JPH11339252A - Powder for base layer of coating type magnetic recording medium and magnetic recording medium using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a nonmagnetic layer having superior surface smoothness by depositing a specified amount of a carboxylic acid on the surface of α- FeOOH particles. SOLUTION: A carboxylic acid as an organic compound is incorporated into the surface of α-FeOOH (iron oxyhydroxide) particles to modify the surface property of the particles, and the particles are used as powder for the base layer of a coating type magnetic recording medium. It is sufficient that the amount of carboxylic acid deposited is only that which is required amount to cover the α-FeOOH particles and is added with respect to the range of 0.1 to 10 wt.% of the α-FeOOH powder to the powder. If the amount is less than 0.1 wt.%, the desired effects are not obtained due to the low viscosity of the coating material, and even if it is added in excess of 10 wt.%, its effects will be saturated and will affect the coating material composition. Thereby, the dispersibility of α-FeOOH particles to the binder resin can be improved, and the viscosity of the coating material can be decreased. Thus, the obtained base layer has superior surface smoothness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated magnetic recording medium having a multilayer structure in which a non-magnetic layer (also referred to as a lower layer) and a magnetic layer (also referred to as an upper layer) are laminated, and a method for forming the non-magnetic layer. It relates to the lower layer powder to be used.

[0002]

2. Description of the Related Art A coating film in which magnetic powder is dispersed and contained in a binder resin (binder) is applied to a support, whereby
In a so-called coated magnetic recording medium in which a magnetic layer is formed on a support, it is desired to reduce the thickness of the magnetic layer in order to obtain high output characteristics with low noise. ), A coating type magnetic recording medium having a multilayer structure in which a coating film of a non-magnetic layer (lower layer) is formed below.

Heretofore, spherical titanium oxide powder or acicular iron oxide powder has been mainly used as a nonmagnetic powder for forming the lower layer. A magnetic recording medium having such a lower layer is disclosed, for example, in JP-A-63-1874.
No. 18, JP-A-4-167225, JP-A-6-167
Japanese Unexamined Patent Application Publication No. 60362/1994 and Japanese Patent Application Laid-Open No. 6-131653. Also, Japanese Patent Application Laid-Open No. 4-167
No. 225, JP-A-6-139553, JP-A-6-215360, JP-A-7-78331, JP-A-7-105530, JP-A-7-182
649, JP-A-7-334835, JP-A-8-329448, JP-A-9-22524, JP-A-9-170003, JP-A-10-21
JP-A-531, JP-A-10-21532, and JP-A-10-21533 disclose such a magnetic recording medium having a multilayer structure in which needle-like hematite or the like is used as a nonmagnetic powder for forming a lower layer. Characteristic values are shown. In these publications, in addition to the needle-like iron oxide powder whose characteristic values are specifically shown, although there is no specific disclosure of the characteristic values, powders made of other substances are also used for the non-magnetic layer for the lower layer. Numerous substance names are exemplified as being usable as powders, including iron oxyhydroxide.

On the other hand, Japanese Unexamined Patent Publication No. 4-167225 discloses a special multi-layer structure in which the thickness of the lower non-magnetic layer is smaller than the thickness of the magnetic layer. When the iron oxyhydroxide powder is used as the powder, the scratch resistance, stiffness and head contact of the tape are evaluated. However, JP-A-6-60362 states that such iron oxyhydroxide cannot be used as a lower layer powder because of its poor dispersibility in a binder resin, and the use of acicular iron oxide is recommended. ing.

Further, examples using iron oxyhydroxide as the lower layer powder are described in JP-A-8-293116 and JP-A-9-180169, but are disclosed in JP-A-8-293116. In the embodiment of the present invention, the tape using iron oxyhydroxide as the lower layer powder as compared with the acicular iron oxide powder has a large surface roughness and low electromagnetic conversion characteristics. Rather, it is used in combination with granular iron oxide, and in any case, it cannot be said that the function of iron oxyhydroxide is sufficiently exhibited.

Further, Japanese Patent Application Laid-Open No. 5-347017 discloses a multilayer structure using an α-FeOOH powder as a lower layer powder. The surface treatment of the α-FeOOH powder includes a Si compound or It is merely desirable to be treated with an Al compound.

