JPH1125449A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a high-density characteristic and durability by incorporating a monoester formed by esterification of a diester of a bivalent alcohol and unsatd. fatty acid and only the one hydroxyl group of the bivalent alcohol with the unsatd. fatty acid into a magnetic layer. SOLUTION: The amt. of the diester and monoester to be added to the magnetic layer is preferably 2 to 10 wt.% of the weight of the magnetic layer and the content of the monoester in the magnetic layer is preferably 8 to 12 wt.% of the weight of the diester. The layers consisting of the magnetic layer and the lower layer contains the monoester preferably at 8 to 12 wt.% of the sum total Swd of the diester and preferably, the monoester is also incorporated into the magnetic layer and the lower layer respectively. The bivalent alcohol which is the constitution raw material of the diester or monoester is HO-R<1> -OH and the unsatd. fatty acid is preferably R<2> -COOH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium having a high recording density. In particular, the present invention relates to a magnetic recording medium for high-density recording, which has a magnetic layer and a substantially nonmagnetic lower layer, and includes a ferromagnetic metal fine powder or a hexagonal ferrite fine powder in the uppermost layer.

[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.

In the field of magnetic tapes, in recent years, with the spread of office computers such as minicomputers, personal computers, and workstations, magnetic tapes (so-called backup tapes) for recording computer data as external storage media.
Research is being actively conducted. In practical use of magnetic tapes for such applications, especially with the downsizing of computers and the increase in information processing capacity, the increase in recording capacity,
In order to achieve miniaturization, improvement in recording capacity is strongly required.

[0004] Conventionally, magnetic recording media have widely been prepared by coating a support with 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. 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, as a large-capacity disk using a ferromagnetic metal fine powder having excellent high-density recording characteristics, a 10 MB MF-2TD and a 21 MB MF-2S are used.
Large-capacity disks using D or hexagonal ferrite include 4 MB MF-2ED, 21 MB 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 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. It is proposed to use a metal fine powder having a Hc of 1000 Oe or more and a specific surface area of 25 to 70 m ² / g. I have.

In order to improve the durability of the disk-shaped magnetic recording medium, Japanese Patent Publication No. 7-85304 proposes to use a fatty acid ester having an ether bond with an unsaturated fatty acid ester, and Japanese Patent Publication No. 7-70045 discloses a branch. It has been proposed to use a fatty acid ester having a fatty acid ester and an ether bond, and JP-A-54-124716 proposes to include a non-magnetic powder having a Mohs hardness of 6 or more and a higher fatty acid ester. Has a volume and surface roughness of 0.005 to 0.025
μm is proposed in Japanese Patent Application Laid-Open No. 61-294637.
It is proposed to use a low melting point and a high melting point fatty acid ester in JP-B-7-36216.
It has been proposed to use an abrasive having a particle size of ４ to ／ and a fatty acid ester having a low melting point, and JP-A-3-203018 proposes to use a metal magnetic material containing Al and chromium oxide.

As a structure 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 structure having a conductive layer and a magnetic layer containing fine metal powder. Has proposed a structure having a magnetic layer and a non-magnetic layer of 1 μm or less.
9337 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 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.
Has proposed a configuration having a magnetic layer having a Hc of 1400 Oe or more and a thickness of 0.5 μm or less and a nonmagnetic layer containing conductive particles, and Japanese Patent Application Laid-Open No. 5-197946 discloses a configuration containing an abrasive larger than the magnetic layer thickness. Japanese Patent Application Laid-Open No. Hei 6-68453 proposes a configuration in which the thickness of a magnetic layer is 0.5 μm or less, the thickness variation of the magnetic layer is within ± 15%, and the surface electric resistance is specified. A configuration has been proposed in which two types of abrasives having different diameters are included and the amount of the abrasive on the surface is regulated.

In recent years, with the spread of office computers such as minicomputers and personal computers, researches on magnetic tapes (so-called backup tapes) for recording computer data as external storage media have been made with respect to tape-shaped magnetic recording media. Is being actively conducted. When a magnetic tape for such a purpose is put to practical use, especially in connection with the miniaturization 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 miniaturization. In addition, the use environment of magnetic tapes is widespread, so it can be used under a wide range of environmental conditions (especially in the circumstance where temperature and humidity fluctuates rapidly). Reliability for performance such as recording and reading is required more than before.

Conventionally, a magnetic tape used in a digital signal recording system is determined for each system, and a so-called DLT type, 3480, 3490, 3590,
Magnetic tapes compatible with QIC, D8 type, or DDS type are known. And in any system, the magnetic tape used has a film thickness of 2.
A magnetic layer containing a ferromagnetic powder, a binder and an abrasive having a relatively thick single layer structure of 0 to 3.0 μm is provided. In order to maintain the condition, a back coat layer is provided. However, in the magnetic layer having a relatively thick single-layer structure as described above, there is a problem of a loss in thickness that the output is reduced.

It is known that the magnetic layer is made thinner in order to improve the decrease in reproduction output due to the thickness loss of the magnetic layer. Comprising a lower nonmagnetic layer dispersed in a binder and an upper magnetic layer having a thickness of 1.0 μm or less formed by dispersing ferromagnetic powder in the binder while the nonmagnetic layer is in a wet state. A recording medium is disclosed.

However, with the rapid increase in capacity and density of magnetic recording media in the form of disks or tapes, it has become difficult to obtain satisfactory characteristics even with such techniques. In particular, it has become difficult to achieve both durability and durability. Conventionally, mineral oils, silicone oils, higher alcohols, higher fatty acids, fatty acid esters, animal oils such as tallow, whale oil, and shark oils and vegetable oils have been used as lubricants, but all have poor durability. In order to improve durability, monoesters of saturated and unsaturated fatty acids and alcohols are widely used, as is well known, including Japanese Patent Publication No. 51-39081. However, in a magnetic recording medium for high-density recording with an ultra-smooth magnetic surface, the durability was insufficient with monoester. In addition, fatty acid esters of polyhydric alcohols are disclosed in JP-B-41-18063 (esters of carboxylic acid and dihydric alcohol) and JP-B-58-18063.
JP-A-31655 (oleic acid glyceride triester), JP-A-54-21806 (fatty acid ester of alcohol containing three or more unsaturated bonds) and JP-A-61-198422 (polyhydric alcohol and fatty acid). Ester) and the like, but none of them can achieve both durability and electromagnetic conversion characteristics.

As the fatty acid monoester having an unsaturated bond, oleyl oleate described in Japanese Patent Publication No. 4917/1992 can be mentioned, but it has insufficient durability. This is presumed to be due to the fact that since it is a monoester, the interaction with the binder resin is inferior and the lubricant volatilizes during long-term storage or use under high-temperature conditions. Japanese Patent Application Laid-Open No. 61-280025 discloses that some polyglycerols are
H is esterified with a fatty acid, but also has insufficient durability. This is because the OH group remains, and the compatibility of the lubricant with the binder resin is too large, so that the lubricant dissolves in the magnetic layer and does not easily leach onto the surface of the magnetic layer, thus exhibiting the function as a lubricant. It is presumed that it is difficult. It is also considered that the polyisocyanate contained in the binder resin as the curing agent reacts with the OH group, so that the reaction between the curing agent and the binder resin is inhibited.

