JPH0487020A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain electromagnetic conversion characteristics of a high level and an excellent traveling property by specifying the stylus type two-dimensional surface roughness on the surface of a nonmagnetic base on the side opposite from the surface to be formed with a magnetic layer. CONSTITUTION:The stylus type two-dimensional surface roughness of the nonmagnetic base on the side opposite from the surface to be formed with the magnetic layer is so specified as to have >=15nm center line average roughness Ra, <=350nm max. height Rmax and <=300nm ten point average roughness Rz. There is the possibility that the traveling durability is deteriorated if the center line average roughness Ra is below 15nm. There is the possibility that the electromagnetic conversion characteristics are deteriorated if the max. height Rmax exceeds 350nm or the ten point average roughness Rz exceeds 300nm. The surface roughness of the back surface of the nonmagnetic base can be set within this range simply by providing an extremely thin layer on at least the back surface by, for example, co-extrusion or inline coating, etc., or by forming microprojections of SiO2, etc., by a vapor deposition method on the back surface side. The electromagnetic conversion characteristics and traveling property are assured at the high level in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic recording media such as video tapes.

[Summary of the invention]

The present invention provides a magnetic recording medium in which a magnetic layer is formed on a non-magnetic support, by optimizing the surface roughness of the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed. The objective is to provide a magnetic recording medium that has both electromagnetic conversion characteristics and excellent running properties.

[Conventional technology]

For example, in order to improve the electromagnetic conversion characteristics of a magnetic tape, it is advantageous to make the surface of the base film as mirror-finished as possible and smooth the surface of the magnetic layer to reduce unevenness.

Therefore, it is necessary to use a base film with good surface properties (low surface roughness) for the nonmagnetic support of a magnetic recording medium that requires high electromagnetic conversion characteristics.

This is because it is reflected in the surface properties of the base film underlying the magnetic layer or the surface properties of the magnetic layer formed thereon.

However, as the nonmagnetic support becomes smoother, running properties are affected, making it difficult for the magnetic tape to run smoothly.

On the other hand, in order to improve runnability and durability,
If a base film (with a large surface roughness) is used, there is a problem of deterioration of electromagnetic conversion characteristics.

All of these are due to the influence of the surface properties of the surface of the base film opposite to the surface on which the magnetic layer is formed. In other words, the runnability and electromagnetic conversion characteristics of a magnetic recording medium are affected more by the surface properties of the surface opposite to the magnetic layer forming surface (hereinafter referred to as the back surface) than by the surface properties of the magnetic layer forming surface of the base film. The influence of superficiality is very large.

This is because the surface properties of the back surface of the base film are transferred to the surface of the magnetic layer due to the heat treatment performed in a roll state after coating the magnetic layer.

[Invention or problem to be solved]

As described above, the surface properties of the back surface of a base film for a magnetic recording medium are very important, and in order to achieve both electromagnetic conversion characteristics and runnability, it is desirable to optimize the surface properties of the back surface.

The present invention was proposed in view of the conventional situation, and it is possible to optimize the surface properties of the back surface of a non-magnetic support and ensure high levels of electromagnetic conversion characteristics and runnability. The purpose of this invention is to provide a magnetic recording medium.

[Failure to solve the problem]

In order to achieve the above object, the magnetic recording medium of the present invention has a magnetic layer formed on a non-magnetic support, in which a magnetic layer is formed on a side of the non-magnetic support opposite to the surface on which the magnetic layer is formed. The two-dimensional stylus surface roughness of the surface is center line average roughness R6≧15 nm, maximum height R3, ≦350 nm,
It is characterized in that the ten-point average roughness R5≦300 nm.

In the magnetic recording medium of the present invention, the surface quality of the back surface of the nonmagnetic support is important. Generally speaking, the evaluation of the surface properties of magnetic recording media is mainly based on the center line average roughness Ra, but as a result of various studies conducted by the present inventors, the center line average roughness Ra It was concluded that the method was insufficient for evaluating the back surface of non-magnetic supports. Therefore, in the present invention, the Japanese Industrial Standard JIS B 060
The two-dimensional surface roughness using a stylus on the back surface of the non-magnetic support was measured in accordance with 1, and the surface roughness at this time was: center line average roughness Ra≧15 nm, maximum height Ra.

The roughness is set to be ≦350 nm, and the ten-point average roughness R5≦300 nm.

