JPH05120671A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability and friction characteristics of a magnetic recording medium forming a magnetic recording layer on a nonmagnetic base material. CONSTITUTION:Fine particles having <=2.5 sp. gr. and 0.1 to 2mum average particle size are incorporated into the magnetic recording layer. Since the specific gravity of the fine particles to be incorporated into the magnetic recording layer is as small as <=2.5 as compared with abrasive materials used heretofore consisting of Al2O3 (3.99 sp. gr.), Cr2O3 (5.21 sp. gr.) and Fe2O3 (5.1 sp. gr.), the volumetric ratio thereof is larger than heretofore when the same mass is incorporated into the magnetic recording layer. The number of projections on the surface of the magnetic recording layer can, therefore, be increased. Even more, the average particle size is as small as 0.1 to 2mum, therefore, the formation of coarse projections is prevented and the degradation in the output by the coarse projections and the degradation in electromagnetic conversion characteristics, such as deterioration in S/N, are suppressed. The many microprojections are formed on the surface of the magnetic recording layer by the fine particles of the relatively small sp. gr. and average particle size. Thus, the durability and friction characteristic of the magnetic recording medium are greatly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tape used in audio equipment, video equipment, computers and the like.
The present invention relates to a magnetic recording medium such as a magnetic sheet and a magnetic disk.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium such as a magnetic disk is manufactured by applying a magnetic coating material composed of magnetic powder, a binder and the like on a support and drying it to form a magnetic recording layer. In recent years, in these magnetic recording media, the surface of the magnetic recording layer has been smoothed more and more in order to reduce the distance loss during high frequency recording / reproduction for high density recording. Further, along with high density recording of such a magnetic recording medium, the magnetic powder used for forming the magnetic recording layer is made into fine particles or high density packing.

[0003]

The above-mentioned conventional magnetic recording media are processed for high density recording, that is, the surface of the magnetic recording layer is smoothed, the magnetic powder is made into fine particles, and high density packing is performed to obtain the required characteristics. It has been difficult to obtain a magnetic recording medium having satisfactory durability and friction characteristics that are sufficiently satisfactory.

Conventionally, in order to obtain a magnetic recording medium having excellent durability and friction characteristics, various kinds of alumina (Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ) and the like are used. Inorganic particles have been used as an abrasive, but the effect of these abrasives on the surface of the magnetic recording layer is not sufficient, and it is difficult to secure friction characteristics such as excellent durability and running stability. Met.

An object of the present invention is to solve the above conventional problems and to provide a magnetic recording medium excellent in durability and friction characteristics.

[0006]

The magnetic recording medium of the present invention is a magnetic recording medium comprising a magnetic recording layer provided on a non-magnetic support, wherein the magnetic recording layer has a specific gravity of 2.5 or less and an average particle diameter. It is characterized by containing fine particles of 0.1 to 2 μm.

That is, the inventors of the present invention have conducted various studies in order to solve the above-mentioned drawbacks of the prior art. As a result, when specific fine particles are used as an abrasive, suitable protrusions are formed on the surface of the magnetic recording layer. The inventors have found that a magnetic recording medium having excellent durability and friction characteristics can be obtained, and completed the present invention.

The present invention will be described in detail below.

In the present invention, the fine particles contained in the magnetic recording layer formed on the non-magnetic support have a specific gravity of 2.5 or less,
It is preferably 1.0 to 2.3, and the average particle size is 0.1 to 2
The fine particles have a size of μm, preferably 0.2 to 1.0 μm.
Specifically, Tospearl 103 (specific gravity 1.32, average particle diameter 0.3 μm), which is a polysiloxane-based silicone resin fine particle manufactured by Toshiba Silicone Co., Ltd., Tospearl 105
(Specific gravity 1.32, average particle diameter 0.5 μm), Tospearl 108 (specific gravity 1.32, average particle diameter 0.8 μm), Tospearl 120 (specific gravity 1.32, average particle diameter 2.0 μm)
Etc.

It is preferable to use such fine particles so that the content thereof in the magnetic recording layer is 0.01 to 20% by weight, preferably 0.1 to 10% by weight. If the content of the fine particles in the magnetic recording layer is too small, the excellent effect of improving durability and friction characteristics according to the present invention cannot be obtained. On the contrary, if the content is too large, the output of the magnetic recording medium and the S / N are obtained. This causes deterioration of electromagnetic conversion characteristics such as a decrease in ratio.

