JPS61192023A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce a friction coefficient over the wide range of temps. and to improve the traveling property of the titled recording medium without decreasing S/N by incorporating a fatty acid ester into the surface layer of a nonmagnetic carrier opposite to the surface on which a magnetic layer is formed. CONSTITUTION:A fatty acid ester shown by the general formula, RCOOR', (where R is a saturated or unsaturated hydrocarbonic group optionally contg. a 7-9C side chain and R' is a saturated or unsaturated hydrocarbonic group optionally contg. a 8-10C side chain) in incorporated into the surface layer of a nonmagnetic carrier opposite to the surface on which a magnetic layer is formed. When the number of C in the fatty acid ester and alcohol exceeds 11, the viscosity is increased and the solidifying point is raised and a sufficient lubricating effect is not obtained. Besides, some troubles such as the deterioration in the durability of the lubricating layer arise at <=7C. The layer contg. a fatty acid ester is composed of the fatty acid ester, carbon black, silicone oil, a binder, a curing agent, etc.

Description

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

[Prior art and its problems]

In general, magnetic recording media used for audio, video, computers, etc. are becoming increasingly denser. In other words, recording signals are becoming increasingly high-frequency, and therefore the spacing loss between the magnetic head and the recording medium has a large effect on the output.

Therefore, the magnetic layer of a magnetic recording medium needs to be as flat as possible.

However, if the surface of the magnetic layer is made too smooth, the increase in the coefficient of friction will make the magnetic tape more likely to cause winding irregularities, and stick-slip will occur due to tension fluctuations, which will not only impair recording and reproducing operations, but also Damage to the magnetic tape may occur at the guide member, flange, etc. of the recording/reproducing device.

In order to overcome these drawbacks, it has been proposed to specially configure the surface layer of the nonmagnetic support of the magnetic recording medium on the side opposite to the magnetic layer forming surface, that is, the back layer.

In other words, in the past, the back layer was made to have a rough surface in order to reduce the coefficient of friction, but when a magnetic tape has a rough back layer, when the magnetic tape is wound, the unevenness of this rough surface is on the magnetic layer. In other words, unevenness is formed on the surface of the magnetic layer, increasing the spacing loss and deteriorating the electromagnetic conversion characteristics. Therefore, the back layer should be made as smooth as possible. That is what is being proposed.

However, simply making the back layer smooth is not enough, and it has been proposed to include lubricants such as fatty acids, fatty acid esters, and silicone oil in the pack layer, but even this is not satisfactory. I haven't been able to do it.

[Disclosure of the invention]

As a result of research on the substance that should be included in the surface layer of the nonmagnetic support opposite to the magnetic layer formation surface, such as the pack layer, the inventor found that this substance has the general formula RCOOR' (where R is 7 carbon atoms A fatty acid ester represented by a saturated or unsaturated hydrocarbon group that may have ~9 side chains, R' is a saturated or unsaturated hydrocarbon group that may have 8 to 10 carbon atoms. It has been found that by selecting the appropriate temperature, the coefficient of friction can be reduced over a wide temperature range without reducing the S/N ratio, and a product with excellent running stability can be obtained.

Here, the reason why the number of carbon atoms of the fatty acid and alcohol in the fatty acid ester is 10 or less is that the number of carbon atoms of these is 1.
This is because if the carbon number exceeds 1, the viscosity and freezing point will increase, making it impossible to obtain a good lubricating effect.The reason why these carbon numbers are 8 or more is that if the carbon number is 7 or less, the lubricating layer will not work properly. This is because problems arise in terms of durability. □Furthermore, fatty acid esters that meet the above conditions have good lubricating properties against environmental temperature changes and are excellent in stability, unlike, for example, fatty acid esters made of lower-intermediate alcohols and higher fatty acids. .

In addition, when carbon black is also included in the pack layer in addition to the above-mentioned fatty acid ester, this carbon black has a specific surface area (BET value) of 7.
It is desirable to select a carbon black with a specific surface area of 00 m"/g or less. In other words, if carbon black with a large specific surface area exceeding roo and t7g is included, this carbon black will have an adverse effect on the fatty acid esters mentioned above. For example, the above-mentioned fatty acid ester is adsorbed on the carbon black surface, and the lubricating effect due to the oozing of the above-mentioned fatty acid ester is reduced.Also, due to the surface roughness, the carbon black It is desirable that the specific surface area of the black be 7oo, 17g or less.

