JP2001250220A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of attaining high output in an ultrahigh band of >9 MHz (recording at a short wavelength of about 0.6 μm). SOLUTION: The magnetic recording medium has a magnetic layer on a nonmagnetic substrate. The magnetic layer contains a magnetic powder and a binder, the coercive force (Hcp) of the magnetic powder satisfies the expression H cm-H cp >=8.5 kA/m in relation to the coercive force (H cm) of the magnetic recording medium and the residual saturation magnetic flux density Br of the magnetic recording medium is >=150 mT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium, and more particularly to a magnetic recording medium having excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art A magnetic recording medium is usually produced by applying a magnetic paint comprising a magnetic powder, a binder (resin binder), an organic solvent and other necessary components to a substrate such as a polyester film and drying.

[0003] The magnetic recording medium manufactured in this manner is desired to have excellent electromagnetic conversion characteristics such as high sensitivity and a high SN ratio, and to have excellent wear resistance. In recent years, it has been desired to increase the output in a so-called ultra-high band (short-wavelength recording) especially in a magnetic recording medium using an iron oxide-based magnetic powder. For this reason, attempts have been made to use extremely fine magnetic powder or to improve the magnetic characteristics of a magnetic recording medium.

[0004] As a prior art related to the present application, Japanese Patent Application Laid-Open No. 9-91683 discloses a coating material for a magnetic layer in order to provide a coating type magnetic recording medium having excellent surface smoothness and hardness of a magnetic layer. It has been proposed to set the coercive force of the dried coating film to be 1 to 6% lower than the coercive force of the magnetic powder used.

[0005]

However, in a magnetic recording medium using an iron oxide-based magnetic powder, in the above-mentioned conventional proposal, for example, an ultra-high band (0.6 μm
Dramatically high output cannot be achieved in short wavelength recording before and after).

The present invention has been made in view of such a situation. The purpose of the present invention is to dramatically increase the output in an ultra-high frequency range exceeding 9 MHz (short wavelength recording of about 0.6 μm). An object of the present invention is to provide a feasible iron oxide magnetic recording medium.

[0007]

According to the present invention, there is provided a magnetic recording medium having a magnetic layer on a non-magnetic support, wherein the magnetic layer comprises a magnetic powder and a binder. And the coercive force (Hcp) of the magnetic powder is Hcm−Hcp ≧ in relation to the coercive force (Hcm) of the magnetic recording medium.
8.5 kA / m is satisfied and the value of the residual saturation magnetic flux density Br of the magnetic recording medium is 150 mT or more.

Further, the magnetic powder in the present invention is constituted as cobalt-containing magnetite.

Conventionally, attempts have been made to fill the magnetic layer with more magnetic powder in order to increase the output of the magnetic recording medium. However, the magnetic powder occupying a unit volume in the medium (particularly, the magnetic layer) has been considered. As the filling rate increases, the value of the residual magnetic flux density Br increases, but the coercive force of the medium is usually lower than the coercive force of the magnetic powder or does not increase so much.

[0010] Recognizing the current situation, the present inventors have studied the relationship between magnetic iron oxides having various characteristics and the output in short-wavelength recording exceeding 9 MHz. It has been found that when the medium configuration is set so that the coercive force difference between the magnetic powder and the medium is equal to or more than a certain value, a great improvement in output is exhibited.

The reason why the output of the present invention can be greatly improved by the configuration of the present invention is unknown, but one of the reasons is that each of the magnetic powders is finely dispersed in the magnetic layer. I think that there is.

[0012]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a sectional view showing a preferred configuration example of a magnetic recording medium 1 according to the present invention. As shown in this figure, the magnetic recording medium 1 of the present invention has a magnetic layer 20 formed by coating on a flexible non-magnetic support 10. The magnetic layer 20 contains a magnetic powder and a binder. The physical properties of the magnetic recording medium according to the present invention are manufactured so as to satisfy the following requirements in relation to the magnetic powder used.

That is, the coercive force (Hcp) of the magnetic powder
Is related to the coercive force (Hcm) of the magnetic recording medium, the coercive force (Hcm) of the magnetic recording medium is larger, and Hcm−Hcp ≧ 8.
It is necessary to satisfy the requirement of 5 kA / m. More preferably, Hcm−Hcp ≧ 9.0 kA / m. If the value indicating this difference is less than 8.5 kA / m, the improvement in the output in the so-called ultrahigh frequency range will not be sufficiently exhibited. Although the upper limit of the value indicating this difference is not particularly limited, it is generally considered that the upper limit is about 15 kA / m from the viewpoint of manufacturing technology.

