JPH01176317A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the title recording medium which is excellent in electromagnetic conversion characteristics such as high-density recording, S/N, etc., by specifying the specific surface area of magnetic metallic powder and the weight ratio of the moisture contained in a magnetic to the weight of the magnetic metallic powder. CONSTITUTION:The magnetic layer 2 is provided on a nonmagnetic base 1 consisting of polyethylene terephthalate, etc., and a back coat layer 3 is provided on the surface of the side opposite to the magnetic layer. The specific surface area of the magnetic metallic powder is >=45m<2>/g and the weight of the moisture contained in the magnetic layer 2 is set larger than 1.0wt.% and <=2.5wt.% of the weight of the magnetic metallic powder. The specific surface area of the magnetic powder is specified preferably to >=50m<2>/g and the upper limit thereof is more preferably specified to 70m<2>/g. The weight of the moisture in the magnetic layer is further preferably specified to 1.2-20wt.%. The high- density recording is thereby enabled and the S/N is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

Prior Art Recently, magnetic recording media such as magnetic tapes have become denser and have higher S/S.
With the shift to nitrogen, magnetic powders with smaller particle diameters are being used.

Generally, it is said that the S/N ratio of a magnetic recording medium is proportional to the square root of the number of particles of magnetic powder in the recording material involved in recording and reproduction. Therefore, when applying the same weight of magnetic powder,
The use of magnetic powder with a smaller particle size is more advantageous in improving the S/N. Further, by making the magnetic powder into fine particles and increasing its BET value, the surface of the magnetic layer becomes smoother and spacing loss is reduced, which is advantageous in obtaining high electromagnetic conversion characteristics. Using metal magnetic powder enables even higher density recording and further improves performance.

However, when magnetic powder is made into fine particles, the dispersibility tends to deteriorate during the series of steps such as dispersion → stagnation → coating. This tendency is particularly strong with metal magnetic powder, and the particles tend to aggregate, resulting in poor coating liquid stability. becomes worse.

As a result of various studies, the inventors of the present invention have discovered that the moisture content of the magnetic layer using metal magnetic powder greatly affects the performance, and has arrived at the present invention.

C.6 Purpose of the Invention The purpose of the present invention is to provide a magnetic recording medium which has excellent electromagnetic characteristics such as high-density recording and S/N ratio, and has improved dispersibility and coating liquid stability.

21 Structure of the invention and its effects, that is, the present invention provides a magnetic recording medium in which a magnetic layer contains a binder and metal magnetic powder dispersed in the binder, the specific surface area of the metal magnetic powder is is 45 m'/p or more, and the amount of water contained in the magnetic layer is greater than 1.0% by weight and less than 2.5% by weight based on the metal magnetic powder. It is related to the medium.

According to the present invention, the magnetic powder has a specific surface area of 45 m"71
Since the metal magnetic powder described above is used, high-density recording is possible, and a medium with excellent S/N ratio etc. can be provided.

In this case, setting the specific surface area to 45w79 or more greatly contributes to improving the performance described above, but on the other hand, since it is a metal powder, the particles tend to aggregate with each other, which affects the dispersibility and coating liquid stability, and ultimately the durability of the medium. Although there is a tendency for the properties to deteriorate, this can be more than solved by controlling the moisture content of the magnetic layer within the above-mentioned specific range based on the present invention.

That is, in the metal magnetic powder itself, active points present on the surfaces of individual particles cause aggregation of the particles, but these active points are inactivated when an appropriate amount of moisture is present or attached to the particle surface. According to the present invention, such inactivation is achieved by increasing the moisture content of the magnetic layer to more than 1.0% by weight (when the metal magnetic powder is 100%). On the other hand, when the water content is 1.0% by weight or less, there is a shortage of water and the active sites cannot be sufficiently crushed, resulting in poor dispersion and agglomeration of particles. However, in the present invention,
If the above water content is too large, it will actually impair the physical properties of the magnetic powder and the performance of the magnetic layer itself, and the dispersion of the magnetic powder will also be poor (poor compatibility with the binder), so the water content should be 2.
It should be less than 5% by weight.

In the above, the specific surface area of the magnetic powder is preferably 50 m'/.9 or more, but the upper limit is preferably 70 m7'fl.

Further, it is desirable that the moisture content of the magnetic layer is further 1.2 to 2.0%.

