JP2584271B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a plurality of magnetic layers, and more particularly to a magnetic recording medium having improved running properties, durability, and electromagnetic conversion characteristics.

[Conventional technology]

Normally, magnetic tapes such as audio tapes and video tapes are prepared by dispersing a ferromagnetic powder in a binder solution together with a suitable additive (dispersant, lubricant, antistatic, etc.) in a binder solution on a non-magnetic substrate such as polyethylene terephthalate ( PET)
It is manufactured by coating and drying on top.

In recent years, video tapes have been recorded at higher densities, and tapes having more excellent electromagnetic conversion characteristics have been demanded.

For this reason, it has been practiced to improve the characteristics by changing the magnetic layer from a single layer to a multilayer. For example, using a low coercive force (Hc) ferromagnetic powder for the lower magnetic layer to provide long wavelength characteristics,
Using a high coercivity (Hc) ferromagnetic powder for the upper magnetic layer,
It has been practiced to provide short wavelength characteristics.

[Problems to be Solved by the Invention] In general, in the case of a multilayer, it is known that the electromagnetic conversion characteristics can be improved by making the magnetic layer of the upper layer thinner, but since the magnetic layer is thinner, the particle size of the abrasive And the amount of the lubricant and the amount of the lubricant are regulated, so that there is a disadvantage that running properties and durability are inferior.

Although a back coat layer is provided on the side opposite to the support to improve running properties and prevent static charge, the lubricant on the magnetic layer is transferred to the back layer and the durability is degraded. .

An object of the present invention is to provide a novel magnetic recording medium having a plurality of magnetic layers and having improved electromagnetic conversion characteristics, running properties, and durability.

[Means for solving the problem]

The present inventors have conducted intensive studies on a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent running properties and durability.As a result, the ferromagnetic powder was dispersed in a binder on one surface of a non-magnetic support. Magnetic recording comprising a plurality of magnetic layers containing at least a lubricant and an abrasive as an additive, and a backcoat layer containing at least a lubricant and an abrasive as an additive in a binder on the other surface. In the medium, the uppermost magnetic layer contains a ferromagnetic metal powder and has a thickness of 0.1 to 2.0.
μm, and the electromagnetic conversion characteristics are attained by forming at least a lubricant and an abrasive of the additives contained in the back coat layer into the same kind of material as the lubricant and the abrasive of the uppermost layer of the plurality of magnetic layers. It has been found that an improved magnetic recording medium having excellent running properties and durability can be obtained.

The present invention relates to a magnetic recording medium having a multilayer structure for improving electromagnetic conversion characteristics, in which the upper magnetic layer is thinned in order to further improve the characteristics, and a lubricant and an abrasive are used in order to further improve running properties and durability. It is used for the upper magnetic layer. However, if the amount of the additive is increased in order to enhance these effects, the magnetic conversion characteristics are deteriorated. Therefore, the amount of the additive in the magnetic layer (upper layer) is such that the magnetic conversion characteristics are not impaired. These are also added to the back coat layer to prevent transfer to the back coat layer and replenish it from the back coat layer. The presence of the back coat layer is also used to ensure the running property and durability of the tape. In this case, the present invention is characterized by using the same type of lubricant and abrasive for the uppermost layer of the magnetic phase and the back coat layer, for the following reasons. In other words, when non-magnetic powders such as abrasives are present in both layers, if these non-magnetic powders are different, the phenomenon of adsorption of the lubricant to the non-magnetic powders is significantly different. There is a big difference in behavior between the two layers. As a result, the durability and running property of the tape are greatly affected. For example, when the amount of the lubricant present on the surface is small, the running property and durability deteriorate. For this reason, in the present invention, the same type of lubricant and at least abrasive is used in both layers, the lubricant behavior on the surface properties of the tape is made similar, and the amount of lubricant present in the surface layer is reduced. Since the same amount can always be maintained, the running property and durability of the tape can be maintained in an improved state without a change with time. The necessity that the lubricant and the non-magnetic powder be the same substance is that if the substance of the non-magnetic powder and the lubricant is different, the adsorption phenomenon of the lubricant to the non-magnetic powder is greatly different, and therefore the existence behavior of the lubricant in the film Big difference. The tape properties greatly affect durability, running durability, and the like. From the above, it is better that the material of the non-magnetic powder and the lubricant is the same, and if the magnetic layer and the back layer are also the same, the lubricant behavior on the tape surface properties will be the same and the tape properties will be better. become.

