JPH1021522A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve both of electromagnetic conversion characteristics and traveling property. SOLUTION: This magnetic recording medium has a magnetic layer having >=2μm thickness which essentially composed of a ferromagnetic metal powder and a binder resin on a nonmagnetic supporting body. The ferromagnetic metal powder particles have <=0.15μm major axial length and 1/4 to 1/9 aspect ratio, and the magnetic layer has >=1000pieces/900 μm<2> projections having 10 to 25nm height measured by an atomic force microscope(AFM), <=250 pieces/900 μm<2> of projections having >=30nm height and 350 to 750nm surface roughness. This magnetic recording medium is suitably used for a magnetic recording system with >=80μm core width of a magnetic head, >=20m/sec relative velocity between the magnetic head and a magnetic recording medium <=1μm shortest recording wavelength.

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, and more particularly to a digital magnetic recording system having a high output.
The present invention also relates to a magnetic recording medium having good running properties.

[0002]

2. Description of the Related Art Generally, as a magnetic recording medium for audio, video, computer (disk, memory tape) and the like, a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support. The provided magnetic recording medium is used. In recent years, in the field of these magnetic recording media, practical use of digital recording with less deterioration of recording during dubbing from conventional analog recording has been progressing. In general, digital recording requires more signals to be recorded than analog recording, and the equipment and magnetic media used must have high image quality and high sound quality, as well as small size and space saving. There is a demand for higher density recording.

In order to achieve high-density recording, a recording wavelength is shortened and a recording track is narrowed.
Therefore, a magnetic medium having a high output and a high C / N ratio is required. The magnetic medium has an output in high density recording, C /
In order to increase the N ratio, the ferromagnetic powder is made finer and more highly filled, and the surface of the magnetic layer is increasingly smoothed. However, when the surface of the magnetic layer becomes smooth, there is a problem that the friction coefficient during running becomes large and running failure occurs. If the surface of the magnetic layer is roughened in order to improve the running performance, the output, C
/ N ratio decreases. Therefore, it is necessary to balance the surface roughness between the electromagnetic conversion characteristics and the traveling performance.

However, the range of surface roughness that can be balanced has been narrowed with the recent increase in recording density.
It is difficult to find the balance range by the conventional surface roughness measuring means. For example, when the center line average roughness Ra becomes 7 nm or less, the output and the C / N ratio do not necessarily increase in proportion to Ra. The center line average roughness Ra is affected by a concave portion which is originally irrelevant to the spacing between the head and the medium, and includes a factor which makes a mistake in the evaluation of the spacing. Rather, emphasis should be placed on convexities for spacing.

[0005] As means for evaluating the protrusions on the surface of the magnetic layer,
The ratio Ns / Ns of the number Ns of protrusions projecting 0.01 μm from the average line of the surface roughness cross-sectional curve measured using a Taristep roughness meter to the number Ns (t) of all peaks projecting from the average line.
It has been proposed to use (t) (Japanese Unexamined Patent Publication No. 3-17 / 1991).
816), since the magnetic medium and the magnetic head are in surface contact with each other, the number of protrusions from the average surface roughness of the magnetic layer surface should be measured.

As a means for evaluating the surface roughness of the magnetic layer, three-dimensional roughness is measured by using an optical non-contact surface roughness meter (HIPOSS), and the area of ± 5 nm from the average plane is traversed from below to above. It has been proposed to count the number of protrusions when the number of protrusions is counted as one (JP-A-3-22412).
7) However, projections that do not cross the region -5 nm from the average plane from below also affect the spacing. Also in this case, since the influence of the concave portion from the average plane is included, the evaluation of the spacing includes a factor that makes a wrong decision.

The broadcast video system has evolved from the D3 system to the D5 system, but the D5 system has a feature not found in the conventional systems, that is, sliding on the magnetic tape in a direction perpendicular to the head running direction. The width of the moving surface (hereinafter also referred to as the core width of the magnetic head) is 12
It is characterized by a width of 0 μm and a very high magnetic tape feed speed. However, it is more difficult to achieve both the wear resistance of the magnetic head and the durability with the magnetic layer when the magnetic head is used for a long time. It has become

That is, in the D5 system, the structure of the magnetic head is of a component type, and not only the relative speed between the magnetic head and the magnetic tape is high, but also the tape feeding speed is very fast, which is twice that of the D3 system. Is 10m per minute. Head wear tends to increase due to an increase in magnetic tape / head relative speed due to high speed transport of the magnetic tape in the VTR and high speed rotation of the head. In order to ensure such head wear within the optimum range, the abrasion or surface hardness of the magnetic tape is adjusted to an appropriate range, and the core width is increased to increase the contact area of the magnetic head core with the tape as described above. Have been dealt with.

However, in order to achieve both the wear resistance of the magnetic head and the durability of the magnetic layer when the magnetic head is used for a long period of time, when the area of the magnetic head is increased, the RF output tends to decrease and increase in fluctuation. There was a problem. This is because the RF output decreases and the output fluctuates because the magnetic tape is drawn into the head mounting window of the cylinder head and the gap between the magnetic tape and the head increases. Further, if the surface hardness of the magnetic layer is excessively increased in order to improve the surface characteristics of the magnetic layer in order to improve the electromagnetic conversion characteristics sacrificed for securing the running durability, the head contact becomes insufficient and the electromagnetic conversion characteristics cannot be improved. There was a problem.

That is, in the D5 system, there has been a demand for a magnetic recording medium having a magnetic layer capable of improving the contact of the magnetic head and ensuring the durability of the magnetic layer.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium in which both the electromagnetic conversion characteristics and the running properties are improved at the same time, and a magnetic recording system to which the magnetic recording medium is applied. It is in.

[0012]

According to the present invention, a ferromagnetic metal powder and a binder resin having a thickness of 2 μm are formed on a non-magnetic support.
m, the ferromagnetic metal powder has a major axis length of 0.15 μm or less and an axial ratio of ４.
１／1/9, and 1000/90 protrusions with a height of 10-25 nm as measured by an atomic force microscope (AFM).
250 μm ² or more and 30 nm or more protrusions 250
/ 900 μm ² or less, and the surface hardness of the magnetic layer is 3
A magnetic recording medium having a thickness of 50 to 750 nm or more.

The present inventors have conducted intensive studies focusing on the protrusions on the surface of the magnetic layer and the surface hardness of the magnetic layer as factors affecting the spacing between the head and the medium. As a result, the magnetic force was measured using an atomic force microscope (AFM). The size and number of protrusions protruding from the average surface roughness of the layer surface greatly affect the electromagnetic conversion characteristics and runnability, and the depth of the groove formed on the surface of the magnetic layer when the surface layer of the magnetic layer is rubbed with a diamond needle. The inventors have found that they affect the electromagnetic conversion characteristics and durability, and have reached the present invention.

In a magnetic recording system in which the core width of the magnetic head is 80 μm or more, the relative speed between the magnetic head and the magnetic recording medium is 20 m / sec or more, and the shortest recording wavelength is 1 μm or less, the major axis length is 0.15 μm or less, preferably 0 μm or less. .11 μm or less, and the axial ratio is 1/4 to 1/9, preferably 1/4 to 1
The number of protrusions having a height of 10 to 25 nm measured by AFM using a ferromagnetic metal powder of
m ² or more, preferably 3000 pieces / 900 μm ² or more 1
The number of protrusions having a height of 0000/900 μm ² or less and a height of 30 nm or more is 250/900 μm ² or less, preferably 1
00/900 μm ² or less The magnetic layer has a surface hardness of 350 to 750 nm or more, preferably 4 to
Excellent electromagnetic conversion characteristics and durability can be obtained by setting the thickness to 00 to 600 nm.

