JPH01196722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the electromagnetic conversion characteristics, traveling property and durability of a medium by incorporating pulverized magnetic powder and a fatty acid and fatty acid ester which are respectively specific in the rate of extraction by cyclohexane into said medium. CONSTITUTION:A binder, the metallic magnetic powder (A), the fatty acid (B) and the fatty acid ester (C) are incorporated into the title medium. The fine particle having >=45m<2>/g specific surface area is used for the component A (e.g.: oleic acid) and the compds. having <=4mg (component B) and 5-100mg (component C) rate of extraction when immersed for 3min in the cyclohexane are used for the component B (e.g.: oleic acid) and the component C (e.g.: butyl stearate). Bleeding and output decrease are liable to arise when the content of the component B exceeds said range and the lubricity is low when the content is too low. Sticking arises or powder dislodgment increases during traveling when the content of the component C exceeds the above-mentioned range. The still-life characteristic is deteriorated if the content is below the above-mentioned range.

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.

9. Prior art Recently, magnetic recording media such as magnetic tapes have become denser and have higher S/S.
As the N ratio increases, 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. In addition, if the magnetic powder is made into fine particles and its BET value is increased, the surface of the magnetic layer will become smoother and the spacing loss will be reduced, which is advantageous in obtaining high electromagnetic conversion characteristics. When used, even higher density recording is possible, and performance is greatly improved.

However, when the magnetic powder is made into fine particles and its BET value is increased, the surface of the magnetic layer becomes smoother, which actually deteriorates the running durability of the tape.

That is, since the recording medium as described above comes into violent sliding contact with the magnetic head during recording and reproduction, the smoothing of the surface increases the sliding contact area and increases the coefficient of friction, which actually deteriorates the running performance. This causes undesirable results such as wear of the magnetic coating film during repeated use, falling off of the magnetic powder contained in the coating film, and clogging of the magnetic head due to the falling magnetic powder. Furthermore, so-called edge folding, in which the edge portion of the tape is damaged by Ti during tape running, is likely to occur.

C5 Purpose of the invention The purpose of the present invention is to provide high-density recording, excellent electromagnetic conversion characteristics such as S/N ratio, good running performance, excellent running durability, reduction of friction coefficient, and prevention of clogging of magnetic heads. An object of the present invention is to provide a magnetic recording medium that can prevent edge bending.

20 Structure of the Invention and Its Effects 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 magnetic layer further contains a fatty acid and a fatty acid ester, and the metal magnetic powder has a specific surface area of 45 m/g or more,
The amount of the fatty acid extracted into the cyclohexane by immersing the magnetic layer in cyclohexane for 3 minutes is
4 or less per rd, and 3 in cyclohexane
The present invention relates to a magnetic recording medium characterized in that the amount of the fatty acid ester extracted in cyclohexane by dipping for a minute is 5 J■ or more and 1001■ or less per magnetic layer l11 (per magnetic layer l11).

According to the present invention, since metal magnetic powder having a specific surface area of 45 m/g or more is used as the magnetic powder, high-density recording is possible and a medium with excellent S/N ratio etc. can be provided.

In the above, the specific surface area of the magnetic powder is preferably 50 r4/g or more, but the upper limit is preferably 70 m/g.

Further, the present invention has a remarkable feature in that fatty acids and fatty acid esters are contained in the magnetic layer that makes strong sliding contact with the magnetic head, and the content of these is regulated by a unique method.

That is, as magnetic powder becomes finer and metal magnetic powder is adopted, problems such as deterioration of running performance, clogging of magnetic heads, and edge breakage, which were mentioned in the section of the prior art, inevitably arise. The lubricating effect of fatty acids and fatty acid esters reduces the coefficient of friction on the surface of the magnetic layer, thereby improving running performance.The tape winding is also stabilized, which prevents edge breakage. It can also prevent powder from falling off and clogging of the magnetic head.

However, what is important here is the content of fatty acids and fatty acid esters and their content state. If these selections are inappropriate, the lubricating effect will not be sufficiently exerted, and bleeding into the magnetic layer will occur. This results in undesirable phenomena such as seepage. On the other hand, the reality is that we have no choice but to experiment and accumulate these choices.

