JP2006107669A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent high recording density characteristics and highly reliable durability by regulating a suitable relation between a thickness dimension of a non-magnetic layer and a particle diameter dimension of non-magnetic powder contained therein. <P>SOLUTION: The non-magnetic powder in the non-magnetic layer has a granular shape having 90 to 200 nm average particle diameter. The average particle diameter L of the non-magnetic powder and the average thickness D of the non-magnetic layer satisfy a relation of L/D≤1/5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tape-type magnetic recording medium.

  Magnetic recording media have various uses such as audio tapes, video tapes, computer tapes, magnetic disks, and magnetic cards. Especially in the field of data backup tapes, as the capacity of hard disks to be backed up increases, 1 Magnetic tapes having a recording capacity of several hundred GB or more per roll have been commercialized. In the future, a large-capacity backup tape exceeding 1 TB has been proposed, and its high recording density is indispensable. In the production of magnetic tapes corresponding to such high recording densities, magnetic powder (hereinafter also referred to as magnetic particles) is finely divided (hereinafter also referred to as fine powder) and high-density filling into the coating film is performed. Advanced techniques such as making the coating, smoothing the coating film and thinning the magnetic layer have been used.

  With regard to the improvement of magnetic powder, in order to cope with short wavelength recording, the magnetic properties are improved along with the formation of fine particles, the needle-like metal magnetic powder having an average particle diameter of 100 nm or less, and the plate shape of 50 nm or less. Hexagonal ferrite magnetic powder, spherical or elliptical rare earth-iron nitride magnetic powder of 50 nm or less has been proposed. Also, in order to prevent a decrease in output due to demagnetization during short wavelength recording, a higher coercive force has been achieved year by year.

  On the other hand, with regard to the improvement of the manufacturing technology of magnetic recording media, the recording wavelength has been shortened along with the recent increase in recording density. The influence of the self-demagnetization loss at the time of reproduction and the thickness loss due to the thickness of the magnetic layer is increased, and the problem that the output is reduced has been increased. Therefore, it has become necessary to reduce the thickness of the magnetic layer. However, if the thickness of the magnetic layer is reduced, the influence of the weakening of the magnetic flux leakage from the magnetic layer and the surface roughness of the nonmagnetic support is greatly reflected on the surface of the magnetic layer, and the surface properties of the magnetic layer are likely to deteriorate. There's a problem. In addition, when thinning the magnetic layer, a method of reducing the solid content concentration of the magnetic coating or reducing the coating amount is conceivable, but depending on these methods, defects during coating and filling of the magnetic powder may occur. There is a problem that it does not improve and weakens the coating strength.

  For this reason, when thinning the magnetic layer by improving the medium manufacturing technology, a nonmagnetic layer is provided between the nonmagnetic support and the magnetic layer, and the upper magnetic layer is applied while the nonmagnetic layer is in a wet state. A so-called simultaneous multilayer coating method has been proposed (see, for example, Patent Document 1).

  In order to weaken the leakage flux from the magnetic layer, in systems using these magnetic recording media, high-sensitivity MR (magnetoresistive effect) type heads are becoming mainstream. . Since the MR type head does not have an induction coil, device noise is small. An excellent C / N can be obtained by reducing the noise of the magnetic recording medium. However, this MR head is more prone to noise (thermal noise) due to the collision between the MR element and minute irregularities on the surface of the magnetic layer, which was not a problem with the magnetic induction type. Need to control.

  Since the magnetic layer is designed to be an extremely thin layer, the surface roughness is greatly influenced by the surface roughness of the nonmagnetic layer. For this problem, the types and sizes of nonmagnetic powders in the nonmagnetic layer have been studied (for example, Patent Documents 2 to 4).

JP-A-5-197946 JP 2001-67650 A JP 2001-184627 A JP-A-8-263829

  In the trend of increasing the capacity of magnetic recording media, in order to increase the recording capacity per unit volume of the magnetic recording medium, it has been studied to reduce the thickness of the magnetic recording medium. Attempts have been made to reduce the thickness of the nonmagnetic layer. In particular, when the thickness of the nonmagnetic layer is reduced, the protrusions on the surface of the nonmagnetic support and the size of the nonmagnetic powder contained in the nonmagnetic layer have greatly influenced the roughness of the surface of the magnetic layer.

  In the above prior art, Patent Document 1 discloses that the magnetic layer contains an abrasive having a Mohs hardness of 6 or more and an average particle diameter larger than the thickness of the magnetic layer. The preferred range of the relationship with the particle size of the nonmagnetic powder contained in the magnetic layer is not disclosed, and in addition, the case where the thickness of the nonmagnetic layer is 1 μm or less has not been specifically examined. Patent Document 2 discloses a preferable relationship between the thickness of the nonmagnetic layer and the particle size of the acicular nonmagnetic powder contained in the nonmagnetic layer, and the amount of granular nonmagnetic powder added at 50 nm or less. However, the preferred relationship between the average particle diameter of the granular nonmagnetic powder having an average particle diameter of 90 nm or more employed in the present invention and the thickness of the nonmagnetic layer is not disclosed. Patent Document 3 discloses that alumina having a particle size of 0.01 to 0.1 μm is contained in a lower layer having a thickness of 1.5 μm or less (1.0 μm or more in the examples). The particle size of a suitable non-magnetic powder when the magnetic layer thickness is less than 1.0 μm is not specifically disclosed. In Patent Document 4, the ratio between the average particle diameter of the abrasive contained in the nonmagnetic layer and the dry film thickness of the magnetic layer is 1.0 to 5.0 in terms of the average particle diameter of the abrasive / the dry film thickness of the magnetic layer. However, the preferred relationship between the average particle size of the nonmagnetic powder and the thickness of the nonmagnetic layer is not disclosed.