[0007]

The primary purpose of providing a non-magnetic layer (lower layer) in which a non-magnetic powder is dispersed between a support and a magnetic layer is to reduce the thickness of the magnetic layer and shorten the recording wavelength. An object of the present invention is to secure an output in an area and to improve excellent electromagnetic conversion characteristics such as erasing characteristics and overwriting characteristics. For this purpose, the magnetic layer itself is required to have a certain characteristic, but the role of the lower nonmagnetic layer side is that a smooth thin magnetic layer with little surface irregularities can be applied thereon, that is, the nonmagnetic layer Mainly, it is excellent in surface smoothness itself, contributes to the strength of the magnetic recording medium, and can sufficiently derive the magnetic characteristics of the upper magnetic layer.

[0008] Spherical titanium oxide, which has been used as a powder for a lower layer, has insufficient strength when formed into a tape and has difficulty in forming fine particles as compared with a needle-shaped one. In addition, needle-like iron oxide (hematite) cannot avoid interparticle sintering due to its manufacturing method, and thus cannot provide sufficient surface smoothness. When iron oxyhydroxide is used for the lower layer powder, the dispersion of the paint becomes difficult because the viscosity of the paint increases, and sufficient surface smoothness cannot be obtained because a smooth paint cannot be formed. In other words, the paint viscosity when the lower layer powder is dispersed in the binder resin depends on the binder resin used, but is affected by the surface characteristics, physical and chemical properties, dimensions and shape of the lower layer powder. In particular, since the effect of surface properties is great, iron oxyhydroxide (α-F
When eOOH) is used as a coating material that can be well coated on a support, the viscosity of the coating material becomes extremely high, and it becomes difficult to disperse the particles, so that sufficient surface smoothness cannot be obtained. Was attached.

In order to solve this problem, inorganic compounds such as Al and Si have so far been contained in α-FeOOH or adhered to the surface of α-FeOOH as disclosed in JP-A-5-347017. Although a method was proposed to improve the dispersibility, it was not sufficient.

[0010] Accordingly, the present invention provides a method for forming a high-strength lower layer having a lower coating viscosity and better surface smoothness when forming iron oxyhydroxide into a coating. It is an object to achieve ultra-thinness and surface smoothness. More specifically, when iron oxyhydroxide powder is applied to the lower layer powder, by modifying not only the chemical / physical properties and shape properties of the powder but also its surface properties, Surface smoothness of magnetic recording media,
It is an object to improve strength, magnetic characteristics, and durability.

[0011]

It has been found that the above problem can be solved by attaching an appropriate amount of carboxylic acid to the surface of α-FeOOH particles as the lower layer powder. That is, according to the present invention, there is provided a powder for a lower layer of a coating type magnetic recording medium in which a carboxylic acid is attached to the surface of α-FeOOH particles.

The carboxylic acids used include oxalic acid,
It is preferably at least one dicarboxylic acid selected from the group consisting of malonic acid, maleic acid, phthalic acid, succinic acid, malic acid, fumaric acid, tartaric acid, adipic acid, and glutamic acid. .1-1
It is advisable to apply it in an amount of 0% by weight.

[0013] Further, by adding an appropriate amount of an inorganic compound of Al or Si to α-FeOOH together with the adhesion of the carboxylic acid, the characteristics of the organic compound and the inorganic compound work well, so that the above-mentioned problem is further solved. I knew I could do it. At this time, the α-FeOOH powder has an average major axis length of 0.01 to 0.50 μm and an average minor axis length of 0.01.
Consisting of needle-like or flat needle-like particles of
More preferably, it contains 0.1 to 2.0% by weight of water released at 0 ° C. The α-FeOOH powder of the present invention treated with a carboxylic acid can lower the powder pH to 7.4 or less.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Heretofore, the surface properties of .alpha.-FeOOH (iron oxyhydroxide) particles have been modified by incorporating a carboxylic acid which is an organic compound into the surface of the particles, and the particles are coated on a coating type magnetic recording medium. No example is found for the lower layer powder. The present inventors have found that on the surface of α-FeOOH,
When the carboxylic acid is contained in an amount of 0.1 to 10% by weight, the dispersibility of the α-FeOOH particles in the binder resin is improved, the viscosity of the paint can be reduced, and a lower layer having excellent surface smoothness can be obtained. I found It has been found that the coating type magnetic recording medium having this lower layer has excellent surface smoothness and strength and improved magnetic properties.

