JPH04163718A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To make it possible to improve the fluidity of powder and to perform highly accurate supply in constant quantity by supplying the mixed powder wherein magnetic powder and bonding agent powder are sufficiently mixed as powder raw material into a continuous-type biaxial kneading machine. CONSTITUTION:As powder raw material 3 which is supplied into a kneading part, mixed powder wherein ferromagnetic powder and bonding agent powder are sufficiently mixed is supplied into a continuous biaxial kneading machine 1 by a constant quantity through a constant-quantity feeding device. Namely, the bonding agent powder is resin powder and has the especially excellent fluidity as the powder characteristic. When the powder is sufficiently mixed with th ferromagnetic powder, the fluidity of the mixed powder is improved. Thus, the bonding agent powder has the better fluidity in comparison with that of other powder. When the powder is sufficiently mixed with the magnetic powder beforehand, the fluidity of the powder is improved, the constant quantity can be supplied and the kneading is performed uniformly.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for manufacturing magnetic recording media such as magnetic tapes and magnetic disks.

BACKGROUND OF THE INVENTION Magnetic recording media are usually manufactured by coating a support such as a polyester film with a magnetic paint containing magnetic powder, an antistatic agent, an abrasive, a binder resin, etc., and drying the coating.

When manufacturing this magnetic recording medium, magnetic powder is dispersed in a solvent solution of binder resin using a dispersing machine such as a ball mill or a sand grinder in order to quickly finish the magnetic paint into a paint with good dispersibility. Previously, a series of steps have been known in which magnetic powder and a small amount of binder resin solution are kneaded using a powerful mixer such as a kneader.

In addition, regarding the manufacturing equipment that performs cross-dispersion when preparing magnetic paint and its operating conditions, there is a method of operating a kneading machine under a specific shear stress (the kneading machine uses Nigu), or a method of operating a dispersion machine under specific conditions. Techniques for increasing dispersibility and RF output are known.

Regarding the above-mentioned crosstalk method, please refer to JP-A Nos. 46-3030, 48-10450, 49-14537, 5
No. 3-9102 No. 53-76012, No. 55-254
It is described in No. 06 and No. 57-141026.

With the recent improvement in the recording density of magnetic recording media, magnetic powders with smaller particle sizes and larger specific surface areas are used. However, dispersion of particles becomes rapidly difficult as the particle size becomes smaller.

In order to solve this problem, it is known to knead magnetic powder and binder in a highly concentrated state using a continuous two-shaft mixer while applying high shearing force. As a conventional technique for manufacturing a magnetic recording medium using a continuous twin-screw kneader, there is
-41274, 64-79274, 64-79
No. 275, JP-A-2-107674, etc.

However, in all of the above-mentioned conventional technologies, it is easy to supply a constant quantity to a continuous twin-screw mixer, so when feeding raw materials to a continuous twin-screw mixer, the binder resin is used as the binder resin, while the ferromagnetic powder is used as the powder raw material. If necessary, it is supplied at the same time as the above binder resin solution together with carbon black, alumina, etc. In this case, since the powder raw material generally has poor fluidity, the constant supply flow rate becomes unstable and varies, and poor dispersion is likely to occur due to non-uniform kneading. Therefore, the quality (electromagnetic conversion characteristics, etc.) of the magnetic recording medium itself is adversely affected.

Furthermore, when all the binder is dissolved in an organic solvent solution and then kneaded, it takes time for the binder solution to evenly permeate the entire ferromagnetic powder.

Furthermore, due to this, the kneading time becomes long, especially in continuous kneading, and the stability and reproducibility of kneading deteriorates.

The purpose of the present invention is to improve the fluidity of powder to enable its highly accurate quantitative supply, and to mix the binder with magnetic powder sufficiently to stabilize the powder in a short period of time. The object of the present invention is to provide a method by which the crosstalk can be obtained.

23. Structure of the Invention In other words, the present invention provides a method for preparing a magnetic coating material through a step of supplying and kneading a powder raw material and a liquid raw material. The present invention relates to a method for producing a magnetic recording medium, in which the powder raw material is supplied to a continuous twin-screw kneader.

