JPH0770057B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium such as a magnetic tape or a magnetic sheet.

B. 2. Description of the Related Art In recent years, there have been increasing demands for high-density recording in general magnetic recording media, and various improvements have been made. Specifically, there is a demand for improving the squareness ratio and the S / N ratio. In order to improve the S / N ratio and the squareness ratio, it is possible to use a ferromagnetic material having a small particle size and a large specific surface area.

Generally, the S / N ratio of a magnetic recording medium is said to be proportional to the square root of the number of particles of the magnetic substance in the recording material related to recording / reproducing. The smaller the magnetic material, the more advantageous the S / N is. S
In order to improve the / N ratio and the squareness ratio, it is necessary to uniformly disperse the ferromagnetic material in the binder resin and smooth the surface properties of the magnetic layer formed by coating.

However, since the surface area of the particles increases in inverse proportion to the square of the particle diameter, the dispersion of the particles becomes rapidly difficult as the particle diameter decreases, and the dispersion stability also deteriorates. This is inconvenient because the orientation of the ferromagnetic material in the magnetic layer, the smoothness of the surface of the magnetic layer, etc. are deteriorated, and the excellent squareness ratio and S / N ratio cannot be obtained.

Usually, in dispersing the magnetic powder, a dispersant sufficient to coat the surface of the magnetic powder particles should be sufficient, but in reality, sufficient dispersibility, stability cannot be obtained,
For this reason, a considerable excess of dispersant is added.

For example, as a dispersant for ferromagnetic powder, various surfactants, particularly fatty acid salts, phosphoric acid esters, alkyl sulfonates, sulfosuccinates, etc. are mainly used.
However, when these conventional dispersants are used, the dispersibility of the ferromagnetic powder at the time of preparation of the magnetic coating is improved, but the magnetic layer obtained by coating the magnetic coating on a support and drying it has high strength. However, the moisture resistance and the like are likely to deteriorate, so that a problem of running property under high temperature and high humidity is likely to occur, and running durability under normal temperature and humidity conditions is often poor. Further, the dispersant which is not adsorbed by the magnetic powder is mixed with a binder resin as a binder in the coating film to plasticize the magnetic layer or prevent the binder resin from being hardened, so that the mechanical strength of the magnetic layer, especially Young's Significantly reduce the rate. Recently, with the long recording time of tapes, there is a tendency to use a thin base film to reduce the total thickness of the tape. However, since the stiffness of the tape is proportional to the cube of the tape thickness, the thickness of the tape decreases. This significantly weakens the waist, which deteriorates the running characteristics of thin tape and the touch of the head of the tape, thus leading to deterioration of the S / N ratio. In order to maintain mechanical properties associated with the reduction in thickness, particularly the rigidity of the tape, a super-stretched base film is used and the Young's modulus of the magnetic layer is increased. Therefore, the decrease in the Young's modulus of the magnetic layer due to an excessive amount of dispersant and other low molecular weight additives significantly deteriorates the mechanical properties of the thin tape.

Various techniques have been disclosed that effectively and stably disperse the magnetic powder and do not impair the mechanical properties of the magnetic layer. For example, JP-A-54-94308, 54-143894, 50
In each of the -92103 publications, the magnetic powder is pretreated with a phosphoric acid ester derivative.

In addition, JP-A-51-134899, 53-51703, 53-7898, 5
Each of the 4-46509 publications discloses a method of coating the surface of the magnetic layer with silicone oil.

Further, JP-A-50-108902, 49-97738, 51-33753,
In each publication such as 53-116114 and 54-24000, the surface is treated with an anion activator. However, the above technique is not effective for small particles, especially for BET 35-40 m ² / g or more magnetic powder.

Also, JP-A-51-103403, 47-33602, 55-125169
No. 55-73929, 55-73930, 57-42888, 57-102
Each of the publications such as No. 6 discloses a technique of coating the surface of the magnetic powder with an oligomer or polymer having a functional group capable of adsorbing to the magnetic powder.

