JPS6069819A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility of magnetic powder in an aq. medium and to improve a squareness ratio by incorporating a copolymer which dissolves at a specific ratio or above in water and the magnetic powder into a magnetic layer. CONSTITUTION:A magnetic layer 3 incorporated therein with a copolymer which dissolves at >=10pts.wt. in 100pts.wt. water and magnetic powder is provided to a magnetic recording medium. The magnetic powder is obtd. by adsorbing the copolymeric polymer on the surface of the magnetic powder in the route A or depositing cobalt thereon in the route B then filtering and washing the magnetic powder, suspending immediately the powder into an aq. soln. contg. the water soluble polymer and adsorbing the polymer on the surface of the magnetic powder. The copolymer consists of monomers contg. negative org. groups as its constituting components. There are, for example, a carboxylic group, residual phosphoric acid group, residual sulfonic acid group, etc. as the negative org. group and above all the carboxylic group and residual phosphoric acid group are preferable. There are ammonium salt, alkali metal salt, etc. as the salt thereof and the ammonium is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field The present invention relates to magnetic recording media such as magnetic tapes and magnetic sheets.

2. Prior Art In recent years, as magnetic materials, especially video and computer recording media, have become more dense and have higher S/N, the particles of magnetic powder used have become smaller - for example, when expressed in terms of surface area per unit weight, VH8 Alternatively, magnetic powder with a BET surface area of 19 to 23 m2/g class is used in the standard grade of beta type magnetic tape, and 23 to 28 m2/g in the high grade class.
m”/g, 29-33 in super high grade class
Magnetic powder of m''/7 class is used. Also, in the near future, powder of -35 to som7.p class is about to appear on the market.

Generally, it is said that the S/N ratio of a magnetic recording medium is proportional to the square root of the number of magnetic particles in the recording material involved in recording and reproduction, so when the same weight of magnetic powder is applied,
The use of a magnetic material with a smaller particle diameter is more advantageous in improving the S/N. However, since the surface area of particles increases in inverse proportion to the square of the particle diameter, dispersion of particles becomes rapidly difficult as the particle diameter decreases, and dispersion stability also deteriorates.

Normally, when dispersing magnetic powder, it should be sufficient to use a dispersant that is sufficient to coat the surface of the magnetic powder particles, but in reality, this does not provide sufficient dispersibility and stability.
For this purpose, a considerable excess of dispersant is added. The dispersant that is not adsorbed to the magnetic powder mixes with the binder in the coating film, and may plasticize the magnetic layer or hinder the curing of the binder. Therefore, the mechanical strength of the magnetic layer, especially Young's modulus, may be significantly reduced. lower. Recently, as tapes have been used for longer recording times, there has been a trend to use thinner base films and to reduce the total thickness of the tape.However, since the stiffness of the tape is proportional to the cube of the tape thickness, it is necessary to make it thinner. As a result, the stiffness becomes noticeably weaker, which impairs the running characteristics of the thin tape, i.e., the head touch of the tape, and thus leads to a deterioration of the S/N ratio.

In order to maintain mechanical properties, particularly the stiffness of the tape, as the tape becomes thinner, a superstretched base film is employed and the Young's modulus of the magnetic layer is increased. Therefore, a decrease 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 damaging the mechanical properties of the magnetic layer.
, No. 3894, and No. 50-92103-, monomagnetic powder is pretreated with a phosphate ester derivative.

In addition, in each publication of JP-A-51-134899, 53-51703, 53-7898, and 54-46509-
Discloses a method of coating the surface of a magnetic layer with silicone oil.

Also, JP-A-50-108902, 49-97738, 51-33753, 53-116114, 54-
In each publication such as No. 24000, the surface is treated with an anionic activator. However, the above technique cannot be said to be effective for small particle magnetic powder, especially for BE'l'' of 35 to 40 rT?/7 or more.

Also, JP-A-51-103403, 47-33602
No.-55-125169, No. 55-73929, 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-polymer having a functional group that can be adsorbed to the magnetic powder.

These techniques involve dissolving the dispersant, mixing with the magnetic powder, stirring, mixing, filtration, drying, pulverization, and sieving in order to mix the dry magnetic powder with a dispersant solution and adsorb the dispersant on its surface. Requires separate steps.

Furthermore, the dried magnetic powder becomes agglomerated and even if a dispersant is added and kneaded, it cannot be dispersed down to the primary particles.Therefore, it is not possible to coat individual primary particles with a polymer. If you try to forcefully disperse it into the primary particles, it will be difficult to break the acicular particles. Therefore, agglomerated clumps of a plurality of particles are surrounded by the polymer, and dispersibility is not improved.

