JPS62125528A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the physical property, wear resistance, toughness, and filler retaining property of the backcoat layer and to prevent the deformation of a tape and generation of abnormality in repeated traveling by incorporating zinc oxide having a single-peak distribution of particles having specified diameter into nonmagnetic powder. CONSTITUTION:A magnetic layer is provided on one surface of a carrier, and the backcoat layer contg. a binder and nonmagnetic powder is furnished on the other surface. The powder contg. zinc oxide and contg. 10-50wt% of particles having >=0.5mu diameter and 60-1wt% of particles having <=0.15mum diameter in a single-peak distribution is used as the nonmagnetic powder. The polyurethane resin to be used in the backcoat layer is synthesized by the reaction of a polyol with a polyisocyanate. Consequently, the traveling stability of the medium under high-temp. and high-humidity conditions can be improved.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to magnetic recording media, and in particular to magnetic tape.

(Background of the invention) Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. When a magnetic tape stored in a cassette is used to record or play back images, the cassette is loaded into a video deck, and the tape runs on a tour while its front and back sides are rubbed by gamma id balls and id rollers. The surface of the magnetic layer is finished to be smooth so that the sliding state of the magnetic tape against the magnetic head does not change when the magnetic tape travels around the magnetic head.

However, the other side surface of the magnetic layer of the magnetic tape has a similar effect on the above fluctuations, and when the running performance and durability of the other side surface are not good, excessive tension may be applied to the running magnetic tape. Not only will damage to the tape and powder fall off occur, but the winding shape will be disturbed and the edges of the tape will become uneven, resulting in poor image or electromagnetic conversion characteristics such as skew, non-taper, and chroma S/N.

Therefore, a back foot layer is provided on the back side of the magnetic tape support to improve running performance and durability against a gap ball, idle roll, guide bin, etc., and this backfoot layer includes a non-magnetic No 8
! There is one in which the layer contains a solid powder as a filler. This is a method in which the surface of the back coat layer is roughened to reduce the contact area with guide balls, etc., and to reduce the frictional resistance.
-161135, 57-53825, 58-2
No. 415 and Japanese Patent Publication No. 50-3927 both show examples using inorganic powders, and many of these also show those with limited particle sizes. However, even those using these inorganic powders not only do not provide sufficient lubricity, but also cause the back coat layer to come into contact with guide bottles, etc., as with the alumina particles described in Japanese Patent Publication No. 50-3927. In particular, when the guide bin etc. is present W1
When using n4 fat parts, this bottle etc. is shaved off,
Although this guides the magnetic tape smoothly, it impairs the function of the tape.

In addition, inorganic powder has a relatively strong affinity with water, so it absorbs moisture from the air during use, and the surface of the back coat layer tends to stick to idol poles, etc., and the adhesion causes the running magnetic tape to suddenly stop. , so-called stick-slip, which is caused by repeated sudden starts, is likely to occur.

Further, the moisture may change the quality of the magnetic powder, resulting in deterioration of performance.

Furthermore, solid powder fillers such as the above-mentioned inorganic powders must be contained in the back coat layer etc. in a well-dispersed state, and the fillers used are required to have good dispersibility. However, inorganic powders generally have poor dispersibility.

On the other hand, with the miniaturization, high performance, and high precision of video equipment, demands for magnetic tape performance have also increased, and a back coat layer has become an essential constituent layer of magnetic tapes to supplement performance.

In response to this, the performance failure of the back coat layer mentioned above can be caused by various factors such as the type of filler, hardness, particle shape, particle size and its distribution, chemical properties, filler used in combination (e.g. carbon blank), combination with binder, etc. For example, regarding zinc oxide filler, JP-A-59-17
No. 2150, No. 59-172151, No. 59-172
No. 1536 and No. 59-58626 disclose technical disclosures regarding the particle size, addition amount, and use of spherical zinc oxide in combination with carbon black.

The combined use of carbon blank is aimed at improving the conductivity and light-shielding properties of the magnetic tape.

