JP2006053974A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium wherein the rigidity of a magnetic tape can be secured even if the magnetic tape is made thin and which has satisfactory electromagnetic transducing characteristics and running stability and can correspond to high recording density. <P>SOLUTION: In the magnetic recording medium formed by providing a magnetic layer containing magnetic powder and a binder resin on at least one surface of a non-magnetic substrate, the non-magnetic substrate is composed essentially of a polyester obtained by performing an esterification reaction of an aromatic dicarboxylic acid having at least three aromatic rings and a diol. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder resin is provided on at least one surface of a nonmagnetic support, and more particularly to an improvement of a nonmagnetic support that is one of its constituent elements. .

  Magnetic recording media have a variety of uses such as audio tapes, video tapes, computer tapes, and magnetic disks. Especially in the field of data backup tapes, the number of magnetic recording media per volume increases as the capacity of hard disks to be backed up increases. Magnetic tapes having a recording capacity of 100 GB or more 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 order to increase the capacity of data that can be recorded on the magnetic tape, (1) a higher recording density in the longitudinal direction of the tape by shortening the recording wavelength, and (2) an increase in the number of data tracks by narrowing the data track, That is, a high recording density in the width direction of the tape, and (3) a high recording density in the thickness direction of the tape by reducing the total thickness of the magnetic tape are being promoted. As a result, the capacity has been increased.

  Among these, the reduction in the total thickness of the magnetic tape (3) is problematic due to a decrease in electromagnetic conversion characteristics and a decrease in running stability due to poor contact with the magnetic head accompanying a decrease in the rigidity of the magnetic tape. ing.

  In order to solve such a problem, studies have been vigorously conducted on a nonmagnetic support that is a dominant factor in securing the rigidity of a magnetic tape. In these studies, polyesters such as polyethylene terephthalate and polyethylene naphthalate, aromatic polyamides, and the like have been proposed as preferred nonmagnetic supports.

  However, with the trend toward higher recording density of magnetic tapes, there is a tendency for non-magnetic supports to become thinner in the future. As a result, even if non-magnetic supports made of the above materials are used, electromagnetic In some cases, conversion characteristics and running stability become insufficient. Therefore, in order to cope with such a problem, the Young's modulus of the nonmagnetic support is increased by providing a reinforcing layer made of a metal, a semimetal, a metal oxide, an inorganic substance, or the like on at least one surface of the nonmagnetic support. It has been proposed to increase the size (for example, Patent Documents 1 to 3).

JP-A-7-272247 JP 11-339251 A JP 2000-11376 A

  However, in a magnetic recording medium in which a layer made of metal, semimetal, metal oxide, inorganic material, etc. is provided on at least one surface of the nonmagnetic support as described above, the processing efficiency is low and the productivity is not increased. There is a problem that becomes high. Further, there is a problem that the performance as a magnetic recording medium is deteriorated when the metal constituting the layer is corroded.

  The present invention has been made in view of such circumstances. The purpose of the present invention is to ensure the rigidity of a magnetic tape even when it is thinned, and to provide a magnetic material suitable for high recording density with good electromagnetic conversion characteristics and running stability. It is to provide a recording medium.

  In order to solve the above problems, the present invention provides a magnetic recording medium having a magnetic layer containing magnetic powder and a binder resin on at least one surface of a nonmagnetic support, wherein the nonmagnetic support has an aromatic ring. The main component is polyester obtained by esterifying at least three aromatic dicarboxylic acids and diols.

  According to the magnetic recording medium of the present invention, since the aromaticity of the polyester, which is the main component of the nonmagnetic support, is large, the Young's modulus of the nonmagnetic support has been used in conventional magnetic recording media. Compared to Accordingly, the rigidity of the entire magnetic recording medium is improved, and a magnetic recording medium having good electromagnetic conversion characteristics and running stability can be obtained.

  The non-magnetic support used in the magnetic recording medium of the present invention is mainly composed of a polyester obtained by esterifying an aromatic dicarboxylic acid having at least three aromatic rings and a diol.

  The diol is preferably an aliphatic diol. The reason why the aliphatic diol is preferable is that if the film formability is good, the raw material is easily available and the cost is low. Examples of such aliphatic diols include polymethylene glycols having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, etc. Furthermore, alicyclic diols such as aliphatic cyclohexanedimethanol can be exemplified.

  The reason why the aromatic dicarboxylic acid has “at least three aromatic rings” is that if the number of aromatic rings is two or less, the required high Young's modulus cannot be obtained in the polyester which is a reaction product. Examples of the aromatic dicarboxylic acid having at least three aromatic rings include anthracene dicarboxylic acid, naphthacene dicarboxylic acid, pentacene dicarboxylic acid, and hexacene dicarboxylic acid. The positions of the carboxyl groups of these aromatic dicarboxylic acids are preferably at both ends in the arrangement direction of the aromatic ring. For example, in the case of anthracene dicarboxylic acid, 2,7-anthracene dicarboxylic acid may be naphthacene dicarboxylic acid. 2,8-naphthacene dicarboxylic acid is preferred. The presence of the carboxyl group at the above position is preferable because the orientation of the molecular chain is increased and the Young's modulus of the resulting polyester is increased. As the number of aromatic rings of the aromatic dicarboxylic acid increases, the aromaticity of the resulting polyester material increases and the Young's modulus increases, which is preferable, but it is difficult to obtain the raw material aromatic dicarboxylic acid, and the cost In general, the upper limit for practical use is 5 because the film-forming property may be lowered or the film-forming property may be lowered when the film is processed into a nonmagnetic support after film-forming. Therefore, considering these circumstances comprehensively, the number of aromatic rings in the aromatic dicarboxylic acid is preferably 3 to 5.

