JP3047668B2 - Nonmagnetic black-brown hydrated iron hydroxide particles, method for producing the same, and underlayer for magnetic recording media using the powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to non-magnetic black-brown particles which are spindle-shaped particles and which comprise a single-phase, iron oxide-containing iron oxide particle having a single-phase goethite structure having a black-brown color. The present invention relates to the iron oxide-containing particles and a method for producing the same, and further relates to light transmission using the non-magnetic black-brown iron oxide particles having a hematite structure obtained by heating and dehydrating the iron oxide-containing particles. The present invention relates to a magnetic recording medium underlayer with improved efficiency.

[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, in recent years, the demand for higher image quality and higher image quality of video tapes has been increasing more and more, and the frequency of carrier signals to be recorded has become higher and higher than that of conventional video tapes, and a shift to a short wavelength region has been made. 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. To make the magnetic recording layer smooth and free of uneven thickness, the surface of the base film must also be smooth. This fact can be found, for example, in the Engineering Information Center Publishing Division, "Magnetic Tape-Factors Arising from Friction and Wear in Head Running System and Troubleshooting-Comprehensive Technical Data Collection (hereinafter referred to as" Comprehensive Technical Data Collection ")," (1987) 18
"The surface roughness of the magnetic layer after curing strongly depends on the surface roughness (back surface roughness) of the base, and both are almost in a proportional relationship. The smoother the surface of the base is, the more uniform and large the head output is obtained, and the higher the S / N ratio is.

[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. In order to improve (reduce) the light transmittance by adding carbon black or the like to a magnetic tape, it is essential to add carbon black or the like to a magnetic recording layer in a current video tape.

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 and JP-A-4-167225.

[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 has focused on these non-magnetic particles, particularly iron compounds, and found that α-iron oxide (α-
When Fe ₂ O ₃ ) is used, the light transmittance cannot be sufficiently reduced, and when the needle-like α-FeOOH disclosed in the above-mentioned embodiment of JP-A-4-167225 is used, However, the light transmittance could not be sufficiently reduced.

[0014] To try to improve the light transmittance (to try to reduce), then used although color of non-magnetic particles is better and has a brown to black, L ^* value as a collection of the particles , A ^* value and b ^* value are calculated according to JIS-Z-8729.
(Hereinafter the same), the color of α-FeOOH is L
^* Value is about 62 to 45, a ^* Value is about 20 to 10, b ^*
The value is yellow-brown having a value of about 55 to 20 and is α-Fe ₂ O ₃
Have an L ^* value of about 50 to 35 and an a ^* value of 50 to 25.
Degree, b ^* value is about 30 to 17 in reddish brown. Therefore, when α-FeOOH or α-Fe ₂ O ₃ is used as the underlayer for a magnetic recording medium, α-FeOOH or α-F
It is necessary that the color of e ₂ O ₃ be brown or black.

Iron oxide having a brown or black color is disclosed in
It is known that it can be obtained by the technical means disclosed in Japanese Patent Publication No. 3-17288. German Patent No. 882,562 discloses that an iron salt is precipitated with a basic agent in the presence of a manganese salt, in which case some of the iron (II) may be blown with air to remove the iron (III). It is proposed that a brown to black pigment is obtained in this case because of the manganese content, the pigment obtained also forming no single phase.灼 A method for producing a temperature-stable manganese-containing iron oxide pigment having a single hematite structure was found by subjecting the obtained pigment kneaded product to {sintering heat treatment at a temperature of about 600 to about 800 ° C.}. It is described that a manganese-containing iron oxide pigment having a single hematite structure is obtained by subjecting a pigment kneaded material that does not form a single phase to a heat treatment.

Technical means for obtaining these brown or black Mn-containing iron compounds include α-FeOOH
It is conceivable to add a Mn compound at the time of producing the compound. As the method, JP-A-49-14400, JP-A-49-15699, and JP-A-49-69104
JP, JP-A-52-134858, JP-A-Showa 56
-104720, JP-A-56-109827, JP-A-57-22121, JP-A-57-34
No. 027 and JP-A-61-9505.

However, according to the technical means described in each of the above publications, a single phase is not formed as described in Japanese Patent Publication No. 43-17288, and JP-A-56-104720 and JP-A-56-104720
As described in JP-A-109827, α-FeOOH has a yellow color.

