JPH0970569A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a magnetic recording medium by which the filtration flow rate is increased even when a filter having a relatively-small-diameter pore is used in filtration, and the clogging of the filter is suppressed. SOLUTION: A magnetic coating material prepared by mixing and dispersing a magnetic powder and a binder in org. solvent is introduced from the coating material inlet 10 of a filter housing 8 contg. a filter 9 and filtered. In this case, a coating material circulating outlet 12 is formed on the housing 8, and a part of the coating material introduced into the housing 8 is discharged from the outlet 12 before being passed through the filter 9 and again introduced from the inlet 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a so-called coating type magnetic recording medium, and more particularly to improvement of a method for filtering magnetic paint.

[0002]

2. Description of the Related Art For example, as a floppy disk, a data cartridge, an audio tape, a video tape,
The so-called coating type magnetic recording medium is predominant. In this coating type magnetic recording medium, a magnetic coating material prepared by mixing and dispersing magnetic powder, a binder and various additives in an organic solvent is coated on a base film and dried to form a magnetic layer. It is a thing.

In such a coating type magnetic recording medium, in recent years, the magnetic layer has been made thinner and the recording wavelength has been shortened.
Therefore, minute defects existing on the surface of the magnetic layer increase noise and dropouts, and often become a serious problem in terms of the quality of the medium.

The surface defects of the magnetic layer are caused by foreign matters such as undispersed agglomerates, reaggregates, and contaminants existing at the stage of magnetic coating. Many of these causative substances are small in size, and how to remove such causative substances becomes an important issue.

As a method for removing the cause of surface defects from the magnetic paint, it is usually adopted to provide a filtration step in a suitable position in the liquid feed system for the magnetic paint.

An example of the filtration system used in this filtration step is shown in FIG.

In this filtration system, a paint stirring device 21 for stirring the paint, a liquid feed pump 26 for controlling the flow rate of the paint, and an annular filter 22 made of a porous material are housed in a filter housing 23. The filter device 27 is formed by being arranged in this order. In this filter device 27, the filter housing 2
3 is formed in a cylindrical shape slightly larger than the filter 22 accommodated therein, and a paint inlet 24 for allowing paint to flow into the filter housing is provided on the upper side of the peripheral surface thereof. A paint outlet 25 is provided on the bottom surface of the filter housing 23 so as to correspond to the space inside the ring of the filter 22.

In this filtration system, the paint stirring device 21
The paint agitated in (1) flows into the filter housing 23 from the paint inlet 24 of the filter device 27 and passes through the filter 22. Foreign substances such as undispersed aggregates, reaggregates, and contaminants are removed from the paint when passing through the filter 22. Then, the paint that has passed through the filter 22 and reached the space inside the ring of the filter is the paint outlet 25.
To the outside, and will be used for the subsequent coating process.

[0009]

As described above, the removal of the causative agent of the surface defect is carried out in the filtration step using a filter. At this time, in order to remove even the causative agent, the pore size of the filter is small, It is necessary to use a highly accurate one.

However, when the pore size of the filter is small, the passage resistance of the paint is increased and the pressure loss is increased. Therefore, if an attempt is made to carry out filtration within the differential pressure limit of the filter, the filtration flow rate will be greatly limited, and the filtration efficiency will inevitably decrease.

Further, when the operation is continued under the condition that the flow rate is small, there is a portion where the paint is stagnant in the line or the filter housing, and gel reaggregates are easily generated in this portion. When this reaggregate is captured by the filter, there is a phenomenon that clogging occurs and the filtration flow rate is accelerated, and it is necessary to frequently stop the coating device and replace the filter. Becomes

For this reason, the workability and the operating rate of the coating device are deteriorated, and the yield of the coating material is lowered, which causes inconveniences.

Therefore, the present invention has been proposed in view of such a conventional situation, and the filtration flow rate can be increased even when a filter having a relatively small pore size is used in the filtration step, and It is an object of the present invention to provide a method for manufacturing a magnetic recording medium in which the clogging of the magnetic recording medium is suppressed.

