JPH06103558A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium inhibiting the damage of the back coat layer, not causing the scraping of a guide and excellent in running durability. CONSTITUTION:Fine zirconia powder as well as carbon black are incorporated into a back coat layer. The fine zirconia powder preferably has 20-90m<2>/g specific surface area and 100-400Angstrom average primary particle diameter. The volume ratio between the fine zirconia powder and the carbon black is regulated to (1:99)-(40:60).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a back coat layer formed thereon, and more particularly to a magnetic recording medium excellent in running durability.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium is placed in a high-speed relative motion with a magnetic head in the process of recording / reproducing a magnetic signal, and at that time, it must be smoothly and stably run. . Therefore, a back coat layer is provided to prevent static electricity and reduce the friction coefficient during running.

As the back coat layer, one mainly containing carbon black or the like is used, and the Mohs hardness of alumina, chromium oxide or the like is about 8.0-9.
Those containing hard pigments having a value of 5 are not used. This is because when the hard pigment is used in the back coat layer, the guide is scraped off, and the abrasion powder is transferred to the magnetic layer to cause dropout. Further, the friction coefficient increases due to the change of the surface due to the scraping of the guide, which causes edge damage and jitter.

[0004]

For this reason, soft pigments having a Mohs hardness of about 5.0 to 6.5 are generally used. However, the durability of the back coat layer against repeated running is insufficient, and there is little effect on scratches and powder falling. Although this is dealt with by using a large particle diameter, it causes the surface roughness.

Therefore, the present invention has been proposed in view of the above circumstances, and an object thereof is to provide a magnetic recording medium having excellent surface smoothness and running durability.

[0006]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the back coat layer contains zirconia fine powder as an abrasive in addition to carbon black. As a result, they have found that the running durability can be improved, and completed the present invention.

That is, the present invention provides a magnetic recording medium having at least a magnetic layer and a back coat layer on a non-magnetic support, wherein the back coat layer contains fine zirconia powder and carbon black. It is characterized by.

The zirconia fine powder has a specific surface area of 20 to
It is preferably 90 m ² / g and the average primary particle diameter is 100 to 400 Å. Further, the volume ratio of the zirconia fine powder to the carbon black is preferably 1:99 to 40:60.

The back surface of the magnetic recording medium containing no zirconia fine powder is easily scratched, and conversely, the zirconia content exceeds 40:60 (carbon black: zirconia fine powder) in volume ratio. Will scrape the sliding guide.

The magnetic recording medium to which the present invention is applied is not particularly limited as long as a magnetic layer is formed on a non-magnetic support and a back coat layer is provided on the surface opposite to the magnetic layer. However, even in the case of a so-called coating type magnetic recording medium in which ferromagnetic powder is dispersed in a binder and coated on a non-magnetic support, a so-called vapor-deposited magnetic film forming a metal magnetic thin film on the non-magnetic support is formed. It may be a recording medium.

For example, when the magnetic recording medium is a coating type, a magnetic powder constituting a non-magnetic support or a magnetic coating film,
Any conventionally known resin binder can be used,
It is not limited in any way. For example, as the non-magnetic support, polyesters, polyolefins,
Polymer substrates made of polymer materials typified by celluloses, vinyl resins, polyimides, polycarbonates, metal substrates made of aluminum alloys and titanium alloys, ceramic substrates made of aluminum glass, glass substrates, etc. Is. The shape is not limited at all, and may be any shape such as a tape shape, a sheet shape, and a drum shape.

As the ferromagnetic powder, ferromagnetic metal materials such as Fe, Co and Ni, Fe-Co, Fe-Ni and Fe- are used.
Co-Ni, Co-Ni, Fe-Mn-Zn, Fe-N
i-Zn, Fe-Co-Ni-Cr, Fe-Co-Ni
-P, Fe-Co-B, Fe-Co-Cr-B, Fe-
Ferromagnetic metal particles made of various ferromagnetic alloy materials containing Fe, Co, and Ni as main components, such as Co-V, are suitable.

In the ferromagnetic powder for the magnetic recording medium, Al, Si, Ti, C are used for the purpose of improving various characteristics.
Elements such as r, Mn, Cu, Zn, Mg and P may be added.

As the binder, polymers such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, etc., or copolymers combining two or more of these, Polyurethane resin, polyester resin, epoxy resin and the like are exemplified. The ferromagnetic powder is dispersed in these binders to form a magnetic layer.

