JPH05242475A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To produce the magnetic recording medium which does not generate trouble in kneading and diluting stages and is improved in dispersibility by using cobalt-contg. iron oxide having a specific moisture content as magnetic powder. CONSTITUTION:This magnetic recording medium is formed by laminating a magnetic layer 12 on one surface of a nonmagnetic base 11 and a back coat layer 13 on the rear surface at need. The cobalt-contg. iron oxide which is expressed by FeOx (where 1.34<=x<=1.42) and has <=0.7wt.% moisture content is used as the magnetic powder. Kneading and dispersing are executed by charging a compsn. for a magnetic coating material into a mixing chamber 1 of a batch type kneading machine and compressing the compsn. with a pressurizing ram 2. A rotor 3 is rotated in this pressurized sate to shear and knead the magnetic powder. The sufficiently kneaded compsn. is diluted by an org. solvent and is taken out of the lower part of the mixing chamber 1. This compsn. enters a diluting and dispersing machine where the compsn. is subjected to dispersion treatment. The displayed compsn. is filtered by a filter and is sent to a coating stage.

Description

Detailed Description of the Invention

[0001]

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 disk, a magnetic tape or a magnetic sheet.

[0002]

2. Description of the Related Art A magnetic recording medium is usually manufactured by coating a support such as a polyester film with a magnetic coating material containing magnetic powder, an antistatic agent, an abrasive, a binder resin and the like and drying it.

In the production of this magnetic recording medium, in order to finish the above magnetic coating material into a coating material which is quick and has good dispersibility, the magnetic powder is placed in a solvent solution of a binder resin by using a dispersing machine such as a ball mill or a sand grinder. Before dispersing
A series of steps is known in which a magnetic powder and a small amount of binder resin solution are kneaded using a powerful kneader such as a kneader.

Regarding the manufacturing apparatus for carrying out the kneading and dispersion in the preparation of the magnetic coating material and the operating conditions thereof, a method of operating the kneading machine under a specific shear stress (a kneader is used for the kneading machine)
Alternatively, a technique of increasing dispersibility and RF output by a method of operating a disperser under specific conditions is known.

Regarding the above-mentioned kneading method, Japanese Patent Publication No. 57-
40566, JP-A-46-3030, 48-10450, 49-
14537, 53-1092, 53-76012, 55-2540
No. 6, No. 56-100871, No. 57-141026, JP-A 1-19
It is described in each publication of No. 0768.

However, the water content of the magnetic powder conventionally used for kneading has not been particularly controlled and often exceeds 1.0% by weight, which is remarkable in the summer. When the amount of water contained in the magnetic powder is large, the kneading cannot be sufficiently performed, so that the kneaded product is not subjected to a high shearing force, resulting in poor dispersion. As a result, the electromagnetic conversion characteristics of the obtained magnetic recording medium deteriorate.

When kneading is performed in a state where the water content is large,
Dilution cannot be carried out smoothly in the next diluting step, and the kneaded product becomes a lump in the diluting / dispersing machine or sticks to the paddle in the kneader and cannot be removed easily by adding the solvent. In particular, when the magnetized magnetic powder is used as the magnetic powder, the cohesive force is stronger than that of other magnetic powders and it is difficult to disperse the magnetic powder, so that the influence of water is large.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a magnetic recording medium which has improved trouble-free dispersibility during the kneading and dilution steps.

[0009]

According to the present invention, in the method for producing a magnetic recording medium having a magnetic layer in which magnetic powder is dispersed in a binder, FeOx (provided that
1.34 ≦ X ≦ 1.42. The present invention relates to a method for producing a magnetic recording medium, which comprises using a cobalt-containing iron oxide having a water content of 0.7% by weight or less and kneading the magnetic powder with the binder and then dispersing the magnetic powder.

According to the method of the present invention, by adjusting the water content of the magnetic powder, especially the magnetized magnetic powder, the kneaded product at the time of kneading is sufficiently sheared, and the kneaded product is adhered to the paddle in the kneader. Alternatively, they have found that troubles such as the formation of lumps (so-called lumps) in the diluting step after kneading are remarkably reduced. In the magnetic recording medium produced by the method of the present invention, the magnetic powder is well dispersed in the magnetic layer.
Tape sliding noise is significantly reduced.

