JPS5818766B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic recording bodies such as magnetic tapes and magnetic disks, and in particular, has few holes and high coercive force,
The present invention relates to a magnetic recording medium using ferromagnetic iron trioxide with excellent dispersibility and orientation.

The production of high-density magnetic recording media requires magnetic materials with high coercive force, excellent acicularity, squareness ratio, and good dispersibility.

As is well known, ferromagnetic iron oxide is iron oxyhydroxide [α-FeOOH (goethite),... β-FeO
OH1r-Fe00H (lepidocrocite)] is dehydrated,
Obtained by reduction and oxidation.

Regarding the above technology, Japanese Patent Publication No. 26-7776, No. 31
-3292, 44-14090, 47-259
No. 59, No. 47-39477, JP-A No. 47-4009
No. 7, No. 49-15699, U.S. Patent No. 2127907
No. 2388659, etc. are known.

In order to increase the coercive force of iron oxide-based magnetic powder, it is effective to incorporate Co into a solid solution.This method is described in U.S. Pat. No. 3,117,333, U.S. Pat.
No. 27719, No. 42-6113, No. 48-1099
No. 4, No. 48-15759, No. 49-4264, JP-A No. 47-22707, No. 48-1998, No. 48
-51297, 48-54497, 48-76
No. 097, No. 48-87397, No. 48-10159
No. 9 is known.

Co-containing magnetic iron oxide has problems such as pressure demagnetization, heat demagnetization, changes in coercive force over time, non-uniformity of coercive force, erasing characteristics, and deterioration of sp ratio, and improvements are being made in these areas.

In addition, ferromagnetic iron oxide has many vacancies as a result of water loss, but the presence of vacancies causes a decrease in the apparent magnetization per unit volume of ferromagnetic iron oxide. This produces several magnetic domains within the particles and causes ferromagnetic iron oxide aggregation in the magnetic film.

The following four methods are known to reduce the number of pores during dehydration, reduction, and oxidation.

(1) Particles are coated with an inorganic substance prior to dehydration, reduction, and oxidation.

(Special Publication No. 38-26278, No. 40-22055,
Japanese Patent Application Laid-open Nos. 47-42396, 48-83100, 48-67197, 49-14400, and US Pat. No. 3,652,334 are known.

)(2) Coating particles with organic matter prior to dehydration, reduction, and oxidation.

(U.S. Patent Nos. 3,394,142, 3,498,748, JP-A-47-40097, JP-A-49-8496, JP-B-41-18786, etc. are known.

) (3) Adding ions effective against dehydration, reduction, and oxidation (Al ions (Japanese Patent Publication No. 38-26278, Japanese Patent Publication No. 49-59137, etc.), Cr ions (% Japanese Patent Publication No. 49-43899) , 49-43900
), Ca ion (Japanese Patent Publication No. 47-31195), other examples include JP-A-47-30477, JP-A-4
No. 8-23752, No. 48-23753, No. 48-237
No. 54, No. 49-7313, JP-A No. 48-97800
There are numbers etc.

] (4) Use special dehydration, reduction, and oxidation conditions.

(Special Publications No. 26-7776, No. 38-26156, No. 39-5009, No. 39-16012, No. 42-2)
No. 4661, JP-A No. 49-43900, U.S. Patent No. 26
No. 89168 is known.

) The above measures have been taken to reduce the number of pores.

When particles are covered with inorganic substances or metal ions are added,
During heat treatment, they become a solid solution in magnetic iron oxide, or the surface properties of iron oxide change, causing sintering to proceed.

There are few vacancies (in order to obtain high coercive force, α Fe2O
500-800℃ at stage 3, 30℃ at stage of Fe3O4
Although it is necessary to heat treat at a high temperature of 0 to 500°C,
Such heat treatment advances the sintering of the magnetic iron oxide.

It is difficult to disperse magnetic iron oxide whose surface properties have changed as a result of sintering to create a magnetic coating solution, and requires a long dispersion time.

The present invention improves these drawbacks.

The first object of the present invention is to have a high coercive force with few pores,
An object of the present invention is to provide magnetic iron oxide having excellent acicular properties.

The second object is to provide magnetic iron oxide that exhibits less decrease in coercive force when highly filled.

Thirdly, it is desirable to provide magnetic iron oxide which has excellent dispersibility and requires a short dispersion time to prepare a magnetic coating liquid.

The fourth object is to provide magnetic iron oxide with excellent orientation.

A fifth object is to provide a magnetic recording body using the above-mentioned magnetic iron oxide, which has excellent squareness ratio and orientation, and is suitable for high-density recording.

In recent years, research on the state of atomic nuclei has been progressing using resonance absorption of gamma rays.

This phenomenon is called the Mössbauer effect, and iron compounds,
Various studies are progressing on the ability of tin compounds.

More information about the Mössbauer effect can be found in the following books:

OH, Frauenfelder, “The M6
ssbauer EEeffect”, (W, A, Be
Njamin, New York, 1962).

