JPH0830967A - Method of manufacturing magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance high density recording ability by coating the top of a substrate with a magnetic coating material contg. magnetic powder as well as a resin binder, drying the coating material, polishing the resultant magnetic layer and carrying out smoothening treatment. CONSTITUTION:The top of a substrate is coated with a magnetic coating material prepd. by mixing and dispersing magnetic powder, a binder, an org. solvent and other necessary components and the coating material is dried. The surface of the resultant magnetic layer 2 is polished and subjected to surface smoothening treatment. The magnetic layer 2 has a rough surface and contains many voids. Protrusions on the surface of the magnetic layer due to solid particles are easily removed by polishing and the surface of the magnetic layer is efficiently smoothened.

Description

Detailed Description of the Invention

[0001]

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 method for manufacturing a high density recording magnetic recording medium in which the magnetic layer has good surface smoothness and excellent short wavelength recording / reproducing output characteristics. Regarding the method.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is coated with a magnetic coating material comprising a magnetic powder, a binder component, an organic solvent and other necessary components on a substrate such as a polyester film and dried, and then a calendar device is used. It is made by surface smoothing.

However, the surface smoothing treatment using the conventional calendering device still fails to sufficiently smooth the surface of the magnetic layer, so that the magnetic layer formed on the substrate 1 as shown in FIG. If the convex portion 13 due to the surface roughness is present on the surface of the layer 2, spacing is generated between the layer 2 and the magnetic head and the signal reproduction output is attenuated.

Further, solid particles 14 are formed on the protrusions on the surface of the magnetic layer 2.
If the solid particles 14 are not sufficiently fixed, the solid particles 14 that are not sufficiently fixed fall off due to sliding with the magnetic head, resulting in dropout, clogging of the magnetic head, and the like. Solid particles such as solid particles contained in the composition or impurities or dust mixed in during the preparation of the magnetic coating exist like the solid particles 15 on the surface of the magnetic layer or the solid particles 16 on the surface of the magnetic layer. Forming convex parts, and further agglomerate 1 of fine powder particles in magnetic paint
If 7 or the like is present on the surface of the magnetic layer to form a convex portion, it may cause dropout and damage the sliding contact surface of the magnetic head.

For this reason, in recent years, JP-A-61-23062 has been proposed.
As in No. 3, a more powerful metal roll-metal roll calender was added to the conventional metal roll-resin roll calender to improve the surface smoothness of the magnetic layer. Is being improved.

Further, as in JP-A-63-259830, polishing treatment is carried out by a polishing tape after surface smoothing treatment of the magnetic layer, or in JP-A-61-131184.
After the surface of the magnetic layer is smoothed, the surface of the magnetic layer is cleaned by polishing with a high hardness tool such as a diamond wheel or sapphire blade.
Dropouts are being reduced.

[0007]

However, in order to further increase the recording density of the magnetic recording medium and to improve the recording / reproducing characteristics of a shorter wavelength, a conventional metal roll-resin roll structure is used. -A method of adding a more powerful metal roll-calender with a metal roll configuration to the calendar,
The method of polishing the surface of the magnetic layer with a polishing tape after the surface smoothing treatment or polishing with a high hardness tool such as diamond wheel or sapphire blade is not sufficient, and relatively small solid The protrusions on the surface of the magnetic layer due to particles or the like attenuate the short wavelength output and further cause dropout.

That is, the conventional metal roll-resin roll
More powerful metal roll for super calender
In the method of adding a calendar of rule-metal roll,
Although the surface of the magnetic layer 2 shown in FIG. 4 is smoothed as shown in FIG. 5, a relatively small convex portion of the surface of the magnetic layer 2 due to solid particles cannot be completely crushed,
Rather, since the local portion of the magnetic layer surface where solid particles and the like are present is more resistant to stress deformation than the peripheral portion, the stronger the calendar treatment is, the higher the protrusions are, and thus the protrusions are formed higher. Since the formed projections have a strong polishing property, the short wavelength output is attenuated and there is a problem that the wear of the magnetic head is increased.