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
As a general method for producing 203, first - ferrous sulfate (
Ferrous hydroxide ((Fe
OH)2) is oxidized in the air and then washed to create α-FeOOH, which becomes the nucleus for crystal growth. Next, separately prepare an aqueous solution of ferrous sulfate and add α-Fe00 to form the nucleus.
When H and metallic iron are added and heated while blowing air, the iron is dissolved by oxidation and α-Fe00H is produced, which is precipitated on the surface of α-Fe00H as a nucleus.
Crystal growth occurs. This growth is, for example, 0.6 to 1.
The length is 0 μm, the width is 0.1 to 0.3 μm, and it is filtered, washed with water, and dried to form a goethite powder. This is further dehydrated and reduced in a H2 stream at about 400°C to obtain F e 3
04 and gradually heated to about 200°C in air, it becomes γ-F 6203 . γ-F thus obtained
To use e2O3 as a nucleus for crystal growth, put it in an aqueous solution of iron sulfate and cobalt sulfate, then add an alkali, and heat it to 60~
Oxidation is performed at 80° C. for 1 to 3 hours to grow cobalt iron oxide on the γ-Fe203i surface. After this, filtration, washing,
Dry -C.

The deposit is γ-Fe203.

As a known technique targeting such Go-coated Fe203, for example, as seen in JP-A-57-138110, a cationic surfactant is added during the process of producing K, magnetic powder - during washing with water after cobalt deposition. There are some products that try to improve the unilateral shape ratio and filling property by doing so. However, even with this, there is still a problem that the dispersibility is insufficient and a good squareness ratio etc. cannot be obtained. Also - JP-A-56-10
No. 903 discloses γ-Fe2O3 coated with co
Although it has been shown to treat with a low-molecular-weight surfactant while it is in a wet state, the dispersibility is still insufficient.

On the other hand, as a processing agent for treating magnetic powder, JP-A-50
-23207 and 50-22603 as a unit, and a part of the carboxyl group is amide (-
CONHR) to impart lipophilicity to the alkyl group (-R), thereby increasing the compatibility of the magnetic powder with the binder during kneading of the magnetic paint. Therefore~
In processes that involve treatment in an aqueous system, such as the above-mentioned CO adhesion - Fe203, it is impossible to surface-treat magnetic powder using the above copolymer; This results in poor dispersion.

3. Purpose of the invention The present inventor has developed a magnetic powder (e.g., cobalt-coated
During the manufacturing process, 3) is dispersed into primary particles in a wet state, but once dried, it forms a hard aggregate and it is very difficult to disperse this into primary particles again, especially when using acicular magnetic powder. Based on the recognition that breakage is likely to occur (therefore, dispersibility will not be improved if surface treatment is performed in an aggregated state), we conducted extensive studies. As a result, we discovered a magnetic powder that can be obtained by surface treatment while exhibiting sufficient dispersibility in an aqueous medium, and thus arrived at the present invention.

4. Structure of the invention and its effects, namely, the present invention provides a magnetic material characterized by containing a magnetic layer of a copolymer and magnetic powder that dissolves at least 10 parts by weight in -100 parts by weight of water. This relates to recording media.

According to the present invention, since the copolymer that acts as a dispersant for magnetic powder exhibits a solubility of 10 parts by weight or more in 100 parts by weight of water, when the magnetic powder is surface-treated in an aqueous medium, (For example, during the step of depositing cobalt on the surface of γ-Fe203: Route 2 in FIG. 1), the copolymer is sufficiently bonded to the hydrophilic surface of the magnetic powder. For this purpose, it is essential that the solubility of the copolymer in water is 10 parts by weight or more, and if it is set within this range, the dispersibility of the magnetic powder will improve as shown in Fig. The mold ratio can be significantly improved. However, if the solubility of the copolymer in water washing is too high, the copolymer will be present in the water rather than adsorbed to the magnetic powder, making it impossible to obtain a sufficient amount of adsorption. Therefore, the solubility is 100 parts by weight per 100 parts by weight of water.
It is desirable that the amount is less than 10 parts by weight, and in order to fully satisfy both dispersibility and adhesion amount, it is 10 to 80 parts by weight/10 parts by weight of water.
It is even more desirable that the amount is 0 parts by weight. The solubility here means the concentration immediately before cloudiness occurs when a copolymer is dissolved in water of a constant weight of m.

In addition, the magnetic powder treated with the above copolymer has secondary particles that are surrounded by an organic polymer (the above copolymer) <1C, and in addition, the hydrophilic groups of the polymer are directed toward the surface of the hydrophilic magnetic powder, and the lipophilic groups are Since the above copolymer is thought to be oriented outward, even when it is made into a magnetic paint, it does not dissolve in the solvent of the magnetic paint because it is a water-soluble polymer, so it is difficult to desorb and has excellent dispersion. While providing stability, it also prevents excess dispersant from being mixed into the binder (i.e. the portion of the copolymer that is not adsorbed to the magnetic powder is removed along with the mother liquor after treatment in the aqueous medium); Does not deteriorate the mechanical properties of the magnetic layer.

In order to obtain the above-mentioned magnetic powder according to the present invention, the copolymer polymer is adsorbed onto the surface of the magnetic powder by route 1 in Figure 1.
Alternatively, after coating with cobalt, it may be filtered and washed, and immediately suspended in an aqueous solution containing the water-soluble polymer of the present invention, and the polymer may be adsorbed on the surface (Route 2 in Figure 1).
.

