JPH11144237A - Magnetic recording disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-capacity magnetic recording disk which is set with a smaller track width and a smaller sector number and is adequate for a recording and reproducing system allowing the substantial increase of a recording capacity by suppressing the anisotropy of thermal shrinkage when the magnetic recording disk is exposed to a high temp. SOLUTION: This magnetic recording disk is constituted by disposing a lower layer which is substantially nonmagnetic and a magnetic layer formed by dispersing ferromagnetic metallic powder or ferromagnetic hexagonal ferrite powder into a binder in this order on a base. In such a case, the magnetic recording disk is <=0.05% in both of the thermal shrinkage rate anisotropy when the disk is placed for 30 minutes under the absolute dry environment at 80 deg.C and the thermal shrinkage rate anisotropy when the disk is placed for 72 hours under the absolute dry environment at 80 deg.C. In addition, the number of the servo sectors existing on one track is 80 to 150 pieces. The magnetic recording disk is used as the recording and reproducing system set at <=10 μm in the track width.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording disk having a high recording density. In particular, the present invention relates to a magnetic recording disk for high-density recording, which has a magnetic layer and a substantially nonmagnetic lower layer, and the magnetic layer contains a ferromagnetic metal powder or a hexagonal ferrite powder.

[0002]

2. Description of the Related Art In the field of magnetic disks, 2 MB MF-2HD floppy disks using Co-modified iron oxide have been standardly mounted on personal computers. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of floppy disks.

Conventionally, a magnetic recording medium has a magnetic layer obtained by dispersing iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder in a binder on a non-magnetic support. Is widely used. Among them, ferromagnetic metal fine powder and hexagonal ferrite fine powder are known to have excellent high density recording characteristics. In the case of a disk, a 10-MB MF-2TD and a 21-MB MF are used as large-capacity disks using ferromagnetic metal fine powder having excellent high-density recording characteristics.
Large-capacity disks using 2SD or hexagonal ferrite include 4MB MF-2ED, 21MB floptical, and the like, but were not sufficient in capacity and performance. Under such circumstances, many attempts have been made to improve the high-density recording characteristics. An example is shown below.

In order to improve the characteristics of magnetic recording disks, 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. It is proposed to use metal fine powder having a specific surface area of 25 to 70 m ² / g, and Japanese Patent Publication No. 6-28106 proposes to determine the specific surface area and the amount of magnetization of a magnetic substance and to include an abrasive.

In order to improve the durability of a magnetic recording disk, Japanese Patent Publication No. 7-85304 proposes to use a fatty acid ester having an unsaturated bond with an unsaturated fatty acid ester, and Japanese Patent Publication No. 7-70045 discloses a branched fatty acid ester. It has been proposed to use a non-magnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester in Japanese Patent Application Laid-Open No. Sho 54-124716. It has been proposed that the volume and surface roughness of the pores containing the agent be 0.005 to 0.025 μm, and Japanese Patent Application Laid-Open No. 61-294637 proposes to use low-melting and high-melting fatty acid esters. Fairness 7-36216 is 1/4 of the thickness of the magnetic layer.
It has been proposed to use an abrasive having a particle size of about 3/4 and a fatty acid ester having a low melting point.
It has been proposed to use a metal magnetic material containing chromium and chromium oxide.

As a configuration of a magnetic recording disk 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 fine powder.
Japanese Patent Application Laid-Open No. 6-290446 proposes a configuration having a magnetic layer and a non-magnetic layer of 1 μm or less.
No. 7 proposes a configuration comprising a carbon intermediate layer and a magnetic layer containing a lubricant, and JP-A-5-290358 proposes a configuration having a nonmagnetic layer having a defined carbon size.

On the other hand, a magnetic recording disk comprising a thin magnetic layer and a functional non-magnetic layer has recently been developed, and has a capacity of 100 MB.
A class floppy disk has appeared. Japanese Patent Application Laid-Open No. 5-109061 discloses these features.
A configuration in which c has a magnetic layer having a thickness of 1400 Oe or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing conductive particles has been proposed, and Japanese Patent Application Laid-Open No. 5-197946 has proposed a configuration containing an abrasive larger than the magnetic layer thickness. Japanese Patent Application Laid-Open No. 5-290354 discloses a magnetic layer having a thickness of 0.5 μm or less and a thickness variation of ± 15%
And the configuration in which the surface electric resistance is specified is disclosed in
68453 proposes a configuration in which two types of abrasives having different particle diameters are included and the amount of the abrasive on the surface is regulated.

It is known that the magnetic layer is made thinner in order to improve the decrease in the reproduction output due to the thickness loss of the magnetic layer. For example, Japanese Patent Application Laid-Open No. Hei 5-182178 discloses that a magnetic layer is formed on a non-magnetic support. A lower nonmagnetic layer containing an inorganic powder and dispersed in a binder, and an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing a ferromagnetic powder in the binder while the nonmagnetic layer is in a wet state. Disclosed a magnetic recording medium.

[0009] The demand for higher capacity and higher density of magnetic recording disks is increasing. By the way, in the current system of a 3.5-inch floppy disk with a recording capacity of 1.4M or 1M, the track servo is supported on the head and the drive side, and there is no servo track on the magnetic recording disk side. Not written. However,
When the capacity is increased and a magnetic recording disk for ZIP manufactured by IOMEGA (Iomega) of the United States is used, accurate tracking cannot be performed only on the head drive side. Therefore, servo tracks are written on the magnetic recording disk in advance.

[0010] The recording location of the magnetic recording disk is on a predetermined track. And the track is divided into several sectors. Information is recorded in units of this sector. Then, the servo signal is written to the exit of this sector, and the head reads this servo signal to correct the head position and perform faithful recording and reproduction. Therefore,
If there are as many sectors as possible on one track (circumference), so many servo signals can be put on one track, so that there are more opportunities to read the servo signals, and the tracking servo is more accurate. I can do it. However, increasing the number of sectors means increasing the number of servo signal areas, which means that the number of places for storing data is reduced and the recording capacity is reduced.

That is, in order to increase the recording capacity of a floppy disk of the same size and the same performance such as a ZIP, it is necessary to reduce the track width and reduce the number of sectors. The problem of the narrow track width and the small number of sectors is the dimensional stability of the magnetic recording disk. In particular, with the recent miniaturization of information electronic devices such as personal computers, magnetic recording disks are exposed to extremely high temperatures due to heat generated in hardware, and the magnetic recording disks shrink.

