JPH0233726A - Magnetic recording medium and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coating type magnetic recording medium, and in particular, it is suitable for high-density recording, with little agglomeration of magnetic fine particles and a high content of magnetic fine particles. The present invention relates to a method for manufacturing a magnetic recording medium and a magnetic recording medium manufactured using the method.

[Conventional technology]

Many methods have been proposed for manufacturing magnetic recording media by coating a non-magnetic substrate with a magnetic paint in which ferromagnetic fine particles are dispersed in a polymeric binder. For example, Tokuko Sho 57-405
No. 66 and Japanese Unexamined Patent Publication No. 5610087],
A method for manufacturing a magnetic recording medium is disclosed that includes a step of cross-talking ferromagnetic fine particles with a cyclohexanone solution such as an epoxy resin under high shear stress.

Since these methods use resin solutions, they have the following problems. First, it is difficult to uniformly mix the ferromagnetic particles and the resin solution.

Unless the ferromagnetic particles and the binder resin are sufficiently mixed and contacted, it is difficult to obtain a magnetic coating film in which the ferromagnetic particles are uniformly dispersed.

Second, the amount of solvent in which the binder resin is dissolved is greater than the amount required for kneading due to the solubility of the resin. Excess solvent may solvate the surface of the ferromagnetic particles, weakening their affinity with the resin, and may also lower the viscosity of the kneaded mixture, making it difficult for the ferromagnetic particles to be exposed to mechanical force. The dispersion effect is weakened.

For these reasons, the ferromagnetic fine particles agglomerated in the resulting coating film, and the smoothness of the coated surface was lost. If the roughness of the coating film before processing is large, noise increases as shown in FIG.

On the other hand, JP-A-63-4422 discloses a method in which a binder resin is pulverized, mixed with ferromagnetic fine particles in a solid state, and a solvent is added thereto and kneaded.

This method improves the mixing state of the ferromagnetic fine particles and the binder resin, and also makes it possible to increase the crosstalk effect by reducing the amount of solvent added. As a result, a magnetic coating film is formed in which the ferromagnetic fine particles are well-dispersed, the surface roughness before processing is extremely low, and the noise is low. However, even in this method), the mixing state of the ferromagnetic fine particles and the binder resin is not necessarily sufficient.

Furthermore, if the amount of binder resin is reduced, it is difficult to cause crosstalk, so if the content of ferromagnetic fine particles is increased, mixing will be required for a very long time, and in some cases, crosstalk will not be possible. Furthermore, when the bulk density of the ferromagnetic fine particles is small, kneading becomes difficult, and a large amount of binder resin and solvent must be added, and it takes a long time to enter the mixed wire.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, it is difficult to achieve a sufficient mixing state even in the method using powdered binder resin, and it is difficult to achieve a sufficient mixing state even in the method using powdered binder resin. There are limits to Therefore, it has been difficult to reduce noise in magnetic recording media and improve flying stability of floating magnetic heads in hard disks. In addition, a large amount of binder resin is required in the kneading process, making it difficult to increase the content of ferromagnetic fine particles, and if the amount of resin is reduced, the crosstalk state will not occur or it will take a long time to reach the crosswire state. That was also a problem. Furthermore, even in the case of ferromagnetic fine particles having a small bulk density, crosstalk cannot occur unless a large amount of binder resin and solvent are added, and furthermore, crosstalk does not occur unless mixed for a long time.

The purpose of the present invention is to improve the cross-crossing process to enable effective cross-crossing of ferromagnetic particles of any bulk density. The purpose is to provide recording media in a short process time.

[Means to solve the problem]

In order to achieve the above objective, we investigated the manufacturing method of magnetic recording media, and found that instead of adding ferromagnetic fine particles and binder resin at the same time as in the past, we decided to swell only the binder resin with a solvent. , or by heating and melting the ferromagnetic material to a highly viscous fluid state, adding 1 ferromagnetic material fine particles in two or more portions, kneading with high shear stress, and then performing ball mill kneading as in the conventional method. A magnetic paint with good dispersibility of ferromagnetic fine particles was obtained regardless of the initial bulk density of the fine particles. Magnetic recording media produced by applying the magnetic paint produced in this way onto a non-magnetic substrate and orienting it in a magnetic field have smaller surface roughness before processing than those produced by conventional methods, and also have fine ferromagnetic particles. The content in the coating film is 8
Even if it is increased to 0 wt%, it is possible to manufacture a magnetic recording medium, and the surface roughness before processing is also 0.04.0 11 m R
We were able to make it as small as a or less. Furthermore, when producing a magnetic recording medium with the same composition as in the conventional method, the time required for the crosstalk process could be reduced by approximately 50%.

