JPH05282658A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium excellent in C-N ratio, overwriting characteristics, head clogging characteristics and running durability. CONSTITUTION:A lower layer having at least one layer contg. nonmagnetic powder or a high permeability material and a magnetic layer contg. magnetic powder and an abrasive material as the uppermost layer are successively laminated on a nonmagnetic substrate. The abrasive material in the uppermost magnetic layer has >=6 new Mohs' hardness and <=0.5mum average particle diameter, the amt. of the abrasive material is 7-20 pts.wt. per 100 pts.wt. of the magnetic powder and the thickness of the magnetic layer is <0.5mum.

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, C / N ratio characteristics, overwrite characteristics,
The present invention relates to a magnetic recording medium having excellent head clog characteristics and running durability.

[0002]

2. Description of the Related Art In the conventional magnetic recording medium, a magnetic layer containing ferromagnetic powder is formed on a non-magnetic support, but a layer containing magnetic powder is used as an upper layer. ,
A multi-layered magnetic recording medium having a layer containing a non-magnetic powder as a lower layer (Japanese Patent Laid-Open No. 63-187418, Japanese Patent Laid-Open No. 6-187418).
No. 3-191315, etc.) has been proposed.

However, in the magnetic recording medium as described above, the non-magnetic layer containing the non-magnetic powder is simply provided as the lower layer, or the abrasive is used. Can not be controlled within a preferable range, and the grain edge from the edge cannot be prevented, and the film thickness of the upper layer is 0.
Since it is 5 μm or more, it is difficult to sufficiently satisfy the high C / N ratio characteristic, the overwrite characteristic, the head clog characteristic, and the running durability required for the digital recording medium.

Therefore, an object of the present invention is to solve the above problems and provide a magnetic recording medium which is excellent in C / N ratio characteristics, overwrite characteristics, head clog characteristics and running durability.

[0005]

In order to solve the above-mentioned problems, the present inventors have studied and found that the uppermost layer of the magnetic layer in the magnetic recording medium has a predetermined new Mohs hardness and an average grain size. While containing the agent in a predetermined ratio, the lower layer has at least one layer containing a non-magnetic powder or a high-permeability material, whereby the surface roughness of the magnetic layer can be controlled within a certain range. As a result, they have found that a magnetic recording medium having excellent high C / N ratio characteristics, overwrite characteristics, head clog characteristics, and running durability can be obtained, and reached the present invention.

That is, the invention according to claim 1 for achieving the above object is such that a lower layer having at least one layer containing a non-magnetic powder or a material having a high magnetic permeability on a non-magnetic support, a magnetic powder, and And an uppermost layer composed of a magnetic layer containing an abrasive in this order, and the uppermost layer composed of the magnetic layer has a new Mohs hardness of 6 or more and an average particle diameter of 0.5 μm or less. The magnetic powder 10
A magnetic recording medium characterized by containing 7 to 20 parts by weight with respect to 0 parts by weight, and having a layer thickness of less than 0.5 μm. The magnetic recording medium according to claim 1, wherein the uppermost layer composed of the magnetic layer contains an abrasive having a new Mohs hardness of 6 or more and an average particle diameter of 0.05 to 0.3 μm,
The invention according to claim 3 is characterized in that the lower layer has at least one layer containing an abrasive having a new Mohs hardness of 6 or more and an average particle diameter of 0.6 μm or less. The magnetic recording medium according to any one of claims 1 to 5, wherein the lower layer contains a non-magnetic powder or a high-permeability material having an average particle diameter of 1 to 300 nm and a spherical shape. The magnetic recording medium according to any one of claims 1 to 3, further comprising an uppermost layer provided when the lower layer is in a wet state. Claim 1
4. The magnetic recording medium according to claim 4, wherein the invention according to claim 6 provides the surface roughness R of the uppermost layer composed of the magnetic layer.
_10. The magnetic recording medium according to claim 1, wherein _10Z is 5 to 20 nm, and the invention according to claim 7 is such that the uppermost layer composed of the magnetic layer has an average particle diameter of 10 to 300 nm. The magnetic recording medium according to claim 1, which contains a fine powder.

The magnetic recording medium of the present invention will be described in detail below. —Structure of Magnetic Recording Medium— The magnetic recording medium of the present invention comprises a non-magnetic support (A),
A lower layer (B) having at least one layer containing a non-magnetic powder or a high magnetic permeability material and an uppermost layer (C) consisting of a magnetic layer containing magnetic powder and an abrasive are laminated in this order.

(A) Non-magnetic support As the 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 and cellulose diacetate. Cellulose derivatives such as polyamide,
Examples thereof include plastics such as polycarbonate. The form of the non-magnetic support is not particularly limited, and mainly includes tape, film, sheet, card, disk, drum and the like.

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. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment. A back coat layer is preferably provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided for the purpose of improving the running property of the magnetic recording medium, preventing electrification, and preventing transfer. Also, an undercoat layer may be provided between the magnetic layer and the non-magnetic support.

(B) Lower Layer (B-1) Description of Lower Layer The lower layer is not particularly limited except that it has at least one layer containing a non-magnetic powder or a high magnetic permeability material, and is formed by various methods. can do. The lower layer is formed of a single layer or a plurality of layers on the non-magnetic support.