In particular, with regard to metal magnetic powder, quantitative compatibility becomes an issue and new consideration is required.

Here, the present inventor adopted a unique method of regulating the amount of fatty acids and fatty acid esters eluted into cyclohexane when a magnetic recording medium is immersed in cyclohexane (solvent) for a predetermined time (3 minutes). At the same time,
We investigated the amount of fatty acids and fatty acid esters extracted in relation to the highly fine-grained metal magnetic powder. As a result, it has been found that, unlike conventional iron oxide magnetic powder, very good results can be obtained by limiting the extraction amount of fatty acids, etc. to the above-mentioned range. That is, as a result, the amount of fatty acids and fatty acid esters present in the vicinity of the medium surface that substantially contributes to the lubricating effect is defined in a manner compatible with the high-fine metal magnetic powder,
While exhibiting the characteristics of each fatty acid and fatty acid ester, it offsets the defects that occur when used alone, improves the lubrication effect, improves running performance, running durability, and S/N ratio, and prevents clogging of the magnetic head. , it is possible to prevent edge breakage, etc.

The amount of fatty acids extracted into cyclohexane was set to be 4 or less per rrf of the magnetic layer, but 0. Old ■ or above, 3n
It is more preferable to set it to less than w. If the fatty acid content is outside this range and the fatty acid content decreases, the lubricity 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 the output decreases.

Further, the amount of fatty acid esters extracted into cyclohexane is 5 mg or more and 1001 square meters or less per m of magnetic R, and more preferably 10 mg or more and 80 square meters or less. If the ester content is outside this range, the still life characteristics will be poor, and if the ester content is too high, it will cause sticking during driving and a lot of powder will fall off.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters extracted into cyclohexane should be set at a ratio of fatty acid/fatty acid ester -0.01/100 to 80.
/100 is preferred.

Fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon 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) Valmitic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Hehenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (I8) Adipic acid (19) Pimelic acid (20) Azelain 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 maleate (4) Butyl stearate (5) Butyl palmitate (6) Butyl myristate (7) Octyl myristate (8) Octyl palmitate ( 9) Amyl stearate (10) Amyl palmitate (11) Isobutyl oleate (12) Stearyl stearate (13) Lauryl oleate (14) Octyl oleate (15) Isobutyl oleate (16) Ethyl oleate (17) Isotridecyl oleate (1B) 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 (29) Oleyl stearate (30) 2-ethylhexyl myristate 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, the average particle size is the same. However, there are some with a large specific surface area and some with a small specific surface area. To measure the specific surface area, for example, first heat the powder at around 250°C for 30 to 6
The powder was degassed while being heated for 0 minutes to remove substances adsorbed on the powder, and then introduced into the measuring device, the initial pressure of nitrogen was set to 0.5'kg/nF, and the powder was heated with nitrogen. Adsorption measurements are carried out at liquid nitrogen temperature (-195°C) (generally referred to as the B, E, T method).
9 (1938)). This specific surface [(BET value)
The measurement device used is the "Powder/Grain Measurement Device (Canterthorpe)" (J, M, DALLAVALLE, CLYDEOI) jointly manufactured by Yuasa Battery ■ and Yuasa Ionics ■.
It is described in detail in ``Chemistry Handbook'' (Application Edition, 1), co-authored by IR Jr.
Pages 170-1171, Nippon Kagakujojo, Kuzen, published on April 30, 1960). However, it is the same as the specific surface area in this specification.

