JP5492039B2 - Magnetic recording medium - Google Patents

Description

  The present invention relates to a high-capacity magnetic recording medium, and more particularly to a magnetic recording medium excellent in recording / reproducing characteristics.

  Magnetic tape, which is a kind of magnetic recording medium, has various uses such as audio tape, video tape, and computer tape. In particular, in the field of data backup tapes for computers, a recording capacity of several hundred GB per volume has been commercialized as the capacity of a hard disk to be backed up increases. In the future, it will be essential to increase the capacity of backup tapes in order to cope with further increases in the capacity of hard disks.

  For magnetic tapes used as backup tapes, the recording wavelength is shortened and the reproduction track pitch is miniaturized as the recording capacity further increases, and noise reduction during recording and reproduction is an important issue. .

  In recent high capacity magnetic recording media, in order to improve short wavelength recording characteristics, a nonmagnetic layer is provided on a nonmagnetic support, and a thin magnetic layer is provided thereon to reduce the thickness loss during recording and reproduction. Reduced.

In order to reduce noise, in addition to making the magnetic powder finer, further smoothing of the magnetic layer surface and further smoothing of the interface between the magnetic layer and the nonmagnetic layer are required.
For example, there are techniques disclosed in Patent Documents 1 and 2 for such problems.

JP-A-11-213379 Japanese Patent No. 2566070

  In Patent Document 1, a nonmagnetic coating material is applied on a nonmagnetic support and dried to form a nonmagnetic layer. After smoothing with a calendar, the radiation is irradiated to cure the nonmagnetic layer. A magnetic coating is applied on the nonmagnetic layer and dried to form a magnetic layer.

However, in this method, although the interface between the nonmagnetic layer and the magnetic layer becomes smooth, there is a problem that productivity is lowered because the magnetic layer is applied after the nonmagnetic layer is applied and dried.
Patent Document 2 uses a nonmagnetic paint in which the ratio of shear stress at a shear rate of 10 ⁴ (1 / s) and 10 (1 / s) is in a specific range, thereby bringing the thixotropy of the magnetic paint closer to it, A magnetic recording medium having a smooth interface between a nonmagnetic layer and a magnetic layer is disclosed. However, the magnetic recording medium disclosed here has a magnetic layer thickness of 0.2 μm or more, and it cannot be said that the short wavelength recording characteristics are sufficient, and the interface between the nonmagnetic layer and the magnetic layer is also sufficient. I couldn't say it would be smooth.

  An object of the present invention is to provide a magnetic recording medium having a thin magnetic layer and having excellent short wavelength recording and reproducing characteristics.

As a result of intensive studies on the configuration of the magnetic recording medium, the present inventors have found that the above-described object can be achieved if the magnetic recording medium is configured as follows.
That is, a nonmagnetic layer containing one kind of nonmagnetic powder, carbon black and a binder on a nonmagnetic support, and a magnetic layer having a thickness of less than 0.1 μm containing magnetic powder and a binder on the nonmagnetic layer 1 ≦ R ≦ 2.5, where R is the ratio of the average particle size of the nonmagnetic powder contained in the nonmagnetic layer to the average particle size of the carbon black. And the shape ratio of the non-magnetic powder is 1-2.

Also, a nonmagnetic layer containing a plurality of types of nonmagnetic powder, carbon black and a binder on a nonmagnetic support, and a magnetic layer having a thickness of less than 0.1 μm containing magnetic powder and a binder on the nonmagnetic layer Wherein the ratio of the average particle diameter of the nonmagnetic powder having the largest average particle diameter to the average particle diameter of the carbon black is R. The shape ratio of the nonmagnetic powder satisfying 1 ≦ R ≦ 2.5 and having the maximum average particle diameter is 1-2.

  According to the present invention, when the ratio of the average particle diameter of the nonmagnetic powder to the average particle diameter of carbon black is R, 1 ≦ R ≦ 2.5 is satisfied, and the shape ratio of the nonmagnetic powder is 1-2. Since the magnetic layer is formed using a paint that is controlled so as to be, a magnetic recording medium having excellent coating suitability and dispersion stability and excellent short-wavelength recording / reproducing characteristics can be provided.