OG, K. Werthe im, “M6s
sbauer Effect: Principle
s and Appl 1cations”, (Aca
demic Press, New Yorkll 96
4), Q. Hirotoshi Sano, “Mössbauer Spectroscopy” (Kodansha, 1972).

When measuring the Mössbauer effect on the magnetic recording medium according to the present invention, we found that it was completely unexpected that the magnetic recording medium of the present invention
rparamagnetic Material)
There was a peak corresponding to .

A superparamagnetic material is a ferromagnetic or antiferromagnetic material that has become fine particles, so it behaves as if it were a paramagnetic material due to thermal motion.

The relationship with the Mössbauer effect can be found on pages 238 to 239 of the aforementioned "Mössbauer Spectroscopy" [When a ferromagnetic material or an antiferromagnetic material becomes fine particles, a significant change is observed in the Mössbauer spectrum.

There are magnetic domains of a certain size in these magnetic bodies, but when they become fine particles, there is only one magnetic domain, for example, and the magnetic field that acts on the position of the nucleus is τ = roexp (KV/kT ) (5, 26).

Here, K is an asymmetry constant and ■ is the particle size.

As we will see, when kT<KV, the magnetic field is oriented in a fixed direction for a long time at that temperature, indicating magnetic splitting, but when kT>KV, the magnetic field at the nuclear position is averaged due to thermal motion. Magnetic splitting is no longer exhibited.

This latter state is similar to the phenomenon in which the magnetic field at the core is averaged out due to the thermal motion of molecules in paramagnetic materials, and is called a superparamagnetic phenomenon.

The particle size can also be estimated using the superparamagnetic phenomenon ((disappearance of magnetic splitting in Mössbauer terms) from the relationship of equations (5, 26).

” is stated.

The term superparamagnetic material used in the present invention does not refer to fine particles that are said to contribute to the transfer effect in magnetic recording materials, but rather refers to superparamagnetic materials (5up) when measuring the Mössbauer effect.
er paramagnetism).

In other words, the superparamagnetic material of the present invention is physically considered to be iron oxide.

Although it is not clear how the superparamagnetic iron oxide is distributed in Examples 1 to 4, due to the difference from the comparative example, one particle (long axis 0.6 μ) contains superparamagnetic iron oxide with a diameter of 100 Å or less. is near the surface.

It is thought that these superparamagnetic iron oxides exist, and when they are made into a paint, they promote the dispersion into single particles, which is the reason for the excellent squareness ratio, high saturation magnetic flux density, and low modulation noise shown in Table 1. It is thought that this is the case.

The proportion of the superparamagnetic substance in the magnetic iron oxide is confirmed from the area of the absorption peak of the magnetic iron oxide and the area of the absorption peak due to the superparamagnetic substance in the Mössbauer spectrum.

It should also be determined by precisely measuring the saturation magnetization (σS), but in this case there is also the influence of non-magnetic impurities, so the relationship between the presence of the superparamagnetic component and the improvement of the characteristics of the magnetic recording medium according to the present invention is This was achieved for the first time using the Mössbauer spectrum.

That is, the present invention provides a magnetic recording material in which a magnetic layer mainly composed of ferromagnetic fine powder and a binder is provided on a substrate.
The present invention is a magnetic recording material characterized in that the ferromagnetic fine powder contains a superparamagnetic material.

In the present invention, the ferromagnetic powder whose main component is iron oxide is maghemite (γ-Fe2O3) or magneta.

(Fe304), a bertolide compound (FeOx, 1
．． 33 <

Co is particularly preferred as the metal ion.

Specifically, Co doped maghemite, Co and M
n doped maghemite, Co and Cr dop
ed maghemite, Co, Mn and Cr doped maghemite, Co doped magnetite, Co and Mn doped magnetite, Co and Crdop
ed magnetite, Co, Mn and Cr doped
7 Gnetite, C.

doped beltlide iron oxide, Co and Mn dop
ed beltlide iron oxide, Co, Mn and Crdope
Examples include d-bertride iron oxide.

The effective range of the superparamagnetic material in the magnetic recording medium is 0.01 to 30 wt.% with respect to magnetic iron oxide, and the generally preferred range is 0.1 to 15 wt.%.

However, if the amount of binder can be reduced, this range can be expanded.

It is known that the coercive force (He) of an iron oxide magnetic material can be increased by containing Co.

The amount of Co added is within a useful range of 0.5% or more and 20% or less in the field of magnetic recording, but the coercive force is 500 to 15%.
In order to be used in high-density magnetic recording media such as 000e (for example, video tapes, master tapes, memory tapes, etc.), the amount of Co is preferably 1 to 10%.

Even in the case of a magnetic recording medium using such an iron oxide magnetic material containing Co, the effective range of the superparamagnetic material is 0.
01-30wt,%, preferably 0.1-30wt%
It is 15wt,%.

In addition, in order to improve the stability over time, pressure demagnetization, heating demagnetization, etc. of iron oxide magnetic materials (including iron oxide magnetic materials containing Co), we have developed belt trines in an intermediate oxidation state between magnetite and maghemite. Compound (FeOX, 1.33<X<1.
5) is used, but in the case of magnetic recording bodies using these, the effective range of superparamagnetic material is 0.01 to 30wt,
%, and a preferable range is 0.1 to 20 wt.%.

