JP3471844B2 - 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
Regarding the coat layer. [0002] In recent years, audio tapes and video tapes have been developed.
And so on, the recording format has been digitized
ing. Digitized signal due to repeated copying
Degradation, that is, from image and sound quality degradation
Therefore, the merit is very large. In this digitization
The amount of data recorded by the magnetic recording medium increases accordingly
As a result, it is unavoidable to increase the recording density,
This is addressed by shortening the wavelength. [0003] A recently developed digital standard
Le Compact Cassette (DCC)
Magnetic tapes, etc.
The tendency of shortening the wavelength is the same. However, higher recording density
And shortening the wavelength, the gap loss increases and the reproduction output
Problems such as a decrease and an increase in the error rate occur. That
To improve the smoothness of the tape magnetic layer surface more than ever
Is required, and measures to stabilize driving performance
The importance of the backcoat layer as a step is increasing. [0004] Audio and video tapes
In the cassette half, stable running of the tape and various heads
To improve the adhesion between the tape and the tape,
There are guides and tape pads on the back coat layer side of the road
There are many. Even for the magnetic tape used for the DCC,
The same is true. [0005] Conventionally, the back coat layer has been used to form a tape.
Chips cut by the tape pad due to repeated long running
There was a point. To resolve such inconveniences,
Add non-magnetic powder with high Mohs hardness to
It is used to increase the durability of the back coat layer.
You. However, the hardness of the back coat layer component increased.
For this reason, there has been a problem that the guide is worn. this
Of the back coat layer, guides, etc.
Foreign matter, generally in the form of fine powder, which is generated,
Clogging and dropping of the head
Cause serious accidents such as out error rates
Cause. Therefore, it is best to reduce as much as possible.
Good. In addition, a text having such a back coat layer
The tape repeatedly for a long time in a high-temperature environment.
Adhere to guides, etc., increasing the torque required for normal rotation.
Therefore, an accident that stops the tape running is likely to occur. [0006] The main object of the present invention
Is abrasion of the back coat layer by tape pad etc.
And wear of guides is small, and stable even in high temperature environments.
Recording medium having a back coat layer with excellent running durability
Is to provide the body. [0007] Such an object is as follows.
This is achieved by the present invention of (1). (1) Ferromagnetic powder bonded to one surface of non-magnetic support
Having a magnetic layer dispersed in an agent, and a back coat on the other surface.
A backing layer, wherein the back coat layer is a conductive inorganic pigment.
And a non-magnetic powder with a viscosity of 20,000 centi
Talks or more silicone oil
The conductive inorganic pigment contains carbon black,
The coating layer contains the conductive inorganic pigment and the nonmagnetic powder.
The weight ratio is 100: 0.5 to 100: 5 by weight.
Magnetic recording medium. The magnetic recording medium of the present invention is made of various materials such as polyester.
Ferromagnetic powder is applied on one side of a non-magnetic support made of seed resin.
Has a magnetic layer dispersed in a binder and has a backing on the other side
It has a coat layer. This back coat layer is
In addition to conductive inorganic pigments such as racks, Mohs hardness of 5-9
The non-magnetic powder in the backcoat layer
Increases durability and prevents scraping by tape pads. That
Top, viscosity at 25 ° C is 20,000 centistokes (CS)
By containing the above silicone oil, the guide
To prevent abrasion of the tape and to adhere to the tape in a high temperature environment.
The tape running stop accident due to the above can be prevented. [0009] Carbon black and silicon
Improves tape runnability etc. by containing corn oil
In Japanese Patent Application Laid-Open No. Sho 59-198533,
Proposed. However, in this proposal, the back coat layer
The purpose of containing silicone oil is to
(The magnetic tape) is wound on the back coat layer while it is wound.
Transfer the silicone oil to the magnetic layer
And supply an appropriate amount of silicone oil to the magnetic layer.
To reduce head wear, head clogging, etc.
It is said that. The publication aims at these effects
That the viscosity of the silicone oil used is 25
Do you state that it is preferable to be 10,000 CS or less at ℃
It is clear that the silicone coating is used for the back coat layer of the present invention.
Irreversible wear due to back coat layer
That have the effect of preventing
Is clearly different. Further, Japanese Patent Application Laid-Open No. 62-183030 discloses
Is a non-magnetic powder with Mohs hardness of 5 or more, Si-O, etc.
