JP2002050023A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a magnetic recording medium having excellent running durability and excellent electromagnetic transducing characteristics which are compatible with each other. SOLUTION: A magnetic layer 3 including pigment having Mohs' hardness of >=3 and <6 and an abrasive is formed on a non-magnetic substrate 1, wherein R>=M and R>r are specified to be satisfied when the mean particle size of the pigment, the mean particle size of the abrasive and the thickness of the magnetic layer 3 are defined as R, r and M, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer, and more particularly, to a magnetic recording medium for broadcasting and computers, such as digital video tapes and data cartridges, which require high reliability. Type magnetic recording medium.

[0002]

2. Description of the Related Art In recent years, magnetic recording media having a magnetic layer containing a magnetic metal powder as a ferromagnetic powder on a non-magnetic support have been actively developed. This magnetic recording medium aims to realize high-density recording by thinning the magnetic layer to minimize self-demagnetization loss, film thickness loss, and the like, and by smoothing the surface of the magnetic layer.

However, when the thickness of the magnetic layer is reduced, the surface shape of the non-magnetic support tends to appear on the surface of the magnetic layer, so that it is difficult to smooth the surface of the magnetic layer. In order to solve such a problem, a magnetic recording medium in which the surface smoothness of a magnetic layer is improved by interposing an undercoat layer between a nonmagnetic support and a magnetic layer has been disclosed in JP-A-57-198536. Is disclosed.

In addition, when a magnetic layer is formed on a non-magnetic support having no coarse protrusions and excellent in smoothness, and the surface of the magnetic layer is intended to be smooth, the winding property of the original tape is deteriorated. Process suitability cannot be satisfied. Therefore, a magnetic recording medium having improved running properties and durability by providing a large number of uniform protrusions on a non-magnetic support has been disclosed in Japanese Patent Laid-Open Publication No. Hei.
176807.

[0005]

However, the magnetic layer,
The thinner the film, the lower the strength and the more likely it is to peel off. The peeling that occurs on the magnetic layer causes dropout, and thus must be reliably prevented. As a method for preventing the peeling of the magnetic layer, there is a wet-on-wet method in which the magnetic layer is formed by applying a magnetic paint while the undercoat layer formed by applying the paint on the non-magnetic support is wet. By a coating method, a magnetic layer is formed on the undercoat layer,
There is a method for improving the adhesion between the magnetic layer and the undercoat layer.

As a method for preventing peeling of the magnetic layer, there is a method of adding a non-magnetic pigment to the magnetic layer to increase the strength of the magnetic layer and improve running durability.

However, when the magnetic layer contains an excessive amount of non-magnetic pigment, the strength of the magnetic layer is increased but the filling degree of the ferromagnetic powder is reduced, so that the output of the magnetic recording medium is reduced and the electromagnetic conversion characteristics are reduced. Had deteriorated. That is, there is a problem that the running durability cannot be improved and high-density recording cannot be achieved.

Further, when the magnetic layer contains an excessive amount of non-magnetic powder, the surface roughness of the magnetic layer becomes large, so that the polishing force on the magnetic head is increased and the magnetic head may be damaged. In particular, magnetic recording media such as magnetic disks and data cartridges having a large capacity for computers are repeatedly recorded and reproduced. Therefore, in order to prevent the magnetic head from being damaged, it has been required that the polishing force of the magnetic recording medium on the magnetic head be as small as possible.

The present invention has been proposed in view of such conventional circumstances, and has as its object to provide a magnetic recording medium having excellent running durability and excellent electromagnetic conversion characteristics. I do.

[0010]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted various studies. As a result, the magnetic layer contains an abrasive and a specific pigment in combination. It has been found that even if the magnetic layer contains a non-magnetic pigment, output deterioration does not occur and a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability can be obtained.

The present invention has been completed based on such findings, and in a magnetic recording medium comprising a nonmagnetic support and a magnetic layer containing a ferromagnetic powder and a binder, the magnetic layer , Containing a pigment having a Mohs hardness of 3 or more and less than 6 and an abrasive, the average particle diameter of the pigment being R, the average particle diameter of the abrasive being r, and the thickness of the magnetic layer being M, ≧ M and R> r.

The strength of the magnetic layer can be enhanced by including a combination of a pigment having a Mohs hardness of 3 or more and less than 6 and having an average particle size satisfying R ≧ M and R> r, and an abrasive. And the polishing force on the magnetic head is optimized.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail.

A magnetic recording medium according to the present invention includes a non-magnetic support, an intermediate layer formed on one main surface of the non-magnetic support, and a magnetic layer formed on the intermediate layer. .

The magnetic layer is formed by applying a magnetic paint prepared by mixing a ferromagnetic powder and a binder on the intermediate layer. The magnetic layer contains a pigment having a Mohs' hardness of 3 or more and less than 6, and an abrasive. The average particle diameter of the pigment is R, the average particle diameter of the abrasive is r, and the thickness of the magnetic layer is Is M, R ≧ M and R> r.

The pigment has a Mohs hardness of 3 or more and less than 6, and is a particle softer than an abrasive, so that it does not polish the magnetic head. In addition, since the average particle size of the pigment is equal to or larger than the thickness of the magnetic layer and larger than the average particle size of the abrasive, the magnetic head contacts the pigment and then the abrasive during recording and reproduction. That is, the pigment is
It serves as a cushion for buffering the contact between the magnetic head and the abrasive during recording and reproduction, and the abrasive buffers the polishing force for polishing the magnetic head.

As described above, the strength of the magnetic layer can be reduced by containing the pigment in which the Mohs' hardness is 3 or more and less than 6 and R ≧ M and R> r in combination with the abrasive. As a result, the polishing force for the magnetic head is optimized.

When the Mohs hardness of the pigment is less than 3, the pigment itself is destroyed by sliding with the magnetic head. If the Mohs hardness of the pigment exceeds 6, the pigment itself will polish the magnetic head.

The average particle size of the pigment having a Mohs' hardness of 3 or more and less than 6 means that the magnetic tape has a thickness of 7 mm in the longitudinal direction.
The cross section obtained by cutting at 00 ° is applied with an applied voltage of 200K.
V: Average value of 500 or more samples randomly selected when observed using a transmission electron microscope with a magnification of 60000.

The thickness of the magnetic layer, that is, M is preferably 0.03 μm or more and 0.3 μm or less, and 0.05 μm or less.
m or more, more preferably 0.3 μm or less,
Most preferably, it is 0.05 μm or more and 0.2 μm or less. If M exceeds 0.3 μm, the electromagnetic conversion characteristics may be degraded due to self-demagnetization loss and film thickness loss.

Pigments having a Mohs hardness of 3 or more and less than 6 include carbon black, graphite, calcium carbonate, antimony, fluorite, barite, silver, dolomite, copper, magnesium oxide, platinum, palladium, opal, and the like. Iron, asbestos, manganese, apatite, nickel and the like can be used.
Further, the average particle size of the pigment having a Mohs hardness of 3 or more and less than 6, that is, R, is preferably 0.03 μm or more and 0.3 μm or less. When R exceeds 0.3 μm, the electromagnetic conversion characteristics may be deteriorated.

