JP2820696B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly, to a magnetic recording medium having good surface smoothness of a magnetic layer and excellent durability and electromagnetic conversion characteristics. And a method for producing the same.

[Conventional technology]

A magnetic recording medium is usually formed by applying a magnetic paint composed of a magnetic powder, an abrasive, a binder resin, an organic solvent and other necessary components on a substrate such as a polyester film and drying to form a magnetic layer. Is made by smoothing the surface.

However, the abrasive contained together with the magnetic powder in the magnetic layer is more difficult to disperse as the particles become finer, and tends to agglomerate. In some cases, projections are formed on the surface of the magnetic layer by such an agglomerated abrasive. is there. Also, in order to sufficiently exert the polishing function of the abrasive, only the abrasive was dispersed in the binder resin solution separately from the magnetic powder, and this abrasive dispersion was dispersed with the magnetic powder together with the binder resin and the like. When adding to magnetic paint and mixing to prepare magnetic paint,
The projections due to the abrasive are easily formed on the surface of the magnetic layer formed by applying and drying this, and when the projections due to the abrasive are formed on the surface of the magnetic layer, recording and reproduction are affected by the projections. Occasionally, local loss of signal occurs, causing many dropouts.

Therefore, in order to correct such protrusions on the surface of the magnetic layer and to suppress the occurrence of dropout, the surface of the magnetic layer formed on the substrate is subjected to a surface smoothing treatment, and then the magnetic layer is further polished using a high-hardness polishing tool. Grinding the surface of the layer has been performed. [Problem to be Solved by the Invention] However, in the polishing of the magnetic layer using a conventional high-hardness polishing tool such as a diamond wheel, projections having a height of 0.01 μm or more are formed. All of them are shaved off, and in extreme cases, the magnetic layer may be damaged. In addition, since the abrasive contained in the magnetic layer and protruding from the surface of the magnetic layer is polished more than necessary and removed, the durability of the magnetic layer becomes insufficient and the cleaning function for the magnetic head in contact with the magnetic layer deteriorates. There are difficulties such as doing.

[Means for solving the problem]

The present invention has been made as a result of conducting various studies in view of the present situation, and forms a magnetic layer by coating a magnetic paint containing a magnetic powder, an abrasive and a binder resin on a substrate, and then forming the magnetic layer. After the layer was smoothed, the tip was cut to make a flat sliding contact surface. The surface was polished with a grinding wheel whose peripheral surface was formed with diamond abrasive grains of # 1500 to # 4000 and projected to the surface of the magnetic layer. 1-10μ diameter mainly composed of abrasive
By making the height of the protrusions m in the range of 0.05 to 0.5 μm and the number of protrusions in the range of 0.1 / mm ^{2 to} 5000 / mm ² , the surface of the magnetic layer is appropriately smoothed, The durability and cleaning function of the magnetic layer are improved without causing dropout, and the durability and electromagnetic conversion characteristics are sufficiently improved.

The polishing wheel used in the present invention is preferably formed such that the peripheral surface is a diamond abrasive having a Mohs hardness of 9 or more and a particle size of # 1500 to # 4000 and using a metal bond as a binder. When the Mohs' hardness is 8 or less, almost no polishing effect is observed on the magnetic layer containing an abrasive such as Al ₂ O ₃ . If the particle size is less than # 1500, the surface roughness becomes too large and the magnetic layer is easily damaged, while if the particle size exceeds # 4000, the polishing effect is extremely reduced.
Further, it is preferable that the diamond abrasive grains be cut at the tip to form a flat sliding contact surface, and that the total area of the sliding contact surface be within a range of 0.5 to 15% of the simple surface area of the outer periphery of the polishing wheel. If the total area is too large, good polishing cannot be performed. If the total area is too small, the magnetic layer is easily damaged, and the abrasive protruding from the surface of the magnetic layer is polished more than necessary, thereby lowering the durability of the magnetic layer. The surface roughness of the peripheral surface is preferably in the range of 0.2 to 2 μm in center line average roughness in order to enable good polishing. With such a grinding wheel, you can use 0.01
without removing all protrusions with a height of μm or more,
The surface of the magnetic layer is appropriately smoothed. Thus, the occurrence of dropout is suppressed, the durability and the cleaning function of the magnetic layer are improved, and the durability and electromagnetic conversion characteristics are sufficiently improved.

When the surface of the magnetic layer is polished by such a polishing wheel, the polishing wheel may be rotated. For example, when the polishing wheel is rotated in a direction opposite to the running direction of the magnetic recording medium, the polishing treatment of the magnetic layer surface becomes more favorable. Good results can be obtained. As described above, when rotating the polishing wheel, it is preferable to rotate the polishing wheel at a peripheral speed of 1 to 700 m / min and run the magnetic recording medium at a traveling speed of 20 to 500 m / min. When the speed of the magnetic recording medium is lower than this range, the polishing effect is small, and when the speed is high, the intervening air layer becomes too thick and polishing cannot be performed.