Japanese Patent Publication No. 47-12950 discloses fatty acid esters of unsaturated alcohols, for example, vinyl stearate, and JP-A-55-139637 discloses fatty acids. Combinations of esters, fatty acid amides and fatty acids are disclosed. JP-A-58-164025 discloses unsaturated fatty acid esters, and JP-A-59-148131 discloses a combination of unsaturated fatty acid esters and hydrocarbons. Disclose unsaturated fatty acid esters of branched alcohols, but all have insufficient durability.

Japanese Patent Application Laid-Open No. 8-167137 discloses that
ATOMM (Advanced Super Thin)
Layer & High Output Meta
1Media Technology) (lower layer is a non-magnetic layer and upper layer is a thin magnetic layer), at least the upper layer contains a diester of a fatty acid having an unsaturated bond and a diol which may have an unsaturated bond as a lubricant. By using the ultra-smoothed magnetic layer, the magnetic recording medium has sufficient runnability, repetitive runnability, and durability, and has high durability even when used and stored in a wide range of environmental conditions and used in dusty environments. It provides a recording medium and a magnetic recording medium having a low error rate even when used and stored under a wide range of environmental conditions and used in a dusty environment. However, the durability evaluation in Japanese Unexamined Patent Publication No. Hei 8-167137 was carried out with a floppy disk drive FD1331 manufactured by NEC Corporation, and was used in a system where the rotation speed of the disk was relatively low. Sufficient durability could not be secured in a high-speed rotation system. In addition, the magnetic material used in the examples is as large as 0.20 μm in major axis diameter, which is advantageous in terms of durability, but insufficient for high-density recording,
If the magnetic material is made finer, sufficient durability cannot be secured.

Japanese Patent Application Laid-Open No. 7-192250 discloses that
The present invention relates to a magnetic recording medium containing a diester of a dihydric alcohol and an unsaturated fatty acid in a magnetic layer, and provides a magnetic disk with less head contamination and excellent torque characteristics and durability. However, JP-A-7-19225
According to the torque / durability evaluation in JP-A No. 0, NEC FD-1
331, Toshiba's PD212 is used, which is in a relatively low-speed rotation system, and sufficient durability could not be obtained in a high-speed rotation system such as Zip.

[0017]

SUMMARY OF THE INVENTION The present invention provides a magnetic recording medium in which the electromagnetic conversion characteristics, especially the high-density recording characteristics are remarkably improved and the durability is excellent, and the running durability is particularly remarkably improved. It is intended to be. In particular, an object of the present invention is to provide a large-capacity disk-shaped magnetic recording medium.

[0018]

Means for Solving the Problems As a result of intensive studies by the present inventors, it has been found that by using the following medium, excellent high-density recording characteristics and excellent durability, which are the objects of the present invention, can be obtained. The present invention has been found. That is, the present invention relates to a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a support, wherein a diester of a dihydric alcohol and an unsaturated fatty acid is contained in the magnetic layer. A magnetic recording medium characterized in that it contains a monoester in which only one hydroxyl group of a polyhydric alcohol is esterified with an unsaturated fatty acid.

Preferred embodiments of the present invention are as follows. (1) A magnetic recording medium comprising the diester in an amount of 1 to 15% by weight based on the weight of the magnetic layer and the monoester in an amount of 1 to 20% by weight or less based on the diester. (2) A substantially nonmagnetic lower layer is formed on a support, and a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder is dispersed in a binder to form a magnetic layer having a thickness of 0.5 μm or less. In the magnetic recording medium, the layer consisting of the magnetic layer and the lower layer contains the diester in an amount of 1 to 15 wt% based on the total weight of the magnetic layer and the lower layer, and the layer consisting of the magnetic layer and the lower layer contains the monoester. 1 to 20% by weight based on the total amount of diesters contained in the magnetic layer and the lower layer
A magnetic recording medium comprising: (3) A magnetic recording medium, wherein each of the magnetic layer and the lower layer contains a diester and a monoester. (4) the dihydric alcohol is HO-R ¹ -OH (R ¹ is - (CH ₂₎ n-or - (CH ₂₎ n-(n is an unsaturated bond derived from 1 to 10) May represent a divalent group, or-(CH ₂ CH (C
H ₃ ))-), wherein the unsaturated fatty acid is R ² -COOH (R
² is a chain unsaturated hydrocarbon group having 12 to 26 carbon atoms, and the units to be bonded to both ends of the dihydric alcohol may be the same or different). (5) A magnetic recording medium wherein the ferromagnetic metal powder is mainly composed of Fe, has an average major axis diameter of 0.15 μm or less, and a crystallite size of 80 to 180 °. (6) The ferromagnetic hexagonal ferrite powder has an average plate diameter of 60
A magnetic recording medium having a plate ratio of 2 to 6 or less. (7) A magnetic recording medium used in a recording / reproducing system having a rotation speed of 700 rpm or more and having a disk shape.

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 the lower layer. The present invention relates to a high-density, large-capacity magnetic recording medium requiring an ultra-smooth magnetic layer (hereinafter, also referred to as an upper layer), which can provide stable running durability both at the beginning of running and during repeated running. . Conventionally, lubricants such as monoesters and diesters have been used as lubricants, but these are used alone, and there was no idea that both should be used in combination.

In the prior art, as described above, diesters of dihydric alcohols were particularly effective for storage durability when a magnetic disk having a very smooth magnetic layer was used under a wide range of environmental conditions. Certainly, it is effective in a conventional system having a relatively low rotational speed as disclosed in the above-mentioned known example. In some cases, the effect was insufficient because of the high speed rotation.

Therefore, in the present invention, when a monoester in which the alcohol hydroxyl group at one terminal of the dihydric alcohol is not esterified is used, a ZIP system {ZIP disk manufactured by IOMEGA (Iomega), USA (area recording density: 96 Mbit / in)
In a system with a rotation speed of 700 rpm or more, such as ch ² ｝, storage durability could be further improved. The mechanism of action is that by mixing the monoester with the diester, the non-esterified -OH of the monoester has an affinity for the magnetic substance or the like, so that the migration of the diester from the magnetic layer by the anchor effect is suppressed. It is thought that it is doing. It is more preferable that the unsaturated fatty acid component of the monoester is the same as the acid component of the diester, and this is considered to have an effect of enhancing the integrity with the monoester.

