JPH0414415B2 - - Google Patents

Description

[Detailed description of the invention]

1. Field of Industrial Application The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic sheets. 2. Prior Art In recent years, as the density and S/N of magnetic materials, particularly video and computer recording media, have increased, the particles of magnetic powder used have become smaller, and for example, in terms of surface area per unit weight, VHS or Beta Magnetic powder with a BET surface area of 19 to 23 m ² /g is used in the standard grade of magnetic tape of this method, 23 to 28 m ² /g in the high grade class, and 29 to 33 m ² /g in the super high grade class. is used. In addition, powder in the 35 to 50 m ² /g class is about to appear on the market in the near future. Generally, 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. Therefore, when applying the same weight of magnetic powder, the particle diameter The smaller the magnetic material used, the more advantageous it is to 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 just enough dispersant to coat the surface of the magnetic powder particles, but in reality, this does not provide sufficient dispersibility and stability. Therefore, 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, plasticizes the magnetic layer, and prevents the hardening of the binder.
Therefore, the mechanical strength of the magnetic layer, especially Young's modulus, is significantly reduced. Recently, as tapes are used for longer recording times, there is a trend to use thinner base films and reduce the total thickness of the tape. As a result, the stiffness becomes noticeably weaker, which deteriorates the running characteristics of thin tapes and the head touch of the tape, leading to a deterioration of the S/N ratio. In order to maintain the mechanical properties associated with thinning, especially the stiffness of the tape, a super-stretched base film is used 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 impairing the mechanical properties of the magnetic layer. For example, JP-A No. 54-94308,
In each of the publications No. 54-143894 and No. 50-92103, magnetic powder is pretreated with a phosphate ester derivative. Also, JP-A-51-134899, 53-51703, 53-
No. 7898 and No. 54-46509 disclose a method of coating the surface of a magnetic layer with silicone oil. Also, JP-A-50-108902, 49-97738, 51-
In publications such as No. 33753, No. 53-116114, and No. 54-24000, the surface is treated with an anionic activator. However, the above technology is suitable for small particles, especially BET35 ~
It cannot be said to be effective against magnetic powder of 40 m ² /g or more. Also, JP-A-51-103403, 47-33602, 55
−125169, 55−73929, 55−73930, 57−
Publications such as No. 42888 and No. 57-1026 disclose techniques for coating the surface of magnetic powder with oligomers and polymers having functional groups that can be adsorbed to the magnetic powder. These techniques involve dissolving the dispersant, mixing with the magnetic powder, stirring, kneading,
Each process of filtration, drying, crushing, and sieving is required.
In addition, dried magnetic powder becomes agglomerated, and even if a dispersant is added and kneaded, it is difficult to disperse down to the primary particles.Therefore, it is difficult and impossible to coat individual primary particles with a polymer. If you try to disperse it into primary particles, the acicular particles will break. Therefore, agglomerated clumps of a plurality of particles are surrounded by the polymer, and dispersibility is not improved. Magnetic powders, particularly Co-coated γ-Fe ₂ O ₃ , are widely used as magnetic materials for video, high performance audio, and computer tapes. As a general method for producing this Co-adhered γ-Fe ₂ O ₃ , first, sodium hydroxide (NaOH) is added to an aqueous solution of ferrous sulfate (FeSO ₄ 7H ₂ O) to produce ferrous hydroxide. Iron ((FeOH) ₂ ) is oxidized in the air and then washed.
Create α-FeOOH, which becomes the nucleus for crystal growth. Next, prepare a separate aqueous solution of ferrous sulfate, add core α-FeOOH and metallic iron, and heat while blowing air.The iron dissolves due to oxidation, producing α-FeOOH. However, this precipitates on the surface of α-FeOOH as a nucleus, and crystal growth occurs. This growth is e.g. 0.6-1.0μ long, 0.1
Keep the width to ~0.3μ, filter, wash with water, and dry to make goethite powder. This is then dehydrated and reduced to Fe 3 O 4 in a H ₂ stream at around 400°C, and then converted to Fe ₃ O ₄ in air.