It is known that during dehydration, reduction, and oxidation of iron oxide-based magnetic materials, the surface of iron oxyhydroxide is coated in advance with various substances in order to reduce the number of pores.

The amount of material covering the surface is 0.1 for γ-Fe2O3
~20wt0% is effective, but the preferred range is 0.5
~10wt0%.

The material ions that coat the iron oxyhydroxide surface include phosphates (for example, H3PO4; Na4P2O7・10H20; NaPO3・12H
2O: (NH4)3PO4・3H20; (NH4)2H
PO4;2HPO4:Na2HPO4;Na2HPO
4・12H20:NH4H2PO4;KH2PO4:N
aH2PO4+H20:NaH2PO4・2H20;L
iH2PO4 etc.); borate (H3PO3, NaBO
4.4H20, etc.); SiO2 sol, Al(OH)3,
Fe(OH)3, AlCl3, KCl, znC12
, titanium chloride, sodium sulfate, aluminum sulfate, Ca (
OH) 2. Silver ions, platinum metal ions, water-soluble fatty acids (stearic acid, palmitic acid, oleic acid, etc.) and their alkali salts, higher alcohols, higher alcohol esters, amides and other derivatives, morpholine, hydrophobic fatty acids These include monocarboxylic acids and coconut oil fatty acids.

In the case of a magnetic recording medium using magnetic iron oxide subjected to surface treatment in this way, the effective range of superparamagnetic material is O, O] ~ 3
0wt, %, preferably in the range 0.1 to 10wt
,%.

If the superparamagnetic component exceeds the effective range, the sensitivity and output of a magnetic tape will be low, and the surface resistance of the magnetic layer will be high, causing noise.

The following eight methods are preferred as methods for producing magnetic iron oxide used in the present invention.

(1) When performing a reaction consisting of a neutralization reaction or an oxidation reaction or a combination thereof in an iron salt solution to form goethite (α-Fe00H), neutralization to 90 to 95% of reaction completion;
After the oxidation reaction and the reaction of this composition proceed, only the neutralization reaction proceeds without performing the oxidation reaction, and α-FeOOH
Three layers of Fe(OH) are formed on top.

When forming the Fe(OH)a layer, a surface coating of iron oxyhydroxide may be present.

The a-FeOOH obtained by washing with water and drying was
Dehydrated at 00℃, Fe50. reduce to

Partial oxidation of Fe3O4 results in Fe0x (1,33<X<1.
5) A bertolide compound.

Alternatively, oxidize Fe3O4 at 200 to 400℃ to create γFe
Let it be 20s.

(2) When forming α-Fe00H, Co is added to form Co-containing α-Fe00H, and the same treatment as in (1) is performed below.

(3) Disperse α-FeOOH in water, add iron salt solution,
By neutralizing this, Fe (OH) on a-Fe00H
A layer is formed, then washed with water, dried, and subjected to the same heat treatment as in (1).

When forming the three Fe(OH) layers, a surface coating of iron oxyhydroxide may be present.

In addition, C in Fe(OH)3 formed on α-FeOOH
C.

α-FeOOH containing α-FeOOH can be obtained.

(4) Disperse α-FeOOH in water, add iron I salt solution, further add oxalic acid or alkali oxalate,
An iron oxalate layer is formed on Fe00H.

This is washed with water, dried, and heat treated in the same manner as in (1).

When an iron salt solution is added and Co is present, an iron oxalate layer containing Co can be formed.

In these cases, an iron oxalate layer may be formed by sharing a surface coating of iron oxyhydroxide and adding oxalic acid or an alkali oxalate.

(5) a Fe20a (especially acicular a-F
α-Fe20 (preferably e203) is dispersed in water and Fe (OH) 3 is provided on the surface in the same manner as in (1).
3 and reduce it at 300-500℃.

The obtained Fe3O4 is partially oxidized to Fe0x(1,33
<X<1.5).

Alternatively, Fe3O4 is oxidized at 200 to 400℃ to produce γ-
Let it be Fe2O3.

In addition, by sharing iron salt and Co salt, Co
Three layers of Fe(OH) can be formed.

(6) a-Fe203 (especially acicular a-Fe20
3 is preferred) in water, and in the same manner as in (4), α-Fe203 with an iron oxalate layer on the surface is obtained, and (5)
Perform the same heat treatment as above.

By coexisting the seasonal salt and the Co salt, an iron oxalate layer containing Co can be provided.

(7) Add urea to the iron salt solution and heat it, or
and acicular β-FeOOH1 or fine particles to which Co is added, obtained by hydrolyzing an iron salt solution containing halogen ions, are heat-treated in a reducing atmosphere,
Further heat treatment is performed in an oxidizing atmosphere to obtain maghemite or codoped maghemite.

(Unexamined Japanese Patent Publication No. 49-104193, No. 49-104194
No. 49-104195, No. 49-104899, No. 49-104900, etc.).