  In order to improve the S / N in the short wavelength region, the magnetic powder is being made finer. For this reason, acicular magnetic powders (metal magnetic powders, etc.) are bundled, and plate-like magnetic powders (hexagonal barium ferrite magnetic powders, etc.) are sufficiently agglomerated in the form of secondary agglomerates to form a magnetic coating. Need to manufacture. Since the viscosity and thixotropy of the paint change depending on the dispersion state of the magnetic paint, it is preferable to appropriately control it. In general, in the fine magnetic powder that easily aggregates in a stack, the thixotropic property of the coating tends to be lowered.

  As described above, recent high-capacity magnetic recording media have a configuration in which a nonmagnetic layer is provided on a nonmagnetic support, and a thin magnetic layer is provided thereon. In order to improve productivity and reduce costs, most magnetic recording media form a nonmagnetic layer by applying a nonmagnetic layer-forming coating (hereinafter also referred to as a nonmagnetic coating) on a nonmagnetic support. When the nonmagnetic layer is in a wet state, it is manufactured by a wet-on-wet method in which a magnetic layer is further applied to form a magnetic layer by applying a coating for forming a magnetic layer (hereinafter also referred to as a magnetic coating). In this manufacturing method, it is important to form each layer without disturbing the interface between the nonmagnetic layer and the magnetic layer. When the interface is disturbed, the recording / reproducing characteristics (S / N, etc.) of the magnetic recording medium may be reduced.

  For this reason, it is preferable to appropriately control the rheological properties of the magnetic paint and the non-magnetic paint.

  As a result of intensive studies on the particle size and shape of the nonmagnetic powder to be included in the nonmagnetic layer and the particle size of carbon black, the inventors of the present invention have the following configurations to make the nonmagnetic layer and the magnetic layer The inventors have found that a magnetic recording medium which is well formed and excellent in recording / reproducing characteristics can be obtained, and has reached the present invention.

  That is, in the nonmagnetic powder and carbon black contained in the nonmagnetic layer, the ratio of the average particle diameter of the nonmagnetic powder to the average particle diameter of the carbon black, that is, R = (average particle diameter of the nonmagnetic powder). / (Average particle diameter of carbon black), preferably 1 ≦ R ≦ 2.5, more preferably 1 ≦ R ≦ 2. It is preferable that R is within this range. If R is less than 1, the nonmagnetic powder is too small and the thixotropic property of the nonmagnetic coating becomes too large, or the voids in the nonmagnetic layer are reduced. The effect of the smoothing treatment due to the calender is reduced, and the supply of lubricant from the nonmagnetic layer to the magnetic layer becomes insufficient. When R exceeds 2.5, the nonmagnetic powder is too large and the magnetic layer This is because the interface with the layer tends to be disturbed.

When a plurality of types of nonmagnetic powder are contained in the nonmagnetic layer, the average particle diameter of the nonmagnetic powder having the maximum average particle diameter can be applied to the above relational expression.
The shape ratio of the nonmagnetic powder applied to the above relational expression is preferably 1 to 2. The shape ratio here means the axial ratio or plate ratio when the nonmagnetic powder has a shape anisotropy such as a needle shape, an ellipse shape, or a plate shape. The ratio of the maximum diameter to the minimum diameter. The reason why the shape ratio is in this range is that if the shape ratio exceeds 2, the thixotropic property becomes too large and the interface may be easily disturbed.

As such non-magnetic powder, inorganic compound powders such as metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, metal sulfide, etc. are used. -Alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, tungsten oxide, zirconium oxide, nitride Boron, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. An organic powder can be added to the nonmagnetic layer according to the purpose. Examples include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluorinated ethylene resin are also included. Can be used. The average particle diameter of the nonmagnetic powder is preferably 10 to 250 nm, and the ratio of the average particle diameter of carbon black preferably satisfies the above relational expression.