When gradually heated to about 200°C, it becomes γ-Fe ₂ O ₃ . The γ-Fe ₂ O ₃ obtained in this way is used as a nucleus for crystal growth, placed in an aqueous solution of iron sulfate and cobalt sulfate, and then an alkali is added and the γ-Fe 2 O 3 is grown at 60-80℃ for 1-3
Oxidation is performed for a period of time to grow cobalt iron oxide on the γ-Fe ₂ O ₃ surface. After that, it is filtered, washed with water, and dried to obtain Co-coated γ-Fe ₂ O ₃ . As a known technique targeting Co-adhered γ-Fe ₂ O ₃ , for example, as seen in JP-A-57-138110, cationic surface activity is Some attempts have been made to increase the squareness ratio and filling properties by adding agents. However, even with this, there is still a problem that the dispersibility is insufficient and a good squareness ratio etc. cannot be obtained. Furthermore, JP-A-56-10903 discloses that γ-Fe ₂ O ₃ coated with Co is treated with a low-molecular surfactant while it is in a wet state. Dispersibility is still insufficient. On the other hand, as processing agents for treating magnetic powder, there are copolymers disclosed in JP-A-50-23207 and JP-A-50-22603. this is,

[Dissociation constant K]

−COOH<−COO ⁻ N ⁺ H ₄ <−COON _a Then, using magnetic powders each surface-treated with each copolymer containing monomer unit A having each of these groups, as will be described in detail later. It was confirmed that the squareness ratio (Bm/Br) of a magnetic recording medium having a magnetic layer prepared by this method is as shown in FIG. 3, for example. That is, compared to the case where a copolymer having simple -COOH is used, -
When using a copolymer in which COOH is a salt,
The squareness ratio is improved. This is because when -COOH is made into a salt and dispersed in a solvent or binder, the copolymer that is not dissolved in the solvent and therefore adsorbed to the magnetic powder is difficult to desorb, and the copolymer itself becomes more hydrophilic. This is thought to be because the processing 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 since it has stronger lipophilicity than salt, it easily dissolves into the solvent and loses its treatment effect, and it also tends to dissolve into the solvent and lose its treatment effect. It is thought that because the particles seep out onto the tape surface, it does not adhere or bond to the surface as a result. Furthermore, among the above organic groups,
From Figure 3, the magnetic properties of ammonium salts are better than those of alkali metal salts, and the use of ammonium salts is the highest, and before and after that, the squareness ratio tends to decrease as the dissociation constant decreases or increases. It turns out that there is. 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. 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 surface of the magnetic powder occurs preferentially due to an appropriate dissociation constant. As the ammonium salt, the above −COO ⁻ N ⁺ H ₄
General formula containing: −COO ⁻ N ⁺ (R ¹ ) (R ² ) (R ³ ) (R ⁴ ) (However, R ¹ , R ² , R ³ , and R ⁴ are each a hydrogen atom, or are the same or (different lower alkyl groups) are applicable. Here above
When R ¹ , R ² , R ³ and R ⁴ are lower alkyl groups,
The total number of carbon atoms of R ¹ to ^{R 4} is 6 or less,
This is desirable because it does not impair the basicity of the ammonium salt due to steric hindrance. The above copolymer has the above monomer unit A.
(also written as [-A]-) and monomer unit B ([-
B
]- is also written. ), [-A]- _n [-
B]-
It can be expressed as _o . However, m and n are each 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 it uniformly in the magnetic layer of the magnetic recording medium, and the performance (for example, output) of the recording medium tends to become partially non-uniform.
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. Here, by selecting the values of m and n and the type of salt of the organic group in unit A, the copolymer can have both hydrophilic and hydrophobic properties.