Here, the major axis length of the ferromagnetic metal powder is 0.15.
If it is larger than μm, the number of protrusions of 30 nm or more of the magnetic layer is 25
Electromagnetic conversion characteristics are deteriorated because the number is larger than 0/900 μm ² . On the other hand, if the axis ratio of the strong powder is more than 1/4, the orientation becomes poor when the magnetic tape is formed, and the electromagnetic conversion characteristics deteriorate.
If the axial ratio of the ferromagnetic metal powder is smaller than 1/9, the degree of filling when formed into a magnetic tape becomes poor, and the electromagnetic conversion characteristics deteriorate.

If the surface hardness is smaller than 350 nm, the electromagnetic conversion characteristics deteriorate. If the surface hardness is more than 750 nm, the scratch resistance of the magnetic layer is reduced, and the magnetic layer is liable to cause problems such as clogging and increase in dropout.
In the present invention, the major axis length of the ferromagnetic metal powder means an average major axis length, and the axial ratio means (average minor axis length / average major axis length).

Next, in the present invention, a measuring method for evaluating the number of protrusions on the surface of the magnetic layer which directly affects the electromagnetic conversion characteristics and running properties and a method for measuring the surface hardness of the magnetic layer will be described. In the present invention, the height of the protrusion is Digi.
The three-dimensional surface roughness is measured using AFM (atomic force microscope) manufactured by tal Instruments, and the distance from the average surface roughness of the magnetic layer to the top of the protrusion is referred to. Here, the average surface is a surface in which the volume of unevenness in the measurement surface is equal. As the number of protrusions, the number of protrusions having the height of the protrusions in the above range is obtained. The measurement conditions are shown below.

Probe: Square cone with 70 ° ridge angle, material SiN ₄ Measurement area: 30 μm × 30 μm Scanning speed: 1 Hz The surface hardness of the magnetic layer is determined by applying a constant load with a diamond needle having a constant tip shape. Of the magnetic layer and measuring the depth of the groove formed on the surface of the magnetic layer. Specifically, the surface property measuring device HEIDO
The magnetic layer was rubbed with a load of 25 g using a diamond needle having a tip shape of 0.1 μmR using N-14 (manufactured by Shinku Kagaku) and then a three-dimensional roughness measuring device TOPO-3
It can be obtained by measuring the depth (Peak-Valley) of the groove generated by the diamond needle with D (manufactured by WYKO).

The magnetic recording medium of the present invention comprises a non-magnetic support, a magnetic layer provided on the support and, if necessary, a back layer provided on the side opposite to the magnetic layer. The magnetic layer is composed of a ferromagnetic metal powder, a powdery component such as an additive filler, a liquid component such as a lubricant if necessary, and a binder in which the powdery component and the like are dispersed. The binder is composed of a resin component and a curing agent further blended as required.

In the present invention, in order to obtain a magnetic recording medium having the above-mentioned distribution of protrusions and surface hardness, the major axis length and the axial ratio of the ferromagnetic metal powder constituting the magnetic layer are set to predetermined ranges, and the binder is used. This can be achieved by adjusting the compounding amounts of the resin and the additive filler such as the abrasive, carbon black, and powdery lubricant, and controlling the calendaring method and conditions.

The powder components such as the ferromagnetic metal powder and the added filler are preferably used in an amount of 0.5 to 40 parts by weight, more preferably 6 to 30 parts by weight, based on 100 parts by weight of the binder resin. . The non-magnetic support used in the present invention has a thickness of about 5 to 20 μm, particularly 6 to 1 μm.
About 5 μm is preferable. Examples of the material include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; and vinyl resins such as polyvinyl chloride. And plastics such as polycarbonate, polyimide, polyamide and polysulfone, but polyethylene terephthalate, polyethylene naphthalate, polyamide and polyimide are preferably used. Prior to coating, these supports may be subjected to corona discharge treatment, plasma treatment, undercoating treatment, heat treatment, dust removal treatment, metal deposition treatment, and alkali treatment. Regarding these supports, see, for example, West German Patent 3,338,854A and JP-A-59-1169.
No. 26, JP-A-61-212973, U.S. Pat.
No. 8368; Yukio Mitsuishi, Textile and Industry, vol. 31, p5
0-55, 1975. The center line average surface roughness of these supports is 0.001 to 0.5 μm
(Cutoff value 0.25 mm) is preferred.

In the ferromagnetic metal powder of the present invention, the metal content in the ferromagnetic metal powder is 75% by weight, of which 80%
Examples of the ferromagnetic metal or ferromagnetic alloy in which at least one wt% is at least one type include Fe, Co, Fe-Al,
Fe-Co, Fe-Ni, Co-Ni, Co-Ni-F
e) and the like. Then, other metal components such as Al, Si, S, Sc, Ti, V, and C within a range of 20% by weight or less of such a ferromagnetic metal or ferromagnetic alloy.
r, Mn, Cu, Zn, Y, Mo, Rh, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
It may contain b, La, Ce, Pr, Nd, B, and P.

The particle size of the ferromagnetic metal powder is about 0.00
The average major axis length and axial ratio of 5 to 0.15 μm, that is, the ratio of average minor axis length / average major axis length is ４ to 1/9. The specific surface area (S-bet) of these ferromagnetic metal powders is 47
-80 m < ² > / g, more preferably 53-70 m < ² > / g, a coercive force (Hc) of 1,250-2,500 Oe, and a water content of 0.1-2.5 mOg.
The pH is preferably 1 to 2.0% by weight and the pH is 3 to 11 (5 g ferromagnetic metal powder / 100 g water). The surface of these ferromagnetic metal powders may be impregnated with a rust inhibitor, a surface treating agent, a dispersant, a lubricant, an antistatic agent, etc., impregnated in a solvent prior to dispersion for each purpose, and adsorbed. Good.

The ferromagnetic metal powder may be composed of Fe alone.
o, Ni, ferromagnetic metal elements, Al, Si, S, S
c, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
d, B, P, N, C and the like can be mentioned. In particular, in order to supplement the strength of metallic iron, it is desirable to provide Al, Si, and Cr alone or in combination on the surface layer. Also,
The ferromagnetic metal may include a small amount of a hydroxide or oxide, an alkali metal element (Na, K, etc.), or an alkaline earth metal element (Mg, Ca, Sr).
Methods for producing these ferromagnetic metal powders are already known,
The ferromagnetic metal powder used in the present invention can also be manufactured according to these known methods.

That is, as an example of a method for producing a ferromagnetic metal powder, the following method can be mentioned. (A) a method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen; and (b) reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles. (C) a method of thermally decomposing a metal carbonyl compound, (d) a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, and (e). A method for separating ferromagnetic metal powder from mercury after electrolytic fermentation using a mercury cathode,
(F) Method of obtaining fine powder by evaporating metal in a low-pressure inert gas When ferromagnetic metal powder is used, its shape is not particularly limited, but usually it is acicular, granular, rice granular, or the like. Are used, and a needle-like shape is particularly preferable. Further, σs of these ferromagnetic materials is preferably 100 to 210 emu / g. The crystallite size is preferably from 100 to 300A. Examples of these ferromagnetic metal powders are described in JP-A-53-70397 and JP-A-5-70397.
8-119609, JP-A-58-130435, JP-A-59-80901, JP-A-59-16903,
JP-A-59-41453, JP-B-61-37761.
No. 4,447,264, US Pat.
No. 1 and U.S. Pat. No. 4,931,198.

