JPH04143924A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent drop out and clogging in a recording medium by demagnetizing the medium either before polishing or before grinding after the magnetic layer is oriented. CONSTITUTION:A magnetic coating material and a coating material for a back coating are applied on a nonmagnetic supporting body 4. This medium as not dried is then subjected to magnetic field orientation treatment with magnets, dried and further treated in a demagnetization zone. First, the medium is passed through a saturation head 1 where the web is hauled for magnetization in one direction. Then the web is passed through an unsaturation head 2 where the web is magnetized in the opposite direction. Finally, the web is passed through an AC head 3 where the charging state is turned to zero state. By performing polishing and grinding as above described, projections are ground and chips produced by grinding do not deposite again on the medium.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a magnetic recording medium having a basic structure consisting of a non-magnetic support and a magnetic layer provided on the support. .

(Background of the Invention) Magnetic recording media in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support are generally used as magnetic recording media for audio, video, or computers. ing.

Such magnetic recording media are produced by coating a magnetic paint, in which a binder component such as a resin component and a granular component such as ferromagnetic powder are dispersed in a solvent, on a non-magnetic support to form a coating layer. It is manufactured by subjecting the coating layer to treatments such as magnetic field orientation treatment, drying treatment, and surface smoothing treatment, and then cutting it into a desired shape.

Generally, the surface of the magnetic layer manufactured in this way is considered to be very smooth with the granular components firmly fixed to the magnetic layer, but according to the study conducted by the present inventor, the surface of the magnetic layer It was found that there were particulate components such as ferromagnetic powder that were insufficiently fixed.

Such poorly fixed particulate components may detach during running and adhere to the magnetic head, causing clogging of the magnetic head, and may also cause dropouts in, for example, video tapes. There is. and,
Since the amount of ferromagnetic powder near the surface of the magnetic layer decreases due to such detachment of the ferromagnetic powder, there is also the problem that electromagnetic conversion characteristics deteriorate (reduction in output) due to repeated running.

The present inventor has invented a method of grinding the surface of a magnetic layer as a method of reducing the occurrence of such dropouts, clogging, and output reduction, and has already filed an application for this invention (Japanese Patent Application Laid-Open No. 172-532-1989). issue).

That is, the present invention removes granular components or the magnetic layer that are easily detached by grinding the smoothed surface of the magnetic layer using a high-hardness grinding tool such as a diamond wheel or a fixed sapphire blade. This removes deposits on the surface and reduces the amount of substances detached from the surface of the magnetic layer.

Against this background, the present inventor further investigated methods for reducing the amount of desorbed substances from the surface of the magnetic layer, and found that
We have discovered that there is an effective method other than grinding the magnetic layer of a magnetic recording medium.

This is a method in which the magnetic layer of a magnetic recording medium is polished using an abrasive tape, and it has been found that this method can produce magnetic recording media with fewer dropouts and clogging, and with better running durability. Ta.

However, in conventional methods, demagnetization treatment is not performed after orientation treatment, so even if wiping treatment is performed after polishing or grinding, it is difficult to remove the shavings and dirt that was ordered. . The reason for this is thought to be that since the magnetic layer had already been subjected to orientation treatment, the individual ferromagnetic powders were magnetized, easily attracted, and could not be removed sufficiently. Therefore, the present inventors found that by demagnetizing the magnetic layer after orienting it and before the polishing or grinding treatment, cleaning debris would not be adsorbed and dropout would be significantly improved. It's arrived.

(Objective of the Invention) An object of the present invention is to provide a method for manufacturing a magnetic recording medium having good running durability.

More specifically, it is an object of the present invention to provide a method for manufacturing a novel magnetic recording medium that is less prone to dropouts and clogging.

