JP2791728B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for high density recording, and more particularly to an improvement in a magnetic recording medium having a coating type magnetic layer.

[0002]

2. Description of the Related Art Magnetic recording technology requires that a medium can be used repeatedly, signals can be easily digitized, and a system can be constructed by combining with peripheral devices.
Video, audio, video, audio, etc.
It has been widely used in various fields including computer applications.

In order to respond to demands for downsizing equipment, improving the quality of recording / reproducing signals, extending recording time, increasing recording capacity, etc., the recording density of recording media has been further improved. Always wanted.

[0004] For example, in audio and video applications, in order to cope with the practical use of a digital recording system for realizing an improvement in sound quality and image quality, and the development of a recording system compatible with a high-definition TV, a conventional system is required. Therefore, a magnetic recording medium capable of recording and reproducing a short wavelength signal has been required.

In addition, in recent years, the spread of personal computers, the advancement of application software, and the processing information processing have been developed for floppy disks having a magnetic layer on a flexible non-magnetic support, which is an external storage medium for microcomputers and personal computers. Due to the trend of increase, it has been strongly required to increase the capacity to 10 Mbytes or more.

[0006] The magnetic recording medium is used in the form of a tape, disk or card depending on the application by forming a magnetic layer on a non-magnetic support. The so-called coating type magnetic layer mainly composed of a ferromagnetic powder obtained by applying and drying a coating solution in which a ferromagnetic powder is dispersed on a non-magnetic support and a binder resin is formed on the magnetic layer by vapor deposition or sputtering. There is a so-called metal thin film type magnetic layer composed of a ferromagnetic metal thin film obtained by vacuum film formation on a non-magnetic support by the vacuum film formation method described above.

[0007] From the viewpoint of recording density, the latter metal thin film type magnetic layer is excellent, and its practical use has been studied for a long time, and has been put to practical use for 8 mm video applications and the like.

However, the metal thin film type magnetic recording medium has problems in characteristics such as durability, running property, corrosion resistance and the like.
In order to deal with the problem, the original excellent characteristics have not been fully utilized. In addition, the production cost is high and there is a problem in economy.

On the other hand, the coating type magnetic layer is superior to the metal thin film type for such a problem and has been put to practical use for various uses since ancient times.
Although many efforts have been made to improve the recording density, which is inferior to the metal thin film type, there is a limit.

From the viewpoint of improving the magnetic characteristics of the magnetic layer, improving the dispersibility of the ferromagnetic powder, and improving the surface properties of the magnetic layer, etc., for achieving high density recording of the coating type magnetic recording medium. Various methods have been studied and proposed.

For example, Japanese Patent Application Laid-Open Nos. 58-122623 and 61-74137 disclose a method of using a ferromagnetic ferromagnetic metal powder or a hexagonal ferrite as a ferromagnetic powder in order to enhance magnetic properties. Japanese Patent Publication No. 62-49656, Japanese Patent Publication No. 60-50323, US Pat.
No. 3, US Pat. No. 4,666,770, and US Pat. No. 4,543,198.

In order to enhance the dispersibility of the ferromagnetic powder, various surfactants (for example, JP-A-52-15660) are used.
No. 6, JP-A-53-15803, JP-A-53-15803
-116114. ) Or various reactive coupling agents (for example,
Nos. 9-59608, JP-A-56-58135, and JP-B-62-28489. ) Has been proposed.

Further, in order to improve the surface properties of the magnetic layer,
There has been proposed a method of improving the surface forming treatment method of a magnetic layer after coating and drying (for example, disclosed in Japanese Patent Publication No. 60-47725).

The above-mentioned ferromagnetic metal powder and hexagonal ferrite are excellent as ferromagnetic powders for high-density recording media, but their electromagnetic conversion characteristics are inferior to metal thin-film magnetic recording media. . In particular, hexagonal ferrite has a problem that its saturation magnetization is small and the magnetic flux density of the magnetic layer cannot be increased. In addition, the dispersibility was poor, and it was difficult to obtain a magnetic layer having excellent surface properties.

However, in spite of the various attempts to achieve high-density recording as described above, in a coating type magnetic recording medium, it is necessary to obtain a magnetic recording medium comparable to a metal thin film type magnetic recording medium. Could not. Therefore, it has been a major task for magnetic recording media to be excellent in practical characteristics such as running properties, durability, and storability, and also excellent in economy, and to meet the demand for high density recording in the future. .

In recent years, in order to increase the short-wavelength output of a magnetic recording medium, a research result focusing on the magnetization reversal mechanism and paying attention thereto has been reported. As one of them, as a measure of the strength of the interaction between the ferromagnetic particles, the remanence curve plotting the remanent magnetization with respect to the applied external magnetic field shows that the AC remanence from the AC demagnetized state and the D
There is a report that a difference ΔM from C remanence is calculated, and for a metal thin film, the difference ΔM is related to noise.
Here, ΔM is ΔM = ｛Id (H) + 2Ir (H) −I
r (∞)｝ / Ir (∞), where Id (H) is the remanent magnetization measured with DC degaussing, Ir (H) is the remanent magnetization measured with AC degaussing, Ir (Ｉ) Is the residual magnetization when the applied magnetic field is 10 kOe (PEKelly et al.
IEEE Trans.MAG.MAG-25 (1989) 3881, PIMayo etal
IEEE Trans. MAG.MAG-26 (1990) 1894, DESpeliotis e
tal J. Appl. Phys 69 (8) 4496 (1991) etc.). In these reports, it is stated that the positive difference ΔM is the direction in which the interaction between the particles is stabilized, and that the negative ΔM indicates the interaction that demagnetizes the magnetic layer. Also, DESpelio
According to tis etal, when a ferromagnetic metal powder is used as a ferromagnetic powder, it is positive when the coercive force is lower than the magnetic recording medium and negative when the coercive force is exceeded.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is excellent in practical characteristics such as running performance, durability and storage properties, economical efficiency, and electromagnetic conversion characteristics. It is an object of the present invention to provide a magnetic recording medium having good recording density and a high recording density, and in particular, to provide a magnetic recording medium having an electromagnetic conversion characteristic comparable to a metal thin film type in a coating type magnetic recording medium. And

[0018]

Means for Solving the Problems The inventor of the present invention focused on the interaction between particles of ferromagnetic powder in the magnetic layer of a coating type magnetic recording medium, and as a result of intensive study to achieve the above object of the present invention, , The difference Δ obtained from the remanence curve
The inventors have found that it is only necessary that the change of M with respect to the applied magnetic field be a specific one, and have found the following configuration of the present invention.