E, Example The present invention will be explained in detail below.

1 to 4 show the apparatus used to carry out the method according to this embodiment.

First, regarding Figures 1 to 3, we will explain the continuous twin-screw kneader used in this example (KEXN manufactured by Kurimoto Iron Works Co., Ltd.).
30) will be explained.

In this continuous twin-screw kneading machine 1, a mixed powder 3 of magnetic powder and binder powder charged from a powder inlet 2 is sent to a mixing section 5 by a screw conveying means 4, where it is injected with liquid. It is sufficiently kneaded with the binder solution 7 from the inlet 6 under the action of shearing force, and is further sent to the mixed line dilution section 11 by the screw type conveying means 10 together with the binder solution or organic solvent solution 9 from the liquid inlet 8. . Here, if there are several types of powder to be introduced, they are mixed uniformly using a mixer such as a ■-type cone mixer or a W-type cone mixer. feeders, etc.) in a fixed amount. As shown in Figure 2, two parallel rotation axes 1
The above-mentioned conveying means 4.10 are fixed to 2A and 12B as 4A and 4B, 10A and 10B, respectively, and in particular, in the kneading section 5 and kneading dilution section 11, paddles 13A and 13B are rotatable in the same direction. , 14A and 14B are configured so that a sufficient shearing force is applied to the material to be kneaded. As shown in FIG. 3, a pair of paddles 13A and 13B
(or 14A and 14B) are provided at angles shifted from each other, and the above shearing force is generated by rotating so that the tip of one paddle always rubs against the other paddle. Regarding the arrangement of the paddles, the angles formed by the front and rear paddles in the axial direction of a common rotation axis may be shifted by, for example, 45 degrees, and the phases of the left and right paddles can always be shifted by 90 degrees. In addition, various other arrangements of the paddles are possible. Further, the kneading section 5 (or the kneading and diluting section 11 in some cases) is made up of a combination of a plurality of unit barrels 15, and the outer wall of each barrel is formed by an inner wall 17 and an outer wall 18 for passing the cold water 16. It consists of a double structure with a cold water channel 19 in between. In the figure, 20 is a cold water inlet, and 21 is a cold water outlet, which are provided in each barrel 15, respectively.
The cold water channel 19 is blocked between each barrel by a partition wall (not shown).

In addition, the kneaded product 24 obtained with the above-mentioned continuous twin-screw kneader 1
As shown in FIG. 4, the solution is introduced into a dilution/dispersion machine 25 equipped with a stirring blade 30, and diluted by the addition of an organic solvent 26.

After that, the diluted dispersion liquid 27 is passed through a dispersion machine 2 equipped with a stirring plate 31.
8, where it is subjected to dispersion treatment, and if necessary, a curing agent,
A lubricant, an organic solvent, etc. are added to the magnetic paint 29, which is sent to a coating section (not shown). Devices used for dilution and dispersion include daysilver, flow jet mixer, line flow, and the like. A ball mill, a sand mill, etc. can be used for the above-mentioned dispersion@28. When using a sand mill, glass, alumina, zirconia, etc. can be used as a dispersion medium, and zirconia is preferable from the viewpoint of improving dispersibility. After the dispersion device 28, it is preferable to introduce the coating device through a filter.The subsequent steps (coating, orientation, drying, calendering) are carried out in the usual manner, so the explanation will be omitted.As the coating device, gravure There are roll coaters, reverse roll coaters, extrusion coaters, etc.

In the continuous twin-screw kneader 1 configured as described above,
The operation according to the invention is as follows.