(Structure of the Invention) That is, the above object of the present invention is to orient a magnetic layer coated on a non-magnetic support and comprising ferromagnetic powder dispersed in a binder, and after surface smoothing treatment, the magnetic layer is coated on a non-magnetic support. Polishing the surface with a polishing tape and/or
Or, in a method of manufacturing a magnetic recording medium characterized by carrying out a grinding treatment, the method comprises demagnetizing the magnetic layer in one of the steps before the polishing treatment and the grinding treatment after the magnetic layer is oriented. This can be achieved by

More preferably, the above-mentioned object of the present invention is to polish the surface of the magnetic layer subjected to the surface smoothing treatment with the polishing tape, then perform the grinding treatment with a blade or a rotating blade, and then wipe off the magnetic layer with a nonwoven cloth. This can be achieved by a method of manufacturing a magnetic recording medium characterized by performing the following steps.

Further, the above object of the present invention can be achieved by a method of manufacturing a magnetic recording medium characterized in that the demagnetization is performed using a saturated head, then an unsaturated head, and finally an AC head.

That is, in the present invention, dust generated by polishing and/or grinding cannot be removed well even by wiping, but a demagnetizing step is included in one of the steps after orientation and before polishing and/or grinding. By doing so, it is possible to significantly prevent dropouts and clogging from occurring due to re-adhesion of shavings magnetized by the orientation process to the magnetic recording medium after the polishing process and/or the grinding process. This demagnetization process can be carried out after orientation treatment and drying, after winding, before or after calender treatment, before or after thermo-treatment, or before and after slitting. Alternatively, the effects of the present invention can be effectively exhibited before the grinding process. The strength of the magnetic field during demagnetization is carried out using several magnets; for example, in the case of metal magnetic powder, the first half is preferably 1,700 to 2,300 Gauss, and the second half is preferably 1,300 to 1,900 Gauss.

In the case of iron oxide magnetic powder, it is desirable that the first half is 900 to 1,500 Gauss and the second half is 400 to 1,100 Gauss. To explain demagnetization more specifically, in the first step, the magnetized support 4 coated with magnetic paint and paint requiring hacking was subjected to magnetic field alignment treatment with a magnet while the magnetic paint was not dry (not shown); After drying, add a degaussing zone.

It first passes through a saturation head 1 to magnetize the web in one direction.

As mentioned above, the magnetic field of the saturation head 1 is preferably 1700 to 2300 Gauss using a permanent magnet. Then, it passes through the unsaturated head 2 and is magnetized in the opposite direction. As mentioned above, the magnetic field of this unsaturated head 2 is preferably a permanent magnet, and it is preferable to use a magnetic field of 1300 to 1700 Gauss.Finally, the web is passed through the AC head 3 to bring the charge to zero. is preferred.

As described above, in the present invention, the protrusions are removed by polishing and/or grinding, and the resulting scraped powder can be effectively removed without re-adhesion.

In the present invention, polishing treatment refers to polishing by sliding a polishing tape in the opposite direction to the running direction of the magnetic tape to eliminate convexities on the surface of the magnetic layer.
Refers to the process of removing the binder layer.

Furthermore, the term "grinding process" refers to a process in which the surface of the magnetic layer is ground using a fixed blade made of sapphire or the like, a carbide blade, a diamond wheel, or the like.

Furthermore, since the number of ferromagnetic powders that separate from the magnetic layer surface is reduced, there is less ferromagnetic powder falling off even after repeated running, and therefore the difference between the reproduction output at the initial stage of running and the reproduction output after repeated running is small. Excellent magnetic recording media can be manufactured.

In addition, when a hardening agent is used as a component for forming the magnetic layer, most of the unreacted hardening agent on the surface of the magnetic layer is removed, so dust and the like will not adhere to the magnetic layer after the magnetic recording medium is manufactured. . Therefore, it is possible to manufacture a magnetic recording medium in which dropouts caused by such deposits are less likely to occur. Furthermore, since the magnetic head is less likely to be contaminated with unreacted hardened material, it is possible to manufacture a magnetic recording medium that is less prone to clogging of the magnetic head due to adhesion of dust to the magnetic head. It is usually produced by applying a magnetic coating onto a non-magnetic support, subjecting it to magnetic field orientation treatment, curing treatment, surface smoothing treatment, etc., and then cutting it into a desired shape.