On the other hand, in order to improve the surface smoothness and strength of the base film, which has been made thinner, it is necessary to use “‥‥ needle-like γ-Fe ₂ O” on page 339 of the aforementioned “General Technical Data Collection”.
Pigment particles considered to be rod-shaped such as ₃ are arranged in parallel to the support when the coating is applied with a shearing force during coating. (4) Bar-shaped particles parallel to the support have greater hiding power and gloss, and lower light and gas permeability than those perpendicular to the support. The difference in the arrangement of the pigments also affects the mechanical properties of the coating film, and the tensile strength is greater and the elongation is smaller as the pigment is horizontal to the support. As described in “‥‥”, particles having an axial ratio (major axis diameter / short axis diameter—the same applies hereinafter), such as needle-shaped or spindle-shaped particles, can be orientated at the time of coating, and are oriented. It is known that particles having an axial ratio have a low light transmittance and improve surface smoothness and strength.

Accordingly, the present invention provides an iron oxide-containing particle powder having a goethite structure, which is a needle-like or spindle-like particle and has a brown to black color. Alternatively, if necessary, the light transmittance is improved using iron oxide particles having a hematite structure exhibiting a brown to black color obtained by heating and dehydrating the hydrous iron oxide particles, and furthermore, the surface smoothness and strength are improved. It is a technical object of the present invention to provide a non-magnetic underlayer for a magnetic recording medium which is excellent in the following.

[0020]

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

That is, according to the present invention, the average major axis diameter is from 0.03 to 0.03.
0.5 μm, particles having an axial ratio of 2 to 15, and an aggregate of the particles having an L ^* value of 30.0 to 0 and an a ^* value of 6.0 to 6.0.
0, b ^* presents a color with a value of 10.0 to -1.7
Nonmagnetic black-brown iron oxide hydroxide particles composed of iron oxide hydroxide particles having a single-phase goethite structure, and a suspension containing an iron-containing precipitate obtained by reacting an aqueous alkali solution and an aqueous ferrous salt solution with oxygen. In the method for producing an iron oxide hydroxide particle powder having a goethite structure by performing an oxidation reaction by passing a gas contained therein, the alkali aqueous solution is obtained by using both alkali aqueous solutions of an alkali hydroxide aqueous solution and an alkali carbonate aqueous solution in combination. The aqueous solution is added to one of the aqueous solution of the alkali hydroxide and the suspension containing the iron-containing precipitate, and the amount of the aqueous alkali carbonate is adjusted to 1 mol of the aqueous solution of the alkali hydroxide (however,
This is the amount excluding the neutralized component of the n compound. ) For 0.4
２20.0 mol, and the total amount of both alkali aqueous solutions is 1.0 equivalent to Fe 2+ in the ferrous salt aqueous solution (however, the amount excluding the neutralized portion of the Mn compound is And the suspension containing the iron-containing precipitate before the oxidation reaction by passing the oxygen-containing gas through the oxygen-containing gas and the oxygen-containing gas. In any one of the suspensions containing the iron-containing precipitate, the oxidation rate of which is less than 50% due to the oxidation reaction by aeration, the Fe
A method for producing the above-mentioned nonmagnetic black-brown iron oxide hydroxide-containing powder, comprising the step of keeping an Mn compound in an amount of 1 to 50 atomic% in terms of Mn with respect to 2+, In a non-magnetic underlayer for a magnetic recording medium comprising a coating composition comprising a magnetic particle powder and a binder resin, wherein the non-magnetic particle powder is the non-magnetic black-brown hydrated iron hydroxide particle powder. A non-magnetic underlayer and a non-magnetic underlayer for a magnetic recording medium comprising a coating composition containing a non-magnetic particle powder and a binder resin formed on a non-magnetic support; Nonmagnetic black-brown iron oxide particles having a single-phase hematite structure obtained by heating and dehydrating magnetic black-brown hydrated iron oxide particles in a temperature range of 270 to 800 ° C. In the stratum .

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

The aqueous ferrous salt solution used in the present invention includes an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution and the like.

Examples of the aqueous alkali hydroxide solution used in the present invention include sodium hydroxide and potassium hydroxide aqueous solutions.

Examples of the aqueous alkali carbonate solution used in the present invention include an aqueous sodium carbonate solution, an aqueous potassium carbonate solution, and an aqueous ammonium carbonate solution.

In the present invention, both alkali aqueous solutions of an alkali hydroxide aqueous solution and an alkali carbonate aqueous solution are used in combination,
The aqueous alkali carbonate solution may be added to any of the aqueous alkali hydroxide solution and the suspension containing the iron-containing precipitate before the oxidation reaction. When added during the oxidation reaction, needle particles and granular particles are mixed in the formed particles, and the particles are not a single phase.

