JPH0927115A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium having excellent electromagnetic conversion characteristics, sufficient overwriting characteristics, compatibility with an ME tape, travelling durability and corrosion resistance. SOLUTION: A magnetic layer essentially comprising a ferromagnetic powder and a binder resin is formed on at least one surface of a nonmagnetic supporting body. In this magnetic recording medium, the magnetic layer is 0.05-0.8μm thick, the average major axial length of the ferromagnetic powder is 0.05-0.20μm, and the binder resin contains such a polyurethane having 5-25nm inertia diameter in cyclohexane.

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, and more particularly to a coating type magnetic recording medium for recording / reproducing digital signals at high density.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks, and the like. The recording density of magnetic recording media has been increasing year by year, and the recording wavelength has been shortened, and recording methods from analog to digital are also being studied.

In order to meet the demand for higher density, a so-called coating type medium in which ferromagnetic powder is dispersed in a binder and coated on a support has a low degree of filling of magnetic material with respect to a metal thin film. Although the electromagnetic conversion characteristics were inferior, the characteristics have been almost the same due to recent advances in magnetic materials and ultra-thin layer coating technology. Further, the coated medium is excellent in terms of productivity and corrosiveness.

As the coating type magnetic recording medium, a magnetic layer in which ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO ₂ , ferromagnetic alloy powder, etc. are dispersed in a binder is coated on a non-magnetic support. Is widely used. Various methods have been proposed to improve the electromagnetic conversion characteristics of the coating type magnetic recording medium, such as improvement of the magnetic characteristics of the ferromagnetic powder and smoothing of the surface. Not a thing. In addition, in recent years, the recording wavelength tends to become shorter with higher density, and the problem of self-demagnetization loss at the time of recording and output loss when the thickness of the magnetic layer is thick and the thickness loss at the time of reproduction are increasing. A coating type magnetic recording medium having an extremely thin layer has also been proposed.

In recent years, Hi-8 and consumer digital VC
In R, a tape on which a metal thin film is deposited, a so-called ME (metal
evaporated) tape has been put to practical use, alloy powder tape, so-called MP (metal particulate) tape and ME.
Systems using both tapes have been put to practical use. In order to coexist with ME tape, MP also ME
Similarly, it is necessary to reduce the thickness of the magnetic layer to achieve high output, and it is necessary to make the relationship between the recording current and the reproduction output the same. Conventionally, the reproduction output of MP decreases due to recording demagnetization as the recording current increases, but this tendency does not appear in ME, and the reproduction output tends to saturate as the recording current increases. . Therefore, in the Hi-8 deck, MP and ME are actually recorded by different recording currents, which has a drawback that the circuit becomes complicated. In order to solve this difficulty, it is necessary to record with the same recording current in a system in which MP and ME coexist, but there is a problem that the output becomes low when recording and reproducing MP with the optimum recording current of ME. It was Moreover, if the ME is recorded and reproduced with the optimum recording current of the MP, the ME cannot exert its ability,
The output will be low. It was required that the optimum recording current of MP be almost the same as that of ME.

Further, in the consumer digital VCR, a signal having a recording wavelength of 22 μm is adopted as a synchronizing signal, and data having a recording wavelength of 0.488 μm is adopted. To reduce the weight, the erase head was omitted and overwrite erase was adopted. To adopt overwrite erase,
It is necessary to erase the synchronizing signal with a data signal, and it is said that the overwrite erasing rate is preferably -20 dB or less. As a characteristic required for a magnetic recording medium, it is desired that the overwrite erasing rate be as low as possible. The overwrite characteristics will be improved as the magnetic layer thickness is made thinner, but the total amount of magnetization will be reduced if the magnetic layer thickness is simply made. Output decreases. In order to improve the output of a long-wavelength signal, a large amount of magnetization is required, and for that purpose, a high magnetic flux density and a certain thickness must be secured. As described above, the overwrite characteristic and the long-wavelength signal output have a conflicting relationship. But,
In order to reduce the overwrite erasing rate, not only can the magnetic layer thickness be made thin, but it can also be improved by recording a short wavelength signal such as a data signal deep into the magnetic layer. To this end, it is effective to supply as much recording current as possible when recording data signals. As mentioned above, M
For compatibility with E, it is desirable that the optimum recording current is as large as ME, but it is also desirable from the viewpoint of overwrite characteristics.

In addition to the above factors, as a method of improving the overwrite characteristics, it is desirable that the surface roughness of the magnetic layer be smooth within the range allowed by running durability, and the squareness ratio of the magnetic layer should be It was found that the higher the SFD and the lower the SFD, the better the overwrite characteristics. In order to improve running durability, it has been conventionally performed to select a binder resin used for the magnetic layer.

[0008] For example, polyurethane was desired to form a strong film having a high glass transition temperature (Tg) from the viewpoint of imparting durability to the magnetic layer, but from the viewpoint of calender moldability, Tg has hitherto been used. Have been chosen to be relatively low. On the other hand, a magnetic recording medium in which the magnetic layer is thinned by providing a magnetic layer on a non-magnetic layer is known.
In order to achieve higher density recording, the magnetic layer needs to be thinner and the ferromagnetic metal powder needs to be finer. The miniaturization of the ferromagnetic metal powder causes a decrease in dispersibility, and consequently causes a problem that the surface properties of the magnetic layer are deteriorated, and the electromagnetic conversion characteristics are likely to be reduced. Further, it becomes difficult to secure durability as the magnetic layer becomes thinner.

Further, in the DVC medium, the magnetic head is preferably a thin film head or an MR head, but when these tapes are used, they are widely used as a binder resin for magnetic recording media. If a vinyl chloride resin (hereinafter also referred to as a vinyl chloride resin) is used, even a slight amount of hydrochloric acid resulting from dehydrochlorination will corrode the head and pose a problem. Therefore, it is desired to make the binder resin non-vinyl chloride.

The present applicant has also proposed an ultrathin layer magnetic recording medium in which a nonmagnetic layer is provided as a lower layer and the upper magnetic layer is made thin. For example, there are the following inventions. In Japanese Patent Laid-Open No. 63-187418, the average major axis length is 0.8 μm.
A magnetic recording medium in which a ferromagnetic powder having a crystallite size of less than 300 m and a crystallite size of less than 300 Å is dispersed and applied on a non-magnetic layer is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 5-298653 discloses a magnetic recording in which the thickness of the magnetic layer is less than 0.3 .mu.m and the standard deviation of the thickness is within a certain range so that the overwrite characteristic and the distortion during digital recording are small. Obtaining a medium is disclosed. However, in these conventional techniques, a system using polyurethane and a vinyl chloride resin as a binder resin is generally used, which is insufficient to improve overwrite characteristics and secure low frequency output, and the running durability It was difficult to achieve both good properties and prevention of head corrosion. That is, running durability cannot be ensured unless a vinyl chloride resin is used, and head corrosion cannot be prevented when a vinyl chloride resin is used. In particular, in the conventional technology, 24 which is adopted in a consumer digital VCR is used.
It was not possible to sufficiently satisfy the running characteristics and the corrosion resistance together with the overwrite characteristics in -25 modulation and compatibility with ME tape. Further, a binder resin system that does not use a vinyl chloride resin has not been found to be a resin that can solve the above problems.