Appropriate control of HLB (Hydrophile Lipophile Balance) is possible. In addition, monomer units other than monomer unit A (hereinafter referred to as monomer unit B) of this copolymer are
It is called. ) Examples include styrene, o-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-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene Examples include styrene and styrene derivatives such as styrene and styrene derivatives. Examples of vinyl monomers other than these include ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, isobutylene, diisobutylene, isononene, and isododecene; vinyl chloride, vinylidene chloride, vinyl bromide, and fluoride. Vinyl halides such as vinyl;
Vinyl acetate; vinyl esters such as vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, acrylic acid Dodecyl, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate , isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate,
α-methylene aliphatic monocarboxylic acid esters such as dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate; derivatives of acrylic acid or methacrylic acid such as acrylonitrile, methacrylonitrile, and acrylamide; vinyl Vinyl ethers such as methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone;
N-vinylpyrrole, N-vinylcarbazole,
Examples include N-vinyl compounds such as N-vinylindole and N-vinylpyrrolidone; vinylnaphthalenes and the like. Next, preferred copolymers (water-soluble polymers) are those in which monomer unit A, when used as a salt of the copolymer, contains at least two carboxyl groups (forming the salt as described above). Examples of such monomer units A include those of the following structural formula, but in the present invention, the following unit (1) is particularly used. (This unit can be formed using maleic anhydride as a starting material under the action of ammonia. n indicates a repeating unit; the same applies hereinafter.) On the other hand, monomer unit B is preferably composed of alkylene, arylalkylene, or a derivative thereof, and alkylene is more preferred (all of these are derived from alkenes or arylalkenes). Particularly branched alkylene is desirable because it has good solubility in organic solvents and can be sufficiently kneaded with the binder. Preferred starting materials for monomer unit B are as follows, but the following unit (4) is particularly used in the present invention. (1) Isobutylene (2) 2,3-dimethyl-1-butene (3) 2,3-dimethyl-1-pentene (4) Isooctene (diisobutylene) (5) Isododecene (6) Isononene The above used in the present invention The copolymer can be produced by copolymerizing the above-mentioned starting materials. for example,
A copolymer of maleic anhydride and alkylene is synthesized, and this copolymer is hydrolyzed to open the ring of the maleic anhydride moiety, and the resulting carboxyl group is treated with ammonia to form the monomer as described above. All carboxyl groups in unit A are converted to ammonium salt. However, in this case, some maleic anhydride moieties that are not ring-opened during the above hydrolysis may remain, but in this case, the maleic anhydride moieties open due to the action of the ammonia and some of the carboxyl groups of monomer unit A are removed. is amidated and the other carboxyl group is ammonium salted, so to speak, resulting in a half-amide state, or even due to the action of ammonia, the maleic anhydride moiety may remain as it is without opening the ring. This is outside the scope of the present invention. The degree of ring opening of the maleic anhydride moiety (and therefore the degree of ammonium saltation of the carboxyl group in monomer unit A) can be controlled by the degree of hydrolysis described above. In addition, depending on the ratio of the above-mentioned half-amidation or maleic anhydride moiety,
It is also possible to control the solubility of the copolymer in water. The obtained copolymer was subjected to GC/Mass
When analyzed, the signal for the part corresponding to an alkene is divided into, for example, isooctene and isobutylene, and the part corresponding to an acid (for example, maleic anhydride) is identified by the signal being divided into toluene, diethylbenzene, styrene, etc. It was done. All of the above-mentioned copolymers used in the present invention alternately exhibit hydrophilicity due to monomer unit A and lipophilicity due to monomer unit B, so that the monomer unit A portion is present on the surface of the magnetic powder. Once bonded, the copolymer does not separate because the monomer unit B portion acts effectively in the aqueous medium. Furthermore, when kneading with the binder, the monomer unit B has sufficient dispersibility. The content of the copolymer relative to the magnetic powder is suitably 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, magnetic powder (e.g. γ-Fe ₂ O ₃ ) is added to an aqueous solution of a Co compound (e.g. CoSO ₄ ) with the addition of an alkali such as NaOH. After soaking Co to adsorb Co on its surface, the pH of the mother liquor is adjusted by adding an inorganic acid such as sulfuric acid.
