JP2008084509A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which has a layer structure and is capable of ensuring a stable recording and reproducing characteristics by extremely high track density in the width direction of the tape and fewer off-track and keeps an adhesive strength between layers increased to improve the durability. <P>SOLUTION: The magnetic recording medium includes a nonmagnetic support body 1 keeping both surfaces of a base film 1a overlaid with reinforcement films 1b which are composed of a single material selected from metals, alloys or their oxides or of a composite material containing these materials. The nonmagnetic support body 1 has a nonmagnetic intermediate layer 7 composed of a nonmagnetic material and a magnetic layer 3 composed of ferromagnetic powder and a binding agent on one surface, and a back layer 5 on the other surface. An easily adhesive layer 2 made of resin for ensuring the adhesion is provided between one reinforcement film 1b and the nonmagnetic intermediate layer 7 and between the other reinforcement film 1b and the back layer 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tape-like magnetic recording medium in which recording / reproduction is performed in the longitudinal direction, and in particular, adhesion strength between layers in a magnetic recording medium having a layer structure that ensures high dimensional stability in the width direction and has excellent off-track characteristics. The present invention relates to a technique for increasing the driving force and improving the running durability.

  In recent years, the amount of information has increased explosively due to the spread of the Internet, digital recording, and the like, and a recording medium for backing up such information as data is moving toward a further increase in capacity and density. As this backup recording medium, a tape medium that is housed in a cartridge in a wound state uses a fixed head in which a large number of magnetoresistive heads are arranged to increase the capacity, and recording and reproduction are performed in the longitudinal direction of the tape. A linear recording system has been put into practical use. To further increase the capacity, the thickness of the magnetic recording layer is reduced and short wavelength recording is performed, the track density in the tape width direction is increased, the tape thickness itself is reduced and the winding length per roll is increased, etc. The measures are taken. In addition, the data transfer speed is increased by arranging a large number of heads and increasing the relative speed between the tape and the head.

  In these measures, if the thickness of the magnetic recording layer is reduced and short wavelength recording is performed, the output becomes small due to slight spacing between the magnetic recording layer and the head, and the running durability deteriorates when running many times. Various improvements are being studied. Also, when the track density in the tape width direction is increased, the track does not exist at the track position that the magnetic head should read due to the dimensional change of the tape itself due to changes in the width direction during tape running and temperature and humidity, etc. A so-called off-track operation such as reading a shifted track position occurs. In a medium having a tape thickness of less than 9.5 μm, the change in the tape width due to the tension factor is further increased, so that the effect of off-track becomes significant and the tape running property becomes unstable. In order to avoid this off-track, a method has been proposed in which a servo signal is recorded on a tape and correct tracking is performed. This servo system includes a system in which a servo signal is magnetically or optically recorded on the tape magnetic layer side or the back layer side.

  By the way, many methods have been proposed in the past for reinforcing a nonmagnetic support in a magnetic recording medium with a reinforcing film made of a metal, an alloy, or an oxide thereof on one or both sides (for example, Patent Documents). 1-6.)

  However, even if a magnetic layer and a back layer are applied by a conventional method on a nonmagnetic support reinforced with a reinforcing film of metal, alloy, or oxide thereof, the adhesive strength is insufficient and the durability as a tape is not improved. There was an insufficient problem.

  Many techniques have been proposed in which an easy-adhesion layer is present in order to increase the adhesive strength between the magnetic layer of the magnetic recording medium and the base film support (see, for example, Patent Documents 7 to 14).

JP 61-13433 A JP-A-11-339250 JP 2000-11364 A JP 2002-304720 A JP 2002-304721 A JP 2003-132525 A Japanese Patent Publication No. 63-57238 Japanese Patent Publication No. 04-49572 Japanese Patent Publication No. 02-13905 Japanese Patent Publication No. 02-13904 Japanese Patent Publication No. 02-13903 Japanese Patent No. 2768863 Japanese Patent No. 2706002 Japanese Patent No. 3205258

  The present invention has been made in view of the problems in the prior art described above, and in a magnetic recording medium having a layer structure capable of ensuring stable recording / reproduction characteristics with very high track density in the tape width direction and low off-track. An object of the present invention is to provide a magnetic recording medium with improved adhesive strength and improved durability.

  The inventors first tried to improve the problem by applying a conventional easy-adhesive to a nonmagnetic support reinforced with a reinforcing film made of a metal, an alloy, or an oxide thereof. However, various problems occurred when applied to the non-magnetic support. For example, when the easy-adhesive is applied with the same thickness as in the prior art, it has been difficult to cause roll adhesion and form a tape in the curing step. The inventors have investigated the causes of these problems, and have intensively studied to solve this problem, thereby achieving the present invention.

  That is, the present invention provided in order to solve the above problems is a non-magnetic support in which a reinforcing film made of a metal, an alloy, or an oxide thereof alone or a composite material thereof is formed on both surfaces of a base film, A magnetic recording medium comprising: a nonmagnetic intermediate layer made of a nonmagnetic material provided on one surface of the nonmagnetic support; a magnetic layer made of ferromagnetic powder and a binder; and a back layer provided on the other surface. The magnetic recording medium is characterized in that an easy-adhesion layer made of a resin for ensuring adhesion is provided between the reinforcing film and the nonmagnetic intermediate layer and between the reinforcing film and the back layer.

  Here, the thickness of the easy-adhesion layer is preferably 5 to 50 nm, and the glass transition temperature Tg of the easy-adhesion layer is preferably 50 to 90 ° C.