(B-2) Composition of Lower Layer The lower layer contains a non-magnetic powder or a high magnetic permeability material. Further, the lower layer may contain an abrasive, a conductive fine powder, a binder and other components.

(B-2-1) Nonmagnetic Powder In the present invention, various known nonmagnetic powders can be appropriately selected and used. Examples of the non-magnetic powder that can be used include carbon black, graphite, titanium oxide, barium sulfate, ZnS, and MgC.
O ₃ , CaCO ₃ , ZnO, CaO, 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, α-iron oxide, garnet, garnet, silica stone, silicon nitride, boron nitride, silicon carbide, molybdenum carbide, boron carbide,
Tungsten carbide, titanium carbide, triboli, diatomaceous earth, dolomite and the like can be mentioned. Of these, preferred are carbon black, CaCO ₃ ,
Inorganic powders such as titanium oxide, barium sulfate, α-Al ₂ O ₃ and α-iron oxide, polymer powders such as polyethylene, and the like.

In the present invention, it is preferable to use a non-magnetic powder having a spherical shape. The average particle size of the non-magnetic powder is usually 1 to 300 nm, preferably 1 to 100 nm, and particularly preferably 1 to 50 nm.
nm. It is preferable to use a non-magnetic powder having a spherical shape and an average particle diameter in the above range, since the non-magnetic powder in the non-magnetic layer does not adversely affect the surface roughness of the magnetic layer.

The content of the nonmagnetic powder in the nonmagnetic layer is 50 to 99% by weight, preferably 60 to 95% by weight, particularly preferably, based on the total of all components constituting the nonmagnetic layer. It is 75 to 95% by weight. When the content of the non-magnetic powder is within the above range, the surface roughness R _10Z of the uppermost magnetic layer can be _excellent .

(B-2-2) High Permeability Material In the present invention, the high magnetic permeability material has a coercive force Hc of 0 <Hc ≦ 1.0 × 10 ⁴ [A / m], preferably 0 <
It is possible to use one having Hc ≦ 5.0 × 10 ³ [A / m]. When the coercive force is within the above range, the effect of stabilizing the magnetized region of the uppermost layer can be well achieved as the high magnetic permeability material. If the coercive force exceeds the above range, the desired properties may not be obtained due to the manifestation of the properties as a magnetic material.

In the present invention, it is preferable to appropriately select a material having a coercive force range as the high magnetic permeability material. Examples of such a high magnetic permeability material include a metal soft magnetic material and an oxide soft magnetic material. As the metal soft magnetic material, Fe-
Si alloy, Fe-Al alloy (Alperm, Alfen
ol, Alfer), permalloy (Ni-Fe binary alloy, and multi-component alloy in which Mo, Cu, Cr, etc. are added), 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 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.

In the present invention, it is preferable to use a high magnetic permeability material having a spherical shape. This high magnetic permeability material is made into a fine powder using a ball mill or other crushing device,
The particle size is 1 to 300 nm, preferably 1 to 1
00 nm, and particularly preferably 1 to 50 nm. 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.

The content of the high magnetic permeability material is 50 to 99% by weight, preferably 60 to 95% by weight, based on the total of all components constituting the layer containing the high magnetic permeability material.
More preferably, it is 75 to 95% by weight. When the content of the high magnetic permeability material is within the above range, the effect of stabilizing the magnetization of the uppermost layer can be sufficiently obtained. If the content of the high magnetic permeability material is less than 50% by weight, the effect of the high magnetic permeability layer may not be obtained, which is not preferable.

In the present invention, the non-magnetic powder and the high-permeability material may be contained at the same time, and the total content thereof constitutes a layer containing the non-magnetic powder and the high-permeability material. It is 50 to 99 parts by weight, preferably 60 to 95 parts by weight, and particularly preferably 75 to 95 parts by weight, based on the total of all components.

(B-2-3) Abrasive The abrasive contained in the lower layer is α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide. , Boron carbide, corundum, zinc oxide, cerium oxide, magnesium oxide, boron nitride and the like. Of these, α-alumina is preferable.

The average particle diameter of this abrasive is usually 0.05 to 0.6 μm, preferably 0.05 to 0.6 μm.
0.5 μm, particularly preferably 0.05 to 0.3
μm. The abrasive preferably has a new Mohs hardness of 6 or more. The new Mohs hardness is an empirical scale for determining the hardness of a sample by comparing it with 15 standard minerals, with 1 being the softest and 1 being the hardest. Let's say 15

When the standard minerals and hardness values are listed, talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, quartz 8, yellow jade 9, garnet 10, zircon 11 , Alumina 12, silicon carbide 13, boron carbide 1
4, diamond 15. By rubbing these reference minerals and specimens against each other, the hardness is compared to 1
Hardness is determined on a scale of -15.