The addition amount of the aqueous alkali carbonate solution is 0.4 to 2 with respect to 1 mol of the aqueous alkali hydroxide solution (however, the amount excluding the neutralized component of the added Mn compound).
It is in the range of 0.0 mole. If less than 0.4 mole,
In some cases, granular particles and the like are mixed in the formed particles and become a single phase. When it exceeds 20.0 mol, iron oxide hydroxide particles having a black-brown goethite structure are not produced.

Further, the total amount of both alkali aqueous solutions is 1.0 equivalent to Fe ²⁺ in the ferrous salt aqueous solution (however,
This is the amount excluding the neutralized component of the Mn compound to be added. ). When the amount is less than 1.0 equivalent, the iron oxide hydroxide particles having a black-brown goethite structure may not be formed. Preferably it is more than 1.0 equivalent and not more than 5.0 equivalents. Although it can be produced even when it exceeds 5.0 equivalents, it is not economical if the amount of expensive alkaline aqueous solution used increases.

In general, when a suspension containing FeCO ₃ using an aqueous alkali carbonate solution is subjected to an oxidation reaction, the pH value is in the range of 7 to 11, and in the present invention, the pH value is within the above range. Well, if the pH value is less than 7,
In some cases, iron oxide hydroxide particles having a black-brown goethite structure are not generated. When the pH value exceeds 11, granular particles and the like are mixed and become a single phase.

The Mn compound used in the present invention may be any soluble Mn salt, such as manganese sulfate and manganese chloride.

The addition amount of the Mn compound is 1 to 50 atomic% in terms of Mn with respect to Fe ²⁺ in the aqueous ferrous salt solution. If it is less than 1 atomic%, iron oxide hydroxide particles having a black-brown goethite structure may not be produced. If it exceeds 50 atomic%, the resulting particles may not be a single phase due to the mixture of granular particles and the like.

The addition time of the Mn compound is determined by passing an aqueous solution of ferrous salt, an aqueous solution of alkali hydroxide, and an oxygen-containing gas by passing a suspension containing an iron-containing precipitate before the oxidation reaction and an oxygen-containing gas. Oxidation rate by oxidation reaction is 50
% In any of the suspensions containing the iron-containing precipitate that is less than 10%. When the oxidation rate due to the oxidation reaction by passing the oxygen-containing gas exceeds 50%, the formed particles may be mixed with granular particles or the like and may not be a single phase.

The Mn compound may be prepared by adding a solid salt to each solution and stirring and dissolving it, or by adding and mixing a separately dissolved aqueous solution.

In the present invention, the suspension containing the iron-containing precipitate is converted to a non-oxidizing solution in the same manner as in the case where the suspension containing FeCO ₃ is oxidized using an ordinary aqueous alkali carbonate solution. Aging may be performed under an atmosphere. The axial ratio of the hydrous iron oxide particles obtained by aging can be increased. The aging is preferably carried out in a non-oxidizing atmosphere at a temperature of usually 40 to 80 ° C. If the temperature is lower than 40 ° C., it is difficult to obtain a sufficient aging effect, so that the axial ratio becomes small.
Granular magnetite may be mixed.

The aging time is in the range of 30 to 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. Although it may be longer than 300 minutes, it does not mean that the time is longer than necessary.

In order to obtain a non-oxidizing atmosphere, an inert gas (such as N ₂ gas) or a reducing gas (such as H ₂ gas) may be passed through the reaction vessel of the suspension.

The temperature at the time of the oxidation reaction in the present invention may be usually set to a temperature of 80 ° C. or less at which the hydrous iron oxide particles are formed. When the temperature is higher than 80 ° C., particulate magnetite particles may be mixed in the spindle-shaped hydrous iron oxide particles having a goethite structure.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid according to a conventional method, and may be accompanied by stirring by mechanical operation if necessary.

The hydrous iron oxide particles obtained in the present invention have an average major axis diameter of 0.03 to 0.5 μm and an axial ratio of 2 to 2.
15, particles having an L ^* value of 30.0 to 0, an a ^* value of 6.0 to 0, and a b ^* value of 10.0 to-
It is a nonmagnetic black-brown hydrated iron hydroxide particle powder having a single-phase goethite structure having a color shown by 1.7.

If the average major axis diameter is less than 0.03 μm, it is not preferable because dispersion in the binder resin becomes difficult. If the average major axis diameter exceeds 0.5 μm, the particle size is too large, which impairs the surface smoothness, which is not preferred.