  Moreover, it is preferable that the said easily bonding layer contains an aromatic polyester resin or an aromatic polyurethane resin.

  Furthermore, it is preferable that OH groups are introduced into the resin of the easy adhesion layer at a concentration of 0.05 to 0.18 mmol / g.

  According to the present invention, by applying an easy-adhesive, it is possible to secure a bonding strength on both sides and to manufacture a magnetic recording medium having excellent durability. Therefore, even when the track density in the width direction is very high, the tape-like shape has a small dimensional change in the width direction due to environmental factors, little off-track, stable recording / reproduction characteristics, and excellent durability. Magnetic recording media can be obtained.

The configuration of the magnetic recording medium according to the present invention will be described below.
FIG. 1 is a cross-sectional view showing a configuration of a magnetic recording medium according to the present invention.
As shown in FIG. 1, the magnetic recording medium of the present invention is a nonmagnetic support in which a reinforcing film 1b made of a metal, an alloy, or an oxide thereof, or a composite material thereof is formed on both surfaces of a plastic film 1a. 1, a nonmagnetic intermediate layer 7 made of a nonmagnetic material provided on one surface of the nonmagnetic support 1, a magnetic layer 3 made of ferromagnetic powder and a binder, and a back layer 5 provided on the other surface. And an easy adhesion layer 2 made of a resin for ensuring adhesion is provided between the reinforcing film 1b and the nonmagnetic intermediate layer 7 and between the reinforcing film 1b and the back layer 5. . A servo signal for tracking control may be recorded on either or both of the magnetic servo signal on the magnetic layer 3 and the optical servo signal on the back layer 5.

  The magnetic recording medium of the present invention is set to a thickness of 3.0 to 9.5 μm as a magnetic tape medium. If the thickness of the tape medium is less than 3.0 μm, not only will the fluctuation in the width direction increase during driving, resulting in unstable running, but also the dimensional change in the width direction caused by the Poisson's ratio effect when tension is applied in the longitudinal direction. The amount of change in creep when the tension is applied in the longitudinal direction for a long time is very large. Further, if the thickness of the tape medium exceeds 9.5 μm, the tape length that can be wound around one cartridge is shortened and the capacity cannot be increased.

  In the present embodiment, as the plastic film 1a constituting the nonmagnetic support 1, polyethylene terephthalate, polyethylene naphthalate, polytetramethylene terephthalate, poly-1,4-cyclohexylenedimethylene terephthalate, polyethylene-p-oxybenzoate Polyimide, polyamide and the like can be mentioned, and polyester plastic films such as polyethylene terephthalate and polyethylene naphthalate are particularly preferable because of high productivity and relatively low cost.

  In addition, these films may have a single layer structure or a multilayer structure, and may be subjected to surface treatment such as corona discharge treatment, electron beam irradiation treatment, easy adhesion layer formation on the surface for the purpose of improving adhesiveness, The surface may be subjected to water repellent treatment for the purpose of reducing the humidity expansion coefficient.

  In addition, inorganic fillers such as calcium carbonate, silica, aluminum oxide, and polystyrene may be internally added for the purpose of controlling surface properties and running stability. The surface roughness Ra is preferably 0.5 to 8 nm, particularly preferably 0.5 to 6 nm, on the magnetic layer coating surface. If the surface roughness is less than 0.5 nm, the friction with the guide roll becomes very high during tape production, which is not preferable because running becomes unstable. Conversely, if it exceeds 8 nm, the tape surface roughness after application of the magnetic layer increases, and the spacing loss with the head increases, which is not preferable.

  On the other hand, the surface roughness Ra of the back layer application surface is preferably 4 to 25 nm, particularly preferably 5 to 15 nm. When the surface roughness is less than 4 nm, it is not preferable because the running becomes unstable in the process as in the case of the magnetic layer coating surface. On the other hand, when the thickness is larger than 25 nm, the tape surface roughness after coating the back layer becomes large, and the roughness of the back layer becomes large when the film is wound and stored in the process or when it is wound and stored in a cartridge. As a result, the roughness of the magnetic layer is increased, resulting in a spacing loss.

  The thickness of the plastic film 1a is preferably 2.0 to 8.0 μm, and particularly preferably 3.0 to 6.0 μm. When the film is thinner than 2.0 μm, not only the film formation itself becomes difficult, but also the strength decreases so much that the running durability decreases, the width change due to the tension change in the longitudinal direction increases, and the creep characteristics Is getting worse. On the other hand, if the thickness is greater than 8.0 μm, the thickness of the magnetic tape itself increases, and the tape length that can be wound per cartridge is shortened, which hinders the increase in capacity.

The longitudinal Young's modulus of the plastic film 1a, preferably 500 kg / mm ² or more, 600 kg / mm ² or more is particularly preferable. If it is less than 500 kg / mm ² , the strength of the magnetic tape itself becomes weak, and the running durability due to repeated running becomes worse. As the Young's modulus in the width direction is preferably 400 kg / mm ² or more, particularly preferably 600 kg / mm ² or more, 650 kg / mm ² or more is more preferred. If it is less than 400 kg / mm ² , the temperature and humidity expansion coefficient of the magnetic tape itself is undesirably increased.

Furthermore, examples of the material of the reinforcing film 1b provided on both surfaces of the plastic film 1a include metals such as Al, Cu, Ni, and Ti, alloys such as Cu—Zn, and oxides such as Al ₂ O ₃ , SiO ₂ , and TiO ₂ . For example, the Young's modulus is 7 × 10E03 kg / mm ² or more and the thermal expansion coefficient is 18 × 10E-06 / ° C. or less. The reinforcing film 1b made of these materials can be formed by a conventionally known method such as a sputtering method, a vacuum deposition method, or an ion plating method. The oxide can be formed by introducing a predetermined oxygen gas at the time of film formation.