These techniques include mixing the dried magnetic powder with a dispersant solution and adsorbing the dispersant on the surface thereof by dissolving the dispersant, mixing with the magnetic powder, stirring, kneading, filtering, drying, pulverizing,
Each step of sieving is required.

Therefore, the conventional dispersants are not sufficient to guarantee good dispersion of various fillers such as magnetic powders which are becoming finer and finer, and the magnetic properties, electromagnetic conversion properties and durability currently required. Was difficult to satisfy.

Further, in order to improve the dispersion of the ferromagnetic material finely divided as described above, a kneading method using various kneading machines (two roll mill, three roll mill, open kneader, pressure kneader, continuous kneader, etc.) is examined. I've been told.

However, as a result of the investigation, it was found that it is difficult to obtain a magnetic coating liquid having a desired degree of dispersion by using any of them, and the tendency becomes stronger as the particle size of the ferromagnetic particles progresses. .

C. OBJECT OF THE INVENTION The object of the present invention is to provide a method for producing a magnetic recording medium in which the dispersion state and orientation of the ferromagnetic powder are good, the electromagnetic conversion characteristics are excellent, the surface properties are good, the friction coefficient is small, and the running property is excellent. Is to provide.

D. Structure of the Invention and Its Effect The present invention is selected from the group consisting of an alkali metal salt of a sulfo group, a phosphate group, a carboxyl group, a sulfo group, an alkali metal salt of a phosphate group and an alkali metal salt of a carboxyl group. Resin containing one or more substituents, BET value 3
A step of preparing a kneaded material by kneading a ferromagnetic powder having a particle size of 5 m ² / g or more, a dispersant, an abrasive, carbon black and a solvent using a roll mill or a kneader; and diluting the kneaded material with at least a solvent. A step of subsequently dispersing; a step of adding at least a solvent and a lubricant to the dispersion after the dispersion to dilute, and thereafter adding a curing agent to obtain a magnetic coating solution; The present invention relates to a method for manufacturing a magnetic recording medium including a step of applying the magnetic recording medium on the magnetic recording medium.

According to the present invention, one or more selected from the group consisting of an alkali metal salt of a sulfo group, a phosphoric acid group, a carboxyl group, a sulfo group, an alkali metal salt of a phosphoric acid group, and an alkali metal salt of a carboxyl group. A resin containing a substituent of, BE
Ferromagnetic powder with T value of 35 m ² / g or more, dispersant, abrasive,
A remarkable feature is that a kneaded product is prepared by kneading carbon black and a solvent. That is, BET of ferromagnetic powder
By setting the value to 35 m ² / g or more, excellent electromagnetic conversion characteristics such as high S / N ratio can be obtained. Here, it is important that the resin contains a sulfo group, a phosphoric acid group, a carboxyl group or an alkali metal salt thereof, and the action of these negative groups improves the dispersibility of the ferromagnetic powder. Moreover, what should be noted is that the ferromagnetic powder and the above resin are kneaded together with other necessary coating liquid materials. If dispersion (pre-dispersion) is performed at this stage, the ferromagnetic powder and the above resin may be mixed. The chance of contact with the (negative group) is significantly reduced, and therefore the effect of the above resin is not sufficiently exhibited. In this respect, according to the present invention, since the ferromagnetic powder and the resin are kneaded in the step of preparing the kneaded material, the dispersing effect of the resin is sufficiently exhibited in this step, and The ferromagnetic powder is evenly dispersed. Therefore, a magnetic coating liquid having a high degree of dispersion can be obtained by adding at least a solvent to the kneaded product to dilute it and then dispersing it.

It is also important that a lubricant is added to the dispersion liquid after dispersion. That is, if a lubricant is added at the stage of the kneading step, the ferromagnetic powder and the lubricant may react or be adsorbed depending on the surface activity of the ferromagnetic powder. It is considered that this causes adverse effects such as a decrease in dispersibility and aggregation, and the lubricating effect is halved. Therefore,
By adding a circulating agent together with a solvent after dispersion, it is possible to improve dispersion efficiency and prevent aggregation during storage of the magnetic coating liquid.

