Claims
- 1. A magnetic recording medium comprising on a non-magnetic support having thereon at least three magnetic layers each layer of which containing a ferromagnetic powder dispersed in a binder, wherein the outermost magnetic layer arranged farthest from the support has a dry thickness of 1 .mu.m or less, and said at least three magnetic layers each exhibit coercive force Hc (Oe) satisfying the following relationships: ##EQU3## wherein R.sub.1 represents Hc of the outermost magnetic layer and is not less than 700 Oe; Hn represents Hc of the magnetic layer which is the n-th layer from said outermost magnetic layer and arrange between the outermost layer and the non-magnetic support; and Dn represents the distance (.mu.m) from the top surface of the outermost magnetic layer to the top surface of the n-th layer.
- 2. A magnetic recording medium as in claim 1, comprising three magnetic layers having a total combined thickness of less than 1 .mu.m.
- 3. A magnetic recording medium as in claim 1, wherein the particles constituting the ferromagnetic powder have a grain diameter along the major access of 0.5 .mu.m or less.
- 4. A magnetic recording medium as in claim 1, wherein the ferromagnetic powder has a specific surface area of from 25 to 80 m.sup.2 /g.
- 5. A magnetic recording medium as in claim 1, wherein the crystalline size of the ferromagnetic powder is in the range of from 100 to 450 .ANG. angstroms.
- 6. A magnetic recording medium as in claim 1, wherein the crystalline size of the ferromagnetic powder contained in the outermost layer is smaller than that of the ferromagnetic powder contained in the lowermost magnetic layer.
- 7. A magnetic recording medium as in claim 1, wherein the binder is selected from a thermoplastic resin, a thermosetting resin, a reactive resin and mixtures thereof.
- 8. A magnetic recording medium as in claim 1, wherein the binder contains at least one polar group in an amount of from 1.times.10.sup.-1 to 1.times.10.sup.-8 mol/g of the binder.
- 9. A magnetic recording medium as in claim 1, wherein the binder is contained in each magnetic layer in an amount of from 5 to 50% by weight based on the weight of the ferromagnetic power contained in the same magnetic layer.
- 10. A magnetic recording medium as in claim 1, wherein the ferromagnetic powder has an H.sub.c of from 200 to 2,000 Oe.
- 11. A magnetic recording medium as in claim 1, wherein the non-magnetic support has a thickness of from 1 to 100 .mu.m.
- 12. A magnetic recording medium as in claim 11, wherein the total thickness of the magnetic layers is 1/100 to 2 times that of the non-magnetic support.
- 13. A magnetic recording medium as in claim 1, wherein H.sub.1 is not less than 900 Oe.
- 14. A process for the preparation of a magnetic recording medium, comprising the steps of kneading and dispersing a first ferromagnetic powder in a binder to prepare a magnetic coating solution having an Hc of a predetermined value for the lowermost layer to be arranged nearest to a non-magnetic support, kneading and dispersing a second ferromagnetic powder in a binder to prepare a magnetic coating solution having an Hc of H.sub.1 for the outermost layer different than Hc of the lowermost layer, mixing the magnetic coating solution for the outermost layer in such ratio as to provide at least one magnetic coating solution for an interlayer having a predetermined Hc intermediate that of the lowermost and outmost layers, simultaneously coating the magnetic coating solution for the lower most layer, the one or more magnetic coating solutions for the interlayer and the magnetic coating solution for the outermost layer on the non-magnetic support to form a plurality of magnetic layers, subjecting the magnetic layers to orienting treatment, drying the magnetic layers, and then calendaring the magnetic recording medium, wherein the outermost magnetic layer arranged farthest from the support has a dry thickness of 1 .mu.m or less, and said magnetic layers each exhibit coercive force Hc (Oe) satisfying the following relationships: ##EQU4## wherein H.sub.1 represents Hc of the outermost magnetic layer and is not less than 700 Oe; Hn represents Hc of the magnetic layer which is the n-th layer from said outermost magnetic layer and arranged between the outermost layer and the non-magnetic support; and Dn represents the distance (.mu.m) from the top surface of the outermost magnetic layer to the top surface of the n-th layer.
- 15. A process as in claim 14, wherein H.sub.1 is not less than 900 Oe.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2-111181 |
Apr 1990 |
JPX |
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Parent Case Info
This is a continuation of application Ser. No. 07/692,346 filed Apr. 26, 1991, now abandoned.
US Referenced Citations (5)
Non-Patent Literature Citations (1)
Entry |
Patent Abstracts of Japan, vol. 9, No. 24 (P-331) (1747) 31 Jan. 1985, & JP-A-59 167845 (Hitachi Maxell K.K.) 21 Sep. 1984. |
Continuations (1)
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Number |
Date |
Country |
Parent |
692346 |
Apr 1991 |
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