  As described above, the magnetic recording media according to each of the above patent publications include a suitable particle size of the nonmagnetic powder to be included in the nonmagnetic layer for a magnetic recording medium having a small nonmagnetic layer thickness corresponding to the increase in capacity. There has not been a sufficient examination of.

  The present invention has been made to achieve the above object, and by defining a suitable relationship between the thickness dimension of the nonmagnetic layer and the particle diameter dimension of the nonmagnetic powder contained therein, for example, one roll of tape. An object of the present invention is to provide a magnetic recording medium excellent in high recording density characteristics capable of corresponding to a recording capacity of 1 TB or more and having high reliability in terms of durability.

  The present invention provides a magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and a magnetic layer containing the magnetic powder and a binder on the nonmagnetic layer. The nonmagnetic powder in the nonmagnetic layer has a granular shape having an average particle size of at least 90 nm and 200 nm. And the average particle diameter L of the said nonmagnetic powder and the said nonmagnetic layer average thickness D satisfy | fill the relationship of L / D <= 1/5.

  According to the present invention, since a nonmagnetic powder having an average particle diameter in a preferred range corresponding to a nonmagnetic layer having a small thickness is included, a magnetic recording medium having a high capacity and excellent recording / reproducing characteristics and durability is obtained. be able to.

(Non-magnetic powder)
In the present invention, the nonmagnetic powder contained in the nonmagnetic layer is preferably in the form of particles having a particle diameter in the range of 90 nm to 200 nm. The granular shape is preferable because the granular shape can form an appropriate protrusion shape on the surface of the magnetic layer and the durability is improved. The term “granular” as used herein means that when the powder particles are needle-shaped, the major axis diameter (the maximum diameter in the longitudinal direction of the needle-shaped particles) and the minor axis diameter (the surface perpendicular to the major axis direction) The maximum diameter when the ring is cut, or the ratio of the major axis diameter / minor axis diameter is 1 to 2 when the rounded surface is elliptical, and the powder particles are plate-like. In the case of, the ratio of the plate diameter (maximum diameter of the plate surface) and the plate thickness, the value of the plate diameter / plate thickness is 1-2, and in the case of indefinite form, the particle diameter The value of the maximum diameter / minimum diameter is 1-2.

  When the shape of the non-magnetic powder is within the above range and is needle-like or plate-like, the major axis direction (or the plate diameter) due to shear stress and film thickness shrinkage during the formation of the non-magnetic layer (at the time of coating and drying) (Direction) tends to be oriented in the coating direction, and it is the minor axis diameter (plate thickness) that affects the durability of the magnetic layer. For this reason, it is preferable to evaluate the said average particle diameter by a short axis diameter (plate thickness). The range of the average particle diameter of the non-magnetic powder is preferable because the durability is insufficient if it is less than 90 nm, and the shape of the surface of the magnetic layer is rough if it exceeds 200 nm, and the electromagnetic conversion characteristics deteriorate. is there. Examples of such nonmagnetic powders include metal salt powders such as carbon black, calcium carbonate, and barium sulfate, metal oxide powders such as iron oxide, chromium oxide, and aluminum oxide, benzoguanamine, crosslinked polystyrene, polyethylene, silicone resin, and Teflon. Conventionally known nonmagnetic powders such as organic powders insoluble in organic solvents such as resins can be used. More preferably, a nonmagnetic powder having a Mohs hardness of 6 or more can be used. In addition to the nonmagnetic powder, other nonmagnetic powders having an average particle size equal to or smaller than the average particle size of the nonmagnetic powder may be used in combination. As the non-magnetic powder, the above-mentioned conventionally known non-magnetic powder can be used, and the shape can be a non-magnetic powder having an arbitrary shape such as a plate shape or a needle shape in addition to a granular shape.

  The addition amount of these nonmagnetic ends is preferably 1 to 30% by weight based on the total weight of the constituent materials of the nonmagnetic layer. If the amount is less than 1% by weight, the durability of the magnetic layer may not be obtained due to the small amount of non-magnetic powder. If the amount exceeds 30% by weight, the surface shape of the magnetic layer becomes too rough, and electromagnetic conversion occurs. This is because the characteristics may deteriorate.