That is, as the powder raw material 3 to be supplied to the above-mentioned kneading section, a mixed powder obtained by sufficiently mixing ferromagnetic powder (magnetic powder) and binder powder is supplied in a fixed quantity through a fixed quantity supply device (not shown). . The present inventor has discovered that binder powder (especially vinyl chloride resin powder) is a resin powder and has particularly good fluidity as a powder characteristic, and that by sufficiently mixing the binder powder and ferromagnetic powder, a mixed powder can be obtained. They found that the fluidity of the powder was greatly improved, and therefore it became possible to supply the powder in a fixed quantity with high accuracy. In other words, binder powder has better fluidity than other powders (e.g. alumina), and if we pay attention to this and mix it thoroughly with magnetic powder before supplying it, the fluidity of the powder can be improved. It was discovered that the performance was improved, fixed quantity supply was possible, and crosstalk could be made uniform.

In addition, the binder solution, which was conventionally supplied dissolved in an organic solvent and kneaded, can be mixed evenly into the ferromagnetic powder as a binder powder, and the remaining binder solution and organic solvent can be added. When using the kneading section and kneading and diluting, the time for sufficient kneading is short and a stable kneaded product can be obtained.In other words, by mixing the binder in powder form with the ferromagnetic powder in advance, Since the binder exists evenly around the magnetic powder at the time of this mixing, the kneading time required to achieve a predetermined dispersion state due to cross-wires can be shortened.

The above-mentioned excellent effects are further achieved by setting the amount of binder powder in the mixed powder to 10 to 80% by weight of the total amount of binder required for the magnetic coating, and preferably 20 to 70% by weight.
It is even better to

Moreover, in the above-mentioned mixed powder, it is desirable that the fluidity index of this mixed powder is 60 to 100, more preferably 70 to 100. This fluidity index is desirable for quantitative supply of powder and can be easily controlled by adjusting the amount of binder powder added. Therefore, there is no need to perform surface treatment on the magnetic powder in order to improve the fluidity index.

It is particularly preferable that the fluidity index is 70 to 100.

The above liquidity index is defined as follows.

In calculating the fluidity index, the powder properties were measured using a powder tester (model: P) manufactured by Hosokawa Micron Co., Ltd.
The measurement was carried out at TE). In addition, the liquidity index is “C
chemical engineering''-Janu
The material described in P163 to P168 of ary18, 1965 was used.

The above-mentioned binder powder is preferably a vinyl chloride resin powder, and it is desirable that the amount of the vinyl chloride resin powder added be the total amount of the vinyl chloride resin required for the magnetic coating material. However, as the resin powder to be added, in addition to vinyl chloride homopolymer, vinyl chloride copolymer, urethane resin powder, etc. can also be used.

There is a desirable range for the particle size of the powder constituting the above mixed powder, and for magnetic powder, BET (20 to 80r
rf/g (even 25 to 75 rrf/g), and for binder powder 10 to 1000 μm (even 20 to 75 rrf/g).
600 μm) is good. In addition, alumina and carbon black can also be added, but alumina generally has the property of reducing fluidity, but according to the present invention, it can be made into powder and conversely improve the fluidity as a mixed powder. It was.

In this embodiment, the kneaded material 24 from the continuous twin-screw kneader 1 is made into a state suitable for the next dilution and dispersion device 25 by the kneading section 5 and the following mixing wire dilution section 11, and further , this secondary dilution is diluted and dispersed in a dilution/dispersion device 25 with the addition of at least an organic solvent 26 (which may be different from the organic solvent in the kneader 1) and adjusted to a secondary dilution 27. Ru.

In the above method, the magnetic powder to be added is, for example, 7-Fe, O,, Co-containing rFezC)+, Co
Adhesion 7-Fegos, Fezoa, CO-containing Fe, O
, Co-coated Fe30a, CrOx, and other oxide magnetic powders. Further, metal magnetic powder may be used, or oxide magnetic powder may be used in combination. Usable metal magnetic powders include Fe, Ni, Co, Fe-Al series, Fe
-Al-Ni system, Fe-Af-Co system, Fe-Aj! −
Zn series, Fe-Af-Ca series, Fe-Ni-Co series, F
e-Mn-Zn system, Fe-Ni system, Fe-N1-Af system, Fe-Ni-Zn system, Fe-Co-Ni-Cr system, F
e-Co-N1-P system, Co-Ni system, Fe, Ni.