As described above, according to the manufacturing method provided by the present invention, the dispersion state of the ferromagnetic powder is good, the orientation can be improved, and the surface smoothness can be improved. Therefore, the friction coefficient is small in combination with the fine particles of the ferromagnetic powder. In addition, it is possible to manufacture a magnetic recording medium which is excellent in running property and has high electromagnetic conversion characteristics.

Hereinafter, the manufacturing method of the present invention will be described more specifically.

FIG. 1 is a flowchart showing a manufacturing method.

First, the kneading step will be described.

The resin used in this step is a sulfo group, a phosphate group,
It can be obtained by copolymerizing a copolymerizable monomer containing an alkali metal salt of a carboxyl group, a sulfo group, an alkali metal salt of a phosphoric acid group, or an alkali metal salt of a carboxyl group with another copolymerizable monomer. This copolymerization method is already known and disclosed in JP-A-60-235814 and JP-A-60-23.
No. 8306, No. 60-238309, No. 60-238371.

Epoxy group-containing monomer and /
Alternatively, a hydroxyl group-containing monomer may be contained. In this case, the running property of the magnetic recording medium is further stabilized. This hydroxyl group may be supplied as a monomer from the beginning, but other copolymerizable monomers (eg, fatty acid vinyl such as vinyl acetate)
It may be produced by partial hydrolysis of the copolymer using.

Further, various copolymerization components can be selected, and the characteristics of the copolymer can be optimally adjusted.

As the alkali metal, sodium, potassium and lithium are preferable, and potassium is particularly preferable in terms of solubility, reactivity and yield.

Examples of the copolymerizable monomer containing a sulfo group or an alkali metal salt of a sulfo group include the following.

_{CH 2 = CHSO 3 M CH 2} = CHCH 2 SO 3 M CH 2 = C (CH 3) CH 2 SO 3 M CH 2 = CHCH 2 OCOCH (CH 2 COOR) SO 3 M CH 2 = CHCH 2 OCH 2 CH ( _{OH) CH 2 SO 3 M CH} 2 = C (CH 3) COOC 2 H 4 SO 3 M CH 2 = CHCOOC 4 H 8 SO 3 M CH 2 = CHCONHC (CH 3) 2 CH 2 SO 3 M phosphoric acid group, Examples of the monomer containing an alkali metal salt of a phosphoric acid group include the following.

_{CH 2 = CHCH 2 OCH 2 CH} (OH) CH 2 -O-PO 3 MY 1 CH 2 = CHCONHC (CH 3) 2 CH 2 -O-PO 3 MY 2 CH ₂ = CHCH ₂ O (CH ₂ CH ₂ O) _m PO ₂ MX ^{2 In the} above, M is an alkali metal or hydrogen atom, R is an alkyl group having 1 to 20 carbon atoms, Y ¹ is M or CH _{2 = CHCH 2 OCH 2 CH (OH} ) CH 2 -, Y 2 is M or _{CH 2 = CHCONHC (CH 3)} 2 CH 2 -, Alternatively, OM and X ² are CH ₂ ═CHCH ₂ O (CH ₂ CH ₂ O) _m −, or OM. Further, n is an integer of 1 to 100 and m is an integer of 1 to 100.

Examples of the carboxyl group and the alkali metal salt-containing monomer of the carboxyl group include acrylic acid, methacrylic acid, maleic acid, and alkali metal salts thereof.

The amount of strong acid radicals in the resulting copolymer is SO ₃ , S
0.1 to 4.0% by weight as O ₄ , PO ₄ , PO _5, etc., preferably 0.3
Used to be ~ 2.0% by weight.

Examples of the above-mentioned monomer having an epoxy group include glycidyl ethers of unsaturated alcohols such as acrylic glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methyl glycidyl itaconate, and glycidyl ethyl malate. , Glycidyl vinyl sulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth) allyl sulfonate, butadiene monooxide, vinyl cyclohexene monooxide,
Examples thereof include epoxide olefins such as 2-methyl-5,6-epoxyhexene. This monomer is generally used in a range such that the amount of epoxy groups in the copolymer is 0.5% by weight or more. If this proportion is less than 0.5% by weight, it becomes difficult to select the conditions for introducing strong acid radicals.

