JPS62104103A - Ferromagnetic powder - Google Patents

Abstract

PURPOSE:To improve an electric resistance without deteriorating magnetic characteristics of a ferromagnetic powder by coating a surface of the ferromagnetic powder with a semiconductive metal oxide gel or mixing it. CONSTITUTION:A semiconductor metal oxide gel includes a peculiar structure and shows a higher electric conductivity (semiconductivity) as compared with a crystal. For example, V2O5.nH2O gel shows the electric conductivity which is 3-4 digits larger than V2O5 crystal. As such semiconductive metal oxide gel, vanadic acid gel, molybdic acid gel, tungstic acid gel etc. can be mentioned and these semiconductor metal oxide gels can be used individually or by combination thereof. For the coating with the above semiconductive metal oxide gel, for example, a ferromagnetic powder such as of gamma-Fe2O3 particles and the above semiconductive metal oxide gel are dispersed in water and after a sufficient stir, it is dehydrated and dried to coat the surface of the ferromagnetic powder with the semiconductor metal oxide gel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferromagnetic powder used in coated magnetic recording media such as magnetic tapes and magnetic disks.

[Importance of the invention]

The present invention relates to a ferromagnetic powder used in a coated magnetic recording medium, and the electrical resistance of the ferromagnetic powder is reduced by depositing or mixing a semiconducting metal oxide gel on the surface of the ferromagnetic powder. This aims to prevent charging when this ferromagnetic powder is used in a magnetic recording medium, and to improve changes in magnetic properties over time and dispersibility.

(Prior Art) Conventionally, TFe203 particles have been widely used as ferromagnetic powder used in coated magnetic recording media.
Feqos particles have advantages such as excellent chemical and magnetic stability and low cost.

In addition, in general, in magnetic recording media, the coercive force He of ferromagnetic powder is an important factor that influences the recording and reproducing characteristics, and by increasing this coercive force Hc, demagnetization can be suppressed and recording density can be improved. It is known that it is possible to Therefore, in order to improve the properties of the magnetic recording medium, it is necessary to further increase the coercive force Hc of the ferromagnetic powder.

Therefore, so-called cobalt-coated γ-Fe2O3 particles, in which cobalt is coated on the surface of the r-Fe203 particles, are also being considered. This cobalt-coated r-Fe2o3
In particles, it has become possible to increase the coercive force Hc by concentrating the effect of cobalt ions on the particle surface.

However, in magnetic recording media using these γ-F6203 particles or cobalt-coated γ-F6203 particles, the electrical resistance of the magnetic layer becomes extremely large. Therefore, when recording and reproducing are performed using the magnetic recording medium, the magnetic layer is likely to be charged, which is undesirable as it causes discharge noise and tape sticking. Also,
In disc-shaped magnetic recording media (so-called magnetic disks), dust tends to adhere due to the charging of the magnetic layer, causing dropouts.

Conventionally, methods for preventing the above-mentioned charging have been proposed, such as improving the mechanical parts of the recording/reproducing device, applying a back coat, or adding carbon into the magnetic layer. However, it is clear that these methods do not essentially solve the above problems, and it has been difficult to reduce the electrical resistance on the surface of the magnetic layer, which is particularly important. Therefore, it is desired to reduce the charging of the magnetic layer by reducing the electrical resistance of the magnetic powder itself.

Therefore, a method of depositing ferrous ions Fe2+ on the surface of the magnetic powder, and a method of depositing or mixing a certain type of conductive hydrate on the magnetic powder are being considered. However,
In this case, there are problems in terms of changes in magnetic properties over time and dispersibility of the magnetic powder.

[Problem that the invention seeks to solve]

As described above, conventional magnetic powders have a high electric resistance, so when used in a magnetic recording medium, the magnetic layer is easily charged, causing discharge noise, sticking, or dropout. Furthermore, when attempting to improve the electrical resistance of magnetic powder, there is a drawback that the magnetic properties change over time or the dispersibility of the magnetic powder deteriorates.

The present invention was proposed in view of the above-mentioned circumstances, and aims to improve the electrical resistance of ferromagnetic powder without impairing its magnetic properties. It is an object of the present invention to provide a ferromagnetic powder in which the magnetic layer is difficult to be charged, the magnetic properties do not change over time, and the dispersibility is excellent.

