JPS60263314A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To realize the decrease in surface resistance with addition of a non- magnetic material in a smaller quantity by mixing >=3 kinds of binders to form a magnetic layer having the surface electric resistance lower than the surface electric resistance of a magnetic layer formed by mixing 2 kinds of binders. CONSTITUTION:The resistance value can be decreased by combining binders of carbon black. More specifically, two kinds of the binders are dissolved in respective solvents to prepare preliminarily solns. The film is formed by mixing these solns. at a specific proportion and drying the same. A polyurethane resin or vinyl chloride acetate copolymer resin is used as the binder having good dispersibility with the carbon black and cellulose acetate butyrate or the like is used as the binder having poor dispersibility with the carbon black. The decrease in the surface electric resistance of the magnetic layer as a result of the incorporation the carbon black therein is considered to arise from the range 4 of the carbon black particles and the generation of the range 4 is made easy by using the binder system mixed with the binder having the good dispersibility and the binder having the poor dispersibility. The surface electric resistance is thus decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic tapes, floppy disks, etc. used in audio equipment, video equipment, computers, etc.
This invention relates to magnetic recording media used in magnetic cards and the like.

Conventional configurations and their problems Recent magnetic recording media used in audio equipment, video equipment, computers, etc. are required to have higher density and higher performance. Comprehensive properties with excellent physical properties and electromagnetic conversion properties are desired.

In particular, high-performance videotapes using iron oxide magnetic powder require a high S/N ratio (which challenges the limits of iron oxide magnetic powder).
Signal-to-noise ratio) is a major concern, and many efforts have been made to find a way to incorporate magnetic powder into the magnetic layer at a high density. However, even with high S/N and high image quality, so-called 0. (
Dropouts) significantly reduce the quality image of the tape. Although the cause of Do is due to the wear resistance of the tape magnetic layer, it is mostly due to surface electrical resistance. That is, needless to say, if the surface electrical resistance is not on the order of a certain value or less, a lot of dust in the air will be attracted by the static electricity charged in the magnetic layer, resulting in significant generation of Do.

Conventionally, in order to counter this problem, the surface electrical resistance has been lowered, and therefore carbon black has been included in the magnetic layer.

came. However, since this carbon blank is a non-magnetic powder, it goes without saying that it is desirable to reduce the content as much as possible from the viewpoint of reproduction output and the like. The same applies to organic conductive materials. However, it is also true that if the content exceeds a certain level, the surface electrical resistance will not fall below a predetermined level. Therefore, the problem was how to reduce the content of the conductive substance and obtain a predetermined surface electrical resistance.

OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that can reduce the surface electrical resistance by adding a non-magnetic material such as carbon as described above with as little amount as possible.

Structure of the Invention The present invention provides a magnetic recording medium in which the surface electrical resistance of the magnetic layer is lowered by mixing carbon black.By mixing three or more types of binders, the magnetic layer has a lower surface resistance than a magnetic layer made of two types of binders. A magnetic recording medium is characterized in that it has a magnetic layer with significantly reduced surface electrical resistance.

In the present invention, there is originally a distinction between binders that have good dispersibility and binders that have poor dispersibility with respect to carbon black, and when carbon black is present in a mixed binder of both, carbon black with the same content in each individual binder.
This was based on the discovery that the surface electrical resistance is significantly lower than when black is present.

Conventionally, the binders that make up the magnetic layer have good compatibility with each other, which improves the dispersibility of the magnetic powder and leads to excellent magnetic properties. A corresponding surface electrical resistance value of the magnetic layer was obtained based on the type and content of the carbon blank. As a result of diligent efforts, the inventor of the present invention has investigated various compositional conditions and process conditions such as the type and content of carbon black, and has found that it is possible to lower the surface electrical resistance by combining them with binders. was easily realized.

6 b/ The basic data for this was the compatibility test between binders described below.

Two types of binders are dissolved in a solvent to prepare a solution, mixed in a fixed ratio, and dried to obtain a film. We investigated the transparency of this film and changes in physical properties when carbon black was added. Based on the results of these compatibility tests, binders with good dispersibility for carbon blanks, such as shitehori urethane resin and salt-vinyl acetate copolymer resin, and binders with poor dispersibility such as CAB (cellulose acetate butyrate), etc. I found out something.

