JP2007048427A - Magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium where reliability in recording and reproduction of data is improved by improve dimensional stability of a tape, particularly in a high-temperature environment, and to provide a method for manufacturing the same. <P>SOLUTION: The magnetic recording medium 10 comprises one or more magnetic layers 16 formed on a non-magnetic substrate 12. The magnetic recording medium has a loss modulus at 0.5 Hz at a temperature of 130°C of 0.18 to 0.39 GPa. The non-magnetic substrate 12 is made of polyethylenenaphthalate, and the non-magnetic substrate 12 has a loss modulus at 0.5 Hz at a temperature of 130°C of 0.15 to 0.37 GPa. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium and a manufacturing method thereof, and more particularly to a magnetic recording medium having improved dimensional stability under a high temperature environment and a manufacturing method thereof.

  Magnetic tape, which is a kind of magnetic recording medium, is used not only for cassette tapes and video tapes but also for computer data backup tapes. In the field of data backup tapes, with the increase in capacity of hard disks to be backed up, those with a storage capacity of 100 GB or more per volume have been commercialized, and the capacity of hard disks will be further increased in the future. In order to respond, it is essential to increase the capacity of the backup magnetic tape.

  At this time, the reliability of data recording and reproduction is extremely important as the capacity is increased. In particular, even in a harsh environment, for example, after storage in a high temperature environment, it is necessary to accurately record data and to accurately reproduce the recorded data.

  In order to deal with such problems, for example, a proposal has been made to improve the durability of the magnetic recording medium, particularly the cycle environment characteristics (see Patent Document 1).

In this proposal, the support of the magnetic recording medium is heat-treated at a temperature lower than the glass transition point of the support for a predetermined time, and the endothermic amount based on the enthalpy relaxation of the support is set to a predetermined value or more. It is said that the reliability of recorded / reproduced data can be improved.
JP-A-11-110735

  However, even the conventional techniques as described above have problems that cannot be solved. That is, in the severe environment as described above, in general, each member constituting the magnetic recording medium may be deformed by creep or the like, resulting in a dimensional change. Playback may not be possible. To solve this problem, the prior art (Patent Document 1, etc.) is insufficient.

  In addition, in order to increase the capacity per one backup tape, it is necessary to reduce the total thickness of the tape and increase the tape length per one roll. In this case, when a thin magnetic recording medium is recorded / reproduced by a drive, non-uniform elongation occurs in the medium due to a tension during driving, and as a result, running stability decreases. Therefore, there has been a strong demand for solving such problems.

  The present invention has been made in view of such circumstances, and improves the dimensional stability of the tape, in particular, the dimensional stability in a high temperature environment, and improves the reliability at the time of data recording / reproduction. It is an object of the present invention to provide a magnetic recording medium that can be used and a method for manufacturing the same.

  In order to achieve the above object, the present invention provides a magnetic recording medium comprising one or more magnetic layers on a nonmagnetic support, and the magnetic recording medium has a 0.5 Hz loss elastic modulus at a temperature of 130 ° C. Provided is a magnetic recording medium characterized by being 0.18 to 0.39 GPa.

  In the magnetic recording medium comprising one or more magnetic layers on a nonmagnetic support, the nonmagnetic support is made of polyethylene naphthalate, and the temperature of the nonmagnetic support is 130 ° C. The magnetic recording medium is characterized in that the loss elastic modulus at 0.5 Hz is 0.15 to 0.37 GPa.

  According to the present invention, since the loss elastic modulus of the magnetic recording medium or the non-magnetic support is controlled within the optimum range, the dimensional stability of the tape is improved, and as a result, the reliability at the time of data recording / reproduction is improved. Can be improved.

  That is, the present inventor paid attention to the non-magnetic support among the members constituting the magnetic recording medium, and proceeded with investigations on the shape stability thereof. It has been found that a magnetic recording medium capable of solving the above problems can be obtained by setting the rate to a specific value.

The loss elastic modulus is one of the evaluation indexes of the vibration damping characteristics of the material, and corresponds to E ₂ when the complex elastic modulus E is expressed by the formula E = E ₁ + iE ₂ . In this case, E ₁ is a value that changes reversibly, E ₂ is a value that changes irreversibly, and i is a display of a complex number.

  The glass transition temperature Tg is also referred to as a glass transition point, and is based on a phenomenon (glass transition) that changes from a hard glassy state to a rubbery state when a polymer substance is heated. This glass transition occurs. Refers to temperature.

  In the present invention, a magnetic or nonmagnetic intermediate layer is preferably provided between the nonmagnetic support and the magnetic layer. Thus, if the nonmagnetic intermediate layer is provided, the shape stability is further improved.

  The present invention also provides a method of manufacturing a magnetic recording medium in which one or more magnetic layers and / or nonmagnetic layers are formed on a nonmagnetic support, before the magnetic layers and / or nonmagnetic layers are formed. A non-magnetic support is heat-treated at a temperature lower by 1 to 25 ° C. than the glass transition temperature Tg of the support, and the heat treatment temperature applied to the support in the subsequent production process is set to the glass transition temperature Tg of the support. Provided is a method of manufacturing a magnetic recording medium, characterized by being maintained below.

  According to the present invention, before forming the magnetic layer and / or the nonmagnetic layer, the nonmagnetic support is heat-treated at a temperature 1 to 25 ° C. lower than the glass transition temperature Tg, and the support is subjected to this support in the subsequent manufacturing process. Since the applied heat treatment temperature is maintained below the glass transition temperature Tg, the dimensional stability of the tape is improved, and as a result, the reliability at the time of data recording / reproduction can be improved.

  As described above, according to the present invention, the dimensional stability of the tape is improved, and as a result, the reliability at the time of data recording / reproduction can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a partially enlarged sectional view for explaining the layer structure of a magnetic recording medium according to the present invention.

  As shown in FIG. 1, in the magnetic recording medium 10 of the present invention, a nonmagnetic intermediate layer 14 is formed on the surface of a nonmagnetic flexible support 12, and a magnetic layer 16 is formed on the intermediate layer 14. Is formed. A back coat layer 18 is formed on the back surface of the nonmagnetic flexible support 12.

  An undercoat layer for improving adhesion may be provided between the nonmagnetic flexible support 12 and the intermediate layer 14 or between the intermediate layer 14 and the magnetic layer 16. When an undercoat layer is provided, the layer thickness is preferably 0.01 to 0.5 μm, more preferably 0.02 to 0.5 μm.