As described above, if the magnetic recording disk is exposed to a high temperature during use or storage, if the anisotropic thermal contraction is large, accurate tracking cannot be performed, the output fluctuates, and good electromagnetic conversion characteristics are obtained. There was a problem that it was difficult to obtain.

[0013]

SUMMARY OF THE INVENTION The present invention suppresses the anisotropy of heat shrinkage when a magnetic recording disk is exposed to a high temperature, thereby setting a smaller track width and a smaller number of sectors. It is an object of the present invention to provide a high-capacity magnetic recording disk suitable for a recording / reproducing system which is capable of substantially increasing the recording capacity.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to form a substantially non-magnetic lower layer on a support and a magnetic layer comprising a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder dispersed in a binder. In the magnetic recording disk provided in this order, the magnetic recording disk was found to have a heat shrinkage anisotropy of 30 minutes at a temperature of 80 ° C. in a dry environment, and a heat shrinkage of 72% at a temperature of 80 ° C. in a dry environment.
Both heat shrinkage anisotropy of 0.05%
The magnetic recording disk according to the present invention is used in a recording / reproducing system in which the number of servo sectors on one track is 80 to 150 and the track width is set to 10 μm or less.

Here, the substantially non-magnetic lower layer means that it may have a magnetic property to such an extent that it does not participate in recording, and is hereinafter simply referred to as a lower layer or a non-magnetic layer. The magnetic layer is also referred to as an upper layer or an upper magnetic layer. The thermal shrinkage anisotropy of the magnetic recording disk of the present invention is determined when the magnetic recording disk is stored at 80 ° C. in an absolutely dry environment for 30 minutes and 72 hours.

The thermal shrinkage anisotropy occurs when a magnetic recording disk shrinks during use or storage, mainly due to the temperature of the environment, causing a tracking error. Usually, the anisotropy often increases with the passage of time. In this case, it is sufficient that the anisotropy is within one hour of 72 hours.
Some of them are large in 0-minute storage but become small in long-term storage, and the heat shrinkage varies with time under absolutely dry conditions. SUMMARY OF THE INVENTION The present invention has been made to address the problem that heat generation increases in a drive having a high degree of integration in a relatively short time, and on the other hand, heat shrinkage for a long time in consideration of storage aging. The rate anisotropy was also evaluated.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The heat shrinkage anisotropy in the present invention indicates a value measured as follows. Head position μm
Using a mechanical drive capable of controlling the magnetic recording disk in the radial direction in units of 12 units, an alignment burst pattern (A, B burst, 100 kHz) is written every 12 degrees at a track position with a radius of 39.5 mm every 30 degrees. A sample of the written magnetic recording disk is stored at 80 ° C. in a dry environment for 30 minutes and 72 hours, respectively. After each period, the recording signal is reproduced by using the facing two-head type drive, the outputs before and after the storage of the A and B burst signals at the 12 points are obtained, and the heat shrinkage γ (%) is obtained from the following equation. . The difference between the maximum value and the minimum value of the total 12 measured values of the heat shrinkage is defined as the heat shrinkage anisotropy.

[0018] _{α = {(X A -X B} ) / (X A + X B)} × TW X β = {(Y A -Y B) / (Y A + Y B)} × TW Y α '= {( _{X A '-X B') /} (X A '+ X B')} × TW X β '= {(Y A' -Y B ') / (Y A' + Y B ')} × TW Y γ = [ {(α '+ β') - (α + β)} / 79000 ] × 100 where counter 2-head drives a, B bursts before storage reproduction output respectively X _a, X _B, and Y _a, Y _B,
X _A after storage playback output, respectively _{', X B', Y A} ',
Y _B ′, and the track widths are TW _X and TW _Y , respectively.

Since the head position of the two-head drive has a radius of 39.5 mm from the center of the magnetic recording disk, the denominator in the last equation is 79000, which is doubled and converted into a diameter, and converted into a unit of μm. It is displayed. Opposite 2
The head type drive is a drive having a pair of magnetic heads arranged symmetrically at the same track position at the center of the magnetic recording disk.

Here, the absolutely dry environment means a very low humidity environmental condition obtained by not supplying moisture to the room for storing the sample and not humidifying, and it is 10% or less when partitioning by humidity. . In the present invention, it is necessary to control the heat shrinkage anisotropy within 0.05%. Means for controlling to such a value is not particularly limited, but it is preferable to select a support made of a material having a small heat shrinkage property,
Thermoforming after punching the web provided with the magnetic layer into a disk shape, thermoprocessing before punching the raw material having the coating layer formed on at least one surface of the non-magnetic support into a disk shape, that is, room temperature or higher. And the like.

The above will be described. As the support, a flexible support is preferable, and the difference in heat shrinkage in the longitudinal direction (MD) and the width direction (TD) at 80 ° C. for 30 minutes is preferably 0.02% or less, and more preferably 0.01% or less. % Or less, particularly preferably 0%. The above and will be described.

The conditions for the thermo-processing of the magnetic recording disk are preferably in the range of 60 to 80 ° C. for 9 to 72 hours, more preferably in the range of 70 ° C. for 24 to 48 hours. It can be selected according to the shrinkage ratio, or can be finely adjusted as appropriate according to the heat shrinkage properties of each of the magnetic recording disk constituting layers provided on the support such as the undercoat layer, the lower layer and the magnetic layer. The physical properties of the constituent layers can be adjusted by selecting the respective compositions, that is, binder resin, various powders, lubricants and the like.

In the present invention, the heat shrinkage anisotropy is 0.0
The range is 5% or less, preferably 0.03% or less, and more preferably 0.01% or less. According to the present invention, by reducing the heat shrinkage anisotropy as described above, in the recording / reproducing system used, the number of servo sectors on one track is 80 to 150, preferably 80 to 100.
Pieces, more preferably 90 to 100 pieces, and the track width can be set to 10 μm or less, preferably 10 to 3 μm, and more preferably 7 to 4 μm. The recording capacity can be increased.

For example, the number of servo sectors is 100 and the track width is 8 μm (that is, the track density is 3170 tp).
i) In a system for recording and reproducing signals under the condition of a linear recording density of 120 kbpi, the areal recording density of the magnetic recording disk of the present invention is about 0.3 Gbit / inch ² .