That is, an object of the present invention is to provide a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder resin on a non-magnetic support, wherein the saturation magnetic flux density B
m is equal to or greater than 2500 Gauss, and the difference ΔM = ΔId between the AC remanence from the AC demagnetized state and the DC remanence from the DC demagnetized state obtained from the remanence curve
(H) + 2Ir (H) −Ir (∞)｝ / Ir (∞) has a range where the measurement magnetic field H that is less than the coercive force Hc of the magnetic layer is negative.
The thickness of the magnetic layer is 1 μm or less,
Magnetic powder is ferromagnetic with coercive force of 1500 to 2500 Oe
A magnetic recording medium characterized by being a metal powder (where Id (H) is the residual magnetization when measured with DC degaussing, Ir (H) is the residual magnetization when measured with AC degaussing, Ir ( ∞) is the residual magnetization when the applied magnetic field is 10 KOe (Oersted).)

The remanence curve in the magnetic recording medium of the present invention is a curve representing a change in residual magnetization (Id (H) and Ir (H)) with respect to an external magnetic field H of a magnetic recording medium in an AC erased or DC erased state. It is. The magnetic recording medium according to the present invention uses the I
With respect to the value of ΔM obtained by substituting d (H) and Ir (H) and Ir (∞), which is the residual magnetization when the applied magnetic field is set to 10 kOe, into the above-mentioned formula, a negative value is obtained in a measurement magnetic field equal to or lower than the magnetic layer Hc. There is a portion having a value of

In the present invention, ΔM was determined as follows. AC degaussing the measurement sample of the magnetic recording medium,
Using VSM-5 (vibrating sample magnetometer manufactured by Toei Kogyo Co., Ltd.), the maximum applied magnetic field is 5000 from the applied magnetic field of 0 Oe in increments of 50 Oe.
Ir (H) was measured up to Oe, and a remanence curve was obtained. Thereafter, an external magnetic field of 10,000 Oe was applied, the magnetic field was reduced to zero, and the saturation residual magnetization Ir (∞) was obtained. Next, a maximum applied magnetic field of -5000 Oe was applied, and the remanence curve was measured from 0 Oe to a maximum applied magnetic field of 5000 Oe in increments of 50 Oe. Id (H) is obtained by reversing the sign of the obtained remanence curve.
MAG.MAG-25 (1989) 388
1, PIMayo etal IEEE Trans.MAG.MAG-26 (1990) 189
4, DESpeliotis etal J. Appl. Phys 69 (8) 4496 (1991)
And a remanence curve measured while demagnetizing after saturation magnetization with direct current described in (1). Such conversion may be performed based on the symmetry of the magnetization curve. ΔM with respect to the applied magnetic field is calculated from the thus obtained remanence curve. Actually, a personal computer is operated by a program that calculates ΔM corresponding to the input measurement value,
Change of ΔM with respect to the strength H of the measured magnetic field (H-ΔM curve)
Is plotted, and it is confirmed from the obtained curve that there is a portion where ΔM becomes negative in the measured magnetic field region below Hc of the magnetic recording medium.

The magnetic recording medium of the present invention is characterized in that ΔM obtained from the remanence curve has a portion where the magnetic layer has a coercive force equal to or lower than Hc and has a negative portion. H-Δ, where the measured magnetic field H is the horizontal axis and ΔM is the vertical axis
It is preferable that the ratio of the range where ΔM is positive in the M curve diagram is limited to 80% or less of the entire region of the magnetic layer where the coercive force Hc is equal to or less than Hc. Furthermore, when comparing the area enclosed by the horizontal axis and the H-ΔM curve in the figure, the area of the area where ΔM is negative (first quadrant) is larger than the area of the area where positive ΔM is positive (second quadrant). Preferably, More preferably, it is negative in all regions of the measurement magnetic field below Hc. If the area where the coercive force Hc of the magnetic layer is less than or equal to Hc is much larger than the area where the area is negative, or if the area of the area where ΔM is positive is larger than the area of the area where the area is negative, excellent electromagnetic conversion characteristics are obtained. Cannot be obtained, and the object of the present invention cannot be sufficiently achieved.

In the magnetic recording medium of the present invention, the saturation magnetic flux density Bm is 2500 gauss or more, preferably 2800 gauss or more, and particularly preferably 3000 gauss or more, while ΔM is the above value. If the saturation magnetic flux density is too small, the output will not increase, which is not preferable as a medium for high density recording. By specifying the values of Bm and ΔM of the magnetic layer in this way, the magnetic recording medium of the present invention has a large output particularly in a short wavelength recording wavelength region and has an excellent C / N, and has a high C / N ratio. It has excellent electromagnetic conversion characteristics as a high-density recording medium that can be compared with a thin-film magnetic recording medium.

The C / C provided by the configuration of the magnetic recording medium of the present invention
Regarding the effect on N, the cause is not clear.
The aforementioned PEKelly etal IEEE Trans.MAG.MAG-25 (198
9) 3881, PIMayo etal IEEE Trans.MAG.MAG-26 (199
0) According to 1894, other reports show that when ΔM is negative, C / N is increased in the present invention, despite the fact that it indicates an interaction that demagnetizes the magnetic layer. . In the magnetic layer of the present invention, it is presumed that the fact that the magnetic energy of the magnetic layer is increased to Bm of 2,500 gauss or more has a synergistic effect with the ΔM specified as described above, thereby increasing the C / N. Is done.