Also, the method shown in FIG. 4 can be applied to the method shown in FIG. 4 in which the surface of the magnetic layer is smoothed and then the surface of the magnetic layer is polished by a polishing tape or by a high hardness tool such as a diamond wheel or a sapphire blade. The surface of the layer 2 is smoothed as shown in FIG. 5, but the relatively small protrusions on the surface of the magnetic layer 2 due to the solid particles or the like are firmly fixed by the binder resin and the solid particles or the like are firmly fixed. Due to their high wear resistance, these relatively small protrusions cannot be sufficiently removed by these polishing processes.

The present invention has been made as a result of various studies in order to overcome the above problems, and it is possible to sufficiently remove the convex portions due to solid particles and the like on the surface of the magnetic layer to sufficiently improve the surface smoothness of the magnetic layer. It is intended to obtain a magnetic recording medium for high-density recording which is excellent and has excellent short-wavelength recording / reproducing output characteristics.

[0011]

In the magnetic recording medium of the present invention, a magnetic coating material containing magnetic powder together with a binder resin is applied onto a substrate and dried to form a magnetic layer, and then the formed magnetic layer is formed. It is manufactured by polishing the surface and then smoothing the surface.

[0012]

Therefore, in the magnetic recording medium obtained by the production method of the present invention, the convex portions due to solid particles on the surface of the magnetic layer are sufficiently removed, the surface smoothness of the magnetic layer is sufficiently improved, and the short wavelength A magnetic recording medium for high-density recording having excellent recording / reproducing output characteristics can be obtained.

Hereinafter, description will be given with reference to an enlarged sectional explanatory view showing an example of a magnetic recording medium obtained by the manufacturing method of the present invention. FIG. 1 is an enlarged sectional view showing a part of the magnetic recording medium of the present invention, in which 1 is a base and 2 is a magnetic layer formed on the base 1.

For the magnetic layer 2, magnetic powder is mixed and dispersed with a binder component, an organic solvent and other necessary components to prepare a magnetic paint, and the magnetic paint is applied onto a substrate.
After drying, the surface of the formed magnetic layer is subjected to a polishing treatment and then a surface smoothing treatment to form the magnetic layer.

At this time, since the surface of the magnetic layer after coating and drying and before the surface smoothing treatment is rough and there are many voids in the magnetic layer, the convex portion due to solid particles on the surface of the magnetic layer is removed by polishing treatment. The surface of the magnetic layer is efficiently smoothed as shown in FIG.

Since the surface of the magnetic layer which has been efficiently smoothed by this polishing treatment is further subjected to the surface smoothing treatment, the magnetic layer 2 having much better surface smoothness is formed as shown in FIG. It

Therefore, the thus-formed magnetic recording medium of the present invention has excellent short-wavelength output characteristics, the occurrence of dropout is sufficiently suppressed, the magnetic head is not clogged, and the magnetic head is not worn. It is suitable for use as a magnetic recording medium for high-density recording, with few head scratches.

When the surface of the magnetic layer thus smoothed by the polishing treatment is further subjected to the surface smoothing treatment, even if the calendar device used for the surface smoothing treatment is continuously used, the roll stains are produced. Does not occur, the smoothness of the magnetic layer surface does not deteriorate with use, and the calendar is discontinued after use.
There is no need to clean the roll.

On the other hand, when the polishing treatment is performed after the surface smoothing treatment, the surface of the magnetic layer, which has been smoothed once by the surface smoothing treatment and has few voids, is difficult to remove.
As shown in FIG. 5 and FIG. 5, protrusions due to solid particles or the like remain on the surface of the magnetic layer.

Further, when the calendar device used for the surface smoothing treatment is continuously used by the conventional method, roll stains are generated, and the use is interrupted to clean the calendar roll. There must be.

In the present invention, the polishing treatment applied to the surface of the magnetic layer formed on the substrate is performed by pressing a polishing film such as a lapping film against the surface of the magnetic layer, or by using a grindstone or a diamond wheel on the surface of the magnetic layer. It is carried out by pressing or the like, and a method of combining these methods is also carried out.