[0012]

DISCLOSURE OF THE INVENTION The present invention is to provide a magnetic recording medium having good electromagnetic conversion characteristics, and has overwriting characteristics, compatibility with ME tape and running durability,
It is an object of the present invention to provide a magnetic recording medium that can sufficiently satisfy corrosion resistance.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder resin is formed on at least one surface of a non-magnetic support. Has a thickness of 0.05 to 0.8 μm,
This can be achieved by a magnetic recording medium characterized in that the ferromagnetic powder has an average major axis diameter of 0.05 to 0.20 μm, and the binder resin contains polyurethane having an inertia radius of 5 to 25 nm in cyclohexanone. .

A feature of the present invention is that polyurethane having an inertia radius of 5 to 25 nm in cyclohexanone is selected as the binder resin, so that the average major axis diameter of the ferromagnetic powder is extremely small at 0.05 to 0.20 μm. In addition, even if the magnetic layer is as thin as 0.05 to 0.8 μm, the dispersibility is good, the surface properties of the magnetic layer can be secured, the running durability can be improved, and head corrosion can be effectively prevented. I found it.

The polyurethane used in the present invention has a radius of gyration of 5 to 25 nm, preferably 5 to 20 nm, more preferably 7 to 20 nm. Here, the radius of gyration is a value measured by a light scattering method in a cyclohexanone solution of polyurethane. As the measurement conditions, a light scattering photometer “DLS700” manufactured by Otsuka Electronics Co., Ltd. is used, and the sample concentration is a cyclohexanone solution. 0.2%, 0.4%,
It was measured at 0.6% and 0.8%.

In the present invention, the radius of gyration is 5 to 25.
Polyurethane controlled to nm is used, but the larger the radius of gyration is, the larger the spread of polyurethane molecules adsorbed on the surface of the ferromagnetic powder in the magnetic coating is, and therefore the dispersibility tends to be good, and the Tg is Larger urethanes tend to have better durability. However, if the radius of gyration is too large for the dark clouds, the dispersibility deteriorates and the orientation decreases.

Conventionally, there is no invention paying attention to the radius of gyration of polyurethane, and urethane of high Tg could not be adopted in order to set the tape Tg to the calender temperature or lower in view of calender moldability, but the radius of gyration is large. By adopting urethane, the dispersibility is improved, and even if high Tg urethane is adopted depending on the calender conditions, the moldability can be ensured, and both the electromagnetic conversion characteristics and the durability can be improved at the same time. It was designed. For example, as a method of controlling the radius of gyration of polyurethane to a predetermined value, a urethane group (-NHCO) contained in polyurethane is used.
Controlling the O-) concentration, the ether group (C-O-C) concentration, etc. may be mentioned.

The concentration of the urethane group is usually 0.5
-5 meq / g, preferably 1.0-4 meq / g, more preferably 1.5-3.0 meq / g. The ether group concentration is usually 0.5 to 9.0 meq / g,
It is preferably 1.0 to 7.0 meq / g, more preferably 2.0 to 6.0 meq / g. The number average molecular weight of polyurethane is usually 20,000 to 150,000,
It is preferably 30,000 to 100,000, more preferably 40,000 to 70,000.

As the calendering conditions, a calender of a combination of metal rolls / metal rolls is preferable, and the temperature is usually 60 to 110 ° C., preferably 70 to 100 ° C.
More preferably, it is 80 to 100 ° C., and the linear pressure is usually 100 to 500 Kg / cm, preferably 200 to 4
00 Kg / cm, more preferably 250-350 Kg
/ Cm. In the present invention, since polyurethane is selected, calendering at high temperature is possible, and therefore, moldability is improved. Examples of the material of the metal roll include chrome steel plated with hard chrome. The center line average surface roughness Ra of the roll is usually 0.001 to 0.05 nm, preferably 0.001.
~ 0.01 nm.

The layer structure of the magnetic recording medium of the present invention is not particularly limited as long as the magnetic layer is provided on at least one surface of the non-magnetic support, but preferably between the magnetic layer and the non-magnetic support. Another example is a structure in which a non-magnetic layer mainly containing an inorganic non-magnetic powder and a binder is provided. The non-magnetic layer and the magnetic layer may have a single-layer structure or a multi-layer structure. In the present invention, the magnetic layer thickness means the total thickness of the magnetic layers. With such a structure, a smooth magnetic layer having more excellent surface properties can be obtained.

Center line average surface roughness Ra of the magnetic layer of the present invention
Is usually 1 to 4 nm, preferably 1 to 3 nm.
The Tg of the magnetic layer of the present invention is usually 80 ° C. or higher, preferably 85 to 95 ° C. When the magnetic recording medium has a multi-layer structure, the uppermost layer preferably has a higher Tg than the other layers. For example, the Tg of the nonmagnetic layer is usually 30 to
The temperature is 90 ° C, preferably 60 to 80 ° C.

The binder resin used in the magnetic layer of the present invention may be the above-mentioned polyurethane alone or a combination of the polyurethane and any other binder resin. The resin that can be used in combination is preferably one in which a corrosive gas generating resin such as a vinyl chloride resin is excluded in order to prevent corrosion of the thin film head or the MR head, and specific examples thereof include polyisocyanate. In the present invention, running durability can be ensured even with polyurethane alone without using a vinyl chloride resin that is generally used for the purpose of strengthening the magnetic layer. Good.

In the present invention, the content of polyurethane in the magnetic layer is usually 50 to 300% by weight, preferably 50 to 150% by weight, based on the ferromagnetic powder, and other resins are usually 20 to 200% by weight, Preferably 40 to 1
50% by weight. When used in combination with a vinyl chloride resin, it is 20 to 150% by weight, preferably 30 to 70% by weight, based on the ferromagnetic powder.

When polyisocyanate is used,
20 to 100% by weight, preferably 3 to the ferromagnetic powder
0 to 70% by weight. The average major axis diameter of the ferromagnetic powder used in the present invention is 0.05 to 0.20 μm, preferably 0.05 to 0.11 μm, and more preferably 0.06 to.
It is 0.09 μm. As the ferromagnetic powder, a ferromagnetic metal powder is preferable.