However, the performance has not yet reached a satisfactory level. In addition, when carbon black is used in combination with the binder properties, durability, abrasion resistance, friction resistance, lubricity, tape bending, tape elongation, winding shape, tape deformation such as adhesiveness at high temperatures, etc. There are still many problems that need to be addressed, such as physical properties related to problems such as problems and runnability abnormalities, as well as production technology problems such as paint stagnation stability and dispersion scratching of fillers.

(Objective of the Invention) The first object of the present invention is to provide a back coat layer with good physical properties, high abrasion resistance, toughness, and filler retention, and no tape deformation or abnormality during repeated running. An object of the present invention is to provide a magnetic recording medium (hereinafter referred to as a magnetic tape) that has high durability over repeated use without causing physical property changes, and therefore does not interfere with electromagnetic conversion characteristics based on physical properties.

Secondly, in the preparation of back coat paints, the filler can be uniformly dispersed easily and stably, the paint has great stagnation stability, it is uniformly dispersed with good reproducibility, and the surface roughness is uniform and fine. An object of the present invention is to provide a magnetic tape having a backfoot layer that does not induce S/N deterioration.

(Structure of the Invention) The object of the present invention is to provide a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer containing a binder and non-magnetic powder on the other side. Particles containing zinc oxide as the magnetic powder and in which the zinc oxide has a particle size of 0.5μIII or more in the particle distribution are 10-50u+t%, 0
．． This is achieved by a magnetic recording medium characterized by a unimodal distribution having 60-1 wL% of particles of 15 μm or less.

In addition, as an aspect of the present invention, a cellulose-based rubber in which polyisocyanate is added to the binder of the back coat layer (
It is preferable that the composition contains a combination of polyurethane-curing type flat resin (fat) and the resin in a weight ratio of 0.1 to 5.0.

The particle size of the zinc oxide (hereinafter referred to as ZnO wood) according to the present invention has a unimodal distribution, and the particles of 0.5 μm or more are 10
~50% by weight, 60~1 particles of 0.15μI11 or less
It is preferable that the weight percent distribution has a tail and the average particle size lies between the tails.

The particle size of the Zn0 particles is expressed as a value determined by the air permeation method described below.

The air permeation method is generally used to calculate the relationship between the permeability of fluid (air) passing through a powder packed bed and the specific surface area of the powder for powder made of spherical uniform particles.
This is a method of determining the average particle diameter using the formula (formula (1) below) (formula (1) below).

In Uni: Sw: Specific surface of powder Jff (cm2/g) ε; Porosity of powder light filling ρ; Powder density (llI/cIfi3) η: Viscosity coefficient of air (g/Cl1l-see) L: Thickness of the powder-filled bed (cfa) Q: Powder-filled x A-layer permeation air amount (c, c) ΔP: Pressure difference between both sides of the filled layer (g/cm2) Cross-sectional area of the slag-filled waste (c+n2)
) L, 'Qc, c, air light chain layer transmission time (sec)
Weight of dust powder (g) In the above formula (1), ρ, 1. Since L, A, and ε can be measured independently, S- can be found by giving Q and L and measuring ΔP for them. The average particle diameter d111 is calculated by entering the value of SW into the following relational expression (2).

Examples of the measuring device include 5S-100 (Shimadzu Corporation).

In the backfoot paint formulation according to the present invention, the ratio of the total filler weight including those other than ZnO* to the total solid weight is 0.2.
-0.9, preferably 0.4-0.85.

Also available as a filler other than ZnO powder! ! A ceramic or inorganic filler may be used in combination, and carbon plastic/rinsing may be used to improve the light-shielding property and conductivity of the porcelain tape.

All kinds of resins conventionally used for magnetic tapes can be used as the binder, but polyurethane resins and cellulose resins to which polyisocyanate is added are particularly preferred.

Furthermore, improving physical properties, electromagnetic conversion characteristics, and productivity,
Various conventionally used additives may be added to improve the performance.