The particle shape of the nonmagnetic powder contained in the nonmagnetic layer may be any of a granular shape, a spherical shape, a plate shape, a needle shape, and a spindle shape, but the shape ratio is 1 to 2 as described above. preferable. Moreover, it is preferable that the particle diameter of nonmagnetic powder is the range which said R fills. Furthermore, in order to form a smooth non-magnetic layer with little thickness unevenness, a non-magnetic powder having a sharp particle size distribution is preferably used. In this specification, the average particle size and shape ratio of the powder mean the number average value of the particle size and shape ratio of 300 powders in a photograph (100,000 times) taken with a transmission electron microscope (TEM). To do.

In order to control the rheological properties of the conductive and nonmagnetic paint, a conventionally known carbon black is included in the nonmagnetic layer. Examples of such carbon black include acetylene black, furnace black, and thermal black. The average particle size of carbon black is preferably 0.01 to 0.1 μm. When the average particle diameter is 0.01 μm or more, a magnetic layer in which carbon black is well dispersed can be formed. On the other hand, when the average particle diameter is 0.1 μm or less, a nonmagnetic layer having excellent conductivity can be formed.

As the binder for the nonmagnetic layer, conventionally known thermoplastic resins, thermosetting resins and the like can be used. Specific examples of the thermoplastic resin include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride- Examples thereof include vinyl acetate-maleic anhydride copolymer resin and vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin. Specific examples of the thermosetting resin include phenolic resins, epoxy resins, polyurethane resins, urea resins, melamine resins, alkyd resins, and the like. These binders preferably have a functional group in order to improve the dispersibility of the nonmagnetic powder and to increase the filling property. Specific examples of such functional groups include COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₃ , and O—P═O (OM) ₂ (M is a hydrogen atom, alkali metal) Salt or amine salt), OH, NR ₁ R ₂ , NR ₃ R ₄ R ₅ (R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are hydrogen or a hydrocarbon group, usually having 1 carbon atom) 10), epoxy groups and the like. When two or more kinds of resins are used in combination, it is preferable to use resins having the same functional group polarity, and among them, a combination of resins having an SO ₃ M group is preferable. The content of these binders is preferably 7 to 50 parts by mass and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the nonmagnetic powder. In particular, the combined use of 5 to 30 parts by mass of vinyl chloride resin and 2 to 20 parts by mass of polyurethane resin is preferable.

Further, a radiation curable resin may be used as a binder instead of or together with the above thermosetting resin. Examples of radiation curable resins include (meth) acrylic monomers and (meth) acrylic oligomers. Among these, a radiation curable resin having two or more double bonds in the molecule and a weight average molecular weight of 50 to 300 per double bond is preferable. Specific examples of such radiation curable resins include 1,3-butanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, and 1,6-hexanediol di (meth) acrylate. ) Acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) Acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, ethoxylated bisphenol A di (meth) acrylate, novolak di (meth) acrylate, propoxylated neopenty Bifunctional (meth) acrylates such as glycol di (meth) acrylate; tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, penta Trifunctional (meth) acrylates such as erythritol tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, propoxylated glyceryl tri (meth) acrylate, caprolactone-modified trimethylolpropane tri (meth) acrylate; pentaerythritol tetra ( (Meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, dipentae Tetrafunctional or higher functional (meth) acrylates such as sitolitol hydroxypenta (meth) acrylate and dipentaerythritol hexa (meth) acrylate; oligomers obtained by extending the above chain with a skeleton such as polyether, polyester, polycarbonate, polyurethane, etc. Is mentioned. The content of the radiation curable resin in the nonmagnetic layer is preferably 5 to 30% by mass with respect to the total amount of the other binder and the radiation curable resin.

Furthermore, it is preferable to use together with the above-mentioned binder, a thermosetting crosslinking agent that binds to a functional group contained in the binder and forms a crosslinked structure. Specific examples of the crosslinking agent include isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; reaction products of isocyanate compounds and compounds having a plurality of hydroxyl groups such as trimethylolpropane; Examples include various polyisocyanates such as condensation products. The content of the crosslinking agent is preferably 10 to 50 parts by mass with respect to 100 parts by mass of the binder.

