JPH03189921A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To solve such problems relating to the dispersibility of carbon black powder and the sliding resistance of a medium and to prevent head from clogging by using polyurethane resin having -SO3Na group as an introduced functional group in a binder. CONSTITUTION:A back coating layer is provided where the carbon black powder of pH 5.5-9.0 is dispersed in a polyurethane resin having -SO3Na group as an introduced functional group so as to improve the dispersibility of the carbon black powder. To improve the sliding strength of the back coating layer, calcium carbonate is added as nonmagnetic powder. In the small amt. of calcium carbonate, sliding strength can not be improved, while in larger amt. of calcium carbonate, the surface of the back coating layer becomes rough. Thereby, it is effective to add calcium carbonate powder by 5-60 wt.% in the whole amt. of nonmagnetic powder. By this method, the dispersibility of the carbon black powder can be improved and the sliding strength of the back coating layer can be improved to prevent head clogging.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferromagnetic metal thin film type magnetic recording medium such as a vapor-deposited tape, and more particularly, to
- Concerning layer improvement.

[Conventional technology]

In recent years, development of ferromagnetic metal thin film type magnetic recording media such as vapor-deposited tapes has been progressing. In the above magnetic recording medium, the surface of the magnetic layer needs to be smooth in order to reduce spacing loss. On the other hand, if the back surface of the magnetic layer is too smooth, the coefficient of friction will increase and the running performance will deteriorate. Therefore, a back coat layer having a certain degree of roughness is provided on the back surface of the magnetic layer. As the back coat layer, a material in which non-magnetic powder such as carbon black powder is dispersed in a binder is used.

However, unlike conventional coated magnetic recording media, the magnetic layer of ferromagnetic metal thin film magnetic recording media is susceptible to corrosion. To prevent this, it is necessary to use p as a non-magnetic powder in the back coat.
It is effective to use carbon black powder with H of 5.5 to 9.0. However, the above-mentioned neutral or weakly alkaline carbon black powder has a drawback of poor dispersibility in a binder.

Generally, the pH value of carbon black powder changes depending on the volatiles (oxides in soil) attached to the surface of the carbon black powder. When there are many oxides, it becomes acidic, and when there are few oxides, it becomes neutral or weakly alkaline. On the other hand, dispersibility is
There is a tendency that it is good when there are many oxides attached, and bad when there are few. Therefore, when carbon black powder with a pH of 5.5 to 9.0 is used, corrosion of the magnetic layer is prevented, but undispersed aggregates remain in Barafco-1-JFi, and these aggregates transfer to the magnetic layer. There is a problem that this causes head clogging and the like.

Furthermore, when carbon black powder is used as the nonmagnetic powder of the back coat layer, there is a drawback that the sliding strength of the film is weak. Therefore, when running for a long time in a VTR or the like, the back coat layer is scraped by sliding against guide pins, etc., causing clogging of the spatula 1'.

[Problems to be solved by the invention] The present invention solves the problems of poor dispersibility and poor sliding resistance of carbon black powder, and has excellent durability with less head clogging. The purpose is to provide a magnetic recording medium.

[Means to solve the problem]

As a result of studying the above-mentioned problems, it was found that by using a polyurethane resin having -5O3N a as a functional group introduced into the binder, the dispersibility of carbon black powder with less oxides attached to the surface can be improved. That is, the above-mentioned problem can be solved by providing a back coat layer in which carbon black powder having a pH of 5.5 to 9.0 is dispersed in a polyurethane resin having -SO*Na as an introduced functional group.

It has also been found that adding calcium carbonate powder as a non-magnetic powder is effective in improving the sliding strength of the back coat layer. If the amount of calcium carbonate powder is too small, it will not be possible to improve the sliding strength, and if it is too large, the surface of the back coat layer will become rough and cause negative effects such as embossing on the magnetic layer. ~(i 3wt%
, more preferably a range of 20 to 4 Qwt%. Addition of calcium carbonate powder reduces abrasion of the back coat layer and reduces clogging of the rad even during long running.

〔Example〕

A ferromagnetic thin film layer of 20 wt % Co80-Ni (1,700 octane) was formed as a magnetic layer on a polyethylene terephthalate film in an oxygen atmosphere using a continuous vacuum evaporation apparatus. Thereafter, a paint in which non-magnetic powder and binder were dispersed using a sand mill device was applied to the other surface to form a back coat layer. Next, this film was slit to a width of 3 mm and assembled into a cassette half to make an 8 mm videotape. pH of carbon black powder of prepared sample
Value 1 Type of binder used during dispersion and its introduced functional group,
Table 1 shows the weight ratio of calcium carbonate powder.

Table 1 For Samples 1 to 6, the surface roughness of the back coat layer (Rmax maximum surface roughness) and 8
The number of head clogging was measured when running 100 passes using mmVTR. A 60 minute tape was used for the running test. The results are shown in Table 2.

table 2 The results are shown in Table 3.

From Table 2, when polyurethane having -303Na as an introduced functional group is used as a dispersion vibrator, sample 1.
It can be seen that in No. 2, the dispersibility of carbon black powder is improved and head clogging is reduced.

Next, for Samples 1 to 2 and 7 to 8, the sliding strength (number of times of sliding until the sliding scratches reach the base film) when the back coat layer was slid with a steel ball with a diameter of 4 mm, and the 8 m
The number of head clogging was measured when running 500 passes using a VTR. Note that a 15-minute tape was used for the running test. As is clear from Table 3, adding calcium carbonate powder improves the sliding strength of the back coat layer and reduces head clogging. I understand that.

The carbon black powder that can be used is Rav
thl 250 (+) H value 6.0. (manufactured by Columbia Carbon) Black Pearls 800
(manufactured by Capot Co., USA, with a pH value of 8.0), etc., and polyurethane such as uR-s310 (i-functional group -3O:+N
a, manufactured by Toyobo Co., Ltd.), and Calflex D (manufactured by Yonejo Co., Ltd., particle size 0.04) as a calcium carbonate powder.
μm).

Homocal D (manufactured by Shiraishi Kogyo Co., Ltd., particle size 0.07 pm)
) etc.

In this example, Co-Ni-071 was used as the magnetic layer, but other ferromagnetic thin film type magnetic layers, such as Co-Cr,
A similar effect can be obtained with co-〇 and the like.

Furthermore, in addition to carbon black and calcium carbonate, the non-magnetic powder in the back coat may include powders such as Fe2O, and the binder may include other polyurethanes, nitrocellulose, etc. as an auxiliary binder.

〔Effect of the invention〕

As described above, the present invention uses a polyurethane resin having -3o3Na as an introduced functional group as a binder.
It is possible to improve the dispersibility of carbon black powder and prevent head clogging due to undispersed carbon black. Furthermore, when calcium carbonate powder is added to the non-magnetic powder of the back coat layer, the sliding strength of the back coat layer can be improved, thereby preventing head clogging due to abrasion of the back coat layer. .

Claims (2)

[Claims] (1) A backing made of a substrate having a magnetic layer made of a ferromagnetic metal thin film on one side and non-magnetic powder containing carbon black powder with a pH of 5.5 to 9.0 dispersed in a binder on the other side. A magnetic recording medium having a coating layer, characterized in that the binder is a polyurethane resin having -SO_3Na as an introduced functional group. (2) The magnetic recording medium according to claim (1), wherein calcium carbonate powder is added as the non-magnetic powder in a weight ratio of 5 wt% to 60 wt% of the total non-magnetic powder.