A magnetic recording medium consists of a nonmagnetic support and a magnetic layer provided on the support. The magnetic layer consists of a particulate component such as ferromagnetic powder and a binder in which the particulate component is dispersed. The binder is composed of a resin component and a curing agent that is further added as desired.

Coating of the magnetic layer can be carried out according to a conventional method. For example, a magnetic paint is prepared by cross-dispersing a resin component, a ferromagnetic powder, and magnetic layer-forming components such as an abrasive and a hardening agent blended as desired with a solvent, and this magnetic paint is applied onto a non-magnetic support. method can be used.

Polyethylene terephthalate (
PET), polyesters such as polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyamide, polyamideimide, polyimide, etc. Non-magnetic metal foil such as aluminum or copper; metal foil such as stainless steel foil; paper, ceramic sheet, etc.

The resin component is selected from resins commonly used as resin components of magnetic paints. Examples of resin components include vinyl chloride copolymers (e.g. vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate/vinyl alcohol copolymer, vinyl chloride/vinyl acetate/acrylic acid copolymer, chloride) Vinyl/vinylidene chloride copolymer, vinyl chloride/acrylonitrile copolymer, ethylene/vinyl acetate copolymer,
5OxNa or -So, vinyl chloride copolymers into which polar groups such as Na and epoxy groups have been introduced), cellulose derivatives such as nitrocellulose resin, acrylic resins,
Polyvinyl acetal resin, polyvinyl butyral resin, epoxy resin, phenoxy resin, polyurethane resin (e.g., polyester polyurethane resin, -3Oz Na
Alternatively, examples thereof include polyurethane resins and polycarbonate polyurethane resins into which polar groups such as -302Na are introduced.

Furthermore, when a curing agent is used, a polyisocyanate compound is usually used. The polyisocyanate compound is selected from those commonly used as curing agent components for polyurethane resins and the like. Examples of polyisocyanate compounds include a reaction product of tolylene diisocyanate and 1 mol of trimethylolpropane (eg, Desmodur L-75 (manufactured by Bayer)), 3 mol of a diisocyanate such as xylylene diisocyanate or hexamethylene diisocyanate. and 1 mole of trimethylolpropane, biuret addition compound of 3 moles of hexamethylene diisocyanate, isocyanurate compound of 5 moles of tolylene diisocyanate, isocyanurate addition compound of 3 moles of birylene diisocyanate and 2 moles of hexamethylene diisocyanate. , isophorone diisocyanate and diphenylmethane diisocyanate.

Further, when performing curing treatment by electron beam irradiation, a compound having a reactive double bond (eg, urethane acrylate) can be used.

In the present invention, it is preferable to use a combination of a highly hard resin such as a vinyl chloride copolymer and a flexible resin such as a polyurethane resin as the resin component.

When using a combination of a hard resin such as a vinyl chloride copolymer and a flexible resin such as a polyurethane resin, the weight ratio of the former to the latter is usually 9.
:1 to 5:5 (preferably 9:1 to 6:4), and when a curing agent is used, the blending weight ratio of the resin component and curing agent is usually 9. :1~5:5(
Preferably, it is set within the range of 9:1 to 6:4).

Generally, when using ferromagnetic powder with low hardness such as ferromagnetic metal fine powder, a larger amount of binder is used than when using high hardness such as 7-Fe, O, etc. . In this case, the amount of flexible resin such as polyurethane resin is usually increased.

Since the binder tends to soften as the amount of polyurethane resin used increases, a method is usually used to maintain the hardness of the binder by increasing the amount of a hardening agent such as a polyisocyanate compound.

When using a polyurethane resin as a resin component and a polyisocyanate compound as a curing agent, the blending weight ratio of the polyurethane resin and the polyisocyanate compound is usually 1:0.8 to 1:2 (preferably 1; 1-1
:1.5). By doing so, even when using fine ferromagnetic metal powder with low hardness, it becomes possible to effectively prevent softening of the binder caused by using polyurethane resin.

