JPH10269573A - Manufacture of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve performance such as an electromagnetic transducing property and durability and productivity by stirring and mixing paste and solvent with a dissolving device having a rotor having a projecting part and a stator, the paste being obtained by mixing at least magnetic powders and connecting agents. SOLUTION: A paste dissolving device includes a rotor 18 having a plurality of projections 22 supported in a stator 20 so as to be freely rotated. The stator 20 has an inner peripheral surface shaped corresponding to the shape of the outer peripheral surface of the rotor 18 with a space A. Supplied paste and solvent are supplied to the space A between the rotor 18 and the stator 20, stirred by the specified number rotation of the rotor 18 and then discharged from an opening part 24. Thus, since magnetic paint is manufactured within a short time, productivity is improved and, also since good quality magnetic paint is provided, performance such as an electromagnetic transducing property and durability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnetic recording medium in which a magnetic paint is applied on a non-magnetic support. Is a method of manufacturing a magnetic recording medium in which the above has been achieved.

[0002]

2. Description of the Related Art In recent years, in a coating type magnetic recording medium,
Development has been actively studied with the aim of achieving high density and large capacity, and high performance has been promoted. Under these circumstances, as the recording wavelength is becoming shorter, the magnetic powder used in the coating type magnetic recording medium is also finely divided.

[0003] The coating type magnetic recording medium includes a non-magnetic support and a magnetic layer formed on the non-magnetic support. This magnetic layer is formed by applying a magnetic coating material in which a magnetic powder, a binder and the like are dispersed in a solvent on a non-magnetic support.

[0004] In order to obtain a magnetic recording medium having excellent magnetic conversion characteristics, a magnetic paint obtained by kneading fine magnetic powder and a binder with a kneader, continuous kneader, extruder or the like having a high shearing force is required. It is. Also,
In order to obtain this magnetic paint, a continuous type is advantageous over a batch type in consideration of productivity. For these reasons, a continuous kneading apparatus is used as an apparatus for producing a magnetic paint in a coating type magnetic recording medium.

[0005]

By the way, when a magnetic coating material is manufactured using this continuous kneading apparatus, the solid content of the treated material is increased to increase the saturation magnetic flux density (Bm) by a high shear. It is possible to do. However, the paste manufactured in this manner is difficult to dissolve in an organic solvent or the like in a subsequent dilution step, and requires a long dissolution time. For this reason,
The conventional method of manufacturing a magnetic recording medium has a problem that the productivity of the magnetic paint is poor.

[0006] In the above-mentioned dilution step, there are cases where the dissolution of the paste is insufficient because the paste is difficult to dissolve. In this case, agglomerates will be mixed in the obtained magnetic paint, which may cause filter clogging or the like in a later manufacturing process, or may cause dropout when a magnetic recording medium such as a magnetic tape is used. In some cases, causing quality problems.

Under such circumstances, development of a technique which is an important issue in sufficiently dispersing these high-performance fine magnetic powders has been awaited. For example, see Japanese Patent Application Laid-Open No. 05-033.
No. 6067 discloses a method in which a solvent is introduced stepwise into a kneader to dilute and dissolve the paste stepwise in the kneader. This is effective as a method for stably dispersing the fine magnetic powder. However, since the paste obtained by this method has a high viscosity, it was difficult to transfer the paste by a pump or the like. For this reason,
In this method, it is necessary to dissolve the paste in a tank installed at the lower part of the kneader, which limits the arrangement of the device,
In addition, the dissolution time was long because the dissolution was performed in a tank. For this reason, this method did not improve productivity.

Further, Japanese Patent Application Laid-Open No. 64-79274 discloses a method for improving dispersibility by using two kneaders continuously. However, even when such a kneading method is used, the dissolution time of the paste cannot be effectively shortened.

