JPH0644341B2 - Magnetic recording medium - Google Patents

Description

Detailed Description of the Invention

 The present invention is durable and reliable when used repeatedly.
Magnets with improved cinching phenomenon, adhesion and wear resistance
Air recording media, especially the electrical properties of the magnetic recording layer.
Higher resistance to improve electromagnetic conversion characteristics and magnetic recording
Coating layer provided on the surface opposite to the surface on which the layer is provided
Drop the electrical resistance of the (back coat layer)
It has a low Young's modulus and a special Young's modulus and surface roughness.
Fixed to solve the scratches on the back surface and reduce the electromagnetic conversion characteristics.
A magnetic recording medium with excellent characteristics
It is a thing. Currently, magnetic recording media are used for audio, video and computer.
Widely used in the field of magnetic disks, magnetic disks, etc.
And recording on magnetic recording media
The amount of information is increasing year by year, and therefore magnetic recording media
There is an increasing demand for higher recording density for the body.
Is coming. The short wavelength recording method is used for high density recording.
This method is apt to cause the dropout problem described below.
That is, the dropout is written on the magnetic recording medium.
Error that misses a pulse that should exist when reading existing information
Which is the space between the magnetic recording medium and the magnetic head.
This is mainly due to the instantaneous increase in sourcing loss.
It That is, the dropout is a magnetic recording medium manufacturing process or
Foreign matter is present on the magnetic surface due to the use process.
Foreign matter has the effect of expanding the spacing between the head and the medium.
These are the sources of foreign matter.
As a result, it was scraped off from the magnetic layer or the base material during running.
Dust, etc., will adhere to the base surface and will be transferred to the magnetic surface.
It is possible to move. By the way, in the current recording method using a magnetic head
Has a tape-head spacing loss of 54.6d.
/ Λ [dB] (d: tape-head distance, λ: recording wave
Long). As you can see from this formula, the recording density
Output due to spacing for short wavelength recording with high
The rate of reduction is significantly greater than that for longer wavelengths. did
Therefore, even if a small foreign substance is on the tape surface, the space is
Ringing loss increases and is detected as a dropout.
Will be issued. On the other hand, on the other hand, the output in short wavelength recording is increased for higher density.
Need to be big, alloy tape has emerged. Immediately
Conventionally, as a ferromagnetic powder, for example, γ-Fe_TwoO_Three,
Co-containing γ-Fe_TwoO_Three, Fe_ThreeO_Four, Co-containing Fe_Three
O_Four, CrO_TwoEtc. were often used, but these strong magnetic
Of coercive force and maximum residual magnetic flux density
Magnetic properties are insufficient for high-sensitivity and high-density recording,
Signals with a short recording wavelength of about 1 μm or less and narrow track width
It is not very suitable for magnetic recording. So as mentioned above
In addition, as the demand for magnetic recording media becomes stricter,
Ferromagnetic powder with suitable properties for high density recording, eg F
e, Co, Fe-Co, Fe-Co-Ni, Co-Ni
Metal or alloy such as Al, Cr, Si, etc.
Alloys and the like have been developed and proposed. Such alloy
A magnetic recording layer made of powder is a high storage material for the purpose of high density recording.
It is necessary to have a magnetic force and a high residual magnetic flux density.
Various manufacturing methods to ensure that the powdery powder meets these criteria
Alternatively, it is preferable to select the alloy composition. The present inventors have manufactured magnetic recording media using various alloy powders.
When made, the specific surface area by BET method is 48m^Two/ G
With the above, the coercive force of the magnetic layer is 1000 Oe or more, and
Surface roughness of the magnetic layer [For measurement by the Taristep described below
With a cut-off of 0.17 mm and R20 (20 times average)
The same applies hereinafter] is less than 0.08μ, the noise level
Magnetic recording is suitable for high density, short wavelength recording.
It was found that a recording medium could be obtained. But consider well
If you look at it, you can wind the magnetic recording medium as a video tape.
The characteristics of the magnetic layer are required to meet the above requirements.
It turns out that the desired effect cannot be achieved simply by satisfying
It was That is, a magnetic recording medium using these ferromagnetic alloy powders
As a result of further research on these magnetic recording media
Has an electrical resistance of 10^TenΩ / cm^TwoBecause it is higher than above, it is suitable for charging
More dust and dirt, dropouts
I found it easy. On the other hand, the electric resistance of the magnetic layer is 10^TenΩ
/ Cm^TwoIn the following cases, the above phenomenon does not occur and 10
^TenΩ / cm^TwoWas found to be a turning point. And when I examined that point further,
The electric resistance of the magnetic recording layer is 10^TenΩ / cm^TwoAbove and high
If not, a substance that can lower the electrical resistance is added to the magnetic recording layer.
Even if you try to solve the above problems due to electrification,
Electromagnetic conversion characteristics have deteriorated due to the mixture of pure substances, and high density
It becomes unsuitable for recording, and the magnetic layer is not supported.
The back of your plastic (usually polyester) film
Surface characteristics to the physical and electrical characteristics of magnetic recording media
It turned out that they have a close relationship. Conventionally,
Forming a back layer by coating on the back surface of the black film substrate,
For example, a carbon black on the base surface opposite the magnetic surface.
Inorganic filler such as graphite or graphite as an organic binder
Coated and kneaded paint applied or antistatic agent applied
To make the base tougher and reduce the electrostatic property.
It is recommended to try to reduce the frictional resistance while driving.
Is being proposed. However, due to these treatments,
Durability against returning and increasing dropout
Has improved considerably, but its level is
However, it is not satisfactory and needs further improvement.
It was. Therefore, as a result of the inventors of the present invention having conducted repeated research on that point,
BE of alloy powder whose S / N of the magnetic recording medium is used for the magnetic layer
Only related to specific surface area by T method and surface roughness of magnetic layer
Not only that, but also the surface roughness of the back layer is concerned.
Phenomenon (loosen winding during rapid stop), back layer wear
There are problems such as friction, friction, and adhesion between the magnetic layer and the back layer.
Electromagnetic conversion characteristics, runnability,
We cannot provide magnetic recording media with excellent durability.
Found that the magnetic tape was
There is a strong winding tightness when wound around the
The surface irregularities of the back layer cut into the magnetic layer and roughen the magnetic surface.