  If necessary, other aromatic dicarboxylic acids such as terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, etc. are used in combination. However, it is preferable that 80 mol% or more of the total dicarboxylic acid component is an aromatic dicarboxylic acid having at least three aromatic rings, and 80 mol% or more of the total diol component is a copolymer of ethylene glycol. . When the ratio of the aromatic dicarboxylic acid having at least three aromatic rings is less than 80 mol% of the total dicarboxylic acid component, or the ratio of ethylene glycol is less than 80 mol% of the total diol component, the required Young's modulus This is because the film cannot be obtained or the film formability is deteriorated.

  Within the range satisfying the above-mentioned constitution ratio, as the dicarboxylic acid, for example, an aliphatic dicarboxylic acid such as adipic acid or sebacic acid; an alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid or the like is included. Also good. In addition, within the range satisfying the above-described composition ratio, the diol may be an aromatic diol such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane, or the like; a fragrance such as 1,4-dihydroxydimethylbenzene. An aliphatic diol having a ring; polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like may be included.

  The nonmagnetic support used in the present invention preferably contains lubricant particles having an average particle diameter of 0.03 to 1.6 μm from the viewpoint of ensuring good electromagnetic conversion characteristics and running durability. If the average particle size of the lubricant particles is smaller than 0.03 μm, the effect of improving the running durability may be insufficient. If the average particle size is larger than 1.6 μm, the electromagnetic conversion characteristics may be deteriorated or the dropout may increase. It is because there is a possibility of doing. Depending on the application of the magnetic recording medium, it is preferable to include a plurality of types of lubricant particles having different particle sizes within the above range. This is because inclusion of plural types of lubricant particles makes it possible to control the height and number of protrusions on the surface of the nonmagnetic support.

Examples of the lubricant particles include silicon dioxide (including hydrates, silica sand, quartz and the like), various crystal forms of alumina, and silicates containing 30 wt% or more of SiO ₂ (for example, amorphous or Crystalline clay minerals, aluminosilicates (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc., oxides of Mg, Zn, Zr, and Ti, sulfates of Ca and Ba, Li , Ba, and Ca phosphates (including monohydrogen and dihydrogen salts), Li, Na, and K benzoates, Ca, Ba, Zn, and Mn terephthalates, Mg, Ca, Ba Zn, Cd, Pb, Sr, Mn, Fe, Co, and Ni titanates, Ba and Pb chromates, carbon (eg, carbon black, graphite, etc.), glass (eg, glass powder, glass beads, etc.) ), Ca, and Mg carbonates, fluorite, ZnS, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked polystyrene particles, crosslinked polyester particles, Teflon particles, polyimide particles, and the like. Among these, crosslinked silicone particles, calcium carbonate, and alumina are preferable. It is preferable to control the height and number of protrusions on the surface of the non-magnetic support by combining a plurality of types of lubricant particles having different average particle diameters depending on the application, from the viewpoint of improving running performance and electromagnetic conversion characteristics. For example, in a nonmagnetic support, 0.0005 to 0.008% by weight of crosslinked silicone particles having an average particle size of 0.8 to 1.6 μm and calcium carbonate having an average particle size of 0.3 to 0.8 μm. It is preferable to add 0.05 to 1.0% by weight of alumina having 0.05 to 0.6% by weight and an average particle size of 0.03 to 0.3 μm because the above characteristics are improved.

  In the present invention, the nonmagnetic support may be composed of a single layer or a plurality of layers. In the case of two layers, the type and amount of lubricant particles contained in each layer can be changed according to the use of the magnetic recording medium. For example, in the case of a non-magnetic support for magnetic tape, the type and amount of lubricant particles are changed on the side where the magnetic layer is provided and on the opposite side. The surface on the opposite side is made larger and the particles on the opposite side are made larger, and the amount added is increased so that the surface has appropriate protrusions. .

  In addition, the non-magnetic support has a three-layer structure, and a middle layer (intermediate layer) is mainly composed of a polyester obtained by esterifying an aromatic dicarboxylic acid having at least three aromatic rings and a diol. It is good also as polyester to do. In this case, the layers on both sides (upper layer and lower layer) are preferably polyesters such as conventionally known polyethylene terephthalate and polyethylene naphthalate. Even in the case of such a three-layer structure, the surface shape of the nonmagnetic support can be controlled by changing the type and amount of lubricant particles contained in each layer.

  Various other additives such as heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, fatty acid esters, waxes and the like within the range not impairing the effects of the present invention. Organic lubricants can also be added.

  In addition, as a method of forming a multilayer film and using it as a nonmagnetic support, for example, a method of laminating a resin melt of each layer by a coextrusion method or the like can be mentioned. These lamination methods include known methods such as lamination in a die, lamination in a composite die, and a method in which one layer is once formed and another layer is formed thereon. Moreover, you may bond each layer formed beforehand.