The above specific surface area is expressed as a BET value, which refers to the surface area per unit weight, and is a physical quantity that is completely different from the average particle size. For example, even if the average particle size is the same, the specific surface area is large. There are some with small specific surface area. To measure the specific surface area, for example, first, the powder is degassed while being heated at around 250°C for 30 to 60 minutes to remove substances adsorbed to the powder, and then introduced into a measuring device. The initial pressure of nitrogen is Q, 5 to 9/rn'
and perform adsorption measurements using nitrogen at the liquid elementary temperature (-195°C) (method for measuring specific surface area, generally referred to as the B, E, T method. For details, see J, Ame, Chem.
Soc, 60309 (1938)). As a device for measuring the specific surface i (BET value), it is possible to use a "powder measuring device (Cantersoap)" jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. A general explanation of the specific surface density and its measurement method can be found in “
granular material constant J (J, M, DALLAVALLE
, co-authored by CLYDEORR Jr., translated by Benta et al.; published by Sangyo Toshosha), and also in ``Chemistry Handbook''.
(Application Edition, pp. 1170-1171, published by Nippon Kagaku Yoshin, Maruzen Co., Ltd. on April 30, 1966).
/gr), which is the same as the specific surface area in this specification. ).

Furthermore, the amount of water in the magnetic layer can be measured using a known measuring method.

Examples of metal magnetic powders that can be used in the present invention include Fe, Ni,
Including Co, Fe-Al system, Fe-Al-Ni system, F
e -A 13- Co system, Fe kl Zn system, Fe-Ni-Co system, Fe-Mn-Zn system, Fe-N
i system, Fe-Ni-A1 system, Fe-Ni-Z
n-based, Fe-Co-Ni-Cr-based, Fe-C
.

-Ni-P system, Co-Ni system, Fe5Ni, C.

Examples include ferromagnetic powders such as metal magnetic powders whose main components are Among them, Fe-based metal magnetic powder containing 80 atm% or more of Fe has excellent electrical properties, and Fe-AJlt and Fe-AlNi are particularly good in terms of corrosion resistance and dispersibility.

Fe-Al-Zn, Fe-Al-Co, Fe-Ni,
F e -N i -A l , F e -N i
-Z n type metal magnetic powder is preferred.

Furthermore, iron-aluminum system (Fe-Al system, Fe
-A l-N i system, F e -A l -Z n system,
Particularly preferred are metal magnetic powders (such as Fe-A1-Co).

Hereinafter, the iron-aluminum system will be simply referred to as the Fe-AA' system.

That is, the uses of video tapes in recent years have expanded to a wide range of uses due to the shift to portable video tapes, and the applications for video tapes are diverse. Therefore, video tapes are required to have high corrosion resistance. In this respect, Fe-A1 magnetic powder exhibits high corrosion resistance and good dispersibility. This is very important for realizing high-density recording because even if the specific surface area of the magnetic powder is increased, its dispersibility can be maintained sufficiently.

Moreover, in the above-mentioned Fe-Al based metal magnetic powder, it is preferable that the AA content of the magnetic powder is within the range of 0.1 to 20 atomic %.

The binder that can be used in the present invention has an average molecular weight of about 1
0000 to 200,000, such as urethane resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, Cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-phtadiene copolymers, polyester resins, various synthetic rubbers,
Phenolic resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic reactive resins, mixtures of high molecular weight polyester resins and incyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols / high molecular weight diol / isocyanate mixture, and mixtures thereof are exemplified.

The above resins are -8o3M, -〇〇〇M, -PO(O
M') 2 (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M' is hydrogen, an alkali metal such as lithium, potassium, or sodium, or a hydrocarbon residue such as an alkyl group); It is preferable that the resin contains the following. In other words, the polar groups in the molecules of these resins improve the compatibility with the metal magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the metal magnetic powder, further improving the stability of the coating liquid. can be done.

The binder used, especially the vinyl chloride copolymer, is a copolymerizable binder containing a vinyl chloride hexamer, a copolymerizable binder containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable binders as necessary. It can be obtained by polymerization.

Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned sulfonic acid or phosphoric acid salt is an alkali metal (sodium, potassium, lithium in percentage), and potassium is particularly preferred in terms of solubility, reactivity, yield, etc.

The above-mentioned copolymerizable polymer containing a sulfonate salt is CH2=CH3O,M.