For this reason, the magnetism of the back layer is not fully utilized.
I also found out. Thus, conventionally, the electric resistance of the magnetic layer is 10^TenΩ / cm^Two
The following was usual, but bound a metal oxide as the magnetic layer
Disperse the agent in the agent and apply it to the substrate to bind the metal powder.
As it is dispersed in the mixture and applied to the substrate,
The electric resistance of the magnetic layer is 10^TenΩ / cm^TwoIncreasing above
However, the electromagnetic conversion characteristics are improved, but on the other hand various
However, the present inventors
Has an electric resistance of the magnetic layer of 10^TenΩ / cm^TwoEven above
The electric resistance of the back coat layer (surface) is 10^TenΩ / cm^TwoSince
By setting it below, unexpectedly dust and dirt will be generated on the magnetic layer.
It becomes difficult to attach, so dropout is drastically reduced and cinch
The sticking phenomenon disappears, the stickiness disappears, and
Young's modulus of the coat layer is 200-1500 kg / mm^Two
By doing so, the back coat surface becomes strong
Increases durability and eliminates scratches due to the brittleness of the back surface
Cut off the surface roughness of the back coat layer
R20 of 0.27 μm or less at 0.17 mm
As a result, the electromagnetic conversion characteristics do not deteriorate and the wear resistance is further improved.
The present invention has been found to improve wear resistance and has reached the present invention.
Is. That is, in the present invention, the electric resistance of the magnetic layer is 10^TenΩ / cm^TwoSince
Keeping the electromagnetic conversion characteristics good by raising the top and back,
Layer electrical resistance 10^TenΩ / cm^TwoBelow E '(Young's modulus)
200-1500 Kg / mm^Two, Its surface roughness is cut
R20 at off 0.17 mm, 0.20 μm or less
By, dropout can be suppressed, and
Breaking strength, cinching phenomenon, adhesiveness and wear resistance, electromagnetic
Providing magnetic recording media with excellent conversion characteristics
The present invention is based on the
Recording layer, magnetic recording medium with backcoat layer on the other side
In the body, the magnetic recording layer is 48m by BET method²/ G or more
Ferromagnetic alloy powder with specific surface area in resin binder
The magnetic recording layer has an electric resistance of 10
^TenΩ / cm²As described above, the coercive force is 1000 Oe or more,
The surface roughness of the magnetic layer is R20 when the cutoff is 0.17 mm,
0.08 μm or less, the back coat layer has an electric resistance of 1
0^TenΩ / cm²Below, E '(Young's modulus) is 200-150
0 kg / mm², Its surface roughness is cut off 0.17 m
R20 at m, 0.20 μm or less
The present invention relates to a magnetic recording medium. In the present invention, E '(Young's modulus) of the back coat layer 40
0 to 1500 Kg / mm^Two, Its surface roughness is cut off
R20 at 0.17 mm, above when 0.10 μm or less
A magnetic recording medium having particularly excellent characteristics is obtained, which is preferable.
Of. The magnetic recording layer of the present invention comprises a ferromagnetic alloy powder and a binder.
The ferromagnetic alloy consists of Fe-Co and Fe-N.
i, Fe-Co-Ni, Co-Ni, Fe-Rh, Fe
-Cu, Fe-Au, Co-Cu, Co-Au, Co-
Y, Co-La, Co-Pr, Co-Gd, Co-S
m, Co-Pt, Ni-Cu, Fe-Co-Nd, Mn
Magnetic alloys such as -Bi, Mn-Sb and Mn-Al are listed.
You can get it. Among them, Fe-C has excellent electromagnetic conversion characteristics.
o, Fe-Co-Ni, Co-Ni, etc.
A fine powder to which Cr, Al, Si, etc. are added is used. This
These are metal salts BH_FourFine powder reduced with a reducing agent such as
After coating the iron oxide surface with a Si compound, H_TwoIn gas
Finely powdered by dry reduction or alloy in low pressure argon
Alloy fine particles obtained by various manufacturing methods such as vacuum evaporation
Particles are used. Electric resistance is 10^TenΩ / cm^TwoMore than
In this case, the electromagnetic conversion characteristics are excellent, but
As mentioned above, as a measure against electric resistance of the coating surface,
Increasing the amount of Si compound processing in 10^TenΩ
/ Cm^TwoIt becomes the following, and put carbon black etc.
10^TenΩ / cm^TwoThe following will reduce the deterioration of electromagnetic conversion characteristics.
As a result, it becomes useless as a high-density magnetic recording medium. The magnetic layer in the magnetic recording medium of the present invention is an alloy containing
Specific surface area of magnetic powder by BET method is 48m^Two/ G or more
When the coercive force (Hc) of the magnetic layer is 1000 Oe or more,
Surface roughness of magnetic layer [Measurement by Taristep described later]
At a cutoff of 0.17 mm, R20 (20 times average
Value), same as below] is 0.08 μm or less
This is the case. The preferred range of coercive force is 1000 to 20.
It is 00 Oe, and if it exceeds this range, the magnetic head is
Is saturated and demagnetization becomes difficult. Specific surface area of magnetic powder
Is larger, the S / N ratio tends to be improved, but the ratio is not so high.
If the surface area is large, the dispersion of the magnetic powder in the binder will be poor.
Found to have a tendency to
It was On the other hand, the surface roughness of the magnetic recording layer affects the recording sensitivity.
If the surface roughness is small, the recording sensitivity of short wavelength is
To rise. As described above, a ferromagnetic alloy that can satisfy the above characteristics
And Fe-Co, Fe-Co-Ni, Co-Ni
Thoroughly, fine powder with Cr, Al, Si, etc. added to it
Used. These are metal salts of BH_FourWhen wet with a reducing agent such as
Reduced fine powder, iron oxide surface was coated with Si compound
After, H_TwoFinely powdered by dry reduction in gas or alloy
Axial ratio of 1: 5, such as fine powder evaporated in pressurized argon.
1:10 and residual magnetic flux density Br = 2000-300
0 Gauss and the above coercive force and specific surface area conditions
To meet. The alloy magnetic powder can be made into a magnetic paint using various binders.
