JPH04288374A - Production of magnetic coating material - Google Patents

Abstract

PURPOSE:To industrially produce the starting material for a magnetic coating material which can be dispersed easily and satisfactory within a short time in the form of a fine magnetic powder (especially one with a mean particle size of 0.2mum or below). CONSTITUTION:A mixture is obtained by kneading a 0.2mum or smaller magnetic powder with a binder resin and an organic solvent on a continuous twin-screw kneader having a ratio of the shaft length of the agitator shaft to its diameter of 25 or above and a clearance between the wall of the barrel and the edge of the paddle of 0.2mm or below, or this mixture is further mixed with an ogranic solvent to obtain a diluted mixture. The metallic magnetic particle powder based on magnetically and chemically unstable ferrous iron-containing magnetic iron oxide or iron can be transported or stored by simply vaccum- packaging it with a plastic film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is useful in producing magnetic paints by using fine magnetic particles, especially those with an average particle diameter of 0.2 μm or less, to quickly and easily achieve excellent dispersibility. The present invention relates to a method for manufacturing a material for magnetic paint that can exhibit the following properties.

0002

[Background Art] In recent years, as magnetic recording and reproducing equipment for video and audio has become longer recording time, smaller and lighter, the performance of magnetic recording media such as magnetic tapes and magnetic disks has improved, that is, high-density recording. There is an increasing demand for higher and lower noise levels.

[0003] Particularly, in recent years, there has been an increasing demand for higher image quality on videotapes, and the frequency of recorded carrier signals has become higher and higher than in conventional videotapes, that is, in the short wavelength region. has been moved to
As a result, the depth of magnetization from the surface of the magnetic tape has become significantly shallower.

[0004] Therefore, efforts are being made to maintain and further improve high output characteristics, especially the CN ratio, even for short wavelength signals.
High dispersion of magnetic particles, (1) smoothing of the magnetic coating surface, and (2) thinning of the magnetic coating layer are required.

[0005] This fact is explained, for example, in ``Development of magnetic materials and high dispersion technology of magnetic particles'' published by Sogo Gijutsu Center Co., Ltd.
1982), p. 312, ``The conditions for high-density recording in coated tapes are to be able to maintain high output characteristics with low noise for short wavelength signals, but to do so, the coercive force Hc and It is necessary for both the residual magnetization Br to be large and the thickness of the coating film to be thinner.'' and Nikkei Electronics (1976) May 3 issue No. 82-1.
"Physical quantities of the tape that are related to the SN ratio (CN ratio) of the luminance signal include the average number of particles per unit volume, their dispersion state (dispersibility), and surface smoothness." on page 05. If the dispersibility is constant, S is proportional to the square root of the average number of particles.
Since the N ratio is better, magnetic powders with smaller particle volumes and higher filling degrees are more advantageous. ” as stated.

[0006] In recent years, there has been a remarkable trend toward finer magnetic particles in order to improve high output characteristics for short wavelength signals, and in particular, finer magnetic particles with an average particle size of 0.2 μm or less have been used. It is used.

On the other hand, as the magnetic particles become finer, the dispersibility of the magnetic particles in the vehicle decreases, and as a result, the surface smoothness of the obtained magnetic coating film becomes worse, making it difficult to make the film thinner. It becomes difficult. Therefore, there is a need for a magnetic paint that can easily exhibit excellent dispersibility even in the case of fine magnetic particles in a short period of time.

In recent years, magnetic particles suitable for high-output and high-density recording, that is, magnetic particles having a high coercive force, such as magnetic iron oxide particles containing ferrous iron and metal magnetic particles mainly containing iron, have been developed. powder is known.

Magnetic iron oxide particles containing ferrous iron have larger coercive force and saturation magnetization than maghemite particles that do not contain ferrous iron, and have high electrical conductivity, so they are suitable for use in magnetic recording media. Magnetite (FeOx ・Fe2 O3
0<x≦1) particles and magnetic iron oxide particles (hereinafter referred to as (referred to as Co magnetized iron oxide particle powder).

Although the magnetic iron oxide particles containing ferrous iron and the metal magnetic particles containing iron as a main component have a high coercive force, they have the disadvantage of being magnetically and chemically unstable. However, it has been pointed out that there are problems with workability and safety when producing magnetic particles, as well as safety and economical issues during transportation and storage.