The content of the abrasive in the lower layer is 3 to 20 parts by weight, preferably 5 to 15 parts by weight, and particularly preferably 5 to 10 parts by weight. In the present invention, when the abrasive satisfies the above-mentioned predetermined average particle diameter, new Mohs hardness and blending amount, grain edge from the edge is prevented and good C / N ratio characteristics and running durability are obtained. You can

(B-2-4) Conductive fine powder The conductive fine powder contained in the lower layer includes carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, organic compounds of silver, copper powder and other metals. Examples thereof include particles and the like, pigments such as metal oxides such as zinc oxide, barium sulfate, and titanium oxide coated with a conductive substance such as a tin oxide coating or an antimony solid solution tin oxide coating. The average particle size of the conductive fine powder used in the lower layer,
It is 5 to 50 nm, and more preferably 5 to 30 nm. As the content of the conductive fine powder, the content of the conductive fine powder is 1 to 20 parts by weight with respect to 100 parts by weight of a non-magnetic powder, a high magnetic permeability material or a combination thereof, and more preferably, 5 to 15 parts by weight.

When the conductive fine powder is contained in the uppermost magnetic layer under the above conditions, more preferable head clog characteristics and running durability can be obtained.

(B-2-5) Binder As the binder used in the lower layer, for example, vinyl chloride resins such as polyurethane, polyester and vinyl chloride copolymer are typical. 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, and M ¹ represents a hydrogen atom, Na, K or
Represents an alkali atom such as Li or an alkyl group.

The above polar group has the function of improving the dispersibility of the magnetic powder, and the content in each resin is 0.1 to 8.0 mol%, preferably 0.5 to 6.0 mol%. When the content is less than 0.1 mol%, the dispersibility of the magnetic powder is deteriorated, and when the content is more than 8.0 mol%, the magnetic coating tends to gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The content of the binder in the non-magnetic layer or the layer containing the high magnetic permeability material in the lower layer is usually 10 to 40 parts by weight, preferably 15 parts by weight with respect to 100 parts by weight of the magnetic powder.
~ 30 parts by weight. The binder is not limited to one type,
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 1 by weight.
It is 0:90, preferably 70:30 to 30:70.

The polar group-containing vinyl chloride copolymer used as a binder in the present invention is a copolymer having a hydroxyl group such as a vinyl chloride-vinyl alcohol copolymer and the following compound having a polar group and a chlorine atom. Can be synthesized by the addition reaction of ClCH 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 ₂ SO ₃ Na is taken as an example, describing the reaction is 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-based 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 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 are cited.
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 the polyol 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, 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 Here, regarding a polar group introduced into the 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 weight of the binder. The resin has a weight average molecular weight of 10,000 to 200,000, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer. Coalesced, polyamide resin,
Polyvinyl butyral, cellulose derivatives (nitrocellulose, etc.), styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, various synthetic rubber resins Etc.

(B-2-6) Other components In the present invention, in order to improve the quality of the lower layer, additives such as a lubricant, a durability improver, a dispersant, an antistatic agent and a filler are added. It can be contained as a component. Fatty acids and / or fatty acid esters can be used as lubricants. In this case, the amount of fatty acid added is 0.2 with respect to the non-magnetic powder or the high magnetic permeability material.
-10 wt% is preferable, and 0.5-5 wt% is more preferable. 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 fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the non-magnetic powder or the high magnetic permeability material. 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, fatty acid ester seeps out to the upper and lower surfaces of the magnetic layer and the output decreases. Is likely to occur.

When it is desired to use 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,
6-30 are preferable and, as for carbon number, the range of 12-22 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, and succinic acid. Acid, maleic acid, glutaric acid, adipic acid,
Examples thereof include 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.

As the lubricant 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 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.

As the dispersant, fatty acids having 12 to 18 carbon atoms such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid;
Salts of these alkali metals or salts of alkaline earth metals or amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefinoxy quaternary ammonium salts; azo compounds having carboxyl groups and sulfonic acid groups, etc. Can be mentioned. These dispersants are usually used in the range of 0.5 to 5% by weight based on the non-magnetic powder or the high magnetic permeability material.

Examples of the antistatic agent include cationic surfactants such as quaternary amines; anionic surfactants containing an acid group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid; aminosulfonic acid and the like. Amphoteric surfactants; natural surfactants such as saponin and the like can be mentioned. The above-mentioned antistatic agent is usually 0.01 to 4 with respect to the binder.
It is added in the range of 0% by weight.

(C) Top layer composed of magnetic layer (C-1) Description of top layer composed of magnetic layer The top layer composed of a magnetic layer is not particularly limited except that it contains a magnetic powder and an abrasive. It can be formed using various methods.

(C-1-1) Thickness of uppermost layer composed of magnetic layer The thickness of the uppermost layer composed of a magnetic layer is less than 0.5 μm, preferably 0.1 to 0.4 μm. .. When the thickness of the magnetic layer is within the above range, various properties required as a digital recording medium are improved in combination with the above-mentioned lower layer containing the non-magnetic powder or the high magnetic permeability material.
Conversely, if the thickness of this layer exceeds 0.5 μm, good C
/ N ratio characteristics cannot be obtained.

(C-1-2) Surface Roughness of _{Uppermost Layer Comprising} Magnetic Layer The surface roughness R _10Z of the uppermost layer comprising magnetic layer is usually 50 nm or less, preferably 30 nm or less,
Particularly preferably, it is 5 to 20 nm. This surface roughness R
It is more preferable that _10Z is in the range of 5 to 20 _nm because good C / N ratio characteristics can be obtained. The surface roughness R
_10Z is a cut surface when the magnetic recording medium is vertically cut by a reference length in the longitudinal direction within a range of ± 2 mm (indicated by R in FIG. 2) from the midpoint P in the width direction as shown in FIG. Of the straight lines parallel to the horizon that cuts the outer surface contour curve at, select the one that passes through the tenth lowest peak from the highest and the one that passes through the tenth shallowest valley bottom from the deeper.
The distance d between the straight lines (L ₁ and L ₂ ) of the book is measured in the direction of the longitudinal magnification of the surface contour curve.