As the above-mentioned monomer containing a hydroxyl group, in other words, X in the monomer having a —X—OH group is Cn.
Examples thereof include organic residues represented by H _2n , OCnH _2n , COOCnH _2n and CONHCnH _2n (n is an integer of 1 to 4).
Examples of the monomer having the -X-OH group include (meth)
Α, such as acrylic acid-2-hydroxyethyl ester and (meth) acrylic acid-2-hydroxypropyl ester
C2-C4 alkanol ester of β-unsaturated acid, maleic acid mono-2-hydroxypropyl ester, maleic acid di-2-hydroxypropyl ester,
Alkanol esters of unsaturated dicarboxylic acids such as itaconic acid mono-2-hydroxybutyl ester, olefinic alcohols such as 3-buten-1-ol and 5-hexen-1-ol, 2-hydroxyethyl vinyl ether, 2-hydroxypropyl Examples thereof include alkanol vinyl ether such as vinyl ether, acrylamide such as N-methylol acrylamide, N-methylol methacrylamide and the like. The amount of hydroxyl groups based on -X-OH groups bonded to the resin is preferably 0.1 to 2.0% by weight. 0.1
If it is less than wt%, the crosslinking effect of the coating film by the isocyanate compound will not be exhibited, and if it is more than 2.0 wt%, the pot life of the paint is too short and it is difficult to use. The amount of the hydroxyl group is much smaller than that of the vinyl chloride-vinyl alcohol-vinyl acetate copolymer which has been heretofore known for magnetic coating materials, but the crosslinking reaction with the isocyanate compound is much smaller. Fully achieved. The reason is not clear, but it is considered that the hydroxyl groups involved in the reaction are separated from the main chain of the copolymer to increase the degree of freedom and that the distribution of the hydroxyl groups in the polymer is uniform. .

Other copolymerizable monomers that can be copolymerized as necessary include known polymerizable monomers, for example, vinyl acetate, various vinyl esters such as vinyl propionate,
Vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, styrene, various acrylic acid esters, methacrylic acid esters, ethylene, propylene, isobutene, butadiene, isoprene, vinyl ether,
Examples include aryl ethers, aryl esters, acrylamides, methacrylamides, maleic acid esters and the like.

The copolymer used in the present invention is emulsion polymerization, solution polymerization,
Polymerization is carried out by a polymerization method such as suspension polymerization or bulk polymerization. In any of the methods, known techniques such as a molecular weight modifier, a polymerization initiator and a monomer may be applied in divided or continuous additions, if necessary.

The amount of the monomer containing the acidic group or the salt thereof in the copolymer used in the present invention is preferably 0.01 to 30 mol%. If the amount of the monomer is too large, the solubility in a solvent is poor and gelation is likely to occur. Further, if the amount of this monomer is too small, desired properties cannot be obtained.

By the way, the vinyl chloride-based copolymer was composed of the following copolymer components.

: Indicates a copolymerization unit.

However, it is considered that the CH ₃ CH—O— group here hardly contributes to the crosslinking reaction with the curing agent or the like. So CH ₃ C
Instead of O, It is preferable to contain an epoxy group such as For example, a copolymer having the following units may be mentioned.

(X: sulfo group, phosphoric acid group, carboxyl group, or monomer unit portion containing an alkali metal salt thereof) As a ferromagnetic powder that can be used in the kneading step, γ-
Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-containing
There are iron oxide magnetic powders such as FeOx (3/4 <x <2/3) and various ferromagnetic powders such as CrO ₂ .