As the organic filler used in combination with the above Z[10],
7 Krylstyrene i? , υ fat, benzoguanamine resin powder, melamine resin powder, and 7 talocyanine pigments are preferred, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin powder, polyfluorinated ethylene resin Particularly benzoguanamine-based and/or melamine-based resin powders are preferred for use in combination with Zn0.

In addition, inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium carbonate, barium sulfate, calcium sulfate, zinc sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, Q FezOv. , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

The polyurethane used in the back coat layer? 4(I
I is synthesized by the reaction of a polyol and a polyisocyanate, but the polyurethane resin according to the present invention has an ether bond in the main chain of the polyurethane and a carbon atom adjacent to it, depending on the selection of the polyol. General ester bond, carbonate ester bond or two of them
A combination of two or more may be included in the urethane bond.

Furthermore, in order to improve lubricity or dispersibility, for example, fluorine, silicon, or sulfone may be introduced into the main chain or side chain.

As the cellulose resin according to the present invention, cellulose ether, cellulose free acid ester, cellulose organic acid ester, etc. can be used. Examples of cellulose ethers include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benylcellulose, shea 7-ethylcellulose, vinyl Cellulose, nitrocarboxymethylcellulose, diethylamide/ethylcellulose, 7mi/ethylcellulose, etc. can be used. As the cellulose free acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used.

In addition, cellulose organic acid esters include acetyl cellulose, propionyl cellulose, butyryl cellulose, methacryloyl cellulose, chloroacetyl cellulose, β-oxybrobionyl cellulose, benzoyl cellulose, p-)luenesulfonate cellulose, acetyl propionyl cellulose, acetyl cellulose, Butyryl cellulose and the like can be used. Among these cellulose-based fats, nitrocellulose is preferable.

The mixing weight ratio of the polyurethane Q (fat and cellulose resin) is 0.05 to 10.0, preferably 0.1 to 5.0.

By using cellulose resin, especially nitrocellulose, as in the present invention, heat resistance, toughness, and wound prong properties can be improved, and the coefficient of friction is small, so it has an outstanding effect on preventing interlayer adhesion, and is particularly effective at high temperatures. Driving stability in humid conditions can be improved.

In addition, in terms of productivity, in paints containing nitrocellulose, the filler is dispersed more quickly than in vinyl chloride paints, the paint itself is stable, and reagglomeration of the filler is less likely to occur.

In the present invention, polyisocyanate is contained as a curing agent in the above-mentioned baingu.

Aromatic polyisocyanates that can be used include, for example, trilenenoisocyanate (TDI) and adducts of these polyisocyanates and active hydrogen compounds, and those with an average molecular weight in the range of 100 to 3,000 are preferable. It is.

Examples of the aliphatic polyinsyanate include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic polyisocyanates and adducts of these polyisocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic polyisocyanates, non-alicyclic polyisocyanates and adducts of these compounds and active hydrogen compounds are preferred.

The amount of the polyisocyanate added to the binder is 0.1 to 0.7, preferably 0.1 of the sum of both weights.
5・-〇, 5.

The carbon black to be mixed in the backfoot layer is suitable for the purpose of improving conductivity, and is preferably carbon black in which the particles are connected to each other like a bunch of grapes. -High level is desirable.

Examples of such carbon blanks include 1, for example, Kongkutex (Codu-ct) manufactured by Columbia Carbon Co., Ltd.
ex) 975 (specific surface tn270tn2/g, particle size 24
+nμ), Congunctex 950 (specific surface 111
245 m2/8, particle size 46 + nμ), Cabot Vulcan XC72 (specific surface area 2
57m2/g, particle size 301oμ), etc. can be used.