Further, in addition to the above-mentioned binder and ferromagnetic powder, a dispersant, an abrasive, an antistatic agent, a rust preventive and the like may be added to the magnetic layer.

On the other hand, even when the magnetic recording medium to which the present invention is applied is of the vapor deposition type, conventionally known materials and manufacturing methods can be used without any limitation. A metal magnetic thin film is formed as a magnetic layer by directly depositing a ferromagnetic metal material on a non-magnetic support, and this metal magnetic material is one that is used for ordinary vapor deposition tape. Anything may be used as long as it is. For example, Fe, Co, Ni and other ferromagnetic metals, Fe-Co, C
o-Ni, Fe-Co-Ni, Fe-Cu, Co-C
u, Co-Au, Co-Pt, Mn-Bi, Mn-A
1, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co
Examples include ferromagnetic alloys such as -Cr, Co-Ni-Cr, and Fe-Co-Ni-Cr.

The metal magnetic thin film may be a single layer film or a multilayer film of these. Further, an underlayer or an intermediate layer may be provided between the non-magnetic support and the metal magnetic thin film, or in the case of a multilayer film, for improving the adhesive force between the layers and controlling the coercive force. Further, for example, the vicinity of the surface of the magnetic layer may be an oxide to improve the corrosion resistance.

As means for forming the metal magnetic thin film, a vacuum vapor deposition method of heating and evaporating a ferromagnetic material under vacuum to deposit it on a non-magnetic support, or an ion plating method of evaporating a ferromagnetic metal material in a discharge. A so-called PVD technique such as a sputtering method in which atoms on a target surface are knocked out by argon ions generated through a glow discharge in an atmosphere containing argon as a main component may be used.

Of course, the structure of the magnetic recording medium according to the present invention is not limited to this, and may be modified within the scope of the present invention, for example, an undercoat layer may be formed on the non-magnetic support, if necessary. There is no problem with forming a layer or forming a layer of a lubricant, a rust preventive, or the like. In this case, as the material contained in the undercoat layer, the lubricant, or the rust preventive agent layer, any conventionally known material can be used.

The material constituting the back coat layer,
The conditions for forming the back coat layer are not particularly limited as long as they are usually applied to this type of magnetic recording medium. Also, when using the zirconia fine powder in the present invention, various addition methods are conceivable, and the method is not limited to the method shown in Examples described later. For example, surface treatment may be performed in advance in order to improve the dispersibility of the zirconia fine powder itself. The treating agent used for this purpose is not limited, but silane-based, tetanate-based, aluminum-based, zirconate-based coupling agents, fatty acids, phosphoric acid esters, anionic surfactants and the like are preferable.

As one of the surface treatments, zirconia fine powder pre-dispersed with a predetermined resin to form a slurry may be used. The resin used at this time is not limited, but a resin having a polar group introduced therein is preferable.
Examples of polar groups include sulfonates such as SO ₃ Na,
Those having a carboxylate or amine salt such as COONa are suitable.

Examples of the disperser used at the time of pre-dispersion include a kneader such as a pressure kneader, an extruder, a cokneader and a triple roll, and a media disperser such as a sand mill, a ball mill, a coball mill and a bin mill. The material of the disperser is not particularly limited, but it is preferably made of ceramic.

Further, the zirconia fine powder may be added to the back coat layer in combination with other pigments. For example, CaCO ₃ , α-Fe ₂ O ₃ , BaSO ₄ , TiO
₂ , it is possible to use in combination with a soft pigment such as ZnO.
In the magnetic recording medium of the present invention, fine zirconia powder may be those containing Y ₂ O _3, this time, no particular limitation is imposed on the amount of the added Y ₂ O _3.

Then, in the magnetic recording medium of the present invention,
The carbon black used is specific surface area, pH, DB
The characteristics such as P oil absorption amount are not particularly limited. However, when a back coat coating material is produced, a method of adding a slurry of zirconia fine powder to a material in which carbon black is dispersed in advance can have the best dispersibility.

[0025]

By including fine zirconia powder in the back coat layer, the back surface of the magnetic recording medium becomes resistant to abrasion. Further, since the zirconia fine powder used in the present invention is ultrafine particles and is excellent in dispersibility, the back surface of the magnetic recording medium using this is excellent in surface smoothness. Therefore, if the amount of zirconia fine powder added is appropriately suppressed, the guide is less likely to be scraped by sliding contact.