Hereinafter, each component of the magnetic recording disk of the present invention will be described. [Magnetic Layer] In the magnetic recording disk of the present invention, the lower layer and the magnetic layer may be provided on only one side or both sides of the support. The upper and lower layers are dried after the lower layer is applied, and the lower layer is dried even when the lower layer is in a wet state ((wet-on-wet method (W / W)) [(wet-on-dry method (W / W
D)), an upper magnetic layer can be provided. From the viewpoint of production yield, simultaneous or sequential wet coating (W / W) is preferable, but in the case of a disk, coating after drying (W / D) can be used sufficiently. In (W / W), since the upper layer and the lower layer can be formed simultaneously, a surface treatment step such as a calendering step can be effectively used, and the surface roughness of the upper magnetic layer can be improved even with an ultrathin layer. The coercive force Hc of the magnetic layer is preferably 1800 Oe or more.
It is preferable that it is 100-3000G (Gauss) and 1000-3000G for barium ferrite powder.

[Ferromagnetic Metal Powder] The ferromagnetic metal powder used in the upper magnetic layer of the present invention may be Fe alone or Fe
Is preferred. These ferromagnetic powders include Al, Si, S, Sc,
Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd,
Ag, Sn, Sb, Te, Ba, Ta, W, Re, A
u, Hg, Pb, Bi, La, Ce, Pr, Nd, P,
It may contain atoms such as Co, Mn, Zn, Ni, Sr, and B. In particular, Al, Si, Ca, Y, Ba, L
a, Nd, Co, Ni, at least one of B and α-Fe
It is preferable to include at least one of Co, Y, and Al. Co content is F
It is preferably from 0 to 40 at%, more preferably from 15 to 35 at%, and even more preferably from 20 to 35 at%. The content of Y is preferably from 1.5 to 12 at%, more preferably from 3 to 10 at%, and still more preferably from 4 to 9 at%. Al is preferably 1.5 atomic% or more and 12 atomic% or less, and more preferably 3 atomic% or less.
It is at least 10 at% and more preferably at least 4 at% and at most 9 at%. These ferromagnetic metal powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion before the dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-1
8372, JP-B-47-22062, JP-B-47-
No. 22513, JP-B-46-28466, JP-B-46
-38755, JP-B-47-4286, JP-B-47
-12422, JP-B-47-17284, JP-B-4
Nos. 7-18509, JP-B-47-18573, JP-B-39-10307, JP-B-46-39639, U.S. Pat. Nos. 3,026,215, 3,031,341 and 31,
No. 00194, No. 3242005, No. 3389014
No. etc.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, reducing iron oxide with a reducing gas such as hydrogen to reduce Fe or F
a method of obtaining e-Co particles or the like, a method of thermally decomposing a metal carbonyl compound, a method of adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal to reduce the metal, And evaporating in a low-pressure inert gas to obtain fine powder. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and 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.

The ferromagnetic metal powder of the magnetic layer of the present invention is
When expressed in terms of specific surface area by the method, it is 45 to 80 m ² / g,
Preferably it is 50-70 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 metal powder of the magnetic layer of the present invention is usually 80 to 180 °, preferably 100 to 180 °, more preferably 110 to 17 °.
5Å. The major axis diameter of the ferromagnetic metal powder is usually 0.01
μm or more and 0.25 μm or less, preferably 0.03 μm
m or more and 0.15 μm or less, more preferably 0.0
3 μm or more and 0.12 μm or less. The needle ratio of the ferromagnetic metal powder is preferably 3 or more and 15 or less, and more preferably 5 or more and 12 or less.
The following is preferred. Σs of ferromagnetic metal powder is usually 100
180 emu / g, preferably 110 emu / g to 17
0 emu / g, more preferably 125-160 emu / g. The coercive force of the ferromagnetic metal powder is 1700 Oe or more and 3500
Oe or less is preferable, and more preferably 1,800 Oe or more and 3
000 Oe or less.

The water content of the ferromagnetic metal 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. It is preferable that the pH of the ferromagnetic metal powder be optimized depending on the combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10. The ferromagnetic metal powder may be subjected to a surface treatment, if necessary, to be in the form of Al, Si, P or an oxide thereof. The amount is 0.1 to 10% by weight based on the ferromagnetic metal powder, 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, C is contained in ferromagnetic metal powder.
a, Fe, Ni, Sr and the like in some cases. These are preferably essentially absent, but 200 pp
If it is less than m, the characteristics are not particularly affected.
The ferromagnetic metal 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. The SFD of the ferromagnetic metal powder itself is preferably small, and is preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic metal powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, and 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.

[Hexagonal Ferrite Powder] As the hexagonal ferrite contained in the uppermost layer of the present invention, there are barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and substituted cobalt ferrite. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, 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, B, Ge, and Nb. Generally, Co-Zn, Co-Ti,
Co-Ti-Zr, Co-Ti-Zn, Ni-Ti-Z
n, Nb-Zn-Co, Sb-Zn-Co, Nb-Zn
And the like can be used. material·
Some production methods contain specific impurities. The particle size is 10 to 200 nm in hexagonal plate diameter, preferably 10 to 200 nm.
To 100 nm, particularly preferably 10 to 80 nm.