  A plastic film occupying most of the thickness of the magnetic tape by providing a reinforcing film 1b made of a material selected from metals, alloys, and oxides and composites thereof on both surfaces of the plastic film 1a as the nonmagnetic support 1 It is possible to block moisture that enters 1a and causes expansion. Further, even if moisture slightly enters from the tape edge portion and causes the expansion of the plastic film 1a, the reinforcing film 1b provided on both surfaces prevents the expansion of the nonmagnetic support and reduces the humidity expansion coefficient in the width direction. Is planned. Without such a film, moisture easily penetrates under high humidity and the tape expands, so that the amount of change caused by environmental factors such as temperature and humidity increases, causing off-tracking. Even if the reinforcing film 1b is provided only on one side, moisture can easily enter from the other side, and the nonmagnetic support is expanded, and the curl and cupping of the magnetic tape are increased.

  The thickness of the reinforcing film 1b provided on each surface of the plastic film 1a is preferably 10 nm or more. When the film thickness is less than 10 nm, a portion that is not completely covered by the unevenness of the plastic film 1a itself is formed, moisture easily enters from the portion, the humidity expansion coefficient increases, and the plastic film 1a expands. The hindering effect becomes very small, and the film is easily peeled off during running in the process, which causes a dropout. The thickness of the reinforcing film 1b provided on the back layer side is preferably 0.5 to 1.5, particularly preferably 0.8 to 1.2, when the thickness of the film provided on the magnetic layer side is 1.0. . If this value is less than 0.5 or more than 1.5, the curl of the non-magnetic support 1 itself becomes severe, which makes the handling of the process inconvenient, and the cupping and curl as a magnetic tape become severe. Therefore, it is not preferable.

The Young's modulus of the reinforcing film 1b is desirably 7 × 10E03 kg / mm ² or more. If the Young's modulus is 7 × 10E03 kg / mm ² or more, the effect of hindering the expansion of the non-magnetic support after the intrusion of moisture is increased. Conversely, if the Young's modulus is less than 7 × 10E03 kg / mm ² , the effect If the change is less and the off-track margin is small and the maximum allowable change amount due to environmental factors is small, off-track is caused.

Furthermore, by setting the Young's modulus of the reinforcing film 1b to 7 × 10E03 kg / mm ² or more, the dimensional change in the width direction caused by the Poisson's ratio effect when tension is applied in the longitudinal direction is reduced, and the longitudinal direction is increased over a long time. The amount of creep change when tension is applied in the direction can also be reduced.

  Further, the temperature expansion coefficient of the reinforcing film 1b is desirably 18 × 10E-06 / ° C. or less. This is because the plastic film 1a is also deformed when there is a temperature change, but the deformation of the nonmagnetic support 1 can be prevented by setting the temperature expansion coefficient of the reinforcing film 1b to 18 × 10E-06 / ° C. or less. This is because the temperature expansion in the width direction can be suppressed.

Next, the easy-adhesion layer 2 will be described.
The easy adhesion layer 2 is formed by applying an adhesive.
Here, the thickness of the easy-adhesion layer 2 used in the present invention is very important because it greatly affects the characteristics. It is desirable that the thickness of the easy-adhesion layer formed on both surfaces of the nonmagnetic support is 5 to 50 nm. If it is smaller than 5 nm, the adhesive strength is insufficient, and if it is larger than 50 nm, roll adhesion occurs at the time of curing, making it difficult to form a tape.

  The resin used for forming the easy-adhesion layer 2 may have a conventionally known structure, for example, an aromatic polyester resin, an aliphatic polyester resin, an aromatic polyester polyurethane. Examples thereof include resins, aliphatic polyester polyurethane resins, alicyclic polyurethane resins, polycarbonate polyurethane resins, polyether polyurethane resins, and acrylic resins. When a resin having a glass transition temperature Tg of 40 ° C. or lower is used, roll adhesion is likely to occur in the curing step, and tape formation becomes difficult. Therefore, the glass transition temperature Tg of the easy-adhesion layer is preferably 50 to 90 ° C., and for example, aromatic polyester resins and aromatic polyurethane resins having a Tg of 50 ° C. or more are desirable.

  Further, in order to increase the adhesive strength with the nonmagnetic intermediate layer 7 or the back layer 5, the structure of the dicarboxylic acid component of the polyester of the adhesive used for the easy-adhesion layer 2 is the bonding of the nonmagnetic intermediate layer 7 or the back layer 5. An aromatic system such as terephthalic acid or isophthalic acid having a structure similar to the agent is desirable.

Further, for the purpose of increasing the adhesion strength of these resins to the support, —SO ₃ M, —OSO ₃ M, —COOM, P═O (OM) ₂ (wherein M is a hydrogen atom or lithium, potassium, an alkali metal such as sodium) ^{or, -NR 1 R 2, -NR 1} R 2 R 3+ X - represented by the side chain amine,> NR ¹ R ²⁺ X ^- mainly represented Chain amine (wherein R ¹ , R ² and R ³ represent a hydrogen atom or a hydrocarbon group, and X ⁻ represents a halogen element ion such as fluorine, chlorine, bromine or iodine, an inorganic ion or an organic ion) Furthermore, polar functional groups such as —OH, —SH, —CN, and an epoxy group may be introduced.

