JPH05242465A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having excellent high-frequency characteristics, satisfactory signal overwriting characteristics and weather resistance and fit for high density recording by forming a magnetic layer on a nonmagnetic substrate with platy ferromagnetic metal powder having an axis of easy magnetization in a direction perpendicular to the plate surface. CONSTITUTION:This magnetic recording medium has plural layers on the nonmagnetic substrate 1, the uppermost layer is a magnetic layer contg. platy ferromagnetic metal powder which is easily magnetizable in a direction perpendicular to the plate surface and at least one layer contg. nonmagnetic powder exists under the uppermost layer. When this medium is produced, a nonmagnetic substrate 1 drawn out of a feed roll 32 is coated with coating materials for the magnetic layer and the lower layer by means of extrusion coaters 10, 11 in a superposed state and the coated substrate 1 is passed magnets 33 for orientation or perpendicular orientation, introduced into a drier 34, dried and introduced into a calendering device 37 composed of calendering rolls 38. In the device 37, the substrate 1 with dried coating layers is calendered and then wound around a winding roll 39. The resulting magnetic film is cut to a tape shape having a desired width.

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,
More specifically, the present invention relates to a magnetic recording medium suitable for high-density recording, which is excellent in high frequency characteristics and has good signal overwriting characteristics and weather resistance (corrosion resistance).

[0002]

2. Description of the Related Art In a conventional magnetic recording medium, a magnetic layer having a magnetic property containing a ferromagnetic powder is formed on a non-magnetic support. There has been proposed a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and containing a ferromagnetic alloy powder in an upper layer (Japanese Patent Laid-Open No. 64-19524, Japanese Patent Laid-Open No. 2-110823). Further, there is also a proposal of a magnetic recording medium in which a layer containing a non-magnetic powder is provided in the lower layer and a ferromagnetic powder is contained in the upper layer (see Japanese Patent Laid-Open No. 63-187418).

However, in the above-mentioned magnetic recording medium, it is still difficult to sufficiently improve the characteristics in a high frequency band, especially in high density recording (digital recording), and even when a non-magnetic layer is provided as a lower layer. It is not expected that the characteristics will be improved sufficiently at high frequencies. On the other hand, when a magnetic layer is provided in the lower layer, the waveform of the reproduced signal is distorted during reproduction due to the residual magnetization of the lower layer (interference between waveforms). As a result, the output peak value decreases and the peak position shifts, and the error rate and the like increase.

Furthermore, if residual magnetization exists in the lower layer, it becomes difficult to record a signal to be re-recorded, so-called deterioration of the overwrite characteristic occurs. In addition, JP-A-4-3316
The publication discloses that an alloy ferromagnetic powder having a plate shape and having an easy axis of magnetization in a direction perpendicular to the plate surface is used. JP-A-57-98136 discloses a magnetic recording medium provided with a magnetic layer containing ferromagnetic particles having a length / width ratio of 1 to 3 in the uppermost layer.

However, in any case, since the magnetic layer is thick or a magnetic layer is used as the lower layer, a thickness loss and a self-demagnetization loss occur, so that a digital VTR is produced.
It was not suitable for high density recording.

Further, although vapor-deposited tapes and the like are promising for high density recording (digital recording), they may have problems in practical use because of poor characteristics such as corrosion resistance. An object of the present invention is to provide a magnetic recording medium which is excellent in high frequency characteristics, and is also excellent in signal overwriting (overwriting) characteristics and weather resistance (corrosion resistance) and suitable for high density recording. ..

[0007]

According to a first aspect of the present invention for attaining the above object, a plurality of layers are formed on a non-magnetic support, and the plurality of layers are made of a ferromagnetic metal. The ferromagnetic metal powder has an uppermost layer composed of a magnetic layer containing a powder and a lower layer having at least one layer containing a nonmagnetic powder, and the ferromagnetic metal powder is plate-shaped and has an easy axis of magnetization in a direction perpendicular to the plate surface. A magnetic recording medium according to the present invention, wherein a plurality of layers are formed on a non-magnetic support, and the plurality of layers are magnetic layers containing ferromagnetic metal powder. And a lower layer having at least one layer containing a soft magnetic powder, wherein the ferromagnetic metal powder is plate-shaped and has an easy axis of magnetization in a direction perpendicular to the plate surface. A recording medium, and the invention according to claim 3 is the top layer. Thickness is a magnetic recording medium according to claim 1 is 0.5μm or less.

