JP5293946B2 - Method for producing nonmagnetic particle powder for nonmagnetic underlayer of magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

A production method for obtaining a nonmagnetic particle powder for a nonmagnetic under layer showing little aggregation among particles and being highly dispersible in a vehicle which comprises freeze-drying in vacuo a liquid-containing material containing geothite particles , thermally treating the dried product to give a hematite particle powder and, if required, coating the surface of the particles constituting the hematite particle powder with a surface coating agent such as aluminum hydroxide or conducting again freeze-drying in vacuo. According to this production method, it is possible to produce a nonmagnetic particle powder for a nonmagnetic under layer from which a magnetic recording medium having a high surface smoothness and showing little dropping out can be obtained.

Description

  The present invention provides a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium having good surface smoothness and low dropout of the magnetic recording medium (tape).

  Conventionally, there has been a demand for smaller, lighter, longer recording time, higher density recording, and increased recording capacity for magnetic recording / reproducing devices for audio, video, and computers. In order to shift the frequency of the carrier signal to a short wavelength region, the magnetization depth from the surface of the magnetic tape becomes remarkably shallow, and to improve the high output characteristics of the magnetic recording medium, particularly the S / N ratio, Tends to be thinned.

  However, the thinning of the magnetic recording layer makes it difficult to smooth the surface of the magnetic recording layer and the strength of the coating film has become a problem. At present, the magnetic recording layer is thinned. In contrast, at least an underlayer (hereinafter referred to as “nonmagnetic underlayer”) in which nonmagnetic particle powder such as hematite particle powder is dispersed in a binder resin on a nonmagnetic support such as a base film. By providing one layer, the surface smoothness and strength of the magnetic recording medium are improved.

  In recent years, there has been a strong demand for further improvement in recording capacity of magnetic tape (backup tape) for recording data as an external storage medium due to the longer recording time of audio tapes and video tapes and the spread of personal computers and office computers. However, in the case of audio tapes, video tapes and backup tapes that have a specified size per tape, for the long-time recording and high recording capacity, the entire tape thickness is reduced to 1 volume. The tape length per hit needs to be increased. Therefore, not only the magnetic recording layer but also the nonmagnetic underlayer and the nonmagnetic support are strongly required to be thinned. For example, the conventional backup tape has a nonmagnetic underlayer thickness of 3 to 5 μm. In recent years, the thickness has been reduced to 1 to 3 μm.

  In particular, when the nonmagnetic underlayer for the nonmagnetic underlayer is thinned, the dispersion level of the nonmagnetic particle powder greatly affects the surface smoothness of the magnetic recording medium. Even if the dispersed particle size of the nonmagnetic particle powder for the magnetic underlayer is reduced, a thin layer causes a protrusion on the surface of the nonmagnetic underlayer, and the protrusion affects the surface of the magnetic recording layer. The surface smoothness of the layer surface is deteriorated, and dropout is likely to occur.

  Therefore, in order to realize a magnetic recording medium suitable for long-time recording and high recording capacity, the individual particles of the non-magnetic particle powder for the non-magnetic under layer are well dispersed in the non-magnetic under layer coating. In addition, it is essential that the surface of the nonmagnetic underlayer be smooth when it is formed. For this purpose, it is necessary that the particles of the nonmagnetic particle powder for the nonmagnetic underlayer are not coagulated firmly, and the individual particles are easily wetted with the binder resin and easily dispersed.

  For the purpose of improving the surface smoothness of the tape, the aluminum-containing acicular goethite particle powder is heat-treated in a temperature range of 100 to 200 ° C. and contained in the aluminum-containing acicular goethite particle powder. A method (Patent Document 1) in which fine particles are absorbed by aluminum-containing acicular goethite particles is disclosed.

Moreover, in order to dry the precipitate of the spindle type hematite particle obtained by hydrolyzing ferric hydroxide, performing freeze-drying (patent document 2) is described.

JP 2000-182236 A Japanese Patent Laid-Open No. 06-340426

  A method for producing a nonmagnetic particle powder for a nonmagnetic underlayer capable of obtaining a magnetic recording medium having a good tape surface smoothness even when the nonmagnetic underlayer is thinned is currently most demanded. However, it has not been obtained yet.

  That is, in the above-mentioned patent document 1, aluminum-containing goethite ultrafine particles contained in the aluminum-containing acicular goethite particle powder by heat-treating the aluminum-containing acicular goethite particle powder in a temperature range of 100 to 200 ° C. contain aluminum. Although the dispersibility of the hematite particle powder is improved by absorbing the needle-like goethite particles, the heat treatment is performed at a high temperature of 550 to 850 ° C. after the heat treatment at a temperature range of 100 to 200 ° C., Because the distance between the particles is short, sintering of the hematite particles occurs, and it is difficult to disperse the hematite particles individually in the nonmagnetic paint when using this as a nonmagnetic paint. When the magnetic underlayer is thinned, it is difficult to obtain a magnetic recording medium having sufficient surface smoothness.

  Further, in the aforementioned Patent Document 2, it is described that freeze drying is performed to dry the precipitate of spindle type hematite particles obtained by hydrolyzing ferric hydroxide. Ferric chloride is used to obtain a ferrous gel suspension, and this ferric chloride is a corrosive substance and corrodes metals, so it is used in industrial production facilities. Is difficult. Moreover, since the hematite particles obtained using ferric chloride as a starting material contain chlorine ions, when the hematite particles are used as the nonmagnetic particle powder for the nonmagnetic underlayer of the magnetic recording medium, the magnetic recording medium is When stored for a long time under high temperature and high humidity, trace amounts of chlorine ions contained in the hematite particles react with the fatty acid used as a lubricant in the magnetic recording medium, and precipitate and crystallize on the surface of the magnetic layer. This is not preferable because it adversely affects the magnetic head and causes corrosion of the magnetic head.

  Accordingly, the present invention provides a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer that can provide a magnetic recording medium with good surface smoothness and low dropout even when the nonmagnetic underlayer is thinned. It is a technical challenge to provide

  The technical problem can be achieved by the present invention as follows.

  That is, the present invention provides a non-magnetic recording medium characterized in that a liquid-containing material containing goethite particles having a solid content concentration of 50% by weight or less is freeze-dried in vacuum, and then the dried material is heat-treated to form hematite particles. This is a method for producing a non-magnetic particle powder for a magnetic underlayer (Invention 1).

  In the present invention, a liquid-containing material containing goethite particles and having a solid content concentration of 50% by weight or less is freeze-dried in vacuum, the dried material is heat-treated to form hematite particles, and then the hematite particles are dispersed in water. An aluminum compound and / or a silicon compound is added to the resulting aqueous suspension, and the particle surface of the hematite particle powder is oxidized with an aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide. A hematite particle powder is obtained by coating with one or two or more types of surface coatings selected from the above, followed by filtration, washing, drying, and pulverization. This is a method for producing magnetic particle powder (Invention 2).

  In the present invention, a liquid-containing material containing goethite particles and having a solid content concentration of 50% by weight or less is freeze-dried in vacuum, the dried material is heat-treated to form hematite particles, and then the hematite particles are dispersed in water. An aluminum compound and / or a silicon compound is added to the resulting aqueous suspension, and the particle surface of the hematite particle powder is oxidized with an aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide. Magnetic recording characterized in that it is coated with one or two or more kinds of surface coatings selected from the products, and then the liquid-containing material having a solid content concentration of 50% by weight or less including the surface-coated hematite particles is vacuum freeze-dried This is a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer of a medium (Invention 3).

  The present invention also provides a nonmagnetic support, a nonmagnetic underlayer comprising a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, and a magnetic particle powder formed on the nonmagnetic underlayer. In a magnetic recording medium comprising a magnetic recording layer containing a binder resin, the nonmagnetic particle powder is obtained by the method for producing a nonmagnetic particle powder for a nonmagnetic underlayer described in any one of the present invention 1 to the present invention 3. The magnetic recording medium is a nonmagnetic particle powder for a nonmagnetic underlayer of the magnetic recording medium thus obtained (Invention 4).

  The hematite particle powder obtained by the method for producing a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium according to the present invention has less aggregation between particles and is easy to disperse. Suitable as non-magnetic particle powder for formation.

  In addition, the magnetic recording medium according to the present invention uses the above-described hematite particle powder as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium, so that the surface of the tape can be smoothed even if the nonmagnetic underlayer is thinned. Therefore, it is suitable as a high-density magnetic recording medium because of its good properties and low dropout.

  The configuration of the present invention will be described in more detail as follows.

  First, a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium according to the present invention will be described.

