JP2007128629A - Nonmagnetic particle powder for nonmagnetic base layer of magnetic recording medium, its production method, nonmagnetic paint for nonmagnetic base layer, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonmagnetic powders for a nonmagnetic base layer of a magnetic recording medium, in which particles are easily dispersed by small dispersion force, and dispersibility is improved in a nonmagnetic paint, a nonmagnetic paint for the nonmagnetic base layer obtained by using the nonmagnetic particle powders for the nonmagnetic base layer, and a magnetic recording medium capable of reducing a dropout even when the nonmagnetic base layer is made thin. <P>SOLUTION: The nonmagnetic particle powders for the nonmagnetic base layer of a magnetic recording medium are prepared such that inorganic particle powders having Mohs hardness of 7.0 to 9.0 and specific gravity of 4.5 or more together with hematite particle powders or hydrous iron oxide particle powders are present by 0.01 to 0.2 w% with respect to the hematite particle powders or the hydrous iron oxide particle powders. The nonmagnetic paint uses the nonmagnetic particle powders. The magnetic recording medium uses the nonmagnetic particle powders. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention uses a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium and a nonmagnetic particle powder for a nonmagnetic underlayer that are easy to loosen particles with a slight dispersion force and have excellent dispersibility in a nonmagnetic paint. Provided are a nonmagnetic paint for a nonmagnetic underlayer and a magnetic recording medium capable of reducing dropout even when the nonmagnetic underlayer is thinned.

  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, a base layer (hereinafter referred to as “non-magnetic base layer”) in which non-magnetic particle powder such as matite particle powder is dispersed in a binder resin on a non-magnetic support such as a base film. ) Is provided to improve the surface smoothness and strength of the magnetic recording medium.

  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, video tapes and backup tapes that have a specified size per tape, for a long recording time 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 non-magnetic underlayer is thinned, the dispersion level of the non-magnetic particle powder greatly affects the surface smoothness of the magnetic recording medium. Even if the particle diameter, by making the layer thin, a protrusion is generated on the surface of the nonmagnetic underlayer, and the protrusion affects the surface of the magnetic recording layer, so that the surface smoothness of the magnetic recording layer is deteriorated, Dropout is likely to occur.

  In addition, since audio tapes, video tapes, and computer backup tapes are repeatedly used at high speed, it is required that the tape strength can be maintained at the same level as before even when the nonmagnetic underlayer is thinned.

  Furthermore, efforts have been made to improve the production rate of magnetic recording media. One of the methods is to improve the dispersibility of non-magnetic particle powder, and there are few secondary agglomerates. There has been a demand for non-magnetic particle powders that are easily wetted by resins and solvents.

  In the past, attempts have been made to use an inorganic compound having a high Mohs hardness as the nonmagnetic particle powder for the nonmagnetic underlayer in order to improve various characteristics of the magnetic recording medium. The method of containing the above plate-like pigment particles (Patent Document 1), the method of containing an inorganic powder having a Mohs hardness of 4 or more in the nonmagnetic underlayer (Patent Document 2), and the two or more types of Mohs hardness of 5 in the nonmagnetic underlayer A method of including the above nonmagnetic powder (Patent Document 3), a method of making the specific gravity of the nonmagnetic powder added to the nonmagnetic underlayer larger than that of the upper ferromagnetic powder (Patent Document 4), etc. are known. Yes.

JP 2004-253069 A JP 2002-15414 A Japanese Patent Laid-Open No. 9-63041 JP-A-4-325916

  Nonmagnetic particle powders for nonmagnetic underlayers, which are excellent in surface smoothness and strength even when the nonmagnetic underlayer is made thin, and can provide a magnetic recording medium with few dropouts, are currently most demanded. By the way, it has not been obtained yet.

  That is, in the above-mentioned patent documents 1 to 3, it is described that an inorganic powder having a high Mohs hardness is included in the nonmagnetic underlayer. However, as shown in a comparative example, a nonmagnetic coating is produced at the stage. When inorganic particle powder with high Mohs hardness is contained or inorganic particle powder with high Mohs hardness is used, secondary particles of nonmagnetic particle powder are not crushed, so that high dispersibility is obtained. However, when the nonmagnetic underlayer is thinned, it is difficult to say that dropout, surface smoothness, and durability of the obtained magnetic recording medium are sufficient.

  Patent Document 4 describes that the specific gravity of the nonmagnetic powder added to the lower layer is 0.5 or more larger than that of the ferromagnetic powder, but the hardness is not particularly mentioned, Since the secondary agglomerates of the nonmagnetic particle powder cannot be efficiently crushed, it is difficult to say that the dropout of the magnetic recording medium obtained using the nonmagnetic particle powder is sufficiently reduced.

  As a result of intensive studies to solve the above problems, the present inventors have found that non-magnetic particle powder in which inorganic particle powder having Mohs hardness of 7.0 to 9.0 is present together with hematite particle powder or hydrous iron oxide particle powder. Since the particles are easy to loosen with a slight dispersion force and are excellent in dispersibility in the nonmagnetic paint, the nonmagnetic paint obtained by using the nonmagnetic particle powder has excellent dispersibility and a thin nonmagnetic underlayer. It has been found that a magnetic recording medium capable of reducing dropout even when layered is obtained, and the present invention has been made.

  That is, the present invention provides a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium, characterized in that an inorganic particle powder having a Mohs hardness of 7.0 to 9.0 is present together with a hematite particle powder or a hydrous iron oxide particle powder. (Invention 1).

  The present invention also provides the nonmagnetic particle powder for a nonmagnetic underlayer of the magnetic recording medium of the present invention 1, wherein the specific gravity of the inorganic particle powder is 4.5 or more (Invention 2).

  The present invention also provides the magnetic recording medium according to the first or second aspect, wherein the inorganic particle powder is present in an amount of 0.01 to 0.2% by weight based on the hematite particle powder or the hydrous iron oxide particle powder. This is a nonmagnetic particle powder for a nonmagnetic underlayer (Invention 3).