CH2=CHCH2SO3M, CH2=C(CH3)CH25o,M.

CH2=CHCH20COCH(CH2COOR)So
,M.

CH2=CHCH20CH2CCH2=CHCH2OC
H2CH(OH)CH2S03M1CH2=C(CH3
)COOC2H4SO3,803M.

Cl-l2=CHCONHC(CH3) 2CH2So
3M, for example.

In addition, as a phosphate, CHCH2=CHCH2OCH2CH(OH)CH2-
0-PO3', CH2=CHC0NHC(CH5) 2
CH,, -0-PO, MY2, CH2=CHCH20(
CH2CH20)m202MX2 In the above, M is an alkali metal, R is an alkyl group having 1 to 20 carbon atoms, ¥
1 is H, M or CH2=CHCH20CH2CH(OH
) CH2-1Y2 is H, M or CH2=CHCONHC(CH3) 2CH2-1X1
is OH or OM, and X2 is CH2=CHCH20(CH2CH20)m-1OH or OM. Further, n is a positive number of 1 to 100, and m is a positive number of 1 to 100.

Copolymerizable heptamers to be copolymerized as necessary include known polymerizable heptamers, such as various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, etc. Examples include acrylic ester, methacrylic ester, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether, aryl ester, acrylamide, methacrylamide, maleic acid, and maleic ester.

The binder according to the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization.

In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of acidic group salts in the binder used in the present invention is preferably 0.01 to 30 mol%. If the amount of the salt-containing monomer is too large, the solubility in solvents will be poor and gelation will likely occur. Furthermore, if the amount of salt-containing monomer is too small, desired characteristics cannot be obtained.

Preferably, the vinyl chloride copolymer further contains an epoxy group or a hydroxyl group.

By the way, conventional vinyl chloride copolymers (for example, U, C, C.

VAGH) manufactured by Co., Ltd. consisted of the following copolymerized components.

: Indicates a copolymerization unit.

However, it is thought that the CH3Co-0- group here does not easily contribute to the crosslinking reaction with the curing agent and the like. Therefore,
It is preferable to contain an epoxy group such as the following instead of CH3Co. For example, a copolymer having the following units may be mentioned.

OH (X: Monomer unit portion containing an alkali metal salt of sulfo or phospho group) In particular, it is preferable to use at least urethane resin, and furthermore, vinyl chloride copolymer, epoxy resin (especially phenoxy resin), polyester resin. Alternatively, it is preferable to use nitrocellulose resin (hereinafter referred to as other resin) in combination.

In this case, the blending ratio of the urethane resin and the other resin is 90 to 10 parts by weight, more preferably 80 to 10 parts by weight.
Preferably, the amount is 20 parts by weight. If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is significantly deteriorated, and the adhesion to the support also deteriorates. Further, if the above-mentioned blending ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

Furthermore, in the present invention, durability can be improved by further adding a polyincyanate curing agent to the magnetic paint containing a binder.

Examples of such polyisocyanate-based curing agents include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate; Any functional incyanate or urethane prepolymer containing isocyanate groups at both ends, which have been conventionally used as a curing agent, or any polyisocyanate that can be used as a curing agent can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
It has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, a BCC 84 is provided on the opposite side of the magnetic layer 2. Also,
As shown in FIG. 2, an overcoat layer (QC layer) 4 may be provided on the magnetic layer 2 of the magnetic recording medium of FIG.

Further, the magnetic recording media shown in FIGS. 1 and 2 may be provided with an undercoat layer (not shown) between the magnetic layer 2 and the support 1, or may be provided with no undercoat layer. (The same applies hereafter). The support may also be subjected to corona discharge treatment.

