JP2001134922A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in electromagnetic conversion characteristics and running durability. SOLUTION: Relating to the magnetic recording medium having a ground layer which is provided on a non-magnetic substrate and includes a non-magnetic powder or ferromagnetic powder and a bonding agent and at least one magnetic layer which is provided on the ground layer and in which the ferromagnetic powder and the bonding agent are dispersed, the ferromagnetic metal powder consists essentially of Fe and contains 10-40 atom% Co, 2-20 atom% Al and 1-15 atom% Y based on Fe and an organophosphorous compound represented by the following formula is contained in at least the magnetic layer. [(R)m-ϕ-O]n- P(=O)(OH)3-n wherein R denotes a substituted or unsubstituted alkyl, aryl or aralkyl group and m=1-5 and n=1 or 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for providing a magnetic layer in which a ferromagnetic fine powder and a binder are dispersed on at least one surface of a nonmagnetic support, The present invention relates to a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability in a magnetic recording medium provided with a nonmagnetic coating layer in which a magnetic layer is dispersed on a nonmagnetic support.

[0002]

2. Description of the Related Art As a magnetic recording medium for audio, video, computer and the like, a magnetic recording medium having a magnetic layer in which a ferromagnetic powder is dispersed in a binder on a non-magnetic support has been used. I have. In recent years, even in the field of home video tape recorders, the practical use of digital recording with less deterioration of recording has been progressing from conventional analog recording, but generally more signals are recorded in digital recording than in analog recording. In addition, the recording / reproducing apparatus and the recording medium to be used are required to have high image quality and high sound quality, and at the same time, to be downsized and space-saving. In order to achieve high-density recording, it is necessary to shorten the wavelength of the recording signal and narrow the track of the recording locus, which requires finer ferromagnetic powder, higher filling, ultra-smoothing of the medium surface, etc. At the same time, the writing speed and reading speed of the recording medium need to be reduced, and the number of rotations of the cylinder and the transport speed of the magnetic tape have been improved.

In a device using a magnetic recording medium, there is a problem that the magnetic head is stained because the medium and the magnetic head are in sliding contact with each other. In particular, in a device for high-density recording, the rotation speed of a magnetic head is increasing, and in a digital video tape recorder, the rotation speed of a magnetic head is 9600 rotations / minute, which is one of the home-use analog video tape recorders.
The rotation speed is much higher than 800 rotations / minute and 5000 rotations / minute for business use. The sliding speed between the magnetic recording medium and the magnetic head increases, and small magnetic heads such as thin-film heads are used. ing. Therefore, while the tape is running repeatedly, dirt adheres to the magnetic head and the reproduction output decreases, causing an increase in errors due to dropout, and significantly reducing the reliability of data recording and reproduction. Happens.

[0004] In order to solve such a problem, ferromagnetic metal powder is highly dispersed in a binder so that magnetic recording can be performed stably even in high-density recording and reproduction. In order to provide a medium, it has been proposed to use a dispersant such as an organic phosphorus compound in a magnetic layer. For example, Japanese Unexamined Patent Publication (Kokai) No. 1-189025 discloses that an acid, an alkali metal salt, a quaternary ammonium salt is used for a magnetic layer comprising a mono- or di-ester or an organic phosphorus compound selected from substituted or unsubstituted alkyl, alkenyl and aryl groups. It describes salts and the like, and specifically, it has been proposed to improve dispersibility by using phenylphosphonic acid. However, there has been a problem in performing a high degree of dispersion of ferromagnetic powder suitable for high-density recording.

Japanese Patent Application Laid-Open No. 58-171720 describes a magnetic recording medium in which a magnetic layer contains an alkyl phosphate having 6 or more carbon atoms. However, there is no description that a magnetic recording medium having excellent characteristics can be obtained by combining an alkyl phosphate and a specific ferromagnetic powder.

It has also been proposed to provide a magnetic recording medium having excellent characteristics by using a ferromagnetic powder having a specific composition in a high-density recording medium.
For example, Japanese Patent Application Laid-Open No. 10-162351 discloses that the long axis length and crystallite size of a ferromagnetic metal powder are specified,
It is described that an excellent balance between input / output characteristics and overwrite characteristics is achieved by specifying the composition, the thickness of the magnetic layer, and the like, and a magnetic recording medium with extremely low noise can be obtained.

However, although the use of a dispersant is described in the specification, the use of a fatty acid ester and a fatty acid is only specifically proposed, and the dispersibility of the ferromagnetic powder is Insufficient. Also, Japanese Patent Application Laid-Open No. 10-208235 discloses that 10
A magnetic recording medium containing Al atoms of up to 20 atm% or further containing Si and Y has been proposed. By using a specific ferromagnetic powder, dirt adhering to a magnetic head can be reduced, and reproduction can be performed even when used repeatedly. It discloses that a recording medium with a small decrease in output and capable of recording and reproducing data stably can be obtained. However, the use of phenylphosphonic acid together with a fatty acid or the like is specifically described as a dispersant, but the dispersibility of the ferromagnetic metal powder is not yet sufficient.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a non-magnetic coating layer in which a non-magnetic powder is dispersed in a binder is provided on at least one surface of a non-magnetic support, and is further bonded to at least a ferromagnetic fine powder. In a magnetic recording medium having a lower non-magnetic layer provided with a magnetic layer in which an agent is dispersed, an object is to provide a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability. It is an object of the present invention to provide a magnetic recording medium that maintains output, is smooth, and has little dropout. More specifically, the present invention provides a magnetic recording medium in which the lower layer has high smoothness and, consequently, the magnetic layer has excellent smoothness and electromagnetic conversion characteristics. It is an object of the present invention to provide a magnetic recording medium excellent in storability and a magnetic recording medium excellent in storability under high temperature and high humidity.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lower layer containing a nonmagnetic powder or a ferromagnetic powder and a binder on a nonmagnetic support, and dispersing the ferromagnetic powder and the binder thereon. In a magnetic recording medium provided with at least one magnetic layer, the ferromagnetic metal powder contains Fe as a main component, and 10 to 40 atomic% of Co, 2 to 20 atomic% of Al,
The problem is solved by a magnetic recording medium containing 1 to 15 atomic% of Y and containing at least the organic phosphorus compound represented by the following formula in the magnetic layer. [(R) _m -φ-O] _n -P (＝ O) (OH) _3-n where R represents a substituted or unsubstituted alkyl group, aryl group or aralkyl group. Further, m = 1 to 5, n = 1 or 2, wherein R in the organic phosphorus compound is an unsubstituted or substituted aryl group or aralkyl group.