Examples of metal magnetic powders that can be used in the present invention include Fe, Ni,
Including Co, Fe-AE system, Fe-Al-Ni system, F
e-Ni-3i system, Fe-Al-Zn system, Fe-Ni-
Co-based, Fe-Mn-Zn-based, Fe-Ni-based, Fe-N
1-Aj! system, Fe-Ni-Zn system, Fe-Ni-Mn
system, Fe-Co-N1-P system, Co-Ni system, Fe, N
Examples include ferromagnetic powders such as metal magnetic powders containing i, Co, etc. as main components. Among them, F with Fe of 3Qa Lm% or more
E-based metal magnetic powder has excellent electrical properties, especially Fe-Aj! in terms of corrosion resistance and dispersibility. , Fe-Aji! -Ni, Fe
-Aff-Zn, Fe-AJ-Co, Fe-NiXFe
-N1-AA! ,,Fe-Ni-Zn,Fe-Ni-
An-31-Zn, Fe-Ni-Af-3i-M
n type metal magnetic powder is preferred.

Furthermore, iron-aluminum series (Fe-Aj! series, Fe-
AE-Ni series, Fe-AE-Zn series, Fe-AJ2-C
Metal magnetic powder (e.g., o-type) is particularly preferred.

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 been wide-ranging as they have become portable, and the conditions for their use have varied. Therefore, video tapes are required to have high corrosion resistance. In this respect, Fe-AA magnetic powder exhibits high corrosion resistance and good dispersibility. This is very important for realizing high-density recording, since even if the specific surface area of the magnetic powder is increased, its dispersibility can be sufficient.

Moreover, in the above-mentioned Fe-AN metal magnetic powder, it is preferable that the Aβ content of the magnetic powder is within the range of 0.1 to 20 at %.

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-butadiene copolymers, polyester resins, various synthetic rubbers,
Phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction 4
Examples include resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

The resins mentioned above are -303M and -COOM.

-PO(OM') 2 (M is hydrogen or alkali gold mud such as lithium, potassium, sodium, etc., M'
is an alkali such as hydrogen, lithium, potassium, sodium, etc.
It is preferable to use a resin containing hydrophilic polar groups such as gold mud or hydrocarbon residues. 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 improved.

The binder used, especially the vinyl chloride copolymer, can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. Can be done.

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 above-mentioned gold mud of a salt of sulfonic acid or phosphoric acid is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferable in terms of solubility, reactivity, yield, etc.

The above copolymerizable monomer containing a sulfonate salt is CHCH2=CH3O 3H2= CHCH2S O3M C) [2=C(CH3)CH2SO3MCHz=CHC
HzOCOCH(CH2COOR)303M CH2=CHCH20CH2CH(OH)CH2S O
s M CHz=C(CH3)COOC2H4SO3MCHz=
CHCOOC4He(CH3)C00C2H4SO3(CH3)2CH2SO3M is mentioned.

In addition, as a phosphate, CH2=CHCH20CH2CH(CH)CH2-0-
P 03M Y' CH2=CHC0NHC(CH3) 2CH2-0-
PO3MY” CH2=CHCH20o (CHz CH20) n0
2MXl CH2=CHCH2O(CH2CH20)m02MX2 In the above, M is an alkali metal, R is the number of carbon atoms 1 to 2
0flW alkyl group, Yl is 8% M or CH2=CH
CH20CH2CH(OH)CH2-1Y2 is H, M, OH or OM; X2 is CH2''CH2H20(CH2CH20)m-2OH or OM; n is a positive number of 1 to 100;

In addition, as the copolymerizable polymer to be copolymerized as necessary, there are known polymerizable polymers, such as various vinyl esters, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, acrylic acid, methacrylic acid, etc. Examples include acrylic esters, methacrylic esters, ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ethers, aryl ethers, aryl esters, acrylamide, methacrylamide, maleic acid, and maleic esters.

It is polymerized by polymerization methods such as polymerization, cloud polymerization, and bulk polymerization. In either method, if necessary, a molecular M regulator,
Known techniques such as divisional addition or continuous addition of a polymerization initiator and a 7-mer can be applied.

The amount of the acid group salt-containing monomer in the binder used in the present invention is preferably from o, oi to 30 mils and 30 moles. 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.

However, it is thought that the CH3CO-〇- group here does not easily contribute to the structural 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.

