JP2924941B2 - Underlayer for magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonmagnetic underlayer for a magnetic recording medium having excellent surface smoothness.

[0002]

2. Description of the Related Art In recent years, as long-term recording and miniaturization of video and audio magnetic recording / reproducing devices have progressed, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved. Demand for noise reduction and noise reduction is increasing.

In particular, recently, demands for higher image quality and higher quality of video tapes have been increasing, and the frequency of a carrier signal to be recorded is higher than that of conventional video tapes. That is, the wavelength shifts to the short wavelength region, and as a result, the magnetization depth from the surface of the magnetic tape becomes extremely shallow.

Therefore, efforts have been made to improve the high-output characteristics, especially the S / N ratio, even for short-wavelength signals. Development and Technology for Highly Dispersing Magnetic Powder "(1982
Year, page 74, “‥‥ Recording / playback characteristics, electromagnetic conversion characteristics, ie, factors for high-density recording, such as noise reduction, S / N ratio, sensitivity, improvement in frequency characteristics, and reduction in output fluctuation. The major issues in the design of the magnetic coating layer imposed to overcome the problems are (1) uniform dispersion of the magnetic particles and improvement of the magnetic field orientation, (2) higher filling ratio of the magnetic particles in the coating,
(3) It is excellent in surface smoothness and has no thickness unevenness. The description for “‥‥” and the condition for high-density recording on the coated tape on page 312 are that high-output characteristics can be maintained with low noise for short-wavelength signals. It is necessary that the coercive force Hc and the residual magnetization Br are both large and that the thickness of the coating film is thinner.
‥‥ ”.

[0005] As the thickness of the magnetic recording layer has been reduced, several problems have arisen. First, there is a problem of smoothing and uneven thickness of the magnetic recording layer. As is well known, in order to make the magnetic recording layer smooth and free of thickness unevenness, the surface of the base film must also be smooth. . This fact can be found, for example, in “Implementation of Engineering Information Center,“ Magnetic Tape-Factor / Wear Occurrence Factors and Trouble Measures for Head Running System-Comprehensive Technical Data Collection (hereinafter referred to as “Comprehensive Technical Data Collection-”) ”(Showa 62)
Years) p. 180 and p. 181 "The surface roughness of the magnetic layer after hardening strongly depends on the surface roughness (back surface roughness) of the base, and both are almost proportional to each other. As the surface of the base is made smoother, a uniform and large head output is obtained and the S / N is improved.

[0006] Second, the base film is also becoming thinner in the same manner as the magnetic layer, and as a result, the strength of the base film is becoming a problem. This fact is described, for example, in the above-mentioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Particles” on page 77, “‥‥ High Density Recording is a major theme that has been imposed on current magnetic tapes. This is important in reducing the length of the tape to reduce the size of the cassette and for long-time recording, which requires reducing the thickness of the film base. . ‥‥
As the tape becomes thinner, the stiffness of the tape sharply decreases, so that smooth running on the recorder becomes difficult. As the video tape becomes thinner, there is a great demand for improvement of the stiffness in both the longitudinal direction and the width direction. ‥‥ ”.

Third, there is a problem that the light transmittance is increased due to the finer magnetic particles and the thinner magnetic recording layer. That is, the stop of the running of a magnetic recording medium such as a magnetic tape, particularly a video tape, is performed by detecting a portion of the magnetic recording medium having a high light transmittance by a video deck. As the light transmittance of the entire magnetic recording layer increases as the magnetic recording medium becomes thinner and the magnetic particles dispersed in the magnetic recording layer become ultrafine, the detection by the video deck becomes difficult. The light transmittance has been reduced by adding carbon black or the like to the glass. Therefore, in current video tapes, the addition of carbon black or the like to the magnetic recording layer is indispensable.

As a prior art relating to a magnetic recording medium having at least one lower layer in which a non-magnetic powder is dispersed in a binder on a non-magnetic support, Japanese Patent Application Laid-Open No. 63-187 discloses a prior art.
418, JP-A-4-167225 and JP-A-5-182177.

[0009]

As described above, in order to solve the problem that the light transmittance is increased by reducing the thickness of the magnetic recording layer, it is necessary to add carbon black or the like to the magnetic recording layer. .

However, the addition of non-magnetic carbon black not only hinders high-density recording but also hinders thinning, and reduces the magnetization depth from the surface of the magnetic tape. In order to further reduce the film thickness, it is not desirable to add non-magnetic particle powders other than the magnetic particle powder to the magnetic recording layer.

Therefore, in the method described in the above-mentioned Japanese Patent Application Laid-Open No. 63-187418, at least one lower layer in which a non-magnetic powder is dispersed in a binder is provided on a non-magnetic support, whereby light transmission is achieved. It is said to solve the problems such as improvement of the efficiency and deterioration of surface properties and electromagnetic conversion characteristics.

This publication describes many substances as non-magnetic powders, and also describes that granular or acicular particle powders having a very wide range of particle diameters can be used.

The present inventor examined each of these non-magnetic particle powders, and found that the surface of the non-magnetic particle powder was smooth even when the granular non-magnetic particle powder was used and also when the needle-shaped non-magnetic particle powder was used. It was found that the properties and strength were still insufficient.

When the acicular α-FeOOH disclosed in the above-mentioned embodiment of JP-A-4-167225 is used, the surface of acicular α-FeOOH particles contains a large amount of crystallization water. Furthermore, the affinity with the binder resin and the solvent is poor, and it is difficult to obtain a desired degree of dispersion.