  Although there is no restriction | limiting in the thickness of a support body, 2-100 micrometers is preferable and 2-80 micrometers is more preferable. Generally, a non-magnetic support for computer tape having a thickness in the range of 3.0 to 10 [mu] m (preferably 3.0 to 9.0 [mu] m, more preferably 3.0 to 8.0 [mu] m) is used. Is done.

  In the magnetic recording medium of the present invention, the average magnetic layer thickness is preferably 40 to 200 nm, more preferably 50 to 200 nm. The magnetic layer 16 can achieve the object of the present invention by a single layer or plural layers.

  The thickness of the intermediate layer that is the lower layer of the magnetic layer 16 in the magnetic recording medium according to the present invention is preferably 0.05 to 5.0 μm, preferably 0.1 to 3.0 μm, and 0.1 to 2.5 μm. Further preferred. The thickness of the backcoat layer 18 is preferably 0.2 to 1.5 μm, and more preferably 0.3 to 0.8 μm.

  Hereinafter, the configuration of each layer of the magnetic recording medium 10 and the method for manufacturing the magnetic recording medium 10 will be described for each item.

[Support]
Examples of the nonmagnetic flexible support 12 used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, Known films such as polyamideimide, polysulfone, aramid, and aromatic polyamide can be used. These supports may be subjected in advance to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like.

In order to achieve the object of the present invention, the 0.5 Hz loss elastic modulus E ₂ of the magnetic recording medium 10 at a temperature of 130 ° C. is required to be 0.18 to 0.39 GPa. When the value of the loss modulus E _2, the support 12 is not limited to polyethylene naphthalate.

In order to achieve the object of the present invention, when the support 12 is made of polyethylene naphthalate, the 0.5 Hz loss elastic modulus E ₂ at a temperature of 130 ° C. of the support 12 is 0.15 to 0.37 GPa. It is required to be.

Magnetic as the recording medium 10 and a method of adjusting the loss modulus E ₂ of the support 12, for example, heat treatment of the support 12 before coating, in advance by 1 to 25 ° C lower temperature than the glass transition temperature Tg of the support 12 And a method of gradually cooling to room temperature after the heat treatment, followed by coating and drying.

  In this case, it is important that the drying temperature after coating does not exceed the glass transition temperature Tg of the support 12. If this drying temperature exceeds the glass transition temperature Tg of the support 12, the relaxed creep characteristics are restored and the 0.5 Hz loss elastic modulus at a temperature of 130 ° C. is also 0.40 GPa or more. is there.

  Next, other characteristics of the support 12 will be described. The range of the center line surface roughness of the surface on which the intermediate layer 14 of the support 12 is applied is 10 nm or less and 0.1 nm or more, preferably 6 nm or less and 0.2 nm or more, more preferably 4.5 nm or less and 0.5 nm or more.

  The Young's modulus (longitudinal elastic modulus) in the longitudinal direction of the support 12 is 5 Gpa or more, preferably 6 Gpa or more, more preferably 8 Gpa or more, and the Young's modulus in the width direction is 3 Gpa or more, preferably 4 Gpa or more. The heat shrinkage rate of the support 12 at 100 ° C for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C for 30 minutes is preferably 1% or less, more preferably. 0.5% or less.

The breaking strength of the support 12 is preferably 5 to 100 kgf / mm ² (≈49 to 980 MPa), and the elastic modulus is preferably 100 to 2000 kgf / mm ² (≈0.98 to 19.6 GPa). The temperature expansion coefficient of the support 12 is 10 ⁻⁴ to 10 ⁻⁸ / ° C., preferably 10 ⁻⁵ to 10 ⁻⁶ / ° C. The humidity expansion coefficient is 10 ⁻⁴ / RH% or less, preferably 10 ⁻⁵ / RH% or less. These thermal characteristics, dimensional characteristics, and mechanical strength characteristics are preferably substantially equal with a difference within 10% in each in-plane direction of the support.

[Magnetic layer]
The thickness of the magnetic layer 16 is preferably 40 to 200 nm, more preferably 50 to 200 nm, and still more preferably 80 to 200 nm. An optimum thickness range can be set according to the recording / reproducing system to be applied. In general, when the thickness is 40 nm or less, the output decreases, and sufficient output and C / N cannot be obtained. On the other hand, when it is 200 nm or more, the noise component becomes high and C / N deteriorates.

  The ferromagnetic powder used for the magnetic layer 16 is preferably a ferromagnetic metal (preferably alloy) powder containing α-Fe as a main component. These ferromagnetic powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, other than predetermined atoms. It may contain atoms such as W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B. In particular, at least one of Al, Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is preferably included in addition to α-Fe, and further includes at least one of Co, Y, and Al. preferable.

  The content of Co is preferably 0 to 40 atomic%, more preferably 15 to 35 atomic%, and more preferably 20 to 35 atomic% with respect to Fe. The content of Y is preferably 1.5 to 15 atomic%, more preferably 3 to 12 atomic%. Al is preferably 1.5 to 15 atomic%, more preferably 3 to 12 atomic%.

  These ferromagnetic powders may be treated in advance with a dispersant, lubricant, surfactant, antistatic agent or the like before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. Sho 46-28466, Japanese Patent Publication No. Sho 46-38755, Japanese Patent Publication No. 47 No. -4286, Japanese Patent Publication No. 47-12422, Japanese Patent Publication No. 47-17284, Japanese Patent Publication No. 47-18509, Japanese Patent Publication No. 47-18573, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 46-39639, US Patent No. 3026215. No. 3033131, No. 3100194, No. 3420005, No. 3338914, and the like.

  The ferromagnetic alloy (fine) powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of ferromagnetic alloy (fine) powder can be used, and the following method can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, a metal carbonyl compound, etc. A method of thermal decomposition, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, evaporating the metal in a low-pressure inert gas to form a fine powder How to get.

  The ferromagnetic alloy powder obtained in this manner is a known slow oxidation treatment, that is, a method of drying after immersing in an organic solvent, and after immersing in an organic solvent, an oxygen-containing gas is fed to form an oxide film on the surface and then dried. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

When the ferromagnetic powder is expressed by a specific surface area (S BET) by the BET method, it is 40 to 80 m ² / g, preferably 45 to 70 m ² / g. Noise is high at 40 m ² / g or less, and surface properties are difficult to obtain at 80 m ² / g or more. The crystallite size of the ferromagnetic powder of the magnetic layer 16 is 80 to 180 mm, preferably 100 to 180 mm, and more preferably 110 to 175 mm. The average major axis length or average plate diameter of the ferromagnetic powder is 30 nm or more and 100 nm or less, preferably 30 nm or more and 75 nm or less.

