JPH09180173A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the durability of a magnetic layer and to also improve the running performance of a magnetic recording medium by forming a protective layer contg. fine bubbles as well as an abrasive material having a prescribed Mohs hardness or above on the side face of the medium. SOLUTION: A magnetic layer 3 is formed on the surface of a film-like substrate 2 by applying and drying a magnetic coating material, the substrate 2 with the layer 3 is cut to a prescribed shape such as a tape or disk shape and a protective layer 6 contg. fine bubbles 5 as well as an abrasive material having a prescribed Mohs hardness or above is formed on the side face of the resultant magnetic recording medium 1. The falling of magnetic powder and damage are hardly caused and the durability of the magnetic layer can be improved. The running performance of the medium is also improved and a fluctuation in audio level can be remarkably suppressed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic tape is formed on a non-magnetic support surface of, for example, polyester, polyimide, polyamide or the like with γ-Fe ₂ O ₃ and Co-containing γ-Fe.
A magnetic coating layer is formed by applying a magnetic coating material containing magnetic powder such as Fe ₂ O ₃ , CrO ₂ or metallic magnetic powder and a binder, and various additives, or wet plating such as electroless plating. It is usually obtained by forming a metal thin film type magnetic layer by means of dry plating means such as vapor deposition or sputtering, and then slitting this into a predetermined width, that is, by slitting or punching. .

By the way, when the magnetic recording medium thus obtained is loaded into a recording / reproducing apparatus and is run, particularly when the magnetic recording medium is run in a cue, review state or repetitive reproducing state, the magnetic recording medium is a recording / reproducing apparatus. The magnetic head, pads, guide pins, cassette halves, etc. are scratched to reduce the mechanical strength and cause magnetic powder to fall off, or the running performance of the magnetic recording medium becomes unstable, resulting in playback output. There is a tendency for problems such as wobbling and deterioration. Further, in the case of a thin tape intended for recording / reproduction for a long time, these problems become remarkable, and in addition, problems such as a large reduction in reproduction output due to a broken edge portion of the tape and a defective running increase.

Therefore, in order to solve such a problem, conventionally, a lubricant or an abrasive is contained in the magnetic layer, or a lubricant is interposed on the surface of the magnetic layer. As disclosed in JP-A-61-2202, a back coat layer is provided on the surface of the support opposite to the magnetic layer, and the above problems are largely solved.

[0005]

However, the recent demands for improving the characteristics such as durability and runnability of magnetic recording media are sufficient only by improving the components contained in the magnetic layer and the back coat layer as described above. It's gone. That is, when a tape-shaped magnetic recording medium is manufactured by slitting after forming the magnetic layer and the back coat layer, stress concentration occurs in the magnetic layer during the slitting work and cracks occur, and as a result, the durability of the magnetic layer is increased. Is deteriorated, or the running performance is deteriorated due to a decrease in head touch. Therefore, for example, as shown in JP-A-60-125929, the slit work is performed in a low temperature and low humidity environment, or as shown in JP-A-61-26937, a raw material of a magnetic recording medium hit by a cutter during slitting. It has been proposed to remove a part of the magnetic layer in advance.

However, these conventional countermeasures have a limit because they are only reluctant to prevent cracking of the magnetic layer during slitting.
Durability and drivability have not been sufficiently improved. The present invention focuses on the above problems and was devised in order to effectively solve them, and the purpose thereof is to provide a protective film containing an abrasive having a Mohs hardness of a predetermined value or more on the end face for durability. An object of the present invention is to provide a magnetic recording medium capable of improving the properties and the like.

[0007]

The present inventor has found that when the magnetic recording medium is running, only the magnetic layer surface of the magnetic recording medium and the back surface opposite to the magnetic layer are in contact with the guide means on the recording / reproducing apparatus side. However, since the end surface which is the slit surface of the magnetic recording medium also contacts with these, if a protective film that improves the running property and durability is also configured on this end surface, the running property of the magnetic recording medium and the The present invention has been accomplished by finding that the durability can be significantly improved as compared with the conventional magnetic recording medium.