However, generally, a thermosetting resin-based binder and
Radiation-curable binders are suitable, and other additives
And use dispersants, lubricants, and antistatic agents according to standard methods
be able to. BET specific surface area is 48m^Two/ G magnetic powder
Therefore, as a dispersant, there is a problem in dispersibility.
When using a surfactant or organic titanium coupling agent, etc.
good. As binder, vinyl chloride, vinyl acetate, vinyl
Nyl alcohol copolymer, polyurethane prepolymer and
And a binder consisting of polyisocyanate, or this
Binder with nitrocellulose added to
For known thermosetting binders or ionization energy
Sensitive acrylic double bond, maleic double bond, etc.
Radiation-curable binders containing as a resin base
Can be used. The alloy magnetic powder was added to the binder and
Mix it with a fixed solvent and various additives to make a magnetic paint.
Apply this to a substrate such as polyester base and heat cure or
Is cured by radiation to form a magnetic film, and
Finishing to a specified surface roughness by performing a durring process
It The backcoat layer of the present invention has an electric resistance of 10^TenΩ / cm^TwoSince
Lower E '(Young's modulus) is 200-1500 Kg / mm^Two,
The surface roughness is R20, 0.
Use the following methods to reduce the thickness to 20 μm or less.
You can That is, the electric resistance is 10^TenΩ / cm^TwoThe following
To do this, 1) Conductive carbon black,
Fight, 2) SiO as an inorganic filler_Two, TiO
_Two, Al_TwoO_Three, Cr_TwoO_Three, SiC, CaO, CaC
O_Three, Zinc oxide, goethite, αFe_TwoO_Three,talc,
Kaolin, CaSO_Four, Boron nitride, graphite fluoride, disulfide
The method of adding molybdenum or the like is mainly adopted. E '
(Young's modulus) is conductive filler, inorganic filler, back coat
It can be changed in various ways depending on the resin used for
Varies depending on the particle size and dispersion method of electrically conductive filler and inorganic filler
You can The dispersion method is a dispersant, a disperser,
It can be changed depending on the time. The electric resistance of the back coat layer is 10^TenΩ / cm^TwoAnd above
If this happens, dust and debris will easily adhere to the
Eut (Young's modulus) of 200
Kg / mm^TwoIn the following, the breaking strength is inferior and during durable running
Scratches on the back surface occur, 1500 Kg / mm^Twothat's all
Is too hard, and it will scrape the magnetic surface, which is not desirable.
Yes. The surface roughness of the back coat layer has a cutoff of 0.1.
R20 at 7 mm, electromagnetic conversion when 0.20 μm or more
Characteristics deteriorate, cinching phenomenon, back coat surface abrasion
As a result, stickiness occurs and dropout becomes large. The binder used in the back coat layer of the present invention is
Thermoplastic and thermosetting used for magnetic recording media
A reactive or reactive resin or a mixture of these is used
A curable resin is preferable from the viewpoint of the strength of the coating film and the like. As a thermoplastic resin, the softening temperature is 150 ° C or less, the average
The amount of material is 10,000 to 200,000, and the degree of polymerization is about 20.
0 to 2,000, for example vinyl chloride-vinegar
Vinyl acetate copolymer (including carboxylic acid introduced),
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer
(Including carboxylic acid introduced), vinyl chloride-chlorinated
Vinylidene copolymer, vinyl chloride-acrylonitrile
Copolymer, acrylic ester-acrylonitrile copolymer
Coalesce, acrylic ester-vinylidene chloride copolymer,
Acrylic ester-styrene copolymer, methacrylic acid
Ester-acrylonitrile copolymer, methacrylic acid
Stell-vinylidene chloride copolymer, methacrylic acid ester
Ru-styrene copolymer, urethane elastomer, Nylo
-Silicon resin, nitrocellulose-polyamide resin
Fat, polyvinyl fluoride, vinylidene chloride-acrylonite
Ryl copolymer, butadiene-acrylonitrile copolymer
Body, polyamide resin, polyvinyl butyral, cellulos
Glucose derivatives (cellulose acetate, cellulose diamond
Cate, cellulose triacetate, cellulose pro
Pionate, nitrocellulose, etc.), styrene-butadiene
Ene copolymer, polyester resin, chlorovinyl ether
-Acrylic ester copolymer, amino resin, various
Synthetic rubber-based thermoplastics and mixtures of these are used.
Be done. As thermosetting resin or reactive resin, in the state of coating liquid
Has a molecular weight of 200,000 or less, and after coating and drying
Molecular weight due to condensation, addition, etc. by heating
Becomes infinite. In addition, among these resins,
Those that do not soften or melt during the thermal decomposition of fat are preferred.
Good Specifically, for example, phenol resin, epoxy resin
Fat, polyurethane curable resin, urea resin, melamine resin
Oil, alkyd resin, silicone resin, acrylic reaction tree
Fat, epoxy-polyamide resin, nitrocellulose melamine
Min resin, high molecular weight polyester resin and isocyanate
Mixtures of prepolymers, methacrylate copolymers and diamines
Mixtures of cyanate prepolymers, polyester poly
A mixture of oat and polyisocyanate, ureaformal
Dehydrate resin, low molecular weight glycol / high molecular weight diol /
Mixture of triphenylmethane triisocyanate, poly
Amine resins, and mixtures thereof. Therefore, particularly preferred are nitrified cotton (fibrous resin) and salt.
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
A thermosetting resin (using a curing agent) consisting of a combination of resins,
Or vinyl chloride-vinyl acetate-vinyl alcohol copolymer
Combined or acrylic modified vinyl chloride-vinyl acetate-vinyl
Made of alcohol alcohol copolymer and urethane acrylate
Radiation-curing resin
For resins, in addition to the above preferred combinations, radicals
Acrylic acid and meta showing unsaturated double bond having polymerizability
Acrylic acid or its ester compounds
Kuryl double bond, allyl such as diallyl phthalate
Unsaturation of double bonds, maleic acid, maleic acid derivatives, etc.
Radiation cross-linking or polymerization drying such as bonding
Group in the molecule of the thermoplastic or thermosetting resin.
Or resin introduced can be used, and other radiation
Those with unsaturated double bonds that undergo cross-linking polymerization upon irradiation
Can be used. Thermoplastic radicals that crosslink or polymerize upon irradiation
The following unsaturated compounds are contained in the molecule of the hydrophilic resin.