A _Talystep roughness meter (Rank Taylor Hobson) was used to measure the surface roughness R _10Z, and a stylus was used to measure 2.5 × 0.1 μm.
m, stylus pressure 2 mg, cut-off filter 0.3
It is possible to adopt a measurement condition of 3 Hz, a measurement speed of 2.5 μm / sec, and a reference length of 0.5 mm. In the roughness curve, the unevenness of 0.002 μm or less is cut.

In _order to control the surface roughness R _10Z , calendering conditions may be set in the manufacturing process to control the surface smoothness of the magnetic layer.
That is, temperature, linear pressure, C as calendar conditions
A factor such as / S (coating speed) may be controlled. Further, the size, amount, etc. of the added particles in the magnetic layer, which is another factor, may be controlled if necessary.

To achieve the object of the present invention, the temperature is usually 50 to 140 ° C. and the linear pressure is 50 to 400 K.
It is preferable to keep g / cm and the above C / S at 20 to 600 m / min. If these numbers are out of range,
It may be difficult or impossible to specify the surface roughness R _10Z of the magnetic layer as described above.

(C-2) Composition of the uppermost layer composed of the magnetic layer The uppermost layer composed of the magnetic layer contains a magnetic powder and an abrasive. Furthermore, the uppermost layer consisting of the magnetic layer is conductive fine powder,
It may contain a binder and other components.

(C-2-1) Magnetic Powder Examples of the magnetic powder used in the present invention include ferromagnetic iron oxide powder, ferromagnetic metal powder, and hexagonal plate-like powder. Among these, the ferromagnetic metal powder and hexagonal plate-like powder described below can be preferably used. Examples of the ferromagnetic iron oxide powder include γ-Fe ₂ O ₃ and Fe ₃ O
₄ or FeO _x (1.33
<X <1.5) or Co-added (cobalt-modified) Co—FeO _x (1.33 <x
The thing etc. which are represented by <1.5) can be mentioned.

As the ferromagnetic metal powder, Fe, Co
, Fe-Al system, Fe-Al-Ni system, Fe-
Al-Zn system, Fe-Al-Co system, Fe-Al-Ca
System, Fe-Ni system, Fe-Ni-Al system, Fe-Ni-
Co-based, Fe-Ni-Si-Al-Mn-based, Fe-Ni
-Si-Al-Zn system, Fe-Al-Si system, Fe-N
i-Zn system, Fe-Ni-Mn system, Fe-Ni-Si
System, Fe-Mn-Zn system, Fe-Co-Ni-P system, N
Ferromagnetic metal powders, such as i-Co type | system | group, metal magnetic powder which has Fe, Ni, Co etc. as a main component, are mentioned. Above all, F
The e-based metal powder has excellent electrical characteristics.

On the other hand, from the viewpoint of corrosion resistance and dispersibility, Fe-Al type, Fe-Al-Ca type, Fe-Al-type.
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Ni-Si-Al-Zn system, Fe-Ni-Si-A
Fe-Al based ferromagnetic metal powder such as 1-Mn based is preferable.

Particularly preferred ferromagnetic metal powder for the purpose of the present invention is metal magnetic powder containing iron as a main component,
1 or Al and Ca, Fe: Al = 100: 0.5 to 100: 20 by weight for Al, and Fe: Ca = 100: 0.1-10 by weight for Ca.
It is desirable to contain it in the range of 0:10.

By setting the ratio of Fe: Al in such a range, the corrosion resistance is remarkably improved, and by setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics are improved and dropout is reduced. Can be made The reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, but it is considered that the coercive force is increased and the agglomerates are decreased due to the improved dispersibility.

The ferromagnetic powder used in the present invention has an average major axis length of 0.2 as observed by a transmission electron microscope.
Less than 5 μm, preferably 0.10 to 0.22 μm, more preferably 0.10 to 0.17 μm, and a crystallite size by X-ray diffractometry of less than 200Å, particularly 100 to 1
It is preferably 80Å. When the average major axis length and the crystallite size of the ferromagnetic powder are within the above ranges, the electromagnetic conversion characteristics can be further improved.

The ferromagnetic powder used in the present invention usually has a coercive force (Hc) of 600 to 5,000 O.
It is preferably in the range of e. This coercive force is 600
If it is less than Oe, the electromagnetic conversion characteristics may deteriorate, and if the coercive force exceeds 5,000 Oe, recording may not be possible with an ordinary head, which is not preferable.

The ferromagnetic powder preferably has a saturation magnetization amount (σ _s ) which is a magnetic property, usually 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, electromagnetic conversion characteristics may deteriorate. Furthermore, according to the present invention, the BET is increased according to the higher recording density.
30 m ² / g or more in terms of specific surface area by the method, especially 45 m ²
A ferromagnetic metal powder having an amount of / g or more is preferably used.