That is, in order to solve the above-mentioned problems, the present invention is configured such that an end face is provided with a protective film containing an abrasive having a Mohs hardness of a predetermined value or more and containing fine bubbles. .

Since the present invention is configured as described above, when the magnetic recording medium is running, not only the magnetic layer of the medium and the back surface on the opposite side but also the end surface of the medium come into contact with the guide means of the recording / reproducing apparatus. Although the vehicle runs, a protective film containing an abrasive and fine bubbles is formed on this end surface, so that the durability can be improved, and powder falling and the like can be greatly reduced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a magnetic recording medium according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of a magnetic recording medium according to the present invention. As shown in the figure, the magnetic recording medium 1 has a film-like non-magnetic support 2 made of a non-magnetic material such as polyethylene terephthalate, and the magnetic layer 3 is formed by coating and drying a magnetic coating on the surface of the support. It is formed. Then, this is formed into a predetermined shape, for example, a tape shape or a disk shape, and one end surface or both end surfaces 4 thereof is formed.
In the illustrated example, the features of the present invention on both end surfaces,
A protective film 6 containing an abrasive having a Mohs hardness of a predetermined value or more and containing fine bubbles 5 is formed, so that the durability and the like of the magnetic recording medium 1 itself can be improved.

To manufacture the magnetic recording medium 1 specifically described above, the coating type magnetic layer 3 or the metal thin film type magnetic layer 3 is used.
A slit of a wide raw material of a magnetic recording medium formed on the surface of the non-magnetic support 2 into a predetermined width, and the end surface 4 which is the slit surface of the magnetic recording medium of a predetermined standard obtained by slitting it.
A coating material containing an abrasive and containing fine open cells is applied and dried by a means such as dip coating to obtain air bubbles 5
For this purpose, a protective film 6 having elasticity was formed to manufacture a magnetic recording medium 1 as shown in FIG. When the magnetic recording medium 1 thus formed was loaded into the recording / reproducing apparatus and the running operation was actually performed, it was found that the running property and durability were remarkably improved. In addition, it has become possible to significantly prevent the magnetic powder from falling off.

Alumina, titanium oxide, α-iron oxide, chromium oxide, etc. are used as the polishing agent in this embodiment, and it is preferable that the Mohs hardness is about 5 or more, and if the Mohs hardness is less than 5, it is sufficient. Does not exhibit excellent polishing properties. The abrasive preferably has an average particle size of 0.5 to 1 μm. If the average particle diameter exceeds 1 μm, the surface smoothness of the end face becomes insufficient, and the abrasive drops off from the end face due to repeated running, causing quality problems such as increased dropout. Further, if the average particle diameter is less than 0.5 μm, the function as an abrasive cannot be sufficiently exhibited. When the protective film 6 is formed by applying an abrasive having a Mohs hardness of about 5 or more together with a binder or the like, the binder forming the protective film has an effect of repairing cracks in the magnetic layer. The results are shown, and it is possible to more effectively prevent the magnetic powder from falling off.

That is, at the stage where a magnetic recording medium of a predetermined standard size is obtained by slitting or punching the raw material of the magnetic recording medium, the slits or cracks generated during punching are small, and
This crack expands with use and the powder drop of magnetic powder etc. becomes severe, but if the crack is repaired with a binder at this early stage, the powder drop of magnetic powder etc. is effectively suppressed. It becomes possible.

In such a case, the abrasive is about 0.5 to 15.0 with respect to 100 parts by weight of the binder.
It is preferable to use it in the range of parts by weight, and it is preferable to use a polyurethane resin as the binder. To obtain a protective film composed of an elastic film having open cells using a polyurethane resin, water that reacts with an isocyanate compound forming a polyurethane resin to generate carbon dioxide gas,
Alternatively, the carboxylic acid is added to the paint forming the film,
It can be provided by a method in which carbon dioxide gas is generated when forming the polyurethane resin film on the end face, and thereby, open cells are formed.