Examples include ferromagnetic powder such as metal magnetic powder containing Co or the like as a main component. Among them, Fe-based metal magnetic powders containing 80 atm% or more of Fe have excellent electrical properties, and are particularly good in terms of corrosion resistance and dispersibility. , Fe-AN-N i, Fe
-Aj! -Zn, Fe-Af-Co, Fe-Ni, Fe
-Ni-A1 and Fe-Ni-Zn metal magnetic powders are preferred. As an additive to these metal magnetic materials, S
i, Cu5ZnSAn.

Elements such as P, Mn, and Cr or compounds thereof may be included. Hexagonal ferrite such as barium ferrite and iron nitride are also used.

Examples of the binder (binder resin) include urethane resin, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer. Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic reactive resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high Examples include mixtures of molecular weight diols/isocyanates and mixtures thereof.

At least one endogenous component of the above-mentioned resin includes -3O3M,
-COOM, -PO(OM')! (However, M, M'
is preferably a resin containing a hydrophilic polar group (negative functional group) represented by hydrogen, an alkali metal such as lithium, potassium, or sodium, or a substituted or unsubstituted hydrocarbon residue. The metal of the salts, such as sulfonic acids, carboxylic acids or phosphoric acids, is an alkali metal (especially sodium, potassium, lithium). The amount of the modified group (polar group) introduced is 0.
．． 01~1.0+wmo j! / g, preferably 0.1 to 0.5 meao l
/H range. The above polar group introduction amount is 1.0 mmo
j! If it exceeds /g, intermolecular or intramolecular aggregation tends to occur, which not only adversely affects dispersibility, but also causes selectivity to the solvent, which may make ordinary general-purpose solvents unusable. The above polar group introduction amount is 0.01m
If it is less than 5+o 12 /g, sufficient effect in dispersing the ferromagnetic powder will not be recognized.

In particular, it is preferable to use at least a urethane resin, and it is also preferable to use a vinyl chloride copolymer, an epoxy resin (especially a phenoxy resin), a polyester resin, or a nitrocellulose resin (hereinafter referred to as other resins). good.

In this case, the blending ratio of the urethane resin and the other resin is 90 to 10 parts by weight, more preferably 80 to 10 parts by weight.
Desirably, the amount is 20 parts by weight. If the above blending ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is significantly deteriorated, and the adhesion to the support is also poor. If the ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

Furthermore, in the present invention, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing the binder resin.

In addition to the magnetic powder and binder resin described above, various additives may be added at any step. As a lubricant, fatty acids and/or fatty acid esters such as myristic acid and butyl stearate can be added. As a result, while demonstrating the respective features of both, it offsets the defects that occur when used alone, improves the lubrication effect, and improves the durability of still images.
Running stability, S/N ratio, etc. can be improved. In addition to fatty acids and fatty acid esters, other lubricants (for example, silicone oil, carboxylic acid modification, ester modification, etc.) may be added. Furthermore, in addition to the above-mentioned lubricants, known abrasives (for example, alumina), antistatic agents (for example, carbon black), etc. may also be added.

When adding each of the above-mentioned additive substances at the time of kneading and dilution, it is preferable to use substances dispersed in a separate process.

Usable solvents include ketones (e.g. methyl ethyl ketone), ethers (e.g. diethyl ether),
Examples include esters (for example, ethyl acetate), aromatic solvents (for example, //yr)Ss), and these can be used alone or in combination.

Next, the method according to this embodiment will be explained in more detail using a specific example.

The apparatus shown in FIGS. 1 to 4 was operated under the following conditions.

According to the flowchart shown in FIG. 5, the steps from kneading to dilution of each component having the composition shown in Tables 1, 2, and 3 were carried out.

The following raw materials were added to the above-mentioned kneaded and diluted solution, diluted to an appropriate viscosity, and then dispersed using a daysilver, sand mill, etc.