[Effect]

A method of kneading ferromagnetic fine particles with a binder resin under high shear stress is an effective means for increasing the dispersibility of ferromagnetic fine particles in magnetic paints and coatings. To perform crosstalk, it is necessary to fill the gaps between the ferromagnetic fine particles with a resin solution or a swollen resin. In order to efficiently fill the voids, it seems that a considerably larger amount of resin is required than the volume of the voids. When ferromagnetic fine particles and resin are added at the same time, the amount of resin for a given amount of voids is small, which is particularly noticeable when the content of ferromagnetic fine particles is high or when the bulk density of the ferromagnetic fine particles is small. Therefore, a large amount of resin and solvent are required to create a crosstalk state, and it takes a long time to reach a crosstalk state. On the other hand, in the method of adding ferromagnetic fine particles in several parts to a resin that has been swollen or heated and melted to a uniform fluid state, the resin is in excess of the initially added fine particles, so There is a crosstalk situation. If a crosstalk occurs, the excess resin other than the minimum required amount remains, and is used for crosstalk of the ferromagnetic fine particles added next. Therefore,
It is thought that an excess amount of resin can be achieved each time ferromagnetic fine particles are added, and crosstalk progresses efficiently. As a result, it is now possible to cross-wire even under conditions where cross-talk was impossible due to lack of resin in the conventional method, and even if the content of ferromagnetic fine particles is increased or ferromagnetic fine particles with a small bulk density are used, there is no problem. There isn't. In addition, even under conditions where crosstalk is possible in the conventional method, the time required for the crosstalk process can be shortened according to the present invention, and when the content of ferromagnetic fine particles is high or the bulk density of ferromagnetic fine particles is small, A time reduction of 50% is possible. As described above, according to the present invention, efficient kneading is possible in a short time, the dispersibility of ferromagnetic fine particles is improved, and a magnetic recording medium with extremely small roughness of the processed surface of the coating film can be produced. Furthermore, by reducing the amount of binder resin added, a magnetic recording medium with a high content of ferromagnetic fine particles can be obtained.

〔Example〕

Examples of the present invention are listed below.

(Example) -) 25 parts by weight of epoxy resin powder having a particle size of about 200 μm was put into a kneader mixer, and 10 parts by weight of cyclohexanone was added to bring the epoxy resin into a swollen state. In addition, ferromagnetic fine particles (acicular γFe2.08 powder, major axis diameter 0.3
[mu]m, axial ratio 5 to 6, bulk density about 0.6 g/mu) and 10 parts by weight of single crystal alumina fine particles were added and kneaded for 30 minutes under high shear stress. Thereafter, 50 parts by weight of ferromagnetic fine particles were added, and crosstalk was continued for another 4 hours.

The time required for the kneader crosstalk was 4 hours and 40 minutes.

” Put the kneaded product in a ball mill pot and add 200% of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane.
After adding the heavy grains and kneading in a ball mill for 5 days, a solution of 25 parts by weight of phenol resin and 6 parts by weight of vinyl resin dissolved in 300 parts by weight of the above mixed solvent was added to prepare a magnetic paint. Next, clean the surface in advance 8, 8
The above paint was spin-coded onto an inch-diameter aluminum substrate, magnetically oriented by a well-known method, and then cured by heating. The obtained disk had no visible defects, the coating thickness was 0.5 μm over the entire surface, and the surface roughness before processing was 0.030 μmRa.

(Example 2) 25 parts by weight of epoxy resin powder having a particle size of about 200 μm was placed in a kneader mixer, and 10 parts by weight of cyclohexanone was added to bring the epoxy resin into a swollen state. To this, ferromagnetic fine particles (hexagonal barium ferrite powder 2 grain size 0.0
5 μm, plate ratio 5°, bulk density approximately 0.8 g/mQ) was added and kneaded under high shear stress. Thereafter, 20 parts by weight of ferromagnetic fine particles were added four times every 15 minutes, and crosstalk was continued for an additional 4 hours. The time required for kneader crosstalk is 5
The time was 10 minutes.