Next, examples and comparative examples performed based on concrete numerical values will be described. (Example 1) Composition of magnetic paint γ-Fe ₂ O ₃ magnetic powder 100 parts by weight Polyurethane resin 15 parts by weight PVC-vinyl acetate copolymer 15 parts by weight Dispersant 1 part by weight Silicone oil 0.4 parts by weight Abrasive 1 Parts by weight carbon black 5 parts by weight toluene 300 parts by weight methyl ethyl ketone 300 parts by weight methyl isobutyl ketone 300 parts by weight

A magnetic coating material having the above composition is sufficiently mixed and dispersed, and then a polyisocyanate curing agent is added to the magnetic coating material, and the magnetic coating material thus obtained is coated on two surfaces of a non-magnetic support such as polyethylene terephthalate. To a predetermined thickness and cured to form a magnetic layer 3 having a thickness of 5 μm, and the magnetic recording medium thus obtained is treated at a temperature of 20 ° C. and a humidity of 50% for 12 minutes. A magnetic recording medium such as a magnetic tape was obtained by slitting to a width of 0.65 mm. Then, while the slitted magnetic recording medium is in the form of a pancake or wound up, a material having the composition of the protective film paint shown below is sufficiently mixed and dispersed on the end surface 4 of the magnetic recording medium, and a polyisocyanate-based curing agent is added thereto. Dip coat the mixed paint.

Composition of Protective Film Paint Al ₂ O ₃ (Mohs hardness 9) having an average particle size of about 0.5 μm 5 parts by weight Pure water 3 parts by weight Carbon black 10 parts by weight Polyurethane resin 100 parts by weight Toluene 500 parts by weight Methyl ethyl ketone 500 Part by weight Methyl isobutyl ketone 500 parts by weight After that, the coating material applied to the end surface was cured to provide a protective film 6 having a thickness of about 1 μm on the end surface 4 to obtain a magnetic recording medium.

Example 2 A magnetic recording medium was obtained in the same manner as in Example 1 except that TiO ₂ (Mohs hardness 7) was used in place of Al ₂ O ₃ in the composition of the protective film paint in Example 1. . (Example 3) A in the composition of the protective film paint in Example 1
A magnetic recording medium was obtained in the same manner as in Example 1 except that α-Fe ₂ O ₃ (Mohs hardness 6) was used instead of l ₂ O ₃ .

On the other hand, the comparative example was formed as follows. (Comparative Example 1) An ordinary magnetic recording medium having no protective film 6 in Example 1 was obtained. As in Example 1 using (Comparative Example 2) Example Al ₂ O ₃ average particle diameter of about 2μm in place of the Al ₂ O ₃ having an average particle diameter of about 0.5μm in the composition of the protective film coating in 1 Then, a magnetic recording medium was obtained. (Comparative Example 3) A magnetic recording medium containing no open cells was obtained in the same manner as in Example 1, except that pure water in the composition of the protective film paint in Example 1 was not used at all.

(Comparative Example 4) In Comparative Example 1, a temperature of 20
A magnetic recording medium was obtained in the same manner except that the slit operation was performed under the conditions of a temperature of 3 ° C. and a humidity of 5% instead of the conditions of the temperature of 50 ° C. and the humidity of 50%. (Comparative Example 5) In Comparative Example 1, an operation of removing the magnetic layer with a blade for removal was added prior to the slitting step of slitting to a width of 12.65 mm, and a magnetic recording medium was similarly obtained.

(Comparative Example 6) In Example 1, Al ₂ O
_A magnetic recording medium was obtained in the same manner by using CaF ₂ (Mohs hardness 4) instead of ₃ . (Comparative Example 7) In Example 1, a coating obtained by adding and mixing a polyisocyanate-based curing agent to the coating for protective film was applied to the surface of the non-magnetic support 1 opposite to the magnetic layer 2 instead of the end surface 4. A magnetic recording medium was obtained in the same manner as above.