As the carboxylic acid adhered to and contained in the α-FeOOH particles, any one having a carboxyl group can be used in principle, but oxalic acid, malonic acid, maleic acid, phthalic acid, succinic acid, malic acid can be used. It is preferably at least one dicarboxylic acid selected from the group consisting of, fumaric acid, tartaric acid, adipic acid and glutamic acid. Among them, the effect of phthalic acid is remarkable, and maleic acid is also good, as shown in Examples described later.

The content of the carboxylic acid attached is α-F
The amount may be an amount necessary to cover the surface of the eOOH particles. In practice, the carboxylic acid may be added to the α-FeOOH powder in a range of 0.1 to 10% by weight based on the α-FeOOH powder. If the amount is less than 0.1% by weight, desired effects such as a decrease in paint viscosity may not be obtained due to insufficient carboxylic acid. Will give.

The most convenient way to make the α-FeOOH particles adhere and contain the carboxylic acid is to add an aqueous solution of the carboxylic acid to the α-FeOOH powder and dry off the water. Therefore, it is preferable to use a dicarboxylic acid having a relatively high solubility in water, but this method can be applied to a low-soluble dicarboxylic acid as long as there is no need to increase the amount of water dried. Carboxylic acid addition treatment is α-F
It can be performed at the final stage of eOOH powder production. For example, after the formation reaction of α-FeOOH, α-FeOOH
The FeOOH powder may be filtered and washed, an aqueous carboxylic acid solution may be added thereto, and moisture may be removed by drying. As another method, the α-FeOOH powder also washed with water may be repulped again in water, a carboxylic acid may be added to the suspension, and then water may be removed by drying. In any case, it is preferable to perform an operation of adjusting the powder water content of the α-FeOOH powder to which the carboxylic acid has been added.

By adding such a carboxylic acid, α-F
The surface modification of the eOOH powder allows the powder p
H can be set to 7.4 or less and the viscosity of the coating film can be remarkably reduced as compared with the case where no carboxylic acid is added. As a result, the surface smoothness and strength of the coating layer are improved. To satisfy the properties required for
It is also affected by the properties of the FeOOH particles themselves. The lower layer powder of the present invention is an α-FeOOH powder having the following characteristics.

Characteristics of α-FeOOH powder [particle size and shape] Needle having average major axis length: 0.01 to 0.50 μm, average minor axis length: 0.01 to 0.05 μm, average axial ratio: 1 to 30 Or flat needle-like particles. Flat needle-shaped particles are substantially unbranched needle-shaped particles whose short-axis cross section cut in the direction perpendicular to the long axis has a longer width and a shorter width. Particles having a short-axis cross-sectional ratio substantially uniformly larger than 1, preferably larger than 1.5 in the long-axis direction. Α-FeOOH having such particle size and shape
By being a powder, the surface smoothness and strength of the coating layer are particularly improved.

[Al or Si Content] The α-FeOOH particles in which Al is dissolved or deposited can maintain good acicularity, and the surface properties of the particles are modified to a desirable state. For this reason, the dispersibility in the paint becomes good, and the heat resistance of the coating layer and also the weather resistance can be improved. A
α-FeOOH containing Si instead of 1 has the same effect. The content of Al or Si may be in the range of 0.1 to 30% by weight. When both are contained simultaneously, the total amount may be in the range of 0.1 to 30% by weight.

[Specific surface area] The specific surface area (BET method) is 10
３００300 m ² / g, preferably 30-150 m ² / g,
When it is more preferably 30 to 120 m ² / g, the amount of fatty acid adsorbed can be reduced and the dispersibility in resin can be improved.

