JP2001351230A - Method for producing magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a magnetic recording medium, in particular, a high-capacity discoid magnetic recording medium, having improved electromagnetic transducing characteristics, particularly improved high- density recording characteristics, low frictional force to a head, superior durability and a lowered error rate particularly in a high density recording region. SOLUTION: In the method for producing the magnetic recording medium, a coating liquid for a lower layer containing a thermosetting resin as a binder and a coating liquid for a magnetic layer are applied on a substrate and dried in a drying zone at 100 deg.C or higher and the web immediately after the drying is cooled to 35 deg.C or lower by passing through a cooling zone, held at 35 deg.C or lower up to a calendering step and calendered to form a magnetic layer having 5 nm or smaller surface roughness (Ra) and 90 nm or smaller surface hardness represented by the depth of a scratch by a scratch method with a surface property testing machine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a coating type magnetic disk having a high recording density, and more particularly to a method of manufacturing a coating type magnetic disk having a magnetic layer and a substantially non-magnetic lower layer. The present invention relates to a method for manufacturing a magnetic disk for high-density recording containing hexagonal ferrite powder.

[0002]

2. Description of the Related Art In the field of magnetic disks, a 2 MB MF-2HD floppy (registered trademark) disk using Co-modified iron oxide has been standardly mounted on a personal computer. However, in today's rapidly increasing data capacity, the capacity is not sufficient, and there has been a demand for a larger floppy disk. In the field of magnetic tapes, in recent years, with the spread of office computers such as minicomputers, personal computers, and workstations, research on magnetic tapes (so-called backup tapes) for recording computer data as an external storage medium has been active. It has been done. When a magnetic tape for such a purpose is put to practical use, especially in order to achieve a large-capacity and small-sized recording in combination with a reduction in the size of a computer and an increase in information processing capacity, an increase in a recording capacity is strongly required. .

Conventionally, a magnetic layer has a magnetic layer in which iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder are dispersed in a binder on a non-magnetic support. Things are widely used. Among them, ferromagnetic metal powder and hexagonal ferrite powder are known to be excellent in high density recording characteristics. In the case of a disk, a 10-MB MF-2TD and a 21-MB MF-2S are used as a large-capacity disk using a ferromagnetic metal powder excellent in high-density recording characteristics.
D has a large capacity disk using hexagonal ferrite, such as 4 MB MF-2ED and 21 MB floptical, but it cannot be said that the capacity and performance are sufficient. Under such circumstances, many attempts have been made to improve the high-density recording characteristics. An example is shown below.

[0004] In order to improve the characteristics of a disk-shaped magnetic recording medium, Japanese Patent Application Laid-Open No. 64-84418 proposes to use a vinyl chloride resin having an acidic group, an epoxy group and a hydroxyl group. Japanese Patent Publication No. 6-28106 proposes to use a metal powder having a Hc of 79.6 kA / m (1000 Oe (Oe)) or more and a specific surface area of 25 to 70 m ² / g. It has been proposed to determine the specific surface area and the amount of magnetization and to include an abrasive.

In order to improve the durability of a disk-shaped magnetic recording medium, Japanese Patent Publication No. 7-85304 proposes to use an unsaturated fatty acid ester and a fatty acid ester having an ether bond, and Japanese Patent Publication No. 7-70045. The publication proposes to use a fatty acid ester having an ether bond with a branched fatty acid ester, as disclosed in JP-A-54-1247.
No. 16 proposes to include a non-magnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester.
No. 9407 proposes that the volume and surface roughness of pores containing a lubricant be 0.005 to 0.025 μm,
Japanese Patent Application Laid-Open No. 61-294637 proposes to use a fatty acid ester having a low melting point and a high melting point.
Japanese Patent No. 6216 proposes to use an abrasive having a particle size of 1/4 to 3/4 of the thickness of a magnetic layer and a fatty acid ester having a low melting point, and Japanese Patent Application Laid-Open No. 3-203018 discloses a metal magnetic material containing aluminum. It has been proposed to use body and chromium oxide.

As a configuration of a disk-shaped magnetic recording medium having a nonmagnetic lower layer and an intermediate layer, Japanese Patent Application Laid-Open No. 3-120613 has proposed a configuration having a conductive layer and a magnetic layer containing metal powder. JP-A-290446 proposes a configuration having a magnetic layer and a non-magnetic layer of 1 μm or less, and JP-A-62-159337 proposes a configuration comprising a carbon intermediate layer and a magnetic layer containing a lubricant. 5-29
No. 0358 proposes a configuration having a nonmagnetic layer having a prescribed carbon size.

On the other hand, a disk-shaped magnetic recording medium comprising a thin magnetic layer and a functional non-magnetic layer has recently been developed.
0MB class floppy disks have appeared. Japanese Patent Application Laid-Open No. 5-109061 shows these features.
In Japanese Patent Application Laid-Open No. H05-205, there is proposed a structure having a magnetic layer having a Hc of 111.4 kA / m (1400 Oe) or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing conductive particles.
Japanese Patent Application Laid-Open No. 197946 proposes a configuration including an abrasive larger than the thickness of the magnetic layer.
A configuration in which the surface electric resistance is defined to be within 15% is proposed. Japanese Patent Application Laid-Open No. 6-68453 proposes a configuration in which two types of abrasives having different particle sizes are included and the amount of the abrasive on the surface is defined. ing.

In recent years, with the spread of office computers such as minicomputers and personal computers, magnetic tapes (so-called backup tapes) for recording computer data as external storage media have also been developed for tape-shaped magnetic recording media. Research is being actively conducted. When a magnetic tape for such a purpose is put into practical use, especially with the downsizing of computers and the increase in information processing capacity, an increase in recording capacity is strongly demanded in order to achieve large-capacity recording and downsizing. In addition, the magnetic tape can be used under a wide range of environmental conditions (especially in the rapidly fluctuating temperature and humidity conditions) due to the wide use environment, reliability in data storage, and data stability in multiple runs by repeated use at high speed. The reliability of the performance of recording, reading, and the like is also required more than before.

