JP3252441B2 - θ-alumina powder, method for producing the same, and magnetic recording medium using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a crystal having substantially the same phase as .theta.
-Made of alumina and having an average primary particle size of 0.1
The present invention relates to a θ-alumina powder having a particle diameter of μm or more, a method for producing the same, and a magnetic recording medium using the θ-alumina powder as an abrasive.

More specifically, when used as an abrasive for a coating type magnetic recording medium, it is possible to provide a magnetic recording medium which is excellent in tape surface smoothness, running durability, and magnetic properties, and has little damage to a magnetic head. The present invention relates to an alumina powder, a method for producing the same, and a magnetic recording medium using the same.

[0003]

2. Description of the Related Art In general, magnetic recording media for audio, video, and computer applications apply a magnetic coating material in which a magnetic material such as ferromagnetic metal oxide or metal powder is dispersed in a binder onto a non-magnetic support. To form a magnetic layer. Since such a magnetic recording medium is used while being in sliding contact with a magnetic head, the magnetic layer needs to ensure sufficient running properties and durability.

If the durability of the magnetic layer is poor, particles that have fallen off the magnetic layer adhere to the vicinity of the magnetic head, hinder smooth contact between the magnetic layer and the magnetic head, and cause deterioration of electromagnetic conversion characteristics and dropout. And the tape is remarkably soiled during still reproduction. In addition, when the running property is poor, a change occurs in the friction of the tape, and the running characteristics deteriorate.

In order to improve the running property and durability of the magnetic layer as described above, an inorganic powder such as alumina, silicon carbide, chromium oxide, titanium oxide, silicon oxide, α-iron oxide or the like is conventionally used as an abrasive in the magnetic layer. Additions have been made.

Alumina, which has been widely used as the abrasive, is mainly α-alumina. Alumina is generally χ → κ → α, γ → δ → θ → α, η → θ by heating aluminum hydroxide such as gibbsite, bayerite and boehmite.
It is known that transition to α-alumina via intermediate alumina, such as → α, ρ → η → θ → α, pseudo γ → θ → α alumina (for example, Electrochemistry, Vol. 28, p. 302, Funaki and Shimizu: For alumina hydrate and alumina, see Table 1 Examples of thermal change of alumina hydrate).

[0007] It has also been found that thermal decomposition of aluminum salts such as aluminum chloride, aluminum sulfate and aluminum nitrate causes a transition from amorphous alumina to α-alumina via intermediate alumina such as γ, δ and θ (for example, mineralogy). (See Magazines, Vol. 19, No. 1, p. 21, p. 41).

However, in any case, it is known that the transition from the above-mentioned intermediate alumina to α-alumina is an exothermic reaction and is accompanied by rapid grain growth, as compared with the grain growth of intermediate alumina. As an abrasive for magnetic recording media, α-alumina has a Mohs hardness of 9 and has a high hardness, which greatly contributes to improving the running properties and durability of the magnetic layer. However, coarse particles are mixed in due to the grain growth that occurs during the phase transition to the α particles. However, the coarse particles reduce the smoothness of the tape surface, damage the head during running, hinder smooth contact of the magnetic head, and lower the electromagnetic conversion characteristics. On the other hand, a method using an intermediate alumina having a particle size of 0.5 μm to 7 μm as an abrasive for a magnetic recording medium is also known (for example, Japanese Patent Application Laid-Open No.
The particle diameter of the intermediate alumina is usually agglomeration of the primary particle diameter of less than 0.1 μm, and the reinforcing effect of the magnetic layer is weak and the running durability is poor.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an alumina as an abrasive capable of providing a magnetic recording medium which is excellent in tape surface smoothness, running durability and electromagnetic conversion characteristics and has little damage to a magnetic head. The aim is to develop the powder and its production method.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a method for preparing a tungsten compound having a .theta.-alumina content of at least 70%, an average primary particle diameter of at least 0.1 .mu.m, and a tungsten compound with respect to alumina of 0.1% by weight to 5% by weight. Another object of the present invention is to provide a .theta.-alumina powder containing 0.1% by weight.