That is, when magnetic iron oxide particles containing ferrous iron are left in the air, the ferrous iron is oxidized to become ferric iron.
Along with this, a phenomenon occurs in which the magnetic properties, particularly the coercive force, decrease over time. This phenomenon tends to become particularly noticeable as the particles become finer.

[0012] In addition, the coercive force of metal magnetic particles whose main component is iron improves as the particle size becomes finer, but on the other hand, the surface activity of the particles becomes extremely large and they rapidly interact with oxygen in the air. Extreme care must be taken when handling it, as it generates heat in response to , and in severe cases, it may ignite, resulting in a decrease in coercive force and saturation magnetization.

[0013] In addition, metal magnetic particles whose main component is iron, which poses the risk of heat generation and ignition, can be prepared by a method in which the magnetic particles are sufficiently wetted with an organic solvent and then sealed in a metal container such as a can. Transportation and storage are carried out by placing the magnetic particles in a metal container, purging it with inert gas, and sealing it, and there are safety issues due to the use of organic solvents, as well as packaging, handling, and transportation. There were operational and economic problems such as space and storage space.

[0014] Therefore, when transporting and storing magnetic iron oxide particles containing ferrous iron and metal magnetic particles whose main component is iron, it is important to transport and store them in a safe and simple packaging with as little risk as possible. An economical method that minimizes transportation and storage space is required.

Conventionally, in order to improve the dispersibility of magnetic particles, magnetic paints are prepared by dispersing magnetic particle powder, binder resin, organic solvent, etc. in a vehicle using a dispersing machine such as a ball mill or a sand grinder. After kneading into a kneaded product using a kneader with high shear force, a planetary mixer, a disper, a twin-screw continuous kneading mixer, etc., the mixture is diluted to an appropriate solid content concentration. There is. (JP-A-62-22867, JP-A-64
-79274, JP-A-64-79275)

[0016]

[Problems to be Solved by the Invention] Magnetic paints that can quickly and easily exhibit excellent dispersibility even with fine magnetic particles are currently in greatest demand. In the case of using the above-mentioned known method, the dispersion of magnetic particles in the magnetic paint obtained is due to the fact that the shear stress on the magnetic particles does not work sufficiently during kneading because the magnetic particles used are fine. Sex was still not enough.

Therefore, in the present invention, the average particle size is 0.2 μm.
To produce a material for magnetic paint that can easily exhibit excellent dispersibility in a short time by applying sufficient shear stress during kneading even with the following fine magnetic particles. is a technical issue.

[0018]

[Means for Solving the Problems] The above technical problems can be achieved by the present invention as follows.

That is, the present invention comprises a container and two rotatable, parallel-bearing stirring shafts disposed inside the container, in which magnetic particles, a binder resin, and an organic solvent are mixed.
In a method for producing a material for a magnetic coating material, which is made into a kneaded material by kneading using a twin-screw continuous kneading mixer in which the stirring shaft has alternating screw parts and paddle parts attached to the stirring shaft. Or, if necessary, in a method for producing a material for a magnetic coating material, the method further comprises adding a solvent to the kneaded material, and then kneading and diluting the kneaded material using the twin-screw continuous kneading mixer to obtain a kneaded diluted product. The average particle size of
or less, and the ratio of the axial length to the axial diameter of the stirring shaft is 2.
5 or more and the clearance between the wall of the container and the end of the paddle is 0.2 mm or less.

Next, various conditions for implementing the present invention will be described.

The magnetic particles used in the present invention include maghemite particles, magnetite particles, and bertolide compounds (FeOx ・Fe2 O3, 0<x<1
), magnetic iron oxide particles containing different metals other than Fe such as Co, Al, Ni, P, and Zn, or magnetic iron oxide particles containing C
metal magnetic particles containing iron as a main component, iron alloy magnetic powder containing other than iron such as Co, Ni, Al, P, B, etc., plate-shaped Ba ferrite particle powder, and resistant to these particles. Divalent metals such as Co, Ni, and Zn, which are magnetic force reducers, and Ti
Any of plate-shaped composite ferrite particles containing one or more of tetravalent metals such as , Sn, and Zr can be used. Further, the shape of the magnetic particles may be acicular, spindle-shaped, cubic, plate-shaped, or the like.