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

The aqueous medium used in the present invention is basically water in the case of Co-containing oxide magnetic powder, with 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 above-mentioned copolymer onto the magnetic powder is greatly influenced by the tIH of the aqueous solution. As shown in Figure 4
H is preferably 7 or less, preferably 5.5 or less, and the amount of adsorption is considerably reduced on the helialkali side.

The adsorption amount of water-soluble polymer is 1 to 10 per 100g of magnetic powder.
g, preferably 1 to 5 g.

In general, the mother liquor after cobalt deposition has a high jH value, so it is best to add an inorganic acid to lower the yH value to 7 or less before adsorbing the water-soluble polymer. The powder exhibits extremely good dispersibility as described above, but in order to further improve dispersion speed and dispersion stability, it may be added with tehalecithin (preferably powdered lecithin),
A small amount of a dispersant such as oleic acid or phosphoric acid ester may be added.

Further, the treatment of magnetic powder with one of the above copolymers may be carried out in a hydrophilic solvent (for example, an aqueous methanol solution) in the final step of obtaining metal-based magnetic powder from γ-Fe20B by a conventional method.

5. Examples The present invention will be described in more detail below with reference to embodiments.

First, in the present invention, the above-mentioned copolymer used for pretreating the surface of magnetic powder 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 sulfo/acid residue, etc. However, a carboxyl group to a phosphoric acid residue is preferable, and salts thereof include ammonium salts, alkali metal salts, etc., and ammonium salts are preferable. Examples of the monomer unino) A include acrylic acid, methacrylic acid,
Examples include maleic anhydride, 2-hydroxyethyl acryloyl phosphate, and the like, with acrylic acid to maleic anhydride being preferred.

The negative organic group is preferably a carboxyl group or a phosphoric acid residue. Acrylic acid and maleic anhydride are preferred as monomer unit A because they are particularly excellent in storage and dispersibility.

In this copolymer, the effect of the salt of the negative organic group is explained as follows: a simple negative organic group (e.g. free -COOH) and its salt (e.g. ammonium salt -Na
Each dissociation constant is different for each salt.

[Dissociation constant K]

-COOH<-COO"-N"H4(-COONa) and using magnetic powders each surface-treated with each copolymer containing monomer unit A having each of these groups,
It was confirmed that the squareness ratio (B m /Br) of a magnetic recording medium having a magnetic layer prepared by the method described in detail later is as shown in FIG. 3, for example.

That is, when a copolymer in which 1000I (is a salt) is used according to the present invention, the squareness ratio is improved compared to the case where a copolymer having just 1 coou is used. ,−
When COO1t is made into a salt and dispersed in a solvent or binder, the copolymer that is not soluble in the solvent and therefore adsorbed to the magnetic powder becomes difficult to desorb, and the copolymer itself becomes more hydrophilic, resulting in a loss of treatment effect. It is thought that this is to prevent the accident. On the other hand, -Coon has the property of easily adhering to or bonding to the surface of magnetic powder, but since it has stronger lipophilicity than salt, it easily dissolves into the solvent and loses its processing effect, so it is easily desorbed. It is thought that because the substance seeps out onto the tape surface, it does not adhere or bond to the surface as a result.

In addition, among the above organic groups according to the present invention, from FIG. 3, the magnetic properties of ammonium salts are better than those of alkali metal salts. It can be seen that the squareness ratio tends to decrease with increase. The reason for this is that alkali metal salts have greater hydrophilicity (possibly due to a considerably larger dissociation constant), which makes them easier to bond to the magnetic powder surface during surface treatment in aqueous systems, as well as being more likely to detach. Although the ammonium salt has less adsorption than the free acid, it has the best dispersibility due to less desorption in the solvent. In other words, this seems to be because binding to the magnetic powder surface occurs preferentially due to an appropriate dissociation constant.

As an ammonium salt, the general formula including the above -coo'''rH4 is: % formula %() (However, R1-R2, R3, and R4 are each a hydrogen atom or a lower alkyl group that is the same or different from each other.) Those expressed are 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 has the above-mentioned monomer unit A (-(-A-) also written -'j.) tomo/-r
If expressed using -unit B (also written as -E-B+), +A-! It can be expressed as -1lii-+B÷Y.

However, m and n are each positive real numbers. (m-)-
The average value of n) is 100 or less, preferably 50 or less. If it exceeds 100, it becomes difficult to be uniformly dispersed in the magnetic layer of the magnetic recording medium, and in the recording medium,
Performance (for example, output, etc.) tends to become partially non-uniform, which is undesirable. Further, (m + n) is particularly preferably 30 or less, and the dispersion effect in this case 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 + n) is preferably 4 or more, for example, from the viewpoint of preventing the blooming phenomenon.

By selecting the values of -m and n, respectively, and selecting the type of salt of the organic group in unit A, both the hydrophilic and hydrophobic properties of the copolymer, that is, HLB (Hydroph
Appropriate control of ile Lipophile Balance) is possible.

