JPH04245022A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium with an improved running property without nearly any shape influence to a magnetic layer with the invention being related to a manufacture of a backcoat of the magnetic recording medium to be applied to information industrial field etc. CONSTITUTION:Although a magnetic recording medium is put into practical application in a configuration shown in figure, an inferior influence such as shape transfer to a magnetic layer 2 can be observed if a manufacturing method is not optimized. Therefore, a paint is obtained by mixing 2-3wt.% urethane binder, 2-3.5wt.% curing agent, 15-18wt.% 2-butanone, 24-30wt.% toluene, and 3-5wt.% cyclohexanone or a method for composing paint such as filtering treatment conditions is optimized, thus achieving a finishing state where the backcoat layer 3 is fully uniform.

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 high recording density magnetic recording medium which is applied to the information industry and the like.

0002

[Prior Art] For the purpose of developing magnetic recording media for magnetic disks, magnetic tapes, etc., γ-Fe2O
3. Instead of coating-type magnetic recording media, which are made by dispersing Co-containing ferromagnetic powder such as γ-Fe2O3 or CrO2 in an organic binder, ferromagnetic metal thin films can be directly deposited on non-magnetic substrates for the purpose of higher density. Metal thin film type magnetic recording media formed by plating, sputtering, vacuum evaporation, ion plating, etc. have been developed.

However, when the metal thin film type magnetic recording medium is used as is, smooth running properties cannot be obtained and the recording and reproduction signals are extremely unstable. The reason for this is that if the non-magnetic substrate is left untreated, there will be large friction with the guide and post portions. Therefore, in the practical application of magnetic recording media, an abrasion-resistant backcoat layer that has excellent friction and abrasion resistance and that maintains these properties under the environmental conditions of use is required. On the other hand, when the magnetic recording layer is a metal thin film layer, the transfer of the shape of the back coat may have a great deal of influence on the quality of the envelope of recording characteristics. Therefore, it is preferable that the back coat surface has a smooth finish.

[0004] For this reason, compared to the conventional back coat material,
For vinyl chloride and vinyl acetate, U.S. Patent No. 456708
3 specification, US Pat. No. 4,587,150, US Pat. No. 4,618,535, US Pat. No. 4,628,009, US Pat. No. 4,639,389, US Pat.
No. 663217, US Pat. No. 4,673,622, US Pat. No. 4,592,942, US Pat. No. 461
8535 specification, U.S. Patent No. 4,448,847 specification,
U.S. Patent No. 4789583, U.S. Patent No. 47865
No. 57 specification, polyester and acrylic systems are described in US Pat. No. 4,687,699, US Pat. No. 4,637,963, and US Pat. , US Pat. No. 4,612,235, US Pat. No. 4,587,150, and the like.

[0005]

[Problems to be Solved by the Invention] However, although these products do show some improvement in running properties, there is a phenomenon in which the back coat peels off during running, resulting in insufficient wear resistance, and the problem is that the magnetic layer There were also many effects of component transfer and shape transfer. Therefore, in consideration of these points, the present invention has excellent abrasion resistance, and overcomes the back coat layer that does not reflect shape transfer by controlling the mixing ratio of paint or filtration, thereby improving running stability, durability, and shape. It was developed with the aim of providing an excellent magnetic recording medium that does not require transfer.

[0006]

[Means for Solving the Problems] Polyurethane having a specific glass transition point, nitrocellulose, an isocyanate hardening agent, and a large particle size and fine particle size carbon fiber are coated on the surface of a nonmagnetic substrate opposite to the magnetic recording layer. Using a mixed solution of BON powder and alumina powder, the particles can be coated with a binder component by mixing them in a preferred composition ratio, or the particles can be coated with a binder component, or magnetic particles with abnormal shapes in the paint can be removed by filtration. A smooth finish is achieved by removing particles that affect the smoothness of the recording layer.

[0007]

[Function] The back coat surface prepared by the above paint mixing operation is a smooth surface with no abnormal particle size or direct exposure of particles, and the shape transfer to the magnetic recording layer is not reflected, and the running condition is An excellent magnetic recording medium becomes possible.

[0008]

[Example] An example of the magnetic recording medium of the present invention (
Figure 1) shows this. The nonmagnetic substrate 1 that can be used includes polymeric materials such as polyamide, polyimide, polysulfone, polycarbonate, polypropylene, polyethylene, polyethylene terephthalate, polycellulose acetate, and polyvinyl chloride, and nonmagnetic materials. It includes films, plates, etc. made of well-known materials such as metal materials, glass, and ceramic materials such as porcelain.

The ferromagnetic material forming the magnetic recording layer 2 is at least one metal selected from Co, Ni, and Fe, or a combination of these with Cr, Mn, Ti, P, and Y.
There are alloys with , Sm, Bi, etc., and alloys with combinations of these oxides. Among them, the magnetic recording layer made of a material selected from at least two or more elements of Co, Cr, and Ni has high magnetic anisotropy energy;
It is preferable because it has high saturation magnetization, and these methods include vacuum evaporation method, sputtering method, ion plating method,
It can be formed by a method such as a plating method. Further, alloys of Co and Cr or metal oxide layers thereof are more preferable from practical points of view such as corrosion resistance. It goes without saying that the magnetic recording layer 2 described in the present invention is not limited to the above composition.