The total weight of the resin component and curing agent is 100% of the ferromagnetic powder.
Usually 10 to 100 parts by weight (15 to 40 parts by weight)
(parts by weight).

Examples of ferromagnetic powders used in the present invention include γ-FezO
ferromagnetic powders based on metal compounds such as , ferromagnetic powders based on dissimilar metals and metal oxides such as γ-Fe20s containing other components such as cobalt, and ferromagnetic metals such as iron, cobalt or nickel. Examples include fine ferromagnetic metal powders containing:

In particular, the present invention is advantageous when used as a method for producing a magnetic recording medium using fine ferromagnetic metal powder. In other words, even if a large amount of hardening agent is used in conjunction with the use of ferromagnetic metal fine powder, the amount of deposits on the magnetic layer or magnetic head can be reduced, thereby preventing drop-outs and magnetic head eyes. A magnetic recording medium with less clogging can be manufactured.

When using a ferromagnetic metal fine powder, it is a ferromagnetic metal fine powder containing iron, cobalt or nickel, and has a specific surface area of 42 m/g or more (particularly preferably 45 m/g).
The above-mentioned ferromagnetic metal fine powder is preferable.

As an example of this ferromagnetic metal fine powder, the metal content in the ferromagnetic gold rr4 fine powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one type of ferromagnetic metal or alloy (e.g. Fe, Co, N15Fe-Co, Fe-
Ni, Co-Ni, Co-N1-Fe), and other components (e.g. Aj2
．． Si, S, Sc, TiXV, Cr, Mn, Cu, Z
n,,Y.

Mo, Rh, Pd, Ag, b Ta, W, Re, Au, HgXPb, P, La.

Mention may be made of alloys that may contain (Ce, Pr, Nd, Te, Bi). Further, the ferromagnetic metal may contain a small amount of water, hydroxide, or oxide.

The methods for producing these ferromagnetic powders are already known, and the ferromagnetic powder used in the present invention can also be produced according to known methods.

There are no particular restrictions on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes are usually used. In particular, it is preferable to use acicular ferromagnetic powder.

The above resin component, curing agent, and ferromagnetic powder are mixed and dispersed together with a solvent (e.g., methyl ethyl ketone, dioxane, cyclohexanone, ethyl acetate) that is normally used in the preparation of magnetic paint to obtain a magnetic paint. Crosstalk dispersion can be performed according to conventional methods.

In addition to the above components, the magnetic paint contains abrasives (e.g. a
A11z 03 , Crz Os ), antistatic agents (e.g., carbon blank), lubricants (e.g., fatty acids, fatty acid esters, silicone oil), dispersants, and other commonly used additives or fillers (agents). Of course, it may be. In particular, when a saturated fatty acid with a carbon number of 10 to 22 is used as a lubricant, the saturated fatty acid tends to be oriented in a layered manner on the surface of the magnetic layer by grinding using a rotating blade described later. Since the oriented fatty acid film has high strength and good lubricity, it has the advantage of improving the running properties of the magnetic recording medium.

The magnetic paint thus prepared is applied onto a non-magnetic support. The coating method can be carried out using a conventional coating method such as a method using a reverse roll.

The coating layer of the magnetic paint is applied so that the thickness of the magnetic layer of the obtained magnetic recording medium is usually within the range of 0.5 to 10 ttm.

Polyethylene terephthalate (
PET), polyesters such as polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyamide, polyamideimide, polyimide, etc. Films or notebooks made of synthetic resin; non-magnetic metal foils such as aluminum and copper;
Gold II foil such as stainless steel foil; selected from paper, ceramic notebook, etc.

In addition, the non-magnetic support generally has a thickness of 3 to 50 μm (
Preferably, those having a weight of 5 to 30 tIm) are used.

A backing layer may be provided on the side of the non-magnetic support used in the present invention that is not coated with magnetic paint. Normally, the bank layer is the side of the non-magnetic support that is not coated with magnetic paint. This is a layer formed by applying a bank layer-forming paint in which particulate components such as abrasives and antistatic agents and the bonding side are dispersed in an organic solvent.