  The unstretched film having a single layer or a plurality of layers is preferably biaxially stretched and biaxially oriented. As the stretching method, a conventionally known method such as sequential biaxial stretching or simultaneous biaxial stretching can be used.

  The thickness of the non-magnetic support is preferably 2 μm or more and less than 7 μm, more preferably 3 μm or more and 6 μm or less, and most preferably 3 μm or more and 5 μm or less from the viewpoint of reducing the thickness while ensuring required rigidity.

The Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.88 GPa (600 kg / mm ² ) or more, more preferably 6.86 GPa (700 kg / mm ² ) or more. The non-magnetic support film should have a Young's modulus in the longitudinal direction of 5.88 GPa (600 kg / mm ² ) or more. If the Young's modulus in the longitudinal direction is less than 5.88 GPa (600 kg / mm ² ), the tape running is unstable. It is because there is a possibility of becoming. In the helical scan type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably in a specific range of 0.30 to 0.80, and more preferably in the range of 0.5 to 0.70. The fact that the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably in a specific range of 0.30 to 0.80 is outside this range, the mechanism is currently unknown, but the magnetic head track This is because the variation (flatness) in output between the incoming side and the outgoing side 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 in the range of 0.70 to 1.30, although the reason is not clear.

  Hereinafter, other components of the present invention and other elements that can be employed in the present invention will be described.

<Magnetic layer>
The thickness of the magnetic layer is preferably 0.01 μm or more and 0.15 μm or less. This range is preferable because when the thickness is less than 0.01 μm, the output obtained is small, and it is difficult to apply a uniform magnetic layer, and when it exceeds 0.15 μm, the resolution of the short wavelength signal is deteriorated. In order to further improve the short wavelength recording characteristics, the thickness of the magnetic layer is more preferably 0.01 to 0.1 μm, and most preferably 0.02 to 0.06 μm.

  In order to increase the capacity of the magnetic recording medium, a configuration may be adopted in which magnetic layers are provided on both sides of the nonmagnetic support.

  The coercive force of the magnetic layer is preferably 80 to 320 kA / m, more preferably 100 to 300 kA / m, and still more preferably 120 to 280 kA / m. This range is preferable because if the recording wavelength is shorter than 80 kA / m, the output is reduced due to demagnetization when the recording wavelength is shortened, and if it exceeds 320 kA / m, recording by the magnetic head becomes difficult.

  As the binder resin used for the magnetic layer (the same applies to the undercoat layer described later), vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate- At least one selected from vinyl alcohol copolymer resins, vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resins, and cellulose resins such as nitrocellulose; The thing etc. which combined with the polyurethane resin are mentioned. 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""" wherein R ', R ", R"" , R ′ ″ ″ and R ″ ″ ″ represent hydrogen or hydrocarbon groups], and binder resins such as vinyl chloride resins and urethane resins made of a polymer having an epoxy group are 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, it is most preferable to use a composite of 5-30 parts by weight of vinyl chloride resin and 2-20 parts by weight of polyurethane resin as the binder 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. In addition, when a magnetic layer is applied by wet-on-wet on an undercoat layer to be described later, a certain amount of polyisocyanate is diffused and supplied from the undercoat paint (coating for forming the undercoat layer). Even without using polyisocyanate, the magnetic layer is crosslinked to some extent.

  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 5 nm or more and less than 60 nm. This range is preferable because when the average particle size is less than 5 nm, the surface energy of the particles becomes large and dispersion becomes difficult, and when the average particle size is 60 nm or more, 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 as described below 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, it may contain at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium and the like (sintering inhibitor). Among these, when cerium, neodymium and samarium, terbium, and yttrium are used, the shape is favorably maintained, and a uniform ceramic layer is formed on the surface of the magnetic powder, which is preferable. The amount of rare earth elements is 0.2 to 25 atomic%, preferably 0.3 to 20 atomic%, more preferably 0.5 to 15 atomic%, based on iron.

  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. However, in order to obtain an iron nitride magnetic powder satisfying the required characteristics as a magnetic powder for magnetic recording with respect to the particle diameter and specific surface area, it is necessary to produce the powder under certain conditions (reference patent: JP 2000-277311 A). Issue gazette).

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 70 to 200 A · m ² / kg (70 to 200 emu / g), 80 to 180 A · m ² / kg (80 to 180 emu / g) is more preferable.

The average particle size of the ferromagnetic iron-based metal magnetic powder and the iron nitride magnetic powder is preferably 5 nm or more and less than 60 nm, and more preferably 15 to 40 nm. If the average particle size is less than 5 nm, the coercive force is lowered, or the surface energy of the particles is increased, so that dispersion in the paint becomes difficult. On the other hand, when the average particle diameter is 60 nm or more, particle noise based on the particle size increases. BET specific surface area of these magnetic powders 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.

  The ferromagnetic iron-based 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) of the hexagonal Ba-ferrite magnetic powder is preferably 10 to 50 nm, more preferably 10 to 30 nm, and still 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 50 nm, particle noise based on the particle size increases. The plate ratio (plate diameter / plate thickness) is preferably 2 to 10, more preferably 2 to 5, and still 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.