In the back coat layer 3 according to the present invention, a material having a polyurethane base material having an average molecular weight (Mw) of 10,000 or more can be used as a binder component. In particular, metal thin films such as Co and Cr as described in the present invention should be selected in consideration of curl suppression, composition, and shape transfer, since these thin films differ in mechanical properties from non-magnetic substrates. is required. Therefore, the average molecular weight of the polyurethane base material is preferably 30,000 or more, and it is more preferable to use a material having physical properties with a glass transition point (Tg) of around 10°C, and from the viewpoint of Young's modulus, thickness, and abrasion resistance, the average molecular weight is 50,000 or more. degree is most preferable. Then, polymers such as nitrocellulose are mixed in to improve mechanical properties and to improve gloss. In the present invention, materials with different molecular weights are mixed, but copolymers with other polymers may also be used. As the curing agent, a trifunctional isocyanate-based reaction product of trimethylolpropane and tolylene diisocyanate can be used. Carbon particles are used to impart conductivity and improve running properties. Since the magnetic recording layer of the present invention has a metal component, the conductivity is 1010~
The mixing amount may be such that a value in the range of 106 Ω/cm2 is achieved, and the particle size is selected from the viewpoint of ease of solution dispersion and ensuring effective runnability. In the present invention, the average diameter is preferably 0.02 to 0.3 μm in order to achieve the synergistic effect of fine particle diameter for imparting conductivity and large particle diameter for imparting runnability. These carbon particles can also be used after surface modification to improve dispersibility and runnability, or surface treatment such as dehalogenation to improve corrosion resistance. The abrasive material used is alumina, titanium, silica alone or their oxides, or a mixture with oxides such as cobalt, chromium, iron, etc., and is used to polish the posts that come in contact with the tape while it is running.
The material and particle size are selected to ensure wear resistance with the guide member. It also has the purpose of imparting surface gloss.

[0011] Addition of these lubricants is more preferable because running properties are further improved. These materials have fatty acids or their salts, amines, esters, amides, alcohols at the ends.
Higher hydrocarbon compounds or fluorinated hydrocarbon compounds having polar groups such as fluorine, liquids such as perfluoropolyether, or molybdenum-based organic lubricants can be used alone or in combination. However, the amount of lubricant to be mixed should be determined taking into account the solution dispersibility, the degree of improvement in runnability, and the effect on component transfer to the magnetic recording layer, and is preferably 1 wt % or less.

[0012] In order to reflect the characteristics of the above materials,
Efforts must be made at the paint mixing stage. That is, depending on the blending ratio of each material, there are many cases where the particle diameters as specified are not mixed, or these particles are exposed during the curing process. As a result, it is obvious that the performance of the backcoat differs in runnability, conductivity, degree of curing, etc., and transfer to the magnetic recording layer, adhesion, etc. may occur.

Therefore, in the present invention, by optimizing the paint preparation stage, a back coat with the above-mentioned excellent performance can be obtained.
The purpose of the present invention is to provide a magnetic recording medium having the following characteristics. It goes without saying that the back coat described in the present invention can be applied not only to the magnetic recording medium described above, but also to cases where a protective layer or a lubricating layer is formed on the surface of the magnetic recording layer.

Examples will be described in detail below. (Example 1) A sample was prepared by coating a polyimide film with a thickness of 10 μm on a polyimide film with a thickness of 0.5 μm based on the following composition and mixing the paints shown in the amounts shown in (Table 1). Each weight percent is based on the total amount, and inorganic substances such as abrasives are not included in (Table 1).

[0015]

[Table 1]

(Basic composition) Polyurethane (Mw 50,000) Nitrocellulose Low molecular weight (1/16 sec) High molecular weight (1/2 sec) (Molecular weight measurement according to JISK6721) Carbon black 0.023 μm 0.3 μm Abrasive material (CoAl2O3) Isocyanate curing agent Methyl ethyl ketone stearate Toluene cyclohexane The manufacturing conditions at this time were: roll mesh 50, roll rotation speed 70 rpm, tape speed 4.5 m/min, and drying temperature 80 to 120°C. .

The results of measuring the surface smoothness using a non-contact three-dimensional surface roughness meter (WYKO, TOPO-3D) are as follows:
From Fig. 2) to (Fig. 7), the surface roughness (Ra, Rms,
PV) is shown in (Table 2), and the mechanical strength was examined using a Young's modulus measuring device (TM-7000 manufactured by Shinku Riko Co., Ltd.), and is also shown in (Table 2).

[0018]

[Table 2]

From (Table 2), sample No. 1, 2, 3
, 6, the back coat was not good because the inorganic particle size was exposed or the mechanical strength was insufficiently improved. On the other hand, sample No. It was carried out in the composition range of 4 and 5, Ra, R
ms and PV value were also small. Young's modulus is also around 550Kg/cm2 when untreated and TD (535Kg/cm2).
cm2) and MD (585 Kg/cm2) directions, but it was found that by applying the back coat, this was strengthened isotropically by about 20%. This is considered to be due to differences in the paint dispersion state and curing process depending on the composition range.