If this is further reduced, magnetite or Codop
Becomes ed magnetite.

(8) Ferrous hydroxide is generated using a ferrous salt solution and an alkaline solution, and oxidized with stirring in air or oxygen at low temperature to generate needle-shaped lepidocrocite (γ-Fe00H), which is heated. and get Maghemite.

If it is further reduced, it becomes magnetite.

In addition, a layer of lepidocrocite is formed on the surface of the ferromagnetic powder obtained by applying force to (1) above, followed by heating and dehydration to obtain a ferromagnetic powder whose surface is coated with a layer of maghemite.

(See Special Publication No. 33-6734 and No. 40-22055).

As the iron salt used in the above method, any water-soluble ferrous salt can be used.

Similarly, any water-soluble salt can be used for CO salt, and it is treated as alkaline.

For example, NaOH, KOH, NH4OH, LiOH, etc. can be used.

In Example 5, an example of a magnetic recording body using only the magnetic material according to the present invention is described, but other magnetic recording materials [
For example, ordinary γ-Fe2O3, )Fe304, FeOx
(1,33<X<1.5), CO-containing iron oxide magnetic material, CrO2, alloy] to form a magnetic recording body.

Furthermore, it is also suitable for use in multi-layer coated magnetic recording bodies;
Can be used for any of the lower layers.

When applying a multilayer coating, it may be mixed with other magnetic materials and used in the same manner as described in j above.

The ferromagnetic iron oxide of the present invention obtained by the above method is dispersed with a binder, coated on a substrate (support) using an organic solvent, and dried to form a magnetic layer to obtain a magnetic recording medium.

Regarding the manufacturing method of the magnetic paint used in the present invention,
-186, 47-28043, 47-28045, 47-28046, 47-28048, 47-3
It is described in detail in publications such as No. 1445.

The magnetic paints described in these documents contain ferromagnetic powder, binder, and coating solvent as main components, and may also contain additives such as dispersants, lubricants, abrasives, and antistatic agents.

The binder used in the present invention is a conventionally known thermoplastic resin, thermosetting resin or reactive resin.

A mixture of Yatore and others is used.

As a thermoplastic resin, the softening temperature is 150°C or less, the average molecular weight is 1oooo to 200,000, and the degree of polymerization is about 200 to 2.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer,
Methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer,
Polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), Methylene butadiene copolymers, polyester resins, chlorovinyl ether acrylate copolymers, amine resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

Examples of these resins are given in Japanese Patent Publication No. 37-6877, 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-20907, No. 41-9463, No. 41-14
No. 059, No. 41-16985, No. 4.2-6428,
42-・11621, 43-4623, 43-15
No. 206, No. 44-2889, No. 44-17947, 4
No. 4-18232, No. 45-14020, 45-145
No. 00, No. 47-18573, No. 47-22063, 4
7-22064, 47-22068, 47-220
No. 69, No. 47-22070, No. 48-27886, U.S. Patent No. 314.4352; No. 3419420; No. 3
No. 499789; No. 3713887.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, but when added after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition.

Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred.

Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, mixture of high molecular weight polyester resin and incyanate prepolymer, Mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof, etc. .

Examples of these resins are given in Japanese Patent Publication No. 39-8103, 40-
No. 9779, No. 41-7192, No. 41-8016, 4
1-14275, 42-18179, 43-120
No. 81, No. 44-28023, No. 45-14501, 4
5-24902, 46-13103, 47-220
No. 65, No. 47-22066, No. 47-22067, 4
No. 7-22072, No. 47-22073, No. 47-280
No. 45, No. 47-28048, No. 47-28922, U.S. Patent No. 3144353: No. 3320090: No. 34
No. 37510; No. 3597273; No. 3781210
No. 3781211.

These binders may be used alone or in combination;
Other additives may be added.

The mixing ratio of the ferromagnetic powder and the binder is 10 to 400 parts by weight, preferably 30 to 200 parts by weight, per 100 parts by weight of the ferromagnetic powder.

In addition to the above-mentioned binder and fine ferromagnetic powder, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent may be added to the magnetic recording layer.

Dispersants include caprylic acid, capric acid, lauric acid,
Fatty acids with 12 to 18 carbon atoms (R, COOH) such as myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, cursic acid, stearolic acid
, R, is an alkyl group having 11 to 17 carbon atoms); metal soaps made of alkali metals (Li, Na, etc.) or alkaline earth metals (Mg, Ca, Ba) of the above fatty acids; lecithin, etc. are used be done.

In addition, higher alcohols having 12 or more carbon atoms and sulfuric esters may also be used.

These dispersants are used in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder.
It is added in a range of parts by weight.

As a lubricant, silicone oil, carbon black, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, carbon number 12-16
fatty acid esters consisting of a monosalt aqueous fatty acid and a monohydric alcohol having 3 to 12 carbon atoms, a monosalt aqueous fatty acid having 17 or more carbon atoms, and a total of 2 carbon atoms in the fatty acid.
Fatty acid esters consisting of 1 to 23 monohydric alcohols can be used.