 Hereinafter, the present invention will be described in detail.

Examples of the ferromagnetic powder used for the plurality of magnetic layers include ferromagnetic iron oxide powder, cobalt-coated ferromagnetic iron oxide powder, ferromagnetic chromium dioxide fine powder, ferromagnetic metal powder, and barium ferrite. However, in the present invention, a ferromagnetic metal powder is used for the uppermost magnetic layer as shown in the examples described later.

The ferromagnetic powder is usually in the form of a needle, and the needle ratio is preferably 2/1 to 20/1 (particularly preferably 5/1 to 20/1).
And an average length (major axis length) of 0.1 to 2.0 μm is used.

The shape of the ferromagnetic powder is not limited to a needle shape,
Usable shapes such as rice grains and plate shapes can be used.

As the ferromagnetic powder, a crystallite size of 300 ° or less by X-ray diffraction with a major axis length of 0.3 μm or less (preferably a major axis length of 0.2 μm
It is particularly preferable to use a ferromagnetic powder having a crystallite size of 200 mm or less).

When a ferromagnetic metal powder is used, at least 75% by weight (preferably at least 80% by weight) of the metal component of the ferromagnetic metal powder is a ferromagnetic metal or alloy (eg, Fe, Co, Ni, Fe).
-Co, Fe-Ni, Co-Ni, Fe-Co-Ni), and are preferably particles having a major axis of 1.0 µm or less.

The holding power (Hc) of these ferromagnetic powders is preferably 350 to 50,000 e, more preferably 600 to 25,000 e, and particularly preferably 800 to 20,000 e.
Is preferred. If it is smaller than 3500 e, the output in a short wavelength range will be reduced, and if it is larger than 50,000 e, recording by a normal head cannot be performed, which is not preferable.

The binder used for the magnetic layer has a softening temperature of 150.
° C or lower, average molecular weight of 10,000-300000, degree of polymerization of about 50-1
About 000, for example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride 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-silicone resin, nitrocellulose-polyamide resin, polyvinyl fluoride, chloride Vinylidene acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose Roast riacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. Is done.

Particularly preferred, -SO ₃ M group in the molecule, -COOM group, -
OM group, -OSO ₃ M group, Vinyl chloride copolymers having functional groups such as groups, polyurethane resins, and polyester resins are preferred.

 Particularly, a hydrophilic group is preferable.

Here, M is hydrogen or an alkali metal (Li, Na, K
Etc.) and M 'represents hydrogen, an alkali metal (Li, Na, K, etc.) or a hydrocarbon group.

JP-A-59-81 discloses resins having these functional groups.
No. 27, No. 57-44227, No. 57-92422, No. 57-92
Nos. 423 and 59-40302 can be used.

A vinyl base copolymer containing an epoxy group together with the above functional group can also be used (Japanese Patent Application Laid-Open No. 62-146432). As a preferable combination of the binder, a combination of the vinyl chloride copolymer having the above functional group and polyurethane is preferable. As polyurethane, polyester polyurethane,
Polyether polyurethane, polyester ether polyurethane, polycaprolactone polyurethane, and polycarbonate polyurethane are preferred, and polyurethane having the above functional group is particularly preferred.

Specific examples of the hydrophilic group-containing binder include a —COOH group-containing polyurethane (“TIM-3005” manufactured by Sanyo Chemical Industries, Ltd.) — SO ₃ Na
Polyurethane (“UR-8300”, “UR” manufactured by Toyobo Co., Ltd.)
−8600 ”) -COOH group-containing vinyl chloride vinyl acetate copolymer (Nippon Zen Co., Ltd., 400 × 110A), -SO ₃ Na-containing polyester (Toyobo Co., Ltd.“ Vylon 530 ”) -SO ₃ Na-containing chloride Vinyl acetate vinyl copolymer (“MR” manufactured by Zeon Corporation)
−110 ”). Hydrophilic group content is 1 to 10000
A range of equivalents / 10 ⁶ gr is preferred. The molecular weight is 3000-200,00
The thickness of the lower magnetic layer is preferably larger than that of the upper magnetic layer, preferably 0.5 μm or more, particularly preferably 1 μm or more.