Therefore, the magnetic recording medium is excellent in running durability and capable of stable recording / reproducing.

[0027]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples. Example 1 First, a magnetic paint having the following composition was prepared. Composition of magnetic paint Magnetic powder: Co-γ-Fe ₂ O ₃ (specific surface area 45 m ² / g) ... 100 parts by weight Binder: Nitrocellulose (Asahi Kasei Co., Ltd., trade name NC1 / 2H) ... 10 Parts by weight Polyurethane (manufactured by Nippon Polyurethane Company, trade name N-2304) ··· 10 parts by weight Abrasive: Alumina (α-Al ₂ O ₃ manufactured by Sumitomo Chemical Co., Ltd., trade name AKP-30) Parts by weight Antistatic agent: conductive carbon (manufactured by Cabot, Vulcan XC-72) 2 parts by weight dispersant: lecithin 2 parts by weight lubricant: butyl stearate 2 parts by weight Myristic acid: 2 parts by weight Solvent: Methyl ethyl ketone: 120 parts by weight Methyl isobutyl ketone: 60 parts by weight Toluene :: 60 parts by weight

The above materials were mixed with a ball mill for 60 hours after stirring with a disper. And the average pore diameter is 1.0 μm
After filtering with a filter, 5 parts by weight of a curing agent (manufactured by Nippon Polyurethane Company, trade name: Coronate L) was added and further stirred. This magnetic paint is a non-magnetic support 14.0.
A magnetic layer was coated on a polyethylene terephthalate (hereinafter referred to as PET) film having a thickness of μm so that the average thickness was 4.5 μm. Then, magnetic field orientation processing was performed, it was made to dry, and calendar processing was given.

Next, a back coat paint having the following composition was prepared. Composition of back coat paint Carbon black (manufactured by Cabot Co., trade name Black Pearls L) ··· 95 parts by weight Abrasive: Zirconia fine powder (ZrO ₂ ) · 5 parts by weight Binder: Vinyl chloride-acetic acid Vinyl copolymer (UCC, trade name VAGH) 35 parts by weight Polyurethane resin 15 parts by weight Solvent: methyl ethyl ketone 300 parts by weight methyl isobutyl ketone 200 parts by weight toluene・ 150 parts by weight

The above materials were kneaded by a pressure kneader and then mixed and dispersed by a sand mill. This has an average pore diameter of 3.0 μm,
After sequentially filtering with a 1.0 μm filter, 10 parts by weight of a curing agent (manufactured by Nippon Polyurethane Company, trade name: Coronate L) was added. The backcoat layer was applied to the surface of the base film on which the magnetic layer had already been formed, opposite to the surface on which the magnetic layer was formed, so that the backcoat layer had an average thickness of 1.0 μm. After being cured for a predetermined time in a curing furnace, it was cut to prepare a sample tape.

The zirconia fine powder used as an abrasive in this example has a specific gravity of 5.73 and a specific surface area of 27 m ² /
g, average primary particle diameter 370Å, Y ₂ O ₃ is not added. On the other hand, the carbon black used had a specific gravity of 1.8 and an average primary particle diameter of 230Å.

Various evaluations were carried out on the sample tape prepared as described above. First, the surface roughness of the above sample tape was measured as a center line average roughness using a stylus type three-dimensional surface roughness meter.

Next, the coefficient of friction was measured as the coefficient of friction between the surface of the back coat layer and 1S stainless steel under the conditions of a load W of 50 g and a low tape speed of 15 mm / sec.

Furthermore, a 30-minute long sample tape
After making the shuttle 0 times, scratches on the guide and scratches on the surface of the back coat layer were visually evaluated. The evaluation is ⊚ when no scraping of the guide or scratches on the backcoat layer surface is observed, ◯ when it is good, and Δ when there is some scraping of the guide or scratches on the backcoat layer surface but is within the allowable range. When there is abrasion of the guide or the surface of the back coat layer, it is represented by ▲, and when the abrasion of the guide or the surface of the back coat layer is extremely severe, it is represented by x, and the results are shown in Table 1.