  The hematite particle powder in the present invention can be obtained by heat-dehydrating the goethite particle powder as a starting material in a temperature range of 200 to 850 ° C. after vacuum freeze-drying.

  A general method for producing goethite particle powder which is a precursor of hematite particle powder in the present invention will be described.

  As described in detail later, the goethite particle powder is obtained by reacting with ferrous salt and either alkali hydroxide or alkali carbonate or mixed alkali of alkali hydroxide and alkali carbonate. It is obtained by generating goethite particles by aerating an oxygen-containing gas such as air through a suspension containing a ferrous iron-containing precipitate such as iron carbonate.

A typical basic reaction of goethite particles includes, as is well known, (1) a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution to a pH value. A method of generating acicular goethite particles by performing an oxidation reaction by bubbling an oxygen-containing gas at a temperature of 11 to 80 ° C., and (2) obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution A method for producing spindle-shaped goethite particles by performing an oxidation reaction by bubbling an oxygen-containing gas after aging the resulting suspension containing FeCO ₃ , if necessary; (3) an aqueous ferrous salt solution; A suspension containing an iron-containing precipitate obtained by reacting an alkali carbonate aqueous solution and an alkali hydroxide is aged as necessary, and then an oxygen-containing gas is passed through to carry out an oxidation reaction to perform a spindle-shaped gate. (4) oxygen-containing gas in ferrous salt aqueous solution containing ferrous hydroxide colloid obtained by adding less than equivalent aqueous alkali hydroxide solution or aqueous alkali carbonate solution to ferrous salt aqueous solution To generate acicular goethite core particles by performing an oxidation reaction, and then to the ferrous salt aqueous solution containing the acicular goethite core particles, an equivalent amount or more with respect to Fe ^{2+ in} the ferrous salt aqueous solution A method of growing the goethite core particles by aeration of an oxygen-containing gas after adding an alkali hydroxide aqueous solution of (5), adding less than an equivalent amount of an alkali hydroxide aqueous solution or an alkali carbonate aqueous solution to the ferrous salt aqueous solution A goethite core particle is generated by performing an oxidation reaction by passing an oxygen-containing gas through an aqueous ferrous salt solution containing the ferrous hydroxide colloid obtained, and then the goethite core particle. And a method of growing the goethite core particles by adding an alkali carbonate aqueous solution equal to or more than the Fe ²⁺ in the ferrous salt aqueous solution to the ferrous salt aqueous solution containing ) By conducting an oxidation reaction by bubbling an oxygen-containing gas into a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding an alkali hydroxide or aqueous carbonate carbonate solution that is less than an equivalent amount to the ferrous salt aqueous solution. There is a method of generating goethite core particles and then growing the goethite core particles in an acidic to neutral region.

  In addition, during the formation reaction of goethite particles, Al, Zr, Ti, P, Si, Sn, Sb, Y, Nb, Mn, etc. are used to improve various characteristics such as the major axis diameter, minor axis diameter, and axial ratio of the particles. These different elements may be added. In particular, considering the improvement of the coating strength of the obtained magnetic recording medium, it is preferable to contain aluminum inside the particles. The total amount of the different elements contained in the particles is preferably 0.05 to 50% by weight in terms of each element, more preferably 0.10 to 40% by weight, still more preferably 0.15 to 30% by weight.

  The particle shape of the goethite particles in the present invention may be any shape such as needle shape, spindle shape, rice granular shape, spherical shape, granular shape, polyhedral shape, flake shape, scale shape, and plate shape. Considering the axial ratio of the resulting hematite particle powder, the axial ratio (ratio of average primary major axis diameter to average primary minor axis diameter) (hereinafter referred to as “axial ratio”) is 2.0 to 20.0. Needle shape, spindle shape, and rice grain shape are preferable, more preferably 2.5 to 18.0, and still more preferably 3.0 to 15.0.

The average primary long axis diameter of the goethite particles in the present invention is 0.005 to 0.40 μm, the BET specific surface area value is 20 to 250 m ² / g, and the volume-based average particle diameter (D ₅₀ ) usually has a lower limit. It has a value exceeding 2.70 μm. The upper limit is preferably 5.00 μm, more preferably 4.50 μm.

  The goethite particles obtained by the above production method can be lyophilized by vacuum using the reaction solution as it is, but usually by filtration, washing, etc. to remove unreacted raw materials and by-products. It is preferable to use the removed one.

  In the present invention, it is preferable to coat the surface of the goethite particle powder with a sintering inhibitor in advance before performing vacuum freeze-drying. The coating treatment with the sintering inhibitor is performed by adding the sintering inhibitor to the aqueous suspension containing the goethite particle powder as a starting material, mixing and stirring the mixture uniformly, and then applying the sintering inhibitor to the surface of the goethite particles. Adjust pH appropriately so that can be coated. The aqueous suspension of goethite particles coated with an anti-sintering agent can be subjected to vacuum freeze-drying as it is after adjusting the solid content, but it is usually not filtered and washed. Vacuum lyophilization may be performed using an aqueous suspension from which reaction raw materials and by-products have been removed.

  Examples of the sintering inhibitor include commonly used phosphorus compounds such as sodium hexametaphosphate, polyphosphoric acid and orthophosphoric acid, No. 3 water glass, sodium orthosilicate, sodium metasilicate, colloidal silica and other silicon compounds, boric acid and the like. Boron compounds, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate, alkali aluminates such as sodium aluminate, aluminum compounds such as alumina sol and aluminum hydroxide, and titanium compounds such as titanium oxysulfate Or 2 or more types can be used. In particular, considering the suppression of sintering of particles by firing at a high temperature, it is more preferable to use one or more compounds containing rare earth elements such as yttrium and neodymium as a sintering inhibitor.

  The amount of anti-sintering agent present on the surface of the goethite particle powder depends on various conditions such as the type and amount of anti-sintering agent, the pH value in the alkaline aqueous solution and the heat treatment temperature, but the total weight of the goethite particle powder. And 0.05 to 20% by weight.

  In the present invention, the goethite particle powder before vacuum freeze-drying is dispersed in a dispersion medium such as water and the solid content concentration is adjusted, followed by vacuum freeze-drying. In the present invention, it is preferable to adjust the concentration (in terms of solid content) of the liquid-containing material containing the goethite particle powder before vacuum freeze-drying to 50% by weight or less. When the solid content of the liquid-containing material exceeds 50% by weight, the particles are condensed after vacuum freeze-drying, which is not preferable. In addition, when the solid content of the liquid-containing material is low, the particles do not condense after vacuum freeze-drying, but it takes time for vacuum freeze-drying and the yield is small and industrially disadvantageous. The solid content is preferably 5% by weight or more.

  The solid content concentration of the liquid-containing material containing the goethite particle powder is measured by weighing 100 g of the liquid-containing material containing the goethite particle powder and drying for 24 hours at a temperature equal to or higher than the temperature at which the liquid constituting the liquid-containing material evaporates. Then, the liquid was volatilized, the weight of the subsequent dried product was measured, and the solid content concentration was calculated from the weight ratio.

  When vacuum-freeze-drying the liquid-containing material containing the goethite particle powder, the liquid-containing material containing the goethite particle powder is pre-frozen at 0 ° C. or less, and after the pre-freezing, the degree of vacuum is 100 Pa or less. Gradually increase the temperature and dry in a temperature range of 0 to 80 ° C. so that the water content is 0.5% or less, or reduce the vacuum of the liquid-containing material containing the goethite particle powder to 100 Pa or less. Then, by evaporating the moisture contained in the goethite particle powder, the temperature of the liquid-containing material containing the goethite particle powder is lowered to 0 ° C. or lower, and the temperature is gradually increased from the frozen state. Any method of drying so that the water content is 3.0% or less within a temperature range of 0 to 80 ° C. can be used.

  The prefreezing temperature of the liquid-containing material containing goethite particle powder is preferably 0 ° C. or lower, more preferably −30 ° C. or lower. When the pre-freezing temperature exceeds 0 ° C., the liquid constituting the liquid-containing material including the goethite particle powder cannot be completely transformed into a solid, and the distance between the particles does not increase, so that heat treatment for producing hematite particles is performed. At this time, it is not preferable because the particles are easily sintered.

  When performing vacuum freeze-drying, the treatment time can be shortened by lowering the layer height of the liquid-containing material containing the goethite particle powder in the container, which is industrially advantageous.

  The degree of vacuum after preliminary freezing of the liquid-containing material containing the goethite particle powder or when self-freezing is preferably 100 Pa or less, and more preferably 80 Pa or less.