These lubricants are used in amounts of 0.2 to 100 parts by weight of binder.
It is added in an amount of 20 parts by weight.

Regarding these, the specifications of Japanese Patent Publication No. 43-23889, Japanese Patent Application No. 42-28647, Japanese Patent Application No. 43-81.543, U.S. Patent No. 3470021;
No. 5; No. 3497411; No. 3523086; No. 3
No. 625760; No. 3630772; No. 363425
No. 3; No. 3642539; No. 3687725: ”
IBM Technical Disclosure
Bulletin” Vnl, 9, A7, P
age779 (December 1966);''``ELEKTRONIK'' 1961, A, 12,
It is described in Page 380 etc.

Commonly used abrasive materials include fused alumina,
silicon carbide chromium oxide, corundum, artificial corundum,
Diamonds, synthetic diamonds, garnet, emery (main ingredients: corundum and magnetite), etc. are used.

These abrasives have an average particle diameter of 0.05 to 5 .mu.m, particularly preferably 0.1 to 2 .mu.m.

These abrasives are used in an amount of 7 to 20 parts by weight per 100 parts by weight of the binder.
Added in parts by weight.

Regarding these, Japanese Patent Application No. 48-26749, US Patent No. 3007807; US Patent No. 3041196, US Pat.
No. 93066; No. 3630910, No. 3687725
No.: British Patent No. 1145349; West German Patent (DT-
PS) No. 853211.

Natural surfactants such as saponin as antistatic agents; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, and
Cationic surfactants such as ammonium salts, pyridine and other heterocycles, phosphonium or sulfoniums; Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups; Amino acids , aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like are used.

Some examples of surfactant compounds that can be used as antistatic agents are disclosed in U.S. Pat.
No. 2288226, No. 2676122, No. 26
No. 76924, No. 2676975, No. 2691566
No. 2727860, No. 2730498, No. 27
No. 42379, No. 2739891, No. 3068101
No. 3158484, No. 3201253, No. 32
No. 10191, No. 3294540, No. 3415649
No. 3441413, No. 3442654, No. 34
No. 75174, No. 3545974, OLS No. 1942665, British Patent No. 1077317
No. 1198450, etc., "Synthesis of surfactants and their applications" by Ryohei Oda et al. (Maki Shoten 1964 edition);
``Surface Active Agents'' by A. W. Peiri (Iatar!;)-I, I-Nshaflication Inc. 1958 edition); ``Encyclopedia of Surface Active Agents'' by T. P. Sisley. , Volume 2'' (Chemical Publishing Co., Ltd., 1964 edition); and ``Surfactant Handbook'', 6th edition (Sangyo Tosho Co., Ltd., December 20, 1964), etc.

These surfactants may be added alone or in combination.

These are used as antistatic agents, but are sometimes used for other purposes, such as dispersion, improving magnetic properties,
It may also be used to improve lubricity and as a coating aid.

The magnetic recording layer is formed by dissolving the above-mentioned composition in an organic solution and coating it on a support as a coating solution.

The thickness of the support is about 5 to 50 μm, preferably 10 to 40 μm.
The diameter is preferably on the order of μm, and the materials used include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and polycarbonate.

The above-mentioned support is coated with a so-called back coat (ba
ckcoat).

Regarding the back coat, for example, US Patent No. 280,440
No. 1, No. 3293066, No. 3617378, No. 3
No. 062676, No. 3734772, No. 347659
No. 6, No. 2643048, No. 2803556, No. 2
No. 887462, No. 2923642, No. 299745
No. 1, No. 3007892, No. 30411'96, No. 3115420, No. 3166688, etc.

Further, the support may be in any form such as a tape, sheet, card, disk, or drum, and various materials may be selected as necessary depending on the form.

Methods for applying the above-mentioned magnetic recording layer onto the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, leaven roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, and spray coating. etc., and other methods are also possible, and detailed explanations of these can be found in "Coating Engineering" published by Asakura Shoten, pages 253-277.
(published on March 20, 1972).

Organic solvents used during coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, Ester systems such as acetic acid glycol monoethyl ether; ether, glycol dimethyl ether, glycol monoethyl ether,
Glycol ethers such as dioxane; tars (aromatic hydrocarbons) such as benzene, toluene, and xylene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. can be used.

By such a method, the magnetic layer coated on the support is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried.

Further, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary.

In this case, the orientation magnetic field is approximately 500 to 20
00 Gauss, and the drying temperature is approximately 50~i o o
℃, and the drying time is about 3 to 10 minutes.

These are, for example, Japanese Patent Publications No. 39-28368, No. 40-
No. 23625, US Pat. No. 3,473,960, etc.

Furthermore, the method disclosed in Japanese Patent Publication No. 13181/1986 is considered to be a basic and important technique in this field.

, FIG. 1 shows a magnetic recording body obtained according to the present invention (Example 1).
) is the Mössbauer spectrum at room temperature.

20 mci of 57Co was used as a source and a Naf dictor was used.