As the curing agent, epoxy-polyamide, epoxy-polycarboxylic acid, polyimine, and polyisocyanate are used. In particular, polyisocyanate is preferred, and -N =
Di, tri and tetra isocyanates selected from aliphatic, aromatic or alicyclic compounds having two or more C ＝ O groups. These isocyanates include ethane diisocyanate, butane diisocyanate, hexane diisocyanate, 2,2-dimethylpentane diisocyanate, 2,2,4-trimethylpentane diisocyanate, decane diisocyanate, ω, ω'-diisocyanate-1,3-dimethyl benzene. Sol, ω, ω'-diisocyanate-1,2-dimethylcyclohexane, ω, ω'-
Diisocyanate-1,4-diethylbenzol, ω,
ω'-diisocyanate-1,5-dimethylnaphthalene,
ω, ω'-diisocyanate-n-propylbiphenyl, 1,3-phenylenediisocyanate, 1-methylbenzol-2,4-diisocyanate, 1,3-dimethylbenzol-2,6-diisocyanate, naphthalene-1,4-diisocyanate , 1,1'-dinaphthyl-2,2 'diisocyanate, biphenyl-2,4'-diisocyanate, 3,3'
-Dimethylbiphenyl-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, 2,2'-dimethyldiphenylmethane-4,4'-diisocyanate,
3,3'-dimethoxydiphenylmethane-4,4'-diisocyanate, 4,4'-diethoxydiphenylmethane-4,4 '
-Diisocyanate, 1-methylbenzol-2,4,6-
Triisocyanate, 1,3,5-trimethylbenzol-
2,4,6-triisocyanate, diphenylmethane-2,4,
4'-triisocyanate, triphenylmethane-4,
4 ', 4 "-triisocyanate, tolylene diisocyanate, 1,5-naphthylene diisocyanate, etc .; dimer or trimer of these isocyanates, or addition of these isocyanates to dihydric or trihydric polyalcohols These are, for example, addition products of trimethylpropane with tolylene diisocyanate or hexanemethylene diisocyanate.

These curing agents are used in an amount of 10-60
It is used in an amount in the range of parts by weight.

Commercially available trade names of these polyisocyanates include Coronate L, Coronate HL, Coronate 20
30, Coronate 2031, Millionate MR, Millionate MT
L (manufactured by Nippon Polyurethane Co., Ltd.), Takenate D-102,
Takenate D-110N, Takenate D-200, Takenate D-202 (manufactured by Takeda Pharmaceutical Co., Ltd.), Death Module L, Death Module IL, Death Module N, Death Module HL
(Manufactured by Sumitomo Bayer), and these can be used alone or in combination of two or more utilizing the difference in curing reactivity.

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 and addition by heating after coating and drying. Among these resins, those which do not soften or melt before the resin is thermally decomposed are preferred.
Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin,
Mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate , Polyamine resins and mixtures thereof.

These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic fine powder and the binder is in the range of 5 to 300 parts by weight of the binder with respect to 100 parts by weight of the ferromagnetic fine powder by weight.

The binder for the upper and lower magnetic layers preferably has good compatibility. If the compatibility is poor, the adhesion between the upper layer and the lower layer is deteriorated, or the interface is disturbed and the surface property is deteriorated.

The coating layer of the magnetic layer on the uppermost layer has a thickness of 0.1 to 2.0 μm, preferably 0.1 to 1.0 μm. If the coating thickness is larger than 2.0 μm, the output in a short wavelength range is decreased due to thickness loss, which is not preferable.

When the thickness is less than 0.1 μm, the effect of the multilayer is reduced, and the effect of improving noise is lost, which is not preferable.