[Moisture Content] The viscosity of the coating film varies depending on the moisture content of the powder. The moisture content detected (released) at 100 ° C. is 0.1 to 2.0% by weight, preferably 0.5%. ~ 2.
When the α-FeOOH powder contains 0% by weight of water, the dispersibility in the coating film is improved.

[Tap density and true specific gravity]
^{3 to} 2.0 g / cm ³ , preferably 0.4 to 1.5 g / cm ³ ,
The true specific gravity is 3.0-6.0 g / cm ³ , preferably 3.5-4.0 g / cm ³ .
3 g / cm ³ . If the α-FeOOH powder has such a true specific gravity and the tap density relative to the true specific gravity is high, the powder tends to be compacted in the coating film when calendered in the tape forming process, and this indicates that It works advantageously to improve smoothness.

[Crystal Grain Size] (Crystallite) It is 10 to 200 angstroms, preferably 50 to 150 angstroms. [Stearate adsorption amount] is preferably 0.1-3.0 mg / ^{m 2.}

In order to produce the α-FeOOH powder according to the present invention, for example, a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution is used. Then, an oxygen-containing gas is passed at a temperature of 80 ° C. or less to carry out an oxidation reaction, and the obtained precipitate is separated by filtration, washed with water, dried and conditioned to obtain an average major axis length of 0.01 to 0.01. 50 μm, average short axis length 0.01 to 0.05
μm α-FeOOH is obtained.

Alternatively, an oxidation reaction is carried out by passing an oxygen-containing gas through a suspension obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an alkali carbonate having an equivalent amount or more, and the resulting precipitate is filtered, washed and dried. By controlling the humidity, the α-FeOOH powder according to the present invention can be similarly produced.

In particular, in order to produce α-FeOOH having a flat needle shape, an aqueous ferric salt solution containing 1.0 to 3.0 μm of Fe ^{3+ is} used.
A suspension containing colloidal hydroxide is formed at 10 to 90 ° C. by adding 5 equivalents of an aqueous alkali hydroxide solution.
After aging for 0 hours, hydrolysis is carried out, and the resulting precipitate can be obtained by filtration, washing with water, drying and conditioning.

In order to contain Al in such α-FeOOH, Al ₂ (SO ₄ ) ₃ , Al (NO ₃ ) ₃ , Al
A compound such as a water-soluble salt such as Cl ₃ or a water-soluble aluminate such as NaAlO ₂ (sodium aluminate) may be allowed to coexist during or after the process of producing α-FeOOH. For example, to deposit Al on the surface of α-FeOOH particles, the above-mentioned Al compound is dissolved in an aqueous alkaline solution, and α-FeOOH is dispersed in this solution. When added and neutralized, Al is deposited on the particle surface as crystalline or amorphous Al ₂ O ₃ .H ₂ O (hydrous aluminum hydroxide). α-
To dissolve (impregnate) Al into FeOOH, α-Fe
The water-soluble Al salt or aluminate may be allowed to coexist in a reaction system for generating OOH, γ-FeOOH, or the like.

To make α-FeOOH contain Si,
For example, a water-soluble compound of sodium silicate or potassium silicate, an aqueous suspension of colloidal silica, or No. 3 water glass is added to a suspension containing α-FeOOH, and p
H can be set to 9 or less.

The α-FeOOH powder thus obtained
To add carboxylic acid to the powder,
Add a carboxylic acid aqueous solution and remove the water by drying.
No. Then, the powder is placed in an inert gas stream containing a small amount of water.
The powder may be treated to adjust the water content. Again
Density of 0.3g / cm³, Preferably 0.4 g / cm
³In order to achieve the above, consolidation treatment was performed using a roller mill or the like.
Good.

Carboxylic acid-containing α-Fe having the above characteristics
When the OOH powder is used as a lower layer powder, a coating layer having reduced coating viscosity and excellent surface smoothness can be formed. The magnetic recording medium using this lower layer has excellent surface smoothness, strength and magnetic properties.

In the coating type magnetic recording medium to which the underlayer according to the present invention is applied, the magnetic layer and the support are not particularly limited, but the magnetic powder for forming the magnetic layer is as follows. Is particularly preferred.

