JPH0481254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media, particularly magnetic disks.

BACKGROUND TECHNOLOGY AND PROBLEMS In conventional magnetic disks, the disk is rotated at high speed and its centrifugal force is used to make it rigid and flat, thereby making it possible to press the magnetic head against the magnetic disk and reducing separation loss. I try to let them do it. Therefore, the purpose of the antistatic layer in conventional magnetic disks was to take into consideration the generation of static electricity caused by the high speed rotation of the disk.

With recent technological advances in high-density and short-wavelength recording of magnetic disks, there has been a trend toward smaller disk diameters and lower rotational speeds.

The decrease in centrifugal force due to the miniaturization of disks and low rotational speeds increases separation loss, so at the same time there is a demand for flattening of the disk itself, it is also necessary to strengthen the pressure bonding pad on the back layer in order to improve the so-called contact characteristics. It becomes necessary to press it. For this reason, the back layer must have durability against the pressure pad that presses the disk against the magnetic head.

Purpose of the Invention In view of the above-mentioned points, the present invention provides a magnetic recording medium in which the magnetic layer is formed mainly of magnetic powder and a binder, that is, a coating type magnetic recording medium, such as a magnetic disk.
By paying special consideration to the back coat layer, warpage of the magnetic disk can be effectively avoided, unstable rotation can be prevented, and the durability of the back layer can be improved.

Summary of the Invention In the present invention, a magnetic layer mainly consisting of magnetic powder and a binder is adhered to one side of a flexible non-magnetic support, and a magnetic layer mainly consisting of an inorganic pigment and a binder is applied to the other side. In particular, the thickness of the non-magnetic support is 20 to 100 μm, and the relationship between the thickness A of the magnetic layer and the thickness A′ of the back coat layer is 0.8A≦. A′≦1.2A, and the average surface roughness is 0.1μm or less.

That is, in the present invention, warping in a coated magnetic recording medium such as a magnetic disk provided with such a back coat layer is caused by the magnetic layer and back coat layer formed on both sides of the nonmagnetic support. Focusing on the fact that this occurs due to the difference in the actual amount of thermal shrinkage due to the difference in film thickness, we calculated the film thickness of the magnetic layer and back coat layer, which are formed by sandwiching a nonmagnetic support. Select to equalize the amount of heat shrinkage.

In other words, in the present invention, in a coating type magnetic recording medium, there is almost no difference in the coefficient of thermal expansion due to the difference in the materials of the magnetic layer and the back coat layer, that is, the amount of thermal contraction is largely dependent on the thickness of the magnetic layer and the back coat layer. Special consideration should be given to the thickness of the magnetic layer and the back coat layer.

Unlike magnetic recording media, the back coat layer of a magnetic disk, especially the antistatic layer, is so-called long or tape-shaped.Due to its structure, it is not required to reduce the winding characteristics and coefficient of friction, which may cause dropouts. Durability of the crimp pad becomes important.

In the present invention, the average surface roughness of the back coat layer is set to 0.1 μm or less, as described above.
This is because it was recognized that the durability was improved when the average surface roughness was set to 0.1 μm.

The back coat layer can be carbon black, graphite, tungsten disulfide, molybdenum disulfide, or high hardness reinforcing materials such as Al ₂ O ₃ , Cr ₂ O ₃ , SiO ₂ , TiO ₂ , CaCO ₃ , CaO, MgO, MnO. Alternatively, it may be filled with relatively soft inorganic particles such as r-Fe ₂ O ₃ , Fe ₃ O ₄ , CrO ₂ or the like. In any case, the average particle size should be approximately 1 μm or less,
The particle size varies depending on the type of particles, and for example, when carbon black is used, it is preferable that the average particle size is about 500 mm or less.

Furthermore, the blending ratio (P/B ratio) between the weight P of the inorganic filler and the weight B of the binder described above can be adjusted over a wide range depending on the inorganic pigment used, but for example, when carbon black is used, P/B ratio B is
A range of 0.1 to 2.0 is preferred.

In addition, the thickness of the flexible non-magnetic film is 20~
The reason for selecting 100 μm is that if it is too thin, it will be difficult to ensure sufficient contact with the magnetic head, and if it is too thick, separation loss will increase.

Figure 1 shows the results of measuring the ratio of the thickness A of the magnetic layer to the thickness A' of the back coat layer and the amount of curl, or warpage, of the magnetic disk, and it is clear from this that 0.8A≦A. ′≦1.2A, the occurrence of the curl could be kept sufficiently small, and the occurrence of unstable rotation and dropout during rotation of the magnetic disk due to this curl could be avoided.

In addition, as a method to reduce the surface roughness to 0.1μm or less,
The pigment is selected by selecting the particle size or composition of the pigment contained in the back layer, by the dispersion method thereof, by calendering, or by a combination of any of these methods. be able to. As shown in FIG. 2, the calendering process can be carried out by meanderingly guiding an original magnetic tape 3 in the form of a wide tape, which will later be cut out as a disk, between a metal roll 1 and an elastic roll 2. However, in this case, the temperature of the metal roll is 60~120℃, and the linear pressure is 150~120℃.
It is desirable to select 300Kg/cm.

Example Example 1 Prepare a mixture with the following composition.

