JP2007294075A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium securing surface properties, suppressing nonuniform elongation even during storage in a high temperature environment, having enhanced dimensional stability and thereby highly reliably recording and reproducing data. <P>SOLUTION: The magnetic recording medium includes at least one magnetic layer provided on a nonmagnetic substrate, wherein the nonmagnetic substrate is made from a polyethylene naphthalate and has a thickness of 6.5 μm or smaller, and the magnetic recording medium has a creep deformation of 0.30% or less in a longitudinal direction of the magnetic recording medium under a tensile stress of 15.7 MPa applied in the longitudinal direction at 60°C for 50 hours. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a magnetic recording medium having improved tape dimensional stability, particularly dimensional stability in a high-temperature environment. Specifically, the surface property can be ensured and the medium is non-uniform even when stored in a high-temperature environment. The present invention relates to a magnetic recording medium in which elongation is suppressed and data can be recorded / reproduced with high reliability.

In the field of data backup tape, as the capacity of the hard disk to be backed up has increased, products with a storage capacity of 100 GB or more per volume have been commercialized. Increasing the capacity of tape is essential.
The reliability of data recording and reproduction along with the increase in capacity described above is an extremely important factor. Even after storage in a harsh environment, for example, in a high temperature environment, it is necessary to accurately record data and to accurately reproduce the recorded data. However, in such an environment, since each member constituting the magnetic recording medium is generally deformed by creep or the like and a dimensional change or the like may occur due to this, accurate data recording / reproduction is possible. May not be possible.
Also, to increase the capacity per volume of backup tape, reduce the total thickness of the tape to 1
It is also necessary to increase the tape length per winding. When a thin magnetic recording medium is recorded / reproduced by a drive, the driving tension causes non-uniform elongation of the medium, which reduces running stability.

In order to solve this problem, for example, in Patent Document 1, one or more magnetic layers are provided on a polyethylene terephthalate support having a thickness of 7 μm or less, and a tensile stress of 19.1 MPa at 50 ° C. is applied in the longitudinal direction of the medium for 25 minutes. A magnetic recording medium is proposed in which the amount of creep deformation in the longitudinal direction of the medium is less than 0.04%. This magnetic recording medium does not generate non-uniform elongation even when stored or used in a harsh environment, and the durability of the medium, particularly the cycle durability, is improved. However, according to the study of the present inventor, when the medium was processed under the heat treatment conditions described in the example of Patent Document 1, the surface roughness Ra was increased and deteriorated, and the high recording density used in recent data backup tapes. The surface properties required for the medium could not be satisfied, and sufficient magnetic tape reproduction output could not be obtained.
JP 2000-251239 A

An object of the present invention is to provide a magnetic recording capable of ensuring surface properties and suppressing uneven distribution of a medium even when stored in a high temperature environment, improving dimensional stability, and recording / reproducing data with high reliability. To provide a medium.

The present inventor paid attention to a non-magnetic support among the materials constituting the magnetic recording medium, and proceeded with studies on the shape stability thereof. As a support, polyethylene naphthalate (PE
It has been found that a magnetic recording medium capable of achieving the above object can be obtained by performing a specific heat treatment using N).
The present invention is as follows.
1) In a magnetic recording medium in which at least one magnetic layer is provided on a nonmagnetic support, the nonmagnetic support is polyethylene naphthalate having a thickness of 6.5 μm or less, and 60 ° C. with respect to the magnetic recording medium. When a tensile stress of 15.7 MPa is applied in the longitudinal direction of the magnetic recording medium for 50 hours, the creep deformation amount in the longitudinal direction is 0.30% or less.
2) The magnetic layer has a center line average surface roughness Ra of 1 to 3 nm.
) Magnetic recording medium.
3) When a tensile stress of 15.7 MPa is applied to the nonmagnetic support at 60 ° C. for 50 hours in the longitudinal direction of the nonmagnetic support, the creep deformation amount in the longitudinal direction is 0.30% or less. The magnetic recording medium described in 1) or 2) above.
4) The above 1) characterized in that a nonmagnetic layer is provided between the nonmagnetic support and the magnetic layer.
To 3).

According to the present invention, magnetic recording that can ensure surface properties, suppress the uneven elongation of the medium even during storage in a high temperature environment, improve the dimensional stability, and can record and reproduce data with high reliability. A medium can be provided.

Hereinafter, the present invention will be described in more detail.
The magnetic recording medium of the present invention is characterized in that when a tensile stress of 15.7 MPa is applied in the longitudinal direction at 60 ° C. for 50 hours, the amount of creep deformation in the longitudinal direction is 0.30% or less.
In order to satisfy the creep deformation amount of the present invention, a method in which the nonmagnetic support before the coating is previously heat-treated at a temperature 25 ° C. or more lower than the glass transition temperature (Tg) of the nonmagnetic support is suitable. This heat treatment is preferably carried out at a temperature 30 ° C. or more lower than the Tg of the nonmagnetic support.
More preferably, it is carried out at a temperature 35 ° C. or more lower than the Tg of the nonmagnetic support. The minimum of the temperature of heat processing is 50-70 degreeC, for example. The heat treatment time is, for example, 1 to 240 hours,
Preferably it is 5-168 hours, More preferably, it is 10-120 hours. A heat treatment temperature lower than 50 ° C. may be used, but the heat treatment time becomes too long. After the heat treatment, it is gradually cooled to room temperature, and then a coating solution for forming each coating layer is applied and dried. The drying temperature after applying the coating solution is desirably set so that the web temperature does not exceed the Tg of the nonmagnetic support. If the web temperature exceeds the Tg of the nonmagnetic support, the creep deformation amount of the present invention may not be satisfied.
In addition, Tg said by this invention is the value measured by the temperature of the maximum value of the loss elastic modulus of the dynamic viscoelasticity measurement measured at 10 Hz. Using a known dynamic viscoelasticity measuring device, for example, DMS6100 connected to EXSTAR6000 station manufactured by Seiko Instruments Inc., the temperature is measured at 10 Hz between 15 ° C. and 200 ° C., and the temperature at the maximum value of the loss elastic modulus is measured. Ask.

The creep deformation amount of the present invention is measured when a tensile stress of 15.7 MPa is applied to the magnetic recording medium at 60 ° C. for 50 hours in the longitudinal direction. The creep deformation is measured as follows. Known creep deformation measuring device, for example, TM-9300 manufactured by ULVAC-RIKO
A sample having a length of 15 mm and a width of 5 mm is cut out from the longitudinal direction. This sample was set in the creep deformation measuring device. First, a tensile stress of 0.6 MPa was applied in the longitudinal direction at a measurement temperature of 60 ° C. for 30 minutes, and then a tensile stress of 15.7 MPa was applied in the longitudinal direction at a measurement temperature of 60 ° C. For 50 hours in the direction, and the elongation of the obtained sample is determined by the initial length of the sample before applying tensile stress (
It is calculated by the following formula as a percentage with respect to the sample length after applying a tensile stress of 0.6 MPa for 30 minutes in the longitudinal direction at a measurement temperature of 60 ° C.
Creep deformation amount = {(length in sample longitudinal direction after applying tensile stress−initial sample length) / initial sample length} × 100 (%)
The creep deformation amount in the present invention is 0.30% or less. By satisfying this creep deformation amount, it is possible to ensure the surface property and improve the dimensional stability. A preferable creep deformation amount is 0.20% or less, and a more preferable creep deformation amount is 0.15% or less.

1. Nonmagnetic Support A nonmagnetic support that can be used in the present invention is polyethylene naphthalate (PEN).
In general, polyethylene terephthalate, polyamide, polyamideimide, aromatic polyamide, and the like are known as nonmagnetic supports for magnetic recording media in addition to PEN, but the amount of creep deformation in the present invention is achieved by the heat treatment. And what produces the desired effect is
The reason is not clear, but only PEN.
PEN may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, and the like. PEN may be biaxially stretched.
In the present invention, the creep deformation amount in the longitudinal direction of PEN is preferably 0.30% or less. The amount of creep deformation of PEN can be measured by the method described above. The preferable creep deformation amount of PEN is 0.20% or less, and the more preferable creep deformation amount is 0.15%.
It is as follows. The amount of creep deformation is determined by providing each coating layer on the front and back surfaces of PEN, drying,
The range is preferably maintained even after the magnetic recording medium is formed. When confirming the amount of creep deformation of PEN after the magnetic recording medium is prepared, the coating layer (including the back layer) is dissolved and removed with methyl ethyl ketone.
The PEN is subjected to the heat treatment described above, but the center line average surface roughness Ra of the PEN before the heat treatment.
Is preferably from 1.0 to 4.0 nm, more preferably from 2.0 to 3.5 nm.

2. Magnetic Layer and Nonmagnetic Layer Binder The binder (binder) used in the magnetic layer, nonmagnetic layer, and back layer of the present invention is a conventionally known thermoplastic resin, thermosetting resin, reactive resin, or a mixture thereof. is there. Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid,
Polymers or copolymers containing acrylic acid esters, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid esters, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as structural units, polyurethane resins, and various rubber resins Can be mentioned.

Examples of thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, and epoxy-polyamide resins. And a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. The thermoplastic resin, thermosetting resin and reactive resin are all described in detail in “Plastic Handbook” issued by Asakura Shoten.

Further, when an electron beam curable resin is used for the magnetic layer, not only the coating film strength is improved and the durability is improved, but also the surface is smoothed and the electromagnetic conversion characteristics are further improved. These examples and their production methods are described in detail in JP-A No. 62-256219.

The above resins can be used alone or in combination. Among them, it is preferable to use a polyurethane resin, and further, a cyclic structure such as hydrogenated bisphenol A or a polypropylene oxide adduct of hydrogenated bisphenol A, a polyol having an alkylene oxide chain with a molecular weight of 500 to 5000, and a chain extender. A polyurethane resin having a cyclic structure and a molecular weight of 200 to 500 and an organic diisocyanate and having a polar group introduced, or an aliphatic dibasic acid such as succinic acid, adipic acid, and sebacic acid; Dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1
Polyester polyols made of aliphatic diols having no alkyl ring side chain such as, 3-propanediol and 2,2-diethyl-1,3-propanediol and having no cyclic structure;
An aliphatic diol having a branched alkyl side chain having 3 or more carbon atoms such as 2-ethyl-2-butyl-1,3-propanediol and 2,2-diethyl-1,3-propanediol as a chain extender; Reaction with an organic diisocyanate compound and introduction of a polar group into a polyurethane resin or a cyclic structure such as dimer diol, a polyol compound having a long chain alkyl chain, and an organic diisocyanate, and introduction of a polar group It is preferable to use a polyurethane resin.

The average molecular weight of the polar group-containing polyurethane resin used in the present invention is 5,000-10.
It is preferably 10,000, and more preferably 10,000 to 50,000. If the average molecular weight is 5,000 or more, it is preferable because the resulting magnetic coating film is not brittle and the physical strength is not lowered, and the durability of the magnetic recording medium is not affected. Also, if the molecular weight is 100,000 or less, the solubility in the solvent will not decrease,
Dispersibility is also good. Further, since the viscosity of the paint at a predetermined concentration does not increase, the workability is good and the handling is easy.

Examples of the polar group contained in the polyurethane resin, for example, -COOM, _-SO 3 M
, —OSO ₃ M, —P═O (OM) ₂ , —OP—O═OM (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base), —OH, —NR ₂ , —N ⁺ R ₃ (R is a hydrocarbon group), an epoxy group, -SH, -CN, etc., and at least one of these polar groups introduced by copolymerization or addition reaction can be used. Moreover, when this polar group-containing polyurethane-based resin has an OH group, it preferably has a branched OH group from the viewpoint of curability and durability, and preferably has 2 to 40 branched OH groups per molecule. 3 to 2 per molecule
More preferably, it has zero. The amount of such polar group is from ¹⁰ -1 ^{to 10 -8} mol / g, preferably ¹⁰ -2 ^{to 10 -6} mol / g.

Specific examples of the binder include, for example, VAGH, VYHH, VMCH, manufactured by Dow Chemical Co., Ltd.
VAGF, VAGD, VROH, VYES, VYNC, VMCC, XYHL, XYSG,
PKHH, PKHJ, PKHC, PKFE, Nissin Chemical Industry MPR-TA, MPR-T
A5, MPR-TAL, MPR-TSN, MPR-TMF, MPR-TS, MPR-TM
, MPR-TAO, manufactured by Denki Kagaku 1000W, DX80, DX81, DX82, DX83
, 100FD, ZEON Corporation MR-104, MR-105, MR110, MR100,
MR555, 400X-110A, Nippon Polyurethane N2301, N23 manufactured by Nippon Polyurethane
02, N2304, Pandex T-5105, T-R3080, T-manufactured by Dainippon Ink
5201, Burnock D-400, D-210-80, Crisbon 6109, 7209,
Byron UR8200, UR8300, UR-8700, RV530, RV2 manufactured by Toyobo Co., Ltd.
80, Daiferamin 4020, 5020, 5100, 5300, 9020 manufactured by Dainichi Seika Co., Ltd.
, 9022, 7020, MX5004 manufactured by Mitsubishi Chemical Co., Ltd., Sanprene SP-15 manufactured by Sanyo Kasei Co., Ltd.
0, Saran F310, F210 manufactured by Asahi Kasei Corporation.

The addition amount of the binder used in the magnetic layer of the present invention is in the range of 5 to 50% by mass, preferably in the range of 10 to 30% by mass with respect to the mass of the ferromagnetic powder. The amount of the binder used in the nonmagnetic layer of the present invention is in the range of 5 to 50% by mass, preferably 10 to 10% by mass of the nonmagnetic powder.
It is in the range of 30% by mass. In the case of using polyurethane, it is preferable to use 2-20% by mass and polyisocyanate in a range of 2-20% by mass.
When head corrosion occurs due to a small amount of dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate. When using a vinyl chloride resin as the other resin, it is preferably in the range of 5 to 30% by mass. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.49 to 98 MPa (0.05 to 10 kg / kg).
mm ² ) and the yield point is preferably 0.49 to 98 MPa (0.05 to 10 kg / mm ² ).

Ferromagnetic powder In the magnetic recording medium of the present invention, as a ferromagnetic powder, an acicular ferromagnetic material having an average major axis length of 20 to 50 nm, a flat magnetic material having an average plate diameter of 10 to 50 nm, or an average diameter of 10 to 50 nm. It is preferable to use a spherical or elliptical magnetic material. Each will be described below.
(1) Acicular ferromagnet As the ferromagnetic powder used in the magnetic recording medium of the present invention, an acicular ferromagnet having an average major axis length of 20 to 50 nm can be used. Examples of the acicular ferromagnet include an acicular ferromagnetic metal powder such as cobalt-containing ferromagnetic iron oxide or ferromagnetic alloy powder, and a BET specific surface area (
S _BET) is preferably 40 to 80 m ² / g, more preferably 50 to 70 m ² / g. The crystallite size is preferably 12 to 25 nm, more preferably 13 to 22 nm, and particularly preferably 14 to 20 nm. The major axis length is 20-50 nm, preferably 20-4
0 nm.

Ferromagnetic powders include yttrium-containing Fe, Fe—Co, Fe—Ni, and Co—Ni.
-Fe is mentioned, and the yttrium content in the ferromagnetic powder is preferably a ratio of yttrium atoms to iron atoms, and Y / Fe is preferably 0.5 atomic% to 20 atomic%, more preferably 5 to 10%.
Atomic%. If it is less than 0.5 atomic%, the ferromagnetic powder cannot be increased in σs, so that the magnetic characteristics are lowered and the electromagnetic conversion characteristics are lowered. If it is larger than 20 atomic%, the iron content decreases, so that the magnetic properties are lowered and the electromagnetic conversion properties are lowered. In addition, 2 per 100 atomic percent of iron
Within the range of 0 atomic% or less, aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper, zinc, molybdenum, rhodium, palladium, tin, antimony, boron, barium, tantalum, tungsten, rhenium, gold Lead, phosphorus, lanthanum,
Can include cerium, praseodymium, neodymium, tellurium, bismuth, and the like. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide.

An example of the manufacturing method of the ferromagnetic powder which introduce | transduced cobalt and yttrium used for this invention is shown.
An example in which iron oxyhydroxide obtained by blowing an oxidizing gas into an aqueous suspension in which a ferrous salt and an alkali are mixed is used as a starting material can be given.
As the kind of this iron oxyhydroxide, α-FeOOH is preferable. As its manufacturing method,
There is a first production method in which ferrous salt is neutralized with alkali hydroxide to form an aqueous suspension of Fe (OH) ₂ , and an oxidizing gas is blown into this suspension to form acicular α-FeOOH. . On the other hand, there is a second production method in which ferrous salt is neutralized with alkali carbonate to form an aqueous suspension of FeCO ₃ , and oxidizing gas is blown into this suspension to form spindle-shaped α-FeOOH. Such an iron oxyhydroxide is obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution to obtain an aqueous solution containing ferrous hydroxide and oxidizing it by air oxidation or the like. Is preferred. In this case, Ni salt, alkaline earth element salt such as Ca salt, Ba salt, Sr salt, Cr salt, Zn salt, etc. may coexist in the ferrous salt aqueous solution, and such salt is appropriately selected. Particle shape (axial ratio)
Etc. can be prepared.

As the ferrous salt, ferrous chloride, ferrous sulfate and the like are preferable. As the alkali, sodium hydroxide, aqueous ammonia, ammonium carbonate, sodium carbonate and the like are preferable. Also,
As the salt that can coexist, chlorides such as nickel chloride, calcium chloride, barium chloride, strontium chloride, chromium chloride, and zinc chloride are preferable.

Next, when introducing cobalt into iron, before introducing yttrium, an aqueous solution of a cobalt compound such as cobalt sulfate or cobalt chloride is stirred and mixed into the iron oxyhydroxide slurry. After preparing a slurry of iron oxyhydroxide containing cobalt, an aqueous solution containing a compound of yttrium can be added to the slurry and mixed by stirring.

In addition to yttrium, neodymium, samarium, praseodymium, lanthanum, and the like can be introduced into the ferromagnetic powder of the present invention. These are yttrium chloride, neodymium chloride,
It can introduce | transduce using chlorides, such as samarium chloride, praseodymium chloride, lanthanum chloride, nitrates, such as neodymium nitrate and gadolinium nitrate, These may use 2 or more types together.

The coercive force (Hc) of the ferromagnetic metal powder is preferably 159.2-238.8 kA / m (2
, 3,000 to 3,000 Oe), more preferably 167.2 to 230.8 kA / m.
(2,100-2,900 Oe).
The saturation magnetic flux density is preferably 150 to 300 mT (1,500 to 3,000 G).
More preferably, it is 160-290 mT (1,600-2,900 G). The saturation magnetization (σs) is preferably 100 to 170 A · m ² / kg (100 to 170 em.
u / g), more preferably 110 to 160 A · m ² / kg (110 to 160 em).
u / g).

SFD (switching field distribution) of magnetic material itself
Is preferably smaller and is preferably 0.8 or less. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, the peak shift is small, and it is suitable for high-density digital magnetic recording. In order to reduce the Hc distribution, there are methods such as improving the particle size distribution of goethite in the ferromagnetic metal powder, using monodispersed α-Fe ₂ O ₃ , and preventing sintering between particles.

(2) Flat magnetic body As the flat magnetic body having an average plate diameter of 10 to 50 nm that can be used in the present invention, hexagonal ferrite powder is preferable.
Hexagonal ferrites include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and substitutions thereof such as Co substitutions thereof. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite partially containing a spinel phase. In addition to other predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo,
Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb, Bi
La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, Nb, Zn
It may contain atoms such as. Generally, Co-Zn, Co-Ti, Co-Ti-Zr
Co-Ti-Zn, Ni-Ti-Zn, Nb-Zn-Co, Sb-Zn-Co, Nb-
A material to which an element such as Zn is added can be used. Some raw materials and manufacturing methods contain specific impurities.

The particle size is preferably 10 to 50 nm in terms of average plate diameter. More preferably 10
It is -40 nm, Most preferably, it is 10-25 nm.
When reproducing with a magnetoresistive head, it is necessary to reduce noise, and the average plate diameter is preferably 40 nm or less. If the plate diameter is in the above range, stable magnetization can be expected without thermal fluctuation. In addition, since noise is reduced, it is suitable for high-density magnetic recording.
The average plate ratio is preferably 1 to 15, and more preferably 2 to 7. In the above range, the orientation is sufficient, stacking between particles hardly occurs, and noise is reduced. The specific surface area according to the BET method in this particle size range is 10 to ²⁰⁰ m ² / g. The specific surface area is generally signified as an arithmetic calculation value from the particle plate diameter and plate thickness. The crystallite size is 50 to 450 mm, preferably 100
~ 350cm. The distribution of the particle plate diameter and plate thickness is generally preferably as narrow as possible. The distribution is often not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average powder size =
0.1-2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improvement process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force Hc measured with a magnetic material is 39.8 to 398 kA / m (500 to 5,000 Oe).
) To the extent possible. A higher Hc is advantageous for high-density recording, but is limited by the capacity of the recording head. Usually, it is about 63.7 to 318.4 kA / m (800 to 4,000 Oe), but preferably 119.4 kA / m (1,500 Oe) or more, 278.6 kA / m (3,
500 Oe) or less. When the saturation magnetization of the head exceeds 1.4 Tesla, 159.2
It is preferable to make it kA / m (2,000 Oe) or more.
Hc can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like. The saturation magnetization σs is 40-80 A · m ² / kg (40-80e
mu / g). σs is preferably higher, but tends to be smaller as the particles become finer.
combining spinel ferrite with magnetoplumbite ferrite to improve s
Selection of the type and amount of elements contained is well known. It is also possible to use W-type hexagonal ferrite.

When dispersing the magnetic material (magnetic powder), the surface of the magnetic material particles is also treated with a material suitable for the dispersion medium and polymer. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% with respect to the magnetic substance. The pH of the magnetic material is also important for dispersion. Usually, about 4 to 12 has optimum values depending on the dispersion medium and polymer, but about 6 to 10 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects the dispersion. There is an optimum value depending on the dispersion medium and polymer, but usually 0.01 to 2.0.
% Is selected.

The hexagonal ferrite can be manufactured by (1) mixing a metal oxide replacing barium oxide, iron oxide, iron and boron oxide as a glass forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method in which a barium ferrite crystal powder is obtained by making an amorphous body and then reheating and then washing and grinding. (2) Hydrothermal reaction method in which barium ferrite composition metal salt solution is neutralized with alkali, by-products are removed, liquid phase heating is performed at 100 ° C or higher, washing, drying, and grinding to obtain barium ferrite crystal powder . (3) There is a coprecipitation method or the like in which a barium ferrite composition metal salt solution is neutralized with an alkali, removed by-products, dried, treated at 1,100 ° C. or less, and pulverized to obtain a barium ferrite crystal powder. However, this invention does not choose a manufacturing method.

(3) Spherical or elliptical magnetic body As the spherical or elliptical magnetic body, an iron nitride-based ferromagnetic powder having Fe ₁₆ N ₂ as a main phase is preferable. In addition to Fe and N atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo,
Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg, Pb, Bi
, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. The content of N with respect to Fe is preferably 1.0 to 20.0 atomic%.
The iron nitride is preferably spherical or elliptical, and the average needle ratio is preferably 1-2. The BET specific surface area (S _BET ) is preferably 30 to 100 m ² / g, more preferably 50 to 70 m.
It is a ² / g. The crystallite size is preferably 12 to 25 nm, more preferably 1
3-22 nm.
The saturation magnetization σs is preferably 50 to 200 A · m ² / kg (emu / g). More preferably, it is 70-150A * m < ² > / kg (emu / g).
The average powder size (average diameter or average long axis length) of the spherical or elliptical magnetic material is preferably 10 to 50 nm, more preferably 10 to 40 nm, and particularly preferably 1
0-25 nm.

In the present specification, the size of the magnetic material (hereinafter referred to as “powder size”) is determined from a high-resolution transmission electron micrograph. That is, the powder size is (1) the length of the long axis constituting the powder when the shape of the powder is needle-like, spindle-like, or columnar (however, the height is larger than the maximum major axis of the bottom). In other words, when the powder has a plate shape or columnar shape (however, the thickness or height is smaller than the maximum long diameter of the plate surface or bottom surface), the maximum of the plate surface or bottom surface is expressed. If the shape of the powder is spherical, polyhedral, unspecified, etc., and the major axis constituting the powder cannot be specified from the shape, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
Further, the average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by measuring as described above for about 350 primary particles. Primary particles refer to an independent powder without aggregation.
The average acicular ratio of the powder is determined by measuring the length of the minor axis of the powder in the above measurement, that is, the minor axis length, and calculating the arithmetic average of the values of (major axis length / minor axis length) of each powder. Point to. Here, the minor axis length is the definition of the powder size in the case of (1), the length of the minor axis constituting the powder, and in the case of (2),
In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
When the shape of the powder is specific, for example, in the case of the definition (1) of the powder size, the average powder size is referred to as an average major axis length, and in the case of the definition (2), the average powder size Is called the average plate diameter, and the arithmetic average of (maximum major axis / thickness to height) is called the average plate ratio. In the case of definition (3), the average powder size is referred to as the average diameter. In powder size measurement, the standard deviation / average value expressed as a percentage is defined as the coefficient of variation.

Further, as described above, the average powder size of the magnetic material is in a preferable range (acoustic ferromagnet is 20 to 5).
0 nm; 10 to 50 nm for a plate-like magnetic body; 10 to 50 nm for a spherical or elliptical magnetic body), thereby improving the surface properties of the medium, increasing the output during signal reproduction, and particles during signal reproduction. Excellent noise conversion characteristics can be obtained due to low noise.
Furthermore, by setting the average powder size of the magnetic material within the above preferable range, the dispersibility of the magnetic material is improved, demagnetization due to thermal fluctuation is suppressed, and electromagnetic conversion characteristics are excellent. If the average powder size exceeds the upper limit of the preferred range, the surface properties become rough, the output tends to be small, or the particulate noise tends to increase, and the electromagnetic conversion characteristics may be deteriorated.

Additives can be added to the magnetic layer in the present invention as necessary. Examples of the additive include an abrasive, a lubricant, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, a solvent, and carbon black.
Examples of these additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Polyolefin, polyglycol, polyphenyl ether, phenylphosphonic acid, benzylphosphonic acid group, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-
Phenethylphosphonic acid, diphenylmethylphosphonic acid, biphenylphosphonic acid, benzylphenylphosphonic acid, α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptyl Aromatic ring-containing organic phosphonic acids such as phenylphosphonic acid, octylphenylphosphonic acid, nonylphenylphosphonic acid and alkali metal salts thereof, octylphosphonic acid, 2-ethylhexylphosphonic acid, isooctylphosphonic acid, isononylphosphonic acid, isodecyl Alkylphosphones such as phosphonic acid, isoundecylphosphonic acid, isododecylphosphonic acid, isohexadecylphosphonic acid, isooctadecylphosphonic acid, isoeicosylphosphonic acid And alkali metal salts thereof, phenyl phosphate, benzyl phosphate, phenethyl phosphate, α-methylbenzyl phosphate, 1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, phosphorus Acid α-
Aromatic phosphate esters such as cumyl, toluyl phosphate, xylyl phosphate, ethyl phenyl phosphate, cumenyl phosphate, propyl phenyl phosphate, butyl phenyl phosphate, heptyl phenyl phosphate, octyl phenyl phosphate, nonyl phenyl phosphate And alkali metal salts thereof, octyl phosphate, 2-ethylhexyl phosphate, isooctyl phosphate, isononyl phosphate, isodecyl phosphate, isoundecyl phosphate, isododecyl phosphate, isohexadecyl phosphate, isooctadecyl phosphate, isoeicosyl phosphate Alkyl phosphate esters and alkali metal salts thereof, alkyl sulfonate esters and alkali metal salts thereof, fluorine-containing alkyl sulfate esters and alkali metal salts thereof, lauric acid, myristic acid, palmitic acid, stearic acid, Monobasic fatty acids which may contain or be branched, such as acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, erucic acid, etc. Or butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate A monobasic fatty acid which may contain or be branched from an unsaturated bond having 10 to 24 carbon atoms such as a rate, and a 1 to 6 valent alcohol which may contain or be branched from an unsaturated bond having 2 to 22 carbon atoms, 12 carbon atoms
A monofatty acid ester, a difatty acid ester or a polyvalent fatty acid ester composed of any one of an alkoxy alcohol which may contain or be branched by ˜22 and / or a monoalkyl ether of an alkylene oxide polymer, 22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms and the like can be used. In addition to the above hydrocarbon groups, alkyl groups, aryl groups, and aralkyl groups substituted with nitro groups and groups other than hydrocarbon groups such as halogen-containing hydrocarbons such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ You may have something.

In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).

The dispersant, lubricant, and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less.
Specific examples of these additives include, for example, NAF-102, castor oil hardened fatty acid, NAA-42, cation SA, Naimine L-201, and nonion E-208 manufactured by NOF Corporation.
, Anon BF, Anon LG, Takemoto Yushi Co., Ltd .: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: Engelbu OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Corporation: Armido P, Duomin TDO, Nissin Oilio: BA-41G, Sanyo Kasei: Profan 2012
E, New Pole PE61, Ionette MS-400, and the like.

Known organic solvents can be used in the magnetic layer of the present invention. The organic solvent is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol and methylcyclohexanol. , Esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, cresol, chlorobenzene, etc. Aromatic hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide,
Hexane or the like can be used.

These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are 3
It is preferably 0% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same in the magnetic layer and the nonmagnetic layer. The amount added may be changed. Use a solvent with high surface tension (cyclohexanone, dioxane, etc.) in the nonmagnetic layer to increase the coating stability. Specifically, the arithmetic average value of the upper layer solvent composition may not exceed the arithmetic average value of the nonmagnetic layer solvent composition. It is essential. In order to improve dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition.
Moreover, it is preferable that a solubility parameter is 8-11.

These dispersants, lubricants, and surfactants used in the magnetic layer of the present invention can be properly used in the magnetic layer and the nonmagnetic layer described later as needed. For example, of course, the dispersant is not limited to the example shown here, but the dispersant has a property of adsorbing or binding with a polar group, and in the magnetic layer, mainly on the surface of the ferromagnetic powder, as will be described later. In the nonmagnetic layer, it is presumed that the organophosphorus compound adsorbed or bonded to the surface of the nonmagnetic powder mainly by the polar group and once adsorbed is difficult to desorb from the surface of metal or metal compound. Accordingly, the surface of the ferromagnetic powder of the present invention or the nonmagnetic powder surface described later is in a state of being coated with an alkyl group, an aromatic group, etc., so the affinity of the ferromagnetic powder or nonmagnetic powder for the binder resin component And the dispersion stability of the ferromagnetic powder or non-magnetic powder is also improved. In addition, since it exists in a free state as a lubricant, the non-magnetic layer and the magnetic layer use fatty acids with different melting points to control the bleeding to the surface, and use esters with different boiling points and polarities to bleed to the surface. It is conceivable that the stability of coating is improved by controlling the amount of the surfactant, and the lubricating effect is improved by increasing the amount of lubricant added in the nonmagnetic layer. All or a part of the additives used in the present invention may be added in any step during the production of the coating solution for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, adding at a kneading step with a ferromagnetic powder, a binder and a solvent, adding at a dispersing step, adding after dispersing, adding just before coating, etc. There is.

In addition, carbon black can be added to the magnetic layer in the present invention as necessary.
As the type of carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. The carbon black of the radiation-cured layer should be optimized for the following characteristics depending on the desired effect, and the effect may be obtained more when used in combination.

The specific surface area of carbon black is 100 to 500 m ² / g, preferably 150 to 400 m ^2.
/ G, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 200 ml / 10
0 g. The particle size of carbon black is 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. The carbon black has a pH of 2 to 10 and a water content of 0.
The tap density is preferably 0.1 to 1 g / ml.

As a specific example of carbon black used in the present invention, BRAC manufactured by Cabot Corporation
KPEARLS 2000, 1300, 1000, 900, 800, 880, 700, V
ULCAN XC-72, manufactured by Mitsubishi Chemical Corporation # 3050B, # 3150B, # 3250B,
# 3750B, # 3950B, # 950, # 650B, # 970B, # 850B, MA-
600, MA-230, # 4000, # 4010, COND made by Columbian Carbon
UCTEX SC, RAVEN 8800, 8000, 7000, 5750, 5250,
3500, 2100, 2000, 1800, 1500, 1255, 1250, and Ketjen Black EC manufactured by Ketjen Black International.

Even if carbon black is surface-treated with a dispersant or grafted with resin,
You may use what made a part of the surface graphitized. Further, carbon black may be dispersed in advance with a binder before it is added to the paint. The carbon black that can be used in the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

These carbon blacks can be used alone or in combination. When using carbon black, it is preferable to use 0.1-30 mass% with respect to the mass of a magnetic body. Carbon black functions to prevent the magnetic layer from being charged, reduce the friction coefficient, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention change the type, amount, and combination in the magnetic layer, and depending on the purpose based on the above-mentioned various characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use them properly, but they should be optimized in each layer.

In addition, 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 A known inorganic powder having a Mohs hardness of 6 or more is used alone or in combination. These can be used as abrasives. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents.

The tap density is preferably 0.3 to ² g / ml, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but those having a corner in a part of the shape are preferable because of high polishing properties.

Specifically, AKP-12, AKP-15, AKP-20, AKP-30 manufactured by Sumitomo Chemical Co., Ltd.
, AKP-50, HIT20, HIT-30, HIT-55, HIT60, HIT70,
HIT80, HIT100, Reynolds, ERC-DBM, HP-DBM, HPS-
DBM, manufactured by Fujimi Abrasive Co., Ltd., WA10000, manufactured by Uemura Kogyo Co., Ltd., UB20, manufactured by Nippon Chemical Industry Co., Ltd., G-5, Chromex U2, Chromex U1, manufactured by Toda Kogyo Co., Ltd., TF100, TF1
40, manufactured by Ibiden Co., Ltd., Beta Random Ultra Fine, Showa Mining Co., Ltd., and B-3.

The surface roughness of the magnetic layer in the present invention is 1 to 3 nm, preferably 1.2 to 2.8 nm, and more preferably 1.5 to 2.8 nm as the center line average surface roughness Ra. The center line average surface roughness Ra of the magnetic layer in the present invention is a general-purpose three-dimensional surface structure analyzer NewV manufactured by ZYGO.
Scan length is 5 μm by scanning white light interferometry according to iee 5022, objective lens is 20 times, intermediate lens is 1.0 times, measurement field is 260 μm × 350 μm, and the measured surface is HPF: 1.65 μm, LPF: It can be obtained by processing with a filter of 50 μm.

Nonmagnetic Layer The magnetic recording medium of the present invention has at least one nonmagnetic layer in which a nonmagnetic powder and a binder are dispersed between a nonmagnetic support and a magnetic layer. The same binder used for the magnetic layer can be used for the nonmagnetic layer.
The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Moreover, you may mix carbon black with a nonmagnetic powder as needed with a nonmagnetic layer.

(Non-magnetic powder)
For the nonmagnetic layer, magnetic powder may be used as long as the nonmagnetic layer is substantially nonmagnetic.
It is preferable to use nonmagnetic powder.
The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina having an α conversion of 90 to 100%, β-
Alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , Ca
CO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination of two or more. Preferable are α-iron oxide and titanium oxide.

The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes.
The crystallite size of the nonmagnetic powder is preferably 4 nm to 1 μm, and more preferably 40 to 100 nm. A crystallite size in the range of 4 nm to 1 μm is preferred because it does not become difficult to disperse and has a suitable surface roughness.
The average particle size of these non-magnetic powders is preferably 5 nm to 2 μm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or even a single non-magnetic powder may have a wide particle size distribution. It can also have an effect. The average particle size of the particularly preferred nonmagnetic powder is 10 to 10
200 nm. The range of 5 nm to 2 μm is preferable because the dispersion is good and the surface roughness is suitable.

The specific surface area of the nonmagnetic powder is preferably 1 to 100 m ² / g, more preferably 5 to 5 m.
A 70m ² / g, more preferably from 10~65m ² / g. Specific surface area of 1-100
If it exists in the range of m < ² > / g, since it has suitable surface roughness and can be disperse | distributed with the desired amount of binders, it is preferable.
The oil absorption using dibutyl phthalate (DBP) is preferably 5 to 100 ml / 100.
g, more preferably 10-80 ml / 100 g, still more preferably 20-60 ml / 10
0 g.
The specific gravity is preferably 1 to 12, more preferably 3 to 6. Tap density is preferably 0
. 05 to 2 g / ml, more preferably 0.2 to 1.5 g / ml. Tap density is 0.
If it is in the range of 05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus.

The pH of the nonmagnetic powder is preferably 2 to 11, but the pH is particularly preferably between 6 and 9. When the pH is in the range of 2 to 11, the friction coefficient does not increase due to high temperature, high humidity, or liberation of fatty acids.
The water content of the nonmagnetic powder is preferably 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, and still more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable.
The ignition loss is preferably 20% by mass or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, durability can be ensured. The nonmagnetic powder has a stearic acid adsorption amount of 1 to 20 μmol / m ² , more preferably ² to 15 μmo.
l / m ² .
The heat of wetting of the nonmagnetic powder into water at 25 ° C. is 20 to 60 μJ / cm ² (200 to 600e).
rg / cm ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used.
The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9.

The surface of these nonmagnetic powders is subjected to surface treatment to produce Al ₂ O ₃ , SiO ₂ , TiO ₂ ,
It is preferable that ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO exist. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ , but more preferred are Al ₂ O ₃ , S
iO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

Specific examples of the nonmagnetic powder used in the nonmagnetic layer of the present invention include, for example, Showa Denko Nanotite, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo DPN-250, D
PN-250BX, DPN-245, DPN-270BX, DPB-550BX, DPN
-550RX Titanium oxide made by Ishihara Sangyo TTO-51B, TTO-55A, TTO-55B
, TTO-55C, TTO-55S, TTO-55D, SN-100, MJ-7, α-iron oxide E270, E271, E300, STT-4D, STT-30D, ST manufactured by Titanium Industry
T-30, STT-65C, Teica MT-100S, MT-100T, MT-150W
, MT-500B, T-600B, T-100F, T-500HD, and the like. Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, D made by Dowa Mining
EFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP, and those fired. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain the desired μ Vickers hardness. Μ Vickers hardness of the nonmagnetic layer is normally 25~60kg / mm ² (0.245~0.588GPa), preferably in order to adjust the head contact, 30~50kg / mm ² (0.294~0.490
GPA), and using a thin film hardness meter (HMA-400 manufactured by NEC), a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm can be used for the tip of the indenter.
It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used.

The specific surface area of the carbon black used for the nonmagnetic layer of the present invention is 100 to 500 m ² / g.
, Preferably 150-400 m ² / g, DBP oil absorption is 20-400 ml / 100 g, preferably 30-200 ml / 100 g. The particle size of carbon black is 5-80nm
The thickness is preferably 10 to 50 nm, more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of carbon black that can be used in the nonmagnetic layer of the present invention include BLACKPEARLS 2000, 1300, 1000, 900, 800, manufactured by Cabot Corporation.
880, 700, VULCAN XC-72, Mitsubishi Chemical Corporation # 3050B, # 3150B
, # 3250B, # 3750B, # 3950B, # 950, # 650B, # 970B, #
850B, MA-600, CONDUCTEX SC, RAV manufactured by Columbian Carbon
EN8800, 8000, 7000, 5750, 5250, 3500, 2100, 200
0, 1800, 1500, 1255, 1250, and Ketjen Black EC manufactured by Ketjen Black International.

Carbon black may be surface-treated with a dispersant, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Further, carbon black may be dispersed in advance with a binder before it is added to the paint. These carbon blacks are in a range not exceeding 50% by mass with respect to the inorganic powder, and 40% of the total mass of the nonmagnetic layer.
Can be used within a range not exceeding%. These carbon blacks can be used alone or in combination. The carbon black that can be used in the nonmagnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

Further, an organic powder can be added to the nonmagnetic layer according to the purpose. Examples of such organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin, and the like. Resin powder and polyfluorinated ethylene resin can also be used. As the production method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

As the binder resin, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the magnetic layer can be applied. In particular, with respect to the binder resin amount, type, additive, and dispersant addition amount and type, known techniques relating to the magnetic layer can be applied.

3. Back layer In general, a magnetic tape for recording computer data is strongly required to have repeated running characteristics as compared with a video tape and an audio tape. In order to maintain such high storage stability, a back layer can be provided on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are provided. The coating liquid for forming the back layer disperses particle components such as an abrasive and an antistatic agent and a binder in an organic solvent. Various inorganic pigments and carbon black can be used as the particulate component. Moreover, as a binder, resin, such as a nitrocellulose, a phenoxy resin, a vinyl chloride resin, a polyurethane, can be used individually or in mixture, for example.

4). Smoothing Layer In the magnetic recording medium of the present invention, a smoothing layer may be provided between the nonmagnetic support and the nonmagnetic layer or magnetic layer. Such a smooth layer is, for example, applied to the surface of a non-magnetic support with a coating solution containing a compound having a radiation curable functional group in the molecule (radiation curable compound), and then irradiated with radiation to apply the coating solution. Can be formed by curing.
The molecular weight of the radiation curable compound is preferably in the range of 200 to 2,000. When the molecular weight is within this range, the molecular weight is relatively low, so that the coating film is easy to flow in the calendar process, has high moldability, and a smooth coating film can be formed.
Preferred as the radiation curable compound is a bifunctional acrylate compound having a molecular weight of 200 to 2000, and more preferred are bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and these alkylene oxide adducts. Acid and methacrylic acid are added.

The radiation curable compound used in the present invention may be used in combination with a polymer-type binder.
As the binder used in combination, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. When ultraviolet rays are used as radiation, it is preferable to use a polymerization initiator in combination. As the polymerization initiator, known radical photopolymerization initiators, cationic photopolymerization initiators, photoamine generators, and the like can be used.

5). Layer Configuration In the configuration of the magnetic recording medium used in the present invention, the thickness of the nonmagnetic support is 6.5 μm.
Or less, preferably 3.0 to 6.0 μm, more preferably 3.0 to 5.5 μm. When the thickness of the nonmagnetic support exceeds 6.5 μm, it is impossible to achieve high capacity as a thin magnetic recording medium. The thickness of the back layer provided on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are provided is 0.1 to 1.0 μm, preferably 0.
2 to 0.8 μm.

The thickness of the magnetic layer is optimized depending on the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is 0.15 μm or less, for example, 0.01 to 0.10 μm, preferably Is 0.02 μm to 0.08 μm, more preferably 0.03 to 0.08.
8 μm. The thickness variation rate of the magnetic layer is preferably within ± 50%, more preferably within ± 40%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

The thickness of the nonmagnetic layer of the present invention is 0.2 to 3.0 μm, preferably 0.3 to 2.5 μm, and more preferably 0.4 to 2.0 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. Note that substantially the same means that the nonmagnetic layer has a residual magnetic flux density of 10 mT (100 G) or less or a coercive force of 7.9.
6 kA / m (100 Oe) or less, preferably means having no residual magnetic flux density and coercive force.

6). Manufacturing Method The process of manufacturing the magnetic layer coating liquid for the magnetic recording medium used in the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes as necessary. Each process may be divided into two or more stages. All raw materials used in the present invention such as hexagonal ferrite ferromagnetic powder or ferromagnetic metal powder, nonmagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent, etc. It may be added. In addition, individual raw materials may be added in two or more steps.
For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventional known manufacturing technique can be used as a partial process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the liquid for the magnetic layer and the liquid for the nonmagnetic layer. Such glass beads are preferably zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

In the method for producing a magnetic recording medium of the present invention, for example, a magnetic layer coating solution is applied to the surface of a nonmagnetic support under running so as to have a predetermined film thickness. Here, a plurality of coating solutions for magnetic layers may be applied sequentially or simultaneously, and a lower magnetic layer coating solution and an upper magnetic layer coating solution may be applied sequentially or simultaneously. As a coating machine for applying the magnetic layer coating liquid or the lower magnetic layer coating liquid, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat,
Transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat and the like can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.

In the case of a magnetic tape, the coating layer of the magnetic layer coating solution is subjected to magnetic field orientation treatment in the longitudinal direction using a cobalt magnet or a solenoid on the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution. In the case of a disk, a sufficiently isotropic orientation may be obtained even without non-orientation without using an orientation device, but known random methods such as alternately arranging cobalt magnets obliquely and applying an alternating magnetic field with a solenoid. It is preferable to use an alignment device. In the case of a ferromagnetic metal powder, the isotropic orientation is generally preferably in-plane two-dimensional random, but can also be three-dimensional random with a vertical component. In the case of hexagonal ferrite, in general, it tends to be in-plane and vertical three-dimensional random, but in-plane two-dimensional random is also possible. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a different-pole counter magnet and making the vertical orientation. In particular, when performing high density recording, vertical alignment is preferable. Moreover, it is good also as circumferential orientation using a spin coat.
It is preferable to be able to control the drying position of the coating film by controlling the temperature, air volume, and coating speed of the drying air, the coating speed is preferably 20 to 1,000 m / min, and the temperature of the drying air is preferably 60 ° C. . Moreover, moderate preliminary drying can also be performed before entering a magnet zone.

After being dried, the coating layer is usually subjected to a surface smoothing treatment or a thermo treatment. For the surface smoothing process, for example, a super calendar roll or the like is used. By performing the surface smoothing treatment, voids generated by removing the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can.
As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like is used. Moreover, it can also process with a metal roll. As the calendering conditions, the temperature of the calendar roll is in the range of 60 to 100 ° C., preferably 7
The range is from 0 to 100 ° C., particularly preferably from 80 to 100 ° C., and the pressure is from 100 to 50
The range of 0 kg / cm (98 to 490 kN / m), preferably 200 to 450 kg / cm (
196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (2
94 to 392 kN / m) is preferable. Here, the calendering temperature is preferably set to Tg or less of the support, and more preferably set such that the web temperature becomes Tg or less.

As heat shrinkage reduction means, there are a method of heat treatment in a web shape while handling at low tension, and a method of heat treatment in a form in which a tape is laminated such as a state of being incorporated in a bulk or a cassette (thermo treatment), both of which can be used. The former is less affected by protrusions on the surface of the back layer, but the heat shrinkage rate cannot be greatly reduced. On the other hand, the latter thermo-treatment can greatly improve the heat shrinkage ratio, but is strongly affected by the projection of the protrusion on the surface of the back layer, so that the magnetic layer becomes rough and causes a decrease in output and an increase in noise. In particular, a high-output, low-noise magnetic recording medium can be supplied as a magnetic recording medium with a thermo process. The obtained magnetic recording medium can be cut into a desired size using a cutting machine, a punching machine, or the like.

7). Physical Properties The saturation magnetic flux density of the magnetic layer of the magnetic recording medium used in the present invention is 100 to 300 mT (1
, 3,000 to 3,000 G). The coercive force (Hc) of the magnetic layer is 143.3 to 318.
. 4 kA / m (1,800 to 4,000 Oe), preferably 159.2 to 278.
. 6 kA / m (2,000 to 3,500 Oe). The coercive force distribution is preferably narrow, and SFD and SFDr are 0.6 or less, more preferably 0.2 or less.

The coefficient of friction with respect to the head of the magnetic recording medium used in the present invention is -10 to 40 ° C,
It is 0.5 or less in the range of humidity 0-95%, Preferably it is 0.3 or less. Also,
The charged position is preferably within −500 to + 500V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa (100 to 2,000 kg / mm ² ) in each in-plane direction,
The breaking strength is preferably 98 to 686 MPa (10 to 70 kg / mm ² ), and the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1,500 k) in each in-plane direction.
g / mm ² ), the residual spread is preferably 0.5% or less, and the thermal shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less, and most preferably 0. .
1% or less.

The glass transition temperature of the magnetic layer (maximum point of loss elastic modulus measured by dynamic viscoelasticity measured at 110 Hz) is preferably 50 to 180 ° C, and that of the nonmagnetic layer is preferably 0 to 180 ° C. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These thermal characteristics and mechanical characteristics are preferably almost equal within 10% in each in-plane direction of the medium.
The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 1
0 mg / m ² or less. The porosity of the coating layer is preferably 30 for both the nonmagnetic layer and the magnetic layer.
It is not more than volume%, more preferably not more than 20 volume%. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example,
In a disk medium where repetitive use is important, the storage stability is often preferable when the porosity is large.

The maximum height R _max of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, the center plane peak height Rp is 0.3 μm or less, and the center plane valley depth Rv is 0.3 μm or less. Center area ratio S
r is preferably 20 to 80%, and the average wavelength λa is preferably 5 to 300 μm. The surface protrusion of the magnetic layer is 0.
One having a size of 01 to 1 μm can be arbitrarily set in the range of 0 to 2,000 per 0.1 mm ² , and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder added to the magnetic layer, the roll surface shape of the calendering treatment, and the like. The curl is preferably within ± 3 mm.

It is easily estimated that these physical characteristics can be changed between the nonmagnetic layer and the magnetic layer in the magnetic recording medium of the present invention depending on the purpose. For example,
For example, the elastic modulus of the magnetic layer is increased to improve the storage stability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

Since the magnetic recording medium of the present invention is particularly effective for increasing the density of the linear recording magnetic recording medium, when recording / reproducing the magnetic recording medium of the present invention by the fixed head method, the track width is 25 μm. Or less, preferably 0.1 to 10 μm, more preferably 0.1 to 6 μm,
The linear recording density can be set to 100 kFCI or more, preferably 100 to 500 kFCI, more preferably 200 to 400 kFCI. Note that a plurality of recording / reproducing magnetic heads in a fixed head type recording apparatus can be arranged as appropriate, and can be arranged at a predetermined angle with respect to the longitudinal direction of the magnetic recording medium.

The magnetic recording medium of the present invention is not particularly limited with respect to a head for reproducing a signal magnetically recorded on the magnetic recording medium, but is preferably used for an MR head. When the MR head is used for reproducing the magnetic recording medium of the present invention, the MR head is not particularly limited, and for example, a GMR head or a TMR head can be used. The head used for magnetic recording is not particularly limited, but the saturation magnetization is 1.0 T or more, preferably 1.5 T or more.

Hereinafter, the present invention will be described specifically by way of examples. It will be readily understood by those skilled in the art that the components, ratios, operation order, and the like shown here can be changed without departing from the spirit of the present invention. Accordingly, the present invention should not be limited to the following examples. In addition, the part in an Example shows a mass part.

[Example 1]
[Preparation of coating liquid for forming upper magnetic layer and coating liquid for forming lower non-magnetic layer]
<Components for forming the upper magnetic layer>
Ferromagnetic metal powder Composition Fe / Co = 100/30 (atomic ratio) 100 parts Hc: 189.6 kA / m (2400 Oe)
Specific surface area by BET method: 70 m ² / g
Average long axis length: 60 nm
Crystallite size: 13 nm (130 cm)
Saturation magnetization σs: 125 A · m ² / kg (125 emu / g)
Surface treatment layer: Al ₂ O ₃ , Y ₂ O ₃
Vinyl chloride copolymer (MR-110 manufactured by Nippon Zeon Co., Ltd.) 12 parts -SO ₃ Na content: 5 × 10 ⁻⁶ eq / g, degree of polymerization: 350
Epoxy group content: 3.5% by weight in monomer units
Polyester polyurethane resin (UR-8200 manufactured by Toyobo) 3 parts α-alumina (average particle diameter: 0.1 μm) 3 parts carbon black (average particle diameter: 0.08 μm) 0.5 part stearic acid 2 parts methyl ethyl ketone 90 parts cyclohexane 30 60 parts of toluene

<Ingredient for forming lower nonmagnetic layer>
Nonmagnetic powder α-Fe ₂ O ₃ hematite 80 parts Average long axis length 0.15 μm
Specific surface area by BET method 110m ² / g
pH 9.3
Tap density 0.98g / ml
Surface treatment layer Al ₂ O ₃ , SiO ₂
Carbon black (Mitsubishi Chemical Corporation) 20 parts Average primary particle size 16nm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method 250 m ² / g
Volatiles 1.5%
Vinyl chloride copolymer (MR-110 manufactured by Nippon Zeon Co., Ltd.) 12 parts Polyester polyurethane resin (UR-8200 manufactured by Toyobo) 12 parts Stearic acid 2 parts Methyl ethyl ketone 150 parts Cyclohexane 50 parts Toluene 50 parts

The components for forming the upper magnetic layer forming coating liquid and the lower nonmagnetic layer were kneaded with a kneader and then dispersed using a sand mill. 1.6 parts of secondary butyl stearate (sec-BS) is added to the obtained dispersion for the upper layer, 3 parts of the above polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) is added to the lower layer dispersion, and each dispersion is further dispersed. 40 parts of a mixed solution of methyl ethyl ketone and cyclohexanone was added to the solution, followed by filtration using a filter having an average pore size of 1 μm, thereby preparing an upper layer forming coating solution and a lower layer forming coating solution, respectively.

[Preparation of coating solution for forming the back layer]
<Back layer forming component>
Particulate carbon black 100 parts Average particle size: 20 nm
Coarse particle carbon black 10 parts Average particle size: 270 nm
Nitrocellulose resin 100 parts Polyester polyurethane resin 30 parts Dispersant Copper oleate 10 parts Copper phthalocyanine 10 parts Barium sulfate (precipitation) 5 parts Methyl ethyl ketone 500 parts Toluene 500 parts α-alumina (average particle size: 0.13 μm) 0.5 parts

The above components were kneaded with a continuous kneader and then dispersed for 2 hours using a sand mill. After adding 40 parts of polyisocyanate [(Coronate L, Nippon Polyurethane Industry Co., Ltd.)] and 1000 parts of methyl ethyl ketone, the obtained dispersion was filtered using a filter having an average pore diameter of 1 μm to form a back layer. A coating solution was prepared.

<Making and manufacturing method of magnetic tape>
Nonmagnetic support made of PEN (polyethylene naphthalate) with a thickness of 6 μm (Tg: 120 ° C.)
Was heat-treated in a heat treatment room at 90 ° C. for 1 day. After the heat treatment, it is cooled to room temperature, and then the upper magnetic layer-forming coating solution and the lower non-magnetic layer-forming coating solution are dried on the support so that the thickness of the lower layer is 1.3 μm. On top of this, simultaneous multilayer coating was performed so that the thickness of the magnetic layer after drying was 0.2 μm. Then, while both layers were still wet, 3000 Gauss (3
The orientation treatment was performed using a cobalt magnet having a magnetic flux density of 00 mT and a solenoid having a magnetic flux density of 1500 gauss (150 mT). Then, the nonmagnetic layer and the magnetic layer were formed by blowing and drying hot air at 80 ° C.
Thereafter, on the other side of the support, the thickness after drying the back layer forming coating solution is 0.5 μm.
m, and dried by blowing hot air of 90 ° C. to provide a back layer, a lower non-magnetic layer and an upper magnetic layer on one side of the support, and a back layer on the other side. Magnetic recording laminate rolls provided respectively were obtained.
The magnetic recording laminate roll thus obtained was passed through a seven-stage calendering machine (temperature 90 ° C., speed 300 m / min) composed of a heated metal roll and an elastic roll coated with a thermosetting resin on the core metal, thereby performing a calendering process. Went. Next, the calendered magnetic recording laminate roll was slit to a width of 0.5 inch, and 650 m was wound around the LTO-G3 cartridge to obtain a magnetic tape cartridge.

[Example 2]
In Example 1, a magnetic tape cartridge was prepared in the same manner as in Example 1 except that the heat treatment of the support was set at 80 ° C. for 2 days.

Example 3
In Example 1, a magnetic tape cartridge was prepared in the same manner as in Example 1 except that the thickness of the support was 4.5 μm.

Example 4
In Example 2, a magnetic tape cartridge was prepared in the same manner as in Example 2 except that the thickness of the support was 4.5 μm.
Example 5
In Example 1, a magnetic tape cartridge was prepared in the same manner as in Example 1 except that the thickness of the support was 3 μm.

[Comparative Example 1]
In Example 1, a magnetic tape cartridge was prepared in the same manner as in Example 1 except that the support was not heat-treated.

[Comparative Example 2]
In Example 3, a magnetic tape cartridge was prepared in the same manner as in Example 3 except that the support was not heat-treated.

[Comparative Example 3]
In Example 1, the support is a non-magnetic support (T) made of PET (polyethylene terephthalate).
g: 90 ° C.) A magnetic tape cartridge was prepared in the same manner as in Example 1.

[Comparative Example 4]
In Example 3, the support is a non-magnetic support made of PET (polyethylene terephthalate) (T
g: 90 ° C.) A magnetic tape cartridge was prepared in the same manner as in Example 3.

<Evaluation method>
[Center line average surface roughness Ra]
Scan Length was measured at 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5022 manufactured by ZYGO. Objective lens: 20 times, intermediate lens: 1.0 times, measurement field of view is 260 μm × 350 μm. The measured surface was HPF: 1.
A center line average surface roughness Ra value was determined by filtering with 65 μm and LPF: 50 μm.

[Creep deformation amount]
A sample having a length of 15 mm and a width of 5 mm from the longitudinal direction was cut out from the magnetic tape cartridge to obtain a magnetic tape sample. Also, the upper and lower layers and the back layer are removed from the magnetic tape using a solvent (methyl ethyl ketone), and only the nonmagnetic support is taken out. A sample 15 mm long and 5 mm wide is cut out from the longitudinal direction of the nonmagnetic support. A support sample was obtained. The measurement was performed using TM-9300 manufactured by ULVAC-RIKO. The measurement temperature was 60 ° C. Tensile stress was applied to the longitudinal direction of the sample in two stages: a first step of 0.6 MPa for 30 minutes and a second step of 15.7 MPa for 50 hours. First step 0.6 MPa The sample length loaded with a tensile stress for 30 minutes was used as the initial sample length, and the sample elongation (percentage) after the second step 50 hours was calculated and used as the amount of creep deformation. 0.30%
The following were considered good.

[Evaluation method of magnetic tape]
Using the LTO-G3 drive, recording and reproduction on the reel outer side and the core side of each of the magnetic tape cartridge samples of (Example 1) to (Example 4) and (Comparative Example 1) to (Comparative Example 4) are performed. The characteristics on the outside of the reel of Comparative Example 1 were set to 0 dB, and the smaller value on the outside of the reel and the core side was set as the reproduction characteristic at the initial stage of storage. Each of the magnetic tape cartridges was stored in an atmosphere of 60 ° C. and 90% RH for 336 hours, and then the recording signals on the reel outer side and the core side (the same position as before the storage) were reproduced. The characteristic on the outer side of the reel is set to 0 dB, and the smaller value on the outer side of the reel and the core side is set as the reproduction characteristic after storage. Regarding the initial value, a value smaller than -1 dB was determined as NG. The reproduction characteristics after storage were determined to be less than −3 dB as NG.
The results are shown in Table 1 below.

From Table 1, the support is polyethylene naphthalate and the creep deformation is 0.30.
It can be seen that the reproduction characteristics at the initial stage and after storage are excellent only when the percentage is less than or equal to%.

Claims (4)

In a magnetic recording medium in which at least one magnetic layer is provided on a nonmagnetic support, the nonmagnetic support is polyethylene naphthalate having a thickness of 6.5 μm or less, and 15% at 60 ° C. with respect to the magnetic recording medium. A magnetic recording medium, wherein when a tensile stress of 0.7 MPa is applied in the longitudinal direction of the magnetic recording medium for 50 hours, the creep deformation amount in the longitudinal direction is 0.30% or less. The magnetic recording medium according to claim 1, wherein the magnetic layer has a center line average surface roughness Ra of 1 to 3 nm. When a tensile stress of 15.7 MPa is applied to the nonmagnetic support at 60 ° C. for 50 hours in the longitudinal direction of the nonmagnetic support, the creep deformation amount in the longitudinal direction is 0.30% or less. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium. 4. A nonmagnetic layer is provided between the nonmagnetic support and the magnetic layer.
A magnetic recording medium according to any one of the above.