Magnetic Powder for Forming Magnetic Layer The magnetic layer formed on the lower layer using the α-FeOOH powder of the present invention is preferably formed using the following ferromagnetic powder. Co: over 3 to 50 at% Al: 0.1 to 30 at% Rare earth element (including Y): 0.1 to 10 at% Group 1a element of the periodic table (Li, Na, K, etc.): 0.05
% By weight or less Group 2a element of the periodic table (Mg, Ca, St, Ba): 0
An iron-based ferromagnetic powder containing 0.1 to 0.1% by weight or less, having an average major axis length of 0.01 to 0.40 μm and an X-ray crystal grain size (Dx) of 50 to 250 angstroms. Magnetic powder.

Further, in this ferromagnetic powder, the short-axis cross section cut in a direction perpendicular to the long axis has a longer width and a shorter width, and the ratio of the short-axis cross section of the long axis to the short axis is the long-axis direction. It is preferable to have a flat needle-like shape which is substantially uniformly larger than 1, preferably 1.5 or more. Further, the ratio (σs) between the saturation magnetic susceptibility (σs) and the X-ray crystal grain size (Dx) / Dx)
Is 0.7 or more.

Further, this ferromagnetic powder has an amount of H ₂ O released at 100 ° C. of 2% by weight or less, an amount of H ₂ O released at 300 ° C. of 4% by weight or less, and a true density of 5.55 g / cm
³ or more, an atmosphere having a specific surface area of 30 to 70 m ² / g by a BET method, a saturation magnetic susceptibility (σs) of 100 to 200 emu / g, a coercive force of 1200 to 3000 (Oe), and a relative humidity of 90% at 60 ° C. Susceptibility (σ)
The reduction rate of s) is preferably 15% or less.

Such a ferromagnetic powder is described in the specification and drawings of Japanese Patent Application No. 9-162061 (June 5, 1997) of the same applicant, and its components and dimensions / shape. Have the above relationship, a magnetic layer suitable for high-density recording can be formed. That is, the shape-maintaining characteristics and the magnetic properties are determined by the combination of the dimensional and shape characteristics of fine particles having an average major axis length of 0.01 to 0.40 μm and the shape of a flat needle, and the specific content of a component. A magnetic layer having compatible characteristics can be formed. In addition, since the lower layer made of α-FeOOH having a needle shape and a flat needle shape according to the present invention is excellent in surface smoothness, the upper layer using the ferromagnetic powder is also excellent in surface smoothness, and the thickness of the magnetic layer is reduced. Therefore, a structure having a sufficient tape strength can be obtained even if the thickness of the magnetic layer is reduced, so that a high-performance magnetic recording medium not available in the related art can be obtained.

Therefore, according to the present invention, the magnetic layer in which the magnetic powder is dispersed in the resin binder is provided through the nonmagnetic layer in which the non-magnetic lower layer powder is dispersed in the resin binder.
In a coating type magnetic recording medium having a multilayer structure formed on a support, the lower layer powder is composed of α-FeOOH powder obtained by adhering a carboxylic acid to the particle surface, and the magnetic powder has a Co: more than 3 ratio. % To 50 at.%, Al: 0.1 to 30 at.%, Rare earth element (including Y): 0.1 to 10 at.%, Group 1a element of the periodic table: 0.05% by weight or less, periodic table Group 2a element: Needle-like ferromagnetic metal powder containing 0.1% by weight or less (including 0% by weight) in Fe, preferably average major axis length: 0.01 to 0.40 μm X Linear crystal grain size (Dx): 50 to 250 angstroms, and more preferably, the short-axis cross section cut in a direction perpendicular to the long axis has a longer width and a shorter width. The short-axis cross-sectional ratio is substantially uniformly greater than 1, preferably 1.5 or more in the long-axis direction. A coating type magnetic recording medium comprising needle-like particles, more preferably a ferromagnetic metal powder having a ratio (σs / Dx) of the saturation magnetization rule (αs) to the X-ray crystal grain size (Dx) of 0.7 or more. I will provide a.

As a support for coating the lower layer and the upper layer for forming such a magnetic recording medium having a baking soda structure,
Known resin films such as polyesters such as poly (ethylene terephthalate) and poly (ethylene naphthalate), polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone / aramid, and aromatic polyamide can be used.

