JPS6066801A - Magnetic powder and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain excellent dispersion characteristic by obtaining magnetic powder through processing with copolymer which dissolves to water in the specific ratio or more. CONSTITUTION:For the processing, those which dissolve 10 weight part or more to water of 100 weight part are used as the copolymer which works as the dispersion agent of magnetic powder. Thereby, this copolymer sufficiently combines with the surface of magnetic powder having affinity at the time of surface processing of magnetic powder in the medium of the water system. For this purpose, it is essential that the copolymer dissolves to water in the 10 weight part or more, and thereby dispersion characteristic of magnetic powder and moreover square ratio can be improved remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field The present invention relates to magnetic powder (particularly magnetic powder contained in a magnetic layer of a magnetic recording medium such as a magnetic tape or a magnetic sheet) and a method for producing the same. be.

2. Prior Art In recent years, with the increasing density and high S/N of magnetic materials, especially video and computer recording media, the particles of magnetic powder used have become smaller, for example, when expressed in terms of surface area per unit weight. The standard grade of VB2 or beta type magnetic tape uses magnetic powder with a BET surface area of 19 to 23tJy2s, and the high grade class uses 23 to 2f+tr? /
l. 28-33W in super high grade class? /1
? Class magnetic powder is used.

In addition, 35 to 5 atyr/f class powder is about to appear on the market in the near future. - In general, the S/N ratio of a magnetic recording medium is said to be proportional to the square root of the number of magnetic particles in the recording material involved in recording and reproduction. When applied, the smaller the particle size and the more magnetic material is used, the more advantageous it will be to improve the S/N. However, since the surface area of particles increases in inverse proportion to the square of the particle diameter, particle dispersion becomes rapidly difficult as the particle diameter decreases, and dispersion stability also deteriorates.

Normally, when dispersing magnetic powder, it should be sufficient to use just enough dispersant to coat the surface of the magnetic powder particles, but in reality, this does not provide sufficient dispersibility and stability. ,
For this purpose, an excessive amount of dispersant is added. The dispersant that is not adsorbed to the magnetic powder mixes with the binder in the coating film to plasticize the magnetic layer, and also hinders the hardening of the binder, thereby significantly reducing the mechanical strength of the magnetic layer, particularly the Young's modulus. Recently, as tapes have been used for longer recording times, thinner base films have been used to reduce the total thickness of the tape, but since the stiffness of the tape is proportional to the cube of the tape thickness, As a result, the tape is considerably stiff, which deteriorates the running characteristics of the thin tape and the flat touch of the tape, leading to a deterioration of the S/N ratio. In order to maintain the mechanical properties of the tape, especially its stiffness, as the tape becomes thinner, ultra-stretched base films are used and the Young's modulus of the magnetic layer is increased. Therefore, a reduction in the Young's modulus of the magnetic layer due to excessive dispersants and other low-molecular additives significantly deteriorates the mechanical properties of the thin tape.

Various techniques have been disclosed for effectively and stably dispersing magnetic powder without impairing the mechanical properties of the magnetic layer. For example, JP-A-54-94308, 54-143
In each of the publications No. 894 and No. 50-92103, magnetic powder is pretreated with a phosphate ester derivative. Also, JP-A-51-134899, 53-51703, 53-7
No. 898 and No. 54-46509 disclose a method of coating the surface of a magnetic layer with silicone oil. or,
JP-A-50-108902, 49-97738,
No. 51-33753, No. 53-116114, 54-2
In each publication such as No. 4000, the surface is treated with an anionic activator. However, the above techniques are not suitable for small particulate matter, especially BE.
T35~40rr? It cannot be said that it is effective for magnetic powder of /S' or more.

Also, JP-A-51-103403, 47-33602
No. 55-73929, No. 55-125169, 55
-73930, 57-42888, 57-1026
Each publication, such as No. 1, discloses a technique for coating the surface of magnetic powder with an oligomer or polymer having a functional group that can be adsorbed to the magnetic powder. These techniques involve mixing dry magnetic powder with a dispersant solution and adsorbing the dispersant on its surface.Therefore, dissolving the dispersant, mixing with the magnetic powder, stirring, crosstalk, filtration, drying, pulverization, Requires static steps. In addition, dried magnetic powder becomes agglomerated, so even if a dispersant is added and kneaded, it is difficult to disperse down to the primary particles, making it difficult to coat individual primary particles with a polymer. If you try to forcefully disperse it into the primary particles, the acicular particles will break. Therefore, the dispersibility cannot be sufficiently improved by enclosing agglomerated particles of a plurality of particles with a polymer.

Magnetic powders, particularly Co-coated Fe203, are widely used as magnetic materials for video, high performance audio, and computer tapes. This Co deposition-F e 20
As a general manufacturing method for No. 3, first, M-iron sulfate (FeS
Sodium hydroxide (NaO
Ferrous hydroxide (Fe(OH)2) produced by taking one sip of H)
is oxidized in the air and then washed to form α-F, which becomes the nucleus for crystal growth.
Create eOOH. Next, prepare a separate IC for 4 types of water-soluble ferrous sulfate, add core α-Fe OOH and Z metal iron, and heat while blowing air. It is dissolved, α-FeOOH is generated, and - is precipitated on the surface of α-FeOOH as a nucleus, and crystal growth occurs. For example, this growth is 0.6 to 1.014
Keep the length and width of 0.1 to 0.3μ, filter, wash,
Dry to make goethite powder. Add this to 40
Dehydration and reduction in a H3 stream at about 0°C yields F e 304, and when it is gradually heated in air to about 200°C, it becomes r7F.
It becomes e203. Thus obtained r −F e203
was used as a nucleus for crystal growth, placed in an aqueous solution of iron sulfate and cobalt sulfate, and then alkali was added and oxidized at 60 to 80°C for 1 to 3 hours to grow cobalt iron oxide on the surface of γ-Fe and 08. let After that, it is E-filtered, washed with water, and dried to obtain Co-coated Fe203.