The average major axis diameter is obtained by 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, and an image analyzer I manufactured by Carl Zeiss.
It can be obtained by appropriately using a method of tracing a transmission electron microscope photograph by BASS1 and reading it. As the ferromagnetic powder, γ-FeOx (x = 1.33 to 1.5), Co-modified γ-
FeOx (x = 1.33 to 1.5), α-Fe or N
Known ferromagnetic powders such as ferromagnetic metal powder containing i or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used, but ferromagnetic metal powder containing α-Fe as a main component is preferable. These ferromagnetic powders include Al, Si, S, Sc, Ca,
Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag,
Sn, Sb, Te, Ba, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, Pr, Nd, P, Co,
It may contain atoms such as Mn, Zn, Ni, Sr, and B. In particular, in the case of ferromagnetic metal powder, Al, Si, C
a, Y, Ba, La, Nd, Co, Ni, B are α-Fe
It is important as an element contained in other than. These ferromagnetic metal powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion before the dispersion. Specifically, Japanese Patent Publication No. 44-090, Japanese Patent Publication No.
45-18372, JP47-22062, JP47-22513, JP46-28466, JP46-38755, JP47-4286
Issue, Japanese Examined Sho 47-12422, Examined Sho 47-17284, Examined Sho 47-1
8509, Japanese Examined Sho 47-18573, Japanese Examined Sho 39-10307, Japanese Examined Sho
48-39639, U.S. Patents 3026215, 3031341, 31
00194, 3242005, 3389014 and the like.

Of the above-mentioned ferromagnetic powder, the ferromagnetic metal fine powder may contain a small amount of hydroxide or oxide. What was obtained by the well-known manufacturing method of a ferromagnetic metal fine powder can be used, and the following method can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic metal powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then sending an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

The BET method was applied to the ferromagnetic powder of the magnetic layer of the present invention.
45-80m in terms of specific surface area ^Two / G and is preferred
Or 50-70m^Two / G. 40m^Two / G or less
Is high noise, 80m^Two / G or more provides surface properties
It is not preferred. Binding of the ferromagnetic powder in the magnetic layer of the present invention
The crystallite size is 350-80 angstroms,
It is preferably 250 to 100Å, more preferably 200 to 1
It is 40Å. The saturation magnetization (σ S) of magnetic metal powder is 10
0 to 180 emu / g is preferable, and 1 is more preferable.
10 emu / g to 170 emu / g, more preferably 125 to 1
It is 60 emu / g. The coercive force of ferromagnetic metal powder is 1,50
0 to 3,500 Oe is preferable, and more preferably 1,80
It is 0 to 3000 Oe. The acicular ratio of the ferromagnetic powder is 4-18
Is preferable, and more preferably 5-12. Ferromagnetic powder
The powdery water content is preferably 0.01 to 2%. Join
The water content of the ferromagnetic powder should be optimized depending on the type of agent.
preferable.

The pH of the ferromagnetic powder is preferably optimized by the combination with the binder used. The range is 4-1
2, but preferably 6 to 10. The ferromagnetic powder may be subjected to a surface treatment with Al, Si, P or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and it is preferable that the surface treatment is performed so that the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. Ferromagnetic powder contains soluble Na, Ca, Fe, Ni,
It may contain an inorganic ion such as Sr. It is preferable that these are essentially absent, but if they are 200 ppm or less, they do not particularly affect the characteristics.

The ferromagnetic powder used in the present invention preferably has a small number of pores, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the above-mentioned characteristics regarding the particle size are satisfied. In order to achieve the SFD of the ferromagnetic powder of 0.6 or less, it is necessary to reduce the Hc distribution of the ferromagnetic powder. For that purpose, there is a method of improving the particle size distribution of goethite and preventing the sintering of γ-hematite.

Next, the detailed contents of the non-magnetic layer (also referred to as the lower layer) will be described. The inorganic non-magnetic powder used in the non-magnetic layer of the present invention includes, for example, metal oxides, metal carbonates,
It can be selected from inorganic compounds such as metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. As the inorganic compound, for example, α-alumina having a conversion of 90% or more, β-
Alumina, γ-alumina, θ-alumina, silicon carbide,
Chromium oxide, cerium oxide, α-iron oxide, goethite,
Corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate,
Molybdenum disulfide and the like are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide, and barium sulfate because of their easy availability, low cost, small particle size distribution, and many means for imparting functions. Titanium dioxide, α are more preferred. It is iron oxide. The particle size of these inorganic non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, the inorganic non-magnetic powders having different particle sizes may be combined, or a single inorganic non-magnetic powder may have a wide particle size distribution. You can also have the effect of. Particularly preferred is a particle size of the inorganic non-magnetic powder of 0.01 μm to 0.2 μm. Tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g /
ml. The inorganic non-magnetic powder has a water content of 0.1 to 5% by weight, preferably 0.2 to 3% by weight, and more preferably 0.3 to 1.5% by weight. PH of inorganic non-magnetic powder
Is 2 to 11, but a pH of 5 to 10 is particularly preferable. The specific surface area of the inorganic non-magnetic powder is 1 to 100 m ² /
g, preferably 5-70 m ² / g, more preferably 10
˜65 m ² / g. The crystallite size of the inorganic non-magnetic powder is preferably 0.004 μm to 1 μm, and 0.04 μm
˜0.1 μ is more preferable. Dibutyl phthalate (DBP
Oil absorption is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100.
g. The specific gravity is 1 to 12, preferably 3 to 6.
The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

The loss on ignition is preferably 20% by weight or less, and it is considered most preferable not to have it. The inorganic nonmagnetic powder used in the present invention preferably has a Mohs hardness of 4 or more and 10 or less. The roughness factor of the surface of these inorganic nonmagnetic powders is preferably 0.8 to 1.5, and more preferably 0.9 to 1.5.
1.2. The amount of SA (stearic acid) adsorbed on the inorganic non-magnetic powder is 1 to 20 μmol / m ² , and more preferably 2 to
It is 15 μmol / m ² . The heat of wetting of the inorganic non-magnetic powder in water at 25 ° C. is preferably in the range of 200 erg / cm ^{2 to} 600 erg / cm ² . Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is appropriately 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 6.

On the surface of these inorganic non-magnetic powders, Al_TwoO
_Three, SiO_Two, TiO_Two, ZrO_Two, SnO_Two, Sb_TwoO _Three, ZnO, Y_TwoO_ThreeTable
Surface treatment is preferred. Especially preferred for dispersibility
Al_TwoO _Three, SiO_Two, TiO_Two, ZrO_TwoHowever, more preferred is
Al_TwoO_Three, SiO_Two, ZrO_TwoIt is. These are used in combination
Or may be used alone. Also the purpose
A surface treatment layer coprecipitated according to may be used.
After treating with alumina, treating the surface layer with silica
The method or vice versa can be adopted. Also, the table
The surface treatment layer may be a porous layer depending on the purpose,
It is generally preferred to be homogeneous and dense.

Specific examples of the inorganic non-magnetic powder used in the non-magnetic layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α hematite manufactured by Toda Kogyo Co., DPN-
250, DPN-250BX, DPN-245, DPN-270BX, Titanium Oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-
55S, TTO-55D, SN-100, α Hematite E270, E271, E30
0, Titanium Industry STT-4D, STT-30D, STT-30, STT-65C
, TAYCA MT-100S, MT-100T, MT-150W, MT-500B,
MT-600B, MT-100F, MT-500HD, Sakai Kagaku FINEX-25, BF
-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R,
Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A
, Y-LOP manufactured by Titanium Industry Co., Ltd. and a product obtained by firing it.