Accordingly, the present invention produces a magnetic recording medium which is used for video tapes, audio tapes, computer tapes and the like, and has improved electromagnetic conversion characteristics, durability and the like, as well as improved productivity. It is an object of the present invention to provide an intended method for manufacturing a magnetic recording medium.

[0010]

A method of manufacturing a magnetic recording medium according to the present invention, which achieves the above object, comprises kneading at least a magnetic powder and a binder, then dispersing the mixture in a solvent to form a magnetic coating material. A method for producing a magnetic recording medium to be applied on a support, wherein a paste obtained after kneading and a solvent are stirred and mixed by a dissolving device including a rotor having a projection and a stator.

According to the method of manufacturing a magnetic recording medium according to the present invention having the above-described structure, the rotor having the protrusion rotates, and the paste and the solvent are poured between the rotor and the stator. Thereby, the paste is uniformly diluted by the solvent. According to the method of the present invention, a large amount of paste can be diluted in a short time by continuously using the dissolving apparatus.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for manufacturing a magnetic recording medium according to the present invention will be described below in detail with reference to the drawings.

[0013] The method of manufacturing a magnetic recording medium according to the present invention comprises:
As shown in FIG. 1, a magnetic recording medium including at least a nonmagnetic support 2 and a magnetic layer 3 formed on the nonmagnetic support 2 is manufactured. The magnetic recording medium may include a top coat layer 4 on the magnetic layer 3 and a back coat layer on the surface of the non-magnetic support 2 opposite to the surface on which the magnetic layer 3 is formed. 5 may be provided. Then, in this magnetic recording medium, the magnetic layer 3
Is formed by applying a magnetic paint obtained by dispersing a magnetic powder, a binder and the like in a solvent onto the non-magnetic support 2. The magnetic paint contains a dispersant, a lubricant, an abrasive, etc. in addition to the magnetic powder and the binder.

In this method, first, a magnetic paint is manufactured as described in detail later, and the magnetic paint is applied on the non-magnetic support 2, dried, calendered, and the like to obtain a predetermined width and length. This is done by cutting to dimensions.

In this method, when a magnetic coating material is produced, a flow chart as shown in FIG. 2 is used.

First, as shown in S1, raw materials are kneaded by a continuous kneader to obtain a paste. At this time, the raw materials include magnetic powder, a part of a binder, a lubricant and the like.

Next, as shown in S2, the paste obtained by the continuous kneader is mixed and diluted with the solvent, the additive and the rest of the binder using a dissolving apparatus.

Next, as shown in S3, the diluted paste is dispersed by using a media disperser represented by a known disperser such as a sand mill, a dyno meal (horizontal sand mill), a basket mill, a ball mill, and a pin mill. Make paint.

Next, as shown in S4, a hardener is added to the paint prepared as described above, and the paint is filtered to obtain a magnetic paint.

The magnetic paint obtained as described above is applied on the non-magnetic support 2 as shown in S5.

[0021] In the manufacturing process of the magnetic paint as described above,
As schematically shown in FIG. 3, an in-line paint production apparatus is used.

This in-line type paint manufacturing apparatus comprises a continuous kneading device 10, a paste dissolving device 11, and a media disperser 12.

In this in-line paint production apparatus,
The continuous kneading apparatus 10 is configured such that a predetermined amount of raw material is continuously supplied from the input port 13 and a predetermined amount of solvent is supplied to the input raw material. In the continuous kneading apparatus 10, when the raw material is supplied from the input port 13, the raw material is sent out at a predetermined speed by the quantitative feeder 14. At this time, the solvent is diluted to a predetermined concentration and stored in the first tank 15.
Continuous kneading device 1 from a tank 15
It is thrown into 0. The amount of this solvent is controlled by the flow meter 17.

The continuous kneading apparatus 10 constructed as described above
Can continuously produce a high-viscosity paste by kneading the raw materials.