may be lowered and treated with the above copolymer under this condition. 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 aqueous solutions of water, methanol, ethanol, propanol, acetone, methyl isobutyl ketone, tetrahydrofuran, dioxane, pyridine, hydroxyquinoline, and the like. After that,
According to a conventional method, the above-mentioned treated magnetic powder is kneaded with a binder and various additives to create a magnetic paint, which is applied onto a support and dried to form a magnetic layer, followed by calendering and slitting. A magnetic recording medium, such as a magnetic tape, is obtained through this process. In the process flow shown in Figure 1, the route includes the step of filtering the dispersion of magnetic powder whose coercive force has been increased by the growth of Co ferrite (Co adhesion), so this step removes unnecessary substances. By removing free Co ions, etc., magnetic powder with good characteristics can be obtained. In addition, with this route, various solvents can be used during the resuspension process, but additives that are compatible with the binder, such as weakly water-soluble dispersants (lecithin, higher fatty acids, etc.), can be added at this time. The physical properties of the magnetic powder can be further controlled by using metal magnetic powder (for example, γ-
Adding the copolymer to a suspension of Fe powder obtained by reduction of Fe ₂ O ₃ , Fe powder obtained by reduction of Fe ₃ O ₄ derived from α-Fe ₂ O ₃ by dehydration of α-FeOOH) do it. Polyurethane can be used as a binder for the magnetic layer in the magnetic recording medium of the present invention, and can be synthesized by reacting a polyol with a polyisocyanate. Usable polyols include organic dibasic acids such as phthalic acid, adipic acid, dimerized linoleic acid, and maleic acid, and glycols such as ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol, or trimethylolpropane, hexanetriol, For reaction with polyhydric alcohols such as glycerin, trimethylolpropane, hexanetriol, glycerin, trimethylolethane, pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols. or lactone polyester polyols synthesized from lactams such as s-caprolactam, a-methyl-1-caprolactam, s-methyl-s-caprolactam, and γ-butyrolactam; or ethylene oxide,
Examples include polyether polyols synthesized from propylene oxide, butylene oxide, and the like. These polyols are reacted with isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, metaxylylene diisocyanate, etc.
As a result, urethanized polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are synthesized. These polyurethanes are usually produced primarily by the reaction of polyisocyanates with polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. (for example, in the form of a urethane elastomer). 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, and the machine target strength increases. 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. Examples of cellulose ethers include methylcellulose, ethylcellulose, propylcellulose, isopropylcellulose, butylcellulose, methylethylcellulose, methylhydroxyethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxymethylcellulose sodium salt, hydroxyethylcellulose, benzylcellulose, cyanoethylcellulose, vinylcellulose, Nitrocarboxymethylcellulose, diethylaminoethylcellulose, aminoethylcellulose, etc. can be used. As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used. In addition, cellulose organic acid esters include acetylcellulose, propionylcellulose, butyrylcellulose, methacryloylcellulose, chloroacetylcellulose, β-oxypropionylcellulose, benzoylcellulose, p-toluenesulfonate cellulose, acetylpropionylcellulose, acetylbutyrylcellulose. etc. can be used. Among these cellulose resins, nitrocellulose is preferred. Specific examples of nitrocellulose include Cellnova BTH1/2 and Nitrocellulose SL-1 manufactured by Asahi Kasei Corporation, Nitrocellulose RS1/2 and Cell Line L-200 manufactured by Daicel Corporation.
Viscosity of nitrocellulose (JIS, K-6703 (1975)
2 to 1/64 seconds, particularly preferably 1 to 1/4 seconds. If it is outside this range, the film adhesion and film strength of the magnetic layer will be insufficient. In addition, the above-mentioned vinyl chloride copolymers that can be used have the general formula: There is something expressed as in this case,

[Formula] Unit and

The molar ratio derived from l and m in the units is 95 to 50 mol % for the former unit and 5 to 50 mol % for the latter unit. In addition, X represents a monomer residue copolymerizable with vinyl chloride, including 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,
Represents at least one member selected from the group consisting of glycidyl acrylate. The degree of polymerization expressed as (l+m) is preferably from 100 to 600; when the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and when it exceeds 600, dispersibility deteriorates. The vinyl chloride copolymer described above may be partially hydrolyzed. The vinyl chloride copolymer is preferably a copolymer containing vinyl chloride-vinyl acetate (hereinafter referred to as "vinyl chloride-vinyl acetate copolymer").
That's what it means. ). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl vinyl acetate-vinyl acetate-
Examples include vinyl alcohol-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers Polymers are preferred. Specific examples of the above vinyl chloride-vinyl acetate copolymer include:
"VAGH" manufactured by Union Carbide,
"VYHH", "VMCH", "Esletsuk M" manufactured by Sekisui Chemical Co., Ltd., "Denkavinyl" manufactured by Denki Kagaku Kogyo Co., Ltd.
1000G", "Denkabinir 100W", etc. can be used. The above vinyl chloride copolymer and cellulose resin may be used in any blending ratio. Regarding the overall binder composition, the proportion of polyurethane and other resins (total amount of cellulose resin and vinyl chloride copolymer) is determined by weight.