Further, as the magnetic metal powder, Fe, Ni, Co, Fe-
Al-based, Fe-Al-Ni-based, Fe-Al-Co-based, Fe-Al-Zn-based, Fe
-Ni-Co system, Fe-An-Zn system, Fe-Ni system, Fe-Ni-Al system,
Fe-Ni-Zn system, Fe-Co-Ni-Cr system, Fe-Co-Ni-P system,
Ferromagnetic powders such as metal magnetic powders containing Co—Ni-based, Fe, Ni, Co, etc. as main components are mentioned. Among them, Fe-based magnetic metal powders containing 80 atomic% or more of Fe are excellent in electrical characteristics, and particularly in terms of corrosion resistance and dispersibility, Fe-Al, Fe-Al-Ni, Fe-Al-Zn, Fe-Al.
-Co, Fe-Ni, Fe-Ni-Al, Fe-Ni-Zn based metal magnetic powders are preferred.

Furthermore, iron-aluminum (Fe-Al, Fe-Al-Ni
(Fe-Al-Zn-based, Fe-Al-Co-based, etc.) metal magnetic powders are particularly preferable.

That is, the use of video tapes in recent years has been diversified as they become portable, and their usage conditions are various. Therefore, the video tape is required to have high corrosion resistance. In this respect, the Fe-Al magnetic powder exhibits high corrosion resistance and good dispersibility. This is very important for realizing high-density recording because the dispersibility can be sufficient even if the specific surface area of the magnetic powder is increased.

Further, in the above Fe-Al-based metal magnetic powder, the Al of the magnetic powder
The content is preferably within the range of 0.5 to 20 atomic%.

The specific surface area of ferromagnetic powder is BET value of 35 m ² / g or more,
It is more preferably 0 m ² / g or more.

In the above, the “BET value” means a surface area per unit weight, and is a physical quantity which is completely different from the average particle diameter. For example, even if the average particle diameter is the same, the specific surface area is large, Some have a small specific surface area. To measure the specific surface area, first, for example, magnetic powder at
Was degassed with 60 minutes heating, to remove what is adsorbed to the powder, then introduced into a measuring device, to set the nitrogen and the initial pressure to 0.5 kg / m ^3, the liquid with nitrogen Adsorption measurement is performed at a nitrogen temperature (-195 ° C) (generally called BET method for measuring specific surface area. For details, see J. Ame. Chem. So.
c. 60 309 (1938)). As a measuring device for the specific surface area (BET value), a “powder and particle measuring device (canter soap)” jointly manufactured by Yuasa Battery Co., Ltd. and Yuasa Ionics Co., Ltd. can be used. "Measurement of powder" for a general explanation of specific surface area and its measurement method
(JMDALLAVALLE, CLYDEORR Jr, co-authored by Benda et al .; published by Sangyo Tosho Publishing Co., Ltd.), and also in "Chemical Handbook" (applied edition, pages 1170 to 1171, edited by The Chemical Society of Japan, Maruzen Co., Ltd., 1966). It is also described in the April 30th issue (note that in the above "Chemical Handbook", the specific surface area is simply the surface area (m ² / g
Although described as r), it has the same specific surface area as used herein. ).

As a dispersant, lecithin; trialkylpolyolefinoxy quaternary ammonium salt (where alkyl is 1 to 5 carbon atoms)
And olefins such as ethylene and propylene) are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfate esters and the like can also be used.

As the abrasive, commonly used materials such as alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, silicon carbide, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide, and boron nitride are used. To be done. The content of this abrasive is 2 per 100 parts by weight of magnetic powder.
The amount is preferably 0 parts by weight or less, particularly 3 parts by weight to 12 parts by weight or less, and the average particle size thereof is preferably 0.6 μm or less.

As the carbon black, all commonly used conductive and light-shielding carbon blacks can be used. The amount of carbon black added to the magnetic layer is preferably in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.

As the solvent, a ketone (for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone),
Alcohols (eg methanol, ethanol, propanol, butanol), esters (eg methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether),
Glycol ether (eg ethylene glycol monoethyl ether, ethylene glycol diethylene ether, dioxane), aromatic hydrocarbon (eg benzene,
Toluene, xylene), aliphatic hydrocarbons (eg, hexane, heptane), nitropropane and the like can be mentioned.

Various kneaders can be used in the kneading step.
For example, a roll mill and a kneader are exemplified.

For kneading and dispersion, TCPATTON “Paint Flow and
Pigment Dispersion "(Published by John Wiley & Sons, 19
64).