The magnetic recording medium of the present invention will be described in detail below. The magnetic recording medium of the present invention has a plurality of layers on a non-magnetic support, and comprises an uppermost layer which is a magnetic layer and a lower layer which is in contact with this magnetic layer. The magnetic recording medium of the present invention is formed by laminating the lower layer and the uppermost layer in this order on a non-magnetic support.

-Non-magnetic support-As a material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Examples thereof include plastics such as cellulose derivatives, polyamide, and polycarbonate. The form of the non-magnetic support is not particularly limited, and specific examples thereof include a tape shape, a film shape, a sheet shape, a card shape, a disk shape, and a drum shape.

The thickness of the non-magnetic support is not particularly limited, but in the case of a film or sheet, it is usually 3 to 1.
00 μm, preferably 5 to 50 μm, about 30 μm to 10 mm in the case of a disk or card, and appropriately selected depending on the recorder etc. in the case of a drum. In addition,
This non-magnetic support may have a single-layer structure or a multi-layer structure. The non-magnetic support may be subjected to surface treatment such as corona discharge treatment. It should be noted that the surface (back surface) on the non-magnetic support on which the magnetic layer is not provided
It is preferable to provide a back coat layer for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer, and providing an undercoat layer between the magnetic layer and the non-magnetic support. You can also

-Uppermost Layer-The uppermost layer is composed of a magnetic layer, and the magnetic layer contains a ferromagnetic metal powder having a plate-like shape and having an easy axis of magnetization in a direction perpendicular to the plate surface. Further, the magnetic layer may contain a binder described below and other components described below. As the ferromagnetic metal powder used in the present invention and having an easy axis of magnetization in the direction perpendicular to the plate surface, a hexagonal alloy strong with other metals mainly containing Co such as Co—Cr and Co—Ni. Magnetic powder, SmC
Alloy ferromagnetic powders of 3d transition metals such as o ₅ and PrCo ₅ and 4d transition metals, and the like, and, for example, Fe—Al alloys and Fe—Nd—B alloys can be included. These may be used alone or in combination.

The average particle size of the ferromagnetic metal powder is usually
40 to 200 nm, preferably 60 to 150 nm
Is. If the average particle size is less than 40 nm, the reproduction output when used as a magnetic recording medium becomes insufficient, and conversely, 200
If the thickness exceeds nm, the surface smoothness of the magnetic recording medium may be significantly deteriorated and the noise level may be too high.

The plate-like ratio (the value obtained by dividing the particle size by the plate thickness) of the ferromagnetic metal powder is usually 2.0 to 10.0, preferably 2.0 to 8.0, and Preferably 2.0
Is about 6.0. If the plate ratio is less than 2.0, a perpendicular orientation ratio suitable for high-density recording cannot be obtained when used as a magnetic recording medium, and conversely, if the plate ratio exceeds 10.0, it is regarded as a magnetic recording medium. The surface smoothness is significantly deteriorated and the noise level becomes too high.

The coercive force (Hc) of the ferromagnetic metal powder is
Usually, it is 800 to 3,000 Oe, preferably 1,000 to 3,000 Oe, and more preferably 1,500 to 3,000 Oe. Holding power is 80
When it is less than 0 Oe, it becomes difficult to hold the recording signal, and when it exceeds 3,000 Oe, the head limit may be saturated and recording may become difficult.

Saturation magnetization amount (σ _s ) of the ferromagnetic metal powder
Is usually in the range of 100 to 200 emu / g,
It is preferably 120 to 200 emu / g, and more preferably 140 to 200 emu / g. When the saturation magnetization amount is less than 100 emu / g, the magnetization amount as the magnetic layer is low and the electromagnetic conversion performance deteriorates. Even when it exceeds 200 emu / g, the dispersion becomes difficult and the electromagnetic conversion performance deteriorates.

As a method for producing such a ferromagnetic metal powder, for example, the following method can be shown. (1) A method in which salts such as metal chlorides and sulfates are reduced with an aqueous solution using a reducing agent such as sodium borohydride and hypophosphite (JP-A-59-170209). (2) A method of heating a plate-shaped metal oxide, hydroxide, or oxyhydroxide in a reducing gas such as hydrogen (JP-A-59-59).
173207 and 60-100606). (3) A method of evaporating an alloy such as Co-Ni, Co-Cr and Sm-Co in a low pressure inert gas to crystallize.