90/10~50/50 is preferable, 85/15~
It has been confirmed that 60/40 is even more desirable. Outside this range, if the polyurethane content is large, poor dispersion tends to occur and still durability tends to deteriorate.
Furthermore, if the amount of other resins increases, the surface properties tend to be poor, and the still properties deteriorate, and especially if the amount exceeds 60% by weight, the physical properties of the coating film become less desirable overall. The magnetic layer of the magnetic recording medium according to the present invention further has a specific surface area (BET value) B ₁ of 40 m ² /gr<B ₁ <
200m ² /gr carbon black (hereinafter referred to as
Sometimes referred to as CB ₁ . ) and specific surface area (BET
It is preferable to contain at least one of carbon black (hereinafter sometimes referred to as CB ₂ ) whose B ₂ value is 200 m ² /gr≦B ₂ <500 m ² /gr. That is, carbon black CB ₁ is added mainly for light shielding, but its specific surface area B ₁ is 40
By specifying the range of m ² /gr<B ₁ <200m ² /gr, it is possible to obtain sufficient light-shielding properties of the layer, and at the same time, it is possible to prevent light from entering the layer.
The dispersibility of CB ₁ can be improved. If the specific surface area of CB ₁ is outside this range and is less than 40 m ² /gr, the particle size will be too large and the light shielding property will tend to deteriorate.
It is necessary to increase the amount added more than necessary,
Moreover, if it is 200 m ² /gr or more, the particle size will be too small and the dispersibility in the layer will tend to be poor. On the other hand, although CB ₂ is added to provide sufficient conductivity, it is also important to specify its specific surface area as 200 m ² /gr≦B ₂ <500 m ² /gr. That is, the specific surface area B ₂ of CB ₂ is
If the particle size is less than 200 m ² /gr, the particle size will be too large and the conductivity will be insufficient even when carbon black is added, and if it is more than 500 m ² /gr, the particle size will be too small and the dispersibility of CB ₂ will deteriorate. becomes susceptible to deterioration. It is desirable to use CB ₁ and CB ₂ together, 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 maintains 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. Due to the specific surface area within the above range, there is no need to increase the amount of carbon black added, and it can be set within 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 improved. ) and also maintain the desired surface electrical resistance (10 ⁹ Ω・cm or less)
and light transmittance (0.05% or less). FIG. 5 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, in which a subbing layer 2 (this layer may not be provided if necessary) and a magnetic layer 3 are provided on a support 1. are laminated. According to the present invention, the above-mentioned treated magnetic powder is contained in the magnetic layer 3. The magnetic powder used in the present invention, especially the ferromagnetic powder, is γ-Fe ₂ O ₃ , Co-containing γ-
Iron oxide magnetic powder such as Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ : Fe, Ni, Co, Fe-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,
Examples include various ferromagnetic powders such as metal magnetic powders containing Ni, Co, etc. as main components. 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 includes a magnetic powder (previously treated with the above copolymer), a binder, the above carbon black, and the above copolymer (the magnetic powder is pretreated with this copolymer). , there is no need to add it again,
Further, from the viewpoint of dispersibility, it may be further added. ) etc. are prepared by kneading and dispersing them together with a coating solvent, and this magnetic coating material is coated on a support to form a magnetic layer, thereby producing a magnetic recording medium according to the present 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. As a thermoplastic resin, the curing temperature is 150℃ or less,
Average molecular weight is 10000~200000, polymerization degree is 200~
About 2000, for example, acrylic ester.
Acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer Coalescence, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, styrene-butadiene copolymer, polyester resin, chlorovinyl ether-acrylic acid ester copolymer, amino resin , various synthetic rubber-based thermoplastic resins, and mixtures thereof. These resins are disclosed in Japanese Patent Publications No. 37-6877 and No. 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-
No. 20907, No. 41-9463, No. 41-14059, No. 41-
No. 16985, No. 42-6428, No. 42-11621, No. 43-
No. 4623, No. 43-15206, No. 44-2889, No. 44-
No. 17947, No. 44-18232, No. 45-14020, No. 45
-14500, 47-18573, 47-22063, 47-22063, 47-18573, 47-22063,
No. 47-22064, No. 47-22068, No. 47-22069,
No. 47-22070, No. 48-27886, U.S. Patent No.