[0039]

EXAMPLES Examples of the lower layer powder according to the present invention will be described below, and the characteristic values in each example were measured as follows.

The average major axis length (l), average minor axis length (d), and axial ratio (l / d) were all determined by the average value of 100 particles measured from a 108.000-fold electron micrograph. Was. The crystal grain size (Dx) was calculated by obtaining the half-value width of a peak corresponding to the (110) plane from a profile obtained using an X-ray diffractometer, and substituting this into Scherrer's equation. The specific surface area was measured by the BET method. The amount of stearic acid adsorbed (shown as STA in Table 1) is determined by dispersing 2% of stearic acid in MEK solution of the sample powder, then sedimenting the sample powder with a centrifuge, and determining the concentration of the supernatant liquid. It was calculated as the amount of adsorption per unit. The resin adsorption was calculated using the same method as the stearic acid adsorption using a 2% MIBK solution of a vinyl chloride resin. Powder pH is JIS K5
Measured according to 101. Tap density (TAP in Table 1)
Was measured in accordance with JIS K5101. The amount of water (in Table 1, denoted as 100 ° C. water amount) is obtained by measuring the separated adsorbed water (% by weight) at 100 ° C.

The coating viscosity was evaluated at a shear rate of 11.5 s ^-1 using an E-type viscometer (RE-110H) manufactured by Toki Sangyo Co., Ltd.

Surface smoothness (referred to as tape roughness in Table 1) was measured by a three-dimensional fine shape measuring instrument (E
T-30HK), the Ra was evaluated by measuring the Ra (roughness) of the tape surface.

The weather resistance test of the magnetic tape was evaluated by the presence or absence of precipitates on the tape after being left for one week in an atmosphere at 60 ° C. and a relative humidity of 90%.

Example 1 10 L of an aqueous solution of FeSO _{4 having a} concentration of 0.2 mol / L (mol / L)
1 liter of an 8 mol / L NaOH aqueous solution and A
1 / FeOOH in a weight ratio of 2.3 wt% Na
AlO ₃ was added, and air was blown for 5 hours while maintaining the solution at 30 ° C. The precipitate formed is separated by solid-liquid separation, and α-F
A powdery precipitate of eOOH was obtained. After the α-FeOOH powder was washed with water, an aqueous solution of phthalic acid was added so that the amount of phthalic acid was 0.3 wt% with respect to the α-FeOOH powder. Thereafter, a drying treatment for sufficiently evaporating water is performed in a dry air stream (110 to 180 ° C. for 1 to 4 hours), and the obtained dry powder is dried in a nitrogen stream at 60 ° C. containing 2 vol. The water content was adjusted by holding for 30 minutes, the phthalic acid content was 0.3 wt% and the separated adsorbed water at 100 ° C was 1.0%.
wt% α-FeOOH powder was obtained. Table 1 shows the properties of the powder (the properties after adding the carboxylic acid and after adjusting the water content).

A paint having the following composition is prepared. Iron oxyhydroxide powder 100 parts by weight Vinyl chloride resin 15 parts by weight Polyurethane resin 5 parts by weight Methyl ethyl ketone 165 parts by weight Cyclohexanone 65 parts by weight Toluene 165 parts by weight Stearic acid 1 part by weight Acetyl acetone 1 part by weight

A coating having the above composition obtained by dispersing in a centrifugal ball mill for 1 hour is applied to a base film made of polyethylene terephthalate using an applicator so that a target thickness is about 3 μm, to form a coating film. did. The roughness of the obtained tape was measured, and the values shown in Table 1 were obtained. The viscosity of a part of the paint was measured to obtain the values shown in Table 1.