Although various methods are conceivable as means for obtaining the magnetic recording medium of the present invention, the most effective method is
An object of the present invention is to use a ferromagnetic powder having a large magnetic property such as a ferromagnetic metal powder by making the filling degree of the ferromagnetic powder relatively high, and to make the thickness of the magnetic layer extremely thin. In particular, the thickness of the magnetic layer is 1 μm or less, preferably 0.05 to 0.5 μm.
It is effective to set the thickness to 8 μm, more preferably 0.1 to 0.5 μm. When the thickness of the magnetic layer is increased, the electromagnetic conversion characteristics are deteriorated. When the thickness is too small, a smooth magnetic layer cannot be obtained, and the output is undesirably reduced.

It is effective to increase the filling degree of the ferromagnetic powder or to use a ferromagnetic metal powder in order to make Bm 2500 gauss or more. The very thin magnetic layer may be formed directly on the non-magnetic support. However, in order to obtain a magnetic layer having a uniform thickness and good surface properties, the non-magnetic layer may be formed on the non-magnetic support. And a magnetic layer is preferably formed thereon. That is, when the magnetic layer is formed directly on the non-magnetic support, the thickness is small, so that the magnetic layer is easily affected by the surface properties of the non-magnetic support, and it is difficult to make the thickness uniform. By first forming a non-magnetic layer on a non-magnetic support and then forming a magnetic layer on it, the influence of the surface properties of the non-magnetic support can be reduced. It becomes easy to make it thick. In particular, a wet-on-wet method in which a coating solution for a magnetic layer is applied thereon while the coating layer for a non-magnetic layer is still wet (simultaneous multilayer coating method;
39929, JP-A-61-54992 and the like. If the upper magnetic layer is formed while the lower non-magnetic layer is in a wet state, the upper magnetic layer can be easily made thinner and coating defects can be reduced. Further, it is preferable because the adhesion to the magnetic layer can be increased.

As described above, in order to obtain the above-mentioned ΔM obtained from the saturation magnetic flux density and the remanence curve of the magnetic layer of the present invention, the thickness of the magnetic layer is considered practically in the conventional coating type. It is necessary to make the magnetic layer in a structure that reduces the effect of demagnetization and enhances the interaction between ferromagnetic powders while keeping the thickness of the ferromagnetic powders as thin as possible and maintaining the degree of filling of the ferromagnetic powders to a certain degree or more. It is considered important.

When the magnetic layer of the present invention is made very thin, the lubricant and the conductive particles cannot be added to the magnetic layer in an excessively large amount in order to make the saturation magnetic flux density Bm be 2500 gauss or more. Forming a magnetic layer on a non-magnetic layer is advantageous because a lubricant or conductive particles can be added to the non-magnetic layer.

In the magnetic recording medium of the present invention, in order to increase the filling degree of the ferromagnetic powder in the magnetic layer, the conditions for applying the magnetic layer on a non-magnetic support and drying and then performing a surface forming treatment with a calender roll are used. It is effective to select as appropriate.
In particular, it is also effective to use a metal or a plastic having a high hardness for the material of the calender roll, or to increase the linear pressure or temperature applied to the magnetic layer.

The calender roll used in the pressure molding process for smoothing the surface of the magnetic layer is epoxy, polyimide, or the like.
Use a heat-resistant plastic roll such as polyamide or polyimide amide. In particular, it is desirable to perform pressure molding with metal rolls in order to obtain a specific value of ΔM obtained from the saturation magnetic flux density and the remanence curve of the magnetic layer of the magnetic recording medium of the present invention. The processing temperature of the pressure molding is 70 ° C. or higher, preferably 80 ° C. or higher. The linear pressure is desirably 200 kg / cm, more preferably 30 kg / cm.
0 kg / cm or more.

Ferromagnetic powder in the magnetic recording medium of the present invention
In order to effectively achieve the object of the present invention , ferromagnetic metal
Use powder. As the ferromagnetic metal powder, Fe or N
i or Co as a main component, Zn, Cr, Mn, Sb,
Mg, Ca, Ba, etc. may be contained. The sintering preventing agent processing when generating the ferromagnetic metal powder in the hydrogen reduction of oxides, alumina, alumina - silica, silica, aluminum
The treatment with a na -boron compound is preferable, and it is preferable to form a stable oxide film by performing a slow oxidation treatment after hydrogen reduction.
As for the particle size of the ferromagnetic metal powder, the average major axis length is 0.05 to 0.4 μm, preferably 0.08 to 0.3 μm, the acicular ratio (average major axis length / average minor axis length) is 3 to 20, Preferably 5 to 15, specific surface area of 35 to 80 m ² / g, preferably 40 to 65 m ² / g, coercive force of 1500 to 2500 Oe, preferably 1500 to 2300 Oe,
The saturation magnetization s is 110 to 160 emu / g, preferably 120 to 155 emu / g. When the particle size is smaller than these ranges, the influence of the surface oxide layer is large and σs is undesirably reduced.

In particular, the saturation magnetic flux density of the magnetic layer of the present invention is 2
In order to attain 500 gauss or more, it is desirable to use a ferromagnetic powder having a saturation magnetization σs of at least 120 emu / g. It is effective to increase the degree of filling (Bm / 4πσs) of the ferromagnetic powder in the magnetic layer as much as possible.

The magnetic properties of the ferromagnetic powder, such as saturation magnetization and coercive force, are values measured using VSM-PI (manufactured by Toei Kogyo Co., Ltd.) at a maximum applied magnetic field of 10 kOe. The specific surface area is Cantersorb (manufactured by Cantarchrome, USA)
Is a value measured by the BET one-point method (partial pressure: 0.30) after dehydration in a nitrogen atmosphere at 250 ° C. for 30 minutes.

The ferromagnetic powder preferably has a water content of 0.01 to 2% by weight. The moisture content is preferably optimized depending on the type of the binder resin. PH of ferromagnetic powder
It is preferable to optimize the combination with the binder resin used. The range is 4 to 12, preferably 5 to 11.

As the binder resin for the magnetic layer in the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As a thermoplastic resin, the glass transition temperature is -1.
00 to 150 ° C, number average molecular weight of 1,000 to 200
000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000.

