JPS6226633A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which has a good electromagnetic conversion characteristic, small coefft. of dynamic friction, substantially less tendency to flawing of a back coat layer and guide pins and good runnability by using alumina or chromium oxide, etc. adsorbed with carbon black on the surface to constitute the back coat layer. CONSTITUTION:This magnetic recording medium is constituted by providing a magnetic layer on one surface side and a resin layer contg. the carbon black-deposited nonmagnetic material adsorbed with the carbon black having >=30m<2>/g specific surface area on the nonmagnetic material having >=6 Mohs' hardness on the other surface side. The resin layer contg. such carbon black-deposited nonmagnetic material is constituted to have the surface which is of 0.005-0.1mum center line average height. The surface roughness of the back coat layer contg. the carbon black-deposited nonmagnetic material is specified to about 0.005-0.1mum because the coefft. of dynamic friction considerably increases after repeated running if the surface roughness thereof is too small and because the surface of the back coat layer is transferred to the surface of the magnetic layer and a decrease of the electromagnetic conversion characteristic is resulted if the surface roughness is conversely too large. The amt. of the carbon black to be adsorbed to the nonmagnetic material is preferably about >=10wt% ratio by the weight of the nonmagnetic material.

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 for video, audio, and computers. Problems] In recent years, technological innovations in magnetic recording and reproducing devices such as video tape recorders have been remarkable. Correspondingly, technological innovations in magnetic recording media have also been remarkable, and high-density recording is being achieved.

Along with this trend towards higher density recording, bases with smooth surfaces are being used as supports for magnetic recording media.

However, a magnetic recording medium formed by providing a magnetic coating layer on a base with a smooth surface has the drawbacks of poor wear resistance and poor running stability.

Therefore, in order to solve these drawbacks, it has been proposed to provide a so-called back coat layer on the base surface opposite to the magnetic coating layer, and this back coat layer contains high-quality materials such as alumina or chromium oxide. Hard powder and carbon black are mixed in.

In other words, by mixing carbon black into the back coat layer, it is possible to prevent static electricity charging, prevent the adhesion of dirt and dust, and prevent irregular winding, and also mix alumina chromium oxide. It is said that it is possible to improve the abrasion resistance and durability by keeping the material in place.

However, it has been discovered that conventional magnetic recording media as described above have new drawbacks.

In other words, although the alumina or chromium oxide contained in the back coat layer improves the abrasion resistance and durability of the magnetic recording medium, it may scratch the guide bins, etc. on the magnetic recording/reproducing device. As a result, a drawback arises in that the running properties of the magnetic recording medium are reduced.

In addition, since carbon black has poor dispersibility, carbon black aggregates may form in the paint for the back coat layer.For this reason, if carbon black aggregates are mixed in BARAFCO-JW, the back coating may be caused. The surface properties of the coat layer are significantly reduced, and in a magnetic recording medium configured with a back coat layer with such poor surface properties, the surface of the back coat layer is transferred to the surface of the magnetic coating layer, and as a result, electromagnetic It has the disadvantage of deteriorating conversion characteristics.

[Disclosure of the invention]

In view of the above-mentioned problems, the present inventors believe that the drawback of reduced runnability that occurs when alumina, chromium oxide, etc. are contained in the back coat layer, Paying attention to the fact that this is caused by the scraping of guide bottles, etc. in the path, some kind of surface treatment should be applied to the highly hard substances such as alumina or chromium oxide that are mixed into the back coat layer. I thought that the above problems could be solved if I kept the carbon black agglomerated, and I also thought that the reduction in surface properties of the back coat layer due to carbon black agglomerations could be solved by preventing the carbon black from agglomerating in the first place. We came to this conclusion and proceeded with research and development in a direction consistent with this technical philosophy.

As a result, the present inventor received the revelation that carbon black could be used as a surface treatment substance for highly hard substances such as alumina or chromium oxide mixed in the back coat layer, and Thinking that it might be possible to kill two birds with one stone by using it as a processing material, we developed a magnetic recording medium in which the back coat layer was made of alumina or chromium oxide with carbon black adsorbed on its surface.