[0017] In this invention, the content of the ferromagnetic alloy powder, magnetic layer uppermost is generally 50 to 99 fold <br/> weight%, preferably 60 to 99 wt% .. The thickness of the uppermost magnetic layer is usually 0.5 μm or less, preferably 0.3 μm or less.

-Lower layer-The lower layer comprises at least one layer containing a non-magnetic powder or a soft magnetic powder. Furthermore, the lower layer may contain a binder described below and other components described below.

Examples of the non-magnetic powder include carbon black, graphite, titanium oxide, barium sulfate, ZnS, MgCO ₃ , CaCO ₃ , ZnO and Ca.
O, α-iron oxide, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂
O ₃ , α-Al ₂ O ₃ , SiC, cerium oxide, corundum, artificial diamond, garnet, garnet, silica, silicon nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, diatomaceous earth , Dolomite and the like.

Of these, preferred are carbon black, CaCO ₃ , titanium oxide, barium sulfate and α-.
Inorganic powders such as Al ₂ O ₃ and α-iron oxide, polymer powders such as polyethylene, and the like.

The preferable particle size of the non-magnetic powder in the present invention is usually 1 to 100 mμ, particularly 1 to 50 mμ. When the particle size of the non-magnetic powder is in the above range, a smooth lower layer can be formed, and the characteristics of the upper magnetic layer can be improved, which is preferable.

In the layer containing the non-magnetic powder,
The content of the non-magnetic powder is 50 to 99% by weight, preferably 60 to 99% by weight, more preferably 80 to 99% by weight. When the content of the nonmagnetic powder is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained. Further, if the content of the non-magnetic powder is less than 50% by weight, the dispersion of the non-magnetic powder may be insufficient, which is not preferable.

The soft magnetic powder has a coercive force Hc of 0.
<Hc ≦ 1.0 × 10 ⁴ [A / m], preferably 0 <H
c ≦ 5.0 × 10 ³ [A / m]. When the coercive force of the soft magnetic powder is within the above range, the effect of stabilizing the magnetization region of the uppermost layer is exhibited. When the coercive force exceeds the above range, desired properties may not be obtained due to manifestation of properties as a magnetic material, which is not preferable.

In the present invention, as the soft magnetic powder,
It is preferable to appropriately select a material within the range of the coercive force. Examples of such soft magnetic powder include metal soft magnetic materials and oxide soft magnetic materials.

Fe-S is used as the soft metal magnetic material.
i alloy, Fe-Al alloy (Alperm, Alfeno
1, Alfer), permalloy (Ni-Fe binary alloy, and multi-component alloy in which Mo, Cu, Cr, etc. are added thereto), sendust (Fe-Si-Al [9.6 wt% Si, 5. 4% Al, the balance being Fe]], Fe—Co alloy, and the like. Among them, sendust is preferable as the preferable metal soft magnetic material. The metal soft magnetic material as the high magnetic permeability material is not limited to those exemplified above, and other metal soft magnetic materials can be used. The high permeability material can be used alone, or
Also, two or more of them can be used in combination.

As the soft oxide magnetic material, spinel type ferrites such as MnFe ₂ O ₄ , Fe ₃ O ₄ and C are used.
oFe ₂ O ₄ , NiFe ₂ O ₄ , MgFe ₂ O ₄ , Li
_0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni-
Zn-based ferrite, Ni-Cu-based ferrite, Cu-Z
n type ferrite, Mg-Zn type ferrite, Li-ZN
Examples include series ferrites. Among these, Mn-Zn type ferrite and Ni-Zn type ferrite are preferable. These soft oxide magnetic materials can be used alone or in combination of two or more.

This soft magnetic powder is made into a fine powder by using a ball mill or other crushing device, and the particle size is 1 mμ-1,
It is preferably 000 mμ, particularly preferably 1 mμ to 500 mμ. In order to obtain such a fine powder, the metal soft magnetic material can be obtained by spraying a molten alloy in a vacuum atmosphere. Further, the soft oxide magnetic material can be made into a fine powder by a glass crystallization method, a coprecipitation firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method or the like.