As a known technique targeting such Co-adhered Fe, 03, for example, as seen in JP-A-57-13811.0, there is a cation interface during washing with water after cobalt adhesion during the magnetic powder manufacturing process. Some attempts have been made to improve the squareness ratio and filling properties by adding an activator. However, even with this, there is still a problem that the dispersibility is insufficient and it is not possible to obtain reeds, good squareness ratio, etc. Also, JP-A-567109
No. 03 discloses γ-F e 203 coated with Co.
Although it has been shown to treat with a low-molecular-weight surfactant while it is in a warm state, the dispersibility of this method is still insufficient.

On the other hand, as a processing agent for treating magnetic powder,
23207 and 50-22603 as a unit, a part of the carboxyl group is amide (-CO
This is an attempt to improve the compatibility of the magnetic powder with the binder when mixing the magnetic paint by converting the magnetic powder into a binder (NHR) and creating a residual oil property due to its alkyl group (-R). Therefore, in a process that involves treatment in an aqueous system, such as the above-mentioned Co-coated Fe203 process, it is impossible to use the above copolymer to treat the surface of magnetic powder. Poor dispersion into the aqueous medium will occur.

3. Purpose of the invention The present inventor has developed a magnetic powder (e.g., cobalt-coated γ-Fe, 1
During the manufacturing process, O8) is dispersed into primary particles in a warm state, but once dried, it forms hard aggregates, which is very difficult to disperse into primary particles again. Based on the recognition that powders are prone to breakage, etc. (therefore, surface treatment in an aggregated state will not improve dispersibility), we conducted extensive studies. As a result, they discovered a magnetic powder that can be surface-treated while exhibiting sufficient dispersibility, particularly in an aqueous medium, and arrived at the present invention.

4. Structure of the invention and its effects, that is, the present invention provides a
! This relates to a magnetic powder treated with a copolymer that dissolves in an amount of 1,000 parts or more.

Further, the present invention provides a method for producing magnetic powder, which is characterized by carrying out metal ion treatment in an aqueous medium, as a method for efficiently obtaining the magnetic powder with good reproducibility.

However, in the present invention, after filtering a magnetic powder dispersion that has been treated to increase coercivity and removing cine-type materials from the dispersion, 1.
The present invention also provides a method for producing magnetic powder, characterized in that the magnetic powder is treated in an aqueous medium with a copolymer that is dissolved in an amount of 10 parts by weight or more per 00 M parts of water.

According to the present invention, since the above-mentioned copolymer which acts as a dispersant for the magnetic powder is used and has a solubility of 10 parts by weight or more in 100 parts by weight of water, the magnetic powder is treated in an aqueous medium. During surface treatment (for example, during the process of depositing CO on the γ-Fe208 surface in the coexistence of Co ions: route ■ in Figure 1), the above copolymer binds sufficiently to the hydrophilic surface of the magnetic powder. do.

For this purpose, it is essential that the solubility of the copolymer in water is 10 parts by weight or more.If it is set within this range, the dispersibility of the magnetic powder will be improved as shown in Fig. The mold ratio can be significantly improved. However, if the solubility of the copolymer in water is too high, the copolymer will exist in water even though it is adsorbed to the magnetic powder, making it impossible to obtain a sufficient amount of adsorption. Therefore, it is desirable that the solubility is 100 parts by weight or less of the copolymer per 100 parts by weight of water, and the K that satisfies both dispersibility and coating amount is 1.
More preferably, the ratio is 0 to 80 parts by weight/100 parts by weight of water. The solubility referred to herein means the concentration immediately before cloudiness occurs when the copolymer is dissolved in a certain amount of water.

In addition, in the magnetic powder treated with the above copolymer, the secondary particles are wrapped in an organic polymer (the above copolymer), and the hydrophilic groups of the polymer face the surface of the hydrophilic magnetic powder, and the lipophilic groups face the outside. Since it is thought that the particles are oriented so that they face the same direction, dispersion is extremely easy even when it is made into a magnetic paint. In addition, since the above copolymer is a water-soluble polymer, it does not dissolve in the solvent of the magnetic paint, and therefore provides excellent dispersion stability when desorbing. (that is, the portion of the copolymer that is not adsorbed by the magnetic powder is removed together with the mother liquor after treatment in an aqueous medium), and the mechanical properties of the magnetic layer are not deteriorated.

In order to obtain the magnetic powder according to the present invention, the copolymer is adsorbed onto the surface of the magnetic powder according to the route (1) in Figure 1, or the cobalt is coated on the surface of the magnetic powder, and then washed five times and washed as necessary. Then, the copolymer may be immediately suspended in an aqueous medium (for example, an aqueous solution) containing the water-soluble copolymer of the present invention, and the copolymer may be adsorbed onto the surface of the copolymer (Route 1 in FIG. 1).

Illegal uses existing magnetic powder manufacturing equipment and does not require any special equipment, so it can be manufactured at low cost.

In the present invention, the aqueous medium is basically water in the case of co-gold-containing oxide magnetic powder, and a small amount of other water-soluble solvents (alcohols, ketones, water-soluble cyclic ethers, amines, etc.). ) may be used together. Further, in the case of metal magnetic powder, a water-soluble solvent such as methanol is used.