  The drying temperature after preliminary freezing or self-freezing of the liquid-containing material containing the goethite particle powder is preferably 0 ° C to 80 ° C, and more preferably 10 ° C to 60 ° C.

  The goethite particle powder that has been subjected to vacuum freeze-drying in the present invention has a particle size and a BET specific surface area that are substantially the same as those of the goethite particle powder before vacuum freeze-drying.

The volume-based average particle diameter (D ₅₀ ) of the goethite particle powder subjected to vacuum freeze-drying in the present invention is 0.01 to 2.70 μm, preferably 0.01 to 2.65 μm, more preferably 0.01. ˜2.60 μm. When the volume-based average particle diameter (D ₅₀ ) exceeds 2.70 μm, it is not preferable because the particles are easily sintered by performing high-temperature heat treatment.

  The hematite particle powder in the present invention is obtained by subjecting the goethite particle powder subjected to vacuum freeze-drying to low-temperature heat dehydration treatment in a temperature range of 200 to 400 ° C. to obtain a low-density hematite particle powder. A densified hematite particle powder obtained by performing high-temperature heat treatment in a temperature range of ˜850 ° C. is preferable.

A low temperature heating dehydration temperature of less than 200 ° C. is not preferable because a long time is required for the dehydration reaction. When the low temperature heating dehydration temperature exceeds 400 ° C., the dehydration reaction may occur rapidly, and the shape of the particles may be easily broken, or sintering between the particles may be caused. The low-density hematite particle powder obtained by low-temperature heat dehydration treatment is composed of low-density particles in which H ₂ O is dehydrated from the goethite particle powder and has many dehydration pores, and the BET specific surface area value is the starting material of the goethite particle powder. 1.2 to 2 times.

  In addition, in the case where the low-density hematite particle powder is heat-treated at 400 to 850 ° C. to obtain a densified hematite particle powder, if the high-temperature heat treatment temperature is less than 400 ° C., the densification is insufficient. For this reason, there are a large number of dehydration holes inside and on the surface of the hematite particles, and it is difficult to disperse in the vehicle, and when a nonmagnetic underlayer is formed, it is difficult to obtain a smooth coating film. When the temperature exceeds 850 ° C., the density of the hematite particles is sufficiently increased. However, since the particles and the particles are sintered with each other, the particle diameter is increased, and similarly, it is difficult to obtain a coating film having a smooth surface. .

  In consideration of the corrosion resistance of the magnetic recording medium, the nonmagnetic underlayer hematite particle powder in the present invention is highly purified by reducing the content of soluble sodium salt, soluble sulfate, etc. in the hematite particle powder. Hematite particle powder is preferred.

The highly purified hematite particle powder preferably has a soluble sodium salt content of 300 ppm or less, more preferably 200 ppm in terms of Na. Further, the content of soluble sulfate is preferably 150 ppm or less, more preferably 100 ppm or less in terms of SO ₄ .

  The highly purified hematite particle powder can be obtained by subjecting the hematite particle powder to a wet dispersion treatment to form a slurry, followed by heat treatment in an alkaline aqueous solution, filtration and washing with water.

  As a dispersing device for wet-dispersing the hematite particle powder, a wet beadless continuous disperser / emulsifier, a wet medium disperser, and a combination thereof can be used.

  The pH value of the alkaline aqueous solution is preferably 13.0 or more. The temperature of the heat treatment is preferably 80 ° C. or higher, more preferably 90 ° C. or higher.

  The hematite particle powder for non-magnetic underlayer in the present invention 2 has one or two or more kinds of hematite particle powders selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. It can be obtained by coating with a surface coating. When the hematite particle powder whose particle surface is coated with a surface coating is dispersed in a vehicle, the hematite particle powder has a good familiarity with the binder resin, and a desired degree of dispersion is more easily obtained.

  The hematite particle powder coated with the surface coating in the present invention 2 is obtained by adding an aluminum compound, a silicon compound or both of the compounds to an aqueous suspension obtained by dispersing the hematite particle powder, and stirring the mixture. Or, if necessary, the particle surface of the hematite particle powder is selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide by adjusting the pH value after mixing and stirring. Or it coats with 2 or more types of surface coatings, Then, it filters, wash | cleans, dries, and grind | pulverizes. If necessary, a deaeration / consolidation process may be further performed.

  As the aluminum compound, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate, and alkali aluminates such as sodium aluminate can be used.

  As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like can be used.

The amount of the surface coating added is 0.01 for aluminum hydroxide and aluminum oxide in terms of Al, and 0.01 for silicon hydroxide and silicon oxide in terms of SiO _{2 with} respect to the hematite particle powder. -50% by weight is preferred. When the amount is less than 0.01% by weight, there is almost no effect of improving dispersibility by coating. When the amount exceeds 50% by weight, the coating effect is saturated, and there is no meaning to cover more than necessary. Considering the effect of improving dispersibility in the vehicle and industrial productivity, 0.05 to 20% by weight is more preferable.

When used in conjunction with an aluminum compound and a silicon compound, 0.01 to 50 wt% in total of Al equivalent amount and SiO ₂ equivalent amount with respect to hematite particles are preferred.

  The hematite particle powder for nonmagnetic underlayer in the present invention 3 is obtained by vacuum-freezing a liquid-containing material in which the hematite particle powder coated with the surface coating is dispersed in a dispersion medium such as water and the solid content concentration is adjusted. It can be obtained by drying. When the hematite particles are freeze-dried in a vacuum, when dispersed in a vehicle, a magnetic recording medium with improved dispersibility and excellent surface smoothness can be obtained.

  The vacuum freeze-drying of the liquid containing the hematite particle powder coated with the surface coating is performed by pre-freezing the liquid containing the hematite particle powder coated with the surface coating at 0 ° C. or lower, In a state of 100 Pa or less, the temperature is gradually raised from the freezing temperature, and a method of drying so that the water content is 0.5% or less within a temperature range of 0 to 80 ° C. or hematite particles coated with a surface coating The temperature of the liquid-containing material containing the hematite particle powder coated with the surface coating is reduced by reducing the vacuum of the liquid-containing material containing the powder to 100 Pa or less and evaporating the water contained in the hematite particle powder. Any of the methods of self-freezing by lowering below 0 ° C., gradually raising the temperature from the frozen state, and drying so that the water content becomes 3.0% or less within the temperature range of 0-80 ° C. It can be also of how to do.

  The treatment conditions for the vacuum freeze-drying of the liquid-containing material containing the hematite particle powder coated with the surface coating may be the same as those for the vacuum freeze-drying of the goethite particle powder.

  The hematite particle powder coated with the surface coating in the present invention 2 and the present invention 3 has substantially the same particle size and BET specific surface area value as the hematite particle powder in the present invention 1 not coated with the surface coating. doing.

  Next, the characteristics of the nonmagnetic particle powder for nonmagnetic underlayer obtained by the method for producing a nonmagnetic particle powder for nonmagnetic underlayer for magnetic recording media according to the present invention will be described.

  The particle shape of the nonmagnetic particle powder for nonmagnetic underlayer in the present invention may be any shape such as needle shape, spindle shape, rice grain shape, spherical shape, granular shape, polyhedron shape, flake shape, scale shape and plate shape. Good.

  The average primary major axis diameter of the nonmagnetic particle powder for a nonmagnetic underlayer in the present invention is 0.005 to 0.30 μm, preferably 0.010 to 0.25 μm, more preferably 0.015 to 0.20 μm. is there.

  When the average primary major axis diameter of the nonmagnetic particle powder for nonmagnetic underlayer in the present invention exceeds 0.30 μm, the surface smoothness of the coating film is impaired when the nonmagnetic underlayer is formed using this. Cheap. When the average primary long axis diameter is less than 0.005 μm, aggregation is likely to occur due to an increase in intermolecular force due to particle miniaturization, which makes it difficult to disperse in the vehicle.

  The axial ratio of the nonmagnetic particle powder for nonmagnetic underlayer in the present invention is preferably 2.0 to 20.0, more preferably 2.5 to 18.0, and still more preferably 3.0 to 15.0. is there.

BET specific surface area of the non-magnetic particles for non-magnetic undercoat layer of the present invention is preferably 10 to 200 m ² / g, more preferably 15~180m ² / g, still more preferably 20~160m ² / g. When the BET specific surface area value is less than 10 m ² / g, when the magnetic recording layer is formed using this, the surface smoothness of the coating film tends to be impaired. When the BET specific surface area value exceeds 200 m ² / g, aggregation tends to occur due to an increase in intermolecular force due to particle miniaturization, and thus dispersion in the vehicle becomes difficult.