Further, since the monoester has one polar ester group in the molecule, its affinity with the binder is not so high, and the monoester is likely to appear on the surface of the magnetic layer without remaining in the layer. Is considered to have a high affinity for the magnetic substance on the surface of the magnetic layer due to the action of the -OH group, and the diester has two polar ester groups in the molecule. Has a property that it is difficult to come out on the surface of the magnetic layer because it is easily retained in the layer, but it is considered that the diester that comes out on the magnetic surface due to the anchor effect of the monoester does not easily leave the surface of the magnetic layer as described above. Can be Therefore, it is considered that the magnetic recording medium of the present invention can obtain extremely good running durability. The diester has extremely good low-temperature durability, and when used in combination with a monoester having good high-temperature durability, extremely excellent running durability from low to high temperatures can be obtained. These effects have a so-called synergistic effect that is more than the effect obtained by simply adding the effect of the monoester and the effect of the diester. Furthermore, it is quite unexpected that the present invention was applied to a magnetic recording medium having both high-density characteristics with an areal recording density equal to or higher than that of ZIP and excellent durability, particularly a disk-shaped magnetic recording medium, and practical characteristics were obtained. That is.

In the present invention, the unsaturated fatty acid for forming a monoester is preferably the same as at least one of the unsaturated fatty acids for forming a diester as described above. The unsaturated fatty acid for forming the diester is preferably a dihydric alcohol in which the same unsaturated fatty acid is ester-bonded to both terminals.

In the present invention, the amount of the diester and monoester added to the magnetic layer is appropriately selected, but is usually 1 to 15% by weight, preferably 1 to 12% by weight based on the weight of the magnetic layer.
t%, more preferably 2 to 10% by weight, and the content of the monoester in the magnetic layer is 1.0 to 20.0% by weight, preferably 5 to 15% by weight, more preferably 8 to 8% by weight based on the diester. It is 12 wt%.

In the present invention, in the case of the ATOMM structure, the distribution of both esters is not particularly limited as long as at least the diester and the monoester are contained in the magnetic layer. It is particularly effective to add to each of the layers. In the layer composed of the magnetic layer and the lower layer, 1 to 15 wt%, preferably 1 to 12
wt%, more preferably 2 to 10 wt%, preferably diester is contained in each of the magnetic layer and the lower layer. Specifically, preferably, the magnetic layer is formed by adding a diester to Swl by 1%.
The lower layer contains 1 to 15% by weight, more preferably 1 to 12% by weight, of the diester based on Swl.

The layer composed of the magnetic layer and the lower layer may contain monoester in an amount of 1 to 20 wt%, preferably 5
-15 wt%, more preferably 8-12 wt%, and preferably a monoester is contained in each of the magnetic layer and the lower layer.
Specifically, preferably, the magnetic layer is made of a monoester of Swd.
1 to 20% by weight, more preferably 5 to 15% by weight, and the lower layer contains 1 to 20% by weight of diester with respect to Swd.
%, More preferably 5 to 15% by weight. By setting the addition amount of the monoester and the diester to the above range, the object of the present invention can be more effectively achieved,
The resulting magnetic recording medium can have both excellent electromagnetic conversion characteristics and excellent running durability.

The dihydric alcohol which is a constituent material of the diester or monoester used in the present invention is HO-R ¹
-OH (R ¹ is - (CH ₂₎ n-or - (CH ₂₎ n- (or n represents the induced unsaturated bond which may contain a divalent group from 1 to 10),
Or-(CH ₂ CH (CH ₃ ))-).
R ² -COOH (R ² is a chain unsaturated hydrocarbon group having 12 to 26 carbon atoms.
The units to be bonded to both terminals of the dihydric alcohol may be the same or different).

Accordingly, the diester used in the present invention is preferably represented by the following general formula (1), and the monoester is preferably a compound represented by the following general formula (2). R ² —COO—R ¹ —OCO—R ² (1) R ² —COO—R ¹ —OH (2) (wherein, R ¹ and R ² are as defined above). the ^second chain unsaturated the chain-like hydrocarbon group, but may be linear or branched, R ² is preferably a straight-chain unsaturated, the case of formula (1), both R ² structure Are preferably the same. Further, as the unsaturated bond, any of a double bond and a triple bond may be used, but a double bond is preferable. The double bond may be either cis or trans.

The carbon number of R ² is 12 to 26, preferably 14 to 22, and more preferably 15 to 19. If the number of carbon atoms is less than 12, the volatility is high, so that it is volatilized from the surface of the magnetic layer during traveling, and the traveling is stopped. 26 carbon atoms
If it is larger, the mobility of the molecules will be low, so that the lubricant will not easily leach onto the surface of the magnetic layer, and the durability will be poor. n is 1
To 10 are preferred. When n is small, the running durability is poor, and when it is too large, the viscosity becomes high, which makes it difficult to use and the durability becomes poor.

The unsaturated fatty acid used in the diester or monoester of the present invention includes 4-dodecenoic acid,
-Dodecenoic acid, 11-dodesenic acid, cis-9-tridecenoic acid, myristoleic acid, 5-myristoleic acid, 6
-Pentadecenoic acid, 7-palmitoleic acid, cis-9
-Palmitoleic acid, 7-heptadecenoic acid, oleic acid, ellagic acid, cis-6-octadecenoic acid, tra
ns-11-octadecenoic acid, cis-11-eicosenoic acid, cis-13-docosenoic acid, 15-tetracosenoic acid, 17-hexacosenic acid, cis-9, cis-12
-Octadienoic acid, trans-9, trans-12
Octadienoic acid, cis-9, trans-11, t
ran-13-octadecatrienoic acid, cis-9,
cis-12, cis-15-octadecatrienoic acid,
Linear unsaturated fatty acids such as stearic acid, 5-methyl-
2-tridecenoic acid, 2-methyl-9-octadecenoic acid,
2-methyl-2-eicosenoic acid, 2,2-dimethyl-1
Examples include branched unsaturated fatty acids such as 1-eicosenoic acid.

The diol used for the diester or monoester of the present invention includes ethylene glycol, trimethylene glycol, 1,4-butanediol,
5-pentanediol, 1,6-hexanediol,
Linear saturated both-terminal diols such as 1,7-pentanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, propylene glycol, 1,2-butanediol, 1,3- Butanediol, 2,4-pentanediol, 2,2-dimethyl-
1,3-propanediol, 2,5-hexanediol, 2-ethyl-1,3-hexanediol, 3-methyl-1,6-hexanediol, 1-methyl-1,7-
Branched saturated diols such as pentanediol, 2,6-dimethyl-1,7-pentanediol, 1-methyl-1,8-nonanediol, 2-butene-1,4-diol,
2,4-hexadiene-1,6-dienediol, 3-
Linear unsaturated diols such as pentene-1,7-diol, 2-methyl-2-butene-1,4-diol,
2,3-dimethyl-2-butene-1,4-diol,
Examples include branched unsaturated diols such as 2,6-dimethyl-3-hexene-1,6-diol.