In order to obtain high surface smoothness in the non-magnetic underlayer, it is necessary to disperse the non-magnetic particles in the binder resin at a very high level . Regarding the dispersibility of the non-magnetic underlayer coating composed of non-magnetic particle powder, binder resin, solvent and the like, see “Elucidation of Dispersion / Agglomeration and Applied Technology”, pp. 94-96, supra.
"‥‥ Many natural and synthetic polymers are adsorbed on the surface of colloidal particles to form a thick adsorption layer, which greatly affects the stability of the dispersion system. 系 Molecular weight of polymer (M) And the saturated adsorption amount (As), the following relationship generally holds: As = K ₁ M ^a (Applicant: Note: a in the formula is α
It means. Here, K ₁ and α are constants peculiar to the system, particularly α is called a molecular weight dependent parameter, and varies from 0 to 1 depending on the structure of the adsorption layer. When ‥‥ α = 1, the polymer is adsorbed at the molecular end, and As is proportional to the molecular weight (M). In this system, the polymer forms a thickest adsorbed layer formed on the particle surface, so that it exhibits a strong steric repulsion effect and more effectively contributes to the stability of the dispersion system. As described in “‥‥”, a molecular weight-dependent parameter α (hereinafter, referred to as α).
Can be represented by

This α is determined by the method of coating the particle surface of an inorganic powder such as α-iron oxide with an inorganic oxide such as Al ₂ O ₃ or SiO ₂ as described in the above-mentioned Japanese Patent Application Laid-Open No. 5-182177. It was found to be about 0.40 to 0.45, and about 0.28 to 0.34 for the case where the coating treatment was not performed as in the above-mentioned JP-A-4-167225.

Accordingly, the present invention provides a non-magnetic recording medium having excellent surface smoothness and strength by using α-Fe ₂ O ₃ particle powder having α larger than 0.50 and excellent dispersibility. It is a technical object of the present invention to provide a magnetic underlayer and to provide a magnetic recording layer having a small light transmittance and a smooth and uniform thickness when a magnetic recording layer is provided on the underlayer.

[0018]

The above technical object can be achieved by the present invention as described below.

That is, the present invention relates to a non-magnetic underlayer for a magnetic recording medium comprising a coating composition comprising a non-magnetic particle powder formed on a non-magnetic support and a binder resin; Al or Si or Al on the particle surface
And the molecular weight dependent parameter α value to which ultrafine particles of oxides of Si or ultrafine particles of hydroxide are fixed is 0.50.
A non-magnetic underlayer for a magnetic recording medium, characterized by using the above-mentioned non-magnetic particle powder of acicular α-Fe ₂ O ₃ particles.

Further, the present invention relates to a method for producing a non-magnetic particle powder, comprising:
Dependent parameter α value is 0.55 or more
The non-magnetic underlayer for a magnetic recording medium described above. Ma
Further, the present invention provides an aqueous suspension containing acicular α-Fe ₂ O ₃ particles.
The pH value of the suspension was adjusted to 10 by adding an aqueous alkali solution to the solution.
As described above, the suspension contains Al or Si or Al and
An aqueous solution containing Si is added, and while stirring, p
Adjust the H value to near neutral to adjust the Al or Si or Al
After the rapid precipitation of the hydroxide of Si and Si, the particles in the liquid
Is filtered with hydroxide to separate the particles and hydroxide from the particles.
After the mixture is washed with water and dried,
The mixture must be compacted by an edge runner.
The surface of the non-magnetic particle powder with Al or Si
Or ultrafine particles or hydroxides of Al and Si oxides
Weight-dependent parameter α value to which ultrafine particles are fixed
Consists of acicular α-Fe ₂ O ₃ particles having a particle size of 0.50 or more
Obtaining a non-magnetic particle powder;
This is a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer. Also,
The present invention relates to an aqueous suspension containing acicular α-Fe ₂ O ₃ particles.
PH value of the suspension is 10 or more by adding an aqueous alkali solution
And the suspension contains Al or Si or Al and Si
PH value of this solution with stirring.
Is adjusted to near neutral to adjust Al or Si or Al and S
After rapidly precipitating the hydroxide of i, the particles in the liquid are washed with water.
It consists of the particles and hydroxide separated by filtration with oxide
A mixture is obtained, and the mixture is washed with water and dried.
To consolidate and pulverize objects with an edge runner?
A non-magnetic particle powder comprising an aqueous suspension containing the particles.
An aqueous alkaline solution was added to the suspension to adjust the pH of the suspension to 1
From the operation of 0 or more, the mixture is
At least two times before performing the compaction crushing process.
By repeating the above, Al
Or ultrafine particles of Si or Al and Si oxides or
Is the molecular weight dependent parameter to which the ultrafine hydroxide particles are fixed.
Needle-like α-Fe ₂ O ₃ particles with a heater α value of 0.55 or more
Magnetism characterized by obtaining non-magnetic particle powder consisting of particles
A method for producing a non-magnetic particle powder for a non-magnetic underlayer of a recording medium.
You.

Next, various conditions for implementing the present invention will be described.

The acicular α-Fe ₂ O ₃ particles according to the present invention are prepared by adding a suspension containing ferrous hydroxide colloid obtained by adding an equivalent or more of an aqueous alkali hydroxide solution to a normal aqueous ferrous salt solution at pH 11; As described above, a method of generating needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower to perform an oxidation reaction, a method of reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution to obtain FeCO ₃ A method of generating spindle-shaped goethite particles by performing an oxidation reaction by passing an oxygen-containing gas through a suspension containing the method,
An oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding a less than equivalent amount of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to an aqueous ferrous salt solution to perform an oxidation reaction. After generating acicular goethite core particles, and then adding an aqueous solution of an alkali hydroxide at least equivalent to Fe ²⁺ in the aqueous ferrous salt solution to the aqueous ferrous salt solution containing the acicular goethite core particles, A method for growing the acicular goethite core particles by passing an oxygen-containing gas and a ferrous hydroxide colloid obtained by adding an aqueous solution of an alkali hydroxide or an alkali carbonate which is less than the equivalent of a ferrous salt aqueous solution; An oxygen-containing gas is passed through the aqueous iron salt solution to perform an oxidation reaction to generate acicular goethite nucleus particles, and then grow the acicular goethite nucleus particles in an acidic to neutral region. Needle-like goethite particles or spindle- like goethite particles obtained by a method or the like are used as precursor particles.