When the axial ratio is less than 2, it is difficult to obtain a desired film strength, which is not preferable. The larger the axial ratio, the better, but in the case of the present invention, it is about 15.

If the L ^* value exceeds 30.0 or is less than 0, the light transmittance increases, which is not preferable.
When the value of a ^* exceeds 6.0 or less than 0, the light transmittance increases, which is not preferable. Also, b
^{* If the} value exceeds 10.0 or less than -1.7, the light transmittance increases, which is not preferable.

In the present invention, if necessary, the obtained nonmagnetic black-brown iron oxide particles may be heated and dehydrated in a temperature range of 270 to 800 ° C. to obtain nonmagnetic black-brown iron oxide particles having a hematite structure. it can. When the temperature is lower than 270 ° C., the heating and dehydration are not sufficient, and black-brown iron oxide particles having a hematite structure are not obtained. When the temperature exceeds 800 ° C., red-brown iron oxide particles are formed, and the light transmittance is undesirably increased.

As the method of heat dehydration, the black-brown iron oxide hydroxide particles are dehydrated in a temperature range of 270 to 500 ° C. or, if necessary, are further annealed by heat treatment in a temperature range of 350 to 800 ° C. It is preferable to obtain nonmagnetic black-brown iron oxide particles having a hematite structure. 350
Annealing by a heat treatment in a temperature range of up to 800 ° C. is performed by annealing pores formed on the particle surface of the black-brown iron oxide particles obtained by dehydration, thereby melting the pole surface of the particles to form pores. This is because it is preferable to cover the surface of the substrate to make it a smooth surface state.

Further, in order to prevent deformation of the particle shape during heating and dehydration and sintering between the particles, P, Si, Al, B, Zr, Sb
And the like.

In the present invention, before the obtained nonmagnetic black-brown hydrated iron hydroxide particles or the nonmagnetic black-brown iron oxide particles are used as an underlayer for a magnetic recording medium, Al, Si, Ti, Mn, Ni, Zn, Zr,
The coating may be performed using one or more compounds selected from Sn and Sb.

Instead of the inorganic metal compound, a coating treatment with a commonly used metal coupling agent such as Al, Si, Ti, Zr, or the like, or a commonly used organic compound such as a phosphoric ester may be performed.

Before the obtained nonmagnetic black-brown hydrated iron oxide particles or the nonmagnetic black-brown iron oxide particles are used as a base layer for a magnetic recording medium, a degassing / consolidation treatment or the like usually performed on each particle powder is used. Processing can also be performed.

In the case of dispersing the non-magnetic black brown hydrated iron oxide particles or the non-magnetic black brown iron oxide particles in a binder resin as an underlayer, the coating treatment and the consolidation treatment may be carried out. By performing each of the above treatments, the affinity with the binder resin is improved, and the desired degree of dispersion can be more easily obtained.

The binder resins used in the present invention include vinyl chloride vinyl acetate copolymers, urethane resins, vinyl chloride vinyl acetate maleate urethane elastomers which are currently widely used in the production of magnetic recording media.
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. be able to. Each binder resin has -O
_{H, -COOH, -SO 3 M,} -OPO 2 M 2, -NH
A polar group such as ₂ (however, M is H, Na, or K) may be contained.

The non-magnetic underlayer for a magnetic recording medium according to the present invention comprises a non-magnetic black-brown iron oxide particle powder or a non-magnetic black-brown iron oxide particle powder obtained according to the present invention and a binder resin on a non-magnetic support. The composition is obtained by applying a coating composition containing It should be noted that 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 to the nonmagnetic underlayer.

As the non-magnetic support, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, 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 coating thickness of the undercoat layer after the coating composition is applied to the nonmagnetic support and dried 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.

Examples of the magnetic particles in the magnetic recording layer include maghemite particles, magnetite particles, magnetic iron oxide particles such as beltlide compound particles which are intermediate oxides of maghemite and magnetite, and magnetic iron oxide particles of these. 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.

[0058]

The operation of the present invention having the above-described configuration is as follows.

As described in the above-mentioned JP-B-43-17288, when an iron salt is precipitated with a basic agent in the presence of a manganese salt and air is blown in to carry out an oxidation reaction, the resulting particles are single. What does not form one phase, for example,
Electron micrograph (× 30000) shown in FIG. 5 of Comparative Example 1 described later when the basic agent was an aqueous alkali hydroxide solution only
This indicates that three phases of needle-like particles, amorphous particles and granular particles are present.