  The magnetic properties of these ferromagnetic powders are all measured with an oscillating sample magnetometer and an external magnetic field of 1273.3 kA / m (16 kOe). In addition, the above average particle diameter is measured from the photograph taken with a transmission electron microscope (TEM), the maximum diameter of each particle (long axis diameter in the case of acicular powder, the maximum value of the plate diameter in the case of plate powder), It is obtained from an average value of 100 pieces.

  A conventionally well-known abrasive | polishing agent can be added to a magnetic layer as needed. These abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, Boron nitride or the like having a Mohs hardness of 6 or higher is used alone or in combination. In general, the particle size of the abrasive is preferably 10 to 200 nm as an average particle size.

  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. The average particle diameter of carbon black is preferably 10 to 100 nm. This range is preferable because when the average particle size is less than 10 nm, it is difficult to disperse the carbon black. When the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. This is because it causes a decrease. If necessary, two or more types of carbon black having different average particle diameters may be used.

<Undercoat layer>
In order to obtain a magnetic layer having a high recording density, it is preferable to reduce the thickness of the magnetic layer. In order to stably obtain a durable thin magnetic layer, the magnetic layer and a non-magnetic support are used. It is preferable to provide an undercoat layer between them. The thickness of the undercoat layer is preferably 0.2 μm or more and 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. If the thickness of the undercoat layer is less than 0.2 μm, the effect of reducing the uneven thickness of the magnetic layer and the effect of improving the durability are small. If the thickness exceeds 1.5 μm, the total thickness of the magnetic tape becomes too thick, and the per-tape tape is too thick. This is because the recording capacity is reduced.

  The undercoat layer contains a nonmagnetic powder. Examples of such non-magnetic powders include titanium oxide, iron oxide, and aluminum oxide. Iron oxide, titanium oxide alone, or a mixed system of iron oxide and aluminum oxide is preferably used. The particle shape of the non-magnetic powder may be spherical, plate-like, needle-like, or spindle-like, but in the case of needle-like or spindle-like, the major axis length is usually 20 to 200 nm and the minor axis length is 5 to 200 nm. preferable. Non-magnetic powder is mainly used, and carbon black having a particle diameter of 0.01 to 0.1 μm and aluminum oxide having a particle diameter of 0.05 to 0.5 μm are often supplementarily contained as necessary. In order to coat and form the undercoat layer smoothly and with little thickness unevenness, it is preferable to use the nonmagnetic particles and carbon black having a sharp particle size distribution.

  A nonmagnetic plate-like powder having an average particle size of 10 to 100 nm may be added to the undercoat layer. As the component of the nonmagnetic plate-like powder, a rare earth element such as cerium, an oxide or a complex oxide of an element such as zirconium, silicon, titanium, manganese, or iron is used. For the purpose of improving the conductivity, a plate-like carbonaceous powder such as graphite having an average particle size of 10 to 100 nm or a plate-like ITO (indium, tin composite oxide) powder having an average particle size of 10 to 100 nm may be added. . By adding the non-magnetic plate-like powder, film thickness uniformity, surface smoothness, rigidity, and dimensional stability are improved.

  The binder resin used for the undercoat layer can be the same as that used in the magnetic layer described above.

<lubricant>
The magnetic layer and the undercoat layer contain 0.5 to 3.0% by weight of fatty acid amide with respect to the total powder contained in the magnetic layer and the undercoat layer, respectively, and 0.5 to 5.0% by weight. It is preferable to contain 0.2 to 3.0% by weight of an ester of higher fatty acid. 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 undercoat 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. Note that this does not exclude the mutual movement of the lubricant in the magnetic layer and the lubricant in the undercoat layer. If the lubricant is contained in the undercoat layer, the magnetic layer may not contain a lubricant. . On the contrary, when the effect is manifested only by being included in the magnetic layer, it may not be included in the undercoat layer.

<Dispersant>
To the undercoat layer and the magnetic layer, a non-magnetic powder, carbon black, and a dispersant for dispersing the magnetic powder contained therein are added. Examples of such dispersants include carbon numbers such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearic acid, etc. Contains 12 to 18 fatty acids (RCOOH, R is an alkyl group or alkenyl group having 11 to 17 carbon atoms), metal soap composed of alkali metal or alkaline earth metal of the fatty acid, fluorine of the fatty acid ester Compound, amide of fatty acid, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonic acid Conventionally known as salts, phosphates, copper phthalocyanine, etc. Or surface treatment with a dispersant, 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.

<Back coat layer>
The magnetic tape which is one embodiment of the present invention is preferably provided with a backcoat layer for the purpose of improving running performance. The thickness of the back coat layer is preferably 0.05 to 0.8 μm. This range is good because if it is less than 0.05 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 storage capacity per roll becomes small. As the back coat layer, a layer having a configuration containing a nonmagnetic powder and a binder resin is usually provided, but a layer having another configuration or form may be used as long as it has an effect of improving running performance. .