[0014]

In order to achieve the above object, in the method of manufacturing a magnetic recording medium of the present invention, magnetic powder and a binder are mixed with an organic solvent from a paint inlet of a filter housing in which a filter is housed. When a magnetic paint prepared by mixing and dispersing in it is filtered and filtered with a filter, a paint circulation outlet is provided in the filter housing, and a part of the paint that has flowed into the filter housing is passed through the filter. It is made to flow out from the circulation outflow port, and again to be made to flow in from the paint inflow port.

At this time, it is preferable that the flow rate of the magnetic paint flowing out from the paint circulation outlet of the filter housing is equal to or higher than the flow rate of the magnetic paint passing through the filter. Further, a paint disperser may be provided immediately before the paint inlet of the filter housing.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described with reference to the drawings.

In the coating type magnetic recording medium, the magnetic layer is formed by coating a non-magnetic support with a magnetic coating material prepared by mixing and dispersing magnetic powder and a binder in an organic solvent and drying. To be done.

In the magnetic layer thus formed, if there are foreign matters such as undispersed agglomerates, reaggregates, and contaminants at the stage of the magnetic coating, these foreign matters cause surface defects, Increases noise and dropouts. Therefore, it is necessary to filter the magnetic paint with a filter in advance before it is formed as a magnetic layer.

In the present invention, such filtration of the magnetic paint is carried out by the filtration system as shown in FIG.

That is, this filtration system comprises a paint stirring device 1 for stirring the paint and a filter device 2 for filtering the paint supplied from the paint stirring device 1.

The paint stirring device 1 comprises a paint tank 3 and
It is composed of a stirring rod 4 for stirring the paint 16 in the paint tank 3. Paint 1 stirred by this paint stirring device 1
6 is discharged from a paint discharge port 6 provided below the paint tank 3, guided to a pipe 7 connected to the paint discharge port 6, and supplied to the filter device 2.

In the filter device 2, the filter housing 8 has an annular filter 9 made of a porous material.
Are housed and configured.

The filter housing 8 is formed in a cylindrical shape having a size slightly larger than the filter 9, and a space 17 is formed between the housed filter 9 and the inner wall of the filter housing 8. It is like this.

The filter housing 8 is provided with a paint inlet 10 on the upper side of its peripheral surface for allowing paint to flow into the filter housing, and on its bottom surface.
A paint outlet 11 is provided corresponding to the space in the ring of the filter. Of these, the paint inlet 10 is connected to the other end of a pipe (hereinafter referred to as a paint inflow pipe) 7 connected to the paint outlet 6 of the paint agitator 1.

Further, in this filter device 2, the paint circulation outlet 12 is provided on the bottom surface of the filter housing 8 corresponding to the annular space 17 between the filter and the inner wall of the filter housing. A pipe (hereinafter referred to as a paint circulation pipe) 14 is connected to the paint circulation outlet 12, and the other end of the paint circulation pipe 14 is connected to a middle portion of the paint inflow pipe 7. ing.

Liquid feed pumps 13 and 15 are provided in the middle of the paint inflow pipe 7 before the connection position with the paint circulation pipe 14 and in the middle of the paint circulation pipe 14. . The liquid feed pumps 13 and 15 can control the flow rate of the paint flowing in from the paint inlet 10 and the flow rate of the paint flowing out from the paint circulating outlet 12.

In order to filter the magnetic paint by such a filtration system, the composition of the magnetic paint is put into the paint tank 3 of the stirrer 1 and stirred.

As the magnetic powder and the binder used in the magnetic paint 16, any of those usually used in a coating type magnetic recording medium can be used.

For example, as magnetic powder, γ-Fe
_{In addition to 2} O ₃ , Fe ₃ O ₄ , Co-modified iron oxide, synthetic fine powder containing iron as a main component, modified barium ferrite, modified strontium ferrite and the like are used.

