JPH0655912B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a magnetic paint prepared by dispersing and mixing needle-shaped magnetic powder (hereinafter, referred to as “magnetic particles”) in a solvent containing a binder is coated on a non-magnetic support to make it magnetic. The present invention relates to a magnetic recording medium manufacturing method for manufacturing a recording medium.

The magnetic coating material used for producing such a magnetic recording medium is usually prepared by dispersing and mixing magnetic particles, polymer binders, additives and the like in a solvent using a mixing device such as a ball mill and a sand mill. .

In the manufacturing process of coating type magnetic recording media used in various equipment including audio and video recorders,
The step of uniformly dispersing and mixing the magnetic particles in the solvent containing the binder occupies a very important position in determining the final performance of the obtained magnetic recording medium. If the dispersion and mixing of magnetic particles is insufficient, aggregates of magnetic particles may form in the coating film and cause noise, or the surface of the coating film that depends on the dispersion state of the magnetic particles in the magnetic coating material Inconvenience arises because the smoothness deteriorates. However, if the mixture is vigorously mixed for sufficient dispersion mixing, the magnetic particles will be destroyed by the physical force during the mixing, so that the magnetic properties such as Hc will be deteriorated and the transfer amount will be increased. The problem arises.

Further, in recent years, the need for high-density recording media has increased, and it has become necessary to increase the dispersion mixing efficiency in accordance with the tendency of magnetic particles to become finer. When mixing conventional magnetic paints, add balls or beads to the magnetic paint and rotate the blade, or rotate or vibrate the entire container to move the balls or beads so that they do not collide with each other. The impact force of was used to loosen the aggregate of magnetic particles. However, in the conventional method, since the material of the balls and beads used is generally steel or glass, if the material is glass, it tends to be crushed at the time of impact to produce glass crushed pieces, and On the contrary, in the case of steel, it is easy to break the particles of the acicular magnetic powder to reduce the axial ratio of the magnetic particles, which gives an unfavorable result to the magnetic recording medium.

That is, since the glass beads have a relatively small impact at the time of bead impact and the mixing efficiency is originally low, the rotational speed of the blade that stirs the beads is increased to increase the efficiency. It is unavoidable that the glass fragments are destroyed during mixing, and if the glass fragments remain in the tape coating, they cause dropout. Although the dropout is improved by using the steel ball beads that are not easily broken by themselves, instead, the particles of the needle-shaped magnetic powder are broken by the collision between the steel ball beads and the magnetic characteristics such as Hc. However, it is difficult to control the mixing conditions. For this reason, when steel ball beads are used, the impact force at the time of collision between beads must be alleviated by increasing the viscosity of the paint. However, if the viscosity of the magnetic paint is increased in this way, a new problem arises that the coating itself becomes difficult.

Therefore, the present invention provides a method of manufacturing a magnetic recording medium, which has improved the drawbacks of the prior art.

The present invention provides a solvent containing a binder and a bead having a predetermined bead diameter which are hollow so as to be within a predetermined bead weight / bead volume ratio range, and a needle-shaped magnetic powder in the method described at the beginning. In addition to the above, by moving the beads, the acicular magnetic powder is uniformly dispersed and mixed in the binder-containing solvent to prepare the magnetic paint, and the beads are separated from the magnetic paint. A magnetic recording medium in which beads are separated is applied onto the non-magnetic support, whereby mixing of crushed pieces of the beads into the magnetic coating and destruction of the acicular magnetic powder are suppressed. It is something that is done.

The beads having a hollow structure used in the present invention have a bead weight / bead volume ratio (called bead weight / bead volume ratio) of 3.0 to 7.0 (g).
/ Cm ³ ) and the bead diameter is 0.8
To 2.5 mm, preferably 1.0 to 2.0 mm. This bead weight / bead volume ratio is
If it is too small, the dispersion efficiency decreases, and if it is too large, the magnetic particles are destroyed, which is not preferable. Further, if the diameter of the beads is too small, the dispersion efficiency is lowered and it becomes difficult to separate the beads with a filter, while if it is too large, the dispersion efficiency is lowered and the magnetic particles are crushed, which is not preferable. In the present invention, the material of the beads having a hollow structure is not particularly limited as long as the above conditions are satisfied, and conventionally, the specific gravity is too large and tends to be shunned because it causes the destruction of the magnetic particles. It is also possible to use metals with a large specific gravity, such as existing stainless steel. Therefore, examples of the material of the beads that can be used in the present invention include metals having a relatively high specific gravity such as steel, titanium, and titanium alloys, and ceramics having a relatively high specific gravity such as zirconium oxide and alumina.