In particular, when reproducing with a magnetoresistive head in order to increase the track density, it is necessary to reduce noise, and the plate diameter is preferably 40 nm or less, but if it is 10 nm or less, stable magnetization cannot be expected due to thermal fluctuation. Above 200 nm, noise is high and none of them are suitable for high-density magnetic recording. The plate ratio (plate diameter / plate thickness) is desirably 1 to 15. Preferably 1 to
7 When the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area of this particle size range by the BET method is 1
0 to 200 m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. It is difficult to quantify, but the particle T
The comparison can be made by randomly measuring 500 particles from an EM photograph. The distribution is often not a normal distribution, but when calculated and expressed as the standard deviation of the average size, σ / average size =
0.1 to 2.0. To sharpen the particle size distribution, make the particle generation reaction system as uniform as possible,
A distribution improvement treatment is also performed on the generated particles. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. Coercive force Hc measured on magnetic material
Can be created up to about 500 Oe to 5000 Oe. A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, Hc is from 1700 Oe to 4000.
Oe, but preferably 1800 Oe or more and 3500
Oe or less. When the saturation magnetization of the head exceeds 1.4 Tesler, it is preferable that the saturation magnetization be 2000 Oe or more. H
c is the particle size (plate diameter / plate thickness), the type and amount of contained elements,
It can be controlled by the substitution site of the element, the particle generation reaction conditions and the like. The saturation magnetization s is 40 emu / g to 80 emu / g. σs
Is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic substance, the surface of the magnetic substance particles is also treated with a substance suitable for the polymer such as a dispersion medium and a binder resin. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include compounds such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% by weight based on the magnetic material.
The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12 depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% is selected. Hexagonal ferrite is produced by mixing barium oxide, iron oxide, and a metal oxide that replaces iron with boron oxide as a glass-forming substance to obtain the desired ferrite composition, then melting, quenching, and then crystallization. And then re-heated, washed and pulverized to obtain a barium ferrite crystal powder, a glass crystallization method, a barium ferrite composition metal salt solution is neutralized with an alkali, and by-products are removed at 100 ° C. or higher. Washing, drying and pulverization after heating in a liquid phase to obtain a barium ferrite crystal powder, a barium ferrite composition metal salt solution is neutralized with an alkali, by-products are removed and then dried and dried at 1100 ° C. or lower , And pulverization to obtain a barium ferrite crystal powder, but the present invention is not limited to a production method.

[Non-magnetic layer] Next, the detailed contents of the lower layer
Will be described. The configuration of the lower layer of the present invention is particularly limited.
Although not to be considered, binder resins and inorganic powders
A body is preferred. None used in the lower layer of the present invention
The material powder is a non-magnetic powder, for example, metal oxide, gold
Genus carbonate, metal sulfate, metal nitride, metal carbide, metal
It can be selected from inorganic compounds such as sulfides.
As the inorganic compound, for example, α-a having an α conversion of 90% or more is used.
Lumina, β-alumina, γ-alumina, θ-alumina,
Silicon carbide, chromium oxide, cerium oxide, α-oxidation
Iron, hematite, goethite, corundum, silicon nitride
Element, titanium carbide, titanium oxide, silicon dioxide, oxidation
Tin, magnesium oxide, tungsten oxide, gill oxide
Conium, boron nitride, zinc oxide, calcium carbonate, sulfur
Calcium oxide, barium sulfate, molybdenum disulfide, etc.
Used alone or in combination. Particularly preferred are grains
Due to the small degree distribution and the many means of adding functions,
Titanium oxide, zinc oxide, iron oxide, barium sulfate,
More preferred are titanium dioxide and α-iron oxide. this
The particle size of the nonmagnetic powder is preferably 0.005 to 2 μm.
However, if necessary, use non-magnetic powders with different particle sizes.
Wide particle size distribution even in combination or single non-magnetic powder
The same effect can be obtained. Especially preferred
What is new is that the particle size of the nonmagnetic powder is 0.01 μm to 0.1 μm.
2 μm. In particular, the nonmagnetic powder is a particulate metal oxide.
In this case, the average particle size is preferably 0.08 μm or less.
In the case of a metallic oxide, the major axis diameter should be 0.3 μm or less.
Preferably, it is 0.2 μm or less. Tap dense
The degree is 0.05-2 g / ml, preferably 0.2-1.5 g / ml
It is. The water content of the non-magnetic powder is 0.1 to 5% by weight, preferably
0.2 to 3% by weight, more preferably 0.3 to 1.
5% by weight. The pH of the non-magnetic powder is 2 to 11
However, the pH is particularly preferably between 5.5 and 10. Non-magnetic powder
Specific surface area of powder is 1-100m^Two/ g, preferably 5 to 80 m
^Two/ g, more preferably 10 to 70 m^Two/ g. Non-magnetic
The crystallite size of the powder is preferably 0.004 μm to 1 μm
And more preferably 0.04 μm to 0.1 μm. DBP
Oil absorption using (dibutyl phthalate) is 5 to 100 ml
/ 100 g, preferably 10-80 ml / 100 g, more preferably
It is 20 to 60 ml / 100 g. Specific gravity is 1 to 12, preferably
Is 3-6. Needle-shaped, spherical, polyhedral, plate-shaped
Either is acceptable. Mohs hardness of 4 or more and 10 or less
Is preferred. SA (stearic acid) adsorption amount of non-magnetic powder
Is 1 to 20 μmol / m^Two, Preferably 2 to 15 μmol /
m^Two, More preferably 3 to 8 μmol / m^TwoIt is. pH
Is preferably between 3 and 6. These non-magnetic powders
The surface of the powder is treated with Al_TwoO_Three, SiO_Two, Ti
O_Two, ZrO_Two, SnO_Two, Sb_TwoO_Three, ZnO, Y_TwoO
_ThreeIs preferably present. Especially preferred for dispersibility
Is Al_TwoO_Three, SiO_Two, TiO_Two , ZrO_TwoIn Although,
More preferred is Al_TwoO_Three, SiO_Two, ZrO_TwoIn
You. These may be used in combination or used alone
Can also be. Also, coprecipitated surface according to the purpose
A treatment layer may be used, or after first treating with alumina
A method of treating the surface layer with silica or vice versa
Can also be taken. Also, the surface treatment layer depends on the purpose
Although it may be a porous layer, it is generally better to be homogeneous and dense
Is preferred.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and α-hematite DPN-250 and DPN-250BX manufactured by Toda Kogyo. , DPN-24
5, DPN-270BX, DPN-500BX, DBN
-SA1, DBN-SA3, Titanium oxide TT manufactured by Ishihara Sangyo
O-51B, TTO-55A, TTO-55B, TTO
-55C, TTO-55S, TTO-55D, SN-1
00, α hematite E270, E271, E300, E
303, titanium industrial titanium oxide STT-4D, STT
-30D, STT-30, STT-65C, α hematite α-40, MT-100S, MT-100 manufactured by Teika
T, MT-150W, MT-500B, MT-600
B, MT-100F, MT-500HD, FI made by Sakai Chemical
NEX-25, BF-1, BF-10, BF-20, S
TM, Dowa Mining DEFIC-Y, DEFIC-R,
AS2BM and TiO2P25 manufactured by Nippon Aerosil, 100A and 500A manufactured by Ube Industries, and baked products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α
-Iron oxide.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. As the type of carbon black, furnace for rubber, thermal 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 10
0 to 500 m ² / g, preferably 150 to 400 m ² / g,
DBP oil absorption is 20-400ml / 100g, preferably 30
４００400 ml / 100 g. The particle size of the carbon black is 5 mμ to 80 mμ, preferably 10 to 50 mμ, more preferably 10 to 40 mμ. PH of carbon black
Is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACK manufactured by Cabot Corporation.
ACKPEARLS 2000, 1300, 1000,
900, 800, 880, 700, VULCAN XC
-72, Mitsubishi Chemical Corporation # 3050B, # 3150B,
# 3250B, # 3750B, # 3950B, # 95
0, # 650B, # 970B, # 850B, MA-60
0, MA-230, # 4000, # 4010, CONDUCTEX SC, RAV manufactured by Columbian Carbon Co., Ltd.
EN8800,8000,7000,5750,525
0,3500,2100,2000,1800,150
0,1255, 1250 and Ketjen Black EC manufactured by Akzo. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by partially graphitizing the surface. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in an amount not exceeding 50% by weight and not exceeding 40% of the total weight of the nonmagnetic layer based on the inorganic powder. These carbon blacks alone,
Or they can be used 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
No. 18,564, and those described in JP-A-60-255827 can be used.