Of these, particularly preferred monoesters and diesters of the present invention are esters of linear unsaturated fatty acids. Specifically, myristoleic acid, 5-myristoleic acid, 7-palmitoleic acid, cis-9-palmitoleic acid, oleic acid, elaidic acid, cis-6-octadecenoic acid (petroceric acid), trans-6-octadecenoic acid (Petroseelaidic acid), trans-
11-octadecenoic acid (basenic acid), cis-11
Linear unsaturated fatty acids such as eicosenoic acid, cis-13-docosenoic acid (erucic acid), cis-9, cis-12-octadienoic acid (linoleic acid) and diethylene glycol, trimethylene glycol, 1,4-butanediol, Esters with 1,5-pentanediol, 1,6-hexanediol, 1,7-pentanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol and the like are preferred, and more preferred. The linear unsaturated fatty acid and 1,4-butanediol, 1,5-
Pentanediol, 1,6-hexanediol, 1,7
-Pentanediol, 1,8-octanediol, 1,
Esters with 9-nonanediol, 1,10-decanediol and the like. Specific examples include neopentyl glycol didecanoate, ethylene glycol dioleyl, and diesters described below. Examples of diesters are as follows.

D-1 C ₁₇ H ₃₃ COO (CH ₂ ) ₂ OCOC ₁₇ H ₃₃ D-2 C ₁₇ H ₃₃ COO (CH ₂ ) ₄ OCOC ₁₇ H ₃₃ D-3 C ₁₇ H ₃₃ COO (CH ₂ ) _{10 OCOC 17 H 33 D-4 C} 12 H 23 COO (CH 2) 2 OCOC 12 H 23 D-5 C 26 H 51 COO (CH 2) 2 OCOC 26 H 51 D-6 C 14 H 27 COOCH 2 CH = CHCH _{2 OCOC 14 H 27 D-7} C 17 H 33 COOCH 2 CH = CHCH 2 OCOC 17 H 33 Further, examples of monoesters is as follows.

M-1 C ₁₇ H ₃₃ COO (CH ₂ ) ₂ OH M-2 C ₁₇ H ₃₃ COO (CH ₂ ) ₄ OH M-3 C ₁₇ H ₃₃ COO (CH ₂ ) ₁₀ OH M-4 C _{12 H 23 COO (CH 2) 2} OH M-5 C 26 H 51 COO (CH 2) 2 OH M-6 C 14 H 27 COOCH 2 CH = CHCH 2 OH M-7 C 17 H 33 COOCH 2 CH = CHCH 2 OH In the present invention, it is preferable that a fatty acid is further contained as a lubricant in at least one of the lower layer and the upper layer, preferably both layers. The fatty acids include any other saturated and unsaturated fatty acids, including the unsaturated fatty acids used to form the diesters or monoesters described above.

The amount of the fatty acid used is preferably 1 to 50% by weight of the diester in both the magnetic layer and the lower layer.
More preferably, it is in the range of 5 to 30% by weight. The inclusion of a fatty acid is particularly effective when the magnetic head is of a contact stop / start type. The magnetic substance to be contained in the magnetic layer of the present invention uses high-output, fine particles of ferromagnetic metal powder or ferromagnetic hexagonal ferrite powder to achieve high capacity, but the ferromagnetic metal powder is mainly composed of Fe,
The average major axis diameter is preferably 0.15 μm or less, the crystallite size is preferably 80 to 180 °, and the ferromagnetic hexagonal ferrite powder preferably has an average plate diameter of 60 nm or less and a plate ratio of 2 to 6.

The shape of the magnetic recording medium of the present invention is arbitrary, but when it is a disk-shaped magnetic recording medium, it may be used in a recording / reproducing system having a rotation speed of 700 rpm or more, preferably 2000 to 5000 rpm. preferable. In the present invention, the merit of making the magnetic layer an ATOMM configuration is considered as follows.

(1) Improvement of electromagnetic conversion characteristics by making the magnetic layer thinner (2) Improvement of durability by stable supply of diester and monoester of the present invention (3) High output by smoothing of magnetic layer (4) ) Easy provision of required functions by separating the functions of the magnetic layer The electromagnetic conversion characteristics as described below can be greatly improved by the thin magnetic layer structure (1).

(1) Improvement of output in high frequency region by improvement of recording demagnetization characteristics (2) Improvement of overwrite (overwrite) characteristics (3) Ensuring window margin

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION

[Magnetic Layer] In the magnetic recording medium of the present invention, the lower layer and the magnetic layer may be provided on only one side or both sides of the support. After applying the lower layer, the upper and lower layers should be provided with a magnetic layer either when the lower layer is in a wet state (W / W = wet-on-wet method) or after drying (W / D = wet-on-dry method). Can be done. From the viewpoint of production yield, simultaneous or sequential wet coating is preferable, but in the case of a disk, coating after drying can be used sufficiently.
Simultaneous or sequential wet coating (W / W) with the multilayer structure of the present invention
Since the upper layer and the lower layer can be formed at the same time, a surface treatment step such as a calendering step can be effectively used, and the surface roughness of the magnetic layer can be improved even with an ultrathin layer. The coercive force Hc of the magnetic layer is 1
It is necessary to be 800 Oe or more, and it is preferable that Bm is 2000-5000G (Gauss) for ferromagnetic metal fine powder and 1000-3000G for hexagonal ferrite fine powder.

[Ferromagnetic Metal Fine Powder] The ferromagnetic metal powder used in the magnetic layer of the present invention is preferably a ferromagnetic alloy powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, T
i, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, S
n, Sb, Te, Ba, Ta, W, Re, Au, Hg,
Pb, Bi, La, Ce, Pr, Nd, P, Co, M
It may contain atoms such as n, Zn, Ni, Sr, and B. In particular, Al, Si, Ca, Y, Ba, La, N
Preferably, at least one of d, Co, Ni, and B is contained other than α-Fe, and more preferably, at least one of Co, Y, and Al is contained. The content of Co is preferably at least 0 at% and at most 40 at% with respect to Fe, more preferably at least 15 at% and at most 35 at%, more preferably 2 at% to 35 at%.
It is 0 atomic% or more and 35 atomic% or less. The content of Y is 1.
The content is preferably from 5 at% to 12 at%, more preferably from 3 at% to 10 at%, more preferably from 4 at% to 9 at%. Al is at least 5 atomic% and 30
Atomic% or less, preferably 10 atomic% or more and 20 atomic% or less, more preferably 12 atomic% or more and 18 atomic% or less.
Atomic% or less. 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, JP-B-44-14090, JP-B-45-183
No. 72, JP-B-47-22062, JP-B-47-22
No. 513, JP-B-46-28466, JP-B-46-3
8755, JP-B-47-4286, JP-B-47-1
No. 2422, JP-B-47-17284, JP-B-47-
18509, JP-B-47-18573, JP-B-39
-10307, JP-B-46-39639, U.S. Pat. Nos. 3,026,215, 3,303,341 and 3,100
194, 3242005 and 3389014.