As shown in FIG. 4, the paste dissolving apparatus 11 of the in-line paint manufacturing apparatus includes a rotor 18 having a projection, a support 19 for supporting the roller 18, and a stator 20. . Further, the paste dissolving device 11 includes cooling devices in the rotor 18 and the stator 20, respectively.

In the paste dissolving apparatus 11, the rotor 18 has a substantially cylindrical shape, and a support bar 21 is provided on the upper surface thereof. Further, the rotor 18 has a plurality of protrusions 22 formed on the outer peripheral surface thereof along the circumferential direction. And in this paste dissolution apparatus 11,
The entire rotor 18 is rotatably supported by a support rod 21. The support portion 19 supports the support rod 21 of the rotor by a rotation support member 23 so as to be rotatable.

In the paste dissolving apparatus 11, the stator 20 has a cylindrical shape having an inner diameter slightly larger than the diameter of the rotor 18 described above.
It is connected to the support 19. This stator 20
The shape of the inner peripheral surface corresponds to the shape of the outer peripheral surface of the roller 18 described above. Further, the stator 20 has an opening 24 formed with a predetermined diameter on the bottom surface.

In the paste dissolving apparatus 11, a roller 18 is provided in the stator 20. In the paste dissolving device 11, the inner peripheral surface of the stator 20 and the outer peripheral surface of the roller 18 have a predetermined interval. That is, the paste dissolving device 11 is configured such that the rotatably supported roller 18 is not in contact with the inner peripheral surface of the stator 20.

In the paste dissolving device 11, the cooling device is formed inside the stator 20 and the rotor 18, and the cooling liquid passage 25 through which the cooling liquid flows.
And a supply device (not shown) for supplying a coolant to the coolant passage 25 at a predetermined flow rate. In this cooling device, the cooling liquid is supplied to the cooling liquid passage 25 from the supply device, and the stator 20 and the rollers 18 are maintained at a predetermined temperature. Thereby, the paste dissolving device 11
The temperature of the space between the stator 20 and the roller 18 can be maintained at a predetermined value.

Further, the paste dissolving device 11
A second tank 26 is provided which is filled with solvent, additives and the remaining binder. The solvent, the additive, and the remaining binder are supplied to the paste dissolving apparatus 11 by the pump 28 while the supply amounts are adjusted by the flow meter 27.

The paste dissolving apparatus 1 configured as described above
In 1, the paste of high viscosity is supplied from the inlet 29 of the continuous kneading apparatus 10. At this time, the high-viscosity paste is supplied from the inlet 30 and is supplied into the paste dissolving apparatus 11 by the third pump 31 together with the solvent and the like supplied from the second tank 26. Then, the supplied paste flows into the space between the stator 20 and the rollers 18 together with the solvent. At this time, the paste dissolving device 11
Then, the paste and the solvent are agitated by rotating the rotor 28 at a predetermined number of rotations. When the paste is dissolved in the solvent by being stirred, the paste flows out of the opening 24.

At this time, the paste dissolving device 11 adjusts the number of rotations of the rotor and the interval between the stator 20 and the roller 18 so that even a hard paste having a high paint viscosity can be dissolved in a short time by stirring with the solvent. it can. Further, by flowing the cooling liquid through both the stator 20 and the rotor 18, it is possible to prevent a rise in the temperature of the paint during high-speed rotation.

In the paste dissolving apparatus 11, the interval between the stator 20 and the rotor 18 (shown by A in FIG. 4).
Is preferably from 0.3 mm to 1.5 mm,
The dissolving ability decreases as the distance increases. Conversely, if the interval is narrowed, the processing temperature of the paint will be
The temperature is preferably from 20 ° C to 60 ° C, more preferably from 30 ° C to 40 ° C, and the processing amount (the flow rate of the paint) is determined based on this temperature.

Further, in this in-line type paint manufacturing apparatus, as the medium, for example, glass, sodaless beads, beads coated with zirconia, titania, alumina or the like, steel balls, etc. are used as the medium in the media dispersing machine 12. It is desirable to use those media suitable for each dispersing machine in view of the dispersing ability.