There is polyester resin. Poly containing radiation-curable unsaturated double bonds in the molecular chain
Ester compounds, such as polybasic acid and polyhydric acid of the following (2)
Saturated polyester resin consisting of ester bond of rucor
Radiation-curable fatigue due to maleic acid as a part of polybasic acid
List unsaturated polyester resins containing Japanese double bonds
be able to. Radiation curable unsaturated polyester resin
One or more polybasic acid components and one or more polyhydric alcohol components
Add maleic acid, fumaric acid, etc. in the usual way, i.e.
180 to 200 ° C under nitrogen atmosphere, dehydration or
Is heated up to 240-280 ℃ after dealcoholation reaction
However, it can be obtained by a condensation reaction under a reduced pressure of 0.5 to 1 mmHg.
You can The content of maleic acid, fumaric acid, etc.
1 to 40 mol% in the acid component due to cross-linking, radiation curing, etc.
It is preferably 10 to 30 mol%. Thermoplastic resins that can be modified into radiation curable resins and thermosetting
The following may be mentioned as examples of the hydrophilic resin.
Wear. (1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer
Coal, vinyl chloride-vinyl alcohol copolymer, salt
Vinyl chloride-Vinyl alcohol-Vinyl propionate
Copolymer, vinyl chloride-vinyl acetate-maleic acid
Copolymer, vinyl chloride-vinyl acetate-terminal OH side chain
Alkyl group copolymers such as VRCC and V manufactured by UCC
YNC, VYBGX, VERR, etc.
By the method described below, acrylic double bond, maleic acid
Radiation-sensitive changes by introducing system double bond and allylic double bond
Do sex. (2) Saturated polyester resin phthalic acid, isophthalic acid, terephthalic acid, succinic acid,
Saturated polybasic acids such as dipic acid and sebacic acid,
Glycol, diethylene glycol, glycerin, g
Trimethylol propane, 1,2 propylene glycol,
1,3 butanediol, dipropylene glycol, 1,
4-butanediol, 1,6-hexanediol, pentae
Reslit, sorbitol, glycerin, neopentyl
Like glycol, 1,4 cyclohexanedimethanol
Obtained by ester bond with various polyhydric alcohols
Polyester resin or these polyester resins
An example is a resin modified with Na or the like (for example, Vylon 53S).
The radiation-sensitive degeneration is also performed in the same manner.
U (3) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin
It is a copolymer of fat, formal resin and these components.
The hydroxyl groups contained in these resins are released by the method described below.
Radiation-sensitive degeneration is performed. (4) Epoxy resin, phenoxy resin bisphenol A, epichlorohydrin, methyl epic
Epoxy resin by reaction of lorhydrin, eg shell
Chemical (Epicoat 152, 154, 828, 1001, 1004, 100
7), made by Dow Chemical (DEN431, DER732, DER51
1, DER331), made by Dainippon Ink (Epiclon 400, 80
0) and UCC, which is a resin with a high degree of polymerization of the above epoxy
Made phenoxy resin (PKHA, PKHC, PKHH),
Copolymerization of brominated bisphenol A and epichlorohydrin
Combined, manufactured by Dainippon Ink and Chemicals (Epiclon 145, 152,
153, 1120) etc. Epoxy contained in these resins
Radiation-sensitive modification is carried out using a silane group. (5) Various fibrin derivatives are used, but the most effective one is nitrification.
Cotton, cellulose acetobutyrate, ethyl cellulose,
Butyl cellulose, acetyl cellulose, etc. are suitable
Radiation by the method described below by utilizing the hydroxyl groups in the resin
Sensitive degeneration. In addition, as a resin that can be used for radiation-sensitive modification
For polyfunctional polyester resin, polyether ester
Resins, polyvinylpyrrolidone resins and derivatives (PVP
(Refin copolymer), polyamide resin, polyimide resin
Fat, phenol resin, spiro acetal resin, hydroxyl group
Acrylic ester and methacrylic ester contained are
Acrylic resins that contain at least one compounding component are also effective
Is. Furthermore, the radiation curable resin has abrasion resistance, adhesiveness and flexibility.
Thermoplastic elastomer or preppo
Limers can be blended into these elastomers
Alternatively, if the prepolymer is similarly radiation-sensitive modified,
Is more effective. Below are the elastomers and prepo
Take the example of a limmer. (1) Polyurethane elastomer and prepolymer poly
The use of urethane is abrasion resistant, and substrate films such as
It is particularly effective in that it has good adhesiveness to a PET film.
As an example of the urethane compound, as an isocyanate,
2,4-toluene diisocyanate, 2,6-toluene
Diisocyanate, 1,3-xylene diisocyanate
1,4-xylene diisocyanate, 1,5-naphth
Tolylene diisocyanate, m-phenylene diisocyanate
, P-phenylene diisocyanate, 3,3'-di
Methyl-4,4'-diphenylmethane diisocyanate
4,4'-diphenylmethane diisocyanate,
3,3'-dimethylbiphenylene diisocyanate,
4,4'-biphenylene diisocyanate, hexamethyi
Diisocyanate, isophorone diisocyanate
G, dicyclohexylmethane diisocyanate, desmo
Various polyisocyanates such as Joule L and Death Module N
And linear saturated polyester (ethylene glycol,
Diethylene glycol, glycerin, trimethylol
Lopan, 1,4-butanediol, 1,6-hexanedi
Oar, pentaerythritol, sorbitol, neopen
Chill glycol, 1,4-cyclohexanedimethanol
Polyhydric alcohols such as phthalic acid, isophthalic acid,
Such as lephthalic acid, succinic acid, adipic acid, sebacic acid
Polycondensation with saturated polybasic acid), linear saturated polyester
Ether (polyethylene glycol, polypropylene green
Cole, polytetramethylene glycol) or caprolact
Tom, hydroxyl-containing acrylic ester, hydroxy
Various polyesters such as sill-containing methacrylic acid ester
Polyurethane elastomer consisting of condensation polymer of
Limmer is effective. Isocyanates at the ends of these urethane elastomers
Group or hydroxyl group, acrylic double bond or allyl double
Radiation by reacting with a monomer that has a bond, etc.