FIG. 3 shows an outline of the case where the lapping film subjected to such a polishing treatment is used. The magnetic recording medium stock 3 having the magnetic layer 2 formed on the substrate 1 is a sending roll 4. Then, the magnetic layer 2 is guided by the guide rolls 5 and 6, and the surface of the magnetic layer 2 is polished by the lapping film 8 wound on the polishing drum 7 and wound on the winding roll 9.

Here, the wrapping film 8 is sent out from the sending roll 10 in a direction opposite to the running direction of the magnetic recording medium original fabric 3, and while being wrapped around the polishing drum 7, the magnetism of the magnetic recording medium original fabric 3 is increased. The surface of the layer 2 is polished and wound on the winding roll 11.

Reference numeral 12 is a touch roll made of an elastic material such as sponge rubber. Like the guide rolls 5 and 6, the surface of the magnetic layer 2 of the magnetic recording medium web 3 is in stable contact with the wrapping film 8. It is provided as needed.

In the lapping film 8 used for such a polishing process, the rougher the surface roughness of the polishing surface, the easier it is to remove the protrusions on the surface of the magnetic layer due to the solid particles and the like. The smoother the surface, the poorer the removal process of the convex portion, but the smoother the finished surface. This is the same when using a grindstone or a diamond wheel.

Therefore, the lapping film 8, the grindstone,
The surface roughness of a polishing tool such as a diamond wheel is only required to be able to remove the convex portions due to solid particles on the magnetic layer surface,
When polishing tools with different surface roughness of the polishing surface are used, and when the polishing surface of the polishing surface is rough to smooth, the removal of the convex portion due to solid particles on the magnetic layer surface can be performed efficiently. That is, the surface of the magnetic layer can be made smoother.

Further, such a polishing treatment may be carried out after the polishing treatment is performed once and then the surface smoothing treatment is carried out. In this case, the polishing treatment before the surface smoothing treatment may be carried out beforehand. Since the surface of the is smoothed and cleaned, the polishing tool used for the polishing treatment after the smoothing treatment can have a relatively smooth polishing surface, and the surface of the magnetic layer can be further smoothed. it can.

The surface smoothing treatment after the polishing treatment is conventionally carried out by using a conventional metal roll-resin roll calender or a metal roll-metal roll calender. Done in.

In this way, the magnetic layer which has been subjected to polishing treatment and further surface smoothing is prepared by mixing and dispersing magnetic powder with a binder resin, an organic solvent and other necessary components to prepare a magnetic coating material. It is made by applying a paint on a substrate and drying.

At this time, the magnetic powder used is γ
-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, intermediate oxide powder of γ-Fe ₂ O ₃ powder and Fe ₃ O ₄ powder, Co-containing γ-F
e ₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder, barium ferrite powder, strontium ferrite powder, and Fe powder, Co powder, and metal powders such as Fe-Ni powders, are generally used in a magnetic recording medium All magnetic powders are used.

As the binder resin, vinyl chloride-
Vinyl acetate copolymer, polyvinyl butyral resin,
Any of those conventionally used for magnetic recording media, such as fibrin-based resins, polyurethane-based resins, polyester-based resins, and isocyanate compounds, can be used.

Further, as the organic solvent, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone,
Ethyl acetate, benzene, toluene, xylene, dimethylformamide, dioxane, tetrahydrofuran, etc.,
Generally, organic solvents used in magnetic recording media are used alone or as a mixture.

In the magnetic paint, a dispersant, an abrasive,
Lubricants, antistatic agents and the like which are generally added to the magnetic paint are added and used as needed.

In this way, a backcoat layer is formed on the back surface of the substrate on which the magnetic layer is formed, if necessary. The backcoat layer is a non-magnetic powder such as carbon black or calcium carbonate. The particles are mixed and dispersed with a binder resin, an organic solvent and other necessary components to prepare a backcoat layer coating material, and the backcoat layer coating material is applied to the back surface of a substrate having a magnetic layer formed on the surface thereof. , Dried and formed.

As the binder resin and the organic solvent used for forming the back coat layer, the same binder resins and organic solvents as those used for forming the magnetic layer are preferably used, and as necessary. , A dispersant, a lubricant and the like are also used.

As a substrate for forming such a magnetic layer and a back coat layer, plastics such as polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates and the like are used. Films made of metal, and metal films made of aluminum alloy, titanium alloy or the like are preferably used.

