KR940006847B1 - Magnetic recording medium - Google Patents

Abstract

The medium enhances the traveling stability and the durability of the magnetic tape. The materials below are used for backcoating layer: the first material, Di-Butyl Phthalate (DBP) solutions of 100-200cc/100g and carbon black of 20-30 nm particle size; the second material, DBP solutions of 80cc/100g and carbon black of 60-100 nm particle size. The first and second material in weight ratio of 1:9 - 5:5, and 50-200 weight ratio of carbon to reference binder 100 weights are used for backcoating layer whose thickness is 0.5-1.5 μm.

Description

Magnetic recording medium

The present invention relates to a magnetic recording medium having excellent running stability and durability.

In general, magnetic recording media such as magnetic tapes, magnetic disks, and the like of audio, computer, or video are formed by applying a magnetic layer containing a magnetic component, a binder, carbon black, and various additives on the surface of a nonmagnetic support such as a polyester film. It is.

In recent years, in accordance with the trend of higher density of magnetic recording, the surface diameter of the magnetic layer is reduced and the surface of the base film is smoothed to increase the smoothness of the surface of the magnetic layer, which increases the residual magnetic flux density, improves recording output, and reduces noise. Give the same effect.

However, when the smoothness of the magnetic layer is increased in this way, the running stability of the magnetic layer is weakened. As a means for solving this problem and preventing foreign matter adhesion due to charging, providing a back coating layer on the surface opposite to the magnetic layer of the nonmagnetic support.

The back coating layer is usually an inorganic compound such as alumina (A1 ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium dioxide (TiO ₂ ), α-iron oxide (α-Fe ₂ O ₃ ), calcium carbonate (CaCO ₃ ) The powder and the particulate carbon black having an average particle diameter of 0.02 μm are adsorbed and dispersed in a binder, and then applied to the opposite side of the magnetic layer on the nonmagnetic support to form a constant surface roughness. When such a back coating layer is provided, not only the antistatic effect is obtained by the conductive carbon black in the back coating layer, but also the running friction coefficient is reduced, the tape winding property is improved, and the running performance of the magnetic tape is greatly improved.

However, it has been found that there is a new problem in the magnetic recording medium having the back coating layer. That is, the surface irregularities formed by the carbon black contained as a main component in the back coating layer are transferred to the opposite magnetic layer in the wound state of the tape, thereby increasing the noise. In order to prevent this, the surface smoothness of the back coating layer is designed, and the friction coefficient of the contact point of the recording / reproducing device (VCR) is increased again by increasing the smoothness of the back coating layer. Problems have arisen.

A technique for including a lubricant in the back coating layer has been proposed for running stability. However, if the lubricant content increases, the adhesion of the back coating layer deteriorates and the binder layer deteriorates, resulting in contamination of the guide roll portion of the VCR. Due to this, the friction coefficient of the guide roll was not sufficiently reduced.

The back coating layer has the following problems in addition to the above-described problems of running stability. That is, in order to maintain an appropriate surface roughness and to ensure driving stability, inorganic compounds such as A1 ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , α-Fe ₂ O ₃ , and CaCO ₃ are mixed with carbon black at a predetermined ratio. When used, the fine particles may be generated during repeated driving of the tape due to the inorganic particles having an uneven shape and poor dispersibility. Occurrence of fine debris increases the contamination of the contact guide and may also increase the drop out.

It is an object of the present invention to solve the above problems, to improve the surface smoothness of the back coating layer to significantly reduce the noise caused by the uneven transfer, and to reduce the friction coefficient with the guide portion of the recording and reproducing apparatus to improve the running stability and It is an object of the present invention to provide a magnetic recording medium having excellent durability.

In order to achieve the above object, in the present invention, a magnetic layer including a magnetic component, a binder, carbon black, and the like is formed on one surface of a nonmagnetic support, and a back coating layer is formed on the opposite side thereof. Oil absorption of Di-Butyl Phthalate (DBP) solution is 100 to 200cc / 100g and carbon black having an average particle diameter of 20 to 30nm, and oil absorption of di-butyl phthalate solution is 80cc / 100g or less and average particle diameter is 60 Provided is a magnetic recording medium comprising carbon black having a thickness of from 100 nm to 100 nm.

In particular, the mixing ratio of the carbon black having the oil absorption amount of the DBP solution of 100 to 200 cc / 100 g and the carbon black having the oil absorption amount of the DBP solution of 80 cc / 100 g or less is preferably 1: 9 to 5: 5 by weight, and the carbon in the back coating layer It is preferable that content of black is 50-200 weight part with respect to 100 weight part of binders. In addition, the back coating layer is preferably a thickness of 0.5 to 1.5μm.

The back coating layer of the magnetic recording medium provided in the present invention contains two kinds of carbon blacks each having a specific DBP oil absorption amount and an average particle diameter instead of not containing a nonmagnetic inorganic substance. Among these two components, carbon black having a DBP oil absorption of 100 to 200cc / l00g and an average particle diameter of 20 to 30nm is a material commonly introduced into a back coating layer, and thus has excellent conductivity due to its excellent structure and shows excellent antistatic effect. This also serves to moderate the surface roughness. In addition, the carbon black having a DBP oil absorption of 80cc / 100g or less and an average particle diameter of 60 to 100nm has a relatively simple structure and thus is easily adsorbed with a binder and exhibits excellent dispersibility. This serves to increase the surface smoothness of the back coating layer.