It is described in the specifications of No. 3144352, No. 3419420, No. 3499789, and No. 3713887. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, 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 resin, epoxy resin, urea resin, melamine resin,
These include alkyd resins, silicone resins, acrylic reactive resins, mixtures of methacrylate copolymers and diisocyanate prepolymers, urea formaldehyde resins, polyamine resins, and mixtures thereof. These resins are listed in Special Publication No. 39-8103 and No. 40-9779.
No. 41-7192, No. 41-8016, No. 41-14275
No. 42-18179, No. 43-12081, No. 44-
No. 28023, No. 45-14501, No. 45-24902, No. 46
−13103, No. 47-22067, No. 47-22072, No.
No. 47-22073, No. 47-28045, No. 47-28048,
Publication No. 47-28922, U.S. Patent No. 3144353, U.S. Pat.
It is described in the specifications of No. 3320090, No. 3437510, No. 3597273, No. 3781210, and No. 3781211. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type,
Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type, hydrocarbon type, etc. The total amount of 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, in order to improve the durability of the magnetic recording medium, various hardening agents can be contained in the magnetic layer.
For example, isocyanate can be contained. Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI) and these isocyanates together with active hydrogen compounds. and adducts with the average molecular weight of 100 to 3000. Specifically, Sumitomo Bayer Urethane Co., Ltd.'s product names Sumizil T80, Sumidil 44S, Sumidil PF, Sumidil L, Sumidil T65, Sumidil 15, Sumidil R, Sumidil RF, Sumidil
SL; Takenate 300S manufactured by Takeda Pharmaceutical Company, Ltd.
500; Product “NDI” manufactured by Mitsui Nisso Urethane Co., Ltd.
"TODI": Desmodyur T100, Millionate MR, MT, Coronate L, manufactured by Nippon Polyurethane Co., Ltd., PAPI-135, manufactured by Kasei Atsupjiyoi Co., Ltd.
TDI65, TDI80, TDI100, Isonate 125M, TDI
Examples include 143L. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. On the other hand, among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. Specifically, for example, Sumidyur N and Desmodyur Z4273 manufactured by Sumitomo Bayer Urethane Co., Ltd., Dulanate 50M and Dulanate 24A-100 manufactured by Asahi Kasei Co., Ltd.
24A-90CX, Coronate HL manufactured by Nippon Polyurethane Co., Ltd., and TMDI manufactured by Hyurus Co., Ltd. Further, as the alicyclic isocyanate among the aliphatic isocyanates, for example, methylcyclohexane-2,4-diisocyanate [structural formula:

[Formula]] 4,4'-methylenebis(cyclohexyl isocyanate) [Structural formula: ], isophorone diisocyanate and adducts of its active hydrogen compounds, and the like. Specifically, the product “IPDI” manufactured by Hyurus Chemical Co., Ltd.
There are IPDI-T1890, IPDI-H2921, IPDI-B1065, etc. In the magnetic recording medium of the present invention, for example, a magnetic coating material is prepared by mixing and dispersing magnetic powder, a binder, and various additives with an organic solvent, and after adding the aromatic isocyanate and/or aliphatic isocyanate, this is applied to a support. It is prepared by coating it on a polyester film (for example, polyester film) and drying it if necessary. It is preferable to use an aromatic isocyanate and an aliphatic isocyanate in combination 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 isocyanate added is 1 to 100% by weight based on the binder. If it is less than 1%, the hardening of the magnetic layer tends to be insufficient, and if it is more than 100%, even if the magnetic layer is hardened, it tends to become "sticky." In order to obtain a more preferable 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 soybean lecithin, soybean oil-free lecithin, caprylic acid,
Capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, etc. with 8 or more carbon atoms
18 fatty acids (represented by R-COOH, where R is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms);
) or alkaline earth metals (Mg, Ca, Ba, etc.)
Examples include metal soaps made of. In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters can 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. As a lubricant, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, carbon atoms 12 or more
Fatty acid esters consisting of 16 monobasic fatty acids and monohydric alcohols having a total of 12 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, and emery (main components: corundum and magnetite). be done. These abrasives have an average particle diameter of 0.05 to 5μ, particularly preferably 0.1 to 2μ.
These abrasives are used in amounts of 1 to 100 parts by weight of magnetic powder.