The volume-based average particle diameter (D ₅₀ ) of the nonmagnetic particle powder for nonmagnetic underlayer in the present invention 1 and the present invention 2 is 0.01-2.80 μm, preferably 0.01-2.70 μm. Preferably it is 0.01-2.60 micrometers. When the volume-based average particle diameter (D ₅₀ ) exceeds 2.80 μm, the surface properties of the obtained magnetic recording medium are lowered and dropout is increased when the nonmagnetic underlayer is thinned. It is not preferable.

The non-magnetic particle powder for non-magnetic underlayer in the present invention 3 can further improve dispersibility by coating the surface of the hematite particles with a surface coating, followed by vacuum freeze-drying. diameter _{(D 50)} is 0.01～2.50Myuemu, preferably 0.01～2.40Myuemu, more preferably 0.01～2.30Myuemu.

  The non-magnetic particle powder for non-magnetic underlayer in the present invention may be one or two kinds selected from hematite particle surfaces selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide if necessary. The surface smoothness of the tape can be improved as compared with the case where it is coated with the above surface coating and not coated with the surface coating.

The coating amount by the surface coating is preferably 0.01 to 50% by weight with respect to the hematite particle powder coated with the surface coating, Al conversion, SiO ₂ conversion or the total of Al conversion amount and SiO ₂ conversion amount, More preferably, it is 0.05 to 20% by weight. If it is less than 0.01% by weight, the effect of improving the surface smoothness of the magnetic recording medium cannot be obtained. Since the effect of improving the surface smoothness of the magnetic recording medium tape can be obtained by the coating amount of 0.01 to 50% by weight, there is no meaning to cover more than necessary beyond 50% by weight.

  Next, the magnetic recording medium according to the present invention will be described.

  The magnetic recording medium in the present invention comprises a nonmagnetic support, a nonmagnetic underlayer formed on the nonmagnetic support, and a magnetic recording layer formed on the nonmagnetic underlayer. If necessary, a back coat layer may be formed on the other surface of the nonmagnetic support with respect to the magnetic recording layer formed on one surface of the nonmagnetic support. In particular, in the case of a backup tape for computer recording, it is preferable to provide a backcoat layer from the viewpoint of preventing winding disturbance and improving running durability.

  As the nonmagnetic support in the present invention, polyesters such as polyethylene terephthalate and polyethylene naphthalate that are currently widely used in magnetic recording media, polyolefins such as polyethylene and polypropylene, polycarbonate, polyamide, polyamideimide, polyimide, aromatic Synthetic resin films such as polyamide, aromatic polyimide, aromatic polyamideimide, polysulfone, cellulose triacetate, and polybenzoxazole, metal foils and plates such as aluminum and stainless steel, and various papers can be used. Considering the strength of the magnetic recording medium to be obtained, polyesters, polyamides or aromatic polyamides are preferable.

  The thickness of the nonmagnetic support varies depending on the material and application, but is usually preferably 1.0 to 300 μm, more preferably 2.0 to 200 μm. In particular, in the case of a backup tape for computer recording which tends to be thinned in order to increase the recording capacity, the thickness is usually preferably from 1.0 to 7.0 μm, more preferably from 2.0 to 6.0 μm. It is.

  Next, the nonmagnetic underlayer in the present invention will be described.

  The nonmagnetic underlayer in the present invention comprises the nonmagnetic particle powder for a nonmagnetic underlayer in the present invention and a binder resin. Further, if necessary, a lubricant, an abrasive, an antistatic agent, etc. that are usually used in the production of magnetic recording media may be added.

As the binder resin, a thermoplastic resin, a thermosetting resin, an electron beam curable resin, etc. that are widely used in the production of magnetic recording media can be used alone or in combination. Specifically, as the thermoplastic resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride polymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene acetate copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic acid Ester-styrene copolymer, methacrylate ester-acrylonitrile copolymer, methacrylate ester-vinylidene chloride copolymer, methacrylate ester-styrene copolymer, urethane elastomer, nylon-silicone resin, nitrocellulose-polyanide resin, Polyvinyl fluoride , Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives such as nitrocellulose, styrene-butadiene copolymer, (saturated) polyester resin, polycarbonate resin, chlorovinyl ether-acrylic acid copolymer Synthetic rubber resins such as polymers, amino resins, and polybutadiene can be used. Thermosetting resins and electron beam curable resins include phenolic resins, phenoxy resins, epoxy resins, polyurethane resins, (unsaturated) polyester resins, polyurethane carbonate resins, urea resins, melamine resins, alkyd resins, silicone resins, polyisocyanates. An electron beam curable acrylic urethane resin or the like can be used. Further, each binder resin has acidic groups such as —COOM, —SO ₃ M and —OPO ₂ M ₂ (where M is H, an alkali metal, an alkaline earth metal or a hydrocarbon group) as a polar group. Groups, phosphate esters and alkylbetaine-type amphoteric groups, —OH, —NH _{2 and the} like may be contained. In consideration of the dispersibility in the vehicle of the nonmagnetic particle powder for the nonmagnetic underlayer in the present invention, a binder resin containing —COOM, —SO ₃ M or an alkylbetaine amphoteric group as a polar group is preferable. , especially considering the tape smoothness, binder resin containing a -SO 3 _M are preferable.

  The blending ratio of the nonmagnetic particle powder for nonmagnetic underlayer and the binder resin in the present invention is 5 to 2000 parts by weight, preferably 100, of nonmagnetic particle powder for nonmagnetic underlayer with respect to 100 parts by weight of binder resin. -1000 parts by weight.

  The coating thickness after calendering of the nonmagnetic underlayer formed on the nonmagnetic support is preferably from 0.1 to 5.0 μm, more preferably from 0.2 to 4.0 μm, even more preferably. Is 0.3 to 3.0 μm. In particular, in the case of a backup tape for recording computer data, which tends to be thinned to increase the recording capacity, the thickness is usually preferably 0.1 to 3.0 μm, more preferably 0.2 to 2. 5 μm, even more preferably 0.3 to 2.0 μm. When the thickness is less than 0.1 μm, it is difficult to improve the surface roughness of the nonmagnetic support, and the strength of the obtained magnetic recording medium tends to be insufficient. When the thickness exceeds 5.0 μm, it is difficult to reduce the thickness of the magnetic recording medium.

  As the antistatic agent, conductive powder such as carbon black, graphite, tin oxide, titanium oxide-tin oxide-antimony oxide, a surfactant, and the like can be used. In addition to antistatic, the effect of reducing the friction coefficient and improving the strength of the magnetic recording medium can be expected. Therefore, it is preferable to use carbon black as the antistatic agent. It is more preferable to use carbon black.

  The nonmagnetic underlayer obtained using the nonmagnetic particle powder for nonmagnetic underlayer in the present invention has a coating film glossiness of 175 to 280%, preferably 180 to 280%, more preferably 185 to 280%. And the surface roughness Ra of a coating film is 2.0-11.0 nm, Preferably it is 2.0-10.5 nm, More preferably, it is 2.0-10.0 nm.

  Next, the magnetic recording layer in the present invention will be described.

  The magnetic recording layer in the present invention contains magnetic particle powder and a binder resin.

As magnetic particle powder, Co or Co and Fe are added to magnetic iron oxide particle powder such as maghemite particle powder (γ-Fe ₂ O ₃ ) and magnetite particle powder ( FeO _x · Fe ₂ O ₃ , 0 <x ≦ 1). Co-coated magnetic iron oxide particle powder deposited, and the Co-coated magnetic iron oxide particle powder contains different elements such as Co, Al, Ni, P, Zn, Si, B, rare earth metals other than Fe Co-coated magnetic iron oxide particle powder, metal magnetic particle powder containing iron as a main component, iron alloy magnetic particles containing Co, Al, Ni, P, Zn, Si, B, rare earth metals, etc. other than iron Plate-like magnetoplumbite type ferrite particle powder containing powder, Ba, Sr, or Ba-Sr and divalent such as Co, Ni, Zn, Mn, Mg, Ti, Sn, Zr, Nb, Cu, and Mo And selected from tetravalent metals Any such one or plate-like magnetoplumbite-type ferrite particles or iron nitride which contains two or more the coercive force reducing agents can be used also.

  In consideration of recent short wavelength recording and high density recording, it contains metal magnetic particle powder mainly composed of iron, Co, Al, Ni, P, Zn, Si, B, rare earth metals, etc. other than iron. Iron alloy magnetic particle powder, plate-like magnetoplumbite type ferrite particle powder, iron nitride and the like are preferable.