Particularly preferred inorganic non-magnetic powders are titanium dioxide and α-iron oxide (α-Fe ₂ O ₃ ). α-Iron oxide (hematite) is carried out under the following conditions. The α-Fe ₂ O ₃ particle powder is a suspension containing ferrous hydroxide colloid obtained by adding an equal amount or more of an aqueous alkali hydroxide solution to a normal ferrous iron solution at a pH of 11 or more.
Method for producing acicular goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of ℃ or less, and a suspension containing FeCO ₃ obtained by reacting an aqueous solution of ferrous salt and an aqueous solution of alkali carbonate A method for producing goethite particles in the form of spindles by carrying out an oxidation reaction by aerating an oxygen-containing gas into the solution, which is obtained by adding less than an equal amount of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to an aqueous ferrous salt solution. Oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid to carry out an oxidation reaction to generate needle-shaped goethite core particles, and then ferrous salt containing the needle-shaped goethite core particles. In the aqueous solution, the F in the aqueous solution of ferrous salt is added.
A method of growing the acicular goethite core particles by adding an oxygen-containing aqueous solution in an amount equal to or more than that of e ²⁺ and then aerating an oxygen-containing gas, and an alkali hydroxide in an amount less than that of the ferrous aqueous solution or A needle-shaped goethite nucleus particle is produced by carrying out an oxidation reaction by passing an oxygen-containing gas through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an alkaline carbonate aqueous solution, and then producing acidic to medium The acicular goethite particles obtained by the method of growing the acicular goethite nucleus particles in the crystalline region are used as precursor particles.

It should be noted that Ni and Z, which are usually added during the reaction for producing goethite particles to improve the characteristics of the particle powder, etc.
There is no problem even if a different element such as n, P or Si is added. Needle-shaped goethite particles, which are precursor particles, are added to 200 to 5
Dehydrate in the temperature range of 00 ° C or, if necessary, further 3
Annealing is performed by heat treatment in the temperature range of 50 to 800 ° C. to obtain acicular α-Fe ₂ O ₃ particles.

There is no problem if the needle-shaped goethite particles to be dehydrated or annealed have a sintering inhibitor such as P, Si, B, Zr or Sb attached to the surface. Annealing by heat treatment in the temperature range of 350 to 800 ° C. is performed by annealing pores generated on the particle surface of the needle-shaped α-Fe ₂ O ₃ particles obtained by dehydration so that the polar surface of the particle is This is because it is preferable that the pores are melted and the pores are closed to form a smooth surface form.

Α-Fe ₂ O ₃ used in the present invention
The particle powder is a suspension obtained by dispersing the acicular α-Fe ₂ O ₃ particles obtained by dehydration or annealing in an aqueous solution,
The Al compound is added to adjust the pH, and the α-Fe ₂ O ₃ is added.
After coating the particle surface of the particles with the additive compound, filtration,
It can be obtained by washing with water, drying, crushing and, if necessary, further performing deaeration and consolidation treatment. As the Al compound used, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate and alkali aluminate salts such as sodium aluminate can be used. In this case, the amount of the Al compound added is 0.01 to 50% by weight in terms of Al based on the α-Fe ₂ O ₃ particle powder. 0.0
When the amount is less than 1% by weight, the dispersion in the binder resin is insufficient, and when the amount exceeds 50% by weight, Al compounds floating on the particle surface interact with each other, which is not preferable. In the inorganic non-magnetic powder of the lower layer in the present invention, starting with the Si compound as well as the Al compound,
It is also possible to coat with one or more compounds selected from P, Ti, Mn, Ni, Zn, Zr, Sn and Sb. The amount of each of these compounds used together with the Al compound is in the range of 0.01 to 50% by weight based on the α-Fe ₂ O ₃ particle powder. If it is less than 0.01% by weight, there is almost no effect of improving dispersibility by addition, and if it is more than 50% by weight, compounds floating on the surfaces other than the particle surface interact with each other, which is not preferable.

The production method of titanium dioxide is as follows. The methods for producing these titanium oxides are mainly a sulfuric acid method and a chlorine method. In the sulfuric acid method, the source ore of illuminite is digested with sulfuric acid, and Ti, Fe, etc. are extracted as sulfates. Iron sulfate is removed by crystallization, and the remaining titanyl sulfate solution is purified by filtration and then subjected to thermal hydrolysis to precipitate hydrous titanium oxide. After filtration and washing, impurities are washed and removed, a particle size regulator and the like are added, and the mixture is calcined at 80 to 1000 ° C. to obtain crude titanium oxide. The rutile type and the anatase type are classified according to the kind of the nucleating agent added at the time of hydrolysis. The crude titanium oxide is prepared by pulverizing, sizing and surface treatment. In the chlorine method, natural rutile or synthetic rutile is used as the raw ore. Ore is chlorinated in high-temperature reduction state, Ti
Fe becomes FeCl _{2 in} iCl ₄ , and iron oxide which has become solid by cooling is separated from liquid TiCl ₄ . The obtained crude TiCl ₄ is purified by rectification, then a nucleating agent is added, and reacted with oxygen instantaneously at a temperature of 1000 ° C. or more,
Obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

The surface treatment is dry pulverization of the titanium oxide material.
After that, add water and dispersant, wet pulverize and centrifuge to obtain coarse particles.
Classification is performed. After that, the fine particle slurry is used in the surface treatment tank.
Where the metal hydroxide surface coating is performed.
You. First, a predetermined amount of Al, Si, Ti, Zr, Sb, S
An aqueous solution of salts such as n and Zn is added to neutralize the acid,
Alternatively, add alkali and use the hydrous oxide produced to
Cover the surface of the tan particles. Water-soluble salts produced as by-products are decane
Removed by filtration, filtration, washing and finally slurry
-Adjust the pH, filter and wash with pure water. Washed
Mi cake is spray dryer or band dryer
To be dried. Finally, this dried product was crushed with a jet mill.
And become a product. Not only water-based but also titanium oxide
AlCl in powder _Three, SiCl_FourThrough the steam of
It is also possible to apply Al, Si surface treatment. Other faces
G.D.Parfitt and K.S.W.Sing ”Ch
aracterization of Powder Surfaces ”Academic Pres
s, 1976 can be referred to.

By mixing carbon black in the non-magnetic layer, it is possible to lower the surface electric resistance Rs, which is a known effect, and to reduce the light transmittance, and it is possible to obtain a desired micro Vickers hardness. The micro-Vickers hardness of the non-magnetic layer is usually 25 to 60 kg / mm ² , preferably 30 to 50 kg / mm ² for adjusting the head contact.
a mm ^2, using a NEC-made film hardness meter HMA-400, an edge angle of 80 degrees, a triangular pyramidal diamond needle tip radius 0.1μm using the indenter tip is measured. The light transmittance is generally such that the absorption of infrared rays having a wavelength of about 900 nm is 3% or less,
For example, VHS is standardized to be 0.8% or less. For this purpose, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used.