In addition to the metal magnetic powder and binder described above, the magnetic layer 2 also contains:
As a lubricant, fatty acids and/or fatty acid esters can be included. This allows us to bring out the strengths of both while offsetting the defects that would occur when used alone.
Improves lubrication effect, still image durability, running stability, S
/N ratio etc. can be increased. In this case, the amount of fatty acid added is ""C002~10 with respect to 100 parts by weight of magnetic powder.
Parts by weight are good, and 0.5 to 8.0 parts by weight is even better. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and output decreases. The amount of fatty acid ester added is preferably 0.1 to 10 parts by weight, and even more preferably 0.2 to 8.5 parts by weight, per 100 parts by weight of the magnetic powder. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be set as fatty acid/fatty acid ester =
10/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30, more preferably 12 to 22 return atoms are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-dodecanedicarboxylic acid (23)
Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Isocetyl stearate (3) Dioleyl manate (4) Butyl stearate (5) Butyl palmitate (6) Butyl myristate (7) Octyl myristate (8) Octyl palmitate (9 ) Amyl stearate (10) Amyl palmitate (11) Eats butyl oleate (12) Stearyl stearate (13) Lauryl oleate (14) Octyl oleate (15) Inbutyl oleate (16) Ethyl oleate (17) Isotridecyl Olate (18) 2-ethylhexyl stearate (19)
Ethyl stearate (20) 2-ethylhexyl palmitate (21)
Isopropyl palmitate (22) Isopropyl myristate (23) Butyl laurate (24) Cetyl-2-ethyl hexalate (25) Dioleyl adipate (26) Diethyl adipate (27) Diisobutyl adipate (28) Diisodecyl adipate In addition to fatty acids and fatty acid esters, other lubricants (for example, silicone oil, carboxylic acid modified, and ester modified), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) may be added to the magnetic layer.

Non-magnetic abrasive particles may also be added, including alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide. , boron nitride, etc. are used. The content of this abrasive is preferably 20 parts by weight or less per 100 parts by weight of the magnetic powder, particularly 3 parts by weight or less.
12 parts by weight or less is preferable, and the average particle size is 0.6μ
m is good, and 0.3 μm or less is even better.

In addition, the magnetic layer further contains an antistatic agent such as graphite.
A dispersing agent such as powdered lecithin or phosphate ester can be added. Further, carbon black can also be used in combination.

If a light shielding carbon black is used as such carbon black, the degree of light shielding can be increased.

As the light-shielding carbon black, Rapen 2000 #35, #30, etc. manufactured by Eva Columbia Carbon Co., Ltd. can be used.

Further, as a conductive carbon blank, for example, Conductex manufactured by Columbia Carbon Co., Ltd.
ex975 (BET value (hereinafter abbreviated as BET) 250m'/
N, DBP oil absorption (abbreviated as DBP below the oil absorption plate) 170rr
J/100gr, particle size 24mβ), Conductex 9
00 (BET 125n+'/j', particle size 27mμ),
Ko7 Dactesox 4O-220 (particle size 20 mμm),
Conductex S C (BET 220rn”/
gr, DBP115m1/100gr, particle size 20mμ
), Cabot Vulca
n) XC-72 (specific surface area 254 m'/, iil,
Particle size 30mμ), Palcuff P (BET 143m'/gr
, DBP118m1/100gr, particle size 20mμ), Raven 1040.420, Blank Pearls 2000
(particle size 15 mμ), #44 manufactured by Mitsubishi Kasei Corporation, etc.

In addition, other carbon blanks that can be used in the present invention include Conductesok, manufactured by Columbia Carbon Co., Ltd. (
(Conductex)-8C, (BET220m/
g, DBP115m1/100N, particle size 20mμ), Vulcan manufactured by Kabonoto 9
(BET 140rn'/,!i', DBP115m1
/100N, particle size 19rnμL #80 manufactured by Asahi-Bon Co., Ltd.
(BET 117m'/7. DBP 113m1/
100 g, particle size 23m=μ), H31 manufactured by Denki Kagaku Co., Ltd.
00 (BET 32m'/g, DBP 180m1
/100! j, particle size 53 mμ), s2 manufactured by Mitsubishi Kasei Corporation
2B (BET55m7'i D B P131 mA!
/Zoo &, particle size 40mμ), s 20B (B E
T56m7/L DBP 115m1/100. F,
particle size 40 mμ), s 3500 (B E T 47r
n7'11, D B P 187 ml/100 fi
, particle size 40 mμ), and in addition, CF-9, #4000, MA-600 manufactured by Mitsubishi Kasei Co., Ltd., and Black Pearls manufactured by Kabonoto Co., Ltd.
) L, Monarch (Monarck) 800, Black* /<-)'I7's 700, Black Pearls 1
000, Black Pearls 880, Flick 11 Harls 900, Black ψ Knolls 1300, Black Pearls 2000, Sterling
) V, Rabe 7 manufactured by Columbian Carbon (R
aven) 410, Raben:y 3200, Raben 430, Rapen 450, Raben 825, Raben 1255, Rapen 1035, Chi Pen 1000. Examples include Raven 5000 and Ketchen Black FC.