Here, as a binder to be used at the time of kneading, it is common to use a vinyl chloride copolymer or a polyurethane resin, and since nitrocellulose has a risk of explosion, a pressure kneader or an extruder is used. It is not suitable for kneading doughs. For this reason, it is common to mix at the stage where the paste obtained by kneading the magnetic powder and the binder is dissolved with a solvent.

The magnetic powder used in the method for manufacturing a magnetic recording medium according to the present invention includes γ-FeOx (x = 1.3).
3-1.5), Co-modified γ-FeOx (x = 1.33-
1.5), Fe or Ni or Co as a main component (75%
Known ferromagnetic materials such as the ferromagnetic alloys described above, bium ferrite, and strontium ferrite can be used. These ferromagnetic powders also contain A
1, Si, S, Sc, Ti, V, Cr, Cu, Y, M
o, Rh, Pd, Ag, Sn, Sb, Te, Ba, N
i, Ta, W, Re, Au, Hg, Pb, Bi, La,
It may contain atoms such as Ce, P, Mn, Zn, Co, Sr, and B.

In addition, in the method for manufacturing a magnetic recording medium according to the present invention, a binder, an abrasive, an antistatic agent, a rust inhibitor or a magnetic material other than the magnetic powder mixed in the nonmagnetic support 2 and the magnetic layer 3 is used. Solvents used to prepare paints include:
Any of the conventionally known ones can be applied.

For example, as the nonmagnetic support 2, those generally used for magnetic recording media can be used. For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, and polyolefins such as polyethylene and polypropylene can be used. , Cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamide imide, other plastics, metals such as aluminum and copper, and aluminum alloys , Light alloys such as titanium alloys, ceramics, single crystal silicon, and the like.

As the binder used for the magnetic layer 3, any known material can be used. That is, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer Coalescence, acrylate-vinylidene chloride copolymer, acrylate-
Acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer , Acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea A formaldehyde resin, a polyvinyl acetal resin, a mixture thereof, or the like can be used.

Of these, polyurethane resins, polyester resins, acrylonitrile-butadiene copolymers and the like, which are supposed to impart flexibility, and cellulose derivatives, phenol resins, epoxy resins, etc., which are supposed to impart rigidity, are desirable. The above-mentioned binder may be one having improved durability by crosslinking an isocyanate compound, or one having a suitable polar group introduced.

In some cases, a layer (undercoat layer) containing the above-mentioned known binder as a main component is provided between the nonmagnetic support 2 and the lower layer for reasons such as increasing the adhesive strength. No problem.

As the carbon black used for the magnetic layer 3, any carbon may be used. The carbon black includes acetylene black, furnace black and the like depending on the production method.

Here, the carbon black is DB
P oil absorption is 30-150ml / 100g, preferably 5
0 to 150 ml / 100 g, and the average particle size is 5 to 150 nm, preferably 15 to 50 nm.
The specific surface area by the ET method 40 to 300 m ² / g, preferably effective ones is 100 to 250 m ² / g. The water content of carbon black is 0.1 to 10%.
And the tap density is 0.1-1 g / cc, pH
Is preferably 2.0 to 10. Carbon black having a higher DBP oil absorption has a higher viscosity and remarkably deteriorates dispersibility. When the amount is small, the dispersibility is poor, so that the dispersing step takes time. The smaller the average particle diameter, the longer the dispersion time is required, but the better the surface properties, and the larger the average particle diameter, the worse the surface properties. For this reason, the above-mentioned range is preferable as the average particle diameter.

