JPH0624060B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk.

[Prior art and its problems]

From the standpoint of achieving high density recording, finely divided magnetic powder has been used for the magnetic recording medium.

However, when the magnetic powder is made into fine particles, there is a drawback that the light transmittance of the magnetic layer containing the fine magnetic particles becomes large, which causes a problem in the operation of the magnetic recording / reproducing apparatus. That is,
For example, in a home-use video tape recorder or the like, when light is transmitted through a transparent leader tape portion provided at an end of a magnetic tape which is a magnetic recording medium, it is detected that the magnetic tape reaches the end. It has a tape edge detection mechanism that stops running, but when the light transmittance of the magnetic tape other than the leader tape section becomes large, light passes through this magnetic tape, and the tape edge detection mechanism malfunctions. There is a problem that makes it easier.

Therefore, in order to prevent such a malfunction of the tape edge detection mechanism, a large amount of carbon black is added to the magnetic layer to reduce the light transmittance of the magnetic layer. Has a problem in that the dispersibility of the magnetic powder is deteriorated and the electromagnetic conversion characteristics are deteriorated by adding a large amount of carbon black to the magnetic paint for forming the magnetic layer.

Therefore, in order not to add a large amount of carbon black to the magnetic layer and to reduce the light transmittance in the magnetic layer constituting portion, a carbon black containing layer, a so-called back coat, is formed on the surface of the support opposite to the magnetic layer constituting side. It is proposed to provide layers.

However, the conventional magnetic recording medium having the back coat layer has a relatively large coefficient of kinetic friction and is not so good in running property, and has a drawback that the screen is shaken when repeatedly reproduced. is there.

[Disclosure of Invention]

The present inventor has conducted detailed research on the cause of the above problems, and as a result, found that these problems are caused by the surface property of the so-called back coat layer, and further researched this surface property. As a result, the specific surface area of carbon black in this back coat layer was 20 to 800 m.
² / g, and projections having a projection height of 2 to 30 nm are 5 × 10 ³ on the surface of the carbon black-containing layer.
If the magnetic recording medium has a sparse ratio of 20 × 10 ³ particles / mm ² or more and 20 × 10 ³ particles / mm ² or less, the dynamic friction coefficient of this magnetic recording medium is small, and the fluctuation of the screen does not occur even when repeatedly reproduced. I found that it rarely happens.

In addition, about 5 × 10 ³ pieces / mm ² or more, about 20 × 10 ³ pieces / mm ²
In order to form the carbon black-containing layer so that the protrusions having a height of about ² to 30 nm are present at a ratio of less than or equal to mm ² , at the time of manufacturing the paint for forming the carbon black-containing layer, the carbon black-containing layer is formed at once in the paint. Rather than adding carbon black, it is added and dispersed in multiple times such as twice, and more specifically, about 60 to 90% of the total amount of carbon black to be added is dispersed. First, the dispersion work is carried out by adding, and the temporary dispersion work is stopped in the middle of the predetermined dispersion time or the remaining carbon black is added while continuing the dispersion work, and the remaining dispersion time is followed by the dispersion work. A carbon black-containing paint is manufactured through a number of steps, and the carbon black-containing paint thus obtained is applied to the surface of the support on which the magnetic layer is not formed. Obtained by the.

Further, the carbon black contained in the so-called back coat layer preferably has a specific surface area (BET value) of about 800 m ² / g or less. That is, when the specific surface area exceeds 800 m ² / g and is too large, even if a lubricant is contained in the so-called back coat layer, the exudation of the lubricant is weakened and the lubrication effect is weakened. Because it will be.

Further, the carbon black contained in the so-called back coat layer is a binder 10 for forming the back coat layer.
It is desirable that the amount is about 25 to 400 parts by weight with respect to 0 parts by weight.

In addition, it is desirable that the so-called back coat layer contains a lubricant in addition to the above carbon black, for example, about 0.5 to 100 parts by weight of the carbon black.
It is desirable that 4.5 parts by weight of fatty acid ester and about 0.5 to 5 parts by weight of silicone oil are contained in the back coat layer.

Further, as the binder for forming the so-called back coat layer, for example, a fibrous resin such as nitrocellulose,
There are thermoplastic polyurethane elastomers, etc., particularly preferable is a combination of 10 to 80 parts by weight of a fibrous resin and 90 to 20 parts by weight of a polyurethane elastomer, and about 10 to 60 parts by weight with respect to 100 parts by weight of a binder resin. It is desirable that one part, especially about 10 to 50 parts by weight of a curing agent, such as an isocyanate curing agent, be used.

Example 1 45 parts by weight of nitrocellulose, polyurethane elastomer
35 parts by weight, polyisocyanate 20 parts by weight, specific surface area 700 m
100 parts by weight of ² / g carbon black, 5 parts by weight of silicone oil, 2 parts by weight of fatty acid ester, 580 parts by weight of an equivalent mixed solvent of toluene, methyl ethyl ketone and methyl isobutyl ketone are kneaded and dispersed in a sand mill, and the required kneading and dispersing time (20 When 2/3 of the time elapses, the remaining (20
(Part by weight) of carbon black is added, and the mixture is kneaded and dispersed for the remaining time.

The coating material prepared as described above is applied to the base film surface on the side opposite to the magnetic coating layer forming surface of the magnetic tape on which the magnetic coating layer is formed, dried and surface treated to about 0.3.
A magnetic black tape is obtained by forming a carbon black-containing layer having a thickness of .about.1.5 .mu.m.