  The magnetic particle powder preferably has an average primary major axis diameter (average primary particle diameter in the case of plate-like particles) of 0.01 to 0.50 μm, more preferably 0.02 to 0.30 μm. The shape of the magnetic particle powder is preferably needle-shaped or plate-shaped. Here, the term “needle” means not only a literal needle shape but also a spindle shape, a rice grain shape, and the like.

  Further, when the particle shape of the magnetic particle powder is needle-shaped, the axial ratio is preferably 2.0 or more, more preferably 3.0 or more, and the upper limit is 15.5 in consideration of dispersibility in the vehicle. 0 is preferable, and 10.0 is more preferable.

  When the particle shape of the magnetic particle powder is plate-like, the plate-like ratio (ratio of average primary particle diameter of particles and average primary thickness of particles) (hereinafter referred to as “plate-like ratio”) is 1.0 or more. The upper limit is preferably 20.0, more preferably 15.0, considering the dispersibility in the vehicle.

The magnetic properties of the magnetic particle powder include a coercive force value of 39.8 to 318.3 kA / m (500 to 4000 Oe), preferably 43.8 to 318.3 kA / m (550 to 4000 Oe), and a saturation magnetization value. Is 40 to 200 Am ² / kg (40 to 200 emu / g), preferably 45 to 180 Am ² / kg (45 to 180 emu / g).

In consideration of high-density recording, etc., when using magnetic metal powder as a magnetic particle powder, iron alloy magnetic particle powder, plate-like magnetoplumbite type ferrite particle powder, iron nitride, etc. The magnetic properties include a coercive force value of 63.7 to 318.3 kA / m (800 to 4000 Oe), preferably 71.6 to 318.3 kA / m (900 to 4000 Oe), and a saturation magnetization value of 40 to 200 Am ² / kg. (40 to 200 emu / g), preferably 45 to 180 Am ² / kg (45 to 180 emu / g).

  As the binder resin, the binder resin used for producing the nonmagnetic underlayer can be used.

  The coating thickness after calendering of the magnetic recording layer provided on the nonmagnetic underlayer is preferably 0.01 to 2.0 μm, more preferably 0.02 to 1.5 μm, and still more preferably. 0.02 to 1.0 μm. In particular, in the case of a backup tape for computer data recording, which tends to be thinned to increase the recording capacity, the thickness is usually preferably from 0.01 to 0.30 μm, more preferably from 0.02 to 0.00. 20 μm. If it is less than 0.01 μm, uniform coating is difficult, and phenomena such as uneven coating tend to occur, which is not preferable. If the thickness exceeds 2.0 μm, the reproduction output becomes small due to the influence of the demagnetizing field, which is not preferable.

  The blending ratio of the magnetic particle powder and the binder resin is 100 to 2000 parts by weight, preferably 200 to 1500 parts by weight with respect to 100 parts by weight of the binder resin.

  In the magnetic recording layer, commonly used lubricants, abrasives, antistatic agents and the like may be added.

  As the antistatic agent, conductive powder such as carbon black, graphite, tin oxide, titanium oxide-tin oxide-antimony oxide, a surfactant, and the like can be used. For the same reason as in the case of forming the nonmagnetic underlayer, it is preferable to use carbon black as the antistatic agent, and it is more preferable to use highly purified carbon black considering the storage stability of the tape.

  Next, the back coat layer in the present invention will be described.

  The back coat layer in the present invention preferably contains an antistatic agent and inorganic particle powder together with the binder resin for the purpose of reducing the surface electrical resistance value and light transmittance of the back coat layer and improving the strength. Further, if necessary, a lubricant, an abrasive and the like used for production of a normal magnetic recording medium may be contained.

  As the binder resin, the binder resin used for producing the nonmagnetic underlayer and the magnetic recording layer can be used.

  As the antistatic agent, conductive powder such as carbon black, graphite, tin oxide, titanium oxide-tin oxide-antimony oxide, a surfactant, and the like can be used. For the same reason as in the case of forming the nonmagnetic underlayer and the magnetic recording layer, it is preferable to use carbon black as the antistatic agent. In consideration of the storage stability of the tape, highly purified carbon black is used. It is more preferable.

  As the inorganic powder, one or more selected from hematite, alumina, calcium carbonate, silicon carbide, cerium oxide, titanium dioxide, silica, zinc oxide, boron nitride, barium sulfate and the like can be used.

  Among backup tapes for recording computer data, when the recording track width is narrowed to increase the recording capacity, a decrease in reproduction output due to off-track becomes a problem, so that a track servo is necessary. In the track servo system, a servo track band is formed on the magnetic recording layer or the backcoat layer, and the servo track band consisting of a concave array is formed on the backcoat layer by laser irradiation, etc. There is an optical servo system that forms, optically reads and servo-tracks it.

  In particular, in the case of a magnetic servo system in which a servo track band is formed on the backcoat layer, it is essential to contain magnetic particle powder in addition to the antistatic agent and inorganic particle powder. As the magnetic particle powder, the magnetic particle powder used in the magnetic layer can be used.

  With respect to the magnetic recording layer formed on one surface of the nonmagnetic support, the coating thickness after calendering of the backcoat layer provided on the other surface of the nonmagnetic support is 0.1 to 4. 0 μm is preferable, more preferably 0.2 to 2.0 μm, and still more preferably 0.2 to 1.5 μm. When the thickness is less than 0.1 μm, the strength of the backcoat layer becomes insufficient, and a phenomenon such as uneven coating tends to occur, which is not preferable. When the thickness exceeds 4.0 μm, the thickness of the back coat layer is too thick, so that the entire thickness of the tape is increased and it is difficult to increase the recording capacity.

    The magnetic recording medium obtained using the magnetic particle powder in the present invention preferably has a coercive force value of 39.8 to 318.3 kA / m (500 to 4000 Oe), more preferably 43.8 to 318.3 kA / m. (550 to 4000 Oe), the glossiness of the coating film is preferably 130 to 300%, more preferably 135 to 300%, still more preferably 140 to 300%, and the surface roughness Ra of the coating film is preferably 11.0 nm or less. , More preferably 2.0 to 10.5 nm, still more preferably 2.0 to 10.0 nm, and the dropout (D / O) of the coating is preferably 18 pieces / msec or less, more preferably 16 pieces / msec. It is as follows.

  In consideration of high recording capacity, acicular metal magnetic particle powder, acicular iron alloy magnetic particle powder, plate-like magnetoplumbite-type ferrite particle powder, iron nitride, etc. are used as magnetic particle powder. In the case of the magnetic recording medium, the coercive force value is preferably 63.7 to 318.3 kA / m (800 to 4000 Oe), more preferably 71.6 to 318.3 kA / m (900 to 4000 Oe). The glossiness is preferably 185 to 300%, more preferably 190 to 300%, still more preferably 195 to 300%, and the coating surface roughness Ra is preferably 8.0 nm or less, more preferably 2.0 to 7.5 nm, even more preferably 2.0 to 7.0 nm, and the dropout (D / O) is preferably 17 pieces / msec or less, more preferably 15 pieces / msec or less.

  Next, a method for manufacturing a magnetic recording medium in the present invention will be described.

    Solvents used in the formation of the nonmagnetic underlayer, magnetic recording layer, and backcoat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and tetrahydrofuran, toluene, xylene, etc. that are widely used in magnetic recording media. Aromatic hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol, esters such as methyl acetate, butyl acetate, isobutyl acetate and glycol acetate, glycol dimethyl ether, glycol monoethyl ether and dioxane Glycol ethers and mixtures thereof can be used.

  The amount of the solvent used is 65 to 1000 parts by weight in total with respect to 100 parts by weight of the nonmagnetic particle powder for nonmagnetic underlayer in the present invention. If it is less than 65 parts by weight, the viscosity becomes too high when applied as a paint, making application difficult. When it exceeds 1000 parts by weight, the volatilization amount of the solvent when forming the coating film becomes too large, which is industrially disadvantageous.

  The nonmagnetic underlayer, the magnetic recording layer, and the backcoat layer are kneaded and dispersed with a kneader and a disperser that generally use components and solvents that constitute each layer, thereby preparing each paint. Using each of the coating materials, a nonmagnetic underlayer and a magnetic recording layer are applied in this order on one surface of the nonmagnetic support, dried, and then calendared. As a coating method at that time, either the Wet on Wet method in which the magnetic layer and the nonmagnetic layer are applied almost simultaneously, or the Wet on Dry method in which the nonmagnetic underlayer is applied and dried and then the magnetic recording layer is applied thereon. But you can. If necessary, if a backcoat layer is provided, a backcoat layer coating is applied on the nonmagnetic support opposite to the nonmagnetic underlayer and the magnetic recording layer, dried, calendered, and magnetically treated. A recording medium is obtained.