Examples of the lubricant used for the nonmagnetic layer include conventionally known fatty acids having 10 to 30 carbon atoms. The fatty acid may be any of linear, branched, and cis / trans isomers, but is preferably a linear type having excellent lubricating performance. Specific examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. These may be used alone or in combination. The fatty acid content in the nonmagnetic layer is preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the nonmagnetic powder. If the fatty acid content is 0.2 parts by mass or more, the fatty acid can be sufficiently leached from the nonmagnetic layer to the magnetic layer, and the long durability under a low humidity environment can be further improved. If content of a fatty acid is 5 mass parts or less, the toughness of a nonmagnetic layer is securable.

The nonmagnetic layer may contain a conventionally known fatty acid ester or fatty acid amide together with the fatty acid as a lubricant. Specific examples of fatty acid esters include n-butyl oleate, hexyl oleate, n-octyl oleate, 2-ethylhexyl oleate, oleyl oleate, n-butyl laurate, heptyl laurate, and myristic acid. Examples include n-butyl, n-butoxyethyl oleate, trimethylolpropane trioleate, n-butyl stearate, s-butyl stearate, isoamyl stearate, and butyl cellosolve stearate. Specific examples of the fatty acid amide include palmitic acid amide and stearic acid amide. These may be used alone or in combination. The total content of fatty acid ester and fatty acid amide in the nonmagnetic layer is preferably 0.2 to 10 parts by mass with respect to 100 parts by mass of the nonmagnetic powder. If these contents are 0.2 parts by mass or more, the lubricant can be sufficiently leached from the nonmagnetic layer to the magnetic layer, and the friction coefficient can be further reduced. When the lubricant content is 15 parts by mass or less, the toughness of the nonmagnetic layer can be ensured. In particular, it is preferable to contain 0.5 to 4 parts by mass of fatty acid and 0.2 to 3 parts by mass of fatty acid ester with respect to 100 parts by mass of nonmagnetic powder.
As long as the nonmagnetic layer contains the nonmagnetic powder, organic acid, binder, and lubricant, the nonmagnetic layer may further contain an additive such as a conventionally known dispersant. Specific examples of such dispersants include, for example, metal soaps composed of alkali metals or alkaline earth metals of the above fatty acids: fluorinated products of the above fatty acid esters; polyalkylene oxide alkyl phosphate esters; lecithins; trialkyl polyolefins. Examples thereof include oxyquaternary ammonium salts (alkyl has 1 to 5 carbon atoms, and olefins include ethylene and propylene); copper phthalocyanine and the like. These may be used alone or in combination. The content of the dispersant is preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the nonmagnetic powder.

  The thickness of the nonmagnetic layer is preferably 0.1 to 3 μm, more preferably 0.1 to 1.2 μm. If the thickness of the nonmagnetic layer is 0.1 μm or more, a sufficient amount of lubricant for ensuring durability can be contained in the nonmagnetic layer. On the other hand, if the thickness of the nonmagnetic layer is 3 μm or less, the total thickness of the magnetic recording medium can be avoided from being unnecessarily increased, and the recording capacity per volume can be improved.

  Specific examples of the magnetic powder used in the magnetic layer include hexagonal ferrite magnetic powder, ferromagnetic metal iron-based magnetic powder, and iron nitride-based magnetic powder. The average particle size of the magnetic powder is preferably 10 to 35 nm, more preferably 15 to 25 nm. If the average particle diameter is 10 nm or more, a magnetic coating material excellent in dispersibility can be prepared. On the other hand, if the average particle diameter is 35 nm or less, particle noise can be reduced. The average particle diameter of the magnetic powder is an average major axis diameter in the case of needles, the largest plate diameter in the case of a plate, and a spherical shape with a ratio of major axis length to minor axis length of 1 to 3.5 In the case of an ellipsoidal shape, it means the maximum passing diameter.