During the formation reaction of the goethite particles, Ni, Z usually added for the purpose of improving the characteristics of the particle powder, etc.
There is no problem even if different elements such as n, P, and Si are added.

Needle-like goethite particles as precursor particles or
The spindle-shaped goethite particles are dehydrated at a temperature in the range of 200 to 500 ° C. or, if necessary, further subjected to 350 to 80.
Annealed by heat treatment in a temperature range of 0 ° C. to obtain acicular α-Fe ₂ O ₃ particles or spindle-shaped α-Fe ₂ O ₃
Particles (hereinafter simply referred to as “acicular α-Fe ₂ O ₃ particles”)
U. Get)

There is no problem even if a sintering inhibitor such as P, Si, B, Zr, or Sb adheres to the surface of the acicular goethite particles to be dehydrated or annealed.

Annealing by heat treatment at a temperature in the range of 350 to 800 ° C. is performed by using a needle-like α obtained by dehydration.
The annealed -fe ₂ O ₃ particles vacancy occurring on the particle surfaces of, because it is preferable to a smooth surface condition blocking the pores to melt the electrode surface of the particles.

In the present invention, an alkaline aqueous solution is added to an aqueous suspension containing acicular α-Fe ₂ O ₃ particles to adjust the pH value of the suspension to 10 or more, and then Al or Si or Al and Si The reason for adding the aqueous solution containing is that the particles are sufficiently and uniformly mixed by utilizing the electric repulsion between the particles in the aqueous suspension.

As the alkaline aqueous solution for adjusting the pH value to 10 or more, an aqueous solution of sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used.

As the aqueous solution containing Al, an aqueous solution of an alkali aluminate such as sodium aluminate or potassium aluminate, or an aluminum salt such as aluminum sulfate, aluminum chloride or aluminum nitrate can be used.

The amount of the compound containing Al is in the form of an acicular α
To -fe ₂ O ₃ particles, in terms of Al 0.01
0.0% by weight. If less than 0.01% by weight,
The dispersibility in the binder resin is insufficient. 20.0
When the amount exceeds 10% by weight, the desired effects of the present invention can be obtained. When considering the dispersibility of the target substance, 0.05 to
10.0% by weight is preferred.

As the aqueous solution containing Si, an aqueous solution of sodium silicate, potassium silicate, colloidal silica, No. 3 water glass or the like can be used.

The amount of the compound containing Si is in the form of an acicular α
To -fe ₂ O ₃ particle powder, 0.01 in terms of SiO ₂
２20.0% by weight. If it is less than 0.01% by weight, dispersibility in the binder resin is insufficient. 2
If the content exceeds 0.0% by weight, the desired effect of the present invention can be obtained, but if it exceeds 0.0% by weight, the effect is saturated, and it is not industrial. In consideration of the dispersibility of the target substance, 0.
It is preferably from 0.05 to 10.0% by weight.

When the mixed aqueous solution containing Al and Si is added in the present invention, the total amount of the acicular α-Fe ₂ O ₃ particles in terms of Al and SiO ₂ is 0.01 to
20.0% by weight, preferably 0.05 to 10.0% by weight
It is.

An aqueous alkali solution is added to the aqueous suspension containing the acicular α-Fe ₂ O ₃ particles to adjust the pH of the suspension to 1
From the operation of 0 or more to the operation of compacting and pulverizing the mixture with an edge runner, the amount of addition of the compound containing Al or Si at one time in the case of repeating at least two times or more, the total amount of the respective addition amounts You only have to consider
Preferably each is 0.05 to 10.0% by weight.

In the present invention, the compound of Al or Si is used as an aqueous solution because it has a needle-like α having a pH value of 10 or more.
In order to sufficiently and uniformly mix in a suspension containing Fe ₂ O ₃ particles, it is also possible to add a compound of Al or Si as a crystal salt and sufficiently dissolve and mix in the suspension. it can.

In the present invention, an aqueous solution containing an Al or Si compound is added to a suspension containing needle-like α-Fe ₂ O ₃ particles having a pH value of 10 or more, and the suspension is rapidly stirred. By adjusting the pH to near neutrality (pH 6.5 to 8.5), almost all of Al and Si can be reduced to ultra-fine particles of each hydroxide .
By fast precipitation as a child acicular _α-Fe 2 _{O 3} particles and a hydroxide
And ultrafine particles of the above.

The time for the quick settling is in the range of 1 to 10 minutes. If the time exceeds 10 minutes, use acicular α-Fe ₂ O
A hydroxide of Al or Si may be formed in a layer on the surface of the _three particles. Therefore, after quick settling, it is quickly separated by filtration. It may be less than 1 minute, but the ultra fineness of Al or Si hydroxide
It takes about one minute to precipitate as particles and mix well.

As the acid for adjusting the pH, sulfuric acid, hydrochloric acid, acetic acid, nitric acid, carbon dioxide gas and the like can be used.