The reason for limitation of the carbon black introduced by this invention is as follows.

First, for carbon black having a DBP oil absorption in the range of 100 to 200 cc / 100 g, the purpose is to obtain appropriate conductivity and roughness. However, since carbon black having a DBP oil absorption of 100cc / 100g or less has a simple structure having almost no conductivity, the antistatic effect is not sufficient, and carbon black having 200cc / 100g or more has an excessively complex structure, and thus binder adsorption on the carbon black surface is not performed. Dispersion is difficult and results in excessively high surface roughness. In addition, carbon black having a DBP oil absorption of 80cc / 100g or less has a relatively simple surface having no developed particle structure, and is easy to adsorb and disperse a binder, thereby improving the surface smoothness of the back coating layer.

In addition, the particle diameters of the carbon blacks are limited to 60 to 100 nm and 20 to 30 nm, respectively, in order to solve the instability of running and friction due to the smoothing of the back coating surface layer. This is because the coefficient of friction can be greatly reduced than in the case of

The mixing ratio of the two kinds of carbon black is obtained by repeated experiments of the present inventors, and the DBP oil absorption is 100 to 200cc / 100g, the average particle diameter is 20 to 30nm and the carbon black and DBP oil absorption is 80cc / 100g or less, and the average particle diameter is 60 It is preferable that the mixing ratio of carbon black of 100 nm to 100 nm is 1: 9 to 5: 5 by weight. If the ratio of the former is larger than the above range, the surface roughness of the back coating layer becomes large, so that the video S / N ratio is greatly decreased, and the contamination due to fine separation during repeated driving increases, resulting in an increase in dropout, and the ratio of the latter is larger than the range. If the surface of the back coating layer is too smooth, the friction coefficient is increased, causing driving instability and the antistatic effect is reduced. Therefore, the mixing ratio of the above range is most suitable.

The total content of carbon black in the back coating layer is 50 to 200 parts by weight relative to 100 parts by weight of the binder, but if the content of carbon black is less than or equal to the above range, the effect sought in the present invention cannot be sufficiently obtained. Since the binding force by the black binder is lacking, the occurrence of separation by the wear resistance fall of the back coating layer itself becomes easy, and it is not preferable.

As a binder for adsorbing and dispersing the two types of carbon black used in the present invention, conventional polymer resins such as nitro cellulose, vinyl chloride copolymer, polyurethane resin, and phenol resin are used, and a polyisocyanate compound is used as a curing agent. do. As an organic solvent, methyl ethyl ketone, cyclohexanone, toluene, etc. are used in combination.

In the back coating layer of the magnetic recording medium of the present invention, a carbon coating component, a binder, an organic solvent, a dispersant, etc. are mixed to prepare a back coating material, which is coated on the opposite side of the magnetic layer of the base film and dried. Can be obtained.

Hereinafter, specific embodiments of the present invention will be described in detail.

Example 1

100 parts by weight of Co-containing α-Fe ₂ O ₃ , 20 parts by weight of a vinyl copolymer, 10 parts by weight of polyurethane, 20 parts by weight of other additives and 300 parts by weight of an organic solvent are mixed to prepare a magnetic paint. The magnetic coating is applied to the surface of the polyester base film to form a magnetic layer.

30 parts by weight of carbon black having a DBP oil absorption of 100 to 200 cc / 100 g and an average particle diameter of 20 to 30 nm, 70 parts by weight of carbon black having a DBP oil absorption of 80 cc / 100 g or less and an average particle diameter of 60 to 100 nm, 50 parts by weight of nitro cellulose, poly 50 parts by weight of a urethane resin, 650 parts by weight of a mixed solvent of methyl ethyl ketone, cyclohexane and toluene, and 5 parts by weight of a dispersant are mixed and then kneaded and dispersed sufficiently by a sand mill. 20 parts by weight of polyisocyanate is added to the mixture to prepare a coating for back coating, and to coat the upper side of the base film and the opposite side of the magnetic layer. Drying and surface treatment are performed to obtain a magnetic tape of the magnetic recording medium of the present invention in which a back coating layer of about 1 탆 is formed.

EXAMPLES 2-4

Perform the same method as in Example 1 except that the amount of carbon black having a DBP oil absorption of 100 to 200 cc / 100 g and an average particle diameter of 20 to 30 nm, and the amount of carbon black having a DBP oil absorption of 80 cc / 100 g or less and an average particle diameter of 60 to 100 nm, respectively. 10 g and 90 g (Example 2), 40 g and 60 g (Example 3), 50 g and 50 g (Example 4) are obtained to obtain the magnetic tape of the magnetic recording medium of the present invention.