In the present invention, the average particle diameter is 0.2μ, which is suitable for improving high output characteristics for short wavelength signals.
Fine magnetic particle powder of less than m is used. The lower limit of the magnetic particle powder is 0.05 μm, and if it is less than 0.05 μm, it becomes difficult to disperse it in the magnetic paint.

The binder resin used in the present invention includes vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate maleate urethane elastomer, butadiene acrylonitrile copolymer, and polyvinyl butyral, which are currently widely used in the production of magnetic recording media. , cellulose derivatives such as nitrocellulose, synthetic rubber resins such as polyester resins and polybutadiene, epoxy resins, polyamide resins, polyisocyanate polymers, electron beam-curable acrylic urethane resins, and mixtures thereof.

[0024] In recent years, instead of the conventionally widely used resins having OH groups, resins having stronger polar functional groups, such as COOH groups, SO3 M(Na, K, H)
, OPO3 H2 groups, etc. are used, and it has been confirmed that these binder resins also exhibit excellent dispersibility.

The organic solvent used in the present invention includes one or more of aromatics such as toluene and xylene, ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and tetrahydrofuran, and esters such as ethyl acetate and butyl acetate. can be used.

In the present invention, the magnetic particle powder, binder resin, and organic solvent are kneaded by a method of simultaneously kneading these raw materials, a method of kneading an organic solvent containing a binder resin prepared in advance, and a magnetic particle powder, a method of kneading the magnetic particle powder in advance, Any method may be used, such as mixing the particle powder and an organic solvent, then adding a binder resin and kneading, but it is preferable to knead the organic solvent containing the binder resin prepared in advance and the magnetic particle powder. .

[0027] The solid content concentration in the kneaded material in the present invention is:
It is 60-85% by weight, preferably 67-80% by weight. If it is less than 60% by weight, the viscosity of the kneaded product will be extremely low and the shear stress necessary for dispersing the magnetic particles will not work. If it exceeds 85% by weight, the particle surfaces of the magnetic particles will not be sufficiently wetted by the solvent or the binder resin, resulting in uneven distribution of the magnetic particles in the kneaded material.

[0028] In the present invention, the amount of binder resin based on the magnetic particle powder in the kneaded product is 5 to 30% by weight. If the amount is less than 5% by weight, sufficient surface adsorption of the binder resin required for dispersing the magnetic particles will not be achieved, resulting in poor dispersion of the magnetic particles in the resulting magnetic paint. 3
When the amount exceeds 0% by weight, the magnetic particles are sufficiently dispersed in the magnetic coating material, but the saturation magnetic flux density of the coating film decreases due to the binder resin which does not participate in magnetism. The kneaded material obtained in the present invention has a columnar or granular shape with an average diameter of about 1 to 20 mm.

The kneaded product of the present invention is diluted by adding an organic solvent to the kneaded product so that the solid content concentration is 30% by weight or more and less than 60% by weight. If it is less than 30% by weight,
Due to rapid dilution, it is not diluted uniformly, and the distribution of magnetic particles in the kneaded material tends to become non-uniform. If it exceeds 60% by weight, dilution will be insufficient and it will be difficult to achieve the optimum viscosity for dispersion in the subsequent dispersion step.

[0030] In the present invention, dispersants, lubricants, abrasives, antistatic agents such as carbon black, etc., which are commonly used in producing magnetic paints, may be added. Carbon black, which is difficult to disperse, is preferably added from the beginning during kneading, and depending on the gap between the magnetic particles, the effect of improving mutual sliding between the magnetic particles can also be obtained.

The twin-screw continuous kneading mixer used in the present invention consists of a container and two rotatable and parallel-bearing stirring shafts disposed inside the container, and the stirring shafts are connected to a screw portion. and paddle parts attached to the stirring shaft, the kneading action is mainly performed by the pair of paddles, and the screw mainly performs the feeding action.

The ratio of the axial length to the axial diameter of the stirring shaft of the twin-screw continuous kneading mixer is 25 or more, preferably 30 to 40 in practice. When the ratio of the axial length to the axial diameter of the stirring shaft is less than 25, it is possible to produce a magnetic paint material that can easily exhibit excellent dispersibility in a short period of time, which is the objective of the present invention. Can not do it.