  Among them, the —OH group has a strong bonding force with the metal —OH group present on the surface of the metal, alloy, or oxide thereof, and is very effective for increasing the adhesive strength with the reinforcing film 1 b. The —OH group concentration is preferably 0.05 to 0.18 mmol / g. If it is less than 0.05 mmol / g, the effect of increasing the adhesive strength is small. On the other hand, if it exceeds 0.18 mmol / g, it tends to be affected by moisture, and the quality after storage under high temperature and high humidity may become unstable.

  Solvents that dissolve the adhesive include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, alcohol solvents such as methanol, ethanol, propanol, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, Ester solvents such as ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, ethylene chloride, carbon tetrachloride, Examples thereof include halogenated hydrocarbon solvents such as chloroform and chlorobenzene, and these are used by being appropriately mixed.

  The magnetic layer 3 is formed by applying a magnetic dispersion in which ferromagnetic powder is dispersed in a binder. The film thickness of the magnetic layer 3 is preferably 0.3 μm or less. This is because if the film thickness of the magnetic layer 3 is 0.3 μm or more, a demagnetizing field with respect to a short wavelength signal is increased, which hinders high recording density.

  Magnetic powders, binders, dispersants, abrasives, antistatic agents, rust preventives, lubricants, and the like mixed in the magnetic layer 3 and the solvents used to adjust these magnetic dispersions are conventionally known. Anything can be used and is not limited at all. Examples of the magnetic powder include ferromagnetic iron powder, ferromagnetic iron-cobalt powder, ferromagnetic iron oxide powder, ferromagnetic chromium dioxide powder, ferromagnetic alloy powder, hexagonal barium ferrite powder and the like.

  Examples of the binder include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer. , Vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin , Phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester Le resins, polyamide resins, phenol resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea - formaldehyde resin or a mixture thereof, and the like. Among these, it is preferable to use each of the vinyl chloride resin and the polyurethane resin alone or in a mixture thereof. Moreover, these may use an isocyanate compound as a crosslinking agent and may improve durability more. Furthermore, the amount of the binder in the magnetic layer is preferably 10 to 50 parts by weight with respect to 100 parts by weight of the magnetic powder.

  Examples of the abrasive include alumina, chromium oxide, titanium oxide, calcium carbonate, and silica. The amount of abrasive in the magnetic layer is preferably 2 to 40 parts by weight and more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the magnetic powder.

  As the antistatic agent, for example, carbon black is generally mentioned. Carbon black is useful not only as an antistatic agent but also for improving running durability, in an amount of 0.2 to 30 parts by weight, preferably 0.5 to 15 parts by weight with respect to 100 parts by weight of the magnetic powder. It is preferable to mix. The average particle diameter varies from about 5 to 500 nm, preferably 5 to 150 nm, more preferably 10 to 100 nm, and it is preferable to use a single particle in combination. Specifically, known materials such as acetylene black, furnace black, and thermal black can be used alone or in combination.

  Examples of the lubricant include higher fatty acids such as myristic acid, palmitic acid, stearic acid, oleic acid, and linoleic acid, fatty acid esters of these fatty acids, fatty acid amides, and the like. Among these, it is preferable to use a combination of fatty acid, fatty acid ester, and fatty acid amide. As addition amounts, 0.1 to 3 parts by weight of fatty acid, 0.1 to 3 parts by weight of fatty acid ester, and 0.1 to 1.5 parts by weight of fatty acid amide with respect to 100 parts by weight of magnetic powder. preferable.

  Furthermore, as a solvent for adjusting the magnetic dispersion, for example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ester, etc. Ester solvents, glycol ether solvents such as glycol monoethyl ether, dioxane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene And organic chlorine compound-based solvents.

  As shown in FIG. 1, the magnetic recording medium of the present invention is provided with a nonmagnetic intermediate layer 7 made of various inorganic powders and a binder between the nonmagnetic support 1 and the magnetic layer 3. The magnetic layer 3 is formed for the purpose of stable application, enhancement of running durability, and the like. The nonmagnetic intermediate layer 7 is preferably nonmagnetic in principle. In the configuration of FIG. 1, the effect of the present invention can be obtained even when the non-magnetic intermediate layer 7 is not provided and the easy adhesion layer 2 and the magnetic layer 3 are in direct contact.

  The nonmagnetic intermediate layer 7 is preferably provided with a thickness of 0.2 to 2.5 μm for the purpose of stable application of the magnetic layer 3 and enhancement of running durability. If the film thickness is less than 0.2 μm, it is difficult to stably apply the magnetic layer. If the film thickness is more than 2.5 μm, the thickness of the magnetic tape increases, and the tape length that can be wound per cartridge is shortened. This hinders the increase in capacity.

  In order to adjust the nonmagnetic inorganic powder mixed in the nonmagnetic intermediate layer 7, the binder, and the dispersant, antistatic agent, rust preventive, lubricant, etc. used as necessary, and these nonmagnetic dispersions Any conventionally known solvent can be used as the solvent, and is not limited in any way.

  Examples of the nonmagnetic inorganic powder include silica, titanium oxide, alumina, carbon black, α-iron oxide, calcium carbonate, chromium oxide and the like. Although the shape of these powders is not limited at all, a plate shape or a needle shape is preferable in order to reduce the temperature and humidity expansion coefficient of the tape. Of these, α-iron oxide and alumina are preferably used in combination for control of tape rigidity and running durability, and carbon black having an antistatic effect is more preferably used in combination.