The value of the residual saturation magnetic flux density Br of the magnetic recording medium of the present invention is 150 mT or more, preferably 160 mT.
mT or more. There is no particular upper limit to this value, but from the viewpoint of manufacturing technology, it is generally considered that the upper limit is about 190 mT.

It has been confirmed that adopting the following manufacturing method is one of the effective methods for manufacturing a medium so as to satisfy the above-mentioned constitutional requirements of the present invention.

(1) Kneading Step In kneading a composition obtained by mixing an additive such as a magnetic powder and an abrasive, a binder (resin binder) and a solvent with a kneader such as a pressure kneader, the kneading process is carried out. Kneading is performed at a temperature several tens of degrees higher than the highest glass transition temperature (Tg) for 10 to 40 minutes.

By doing so, the viscosity of the binder (resin binder) is reduced to facilitate movement, and good contact with the magnetic powder is achieved, enabling uniform dispersion. However, if the kneading time at a temperature higher than the glass transition temperature (Tg) is too long, the filling ratio of the magnetic powder in the composition increases, and the residual saturation magnetic flux density Br improves, but the coercive force (Hcm) of the medium increases. Care must be taken as it will decrease.

(2) Coating / Orientation Step A magnetic coating obtained by adding a solvent or the like to the kneaded composition and then dispersing the composition is applied to a nonmagnetic support to form a magnetic layer, and then a permanent magnet such as a ferrite magnet or a rare earth magnet is prepared. A magnetic field is applied by a magnet, electromagnet, solenoid or the like to orient the magnetic particles in the magnetic layer in the running direction (longitudinal direction) of the non-magnetic support.

In order to form the coercive force value of the present invention, the value of this magnetic field needs to be 450 mT or more, preferably 500 mT or more. If the value of the magnetic field is less than 450 mT, the values of the coercive force and the saturation magnetic flux density in the magnetic layer will not be sufficiently high, and it will be difficult to satisfy the scope of the present invention (the constituent elements of the present invention). Further, an orientation operation may be performed by providing an appropriate drying step in advance before the orientation or performing drying at the same time as the orientation so that the orientation after the drying becomes the highest.

Next, it has been confirmed that the following method is effective in satisfying the constituent requirements of the present invention from the viewpoint of manufacturing magnetic powder.

That is, the magnetic powder in the present invention can be produced in a conventionally known direction. However, according to the following method, the magnetic powder within the scope of the present invention can be easily obtained, which is preferable. For example, after an aqueous solution containing FeCO ₃ obtained by reacting an aqueous alkali carbonate solution and an aqueous ferrous salt solution is aged in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the suspension containing FeCO ₃ . And oxidize to grow goethite particles. At this time, when the ripening temperature in the ripening is 40 to 60 ° C., goethite particles having a large axial ratio (major axis diameter / short axis diameter) can be obtained.

Further, the obtained goethite particles or hematite particles obtained by heating and calcining the same are heated and reduced at 250 to 400 ° C. in a reducing gas to obtain desired magnetite particles. The shape of the obtained particles is basically acicular, but may be a spindle shape. The magnetic iron oxide powder of the present invention can be obtained by coating a cobalt compound or a cobalt compound and another metal compound on the surface of the magnetite particles obtained as described above.

As a method of applying a cobalt compound or a cobalt compound and another metal compound, (1) magnetite particles are dispersed in an aqueous solution of cobalt or cobalt and another metal salt, and an alkali aqueous solution is added thereto.
(2) magnetite particles are dispersed in an aqueous alkaline solution,
To this, there is a method of adding cobalt or an aqueous solution of cobalt and another metal salt.

The atmosphere during the deposition may be either an oxidizing atmosphere or an inert atmosphere.
It is important to control to 5-45 ° C. By performing such control, it becomes easy to satisfy the desired requirements of the present invention.

The average major axis length of the magnetic powder is 0.08 to 0.5.
It is set to about 35 μm. The SSA value, which is the specific surface area of the magnetic powder by the BET method, is 25 to 50 m ² / g.
Degree.