[0035]

[Table 1]

[0036] Sample tapes of Examples 2-5 back except for changing the volume ratio of the fine zirconia powder is carbon black and abrasives contained in the coat layer in the same manner as in Example 1 Examples 2-5 Was produced.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the back coat layer surface were evaluated. Table 1 also shows the volume ratio of carbon black and zirconia fine powder and the evaluation results for each sample tape.

Examples 6 to 8 In this example, the zirconia fine powder contained in the back coat layer contained Y ₂ O _{3 in an amount} of 3 mol%.
It differs from Example 1 in having a specific surface area of 50 m ² / g and an average primary particle size of 200Å, but is similar to Example 1 except that the volume ratio of carbon black and zirconia fine powder was changed. Then, the sample tapes of Examples 6 to 8 were produced.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated. Table 1 shows the volume ratios of carbon black and zirconia fine powder as an abrasive and the results of each evaluation for each sample tape.

Comparative Example 1 For comparison with the above example, the back coat layer did not contain zirconia fine powder and the main component was carbon black 1.
The sample tape of Comparative Example 1 was prepared in the same manner as in Example 1 except that the amount was set to 00 parts by weight.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated, and the results are also shown in Table 1.

Comparative Example 2 The back coat layer contained rutile type titanium oxide (TiO ₂ ) as an abrasive instead of fine zirconia powder,
A sample tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the volume ratio of carbon black to the above rutile-type titanium oxide was 95: 5.

The used rutile titanium oxide (TiO 2
₂ ) has an average primary particle diameter of 0.2 μm and a specific gravity of 4.2.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated, and the results are also shown in Table 1.

[0045]Comparative Example 3 The back coat layer contains zirconia fine powder as an abrasive.
Instead of α-Al₂O ₃Contains carbon black
And the above α-Al₂O₃The composition ratio with is 90:10 by volume.
Comparative Example 3 as in Example 1 except that
A sample tape of was prepared.

The α-Al ₂ O _{3 used} had an average primary particle diameter of 0.05 μm and a specific gravity of 4.0.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated, and the results are also shown in Table 1.

Comparative Example 4 The back coat layer contains zinc oxide (ZnO) instead of zirconia fine powder as an abrasive so that the volume ratio of carbon black to zinc oxide is 80:20. A sample tape of Comparative Example 3 was produced in the same manner as in Example 1 except that the above was used.

The zinc oxide (ZnO) used was 1 on average.
It has a secondary particle diameter of 0.01 μm and a specific gravity of 5.47.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated, and the results are also shown in Table 1.

Comparative Example 5 The back coat layer contained fumed silica (SiO ₂ ) as an abrasive instead of fine zirconia powder, and the composition ratio of carbon black to the fumed silica (SiO ₂ ) was a volume ratio. A sample tape of Comparative Example 3 was prepared in the same manner as in Example 1 except that the sample tape was 80:20.

The fumed silica (Si
O ₂ ) has an average primary particle size of 220Å and a specific gravity of 2.21.

In the same manner as in Example 1, the surface roughness of the sample tape, the coefficient of friction, the abrasion of the guide and the degree of scratches on the surface of the back coat layer were evaluated, and the results are also shown in Table 1.

From the results shown in Table 1 above, it can be seen that the back surface is less likely to be scratched by incorporating zirconia fine powder as an abrasive in the back coat layer. The fine zirconia powder is TiO ₂ , α
-Al ₂ O _3, ZnO, it is highly effective as compared to SiO ₂ or the like can be seen.

[0055]

As is apparent from the above description, since the magnetic recording medium of the present invention contains fine zirconia powder in the back coat layer, the strength against friction of the back surface of the magnetic recording medium is improved, It can be seen that the back surface is less likely to be scratched. Further, since the magnetic recording medium of the present invention is excellent in surface smoothness, the friction is small and the guide which is in sliding contact is hardly scraped and worn.

Therefore, it is possible to provide a magnetic recording medium which is excellent in running durability and capable of stable recording and reproduction.

Claims (3)

[Claims] 1. A magnetic recording medium having at least a magnetic layer and a back coat layer on a non-magnetic support, wherein the back coat layer contains fine zirconia powder and carbon black. . 2. A zirconia fine powder having a specific surface area of 20 to 90.
m ² / g, the magnetic recording medium of claim 1, wherein the average is a primary particle size 100～400A. 3. The magnetic recording medium according to claim 1 or 2, wherein the volume ratio of the zirconia fine powder to the carbon black is 1:99 to 40:60.