However, with the rapid increase in capacity and recording density of magnetic recording media in the form of disks or tapes, it has become difficult to obtain satisfactory characteristics even with such techniques. Also, it is becoming difficult to achieve both durability and durability.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to significantly improve the electromagnetic conversion characteristics, particularly the high-density recording characteristics, and have a low frictional force with the head, and have excellent durability. An object of the present invention is to provide a method for manufacturing a magnetic recording medium in which an error rate in a region is significantly improved. Another object of the present invention is to have the above-mentioned properties,
An object of the present invention is to provide a method of manufacturing a disk-shaped magnetic recording medium having a large capacity of Gbit.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to obtain a magnetic recording medium having good electromagnetic conversion characteristics and durability and a particularly improved error rate in a high-density recording area. The present inventors have found that a magnetic recording medium manufactured by the following method has excellent high-density recording characteristics and excellent durability, and have led to the present invention. That is, according to the present invention, a method of manufacturing a magnetic recording medium having the following configuration and a magnetic recording medium are provided. 1. A method for producing a magnetic recording medium, wherein a non-magnetic layer substantially non-magnetic on a support and a magnetic layer formed by dispersing a ferromagnetic powder in a binder thereon are formed in this order,
A lower layer coating solution containing a thermosetting resin as a binder and a magnetic layer coating solution are coated on a support, dried in a drying zone at 100 ° C. or more, and the web immediately after drying is passed through a cooling zone to reduce the web temperature. The web was cooled to 35 ° C. or less, the temperature of the web until the calendering treatment was maintained at 35 ° C. or less, and then the calendering treatment was performed to reduce the surface roughness (Ra) of the magnetic layer to 5 nm or less and the surface hardness to the surface hardness. A method for manufacturing a magnetic recording medium, characterized in that the scratch depth is 90 nm or less, expressed as a scratch depth by a scratch test method using a testing machine. 2. A magnetic recording medium manufactured by the above method.

Generally, after the magnetic layer / non-magnetic layer is applied, heat is applied to remove the organic solvent used in preparing the coating solution, followed by drying. If the organic solvent remains in the magnetic layer / non-magnetic layer, the magnetic layer / non-magnetic layer is plasticized and the durability of the magnetic recording medium is reduced. On the other hand, when a thermosetting resin is used as a binder in order to obtain excellent durability, after applying the magnetic layer / nonmagnetic layer, heat is applied for drying, and thus the curing proceeds. As the curing proceeds, the moldability in the calendar decreases, the surface roughness of the magnetic layer after treatment, the degree of filling deteriorates, the surface hardness becomes soft, the electromagnetic conversion characteristics decrease, and the durability decreases. . According to the method of the present invention, in order to sufficiently remove the residual solvent, the drying temperature is set to 100 ° C. or higher, and immediately thereafter, the web temperature is lowered by passing the web through a cooling zone, and the temperature from winding to calendering is reduced. Is kept at a low temperature, the curing of the thermosetting resin is suppressed, and the above problem is solved. You. Although there is no regulation on the cooling zone temperature and staying time,
The temperature must be 5 ° C or lower, preferably 30 ° C or lower. The temperature during winding and the temperature until calendering are also 35 ° C.
Desirably, the temperature must be 30 ° C. or lower. According to the present manufacturing method, the surface roughness of the magnetic recording layer is 5 nm or less, preferably 4 nm.
nm or less, by setting the scratch depth by a scratch test method using a surface property tester, which is an index of surface hardness, to 90 nm or less, preferably 70 nm or less, a magnetic recording medium having both excellent electromagnetic conversion characteristics and durability can be obtained. Obtainable.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention has a substantially non-magnetic lower layer formed on a support and a magnetic layer formed by dispersing a ferromagnetic powder in a binder on the lower layer. It is a magnetic recording medium. Hereinafter, the components of each layer constituting the magnetic recording medium, the layer configuration, a specific method for manufacturing the magnetic recording medium, and the like will be described.

[Magnetic Layer] The average surface roughness (Ra) of the magnetic layer of the magnetic recording medium of the present invention is HD200 manufactured by WYKO.
The value measured by 0 is 5 nm or less, preferably 4 nm or less, more preferably 0.5 to 4 nm. If it exceeds 5 nm, the spacing loss between the magnetic disk and the head becomes large, the output is low and the noise is high, and the medium performance of the magnetic disk of the present invention cannot be exhibited. If the thickness is less than 0.5 nm, the magnetic layer is easily damaged by the magnetic head, which is not preferable. In addition, the scratch depth by a scratch test method using a surface property tester, which is an index of the surface hardness of the magnetic layer, is 90 nm or less, preferably 70 nm or less. The smaller the depth of the flaw, the larger and harder the surface hardness. The surface of the magnetic layer having a scratch depth exceeding 90 nm is soft, and the magnetic layer is easily damaged by the magnetic head. In order to make the average surface roughness and hardness of the surface of the magnetic layer as described above, a thermosetting resin is used as a binder contained in the coating solution for forming the magnetic layer and the lower layer, and the coating solution is applied to the support. After applying, drying is carried out at a temperature of 100 ° C. or more in a drying zone for removing the solvent, the web immediately after drying is cooled to 35 ° C. or less, and the temperature of the web is kept at 35 ° C. or less until calendering is performed. Thereafter, it can be performed by a method of performing a calendar process. This will be described in more detail later.

The coercive force (Hc) of the magnetic layer of the magnetic disk of the present invention is preferably 143.3 kA / m (1800 Oe) or more, and more preferably 159.2 kA / m.
A / m (2000 Oe) or more, more preferably 183.1 to 278.6 kA / m ((2300 to
3500 Oersted). 143.3 kA / m
If it is less than (1800 Oersteds), it is difficult to achieve a high recording density.

(Ferromagnetic Powder) The ferromagnetic powder used in the upper magnetic layer of the present invention is preferably a ferromagnetic metal powder or a hexagonal ferrite powder. As ferromagnetic metal powder,
A ferromagnetic alloy powder containing α-Fe as a main component is preferable. These ferromagnetic powders include Al, Si,
S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
It may contain atoms such as d, Sm, P, Co, Mn, Zn, Ni, Sr, and B. In particular, Al, Si, C
It is preferable that at least one of a, Y, Ba, La, Nd, Sm, Co, Ni, and B be contained in addition to α-Fe.
More preferably, it contains at least one of o, Y, Al, Nd, and Sm. The content of Co is 0 to Fe.
It is preferably 40 at%, more preferably 15 to 35 at%, and still more preferably 20 to 35 at%. The content of Y is preferably 1.5 to 12 atomic%, more preferably 3 to 10 atomic%, and still more preferably 4 to 9 atomic%. Al is preferably 1.5 to 30 atomic%, more preferably 5 to 20 atomic%, and more preferably 8 to 15 atomic%.

These ferromagnetic powders may be treated in advance with a dispersant, a lubricant, a surfactant, an antistatic agent and the like described below before dispersion. Specifically, JP-B-44-14090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513,
JP-B-46-28466, JP-B-46-38755
No., JP-B-47-4286, JP-B-47-12422
No., JP-B-47-17284, JP-B-47-1850
No. 9, JP-B-47-18573, JP-B-39-103
07, Japanese Patent Publication No. 46-39639, U.S. Pat.
No. 6215, No. 3031341, No. 3100194
Nos. 3,242,005 and 3,389,014.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder, those obtained by a known production method can be used, and the following production methods can be mentioned. -A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen-A method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles-Metal carbonyl compound・ A method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal ・ Evaporating the metal in a low-pressure inert gas to form a powder How to get. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

When the ferromagnetic powder contained in the magnetic layer is represented by a specific surface area (S _BET ) by a BET method, it is usually 45 to 80.
a m ² / g, preferably from 50 to 70 m ² / g.
If it is less than 45 m ² / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable. The crystallite size of the ferromagnetic powder is usually from 80 to 180 °, preferably from 100 to 180 °, more preferably from 110 to 175 °. The average major axis length of the ferromagnetic powder is preferably 30 to 1
It is 50 nm, and more preferably 30 to 100 nm. The needle ratio of the ferromagnetic powder is preferably from 3 to 15, and more preferably from 5 to 12. Saturation magnetization of ferromagnetic powder (σ
S) is usually 100 to 200 A · m ² / kg (emu /
g), preferably 120 A · m ² / kg (emu
/ G) to 180 A · m ² / kg (emu / g).