Magnets with a backcoat layer having a compound in the structure
The air recording medium has good running properties, and
There is a suggestion that both members have little damage. But this
Is a compound of the general formula
Are compounds having different chemical structures represented by In addition,
From the maximum molecular weight of the general formula given, the viscosity of this compound is
It is outside the scope of the invention. The magnetic recording medium according to the present invention comprises a non-magnetic support.
Layer with ferromagnetic powder dispersed in binder on one side of
Having a back coat layer on the other surface,
The coating layer is made of a conductive inorganic pigment, a non-magnetic powder,
Contains corn oil. Non-magnetic support used in the magnetic recording medium of the present invention
There are no particular restrictions on the body, depending on the purpose various flexible materials, each
The material selected from the various types of rigid materials can be
What is necessary is just to make it predetermined shape and dimensions, such as a loop shape. For example,
Flexible materials such as polyethylene terephthalate
Polyester. [Backcoat layer] Backcoat of the present invention
The layer is a conductive inorganic pigment and enhances the mechanical strength
Inorganic pigments such as non-magnetic powder for the main purpose, further additives,
It is composed of a binder, a curing agent and the like. A conductive inorganic pigment used for the back coat layer;
It is usually magnetic, such as carbon black and graphite.
It is used for the back coat layer etc. of the recording medium.
Any price, light transmittance, electricity
It is preferable to include carbon black in terms of resistance, etc.
No. In addition, conductive inorganic pigments such as carbon black
May have any shape, and the average particle size is 20 to
About 100μm, BET value is 40 ~ 200m ^Two / g
Preferably, there is. Average particle size and BET value
Those smaller than the range are difficult to obtain industrially, and
Ra value of the back coat layer is too low and friction is large.
You. On the other hand, if it is too large, the surface smoothness of the back coat layer
Deteriorates the surface properties of the magnetic layer surface,
Deteriorate characteristics. [0015] Among the inorganic pigments, non-magnetic powders include:
SiO with Mohs hardness of about 5 to 9 _Two , TiO _Two , Al _Two O
_Three , Α-Fe _Two O _Three , Cr _Two O _Three , SiC, CaO, etc.
Can be used. Mohs hardness in the range of about 5 to 9
The lower one is the back coat layer by tape pad etc.
If there is a lot of shaving, and the
The amount of wear is large, which is not preferable. The shape of these non-magnetic powders is spherical, granular,
What is the usual shape such as shape, needle shape
The average particle size is about 10 to 200 nm
Is preferred. If the particle size is too large, Ra will increase.
Too much, and the error rate worsens. Also, if it is too small,
It is necessary to contain a large amount because of insufficient strength.
Id wear increases. The conductive inorganic pigment in these inorganic pigments is
The content ratio with the magnetic powder is 100: 0.5 to 10 by weight.
0: 5 is preferred. If too little non-magnetic powder
The mechanical strength of the coating layer decreases and the backcoat layer is scraped.
Increase. On the other hand, if too large, the mechanical strength is too high and gas
Id wear increases. The content of such an inorganic pigment is
The content is preferably about 30 to 60% by weight of the back coat layer. inorganic
Too much pigment makes the backcoat layer brittle
If too small, the magnetic layer and the back coat layer interface
This causes problems such as sticking. The lubricant used for the back coat layer is
In the clear, silicone oil with a viscosity at 25 ° C of 20,000 CS or more
Ill. Silicone oil with such viscosity
Generally has an average degree of polymerization of about 100 or more. About this
If the viscosity is too low, guide wear will increase and lubrication will increase.
The effect of adding silicone oil as an agent has no effect.
Therefore, the effect of the back coat layer of the present invention cannot be obtained. Also,
The viscosity of the silicone oil used has no particular upper limit,
It is usually about 1,000,000 CS. Examples of such silicone oils include
For example, dimethylpolysiloxane, diphenylpolysiloxane
Fatty acids such as myristic acid, oxyethylene
Silicone modified with epoxy, epoxy-modified silicone, etc.
Known silicone oils commonly used for magnetic recording media
Can be used. In addition, the silicone oil contains
The amount is 0.5 to 100 parts by weight of the inorganic pigment.