(Nonmagnetic layer)
The thickness D of the nonmagnetic layer is preferably 0.5 μm or more. When the thickness of the nonmagnetic layer is less than 0.5 μm, the influence of the surface shape of the nonmagnetic support greatly affects the surface of the magnetic layer, leading to a decrease in electromagnetic conversion characteristics. In addition, the amount of lubricant supplied from the nonmagnetic layer may be insufficient, leading to a decrease in durability of the magnetic recording medium. Further, the thickness D of the nonmagnetic layer is preferably 1 μm or less. This is because when the thickness of the nonmagnetic layer exceeds 1 μm, the total thickness of the magnetic recording medium increases, and the recording per volume of the recording medium This is due to the smaller capacity.

  In addition to the above nonmagnetic powder, the nonmagnetic layer can contain a nonmagnetic powder having an average particle size smaller than that of the above nonmagnetic powder as necessary, such as imparting conductivity. These nonmagnetic powders can be used in any shape, regardless of shape, such as granular, needle-like, and plate-like nonmagnetic powders. As the non-magnetic powder, a conventionally known non-magnetic powder similar to the above can be used.

  In addition, in the present invention, it is noted that the thickness D of the nonmagnetic layer and the average particle diameter L of the nonmagnetic powder contained in the nonmagnetic layer satisfy the relationship of L / D ≦ 1/5. The The average particle diameter L here is assumed to be evaluated with a minor axis diameter (plate thickness) in the needle shape (plate shape) as described above. This numerical range is preferable because when the value of L / D exceeds 1/5, the particles having a large particle diameter in the particle size distribution of the powder particles cause the surface shape of the magnetic layer to become rough, or the electromagnetic conversion characteristics deteriorate. (Refer to Table 1 and FIG. 3 below.) In that respect, as in the present invention, the thickness D of the nonmagnetic layer and the average particle diameter L of the nonmagnetic powder contained in the nonmagnetic layer satisfy the relationship of L / D ≦ 1/5. As described above, in combination with the non-magnetic powder having a particle diameter in the range of 90 nm to 200 nm, the magnetic recording is excellent in high recording density characteristics and highly reliable in terms of durability. A medium can be obtained.

<Non-magnetic support>
The thickness of the magnetic support varies depending on the application, but usually 1.5 to 11.0 μm is used. More preferably, it is 2.0-7.0 micrometers, Most preferably, it is 2.0-6.0 micrometers. Nonmagnetic supports with a thickness in this range are used when film thickness is less than 1.5 μm, and film strength is difficult, and tape strength decreases. This is because the recording capacity per unit becomes small.

Longitudinal Young's modulus of the nonmagnetic support is preferably 5.8GPa (590kg / mm ²⁾ or more, more preferably 7.1GPa (720kg / mm ²⁾ or more, 7.8GPa (800kg / mm ²⁾ or more and most preferable. The non-magnetic support preferably has a Young's modulus in the longitudinal direction of 5.8 GPa (590 kg / mm ² ) or more. If the Young's modulus in the longitudinal direction is less than 5.8 GPa (590 kg / mm ² ), the tape running becomes unstable. Because. In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction preferably ranges from 0.60 to 0.80, and ranges from 0.65 to 0.75. Is more preferable. The specific range of Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably in the range of 0.60 to 0.80. When the ratio is less than 0.60 or exceeds 0.80, the mechanism is currently unknown. This is because the output variation (flatness) between the entrance side and the exit side of the track of the magnetic head becomes large. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70. Further, in the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.70 to 1.30, although the reason is not clear.

The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 ⁻⁶ , and the humidity expansion coefficient is preferably 0 to 10 × 10 ⁻⁶ . The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate increases.

  The nonmagnetic support is preferably roughened by providing a smooth surface on the side where the magnetic layer is provided and forming protrusions on the other surface. In order to achieve such a configuration, the non-magnetic support has a two-layer structure, the powder layer is not added to the layer forming the magnetic layer, or a very small amount is added, and the other layer is added to the other layer. Preferably, powder particles are added to form protrusions. In order to obtain such a two-layer structure, a known method, for example, lamination in a die, lamination in a composite die, or a method in which one layer is once formed and another layer is formed thereon. and so on. Moreover, you may bond each layer formed beforehand.

  Nonmagnetic supports satisfying such properties include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, aromatic polyimide film and the like.

<lubricant>
The magnetic layer and nonmagnetic layer contain 0.5 to 3.0% by weight of fatty acid amide based on the total powder contained in the magnetic layer and nonmagnetic layer, respectively, and 0.5 to 5.0% by weight. It is preferable that a higher fatty acid is contained and 0.2 to 3.0% by weight of an ester of a higher fatty acid is contained. Fatty acid amides in this range are preferred if the amount is less than 0.5% by weight, the direct contact at the head / magnetic layer interface is likely to occur, and the effect of preventing seizure is small. This is because defects such as out may occur. The addition of higher fatty acids within this range is preferable when the content is less than 0.5% by weight, and the effect of reducing the friction coefficient is small. When the content exceeds 5.0% by weight, the nonmagnetic layer may be plasticized and the toughness may be lost. Because. The addition of higher fatty acid esters within this range is preferred because if the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, the amount transferred into the magnetic layer is too large. This is because side effects such as sticking to the head may occur. The higher fatty acid is preferably a fatty acid having 10 or more carbon atoms, and the higher fatty acid ester is preferably an ester of the higher fatty acid. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable. In addition, the mutual movement of the lubricant in the magnetic layer and the lubricant in the nonmagnetic layer is not excluded, and when the lubricant is included in the nonmagnetic layer, the magnetic layer may not include the lubricant. . On the contrary, when the effect is manifested only by being included in the magnetic layer, it may not be included in the nonmagnetic layer. Moreover, you may supply the lubricant used for a magnetic layer and a nonmagnetic layer by application | coating from on a carbon layer as needed.