The water content of the ferromagnetic powder is preferably 0.01 to 2% by weight. It is preferable to optimize the water content of the ferromagnetic metal powder depending on the type of the binder. Preferably, the pH of the ferromagnetic powder is optimized by the combination with the binder used. The range is usually from 4 to 12, preferably from 6 to 10. Ferromagnetic powder, if necessary,
The surface treatment may be performed with Al, Si, P, or an oxide thereof. The amount is usually based on the ferromagnetic powder.
The surface treatment is 0.1 to 10% by weight, and the surface treatment is preferable because the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. Soluble Na, Ca, Fe, N
It may contain inorganic ions such as i and Sr. It is preferable that these are essentially absent, but if they are 200 ppm or less, they do not particularly affect the characteristics. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and its value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of a needle shape, a rice grain shape, and a spindle shape as long as the characteristics of the particle size described above are satisfied.

SFD (switching fiel) of the ferromagnetic powder itself
d distribution) is preferably small, more preferably 0.8 or less. It is preferable to reduce the distribution of Hc in the ferromagnetic powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, and the peak shift is small, which is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods of improving the particle size distribution of goethite in the ferromagnetic metal powder and preventing sintering.

(Abrasive) A known abrasive can be used for the magnetic layer of the magnetic disk, but diamond particles or alumina particles are preferably used.

<Diamond and Alumina> In the case of diamond, natural diamond is expensive, and artificial diamond is usually used. Methods for producing diamond include a method of producing graphite and iron, Co, Ni, etc. under high temperature and high pressure, a method called static synthesis in which graphite or furan resin carbon is reacted under high temperature and high pressure, and a dynamic synthesis method. ,
There is a gas phase synthesis method. In the present invention, the method for producing diamond is not limited. The average particle size of the diamond particles is preferably 0.05 to 1 μm, more preferably 0.07 to 0.5 μm.
m. The amount of the diamond is from 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, based on the ferromagnetic powder. Industrially, it is possible to use a diamond which has been used for cutting and polishing, in which impurities are discriminated and cleaned from secondary use. As a method for classifying diamond particles, there is a method using a special mesh filter using centrifugal force from a dispersion liquid, and the like. As the alumina particles, α-alumina, β-alumina or the like having an α conversion of 90% or more is used. The average particle size of the alumina particles is preferably 0.05 to 1.0 μm, more preferably 0.1 to 0.1 μm.
3 μm. The compounding amount of the alumina particles is 1 to 15% by weight, and preferably 5 to 12% by weight, based on the ferromagnetic powder.

<Carbon Black> As carbon black to be blended in the magnetic layer, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DB
The P oil absorption is 10 to 400 ml / 100 g, the average particle diameter is 5 nm to 300 nm, the pH is 2 to 10, and the water content is 0.1.
Preferably, the tap density is 0.1 to 1 g / cc. Specific examples of carbon black to be used include BLACKPEARLS-130 manufactured by Cabot Corporation.
# 55, # 50, # 35 manufactured by Asahi Carbon Co., N660 manufactured by Mitsubishi Kasei Kogyo Co., Ltd., RAVE manufactured by Columbia Carbon Co.
N 410, 420, 500, 22 and the like.
Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination.

When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the amount of ferromagnetic material. Carbon black has functions such as antistatic of the magnetic layer, reduction of friction coefficient, addition of light-shielding property, improvement of film strength, and the like.
These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the upper magnetic layer and the lower layer, and are used for the purpose based on the characteristics shown above such as particle size, oil absorption, conductivity, and pH. It is, of course, possible to use them properly according to the conditions, but rather to optimize each layer. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

<Other Abrasives> The magnetic layer of the magnetic disk of the present invention may optionally contain other abrasives than those described above. Such abrasives include aluminum oxide,
Silicon carbide, chromium oxide, cerium oxide, α-iron oxide,
Corundum, silicon nitride, silicon carbide, titanium carbide,
Known materials mainly having a Mohs hardness of 6 or more, such as titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (a surface of which is 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% by weight or more. The average particle size of the abrasive used in combination is usually 0.01 to 2 μm, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. In order to improve the durability, it is also possible to combine particles having different particle sizes as needed, or to achieve the same effect by broadening the particle size distribution by using a single abrasive. Abrasives used for the magnetic layer, including diamond and alumina, have a tap density of 0.3 to 2 g / cc and a water content of 0.1 g / cc.
1-5% by weight, pH 2-11, specific surface area 1-30m
It is preferably ² / g. The shape of the abrasive 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 abrasive include AKP-12 and AKP manufactured by Sumitomo Chemical Co., Ltd.
-15, AKP-20, AKP-30, AKP-50,
HIT-20, HIT-30, HIT-55, HIT-
60, HIT-70, HIT-80, HIT-100;
ERC-DBM, HP-DBM, HP manufactured by Reynolds
S-DBM; manufactured by Fujimi Abrasives Co., Ltd., WA10000; manufactured by Uemura Kogyo Co., Ltd., UB20; manufactured by Nippon Chemical Industry Co., Ltd., G-5, Chromex U2, Chromex U1;
100, TF140; manufactured by Ibiden Co., Ltd., Beta Random Ultra Fine; B-3 manufactured by Showa Mining Co., Ltd. These abrasives can be added to the lower layer as needed. By controlling the surface shape by adding it to the lower layer,
For example, the projecting state of the abrasive can be controlled. The particle size and amount of the abrasive used together with the magnetic layer or added to the lower layer should of course be set to optimal values.

[Non-Magnetic Layer (Lower Layer)] Next, the details of the lower layer will be described. The structure of the lower layer of the magnetic disk of the present invention is not particularly limited as long as it is substantially non-magnetic, but it is usually composed of at least a resin, preferably a powder such as an inorganic powder or an organic powder. And those dispersed in The inorganic powder is usually preferably a non-magnetic powder, but a magnetic powder can also be used as long as the lower layer is substantially non-magnetic. That the lower layer is substantially non-magnetic means that the lower layer is allowed to have magnetism as long as the electromagnetic conversion characteristics of the upper layer are not substantially reduced. Specifically, for example, the lower layer has a residual magnetic flux density of 0.01 Tesla (100 Gauss (G)) or less or a coercive force of 7.96 kA / m (100 Oersteds) or less.