In the layer containing the soft magnetic powder,
The content of the soft magnetic powder is 10 to 100% by weight, preferably 50 to 100% by weight, more preferably 60 to 100% by weight. When the content of the soft magnetic powder is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained.
Further, if the soft magnetic powder is less than 50% by weight, the effect as a layer containing the soft magnetic powder may not be obtained, which is not preferable.

The layer containing the soft magnetic powder contains
It may contain non-magnetic particles.

-Binder- As the binder used in the present invention, for example, vinyl chloride resins such as polyurethane, polyester and vinyl chloride copolymer are typical, and these resins are -S.
_{O 3 M, -OSO 3 M,} -COOM and -PO (OM
¹ ) It is preferable to include a repeating unit having at least one polar group selected from ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal such as Na, K or Li,
M ¹ represents a hydrogen atom, an alkali atom such as Na, K or Li, or an alkyl group. The polar group has a function of improving the dispersibility of the ferromagnetic metal powder in the magnetic layer and the non-magnetic powder or the soft magnetic powder in the lower layer, and the content ratio in each resin is 0.1 to 8.0 mol%, preferably Is 0.5 to 6.0 mol%. If this content is less than 0.1 mol%, the dispersibility of the ferromagnetic metal powder in the magnetic layer and the non-magnetic powder or soft magnetic powder in the lower layer will decrease, and the content will exceed 8.0 mol%. Then, the magnetic paint and the lower layer paint are easily gelated. The weight average molecular weight of each resin is 15,000 to 50,000.
A range of 0 is preferred.

The content of the binder in the magnetic layer or the lower layer is usually 10 to 100 parts by weight of the ferromagnetic metal powder or the lower layer of the non-magnetic powder or the soft magnetic powder.
40 parts by weight, preferably 15 to 30 parts by weight. The binder is not limited to one kind alone, and two or more kinds may be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is usually 90:10 to 10: by weight. 90, preferably 70:
It is in the range of 30 to 30:70.

The polar group-containing vinyl chloride copolymer used as a binder in the present invention has a hydroxyl group-containing copolymer such as a vinyl chloride-vinyl alcohol copolymer and the following polar group and chlorine atom. It can be synthesized by an addition reaction with a compound. Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₃ M, Cl-CH ₂ COOM, Cl-CH ₂ -P (= O) (OM ¹ ) _{2 From} these compounds Cl-CH ₂ CH Taking ₂ SO ₃ Na as an example, the above reaction is explained as follows. _{-CH 2 C (OH) H -} + ClCH 2 CH 2 SO 3 Na → - CH 2 C (OCH 2 CH 2 SO 3 Na) H-.

In addition, in the polar group-containing vinyl chloride copolymer, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is charged into a reaction vessel such as an autoclave to start a general polymerization. Agents, eg BPO
(Benzoyl peroxide), AIBN (azobisisobutyronitrile) and other radical polymerization initiators, redox polymerization initiators, cationic polymerization initiators and the like can be obtained by carrying out a polymerization reaction.

Specific examples of the reactive monomer for introducing the sulfonic acid or its salt include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid, and the like. Mention may be made of salt. When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used, and when introducing a phosphoric acid or a salt thereof,
For example, (meth) acrylic acid-2-phosphate ester may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so. When introducing an epoxy group, the content of the repeating unit having an epoxy group in the copolymer is preferably 1 to 30 mol%,
20 mol% is more preferable. For example, glycidyl acrylate is preferable as the monomer for introducing the epoxy group.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-57-42427 can be used.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
No. 8306, No. 60-238371, No. 62-121
No. 923, No. 62-146432, No. 62-1464.
No. 33 and the like are described, and these can be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting a polyol with a polybasic acid. By using this known method, a polyester (polyol) having a polar group can be synthesized from a polybasic acid partially having a polar group.

Examples of polybasic acids having polar groups include 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Examples thereof include sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and their sodium salts and potassium salts.

Examples of polyols include trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol.
1,3-butanediol, 1,4-butanediol
1,6-hexanediol, diethylene glycol
And cyclohexane dimethanol. Note that other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described. It results from the reaction of polyols with polyisocyanates. As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, if a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like can be mentioned.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective. Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ CH ₂ OSO ₂ M, Cl-CH ₂ COOM, Cl-CH ₂ -P (= O) (OM ¹ ) ₂ Regarding the introduction of polar groups into polyurethane As the technology, Japanese Patent Publication No. 58-41565 and Japanese Patent Laid-Open No. 57-9242.
No. 2, No. 57-92423, No. 59-8127, No. 59-5423, No. 59-5424, No. 62-12.
It is described in the publications such as 1923, and these can be used in the present invention.