The ferromagnetic metal powder has a major axis length of 0.05 μm.
Not less than 0.13 μm and crystallite size of not less than 8 nm and not more than 20
nm or less, and the thickness of the magnetic layer is 0.05 μm or more and 0.5 μm or less. The coercive force of the ferromagnetic metal powder is 155 to 219 kA / m, σ
_The above magnetic recording medium, wherein _S is 140 to 170 Am ² / kg and the specific surface area by the BET method is 30 m ² / g or more and 50 m ² / g or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention is made strong by using a specific organic phosphorus compound as a dispersant and an iron alloy having a specific composition of Co, Al and Y as a ferromagnetic powder. An object of the present invention is to provide a magnetic recording medium that has improved dispersibility of magnetic powder and excellent electromagnetic conversion characteristics.

The organic phosphorus compound that can be used as a dispersant in the present invention is represented by the following general formula. [(R) _m -φ-O] _n -P (＝ O) (OH) _3-n where R represents a substituted or unsubstituted alkyl group, aryl group or aralkyl group. m = 1 to 5 (where m ≧ 2
In the case, the substituents may be the same or different.) N = 1 or 2.

In the organic phosphorus compound of the present invention, the alkyl group preferably has 1 to 22 carbon atoms, and may be linear or branched. Specifically, methyl, ethyl, (iso) propyl, (iso, s-, t
-) Butyl group, (iso, neo, t-) pentyl group, 1-
Methylbutyl group, (iso) hexyl group, (iso) heptyl group, (iso) octyl group, 2-ethylhexyl group,
(Iso) nonyl group, (iso) decyl group, (iso) undecyl group, (iso) dodecyl group, (iso) hexadecyl group, (iso) octadecyl group, (iso) eicosyl group and the like. In addition, (iso) such as (iso) propyl group indicates any of propyl group, isopropyl group and the like.

The aryl group includes a phenyl group, a toluyl group, a xylyl group, an ethylphenyl group, a cumenyl group,
And a biphenylyl group. Examples of the aralkyl group include a benzyl group, a phenethyl group, an α-methylbenzyl group, a 1-methyl-1-phenethyl group, and a diphenylmethyl group. Examples other than the hydrocarbon group include a methoxy group, a butoxy group, an amino group, a nitro group, and a halogen-containing hydrocarbon such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ . Further, an alkyl group, an aryl group, or an aralkyl group substituted with a group other than the above-mentioned hydrocarbon group may be used.

Among the above specific examples, a substituent having an aromatic ring is preferable, and a phenyl group, a benzylphenyl group and a 1-methyl-1-phenethyl group are particularly preferable. Specific examples include the following mono-1-methyl-1-phenylethylphenyl phosphate, monooctylphenyl phosphate, and mono-tert-butylphenyl phosphate.

[0016]

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Such an organic phosphorus compound has a property of adsorbing or bonding with the above-mentioned polar group, and is mainly located on the surface of the ferromagnetic powder in the magnetic layer, and is mainly located on the surface of the non-magnetic powder in the non-magnetic layer. It is presumed that they exist in a state of being adsorbed or bonded by the polar group on the surface of the polymer. In particular, the adsorptive power of metal surfaces, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. on metal compound surfaces is higher than that of carboxylic acids and sulfonic acids. Since the organic phosphoric acid compound used in the present invention has a strong adsorbing power, the organic phosphorus compound once adsorbed is difficult to desorb from the surface of the metal or the metal compound. Therefore, the surface of the ferromagnetic powder or non-magnetic powder of the present invention is in a state in which the organophosphorus compound is strongly adsorbed and is covered with an aromatic ring or the like. It is presumed that the affinity for the ferromagnetic powder or non-magnetic powder is improved, and the dispersion stability of the ferromagnetic powder or non-magnetic powder is also improved.

Further, since the ferromagnetic powder or non-magnetic powder and the binder cause a strong interaction due to the action of the organic phosphorus compound, desorption of the ferromagnetic powder or non-magnetic powder does not occur, so that the running property and running durability can be improved. It is considered that the property is significantly improved. Furthermore, since the organic phosphorus compound used in the present invention has lower water absorption than other organic compounds such as sulfonic acid, it has good water resistance and durability.

The effect of adding the organic phosphorus compound used in the present invention can be seen even when used in a nonmagnetic layer. The thickness of the magnetic layer is about 0.2 μm, which is very thin compared to about 2 μm of the non-magnetic lower layer. Will be reflected.

In addition, during storage for a long period of time or under high temperature and high humidity, a binder component and the like free from the magnetic layer or the lower non-magnetic layer oozes out on the surface of the magnetic layer and causes dropout, head and running system stains, and the like. In some cases, however, it was found that this can be prevented by adding the organic phosphorus compound of the present invention also to the lower nonmagnetic layer.