Other additives may be added to the magnetic layer.

For example, as the antistatic agent, conductive fine powder such as carbon black graft polymer; natural surfactant such as saponin; nonionic surfactant such as alkylene oxide type, glycerin type and glycidol type; higher alkylamines, fourth Cationic surfactants such as primary ammonium salts, pyridine and other heterocycles, and phosphoniums;
Anionic surfactants containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group and phosphoric acid ester group;
Amino acids sold, amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohol, etc. are used. The conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the magnetic powder. You may add these surfactant individually or in mixture. These are used as antistatic agents, but sometimes for other purposes, such as dispersion,
It may be applied as an improvement of magnetic properties, an improvement of lubricity, or a coating aid.

In addition, the following may be used as an additive. Phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used, but especially dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine phosphate, cyclohexyl ammonium carbonate, hexane. The use of methylenediamine carbonate, propylenediamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate (inorganic acid salt of amine, amide or imide or organic acid salt) improves the rust preventive effect.
These are used within the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the ferromagnetic fine powder.

The magnetic layer can also be used in combination with other resins. Resins that can be used in combination have an average molecular weight of about 10,000 to 20,000.
0, for example vinyl chloride-vinyl acetate copolymer,
Vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral,
Cellulose derivative (cellulose acetate butyrate,
Cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubber phenolic resins, epoxy resins,
Urea resin, melamine resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / isocyanate, and These mixtures etc. are illustrated.

In the diluting step, the above solvent may be used, or the resin of the present invention may be dissolved in the above solvent and the solution may be added to the kneaded product.

Various dispersing machines can be used in the dispersing step, and examples thereof include a medium dispersing machine represented by a sand grinder, an attritor and a ball mill, a high speed impeller dispersing machine, and an impact dispersing machine represented by a colloid mill.

In the next diluting step, a lubricant and a solvent (and a binder resin if necessary) are added to the dispersion liquid to dilute it.

Examples of the lubricant include fatty acids and / or fatty acid esters. By using these together, it is possible to offset the defects that occur when used alone, improve the lubrication effect, and enhance still image durability, running stability, S / N ratio, etc. while exhibiting the respective characteristics of both. it can. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight per 100 parts by weight of the magnetic powder,
5 to 8.0 parts by weight is even better. If the amount of fatty acid deviates from this range, the dispersibility of the magnetic powder decreases, and the running property of the medium tends to decrease. If the amount of fatty acid increases, the fatty acid tends to exude or the output tends to decrease. Further, the amount of the fatty acid ester added is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder,
2 to 8.5 parts by weight is even better. If the amount of ester is less than this range, the effect of improving the running property is poor, and if the amount of ester is too large, the ester exudes or the output is apt to decrease.

Also. In order to achieve the above effects better, the weight ratio of fatty acid to fatty acid ester is fatty acid / fatty acid ester =
10/90 to 90/10 is preferable. It should be noted that fatty acids also have a dispersive effect, and it is considered that the use of fatty acids can reduce the amount of another low-molecular weight dispersant used, and the Young's modulus of the magnetic recording medium can be improved accordingly.

The fatty acid may be monobasic or dibasic.
Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms are preferable.
Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Palmitic acid (7) Stearic acid (8) Isostearic acid (9) Linolenic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-Dodecanedicarboxylic acid (23) Octanedicarboxylic acid Examples of the above fatty acid ester are as follows.

(1) Oleyl oleate (2) Isocetyl stearate (3) Dioleyl maleate (4) Butyl stearate (5) Butyl palmitate (6) Butyl myristate (7) Octyl myristate (8) Octyl palmitate ( 9) Amyl stearate (10) Amyl palmitate (11) Isobutyl oleate (12) Stearyl stearate (13) Lauryl oleate (14) Octyl oleate (15) Isobutyl oleate (16) Ethyl oleate (17) Isotridecyl oleate (18) 2-Ethylhexyl stearate (19) Ethyl stearate (20) 2-Ethylhexyl palmitate (21) Isopropyl palmitate (22) Isopropyl myristate (23) Butyl laurate (24) Cetyl-2-ethyl hexalate (25) Georail Adipate (2 6) Diethyl adipate (27) Diisobutyl adipate (28) Diisodecyl adipate In addition to the above fatty acids and fatty acid esters, other lubricants (for example, silicone oil (which may be carboxylic acid modified or ester modified), graphite, fluorinated) Carbon, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc.) are exemplified.