Among these pigments, it is particularly preferable to use carbon black having an average particle size of 0.03 μm or more and 0.3 μm or less. As such carbon black, Asahi Carbon Black's # 60 (51
nm), $ 55 (77 nm), thermal (90 nm),
# 50 (94 nm), # 35 (115 nm), Diablack G (84 nm) manufactured by Mitsubishi Kasei, Regal SRF-S (60 nm) manufactured by Cabot, Stirling NS
(75 nm), HS100 (53n) manufactured by Denki Kagaku
m), MT-CI (270 nm) manufactured by SEBA CARBON, or the like can be used.

By including carbon black or graphite in the magnetic layer, an effect of preventing the magnetic layer from being charged can be obtained.

As the polishing agent, Mohs hardness of 6 or more, 1
0 or less, specifically α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, tungsten carbide, molybdenum carbide, boron carbide,
Corundum, zinc oxide, cerium oxide, magnesium oxide, boron nitride and the like can be used.

The average particle size of the abrasive, that is, r, is not particularly limited as long as the relationship of R> r is satisfied.
It is preferable that it is not less than 03 μm and not more than 0.2 μm.

The weight ratio of the abrasive is preferably 6 or more and 20 or less for the pigment having a Mohs hardness of 3 or more and less than 6 contained in the magnetic layer.

When the weight ratio of the abrasive to the pigment having a Mohs hardness of 3 or more and less than 6 is less than 6, the abrasive power for the magnetic head is insufficient, and there is a possibility that head clogging and output reduction may occur. On the other hand, if the weight ratio of the abrasive exceeds 20, the polishing power on the magnetic head is too large, and the magnetic head may be damaged.

As the ferromagnetic powder, Fe, Co, Fe-
Al-based, Fe-Al-Ni-based, Fe-Al-Zn-based, F
e-Al-Co system, Fe-Al-Ca system, Fe-Ni
System, Fe-Ni-Co system, Fe-Ni-Si-Al-M
n-based, Fe-Ni-Si-Al-Zn-based, Fe-Al-
Si-based, Fe-Ni-Zn-based, Fe-Ni-Mn-based, F
e-Ni-Si system, Fe-Mn-Zn system, Fe-Co-
It is possible to use a magnetic metal powder such as a Ni-P-based material mainly containing Fe, Ni or Co.

Among these ferromagnetic powders, it is particularly preferable to use an Fe-based metal magnetic powder having excellent electric characteristics. Further, among these ferromagnetic powders, Fe-Al-based and Fe-Al-Ca excellent in corrosion resistance and dispersibility are excellent.
System, Fe-Al-Ni system, Fe-Al-Zn system, Fe-
Al-Co system, Fe-Ni-Si-Al-Zn system, Fe
It is preferable to use Fe-Al-based metal magnetic powder such as -Ni-Si-Al-Mn-based.

The content of Al contained in the metallic magnetic powder mainly composed of Fe is expressed by weight ratio of Fe: Al = 100: 0.
Preferably, the ratio is 5 to 100: 20. The content of Ca is Fe: Ca = 100: 0.1 to 10 by weight.
It is preferably 0:10.

By setting the Al content within the above range, the corrosion resistance is remarkably improved. Further, by setting the content of Ca to the ratio in the above range, the dispersibility of the metal magnetic powder is improved, so that the coercive force is improved and the aggregates are reduced, the electromagnetic conversion characteristics are improved, and the dropout is reduced. Decrease.

It is preferable that the metal magnetic powder contains Fe and Al and at least one of rare earth elements such as Sm, Nd, Y, Pr, and La. A
The content of Al and the rare earth element is such that the Al content is 1 to 100 parts by weight of Fe contained in the metal magnetic powder.
It is preferable that the content of the rare earth element is 1 part by weight to 16 parts by weight. Further, regarding the atomic ratio of Al and rare earth elements on the surface of the metal magnetic powder, the number of Al atoms is 70 to 300, and the number of rare earth elements is 0.5 to 0.5 with respect to 100 Fe atoms.
It is preferably from 100 to 100.

Furthermore, the metal magnetic powder preferably contains at least one of Fe, Al, and rare earth elements such as Sm, Nd, Y, Pr, and La, and preferably contains Na and Ca. The content of Al and rare earth elements, Na and Ca is 2 parts by weight to 10 parts by weight with respect to 100 parts by weight of Fe contained in the metal magnetic powder, and the content of rare earth element is 1 part by weight. It is preferable that the content of Na is less than 0.1 part by weight, and the content of Ca is 0.1 part by weight to 2 parts by weight.
In addition, Al, rare earth elements on the surface of the metal magnetic powder,
As the atomic ratio of Na and Ca, the number of Fe atoms is 1
On the other hand, the number of atoms of Al is 70 to 200, the number of atoms of the rare earth element is 0.5 to 30, the number of atoms of Na is 2 to 30, and the atomic weight of Ca is 5 to 30. Is preferred.

Further, the metallic magnetic powder may be Fe, A
l, at least one element selected from the group consisting of rare earth elements such as Sm, Nd, Y, Pr, and La; Na and Ca;
And at least one of Ni and Si. The content of Al is 1 to 20 parts by weight, and the content of rare earth element is 1 to 16 parts by weight with respect to 100 parts by weight of Fe contained in the metal magnetic powder. The content of Na is less than 0.1 part by weight, the content of Ca is 0.1 to 2 parts by weight, the content of Co is 2 to 40 parts by weight,
Is preferably 2 to 20 parts by weight, and the Si content is preferably 0.3 to 5 parts by weight. In addition, Al, rare earth element, N on the surface of the metal magnetic powder
a, Ca, and the atomic ratio of at least one of Co, Ni, and Si, the number of atoms of Al is 70 to 300, and the number of atoms of the rare earth element is 0.1 to 100 for the number of atoms of Fe. 5 to 100, and the number of atoms of Na is 2 to 3
0, the atomic weight of Ca is 5 to 30, the atomic number of Co is less than 0.1, the atomic number of Ni is less than 0.1, and the atomic number of Si is 20 to 130. preferable.

The average major axis length of the ferromagnetic powder is 0.03 μm
0.15 μm, preferably 0.05 μm
More preferably, it is 0.12 μm. Further, the X-ray particle size of the ferromagnetic powder, that is, the crystallite size is preferably less than 20 nm, and more preferably 5 nm to 17 nm. Further, the axis ratio of the ferromagnetic powder is preferably 12 or less, more preferably 10 or less, and 4 or less.
Most preferably, it is from 9 to 9. When the average major axis length, crystallite size, and axial ratio of the ferromagnetic powder are in the above ranges, high-frequency characteristics, particularly output of a perpendicular recording component, can be increased.