[Means for solving problems]

As a result of intensive research to achieve the above object, the present inventors discovered that semiconducting metal oxide gel has a considerably high electrical conductivity. We have come to the knowledge that by adhering to or mixing with ferromagnetic powder, the electrical resistance can be improved without impairing the magnetic properties of the ferromagnetic powder.

The ferromagnetic powder of the present invention was developed based on this knowledge, and is characterized by having a semiconductive metal oxide gel adhered to or mixed on the surface of the ferromagnetic powder.

Here, the semiconductive metal oxide gel used in the present invention is
It has a unique structure and has good electrical conductivity (
semiconductivity). For example, V2O5·n H20 gel exhibits electrical conductivity that is 3-4 orders of magnitude higher than that of V2O5 crystals. Examples of the semiconductive metal oxide gel include vanadate gel, molybdate gel, and tungstate gel, and these semiconductive metal oxide gels can be used alone or in combination.

The method for depositing the semiconducting metal oxide gel is, for example, by dispersing magnetic powder such as γ-F8203 particles and the semiconducting metal oxide gel in water, stirring thoroughly, and then dehydrating and dispersing the semiconducting metal oxide gel.
By drying, a semiconductive metal oxide gel may be deposited on the surface of the ferromagnetic powder.

In addition, a solution prepared by dispersing a semiconducting metal oxide in water and turning it into a gel is mixed into the /8 liquid in which magnetic powder is dispersed in advance.
By dispersing it, a ferromagnetic powder containing the above-mentioned oxide gel can be produced.

On the other hand, the ferromagnetic powder serving as the starting material may be any commonly used powder, including ferromagnetic iron oxide particles 1, ferromagnetic chromium dioxide, ferromagnetic alloy powder, and hexagonal barium ferrite fine particles.

Examples include iron nitride.

The above-mentioned ferromagnetic iron oxide particles are those whose X value is in the range of 1.33≦X≦1.50 when expressed by the general formula Fe0X, that is, maghematite (γ-p e203,
x-1,50), magnetite (Fe30a,
= 1.33) and their solid solutions (FeOx, 1.33
<x<1.50). Furthermore, ferromagnetic iron oxide has
Cobalt may be added for the purpose of increasing coercive force. There are two types of cobalt-containing iron oxide: doped type and deposited type.

The above-mentioned ferromagnetic chromium dioxide may include cro2 or Ru for the purpose of improving the coercive force thereof.

A material containing at least one of Sn, Te, Sb, Fe, Ti, V, Mn, etc. can be used.

Examples of the ferromagnetic alloy powder include Fe, Co, and Ni.

Fe-Co, Fe-Ni, Fe-Co-Ni, C.

-Ni, Fe-Co-B, Fe-Co-Cr-B.

Mn-B1. Mn-ACFe-Co-V etc. can be used,
In addition, ACSi, T
Total bending components such as i, Cr, Mn, Cu, and Zn may be added.

In addition, the ferromagnetic powder of the present invention is kneaded with a binder, an organic solvent, or various additives to make a magnetic paint, and this paint is applied onto a non-magnetic support and dried to form a magnetic layer. Used in magnetic recording media.

The binder, which is one of the main components constituting the magnetic layer, may be one that has been conventionally used as a binder for magnetic recording media, such as 1m-hinyl-hinyl acetate co-m combination, IP Vinyl-vinyl acetate-vinyl alcohol copolymer L tH17 Ni-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester - Vinylidene chloride copolymer, methacrylic acid ester - Vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer Polymers, acrylonitrile-butadiene-methacrylic acid copolymers, polyvinyl butyral, cellulose derivatives, styrene-butadiene copolymers, polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins.

Examples include urea-formaldehyde resins and mixtures thereof.

In addition to the ferromagnetic powder of the present invention and the binder, additives such as a dispersant, an ifJ lubricant, an abrasive, and a rust preventive may be added to the magnetic paint.

These materials constituting the magnetic layer are dissolved in an organic solvent to prepare a magnetic paint, which is then applied onto a non-magnetic support. Examples of the organic solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. Ketone series, methyl acetate.

Ester types such as ethyl acetate, butyl acetate, ethyl lactate, and acetic acid glycol monoethyl ether, glycol ether types such as glycol dimethyl ether, glycol monoethyl ether, and dioxane, aromatic hydrocarbons such as benzene, toluene, and quinolene, hexane, and heptane. Aliphatic hydrocarbons such as ethylene chloride, carbon tetrachloride, chloroform.