Further, the present invention relates to the present invention, wherein the content of the tungsten compound relative to alumina after firing the tungsten or the tungsten compound is 0.1% as tungsten oxide.
The aluminum compound contained in the range of 1 to 5% by weight is calcined at a temperature of 1100 ° C to 1300 ° C, the content of θ-alumina is 70% or more, and the average primary particle diameter is 0.1 µm
As described above, an object of the present invention is to provide a method for producing θ-alumina powder, characterized by obtaining an alumina powder containing 0.1% to 5% by weight of a tungsten compound as a tungsten oxide with respect to alumina.

The present invention also relates to a magnetic recording medium comprising a magnetic layer containing a magnetic substance, a binder and an abrasive formed on a non-magnetic support, wherein the abrasive has at least a .theta.-alumina content of 70%. As described above, the average primary particle diameter is 0.1 μm or more.
Another object of the present invention is to provide a magnetic recording medium characterized by using 0.5 μm θ-alumina powder.

Hereinafter, the present invention will be described in more detail. The alumina powder in the present invention is an alumina powder having at least 70% or more, preferably 80% or more of the crystal phase of alumina in the powder having a θ phase and having an average primary particle diameter of 0.1 μm or more.

Conventionally, alumina powder having a θ phase as a crystal phase is known, but θ-alumina powder, which is known for industrial production, has an average primary particle diameter of at most about 0.03 μm, In order to obtain particles having larger particles, the alumina particles are rapidly transformed into α-alumina. Therefore, there is no known alumina powder having an average primary particle diameter of 0.1 μm or more and substantially consisting of a θ phase and formed by heating grains.

When θ-alumina is used as an abrasive for a magnetic recording medium, the hardness of θ-alumina is about 8, and silicon oxide, titanium oxide, α-oxide Because hardness is higher than iron,
In addition to having a sufficient head cleaning effect, α-
Since the hardness is lower than that of alumina, there is an effect that the head is hardly damaged.

Θ-alumina used as an abrasive has an average primary particle diameter of 0.1 μm or more, usually 0.1 μm to 0.5 μm.
μm, preferably 0.12 μm to 0.3 μm
-Any alumina powder may be used, and its production method is not particularly limited, but can be obtained by the following method.

Tungsten or a starting aluminum compound containing the tungsten compound in an amount of 0.1 to 5% by weight, preferably 1 to 3% by weight as tungsten oxide based on alumina after firing the tungsten compound at 1100 ° C. 10 minutes to 4 at a temperature of ~ 1300 ° C
8 hours, preferably at a temperature of 1150 ° C. to 1250 ° C.
It can be obtained by baking for 0 minutes to 24 hours.
Since the crystal form of the obtained alumina powder changes not only by the sintering temperature and time but also by the type of aluminum compound or tungsten used as a raw material and the amount of alumina present, the raw material conditions to be used are selected.
It is recommended that the firing conditions be determined within a simple range by a simple preliminary experiment. When the firing is performed in the presence of water vapor, for example, using a gas firing furnace, θ-alumina powder having a large particle diameter, for example, exceeding about 0.2 μm can be easily obtained.

The method of containing tungsten or the tungsten compound in the aluminum compound as the raw material may be such that tungsten or the tungsten compound is dispersed as uniformly as possible in the raw aluminum compound. The method is not particularly limited. Tungsten or a tungsten compound is calcined in a solution containing an aluminum halide such as aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum perchlorate, and ammonium alum. After adding and uniformly mixing in an amount of 1 to 5% by weight, an aluminum compound is obtained by a neutralization method, a recrystallization method, a method of precipitating as a carbonate by ammonium bicarbonate or the like, and calcining. Law, and the like.