In the present invention, known abrasives such as alumina, chromium oxide and iron oxide may be used in combination with the fine particles. When these known abrasives are used in combination, the amount used is such that the content in the magnetic recording layer is 0.5 to 2
It is desirable to set it in the range of 0% by weight, preferably 1 to 10% by weight.

The magnetic recording medium of the present invention uses a magnetic coating material comprising a ferromagnetic powder and a binder resin, and the above fine particles and, if necessary, an abrasive such as alumina in the above proportions on a non-magnetic support. The magnetic recording layer can be easily manufactured.

The ferromagnetic powder used for forming the magnetic recording layer is a ferromagnetic alloy powder containing iron as a main component, γ-Fe _{2
O 3, Fe 3 O 4,} Co-γ-Fe 2 O 3, other CrO _2, modified barium ferrite, modified strontium ferrite, and the like. The content of these ferromagnetic powders in the magnetic recording layer is 50 to 90% by weight, particularly 55 to 85% by weight.
It is preferable to use it so as to be in a weight percentage.

On the other hand, the binder resin is not particularly limited, and one having excellent adhesiveness to the non-magnetic support and abrasion resistance is appropriately used. Examples thereof include polyurethane resin, polyester resin, fibrin resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-acrylic copolymer, epoxy resin, phenoxy resin, and the like. Can be used alone or in combination of two or more. These binder resins are preferably used so that the content in the magnetic recording layer is 2 to 50% by weight, particularly 5 to 35% by weight.

In the magnetic recording medium of the present invention, a low molecular weight polyisocyanate compound having a plurality of isocyanate groups is further contained in the magnetic paint to form a three-dimensional network structure in the magnetic recording layer, and the mechanical properties The strength can be improved. Examples of the low molecular weight polyisocyanate compound include trimethylolpropane adduct of tolylene diisocyanate. Such a low molecular weight polyisocyanate compound is preferably used in a proportion of 5 to 100% by weight with respect to the binder resin.

If desired, various additives such as lubricants and antistatic agents can be used in the magnetic coating material forming the magnetic recording layer. Here, as the lubricant, known lubricants such as fatty acids, fatty acid esters, higher alcohols, fluorine oil and silicone oil can be used. The content of the lubricant in the magnetic recording layer is 0.5.
It is preferably in the range of ˜20% by weight, particularly 1 to 10% by weight. As the antistatic agent, in addition to inorganic particles such as carbon black and graphite, an organic antistatic agent can be used, and the amount thereof used is appropriately determined according to the required characteristics.

Solvents used when kneading the magnetic paint containing the above components are toluene, methyl ethyl ketone,
Solvents that are commonly used in the preparation of magnetic paints such as cyclohexanone, butyl acetate and tetrahydrofuran can be used. Further, the kneading method, the order of addition of the respective components, and the like may be the same as those generally used for kneading magnetic paints.

The magnetic coating material thus prepared is coated on a non-magnetic support such as polyethylene terephthalate, polypropylene, polycarbonate, polyamide or polyimide by a conventional method and dried to obtain the magnetic recording medium of the present invention. .

The thickness of the magnetic recording layer formed on the non-magnetic support is, after drying, preferably in the range of 0.1 to 5 μm, particularly 0.2 to 3 μm.

After the formation of the magnetic recording layer, an alignment treatment, a random treatment, a smoothing treatment or the like may be further performed, if necessary.

[0021]

In the present invention, the fine particles contained in the magnetic recording layer are the abrasives (Al ₂ O ₃ (specific gravity: 3.
99), Cr ₂ O ₃ (specific gravity 5.21), Fe ₂ O ₃ (specific gravity 5.1)), its specific gravity is 2.5 or less, so the same weight was mixed in the magnetic recording layer. In that case, the volume ratio becomes larger than that of the conventional one. Therefore, the number of protrusions on the surface of the magnetic recording layer can be increased. Moreover, since the average particle size is as small as 0.1 to 2 μm, the formation of coarse protrusions is prevented, and the output decreases due to the coarse protrusions and S
It is possible to suppress deterioration of electromagnetic conversion characteristics such as deterioration of / N ratio.

As described above, according to the present invention, a large number of minute projections are formed on the surface of the magnetic recording layer by the fine particles having a relatively small specific gravity and an average particle diameter, and the durability and friction characteristics of the magnetic recording medium are greatly improved. It is possible to improve.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Example 1 A magnetic coating material having the following composition was prepared, and was coated on a polyethylene terephthalate film having a thickness of 75 μm by a conventional method so that the thickness of the magnetic recording layer after drying was 1.5 μm and dried. .. Then, after performing a surface smoothing treatment, 3.5
Floppy disks were manufactured by punching into inch disks.