  A conventionally known binder can be used as the binder for the magnetic layer. Among these, considering the dispersibility of the magnetic powder and the rigidity of the magnetic layer, the same binder as that used for the nonmagnetic layer is preferable. The content of the binder in the magnetic layer is preferably 7 to 50 parts by mass and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the magnetic powder. In particular, when the vinyl chloride resin and the polyurethane resin are used in combination, it is preferable to use 5 to 30 parts by mass of the vinyl chloride resin and 2 to 20 parts by mass of the polyurethane resin. Further, like the nonmagnetic layer, it is preferable to use a crosslinking agent such as polyisocyanate in order to crosslink the binder and improve the strength of the magnetic layer. The content of the crosslinking agent is preferably 10 to 50 parts by mass with respect to 100 parts by mass of the binder.

  As long as the magnetic layer contains magnetic powder and a binder, it may further contain known additives such as abrasives, lubricants, and dispersants. In particular, abrasives and lubricants are preferably used from the viewpoint of durability. Specific examples of the abrasive include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, and oxide. Examples include titanium, silicon dioxide, and boron nitride. These may be used alone or in combination. Among these, an abrasive having a Mohs hardness of 6 or more is more preferable. The average particle size of the abrasive is preferably 10 to 200 nm, although it depends on the type of abrasive used. The content of the abrasive is preferably 5 to 20 parts by mass and more preferably 8 to 18 parts by mass with respect to 100 parts by mass of the magnetic powder. As the lubricant, the same lubricant as that used in the nonmagnetic layer can be used. Among these, the combined use of a fatty acid ester and a fatty acid amide is preferable. In particular, when a lubricant is contained in the magnetic layer, the fatty acid ester is 0.2 to 3 parts by mass and the fatty acid amide is 0.1% with respect to 100 parts by mass of the total amount of the magnetic powder and abrasive in the magnetic layer. It is preferable to use 5 to 5 parts by mass.

  Further, the magnetic layer may contain conventionally known carbon black for the purpose of improving conductivity and surface lubricity, if necessary. Specific examples of such carbon black include acetylene black, furnace black, and thermal black. The average particle size of carbon black is preferably 0.01 to 0.1 μm. When the average particle diameter is 0.01 μm or more, a magnetic layer in which carbon black is well dispersed can be formed. On the other hand, when the average particle size is 0.1 μm or less, a magnetic layer having excellent surface smoothness can be formed. If necessary, two or more carbon blacks having different average particle diameters may be used. The content of carbon black is preferably 0.2 to 5 parts by mass and more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the magnetic powder.

  The thickness of the magnetic layer is less than 0.1 μm for the purpose of improving short wavelength recording characteristics, preferably 10 to 90 nm, more preferably 20 to 90 nm, and still more preferably 30 to 90 nm. With the thickness of the magnetic layer, it is possible to reduce the thickness loss at the time of recording / reproducing due to the self-demagnetizing action even in short wavelength recording. For this reason, high output can be obtained even in a system having a shortest recording wavelength of 0.5 μm or less. In particular, since such a thin magnetic layer cannot contain a large amount of lubricant, the magnetic recording medium of the present embodiment is suitable.

  The product of the residual magnetic flux density in the longitudinal direction of the magnetic layer and the thickness of the magnetic layer is preferably 0.0018 to 0.05 μTm, more preferably 0.0036 to 0.05 μTm, and still more preferably 0.004. ~ 0.05 μTm. If the product is too small, the reproduction output tends to be small when an MR head is used as the reproduction head. On the other hand, if the product is too large, the MR head is saturated and the reproduction output is easily distorted.

  The surface roughness of the magnetic layer is a center line average roughness (Ra), and is preferably 2.0 nm or less. The higher the surface smoothness of the magnetic layer, the higher the output can be obtained. However, if the surface of the magnetic layer is too smooth, the friction coefficient increases and the running stability decreases. For this reason, the surface roughness of the magnetic layer is a center line average roughness (Ra), preferably 1.0 nm or more.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. In the following, “part” means “part by mass”.

