JPH0363592B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a magnetic paint for magnetic recording media, and more specifically, the present invention relates to a method for producing a magnetic paint for magnetic recording media, and more specifically,
This invention relates to a method for producing a magnetic paint for magnetic recording media using silicon nitride and/or silicon carbide beads of ~2 mm. Magnetic paint is usually made by mixing magnetic particles, polymer binder,
It is prepared by dispersing and mixing additives in a solvent. In the manufacturing process of coated magnetic recording media used in various devices such as audio and video recorders, the process of uniformly dispersing and mixing magnetic particles in a solvent containing a binder improves the final performance of the resulting magnetic recording media. It occupies an extremely important position in making decisions. If the dispersion and mixing of the magnetic particles is insufficient, aggregates of magnetic particles may form in the paint film, causing noise, or the surface of the paint film may be affected, which depends on the dispersion state of the magnetic particles in the magnetic paint. This may cause problems such as deterioration of smoothness. However, if you mix strongly to ensure sufficient dispersion, the magnetic particles will be destroyed by physical force during mixing.
Problems arise such as deterioration of magnetic properties such as Hc and an increase in the amount of transfer. In addition, the need for high-density recording media has increased in recent years,
As magnetic particles tend to become finer, it is necessary to increase the dispersion mixing ratio. When mixing conventional magnetic paints, balls or beads are added to the magnetic paint and the blade is rotated or the entire container is rotated and vibrated to move the balls or beads and reduce the impact force when they collide with each other. was used to loosen aggregates of magnetic particles. However, in conventional methods, the materials used for the balls and beads used are generally steel or glass, so the materials do not shatter under impact like glass, or conversely can generate particles of magnetic powder like steel. This has caused undesirable effects on magnetic recording media, such as destruction. In other words, since glass beads have a relatively low impact when they collide and have low mixing efficiency, the efficiency is increased by increasing the rotational speed of the blade that stirs the beads. If glass fragments cannot be avoided and remain in the tape coating, they cause dropouts. Furthermore, if steel ball beads that are difficult to break themselves are used, dropout will be improved, but instead, the magnetic powder particles will be destroyed due to collisions between the steel ball beads, resulting in deterioration of magnetic properties such as Hc, and transfer amount. This makes it extremely difficult to control the mixing conditions. Therefore, when using steel ball beads, it is necessary to reduce the impact force when the beads collide with each other by increasing the viscosity of the paint. However, if the viscosity of the magnetic paint is increased in this way, a new problem arises in that the coating itself becomes difficult. Therefore, the present invention provides a method for producing a magnetic coating material for magnetic recording media, which improves the various drawbacks of the prior art. The method according to the invention consists of stirring and mixing magnetic particles with silicon nitride and/or silicon carbide beads having a bead diameter of 1 to 2 mm. These silicon nitride and/or silicon carbide beads with a bead diameter of 1 to 2 mm are originally used as materials for beads used for mixing magnetic paints, and have the following characteristics: they do not break during mixing, they have low friction, and they do not contain magnetic particles. It satisfies the characteristics of being able to obtain enough impact force to loosen agglomerations without breaking them, and being easy to process into beads. That is, these beads have a diameter of 1 to 2
mm silicon nitride and/or silicon carbide beads are significantly stronger than conventionally used glass beads, but they are not as dense as steel and have superior durability compared to metal materials. Because it has abrasive properties, the particles themselves are hard but extremely brittle, especially like oxide-based magnetic powders, and if the particles are broken during mixing, the acicularity of the particles is lost and the magnetic properties immediately deteriorate. It is suitable for dispersive mixing of materials that may lead to deterioration of the product. The magnetic powder used in this invention includes:
In particular, it is not limited in any way as long as it is used in coating type magnetic recording media, for example, γ-
Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Iron oxide in an oxidation state intermediate between Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing γ
- Iron oxide in an oxidation state intermediate between _{Fe 2} O ₃ and Fe ₃ O ₄ , iron oxide containing one or more metal elements (particularly transition metal elements), iron oxide containing Co
Those with a coating layer mainly composed of oxides or hydroxides, CrO ₂ , CrO ₂ by reducing the surface _of CrO ₂
Oxide-based magnetic powder such as layer-formed powder or
Metals such as Fe, Co, Ni, etc. Or Fe-Co alloy,
Fe-Ni alloy, Fe-Co-Ni alloy, Co-Ni-P alloy, Co-Ni-Fe-B alloy, Fe-Ni-Zn alloy,
Examples include ferromagnetic fine powder of alloys such as Fe-Mn-Zn alloy and Fe-Co-Ni-P alloy. Magnetic paint also uses aluminum oxide as an abrasive.
Chromium oxide, silicon oxide, etc., antistatic agents such as carbon black, lubricants such as molybdenum disulfide, graphite, silicone oil, olive oil, etc., and dispersants such as lecithin can be added. In addition, examples of binders 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 Polymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-
vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, vinylidene chloride-acrylonitrile copolymer, putadiene-acrylonitrile copolymer, acrylonitrile-ptadiene-acrylic acid copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, Styrene-butadiene copolymer, formal resin, acetal resin,
Examples include butyral resin, phenolic resin, polyester resin, polyurethane resin, polyamide resin, urea resin, urea-formaldehyde resin, melamine resin, epoxy resin, alkyd resin, phenoxy resin, polyvinyl fluoride, and mixtures thereof. Furthermore, solvents that can be used 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 ether, ethylene glycol dimethyl ether, dioxane, etc. Examples include glycol ethers, 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 by a conventional coating method such as a doctor blade method or a gravure coating method to form a desired magnetic recording medium. Examples of the nonmagnetic support used include polyesters such as polyethylene tereftate, polyolefins such as polypropylene, cellulose derivatives such as cellulose diacetate and cellulose triacetate, polycarbonate, polyvinyl chloride, polyimide,
Examples include polyamide, metals such as aluminum and copper, and paper. Hereinafter, the present invention will be explained by Examples with reference to Comparative Examples. Examples 1-2 and Comparative Examples 1-2 Magnetic paints having the following compositions were prepared as follows. Composition (parts by weight) Co−γ−Fe ₂ O ₃ (Hc = 600 Oe, particle size 0.3 to 0.4 μm,
Axial ratio = 10) 100 Composition (parts by weight) Vinyl chloride-vinyl acetate copolymer (product name "VYHH"; manufactured by UCC) 18 Thermoplastic polyurethane (product name "Estan")
5701”; Manufactured by B.F. Gutdoritsu)
7 Cr ₂ O ₃ 3 PHP Lecithin 1.5PHP Hexyllaurate 1.5PHP Methyl ethyl ketone:Toluene (1:1)
300 After pre-stirring about 15 liters of magnetic paint having the above composition, it was mixed in a 25 liter sand mill.
Mixing was carried out for about 3 hours using beads having the materials and properties shown in the table below. The amount of beads is approximately 10 by volume.
It was a little hot. The material of the rotating blade of the mixer was steel, and the rotation speed was 1200 rpm. The magnetic paint thus obtained was placed on a 5 inch wide polyethylene terephthalate film.
It was coated to a thickness of 4 μm and cut into 1/2 inch width for video use. Various properties were measured using this magnetic tape, and the results are shown in the table below.

