JPS63166009A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain sufficient wear resistance and electromagnetic conversion characteristic by coating a magnetic coating compd. prepd. by subjecting the same to primary dispersion with a polyurethane resin into which a hydrophilic group is introduced, then to secondary dispersion with a vinyl chloride resin on a nonmagnetic base, thereby forming a magnetic layer. CONSTITUTION:The amt. of the polyurethane resin to be adsorbed can be increased to the amt. of the vinyl chloride resin to be adsorbed or above by introducing the hydrophilic group into the molecules of said resin. The secure adsorption of the polyurethane resin having the wear resistance better than the wear resistance of the vinyl chloride resin to the magnetic powder is, therefore, permitted by the hydrophilic group in the molecules. The better durability is thus obtd. with the magnetic coated film formed by the primary dispersion with the polyurethane resin having the hydrophilic group and the secondary dispersion with the vinyl chloride resin than the magnetic coated film obtd. by the reverse sequence.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium that can be used for magnetic disks and the like.

BACKGROUND OF THE INVENTION In recent years, particularly in the field of video tapes, research and development of magnetic materials has progressed from conventional iron oxide to metal-2 alloy systems in order to achieve high-density recording. Among these, the composition and manufacturing conditions of metal 1 alloy magnetic materials have been improved to achieve uniform fine particles, and the BET specific surface area has been reduced to 60 m2.
/g or more can now be stably produced. Furthermore, the BET specific surface area of iron oxide magnetic material is 50 m
Products with a ratio of 2/i or higher 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 a polyurethane resin and a vinyl chloride resin, primary dispersion using a polyurethane resin is superior to primary dispersion using a vinyl chloride resin, as disclosed in JP-A-56-167771.

Problems that the invention attempts to solve However, such conventional methods have poor superficiality, and the BET
If the specific surface area is 30 m279 or less, the electromagnetic conversion characteristics are satisfactory, but if the specific surface area is 50 m27 g or more, the electromagnetic conversion characteristics deteriorate.

An object of the present invention is to provide a magnetic recording medium that satisfies both wear resistance and electromagnetic conversion characteristics by using fine particle magnetic material having a BET specific surface area of 50 m2/g or more.

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
It is characterized in that a magnetic layer is formed by coating a magnetic paint secondary dispersed with vinyl chloride resin on a non-magnetic support.

Function: This configuration makes it possible to satisfy both electromagnetic conversion characteristics based on dispersibility and abrasion resistance based on coating film strength.

In order to achieve a high-density recording medium using fine particle magnetic material with a BET surface area of 50 m279 or more, high dispersion reduces the surface roughness and improves electromagnetic conversion characteristics, and the coating strength is improved to improve running performance. Durability must be satisfied. The present inventor has intensively studied the binder system of polyurethane resin and vinyl chloride resin from the viewpoint of adsorption of the resin to the magnetic material, and found that it is better to perform primary dispersion with polyurethane resin having hydrophilic groups and secondary dispersion with vinyl chloride resin. It has been found that, rather than the reverse, a magnetic coating film with excellent durability can be obtained with almost no change in C/N.

This is because polyurethane resin, which has better abrasion resistance than vinyl chloride resin, can be strongly adsorbed to magnetic powder by the hydrophilic groups in its molecules. Conventionally,
Many polyurethane resins have a lower adsorption amount than vinyl chloride resins, but by introducing hydrophilic groups into their molecules, it has become possible to make the adsorption amount equal to or higher than that of vinyl chloride resins, and the present invention The distribution order was determined based on the results with good durability.

The magnetic material used in the present invention is iron oxide.

Examples include CO-adhered iron oxide, iron nitride, metal or alloy magnetic material, and the BET specific surface area is 50W12/! 9 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.

Examples of the vinyl chloride resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride resin derivatives having a hydrophilic group in one molecule.

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, and chromium oxide are used as abrasive materials.

Titanium oxide or the like is used.

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, a three-roll mill, a pressure kneader, a double planetary mill, a ball mill Henschel mixer, a double moving mill, a disper mill, and a pebble mill.

Agitator mill attritor, sand grinder.

Coball mill, Combimix, line mill, line flow, bottle mill, etc. are used alone or in combination.

Example The present invention will be further explained in detail below.

Example 1 Ferromagnetic Co-coated r Fe20s 10 parts by weight Polyurethane resin α-alumina (average particle size 0.3 μm) having sodium sulfonate group 5 parts by weight Stearic acid 2 parts by weight n-butyl stearate 1 part by weight MEK −)
Luene-cyclohexane 1 ooit part non(2:2:
1) The above composition is mixed in a pressure kneader and then primary dispersed in a Copol mill. Next, 10 parts by weight of vinyl chloride-vinyl alcohol-maleic acid copolymer 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. After adding 4 parts by weight of Coronate L (polyisocyanate manufactured by Nippon Polyurethane) and mixing and dispersing with a disper, the mixture was filtered through a filter with an average pore size of 1 μm, coated on a 14 μm thick polyethylene terephthalate film, oriented, and dried.

Hardened after mirror polishing. 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 the vinyl chloride-vinyl alcohol-maleic acid copolymer were replaced.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the ferromagnetic CO-coated r-Fe2o3 was changed to ferromagnetic alloy powder.

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 the vinyl chloride-vinyl alcohol-maleic acid copolymer were replaced.

The obtained runner magnetic tape was cut into inch pieces, wound into a cassette half, and the C/N at 5 MHz was measured. The video tape for C/N measurement was a VHS video tape recorder (NV-8800, manufactured by Matsushita Electric Industrial Co., Ltd.), and in the case of alloy magnetic material, the recording/reproducing head was changed to Sendust alloy. National Video Chive and Super HG tape (NV-TI 20HGA) manufactured by Matsushita Electric Industrial Co., Ltd. were used as standard tapes, and the C/N was set to OdB. The durability of the tape is 200℃ under an environment of 40℃ and ao%RH.
The condition was observed after passing. 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.

As is clear from the examples and corresponding comparative examples, C/N hardly changes when primary dispersion is performed using a polyurethane resin having hydrophilic groups and secondary dispersion is performed using vinyl chloride resin, and vice versa. It has excellent durability.

Effects of the Invention As described above, according to the present invention, a magnetic recording medium that satisfies both 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 vinyl chloride resin on a non-magnetic support.