The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. A ferromagnetic metal 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 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, and immersing in an organic solvent and then sending 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 was
When expressed in terms of specific surface area by the method, it is usually 45 to 80 m ² / g.
And preferably 50 to 70 m ² / g. 45m ²
If it is less than 80 m ² / g, the surface property is difficult to obtain, which is not preferable. The crystallite size of the ferromagnetic metal powder of the magnetic layer of the present invention is generally 80 to 180 °, preferably 100 to 180 °, more preferably 11 °.
0-175 °. The average 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 or more and 0.15 μm or less, and more preferably 0.03 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. Σs of the ferromagnetic metal powder is usually 100 to 180 emu / g, preferably 110 emu / g.
mu / g to 170 emu / g, more preferably 125 to 160 e
mu / g. The coercive force of ferromagnetic metal powder is usually 170
It is preferably from 0 Oe to 3500 Oe, more preferably from 1,800 Oe to 3000 Oe.

The water content of the ferromagnetic metal powder is 0.01 to 2%.
(Hereinafter, "%" means "% by weight")
Is preferred. Inclusion of ferromagnetic metal powder depending on the type of binder
The water content is preferably optimized. PH of ferromagnetic metal powder
Is preferably optimized by the combination with the binder used.
Good. The range is from 4 to 12, preferably from 6 to
It is 10. The ferromagnetic metal powder can be made of Al, S
surface treatment with i, P or their oxides
I don't care. The amount is 0.1 to 1 with respect to the ferromagnetic metal powder.
0%, surface treatment gives lubricant absorption such as fatty acids
Is 100 mg / m ^TwoThe following is preferred. Ferromagnetic metal powder
At the end there is no soluble Na, Ca, Fe, Ni, Sr, etc.
May contain machine ions. These are essentially none
Is preferable, but if it is 200 ppm or less, it particularly affects the characteristics.
It is rare to give. In addition, the ferromagnetic
It is preferable that the porous metal powder has few pores,
%, More preferably 5% by volume or less. Ma
Characteristics for particle size shown above
If it satisfies the requirements, it can be needle-shaped, rice-granular, or spindle-shaped.
Absent. The smaller the SFD of the ferromagnetic metal powder itself, the better
And 0.8 or less is preferable. Hc content of ferromagnetic metal powder
The cloth needs to be small. If the SFD is 0.8 or less,
If it is, the electromagnetic conversion characteristics are good, the output is high, and
Inversion is sharp, peak shift is small, and high density
Suitable for digital magnetic recording. Decrease Hc distribution
In order to achieve this, in ferromagnetic metal powder,
There are methods for improving the degree distribution and preventing sintering.

[Ferromagnetic Hexagonal Ferrite Powder] Examples of the hexagonal ferrite contained in the magnetic layer of the present invention include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and Co substitution. Specifically, magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel,
Further, a magnetoplumbite type barium ferrite and a strontium ferrite containing a part of a spinel phase, and the like, other than predetermined atoms, Al, Si, S,
Sc, 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, B, Ge, and Nb. Generally, Co-Zn, Co
-Ti, Co-Ti-Zr, Co-Ti-Zn, Ni-
Ti-Zn, Nb-Zn-Co, Sb-Zn-Co, N
Those substituted with an element such as b-Zn can be used. Some raw materials and production methods contain specific impurities. Particle size is usually 10 to 200 n in average plate diameter
m, preferably 60 nm or less, particularly preferably 10 nm or less.
４０40 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 2
6. 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 Tesla, it is preferable to set it to 2000 Oe or more. Hc
Can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions and the like. The saturation magnetization 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 material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. The main compound is S
Representative examples include oxides or hydroxides of i, Al, P, etc., various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% 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. A glass crystallization method of obtaining a barium ferrite crystal powder by washing and pulverizing after reheating and then barium ferrite-containing metal salt solution is neutralized with an alkali to remove by-products.
The liquid phase is heated at a temperature of at least 100 ° C. and then washed, dried and pulverized to obtain a barium ferrite crystal powder. There is a coprecipitation method in which the barium ferrite crystal powder is obtained by treating at a temperature of not more than ° C and pulverizing, but the present invention is not limited to a production method.

[Lower Layer] Next, the details of the lower layer will be described. The configuration of the lower layer of the present invention is not particularly limited as long as it is substantially non-magnetic. Examples include: 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.

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. As the inorganic compound, for example, α having an α conversion of 90% or more is used.
-Alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, silicon nitride,
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 and the like 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 particle size of these non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have the same effect by widening the particle size distribution. You can also. Particularly preferably, the particle size of the nonmagnetic powder is 0.01 μm to 0.2 μm.
μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle size is preferably 0.08 μm or less, and when the nonmagnetic powder is a needle-shaped metal oxide, the major axis length is preferably 0.3 μm or less, and 0.2 μm or less. Is more preferred. The tap density is 0.05-2 g / ml, preferably 0.2-1.5 g / ml. The water content of the nonmagnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.3 to 1.5% by weight.
% By weight. The pH of the nonmagnetic powder is usually from 2 to 11, but the pH is particularly preferably from 5.5 to 10. The specific surface area of the non-magnetic powder is generally 1 to 100 m ² / g, preferably 5 to 100 m ² / g.
８０80 m ² / g, more preferably 10-70 m ² / g. The crystallite size of the non-magnetic powder is preferably from 0.004 μm to 1 μm, more preferably from 0.04 μm to 0.1 μm. D
The oil absorption using BP (dibutyl phthalate) is usually 5
１００100 ml / 100 g, preferably 10-80 ml / 100 g, more preferably 20-60 ml / 100 g. Specific gravity is usually 1
-12, preferably 3-6. Needle-shaped, spherical,
Any of a polyhedral shape and a plate shape may be used. The Mohs' hardness is preferably 4 or more and 10 or less. The nonmagnetic powder has an SA (stearic acid) adsorption amount of 1 to 20 μmol / m ² , preferably 2 to ² μmol / m ² .
It is 15 μmol / m ² , more preferably 3 to 8 μmol / m ² . Preferably, the pH is between 3 and 6. Al ₂ O ₃ , SiO ₂ , Ti
O ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, Y ₂ O
It is preferable to perform the surface treatment in ₃ . Particularly preferred dispersibility _{Al 2 O 3, SiO 2,} TiO 2, is a ZrO _2, more preferred _{Al 2 O 3, SiO 2,} ZrO
₂ These may be used in combination or may be used alone. Further, a co-precipitated surface treatment layer may be used according to the purpose, or a method of first treating with alumina and then treating the surface layer with silica, or vice versa, may be employed. 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 and ZA-G1 manufactured by Sumitomo Chemical Co., Ltd., 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 reduce 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 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 / 100 g,
Preferably, it is 30 to 400 ml / 100 g. The particle size of the carbon black is usually 5 mμ to 80 mμ, preferably 10 mμ to 80 mμ.
It is 50 mμ, more preferably 10 to 40 mμ. The pH of carbon black is usually 2 to 10, and the water content is usually
Preferably, the tap density 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 BLACKPEARLS manufactured by Cabot Corporation.
2000, 1300, 1000, 900, 800, 88
0,700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050B, # 3150B, # 3250B, #
3750B, # 3950B, # 950, # 650B, #
970B, # 850B, MA-600, MA-230,
# 4000, # 4010, manufactured by Columbian Carbon
CONDUCTEX SC, RAVEN 8800,8
000,7000,5750,5250,3500,2
100, 2000, 1800, 1500, 1255, 1
250 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 lower layer based on the inorganic powder.
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).