The binder resin, lubricant, dispersant, additive, solvent, dispersing method and other known techniques for the lower layer can be applied to the magnetic layer within the scope of the present invention. [Binder]

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As a thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1.0.
00 to 200,000, preferably 10,000 to 10
000 and a degree of polymerization of 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 acetal,
There are polymers or copolymers containing vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

The thermosetting resin or the reactive resin includes phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin. , A mixture of a polyester resin and an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, and a mixture of a polyurethane and a polyisocyanate. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in JP-A-62-256219.
In more detail. The above resins can be used alone or in combination, but preferred are vinyl chloride resins, vinyl chloride vinyl acetate copolymers, vinyl chloride vinyl acetate vinyl alcohol copolymers, and vinyl chloride vinyl acetate maleic anhydride copolymers. And a combination of at least one of the above and a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, -COO is required to obtain better dispersibility and durability.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2,
-OP = O (OM) ₂ , where M is a hydrogen atom,
Or alkali metal base), —OH, —NR ₂ , —N ⁺
R ₃ (R is a hydrocarbon group), epoxy group, —SH, —C
It is preferable to use one obtained by introducing at least one or more polar groups selected from N and the like by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g.
And preferably 10 ⁻² to 10 ⁻⁶ mol / g.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, ZEON Corporation MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9,7209, Toyobo Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Daiferamine 4020, 5020, 5 manufactured by Dainichi Seika
100, 5300, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Co., Ltd., MX5004, Samprene S manufactured by Sanyo Kasei Co., Ltd.
P-150 and Saran F310, F210 manufactured by Asahi Kasei Corporation.

The binder used in the nonmagnetic layer and the magnetic layer of the present invention is used in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, based on the inorganic powder or the magnetic powder. 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin,
The polyisocyanate is preferably used in combination in the range of 2 to 20% by weight. For example, when head corrosion occurs due to a slight amount of dechlorination, it is also possible to use only polyurethane or only polyurethane and isocyanate. . In the present invention, when polyurethane is used, the glass transition temperature is -50 to 150C, preferably 0C to 100C, and the elongation at break is 100 to 2000.
%, The breaking stress is 0.05 to 10 kg / mm ² , and the yield point is 0.
It is preferably from 0.05 to 10 kg / mm ² .

The magnetic recording medium of the present invention comprises two or more layers. Therefore, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the resin described above. It is of course possible to change the physical characteristics of the non-magnetic layer and the magnetic layer as needed, and rather, it should be optimized for each layer, and a known technique for a multilayer magnetic layer can be applied. For example, when changing the amount of the binder in each layer, it is effective to increase the amount of the binder in the magnetic layer in order to reduce abrasion on the surface of the magnetic layer,
In order to improve the head touch with the head, the amount of the binder in the nonmagnetic layer can be increased to provide flexibility.

The polyisocyanates used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Use of isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can do. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M
R, Millionate MTL, Takeda Yakuhin, Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, manufactured by Sumitomo Bayer Co., Ltd., Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These are used alone or in combination of two or more using the difference in curing reactivity. Each layer can be used in combination.

[Carbon Black, Abrasive] As the carbon black used in the magnetic layer of the present invention, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5-50
0 m ² / g, DBP oil absorption 10-400 ml / 100
g, particle size 5mμ ~ 300mμ, pH 2 ~ 10, water content 0.1 ~ 10%, tap density 0.1 ~ 1g / cc,
Is preferred. Specific examples of the carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 90
5, 800, 700, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3
5, # 2400B, # 2300, # 90, manufactured by Mitsubishi Chemical Corporation
0, # 1000 # 30, # 40, # 10B, manufactured by Columbian Carbon Co., Ltd., CONDUCTEX SC, RAVE
N 150, 50, 40, 15, RAVEN-MT-
P, manufactured by EC Japan, Ketjen Black EC, 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 one obtained by partially graphitizing the surface. 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 magnetic substance. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination in the upper magnetic layer and the non-magnetic layer, and the particle size, oil absorption,
It is, of course, possible to selectively use them according to the purpose based on the above-mentioned various properties such as the electric conductivity and the pH. Rather, each layer should be optimized. Carbon black that can be used in the magnetic layer of the present invention is, for example, "Carbon Black Handbook"
(Edited by the Carbon Black Association).

As the abrasive used in the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized carbon having an α conversion of 90% or more are used. Known materials mainly having a Mohs hardness of 6 or more such as silicon, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been 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, and in particular, in order to enhance the electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as needed, or to achieve the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention is needle-like, spherical, dice-like,
Although any of these may be used, those having a corner in a part of the shape are preferable because of high abrasiveness. Specifically, AKP- manufactured by Sumitomo Chemical Co., Ltd.
12, AKP-15, AKP-20, AKP-30, A
KP-50, HIT-20, HIT-30, HIT-5
5, HIT-60, HIT-70, HIT-80, HI
T-100, manufactured by Reynolds, ERC-DBM, HP-
DBM, HPS-DBM, manufactured by Fujimi Abrasives, WA10
000, Uemura Industry Co., Ltd., UB20, Nippon Chemical Industry Co., Ltd.,
G-5, Chromex U2, Chromex U1, Toda Kogyo Co., Ltd., TF100, TF140, Ibiden Co., Ltd., Beta Random Ultra Fine, Showa Mining Co., Ltd., B-3 and the like. These abrasives can be added to the nonmagnetic layer as needed. By adding to the non-magnetic layer, the surface shape can be controlled, and the projected state of the abrasive can be controlled. The particle size and amount of the abrasive added to the magnetic layer and the non-magnetic layer should of course be set to optimal values.