<Example 1>
[Preparation of non-magnetic paint]
The nonmagnetic coating component (1) shown in Table 1 was kneaded with a batch kneader to prepare a kneaded product. The obtained kneaded material and the nonmagnetic paint component (2) shown in Table 2 were stirred using a dispaper to prepare a mixed solution. The obtained mixed liquid was dispersed with a sand mill (retention time: 60 minutes) to prepare a dispersion, and the dispersion and the nonmagnetic coating component (3) shown in Table 3 were stirred using a dispaper. Was filtered with a filter to prepare a non-magnetic paint.

[Preparation of magnetic paint]
The magnetic paint component (1) shown in Table 4 was mixed at high speed with a high-speed stirring mixer, and the resulting mixture was kneaded with a continuous biaxial kneader. Next, a magnetic paint component (2) shown in Table 5 was added in two stages to a continuous biaxial kneader to dilute the kneaded material, thereby preparing a slurry. After this slurry was dispersed in a sand mill (residence time: 45 minutes), the obtained dispersion and the magnetic coating component (3) shown in Table 6 were stirred using a disperser, and this was filtered through a filter. A magnetic paint was prepared.

[Preparation of paint for back coat layer]
The mixed liquid in which the coating components for the backcoat layer shown in Table 7 below were mixed was dispersed (sand retention time: 45 minutes) with a sand mill. 15 parts of polyisocyanate was added to the obtained dispersion, stirred, and filtered through a filter to prepare a coating material for a backcoat layer.

[Production of magnetic tape for evaluation]
On the non-magnetic support (polyethylene naphthalate film, thickness: 6.1 μm), the above-mentioned non-magnetic paint and magnetic paint were dried and calendared so that the thicknesses after being 1.5 μm and 90 nm, respectively. A non-magnetic layer and a magnetic layer were formed by simultaneous multilayer coating with an extrusion type coater. At this time, in-plane orientation treatment was performed while applying an orientation magnetic field (400 kA / m) using a solenoid magnet.

Next, the above-mentioned coating material for the backcoat layer is applied to the surface opposite to the surface on which the magnetic layer of the nonmagnetic support is formed so that the thickness after drying and calendering is 0.5 μm and dried. Thus, a back coat layer was formed. A raw roll having a nonmagnetic layer and a magnetic layer formed on one side of the nonmagnetic support and a back coat layer formed on the other side was calendered with a calender apparatus having seven metal rolls (temperature: 100). ° C, linear pressure: 196 kN / m).
The obtained raw fabric roll was cured at 70 ° C. for 72 hours to produce a magnetic sheet. This magnetic sheet was cut to a width of 1/2 inch, and a servo signal compliant with the LTO standard was written to produce a magnetic tape for evaluation.

<Example 2>
A magnetic tape for evaluation was produced in the same manner as in Example 1 except that the average particle diameter of barium sulfate in the nonmagnetic paint component (1) was changed to 40 nm.

<Example 3>
Except that the average particle size of barium sulfate in the nonmagnetic paint component (1) was changed to 50 nm and the average particle size of carbon black in the nonmagnetic paint component (1) was changed to 25 nm, the same as in Example 1. Thus, a magnetic tape for evaluation was produced.

<Example 4>
Except for changing barium sulfate in non-magnetic paint component (1) to granular iron oxide (average particle size: 100 nm) and changing the average particle size of carbon black in non-magnetic paint component (1) to 75 nm. A magnetic tape for evaluation was produced in the same manner as in Example 1.

<Comparative Example 1>
A magnetic tape for evaluation was produced in the same manner as in Example 1 except that the average particle diameter of barium sulfate in the nonmagnetic paint component (1) was changed to 50 nm.

<Comparative example 2>
A magnetic tape for evaluation was produced in the same manner as in Example 4 except that the granular iron oxide in the nonmagnetic coating component (1) was changed to granular alumina (average particle diameter: 200 nm).

<Comparative Example 3>
A magnetic tape for evaluation was produced in the same manner as in Example 4 except that the granular iron oxide in the nonmagnetic coating component (1) was changed to barium sulfate (average particle diameter: 60 nm).