As the resin component of the binder used in the magnetic layer and the back layer of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, electron beam-curable resins, ultraviolet-curable resins, visible light Light curable resins and mixtures thereof are used. As a thermoplastic resin, the softening temperature is 150 ° C or less,
Average molecular weight of 10,000 to 300,000, degree of polymerization of about 5
About 0 to 2000, more preferably 200 to 60
0, for example, vinyl chloride vinyl acetate copolymer,
Vinyl chloride copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl alcohol copolymer, vinyl chloride vinylidene copolymer, vinyl chloride acrylonitrile copolymer, acrylate acrylonitrile copolymer, acrylate Vinylidene chloride copolymer, acrylate styrene copolymer, methacrylate acrylonitrile copolymer, methacrylate vinylidene chloride copolymer, methacrylate styrene copolymer, urethane elastomer, nylon-silicon resin, nitrocellulo -Polyamide resin, polyfukka vinyl, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer,
Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose striacetate, cellulose propionate, nitrocellulose, ethyl cellulose)
, Methylcellulose, propylcellulose, methylethylcellulose, carboxymethylcellulose, acetylcellulose, etc.), styrene-butadiene copolymer, polyester resin, polycarbonate resin, chlorovinyl ether acrylate copolymer , Amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof. Examples of these resins are described in JP-B-37-6877.
No., JP-B-39-12528, JP-B-39-1928
No. 2, Japanese Patent Publication No. 40-5349, Japanese Patent Publication No. 40-2090
No. 7, Japanese Patent Publication No. 41-9463, Japanese Patent Publication No. 41-1405
No. 9, JP-B-41-16985, JP-B-42-642
8, Japanese Patent Publication No. 42-11621, Japanese Patent Publication No. 43-462
No. 3, JP-B-43-15206, JP-B-44-288
No. 9, JP-B-44-17947, JP-B-44-182
No. 32, JP-B-45-14020, JP-B-45-14
500, JP-B-47-18573, JP-B-47-2
2063, JP-B-47-2264, JP-B-47-
22068, JP-B-47-22069, JP-B-47
-22070, JP-B-47-27886, JP-A-5
7-133521, JP-A-58-137133, JP-A-58-166533, JP-A-58-222433
No. JP-A-59-58642, U.S. Pat.
No. 4, U.S. Pat. No. 4,752,530.

The thermosetting resin or the reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and becomes infinite by a reaction such as condensation or addition by heating and humidifying after coating and drying. . Among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, phenoxy resin, epoxy resin, polyurethane resin, polyester resin, polyurethane polycarbonate resin, urea resin, melamine resin, alkyd resin,
Silicon resin, acrylic reaction resin (electron beam curable resin), epoxy-polyamide resin, nitrocellulose-melamine resin, high molecular weight polyester resin and isocyanate
A mixture of a toppolymer, a mixture of a methacrylate copolymer and a diisocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a urea formaldehyde resin, a low molecular weight glycol / high molecular weight geo-polymer.
/ Triphenylmethane triisocyanate mixture,
And polyamine resins, polyimine resins, and mixtures thereof. Examples of these resins are described in JP-B-39-8103.
No., JP-B-40-9779, JP-B-41-7192
No., JP-B-41-8016, JP-B-41-14275
No., JP-B-42-18179, JP-B-43-1208
No. 1, Japanese Patent Publication No. 44-28023, Japanese Patent Publication No. 45-145
No. 01, JP-B-45-24902, JP-B-46-13
103, JP-B-47-2265, JP-B-47-2
No. 2066, JP-B-47-22067, JP-B-47-
22072, JP-B-47-22073, JP-B-47
-28045, JP-B-47-28048, JP-B-4
It is described in publications such as 7-28922. These thermoplastic resins, thermosetting resins, and reactive resins include carboxylic acid (COOM), sulfinic acid, sulfenic acid, sulfonic acid (SO ₃ M), and phosphoric acid (PO (OM)) as functional groups other than the main functional groups. (OM)), phosphonic acid, sulfuric acid (OS
O ₃ M) and acidic groups such as ester groups thereof (M is H, an alkali metal, an alkaline earth metal, a hydrocarbon group),
Amino acids; aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohol, amphoteric groups such as alkyl betaine type, amino groups, imino groups, imide groups, amide groups, etc .; hydroxyl groups, alkoxyl groups, thiol groups , An alkylthio group, a halogen group (F, Cl, Br, I), a silyl group,
It usually contains at least one type of siloxane group, epoxy group, isocyanato group, cyano group, nitrile group, oxo group, acryl group, and phosphine group.
It is preferable to contain 1 × 10 ⁻⁶ eq to 1 × 10 ⁻² eq per g.

As the curing agent, a polyisocyanate compound is usually used. Examples of the polyisocyanate compound used in the magnetic layer and / or the back layer of the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate. Isocyanates such as naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and isophorone diisocyanate; Further, a product of the isocyanate and the polyalcohol, a polyisocyanate of 2 to 10 mer formed by the condensation of the isocyanate, and a product of the triisocyanate and the polyurethane, which have a terminal functional group. Is an isocyanate. The average molecular weight of these polyisocyanates is 100 to 20.
000 are preferred. Commercially available trade names of these polyisocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 203
1, Millionate MR, Millionate MTL (manufactured by Nippon Polyurethane Co., Ltd.), Takenet D-102, Takenet D
-110N, Takenet D-200, Takenet D-2
02, Takenate 300S, Takenate 500 (manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T-80, Sumidur 44
S, Sumidur PF, Sumidur L, Sumidur N, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, Desmodur T6
5, Desmodule 15, Desmodule R, Desmodule RF, Desmodule SL, Desmodule Z4
273 (manufactured by Sumitomo Bayer), and these can be used alone or in combination of two or more using the difference in curing reactivity. Compounds having a hydroxyl group (butanediol, hexanediol, polyurethane having a molecular weight of 1,000 to 10,000, water, etc.), an amino group (monomethylamine, dimethylamine, trimethylamine, etc.) and metal oxides for the purpose of accelerating the curing reaction. A catalyst such as a product catalyst or a catalyst such as iron acetylacetonate can be used in combination. It is desirable that these compounds having a hydroxyl group or an amino group are polyfunctional. These polyisocyanates are preferably used in an amount of 2 to 70 parts by weight, more preferably 5 to 50 parts by weight, per 100 parts by weight of the total amount of the binder resin and the polyisocyanate for both the magnetic layer and the back layer. These examples are described in JP-A-60-131622.
And JP-A-61-74138.

These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic metal powder and the binder in the magnetic layer is preferably from 5 to 25 parts by weight based on 100 parts by weight of the ferromagnetic metal powder.
Parts by weight, more preferably in the range of 8 to 22 parts by weight. The mixing ratio of the fine powder and the binder in the back layer is usually from 8 to 400 parts by weight, preferably from 50 to 300 parts by weight, based on 100 parts by weight of the fine powder. Additives include carbon black, abrasives, lubricants, dispersants / dispersion aids, fungicides, antistatic agents, solvents and the like.