In this case, the adsorption of the water-soluble polymer (the above-mentioned copolymer) by the magnetic powder is greatly influenced by the pH of the mother liquor.

As shown in FIG. 4, the pH is preferably 7 or less, preferably 6 or less, and on the alkaline side, the amount of adsorption decreases considerably.

The adsorption amount of water-soluble polymer is 1 to 1 per 100 g of magnetic powder.
07, preferably 1 to 52. Generally, the mother liquor after cobalt deposition has a high pH, so it is best to add an inorganic acid to lower the pH to 7 or less before adsorbing the water-soluble polymer. It is preferable to perform the treatment of the present invention after the magnetic powder is filtered and washed with water to remove by-products.

The magnetic powder according to the present invention exhibits extremely good dispersibility as described above, but in order to further improve fractional speed and dispersion stability, lecithin (preferably powdered lecithin), oleic acid, phosphorus, etc. may be added in some cases. A small amount of a dispersant such as an acid ester may be added.

Further, the surface treatment of the magnetic powder with the above copolymer may be carried out, for example, in a hydrophilic solvent (for example, an aqueous methanol solution) in the final step of obtaining metal-based magnetic powder from γ-Fe2O3 by a conventional method.

5. Examples Hereinafter, the present invention will be explained in more detail with reference to examples.

First, the above-mentioned copolymer used for pretreating the surface of magnetic powder in the present invention will be explained in detail. This copolymer has a monomer containing a negative organic group (hereinafter referred to as monomer unit A) as a constituent component, and the negative organic group includes, for example, a carboxyl group, a phosphoric acid residue, a sulfonic acid residue, etc. However, carboxyl groups and phosphoric acid residues are preferable, and the salts thereof are preferably ammonium salts, alkali metal salts, and the like. Examples of the monomer A include acrylic acid, methacrylic acid, maleic anhydride, and 2-hydroxyethyl acryloyl phosphate, with acrylic acid and maleic anhydride being preferred.

The negative 8f group is preferably a carboxyl group or a phosphoric acid residue, and the salt is preferably an ammonium salt.

The reason why acrylic acid and maleic anhydride are preferable as the 7-mer unit A is because they have particularly excellent storage stability and dispersibility. In the case of additives conventionally used to improve the phenomenon of pluming, etc., they can improve the phenomenon to some extent, but they have poor storage stability, tend to stick together, and tend to aggregate during dispersion. However, the copolymer used in the present invention is excellent in these points.

In this copolymer, the effect of the salt of the negative organic group can be explained as follows.
Each dissociation constant is different for a salt).

[Dissociation constant K]

Then, the corner of a magnetic recording medium comprising a magnetic layer prepared by a method described in detail later, using magnetic powder surface-treated with each copolymer containing monomer unit A having each of these groups as a component. It was confirmed that the mold ratio (Bm/Br) was as shown in FIG. 3, for example.

That is, when a copolymer in which -COOH is a salt according to the present invention is used, the squareness ratio is improved compared to the case where a copolymer having only one COOH is used. This is -CO
This is thought to be because when OH is used as a salt, it is difficult to desorb when dispersed in a solvent or binder, and the copolymer itself becomes more hydrophilic, so that the treatment effect is not lost. On the other hand, -COOH has the property of easily adhering to or bonding to the surface of magnetic powder, but because it has stronger lipophilicity than salt,
It is thought that the treatment effect is likely to be lost due to the dissolution in the solvent, and that the desorbed materials seep out onto the tape surface, resulting in them not adhering to or bonding to the surface.

In addition, among the organic groups according to the present invention, as shown in Figure 3, ammonium salts have better magnetic properties than alkali metal salts, and the use of ammonium salts is the best, and before and after that, the dissociation constant decreases or increases. It can be seen that the squareness ratio tends to decrease as the squareness increases. The reason for this is that alkali metal salts have greater hydrophilicity (possibly due to a larger dissociation constant), which makes them more likely to bond to the magnetic powder surface during surface treatment in an aqueous system, but at the same time, they also have the property of being more likely to detach. However, the adsorption of ammonium salts is not as great as that of free acids, but since there is less desorption in the solvent, the dispersibility is the best. In other words, this seems to be because binding to the magnetic powder surface occurs preferentially due to an appropriate dissociation constant.

General formula: %formula% are mutually the same or different lower alkyl groups.

) is applicable. Here, the above R1
, R2, R3, R4 are lower alkyl groups, R1
The total number of carbon atoms in -R4 is desirably 6 or less, since the basicity of the ammonium salt is not impaired by steric hindrance.

The above-mentioned copolymer used in the present invention comprises the above-mentioned monomer unit A (also written as (l-A+)) and monomer unit B.
Also written as (-E-B-). ) to express/death, soA purple pregnancy B.

It can be expressed as However, m and n are positive real numbers. The average value of (m+n) is 100 or less, preferably 50 or less. If it exceeds 100, it becomes difficult to disperse uniformly in the magnetic layer of the magnetic recording medium.
In the recording medium, performance (for example, output, etc.) tends to be partially uneven, which is undesirable. Also, (m+n
) is particularly preferably 30 or less, in which case the dispersion effect is particularly excellent and the performance of the magnetic recording medium according to the present invention is particularly significantly improved. Note that the average value of (m+rl) is, for example, 4 in order to prevent the pluming phenomenon.
It is preferable that it is above.

Here, by selecting the values of m and n, respectively, and by controlling the moderation of the salts of the organic groups in unit A, - both the hydrophilic and hydrophobic properties of the copolymer, i.e. HLB (Hydrop
It is possible to appropriately control the heliophile balance (Lipophile Balance).