  In addition, the present invention is the nonmagnetic particle powder for a nonmagnetic underlayer of the magnetic recording medium according to any one of the present invention 1 to 3, wherein the inorganic particle powder is tungsten carbide (Invention 4).

  In addition, the present invention provides a hematite particle powder or one or more particle surfaces of a hydrous iron oxide particle powder and an inorganic particle powder having an aluminum hydroxide, an aluminum oxide, a silicon hydroxide, and a silicon oxide. A nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium according to any one of the first to fourth aspects of the present invention, wherein the nonmagnetic underlayer powder is coated with a compound composed of at least one selected from the above (Invention 5).

  In addition, the present invention provides a non-magnetic under magnetic recording medium according to any one of the present inventions 1 to 4, wherein the inorganic particle powder is added to the hematite particle powder or the hydrous iron oxide particle powder, followed by wet dispersion treatment. This is a method for producing a nonmagnetic particle powder for formation (Invention 6).

  In the present invention, the inorganic particle powder is added to the hematite particle powder or the hydrous iron oxide particle powder, and after performing the wet dispersion treatment, any one of the hematite particle powder, the hydrous iron oxide particle powder, and the inorganic particle powder is used. The magnetic recording medium according to the fifth aspect of the present invention, wherein the particle surface is coated with a compound comprising at least one selected from aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide. This is a method for producing a nonmagnetic particle powder for a nonmagnetic underlayer (Invention 7).

  Further, the present invention is a nonmagnetic particle powder, a nonmagnetic coating material containing a binder resin and a solvent, wherein the nonmagnetic particle powder is the nonmagnetic particle powder for a nonmagnetic underlayer according to any one of the present invention 1 to 5. (Invention 8).

  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. A magnetic recording medium comprising a magnetic recording layer containing a binder resin, wherein the nonmagnetic particle powder is the nonmagnetic particle powder for a nonmagnetic underlayer according to any one of the first to fifth aspects of the invention. (Invention 9).

  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 and a backcoat layer formed on the other surface of the nonmagnetic support, the nonmagnetic particle powder is any one of the inventions 1 to 5. A magnetic recording medium characterized by being a nonmagnetic particle powder for a magnetic underlayer (Invention 10).

  The non-magnetic particle powder according to the present invention is suitable as a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium because the particles are easily loosened with a slight dispersion force and excellent in dispersibility in a non-magnetic coating material. .

  The nonmagnetic paint according to the present invention provides a nonmagnetic underlayer having high surface smoothness and strength by using the nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium excellent in dispersibility according to the present invention. Therefore, it is suitable as a nonmagnetic paint for a nonmagnetic underlayer of a magnetic recording medium.

  The magnetic recording medium according to the present invention is excellent in productivity and can reduce dropout even when the nonmagnetic underlayer is thinned by using the nonmagnetic particle powder according to the present invention. Therefore, it is suitable as a high-density magnetic recording medium.

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

  First, the nonmagnetic particle powder for nonmagnetic underlayer for magnetic recording media according to the present invention (hereinafter referred to as “nonmagnetic particle powder”) will be described.

  The nonmagnetic particle powder according to the present invention comprises a nonmagnetic particle powder in which inorganic particle powder having a hardness of 7.0 to 9.0 is present together with hematite particle powder or hydrous iron oxide particle powder.

  The hematite particles or hydrous iron oxide particles in the present invention may contain different elements such as Al, Zr, Ti, P, Sn, Sb or Mn inside the particles. In particular, in view of improving the strength of the obtained magnetic recording medium, it is preferable to use hematite particles or hydrous iron oxide particles containing aluminum inside the particles. The different elements contained in the particles are preferably 0.05 to 50% by weight in terms of each element, more preferably 0.10 to 40% by weight, and still more preferably 0.15 to 30% by weight.

  The particle shape of the hematite particles or hydrous iron oxide 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 coating film strength of the obtained magnetic recording medium, 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-like, spindle-like, and rice grain are preferred, more preferably 2.25 to 18.0, and even more preferably 2.5 to 15.0.

  The average primary long axis diameter of the hematite particle powder or the hydrous iron oxide particle powder 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. It is.

The BET specific surface area value of the hematite particle powder or the hydrous iron oxide particle powder in the present invention is usually 25 to 300 m ² / g.

The volume reference average diameter (D ₅₀ ) of ₅ bar at a dispersion pressure of 5 bar of the hematite particle powder or the hydrous iron oxide particle powder in the present invention usually has a value exceeding 2.70 μm. In the present _{invention, (D 50) 5 bar} in order to obtain a non-magnetic particles below 2.70μm are the particles _{(D 50) 5 bar} also lower is preferable as possible. The upper limit is more preferably 5.00 μm, and even more preferably 4.50 μm.

The volume-based average diameter (D ₅₀ ) ₃ bar at a dispersion pressure 3 bar of the hematite particle powder or the hydrous iron oxide particle powder in the present invention usually has a value exceeding 3.00 μm. In the present _{invention, (D 50) 3 bar} in order to obtain a non-magnetic particles below 3.00μm are the particles _{(D 50) 3 bar} also lower is preferable as possible. The upper limit is more preferably 6.00 μm, and even more preferably 5.50 μm.

Any inorganic particle powder may be used as long as it has a Mohs hardness of 7.0 to 9.0, preferably 7.5 to 9.0, more preferably 8.0 to 9.0. is there. Specifically, tungsten carbide (WC) having a Mohs hardness of 9, boron carbide (B ₄ C), silicon carbide (SiC), alumina (Al ₂ O ₃ ), zirconium carbide (ZrC), thallium carbide (TaC), Examples include titanium nitride (TiN), titanium carbide (TiC) with Mohs hardness of 8, zirconium oxide (ZrO) with Mohs hardness of 7, chromium (III) oxide (Cr ₂ O ₃ ), quartz (SiO ₂ ), and the like. It is done. When the Mohs hardness is less than 7.0, it is difficult to obtain an agglomerate of the hematite particle powder or the hydrous iron oxide particle powder in the present invention, and it is difficult to obtain a nonmagnetic particle powder in which the particles are loosened with a slight dispersion force. Become. In addition, when the Mohs hardness exceeds 9.0, the effect of pulverizing the aggregate of the hematite particle powder or the hydrous iron oxide particle powder does not change greatly, and it becomes expensive like diamond. Not suitable.