If the center line average roughness R6 is less than 15 nm, there is a risk that the running durability will deteriorate. Also, the maximum height R,,8
or exceeds 350nm, or the ten-point average roughness Ra is 300n.
If it exceeds m, there is a risk that the electromagnetic conversion characteristics will deteriorate.

In order to set the surface roughness of the back surface of the non-magnetic support within the above-mentioned range, for example, it is necessary to provide at least an extremely thin layer on the back surface by co-extrusion or in-line coating, or to coat the back surface with a material such as 5i02 by vapor deposition. What is necessary is to form minute protrusions.

For example, coextruded films can be produced by plasticizing the resin materials making up each layer in separate extruders, collecting them through separate conduits and extruding them through a single die onto a cooling drum, which is then biaxially stretched under normal conditions. The surface properties of the back surface can be controlled by mixing non-magnetic fine particles into the ultra-thin layer on the back surface side.

The non-magnetic fine particles preferably have a narrow particle size distribution and can be monodispersed, such as spherical silica, benzoguanamine resin, styrene resin, acrylic resin fine particles, etc., and the average particle size and amount added can be adjusted. Any superficiality can be obtained.

Of course, on the back surface on which the ultra-thin layer or minute protrusions are formed,
Furthermore, it is also possible to form a back coat layer. In this case, by reducing the thickness of the back coat layer, the surface properties of the back surface of the base film can be utilized, which is suitable for controlling the surface properties.

Furthermore, as the material for the non-magnetic support, any material normally used for this type of magnetic recording medium can be used, including polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and other materials. A polyester base film, such as one copolymerized with monomers in a proportion of 15 mol % or less, is suitable.

On the other hand, the binder, magnetic powder, various additives, etc. contained in the magnetic paint for forming the magnetic layer may be those used in ordinary coated magnetic recording media, and are not limited in any way. do not have.

[Effect]

In magnetic recording media, the surface roughness of the back surface of the non-magnetic support has a large influence on electromagnetic conversion characteristics and running properties, but even if one attempts to determine the optimum surface roughness only by the center line average roughness R6, In many cases, either the electromagnetic conversion characteristics or the running performance deteriorate.

In the magnetic recording medium of the present invention, not only the center line average roughness Ra, but also the maximum height R Since the surface properties have been optimized, a high level of both electromagnetic conversion characteristics and runnability can be achieved.

〔Example〕

The present invention will be explained below based on specific experimental results.

The compositions of the magnetic paint and back coat paint used in each Example and Comparative Example are as follows.

Magnetic paint Metal magnetic powder...100 parts by weight (specific surface area 55n(/g) Vinyl chloride vinyl acetate copolymer...12 parts by weight (U
, manufactured by C, C Company, VYHH) Polyurethane resin... 7 parts by weight (manufactured by Nippon Polyurethane Company, N-3109) Alumina
... 5 parts by weight (product name AKP-5
0) Carbon...2 parts by weight (product name Conductex SC) Butyl stearate...2.5 parts by weight Myristic acid...1 part by weight Methyl ethyl ketone...150 parts by weight Toluene
... 50 parts by weight Back coat paint Carphone ... 97 parts by weight (manufactured by Mitsubishi Kasei Co., Ltd., #980B) Additives ... 3 parts by weight (manufactured by Capot Co., Ltd., 5TERLING NS) Vinyl chloride vinyl acetate copolymer ... 80 parts by weight (manufactured by U, C, C Company, VAGH) Polyurethane resin ... 20 parts by weight (manufactured by Nippon Polyurethane Co., Ltd., N-2304) Oleic acid
...0.3 parts by weight methyl ethyl ketone ...700 parts by weight toluene
...300 parts by weight Examples 1 to 5 In this example, an ultrathin layer in which non-magnetic fine particles were dispersed was formed by co-extrusion on the back surface opposite to the magnetic surface on which the magnetic layer was formed. coextruded film (thickness 7.5μm)
) is used as a nonmagnetic support. The thickness of the ultra-thin layer of the coextruded film used in each example, the type of nonmagnetic fine particles, and the average particle size are as shown in Table 1. Note that the amount of nonmagnetic fine particles added was uniformly 0.4%. The thickness of the ultra-thin layer was measured using a transmission electron microscope, and the average particle diameter of the added non-magnetic fine particles was determined by observing the particles using a transmission electron microscope and obtaining the average value of 100 particles. Ta.