In addition, monomer units other than the monomer unit A of this copolymer (hereinafter referred to as monomer units) B. ) Examples include styrene, 0-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n -hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-tethylstyrene, p-n-dode'/lustyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene , 3,4-dichlorostyrene and other styrene-oyohistyrene derivatives. Other vinyl monomers other than these include, for example, ethylene,
Ethylenically unsaturated monoolefins such as propylene, butylene, isobutylene, diisobutylene, isononene, isododecene, etc.; vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride, etc.; Vinyl esters such as vinyl acid, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, acrylic acid 2 -ethylhexyl, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate,
Methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, inbutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate , α-methylene aliphatic monocarboxylic acid esters such as phenyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate; conductors of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, and acrylamide; vinyl methyl ether,
Vinyl ethers such as vinyl ethyl ether and vinyl impropenyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl impropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinylindole, N-vinyl bisdon Examples include N-vinyl compounds such as; vinylnaphthalenes, and the like.

Next, a preferable co-7fi:copolymer (water-soluble polymer) is one in which the copolymer unit A has at least two carboxyl groups (forming the salt as described above) when used as a copolymer salt. It includes. Examples of such monomer units A include those having the following structural formula.

(This unit can be formed using maleic anhydride as a starting material under the action of ammonia. n indicates a repeating unit; hereinafter.) Coo -NHCH.

(2), -(-C-□ CH ya Coo @NHCH3 CH.

On the other hand, monomer units B are preferably composed of alkylene, arylalkylene or conductors thereof, with alkylene being more preferred (all of these are derived from alkunes or arylalkenes). In particular, alkylene having branches is desirable because it has good solubility in organic solvents and can be sufficiently mixed with a binder. Preferred starting materials for monomer unit B are as follows.

(1), isobutylene (2), 2,3-dimethyl-1-butene (3), 2,3
-dimethyl-1-pentene (4), inocte/(diisobutylene) (5), isododecene (6), isononene The above-mentioned copolymers used in the present invention can be produced by copolymerization of the above-mentioned starting materials. The obtained co-M [coalescence is
If analyzed by GC/Mass, the signal will be separated into inoctene and imbutylene in the part corresponding to an alkene, and the signal will be separated into toluene, diethylbenzene, styrene, etc. in the part corresponding to an acid (for example, maleic anhydride). Identified by.

All of the copolymers exemplified above used in the present invention are
Hydrophilicity due to monomer unit A and monomer unit) H
Since the lipophilicity and lipophilicity of
Since the monomer unit (H) part acts effectively in the aqueous medium, there is no possibility that the copolymer will separate. Furthermore, when mixed with the binder, the monomer binit B portion provides sufficient dispersibility. The appropriate content of the copolymer to the magnetic powder is 1 to 20 parts by weight per 100 parts by weight of the former. If the amount of the copolymer is too small outside this range, the dispersion effect will be poor, and if it is too large, it is undesirable in terms of strength and recording performance of the magnetic layer.

To surface-treat magnetic powder with this copolymer, Na
Magnetic powder (e.g. γ-Fe2
0B) to adsorb Co on its surface, the pH of the mother liquor is lowered by adding an inorganic acid such as sulfuric acid, and under this condition the mother liquor is treated with the above copolymer. Alternatively, after adsorbing co, reaction by-products may be removed by filtering and if necessary, followed by treatment with the copolymer. Examples of the solvent used here include aqueous solutions of water, methanol, ethanol, propatool, acetone, methyl in butyl ketone, tetrahydrofuran, dioxane, pyridine, hydroxyquinoline, and the like. Thereafter, according to a conventional method, the above-mentioned treated magnetic powder is mixed with a binder and additives as described above to prepare a magnetic paint, which is coated on a support, dried to form a magnetic layer, and calendered. A magnetic recording medium, such as a magnetic tape, is obtained through processing and slitting.

In the process flow shown in Figure 1, especially ■root ll'
Since a step is added to filter the dispersion of magnetic powder whose coercive force has been increased by the growth of iCo ferrite (Go adhesion), unnecessary substances and free C are removed in this step.

Ions etc. can be removed and magnetic powder with good properties can be obtained. In addition, in the (2) route, various solvents can be used during the resuspension process, but at this time, additives that are compatible with the binder, such as weakly water-soluble dispersants (lecithin, higher fatty acids, etc.), can be used. It can also be added to further control the physical properties of the magnetic powder. Also, in the ■ route,
Metal magnetic powder (e.g. γ-Fe2) prepared by a known method
The copolymer may be added to a suspension of Fe powder obtained by reduction of O3 or Fe powder obtained by reduction of Fe3O4 derived from α-F+403 by dehydration of α-FeOOH.

In a magnetic recording medium containing the magnetic powder of the present invention in the magnetic layer, polyurethane can be used as a binder for the magnetic layer, and polyurethane can be synthesized by reacting polyol and polyisocyanate. Polyols that can be used include:
7 Organic dibasic acids such as talic acid, adipic acid, double lyluic acid, and maleic acid,! : Glycols such as ethylene glycol, flopylene glycol, ethylene glycol, diethylene glycol, or polyhydric compounds such as trimethylolpropane, hexanetriol, chrycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, etc. A polyester polyol synthesized by reacting alcohols or their glycols and polyhydric alcohols with any two or more selected polyols;
Or, a lactone polyester polyol synthesized from tscutams such as S-capro2cutam, a-methyl-1-caglolactam, S-methyl-8-capro2cutam, and γ-butyro2cutam; or ethylene oxide, propylene oxide Examples include polyether polyols synthesized from , datelene oxide, and the like.