  Examples of the binder include the binders described above as the binder for the magnetic layer. Among these, it is preferable to use each of the vinyl chloride resin and the polyurethane resin alone or in a mixture thereof. Moreover, these may use isocyanate as a crosslinking agent and may improve durability more. Furthermore, the amount of the binder in the nonmagnetic intermediate layer is preferably 10 to 50 parts by weight with respect to 100 parts by weight of the nonmagnetic inorganic powder.

  Examples of the lubricant include the lubricant described above as the lubricant for the magnetic layer. Among these, it is preferable to use a combination of fatty acids and fatty acid esters. The addition amount is preferably 0.1 to 3 parts by weight for each fatty acid and fatty acid ester with respect to 100 parts by weight of the nonmagnetic inorganic powder. Similarly, examples of the solvent for adjusting the nonmagnetic dispersion include those described above as the solvent for adjusting the magnetic dispersion.

  The back layer 5 is formed by applying a dispersion liquid in which an inorganic pigment is dispersed in a binder. The back layer 5 is preferably formed with a thickness of 0.1 to 1.5 μm. If the thickness is less than 0.1 μm, the strength of the back layer is not sufficiently increased, and consequently the strength of the magnetic tape is not increased, so that not only the temperature expansion coefficient and humidity expansion coefficient in the width direction are increased, but also the width with the tension applied in the longitudinal direction. The change also increases, and the amount of creep change under a 1N load also increases. On the other hand, if the thickness is greater than 1.5 μm, the thickness of the magnetic tape itself increases, which hinders the increase in capacity.

  The inorganic powder, the binder, and the dispersant, lubricant, and the like used as necessary, and the solvent used for adjusting the back dispersion are conventionally known ones mixed in the back layer 5. Either can be used and is not limited at all. The inorganic powder preferably contains a plate-like or needle-like inorganic powder for the purpose of increasing the strength of the back layer, particularly in the width direction.

  Examples of the plate-like inorganic powder include mica and kaolin as natural products, and barium sulfate and iron oxide as synthetic products. The average particle diameter (in the plate surface direction) of the plate-like inorganic powder is preferably 0.15 to 2.0 μm, and the average thickness is preferably 0.005 to 0.1 μm. Examples of the acicular inorganic powder include iron oxide. The major axis length of the acicular inorganic powder is preferably 0.08 to 0.8 μm, and the minor axis length is preferably 0.005 to 0.05 μm.

  In addition to the plate-like or needle-like inorganic powder, carbon black is preferably added to the back layer 5 to prevent charging. The average particle diameter varies from about 5 to 500 nm, preferably 5 to 150 nm, more preferably 10 to 100 nm, and it is preferable to use a single particle in combination. Specifically, known materials such as acetylene black, furnace black, and thermal black can be used alone or in combination. Furthermore, carbon black may be surface-treated and coated on a plate-like or needle-like inorganic powder for the same purpose.

  Further, for the purpose of preventing the surface change of the back layer 5 during repeated running, or for the purpose of controlling the signal when the servo signal is optically recorded on the back layer 5 in particular, alumina, titanium oxide, Inorganic powders such as calcium carbonate, barium sulfate, chromium oxide, and iron oxide may be mixed.

  Examples of the binder include a binder for a magnetic layer and the binder described above for a nonmagnetic intermediate layer. Among these, it is preferable to use a mixture of a polyurethane resin and a cellulose resin. Moreover, these may use isocyanate as a crosslinking agent and may improve durability more. Furthermore, the amount of the binder in the back layer is preferably 20 to 150 parts by weight with respect to 100 parts by weight of the back layer inorganic powder. Similarly, examples of the solvent for adjusting the back layer dispersion include those described above as the solvent for adjusting the magnetic dispersion and the nonmagnetic dispersion.

  The above-described magnetic powder and binder, non-magnetic inorganic powder and binder, and back layer inorganic powder and binder can be adjusted by a conventionally known method. For example, a sand mill, a roll mill, etc. A ball mill, a kneader, a pressure kneader, an extruder, a homogenizer, a disper, an ultrasonic disperser, or the like can be used. Among these, it is preferable to use a combination of adjustment for kneading such as a kneader and adjustment for dispersion such as a sand mill.

  As a method for forming a magnetic dispersion on the nonmagnetic support 1 and, if necessary, a nonmagnetic dispersion between them simultaneously or sequentially, a conventionally known method such as blade coating, gravure coating, die coating or the like is used. Can do. The same applies to the back layer dispersion. Further, the application onto the nonmagnetic support 1 may be performed first on the magnetic layer side or the back layer side, or simultaneously.

  Further, a water repellent effect may be applied to the tape edge for the purpose of reducing the humidity expansion coefficient. Methods for applying a water repellent effect to the edge include supplying a water repellent to the slitter knife during slitting, or applying a woven cloth soaked with water repellent to the edge of the slit media after slitting, etc. Is mentioned. Examples of the water repellent include perfluoropolyether and carboxylic acid ester compounds, carboxylic acid perfluoroalkyl esters, and fluorinated alkyl succinic acid esters.

As described above, in the present embodiment, a reinforcing film is provided on both surfaces of a plastic film serving as a nonmagnetic support, the Young's modulus of the reinforcing film is 7 × 10E03 kg / mm ² or more, and the thermal expansion coefficient is 18 × 10E. By setting the temperature to −06 / ° C. or less, the dimensional change in the width direction of the tape itself due to environmental factors such as temperature and humidity changes, tension changes, and creep can be reduced as a whole. As a result, even when the track density in the tape width direction is very high, stable recording / reproducing characteristics with less off-track can be ensured. In addition, the easy-adhesion layer can ensure the adhesive strength between the reinforcing film and the nonmagnetic intermediate layer, and between the reinforcing film and the back layer, making it possible to produce a magnetic recording medium with excellent durability. .