The clearance between the container wall and the paddle end is 0.2
mm or less, preferably 0.18 mm or less. When the clearance between the wall of the container and the end of the paddle exceeds 0.2 mm, the objective of the present invention is to produce a magnetic paint material that can easily exhibit excellent dispersibility in a short period of time. I can't.

As the twin-screw continuous kneading mixer in the present invention, commercially available KEX-30 and KE manufactured by Kurimoto Iron Works Co., Ltd.
X-40, KEX-50, KEX-65, KEX-80
, KEX-100, KEX-125, and KEX-160 can be used.

[0035]

[Operation] First, the most important point in the present invention is that the magnetic particles, the binder resin, and the organic solvent are mixed using a container and two rotatable stirring shafts mounted in parallel that are disposed inside the container. A magnetic paint material which is made into a kneaded product by kneading it using a twin-screw continuous kneading mixer, the stirring shaft of which has alternating screw parts and paddle parts attached to the stirring shaft. In the manufacturing method, when a twin-screw continuous kneading mixer is used, the ratio of the axial length of the stirring shaft to the shaft diameter is 25 or more, and the clearance between the container wall and the paddle end is 0.2 mm or less. Even with fine magnetic particles, especially 0.2 μm or less, sufficient shear stress is applied during kneading, so that magnetic paint can be manufactured quickly and easily. The fact is that it is possible to obtain a magnetic coating material that can exhibit excellent dispersibility.

In the present invention, the dilution of the kneaded material is carried out using a two-screw type continuous kneading mixer in which the ratio of the axial length to the shaft diameter of the stirring shaft is 25 or more, and the clearance between the wall of the container and the end of the paddle is 0.2 mm or less. When a magnetic paint is produced using a machine, a magnetic paint material that can easily exhibit superior dispersibility can be obtained in a short period of time.

The kneaded product obtained in the present invention contains magnetically and chemically unstable magnetic particle powders such as acicular magnetic iron oxide particles containing ferrous iron and metal magnetic particles containing iron as a main component. Even in this case, as shown in the Examples below, oxidation by oxygen in the air is sufficiently prevented, and it is extremely stable magnetically and chemically.

The reason why the magnetic particles in the kneaded product obtained in the present invention are magnetically and chemically stable is that the reason is that the shear stress is sufficiently applied during kneading.
．． Even with fine magnetic particles of 2 μm or less, the surface of the particles is thoroughly wetted with organic solvent, and a continuous coating of binder resin is formed, which sufficiently prevents oxidation due to oxygen in the air, etc. I think this is probably because they were able to do so.

[0039] Conventionally, a biaxial continuous kneading mixer is used for kneading magnetic particles, binder resin, and organic solvent, as disclosed in the above-mentioned JP-A-64-79274 and JP-A-64-79275. There is a method described, but this twin-screw continuous kneading mixer has a ratio of the axial length to the shaft diameter of the stirring shaft of 10.
The clearance between the container wall and the end of the pawl is 0.5 mm or more, making it impossible to achieve the object of the present invention.

[0040]

EXAMPLES Next, the present invention will be explained with reference to Examples, Comparative Examples, and Usage Examples. The long axis and axial ratio (long axis diameter/short axis diameter) of the magnetic particles in the following Examples, Comparative Examples, and Usage Examples are shown as average values of values measured from electron micrographs. The magnetic properties of the magnetic particles and the magnetic recording medium were measured using a "Vibrating Sample Magnetometer VSM-3S-15" (manufactured by Toei Kogyo Co., Ltd.) by applying an external magnetic field of up to 10 KOe.

In addition, when a magnetic recording medium is manufactured using plate-shaped Ba ferrite fine particles as magnetic particles, the values of coercive force, residual magnetic flux density, and squareness are determined by magnetic field orientation perpendicular to the tape surface. Perpendicular coercive force, saturation magnetic flux density, residual magnetic flux density, and square shape (Br/Bm) of magnetic recording media
), and the coercive force is shown as the measured value, and the saturation magnetic flux density, residual magnetic flux density, and square shape are shown as the values after demagnetizing field correction.