Examples of the carbon black satisfying the above conditions include, for example, Raven 1250 (particle size: 23 nm, BET value: 1) manufactured by Columbian Carbon Co., Ltd.
35.0 m ² / g, DBP oil absorption 58.0 ml / 100
g), 1255 (particle size: 23 nm, BET value: 125.0 m)
² / g, DBP oil absorption 58.0 ml / 100 g), 10
20 (particle diameter 27 nm, BET value 95.0 m ² / g, DB
P oil absorption 60.0 ml / 100 g), 1080 (particle size 2
8 nm, BET value 78.0 m ² / g, DBP oil absorption 6
5.0 ml / 100 g), raben 1040, raben 1060, raben 3300, raben 450, raben 780, etc., or CONDUCT
EX) SC (particle size: 20 nm, BET value: 220.0 m ² /
g, DBP oil absorption 115.0 ml / 100 g). Asahi Carbon # 22B (particle size 23 nm, B
ET value 5.0 m ² / g, DBP oil absorption 113.0 ml /
100g), Mitsubishi Kasei # 22B (particle size 40nm, BE
T value 5.0 m ² / g, DBP oil absorption 131.0 ml / 1
00g), # 20B (particle size 40 nm, BET value 56.0)
m ² / g, DBP oil absorption 115.0 ml / 100 g),
Black Pearls (BLACK PEA) manufactured by Cabot
RLS) L (particle diameter 24 nm, BET value 250.0 m ² /
g, DBP oil absorption 60.0 ml / 100 g), Black Pearls 800 (particle size 17 nm, BET value 240.0 m)
² / g, DBP oil absorption 75.0 ml / 100 g), Black Pearls 1000, Black Pearls 1100, Black Pearls 700, Black Pearls 905, etc.

In this magnetic recording medium, a nonmagnetic back coat layer 5 may be provided on the surface of the nonmagnetic support 2 opposite to the magnetic layer 3 side. The thickness of the back coat layer 5 is 0.
The thickness is 1 to 2.0 μm, preferably 0.3 to 1.0 μm, and known ones can be used.

As the lubricant, conventionally known lubricants can be used. For example, higher fatty acid esters, silicone oils, fatty acid-modified silicones, fluorine-containing silicones or other fluorine-based lubricants, polyolefins, polyglycols, amine-based lubricants such as alkyl acid amine salts and fluorinated alkyl carboxylic acid amine salts, and 12-14 carbon atoms
(Which may be unsaturated or branched), and higher fatty acids having 12 to 14 carbon atoms.

The higher fatty acid ester component is a higher fatty acid ester having 12 to 32 carbon atoms (which may be unsaturated or branched), such as lauric acid, myristic acid, palmitic acid, and stearic acid. Acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid, methyl ester such as linoleic acid, ethyl ester, propyl ester, isopropyl ester, butyl ester, pentyl ester, hexyl ester, heptyl ester ,
Octyl ester and the like. Specific compound names include butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, butoxyethyl stearate, octyl myristate, isooctyl myristate, butyl palmitate, and the like. The lubricant may be a mixture of a plurality of lubricants.

Examples of the abrasive include α-alumina,
Mainly β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, quartzite, garnet, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, etc. As a component, a known material having a Mohs hardness of 6 or more is used alone or in combination.

The average particle size of these abrasives is 0.01 to 2
Although μm is preferable, abrasives having different particle sizes may be combined as needed, or a single abrasive may be used by broadening the particle size distribution.

Similarly, as the antistatic agent, known antistatic agents such as natural surfactants, nonionic surfactants and cationic surfactants can be used in addition to the above-mentioned carbon black.

Further, a coupling agent may be used in this magnetic recording medium. Examples of the coupling agent include a silane coupling agent, a titanate-based coupling agent, and an aluminum-based coupling agent. Here, the addition amount of the coupling agent is preferably 0.05 to 10.0 parts, more preferably 0.1 to 5.0 parts, per 100 parts by weight of the magnetic powder.