About 10 parts by weight, more preferably about 1 to 3 parts by weight
It is. If the content is too small, the above effect is reduced,
If it is too large, the effect cannot be expected to increase. The back coat layer of the present invention is characterized in that
Machine pigment, the non-magnetic powder and the silicone oil
Each is included within the above conditions. Thereby, for example,
Higher recording signal density and shorter wavelength, such as magnetic tape for DCC
Especially for applications that require smoothing of the magnetic layer surface.
Tape pad provided on the cassette half of the air tape
Back coat layer due to sliding contact with
It is possible to prevent the generation of a foreign substance that causes the above. Furthermore, high
It is possible to effectively prevent the occurrence of accidents during long-time driving.
Will be possible. As additives such as lubricants and dispersants,
In addition to silicone oil, this type of backcoat layer
Any of the types used can be used
You. For example, a monobasic fatty acid having 12 to 16 carbon atoms and carbon
Fatty acid esthetics consisting of several 3 to 12 monohydric alcohols
Monobasic fatty acids having 17 or more carbon atoms and the fatty acids
Of carbon atoms of 21 to 23 in total
Fatty acid esters composed of polyhydric alcohols are used.
You. These lubricants are used in an amount of 100% by weight of the inorganic pigment.
Parts by weight in the range of about 0.1 to 1 part by weight.
No. If the content of these additives is too high, running at high temperatures
Accidents are likely to occur at the time of the run.
This is likely to happen. Binder used in the back coat layer of the present invention
Are thermoplastic resins, thermosetting resins, reactive resins, electron beams
Irradiation curable resin, or a mixture thereof
You may. As the thermoplastic resin, for example, vinyl chloride
Nyl-acrylate copolymer, vinyl chloride-vinegar
Vinyl acid copolymer, vinyl chloride-vinylidene chloride copolymer
Polymer, vinyl chloride-acrylonitrile copolymer,
Acrylate-acrylonitrile copolymer,
Lylic acid ester-vinylidene chloride copolymer, methacrylic acid
Lulic acid ester-vinylidene chloride copolymer, methacryl
Acid ester-ethylene copolymer, polyvinyl fluoride-salt
Vinylidene fluoride-acrylonitrile copolymer, acrylo
Nitrile-butadiene copolymer, polyamide resin,
Livinyl butyral, cellulose derivatives (cellulose
Acetate butyrate, cellulose diacetate, cell
Roast rear acetate, cellulose propionate, d
Styrene, butadiene-based copolymer,
Polyester resin-chlorovinyl ether acrylic acid
Heating of stell copolymer, amino resin and synthetic rubber
Plastic resins and the like can be given. These are a kind alone
May be used in combination with two or more
May be. Further, the thermosetting resin or the reactive resin
Examples include, for example, phenolic resin, epoxy resin,
Urethane-curable resin, urea resin, melamine resin, aluminum
Kid resin, silicone resin, acrylic reaction resin, high
Molecular weight polyester resin and isocyanate prepolymer
With methacrylate copolymer and diisocyanate
Mixture with toprepolymer, urea-formaldehyde resin
And polyamine resins. These are just a kind
It may be used alone or in combination of two or more.
May be used. Further, the binder may be hardened by electron beam irradiation.
Cured compound, that is, electron beam irradiation curing type
Those using a resin are also suitable. Including these binders used in the back coat layer
The amount is 50 to 30 parts by weight based on 100 parts by weight of the inorganic pigment.
The range may be about 0 parts by weight, and more preferably 6 parts by weight.
It is about 0 to 200 parts by weight. Too much binder content
This increases friction with the tape pad and guide,
It is easy to cause damage, while back coat is too small
The strength of the layer decreases, the coating becomes brittle, and the running durability is poor.
Become There are no particular restrictions on the solvent used for the back coat layer.
No solubility and phase of binders and other additives
It is appropriately selected in consideration of solubility and the like. Commonly used solvents, for example
For example, cyclohexanone, methyl ethyl ketone, methyl iso
Ketones such as butyl ketone and isophorone, and toluene
Various types such as aromatics and furans such as tetrahydrofuran
If one or two or more solvents are selected according to the purpose,
Good. Such a solvent is added to 100 parts by weight of the inorganic pigment.
About 500 to 1500 parts by weight. The components of such a back coat layer coating layer are
As a paint, the above-mentioned non-magnetic
Is applied to the back side of the magnetic layer side of the conductive support.
Any method that is commonly used can be used.
No particular restrictions. The thickness of such a back coat layer is 0.3
It is preferably about μm or more. Back coat layer
If the thickness is too small, the effect of the surface smoothness of the support will increase.