As the average major axis length and average minor axis length of the ferromagnetic powder, the average value of the major axis length per 500 particles randomly selected from a transmission electron micrograph is adopted. In addition, the axial ratio is a ratio of the average major axis length to the average minor axis length. In addition, the crystallite size is obtained by measuring the (110) diffraction line of Fe using an X-ray diffractometer and calculating the S
It is measured by the Scherrer method based on i powder. In addition, as a method of obtaining, the spread of double lines was corrected by A. Jones correction (integral width) by the method described in the X-ray diffraction guide (Rigaku Denki Co., Ltd.).

The coercive force of the ferromagnetic powder is from 600 Oe to 50
It is preferably 00Oe. If the coercive force is less than 600 Oe, the electromagnetic conversion characteristics may deteriorate,
If the coercive force exceeds 5000 Oe, recording may not be possible with a normal magnetic head.

Further, the saturation magnetization of the ferromagnetic powder (hereinafter referred to as
Called σ _s . ) Is preferably 120 emu / g or more, more preferably 130 emu / g to 170 emu / g. Furthermore, the specific surface area of the ferromagnetic powder measured by the Brunauer-Emmett-Teller method is preferably 30 m ² / g or more, more preferably 45 m ² / g or more.

As the binder contained in the magnetic layer, a conventionally known resin used as a binder for a magnetic recording medium can be used, and specifically, a vinyl chloride copolymer,
Resins such as polyester, polyurethane, phenoxy resin and cellulose resin can be used. The weight average molecular weight of these resins is preferably from 15,000 to 50,000.

The content of the binder in the magnetic layer is preferably from 10 to 40 parts by weight, more preferably from 15 to 30 parts by weight, based on 100 parts by weight of the ferromagnetic powder.
In addition, one of the above resins may be used alone as a binder, or two or more may be used in combination. When two or more kinds are used in combination, the weight ratio between the polyurethane and / or polyester and the vinyl chloride-based copolymer is preferably from 90:10 to 10:90, and more preferably from 70:30 to 30:70. Is more preferable.

These resins used as binders include -SO ₃ M, -OSO ₃ M, -COOM, -P = O
It is preferable to introduce at least one kind of polar group among (OM ₁ ) ₂ and —OPO (OM ₁ ) ₂ (where M represents a hydrogen atom or an alkali metal such as lithium, potassium, and sodium. Wherein M ₁ represents a hydrogen atom or an alkali metal such as lithium, potassium, or sodium, or an alkyl group.) The resin having the polar group introduced therein improves the dispersibility of a non-magnetic pigment such as a non-magnetic powder.

The amount of these polar groups introduced into the binder is 0.1 mmol based on the weight of the resin used as the binder.
/ G to 8.0 mmol / g, preferably 0.1 mmol / g to 8.0 mmol / g.
More preferably, it is 5 mmol / g to 6.0 mmol / g. When the introduction amount of the polar group is less than 0.1 mmol / g, the dispersibility of the ferromagnetic powder may be reduced. On the other hand, when the introduction amount of the polar group exceeds 8.0 mmol / g, the magnetic coating material may be easily gelled.

The polar group-containing chloride into which these polar groups are introduced
The vinyl copolymer is, for example, vinyl chloride-vinyl alcohol.
Having a hydroxyl group, such as
H_TwoCH_TwoSO_ThreeM or Cl-CH_TwoCH_TwoOSO_TwoM, Cl-
CH_TwoCOOM, Cl-CH _Two−P (= O) (OM₁)_Twoetc
Reaction with a compound containing a polar group and a chlorine atom
Synthesize more.

For example, as a copolymer having a hydroxyl group,
And CH ₂ C (OH) H-, by addition reaction of ClCH ₂ CH ₂ SO ₃ Na as a compound containing a polar group and a chlorine _{atom, -CH 2 C (OCH 2 CH} 2 SO 3 Na) H- synthetic Is done.

The vinyl chloride copolymer containing a polar group is prepared by introducing a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced into a reaction vessel such as an autoclave or the like. It is synthesized by performing a polymerization reaction using a polymerization initiator such as a radical polymerization initiator such as azobisisobutyronitrile, a redox polymerization initiator, and a cationic polymerization initiator.

As the reactive monomer for introducing sulfonic acid or a salt thereof, unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid and salts thereof are used. It is possible.

When introducing a carboxylic acid or a salt thereof,
For example, when (meth) acrylic acid or maleic acid is used and phosphoric acid or a salt thereof is introduced, for example, (meth) acrylic acid-2-phosphate may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. A vinyl chloride copolymer into which an epoxy group has been introduced has excellent thermal stability.
The content of the repeating unit having an epoxy group in the vinyl chloride copolymer is preferably 1 to 30 mmol / g, more preferably 1 to 20 mmol / g. As monomers for introducing epoxy groups,
For example, glycidyl acrylate is preferred.

As a method for introducing a polar group into a vinyl chloride copolymer, JP-A-57-44227, JP-A-58-108052, and JP-A-59-8
127, JP-A-60-101161, JP-A-60-235814, JP-A-60-23830
No. 6, JP-A-60-238371, JP-A-60-238371
The introduction methods disclosed in JP-A-2-121923, JP-A-62-146432, JP-A-62-146433, and the like are applicable.

The polyester used as the binder is
It is synthesized by a reaction between a polyol and a polybasic acid. Further, a polar group-containing polyester can be synthesized from a polyol and a polybasic acid into which a polar group is partially introduced.

The polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol,
1,3-butanediol, 1,4-butanediol, 1,
6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like can be used.

Examples of the polybasic acid partially introduced with a polar group include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfoisophthalic acid, dialkyl 5-sulfoisophthalate, -Dialkyl sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and sodium and potassium salts thereof can be used.

It should be noted that a polyester having another polar group introduced therein can be synthesized by a conventionally known method.

The polyurethane used as a binder is
It is synthesized by a reaction between a polyol and a polyisocyanate.

As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. If a polyester polyol having a polar group is used as a raw material for synthesis, a polyurethane having a polar group can be synthesized. As the polyisocyanate, diphenylmethane-4,4'-diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, 1,5-naphthalene diisocyanate, tolidine diisocyanate, lysine diisocyanate methyl ester and the like can be used. In the present invention, it is preferable to use an aromatic polyester polyurethane synthesized using a polyester polyol having an aromatic ring and / or a polyester polyol containing a cyclic hydrocarbon residue.

Further, a polyurethane having a hydroxyl group and C
l-CH_TwoCH_TwoSO_ThreeM or Cl-CH_TwoCH_TwoOSO_TwoM,
Cl-CH_TwoCOOM, Cl-CH_Two−P (= O) (OM
₁) _TwoWith compounds containing polar groups and chlorine atoms
Synthesize polyurethane with polar groups introduced by reaction
It is also possible.

As a method for introducing a polar group into polyurethane, Japanese Patent Publication No. 58-41565, Japanese Patent Application Laid-Open No. 57-92422, Japanese Patent Application Laid-Open No. 57-92423, Japanese Patent Application Laid-Open No. 59-8127, Kaihei 59-54
No. 23, JP-A-59-5424, JP-A-62
The method disclosed in JP-A-121923 or the like can be applied.