It is added in an amount of 20 parts by weight. Other antistatic agents that may be used include graphite, tin oxide-antimony oxide compounds,
Conductive powders such as titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts , pyridine, other heterocycles, phosphonium or sulfonium; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group; amino acids, amino acids Examples include amphoteric activators such as sulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like. 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, propanol, and butanol; methyl acetate, ethyl acetate, and acetic acid. Esters such as butyl, ethyl lactate, ethylene glycol monoacetate;
Ethylene glycol dimethyl ether, diethylene glycol monoethyl ether, dioxane,
Ethers such as tetrahydrofuran; benzene,
Aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used. In addition, materials for the support 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, Al, Zn
metals, glass, boron nitride, silicon carbide, etc.
Ceramics such as porcelain and pottery 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 disks and cards, it is 30 μm ~
It is about 10mm, and if it is drum-shaped, it should be cylindrical.
The type is determined depending on the recorder used. The support is preferably coated with a so-called backcoat 4 as shown in FIG. 6 on the side opposite to the side on which the magnetic layer is provided for the purpose of preventing static electricity, preventing transfer, and the like. Coating methods for forming a magnetic layer by applying the magnetic paint onto the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, and gravure coating. , kiss coat, cast coat, spray coat, etc., 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. Furthermore, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing processing or cutting it into a desired shape, if necessary. 5 Examples The present invention will be described below 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, all "parts" in the following examples represent "parts by weight." Example 1 Co-coated Co-γ-Fe ₂ O ₃ was filtered and washed,
Co-γ-Fe ₂ O ₃ in a wet state is mixed with the copolymer of the present invention (unit A, in which two carboxyl groups of alkylene derived from maleic anhydride are converted to quaternary ammonium salts, and unit B, which is composed of diisobutylene). (a copolymer composed of) was suspended in an aqueous solution. The amount added in this case was 21 parts of copolymer to 79 parts of water. The physical properties of this copolymer are m = 2, n = 3 (the molecular weight of the copolymer is 636), where the repeating units of the copolymer are expressed as [-unit A] _-n [-unit B] _-o . It was hot. Next, the pH of the adsorption bath
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. 0.8g of polymer was adsorbed to 100g of magnetic powder. This was dried and sieved. In order to produce the above copolymer, first, approximately equal amounts of maleic anhydride and diisobutylene were added and subjected to addition polymerization. In the resulting copolymer, the maleic anhydride was sufficiently ring-opened with a small amount of amine. Then, aqueous ammonia was added to this maleic acid to convert all the carboxyl groups of maleic anhydride into ammonium salts. In this way, the above-mentioned copolymer containing a carboxyl group converted into ammonium salt was obtained. The aqueous solution of this copolymer had a pH of 8.5 to 9, a viscosity of 125 cps, and a copolymer concentration of 21 wt%. Next, the following magnetic paint was prepared and a 1/2 inch videotape was made according to a conventional method. Surface treatment Co-γ-Fe ₂ O ₃ 100 parts Niporan N-2304 (polyurethane) 10 parts S-leCA (vinyl chloride-vinyl acetate copolymer) 10 parts myristic acid 0.5 parts palmitic acid 0.5 parts Al ₂ O ₃ 4.0 parts Vulcan XC-72 (conductive carbon black)
5.0 parts Coronate (hardening 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 added to the magnetic coating material per 100 parts of magnetic powder. Example 4 In Example 1, Co-modified γ-Fe ₂ O ₃ powder 100
After drying, the copolymer aqueous solution was added, the pH was adjusted to 6, the treated magnetic powder was adsorbed, filtered, dried, crushed, and sieved, and the treated magnetic powder was kneaded in the same manner as Example 1. It was made into a tape according to the law. Comparative Example 1 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 9. Comparative Example 2 A sample was prepared in the same manner as in Example 1 using the same copolymer as in Example 1 (but having a free carboxyl group instead of an NH ₄ salt and having a solubility in water of 10% or less). Ivy. Comparative Example 3 The copolymer disclosed in JP-A-50-23207 (the compound of Example 1 having the same basic structure as Example 1 is an ammonium salt of maleic acid; Half amide (one is a carboxyl group and the other is an acid amide).
was dissolved in methanol and treated according to the method of Example 4 to prepare a sample. The coercive force (He), residual magnetic flux density (Br), squareness ratio (Sq), gloss, and video characteristics of each of the magnetic tapes obtained above were measured, and the results shown in the table below were obtained. The method of these measurements was as follows. Gloss (glass): Measured using a variable angle photometer manufactured by Murakami Color Research Institute at an input/output angle of 60° and expressed as 100% of the standard plate. Video S/N: 0.36V _PP 50% white signal was recorded and played back and directly read using a Shibasoku 725D/1 noise meter. Color S/N: 100% superimposed on 0.36V _PP white signal
Shibasoku 925D/1 by recording and reproducing color signals
I read it directly on the noise meter.