(X: Monomer unit portion containing an alkali gold mud salt of sulfo or phospho group) In particular, it is preferable to use at least a urethane resin, and further a vinyl chloride copolymer, an epoxy resin (particularly a phenoxy resin), a polyester resin or 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 polyisocyanate 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;
41@), trifunctional isocyanates such as Desmodur L (manufactured by Bayer AG), or urethane prepolymers containing isocyanate groups at both ends, which are conventionally used as curing agents, and also used as curing agents. Any possible polyisocyanate 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 BCCa 2 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 shown in 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. It's okay. The support may also be subjected to corona discharge treatment.

In addition to the above-mentioned fatty acids and fatty acid esters, the magnetic layer may also contain other lubricants (such as silicone oil, carboxylic acid-modified or ester-modified molybdenum, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.). etc. can be added. Non-magnetic abrasive particles may also be added, including alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, shifconium oxide, zinc oxide, cerium oxide, acid Magnesium/gnesium, boron nitride, etc. are used. This r1
The content of the 7F abrasive material is preferably 20 parts by weight or less per 100 parts by weight of the magnetic powder, particularly 3 parts by weight to 12 parts by weight or less, and the average particle diameter is preferably 0.6 μm or less.
．． Even better is 3 μm or less.

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. Furthermore, a carbon blank can also be used in combination.

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

As a light-shielding carbon blank, for example, Lahen 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 190n (/
g, particle size 18 mμ), 2100.1170.1000
, Mitsubishi Kasei 0 remanufactured #100, #75, #40, #3
5, #30, etc. can be used.

Further, as a conductive carbon blank, for example, Conductex (Columbia Carbon Co., Ltd.) is used.
x ) 975 (BET value (hereinafter abbreviated as BET) 2
50rr? /g, DBP oil absorption (hereinafter abbreviated as DBP)
170me/100gr, particle size 24mμ), Conductesox 900 (BET125m/g, particle size 27
mμ), Near 7 Dactex 40-220 (particle size 20 mμm), Conductenox SC (B ET22
0 m/gr, D B P115 m7! / 100
gr, particle size 20 mμ), Palcan manufactured by Cabosoto (
Cabot Vulcan) X C-72 (specific surface area 2541/g1 particle size 30 mμ), Palcan P
T143m/gr, D B P118ml/
100gr, particle size 20rncr) Raven 1040.
420, Blasoku Pearls 2000 (grain i stripe 15mmμ
), #44 manufactured by Mitsubishi Kasei GI Candle, etc.

Other carbon blacks that can be used in the present invention include Conductex (made by Columbia Carbon Co., Ltd.).
Conductex ) -3C, (BET220m/
g, DBP115 mj2/100 g1 particle size 20mμ
), Vulcan 9 manufactured by Cabosoto
(BE T140 ra/g, DBP114 mj
? /100 g, particle size 19 mμ), # manufactured by Asahi Carbon Co., Ltd.
80 (B E 7117 m/g, D B P1
13 m 1. /100 g, particle size 23 mμ), H3100 manufactured by Denki Kagaku Co., Ltd. (BET32 m/g SDBP1
80mff/100g, particle size 53mμ), Mitsubishi Chemical #22B (BET55n?/g, DBP131
m/! /100 g1 particle size 40 m u), #20B
(BE 756m/g, DBP115ml
/100 g, particle size 40 mμ), #3500 (
B ET47rJ/g, DBP187 m//100
g, particle size 40 mμ), and also CF-9, #4000. manufactured by Mitsubishi Chemical Corporation. ．． MA-600, Kisabot's Black Pear
ls) L, Monarch (Monarck) 800
, Black Burls 700, Black Pearls 10
00, Black Pearls 880, Black Pearls 900, Black Pearls 1300, Black Burls 2000, Sterling ■,
Raven manufactured by Columbia Carbon
) 410, Lachen 3200, Laben 430, Laben 450, Lachen 825, Laben 1255, Laven 1035, Lachen 1000, Laven 5000, Kefchenbrak FC, etc.

In addition, the non-magnetic particles contained in the bank coat layer are
It is more preferable that 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 a carbon blank together with the above-mentioned non-magnetic particles. This makes it possible to further stabilize the running properties of the medium, and in combination with the effect of the non-magnetic particles mentioned above, 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 addition, in the following examples, all "parts" represent parts by weight.