The following resins are used as the binder, and the content in the binder is 20% by weight or less.
It can be used in combination with the above-mentioned resins. Specifically, the weight average molecular weight is 10,000 to 200,000
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer,
Cellulose derivatives such as polyamide resin, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, various synthetic rubbers, etc. Can be used.

The magnetic layer preferably contains a lubricant. Fatty acids, fatty acid esters and the like can be used as the lubricant.

The content of the fatty acid as a lubricant is preferably from 0.2% by weight to 10% by weight, more preferably from 0.5% by weight to 5% by weight, based on the ferromagnetic powder contained in the magnetic layer. More preferably, there is. When the content of the fatty acid is less than 0.2 weight, there is a possibility that the running property may be reduced. On the other hand, when the content of the fatty acid exceeds 10% by weight, there is a possibility that the excess fatty acid may seep to the surface of the magnetic layer or output may be easily deteriorated.

The content of the fatty acid ester as a lubricant is preferably from 0.2% by weight to 10% by weight, more preferably from 0.5% by weight to 10% by weight, based on the ferromagnetic powder contained in the magnetic layer.
More preferably, it is 5% by weight. When the content of the fatty acid ester is less than 0.2 weight, the still durability may be easily deteriorated. On the other hand, when the content of the fatty acid ester exceeds 10% by weight, the fatty acid ester may ooze onto the surface of the magnetic layer or output may be easily deteriorated.

When a fatty acid and a fatty acid ester are used in combination, the weight ratio between the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10.

The fatty acids include, for example, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, pentadecylic acid, heptadecylic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, Arachiic acid, lignoceric acid,
Cerotic acid, heptacosanoic acid, montanic acid, melicic acid, lacceric acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid Etc. can be used.

In particular, it is preferable to contain a fatty acid having a melting point of 50 ° C. or more, and specifically, myristic acid, palmitic acid, pentadecylic acid, heptadecylic acid, stearic acid, behenic acid, arachinic acid, lignoceric acid, and cerotic acid. It is preferable to use heptacosanoic acid, montanic acid, melicic acid, laccelic acid, etc., and it is most preferable to use stearic acid.

The fatty acid may be a monobasic acid or a dibasic acid. The fatty acid preferably has 6 to 30 carbon atoms, and more preferably 12 to 22 carbon atoms.

Examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmylate, Isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol mono-butyl ether palmitate, etc. can be used. is there.

The magnetic layer can contain conductive particles, conductive resin and the like as an antistatic agent, and various conventionally known additives can be added.

As the conductive particles, SnO ₂ can be used. In addition, silver powder, silver oxide, silver nitrate, organic compounds of silver, metal particles such as copper powder, metal oxides such as zinc oxide, barium sulfate, titanium oxide, etc. are converted into conductive materials such as tin oxide or antimony solid solution tin oxide. Can be used, but it is particularly preferable to use conductive particles coated with a conductive substance.

The average particle size of these conductive particles is 30 n
m to 500 nm, preferably 45 nm to 30 nm.
More preferably, it is 0 nm. The amount of the conductive particles to be added is preferably 0.1 to 2.0 parts by weight based on 100 parts by weight of the magnetic powder.

Examples of antistatic agents include cationic surfactants such as quaternary amines, anionic surfactants containing bases such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid, and aminosulfonic acid. An amphoteric surfactant, a natural surfactant such as saponin and the like can be used, and the content thereof is preferably 0.01% by weight to 40% by weight based on the binder contained in the magnetic layer.

In the magnetic layer, a polyisocyanate for crosslinking and curing a binder may be used in combination as a curing agent.
As the polyisocyanate, an aromatic polyisocyanate which is an adduct of tolylene diisocyanate or the like and an active hydrogen compound, and an aliphatic polyisocyanate which is an adduct of a hexamethylene diisocyanate or the like and an active hydrogen compound can be used. The weight average molecular weight of these polyisocyanates is preferably from 100 to 3,000.

Further, the magnetic layer can contain various additives such as conventionally known dispersants and fillers. The amount of the dispersant added is preferably 0.5% by weight to 5% by weight based on the ferromagnetic powder.

The intermediate layer is formed by applying a non-magnetic paint prepared by mixing a non-magnetic powder and / or a magnetic powder with a binder on one main surface of a non-magnetic support.

The thickness of the intermediate layer is from 0.2 μm to 2.5 μm
Is more preferable, and more preferably 0.5 μm to 2.0 μm. By setting the thickness of the intermediate layer to the above range, the surface roughness of the magnetic layer formed on the intermediate layer is increased, that is, the occurrence of so-called multilayer surface roughness is prevented, and excellent surface smoothness is obtained by the calendar treatment. Is obtained, so that the electromagnetic conversion characteristics of the magnetic recording medium are further improved.

As the non-magnetic powder, titanium oxide, boron nitride, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α
-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide,
Corundum, artificial diamond, garnet, garnet, quartzite, silicon nitride, silicon carbide, barium sulfate and the like can be used. Among them, titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOO
H, Cr ₂ O ₃ is preferably used, and α-Fe
More preferably, ₂ O ₃ , α-FeOOH is used,
Most preferably, α-FeOOH is used. In particular,
By using the nonmagnetic powder having a needle shape, the surface smoothness of the intermediate layer is improved, and the surface smoothness of the magnetic layer formed on the intermediate layer is also improved.

The content of the nonmagnetic powder in the intermediate layer is from 50% by weight to 99% by weight based on all the components constituting the intermediate layer.
Is preferably 60 to 95% by weight, and more preferably 70 to 95% by weight. By setting the content of the nonmagnetic powder in the above range, the surface smoothness of the intermediate layer is improved, and the surface smoothness of the magnetic layer formed on the intermediate layer is also improved.

The nonmagnetic powder has a crystallite size of 10 nm to 1
The thickness is preferably 00 nm, more preferably 15 nm to 80 nm, and most preferably 20 nm to 60 nm. The Mohs hardness of the nonmagnetic powder is 5
It is preferably from 10 to 10. Furthermore, the specific surface area of the nonmagnetic powder is more preferably preferably 20m ² / g~150m ² / g It is 10m ² / g~250m ² / g, at 30m ² / g~100m ² / g Most preferably.

When the shape of the nonmagnetic powder is not acicular, the number average particle diameter is preferably 20 nm or more and 250 nm or less, more preferably 220 nm or less, and most preferably 200 nm or less. .

On the other hand, when the shape of the nonmagnetic powder is acicular, the average major axis length is preferably 20 nm or more and 250 nm or less, more preferably 220 nm or less, and most preferably 200 nm or less. preferable.
The average short axis length is preferably 10 nm or more and 100 nm or less, more preferably 80 nm or less, and most preferably 60 nm or less.
Further, the ratio of the average major axis length to the average minor axis length, that is, the axial ratio expressed by major axis length / minor axis length is preferably 2 to 20, more preferably 5 to 15, and 5 to 15. Most preferably, it is from 10 to 10.