Magnetic coating composition (parts by weight) Co-γ-Fe ₂ O ₃ (Hc = 700 Oe, SSA = 20 m ² / g): 100 Vinyl chloride-acrylic copolymer ("MR110" manufactured by Zeon Corporation): 18 Methylene diisocyanate-based polyester polyurethane (“N-2304” manufactured by Nippon Polyurethane Co., Ltd.): 18 Tolylene diisocyanate adduct of trimethylolpropane (“Coronate L” manufactured by Nippon Polyurethane Co.): 10 Silicone resin fine particles (“Tospearl” manufactured by Toshiba Silicone Co., Ltd.) 103 ″ Specific gravity = 1.32, average particle size = 0.3 μm): 5 α-Al ₂ O ₃ fine particles (specific gravity = 3.99, average particle size = 0.3 μm): 5 Carbon black fine particles (specific gravity = 1. 8, average particle diameter = 0.03 μm): 8 butyl stearate: 5 methyl ethyl ketone: 195 cyclo Hexanone: 195 The static friction between the magnetic recording layer of the obtained floppy disk and the head was measured by a rotary torque meter, while the dynamic friction was determined from the load current value of the 3.5-inch floppy disk drive during rotation.

After being kept in an environment of a temperature of 45 ° C. and a relative humidity of 80% for 7 hours, an environment of a temperature of 5 ° C. and a relative humidity of 50% is taken over 5 hours, and after being kept in this environment for 7 hours,
A durability test was conducted by repeating a cyclic environment change, which is one cycle of a total of 24 hours of returning to the initial environment over 5 hours. The evaluation was performed with or without deterioration such as output reduction (80% or less of the initial value) or occurrence of scratches on the medium, and was expressed by the number of cycles that could be performed without deterioration.

Further, a ferrite head having a head gap of 0.9 μm was used and rotated at 300 rpm to obtain 250
The S / N ratio was obtained by recording a KHz digital signal and measuring the ratio of the signal and noise during reproduction. The respective measurement results are shown in Table 1.

Example 2 Instead of silicone resin fine particles "Tospearl 103", "Tospearl 105" (specific gravity = 1.32, average particle diameter =)
A floppy disk was manufactured in the same manner as in Example 1 except that 0.5 μm) was used, and various characteristic values were determined in the same manner, and the results are shown in Table 1.

Example 3 Instead of silicone resin fine particles "Tospearl 103", "Tospearl 108" (specific gravity = 1.32, average particle diameter =)
A floppy disk was manufactured in the same manner as in Example 1 except that 0.8 μm) was used, and various characteristic values were determined in the same manner. The results are shown in Table 1.

Comparative Example 1 The same as Example 1 except that α-Al ₂ O ₃ fine particles (specific gravity = 3.99, average particle size = 0.3 μm) were used in place of the silicone resin fine particles “Tospearl 103”. A floppy disk was manufactured in the same manner as above, and various characteristic values were determined in the same manner, and the results are shown in Table 1.

Comparative Example 2 Instead of the silicone resin fine particles “TOSPEARL 103”, Cr ₂ O ₃ fine particles (specific gravity = 5.21, average particle diameter =)
A floppy disk was manufactured in the same manner as in Example 1 except that 0.4 μm) was used, and various characteristic values were determined in the same manner, and the results are shown in Table 1.

Comparative Example 3 Instead of silicone resin fine particles "Tospearl 103", "Tospearl 145" (specific gravity = 1.32, average particle diameter =)
A floppy disk was manufactured in the same manner as in Example 1 except that 4.5 μm) was used, and various characteristic values were determined in the same manner. The results are shown in Table 1.

[0033]

[Table 1]

From Table 1, it is clear that the present invention provides a high-performance magnetic recording medium which is excellent in both durability and friction characteristics and has a good S / N ratio.

[0035]

As described in detail above, according to the magnetic recording medium of the present invention, it is possible to obtain a magnetic recording medium having excellent durability and friction characteristics and a high S / N ratio.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic recording layer provided on a non-magnetic support, wherein the magnetic recording layer has a specific gravity of 2.5.
Hereinafter, a magnetic recording medium containing fine particles having an average particle diameter of 0.1 to 2 μm.