Ferromagnetic acicular alloy (coercive force: 1180Oe, BET specific surface area: 45m ² /g) ...100 parts by weight Vinyl chloride-vinyl acetate copolymer (product name
VYHH Union Carby Co., Ltd.) ... 10 parts by weight thermoplastic polyurethane resin (product name Estan
5701, manufactured by B.F. Gutdoritsu)
...6 parts by weight Cr ₂ O ₃ ...10 parts by weight lecithin ...2 parts by weight fatty acid ester ...1 part by weight toluene ...50 parts by weight methyl ethyl ketone ...50 parts by weight cyclohexanone ...50 parts by weight A mixture having the above composition After kneading in a ball mill for 24 hours, 5 parts by weight of an isocyanate compound (trade name Coronate L, manufactured by Nippon Polyurethane Industries, Ltd.) was added and dispersed with high speed shearing for 1 hour to prepare a magnetic paint.

This magnetic paint was coated on a non-magnetic support made of polyethylene terephthalate film with a thickness of 36 μm at a coater speed of 20 so that the thickness after drying was 4 μm.
A raw magnetic tape was prepared by applying the film at a rate of m/min and passing it through an alternating current solenoid (frequency 50 Hz, 5 A) while the film was in a fluid state.

Next, in order to form a back coat layer, a paint having the following composition was first prepared.

Carbon black (Asahi Carbon #55 manufactured by Asahi Carbon Co., Ltd., furnace type: average particle size approximately 100μm)
...50 parts by weight of polyurethane resin (Estan manufactured by Gutsudoritsuchi Co., Ltd.)
5702, thermoplastic polyurethane) ...70 parts by weight Epoxy resin (trade name Epicron 351, manufactured by Dainippon Ink Co., Ltd.) ...30 parts by weight Toluene ...150 parts by weight Methyl ethyl ketone ...150 parts by weight Cyclohexanone ...100 parts by weight Each of these After mixing the raw materials in a ball mill for 15 hours, 10 parts by weight of an isocyanate compound (trade name: Coronate L manufactured by Nippon Polyurethane Industries, Ltd.) was added.
Stir in a stirrer for 30 minutes to prepare a paint for the back coat layer. This back coat layer paint was applied to the back side of the above-mentioned original magnetic tape so that the thickness after drying was 3.5 μm.
The coating was applied at a coater speed of 20 m/min so that the coating thickness was 20 m/min, and supercalender treatment was performed. This supercalendar process, as shown in Figure 2,
Elastic rolls 2 and metal rolls 1, each having an elastic urethane coating 2a applied to the circumferential surface of a metal core 2a, are alternately 7
The raw magnetic tape 3 is compressed and run in a meandering manner between adjacent rolls 1 and 2 with the magnetic layer side facing the metal roll by means of calendering means arranged in stages. In this case, the temperature applied to the metal roll 1 is 100℃, and the linear pressure is 300Kg/
cm, and the calendar speed was 40 m/min. Next, this tape 3 was punched out to a diameter of 47 mm to produce a magnetic disk.

Examples 2 to 4 Magnetic disks were prepared in the same manner as in Example 1, but the thicknesses A and A' and surface roughness of the magnetic layer and backcoat layer were varied. Those numerical values are as described in each example column of the table in FIG. The results of measuring the amount of curl, powder falling off of the back coat layer, and number of dropouts for each of these magnetic disks are shown in the table of FIG. In the same table, Comparative Examples 1 to 4 are magnetic disks prepared by the same method as in Example 1, but the respective thicknesses A and A' of the magnetic layer and the back coat layer are within the range not based on the structure of the present invention. and surface roughness, these values are as entered in each column of the same table. Note that the surface roughness was measured using a stylus type roughness meter manufactured by Kosaka Ken Co., Ltd. In addition, when measuring the amount of powder falling off, ◎ indicates that there was very little powder falling off, ○ mark means that there is little powder falling off, △ mark means that some powder falling off is observed, × mark means that there is a lot of powder falling off, and XX mark was extremely remarkable.

As mentioned above, in the present invention,
It can be seen that the effects of a small amount of curl, little powder falling, and small dropout can be obtained.

In each of the examples according to the present invention, the pad was applied from the side of the back coat layer, and after running on a rotating sheet record, scratches on the surface of the back coat layer were visually evaluated. When the surface roughness was selected to be 0.1 μm or less, these scratches were not visible at all, but when the surface roughness of the back coat layer was set to 0.2 to 0.3 μm,
In the case where the diameter was m, numerous scratches on concentric circles were visually observed.

Effects of the Invention According to the magnetic recording medium according to the present invention, a magnetic recording medium with less curling can be obtained, so that a magnetic disk formed thereby has the disadvantage of exhibiting unstable rotation during rotation. It is possible to effectively avoid the occurrence of dropouts, to form a back layer with excellent durability, and to make the pad pressure sufficiently large, making it an excellent choice for small, low-speed rotating magnetic disks. characteristics can be obtained.

[Brief explanation of the drawing]

Figure 1 is a measurement curve of the amount of curl used to explain the present invention, Figure 2 is a diagram used to explain calendering of a magnetic head according to the present invention, and Figure 3 is a table showing the measurement results of each characteristic of each example. It is a diagram. 1 is a metal roll, 2 is an elastic roll, and 3 is an original magnetic tape.

Claims (1)

[Claims] 1. A magnetic layer mainly composed of magnetic powder and a binder is formed on one side of a flexible non-magnetic support, and a back coat mainly composed of an inorganic pigment and a binder is formed on the other side. In the magnetic recording medium formed with a layer, the thickness of the non-magnetic support is 20 to 100 μm, and the thickness A of the magnetic layer and the thickness A′ of the back coat layer are 0.8A≦A′≦ 1.2A and an average surface roughness of 0.1 μm or less.