  Carbon black is added to the back coat layer for the purpose of improving running performance. 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 in combination. As the small particle size carbon black, those having an average particle size of 5 to 200 nm are preferably used, and those having an average particle size of 10 to 100 nm are more preferably used. If the average particle size of the small particle size carbon black is 10 nm or less, it is difficult to disperse the carbon black. If 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 becomes rough. This is because it causes a back-off (embossing) to the magnetic layer. If the large particle size carbon black used in combination with the small particle size carbon black is a large particle size carbon black having an average particle size of 200 to 400 nm at a ratio of 5 to 15% by weight of the small particle size carbon black, the surface will not become rough. In addition, the driving performance improvement effect is increased. The total addition amount of the small particle size carbon black and the large particle size carbon black is preferably 60 to 100% by weight, more preferably 70 to 100% by weight, based on the weight of the inorganic powder contained in the back layer. The center line average surface roughness Ra of the back layer is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

  A nonmagnetic plate-like powder having an average particle diameter of 10 nm to 100 nm can be added to the backcoat 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 to 100 nm, a plate-like ITO powder having an average particle size of 10 to 100 nm, or the like may be added. Moreover, you may add the granular iron oxide powder whose average particle diameter is 0.1-0.6 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 backcoat layer. 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 coat layer, the same resin as that used for the magnetic layer and the undercoat layer described above can be used as the binder resin. Among these, in order to reduce the coefficient of friction and improve the runnability, cellulose resin and polyurethane resin are used. It is preferable to combine and use resin. 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. If the binder resin content is less than 50 parts by weight, the strength of the backcoat layer tends to be 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. Furthermore, it is preferable to use a crosslinking agent such as a polyisocyanate compound in order to cure the binder resin.

  For the backcoat layer, a crosslinking agent similar to the crosslinking agent used for the magnetic layer and the undercoat layer described above can be 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. If the amount of the cross-linking agent is less than 10 parts by weight, the coating strength of the backcoat layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction against a guide roller (material is, for example, SUS304) provided in the running system of the tape drive. The coefficient tends to increase.

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

[Example]
Examples of the present invention will be described below. In the following Examples and Comparative Examples, “parts” represents parts by weight, and the average particle diameter (average particle diameter) represents the number average particle diameter.

<Production of non-magnetic support>
Composition <1>
・ 70 parts of methyl ester of 2,7-anthracene dicarboxylic acid (aromatic dicarboxylic acid)
・ Ethylene glycol (diol) 30 parts ・ Manganese acetate ・ Tetrahydrate (transesterification catalyst) 0.02 parts ・ Cross-linked silicone particles (average particle size 1.2 μm, lubricant particles) 0.001 parts ・ Calcium carbonate particles (average) Particle size 0.6 μm, lubricant particles) 0.2 parts Alumina particles (average particle size 0.1 μm, lubricant particles) 0.2 parts

  The above composition <1> is supplied to a transesterification reactor equipped with a stirrer, a rectifying column, and a condenser, and the temperature is gradually raised to 180 ° C. to 240 ° C., and simultaneously generated methanol is continuously reacted in the reaction system. The ester exchange reaction was carried out while distilling out. To the reaction product thus obtained, 0.025 part of trimethyl phosphate was added and reacted for 15 minutes to complete the transesterification reaction, and then 0.02 part of antimony trioxide was added and reacted for another 5 minutes. Subsequently, while continuously distilling ethylene glycol, the temperature was raised to 290 ° C., and at the same time, the pressure was reduced to 0.2 mmHg to carry out the polycondensation reaction, and the intrinsic viscosity (measuring solvent orthochlorophenol, 35 ° C.) 0.54 dl / g of polyethylene anthracenecarboxylate (PEA1) was obtained. The lubricant particles are each dispersed in ethylene glycol to form a slurry having a concentration of 10% by weight. The slurry is filtered using a filter having an average pore diameter of 1.0 μm, and coarse particles separated from the average particle diameter are obtained. Removed and added.

  The PEA1 pellets were dried at 170 ° C. for 3 hours, then fed to an extruder hopper, melted at a melting temperature of 320 to 340 ° C., and the melted polymer was passed through a 0.3 mm slit die to obtain a surface finish of 0.3 s. Extruded onto a rotary cooling drum having a surface temperature of 20 ° C. to obtain an unstretched film having a thickness of 70 μm. Subsequently, this unstretched film is preheated at 180 ° C., further heated by three IR heaters having a surface temperature of 800 ° C. from 15 mm above between low-speed and high-speed rolls, stretched 4.2 times, and rapidly cooled. did. Subsequently, it was supplied to a stenter and stretched 3.3 times in the transverse direction at 220 ° C. The obtained biaxially oriented film was heat-set at a temperature of 255 ° C. for 5 seconds, and a biaxially oriented polyester film having a thickness of 5.0 μm (Young's modulus: MD (longitudinal) / TD (lateral)) = 12.4 / 7. .3 (GPa)) was obtained.