These polyols are reacted with incyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, meta-xylene diyne heptaanate, etc., and thereby urethanized polyester polyurethane, polyether polyurethane, or carbonated with phosgene or diphenyl carbonate. These polyurethanes are usually prepared primarily by the reaction of polyisocyanates with polyols and are in the form of urethane trees or urethane prepolymers containing free incyanate groups and/or hydroxyl groups. Alternatively, it may be in the form of a urethane elastomer, or may not contain these reactive end groups.

Polyurethane, urethane prepolymer, urethane elastomer manufacturing methods, curing and crosslinking methods, etc. are well known, so detailed explanation thereof will be omitted. In addition, in the present invention, in addition to the above-mentioned polyurethane as a binder, cellulose resin and/or Alternatively, if a vinyl chloride copolymer is also included, the dispersibility of the magnetic powder will be improved when applied to a magnetic layer, and its mechanical strength will be increased. However, if only the cellulose resin and/or vinyl chloride copolymer is used, the layer becomes too hard, but this can be prevented by containing polyurethane.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. Cellulose ether, methylcellulose, ethylcellulose, propylcellulose, improvylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose,
Cyanethyl cellulose, vinyl cellulose, nitrocarboxymethyl cellulose, diethylaminoethyl cellulose, aminoethyl cellulose, etc. can be used. Cellulose inorganic acid esters, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can also be used.
Cellulose organic acid esters include acetylcellulose, globionylcellulose, butyrylcellulose, methacryloylcellulose, chloroacetylcellulose,
β-oxypropionyl cellulose, pensoyl cellulose, p-)luenesulfonate cellulose, acetylpropionyl cellulose, acetyl butyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose is preferred. A specific example of nitrocellulose is
Seltsuba BTHT, Nitrocellulose 5L-1 manufactured by Asahi Kasei Corporation, Nitrocellulose R8 manufactured by Daicel (a)
-2 and cell line L-200. Viscosity of nitrocellulose (JIS, Ni-6703 (1975)
2 to 1 second is preferable, and 41 to 1 second is particularly good. If it is outside this range, the film adhesion and film strength of the magnetic layer will be insufficient.

In addition, as for the vinyl chloride copolymer that can be used, the molar ratio derived from t and m is 95 to 50 molty for the former unit, and 5 to 50 molty for the latter unit. It is. In addition, X represents a monomer residue that can be copolymerized with vinyl chloride, vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride, maleic acid, maleic ester, vinylidene chloride, acrylonitrile, acrylic acid. , acrylic ester, methacrylic acid, methacrylic ester, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate. The degree of polymerization expressed as (t+m) is preferably 1OO~600 υ; if the degree of polymerization is less than 100, the magnetic layer etc. tends to become sticky, and if it exceeds 600, the dispersibility deteriorates. The copolymer may be partially hydrolyzed. The vinyl chloride copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as F) "vinyl chloride-vinyl acetate copolymer". ). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride p, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, vinyl chloride-acetic acid Examples include vinyl-vinyl alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers,
Partially hydrolyzed copolymers are preferred. Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include r VAG) (J, r VYHH manufactured by Union Carbide Co., Ltd.
J, rVMCHJ, "S-LEC A" manufactured by Block Chemical Co., Ltd.
”, “S-Lec A-5J, r-S-Lec CJ, r-S-lec M”, “Denkabinir 1” manufactured by Denki Kagaku Kogyo Co., Ltd.
000 G J, "Denkabinir 100OWJ, etc. can be used.

The above vinyl chloride copolymer and cellulose resin may be used in any blending ratio.

Regarding the entire binder composition, the ratio of polyurethane to other resins (total amount of cellulose resin and vinyl chloride copolymer) is 90/lo to so
/ so is desirable, 85/15 to 60/40
has been confirmed to be even more desirable.

Outside this range, if there is a large amount of polyurethane, poor dispersion tends to occur and the still properties are poor and it is easy to scratch, and if other resins are too large, the surface properties are likely to be poor and the still properties are poor, especially 6off&%. If it exceeds this value, the physical properties of the coating film become unfavorable overall.

The magnetic layer of the magnetic recording medium further has a specific surface area (BET value) B1 of 40 m'/ f r < Bt < 200.
rr? /S'r carbon black (hereinafter referred to as C
It is sometimes called B. ) and specific surface [(BET value) B
Z is 200rr? /fr≦B, (500m'/tr
It is preferable to contain at least one of carbon black CB (hereinafter sometimes referred to as CB2). That is, carbon black CB is added mainly for light shielding, but its specific surface fItB, 4On?/
tr < Bl (200rr?/ 11 of tr [≧
By specifying the above, the light-shielding property of the layer can be sufficiently achieved, and at the same time, the dispersibility of CB in the layer can be improved. Outside this range, the specific surface area of CB1 is 40rr? /gr or less, the particle size is too large and the light-shielding properties tend to deteriorate, and it is necessary to increase the amount added more than necessary.
0rr? /7r or more, the particle size is too small and dispersibility in the layer tends to be poor. On the other hand, CB is added to provide sufficient conductivity, but its specific surface area is 200 rr.
? / tr≦B2 (500r#/7r is also important to specify. That is, the specific surface area B of CB is 200 m'
If the particle size is less than /7r, the particle size will be too large and the conductivity will be insufficient even with the addition of carbon black.
? /fr or more, the particle size is too small and the dispersibility of CB tends to deteriorate.

Although it is preferable to use CB and CB in combination, depending on the properties of the magnetic powder and the recording/reproduction method, sufficient effects may be obtained even when each is used alone.