(Non-Magnetic Powder) The non-magnetic powder can be selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and nitride having an α conversion of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. . Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α-iron oxide.

The average particle size of these non-magnetic powders is
The thickness 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 have the same effect by broadening the particle size distribution. Particularly preferred average particle diameter of the non-magnetic powder is 0.01 μm to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is 0.08.
μm or less, and in the case of an acicular metal oxide, the average major axis length is preferably 0.3 μm or less, and more preferably 0.2 μm or less. Tap density is usually 0.05-2g
/ Ml, preferably 0.2 to 1.5 g / ml. The water content of the nonmagnetic powder is usually 0.1 to 5% by weight, preferably 0.2 to 3% by weight, and more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic powder is usually 2 to 11, but the pH is particularly preferably in the range of 3 to 10. The specific surface area of the non-magnetic powder is usually 1 to 100 m ² / g, preferably 5 to 100 m ² / g.
It is -80 m < ² > / g, More preferably, it is 10-70 m < ² > / g. The crystallite size of the non-magnetic powder is 0.004 μm to 1 μm
m is preferable, and 0.04 μm to 0.1 μm is more preferable. The oil absorption using DBP (dibutyl phthalate)
Usually 5 to 100 ml / 100 g, preferably 10 to 80
ml / 100 g, more preferably 20-60 ml / 10
0 g. The specific gravity is usually 1 to 12, preferably 3 to 6.
It is. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The Mohs' hardness is preferably 4 or more and 10 or less. The SA (stearic acid) adsorption amount of the nonmagnetic powder is usually 1 to 20 μmol / m ² , preferably ² to 15 μmol.
1 / m ² , more preferably 3 to 8 μmol / m ² .

The surface of these non-magnetic powders is subjected to a surface treatment, and the surfaces are treated with Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ ,
Preferably, SnO ₂ , Sb ₂ O ₃ , ZnO, and Y ₂ O ₃ are present. Particularly preferable for dispersibility are Al ₂ O ₃ and SiO _2.
2 , TiO ₂ and ZrO ₂ , more preferably Al ₂
O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Also,
Depending on the purpose, a co-precipitated surface treatment layer may be used,
It is also possible to adopt a method in which alumina is first present and then silica is present in the surface layer, or vice versa.
Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used in the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical; α-hematite DPN-250, DPN- manufactured by Toda Kogyo. 250BX, DPN-2
45, DPN-270BX, DPN-500BX, DB
N-SA1, DBN-SA3; Ishihara Sangyo Titanium Oxide T
TO-51B, TTO-55A, TTO-55B, TT
O-55C, TTO-55S, TTO-55D, SN-
100, α-hematite E270, E271, E30
0, E303; titanium oxide STT-4D manufactured by Titanium Industry,
STT-30D, STT-30, STT-65C, α-hematite α-40, MT-100S manufactured by Teica, MT-1
00T, MT-150W, MT-500B, MT-60
0B, MT-100F, MT-500HD; Sakai Chemical F
INEX-25, BF-1, BF-10, BF-20,
ST-M; Dowa Mining DEFIC-Y, DEFIC-
R: AS2BM, TiO2P25 manufactured by Nippon Aerosil; 100A, 500A manufactured by Ube Industries, and baked products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

(Carbon black compounded in lower layer)
By mixing carbon black in the lower layer, the surface electric resistance (Rs), which is a known effect, can be reduced, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. In addition, the effect of storing lubricant can be brought about by including carbon black in the lower layer. As the type of carbon black, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

The specific surface area of the lower carbon black is usually 100 to 500 m ² / g, preferably 150 to 400 m ² / g.
m ² / g, DBP oil absorption is usually 20 to 400 ml / 1
00 g, preferably 30 to 400 ml / 100 g. The average particle size of carbon black is usually 5 to 80 n.
m, preferably 10 to 50 nm, more preferably 10
４０40 nm. PH of carbon black is 2-1
0, water content is 0.1-10% by weight, tap density is 0.1
〜1 g / ml is preferred.

Specific examples of the carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72; manufactured by Mitsubishi Kasei Corporation # 3050B, # 3150B, # 325
0B, # 3750B, # 3950B, # 950, # 65
0B, # 970B, # 850B, MA-600, MA-
230, # 4000, # 4010; CONDUCTEX SC, RAVEN 88 manufactured by Columbian Carbon Co., Ltd.
00, 8000, 7000, 5750, 5250, 35
00, 2100, 2000, 1800, 1500, 12
55, 1250; Ketjen Black EC manufactured by Akzo
And so on. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. The carbon black may be dispersed with a binder before adding the carbon black to the paint. These carbon blacks are 50% by weight based on the inorganic compound powder.
And a range not exceeding 40% by weight of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination. 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).

In the lower layer, an organic powder is used according to the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. The manufacturing method is disclosed in
For example, the methods described in JP-A-185564 and JP-A-60-255827 can be used.

[Binder] As a binder used in each layer of the magnetic recording medium, a conventionally known thermosetting resin is used. Examples of the thermosetting resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, an epoxy-polyamide resin, and a polyisocyanate. Is mentioned. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Among them, polyisocyanates are particularly preferred.

Examples of the polyisocyanate include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1, 5- Isocyanates such as diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, and products of these isocyanates and polyalcohols And polyisocyanates formed by condensation of isocyanates.
Can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2
030, Coronate 2031, Millionate MR, Millionate MTL; Takedate D-10, manufactured by Takeda Pharmaceutical Co., Ltd.
2, Takenet D-110N, Takenet D-200,
Takenate D-202; Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc., manufactured by Sumitomo Bayer Co., Ltd., either alone or by utilizing the difference in curing reactivity. Each layer can be used in more combinations.

As the binder, a thermoplastic resin can be used together with the thermosetting resin. As such a thermoplastic resin, the glass transition temperature is usually -100 to 15
0 ° C., the number average molecular weight (in terms of polystyrene by GPC method) is usually 1,000 to 200,000, preferably 1
000-100,000, degree of polymerization is usually about 50-1
About 000 is preferable. Examples of such thermoplastic resins include vinyl chloride, vinyl acetate, vinyl alcohol, maleic anhydride, maleic acid, acrylic acid, acrylate, vinylidene chloride, acrylonitrile,
Methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal
And polymers or copolymers containing structural units derived from monomers such as toluene and vinyl ether, polyurethane resins, and various rubber-based resins. The above thermoplastic resins can be used alone or in combination with the thermosetting resin.