In the present invention, in order to improve the strength and durability by reducing the amount of residual solvent after drying the coating film in the non-magnetic underlayer for a magnetic recording medium, in addition to Al and Si, Zn, Co, Ni, V, Mg, Ca, Sr, B
It is more preferable to add a compound selected from a, Bi, P and the like. In order to improve the running durability by reducing the mechanical strength (scratch characteristics) and the coefficient of friction, Al
It is more preferable to add a compound selected from Zr, Ti, Hf, Mo and the like in addition to Si and Si. Further, when the surface resistance is reduced to improve the surface smoothness and the chargeability, Sn, Sb, Ag, Pd, C
It is more preferable to add a compound selected from u, Fe and the like. Each of these compounds is a sulfate of each element,
Water soluble salts such as chlorides, nitrates and acetates can be used.

These compounds may be added in appropriate combination in accordance with the purpose of addition and the properties of the element, and the amount of the compound added to the acicular α-Fe ₂ O ₃ particle powder may be It is 0.01 to 20.0% by weight in conversion.
If it is less than 0.01% by weight, dispersibility in the binder resin is insufficient. When the content exceeds 20.0% by weight, the effects aimed at by the present invention can be obtained, but when it exceeds 20.0% by weight, the effect saturates and is not industrial. In consideration of the dispersibility of the target substance, the content is preferably 0.05 to 10.0% by weight.

It is desirable to carry out the following operations for Ca, Sr, and Ba among the above-mentioned compounds which may be eluted by washing after substantially the entire amount is precipitated as hydroxide. When Ca is neutralized with the above-mentioned acid other than carbon dioxide, it is possible to make it difficult to elute Ca ions as CaCO ₃ by bubbling by blowing a little carbon dioxide after adjusting the pH. When Sr is also neutralized with the above-mentioned acid other than carbon dioxide, it is possible to make it difficult to elute Sr ions as SrCO ₃ by bubbling by blowing a little carbon dioxide after adjusting the pH. B
a is desirably neutralized with sulfuric acid. When neutralized with the above-mentioned acid other than sulfuric acid, the pH is adjusted and sulfuric acid is again used with sulfuric acid.
It is preferable to make it difficult to elute as aSO ₄ .

Further, in the present invention, acicular α-Fe ₂ O ₃
The mixture of the particles and the hydroxide may be filtered, washed with water, and dried in a conventional manner.

Since the above-mentioned mixture is present by interaction, the filtration, washing and drying can be carried out as usual, and the workability is not particularly deteriorated.

As the edge runner used in the compaction pulverization treatment in the present invention, "Sandmill" manufactured by Matsumoto Cast Iron Works, "Mix Muller" manufactured by Shinto Kogyo KK, or the like can be used.

The weight of the edge runner is 15 to 80 kg.
/ Cm, more preferably 30 to 60 kg / cm. When it is less than 15 kg / cm, the shearing force due to the grinding is too weak, so that the mechanochemical effect cannot be obtained. 8
If it exceeds 0 kg / cm, the shearing force due to the grinding is too strong, and the particles themselves may be broken. The processing time is 15 to 120 minutes, preferably 3 minutes.
0-60 minutes.

In the present invention, the operation of compacting and pulverizing the mixture of the acicular α-Fe ₂ O ₃ particles and the hydroxide with an edge runner at least twice or more is performed in the present invention.
Preferably, it may be repeated 2 to 5 times. The effect can be obtained when the number of times exceeds 5, but the effect tends to be saturated.
It is no longer industrial.

In the present invention, the surface-treated acicular α
The average major axis diameter of the Fe ₂ O ₃ particles is 0.05 to 0.25 μ;
m, the minor axis diameter is 0.010 to 0.035 μm, the particle size distribution is 1.40 or less in geometric standard deviation, and the axial ratio (major axis diameter / minor axis diameter—the same applies hereinafter) is 2 to 20.

If the average major axis diameter is less than 0.05 μm, it is not preferable because dispersion in the binder resin becomes difficult. When the average major axis diameter exceeds 0.25 μm,
Since the particle size is too large, surface smoothness is impaired, which is not preferable.

If the average minor axis diameter is less than 0.010 μm, it is not preferable because dispersion in the binder resin becomes difficult. If the average minor axis diameter exceeds 0.035 μm, the particle size is too large, which impairs surface smoothness, which is not preferred.

If the particle size distribution exceeds 1.40 in terms of geometric standard deviation, it is not preferable because the existing coarse particles adversely affect the surface smoothness of the coating film.

When the axial ratio is less than 2, it is difficult to obtain a desired coating strength, which is not preferable. If the axial ratio exceeds 20, the interaction between particles increases, which adversely affects the dispersion.

As the binder resin in the present invention, vinyl chloride vinyl acetate copolymer, urethane resin, vinyl chloride vinyl acetate maleate urethane elastomer, butadiene acrylonitrile copolymer, Polyvinyl butyral,
Cellulose derivatives such as nitrocellulose, polyester resins, synthetic rubber resins such as polybutadiene, epoxy resins, polyamide resins, polyisocyanate polymers, electron beam-curable acrylic urethane resins and the like and mixtures thereof can be used. Also, each binder resin has -OH,-
_{COOH, -SO 3 M, -OPO 2} M 2, polar groups such as -NH ₂ (where, M is H, Na, a K.) May be contained.

The non-magnetic underlayer for a magnetic recording medium according to the present invention comprises a needle-like α-Fe ₂ O ₃ surface-treated on a non-magnetic support.
It is obtained by applying a coating composition containing the particle powder and the binder resin to form a coating. The non-magnetic underlayer has
There is no problem even if a lubricant, an abrasive, an antistatic agent or the like used in the manufacture of a normal magnetic recording medium is added.