” The kneaded product obtained in Example 2 was made into a magnetic paint in the same manner as in Example 1,
After coating on an aluminum substrate with a diameter of 5 or 25 inches, the surface of which had been cleaned in advance, it was magnetically aligned in the in-plane direction using a well-known method. As a result of observation using an electron microscope, it was confirmed that the plate surface of the barium ferrite powder was oriented perpendicular to the aluminum substrate. Furthermore, the squareness ratio in the in-plane direction was 0.7 as measured by a vibrating sample magnetometer. The disk obtained by heating and curing the coating film had no visible defects, the coating thickness was 0.5 μm over the entire surface, and the surface roughness before processing was 0.038 μmRa.

(Example 3) A magnetic paint prepared in the same manner as in Example 2 was applied to a 5.25-inch diameter aluminum substrate whose surface had been cleaned in advance, and then a vertical magnetic field was partially applied to the substrate. The direction of the ferromagnetic particles was made irregular. As a result of measurement using a vibrating sample magnetometer, the squareness ratio is 0 in all directions.
．． It was 42-0.46. The coating was heat cured at 230'C. The obtained disk had no visible defects, the coating thickness was 0.5 μm over the entire surface, and the roughness before processing was 0.030 μm Ra.

(Example 4) 11 parts by weight of epoxy resin powder having a particle size of about 200 μm was put into a kneader-kneader, and 20 parts by weight of cyclohexanone was added to bring the epoxy resin into a swollen state. In addition, ferromagnetic fine particles (acicular γ-Fe2O3 powder, long axis diameter 0.3 μm,
Axial ratio 5 to 6, bulk density 0, 6 g/m Q) was added in 20 parts by weight every 30 minutes, a total of 100 parts by weight, under high shear stress, and crosstalk was further performed for 4 hours.

Put the above mixture into a ball mill pot, and put the mixed solvent consisting of cyclohexanone, isophorone, and dioxane]-5
After adding 0 parts by weight and performing ball mill kneading for 5 days,
A magnetic paint was prepared by adding a solution in which parts by weight of phenolic resin and 3 parts by weight of vinyl resin were dissolved in 200 parts by weight of the above mixed solvent.

Next, the above coating material was spin-coded onto an 8.8 inch diameter aluminum substrate whose surface had been previously cleaned, and after magnetic field orientation was performed by a well-known method, the coating film was cured by heating. The coating film thickness is 0.5 μm at the R65mm position, R
The surface roughness before machining is 0.6μm at the 105mm position.
The content of ferromagnetic fine particles is 80 wt% (5QvoD, %)
0.040 μmRa despite the increase in
This was a small value.

(Example 5) 20 parts by weight of epoxy resin powder having a particle size of about 200 μm was placed in a kneader mixer, and cyclohexanone]O was added to make the epoxy resin swollen. In addition, ferromagnetic particles (acicular γ-Fe2O3 powder, major axis diameter 0.3 μm,
Axial ratio 5-6, bulk density 0, 6 g/m Q)
was added in 20 parts by weight every 20 minutes, for a total of 100 parts by weight, and kneaded for an additional 4 hours under high shear stress. The time required for crosstalk was approximately 6 hours.

The above mixture was placed in a ball mill pot, 180 parts by weight of a mixed solvent consisting of cyclohexanone, isophorone, and dioxane was added, and kneaded in a ball mill for 5 days. 20 parts by weight of phenol resin and 5 parts by weight of vinyl resin were added to 240 parts by weight of the above mixed solvent. A magnetic paint was prepared by adding a solution dissolved in the sample. Using this, a magnetic disk was prepared in the same manner as in Example 4. The surface roughness of the coating film before processing is 0.038
It was μmRa.

(Example 6) 25 parts by weight of epoxy resin powder having a particle size of about 200 μm was placed in a kneader mixer, and 10 parts by weight of cyclohexanone was added to bring the epoxy resin into a swollen state. To this was added 20 parts by weight of ferromagnetic fine particles (acicular Fe powder, long axis diameter 0.5 μm, axial ratio 6 to 8, bulk density 0.4 g/mfl), and kneaded under high shear stress. 20 every 15 minutes thereafter
Parts by weight of ferromagnetic fine particles were added four times, and kneading was continued for an additional 4 hours. The time required for the kneader crosstalk was 5 hours and 10 minutes.