As the binder, a modified or non-modified vinyl chloride resin, polyurethane resin or polyester resin may be used alone or in combination. Further, a fibrous resin, a phenoxy resin or a thermoplastic resin having a specific usage, a thermosetting resin, a reactive resin, or an electron irradiation curable resin may be used in combination. The group to be introduced for modification of the resin, -SO ₃ M, -OSO ₃ M and improving dispersibility of the magnetic powder for the purpose, -COO
M and —PO (OM ′) ₂ (where M represents an alkali metal atom such as Na and M ′ represents an alkali metal atom such as Na or an alkyl group) and the like are preferable.

The solvent for forming the coating material may be an organic solvent selected from ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons and the like.

If necessary, a dispersant such as lecithin, a lubricant such as stearic acid, an antistatic agent such as carbon black, an abrasive such as chromium oxide, and an anticorrosive agent may be added to the magnetic paint. Is also good. As the dispersant, the lubricant, the antistatic agent, and the rust preventive, any conventionally known materials can be used other than those exemplified above.

The magnetic paint 16 prepared by stirring such a paint composition in the paint tank 3 flows out from the paint discharge port 6 into the paint inflow pipe 7, is guided to this pipe 7 and is guided to the filter housing. 8 reaches the paint inlet 10. Then, it is supplied into the filter housing 8 from the paint inlet 10. The magnetic paint supplied into the filter housing 8 first flows into the annular space 17 between the filter 9 and the inner wall of the filter housing 8. Here, in this filter device 2, since the paint circulation outlet 12 is provided in the filter housing 8, a part of the magnetic paint that has flowed into the annular space 17 is coated from the paint circulation outlet 12. It flows out to the circulation pipe 14. Then, it is guided to the paint circulation pipe 14, reaches the connection portion with the paint inflow pipe 7, merges with the magnetic paint from the paint stirring device 1, and again from the paint inlet 10 of the filter housing 8 to the filter housing. It flows into 8. On the other hand, of the magnetic paint that has flowed into the annular space 17 between the filter 9 and the inner wall of the filter housing 8, the magnetic paint that has not flowed out of the paint circulation outlet 12 passes through the filter 9. This filter 9
Foreign substances such as undispersed agglomerates, reaggregates, and contaminants are removed from the paint when passing through. Then, the paint that has passed through the filter 9 and reached the space inside the ring of the filter 9 flows out from the paint outlet 11 to the outside, and is used for the subsequent coating step.

In such a filtration system, as described above, a part of the magnetic paint once flowing into the filter housing 8 flows out from the paint circulation outlet 12 before passing through the filter 9, and the paint again. It flows into the filter housing 8 from the inflow port 10. That is, in the annular space 17 between the filter and the inner wall of the filter housing 8, the paint inlet 10 to the paint circulation outlet 12 are provided.
A flow of paint is formed toward and the fluidity is always maintained in this space.

Therefore, the paint does not stagnate in front of the filter 9, and the generation of reaggregates caused by the stagnation of the paint is suppressed. Therefore, even in a relatively low flow pressure range, the flow rate of paint passing through the filter can be increased, and stable and high filtration efficiency can be obtained. Further, since the reaggregates are less likely to be captured by the filter 9, the filter life is extended and the frequency of filter replacement is reduced. Therefore, the workability and the operation rate of the device are improved. In addition, since the filter 9 having a relatively small pore size can be naturally selected, it becomes possible to remove the minute cause of the surface defect.

In order to obtain such an effect sufficiently,
It is desirable that the flow rate of the paint flowing out from the paint circulation outlet 12 be equal to or higher than the flow rate of the paint passing through the filter 9 (filtering flow rate). Practically, the flow rate flowing out from the paint circulation outlet 12 is 2 to 5 times the filtration flow rate, and preferably 2 times.
It is better to triple.