The specific surface area of carbon black is 100 to 5
00 m ² / g, preferably 150 to 400 m ² / g, D
BP oil absorption is 20-400 ml / 100g, preferably 30-
It is 200 ml / 100 g. The particle size of carbon black is 5
mμ-80 mμ, preferably 10-50 mμ, and more preferably 10-40 mμ. PH of carbon black
Is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is 0.1 to 1 g / ml. As a specific example of carbon black used in the present invention, manufactured by Cabot Corporation,
BLACKPEARLS 2000, 1300, 100
0, 900, 800, 880, 700, VULCAN
XC-72, Mitsubishi Kasei Co., Ltd., # 3050B, 315
0B, 3250B, # 3750B, # 3950B, # 9
50, # 650B, # 970B, # 850B, MA-6
00, MA-230, # 4000, # 4010, manufactured by Columbian Carbon Co., CONDUCTEX SC, RA
VEN 8800,8000,7000,5750,5250,3500,2100,2000,18
Examples include 00,1500,1255,1250 and Ketjen Black EC manufactured by Akzo. Even if carbon black is surface-treated with a dispersant or grafted with a resin,
A part of the surface of which is graphitized may be used. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used within a range not exceeding 50% by weight based on the inorganic non-magnetic powder and not exceeding 40% by weight of the total weight of the non-magnetic layer. These carbon blacks can be used alone or in combination.

The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association. In addition, an organic powder can be added to the non-magnetic layer according to the purpose. For example, acrylic styrene resin powder, benzoguanamine resin powder,
Melamine-based resin powders and phthalocyanine-based pigments can be mentioned, but polyolefin-based resin powders, polyester-based resin powders, polyamide-based resin powders, polyimide-based resin powders, and polyfluoroethylene resins can also be used. As the manufacturing method, those described in JP-A-62-18564 and JP-A-60-255827 can be used. The undercoat layer is provided in a general magnetic recording medium, but it is provided in order to improve the adhesive force between the support and the magnetic layer, and the thickness is generally 0.5 μm or less. Target.

Binder, lubricant, dispersant for the non-magnetic layer,
As for the additive, solvent, dispersion method and the like, those of the magnetic layer (also referred to as upper layer) can be applied. In particular, the amount of binder, type,
As for the amounts and types of additives and dispersants to be added, known techniques for magnetic layers can be applied. As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,000 to 20.
0000, preferably 10,000 to 100,00
0, the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins.

As the thermosetting resin or reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin. , A mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Further, a known electron beam-curable resin can be used for the non-magnetic layer or the magnetic layer.

These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin,
At least one selected from vinyl chloride vinyl acetate vinyl alcohol resin and vinyl chloride vinyl acetate maleic anhydride copolymer may be used in combination with a polyurethane resin, or a combination of these with polyisocyanate. The structure of polyurethane resin is polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane,
Known materials such as polyester polycarbonate polyurethane, polycaprolactone polyurethane, and polyolefin polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and durability, -COOM, -SO ₃ M, -OSO
₃ M, -P = O (OM) ₂ , -OP-O (OM)
_2, (wherein M represents a hydrogen atom or an alkali metal _{salt,), - OH, -NR 2} , -N + R 3 (R is a hydrocarbon group), epoxy group, -SH, -CN, sulfobetaine,
It is preferable to use one in which at least one or more polar groups selected from phosphobetaine, carboxybetaine and the like are introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably ¹ to 10 ^-8 mol / g.
0 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbide.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, manufactured by Denki Kagaku Co., Ltd. 1000
W, DX80, DX81, DX82, DX83, 100
FD, ZEON MR-104, MR-105,
MR110, MR100, 400X-110A, Nipporan N2301, N2302, N
2304, Pandex T-510 manufactured by Dainippon Ink and Chemicals, Inc.
5, T-R3080, T-5201, Burnock D-4
00, D-210-80, Crisbon 6109, 720
9, Toyobo Co. Byron UR8200, UR8300,
RV530, RV280, manufactured by Dainichiseika, Daiferamine 4020, 5020, 5100, 5300, 902
0,9022,7020, Mitsubishi Kasei, MX500
4, Sampren SP-150, TIM-3 manufactured by Sanyo Kasei Co., Ltd.
003, Saran F310, F210 and the like manufactured by Asahi Kasei. Among them, MR-104, MR110, MPR
-TA, UR-8200 and UR8300 are preferable.

The binder used in the magnetic layer of the present invention is in the range of 5 to 25% by weight, preferably 8 to 8% by weight based on the ferromagnetic powder.
It is used in the range of 22% by weight. 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, 2 to 20% by weight of polyisocyanate
It is preferable to use them in combination in the range of weight%. In particular, it is desirable that the magnetic layer does not contain polyisocyanate and the non-magnetic layer contains polyisocyanate.

In the present invention, when polyurethane is used,
Glass transition temperature is -50 to 100 ° C and elongation at break is 1
0 to 2,000%, breaking stress 0.05 to 10 kg /
cm ^Two , Yield point is 0.05 to 10 kg / cm^Two Is preferred
Yes. When the magnetic recording medium of the present invention is composed of two or more layers
Is the amount of binder, the vinyl chloride resin,
Polyurethane resin, polyisocyanate or higher
Amount of resin outside, molecular weight of each resin forming the magnetic layer, polarity
Basic amount or physical properties of resin mentioned above are required
It is of course possible to change between the non-magnetic layer and the magnetic layer.
Therefore, a publicly known technique regarding the multilayer magnetic layer can be applied. example
For example, when changing the amount of binder in each layer,
Increase the amount of binder in the magnetic layer to reduce scratches
Is effective and good head touch to the head
In order to achieve this, increase the amount of binder in layers other than the magnetic layer.
It is achieved by having flexibility.

As the polyisocyanate used in the present invention, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates are used. can do. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate M
R, Millionate MTL, Takeda Yakuhin, Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, Sumitomo Bayer, Death Module L, Death Module IL, Death Module N, Death Module HL, Dainippon Ink Burnock D
502 and the like can be used as the non-magnetic layer and the magnetic layer in combination of two or more by utilizing the difference in curing reactivity.

The carbon black used in the present invention is a furnace for rubber, a thermal for rubber, a black for color,
Acetylene black and the like can be used. Specific surface area is 5-500 m ² / g, DBP oil absorption is 10-400
ml / 100 g, particle size is 5 μm to 300 μm, pH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1 μm.
1 to 1 g / CC is preferable. Specific examples of the carbon black used in the present invention include BLA manufactured by Cabot Corporation.
CKPEARLS 2000, 1300, 1000, 9
00, 800, 700, VULCAN XC-72, Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3.
5, # 2400B, # 2300, #, manufactured by Mitsubishi Chemical Corporation
5, # 900, # 950, # 970, # 1000, # 3
0, # 40, # 10B, Colombian Carbon Co., C
ONDUCTEX SC, RAVEN 150, 50,
40, 15 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 one obtained by partially graphitizing the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance.
These carbon blacks can be used alone or in combination. When carbon black is used, it is preferable to use 0.1 to 30% of the amount based on the ferromagnetic powder. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the non-magnetic layer, and are based on the above-mentioned characteristics such as particle size, oil absorption, electric conductivity, and pH. Of course, it is possible to use them properly according to the purpose. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

As the abrasive used in the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized having an α conversion of 90% or more. Known materials such as silicon-titanium carbide, titanium oxide, silicon dioxide, and boron nitride, which are mainly Mohs 6 or more, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is 0.0
The thickness is preferably from 1 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or even a single abrasive may have the same effect by broadening the particle size distribution. Tap density is 0.3-2g / cc, water content is 0.1-5%,
PH is preferably ^{2 to} 11, and specific surface area is preferably 1 to 30 m ² / g.