The carbon black used in the magnetic layer and the back layer of the present invention may be a furnace black for rubber, a thermal black for rubber,
Color black, acetylene black and the like can be used. These carbon blacks are used for the purpose of improving the durability of the tape, such as an antistatic agent, a light shielding agent, a friction coefficient adjusting agent, and the like. Specific examples of abbreviations of carbon black in the United States include SAF, ISAF and IISA.
F, T, HAF, SPF, FF, FEF, HMF, GP
F, APF, SRF, MPF, ECF, SCF, CF,
FT, MT, HCC, HCF, MCF, LFF, RCF
And the like, and the US ASTM standard D-1765-82a
Can be used. The average particle size of these carbon blacks used in the present invention is 5 to 1000 nm (electron microscope), the specific surface area by the nitrogen adsorption method is 1 to 800 m ² / g, and the pH is 4 to 11 (JIS K-6221-1982). Method), dibutyl phthalate (D
BP) The oil absorption is 10-800 ml / 100 g (JIS K-6221-1982 method). The size of the carbon black used in the present invention is 5 to 100 nm for the purpose of reducing the surface electric resistance of the coating film, and 50 to 1000 when controlling the strength of the coating film.
nm carbon black. For the purpose of controlling the surface roughness of the coating film, carbon black (100 n) of fine particles is used for smoothing to reduce spacing loss.
m) is used for the purpose of roughening the surface to lower the coefficient of friction. As described above, the type and amount of carbon black are properly used depending on the purpose required for the magnetic recording medium. Further, these carbon blacks may be surface-treated with a dispersant described below or grafted with a resin for use. Also,
The furnace temperature for producing carbon black was 2000
A material obtained by treating at a temperature of at least ℃ and partially graphitizing the surface can also be used. Also, hollow carbon black can be used as a special carbon black. These carbon blacks are used in the case of a magnetic layer in the form of ferromagnetic metal powder 100.
Preferably, it is used in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on parts by weight. In the case of the back layer, it is generally desirable to use 20 to 400 parts by weight, preferably 50 to 350 parts by weight, based on 100 parts by weight of a resin described later. Carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook", edited by Carbon Black Association (issued in 1971). Examples of these carbon blacks are described in U.S. Pat.
No. 5,39,257, U.S. Pat.
No. 1-92424 and JP-A-61-99927.

The abrasive used in the magnetic layer and the back layer according to the present invention is used for improving the durability of the magnetic recording medium and the effect of cleaning the head of the VTR, and is generally a material having an abrasive action or a polishing action. -Alumina,
γ-alumina, α, γ-alumina fused alumina, silicon carbide, chromium oxide, cerium oxide, corundum, artificial diamond, diamond, α-iron oxide, garnet, emery (main component: corundum and magnetite), garnet ,
Silica stone, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly,
Materials such as diatomaceous earth and dolomite having a Mohs hardness of 6 or more, preferably a Mohs hardness of 8 or more, are used in combinations of 1 to 4 types. These abrasives have an average particle size of 0.005 to 5 μm,
Particularly preferably, it is 0.01 to 2 μm. In the case of a magnetic layer, these abrasives are preferably 0.1 to 25 parts by weight, more preferably 5 to 25 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.
It is added in the range of 20 parts by weight. In the case of the back layer, it is usually used in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, based on 100 parts by weight of a resin described later. Specific examples of these include A manufactured by Sumitomo Chemical Co., Ltd.
KP1, AKP15, AKP20, AKP30, AKP
50, AKP80, Hit50, Hit100 and the like. About these, JP-B No. 52-28642,
JP-B-49-39402, JP-A-63-98828
No. 3,687,725, U.S. Pat.
7, U.S. Pat. No. 3,041,196, U.S. Pat.
No. 66, U.S. Pat. No. 3,630,910, U.S. Pat.
No. 412, US Pat. No. 4,117,190, British Patent 114
No. 5349 and West German Patent No. 853211.

The powdery lubricant used for the magnetic layer and the back layer of the present invention includes graphite, molybdenum disulfide, boron nitride, graphite fluoride, calcium carbonate, barium sulfate, silicon oxide, titanium oxide, zinc oxide, and the like. Inorganic fine powder such as tin oxide and tungsten disulfide, acrylic styrene resin fine powder, benzoguanamine resin fine powder, melamine resin fine powder, polyolefin resin fine powder, polyester resin fine powder, polyamide resin fine powder, polyimide resin, polyimide And fine resin powder such as fine resin powder and polyfluorinated ethylene resin fine powder.

Silicone oils (dialkyl polysiloxanes, dialkoxy polysiloxanes, phenyl polysiloxanes, fluoroalkyl polysiloxanes (KF96 and KF69 manufactured by Shin-Etsu Chemical Co., Ltd.) can be used as organic compound-based lubricants.
Etc.)), fatty acid modified silicone oil, fluorine alcohol
, Polyolefin (polyethylene wax, polypropylene, etc.), polyglycol (ethylene glycol, polyethylene oxide wax, etc.), tetrafluoroethylene oxide wax, polytetrafluoroglycol
Perfluoroalkyl ether, perfluoro fatty acid, perfluoro fatty acid ester, perfluoroalkyl sulfate, perfluoroalkyl sulfonate, perfluoroalkyl benzene sulfonate, perfluoroalkyl phosphate, etc. And compounds containing silicon, alkyl sulfate, alkyl sulfonate, alkyl phosphonate triester,
Organic acids and organic acid ester compounds such as alkyl phosphonic acid monoesters, alkyl phosphonic acid diesters, alkyl phosphate esters, succinate esters, triazaindolizine, tetraazaindene, benzotriazole, benzotriazine, benzodiazole, EDTA, etc. Heterocyclic compounds containing nitrogen and sulfur, C10-4
0 monobasic fatty acid and any of monohydric alcohols having 2 to 40 carbon atoms, dihydric alcohols, trivalent alcohols, tetravalent alcohols, and hexavalent alcohols Fatty acid esters composed of at least one or two or more carbon atoms having 10 carbon atoms
Fatty acid esters comprising mono- to hexavalent alcohols having a total of 11 to 70 carbon atoms in total with at least one monobasic fatty acid and the number of carbon atoms of the fatty acid, a fatty acid or fatty acid having 8 to 40 carbon atoms Amides, fatty acid alkylamides, and aliphatic alcohols can also be used.

Specific examples of these compounds include butyl caprylate, octyl caprylate, ethyl laurate, butyl laurate, octyl laurate, ethyl myristate, butyl myristate, octyl myristate, 2-ethylhexyl myristate, Ethyl palmitate, butyl palmitate, octyl palmitate, 2 ethylhexyl palmitate, ethyl stearate, butyl stearate, isobutyl stearate, octyl stearate, 2 ethyl hexyl stearate, amyl stearate, isoamyl stearate, 2 stearic acid
Ethylpentyl, 2-hexyldecyl stearate, isotridecyl stearate, stearic acid amide, alkyl stearate, butoxyethyl stearate,
Anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, anhydrosorbitan tetrastearate
Oleyl oleate, oleyl alcohol, lauryl alcohol, montan wax, carnauba wax,
Can be used alone or in combination.

As the lubricant used in the present invention, a so-called lubricating oil additive can be used alone or in combination.
Antioxidants (metal chelating agents such as alkylphenols, benzotriazines, tetraazaindenes, sulfamides, guanidines, nucleic acids, pyridines, amines, hydroquinones, EDTA, etc.), rust inhibitors (naphthenes) Acid, alkenyl succinic acid, phosphoric acid, dilauryl phosphate, etc., oil agent (rapeseed oil, lauryl alcohol, etc.), extreme pressure agent (dibenzyl sulfide, tricresyl phosphate, tributyl phosphite, etc.) ), Cleaning dispersants, viscosity index improvers, pour point depressants, foaming agents and the like. These lubricants are generally added in an amount of 0.01 to 30 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the binder. About these,
-23889, JP-B-48-24401, JP-B-4
Nos. 8-18482, JP-B-44-18221, JP-B-47-28043, JP-B-57-56132, JP-A-59-8136, JP-A-59-8139, and JP-A-6-18
No. 1-85621, U.S. Pat. No. 3,423,233, U.S. Pat. No. 3,470,235, U.S. Pat. No. 3,492,235, U.S. Pat. No. 3,497,411, U.S. Pat.
U.S. Pat. No. 3,634,253, U.S. Pat.
No. 3,687,725, U.S. Pat.
No. 1, US Pat. No. 4,497,864, US Pat.
No. 94, IBM Technical Disclosure Bulletin (IBM Technical Disclosure)
ure Bulletin) Vol. 9, No7, p7
79 (December 1966), Electronic (ELEK)
TRONIK) No. 12 in 1961, p380, Chemical Handbook, Applied Edition, p954-967, issued in 1980 by Maruzen Stock, and the like.