Note that an adhesive layer may be attached to the surface of the nonmagnetic support on which the magnetic paint and the back layer forming paint are applied.

Usually, the coated layer of magnetic paint is dried after being subjected to a treatment for orienting the ferromagnetic powder contained in the coated layer of magnetic paint, that is, a magnetic field orientation treatment.

After being dried in this manner, the coated layer is subjected to surface smoothing treatment. For example, a super calender roll is used for the surface smoothing treatment.By performing the surface smoothing treatment, the pores created by the removal of the cutting during drying are eliminated, and the ferromagnetic powder in the magnetic layer is filled. Since the ratio is improved, a magnetic recording medium with high electromagnetic conversion characteristics can be obtained.

In the manufacturing method of the present invention, the surface of the magnetic layer that has been demagnetized, or the surface of the magnetic layer and the surface of the hack layer, is polished using a polishing tape. In particular, it is preferable to perform wiping treatment with a non-woven cloth after grinding the surface polished with an abrasive tape with a rotating blade, etc. However,
The order of polishing, grinding, and wiping is not limited to the above order.

At the stage where the surface is smoothed, if a hardening agent is used as a component forming the binder, usually 90% by weight or more of the hardening agent contained in the magnetic layer is contained in the magnetic layer in an unreacted state. Therefore, it is preferable to perform a curing treatment to react at least 50% by weight (particularly preferably 80% by weight or more) of the curing agent before carrying out the subsequent treatment.

The curing treatment includes heat curing treatment and electron beam irradiation curing treatment, and either method can be used in the present invention.

Through this curing treatment, the unreacted curing agent contained in the surface-smoothed magnetic layer forms a three-dimensional network crosslinked structure with resin components such as vinyl chloride copolymer and polyurethane resin. react to.

The heat treatment process itself is already well known, and the heat treatment can also be performed in the present invention according to these methods.

For example, in heat treatment, the heating time is usually 40°C or higher (
(preferably within the range of 50 to 80°C), and the heating time is usually set to 20 hours or more (preferably 24 hours to 7 days). Further, the process of curing treatment by electron beam irradiation itself is already known, and the heat treatment can be performed according to these methods in the present invention as well.

The thus cured laminate is then cut into a desired shape.

The cutting can be carried out under normal conditions using a normal cutting machine such as a slitter.

The surface of the magnetic layer of the thus hardened and cut laminate, or the surface of the magnetic layer and the surface of the bank layer, is polished by slowly rotating the belt of the polishing tape. At this time, the polishing process is performed at a peripheral speed of the belt of 1 to 3 cm and 7 minutes in the opposite direction to the winding direction of the tape of the magnetic recording medium.

The first circle shows the demagnetization treatment according to the present invention, and the second circle shows the polishing treatment.
It is a schematic diagram showing an example of a grinding process and a wiping process.

As shown in Figure 1, 1700 to 2 at saturation end 1
Magnetized to maximum residual flux density using a 300 Gauss permanent magnet, followed by 130 Gauss in the unsaturated head 2.
It is magnetized in the opposite direction using a permanent magnet of 0 to 1900 Gauss so that the residual magnetic flux density is almost O. Finally, an alternating current magnetic field of 900 to 1,500 Gauss is applied with an alternating current head 3, which is a t-magnet having a source 6, so that the amplitude is attenuated, so that the residual magnetic flux density becomes almost completely zero.

As shown in FIG. 2, the tape is fed out from a feeding roll 14, polished with an abrasive tape 15, ground with a fixed blade 16, wiped off with a nonwoven cloth 7, and then wound up with a winding roll 8. Processing is complete. 13
The tape is fed smoothly using a feed roll.

The polishing tape 16 is moved by the rotating roll 11 at a speed of 1 to 3 cmZ in the opposite direction to the tape feeding, and the polishing tape 16 is held down by the pad 9 and comes into contact with the surface of the magnetic layer to perform the polishing process.