Example 2 The amount of phthalic acid was α-FeOO
The same processing as in Example 1 was performed, except that an aqueous solution of phthalic acid was added so as to be 1.0 wt% with respect to the H powder.
Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 3 The amount of phthalic acid was α-FeOO
The same process as in Example 1 was performed except that an aqueous solution of phthalic acid was added so as to be 2.0 wt% with respect to the H powder.
Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 4 The amount of phthalic acid was α-FeOO
The same processing as in Example 1 was performed except that an aqueous solution of phthalic acid was added so as to be 3.0 wt% with respect to the H powder.
Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 5 The amount of phthalic acid was α-FeOO
The same process as in Example 1 was performed except that an aqueous solution of phthalic acid was added so as to be 5.0 wt% with respect to the H powder.
Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 6 Instead of the aqueous solution of phthalic acid,
Maleic acid content is 1.0 wt% with respect to α-FeOOH powder
%, Except that an aqueous solution of maleic acid was added
The same processing as in Example 1 was performed. Various properties of the obtained powder,
Table 1 also shows the paint viscosity and the tape roughness.

[Example 7] Instead of the aqueous solution of phthalic acid,
Oxalic acid content is 1.0 wt% based on α-FeOOH powder
The same treatment as in Example 1 was performed, except that an oxalic acid aqueous solution was added so that Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 8 Instead of an aqueous solution of phthalic acid,
Malonic acid content is 1.0 wt% based on α-FeOOH powder
The same treatment as in Example 1 was performed except that the malonic acid aqueous solution was added so as to obtain Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 9 Instead of an aqueous solution of phthalic acid,
Succinic acid content is 1.0 wt% based on α-FeOOH powder
The same treatment as in Example 1 was performed, except that an aqueous succinic acid solution was added so that Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Example 10 Instead of an aqueous solution of phthalic acid, the amount of malic acid was 1.0 w / α-FeOOH powder.
The same treatment as in Example 1 was performed, except that the malic acid aqueous solution was added so as to be t%. Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

[Example 11] Instead of the aqueous solution of phthalic acid, the amount of fumaric acid was 1.0 w / α-FeOOH powder.
The same treatment as in Example 1 was performed except that an aqueous solution of fumaric acid was added so that the concentration became t%. Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Comparative Example 1 The same treatment as in Example 1 was performed except that the aqueous solution of phthalic acid was not added. Various properties, paint viscosity and tape roughness of the obtained powder are also shown in Table 1.

Comparative Example 2 αFe ₂ O having the characteristics shown in Table 1
_{Using 3} powders, a paint having the same composition as in Example 1 was prepared.
Taped. The paint viscosity and tape roughness are also shown in Table 1.

Comparative Example 3 A coating material having the same composition as in Example 1 was prepared using TiO ₂ powder having the characteristics shown in Table 1 and taped. The paint viscosity and tape roughness are also shown in Table 1.

[0060]

[Table 1]

From the results in Table 1, it can be seen that the stearic acid adsorption amount and the pH of the carboxylic acid-added products of Examples 1 to 11 were lower than those of Comparative Example 1 in which no carboxylic acid was added. It can be seen that even when dispersed, the viscosity of the coating material is reduced and the surface roughness when taped is remarkably improved. Further, as can be seen from Examples 1 to 5, it can be seen that as the amount of the carboxylic acid added increases, the paint viscosity decreases and the surface roughness of the tape improves. When αFe ₂ O ₃ powder and TiO ₂ powder are used, the paint viscosity is low but the surface roughness when taped is poor.

Example 12 A magnetic tape having the following composition was applied on the lower tape obtained in Example 4 to prepare a magnetic tape. The composition and characteristics of the metal magnetic powder used are as follows.

[Composition of magnetic paint] Metal magnetic powder 100 parts by weight Vinyl chloride resin 20 parts by weight Polyurethane resin 10 parts by weight Methyl ethyl ketone 190 parts by weight Cyclohexanone 80 parts by weight Toluene 110 parts by weight Stearin butyl 1 part by weight Acetyl acetone 1 part by weight α- Alumina 3 parts by weight Carpon black 2 parts by weight

[Composition of Metallic Magnetic Powder] Co: 30 at%,
Al: 10 at%, Y: 4.0 at%, Na: 0.002
at%, Ca: 0.004 at%, balance: Fe.

[Powder Characteristics of Metal Magnetic Powder] Long axis length = 0.0
8 μm, axial ratio = 5, BET = 49 m ² / g, crystallite =
170 angstroms, powder pH = 9.4, STA = 101m
g / m ² .