The plurality of magnetic layers of the present invention may be two layers of an upper layer and a lower layer,
Upper layer, middle layer, lower layer, or more layers,
Further, a non-magnetic intermediate layer may be provided between the upper layer and the lower layer. Further, an undercoat layer may be provided between the lower layer and the support.

Examples of the material forming the nonmagnetic support include polyester resins, polyolefin resins, cellulose derivatives, polycarbonate resins, polyimide resins, and polyamideimide resins. Also,
Depending on the application, nonmagnetic metals such as aluminum, copper, tin and zinc, or nonmagnetic metals containing these, plastics on which metals such as aluminum are deposited, paper such as paper and paper coated or laminated with polyolefins, etc. Can also be used. The form of the nonmagnetic support is not particularly limited, but usually a sheet-like one is used. However, the non-magnetic support may be in the form of a film, tape, disk, card or drum.

When a sheet-shaped non-magnetic support is used, the non-magnetic support generally has a thickness in the range of 5 to 100 μm.

On the other hand, a backcoat layer is formed on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is provided.

The binder used for forming the back layer of the present invention is not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and the like conventionally used as binders for magnetic recording media have been used. Can be used.

As the thermoplastic resin, the softening temperature is 150 ° C. or less,
With an average molecular weight of about 10,000 to 300,000, for example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride 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-silicone resin , Nitrocellulose-polyamide resin, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, Such as cellulose diacetate, cellulose triacetate, cellulose propionate, and nitrocellulose), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, and various synthetic rubber thermoplastic resins. Can be Further, the thermosetting resin or,
The reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, and becomes extremely large in molecular weight when heated after coating and drying.For example, phenol resin, phenoxy resin, epoxy resin, polyurethane cured Mold resin, urea resin, melamine resin, alkyd resin, silicone resin, cyclyl-based reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and diisocyanate Prepolymer mixtures, polyester polyol and polyisocyanate mixtures, urea formaldehyde resins, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixtures, polyamine resins, and mixtures thereof. It is.

Further, these binders may have other functional groups known per se, and among those functional groups,
At least one functional group selected from the group consisting of —SO ₃ M, —SO ₂ M, —COOM, —NH ₂ , —N ⁺ R ₄ , —OH, a phosphate group, and a phosphate group (where M Represents a hydrogen atom or an alkali metal atom, and R represents a lower alkyl group having 10 or less carbon atoms). These functional groups are preferably contained in an amount of 1 × 10 ⁻⁶ to 1 × 10 ⁻² equivalent per 1 g of the resin. As the binder, the glass transition temperature Tg is 40
C. or higher, particularly preferably 60.degree. C. or higher.

The binder may further contain a compound having two or more isocyanate groups (polyisocyanate). As such a polyisocyanate, for example,
Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate,
Xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, isocyanates such as triphenylmethane triisocyanate, reaction products of these isocyanates with polyalcohols, and condensation of these isocyanates The resulting polyisocyanate can be mentioned. The polyisocyanates are, for example, from Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031,
Takerate D-102, Takenate D-110 from Millionate MR, Millionate MLT, Takeda Pharmaceutical Co., Ltd.
N, Takenate D-200, Takenate D-202, and Sumitomo Bayer Co., Ltd., under the trade names such as DeathModule L, DeathModule L, DeathModule IL, DeathModule N, and DeathModule HL.

The mixing ratio of the binder and the inorganic powder in the back layer of the magnetic recording medium of the present invention is preferably 40 to 200 parts by weight, more preferably 50 to 130 parts by weight, per 100 parts by weight of the inorganic powder. If the mixing ratio of the binder is less than the above range,
If the running durability of the magnetic recording medium is deteriorated, and if it exceeds the above range, the packing density of the inorganic powder becomes low, so that the desired surface electric resistance cannot be obtained in the back layer of the magnetic recording medium or the friction coefficient Tend to increase.

The thickness of the back layer of the axial recording medium of the present invention is 1.5 μm or less, preferably 0.5 to 1.0 μm. If the thickness of the back layer is larger than the above range, the running property of the tape becomes unstable.