On the other hand, as light-shielding carbon black, those with small particle size, relatively low stracture level, and relatively low specific surface area, such as Reven 2000 (specific surface area 180+n2/
g1 particle size 19 mμ), 430,420.14.210
0.1170.1000.1255.1250.320
0.3500.5250.5750.7000; #30, #35, #40, #44, #75 manufactured by Mitsubishi Kasei Corporation
, #100, #970, #tooo, #2200
%# 2350, $2400, MA7, MA8JA1
．． 1, HΔ100; Black Pearl 7 manufactured by Cabot
00.800.1100.1300, reel 40
0.500.660 etc. can be used.

Furthermore, in the present invention, 1] (I is preferably 7 or less,
Gives good uniform dispersion.

The carbon black having a pH of 7 or less is manufactured by Columbia Carbon Co., Ltd.; Raven 1000.1170.1250.1255.2
000.3200.3500.5250.5750.7
000° Fungkutex 975, manufactured by Cabot; Blank crowbar 1000.1100.1300, L.

Manufactured by Mitsubishi Kasei Corporation; #100, #970, #1000, I2200B,
#2350, #z46oa, 7 to H, 8 to H, M^
11, H^100 Kasa is mentioned.

The paint used to form the aged back coat layer may contain additives such as a dispersant and an antistatic agent, if necessary.

Dispersants used in the back coat layer according to the present invention include lecithin, phosphoric acid ester, amine compound, alkyl sulfate, fatty acid amide, higher alcohol, polyethylene oxide, sulfosuccinic acid, sulfofluoromonophosphate, and known surfactants. and their salts, as well as negative aiso groups (e.g. -C00I+, -r'0.
It is also possible to use salts of polymeric dispersants with 1+). These dispersants can be used alone or in combination.
More than one type may be used in combination.

These dispersants are used in an amount of 1 to 2 parts by weight per 100 parts by weight of Bangu.
It is added in an amount of 0 parts.

Examples of antistatic agents that may be used include the above-mentioned carbon black, conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin. ; 7-ion surfactants such as alkylene oxide, glycerin, and glycidol; cationic surfactants such as higher alkyl amines, tjS quaternary ammonium salts, pyrinone, other heterocycles, phosphonium or sulfonium; carboxylic acids, Examples include anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as sulfuric acid or phosphoric esters of amino acids, ami/sulfonic acids, and ami/alcohols.

A unique feature of the present invention is that it does not use a commonly used lubricant. The use of conventionally known lubricants increases the coefficient of friction, which causes abnormal running due to increased torque and reduces running durability.

The backfoot paint configured as above has a dry thickness of 0.
．． The coating is applied to a thickness of 3-2.0 μm, preferably 0.4-1.5 μm.

The magnetic layer according to the present invention may be a coated magnetic layer using magnetic powder, a binder and dispersion, a lubricant, etc., or a three-layer film formed by a vapor deposition method, a sputtering method, a paper debonition method, etc. It may also be a type magnetic layer.

Examples of magnetic materials include γ-Fe2O3, Co-containing-Fe201, Co-coated-Fe, 03, Fe:1O, Co-containing Fe, O,, Co-coated IFe-0. , CrO2 and other oxide magnetic materials, such as Fe, Ni, Co, Fe-Ni
alloy, Fe-Co alloy, Fe-N1-I' gold alloy Fe-
Ni-Co alloy, Fc-Mn-Zn alloy, Fe-N
1-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-C
o -N i-P alloy, Co-N1Q gold, Co-P alloy, Co-Cr: gold, etc. Various ferromagnetic powders such as metal magnetic powders mainly composed of Fe, Ni, Co, etc.
-4q7-''-↓1?-111ノf'トIJrdJjト7mu'1-8-←?-Additives include Si, CuSZn,
^9 Elements such as P, Mu, and Cr or compounds thereof may be included. Also used are hexagonal ferrites such as barium ferrite, and iron nitride.

In addition, binders, curing agents, dispersants, and
As for the antistatic agent and the filler, those explained in 1ifj for the bank coat layer can be used.

Furthermore, conventionally used lubricants can be used.

Furthermore, an abrasive can be added if necessary.

