JPH03157810A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve mechanical properties and electromagnetic conversion characteristics of the medium by incorporating a specified amt. of nonmagnetic powder of rigid particles into an upper layer part from the surface to the half depth of a magnetic layer. CONSTITUTION:The nonmagnetic powder of rigid particles is incorporated into the magnetic layer in a manner that >=70wt.% of the powder is incorporated into an upper layer part from the surface to the half depth of the magnetic layer. Namely, the nonmagnetic powder of rigid particles is not uniformly dispersed, different from conventional method, but dispersed in a manner that the upper layer part from the surface to the half depth of the magnetic layer contains >=70wt.% of the powder. Thereby, the total amt. of the powder incorporated into the magnetic layer can be decreases than in a layer with uniformly dispersed powder, and both of mechanical properties and electromagnetic conversion characteristics of the medium can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to magnetic tapes, magnetic disks, etc. in which a coating-type magnetic layer containing magnetic powder and a binder is formed on a non-magnetic support. Concerning recording media and their manufacturing methods.

[Conventional technology]

This type of magnetic recording medium has improved mechanical properties such as durability, abrasion resistance, and running stability because the magnetic layer comes into sliding contact with the magnetic head and guide member of the recording/reproducing device at a high relative speed during recording and reproduction. For this purpose, conventional methods have been employed to uniformly disperse various non-magnetic solid powders in the magnetic layer.

Examples of such non-magnetic solid powder include A'2
()+ , Cr2 0s , α Fe2 0
3. Oxides such as TiO□, Sing, SiC, T
ic.

Carbide such as WC, nitride such as TiN, Si3N4,
In addition to borides such as TiBz and ZrBz, powders such as graphite are commonly used.

[Problem to be solved by the invention]

However, with the conventional means, durability, wear resistance,
In order to sufficiently improve mechanical properties such as running stability, it is necessary to incorporate a large amount of non-magnetic solid powder into the magnetic layer; for example, in floppy disks, the amount of non-magnetic solid powder is 20% by weight or more based on the magnetic powder. Non-magnetic solid powder may be blended.

However, when the amount of non-magnetic solid powder blended is increased in this way, the proportion of non-magnetic components in the magnetic layer inevitably increases, and magnetic properties such as saturation magnetization and square shape decrease accordingly.
This has caused a problem in that the electromagnetic conversion characteristics of the magnetic recording medium deteriorate.

The object of the present invention is to solve the above-mentioned conventional problems and to obtain a magnetic recording medium having excellent mechanical properties and electromagnetic conversion properties.

[Means to solve the problem]

In the process of conducting intensive studies to achieve the above object, the inventors discovered that in video tapes, floppy disks, etc., which are in sliding contact with the magnetic head at high speed during recording and reproduction, the We learned that the behavior of the existing nonmagnetic solid powder greatly controls the mechanical properties of magnetic recording media.

Therefore, after further consideration based on this knowledge, we found that
Instead of dispersing the non-magnetic solid powder uniformly in the magnetic layer as in the past, by unevenly distributing the solid powder near the surface of the magnetic layer, the amount of the solid powder mixed in the entire magnetic layer can be reduced. As a result, it is possible to improve the magnetic properties by reducing the proportion of non-magnetic components in the magnetic layer, resulting in a magnetic material with excellent mechanical properties and electromagnetic conversion properties. They discovered that it was possible to realize a recording medium and came up with this invention.

That is, in order to achieve the above object, the magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic layer containing magnetic powder, nonmagnetic solid powder, and a binder is formed on a nonmagnetic support. , the magnetic layer is characterized in that 70% by weight or more of the non-magnetic solid powder is contained in the upper layer half of the depth from the surface of the magnetic layer.

Further, for the above-mentioned purpose, the method for manufacturing a magnetic recording medium according to the present invention includes hydrophobicizing non-magnetic solid powder, and mixing the treated non-magnetic solid powder with an organic solvent together with magnetic powder and a binder. The method is characterized by preparing a magnetic coating material, coating the magnetic coating material on a non-magnetic support, and drying it to form a magnetic layer.