<Undercoat paint component>
(1)
-Acicular iron oxide (average particle size: 100 nm) 68 parts-Granular alumina powder (average particle size: 80 nm) 8 parts-Carbon black (average particle size: 25 nm) 24 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)
・ 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 component》
(1) Kneading process / Acoustic ferromagnetic iron metal powder 100 parts (Co / Fe: 24 at%,
Y / (Fe + Co): 7.9 at%,
Al / (Fe + Co): 4.7 at%,
σs: 119 A · m ² / kg (119 emu / g),
Hc: 181 kA / m (2280 Oe),
Average axial length: 60 nm, axial ratio 6)
14 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin (PU) 5 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)
-Particulate alumina (average particle size: 80 nm) 10 parts-Carbon black (average particle size: 75 nm) 5 parts-Methyl acid phosphate (MAP) 2 parts-Tetrahydrofuran (THF) 20 parts-Methyl ethyl ketone / cyclohexanone (MEK / A) 9 Parts (2) Diluting process components Palmitic acid amide (PA) 1.5 parts N-butyl stearate (SB) 1 part Methyl ethyl ketone / cyclohexanone (MEK / A) 350 parts (3) Blending process components Polyisocyanate 1 5 parts, 29 parts of methyl ethyl ketone / cyclohexanone (MEK / A)

  After kneading (1) with a batch kneader in the above-mentioned undercoat paint component, add (2) and stir, and then disperse with a sand mill with a residence time of 60 minutes. Add (3) to this and stir and filter After that, an undercoat paint (undercoat layer paint) was obtained.

  Apart from this, in the above-mentioned components of the magnetic coating, (1) the mixing process components are mixed in advance at high speed, the mixed powder is kneaded with a continuous biaxial kneader, and (2) the dilution process components are 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, (3) ingredients of the blending step were added thereto, and the mixture was stirred and filtered to obtain a magnetic paint.

  The undercoat paint is applied on the prepared nonmagnetic support (biaxially oriented polyester film) so that the thickness after drying and calendering is 0.9 μm, and further on the undercoat layer, The magnetic coating was applied wet-on-wet so that the magnetic layer thickness after the magnetic field orientation treatment, drying, and calendar treatment was 0.09 μm, and a magnetic sheet was obtained through magnetic field orientation treatment and drying.

《Paint component for back coat layer》
Carbon black (average particle size: 25 nm) 80 parts Carbon black (average particle size: 0.35 μm) 10 parts Granular iron oxide (average particle diameter: 50 nm) 10 parts Nitrocellulose 45 parts Polyurethane resin (-SO ₃ containing Na group) 30 parts ・ Cyclohexanone 260 parts ・ Toluene 260 parts ・ Methyl ethyl ketone 525 parts

  After the coating component for the backcoat layer is dispersed in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate is added to adjust the coating for the backcoat layer, and after filtration, on the opposite side of the magnetic layer of the magnetic sheet prepared above , Dried and coated so that the thickness after calendering was 0.5 μm and dried.

  The magnetic sheet thus obtained was mirror-finished at 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 on a core at 70 ° C. for 72 hours. Aging was performed to produce a magnetic sheet.

  The magnetic sheet is cut to 1/2 inch (about 12.65 mm) width, and the post-processing of lapping tape polishing, blade polishing and surface wiping is performed on the magnetic layer surface while running the cut tape at 200 m / min. A magnetic tape was prepared. At this time, K10000 was used for the wrapping tape, a carbide blade was used for the blade, and Toraysee (trade name) manufactured by Toray was used for surface wiping, and the treatment was performed with a running tension of 0.294N. The magnetic tape obtained as described above was written with a servo signal on the backcoat layer with a servo writer for S-DLT, and then 4 pieces of cotton having a short fiber diameter of 4 μm were twisted on the backcoat layer. The tape was run while contacting a velvet planted with 2.5 mm long fibers to remove the burning residue at the time of servo signal writing, and it was incorporated into a cartridge to produce a computer tape.

  A computer tape of Example 2 was produced in the same manner as in Example 1 except that the biaxially oriented polyester used for the nonmagnetic support was changed from PEA to PENA produced as follows.

<Production of non-magnetic support>
Composition <2>
・ Methyl ester of naphthacene dicarboxylic acid 75 parts (aromatic dicarboxylic acid)
・ Ethylene glycol (diol) 25 parts ・ Manganese acetate ・ Tetrahydrate (transesterification catalyst) 0.02 part ・ Cross-linked silicone particles (average particle size 1.2 μm, lubricant particles) 0.001 part ・ Calcium carbonate particles (average) Particle size 0.6 μm, lubricant particles) 0.2 parts Alumina particles (average particle size 0.1 μm, lubricant particles) 0.2 parts

  The above composition <2> is supplied to a transesterification reactor equipped with a stirrer, a rectifying column, and a condenser, and the temperature is gradually raised to 180 ° C. to 240 ° C., and the produced methanol is continuously reacted in the reaction system. The ester exchange reaction was carried out while distilling out. To the reaction product thus obtained, 0.025 part of trimethyl phosphate was added and reacted for 15 minutes to complete the transesterification reaction, and then 0.02 part of antimony trioxide was added and reacted for another 5 minutes. Subsequently, the temperature was raised to 290 ° C. while continuously distilling ethylene glycol, and at the same time, the pressure was reduced to 0.2 mmHg to carry out the polycondensation reaction, and the intrinsic viscosity (measuring solvent orthochlorophenol, measuring temperature 35 ° C.) 56 dl / g of polyethylene naphthacene carboxylate (PENA) was obtained. The lubricant particles are each dispersed in ethylene glycol to form a slurry having a concentration of 10% by weight, and the slurry is filtered using a filter having an average pore diameter of 1.0 μm to obtain coarse particles far from the average particle diameter. And then added.