It is very effective to transform it to be line-sensitive. (2) Acrylonitrile-butadiene copolymer elastomer
-Sinclair Petrochemical's poly BD retired cash register
Acrylonite with a terminal hydroxyl group that is commercially available
Ryl butadiene copolymer prepolymer or Nippon Zeo
Elastomers such as the Hiker 1432J manufactured by
The double bond in ene produces radicals by radiation and crosslinks
It is suitable as an elastomer component to be polymerized. (3) Polybutadiene Elastomer Poly BD Retied Resin manufactured by Sinclair Petrochemical
R-15 and other prepolymers having low molecular weight terminal hydroxyl groups
Is particularly preferable in terms of compatibility with the thermoplastic resin. R
In the -15 prepolymer, the molecular end becomes a hydroxyl group.
Therefore, an acrylic unsaturated double bond is added to the end of the molecule.
It is possible to increase the radiation sensitivity by
Therefore, it is more advantageous as a binder. In addition, cyclized polybutadiene, CBR- made by Japan Synthetic Rubber
M901 also has excellent properties when combined with a thermoplastic resin.
Have In addition, thermoplastic elastomers and their prepolymers
Suitable for the system are styrene-butadiene rubber,
Chlorinated rubber, acrylic rubber, isoprene rubber and their cyclization
There is a product (CIR701 made by Japan Synthetic Rubber), and epoxy modified
Rubber, internally plasticized saturated linear polyester (Toyobo Viro
# 300) and other elastomers are also
It can be effectively used by subjecting it to a modification treatment. Next, a synthesis example of the radiation sensitive binder will be described. a) Acrylic vinyl chloride vinyl acetate copolymer resin
Synthesis of modified resin (radiation-sensitive modified resin) Partially saponified vinyl chloride-vinyl acetate copolymer (UCC) having OH group
750 parts of vinylide VAGH) and toluene 1250
Parts, 500 parts of cyclohexanone into a 51 four-necked flask
Charged and melted, heated to 80 ° C and tolylene diisocyanate
2-hydroxyethyl methacrylate adduct *
61.4 parts, 0.012 parts tin octylate, hydro
Add 0.012 parts of quinone and N at 80 ℃_TwoNCO reaction in air flow
Let react until the rate reaches 90%. Cooling after the reaction
Then, 1250 parts of methyl ethyl ketone is added and diluted.

[* Preparation of 2-hydroxyethylmethacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) 348 parts of TDI 8 in 11 four-neck flask in N ₂ stream
After heating to 0 ° C., 260 parts of 2-ethylene methacrylate,
After completion of dropping, 0.07 part of tin octylate and 0.05 part of hydroquinone are cooled and controlled so that the temperature in the reaction vessel is 80 to 85 ° C, and the reaction is completed by stirring at 80 ° C for 3 hours. After completion of the reaction, the product was taken out and cooled, and 2HEMA of white paste TDI was obtained. B) Synthesis of butyral resin acrylic modified product (radiation sensitive modified resin) Butyral resin 100 parts of BM-S manufactured by Sekisui Chemical Co., Ltd.
4 in 51 with 91.2 parts and cyclohexane 71.4 parts
Charge into a two-necked flask, melt by heating, and raise the temperature to 80 ° C. Then add 7.4 parts of 2HEMA adduct * of TDI, 0.015 parts of tin octylate and 0.015 parts of hydroquinone, and add NCO in N ₂ stream at 80 ° C. The reaction is continued until the reaction rate becomes 90% or more. After the reaction is complete, it is cooled and diluted with methyl ethyl ketone. c) Synthesis of Saturated Polyester Resin Acrylic Modified Body (Radiation Sensitive Modified Resin) Saturated polyester (Vylon RV-200 manufactured by Toyobo),
100 parts of toluene 116 parts, methyl ethyl ketone 11
After heat-dissolving in 6 parts and heating to 80 ° C, 3.55 parts of 2HEMA adduct * of TDI was added, and tin octylate 0.007 was added.
Part, hydroquinone 0.007 part, and 80 ° C., N ₂
The reaction is performed until the NCO reaction rate in the air flow is 90% or more. d) Synthesis of acrylic modified epoxy resin (radiation-sensitive modified resin) Bisphenol-based epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.), 400 parts by heating and dissolving in 50 parts of toluene and 50 parts of methyl ethyl ketone, and then N, N-dimethylbenzylamine 0 0.006 parts and hydroquinone 0.003 parts are added to 80 ° C., and 69 parts of acrylic acid is added dropwise to react at 80 ° C. until the acid value becomes 5 or less. e) Synthesis of urethane elastomer acrylic modified product (radiation-curable elastomer) 250 parts of diphenylmethane diisocyanate (MDI) -based urethane prepolymer (Nipporan 4040 manufactured by Nippon Polyurethane) having a terminal isocyanate, 2HEMA32.
5 parts, hydroquinone 0.07 parts, tin octylate 0.
Put 009 parts in a reaction can and heat it to 80 ° C. to dissolve it, then TDI4
3.5 parts was added dropwise while cooling so that the temperature in the reaction vessel was 80 to 90 ° C, and after completion of the dropping, the reaction rate was 95% at 80 ° C.