Here, the average major axis length, average uniaxial length, and number average particle size of the nonmagnetic powder are defined as the major axis length, uniaxial length per 500 particles randomly selected from a transmission electron micrograph. And the average value of particle size and the like. The crystallite size is a value obtained by measuring the (110) diffraction line of Fe using an X-ray diffractometer and measuring the integrated width by the Scherrer method based on Si powder. In addition, as a method of obtaining this, the method described in the X-ray diffraction guide (Rigaku Denki Co., Ltd.)
The correction of the spread due to the double line was obtained by the correction (integral width) by A. Jones.

By using a non-magnetic powder having a specific surface area, a major axis length, an average minor axis length, an axial ratio and the like within the above ranges, the surface smoothness of the intermediate layer is improved, and the intermediate layer is formed on the intermediate layer. The surface properties of the magnetic layer are also improved. When synthesizing the nonmagnetic powder, it is possible to control the shape and the axial ratio of the nonmagnetic powder by appropriately combining known methods such as selection of starting materials, oxidation-reduction conditions, and sintering inhibitors. It is.

The non-magnetic powder is preferably subjected to a surface treatment with a Si compound and / or an Al compound. By using a non-magnetic powder surface-treated with the above compound, the surface state of the magnetic layer is improved. Si and Al contained in the nonmagnetic powder preferably have a weight ratio relationship of Si <Al. Further, specific contents of Si and Al in the non-magnetic powder include:
Si is 0.1% by weight to 10% by weight, and Al is 0.1% by weight.
% By weight, preferably 0.1 to 10% by weight.
1 wt% to 5 wt%, Al is more preferably 0.1 wt% to 5 wt%, and Si is 0.1 wt% to 5 wt%.
Most preferably, the Al content is 0.1% to 2% by weight. As a method of the surface treatment, a method disclosed in JP-A-2-83219 can be applied.

As the binder contained in the intermediate layer, the same resin as the binder contained in the above-mentioned magnetic layer can be used.

It is preferable that the intermediate layer contains a lubricant. By including a lubricant in both the magnetic layer and the intermediate layer, a smoother lubricating effect can be obtained. Specifically, it is preferable that a fatty acid ester such as oleyl oleate composed of an unsaturated fatty acid and an unsaturated alcohol, or a glycerin ester such as glycerin triolate be contained in the intermediate layer.

As the unsaturated fatty acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and the like can be used, and it is particularly preferable to use oleic acid. Oleyl alcohol and the like can be used as the unsaturated alcohol. As the fatty acid ester comprising an unsaturated fatty acid and an unsaturated alcohol, for example, oleyl oleate, oleyl elaidate, oleyl linoleate, oleyl linolenate and the like can be used.

As the glycerin ester, the following esters can be used. (1) Ester of glycerin and palmitic acid containing 16 carbon atoms (2) Ester of glycerin and stearic acid containing 18 carbon atoms (3) Glycerin and unsaturated carbon containing 18 carbon atoms -Ester with oleic acid containing one carbon double bond (4) ester of glycerin with linoleic acid containing 18 carbon atoms and containing two unsaturated carbon-carbon double bonds (5) natural product Olive oil which is a mixture of various fatty acid esters (6) ester of glycerin and lauric acid containing 10 carbon atoms (7) ester of glycerin and myristic acid containing 14 carbon atoms (8) glycerin, Ester with isostearic acid containing 18 carbon atoms (9) Ester with glycerin and behenic acid containing 22 carbon atoms (10) 2-Ethyl ester Triglyceride sanate (11) monoglyceride behenate (12) monodiglyceride stearate oleate (13) glyceride diacetylcaprate (14) glyceride of fatty acid fatty acid (15) glyceride diacetylstearate (16) glyceride diacetylcaprate (17) capryl Acid monodiglyceride (18) acetylstearic acid glyceride (19) caprylic acid triglyceride (20) fatty acid triglyceride containing 8 or 10 carbon atoms The glycerin ester may be any of monoester, diester and triester. good. Also,
One type of glycerin ester can be used alone, or two or more types can be used in combination. Further, in addition to the glycerin ester, an ester of a polyhydric alcohol such as sorbitan can be used in combination.

In the intermediate layer, R ₁ C =
OO (CHR ₂ CHR ₃ O) _n R ₄ (wherein, R ₁ is a linear or branched hydrocarbon group having 11 to 22 carbon atoms, R ₂ and R ₃ are H or CH ₃ , R ₄ has 1 to 2 carbon atoms
2 saturated or unsaturated hydrocarbon groups, 1 ≦ n ≦ 10
It is. ) And a compound represented by, R ₅ OC = OR ₆ (where wherein R ₅ is a straight, linear or branched hydrocarbon group having 1 to 18 carbon atoms, R ₆ has a carbon number 11 to 22 A chain or branched hydrocarbon group).

As described above, by including several kinds of different fatty acid esters and glycerin esters in the intermediate layer, these lubricants can be appropriately supplied to the magnetic layer.
Even under a wide range of temperatures from low to high,
A stable lubrication action is obtained, and the durability is significantly improved.

Further, the intermediate layer preferably contains a plurality of fatty acids having different melting points as a lubricant in addition to the fatty acid ester and the glycerin ester. Thereby, the durability is further improved. As described above, by using a hybrid lubricant system in which many kinds of lubricants are combined, a high-density recording is achieved, a durability is increased, and a magnetic recording medium with a sufficiently reduced error rate can be realized.

In the intermediate layer, as a lubricant other than the above-mentioned fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide,
Tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

As in the case of the magnetic layer, the intermediate layer contains the above-described curing agent, various additives such as a conventionally known dispersant and filler, and conductive particles such as carbon black as an antistatic agent. It is possible to do.

The average particle size of the conductive particles contained in the intermediate layer is preferably 5 nm to 50 nm, and more preferably 10 nm to 50 nm.
４０40 nm, more preferably ｎｍ40 nm.
nm is more preferable. The content of the conductive particles is determined by the amount of filler 1 such as non-magnetic powder contained in the intermediate layer.
It is preferably 1.0% to 50% by weight, more preferably 3.0% to 30% by weight, and more preferably 5.0% to 20% by weight with respect to 00% by weight. Most preferred.

Examples of carbon black that can be contained in the intermediate layer include Seagull 600 (23 nm), Seast 6H (24 nm), Seast 6H (28 nm) manufactured by Tokai Electrode Co., Ltd.
Seast 116 (30 nm), # 80 (23 nm) manufactured by Asahi Carbon Black, Conductex SC (17 nm) manufactured by Colombian Carbon, Conductex 9
75 (20 nm), Conductex 40-220 (2
0 nm), Diablack A (18n) manufactured by Mitsubishi Kasei Corporation
m), Diablack I (21 nm), Diablack H (30 nm), Showa Black O manufactured by Showa Denko KK
(21 nm), Monarch 1300 (1
3 nm), Regal 400 (25 nm), Vulcan XC
-72 (30 nm), Vulcan P (20 nm), Vulcan 9 (19 nm), Black Pearls 2000 (15n
m) etc. can be used. One type of these carbon blacks may be used alone, or two or more types may be used in combination.