The average needle ratio or average plate diameter ratio of the ferromagnetic powder is preferably 5 to 15, and more preferably 6 to 12. The acicular ratio is represented by the ratio between the average major axis length measured by transmission electron microscope and the crystallite size obtained by X-ray diffraction. The σs of the magnetic metal powder is 70 to 180 A · m ² / kg, preferably 80 to 170 A · m ² / kg. The coercive force of the metal powder is preferably 119 to 318 kA / m, more preferably 159 to 279 kA / m, and still more preferably 183 to 239 kA / m.

The moisture content of the ferromagnetic metal powder is preferably 0.1 to 2%. It is preferable to optimize the moisture content of the ferromagnetic powder depending on the type of binder. The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 6-12, preferably 7-11. If necessary, the ferromagnetic powder may be surface-treated to form Al, Si, P, or an oxide thereof. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less.

Ferromagnetic metal powder SA (stearic acid) adsorption amount (a measure of the basic points of the surface) is 1~15μmol / ^{m 2,} preferably not 2~10μmol / ^{m 2,} more preferably at 3 to 8 [mu] mol / ^{m 2.} When using a ferromagnetic metal powder having a large amount of stearic acid adsorption, it is preferable to prepare a magnetic recording medium by modifying the surface with an organic substance that strongly adsorbs to the surface.

  The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially absent, if they are 300 ppm or less, they do not particularly affect the characteristics. The ferromagnetic powder used in the present invention preferably has fewer pores, and its value is 20% by volume or less, more preferably 5% by volume or less. As for the shape, any of needle shape, rice grain shape, or spindle shape may be used as long as the above-mentioned characteristics regarding the particle size are satisfied.

The SFD (Switching Field Distribution) of the ferromagnetic powder itself is preferably small, and preferably 0.6 or less. It is necessary to reduce the Hc distribution of the ferromagnetic powder. When the SFD is 0.6 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods such as improving the particle size distribution of getite in the ferromagnetic metal powder, using monodispersed α-Fe ₂ O ₃ , and preventing sintering.

Examples of the carbon black used in the magnetic layer 16 include rubber furnace, rubber thermal, color black, acetylene black, and the like. Specific surface area (SBET) is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, average particle (child) diameter is 5 nm to 300 nm, pH is 2 to 10 and water content is 0.1 to 10% by mass. The tap density is preferably 0.1 to 1 g / ml.

  Specific examples of carbon black include Cabot Corporation, BLACKPEARLS 2000, 1300, 1000, 900, 800, 700, VULCAN XC-72, Asahi Carbon Corporation, # 80, # 60, # 55, # 50, # 35, manufactured by Mitsubishi Chemical Corporation, # 2400B, # 2300, # 900, # 1000 # 30, # 40, # 10B, manufactured by Konlon Beer Carbon, CONDUCTEX SC, RAVEN 150, 50, 40, 15 etc. It is done.

  Carbon black may be surface-treated with a dispersant or the like, or may be grafted with a resin or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed with a binder in advance before being added to the magnetic coating solution. These carbon blacks can be used alone or in combination.

  When carbon black is used, it is preferably used in an amount of 0.1 to 30% by mass with respect to the ferromagnetic powder. The carbon black functions to prevent the magnetic layer 16 from being charged, reduce the coefficient of friction, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention change the kind, amount, and combination in the magnetic layer 16 and the intermediate layer 14, and exhibit the above-mentioned characteristics such as particle size, oil absorption, conductivity, pH, and the like. Of course, it is possible to use properly according to the purpose. The carbon black that can be used in the magnetic layer 16 of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

[Middle layer]
Next, the detailed content regarding the intermediate | middle layer 14 is demonstrated. The inorganic powder used for the intermediate layer 14 is a non-magnetic powder, and may be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. it can.

  Examples of inorganic compounds include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and nitridation with an α conversion rate of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. The

  Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and alpha iron oxide. The particle size of these non-magnetic powders is preferably 0.005 to 0.5 μm, but if necessary, non-magnetic powders with different particle sizes can be combined, or even a single non-magnetic powder can have the same effect by widening the particle size distribution. Can also be given.

  The particle size of the nonmagnetic powder is particularly preferably 0.01 to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is preferably 0.08 μm or less, and when the nonmagnetic powder is an acicular metal oxide, the major axis length is 0.2 μm or less, preferably 0.15 μm or less. More preferably, it is 0.1 μm or less.

  The acicular ratio of the nonmagnetic powder is 2 to 20, preferably 3 to 10. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. The pH of the non-magnetic powder is 2 to 11, and the pH is particularly preferably between 5.5 and 10. Since these have high adsorptivity to functional groups, they are well dispersed and the mechanical strength of the coating film is also high.

The specific surface area of the nonmagnetic powder is 1 to 100 m ² / g, preferably 5 to 80 m ² / g, and more preferably 10 to 70 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 to 1 μm, and more preferably 0.04 to 0.1 μm. The oil absorption using DBP (dibutyl phthalate) is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g.

The specific gravity of the nonmagnetic powder is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedron shape, and a plate shape. The Mohs hardness is preferably 4 or more and 10 or less. The non-magnetic powder SA (stearic acid) adsorption of 1 to 20 [mu] mol / ^{m 2,} preferably not 2 to 15 [mu] mol / ^{m 2,} more preferably at 3 to 8 [mu] mol / ^{m 2.} The pH is preferably between 3-6.

The surface of these non-magnetic powders is preferably surface-treated and Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ are present. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ , but more preferred are Al ₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used depending on the purpose, and after treating with alumina first, the surface layer may be treated with silica, or vice versa. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

  Specific examples of the non-magnetic powder used for the intermediate layer 14 include Showa Denko Nano Tight, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo α-Hematite DPN-250, DPN-250BX, DPN-245. , DPN-270BX, DPN-500BX, DBN-SA1, DBN-SA3, Ishihara Sangyo Titanium oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, α-Hematite E270, E271, E300, E303, Titanium Industry Titanium Oxide STT-4D, STT-30D, STT-30, STT-65C, α-Hematite α-40, Teica MT-100S, MT-100T, MT-150W , MT-500B, MT-600B, MT-100F, MT-500HD Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, and the like Can be mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

  Carbon black is mixed with the intermediate layer 14 to reduce the surface electrical resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. As the type of carbon black, rubber furnace, rubber thermal, color black, acetylene black, and the like can be used.