  The PEN pellets are dried at 170 ° C. for 3 hours and then supplied to an extruder hopper and melted at a melting temperature of 330 to 350 ° C. The surface of the melted polymer is passed through a 0.3 mm slit die for about 0.3 s. The film was extruded onto a rotary cooling drum having a surface temperature of 20 ° C. to obtain an unstretched film having a thickness of 70 μm. Subsequently, this unstretched film is preheated at 200 ° C., further heated by three IR heaters with a surface temperature of 800 ° C. from 15 mm above between low-speed and high-speed rolls, stretched 5.0 times, and rapidly cooled. did. Subsequently, it was supplied to a stenter, and stretched 3.5 times in the transverse direction at 240 ° C. The obtained biaxially oriented film was heat-fixed at a temperature of 275 ° C. for 5 seconds, and a biaxially oriented polyester film having a thickness of 4.0 μm (Young's modulus: MD (longitudinal) / TD (lateral)) = 12.6 / 7. .5 (GPa)) was obtained.

  The biaxially oriented polyester used for the non-magnetic support is changed from a single layer configuration to a two-layer configuration prepared as follows, a magnetic layer is provided on the PEA2 layer side, and a backcoat layer is provided on the opposite side. A computer tape of Example 3 was produced in the same manner as Example 1 except that it was provided.

<Production of non-magnetic support>
PEA1 pellets and PEA2 pellets prepared in the same manner as PEA1 except that no lubricant particles were added were dried at 170 ° C. for 3 hours, and then supplied to two extruder hoppers at a melting temperature of 320 to 340 ° C. 2 layers are laminated using a multi-manifold type co-extrusion die, and the thickness ratio of PEA1 / PEA2 is 1/2 on a rotary cooling drum having a surface finish of about 0.3 s and a surface temperature of 20 ° C. through a slit die. And an unstretched film having a total thickness of 70 μm was obtained. The layer thickness configuration was adjusted by the discharge amount of two extruders. The subsequent stretching step is carried out in the same manner as in Example 1, and a biaxially oriented polyester film having a thickness of 5.0 μm (PEA1 layer 1.0 μm, PEA2 layer 4.0 μm) (Young's modulus: MD (longitudinal)) / TD (width) = 12.4 / 7.4 (GPa)).

  The biaxially oriented polyester used for the non-magnetic support is changed from a single-layer configuration to a three-layer configuration prepared as follows, a magnetic layer is provided on the PEN2 layer side, and a backcoat layer is provided on the opposite side. A computer tape of Example 4 was produced in the same manner as Example 1 except that it was provided.

<Production of non-magnetic support>
Polyethylene-2,6-naphthalate pellets (PEN2) containing no lubricant particles (PEN2) (inherent viscosity 0.61 dl / g, measurement solvent orthochlorophenol, measurement temperature 25 ° C.), PEA2 pellets, and average particle size in PEN2 It contains 0.001% by weight of crosslinked silicone particles of 1.2 μm, 0.2% by weight of calcium carbonate particles having an average particle diameter of 0.6 μm, and 0.2% by weight of alumina particles having an average particle diameter of 0.1 μm. The prepared PEN1 pellets are dried at 170 ° C. for 3 hours, then supplied to three extruder hoppers, melted at a melting temperature of 300 to 340 ° C., and laminated using a multi-manifold coextrusion die, Extruded through a slit-shaped die onto a rotating cooling drum with a surface finish of about 0.3 s and a surface temperature of 20 ° C. so that the thickness ratio of PEN2 / PEA2 / PEN1 is 0.5 / 4 / 0.5. To obtain an unstretched film of 70μm. The layer thickness configuration was adjusted by the discharge amount of three extruders. Subsequent stretching steps were carried out in the same manner as in Example 1, and a biaxially oriented polyester film (Young) with a thickness of 5.0 μm (PEN2 layer 0.5 μm, PEA2 layer 4.0 μm, PEN1 layer 0.5 μm). Rate: MD (longitudinal) / TD (width) = 12.3 / 7.1 (GPa)).

[Reference example]
A computer tape (magnetic tape) was produced in the same manner as in Example 1 except that the thickness of the nonmagnetic support was changed to 5.2 μm.

[Comparative Example 1]
A computer tape of Comparative Example 1 was produced in the same manner as in Example 1 except that the biaxially oriented polyester used for the nonmagnetic support was changed from PEA to polyethylene terephthalate (PET) produced as follows.

<Production of non-magnetic support>
To PET pellets containing no lubricant particles (intrinsic viscosity 0.60 dl / g, measurement solvent orthochlorophenol, measurement temperature 35 ° C.), cross-linked silicone particles having an average particle diameter of 1.2 μm are 0.001% by weight, average particles PET1 pellets prepared by adding 0.2% by weight of calcium carbonate particles having a diameter of 0.6 μm and 0.2% by weight of alumina particles having an average particle diameter of 0.1 μm were dried at 170 ° C. for 3 hours, and then an extruder. Supplied to the hopper and melted at a melting temperature of 280 to 300 ° C., and the melted polymer was extruded through a slit die having a thickness of 0.3 mm onto a rotating cooling drum having a surface finish of about 0.3 s and a surface temperature of 20 ° C. An unstretched film was obtained. Subsequent stretching steps were performed in the same manner as in Example 1, and a biaxially oriented polyester film having a thickness of 5.0 μm (Young's modulus: MD (longitudinal) / TD (width)) = 7.4 / 4.9 (GPa) )

[Comparative Example 2]
A computer tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the biaxially oriented polyester used for the nonmagnetic support was changed from PEA to polyethylene naphthalate (PEN) produced as follows.