That is, a magnetic recording medium provided with a back coat layer of a resin layer containing a non-magnetic substance adhered to carbon black in which carbon black with a specific surface area of 30 rn'/g or more is adsorbed to a non-magnetic substance with a Mohs hardness of 6 or more is The carbon black is adsorbed by the non-magnetic material, resulting in a more appropriate hardness, and the guide bottle etc. will not be scratched. Furthermore, the adsorbed carbon black plays the role of a solid lubricant, improving running properties and has good wear resistance. They found that the dispersibility is better and the surface properties are better as well.

Here, as the carbon black to be adsorbed to a non-magnetic substance having a Mohs hardness of 6 or more, carbon black with a specific surface area of 3o, z7
If the material is much smaller than this, the carbon black will easily separate from the non-magnetic material.
This is because the effect will be weak.

The reason why the Mohs hardness of the non-magnetic material that adsorbs carbon black is set to be 6 or more is because if the Mohs hardness is too small, the back coat layer will be scratched.

Furthermore, if the surface roughness Ra of the back coat layer containing the non-magnetic substance adhered to carbon black is too small, the coefficient of dynamic friction will greatly increase after repeated running; The surface of the layer is transferred to the surface of the magnetic layer, resulting in a decrease in electromagnetic conversion characteristics.
It has also been found that it is important that the thickness be about 0.000 to 0.1 μm.

The amount of carbon black adsorbed to the non-magnetic material is
The ratio of carbon black-adhered non-magnetic material to resin is preferably about 10% by weight or more based on the non-magnetic material, and the ratio of carbon black-adhered non-magnetic material to resin is about 1%. It is desirable that the weight ratio be within the range of /10 to 10/1 (weight ratio).

The non-magnetic substance to which carbon black is adsorbed preferably has an average particle size of about 0.01 to 2 μm, and the back coat layer, which is a resin layer containing a non-magnetic substance to which carbon black is adhered, Its thickness is about 0.3 ~
It is desirable that the thickness is 4 μm.

[Example 1] Co coating - 100 parts by weight of Fetus, 1 part by weight of lecithin, 10 parts by weight of nitrocellulose, 10 parts by weight of polyurethane elastomer, 5 parts by weight of Ti0, and 270 parts by weight of a mixed solvent of toluene, methyl ethyl ketone, and cyclohexanone were mixed in a ball mill. A magnetic paint is obtained by mixing and dispersing, and this magnetic paint is applied to a polyethylene terephthalate base film to a predetermined thickness, and subjected to magnetic field orientation treatment and calender treatment.

In addition, carbon black with a specific surface area of 3o and t7g was At2
Approximately 10 to 0g (Mohs hardness 9, average particle size 0.3μm)
For carbon black adsorption by weight%! , 20s
A mixture of 10 parts by weight, 5 parts by weight of nitrocellulose, 5 parts by weight of polyurethane elastomer, methyl isobutyl ketone, and 40 parts by weight of cyclohexanone was mixed and dispersed in a sand mill for a predetermined time to obtain a paint, and this paint was coated with the above magnetic paint. Specified thickness on the opposite side of the base film,
For example, it is coated to a thickness of 1 μm and dried.

Then, the product obtained in the above manner is heated to 40℃ for example.
The material is left to stand for 8 hours to undergo a curing reaction, and then slit into 1-inch widths to obtain a magnetic recording medium such as a video magnetic tape.

[Example 2] In Example 1, the carbon black used for the carbon black coating A7zOz had a specific surface area of 100ml/g.
A magnetic recording medium is obtained by carrying out the same procedure using a magnetic recording medium.

[Comparative Example 1] A magnetic recording medium is obtained by carrying out the same procedure as in Example 1 using AA203 to which no carbon black is adsorbed instead of the carbon black-adsorbed ALzOs.

[Comparative Example 2] The same procedure as in Example 1 was carried out using CaFt (Mohs hardness: 4, average particle size: 0.3 μm) on which carbon black was not adsorbed instead of the carbon black-adhered AlaOs, and a magnetic recording medium was prepared. obtain.

[Comparative Example 3] In Example 1, carbon black adhesion A! The carbon black used in Aos has a specific surface area of 20 m1/g.
A magnetic recording medium is obtained by carrying out the same procedure using a magnetic recording medium.