[Additives] As the additives used in the magnetic layer and the nonmagnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, 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, polyphenyl ether, phenyl phosphonic acid, α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, p-ethylbenzene phosphonic acid, phenyl phosphinic acid , Aminoquinones, various silane coupling agents, titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, having 10 to 24 carbon atoms
Monobasic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (L
i, Na, K, Cu, etc., or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (including an unsaturated bond or a branched alcohol) Absent),
Alkoxy alcohols having 12 to 22 carbon atoms (which may contain an unsaturated bond or may be branched), monobasic fatty acids having 10 to 24 carbon atoms (including an unsaturated bond,
It may be branched or any one of mono-, di-, tri-, tetra-, penta-, and hexa-hydric alcohols having 2 to 12 carbon atoms (including an unsaturated bond, A mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester, a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer,
Fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

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. Can be Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, oleyl alcohol, stearyl Alcohol, lauryl alcohol and the like.
Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Heterocycles, cationic surfactants such as phosphoniums or sulfoniums, carboxylic acids, sulfonic acids, phosphoric acids,
Anionic surfactants containing acidic groups such as sulfate groups, phosphate groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and alkylbedine types can also be used. . These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are always 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

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.
To control leaching to the surface by using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control leaching to the surface by using esters with different boiling points, melting points and polarities, and to adjust the amount of surfactant It is conceivable to improve the stability of the coating and to improve the lubrication effect by increasing the amount of the lubricant added in the lower layer, and it is needless to say that the present invention is not limited to the examples shown here. Generally, the total amount of the lubricant is 0.1% by weight to 50% by weight, preferably 2% by weight, based on the magnetic powder or the inorganic powder.
It is selected in the range of 25% by weight to 25% by weight.

All or some of the additives used in the present invention may be added at any step in the production of magnetic and non-magnetic paints. There are a case where it is added in a kneading step using a body, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. 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 or after the slit is completed.

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

[Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the support has a thickness of 2 to 100 μm, preferably 2 to 80 μm.

An undercoat layer may be provided between the support and the nonmagnetic layer or the magnetic layer to improve the adhesion. The thickness of the undercoat layer is 0.01 to 0.5 μm, preferably 0.02 to
0.5 μm. The present invention may be a double-sided magnetic layer disk-shaped medium in which a nonmagnetic layer and a magnetic layer are provided on both sides of a support, or may be provided on only one side. In this case, a non-magnetic layer,
A back coat layer may be provided on the side opposite to the magnetic layer side. This thickness is 0.1 to 4 μm, preferably 0.3 to
2.0 μm. Known undercoat layers and backcoat layers can be used.

The thickness of the magnetic layer of the medium of the present invention is optimized according to the saturation magnetization of the head to be used, the head gap length, and the band of the recording signal.
Not less than 0.25 μm, preferably 0.05 μm
It is not less than 0.20 μm. The magnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the non-magnetic layer as the lower layer of the medium according to the present invention is 0.2 μm or more and 5.0 μm or less, preferably 0.1 μm or less.
3 μm or more and 3.0 μm or less, more preferably 1.0 μm
m or more and 2.5 μm or less. The lower layer of the medium of the present invention exerts its effect if it is substantially non-magnetic.For example, even if a small amount of a magnetic substance is included as an impurity or intentionally, it exhibits the effect of the present invention, It goes without saying that the configuration can be regarded as substantially the same as that of the present invention. Substantially non-magnetic means that the lower layer has a residual magnetic flux density of 100 G or less or a coercive force of 100 Oe or less, and preferably has no residual magnetic flux density and coercive force.

[Support] The support used in the present invention is preferably non-magnetic and flexible. These supports are polyethylene terephthalate, polyethylene naphthalate,
Known films such as polyesters, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, polyaramid, aromatic polyamide, 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.

In order to attain the object of the present invention, as a support, Mira of a surface roughness meter TOPO-3D manufactured by WYKO is used.
The center plane average surface roughness SRa measured by the u method is 8.0 nm or less, preferably 4.0 nm or less, more preferably 2.0 nm or less.
It is preferable to use one having a diameter of nm or less. These supports not only have low center plane average surface roughness, but also have
It is preferable that there are no coarse protrusions of 5 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include Ca, S
In addition to oxides and carbonates such as i and Ti, organic fine powders such as acryl-based can be used. The maximum height SRmax of the support is 1 μm or less, the ten-point average roughness SRz is 0.5 μm or less, the height of the center plane is SRp is 0.5 μm or less, and the center plane valley depth SRv
Is 0.5 μm or less, center plane area ratio SSr is 10% or more, 9
0% or less, and the average wavelength Sλa is preferably 5 μm or more and 300 μm or less. To obtain the desired electromagnetic conversion characteristics and durability,
The distribution of surface protrusions of these supports can be arbitrarily controlled by a filler. Each of the supports having a size of 0.01 μm to 1 μm has a size of 0 to 2000 per 0.1 mm ^2.
You can control in a range.

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² . Breaking strength is 5-100
Kg / mm ^2, the elastic modulus is preferably from 100 to 2,000 kg / mm ^2. 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.