The magnetic powder used in the present invention is not particularly limited as long as it is used for a coating type magnetic recording medium, and for example, γ-Fe ₂ O ₃ , Fe.
₃ O ₄ , iron oxide in an intermediate oxidation state between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃
O ₄ , iron oxide in an oxidation state intermediate between Co-containing γ-Fe ₂ O ₃ and Fe ₃ O ₄ , the iron oxide further containing one or more metal elements (particularly transition metal elements), Oxide-based magnetic powder such as iron oxide having a coating layer mainly composed of Co oxide or hydroxide, CrO ₂ or CrO ₂ surface-treated to form a Cr ₂ O ₃ layer, or Fe , Co, Ni and other metals or Fe-Co alloys, Fe-Ni alloys, Fe-Co-Ni alloys, Co-N
i-P alloy, Co-Ni-Fe-B alloy, Fe-Ni-
Zn alloy, Fe-Mn-Zn alloy, Fe-Co-Ni-
Examples include ferromagnetic fine powders such as P alloys. In addition, aluminum oxide, chromium oxide, silicon oxide, etc. as abrasives, carbon black, etc. as antistatic agent, molybdenum disulfide, graphite, silicone oil, olive oil, etc. as lubricant, lecithin etc. as dispersant, etc. It can be added. Examples of the binder that can be used include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl propionate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate. -Vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-chloride Vinylidene copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-
Styrene copolymer, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-methacrylic acid copolymer,
Styrene-butadiene copolymer, formal resin, acetal resin, butyral resin, phenol resin, polyester resin, polyurethane resin, polyamide resin, urea resin, urea-formaldehyde resin, melamine resin, epoxy resin, alkyd resin, phenoxy resin, polyfluoride Examples thereof include vinyl and mixtures thereof. Further, usable solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as methanol and ethanol, esters such as methyl acetate, ethyl acetate, butyl acetate and ethyl butyrate, ethylene glycol monoethyl. Examples thereof include ethers, glycol ethers such as ethylene glycol dimethyl ether and dioxane, aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic hydrocarbons such as hexane and heptane.

The magnetic coating material obtained as described above is applied to a non-magnetic support according to a usual coating method such as a doctor blade method or a gravure coating method to obtain a desired magnetic recording medium. The non-magnetic support used, for example, polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose diacetate, cellulose derivatives such as cellulose triacetate, polycarbonate, polyvinyl chloride, polyimide,
Examples thereof include polyamide, metals such as aluminum and copper, and paper.

Hereinafter, the present invention will be described with reference to comparative examples and examples.

Examples 1 to 4 and Comparative Examples 1 to 6 Magnetic paints having the following compositions were prepared as follows.

After preliminarily stirring 10 liters of the magnetic coating material having the above composition, the diameter of each of the materials and structures shown in Table 1 was 1.4 to 1.6 in a 25 liter capacity sand mill.
Each of the 10 types of spherical beads in the range of mm was used and mixed for about 3 hours. The amount of beads was 10 liters in volume. The material of the rotary blade of the mixer was steel and the rotation speed was 1,200 rpm.

The 10 kinds of magnetic paints thus obtained were applied on a polyethylene terephthalate film to a thickness of 6 μm to prepare 10 kinds of magnetic tapes.
When the magnetic characteristics were measured using each of these 10 types of magnetic tapes, the results were as shown in Table 1.

In place of the hollow-structured steel ball beads used in the above-mentioned Examples 1 to 4, it is made of aluminum alloy, heavy silica flint glass, silicon nitride and silicon carbide, and has the same diameter as the steel ball beads and is not hollow. Four types of magnetic tapes were prepared in the same manner as in Examples 1 to 4 except that four types of spherical beads were used. When the dropout characteristics were measured using these four types of magnetic tapes, the four types of magnetic tapes were more likely to cause dropouts than the magnetic tapes of Examples 1 to 4, and the beads were crushed. It was found that the pieces tended to remain in the magnetic coating.

Comparative Examples 7 to 14 In the same manner as in Example 1, solid zircon oxide beads (bead weight / bead volume [gr / cm ³ ] is about 5.6) were changed in diameter to 8 types and stirred. Eight types of magnetic tapes were prepared using the magnetic paints obtained as described above. Then, the presence or absence of crushing of the magnetic particles and the gloss of the eight kinds of magnetic tapes were observed by an electron microscope, and the results were as shown in Table 2.

From this Table 2, it was possible to easily deduce that in the present invention, the bead diameter must be within the range of 0.8 to 2.5 mm.

As described above in detail, according to the present invention, the acicular magnetic powder can be dispersed and mixed extremely uniformly in the binder-containing solvent.

Further, it is possible to extremely effectively reduce the dropout of the magnetic recording medium (that is, the defect such as the conventional glass beads) caused by the crushing of the beads upon impact and the crushed pieces remaining in the magnetic coating film. .

Further, since the impact force on the acicular magnetic powder is too strong, the acicular magnetic powder is destroyed and the magnetic properties such as the coercive force (Hc) of the magnetic recording medium are deteriorated, and the transfer amount is increased. (That is, the drawbacks of conventional solid steel beads and the like) can be very effectively prevented.

Claims (1)

[Claims] 1. A method for producing a magnetic recording medium, comprising: applying a magnetic coating material, in which acicular magnetic powder is dispersed and mixed in a solvent containing a binder, onto a non-magnetic support to produce a magnetic recording medium. , The bead weight / bead volume ratio is in the range of 3.0 to 7.0, and the bead diameter is in the range of 0.8 to 2.5 mm. The beads and the acicular magnetic powder are added to the binder-containing solvent and the beads are moved to uniformly disperse and mix the acicular magnetic powder in the binder-containing solvent. Was prepared, and the beads were separated from the magnetic paint, and the magnetic paint from which the beads had been separated was applied onto the non-magnetic support, whereby the fragments of the beads were mixed into the magnetic paint. And the above needle breaks the magnetic powder. Preparation of magnetic recording medium but which is adapted to produce a magnetic recording medium is suppressed.