Examples of such a binder resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester,
Styrene, butadiene, ethylene, vinyl butyral,
There are polymers or copolymers containing vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins.

As the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate.

In order to obtain a better dispersing effect of ferromagnetic powder in the binder resin and the durability of the magnetic layer, COOM, SO3M, OSO3M, P = O (OM)
2, OP = O (OM) 2, (where M is a hydrogen atom,
Or an alkali metal base), OH, NR ² , N ⁺ R ³ (R
Is preferably a hydrocarbon group) obtained by introducing at least one or more polar groups selected from epoxy groups, SH, CN, and the like by copolymerization or addition reaction. The amount of such a polar group is from 10 ^{-1 to} 10 ^-8 mol / g, preferably from 10 ^{-2 to} 10 ^-6 mol / g.

The binder resin used in the magnetic recording medium of the present invention is in the range of 5 to 50% by weight based on the ferromagnetic powder.
Preferably, it is used in the range of 10 to 30% by weight. It is preferable to use 5 to 100% by weight when using a vinyl chloride resin, 2 to 50% by weight when using a polyurethane resin, and 2 to 100% by weight for polyisocyanate in combination.

The filling degree of the ferromagnetic powder in the magnetic layer can be calculated from the maximum saturation magnetization σs and the maximum magnetic flux density Bm of the ferromagnetic powder used (Bm / 4πσs). It is preferably at least 1.7 g / cc, more preferably at least 1.9 g / cc, most preferably at least 2.1 g / cc.

In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 k.
g / cm ² , and the yield point is preferably 0.05 to 10 kg / cm ² .

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate;
Products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL,
CORONATE 2030, CORONATE 2031, Millionet
MR Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenet D-102, Takenet D-110N, Takenet D-
200, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N Desmodur HL, etc. These are used alone or by utilizing the difference in curing reactivity. One or more combinations can be used.

In the magnetic layer of the magnetic recording medium of the present invention, various functions such as a lubricant, an abrasive, a dispersant, an antistatic agent, a dispersant, a plasticizer, an antifungal agent and the like are usually provided. Materials to be contained according to the purpose.

As the lubricant used in the magnetic layer of the present invention, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy poly Siloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms), phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1 to 5 carbon atoms)
Conductive oil such as graphite; inorganic powder such as molybdenum disulfide, tungsten disulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α -An olefin polymer; an unsaturated aliphatic hydrocarbon liquid at room temperature (a compound in which an n-olefin double bond is bonded to a terminal carbon, having about 20 carbon atoms); a monobasic fatty acid having 12 to 20 carbon atoms and carbon Equations 3 to 12
Fatty acid esters, fluorocarbons, etc. composed of individual monohydric alcohols can be used.

Among them, fatty acid esters are more preferred.
The alcohols used as raw materials for fatty acid esters include ethanol, butanol, phenol, benzyl alcohol, 2-methylbutyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, Examples include system monoalcohols such as s-butyl alcohol, and polyhydric alcohols such as ethylene glycol, diethylene glycol, neopentyl glycol, glycerin, and sorbitan derivatives. Similarly, fatty acids include acetic acid, propionic acid, octanoic acid,
Examples include aliphatic carboxylic acids such as ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachinic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid, and mixtures thereof.

Specific examples of the fatty acid ester include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, and 2-hexyldecyl. Stearate, butyl palmitate, 2-ethylhexyl myristate,
A mixture of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol monobutyl ether acylated with stearic acid, diethylene glycol dipalmitate, and hexamethylene diol myristic acid And various ester compounds such as glycerin oleate.

Further, in order to reduce the hydrolysis of fatty acid esters which often occur when the magnetic recording medium is used under high humidity, the fatty acid and alcohol used as the raw material are branched / straight chain, isomer structure such as cis / trans and the like, branch position. A choice is made. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

The following compounds can also be used as the lubricant. That is, silicon oil, graphite, molybdenum disulfide, boron nitride, graphite fluoride, fluorinated alcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide, and the like.

The abrasive used for the magnetic layer of the present invention may be a commonly used material such as fused alumina, silicon carbide,
Chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite) and the like are used.
These abrasives have a Mohs hardness of 6 or more. Specific examples include AKP-10 and AKP-1 manufactured by Sumitomo Chemical Co., Ltd.
2, AKP-15, 20AKP-30, AKP-50,
AKP-1520, AKP-1500, HIT-50,
HIT-100, manufactured by Nippon Chemical Industry Co., Ltd., G5, G7, S-
1, Chromium oxide K, UB40B manufactured by Uemura Kogyo Co., Ltd., WA8000 and WA10000 manufactured by Fujimi Abrasives Co., Ltd., and TF140 and TF180 manufactured by Toda Kogyo Co., Ltd. Those having an average particle size of 0.05 to 3 μm are effective, and preferably 0.1 to 1.5 μm. These abrasives are added in an amount of 1 to 20 parts by weight, preferably 1 to 15 parts by weight, based on 100 parts by weight of the magnetic material. If the amount is less than 1 part by weight, sufficient durability cannot be obtained. If the amount is more than 20 parts by weight, the surface properties and the degree of filling deteriorate, and the structure of the present invention cannot be taken in terms of the saturation magnetic flux density Bm and ΔM. .
These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

The magnetic layer of the magnetic recording medium of the present invention may contain conductive particles as an antistatic agent in addition to the nonmagnetic powder. Particularly, addition of carbon black is preferable from the viewpoint of lowering the surface electric resistance of the entire medium. The carbon black that can be used in the present invention includes furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 1500 m
1/100 g, a particle diameter of 5 to 300 mμ, a PH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / cc are preferable. Specific examples of the carbon black used in the present invention are BLACKPEARLS 2000, 1300, 1 manufactured by Cabot Corporation.
000, 900, 800, 700, VULCAN XC
-72, manufactured by Asahi Carbon, # 80, # 60, # 55, #
50, # 35, manufactured by Mitsubishi Chemical Corporation, # 3950B, # 2
400B, # 2300, # 900, # 1000 # 30,
# 40, # 10B, manufactured by Conlon Via Carbon, CON
DUCTEXT SC, RAVEN 150, 50, 4
0,15, Lion Azo Ketjen Black E
C, Ketjen Black ECDJ-500, Ketjen Black ECDJ-600, and the like.
Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. When carbon black is used for the magnetic layer, the amount based on the magnetic material is 0.1 to 30% by weight.
It is preferable to use it. Further, the nonmagnetic layer preferably contains 3 to 20% by weight based on the total nonmagnetic powder.