[Production Method] The step of producing the magnetic coating material of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as magnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention 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, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventionally known manufacturing technique can be used as a part of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, and an extruder. When a kneader is used, the magnetic powder or the non-magnetic powder and all or a part of the binder (30% of the total binder) are used.
% By weight) and 15 to 500 parts by weight with respect to 100 parts by weight of the magnetic powder. The details of these kneading treatments are described in JP-A-1-10633.
8, JP-A-1-79274. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When applying a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. First, the lower layer is first applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like generally used in the application of a magnetic paint, and the lower layer is wet in a wet state. Showa 60-238
179, Japanese Patent Application Laid-Open No. 2-265672, a method of coating an upper layer by a support pressure type extrusion coating apparatus.
No. 17971, Japanese Patent Application Laid-Open No. 2-265672, a method for applying the upper and lower layers almost simultaneously by one coating head having two built-in slits for passing a coating liquid, and a third method disclosed in Japanese Patent Application Laid-Open No. 2-174965. This is a method in which the upper and lower layers are applied almost simultaneously by an extrusion coating device with a backup roll. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to agglomeration of the magnetic particles, Japanese Patent Application Laid-Open Nos. 62-95174 and 1-236968 are known.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in US Pat. Further, the viscosity of the coating liquid must satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the constitution of the present invention, it is of course possible to use a sequential multi-layer coating in which a lower layer is applied and dried, and then a magnetic layer is provided thereon, and the effect of the present invention is not lost. 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 the case of a disk, a sufficient isotropic orientation may be obtained even without orientation without using an orientation device. However, alternately arranging cobalt magnets diagonally, applying an alternating magnetic field with a solenoid, etc. It is preferable to use a known random alignment device. In the case of the ferromagnetic metal fine powder, isotropic orientation is generally preferred to be in-plane two-dimensional random,
Three-dimensional randomness can be obtained by adding a vertical component. In the case of hexagonal ferrite, three-dimensional randomness in the in-plane and vertical directions generally tends to occur, but in-plane two-dimensional randomness is also possible. In addition, isotropic magnetic characteristics can be imparted in the circumferential direction by using a known method such as a different polarity opposed magnet and making the magnets vertically oriented. In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

It is preferable that the drying position of the coating film can be controlled by controlling the temperature, amount of air, and coating speed of the drying air. The coating speed is 20 m / min to 1000 m / min, and the temperature of the drying air is 60 ° C. The above is preferable, and a suitable preliminary drying can be performed before entering the magnet zone.

As a calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll is used.
In particular, in the case of forming a double-sided magnetic layer, it is preferable to perform the treatment with metal rolls. The processing temperature is preferably 50 ° C. or higher,
More preferably, the temperature is 100 ° C. or higher. The linear pressure is preferably at least 200 kg / cm, more preferably at least 300 kg / cm.

[Physical Characteristics] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is 2,000 G or more and 5,000 G or less when ferromagnetic metal fine powder is used, and 1000 G or more and 3000 G or less when hexagonal ferrite is used. Is preferred. The coercive force Hc is usually 1500 Oe or more and 50
00 Oe or less, preferably 1700 Oe or more,
It is 3000 Oe or less. The narrower the coercive force distribution is, the better the switching-field distribution (SFD) is.
6 or less is preferred. The squareness ratio is 0 for two-dimensional randomness.
55 or more and 0.67 or less, preferably 0.58 or more,
0.64 or less, 0.45 or more for three-dimensional random,
It is preferably 0.55 or less, 0.6 or more, preferably 0.7 or more in the vertical direction in the case of vertical alignment, and 0.7 or more, preferably 0.8 or more when demagnetizing field correction is performed. The orientation ratio is preferably 0.8 or more for both two-dimensional random and three-dimensional random. In the case of two-dimensional randomness, it is preferable that each of the squareness ratios, Br, and Hc in the vertical direction be within 0.1 to 0.5 times the in-plane direction.

The coefficient of friction for the head of the present invention is expressed by the following equation.
0.5 or less, preferably 0.3 or less, in the range of 10 ° C. to 40 ° C. and humidity of 0% to 95%, the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq, and the charge potential is −5.
It is preferably within the range of 00V to + 500V. 0.5% of magnetic layer
The elastic modulus at elongation is preferably 100 to 20 in each direction in the plane.
00Kg / mm ² , breaking strength is preferably 10-70Kg / m
m ² , the elastic modulus of the magnetic recording medium in each in-plane direction is preferably 100 to 1500 kg / mm ² , and the residual growth is preferably 0.1 kg / mm ² .
The heat shrinkage at any temperature of 5% or less and 100 ° C or less is preferably 0.3% or less, more preferably 0.2% or less, and 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 nonmagnetic layer is preferably from 0 ° C to 100 ° C. The loss modulus is preferably in the range of 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 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, a larger porosity is often preferable in running durability.

The center plane surface roughness Ra of the magnetic layer is WYKO.
It is obtained by measuring the area of 250 μm × 250 μm by the mirau method using a surface roughness meter TOPO-3D manufactured by the company, and is usually 4.0 nm or less, preferably 3.8 nm or less, more preferably 3.5 nm or less. is there. Maximum height SRma of the magnetic layer
x is 0.5 μm or less, ten-point average roughness SRz is 0.3 μm or less, center plane peak height SRp is 0.3 μm or less, center plane trough depth SRv is 0.3 μm or less, and center plane area ratio SSr is 20%. Not less than 80%, and the average wavelength Sλa is not less than 5 μm and not more than 300 μm.
m or less is preferable. The surface protrusions of the magnetic layer can be arbitrarily set in the range of 0 to 2000 with a size of 0.01 μm to 1 μm, and it is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient. . These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder to be added to the magnetic layer, the roll surface shape of the calendering treatment, and the like. The curl is preferably within ± 3 mm. The curl value was determined by the displacement of the peripheral edge when the 3.5-inch magnetic recording disk was fixed vertically and fixed at the center.

When the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed 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 non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0068]

EXAMPLES <Preparation of paint> Magnetic paint Ferromagnetic metal fine powder 100 parts Composition: Fe 90%, Co 10% (atomic ratio) Hc2350Oe, specific surface area 55 m ² / g, σs 150 emu / g Crystallite size 140 °, major axis diameter 0 0.090 μm Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin UR5500 (manufactured by Toyobo) 4 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co.) 10 parts Carbon black # 50 (manufactured by Asahi Carbon Co.) 2 parts Phenyl Phosphonic acid 3 parts Ethylene glycol dioleil 10 parts Stearic acid 2 parts Methyl ethyl ketone 180 parts Cyclohexanone 180 parts Non-magnetic paint Non-magnetic powder α-Fe ₂ O ₃ hematite 100 parts Long axis diameter 0.15 μm, BET specific surface area 50 m ² / g pH 9, Al ₂ O ₃ is with respect to the entire particles to the surface 8 wt% presence Carb Black # 950B (manufactured by Mitsubishi Kasei) 18 parts Vinyl chloride copolymer MR104 (manufactured by Zeon Corporation) 15 parts Polyurethane resin UR5500 (manufactured by Toyobo) 7 parts Phenylphosphonic acid 4 parts Ethylene glycol dioleyl 15 parts Oleic acid 1. 2 parts Stearic acid 1.2 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts For each of the above paints, each component was kneaded with a kneader, and then dispersed using a sand mill. Polyisocyanate was added to the resulting dispersion, and 10% to the coating solution for the non-magnetic layer.
Parts and 5 parts of the coating solution for the magnetic layer, and 40 parts of cyclohexanone were added to each, and the mixture was filtered using a filter having an average pore diameter of 1 μm to obtain a coating solution for forming the nonmagnetic layer and the magnetic layer. Each was prepared.