The dispersing agents and dispersing agents used in the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearoyl. -Fatty acids having 2 to 40 carbon atoms (R1 COOH, R1 is an alkyl group having 1 to 39 carbon atoms, phenyl group, aralkyl group) such as carboxylic acid, behenic acid, maleic acid, phthalic acid, etc .; (Li, Na, K, NH4 +, etc.) or alkaline earth metals (Mg, Ca, Ba, etc.), metal soap (copper oleate) composed of Cu, Pb, etc., fatty acid amide; lecithin (soybean oil lecithin), etc. Is done. In addition, higher alcohols having 4 to 40 carbon atoms (butanol, octyl alcohol, myristyl alcohol, stearyl alcohol) and their sulfates, sulfonic acids, phenylsulfonic acids, and alkylsulfonic acids. Sulfonic acid ester, phosphoric acid monoester, phosphoric acid diester, phosphoric acid triester, alkylphosphonic acid, phenylphosphonic acid, amine compound and the like can also be used. Further, polyethylene glycol, polyethylene oxide, sulfosuccinic acid, metal sulfosuccinate, sulfosuccinate, and the like can also be used. These dispersants are usually used in one or more types,
One kind of dispersant is usually used for 100 parts by weight of the binder.
It is added in the range of 0.005 to 20 parts by weight, preferably 0.01 to 5 parts by weight. Regarding the method of using these dispersing agents, the dispersing agent may be applied in advance to the surface of the ferromagnetic fine powder or the non-magnetic fine powder, or may be added during the dispersion. Such materials are disclosed, for example, in JP-B-39-28369 and JP-B-44-1.
7945, JP-B-44-18221, JP-B-48-
7441, JP-B-48-15001, JP-B-48-
15002, JP-B-48-16363, JP-B-49
No. 39402, U.S. Pat.
No. 0021 and the like.

As the antifungal agent used in the present invention, 2- (4-
Thiazolyl) -benzimidazole, N- (fluorodichloromethylthio) -phthalimide, 10,10'-oxybisphenoxalcin, 2,4,5,6-tetrachloroisophthalonitrile, P-tolyldiiodomethylsulfone, tri- Examples include iodoallyl alcohol, dihydroacetoacid, mercury phenyloleate, bis (tributyltin oxide), and saltylanilide. Such a substance is described in, for example, "Microbial Disaster and Prevention Technology", Engineering Books, 1972, "Chemistry and Industry", 32, 904 (1979).

As the antistatic agent other than carbon black used in the present invention, graphite, modified graphite, carbon black graft polymer, tin oxide-antimony oxide, tin oxide, titanium oxide-tin oxide-antimony oxide,
Nonionic surface activity such as alkylene oxide, glycerin, glycidol, polyhydric alcohol, polyhydric alcohol ester, alkylphenol EO adduct, etc. Agents; higher alkyl amines, cyclic amines, hydantoin derivatives, amidoamines, ester amides, quaternary ammonium salts, pyridine and other heterocycles, cationic surfactants such as phosphoniums or sulfoniums; carboxylic acids, sulfonic acids, phosphonic acids Surfactants containing acidic groups such as carboxylic acid, phosphoric acid, sulfate group, phosphonate ester, phosphate group; amino acids; amphoteric interface such as aminosulfonic acid, sulfuric acid or phosphate ester of amino alcohol, alkyl betaine type, etc. Activators and the like are used. Some examples of the surfactant compound which can be used as the antistatic agent are described in JP-A-60-28025, U.S. Pat.
Nos. 2240472, 2288226, 2676
No. 122, No. 2676924, No. 2676975,
No. 2691566, No. 2727860, No. 2730
No. 498, No. 2742379, No. 2739891,
No. 3068101, No. 3158484, No. 3201
No. 253, No. 3210191, No. 3294540,
No. 3415649, No. 3441413, No. 3442
No. 654, No. 3475174, No. 3545974,
West German Patent Publication (OLS) 1942665, British Patent 1
Ryohei Oda et al., "Synthesis of Surfactants and Their Applications" (Maki Shoten 19)
A. 72 edition); W. Beili, "Surface Active Agents" (Interscience Publishing)
S. Co., Ltd., 1985); P. By Shisley, "Encyclopedia of Surfactive Agents, Vol. 2," (Chemical Publish Company, 1964 edition); "Surfactant Handbook," 6th printing (Sangyo Tosho Co., Ltd., December 1966. March 20); written by Hideo Marumo, "Antistatic Agent", written books such as Koshobo (1968). These surfactants may be added alone or as a mixture. The amount of these surfactants used in the magnetic recording medium is usually 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, per 100 parts by weight of the ferromagnetic metal powder. The amount used in the back layer is 0.01 to 30 parts by weight per 100 parts by weight of the binder. These are used as antistatic agents, but are sometimes applied for other purposes, such as dispersion, improved magnetic properties, improved lubricity, coating aids, wetting agents, curing accelerators, and dispersion accelerators. In some cases.

The formation of the magnetic layer can be performed according to a usual method. For example, a magnetic coating material is prepared by mixing and dispersing the above-mentioned ferromagnetic metal powder and a resin component, and a magnetic layer forming component such as a polishing agent and a curing agent, which are blended as required, together with a solvent to prepare a magnetic coating material. A method of applying on the body can be used. Dispersion of the present invention, kneading, as the organic solvent used in the application, acetone in any ratio,
Ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran; methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol
And alcohols such as methylcyclohexanol; methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate;
Ester systems such as isopropyl acetate, ethyl lactate, and glycol monoethyl ether; ether systems such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene, toluene, xylene, and cresol Tar (aromatic hydrocarbons) such as chlorobenzene, chlorobenzene and styrene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, N, N -Dimethylformaldehyde, hexane and the like can be used. These solvents are generally used in two or more kinds at an arbitrary ratio. Further, a trace amount of impurities (polymer of the solvent itself, moisture, raw material components, etc.) may be contained in an amount of 1% by weight or less.

These solvents are a magnetic liquid or a back liquid,
Usually, 100 parts by weight of the total solid content of the undercoat liquid is 100 parts by weight.
Used at で 20,000 parts by weight. The preferred solid content of the magnetic liquid is 10 to 40% by weight. The preferable solid content of the back solution is usually 5 to 20% by weight. An aqueous solvent (water, alcohol, acetone, etc.) can be used instead of the organic solvent.

