# US 5,702,821 A · Magnetic recording medium comprising ferromagnetic powder and a specified polyurethane resin

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- Number: US 5,702,821 A
- Document ID: US5702821A
- Status: Granted
- Kind: A
- Application number: 08/555,447
- Filed: 1995-11-09
- Granted: 1997-12-30
- Earliest claimed: 1995-02-24
- Assignees: Fuji Photo Film Co., Ltd.
- Inventors: Yuichiro Murayama; Masaki Satake; Hiroshi Hashimoto; Tsutomu Okita
- Web page: https://patentgrep.com/patent/US5702821A

## CPC

- G11B 5/7021: {containing a polyurethane or a polyisocyanate}
- Y10S 428/90: Magnetic feature
- Y10T 428/31609: Particulate metal or metal compound-containing
- 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

In a binder for a magnetic recording medium for forming a magnetic layer with ferromagnetic powder dispersed therein being arranged on a non-magnetic support member, whereby said binder consists of a polyurethane resin, which is a reaction product of diol and organic diisocyanate as principal materials, said polyurethane resin contains a short-chain diol having cyclic structure by 17 to 40 weight %, and said polyurethane resin contains a long-chain diol comprising 1.0 to 5.0 mmol/g of ether group to total urethane resin by 10 to 50 weight %. According to a binder for a magnetic recording medium and a magnetic recording medium using said binder of the present invention, good dispersion property, high running durability and preservation property can be obtained.

## Claims

### Claim 1

A magnetic recording medium comprising a magnetic layer formed on a non-magnetic support member, said magnetic layer comprising ferromagnetic powder and a binder comprising a polyurethane resin which is a reaction product of diol and organic diisocyanate, wherein said diol comprises short chain diol and long chain diol, said short-chain diol has a cyclic structure and said short chain diol forms 17 to 40 weight % of said polyurethane resin, said long-chain diol contains 1.0 to 5.0 mmol/g of an ether group and said long-chain diol forms 10 to 50 weight % of said polyurethane resin, and the thickness of said magnetic layer is 1 .mu.m or less, wherein said short-chain diol has a molecular weight less than 500, and said long-chain diol has a molecular weight of 500 to 5,000.

### Claim 2 (depends on 1)

A magnetic recording medium according to claim 1, wherein said polyurethane resin contains 3 to 20 OH groups per molecule.

### Claim 3 (depends on 2)

A magnetic recording medium according to claim 2, wherein said polyurethane resin contains at least one polar group selected from the group consisting of --SO.sub.3 M, --OSO.sub.3 M, --COOM, --P.sub.3 M'.sub.2, --OP.sub.3 M'.sub.2, --NR.sub.2, --N+R.sub.2 R'COO--, wherein M represents a hydrogen atom, an alkali metal, an alkali earth metal or an ammonium salt, M' represents a hydrogen atom, an alkali metal, an alkali earth metal or an ammonium salt, and R and R' each represents an alkyl group having 1 to 12 carbon atoms.