JPH04153914A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the surface smoothness of a magnetic layer and to enhance output characteristics as well as to reduce the coefft. of friction and rotational torque and to enhance travelling performance by incorporating nonmagnetic inorg. powder having average particle size within a specified range and a specified particle size distribution into the magnetic layer. CONSTITUTION:Nonmagnetic inorg. powder having average particle size D50 within the range of 1/2 of the thickness of a magnetic layer to the thickness of the layer is relatively coarse in the magnetic layer having <=1.0mum thickness and has such a narrow particle size distribution as D25/D75<=1.4. When the nonmagnetic inorg. powder is incorporated into the magnetic layer, the surface smoothness of the magnetic layer is improved and output characteristics are enhanced. The coefft. of friction and the rotational torque are reduced and the travelling performance of a digital magnetic recording medium, especially a floppy disk having <=1.0mum thickness of the magnetic layer is further enhanced.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium, and more specifically, the magnetic layer has good surface smoothness and excellent eight characteristics, and has a small friction coefficient and rotational torque. This invention relates to a magnetic recording medium with excellent running properties.

[Prior Art] In general, magnetic recording media, which are made by coating and drying a magnetic paint consisting of magnetic powder, bonding resin, organic solvent, and other necessary components on a substrate, are subjected to violent contact with magnetic heads etc. during recording and reproduction. Since the magnetic layer runs while sliding, it is required that the coefficient of friction of the magnetic layer is small and the running performance is excellent. In particular, floppy disks are required to have a sufficiently low rotational torque.

For this reason, 11! of the magnetic layer! As a measure to reduce the coefficient of friction and rotational torque, various non-magnetic inorganic powders are mixed into the magnetic layer, such as large particle carbon black, molybdenum disulfide, graphite powder, alumina, and silica. , non-magnetic inorganic powder such as silicon carbide is mixed in.

[Problem to be solved by the invention]

However, in recent years, especially in digital magnetic recording media such as floppy disks, there has been a tendency to reduce the thickness of the magnetic layer as recording density has improved. However, general large-particle non-magnetic inorganic powders have a wide particle size distribution, and there are particles whose particle size is larger than the thickness of the magnetic layer. Addition of this compound has the disadvantage that the surface smoothness of the magnetic layer deteriorates and the output characteristics deteriorate.

(Means for Solving the Problems) The present invention was made as a result of various studies in view of the above circumstances.
The average particle size (D50) is within the range of 1/2 of the thickness of the magnetic layer to the thickness of the magnetic layer, and the particle size distribution (025/D, 5)
By containing a non-magnetic inorganic powder with a coefficient of 1.4 or less, the coefficient of friction and rotational torque can be reduced to sufficiently improve running performance, and the surface smoothness of the magnetic layer can also be improved to improve output characteristics. This is a sufficient improvement.

The non-magnetic inorganic powder used in this invention has an average particle diameter (D50) within the range of 1/2 of the thickness of the magnetic layer with a thickness of 1.0 μm or less to the thickness of the magnetic layer, It is preferable that the particle size distribution (D25/D?S) is 1.4 or less, and in this way, the average particle size (D,.) ranges from 1/2 of the thickness of the magnetic layer to 1/2 of the thickness of the magnetic layer. Non-magnetic inorganic powder within the range of
'rs) is 1.4 or less, so the particle size distribution is narrow.

However, when this kind of non-magnetic inorganic powder is contained in the magnetic layer, the friction coefficient and rotational torque are reduced, and this is especially true for digital magnetic devices such as Fronby disks with a magnetic layer thickness of 1.0 μm or less. The running properties of the recording medium are further improved, and the surface smoothness of the magnetic layer having a thickness of 1.0 μm or less is improved, resulting in improved output characteristics. Note that this type of non-magnetic inorganic powder has a recording density of 15 kfci.
Favorable results can be obtained when used in the above magnetic recording media.

On the other hand, when the particle size distribution (D 25 / D ts ) is 1
．． Conventionally known non-magnetic inorganic powders with a wide distribution larger than 4 can achieve the desired effect when the thickness of the magnetic layer is 1.0 μm or more, but when the thickness of the magnetic layer is 1.0 μm or less, The desired effect cannot be obtained, and in particular, if the thickness is less than 0.7 μm, the surface smoothness of the magnetic layer deteriorates, making it impossible to prevent the output characteristics from deteriorating. In addition, if the average particle size of the non-magnetic inorganic powder is smaller than 1/2 of the thickness of the magnetic layer with a thickness of 1.0 μm or less, the friction coefficient and rotational torque will not be sufficiently reduced; If the particle size is larger than the thickness of the magnetic layer, which is 1.0 um or less, it is not preferable because the surface smoothness of the magnetic layer will be impaired.

Examples of such non-magnetic inorganic powders include those whose average particle diameter (D5°) is within the range from 1/2 of the thickness of the magnetic layer with a thickness of 1.0 μm or less to the thickness of the magnetic layer. A carbon blank with a particle size distribution (D 25 / D '+5) of 1.4 or less, α-iron oxide powder, alumina powder, zirconia powder, silicon carbide powder, garnet powder, silicon oxide powder, chromium oxide powder, oxidized Titanium powder or the like is preferably used. The amount used is 0 for magnetic powder.
．． The amount is preferably within the range of 1 to 20.0% by weight; if it is too small, the desired effect cannot be obtained, and if it is too large, the magnetic powder will be relatively reduced, which may lead to deterioration of electromagnetic conversion characteristics. .