Incidentally, the polyurethane resin may be
Steal polyurethane, polyether polyurethane, poly
Ether polyester polyurethane, polycarbonate
Polyurethane, polyester polycarbonate-polyurethane
Contains Tan, Polycaprolactone Polyurethane, etc.
You. Glass transition temperature when using polyurethane resin
Degree of -50 to 150 ° C, further 0 to 100 ° C, breaking elongation
100-2000%, breaking stress 0.49-98N
/ Mm^Two(0.05 to 10 kg / mm^Two), The yield point is 0.
49-98 N / mm ^Two(0.05 to 10 kg / mm^Two)so
Preferably, there is.

The above-mentioned thermosetting resin and the thermoplastic resin used in combination therewith may be -COOM, -SO ₃ M, -OSO in order to obtain more excellent dispersibility and durability.
₃ M, -P = O (OM) ₂ , -OP = O (OM) ₂ (where M represents a hydrogen atom or an alkali metal), -O
H, -NR ₂ , -N ⁺ R ₃ (R is a hydrocarbon group), an epoxy group, -SH, -CN or the like into which at least one or more polar groups are introduced by copolymerization or addition reaction are used. Is preferred. The amount of such a polar group is preferably 10 ^-1 to 10 ^-8 mol / g, more preferably ¹ to 10 ^-8 mol / g.
0 ^-2 to 10 ^-6 mol / g.

Specific examples of the binder as the thermoplastic resin used in combination with the thermosetting resin include VAGH, VYHH, VMCH, VAGF, VA manufactured by Union Carbide Co., Ltd.
GD, VROH, VYES, VYNC, VMCC, XY
HL, XYSG, PKHH, PKHJ, PKHC, PK
FE: manufactured by Nissin Chemical Industries, MPR-TA, MPR-TA
5, MPR-TAL, MPR-TSN, MPR-TM
F, MPR-TS, MPR-TM, MPR-TAO; 1000 W, DX80, DX81, DX8 manufactured by Denki Kagaku
2, DX83, 100FD; MR-10 manufactured by Zeon Corporation
4, MR-105, MR110, MR100, MR55
5, 400X-110A; Nipporan N2301, N2302, N2304 manufactured by Nippon Polyurethane Co., Ltd .; Pandex T-5105, T-R3080, T manufactured by Dai Nippon Ink Co., Ltd.
-5201, Burnock D-400, D-210-8
0, Chris Bon 6109, 7209; Toyobo Co., Ltd. Byron UR8200, UR8300, UR-8700, RV
530, RV280, manufactured by Dainichi Seika, Diferamine 4
020, 5020, 5100, 5300, 9020, 9
022, 7020; MX5004, manufactured by Mitsubishi Kasei Co., Ltd., Samprene SP-150, manufactured by Sanyo Chemical Co., Ltd .; Saran F, manufactured by Asahi Kasei Corporation
310, F210 and the like.

The thermosetting resin as a binder used for the lower layer and the magnetic layer of the magnetic recording medium is usually 5 to 5 times for the non-magnetic powder in the lower layer and 5 to the ferromagnetic metal powder in the magnetic layer. It is used in a range of 50% by weight, preferably in a range of 10 to 30% by weight. The polyisocyanate is preferably used in the range of 2 to 20% by weight. When a vinyl chloride resin is used in combination, the content is preferably in the range of 5 to 30% by weight, and when a polyurethane resin is used in combination, the content is preferably 2 to 30% by weight.
It is used in the range of 20% by weight. In particular, it is preferable to use these three in combination. When head corrosion occurs due to a small amount of dechlorination, polyurethane alone may be used in combination with polyisocyanate.

The magnetic recording medium according to the present invention basically comprises a lower layer and a magnetic layer. However, the lower layer and / or the magnetic layer may have a multilayer structure. Therefore, the amount of the binder, the amount of the thermosetting resin or other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the physical properties of the resin described above are required. Of course, it is possible to change between each layer according to the situation, but rather it should be optimized for each layer, and a known technique concerning a multilayer structure can be applied. For example, when changing the amount of the binder in each layer, to reduce the scratches on the surface of the magnetic layer, to increase the amount of the binder in the magnetic layer,
In order to improve the head touch to the head, it is possible to increase the amount of the binder in the lower layer so as to have flexibility, but upon application, it is optimized within a range where the effects of the present invention are exhibited. It is not necessary to say that it is preferable to do so.

[Additives] The additives used for the magnetic layer and the lower layer of the magnetic recording medium include a lubricating effect, an antistatic effect,
Those having a dispersing effect, a plasticizing effect and the like are used. Additives include molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, polar group-containing silicone, fatty acid-modified silicone,
Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenylether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, Diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms It may contain a saturated bond or may be branched), and a metal salt thereof (Li, Na, K, Cu, etc.) or a monovalent, divalent, trivalent, tetravalent carbon having 12 to 22 carbon atoms. Trivalent, pentavalent, hexavalent alcohols (unsaturated Or an alcohol having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched), a monobasic fatty acid having 10 to 24 carbon atoms. (Which may contain an unsaturated bond or may be branched) and any one of mono-, di-, tri-, tetra-, penta-, and hexa-hydric alcohols having 2 to 12 carbon atoms (unsaturated A monofatty acid ester or a difatty acid ester or a trifatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, a fatty acid amide having 8 to 22 carbon atoms, Carbon number 8
To 22 aliphatic amines.

The following are specific examples of these. Fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and isostearic acid. Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate,
Octyl myristate, butoxyethyl stearate,
Butoxydiethyl stearate, 2-ethylhexyl stearate, 2-octyldodecyl palmitate, 2-hexyldodecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl Glycol didecanoate, ethylene glycol dioleyl and the like. For alcohols, oleyl alcohol
, Stearyl alcohol, lauryl alcohol and the like.

Alkylene oxide, glycerin,
Nonionic surfactants such as glycidol-based and alkylphenol-ethylene oxide adducts, and cationic surfactants such as cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums and sulfoniums Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, alkylbedine type, etc. And the like can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
It is not 0% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% by weight or less,
More preferably, it is at most 10% by weight.

These lubricants and surfactants used in the present invention each have a different physical action.
The type, amount, and combination ratio of the lubricant that produces a synergistic effect should be optimally determined according to the purpose.
Controlling leaching to the surface using fatty acids with different melting points in the lower layer and magnetic layer, controlling leaching to the surface using esters with different boiling points, melting points and polarities, coating by adjusting the amount of surfactant It is conceivable that the lubricating effect is improved by increasing the stability of the lubricant and increasing the amount of the lubricant added in the lower layer, and is not limited to the examples shown here.
Generally, the total amount of the lubricant is from 0.1% by weight to 50% by weight based on the ferromagnetic powder of the magnetic layer or the non-magnetic powder of the lower layer.
Preferably, it is selected in the range of 2% by weight to 25% by weight.

All or a part of the additives used in the present invention may be added at any step in the production of magnetic and non-magnetic paints. For example, when mixing with a magnetic substance before the kneading step, when adding in a kneading step with a magnetic substance and a binder and an organic solvent, when adding in a dispersing step, when adding after dispersing, when adding just before coating, etc. is there.
In some cases, the purpose may be achieved by applying a part or all of the additive 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 calendering (heating and pressurizing with a calender roll) or after slitting.