Mosquito intermediate layer 14 - specific surface area (S BET) of carbon black is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption 20 to 400 ml / 100 g, preferably 30 to 400 ml / 100 g is there. The average particle (child) diameter of carbon black is 5 nm to 80 nm, preferably 10 to 50 nm, more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

  Specific examples of carbon black include BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, Mitsubishi Chemical Corporation # 3050B, # 3150B, # 3250B, # 3750B, manufactured by Cabot Corporation. # 3950B, # 950, # 650B, # 970B, # 850B, MA-600, MA-230, # 4000, # 4010, CONDUCTEX SC, RAVEN 8800, 8000, 7000, 5750, 5250, 3500, manufactured by Conlon Beer Carbon 2100, 2000, 1800, 1500, 1255, 1250, and Ketjen Black EC manufactured by Ketjen Black International.

  Carbon black may be surface-treated with a dispersant or the like, or may be grafted with a resin or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in advance with a binder before being added to the coating solution. These carbon blacks can be used in a range not exceeding 50% by mass and not exceeding 40% of the total mass of the intermediate layer with respect to the inorganic powder. These carbon blacks can be used alone or in combination.

  In addition, an organic powder can be added to the intermediate layer 14 according to the purpose. For example, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment, polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, and polyfluorinated ethylene resin Can be used. As the production method, those described in JP-A Nos. 62-18564 and 60-255827 can be used.

  The binder resin, lubricant, dispersant, additive, solvent, dispersion method, etc. of the intermediate layer 14 can be applied to those of the magnetic layer 16 described below. In particular, with respect to the binder resin amount, type, additive, dispersant addition amount, and type, known techniques relating to the magnetic layer 16 can be applied.

[Back coat layer]
The back coat layer 18 has a number of protrusions having a height of 50 nm or more from the root mean square when the layer is measured with an optical surface roughness meter, of 0.03 / 100 μm ^{2 to} 0.2 / 100 μm ^2. It is preferable that

  In general, a magnetic tape for recording computer data is strongly required to have repeated running characteristics as compared with a video tape and an audio tape. In order to maintain such high running durability, the backcoat layer preferably contains carbon black.

  It is preferable to use a combination of two types of carbon black having different average particle sizes. In this case, it is preferable to use a combination of fine particle carbon black having an average particle size of 10 to 50 nm and coarse particle carbon black having an average particle size of 70 to 300 nm.

  In general, by adding fine carbon black as described above, the surface electrical resistance of the backcoat layer can be set low, and the light transmittance can also be set low. Some magnetic recording devices utilize the light transmittance of the tape and are used for the operation signal. In such a case, the addition of particulate carbon black is particularly effective. In addition, particulate carbon black is generally excellent in retention of liquid lubricants, and contributes to reduction of the friction coefficient when used in combination with lubricants.

  Specific products of the particulate carbon black include the following. RAVEN2000B (18nm), RAVEN1500B (17nm) (above, Columbia Carbon Co., Ltd.), BP800 (17nm) (Cabot Corp.), PRINTEX90 (14nm), PRINTEX95 (15nm), PRINTEX85 (16nm), PRINTEX75 (17nm) (above, Degussa), # 3950 (16 nm) (Mitsubishi Chemical Corporation), Asahi # 51 (Asahi Carbon Co.) (38 nm).

  Examples of specific products of coarse particle carbon black include Regal 99 (Cabot) (100 nm), Thermal Black (270 nm) (Kerncarb), RAVEN MTP (275 nm) (Columbia Carbon). Can do.

  When two types of back coat layers 18 having different average particle sizes are used, the content ratio (mass ratio) of fine particle carbon black of 10 to 50 nm and coarse particle carbon black of 70 to 300 nm is the former / the latter. = 1/100 to 1/1, more preferably 1/20 (5/100) to 1/2 (50/100).

  The content of carbon black in the back coat layer 18 (the total amount when two types are used) is usually in the range of 30 to 100 parts by mass with respect to 100 parts by mass of the binder, preferably It is the range of 45-95 mass parts.

  An inorganic powder can be used for the back coat layer 18. It is preferable to use two types of inorganic powders having different hardnesses. Specifically, it is preferable to use a soft inorganic powder having a Mohs hardness of 3 to 4.5 and a hard inorganic powder having a Mohs hardness of 5 to 9. By adding a soft inorganic powder having a Mohs hardness of 3 to 4.5, the friction coefficient can be stabilized by repeated running. Moreover, when the hardness is within this range, the sliding guide pole is not scraped. The average particle size of the inorganic powder is preferably in the range of 30 to 50 nm.

  Examples of the soft inorganic powder having a Mohs hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more. Among these, calcium carbonate is particularly preferable.

  The content of the soft inorganic powder in the back coat layer 18 is preferably in the range of 0 to 140 parts by mass, more preferably 0 to 100 parts by mass with respect to 100 parts by mass of the carbon black.

  By adding a hard inorganic powder having a Mohs hardness of 5 to 9, the strength of the backcoat layer 18 is enhanced and the running durability is improved. When these inorganic powders are used together with carbon black or the soft inorganic powder, there is little deterioration even with repeated sliding, and a strong back coat layer 18 is obtained. In addition, the addition of the inorganic powder provides an appropriate polishing force and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with a soft inorganic powder (especially calcium carbonate), the sliding characteristics with respect to the guide pole having a rough surface can be improved, and the friction coefficient of the backcoat layer can be stabilized.

The hard inorganic powder preferably has an average particle size in the range of 80 to 250 nm (more preferably, 100 to 210 nm). Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Among these, α-iron oxide or α-alumina is preferable. Content of hard inorganic powder is 0-30 mass parts normally with respect to 100 mass parts of carbon black, Preferably, it is 0-20 mass parts.

  When the soft inorganic powder and the hard inorganic powder are used in combination in the back coat layer 18, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, particularly 3 or more. It is preferable to select and use a soft inorganic powder and a hard inorganic powder.

  The backcoat layer 18 preferably contains two types of inorganic powders each having a specific average particle size and different Mohs hardness and two types of carbon blacks having different average particle sizes. In particular, in this combination, it is preferable that calcium carbonate is contained as the soft inorganic powder.

  The back coat layer 18 can contain a lubricant. The lubricant can be appropriately selected from the lubricants listed as the lubricant that can be used for the intermediate layer 14 or the magnetic layer 16 described above. In the backcoat layer 18, the lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder.

[Other materials used in the manufacture of magnetic recording media]
Next, other materials used for manufacturing the magnetic recording medium 10 will be described.