Hereinafter, the present invention will be described in more detail with reference to examples.
<Example 1>
First, as shown below, an aluminum oxide film was formed on both surfaces of polyethylene terephthalate (PET) as a nonmagnetic support so as to have a thickness of 90 nm per side by vacuum deposition.
[Non-magnetic support]
Plastic film 1a: PET (thickness: 4.9 μm, Young's modulus: longitudinal direction (MD) / width direction (TD) = 650/500 kg / mm ² )
-Reinforcing film 1b: Aluminum oxide film (film thickness: 90 nm)

Next, a dispersion composition for forming the magnetic layer 3, the nonmagnetic intermediate layer 7, and the back layer 5 was prepared according to the following composition. Furthermore, the dispersion liquid for forming the easily bonding layer 2 was adjusted.
[Magnetic dispersion]
{Magnetic powder}
・ Iron-cobalt alloy metal ferromagnetic powder (average major axis length: 45 nm) / 100 parts by weight {binder}
Polyester polyurethane resin (number average molecular weight: 22000) / 8 parts by weight Vinyl chloride copolymer (average degree of polymerization: 300) / 10 parts by weight {abrasive agent}
・ Α-alumina (average particle size: 0.3 μm) / 10 parts by weight {antistatic agent}
・ Carbon black (average particle size: 50 nm) / 3 parts by weight {lubricant}
・ Stearic acid / 1 part by weight ・ Butyl stearate / 1 part by weight ・ Stearic amide / 0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Toluene / 20 parts by weight ・ Cyclohexanone / 10 parts by weight The above materials are kneaded with an extruder and three rolls, further diluted with methyl ethyl ketone, toluene and cyclohexanone, then dispersed in a sand mill, and filtered. I applied. Subsequently, 4 parts by weight of polyisocyanate (Japanese polyurethane curing agent “Coronate L”) was added, and after stirring, this was used as a magnetic dispersion.

[Non-magnetic dispersion]
{Nonmagnetic inorganic powder}
・ Acicular α-iron oxide (average major axis length: 0.10 μm) / 100 parts by weight ・ α-alumina (average particle size 0.3 μm) / 6 parts by weight {binder}
Polyester polyurethane resin (number average molecular weight: 22000) / 8 parts by weightVinyl chloride copolymer (average polymerization degree: 300) / 8 parts by weight {Antistatic agent}
・ Carbon black (average particle size: 20 nm) / 20 parts by weight {lubricant}
・ Stearic acid / 1 part by weight ・ Butyl stearate / 2 part by weight {solvent}
Methyl ethyl ketone / 70 parts by weight Toluene / 70 parts by weight Cyclohexanone / 40 parts by weight The above materials were kneaded with an extruder, further diluted with methyl ethyl ketone, toluene, and cyclohexanone, and then dispersed in a sand mill and filtered. Next, 3 parts by weight of polyisocyanate (Japanese polyurethane curing agent “Coronate L”) was added, and after stirring, this was used as a nonmagnetic dispersion.

[Back layer dispersion]
{Inorganic powder}
Carbon black (average particle size: 20 nm) / 100 parts by weight Carbon black (average particle size: 70 nm) / 15 parts by weight Plate-like α-iron oxide (average particle size: 0.9 μm, average thickness: 0.015 μm) ) / 15 parts by weight. Titanium oxide (average particle size: 100 nm) / 1 part by weight {binder}
Polyester polyurethane resin (number average molecular weight: 35000) / 25 parts by weight Nitrocellulose resin (molecular weight: equivalent to 1 / 2H) / 25 parts by weight {solvent}
-Methyl ethyl ketone / 200 parts by weight-Toluene / 200 parts by weight-Cyclohexanone / 50 parts by weight After mixing the above materials, sand mill dispersion, filter, and polyisocyanate (Japanese polyurethane curing agent "Coronate L") 10 weights After adding part and stirring, this was made into the back layer dispersion.

[Easily adhesive layer dispersion]
{Easy Adhesive 1}
Aromatic polyester resin (number average molecular weight 19000, Tg: 60 ° C., isophthalic acid, terephthalic acid polyester, OH group concentration: 0.11 mmol / g) /0.5 part by weight {solvent}
-Methyl ethyl ketone / 20 parts by weight-Cyclohexanone / 80 parts by weight The above materials were mixed and dispersed with a disperser, and filtered to obtain an easily adhesive layer dispersion (adhesive).

  First, an easy-adhesion layer dispersion (adhesive) was applied on one surface of a non-magnetic support on which aluminum oxide was vacuum-deposited on both surfaces, and dried to adjust the thickness to 20 nm. Next, in the order of the non-magnetic dispersion and the magnetic dispersion, die coating was simultaneously performed so that the dry thicknesses were 1.1 μm and 0.1 μm, respectively, and then magnetic field orientation treatment and drying treatment were performed and wound as a roll. Then, after applying and drying the easy-adhesion layer dispersion (adhesive) on the other surface of the nonmagnetic support (dry thickness 20 nm), the back layer dispersion is die-coated so that the dry thickness is 0.5 μm. Then, it was dried and wound up as a roll. And after performing a calendar process and a hardening process, it slitted so that it might become a 1/2 inch width | variety, and wound up, and it was set as the sample.