React until the above is reached. f) Synthesis of Polyether-based Urethane Modified Elastomer Acrylic Modified Body (Radiation Curable Elastomer) Polyether PTG-500, 2 manufactured by Nippon Polyurethane Company
50 parts, 2HEMA 32.5 parts, hydroquinone 0.0
07 parts, 0.009 parts tin octylate were put into a reaction can,
After heating and melting at 80 ° C., 43.5 parts of TDI is added dropwise while cooling so that the temperature in the reaction vessel is 80 to 90 ° C. After completion of the dropping, the reaction is allowed to proceed at 80 ° C. until the reaction rate reaches 95% or more. g) Synthesis of acrylic modified polybutadiene elastomer (radiation-curable elastomer) Low molecular weight terminal hydroxyl group polybutadiene PO BD LIQUIT resin R-15, 250 manufactured by Sinclair Petrochemical
Parts, 2HEMA 32.5 parts, hydroquinone 0.007
Parts, tin octylate 0.09 parts in a reaction can, 80 ℃
After melting by heating to 43.5 parts of TDI, the temperature in the reaction vessel is 80
It is added dropwise while cooling so as to be ˜90 ° C. After completion of the addition, the reaction is allowed to proceed at 80 ° C. until the reaction rate reaches 95% or more. It is known that a polymer is one that is disintegrated by irradiation with radiation and one that causes intermolecular crosslinking. Polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein are examples of those that cause cross-linking between molecules. With such a cross-linking polymer, the cross-linking reaction occurs even if the above-mentioned modification is not particularly performed. Therefore, in addition to the modified product, these resins can be used as they are as a back coating resin for radiation cross-linking. is there. Furthermore, according to this method, even a solventless resin that does not use a solvent can be cured in a short time,
Such a resin can be used for the back coat. The active energy rays used for crosslinking the resin used in the back coat layer of the present invention include an electron beam having a radiation accelerator as a radiation source, γ-rays having Co60 as a radiation source, and β-rays having Sr90 as a radiation source. X-rays, ultraviolet rays or the like having an X-ray generator as a radiation source are used. Particularly, as a radiation source, a method of using radiation by a radiation heater is advantageous from the standpoints of controlling absorbed dose, introducing it into a manufacturing process line, and shielding ionizing radiation. The radiation characteristics used for curing the backcoat layer are: an absorption voltage of 0.5 to 2.0 megarads using a radiation accelerator having an accelerating voltage of 100 to 750 KV, preferably 150 to 300 KV, from the viewpoint of penetrating power. It is convenient to irradiate. When curing the backcoat layer of the present invention, a low-dose type radiation accelerator (electro curtain system) manufactured by US Energy Science Co., Ltd. is introduced into the tape coating processing line, and secondary X-rays inside the accelerator are shielded. Etc. is extremely advantageous. Of course, a van de Graaff type accelerator, which has been widely used as a radiation accelerator, can be used. Further, at the time of radiation crosslinking, it is important to irradiate the backcoat layer with radiation in a stream of an inert gas such as N ₂ gas or He gas. It is important to irradiate the backcoat layer with radiation in the air when crosslinking the binder component. O ₃ generated by irradiation
This is extremely disadvantageous because radicals generated in the polymer under the influence of the above influence the crosslinking reaction advantageously. Therefore, it is important to maintain the atmosphere of the portion irradiated with the active energy ray in an atmosphere of an inert gas such as N ₂ , He or CO ₂ having an oxygen concentration of 5% at maximum. Other usable binder components include acrylic acid, methacrylic acid, acrylamide and methacrylamide as monomers. As the binder having a double bond, various polyesters, polyols, polyurethanes and the like can be modified with a compound having an acrylic double bond. Various molecular weights can be obtained by blending a polyhydric alcohol and a polycarboxylic acid as needed. As for the radiation sensitive resin, the above description is only a part. These may be mixed. Magnetic tape bases such as polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, etc. tend to use thin plastic films with a thickness of about 11μ or less, so the winding tightness when winding the tape is large and the roughness of the back surface is large. Are easily transferred to the magnetic surface, which easily causes a decrease in output. On the other hand, when a radiation curable resin and a back layer in which a predetermined filler is dispersed as required are used, the winding tightness when cut and wound into a tape shape is reduced, and therefore the roughness of the back surface is magnetic. There is no risk of transfer to the surface, the electromagnetic characteristics are improved, the adhesiveness is also greatly improved, the cinching phenomenon is suppressed, and the backing is strong. When a radiation curable binder is used for both the magnetic surface and the back surface, continuous curing is possible in production, and since there is no back mold transfer as described above, dropout can be prevented, which is more preferable. In addition, since radiation curing can be processed online, it helps save energy, reduces the number of personnel during manufacturing, and reduces costs. In terms of characteristics, in addition to the dropout due to winding tightness during thermosetting, there is no difference in output due to the distance in the lengthwise direction of the magnetic tape due to the difference in pressure at the inner and outer diameter portions when wound in a roll shape. The problem caused by the winding tightening is that the base thickness becomes as thin as 11 μm or less, and the hardness of the metal magnetic powder is smaller than that of the magnetic oxide such as γ-Fe ₂ O _3, so that the surface hardness of the magnetic layer is small and the winding tightness is small. The radiation-curable back coat layer is particularly preferable because it can be removed and the output difference and the dropout difference between the inner and outer diameters can be removed. The non-magnetic powder contained in the back coat layer of the present invention includes fillers, dispersants, lubricants and the like. As the filler, 1) conductive carbon black,
Graphite, or 2) SiO ₂ , T as an inorganic filler
iO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ , SiC, CaO, C
There are aCO ₃ , zinc oxide, goethite, αFe ₂ O ₃ , talc, kaolin, CaSO ₄ , nitrogen nitrogen, black fluoride, molybdenum disulfide, etc. Among them, CaCO ₃ and carbon are used. The amount of such a filler used is appropriately 20 to 200 parts by weight with respect to 100 parts by weight of the binder for 1), and 10 to 300 parts by weight for 2). The film becomes brittle,
On the contrary, there is a drawback that the number of dropouts increases. As the dispersant, any of the types conventionally used for this type of back coat layer can be used, but caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, and elaidin. A fatty acid having 12 or more carbon atoms (RCOOH, R is an alkyl group having 11 or more carbon atoms) such as acid, linoleic acid, linolenic acid, and stearolic acid; an alkali metal (L
i, Na, K, etc.) or alkaline earth metal (Mg, C)
a, Ba, etc.) metal soap; lecithin, etc. are used. In addition to these, higher alcohols having 12 or more carbon atoms, and sulfuric acid esters thereof, surfactants, titanium coupling agents, silane coupling agents and the like can also be used. These dispersants are 1 to 20 parts by weight with respect to 100 parts by weight of the binder.
It is added in the range of parts by weight. As the lubricant, silicon oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters composed of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohol having 3 to 12 carbon atoms, 17 carbon atoms The total number of carbon atoms of the above monobasic fatty acid and the fatty acid is 21
A fatty acid ester consisting of ~ 23 monohydric alcohols is used. These lubricants are binder 1
It is added in the range of 0.2 to 20 parts by weight with respect to 00 parts by weight. Also, antistatic agents such as saponin and other natural surfactants;
Nonionic surfactants such as alkylene oxide-based and glycerin-based glycidol-based; higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, cation surfactants such as phosphonium or sulfoniums; carboxylic acids, sulfonic acids, Phosphoric acid, sulfate group,
An anionic surfactant containing an acidic group such as a phosphate ester group;
Amphoteric activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The thickness of the back coat layer of the present invention after coating and drying was 0.