In addition, the non-magnetic particles contained in the back coat layer are
More preferably, the average particle size is within the range of 10 mμ to 1000 mμ. This is because within the above range, the non-magnetic particles will not become too fine and the addition effect will be good.

Non-magnetic particles include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide,
Examples include zinc oxide, α-Fe203, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbide, barium sulfate, and the like. In addition, organic powders such as benzoguanamine resins, melamine resins, phthalocyanine pigments, etc. can also be used, and organic powders and the above-mentioned inorganic powders can also be used in combination.

Furthermore, it is more preferable to use carbon black in combination with the above-mentioned non-magnetic particles. This further stabilizes the running properties of the medium, and in combination with the effect of the non-magnetic particles described above, it is possible to further improve the durability of the medium.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In the Examples below, all "parts" are parts by weight, and a magnetic layer was formed on a 10 μm thick polyethylene terephthalate base film as a support in the following manner.

That is, after using a predetermined alloy metal magnetic powder and dispersing each of the components shown in FIG. Apply to .5μm and apply super calendar.
Magnetic layers having various compositions shown in FIG. 3 were prepared.

However, the Al content in each alloy metal magnetic powder was 5 at %.

Thereafter, a paint for the BC layer having the following composition was applied to the opposite surface of the magnetic layer to a dry thickness of 0.4 μm.

Carbon black 40 parts (average particle size 5
0mμ) Barium sulfate 10 parts Nitrocellulose 25 parts N・2301 (日2EHo'J')Vtoughm) 2 ss Coronate L (
) 10 parts cyclohexanone 400 parts methyl ethyl ketone 250 parts toluene
250 parts of the magnetic layer of a predetermined thickness, BC
A wide magnetic film having r@ was obtained and wound up.

This film was cut into 8 squares to make the following video tapes (corresponding to the numbers of each Example and Comparative Example). However, the numbers after the second column in FIG. 3 represent parts by weight.

In addition, when measuring the frequency of scratches on the tape, H inch (
It was made into a videotape with a width of 12.65 m).

The results of measuring the performance of the tape obtained as described above are shown below. However, evaluation items are measured and displayed according to the following standards.

Lumi S/N: Color video noise meter rshiba
Measured by sc925 D/IJ. Bypass filter is 10KHz, low pass filter is 4.2M
It was done in Hz. The VTR used was an 8-video deck.

Decrease in RF output: The RF output was measured using an 8mm video deck, and after 100 playbacks, the value showed a decrease compared to the initial output. (Unit: dB)Still image lifespan:
Shows the time in minutes for a still image to degrade by 2 dB. The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

Frequency of scratches on tape: Using a commercially available VH8 type VTR, set the tape and
I ran it for a minute. After that, the running was stopped, the tape was taken out, and the running part and the part used for loading and unloading were visually inspected to determine whether there were any scratches on the tape surface. Calculate as number of scratches/number of tests x 100 (%). The number of tests was 20 or more.

)ku Saturation magnetization: The saturation magnetization of the sample tape is expressed in Gauss.

Remaining rate of saturation magnetization: The saturation magnetization measured after the sample tape was left in an atmosphere of 60° C. and 80% RH for one week corresponds to what percentage of the saturation magnetization measured before being left.

Powder removal after running 100 times: ◎ Very good ○ Good Δ Fairly good . That is, the BET value of the metal magnetic powder is 45 m''/,
It is extremely important that li' or more and the water content of the magnetic layer be greater than 1.0 and less than 2.5% by weight.

(1) Brief Description of the Drawings - FIGS. 1 and 2 are partially enlarged cross-sectional views showing examples of the magnetic recording medium of the present invention.

FIG. 3 is a graph showing changes in characteristics depending on the composition of the magnetic layer.

In addition, in the symbols shown in the drawings, 1......Nonmagnetic support 2...
...... Magnetic layer 3 ...... Back coat layer (BC layer)
4...... Overcoat layer (QC layer).

Agent: Patent Attorney Hiroshi Aisaka

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer contains a binder and metal magnetic powder dispersed in the binder, in which the specific surface area of the metal magnetic powder is 45 m^2/g or more, and the magnetic A magnetic recording medium characterized in that the amount of water contained in the layer is greater than 1.0% by weight and less than 2.5% by weight based on the metal magnetic powder.