JPS61182630A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce dispersion time, to decrease the amt. of the resin to be adsorbed to nonmagnetic powder and to make smaller the coefft. of friction by dispersing the nonmagnetic powder into a binder soln. at a low ratio and coating the soln. on the surface of a nonmagnetic base on the side opposite from the surface on which a magnetic layer is provided then subjecting the surface to a highly smoothing treatment. CONSTITUTION:The coating liquid is prepd. by combining 1 or >=2 kinds of nonmagnetic inorg. powders such as carbon black, graphite, CaCO3, BaSO4, ZnO and TiO2 and dispersing the same into the binder resin soln. and such coating liquid is coated on the surface of the base on the side opposite from the surface on which the magnetic layer such as magnetic tape or magnetic sheet is provided. The kneading time for the inorg. powder and resin soln. in a ball mill is made half the kneading time of the conventional practice or below to obtain the low dispersed and kneaded matter in the stage of the preparing the above-mentioned coating liquid. The kneaded matter is filtered with a filter having average 3mu grain size by which the paint for the back coat layer is obtd. Such paint is coated on the base and after drying, the surface is treated with a super calender roll by which the back coat layer having the surface roughness within the 0.25-0.35 range of the average roughness of the 'surface roughness' specified in JIS B6001 + point surface roughness RZ is obtd. The magnetic recording medium having the small coefft. of friction, excellent video S/N and good running stability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic sheets used in audio/video equipment, computers, and the like.

BACKGROUND OF THE INVENTION Magnetic recording media are increasingly becoming more densely packed year by year. As a result, it is necessary to reduce recording and reproducing losses in the short wavelength region, and measures are being taken to further reduce the gap between the magnetic head and the magnetic recording medium. That is, making the surface of the magnetic recording medium highly smooth, making the magnetic powder finer, etc.

However, such a measure causes the following problem. That is, as the surface of the magnetic recording medium becomes highly smooth, the coefficient of friction of the magnetic recording medium increases, so that running performance and durability deteriorate compared to conventional ones.

As a method for solving this problem, it is generally known to provide a back coat layer on the surface of the magnetic recording medium opposite to the magnetic layer on the nonmagnetic support. [For example, Japanese Patent Publication No. 55-80830] This back coat layer consists of nonmagnetic powder and a binder. Nonmagnetic powder is used as a filler to adjust coating strength, surface electrical resistance, etc.

Problems to be Solved by the Invention The basic characteristics required of the back coat layer are a low coefficient of friction and excellent wear resistance. However, conventional backcoat layers do not satisfy these two requirements at the same time, and a backcoat layer with sufficient characteristics such as an increase in the coefficient of friction or peeling of the backcoat layer during running has not yet been obtained. . In particular, if the surface of the back coat layer is made excessively rough with emphasis on runnability, this roughness will be transferred to the magnetic layer on the back surface of the support when the magnetic recording medium is wound up into a roll. As a result, the surface of the magnetic layer becomes rough and the air gap with the magnetic head increases, resulting in increased air gap loss and deterioration of the electromagnetic conversion characteristics of the magnetic layer.

Means for Solving the Problems In order to solve the above problems, the method of the present invention combines a magnetic layer on one main surface of a non-magnetic support and a non-magnetic powder on the other main surface. In a magnetic recording medium each provided with a back coat layer dispersed in a coating agent, when forming the back coat layer, the dispersion time of the coating material is shortened compared to the conventional method, and a highly smoothing treatment is performed after coating. As a result, a magnetic recording medium with a back coat layer having a low coefficient of friction and excellent wear resistance can be obtained.

The surface roughness of the back coat layer in the present invention is Japanese Industrial Standards ()Is) Baoo1r surface roughness + point average roughness H
In, it is 0.25 to 0.35.

By shortening the dispersion time of the functional paint and performing a highly smoothing treatment after application, the following characteristics are exhibited.

First, by shortening the dispersion time, the amount of resin adsorbed on the filler surface is reduced compared to the conventional method, so that the running system and the filler surface in contact with it are reduced on the surface of the formed back coat layer. The coefficient of friction decreases. Therefore, even after performing the high smoothing treatment, the coefficient of friction is lower than that obtained by conventional means even if the surface roughness is the same.

Secondly, by shortening the dispersion time, the viscosity of the produced coating material is lower than that obtained conventionally, and there is less change over time, resulting in excellent coatability and mass production.

Fillers for the back coat layer to which the present invention is applied include carbon black, graphite, CaCO3, Ba5O.
ZnO, Tie. These inorganic powders can be used singly or in combination of two or more. Furthermore, small amounts of lubricants, dispersants, etc. may be included as necessary. Furthermore, as the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and the like can be used alone or in combination.

EXAMPLE An example of the method for manufacturing a magnetic recording medium of the present invention will be described using a magnetic tape as an example. It should be noted that all values of component ratios stated in the Examples indicate parts by weight.

(Example 1) A magnetic paint and a back coat paint were prepared as follows.