<Dispersant>
The nonmagnetic powder, carbon black, and magnetic powder contained in the nonmagnetic layer and the magnetic layer are, for example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, and oleic acid. Fatty acids having 12 to 18 carbon atoms such as elaidic acid, linoleic acid, linolenic acid, stearolic acid (RCOOH, R is an alkyl group or alkenyl group having 11 to 17 carbon atoms), alkali metals or alkalis of the fatty acids Metal soap made of earth metal, fluorine-containing compound of fatty acid ester, amide of fatty acid, polyalkylene oxide alkyl phosphate ester, lecithin, trialkylpolyolefinoxy quaternary ammonium salt 5 olefins include ethylene, propylene, etc.), sulfate, sulfur Emissions salt, phosphate salt, and may be surface treated with a conventionally known dispersant such as copper phthalocyanine may be performed paint manufacturing process with a dispersant. These may be used alone or in combination. The dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder in any layer.

<Magnetic layer>
The thickness of the magnetic layer is 10 nm or more and less than 100 nm. If the output is less than 10 nm, it is difficult to apply a uniform magnetic layer, and if it exceeds 100 nm, the self-demagnetization and the thickness loss become too large and the short wavelength recording / reproducing characteristics deteriorate. .

  The roughness of the magnetic layer is preferably 3 to 7 nm, more preferably 3 to 6 nm, in terms of the center line average roughness Ra. This range is preferable because when the Ra is less than 3 nm, the friction coefficient of the magnetic layer becomes too large, which may cause problems in running stability and durability. Because it gets worse.

  The coercive force of the magnetic layer is preferably 80 to 320 kA / m, more preferably 100 to 320 kA / m, and still more preferably 120 to 320 kA / m. This range is preferable because if the recording wavelength is shorter than 80 kA / m, the output is reduced due to demagnetization, and if it exceeds 320 kA / m, recording by the magnetic head becomes difficult.

  The binder resin used for the magnetic layer (the same applies to the nonmagnetic layer) includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol. A polyurethane resin, at least one selected from a copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose; And a combination of these. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, and polyester polycarbonate polyurethane resin.

-COOH as a functional _{group, -SO 3 M, -OSO 3 M} , -P = O (OM) 3, -O-P = O (OM) 2 [ In these formulas, M represents a hydrogen atom, an alkali metal base or Represents an amine salt], —OH, —NR′R ″, —N + R ′ ″ R ″ ″ R ′ ″ ″ [in these formulas, R ′, R ″, R ″ ', R ″ ″, R ′ ″ ″ represent hydrogen or a hydrocarbon group], and a binder resin such as a urethane resin made of a polymer having an epoxy group is used. The reason why such a binder resin is used is that the dispersibility of the magnetic powder and the like is improved as described above. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  These binder resins are used in the range of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder. In particular, as the binder resin, it is most preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin.

  Along with these binder resins, it is preferable to use a thermosetting crosslinking agent which is bonded to a functional group contained in the binder resin and crosslinked. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used in a proportion of 1 to 30 parts by weight with respect to 100 parts by weight of the binder resin. More preferably, it is 5 to 20 parts by weight. However, when a magnetic layer is applied on the nonmagnetic layer by wet-on-wet, a certain amount of polyisocyanate is diffused and supplied from the nonmagnetic coating material. Cross-linked.

  Instead of the thermosetting binder resin as described above, a radiation curable resin may be used. As the radiation curable resin, those obtained by acrylic modification of the thermosetting resin to give a radiation sensitive double bond, acrylic monomers, and acrylic oligomers are used. The average particle size of the magnetic powder contained in the magnetic layer is preferably in the range of 10 to 100 nm, more preferably in the range of 15 to 80 nm. This range is preferred because if the average particle size is less than 10 nm, the surface energy of the particles becomes large and dispersion becomes difficult, and if the average particle size exceeds 100 nm, noise increases. As the magnetic powder, ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder, plate-shaped hexagonal Ba-ferrite magnetic powder, and the like are preferable.

  The ferromagnetic iron-based metal magnetic powder may contain transition metals such as Mn, Zn, Ni, Cu, and Co as an alloy. Among these, Co and Ni are preferable, and Co is particularly preferable because it can improve saturation magnetization most. As a quantity of said transition metal element, it is preferable to set it as 5-50 atomic% with respect to iron, and it is more preferable to set it as 10-30 atomic%. Further, at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium, and the like may be included. Among these, when cerium, neodymium and samarium, terbium, and yttrium are used, a high coercive force is obtained, which is preferable. The amount of rare earth elements is 0.2 to 20 atomic%, preferably 0.3 to 15 atomic%, more preferably 0.5 to 10 atomic%, based on iron. Ferromagnetic iron-based metal magnetic powders are usually needle-shaped, spindle-shaped, or rice-grained, but the average particle diameter (major axis diameter) is preferably 10 nm or more and less than 100 nm. If the average particle size is less than 10 nm, the coercive force is not within the preferred range, or the specific surface area is large, so that dispersion becomes unstable, and favorable recording / reproducing characteristics cannot be obtained. The axial ratio (major axis diameter / minor axis diameter) of the ferromagnetic iron-based metal magnetic powder is preferably 2 or more and less than 10, and more preferably 2 or more and 5 or less.