The specific gravity of the inorganic particle powder in the present invention is preferably 4.5 or more. Particularly, when the hydrous iron oxide particle powder is used, the specific gravity is preferably 4.5 or more, and when the hematite particle powder is used, the specific gravity is 5 More than 5 is preferable. As specific gravity of 5.5 or more, specifically, tungsten carbide (WC) specific gravity: 15.6, thallium carbide (TaC) specific gravity: 14.5, zirconium carbide (ZrC) specific gravity: 6.9, zirconium oxide (ZrO) ₂ ) Specific gravity: 5.9 and the like, and specific gravity of 4.5 to 5.5 includes titanium nitride (TiN) specific gravity: 5.2, chromium oxide (III) (Cr ₂ O ₃ ) specific gravity. : 5.2, titanium carbide (TiC) specific gravity: 4.9, and the like. The higher the specific gravity of the inorganic particle powder, the more efficiently the agglomerates of hematite particle powder or hydrous iron oxide particle powder can be pulverized in the presence of a small amount. Therefore, tungsten carbide (WC) having a specific gravity of 15.6 is preferable. Used for.

  The particle size of the inorganic particle powder present in the hematite particle powder or the hydrous iron oxide particle powder of the present invention is preferably 0.08 to 1.20 μm, more preferably 0.09 to 1.10 μm, still more preferably. 0.10 to 1.00 μm.

  The shape of the inorganic particles of the present invention may be any of granular, acicular, and spherical.

The abundance of the inorganic particle powder in the present invention is preferably 0.01 to 0.20% by weight, more preferably 0.02 to 0.15% by weight, even more based on the hematite particle powder or the hydrous iron oxide particle powder. Preferably it is 0.03-0.10 weight%. If it is less than 0.01% by weight, the effect of loosening the aggregates present in the hematite particle powder or the hydrous iron oxide particle powder to the primary particles is low, and it is difficult to obtain the nonmagnetic particle powder targeted by the present invention. is there. The volume-based average particle diameter (D ₅₀ ) at a dispersion pressure of 3 _bar can be sufficiently reduced by the abundance of 0.01 to 0.20% by weight, so that it exceeds 0.20% by weight and is present more than necessary. There is no point in making it happen.

  The average primary long axis diameter of the nonmagnetic particle powder according to the present invention excluding the inorganic particle powder having a Mohs hardness of 7.0 to 9.0 is preferably 0.005 to 0.30 μm, more preferably 0.010 to 0. .25 μm, still more preferably 0.015 to 0.20 μm.

  When the average primary major axis diameter exceeds 0.30 μm, the non-magnetic particles become large particles, and when the non-magnetic underlayer is formed using this, the surface smoothness of the coating film tends to be impaired. 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 the refinement of the particles. As a result, coarse particles are generated and are introduced into the vehicle during the production of the nonmagnetic paint. Uniform dispersion becomes difficult.

  The particle shape of the nonmagnetic particles according to 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. Considering the coating strength of the resulting magnetic recording medium, needles, spindles and rice grains having an axial ratio of 2.0 to 20.0 are preferred, more preferably 2.5 to 18.0, and even more preferably. Is 3.0-15.0.

The nonmagnetic particle powder according to the present invention has a BET specific surface area value of 25 to 300 m ² / g.

The volume-based average diameter (D ₅₀ ) ₅ bar of the nonmagnetic particle powder according to the present invention at a dispersion pressure of 5 bar is 0.01 to 2.70 μm, preferably 0.01 to 2.60 μm, more preferably 0.01. ˜2.50 μm.

The volume-based average diameter (D ₅₀ ) ₃ bar at a dispersion pressure of 3 bar of the nonmagnetic particle powder according to the present invention is 0.01 to 3.00 μm, preferably 0.01 to 2.90 μm, more preferably 0.01. ˜2.80 μm. When the volume-based mean diameter in the dispersion pressure _3bar (D ₅₀₎ 3bar exceeds 3.00μm, when the non-magnetic undercoat layer is made thin, the surface of the resulting magnetic recording medium is reduced, dropout Is unfavorable because of an increase. In particular, in the case of non-magnetic particle powder in which inorganic particle powder having a specific gravity of 4.5 or more according to the present invention is present, the volume-based average diameter (D ₅₀ ) at _{3 bar} of _{3 bar} is 0.01 to 2.90 μm. More preferably, it is 0.01-2.80 micrometers or less, More preferably, it is 0.01-2.70 micrometers. When the specific gravity of the inorganic particle powder is less than 4.5, a strong dispersion force is required to loosen the secondary aggregate of the hematite particle powder or the hydrous iron oxide particle powder, which is not preferable because the production capacity is lowered.

If necessary, the nonmagnetic particle powder according to the present invention may have a hematite particle powder, or one or more particle surfaces of a hydrous iron oxide particle powder and an inorganic particle powder, an aluminum hydroxide, an aluminum oxide, a silicon One or two or more compounds selected from hydroxides and silicon oxides may be coated, and the volume-based average particle diameter (D ₅₀ ) _{3 bar} at a dispersion pressure of 3 _bar is smaller than when not coated with a compound. can do.

The coating amount by the compound is preferably 0.01 to 20% by weight in terms of Al, SiO ₂ or the total of the Al conversion and the SiO ₂ conversion with respect to the nonmagnetic particle powder coated with the compound.