The magnetic powder used in the present invention is cobalt-containing iron oxide represented by FeOx, so-called magnetized magnetic powder. X is 1.34 to 1.42, preferably 1.36 to 1.40. When X is less than 1.34, the amount of Fe ²⁺ increases, so that the stability of the magnetic powder itself with time deteriorates and the electromagnetic conversion characteristics deteriorate with time when formed into a tape. On the other hand, when it exceeds 1.42, the amount of Fe ²⁺ becomes small, the light transmittance becomes large, and the spec of the light transmittance is exceeded, and troubles such as the tape not running occur.

The water content of the magnetized magnetic powder used in the present invention is adjusted to 0.7% by weight or less, preferably 0.05 to 0.5% by weight. When the water content exceeds 0.7% by weight, the kneading becomes insufficient as described above, and troubles frequently occur in the diluting step.

As a method of adjusting the water content, the drying condition may be set by a known method in the manufacturing process of the magnetic powder. The magnetic powder produced must be controlled in humidity around the equipment in order to maintain a water content of 0.7% by weight or less until the magnetic powder preparation process. If there is a waiting time before the magnetic paint preparation step, it is advisable to seal the container containing the magnetic powder or the container bag with nitrogen.

In kneading the composition of the magnetic paint components, the magnetic powder and the other magnetic paint components are added to the kneader at the same time or individually. For example, first, magnetic powder is added to a solution containing a dispersant, and after kneading for a predetermined time, the remaining components are added and the kneading is further continued to obtain a magnetic paint.

For kneading and dispersing, various kneaders can be used. Examples of this kneader include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sand glider, a Sqegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill,
Disper kneader, high speed mixer, homogenizer,
Examples thereof include an ultrasonic disperser, and a kneader, particularly a pressure kneader or a continuous kneader, is preferable from the viewpoint of kneading ability.

An example of the pressure type kneader is a batch type kneader having a structure as shown in FIG. The composition for magnetic paint is charged into the mixing chamber 1 and compressed by the pressure ram 2. In this pressurized state, the rotor 3 is rotated to shear the magnetic powder,
Knead. The kneading temperature is preferably 20 to 60 ° C. in order to keep the viscosity of the kneaded product within an appropriate range and prevent evaporation of the solvent, and the kneading time is required to be about 30 minutes to 120 minutes. The sufficiently kneaded composition is diluted with an organic solvent (because it adheres to the inside of the machine), and is dropped to a viscosity at which it can be discharged, and then taken out from the lower part of the mixing chamber.

The composition discharged from the kneader enters a diluting / dispersing machine and is diluted with an organic solvent. As a device used for dilution and dispersion, there are a dissolver, a flow jet mixer, a line flow, and the like. After that, the composition is subjected to dispersion treatment with a disperser, filtered with a filter, and sent to a coating step.

The binder used in the method of the present invention includes:
The average molecular weight is preferably about 10,000 to 200,000, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, polyvinyl chloride, polyurethane resin, 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 synthesis Rubber polymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy 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 , Low molecular weight glycol / high molecular weight diol / isocyanate mixtures, and mixtures thereof.

These binders are --SO ₃ M, --COO.
M, —PO (OM ′) ₂ (where M is hydrogen or lithium,
Alkali metals such as potassium and sodium, M'is hydrogen,
A resin containing a hydrophilic polar group such as an alkali metal such as lithium, potassium, sodium or a hydrocarbon residue) is preferable. These resins improve the compatibility with the magnetic powder due to the polar group in the molecule, thereby further improving the dispersibility of the magnetic powder and preventing the aggregation of the magnetic powder to further improve the coating liquid stability. It is possible to improve the durability of the medium.

Such a binder, particularly a vinyl chloride-based copolymer, is prepared by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and optionally other copolymerizable monomer. Obtainable. Since this copolymer is produced by vinyl synthesis, it is easy to synthesize, various copolymerization components can be selected, and the properties of the copolymer can be optimally adjusted.

The magnetic recording medium of the present invention has, for example, as shown in FIG. 2, a magnetic layer 12 on one surface of a non-magnetic support 11, and a back coat layer 13 on the back surface if necessary. ..