The abrasive used in the present invention has a needle shape,
It may have a spherical shape or a dice shape, but one having a corner in a part thereof is preferable because of high abrasivity. Specific examples of the abrasive used in the present invention include those manufactured by Sumitomo Chemical Co., Ltd., A
KP-20, AKP-30, AKP-50, HIT-5
0, HIT-60, HIT-80, HIT-80G, H
IT-100, Nippon Kagaku Kogyo KK, G5, G7, S-
1, manufactured by Toda Kogyo Co., Ltd., TF-100, TF-140 and the like. The abrasives used in the present invention can be of different types, amounts and combinations in the non-magnetic layer and the magnetic layer and can be used properly according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. The abrasive present on the surface of the magnetic layer and the end face of the magnetic layer of the magnetic recording medium of the present invention is 5/100 μm ^2.
The above is preferred.

As the additive used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ethers, fluorine-containing alkyl sulfates and alkali metal salts thereof, containing 10 to 24 carbon atoms Basic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (Li,
Na, K, Cu, etc., or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms (including unsaturated bonds and may be branched) ),
C12-C22 alkoxy alcohol, C10
~ 24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and monovalent fatty acids having 2 to 12 carbon atoms,
Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid consisting of any one of dihydric, trihydric, tetrahydric, pentahydric, and hexahydric alcohol (whether or not unsaturated bond is contained or branched) Ester, fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid amide having 8 to 22 carbon atoms, aliphatic amine having 8 to 22 carbon atoms, and the like can be used.

Specific examples thereof 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 and stearic acid. Examples thereof include isooctyl, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol and lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. 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, alkylbedine type, etc. Can be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are always 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

The types and amounts of these lubricants and surfactants used in the present invention can be appropriately selected for each layer. For example, fatty acids having different melting points in the non-magnetic layer and magnetic layer are used to control bleeding to the surface, esters having different boiling points and polarities are used to control bleeding to the surface, and the amount of surfactant is adjusted. Therefore, it is considered that the stability of coating is improved, the amount of the lubricant added is increased in the non-magnetic layer, and the lubrication effect is improved. Of course, the present invention is not limited to the examples shown here.

All or part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with a ferromagnetic powder before the kneading step, a ferromagnetic powder is used. There are cases where it is added in a kneading step using a binder and a solvent, when it is added in a dispersion step, when it is added after dispersion, and when it is added immediately before coating. In some cases, the purpose may be achieved by applying a part or all of the additives simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after the slit is completed.

Examples of commercial products of these lubricants used in the present invention are NAA-102 and NAA-4 manufactured by NOF CORPORATION.
15, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, Cation SA, Cation MA, Cation A
B, cation BB, Nimeen L-201, Nimeen L-202, Nimeen S-202, Nonion E-20
8, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku, oleic acid, manufactured by Takemoto Yushi, FAL-205, FAL-123,
Engelbu LO, Enjorbu IP, manufactured by Shin Nippon Rika Co., Ltd.
M, Sansocizer-E4030, manufactured by Shin-Etsu Chemical Co., Ltd., TA
-3, KF-96, KF-96L, KF96H, KF4
10, KF420, KF965, KF54, KF50,
KF56, KF907, KF851, X-22-81
9, X-22-822, KF905, KF700, KF
393, KF-857, KF-860, KF-865,
X-22-980, KF-101, KF-102, KF
−103, X-22-3710, X-22-3715,
KF-910, KF-3935, manufactured by Lion Armor Company, Armid P, Armid C, Armoslip C
P, manufactured by Lion Oil & Fat Co., Ltd., Deuomin TDO, manufactured by Nisshin Oil Co., Ltd., BA-41G, manufactured by Sanyo Chemical Co., Ltd., Profan 2012
E, Newpole PE61, Ionnet MS-400,
IONET MO-200 IONET DL-200, IONET DS-300, IONET DS-1000 IONET DO-200 and the like.

The organic solvent used in the present invention is any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. , Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, and other glycol ethers, benzene, etc. Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chlorine Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
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 organic solvent used in the present invention is preferably the same type in the magnetic layer and the non-magnetic layer. The amount added may be changed. Solvents with high surface tension in the non-magnetic layer (cyclohexanone, dioxane, etc.)
It is important that the stability of coating is increased by using, specifically, the arithmetic average value of the solvent composition of the magnetic layer does not fall below the arithmetic average value of the solvent composition of the non-magnetic layer. In order to improve the dispersibility, it is preferable that the polarity is strong to some extent, and it is preferable that the solvent composition contains 50% by weight or more of a solvent having a dielectric constant of 15 or more and 20 or less. Further, the dissolution parameter is preferably from 8 to 11.

The thickness of the magnetic recording medium of the present invention is such that the non-magnetic support has a thickness of 1 to 100 μm, and is particularly effective when a thin non-magnetic support having a thickness of 1 to 8 μm is used. The total thickness of the magnetic layer and the non-magnetic layer is 1/1 of the thickness of the non-magnetic support.
It is used in the range of 0 to 2 times. Further, an adhesive layer for improving adhesion is provided between the non-magnetic support and the non-magnetic layer coating layer.

The thickness of the adhesive layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. Further, a back coat layer may be provided on the non-magnetic support on the side opposite to the magnetic layer side. This thickness is 0.1-2 μm, preferably 0.3
Is about 1.0 μm. Known adhesive layers and back coat layers can be used. The non-magnetic support used in the present invention has a micro Vickers hardness of 75 kg / mm ² or more, and biaxially stretched polyethylene naphthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenzoxdazole. A publicly known film such as the above can be used. In particular, a nonmagnetic support using aramid resin or polyethylene naphthalate is preferable.

Corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment and the like may be performed on these non-magnetic supports in advance. In order to achieve the object of the present invention, the center line average surface roughness of the surface of the non-magnetic support on which the magnetic layer is coated is 10 nm or less, 0.1 nm or more, preferably 6 nm or less, 0.2 nm or more, more preferably 4 nm or less. It is necessary to use one having a thickness of 0.5 nm or more. Also,
These non-magnetic supports preferably have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more. The surface roughness shape 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 of Al, Ca, Si, Ti and the like, whether crystalline or amorphous, and organic fine powders such as acrylic or melamine. Further, in order to achieve compatibility with running durability, it is preferable that the surface on which the back layer is applied be rougher than the surface on which the magnetic layer is applied.
The center line surface roughness of the back layer coating surface is preferably 1 nm or more, more preferably 4 nm or more. When changing the roughness between the magnetic layer-coated surface and the back layer-coated surface, a dual-structured support may be used, or a coating layer may be provided.