The Mössbauer effect measuring device is AME- manufactured by Elsinto.
30 model, and the wave height analyzer used was MS-71,0 model manufactured by Northern Scientific.

In FIG. 1, peaks 1, 2, 3, 4, 5, and 6 are peaks corresponding to trivalent iron, and peak 7 is a peak corresponding to superparamagnetic material.

FIG. 2 shows an example of the magnetic recording material of Example 3, in which a peak 29 of superparamagnetic material is observed.

Due to the coexistence of Fe(II) and Fe(JIJ), more complex peak groups 21 to 29 than in FIG. 1 were obtained.

FIG. 3 shows the Messbauer spectrum of a normal magnetic recording material (Comparative Example 1). In FIG. 3, peak 7 does not exist, and it is clear that no superparamagnetic material exists.

Effects and advantages of the present invention are as follows: (1) A magnetic recording medium using magnetic iron oxide with few pores, high coercive force, and good acicularity was obtained.

(2) A magnetic recording medium using magnetic iron oxide with less decrease in coercive force even if the filling dust was thickened was obtained.

(3) A magnetic recording material using magnetic iron oxide with excellent dispersibility and short dispersion time for preparing a magnetic coating liquid was obtained.

(4) Magnetic iron oxide with excellent orientation was obtained.

(5) When such magnetic iron oxide was used, a magnetic recording medium with excellent squareness ratio and orientation was produced.

The magnetic recording medium using magnetic iron oxide of the present invention has low modulation noise, excellent sensitivity and frequency characteristics, and can be used for broadcasting video tapes, home video tapes, computer memory tapes, memory cassette tapes, and digital cassettes. tape, high-grade saran.

It is an excellent magnetic recording material that can be used for hard tapes, etc.

The present invention will be explained in more detail below using examples.

The components, proportions, order of operations, etc. shown herein may be modified without departing from the spirit of the invention.

It is easily understood by those involved in this industry that this is the case.

Therefore, the invention should not be limited to the examples below.

In the following examples, all parts are by weight.

・Example l NaOH62? into a 51 beaker, add 1 liter of water, and 1 ol of water.
Added and dissolved.

20,500 g of FeSO4.7H was dissolved in 1.51 g of water and added to the NaOH solution.

Keep the liquid temperature at 40℃ and add air at about 1Ol/m while stirring.
The reaction continued until the solution became oxidized and turned yellow, and the pH stabilized around 4.

Next, the temperature of the above reaction solution was raised to 85° C., NaOH751 dissolved in water 0.51, and added while adjusting the pH to ¥4.5, and air oxidation was performed.

After the addition of NaOH, stirring was continued for 30 minutes to perform air oxidation.

After that, air oxidation was stopped and NaOH2]-ff was dissolved in water 0
．． A solution dissolved in No. 51 was added, stirred for 60 minutes, washed with water, and dried.

Goethite (α-Fe00H) with a Fe(OH)s layer on the surface in this way], 55? I got it.

The goethite obtained above was dehydrated at 380°C for 2 hours, and then reduced at 410°C for 2 hours to obtain magnetite.

The obtained magnetite was oxidized at 280° C. for 3 hours to obtain maghemite.

The magnetic property of this maghemite is that the coercive force (He) is 415
oe, saturation magnetization (σS) is 73.4 emu/? Met.

Observation of the obtained particles using an electron microscope revealed that the average particle size was 0.6μ in the long axis and the acicular ratio was 1:8 to 1:10. There was one.

Example 2 Goethite seeds were formed in the same manner as in Example 1, and goethite was grown.

Na4P2O7H10H208S' was dissolved in 100 ml of water and added.

Stop air oxidation and use NaOH21? A solution prepared by dissolving 0.5% of water in 0.5% of water was added, stirred for 60 minutes, washed with water, and dried.

In this way, the surface becomes Na4 p2o7+ 10 H2
156f was obtained by treatment with O to form a Fe(OH)s layer.

Hereinafter, dehydration, reduction, and oxidation were carried out under the same conditions as in Example 1.
Obtained Maghemite.

The magnetic properties of this maghemite include coercive force (He) of 41
208. The saturation magnetization (σS) was 72.8 emu/g.

When the obtained particles were observed with an electron microscope, the average particle size was 0.6μ in the long axis and the acicular ratio was 1:8 to 1:10.
On average, the number of vacancies in the particles is 1 for every 2 particles.
There were several.

Example 3 1.50P of goethite (particle size 0.5μ) was added to 1.50P of water.
It was distributed in 51.

FeSO4・7H20100g and CoSO4・7H2
0121 with water 0. 1 was added to the goethite slurry.

A solution of 55 g of sodium oxalate dissolved in 1.5 l of water was added to the above slurry, stirred, and poured onto the goethite.

An iron acid containing .

After washing with water and drying, the yield was 203 grams.

35 Goethite with iron oxalate layer containing Co
After dehydration at 0°C for 2 hours, the mixture was reduced at 400°C for 2 hours to obtain magnetite.