In general, carbon black functions not only as an antistatic agent but also to reduce the coefficient of friction, impart light-shielding properties, improve film strength, and the like, and these differ depending on the carbon black used. Therefore, these cars used in the present invention
Bon blacks can be used in different types, amounts and combinations depending on the purpose, based on the above-mentioned various properties such as particle size, oil absorption, conductivity and pH. Carbon black that can be used can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

When a non-magnetic layer is formed below the magnetic layer of the magnetic recording medium of the present invention, the non-magnetic layer is a layer in which ferromagnetic powder is dispersed in a binder resin. Various nonmagnetic powders can be used for the nonmagnetic layer. For example,
α-alumina, β-alumina, γ-
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, corundum, silicon nitride, titanium carbide,
Titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate and the like are used alone or in combination. The particle size of these non-magnetic powders is preferably 0.01 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have a similar particle size distribution to achieve the same effect. You can also. Tap density is 0.3 to 2 g / cc,
It is preferable that the water content is 0.1 to 5% by weight, the pH is 2 to 11, and the specific surface area is 1 to 60 m ² / g. The shape of the nonmagnetic powder may be any of a needle shape, a spherical shape, and a die shape. Specific examples of the nonmagnetic powder used in the present invention include AKP-20, AKP-30, and AK manufactured by Sumitomo Chemical Co., Ltd.
P-50, HIT-50, manufactured by Nippon Chemical Industry Co., Ltd., G5, G
7, S-1, manufactured by Toda Kogyo Co., Ltd., TF-100, TF-12
0, TF-140, Ishihara Sangyo TT055 series,
ET300W, STT30 manufactured by Titanium Industry Co., Ltd., and the like.

The addition of the above-mentioned lubricant or conductive particles which can be used for the magnetic layer to the non-magnetic layer can reduce the thickness of the magnetic layer so that the saturation magnetic flux density Bm of the magnetic layer is maintained at 2500 gauss or more. In order to make ΔM a specific value, it is effective only because the amount of addition to the magnetic layer is limited,
preferable.

These lubricants can be selected and added to the non-magnetic layer in the same manner as the magnetic layer. The amount of the lubricant ranges from 0.2 to 30 parts by weight based on 100 parts by weight of the whole non-magnetic powder. Is added. By adding a lubricant to the non-magnetic layer, a portion lacking in the magnetic layer can be compensated.
In particular, this effect is effective when the magnetic layer is as thin as 1 μm or less because the amount of the lubricant that the magnetic layer can hold is limited. The binder resin for the non-magnetic layer may be the same as that for the magnetic layer.

The coating method for forming the nonmagnetic layer between the magnetic layer and the nonmagnetic support of the magnetic recording medium of the present invention is not particularly limited, and a conventionally known coating method can be used. However, while the coating layer for the non-magnetic layer coated on the non-magnetic support is still wet, the so-called wet-on-coating method such as a wet simultaneous multilayer coating method in which a coating solution for the magnetic layer is coated thereon is applied. Wet systems are most preferred. By adopting this coating method, the adhesion of the magnetic layer to the non-magnetic layer can be increased, and the thickness of the magnetic layer can be reduced to 1.0 μm.
Even if the thickness is very small, the magnetic layer does not peel off, and a magnetic recording medium with excellent running durability in which dropout does not easily occur can be obtained.

In another coating method, for example, a method of applying a non-magnetic coating solution, drying it once to form a non-magnetic layer, and then coating the magnetic layer thereon, if the magnetic layer becomes thinner, The adhesion between the magnetic layer and the magnetic layer was reduced, and it was difficult for the two layers to form an integrated structure as a layer formed on the nonmagnetic support.

As a specific method of the above wet-on-wet method,

(1) First, a lower layer is applied by a gravure coating, roll coating, blade coating, or extrusion coating device which is generally used as a magnetic paint, and while the layer is still in a wet state, for example, -46186, JP-A-60-238179 and JP-A-2-2-2.
No. 65672, a method of applying an upper layer by a non-magnetic support pressurized extrusion coating apparatus,

(2) JP-A-63-88080, JP-A-2-17971 and JP-A-2-265672
A method of applying a lower layer coating liquid and an upper layer coating liquid almost simultaneously by a coating head incorporating two coating liquid passage slits as disclosed in JP

(3) A method in which an upper layer and a lower layer are coated almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In the case of coating by a wet-on-wet method, the flow characteristics of the coating solution for the magnetic layer and the coating solution for the non-magnetic layer should be as close as possible to avoid disturbance of the interface between the coated magnetic layer and the non-magnetic layer. A magnetic layer having a uniform thickness and a small thickness variation can be obtained. Since the flow characteristics of the coating solution strongly depend on the combination of the powder particles and the binder resin in the coating solution,
In particular, it is necessary to pay attention to the selection of the non-magnetic powder used for the non-magnetic layer.

The non-magnetic support of the magnetic recording medium is usually
The thickness is 1 to 100 μm, preferably 3 to 20 μm, and the nonmagnetic layer is 0.5 to 10 μm. It is permissible to form layers other than the magnetic layer and the non-magnetic layer according to the purpose as long as the magnetic layer is the uppermost layer and the non-magnetic layer is the lower layer. For example,
An undercoat layer for improving adhesion may be provided between the nonmagnetic support and the lower layer. This thickness is 0.01 to 2μ
m, preferably 0.05 to 0.5 μm. Also,
A back coat layer may be provided on the side opposite to the magnetic layer side of the non-magnetic support. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known materials can be used for the intermediate layer and the back coat layer. In the case of a disk-shaped magnetic recording medium, the above-mentioned layer structure can be provided on both surfaces or both surfaces.