Examples of the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Can be used.

As the shape of the nonmagnetic support, any shape such as a tape shape, a film shape, a sheet shape, a card shape, a disk shape and a drum shape can be used. The thickness of the non-magnetic support is, for example, from 3 μm to
It is preferably 100 μm, more preferably ⁵ μm to 50 μm, and in the case of a disk or card, it is preferably 30 μm to 104 μm. Also,
In the case of a drum shape, the thickness is appropriately selected according to the recording / reproducing device.

The center line average roughness (hereinafter referred to as R
a. ) Is preferably from 12 nm to 28 nm, more preferably from 14 nm to 26 nm,
Most preferably, it is 16 nm to 24 nm. Also,
The maximum roughness (hereinafter referred to as Rt) of the nonmagnetic support is 9
5 nm to 220 nm, preferably 110 nm
To 200 nm, more preferably 120 nm to
Most preferably, it is 180 nm. Also, Rt / R
a is preferably from 5 to 9, more preferably from 7 to 9. Further, the number of protrusions present on the surface of the non-magnetic support and having a height of 0.01 μm or more is measured length 1 m
The number is preferably 200 or more per m, and more preferably 250 to 1000.

As a method of controlling Ra, Rt, and the number of protrusions on the nonmagnetic support, for example, the content of particles having a substantially uniform particle size and a substantially spherical shape is 0.1% by weight to 10% by weight. Non-magnetic, smooth, undulation-free protrusion layer having an average film thickness of 0.01 μm to 1 μm, preferably 0.01 to 0.5 μm. A method of forming on the other main surface of the support may be mentioned. This projection layer does not necessarily have to form a film as long as the particles are wrapped with a polymer, and may be, for example, a mesh. Also, without forming such a protrusion layer, it is also possible to control the Ra, Rt, and the number of protrusions by mechanically forming irregularities on the other main surface of the nonmagnetic support.

In the non-magnetic support, the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is 1300 kg /
mm ² or more, preferably 1400 kg / mm ²
More preferably, it is で 4000 kg / mm ² .

The nonmagnetic support is not limited to a single-layer structure, but may have a multilayer structure. Further, as the non-magnetic support, those subjected to a surface treatment such as corona discharge treatment can be used, and those provided with an undercoat layer for the purpose of improving the adhesive strength can also be used.

Further, it is preferable to form a back coat layer on the other main surface of the non-magnetic support. By forming the back coat layer, the runnability of the magnetic recording medium is improved,
Charging of the magnetic layer and transfer of recorded contents are prevented.

Furthermore, it is also possible to form a writing layer, a print recording layer, and a forgery prevention layer on the other main surface of the nonmagnetic support. It is also possible to form an undercoat layer between the nonmagnetic support and the intermediate layer, or to form an overcoat layer on the magnetic layer.

In manufacturing the magnetic recording medium constituted as described above, first, a nonmagnetic powder and / or a magnetic powder and a binder are dispersed in a solvent on a nonmagnetic support. The applied intermediate paint is applied to form an intermediate layer. Next, on the intermediate layer, a ferromagnetic powder, a binder, Mohs hardness of 3 or more,
A magnetic layer is formed by applying a magnetic paint prepared by dispersing a pigment having less than 6 and an abrasive in a solvent. And
After drying the intermediate layer and the magnetic layer, a calendering process for smoothing the surface of the magnetic layer is performed.

In preparing the magnetic coating material and the intermediate coating material, examples of the solvent for mixing the above-mentioned various components to form a coating material include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol, and the like. Alcohols such as propanol and butanol, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran; benzene, toluene and xylene And aromatic hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene. These solvents may be used alone or in combination of two or more.

The magnetic paint and the intermediate paint are prepared by kneading and dispersing with a kneading and dispersing machine. As the kneading / dispersing machine, conventionally known various kneading / dispersing machines can be used. For example, as a kneading and dispersing machine capable of providing a power consumption load of 0.05 kW to 0.5 kW, a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, a three-roll mill, or the like can be used.

When preparing a magnetic coating material, for example, as a method of adding carbon black as a pigment having a Mohs' hardness of 3 or more and less than 6, a method in which fine particles and coarse particles of carbon black are simultaneously charged into a disperser and mixed. Alternatively, a method may be employed in which only a part of the remaining amount is input first, and the remaining amount is input when dispersion has progressed to some extent.

When the emphasis is placed on the dispersion of carbon black, a method may be used in which carbon black, a filler such as ferromagnetic powder, and a binder are kneaded using the above-described three-roll mill or the like, and further dispersed using a disperser. When importance is placed on conductivity, if carbon black is added in the latter half of the dispersion step and the liquid preparation step, the structure structure of the carbon black is less likely to be cut. It is also possible to use a so-called carbon master patch in which carbon black has been kneaded with a binder in advance.

As a coating method for applying the intermediate paint and the magnetic paint prepared as described above, any of conventionally known coating methods can be used. However, the magnetic paint is overlaid on the wet intermediate layer. It is preferable to apply a wet multi-layer coating method of applying a so-called wet-on-wet coating method. When the wet multilayer coating method is applied, the surface smoothness of the intermediate layer is improved, so that the surface smoothness of the magnetic layer is also improved, and the dropout is reduced, resulting in a highly reliable magnetic recording medium. Further, since the adhesiveness between the intermediate layer and the magnetic layer is also improved, the strength of the magnetic layer is increased, and the magnetic recording medium is prevented from peeling and has excellent running durability.

In the case of applying the intermediate paint and the magnetic paint by the wet overlay coating method, first, the intermediate paint and the magnetic paint are applied by an extrusion-type extrusion coater onto the film-like non-magnetic support taken out from the supply roll. Thus, an intermediate layer and a magnetic layer are formed.

Next, a magnetic field orientation treatment is performed using an orientation magnet or an oblique orientation magnet, and further, the intermediate layer and the magnetic layer are dried by passing through a dryer in which hot air is blown from a nozzle to obtain a raw material. . The magnetic field when performing the magnetic field orientation treatment is 2
It is preferably 0 gauss to 10000 gauss. The drying temperature in the dryer is preferably 30C to 120C, and the drying time is preferably 0.1 minute to 10 minutes.

The raw material is heated and pressurized by passing it between a pair of rolls of a combination of a resin elastic roll and a metal roll or between a pair of rolls of a combination of a metal roll and a metal roll. Perform calendar processing. The temperature at the time of performing the calendar processing is 50 ° C. to 14 ° C.
0 ° C., and a linear pressure of 50 kg / cm to
The coating speed is preferably 400 kg / cm, and the coating speed is preferably 20 m / min to 1000 m / min.

The raw material subjected to the calendar processing as described above is taken up by a take-up roll, slit into a desired width, for example, and becomes a tape-shaped magnetic recording medium.