Further, an organic powder can be added to the lower layer according to the purpose. 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.

For the binder resin, lubricant, dispersant, additive, solvent, dispersing method, etc. of the lower layer, those of the magnetic layer described below can be applied. In particular, binder resin amount, type, additives,
Known techniques for the magnetic layer can be applied to the amount and type of the dispersant. [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,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. In addition, as a thermosetting resin or a reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin,
Examples include epoxy-polyamide resins, mixtures of polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates. 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 detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resins,
A combination of at least one selected from vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer and a polyurethane resin, or a combination of these with a polyisocyanate Is raised.

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, Mitsubishi Kasei Co., Ltd., MX5004, Sanyo Chemical Co., Ltd. Samprene S
P-150, Saran F310, F210 manufactured by Asahi Kasei Corporation and the like.

The binder used in the lower layer and the magnetic layer of the present invention is used in a range of 5 to 50%, preferably 10 to 30% based on the nonmagnetic powder or the magnetic powder. It is preferable to use 5 to 30% when using a vinyl chloride resin, 2 to 20% when using a polyurethane resin, and 2 to 20% of a polyisocyanate in combination. When head corrosion occurs, 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, the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 1.
0 kg / mm ² , and the yield point is preferably 0.05 to 10 kg / mm ² .

The magnetic recording medium of the present invention can be composed of two or more lower layers and magnetic layers. The magnetic layer may be composed of a plurality of layers having different thicknesses, compositions, and the like. In the case of the ATOMM type, the total of the magnetic layers is preferably 0.5 μm or less. 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. Of course, it is possible to change the physical characteristics of the lower layer, the magnetic layer or each magnetic layer as necessary, and rather, it should be optimized in each layer,
Known techniques for the multilayer magnetic layer can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. The amount 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, #, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
900, # 1000, # 30, # 40, # 10B, manufactured by Columbian Carbon, CONDUCTEX SC, R
AVEN 150, 50, 40, 15, RAVE-M
TP, 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% of the amount based on the magnetic material. 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, the magnetic layer, its type in the lower layer,
Change the amount and combination, particle size, oil absorption, conductivity, pH
It is, of course, possible to selectively use them according to the purpose based on the above-mentioned various characteristics, but rather, it should be optimized in 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).

The abrasives used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, and carbonized material having an α conversion of 90% or more. 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 average particle size of these abrasives is 0.01
To 2 μm, more preferably 0.4 μm or less, 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. Tap density is 0.3-2g /
The water content is preferably 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specifically, AKP-12 and AKP-1 manufactured by Sumitomo Chemical Co., Ltd.
5, AKP-20, AKP-30, AKP-50, HI
T-20, HIT-30, HIT-55, HIT-6
0, HIT-70, HIT-80, HIT-100, manufactured by Reynolds, ERC-DBM, HP-DBM, HPS
-DBM, manufactured by Fujimi Abrasives, WA10000, manufactured by Uemura Kogyo Co., Ltd., UB20, manufactured by Nippon Kagaku Kogyo Co., Ltd., G-5, Chromex U2, Chromex U1, Toda Kogyo Co., Ltd., TF1
00, TF140, manufactured by IBIDEN, Beta Random Ultra Fine, manufactured by Showa Mining Co., Ltd., B-3, etc. These abrasives can be added to the lower layer as needed. By controlling the surface shape by adding to the lower layer,
For example, the projecting state of the abrasive can be controlled. The particle size and amount of the abrasive added to the magnetic layer and the lower layer should of course be set to optimal values.

[Additives] As additives used in the magnetic layer and the lower 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 graphite disulfide, 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 salts, alkyl sulfates and their alkali metal salts, polyphenyl ether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents , A titanium coupling agent, a fluorine-containing alkyl sulfate and an alkali metal salt thereof, a monobasic fatty acid having 10 to 24 carbon atoms (whether an unsaturated bond may be contained or branched. There), and, these metal salts (Li,
Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms (including unsaturated bonds and may be branched) , An alkoxy alcohol having 12 to 22 carbon atoms, 10 to 10 carbon atoms
24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and any one of mono-, tri-, tetra-, penta-, and hexa-hydric alcohols having 2 to 12 carbon atoms (Which may or may not contain an unsaturated bond), mono-fatty acid esters or poly-fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, carbon Aliphatic amines of the formulas 8 to 22 can be used in combination with the monoester and diester of the present invention.

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% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention each have different physical actions.
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 lubrication effect is improved by increasing the stability of the intermediate layer and by increasing the amount of the lubricant added in the intermediate 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 selected in the range of 0.1% to 50%, preferably 2% to 25% based on the magnetic powder or the non-magnetic powder.

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. 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 for improving adhesion may be provided between the support and the lower layer or the magnetic layer. This undercoat layer thickness is 0.01 to 0.5 μm, preferably 0.02 to 0.5 μm
It is.

The disk-shaped magnetic recording medium is usually provided with coating layers on both sides of the support in order to maintain its planarity. In the case of a single-sided recording medium, a coating layer having the same composition as the magnetic layer may be provided on the back surface, or a well-known back coat layer of a tape-shaped medium may be provided. The thickness of the back coat layer is usually 0.1 to 4 μm, preferably 0.3 to 4 μm.
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 depending on the saturation magnetization of the head used, the head gap length, and the band of the recording signal.
50 μm or less, preferably 0.1 μm or more and 0.3
0 μm or less. The magnetic layer having different magnetic properties 2
It does not matter if it is separated into layers or more, and a known configuration relating to a multilayer magnetic layer can be applied.

The thickness of the lower layer of the medium according to the present invention is 0.2 μm.
m to 5.0 μm, preferably 0.3 μm to 3.
0 μm or less, more preferably 1.0 μm or more and 2.5 μm
m or less. Incidentally, the lower layer of the medium of the present invention exhibits its effect if it is substantially non-magnetic.
It shows the effect of the present invention, and it goes without saying that the configuration can be regarded as substantially the same as 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 includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, polyaramide, and aromatic polyamide. And known films such as polybenzoxazole. 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, mir of TOPO-3D, a surface roughness meter manufactured by WYKO, is used.
The center plane average surface roughness Ra measured by an au method in an area of about 250 μm × 250 μm is preferably 8.0 nm or less, more preferably 4.0 nm or less, and particularly preferably 2.0 nm or less. It is preferable that these supports not only have a small center plane average surface roughness but also have no coarse protrusions of 0.5 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 oxides and carbonates such as Ca, Si and Ti, and organic fine powders such as acryl.
The maximum height SRmax of the support is 1 μm or less, and the ten-point average roughness S
Rz is 0.5 μm or less, and peak height of the center plane is SRp 0.5 μm.
Hereinafter, it is preferable that the center plane valley depth SRv is 0.5 μm or less, the center plane area ratio SSr is 10% or more and 90% or less, and the average wavelength Sλa is 5 μm or more and 300 μm or less. In order to obtain desired electromagnetic conversion characteristics and durability, the distribution of surface projections of these supports can be arbitrarily controlled by a filler.
It can be controlled in the range of 0 to 2000 per mm ² .