When the content is less than 0.01% by weight, an effect of improving the volume-based average particle diameter (D ₅₀ ) of _{3 bar} at _{3 bar} cannot be obtained. Since the effect of improving the volume-based average particle diameter (D ₅₀ ) of ₃ bar at a dispersion pressure of 3 bar is obtained by the coating amount of 0.01 to 20% by weight, it is meaningless to cover more than 20% by weight.

The nonmagnetic particle powder according to the present invention coated with a compound (hereinafter referred to as “nonmagnetic particle powder according to the present invention 5”) is nonmagnetic according to the present invention 1 to present invention 4 not coated with a compound. It has a particle size and a BET specific surface area value almost the same as those of the particle powder. Further, the dispersion volume-based mean diameter _{(D 50)} in the pressure 5 bar volume-based mean diameter in the _{5 bar} and _{3bar (D 50)} 3bar is improved by coating the compound, volume-based mean diameter in the dispersion pressure _{5bar (D 50)} 5bar Is preferably 0.01 to 2.50 μm, more preferably 0.01 to 2.40 μm, and still more preferably 0.01 to 2.30 μm. Further, the volume reference average diameter (D ₅₀ ) ₃ bar at the dispersion pressure of 3 _bar is preferably 0.01 to 2.80 μm, more preferably 0.01 to 2.70 μm, and still more preferably 0.01 to 2.60 μm. .

  Next, the nonmagnetic paint for a nonmagnetic underlayer according to the present invention will be described.

  The nonmagnetic paint for a nonmagnetic underlayer according to the present invention comprises a nonmagnetic particle powder, a binder resin, and a solvent. 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, and the like that are widely used in the manufacture 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. Considering the dispersibility in the vehicle of the nonmagnetic particle powder according to the present invention, a binder resin containing —COOM, —SO ₃ M or an alkylbetaine type amphoteric group as a polar group is preferable.

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

  Examples of the solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone and tetrahydrofuran, aromatic hydrocarbons such as toluene and xylene, methanol, ethanol, propanol, butanol, isobutyl alcohol and the like, which are widely used in magnetic recording media. Alcohols such as isopropyl alcohol, esters such as methyl acetate, butyl acetate, isobutyl acetate and glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether and dioxane, and mixtures thereof can be used.

  The total amount of the solvent used is 65 to 1000 parts by weight with respect to 100 parts by weight of the nonmagnetic particle powder. 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.

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

  The magnetic recording medium according to 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 back coat layer from the viewpoint of preventing winding disturbance and improving running durability.

  As the non-magnetic 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 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.

  The nonmagnetic underlayer in the present invention is formed using the above-described nonmagnetic paint for a nonmagnetic underlayer according to the present invention.

  The coating thickness of the nonmagnetic underlayer formed on the nonmagnetic support after calendering is preferably from 0.1 to 5.0 μm, more preferably from 0.3 to 4.0 μm, even more preferably. Is 0.5 to 3.0 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 0.1 to 3.0 μm, more preferably 0.3 to 2. 5 μm, even more preferably 0.5 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.

  The nonmagnetic underlayer obtained from the nonmagnetic coating for a nonmagnetic underlayer using the nonmagnetic particle powder according to the present invention has a coating film glossiness of 180 to 300%, preferably 185 to 300%, more preferably The surface roughness Ra of the coating film is 190 to 300%, 0.5 to 7.5 nm, preferably 0.5 to 7.0 nm, more preferably 0.5 to 6.5 nm. The Young's modulus (relative value) is 126-160, preferably 128-160.

  The nonmagnetic underlayer obtained from the nonmagnetic coating material for a nonmagnetic underlayer using the nonmagnetic particle powder according to the present invention with an inorganic particle powder having a specific gravity of 4.5 or more has a glossiness of the coating film of 185 to 300%, Preferably it is 190-300%, More preferably, it is 195-300%, Comprising: Surface roughness Ra of a coating film is 0.5-7.0 nm, Preferably it is 0.5-6.5 nm, More preferably, it is 0.5 It is -6.0nm, Comprising: As for the intensity | strength of a coating film, Young's modulus (relative value) is 126-160, Preferably it is 128-160.

  For non-magnetic underlayer using non-magnetic particle powder according to the present invention coated with at least one compound selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide The nonmagnetic underlayer obtained from the nonmagnetic paint has a coating film gloss of 190 to 300%, preferably 195 to 300%, more preferably 200 to 300%, and the coating film has a surface roughness Ra. 0.5 to 6.5 nm, preferably 0.5 to 6.0 nm, more preferably 0.5 to 5.5 nm, and the strength of the coating film is Young's modulus (relative value) of 130 to 160, preferably Is 132-160.

  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 and coercive force reducing agents one or the like plate-shaped magnetoplumbite ferrite particles which contains two or more can be used.

  In consideration of recent short wavelength recording and high density recording, acicular metal magnetic particle powder mainly composed of iron, Co, Al, Ni, P, Zn, Si, B, rare earth metal other than iron, etc. Needle-like iron alloy magnetic particle powder, plate-like magnetoplumbite type ferrite particle powder, 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 0.03 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 5.0 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 2.0 or more. The upper limit is preferably 20.0, and 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 50 to 180 Am ² / kg (50 to 180 emu / g).

In consideration of high-density recording and the like, the magnetic characteristics when the acicular metal magnetic particle powder or acicular iron alloy magnetic particle powder mainly containing iron is used as the magnetic particle powder have a coercive force value of 63.7. To 278.5 kA / m (800 to 3500 Oe), preferably 71.6 to 278.5 kA / m (900 to 3500 Oe), and a saturation magnetization value of 90 to 200 Am ² / kg (90 to 200 emu / g), preferably 90 -180 Am < ² > / kg (100-180 emu / g).

  As the binder resin, the binder resin used for producing the nonmagnetic coating material for 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 2.00 μm, more preferably 0.02 to 1.50 μm, and still more preferably. 0.02 to 1.00 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 it exceeds 2.00 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.