This specific surface area and its measuring method are described in detail in “Measurement of powder” (JMDallavelle, Clyeorr Jr., co-authored, Muta et al., Published by Sangyo Tosho Publishing Co., Ltd.),
It is also described in "Chemical Handbook", Applied Edition, P1170 to 1171 (edited by The Chemical Society of Japan; Maruzen Co., Ltd., published April 30, 1966).

The specific surface area is measured, for example, by using a powder of 105
Degassed while being heated at around 13 ° C for 13 minutes to remove those adsorbed on the powder, and then introduce this powder into the measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² .
Measurement is carried out with nitrogen at liquid nitrogen temperature (-105 ° C) for 10 minutes. As a measuring device, for example, a counter soap (manufactured by Yuasa Ionics Co., Ltd.) is used.

Further, as a preferable structure of the ferromagnetic powder, the content ratio of Fe atoms and Al atoms contained in the ferromagnetic powder is Fe: Al = 100: 1 to 1 in terms of atomic number ratio.
The content ratio of Fe atoms and Al atoms in the surface region of 00:20 and ESCA analysis depth of the ferromagnetic powder of 100 Å or less is Fe: Al = 30.
It has a structure of 0:70 to 70:30.
Alternatively, Fe atoms, Ni atoms, Al atoms, and Si atoms are contained in the ferromagnetic powder, at least one of Zn atoms and Mn atoms is further contained in the ferromagnetic powder, and the content of Fe atoms is 90 atomic%. Above, the content of Ni atoms is 1 atomic%
Or more and less than 10 atomic%, the content of Al atoms is 0.1 atomic% or more and less than 5 atomic%, the content of Si atoms is 0.1 atomic% or more and less than 5 atomic%, the content of Zn atoms and / Or the content of Mn atoms (however, the total amount when both Zn and Mn atoms are contained) is 0.1 atom% or more and less than 5 atom%, and the analysis depth of the ferromagnetic powder by ESCA And Fe atom, Ni atom, Al atom, Si atom, Zn atom and /
Alternatively, the content ratio of Mn atoms is Fe: Ni: A in terms of atomic number ratio.
1: Si (Zn and / or Mn) = 100: (4 or less): (10-60): (10-70): (20-8)
Examples thereof include a ferromagnetic powder having a structure of 0).

Examples of the hexagonal plate-like powder include hexagonal ferrite. Such a hexagonal ferrite is composed of, for example, a strontium ferrite and a bismuth ferrite, and a part of the iron element is another element (for example, Ti, Co, Zn, In, Mn, Ge, Hb).
Etc.). Regarding this ferrite magnetic material, the IEEE trans on MAG-18 1
6 (1982).

Of these, barium ferrite can be preferably used in the present invention. As an example of the barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder preferably used in the present invention, an average particle size in which a part of Fe is replaced with at least Co and Zn (of the plate surface of the hexagonal ferrite) The height of the diagonal line is 400 to 900Å, and the plate ratio (value obtained by dividing the length of the diagonal line of the plate surface of the hexagonal ferrite by the plate thickness) is 2.
There can be mentioned Ba-ferrite having a coercive force (Hc) of 450 to 1500, which is 0 to 10.0, preferably 2.0 to 6.0.

The coercive force of the Ba-ferrite powder is controlled to an appropriate value by partially substituting Fe for Co, and further by partially substituting for Zn, it cannot be obtained only by Co substitution. It is possible to obtain a magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. Further, in the Ba-ferrite used in the present invention, a part of Fe is T
It may be substituted with a transition metal such as i, In, Mn, Cu, Ge and Sn.

The Ba-ferrite used in the present invention is represented by the following general formula. _{BaO · n ((Fe 1-} m M m) 2 O 3) { However, m> 0.36 (However, Co + Zn = 0.08
˜0.3, Co / Zn = 0.5 to 10), n is 5.4 to 11.0, preferably 5.4 to 6.0, and M represents a substituted metal, and the average. Magnetic particles that are a combination of two or more elements, the number of which is 3, are preferable. } In order to obtain a sufficient reproduction output when used as a magnetic recording medium,
The average particle size of the Ba-ferrite is preferably 300 Å or more, and is preferably 900 Å or less in order to improve the surface smoothness and reduce the noise level. Also,
By setting the plate ratio to 2.0 or more, a perpendicular orientation ratio suitable for high density recording when used as a magnetic recording medium can be obtained, and the plate ratio can be improved to improve the surface smoothness and reduce the noise level. Is preferably 10.0 or less. Further, the coercive force is preferably 450 Oe or more in order to retain the recording signal, and the coercive force is 1500 in order to prevent the head from being saturated.
Oe or less is preferable.

The barium ferrite magnetic powder used in the present invention usually has a saturation magnetization (σ _S ) which is a magnetic characteristic.
It is preferably 50 emu / g or more. This is because if the saturation magnetization is less than 50 emu / g, the electromagnetic conversion characteristics may deteriorate. Further, in the present invention, it is desirable to use Ba-ferrite magnetic powder having a specific surface area of 30 m ² / g or more by the BET method according to the higher recording density.