As the organic solvent used above, known ones can be used, and for example, solvents described in JP-A-6-68453 can be used.

[Layer Structure] The layer structure of the magnetic recording medium according to the present invention will be described in more detail. The thickness of the support of the magnetic recording medium is preferably 10 to 100 μm, more preferably 20 to 80 μm. An undercoat layer for improving adhesion may be provided between the support and the lower layer. The thickness of the undercoat layer is preferably 0.01 to 0.5 μm, more preferably 0.02 to 0.5 μm. The magnetic recording medium according to the present invention may be a double-sided magnetic layer disk-shaped medium in which a lower layer and a magnetic layer are provided on both sides of a support, or a disk-shaped medium in which they are provided only on one side. In the latter case, a back coat layer may be provided on the lower layer, the side opposite to the magnetic layer side, in order to obtain effects such as antistatic and curl correction. This thickness is 0.1-4 μm, preferably 0.3
２．０2.0 μm. Known undercoat layers and backcoat layers can be used.

The thickness of the magnetic layer of the magnetic recording medium is optimized depending on the saturation magnetization of the head used, the head gap length, and the band of the recording signal, but is preferably 0.02.
To 0.5 μm, more preferably 0.7 to 0.25 μm. The magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the lower layer is usually 0.2 to 5 μm, preferably 0.3 to 3 μm, more preferably 1 to 2.5 μm.
m. The lower layer exhibits its effect if it is substantially non-magnetic. For example, the lower layer exhibits the effects of the present invention even if it contains impurities or a small amount of a magnetic substance intentionally. It has already been mentioned that the same configuration can be regarded as the same. Specifically, for example, the residual magnetic flux density of the lower layer is 0.01 Tesla (100 gauss (G)) or less, or the coercive force is 7.96 kA / m (100
Oersted) or less, and preferably has no residual magnetic flux density and coercive force.

(Support) The support used for the magnetic disk of the present invention is preferably non-magnetic. As non-magnetic supports, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate,
Polyamides (including aromatic polyamides such as aliphatic polyamides and aramids), polyimides, polyamideimides,
Known films such as polysulfone and polybenzoxazole can be used. It is preferable to use a high-strength support such as polyethylene naphthalate or polyamide.
If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. In addition, an aluminum or glass substrate can be used as the support of the present invention.

The F-5 value of the support is preferably 49 to 4
90 N / mm ² (5 to 50 kg / mm ² ), and the heat shrinkage of the support at 100 ° C. for 30 minutes is preferably 3% or less,
More preferably, it is 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is preferably 0.5% or less, more preferably 0.1% or less.
1% or less. The breaking strength is 5 to 980 N / mm ² (5
-100 kg / mm ² ), and the elastic modulus is 980-19600.
N / mm ² (100 to 2000 kg / mm ² ) is preferred. The coefficient of thermal expansion is from 10 ^-4 to 10 ^-8 / ° C, preferably from 10 ^-5 to 10 ^-6 / ° C. Humidity expansion coefficient is 10 ^-4
/ RH% or less, preferably 10 ⁻⁵ / RH% or less. These thermal characteristics, dimensional characteristics and mechanical strength characteristics are preferably substantially equal to each other in the in-plane direction of the support with a difference of 10% or less.

[Method of Manufacturing Magnetic Recording Medium] The method of manufacturing a magnetic recording medium of the present invention comprises preparing a coating solution for forming each layer, applying the coating solution to a support, orienting, drying, cooling,
The process of producing a magnetic coating material (coating solution) or a lower layer coating material (coating solution) for a magnetic recording medium, which includes processes such as calendaring, post-curing, and polishing, includes at least a kneading process, a dispersing process, and a process before and after these processes. It consists of a mixing step provided as needed. Each step may be divided into two or more steps. All raw materials such as ferromagnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, the polyisocyanate may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. Also,
Conventionally known manufacturing techniques can be used as some of the steps. In the kneading step, it is preferable to use an open kneader, a continuous kneader, a pressure kneader, an extruder or the like having a strong kneading force. When a kneader is used, the magnetic powder or non-magnetic powder and all or a part of the binder (preferably 30% by weight or more of the total binder) and 15 to 500 parts by weight are mixed with 100 parts by weight of the magnetic powder. It is processed. The details of these kneading processes are described in JP-A-1-106338 and JP-A-1-79274.
No., published in Japanese Unexamined Patent Publication No. Further, glass beads can be used to disperse the magnetic layer paint and the lower layer paint, but zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media, are preferable. The particle size and filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

In the case of the magnetic recording medium having a multilayer structure according to the present invention,
When coating on a support, the following method is preferably used. First, the lower layer is first applied by a gravure coating, a roll coating, a blade coating, an extrusion coating device, etc., which are generally used in applying a magnetic paint.
While the lower layer is in a wet state, Japanese Patent Publication No. 46186/1985, Japanese Patent Laid-Open No. 238179/1985,
This is a method of applying an upper layer using a support pressure-type extrusion coating apparatus disclosed in Japanese Patent No. 5672.
Second, JP-A-63-88080 and JP-A-2-1
No. 7971 and Japanese Patent Application Laid-Open No. 2-265672 disclose a method in which upper and lower layers are coated almost simultaneously by one coating head having two built-in coating liquid passage slits. Thirdly, there is a method of applying the upper and lower layers almost simultaneously using an extrusion coating apparatus with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic disk from deteriorating due to the aggregation of magnetic particles, Japanese Patent Application Laid-Open No.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in JP-A-74-174 and JP-A-1-236968. Further, the viscosity of the coating solution preferably satisfies the numerical range disclosed in JP-A-3-8471. In order to realize the layer structure of the magnetic recording medium according to the present invention, the lower layer is applied and dried, and then the magnetic layer is provided thereon. Not something. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

In a magnetic recording medium, sufficient isotropic orientation may be obtained even without orientation without using an orientation device. However, alternately arranging cobalt magnets diagonally and applying an alternating magnetic field with a solenoid. It is preferable to use a known random alignment device. In general, the isotropic orientation is preferably two-dimensional random in a plane, but may be three-dimensional random with a vertical component. In addition, circumferential orientation may be performed using spin coating.

In the drying step, the temperature of the drying zone is 4
The temperature is desirably set to 0 ° C. or higher, preferably 100 to 130 ° C. At this time, it is preferable that the drying position of the coating film can be controlled by controlling the temperature, the flow rate, and the application speed of the drying air. Coating speed is 20-1000m
The temperature of the drying air is preferably 40 ° C. or more, more preferably 100 ° C. to 130 ° C., and an appropriate preliminary drying can be performed before the alignment step.