In addition, monomer units other than monomer unit A of this copolymer (hereinafter referred to as monomer unit B).
Examples include styrene, 0-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene-pn- Hexylstyrene-p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene-p-chlorostyrene, 3, Examples include styrene and styrene derivatives such as 4-cyclostyrene.

Other vinyl monomers other than these include, for example, ethylenically unsaturated monoolefins such as ethylene, globylene, butylene, isobutylene, diisobutylene, isononene, and indodesenbu Z; vinyl chloride, vinylidene chloride, vinyl bromide, and fluoride. Vinyl halides such as vinyl; Vinyl h-acid ≦ Vinyl esters such as vinyl glopionate, vinyl penzoate, vinyl butyrate; Methyl acrylic, ethyl acrylate, butyl acrylic, isobutyl acrylate, propyl acrylate, acrylic Octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, meth Acrylic "Th butyl - Ibutyl methacrylate, Gintheoctyl methacrylate, Dodecyl methacrylate, 2-ethylhexyl methacrylate, Stearyl methacrylate, Phenyl methacrylate, Dimethylaminoethyl methacrylate - Dimethylaminoethyl methacrylate α-methylene aliphatic monocarboxylic acid esters such as 7 and diethylaminoethyl methacrylate; derivatives of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, and acrylamide:
vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone/, methyl isopropenyl ketone; N-vinyl pyrrol, N-vinyl carbazole, N-vinylindole;
Examples include N-vinyl compounds such as N-vinylpyrrolidone; vinylnaphthalenes, and the like.

Next, the preferable copolymer (water-soluble polymer) is mono-r-u= when used as a copolymer salt.
y) A contains at least two carboxyl groups (forming a salt as described above). Examples of such monomers (unino)A include those of the following structural formula.

Coo-NH, COO・NH4 (This unit can be formed using monomaleic anhydride as a starting material ~ under the action of ammonia. n indicates a repeating unit and is the same below or equal to 2.) COO・NHCH3 (2) (- C-CH-)-.

COO・NHCH.

H3 COO itself NH4Coo-NH4 On the other hand, monomer unit B is preferably composed of alkylene, aryl alkylene or derivatives thereof, and alkylene is more preferred (all of these are derived from alkenes or aryl alkenes). ). ! It is desirable because it has good IC separation properties and can sufficiently cross-wire with the binder. Preferred starting materials for the monomer unit)H are as follows.

(1), isobutylene (2), 2.3-dimethyl-1-butene (3), 2.3
-Dimethyl-1-pentene (4), inoctene (diisobutylene) (5), indodecene (6), isononene The above-mentioned copolymers used in the present invention can be produced by copolymerization of the above-mentioned starting materials. The obtained copolymer is
If analyzed by GC/Mass, the signal will be separated into isooctene and isobutylene 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). Therefore, it was identified.

All of the copolymers exemplified above used in the present invention are
Hydrophilicity due to monomer Uniso) A and monomer unit B
Since the lipophilicity and lipophilicity are exhibited alternately and repeatedly, once the monomer unit A portion is bonded to the magnetic powder surface,
Since the monomer unit (B) effectively acts in the aqueous medium, the copolymer does not separate. Furthermore, when mixed with a binder, the -monomer unit B portion has sufficient dispersibility. The content of the copolymer to the magnetic powder is suitably 1 to 20 parts by weight per 10 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, KN in an aqueous solution of a Co compound (e.g. Co 804) is prepared according to a conventional method.
Magnetic powder (e.g. γ-Fe
2O3) to adsorb KCO on its surface, the pH of the mother liquor may be lowered by adding an inorganic acid such as sulfuric acid, and under this condition it may be treated with the above copolymer. Alternatively, the copolymer may be adsorbed after the magnetic powder coated with Co is filtered and, if necessary, washed to remove impurities. Examples of the solvent used here include water, methanol, ethanol, propatool, acetone, methyl isobutyl ketone, tetrahydrofuran, and aqueous solutions of dioxane, pyridine, and hydroxyquinoline. Thereafter, the above-mentioned treated magnetic powder was kneaded with a binder and various additives according to a conventional method to prepare a magnetic paint.
A magnetic layer is formed by applying C and drying, followed by calendering and slitting to obtain a magnetic recording medium, such as a magnetic tape.

In the process 70- of FIG. 1, especially the ■ route is Co.
Since a step is added to filter the dispersion of magnetic powder whose coercive force has been increased by the growth of ferrite (Co 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, with this route (1), 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 added. At the very least, it is possible to further control the physical properties of the magnetic powder.Also, in the case of ◎Ru), metal magnetic powder (for example, γ-Fe
The copolymer may be added to a suspension of Fe powder obtained by reduction of 2O3 or Fe powder obtained by reduction of Fe 304 derived from α-Fe203 by dehydration of α-Fe00H.

Polyurethane can be used as a binder for the magnetic layer in the magnetic recording medium of the present invention - it can be synthesized by reaction of a polyol and a polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid-ardipic acid, dimerized sulfuric acid, and maleic acid; glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol; and trimethylolpropane. Polyalcohols such as hexanetriol, chrycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. Polyester polyols synthesized by reaction with; or lactone polyester polyols synthesized from lactams such as 4-caprolactam, S-caprolactam, and γ-butyrolactam; or lactone-based polyester polyols synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. Examples include polyether polyols and the like.