Stearic acid 1.0 parts by weight Oleic acid 1.0 parts by weight Butyl stearate 1.0 parts by weight Cyclohexanone Appropriate amount Methyl ethyl ketone
Appropriate amount of toluene 5.0 parts by weight of a polyisocyanate compound was added to the obtained magnetic paint in an appropriate amount, and the mixture was coated on a polyethylene terephthalate base, oriented, dried, and cut into % inch width to obtain a magnetic tape.

(Margin below) Table 1 (powder) *1) C is compression degree.

Table 2 $2) E620 is methyl ethyl ketone/toluene = 17
1 with a solid content of 40% by weight solution (polyurethane with no polar groups in the resin) l iτA-r'-+ N It was made into a tape.

Table 4 Examples and comparative examples "Actual" indicates an example, and "ratio" indicates a comparative example (the same applies hereinafter).

The following measurements were performed on each sample or tape obtained above, and the results are shown in the table below.

<Output and comparison example during playback with 100% RF ratio output white signal -
] was used as a standard for comparison.

<Chroma output> 500 KHz using a VTR deck for measuring chroma output
The chroma output was measured (unit: dB).

<Chroma S/N> Using a noise meter (manufactured by Shibatsu), the difference in S/N of the sample in a 100% white signal was determined in comparison with a reference tape (Comparative Example-1).

Necessary residence time during kneading> The raw materials for the mixed powder, the binder dissolved in the organic solvent, and the organic solvent were started to be supplied, and the glossiness after dispersion was determined.The time required to obtain the kneaded product was determined.

The results are shown in Table 5 below.

(Hereinafter referred to as margin) Table 5 From this result, by performing crosstalk based on the present invention,
Sufficient and uniform crosstalk and dilution can be performed during the short sewing time Z, and the electromagnetic conversion characteristics of the medium can be greatly improved.

The embodiments described above can be modified in various ways based on the technical idea of the present invention.

For example, the above-mentioned continuous twin-screw kneader is
The kneader described in No. 1274 (no kneading/dilution section) may be used, or a single-screw kneader may be used.

A continuous twin-screw kneader may be followed by a dilution kneader. The configuration of the continuous twin-screw kneader may be varied in various ways; for example, the shape and arrangement of the paddles are not limited to those described above.

As described above, the present invention supplies a mixed powder obtained by sufficiently mixing magnetic powder and binder powder as the powder raw material supplied to the kneading section. The fluidity of the mixed powder is particularly good, and by sufficiently mixing the powder with the magnetic powder, the fluidity of the mixed powder becomes thicker (improved), thus making it possible to supply the powder in a fixed quantity with high precision.

In addition, by uniformly mixing the binder powder into the magnetic powder in advance, when adding and kneading the remaining binder solution or organic solvent, the time required for sufficient kneading can be shortened, and A stable kneaded product can be obtained.

[Brief explanation of drawings]

The drawings illustrate the present invention; Fig. 1 is a schematic cross-sectional view of a continuous twin-screw kneader used for manufacturing magnetic recording media, and Fig. 2 is a schematic cross-sectional view of the kneader. Fig. 3 is a cross-sectional perspective view of a part of the same heating kneader, Fig. 4 is a schematic flow chart showing the main steps for preparing magnetic paint, and Fig. 5 is a schematic flow chart during kneading and kneading dilution. . In addition, in the symbols shown in the drawings, 1... Continuous twin-screw kneader (kneader) 2
......Powder inlet 3...Powder 4.10...Screw type conveyance means 5.
Kneading section 6.8 Inlet a... Binder solution 9 Binder solution Or organic solvent 11...
......Kneading and diluting section 12.12A, 12B...Rotating shaft 13.
13A, 13th, 14.14A, 14B...
...Paddle 15...Barrel 24...Kneaded material 25...Dilution and dispersion machine 28...Dispersion It is a machine. Agent Patent Attorney Hiroshi Renkan Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] 1. When preparing a magnetic paint through the step of supplying and kneading powder raw materials and liquid raw materials, a mixed powder in which magnetic powder and binder powder are sufficiently mixed is used as the powder raw material in a continuous method 2. A method of manufacturing a magnetic recording medium to be supplied to an axial kneader.