The method of dispersion and kneading is not particularly limited, and the order of addition of each component (resin, powder, lubricant, solvent, etc.)
The addition position during dispersion / kneading, the dispersion temperature (0 to 80 ° C.), and the like can be appropriately set. For preparing the magnetic coating material and the back layer coating material, a conventional kneader such as a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder, a Zegva (Szegva) is used.
ri) Attritor, high-speed impeller, disperser, high-speed stone mill, high-speed impact mill, disperser, kneader,
High-speed mixer, ribbon blender, coneder, intensive mixer, tumbler, blender, disperser
A screw, a homogenizer, a single-screw extruder, a twin-screw extruder, and an ultrasonic disperser can be used. Usually, a plurality of these dispersing and kneading machines are provided for dispersing and kneading, and the treatment is continuously performed. For details of the kneading and dispersing technique, see C. "Paint Flow and Pi" by Patton (T.C. Patton)
gment Dispersion ”(paint flow and pigment day dispersion) 1964
John Wiley & Sons, Inc. (John Wiley & Sons), Shinichi Tanaka, Industrial Materials, Vol. 25, 37 (1977), and other references cited in the book. In order to efficiently promote dispersion and kneading as an auxiliary material for these dispersion and kneading, the equivalent spherical diameter is 10 cm.
Steel balls, steel beads, ceramic beads, glass beads, and organic polymer beads having a diameter of φ to 0.05 mmφ can be used. These materials are not limited to spherical shapes. It is also described in specifications such as U.S. Patent Nos. 2,581,414 and 2,855,156. Also in the present invention, the magnetic coating material and the back layer coating material can be prepared by kneading and dispersing according to the method described in the above-mentioned book or the cited document of the book.

As a method of applying the above-mentioned coating solution for the magnetic recording layer and the coating solution for the back layer onto the support, the viscosity of the coating solution is adjusted to 1 to 20,000 centistokes (25 ° C.), and the air doctor -Coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat , Spray coat,
Rod coat, forward rotation roll coat, carten coat,
Extrusion coating, bar coating, and the like can be used, and other methods are also possible. Specific descriptions of these methods are described in "Coating Engineering", pages 253 to 277, published by Asakura Shoten (Showa 46.3.
20. Issuance). The order of application of these coating liquids can be arbitrarily selected, and a corona discharge treatment or the like may be performed before application of a desired liquid to improve adhesion to an undercoat layer or a support. When it is desired to form the magnetic layer or the back layer with multiple layers, simultaneous multilayer coating, sequential multilayer coating, or the like may be performed. These are described, for example, in JP-A-57-123532, JP-B-62-37451, JP-A-59-142741 and JP-A-59-142741.
This is described in the specification of JP-A-165239.

According to such a method, usually,
The magnetic liquid applied at about 1 to 200 μm, preferably about 20 to 100 μm is used to immediately dry the magnetic powder in the layer as needed, usually at 20 to 130 ° C., preferably at 40 to 120 ° C. while drying at 500 to 5000 G while drying in multiple stages. After performing a process for orienting in a desired direction (vertical, longitudinal, width, random, oblique, etc.), that is, performing a magnetic field orientation process, the formed magnetic layer is 2 μm or more, usually 2 to 30 μm, preferably 2.5 μm.
Dry to a thickness of 〜１０10 μm. At this time, the transfer speed of the support is usually 100 m / min to 600 m / min, and the drying temperature in a plurality of drying zones is usually controlled at 20 ° C. to 130 ° C., and the residual solvent amount of the coating film is usually 0 ° C. 0.1 to 40 mg /
(１ ／ inch) / m ² , preferably 0.1 to 15 mg /
(1/2 inch) / m ² .

After being dried in this manner, the coating layer is subjected to a calender treatment if necessary. For the calendar process, for example, a spar calendar roll is used. By performing the calendering process, vacancies generated by removing the solvent during drying are reduced and the filling rate of the ferromagnetic metal powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. .

As a combination of calendar rolls,
A combination of a metal roll and an elastic roll is preferable. As the metal roll, for example, preferably, a steel material is subjected to hard chrome plating, and the surface roughness Ra is 15 nm.
Examples of the elastic roll include, for example, preferably those made of plastic resin such as nylon, urethane, epoxy, and polyesteramide and having a surface roughness of 5
And those having a thickness of 0 nm or less.

The calendering condition is preferably a temperature of 60 to 120 ° C., more preferably 70 to 100 ° C.
The linear pressure is preferably from 200 to 500 kg / cm, more preferably from 270 to 350 kg / cm. When a curing agent is used as a binder-forming component in the above-mentioned calendering step, 90% by weight or more of the curing agent contained in the magnetic layer is usually contained in the magnetic layer in an unreacted state. Therefore, by performing a curing process, at least 50
It is desirable to carry out the subsequent treatment after reacting by weight% (particularly preferably 80% by weight or more). The curing treatment includes a heat curing treatment and an electron beam curing treatment. In the present invention, any method can be used. The unreacted curing agent contained in the magnetic layer calendered by this curing treatment reacts with a resin component such as a vinyl chloride copolymer and a polyurethane resin to form a three-dimensional network crosslinked structure. I do. The heat treatment process itself is already known, and in the present invention, the heat treatment can be performed according to these methods. For example,
In the heat treatment, the heating time is usually 40 ° C. or more (preferably 5 ° C.).
The heating time is usually set to 20 hours or more (preferably 24 hours to 7 days).
Further, the step of curing treatment by electron beam irradiation is already known, and the curing treatment can be performed according to these methods in the present invention.

In the present invention, the magnetic recording medium produced in this manner is cut into a desired shape under ordinary conditions using a usual cutting machine such as a slitter, and then wound on a plastic or metal reel. In the present invention, the magnetic recording medium (magnetic layer, back layer, edge end face, base face) may be formed in a process immediately before or before winding the surface of the magnetic layer or the surface of the magnetic layer and the surface of the back layer. May be burnished with a polishing tape. These are described, for example, in JP-A-63-259830.
JP-A-62-172532 and JP-A-63-9
88345 and the like.

In the wiping process of the magnetic recording medium, the surface layer of the magnetic recording medium is made of a nonwoven fabric or the like with a magnetic layer surface, a back layer surface,
This is performed by wiping the edge end surface and the base surface on the back side. Examples of such wiping materials include various types of virgin made by Japan Vilene, Toraysee made by Toray, Kuraray WRP series made by Ecseine and Kuraray, and nonwoven fabric made of nylon, nonwoven fabric made of polyester, nonwoven fabric made of rayon, nonwoven fabric made of acrylonitrile, mixed spinning Non-woven fabrics can also be used. In addition, tissue paper, Kimwipe, and the like can be used. These are described, for example, in JP-B-46-39309, JP-B-58-46768, JP-A-56-90429, JP-B-58-46767, JP-A-63-259830, JP-A-1-201824 and the like. Have been. By this wiping treatment, deposits and organic substances on the magnetic layer and / or the back layer are completely removed, and the frequency of dropout or clogging is reduced.

These production methods include pretreatment / surface treatment of powder, kneading / dispersion, application / orientation / drying, calendering, curing (heat treatment, EB treatment), cutting, burnishing, wiping and winding. Is desirably performed continuously. These are, for example,
No. 23625, JP-B-39-28368, JP-B-47-38802, UK Patent 11919124
JP-B-48-11336, JP-A-49-53
No. 631, JP-A-50-110005, JP-A-51-1
No. 77303, JP-B-52-17404, JP-A-60
-70532, JP-A-2-265672, U.S. Pat. No. 3,473,960, U.S. Pat. No. 4,728,569.
And U.S. Pat. No. 4,746,542. The method disclosed in Japanese Patent Publication No. 41-13181 is considered to be a basic and important technique in this field. However, the order in which the processing is performed is not limited to the above order.

The ferromagnetic metal powder, binder, and additives (lubricants, dispersants, antistatic agents, surface treatment agents, carbon black, abrasives, light shielding agents, antioxidants,
For antifungal agents, solvents and supports (may have an undercoat layer, a back layer, a back undercoat) or a method for producing a magnetic recording medium, refer to those described in JP-B-56-26890. Can be.

[0051]

The present invention will be described more specifically with reference to the following examples. It is easily understood by those skilled in the art that the components, ratios, operation orders, and the like shown here can be changed without departing from the spirit of the present invention. Therefore, the present invention should not be limited to the following examples. In each example, “parts” means “parts by weight” unless otherwise specified.