The surface of the carbon black-containing layer of the magnetic tape thus obtained was measured by a three-dimensional roughness measuring instrument manufactured by Kosaka Laboratory, and there were 14250 protrusions / mm ² with a height of about 2 to 30 nm. is doing.

[Example 2] A magnetic tape is obtained in the same manner as in Example 1, except that the initial amount of carbon black added in the paint preparation step is 80 parts by weight and the amount of carbon black added during kneading and dispersion is 40 parts by weight.

The surface of the carbon black-containing layer of the magnetic tape thus obtained was measured with a three-dimensional roughness measuring instrument manufactured by Kosaka Laboratory, and protrusions with a height of about ² to 30 nm were present at a rate of 13820 pieces / mm ^2. is doing.

[Example 3] In Example 1, the time of adding carbon black during the kneading and dispersing in the paint adjusting step is 1 / the required kneading and dispersing time.
After three lapses, magnetic tape is obtained in the same manner.

The surface of the carbon black-containing layer of the magnetic tape thus obtained was measured with a three-dimensional roughness measuring instrument manufactured by Kosaka Laboratory, and there were 15260 protrusions with a height of about ² to 30 nm / mm ^2. is doing.

Example 4 In Example 1, carbon black having a specific surface area of 250 m ² / g was used, and projections having a height of about 2 to 30 nm were 19 pieces.
A tape having a dynamic friction coefficient of about 0.268 was obtained at 820 pieces / mm ² .

Example 5 In Example 1, a carbon black having a specific surface area of 30 m ² / g is used, and a protrusion having a height of about ² to 30 nm is 528.
A tape having a dynamic friction coefficient of about 0.272 was obtained at 0 pieces / mm ² .

[Comparative Example 1] In Example 1, the total amount of carbon black (120 parts by weight) was added from the beginning and kneaded and dispersed to obtain a magnetic tape in the same manner.

When the surface of the carbon black-containing layer of the magnetic tape thus obtained was measured by a three-dimensional roughness measuring instrument manufactured by Kosaka Laboratory, there were 27200 protrusions with a height of about ² to 30 nm / mm ^2. is doing.

Comparative Example 2 In Example 1, a carbon black having a specific surface area of 30 m ² / g was used, the entire amount (120 parts by weight) was added from the beginning, and 22840 protrusions having a height of about 2 to 30 nm / mm.
^{At 2} , a tape having a dynamic friction coefficient of about 0.305 was obtained.

[Comparative Example 3] In Example 1, without using the carbon black,
120 parts by weight of calcium carbonate having an average particle size of 0.15 μm and a specific surface area of 11.5 m ² / g, and a height of about 2 to 30
The number of protrusions of nm was 12,500 / mm ² , and a tape having a dynamic friction coefficient of about 0.316 was obtained.

[Comparative Example 4] In Example 1, 20 parts by weight of carbon black having a specific surface area of 250 m ² / g was used, and the entire amount (20 parts by weight) was added from the beginning, and projections having a height of about 2 to 30 nm were 4260.
A tape having a coefficient of dynamic friction of about 0.345 was obtained at the number of pieces / mm ² .

〔Characteristic〕

The dynamic friction coefficient and jitter of the magnetic tapes obtained in the above examples are shown in the table.

The dynamic friction coefficient μ _k was determined by winding a magnetic tape around a stainless steel pin with a diameter of 6 mm with the carbon black containing layer side inside at a wrap angle of 180 °, back tension 50 g, speed 10 mm.
When traveling at / s, the ratio T ₂ / T ₁ of the tension T ₁ on the inlet side and the tension T ₂ on the outlet side to the stainless steel pin It was inserted and asked for.

Also, the jitter can be recorded at a temperature of 40 using a video tape recorder.
Repeatedly run 100 times in an environment of ℃ and 80% RH,
It was judged by visually observing the screen fluctuation.

As can be seen from this table, in the present embodiment, the dynamic friction coefficient is small and the running property is good, and further, the jitter property is good without the screen fluctuation, and the recording / reproducing property is good. The examples have a large dynamic friction coefficient and are inferior in running property, and also have screen fluctuations and poor recording and reproducing characteristics.

〔effect〕

The magnetic recording medium according to the present invention has about 5 × 10 ³ protrusions / m having a protrusion height of about 2 to 30 nm on the surface of a so-called back coat layer.
since it is configured to present at about 20 × 10 sparse proportion of ³ / mm ² or less m ² or more, as a good running properties and small dynamic friction coefficient, also like hardly occur shaking of the screen during playback The recording and playback characteristics are also excellent,
In addition, the magnetic recording medium can be manufactured in the same manner as the conventional method except that the time of adding the carbon black is adjusted when the coating material is adjusted. Therefore, the magnetic recording medium can be easily manufactured.

 ─────────────────────────────────────────────────── --- Continued from the front page (72) Inventor Kumiko Kojima 3-12 Moriyacho, Kanagawa-ku, Yokohama, Kanagawa Nihon Victor Co., Ltd. (56) References JP-A-59-203237 (JP, A) JP-A-SHO 59-2228 (JP, A) JP 61-5431 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on one surface side and a carbon black-containing layer on the other surface side, wherein the specific surface area of the carbon black is 20 to 800 m ² / g, and the carbon It is characterized in that projections having a projection height of 2 to 30 nm are present on the surface of the black-containing layer at a sparse ratio of 5 × 10 ³ pieces / mm ² or more and 20 × 10 ³ pieces / mm ² or less. Magnetic recording medium.