After drying, the web is introduced into a cooling zone, the temperature of the web is cooled to 35 ° C. or less, preferably 30 ° C. or less, and the temperature of the web is maintained in this temperature range until it is calendered. The web is usually wound up in a roll and the roll is maintained in the above temperature range. By keeping the web at a low temperature in this manner, the curing reaction of the thermosetting resin contained in the coating layer of the web does not substantially occur before the calendaring treatment, so that the web has sufficient flexibility, Processing is performed smoothly. As a result, the surface of the magnetic layer after the calendering treatment becomes appropriately smooth, the degree of filling of the magnetic powder increases, and the surface hardness also increases. In this specification, the term “web” refers to a state in which a support or a coated support is being conveyed to a coating machine or a state in which the support is rolled.

The roll used for the calendar processing is as follows.
Heat-resistant plastic or metal rolls such as epoxy, polyimide, polyamide, and polyimideamide
Is used. In particular, when a double-sided magnetic layer is used, the metal layer
It is preferred that the treatment be performed by each other. The treatment temperature is preferably at least 50 ° C, more preferably at least 100 ° C. The linear pressure is preferably 1960 N / cm (200 kg
/ Cm) or more, more preferably 2940 N / cm (3
00 kg / cm) or more. After calendering, punching into a disk shape, putting it into a cartridge with a liner installed inside, adding predetermined mechanical components, and manufacturing a magnetic disk, but if necessary, punching out the disk shape, A post-treatment such as a thermo-treatment (usually at 50 to 90 ° C.) to accelerate the curing treatment of the coating layer or a burnishing treatment with a polishing tape to remove surface protrusions may be performed.

[Physical Properties] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is usually 0.2 to 0.6 Tesla (2000 to 6000 Gauss). The distribution of coercive force is preferably narrow, and SFD and SFDr are preferably 0.6 or less. The squareness ratio is usually 0.45 in random orientation.
~ 0.55, 0.6-0.6 for two-dimensional random
7 or less. In the case of vertical alignment, it is usually 0.5 or more.

The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is preferably 0.5 or less, more preferably 0.3 or less in a temperature range of -10 ° C. to 40 ° C. and a humidity of 0% to 95%. , The surface resistivity is preferably the magnetic surface 1
0 ⁴ to 10 ¹² ohm / sq, and the charged potential is -500 V
To +500 V or less. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 980 to 196 in each direction in the plane.
^{00N / mm 2 (100~2000kg / mm} 2), the breaking strength is preferably 98~686N / mm ² (10~7
0 Kg / mm ² ), and the elastic modulus of the magnetic disk is preferably 980 to 14700 N / mm ² (100
, 1500 kg / mm ² ), the residual elongation is preferably 0.5% or less, and the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less.
Or less, most preferably 0.1% or less. The glass transition temperature (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) of the magnetic layer is preferably from 50 ° C to 120 ° C, and that of the lower layer is preferably from 0 ° C to 100 ° C. The loss modulus is 1 × 10 ³ to 1 × 10 ⁴ N / cm ² (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. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the nonmagnetic lower layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a disk medium in which repeated use is emphasized, it is often the case that a larger porosity has a higher running durability.

In the magnetic recording medium of the present invention, these physical characteristics can be changed between the lower layer and the magnetic layer according to the purpose. 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 layer is made lower than that of the magnetic layer to improve the contact of the magnetic disk with the head.

[0064]

EXAMPLES Hereinafter, the present invention will be described specifically based on examples, but the present invention should not be construed as being limited thereto. In the following, “parts” means “parts by weight”.

(Example 1) <Preparation of paint (coating liquid)> Magnetic paint Ferromagnetic metal powder 100 parts Composition: 70% Fe, 30% Co Hc: 203 kA / m (2550 Oersted) Specific surface: 55 m ² / g Long axis Length: 0.048 μm Needle ratio: 4 Crystal size: 120 nm σs: 140 Am ² / kg (emu / g) Sintering inhibitor Al compound (Al / Fe atomic ratio 8%) Y compound (Y / Fe atomic ratio) Vinyl chloride copolymer 12 parts MR110 (manufactured by Zeon Corporation) polyurethane resin 3 parts UR8200 (manufactured by Toyobo Co., Ltd.) α-alumina 10 parts HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) carbon black 5 parts # 50 ( Asahi Carbon Co., Ltd.) Phenylphosphonic acid 3 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 Part Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts

Non-magnetic paint NU-1 (using spherical inorganic powder) Non-magnetic powder TiO ₂ crystalline rutile 80 parts Average primary particle size: 0.035 μm Specific surface area by BET method: 40 m ² / g pH: 7 containing TiO ₂ Amount: 90% or more DBP oil absorption: 27 to 38 g / 100 g Surface treatment agent Al ₂ O ₃ : 8% by weight Carbon black 20 parts Conductex SC-U (manufactured by Columbia Carbon Co.) Vinyl chloride copolymer 12 parts MR11O (Japan) Polyurethane resin 5 parts UR8200 (manufactured by Toyobo Co., Ltd.) Phenylphosphonic acid 4 parts Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 2 parts Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8 / 2 mixed solvent) 250 parts

Each of the above-mentioned paints was kneaded with a kneader, and then dispersed using a sand mill. Polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the obtained dispersion as a thermosetting resin, and 10 parts was added to the nonmagnetic layer coating liquid and 10 parts to the magnetic layer coating liquid. Further, 40 parts of cyclohexanone was added to each, and the mixture was filtered using a filter having an average pore diameter of 1 μm to prepare coating solutions for forming a lower layer (nonmagnetic layer) and a magnetic layer, respectively.

<Preparation of Magnetic Disk> The obtained coating solution for the non-magnetic layer was coated with a magnetic layer having a thickness of 0.15 μm immediately after drying so that the thickness after drying was 1.5 μm. To a thickness of 62 μm and a polyethylene terephthalate support having a center plane average surface roughness of 3 nm. While both layers are still wet, the frequency is 50 Hz and the magnetic field strength is 0.025 Tesla. (250 gauss) Also, pass through two AC magnetic field generators with a frequency of 50 Hz and a magnetic field strength of 0.012 tesla (120 gauss), perform random orientation treatment, dry at 100 ° C, and set the web temperature to 35 ° C through the cooling zone. Winding the web into a roll and maintaining the temperature of the subsequent roll at 35 ° C.
Calendar temperature 90 ° C, linear pressure 2940N / cm (300k
g / cm), punched out to 3.5 inches, polished the surface, and then a 3.7-inch cartridge (zip-disk manufactured by Iomega, USA) with a liner installed inside.
Cartridge) and add predetermined mechanical parts.
A 7-inch floppy disk was obtained. The performance of each of the magnetic disks prepared above was evaluated by the following measurement methods, and the results are shown in Table 1.