The above-mentioned crosstalk was made into a magnetic paint in the same manner as in Example 1, and after coating on a 5.25 inch diameter aluminum substrate whose surface had been previously cleaned, it was oriented in a magnetic field by a well-known method. The coating film was cured by heating in an inert gas to obtain a magnetic disk. The obtained disk had no visible defects, the coating film was 0.5 μm on the entire surface, and the roughness before processing was 0.
．． It was 040 μm Ra.

Below, as a comparative example, a state in which magnetic powder was kneaded by a conventional method not based on the present invention is listed.

(Comparative Example 1) Ferromagnetic fine particles (acicular γ-FezOs powder, major axis diameter 0.3
μm, axial ratio 5-6, bulk density 0.6g/mQ) 1-00
Parts by weight and 10 parts by weight of single-crystal alumina fine particles were put into a kneader mixer and mixed, and then a solution of 15 parts by weight of epoxy resin dissolved in 22 parts by weight of cyclohexanone was added and mixing was continued. Further, a solution of 5 parts by weight of epoxy resin dissolved in 8 parts by weight of cyclohexanone was added and kneaded for 4 hours under high shear stress. The time required for crosstalk was 5 hours.

Put the above mixture into a ball mill bot and use epoxy resin 5.
Weight parts and cyclohexanone, isophorone.

180 parts by weight of a mixed solvent consisting of dioxane was added, and ball milling was carried out for 5 days. Next, a solution of 25 parts by weight of phenol resin and 6 parts by weight of vinyl resin dissolved in 300 parts by weight of the above mixed solvent was added to prepare a magnetic paint. Next, the above coating material was spin-coded onto an 8.8 inch diameter aluminum substrate whose surface had been previously cleaned, and after magnetic field orientation was performed by a well-known method, the coating film was cured by heating.

The obtained magnetic disk has a film thickness of 0.7 μm with R65 mm.
, R was 105 mm, and the thickness was 0.9 μm, and the surface roughness before processing was also a large value of 0.07 μm R,a.

(Comparative Example 2) 25 parts by weight of epoxy resin powder with a particle size of approximately 200 μm and ferromagnetic fine particles (acicular γ-Fe2O3 powder, major axis diameter 0.3
μm, axial ratio 5-6, bulk density 0.6 g/mQ) was put into a kneader-mixer and mixed, then 10 parts by weight of cyclohexanone was added and mixing was continued under high shear stress. Ta. After about 3 hours, the lines became interfering, and the interfering continued for another four hours.

The time required for kneader crosstalk was 8 hours.

The above mixed wire was made into a magnetic paint in the same manner as in Example 1, and a magnetic disk was produced. The coating film thickness was 0.5 μm on the entire surface.
The surface roughness before processing was 0.030 μm Ra.

(Comparative Example 3) Ferromagnetic fine particles (hexagonal barium ferrite powder, particle size 0
．． 05μm, plate ratio 5, bulk density 0.8g/rr+Q)
was made into a magnetic paint using the same method as in Comparative Example 2, and spin-coded onto a 5- or 25-inch diameter aluminum substrate whose surface had been previously cleaned.Then, the magnetic field was oriented in the in-plane direction using a well-known method, and the coating film was cured by heating. did. The resulting disc is
Coating film thickness is 0.5 μm on the entire surface, surface roughness before processing is 0.0
It was 42 μmRa.

(Comparative Example 4) Ferromagnetic fine particles (acicular γ-F”ezO8 powder, long axis diameter 0.
3 μm, axial ratio 5-6, bulk density 0.6 g/mQ, )1
00 parts by weight and epoxy resin powder 1 with a particle size of approximately 200 μm
1 part by weight was put into a kneader mixer and mixed, 20 parts by weight of cyclohexanone was added and mixing was continued.
No crosstalk occurred even after 6 hours had passed. An additional 5 parts by weight of cyclohexanone was added and mixing was continued for 4 hours, but no crosstalk occurred.