[Comparative Example 4] In Example 1, carbon black with a specific surface area of 10 o@'/g was used instead of At203 coated with carbon black.
A magnetic recording medium is obtained by carrying out the same procedure using carbon black-adhered CaF2 adsorbed in an amount of about 10% by weight on aF=(same particle size as Comparative Example 2).

〔Characteristic〕

Regarding the magnetic recording medium obtained as described above, the center line average roughness Ra%C-5/N of the back coat layer, the coefficient of dynamic friction, the degree of damage to the back coat layer by repeated running tests, and the guide in the running path. Examining the degree of damage to the bottle, it is as shown in the table.

As can be seen from this table, if a material with a high Mohs hardness, such as Az*Os, is selected to be mixed into the back coat layer, damage to guide bottles, etc. in the travel path of the magnetic recording medium can be avoided. As a result, the running properties will be deteriorated.Also, if a material with low Mohs hardness such as CaFt is included in the back coat layer, it will not damage the guide bins etc. in the running route, but the back coat will be damaged. The coating layer itself is severely damaged, and as the running is repeated, the coefficient of dynamic friction increases, resulting in poor running properties.
Unlike the case where a F 2 is mixed into the back coat layer, as shown in Comparative Example 3, carbon black deposited A
Even if t203 is mixed into the back coat layer, if the specific surface area of this carbon black is small, such as 20 ml g, the coefficient of kinetic friction will increase as the running is repeated. The back coat layer and the guide bottles in the travel path may be slightly scratched, and as shown in Comparative Example 4, carbon black adhering non-magnetic material mixed in the back coat layer Even if carbon black has a large specific surface area of 100 m/g, if the non-magnetic material to which carbon black is adsorbed has a small Mohs hardness, the back coat layer will be severely damaged. be.

On the other hand, a mukhak coat layer containing a non-magnetic substance adhered to carbon black, which is made by adsorbing carbon black with a specific surface area of 30 m2/g or more to a non-magnetic substance with a Mohs hardness of 6 or more, is provided, and the surface of this back coat layer is The magnetic recording medium of the above example, which has a center line average roughness Ra of 0.005 to 0.1 μm, has good electromagnetic conversion characteristics such as C-5/N, and has a small coefficient of dynamic friction, and is particularly suitable for repeated running. Even after the test, the increase in the coefficient of dynamic friction is small, and furthermore, the back coat layer and the guide bins in the running path are hardly scratched, and the running performance is also good.

〔effect〕

The magnetic recording medium of the present invention has a magnetic layer on one side of a base support, and carbon black with a specific surface area of 30 m/g or more adsorbed on the other side of a non-magnetic material with a Mohs hardness of 6 or more. A resin layer containing a non-magnetic substance adhered to carbon black, that is, a back coat layer is provided, and the surface of this back coat layer has a center line average roughness of 0.005 to 0.1 μm.
Since it is made of M, it has good electromagnetic conversion characteristics such as C-5/N, and since carbon black is coated on the abrasive with a high Mohs hardness, it is difficult to use the back coat layer and guide bottles in the travel path. The carbon black is less likely to be scratched, and the specific surface area of the adsorbed carbon black is 30
, Z7g or more is used, so the effect is large, and the coefficient of dynamic friction is small, resulting in good running properties.Furthermore, since carbon platters are included, the surface electrical resistance is small, which reduces static electricity. Since carbon black is not easily charged and is adsorbed in advance to a non-magnetic substance, it has good dispersibility when producing a paint with a back coat layer structure, and can be provided more efficiently.

Patent applicant: Victor Japan Co., Ltd.7, agent: Katsumi Utaka.

Claims (1)

[Claims] A magnetic layer is placed on one side of the support, and the specific surface area is 30 m on the other side.
^2/g or more of carbon black is adsorbed to a non-magnetic material with a Mohs hardness of 6 or more, and a resin layer containing a carbon black-adhered non-magnetic material is provided, and the resin contains the carbon black-adhered non-magnetic material. A magnetic recording medium characterized in that the surface of the layer has a center line average roughness of 0.005 to 0.1 μm.