  Boron may be included in the ferromagnetic iron-based metal magnetic powder. By containing boron, granular or elliptical ultrafine particles having an average particle diameter of less than 25 nm can be obtained. The amount of boron is 0.5 to 30 atomic%, preferably 1 to 25 atomic%, more preferably 2 to 20 atomic%, based on iron in the entire magnetic powder. Both the atomic% are values measured by fluorescent X-ray analysis (reference patent: Japanese Patent Application Laid-Open No. 2001-181754). The axial ratio of the magnetic powder is preferably 1 or more and 2 or less.

  As the iron nitride magnetic powder, a known one can be used, and the shape can be an indeterminate shape such as a spherical shape or a cubic shape in addition to a needle shape. The average particle size is preferably 20 nm or less. The axial ratio of the magnetic powder is preferably 1 or more and 2 or less. (Reference patent: WO03079333A1)

The coercive force of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably 80 to 320 kA / m, and the saturation magnetization is preferably 80 to 200 A · m ² / kg (80 to 200 emu / g), 100 to 180 A · m ² / kg (100 to 180 emu / g) is more preferable. Further, BET specific surface area of the ferromagnetic powder is preferably at least 35m ² / g, more preferably at least 40 m ² / g, most preferably at least 50 m ² / g. Usually, it is 100 m ² / g or less. Further, the ferromagnetic iron metal temporal powder and the iron nitride magnetic powder may be used after being surface-treated with Al, Si, P, Y, Zr, or an oxide thereof.

The coercive force of the hexagonal Ba-ferrite magnetic powder is preferably 120 to 320 kA / m, and the saturation magnetization is preferably 40 to 70 A · m ² / kg (40 to 70 emu / g). The particle size (size in the plate surface direction) is preferably 10 to 25 nm, more preferably 10 to 20 nm. When the particle size is less than 10 nm, the surface energy of the particles increases, so that dispersion in the paint becomes difficult. When the particle size exceeds 25 nm, particle noise based on the particle size increases. The plate ratio (plate diameter / plate thickness) is preferably 2 to 5, and more preferably 2 to 4. The BET specific surface area of the hexagonal Ba-ferrite magnetic powder is preferably 1 to 100 m ² / g. Note that the magnetic properties of these ferromagnetic powders all refer to values measured with an external magnetic field of 1273.3 kA / m (16 kOe) using a sample vibration type magnetometer. In addition, the above average particle diameter was measured by measuring the maximum diameter of each particle (major axis diameter for needle-like powder and plate diameter for plate-like powder) from a photograph taken with a transmission electron microscope (TEM). The average value is obtained.

  As the non-magnetic powder, conventionally known powders are used, and α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium car Those having a Mohs hardness of 6 or more such as bite, titanium oxide, silicon dioxide and boron nitride are preferably used alone or in combination. As the particle size of the nonmagnetic powder, a nonmagnetic powder having an average particle diameter of 9 nm to 250 nm satisfying the above relationship is used for a magnetic layer having a thickness of 0.01 to 0.1 μm.

  Furthermore, if necessary, conventionally known carbon black may be added for the purpose of improving conductivity and improving surface lubricity. As carbon black, acetylene black, furnace black, thermal black, etc. can be used. In addition, a thing with an average particle diameter of 10 nm-100 nm is preferable. This range is preferable because when the average particle size is 10 nm or less, it is difficult to disperse the carbon black. When the average particle size is 100 nm or more, it is necessary to add a large amount of carbon black. In any case, the surface becomes rough and the output decreases. This is because it causes. Moreover, you may use two or more types of carbon black of a different average particle diameter as needed. In addition, it is preferable that the average particle diameter of carbon black also exists in the range of said relationship.

<Back layer>
A back layer can be provided on the other surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support constituting the magnetic tape of the present invention for the purpose of improving running performance. . The back layer is usually provided as a back layer containing a nonmagnetic powder mainly composed of carbon black and a binder resin.

  The thickness of the back layer is preferably 0.2 to 0.8 μm. This range is good because if the thickness is less than 0.2 μm, the effect of improving running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the recording capacity per roll becomes small. As carbon black, acetylene black, furnace black, thermal black, etc. can be used. Usually, small particle size carbon black and large particle size carbon black are used. As the small particle size carbon black, those having an average particle size of 5 nm to 200 nm are used, and those having an average particle size of 10 nm to 100 nm are more preferable. This range is more preferable because when the average particle size is 10 nm or less, it is difficult to disperse the carbon black, and when the average particle size is 100 nm or more, it is necessary to add a large amount of carbon black. In either case, the surface is rough. This is because it causes the back-off (embossing) of the magnetic layer. When a large particle diameter carbon black having a large particle diameter of 5 to 15% by weight and an average particle diameter of 200 to 400 nm is used as the large particle diameter carbon black, the surface is not roughened and the effect of improving running performance is increased. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder. The center line average surface roughness Ra is preferably 3 to 8 nm, and more preferably 4 to 7 nm. Since the magnetic signal of the magnetic recording layer may be disturbed if the back layer is magnetic, the back layer is usually non-magnetic.