In FIG. 2, there may be two or more polishing points with the polishing tape, and when polishing not only the surface of the magnetic layer but also the surface of the bank layer, a similar polishing point with the polishing tape is provided on the opposite side.

The fixed blade 16 for the grinding process may not be used, or a rotating blade may be used instead of the fixed blade. Also, both fixed blades and rotating blades may be used.

Further, when grinding not only the surface of the magnetic layer but also the surface of the bank layer, a fixed blade and/or a rotating blade is provided on the opposite side.

The nonwoven fabric 7 is rolled by a rotating roll 12 in a direction opposite to the tape feeding direction. Moving at a speed of 5 to 10 CI/min, the nonwoven fabric 7 is held down by the pad 10 and comes into contact with the surface of the magnetic layer to perform a wiping process.

Further, there may be two or more locations to be wiped off with a nonwoven fabric, and if the wiping process is performed not only on the surface of the magnetic layer but also on the surface of the back layer, a similar location on the opposite side is also provided with a wiping location using a nonwoven fabric.

The polishing tape used in the polishing process of the present invention is preferably a tape for polishing heads of cassette decks, video decks, etc. The main purpose of this polishing tape is to finish the head surface, create the tip shape of the head,
and eliminating head chipping.

The polishing tape used in these polishing processes has an abrasive hardness in the range of 5 to 9 on the Mohs scale, such as α-A 1 t Os , S i O! , Crt.
O3, tx Fet OH, Diamond, Z n
It contains at least one type of abrasive selected from the group of Oz and T i Oz.

The polishing tape used in the present invention is manufactured, for example, as follows. The abrasive material is dispersed in a binder containing a binder, additives, etc., applied to a support, dried, and then cut into a predetermined size.

As the binder, thermosetting resins, thermosetting resins, and reactive resins may be used alone or in combination. The mixing ratio of the abrasive material and the binder is 10 to 200 parts by weight based on 100 parts by weight of the abrasive material. The material for the support is polyethylene terephthalate (PET).
), polyolefins such as polypropylene, cellulose derivatives, vinyl resins, polycarbonates, polyamides, and other synthetic resins; non-magnetic metal foils such as aluminum and copper; metal foils such as stainless steel foils; paper , ceramic sheet, etc.

The surface roughness (center line average roughness) Ra of the abrasive tape used in the present invention is preferably within the range of 0.07 to 0°9. The measurement conditions for roughness) Ra are as follows.

Center line average roughness measuring machine Safcom 400B, 403B, 4
Using the 04B system, cutoff value: 0.8 kaku,
Operating speed: 0.3m, needle pressure: 0°07g, needle diameter: 2μR
, the measurement was carried out under the conditions of range=20 and 10.5.

The polishing tape is not particularly limited as long as it has the above performance (although commercially available polishing tapes can also be used).

The polishing process using the polishing tape described above removes particulate components such as ferromagnetic powder or abrasive material protruding from the surface of the magnetic layer, as well as unreacted hardening material existing on the surface of the magnetic layer, and the surface of the magnetic layer. Deposits (for example, dust in the air that adheres to the surface during the manufacture of magnetic recording media) are scraped off together with the binder near the surface of the magnetic layer (generally at a height of 0.01 to 5 μm), and the magnetic layer is removed. The surface is smoothed.

If the back layer is also polished, polishing the back layer reduces the detachment of particulate components such as non-magnetic powder, so for example, magnetic recording media cut into tape shapes can be used in a wound state. Even if the granular component is detached from the surface of the bank layer, it is less likely that the particulate component will adhere to the surface of the magnetic layer and cause dropout or clogging.

An example of a material used for the wiping process is a suede-like nonwoven fabric with a single layer structure consisting of densely intertwined bundles of polyester fibers without substantially containing a binding component such as polyurethane (e.g., Ecsaine). Product name)
, manufactured by Toshi ■; Clarino 1 product name), manufactured by Kuraray ■), and nonwoven fabrics made of polyester fibers bonded with a binding component such as polyurethane (for example, Hi-Lean (product name), manufactured by Nippon Vilene ■), etc. can.

