Magnetic recording media and thermoplastic polyurethane resins therefor

• US 20030022022A1
• Filed: 03/07/2000
• Published: 01/30/2003
• Est. Priority Date: 03/08/1999
• Status: Active Grant

• Current Assignee: Toyoda Gosei Company Limited (Toyota Motor Corporation)
• Original Assignee: Toyoda Gosei Company Limited (Toyota Motor Corporation)
• Inventors: Yatsuka, Takeshi, Sugitawa, Chikara, Doi, Kuniyuki, Kizumoto, Hirotoshi
• Granted Patent: US 6,545,119 B2
• Time in Patent Office: Days
• US Class Current: 428/694BU
• CPC Class Codes: C08G 18/4202 Two or more polyesters of different physical or chemical nature C08G18/44 takes precedence
• CPC Class Codes: C08G 18/4211 derived from aromatic dicarboxylic acids and dialcohols
• CPC Class Codes: C08G 18/4238 derived from dicarboxylic acids and dialcohols
• CPC Class Codes: C09D 175/06 from polyesters
• CPC Class Codes: G11B 5/7021 containing a polyurethane or a polyisocyanate

Abstract

A magnetic recording medium possessing a magnetic layer formed by application onto a non-magnetic support, of a magnetic coating containing magnetic particles dispersed in a binder which contains a polyurethane resin, together with carbon black particles at 5% by weight or higher, based on the weight of the magnetic particles. The polyurethane resin to be used herein is composed of: (a) a polyester polyol having a molecular weight of 2000 or lower and containing at least one selected from the group consisting of aromatic dibasic acids and alicyclic dibasic acids at a ratio of 90 mol % or higher of acid components; (b) a high molecular weight polyol having a molecular weight of 5000 or lower, which is at least one selected from the group consisting of (b1) polyester polyols each containing an aliphatic dibasic acid at a ratio of 90 mol % or higher of acid components, (b2) polylactones, (b3) polyester polyols, and (b4) polycarbonate polyols; (c) an organic diisocyanate compound; and (d) an optional compound having a molecular weight of 500 or lower and containing at least two functional groups in one molecule, which are reactive with isocyanate groups.

Claims

1. A magnetic recording medium comprising a magnetic layer formed by application onto a non-magnetic support, of a magnetic coating containing magnetic particles dispersed in a binder,

said binder comprising a polyurethane resin composed of:

(a) a polyester polyol having a molecular weight of 2000 or lower and containing at least one selected from the group consisting of aromatic dibasic acids and alicyclic dibasic acids at a ratio of 90 mol % or higher of acid components;

(b) a high molecular weight polyol having a molecular weight of 5000 or lower, which is at least one selected from the group consisting of (b1) polyester polyols each containing an aliphatic dibasic acid at a ratio of 90 mol % or higher of acid components, (b2) polylactones, (b3) polyether polyols, and (b4) polycarbonate polyols;

(c) an organic diisocyanate compound; and

(d) an optional compound having a molecular weight of 500 or lower and containing at least two functional groups in one molecule, which are reactive with isocyanate groups;

and said binder further comprising 5% by weight or higher carbon black particles, based on the weight of the magnetic particles.

14. The magnetic recording medium according to claim 1, wherein said binder comprises a polyurethane resin according to any one of claims 2, 6, 10, and 12.

2. A thermoplastic polyurethane resin for use in magnetic recording media, which is obtained by reaction in molten state of starting materials, said thermoplastic polyurethane resin having a glass transition temperature of 80°

C. or higher and an urethane bonding group concentration of lower than 3000 eq./10⁶ g.

3. The thermoplastic polyurethane resin according to claim 2, wherein said component B is at least one selected from the group consisting of diols having a molecular weight of 200 or higher and diols in liquid form at 20°

C.

4. The thermoplastic polyurethane resin according to claim 2, having a molecular weight distribution (Mw/Mn) as determined by a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of 4 or lower.

5. The thermoplastic polyurethane resin according to claim 2, comprising as the starting materials a polyester resin containing at least one selected from the group consisting of aromatic dicarboxylic acids and alicyclic dicarboxylic acids at a ratio of 80 mol % or higher of acid components.

6. A thermoplastic polyurethane resin for use in magnetic recording media, which is obtained by reaction in molten state of a polyester (component A) containing at least one selected from the group consisting of aromatic dicarboxylic acids and alicyclic dicarboxylic acids at a ratio of 80 mol % or higher of acid components;

a low molecular weight diol (component B) having a molecular weight of 500 or lower; and

an optional high molecular weight polyol (component C), which is at least one selected from the group consisting of (C1) polyester polyols each composed mainly of an aliphatic dicarboxylic acid as an acid component, (C2) polylactones, (C3) polyether polyols, and (C4) polycarbonate polyols, with an organic diisocyanate compound;

said component A meeting at least one of the following conditions (i) and (ii);

(i) 10 to 50 mol % of glycol components comprises 1,6-hexanediol;

(ii) 80 mol % or higher of acid components comprises at least one dicarboxylic acid selected from the group consisting of isophthalic acid, o-phthalic acid, 1,3-cyclohexanedicarboxylic acid (hydrogenated isophthalic acid), and 1,2-cyclohexanedicarboxylic acid (hydrogenated phthalic acid).

7. The thermoplastic polyurethane resin according to claim 6, wherein said component A meets both conditions (i) and (ii).

8. The thermoplastic polyurethane resin according to claim 6, having a glass transition temperature of 80°

C. or higher and an urethane bonding group concentration of lower than 3000 eq./10⁶ g.

9. The thermoplastic polyurethane resin according to claim 6, wherein said component B is at least one selected from the group consisting of diols having a molecular weight of 200 or higher and diols in liquid form at 20°

C.

10. A thermoplastic urethane resin for use in recording media, which is obtained by reaction in molten state of a polyester polyol (component A) and a low molecular weight diol (component B) having a molecular weight of 500 or lower with an organic diisocyanate compound, said component B being at least one selected from the group consisting of diols having a molecular weight of 200 or higher and diols in liquid form at 20°

C.

11. The thermoplastic polyurethane resin according to claim 10, comprising as the starting materials a polyester resin containing at least one selected from the group consisting of aromatic dicarboxylic acids and alicyclic dicarboxylic acids at a ratio of 80 mol % or higher of acid components.

12. A thermoplastic polyurethane resin for use in magnetic recording media, which is obtained by reaction in molten state of starting materials, said thermoplastic polyurethane resin having a molecular weight distribution (Mw/Mn) as determined by a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of 4 or lower.

13. The thermoplastic polyurethane resin according to claim 12, comprising as the starting materials a polyester resin containing at least one selected from the group consisting of aromatic dicarboxylic acids and alicyclic dicarboxylic acids at a ratio of 80 mol % or higher of acid components.