Next, the binder (resin binder) used in the present invention will be described. As the binder, a thermoplastic resin, a thermosetting or reactive resin, an electron beam-sensitive modified resin, or the like is used, and a combination thereof is appropriately selected and used according to the characteristics of the medium and the process conditions.

As the thermoplastic resin, the softening temperature is 150
° C or lower, average molecular weight of 5,000 to 200,000, degree of polymerization of about 50 to 2,000, and thermosetting resin, reactive resin, or electron beam functional type modified resin have the same average molecular weight and polymerization as thermoplastic resin. Degree of application, drying,
By heating and / or irradiating with an electron beam after calendering, the molecular weight becomes infinite due to reactions such as condensation and addition.

Among these, a combination preferably used is a combination of a vinyl chloride copolymer and a polyurethane resin.

The vinyl chloride copolymer preferably has a vinyl chloride content of 60 to 95 wt%, particularly preferably 60 to 90 wt%, and the average degree of polymerization is preferably about 100 to 500.

Examples of such vinyl chloride resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-maleic acid, vinyl chloride -Vinyl acetate-vinyl alcohol-maleic acid,
Vinyl chloride-vinyl acetate-hydroxyalkyl (meth)
Acrylate, vinyl chloride-vinyl acetate-hydroxyalkyl (meth) acrylate-maleic acid, vinyl chloride-vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate, chloride There are copolymers such as vinyl-vinyl acetate-vinyl alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-allyl glycidyl ether, and vinyl chloride-vinyl acetate-vinyl alcohol-allyl glycidyl ether. However, a copolymer of vinyl chloride and a monomer containing an epoxy (glycidyl) group is particularly preferred.

The polyurethane resin used in combination with such a vinyl chloride resin is particularly effective in that it has good abrasion resistance and adhesion to a support, and has a polar group, a hydroxyl group or the like in a side chain. It may be one having a polar group containing sulfur or phosphorus.

The term "polyurethane resin" is a general term for resins obtained by the reaction of a hydroxy group-containing resin such as a polyester polyol and / or a polyether polyol with a polyisocyanate-containing compound. It is polymerized to a degree.

The vinyl chloride copolymer and the polyurethane resin have a weight mixing ratio of 10:90 to 9: 9.
It is preferable to mix them so that the ratio becomes 0:10.

Examples of other thermoplastic resins include (meth) acrylic resin, polyester resin, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymer, and polyvinyl alcohol resin. , Acetal resin, epoxy resin, phenoxy resin, polyether resin, polyfunctional polyethers such as polycaprolactone, polyamide resin, polyimide resin, phenol resin, polybutadiene elastomer, chloride rubber, acrylic rubber, isoprene rubber, epoxy modified Rubber and the like can be given.

Examples of the thermosetting resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a butyral resin, a polymer resin, a melanin resin, an alkyd resin, a silicone resin, an acrylic reaction resin, and a polyamide resin which undergo condensation polymerization. , An epoxy-polyamide resin, a saturated polyester resin, a urea formaldehyde resin and the like.

Among the above resins, those having a hydroxyl group at the terminal and / or the side chain are preferred as the reactive resin because crosslinking using isocyanate and electron beam crosslinking modification can be easily used. Amino group (-NR ₂ ), ammonium base (-NR
₃ X), a sulfate group (—SO ₄ Y), a sulfo group (—SO ₄ Y)
₃ Y), -COOY group, -OPO ₂ Y group, -OPO ₃ Y
_Two , (R represents H, methyl, ethyl, X represents a halogen, Y represents H, an alkali metal), an acidic polar group, a basic polar group, or the like; These contents are suitable for improving dispersibility. These may be used alone or in combination of two or more.

As the crosslinking agent for curing the binder resin, various polyisocyanates can be used. One or more of tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate and the like can be used in combination with trimethylolpropane and the like. It is preferable to use a cross-linking agent modified to one having a plurality of hydroxyl groups or an isocyanurate-type cross-linking agent in which three molecules of a diisocyanate compound are bonded. The content of the cross-linking agent is 1 to 5 with respect to 100% by weight of the resin.
The content is preferably 0% by weight, and the crosslinking agent three-dimensionally binds to a hydroxyl group or the like contained in the binder resin, so that the durability of the coating film layer can be improved.

