JPH0489615A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium which is less changed in coefft. of friction with time and has an excellent traveling property and durability by incorporating a carbon black subjected to an adsorption treatment of a fatty acid into a magnetic layer. CONSTITUTION:The carbon black which is previously subjected to the adsorption treatment of the fatty acid is incorporated into the magnetic layer. Since the fatty acid is already adsorbed into the carbon black to be incorporated into the magnetic layer in this case, the excess transfer of the fatty acid is limited and the min. fatty acid necessary for maintaining the low coefft. of friction is supplied gradually from the inside of the carbon black to the surface of the magnetic layer even if the fatty acid transfers partly to the layer of the opposite surface from the surface of the magnetic layer. Then, the transfer quantity, i.e. the quantity of the fatty acid to be lost is minimized and the fatty acid quantity on the surface of the magnetic layer is maintained constant nearly over a long period of time. The magnetic recording medium which is less changed in the coefft. of friction and has the excellent traveling property and durability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape used in audio/video equipment or computers.

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, when magnetic recording media are manufactured using such measures, the following problems arise. In other words, by making the surface of the magnetic recording medium highly smooth, the coefficient of friction (
Since running resistance) increases, running performance and durability deteriorate compared to conventional ones.

Specifically, magnetic tape causes problems such as increased jitter, wow, and flutter, as well as stoppage and damage to the magnetic tape.

Several measures have been taken to solve this problem. For example, (1) the coefficient of friction is reduced by adjusting the content of lubricant such as fatty acid mixed in the VA magnetic layer. (2) A filler with high lubricity such as carbon blank is included in the magnetic layer to reduce the coefficient of friction. (3) A hack coat layer having a low coefficient of friction is provided on the surface of the magnetic recording medium opposite to the magnetic layer on the nonmagnetic support (for example, Japanese Patent Publication No. 80830/1983).

Problems to be Solved by the Invention When fatty acids and carbon black are added to a magnetic layer using the above-mentioned conventional technique, the following problems arise.

In other words, when a magnetic layer is applied on the support layer and then wound up into a roll, or when a hack coat layer is applied on the opposite side of the support layer and then wound up into a roll, the fatty acids present on the surface of the magnetic layer A portion of the magnetic layer is gradually transferred to the support layer or backcoat layer that is in contact with the magnetic layer, and the amount of fatty acids contained in the magnetic layer gradually decreases. The deficient fatty acids are supplied by gradually rising from the inside of the magnetic layer to the surface, but the transfer of fatty acids continues thereafter, and finally the amount of fatty acids on the surface of the magnetic layer becomes insufficient. For this reason,
The friction coefficient of the magnetic layer gradually increases over time, improving running performance and
Durability deteriorates.

In order to avoid this, if the content of lubricants such as fatty acids is increased excessively, the binding force between the binder and the magnetic powder will decrease, the strength of the magnetic layer will decrease, and the still life of the tape will be shortened. was there.

The present invention solves the above-mentioned conventional problems and provides a magnetic recording medium that maintains a low coefficient of friction over a long period of time and has excellent blood durability.

In order to solve the second problem, the present invention takes a method of incorporating carbon black into which a fatty acid has been adsorbed in advance into the magnetic layer.

Effect: Because fatty acids are already adsorbed inside the carbon black contained in the magnetic layer by the above means, excessive movement of fatty acids is restricted, and some fatty acids are transferred from the surface of the magnetic layer to the layer on the opposite side. However, the minimum amount of fatty acids necessary to maintain a low coefficient of friction is gradually supplied from the inside of the carbon blank to the surface of the magnetic layer, which minimizes the amount of transferred fatty acids, that is, the amount of fatty acids that are lost, and the magnetic layer The amount of fatty acids on the surface remains almost constant over a long period of time.

As a result, it is possible to provide a magnetic recording medium with extremely little temporal change in the coefficient of friction and excellent running performance and durability.

EXAMPLE The treatment of a carphone blank in the present invention is carried out, for example, by mixing and dispersing carphone black and a fatty acid in a solvent such as toluene or methyl ethyl ketone for several hours.

The carphone blank used here may be manufactured by any method such as thermal, furnace, channel, graphitized carbon black, etc., but those having a specific surface area of 10 to 200 m27H are preferable.

When the specific surface area of carbon black is smaller than 10 m2/g, the amount of fatty acid adsorption is small, so that no fatty acid supply effect can be expected. If the specific surface area is larger than 200 m27 g, it will be difficult to disperse, and therefore it is not suitable for magnetic paint.

Moreover, as the fatty acid, a saturated or unsaturated fatty acid having 10 to 22 carbon atoms is preferable. If the number of carbon atoms is less than 10, the lubricity will be low, and if the number of carbon atoms is more than 22, the compatibility with the resin will be poor, so it is not suitable. The number of fatty acids mixed with the carbon blank may be one or more.

Also, the amount of carbon black to be included is 1 to 5 of the magnetic powder.
Weight % is appropriate. If it is less than 1%, the durability will be somewhat insufficient, and if it exceeds 5%, the strength of the magnetic layer will be insufficient.