The amount of carbon black to be added is determined within a range that can maintain the mechanical strength of the magnetic layer, but it is usually necessary to add 5 to 35% by weight (preferably 10 to 25% by weight) of carbon black to the binder. With the specific surface area in the above range, it is not necessary to increase the carbon black addition; d-, and it can be set in the above range of 5 to 35% by weight, and the mechanical properties of the magnetic layer (e.g. powder removal of the magnetic layer) are improved. ) can be maintained well, and the desired surface electrical resistance (10°Ω・
(below 0.05) and light transmittance (below 0.05).

FIG. 5 shows a magnetic recording medium, for example a magnetic tape, having a magnetic layer containing magnetic powder according to the present invention, in which a subbing layer 2 (this layer is not provided if necessary) is provided on a support 1. (in some cases), magnetic W13 is laminated.

The magnetic layer 3 contains the above-mentioned treated magnetic powder.

The magnetic powder used in the present invention, particularly the ferromagnetic powder, includes 1-Fe203, Co-containing 1-Fe203,
Fe50. , Co-containing iron oxide magnetic powder such as Fe3O4, CrO2; FeXNi, CoXFe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-
Ni-P alloy, Co-Ni alloy, etc. Fe, Ni, C
Examples include various ferromagnetic powders such as metal magnetic powders whose main component is ferromagnetic powder. In the case of metal magnetic powder, it can be treated with a copolymer according to route C in FIG.

The magnetic paint consists of magnetic powder (previously treated with the above copolymer), binder, above carbon black, and above copolymer (the magnetic powder has already been treated with this copolymer, so there is no need to add it again). (or may be further added from the viewpoint of dispersibility), etc. are mixed and dispersed together with a coating solvent, and this magnetic coating is coated on a support to form a magnetic layer, which is then used as a magnetic recording medium. As the binder for the magnetic layer, in addition to the above-mentioned binder,
A mixture of this binder and a thermoplastic resin, a heat-curable resin, a reactive resin, or an electron beam irradiation-curable resin may be used.

The thermoplastic resin has a softening temperature of 150°C or less, an average molecular weight of io, ooo to 200,000, and a polymerization degree of about 2.
00 to 2,000, such as acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene inide-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer Polyester resins, chlorovinyl ether-acrylic ester/copolymers, amine resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used.

These resins are disclosed in Japanese Patent Publications Nos. 37-6877 and 39-1.
No. 2528, No. 39-19282, No. 40-5349
No. 40-20907, No. 41-9463, No. 4
No. 1-14059, No. 4l-1698s, No. 42-6
No. 428, No. 42-11621, No. 43-4623, No. 43-15206-, No. 44-2889, No. 4
No. 4-17947, No. 44-18232, No. 45-1
No. 4020, No. 45-14500, No. 47-1857
No. 3, No. 47-22063, No. 47-22064,
No. 47-22068, No. 47-22069, No. 47
-22070, US Patent No. 48-27886, US Patent No. 3,144,352, US Patent No. 3,419,420,
It is described in the specifications of the same No. 3,499,789 and the same No. 3,713,887.

The thermosetting resin or reactive resin has a molecular weight of less than zoo or ooo in the state of a coating solution, but after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those which soften but do not melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, mixture of methacrylate copolymer and diisocyanate prepolymer, urea formaldehyde resin,
These resins are polyamine resins and mixtures thereof.
No. 79, No. 41-7192, No. 41-8016, No. 41-14275, No. 42-18179, No. 43-
No. 12081, No. 44-28023, No. 45-145
No. 01, No. 45-24902, No. 46-13103, No. 47-22067, No. 47-22072, No. 4
No. 7-22073, No. 47-28045, No. 47-2
No. 8048, No. 47-28922, U.S. Patent No. 3
．． No. 144,353, No. 3,320,090, No. 3,437,510, No. 3.597. ．． No. 273,
It is described in the specifications of the same No. 3,781,210 and the same No. 3,781,211.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, maleic anhydride type, urethane acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type pipe, polyfunctional fI ≧ monomer, ether acrylic type, urethane acrylic type, phosphate ester acrylic Type, aryl type, hydrocarbon type, etc. are praised.

The total amount of binder used above is 1 magnetic powder.
From the viewpoint of recording density, strength, etc., it is desirable that the amount is 95 to 50 parts by weight per part of 00M.

Furthermore, in order to improve the durability of the magnetic recording medium, the magnetic layer can contain a lit N-forming agent, for example, an isocyanate.

Aromatic incyanates that can be used are, for example, tolylene diisonoanate (TDI), 4,4'-diphenylmethane diinocyanate (MD I,'), xylylene diisocyanate (XDI), meta-xylylene diisocyanate (MXDI) There are also adducts of these isocyanates and active hydrogen compounds, and those having an average molecular weight of 100 to 3,000 are suitable.

Specifically, the product name Sumiseal T80. manufactured by Sumitomo Bayer Urethane Co., Ltd. is used. Same 44s1 Same PF, Same L1 Desmosir T65, Same 15, Same R1 Same RF, Same IL1 Same SL
; Takenate 300S and 500 manufactured by Takeda Pharmaceutical Company
; Mitsui Nisso Urethane Co., Ltd. products rNDIJ, rTODIj
; Desmodule T/CO% manufactured by Nippon Polyurethane Co., Ltd.
Millionaire) MR, same MT.

70 Net L1 Product manufactured by Kasei Upjiyon Co., Ltd. F A T
) I-135, TDI65, TDI80, TDI100. Examples include Isonate 125M and Isonate 143L.