In the magnetic layer or the lower non-magnetic layer of the present invention, the organic phosphorus compound is contained in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the ferromagnetic powder or the non-magnetic powder. include. Especially when its content is 0.5
By setting the content within the range of ~ 15 parts by weight, a phenomenon such as an increase in the glossiness of the surface of the magnetic layer or the non-magnetic layer appears,
It can be seen that the ferromagnetic powder or non-magnetic powder has a good dispersion state. Further, by setting the content in the range of 1 to 10 parts by weight, the electromagnetic conversion characteristics are remarkably improved. If the content is less than 0.1 part by weight, the effect of the compounding may not be effectively exhibited, and if the content is more than 20 parts by weight, the dispersion state of the ferromagnetic powder or the nonmagnetic powder is further improved. May not.

As a method for improving the dispersibility of the ferromagnetic powder or non-magnetic powder by incorporating the above-mentioned organic phosphorus compound in a magnetic layer or a non-magnetic layer, the organic phosphorus compound is dissolved in a low boiling point organic solvent or After the ferromagnetic powder or non-magnetic powder is put into the solution and mixed therein, the organic solvent is removed to prepare a ferromagnetic powder or non-magnetic powder which has been pre-treated with an organic phosphorus compound. A method for producing a magnetic recording medium using the treated ferromagnetic powder, and when preparing a coating solution for a magnetic layer or a coating solution for a non-magnetic layer, the organic phosphorus compound directly or preferably for the magnetic layer A method of kneading and dispersing the mixture by dissolving or dispersing it in a part of the solvent for the coating liquid or the coating liquid for the nonmagnetic layer can be used. In particular, when the organic phosphorus compound of the present invention is kneaded and dispersed in a solvent with a magnetic or non-magnetic powder, it is extremely strongly adsorbed on the powder surface.

In addition, by using a ferromagnetic powder containing iron, cobalt, aluminum and yttrium as a main component together with a dispersant comprising an organic phosphorus compound in the present invention, the electromagnetic conversion characteristics can be improved. An excellent magnetic recording medium can be obtained.

In the ferromagnetic powder, besides these predetermined atoms, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
It may contain atoms such as d, P, Co, Mn, Zn, Ni, Sr, and B. More specifically, Co
Is 10 to 40 atomic%, Al is 2 to 20 atomic%, and Y is 1 to
Those containing 15 atomic% are preferred.

These ferromagnetic powders include a dispersant, a lubricant,
The treatment may be carried out in advance with a surfactant, an antistatic agent or the like before dispersion. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The water content of the ferromagnetic powder is preferably 0.01 to 2%. The moisture content of the ferromagnetic powder can be adjusted depending on the type of the binder.

The specific surface area (S _BET ) of the ferromagnetic powder used in the magnetic layer of the present invention by the BET method is 30 m ² / g or more.
It is preferably less than 0 m ² / g. Furthermore, 38 to 48 m ² / g
Is preferred. This makes it possible to achieve both good surface properties and low noise.

It is preferable that the pH of the ferromagnetic powder is optimized by a combination with the binder used. The range is 4-1
2, but preferably 7 to 10. The ferromagnetic powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof. The amount is 0.1 to
When the surface treatment is performed, the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less, which is preferable.

Soluble Na, Ca, F is contained in the ferromagnetic powder.
may contain inorganic ions such as e, Ni, and Sr.
If it is not more than 00 ppm, there is little influence on the characteristics. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. Further, the shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the characteristics of the particle size described above are satisfied. In the case of acicular ferromagnetic powder, the acicular ratio is preferably from 4 to 12, more preferably from 5 to 12.

The major axis length of the ferromagnetic metal powder is 0.05 μm or more.
0.13 μm, preferably 0.07 μm to 0.1
2 μm, particularly preferably 0.08 μm to 0.11
μm. The crystallite size is from 8 nm to 20 nm, preferably from 10 nm to 18 nm, particularly preferably 12 n
m to 16 nm. The major axis diameter is determined by, for example, taking a transmission electron microscope photograph and directly reading the minor axis diameter and the major axis diameter of the ferromagnetic powder from the photograph, a method of reading the transmission electron microscope photograph with an image analyzer, or the like. Can be The thickness of the magnetic layer is 0.05 μm or more in order to improve the input / output characteristics in high output, especially in a high frequency range exceeding 20 MHz.
0.5 μm is required, preferably 0.1 μm
0.3 μm, more preferably 0.11 μm to 0.27 μ
m.

In order to stably apply this ultra-thin magnetic layer, a lower non-magnetic layer containing an inorganic powder is interposed on a support, and a magnetic layer is applied thereon on a wet-on-wet basis. It is desirable. Coercive force Hc of ferromagnetic metal powder
Is preferably 155~219kA / m, further preferably 159~183kA / m, the sigma _s, preferably 140~170Am ² / kg, more preferably 145
１６０160 Am ² / kg.

The magnetic recording medium of the present invention has a non-magnetic lower layer coated with a non-magnetic powder dispersed in a binder on a non-magnetic support. The nonmagnetic powder that can be used for the nonmagnetic lower layer may be an inorganic substance or an organic substance. Further, carbon black or the like can be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α
Α-alumina, β-alumina, γ with a conversion of 90 to 100%
-Alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium sulfate, silicon carbide, carbonized Titanium or the like is used alone or in combination of two or more. Of these, α-iron oxide and titanium oxide are preferred.

The average particle size of these non-magnetic powders is 0.005.
The thickness is preferably from 2 μm to 2 μm, but if necessary, nonmagnetic powders having different average particle diameters may be combined, or even a single nonmagnetic powder may have the same effect by broadening the particle size distribution.
Particularly preferred is 0.01 μm to 0.2 μm. If it is less than 0.005 μm, dispersion tends to be difficult, and if it is more than 2 μm, the surface roughness tends to increase.

The pH of the nonmagnetic powder is preferably from 2 to 11, and the pH is particularly preferably from 6 to 9. If the pH is less than 2, the friction coefficient under high temperature and high humidity tends to increase. On the other hand, when the pH is higher than 11, the release amount of the fatty acid decreases, and the friction coefficient tends to increase.