<Example 2>
In Example 1, a sample was obtained in the same manner as in Example 1 except that the thickness of the easy adhesion layer was 45 nm.

<Example 3>
In Example 1, a sample was obtained in the same manner as in Example 1 except that the thickness of the easy-adhesion layer was 10 nm.

<Example 4>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 2 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. A sample was obtained.

[Easily adhesive layer dispersion]
{Easily adhesive 2}
Aromatic polyester resin (number average molecular weight 18000, Tg: 68 ° C., isophthalic acid, terephthalic acid polyester, OH group concentration: 0.12 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Example 5>
In Example 1, as the nonmagnetic support, a sample having the same Young's modulus and the like as described below and having a thickness of 4.9 μm obtained by vacuum-depositing Al was used. Got.

[Non-magnetic support]
Plastic film 1a: PET (thickness: 4.9 μm, Young's modulus: longitudinal direction (MD) / width direction (TD) = 650/500 kg / mm ² )
Strengthening film 1b: Al (film thickness: 90 nm)

<Example 6>
In Example 1, as the nonmagnetic support, a sample having the same Young's modulus and the like as described below and having a thickness of 4.9 μm and Cu deposited on both sides of the vacuum was used. Got.

[Non-magnetic support]
Plastic film 1a: PET (thickness: 4.9 μm, Young's modulus: longitudinal direction (MD) / width direction (TD) = 650/500 kg / mm ² )
Strengthening film 1b: Cu (film thickness: 90 nm)

<Example 7>
In Example 1, as a nonmagnetic support, the same Young's modulus and the like as described below were used, and copper oxide was vacuum-deposited on both sides of PET having a thickness of 4.9 μm. Otherwise, the same procedure as in Example 1 was used. A sample was obtained.

[Non-magnetic support]
Plastic film 1a: PET (thickness: 4.9 μm, Young's modulus: longitudinal direction (MD) / width direction (TD) = 650/500 kg / mm ² )
Strengthening film 1b: Copper oxide (film thickness: 90 nm)

<Example 8>
In Example 1, as a nonmagnetic support, the same Young's modulus and others as described below were used, and titanium oxide was vacuum-deposited on both sides of PET having a thickness of 4.9 μm. A sample was obtained.

[Non-magnetic support]
Plastic film 1a: PET (thickness: 4.9 μm, Young's modulus: longitudinal direction (MD) / width direction (TD) = 650/500 kg / mm ² )
Strengthening film 1b: titanium oxide (film thickness: 90 nm)

<Example 9>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 3 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. Sample.

[Easily adhesive layer dispersion]
{Easy Adhesive 3}
Aromatic polyester polyurethane resin (number average molecular weight 18000, Tg: 79 ° C., isophthalic acid, terephthalic acid polyester, OH group concentration: 0.16 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Example 10>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 4 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. Sample.

[Easily adhesive layer dispersion]
{Easily adhesive 4}
Aromatic polyester polyurethane resin (number average molecular weight 18000, Tg: 68 ° C., isophthalic acid, terephthalic acid polyester, OH group concentration: 0.07 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Comparative Example 1>
In Example 1, a sample was obtained in the same manner as in Example 1 except that the easy adhesion layer was not provided on the nonmagnetic support.

<Comparative example 2>
In Example 1, a sample was obtained in the same manner as in Example 1 except that the thickness of the easy adhesion layer 2 was 100 nm.

<Comparative Example 3>
In Example 1, a sample was obtained in the same manner as in Example 1 except that the thickness of the easy-adhesion layer 2 was 4 nm.

<Comparative Example 4>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 5 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. Sample.

[Easily adhesive layer dispersion]
{Easily adhesive 5}
Aliphatic polyester resin (number average molecular weight 28000, Tg: −15 ° C., adipic acid polyester, OH group concentration: 0.07 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Comparative Example 5>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 6 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. Sample.

[Easily adhesive layer dispersion]
{Easily adhesive 6}
Aliphatic + aromatic polyester resin (number average molecular weight 20000, Tg: 35 ° C., isophthalic acid, adipic acid polyester, OH group concentration: 0.20 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Comparative Example 6>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 7 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. A sample was obtained.

[Easily adhesive layer dispersion]
{Easily adhesive 7}
Aromatic polyester polyurethane resin (number average molecular weight 18000, Tg: 95 ° C., terephthalic acid isophthalic acid polyester, OH group concentration: 0.07 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

<Comparative Example 7>
In Example 1, the easy-adhesive was changed to the following easy-adhesive 8 to prepare an easy-adhesive layer dispersion (adhesive), and the thickness of the easy-adhesive layer was 20 nm. Sample.

[Easily adhesive layer dispersion]
{Easily adhesive 8}
Aromatic polyester polyurethane resin (number average molecular weight 5000, Tg: 60 ° C., terephthalic acid isophthalic acid polyester, OH group concentration: 0.03 mmol / g) /0.5 part by weight {solvent}
・ Methyl ethyl ketone / 20 parts by weight ・ Cyclohexanone / 80 parts by weight

  Various properties of the reinforcing films of the nonmagnetic support in the above Examples and Comparative Examples and the obtained magnetic tape were measured as follows.

[Measurement of film thickness of easy adhesion layer]
Spectral ellipsometry is used for samples that are simply coated with an easy-adhesion layer dispersion (adhesive) and dried, and the thickness of the easy-adhesion layer is determined from the difference in refractive index between the base film and the easy-adhesion layer. Asked.