These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diinocyanate-methylene diisocyanate, metaxylylene diisocyanate, etc., resulting in urethanized polyester polyurethane, polyneedle polyurethane, and carbonate with phosgene or diphenyl carbonate. Polycarbonate polyurethane is synthesized.

These polyurethanes are usually produced primarily by the reaction of polyisocyanates and polyols and are also in the form of urethane resins or urethane polymers containing free isocyanate groups and/or hydroxyl groups, or reactive end groups thereof. It may also be one that does not contain (for example, a urethane ester).

Since the methods for producing polyurethane-urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted.

In addition, in the present invention, if a cellulose resin and/or a vinyl chloride copolymer is also included as a binder in addition to the above-mentioned polyurethane, the dispersibility of the magnetic powder will be improved when applied to the magnetic layer. target strength increases. However, if the cellulose resin and/or vinyl chloride copolymer alone is used, the layer becomes too hard, but this can be prevented by the polyurethane content.

Usable cellulose resins include cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester, and the like. Cellulose knee □ Tertoshi contains methylcellulose, ethylcellulose, clovircellulose, inclovircellulose, methylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylcellulose, carboxymethylcellulose.
Sodium salts, hydroxyethylcellulose, benzylcellulose, cyanoethylcellulose, vinylcellulose, nitrocarboxymethylcellulose, diethylaminoethylcellulose, and minoethylcellulose can be used. As the cellulose inorganic acid ester, nitrocellulose-He cellulose, cellulose phosphate, etc. can be used. Cellulose organic acid esters include acetyl cellulose, clopionyl cellulose, phthyryl cellulose, methacryloyl cellulose, chloroacetyl cellulose, β-oxypropionyl cellulose, benzoyl cellulose, p-toluenesulfonate cellulose, acetyl cellulose, Killed by using pionyl cellulose, acetyl butyryl cellulose, etc. Among these cellulose resins, nitrocellulose is preferred. A specific example of nitrocellulose is Cellutuba BTHI manufactured by Asahi Kasei Co., Ltd.
/2, Nitrocellulose 5L-1, Daicel U) 2) o-1z Rulose RS 1/2 to Cell Line L -
200 seconds are gone. Viscosity of nitrocellulose (JI
S-6703 (1975) K)
is preferably 2 to -2 seconds, particularly preferably 1 to 1/1 second.

If it is outside this range, the film adhesion and film strength of the magnetic layer will be insufficient.

The above-mentioned vinyl chloride copolymers that can also be used include those represented by the general formula: In this case, the molar ratio derived from l and m is between 95 and 50 molar for the former units and between 5 and 50 molar for the latter units.

-X represents a monomer residue copolymerizable with vinyl chloride, vinyl acetate, vinyl alcohol, maleic anhydride,
At least one selected from the group consisting of maleic anhydride, maleic acid, maleic ester, vinylidene chloride, acrylonitrile, acrylic acid, acrylic ester, methacrylic acid-methacrylic ester, vinyl propionate glycidyl methacrylate, and glycidyl acrylate. Represents a species. The degree of polymerization expressed as i+m) is preferably from 100 to 600, and when the degree of polymerization is 100
If it is less than 600, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the dispersibility becomes poor. The vinyl chloride copolymer described above may be partially hydrolyzed. Examples of vinyl chloride copolymers include copolymers containing vinyl chloride and vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymers"). Examples of vinyl chloride-vinyl acetate copolymers are vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, vinyl chloride-vinyl acetate. Examples include copolymers of -vinyl alcohol-maleic anhydride-maleic acid, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferred. As a specific example of the above-mentioned vinyl chloride-vinyl acetate copolymer, “VAGI (J,
[VYHHJ-"VMcHJ, Building Block Chemical ("Eslenoku M" made by vermilion, "Denkabinir 100" made by Denki Kagaku Kogyo Co., Ltd.)
0G'', [Denkabinir 100WJ, 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 90/10 to so/s by weight.
o, preferably 85/15 to 6Q/! It has been confirmed that 0 is more desirable. Outside this range,
If there is too much polyurethane, poor dispersion tends to occur and still durability tends to deteriorate, and when other resins are too large, surface properties tend to be poor and still properties deteriorate, especially when polyurethane is used.
When it exceeds 0% by weight, the physical properties of the coating film become less favorable overall.

The magnetic layer of the magnetic recording medium according to the present invention further has a specific surface area (BET value) Bo of 40 m71 r<B t<20
0 m”ノ.

carbon black (hereinafter sometimes referred to as CBl) and specific surface area (BET value) B2 of 200m7ir.
≦B 2 (500I'll''/jilr carbon black (hereinafter sometimes referred to as CB2).
It is preferable to contain at least one of the following. That is,
Carbon black CB1 is added mainly for light shielding, but its specific surface 9B1 is 40 m/, 9r < Bl
<20 om'/ ,! By specifying the amount in the range of 9r, the layer can have sufficient light-shielding properties, and at the same time, the dispersibility of CB1 in the layer can be improved. Outside this range, CB
If the specific surface area of
If it is more than fl r, the particle size will be too small and the dispersibility in the layer will tend to be poor.