Specifically, Coronate L, HL, 3041 manufactured by Nippon Polyurethane Industry Co., Ltd., 24A-100, TPI-100, B.I. F. Go
Death modules L and N manufactured by Odrich.

In general, such a reactive or thermosetting resin is cured by heating in a heating oven at 50 to 80 ° C. for 6 to 100 hours, or at a low speed for 8 to 100 hours.
Or run in an oven at 0 to 120 ° C.

Further, the above-mentioned copolymer is obtained by a known method.
It is also possible to use a (meth) acrylic double bond-introduced electron beam-sensitive modified product

In order to carry out the electron beam-sensitive modification, a urethane-modified and ethylenically-unmodified product in which a reaction product (adduct) of tolylene diisocyanate (TDI) and 2-hydroxyethyl (meth) acrylate (2-HEMA) is reacted. One or more saturated double bonds and one isocyanate group
An improved urethane modification using a monomer having a urethane bond in the molecule and having no urethane bond in the molecule (such as 2-isocyanatoethyl (meth) acrylate) and a resin having a hydroxyl group or a carboxylic acid group having a (meth) acryl group A method of reacting a compound having a carboxylic anhydride or a dicarboxylic acid to modify the ester is well known. Among these, modified urethane modification is preferable because even if the content ratio of the vinyl chloride resin is increased, the coating does not become brittle and a coating film having excellent dispersibility and surface properties can be obtained.

An electron beam is used as a radiation source at the time of curing when an electron beam-sensitive modified resin is used as a binder, from the viewpoint of controlling the absorbed dose, introducing the resin into the production process line, and shielding ionizing radiation. A method using ultraviolet light and / or a method using ultraviolet light is advantageous. In the case of an electron beam, the acceleration voltage is 100 KV to 750 KV, preferably 150 to 30 KV.
Using an electron beam accelerator of 0 KV, adjust the absorbed dose to 20 to 200
It is convenient to illuminate to be kilogray.

The solvent contained in the magnetic paint for forming the magnetic layer is not particularly limited, but is appropriately selected in consideration of the solubility, compatibility and drying efficiency of the binder. Ketones such as isobutyl ketone and cyclohexanone, aromatic hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, alcohols such as isopropanol and butanol, dioxane, tetrahydrofuran, dimethylformamide, hexane and chlorine A diluent or solvent such as substituted hydrocarbons is used as a single solvent or a mixed solvent of any ratio thereof.

The magnetic coating material for forming the magnetic layer usually contains a lubricant. As the lubricant to be used, it is preferable to use fatty acids and / or fatty acid esters among various known lubricants.

Examples of the fatty acid include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid.
Butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate,
Sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate,
Octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate and the like can be mentioned.

The content of the fatty acid and / or fatty acid ester in the magnetic layer is preferably from 0.1 to 20% by weight, more preferably from 1 to 15% by weight, more preferably from 1 to 12% by weight based on the magnetic powder. .

The magnetic coating material may contain various additives for exhibiting a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like. For example, silicone oils, fluorine oils, alcohols containing fluorine-substituted hydrocarbon groups, fatty acids, esters, ethers, paraffins,
Metals of the monobasic fatty acids (Li, Na, K, Ca,
Ba, Cu, Pb, etc.) salts, alcohols for producing fatty acid esters, alkoxy alcohols, fatty acid esters of polyethylene oxide-added monoalkyl ethers, aliphatic or cyclic amines, fatty acid amides, quaternary ammonium salts, polyolefins , Polyglycols, polyphenyl ethers, fluorine-containing alkyl sulfates and alkali metal salts thereof, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, and cationic interfaces such as phosphonium or sulfonium Surfactants and their alkali metal salts, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group and phosphate group and their alkali metal salts, amino acids and amino acids Sulfonic acids, sulfuric or phosphoric esters of amino alcohols, amphoteric surface active agents such as alkyl betaines.

Further, the magnetic paint may contain an inorganic compound. Examples of usable inorganic powders include inorganic powders such as metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.

Further, carbon black may be contained in the magnetic paint. Furnace carbon black, thermal carbon black,
Acetylene black or the like can be used.

The thickness of such a magnetic layer 20 is usually set to 0.1.
It is set to about 05 to 5 μm.