In this manner, the magnetic layer polished using the polishing wheel has a protrusion that is mainly composed of an abrasive and protrudes from the surface.
It is preferably in the range of 0.05 to 0.5 μm, the diameter of these projections is 1 to 10 μm, the number is preferably in the range of 0.1 / mm ^{2 to} 5000 / mm ² , and the height of the projections is low. If the diameter is too small, the diameter is too small, or the number is too small, the durability and cleaning function of the magnetic layer cannot be improved, and the height of the projections is too high, the diameter is too large, If there are too many, the occurrence of dropouts will increase.

Here, as the abrasive contained in the magnetic layer, Al ₂ O
₃ , Cr ₂ O ₃ , TiO ₂ , SiO ₂ , SiC and the like are preferably used, and each is used alone or in combination of two or more. These abrasives have an average particle size of 0.05 to 1 μm.
m is preferably used, and at the time of use, the magnetic powder, the binder resin, the organic solvent and the like are mixed and dispersed at the same time. In addition, in order to sufficiently exert the function as an abrasive, only the abrasive is used. Is dispersed in a binder resin solution to prepare an abrasive dispersion, and this is added to a magnetic paint prepared by mixing and dispersing a magnetic powder together with a binder resin and other necessary components, followed by mixing. But also used. In particular, when the abrasive dispersion is added to a magnetic paint in which magnetic powder is mixed and dispersed, and mixed and used, the dispersion of the abrasive is appropriately adjusted and the function as the abrasive is sufficiently exhibited. On the other hand, large protrusions are formed on the surface of the magnetic layer, and a large number of dropouts are likely to occur.Therefore, it is necessary to perform polishing using the polishing wheel. By being polished, the durability and the cleaning function of the magnetic layer are improved, and the durability and the electromagnetic conversion characteristics are sufficiently improved.

Examples of the magnetic powder include γ-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder, Fe powder, and Co powder. Various conventionally known magnetic powders are widely encompassed, and as the binder resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin,
Conventionally widely used binder resins such as cellulose resin, polyurethane resin, polyester resin and isocyanate compound are widely used.

As the organic solvent, conventionally used organic solvents such as toluene, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, and ethyl acetate are used alone or in combination of two or more.

In the magnetic paint, various commonly used additives such as a dispersant, a lubricant, an antistatic agent and the like may be arbitrarily added and used.

〔Example〕

 Next, an embodiment of the present invention will be described.

Example 1 α-Al ₂ O ₃ powder 9 parts by weight Vinyl chloride-vinyl acetate copolymer 1 シ ク ロ Cyclohexanone 5 メ チ ル Methyl ethyl ketone 5 〃Toluene 5 混合 The composition was mixed and dispersed by a ball mill for 48 hours to form α-Al.
A dispersion of ₂ O ₃ was prepared.

Then, Co-containing γ-Fe ₂ O ₃ magnetic powder (specific surface area 40 m ² / g) 100
Parts by weight Nitrocellulose (HIG1 manufactured by Asahi Kasei) 10 〃 Polyurethane (Estan 5702 manufactured by Goodrich)
9 ポ リ Polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) 〃 Carbon black 5 亜 鉛 Zinc stearate 0.5 −-N-butyl stearate 0.5 シ ク ロ Cyclohexanone 80 メ チ ル Methyl ethyl ketone 80 〃 Toluene 80 混 Kneading with ball mill for 48 hours Disperse to prepare a magnetic paint, into which the above-mentioned α-Al ₂ O ₃ dispersion is added to α-Al ₂ O ₃
Was added so as to be 5% by weight with respect to the magnetic powder, and mixed to prepare a magnetic paint. Next, the magnetic paint obtained by adding α-Al ₂ O ₃ in this manner was
m on a polyester film support with a dry thickness of 5 μm
After coating and drying so as to obtain a mirror tape by a super calender, a magnetic tape was cut by cutting to a predetermined width.

Next, the magnetic tape was run at a running speed of 150 m / min, and the total area of the flat sliding contact surface having a Mohs' hardness of 10 and a grain size of # 2000 was cut off at the tip of the grinding wheel. 3% of the simple surface area, the diameter of the peripheral surface is 1 so that the surface roughness is 0.6 μm in center line average roughness Ra.
A 00 mm polishing wheel was rotated at a peripheral speed of 360 m / min in a direction opposite to the running direction of the magnetic tape, and brought into sliding contact with each other to polish.