The range of 3 to 10 μm is general. The magnetic recording medium of the present invention is widely used in the fields of audio tapes, video tapes, computer tapes, endless tapes, magnetic disks, etc. Among them, the video tape in which dropout is one of the most important characteristics,
It is quite effective to use for computer tape. Examples of the present invention will be shown below. It should be understood that the present invention is not limited to this embodiment. Example Several magnetic layers and a back layer were formed as follows, and the magnetic recording medium was manufactured by combining these, and the effects of the present invention were observed. Formation of Magnetic Layer Various alloy powders were manufactured by the wet reduction method. These consist of acicular particles with an axial ratio (minor axis / major axis) of 1/5 to 1/10, residual magnetic flux density of 2000 to 3000 gauss, coercive force of 1000 to 2000 Oe: BET specific surface area of 48 to 70 m.
^{It had 2} / g. These magnetic powders were mixed in the following mixing ratio by a usual method to form each magnetic layer. Magnetic layer 1 part by weight Fe—Co—Ni alloy powder 100 (Hc = 1200 Oe, major axis 0.4 μm, minor axis 0.05 μm BET
Specific surface area 52 m ² / g) Vinyl chloride / vinyl acetate / vinyl alcohol copolymer (VAGH manufactured by UCC, USA) 15 Polyurethane prepolymer 10 (Desmocoll 22 manufactured by Bayer) Methyl ethyl ketone / toluene (1/1) 250 Myristic acid 2 Sorbitan stearate 2 To this mixture was added 30 parts by weight of polyisocyanate (Desmodur L manufactured by Bayer Co.) to form a magnetic paint, which was formed into a polyester film with a thickness of 3.5 μm and calendered. Magnetic layer 2 Using the same magnetic alloy powder and base as in magnetic layer 1, the following mixture parts by weight Fe-Co-Ni alloy powder 100 (same as magnetic layer 1) vinyl chloride / vinyl acetate / vinyl alcohol copolymer (US UCH VAGH) 15 polyvinyl butyral resin 10 acrylic double bond-introduced urethane 10 methyl ethyl ketone / toluene (50/50) 250 was applied to a polyester film to a thickness of 3.5 μm, and electron beam curing and calendaring were performed. Magnetic Layer 3 A magnetic layer was formed using the following composition by using the same method as the magnetic layer 2 manufacturing method. Parts by weight Fe-Co-Ni alloy powder (BET 60 m ² / g) 100 Saturated polyester resin 5 Acrylic-introduced vinyl chloride alcohol copolymer (degree of polymerization 300) 10 Acrylic double bond-introduced polyether urethane elastomer 10 Mixed solvent (magnetic layer Same as 1) 250 Formation of Back Layer Back Layer 1 The following mixture was dispersed in a ball mill for 5 hours. Parts by weight Carbon black 40 mμ (Furnace method) 50 Curing agent Coronate L 20 Lubricant Stearic acid 4 Butyl stearate 2 Nitrified cotton 40 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (Sekisui Chemical Co., Ltd., Eslec A) 30 Polyurethane elastomer 30 (Nippon Polyurethane, Essen 5703) Mixed solvent (MIBK / toluene) 250 The mixture after dispersion is applied to the opposite surface side of the base material on which the magnetic recording layer is formed so that the dry thickness is 1 μm, and dried. After surface smoothing with a calendar,
It was cured by heating at a temperature of 0 ° C. for 24 hours. Back layer 2 parts by weight CaCO ₃ (particle size 80 mμ) 30 αFe ₂ O ₃ (150 mμ) 20 Acrylic modified polyvinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 Acrylic modified polyurethane elastomer 30 Mixed solvent (MIBK / toluene = 1/1) 300 The above mixture was mixed in a ball mill for 5 hours, and dried on the back surface of the polyester film having a magnetic surface to a dry thickness of 1.
After coating so as to have a thickness of 5 μm, accelerating voltage of 150 KeV, electrode current of 10 mA, absorbed dose of 5 Mrad, electron beam irradiation of the back coat layer in N ₂ gas using an electron curtain type electron beam accelerator, and after curing It was calendered, wound up, and cut into 1/2 ″ video width. Back layer 3 parts by weight carbon black (80 mμ) 15 CaCO ₃ (40 mμ) 35 acrylic modified polyurethane elastomer 30 vinyl chloride-vinyl acetate-vinyl alcohol copolymer (UCCVAGH) 70 Mixed solvent (MIBK / toluene = 1/1) 300 The above mixture was prepared in the same manner as the back layer 2. Electric resistance of these magnetic layers, and dropout when the back layer was not provided. Table 1 shows the electric resistance, E '(Young's modulus) and surface roughness of the back layer. Regarding the magnetic recording medium in which the magnetic layer 2 and the back layer 3 are combined, the ratio of the pigment to the binder in the back layer is changed, and the E '(Young's modulus), electric resistance, and back surface roughness of the back layer are adjusted. Table 2 shows the results of the changes in each characteristic accompanying the changes. From Table 2, the electric resistance of the magnetic layer is 10 ¹⁰ Ω / cm ² or more, the back surface has an electric resistance of 10 ¹⁰ Ω / cm ² or less, and E ′.
It can be seen that those having a surface roughness of 200 to 1500 Kg / mm ² and a surface roughness of R20 of 0.27 or less at a cutoff of 0.17 mm (No. 3 to 7) are good in all properties. Then, the magnetic layers 1, 2, and 3 and the back layers 1, 2, and 3 described above are used.
Were appropriately combined and the order of formation was changed to manufacture a magnetic recording medium. However, in this case, calendering was performed every time each layer was formed. The measurement results of each characteristic are shown in Table 3. In the table, indicates the order of formation. As a comparative example, a magnetic recording medium in which a magnetic layer 1 and a back layer excluding the pigment in the back layer 1 were combined was adopted. The following can be seen from Table 3. That is, the dropout is
When either the magnetic layer or the back layer is radiation-curable (B, C), both layers are better than the heat-curable type (A) because there is no back mold transfer, and the output is also large. . In the case where the magnetic surface and the back coat surface are radiation-cured (D), it is further excellent in terms of electric conversion characteristics and the like.