As a method for producing the hexagonal magnetic powder used in the present invention, for example, the oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite can be prepared, for example, from boric acid. Such a glass-forming substance is melted, the resulting melt is rapidly cooled to form a glass, and the glass is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component. In addition to the glass crystallization method of removing by heat treatment,
A coprecipitation-firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method and the like can be applied.

In the present invention, the content of the above-mentioned magnetic powder is 50 to 99% by weight, preferably 60 to 99% by weight, particularly preferably 75 to 90% by weight.
% By weight.

(C-2-2) Abrasive agent In the present invention, examples of the abrasive agent used for the uppermost layer composed of the magnetic layer include those exemplified in the above (B-2-3). .. Among them, α-alumina is preferable.

The average particle size of the abrasive is usually 0.5 μm or less, preferably 0.05 to 0.5 μm.
m, and particularly preferably 0.05 to 0.3 μm. The abrasive has a new Mohs hardness of 6 or more.

The content of the abrasive in the uppermost layer composed of the magnetic layer is 7 to 100 parts by weight of the magnetic powder.
It is 20 parts by weight, preferably 7 to 15 parts by weight, and particularly preferably 7 to 12 parts by weight. In the present invention, the C / N ratio characteristics and running durability can be obtained by satisfying the conditions of the above-mentioned predetermined average particle diameter, new Mohs hardness and blending amount of the abrasive.

(C-2-3) Conductive fine powder As the conductive fine powder used in the present invention, the compounds exemplified in the above (B-2-4) can be mentioned.

The conductive fine powder used in the uppermost layer of the magnetic layer has an average particle diameter of 10 to 300 nm, preferably 30 to 300 nm, and particularly preferably 40 to 300 nm. Regarding the content of the conductive fine powder, the content of the conductive fine powder is 2 parts by weight or less, preferably 1 part by weight or less, relative to 100 parts by weight of the magnetic powder. When the conductive fine powder is contained in the uppermost magnetic layer under the above conditions, more preferable head clog characteristics and running durability can be obtained.

(C-2-4) Binder The binder contained in the uppermost layer of the magnetic layer is (B-
It is as described above in 2-5). The content of the binder in the uppermost layer composed of the magnetic layer is usually 10 to 40 parts by weight, preferably 15 to 30 parts by weight, based on 100 parts by weight of the magnetic powder.

(C-2-5) Other Components The other components contained in the uppermost layer composed of the magnetic layer are (B
It is as described above in 2-6). The content of the lubricant is 0.2 to 10% by weight based on the magnetic powder.
Is preferred, and 0.5 to 5% by weight is more preferred. The content of the dispersant is 0.5 to 5 relative to the magnetic powder.
% By weight.

-Manufacture of Magnetic Recording Medium- In the magnetic recording medium of the present invention, it is preferable that the magnetic layer is coated by a so-called wet-on-wet system in which the lower layer is in a wet state. 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 magnetic 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 paint, and then the high-concentration magnetic paint is diluted to obtain a magnetic powder. After the paint is prepared, this magnetic paint is applied to the surface of the non-magnetic support.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and cyclohexanone; alcohols such as methanol, ethanol and propanol; esters such as methyl acetate, ethyl acetate and butyl acetate. Cyclic ethers such as tetrahydrofuran and the like; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene can be used.

In kneading and dispersing the components for forming the magnetic layer,
Various kneading dispersers can be used. Examples of this kneading disperser include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a cobol mill, a tron mill, a sand mill, a sand grinder, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a disper, and a high speed. Examples thereof include a mixer, a homogenizer, an ultrasonic disperser, an open kneader, a continuous kneader, and a pressure kneader. Among the above-mentioned kneading dispersers, kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) include a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, and a three-roll mill. This is a roll mill.

In order to coat the uppermost magnetic layer and the lower layer on the non-magnetic support, specifically, as shown in FIG. 2, first, the non-magnetic support 1 fed from the supply roll 32 is fed.
Extrusion type extrusion coater 10,
11, wet the top layer paint and the lower layer paint-
After the multi-layer coating by the on-wet method, it passes through the magnet for orientation or the magnet for vertical orientation 33 and is introduced into the dryer 34,
Here, hot air is blown from the nozzles arranged above and below to dry. 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-mentioned method, each paint was extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. It should be noted that in the figure, the arrow indicates the conveying direction of the non-magnetic support. Extrusion coaters 10 and 11 are provided with liquid pools 13 and 14, respectively, and the coating materials from the coaters are stacked in a wet-on-wet system. That is, the uppermost magnetic layer coating material is applied in multiple layers immediately after the lower layer coating material is applied (when it is in an undried state). As the extrusion coater, in addition to the two extrusion coaters 5a and 5b shown in FIG. 3, the extrusion coaters 5c and 5d of the types shown in FIGS. 4 and 5 can be used.
Of these, the extrusion coater 5d shown in FIG. 5 is preferable in the present invention. The lower layer application material 2 and the uppermost layer coating material 4 are co-extruded by an extrusion coater 5d to apply multiple layers.