The layer containing the fatty acid ester mentioned above is composed of the fatty acid ester mentioned above, carbon black, silicone oil, a binder, a hardening agent, etc. In this case, the fatty acid ester is approximately 0.5
~5% by weight, carbon black is about 0.5 to 4% by weight based on the binder, silicone oil is about 5% by weight or less based on the non-magnetic powder, and hardeners such as incyanate hardeners are about about 5% by weight based on the binder. Desirably it is 10 to 60% by weight, more preferably about 10 to 50% by weight.

Examples of the binder include cellulose resins such as nitrocellulose, thermoplastic polyurethane elastomers, etc. Particularly preferred are binders that are a combination of 10 to 80 parts by weight of cellulose resins and 90 to 20 parts by weight of polyurethane elastomers. preferable.

Further, the thickness of the fatty acid ester-containing layer formed from such a composition is preferably about 0.3 to 1.5 μm.

[Example 1] 45 parts by weight of nitrocellulose, 35 parts by weight of polyurethane resin, 20 parts by weight of polyisocyanate, specific surface area 700
7Fl! /g carbon black powder 120 parts by weight, silicone oil 5 parts by weight, octyl octanoate 2t
580 parts by weight of a mixed solvent of equal amounts of luene, methyl ethyl ketone, and methyl isobutyl ketone are thoroughly cross-dispersed in a sand mill to make a paint, and this octyl octanoate-containing paint is applied to a magnetic tape on which a magnetic layer is formed. A magnetic tape is produced by applying the mixture to the opposite side to the magnetic layer forming side, drying and surface treatment to form an octyl octanoate-containing back layer having a thickness of about 0.5 to 1.2 μm.

[Example 2] In Example 1, 2 was used instead of octyl octanoate.
- Perform the same procedure using ethylhexyl octanoate. 1. Make magnetic tape.

[Example 3] A magnetic tape is produced in the same manner as in Example 1 using decyl decanoate instead of octyl octanoate.

[Example 4] A magnetic tape is produced in the same manner as in Example 1 except that carbon black with a specific surface area of 3oo and t7g is used instead of carbon black with a specific surface area of 700@7g.

[Comparative Examples 1 to 8] In Example 1, instead of octyl octanoate,
Butyl stearate (Comparative example 1), isopropyl palmitate (Comparative example 2), butyl capronate (Comparative example 3)
, isopropylhexanoate (Comparative Example 4), oleyl capronate (Comparative Example 5), stearylhexanoate (Comparative Example 6), oleyl oleate (Comparative Example 7), or isocetyl palmitate (Comparative Example 8). A magnetic tape is produced in the same manner.

[Characteristics test]

The dynamic friction coefficient and jitter of the magnetic tapes obtained on each side were measured as shown in the table.

The coefficient of dynamic friction μ is determined by wrapping a magnetic tape around a 61-diameter stainless steel bottle with the pack layer inside at a wrapping angle of 180°, pack tension 50 g, and speed 10 m/s.
When running the magnetic tape, the ratio of the tension T1 on the inlet side and the tension Tl on the outlet side with respect to the stainless steel pin is expressed as μ = An('r*/ Tl
) is calculated by inserting it into π.

Further, jitter was determined by running a commercially available video tape recorder 100 times in an environment of a temperature of 40° C. and a humidity of 8096 RH, and visually observing screen shake.

O: No shaking, Δ: Slight shaking, ×... Shaking As shown in this table, the temperature of this example was -5℃ to 4℃.
Even with wide environmental changes over 0°C, there is little variation in the coefficient of dynamic friction, the coefficient of dynamic friction is small, and the jitter characteristics are also good, whereas the comparative example has a coefficient of dynamic friction that changes greatly depending on environmental changes and a coefficient of dynamic friction that is small. The value itself is large, and the jitter characteristics are also poor.

〔effect〕

It has good running properties and is less prone to jitter.

°2, no

Claims (1)

[Claims] The surface layer on the side opposite to the magnetic layer forming surface of the nonmagnetic support is coated with the general formula RCOOR' (where R is a saturated or unsaturated hydrocarbon group that may have a side chain having 7 to 9 carbon atoms, R' A magnetic recording medium characterized in that it contains a fatty acid ester represented by a saturated or unsaturated hydrocarbon group (which may have a side chain having 8 to 10 carbon atoms).