The non-magnetic support used in the present invention is not particularly limited, and those commonly used can be used. Examples of the material forming the nonmagnetic support include films of various synthetic resins such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, polysulfone, polyethersulfone, and aluminum foil. And metal foils such as stainless steel foils.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is 0.03 μm or less, preferably 0.02 μm in terms of center line average surface roughness Ra (cutoff value 0.25 mm). The thickness is more preferably 0.01 μm or less. Further, it is preferable that these non-magnetic supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and fine organic resin powders such as acryl. The F-5 value of the non-magnetic support used in the present invention in the web running direction is preferably 5 to 50 kg / m.
m ² , the F-5 value in the web width direction is preferably 3 to 30.
kg / mm ² , and the F-5 value in the long hand direction of the web is generally higher than the F-5 value in the web width direction.
This is not always the case when it is necessary to increase the strength in the width direction.

The heat shrinkage of the support in the web running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is 30%. Preferably it is 1% or less, more preferably 0.1%.
5% or less. Breaking strength 5 to 100k in both directions
g / mm ² and an elastic modulus of 100 to 2000 kg / mm ² .

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc.
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate Esters such as glycerol, glycol dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc .;
N-dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The kind and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the intermediate layer if necessary. Using a highly volatile solvent for the first layer to improve the surface properties, using a solvent having a high surface tension (cyclohexanone, dioxane, etc.) for the first layer to improve the coating stability, and dissolving parameters of the second layer. Examples of such a method include increasing the degree of filling using a solvent having a high value, but it is a matter of course that the present invention is not limited to these examples.

The magnetic recording medium of the present invention is prepared by kneading and dispersing the above-mentioned ferromagnetic powder, a binder resin, and other additives, if necessary, using an organic solvent, applying a magnetic paint on a non-magnetic support, It is obtained by orientation and drying as required.

The step of producing the magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All raw materials such as a magnetic substance, a binder, carbon black, an abrasive, an antistatic agent, a lubricant and a solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

For kneading and dispersing the magnetic paint, various kneaders are used. For example, two-roll mill, three-roll mill, ball mill, pebble mill, tron mill, sand grinder, Segvari, attritor, high-speed impeller disperser, high-speed stone mill, high-speed impact mill, disper, kneader, high-speed mixer, homogenizer, ultra A sound disperser or the like can be used.

In order to achieve the object of the present invention, it is needless to say that a known manufacturing technique can be used as a part of the process. However, in the kneading process, a continuous kneader or a pressure kneader is used. By using a material having a strong kneading force such as a die, the high Bm of the magnetic recording medium of the present invention can be obtained for the first time. When a continuous kneader or a pressure kneader is used, all or a part of the magnetic substance and the binder (however, 30% or more of the total binder is preferable) and 15 to 500 parts by weight based on 100 parts by weight of the magnetic substance Is kneaded within the range. Details of these kneading processes are described in JP-A No. 1-10.
No. 6338 and JP-A-64-79274. In the present invention, more efficient production can be achieved by using a simultaneous multilayer coating method as disclosed in JP-A-62-212933.

The residual solvent contained in the magnetic layer of the magnetic recording medium of the present invention is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and the residual solvent contained in the magnetic layer is contained in the non-magnetic layer. It is preferable that the amount is smaller than the contained residual solvent.

The porosity of the magnetic layer is preferably 30% by volume or less for both the non-magnetic layer and the magnetic layer, and more preferably 10% or less.
% By volume or less. The porosity of the non-magnetic layer is preferably larger than the porosity of the magnetic layer, but may be small as long as the porosity of the non-magnetic layer is 5% by volume or more.

Although the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

According to such a method, the magnetic layer coated on the support is subjected to a treatment for orienting the ferromagnetic powder in the layer if necessary, and then the formed magnetic layer is dried. If necessary, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape. The composition for the magnetic layer and the composition for the non-magnetic layer are dispersed together with a solvent, and the obtained coating solution is applied on a non-magnetic material, orientation-dried, and the magnetic layer is placed on the non-magnetic support. To obtain a magnetic recording medium.

The elastic modulus of the magnetic layer at 0.5% elongation is
Desirably 100 to 2000 in both application direction and width direction
kg / mm^TwoAnd the breaking strength is desirably 1 to 30 kg /
cm ^TwoThe elastic modulus of the magnetic recording medium depends on the web application direction and width.
Preferably in the direction of 100 to 1500 kg / mm^TwoThe rest
The run is preferably 0.5% or less and 100 ° C or less.
The heat shrinkage at any temperature is desirably 1% or less,
Preferably 0.5% or less, most preferably 0.1%
It is as follows.

The magnetic recording medium of the present invention may be a tape for video use or audio use, or a floppy disk or magnetic disk for data use.
This is particularly effective for a disk-shaped medium for data recording in which the loss of a signal due to the occurrence of dropout is fatal. Further, by setting the thickness of the magnetic layer to 1 μm or less, it is possible to obtain a high-density, high-capacity magnetic recording disk having high electromagnetic conversion characteristics and excellent overwriting characteristics.

The novel features of the present invention will be specifically described in the following examples.

[0078]

EXAMPLES The present invention will be specifically described with reference to Examples.
In the examples, “parts” indicates “parts by weight”.