As the support used in the magnetic recording medium 1 of the present invention, polyethylene terephthalate (PET),
Known films such as polyesters such as polyethylene naphthalate (PEN), polyolefins, polyamide, polyimide, polyamideimide, polysulfone cellulose triacetate, and polycarbonate can be used, and PET, PEN, and aromatic polyamide are preferable. .

In the magnetic recording medium 1 of the present invention, various known backcoat layers may be provided on the back surface (the surface opposite to the surface on which the magnetic layer is formed) of the nonmagnetic support 10.

The application of the magnetic paint to the non-magnetic support 10 is as follows:
Various known coating means such as a gravure coat, a reverse roll coat, and an extrusion nozzle coat can be used.

After such a coating process, various processes for smoothing the wet film surface of the magnetic paint applied on the non-magnetic support 10 and regulating the coating film may be appropriately performed as the next process.

After the magnetic layer is formed and dried as described above, a calendar process is performed as a surface smoothing process, if necessary. As a calendering roll, a combination of a heat-resistant plastic roll such as epoxy, polyester, nylon, polyimide, polyamide, or polyimideamide (which may be kneaded with carbon, metal or other inorganic compound) and a metal roll ( (Combinations of 3 to 7 stages) or metal rolls. The processing temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and the linear pressure is preferably 196 ° C.
0 N / cm, more preferably 2940 N / cm or more,
Its speed ranges from 20 m / min to 700 m / min.

After the calendering treatment, a heat curing treatment at 40 ° C. to 80 ° C. is usually performed in order to accelerate the curing of the magnetic layer. Next, the magnetic recording medium is manufactured by slitting into a predetermined shape.

[0058]

The present invention will be described in more detail with reference to specific examples below.

(Example 1) Preparation of magnetic powder A magnetic powder was prepared in the following manner. 1.16 mo in a reaction vessel held under a non-oxidizing atmosphere under a nitrogen gas flow.
Put aqueous solution of Na ₂ CO ₃ l / L, Na ₂ CO ₃ amount of Fe
Fe ²⁺ 1.5m so as to correspond to 2.0 times equivalent
An aqueous solution of ferrous sulfate containing ol / L was added and mixed, and FeCO ₃ was produced at a temperature of 45 ° C. This Fe
While flowing nitrogen gas into the suspension containing CO ₃ , 45
C. for 70 minutes.

Thereafter, air was passed through the suspension containing FeCO ₃ at a temperature of 45 ° C., followed by filtration and drying to obtain goethite particle powder. This goethite particle powder was heat-treated at 600 ° C. in air to obtain hematite particle powder.
Thereafter, the hematite particle powder is charged into a reduction vessel, and hydrogen gas is passed at a rate of 1.0 L / min.
C. for 3 hours to obtain magnetite particle powder.

While blowing nitrogen gas at room temperature into 100 g of a slurry in which the obtained magnetite particle powder is dispersed in water, a 0.85 mol / L aqueous solution of cobalt sulfate 70 was blown.
mL and 0.90 mol / L ferrous sulfate aqueous solution 140
The mixture was further added with 67 mL of a 10 mol / L aqueous sodium hydroxide solution, heated to 45 ° C., and stirred for 5 hours. After adjusting this slurry to pH 8.5, filtration,
After washing with water and drying at 120 ° C. in nitrogen gas, a magnetite powder coated with cobalt was obtained.

Preparation of Magnetic Coating <Preparation of Binder (Resin Binder) Solution A> Vinyl Chloride Copolymer: 10 parts by weight (manufactured by Zeon Corporation: MR110, Tg = 70 ° C.) Polyester polyurethane resin 5 parts by weight (containing -SO ₃ Na, Tg = 20 ° C.) methyl ethyl ketone 21 parts by weight toluene 21 parts by weight cyclohexanone 21 parts by weight The above composition was stirred and dissolved with a hypermixer for 6 hours.

[0063] <kneading mixing treatment-dispersion treatment> · Co-coated magnetite magnetic powder (as mentioned above) ... 100 parts by weight ^{(2 / BET = 38m g)} · α-Al 2 O 3 ( manufactured by Sumitomo Chemical Co., Ltd. : HIT-50) ... 5 parts by weight Cr ₂ O ₃ Nippon Chemical Industrial Co., Ltd.; U-1) ... 5 parts by weight binder (resin binder) solution (above A) ... 40 parts by weight

The above composition was put into a pressure kneader and kneaded for 1 hour. The liquid temperature is 60 during the first 30 minutes of the kneading process.
The rotation speed of the pressurized kneader and the flow rate of the cooling water were adjusted so as to maintain the temperature at 80 to 90 ° C. for 30 minutes in the latter half of the temperature. Next, after the following composition was charged and the viscosity was adjusted, dispersion was performed with a sand grinder mill.