A solution containing aluminum alkoxides such as aluminum methoxide, aluminum ethoxide and aluminum isopropoxide; alkyl aluminum such as trimethyl aluminum and triethyl aluminum; and organic aluminum compounds such as aluminum carboxylate and aluminum dicarboxylate. Tungsten or a tungsten compound is added in a range where the amount of the tungsten compound with respect to alumina after calcination is 0.1 to 5% by weight as tungsten oxide, uniformly mixed, and then an aluminum compound is obtained by hydrolysis. Is fired.

Further, only the aluminum compound obtained by a neutralization method, a recrystallization method or a method of precipitating as a carbonate by ammonium bicarbonate or the like, or an organic aluminum compound alone by a hydrolysis method or a thermal decomposition method. A method in which tungsten or a tungsten compound is mixed with the obtained aluminum compound in a wet or dry manner in a range where the abundance of the tungsten compound with respect to alumina after firing is 0.1 to 5% by weight as tungsten oxide, and firing is performed. Can be In particular, aluminum hydroxide having an average primary particle size of 0.05 μm or less obtained by a method of hydrolyzing an organic aluminum compound was preferred.

If the amount of tungsten or tungsten compound added to the starting aluminum compound is outside the above range, a desired θ-alumina powder having a large average primary particle diameter cannot be obtained.

The tungsten compound used as a raw material is not particularly limited as long as it can be uniformly dispersed or mixed with the raw material aluminum compound. Examples thereof include ammonium tungstate such as ammonium metatungstate and ammonium paratungstate; Examples thereof include tungsten halide such as tungsten, and tungsten oxyhalide compound such as tungsten oxychloride.

The magnetic recording medium of the present invention is characterized by using the thus obtained θ-alumina powder as an abrasive. That is, in a magnetic recording medium in which a magnetic layer containing a magnetic substance, a binder, and an abrasive is formed on a nonmagnetic support, the abrasive has at least a θ-alumina content of 70% or more and an average primary particle diameter of at least 70%. 0.1 μm
A magnetic recording medium characterized by using θ-alumina powder having a thickness of about 0.5 μm.

When the abrasive has an average primary particle diameter of less than 0.1 μm as observed by TEM, the reinforcing effect is weak,
If the running durability is reduced, and if it exceeds 0.5 μm, the magnetic properties are reduced, the head is damaged, and the electromagnetic conversion properties are deteriorated. Also, the content of θ-alumina is 70%
If the content of α-alumina exceeds 30%, the surface smoothness of the tape may be reduced, or the head may be damaged during running.

In the magnetic recording medium of the present invention, the amount of the alumina added to the magnetic layer is generally 1 to 20 parts by weight, preferably 1 to 15 parts by weight, per 100 parts by weight of the magnetic material. If the amount is more than 20 parts by weight, the surface smoothness of the tape and the magnetic properties are deteriorated, and the head is damaged. If the amount is less than 1 part by weight, the reinforcing effect is insufficient and the running durability is lowered, which is not preferable. .

As the magnetic material, a known magnetic material, for example,
γ-Fe_TwoO_Three, Co-containing γ-Fe _TwoO_Three, Co deposition γ
-Fe_TwoO_Three, Fe_ThreeO_Four, Co-containing γ-Fe_ThreeO_Four,
Co deposited γ-Fe_ThreeO_Four, CrO_TwoOxide magnetic materials such as
For example, Fe, Ni, Co, Fe-Ni alloy, Fe-Co
Alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, F
e-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-C
o-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co
-Ni alloy, Co-P alloy, Co-Cr alloy, etc., Fe,
Various magnetic powders such as metal magnetic powders mainly composed of Ni and Co
Is used.

The particle size (average primary particle size) of the magnetic material is not particularly limited, but is generally in the range of about 0.05 to about 5 μm.

Additives to these metal magnetic materials include Si, C within the range used in the art.
Elements such as u, Zn, Al, P, Mn, and Cr, or compounds thereof may be included.

It is also possible to contain hexagonal ferrites such as barium ferrite, iron nitride and iron carbide.