[Table] Comparative Example 4 A magnetic tape was prepared in the same manner as in Example 1 except that carbon black (Vulcan XC-72) was not added to the magnetic paint. Comparative Example 5 In Example 1, magnetic powder was prepared in the same manner as in Example 1, except that the copolymer used was not applied to the surface treatment of the magnetic powder, but was added to the paint together with the magnetic powder during the preparation of the magnetic paint (the amount added was 0.8 parts). I made a tape. Comparative Example 6 In Example 1, magnetic powder was treated in the same manner as in Example 1 using styrene-acrylamide having no free carboxyl groups as a copolymer to produce a magnetic tape. Comparative Example 7 In Comparative Example 6, magnetic powder was prepared in the same manner as in Comparative Example 6, except that the copolymer used was not applied to the surface treatment of the magnetic powder, but was added to the paint together with the magnetic powder during the preparation of the magnetic paint (the amount added was 0.8 parts). I made a tape. The results of Comparative Examples 4 to 7 are compared with Example 1 and shown in the table below.

[Table] The output drop in the above table indicates how much the output has changed after the tape has been run from the initial value when the tape is loaded into a VHS cassette and played 100 times on a video deck. From the above results, the magnetic powder surface-treated with the copolymer of the present invention without drying the magnetic powder after Co adsorption treatment has excellent dispersibility, and therefore has excellent magnetic properties.
It can be seen that it has excellent electrical properties. In addition, the amount of copolymer adsorbed is affected by the pH of the adsorption reaction solution, and those treated at pH=6 are better, while those treated at pH=9 tend to have poor adsorption. Furthermore, it can be seen that the dispersibility of the magnetic powder that is filtered and dried after adsorbing Co tends to deteriorate, probably because the polymer is adsorbed in an aggregated state. Based on the above results, based on the present invention, if magnetic powder is surface-treated in advance with a copolymer having a salt of a negative group, that is, a quaternary ammonium salt of a carboxyl group, the dispersibility of the magnetic powder can be improved. It can be seen that various properties are improved. In addition, by adding carbon black to the magnetic paint (Example 1), the output reduction after 100 runs was -0.8 dB in Example 1 and in Comparative Example 4, compared to when carbon black was not added (Comparative Example 4). It was confirmed that it was -3dB. This shows that the presence of carbon black significantly reduces powder falling from the magnetic layer.

[Brief explanation of drawings]

The drawings show examples of the present invention, in which Fig. 1 is a flowchart of the manufacturing process of a magnetic recording medium, and Fig. 2 is a flowchart of the manufacturing process of the magnetic recording medium, and Fig. 2 shows the angular shape of the magnetic recording medium due to the solubility of the magnetic powder surface treatment agent (copolymer). 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 depending on PH, Figures 5 and 3 are graphs showing the shape ratio and adhesion amount. FIG. 6 is an enlarged sectional view of a portion of two examples of magnetic tapes. In addition, in the symbols shown in the drawings, 1... non-magnetic support, 2... subbing layer, 3... magnetic layer, 4...
...This is a back coat layer.

Claims (1)

[Claims] 1 Dissolved in 10 parts by weight or more in 100 parts by weight of water,
A step of preparing an aqueous solution of a copolymer composed of a unit in which two carboxyl groups of an alkylene derived from maleic anhydride are converted into quaternary ammonium salts and a unit consisting of diisobutylene; a step of treating the magnetic powder prepared and suspended in the aqueous solution; a step of obtaining magnetic powder surface-treated with the copolymer through this treatment; and a step of treating the surface-treated magnetic powder and carbon. A method for manufacturing a magnetic recording medium, comprising: preparing a magnetic paint containing black; and obtaining a magnetic recording medium using the magnetic paint.