Binder (resin binder) solution (A): 40 parts by weight Methyl ethyl ketone: 15 parts by weight Toluene: 15 parts by weight Cyclohexanone: 15 parts by weight

<Viscosity adjusting step>-Stearic acid ... 0.5 parts by weight-Myristic acid ... 0.5 parts by weight-Butyl stearate ... 0.5 parts by weight-Methyl ethyl ketone ... 65 parts by weight-Toluene ... 65 parts by weight-Cyclohexanone … 65 parts by weight

The above composition was charged into a hyper mixer,
The mixture was mixed and stirred for 1 hour to obtain a viscosity adjusting solution. The viscosity-adjusted solution and the liquid after the dispersion treatment were dispersed in a sand grinder mill, followed by circulating filtration, and an isocyanate compound (manufactured by Nippon Polyurethane Co .; Coronate L) 0.8 parts by weight based on 100 parts by weight of the paint. Parts by weight were added and mixed with stirring to obtain a coating material for forming a magnetic layer.

Preparation of Back Coating Paint <Preparation of Binder (Resin Binder) Solution B> Vinyl chloride copolymer: 45 parts by weight Polyester polyurethane resin (containing -SO ₃ Na): 45 parts by weight Methyl ethyl ketone: 100 Parts by weight Toluene 80 parts by weight Cyclohexanone 100 parts by weight The above composition was stirred for 6 hours with a hypermixer and dissolved.

<Kneading and mixing treatment to dispersion treatment> Carbon black (Mitsubishi Chemical Corporation; # 47B): 100 parts by weight α-Fe ₂ O ₃ (Toda Kogyo Co., Ltd .: TF-100): 0.8 parts by weight -Binder (resin binder) solution (B above) ... 150 parts by weight

The above composition was put into a pressure kneader and kneaded for 2 hours. Next, the following composition was charged, and the viscosity was adjusted to an optimum for the dispersion treatment. Next, dispersion treatment was performed with a sand grinder mill.

Binder (resin binder) solution (B): 200 parts by weight Methyl ethyl ketone: 135 parts by weight Toluene: 120 parts by weight Cyclohexanone: 135 parts by weight

<Viscosity Adjusting Step> Binder (resin binder) solution (B): 66 parts by weight Stearic acid: 1 part by weight Myristic acid: 1 part by weight butyl stearate: 1 part by weight Methyl ethyl ketone: 235 Parts by weight Toluene 235 parts by weight Cyclohexanone 235 parts by weight

The above composition was charged into a hyper mixer,
The mixture was mixed and stirred for 1 hour to obtain a viscosity adjusting solution. After mixing the viscosity-adjusted solution and the slurry after the dispersion treatment, the mixture was dispersed in a sand grinder mill, and then circulated and filtered, and an isocyanate compound (manufactured by Nippon Polyurethane Co .; Coronate L) was used for 100 parts by weight of the paint. 1.0 part by weight was added and mixed by stirring to obtain a coating material for forming a back coat layer.

The above magnetic coating material was applied to one side of a PET film having a thickness of 15 μm so that the coating thickness after drying was 2.2 μm, and the coating was oriented in a longitudinal direction with a 600 mT orientation magnet, and then dried. I let it. Thereafter, the coating for forming the back coat layer is dried on the opposite surface to a thickness of 0.
It was applied and dried to a thickness of 5 μm. Then, at 100 ° C
Then, the magnetic tape sample was prepared by slitting to a 1/2 inch width (sample of Example 1).

(Example 2) In Example 1, the temperature at which the goethite particles were obtained was changed from 45 ° C to 35 ° C, except that the magnetic powder used in Example 2 was the same as in Example 1. Obtained. A magnetic tape sample of Example 2 was produced in the same manner as in Example 1 except that the characteristics of the magnetic powder were changed from the aspect of manufacturing the magnetic powder (sample of Example 2).

