JPS63166011A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease powder dislodgment from a magnetic layer and to improve running durability by forming the magnetic layer which is formed by post-adding a fatty acid to a metal or alloy magnetic material of >=7.5 pH value on a nonmagnetic base. CONSTITUTION:The magnetic layer which is formed by post-adding the fatty acid to the metal or alloy magnetic material of >=7.5 pH value is formed on the nonmagnetic base. The coefft. of friction of the magnetic coated film obtd. from the metal or alloy magnetic material of >=7.5 pH value is heretofore high and the running durability is poor, but if the fatty acid is post-added to the coating compd. without adding the same thereto from the beginning, the amt. of the fatty acid to be adsorbed to said magnetic material is decreased and the magnetic coated film having the low coefft. of friction is obtd. The coefft. of friction of the magnetic layer is thereby decreased and the powder dislodgment is decreased, by which the running durability is improved.

Description

[Detailed description of the invention] Industrial applications The present invention relates to audio tapes and video tapes.

The present invention relates to magnetic recording media that can be used for magnetic cards, magnetic disks, etc., and particularly relates to magnetic recording media made of metal powder with improved running durability.

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'.
/r or higher can now be stably manufactured. Furthermore, as a measure against moisture resistance, which is a problem unique to metal/alloy magnetic materials, metal/alloy magnetic materials with a pH value of 7.6 or higher are being considered, as disclosed in JP-A-60-32123◇ Problems to be Solved by the Invention However, with such a conventional configuration, the magnetic coating film obtained had a high coefficient of friction and poor running properties.

As a result, there was a problem in that there was a lot of powder falling off from the magnetic layer, and the condition was not yet satisfactory for improving running durability.

An object of the present invention is to provide a magnetic recording medium that has a lower coefficient of friction, less dust falling from a magnetic layer, and improved running durability.

Means for Solving the Problem In order to solve this problem, the magnetic recording medium of the present invention has a magnetic layer formed by adding a fatty acid to a metal or alloy magnetic material having a pH value of 7.5 or more on a non-magnetic support. It is characterized by being formed on the top.

Function: With this configuration, it is possible to lower the friction coefficient of the magnetic layer, reduce powder falling, and improve running durability.

Although metal or alloy magnetic materials with a pH value of 7.5 or higher have various features, one of the problems that prevents them from being widely used is that the resulting magnetic coating has a high coefficient of friction and poor running durability. ◎The present inventor analyzed the adsorption phenomenon of fatty acids as a lubricant, and by adding fatty acids later to the paint instead of adding them from the beginning, the amount of fatty acids adsorbed by the magnetic material was reduced. It was discovered that a magnetic coating film with a low coefficient of friction can be obtained, leading to the present invention.

The metal or alloy magnetic material used in the present invention is F
e, Fe-Co, Fe-Ni, Co-Ni
, Fe-Co-Nl, etc.

Those having a pH value of 7.5 or more can be easily obtained through a dry oxidation process during the production of metal or alloy magnetic materials. This is thought to be due to the precipitation of alkaline roots on the surface of the magnetic powder due to dry oxidation.

As a binder, polyurethane resin, polyurethane resin with hydrophilic groups introduced, polyester resin with hydrophilic groups introduced,
Vinyl chloride resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride derivatives with hydrophilic groups introduced,
Butyral resin, phenoxy resin, etc. can be 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, and chromium oxide are used as abrasive materials.

Titanium oxide or the like is used. As an anti-static agent, conductive carbon such as Ketchinplak E and C0 can be added, and graphite carbon black can also be used.

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

For example, three-roll mill, pressure kneader, double planetary mixer, ball mill, Henschel mixer, vibration mill, disper mill, and pebble mill.

Agitator mill, attritor, sand grinder, cobal mill, combination mix, line mill.

Line flow, pin mill, etc. are used alone or in combination.

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

Example 1 Ferromagnetic metal iron powder (PH: 8.5) Lecithin 1 part by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 1
0 parts by weight α-alumina (average particle size 0.3 μm) 5 parts by weight Stearic acid Nibutyl 1 part by weight Carbon black 2 parts by weight MEK-
200 parts by weight of luene-cyclohexanone (2:2:1) The above composition was dispersed using a pressure kneader and a cobal mill to obtain a magnetic coating material. Next, 2 parts by weight of stearic acid as a lubricant and 4 parts by weight of Coronate L (Japan Polyurethane Polyisocyanate) as a hardening agent were added and mixed and dispersed with a disper, and then filtered through a filter with an average pore size of 1 μm to form a polyethylene terephthalate film with a thickness of 10 μm. It was coated on top, oriented, dried, mirror-finished, and then cured. Furthermore, a back coat layer mainly composed of carbon black was provided on the polyethylene terephthalate film on the side opposite to the magnetic layer to obtain a magnetic tape. ◎ Comparative Example 1 In Example 1, stearic acid was not added afterward, but magnetic paint was manufactured. A magnetic tape was obtained in the same manner except that it was added during the process.

Example 2 In Example 1, the ferromagnetic metal iron powder was replaced with Fe-Co-Ni
A magnetic tape was obtained in the same manner except that an alloy was used.

Comparative Example 2 A magnetic tape was obtained in the same manner as in Example 2, except that stearic acid was added during the magnetic paint manufacturing process (pre-addition).

Each of the obtained magnetic tapes was cut into pieces of % inch, wound into cassette halves, and subjected to a durability test. The environment is 40℃, a
The state after running the tape for 200 passes at o%RH was observed. The VTR used was a VHS video tape recorder (NV-8800 manufactured by Kishita Denki Sangyo Co., Ltd.), and the recording/reproducing head was changed to a Sendust alloy.

The results are shown below.

As is clear from the Examples and the corresponding Comparative Examples, post-addition of fatty acids as a lubricant has effects such as lowering the coefficient of dynamic friction, reducing powder falling, and preventing clogging. This is because we focused on the phenomenon that fatty acids are easily adsorbed because magnetic powder has a pH of 7.6 or higher and is alkaline, and by adding it later, we succeeded in reducing the amount of adsorption and lowering the coefficient of friction. .

Effects of the Invention As described above, according to the present invention, it is possible to prevent the lubricant from adhering to the magnetic powder, thereby improving the running durability of the recording medium.

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] 1. A magnetic recording medium comprising a magnetic layer formed by adding a fatty acid to a metal or alloy magnetic material having a pH value of 7.5 or higher on a non-magnetic support.