Abrasives that may be used include commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond,
Garnet, emery (main components: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05 μm.
Those with a size of 0 to 5 μm are used, particularly preferably 0 to 5 μm.
．． 1 to 2 μII+. These abrasives have a binder of 10
It is added in an amount of 1 to 20 parts by weight based on 0 parts by weight ffi.

7. Contained in the above bank coat and magnetic paint. Examples of solvents or diluting solvents used when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; methanol, ethanol, propyl, and butyl. Alcohols such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cephacetate, and other esters; Ethers such as glyfurt methyl ether, glycol monoethyl ether, dioxane, and tetrahydro-7rane; benzene, toluene, Aromatic hydrocarbons such as xylene; methylene chloride, ethylene chloride, RZ tetrachloride, chloroform,
Halogenated hydrocarbons such as dichlorobenzene can be used.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose guiacetate, and plastics such as polyamide and polycarbonate. metal,
Plus, BN.

Ceramics such as S1 carbide, porcelain, and earthenware can also be used.

The thickness of these supports is about 3 to 100 μIo in the case of a film or sheet, preferably 5 to 50 μm,
30 μm or more for disks and cards], Om m
In the case of a drum shape, a cylindrical shape is used, and the shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the bank foot layer or magnetic layer.

The coating method for forming the above layer on the support is as follows:
Air doctor coat, blade foot, air knife coat, squeeze foot, gold coat, reverse roll coat, trans7 roll coat, gravure foot, kiss foot, cast coat, spray coat, etc. can be used, but are not limited to these.

(Example) The present invention will be specifically explained using examples.

Example 1 A magnetic paint having the following formulation I was thoroughly mixed and dispersed in a ball mill, 5 parts of polyfunctional incyanate was added as a hardening agent, and 1
The mixture was filtered through a μIl+ filter and coated onto a 13 μm thick polyethylene terephthalate base using a reverse roll coater to a dry film thickness of 4.5 μm to obtain a sample film. The film was subjected to supercalender treatment.

Next, compositions of different backcoat paint formulations H for each sample shown in Table 1 were dispersed in a ball mill for 5 hours to obtain backcoat paints for each sample. The paint was coated on the back side of the 'Jb n film with a reverse roll coater to form a dry film of 1'7.0.
．． Apply to 7μIfi, +2. They were dried, a back coat layer was formed on each, and slits were made into 172-inch widths to obtain Example sample tapes 1 to 5 and Comparative example sample tapes (1) to (
8).

Formulation I (Magnetic paint) (Parts by weight) Co-containing - FezOz 100 Polyurethane 12 PVC, vinyl acetate, 8 Butyl stearate 0.8 Myristic acid 0.8 Alumina
5 Carbon black 5 Lecithin 4 Cyclohexanone 100 Methyl ethyl ketone 50 Toluene 10 Prescription■ (Back coat paint) The particle size distribution (%) of Zn0 according to the present invention is as follows. pass, vernon tape) and 200 repeated runs f&(Zo
The tape condition, physical properties, and special electromagnetic conversion were checked for the (o-pass) tape, and the results are listed in Table 2.

Examples 1 to 5 in which ZnO wood powder and rice powder with an average particle size of 0.5 μIff were used in the following margins were
Comparative example (1) in which ZnO* and coarse particles (average particle size 0.5 μm) were simply used in combination, Comparative example (2) in which zinc oxide having a particle size distribution different from that of ZnO* according to the present invention was used, and Comparative example using simply a combination of fine particles and coarse particles of titanium dioxide (
:Compared to 2 and 1 of 3), after repeated running, there is less output fluctuation, less tape damage, less increase in deck tension, and not only is it superior in running and durability,
Compared to the case where fine particles and 4-inch particles are simply used together, uniform dispersion is excellent and the chroma S/N ratio is extremely small.