A method of forming a back layer on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed is already known, and the back layer of the magnetic recording medium of the present invention is basically formed on the support surface by the same operation. can do. That is, for example, after preparing a coating solution in which the inorganic powder and the binder component, and other additives to be added, are dispersed or dissolved in an organic solvent, and applying the coating solution on the surface of the support,
The back layer is formed by drying, evaporating the solvent, and further curing the binder component.

In preparing the coating liquid, the organic solvent, the method and the apparatus for dispersion and kneading, the method and the apparatus for coating the coating liquid on the support, and the like can be the conventional techniques known per se.

Either attachment of the magnetic layer to the support or attachment of the back layer may be performed first or may be performed simultaneously.

In the present invention, at least the same kind of lubricant and abrasive are contained as additives in the uppermost layer and the back coat layer of the plurality of magnetic layers of the magnetic recording medium configured as described above. In this case, the additives of the other magnetic layers may be the same or different from those of the uppermost layer, and may not contain a lubricant or an abrasive. When both layers contain other additives such as an antistatic agent, they may be the same or different.

Lubricants used in the present invention include, for example, saturated or unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils and the like.Abrasives include alumina, silicon carbide, titanium oxide, Magnesium oxide, titanium carbide, silicon nitride, silicon oxide, zirconia, and the like having a Mohs hardness of 5 or more can be used, and the particle size is preferably 10 μm or less, particularly preferably 0.5 μm or less.

In the present invention, the method of applying the magnetic paint in a superimposed manner in a wet state, that is, a wet-on-wet coating method, is to apply a next layer on the first layer as soon as possible after applying one layer in a wet state. And a multi-layer simultaneous application method by an extrusion coating method.

The magnetic layer coated on the non-magnetic support is usually dried after the treatment for orienting the ferromagnetic powder in the magnetic layer, that is, the magnetic field orientation treatment. Further, usually, after curing the resin component by heating or the like to obtain a cured product,
If necessary, a surface smoothing treatment can be performed. The magnetic recording medium that has been subjected to a surface smoothing treatment or the like is then subjected to a blade treatment as desired, and then cut into a predetermined shape.

〔Example〕

 Hereinafter, the present invention will be described specifically with reference to Examples.

 All expressions “parts” indicate “parts by weight”.

Ferromagnetic powder for lower layer: Co-doped γ-FeOx (x = 1.4
5) Long axis 0.3μm, crystallite size 400mm, Hc 600 Oe Ferromagnetic powder for upper layer (used for sample 1): Co-doped
FeOx (x = 1.45) long axis length 0.2μm, crystallite size 300
Å, Hc 850 Oe Ferromagnetic powder for upper layer (used for sample 2): Fe-Zn-Ni
Alloy, long axis length 0.2 μm, crystallite Hc 1500 Oe formulation Ferromagnetic powder for lower layer 100 parts Vinyl chloride / vinyl acetate / vinyl alcohol = 92: 2: 6 copolymer, degree of polymerization 400 15 parts Polyester polyurethane (NM = 5) 10,000 parts Desmodur L-75 (75% solution of isocyanate-based curing agent) 6.7 parts Conductive carbon (granular 7 mμ) 2 parts Methyl ethyl ketone 250 parts Ferromagnetic powder for magnetic layer upper layer 100 parts Vinyl chloride / vinyl acetate / vinyl alcohol = 92: 2: 6 copolymer, degree of polymerization 400 15 parts Polyester polyurethane (NM = 50,000) 5 parts Desmodur L-75 (75% solution of isocyanate-based curing agent) 6.7 parts Industrial myristic acid 1 part Oleic acid modified Silicone 1 part Butyl stearate 1 part Conductive carbon 0.2 part α-alumina 2 parts Methyl ethyl ketone 250 parts (back layer) Carbon black 10 parts Nitro cellulose S 25 parts Urethane resin 15 parts Polyisocyanate 40 parts α-alumina 5 parts Myristic acid 2 parts Oleic acid-modified silicone 2 parts Butyl stearate 2 parts Solvent MEK 300 parts
Using an extrusion type coating head having two slits in one head, the lower layer is simultaneously coated to 4 μm and the upper layer is 1.5 μm, and the magnetic layer is distributed and dried. Then, the back layer having the above composition is applied and dried. To perform calendar processing,
Slit to 1/2 inch width, VHS type video tape (Sample N
o.1-2) were obtained.