The above is the basic configuration of the filtration system. In this filtration system, as shown in FIG.
A paint disperser 18 may be provided immediately before the paint inlet 10 of the filter device 2. The paint disperser 18 applies a high shearing force to the paint to break up the agglomerates and reaggregates in the paint. By disposing such a paint disperser immediately before the paint inlet 10 of the filter device 2, the flow rate of the paint to be filtered can be further increased, and clogging of the filter can be suppressed.

Examples of the paint disperser 18 include a high speed grinder, an ultrasonic disperser, and a high pressure homogenizer.

The magnetic coating material thus filtered is then introduced into a coating step, coated on a non-magnetic support and dried to form a magnetic layer.

The coating method used in this coating step is a coating method generally used for coating type magnetic recording media, such as a gravure roll method, a reverse roll method or other roll-type coating method, or a die head-based extrusion coating method or the like. It can be a method.

The magnetic layer formed in this manner has good surface properties because the cause of surface defects such as agglomerates and foreign substances is removed from the magnetic paint in the previous filtration step, and the dropout Noise can be suppressed and a high S / N ratio can be obtained.

[0042]

EXAMPLES Specific examples of the present invention will be described based on experimental results.

Example 1 The compositions of various magnetic paints were measured based on the following composition, and the filtration system shown in FIG. 1, that is, the filter device had a paint circulation path from the paint inlet to the paint circulation outlet. A magnetic paint was prepared by stirring and filtering with a filtration system.

Composition of magnetic paint Magnetic powder: Fe-based metal powder (specific surface area 45 m ² / g) 100 parts by weight Binder: Vinyl chloride-vinyl acetate copolymer 10 parts by weight (UCC trade name VAGH) Polyurethane 10 parts by weight Part (Nippon Polyurethane Co., trade name N-2304) Abrasive: Chromium oxide 2 parts by weight Carbon: Vulcan XC-72 (manufactured by Cabot Co.) 3 parts by weight Solvent: Cyclohexanone Appropriate amount Methyl ethyl ketone Appropriate amount The filter used in the filter device is: There are three types of absolute accuracy: 3.0 μm, 1.5 μm, and 1.0 μm. The flow pressure of the paint was 3.2 kg with a pressure gauge placed just before the paint inlet of the filter device (position A in FIG. 1).
/ Cm ² .

Comparative Example 1 The compositions of various magnetic paints similar to those in Example 1 are weighed and stirred and filtered by the filtration system shown in FIG. 3, that is, the filtration system having no circulation route in the filter device. To prepare a magnetic paint.

The filters used in the filter device have three types of absolute accuracy of 3.0 μm, 1.5 μm and 1.0 μm. The flow pressure of the paint was 3.2 kg / cm ² with a pressure gauge arranged immediately before the paint inlet of the filter device (position A in FIG. 3).

Table 1 shows the filtration flow rates in the process of preparing the above magnetic paint. Table 2 shows changes over time in the flow pressure when the filtration flow rate was fixed at 1.0 liter / min using a filter with an absolute accuracy of 1.0 μm.

[0048]

[Table 1]

[0049]

[Table 2]

As shown in Table 1, the filter system of FIG. 1 having a circulation path of the paint flowing from the paint inlet to the paint circulation outlet is shown in FIG. 3 having no such circulation path. Compared to the filtration system, a large filtration flow rate can be obtained by using either filter.

Further, as shown in Table 2, the absolute accuracy is 1.0
Looking at the change over time in the flow pressure when a μm filter was used, in the filtration system of FIG. 1, the flow pressure after 5 hours (hours) was almost the same as the initial flow pressure.
In the filtration system shown in (1), the flow pressure is high from the beginning, and the change with time of the flow pressure is large.

From this, it is effective to increase the filtration flow rate and obtain stable filtration efficiency by providing the filter device with a circulation path for the paint flowing from the paint inlet to the paint circulation outlet. all right.

Example 2 The compositions of various magnetic paints similar to those in Example 1 were weighed out, and the filtration system shown in FIG. 2, that is, the filter device had a circulation path and a disperser was installed immediately before the paint inlet. A magnetic paint was prepared by stirring and filtering with the filtration system.