Table 1 On the other hand, on the magnetic side, non-magnetic fine particles with an average particle size of 0.
0.01% of 1 μm spherical silica was added, and the center line average roughness R was −5 nm, the maximum height Ra was 6 Onm, and the ten point average roughness R was 50 nm.

After kneading the above magnetic paint in a sand mill for 5 hours, 2 parts by weight of a hardening agent (trade name: Coronate) was added to the magnetic surface of each coextruded film so that the film thickness after drying was 4.0 μm. Coated. Next, perform calendar processing,
Heat treatment was performed at 80°C for 48 hours.

Thereafter, the previous back coat paint was applied to the back surface so that the film thickness after drying was 1.0 .mu.m, and an 8-line slit was made to incorporate it into a cassette. The back coat paint was kneaded in a ball mill for 48 hours, and after adding 10 parts by weight of a hardening agent (trade name: Coronate), it was applied to the back surface.

The thickness of the ultra-thin layer, the type of coating resin, the type of non-magnetic fine particles, and the average particle size of the in-line coated film are as shown in Table 2. Note that the amount of nonmagnetic fine particles added was uniformly 0.35%. In addition, on the magnetic surface side, 0.01% of spherical warping force with an average particle diameter of 0.1 μm was added as non-magnetic fine particles as in the previous example, and the center line average roughness R,=
5 nm, maximum height Rm a = 60 nm, and ten point average roughness R, = 50 nm.

The method of forming the magnetic layer and back coat layer is also the same as in the previous example.

Table 2 Example 6 to Example IO This example is an in-line coating in which an ultra-thin layer in which non-magnetic fine particles are dispersed is formed by in-line coating on the back surface opposite to the magnetic surface on which the magnetic layer is formed. This is an example in which a film (thickness: 7.5 μm) was used as a nonmagnetic support. Used in each Example In this example, a single-layer base film was used as the non-magnetic support.

The method of forming the magnetic layer and back coat layer is the same as in the previous example.

For each of the above-mentioned Examples and Comparative Examples, the centerline average roughness Ra and maximum height R+m of the back surface of the non-magnetic support, respectively.
ay and ten point average roughness Ra were measured.

For measurement, ET-30HK+5PA-1 manufactured by Koita Research Institute
1 was used to determine the two-dimensional roughness by a contact method. The measurement conditions are as follows.

Measurement condition Needle pressure 6■ (needle diameter 2μmR) Magnification Height direction X50000 Cutoff 0.0’8mm Measurement speed: 20μm/sec The results are shown in Table 3.

Furthermore, electromagnetic conversion characteristics, dropout, and running durability were measured for the sample tapes obtained in each of the above Examples and Comparative Examples.

For electromagnetic conversion characteristics, a 7 MHz signal was recorded, and the 7 μm output and 6.5 MHz output (noise) were measured.

As for dropouts, after inputting a white 50% signal, playback was performed and dropouts of -16 dB/μsec or more were counted. The running durability was determined by measuring the number of passes when the output level decreased by 3 dB when running in an environment with a temperature of 40° C. and a relative humidity of 80%.

The results are shown in Table 4.

(Leaving space below) Table 3 Table 4 As is clear from this table, the sample tapes of each example achieved good runnability and electromagnetic conversion characteristics, and there were few dropouts. It has become a thing.

On the other hand, in Comparative Example 1, for example, where the center line average roughness R8 is less than 15 nm, although the deterioration of the electromagnetic conversion characteristics is suppressed, the runnability is significantly inferior. On the other hand, Comparative Example 2 has a large maximum height Ra, 1 and a ten-point average roughness R8. In Comparative Example 3, although running performance was secured to some extent, deterioration of electromagnetic conversion characteristics was observed.

〔Effect of the invention〕

As is clear from the above explanation, in the magnetic recording medium of the present invention, the surface roughness of the back surface of the nonmagnetic support is
Since not only the centerline average roughness but also the maximum height and ten-point average roughness are optimized, it is possible to achieve both high levels of electromagnetic conversion characteristics and runnability.

Procedural amendment (voluntary) November 5, 1990

Claims (1)

[Scope of Claims] A magnetic recording medium in which a magnetic layer is formed on a non-magnetic support, comprising: a stylus-type two-dimensional surface roughening of a surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed; center line average roughness R_a≧1
5 nm, maximum height R_m_a_x≦350 nm) and ten-point average roughness R_■≦300 nm.