JPS6040531A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent surface smoothness without blooming or without deteriorating various electrical and mechanical properties by adding a suitable amt. of a volatile siloxane monomer as a leveling agent into a magnetic coating thereby evaporating said monomer in the stage of drying the coated film. CONSTITUTION:The magnetic coating is prepared by adding the volatile siloxane monomer expressed by the formulas I , II (R is alkyl, n<=1 in the formula I of straight chain structure, n<=5 in the formula II of the cyclic structure) and having <=200 deg.Cb.p. and >=1mm.Hg vapor pressure at 25 deg.C into ferromagnetic powder at about 0.1-10wt%. Such coating is applied on a base consisting of a polyester film, etc. and is dried to form a magnetic layer. The volatile siloxane monomer has good compatibility with the coating, requires the smaller amt. of the solvent to be added to the coating in the stage of preparing the same to an adequate viscosity, evaporates in the drying stage and obviates whitening of the surface of the coated film. The excellent magnetic recording medium is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium with excellent surface smoothness.

Magnetic recording media such as audio tapes are usually manufactured by kneading magnetic powder with a binder, various additives, etc., and coating the mixture onto a non-magnetic support such as polyethylene terephthalate.

As described above, ensuring surface smoothness (1) in coated magnetic recording media is essential to achieving high-density recording.
This is accomplished by adding a leveling agent to the magnetic paint or by mechanical treatment (for example, supercalender treatment) after coating.

However, mechanical processing alone is not enough.

It is not possible to obtain satisfactory smoothness. Also.

Polydimethylsiloxane or its derivatives, which are the most common leveling agents, have problems with compatibility with magnetic paints, and if too much is added, blooming may occur.2 Mechanical strength and electromagnetic conversion It is difficult to use because it causes deterioration of characteristics.

The present invention aims to provide a method for manufacturing a magnetic recording medium that eliminates these drawbacks.

One aspect of the present invention is to use a volatile siloxane monomer as a leveling agent in the magnetic coating in a method of manufacturing a magnetic recording medium by coating a magnetic coating on a non-magnetic support.

This volatile siloxane monomer not only sufficiently functions as a leveling agent in magnetic paints, but also volatilizes during the coating film drying stage, so even if too much is added.

It has the great advantage of not causing pluming or deteriorating electrical and mechanical characteristics.

The volatile siloxane monomer used in the present invention is a linear polyalkylsiloxane with n≦1 having a boiling point of 200°C or less, a vapor pressure (25°C), and taHg or more and having the following structure, or n ≦5 cyclic alkylsiloxane, as a specific example.

Examples include octamethyltrisiloxane and octamethylcyclotetrasiloxane.

R (R: alkyl group) R (R: alkyl group) The amount of the volatile siloxane monomer used in the present invention is based on the magnetic powder. , 1~]-0wt% or more, and the viscosity of the magnetic paint decreases as the amount added decreases, making it possible to reduce the amount of solvent required to form a paint. However, if too much is added, the drying time will increase. Since it takes a long time, it is preferable to use it at a ratio of 5 or less.

Next, examples of the present invention will be described.

Example 1 γ-Fe2O3"' 80 parts by weight Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
UCC VAGH) -12 Urethane resin...8 Dispersant (lecithin)...1.6 Methyl ethyl ketone...50 Toluene...50 Cyclohexanone...50 Octamethylcyclotetrasiloxane...4- After kneading the above composition in a ball mill for 24 hours, Coronae 1-3
041 (Incyanate compound manufactured by Nippon Polyurethane Co., Ltd.)
5 parts by weight were added and kneaded for an additional hour to obtain a magnetic paint. The magnetic paint obtained in this way was coated in a 1211 m thick
The magnetic tape was coated onto a JP Literene terephthalate film so that the thickness after drying was 6 μm.

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1 except that 4 parts of octamethylcyclotetrasiloxane in Example 1 was replaced with 4 parts of polydimethylsiloxane having a viscosity of 300 cps (25°C).

Specific Gravity I A magnetic tape was obtained in the same manner as in Example 1, except that 4 parts of octamethyltetrasiloxane in Example 1 was replaced with 4 parts of stearic acid-terminated polydimethylsiloxane (solid to paste at 25°C). Ta.

These samples were observed for leveling properties and degree of pluming. The results are shown in Table 1. Here, the leveling property is determined by comprehensively determining the center line average roughness measurement results using a surface roughness meter, as well as visual evaluation using a scanning electron microscope.

For blooming, 10% at room temperature and 70% relative humidity.
These are the results of observations made when sliding with the time head.

In Comparative Example 1, the compatibility of polydimethylsiloxane with magnetic paint was so poor that it was impossible to form it into a paint, and in Comparative Example 2, although the leveling properties were good, blooming occurred extremely frequently.

Chalking on the surface of the magnetic coating film was observed.

As can be seen from Table 1, according to the present invention, a magnetic recording medium with excellent surface smoothness that eliminates the conventional drawbacks can be obtained.

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Claims (1)

[Claims] 1. In a method of manufacturing a magnetic recording medium by cross-dispersing ferromagnetic powder in a binder to make a magnetic paint and coating it on a non-magnetic support, a volatile siloxane monomer is added to the magnetic paint. A method of manufacturing a magnetic recording medium characterized by: