JPH0830957A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having satisfactory electromagnetic transducing characteristics, to especially improve overwriting characteristics, to increase output in a low frequency region, to ensure the optimum recording current almost equal to that for ME and to obtain a medium having satisfactory interchangeability with ME. CONSTITUTION:A lower nonmagnetic layer contg. at least nonmagnetic powder and a binder is formed on a nonmagnetic substrate and a magnetic layer contg. at least ferromagnetic metal powder and a binder is formed on the nonmagnetic layer to obtain the objective magnetic recording medium. The magnetic layer has 0.07-0.20mum thickness, 3,700-6,000G Bm measured in an external magnetic field of 10kOe and 2,000-3,000Oe Hc. The center line surface roughness Ra of the magnetic layer is 1.0-3.0nm and that of the surface of the nonmagnetic substrate coated with the nonmagnetic layer is 0.5-7.0nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium for recording / reproducing digital signals at a high density. More specifically, it is excellent in high frequency output and CN ratio and low frequency output. And a high overwrite erasing rate and good compatibility with a vapor deposition type magnetic tape.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks and the like. Magnetic recording media have become denser year by year and the recording wavelength has become shorter, and the recording method is being studied from analog to digital. In order to meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer are being studied, but ferromagnetic powder is dispersed in the binder in terms of practical reliability such as productivity and corrosion. The so-called coating type magnetic recording medium coated on the support is excellent. However, the coating type magnetic recording medium is inferior in electromagnetic conversion characteristics to the metal thin film because the filling degree of the magnetic substance is low. As the coating type magnetic recording medium, ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO ₂ ,
A non-magnetic support coated with a magnetic layer in which a ferromagnetic alloy powder or the like is dispersed in a binder is widely used. Various methods have been proposed for improving the electromagnetic conversion characteristics of the coating type magnetic recording medium, such as improving the magnetic characteristics of the ferromagnetic powder and smoothing the surface of the magnetic layer. Not enough. In addition, in recent years, the recording wavelength tends to become shorter with higher density, and the problem of self-demagnetization loss at the time of recording and output loss when the thickness of the magnetic layer is thick and the thickness loss at the time of reproduction are increasing. A coating type magnetic recording medium having an extremely thin layer has also been proposed. In recent years, a Hi-8 or a consumer digital VCR (hereinafter referred to as DVC) has been put into practical use as a tape obtained by vapor-depositing a metal thin film, a so-called ME (metal evaporated) tape. MP (metal particula
te) and ME tapes have been put to practical use. In order to coexist with the ME tape, the MP, like the ME, must have a thin magnetic layer to achieve a high output, and the relationship between the recording current and the reproduction output must be the same. Conventionally, the reproduction output of MP decreases due to recording demagnetization as the recording current increases, but this tendency does not appear in ME, and the reproduction output tends to saturate as the recording current increases. . Therefore, in the Hi-8 deck, MP and ME are actually recorded by different recording currents, which has a drawback that the circuit becomes complicated. In order to solve this difficulty, it is necessary to record with the same recording current in a system in which MP and ME coexist, but there is a problem that the output becomes low when recording and reproducing MP with the optimum recording current of ME. It was Also, M
When the ME is recorded / reproduced with the optimum recording current of P, the ME cannot exert its ability and the output becomes low. It was required that the optimum recording current of MP be almost the same as that of ME.

Further, the DVC employs a method of overwriting (overwriting) a data signal of 0.5 μm on a tracking signal of a recording wavelength of 22 μm and recording while erasing the tracking signal. That is, in the DVC, overwriting erasing is adopted by omitting the erasing head for weight reduction. In order to adopt the overwrite erasing, it is necessary to erase the synchronization signal with the data signal, and it is said that the overwrite erasing rate is preferably -20 dB or less.

As a characteristic required for a magnetic recording medium, it is desired that the overwrite erasing rate be as low as possible.
The overwrite characteristics will be improved as the magnetic layer thickness is made thinner, but the total amount of magnetization will be reduced if the magnetic layer thickness is simply made. Output decreases. As described above, the overwrite characteristic and the long-wavelength signal output have a contradictory relationship. That is, it is a trade-off to make the erasing higher to satisfy the overwrite characteristic and to secure the output of each signal, and a means for satisfying both has not been found.

By the way, the present applicant has proposed an ultrathin layer magnetic recording medium in which a nonmagnetic layer is provided as a lower layer and the upper magnetic layer is made thin. For example, in Japanese Patent Laid-Open No. 63-187418,
The average major axis length is less than 0.3 μm and the crystallite size is 300Å
Disclosed is a magnetic recording medium in which a ferromagnetic powder of less than 100 is dispersed and coated on a non-magnetic layer. In addition, JP-A-63-19131
5 discloses a magnetic recording medium having a lower layer thickness of 0.5 μm or more and a magnetic layer thickness of 1 μm. These do not disclose the requirements for satisfying the overwrite erasing rate in question here.

Further, in Japanese Patent Laid-Open No. 5-298653, the overwrite characteristic (1.9 MH) is set by setting the magnetic layer thickness to less than 0.3 μm and keeping the standard deviation of the thickness within a certain range.
It is disclosed that a z signal is overwritten with a 7.6 MHz signal) and a magnetic recording medium with less distortion during digital recording is obtained. Japanese Unexamined Patent Publication (Kokai) No. 5-73883 discloses a high magnetic layer having a thickness of 1 μm or less and regulating its thickness variation to reduce self-demagnetization loss in the short wavelength region and a smooth magnetic layer to eliminate space loss. M with performance comparable to ME tape that can achieve output from low range to high range
There is a disclosure that a P tape can be provided, and it is stated that a magnetic recording medium having good head contact, excellent storage stability and running durability, low dropout and block error rate, and little edge damage is provided. . Japanese Unexamined Patent Publication (Kokai) No. 5-28464 discloses a magnetic recording medium in which a non-magnetic layer is composed only of a binder and a semi-solid or liquid additive, and the thickness of the magnetic layer is 1 μm or less. Characteristics, overwrite characteristics (10MHz signal at 20MH
It is said that the output at 40 MHz, etc. will be improved.

[0007] These prior arts are insufficient for improving the overwrite characteristics and securing a low frequency output. In particular, satisfactory results were not obtained in the overwrite characteristics in the 24-25 modulation adopted in DVC. Further, these conventional techniques are not sufficiently compatible with the ME tape described above, and a magnetic recording medium satisfying the compatibility has been desired.

[0008]

DISCLOSURE OF THE INVENTION The present invention is to provide a magnetic recording medium having a good electromagnetic conversion characteristic, in particular, an improved overwrite characteristic, a high low frequency output, and an optimum recording current of ME. Obtained the same optimum recording current as
The purpose is to obtain a magnetic recording medium having good compatibility with E.

[0009]

An object of the present invention is to provide a lower non-magnetic layer mainly containing a non-magnetic powder and a binder on a non-magnetic support, on which at least a ferromagnetic metal powder and a binder are provided. In a magnetic recording medium provided with a magnetic layer containing
The thickness of the magnetic layer is 0.07 to 0.20 μm, and the Bm of the magnetic layer measured with an external magnetic field of 10 kOe is 3700 to 600.
0 Gauss, Hc of the magnetic layer is 2000 to 3000 Oe, and the center line surface roughness Ra of the magnetic layer is 1.0 to
This is achieved by a magnetic recording medium characterized in that the center line surface roughness of the surface on which the lower non-magnetic layer of the non-magnetic support is coated is 0.5 to 7.0 nm.

According to the present invention having the above-mentioned structure, as described above, the overwrite characteristic is good, the low-frequency output is high, the relationship between the recording current and the reproducing output is the same as ME, and an optimum recording current of the same level is obtained. It is possible to obtain a magnetic recording medium having excellent compatibility. In addition, the present invention can provide a magnetic recording medium that satisfies both the overwrite characteristic and the output of a long-wavelength signal particularly in DVC.

That is, according to the present invention, in order to satisfy both the overwrite characteristic and the long wavelength signal output, the thickness of the magnetic layer is set to 0.
The magnetic layer has a maximum magnetic flux density Bm of 3700 to 6000 Gauss, a coercive force Hc of 2000 to 3000 Oe, and a center line surface roughness Ra of the magnetic layer. 1.0-3.0
and the surface of the lower non-magnetic layer coated with Ra is 0.5 to 7 nm as the non-magnetic support.

Hereinafter, the respective defining elements will be sequentially described in detail.
In the present invention, the magnetic layer has a thickness of 0.07 to 0.20 μm.
m. If the thickness of the magnetic layer is less than 0.07 μm, the long wavelength signal output is reduced, and if it exceeds 0.20 μm, the overwrite characteristic cannot be secured. The thickness of the magnetic layer is preferably 0.08 to 0.15 μm, more preferably 0.09 to 0.14 μm μm. As a method for measuring the thickness of the magnetic layer, a thickness of about 0.1 μm is cut out along the longitudinal direction of the magnetic recording medium with a diamond cutter, observed with a transmission electron microscope at a magnification of 30,000 and photographed. The print size of the photograph is A4 size. afterwards,
Paying attention to the shape difference between the ferromagnetic powder and the non-magnetic powder in the magnetic layer and the non-magnetic layer, the interface is visually judged to be blackened, and the surface of the magnetic layer is also blackened. After that, the distance between the lines bordered by the image processing device IBAS2 manufactured by Zeiss Co. is measured by taking measurement points. The simple average value of the measured values at that time is taken as the thickness of the magnetic layer.

In the present invention, Bm is 3700-60.
It is 00 gauss. When Bm is less than 3700 gauss, the long wavelength signal output is lowered, and when it exceeds 6000 gauss, the overwrite characteristic is deteriorated. Bm is preferably 4
000-5700 gauss, more preferably 4500
It is 5500 gauss. In the present invention, Hc is 200
It is 0 to 3000 Oe. Here, Hc means the tape running direction. When Hc is less than 2000, short wavelength output cannot be secured, and when Hc is greater than 3000, the head used for recording is saturated, so that output cannot be secured.
Hc is preferably 2050 to 2700 Oe, and more preferably 2100 to 2500 Oe.

Bm and Hc are measured with a vibrating sample type magnetometer (manufactured by Toei Industry Co., Ltd.) at Hm of 10 kOe. Further, in the present invention, the higher the squareness ratio of the magnetic layer, the more S
The lower the FD, the better the overwrite characteristics. The squareness ratio in the tape running direction is usually 0.75 or more, preferably 0.80 or more, and more preferably 0.85 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less, more preferably 0.5 or less, and ideally 0.

In the present invention, Ra of the magnetic layer is 1.0
Is about 3.0 nm. In general, Ra is preferably as small as possible in order to improve electromagnetic conversion characteristics, and is preferably as large as in order to improve running durability.
Was set within a range of small values within the range where running performance is secured, and a range that satisfies the aspects of securing output and overwriting characteristics. When Ra exceeds 3.0 nm, both output and overwrite characteristics are deteriorated due to spacing loss, but it is particularly difficult to overwrite a long wavelength signal recorded deep in the magnetic layer with a short wavelength signal.

The RMS surface roughness RRMS obtained by the AFM evaluation is preferably in the range of 2 nm to 15 nm. In the present invention, Ra of the non-magnetic support is 0.
It is 5 to 7.0 nm, which reduces the roughness of the interface between the lower non-magnetic layer and the magnetic layer, and thus improves the surface property of the magnetic layer.
When it is less than 0.5 nm, the friction coefficient of the surface of the non-magnetic support becomes high, the handling becomes difficult in the film forming process and the coating process, and the winding shape of the raw fabric becomes poor. On the other hand, if it is larger than 7.0 nm, the surface roughness of the magnetic recording medium becomes large and the output and the CN ratio decrease. Ra of the non-magnetic support is preferably 0.6 to 4 nm, more preferably 1.0 to 3 n.
m.

Ra of the magnetic layer and the non-magnetic support is WY
Using TOPO3D manufactured by KO, Ra of an area of about 250 nm × 250 nm is measured on the surface by the MIRAU method. The measurement wavelength is about 650 nm, and spherical correction and cylindrical correction are added. This method is a non-contact surface roughness meter that measures by optical interference. The magnetic recording medium of the present invention simultaneously records a signal having a recording wavelength of 22 μm which is a synchronizing signal and a signal having a recording wavelength of 0.488 μm, which is a synchronizing signal, in the DVC, and at the same time, an erasing rate when a part of the former is overwritten by the latter -20
It can be dB or less, preferably -21 dB or less, and more preferably -22 dB or less, and can secure the output of the long wavelength signal together with the recording of the short wavelength signal.
Further, the present invention could be improved not only by reducing the thickness of the magnetic layer in order to reduce the overwrite erasing rate, but also by recording a short wavelength signal such as a data signal deep into the magnetic layer. In the present invention, it is effective to pass as much recording current as possible when recording a data signal.
The compatibility with E can be secured, and the optimum recording current can be increased to the same level as ME. This is also desirable from the viewpoint of overwrite characteristics.

Preferred embodiments of the present invention are as follows. (1) The total thickness of the magnetic recording medium of the present invention is 4.5 to 8.5.
Must be μm. (2) The support used in the magnetic recording medium of the present invention is a polyethylene naphthalate resin or a polyaramid resin. (3) The nonmagnetic powder contained in the nonmagnetic layer of the present invention is at least one selected from titanium oxide, α-iron oxide, barium sulfate, zinc oxide, and alumina. (4) The coating solution for the magnetic layer in the magnetic recording medium should not contain polyisocyanate. (5) The binder content of the magnetic layer coating liquid in the magnetic recording medium is 8 to 24 parts by weight with respect to 100 parts by weight of the ferromagnetic metal powder, and the content of the non-magnetic powder contained in the magnetic layer is the ferromagnetic metal powder. 3 to 15 parts by weight with respect to 100 parts by weight. (6) The magnetic recording medium has a lower non-magnetic layer and at least a magnetic layer in contact with the lower non-magnetic layer formed by a wet-on-wet coating method.

The reason why the above embodiment is suitable for the present invention will be explained by incorporating it in the following series of description. Next, the detailed contents of the lower non-magnetic layer will be described. The non-magnetic powder used in the lower non-magnetic layer of the present invention can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides. As the inorganic compound, for example, α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide having a conversion rate of 90% or more. -Bite, titanium oxide, silicon dioxide, tin oxide, magnesium oxide,
Tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Especially preferred are availability, price, and 0.
The above-mentioned titanium oxide, α-iron oxide, barium sulfate, zinc oxide, and alumina are preferable because powders of fine particles having a sharp particle size distribution of 1 μm or less are obtained, and titanium dioxide and α-iron oxide are more preferable. The particle size of these non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or a single non-magnetic powder may be used to broaden the particle size distribution and achieve the same effect. You can also Particularly preferably, the particle size of the non-magnetic powder is 0.01 μm to 0.2 μm, especially 0.0
It is 2 to 0.08 μm. Tap density is 0.05-2g
/ Ml, preferably 0.2-1.5 g / ml. The water content of the non-magnetic powder is 0.1 to 5% by weight, preferably 0.1.
It is 2 to 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the non-magnetic powder is 2 to 11, but the pH is 5
Particularly preferred is between 10 and 10. Specific surface area of non-magnetic powder is 1
˜100 m ² / g, preferably 5-70 m ² / g, more preferably 10-65 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 μm to 1 μm, and 0.0
75 μm to 0.2 μm is more preferable. Oil absorption using DBP is 5-100ml / 100g, preferably 10-80ml / 10
It is 0 g, more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be needle-like, spherical, polyhedral or plate-like.

The loss on ignition is preferably 20% by weight or less, and most preferably not present. The Mohs hardness of the non-magnetic powder used in the present invention is 4 or more,
It is preferably 10 or less. The roughness factor of the powder surface is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. SA (stearic acid) adsorption amount of non-magnetic powder is 1 to 20 μmol / m
² , more preferably ² to 15 μmol / m ² . The heat of wetting of the non-magnetic powder used in the lower non-magnetic layer in water at 25 ° C. is preferably in the range of 200 erg / cm ^{2 to} 600 erg / cm ² . In addition, a solvent having a heat of wetting in this range can be used. The amount of water molecules on the surface at 100 to 400 ° C is appropriately 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 6.

Al ₂ O ₃ and SiO are formed on the surface of these non-magnetic powders.
Surface treatment with ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , and ZnO is preferable. Al ₂ O ₃ , SiO ₂ , and T are particularly preferable for dispersibility.
iO ₂ , ZrO ₂ , and more preferably Al ₂ O ₃ , SiO ₂ ,
It is ZrO ₂ . You may use these in combination,
It can also be used alone. In addition, a co-precipitated surface-treated layer may be used depending on the purpose, or a method of first treating with alumina and then treating the surface layer with silica or vice versa can be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that it is homogeneous and dense.

Specific examples of the non-magnetic powder used in the lower non-magnetic layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, DPN-250, DPN- manufactured by Toda Kogyo Co., Ltd. 250BX
, DPN-245, DPN-270BX, Titanium oxide TTO-51B made by Ishihara Sangyo
, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D,
SN-100, α-iron oxide E270, E271, E300, TTT manufactured by Titanium Industry
-4D, STT-30D, STT-30, STT-65C, TAYCA MT-100S,
MT-100T, MT-150W, MT-500B, MT-600B, MT-100F,
MT-500HD. Sakai Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M,
Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM,
Examples include TiO2P25, Ube Industries 100A and 500A, Titanium Industry Y-LOP, and fired products thereof.

Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide. For α-iron oxide (hematite), the method for synthesizing γ-iron oxide can be referred to. The α iron oxide (hematite) is implemented under the following conditions. That is, the α-Fe ₂ O ₃ particle powder in the present invention is
Oxidation reaction of a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an ordinary ferrous iron solution at a pH of 11 or more and at a temperature of 80 ° C. or less by aerating an oxygen-containing gas. A method of generating needle-shaped goethite particles by carrying out the method, and a suspension containing FeCO ₃ obtained by reacting an aqueous solution of ferrous iron with an aqueous solution of alkali carbonate is passed through an oxygen-containing gas to carry out an oxidation reaction to carry out the spindle reaction. A method of producing goethite particles in the shape of a ferrous salt, an aqueous solution of a ferrous salt containing ferrous hydroxide colloid obtained by adding an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate of less than equivalent to the ferrous salt solution is oxygen. The needle-shaped goethite core particles are generated by carrying out an oxidation reaction by aerating a containing gas, and then, the ferrous salt aqueous solution containing the needle-shaped goethite core particles is mixed with the aqueous solution of the ferrous salt. After the addition of equivalent amount or more of an aqueous alkali hydroxide solution to Fe ²⁺ in the process by passing an oxygen-containing gas to grow the acicular goethite nucleus particles and the ferrous solution and an alkali hydroxide is less than equivalent amount Alternatively, acicular goethite core particles are generated by aerating an oxygen-containing gas through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an alkaline carbonate aqueous solution to generate acicular goethite nucleus particles, and then acid or acid. The acicular goethite particles obtained by the method of growing the acicular goethite nucleus particles in a neutral region are used as precursor particles.

It should be noted that Ni and Z, which are usually added during the reaction for producing goethite particles to improve the characteristics of the particle powder, etc.
There is no problem even if a different element such as n, P or Si is added. Needle-shaped goethite particles, which are precursor particles, are added to 200 to 5
Dehydrate in the temperature range of 00 ° C or, if necessary, further 3
Annealing is performed by heat treatment in the temperature range of 50 to 800 ° C. to obtain acicular α-Fe ₂ O ₃ particles.

There is no problem even if the acicular goethite particles to be dehydrated or annealed have a sintering inhibitor such as P, Si, B, Zr or Sb attached to the surface. Annealing by heat treatment in the temperature range of 350 to 800 ° C. is performed by annealing pores generated on the particle surface of needle-shaped Fe ₂ O ₃ particles obtained by dehydration to melt the polar surface of the particle. This is because it is preferable to close the pores to form a smooth surface morphology.

Α-Fe ₂ O ₃ used in the present invention
The particle powder is obtained by dispersing the acicular α-Fe ₂ O ₃ particles obtained by dehydration or annealing in an aqueous solution to form a suspension, adding an Al compound, and adjusting the pH to obtain the α-Fe.
After coating the additive compound on the particle surface of ₂ O ₃ particles,
It can be obtained by filtering, washing with water, drying, pulverizing, and if necessary, further performing deaeration and consolidation treatment. As the Al compound used, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate and alkali aluminate salts such as sodium aluminate can be used. In this case, the amount of the Al compound added is 0.01 to 50% by weight in terms of Al based on the α-Fe ₂ O ₃ particle powder.
When it is less than 0.01% by weight, the dispersion in the binder resin is insufficient, and when it exceeds 50% by weight, Al compounds floating on the particle surface interact with each other, which is not preferable. In the non-magnetic powder of the lower non-magnetic layer in the present invention, not only Al compounds but also Si compounds, P, Ti, Mn, Ni, Zn, Zr, Sn and Sb are contained.
It is also possible to coat with one or more compounds selected from the above. The amount of each of these compounds used together with the Al compound is in the range of 0.01 to 50% by weight based on the α-Fe ₂ O ₃ particle powder. When it is less than 0.01% by weight, the effect of improving the dispersibility by addition is scarce, and when it exceeds 50% by weight, the compounds floating on other than the particle surface interact with each other, which is not preferable.

Next, titanium dioxide will be described in detail. The methods for producing these titanium oxides are mainly the sulfuric acid method and the chlorine method.
In the sulfuric acid method, the source ore of illuminite is digested with sulfuric acid to produce Ti,
Extract Fe and the like as sulfate. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration and then subjected to thermal hydrolysis to precipitate hydrous titanium oxide. After this is filtered and washed, impurities are washed and removed, and a particle size adjusting agent and the like are added, and then calcined at 80 to 1000 ° C. to obtain crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the nucleating agent added at the time of hydrolysis. This crude titanium oxide is prepared by crushing, sizing, surface treatment and the like. In the chlorine method, natural or synthetic rutile is used as the raw ore.
The ore is chlorinated in a high-temperature reduced state, Ti becomes TiCl ₄ and Fe becomes FeCl ₂ , and iron oxide which is solidified by cooling is separated from liquid TiCl ₄ . Obtained crude TiC
l ₄ was purified by rectification and added with a nucleating agent to give 100
Crude titanium oxide is obtained by instantaneously reacting with oxygen at a temperature of 0 ° C. or higher. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

For the surface treatment, coarse particles are classified by dry pulverizing the titanium oxide material, adding water and a dispersant, wet pulverizing and centrifuging. After that, the fine particle slurry is transferred to a surface treatment tank, where the surface coating of the metal hydroxide is performed. First, a predetermined amount of Al, Si, Ti, Zr, Sb, S
An aqueous solution of salts such as n and Zn is added to neutralize the acid,
Alternatively, alkali is added to cover the surface of the titanium oxide particles with the hydrous oxide produced. By-produced water-soluble salts are removed by decantation, filtration and washing, and finally the slurry pH is adjusted and filtered, followed by washing with pure water. The washed cake is dried with a spray dryer or band dryer. Finally, the dried product is crushed with a jet mill to obtain a product. Further, not only the water system but also the titanium oxide powder can be subjected to AlCl ₃ and SiCl ₄ vapor, and then steam can be introduced to perform the Al and Si surface treatment. For other pigment manufacturing methods, see GD Parfitt and KSW Sing ”Cha
racterization of Powder Surfaces ”Academic Press, 1
You can refer to 976.

By mixing carbon black in the lower non-magnetic layer, the known effect of lowering the surface electric resistance Rs,
The light transmittance can be reduced and a desired micro Vickers hardness can be obtained. The micro Vickers hardness of the lower non-magnetic layer is usually 25 to 60 kg /
mm ² , preferably 30 to adjust head contact
~ 50 Kg / mm ² , NEC thin film hardness meter HMA
Using -400, a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm is used for the tip of the indenter for measurement.

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 VHS. For this purpose, a furnace for rubber, a thermal for rubber, a black for color, acetylene black, etc. can be used.

The BET specific surface area of carbon black is 10
0 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 / 100 g. The particle size of carbon black is 5 to 80 nm, preferably 10 to 50 nm, and 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 the carbon black used in the present invention include BLACKPEARLS 2000, 1300, 1 manufactured by Cabot Corporation.
000, 900, 800, 880, 700, VULCA
N XC-72, manufactured by Mitsubishi Kasei Kogyo, # 3050B, 3
150B, 3250B, # 3750B, # 3950B,
# 950, # 650B, # 970B, # 850B, MA
-600, manufactured by Conlon Bia Carbon, CONDUCT
EX SC, RAVEN 8800,8000,7000,5750,5250,3
500,2100,2000,1800,1500,1255,1250, Ketjen Black EC manufactured by Akzo, etc. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the paint. These carbon blacks are in the range of not more than 50% by weight with respect to the above inorganic powder, and the total weight of the nonmagnetic layer is 40
It can be used in a range not exceeding%. These carbon blacks can be used alone or in combination.

The carbon black which can be used in the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association. In addition, an organic powder may be added to the lower non-magnetic layer according to the purpose. Examples include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine resin powder, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, 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.

The undercoat layer is provided in a general magnetic recording medium, but it is provided in order to improve the adhesive force between the support and the magnetic layer and has a thickness of 0.5 μm. The following are common:

As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the lower non-magnetic layer, those of the magnetic layer can be applied. In particular, with regard to the amount and kind of binder, the amount and kind of additive and dispersant added, known techniques for the magnetic layer can be applied.

Next, the magnetic layer will be described in detail. The ferromagnetic metal powder used in the magnetic layer of the present invention includes α-
Examples thereof include ferromagnetic metal powders containing Fe, Ni or Co as a main component (75% or more), and ferromagnetic alloy powders containing α-Fe as a main component are preferable. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, T
i, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It may contain atoms such as n, Zn, Ni, Sr, and B. In particular, Al, Si, Ca, Y, Ba, La, N
d, Co, Ni and B are important as elements contained in addition to α-Fe. These ferromagnetic metal powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before the dispersion. Specifically, Japanese Patent Publication Nos. 44-14090, 45-18372, and 47-2
2062, Japanese Examined Sho 47-22513, Japanese Examined Sho 46-28466, Japanese Examined Sho
46-38755, JP-B 47-4286, JP-B 47-12422, JP-B 47-17284, JP-B 47-18509, JP-B 47-18573
No. 3, Japanese Patent Publication No. 39-10307, Japanese Patent Publication No. 48-39639, US Patent 30
26215, 3031341, 3100194, 3242005
No. 3389014, etc.

The ferromagnetic metal fine powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal fine powder, those obtained by a known manufacturing method can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, or reducing Fe oxide with a reducing gas such as hydrogen to Fe or F
a method for obtaining e-Co particles and the like, a method for thermally decomposing a metal carbonyl compound, a method for reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, a metal For example, a method of obtaining fine powder by evaporating in a low-pressure inert gas. The ferromagnetic metal powder thus obtained is subjected to a known gradual oxidation treatment, that is, a method of immersing it in an organic solvent and then drying it, and immersing it in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and then drying it. Any of the method of forming the oxide film on the surface by adjusting the partial pressure of oxygen gas and the inert gas without using an organic solvent can be used.

The Hc of the ferromagnetic metal powder contained in the upper magnetic layer is usually 1500 to 4000 Oe, preferably 1
800-3500 Oe, more preferably 2000-30
00 Oe and σ _S is usually 110 to 200 emu / g, preferably 125 to 180 emu / g, more preferably 13
5 to 160 emu / g, major axis length is usually 0.03 to 0.20
μm, preferably 0.04 to 0.15 μm, more preferably
0.06-0.11 μm, crystallite size is usually 80-
It is 300Å, preferably 100 to 200Å, more preferably 120 to 190Å. The acicular ratio of the ferromagnetic metal powder is preferably 4-18, more preferably 5-12. The water content of the ferromagnetic metal powder is preferably 0.01 to 2%. It is preferable to optimize the water content of the ferromagnetic metal powder depending on the type of binder.

BET was used for the ferromagnetic metal powder of the magnetic layer of the present invention.
The specific surface area according to the method is 45 to 80 m ² / g,
It is preferably 50 to 70 m ² / g. When it is 25 m ² / g or less, noise becomes high, and when it is 80 m ² / g or more, sufficient dispersibility cannot be obtained, which is not preferable. The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4 to 12, preferably 6 to 10.
Is. Ferromagnetic metal powder may be Al, Si, P
Alternatively, surface treatment may be performed with these oxides or the like. The amount is 0.1 to 10% with respect to the ferromagnetic metal powder, and when surface treatment is applied, the adsorption of lubricant such as fatty acid is 10
It is preferably 0 mg / m ² or less, which is preferable. The ferromagnetic metal powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but the characteristics are not particularly affected as long as the content is 200 ppm or less.

The ferromagnetic metal powder used in the present invention preferably has few voids, and the value is 20% by volume or less, more preferably 5% by volume or less. The shape may be needle-like, rice-like, rod-like, or spindle-like, as long as the characteristics of the particle size shown above are satisfied.
In order to achieve the SFD of the ferromagnetic metal powder of 0.6 or less, it is necessary to reduce the Hc distribution of the ferromagnetic metal powder. For that purpose, there is a method of improving the particle size distribution of goethite and preventing the sintering of γ-hematite.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,0.
00-200,000, preferably 10,000-10
The degree of polymerization is about 50,000 and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile,
Methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetate
There are polymers or copolymers containing polyurethane, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

Further, as the thermosetting resin or the reaction type resin, a phenol resin, an epoxy resin, a polyurethane curing type resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Further, a known electron beam curable resin can be used for the lower non-magnetic layer or the magnetic layer.

These examples and the method for producing them are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin,
Examples thereof include a combination of at least one selected from vinyl chloride vinyl acetate vinyl alcohol resin and vinyl chloride vinyl acetate maleic anhydride copolymer, and a polyurethane resin, or a combination of these with polyisocyanate. As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate carbonate polyurethane, polyester polycarbonate carbonate polyurethane, polycaprolactone polyurethane and polyolefin polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and durability, -COOM, -SO ₃ M, -OS
_{O 3 M, -P = O (} OM) 2, -O-P = O (OM)
_2, (wherein M represents a hydrogen atom or an alkali metal _{salt,), - OH, -NR 2} , -N + R 3 (R is a hydrocarbon group) epoxy group, -SH, -CN, sulfobetaine, phosphobetaine, It is preferable to use one having at least one polar group selected from carboxybetaine and the like introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ⁻¹ to 10 ⁻⁸ mol / g, preferably 10
^{It is -2} to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbite Corporation.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku Co., Ltd. 1000
W, DX80, DX81, DX82, DX83, 100
FD, MR-104, MR-105 manufactured by Nippon Zeon Co., Ltd.
MR110, MR100, 400X-110A, Nippon Polyurethane Nipporan N2301, N2302, N
2304, Pandex T-510 manufactured by Dainippon Ink and Chemicals, Inc.
5, T-R3080, T-5201, Barnock D-4
00, D-210-80, Crisbon 6109, 720
9. Byron UR8200, UR8300, manufactured by Toyobo Co., Ltd.
UR-8600, UR-5500, UR-4300, R
V530, RV280, FB-84, FB-79, manufactured by Dainichiseika, Daiferamine 4020, 5020, 510
0, 5300, 9020, 9022, 7020, Mitsubishi Kasei Corp., MX5004, Sanyo Kasei Samprene SP-
150, TIM-3003, TIM-3005, Saran F310, F210 and the like manufactured by Asahi Kasei Corporation. Among them, MR-104, MR110, UR-8200, UR
8300, UR-8600, UR-5500, UR-4
300 and TIM-3005 are preferable.

The binder used in the magnetic layer of the present invention is used in the range of 8 to 24% by weight, preferably 12 to 24% by weight, based on the ferromagnetic metal powder. When vinyl chloride resin is used, it is 5 to 30% by weight, when polyurethane resin is used, it is 2 to 20% by weight, and polyisocyanate is 2% by weight.
It is preferable to use these in combination within the range of 20 wt%. In particular, it is preferable that the magnetic layer does not contain polyisocyanate and the lower non-magnetic layer contains polyisocyanate. The reason for this is that it is effective in preventing the polyisocyanate of the magnetic layer from undergoing a curing reaction in the liquid and causing aggregation of the ferromagnetic metal powder.

In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100 ° C. and the elongation at break is 1.
0 to 2,000%, breaking stress 0.05 to 10 kg /
The cm ² and the yield point are preferably 0.05 to 10 kg / cm ² . The magnetic recording medium of the present invention comprises at least two layers, a lower non-magnetic layer and a magnetic layer. The lower non-magnetic layer and the magnetic layer may each have a single layer or a multilayer structure. Therefore, the amount of binder, the amount of vinyl chloride resin, polyurethane resin, polyisocyanate, or other resin in the binder, the molecular weight of each resin forming each layer, the amount of polar groups, or the resins described above. It is of course possible to change the physical properties and the like of each layer depending on the need, and known techniques relating to the multilayer magnetic layer can be applied. For example, when changing the amount of binder in the upper layer (magnetic layer), lower layer (non-magnetic layer), and intermediate layer (magnetic layer or non-magnetic layer), increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. In order to improve the head touch with respect to the head, it is achieved by increasing the amount of the binder in the intermediate layer other than the magnetic layer to give flexibility.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate and naphthylene-1. ，
5-diisocyanate, o-toluidine diisocyanate
, Isophorone diisocyanate, triphenylmethane triisocyanate, and the like, products of these isocyanates with polyalcohols, and polyisocyanates formed by condensation of isocyanates. -, Etc. can be used. Commercially available trade names of these isocyanates are Nippon Polyurethane Co., Ltd., Coronate L, Coronet HL, Coronet 2030, Coronet 2031, Millionate MR.
Millionate MTL, Takeda Pharmaceutical Co., Takenet D-1
02, Takenate D-110N, Takenate D-20
0, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodule L, Desmodule IL, Desmodule N Desmodule HL, etc., and these are used alone or by utilizing the difference in curing reactivity. The lower non-magnetic layer and the magnetic layer can be used in one or more combinations.

The carbon black used in the magnetic layer of the present invention may be a furnace for rubber, thermal for rubber, black for color, acetylene black or the like. Specific surface area is 5-500 m ² / g, DBP oil absorption is 1
0-400ml / 100g, particle size 5nm-300n
m, pH is 2 to 10, water content is 0.1 to 10%, and tap density is preferably 0.1 to 1 g / CC. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 1300 manufactured by Cabot Corporation.
1000, 900, 800, 700, VULCAN X
C-72, Asahi Carbon Co., Ltd., # 80, # 60, # 55,
# 50, # 35, Mitsubishi Kasei Co., Ltd., # 2400B, #
2300, # 900, # 1000 # 30, # 40, # 1
0B, manufactured by Conlon Bia Carbon Co., Ltd., CONDUCTEX
SC, RAVEN 150, 50, 40, 15 and the like. Carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the ferromagnetic powder. Carbon black has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving the film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different characteristics, such as particle size, oil absorption, electric conductivity, pH, etc., in the magnetic layer and the lower non-magnetic layer by changing the kind, amount and combination thereof. Of course, it is possible to use them properly according to the purpose. Carbon black which can be used in the magnetic layer of the present invention includes, for example, "carbon black".
You can refer to the “Bon Black Handbook” edited by the Carbon Black Association. The abrasive used in the present invention is α
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 having a conversion of 90% or more. , Etc., mainly known materials having a moth of 6 or more are used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably 0.01 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution and obtain the same effect. . Tap density is 0.3 to 2 g / cc, water content is 0.1
~ 5%, pH 2-11, specific surface area 1-30 m ² /
g is preferred. 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 a shape having a part of a corner is preferable because of high abrasiveness. Specific examples of the polishing agent used in the present invention include AKP-20, AKP-30, AKP-50 and HI manufactured by Sumitomo Chemical Co., Ltd.
T-50, HIT-60, HIT-60A, HIT-70A,
HIT-80, HIT-80G, HIT-100, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo KK, T
Examples include F-100 and TF-140. The abrasive used in the present invention can be of different types, amounts and combinations in the lower non-magnetic layer and the magnetic layer and can be used properly according to the purpose. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint.
The number of abrasives present on the magnetic layer surface and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5 pieces / 100 μm ² or more.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten disulfide graphite, boron nitride, graphite fluoride, silicon
Oil, polar group-containing silicone, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing ester, polyolefin, polyglycol
, Alkyl phosphates and their alkali metal salts,
Alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt, monobasic fatty acid having 10 to 24 carbon atoms (may contain unsaturated bond, or may be branched) ) And their metal salts (Li, Na,
K, Cu, etc., or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (may contain an unsaturated bond or may be branched. ), An alkoxy alcohol having 12 to 22 carbon atoms, and 10 to 24 carbon atoms
A monobasic fatty acid (which may contain an unsaturated bond or may be branched) and a monovalent or divalent one having 2 to 12 carbon atoms,
Any one of trivalent, tetravalent, pentavalent, and hexavalent alcohol (may contain an unsaturated bond or may be branched)
A mono-fatty acid ester, a di-fatty acid ester or a tri-fatty acid ester, a mono-alkyl ether fatty acid ester of an alkylene oxide polymer, and 8 to 8 carbon atoms
22 fatty acid amides, aliphatic amines having 8 to 22 carbon atoms,
Etc. can be used.

Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, Examples include isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol. To be Further, nonionic surfactants such as alkylene oxide-based, glycerin-based, glycidyl-based, and alkylphenol-ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium. Or a cationic surfactant such as sulfonium, carboxylic acid, sulfonic acid,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfuric acid ester groups, phosphoric acid ester groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, alkylbedine type, etc. Etc. can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants and antistatic agents are not always 100%
Impurities such as isomers, unreacted products, by-products, decomposed products, and oxides may be included in addition to the main component. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in the lower non-magnetic layer and the magnetic layer in different types and amounts according to need. For example, the lower non-magnetic layer,
Stabilization of coating by controlling bleeding to the surface using fatty acid whose melting point is different in the magnetic layer, controlling bleeding to the surface using esters with different boiling points and polarities, and adjusting the amount of surfactant And the amount of lubricant added in the lower non-magnetic layer may be improved to improve the lubrication effect. Of course, the present invention is not limited to the examples shown here.

All or part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. There are cases where it is added in a kneading step using a binder and a solvent, when it is added in a dispersion step, when it is added after dispersion, and when it is added immediately before coating. In some cases, the purpose may be achieved by applying a part or all of the additives simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendaring or after slitting.

Examples of commercial products of these lubricants used in the present invention are NAA-102 and NAA-4 manufactured by NOF CORPORATION.
15, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, cation SA, cation MA, cation A
B, cation BB, nymine L-201, nymine L-202, nymine S-202, nonion E-20
8, nonion P-208, nonion S-207, nonion K-204, nonion NS-202, nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monoguri MB, Nonion DS-6
0, anon BF, anon LG, butyl stearate, butyl laurate, erucic acid, Kanto Chemical Co., oleic acid, Takemoto Yushi Co., FAL-205, FAL-123,
Made by Shin Nippon Rika Co., Ngerb LO, Njorbu IP
M, Sansosizer-E4030, Shin-Etsu Chemical Co., TA
-3, KF-96, KF-96L, KF96H, KF4
10, KF420, KF965, KF54, KF50,
KF56, KF907, KF851, X-22-81
9, X-22-822, KF905, KF700, KF
393, KF-857, KF-860, KF-865
X-22-980, KF-101, KF-102, KF
-103, X-22-3710, X-22-3715,
KF-910, KF-3935, Lion Armor Co., Amid P, Amid C, Amoslip C
P, Lion Oil and Fat Co., Deuomin TDO, Nisshin Oil Co., BA-41G, Sanyo Kasei Co., Profan 2012
E, Newpole PE61, Ionette MS-400,
Ionet MO-200 Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionet DO-200 and the like.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., and methanol.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc., methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycoacetate -Esters such as glycol, dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,
Those such as N-dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted substances, by-products, decomposition products, oxides, and water in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same type in the magnetic layer and the intermediate layer. The addition amount may be changed. Use a solvent with high surface tension (such as cyclohexanone and dioxane) for the intermediate layer to improve coating stability. Specifically, the arithmetic mean value of the solvent composition of the magnetic layer should not be lower than that of the solvent composition of the lower non-magnetic layer. Is essential. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and it is preferable that the solvent composition contains 50% by weight or more of a solvent having a dielectric constant of 15 or more and 20 or less. The dissolution parameter is preferably 8-11.

The thickness constitution of the magnetic recording medium of the present invention is usually 2.0 to 8.0 μm, preferably 3.
0-7.5 μm, more preferably 4.0-7.0 μm
And the lower non-magnetic layer is usually 0.2 to 4.0 μm, preferably 0.3 to 2.0 μm, and more preferably 0.
It is 5 to 1.5 μm. Further, an adhesive layer for improving adhesion is provided between the non-magnetic support and the lower non-magnetic layer. The thickness of the adhesive layer is 0.01-2 μm, preferably 0.02-
It is 0.5 μm. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known adhesive layers and back coat layers can be used.

The total thickness of the magnetic recording medium of the present invention is
Usually, it is 4.5 to 8.5 μm, preferably 5.0 to 7.
3 μm, and more preferably 6.3 to 7.3 μm.
Here, if it is less than 4.5 μm, the stiffness of the tape decreases, sufficient running durability cannot be obtained, and the head tape interface may become unstable, which is not preferable, and if it is more than 8.5 μm, the tape The rigidity is too high, and it may not be possible to obtain a smooth head tape interface, which is not preferable.

The non-magnetic support used in the present invention has a micro Vickers hardness of usually 75 to 150 kg / mm ² , preferably 50 to 100 kg / mm ² , and biaxially stretched polyethylene naphthalate. Known films such as polyamide, polyimide, polyamideimide, aromatic polyamide, and polybenzoxidazole can be used.
In particular, a non-magnetic support made of aramid resin or polyethylene naphthalate is more preferable because sufficient rigidity can be obtained even if the support is thin to some extent.

Corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, etc. may be performed on these non-magnetic supports in advance. The center line average surface roughness of the surface coated with the lower non-magnetic layer of the non-magnetic support is controlled to 0.5 to 7.0 nm in the present invention as described above. Further, it is preferable that the non-magnetic support has not only a small center line average surface roughness but also no large protrusions of 1 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the non-magnetic support, if necessary. Examples of these fillers include oxides and carbonates of Al, Ca, Si, Ti and the like, which may be crystalline or amorphous, and organic fine powders of acrylic or melamine type. Further, in order to achieve compatibility with running durability, it is preferable that the surface on which the back layer is applied be rougher than the surface on which the magnetic layer is applied. The center line surface roughness of the back layer coated surface is preferably 1 nm or more,
More preferably, it is 4 nm or more. When changing the roughness between the magnetic layer-coated surface and the back layer-coated surface, a dual-structured support may be used, or a coating layer may be provided.

The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 10 to 50 kg / mm.
² , F-5 value in the tape width direction is preferably 10 to 30K
g / mm ² and the tape F-5 value in the longitudinal direction of the tape is
It is generally higher than the F-5 value in the width direction, but this is not the case when it is necessary to particularly increase the strength in the width direction. The heat shrinkage ratio of the non-magnetic support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less,
More preferably 1.5% or less, the heat shrinkage ratio at 80 ° C. 30 minutes is preferably 1% or less, more preferably 0.5%.
It is the following. Breaking strength is 5 to 100 kg / m in both directions
The m ² and the elastic modulus are preferably 100 to 2,000 Kg / mm ² . The light transmittance at 900 nm in the present invention is 30%.
The following is preferable, and 3% or less is more preferable.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant and solvent used in the present invention may be added at the beginning or in the middle of any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong force such as a continuous kneader or a pressure kneader is used. The high B of the magnetic recording medium of the present invention can be obtained by using a material having a kneading power.
r can be obtained. When a continuous kneader or a pressure kneader is used, all or part of the ferromagnetic metal powder and the binder (however, 30% or more of the total binder is preferable) and 15 to 100 parts of the ferromagnetic metal powder are used. Kneading is performed in the range of 500 parts. Details of these kneading treatments are described in JP-A-1-166338 and JP-A-64-79274. Further, when preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity,
Zirconia beads are preferred.

A wet-on-wet coating method is preferable for producing a magnetic recording medium having a multi-layered structure as in the present invention, and the following structure can be proposed. 1. The lower non-magnetic layer is first coated by gravure coating, roll coating, blade coating, extrusion coating equipment, etc. commonly used for coating magnetic coatings, and the lower non-magnetic layer is in a wet state. The magnetic layer is coated by a support pressure type extrusion coating apparatus disclosed in JP-A-46186, JP-A-60-238179 and JP-A-2-265672.