(Comparative Example 1) In Example 1, the condition for depositing cobalt on the magnetite particles was 45 ° C.
The magnetic powder used in Comparative Example 1 was obtained by changing from 5 hours to 100 ° C. for 10 hours. A magnetic tape sample of Comparative Example 1 was prepared in the same manner as in Example 1 except that the characteristics of the magnetic powder were changed from the aspect of manufacturing the magnetic powder.

Comparative Example 2 In Example 1, the number of revolutions of the pressure kneader was controlled so that the liquid temperature during kneading was 40 to 50 ° C. even at a high temperature. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Comparative Example 2 was produced (Comparative Example 2 sample).

(Comparative Example 3) In Example 1, the kneading time was 1 hour and 30 minutes, and the liquid temperature for 30 minutes from the start of kneading was 60 ° C or less, and then the state where the liquid temperature was 80 to 90 ° C was 6 hours.
The rotation speed of the pressure kneader and the flow rate of the cooling water were adjusted so as to be 0 minutes. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Comparative Example 3 was produced (Comparative Example 3 sample).

(Example 3) In Example 1, the orientation magnetic field by the orientation magnet after applying the magnetic paint was 600 m.
T was changed to 450 mT. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Example 3 was produced (Sample of Example 3).

Example 4 In Example 1, the orientation magnetic field of the orientation magnet after application of the magnetic paint was 600 m.
Changed from T to 500 mT. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Example 4 was produced (Sample of Example 4).

(Comparative Example 4) In Example 1, the orientation magnetic field of the orientation magnet after application of the magnetic paint was 600 m.
Changed from T to 300mT. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Comparative Example 4 was produced (Comparative Example 4 sample).

(Comparative Example 5) In Example 1, the kneading time was 2 hours, and the liquid temperature for 30 minutes from the start of kneading was 60 hours.
℃ or lower, then the liquid temperature of 80 to 90 ℃ for 1 hour 3
The rotation speed of the pressure kneader and the flow rate of the cooling water were adjusted so as to be 0 minutes. Otherwise, in the same manner as in Example 1, a magnetic tape sample of Comparative Example 5 was produced (Comparative Example 5 sample).

The samples thus prepared (Examples 1 to 4; Comparative Examples 1 to 5) were evaluated for (1) electromagnetic conversion characteristics RF-9.6 MHz in the following manner.

(1) Electromagnetic Conversion Characteristics RF-9.6 MHz VTR BR-S711 manufactured by Victor Company of Japan, Ltd.
The reproduction output at 6 MHz was measured, and the difference from the S-VHS standard tape (SRT-1) was indicated in dB.

During the preparation of the sample, the coercive force (Hcp) of the magnetic powder and the coercive force (Hc) of the magnetic recording medium
m) and the magnetic characteristic values of the residual saturation magnetic flux density Br of the magnetic recording medium were measured using a vibrating sample magnetometer (Toei Kogyo Co., Ltd .; VSN
-V type). At that time, the maximum external magnetic field is 1
T.

The evaluation results are shown in Table 1 below.

[0087]

[Table 1]

[0088]

The effects of the present invention are clear from the results shown in Table 1. That is, the present invention relates to a magnetic recording medium having a magnetic layer on a nonmagnetic support, wherein the magnetic layer contains a magnetic powder and a binder, and the coercive force (Hcp) of the magnetic powder is magnetically recorded. Since the relationship with the coercive force (Hcm) of the medium is satisfied, Hcm−Hcp ≧ 8.5 kA / m and the value of the residual saturation magnetic flux density Br of the magnetic recording medium is 150 mT or more. For example, in an ultra-high frequency range exceeding 9 MHz (recording of a short wavelength of about 0.6 μm), a higher output which has not been seen conventionally can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a preferred configuration example of a magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium 10 ... Non-magnetic support 20 ... Magnetic layer

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic layer on a non-magnetic support, wherein the magnetic layer contains a magnetic powder and a binder, and the coercive force (Hcp) of the magnetic powder is a magnetic recording medium. A magnetic recording medium characterized by satisfying Hcm−Hcp ≧ 8.5 kA / m in relation to the coercive force (Hcm) and having a residual saturation magnetic flux density Br of the magnetic recording medium of 150 mT or more. 2. The magnetic recording medium according to claim 1, wherein said magnetic powder is cobalt-containing magnetite.