The obtained non-magnetic layer coating solution was coated with the following support so that the thickness after drying was 1.5 μm, and immediately thereafter, the thickness of the magnetic layer was 0.25 μm thereon. B
Simultaneous multi-layer coating on -1, while both layers are still wet, pass through an AC magnetic field generator with frequency 50Hz, magnetic field strength 250gauss or frequency 50Hz, magnetic field strength 250gauss to perform random orientation treatment After drying,
Processing is performed at a temperature of 90 ° C. and a linear pressure of 300 kg / cm using a 7-stage calender, and punched into a 3.5 inch thermo-treatment (70 ° C., 4 ° C.).
After 8 hours), the cartridge was placed in a 3.5-inch cartridge with the liner installed inside, and predetermined mechanical components were added to obtain a 3.5-inch floppy disk.

With respect to the obtained sample, the heat shrinkage anisotropy was measured by the method described above. Each track width TW _x and TW _y of the magnetic head used for measurement 120μ
m and 114 μm. Support B-1: Material Polyethylene terephthalate Thickness 62 μm Center-surface average surface roughness 5 nm Heat shrinkage (80 ° C., 30 minutes): MD 0.12%: TD 0.10% Heat shrinkage (100 ° C., 30 minutes) ): MD 0.5%: TD 0.4% (Example 2) In Example 1, the following support B-2 was used in place of the support B-1.

Support B-2: Material Polyethylene terephthalate Thickness 62 μm Center-surface average surface roughness 4 nm Heat shrinkage (80 ° C., 30 minutes): MD 0.05%: TD 0.05% Heat shrinkage (100 ° C.) , 30 minutes): MD 0.1%: TD 0.1% (Example 3) In Example 1, the thermoprocessing after punching out to 3.5 inches was performed at 70 ° C. for 24 hours (H). Example 4 In Example 1, the following support B-3 was used in place of the support B-1.

Support B-3: Material Polyethylene naphthalate Thickness 62 μm Center-surface average surface roughness 5 nm Heat shrinkage (80 ° C., 30 minutes): MD 0.03%: TD 0.02% Heat shrinkage (100 (° C., 30 minutes): MD 0.1%: TD 0.1% (Example 5) In Example 4, the thermotreatment after punching into 3.5 inches was not performed. Comparative Example 1 The following support B-4 was used in Example 1 in place of the support B-1.

Support B-4: Material Polyethylene terephthalate Thickness 62 μm Center-surface average surface roughness 5 nm Heat shrinkage (80 ° C., 30 minutes): MD 0.15%: TD 0.19% Heat shrinkage (100 ° C.) , 30 minutes): MD 0.5%: TD 0.9% (Comparative Example 2) In Comparative Example 1, the thermotreatment after punching into 3.5 inches was not performed. (Comparative Example 3) In Example 1, the thermotreatment after punching into 3.5 inches was not performed. (Comparative Example 4) In Example 1, the thermotreatment after punching into 3.5 inches was performed at 55 ° C and 24H. (Comparative Example 5) In Example 2, the thermoprocessing after punching into 3.5 inches was not performed.

The evaluation of each material was based on the following. (1) Magnetic properties (Hc): Measured using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) with Hm10KOe. (2) The long axis diameter of each of the ferromagnetic metal powder and the non-magnetic powder in the lower layer is 100,000 times or 200,000 times. And the image was analyzed using a KS400 manufactured by Carl Zeiss Co., Ltd., and the average value of the major axis diameter was determined. (3) Center plane average surface roughness (Ra): 3D-MIRAU
Surface roughness (Ra): Ra value of an area of about 250 μm × 250 μm was measured by MIRAU method using TOPO3D manufactured by WYKO. Spherical correction and cylindrical correction are added at a measurement wavelength of about 650 nm. This method is a non-contact surface roughness meter that measures by light interference. (4) The thickness of the magnetic layer is cut out to a thickness of about 0.1 μm with a diamond cutter over the magnetic recording medium in the longitudinal direction.
Magnification of 10,000 to 100,000 by transmission electron microscope
The images were observed at a magnification of, preferably 20,000 to 50,000, and photographed. Photo print size is A
4-A5. Thereafter, the interface was visually determined by paying attention to the shape difference between the ferromagnetic powder and the nonmagnetic powder of the magnetic layer and the lower nonmagnetic layer, and the magnetic layer surface was similarly blackened. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. Sample photo length is 2
In the case of 1 cm, the measurement was performed 85 to 300 times. The average of the measured values at that time was defined as the magnetic layer thickness.

The heat shrinkage anisotropy of each of the above samples was determined.
It was shown to.

[0076]

[Table 1] From the above table, the comparative examples are 80 ° C, 30 minutes and 80 ° C, 72H.
Is not within the range of the heat shrinkage anisotropy of the present invention of 0.05% or less, and it is understood that both of the examples are within the range of the heat shrinkage anisotropy of the present invention.

[0077]

According to the present invention, a substantially nonmagnetic lower layer and a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder dispersed in a binder are provided in this order on a nonmagnetic support. In the magnetic recording medium, by controlling the heat shrinkage anisotropy of the magnetic recording disk to 0.05% or less, the number of servo sectors on one track is not increased in the recording / reproducing system to be used. The width can be reduced, and the recording capacity can be substantially increased while maintaining good electromagnetic conversion characteristics.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Saito 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (1)

[Claims] 1. A magnetic recording disk comprising a support and a substantially nonmagnetic lower layer and a magnetic layer obtained by dispersing a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder in a binder in this order. The magnetic recording disk had a heat shrinkage anisotropy of 8% when placed in a dry environment at 80 ° C. for 30 minutes.
Both the heat shrinkage anisotropy when placed in a completely dry environment at 0 ° C. for 72 hours is 0.05% or less, and the number of servo sectors on one track is 80 to 150. A magnetic recording disk used in a recording / reproducing system having a width set to 10 μm or less.