This is disadvantageous in characteristics such as running characteristics and modulation noise. Also,
The thickness of the back coat layer provided for the purpose such as the present invention
Is usually 3 μm or less. The back cover provided in this manner is
The surface roughness Ra of the coating layer is about 10 to 70 nm. Ra
Is too large, the surface smoothness is poor and the magnetic layer
Is also not preferable in terms of the electromagnetic conversion characteristics. Also, it ’s too small
For example, the coefficient of friction on the backcoat layer surface increases,
When running at high temperatures, magnetic tape adheres to guides and stops running.
Stopping accidents are more likely to occur. In addition, Ra value is tailor
-A stylus type surface shape measuring device manufactured by Hobson, TALYS
What is necessary is just to measure by a TEP system. Ra is JIS-
B0601. Further, the friction coefficient μ of the back coat layer is
It is preferably about 0.30 or less, usually 0.15
About 0.20. Friction of the back coat layer of the present invention
The coefficient depends on the surface properties of the backcoat layer and the silicon
Oil and other lubricants, but the friction coefficient is large.
If it is too high, the magnetic tape may adhere to guides, especially when running at high temperatures.
Because it is easy to cause
Not good. The value of friction coefficient μ is a tape manufactured by Yokohama System Co., Ltd.
Apply a constant back tension with a friction tester and
Teflon on back coat surface with speed of 4.76m / sec
Can be measured by contacting a tape pad made of
You. [Magnetic Layer] The magnetic layer used in the present invention is a known magnetic layer.
May be various coating type magnetic layers. Magnetic powder used
For example, γ-Fe _Two O _Three , Co-containing γ-Fe _Two O
_Three , Fe _Three O _Four , Co-containing Fe _Three O _Four , CrO _Two Etc. acid
Fine powder, Fe, Co, Ni or their alloys
From known magnetic powders such as fine powders, suitable ones according to the purpose
And its coercive force Hc, saturation magnetization σs, etc.
What is necessary is just to select suitably according to the objective. The magnetic powder is 70 to 85 layers in the magnetic layer.
It may be contained in an amount of about%. With respect to the binder used for the magnetic layer,
The binder used for the back coat layer can be preferably used.
Wear. The content of the binder is 100 parts by weight of the magnetic powder.
It is sufficient that about 15 to 30 parts by weight is contained. Join
If the content of the agent is too large, the electromagnetic conversion characteristics decrease and the friction
It may cause driving accidents due to the increase in numbers,
If the amount is too small, the adhesive strength to the support or the bond in the magnetic layer
The resultant force weakens. When a crosslinking agent is also used, such a magnetic material is used.
Any material can be used for the conductive layer
The content is 1 to 100 parts by weight of the binder.
It may be about 0 to 30 parts by weight. The magnetic layer is used for the back coat layer.
Inorganic pigments such as conductive inorganic pigments and non-magnetic powders
It may be rare. Carbon black is a conductive inorganic pigment.
Rack, graphite, graphitized carbon black
, Etc., and SiO as nonmagnetic powder _Two , TiO _Two , Al
_Two O _Three , Cr _Two O _Three , SiC, CaO, CaCO _Three ,acid
Zinc oxide, α-Fe _Two O _Three , Talc, kaolin, CaSO
_Four , Boron nitride, graphite fluoride, molybdenum disulfide, ZnS
Etc. Such a conductive inorganic pigment and non-magnetic powder
Etc. are 0.1 to 10 with respect to 100 parts by weight of the magnetic powder.
It only needs to be included in parts by weight, these will be too much
And the coating film becomes brittle, with many dropouts
Disadvantage. The conductive inorganic pigment and the nonmagnetic
The diameter of the powder or the like is preferably about 0.5 μm or less. As the magnetic paint, other than the above,
Agents, dispersants, lubricants and the like may be included. There is no particular limitation on the solvent, and the solvent
What is necessary is just to select suitably in consideration of resolvability, compatibility, etc. An example
For example, acetone, methyl ethyl ketone, methyl isobutyl
Ketones, ketones such as cyclohexanone, ethyl formate,
Esters such as ethyl acetate and butyl acetate, methanol,
Alcohols such as ethanol, isopropanol and butanol
Aromatics such as toluene, xylene and ethylbenzene
Group hydrocarbons, isopropyl ether, ethyl ether
, Ethers such as dioxane, tetrahydrofuran,
One or more kinds of furans such as furfural
Mix and use. These solvents were used in an amount of 100 parts by weight of the magnetic powder.