On the other hand, examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (TM
Examples include I) I) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these incyanates and active hydrogen compounds, those with a molecular weight of 1 are preferable.
00 to 3,000.

On the other hand, among the aliphatic incyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. Specifically, for example, Sumitomo Bayer Urethane Co., Ltd. product Sumijyu kN.

Asmosur Z4273, Duranate 50M1 24A-100, 24A-90CX%B manufactured by Mukasei Co., Ltd.
Examples include Coronate HL manufactured by Polyurethane Co., Ltd. and TMDI manufactured by Hüls.

Examples of alicyclic incyanates among the aliphatic isocyanates include methylcyclohexa-4,4-methylenebis(cyclohexyl isoanate), inphorone diisocyanate, and adducts of active hydrogen compounds thereof.

Specifically, products rIPDIJ and IP manufactured by Heals Chemical Co., Ltd.
DI-T1890. Same-H2921, Same-B1065
and so on.

For magnetic recording media, for example, a magnetic paint is prepared by mixing and dispersing magnetic powder, a binder, and various additives in an organic solvent, and after adding the above-mentioned aromatic isocyanate and/or aliphatic incyanate, the stiffness is applied to a support (e.g. polyester film) on top of c? Fabric, dry and prepare as needed. It is preferable to use an aromatic incyanate and an aliphatic incyanate together in order to maintain the physical properties of the magnetic coating material so that it is easy to apply and to improve the physical properties of the magnetic layer formed.

The amount of incyanate added is 1 to 10 to the binder.
Add 0% by weight. If the amount is less than 1%, the hardening of the magnetic layer will be insufficient. If it is more than 10%, the magnetic layer will be easily "sticky" even if it is hardened. In order to maintain a desirable magnetic layer, the amount of isocyanate added is preferably 5 to 30% by weight based on the binder.

The coating material used to form the magnetic layer may contain other additives such as dispersants, lubricants, abrasives, and other antistatic agents, if necessary.

Other dispersants that may be used include lentin, caprylic acid, capric acid, diuric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid,
Fatty acids having 8 to 18 carbon atoms such as linoleic acid and rinnic acid (represented by R-COOH, where R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); Alkali gold 17A of the above fatty acids (Li, Na, etc.) or metal soaps made of potash earth metals (Mg + Ca, Ba, etc.). In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters may also be used.

Moreover, commercially available general surfactants can also be used.

These dispersants may be used alone or in combination of two or more. Examples of lubricants include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 1 G of carbon atoms, and monobasic fatty acids with a total number of carbon atoms of 21 to 23 carbon atoms. Fatty acid esters consisting of alcohols of different types can also be used. These lubricants are added in an amount of 0.2 to 20 M parts per 100 M parts of the magnetic powder.

Abrasive materials that may be used include commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond,
Zaku Shiho, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05~
A size of 5μ is used, particularly preferably a size of 0.
It is 1 to 2μ.

These abrasives are 1 to 2
It is added in an amount of 0 parts by weight.

Other antistatic agents that may be used include conductive powders such as graphite, tin oxide-antimony oxide compounds, and titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; and alkylene oxide compounds. , nonionic surfactants such as glycerin and glycidol; cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphonium and sulfonium; carboxylic acids,
Examples include anionic surfactants containing acidic groups such as sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols.

Solvents for magnetic paint or solvents used when applying magnetic paint include ketones such as acetone, methyl ethyl lactone, methyl ibutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, globanol, butanol; methyl acetate, acetic acid. Esters such as ethyl, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; Ethers such as ethylene glycol dimethyl ether, diethylene glycol monoether ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, and xylene; Methylene chloride, and ethylene Halogenated hydrocarbons such as chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

Materials for the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-7-talate, polyolefins such as polypropylene, cellulose conductors such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, etc. , t, metals such as Zn, glass, boron nitride,
Ceramics such as silicon carbide, porcelain, and earthenware are used.

The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
In the case of a disk or card, the thickness is approximately 30 μm to 10 mm, and in the case of a drum, the shape is cylindrical, and the shape is determined depending on the recorder used.

The surface of the support opposite to the side on which the magnetic layer is provided is preferably coated with a so-called backcoat 4 as shown in FIG. 6 for the purpose of preventing static electricity, preventing transfer, and the like.

Coating methods for coating the magnetic paint onto the support to form a magnetic layer include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coat, cast coat,
Spray coating, etc. can be used, and other methods are also possible.

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

Further, the tAIFr is molded into a desired shape, subjected to surface smoothing processing if necessary, to produce a magnetic recording medium.

Hereinafter, the present invention will be explained with reference to specific examples.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

In the examples below, all "parts" refer to "parts by weight."
represents.

Example 1 Co was deposited by a conventional method, and the copolymer of the present invention (unit A in which two carboxyl groups of alkylene derived from maleic anhydride were converted to quaternary ammonium salts and diisobutylene) was deposited on the reaction solution. An aqueous solution of a copolymer composed of Uni)) and B was also added. The amount added in this case was 21 parts of copolymer to 79 parts of water. Next, the pH of the adsorption tower was adjusted to 7K by adding sulfuric acid, stirred at room temperature for 1 hour, filtered, and washed with water to remove unadsorbed polymer. 0.82 of the polymer was adsorbed to 1002 of the magnetic powder.

This was dried and sectioned.

Next, the following magnetic paint was prepared and a b-inch video chive was prepared in accordance with a conventional method.