When only the aqueous alkali carbonate solution was used as the basic agent, the obtained powdery particles had a yellow-brown color, as shown in Comparative Example 2 below, and the desired black-brown powdery particles were not obtained. I can't.

On the other hand, when the alkaline aqueous solution of the present invention was used in combination, the X in FIG.
It shows that the particles have a goethite structure in the line diffraction, and it can be confirmed from the electron micrograph (× 30000) shown in FIG.

Although the reasons for these are not yet clear, the combined use of the aqueous alkali hydroxide solution and the aqueous alkali carbonate solution of the present invention causes the added Mn compound to become black-brown with the aqueous alkali hydroxide solution, It is considered that a single phase was formed because the Mn compound was formed into a solid solution in the iron oxide hydroxide particles having a goethite structure by the aqueous solution.

When obtaining nonmagnetic black-brown hydrated iron hydroxide particles having a goethite structure, the addition of the Mn compound involves the reaction of the Mn compound with the aqueous alkali hydroxide solution. It is necessary to add a Mn compound to each of the above solutions,
It is believed that the present invention could be completed by making the reaction into a solid solution in the iron oxide-containing particles using an aqueous alkali carbonate solution.

As a result of the solid solution of the Mn compound in the iron oxide-containing particles, the color of the ordinary goethite particles is L ^* value of 6
About 2 to 45, a ^* value is about 20 to 10, b ^* value is 55
In contrast to the yellow-brown color of about 20 to about 20, the L ^* value of the iron oxide hydroxide particles having a goethite structure of the present invention is 30.0%.
~0, a ^* value is 6.0~0, b ^* value is 10.0-1.
It has a dark brown color of 7.

The color of the hematite particle powder obtained by heating and dehydrating the ordinary goethite particle powder has an L ^* value of 5
About 0 to 35, a ^* value is about 50 to 25, b ^* value is 30
While the iron oxide particles having a hematite structure of the present invention have an L ^* value of 30.0 to
0, a ^* value is 6.0 to 0, b ^* value is 10.0 to -1.7.
Has a dark brown color.

Therefore, when the nonmagnetic black-brown iron oxide hydroxide particles or the nonmagnetic black-brown iron oxide particles obtained in the present invention are used as an underlayer for a magnetic recording medium, the light transmittance is improved, and Also excellent in surface smoothness, strength, electric resistance, etc.

As described above, the non-magnetic underlayer for a magnetic recording medium according to the present invention is excellent in surface smoothness and strength.
Spindle-shaped particles can be oriented during application,
The oriented spindle-shaped particles have low transmittance,
It is believed that the surface smoothness and strength could be improved.

On the other hand, the above-mentioned “General Technical Data Book”, p. 343, “‥‥ Poor dispersibility of magnetic powder particles leads to poor surface smoothness, but also influences the orientation and deteriorates the magnetic properties. As described in “‥‥”, the dispersibility of the particle powder is a problem.

However, in the present invention, since each of the particles has a spindle shape, the particles are rounded. Therefore, the particles are unlikely to adhere to each other, are likely to be separated one by one, and have excellent dispersibility. Particle powder. In addition, since the particles have a spindle shape with an axial ratio of 2 to 15, it is considered that the particles are easily oriented by the coating process and surface smoothness and strength are obtained.

In the present invention, the nonmagnetic black-brown iron oxide hydroxide powder or the nonmagnetic black-brown iron oxide particle powder contains a single phase of only spindle-shaped particles that do not contain irregular particles or granular particles. Therefore, it is considered that orientation is easy when the underlayer is used for a magnetic recording medium, and desired surface smoothness and strength are obtained.

As a result, the nonmagnetic underlayer for a magnetic recording medium according to the present invention has excellent surface smoothness and strength.
When a coating composition containing magnetic particle powder and a binder resin is applied to the surface to form a magnetic recording medium, a thin magnetic recording layer having a small light transmittance and a uniform thickness is obtained.

[0072]

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 by the average values of the values measured from electron micrographs. The specific surface area was indicated by a value measured by the BET method. The amount of Mn and the amount of each element were measured by X-ray fluorescence analysis.

The color measurement of the aggregate of particles is performed by measuring the particle
After compression-molding a ring having a thickness of 0 mm and a thickness of 3 mm at 15 tons / cm ² , the measurement was performed using a multi-source spectrophotometer MSC-IS-2D (manufactured by Suga Test Instruments Co., Ltd.).