[0042]S. F. The measurement of D was obtained by obtaining a differential curve of the demagnetization curve of the magnetic hysteresis curve using the differential circuit of the magnetic measuring instrument, measuring the half-width of this curve, and dividing this value by the coercive force. .

When the magnetic particles contained in the kneaded product are magnetic iron oxide particles containing ferrous iron or metal magnetic particles whose main component is iron, the oxidation stability is determined between the kneaded product immediately after production and the one immediately after production. The coercive force value and saturation magnetic flux density value of the coating film obtained using each of the kneaded products after 7 days of vacuum packaging the kneaded products in an atmosphere with a temperature of 60 ° C. and a relative humidity of 90%. It was determined by multiplying the change value by the saturation magnetic flux density value and coercive force value immediately after manufacture.

The glossiness of the coating film is a value measured with a gloss meter manufactured by Nippon Denshoku Kogyo Co., Ltd. at an incident angle of 45°.
The value is expressed in percentage when the standard plate gloss is 86.3%.

The surface roughness of the coating film was measured using a surface roughness meter Surfcom 570A (manufactured by Tokyo Seimitsu Co., Ltd.) using a JIS B
Surface roughness was measured according to 0601. Surface roughness is "center line average roughness (Ra)" and "root mean square roughness (RMS)"
”.

<Production of kneaded product> Examples 1 to 8 Comparative Examples 1 to 8; Example 1 The ratio of the axial length to the shaft diameter of the stirring shaft was 38, and the clearance between the wall of the container and the end of the paddle was Using a twin-shaft continuous kneading mixer "KEX-30" (manufactured by Kurimoto Iron Works Co., Ltd.) with a diameter of 2 mm, the long axis was 0.15 μm, the axial ratio (long axis diameter: short axis diameter) was 8, and the coercive force was 1590. Oe, saturation magnetization 135e
Acicular alloy magnetic particle powder mainly composed of iron of mu/g 10
Kg and carbon black #3150 (Mitsubishi Kasei Corporation)
3.83Kg of mixed powder with 0.3Kg from the powder supply port
/ hour, and the resin liquid (ME) with a concentration of 17.1%
K/Anon=1/1) MR-110 (Nippon Zeon Co., Ltd.)
) was continuously supplied from the liquid side supply port at a rate of 2.17 kg/hour, and kneaded and mixed at a rate of 6.5 kg/hour to obtain a pellet-like kneaded product with a solid content concentration of 70% by weight. .

Examples 2 to 8, Comparative Examples 1 to 8 Same as Example 1 except that the type of magnetic particles, the amount of carbon black, the type of resin liquid, the type of kneader, and the amount of kneading were varied. A kneaded product was obtained in the same manner. Table 1 shows the main manufacturing conditions.

<Production of kneaded diluted product> Examples 9 to 19 Comparative Examples 9 to 16; Example 9 19.4 g of the kneaded product obtained in Example 1 (acicular metal magnetic particle powder containing iron as the main component) 12g, resin: 1.44g,
Carbon black: 0.36g, mixed solvent of methyl ethyl ketone and cyclohexanone (mixing ratio 1:1): 5
．． 6g) and 8.2g of the above mixed solvent (mixing ratio 1:1) were kneaded and diluted for 2 hours using a paint conditioner (manufactured by Toyo Seiki Co., Ltd.) to obtain a kneaded dilution with a solid content concentration of 50% by weight. .

Examples 10 to 19, Comparative Examples 9 to 16 The same procedure as in Example 9 was carried out except that the type and amount of the kneaded product, the amount of organic solvent, the type of kneading diluter, and the kneading dilution time were varied. A kneaded dilution was obtained. Table 2 shows the main manufacturing conditions at this time.
Shown below.

<Manufacture of magnetic coating film> Usage Examples 1 to 19 Usage Example 1 27.6 g of the kneaded dilution obtained in Example 9 and auxiliary raw materials in proportions to form a magnetic paint having the following composition were mixed into a 1.5 mm diameter The mixture was added to a 140 ml glass bottle along with 95 g of glass beads, and dispersed in a paint conditioner for 12 hours to obtain a magnetic paint with a solid content concentration of 30% by weight.