<Comparative Example 4>
A magnetic tape for evaluation was prepared in the same manner as in Example 4 except that the granular iron oxide in the nonmagnetic coating component (1) was changed to acicular iron oxide (average particle size: 110 nm, acicular ratio: 6.1). Produced.

<Examples 5 to 8>
Magnetic powder of magnetic coating component (1) is barium ferrite magnetic powder (Ba-Fe) (σs: 50 A · m 2 / kg (50 emu / g), Hc: 159 kA / m (2000 Oe), average particle diameter (plate diameter) : An evaluation magnetic tape was prepared in the same manner as in Examples 1 to 4 except that the change was made to 20 nm.

<Comparative Examples 5-8>
Magnetic powder of magnetic coating component (1) is barium ferrite magnetic powder (Ba-Fe) (σs: 50 A · m 2 / kg (50 emu / g), Hc: 159 kA / m (2000 Oe), average particle diameter (plate diameter) : A magnetic tape for evaluation was produced in the same manner as in Comparative Examples 1 to 4 except that the thickness was changed to 20 nm.

<Examples 9 to 12>
Magnetic powder of magnetic coating component (1) is converted into iron nitride magnetic powder (YN-Fe) (Y / Fe: 5.5 at%, N / Fe: 11.9 at%, σs: 103 A · m 2 / kg (103 emu) / G), Hc: 211.0 kA / m (2650 Oe), average particle diameter: 16 nm, axial ratio: 1.1), except that the magnetic tape for evaluation was prepared in the same manner as in Examples 1 to 4, respectively. Produced.

<Comparative Examples 9-12>
Magnetic powder of magnetic coating component (1) is converted into iron nitride magnetic powder (YN-Fe) (Y / Fe: 5.5 at%, N / Fe: 11.9 at%, σs: 103 A · m 2 / kg (103 emu) / G), Hc: 211.0 kA / m (2650 Oe), average particle diameter: 16 nm, axial ratio: 1.1), except that the magnetic tape for evaluation was prepared in the same manner as in Comparative Examples 1 to 4, respectively. Produced.

  The following evaluation was performed using the obtained magnetic tape, and the results are shown in Tables 8-10.

<S / N measurement>
Using a Hitachi Maxell linear tape electrical measuring device, an HP LTO3 drive head was attached to the tape, and a tape speed of 1.5 m / sec was recorded on a magnetic tape with a recording wavelength of 390 nm. After amplification with a commercially available Read amplifier for MR head, the fundamental component output (C) and noise component (N) of the signal were measured using a spectrum analyzer N9020A manufactured by Agilent Technologies. And it evaluated by relative value by making S / N of the comparative example 1, the comparative example 5, and the comparative example 9 into the reference | standard (0 dB), respectively.

As is apparent from the table, Examples 1 to 12 satisfying the claims of the present invention have good S / N, and Comparative Examples 1 to 12 that do not satisfy the claims have poor S / N.

  The magnetic recording medium of the present invention can be used as a magnetic recording medium having a high capacity and excellent running characteristics.

Claims (2)

A nonmagnetic layer containing one kind of nonmagnetic powder, carbon black and a binder on a nonmagnetic support, and a magnetic layer having a thickness of less than 0.1 μm containing magnetic powder and a binder on the nonmagnetic layer. A magnetic recording medium comprising:
When the ratio of the average particle diameter of the nonmagnetic powder contained in the nonmagnetic layer to the average particle diameter of the carbon black is R, 1 ≦ R ≦ 2.5 is satisfied, and the shape ratio of the nonmagnetic powder is A magnetic recording medium characterized by being 1 to 2. A nonmagnetic layer comprising a plurality of types of nonmagnetic powder, carbon black and a binder on a nonmagnetic support; and a magnetic layer having a thickness of less than 0.1 μm comprising magnetic powder and a binder on the nonmagnetic layer. A magnetic recording medium comprising:
1 ≦ R ≦ 2.5 is satisfied, where R is the ratio of the average particle size of the nonmagnetic powder having the maximum average particle size to the average particle size of the carbon black. A magnetic recording medium wherein the shape ratio of the nonmagnetic powder having the maximum average particle diameter is 1 to 2 .