Examples include chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene.

Examples of the dispersant include caprylic acid and capric acid.

Fatty acids having 12 to 18111 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lyrinic acid, and stearolic acid (RtCOOHlRl is an alkyl or alkenyl having 11 to 17 carbon atoms) group), alkali gold of the above fatty acids
A full-strength soap consisting of fA (Li, Na, K, etc.) or alkaline earth gold H (Mg, Ca, B; 1, etc.), a fluorine-containing compound of the above fatty acid ester,
Amides of the above-mentioned fatty acids, polyalkylene oxide alkyl phosphates, trialkyl polyolefin oxy quaternary ammonium salts (alkyl has 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), and the like are used.

In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used.

The above lubricants include dialkylpolysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxypolysiloxane (alkoxy has 1 to 4 carbon atoms), heptanoalkylmonoalkoxyborisiloxane (alkyl has 1 to 5 carbon atoms). Individual,
Alkoxy has 1 to 4 carbon atoms (solid), silicone oil such as phenyl J revorisiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms), conductive fine powder such as graphite, molybdenum disulfide, disulfide Inorganic fine powder such as tungsten, polyethylene, polypropylene.

Polyethylene vinyl chloride copolymer, polytetrafluoroethylene, etc. fine powder, α-olefin polymers, unsaturated aliphatic hydrocarbons that are liquid at room temperature (compounds in which a 0-olefin double bond is bonded to the terminal carbon) , carbon number 2
0 (solid), monobasic fatty acids having 12 to 20 carbon atoms, fatty acid esters consisting of alcohols having 1 side of carbon atoms, and fluorocarbons can be used.

As the abrasive, fused alumina, silicon carbide, chromium oxide (Cr203), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are used.

As the rust preventive agent, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used, but in particular, dicyclohexylamine nitrite,
Volatile rust inhibitors (amine , amide or imidono-inorganic acid salts or organic acid salts), the rust prevention effect is improved.

Furthermore, examples of the non-magnetic support to which the magnetic paint is applied include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, and polyvinyl chloride. , vinyl resins such as polyvinylidene chloride, and plastics such as polycarbonate, polyimide, and polyamideimide. The nonmagnetic support may be in any form such as a film, tape, disk, card, or drum. Alternatively, the non-magnetic support may be a so-called hard disk by using light alloys such as aluminum alloys and titanium alloys, thermoplastic resins such as polystyrene and ABS resins, ceramics such as alumina glass, single crystal silicon, and the like. In this case, it is preferable that the surface of the support is hardened by providing an N1-P plating layer or alumite treatment in advance.

[Effect]

By coating or mixing a semiconducting metal oxide gel with high electrical conductivity on the surface of the ferromagnetic powder, the electrical resistance of the ferromagnetic powder can be extremely reduced without changing its magnetic properties. .

〔Example〕

Next, the present invention will be explained using specific examples, but the present invention is not limited to these examples.

Example 1 First, 1.2 mol of vanadyl oxytrichloride was hydrolyzed to prepare a vanadate gel. 130 g of this vanadate gel was recovered in terms of dry mass.

Next, the above vanadate gel and γ-Fe2O3 (coercive force Hc = 368 oersted, saturation magnetization σ5-73
．． Oemu/g) 8.0kg and water 25. After dispersing in Ol and stirring for about 1 hour, it was dehydrated and dried to produce a ferromagnetic powder.

It was confirmed by atomic absorption spectrometry that vanadium was deposited or mixed in the obtained ferromagnetic powder.

The magnetic properties of this ferromagnetic powder were Hc of 371 oersted and σS of 72.5 emu/g, which were comparable to those of T-Fe203 before coating with vanadate gel.

Example 2 First, 7.0% by weight sodium tungstate solution 12
．． 0Il and IN-H (1 (1N hydrogen chloride solution) 6
．． A tungstic acid gel was prepared by mixing with 01 (
Co-authored by Furusawa and Ren, Journal of the Chemical Society of Japan 87 (1966) 1
(see 18). 220 g of this tungstic acid gel was recovered in terms of dry weight.