<Production of non-magnetic support>
PEN1 pellets are dried at 170 ° C. for 3 hours, then fed to an extruder hopper, melted at a melting temperature of 300 to 320 ° C., and the melted polymer is passed through a 0.3 mm slit die to have a surface finish of about 0.3 s and a surface temperature. The film was extruded on a rotary cooling drum at 20 ° C. to obtain an unstretched film having a thickness of 70 μm. Subsequent stretching steps were carried out in the same manner as in Example 1, and a biaxially oriented polyester film having a thickness of 5.0 μm (Young's modulus: MD (longitudinal) / TD (lateral)) = 10.8 / 6.1 (GPa) )

[Evaluation of properties]
The characteristics of the obtained computer tapes (magnetic tapes) and the nonmagnetic support sheets used for them were evaluated by the following methods.

<Measurement of thickness of each component layer of non-magnetic support>
The total thickness of the nonmagnetic support is measured at 10 points with a micrometer at random, and the average value is used. When the nonmagnetic support has a two-layer or three-layer structure, the thickness of the film is in the range of the surface layer excluding the coating layer to a depth of 5000 nm using a secondary ion mass spectrometer (SIMS). The concentration ratio (M + / C +) between the metal element (M +) and the hydrocarbon (C +) of the thermoplastic resin due to the highest concentration of the particles is defined as the particle concentration, and from the surface to the depth of 5000 nm in the thickness direction. Perform analysis. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the present invention, as shown in FIG. 1, when M + / C + is viewed from the surface to the inside, the particle concentration becomes higher after entering the inside from the surface, and then becomes a stable value, and thereafter the particle concentration becomes lower. M + / C + decreases (FIG. 1). Based on this distribution curve, the thickness of the surface layer (μm) having a depth at which the particle concentration is ½ of the stable value (this depth is deeper than the depth giving the stable value) (“a” in FIG. "Thickness of the layer"). This thickness. The other layer thickness is obtained by subtracting the layer thickness obtained from the total thickness.

  In addition, when the most abundant particles in the range of 5000 nm from the surface layer are organic polymer particles other than silicone resin, it is difficult to measure by the SIMS, so FT-IR (Fourier transform infrared spectroscopy) while etching from the surface. Depending on the particle, a concentration distribution curve similar to the above is measured by XPS (X-ray photoelectric spectroscopy) or the like to determine the layer thickness (μm). The layer thickness in the case of the three-layer structure is obtained by subtracting the layer thicknesses of both surface layers from the total thickness described above.

<Measurement of Young's modulus (width direction)>
A sample with a length of 15 mm and a width of 4 mm is cut out from the non-magnetic support sheet in each of the longitudinal direction and the width direction, and the strain / tensile stress at 25 ° C. is measured using a small tensile testing machine (manufactured by Yokohama System). did. The measurement length was 10 mm, the tensile rate was 10% strain / min, and the 0.3% elongation modulus (Young's modulus) was evaluated based on the 0.3% strain value of the obtained stress.

<C / N measurement>
A drum tester was used to measure the electromagnetic conversion characteristics of the magnetic 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). Recording was performed with the induction head, and reproduction was performed with the MR head. These electromagnetic induction type head and MR head are installed at different locations with respect to the rotating drum, and the two heads can be operated in the vertical direction so that tracking can be matched. 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 computer tape of Comparative Example 1.

<Durability test>
The error rate before running is obtained by recording (recording wavelength 0.37 μm) and playback in the test mode using an S-DLT drive modified so that thin tape can be measured, and at 25 ° C. and 55% RH. Under the environment, the error rate after running the entire length and all tracks for 300 hours was obtained.

  Table 1 shows the above evaluation results.

  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 and 2, and the error rate after the endurance running test. There is little increase. Further, the thickness of the nonmagnetic support in the computer tape is smaller in Example 2 than in Comparative Examples 1 and 2, and in Examples 1, 3, and 4 are those in Comparative Examples 1 and 2. Although it is equal, it can also be seen that the Young's modulus of the non-magnetic support is higher in each example than in Comparative Examples 1 and 2. For the computer tape of the reference example, C / N could be measured, but when the tape length was the same as in Examples 1 to 4, the winding diameter was relatively large, so it could not be incorporated into the current standard cartridge. The durability running test could not be performed.

It is explanatory drawing used when measuring the layer thickness of a nonmagnetic support body.

Claims (1)

A magnetic recording medium provided with a magnetic layer containing magnetic powder and a binder resin on at least one surface of a nonmagnetic support,
A magnetic recording medium, wherein the non-magnetic support comprises, as a main component, a polyester obtained by an esterification reaction of an aromatic dicarboxylic acid having at least three aromatic rings and a diol.

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