For the gloss, “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 “Surfcom
The center line average roughness of the coating film was measured using "-575A" (manufactured by Tokyo Seimitsu Co., Ltd.).

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 light transmittance of the magnetic sheet was represented by a linear absorption coefficient measured using a “photoelectric spectrophotometer UV-2100” (manufactured by Suga Test Instruments Co., Ltd.). 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.

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

<Production of Hydrous Iron Oxide Particle Powder Having Goethite Structure> Examples 1 to 6 and Comparative Examples 1 to 3;

Example 1 A 9.3 mol / l NaOH aqueous solution was placed in a reaction vessel.
5 l and 2.5 mol / l Na ₂ CO ₃ aqueous solution
3 l (corresponding to 1.2 mol with respect to NaOH) is added (the total amount of NaOH and Na ₂ CO ₃ corresponds to 2.5 equivalents to the amount of Fe excluding the neutralized Mn compound). After that, 1025 g of manganese sulfate (corresponding to 20 atomic% with respect to Fe ^{2+ in} the ferrous salt aqueous solution) was dissolved and mixed.
2.2 l (reaction Fe ²⁺ concentration corresponds to 0.6 mol / l) was added and mixed to form a suspension containing an iron-containing precipitate at a temperature of 50 ° C.

The suspension containing the iron-containing precipitate was blown with 100 l / min of air at a temperature of 50 ° C. for 5.0 hours to produce black-brown precipitate particles. In addition, pH during air ventilation
Was 8.0 to 11.0.

The black-brown precipitate particles were separated by filtration, washed with water, dried and pulverized by a conventional method. The resulting black-brown particle powder is shown in FIG.
Has a goethite structure as is clear from the X-ray diffraction results shown in FIG.
As is clear from 0), it is a single phase composed of only spindle-shaped particles having an average major axis diameter of 0.30 μm and an axial ratio of 7, having a uniform particle size and having no dendritic particles. Was. The Mn content is 20 atom% in terms of Mn with respect to Fe, L ^* value is 22.9, a ^* value is 1.0, b ^*
It was a non-magnetic black-brown particle powder having a color of -0.24. Incidentally, the saturation magnetization σs was 0.1 emu / g or less.

Examples 2 to 6, Comparative Examples 1 to 3 Kind, concentration and amount of alkali hydroxide, kind, concentration, amount of alkali carbonate aqueous solution, molar ratio to alkali hydroxide (mixing ratio) and timing of addition, Equivalent ratio (total amount of alkali) of both alkali aqueous solutions (the amount excluding the Mn compound neutralized component) to Fe, type, concentration and use amount of ferrous salt aqueous solution, reaction concentration, type of Mn compound, addition amount and addition Iron-containing hydroxide particles having a goethite structure were obtained in the same manner as in Example 1 except that the time, presence or absence of aging, and the reaction temperature were variously changed. Tables 1 and 2 show the main production conditions and various characteristics at this time.

[0084]

[Table 1]

[0085]

[Table 2]

<Production of Iron Oxide Particle Powder Having Hematite Structure> Examples 7 to 14;

Example 7 1.5 kg of the iron oxide hydroxide particles having a goethite structure obtained in Example 1 was dispersed in 40 l of water to form a suspension, and 21 ml of No. 3 water glass was added to the suspension. 0.58% by weight in terms of Si with respect to the particle powder), and then a 1.0 mol / l H ₂ SO ₄ aqueous solution was added.
The mixture was adjusted to pH 6.5 and mixed and stirred for 30 minutes. After mixing and stirring, the mixture was filtered, washed with water and dried by a conventional method to obtain a powder of hydrous iron oxide particles having a goethite structure coated with Si.

Next, the obtained powdered iron oxide hydroxide particles
0 kg was placed in a one-end open-type retort container, and heated and dehydrated at 300 ° C. for 60 minutes in the air while rotating and then further annealed at 550 ° C. for 60 minutes to obtain black-brown particles.

The obtained black-brown particles had a hematite structure as a result of X-ray diffraction. As is clear from the electron micrograph (× 30000) shown in FIG. 3, the average major axis diameter was 0.23 μm, and the average particle diameter was 0.23 μm. It is a single phase consisting of only spindle-shaped particles having a ratio of 5.5, and the Mn content is M
The powder was non-magnetic black-brown iron oxide particles having a color of n = 20 at%, L ^* value of 22.0, a ^* value of 1.7, and b ^* value of -0.14.