[Structure and operation of the invention]

In the magnetic recording medium of the present invention, the non-magnetic solid powder blended into the magnetic layer is not uniformly dispersed throughout the magnetic layer as in the conventional case, but is distributed at a depth of about half from the surface of the magnetic layer as described above. Since the solid powder is unevenly distributed with more than 70% by weight being contained in the upper layer, the overall amount of the solid powder in the magnetic layer is much smaller than in the case of conventional uniform dispersion. Both mechanical properties and electromagnetic conversion properties can be improved.

This is because the mechanical properties of this type of magnetic recording medium, such as durability, abrasion resistance, and running stability, are solely carried by the nonmagnetic solid powder that exists near the surface of the magnetic layer that comes into sliding contact with the magnetic head during recording and reproduction. The higher the density of the solid powder near the surface of the magnetic layer, the better the mechanical properties. However, in this invention, as described above, the solid powder is unevenly distributed in the upper layer of the magnetic layer. Even if the total amount of solid powder blended is small, the density of the solid powder near the surface of the magnetic layer can be set high, and this allows the same or better mechanical properties to be achieved with a much smaller amount than in the case of conventional uniform dispersion. It is thought that this can be obtained. In addition, by reducing the amount of non-magnetic magnetic powder blended, the proportion of non-magnetic components in the magnetic layer becomes smaller, which greatly improves magnetic properties such as saturation magnetization and square shape. It is thought that electromagnetic conversion characteristics such as output characteristics will be significantly improved.

In order to achieve such effects, it is necessary to achieve an uneven distribution state in which 70% by weight or more of the non-magnetic solid powder is contained in the upper layer at a depth of half from the surface of the magnetic layer, as described above. . That is, the content of this upper layer is 70% by weight.
If the magnetic layer is less than This results in deterioration of magnetic properties and, ultimately, of electromagnetic conversion characteristics.

In the present invention, the means for unevenly distributing the nonmagnetic solid powder toward the upper layer side of the magnetic layer as described above is not particularly limited, but the method of the present invention in which the solid powder is hydrophobized is the simplest. In other words, this hydrophobization treatment lowers the surface energy of the solid powder, resulting in a large difference in interfacial energy between the solid powder and the binder solution in the magnetic coating, and this difference in interfacial energy causes a Since a force acts to levitate the solid powder in the paint, the solid powder moves toward the surface of the paint film in the magnetic paint film that is formed when the magnetic paint is applied to a non-magnetic support. After drying, the magnetic layer has the solid powder unevenly distributed on the upper layer side, particularly near the surface.

The above hydrophobization treatment can be carried out by simply dispersing a non-magnetic solid powder in a solution of a hydrophobization treatment agent dissolved in an organic solvent, whereby the hydrophobization treatment agent is chemically adsorbed onto the surface of the solid powder and filtered. After drying, a non-magnetic solid powder with low surface energy is obtained.

As the hydrophobizing agent, various existing hydrocarbon-based and fluorine-based agents can be used, but silane-based, titanate-based, aluminum-based, etc., which have excellent chemical adsorption properties on the solid powder surface, can be used. Coupling agents as well as organosilazanes are suitable. Further, as a solvent for dissolving such a hydrophobizing agent, the same solvent as that used for the magnetic paint described below can be used.

As the non-magnetic solid powder, any of the various materials conventionally used in the magnetic layer of this type of magnetic recording medium can be used, but powders consisting of inorganic particles with a Mohs hardness of 8 or more are particularly suitable. . In other words, if the Mohs hardness is too low, the polishing ability for the magnetic head will be insufficient and the strength of the magnetic layer will also be insufficient, and the magnetic layer will be easily worn out due to sliding contact with the magnetic head during recording and reproduction, and this abrasion powder will cause Clogging of the magnetic head occurs frequently, and both the durability and electromagnetic conversion characteristics of the magnetic recording medium deteriorate.

A preferable specific example of such a non-magnetic solid powder having a Mohs hardness of 8 or more is Aj! z 03 , Crz Oz ,
3AIlt Os・2S ioz, A7! z O
3. Oxides such as Ti02(7), TiC, SiC, WC
carbides such as 5f3N4, nitrides such as TiN, Ti
Examples include powders of inorganic compounds such as borides such as Bt and ZrBz.

Further, the size of the non-magnetic solid powder is an average particle size of 0.
The thickness is preferably in the range of about 1 to 1.0 μm. In other words, if the average particle diameter is too large, the amount of wear on the magnetic head will be excessive and the damage to the magnetic head will be significant.On the other hand, if the average particle diameter is too small, the sliding contact resistance between the magnetic layer surface and the magnetic head will increase. This leads to a decrease in running stability and a decrease in the strength of the magnetic layer.