The binder used in the magnetic phase of the present invention may be any known binder used for magnetic recording media, such as a thermoplastic resin, a thermosetting resin, a reactive resin, and an electron beam. An irradiation-curable resin or a mixture thereof is used.

More specifically, units of urethane resin, vinyl chloride resin, epoxy resin, urea resin, amide resin, silicone resin, polyester resin, phenol resin, vinyl resin, cellulose derivative resin, rubber-based resin, or these resins Or a mixture thereof.

Examples of the material for the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyvinyl chloride resins, polycarbonates, polyamides, and the like. In addition to plastics such as polysulfone, metals such as aluminum and copper, and ceramics such as glass can also be used.

The production of the magnetic recording medium may be in accordance with a known method, and is not particularly limited. However, the above-mentioned magnetic powder, binder and abrasive have substantially a θ phase as a main crystal phase. Alumina is mixed and dispersed with an organic solvent together with various additives to prepare a magnetic paint, applied on a non-magnetic support, dried and, if necessary, subjected to heat treatment, surface treatment, etc. Good.

The θ-alumina powder obtained by the present invention can be used as a backing additive for a magnetic recording medium, a filler for a paint, a PET film, or various fibers in addition to the above-mentioned abrasive for a magnetic recording medium. Can also be used.

[0035]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. In the present invention, the analysis was performed by the following method.

Square ratio; vibrating sample magnetometer (RIKEN ELECTRONICS B
HV-50) with a sweeping magnetic field of 15K Gauss.

Surface gloss: An incident angle of 60 ° with respect to the longitudinal direction of the sample tape was measured by a standard gloss meter at an angle of reflection of 60 °, and the specular gloss at an incident angle of 60 ° of glass with a refractive index of 1.56 was measured according to JISZ8741. The relative value was determined with the degree as 100.

Still characteristics: 4 MHz signal was recorded on a sample tape to be measured at 25 ° C., 60% RH, and back tension 40 g using a video deck modified for still measurement.
When playback is performed in a stationary state under the condition of
The time until the drop was measured.

Observation of head adhesion and head wear, observation of adhesion to magnetic head when running sample tape for 100 hours at 40 ° C. and 80% RH atmosphere using Matsushita VCR NV-G21, head wear The amount was measured.

Average primary particle diameter: The average primary particle diameter is determined by reading the particle diameter from a TEM (transmission electron microscope) and converting the weight to a cumulative frequency distribution chart.

[0041] BET specific surface area: using Quantachrome Co. direct reading specific surface area measuring apparatus, the N ₂ was desorbed at N ₂ -He carrier gas, measure the measured surface area of a heat conductive detector N ₂ desorption amount I do.

Θ alumina content: X-ray intensity of the sample was measured, and the diffraction intensity at the plane index of the θ alumina was measured simultaneously. The diffraction intensity of the standard sample (X intensity of the sample in which θ alumina and α alumina were mixed 1: 1) was measured. The line intensity is compared with 50) and expressed in% by the intensity ratio.

EXAMPLE 1 An ammonium metatungstate solution was hydrated on an alumina hydrate having an average primary particle diameter of 0.01 μm and obtained by hydrolyzing aluminum isopropoxide. And then uniformly dispersed and mixed. The mixture was placed in a heat-resistant sheath made of alumina, and placed in a gas firing furnace at 1230.
Calcination was performed at 3 ° C. for 3 hours. After cooling, the obtained alumina powder had an average primary particle diameter of 0.2 μm, and the crystal phase of the particles determined by X-ray diffraction was 89% θ-alumina and the others were α-alumina.

Using 5 parts by weight of the alumina powder thus obtained, a magnetic paint was prepared at the following weight ratio. Co-coated γ-iron oxide 100 parts by weight Polyurethane resin 10 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Carbon 2 parts by weight Lubricant (butyl stearate) 1 part by weight Curing agent (polyisocyanate) 2 parts by weight Solvent Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight

The above composition was dispersed in a sand grinder for 5 hours, and then filtered through a filter having an average diameter of 5 μm.
On a 4 μm thick polyethylene terephthalate film,
The magnetic layer was dried and coated so as to have a thickness of 3 μm, calendered, cured at 70 ° C. for 24 hours, and cut into イ ン チ inch width to prepare a magnetic tape. The surface gloss, still characteristics, head adhesion amount, and head wear amount of the obtained magnetic tape were measured, and the results are shown in Table 2.