Example 1 A magnetic paint (1) having the composition shown below was kneaded with an open kneader, added with a composition (2), dispersed in a sand mill, and adjusted by adding (3) before coating. It was coated on a 10 μm-thick non-magnetic support polyethylene terephthalate which had been previously provided with an undercoat layer so that the thickness of the magnetic layer after drying was 3 μm.

Magnetic coating composition (1) Ferromagnetic alloy powder 100 parts (Fe metal powder, major axis length 0.11 μm, axial ratio 1/6, Hc1810 Oe, σs140 emu / g) Carbon black (Asahi Carbon black # 50) 1 Part Phosphoric acid ester (phenylsulfonic acid) 3 parts Vinyl chloride copolymer resin (manufactured by Nippon Zeon: MR110) 10 parts Urethane resin (manufactured by Toyobo: UR8400) 4 parts Cyclohexanone 130 parts Methyl ethyl ketone 75 parts Toluene 50 parts (2) Abrasive ( Sumitomo Chemical: Hit-60) 14 parts Methyl ethyl ketone 5 parts (3) Polyisocyanate 4 parts (Nippon Polyurethane: Coronate 3041) Toluene 30 parts Stearic acid 1 part 2-ethylhexyl stearate 1 part Stearamide 0.5 part Magnetic Non-magnetic support with paint The body, cobalt magnets and 300 magnetic paint has a 3000G of magnetic force in the state of undried
A magnetic field orientation treatment and drying were performed using a solenoid having a magnetic force of 0 G, and subsequently, (5) was added to the following back coating (4) immediately before coating to apply a dry thickness of 0.6 μm.

Back coating composition (4) Carbon black (Cabot: BP800) 95 parts Carbon black (Cancarb: MTCI) 5 parts α-Al ₂ O ₃ (Sumitomo Chemical: Hit-55) 0.1 parts Barium sulfate (Manufactured by Sakai Chemical: BF1) 0.1 part 2 ethylhexyl stearate 0.5 part Copper oleate 0.1 part Vinyl chloride copolymer resin (manufactured by Zeon Corporation: MR110) 50 parts Polyurethane resin (manufactured by Toyobo: UR8300) 40 Part Cyclohexanone 200 parts Methyl ethylyl ketone 300 parts (5) Polyisocyanate 20 parts (Nippon Polyurethane: Coronate 3040) Methyl ethyl ketone 3500 parts Toluene 200 parts Silicone compound (Shin-Etsu Chemical: KF69) 0.1 part Further drying, metal roll And elastic roll 7
Using a stage calender, temperature 90 ° C, linear pressure 260Kg
/ Cm at a speed of 80 m / min to produce a laminate comprising a nonmagnetic support, a magnetic layer and a back layer. After heating this laminate at 70 ° C. for 48 hours to cure the polyisocyanate compound contained in the laminate,
After slitting to a width of 1/2 inch and performing burnishing on the surface of the magnetic layer with a polishing tape (K10000, manufactured by Fuji Film), wiping using a wiping material (WRP736, manufactured by Kuraray) was performed, and the surface was halved. Inch videotapes were made.

Example 2 In Example 1, calendering was performed at a temperature of 80 ° C., a linear pressure of 260 kg / cm, and a speed of 80 kg / cm.
A process similar to that of Example 1 was performed except that the measurement was performed at m / min, to produce a 1/2 inch video tape. Example 3 A 1/2 inch video tape was prepared by performing the same process as in Example 1 except that the calendering process was performed at a temperature of 90 ° C., a linear pressure of 300 kg / cm, and a speed of 50 m / min. did.

[Embodiment 4] In Embodiment 1, an axial ratio of 1/6, Hc1840 Oe, and ss1 were obtained at a major axis length of 0.08 μm.
Except for using a 40 emu / g ferromagnetic alloy powder, the same processing as in the example was performed to produce a 1/2 inch video tape. [Example 5] In Example 1, the major axis length was 0.08 µm,
Axial ratio 1/4, Hc1830 Oe, s142 emu / g
Except for using the ferromagnetic alloy powder, the same process as in the example was performed to produce a 1/2 inch video tape.

Embodiment 6 In Embodiment 1, the major axis length is 0.06 μm, the axial ratio is ４, Hc1850 Oe, σs1
Except that 45 emu / g of ferromagnetic alloy powder was used, the same processing as in the example was performed to produce a 1/2 inch video tape. [Example 7] In Example 1, the major axis length was 0.13 µm,
Axial ratio 1/8, Hc1800 Oe, ss138 emu / g
Except for using the ferromagnetic alloy powder, the same process as in the example was performed to produce a 1/2 inch video tape.

Embodiment 8 In Embodiment 1, the major axis length is 0.13 μm, the axial ratio is 比, Hc1800 Oe, σs1
Using a 38 emu / g ferromagnetic alloy powder, calendering was performed at a temperature of 80 ° C., a linear pressure of 260 kg / cm, and a speed of 80 m.
/ Min, the same processing as in the example was performed.
A 1/2 inch video tape was produced.

Ninth Embodiment In the first embodiment, the major axis length is 0.15 μm, the axial ratio is 1/9, Hc1800 Oe, σs1
Using a ferromagnetic alloy powder of 40 emu / g, calendering was performed at a temperature of 80 ° C., a linear pressure of 260 kg / cm, and a speed of 80 m.
/ Min, the same processing as in the example was performed.
A 1/2 inch video tape was produced.

Example 10 A 1/2 inch video tape was produced in the same manner as in Example 1, except that the magnetic coating composition was changed to the following composition. Magnetic paint composition (1) Ferromagnetic alloy powder 100 parts (Fe metal powder, major axis length 0.11 μm, axial ratio 1/6, Hc1810 Oe, σs140 emu / g) Carbon black (Asahi Carbon black # 50) 1 part Phosphate ester (Phenylsulfonic acid) 3 parts Vinyl chloride copolymer resin (manufactured by Zeon Corporation: MR110) 7 parts Urethane resin (manufactured by Toyobo: UR8400) 12 parts Cyclohexanone 130 parts Methyl ethyl ketone 75 parts Toluene 50 parts (2) Abrasive (manufactured by Sumitomo Chemical) : Hit-60) 14 parts Methyl ethyl ketone 5 parts (3) Polyisocyanate 4 parts (Nippon Polyurethane: Coronate 3041) Toluene 30 parts Stearic acid 1 part Stearic acid 2 ethylhexyl 1 part Stearamide 0.5 part [Example 11] In Example 1, the magnetic paint Except for changing the Narubutsu the following composition performs the same processing as in Example 1, 1
A 1/2 inch video tape was produced.

Magnetic paint composition (1) Ferromagnetic alloy powder 100 parts (Fe metal powder, major axis length 0.11 μm, axial ratio 1/6, Hc1810 Oe, σs140 emu / g) Carbon black (Asahi Carbon black # 50) 1 Part Phosphoric ester (phenylsulfonic acid) 3 parts Vinyl chloride copolymer resin (manufactured by Nippon Zeon: MR110) 5 parts Urethane resin (manufactured by Toyobo: UR8400) 15 parts Cyclohexanone 130 parts Methyl ethyl ketone 75 parts Toluene 50 parts (2) Abrasive ( Sumitomo Chemical: Hit-60) 14 parts Methyl ethyl ketone 5 parts (3) Polyisocyanate 4 parts (Nippon Polyurethane: Coronate 3041) Toluene 30 parts Stearic acid 1 part Stearic acid 2 ethylhexyl 1 part Stearamide 0.5 part [Comparison Example 1 In Example 1 Carbon black (Asahi Carbon Co. Black # 50) to be added to the magnetic layer except for using 3 parts performs the same processing as in Example 1 to produce a 1/2 inches videotape.