  The binder, lubricant, dispersant, additive, solvent, dispersion method, etc. of the magnetic layer 16, the intermediate layer 14, and the back coat layer 18 are commonly applied to the magnetic layer 16, the intermediate layer 14, and the back coat layer 18, respectively. it can. In particular, with respect to the binder amount, type, additive, dispersant addition amount and type, known techniques relating to the magnetic layer 16 can be applied.

  As the binder, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a polymerization degree of about 50 to 1,000. It is.

  Examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetate. There are polymers or copolymers containing polyurethane, vinyl ether, etc. as structural units, polyurethane resins, and various rubber resins.

  Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamides. Examples thereof include a resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate.

  These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219.

  The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer, A combination of at least one selected from the group consisting of a polyurethane resin and a combination of these with a polyisocyanate may be mentioned.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and _{durability, -COOM, -SO 3 M, -OSO} 3 M, -P = O (OM) 2, - O—P═O (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), —OH, —NR ₂ , —N ₊ R ₃ (R is a hydrocarbon group), an epoxy group, —SH, It is preferable to use one in which at least one polar group selected from —CN, etc. is introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.

  Specific examples of these binders include VAGH, VYHH, VMCH, VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG, PKHH, PKHJ, PKHC, PKFE, Nissin Chemical Industry Co., Ltd. Manufactured, MPR-TA, MPR-TA5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM, MPR-TAO, manufactured by Denki Kagaku 1000W, DX80, DX81, DX82, DX83, 100FD, MR-104, MR-105, MR110, MR100, MR555, 400X-110A manufactured by Nippon Zeon Co., Ltd. Nipponran N2301, N2302, N2304 manufactured by Nippon Polyurethane Co., Ltd. Pandex T-5105, T-R3080 manufactured by Dainippon Ink, Inc. 5201, Barnock D- 00, D-210-80, Crisbon 6109, 7209, Byron UR8200, UR8300, UR-8700, RV530, RV280, manufactured by Toyobo Co., Ltd., Daiichi Seika Co., Ltd. Examples include Mitsubishi Chemical Co., Ltd., MX5004, Sanyo Chemical Co., Ltd. Samplen SP-150, Asahi Kasei Co., Ltd. Saran F310, F210, and the like.

  In the present invention, the binder used for the intermediate layer 14 and the magnetic layer 16 is used in the range of 5 to 50%, preferably in the range of 10 to 30% with respect to the nonmagnetic powder or the magnetic powder. It is preferable to use a combination of 5 to 30% when using a vinyl chloride resin, 2 to 20% when using a polyurethane resin, and 2 to 20% of a polyisocyanate. When head corrosion occurs due to dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate.

When polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 ° C. to 100 ° C., the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10 kgf / mm ² (≈0.49). ~ 98 MPa), and the yield point is preferably 0.05 to 10 kgf / mm ² (≈0.49 to 98 MPa).

  The magnetic recording medium 10 of the present invention consists of two or more layers. Accordingly, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming the magnetic layer 16, the amount of polar groups, or the above-mentioned Of course, it is possible to change the physical characteristics of the resin between the intermediate layer 14 and the magnetic layer 16 as necessary, and rather, it should be optimized in each layer, and a known technique relating to a multilayer magnetic layer can be applied. For example, when the binder amount is changed in each layer, it is effective to increase the binder amount of the magnetic layer 16 in order to reduce scratches on the surface of the magnetic layer, and in order to improve the head touch to the head, the intermediate layer The amount of the binder of 14 can be increased to give flexibility.

  Examples of the polyisocyanate used include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene-1,5-diisocyanate. , O-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and the like, products of these isocyanates and polyalcohols, Polyisocyanate produced by condensation of isocyanates can be used.

  Commercially available product names of these isocyanates include: Nippon Polyurethane, Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Made, Takenet D-102, Takenet D-110N, Takenet D-200, Takenet D-202, manufactured by Sumika Bayer, Death Module L, Death Module IL, Death Module N , Desmodur HL, etc., and these can be used for each layer alone or in combination of two or more utilizing the difference in curing reactivity.

  The abrasive used is α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide having an α conversion rate of 90% or more, Known materials having a Mohs hardness of 6 or more, such as titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination.

Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% by mass or more. The tap density is preferably 0.3 to ² g / ml, the water content is 0.1 to 5% by mass, the pH is 2 to 11, and the specific surface area (SBET) is preferably 1 to 30 m ² / g.

  The shape of the abrasive used may be any of a needle shape, a spherical shape, and a dice shape, but those having a corner in a part of the shape are preferable because of high polishing properties. Specific examples of the abrasive used include AKP-20, AKP-30, AKP-50, HIT-50, HIT-55, HIT-60A, HIT-70, HIT-100, Japan, manufactured by Sumitomo Chemical Co., Ltd. Chemical industry company make, G5, G7, S-1, Toda Kogyo company make, TF-100, TF-140 etc. are mentioned. Of course, it is possible to change the type, amount and combination of the abrasive in the magnetic layer 16 and the intermediate layer 14 and use them properly according to the purpose. These abrasives may be added to the magnetic coating solution after being previously dispersed with a binder.

  As the additive, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like can be used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, fluorinated graphite, silicone oil, silicone with polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Polyolefin, polyglycol, alkyl phosphate ester and alkali metal salt thereof, alkyl sulfate ester and alkali metal salt thereof, polyphenyl ether, fluorine-containing alkyl sulfate ester and alkali metal salt thereof, monobasic fatty acid having 10 to 24 carbon atoms ( May contain an unsaturated bond or may be branched) and a metal salt thereof (Li, Na, K, Cu, etc.) or a monovalent, divalent, or trivalent carbon having 12 to 22 carbon atoms, Tetravalent, pentavalent, hexavalent alcohol (may contain unsaturated bonds or branched), carbon number Alkoxy alcohol having 2 to 22 carbon atoms, monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or branched), and monovalent, divalent or trivalent carbon atoms having 2 to 12 carbon atoms Monofatty acid ester or difatty acid ester or trifatty acid ester comprising any one of monovalent, tetravalent, pentavalent and hexavalent alcohols (which may contain an unsaturated bond or may be branched), A monoalkyl ether fatty acid ester of an alkylene oxide polymer, a fatty acid amide having 8 to 22 carbon atoms, an aliphatic amine having 8 to 22 carbon atoms, and the like can be used.

  Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate. Octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol.

  Nonionic surfactants such as alkylene oxide, glycerin, glycidyl, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, phosphonium Or cationic surfactants such as sulfoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group, amino acids, aminosulfonic acids, amino alcohol Also usable are amphoteric surfactants such as sulfuric acid or phosphoric acid esters, alkylbedine type, and the like.