[0037]

EXAMPLES Next, examples of the present invention will be described. Example 1 Ferromagnetic metal powder (coercive force 1600 oersted, saturation magnetization 100 100 parts by weight 120 emu / g, major axis diameter 0.13 μm, axial ratio 9) Hydroxyl group-containing vinyl chloride resin 10〃 thermoplastic polyurethane resin 7〃 alumina (grains Diameter 0.3 μm) 8 〃 Myristic acid 2 〃 Red iron oxide (particle size 0.8 μm) 2 〃 Carbon black (Tokai Carbon Co., Ltd., cast 5H, particle size 2 〃 20 mμm) Cyclohexanone 160 〃 Toluene 160 〃 After the mixture was mixed and dispersed with a ball mill for 96 hours, 5 parts by weight of a trifunctional polyisocyanate compound was further added and stirred to prepare a magnetic coating material.

The magnetic coating material obtained was applied onto a biaxially oriented polyethylene terephthalate film to give a thickness of 2.5 μm after drying.
It was applied by using a reverse roll coater so that the magnetic layer had a thickness of m, and was passed through a counter-magnet having the same pole and dried to form a magnetic layer.

Then, the surface of the magnetic layer immediately after drying was polished with a wrapping film of # 4000.
After polishing, the roll temperature was 90 ° C. and the roll linear pressure was 250 kg / cm using a calender made of metal roll and resin roll.
Calendar processing was carried out.

Next, the following backcoat layer composition was mixed and dispersed in a ball mill for 96 hours, 15 parts by weight of a trifunctional polyisocyanate compound was further added, and the mixture was stirred to prepare a coating material for the backcoat layer. On the back surface of the biaxially oriented polyethylene terephthalate film having a magnetic layer formed on the surface thereof.
A back coat layer was formed by coating and drying so as to have a thickness of 1.0 μm. Then, it was cut into a width of 8 mm to form a magnetic tape.

Backcoat layer composition Carbon black (manufactured by Tokai Carbon Co., Ltd., cast 5H, particle size 60 parts by weight 20 mμm) Bengala (particle size 0.8 μm) 2.5 〃 calcium carbonate (particle size 0.05 μm) 30 〃 Thermoplastic polyurethane resin 45 〃 Nitrocellulose 40 〃 Cyclohexanone 330 〃 Toluene 330 〃

Example 2 In the polishing treatment of the magnetic layer surface in Example 1, the step # 20 was used instead of the step # 4000 lapping film.
Example 1 except that the 00 wrapping film was used
The surface of the magnetic layer was polished in the same manner as in 1. to produce a magnetic tape.

Example 3 Example 2 was the same as Example 2 except that the polishing treatment of the magnetic layer surface in Example 2 was performed with a lapping film of # 2000 and then with a lapping film of # 8000. Similarly, the surface of the magnetic layer was polished to prepare a magnetic tape.

Example 4 In the calendering process in Example 1, a metal roller was used.
Instead of a calendar with a roll of resin roll, a metal roll
A calender treatment was carried out in the same manner as in Example 1 except that calender treatment was carried out at a roll temperature of 110 ° C. and a roll linear pressure of 300 kg / cm using a calendar having a roll metal roll configuration. A magnetic tape was produced.

Example 5 A magnetic tape was produced in the same manner as in Example 3 except that calendering was carried out and then lapping film No. 20000 was further used for polishing.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the polishing treatment on the surface of the magnetic layer was omitted.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 5 except that the polishing treatment on the surface of the magnetic layer was omitted.

Comparative Example 3 In Example 5, except that the polishing treatment of the surface of the magnetic layer was omitted, and the polishing treatment after the calendar treatment was changed from the lapping film of # 2000 to the lapping film of # 4000. In the same manner as in Example 5, a magnetic tape was manufactured.

Comparative Example 4 The same procedure as in Example 4 was carried out except that the magnetic layer surface was abraded and the calendered magnetic layer surface was abraded with a lapping film of # 10000. A magnetic tape was produced.