  In addition, a nonmagnetic plate-like powder having an average particle diameter of 10 nm to 100 nm can be added to the back layer for the purpose of improving strength, temperature / humidity dimensional stability, and the like. The component of the nonmagnetic plate-like powder is not limited to aluminum oxide, and rare earth elements such as cerium, and oxides or composite oxides of elements such as zirconium, silicon, titanium, manganese, and iron are used. For the purpose of improving conductivity, a plate-like carbonaceous powder having an average particle size of 10 nm to 100 nm, a plate-like ITO powder having an average particle size of 10 nm to 100 nm, or the like may be added. Moreover, you may add the granular iron oxide powder whose average particle diameter is 0.1 micrometer-0.6 micrometer as needed. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the total inorganic powder in the back layer. Moreover, it is preferable to add alumina having an average particle size of 0.1 μm to 0.6 μm because durability is further improved.

  For the back layer, the same resin as that used for the magnetic layer and non-magnetic layer described above can be used as the binder resin, but among these, in order to reduce the coefficient of friction and improve the runnability, cellulose resin and polyurethane resin Are preferably used in combination. The content of the binder resin is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight with respect to 100 parts by weight of the total amount of the carbon black and the inorganic nonmagnetic powder. More preferably, it is 70 to 110 parts by weight. The above range is preferable because if the amount is less than 50 parts by weight, the strength of the back layer is insufficient, and if it exceeds 120 parts by weight, the friction coefficient tends to increase. It is preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin. Further, in order to further cure the binder resin, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

  For the back layer, the same cross-linking agent as that used for the magnetic layer and the non-magnetic layer is used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, preferably 10 to 35 parts by weight, and more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder resin. The above range is preferable because if the amount is less than 10 parts by weight, the coating strength of the back layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction coefficient against SUS increases. In the back layer, in order to crosslink and cure the coating film, the same electron beam curable resin as that of the magnetic layer and the nonmagnetic layer can be used as a crosslinking agent.

  When the thickness of the nonmagnetic layer is 0.5 μm or less, the lubricant component supplied from the nonmagnetic layer may be insufficient. In that case, it is preferable to include a lubricant in the back layer and supply the lubricant from the back layer to the surface on the magnetic layer side. The type of lubricant used is the same as that used for the magnetic layer and nonmagnetic layer. Addition amount is 0.5 to 3.0% by weight of fatty acid amide, 0.2 to 3.0% by weight of higher fatty acid ester, 0.5 to 5.0% by weight based on the total amount of nonmagnetic powder in the back layer. It is preferable to contain a higher fatty acid.

<Organic solvent>
Examples of organic solvents used in magnetic paints, nonmagnetic paints, back layer paints, and nonmagnetic layers include ketone solvents such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, ethyl acetate, Examples thereof include acetate solvents such as butyl acetate. These solvents are used alone or in combination, and further mixed with toluene or the like.

  The present invention will be described in detail by the following examples, but the present invention is not limited thereto. In the following, examples and comparative examples are parts by weight. Moreover, the average particle diameter of an Example and a comparative example shows a number average particle diameter.

Example 1
《Non-magnetic paint component》
(1)
・ Nonmagnetic acicular iron oxide powder (average major axis diameter: 50 nm, axial ratio 5) 68 parts ・ Particulate alumina powder (average particle diameter: 100 nm) 12 parts ・ Carbon black (average particle diameter: 25 nm) 20 parts ・ Stearic acid 2.0 parts / vinyl chloride-hydroxypropyl acrylate copolymer 8.8 parts (containing-SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Cyclohexanone 25 parts ・ Methyl ethyl ketone 40 parts ・ Toluene 10 parts (2)
・ Stearic acid 1 part ・ Butyl stearate 1 part ・ Cyclohexanone 70 parts ・ Methyl ethyl ketone 50 parts ・ Toluene 20 parts (3)
・ Polyisocyanate 1.4 parts ・ Cyclohexanone 10 parts ・ Methyl ethyl ketone 15 parts ・ Toluene 10 parts << Magnetic paint ingredients >>
(1) Kneading process / magnetic powder (Co—Fe—Al—Y) 100 parts (Co / Fe: 24 at%,
Al / (Fe + Co): 4.7 wt%
Y / (Fe + Co): 7.9 at%
σs: 119 A · m ² / kg (119 emu / g),
Hc: 181.4 kA / m (2280 Oe),
Average particle diameter: 60 nm, axial ratio: 5)
-13 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin (PU) 4.5 parts (containing -SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g)
-Methyl acid phosphate (MAP) 2 parts-Tetrahydrofuran (THF) 20 parts-Methyl ethyl ketone / cyclohexanone (MEK / A) 9 parts (2) Dilution step-Palmitic acid amide (PA) 1.5 parts-N-butyl stearate ( SB) 1 part ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 350 parts (3) Blending process ・ Polyisocyanate 1.5 parts ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts

  After kneading (1) with a batch kneader in the above nonmagnetic coating component, (2) is added and stirred, and then a dispersion treatment is performed using a sand mill with a residence time of 60 minutes. After filtration, a nonmagnetic paint (nonmagnetic layer paint) was obtained.