On the other hand, CB2 is added to provide sufficient conductivity, but its specific surface area is
0m2/? It is also important to specify rK. That is -C
If the specific surface area B2 of B2 is less than 200 m'/f/r, the particle size is too large and conductivity is insufficient even with the addition of carbon black, and if it is more than 500 m'/gr, the particle size is too small. On the contrary, the dispersibility of CB2 tends to deteriorate.

It is preferable to use Ca11 and CB2 in combination, but even if each is used alone, sufficient effects may be obtained depending on the properties of the magnetic powder and the recording/reproducing method.

The amount of carbon black to be added is determined within a range that can maintain the mechanical strength of the magnetic layer, and 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, there is no need to increase the amount of carbon blank added, and it can be set in the above range of 5 to 35% by weight, and the mechanical properties of the magnetic layer (for example, powder falling off of the magnetic layer) can be reduced. Not only can it be held well, but it also has the desired surface electrical resistance (109 Ω・cm or less) and light transmittance (0,0
5% or less).

This shows a magnetic tape, with a subbing layer 2 on a support 1.
(This layer may not be provided if necessary.)

)-The magnetic layer 3 is laminated.

According to the present invention, the above-mentioned treated magnetic powder is contained in the magnetic layer 3.

In particular, as the ferromagnetic powder for the magnetic floating bed used in the present invention, -γ-Fe203, Co-containing -Fe203-F
e304- Iron oxide magnetic powder such as Co-containing F@304:
Fe, Ni-co, Fe-Ni-Co alloy, Fe −
Mn-, Zn alloy, Fe-Ni-Zn alloy,
Fe-Co-Ni-Cr alloy, Fe-Co-N
i-P alloy, Co-Ni alloy, etc., Fe-Ni,
C.

Examples include various ferromagnetic powders such as metal magnetic powders whose main components are In the case of metal magnetic powder, it can be treated with a copolymer by route C in FIG.

The magnetic paint according to the present invention consists of a magnetic powder (previously treated with the above copolymer), a binder, the above carbon blank, and the above copolymer (the magnetic powder is pretreated with this copolymer). It is not necessary to add it, or it may be further added from the viewpoint of dispersibility. A magnetic recording medium according to the invention.

As the binder for the magnetic layer of the present invention, in addition to the binders described above, a mixture of this binder and a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam curable resin may be used.

The thermoplastic resin has a softening temperature of 15'0"C, an average molecular weight of io, ooo to 200,000, and a polymerization degree of about 200 to 2,000, such as acrylic ester-acrylotolyl. Copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer , polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer to acrylonitrile-butadiene copolymer,
Polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin-chlorovinyl ether-acrylic acid ester co-M combination-7mino resin, 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. 41-9463-41-14059, No. 41-16985, No. 42-
No. 6428, No. 42-11621, No. 43-4623
No. 43-15206, No. 44-2889, No. 4
．． No. 1-17947-, No. 44-18232, No. 45
-No. 14020, No. 45-1402 - No. 47-185
No. 73-47-220G3, No. 47-22064
No. 47-22068, No. 47-22069, No. 47-22070, No. 48-27886, U.S. Patent No. 3,144,352, U.S. Patent No. 3,419,420
No., No. 3.499.789 - No. 3,713,88
It is written in No. 7 Meibun 1 sho.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a single coating solution, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenolic resins, epoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, aryl-based reactive resins, mixtures of methacrylate copolymers and diisocyanate prepolymers, urea-formaldehyde resins, and polyamines. resins, mixtures thereof, etc.

These resins are disclosed in Japanese Patent Publications Nos. 39-8103 and 40-97.
No. 79, No. 41-7192, No. 41-8016, No. 41-14275, No. 42-18179, No. 43-
No. 12081, No. 44-28023, No. 4s-145
No. 01, No. 45-24902, No. 46-13103, No. 47-22067 to 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. 3,597,273, No. 3.781.210, No. 3.7 '81. 211
It is stated in the specification of the No.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
For example, maleic anhydride type, urethane polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., or polyfunctional monomers such as ether acrylic type, urethane acrylic type, phosphoric acid ester decryl type, Ryorir type-hydrocarbon type, etc. Can be mentioned.

Note that the total amount of the binder used in the present invention is desirably 5 to 50 parts by weight per 100 parts by weight of magnetic powder from the viewpoint of recording density, strength, etc.

Furthermore, magnetic W is used to improve the durability of magnetic recording media.
IVC may contain various curing agents, such as isocyanates.

Aromatic incyanates that can be used are, for example, tolylene diisocyanate (TDI), 4,4'-diphenylmethane diincyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (
, MXDI) and adducts of these incyanates with active hydrogen compounds, etc., and the average molecular weight is 10.
A range of 0 to 3,000 is preferred.