In addition, when Zn00000 powder and carbon black are used in combination, as in Example 5, when one having p117 or less is used, uniform dispersion is better than in Comparative Example (4), and the chroma S/N is better.

Furthermore, compared to Examples 1 to 5, polyurethane 8f1
]7? / Comparative Example (5) in which the weight ratio of nitrocellulose is 6.00 is that the nitrocellulose content is too small.
It has a high coefficient of running friction and does not cause interlayer adhesion. In addition,
When the amount of polyurethane resin is large, uniform dispersibility becomes a problem, the surface density Ra increases, and the chroma S/N deteriorates significantly.

On the other hand, in Comparative Example (6) where the weight ratio of polyurethane resin/nitrocellulose was 0.13 and the amount of nitrocellulose was large,
There is a lot of BC scraping, and friction resistance becomes a problem.

Comparative Example (7) in which a vinyl chloride-vinyl acetate copolymer was used instead of nitrocellulose as a binder required a long time for dispersion, had a large surface roughness Ra, and suffered from a decrease in chroma S/N. big. In addition, there is a lot of BC abrasion, which causes problems in running durability.

Furthermore, in Comparative Example (8) in which stearic acid and butyl stearate were added as lubricants, the friction coefficient increased significantly;
Running torque increases and tape damage becomes a problem.

Measurement method for Examples and Comparative Examples (a) The tape was packed in a VIIS cassette and heated at 20°C.
A 2oO bus was run repeatedly using an NV-6200 (manufactured by Matsushita Electric) deck in a 60% old 1 vehicle. At the same time, R
The F output drop was also measured.

(1)) Tape damage was visually evaluated after running 200 passes.

(c) Coefficient of dynamic friction...at 23°C and 60%RH,
Yokohama System Co., Ltd. running performance test TFI (TBT-30
0-D), set the inlet tension to 20g,
Place 1 sample tape in a stainless steel bottle with a diameter of 3.3+n+n.
It was wound at 80 degrees and run at 3.3 cω/sec, and the outlet tension of -minute diameter was measured and calculated from the following formula.

(d) Coefficient of interlaminar friction: 23°C, 60% III, using the same equipment as in (C), with a large tension of 20%.
g, and wrap it around a stainless steel drum with a diameter of 62 II m with the magnetic layer facing upward, and then place the sample tape on top of it at a diameter of 180 mm.
After winding, the outlet tension was measured after one minute by running on the DC surface at 0.2 cω/sec, and was calculated from equation (1).

(e) Surface roughness Ra (μm): Cant-off 0.2 using three-dimensional roughness measuring instrument 5E-3FK (Koita Institute)
5. Obtained by measuring 2.5+nm of the sample surface with a needle pressure of 30 mH.

(r) Measurement of chroma S/N-) 4.5M at maximum recording current using IR-7100 (Japan 1:'ri9-ti)
1 lz was recorded and the /is delivered pressure during playback was measured.

(++) Gfl adhesion test with / Wrap 172 inch wide tape with IK pressure, 60°C 180%l'
After being left at tl+ for 2.4 hours, it was left at room temperature for an additional 24 hours and rewound, and those with resistance when pulled apart were evaluated as "Yes" and those without were evaluated as "No."

(11) Electrical tension: Using a VHS video cheap recorder IIR-6500 (Japan Victor Co., Ltd.), measure the opening tension (T1) and the exit tension (1'l). I asked for it.

Claims (2)

[Claims] (1) A magnetic recording medium having a magnetic layer on one side of a support and a back coat layer containing a binder and non-magnetic powder on the other side, which contains zinc oxide as the non-magnetic powder and A magnetic recording medium characterized in that zinc oxide has a monomodal particle distribution having 10 to 50 wt% of particles of 0.5 μm or more and 60 to 1 wt% of particles of 0.15 μm or less. (2) A cellulose resin in which polyisocyanate is added to the binder of the back coat layer and 0.1 of the resin.
The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium contains a combination of polyurethane curable resins in a weight ratio of 5.0 to 5.0.