[0051] A part of the kneaded material was taken out 6 hours after the start of dispersion, and the gloss of the magnetic coating film produced in the same manner as described below was 123%, indicating that it was dispersed in a short time. It was recognized that

[0052] Apply the magnetic paint using an applicator.
After coating on the ET film, it is oriented, dried, and then 1/
After slitting it into 2-inch widths, it was cured at 60° C. for 24 hours to produce a magnetic coating film.

Composition of magnetic paint Acicular alloy magnetic particle powder mainly composed of iron
12g resin

2.88g carbon black
0.36g alumina
1.2g
lubricant

0.3g hardening agent

0.6g MEK

20.44g toluene

12.27g cyclohexanone

8.18g

The magnetic coating has a coercive force of 1559 Oe, a square shape of 0.85, an orientation degree of 2.95, a saturation magnetic flux density of 3690 Gauss, a residual magnetic flux density of 3140 Gauss, and a S.O. F. D. is 0.
493, gloss is 139, and surface roughness Ra is 25.
8 nm, RMS was 32.0 nm.

[0055] Oxidation stability is also determined by the rate of change in coercive force -
3.2%, the rate of change in saturation magnetic flux density is -6.8%,
It was recognized that the oxidation stability was excellent.

Use Examples 2 to 19 Magnetic paints were produced in the same manner as Use Example 1, except that the type of kneading diluent and the dispersion time were varied. Table 3 shows the main manufacturing conditions and various properties of the magnetic coating material obtained. The gloss of the magnetic coating films produced in Use Examples 10, 11, and 18 showed values of 2-hour and 6-hour dispersion, respectively.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

[0060]

[Effects of the Invention] According to the method for producing a material for magnetic paint according to the present invention, as shown in the above example, fine magnetic particles can be easily produced in a short time when producing a magnetic paint. Since it is possible to produce a magnetic coating material that exhibits excellent dispersibility, it is ideal for high-density recording and low noise level, which are currently most required.

[0061] In the present invention, the particle surfaces of the magnetic particles in the obtained kneaded material are sufficiently wetted with an organic solvent, and a continuous coating of binder resin is formed on the particle surfaces, so that In particular, it is possible to sufficiently prevent magnetic iron oxide particles containing ferrous iron and metal magnetic particles whose main component is iron from being oxidized by oxygen in the air, so wet the magnetic particles sufficiently with an organic solvent. Without sealing a metal container such as a can or purging an inert gas into the metal container such as a can, the oxygen permeability resistance,
It also has the effect of being able to be transported and stored simply by packaging it with a plastic film that is water resistant (not easily permeable to water and water vapor) and solvent resistant.

Claims (2)

[Claims] Claim 1: Magnetic particle powder, binder resin, and organic solvent are mixed into a container and two rotatable stirring shafts mounted in parallel and arranged inside the container, the stirring shafts having a screw portion. In a method for producing a material for magnetic paint, the magnetic particle powder is kneaded into a kneaded material by using a twin-screw continuous kneading mixer having alternating paddle parts attached to the stirring shaft. The average particle size is 0.2 μm or less, the ratio of the axial length to the shaft diameter of the stirring shaft is 25 or more, and the clearance between the wall of the container and the end of the paddle is 0.2 mm or less. A method for producing a magnetic paint material, characterized by using the twin-screw continuous kneading mixer. 2. Magnetic particle powder, binder resin, and organic solvent are mixed into a container and two rotatable stirring shafts mounted in parallel and arranged inside the container, the stirring shafts having a screw portion. A kneaded product is obtained by kneading using a two-screw type continuous kneading mixer which has alternating paddle parts attached to the stirring shaft, and then, after adding a solvent to the kneaded material, the two-screw continuous kneading mixer is used. In a method for producing a magnetic paint material, which is kneaded and diluted using a type continuous kneading mixer to obtain a kneaded diluted product,
The average particle size of the magnetic particles is 0.2 μm or less,
Further, the ratio of the axial length to the axial diameter of the stirring shaft is 25 or more, and the clearance between the wall of the container and the end of the paddle is 0.
A method for producing a material for magnetic paint, characterized in that the above-mentioned twin-screw continuous kneading mixer having a diameter of 2 mm or less is used.