Comparative Example 1 In the same manner as in Sample No. 1 of the example, a magnetic layer was applied in multiple layers, and a back layer having a composition in which only the additive was removed from the composition of the back layer was applied. Sample No. 3 Comparative Example 2 In the same manner as in Example 1, a magnetic layer was coated in multiple layers to prepare a magnetic layer without a back layer. (Sample No. 4) Comparative Example 3 As Comparative Example 3, the composition of the back layer was as follows.
Samples were prepared in the same manner as in the examples using the same magnetic layer composition as the examples for both the upper layer and the lower layer (sample N
o.5) Back layer Carbon black 10 parts Nitrocellulose 25 parts Urethane resin 15 parts Polyisocyanate 40 parts Chromic oxide 5 parts Myristic acid 2 parts Oleic acid modified silicone 2 parts Butyl stearate 2 parts Methyl ethyl ketone 300 parts Comparative example 4 Comparative example 4 For the composition of the back layer and the composition of the upper layer of the magnetic layer, the following composition was used, and the lower layer of the magnetic layer had the same composition as that of the example, and a sample was prepared in the same manner as in the example. (Sample No.6) Upper layer of magnetic layer Ferromagnetic powder 100 parts Vinyl chloride / vinyl acetate / vinyl alcohol = 92: 2: 6 copolymer Degree of polymerization 400 15 parts Polyester polyurethane (NM = 50,000) 5 parts Desmodur L- 75 (75% solution of isocyanate-based curing agent) 6.7 parts Industrial myristic acid 1 part Stearic acid 1 part Butyl stearate 1 part Conductive carbon 0.2 part Chromium oxide 2 parts Methyl ethyl ketone 250 parts Back layer carbon black 10 parts Nitrocellulose 25 parts Urethane Resin 15 parts Polyisocyanate 40 parts α-alumina 5 parts Myristic acid 2 parts Oleic acid-modified silicone 2 parts Butyl stearate 2 parts Methyl ethyl ketone 300 parts Each sample was evaluated by the following method, and the results are shown in Table 1. Show.

Electromagnetic conversion characteristics (Y-S / N, C-S / N) Y-S / N is S / N ratio at 5MHz, SHG made by Fuji Photo Film KK
The comparison was made with the tape set to 0 dB.

C / S / N is S / N ratio at 0.75MHz, Fuji Photo Film KK S
HG tape was compared with 0dB.

Measuring machine: HR-D555 type deck made by Victor Company of Japan KK Driving durability T-120 video tape VHS type under conditions of 40 ° C and 80% RH
The test was performed on a VTR, and a full-length running test was performed. The number of runs before the signal recorded beforehand did not appear on the monitor due to head clogging was indicated.

Still durability The durability was examined in steel mode. Table 1 shows the evaluation results.

[Effects of the Invention] From the results in Table 1, the video tapes obtained in each of the examples have excellent electromagnetic conversion characteristics, superior running durability and durability in comparison with the video tapes obtained in each of the comparative examples. It is clear that it shows.

Claims (1)

(57) [Claims] 1. A non-support having, on one surface, a plurality of magnetic layers in which a ferromagnetic powder is dispersed in a binder and containing at least a lubricant and an abrasive as additives, and the other surface. In a magnetic recording medium having a back coat layer containing at least a lubricant and an abrasive in a binder as an additive,
The uppermost magnetic layer contains a ferromagnetic metal powder, and has a thickness of 0.1 to 2.0 μm, and at least a lubricant and an abrasive of the additives contained in the back coat layer are formed of the plurality of magnetic layers. A magnetic recording medium characterized by being the same kind of substance as the lubricant and the abrasive in the uppermost layer.