The specific surface area of the non-magnetic powder is 1 to 100 m ² /
g, preferably 5 to 70 m ² / g. And more preferably it is 10-65 m < ² > / g. If it is less than 1 m ² / g, the surface roughness tends to increase,
If it is more than 0 m ² / g, dispersion tends to be difficult, for example, the desired amount of binder cannot be dispersed.

The tap density is 0.05 g / ml to 2 g / m
1, preferably from 0.2 g / ml to 1.5 g / ml. If it is less than 0.05 g / ml, the amount of particles scattered tends to be large, making the operation difficult. If it is larger than 2 g / ml, it tends to stick to the device and the operation tends to be difficult.

The water content of the nonmagnetic powder is 0.1 to 5% by weight,
Preferably 0.2 to 3% by weight, more preferably 0.3 to 3% by weight.
1.5% by weight. If it is less than 0.1% by weight, dispersion tends to be difficult. If it is more than 5% by weight, the viscosity of the paint after dispersion tends to be unstable.

The nonmagnetic powder has a crystallite size of 0.004 μm.
m to 1 μm is preferable, and 0.04 to 0.1 μm is more preferable. If it is smaller than 0.004 μm, dispersion tends to be difficult. If it is larger than 1 μm, the surface roughness tends to increase. In addition, dibutyl phthalate (DB
The oil absorption using P) is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 100 ml / 100 g.
６０60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. Further, the shape of the nonmagnetic powder may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. Ignition loss is 20
% By weight or less, and a material having a small ignition loss is preferable. When the non-magnetic powder is an inorganic powder, the Mohs' hardness is preferably 4 or more and 10 or less.
If the Mohs hardness is smaller than 4, durability tends to be insufficient. The stearic acid adsorption amount of the inorganic powder is 1 to 20
μmol / m ² , more preferably ^{2 to} 15 μmol / m ²
It is. The heat of wetting in water at 25 ° C. of the lower coating layer Non-magnetic powder is preferably in the range of ^{0.2J / m 2 ~0.6J / m 2} .

A solvent having a heat of wetting within this range can be used. The amount of water molecules on the surface at 100 to 400 ° C is suitably 1 to 10/10 nm. The pH of the isoelectric point in water is preferably between 3 and 9.

On the surface of these nonmagnetic powders, Al_TwoO_Three,
SiO_Two, TiO_Two, ZrO_Two, SnO_Two, Sb_TwoO_Three, Z
It is preferable to perform surface treatment with nO. Especially preferred for dispersibility
What's new is Al_TwoO_Three, SiO_Two, TiO_Two, ZrO_TwoIs
However, more preferred is Al_TwoO _Three, SiO_Two, ZrO_Two so
is there. These may be used in combination or used alone.
You can also. Also, coprecipitated surface treatment
A physical layer may be used.
Treatment of the surface layer with silica or vice versa
Can also be taken. In addition, there are many surface treatment layers depending on the purpose.
Although it may be a porous layer, it is generally better to be homogeneous and dense.
Is preferred.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotight manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and DPN-2 manufactured by Toda Kogyo.
50, DPN-250BX, DPN-245, DPN-
270BX, DPB-550BX, DPN-550RX
Titanium oxide TTO-51B, TTO-55 manufactured by Ishihara Sangyo
A, TTO-55B, TTO-55C, TTO-55
S, TTO-55D, SN-100, MJ-7, α-iron oxide E270, E271, E300, ST manufactured by Titanium Industry
T-4D, STT-30D, STT-30, STT-6
5C, Teika MT-100S, MT-100T, MT
-150W, MT-500B, MT-600B, MT-
100F, MT-500HD, FINEX-2 manufactured by Sakai Chemical
5, BF-1, BF- 10, BF-20, ST-M, Dowa Mining Ltd. DEFIC-Y, DEFIC-R, manufactured by Japan Aerosil AS2BM, TiO ₂ P25, manufactured by Ube Industries, Ltd. 100
A, 500A, Y-LOP manufactured by Titanium Kogyo Co., Ltd. and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

The lower non-magnetic layer is coated with a non-magnetic powder together with a non-magnetic powder.
By mixing Bon Black, the surface electric resistance (Rs) can be reduced, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. The micro Vickers hardness of the lower non-magnetic layer is usually 245 to 245.
588 MPa, preferably 294 to 490 MPa for adjusting the head contact, using a thin film hardness tester (NEC HMA-400) to indent a diamond triangular pyramid needle with a ridge angle of 80 degrees and a tip radius of 0.1 μm. It can be measured using the tip.

It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a magnetic tape for VHS. For this purpose, carbon black such as furnace black for rubber, thermal black for rubber, carbon black for color, and acetylene black can be used.

[0043] The specific surface area of carbon black employed in the nonmagnetic layer of the present invention is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption amount from 20 to 40
0 ml / 100 g, preferably 30-200 ml / 10
0 g. Particle size of carbon black is 5-80n
m, preferably 10 to 50 nm, more preferably 10 to
40 nm. PH of carbon black is 2-10,
Moisture content is 0.1-10%, tap density is 0.1-1g /
ml is preferred. Specific examples of carbon black used in the present invention include BLACKPE manufactured by Cabot Corporation.
ARLS 2000, 1300, 1000, 900, 8
00, 880, 700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd., # 3050B, 3150B, 3250
B, # 3750B, # 3950B, # 950, # 650
B, # 970B, # 850B, MA-600, manufactured by Columbia Carbon, CONDUCTEX SC, RAVE
N 8800, 8000, 7000, 5750, 525
0,3500,2100,2000,1800,150
0, 1255, 1250, manufactured by Akzo Ketjen Black EC, and the like. Carbon black may be surface-treated with a dispersant or the like, grafted with a resin, or used, or a part of the surface may be graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in a range not exceeding 50% by weight based on the inorganic powder and in a range not exceeding 40% of the total weight of the nonmagnetic layer. These carbon blacks can be used alone or in combination.