  Apart from this, in the above-mentioned components of the magnetic paint, (1) the mixing process component is previously mixed at high speed, the mixed powder is kneaded with a continuous biaxial kneader, and (2) the dilution process component is added. The mixture was diluted in at least two stages using a continuous biaxial kneader, dispersed in a sand mill with a residence time of 45 minutes, added with (3) blending step components, stirred and filtered to obtain a magnetic paint. Further, the above nonmagnetic paint components were mixed with stirring to obtain a nonmagnetic paint.

  Nonmagnetic support (base) made of an aromatic polyamide film (thickness 6.0 μm, MD = 7.8 GPa, MD / TD = 1.23, trade name: Teonex, manufactured by Teijin DuPont) The film is coated on the non-magnetic layer so that the thickness after drying and calendering is 0.9 μm, and the magnetic layer is further coated with magnetic coating on the nonmagnetic layer after the magnetic field orientation treatment, drying and calendering treatment. The film was applied wet-on-wet with an extrusion coater so that the thickness was 0.06 μm, and after magnetic field orientation treatment, it was dried using a dryer and far infrared rays to obtain a magnetic sheet.

<Back layer paint component>
Carbon black (average particle size: 25 nm) 80 parts Carbon black (average particle size: 350 nm) 10 parts Nonmagnetic granular iron oxide powder (average particle size: 100 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin (- SO ₃ Na group-containing) 30 parts ・ Cyclohexanone 260 parts ・ Toluene 260 parts ・ Methyl ethyl ketone 525 parts

  After dispersing the coating component for the back layer in a sand mill with a residence time of 45 minutes, after adding 15 parts of polyisocyanate to adjust the coating for the back layer and filtering, drying on the opposite side of the magnetic layer of the magnetic sheet prepared above, It was applied so that the thickness after calendering was 0.5 μm and dried.

  The magnetic sheet thus obtained was mirror-finished under the conditions of a temperature of 100 ° C. and a linear pressure of 196 kN / m with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound around the core at 70 ° C. at 72 ° C. Time-aging was performed to obtain a magnetic sheet with a back layer. The obtained magnetic sheet with a carbon layer was cut into a 1/2 inch width by a slit machine.

  A slit machine (an apparatus for cutting a magnetic tape original into a magnetic tape having a predetermined width) was used in which various constituent elements were improved as follows. A tension cut roller was provided in the web path from the unwinding raw fabric to the slit blade group, this tension cut roller was a suction type, and the suction part was a mesh suction in which a porous metal was embedded. A direct drive directly connected to a motor without a mechanism for transmitting power to the blade drive unit was used. Thereafter, a servo signal was written on the back layer with a laser spot to obtain a magnetic tape. The magnetic tape obtained as described above was assembled in a cartridge to produce a computer tape.

(Example 2)
Except that the granular alumina powder (average particle size: 100 nm) in the nonmagnetic coating component was changed to granular alumina powder (average particle size: 150 nm) and the thickness of the nonmagnetic layer was changed from 0.9 μm to 0.75 μm. A computer tape of Example 2 was produced in the same manner as Example 1.

(Example 3)
Except that the granular alumina powder (average particle size: 100 nm) in the nonmagnetic paint component was changed to granular alumina powder (average particle size: 200 nm) and the thickness of the nonmagnetic layer was changed from 0.9 μm to 1.0 μm. A computer tape of Example 3 was produced in the same manner as Example 1.

Example 4
A computer tape of Example 4 was produced in the same manner as in Example 1 except that the thickness of the nonmagnetic layer was changed from 0.9 μm to 0.5 μm.

(Comparative Example 1)
A computer tape of Comparative Example 1 was produced in the same manner as in Example 1 except that the thickness of the nonmagnetic layer was changed from 0.9 μm to 0.4 μm.

(Comparative Example 2)
Except that the granular alumina powder (average particle size: 100 nm) in the nonmagnetic coating component was changed to granular alumina powder (average particle size: 150 nm) and the thickness of the nonmagnetic layer was changed from 0.9 μm to 0.7 μm. A computer tape of Comparative Example 2 was produced in the same manner as Example 1.

(Comparative Example 3)
Except that the granular alumina powder (average particle size: 100 nm) in the nonmagnetic coating component was changed to granular alumina powder (average particle size: 80 nm) and the thickness of the nonmagnetic layer was changed from 0.9 μm to 0.4 μm. A computer tape of Comparative Example 3 was produced in the same manner as Example 1.

(Comparative Example 4)
A computer tape of Comparative Example 4 was produced in the same manner as Comparative Example 3 except that the thickness of the nonmagnetic layer was changed from 0.4 μm to 0.8 μm.