In the present invention, the following resins can be used together as a binder in an amount of 20% by weight or less based on the total amount of the binder. The resin has a weight average molecular weight of 1
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (nitrocellulose etc.), styrene-butadiene copolymers, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins, various synthetic rubber resins, etc. ..

-Other Components- In the present invention, in order to improve the quality of the magnetic layer and the lower layer, additives such as a lubricant, a durability improver, a dispersant, an abrasive, an antistatic agent and a filler are added to the other components. It can be contained as an ingredient. As a lubricant, fatty acid and / or
Alternatively, fatty acid esters can be used. In this case, the amount of the fatty acid added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic metal powder or the lower layer non-magnetic powder or soft magnetic powder. If the addition amount is less than 0.2% by weight, the running property tends to decrease, and if the addition amount exceeds 10% by weight, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to decrease.

The amount of the fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic metal powder or the lower layer non-magnetic powder or soft magnetic powder.
Is more preferable. If the addition amount is less than 0.2% by weight, the still durability is apt to deteriorate, and if it exceeds 10% by weight, the fatty acid ester exudes on the surface of the magnetic layer,
The output tends to decrease. When using a fatty acid and a fatty acid ester together to further enhance the lubricating effect, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10.

The fatty acid may be a monobasic acid or a dibasic acid and preferably has 6 to 30 carbon atoms.
The range of -22 is more preferable. Specific examples of fatty acids include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid. Examples thereof include acids, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid and octanedicarboxylic acid.

Specific 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 palmiate. Tate, 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, diethylene glycol mono- Butyl ether palmitate and the like can be mentioned. Also,
Lubricants other than the above 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 also be used.

Examples of the durability improver include polyisocyanate, and examples of the polyisocyanate include:
For example, there are aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

Examples of the dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, and other fatty acids having 12 to 18 carbon atoms; salts of these alkali metals or alkaline earth metals. Examples thereof include salts or amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having a carboxyl group and a sulfonic acid group. These dispersants are usually added to the ferromagnetic metal powder or the lower non-magnetic powder or soft magnetic powder at 0.5%.
Used in the range of up to 5% by weight.

Specific examples of the polishing agent include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide and boron nitride. The abrasive has an average particle size of 0.05 to 0.6.
Those having a thickness of μm are preferable, and those having a thickness of 0.1 to 0.3 μm are more preferable.

As the antistatic agent, carbon black,
Conductive powder such as graphite; cationic surfactant such as quaternary amine; anionic surfactant containing acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid;
Examples thereof include amphoteric surfactants such as aminosulfonic acid; natural surfactants such as saponin. The above-mentioned antistatic agent is usually added in the range of 0.01 to 40% by weight with respect to the binder.

—Manufacture of Magnetic Recording Medium— In the magnetic recording medium of the present invention, the uppermost magnetic layer and the lower layer are coated by a wet-on-wet system. As the wet-on-wet system, a known method used for manufacturing a multilayer structure type magnetic recording medium can be appropriately adopted. For example, generally, a ferromagnetic metal powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent, and the like are kneaded with a solvent to prepare a high-concentration magnetic layer magnetic coating, and then this high-concentration magnetic layer is prepared. The magnetic paint for the magnetic layer is diluted to prepare the magnetic paint for the magnetic layer. Further, in general, a non-magnetic powder or soft magnetic powder of the lower layer, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent and the like and a solvent are kneaded to prepare a high-concentration lower layer coating material, and then This high-concentration lower layer coating material is diluted to prepare a lower layer coating material. Then, the magnetic coating material for the magnetic layer and the coating material for the lower layer are applied on the non-magnetic support.

Examples of the solvent include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MK).
IBK), ketones such as cyclohexanone; alcohols such as methanol, ethanol, propanol; esters such as methyl acetate, ethyl acetate, butyl acetate; cyclic ethers such as tetrahydrofuran; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform ,
Halogenated hydrocarbon such as dichlorobenzene can be used.