As the solvent to be blended in the above paint or a diluent solvent when applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; alcohols such as methanol, ethanol, propanol, 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, since the upper magnetic layer is coated while the layer located under the uppermost layer is in a wet state, the surface of the lower layer (that is, the uppermost layer). The boundary surface) and the surface properties of the uppermost layer are improved, and the adhesiveness between the upper and lower layers is also improved. As a result, especially for high-density recording, the performance required for high output and low noise, such as a magnetic tape, is satisfied, and film durability is also required for film peeling. It is eliminated, the film strength is improved, and the durability is sufficient. Wet-on-
The wet multi-layer coating method can 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 calendar conditions. In the present invention, the temperature is usually 50 to 120 ° C., and the linear pressure is 50 to 4
It is preferable to maintain 00 kg / cm and the above C / s at 20 to 600 m / min. If these numbers are not satisfied,
It may be difficult or impossible to keep the surface roughness R _10Z of the magnetic layer in a specific range.

The thickness of the uppermost layer obtained as a result of the above treatment is 0.5 μm or less, preferably 0.1 to 0.4.
μm. When the thickness of the layer exceeds 0.5 μm, the high frequency characteristics and the overwrite characteristics are deteriorated, which is no different from the magnetic recording medium having a single layer structure, and the object of the present invention cannot be achieved.

[0093]

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.

Example 1 The following components of the magnetic composition for the uppermost layer were kneaded and dispersed using a kneader sand mill to prepare a magnetic layer coating material for the uppermost layer and a coating material for the lower layer.

{Magnetic coating material A for the uppermost layer} Fe-Al based ferromagnetic metal powder ... 100 parts (Fe: Al weight ratio = 100: 8, average major axis length 0) 16 μm, Hc1,580 Oe, σ _s 120 emu / g, crystallite size 170 Å) Vinyl chloride resin containing sulfonic acid metal salt ········· 10 parts (Nippon Zeon Co., Ltd. MR-110) Polyurethane resin containing sulfonic acid metal salt: 5 parts (Toyobo Co., Ltd., UR-8700) Alumina:・ ・ ・ ・ ・ ・ 8 parts (α-Al ₂ O ₃ , average particle size 0.2 μm, new Mohs hardness: 12) Carbon black (average particle size 40 nm) ・ ・ ・ ・ ・ ・ 0.5 parts Stearic acid ... 1 part Myristic acid・ ・ ・ ・ ・ ・ 1 part Butyl stearate ・ ・ ・ ・ ・ ・ 1 part Cyclohexanone ・ ・ ・100 parts Methyl ethyl ketone ... 100 parts Toluene ... ...... 100 parts {magnetic paint B for uppermost layer} In the above magnetic paint A for uppermost layer, SnO ₂ (average particle diameter 40 nm) is used in place of carbon black, except that It was prepared in the same manner as the magnetic coating material A for the upper layer.

{Magnetic coating C for the uppermost layer} In the magnetic coating A for the uppermost layer, 8 parts of Cr ₂ O ₃ (average particle diameter 0.2 μm, new Mohs hardness: 11) was used instead of alumina. It was prepared in the same manner as the magnetic coating material A for the uppermost layer.

{Magnetic paint D for the uppermost layer} In the above magnetic paint A for the uppermost layer, Co-substituted barium ferrite (Hc: 1,100) was used in place of the Fe--Al based ferromagnetic metal powder.
Oe, BET 45 m ² / g, σ _s : 64 emu / g, and plate ratio 4) were used, except that the above magnetic coating material A for top layer was prepared.

{Coating E for lower layer} TiO ₂ (spherical, average particle size 30 nm) ... 90 parts Carbon black (average particle size 27 nm) ... 10 parts Vinyl chloride-based resin containing sulfonic acid metal salt: 6 parts (MR-110 manufactured by Nippon Zeon Co., Ltd.) Polyurethane resin containing sulfonic acid metal salt: 3 Part (Toyobo Co., Ltd., UR-8700) Alumina: 6 parts (α-Al ₂ O ₃ , average particle) Diameter 0.2 μm, new Mohs hardness: 12) Myristic acid: 1 part Butyl stearate:・ ・ ・ ・ ・ ・ ・ ・ 1 part Cyclohexanone ・ ・ ・ ・ 100 parts Methyl ethyl ketone ・・ ・ ・ 100 parts Toluene ・ ・ ・ 100 parts {Paint F for lower layer} The lower layer coating material E was prepared in the same manner as the lower layer coating material E except that SnO ₂ (average particle diameter 40 nm) was used instead of carbon black.

{Lower layer coating material G} The lower layer coating material E was prepared in the same manner as the lower layer coating material E except that CaCO ₃ (spherical, average particle diameter 30 nm) was used in place of TiO ₂ . ..

{Lower layer coating material H} In the same manner as in the preparation of the lower layer coating material E except that 100 parts of carbon black (spherical, average particle diameter 27 nm) was used in place of TiO ₂ in the lower layer coating material E. Prepared.

{Lower layer coating material I} In the lower layer coating material E, instead of TiO ₂ , Fe--Si--Al sendust alloy powder (coercive force Hc = 40 A / m, Mi = 200 H /
m, spherical, average particle diameter 50 nm) was used in the same manner as in the preparation of the lower layer coating material E.

{Magnetic coating material J for the uppermost layer} In the magnetic coating material A for the uppermost layer, ZnO (average particle diameter 0.2 μm, new Mohs hardness: 5) was used in place of alumina, except that the magnetic material for the uppermost layer was formed. It was prepared in the same manner as the paint A.