Therefore, as described in the present invention, when a back coat containing polyurethane having the above-mentioned composition range is applied to the opposite side of the non-magnetic substrate having a magnetic recording layer, a running surface with improved smoothness and mechanical strength can be obtained. It can be seen that a magnetic recording medium with excellent properties can be obtained. (Example 2) Next, the back coat surface before and after filtration was examined at the paint preparation stage. The purpose of this is to achieve flatness by removing abnormal particle diameters.

[0021] This is shown in (Table 3). Note that the filter material manufactured by Nippon Roki Co., Ltd. was used.

[0022]

[Table 3]

Observation of these results shows that sample No. When the average filtration diameter used in Examples 7 to 9 was 0.4 μm and the maximum filtration diameter was 1.0 μm, the presence of abnormal particle diameters was hardly observed. On the other hand, sample No. In the filter media used in Examples 10 and 11, the presence of particles with large average and maximum filtration diameters was occasionally observed. On the other hand, the filtration pressure is 2Kg/cm2
If the flow rate is above 1000 g/min and the processing time is less than 60 min, the selection of the filter material was insufficient. Therefore, filtration conditions need to be optimized.

(Example 3) The composition of the back coat was within the composition range of (Example 1) and was filtered to form a film with a thickness of 0.6 μm. At this time, as an example, the magnetic layer was formed by sequentially forming CoCr and CoO on a 9 μm polyimide film under the conditions shown in Table 4 to prepare a magnetic recording medium.

[0025]

[Table 4]

In the magnetic recording medium produced at this time, when the compounding operation described in the present invention was not performed (sample No. 12), some depressions were formed in the magnetic recording layer as shown in FIG. 8. On the other hand, in the magnetic recording medium (sample No. 13) produced by this operation, the magnetic recording layer was flat as shown in FIG. 9.

From the above, it is possible to provide a magnetic recording medium that is free from transfer to the magnetic layer and has extremely excellent running conditions with the back coat produced by optimizing the paint preparation process according to the present invention. From the above, it can be seen that the magnetic recording medium can obtain excellent wear and friction resistance only by having the back coat described in the present invention.

[0028]

According to the present invention, a magnetic recording layer made of a mixture of Co and Cr or a metal oxide containing these is formed on one surface of a non-magnetic substrate, and a polyurethane layer is formed on the opposite surface of the non-magnetic substrate. A magnetic recording medium with enhanced surface smoothness and improved Young's modulus and good runnability can be realized by applying a solution containing as the main component in an appropriate composition range and using a filtered paint. Further, by using the back coat of the present invention, a magnetic recording medium having a flat shape with improved curl correction can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a magnetic recording medium of the present invention.

[Figure 2]
(Example 1) Sample No. 3D view when measuring 1 with a non-contact 3D surface roughness meter with 20x magnification

FIG. 3: Sample No. of (Example 1). 3D view when measuring 2 with a non-contact 3D surface roughness meter with 20x magnification

[Figure 4] (Example 1)
Sample No. 3D view when measured with a non-contact 3D surface roughness meter with 20x magnification

FIG. 5: Sample No. of (Example 1). 3D view when measuring 4 with a non-contact 3D surface roughness meter with 20x magnification

[Figure 6] Sample N of (Example 1)
o. 3D view when measuring 5 with a non-contact 3D surface roughness meter with 20x magnification

FIG. 7: Sample No. of (Example 1). 6
3D view when measured with a non-contact 3D surface roughness meter with 20x magnification

FIG. 8: Sample No. of (Example 3). A three-dimensional view of the back coat and magnetic surface when measuring No. 12 with a non-contact three-dimensional surface roughness meter at 200x magnification.

FIG. 9: Sample No. of (Example 3). 13 to magnification 20
3D view of the back coat and magnetic surface measured with a 0x non-contact 3D surface roughness meter

[Explanation of symbols]

1 Non-magnetic substrate 2 Magnetic layer 3 Back coat layer

Claims (2)

[Claims] 1. A magnetic recording layer made of a Co-based alloy or a metal oxide layer containing these is provided on one surface of a non-magnetic substrate, and a glass dot is provided on the surface of the non-magnetic substrate opposite to the magnetic recording layer. A solution containing polyurethane with a transition temperature of around 10°C, nitrocellulose, an isocyanate curing agent, carbon powder with large and fine particle sizes, alumina powder, and a lubricant was used, and the composition ratio was adjusted to urethane. 2-3 with binder
wt%, curing agent 2 to 3.5 wt%, 2-butanone 15 to
1. A method for manufacturing a magnetic recording medium, characterized in that it is manufactured using a paint mixture of 18 wt%, toluene, 24 to 30 wt%, and cyclohexanone, 3 to 5 wt%. [Claim 2] The average diameter of the paint passing through the filtration is 0.4 μm.
, filtration pressure 2Kg/cm using a filter medium with a maximum diameter of 1.0μm
2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is manufactured using a paint treated with a flow rate of about 1000 g/min and a processing time of 60 min or more.