Comparing A-1 and A-2 in the groups in the table,
In the case of A-2, the thin base was reinforced due to the backcoat layer formed first, and the Young's modulus of the base was large. It can be seen that the difference in the electromagnetic conversion characteristics between the outside and inside of the tape is small. This tendency is the same in that B and C are also superior in C. Further, in the group D, since the hardening is performed during continuous running, there is no influence of winding tightness. Further, by adding a fatty acid (a fatty acid ester in some cases), the abrasion of the back coat surface and the occurrence of jitter which is a problem on the image are suppressed, and for example, the friction coefficient at D-1 is 0.
However, when 3 parts by weight of fatty acid is added to D-1, the friction coefficient becomes 0.15, and the friction is low under high temperature running, so that the back coat surface is not scraped or jittered, and the running property becomes smooth. . In this way, putting lubricant in the back layer achieves smooth running under high temperatures,
It is preferable. Next, the surface roughness of the video tape in Table 2 above was examined. Figure 1 shows a videotape of 3.8 m / se
The following shows the S / N ratio (relative value) in the case of driving at c and recording / reproducing at a center frequency of 4.5 MHz. However, the subscript of the curve is the surface roughness of the magnetic layer. As can be seen from this, when the surface roughness of the magnetic layer is 0.08 μm or less and the surface roughness of the back coat layer is 0.6 μm or less, the S / N ratio can be kept high. The same was true for other combinations. In the above video tape, the surface roughness of the magnetic layer is 0.
08 μm or less and the surface roughness of the back coat layer is 0.0
When the relationship between the BET specific surface area of the alloy powder and the S / N was investigated in the range of 5 to 0.6 μm, the results shown in FIG. 2 were obtained. However, the standard was 55 dB. From this, it is understood that excellent characteristics can be obtained when the BET value is 48 m ² / g or more. The same was true in other cases. Furthermore, when the tightness of winding was measured, it was 40 ° C and 80% RH.
Then everything was good. The above-mentioned characteristics were measured as follows. 1) Cinching phenomenon, winding form Using a commercially available VHS system VTR, fast forward the full tape length, then fast reverse, stop at the remaining 50 m,
Further rewind to the end. After that, the winding state of the tape was visually observed. When there was no gap between the tape layers and the wound state was good, it was marked with ◯ or ⊚, and when a gap occurred between the tape layers, it was marked with x. 2) Scraping of back coat surface Using a commercially available VHS type VTR, after running 100 times in an environment of 40 ° C. and 60%, the stain in the cassette case was observed. ○ indicates that there is no stain, and × indicates that the stain is severe. 3) Adhesion of guide during traveling After traveling 100 times in an environment of 40 ° C. and 60% using a general commercially available VHSVTR, the adherence of the guide in the cassette case and the guide on the VHS deck was observed. 4) Adhesion A double-sided tape was attached to the fixing plate, the back coat surface was attached thereto, and when pulled in the 180 ° direction, the peeling tension of the back coat surface was read. The measurement was carried out at 20 ° C. by Shimadzu Autograph. 5) Calender stain during production The calendar adhesion was observed when calendering was performed at 70 ° C during production. 6) Young's modulus Measured at 20 ° C. with a viscoelasticity spectrometer (Iwaki Seisakusho, Toyo Boat Win, Toyo Seiko Co., Ltd.). 7) Dropout Using a VHS deck at 20 ° C, 60% RH, a single signal of 4MHz is recorded and reproduced, and the number of times that the signal drops by 18dB or more from the average playback level is 15μs or more. , 10 samples were counted per minute, and the average was taken. The magnetic tape before running (first) and after running 100 times were measured. 8) Surface Roughness The surface roughness was determined by a 20-point average method from a chart obtained by using Talystep (manufactured by TAYLOR-HOBSON). A cutoff of 0.17 mm and a needle pressure of 0.1 × 2.5 μ were used. 9) Electromagnetic conversion characteristics The S / N ratio (relative value) when recording and reproducing at a center frequency of 5 MHz is shown. The VHS VTR was modified to measure up to 5 MHz. 10) Electron microscope imaging method a) The average particle size is measured by an extraction method from a tape by transmission electron microscopy. b) By a cross-sectional photographic method using a scanning electron microscope. In this case, the particles may be aggregated, and therefore, when the variation is large, the minimum particle size is set as the average particle size. 11) Coefficient of friction Wrap it around an aluminum cylinder with a polished surface of 4 mm in diameter with the back surface of the magnetic tape facing inward at a wrap angle of 180 °.
It was run at cm / sec, and the tensions on the sending side and the winding side were measured and calculated.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the surface roughness of the magnetic layer and back coat layer of the magnetic recording medium and the S / N ratio, and FIG. 2 is a graph showing the relationship between the BET specific surface area of the alloy magnetic powder and the S / N ratio. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Arioka 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Yuichi Kubota 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Incorporated (56) References JP-A-49-11305 (JP, A) JP-A-57-200937 (JP, A) JP-A-57-130234 (JP, A) JP-A-58-91528 (JP, A) JP-A-57-200938 (JP, A) JP-A-57-154618 (JP, A) JP-A-57-143733 (JP, A)

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic recording layer on one surface of a non-magnetic substrate and a back coat layer on the other surface,
The magnetic recording layer is formed by dispersing a ferromagnetic alloy powder having a specific surface area of 48 m ² / g or more by a BET method in a resin binder, and the magnetic recording layer has an electric resistance of 10 ¹⁰ Ω / cm ² or more and a coercive force. Is 1000 Oe or more, and the surface roughness of the magnetic layer is R20, 0.08 μm with a cutoff of 0.17 mm.
And the back coat layer has an electric resistance of 10 ¹⁰ Ω / cm ²
E '(Young's modulus) is 200 to 1500 Kg / mm
² , R20 with a surface roughness of 0.17mm cutoff
A magnetic recording medium having a thickness of 0.20 μm or less.