  These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposed products, and oxides in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

  These lubricants and surfactants to be used can be used properly in the intermediate layer 14 and the magnetic upper layer according to necessity and amount. For example, the intermediate layer 14 and the magnetic upper layer use fatty acids having different melting points to control the bleeding to the surface, use esters having different boiling points and polarities to control the bleeding to the surface, and adjust the amount of the surfactant. In this case, it is conceivable to improve the stability of coating and increase the lubricating effect by increasing the additive amount of the lubricant in the intermediate layer. Of course, it is not limited to the examples shown here. Further, all or a part of the additives used in the present invention may be added in any step of the magnetic coating liquid production. For example, when mixed with the ferromagnetic powder before the kneading step, the additive is combined with the ferromagnetic powder. When adding in a kneading step with an agent and a solvent, adding in a dispersing step, adding after dispersing, adding in just before coating, and the like. Further, after the magnetic layer 16 is applied according to the purpose, the purpose may be achieved by applying a part or all of the additive by simultaneous or sequential application. Further, depending on the purpose, a lubricant can be applied to the surface of the magnetic layer after calendering or after completion of the slit.

  As examples of products of these lubricants used, NAA-102, NAA-415, NAA-312, NAA-160, NAA-180, NAA-174, NAA-175, NAA-222, NAA manufactured by NOF Corporation -34, NAA-35, NAA-171, NAA-122, NAA-142, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB Nimine L-201, Nimine L-202, Nimine S-202, Nonion E-208, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS- 210, Nonion HS-206, Nonion L-2, Nonion S-2, Nonion S-4, Nonion O- , Nonion LP-20R, Nonion PP-40R, Nonion SP-60R, Nonion OP-80R, Nonion OP-85R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-60, Anon BF, Anon LG, Butyl stearate, Butyl laurate, Erucic acid, Manufactured by Kanto Chemical Co., Ltd., Oleic acid, Takemoto Yushi Co., Ltd., FAL-205, FAL-123, Shin Nippon Rika Co., Ltd. -E4030, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-96, KF-96L, KF96H, KF410, KF420, KF965, KF54, KF50, KF56, KF907, KF851, X-22-819, X-22-822, KF905, KF700, KF393, KF 857, KF-860, KF-865, X-22-980, KF-101, KF-102, KF-103, X-22-3710, X-22-3715, KF-910, KF-3935, Lion Corporation Manufactured, Armide P, Armide C, Amoslip CP, Lion Oil & Fats, Duomin TDO, Nisshin Oillio, BA-41G, Sanyo Chemical, Profan 2012E, New Pole PE61 , Ionette MS-400, Ionet MO-200 Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionette DO-200, and the like.

  The organic solvent used can be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol. Alcohol, isopropyl alcohol, methylcyclohexanol, etc., esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether , Glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene Chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N, N- dimethylformamide, those hexane and the like can be used.

  These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

  The organic solvent is preferably the same type in the magnetic layer 16 and the intermediate layer 14. The amount added may be changed. A high surface tension solvent (cyclohexanone, dioxane, etc.) is used for the intermediate layer 14 to improve the coating stability. Specifically, the arithmetic average value of the solvent composition of the magnetic layer 16 is the arithmetic average value of the solvent composition of the intermediate layer 14. It is important not to fall below.

  In order to improve dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition. The dissolution parameter is preferably 8-11.

[Method of manufacturing magnetic recording medium]
The magnetic recording medium of the present invention can be produced by applying and drying a coating solution for forming each layer. The process for producing the coating liquid comprises at least a kneading process, a dispersing process, and a mixing process provided as necessary before and after these processes. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

  In order to manufacture the magnetic recording medium of the present invention, it can of course be used as a part of the conventional known manufacturing technique, but the kneading process is strong such as continuous or pressure kneader. By using a material having a kneading force, a magnetic recording medium having a high residual magnetic flux density (Br) can be obtained. When using a continuous kneader or a pressure kneader, all or a part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferred) and 15 to 500 parts by weight with respect to 100 parts by mass of the ferromagnetic powder. The kneading process is performed in the range of parts by mass.

  Details of these kneading treatments are described in JP-A-1-106338 and JP-A-64-79274. Moreover, when adjusting the coating liquid for the intermediate | middle layer 14, it is desirable to use the dispersion medium of high specific gravity, and a zirconia bead is suitable.

  A coating solution for forming the intermediate layer 14 containing nonmagnetic powder and a binder on the nonmagnetic flexible support 12 and a coating solution for forming the magnetic layer 16 containing ferromagnetic powder and a binder are intermediately used. The magnetic layer 16 is formed on the layer 14 so that the magnetic layer 16 is formed on the support 12 simultaneously or sequentially (so-called wet-on-wet coating), and the smoothing process and the magnetic field are applied while the coating layer is in a wet state. A method of performing orientation can be used.

  Examples of the apparatus and method for applying the magnetic recording medium having the multilayer structure as described above include the following methods and apparatuses.

  1) First, the intermediate layer 14 is applied by a gravure coating, roll coating, blade coating, extrusion coating apparatus or the like generally used in the application of the magnetic coating solution, and the intermediate layer 14 is in a wet state. The upper layer is applied by a support pressure type extrusion coating apparatus disclosed in Japanese Patent No. 46186, Japanese Patent Laid-Open No. 60-238179, and Japanese Patent Laid-Open No. 2-265672.

  2) The upper and lower layers are formed by a single coating head having two slits through which coating liquid passes, as disclosed in JP-A-63-88080, JP-A-2-17971, and JP-A-2-265672. Are applied almost simultaneously.

  3) The upper and lower layers are applied almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

  In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of the magnetic particles, the inside of the coating head is formed by a method as disclosed in Japanese Patent Application Laid-Open Nos. 62-95174 and 1-2236968. It is desirable to apply shear to the coating solution. Furthermore, it is appropriate for the viscosity of the coating solution to satisfy the numerical range disclosed in JP-A-3-8471.

  Further, the smoothing treatment can be performed, for example, by applying a stainless steel plate to the surface of the coating layer on the support 12, but in addition to this, a method using a solid smoother as described in JP-B-60-57387. , A method of scraping and measuring the coating liquid with a rod that is stationary or rotating in the direction opposite to the traveling direction of the support 12, a method of smoothing the surface of the coating liquid film by bringing a flexible sheet into surface contact, etc. Can also be adopted.