(Comparative Example 5) Ferromagnetic fine particles (acicular γ-Fe2O3 powder, major axis diameter 0.3
μm, axial ratio 5-6, bulk density 0.6g/m(1)10
0 parts by weight and 20 parts of epoxy resin powder with a particle size of approximately 200 μm.
Parts by weight were put into a kneader mixer and mixed, 10 parts by weight of cyclohexanone was added, and mixing was continued. After about 5 hours, the wires were crossed, and the wires continued to be crossed under high shear stress for another 4 hours. The crosstalk process takes nine hours.

A magnetic disk was produced in the same manner as in Example 5 using the above-mentioned interfering material. The roughness of the processed front surface of the coating film is 0.038μmR
It was a.

(Comparative Example 6) 100 parts by weight of ferromagnetic fine particles (acicular Fe powder, long axis diameter 0.5 μm, axial ratio 6 to 8, bulk density 0.4 g/mQ) and 25 parts by weight of epoxy resin powder were mixed in a kneader. After the mixture was put into the machine and mixed, 10 parts by weight of cyclohexanone was added, but no crosstalk occurred even after 3 hours. 10 more
After adding part by weight of cyclohexanone, a crosstalk state occurred after about 3 hours. The line continued to be mixed up for another four hours. The time required for kneader crosstalk was about 10 hours.

The above mixed wire was made into a magnetic paint in the same manner as in Example 6, and a magnetic disk was produced. The coating film thickness is 0.5pm on the entire surface.
The surface roughness before processing was 0.060 μm Ra.

In the above embodiments of the present invention, a kneader crosstalk machine is used, but other devices capable of crosstalk under high shear stress include:
A roll mill, side mill, ball mill, etc. can also be used.

As mentioned above, one of the advantages of the present invention is that the surface roughness of the magnetic recording medium before processing can be reduced. Figure 1 shows the relationship between the surface roughness and disk noise of a magnetic disk using γ-Fe2O3 powder, but the tendency is the same for other magnetic powders, and the present invention By using this method, the surface roughness can be significantly reduced compared to the conventional method, and a magnetic disk with low noise can be obtained.

Another advantage of the present invention is that it can shorten the time required for the magnetic recording medium manufacturing process, and as shown in Figure 2, the time required is up to 50% compared to the conventional method (comparative example). Can be shortened. Furthermore, there is no increase in surface roughness as in Comparative Example 1.

〔Effect of the invention〕

As described above, according to the present invention, for example, when a magnetic disk is manufactured using an aluminum substrate with a diameter of 5.25 inches or 8.8 inches, the roughness of the coated surface is reduced to 0.04.
It can be suppressed to 0 μmRa or less, and noise can be expected to be reduced. Also, the roughness of the coated surface is 0.040 μm
It is possible to increase the content of ferromagnetic fine particles to 80 wt% while maintaining a small value of Ra.

Furthermore, the time required for the crosstalk process can be shortened without adding excessive solvent, and in particular, ferromagnetic fine particles of 70 wt.
% or more, or a bulk density of 0.4 g/
When using ferromagnetic fine particles with a large number of voids on the order of mQ, the time required for the crosstalk process can be reduced by 50%.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the surface roughness of a magnetic disk before processing and magnetic disk noise. Figure 2 is a graph showing the ferromagnetic fine particle content in the magnetic coating and the amount of time required to produce the coating. It is a graph showing the relationship with time of the kneading process.

Claims (1)

[Claims] 1. A method for manufacturing a magnetic recording medium in which a magnetic layer in which ferromagnetic particles, or ferromagnetic particles and non-magnetic particles are dispersed in a polymeric binder, is provided on a non-magnetic substrate. In this step, at least one kind of the polymeric binder is swollen with an organic solvent or heated and melted to form a highly viscous fluid state, and the ferromagnetic fine particles or ferromagnetic fine particles are added to the polymeric binder. A method for producing a magnetic recording medium, comprising the step of adding non-magnetic fine particles in at least two portions and kneading them under high shear stress. 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the ferromagnetic fine particles are at least one of iron oxide powder, Co-coated iron oxide powder, metal powder, and barium ferrite powder. 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the polymer binder includes at least one of epoxy resin, phenol resin, and vinyl resin. 4. A magnetic recording medium manufactured by the method described in claims 1 to 3. 5. The magnetic recording medium according to claim 4, wherein the magnetic recording medium is a magnetic disk. 6. The magnetic recording medium according to claim 4, wherein the magnetic recording medium contains 50 volume percent or more of ferromagnetic fine particles in the magnetic layer.