Embodiments of the magnetic recording medium of the present invention will be specifically 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 I) 1. Treatment of carbon blank Carbon black Specific surface area 150 m''/g 2 parts Fatty acid nistearic acid 2 parts Methyl ethyl ketone 10 parts The above composition was subjected to sound dispersion in a ball mill for 20 hours to prepare a paint. Let it be A.

2. Preparation of magnetic paint B Co-containing T-Fe208 100 parts magnetic iron oxide powder Average particle size Length - 0.1 μm μm ratio - 10/1 Coercive force 9000e Polyurethane resin 10 parts Blue chloride vinyl acetate copolymer 10 parts aluminum oxide powder
5 parts Average particle size 0.2 μm Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene
After mixing and dispersing 100 parts of the above composition and paint A in a ball mill for 48 hours, 6 parts of the curing agent (Coronate L) was added.
Magnetic coating material B was prepared by filtering the kneaded material obtained by adding 1.5 µm of the mixture through a filter having an average particle size of 3 μm.

3. Preparation of paint for back coat layer Carbon powder average particle size 0.1 μm Polyurethane resin Nitrocellulose resin Methyl ethyl carbon 100 parts 30 parts 30 parts 250 parts Toluene 180 parts Cyclohexanone 70 parts The above composition was heated in a ball mill for 36 hours. After mixing and dispersing and taking out the kneaded material, 15 parts of a hardening agent (coronate) was added, and the mixture was mixed and dispersed for about 30 minutes using a high-speed dissolver, and then filtered through a filter with an average particle size of 3 μm to prepare a back coat layer. Prepared the paint.

Next, the magnetic paint B was applied onto a 14 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 4 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, surface treatment was performed using a super calendar roll to form a hack coat layer with a thickness of 0.7 μm.

This was cut into 1/2 inch width to produce a videotape.

(Example 2) A videotape was produced in the same manner as in Example 1 except that the specific surface area of the carpump thick was set to 60 m2/g in the paint of Example 1.

(Example 3) In the paint A of Example 1, 1 part of stearic acid was added,
A videotape was produced in the same manner as in Example 1 except for the above.

(Example 4) A videotape was produced in the same manner as in Example 1, except that in paint A of Example 1, 2 parts of stearic acid and 2 parts of myristic acid were used.

(Comparative Example 1) In Example 1, no carbon black treatment was performed,
The composition of magnetic paint B is as follows.

Carphone black Specific surface area 150 m''/g Contains 2 parts fatty acid nistearic acid 2 parts co
-Fe203 Magnetic iron oxide powder 100 parts Average particle size Length - 0.1 μm Acicularity ratio - 10/1 Coercive force 9000e Polyurethane resin 10 parts Vinyl chloride-vinyl acetate copolymer 10 parts Aluminum oxide powder
5 parts Average particle size 0.2 μm Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene
After mixing and dispersing 100 parts of this in a ball mill for 48 hours, 6 parts of a hardening agent (Coronet L) was added, and the resulting kneaded product was filtered through a filter having an average particle size of 3 μm to prepare magnetic paint B. The following steps are Example 1
A videotape was made in the same manner.

(Comparative Example 2) A videotape was produced in the same manner as in Comparative Example 1 except that the amount of carbon black added was 0 parts in the magnetic paint B of Comparative Example 1.

(Comparative Example 3) A videotape was produced in the same manner as in Comparative Example 1 except that the amount of stearic acid added was 4 parts in the magnetic paint B of Comparative Example 2.

The friction coefficient, zinc, and still life immediately after the production of the giant tape and after three months of release are shown in the attached table.

In this table, (D) The coefficient of friction (μk) is determined by the tension at the entrance (Ti) and the tension at the exit ( The value of T o ) was read out and calculated from the following equation.

μ = j2n (To/T i) /rt(2) The jitter was measured using a VH3 type VTR (NVM21 manufactured by Matsushita Electric Industrial ■) at 5°C and 80%RH (7nlt).
The amount of jitter when recording and reproducing a video signal by a signal generator was measured using a thick meter (unit: μ5ec).

(3) Still lifespan indicates that the image quality deteriorates significantly when a VH3 type VTR (NV-MIO manufactured by Matsushita Electric Industrial ■) is used to record a video signal in an environment of -10°C and is played back in still mode. It was determined by measuring the time until the end (unit: minutes).

As is clear from the two tables, the magnetic tape obtained in the above manner shows less change over time in the coefficient of friction and less jitter than the conventional comparative example, so it has excellent runnability and durability. It can be said that it has excellent characteristics.

In addition, 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 other magnetic recording media such as magnetic sheets.

Effects of the Invention As detailed above, according to the present invention, since an appropriate amount of fatty acid is supplied to the magnetic layer from carbon black treated with fatty acids, there is very little change in the coefficient of friction over time, and running properties and Since a magnetic recording medium with excellent durability can be obtained, it has great practical value.

Claims (2)

[Claims] (1) A magnetic recording medium characterized in that a magnetic layer contains carbon black to which fatty acids have been adsorbed. (2) The magnetic recording medium according to claim (1), wherein the magnetic layer contains carbon black in an amount of 1 to 5% by weight based on the magnetic powder.