Various kneading and dispersing machines can be used for kneading and dispersing the forming components of the magnetic layer and the lower layer. As this kneading disperser, for example, a two-roll mill,
Three roll mill, ball mill, pebble mill, cobol mill, tron mill, sand mill, sand grinder, Sq
Examples include egvari attritors, high speed impeller dispersers, high speed stone mills, high speed impact mills, dispersers, high speed mixers, homogenizers, ultrasonic dispersers, open kneaders, continuous kneaders and pressure kneaders. Among the above-mentioned kneading dispersers, 0.05 to 0.5 kW (magnetic powder 1K
Kneading dispersers capable of providing a power consumption load (per g) are pressure kneaders, open kneaders, continuous kneaders, two roll mills, three roll mills.

To coat the uppermost magnetic layer and the lower layer on the non-magnetic support, specifically, as shown in FIG.
First, the magnetic coating for the magnetic layer and the coating for the lower layer are multi-layered by the wet-on-wet method on the non-magnetic support 1 fed from the supply roll 32 by the extrusion-type extrusion coaters 10 and 11, and thereafter, for the orientation. After passing through the magnet or the vertical orientation magnet 33, it is introduced into the dryer 34, and hot air is blown from the nozzles arranged above and below to dry it. Next, the dried non-magnetic support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered and then wound on a winding roll 39. The magnetic film thus obtained is cut into a tape having a desired width, for example, 8 m.
Magnetic recording tapes for m-video cameras can be manufactured.

In the above method, each paint was extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. In addition, in the figure, the arrow indicates the transport direction of the non-magnetic support film. Extrusion coater 1
Nos. 0 and 11 are provided with liquid reservoirs 13 and 14, respectively, to wet-on-paint the paint from each extrusion coater.
Wet method is used. That is, immediately after the coating of the lower layer coating material (in the undried state), the uppermost magnetic layer magnetic coating material is applied in multiple layers. As the extrusion coater, the extrusion coater 15 shown in FIG. 2 is preferable in the present invention. The lower layer coating material 2 and the magnetic layer magnetic coating material 3 are co-extruded from the extrusion coater 15 and coated in multiple layers on the non-magnetic support 1.

As the solvent to be added to the above paint or a diluent solvent for applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, xylene; methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
A halogenated hydrocarbon such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more. The magnetic field in the orienting magnet or the vertically orienting magnet is about 20 to 5,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.
It is about 1 to 10 minutes.

In the wet-on-wet system, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, etc. can also be used. Furthermore, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, etc. can be combined.

In the multi-layer coating in the wet-on-wet system, the upper magnetic layer is coated while the layer located under the uppermost layer is in a wet state, so that the surface of the lower layer (that is, the uppermost layer). And the surface property of the uppermost layer is improved, and the adhesion between the upper layer and the lower layer is improved. As a result, especially for high-density recording, high output and low noise are satisfied, for example, the performance required as a magnetic tape is satisfied, and high durability performance is required. , The film strength is improved, and the durability is sufficient. Further, the wet-on-wet multi-layer coating method can also reduce dropout and improve reliability.

-Surface Smoothing-In the present invention, it is also possible to carry out a surface smoothing process by calendering. After that, if necessary, burnishing or blade processing is performed for slitting. In the surface smoothing treatment, temperature, linear pressure, C / S (coating speed) and the like can be mentioned as calendering conditions.

In the present invention, the above temperature is usually set to 5
0 to 120 ° C, the linear pressure is 50 to 400 kg / cm,
It is preferable to keep the C / S at 20 to 600 m / min. The thickness of the top layer resulting from the above treatment is
The thickness is 1.0 μm or less, preferably 0.8 μm or less. When the layer thickness exceeds 1.0 μm, the high frequency characteristics and the signal overwriting (overwriting) characteristics deteriorate, and the magnetic recording medium is the same as a single-layer magnetic recording medium, and the object of the present invention is achieved. I can't.

[0063]

Embodiments of the present invention will be described below. The components, ratios, and operation sequences shown below can be variously modified without departing from the scope of the present invention. In the following examples, all "parts" are parts by weight.

A magnetic paint having the following composition was prepared. <Magnetic coating for the top magnetic layer> Plate-shaped ferromagnetic metal powder (shown in Table 1) 100 parts Vinyl chloride resin (MR110 manufactured by Zeon Corporation) 5 parts Polyurethane resin (UR8700 manufactured by Toyobo) 3 parts Cr ₂ O ₃ powder 5 parts carbon black 0.5 part (average particle size 40 nm) butyl stearate 1 part stearic acid 1 part methyl ethyl ketone 100 parts cyclohexanone 100 parts After kneading and dispersing the above composition, a polyisocyanate compound (Coronate L ) 5 parts were added.