Should be contained in an amount of about 100 to 300 parts by weight. As the lubricant (including the dispersant),
Any of the types used for this type of magnetic layer
Caprylic acid, capric acid, lauric acid
Acid, myristic acid, palmitic acid, stearic acid,
Acid, oleic acid, elaidic acid, linoleic acid, linoleic acid
Fatty acids having 12 or more carbon atoms such as stearic acid
And the alkali metals of the fatty acids (Li, Na, K, etc.)
Or alkaline earth metals (Mg, Ca, Ba, etc.)
Metal soap; lecithin and the like are used. In addition, a higher alcohol having 12 or more carbon atoms
And their sulfates, surfactants, titanium
Coupling agents, silane coupling agents, etc. can also be used
is there. These lubricants (dispersants) are used in the magnetic powder.
Contained in the range of about 1 to 10 parts by weight based on 100 parts by weight
Just do it. As the lubricant, in addition to the above, silicone oil
Il, graphite, molybdenum disulfide, tongue disulfide
Stainless steels and fatty acid esters are used. These lubricants were used in an amount of 100 wt.
Parts by weight of about 0.5 to 20 parts by weight.
Just do it. As other additives, this type of
Any material can be used for the magnetic layer.
For example, antistatic agents such as saponin
Agents, nonionic surfactants, heterocycles, cationic
Surfactants, anionic surfactants containing acidic groups, amphoteric activities
Agents and the like are used. Such a magnetic paint is coated on a non-magnetic support.
Although there is no particular limitation on the application method,
Knife coating method, reverse roll coating method,
Commonly used such as via roll coating method or extrusion coating method
Any of the methods that have been used. The magnetic layer is a single layer
In addition, it may have a multilayer structure of two or more layers. Sa
In addition, a non-magnetic paint film layer is provided between the magnetic layer and the non-magnetic support.
Or to improve the adhesion between the nonmagnetic support surface and the magnetic layer.
Magnetic recording medium to be manufactured
May be determined based on the performance, application, and the like required by the user. The dry thickness of the magnetic layer thus provided is
Usually, it may be about 0.15 to 5 μm. EXAMPLES Hereinafter, specific examples of the present invention will be described together with comparative examples.
explain. Example 1 A back coat layer and a magnetic layer were provided as follows.
A magnetic tape for DCC, which is a magnetic recording medium, was manufactured. What
The numerical values of the compositions are expressed in parts by weight. <Magnetic Layer> Co-Coated γ-Fe _Two O _Three (BET value 40m ^Two / g · Hc720Oe) 100 α-alumina (particle size 0.2 μm) 1.5 vinyl chloride-vinyl acetate-vinyl alcohol copolymer 12 polyurethane 5 methyl ethyl ketone 290 cyclohexanone 90 myristic acid 0.5 polyisocyanate 5 Prepare magnetic paint of composition, 10μm
Coating on thick polyester non-magnetic support, magnetic field orientation,
Drying and calendering to form a magnetic layer with a thickness of 2μm
Then, a heating heat treatment was performed at 60 ° C. for 24 hours. Next, on the back surface of the magnetic layer of the non-magnetic support,
A back coat layer having the following composition was formed. <Backcoat Layer> Carbon black (BET value 180 m ^Two / g, average particle size 0.03μm) 97 Non-magnetic powder (SiO _Two Powder; average particle diameter 60 μm, Mohs hardness 7) 3 vinyl chloride-vinyl acetate-vinyl alcohol copolymer 70 polyurethane 30 methyl ethyl ketone 840 toluene 560 silicone oil 2 (polydimethylsiloxane; viscosity at 25 ° C., 20,000 SC) polyisocyanate 30 Prepare a backcoat layer paint of the above composition,
Perform coating, drying and calendaring, and heat at 60 ° C for 24 hours
Heat treatment formed a 0.5 μm thick layer. Example 2 Silicone oil in the backcoat layer coating composition of Example 1
And the viscosity at 25 ° C of 50,000 CS
Other than that, a magnetic tape for DCC was prepared in the same manner as in Example 1.
did. Example 3 Silicone oil in the backcoat layer coating composition of Example 1
The same as in Example 1 except that the viscosity of
Thus, a magnetic tape for DCC was produced. Comparative Example 1 Silicone oil in the backcoat layer coating composition of Example 1
And SiO _Two Without adding powder (non-magnetic powder)
Produced a magnetic tape for DCC in the same manner as in Example 1. Comparative Example 2 Silicone oil in the backcoat layer coating composition of Example 1
The magnetic tape for DCC was the same as in Example 1 except that no
Made the soup. Comparative Example 3 Silicone oil in the backcoat layer coating composition of Example 1
Except that the viscosity of the oil was 100 CS.