(Comparative Example 5)
The same as Example 1 except that the granular alumina powder (average particle size: 100 nm) in the nonmagnetic coating component was changed to acicular nonmagnetic iron oxide powder (average major axis diameter: 230 nm, average minor axis diameter: 30 nm). Thus, a computer tape of Comparative Example 5 was produced.

The evaluation method was performed as follows.
<C / N measurement>
A drum tester was used for measuring the electromagnetic conversion characteristics of the tape. The drum tester was equipped with an electromagnetic induction head (track width 25 μm, gap 0.2 μm) and an MR head (track width 8 μm), and recording was performed with the induction head and reproduction was performed with the MR head. Both heads are installed at different locations with respect to the rotating drum, and tracking can be adjusted by operating both heads in the vertical direction. An appropriate amount of the magnetic tape was withdrawn from the state of being wound in the cartridge and discarded, and further 60 cm was cut out, further processed into a width of 4 mm, and wound around the outer periphery of the rotating drum.

  For the output and noise, a rectangular wave was input to the recording current / current generator by a function generator, a signal having a wavelength of 0.2 μm was written, the output of the MR head was amplified by a preamplifier, and then read into a spectrum analyzer. The carrier value of 0.2 μm was set as the medium output C. Further, when a rectangular wave of 0.2 μm was written, the integrated value of the value obtained by subtracting the output and system noise from the spectral component corresponding to the recording wavelength of 0.2 μm or more was used as the noise value N. Furthermore, the ratio of both was taken as C / N, and both C and C / N were determined relative to the value of the tape of Comparative Example 1.

<Error rate>
Using a Quantum DLT7000 drive, run the entire track for 300 hours continuously in a room temperature environment, read the error information output by the drive after running via the RS-232C interface, and record an error per 1 MB of recording capacity. Rated as a number.

<Non-magnetic layer thickness>
The sample magnetic recording medium was filled with resin, and the cross section in the thickness direction was cut out with a focused ion beam processing apparatus, and the cross section was photographed with 10 fields of view at 10,000 times with a scanning electron microscope (SEM). Borders the boundary between the magnetic layer and the nonmagnetic layer and the boundary between the nonmagnetic layer and the nonmagnetic support. Next, select any five locations (total of 50 locations) where no nonmagnetic powder is applied to the interface per field of view, measure the distance between the bordered lines as the thickness of the nonmagnetic layer, and average them. Thus, the nonmagnetic layer thickness was obtained.

<Granular non-magnetic powder particle size>
As in the case of obtaining the thickness of the magnetic layer described above, the cross section of the nonmagnetic layer was taken 10,000 times with a scanning electron microscope (SEM), and the required number of photographs were taken with a continuous field of view. The outline of the granular nonmagnetic powder contained is trimmed. The minimum of the outer diameter is measured as the particle diameter. Fifty nonmagnetic powders were measured, and the average value was taken as the average particle size.

  Table 1 shows the evaluation results of each computer tape. As is apparent from Table 1, the computer tapes of Examples 1 to 4 according to the present invention have better C / N than the computer tapes of Comparative Examples 1 to 5 that do not satisfy Claim 1. Durability is also great.

  Next, the critical significance of various numerical values of the present invention will be clarified with reference to FIGS. FIG. 1 shows the relationship between L and D values and C / N. The experiment was conducted with Example 1 as the basic composition, with the average particle size of the nonmagnetic powder being changed in the range of 80 to 200 nm and the thickness of the nonmagnetic layer in the range of 300 to 1200 nm. The C / N value (dB) of the obtained computer tape is shown with each point. As is clear from the figure, it can be seen that C / N decreases in the region above the line (shown by a solid line) with L / D of 1/5 in the figure.

  FIG. 2 shows the relationship between the values of L and D and the error rate (ER) after the durability running test. The experiment was conducted with Example 1 as the basic composition, with the average particle size of the nonmagnetic powder being changed in the range of 80 to 200 nm and the thickness of the nonmagnetic layer in the range of 300 to 1200 nm. The error rate value (pieces / MB) of the obtained computer tape is shown with each point. As is apparent from the figure, the error rate after the endurance running test increases when L / D is in the upper region in the figure than the line where D is 1/5 (shown by a solid line). It can also be seen that when the average particle size of the non-magnetic powder is less than 90 nm, the error rate after the durability running test increases.

  FIG. 3 shows the results of FIGS. 1 and 2 collectively. It can be seen that the range of L and D surrounded by each line of L / D = 1/5 and L = 90 nm indicates a range with good C / N and durability.

The figure which shows the relationship between L / D and a magnetic tape characteristic (C / N) The figure which shows the relationship between L / D and magnetic tape characteristic (error rate after running) Diagram showing the relationship between L / D and magnetic tape characteristics

Claims (1)

A magnetic recording medium comprising a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and a magnetic layer containing the magnetic powder and a binder on the nonmagnetic layer.
The nonmagnetic powder in the nonmagnetic layer is a granule having an average particle diameter of at least 90 nm and 200 nm,
A magnetic recording medium, wherein an average particle diameter L of the nonmagnetic powder and an average thickness D of the nonmagnetic layer satisfy a relationship of L / D ≦ 1/5.

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