<Action>
The most important point in the present invention is that the liquid containing the goethite particle powder is freeze-dried in vacuum, and then the dried hematite particle powder obtained by heat treatment is sintered between particles. The magnetic recording medium obtained by using this is the fact that even if the nonmagnetic underlayer is thinned, the tape surface smoothness is good and the dropout is small.

  As a reason why the magnetic recording medium obtained using the nonmagnetic particle powder for a nonmagnetic underlayer in the present invention has good surface smoothness even when the nonmagnetic underlayer is thinned, the present inventor Is estimated.

  In other words, by performing vacuum freeze-drying on the liquid-containing material containing the goethite particle powder, the liquid constituting the liquid-containing material can be removed from the solid state by sublimation. Compared with the case of the above, it is possible to suppress the aggregation of particles between the goethite particles, it is possible to suppress the sintering of the particles when the dried product is heat-treated at a high temperature to form hematite particles, Even liquids that are difficult to dry, such as recesses, can be efficiently removed. As a result, the present inventor believes that the hematite particle powder is well dispersed in the vehicle because the wettability of the individual hematite particles with the solvent and the binder resin is efficiently performed.

  Examples of the present invention are shown below, and the present invention will be specifically described.

  The average primary major axis diameter, average primary minor axis diameter, average primary particle diameter, and average primary thickness of the particles were measured by the following procedure. First, the particles were observed using a transmission electron microscope. The magnification was adjusted so that about 400 particles existed in a field where the individual particles did not overlap and were dispersed, and a photograph was taken. Next, after enlarging the obtained photograph four times in length and width, the major axis diameter, minor axis diameter, particle diameter, or thickness of about 350 particles was measured using DIGITIZER (model: KD 4620, manufactured by Graphtec Corporation). Each was measured, and the average primary long axis diameter, average primary short axis diameter, average primary particle diameter, and average primary thickness of the particles were shown by the average value. When measuring the particle size, the longest part was measured in the major axis, minor axis, particle, and thickness. In addition, on the photograph, those in which the outline of the particles was not clear or those in which the particles overlapped to make it difficult to distinguish individual particles were excluded from the measurement of the particle diameter.

  The axial ratio was indicated by the ratio of the average primary major axis diameter to the average primary minor axis diameter, and the plate ratio was indicated by the ratio of the average primary particle diameter to the average primary thickness.

  The specific surface area value was indicated by a value measured by the BET method.

Each of the Al amount, P amount, SiO ₂ amount, and Y amount present inside or on the surface of the goethite particle powder or hematite particle powder is “X-ray fluorescence analyzer 3063M type” (manufactured by Rigaku Corporation). Was measured in accordance with “General X-ray fluorescence analysis rules” of JIS K0119. Further, the Ti amount, Ni amount and Fe amount of the plate-like magnetoplumbite type ferrite particle powder were measured in the same manner as described above.

The volume-based average particle diameter (D ₅₀ ) of the goethite particle powder and hematite particle powder was determined by passing the sample through a sieve of 60 mesh (aperture 250 μm) in advance and drying the sample that passed through the sieve at 80 ° C. for 3 hours. Then, using a dry dispersion unit of “Laser diffraction type particle size distribution measuring device model HELOS LA / KA” (manufactured by SYMPATEC), the dispersion pressure was measured at 0.5 MPa (5 bar).

  The solid content concentration of the liquid-containing material containing goethite particles or hematite particles is 24 above the temperature at which 100 g of liquid-containing material containing goethite particles or hematite particles is weighed and the liquid constituting the liquid-containing material evaporates using a dryer. It was dried for hours and the liquid was evaporated. Thereafter, the weight of the dried product was measured, and the solid content concentration was calculated from the weight ratio.

  The magnetic properties of the magnetic particle powder are values measured under an external magnetic field of 795.8 kA / m (10 kOe) using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) The characteristics of the magnetic tape are the results of measurement under an external magnetic field of 795.8 kA / m (10 kOe).

  The surface glossiness of the coating film is a value measured by using “Glossmeter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.) at an incident angle of 45 °, and the value when the standard plate glossiness is 86.3%. In%.

  Surface roughness Ra measured the centerline average roughness Ra of the coating film using "Surfcom-575A" (made by Tokyo Seimitsu Co., Ltd.).

  For magnetic recording medium dropout, the magnetic tape is applied to “Drum Tester BX-3168” (manufactured by Verdex), and the number of dropouts per unit time is counted from the envelope obtained at a relative speed of 2.5 m / sec. Was determined by

  The thicknesses of the nonmagnetic support, the nonmagnetic underlayer and the magnetic recording layer constituting the magnetic recording medium were measured as follows.

  First, the film thickness (A) of the nonmagnetic support is measured using “Digital Electronic Micrometer K351C” (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support (the sum of the thickness of the nonmagnetic support and the nonmagnetic underlayer) was measured in the same manner. To do. Further, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer). ) Is measured in the same manner. The thickness of the nonmagnetic underlayer is indicated by (B)-(A), and the thickness of the magnetic recording layer is indicated by (C)-(B).

  Further, when a back coat layer is provided on the other surface of the nonmagnetic support with respect to the magnetic recording layer formed on one surface of the nonmagnetic support, as in the above, “digital electronic micrometer K351C”. ”(Manufactured by Anritsu Electric Co., Ltd.), first, the film thickness (A) of the nonmagnetic support is measured. Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support (the sum of the thickness of the nonmagnetic support and the nonmagnetic underlayer) was measured in the same manner. To do. Further, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer). ) Is measured in the same manner. Further, the thickness (D) of the backcoat layer provided on the surface of the nonmagnetic support opposite to the magnetic recording layer (the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, the thickness of the magnetic recording layer, and the thickness of the backcoat layer) The total thickness) is measured in the same manner. The thickness of the nonmagnetic underlayer is indicated by (B)-(A), the thickness of the magnetic recording layer is indicated by (C)-(B), and the thickness of the backcoat layer is indicated by (D)-(C). It was.

<Example 1-1: Production of nonmagnetic particle powder for nonmagnetic underlayer>
Precursor 1 obtained using a ferrous sulfate aqueous solution and a mixed aqueous solution of sodium hydroxide and sodium carbonate (type: goethite particles, particle shape: spindle shape, average primary major axis diameter: 0.130 μm, average primary Short axis diameter: 0.0170 μm, axial ratio: 7.6, BET specific surface area value: 145.4 m ² / g, volume-based average particle diameter D ₅₀ : 3.75 μm, aluminum content (Al conversion): 0.7. (05 wt%) 17 kg of slurry (solid content concentration: 31 g / l) 550 l was heated to a temperature of 60 ° C., and 0.1 N NaOH aqueous solution was added to adjust the pH value of the slurry to 10.0.

  Next, an aqueous solution in which 400 g of sodium hexametaphosphate was dissolved as a sintering inhibitor was gradually added to the slurry, and after the addition was completed, aging was performed for 60 minutes. Next, a 0.1N acetic acid solution was added to the slurry to adjust the pH value of the slurry to 6.5. Then, it washed with water and filtered by the conventional method, and obtained the hydrated substance (solid content concentration 31 weight%) containing goethite particle powder.

Next, the hydrous material containing the goethite particle powder obtained by performing the above-mentioned sintering prevention treatment was frozen at −50 ° C. (preliminary freezing). After freezing, raise the degree of vacuum to 50 Pa, and in that state, gradually raise the temperature from the freezing temperature −50 ° C. to 50 ° C., and dry until the water content is 0.5% or less. 16 kg of goethite particle powder in which the surface of the compound was coated was obtained. Obtained goethite particles (particles 1) the content of phosphorus 0.70% by weight P in terms of a volume-based average particle diameter _{D 50} was 2.10.

  Next, the obtained goethite particle powder is put in a ceramic rotary furnace, and heated and dehydrated at 280 ° C. for 60 minutes in the air while being driven to rotate. The goethite particle powder is dehydrated to obtain a low-density hematite particle powder. It was.

  Next, 13 kg of the above low-density hematite particle powder was again put into a ceramic rotary furnace, heat-treated in air at 570 ° C. for 30 minutes while being rotationally driven, and sealing of the dehydration holes was carried out. -1 nonmagnetic particle powder for nonmagnetic underlayer was obtained.