Examples of the silane coupling agent include vinylsilane compounds such as γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane, and β- (3,4
Epoxysilane compounds such as -epoxycyclohexyl) ethyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane, and aminosilane compounds such as γ-aminopropyltriethoxysilane and N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane And mercaptosilane compounds such as γ-mercaptopropyltrimethoxysilane can be suitably used.

As the titanate coupling agent, tetra-n-butoxytitanium, tetraisopropoxytitanium, bis [2-[(2-aminoethyl) amino] ethanolate] [2-[(2-aminoethyl) amino] Ethanolate-0] (2-propanolate) titanium, tris (isooctadecanoate-0) (2-propanolate) titanium, bis (ditridecyl phosphite)
0 ") tetrakis (2-propanolate) dihydrozentitanate, tris (dioctylphosphite-
0 ") (2-propanolate) titanium, bis (dioctylphosphite-0") [1,2-ethanediolate (2-)-0,0 "] titanium, tris (dodecylbenzenesulfonate-0) ( 2-propanolate)
Titanium, tetrakis [2,2-bis [(2-propenyloxy) methyl] -1-butanolate titanate, and the like can be mentioned. Commercially available products are Ajinomoto Co., Inc., Prenact KR TTS, KR 46B, KR 55, and KR 41.
B, KR 38S, KR 138S, KR 238S,
338X, KR 12, KR 44, KR 9SA, K
R34S or the like can be suitably used.

As the aluminum-based coupling agent,
Acetoalkoxyaluminum diisopropylate and the like.
LM and the like can be suitably used.

When the magnetic paint is applied, an undercoat layer such as an adhesive layer is applied on the non-magnetic support 2 or a pre-treatment such as corona discharge treatment or electron beam irradiation treatment is applied on the non-magnetic support 2. No problem.

The method of coating on the non-magnetic support 2 includes air doctor coating, blade coating, rod coating, extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, gravure coating, transfer roll coating, Methods such as cast coating can be mentioned, and methods other than these can also be used. Further, simultaneous multilayer coating by extrusion coating may be used.

In this magnetic recording medium, a polyol adduct of an isocyanate having an average number of functional groups of 2 or more can be suitably used in order to impart more solvent resistance.

In the present invention, when an isocyanate group is introduced, performance excellent in heat resistance and durability can be exhibited.
Here, when a certain ratio of isocyanurate groups and / or other isocyanate polymers are contained in the polyisocyanate compound molecule, it is possible to introduce a branching point to such an extent that gelation is not reached in the produced polyurethane-based component.

Examples of the curing agent include fragrance polyisocyanates and aliphatic polyisocyanates, and adducts of these with active hydrogen compounds are preferred. As the aromatic polyisocyanate, toluene diisocyanate (TD
I), 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl diisocyanate, and the like. . Also,
Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, and isophorone diisocyanate (IPDI). Active hydrogen compounds which form adducts with these include ethylene glycol, 1,4-butanediol,
There are 1,3-butanediol, neopentyl glycol, diethylene glycol, trimethylolpropane, glycerin and the like, and the average molecular weight is preferably in the range of 100 to 5,000.

The amount of the curing agent to be added is generally 0 to 20 parts by weight of the binder resin.
0 to 10 parts. Here, theoretically, a sufficient amount of the curing agent is used in terms of the weight of the curing agent that is equivalent to the amount of the active hydrogen in the polyutalen resin composition (or the binder resin composition). However, in actual production, the isocyanate of the curing agent component reacts with moisture and the like,
In many cases, the amount of isocyanate equivalent to active hydrogen is insufficient, so that it is 10% to 50% higher than the equivalent amount of active hydrogen.
It is effective to add an excessive amount of the curing agent.

Further, when using a curing agent composed of a polyisocyanate, the magnetic paint is coated at 40% after coating.
By promoting the effect reaction for several hours at a temperature of ８０80%, stronger adhesion is obtained.