[Example 1] (Composition for nonmagnetic layer) Nonmagnetic powder 80 parts of acicular α-Fe2O3 (average particle length 0.25 µm, average acicular ratio 12 BET surface area 35 m ² / g pH4. 0) Carbon black 20 parts (Average primary particle diameter 16 nm, DBP and oil amount 80 ml / 100 g Surface area by BET method 235 m ² / g pH 8.0) Binder resin Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts (- 5 × 10 ⁻⁶ eq / g polar group of N (CH ₃ ) ³⁺ Cl ⁻ Monomer composition ratio 86: 13: 1 Polymerization degree 400) Polyester polyurethane resin 8 parts (Basic skeleton: 1,4-BD / phthalic) Acid / HMDI Molecular weight: 10200 Hydroxyl group: 0.23 × 10 ^-3 eq / g contained -SO ³ Na group: 1 × 10 ^-4 eq / g butyl stearate 1 part stearyl Acid 2.5 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

(Composition for Magnetic Layer) 100 parts of ferromagnetic powder (composition: Fe / Ni / Co 91/4/5 sintering inhibitor: aluminum-silica Hc: 1580 Oe, σs 130 emu / g Specific surface area 57 m ² / g Average major axis length 0.18 μm Needle ratio 10 Crystallite size 170 Å Binder resin Vinyl chloride copolymer 12 parts (containing 1 × 10 ^-4 eq / g of -SO3Na group) Polymerization degree 300 Polyester polyurethane resin 3 parts ( Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group containing 1 × 10 ^-4 eq / g α-alumina (average particle size 0.2 μm) 1.5 parts carbon Black (average particle size 100 nm) 0.5 part Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 200 parts

Each of the composition for the non-magnetic layer and the composition for the magnetic layer was kneaded with a kneader, and then dispersed using a sand grinder. To the resulting dispersion, 5 parts of a polyisocyanate was added to the coating solution for the non-magnetic lower layer, 6 parts to the coating solution for the second layer, and 20 parts of a mixed solvent of 1: 1 methyl ethyl ketone and cyclohexanone. Filtration was performed using a filter having a pore size to prepare a coating solution for forming a nonmagnetic layer and a magnetic layer.

The obtained coating solution for the non-magnetic layer was applied to a thickness of 2 μm after drying, and immediately thereafter, while the coating layer for the non-magnetic layer was still wet, Wet simultaneous multi-layer coating is performed on a 7 μm thick polyethylene terephthalate support so that the layers have a predetermined thickness. While both layers are still wet, an Sm-Co magnet (3000 gauss surface flux) and a solenoid are applied. The magnetic field of the ferromagnetic powder is oriented by an electromagnet (surface magnetic flux of 1500 Gauss), and then the magnetic layer is dried, calendered at a roll temperature of 90 ° C. using a seven-stage calender composed of metal rolls, and subjected to calendering. The magnetic recording medium of Example 1 was slit, and it was slit into an 8 mm width to prepare a sample of an 8 mm video tape (Examples 1-1 to 1-3).

[0083] Separately, Comparative Example to create a sample applied directly to the non-magnetic support as a magnetic layer thickness without forming a nonmagnetic layer of the lower layer is 1.5μm or 2.5 [mu] m 1-1 or
The other was 1-2. The magnetic properties were measured using a vibrating sample magnetometer VSM-5 manufactured by Toei Kogyo with an applied magnetic field of 5 kOe.

Further, ΔM was measured for the obtained sample. The results are shown in FIGS. Figure 1 shows the actual 1-2.
FIG. 2 is a diagram showing an H-.DELTA.M curve of the ratio 1-3 and FIG. The ΔM of the actual 1-1 was almost the same as that of FIG. 1, and the ΔM of the ratio 1-1 was almost the same as that of FIG. From the graph of ΔM, the coercive force Hc of each sample is 1
The results of reading the ΔM at a magnetic field of × 2, 1 × and 1.5 × are shown in Tables 1 and 2 below.

Using a FUJIX8 8-mm video deck manufactured by Fuji Photo Film Co., Ltd., signals of 1 MHz and 7 MHz were recorded, and the reproduction output when reproducing these signals was read from an oscilloscope and measured.

On the other hand, C / N was determined from the video sensitivity of 7 MHz obtained by reading the peak value of the RF output from the oscilloscope, and the noise of 6 MHz measured by the 925R-1 NTSC color noise meter manufactured by Shibasoku. The measurement results are shown in Table 1 below.

[0087]

[Table 1]

[0088]

[Table 2]

[Example 2] (Composition of magnetic layer) 100 parts of ferromagnetic powder (Composition: Fe / Ni / Co 91/4/5 Sintering inhibitor: Aluminum-silica Hc: 1610 Oe, σs 135 emu / g Specific surface area 40 m ² / g Average major axis length 0.30 μm Needle ratio 12 Crystallite size ２３０ 230 Å Binder resin 12 parts of vinyl chloride copolymer (containing 1 × 10 ⁻⁴ eq / g of —SO 3 Na group) Polymerization degree 300 Polyester Polyurethane resin 3 parts (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group containing 1 × 10 ^-4 eq / g) α-alumina (average particle size 0.2 μm) 1.5 parts Carbon black (average particle size 100 nm) 0.5 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone and silicone Clohexanone 1: 1 mixed solvent 200 parts

A coating solution for a magnetic layer having the above composition was prepared under the same conditions as in Example 1, and the coating solution for a non-magnetic layer prepared in Example 1 was further dried to a thickness of 3 μm after drying. Immediately after the non-magnetic layer coating layer is in a wet state, the thickness of the non-magnetic layer is adjusted so that the thickness of the dried magnetic layer is 0.4 μm.
A wet simultaneous multi-layer coating was performed on a non-magnetic support of μm polyethylene terephthalate, and the layers were randomly oriented and dried while both layers were still wet. Then, on the uncoated side, the thickness of the non-magnetic lower layer coating solution prepared in Example 1 after drying was 3 μm, and immediately thereafter, the thickness of the upper magnetic layer was 0.4 μm thereon. Was applied simultaneously, and while both layers were still in a wet state, they were oriented in a random magnetic field and dried. A calendering process was performed at a roll temperature of 70 ° C. using a seven-stage calender composed of metal rolls, and punched out into a 3.5-inch disk to prepare a floppy disk sample.