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² ,
The heat shrinkage rate per minute is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. The breaking strength is 5-100 kg / mm ² , and the elastic modulus is 100-2000.
Kg / mm ² is preferred. The coefficient of thermal expansion is 10 ^-4 to 10 ^-8 / ° C.
And preferably 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 paint 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.
% Or more) and 15 parts per 100 parts of magnetic powder.
The kneading process is performed in a range of up to 500 parts. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-106338.
79274. Glass beads can be used to disperse the magnetic layer solution and the lower layer solution, and zirconia beads, titania beads, and steel beads, which are dispersion media having a high specific gravity, 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, there is a method of coating the upper layer by a support pressurization type extrusion coating apparatus. Secondly, Japanese Patent Application Laid-Open Nos. 63-88080, 2-17971 and 2-265672 Japanese Patent Application Laid-Open No. 2-174965 discloses a method of applying upper and lower layers almost simultaneously using one coating head having two built-in coating liquid passage slits. This is a method in which the upper and lower layers are applied almost simultaneously by a lubrication coating apparatus. Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open Nos.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in 236968.
Further, regarding the viscosity of the coating solution, see Japanese Patent Application Laid-Open No. 3-8471.
It is necessary to satisfy the numerical range disclosed in US Pat. To realize the configuration of the present invention, after applying and drying the lower layer,
It goes without saying that a sequential multilayer coating in which a magnetic layer is provided thereon may be used, 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, a cobalt magnet may be alternately arranged diagonally, or an alternating magnetic field may be applied by a solenoid. 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.

A calendering roll is treated with a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll.
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 preferably 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. . Coercive force Hc and Hr are 1500 Oe or more and 5000
Oe or less, preferably from 1700 Oe to 30
00 Oe or less. The distribution of coercive force is preferably narrow, and SFD and SFDr are preferably 0.6 or less. The squareness ratio is 0.55 or more and 0.67 or less in the case of two-dimensional random, preferably 0.58 or more and 0.64 or less. In the case of three-dimensional random, it is preferably 0.45 or more and 0.55 or less. The orientation is 0.6 or more, preferably 0.7 or more in the vertical direction, 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, the squareness ratio in the vertical direction, Br, Hc and Hr
Is preferably within 0.1 to 0.5 times the in-plane direction.

The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is -10 ° C. to 40 ° C., and the humidity is 0% to 95%.
0.5 or less, preferably 0.3 or less, and the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / s.
q, the charge potential is preferably within the range of -500V to + 500V.
Preferably 100 to 2,000 kg / mm ² in elastic modulus plane directions at 0.5% elongation of the magnetic layer, the breaking strength is preferably 10 to 70 kg / mm ^2, the modulus of elasticity of the magnetic recording medium is plane directions in preferably 100 to 1,500 / mm ^2, the residual elongation is preferably 0.5% or less, the thermal shrinkage rate at all temperatures 100 ° C. or less, preferably 1% or less, more preferably 0.5% or less, most preferably Is 0.1% or less. The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is 50 ° C or more and 120 ° C or more.
C. or lower, and that of the lower layer is preferably from 0.degree. Loss modulus is 1 × 10 ⁶ 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 lower layer and the magnetic layer. The porosity is preferably small to achieve high output,
Depending on the purpose, it may be better to secure a certain value.
For example, in a disk medium in which repeated use is emphasized, a larger porosity is often preferable in running durability.

The center plane average surface roughness Ra of the magnetic layer is WYC
Approximately 250 using the Mirau method of TOPO-3D manufactured by Company O
Usually, it is 4.0 nm or less, preferably 3.8 nm or less, and more preferably 3.5 nm or less when measured in an area of μm × 250 μm.
nm or less. The maximum height SRmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness SRz is 0.3 μm or less, the center plane height SRp is 0.3 μm or less, and the center plane valley depth SRv is 0.3 μm.
Hereinafter, the center plane area ratio SSr is 20% or more and 80% or less,
The average wavelength Sλa is preferably 5 μm or more and 300 μm or less. 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.

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

[0084]

Examples <Preparation of paint> Upper paint A Ferromagnetic metal fine powder 100 parts Composition: 70% Fe, 30% Co (atomic ratio) Hc: 2300 Oe Average major axis diameter: 0.10 μm Crystallite size: 145 ° σs: 150 emu / g Sintering inhibitor Al compound (Al / Fe atomic ratio 12%) Y compound (Y / Fe atomic ratio 6%) Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 4 Part α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 5 parts Carbon black # 50 (manufactured by Asahi Carbon Co., Ltd.) 1 part phenylphosphonic acid 3 parts butyl stearate 4 parts butoxyethyl stearate 4 parts Diester of Table 1 or 2 Table 1 or 2 Description Monoester of Table 1 or 2 Description of Table 1 or 2 Stearic acid 1 part Oleic acid 1 part Methyl ethyl ketone 14 Part Cyclohexanone 200 parts Upper coating B Same composition as upper coating A except that the average major axis diameter of the ferromagnetic metal fine powder was changed to 0.065 μm and the crystallite size was changed to 110 °. Upper coating C: average long axis of ferromagnetic metal fine powder The same composition as the upper layer paint A except that the diameter was changed to 0.15 μm and the crystallite size was changed to 180 °. Upper layer paint D Barium ferrite magnetic powder 100 parts: Ba molar ratio composition: Fe 9.10, Co 0.20, Zn 0.77 Hc 2500 Oe, Specific surface area 50 m ² / g, σs 58 emu / g Average plate diameter 35 nm, Plate ratio 4 Vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) 6 parts Polyurethane resin UR8200 (manufactured by Toyobo) 3 parts α-alumina HIT55 (Sumitomo Chemical Co., Ltd.) 5 parts Carbon black # 50 (manufactured by Asahi Carbon Co., Ltd.) 1 part Phenylphosphonic acid 3 parts Butyl stearate 4 parts Butoxy Chill stearate 4 parts Diester of Table 2 Monoester of Table 2 Monoester of Table 2 Table 2 Stearic acid 1 part Oleic acid 1 part Methyl ethyl ketone 125 parts Cyclohexanone 125 parts Top coating E Barium ferrite magnetic powder has an average plate diameter of 20 nm and a plate diameter. The same composition as the upper coating D except that the composition was changed to 3. Upper coating F The same composition as the upper coating D except that the average plate diameter of the barium ferrite magnetic powder was changed to 50 nm and the plate diameter to 5. Lower coating 1 Non-magnetic powder TiO _2- crystal rutile 100 parts Average primary particle diameter 0.035 μm, specific surface area 40 m ² / g pH 7 TiO ₂ content 90% or more, DBP oil absorption 27-38 g / 100 g, surface treatment agent Al ₂ O ₃ , SiO ₂ -Bon Black Ketjen Black EC 13 parts Vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 17 parts Polyurethane Fat UR8600 (manufactured by Toyobo) 6 parts Phenylphosphonic acid 3 parts n-butyl stearate 5 parts Butoxyethyl stearate 5 parts Diester of Table 1 or 2 Table 1 or 2 Monoester of Table 1 or 2 Table 1 or 2 Oleic acid 1 part Stearic acid 1 part Methyl ethyl ketone 120 parts Cyclohexanone 180 parts Lower layer paint 2 Non-magnetic powder α-Fe ₂ O ₃ hematite 100 parts Long axis 0.15 μm, BET specific surface area 50 m ² / g pH 9 Surface treatment agent Al ₂ O ₃ 8% by weight Carbon black Conductex SC-U (manufactured by Columbian Carbon Co.) 18 parts Vinyl chloride copolymer MR110 (vinyl chloride copolymer) 16 parts Polyurethane resin UR8200 (manufactured by Toyobo Co., Ltd.) 7 parts phenylphosphonic acid 4 parts butyl stearate 5 parts butoxyethyl 5 parts of diester of Table 2 List of monoester of Table 2 List of monoester of Table 2 List of Table 2 Stearic acid 1 part Oleic acid 1 part Methyl ethyl ketone 140 parts Cyclohexanone 200 parts For each of the above coating materials, each component is kneaded with a kneader and then sand milled. And dispersed. 10 parts of polyisocyanate was added to the resulting dispersion,
To the coating liquid for the magnetic layer, 10 parts were added, and 40 parts of cyclohexanone was further added to each, followed by filtration using a filter having an average pore diameter of 1 μm to prepare coating liquids for forming the lower layer and for forming the magnetic layer, respectively.