This wiping process completely removes deposits and organic substances from the magnetic layer and/or backing layer, reducing dropouts or clogging.

Regarding the grinding treatment method, it is more preferable to perform the grinding treatment before performing the wiping treatment of the nonwoven fabric.
It is described in Japanese Patent Application No. 13184/1984. Thus, examples of grinding tools that may be used include fixed blades, diamond wheels and rotating blades.

Here, the fixed blade is a blade whose portion that contacts the surface of the magnetic layer or back layer to be ground is made of a highly hard material. Blades are typically made of sapphire, alumina, cermet, or zirconia (zirconium oxide)
, silicon nitride, silicon carbide, diamond, and cemented carbide.

Furthermore, a diamond wheel refers to a rotating cylindrical grinding tool with sintered diamonds around the circumference.

Further, the rotary blade body is a grinding tool that includes a rotary body and at least one blade provided on the outer circumference of the rotary body along the rotation axis of the rotary body.

The above-described treatment can further enhance the effect of polishing using a polishing tape.

The above description mainly describes a method in which the surface of the magnetic layer or the surfaces of the magnetic layer and back layer is polished using a polishing tape after cutting the laminate that has been subjected to surface smoothing treatment. The order is not limited to this, and for example, a method of polishing while cutting or a method of polishing before cutting can be used.

Furthermore, since the curing reaction proceeds gradually even without a curing process, after the surface-smoothed sample, the surface of the magnetic layer or the surfaces of the magnetic layer and back layer can be polished with a polishing tape without any curing process. It is also possible to do so.

(Effects of the Invention) The present invention provides a demagnetizing step after the magnetic layer is oriented and before the polishing or grinding treatment, so that the generated shavings are not magnetized and are therefore reattached to the magnetic recording medium. Dropout is noticeably improved without any problems.

(Example) Next, Examples and Comparative Examples of the present invention will be shown. Note that "parts" in Examples and Comparative Examples indicate "parts by weight."

[Example 1] A magnetic paint was prepared by cross-dispersing the following magnetic paint composition in a ball mill until it became uniform.

After adjusting the viscosity of the obtained magnetic paint, it was applied onto the surface of a polyethylene terephthalate support with a thickness of IOam using a reverse roll so that the thickness of the magnetic layer was 3.0 μm.

■Fine ferromagnetic metal powder (composition: Fe96wtX, Ni4w)
tχ, specific surface area = 45 po/g) 100 parts Vinyl chloride/vinyl acetate/maleic anhydride copolymer (400X110A, manufactured by Nippon Zeon ■) 14 parts Polyurethane resin with Tuboran N-2304, manufactured by Nippon Polyurethane ■) 12 parts Polyisocyanate compound (Desmodur L-75, manufactured by Bayer AG) 12 parts α
-Alumina 10 parts Stearic acid 5 parts Butyl stearate
6 part carbon blank
1 part methyl ethyl ketone
A back layer forming paint was prepared by cross-dispersing 325 parts of the following back layer forming paint composition using a ball mill until uniform.

After adjusting the viscosity of the obtained back layer forming coating material, it was coated on the back surface of the support coated with the above magnetic coating material using a reverse roll so that the thickness of the back layer was 0.7 μm.

Carbon black (average particle size: O, O5 μm) 35 parts α-alumina (average particle size: 0.15 μm, maximum particle size: 0.3 μm) 1.8 parts nitrocellulose 20 parts Polyurethane resin with Tuboran N -2304, manufactured by Nippon Polyurethane ■) 10 parts polyisonanate compound (Coronate 1 manufactured by Nippon Polyurethane ■) 10 parts methyl ethyl ketone 600 parts In this state, a magnetic field orientation treatment was performed using a 3000 Gauss magnet, and after drying, a demagnetization zone was installed as shown in FIG. 1 before being wound up.