Further, an organic powder may be added to the lower layer for the purpose of, for example, adjusting the micro Vickers hardness to adjust the head contact or the paint viscosity. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used.

Also, in the magnetic recording medium of the present invention,
An undercoat layer may be provided. By providing the undercoat layer, the adhesive strength between the support and the magnetic layer or the lower non-magnetic layer can be improved. As the undercoat layer, a polyester resin or the like which is soluble in a solvent is used. The undercoat layer preferably has a thickness of 0.5 μm or less. In the magnetic recording medium of the present invention, a polar group-containing vinyl chloride resin and a polar group-containing polyurethane resin can be used as a binder used for forming the nonmagnetic lower layer or the magnetic layer.

As the polar group of the binder, -SO ₃ M, -PO (OM) ₂ , and -COOM (M is used to improve the dispersibility of the ferromagnetic fine powder and the nonmagnetic powder. A hydrogen atom, an alkali metal or an ammonium salt), an amino group, or a quaternary ammonium base. Among them -SO ₃ M is preferred particularly excellent dispersibility. The preferred polar group content is 1 × 10 ⁻⁵ to 50 × 10 ⁻⁵ eq / g, more preferably 1 × 10 ⁻⁴ to 1 × 10 ⁻⁶ eq / g-binder. If less than 1 × 10 ⁻⁵ eq / g, no effect can be obtained,
If it exceeds ^10-5 eq / g, the viscosity of the coating material for forming the nonmagnetic layer or the magnetic layer becomes high, the workability becomes extremely poor, and the handling becomes difficult. Furthermore, polar groups to be introduced may be two or more, for example, in addition to be performed to introduce -COOM of -SO ₃ M.

The method for introducing a polar group into a polar group-containing vinyl chloride resin used in the present invention can be, for example, a method in which the polar group is added to a vinyl chloride resin containing no polar group by a reaction to synthesize the resin. Specifically, when -SO ₃ M is introduced into a vinyl chloride resin, first, a vinyl chloride monomer and a copolymerizable compound having a glycidyl group and, if necessary, another compound copolymerizable with these are copolymerized. Let
It is obtained by reacting a compound having a -SO ₃ M after obtaining a copolymer simultaneously or copolymers. As a copolymerizable compound for introducing a glycidyl group,
Glycidyl acrylate, glycidyl methacrylate,
Glycidyl vinyl ether, etc., may be used alone or in combination of two or more.

Further, a copolymerizable polar group-containing compound may be copolymerized with a vinyl chloride monomer and other copolymerizable compounds. As the copolymerizable polar group-containing compound, a copolymerizable compound containing the polar group can be used. The copolymerizable compound for introducing a -SO ₃ M 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acrylic acid, methacrylic acid, unsaturated hydrocarbons such as p- styrenesulfonate Examples thereof include sulfonic acids and salts thereof, and sulfoalkyl esters of acrylic acid or methacrylic acid such as sulfoethyl methacrylate and sulfopropyl methacrylate, and salts thereof. These may be used alone or in combination of two or more. Further, when the polar group to be introduced is two or more, for example, the -SO ₃ besides copolymerizable compounds containing -COOM when introducing -COOM is required M, specifically acrylic acid, Methacrylic acid, maleic acid, and the like, and salts thereof can be used.

The polar group-containing vinyl unit of the polar group-containing vinyl chloride resin used in the present invention is 0.05 to 5% by weight.
Is less than 0.05% by weight, there is no effect of improving the dispersibility of the nonmagnetic powder or the magnetic powder.
On the other hand, when the content exceeds 5% by weight, the viscosity of the coating material becomes high, and the pot life when the isocyanate compound is added becomes short, so that the workability of forming a layer is deteriorated. The vinyl chloride unit is preferably from 57 to 98% by weight. If the amount is less than 57% by weight, the strength of the obtained resin coating film is reduced.

Other copolymerizable monomers include vinyl acetate, vinyl propionate, (meth) acrylic acid ester, (meth) acrylic acid, (maleic anhydride), maleic acid, acrylonitrile, vinylidene chloride, hydroxyethyl (meth) acrylate, and glycidyl. (Meth) acrylate and the like. Here, (meth) acryl means a material containing at least one of acryl and methacryl, and (maleic anhydride) means a material containing at least one of maleic acid and maleic anhydride. When other vinyl units are contained, the content is preferably 26% by weight or less. If it exceeds this range, the mechanical properties and dispersibility of the entire resin will be reduced. Further, the obtained vinyl chloride copolymer can be saponified to convert vinyl acetate, vinyl propionate, and the like into a vinyl alcohol component. The content of the vinyl alcohol unit is preferably 2 to 16% by weight. If the amount is less than 2% by weight, solubility of the coating material in organic solvents such as ketones and esters, dispersibility of non-magnetic powder and magnetic powder, reactivity with the isocyanate compound used in combination with the present resin, etc. No effect on the compatibility with the resin can be obtained, and if it exceeds 16% by weight, the viscosity of the coating becomes too high, and the pot life when the isocyanate compound is added becomes short, which is disadvantageous in practical use.

The average polymerization degree of the polar group-containing vinyl chloride resin used in the present invention is preferably from 200 to 800. Further, 250 to 700 is preferable. If it is less than 200, the resulting magnetic coating film becomes brittle, and the obtained magnetic coating film becomes brittle, resulting in a decrease in physical strength, which also affects the durability of a magnetic tape or the like. If it exceeds 800, the viscosity of the paint at a predetermined concentration becomes high, the workability becomes extremely poor, and the handling becomes difficult. The polar group-containing vinyl chloride resin used in the present invention is produced by adding compounds such as a polymerization initiator, a suspension stabilizer, an emulsifier, and a molecular weight modifier.