The amount of non-magnetic solid powder used is about 2 to 15 parts by weight per 100 parts by weight of magnetic powder, but compared to the conventional case where the solid powder is uniformly dispersed in the magnetic layer. The same or better mechanical properties can be imparted with less than half the amount used.

As described above, the magnetic recording medium of the present invention includes a special magnetic layer in which non-magnetic solid powder is unevenly distributed on the upper layer side, and the method of the present invention uses a hydrophobized solid powder as the solid powder. According to the method, it can be easily manufactured according to a conventional method.

That is, in the method of the present invention, a magnetic paint is prepared by adding and mixing a hydrophobized non-magnetic solid powder, a magnetic powder, a binder, and various additives blended as necessary in an organic solvent. This paint is applied onto a non-magnetic support.

After drying to form a magnetic layer of a desired thickness, appropriate post-processing such as calendering may be performed to form the desired shape of the magnetic recording medium.

0 The above magnetic powders include γ-F eg 03, Fe3
O4, co-containing r F ez Os , Co-containing γ
Various conventionally known magnetic powders can be used, including oxide-based magnetic powders such as Fe3O4, CrO□, and barium ferrite, as well as metal-based magnetic powders such as Fe, Co, and FeNi.

In addition, the above-mentioned binders include vinyl chloride-vinyl acetate copolymers, polyvinyl brachyl resins, cellulose resins, polyurethane resins, polyester resins, polyisocyanate compounds as crosslinking agents, and radiation-curable resins. Any of the binders conventionally known as binders for magnetic layers of magnetic recording media can be used alone or in combination of two or more.

Organic solvents used to prepare magnetic paints include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and isopropyl. Solvents suitable for dissolving the binder used are particularly limited, such as alcoholic solvents such as alcohol, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and dioxane. They can be used alone or in combination of two or more.

Additionally, additives that may be added as necessary include dispersants, lubricants, antistatic agents, and the like.

According to the method of the present invention, since the nonmagnetic solid powder is unevenly distributed near the surface of the magnetic layer, a magnetic recording medium that highly satisfies both mechanical properties and electrical conversion properties can be obtained. It is also conceivable that due to poor interaction between the chemically treated solid powder and the binder of the magnetic layer, the solid powder exposed on the surface of the magnetic layer tends to fall off.

In this case, a binder for the magnetic layer is used that has a bond capable of electron beam crosslinking, such as a C=C bond or a C-CZ bond, in its molecule, while a binder for the above bond is used on the particle surface of the nonmagnetic solid powder. If a C=C bond that can be cross-linked by an electron beam is chemically fixed in advance,
The solid powder exposed on the surface of the magnetic layer can be firmly held in the magnetic layer by electron beam irradiation after coating the magnetic layer. C=C on the particle surface of such a solid powder
The bond can be easily fixed by using a hydrophobizing agent containing a C═C bond during the hydrophobizing treatment, or by using a hydrophobizing agent and a surface treating agent containing a C═C bond in combination.

〔Effect of the invention〕

The magnetic recording medium of the present invention has a magnetic layer in which the non-magnetic solid powder contained in the magnetic layer is unevenly distributed on the surface side of the magnetic layer. Even though the amount of solid powder used is much smaller than that of the conventional powder, it has excellent mechanical properties such as durability, wear resistance, and running stability, and the magnetic properties are improved due to the reduction in the amount used. By improving this, it is possible to demonstrate high electromagnetic conversion characteristics.

Further, according to the method for manufacturing a magnetic recording medium according to the present invention,
A magnetic recording medium having a magnetic layer in which the above-mentioned non-magnetic solid powder is unevenly distributed on the surface side can be easily manufactured according to a conventional method.

〔Example〕

Next, embodiments of the present invention will be specifically described.

In addition, in the following, parts mean parts by weight.

Example 1 Methyl isobutyl ketone 60 parts toluene
After partially dispersing 60 parts of the above composition in a pebble mill for about 100 hours, it was filtered and dried to obtain a hydrophobized α-AIlzO:+ powder. Then,
A magnetic coating material was prepared by partially dispersing the following composition using the hydrophobized α-A Ilt Os powder in a ball mill for about 100 hours.

