JPS5916138A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility, surface smoothness, and video S/N ratio, by mixing vinyl monomer with antistatic carbon black to be added to a magnetic layer, and after adsorption of the vinyl monomer, polymerizing it by heat or irradiation of electron beams, or the like. CONSTITUTION:As carbon black, a carbon high in electric conductivity having a well-grown structure in antistatic performance is used, and as the vinyl monomer, an unsaturated monomer capable of thermal or electron beam polymn. is used. The thermal polymn. is carried out at 60-200 deg.C, and the electron beam polymn. is executed by 1-2 Mrad irradiation. As the monomer, styrene, methyl methacrylate, butyl methacrylate, vinyl stearate, and mixtures of them are suitable. The use of the graft carbon thus obtained forms an extremely uniformly dispersed magnetic coating material in a short time, and a magnetic tape having good antistatic effect as well as good surface smoothness and high video S/N ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic recording tape, and particularly to antistatic conductive particles contained in a magnetic layer.

As video tape recorders and other devices become smaller and lighter, and high-density recording progresses, the recording media used are
Extreme smoothness of the magnetic layer surface, high S/N characteristics, etc. are increasingly required.

The magnetic layers of magnetic tapes, floppy disks, etc. are generally composed of magnetic powder and small amounts of abrasives, antistatic agents, lubricants, and dispersants dispersed in a binder resin. Fine powders such as aluminum oxide and chromium dioxide are used as abrasives, and carbon black is used as an antistatic agent.

In the magnetic recording medium described above, in order to make the magnetic layer surface extremely smooth and achieve a high S/N ratio, magnetic powder, abrasives,
It is necessary to uniformly disperse inorganic fine particles such as antistatic agents in the resin. However, carbon black, which is added as an antistatic agent, has a large interparticle cohesive force because it is a fine particle, and it is difficult to uniformly disperse it to the level of sub-particles, which may cause a decrease in surface smoothness and S/H. It had become.

An object of the present invention is to improve the performance of magnetic recording media due to the dispersibility of carbon black.

As a result of various studies on the dispersion of carbon black, the present inventors have found that dispersibility can be extremely improved by bonding a polymer to the surface of carbon black particles in advance, leading to the present invention.

That is, the present invention is characterized in that the magnetic layer of the magnetic recording medium contains grafted carbon in which a polymer is bonded in advance to the surface of carbon black particles.

The present invention will be explained in more detail below.

The grafted carbon applied to the present invention is obtained by mixing and adsorbing vinyl monomers on carbon black and then polymerizing the monomers with heat or electron beams. That is, it is a state in which vinyl groups are chemically bonded to the surface of carbon black particles and at the same time monomers are polymerized to form a polymer.

Various kinds of carbon black can be applied to the present invention, but highly conductive carbon with developed struttles, such as Ketjenblack EC manufactured by Amatsu Corporation and Asahi Carbon Corporation, are highly effective in antistatic performance. No. 8
-500 etc. are preferable.

Next, as the vinyl monomer, a monomer having vinyl unsaturation that can be thermally polymerized or electron beam polymerized can be used. The thermal polymerization treatment can be carried out at a temperature of about 60°C to 20°C. In addition, in the case of electron beam irradiation polymerization, about 1 to 2 Mra
It can be polymerized by irradiation of d.

Suitable monomers include styrene, methyl methacrylate, butyl methacrylate, vinyl stearate,
and mixtures thereof and many others are applicable. It is preferable that these vinyl monomers have excellent compatibility with the binder resin forming the magnetic layer.

In the grafting reaction, carbon black and the monomer are thoroughly mixed by a mixing operation, the monomer is uniformly adsorbed onto the surface of the carbon particles, and then polymerized under the above conditions.

After polymerization, if a portion of the polymer is too large for the carbon black and it would be inconvenient to add it to the magnetic layer as it is, dissolve the polymerized grafted carbon in a solvent and remove and concentrate the portion of the polymer by means such as filtration. It is preferable to use

Using the grafted carbon obtained by the above method, compared to untreated carbon black, an extremely uniformly dispersed magnetic coating can be achieved in a short time, and it not only has an antistatic effect but also improves surface smoothness and S/N.

Good will be done.

Next, the effects of the present invention will be specifically explained in Examples.

(Example 1) Ketjenblack EC...100 parts Methyl methacrylate...800 parts were mixed well and reacted at 100'C for 5 hours.

Thereafter, it was dissolved in methyl ether ketone, filtered using paper to remove a portion of the polymer that was not directly bonded to carbon, and dried. Grafted carbon was obtained in a ratio of 96 parts of polymethyl methacrylate to 100 parts of carbon.

(Example 2) 100 parts of Ketteen Black 7EC 800 parts of styrene were thoroughly mixed and reacted at 140° C. for 2 hours.

Thereafter, it was dissolved in toluene, excess polystyrene was removed by filtration and dried in the same manner as in Example 1. Grafted carbon was obtained in a ratio of 150 parts of polystyrene to 100 parts of carbon.

(Example 3) Ketjenblack EC...100 parts Styrene...400 parts Butyl methacrylate...400 parts were mixed well and reacted at 100°C for 3 hours. Ta. Thereafter, it was dissolved in a 1:1 mixed solvent of toluene and methyl ether ketone, and the excess styrene-butyl methacrylate copolymer was removed and dried in the same manner as in Example 1. A grafted carbon consisting of 200 parts of polymer to 100 parts of carbon was obtained.

Using the grafted carbon obtained in the above examples, the components shown below were mixed and dispersed for 4 hours using a vibrating mill to obtain a magnetic paint. The paint was then applied onto a polyester base film in a conventional manner and dried to form a videotape.

Magnetic powder (Co coated - Fe20a)...
・100 parts urethane resin ・・・・・・
9 parts (Japan Polyurethane, 2304) Nitrocellulose 9 parts (
R81h) Hardening agent: 2 parts (Coronate L2 manufactured by Nippon Polyurethane) Dispersant (lecithin)
... 1 part oil lubricant (stearic acid) 1 part abrasive (alumina powder)
・・・・・・ Part 3 Craft Carbon
...... 3 parts (converted to the amount of carbon in the grafted carbon) As a comparative example, untreated Ketjen Black EC was used and made into a paint with the same composition and dispersion conditions as in the example. It was made into a videotape under certain conditions.

The surface roughness of the magnetic layer surface of these tapes, video S/N,
The measurement results of surface electrical resistance are shown in the table below.

The video S/N of the comparative example is shown as odB.

As seen in the table above, the present invention is extremely effective in improving the surface smoothness and video S/N of magnetic recording media. In the examples, the carbon content was concentrated by dissolving and filtering after the grafting reaction, but the polymer itself produced by the grafting reaction can also be used as the binder resin for the magnetic layer. . Further, in the examples, the effect was shown with Ketjenblack EC, but it is not limited to Ketjenblack.

As is clear from the above description, according to the present invention, a magnetic recording medium with improved surface smoothness and video S/N ratio can be obtained, and therefore has great industrial value.

Claims (2)

[Claims] (1) A magnetic layer in which magnetic powder is dispersed in a binder resin is formed on a non-magnetic support, and grafted carbon in which a polymer is bonded to the surface of carbon black particles is included in the magnetic layer. A magnetic recording medium characterized by: (2) The magnetic recording medium according to claim (1), wherein the graft carbon is formed by thermal polymerization or t-ray polymerization of carbon black and a vinyl monomer.