  The back coat layer in the present invention preferably contains an antistatic agent and a filler material 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 coating material for the nonmagnetic underlayer can be used.

  As the filler material, 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 computer data recording backup tapes, 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 filler material. 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 blending ratio of the carbon black and the filler material and the binder resin is 40 to 250 parts by weight, preferably 50 to 200 parts by weight as the total amount of carbon black and the filler material with respect to 100 parts by weight of the binder resin. Part.

  The magnetic recording medium according to 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 is preferably 165 to 300%, more preferably 170 to 300%, still more preferably 175 to 300%, and the coating surface roughness Ra is preferably 11.5 nm or less, more preferably 2.0 to 11.0 nm, still more preferably 2.0-10.5 nm, Young's modulus is preferably 126-160, more preferably 128-160, and dropout (D / O) is preferably 18 / msec or less, more preferably Is 16 pieces / msec or less.

  In consideration of the increase in recording capacity, the present invention uses acicular metal magnetic particle powder, acicular iron alloy magnetic particle powder or plate-like magnetoplumbite type ferrite particle powder containing iron as a main component as magnetic particle powder. In the case of a 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 9.0 nm or less, more preferably 2.0 to 8%. 0.5 nm, still more preferably 2.0 to 8.0 nm, and Young's modulus is preferably 128 to 160, more preferably 130 to 160, and the dropout (D / O) is 16 / m. Preferably equal to or less than ec, more preferably less than or equal to 14 / msec.

  In the case of the magnetic recording medium according to the present invention using the non-magnetic particle powder obtained by using the inorganic particle powder having a specific gravity of 4.5 or more, the coercive force value is 63.7 to 318.3 kA / m (800 to 4000 Oe), more preferably 71.6 to 318.3 kA / m (900 to 4000 Oe), and the gloss of the coating film is preferably 190 to 300%, more preferably 195 to 300%, still more preferably 200 to 300%, surface roughness Ra of the coating film is preferably 8.5 nm or less, more preferably 2.0 to 8.0 nm, still more preferably 2.0 to 7.5 nm, and Young's modulus is preferably 130 to 160, More preferably, it is 132 to 160, and the dropout (D / O) is preferably 14 pieces / msec or less, more preferably 12 pieces / msec or less.

  Next, a method for producing the nonmagnetic particle powder according to the present invention will be described.

  The nonmagnetic particle powder for a nonmagnetic underlayer for a magnetic recording medium according to the present invention is wet-dispersed after adding inorganic particle powder having a Mohs hardness of 7.0 to 9.0 to hematite particle powder or hydrous iron oxide particle powder. Can be obtained.

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

  The addition amount of the inorganic particle powder having a Mohs hardness of 7.0 to 9.0 is 0.01 to 0.20 part by weight with respect to 100 parts by weight of the hematite particle powder or the hydrous iron oxide particle powder. When the added amount of the inorganic particle powder is out of the above range, the nonmagnetic particle powder targeted by the present invention cannot be obtained.

  After the wet dispersion treatment, it is filtered, washed with water, dried and pulverized. If necessary, a deaeration / consolidation process may be further performed.

  The non-magnetic particle powder according to the present invention is optionally added with inorganic particle powder having a Mohs hardness of 7.0 to 9.0, and after wet dispersion treatment, aluminum hydroxide, aluminum oxide, silicon hydroxide. You may coat | cover with the compound of 1 type, or 2 or more types chosen from the thing and the oxide of silicon.

  The coating with the compound is performed by adding an inorganic particle powder having a Mohs hardness of 7.0 to 9.0 to a hematite particle powder or a hydrous iron oxide particle powder, and a water suspension of a nonmagnetic particle powder obtained by wet dispersion. An aluminum hydroxide, a silicon compound, or both of these compounds are mixed and stirred, or if necessary, the pH value is adjusted after mixing and stirring, whereby the particle surface of the nonmagnetic particle powder is treated with an aluminum hydroxide. And coating with one or more compounds selected from aluminum oxide, silicon hydroxide and silicon oxide, followed by filtration, washing with water, drying and grinding. 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.

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

  Solvents used for forming the magnetic recording layer and the back coat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and tetrahydrofuran, which are widely used in magnetic recording media, and aromatic hydrocarbons such as toluene and xylene. 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 ethers such as glycol dimethyl ether, glycol monoethyl ether and dioxane And mixtures thereof.

  The total amount of the solvent used is 65 to 1000 parts by weight with respect to 100 parts by weight of the particle powder. 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 magnetic recording layer is applied on the nonmagnetic underlayer after coating and drying. 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 nonmagnetic particle powder obtained by adding an inorganic particle powder having a Mohs hardness of 7.0 to 9.0 to a hematite particle powder or a hydrous iron oxide particle powder and performing a wet dispersion treatment is as follows: The fact is that the particles are easily loosened with a slight dispersion force.

  The present inventor considers the reason why the nonmagnetic particle powder according to the present invention is easily loosened with a slight dispersion force as follows. By adding an inorganic particle powder having a Mohs hardness of 7.0 to 9.0 to the hematite particle powder or the hydrous iron oxide particle powder and subjecting it to a wet dispersion treatment, a strong secondary existing in the hematite particle powder or the hydrous iron oxide particle powder is obtained. It is considered that the aggregate is loosened to primary particles by impact grinding with inorganic particle powder having higher Mohs hardness than hematite particle powder or hydrous iron oxide particle powder. In addition, in the case where the specific gravity of the inorganic particle powder is larger than that of the hematite particle powder or the hydrous iron oxide particle powder, the impact force becomes higher, so that it can be more effectively loosened to primary particles with a small abundance. it can.

  In addition, when the surface is coated with one or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, there are few secondary aggregates and primary Since the particle powder surface loosened to the particles could be uniformly covered with one or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, It is believed that a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium excellent in dispersibility in a nonmagnetic paint can be obtained.