2. JP-A-63-88080, JP-A-2-17971
No. 2, JP-A-2-265672, the upper layer and the lower layer are coated almost simultaneously by a single coating head having two slits for passing the coating liquid therein. 3. The upper and lower layers are coated almost simultaneously by the extrusion coating device with a backup roll disclosed in Japanese Patent Laid-Open No. 2-174965.

In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the agglomeration of magnetic particles, it is disclosed in JP-A-62-951.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in JP-A-74-36968. Furthermore, regarding the viscosity of the coating liquid, see
It is necessary to satisfy the numerical range disclosed in No. 8471.

In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1,000 G or more and a cobalt magnet of 2,000 G or more together with the same poles facing each other, and further to provide an appropriate drying step before orientation so that the orientation after drying becomes the highest. preferable. In order to perform high-density recording, it is known that it is effective to incline the easy axis of magnetization in the vertical direction regardless of the needle shape or the plate shape, and it is also effective to combine with this. In addition, it is preferable to provide an adhesive layer containing a polymer as a main component before the simultaneous multi-layer coating of the non-magnetic layer and the magnetic layer, or to combine known methods for increasing the adhesiveness by corona discharge, UV irradiation, and EB irradiation. .

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, it is also possible to treat with metal rolls. The treatment temperature is preferably 70 to 120 ° C., more preferably 80 to 100.
℃ or above. Linear pressure is preferably 200-500 Kg
/ Cm, more preferably 300 to 400 Kg / cm or more.

The magnetic layer surface and its surface of the magnetic recording medium of the present invention.
The coefficient of friction on the opposite surface of SUS420J is preferable
Is 0.1 to 0.5, more preferably 0.2 to 0.3
is there. The surface resistivity is preferably 10^Four-10¹²Homme
/ Sq, the elastic modulus at 0.5% elongation of the magnetic layer is the running direction,
Preferably in the width direction 100 to 2,000 Kg / m
m ², Breaking strength is preferably 1 to 30 Kg / cm², Magnetic
The elastic modulus of the recording medium is preferably 1 in both the running direction and the width direction.
00-1,500Kg / mm², The residual elongation is preferably
Heat shrink at any temperature below 0.5% and below 100 ° C
The rate is preferably 1% or less, more preferably 0.5% or less.
Lower, most preferably 0.1% or less, ideally 0%
is there. Glass transition temperature of magnetic layer (dynamic viscosity measured at 110HZ
The maximum point of the loss modulus of elasticity measurement is 50 ° C or more and 120 ° C
The following is preferable, and that of the lower non-magnetic layer is 0 ° C to 100 ° C.
Is preferred. Loss elastic modulus is 1 × 10⁸~ 8 × 10⁹dyne / c
m²The loss tangent is preferably 0.2 or less.
It is preferably below. Sticking if loss tangent is too large
Breakdown is easy. The residual solvent contained in the magnetic layer is preferably
Kuha 100 mg / m²Or less, more preferably 10 mg
/ M²Below, the residual solvent contained in the magnetic layer is
It is preferably less than the residual solvent contained in the magnetic layer.
The porosity of the magnetic layer is preferable for both the lower non-magnetic layer and the magnetic layer.
30% by volume or less, more preferably 20% by volume or less
Below. Porosity should be small to achieve high output
It is preferable, but it is better to secure a certain value depending on the purpose
There are cases. For example, data where repeated use is important
In magnetic recording media for recording, the higher the porosity, the longer the running durability
Is often preferred.

Although the magnetic recording medium of the present invention has a lower non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the lower non-magnetic layer and the magnetic layer can be changed according to the purpose. is there. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the lower non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. Further, it is effective in the present invention to improve the head contact by changing the method of tensing the support, and the support which is tensified in a direction perpendicular to the tape longitudinal direction has better head contact. It often becomes.

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EXAMPLES The present invention will now be specifically described with reference to Examples of the present invention and Comparative Examples, but the present invention is not limited thereto.
In the examples, the indication "part" means "part by weight".

Example 1: Lower non-magnetic layer (lower layer) Non-magnetic powder αFe ₂ O ₃ hematite 80 parts Long axis length 0.15 μm Specific surface area by BET method 52 m ² / g pH 6 Tap density 0.8 DBP oil absorption 27-38g / 100g, surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle size 16nm DBP oil absorption 80ml / 100g pH 8.0 BET specific surface area 250m ² / g Volatile content 1.5% Vinyl chloride copolymer 12 parts MR-110 polyester polyurethane resin manufactured by Zeon Corporation 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1; -SO ₃ Na group 1 × 10 ^-4 eq / g-containing α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Magnetic layer (upper layer) Ferromagnetic metal fine powder Composition Fe / Co = 80/20 100 parts Hc 2200 Oe, specific surface area by BET method 59 m ² / g Crystallite size 170 Å Surface treatment agent Al ₂ O ₃ , SiO ₂ Particle size (long axis length) 0. 08 μm Needle ratio 8 σs: 137 emu / g Polyester polyurethane resin 12 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1; -SO ₃ Na group 1 × 10 ^-4 eq / g content α- Al ₂ O ₃ (average particle size 0.15 μm) 5 parts Carbon black (average particle size 0.08 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts

Each component of each of the above paints was kneaded with an open kneader and then dispersed using a sand mill. To the obtained lower layer dispersion liquid, 5 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added, and to the upper layer dispersion liquid, 1 part of the same polyisocyanate was added. Add 40 parts of mixed solvent,
Filtration was performed using a filter having an average pore size of μm to prepare coating solutions for forming the lower non-magnetic layer and the magnetic layer, respectively.

The resulting lower non-magnetic layer coating solution was dried to a thickness of 1 μm, and immediately after that, a magnetic layer thickness of 0.12 μm was added to form a thickness of 5. 5μ
The magnetic layer coated surface has a center line surface roughness of 0.002 μm and is simultaneously multilayer coated on a polyethylene naphthalate support. While both layers are still wet, a cobalt magnet having a magnetic force of 3000 G and 1500 G After being oriented by a solenoid with magnetic force and dried, a 7-stage calender consisting of only metal rolls at a temperature of 90 ° C and a speed of 200 m / mi / min.
Then, a back layer having a thickness of 0.5 μm was applied. An 8 mm video tape was manufactured by slitting a width of 8 mm.

Examples 2 to 7 and Comparative Examples 1 to 6 In Example 1, various conditions were changed to prepare samples. Example 2 The lower limit of the thickness of the magnetic layer of Example 1 is 0.0
Thinned to 7 μm. Example 3 The magnetic layer thickness of Example 1 is the upper limit, that is, 0.2.
It was thickened to 0 μm. Comparative Example 1 The thickness of the magnetic layer was 0.06 μm as compared with Example 2.
And thinned it.

Comparative Example 2 The magnetic layer thickness was increased to 0.22 μm as compared with Example 3. Example 4 Bm was lowered by adjusting the amount of polyester polyurethane contained in the magnetic layer of Example 1 to 16 parts by weight. Example 5 The following were used as the ferromagnetic metal powder of Example 1, and the polyester polyurethane was reduced to 9 parts by weight.

Ferromagnetic fine metal powder composition Fe / Co = 70/30 Hc 2500 Oe, specific surface area by BET method 62 m ² / g crystallite size 190 Å surface treatment agent Al ₂ O ₃ , SiO ₂ , Y particle size (long axis length ) 0.11 μm needle-like ratio 10 σs: 160 emu / g Comparative Example 3 The polyester polyurethane of Example 1 was 12
The amount was increased from 2 parts by weight to 24.5 parts by weight to reduce Bm.