The magnetic layer 12 may be a single layer or a multilayer of two or more layers. If necessary, it may be further provided with an overcoat layer (not shown) or a non-magnetic support 11. May be provided with an undercoat layer (not shown). Further, in order to improve the adhesiveness with the magnetic layer 12, the nonmagnetic support 11 may be subjected to corona discharge treatment.

In order to form the above magnetic layer, other additives such as a dispersant, a lubricant, an abrasive, an antistatic agent and a filler may be added, if necessary.

As the dispersant, caprylic acid, capric acid,
Fatty acids having 12 to 18 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, etc., and salts of these alkali metals or alkaline earth metals or their amides; polyalkylene oxide alkylphosphoric acids Esters; lecithin; trialkylpolyolefinoxy quaternary ammonium salts; azo compounds having a carboxyl group and a sulfonic acid group and the like are used. These dispersants are preferably added within the range of 0.5 to 5% by weight with respect to the ferromagnetic powder.

As the lubricant, fatty acids and fatty acid esters are mainly used, and the combined use of both is particularly effective. Examples of fatty acids include caproic acid, caprylic acid, capric acid,
Lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid. , Sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicarboxylic acid and the like.

Examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate and the like.

In addition to the above fatty acids and fatty acid esters, other lubricants such as silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide, etc. are added to the magnetic layer. You may.

In addition, non-magnetic abrasive particles may also be added, which include alumina (α-Al ₂ O ₃ , β-Al ₂ O).
₃ , γ-Al ₂ O ₃ , δ-Al ₂ O ₃ , ζ-Al
₂ O ₃ , η-Al ₂ O ₃ , θ-Al ₂ O ₃ , κ-Al ₂
O ₃ , χ-Al ₂ O ₃ , ρ-Al ₂ O _3, etc.), alumina hydrate, alumina silicate, other silicates, silicon carbide,
Boron carbide, other carbides, non-magnetic oxides such as chromium oxide and iron oxide, boron nitride, titanium oxide, silicon oxide, silicon nitride, zirconium oxide, zinc oxide, cerium oxide, magnesium oxide and the like are used. The content of the abrasive is preferably 20 parts by weight or less with respect to 100 parts by weight of the magnetic powder, and the average particle diameter thereof is preferably 0.05 to 6 μm.

As the antistatic agent, carbon black,
Conductive powder such as graphite; cationic surfactant such as quaternary amine; anionic surfactant containing acidic group such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester, carboxylic acid; amphoteric interface such as aminosulfonic acid Activator: A natural surfactant such as saponin is used. The above antistatic agent is preferably added in the range of 0.01 to 40% by weight with respect to the binder.

In order to improve the durability of the constituent layers such as the magnetic layer of the magnetic recording medium of the present invention, various curing agents can be contained, for example, isocyanate can be contained.

Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI) and the like, and adducts of these isocyanates with active hydrogen compounds.
The average molecular weight is preferably in the range of 100 to 3,000.

Examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates with active hydrogen compounds. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds and active hydrogen compounds are preferable.

Examples of the solvent to be added to the coating material for forming the magnetic layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone;
Aromatic hydrocarbons such as benzene, toluene, xylene; alcohols such as methanol, ethanol, propanol, butanol; esters such as methyl acetate, ethyl acetate, butyl acetate; cyclic ethers such as tetrahydrofuran; methylene chloride, ethylene chloride, Examples thereof include halogenated hydrocarbons such as carbon tetrachloride, chloroform and dichlorobenzene.

Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate.

Metals such as Cu, Al and Zn, glass, ceramics such as boron nitride and Si carbide can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or sheet.
It is about 30 μm to 10 mm in the case of a disc or a card, and is cylindrical in the case of a drum, and its shape is determined according to the recorder to be used.

[0037]

EXAMPLES Examples of the present invention will be described below together with comparative examples. The components, ratios, operation sequences, etc. can be variously modified without departing from the spirit of the present invention. In the following examples, all "parts" are parts by weight.