<Measurement Method> (1) Surface Roughness (Ra) Using a model WYKO HD2000, R was measured under the following conditions.
a was measured. Objective lens: × 50, Intermediate lens: × 0.5 Measurement range: 242 μm × 184 nm Pixels: 368 × 240 Filter: Cylinder correction and tilt correction (2) Surface hardness Using a Shinto Kagaku HEDON14 surface property measuring instrument 2
The surface of the magnetic recording layer is scratched in the environment of 3 ° C. and 50% under the following conditions. Stylus load 10 g Needle R = 0.1 mm diamond needle Scratch length 3 cm Scratch speed 100 mm / min The above scratches were measured for PV on 8 lines under the following conditions using TOP03D manufactured by WYKO, and the average value was deepened. I did it.
The smaller the depth of the scratch, the harder it is. Objective lens: × 40 Measurement range: 250 μm × 250 μm Number of pixels: 256 × 256 Filter: cylinder correction and tilt correction

(3) Electromagnetic conversion characteristics (output) Floppy disk drive ZIP manufactured by Iomega
100 (rotation speed 2968 rpm), radius 38 mm
After recording at a recording density of 34 kfc, the signal was reproduced and the output at that time was measured.
The output of Fuji Photo Film's ZIP100 disk is 1
00% and expressed by the ratio. (4) Durability Ioppa's floppy disk drive ZIP1
After recording at a recording density of 34 kfc with the head fixed at a position of a radius of 38 mm using 00 (2968 rpm), the signal is reproduced and the output at that time is measured to be 100%. After that, the vehicle continuously runs in an environment of 50 ° C and 20% and the output is
The time until it reached 0% was measured. (5) Error rate Fuji Photo Film HiFD drive (3600 rpm)
rpm), a signal having a linear recording density of 89 kfci was recorded, and the error rate was measured.

Example 2 A magnetic disk was manufactured in the same manner as in Example 1 except that the web winding temperature was 30 ° C. and the roll holding temperature until the calender treatment was 30 ° C. A disk was prepared and evaluated. The results are shown in Table 1. (Embodiment 3) In manufacturing the magnetic disk of Embodiment 1,
A magnetic disk was prepared and evaluated in the same manner as in Example 1 except that the web winding temperature was 25 ° C. and the roll holding temperature up to the calender treatment was 25 ° C. Table 1 shows the results
It was shown to.

Example 4 In the manufacture of the magnetic disk of Example 1, the drying temperature was 130 ° C., the web winding temperature was 30 ° C., and the roll holding temperature until the calendering process was 30.
A magnetic disk was prepared and evaluated in the same manner as in Example 1 except that the temperature was changed to ° C. The results are shown in Table 1. (Example 5) In manufacturing the magnetic disk of Example 1,
A magnetic disk was prepared and evaluated in the same manner as in Example 1 except that the drying temperature was 130 ° C., the web winding temperature was 25 ° C., and the roll holding temperature up to the calender treatment was 35 ° C. The results are shown in Table 1.

Example 6 In the manufacture of the magnetic disk of Example 1, the drying temperature was 130 ° C., the web winding temperature was 35 ° C., and the roll holding temperature until calendering was 25.
A magnetic disk was prepared and evaluated in the same manner as in Example 1 except that the temperature was changed to ° C. The results are shown in Table 1. (Example 7) A magnetic disk was prepared in the same manner as in Example 1 except that in the preparation of the coating material of Example 1, the thermosetting resin was Burnock D802F (manufactured by Dainippon Ink and Chemicals, Inc.). And evaluated. The results are shown in Table 1.

Comparative Example 1 A magnetic disk was prepared and evaluated in the same manner as in Example 1, except that the coating material was prepared without using a thermosetting resin. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the drying temperature was 90 ° C. in the manufacture of the magnetic disk of Example 1.
A magnetic disk was prepared and evaluated in the same manner as described above. The results are shown in Table 1. Comparative Example 3 In the manufacture of the magnetic disk of Example 1,
A magnetic disk was prepared and evaluated in the same manner as in Example 1, except that the web winding temperature was 40 ° C and the roll holding temperature until the calendering process was 40 ° C. Table 1 shows the results
It was shown to.

Comparative Example 4 A magnetic disk was manufactured in the same manner as in Example 1 except that the web winding temperature was 45 ° C. and the roll holding temperature until calendering was 45 ° C. A disk was prepared and evaluated. The results are shown in Table 1.

(Comparative Example 5) A magnetic disk was manufactured in the same manner as in Example 1 except that the web winding temperature was 45 ° C and the roll holding temperature until calendering was 25 ° C in the manufacture of the magnetic disk of Example 1. A disk was prepared and evaluated. The results are shown in Table 1. (Comparative Example 6) In manufacturing the magnetic disk of Example 1,
A magnetic disk was prepared and evaluated in the same manner as in Example 1, except that the web winding temperature was 25 ° C and the roll holding temperature until the calendering process was 45 ° C. Table 1 shows the results
It was shown to.

[0078]

[Table 1]

(In the table, thermosetting resin A represents Coronate L, and thermosetting resin B represents Burnock D802F.)

From the results shown in Table 1, the following is clear. The magnetic disks manufactured in Examples 1 to 7 have excellent electromagnetic conversion characteristics and durability. On the other hand, in the case of Comparative Example 1 in which no thermosetting resin was used as the binder, the durability was significantly poor. In the case of Comparative Example 2 in which the drying temperature does not satisfy the conditions of the present invention, Comparative Examples 3 to 3 in which the temperature conditions of the web after further drying and before the calendering treatment are not satisfied are satisfied.
In the case of No. 6, both the electromagnetic conversion characteristics and the durability are inferior.

[0081]

The magnetic recording medium produced by the method of the present invention has significantly improved electromagnetic characteristics, especially high-density recording characteristics, low frictional force with the head, and excellent durability. The error rate in the high-density recording area is remarkably improved. Therefore, the magnetic recording medium manufactured by the method of the present invention can be suitably used as a disk-shaped magnetic recording medium having a large capacity of 0.35 to 2 Gbit.

Claims (2)

[Claims] 1. Production of a magnetic recording medium in which a non-magnetic layer substantially non-magnetic on a support and a magnetic layer on which a ferromagnetic powder is dispersed in a binder are formed in this order. In the method, a lower layer coating solution containing a thermosetting resin as a binder and a magnetic layer coating solution are coated on a support, dried in a drying zone at 100 ° C. or higher, and the web immediately after drying is passed through a cooling zone. The temperature of the web is cooled to 35 ° C. or less, and the temperature of the web up to the calendering treatment is maintained at 35 ° C. or less. Thereafter, the calendering treatment is performed, the surface roughness (Ra) of the magnetic layer is 5 nm or less, and the surface hardness is reduced. A method for producing a magnetic recording medium, wherein the depth is determined to be 90 nm or less by a scratch test method using a surface tester. 2. A magnetic recording medium manufactured by the method according to claim 1.