  The nonmagnetic coating material for the nonmagnetic underlayer containing the nonmagnetic particle powder is a fact that a coating material having excellent dispersibility can be obtained with a slight dispersion force.

Regarding the reason why a non-magnetic coating for a non-magnetic underlayer according to the present invention can provide a coating material having excellent dispersibility with a slight dispersion force, the present inventor has obtained, as the non-magnetic particle powder, the non-magnetic particles according to the present invention described above. Non-magnetic particles whose volume-based average particle diameter (D ₅₀ ) at _{3 bar} is almost the same as the volume-based average diameter (D ₅₀ ) _{5 bar} at a dispersion pressure of 5 _bar, and which are loosened to primary particles with a weaker dispersion force than before. This is thought to be due to the use of powder.

  In addition, the magnetic recording medium according to the present invention is excellent in productivity and can reduce dropout even when the nonmagnetic underlayer is thinned.

  The magnetic recording medium according to the present invention is obtained from a nonmagnetic coating material having excellent dispersibility as the reason why the surface smoothness is excellent and the dropout is reduced even when the nonmagnetic underlayer is thinned. This is considered to be due to the fact that the secondary agglomerated particle mass protruding on the surface could be reduced by using the coated film as the nonmagnetic underlayer even when the nonmagnetic underlayer was thinned.

  Hereinafter, the present invention will be described in detail with reference to examples.

  The average primary long axis diameter, average primary short axis diameter and average primary particle diameter of the particles are measured for the primary major axis diameter, primary minor axis diameter or primary particle diameter for about 350 particles shown in the electron micrograph, respectively. The average value is shown.

  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.

  Al amount, Si amount, and inorganic particle powder present in hematite particle powder and hydrous iron oxide particle powder, Ti amount, Zr amount, Al The amount, Ca amount, and the like were measured using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to JIS K0119 “General Rules for Fluorescent X-ray Analysis”. Further, the Co amount of the Co-coated magnetite particle powder and the Co-coated maghemite particle powder and 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.

Hematite particle powder, hydrous iron oxide particle powder, and non-magnetic particle powder of the present invention have a volume-based average diameter (D ₅₀ ) at a dispersion pressure of 5 bar. _{5 bar} passes the sample through a sieve of 60 mesh (opening 250 μm) in advance and passes through the sieve The sample thus obtained was dried at 80 ° C. for 3 hours in a dryer, and then a dispersion pressure of 0.5 MPa (with a dry dispersion unit of “laser diffraction particle size distribution measuring device model HELOS LA / KA” (manufactured by SYMPATEC) was used. 5 bar). Volume-based mean diameter in the dispersion pressure _{3bar (D 50)} 3bar was determined by the dispersed pressure to 0.3 MPa (3 bar) in a similar manner.

  The magnetic properties of the magnetic particle powder are as follows: an external magnetic field 795.8 kA / m (10 kOe) using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) (Co-coated magnetic oxidation) In the case of using iron particle powder, it is a value measured under 39.79 kA / m (5 kOe)), and various characteristics of the magnetic tape are external magnetic fields 795.8 kA / m (10 kOe) (however, Co-coated type) When magnetic iron oxide particle powder is used as magnetic particle powder, it is the result of measurement under 39.79 kA / m (5 kOe)).

The paint viscosity was determined by measuring the paint viscosity E ₀ at 25 ° C. of the obtained paint using an “E-type viscometer EMD-R” (manufactured by Tokyo Keiki Co., Ltd.), and at a shear rate D = 1.92 sec ⁻¹ . Indicated by value.

  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 of the coating film using "Surfcom-575A" (made 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). The Young's modulus was expressed as a relative value with a commercially available video tape “AV T-120” (manufactured by Victor Company of Japan). It shows that the intensity | strength of a coating film is so favorable that a relative value is high.

  The dropout (D / O) of the magnetic recording medium is a dropout per unit time from an envelope obtained by applying a magnetic tape to “Drum Tester BX-3168” (manufactured by Verdex) at a relative speed of 2.5 m / sec. It was obtained by counting the number of.

  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. Furthermore, 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, 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 non-magnetic particle powder>
Particle powder 1 (type: hematite particle powder, particle shape: needle shape, average primary major axis diameter: 0.142 μm, average primary minor axis diameter: 0.0209 μm, axial ratio: 6.8, BET specific surface area value: 49. In order to release aggregation, 12 kg of 8 m ² / g, volume-based average diameter (D ₅₀ ) at a dispersion pressure of 5 bar (D ₅₀ ), _{5 bar} : 3.71 μm, volume-based average diameter at a dispersion pressure of 3 bar (D ₅₀ ) _{3 bar} : 4.53 μm) Inorganic water 1 (type: tungsten carbide (product name WC-10, manufactured by Allied Material Co., Ltd.), particle shape: granular, Mohs hardness: 9.0, specific gravity: 15.4 an average primary particle size: 0.95 .mu.m, BET specific surface area: after the 1.2 m ² / g) was added 6 g, further, "TK pipeline homomixer" (product name, special Manufactured by Chemical Industry Co., Ltd.) through 60 minutes at a rotation speed of 3600 rpm, to obtain a slurry of hematite particles which exist tungsten carbide particles.

  Subsequently, the slurry of the hematite particle powder in which the tungsten carbide particle powder is present is 5 at a shaft rotation speed of 2000 rpm using a vertical sand grinder “Mighty Mill MHG-1.5L” (product name, manufactured by Inoue Seisakusho Co., Ltd.). A pass slurry was obtained to obtain a dispersed slurry of hematite particle powder containing tungsten carbide particle powder.