3 4 Hydrophobized α-A7!203 powder 4 parts myristic acid 3 parts cyclohexanone
100 parts toluene 10
Next, this magnetic paint was applied onto a polyester film with a thickness of 13 μm so that the film thickness after drying was approximately 4 μm, dried to form a magnetic layer, and mirror-finished by calendering. A magnetic tape was produced by cutting it into a predetermined width.

Comparative Example 1 Instead of α-AJzOs powder subjected to hydrophobization treatment, untreated α-Aj! A magnetic tape was produced in the same manner as in Example 1 except that the same amount of Gos powder was used.

Comparative Example 2 Except that 10 parts of untreated α-Aflzos powder was used instead of α-AjlzOs powder subjected to hydrophobization treatment.
A magnetic tape was produced in the same manner as in Example 1.

Example 2 Hydrophobization treatment was performed in the same manner as in Example 1 using the same amount of SiC powder (average particle size 0.2 μm) instead of α-Aβgos powder, and the SiC powder after this treatment was used as α-AItzO.
Except that the same amount of magnetic paint was used instead of S powder.
A magnetic tape was produced in the same manner as in Example 1.

Example 3 Hydrophobic treatment was performed in the same manner as in Example 1 using the same amount of TiB powder (average particle size 0.2 μm) instead of α-ANzO3 powder, and the TiB2 powder after this treatment was used as α-A1t.
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of magnetic paint was used in place of the Oz powder.

For each of the magnetic tapes obtained in the above Examples and Comparative Examples, a VH3 type video tape recorder equipped with a Victor magnetic head was used to determine the still durability at -10°C and the tape speed of 2 m/min. The amount of wear on the head after running for 100 hours, the number of runs until the magnetic head became clogged at the same tape speed, and the output at 8 MHz were measured. The results are shown in the table below along with the ratio of the non-magnetic solid powder contained in the upper layer half deep from the surface of the magnetic layer of each magnetic tape.

Note that the output is shown as a relative value with the magnetic tape of Example 1 as a reference (OdB). Further, the ratio of the nonmagnetic solid powder contained in the upper layer of the magnetic layer was measured by electron microanalysis of a cross section of the magnetic layer.

From the results in the above table, it can be seen that the magnetic tape of the present invention (Examples 1 to 3)
) is equivalent to or better than the conventional magnetic tape (Comparative Example 2) in which non-magnetic solid powder is uniformly dispersed throughout the magnetic layer, although the amount of solid powder used is less than 1/2. It is clear that the material has excellent mechanical properties and also exhibits excellent electromagnetic conversion properties. In addition, in a magnetic tape (Comparative Example 1) in which non-magnetic solid powder was uniformly dispersed throughout the magnetic layer and the amount of the solid powder used was small as in Examples 1 to 3 (Comparative Example 1), the mechanical properties were extremely poor. Moreover, it can be seen that the electromagnetic conversion characteristics are also inferior to the magnetic tape of the present invention.

7 8

Claims (5)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing magnetic powder, non-magnetic solid powder, and a binder is formed on a non-magnetic support, the above-mentioned non-magnetic A magnetic recording medium comprising 70% by weight or more of magnetic solid powder. (2) The magnetic recording medium according to claim 1, wherein the nonmagnetic solid powder comprises inorganic particles having a Mohs hardness of 8 or more. (3) The average particle diameter of the non-magnetic solid powder is 0.1 to 1.0μ
The magnetic recording medium according to claim 2, wherein the magnetic recording medium is within the range of m. (4) Non-magnetic solid powder is Al_2O_3, Cr_2O_
3, 3Al_2O_3・2SiO_2, Al_2O_3
・TiO_2, TiC, SiC, WC, Si_3N_4
, TiN, TiB_2, and ZrB_2. The magnetic recording medium according to claim 2, comprising a powder of at least one inorganic compound selected from TiN, TiB_2, and ZrB_2. (5) Hydrophobize the non-magnetic solid powder, mix the treated non-magnetic solid powder with magnetic powder and a binder together with an organic solvent to prepare a magnetic paint, and apply this magnetic paint on a non-magnetic support. A method for manufacturing a magnetic recording medium, which comprises coating and drying to form a magnetic layer.