Subsequently, the obtained iron oxide particle powder was dry-pulverized by an edge runner type pulverizer (Sandmill: manufactured by Matsumoto Cast Iron Works), and the pulverized material was stirred and mixed in water to form a line mill. Wet pulverization was performed by a mold pulverizer (Homomic Line Mill: manufactured by Tokushu Kikai Kogyo KK) to obtain a suspension containing iron oxide particles.

To the obtained suspension was added 140 ml of a 2.5 mol / l aqueous solution of aluminum sulfate (corresponding to 1.8% by weight in terms of Al with respect to the particle powder), and then 1.0 mol / l. NaOH aqueous solution
The mixture was adjusted to 6.0 and mixed and stirred for 30 minutes.

After mixing and stirring, the mixture was filtered, washed with water and dried by a conventional method, and then subjected to a consolidation treatment using an edge runner type pulverizer (Sandmill: manufactured by Matsumoto Cast Iron Works).

The obtained iron oxide particles coated with an Al compound are a single phase composed of only spindle-shaped particles having an average major axis diameter of 0.23 μm and an axial ratio of 5.5. And no dendritic particles were mixed. The Mn content is 20 atomic% in terms of Mn with respect to Fe, and a nonmagnetic black-brown color having an L ^* value of 22.9, an a ^* value of 1.0, and a b ^* value of -0.2. It was a particle powder. Incidentally, the saturation magnetization σs was 0.1 emu / g or less.

Examples 8 to 14 Except that the type of the powder to be treated, the type and amount of the compound for the sintering prevention treatment, and the type, the amount and the pH of the coating compound after the dehydration and annealing treatment were variously changed. In the same manner as in Example 7, iron oxide particles were produced.

Tables 3 and 4 show the main production conditions and various characteristics at this time.

[0096]

[Table 3]

[0097]

[Table 4]

<Production of Non-magnetic Underlayer for Magnetic Recording Medium> Examples 15 to 28 and Comparative Example 4;

Example 15 Using the hydrated iron oxide particles obtained in Example 1, the hydrated iron oxide particles were first mixed with a binder resin and a solvent. 30 using
Kneaded for minutes. After that, take out a predetermined amount of kneaded material,
The mixture was 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. Hydrous iron oxide particles 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group 10 parts by weight Polyurethane resin having a 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 applied on a polyethylene terephthalate film having a thickness of 14 μm to a thickness of 55 μm using an applicator, and then dried to obtain a sheet-shaped sample piece.

The Young's modulus of the obtained sheet sample was 98,
The gloss was 110%, the surface roughness was 30.6 nm, and the linear absorption coefficient was 0.88 μm ⁻¹ .

Examples 16 to 28 and Comparative Example 4 The same procedure as in Example 15 was repeated except that the powders of the iron oxide particles and the iron oxide particles obtained in Examples 2 to 14 and Comparative Example 2 were used. A magnetic underlayer was obtained.

Table 5 shows the characteristics at this time.

[0105]

[Table 5]

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

Reference Example 1 On the nonmagnetic underlayer for a magnetic recording medium obtained in Example 15, Co-coated magnetic iron oxide particles (average major axis diameter 0.25
μm, average minor axis diameter 0.037 μm, Hc850Oe, σ
s81.3 emu / g, Co content 4.52%, Fe ²⁺
(16.5%), magnetic particles, a binder resin, and a solvent were first mixed and kneaded at a solid content of 76% by weight using a plast mill for 30 minutes. Thereafter, a predetermined amount of the kneaded material is taken out, added to the glass bottle together with the glass beads and the solvent, and mixed for 6 hours with a paint conditioner.
Dispersion was performed.

Thereafter, an abrasive, a lubricant and a curing agent were added, and the mixture was further mixed and dispersed for 15 minutes. The composition of the coating composition 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 coating composition was applied on a polyethylene terephthalate film having a thickness of 14 μm using an applicator to a thickness of 15 μm, and then dried to obtain a sheet-like 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 resulting magnetic tape has an Hc of 890 Oe,
Squareness ratio is 0.90, gloss is 140%, surface roughness Ra is 1
2.2 nm, Young's modulus is 121, and linear absorption coefficient is 1.31
Met.

Reference Examples 2 to 10 Using the nonmagnetic underlayers for magnetic recording media obtained in Examples 15, 20, 26 and 27 and Comparative Example 4, the magnetic particle powder was used to obtain the Co-coated magnetic oxide of Reference Example 1. Iron particle powder and metal magnetic particle powder (average major axis diameter 0.13 μm, average minor axis diameter 0.
017 μm, Hc1560e, σs 128.9 emu /
g, BET specific surface area 52.9 m ² / g, Co content 5.
9%, Al content 1.1%, B content 1.0%) to obtain a magnetic recording medium in the same manner as in Reference Example 1.