Examples 1-10, Comparative Examples 1-8 Co-γ-FeOx 100 parts Carbon black (average particle size 20 μm) 5 parts α-Al ₂ O ₃ 5 parts Vinyl chloride resin (manufactured by Nippon Zeon Co., Ltd .: MR110) 10 parts Polyurethane resin (as solid content) 10 parts Methyl ethyl ketone Amount Amount Toluene Amount

The above components were kneaded in a pressure kneader (MS pressure kneader manufactured by Moriyama Seisakusho Co., Ltd.) or a continuous kneader (KEX N-30 extruder manufactured by Kurimoto Iron Works Co., Ltd.), and then the following composition Diluted with. (However, Comparative Example 7 does not have a kneading step.) Cyclohexanone Amount Methyl ethyl ketone Amount Toluene Amount Myristic acid 1.5 parts Stearic acid 1.5 parts Butyl stearate 1 part

A polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to this mixture, and the mixture was stirred, dispersed, coated on a polyethylene terephthalate support, oriented with a magnet, and then dried. Further, this was cut into a magnetic recording medium.

Table 1 shows the magnetic powder composition, water content, polyurethane resin type, and kneading method of each example. Also,
The performance evaluation of each example is shown in Table 2.

Each evaluation method is as follows. (A) Glossiness: The glossiness of the sample film (without calendar treatment) after coating was measured at an incident angle of 60 ° at right angles to the coating direction, and displayed with the standard plate as a reference. (B) RF output: The RF output at 4 MHz was measured using a VTR deck for measuring RF output, and the Konica standard tape after 100 times reproduction was shown as the reference tape. (Unit: d
B).

(C) Lumi S / N: A noise meter (925 D / 1) manufactured by Shibasoku Co., Ltd. was used as a measuring instrument, and a standard tape manufactured by Konica was used as a standard tape (0 dB), and the difference was displayed. The high pass filter was 4.2 MHz and the low pass filter was 10 KHz. As the VTR, HR-D120 manufactured by Victor Company of Japan, Ltd. was used (unit: dB).

(D) Chroma S / NAM (C- in Table 2)
Abbreviated as AM); Noise meter 925e manufactured by Shibasoku Co., Ltd. was used, and measurement was performed using an HR-S7000 deck manufactured by Victor Company of Japan (unit: dB).

(E) Sliding noise; (i) Playback is performed without running the tape, and system noise is measured with a spectrum analyzer. (ii) Read the value of the first pass (playback) of the sample tape. (iii) Play the sample tape 10 times for 1 minute each, and
The sliding noise is the difference between the 1st pass and the 10th pass at a noise level near -8MHz.

(F) Diluting trouble after kneading: In the diluting step after kneading, it was checked whether or not there was a work problem due to generation of lumps of the kneaded product, sticking of paddles in the kneader and the like.

The water content of the magnetic powder was measured as follows. That is, Mitsubishi Kasei Micro moisture analyzer CA-
Using O6 type and moisture vaporizer VA-O6 type, magnetic powder approx.
0.1 g was weighed out, vaporized at 120 ° C., the water content obtained at this time was divided by the sample quantity, and this value was expressed as a percentage.

[0048] * 1 Takeda Pharmaceutical Co., Ltd .: Methyl ethyl ketone / toluene solution with a solid content of 40% by weight. * 2 Toyobo Co., Ltd .: Toluene solution with a solid content of 30% by weight.

[0049]

As is clear from the results in Table 2, according to the method of the present invention, no trouble occurs during the dilution after kneading, so that the process control is greatly facilitated. Further, the obtained magnetic recording medium has low sliding noise and exhibits high electromagnetic conversion characteristics.

[Brief description of drawings]

FIG. 1 is an example showing the structure of a pressure kneader.

FIG. 2 is an example of a cross-sectional view of a magnetic recording medium.

[Explanation of symbols]

 1 mixing chamber 2 pressure ram 3 rotor 11 support 12 magnetic layer 13 backcoat layer

Claims (1)

[Claims] 1. A method for producing a magnetic recording medium having a magnetic layer in which magnetic powder is dispersed in a binder, wherein FeOx (where 1.34 ≦ X ≦ 1.42) is used as the magnetic powder. A method for producing a magnetic recording medium, which comprises using a cobalt-containing iron oxide having a water content of 0.7% by weight or less, which is represented, and kneading the magnetic powder with the binder and then dispersing the magnetic powder.