<Lower layer non-magnetic powder-containing layer coating> The above-mentioned magnetic coating for the uppermost layer was used except that 100 parts of the non-magnetic powder shown in Table 1 was used instead of the plate-like ferromagnetic metal powder in the magnetic coating for the uppermost layer. It was prepared in the same manner as the paint.

<Coating for lower soft magnetic powder-containing layer> The above-mentioned magnetic coating for the uppermost layer except that 100 parts of the soft magnetic powder shown in Table 1 was used instead of the plate-like ferromagnetic metal powder in the magnetic coating for the uppermost layer. It was prepared in the same manner as the paint.

<Lower magnetic layer coating material> Same as the above uppermost magnetic coating material except that 100 parts of the ferromagnetic powder shown in Table 1 was used instead of the plate-like ferromagnetic metal powder in the above uppermost magnetic coating material. Was prepared.

[0068]

[Table 1]

(Examples 1 to 10 and Comparative Examples 1 to 5) With the composition of the coating film shown in Table 1, wet-on-
A magnetic recording medium having a width of 8 mm was prepared by the wet method. The following evaluation tests were conducted on this magnetic recording medium, and the results are summarized in Table 2. <C / N characteristics> A 9 MHz single wave was recorded using a commercially available 8 mm video tape recorder, and the output level when the signal was reproduced was expressed by comparison with a reference sample (Comparative Example 1). <Overwrite characteristics> A residual output level of a 2 MHz signal was measured when a 2 MHz signal was recorded at a saturation level and then a 9 MHz signal was (overwritten) recorded. The lower the residual output level, the better the overwrite characteristics. <Weather resistance> The output level at 9 MHZ was measured in advance, the magnetic recording medium as a sample was left for 7 days in an environment of 60 ° C. and 80% (humidity), and then the output level of 9 MHz was measured again. The difference from the initial measured value was obtained.

(Comparative Example 6) Co-Ni was coated on a non-magnetic support.
A vapor-deposited magnetic recording medium prepared by vapor-depositing an alloy was prepared, and an evaluation test was conducted in the same manner as in the above-mentioned examples.

[0071]

[Table 2]

[0072]

According to the present invention, it is possible to provide a magnetic recording medium which is excellent in high frequency characteristics and has good signal overwriting (overwriting) characteristics and weather resistance (corrosion resistance) and which is suitable for high density recording. You can

[Brief description of drawings]

FIG. 1 is a diagram for explaining multi-layer coating of a magnetic layer and a lower layer by a wet-on-wet coating method.

FIG. 2 is a diagram of an extrusion coater for applying the magnetic coating material for the magnetic layer and the coating material for the lower layer.

[Explanation of sign]

 DESCRIPTION OF SYMBOLS 1 Non-magnetic support 2 Lower layer coating material 3 Magnetic layer magnetic coating material 10 Extrusion coater 11 Extrusion coater 13 Liquid pool section 14 Liquid pool section 15 Extrusion coater 32 Supply roll 33 Orientation magnet or vertical orientation magnet 34 Dryer 37 Super calendar Equipment 38 Calender roll 39 Winding roll

Claims (3)

[Claims] 1. A plurality of layers are formed on a non-magnetic support, and the plurality of layers are at least an uppermost layer composed of a magnetic layer containing a ferromagnetic metal powder and a layer containing a non-magnetic powder. Consisting of a lower layer having one layer, the ferromagnetic metal powder,
A magnetic recording medium having a plate-like shape and having an easy axis of magnetization in a direction perpendicular to the plate surface. 2. A plurality of layers are formed on a non-magnetic support, and the plurality of layers are at least an uppermost layer composed of a magnetic layer containing a ferromagnetic metal powder and a layer containing a soft magnetic powder. Consisting of a lower layer having one layer, the ferromagnetic metal powder,
A magnetic recording medium having a plate-like shape and having an easy axis of magnetization in a direction perpendicular to the plate surface. 3. The magnetic recording medium according to claim 1, wherein the thickness of the uppermost layer is 0.5 μm or less.