[Measurement of roll adhesion]
In each of the above Examples and Comparative Examples, an easy-adhesion layer, a nonmagnetic intermediate layer + magnetic layer, and a back layer were formed, and a roll at the stage of calendar treatment was prepared. Note that the magnetic layer and the back layer were not formed on the roll ear. The roll was cured in a curing oven at 70 ° C./20 hours. Thereafter, the roll was taken out and rewound, and the degree of adhesion between the magnetic layer forming surface and the back layer forming surface and the degree of adhesion of the ear portion where the magnetic layer and the back layer were not formed were measured. The case where it was easily peeled off by the rewinding machine was judged as having no adhesion, and the case where it could not be peeled off by the rewinding machine was judged as having adhesion.

[Measurement of adhesive strength]
The magnetic surface of the sample tape (magnetic layer forming surface) and the dedicated adhesive tape are bonded with a force of 1.0 N, and peeled off at a speed of 254 mm / min using a peel method tester, and the magnetic surface is not The force when peeled from the magnetic support was measured as the adhesive strength. The adhesive strength was set to 1.0 N or more as a standard value (pass).

[Measurement of initial MP (missing pulses)]
A modified HP LTO drive (Ultraun 960) was used as the measuring device. First, a 2T signal was recorded in a constant environment of 25 ° C. and 50% RH, and was reproduced in this environment immediately after recording. A signal at the time of 35% decrease from the average value of the base-to-peak output of the reproduction signal was defined as Missing Pulse. The number of missing pulses per 1 m track was measured. The standard (accepted) was 1 or less per 1 m per track.

[Measurement of MP (missing pulses) after storage]
In the above drive, the recorded cartridge was stored for one week in a constant environment of 50 ° C. and 80% RH. Thereafter, reproduction was performed with a drive (Ultriun 960) in an environment of 25 ° C. and 50% RH. The signal at the time of 35% reduction from the average value of the base-to-peak output of the reproduction signal was defined as Missing Pulse, and the number of Missing Pulses per 1 m track was measured.

[Measurement of ERT (Error Rate) after storage]
Under an environment of 25 ° C. and 50% RH, a random signal was recorded over the entire length using an HP LTO drive (Ultraun 960) as a measuring device. Next, the cartridge was stored in an environment of 50 ° C. and 80% RH for 7 days. After the cartridge was stored at room temperature for one day, the full length was reproduced, and the error rate of the signal at the time of reproduction was measured. The standard value of ERT is 1 * 10 ⁻³ or less.

  Table 1 shows the measurement results for the examples, and Table 2 shows the measurement results for the comparative examples.

  As shown in Table 1, the film made of the above material on both surfaces of the non-magnetic support and the easy-adhesion layer applied with an appropriate thickness were free from roll sticking by the curing process, and the adhesive strength satisfied the standard. As the durability of the tape, stable characteristics were obtained with a small number of Missing Pulses after storage at 50 ° C./80% RH for 1 week. After storage of the tape, the Tg and -OH group concentration of the easy-adhesion layer was within the scope of the claims, and the error rate satisfied the standard value, and a magnetic recording medium excellent in running durability could be obtained.

In Comparative Example 1 in which no easy-adhesion layer was provided, and in Comparative Example 3 in which the easy-adhesion layer deviated from the thickness range defined in the present invention, the adhesive strength did not satisfy the standard. In addition, Comparative Examples 4 and 5 in which the glass transition temperature Tg of the easy-adhesion layer is lower than the lower limit defined in the present invention have a large amount of Missing Pulse after initial storage, and an increase in Error Rate after storage. There was a problem with running durability. In Comparative Example 6 in which the glass transition temperature Tg of the easy-adhesion layer is higher than the upper limit defined in the present invention, the adhesive strength could not satisfy the standard.
In Comparative Example 2 in which the easy-adhesion layer deviates from the thickness range defined in the present invention, roll adhesion at the time of curing was severe and it was difficult to produce a tape. When the —OH group concentration was as low as 0.03 mmol / g as in Comparative Example 7, the adhesive strength was low and the standard could not be satisfied. Further, as in Comparative Example 5, when the —OH group concentration was as high as 0.20 mmol / g, the adhesive strength satisfied the standard, but the number of MP after storage increased and the standard could not be satisfied.

It is sectional drawing which shows the structure of the magnetic-recording medium based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 1a ... Plastic film, 1b ... Reinforcement film, 2 ... Easy adhesion layer, 3 ... Magnetic layer, 5 ... Back layer, 7 ... Non Magnetic intermediate layer

Claims (5)

From a nonmagnetic support in which a reinforcing film made of a metal, an alloy or an oxide thereof alone or a composite material thereof is formed on both surfaces of the base film, and a nonmagnetic material provided on one surface of the nonmagnetic support In a magnetic recording medium comprising a nonmagnetic intermediate layer and a magnetic layer comprising a ferromagnetic powder and a binder, and a back layer provided on the other surface,
A magnetic recording medium comprising an easy adhesion layer made of a resin for ensuring adhesion between the reinforcing film and the nonmagnetic intermediate layer and between the reinforcing film and the back layer.   The magnetic recording medium according to claim 1, wherein the easy-adhesion layer has a thickness of 5 to 50 nm.   The magnetic recording medium according to claim 1, wherein the easy-adhesion layer has a glass transition temperature Tg of 50 to 90 ° C.   The magnetic recording medium according to claim 1, wherein the easy adhesion layer includes an aromatic polyester resin or an aromatic polyurethane resin.   2. The magnetic recording medium according to claim 1, wherein an OH group is introduced into the resin of the easy adhesion layer at a concentration of 0.05 to 0.18 mmol / g.

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