  For magnetic field orientation, it is preferable to use a solenoid of 1000G or more and a cobalt magnet of 2000G or more in the same polarity. In addition, when the present invention is applied as a disk medium, an orientation method that randomizes the orientation is necessary.

  Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyimide amide or the like can be used as a calendering roll. Moreover, it can also process with a metal roll. The treatment temperature is preferably 30 ° C or higher, more preferably 35 ° C or higher and 100 ° C or lower. The linear pressure is preferably 200 kgf / cm, more preferably 300 kgf / cm or more.

The friction coefficient with respect to SUS420J on the magnetic layer surface and the opposite surface of the magnetic recording medium of the present invention is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq. The elastic modulus at 0.5% elongation of the layer 16 is preferably 100 to 2000 kgf / mm ² (≈0.98 to 19.6 GPa) in both the running direction and the width direction, and the breaking strength is preferably 1 to 30 kgf / cm ² ( ≈0.098 to 2.94 MPa), the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kgf / mm ² (≈0.98 to 14.7 GPa) in both the running direction and the width direction, and the residual elongation is preferably 0.5. %, And the thermal shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. It is appropriate.

  The glass transition temperature of the magnetic layer 16 (the maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 50 ° C. or more and 120 ° C. or less, and that of the intermediate layer 14 is 0 ° C. to 100 ° C. preferable. The loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur.

The residual solvent contained in the magnetic layer 16 is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity of the magnetic layer 16 is preferably 30% by volume or less, more preferably 20% by volume or less for both the intermediate layer 14 and the magnetic layer 16. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example, in a data recording magnetic recording medium in which repetitive usage is important, a larger porosity is often preferable for running durability.

  When the magnetic properties of the magnetic recording medium 10 of the present invention are measured with a magnetic field of 398 kA / m (5 KOe), the squareness ratio in the tape running direction is 0.70 or more, preferably 0.80 or more, more preferably 0.8. It is suitable that it is 90 or more.

  The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD (Switching Field Distribution) of the magnetic layer 16 is preferably 0.6 or less.

  Although the magnetic recording medium 10 of the present invention has the intermediate layer 14 and the upper magnetic layer 16, it is easily estimated that these physical characteristics can be changed by the intermediate layer 14 and the magnetic layer 16 depending on the purpose. . For example, the elastic modulus of the magnetic layer 16 is increased to improve running durability, and the elastic modulus of the intermediate layer 14 is made lower than that of the magnetic layer 16 to improve the contact of the magnetic recording medium 10 with the head.

  When two or more magnetic layers 16 are used, it is possible to refer to a known technique related to the magnetic layer multilayer to determine what physical characteristics are brought to each of these magnetic layers. For example, there are many inventions such as Japanese Patent Publication No. 37-2218, Japanese Patent Application Laid-Open No. 58-56228, etc. that make Hc of the upper magnetic layer higher than Hc of the intermediate layer 14. By making 16 a thin layer, recording is possible even with a magnetic layer 16 having a higher Hc.

  As mentioned above, although the example of embodiment of the magnetic recording medium which concerns on this invention, and its manufacturing method was demonstrated, this invention is not limited to the example of the said embodiment, Various aspects can be taken.

  Hereinafter, the present invention will be specifically described by way of examples. It will be readily understood by those skilled in the art that the components, ratios, operation order, and the like shown here can be changed without departing from the spirit of the present invention.

  Accordingly, the present invention should not be limited to the following examples. In addition, the part in an Example shows a weight part.

[Components of coating solution for magnetic layer]
Ferromagnetic metal powder Composition: Fe / Co = 100/30 (atomic ratio) 100 parts Hc: 189.600 kA / m (2400 Oe)
Specific surface area by BET method 70m ² / g
Average long axis length: 60 nm
Crystallite size: 13 nm (130 cm)
Saturation magnetization σs: 125 A · m ² / kg (125 emu / g)
Surface treatment agent: Al ₂ O ₃ , Y ₂ O ₃
Vinyl chloride copolymer (manufactured by Nippon Zeon Co., Ltd., MR-110) 12 parts -SO ₃ Na content: 5 × 10 ^-6 eq / g), degree of polymerization: 350
Epoxy group (3.5% by weight in monomer units)
Polyester polyurethane resin 3 parts
UR-8200, manufactured by Toyobo
α-alumina (average particle size: 0.1 μm) 5 parts carbon black (average particle size: 0.08 μm) 0.5 parts stearic acid 2 parts methyl ethyl ketone 90 parts cyclohexanone 30 parts toluene 60 parts [of intermediate layer coating solution component]
Nonmagnetic powder αFe ₂ O ₃ hematite 80 parts Long axis length: 0.15 μm
Specific surface area of 110 m ² / g by BET method
pH: 9.3
Tap density: 0.98
Surface treatment agent: Al ₂ O ₃ , SiO ₂
Carbon black (Mitsubishi Carbon Co., Ltd.) 20 parts Average primary particle size: 16 nm
DBP oil absorption: 80ml / 100g
pH: 8.0
Specific surface area by BET method 250m ² / g
Volatile content: 1.5%
12 parts vinyl chloride copolymer MR-110 manufactured by Nippon Zeon
Polyester polyurethane resin 12 parts Toyobo, UR-8200
Stearic acid 2 parts Methyl ethyl ketone 150 parts Cyclohexanone 50 parts Toluene 50 parts Each component forming the upper layer (magnetic layer) or lower layer (intermediate layer) was kneaded with a kneader and then dispersed using a sand mill. 1.6 parts by weight of secondary butyl stearate (sec-BS) is added to the obtained dispersion for the upper layer, and 3 parts of the polyisocyanate (manufactured by Nippon Polyurethane Co., Ltd., trade name: Coronate L) is added to the lower layer dispersion. 40 parts of a methyl ethyl ketone / cyclohexanone mixed solution was added to each dispersion, followed by filtration using a filter having an average pore diameter of 1 μm to prepare an upper layer forming coating solution and a lower layer forming coating solution, respectively.

[Components of coating solution for back layer]
Particulate carbon black 100 parts Average particle size: 20 nm
Coarse particle carbon black 10 parts Average particle size: 270 nm
Nitrocellulose resin 100 parts Polyester polyurethane resin 30 parts Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts α-Al ₂ O ₃ 0.5 parts Average particle size 0.13 μm
The above components were kneaded with a continuous kneader and then dispersed for 2 hours using a sand mill. After adding 40 parts of polyisocyanate (trade name: Coronate L 1 manufactured by Nippon Polyurethane Co., Ltd.) and 1000 parts of methyl ethyl ketone, the obtained dispersion was filtered using a filter having an average pore diameter of 1 μm to form a coating solution for forming a back layer. Was prepared.