[Comparative Example 2] In Example 1, calender treatment was performed at a temperature of 90 ° C, a linear pressure of 260 kg / cm, and a speed of 20 m / m, with 0 parts of carbon black added to the magnetic layer.
The same processing as in Example 1 was performed except for performing
A 2 inch video tape was made. Comparative Example 3 A 1/2 inch video tape was produced in the same manner as in Example 1, except that a ferromagnetic alloy powder having a major axis length of 0.18 μm and an axial ratio of 1/9 was used. .

Comparative Example 4 In Example 1, the major axis length was 0.08 μm, the axial ratio was 1/3, Hc1820 Oe, σs1
Except for using a 40 emu / g ferromagnetic alloy powder, the same processing as in the example was performed to produce a 1/2 inch video tape. [Comparative Example 5] In Example 1, the major axis length was 0.14 µm,
Axial ratio 1/10, Hc 1800 oe, σs 138 emu /
Except that g of the ferromagnetic alloy powder was used, the same processing as in the example was performed to produce a 1/2 inch video tape.

Comparative Example 6 A 1/2 inch video tape was produced in the same manner as in Example 1 except that the magnetic coating composition was changed to the following composition. Magnetic paint composition (1) Ferromagnetic alloy powder 100 parts (Fe metal powder, major axis length 0.11 μm, axial ratio 1/6, Hc1810 Oe, σs140 emu / g) Carbon black (Asahi Carbon black # 50) 1 part Phosphate ester (Phenylsulfonic acid) 3 parts Vinyl chloride copolymer resin (manufactured by Nippon Zeon: MR110) 15 parts Urethane resin (manufactured by Toyobo: UR8400) 4 parts Cyclohexanone 130 parts Methyl ethyl ketone 75 parts Toluene 50 parts (2) Abrasive (manufactured by Sumitomo Chemical) : Hit-60) 14 parts Methyl ethyl ketone 5 parts (3) Polyisocyanate 15 parts (Nippon Polyurethane: Coronate 3041) Toluene 30 parts Stearic acid 1 part Stearic acid 2 ethylhexyl 1 part Stearamide 0.5 part [Comparative Example 7] In Example 1, a metal low The seven-stage constituted by only using the calendar, temperature 90 ° C., linear pressure 2
Except for processing at 60 Kg / cm and a speed of 80 m / min, the same processing as in Example 1 was performed to produce a 1/2 inch video tape.

[Comparative Example 8] In Example 1, three parts of carbon black were added to the magnetic layer, and seven stages composed of only metal rolls were used with a calender.
The same processing as in Example 1 was performed except that the processing was performed at a linear pressure of 260 Kg / cm and a speed of 80 m / min, to produce a 1/2 inch video tape.

Comparative Example 9 A 1/2 inch video tape was produced in the same manner as in Example 1, except that the magnetic coating composition was changed to the following composition. Magnetic paint composition (1) Ferromagnetic alloy powder 100 parts (Fe metal powder, major axis length 0.11 μm, axial ratio 1/6) Carbon black (Asahi Carbon black # 50) 1 part Phosphoric acid ester (phenylsulfonic acid) 3 Part: vinyl chloride copolymer resin (manufactured by Zeon Corporation: MR110) 5 parts urethane resin (manufactured by Toyobo: UR8400) 25 parts cyclohexanone 130 parts methyl ethyl ketone 75 parts toluene 50 parts (2) abrasive (Sumitomo Chemical: Hit-60) 14 Part methyl ethyl ketone 5 parts (3) polyisocyanate 3 parts (manufactured by Nippon Polyurethane Co., Ltd .: Coronate 3041) toluene 4 parts stearic acid 1 part stearic acid 2 ethylhexyl 1 part stearic acid amide 0.5 part In this example and comparative examples, Was used.
Table 1 shows the evaluation results of the samples.

[Long axis length and axis ratio of magnetic material] A 100,000-fold photograph was taken with a transmission electron microscope of 300 kV, and the electron microscope photograph was traced with an image analyzer (IBASS-1 manufactured by Carl Zeiss) to obtain a long axis length. And the short axis length (n = 500
G), major axis length, and axial ratio were determined. [Magnetostatic properties] Measurement was performed using a vibrating sample magnetometer (manufactured by Toei Kogyo) at a maximum magnetic field of 5 kOe. Bs indicates the saturation magnetic flux density, and SQ indicates the squareness ratio.

[Micro Projection] Digital Instr
30 using an AFM (atomic force microscope) manufactured by U.S.
The three-dimensional surface roughness of μm square angle (900 μm ² ) was measured, and 5 nm from the average surface roughness of the magnetic layer to 60 nm.
The number of protrusions for each was measured. The measurement conditions are shown below.

Probe: Square cone with 70 ° ridge angle, material SiN ₄ Measurement area: 30 μm × 30 μm Scanning speed: 1 Hz [Magnetic layer surface hardness] The magnetic layer surface hardness is a constant load with a diamond needle having a constant tip shape. , The surface of the magnetic layer was rubbed while measuring the depth of a groove formed on the surface of the magnetic layer. Surface property measuring device HEIDON-
14 (manufactured by Shinku Kagaku) using a diamond needle having a tip shape of 0.1 μmR, rubbing the magnetic layer with a load of 25 g, and then a three-dimensional roughness measuring device TOPO-3D
The depth (Peak-Valley) of the groove formed by the diamond needle was measured by using (manufactured by WYKO), and this was defined as the surface hardness of the magnetic layer.

[Output] D3VTR (Matsushita Electric AJ-D)
350, a magnetic head core width of 120 μm, a relative speed between the magnetic head and the magnetic tape of 21.4 m / sec) and a recording wavelength of 0.7
The reproduction output when recording and reproducing a signal of μm was measured.
The reference tape used was a D3 reference tape manufactured by our company.

[Coefficient of friction] SUS of 420 J of 4 mmφ
Pass the tape at an angle of 180 degrees using a rod and apply a load of 50
g, sliding 100 passes at 42 mm / sec, and the friction coefficient at the 100th pass was determined based on Euler's equation. [Scratch resistance of magnetic layer] Using a 4 mmφ 420J SUS rod, pass the tape at an angle of 180 ° and apply a load of 50 g to 4 g.
After sliding for 500 passes at 2 mm / sec, the sliding surface of the magnetic layer after 500 passes was observed with an optical microscope (magnification: 50), and the degree of scratch was judged.

No scratch in one visual field A (very good) 1 to 3 scratches in one visual field B (good) 4 to 8 scratches in one visual field C (practical) No scratch in one visual field 9 or more D (not practical)

[0073]

[Table 1]

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic layer having a thickness of 2 μm or more mainly composed of a ferromagnetic metal powder and a binder resin on a nonmagnetic support, wherein the ferromagnetic metal powder has a major axis length of 0.15 μm. Hereinafter, the axial ratio is 1/4 to 1/9, and the height measured by an atomic force microscope (AFM) is 10 to 25 n.
m projections are more than 1000/900 μm ² and 30
A magnetic recording medium, wherein the number of protrusions of not less than 250 nm is not more than 250/900 μm ² , and the surface hardness of the magnetic layer is 350 to 750 nm. 2. The magnetic recording medium according to claim 1, wherein the core width of the magnetic head is 80 μm or more, the relative speed between the magnetic head and the magnetic recording medium is 20 m / sec or more, and the shortest recording wavelength is 1 μm or less. A magnetic recording system, which is the magnetic recording medium according to claim 1.