Examples of the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and the like which are currently widely used for magnetic recording media.
Synthetic resin film such as polyimide and aluminum,
Metal foils and plates such as stainless steel and various types of paper can be used.

In the present invention, the thickness of the undercoat layer after coating the coating composition on the non-magnetic support and drying the coating composition is 1 to 3.
It is in the range of 10 μm. If it is less than 1 μm, not only the surface roughness of the base film cannot be improved, but also the strength is insufficient. Although it may exceed 10 μm,
In order to obtain a thin-film magnetic recording medium, the thickness needs to be 10 μm or less, and preferably in the range of 2 to 4 μm.

A magnetic recording medium is obtained by applying a coating composition containing magnetic particles and a binder resin on the non-magnetic underlayer for a magnetic recording medium according to the present invention to form a magnetic recording layer. Can be.

A commonly used lubricant, abrasive, antistatic agent and the like may be added to the magnetic recording layer.

The magnetic particles in the magnetic recording layer include magnetic iron oxide particles such as maghemite particles, magnetite particles, and a beltlide compound particle which is an intermediate oxide between maghemite and magnetite; Co, Al, Ni other than Fe
Particles containing different elements such as P, Zn, Si, and B or particles obtained by coating these magnetic iron oxide particles with Co or the like;
Iron-based metal magnetic particles, Co, Al other than iron,
Iron alloy magnetic particles containing Ni, P, Zn, Si, B, etc., plate-like Ba ferrite particles, and divalent metals (Co, Ni, Zn, etc.) as coercive force reducing agents and tetravalent metals (Ti , Sn, Zr, etc.) in the form of a plate-like composite ferrite particle powder. Also,
The magnetic particle powder may be in any of a needle shape, a spindle shape, a cubic shape, a plate shape, and the like.

As the binder resin in the magnetic recording layer, those used for forming the underlayer can be used.

[0060]

The non-magnetic underlayer for a magnetic recording medium according to the present invention comprises:
Since the surface smoothness and strength are excellent, the light transmittance is small when the coating composition containing the magnetic particle powder and the binder resin is applied to the surface to form a magnetic recording medium, and the surface is smooth. As a result, a thin magnetic recording layer having excellent strength without thickness unevenness can be obtained.

The non-magnetic underlayer for a magnetic recording medium according to the present invention has excellent surface smoothness and strength for the following reasons.

In other words, “Pigment particles considered to be rod-like, such as needle-like γ-Fe ₂ O ₃ ,” p. Then, the rod-shaped particles parallel to the support have greater hiding power and gloss and less light and gas permeability than the case where they are perpendicular to each other. It also affects the mechanical properties of the coating, with the tensile strength increasing and the elongation decreasing as the level increases.
As described in “‥”, it has been found that the acicular particles can be oriented at the time of coating, and the oriented acicular particles have reduced light transmittance and improved surface smoothness and strength.

However, if the dispersibility of the magnetic powder particles is poor, the smoothness of the surface is poor, but the magnetic properties are deteriorated due to the influence of the orientation. As described in “‥‥”, the dispersibility of the particle powder is a problem.

The present inventors have studied various non-magnetic acicular particle powders capable of improving the surface smoothness and strength. As a result, the non-magnetic particle powder used for the non-magnetic underlayer for the magnetic recording medium was also changed to the magnetic recording layer. If the same iron oxide particle powder as the magnetic particle powder used for the base film is formed by coating on the base film, the affinity with the binder resin increases and the good adhesion and durability are obtained and a good one is obtained. Think, non-magnetic acicular α-
Fe ₂ O ₃ particles were selected.

However, it was found that simply applying the α-Fe ₂ O ₃ particles dispersed in a binder resin and applying the resulting mixture did not provide sufficient orientation, did not provide sufficient surface smoothness, and did not have sufficient strength. Therefore, various studies were conducted to make the acicular α-Fe ₂ O ₃ particles easy to disperse in the binder resin.

First, the dispersibility will be described. As described above, α is obtained by coating the particle surface with an Al compound or a Si compound by the method described in the above-mentioned JP-A-5-182177.
The reason why the α of the Fe ₂ O ₃ particle powder is as low as about 0.40 to 0.45 is that “‥‥ The surface treatment layer may be a porous layer depending on the purpose, It is generally preferred that the density be higher than that of Si.
In order to coat the compound and Al compound uniformly and densely on the particle surface, the hydroxide of the compound is deposited and coated over a relatively long time, so that the number of polymer adsorption points on the particle surface is small. Then, it was considered that the dispersibility when the particle powder was dispersed in the polymer resin was insufficient.

The application field differs in that the coating is performed uniformly over a relatively long period of time, for example, as described in each of the examples of the above-mentioned JP-B-54-7292. After the addition was completed, stirring was continued for about 30 minutes. "And the above-mentioned JP-A-51-479.
No. 23 and JP-A-51-66320, the surface of iron oxide particles is coated over a relatively long period of time as described in the description of "{1 hour after neutralization}". Is a common practice.

Therefore, the present inventor has proposed that acicular α-Fe ₂ O ₃
A method for increasing the thickness of the polymer adsorption layer by increasing the number of polymer adsorption points on the particle surface as much as possible was studied.

As a result, in the present invention, Al or S
Considering that ultrafine particles of i or Al and Si oxides or hydroxides need to be adsorbed on the surface of the needle-like α-Fe ₂ O ₃ particles as much as possible, and it is necessary to chemically adsorb these particles. Ultrafine particles of Al or Si or hydroxides of Al and Si are uniformly precipitated and mixed in the suspension containing, and the mechanochemical effect of consolidating the mixture causes Al or Si or Al and Since oxide or hydroxide ultrafine particles of Si could be firmly fixed, α was 0.50 or more,
In particular, it could be increased to about 0.50 to 0.70. This is thought to be the result of increasing the number of polymer adsorption points on the particle surface.

