1, wherein a backcoat layer is provided on the reverse side of the nonmagnetic support opposite said plurality of magnetic layers. ### Claim 6 (depends on 1) The magnetic recording medium according to claim 1, wherein the ferromagnetic metal powder has a coercive force of 1600 to 2500 Oe. ### Claim 7 (depends on 1) The magnetic recording medium according to claim 1, wherein the hexagonal ferrite powder has a coercive force of 1300 to 2300 Oe. ### Claim 8 (depends on 1) The magnetic recording medium according to claim 1, wherein the ferromagnetic metal powder has a metal content of not less than 50% by weight and said metal consists of 60% or more by weight of Fe. ### Claim 9 (depends on 4) The magnetic recording medium according to claim 4, wherein the top magnetic layer has a thickness of 0.05 to 0.8 .mu.m. ### Claim 10 (depends on 1) The magnetic recording medium according to claim 1, wherein the soft magnetic oxide powder is a spinel ferrite powder. ### Claim 11 (depends on 10) The magnetic recording medium according to claim 10, wherein the soft magnetic oxide powder has a coercive force of 0.1 to 150 Oe and a saturation magnetization of 30 to 90 emu/g. ### Claim 12 (depends on 1) The magnetic recording medium according to claim 1, wherein the soft magnetic metal powder has a coercive force of 0.02 to 100 Oe and a saturation magnetization of 50 to 500 emu/g. ### Claim 13 (depends on 1) The magnetic recording medium according to claim 1, wherein the soft magnetic oxide powder and soft magnetic metal powder are selected from the group consisting of spherical, tabular or amorphous powder. ### Claim 14 (depends on 1) The magnetic recording medium according to claim 1, wherein the lower magnetic layer further contains nonmagnetic powder. ### Claim 15 (depends on 1) The magnetic recording medium according to claim 1, wherein the lower magnetic layer has a thickness of 0.2 to 5 .mu.m. ### Claim 16 (depends on 1) The magnetic recording medium according to claim 1, wherein the top magnetic layer contains the ferromagnetic metal powder and has a coercive force of 1800 to 2400 Oe. ### Claim 17 (depends on 16) The magnetic recording medium according to claim 16, wherein the top magnetic layer has a saturation flux density of 3000 to 4500 gauss. ### Claim 18 (depends on 1) The magnetic recording medium according to claim 1, wherein the top magnetic layer contains hexagonal ferrite powder and has a coercive force of 1600 to 2200 Oe. ### Claim 19 (depends on 18) The magnetic recording medium according to claim 18, wherein the top magnetic layer has a saturation flux density of 1500 to 2500 gauss.