The obtained lower layer coating liquid was applied to a thickness of 62 μm so as to have a thickness of 1.5 μm after drying, and immediately thereafter, a thickness of 62 μm so that the thickness of the magnetic layer was 0.15 μm thereon. Polyethylene terephthalate having a surface average surface roughness of 3 nm
After the two layers are simultaneously coated on the support, while both layers are still in a wet state, they are passed through an AC magnetic field generator at a frequency of 50 Hz and a magnetic field strength of 250 gauss, subjected to random orientation treatment, dried, and dried. 90 temperature in the stage calendar
C. and a linear pressure of 300 kg / cm, punched into a 3.7-inch cartridge, and placed in a 3.7-inch cartridge (zip-disk cartridge manufactured by Iomega, USA) with a liner installed inside, and specified mechanical parts Was added to obtain a 3.7 inch floppy disk. However, the lower layer and the magnetic layer were coated and treated in the same manner as described above, respectively, on the back surface of the support using a coating solution having the same formulation as above, to provide magnetic layers on both surfaces.

[0086] If necessary, after punching into a disk shape, a high temperature thermo-treatment (usually 50 ° C to 90 ° C) is performed to accelerate the curing of the coating layer. Post-processing such as shaving of the projections may be performed. Sample Nos. 1 to 25 were prepared according to the changing factors described in Tables 1 and 2. Sample Nos. 15 to 19 are
It was a single layer of only the upper layer paint.

The samples obtained were evaluated as follows and are shown in Tables 1 and 2. The diesters used are as follows. _{D-1 C 17 H 33 COO} (CH 2) 2 OCOC 17 H 33 D-2 C 17 H 33 COO (CH 2) 4 OCOC 17 H 33 D-3 C 17 H 33 COO (CH 2) 10 OCOC 17 H _{33 D-4 C 12 H 23} COO (CH 2) 2 OCOC 12 H 23 D-5 C 26 H 51 COO (CH 2) 2 OCOC 26 H 51 Further, monoester used were as follows.

M-1 C ₁₇ H ₃₃ COO (CH ₂ ) ₂ OH M-2 C ₁₇ H ₃₃ COO (CH ₂ ) ₄ OH M-3 C ₁₇ H ₃₃ COO (CH ₂ ) ₁₀ OH M-4 C ₁₂ H ₂₃ COO (CH ₂ ) ₂ OH M-5 C ₂₆ H ₅₁ COO (CH ₂ ) ₂ OH Reproduction output / S / N measurement The output / S / N measurement was performed by RWA1 manufactured by GUZK in the United States.
001 type disk evaluation device and Kyodo Electronic System Co., Ltd.
With a gap length of 0.3μ
m metal in gap head, radius 24.6mm
At the position of, the reproduction output (TAA) at a linear recording density of 90 kbpi and the noise level after DC erase were measured,
The reproduction output / S / N value was determined. Evaluation of running durability Floppy disk drive (manufactured by Imega in the United States)
Radius 38 using ZIP100: rotation number 2968 rpm)
After the head was fixed at the mm position and recording was performed at a recording density of 34 kbpi, the signal was reproduced and set to 100%. afterwards
The vehicle was run for 1500 hours in a thermocycle environment in which the following flow was defined as one cycle. The output was monitored every 24 hours of running, and the point when the output became 70% or less of the initial value was regarded as NG. "Thermo cycle flow" 25 ° C, 50% RH 1 hour → (Temperature rise 2 hours) → 60 ° C, 20% RH 7 hours →
(Temperature drop 2 hours) → 25 ° C., 50% RH 1 hour → (Temperature drop 2 hours) → 5 ° C., 50% RH 7 hours → (Temperature rise 2
Time) → <Repeat this> Liner wear evaluation Run the sample for 1000 hours in the same environment as the running durability with the head off, open the cartridge case after running the completed sample, and visually observe the magnetic layer surface of the magnetic disk Was evaluated.

：: No defect on the magnetic layer surface Δ: Fine scratches on a part of the magnetic layer surface ×: Fine scratches on the entire magnetic layer surface Evaluation of liner adhesion Head-off state In the same environment as the running durability, the sample was run for 1000 hours. After running the completed sample, the cartridge case was opened and the magnetic layer surface of the magnetic disk was visually observed for evaluation.

：: No defect on the surface of the magnetic layer Δ: A liner adhered to a part of the surface of the magnetic layer ×: A liner adhered to the entire surface of the magnetic layer

[0091]

[Table 1]

[0092]

[Table 2]

[0093]

The present invention is particularly applicable to a magnetic layer composition containing a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder of a fine particle magnetic substance, or preferably, to a magnetic layer comprising a substantially non-magnetic underlayer. With the ATOMM configuration provided and the magnetic layer thickness as thin as 0.5 μm or less, excellent electromagnetic conversion characteristics suitable for high-density recording are ensured, and diesters and monoesters of dihydric alcohol and unsaturated fatty acids are used. By including a predetermined amount in both layers, a magnetic recording medium having extremely excellent running durability can be provided.

Claims (2)

[Claims] In a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder formed on a support, a diester of a dihydric alcohol and an unsaturated fatty acid is contained in the magnetic layer. A magnetic recording medium comprising a monoester in which only one hydroxyl group of a polyhydric alcohol is esterified with an unsaturated fatty acid. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is used in a recording / reproducing system having a rotation speed of 700 rpm or more and has a disk shape.