JPS6226632A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide magnetic recording medium which has a good electromagnetic conversion characteristic, small surface electric resistivity, less tendency to electrostatic charging, good runnability, resistance to flawing and less tendency to drop-out by constituting a back coat layer by using alumina or chromium oxide, etc. adsorbed with carbon black on the surface. CONSTITUTION:A magnetic layer is provided on one surface side of a base and a resin layer contg. the carbon black-deposited nonmagnetic material adsorbed with the carbon black having >=30m<2>/g specific surface area and >=30ml/100g DBP oil absorption on the nonmagnetic material having >=6 Mohs' hardness is provided on the other surface side. The Mohs' hardness of the nonmagnetic material is specified to >=6 Mohs' hardness because the flawing of the back coat layer is admitted if the Mohs' hardness is too small. The amt. of the carbon black to be adsorbed on the nonmagnetic material is about >=10wt% ratio by the weight of the nonmagnetic material and the ratio at which the carbon black-deposited nonmagnetic material is incorporated into the resin is in an about 1/10-10/1 range between the carbon black-deposited nonmagnetic material and the resin.

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 use in video, audio, computers, etc., for example.

[Prior art and its 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 incorporating carbon black into the back coat layer, it is possible to prevent static electricity charging, prevent dirt and dust from adhering, and prevent irregular winding. It is said that by mixing it in, wear resistance and durability can be improved.

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

That is, although the alumina or chromium oxide contained in the back coat and layer improves the abrasion resistance and durability of the magnetic recording medium, the guide bins, etc. on the magnetic recording/reproducing device are scratched. This results in a drawback that the running properties of the magnetic recording medium are reduced.

Also, 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 the back coat layer, the back coat The surface properties of the 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 the 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 included in the back coat layer is due to the alumina, chromium oxide, etc. Paying attention to the fact that this is caused by scraping of the dirt bins etc. in the path, some kind of surface treatment is applied to the highly hard substances such as alumina or chromium oxide mixed in the back coat layer. We thought that the above problems could be solved if we kept the carbon black agglomerated, and that the reduction in the surface properties of the back coat layer due to carbon black agglomerations could be solved by preventing carbon black from agglomerating in the first place. After reaching this conclusion, we 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 developed the idea of carbon black. Thinking that it might be possible to kill two birds with one stone by using it as a surface treatment material, we developed a magnetic recording medium in which the back coat layer was made of alumina or chromium oxide with carbo black adsorbed on the surface.

In other words, carbon black with a specific surface area of 30, 17 g or more and a DBP oil absorption of 30 ml/100 g or more is adsorbed on a non-magnetic material with a Mohs hardness of 6 or more. A magnetic recording medium provided with a coat layer has appropriate hardness because carbon black is adsorbed to a non-magnetic substance, and guide pins and the like are not scraped. Furthermore, the adsorbed carbon black plays the role of a solid lubricant, improving runnability and has good wear resistance.Furthermore, carbon black agglomerates during the production of paint for the hard coat layer. They found that the dispersibility and surface properties of the material were also better.

Here, as carbon black to be adsorbed to a non-magnetic substance with a Mohs hardness of 6 or more, in particular, carbon black with a specific surface area of 30 m"
/g or more, the DBP oil absorption amount is 30ml/100g
The reason for the above is that if carbon black smaller than this is used, the carbon black will easily separate from the non-magnetic material, causing the disadvantage that guide pins etc. will be scraped off and running performance will deteriorate. This is because there are drawbacks such as an increase in surface electrical resistance and a decrease in light-shielding properties.

Further, the reason why the Mohs hardness of the nonmagnetic material to which carbon black is adsorbed is set to be 6 or more is because if this Mohs hardness is too small, damage to the bank coat layer will be observed.

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 material 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 non-magnetic material-containing layer to which carbon black is adhered, Thickness is approximately 0.3~4μ
It is desirable that it be of m.

[Example 1] Co deposition 7 3100 parts by weight of FezO, 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, 270 parts by weight of a mixed solvent of toluene, methyl ethyl ketone and cyclohexanone
A magnetic paint is obtained by mixing and dispersing parts by weight in a ball mill, and this magnetic paint is applied to a polyethylene terrestrial base film to a predetermined thickness, and subjected to a magnetic field orientation treatment and a calender treatment.

Also, the specific surface area is 30yr? /g, DBP oil absorption 30ml
/100g of carbon black adsorbed on A-Laos (Mohs hardness 9, average particle size 0.3μm) by about 10% by weight, A t20s 10 parts by weight,
A paint was obtained by mixing and dispersing 5 parts by weight of nitrocellulose, 5 parts by weight of a polyurethane elastomer, and 40 parts by weight of a mixed solvent of methyl isobutyl ketone and cyclohexanone for a predetermined time using a sand mill, and this paint was applied to the opposite side of the base film coated with the magnetic paint. A predetermined thickness, for example, 1 μm, is applied onto the surface of the substrate and dried.