In the above-described coating method, the intermediate paint and the magnetic paint can be supplied to an extrusion coater through an inline mixer. Each of the extruder coaters is provided with a liquid pool portion, and paints from the respective coaters are overlapped by a multi-layer coating method.

In the wet multilayer coating method, a combination of a reverse roll and an extrusion coater or a combination of a gravure roll and an extrusion coater is also applicable.
Furthermore, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater and the like can be combined.

The magnetic recording medium manufactured as described above includes a magnetic layer containing a pigment having a Mohs hardness of 3 or more and less than 6 and an abrasive, and the average particle diameter of the pigment is R.
When the average particle size of the abrasive is r and the thickness of the magnetic layer is M, R ≧ M and R> r, so that the strength of the magnetic layer is sufficiently increased and the polishing force for the magnetic head is optimized. Is done. Therefore, this magnetic recording medium has excellent running durability and also has a good electromagnetic conversion characteristic because the magnetic layer can be made thinner, and is optimal for high-density recording.

Further, by setting the weight ratio of the abrasive to 6 or more and 20 or less for the pigment having a Mohs' hardness of 3 or more and less than 6, the polishing power for the magnetic head is extremely optimized. In addition, it has excellent running durability over a long period of time under any temperature environment, and has good electromagnetic conversion characteristics.

The above-described magnetic recording medium is a multilayer coating type magnetic recording medium in which one intermediate layer is interposed between a non-magnetic support and a magnetic layer, but the present invention is not limited to this. Instead, a structure having a plurality of intermediate layers is also possible, and the present invention is also applicable to a single-layer coating type magnetic recording medium in which a magnetic layer is formed directly on a nonmagnetic support. In a single-layer coating type magnetic recording medium, the thickness of the magnetic layer is preferably 0.1 μm to 0.3 μm.

[0117]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described.
This will be described in detail based on specific experimental results.

First, as shown in FIG.
A plurality of multilayer coating type magnetic tapes each including the intermediate layer 2 and the magnetic layer 3 were produced as described below.

Example 1-1 [Preparation of Magnetic Coating] First, each component was weighed according to the following composition, and kneaded and dispersed using a kneader and a sand mill to prepare a magnetic coating.

<Magnetic paint composition>-Ferromagnetic powder: 100 parts by weight of Fe-Al-based metal magnetic powder-Binder: vinyl chloride-based copolymer containing metal sulfonic acid salt (manufactured by Zeon Corporation: MR-105) 10 parts by weight Sulfonic acid metal salt-containing aromatic polyester polyurethane (manufactured by Toyobo Co., Ltd .: UR-8200) 10 parts by weight ・ Carbon black (average particle size: 0.3 μm) 0.8 parts by weight ・ Abrasive: Alumina (Α-Al ₂ O ₃ , average particle size: 0.18 μm) 5 parts by weight ・ 100 parts by weight of cyclohexanone ・ 100 parts by weight of methyl ethyl ketone ・ 100 parts by weight of toluene ・ 1 part by weight of myristic acid ・ 1 part by weight of stearic acid ・ butyl stearate 1 part by weight The composition of the ferromagnetic powder is Fe: Co: A in weight ratio.
1: Y = 100: 20: 8: 5, the average major axis length was 0.1 μm, the axial ratio was 5, the coercive force was 2390 Oe, the saturation magnetization was 150 emu / g, and the crystallite size was 12 nm. . Carbon black was used as a pigment having a Mohs hardness of 3 or more and less than 6.

[Preparation of Intermediate Paint] Next, each component of the intermediate paint was weighed according to the following composition, and kneaded and dispersed using a kneader and a sand mill to prepare an intermediate paint.

<Intermediate coating composition> Non-magnetic powder: 100 parts by weight of acicular powder mainly composed of α-Fe ₂ O ₃ Binder: vinyl chloride copolymer containing sulfonic acid metal salt (Nippon Zeon Co., Ltd.) 6 parts by weight Metallic sulfonic acid salt-containing aromatic polyester polyurethane (UR-8300 manufactured by Toyobo Co., Ltd.) 3 parts by weight Carbon black (average particle size: 0.02 μm) 16 parts by weight Abrasive: 6 parts by weight of alumina (α-Al ₂ O ₃ , average particle size: 0.3 μm) ・ 100 parts by weight of cyclohexanone ・ 100 parts by weight of methyl ethyl ketone ・ 100 parts by weight of toluene ・ 1 part by weight of myristic acid ・ 1 part by weight of stearic acid 1 part by weight of butyl stearate The average major axis length of the nonmagnetic powder is 0.15 μm, the average minor axis length is 0.015 μm, the axial ratio is 10, and the crystallite size is
It was 8 nm. The content of Si in the nonmagnetic powder is 0.2% by weight with respect to α-Fe ₂ O ₃ ,
Al content is 1.0% by weight relative to α-Fe ₂ O ₃
Met.

Then, 5 parts by weight of a polyisocyanate (manufactured by Nippon Polyurethane Co., Ltd .: Coronate L) was added as a curing agent to the magnetic coating material and the intermediate coating material prepared as described above. The magnetic paint and the intermediate paint were applied on a non-magnetic support 1 made of a certain polyethylene terephthalate by wet superposition. And
Intermediate layer 2 having a thickness of 2.0 μm and a thickness of 0.3 μm
Was formed, and a magnetic field orientation treatment was performed while the intermediate layer 2 and the magnetic layer 3 were not dried. Next, the middle layer 2
After the magnetic layer 3 was dried, the surface of the magnetic layer 3 was smoothed by calendering to obtain a raw material.

The raw material formed as described above was slit to obtain a multilayer coating type magnetic tape having a width of 8 mm. Then, this multilayer coating type magnetic tape was assembled in a cassette to produce an 8 mm cassette tape.

Examples 1-1 to 1-12, Comparative Example 1
-1 to 1-5 In the same manner as in Example 1-1 except that the average particle size of the carbon black and the abrasive contained in the magnetic paint and the thicknesses of the magnetic layer and the intermediate layer were as shown in Table 1, 8mm
A cassette tape was produced.

[0126]

[Table 1]

Next, a plurality of single-layer coated magnetic tapes each having a magnetic layer on a non-magnetic support were produced as described below.

Example 2-1 The same magnetic paint as in Example 1-1 was applied on a non-magnetic support to form a magnetic layer having a thickness of 0.2 μm. Then, after subjecting to magnetic field orientation treatment, drying, calendering treatment and the like, slitting was performed to obtain a single-layer coating type magnetic tape having a width of 8 mm. Then, this single-layer coating type magnetic tape was assembled in a cassette to produce an 8 mm cassette tape.

Examples 2-2 to 2-3, Comparative Example 2-
1 to Comparative Example 2-5 8 mm in the same manner as in Example 1-1 except that the average particle size of the carbon black and the abrasive contained in the magnetic paint and the thickness of the magnetic layer were as shown in Table 2. A cassette tape was produced.