Example 2, Comparative Examples 1 to 6 In the method of Example 1, an alumina powder having the physical properties shown in Table 1 was obtained by changing the tungsten oxide content and the firing conditions (Comparative Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that these alumina powders were used (commercially available from Degussa (Germany), trade name: Al ₂ O ₃ —C). Surface gloss of the obtained magnetic tape,
The still characteristics, the head adhesion amount, and the head wear amount were measured, and the results are shown in Table 2.

Example 3 Ammonium metatungstate was added to an aqueous solution of ammonium alum so as to be 4% by weight of tungsten oxide with respect to alumina after calcining. Ammonium alum was precipitated and calcined at 1230 ° C. for 3 hours in a gas calcining furnace to obtain θ-alumina powder having the physical properties shown in Table 1. Using this θ-alumina powder, a magnetic tape was prepared in the same manner as in Example 1. The surface gloss, still characteristics, head adhesion amount, and head wear amount of the obtained tape were measured, and the results are shown in Table 2.

Example 4 Tungsten methoxide was added to an isopropyl alcohol solution of aluminum isopropoxide so as to be 1% by weight as tungsten oxide based on calcined alumina, and after uniform mixing, hydrolyzed to contain tungsten. Alumina hydrate was obtained, which was heated at 1170 ° C. in a gas firing furnace.
The mixture was fired for 3 hours to obtain θ-alumina powder having the physical properties shown in Table 1. Using this θ-alumina powder, a magnetic tape was prepared in the same manner as in Example 1. The surface gloss, still characteristics, head adhesion amount, and head wear amount of the obtained tape were measured, and the results are shown in Table 2.

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

According to the present invention described in detail above, alumina powder having a large average primary particle diameter substantially consisting of the .theta. Phase can be obtained by a specific method, and this can be used as an abrasive for magnetic recording media. Supplying a magnetic recording medium that is excellent in durability, magnetic properties, and surface smoothness of a magnetic layer, and is excellent in a magnetic head cleaning effect and a magnetic head abrasion suppressing effect by being used in place of the α-alumina powder that has been used. The industrial value is extremely large.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-275409 (JP, A) JP-A-4-146987 (JP, A) JP-A-54-103308 (JP, A) JP-A-2- 128319 (JP, A) US Patent 3,714,343 (US, A) US Patent 4,731,278 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01F ^7/ 00-7/47 G11B 5/708 CA (STN) JICST file (JOIS) WPI (DIALOG)

Claims (3)

(57) [Claims] 1. The content of θ-alumina is 70% or more, the average primary particle diameter is 0.1 μm or more, and a tungsten compound is 0.1% by weight or more based on alumina as tungsten oxide.
Θ-alumina powder containing 5% by weight. 2. Tungsten or an aluminum compound containing the tungsten compound in an amount of 0.1 wt% to 5 wt% as tungsten oxide with respect to alumina after firing the tungsten compound at 1100 ° C.
Calcined at a temperature of ~ 1300 ° C and a θ-alumina content of 7
Production of θ-alumina powder characterized by obtaining an alumina powder having 0% or more, an average primary particle diameter of 0.1 μm or more, and containing 0.1 to 5% by weight of a tungsten compound as tungsten oxide with respect to alumina. Method. 3. A magnetic recording medium in which a magnetic layer containing a magnetic material, a binder and an abrasive is formed on a non-magnetic support, wherein the abrasive has at least a θ-alumina content of 70%.
% Or more, and the average primary particle diameter is 0.1 μm to 0.5 μm.
-A magnetic recording medium characterized by using alumina powder.