The circulating agent may be added immediately before the curing agent is added to the dispersion liquid.

The durability of the magnetic layer can be improved by adding a curing agent to the dispersion in the curing agent addition step.
The curing agent is preferably a polyisocyanate curing agent. Examples of the polyisocyanate-based curing agent include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Desmodur L (manufactured by Bayer).
Any of functional isocyanates, urethane prepolymers having isocyanate groups at both ends, which have been conventionally used as a curing agent, and polyisocyanates usable as a curing agent can be used. The amount of the polyisocyanate-based curing agent used is 5 to 80 parts by weight based on the total amount of the binder.

In the coating step, the magnetic coating liquid is coated on the non-magnetic substrate.

This non-magnetic substrate includes polyester (eg polyethylene terephthalate, polyethylene-2,6-naphthalate), polyolefin (eg polyethylene, polypropylene), cellulose derivative (eg cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate). ), Polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazites, metals (eg aluminum, copper), paper and the like.

Examples of the method for applying the magnetic coating liquid onto the non-magnetic substrate include blade coating, reverse roll coating, gravure coating, spray coating, cast coating, air doctor coating, and air knife coating. Specifically, it is described on pages 253 to 277 of "Coating Engineering" (published by Asakura Shoten, 1972).

In the post-treatment process, orientation treatment, drying treatment, surface smoothing treatment, curing and cutting are carried out as necessary to manufacture a magnetic recording medium.

E. EXAMPLES Hereinafter, the present invention will be described with reference to specific examples. The components, ratios, operation sequences and the like shown below can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" represent "parts by weight".

<Manufacture of Video Tape> First, Examples 1 and 2 and Comparative Examples 1 to 3 are performed as follows.
Each video tape of was produced.

Examples 1, 2 and Comparative Example 1 Video tapes were produced according to the steps shown in FIG.

(Kneading step) The following composition was kneaded in an open kneader for 1 hour to prepare a kneaded product.

Co-deposited iron oxide 100 parts (however, Example 1 has a BET value of 40 m ² / g, Example 2 has a BET value of 45 m ² / g, Comparative Example 1 has a BET value of 25 m ² / g) Sulfo group-containing vinyl chloride system Copolymer resin 10 parts Carbon black 3 parts RP-710 (phosphate ester) 3 parts Al ₂ O ₃ 4 parts Methyl ethyl ketone 50 parts (dilution step) 170 parts of a kneaded product was diluted with the following composition.

Urethane resin 6 parts Methyl ethyl ketone 30 parts Toluene 40 parts (dispersing step) After the kneaded product was diluted, it was dispersed for 2 hours with a sand grinder.

(Diluting Step) 246 parts of the dispersion liquid was diluted with the following composition.

MA (myristic acid) 1 part SA (stearic acid) 1 part Bust (butyl stearate) 2 parts Methyl ethyl ketone 40 parts Toluene 40 parts (curing agent addition process) Polyisocyanate (“Coronate L” manufactured by Nippon Polyurethane Co., Ltd.) 10 parts added To obtain a magnetic coating liquid.

(Coating process and post-treatment process) The magnetic coating liquid was applied onto a 14 μm polyester base film,
It was applied by a reverse roll coater so as to have a dry film thickness of 5.0 μm and dried. This was further subjected to surface smoothing treatment, followed by curing and cutting into 1/2 inch width.

Comparative Examples 2 and 3 Video tapes were produced according to the steps shown in FIG.