The obtained nonmagnetic particle powder for nonmagnetic underlayer of Example 1-1 has a spindle shape, an average primary major axis diameter of 0.099 μm, an average primary minor axis diameter of 0.0161 μm, and an axial ratio of 6 0.1, the BET specific surface area value was 58.9 m ² / g, the volume-based average particle diameter D ₅₀ was 2.15, and the phosphorus content (P conversion) was 0.62% by weight.

<Example 2-1: Production of nonmagnetic particle powder for nonmagnetic underlayer>
To disaggregate the 12 kg of the hematite particles obtained in Example 1-1, the mixture was stirred in 70 l of pure water using a stirrer, and “TK Pipeline Homomixer” (product name, Special Machine Industries Co., Ltd.). The slurry containing the hematite particle powder of Example 1-1 was obtained.

  Subsequently, the slurry containing the hematite particle powder of Example 1-1 was subjected to 5 times at a shaft rotational speed of 2000 rpm using a horizontal sand grinder “Mighty Mill MHG-1.5L” (product name, manufactured by Inoue Seisakusho Co., Ltd.). A dispersion slurry containing the hematite particle powder of Example 1-1 was obtained by passing.

  The dispersion slurry concentration containing the obtained hematite particle powder of Example 1-1 was 62 g / l, and 180 l of the slurry was collected. While stirring the slurry, 6N NaOH aqueous solution was added to adjust the pH value of the slurry to 13.4. Next, this slurry was heated with stirring to a temperature of 95 ° C. and held at that temperature for 3 hours.

  Next, this slurry was washed with water by a decantation method to obtain a slurry having a pH value of 10.5. The weight of the hematite particle powder at this time was 10.5 kg.

  Next, 346.5 g of sodium aluminate was gradually added to the alkaline slurry, followed by aging for 20 minutes. Next, a 0.1N acetic acid solution was added to the slurry to adjust the pH value of the slurry to 9.1. Thereafter, filtration, washing with water, and drying were performed by a conventional method to obtain a nonmagnetic particle powder for a nonmagnetic underlayer of Example 2-1.

The obtained nonmagnetic particle powder for nonmagnetic underlayer of Example 2-1 had a spindle shape, an average primary major axis diameter of 0.100 μm, an average primary minor axis diameter of 0.0161 μm, and an axial ratio of 6 .2, BET specific surface area value is 59.2 m ² / g, volume-based average particle diameter D ₅₀ is 2.16, phosphorus content (P conversion) is 0.62% by weight, aluminum content (Al Conversion) was 1.14% by weight.

<Example 3-1: Production of nonmagnetic particle powder for nonmagnetic underlayer>
Next, the water-containing material (solid content concentration: 29% by weight) containing the hematite particle powder after filtering and washing with water (before drying) in Example 2-1 was completely frozen at −50 ° C., and after freezing The degree of vacuum was raised to 50 Pa, the temperature was gradually raised from this state to 60 ° C., and then drying was performed until the water content became 0.5% or less. 10.0 kg of this dry powder was put into an edge runner “MPUV-2 type” (product name, manufactured by Matsumoto Casting Iron Works Co., Ltd.), mixed and stirred at 392 N / cm for 20 minutes to loosen the particles agglomerate, A nonmagnetic particle powder for a nonmagnetic underlayer of Example 3-1 was obtained.

The obtained nonmagnetic particle powder for nonmagnetic underlayer of Example 3-1 has a spindle shape, an average primary major axis diameter of 0.099 μm, an average primary minor axis diameter of 0.0160 μm, and an axial ratio of 6 .2, BET specific surface area value is 59.1 m ² / g, volume-based average particle diameter D ₅₀ is 1.86 μm, phosphorus content (P conversion) is 0.61% by weight, aluminum content (Al Conversion) was 1.13 wt%.

<Nonmagnetic Underlayer 1: Production of Nonmagnetic Underlayer>
12 g of nonmagnetic particle powder for nonmagnetic underlayer of Example 1-1, binder resin solution (30% by weight of vinyl chloride copolymer resin having potassium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone were mixed. The mixture was kneaded for 30 minutes using an automatic mortar to obtain a kneaded product.

  This kneaded product was mixed with 95 g of 1.5 mmφ glass beads, an additional binder resin solution (polyurethane resin having a sodium sulfonate group 30 wt%, solvent (methyl ethyl ketone: toluene = 1: 1) 70 wt%), cyclohexanone, methyl ethyl ketone and toluene. The mixture was added to a 140 ml glass bottle and mixed and dispersed for 6 hours with a paint shaker to obtain a coating composition. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a nonmagnetic paint for a nonmagnetic underlayer.

  The composition of the obtained nonmagnetic coating material for the nonmagnetic underlayer was as follows.

100.0 parts by weight of nonmagnetic particle powder for nonmagnetic underlayer,
11.8 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
11.8 parts by weight of a polyurethane resin having a sodium sulfonate group,
78.3 parts by weight of cyclohexanone,
195.8 parts by weight of methyl ethyl ketone,
117.5 parts by weight of toluene,
Curing agent (polyisocyanate) 3.0 parts by weight,
Lubricant (butyl stearate) 1.0 part by weight.

  The nonmagnetic coating for the nonmagnetic underlayer was applied onto an aromatic polyamide film having a thickness of 4.5 μm, and then dried to form a nonmagnetic underlayer. In order to evaluate the characteristics of the nonmagnetic underlayer, the half of the obtained coated piece was calendered and then cured at 60 ° C. for 24 hours.

  The obtained nonmagnetic underlayer 1 had a film thickness of 1.3 μm, a coating film glossiness of 200%, and a surface roughness Ra of 6.5 nm.

<Example 4-1: Production of magnetic recording medium>
Magnetic particles (1) (Type: metal magnetic particles containing iron as a main component, particle shape: needle shape, average primary major axis diameter: 0.063 μm, average primary minor axis diameter: 0.0116 μm, axial ratio: 5.4 , Coercive force value: 187.0 kA / m (2,350 Oe), saturation magnetization value: 131.8 Am ² / kg (131.8 emu / g)) 12 g, abrasive (trade name: AKP-50, Sumitomo Chemical Co., Ltd.) (Product made) 1.2g, carbon black 1 0.12g, binder resin solution (30% by weight of vinyl chloride copolymer resin having potassium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone are mixed and an automatic mortar is used. And kneaded for 30 minutes to obtain a kneaded product.

Here, the used carbon black 1 was highly purified with the following contents. Commercially available carbon black (particle shape: granular, average primary particle size: 0.025 μm, BET specific surface area value: 85.6 m ² / g, DBP oil absorption: 55 ml / 100 g, soluble sodium salt content (as Na ): 147 ppm, soluble sulfate content (SO ₄ conversion: 1105 ppm) was crushed by an edge runner “MPUV-2 type” (product name, manufactured by Matsumoto Foundry Co., Ltd.). Water was added to 2 kg of crushed carbon black to a concentration of 98 g / l, and while stirring, an aqueous 18N NaOH solution was added to adjust the pH value of the slurry to 13.7. Next, the slurry was heated with stirring to 95 ° C., held at that temperature for 180 minutes, and then washed with pure water by decantation. Next, the water-washed slurry obtained was filtered off using a Buchner funnel, passed through pure water, washed with water until the electric conductivity of the filtrate was 60 μS / cm or less, and then dried by a conventional method. To obtain high-purity carbon black 1.

The obtained carbon black 1 has an average primary particle size of 0.025 μm, a BET specific surface area value of 82.3 m ² / g, a DBP oil absorption of 49 ml / 100 g, and a soluble sodium salt content of 20 ppm in terms of Na, soluble. The sulfate content was 42 ppm in terms of SO ₄ .

  Together with 95 g of 1.5 mmφ glass beads, an additional binder resin solution (30% by weight of polyurethane resin having sodium sulfonate group, 70% by weight of solvent (methyl ethyl ketone: toluene = 1: 1)), cyclohexanone, methyl ethyl ketone and toluene It was added to a 140 ml glass bottle and mixed and dispersed for 6 hours with a paint shaker to obtain a magnetic paint. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a magnetic coating material for a magnetic recording layer.

The composition of the obtained magnetic coating material for the magnetic recording layer was as follows.
100.0 parts by weight of metal magnetic particle powder containing iron as a main component,
10.0 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
10.0 parts by weight of a polyurethane resin having a sodium sulfonate group,
Abrasive (AKP-50) 10.0 parts by weight,
1.0 part by weight of carbon black 1,
Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight,
Curing agent (polyisocyanate) 5.0 parts by weight,
65.8 parts by weight of cyclohexanone,
164.5 parts by weight of methyl ethyl ketone,
98.7 parts by weight of toluene.