  The obtained dispersion slurry had a sieve residue of 0% at 325 mesh (aperture 44 μm). The dispersion slurry was filtered and washed with water to obtain a cake of hematite particle powder having tungsten carbide particle powder. After drying the cake of hematite particle powder containing tungsten carbide particle powder at 120 ° C., 11.0 kg of the dried powder was put into Edge Runner “MPUV-2 type” (product name, manufactured by Matsumoto Foundry Co., Ltd.). Then, the mixture was stirred at 392 N / cm (40 Kg / cm) for 20 minutes to loosen the agglomeration of the particles.

The obtained nonmagnetic particle powder had a needle shape, an average primary major axis diameter of 0.143 μm, an average primary minor axis diameter of 0.0211 μm, and an axial ratio of 6.8. The BET specific surface area value was 48.1 m ² / g, the volume standard average diameter (D ₅₀ ) at a dispersion pressure of 5 _{bar, 5 bar} was 1.99 μm, and the volume standard average diameter (D ₅₀ ) at _{3 bar} was _{3 bar} . The abundance of tungsten carbide in the nonmagnetic particle powder was 0.041% by weight in terms of W.

<Example 2-1: Production of nonmagnetic underlayer (configuration: nonmagnetic underlayer 1)>
12 g of the non-magnetic particle powder, a 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 to obtain a mixture (solid content rate: 72%). The mixture was further kneaded with a plastmill for 30 minutes 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 non-magnetic particle powder,
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,
44.6 parts by weight of cyclohexanone,
111.4 parts by weight of methyl ethyl ketone,
66.9 parts by weight of toluene,
Curing agent (polyisocyanate) 3.0 parts by weight,
Lubricant (butyl stearate) 1.0 part by weight.

  The resulting nonmagnetic paint had a paint viscosity of 230 mPa · s.

  Example 2-1 was formed by applying the nonmagnetic coating material for a nonmagnetic underlayer on a polyethylene terephthalate film having a thickness of 6.3 μm and then drying it. 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.

  In Example 2-1 obtained, the film thickness was 2.5 μm, the glossiness of the coating film was 217%, the surface roughness Ra was 5.1 nm, and the Young's modulus (relative value) was 133.

<Example 2-7: Production of nonmagnetic underlayer (configuration: nonmagnetic underlayer 2)>
Example 2-6 was formed by applying a nonmagnetic coating for a nonmagnetic underlayer prepared in the same manner as described above onto an aromatic polyamide film having a thickness of 4.5 μm and then drying. 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.

  In Example 2-7 obtained, the film thickness was 1.7 μm, the glossiness was 210%, the surface roughness Ra was 5.6 nm, and the Young's modulus (relative value) was 131.

<Example 3-1: Production of magnetic recording medium (configuration: magnetic recording medium layer 1)>
Magnetic particles (1) (type: acicular metal magnetic particle powder containing iron as a main component, average major axis diameter: 0.063 μm, average 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-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2 g Carbon black (trade name: # 3250B, manufactured by Mitsubishi Kasei Co., Ltd.) 0.12 g, binder resin solution (30% by weight of vinyl chloride copolymer resin having potassium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone The mixture (solid content ratio 78%) was obtained by mixing, and this mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

  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-30) 10.0 parts by weight,
1.0 part by weight of carbon black (# 3250B)
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.

  After coating the magnetic recording layer coating on Example 2-1, the film was oriented and dried in a magnetic field, and then calendered, followed by a curing reaction at 60 ° C. for 24 hours to a width of 12.7 mm. The magnetic recording medium 1 (Example 3-1) was obtained by slitting.

  The obtained magnetic recording medium (Example 3-1) had a magnetic recording layer thickness of 0.2 μm, a coercive force value of 192.1 kA / m (2414 Oe), a glossiness of 215%, and a surface roughness Ra. The Young's modulus (relative value) was 5.4 nm, the D / O was 9 / msec.

<Example 3-7: Production of magnetic recording medium (configuration: magnetic recording medium layer 2)>
A magnetic coating material for magnetic recording layer prepared in the same manner as described above was applied on Example 2-7 and then oriented and dried in a magnetic field.

  Carbon black (average primary particle size 25 nm) 12.0 g, carbon black (average primary particle size 370 nm) 1.8 g, iron oxide 1.8 g, binder resin solution (nitrocellulose 30 wt% and cyclohexanone 70 wt%) and cyclohexanone Were mixed to obtain a mixture (solid content ratio 78%), and this mixture was further kneaded with a plast mill for 30 minutes to obtain a kneaded product.

  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 (primary particle size 25 nm) 100.0 parts by weight,
Carbon black (primary particle size 370 nm) 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 slitting to a width of 0.5 inch gave the magnetic recording layer 2 (Example 3-7).

  The obtained magnetic recording medium (Example 3-7) has a magnetic recording layer thickness of 0.2 μm, a coercive force value of 192.2 kA / m (2415 Oe), a glossiness of 211%, and a surface roughness Ra. It was 5.7 nm, Young's modulus (relative value) was 133, and D / O was 10 / msec.

  In accordance with Examples 1-1, 2-1, 2-7, 3-1, and 3-7, nonmagnetic particle powder, nonmagnetic underlayer and magnetic recording medium were prepared. Various manufacturing conditions and various characteristics of the obtained nonmagnetic particle powder, nonmagnetic underlayer and magnetic recording medium are shown.

Particle powder 1-5:
Various hematite particle powders and goethite particle powders were prepared, and hematite particle powders and goethite particle powders that were deagglomerated in the same manner as in Example 1-1 were obtained.

  Table 1 shows various characteristics of the hematite particle powder and the goethite particle powder.

Inorganic particle powders 1-7:
An inorganic particle powder having the characteristics shown in Table 2 was prepared as the inorganic particle powder.

Examples 1-2 to 1-6, Comparative Examples 1 and 2:
A nonmagnetic particle powder was obtained in the same manner as in Example 1-1 except that the type of particle powder, the type of inorganic particle powder added in the wet dispersion treatment step, and the amount added were variously changed.
In addition, the comparative example 1 does not add inorganic particle powder to the particle powder 1, but performs the wet dispersion process process.