(Pre-dispersion step) Co-deposited iron oxide 100 parts obtained by dispersing the following composition in a sand grinder for 4 hours (however, Comparative Example 2 has a BET value of 25 m ² / g and Comparative Example 3 has a BET value of 40 m ² / g) sulfo group Containing vinyl chloride copolymer resin 10 parts Carbon black 3 parts RP-710 (phosphate ester) 3 parts Al ₂ O ₃ 4 parts Methyl ethyl ketone 80 parts Toluene 40 parts (dilution step and post-dispersion step) To 240 parts of the above dispersion liquid The following composition was added and diluted, and then dispersed again with a sand grinder for 1 hour.

Urethane resin 6 parts MA (myristic acid) 1 part SA (stearic acid) 1 part Bust (butyl stearate) 2 parts Methyl ethyl ketone 40 parts Toluene 40 parts (curing agent addition step) To 330 parts of magnetic coating liquid after the post-dispersion step , Polyisocyanate (“Coronate L” manufactured by Nippon Polyurethane Co., Ltd.) 10
Parts to make a magnetic coating solution.

(Coating process and post-treatment process) The magnetic coating liquid was applied onto a 14 μm polyester base film,
It was applied by a reverse roll coater so as to have a dry film thickness of 5.0 μm and dried. This was further subjected to surface smoothing treatment, followed by curing and cutting into 1/2 inch width.

Comparative Examples 4 and 5 The same procedure as in Comparative Examples 1 and 2 except that the ferromagnetic powder having a BET value of 30 m ² / g was used.

<Evaluation> For each of the video tapes of Examples 1 and 2 and Comparative Examples 1 to 5, the squareness ratio, video S / N, running property, and dynamic friction coefficient were measured. The measurement and evaluation methods are as follows.

Squareness: Using a vibrating sample type magnetometer (Toei Kogyo), Br / B at Hm5KOe
I asked for m.

Video S / N: A Shiba Soku noise meter (925C) was used, the reference tape was used as the tape of Comparative Example 2, and the difference in S / N ratio was determined.

The noise level was measured with a high pass filter of 10 KHz and a low pass filter of 4 MHz.

The VTR used is Matsushita NV-8300.

Running property: The sample tape was run on a video deck continuously at 40 ° C and 80% for 200 hours, and RF output drop, skew, and powder drop were measured. A indicates good, B indicates normal, and C indicates insufficient.

Dynamic friction coefficient: 25 ° C, tape running tester TBT-300D (Yokohama System Research Institute) was used to wrap the tape 180 ° around the chrome-plated stainless steel 4φ pin, tape speed 1cm / sec,
The measurement was performed at an inlet tension of 20 g, and μk was calculated by the following formula.

The measurement results of each video tape are shown in the table.

As is clear from the table, by producing a magnetic recording medium according to the present invention, good dispersibility, squareness ratio, S / N
It can be seen that it is possible to obtain a video tape having a high ratio, good surface properties, a small friction coefficient, and excellent running properties.

[Brief description of drawings]

FIG. 1 is a flow chart showing the manufacturing process of the present invention. FIG. 2 is a flowchart showing the manufacturing process of the comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Ando 1 Sakura-cho, Hino-shi, Tokyo Konica stock company (72) Inventor Atsuko Matsuda 1 Sakura-cho, Hino-shi, Tokyo Konica stock company (56) References JP-A-62-143230 (JP, A) JP-A-61-230624 (JP, A)

Claims (1)

[Claims] 1. One or more kinds selected from the group consisting of an alkali metal salt of a sulfo group, a phosphoric acid group, a carboxyl group, a sulfo group, an alkali metal salt of a phosphoric acid group and an alkali metal salt of a carboxyl group. A resin containing a substituent, a step of preparing a kneaded product by kneading a ferromagnetic powder having a BET value of 35 m ² / g or more, a dispersant, an abrasive, carbon black and a solvent using a roll mill or a kneader; A step of adding at least a solvent to the kneaded product to dilute, and then dispersing; a step of adding at least a solvent and a lubricant to the dispersion liquid after the dispersion to dilute, and then adding a curing agent to obtain a magnetic coating liquid And; a method for producing a time recording medium, which comprises a step of applying this magnetic coating liquid onto a non-magnetic substrate.