Next, the above tungstic acid gel was used in the T
-Fe2038. With Okg, water 25. After dispersing in Ol and stirring for about 1 hour, it was dehydrated and dried to produce a ferromagnetic powder.

It was confirmed by atomic absorption spectrometry that tungsten was deposited or mixed in the obtained ferromagnetic powder. Further, the magnetic properties of this ferromagnetic powder were Hc of 367 oerstesod and σS of 72.3 emu/g, which were comparable to those of γ-Fe2O3 before coating with tungstate gel.

Example 3 Mixed solution of 6.0ffit 1% sodium tungstate solution and 0.7% by weight sodium molybdate solution 12.07! and I N -HC1 solution 6.01 were mixed to prepare a mixed gel of tungstic acid and molybdic acid. 21 og of the above-mentioned mixed gel could be recovered in terms of dry mass.

Next, the above mixed gel was mixed with γ-Fe20 used in Example 1.
38. With Okg, water 25. After dispersing in ON and stirring for about 1 hour, the mixture was dehydrated and dried to produce a ferromagnetic powder.

It was confirmed by atomic absorption spectrometry that tungsten and molybdenum were attached or mixed in the obtained ferromagnetic powder. Moreover, the magnetic properties of this ferromagnetic powder are H
c was 368 oersted and 5σS was 72.3 emu/g, which was comparable to that of r-Fe203 before coating with tungstate gel and molybdate gel.

Subsequently, the ferromagnetic powder produced in each of the above examples was dissolved in a solvent together with a vinyl chloride-vinyl acetate copolymer resin (VAGH manufactured by Union Carbide) and a dispersant (trade name: Prysurf). A sample tape was prepared by coating the magnetic paint on a polyethylene terephthalate substrate to form a magnetic layer. Each issue of these samples.

The coercive force HC1, residual magnetic flux density Bs, and surface electrical resistance were measured. The results are shown in Table 1. For comparison, a sample tape (Comparative Example 1) using ferromagnetic powder without any treatment on the γ-FCq03 used in Example 1, and a sample tape using this ferromagnetic powder and carbon as an antistatic agent were used. Similar measurements were also carried out on a sample tape containing 2.0% by weight (Comparative Example 2).

Table 1 As is clear from this Table 1, magnetic powder can be obtained by adhering or mixing a small amount of vanadate gel, tungstate gel, or semiconductive metal oxide gel such as vanadate gel with magnetic powder. The magnetic recording medium was able to reduce the surface electrical resistance by more than one order of magnitude without impairing magnetic properties such as coercive force and residual magnetic flux density.

Further, no change over time was observed in the coercive force and residual magnetic flux density in the sample tapes of each Example.

Furthermore, it was confirmed that by using the semiconductive metal oxide gel of the present invention, the surface electrical resistance could be lowered to a greater extent than carbon.

Therefore, the magnetic tape using the ferromagnetic powder of this example is less likely to cause discharge noise or sticking, and can provide good recording and reproducing characteristics. Furthermore, in the case of magnetic disks, adhesion of dust and the like can be significantly reduced, making dropouts less likely to occur.

〔Effect of the invention〕

As is clear from the above explanation, by depositing or mixing semiconducting metal oxide gel with high electrical conductivity on the surface of ferromagnetic powder, it is possible to maintain electrical resistance while maintaining the magnetic properties of ferromagnetic powder. can be made extremely small compared to conventional ferromagnetic powders.

Further, the present cobalt deposition technology can be used to deposit or mix the above-mentioned semiconductive metal oxide gel, and there is an advantage that large-scale equipment is not required.

Furthermore, if the ferromagnetic powder of the present invention is used in a magnetic recording medium, the electrical resistance on the surface of the magnetic layer can be suppressed while maintaining the magnetic properties of the magnetic powder, thereby eliminating discharge noise, tape sticking, or dropouts. It's improved. Also,
Since changes in magnetic properties over time are suppressed and dispersibility is improved, good recording and reproducing properties can be obtained over a long period of time.

Moreover, since the same effect can be obtained by adding a smaller amount than carbon, it is possible to increase the packing density of ferromagnetic powder in the magnetic layer, which is advantageous for high-density recording.

Claims (1)

[Claims] A ferromagnetic powder characterized by having a semiconducting metal oxide gel adhered to or mixed on the surface of the ferromagnetic powder.