Specifically, Sumiseal T80, 448-PF, and L1 Desmoji manufactured by Sumitomo Bayer Urethane Co., Ltd.
- kT65, 15, R1 RF - IL - SL;
Takeda Pharmaceutical Co., Ltd. product Tagane) 300S, 500
Mitsui Nisso V Product manufactured by Thai company "NDIJ," T.

DIJ; Commercial W Desmosir T manufactured by Nippon Polyurethane Co., Ltd.
100, Millionate MR, Same MT, Coronate L.

Kasei Upjoy products PAPI-135, TDI6
5, 80-Zoo, Isone) 125M,, 14
Examples include 3L.

On the other hand, examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, and trimethylhexamethylene diisocyanate (TMD).
I) and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these isocyanates and active hydrogen compounds, those with a molecular weight of 100 are preferable.
~3,000. On the other hand, adducts of monoaliphatic isocyanates and active hydrogen compounds are preferred.

Specifically, for example, Sumidur N1 Desmodur Z 4273 manufactured by Sumitomo Bayer Urethane Co., Ltd., Puranate 50M, 24A-100, and 24A manufactured by Asahi Kasei Co., Ltd.
-90CX, Product Coronae manufactured by Nippon Polyurethane Co., Ltd.) H
L, TMDI manufactured by Heels, etc.

Examples of alicyclic incyanates among the aliphatic incyanates include methylcyclohexaGO 4,4'-methylenebis (cyclohexyl incya isophorone diisocyanate and its adduct of an active hydrogen compound).

Specifically, products manufactured by Heals Chemical Co., Ltd. [IPDIJ~IP
There are DI-T1890, DI-H2921, DI-B1065, etc.

In the magnetic recording medium of the present invention, for example, a magnetic paint is prepared by mixing and dispersing magnetic powder, a binder, and various additives with an organic solvent, and after adding the aromatic incyanate and/or aliphatic incyanate, this is prepared. It is prepared by coating it on a support (for example, a polyester film) and drying it if necessary.

The combination of aromatic isocyanate and aliphatic isocyanate maintains the physical properties of the magnetic paint so that it is easy to apply.
It is also preferable in terms of improving 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 it is less than 1 inch, the hardening of the magnetic layer tends to be insufficient, and if it is more than 100 inches, even if the magnetic layer is hardened, it tends to become "sticky". In order to obtain a more preferable magnetic layer, the amount of incyanate 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 soybean lecithin, soybean oil-free lecithin, caprylic acid-puric acid,
Fatty acids having 8 to 18 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, and linuric acid (represented by R-COOH, where R is 7 to 17 carbon atoms) saturated or unsaturated alkyl groups); alkali metals (Li, N
a, etc.) or alkaline earth metals (Mg, Ca, Ba, etc.) or alkaline earth metals (Mg, Ca, Ba, etc.)
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. Lubricants include silicone oil, graphite, and molyph disulfide.

Den, tungsten disulfide - monobasic fatty acid having 12 to 16 carbon atoms and the total number of carbon atoms of the fatty acid.

Fatty acid esters made of monohydric alcohols having 21 to 23 carbon atoms can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight 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,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives have an average particle size of 0.05
~5μ in size is used, particularly preferably 0
．． It is 1 to 2μ.

These abrasives are used in an amount of 1 to 20 parts by weight per 100 parts by weight of magnetic powder.
It is added in a range of parts by weight.

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

Solvents for magnetic paint or solvents used when applying magnetic paint 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, Esters such as butyl acetate, ethyl lactate, and ethylene glycol monoacetate; Ethers such as ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane, and tetrahydrofuran; Aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, Carbon tetrachloride, chloroform, dichlorobenzene, and other halogenated hydrocarbons can be used.

Support materials include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, AIJ-Zn, etc. metals, glass, boron nitride, silicon carbide, ceramics such as porcelain-ceramics, etc. are used.

The thickness of these supports is about 3 to 100 μm to preferably 5 to 50 μm in the case of a film or sheet,
In the case of a disk or card shape, the diameter is about 30 μm to 10 mm, and in the case of a drum shape, it 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 purposes such as antistatic and antitransfer purposes.

Coating methods for forming a magnetic layer by coating the magnetic paint on the support include air doctor coating, blade coating, air knife coating, squeeze coat), f.
Fl coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, 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 magnetic recording medium of the present invention is manufactured by performing surface smoothing processing or cutting into a desired shape as necessary.

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 addition, in the following examples, all "parts" are "parts by weight".
represents.

Example 1 ゛CO-γ-Fe203 coated with Co was filtered and washed,
The copolymer of the present invention is Co-γ-F e 203 in a wet vortex state. (Copolymer composed of unit A, in which two carboxyl groups of alkylene derived from maleic anhydride are converted into quaternary ammonium salts, and unit B, which is composed of diisobutylene) was suspended in an aqueous solution. The amount added in this case was 21 parts of copolymer to 79 parts of water.