【table】

[Table] From the results in the table above, in Examples 1 and 2 using non-oxide ceramic beads, the density is slightly higher than that of glass beads.
Since the impact force caused by the collision between the beads was approximately the same as that for glass beads, almost no fragmentation of the magnetic particles was observed. Furthermore, since silicon nitride and/or silicon carbide beads with a bead diameter of 1 to 2 mm are significantly stronger than glass beads,
No fracture of the beads themselves, which would cause dropout, was observed. In contrast to the examples, in the glass beads of Comparative Example 1, no fracture of the magnetic powder was observed and the tape squareness ratio was satisfactory, but a large number of broken pieces of glass beads were present and the number of dropouts was significant. In addition, in the case of the steel ball shown in Comparative Example 2, the beads were not crushed, so there was very little dropout, but the tape squareness ratio decreased due to the destruction of the magnetic particles. As mentioned above, the method according to the present invention uses silicon nitride and/or silicon carbide beads with a bead diameter of 1 to 2 mm, thereby eliminating bead breakage, which is a drawback of conventionally used glass beads. The usefulness of a magnetic paint that solves both the increase in dropout and the decrease in tape squareness ratio due to magnetic particle destruction due to too strong impact force on the magnetic particles due to the high density, which is a disadvantage of steel ball beads. It is a manufacturing method.

Claims (1)

[Claims] 1. In a method for producing a magnetic paint for magnetic recording media, in which a magnetic paint is prepared by dispersing and mixing at least magnetic particles and a polymeric binder in a solvent, when preparing the magnetic paint, the diameter of the beads is 1~2mm
1. A method for producing a magnetic paint for magnetic recording media, which comprises adding silicon nitride and/or silicon carbide.