The magnetic recording medium of the present invention can be manufactured according to a conventional method (for example, when the average grain size (Di.) is 1.0
The particle size distribution (Dz, /D-s) is within the range of 1/2 of the thickness of the magnetic layer to 1/2 of the thickness of the magnetic layer of μm or less, and the particle size distribution (Dz, /D-s) is 1.
4 or less non-magnetic inorganic powder is mixed and dispersed with magnetic powder, binder resin, organic solvent, etc. to prepare a magnetic paint, and this is applied onto a substrate such as a polyethylene terephthalate film using any coating method such as a roll coater. and dry it.

Here, as the magnetic powder, for example, γ-Fe203
In addition to powder, Fe:Ion powder, CO-containing T-Fe, O8 powder, Co-containing Fesoa powder, Cr○2 powder, various conventionally known magnetic powders such as Fe powder, Co powder, Fe-Ni powder, barium ferrite powder, etc. Widely used.

In addition, binder components include vinyl chloride-vinyl acetate copolymers, cellulose resins, polyurethane resins, polyester resins, acrylic resins, rubber resins, and isocyanate compounds, which are usually magnetic powder binders. Those used as ingredients are widely used.

In addition, various additives commonly used in magnetic paints,
For example, a lubricant, a dispersant, an antistatic agent, etc. may be optionally added.

〔Example] Next, embodiments of the invention will be described.

Example 1 α-F eliff powder (coercive force 1630, 100 parts by weight Oersted, saturation magnetization 135 emu/g, specific surface area 45rd/g) vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
Polyurethane resin (Nippon Boliu 8.5; manufactured by Rethan Kogyo Co., Ltd.; Nimboran N2301) Trifunctional low molecular weight isocyanate-5,6 compound (manufactured by Nippon Polyurethane Kogyo Co., Ltd.; Coronate L) Seahosta KE -E50 (Nippon Shokubai 5,0 manufactured by Soda Kagaku Co., Ltd.; SiO□Inorganic powder oleyl oleate 7.0〃Cyclohexanone 120〃Toluene
120 This composition was kneaded and dispersed in a ball mill for 72 hours to prepare a magnetic paint. This magnetic paint was applied onto a polyethylene terephthalate film with a thickness of 62 μm so that the thickness after drying would be 0.6 μm. After drying and calendering, this was punched out into a disk shape to produce a magnetic disk. did.

Comparative Example 1 A magnetic disk was prepared in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of Sehacarb MT-CI (manufactured by Columbia Carbon Co., Ltd. - carbon black) was used in place of Seahosta KE-E50. was created.

Comparative Example 2 In the composition of the magnetic paint in Example 1, the same amount of Seahosta KEE30 (manufactured by Nippon Shokubai Chemical Co., Ltd.; 5in2 inorganic powder) was used instead of Seahosta KE-E50.
A magnetic disk was produced in the same manner as in Example 1.

Comparative Example 3 A magnetic disk was produced in the same manner as in Example 1, except that in the composition of the magnetic paint in Example 1, the same amount of alumina AESI2 (manufactured by Sumitomo Chemical Co., Ltd.; alumina) was used in place of Seahosta KE-E50. .

For the magnetic disks obtained in each example and comparative example, the surface roughness of the magnetic layer, output level, rotational torque, average particle size and particle size distribution of the non-magnetic inorganic powder contained in the magnetic layer were measured using the following method. It was measured.

<Surface Roughness of Magnetic Layer> Using a stylus type surface roughness meter, the center line roughness (Ra value) of the magnetic disk was measured under conditions of stylus R = 2 μm and cutoff 0.08 mm.

<Output level, rotational torque> Manufactured by NEC; Floppy disk drive FD133
1, the output when recording and reproducing the signal (34.9 kfci) on the innermost circumference 2F was taken as the output level, and the torque during rotation was measured.

<Average particle size and distribution of inorganic powder in the magnetic layer> The size of 1000 non-magnetic inorganic powders was counted from a transmission electron micrograph of a cross section of the magnetic layer, and the average particle size was determined from the cumulative curve. and particle size distribution. /D7. I asked for

Table 1 below shows the results.

Table 1 [Effects of the Invention] As is clear from Table 1 above, the magnetic disks obtained in the example process had a higher surface roughness than the magnetic disks obtained in Comparative Examples 1 and 3. The magnetic recording medium obtained by this invention has a small size, a high output level, and a small rotational torque (and a small rotational torque compared to the magnetic disk obtained in Comparative Example 2). Good, excellent output characteristics, and low rotational torque.
It can be seen that the running performance is excellent.

Patent applicant: Hitachi Maxell, Ltd.

Claims (1)

[Claims] 1. The average grain size (D
_5_0) is within the range of 1/2 of the thickness of the magnetic layer to the thickness of the magnetic layer, and the particle size distribution (D_2_5/D_7_5)
A magnetic recording medium characterized in that it contains a non-magnetic inorganic powder having a magnetic flux of 1.4 or less.