[Magnetic Properties of Metal Magnetic Powder] Hc = 2340
(Oe), σs = 146 emu / g, σr / σs = 0.
52, Δσs = 9.2.

When preparing a magnetic tape, a magnetic paint having the above composition obtained by dispersing for 1 hour in a centrifugal ball mill was used.
A sheet-like sample was prepared by applying the lower layer tape obtained in Example 4 by using an applicator, and the sheet-like sample was further calendered, and slit to a width of 8 mm to obtain a magnetic tape. Table 2 shows properties of the obtained magnetic tape.

Example 13 Example 6 was used as a lower layer tape.
Example 12 was repeated except that Table 2 shows properties of the obtained magnetic tape.

[Comparative Example: A] Comparative Example 1 as a lower layer tape
Example 12 was repeated except that Table 2 shows properties of the obtained magnetic tape.

Comparative Example B Comparative Example 2 as a lower layer tape
Example 12 was repeated except that Table 2 shows properties of the obtained magnetic tape.

[0071]

[Table 2]

From the results shown in Table 2, the results of Examples 12 and 13 using the lower layer formed of α-FeOOH with added carboxylic acid were lower than the lower layer formed with α-FeOOH without added carboxylic acid as in Comparative Example A. It can be seen that the magnetic tape has a low surface roughness, a high strength, and a high output and a high C / N ratio. Further, the magnetic tape using the lower layer formed of αFe ₂ O ₃ as in Comparative Example B has poor roughness, low strength, and low output and C / N ratio.

[0073]

As described above, the powder for the lower layer of the coating type magnetic recording medium according to the present invention can form a non-magnetic layer having excellent surface smoothness and strength. A magnetic recording medium having a suitable multilayer structure can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shuichi Mafune 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Naoki Sato 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd.

Claims (8)

[Claims] A powder for a lower layer of a coating type magnetic recording medium in which a carboxylic acid is attached to the surface of α-FeOOH particles. 2. The carboxylic acid is oxalic acid, malonic acid, maleic acid, phthalic acid, succinic acid, malic acid, fumaric acid,
At least one dicarboxylic acid selected from the group consisting of tartaric acid, adipic acid and glutamic acid;
2. The lower layer powder according to claim 1, wherein the powder is attached in an amount of 0.1 to 10% by weight based on the OH powder. 3. The α-FeOOH powder has an average major axis length of 0.01 to 0.50 μm and an average minor axis length of 0.01 to 0.05.
3. A needle or flat needle-like particle having a particle diameter of μm.
The powder for a lower layer according to the above. 4. The α-FeOOH particles contain 0.1 to 30% by weight of Al or Si, and the powder contains 0.1 to 2.0% by weight of water released at 100 ° C. The lower layer powder according to claim 3. 5. The α-FeOOH powder has a powder pH of 7.
The powder for a lower layer according to claim 1 or 2, which is 4 or less. 6. A multilayer structure formed on a support through a non-magnetic layer in which magnetic powder is dispersed in a resin binder and a non-magnetic lower layer powder is dispersed in a resin binder. A coating type magnetic recording medium, wherein the lower layer powder comprises an α-FeOOH powder obtained by adhering a carboxylic acid to the particle surface. 7. The magnetic powder comprises: Co: more than 3 to 50 at.%, Al: 0.1 to 30 at.%, Rare earth element (including Y): 0.1 to 10 at.%, Group 1a of the periodic table 7. An acicular ferromagnetic metal powder containing Fe in an element: 0.05% by weight or less, Group 2a element in the periodic table: 0.1% by weight or less (including 0% by weight) in Fe. Coating type magnetic recording medium. 8. The magnetic powder has an average major axis length of 0.01 to 0.40 μm, an X-ray crystal grain size (Dx) of 50 to 250 angstroms, and a short axis cross section cut in a direction perpendicular to the major axis. Consist of flat needle-like particles having a longer width and a shorter width, and a short-axis cross-sectional ratio of the long axis and the short axis is almost uniformly greater than 1 in the long axis direction. 8. The coating type magnetic recording medium according to claim 7, wherein a ratio (σs / Dx) of (X) to the X-ray crystal grain size (Dx) is 0.7 or more.