The magnetic recording media obtained in each of the above examples and each comparative example were loaded into a recording / reproducing apparatus, and the degree of audio level fluctuation, dropout, drop of magnetic powder and damage to the end face portion were examined. Table 1 shows the results.

[0023]

[Table 1]

For the audio level fluctuation, a BR-7000 type video tape recorder manufactured by Victor Company of Japan, Ltd. was used to record a 7 KHz sine wave signal, and then it was run at a high speed for 10 round trips in a cue and review state. It was regenerated and measured. As for the dropout, a dropout (width 5 μs, depth 20 dB) before and after repeatedly running 10 times using an HR-7100 type video tape recorder manufactured by Victor Company of Japan, Ltd.
Measured with a dropout counter. Also,
The degree of the magnetic powder falling off and the damage on the end face portion was determined by observing with a microscope after repeatedly running 100 times using an HR-7650 type video tape recorder manufactured by Victor Company of Japan, Ltd.

As can be seen from Table 1, regarding the magnetic recording media of Examples 1 to 3, the fluctuation of the audio level is 0.
Within the range of 3 to 0.5, the fluctuation is small, and the difference between dropout before running and after running is zero, so dropout is unlikely to occur, and there is no powder drop in the magnetic layer. It is good enough. Moreover, almost no damage was observed on the end surface of the magnetic recording medium, and it was found that the magnetic recording medium was excellent in running property and durability of the magnetic layer.
On the other hand, as shown in Comparative Example 1, when the protective film is not provided on the end surface of the magnetic recording medium, the fluctuation of the audio level is 2.0 dB, which is large, and the number of dropouts is also large. The number was 53, which was large, and the magnetic layer also had many powder drops and damages, which was not preferable in terms of characteristics.

Even if the end surface of the magnetic recording medium is not provided with a protective film, the structure shown in Comparative Examples 4 and 5 is better than that of Comparative Example 1 in any case. Although good results are shown, good results as in Examples 1 to 3 are not obtained. That is, when the protective film 6, which is a feature of the present invention, is not applied, there is a large limit to the degree of performance of the result.

Further, as shown in Comparative Example 2 or Comparative Example 3, when the protective film does not contain a predetermined average particle size or when the protective film does not have open cells, the fluctuation of the audio level is recognized to be relatively large. Also, the durability of the magnetic layer was not good, as is clear from the data of dropout, drop of magnetic powder, and damage data.

Further, as shown in Comparative Example 6, when the Mohs hardness of the abrasive contained in the protective film is not more than the predetermined value, dropout after repeated running and powder falling off of the magnetic layer are inferior.
The durability of the magnetic layer was not good. Then, as shown in Comparative Example 7, when the protective film was provided on the surface opposite to the support, the end surface portion was particularly damaged.

In the above embodiment, the case where the protective film 6 is provided on both end faces of the magnetic recording medium has been described as an example, but the protective film 6 may be provided on only one end face. But good results were observed. Further, in the above-mentioned embodiment, the case of the magnetic tape has been described, but the present invention is not limited to this, and it is needless to say that the same can be applied to the case of other magnetic recording media such as a magnetic disk.

[0030]

As described above, according to the magnetic recording medium of the present invention, the following excellent operational effects can be exhibited. Since a protective film containing an abrasive and fine open cells is formed on the end surface, dropout is less likely to occur, magnetic powder is less likely to fall off, and damage is less likely to occur, resulting in a magnetic layer. The durability of the magnetic recording medium can be improved, the running property of the magnetic recording medium can be improved, and the fluctuation of the audio level can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a magnetic recording medium according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium, 2 ... Non-magnetic support, 3 ... Magnetic layer, 4
... end faces, 5 ... bubbles, 6 ... protective film.

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that an end face is provided with a protective film containing an abrasive having a Mohs hardness of a predetermined value or more and containing fine bubbles.