The filter used in the filter device has an absolute accuracy of 3.0 μm, 1.5 μm, 1.0 μm,
There are five types, 0.7 μm and 0.5 μm, and the disperser is a high-speed grind device. The flow pressure of the paint was 3.2 kg / cm ² with a pressure gauge arranged immediately before the paint inlet of the filter device (position A in FIG. 2).

Table 3 shows the filtration flow rates in the process of preparing the magnetic paint as described above, together with the filtration flow rates of Comparative Example 1 above.

[0056]

[Table 3]

As shown in Table 3, the filtration system of FIG. 2 having a circulation path in the filter device and a disperser provided immediately in front of the paint inflow port is better than the case of the filtration system of FIG. 1 (Example 1). Even greater filtration flow rates can be obtained. In particular, even when using a filter having an extremely high absolute accuracy of 0.5 μm, a sufficiently practical filtration flow rate of 1.34 liters / minute can be obtained.

From this, it was found that the filtration flow rate can be further increased by providing the filter device with a circulation path and providing a disperser immediately before the paint inlet.

Further, Table 4 shows the magnetic properties and glossiness of the magnetic layer formed by using the magnetic coating materials prepared in Example 2 and Comparative Example 1.

The magnetic characteristics were measured for saturation magnetic flux density Bm, residual magnetic flux density Br, and squareness ratio Rs using a vibrating sample magnetometer (manufactured by VSM Toei Industry Co., Ltd.).

The glossiness is an index of the dispersibility of the magnetic layer and was measured by a gloss meter at an incident angle of 60 °.

[0062]

[Table 4]

As shown in Table 4, in comparison with the magnetic layer using the magnetic coating material prepared by the filtration system of FIG. 3, the magnetic layer prepared by the magnetic coating material prepared by the filtration system of FIG. Is also excellent. Further, the glossiness is high, and it is judged that the magnetic powder is highly dispersed in the magnetic layer.

From these facts, the effect of providing the filter device with a circulation path and providing the disperser immediately before the paint inlet is actually reflected in the characteristics of the magnetic layer, whereby a magnetic layer having excellent characteristics is formed. It was confirmed that

[0065]

As is apparent from the above description, in the method of manufacturing a magnetic recording medium according to the present invention, when the magnetic paint is filtered, a paint circulation outlet is provided in the filter housing, and the paint flowing into the filter housing is introduced. A part of the water is discharged from this paint circulation outlet before passing through the filter and then flowed again from the paint inlet, so even if a filter with a relatively small pore size is used in the filtration process, increase the filtration flow rate. It also prevents clogging of the filter. Therefore, the filtration accuracy of the magnetic paint can be reasonably improved, and the workability and the operation rate of the device can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing one configuration example of a filtration system to which the present invention is applied.

FIG. 2 is a schematic diagram showing another configuration example of the filtration system to which the present invention is applied.

FIG. 3 is a schematic diagram showing a conventional filtration system.

[Explanation of symbols]

 2 Filter device 8 Filter housing 9 Filter 10 Paint inlet 12 Paint circulation outlet

Claims (3)

[Claims] 1. When a magnetic paint prepared by mixing and dispersing magnetic powder and a binder in an organic solvent is introduced from a paint inlet of a filter housing containing the filter and filtered by the filter, the paint is applied to the filter housing. A circulation outlet is provided, and a part of the paint flowing into the filter housing is caused to flow out from the paint circulation outlet before passing through the filter.
A method of manufacturing a magnetic recording medium, characterized in that the coating material is made to flow again through the paint inlet. 2. The magnetic paint flows out of the filter housing from the paint circulation outlet at a flow rate equal to or higher than the flow rate of the magnetic paint passing through the filter.
The manufacturing method of the magnetic recording medium according to the above. 3. The method for producing a magnetic recording medium according to claim 1, wherein a paint disperser is provided immediately before the paint inlet of the filter housing.