In particular, A is added to the surface of the acicular α-Fe ₂ O ₃ particles.
In the case where l or Si or an oxide or hydroxide of Al and Si is fixed, there is a great effect in compatibility with the binder resin, and the needle-like α-F
It has good dispersibility in a coating composition containing e ₂ O ₃ particles and a binder resin, and when applied on a base film, mechanical orientation is smoothly performed on the base film. The non-magnetic underlayer for a magnetic recording medium was found to have excellent surface smoothness and excellent strength.

As a result of further study, it was found that acicular α-Fe
_{When the 2} O ₃ particles have an average major axis diameter of 0.05 to 0.25 μm, an average minor axis diameter of 0.010 to 0.035 μm, and a particle size distribution of 1.40 or less in geometric standard deviation and an axial ratio of 2 to 20. It was found that the obtained nonmagnetic underlayer for a magnetic recording medium had better surface smoothness and better strength.

Such a result was obtained because needle-like α-
By fixing ultrafine particles of Al or Si or oxides of Al and Si or ultrafine particles of hydroxide on the surface of Fe ₂ O ₃ particles, the affinity with the binder resin is improved and the dispersibility is improved. I believe.

JP-A-62-295217 discloses that a magnetic layer contains α-Fe ₂ O ₃ powder whose particle surface is coated with a compound containing at least one element of Si, Cr and Al. A magnetic recording medium is disclosed, but in this case, as in the case of adding non-magnetic carbon black or the like, not only does high-density recording be hindered, but it also hinders thinning. . Therefore, as described above, the magnetization depth from the surface of the magnetic tape is made shallow, and the thickness of the magnetic tape becomes insufficiently thin.

[0074]

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

The average major axis diameter, average minor axis diameter, and axial ratio of the particles in the following Examples and Comparative Examples are all shown as average values of numerical values measured from electron micrographs.

The particle size distribution of the particles was represented by a geometric standard deviation (σg) obtained by the following method. That is, the major axis diameter of 350 particles shown in a 120,000-fold electron micrograph was measured, and the logarithmic normal was calculated from the actual major axis diameter and the number of particles calculated from the measured value according to a statistical method. On the probability paper, the horizontal axis represents the major axis diameter of the particles, and the vertical axis represents the percentage of the cumulative number of particles belonging to each of the _ major axis diameter sections. The graph shows that the number of particles is 50% and 84.13.
%, And read the value of the major axis diameter corresponding to each of the%, and when the geometric standard deviation value (σg) = 84.13% of the number, the major axis diameter (μ)
m) / 50% of the number is shown as a value calculated according to the major axis diameter (μm).

The specific surface area is shown by a value measured by the BET method.

The amount of each element of the compounds such as Al, Si, Zn, Mg, P, Zr, Ti, and Sb fixed or coated on the acicular α-Fe ₂ O ₃ particles was measured by X-ray fluorescence analysis.

The evaluation of the dispersibility in the present invention is carried out by the value of α, and the value of α is determined by the binder having different molecular weights (M =
15,000, 28000, 42000), and the saturated adsorption amount (As) of each binder to the goethite particle powder or the hematite particle powder was measured by an ordinary method,
A linear relationship was obtained by plotting the obtained As and M on a log-log table, and the value of α was determined from the slope of the straight line.

The gloss was measured using a gloss meter UGV-5.
D "(manufactured by Suga Test Instruments Co., Ltd.) to measure the 45 ° gloss of the coating film.

The surface roughness Ra is expressed by “Surfcom-57
5A "(manufactured by Tokyo Seimitsu Co., Ltd.) was used to measure the center line average roughness of the coating film.

The strength of the coating film was determined by measuring the Young's modulus of the coating film using “Autograph” (manufactured by Shimadzu Corporation). Young's Modulus is a commercial videotape "AV T-120
(Manufactured by JVC) ". The higher the relative value, the better.

The magnetic characteristics are described in “Vibrating sample magnetometer VSM-
3S-15 "(manufactured by Toei Industry Co., Ltd.) using an external magnetic field of up to 10 KOe.

The light transmittance of the magnetic sheet was represented by a linear absorption coefficient measured using a “photoelectric spectrophotometer UV-2100” (manufactured by Shimadzu Corporation). The linear absorption coefficient is defined by the following equation, and the larger the value, the more difficult it is to transmit light. Linear absorption coefficient (μm ⁻¹ ) = ln (1 / t) / FT t: Light transmittance at λ = 900 nm (−) FT: Thickness of coating film composition layer of film used for measurement (μ)
m) If the linear absorption coefficient is 1.2 or more (film thickness 4.0 μm), the light transmittance 0.8% or less defined by the VHS standard can be satisfied.

<Production of Acicular α-Fe ₂ O ₃ > Examples 1 to 8 and Comparative Examples 1 to 7;

Example 1 Acicular α-FeOOH particle powder (average major axis diameter 0.20 μm)
m, average short axis diameter 0.019 μm, axial ratio 10.5, BET
10 kg of a specific surface area of 134.4 m ² / g) was put into an open-type retort container, and 5 kg in air while being driven to rotate.
The resultant was dehydrated by heating at 00 ° C. for 75 minutes, and further annealed at 630 ° C. for 100 minutes to obtain acicular α-Fe ₂ O ₃ particles.

The obtained acicular α-Fe ₂ O ₃ particles had an average major axis diameter of 0.13 μm and an average minor axis diameter of 0.023 μm.
m and the axial ratio were 5.7.