The polar group-containing polyurethane resin of the present invention comprises
It can be produced from a polar group-containing polyol such as a polyester polyol having a polar group, a polycarbonate polyol or a polyether polyol, and a polyol having no polar group such as a polyester polyol, a polycarbonate polyol or a polyether polyol, and a diisocyanate. For example, it can be produced by changing a part of dihydric alcohol or dibasic acid to polar group-containing diol or polar group-containing dibasic acid. The polar group-containing polyol has a polar group represented by the above general formula in the main chain or side chain of the polyol described below.

The above polyester polyol is, for example,
Examples thereof include those obtained by polycondensation of a dihydric alcohol and a dibasic acid, and those obtained by ring-opening polymerization of lactones, for example, caprolactone. Typical dihydric alcohols include glycols such as ethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, and cyclohexanedimethanol. Typical dibasic acids include adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, and the like.

The polycarbonate polyols have a molecular weight of 300 to 2 synthesized by condensation or transesterification of a polyhydric alcohol with phosgene, chloroformate, dialkyl carbonate or diallyl carbonate.
0000, a polycarbonate polyol having a hydroxyl value of 200 to 300, or 2
Molecular weight 400 to 3 obtained by condensation with a polyvalent carboxylic acid
0000, a polycarbonate polyester polyol having a hydroxyl value of 5 to 300.

Examples of the polyether diol include bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, and other polyethylene oxide and / or polypropylene oxide adducts, and molecular weights of 500 to 5000 such as polypropylene glycol, polyethylene glycol, and polytetramethylene glycol. Can be used.

As the polyol, bisphenol A,
Hydrogenated bisphenol A and their ethylene oxides,
25% by weight of ether groups in propylene oxide adduct
Polyether polyols containing 45% by weight, more preferably in the range of 30% to 40% by weight, are preferred. If the content is less than 25% by weight, the solubility in a solvent is reduced, and the dispersibility is reduced. If the content exceeds 45% by weight, the strength of the coating film is reduced, so that the durability is reduced. Other polyols may be blended with the above polyol up to 90% by weight of the above polyol and used in combination.

Examples of the polyisocyanate used to form a polyurethane by reacting with the above polyol include hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate cyclohexane diisocyanate, Toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,
Examples thereof include 5-naphthalenediisocyanate and 3,3-dimethylphenylenediisocyanate.

As the chain extender, substances known per se, polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like can be used. Among them, polyhydric alcohols having a molecular weight of 50 to 500 are preferable. If it is less than 50, the coating film becomes brittle and the durability is reduced. If it is 500 or more, the glass transition temperature Tg of the coating film decreases, and the coating film becomes soft, so that the durability decreases.

Examples of polyhydric alcohols include bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, and ethylene oxide and propylene oxide adducts thereof, cyclohexanedimethanol, cyclohexanediol, hydroquinone, bis (2-hydroxyethyl) tetrabromobisphenol. A, bis (2-hydroxyethyl) tetrabromobisphenol S, bis (2-hydroxyethyl) tetramethylbisphenol S, bis (2-hydroxyethyl) diphenylbisphenol S, bis (2-hydroxyethyl) diphenylbisphenol, bis (2 -Hydroxyethyl)
Short-chain diols having a cyclic structure such as thiodiphenol, bis (2-hydroxyethyl) bisphenol F, biphenol, bisphenol fluorene, and bisphenol fluorene hydroxyethyl ether are preferred. More preferred are bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and diols having an aromatic or alicyclic group such as ethylene oxide, propylene oxide adduct thereof, cyclohexane dimethanol and cyclohexane diol.

The average molecular weight of the polar group-containing polyurethane resin used in the present invention is preferably 5,000 to 100,000. Further, it is preferably 10,000 to 50,000. 500
If it is less than 0, the resulting magnetic coating film becomes brittle, and the resulting magnetic coating film becomes brittle, resulting in a decrease in physical strength, which also affects the durability of a magnetic tape or the like. When the molecular weight exceeds 100,000, the solubility in a solvent decreases, and the dispersibility decreases. Further, the viscosity of the paint at a predetermined concentration becomes high, so that workability is remarkably deteriorated and handling becomes difficult. As the OH group of the polar group-containing polyurethane resin used in the present invention, a branched O
Having an H group is preferable in terms of curability and durability,
The number is preferably 2 to 40 per molecule, more preferably 3 to 20 per molecule.

Other binders used in the present invention include:
Along with the above-mentioned polar group-containing vinyl chloride resin and polar group-containing polyurethane resin, a binder having another polar group may be used in an amount equal to or less than the total amount of these. Other resins that can be used in combination are not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof, which are conventionally used as binders for magnetic recording media, can be used. In particular,
As a thermoplastic resin, the glass transition temperature is -100 to 1
50 ° C., number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and degree of polymerization of 50 to 10
It is about 00. Examples of such a polymer include acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, a polymer containing vinyl ether, and the like as constituent units, and copolymers. There are coalescing, polyurethane resin and various rubber resins. In addition, as the thermosetting resin or the reactive resin, phenol resin, phenoxy resin, epoxy resin,
Examples include urea resins, melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, and mixtures of polyester resins and isocyanate prepolymers.

In the magnetic recording medium of the present invention, a lubricating effect, an antistatic effect,
An additive for providing a dispersing effect, a plasticizing effect, and the like may be contained. These additives include molybdenum disulfide,
Tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, polar group silicone,
Fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and Its alkali metal salt, carbon number 1
Monobasic fatty acids which may contain 0 to 24 unsaturated bonds and may be branched, and metal salts thereof (Li,
Na, K, Cu, etc.) or containing an unsaturated bond having 12 to 22 carbon atoms, or a branched or branched 1 to 6 alcohol, containing an unsaturated bond having 12 to 22 carbon atoms,
In addition, an alkoxy alcohol which may be branched, containing an unsaturated bond having 10 to 24 carbon atoms, or containing a monobasic fatty acid which may be branched and an unsaturated bond having 2 to 12 carbon atoms, Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester composed of any one of 1 to 6 alcohols which may be a fatty acid ester of a monoalkyl ether of an alkylene oxide polymer, a fatty acid amide having 2 to 22 carbon atoms, An aliphatic amine having 8 to 22 carbon atoms can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, myristin Octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol.