  A magnetic recording layer coating was applied on the nonmagnetic underlayer, and then oriented and dried in a magnetic field.

<Manufacture of back coat layer>
Carbon black 1 12.0 g, carbon black 2 (average primary particle size: 0.37 μm) 1.8 g, iron oxide 1.8 g, binder resin solution (nitrocellulose 30 wt% and cyclohexanone 70 wt%) and cyclohexanone The mixture was kneaded for 30 minutes using an automatic mortar to obtain a kneaded product. Carbon black 2 was obtained by purifying carbon black having an average primary particle size of 0.37 μm under the same cleaning conditions as carbon black 1. The obtained carbon black 2 had a soluble sodium salt content of 18 ppm in terms of Na and a soluble sulfate content of 25 ppm in terms of SO ₄ .

  Together with 95 g of 1.5 mmφ glass beads, an additional binder resin solution (30% by weight of polyurethane resin having sodium sulfonate group, 70% by weight of solvent (methyl ethyl ketone: toluene = 1: 1)), cyclohexanone, methyl ethyl ketone and toluene The resultant was added to a 140 ml glass bottle and mixed and dispersed for 6 hours with a paint shaker to obtain a back coat paint. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a backcoat layer coating material.

The composition of the obtained coating material for the back coat layer was as follows.
Carbon black 1 (average primary particle size 0.025 μm) 100.0 parts by weight,
Carbon black 2 (average primary particle size 0.37 μm) 15.0 parts by weight,
15.0 parts by weight of iron oxide,
55.0 parts by weight of nitrocellulose resin,
35.0 parts by weight of a polyurethane resin having a sodium sulfonate group,
Curing agent (polyisocyanate) 18.0 parts by weight,
325.0 parts by weight of cyclohexanone,
655.0 parts by weight of methyl ethyl ketone,
325.0 parts by weight of toluene.

  The backcoat layer paint obtained above was applied onto a nonmagnetic support on the side opposite to the magnetic recording layer, dried, and then subjected to a calendar treatment. The thickness of the back coat layer was 0.5 μm. Thereafter, a curing reaction was performed at 60 ° C. for 24 hours, and a magnetic recording medium was obtained by slitting to 12.7 mm width.

  The obtained magnetic recording medium had a magnetic recording layer thickness of 0.27 μm, a coercive force value of 194.2 kA / m (2,440 Oe), a glossiness of 217%, a surface roughness Ra of 5.8 nm, D / O was 15 / msec.

  Nonmagnetic particle powder for nonmagnetic underlayer, nonmagnetic underlayer, and magnetic recording medium according to Example 1-1, Example 2-1, Example 3-1, nonmagnetic underlayer 1, and Example 4-1. Was made. Various manufacturing conditions and various characteristics of the obtained nonmagnetic particle powder for nonmagnetic underlayer, nonmagnetic underlayer and magnetic recording medium are shown.

Precursors 2-4:
Precursors 2 to 4 were prepared as goethite particles which are precursors for producing hematite particles. Various properties of the goethite particles are shown in Table 1.

Particles 2-4:
Except for various changes in the type of goethite particles that are precursors, the type and coating amount of the sintering inhibitor, the solid content concentration in the vacuum freeze-drying process, the freezing temperature, the degree of vacuum, and the drying temperature, the same as in particle 1 Goethite particles were obtained.

Table 2 shows the production conditions at this time and the volume-based average particle diameter D ₅₀ of the obtained goethite particles.

Particle 5:
The hydrous material containing the goethite particles was obtained by subjecting the hydrous material containing the goethite particles obtained by carrying out the sintering prevention treatment to pre-freezing without increasing the vacuum to 50 Pa. The freezing temperature at that time was −40 ° C. Next, goethite particles were obtained in the same manner as the particles 1 except that the temperature was gradually raised from -40 ° C to 50 ° C and drying was performed until the water content became 3% or less.

Particle 6:
Goethite particles were obtained in the same manner as the particles 1 except that the drying after the sintering prevention treatment was not performed by vacuum freeze-drying but by a normal dryer.

Table 2 shows the production conditions of the particles 5 and 6 and the volume-based average particle diameter D ₅₀ of the obtained goethite particles.

Examples 1-2 to 1-5 and Comparative Example 1-1
A nonmagnetic particle powder for a nonmagnetic underlayer was obtained in the same manner as in Example 1-1, except that the type of goethite particles, the temperature and time of low density heat treatment, and the temperature and time of high density heat treatment were variously changed. It was.

  Table 3 shows the manufacturing conditions and various characteristics of the nonmagnetic particle powder for the nonmagnetic underlayer.

Examples 2-2 to 2-5 and Comparative Example 1-2:
A nonmagnetic particle powder for a nonmagnetic underlayer was obtained in the same manner as in Example 2-1, except that the type of hematite particles and the type and amount of the surface treatment additive were variously changed.

  The production conditions at this time are shown in Table 4, and various characteristics of the obtained nonmagnetic particle powder for nonmagnetic underlayer are shown in Table 5.

Examples 3-2 to 3-5 and Comparative Examples 1-3 to 1-4:
A nonmagnetic particle powder for a nonmagnetic underlayer was prepared in the same manner as in Example 3-1, except that the type of hematite particles, the solid concentration in the freeze-drying treatment, the freezing temperature, the degree of vacuum, and the drying temperature were variously changed. Obtained.

  The production conditions at this time are shown in Table 6, and the characteristics of the obtained nonmagnetic particle powder for nonmagnetic underlayer are shown in Table 7.

<Manufacture of nonmagnetic underlayer>
Nonmagnetic underlayers 2-9, comparative nonmagnetic underlayers 1-4:
A nonmagnetic underlayer was obtained in the same manner as the nonmagnetic underlayer 1 except that the type of nonmagnetic particle powder for the nonmagnetic underlayer was variously changed.

  Table 8 shows the manufacturing conditions and the characteristics of the obtained nonmagnetic underlayer.

<Manufacture of magnetic recording media>
Examples 4-2 to 4-9 and comparative examples 2-1 to 2-4:
A magnetic recording medium was manufactured in the same manner as in Example 4-1 except that the type of the nonmagnetic underlayer and the type of the magnetic particles were variously changed.

  Table 9 shows various characteristics of the magnetic particles (1) to (3) used.

  Table 10 shows the manufacturing conditions and various characteristics of the obtained magnetic recording medium.

The non-magnetic particle powder for non-magnetic underlayer of the magnetic recording medium obtained by the production method according to the present invention has less aggregation between particles and is easy to disperse. Therefore, the magnetic recording medium using the non-magnetic particle powder is non-magnetic. Even if the magnetic underlayer is made thin, the tape has good surface smoothness, little dropout, and is suitable as a high-density magnetic recording medium.

Claims (4)

A non-magnetic underlayer for a non-magnetic underlayer of a magnetic recording medium, characterized in that a liquid-containing material containing goethite particles having a solid content concentration of 50% by weight or less is freeze-dried in vacuum, and then the dried material is heat-treated into hematite particle powder Manufacturing method of particle powder. Water suspension obtained by vacuum freeze-drying a liquid-containing material containing goethite particles and having a solid content concentration of 50% by weight or less, heat-treating the dried material into hematite particle powder, and then dispersing the hematite particle powder in water An aluminum compound and / or a silicon compound is added to the liquid, and the surface of the hematite particles is selected from one or two selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. A method of producing a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium, wherein hematite particle powder is obtained by coating with a surface coating of at least seeds, and then filtering, washing, drying and grinding. Water suspension obtained by vacuum freeze-drying a liquid-containing material containing goethite particles and having a solid content concentration of 50% by weight or less, heat-treating the dried material into hematite particle powder, and then dispersing the hematite particle powder in water An aluminum compound and / or a silicon compound is added to the liquid, and the particle surface of the hematite particle powder is selected from the group consisting of aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide, or A non-magnetic underlayer for a magnetic recording medium, characterized in that the liquid-containing material having a solid content concentration of 50% by weight or less containing the surface-coated hematite particles is vacuum lyophilized. For producing non-magnetic particle powder for use. Nonmagnetic support, nonmagnetic underlayer containing nonmagnetic particle powder and binder resin formed on nonmagnetic support, and magnetic particle powder and binder resin formed on nonmagnetic underlayer A magnetic recording medium comprising a magnetic recording layer, wherein the nonmagnetic particle powder is obtained by the method for producing a nonmagnetic particle powder for a nonmagnetic underlayer according to any one of claims 1 to 3. A magnetic recording medium, which is a nonmagnetic particle powder for a nonmagnetic underlayer.