The F-5 value in the tape running direction of the non-magnetic support used in the present invention is preferably 10 to 50 kg / mm.
^2. The F-5 value in the tape width direction is preferably 10 to 30K.
g / mm ² , and the F-5 value in the longitudinal direction of the tape is generally higher than the F-5 value in the tape width direction. However, especially when the strength in the width direction needs to be increased, Not. The heat shrinkage ratio of the non-magnetic support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less at 80 ° C. for 30 minutes. Is preferably 1% or less, more preferably 0.5% or less. Breaking strength 5-100 in both directions
Kg / mm ² , elastic modulus is 100 to 2,000 Kg / mm
² is preferred. The light transmittance at 900 nm in the present invention is preferably 30% or less, more preferably 3% or less.

The process for producing the magnetic coating material for the magnetic recording medium of the present invention comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes, if necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and 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. In order to achieve the object of the present invention, it goes without saying that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong kneading force such as a continuous kneader or a pressure kneader is used. It is preferable to use one. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (preferably 30% or more of the total binder) and 15 to 500 parts of kneading with 100 parts of the ferromagnetic powder are kneaded. It is processed. Details of these kneading processes are described in JP-A-1-106338 and JP-A-64-79274. Further, in the case of preparing the magnetic layer liquid and the non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity in order to increase the degree of dispersion, and zirconia beads are preferable. Also, zirconia beads can be used when the abrasive is separately dispersed.

The following constitution can be proposed as an example of an apparatus and method for coating a magnetic recording medium having a multilayer constitution as in the present invention. 1. First, the non-magnetic layer coating layer is coated by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for coating a magnetic coating material, and the non-magnetic layer coating layer is kept in a wet state. The magnetic layer is coated by the support pressure type extrusion coating apparatus disclosed in JP-B-1-46186, JP-A-60-238179 and JP-A-2-265672.

2, JP-A-63-88080, JP-A-2-17971
The upper and lower layers are applied almost simultaneously by one coating head having two built-in slits for passing the coating liquid as disclosed in JP-A-2-265672. 3. The upper and lower layers are coated almost simultaneously by the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the agglomeration of magnetic particles, it is disclosed in JP-A-62-951.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in JP-A No. 74 and JP-A-1-236968. Further, regarding the viscosity of the coating liquid,
It must satisfy the numerical range disclosed in 8471.

In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1,000 G or more and a cobalt magnet of 2,000 G or more in the same polarity facing each other, and to provide an appropriate drying step before orientation so that the orientation after drying is the highest. preferable. It is known that in order to perform high-density recording, it is effective to incline the axis of easy magnetization in the vertical direction regardless of the needle shape or the plate shape, and it is also effective to combine it with this.

In addition, a known method for improving the adhesiveness is provided by providing an adhesive layer containing a polymer as a main component before the simultaneous multi-layer coating of the non-magnetic layer and the magnetic layer, or by corona discharge, UV irradiation, and EB irradiation. It is preferable.

Further, a heat-resistant plastic roll of epoxy, polyimide, polyamide, polyimide amide or the like is used as the calendering roll. Further, the treatment can be performed between metal rolls. The treatment temperature is preferably 70 to 120 ° C, more preferably 80 to 100 ° C.
℃ or above. Linear pressure is preferably 200-500 kg
/ Cm, more preferably 300 to 400 kg / cm or more.

The magnetic layer surface and its surface of the magnetic recording medium of the present invention.
The coefficient of friction of SUS420J on the opposite side of
Is 0.1 to 0.5, more preferably 0.2 to 0.3
is there. The surface resistivity is preferably 10^Four -10¹²Ohm
/ Sq, the elastic modulus at 0.5% elongation of the magnetic layer is the running direction,
Preferably in the width direction 100-2,000 Kg / mm
^Two , Breaking strength is preferably 1 to 30 kg / cm^Two , Magnetic
The elastic modulus of the recording medium is preferably in both the running direction and the long direction.
100-1500Kg / mm^Two , The residual elongation is preferable
Is less than 0.5% and heat absorption at all temperatures below 100 ° C
Reduction ratio is preferably 1% or less, more preferably 0.5%
Below, most preferably below 0.1%, 0% is ideal
It is. Glass transition temperature of magnetic layer (dynamic measured at 110 Hz
The maximum point of loss elastic modulus in viscoelasticity measurement) is 50 ° C or more 120
The temperature of the nonmagnetic layer is preferably 0 ° C to 100 ° C.
preferable. Loss modulus is 1 × 10⁸ ~ 8 × 10⁹dyne / cm
^TwoAnd the loss tangent is 0.2 or less.
It is preferred that If the loss tangent is too large, it will stick
Easy to get hindered. The residual solvent contained in the magnetic layer is preferably
Is 100 mg / m^Two Or less, more preferably 10 mg /
m^Two And the residual solvent contained in the magnetic layer is
It is preferable that the amount is less than the residual solvent contained in. Magnetic layer
The porosity of each of the non-magnetic layer and the magnetic layer is preferably 30.
It is not more than 20% by volume, more preferably not more than 20% by volume.
Porosity is preferably small to achieve high output
However, it may be better to secure a certain value depending on the purpose.
You. For example, data recording magnets for which repeated use is important
For air recording media, the larger the porosity, the better the running durability.
Often

The magnetic characteristic of the magnetic recording medium of the present invention is the magnetic field 1
When measured by VSM at 0 kOe, H in the tape running direction
c is 2000 to 3000 Oe, and more preferably 2100 to
It is 2500 Oe. The squareness ratio (SQ) is 0.75 or more, preferably 0.80 or more, and more preferably 0.85 or more. The squareness ratio in the two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less, more preferably 0.5 or less, and ideally 0. The remanence coercive force Hr in the longitudinal direction is also preferably 1800 Oe or more and 3000 Oe or less. Hc and Hr in the vertical direction
Is preferably 1000 Oe or more and 5000 Oe or less.

RMS determined by AFM evaluation of magnetic layer
The surface roughness RRMS is preferably in the range of 2 nm to 15 nm.

The magnetic recording medium of the present invention can have a non-magnetic layer and a magnetic layer, but it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. Is. 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. It is also effective in the present invention to improve the head contact by changing the method of tensifying the support, and the support tensified in the direction perpendicular to the longitudinal direction of the tape has better head contact. Often.