[0130]

[Table 2]

Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-5, which are multilayer coating type magnetic tapes produced as described above, and a single-layer coating type magnetic tape Various measurements were performed on Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-5, and the following characteristics were evaluated.

<Electromagnetic conversion characteristics> Magnetic tape recording / reproducing device (Sony: 8 mm video camera CCDV-900)
Was used to measure the RF reproduction output at 7 MHz to evaluate the electromagnetic conversion characteristics.

<Driving durability> In a high temperature environment After recording the entire length using a magnetic tape recording / reproducing apparatus (S-550, manufactured by Sony Corporation) in an environment of a temperature of 40 ° C. and a relative humidity of 20% 50 full-length runs were performed. And 50
The output decrease value after the first run after the first run was measured, and the running durability under a high temperature environment was evaluated.

In a low-temperature environment In an environment where the temperature is 5 ° C. and the relative humidity is 20%, full-length recording and reproduction are performed using a magnetic tape recording / reproducing apparatus (S-550, manufactured by Sony Corporation). The case where the output decrease continued for 1 second or more was regarded as a head clog, and the running durability under a low temperature environment was evaluated by measuring the presence or absence of the head clog.

<Polishing Power for Magnetic Head>
Five magnetic tapes with a length of 0 minutes were reproduced and run. The change in the amount of protrusion of the head before and after the tape travels, that is, the headwear is changed to BELDEX manufactured by Tohodenshi Kogyo.
And the polishing force on the magnetic head was evaluated.

<Surface Smoothness> Using a three-dimensional surface roughness meter ET-30HK manufactured by Kosaka Laboratory, the cut-off was 0.25 m.
The center line average roughness (Ra) was measured as m. In addition,
Ra was defined using JIS surface roughness (B061).

Tables 3 and 4 show the above measurement results.

[0138]

[Table 3]

[0139]

[Table 4]

As is clear from Tables 3 and 4, a magnetic layer containing carbon black as a pigment having a Mohs hardness of 3 or more and less than 6 and an abrasive was provided. , The average particle size of the abrasive is r,
When the thickness of the magnetic layer is M, Examples 1-1 to 1-12 and Examples 2-1 to 2-3 in which R ≧ M and R> r have good reproduction output. It was found that there was no reduction in output or head clog, and that the headwear was optimal. It was also found that the same effect as that of the magnetic tape of the multilayer coating type can be obtained even with the magnetic tape of the single layer coating type.

Therefore, since the magnetic layer contains a combination of an abrasive and a specific pigment, the magnetic layer has excellent running durability for a long time even under a wide temperature environment, and has good electromagnetic conversion characteristics. Thus, it was found that a magnetic recording medium having an optimized polishing force for the magnetic head can be obtained.

On the other hand, if R is smaller than M and r
Comparative Examples 1-1 to 1-6 and Comparative Examples 2-1 to 3 having a magnetic layer containing smaller carbon black
It was found that the sample had poor running durability and had a large abrasive force against the magnetic head.

Further, Comparative Examples 1-7 and 2-2, 4 provided with a magnetic layer containing carbon black in which R is smaller than M but satisfying R> r have good electromagnetic conversion characteristics. However, the running durability was found to be poor.

Further, in Comparative Examples 1-8 and 2-6 each having a magnetic layer having a carbon black satisfying R ≧ M but R is equal to or less than r, head clog was prevented. It was found that the polishing power for the magnetic head was too large.

Next, in order to consider the optimum weight mixing ratio of the abrasive and carbon black, a multilayer coating type in which the weight mixing ratio of the abrasive to carbon black (hereinafter simply referred to as weight mixing ratio) was changed. A plurality of magnetic tapes were produced.

Examples 3-1 to 3-12 Same as Example 1-1 except that the magnetic paints in which the amounts of the abrasive and carbon black were changed as shown in Table 5 below were used. Thus, an 8 mm cassette tape was produced.

[0147]

[Table 5]

In addition, Example 3 manufactured in this manner was used.
The above-described various measurements were performed in the same manner on Examples 1 to 3 to evaluate the characteristics. Table 6 shows the above measurement results.
Shown in

[0149]

[Table 6]

Although Examples 3-1 and 2 have good electromagnetic conversion characteristics, it has been found that a head clog occurs in a low-temperature environment and the output may decrease. Further, it has been found that when the magnetic head has too little polishing power and powder falling off the magnetic layer clogs the magnetic head, the magnetic head cannot be polished and the output may decrease.

A comparison between Example 3-4 and Example 3-3 shows that Example 3-4 having a weight blending ratio of 6 has a higher output than Example 3-3 having a weight blending ratio of less than 6. It was found that there was no decrease and there was no head clog, and that the magnetic head had an appropriate polishing force.

Further, Embodiments 3-10 and 3-11
In comparison with Example 3-4, the weight ratio was 20.
Was found to be more excellent in reproduction output than Example 3-11 in which the weight ratio was larger than 20.

In Example 3-12, it was found that the polishing force on the magnetic head was too large, and the magnetic head could be damaged.

Accordingly, by setting the weight ratio of the abrasive to carbon black in the magnetic layer in the range of 6 or more and 20 or less, the polishing power for the magnetic head is extremely optimized. As a result, it has been found that the magnetic recording medium has excellent running durability for a long time even under a wide temperature environment, has good electromagnetic conversion characteristics, and has high reliability.

[0155]

As is clear from the above description, the magnetic recording medium according to the present invention comprises a magnetic layer containing a pigment having a Mohs hardness of 3 or more and less than 6 and an abrasive, When the average particle size is R, the average particle size of the abrasive is r, and the thickness of the magnetic layer is M, since R ≧ M and R> r, the strength of the magnetic layer is sufficiently increased and The polishing power for the head is optimized. Therefore, this magnetic recording medium has excellent running durability and also has a good electromagnetic conversion characteristic because the magnetic layer can be made thinner, and is optimal for high-density recording.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a magnetic recording medium.

[Explanation of symbols]

 1 Non-magnetic support, 2 Intermediate layer, 3 Magnetic layer

Claims (6)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer containing a ferromagnetic powder and a binder, wherein the magnetic layer has a Mohs' hardness of 3 or more and less than 6; When the average particle size of the pigment is R, the average particle size of the abrasive is r, and the thickness of the magnetic layer is M, R ≧ M and R> r. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, wherein the pigment is carbon black. 3. The abrasive has a Mohs hardness of 6 or more and 1 or more.
2. The magnetic recording medium according to claim 1, wherein the value is 0 or less. 4. The magnetic recording medium according to claim 1, wherein a weight ratio of the abrasive to the pigment is 6 or more and 20 or less. 5. The method according to claim 1, wherein at least one intermediate layer containing a nonmagnetic powder and / or a magnetic powder and a binder is provided between the nonmagnetic support and the magnetic layer. Item 7. The magnetic recording medium according to Item 1. 6. The M is 0.03 μm or more and 0.3 μm or more.
6. The magnetic recording medium according to claim 5, wherein m is equal to or less than m.