Thereafter, the product obtained as described above is heated for example at 4°C.
The mixture is left to stand for 8 hours for a curing reaction, and then slit into i-inch widths to obtain a magnetic recording medium such as a video magnetic tape.

[Example 2] In Example 1, A to adsorb carbon black
Carbon black adhesion T using Tie- (Mohs hardness 6-7, average particle size 0.25 μm) instead of At O*
i O! A magnetic recording medium is obtained by carrying out the same procedure using .

[Comparative Example 1] In Example 1, carbon black adhesion A At O
A t2 that does not adsorb carbon black instead of s
The same procedure is performed using 0 s to obtain a magnetic recording medium.

[Comparative Example 2] In Example 1, carbon black adhesion A t20s
The same procedure was repeated twice using 5 parts by weight of At20i and 5 parts by weight of carbon black instead of 10 parts by weight to obtain a magnetic recording medium.

' [Comparative Example 3] In Example 1, carbon black coating A L203
The specific surface area of the carbon black used in
A magnetic recording medium is obtained by carrying out the same procedure using a DBP oil absorption amount of 26 ml and 7100 g.

[Comparative Example 4] In Example 1, carbon black adhesion A! A O
The same procedure was carried out using carbon black-adhered CaFz (Mohs hardness 4, average particle size 0.3 μm, 1 force-bon black adsorption amount 10% by weight, the characteristics of carbon black were the same as in Example 1) instead of No. 3, and a magnetic recording medium was obtained. get.

〔Characteristic〕

Regarding the magnetic recording medium obtained as described above, Y-
3/N, C-5/N, surface electrical resistance of back coat layer,
The coefficient of dynamic friction, the extent of scratches on the surface of the back coat layer through repeated running tests, and dropouts were examined as shown in the table.

・Y-5/N and C-5/N are H manufactured by Japan Victor ■
Recorded and played back using an R-2200 video tape recorder and measured with a noise meter.

・The coefficient of dynamic friction indicates what acts between the back coat layer and the chrome-plated surface of the guide bin in the travel path.

- Dropout is indicated by the number of times a phenomenon in which the reproduced output signal decreases by 20 dB or more for 15 μsec or more occurs.

As can be seen from this table, when the substance mixed in the back coat layer is simply A4203, as shown in Comparative Example 1, the surface electrical resistance is high and it is easy to be charged with static electricity. However, even if carbon black is simply mixed into the back coat layer together with A At Os in order to reduce the surface electrical resistance, as shown in Comparative Example 2, The magnetic properties of the product, such as ¥-5/N and C-5/N, have significantly deteriorated, and repeated running tests have shown that the coefficient of dynamic friction has increased significantly, resulting in poor running performance.
Furthermore, dropouts occur frequently, so there is no benefit from mixing carbon black.

Further, even if a back coat layer mixed with a non-magnetic substance adhered to carbon black is provided as in the present invention, if this carbon black is not as specified in the present invention, Comparative Example 3 As shown, Y-5/N, C-
The electromagnetic conversion characteristics such as 5/N are poor and there are many dropouts, and if the non-magnetic material is not as specified in the present invention, as shown in Comparative Example 4, The disadvantage is that the Tsukuyodo layer is scratched.

On the other hand, the magnetic recording medium of this example has Y-5/N
, C-5/N, etc. have good electromagnetic conversion characteristics, and the surface electrical resistance is small, making it difficult to be charged with static electricity.Furthermore, the coefficient of dynamic friction is small, making it easy to run and not easily scratched. Furthermore, dropout is less likely to occur.

〔effect〕

The magnetic recording medium of the present invention has a magnetic layer on one side of a support serving as a base, and a specific surface area of 30 g and a t7 g on the other side.
In the above, a resin layer containing a non-magnetic substance coated with carbon black in which carbon black with a DBP oil absorption of 30 mL/100 g or more is adsorbed on a non-magnetic substance with a Mohs hardness of 6 or more;
In other words, since the back coat layer was provided, C-5/N, Y
It has good electromagnetic conversion characteristics such as -5/N, and carbon black is coated on the abrasive with a high Mohs hardness, making it difficult to scratch the back coat layer and guide pins in the travel path. The carbon black to be adsorbed has a specific surface area of 30 ml g or more and a DBP oil absorption of 3
0 ml, / 100 g or more, the effect of carbon black adhesion is large, and it also has excellent light shielding properties.Furthermore, the surface electrical resistance is small, making it difficult to be charged with static electricity, and it has good running properties. Furthermore, since carbon black is adhered to a non-magnetic material, it is difficult to form carbon black agglomerates, the surface properties of the back coat layer are good, and the dispersibility is improved when preparing the paint for the back coat layer. It has the advantage of being able to provide information efficiently and efficiently.

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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 and a DBP oil absorption of 30 ml/100 g or more is adsorbed onto a non-magnetic material with a Mohs hardness of 6 or more, and is characterized by having a resin layer containing a non-magnetic substance adhered to the carbon black. magnetic recording medium.