JPH01290122A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable the smooth operation of a sand mill and to enhance dispersion degree and dispersion efficiency so that the good characteristics of the magnetic recording medium are obtd. by using zirconia beads and applying shearing stresses within a specific range in the state of a specific packing ratio to magnetic particles to disperse said particles, then coating the resulted magnetic coating compd. on a base. CONSTITUTION:The zirconia beads are used and the shearing stresses are applied to the magnetic particles within the 1X10<4>-1X10<5>dyne/cm<2> range in the state of >=55% packing ratio of the beads to disperse the magnetic particles. The resulted magnetic coating compd. is coated on the base. The zirconia beads specified in the surface roughness to <=1.5, more preferably <=0.7, further more preferably <=0.35 max. height Rmax are adequately used. The dense zirconia beads having >=5.5 sp. gr. are preferably used. The magnetic coating compd. having the excellent dispersibility of the magnetic particles is thereby obtd. and the sure operation of the sand mill is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a magnetic recording medium, and particularly to a method for obtaining a magnetic paint by dispersing magnetic particles using a sand mill.

[Conventional technology]

As is well known, magnetic recording media are produced by dispersing magnetic particles in a dispersion consisting of a solvent, a binder, and other additives.
It is generally obtained by coating a support.

In this case, the method for dispersing magnetic particles is (1)
There are two methods: kneading with a high viscosity kneading device such as a kneader and then dispersing using a media dispersion device such as a sand mill or attritor; and (2) using a daysilver, high-speed disperser, homogenizer, etc. without using a kneading device. It can be roughly divided into two methods: pre-mixing at a relatively low viscosity and then dispersing using the above-mentioned media dispersing machine.

In recent years, sand mills have become mainstream as the above-mentioned medium dispersion machine because of their strong dispersion power. The sand mill is a 194-year-old development of the attritor.
It was developed and improved from 1960 to 1960. The dispersion principle is to fluidize the magnetic coating liquid and beads using several rotating disks, and use the impact force and shear force of the beads to disperse the magnetic particles.

At the beginning of the development of the sand mill, it was used as a bead, as the name suggests, Ottawa 5 and
However, due to problems with the particles being dispersed, the viscosity of the dispersion liquid, or contamination, beads (
Glass, steel, alumina, zirconia, etc. are used as dispersion media.

The surface roughness of the beads in this case is 2. O8 or higher, usually 3. O8 or higher is used. 3. The glass should be coated with 3. There are some that are O8 or higher, but it is 3.0 in one use. It becomes O8 or higher.

On the other hand, with the increase in magnetic recording density in recent years, magnetic particles have become increasingly finer, and currently the BTE value is 5.
Particles of about 0 rrr/g are at a common level.

In such cases, the dispersion level of fine particles is as follows:
It is considered to be completely on the order of submicrons.

It is becoming clear that the dispersibility of such fine particles is also controlled by the beads of the media disperser, and attempts have been made to improve the dispersibility by modifying the shape of the beads.

[Problem to be solved by the invention]

However, although the beads used in media dispersion machines such as sand mills have a large effect on dispersibility, the present inventors have found that the shape of the beads is not so dominant, but rather the material and surface roughness of the beads. is dominant.

On the other hand, as a media dispersing machine, a sand mill is suitable because of its high dispersion power, but it has an effective volume of 30 mm, especially for production lines. !
When installing the above items and using zirconia beads with a high specific gravity as beads, a considerable load is applied to the bottom of the vertical sand mill, resulting in an overload during start-up operation and making it impossible to start up.

Therefore, it may be possible to start up the vertical sand mill by lowering the filling rate of zirconia beads, but the degree of dispersion and dispersion efficiency are low and there are many practical problems.

Therefore, the main object of the present invention is to provide a method for manufacturing a magnetic recording medium that allows smooth operation of a sand mill, has a high degree of dispersion and high dispersion efficiency, and exhibits good magnetic recording medium characteristics. .

[Means to solve the problem]

The above problem is that the effective volume of the magnetic particles in the dispersion liquid is 3.
In a sand mill of 01 or more, using zirconia beads and with a filling rate of 55% or more, shear stress is applied within the range of IXIO' to IX10'dyne/- to disperse the magnetic particles, This problem can be solved by applying the resulting magnetic paint onto a support.

[Specific structure of the invention]

The present invention will be explained in more detail below.

As the medium disperser in the present invention, a sand mill, particularly a horizontal sand mill, is used. In addition, the present invention is applied to those whose effective volume is 3Of or more.

Zirconia beads are particularly used as the dispersion medium, and the surface roughness of the beads is 1.5 or less in maximum height Rmax, more preferably 0.7 or less, and more preferably 0.3.
5 or less is preferably used. The conventionally used zirconia beads are 3. The OS is even rougher than that. It is desirable to use dense zirconia beads with a specific gravity of 5.5 or more.

The particle size of the zirconia beads is preferably 0.5 to 3.0 mm.

Conventionally, glass beads have been the mainstream as beads for sand mills, but after one use, their surface roughness Rmax is no longer as high as 3. It becomes rougher than O8,
There are restrictions from the material standpoint. Also, with steel, it is not possible to obtain a material with low surface roughness.