Separately, for comparison, a magnetic layer was coated directly on a non-magnetic support so that the thickness of the magnetic layer was 2 μm without providing a non-magnetic layer on both sides, and a random magnetic field was oriented and dried. The roll temperature was set to 70 ° C. using a seven-stage calender composed of metal rolls, and calendering was performed to prepare a 3.5-inch floppy disk sample. The magnetic properties were measured using a vibrating sample magnetometer VSM-5 manufactured by Toei Kogyo with an applied magnetic field of 5 kOe. ΔM of the obtained sample was measured under the same conditions as in Example 1. FIG. 4 shows the second embodiment.
-1 and the ΔM of Comparative Example 2 showed almost the same changes as in FIG. From these figures, it can be seen that the coercivity Hc of the magnetic layer is 1/2 times, 1
Tables 3 and 4 show the results of reading the ΔM at the measurement magnetic field of 1.5 times and 1.5 times.

A modified drive for a 3.5-inch floppy disk (MIG with a head gap of 0.25 μm)
The output when recording and reproducing signals of 15 kFRPI and 100 kFRPI using a head was measured.

Comparative Example 3 An 8-mm video was produced under the same conditions as in Example 1-2, except that the ferromagnetic powder was changed to ferromagnetic barium ferrite powder comprising the following plate-like particles. A tape sample was made. FIG. 5 shows an H-ΔM curve of the magnetic layer. Part of Fe ³⁺ is Co-
Hexagonal barium ferrite substituted with Ti (Average particle diameter (plate diameter): 0.05 μm, average plate ratio (plate diameter / plate thickness): 3, specific surface area: 35 m ² / g, coercive force Hc:
1150 Oe, saturation magnetization: 60 emu / g)

[0094]

[Table 3]

[0095]

[Table 4]

Example 3 (Composition for Magnetic Layer) An 8 mm video tape sample was prepared under the same conditions as in Example 1 except that the composition of the magnetic layer was changed to the following. did. (Composition of magnetic layer) 100 parts of ferromagnetic powder (Composition: Fe / Ni / Co 91/4/5 Sintering inhibitor: Aluminum-silica Hc: 1550 Oe, σs 120 emu / g Specific surface area 53 m ² / g Average major axis length 0.15 μm Needle ratio 10 Crystallite size 子 160 Å Binder resin Vinyl chloride copolymer 15 parts (containing 1 × 10 ⁻⁴ eq / g of —SO 3 Na group) Polymerization degree 300 Polyester polyurethane resin 5 parts (neopentyl glycol) / Caprolactone polyol / MD I = 0.9 / 2.6 / 1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g α-alumina (average particle size 0.2 μm) 10 parts carbon black (average particle size) 2.5 parts Butyl stearate 1 part Stearic acid 2 parts 1: 1 mixed solution of methyl ethyl ketone and cyclohexanone 200 parts

Comparative Example 4 (Composition for Magnetic Layer) An 8 mm video tape sample was prepared under the same conditions as in Example 1 except that the composition of the magnetic layer was changed to the following. did. (Composition of magnetic layer) 100 parts of ferromagnetic powder (Composition: Fe / Ni / Co 91/4/5 Sintering inhibitor: Aluminum-silica Hc: 1550 Oe, σs 120 emu / g Specific surface area 53 m ² / g Average major axis length 0.15 μm Needle ratio 10 Crystallite size 子 160 Å Binder resin Vinyl chloride copolymer 15 parts (containing 1 × 10 ⁻⁴ eq / g of —SO 3 Na group) Polymerization degree 300 Polyester polyurethane resin 5 parts (neopentyl glycol) / Caprolactone polyol / MD I = 0.9 / 2.6 / 1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g α-alumina (average particle size 0.2 μm) 15 parts carbon black (average particle size) 100 nm) 4 parts Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone and cyclohexanone 1: 1 mixed solvent 2 00 parts Evaluation results of Example 3 and Comparative Example 4 are shown in Tables 5 and 6.

[0098]

[Table 5]

[0099]

[Table 6]

[0100]

The saturation magnetic flux density Bm of the magnetic layer is set to 2500 Gauss or more, and the AC remanence from the AC demagnetized state and the D from the DC demagnetized state obtained from the remanence curve are obtained.
By making the difference ΔM from the C remanence have a negative region in the range of the measured magnetic field below Hc of the magnetic layer,
The C / N of the coating type magnetic recording medium can be made to have characteristics comparable to those of the metal thin film type magnetic recording medium.

[Brief description of the drawings]

FIG. 1 is a graph showing an H-ΔM curve of Example 1-2.

FIG. 2 is a graph showing an H-ΔM curve of Example 1-3.

FIG. 3 is a graph showing an H-ΔM curve of Comparative Example 1-2.

FIG. 4 is a graph showing an H-ΔM curve of Example 2-1.

FIG. 5 is a graph showing an H-ΔM curve of Comparative Example 3.

Claims (4)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder resin on a nonmagnetic support, wherein the saturation magnetic flux density Bm of the magnetic layer is 2500 gauss or more, and the remanence curve △ M = ｛Id (H) + 2Ir (H) -I between AC remanence from the AC demagnetized state and DC remanence from the DC demagnetized state obtained from
r (∞)} / Ir ( ∞) have a range which is negative with coercivity Hc less measurement magnetic field H of the magnetic layer, the thickness of the magnetic layer is 1
μm or less, and the ferromagnetic powder has a coercive force of 150
A magnetic recording medium characterized by being a ferromagnetic metal powder of 0 to 2500 Oe . Here, Id (H) is the residual magnetization when measured with DC degaussing, Ir (H) is the residual magnetization when measured with AC degaussing, and Ir (∞) is the applied magnetic field.
This is the residual magnetization when KOe (Oersted) is used. 2. Between the magnetic layer and the non-magnetic support.
The magnetic recording medium according to claim 1, further comprising a nonmagnetic layer mainly composed of a nonmagnetic powder and a binder . 3. The magnetic layer , wherein the coating layer of the nonmagnetic layer is
While in the wet state, apply the coating solution for the magnetic layer on the coating layer.
3. The magnetic recording medium according to claim 2 , wherein the magnetic recording medium is formed by fabric . 4. The non-magnetic layer contains conductive particles.
The magnetic recording medium according to claim 2 .