[0075]

Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. In the examples,
The indication “parts” indicates “parts by weight”. Examples 1 to 20, Comparative Examples 1 to 5: Lower coating layer (nonmagnetic layer): Coating formulation a: Inorganic nonmagnetic powder: α-Fe ₂ O ₃ hematite 80 parts Long axis length 0.15 μm Specific surface area by BET method 52 m ² / g pH 6 Tap density 0.8 Surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatilization min 1.5% vinyl chloride copolymer 12 parts (manufactured by Nippon Zeon Co., Ltd. MR-104) polyester polyurethane resin 5 parts neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO 3 Na group containing 1 × 10 ^-4 eq / g α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 1 part Methyl ethyl ketone 100 parts 1 part butyl stearate 1 part stearic acid Rohekisanon 50 parts Toluene 50 parts lower coating layer (nonmagnetic layer): coating formulation b: inorganic non-magnetic powder: specific surface area by the TiO ₂ Titanium oxide 80 parts particle size 0.022 BET method 75m ² / g pH 7.5 DBP oil absorption Amount 27-38 g / 100 g Surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle size 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET specific surface area 250 m ² / g Volatile content 1.5% Vinyl chloride-based copolymer 12 parts (MR-104 manufactured by Zeon Corporation) Polyester polyurethane resin 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g content α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Butyl stearate 1 part Stearic acid 1 part Methyl ether Cylketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Magnetic paint (magnetic layer): Coating formulation a Ferromagnetic metal powders A to E (listed in Table 1) 100 parts Polyurethane A to G (listed in Table 2) or H (table 3) 12 parts α-alumina (average particle size 0.15 μm) 5 parts Carbon black (average particle size 0.08 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts Magnetic paint (magnetic layer) ): Coating formulation b Ferromagnetic metal powders A to E (described in Table 1) 100 parts Vinyl chloride-based copolymer 12 parts MR-110 polyurethane A to G (described in Table 2) manufactured by Zeon Corporation 5 parts α-alumina (average) Particle size 0.2 μm) 1 part Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts

[0076]

[Table 1]

[0077]

[Table 2]

[0078]

[Table 3]

The components of each of the above paints were kneaded with an open kneader and then dispersed using a sand mill. To the obtained dispersion, 5 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the lower non-magnetic paint and 5 parts to the magnetic paint, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was further added to 1 μm. A non-magnetic paint and a magnetic paint were prepared by filtering using a filter having an average pore size of.

The thickness of the obtained non-magnetic coating material after drying is
The magnetic coating is applied at a thickness of 5.5 μm so that the magnetic coating has a thickness of 1.2 μm and, immediately thereafter, the thickness of the magnetic layer after drying is the thickness shown in Tables 4 to 9. Simultaneous multilayer coating is performed on a polyethylene naphthalate support having a surface center surface roughness of 0.002 μm, and while both layers are still in a wet state, a cobalt magnet having a magnetic force of 3000 G and a solenoid having a magnetic force of 1500 G are used. After orienting and drying, a 7-stage calender consisting of only metal rolls was used to perform treatment at a temperature of 90 ° C. at a speed of 200 m / min and a linear pressure of 270 Kg / cm, and then a back layer having a thickness of 0.5 μm was applied. Slit to a width of 8 mm, various 8 in Tables 4-9
mm video tapes were manufactured and evaluated by the following, and the results are shown in Tables 4-9.

[0081]

[Table 4]

[0082]

[Table 5]

[0083]

[Table 6]

[0084]

[Table 7]

[0085]

[Table 8]

[0086]

[Table 9]

[Evaluation Method] <Method for Measuring Thickness of Magnetic Layer> A magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter over the longitudinal direction, and observed with a transmission electron microscope at a magnification of 30,000. I took the picture. The print size of the photo is A4 size. After that, paying attention to the shape difference between the ferromagnetic powder and the non-magnetic powder in the magnetic layer and the non-magnetic layer, the interface is visually judged and bordered in black.
Further, the surface of the magnetic layer was similarly trimmed in black, and then the distance between the trimmed lines was measured by an image analyzer (IBAS-2 manufactured by Carl Zeiss). The measurement point was measured over a range of 21 cm in the length of the sample photograph. The simple arithmetic mean of the measured values at that time was divided by the magnification to obtain the thickness of the magnetic layer. <Surface roughness Ra of magnetic layer> Using a light interference three-dimensional roughness meter "TOPO3D" manufactured by WYKO (Arizona, USA), the surface of the magnetic layer was about 250 nm × 250 by MIRAU method.
The Ra in the area of nm was measured. Measurement wavelength is about 650nm
Adds spherical and cylindrical corrections. <Electromagnetic conversion characteristics> “Output at recording wavelengths of 0.488 μm and 22 μm” Outputs at recording wavelengths of 0.488 μm and 22 μm are measured as follows. The reference tape is our reference ME tape (vapor deposition tape for 8 mm video tape).
Then, using an external drum tester, the relative speed is 10.2
The signal corresponding to the recording wavelength is recorded at m / sec,
The reproduction output was measured. The head used was an Fe-based head B
s is 1.5T. The recording current was set to the reference optimum recording current.

The higher the output of the recording wavelength of 0.488 μm, the more preferable. The output of 22 μm is preferably in the range of a reference ratio of −2 dB or more and +2 dB or less. <Overwrite erasing rate> After recording a rectangular wave signal having a recording wavelength of 22 μm using an externally applied drum tester, the output is reproduced and measured. A rectangular wave signal having a recording wavelength of 0.488 μm was superimposed on the signal, recorded, reproduced, and then recorded.
Read the output of 2μm with a spectrum analyzer,
The ratio of the output of the wavelength of 22 μm before and after the overlapping recording is defined as the overwrite erasing rate. The absolute value is preferably −20 dB or less. <Head corrosion> A magnetic layer was brought into contact with a test piece in which a permalloy sputtered film was formed on a PET base, and the temperature was 60% at 90 ° C.
It was stored in an RH environment for 1 week, and the corrosion of the permalloy sputtered film was evaluated. As for the evaluation rank, 10 fields were observed under a microscope field of view of 50 times, and those with no corrosion were evaluated as ◯, corrosion at one location was evaluated as Δ, and higher than that were evaluated as x. <Running Durability> The tape was run in an atmosphere of 23 ° C. and 70% RH with 10 units of 8 mm video deck FUJIX8 manufactured by Fuji Photo Film Co., Ltd. 100 times each. During that time, the output reduction was measured, and the contamination of each part in the deck after running was evaluated. ◯: Output decrease was within 3 dB, and stains on various parts inside the deck were not visually observed. Δ: Output decrease was within 3 dB, but a lot of stains on each part in the deck were visually observed. Poor: The output was reduced by 3 dB or more, and there were many stains on various parts inside the deck.

[0089]

INDUSTRIAL APPLICABILITY According to the present invention, high density recording is possible by using a binder resin containing polyurethane having a specific radius of gyration and forming a magnetic layer having an extremely thin magnetic layer and containing minute ferromagnetic powder. A magnetic recording medium having excellent overwrite characteristics, running durability, and corrosion resistance can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroaki Takano 2-2-1-1, Ogimachi, Odawara-shi, Kanagawa Inside Fuji Photo Film Co., Ltd.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder resin is formed on at least one surface of a non-magnetic support, and the magnetic layer has a thickness of 0.05 to
0.8 μm, and the average major axis diameter of the ferromagnetic powder is 0.0
The magnetic recording medium is characterized in that the binder resin contains polyurethane having a radius of gyration of 5 to 25 nm in cyclohexanone.