Next, 6 kg of the obtained α-Fe ₂ O ₃ particle powder is stirred and mixed in water, and wet-pulverized by a line mill type pulverizer (Homomic Line Mill, manufactured by Tokushu Kiko Kogyo KK) to perform α-Fe ₂ O ₃ particle powder. A suspension containing Fe ₂ O ₃ particles was obtained.

While stirring the suspension, 0.1 mol /
One liter of aqueous NaOH solution was added until the pH value was 10.5. After stirring and mixing the above mixed suspension, 1.0 mo
667 ml of 1 / l aqueous sodium aluminate solution (α-F
This corresponds to 3.00 wt% in terms of Al with respect to the e ₂ O ₃ particle powder. ) Was added and stirred and mixed. Then, a 1.0 mol / l HCl aqueous solution was added to the suspension while stirring to adjust the pH value to 7.1. The required time at that time was 5 minutes. Immediately, it was filtered, washed with water and dried by a conventional method to obtain acicular α-Fe ₂ O ₃ particles.

The obtained acicular α-Fe ₂ O ₃ particles powder 5k
g was put into an edge runner "MPUV-2" (manufactured by Matsumoto Cast Iron Works) and compacted and pulverized at a linear load of 60 kg / cm for 60 minutes.

The obtained acicular α-Fe ₂ O ₃ particles powder was A
1 The amount of fixation was 2.99% by weight, and α was 0.55.

Further, 4.5 kg of the obtained acicular α-Fe ₂ O ₃ particle powder was mixed and stirred again with water, and then 0.1 mol
The pH value was adjusted to 11.0 by adding 1 l of aqueous NaOH solution.
Next, 311.4 g of the No. 3 water glass solution (α-Fe ₂ O ₃
This corresponds to 2.00 wt% in terms of SiO ₂ with respect to the particle powder. ) Was added and stirred and mixed to obtain a suspension. Subsequently, the suspension was stirred and 1.0 mol / l of HC was added.
The pH was adjusted to 7.5 with 1 aqueous solution. The required time at that time was 4 minutes. Immediately, it was filtered, washed with water and dried by a conventional method to obtain acicular α-Fe ₂ O ₃ particles.

The obtained acicular α-Fe ₂ O ₃ particles powder 4k
g was put into an edge runner "MPUV-2" (manufactured by Matsumoto Cast Iron Works) and compacted and pulverized at a linear load of 60 kg / cm for 30 minutes.

The average long axis diameter of the obtained acicular α-Fe ₂ O ₃ particles having the Al compound and the Si compound fixed thereto is 0.
13 μm, average minor axis diameter 0.023 μm, axial ratio 5.
7. The particle size distribution has a geometric standard deviation of 1.36.
The specific surface area was 59.8 m ² / g. Also, p
The H value was 7.8 and α was 0.58.

Examples 2 to 8 and Comparative Examples 1 to 7 Types of particles to be treated, temperature and time of dehydration treatment, temperature and time of annealing treatment, type and amount of compound to be added, treatment pH, addition / stirring Except that the adjustment time, the linear load and time of the consolidation treatment, and the number of treatments were variously changed, needle-like α-Fe ₂ O ₃ particles to which Al, Si, and other compounds were fixed were produced in the same manner as in Example 1. I let it.

Comparative Example 6 is acicular goethite particles, and Comparative Example 7 is granular α-Fe ₂ O ₃ particles obtained by firing magnetite particles.

Tables 1 to 4 show the main manufacturing conditions and various characteristics at this time.

[0098]

[Table 1]

[0099]

[Table 2]

[0100]

[Table 3]

[0101]

[Table 4]

<Production of Non-magnetic Underlayer for Magnetic Recording Medium> Examples 9 to 16 and Comparative Examples 8 to 14;

Example 9 Using the acicular α-Fe ₂ O ₃ particle powder obtained in Example 1, first, the α-Fe ₂ O ₃ particle powder, a binder resin,
The mixture was mixed with a solvent and kneaded at a solid content of 75% by weight using a plastmill for 30 minutes. Thereafter, a predetermined amount of the kneaded material was taken out, added to a glass bottle together with glass beads and a solvent, and mixed and dispersed for 6 hours with a paint conditioner.

The final composition of the obtained coating composition is as follows. Acicular α-Fe ₂ O ₃ particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Cyclohexanone 40.9 parts by weight Methyl ethyl ketone 102. 2 parts by weight Toluene 61.3 parts by weight

The obtained coating composition was coated on a polyethylene terephthalate film having a thickness of 14 μm using an applicator to a thickness of 45 μm, and then dried to obtain a nonmagnetic underlayer.

The gloss of the obtained nonmagnetic underlayer was 226%,
The surface roughness Ra was 8.8 nm, and the Young's modulus was 125.

Examples 10 to 16 and Comparative Examples 8 to 14 Needle-like α-Fe obtained in Examples 2 to 8 and Comparative Examples 1 to 7
_A nonmagnetic underlayer was obtained in the same manner as in Example 9 using ₂ O ₃ particles (however, Comparative Example 6 was acicular goethite particles, and Comparative Example 7 was granular α-Fe ₂ O ₃ particles). Was.

Table 5 shows various characteristics at this time.

[0109]

[Table 5]

<Manufacture of Magnetic Tape> Reference Examples 1 to 10;

REFERENCE EXAMPLE 1 Co-coated magnetic iron oxide particles (average major axis diameter: 0.19 μm, average minor axis diameter: 0.026 μm, Hc: 912 Oe, .sigma.
0 emu / g. ), First, the magnetic particle powder, the binder resin, and the solvent are mixed, and the solid content is 76% by weight.
And kneaded using a plast mill for 30 minutes. After a while
A predetermined amount of the kneaded material is taken out, added to a glass bottle together with a glass bead and a solvent, and mixed with a paint conditioner.
Mixing and dispersion were performed for a time.