On the other hand, zirconia beads have high wear resistance and
The surface roughness hardly changes even after long-term use.
Rather, the surface roughness tends to decrease due to mutual rubbing. Moreover, although there are various grades of zirconia beads, their surface roughness is limited to the maximum height Rmax.
If the value is 1.5 or less, the dispersibility will be further improved.

The filling rate of zirconia beads is 55% or more, and the filling rate is 55% or more.
80% is preferred. The filling rate is 100Vt/1, where the apparent volume when a group of beads is put into a certain container is 1, the true volume of the beads is 2, and the volume of the dispersion is 2.
CVt +V).

In the present invention, magnetic particles are dispersed in a dispersion liquid using a horizontal sand mill, and the shear stress at that time is IXI
O' 〜I X10'dyne /an! It is said that

The shear stress is measured by measuring the viscosity of the coating liquid using a precision viscometer such as Hague. It can be determined by the following equations (11 and (2)).

Shear stress τ=ηγ...(2
) Magnetic particles in the present invention include γ-Fe2O3,
Co-containing r FezO, 1% Co coated T Fez
O:+, Fe30=, Co-containing Fe3O4, Crow
oxide ferromagnetic powder, Fe-Co-Ni alloy, Fe
-11! alloy, Mn-B1 alloy, Fe-Al-P alloy, Fe-Co-Ni-Cr alloy, Fe-Ni-Zn alloy, Fe-Co-N1-P alloy, Fe-Ni alloy, Co
-N1-P alloy, Co-Ni alloy, Co-P alloy, Fe
-Mn -Zn alloy, Fe-Ni-Mn alloy, Fe-
Various ferromagnetic powders such as Ni-Cr-P alloy, Fe-Ni-Co-Zn alloy, metal ferromagnetic powder whose main component is Fes Nix C0% Cr, etc. can be used.

The magnetic particles are dispersed into a dispersion liquid through a dispersion process using a medium disperser according to the method (1) or (2) described above.

The dispersion liquid mainly contains a binder and an organic solvent, and examples of the binder include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinylidene chloride-acrylonitrile copolymer, butyl acrylate-acrylonitrile. copolymers, cellulose resins, epoxy resins,
Polyvinyl butyral resin, polyurethane resin, polyester resin, synthetic rubber resin, etc. can be used.

Examples of solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl acetate, ethyl acetate, butal acetate, ethyl lactate, ethylene glycol monoacetate, etc. esters; ethers such as ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, etc. Halogenated hydrocarbons and the like can be used.

The above magnetic paint may contain dispersants, lubricants,
Abrasives, antistatic agents, curing agents, plasticizers, surfactants, etc. may be added.

Coating methods for coating the magnetic paint onto the support to form a magnetic layer include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coat, cast coat,
Spray coat, extrusion type coating method JP-A-57-847
No. 71, No. 58-104666, No. 60-23817
An extrusion type coating method such as No. 9 is preferable from the viewpoint of uniformity of film thickness.

A magnetic layer formed by coating a magnetic paint on a support by such a method is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried. Further, a magnetic recording medium is manufactured by performing surface smoothing processing or cutting into a desired shape if necessary.

Supports include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose acetate and cellulose diacetate, plastics such as polycarbonate, metals such as AlXZn, and glass BN.

Ceramics such as Si carbide, porcelain, and earthenware are used.

The thickness of the support is approximately 3 to 100 mm in the case of a sheet.
The thickness is about μm, preferably 5 to 50 μm.

Note that the present invention is particularly effectively applied when the magnetic particles have a BET value of 40 g/M or more.

〔Example〕

Next, the effects of the present invention will be clarified by examples.

Co-Fed with a BET value of 45rd/g as magnetic powder,
Using powder and various beads with an average particle size of 1.2,
After dispersing various types using a sand mill, 14
A magnetic tape was obtained after coating on a μm polyethylene terephthalate (PET) base using an extrusion type coating device.

Table 1 shows the beads, sand mill and dispersion conditions used, as well as the measurement results of the squareness ratio of the obtained magnetic tape.

According to the above results, the smaller the surface roughness of zirconia beads, the higher the squareness ratio, which is an index of dispersibility, and the higher the filling rate and using a horizontal sand mill, the higher the squareness ratio. I also know it's expensive.

(Effects of the Invention) As described above, according to the present invention, a magnetic paint with excellent dispersibility of magnetic particles can be obtained, and a sand mill can be operated reliably.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic explanatory diagram of a simple method for measuring shear effectiveness. Figure 1

Claims (1)

[Claims] (1) Magnetic particles are applied to a dispersion liquid in a horizontal sand mill with an effective volume of 30 liters or more, using zirconia beads and at a filling rate of 55% or more, with a shear stress of 1×10^4 to 1× A method for manufacturing a magnetic recording medium, which comprises adding the magnetic particles within a range of 10^5 dyne/cm^2, dispersing the magnetic particles, and applying the obtained magnetic paint onto a support.