The magnetic tape obtained in each Example and Comparative Example
The recording / reproducing output, the height of the maximum convex portion on the surface of the magnetic layer, the dropout, the amount of wear of the magnetic head, and the scratch on the magnetic head were examined for the magnetic recording medium by the following methods.

<Recording / reproducing output> Using a drum type tester,
The recording / reproducing output of a single sine wave signal having recording wavelengths of 0.5 μm and 0.4 μm was measured, and the output of the magnetic tape of Comparative Example 1 was set to 0, and the ratio was expressed in dB.

<The height of the maximum convex portion on the surface of the magnetic layer> In the optical interference type three-dimensional surface shape measuring apparatus Hi-ResTOPO (manufactured by WYKO, USA) according to US Pat. No. 4,639,139, V
An LX100 objective head (manufactured by WYKO, USA) is attached, shape measurements are performed at a spatial sampling interval of 0.068 μm in a 70 μm square area of the surface of the magnetic layer, and the obtained shape data is used for the following inclination correction, spherical correction and cylindrical surface. After correction, the three-dimensional shape of the magnetic layer surface was measured. Here, a plane having a height of 0 in the three-dimensional shape after each correction is called an average plane. Then, the height of the highest point from the average plane was defined as the maximum convex height.

Inclination correction After calculating a plane that minimizes the square root of the deviation in the height direction from the three-dimensional data at each coordinate, the three-dimensional data is calculated.
Divide the height of the plane from the height of the plane.

Spherical correction After calculating a spherical surface that minimizes the square root of the deviation in the height direction from the three-dimensional shape data at each coordinate after inclination correction, the height of the three-dimensional data is calculated. Divide the height of the sphere.

Cylindrical surface correction A cylindrical surface having a central axis parallel to the average surface that minimizes the square root of the deviation in the height direction from the three-dimensional shape data at each coordinate after spherical surface correction was calculated. After that, the height of the cylindrical surface is divided from the height of the three-dimensional data.

<Dropout> A magnetic tape was wound into an 8 mm video cassette to produce a P6-120 (2 hours) cassette tape, manufactured by Sony; Hi8VTR.
It was mounted on an EV-S900, and the number of dropouts per minute during which the reproduction output time was 15 μs or more and the output decreased by −18 dB was counted.

<Magnetic Head Abrasion and Magnetic Head Scratch> A cassette tape was prepared in the same manner as in the still durability measurement, and a new head was replaced for each measurement; manufactured by Sony Corporation; Hi
It was mounted on an 8VTR / EV-S900 and repeatedly run in PLAY mode for 2 hours x 50 times (total 100 hours). Then, the change in the head protrusion amount before and after the running was measured, and the resignation head scratch was observed. Table 1 below shows the results.

[0058]

[0059]

As is clear from Table 1, the magnetic tape obtained by the present invention has excellent surface smoothness, high short-wavelength output, little dropout, and little head wear. , There is no scratch on the head.

From these facts, according to the present invention, the surface smoothness is excellent, the short wavelength recording / reproducing output characteristics are excellent, the dropout is small, the head wear is small, and the head is not scratched. It can be seen that a magnetic recording medium for density recording can be obtained.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional explanatory view of a magnetic recording medium obtained by a manufacturing method of the present invention.

FIG. 2 is a partially enlarged cross-sectional explanatory view of the magnetic recording medium during the process of the method for manufacturing the magnetic recording medium of the present invention.

FIG. 3 is an explanatory diagram showing an outline of a polishing apparatus when manufacturing the magnetic recording medium of the present invention.

FIG. 4 is a partially enlarged cross-sectional explanatory view of a magnetic recording medium obtained by a conventional manufacturing method.

FIG. 5 is a partially enlarged cross-sectional explanatory view of a magnetic recording medium obtained by a conventional manufacturing method.

[Explanation of symbols]

 1 substrate 2 magnetic layer 3 magnetic recording medium material 8 lapping film

Claims (1)

[Claims] 1. A magnetic coating material containing magnetic powder together with a binder resin is applied on a substrate and dried to form a magnetic layer, and then the surface of the formed magnetic layer is subjected to polishing treatment and then surface smoothing treatment. A method of manufacturing a magnetic recording medium, characterized by