After the firing furnace was cooled, the surface of this magnetite was slowly oxidized with air, and after being adapted to the air, it was taken out and kept in a constant temperature bath at 60° C. for 48 hours.

Coercive force (He) is 59008, saturation magnetization (σS) is 81
emu/fI oxidation degree M=1. '39, Co content is 1
．． A bertride iron oxide magnetic material of 95 atomic % was obtained.

Here, M is defined by the following equation. When the obtained particles were observed with an electron microscope, the average particle size was 0.5μ along the long axis.
The acicular ratio is 1:10 to 1:13, and the pores in the particles are average.

There was one for each child.

Example 4 Acicular goethite (particle size 0.5μ) was heated at 350°C for 2 hours and dehydrated to form the starting material hematite (α-F
e203) was obtained.

This hematite :) 300S' was dispersed in water 21 to form a slurry.

A solution of FeSO4.7H201101 in 11 parts of water was added to the slurry.

More Na2 BO410? was dissolved in 0.51 g of water and added.

NaOH35? A solution prepared by dissolving 0.5% of water in 0.5% of water was gradually added, and after the addition was complete, the mixture was stirred for 60 minutes.

After washing with water and drying, hematite 3351 with Fe(OH)3 formed on the surface was obtained.

After dehydration at 350°C for 1 hour, reduced magnetite was obtained at 410°C for 2 hours, and oxidized at 280°C for 2 hours.

Coercive force (He) is 425 oe, saturation magnetization. Maghemite with (σS) of 73 and Oe mu/ff was obtained.

When the obtained particles were observed with an electron microscope, the average particle size was 0.5 μ on the long axis, and the acicular ratio was 1:10 to 1:1.
3, and the number of pores in the particles is on average.

One hole was present for every two particles.

Comparative example l NaOH62? was placed in a 51 beaker, and 11 parts of water was added to dissolve it.

F e SO4・7 H20500? was dissolved in 1.5 liters of water and added to the NaOH solution.

Keep the liquid temperature at 40°C and add about 10 liters of air while stirring.
/viyt.

The solution was oxidized while being blown in, and the reaction continued until the solution turned yellow and the pH stabilized around 4.

Next, the temperature of the reaction solution was raised to 80°C, 82 g of NaOH was dissolved in 11 g of water, and the solution was added while adjusting the pH to 4.5.
Further air oxidation was performed.

After the reaction was completed, the mixture was further stirred for 30 minutes, washed with water, and dried to obtain 157S'.

This goethite was dehydrated at 380°C for 2 hours, and then
It was reduced at 0°C for 2 hours and oxidized at 280°C for 2 hours to obtain maghemite.

As for magnetic properties, coercive force (He) is 375 oe1 saturation magnetization (σ
s) was 74.6 layers mu/g.

When the obtained particles were observed with an electron microscope, the average particle size was found to be 0.6 μm on the long axis, and the acicular ratio was 1 to 1:10, with an average of 7 pores per particle. did.

Comparative example 2 By performing the same operation as in Example 1, on the surface, We made goethite with three layers of Fe (OH).

This goethite was dehydrated at 450°C for 2 hours, and then
Reduction was performed at 0°C for 3 hours to obtain magnetite.

This magnetite was oxidized at 280° C. for 2 hours to obtain maghemite.

The magnetic properties of this maghemite include coercive force (He) of 395
oe, saturation magnetization (σs) is 745 emu/? Met.

When the obtained particles were observed with an electron microscope, the average particle size was 0.55μ in the long axis, and the acicular ratio was 1:6 to 1:8, with an average of 1 hole per particle. There were individuals.

Example 5 Magnetic iron oxide 6 obtained in Example 1.2.3.4 Comparative Example 1.2
300 parts of each species were sufficiently mixed and dispersed with the following composition using a ball mill.

This is followed by Dismodule L-75 (product name, Bayer
20 parts of a 75 wt% ethyl acetate solution of an adduct of 3 moles of toluene diisocyanate and 1 mole of trimethylolpropane (polyisocyanate compound manufactured by A.G.) were added and uniformly mixed and dispersed to obtain a magnetic paint.

Apply this paint to a polyethylene terephthalate base (thickness 2
5mμ) to a dry thickness of 10mμ,
The tape was oriented in a magnetic field at 000 oe, dried, and slit to obtain a magnetic tape.

The slit width was 1/2 inch. The magnetic properties of the obtained magnetic tape were investigated.

In order to investigate the uniformity of the coercive force distribution, we took the differential waveform of the B-H curve and determined its half-width (△He) (Table 1, c
f, 1).

The degree of orientation is determined by calculating the squareness ratio P (Br78m) when the magnetic field alignment direction and the applied magnetic field direction match and the squareness ratio V (Br78m) when the orientation direction and the magnetic field direction are perpendicular, and
(Br78m)/P(Br78m) (Table 1, cf, 2).

Furthermore, using a frequency spectrum analyzer (manufactured by Ando Electric KK, FSA-IB type), the relative velocity was 11 ml se
Recording and reproduction were performed using C, frequency analysis was performed, noise levels were compared, and modulation noise and sensitivity were investigated.