[Method for Producing Magnetic Tape (Examples 1-4, Comparative Examples 1-4)]
A 6 μm thick PEN (polyethylene naphthalate) nonmagnetic support (Tg: 120 ° C.) was heat-treated at 110 ° C. for 1 day in a heat treatment chamber. After the heat treatment, it is cooled to room temperature, and then the upper layer forming coating solution and the lower layer forming coating solution are dried on the support so that the thickness of the lower layer (intermediate layer) is 1.3 μm. A simultaneous multilayer coating was performed so that the thickness of the magnetic layer after drying was 0.2 μm.

  Next, while both layers were still wet, orientation treatment was performed using a cobalt magnet having a magnetic flux density of 3000 gauss and a solenoid having a magnetic flux density of 1500 gauss. Then, the nonmagnetic intermediate layer and the magnetic layer were formed by drying at a temperature not exceeding the Tg of the support.

  Thereafter, the back layer-forming coating solution is applied to the other side of the support so that the thickness after drying is 0.5 μm, and dried at a temperature not exceeding the Tg of the support to provide a back layer. Thus, a magnetic recording laminate roll having a lower layer (intermediate layer) and a magnetic layer on one side of the support and a back layer on the other side was obtained.

  The obtained magnetic recording laminate roll was passed through a seven-stage calendering machine (temperature 90 ° C., speed 300 m / min) composed of a heated metal roller and an elastic roller coated with a thermosetting resin on a core metal. Calendar processing was performed. Next, the magnetic recording product roll after the calendar process was slit to 12.7 mm (0.5 inch width) to obtain a magnetic tape. This is the sample of Example 1.

[Example 2]
In Example 1, the heat treatment of the support was set at 115 ° C. for 2 days. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Example 3]
In Example 1, the heat treatment of the support was set at 110 ° C. for 4 days. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Example 4]
In Example 1, the heat treatment of the support was set at 90 ° C. for 7 days. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Comparative Example 1]
In Example 1, the support was not heat-treated. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Comparative Example 2]
In Example 1, the heat treatment of the support was set at 60 ° C. for 4 days. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Comparative Example 3]
In Example 1, the heat treatment of the support was set at 65 ° C. for 4 days. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Comparative Example 4]
In Example 1, the drying temperature of the coating film was set to a temperature exceeding the Tg of the support. A magnetic tape was prepared in the same manner as in Example 1 except for the above conditions.

[Evaluation 1: Measurement of loss modulus E ₂ ]
A sample having a length of 10 mm and a width of 3.35 mm was cut out from the longitudinal direction of the magnetic tape to obtain a magnetic tape sample. Further, the upper and lower layers and the back layer were removed from the magnetic tape using a solvent, and only the support was taken out. A sample having a length of 110 mm and a width of 3.35 mm was cut out from the longitudinal direction of the support and used as a sample for measurement.

The loss modulus _{E 2} of the dynamic viscoelasticity measurement at a frequency 0.5 Hz, manufactured by Seiko Instruments Inc. of the measuring station (model number: EXSTAR6000) connected to the company manufactured a dynamic viscoelasticity measuring device (model number: DMS6100) a The temperature was measured between 15 ° C. and 200 ° C., and the loss modulus E ₂ at 130 ° C. was read.

[Evaluation 2: Measurement of creep deformation]
A sample having a length of 15 mm and a width of 5 mm was cut out from the longitudinal direction of the magnetic tape. The amount of creep deformation was measured using a testing machine (model number: TM-9300) manufactured by ULVAC-RIKO. The measurement temperature was 50 ° C. The stress was applied in two stages, a first step of 0.6 MPa for 30 minutes and a second step of 15.7 MPa for 50 hours. Using the sample length loaded with the stress of 15.7 MPa as the initial sample length, the sample elongation (percentage) after the second step 50 hours was calculated and used as the creep amount. A creep amount of 0.10% or less was judged good.

[Evaluation results of Examples and Comparative Examples]
The evaluation results of Examples 1 to 4 and Comparative Examples 1 to 4 are summarized in the table of FIG.

Loss modulus _{E 2} of the magnetic tapes of Examples 1 to 4 (the magnetic recording medium 10) was 0.20～0.34GPa. Furthermore, loss modulus _{E 2} of the support 12 of Examples 1 to 4 was 0.16～0.32GPa. And the amount of creep deformation was in the range of 0.03 to 0.10%, and all showed good results.

On the other hand, the loss modulus _{E 2} of the magnetic tapes of Comparative Examples 1 to 4 (the magnetic recording medium 10) was 0.40～0.44GPa. Furthermore, loss modulus _{E 2} of the support 12 of Comparative Examples 1 to 4 was 0.38～0.40GPa. And the amount of creep deformation was in the range of 0.25 to 0.40%, and all showed poor results.

  From the above results, according to the present invention, it was confirmed that the dimensional stability of the tape was improved, and as a result, the reliability at the time of data recording / reproduction could be improved.

Partial expanded sectional view explaining the layer structure of the magnetic recording medium according to the present invention Table showing evaluation results of Examples and Comparative Examples

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Magnetic recording medium, 12 ... Support body, 14 ... Intermediate | middle layer, 16 ... Magnetic layer, 18 ... Backcoat layer

Claims (4)

In a magnetic recording medium comprising one or more magnetic layers on a nonmagnetic support,
A magnetic recording medium, wherein the magnetic recording medium has a loss elastic modulus of 0.5 Hz at a temperature of 130 ° C. of 0.18 to 0.39 GPa. In a magnetic recording medium comprising one or more magnetic layers on a nonmagnetic support,
A magnetic recording medium, wherein the nonmagnetic support is made of polyethylene naphthalate, and the nonmagnetic support has a 0.5 Hz loss elastic modulus at a temperature of 130 ° C. of 0.15 to 0.37 GPa.   The magnetic recording medium according to claim 1, wherein a magnetic or nonmagnetic intermediate layer is provided between the nonmagnetic support and the magnetic layer. In a method of manufacturing a magnetic recording medium, in which one or more magnetic layers and / or nonmagnetic layers are formed on a nonmagnetic support,
Before forming the magnetic layer and / or nonmagnetic layer, the nonmagnetic support is heat-treated at a temperature 1 to 25 ° C. lower than the glass transition temperature Tg of the support,
A method for producing a magnetic recording medium, characterized in that a heat treatment temperature applied to the support in a subsequent production process is maintained below the glass transition temperature Tg of the support.

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