JPS63175221A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic transducing characteristic and wear resistance of the title medium by primarily dispersing a magnetic substance with the polyurethane resin incorporated with a hydrophilic group, then secondarily dispersing the substance with nitrocellulose to obtain a magnetic paint, and then coating the magnetic paint on a nonmagnetic supporting body to form the magnetic layer. CONSTITUTION:A magnetic substance is primarily dispersed with the polyurethane resin incorporated with a hydrophilic group, and then secondarily dispersed with nitrocellulose to obtain a magnetic paint. The paint is coated on a nonmagnetic supporting body along with a binder to form a magnetic layer. Iron oxide, Co-coated iron oxide, iron nitride, etc., can be exemplified as the magnetic substance, and the BET specific surface is controlled to >=30m<2>/g. The binder is the polyurethane resin incorporated with a hydrophilic group, and has a phosphoric group or a sulfonic group or the metal salt of the group in the molecule. Nitrocellulose resin, the nitrocellulose resin having a phosphoric group or a sulfonic group in the molecule as the hydrophilic group, etc., can be used as the nitrocellulose, and lecithin, oleic acid, etc., are used as the dispersant. By this method, the electromagnetic transducing characteristic and durability are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium that can be used for audio tapes, video tapes, magnetic cards, magnetic disks, and the like.

BACKGROUND OF THE INVENTION In recent years, research and development of magnetic materials has progressed from conventional iron oxide to metal/alloy systems, particularly in the field of video tapes, in order to achieve high-density recording. Among these, improvements have been made to the composition and manufacturing conditions of metal/alloy magnetic materials in order to achieve uniform particle size, and the BET specific surface area has increased to 60 m'.
/f or higher can now be stably manufactured. Furthermore, the BET specific surface area of iron oxide magnetic material is 50 m''
/2 or more are now being manufactured. In order to obtain a high-density recording medium with excellent durability using such fine-grained magnetic material, the problem of the interface between the tape and the head becomes important.

Among these, the binder system and dispersion order determine wear resistance and electromagnetic conversion characteristics.

In a system using polyurethane resin and nitrocellulose, as disclosed in JP-A-56-167769, primary dispersion with nitrocellulose provides better dispersibility and lower surface roughness than primary dispersion with polyurethane resin. As a result, electromagnetic conversion characteristics are improved. But 30rr? /
The running durability of a fine particle magnetic material having a BET specific surface area of 30 yf/ or more was not satisfactory in terms of running durability. The objective is to provide a magnetic recording medium that satisfies both abrasion resistance and electromagnetic conversion characteristics.

Means for Solving the Problem In order to solve this problem, the magnetic recording medium of the present invention is made by first dispersing the polyurethane resin into which hydrophilic groups have been introduced, and then
A magnetic layer is formed by coating a magnetic paint secondary dispersed with nitrocellulose on a non-magnetic support.

Function: With this configuration, it is possible to satisfy both electromagnetic conversion characteristics based on dispersibility and abrasion resistance based on coating film strength.

Example BET specific surface area is 30PF? In order to achieve a high-density recording medium using a magnetic material with fine particles of / or more, it is necessary to reduce surface roughness through high dispersion and improve electromagnetic conversion characteristics, and to improve running durability by increasing coating strength. must be satisfied. The present inventor has intensively studied the binder system of polyurethane resin and nitrocellulose from the viewpoint of adsorption of the resin to the magnetic material, and has arrived at the present invention.

The magnetic material used in the present invention includes iron oxide, Co-coated iron oxide, iron nitride, etc., and has a BET specific surface area of 30
rr? /P or higher.

A polyurethane resin into which a hydrophilic group as a binder is introduced has a phosphoric acid group, a sulfonic acid group, or a metal salt thereof in the molecule.

Nitrocellulose resin, nitrocellulose resin having a phosphoric acid group or sulfonic acid group as a hydrophilic group in the molecule, etc. are used. Lecithin, oleic acid, etc. are used as the dispersant.

Higher fatty acids such as myristic acid, palmitic acid, stearic acid, and behenic acid can be used as lubricants.

