Magnetic recording medium and production process therefor
View Patent ↗A magnetic recording medium is provided that includes a non-magnetic support, and at least one magnetic layer provided above the non-magnetic support, the magnetic layer having a ferromagnetic powder dispersed in a binder, all or part of the binder being a polyurethane resin obtained by a reaction of a polyol and a polyisocyanate, the polyurethane resin having a glass transition temperature (Tg) of 70° C. to 200° C., and part of the polyol being a diol having at least one epoxy group and two hydroxyl groups per molecule. There is also provided a process for producing the magnetic recording medium, the process including a step of kneading the ferromagnetic powder and the polyurethane resin.
1. A magnetic recording medium comprising:
a non-magnetic support;
at least one magnetic layer provided above the non-magnetic support, the magnetic layer comprising a ferromagnetic powder dispersed in a binder;
all or part of the binder being a polyurethane resin obtained by a reaction of a polyol and a polyisocyanate;
the polyurethane resin having a glass transition temperature (Tg) of 70° C. to 200° C.; and
part of the polyol being a diol having at least one epoxy group and two hydroxyl groups per molecule.
2. The magnetic recording medium according to claim 1 , wherein the diol is an epoxy-modified tri- or higher-hydric alcohol.
3. The magnetic recording medium according to claim 1 , wherein the diol is selected from the group consisting of compounds (I) to (VIII) below:
wherein, among X 1 , X 2 , and X 3 , one thereof is a glycidyl ether group and two thereof are hydroxyl groups,
wherein, among X 1 to X 4 , two thereof are glycidyl ether groups and two thereof are hydroxyl groups, and
wherein, among X 1 to X 6 , four thereof are glycidyl ether groups and two thereof are hydroxyl groups.
4. The magnetic recording medium according to claim 1 , wherein the diol is selected from the group consisting of the above compounds (I), (IV), and (VII).
5. The magnetic recording medium according to claim 1 , wherein the medium comprises at least one non-magnetic layer provided between the non-magnetic support and the magnetic layer, the non-magnetic layer comprising a non-magnetic powder dispersed in a binder, all or part of the binder being a polyurethane resin obtained by a reaction of a polyol and a polyisocyanate, the polyurethane resin having a glass transition temperature (Tg) of 70° C. to 200° C., and part of the polyol being a diol having at least one epoxy group and two hydroxyl groups per molecule.
6. The magnetic recording medium according to claim 1 , wherein the polyurethane resin has an epoxy group content of 2×10 −5 to 8×10 −4 eq/g.
7. The magnetic recording medium according to claim 1 , wherein the polyol comprises a long chain diol and, as a chain extending agent, a short chain diol.
8. The magnetic recording medium according to claim 1 , wherein the polyisocyanate is a diisocyanate compound.
9. The magnetic recording medium according to claim 1 , wherein the polyurethane resin contains a polar group selected from the group consisting of —SO 3 M, —SO 4 M, —PO(OM) 2 , —OPO(OM) 2 , —COOM, >NSO 3 M, —NR 1 SO 3 M, —NR 1 R 2 , and —N + R 1 R 2 R 3 X − (M denotes a hydrogen atom, an alkali metal, or an ammonium, R 1 , R 2 , and R 3 independently denote a hydrogen atom or an alkyl group, and X denotes a monovalent halide ion).
10. The magnetic recording medium according to claim 1 , wherein the ferromagnetic powder is a ferromagnetic metal powder.
11. The magnetic recording medium according to claim 1 , wherein the ferromagnetic powder is a ferromagnetic hexagonal ferrite powder.
12. The magnetic recording medium according to claim 10 , wherein the ferromagnetic metal powder has a major axis length of 35 to 70 nm.
13. The magnetic recording medium according to claim 11 , wherein the ferromagnetic hexagonal ferrite powder has a plate size of 5 to 40 nm.
14. The magnetic recording medium according to claim 1 , wherein the non-magnetic support is selected from the group consisting of polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamideimide, aromatic polyamide, and polybenzoxazole.
15. The magnetic recording medium according to claim 1 , wherein the non-magnetic support has a center line average surface roughness of 0.1 to 20 nm for a cutoff value of 0.25 mm.
16. The magnetic recording medium according to claim 1 , wherein the magnetic layer has a thickness of 0.01 to 0.10 μm.
17. The magnetic recording medium according to claim 1 , wherein the magnetic recording medium has a center line average surface roughness of 0.1 to 4 nm for a cutoff value of 0.25 mm.
18. The magnetic recording medium according to claim 1 , wherein the epoxy group introduced into the polyurethane resin is subjected to a curing reaction by heating the magnetic recording medium.