Comparative Example 4 A polyester polyurethane of Example 5 was prepared by reducing the amount to 7.5 parts by weight. Example 6 The ferromagnetic metal powder of Example 1 was changed to the following. Ferromagnetic metal fine powder Composition Fe / Co = 90/10 Hc 1960 Oe, specific surface area by BET method 58 m ² / g Crystallite size 170 Å Surface treatment agent Al ₂ O ₃ , SiO ₂ , Y Particle size (long axis length) 0. 08 μm acicular ratio 8 σs: 134 emu / g Example 7 The ferromagnetic metal powder of Example 1 was changed to the following.

Ferromagnetic metal fine powder composition Fe / Co = 70/30 Hc 2800 Oe BET specific surface area 65 m ² / g crystallite size 130 Å surface treatment agent Al ₂ O ₃ , SiO ₂ , Y particle size (long axis length) 0.08 μm Needle ratio 12 σs: 130 emu / g Comparative Example 5 The ferromagnetic metal powder of Example 1 was changed to the following.

Ferromagnetic fine metal powder composition Fe / Co = 90/10 Hc 1850 Oe, specific surface area by BET method 57 m ² / g crystallite size 170 Å surface treatment agent Al ₂ O ₃ , SiO ₂ , La particle size (long axis length ) 0.11 μm Needle ratio 10 σs: 137 emu / g Comparative Example 6 The ferromagnetic metal powder of Example 1 was changed to the following.

Ferromagnetic metal fine powder composition Fe / Co = 70/30 Hc 2900 Oe, specific surface area by BET method 54 m ² / g crystallite size 160 Å surface treatment agent Al ₂ O ₃ , SiO ₂ , La particle size (long axis length ) 0.13 μm acicular ratio 15 σs: 134emu / g

The materials and the prepared samples were evaluated as follows. Evaluation Method <Magnetic Layer Thickness Measuring Method> A magnetic cutter was cut out to a thickness of about 0.1 μm in the longitudinal direction of the magnetic recording medium, observed with a transmission electron microscope at a magnification of 30,000, and photographed. . The print size of the photograph is A4 size. After that, paying attention to the shape difference between the ferromagnetic powder and the non-magnetic powder in the magnetic layer and the non-magnetic layer, the interface is visually judged and bordered in black.
Moreover, the surface of the magnetic layer also had a black border. Then Zei
The distance between the bordered lines was measured by an image processing apparatus IBAS2 manufactured by ss. The length of the sample photograph was in the range of 21 cm, 200 to 500 measurement points were taken, and the simple addition average value of the measurement values at that time was taken as the thickness of the magnetic layer.

<Specific surface area by BET method> Canter soap (manufactured by US Canter Chrome Co., Ltd.) was used. 250 ° C, 3
BET single point method (partial pressure 0.3
It was measured in 0). <Magnetic characteristics Hc, Br, Bm> Using a vibrating sample type magnetometer (manufactured by Toei Industry Co., Ltd.), Hm was measured at 10 kOe. <Centerline average surface roughness Ra> TOPO3D manufactured by WYKO
By using the MIRAU method to measure the surface of the medium to about 250 nm × 2
Ra of an area of 50 nm was measured. Measurement wavelength is about 650
Spherical correction and cylindrical correction are added in nm. This method is a non-contact surface roughness meter that measures by optical interference.

<Particle Diameter of Ferromagnetic Powder and Non-Magnetic Powder> A method of taking a transmission electron microscope photograph and directly reading the minor axis diameter and the major axis diameter of the ferromagnetic powder from the photograph, and an image analyzer Carl Zeiss. The average particle diameter was determined by appropriately using a method of tracing and reading a transmission type micrograph with IBASS1 manufactured by the company.

<Ferromagnetic metal powder crystallite size> It was determined from the half-width broadening of the diffraction lines of the (1,1,0) plane and the (2,2,0) plane by X-ray diffraction.

<Electromagnetic conversion characteristics> The “output of recording wavelengths 0.488 μm and 22 μm” reference is a prototype reference ME tape, and the output is measured at a relative speed of 10.2 m / sec using an externally applied drum tester. did. The head used was an Fe-based head and had a Bs (saturation magnetization amount) of 1.5 T (tesla). It is a value when recording / reproducing with the optimum recording current defined below.

The higher the output of the recording wavelength of 0.488 μm, the more preferable. The 22 μm output is preferably in the range of −2 dB to +2 dB. “Overwrite erasure rate” After recording a rectangular wave signal having a recording wavelength of 22 μm by using an externally applied drum tester, its output is reproduced and measured. After recording a rectangular wave signal having a recording wavelength of 0.488 μm by superimposing it on the recording medium, the recording wavelength 2 is reproduced.
Read the output of 2μm with a spectrum analyzer,
The ratio of the output of the wavelength of 22 μm before and after the overlapping recording is defined as the overwrite erasing rate. The absolute value is preferably −20 dB or less. “Input / output characteristics” Using the external contact type drum tester, a rectangular wave signal having a recording wavelength of 0.488 μm was recorded and reproduced by changing the recording current. 90 of the maximum reproduction output of the "optimum recording current" input / output characteristic curve
The recording current value is +4 dB larger than the recording current value at the output at which%. It is preferably in the range of ± 1.0 dB from the reference.

The obtained results are shown below.

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[Table 1]

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[Table 2]

Examples 8 to 11 and Comparative Examples 7 to 10 Samples were prepared by changing various conditions in Example 1. Comparative Example 7 The surface roughness of the magnetic layer was increased by treating with a calender composed of a plastic roll and a metal roll at a temperature of 50 ° C.

Comparative Example 8 The particle size of the filler of the non-magnetic support used in Example 1 was about 2
The surface roughness of the support was increased by doubling and increasing the amount of non-filler 1.5 times. Comparative Example 9 The amount of filler in the non-magnetic support used in Example 8 was about 30%.
Increased support was used.

Example 9 The particle size of the filler of the non-magnetic support used in Example 1 was set to 1 /
The surface property of the base was smoothed by doubling the amount of addition to 1/2. Comparative Example 10 The particle size of the filler in the non-magnetic support of Example 1 was halved and the addition amount was reduced to 1/10 to further reduce the surface roughness of the non-magnetic support.

Example 10 The thickness of the non-magnetic support of Example 1 was changed from 5.5 μm to 6.9.
thickened to μm. Example 11 The thickness of the non-magnetic support of Example 1 was changed from 5.5 μm to 2.9.
Thinned to μm. The results obtained are shown in the table below.

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[Table 3]

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[Table 4]

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Front page continued (72) Inventor Hiroaki Takano 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (3)

[Claims] 1. A magnetic recording in which a lower non-magnetic layer mainly containing a non-magnetic powder and a binder is provided on a non-magnetic support, and a magnetic layer containing at least a ferromagnetic metal powder and a binder is provided thereon. In the medium, the thickness of the magnetic layer is 0.07 to
0.20 μm, Bm of the magnetic layer measured with an external magnetic field of 10 kOe is 3700 to 6000 gauss, and Hc of the magnetic layer is 20.
Is 0 to 3000 Oe, the center line surface roughness Ra of the magnetic layer is 1.0 to 3.0 nm, and the center line surface roughness of the surface on which the lower non-magnetic layer of the non-magnetic support is coated is A magnetic recording medium having a thickness of 0.5 to 7.0 nm. 2. The total thickness of the magnetic recording medium is 4.5 to
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 8.5 μm. 3. The magnetic recording medium according to claim 1, wherein the coating solution for the magnetic layer in the magnetic recording medium does not contain polyisocyanate.