First, a magnetic layer was formed on a polyethylene terephthalate heath film having a thickness of 10 μm as a support in the following manner.

That is, after using the specified alloy metal magnetic powder shown in the table below and dispersing each component shown in the table below, apply this magnetic paint to 1 μm.
The mixture was filtered through an M filter, 5 parts of polyfunctional isocyanate was added, and the mixture was coated onto a support to a thickness of 2.5 μm and supercalendered to obtain magnetic layers having various compositions shown in the table below.

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

For fatty acids and fatty acid esters, immerse the magnetic tape in cyclohexane for 3 minutes, and extract the fiffl (=g) (weight per 1% magnetic layer) in cyclohexane.
are shown in the table.

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 blank (average particle size 50 mμ) 40 parts Barium sulfate 10 parts Nitrocellulose 25 parts N-2301 (
Made by Nippon Polyurethane) 25 parts Coronate L (〃
) 10 parts cyclohexanone
400 parts methyl ethyl ketone
250 parts toluene
250 parts A wide magnetic film having a magnetic layer of a predetermined thickness and BcR was obtained in this way, and this was wound up.

This film was cut into 8 am width to make each videotape in the table below (corresponding to the numbers of each example and comparative example).
. However, the numerical values after the second column in the table below represent parts by weight.

In addition, when measuring the frequency of scratches on the tape, a 2-inch (
12.65m) @videotape.

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

Lumi S/N: Color video noise meter rshiba
Measured using soku 925 D/IJ. Bypass filter is 10kHz, low pass filter is 4
．． It was performed at 2MHz. The VTR used was an 8n video deck.

Still Image Lifespan: Shows the time in minutes for a still image to degrade by 2 dB. The larger the value, the more durable the magnetic recording medium is.
High wear resistance.

Frequency of Scratches on Tape 2 Using a commercially available VH3 type VTR, the tape was set and run for 1 minute.

After that, the running was stopped, the tape was taken out, and the parts where it ran and the parts 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.

Saturation magnetization: The saturation magnetization of the sample tape is shown in Gauss.

Powder shedding: The sample tape was run on a video deck for 200 hours continuously at 40° C. and 80% to measure powder shedding.

◎ Very good ○ Good △ Fairly good

After running the tape on a video deck for 200 cycles in an atmosphere with edge bending of 23° C./60%, the tape was taken out and the surface was observed to see if there was any bending at the edges.

Dynamic friction coefficient: Tape runability tester TBT-3 at 25°C
00D (Yokohama System Research Institute) Attach tape to chrome-plated stainless steel 4φ pin at 180"! Tape speed l cm/sec % Rotation 2
It was measured at 0 g, and μk was calculated using the following formula.

(The following margins continue on the next page.) From the results shown, it can be seen that by constructing a magnetic tape based on the present invention, tape performance is significantly improved. That is, it is extremely important to set the BET value of whole urine magnetic powder to 45 m/g or more and to limit the amount of fatty acids and fatty acid esters extracted by cyclohexanone.

[Brief explanation of the drawing]

FIGS. 1 and 2 are partially enlarged sectional views showing examples of the magnetic recording medium of the present invention. In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2...Magnetic layer 3...Bank coat layer (80 layers) )4...
...... Overcoat layer (QC layer).

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer contains a binder and metal magnetic powder dispersed in the binder, the magnetic layer further contains a fatty acid and a fatty acid ester, and the ratio of the metal magnetic powder is The magnetic layer has a surface area of 45 m^2/g or more, and the amount of the fatty acid extracted into cyclohexane by immersion in cyclohexane for 3 minutes is 1 m^
4 mg or less per 2 and 3 in cyclohexane
The amount of the fatty acid ester extracted into cyclohexane by immersion in cyclohexane for 5 minutes per 1 m^2 of the magnetic layer is
A magnetic recording medium characterized in that the amount is 100 mg or more and 100 mg or less.