Example 1-7:
Using 12 kg of acicular hematite particle powder of particle powder 1 and 120 l of water, a slurry containing acicular hematite particle powder and tungsten carbide particle powder was obtained in the same manner as in Example 1-1. The pH value of the re-dispersed slurry of the non-magnetic particle powder containing the tungsten carbide particle powder thus obtained was set to 10.5.

Next, water was added to the slurry to adjust the slurry concentration to 98 g / l. 120 l of this slurry was heated to 60 ° C., 5737 ml of a 1.0 mol / l NaAlO ₂ solution (corresponding to 1.3% by weight in terms of Al with respect to acicular hematite particle powder) was added to this slurry, and 30 After holding for a minute, the pH value was adjusted to 7.5 with acetic acid. After holding in this state for 30 minutes, nonmagnetic particle powder of Example 1-7 in which the particle surface was coated with aluminum hydroxide was obtained by filtration, washing with water, drying and grinding.

Examples 1-8 to 1-11:
Nonmagnetic particles in the same manner as in Example 1-7, except that the type of the particle powder, the type and addition amount of the inorganic particle powder in the wet dispersion treatment step, and the type and addition amount of the coating in the surface treatment step were variously changed. A powder was obtained.

  The production conditions at this time are shown in Table 3, and various characteristics of the obtained nonmagnetic particle powder are shown in Table 4.

<Manufacture of nonmagnetic underlayer>
Examples 2-2 to 2-6, 2-8 to 2-13, Comparative Examples 3 to 8:
A nonmagnetic paint was obtained in the same manner as in Example 2-1 or 2-7, except that the type of nonmagnetic particle powder was variously changed. For Comparative Examples 5 and 8, 0.05 parts by weight of the inorganic particle powder 2 was added to 100 parts by weight of the nonmagnetic particle powder at the stage of preparing the nonmagnetic paint, and the above Examples 2-1 or 2-7. In the same manner as above, a nonmagnetic underlayer was obtained.

  Table 5 shows the manufacturing conditions and the characteristics of the obtained nonmagnetic paint and nonmagnetic underlayer.

<Manufacture of magnetic recording media>
Examples 3-2 to 3-6, Examples 3-8 to 3-13 and Comparative Examples 15 to 20:
A magnetic recording medium was manufactured in the same manner as in Example 3-1 or 3-7, except that the type of nonmagnetic underlayer and the type of magnetic particle powder were variously changed.

  Table 6 shows the characteristics of the magnetic particles 1 to 4 used.

  Table 7 shows the manufacturing conditions at this time and various characteristics of the obtained magnetic recording medium.

Since the non-magnetic particle powder according to the present invention has a small volume-based average particle diameter (D ₅₀ ) of ₃ bar at a dispersion pressure of 3 bar and particles are easily loosened with a slight dispersion force, it has excellent dispersibility in non-magnetic paints. It is suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium.

  The nonmagnetic coating material according to the present invention is suitable as a nonmagnetic coating material for a nonmagnetic underlayer of a magnetic recording medium because a nonmagnetic underlayer having excellent dispersibility and high surface smoothness and strength can be obtained. .

The magnetic recording medium according to the present invention is excellent in productivity by using a coating film obtained from a non-magnetic paint having excellent dispersibility as a non-magnetic under layer, and when the non-magnetic under layer is thinned. Since the dropout can be reduced, it is suitable as a high-density magnetic recording medium.

Claims (10)

A nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium, wherein an inorganic particle powder having a Mohs hardness of 7.0 to 9.0 is present together with a hematite particle powder or a hydrous iron oxide particle powder. 2. The nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium according to claim 1, wherein the specific gravity of the inorganic particle powder is 4.5 or more. The nonmagnetic property of the magnetic recording medium according to claim 1 or 2, wherein the abundance of the inorganic particle powder is 0.01 to 0.2% by weight with respect to the hematite particle powder or the hydrous iron oxide particle powder. Nonmagnetic particle powder for underlayer. The nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium according to any one of claims 1 to 3, wherein the inorganic particle powder is tungsten carbide. The surface of one or more of the hematite particle powder or the hydrous iron oxide particle powder and the inorganic particle powder is at least one selected from aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide. The nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium according to any one of claims 1 to 4, wherein the nonmagnetic particle powder is coated with a compound. 5. The nonmagnetic underlayer for a magnetic recording medium according to any one of claims 1 to 4, wherein the inorganic particles are added to the hematite particles or the hydrated iron oxide particles and then wet dispersion is performed. Method for producing non-magnetic particle powder. After adding the inorganic particle powder to the hematite particle powder or the hydrous iron oxide particle powder and performing a wet dispersion treatment, the surface of any one or more of the hematite particle powder or the hydrous iron oxide particle powder and the inorganic particle powder is made of aluminum. 6. The nonmagnetic underlayer for a magnetic recording medium according to claim 5, wherein the magnetic recording medium is coated with a compound consisting of at least one selected from the group consisting of hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide. Method for producing non-magnetic particle powder. A nonmagnetic particle powder, a nonmagnetic coating material containing a binder resin and a solvent, wherein the nonmagnetic particle powder is the nonmagnetic particle powder for a nonmagnetic underlayer according to any one of claims 1 to 5. Non-magnetic paint. 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 the nonmagnetic particle powder for a nonmagnetic underlayer according to any one of claims 1 to 5. Nonmagnetic support, nonmagnetic underlayer containing nonmagnetic particle powder and binder resin formed on the nonmagnetic support, and magnetic particle powder and binder resin formed on the nonmagnetic underlayer 6. The magnetic recording medium comprising a magnetic recording layer and a backcoat layer formed on the other surface of the nonmagnetic support, wherein the nonmagnetic particle powder is nonmagnetic under the magnetic recording medium according to any one of claims 1 to 5. A magnetic recording medium characterized by being a non-magnetic particle powder for formation.