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums or sulfoniums,
Such as cationic surfactants, carboxylic acids, sulfonic acids,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfate ester groups, phosphate ester groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, alkyl betaine type, etc. Etc. can also be used. These lubricants, antistatic agents and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

The type and amount of these lubricants and surfactants used in the present invention can be selected as needed in the non-magnetic layer and the magnetic layer. For example, to control bleeding to the surface using fatty acids having different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface using esters having different boiling points and polarities, and to adjust the amount of surfactant. It can be considered to improve the stability of coating and improve the lubricating effect by increasing the amount of the lubricant added to the non-magnetic layer. Of course, the present invention is not limited to the examples shown here. Further, all or a part of the additives used in the present invention may be added in any step of producing a coating solution for the magnetic layer or the lower layer. For example, when mixing with a ferromagnetic powder before a kneading step, when adding in a kneading step with a ferromagnetic powder, a binder and a solvent, when adding in a dispersing step, when adding after dispersing, when adding just before coating, and the like. There is.

Specific examples of these lubricants used in the present invention include: NAA-102, castor oil-cured fatty acid, NAA-42, cation SA, Nymeen L-201, Nonion E-208, manufactured by NOF Corporation. Anon BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku: oleic acid, manufactured by Takemoto Yushi: FA
L-205, FAL-123, Nippon Rika Co., Ltd .: Nujielbu OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Armor Co .: Armide P, Lion Co., Ltd., Duomin TD
O, manufactured by Nisshin Oil Co., Ltd .: BA-41G, manufactured by Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionnet MS-400. The coating solution prepared from the above materials is coated on a non-magnetic support to form a lower coating layer or a magnetic layer.

Examples of the nonmagnetic support that can be used in the present invention include biaxially stretched polyethylene naphthalate,
Known materials such as polyethylene terephthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, and polybenzoxdazole can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, or the like in advance.
The non-magnetic support that can be used in the present invention has a center line average surface roughness of 0.2 at a cutoff value of 0.25 mm.
The surface preferably has excellent smoothness in the range of 1 to 20 nm, preferably 1 to 10 nm. Also,
These non-magnetic supports preferably have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more.

The value of the arithmetic average roughness (Ra) of the obtained support [JIS B0660-1998, ISO 4287
-1997] is preferably 0.1 μm or less, since noise of the obtained magnetic recording medium is reduced. The preferable thickness of the nonmagnetic support in the magnetic recording medium of the present invention is 3 to 80 μm as the thickness after drying.

The back coat layer (backing layer) is formed on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied.
May be provided. The back coat layer is provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent on a surface of the non-magnetic support on which the magnetic paint is not applied. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . An adhesive layer may be provided on the surface of the non-magnetic support of the present invention where the magnetic paint and the back coat layer forming paint are applied.

In the method of manufacturing a magnetic recording medium of the present invention, for example, the lower layer coating solution and the magnetic layer coating solution may be sequentially or simultaneously multi-layer coated. Coating machines for applying the magnetic coating liquid or the lower layer coating liquid include air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, Cast coat, spray coat, spin coat and the like can be used.

For these, reference can be made, for example, to “Latest Coating Technology” (May 31, 1983) issued by Sogo Gijutsu Center. When applied to the magnetic recording medium of the present invention, the following can be proposed as an example of a coating apparatus and method. (1) First, a lower layer is applied by a coating apparatus such as gravure, roll, blade, or extrusion which is generally applied in the application of a magnetic layer coating liquid, and the lower layer is dried while the lower layer is in an undried state. No., JP-A-60-2
The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in JP-A-38179, JP-A-2-265672 and the like. (2) JP-A-63-88080, JP-A-2-17
No. 971 and Japanese Unexamined Patent Publication No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965.

The coating layer of the magnetic layer coating solution is dried after subjecting the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution to a magnetic field orientation treatment. After being dried in this manner, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as an epoxy resin, a polyimide resin, a polyamide resin, or a polyamideimide resin is used. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a center line average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
It is preferable that the surface has an extremely excellent smoothness of 4 nm, preferably 1 to 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the above calendering treatment. As the calendering conditions, the temperature of the calender roll is in the range of 60 to 100 ° C, preferably in the range of 70 to 100 ° C, particularly preferably 80 to 10 ° C.
0 ° C. range and the pressure is a linear pressure, 98-490 kN /
m, preferably in the range of 196 to 441 kN / m, particularly preferably in the range of 294 to 392 kN / m. The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

[0073]