[0062]

Next, an embodiment actually manufactured by applying the method for manufacturing a magnetic recording medium according to the present invention will be described in detail. Further, a magnetic recording medium of a comparative example was also manufactured and compared with the magnetic recording medium of the example. However, the method for manufacturing a magnetic recording medium according to the present invention is not limited to these examples. In the following description, “part” and “%” mean “part by weight” and “% by weight”, respectively, unless otherwise specified.

Example 1 In Example 1, a magnetic paint as shown below was prepared and applied on a non-magnetic support 2.

Preparation of Magnetic Paint A magnetic paint for forming the magnetic layer 3 was prepared according to the following composition.

<Magnetic coating liquid composition> Metal magnetic powder 100 parts by weight (σs = 150 Am ² / kg, 56 m ² / g, Hc = 127 kA / m) Strong vinyl chloride polymer (MR-110 manufactured by Zeon Corporation) 10 5 parts by weight Polyurethane resin (N-5033, Japan Polyurethane Industry) 5 parts by weight Nitrocellulose (NC-1 / 2H, Asahi Kasei Corporation) 5 parts by weight Carbon black (BP-L, Cabot Corporation) 2 parts by weight Alumina (Sumitomo Chemical Co., Ltd.) AKP-30) 5 parts by weight 1 part by weight of butyl stearate 80 parts by weight of methyl ethyl ketone 80 parts by weight of methyl isobutyl ketone 80 parts by weight of toluene <Magnetic paint production process> In this Example 1, the magnetic material was prepared according to the flowchart shown in FIG. Paint was created.

First, a metal magnetic powder, a vinyl chloride-based copolymer, a polyurethane resin, carbon black, and alumina were added to a planetary mixer, and the solid content was adjusted to 85 wt% by a twin-screw extruder.
The mixture was diluted and kneaded to 0 wt%.

Thereafter, nitrocellulose, butyl stearate and the remaining solvent were added in-line to the kneaded paste, and the mixture was diluted with a paste dissolving apparatus shown in FIG. 4 so that the final coating solid content was 35 wt%. At this time, in the paste dissolving apparatus, the distance between the rotor and the stator is 0.3 mm.

Thereafter, the uniformly dissolved paste was dispersed using a sand mill. To the magnetic paint thus obtained, 4 parts by weight of polyisocyanate and 1 part by weight of myristic acid were added, and the mixture was filtered through a filter having an average diameter of 1 μm to obtain a magnetic paint.

The dispersed magnetic coating liquid was applied as a non-magnetic support 2 having a thickness of 10 μm to a polyethylene terephthalate film with a thickness of 3.0 μm by die coating. After curing the obtained wide magnetic film, it was cut into a 1/2 inch width to prepare a video tape, and Example 1 was used.

Examples 2 to 5 Examples 2 to 5 were produced in the same manner as in Example 1 except that the distance between the rotor and the stator in the paste dissolving apparatus was changed as follows. Was done.

Example 2 ... 0.6 mm spacing Example 3 ... 1.0 mm spacing Example 4 ... 1.5 mm spacing Example 5 ... 2.0 mm spacing Comparative Example The paste having the same magnetic coating composition as in Example 1 and kneaded by an extruder was dissolved in a tank equipped with a stirrer containing nitrocellulose, butyl stearate and a diluting solvent to obtain a magnetic coating. In addition, about 4
It took hours of time. Thereafter, a video tape was prepared in the same manner as in the example, and was used as a comparative example.

Examples 1 to 5 produced as described above
The following characteristics were evaluated for each video tape of the comparative example.

Evaluation of Properties [ Evaluation of Paste Solubility] In the examples, the dissolution state of the paste when the gap clearance of the in-line paste dissolution apparatus was changed was evaluated according to the following criteria.

；: Uniform state without visual agglomerates △: Almost complete dissolution with agglomerates ×: Separation of solvent and paste [Dispersibility] A polyethylene terephthalate film (14.0 μm thick) After coating and drying with a doctor blade 2MIL, the glossiness (gloss) of the coated surface was measured using a digital variable-angle gloss meter VG-1D manufactured by Nippon Denshoku Industries Co., Ltd.
Was measured at 45 ° C.