5 parts of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the obtained upper layer magnetic coating material and lower layer coating material.

(Examples 1 to 16 and Comparative Examples 1 to 10)
According to the coating composition of the composition shown in Table 1, the composition was applied on a polyethylene terephthalate film having a thickness of 10 μm by a wet-on-wet method, and then a magnetic field orientation treatment was carried out while the coating was not dried. After drying,
The surface is smoothed with a calendar, and the thickness is 2.0 μm.
To form a magnetic layer composed of a lower layer and a top layer having a thickness of 0.4 μm.

Further, a coating material having the following composition is applied to the surface (back surface) of the polyethylene terephthalate film on the side opposite to the magnetic layer, the coating film is dried and calendered according to the above-mentioned calendering conditions. As a result, a back coat layer having a thickness of 0.8 μm was formed to obtain a wide original anti-magnetic tape.

Carbon black: 40 parts (Raven 1035) Barium sulfate:・ ・ ・ 10 parts (average particle size 300 nm) Nitrocellulose ・ ・ ・ ・ ・ ・ 25 parts Polyurethane resin ・ ・ ・ ・25 parts (N-2301 manufactured by Nippon Polyurethane Co., Ltd.) Polyisocyanate compound: 10 parts (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) Cyclohexanone ... 400 parts Methyl ethyl ketone ... 250 parts Toluene ...・ ・ ・ ・ ・ ・ ・ ・ ・ 250 copies Slit the original magnetic tape Then 8 mm
A wide width magnetic recording medium for video was prepared. The following evaluation tests were conducted on this magnetic recording medium. The results are shown in Table 1.

<C / N Ratio Characteristic> A single wave of 9 MHz was recorded and the output level when the signal was reproduced was expressed by comparison with a reference sample.

<Overwrite Characteristics> A residual output level of a 2 MHz signal when a 2 MHz signal was recorded at a saturation level and then a 9 MHz signal was (overwritten) recorded, was measured. The lower the residual output level, the better the overwrite characteristics.

<Running Durability> Under the environment of 20 ° C. and 60% RH, S-550 (manufactured by Sony Corporation) was used to repeat the reproduction for 5 minutes at the beginning of the tape for 200 passes or more, and there was no edge damage. Was observed.

<Head Clog Characteristics> 40 ° C., 20% R
Under the environment of H, the tape was run for the full length using S-550 (manufactured by Sony Corp.), and the case where the decrease of the RF output was 2 dB or more and 1 second or more continuously was taken as the head clogging. Counted.

[0111]

[Table 1]

[0112]

According to the present invention, excellent C / N ratio characteristics,
A magnetic recording medium having overwrite characteristics, head clog characteristics, and running durability can be provided.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the situation when measuring the surface roughness R _10Z of a magnetic layer.

FIG. 2 is a diagram for explaining multi-layer coating of a magnetic layer by a wet-on-wet coating method.

FIG. 3 is a diagram showing an example of an extrusion coater for applying a magnetic paint.

FIG. 4 is a diagram showing an example of an extrusion coater for applying a magnetic paint.

FIG. 5 is a diagram showing an example of an extrusion coater for applying a magnetic paint.

[Explanation of sign]

 1 non-magnetic support 2 lower layer paint 4 uppermost layer coating 5a extrusion coater 5b extrusion coater 5c extrusion coater 5d extrusion coater 6 uppermost magnetic layer 7 lower layer 8 backcoat layer 10 extrusion coater 11 extrusion coater 13 liquid pool part 14 liquid Reservoir part 32 Supply roll 33 Magnet for orientation or magnet for vertical orientation 34 Dryer 37 Super calender device 38 Calender roll 39 Winding roll

Claims (7)

[Claims] 1. A lower layer having at least one layer containing a non-magnetic powder or a high magnetic permeability material on a non-magnetic support, and an uppermost layer consisting of a magnetic layer containing a magnetic powder and an abrasive in this order. 7 to 20 parts by weight of an abrasive having a new Mohs hardness of 6 or more and an average particle diameter of 0.5 μm or less is laminated on the uppermost layer composed of the magnetic layer with respect to 100 parts by weight of the magnetic powder. And a layer thickness of less than 0.5 μm. 2. The uppermost layer composed of the magnetic layer has a new Mohs hardness of 6 or more and an average particle size of 0.05 to 0.3.
The magnetic recording medium according to claim 1, containing an abrasive having a thickness of μm. 3. The method according to claim 1, wherein the lower layer has at least one layer containing an abrasive having a new Mohs hardness of 6 or more and an average particle size of 0.6 μm or less. The magnetic recording medium described. 4. The lower layer has an average particle size of 1 to 300 nm.
The magnetic recording medium according to any one of claims 1 to 3, further comprising at least one layer containing a non-magnetic powder or a material having a high magnetic permeability, which is spherical and is spherical. 5. The magnetic recording medium according to claim 1, wherein an uppermost layer is provided when the lower layer is in a wet state. 6. The surface roughness R of the uppermost layer formed of the magnetic layer.
The magnetic recording medium according to claim 1, wherein _10Z is 5 to 20 nm. 7. The magnetic recording medium according to claim 1, wherein the uppermost layer composed of the magnetic layer contains conductive fine powder having an average particle diameter of 10 to 300 nm.