The present invention will be described below with reference to examples. In the examples, "parts" indicates "parts by weight" unless otherwise specified. Example 1 (Preparation of Upper Layer Magnetic Coating Liquid) Ferromagnetic Alloy Powder 100 parts Composition: Fe / Co / Al / Y = 57/30/7/6, Surface Treatment Agent: Al ₂ O ₃ , Y ₂ O ₃ , Hc : 190 kA / m, crystallite size: 13.7 nm, major axis diameter: 0.11 μm, acicular ratio: 8, BET specific surface area: 47 m ² / g, σ _s : 153 Am ² / kg 12 parts of polyurethane resin (UR8200: Sulfonic acid group-containing polyurethane resin manufactured by Toyobo Co., Ltd. 6 parts of vinyl chloride resin (MR110: manufactured by Zeon Corporation, sulfonic acid group-containing vinyl chloride resin) 3 parts of monobiphenyl phosphate α-Al ₂ O ₃ (particle size of 0. 15 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearin 1 parts (Preparation of lower layer non-magnetic coating solution) non-magnetic inorganic powder 85 parts (alpha-iron oxide surface treatment _{agent: Al 2 O 3, SiO 2} , major axis length: 0.15 [mu] m, power strips Density: 0 0.8, needle ratio: 7, BET specific surface area 52 m ² / g, pH 8, DBP oil absorption: 33 g / 100 g) Carbon black 20 parts (DBP oil absorption: 120 ml / 100 g, pH: 8, BET specific surface area, 250 m) ² / g, volatile matter: 1.5%) Polyurethane resin 12 parts (UR8200: Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin) Vinyl chloride resin 6 parts (MR110: Nippon Zeon, sulfonic acid group-containing vinyl chloride resin) Resin) α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Monobiphenyl phosphate 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts 1 part of theearic acid

Each of the above-mentioned upper layer magnetic paint and lower layer non-magnetic paint composition was kneaded with an open kneader for 60 minutes, and then dispersed in a sand mill for 120 minutes. A trifunctional low molecular weight polyisocyanate compound (Coronate 304 manufactured by Nippon Polyurethane) is added to the obtained dispersion.
6 parts of 1) was added, and the mixture was further stirred and mixed for 20 minutes.
Filtration was performed using a filter having an average pore size of μm to prepare a magnetic paint and a non-magnetic paint.

Further, the above-mentioned non-magnetic paint was applied so that the thickness after drying became 1.8 μm, and immediately thereafter, the magnetic paint was applied simultaneously and in layers so that the thickness after drying became 0.2 μm. In a state where both layers are not dried, a magnetic field orientation is performed with a magnet of 0.3 T, and after drying, a 7-stage calender consisting only of a metal roll is used at a speed of 100 m / min, a linear pressure of 294.2 kN / m, and a temperature of 90. After performing a surface smoothing treatment at 70 ° C., a heat curing treatment is performed at 70 ° C. for 24 hours, and 6.3.
The tape was cut into a width of 5 mm to produce a magnetic tape.

Examples 2 to 11 Examples 2 to 11 were produced in the same manner as in Example 1 except that the thickness of the magnetic material, dispersant and magnetic layer was changed as shown in Table 1.

Comparative Examples 1 to 5 Comparative examples 1 to 5 were prepared in the same manner as in Example 1 except that the thickness of the magnetic substance, dispersant and magnetic layer was changed as shown in Table 1.

[Measurement Method] (1) Magnetic Properties [Small axis diameter and long axis diameter] A method of taking a transmission electron micrograph and directly reading the short axis diameter and the long axis diameter of the ferromagnetic powder from the photograph. And image analyzer (IB manufactured by Carl Zeiss)
ASSI) and a method of tracing and reading transmission electron micrographs. [Crystallite size] X-ray diffractometer (Rigaku RINT
The average value obtained by the Scherrer method from the half width of the diffraction peak under the conditions of a radiation source CuKα1, a tube voltage of 50 kV, and a tube current of 300 mA was used. (2) Electromagnetic conversion characteristics Output, output decrease: The obtained tape was heated at 23 ° C. and 50% RH.
Record a signal with a frequency of 4.7 MHz and reproduce it. The output at the time of the first reproduction was evaluated based on the output relative to the tape of Example 1. The output was continuously reproduced 1000 times more and the output was continuously reproduced. The output of each sample was set to 0 dB for the first output, and the output reduction was measured.

[0079]

[Table 1]

[0080]

As described above, according to the present invention, a non-magnetic coating layer in which at least a non-magnetic powder and a binder are dispersed is provided on at least one surface of a non-magnetic support. In a magnetic recording medium having a lower non-magnetic layer provided with a magnetic layer formed by dispersing a binder, at least at least a specific organic phosphoric acid compound is added to the lower non-magnetic layer, thereby improving the smoothness of the coating film. Electromagnetic conversion characteristics are improved, the surface of the magnetic layer is hardly scraped, head dirt is reduced, storage stability is greatly improved, dropout is reduced, running durability is excellent, and surface smoothness of the magnetic recording medium is excellent. As a result, it is possible to provide a magnetic recording medium capable of obtaining a high output, so that a remarkable effect is recognized as compared with the conventional method.

Claims (4)

[Claims] 1. A magnetic device comprising: a lower layer containing a non-magnetic powder or a ferromagnetic powder and a binder provided on a non-magnetic support; and at least one magnetic layer in which the ferromagnetic powder and the binder are dispersed. In the recording medium, the ferromagnetic metal powder contains Fe as a main component, and 10 to 40 atomic% of Co with respect to Fe,
A magnetic recording medium comprising 2 to 20 atomic% of Y and 1 to 15 atomic% of Y, and at least the magnetic layer contains an organic phosphorus compound represented by the following formula. [(R) _m -φ-O] _n -P (＝ O) (OH) _3-n where R represents a substituted or unsubstituted alkyl group, aryl group or aralkyl group. Also, m = 1 to 5, n = 1 or 2 2. The magnetic recording medium according to claim 1, wherein R of the organic phosphorus compound is an unsubstituted or substituted aryl group or aralkyl group. 3. The ferromagnetic metal powder has a major axis length of 0.05 μm.
m to 0.13 μm and crystallite size of 8 nm to 2
3. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic layer is 0 nm or less, and the thickness of the magnetic layer is 0.05 μm or more and 0.5 μm or less. 4. The coercive force of the ferromagnetic metal powder is 155 to
219 kA / m, σ _SIs 140-170 Am^Two/ Kg
The specific surface area by the BET method is 30m^Two/ G or more 50m^Two
/ G or less.
The magnetic recording medium according to claim 1.