Sensitivity and modulation noise measurements were made using a standard tape as a reference, all OdB, and expressed as relative values (Table 1, cf, 3).

The above data are shown in Table 1 along with other characteristics.

Mössbauer spectra were measured for the magnetic recording bodies using magnetic iron oxide obtained in Example 1.2.3.4 and Comparative Example 1.2.

57C0 (20mC1) was used as a radiation source, and a NaI detector was used as a detector.

The Mössbauer effect measuring device used was Model AME-30 manufactured by El Sinto (Israel), and the wave height analyzer was Model MS-710 manufactured by Northern Scientific (USA).

As a representative example, the Mössbauer spectra obtained for Example 1.3 and Comparative Example 1 are shown in Fig. 1, Fig. 2, and Fig. 2, respectively.
It is shown in Figure 3.

Examples 2.4 also had the same spectra as Example 1.

In Figure 1, six peaks 1 to 6 corresponding to Fe@,
A peak 7 indicating superparamagnetism exists in the center.

Figure 2 also shows a peak 29 showing superparamagnetism in the center, similar to Figure 1.
exists.

Because Fe(II) and FeQI]) coexist, the first
It is more complex than the figure and some peaks are split.

21-28 Figure 3 shows the Mössbauer spectrum of Comparative Example 1, with only six peaks 31-36 indicating Fe(III).
There are no peaks indicating superparamagnetism.

The Mössbauer spectrum of magnetic iron oxide obtained in Comparative Example 2 was the same Mössbauer spectrum as in FIG. 3 (Comparative Example 1), and there was no peak corresponding to superparamagnetism.

The reason why a peak corresponding to superparamagnetism was not observed in the magnetic recording medium obtained using the powder obtained in Comparative Example 2 is not clear, but the reduction temperature was as high as 54.0°C, so sintering progressed. , it is thought that it disappeared because it promoted the growth of particles exhibiting superparamagnetism (particles with a diameter of 100λ or less grow to a particle size of 500A or more).

Further, the progress of sintering is also evident from the fact that the acicular ratio is deteriorated when compared with the particles of Example 10.

The magnetic tape using the magnetic material according to the present invention has a squareness ratio (B
r/8m), and it can be seen that the degree of orientation is extremely superior to that of the comparative example.

In addition, although the saturation magnetic flux density (Br) is extremely high, in other words, the degree of filling is extremely high, there is little decrease in coercive force.

In general, iron oxide-based magnetic materials have shape anisotropy that increases their coercive force, so when the degree of filling is increased, the coercive force usually decreases.

From this result, it can be said that the magnetic iron oxide according to the present invention is a magnetic material with little decrease in coercive force even when it is highly filled.

When considering the dispersion time, the magnetic iron oxide according to the present invention has a short dispersion time and can be dispersed in 75% of the time of the comparative example.

The industrial advantage of a short dispersion time when producing magnetic recording media is significant.

Looking at the properties when made into a magnetic tape, the magnetic recording material according to the present invention is characterized by high sensitivity corresponding to the ability to make a tape with a high degree of filling.

Furthermore, considering modulation noise, compared to standard tape, it is 2.0 to 2.5 dB at 3.5 MHz and 2.0 to 2.5 dB at 3.5 MHz.
．． The noise level is low (3 to 2.5 dB), and this difference is even larger when compared with the comparative example.

Due to its high sensitivity and low noise level, the magnetic recording medium according to the present invention has an extremely excellent signal-to-noise ratio.

The magnetic recording material using the magnetic material obtained in Comparative Example 2 has a low saturation magnetic flux, and accordingly, the sensitivity is also lower than that of the magnetic recording material according to the present invention, and is almost equivalent to that of Comparative Example 1 obtained by a conventional method. be.

Furthermore, the modulation noise is about 3 to 4 dB inferior to the magnetic recording material according to the present invention, but this is because sintering progresses during the dehydration, reduction, and oxidation processes, and the surface properties of the magnetic recording material deteriorate. it is conceivable that.

The magnetic iron oxide according to the present invention containing a superparamagnetic material does not undergo much sintering, has excellent dispersibility, and has a good degree of orientation.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the Mössbauer spectrum at room temperature of the magnetic recording material according to the present invention (Example 1), in which peaks 1 to 6 correspond to Fe (Ill), and peak 7 is a peak indicating superparamagnetism. FIG. 2 is a graph showing the Mössbauer spectrum at room temperature of the magnetic recording material according to the present invention (Example 3), in which peaks 21 to 28 are peaks indicating the coexistence of Fe(TI) and Fe(Ill); Peak 29 is a peak indicating a superparamagnetic material. Fig. 3 is a graph showing the Mössbauer spectrum at room temperature of a magnetic recording medium manufactured by a conventional method.
Peaks 31 to 36 are peaks indicating Fe(II).

Claims (1)

[Claims] 1. A magnetic recording body comprising a magnetic layer mainly composed of ferromagnetic iron oxide powder and a binder provided on a substrate, characterized in that the magnetic layer contains a superparamagnetic material.