A magnetic tape for CC was produced. Comparative Example 4 Silicone oil in the backcoat layer coating composition of Example 1
Except that the viscosity of the oil was 3000 CS.
A magnetic tape for DCC was produced. Comparative Example 5 Silicone oil contained in the backcoat layer coating composition of Example 1
As in Example 1 except that the viscosity of
The magnetic tape for DCC was produced. Comparative Example 6 SiO in the backcoat layer coating composition of Example 1 _Two Powder
(Non-magnetic powder) without adding silicone oil
Except that the viscosity was 50,000 CS, D
A magnetic tape for CC was produced. Comparative Example 7 Silicone oil contained in the coating composition of the back coat layer of Example 1
Can be used as described in JP-A-62-183030.
Except for using the compound represented by the formula,
A magnetic tape for DCC was produced. The magnetic tape for each DCC manufactured in this manner was used.
Were evaluated in the following manner. <Evaluation method for back coat layer scraping> DCC90
Using a 0 tape recorder (manufactured by Philips)
℃, continuously run for 24 hours, back coat layer
The degree of foreign matter adhered to the tape pad due to scraping
Observed more. As a result, shavings on the tape pad
If there is almost no adhesion, remove the tape.
If there is significant adhesion of shavings to the
Was. <Evaluation method of guide wear> DCC900
-Using a precoder (manufactured by Philips) at 0 ° C,
Perform continuous running for 24 hours repeatedly, and guide (Styrol
Abrasion), a contact-type profile measuring machine manufactured by Tokyo Seimitsu Co., Ltd.
It was measured with Surfcom 605A. <High temperature running test evaluation method> TD-R631
Type audio tape recorder (made by Victor Company of Japan)
Repeat for 24 hours at 55 ° C and 80% RH
Continue running and stop running due to high torque.
If there was an accident, it was considered an accident. Table 1 summarizes the above evaluation results. [Table 1] The content of the nonmagnetic powder shown in Table 1 is based on the content of the inorganic pigment.
% By weight of the non-magnetic powder. As shown in Table 1, non-magnetic
Backcoat layers of Comparative Examples 1 and 6 without addition of conductive powder
Indicates that the back coat layer is scraped,
Non-magnetic powder was added when no oil was used.
It can be seen that the amount of guide wear of each of Comparative Examples 2 to 5 was large.
Call Also, do not use the silicone oil
Or in Comparative Examples 1 to 3 using very low viscosity,
Adhesion to the guide occurs due to high temperature running. Further
In addition, in Comparative Example 7, backcoat layer scraping was observed.
Although there was no
The test resulted in an accident. Note that conductive inorganic pigments and non-magnetic
Content ratio with conductive powder, guide wear and back coat
Table 2 shows the relationship with the layer wear. [Table 2] The use of the back coat layer of the present invention
From the back coat layer with a tape pad, etc.
And wear of guides are stable, even in high temperature environments
Recording with backcoat layer with improved running durability
A medium can be provided.

Continuation of the front page (72) Inventor Souichi Yawata 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-59-167847 (JP, A) JP-A-1-176320 ( JP, A) JP-A-1-276425 (JP, A) JP-A-4-114314 (JP, A) JP-B-50-3927 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G11B 5/62

Claims (1)

(57) [Claim 1] A nonmagnetic support has a magnetic layer in which a ferromagnetic powder is dispersed in a binder on one surface and a backcoat layer on the other surface. The back coat layer contains a conductive inorganic pigment, a nonmagnetic powder, and a silicone oil having a viscosity at 25 ° C. of 20,000 centistokes or more. The conductive inorganic pigment contains carbon black. In the coat layer, the content ratio of the conductive inorganic pigment to the nonmagnetic powder is 100: 0.5 to 10 by weight.
0: 5 magnetic recording medium.