First, the web 4 entering the degaussing zone is magnetized to the maximum residual magnetic flux density by a saturation head made of a 2000 Gauss permanent magnet, and then the residual magnetic flux density is reduced to almost 0 by an unsaturated head 2 made of a 1600 Gauss permanent magnet. It is magnetized in the opposite direction so that

And finally, an electromagnet with 1200 Gauss AC power (
An alternating current magnetic field whose amplitude is attenuated is applied by the alternating current head (3), which is a ferrite yoke, and the residual magnetic flux density becomes almost completely zero.

In this embodiment, the residual magnetic flux density of the web is 0.02 Gauss even without passing through an AC head, and the object of the present invention is achieved.

Thereafter, a calender treatment was performed to prepare a laminate consisting of a nonmagnetic support, a magnetic layer, and a back layer.

This laminate was heat-treated at 60°C for 24 hours to harden the polyisocyanate compound contained in the magnetic layer, and then slit into 8 pieces. As shown in FIG. 2, a material Cr2O, manufactured by Fuji Photo Film ■) was polished and then wiped using a suede-like nonwoven fabric to produce an 8 mm video tape.

Processing conditions The polishing tape 5 is moved by the rotating roll II at a speed of 1.5 cm/min in the opposite direction to the tape feeding, and is pressed from above by the pad 9 to come into contact with the surface of the magnetic layer of the tape, and the polishing process is carried out. After that, the surface of the magnetic layer was cut with a sapphire blade (width: 5cm,
Length 35cm, manufactured by Kyocera■), contact angle 80 degrees, tension 5
Grinding was carried out by contacting at 0 g/8■.

Note that the contact between the magnetic layer and the sapphire blades was made once using a set of four sapphire blades.

Comparative Example 1 8 was carried out in the same manner as in Example 1 except that in Example 1, the polishing treatment with the polishing tape, the sapphire blade treatment, and the wiping treatment using the suede-like nonwoven fabric were not performed.
Produced millimeter videotape.

Comparative Example 2 An 8 mm videotape was produced in the same manner as in Example 1 except that the demagnetizing zone was not provided.

Evaluation method The obtained 8 mm videotape was used to record a length of 10 minutes on a VTR, and the number of dropouts occurring per minute at 15 μS - 18 dB during playback was measured.

As is clear from the results in Table 1, there is a difference of about 14 to 24 times in terms of the number of O between Example 1 and Comparative Example 2.
This is a remarkable effect of demagnetization.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a degaussing process according to the present invention. FIG. 2 is a schematic diagram of an example of polishing, grinding, and wiping steps according to the present invention. 1: Saturated head (permanent magnet) 2: Unsaturated head (permanent magnet) 3: AC head (ferrite yoke) 4: Web 5: Coil 6: AC power supply 7: Nonwoven fabric 8: Winding roll 9: Pad (for polishing tape) ) 10: Pad (for non-woven fabric) ll: Rotating roll (for polishing tape) 12: Rotating roll (for non-woven fabric) 13: Feeding roll 14: Feeding roll 15: Polishing tape 16: Fixed blade patent applicant Fuji Photo Film Co., Ltd. figure

Claims (2)

[Claims] (1) After orienting a magnetic layer coated on a non-magnetic support and comprising ferromagnetic powder dispersed in a binder and subjecting it to surface smoothing treatment, the surface of the magnetic layer is polished using an abrasive tape. A method for manufacturing a magnetic recording medium characterized in that the magnetic recording medium is subjected to a grinding treatment, and the magnetic recording medium is demagnetized in any one of the steps after orienting the magnetic layer and before the polishing treatment and/or the grinding treatment. Production method. (2) After the surface of the magnetic layer subjected to the surface smoothing treatment is polished with the polishing tape, the grinding treatment is performed with a blade or a rotating blade, and then the magnetic layer is wiped off with a nonwoven cloth. The method for manufacturing a magnetic recording medium according to claim (1). (3) The method for manufacturing a magnetic recording medium according to claim (1), wherein the demagnetization is performed using a saturated head, then an unsaturated head, and finally an AC head.