Comparative Example 1

Performed in the same manner as in Example 1, using 100 parts by weight of carbon black having a DBP oil absorption of 100 to 200cc / 100g and an average particle diameter of 20 to 30nm, carbon having a DBP oil absorption of 80cc / 100g or less and an average particle diameter of 60 to 100nm Instead of black, 10 parts by weight of Al ₂ O ₃ , a nonmagnetic inorganic additive, is added to obtain a magnetic tape of the magnetic recording medium of the present invention.

Comparative Example 2

Performed in the same manner as in Example 1, using 100 parts by weight of carbon black having a DBP oil absorption of 80cc / 100g or less and an average particle diameter of 60 to 100nm, carbon having a DBP oil absorption of 100 to 200cc / 100g and an average particle diameter of 20 to 30nm Instead of black, 10 parts by weight of Al ₂ O ₃ , a nonmagnetic inorganic additive, is added to obtain a magnetic tape of the magnetic recording medium of the present invention.

For the magnetic tapes manufactured through the above examples and comparative examples, the dropout occurrence rate, the friction coefficient, the video S / N ratio during the initial and repeated running, the contamination degree due to the occurrence of the breakage during the repeated running, and the runability were evaluated. Indicated.

TABLE 1

In Table 1, the dropout occurrence rate is a count of the number of times the reproduction output signal drops by 20 dB or more over 15 µsec.

Coefficient of friction is the ratio of the load hanging on a chrome-plated original plate by an angular contact a back coating layer on the chromium-plated mirror-finished with a diameter of 120mm to the inside and winding the magnetic tape to 180 ° on a load of 10g by rotating at a speed of 150rpm T ₂ / 10g Expression The value obtained by inserting into.

In addition, the video S / N ratio was recorded and reproduced using the BR6400 VTR manufactured by Victor Nippon Co., Ltd. using Shiba Sok noise meter, and the contamination level caused by the occurrence of separation after repeated driving was rotated 62mm using the Yokohama MCS testability tester. After the drum cleaning tape was attached, the vehicle was repeatedly run for 100 times while rotating backward at 40 rpm, and the degree of contamination on the cleaning tape was visually determined.

The running time is expressed as the sum of the time taken by fast forwarding and rewinding the 120-minute tape in the BR6400 VTR.

The results shown in Table 1 are as follows.

For example, in Comparative Example 1 using carbon black having a DBP oil absorption of 100 to 200cc / 100g alone in the back coating layer and using an existing inorganic additive, the contamination due to the occurrence of fine separation during repeated driving is large, and thus the dropout suddenly occurs. It is increasing. In addition, it can be seen that the video S / N ratio of the magnetic layer due to the surface irregularities is also greatly reduced.

In addition, in the case of using carbon black having a DBP oil absorption amount of 80cc / 100g or less and a conventional inorganic additive of Comparative Example 2, there is a problem that the contamination due to the delamination of the inorganic additive is fine, but the driving becomes suddenly unstable due to the increase of the friction coefficient. have.

Compared with the comparative examples, it can be seen that the magnetic tape according to the exemplary embodiment of the present invention has no pollution during repeated driving, suppresses the sudden increase in dropout, and has excellent video S / N ratio characteristics, friction coefficient, and running performance. .

As described above, in the present invention, a carbon black having a DBP oil absorption of 100 to 200cc / 100g and an average particle diameter of 20 to 30nm and a DBP hop flow rate of 80cc / 100g or less are used without using a nonmagnetic inorganic additive on the opposite side of the magnetic layer. By providing a back coating layer containing two types of carbon black having a particle diameter of 60 to 100 nm, not only the surface smoothness is maintained and the noise increase is suppressed, but also the carbon black having different surface structures and particle diameters is joined to each other. The driving stability could be maintained by reducing the contact friction of the guide, and it was possible to prevent the micro-split caused by the use of the existing nonmagnetic minerals and the sudden drop out due to the drop.

Claims (4)

In a magnetic recording medium having a magnetic layer containing a magnetic component, a binder, carbon black, and the like formed on one surface of a nonmagnetic support, and a back coating layer formed on the opposite side thereof, the oil absorption amount of the di-butyl phthalate solution in the back coating layer is 100. A magnetic recording medium comprising carbon black having a mean particle size of 20 to 30 nm and a carbon particle having a mean particle size of 60 to 100 nm while having an oil absorption amount of 80 cc / 100 g or less and an average particle diameter of 20 to 30 nm. According to claim 1, wherein the oil absorption of the di- butyl phthalate solution is 100 to 200cc / 100g, the average particle diameter of 20 to 30nm, the oil absorption of carbon black and di-butyl phthalate solution is 80cc / 100g or less and the average particle diameter is 60 to 100nm A magnetic recording medium, wherein the mixing ratio of phosphorus carbon black is 1: 9 to 5: 5 by weight. The magnetic recording medium according to claim 1, wherein the content of the carbon black in the back coating layer is 50 to 200 parts by weight based on 100 parts by weight of the binder. The magnetic recording medium according to any one of claims 1 to 3, wherein the back coating layer has a thickness of 0.5 to 1.5 m.