DESCRIPTION OF EXAMPLES The present invention will be specifically explained below with reference to Examples. All figures in the middle part of the examples are parts by weight. In addition, barium ferrite (barium ferrite) is used as a magnetic powder for perpendicular magnetic recording media.
BaO.eFe-203) was used.

Example 1-(1) to (-1, Example 2-(11 to (41)
The common material composition and film forming method except for the binder system and carbon black 3 are as follows.

6benomagnetic iron oxide (BaO・6Fe203) 100 parts Abrasive (α-mu Jl?zO3) 3 parts Lecithin (made from soybean) 1 part Silistic acid 2 parts Stearic acid 2 parts Methyl ether titone 400 parts Toluene 100 parts Cyclohexanone IQO part The binder and carbon black of each example were added to the above composition, kneaded in a ball mill for 114 hours, and then filtered through a filter with an average pore size of 3 μm.

Next, 8 parts of Coronate L (trade name: manufactured by Nippon Polyurethane Co., Ltd.) as a hardening agent was added to this magnetic paint, which was coated onto a 15 μm thick polyethylene terephthalate film 1, dried, calendered, and then heated to make it magnetic. The layer was cured to form a magnetic layer 2 with a thickness of 5 μm. After that μ
It was cut into inch width pieces to obtain magnetic tape.

The surface electrical resistance values of the magnetic layers of the above samples were measured using the following two methods.

7, -7 (1) Measurement using a high resistance measuring device Insulation resistance meter (YHP4329A, capable of measuring up to a minimum of 108 Ω) Sample tape width Inches Applied voltage 500V Distance between electrodes 5C1n If the actual value of the resistance meter is The surface electrical resistance value was calculated to be 0.29 x (Q/ci).

(2) Measurement using a simple tester The resistance value was actually measured using a commercially available tester (capable of measuring up to 106Ω) at a distance of 1 m between the probes.

If the resistance value is (1), it is too low, and if it is (≧), it is too high to be measured, this is indicated by marking it in the table with an x.

In addition, the following binderms, B, 0, and carbon black in Tables 1 and 2 were used.

5.9ia 7- □ Cellulose acetate phthylate resin (product number CAB-
553-0,4) Binder B manufactured by Eastman Kodax Polyurethane resin (Product number N-2304) ■ Binder C manufactured by Nippon Polyurethane Vinyl chloride/vinyl acetate copolymer resin (Product name V4G
H) Carbon black manufactured by UCC Corporation (product number VULCjAN XC-72) manufactured by Cabot Corporation (
Space below) 9 beno 10 peno 11 beno In addition, regarding the growth of Do (drop out), run in the following method, D, 0. Measured with a counter.

Equipment used: VTR deck manufactured by Matsushita Electric Industrial Co., Ltd. (MV
-8200) Atmosphere: 26℃, 60%RH Number of runs: 2o passes (2 hour mode, Zhang Kanying 401
i', Out 9of/), Measurement Effects of the Invention The effects of the invention are clear from the results shown in the above examples. In other words, the decrease in the surface electrical resistance of the magnetic layer due to the inclusion of carbon black is thought to be due to the arrangement of carbon black particles 4 as shown in Figure 2. In order to realize such a series, it is necessary to A mixed binder system with a binder that has good dispersibility and a binder that does not have good dispersibility for black! 1 6 and f'-& y 7' 7 y
l y)'-"0AW7'X--, it is thought that unlucky lines are more likely to occur and the surface electrical resistance value decreases.On the other hand, the difference between carbon black and dispersibility. It is thought that a mixed binder system of good binders will make it difficult to generate porosity and reduce the surface electrical resistance.In this example, the orientation of the Ba ferrite magnetic powder and the magnetic layer There was almost no difference in the surface properties.In other words, only the surface electrical resistance of the magnetic layer was significantly changed by a series of changes in carpump sickness, and after the running test, it was possible to reduce the amount of oxide and O1 growth. We were able to obtain a magnetic recording medium.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing models of the particle morphology of carbon black in the magnetic layer. Figure 1...Example 2-(3) Figure 2...
......N2-(4) is shown respectively. 1...Base film, 2...Magnetic layer,
3... Carbon black particles, 4...
A series of carbon black particles.

Claims (1)

[Claims] In magnetic recording media in which the surface electrical resistance of the magnetic layer is lowered by mixing carbon black, the surface electrical resistance is lowered by mixing three or more types of binders compared to a magnetic layer made by mixing two types of binders. 1. A magnetic recording medium characterized by realizing a magnetic layer with a further reduced .