Table 6 shows the characteristics at this time.

[0113]

[Table 6]

[0114]

The hydrous iron oxide particles according to the present invention are non-magnetic black brown iron oxide particles having a goethite structure having a spindle shape and exhibiting a black brown color with an appropriate axial ratio or, if necessary, the hydrous iron oxide particles. Since the iron oxide particle powder having a hematite structure exhibiting a black-brown color obtained by heating and dehydrating the iron oxide particle powder, the light transmittance is small, and
An underlayer for a magnetic recording medium having excellent surface smoothness, strength, electric resistance and the like can be provided.

The non-magnetic underlayer for a magnetic recording medium according to the present invention has excellent strength and surface properties as a base film as shown in the above-described embodiment. When used as a medium, a thin magnetic recording layer having a small light transmittance and a smooth thickness without unevenness can be obtained.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a powder of hydrous iron oxide having a goethite structure obtained in Example 1.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the iron oxide hydroxide particles having a goethite structure obtained in Example 1.

FIG. 3 is an X-ray diffraction diagram of the iron oxide particle powder having a hematite structure obtained in Example 7.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the iron oxide particle powder having a hematite structure obtained in Example 7.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the particle powder obtained in Comparative Example 1.

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the hydrous iron oxide particles having a goethite structure obtained in Comparative Example 2.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Katsumi Yamashita Inventor, Hitoshi Misaki, Creative Center, 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima, Japan (56) References JP-A-2-180718 (JP, A) JP-A-2-224302 (JP, A) JP-A-4-144924 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 49/00-49 / 08

Claims (4)

(57) [Claims] 1. Particles having an average major axis diameter of 0.03 to 0.5 μm, an axial ratio (major axis diameter / minor axis diameter) of 2 to 15, and an aggregate of the particles having an L ^* value. 30.0-0, a ^* value6.
0 to 0, b ^* value 10.0 to -1.7 (however, L ^* value, a ^*
The value, b ^* value is a value according to JIS-Z-8729. )
Non-magnetic black-brown iron oxide hydroxide particles comprising iron oxide hydroxide particles having a single-phase goethite structure and exhibiting a color represented by the following formula: 2. An oxidation reaction having a goethite structure by passing an oxygen-containing gas through a suspension containing an iron-containing precipitate obtained by reacting an aqueous alkali solution and an aqueous ferrous salt solution to carry out an oxidation reaction. In the method for producing iron particle powder, the alkali aqueous solution is used in combination with both alkali aqueous solutions of an alkali hydroxide aqueous solution and an alkali carbonate aqueous solution, and the alkali carbonate aqueous solution is a suspension of the aqueous solution containing the alkali hydroxide aqueous solution and the iron-containing precipitate. While being added to any of the liquids, the amount of the aqueous alkali carbonate solution added is 0.4 with respect to 1 mol of the aqueous alkali hydroxide solution (however, the amount excluding the neutralized component of the added Mn compound). and 20.0 mols, moreover, the 1.0 equivalents relative to Fe ²⁺ of the total amount the ferrous salt aqueous solution of both an alkaline aqueous solution (where, in the Mn compound And a suspension containing the ferrous salt aqueous solution, the alkali hydroxide aqueous solution, and the iron-containing precipitate before the oxidation reaction by passing the oxygen-containing gas through. In any of the suspensions containing the iron-containing precipitate, the oxidation rate of which is less than 50% due to the oxidation reaction by passing the liquid and the oxygen-containing gas through, the Fe ^{2 + To} 50 in Mn conversion
2. The method for producing nonmagnetic black-brown iron oxide hydroxide particles according to claim 1, wherein a Mn compound is present in an amount in the range of atomic%. 3. A non-magnetic underlayer for a magnetic recording medium comprising a coating composition containing a non-magnetic particle powder formed on a non-magnetic support and a binder resin, wherein the non-magnetic particle powder is used. A non-magnetic underlayer for a magnetic recording medium, which is the non-magnetic black-brown hydrated iron hydroxide particles described above. 4. 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 used. 270 particles of the non-magnetic black-brown hydrated iron hydroxide particles described above.
A nonmagnetic underlayer for a magnetic recording medium, which is a single-phase nonmagnetic black-brown iron oxide particle powder having a hematite structure and obtained by heating and dehydrating at a temperature in the range of -800 ° C.