1. Preparation of magnetic paint Co containing r Fe2O2 magnetic iron oxide powder 10 parts Average particle size Length = 0.3 μm Acicular ratio = 10/1 Coercive force 6500e Polyurethane resin 15 parts Vinyl chloride-vinyl acetate copolymer 5 parts Nitro Cellulose resin 5 parts Aluminum chloride powder
3 parts Average particle size 0.3 μm Lecithin 2 parts Methyl ethyl ketone 100 parts Methyl isobutyl ketone 100 parts Toluene
After mixing and dispersing 100 parts of the above composition in a ball mill for 48 hours, 6 parts of a hardening agent (Coronate L) was added, and the resulting mixture was filtered through a filter having an average particle size of 3 μm to prepare a magnetic coating solution. .

2. Preparation of paint for back coat layer Ca COs powder 100 parts Average particle size 0.1 μm Polyurethane resin 60 parts Nitrocellulose resin 60 parts Methyl ethyl ketone 250 parts Toluene
180 parts cyclohexanone
After mixing and dispersing 70 parts of the above composition in a ball mill for 36 hours and removing the contaminants, 15 parts of a hardening agent (Coronate L) was added and mixed and dispersed for about 30 minutes in a high-speed dissolver.
Further, the mixture was filtered through a filter having an average particle size of 3 μm to prepare a back coat layer paint.

Next, the above magnetic paint was applied onto a 15 μm thick polyester film, oriented and dried, and then the magnetic layer was surface treated using a super calendar roll to obtain a wide jumbo roll with a magnetic layer thickness of 5 μm.

Using this jumbo roll, the above paint for the back coat layer was applied to the surface opposite to the magnetic layer, and after drying, the surface was treated with a super calendar roll to form a back coat layer with a thickness of 0.7 μm. . This was cut into 1/2 inch width to produce a videotape.

(Example 2) In the back coat layer paint of Example 1, 100 parts of carbon black (average particle size 0.1 μm) was used as a filler instead of CaCos, and the other conditions were the same as in Example 1. A videotape was made.

(Comparative Example 1) A videotape was produced in the same manner as in Example 1 except that the back coat layer paint of Example 1 was not subjected to surface treatment using a super calendar roll.

(Comparative Example 2) Example 20 A videotape was produced in the same manner as in Example 2 except that the coating for the back coating layer was not subjected to surface treatment using a super calendar roll.

(Comparative Example 3) A videotape was produced in the same manner as in Example 1 except that the dispersion time in the ball mill was 1 hour for the back coat layer paint of Example 1.

(Comparative Example 4) A videotape was produced in the same manner as in Example 2 except that the dispersion time in the ball mill was 1 hour for the back coat layer paint of Example 2.

(Comparative Example 6) A videotape was produced in the same manner as in Example 1 except that the dispersion time in the ball mill was 96 hours for the back coat layer paint of Example 1.

(Comparative Example e) A videotape was produced in the same manner as in Example 2 except that the dispersion time in the ball mill was 96 hours for the back coat layer paint of Example 2.

The scratch resistance, surface roughness, friction coefficient, and video S/N of the back coat layer of each of the above samples are shown in the attached table. In this table, 1) Scratch resistance is determined by applying a load of 40 (ii+) to a 6φ steel ball and reciprocating the sample tape surface 50 times on the same track at a speed of 20 mm/sec. They were observed and evaluated on a 6-level scale.

1 means the most damage, and 5 means the least damage.

2) Surface roughness is measured using a stylus type surface roughness meter, and is based on the "surface roughness" of Japanese Industrial Standards (JIS) Beool.
Then, the ten-point average roughness R was calculated.

3) The coefficient of friction (μK) is the value of the inlet tensicon (Ti) and the outlet tension (To) when the sample is wound around a 4φ stainless steel pin at a 180 degree angle and is run at 4 Cm/sec. It was read out and calculated using the following formula.

p K = I n (To/T i )/π4) bidet, t-S is a VH8 type VTR (under desk [Kisei Sangyo Co., Ltd. N
V8200), record the specified brightness signal (60% white level signal) from the TV signal generator at the optimal recording current of the reference tape, and use a video color noise meter to compare the signal and noise contained in the demodulated signal during playback. The ratio was measured and compared with that of the reference tape as odB.

As is clear from the above table, the magnetic tape obtained as described above has a better balance between wear resistance and running stability than conventional products.

Although the above embodiments have been described with reference to magnetic tapes, it goes without saying that the present invention is applicable not only to magnetic tapes but also to other magnetic recording media such as magnetic sheets.

Effects of the Invention As detailed above, according to the present invention, it is possible to obtain a magnetic recording medium having a back coat layer that has excellent wear resistance, a low coefficient of friction, and stable running, so its practical value is There is something big.

Claims (1)

[Claims] A method for manufacturing a magnetic recording medium, wherein a magnetic layer is provided on one main surface of a non-magnetic support, and a back coat layer made of non-magnetic powder dispersed in a binder is provided on the other main surface. When forming the back coat layer, the paint is subjected to a low dispersion treatment, and after application, the back coat layer surface is subjected to a high smoothing treatment to meet Japanese Industrial Standards (JIS) B6001.
A method for manufacturing a magnetic recording medium, characterized in that "surface roughness" + point average roughness R_2 is 0.25 to 0.35.