Thereafter, an abrasive, a lubricant and a hardener were added, and the mixture was further mixed and dispersed for 15 minutes. The composition of the magnetic paint was as follows. Co-coated magnetic iron oxide particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Abrasive 10 parts by weight Lubricant 2.5 Parts by weight Hardener 5 parts by weight Cyclohexanone 52.2 parts by weight Methyl ethyl ketone 130.5 parts by weight Toluene 78.3 parts by weight

The obtained magnetic paint was applied on the nonmagnetic underlayer obtained in Example 9 to a thickness of 15 μm using an applicator, and then dried to obtain a sheet-shaped sample piece. After calendering the obtained sheet sample piece, a curing reaction was performed at 60 ° C. for 24 hours, and a 0.5-inch width slit was obtained to obtain a magnetic tape.

The thickness of the magnetic coating film of the obtained magnetic tape was 1.3 μm, Hc was 951 Oe, and squareness ratio was 0.9.
0, gloss was 185%, surface roughness Ra was 5.6 nm, Young's modulus was 135, and linear absorption coefficient was 1.24.

Reference Examples 2 to 10 Using the nonmagnetic underlayers obtained in Examples 9, 11 and 14 and Comparative Examples 8 and 13, magnetic recording media were obtained in the same manner as in Reference Example 1.

Table 6 shows the characteristics at this time.

[0117]

[Table 6]

[0118]

According to the present invention, the non-magnetic underlayer for a magnetic recording medium according to the present invention has an Al or Si
Alternatively, since an α or Fe ₂ O ₃ particle powder having a large α of 0.50 or more and excellent dispersibility was used by fixing oxides or hydroxides of Al and Si, a non-magnetic recording medium was used. It has excellent strength and surface properties as a magnetic underlayer. As shown in the reference example above, when a magnetic paint containing magnetic particle powder and a binder resin is applied to its surface to obtain a magnetic recording medium, A thin magnetic recording layer having a small transmittance, a smooth surface, and excellent strength without uneven thickness can be obtained.

Continued on the front page (72) Inventor Hiroko Morii 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Prefecture Toda Kogyo Co., Ltd. Creative Center (72) Minoko Sakota 4-chome, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima No. 2 Toda Kogyo Co., Ltd. Creative Center Examiner Naoya Matsuda (56) References JP-A-4-285726 (JP, A) JP-A-4-325915 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G11B 5/704 C01G 49/06

Claims (4)

(57) [Claims] 1. A non-magnetic underlayer for a magnetic recording medium comprising a coating composition comprising a non-magnetic particle powder formed on a non-magnetic support and a binder resin, wherein the non-magnetic particle powder is formed on the particle surface. ultrafine particles are fixed in the ultrafine particles or hydroxide of an oxide of Al or Si or Al and Si
A non-magnetic underlayer for a magnetic recording medium, wherein non-magnetic particles comprising needle-like α-Fe ₂ O ₃ particles having a molecular weight-dependent parameter α value of 0.50 or more are used. 2. A molecular weight-dependent parameter of a non-magnetic particle powder.
2. The method according to claim 1, wherein the α value is 0.55 or more.
A nonmagnetic underlayer for a magnetic recording medium according to the above . 3. An aqueous suspension containing acicular α-Fe ₂ O ₃ particles.
The pH value of the suspension was adjusted to 10 by adding an aqueous alkali solution to the solution.
As described above, the suspension contains Al or Si or Al and
An aqueous solution containing Si is added, and while stirring, p
Adjust the H value to near neutral to adjust the Al or Si or Al
After the rapid precipitation of the hydroxide of Si and Si, the particles in the liquid
Is filtered with hydroxide to separate the particles and hydroxide from the particles.
After the mixture is washed with water and dried,
The mixture must be compacted by an edge runner.
The surface of the non-magnetic particle powder with Al or Si
Or ultrafine particles or hydroxides of Al and Si oxides
Weight-dependent parameter α value to which ultrafine particles are fixed
Consists of acicular α-Fe ₂ O ₃ particles having a particle size of 0.50 or more
Obtaining a non-magnetic particle powder;
A method for producing a nonmagnetic particle powder for a nonmagnetic underlayer. 4. An aqueous suspension containing acicular α-Fe ₂ O ₃ particles.
The pH value of the suspension was adjusted to 10 by adding an aqueous alkali solution to the solution.
As described above, the suspension contains Al or Si or Al and
An aqueous solution containing Si is added, and while stirring, p
Adjust the H value to near neutral to adjust the Al or Si or Al
After the rapid precipitation of the hydroxide of Si and Si, the particles in the liquid
Is filtered with hydroxide to separate the particles and hydroxide from the particles.
After the mixture is washed with water and dried,
The mixture must be compacted by an edge runner.
In the non-magnetic particle powder consisting of:
PH value of the aqueous suspension
From the operation of making the mixture 10 or more
Until operation of the compacted grinding process, even a small 2
Over the non-magnetic particle powder
Ultrafine particles of Al or Si or oxides of Al and Si
Alternatively, the molecular weight-dependent pattern to which ultra-fine hydroxide particles are fixed
Needle-like α-Fe ₂ O having a parameter α value of 0.55 or more
Characterized by obtaining non-magnetic particle powder consisting of _three particles
Production of non-magnetic particle powder for non-magnetic underlayer of magnetic recording media
Law.