In Example 1, adding a dispersion of alpha-Al ₂ O _3, without mixing, in the magnetic coating composition comprising magnetic powder, the alpha-Al ₂ O ₃ by adding 5 parts by weight, bulk A magnetic tape was prepared and polished in the same manner as in Example 1 except that the magnetic tape was mixed and dispersed.

Comparative Example 1 In the polishing treatment in Example 1, Mohs hardness was 1
0, a diamond abrasive with a particle size of # 2000, the total area of the flat sliding contact surface whose tip is cut is 3% of the simple surface area of the outer periphery of the polishing wheel, and the surface roughness is 0.6 μm in center line average roughness Ra. Instead of a 100 mm diameter grinding wheel with a peripheral surface, it is a diamond abrasive with a Mohs hardness of 10 and a grain size of # 2000, with almost no flat portion at the tip (0.1% of the simple surface area of the grinding wheel periphery) Polishing was performed in the same manner as in Example 1 except that a polishing wheel having a diameter of 100 mm and a peripheral surface formed so that the surface roughness was 3 μm in center line average roughness Ra was used.

Comparative Example 2 In the polishing treatment in Example 2, Mohs hardness was 1
0, a diamond abrasive with a particle size of # 2000, the total area of the flat sliding contact surface whose tip is cut is 3% of the simple surface area of the outer periphery of the polishing wheel, and the surface roughness is 0.6 μm in center line average roughness Ra. Instead of a 100 mm diameter grinding wheel with a peripheral surface, it is a diamond abrasive grain with a Mohs hardness of 10 and a grain size of # 5000. Polishing was performed in the same manner as in Example 2 except that a polishing wheel having a diameter of 100 mm and a peripheral surface formed so that the surface roughness was 20 μm of the surface area and the center line average roughness Ra was 0.1 μm was used. Was.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that the polishing treatment was omitted.

Comparative Example 4 A magnetic tape was produced in the same manner as in Example 2 except that the polishing treatment was omitted.

The magnetic tapes obtained in each of the examples and comparative examples were examined for the number of dropouts, steel properties, wear of the magnetic head, and damage to the magnetic layer. The number of dropouts was determined by assembling a magnetic tape into a VHS cassette, recording and reproducing using a VTR, VT-8000 manufactured by Hitachi, Ltd., and checking the number of dropouts of 5 μs or more. In addition, steel characteristics,
Using a VTR, VT-8000 manufactured by Hitachi, Ltd., record at 40 ° C and 80% RH, leave it sufficiently at 5 ° C and 40% RH, play it back, and play it on a monitor-TV. The time until the part disappeared was measured. The wear of the magnetic head was measured by measuring the change in the amount of protrusion of the magnetic head from the cylinder when the magnetic tape was run at room temperature for 20 hours. For the scratches on the magnetic layer, the surface of the magnetic layer of the magnetic tape was observed with a differential interference microscope to check for any scratches in the running direction.

 Table 1 below shows the results.

[Effects of the Invention] As is clear from Table 1 above, the magnetic tapes (Examples 1 and 2) obtained by the present invention were compared with Comparative Examples 1 to 4.
Compared with the magnetic tape obtained in the above, the dropout is small, the steel properties are good, the wear of the magnetic head is small, and the magnetic layer is not scratched. It can be seen that the surface smoothness of the magnetic layer was good and the electromagnetic conversion characteristics and durability were excellent.

Claims (5)

(57) [Claims] 1. A magnetic layer containing a magnetic powder, an abrasive and a binder resin is applied on a substrate to form a magnetic layer, and then the magnetic layer is smoothed, and then its tip is cut. Polished with a grinding wheel whose peripheral surface is formed with diamond abrasive grains with a particle size of # 1500 to # 4000 on a flat sliding contact surface.
A method for manufacturing a magnetic recording medium, comprising: setting the height of m projections within a range of 0.05 to 0.5 μm and the number of projections within a range of 0.1 / mm ^{2 to} 5000 / mm ^2. 2. A binder resin solution prepared by mixing and dispersing a magnetic paint containing a magnetic powder, an abrasive and a binder resin with a magnetic powder together with a binder resin and other necessary components. 2. The method for producing a magnetic recording medium according to claim 1, wherein an abrasive dispersion liquid dispersed therein is added and mixed. 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the total area of the sliding contact surface on which the diamond abrasive grains are cut is within a range of 0.5 to 15% of the simple surface area of the outer periphery of the polishing wheel. 4. The method for manufacturing a magnetic recording medium according to claim 1, wherein the binder of the diamond abrasive grains is a metal bond. 5. A surface roughness of a peripheral surface of a polishing wheel formed of diamond abrasive grains is 0.2 to 2 μm in center line average roughness.
The method for manufacturing a magnetic recording medium according to claim 1, 2, 3, or 4, wherein