Alumina, red iron oxide, chromium oxide, titanium oxide, etc. are used as the abrasive. As an antistatic agent, conductive carbon such as Ketchinplak E, C, etc. can also be added. Furthermore, graphitized carbon black can also be used.

Various types of dispersion machines are used to disperse crosstalk in magnetic paint.

For example, three-roll, pressure kneader, double planetary mixer, ball mill, Henschel mixer, vibration mill, disper mill, pebble mill, agitator tile, attritor, sand grinder, copole mill, conhimix, line mill, line flow, pin mill, etc. Used alone or in combination.

The present invention will be further explained in detail below.

Example 1 Ferromagnetic CO-coated γ-F e203 carbon blank 3 parts by weight Polyurethane resin 10 having sodium sulfonate groups
Parts by weight α-alumina (average particle size 0.3 μm) 5 parts by weight Stearic acid 2 parts by weight Stearic acid n-Butyl 1 part by weight MEK-Toluene-Cyclohexanone (2:2:1
) 100 parts by weight of the above composition was mixed in a pressure kneader and then primarily dispersed in a Copol mill.

10 parts by weight of nitrocellulose and 100 parts by weight of MEK-toluene-cyclohexanone (2:2:1) were added and secondary dispersed using a sand grinder to obtain a magnetic paint.

4 parts by weight of Coronate L (polyisocyanate manufactured by Nippon Polyurethane) was added and mixed and dispersed with a disper, followed by filtration with a filter having an average pore size of 1 μm.

It was coated on a 14 μm thick polyethylene terephthalate film, oriented, dried, mirror-finished, and then cured.

Furthermore, a back coat layer containing carbon black as a main component was provided on the polyethylene terephthalate film on the side opposite to the magnetic layer to obtain a magnetic tape.

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1, except that the polyurethane resin having a sodium sulfonate group and nitrocellulose were replaced.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the ferromagnetic Co-coated γ-Fe 203 was changed to the following ferromagnetic iron nitride.

Comparative Example 2 A magnetic tape was obtained in the same manner as in Example 2, except that the polyurethane resin having a sodium sulfonate group and nitrocellulose were replaced.

Each of the obtained magnetic tapes was cut into % inch pieces, wound into a cassette half, and the C/N at 5 MHz was measured.

For C/N measurement, a VHS video tape recorder (NV-8800 manufactured by Matsushita Electric Industrial Co., Ltd.) was used.The standard tapes used were National Videotape and Super HG-tape (NV-8800).
-TI20HGA) manufactured by Matsushita Electric Industrial ■, its C/
N was set as odB. Durability: tape 40″C, 80%
The state of the bus was observed after running it 200 times in a RH environment. The surface roughness was measured using Talysurf manufactured by Rank Taylor Hopson and expressed in Ra. Ra means the arithmetic mean of the deviations of the surface roughness from the center line. The measurement results are shown in the table below.

As is clear from the examples and corresponding comparative examples, primary dispersion with a polyurethane resin having hydrophilic groups and secondary dispersion with nitrocellulose results in better durability with almost no change in C/N than the reverse. Excellent in nature. This is because polyurethane resin, which has better abrasion resistance than nitrocellulose, can be strongly adsorbed to magnetic powder by the hydrophilic groups in its molecules.

Conventionally, many polyurethane resins had a lower adsorption amount than nitrocellulose, but by introducing hydrophilic groups into their molecules, it is now possible to make the adsorption amount equivalent to or higher than that of nitrocellulose.As a result, the surface roughness , C/N is no longer affected by the dispersion order, and the dispersion order is determined based on results with good durability.

Effects of the Invention As described above, according to the present invention, a magnetic recording medium that satisfies electromagnetic characteristics and durability can be obtained.

In addition, in the above embodiment, a magnetic tape was explained, but
It goes without saying that the present invention is applicable not only to magnetic tapes but also to magnetic recording media such as magnetic disks and magnetic cards.

Claims (1)

[Claims] After primary dispersion using polyurethane resin with hydrophilic groups introduced,
A magnetic recording medium characterized in that a magnetic layer is formed by coating a magnetic paint secondary dispersed with nitrocellulose on a non-magnetic support.