[Magnetostatic Properties] The prepared tape was measured at 20 ° C. at 5 ° C. using an ultra-high-vibration sample magnetometer (VSM-P10-15auto) manufactured by Toei Kogyo Co., Ltd.
It was measured under the condition of 0% RH.

[Still durability] Using a Betacam VTR (BVW-75, manufactured by Sony Corporation) at 20 ° C. and 50 ° C.
After performing still reproduction for 60 minutes under the condition of% RH, the results were expressed according to the following evaluation criteria.

；: Completed for 120 minutes without head clogging △: Completed for 120 minutes but clogged x: Visually scratched tape surface [Electromagnetic conversion characteristics] Electromagnetic conversion characteristics Is measured using a digital beta cam VTR (DVW-500, manufactured by Sony Corporation)
The output difference from this comparative example was measured by setting the measurement frequency to 32 MHz and setting the output to 0 dB for the comparative example.

Table 1 shows the results of the evaluation of each evaluation item.

[0079]

[Table 1]

From the results shown in Table 1, a high-performance magnetic recording medium was obtained by the method for manufacturing a magnetic recording medium according to the present invention. Here, it became clear that the solubility can be improved by adjusting the gap clearance of the in-line paste dissolution apparatus. In the embodiment, the time required for dissolving the paste can be eliminated. For this reason, the method for manufacturing a magnetic recording medium according to the present invention exhibits significantly improved productivity.

[0081]

As described above in detail, according to the method of manufacturing a magnetic recording medium according to the present invention, the paste and the solvent obtained after kneading are mixed with the dissolving device including the rotor having the protrusion and the stator. With stirring. Therefore, according to this method, the magnetic paint can be manufactured in a short time, so that the productivity can be improved. Further, according to this method, since the magnetic coating material becomes favorable, it is possible to manufacture a magnetic recording medium with improved performance such as electromagnetic conversion characteristics and durability.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an example of a magnetic recording medium manufactured by a method for manufacturing a magnetic recording medium according to the present invention.

FIG. 2 is a flowchart for producing a magnetic paint in the method for producing a magnetic recording medium according to the present invention.

FIG. 3 is a schematic configuration diagram illustrating a configuration of an in-line type paint manufacturing apparatus.

FIG. 4 is a sectional view of a main part of the paste dissolving apparatus.

[Explanation of symbols]

10 continuous kneading device, 11 paste melting device, 12
Media disperser, 18 rotor, 19 support, 20
Stator

Claims (6)

[Claims] 1. A method for producing a magnetic recording medium, comprising kneading at least a magnetic powder and a binder, dispersing the mixture in a solvent to form a magnetic coating material, and coating the magnetic coating material on a nonmagnetic support. A method for producing a magnetic recording medium, wherein a paste and a solvent obtained after kneading are stirred and mixed by a dissolving device including a stator having a concave portion corresponding to a protrusion. 2. The melting apparatus according to claim 1, wherein a protrusion of the rotor is formed in a circumferential direction on an outer circumferential surface thereof, and a recess of the stator is formed in a circumferential direction of an inner circumferential surface thereof in correspondence with the protrusion. 2. The method for producing a magnetic recording medium according to claim 1, wherein the paste obtained later flows between the rotor and the stator together with the solvent in the axial direction. 3. The method according to claim 1, wherein a distance between the rotor and the stator is 0.3 mm or more and 1.5 mm or less. 4. The method according to claim 1, wherein the solvent comprises an organic solvent, a binder, and an additive. 5. The method according to claim 1, wherein the melting device has a cooling device in at least one of a rotor and a stator. 6. The method according to claim 5, wherein the cooling device comprises a cooling circuit through which a cooling liquid circulates.