Surface treatment Cor-Fe203 10 (1 part Niborane N-230'4 (manufactured by Polyurethane Japan Polyurethane Co., Ltd.) 10 parts Myristic acid 0.5 parts Valmitic acid 0.5 parts At, 0.4.0 parts Palcan XC-72 (Conductive carbon blank) S,
0 parts Coronate (curing agent) 5.4 parts Example 2 A magnetic tape was prepared in the same manner as in Example 1, except that the pH of the reaction solution during the magnetic powder surface treatment was set to 6.

Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that 1 part of lecithin powder was further added to the magnetic paint based on 100 parts of magnetic powder.

Example 4 In Example 1, Co-modified 1-Fezσ8 powder 100
After filtration and drying, the aqueous copolymer solution was added to 2, and the pH was adjusted to 6. A, 3 filtration, drying,
The pulverized and sieved treated magnetic powder was kneaded in the same manner as in Example 1 to form a tape according to the method.

Example 5 In Example 1, the pH of the mother liquor during magnetic powder surface treatment was changed to 9.
A magnetic tape was made in the same manner as above.

Comparative Example 1 The same copolymer as Example 1 (but not an NH4 salt, but having a free carboxyl group and a water solubility of 10-
A sample was prepared in the same manner as in Example 1 using the following materials.

Comparative Example 2 A copolymer disclosed in JP-A No. 50-23207 (
The compound in this example with the same basic structure as Example 1 is an ammonium salt of maleic acid, but in this comparative example, it is a half amide of maleic acid (one is a carboxyl group and the other is an acid amide). : It has become. ) was dissolved in methanol and treated according to the method of Example 4 to prepare a sample.

For each magnetic tape obtained above, the coercive force (He)
, residual magnetic flux density (Br), ski (S), optical selectivity, and video characteristics were measured, and the results shown in the table below were obtained. The method for these measurements was as follows.

Gloss ($) -: Using a variable angle photometer manufactured by Murakami Color Research PJr, a standard plate was determined at 1llll at an exit angle of 6o0.
Displayed in CH.

Video "4: A 50% white signal of 0.36 Vpp was recorded and reproduced and directly read using a Shibaku 725D/l noise meter.

Color%: lo superimposed on O-36Vpp white signal
The multi-color signals were recorded and reproduced and directly read using a Shibaku 925% noise meter.

These results show that the magnetic powder surface-treated with the copolymer of the present invention without drying the magnetic powder after the co adsorption treatment has excellent dispersibility and therefore has excellent magnetic and electrical properties. In addition, due to the influence of pH during copolymer adsorption, pH = 6
Those treated with pH = 9 are good, and those treated with pH = 9 tend to have poor adsorption. Also, after completing the "CO adsorption", E? It can be seen that the dispersibility of the filter-dried magnetic powder tends to deteriorate because the polymer is adsorbed in an aggregated state.

[Brief explanation of the drawing]

The drawings show examples of the present invention, and FIG. 1 is a diagram showing a manufacturing process 70 of a magnetic recording medium, and FIG. Figure 3 is a graph showing the squareness ratio of magnetic recording media depending on the type of copolymer, Figure 4 is a graph showing the copolymer adsorption rate by pHK, Figure 5 is a graph showing the squareness ratio and attached pieces.
This figure and FIG. 6 are enlarged sectional views of a portion of the second side of the magnetic tape. In addition, in the symbols shown in the drawings, l...Non-magnetic support 2...-... Subbing layer 3...Magnetic Layer 4: Back coat layer. Agent: Patent attorney Aisaka *(1 other person) Figure 1 Figure 20 Copolymer melt angle amount (weight platform P/water/θρ weight sound Is)
Elementary □ -- □ Person fII Separation Reciprocal 4th Day H 5th (Spontaneous) Hiraito Ri' and Ne I ↑ Positive Flf 2 Commissioner of the Patent Office Kazuo Wakasugi Tono 2, Igomei's name Magnetic powder and its manufacturing method 3 , Relationship to the case of the person making the amendment Patent applicant address 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name
(127) Konishi Rokushago Kogyo Co., Ltd. 4, Agent Su, Sode Masa (i9 Number of inventions to be added 7, Subject of amendment Detailed explanation of the invention in i+++ document 8, Contents of amendment (2) , p. 21, line 13, "1M can be produced." The acid moiety is ring-opened, and ammonia is applied to the resulting carboxyl group to convert all the carboxyl groups in the monomer A into ammonium salts as described above. A part of the maleic anhydride moiety may remain. In this case, the maleic anhydride moiety is ring-opened by the action of ammonia as described in -, part of the carboxyl group to the monomer unit is amidated, and other carboxyl groups are The maleic anhydride moiety may be converted into a so-called half-amide state by ammonium salt, or the maleic anhydride moiety may remain as it is without being ring-opened by the action of ammonia. Therefore, the degree of ammonium saltation of the carboxyl group in monomer unit A)
can be controlled by the amount of hydrated molecules W mentioned above. Furthermore, the solubility of the copolymer in water can be controlled by changing the ratio of the half-amidation or maleic anhydride moiety described above. ” I corrected myself. Part top

Claims (1)

[Claims] 1. Magnetic powder treated with a copolymer that dissolves at least 10 parts by weight in 100 parts by weight of Jji: parts of water. 2. In the presence of metal ions in an aqueous medium,
A method for producing magnetic powder, which comprises treating magnetic powder with a copolymer that dissolves at least 10 parts by weight in 100 parts by weight of water. 3. A copolymer that dissolves at least 10 parts by weight in 100 parts by weight of water after filtering a magnetic powder dispersion treated to increase coercivity to remove cine essentials from the dispersion. A method for producing magnetic powder, comprising treating the magnetic powder in an aqueous medium.