Next, the pH of the adsorption valley was adjusted to pH 7 by adding sulfuric acid, stirred at room temperature for 1 hour, filtered and washed with water to remove unadsorbed polymer.

0.8 g of polymer was adsorbed to 100 g of magnetic powder. This was dried and sieved.

Next, the following magnetic paint was prepared and one copy of a 2-inch videotape was made according to a conventional method.

S-7IeCA (vinyl chloride vinyl acetate copolymer) 10 parts myristic acid 0.5 parts valmitic acid 0.5 parts AA+20z, 4.0 parts Palcan XC-72 (conductive carbon black) 5.
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 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-Fe 203 powder 1
After drying against 00I, adding the copolymer aqueous solution,
The treated magnetic powder, which had been adsorbed after adjusting the pH to 6, was filtered, dried, crushed, and sieved, was kneaded in the same manner as in Example 1 and made into a tape according to a conventional method.

Example 5 A magnetic tape was produced in the same manner as in Example 1, except that the pH of the reaction solution during magnetic powder surface treatment was set to 9.

Comparative Example 1 A sample was prepared in the same manner as in Example 1 using the same copolymer as in Example 1 (but having free carboxyl groups instead of NH4 salts and having a solubility in water of 10 or less). .

Comparative Example 2 Copolymer disclosed in JP-A-50-23207 (
The compound of Example fi11, which has the same basic structure as Example 1, is an ammonium salt of maleic acid, but in this comparative example, the compound of )·-famid (one of which is a carboxyl group,
The other is an acid amide). ) 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), squareness ratio (Sq)-gloss-video characteristics were measured, and the results shown in the table below were obtained.

The method for these measurements was as follows.

Brightness: Measured using a variable angle photometer manufactured by Murakami Color Research Institute (
glass) Measured at an angle of incidence of 60° and the standard plate is displayed as 100%.

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, accordingly, excellent magnetic properties and electrical properties.

In addition, the amount of copolymer adsorption is affected by the pH of the adsorption reaction solution.
Those treated with pi (= 6) are better, and those treated with pH = 9 tend to have poor adsorption. In addition, the magnetic powder that was filtered and dried after Co adsorption may be because the polymer was adsorbed in an aggregated state. It can be seen that the dispersibility tends to deteriorate.

[Brief explanation of the drawing]

The drawings show examples of the present invention, in which Fig. 1 is a flow diagram of the manufacturing process of a magnetic recording medium, and Fig. 2 is a magnetic recording method using the solubility properties of a magnetic powder surface treatment agent (copolymer). Graph showing the squareness ratio and adhesion amount of the media, 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 6 and 6 are enlarged cross-sectional views of a portion of an example magnetic desk. In addition, in the symbols shown in the drawings - I...--Nonmagnetic support 2--
. . . Subbing layer 3 . . . Magnetic layer 4 . . . Bank coat layer. Agent: Patent attorney Hiroshi Osaka (and 1 other person) Kyokakura body 0 retaining amount (electricity instant/water 100 volume sound p) @3
Small person 1g + Distance constant Figure 4 H @50 (Voluntary) Procedural formalities Commissioner of the Patent Office Kazuo Wakasugi 2. Name of the invention Magnetic recording medium 3. Relationship with the case to be amended Patent applicant Address: 1-26-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name:
('127) Roku Konishi Photo Industry Co., Ltd. 46 Agent 6, Number of inventions increased by amendment 7, Column 8 for detailed explanation of the invention in the specification subject to amendment, Contents of amendment C00-N I(tc Hi Correct "r -1-C-C11-Monkey-". 1 COO-NH,COO・N1(.
Can be manufactured. For example, by synthesizing an Ii aggregate of maleic anhydride and al-1-lene, the polymer can be hydrolyzed (as described in 1-1). 1 to open the ring of the maleic acid moiety in water, and to react with ammonia to the generated carboxyl λ1, all of the carboxyl groups in the monomer Uni 71-A are converted into ammonium salts in a double manner.However, in this case, during the above hydrolysis, A portion of the maleic anhydride moiety that is not ring-opened may remain; in this case, the maleic anhydride moiety is ring-opened by the action of the ammonia, and some of the carboxyl groups to the monomer unit are amidated, and other carboxyl groups are The maleic anhydride acid moiety may remain as it is without ring-opening due to ammonium salt formation, so to speak, a half-amide state, or due to the action of the ammonia mentioned above.The degree of ring-opening of the maleic anhydride moiety (Therefore, the degree of ammonium saltation of the carboxyl group in monomer unit A) is
It can be controlled by the degree of W. In addition, depending on the ratio of the half-amidation or maleic anhydride moiety described above, the water content of the copolymer may be affected. ii: You can also control your sexuality. ” I corrected myself. (4), p. 44, lines 11-12, "copolymer." has been corrected to "copolymer." Part”21

Claims (1)

[Claims] 1. A magnetic recording medium characterized in that a magnetic layer contains a copolymer that dissolves in an amount of 10 parts by weight or more in 100 parts by weight of water, and a magnetic powder.