JPH04265512A - Method for manufacturing magnetic recording media - 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]

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.In place of coating-type magnetic recording media, which are manufactured by dispersing Co-containing ferromagnetic powder such as γ-Fe2O3 or CrO2 in an organic binder, currently magnetic recording media are made directly on a non-magnetic substrate with the aim of achieving even higher densities. Plating method with magnetic metal thin film,
Metal thin film magnetic recording media formed by sputtering, vacuum evaporation, ion plating, etc. are actively being developed.

However, if 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 in which it is used is required. For this reason, compared to conventional back coat materials, vinyl chloride and vinyl acetate materials are disclosed in US Pat. No. 4,567,083, US Pat. No. 4,587,150, US Pat.
No. 628009, US Pat. No. 4,639,389, US Pat. No. 4,663,217, US Pat. No. 467
No. 3622, US Pat. No. 4,592,942,
US Pat. No. 4,618,535, US Pat. No. 44,488
No. 47, US Pat. No. 4,789,583, and US Pat. No. 4,786,557; for polyester and acrylic systems, US Pat. No. 4,687,699 and US Pat.
637963, U.S. Pat. No. 4,443,514, and for polyurethane systems, U.S. Pat. No. 4,567,063, U.S. Pat. No. 4,612,244, and U.S. Pat.
Its manufacture has been carried out as described in the specification of No. 12235, the specification of US Pat. No. 4,587,150, etc.

0004

[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, the present invention takes this point into consideration and provides an excellent magnetic recording medium that has running stability and durability and is free from transfer to the magnetic recording layer by forming a back coat layer that has excellent wear resistance. With the goal.

[0005]

[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 solution containing a mixture of carbon powder, alumina powder, and lubricant, back coating is achieved by finding optimal coating conditions such as tape application speed, roll selection, and blade pressure. Create.

[0006]

[Effect] When formed under the above-optimized coating conditions, a finished state with uniformity and smoothness over a large area is obtained, and the shape transfer to the magnetic recording layer and the edges of the envelope during recording and reproduction are also prevented. By obtaining a flat surface, an excellent magnetic recording medium can be obtained.

[0007]

Embodiment An embodiment of the method for manufacturing a magnetic recording medium of the present invention is shown in FIG. 1. The non-magnetic substrate 1 that can be used is
Polymeric materials such as polyamide, polyimide, polysulfone, polycarbonate, polypropylene, polyethylene, polyethylene terephthalate, polycellulose acetate, and polyvinyl chloride, non-magnetic metal materials, ceramics such as glass and porcelain. Including films, plates, etc. made of well-known materials.

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.
, Sm, Bi, etc., or alloys containing these oxides. Among them, a magnetic recording layer made of a material selected from at least two or more elements of Co, Cr, and Ni,
It is preferable in that it has high magnetic anisotropy energy and high saturation magnetization, and these are
It can be formed by a method such as a sputtering method, an ion plating method, or a plating method. And further Co
, Cr, or metal oxide layers thereof are more preferable from practical points of view such as corrosion resistance. Needless to say, the magnetic recording layer 2 described in the present invention is not limited to the above composition.

The back coat layer 3 described in the present invention has an average molecular weight (M
A material having w) of 10,000 or more can be used. 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 from non-magnetic substrates in mechanical properties. is required. Therefore, the average molecular weight of the polyurethane base agent is preferably 30,000 or more,
A material having physical properties with a glass transition point (Tg) of around 10° C. is more preferable, and an average molecular weight of about 50,000 is most preferable from the viewpoints of Young's modulus, thickness, and abrasion resistance. 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 to 106.
The mixing amount may be such that a value in the range of Ω/cm 2 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 has excellent wear resistance with posts and guide members that come in contact with the tape while it is running. The material and particle size are selected to the extent that they are ensured. It also has the purpose of imparting surface gloss.

[0010] 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 running performance improvement, and the effect of component transfer to the magnetic recording layer, and should be 1 wt%.
The following are preferred.

[0011] It is necessary to optimize the coating conditions applied to the medium in order to maximize the effectiveness of the above-mentioned characteristics of the composition. For example, in addition to adjusting the paint,
The finished surface varies greatly depending on the coating conditions, such as the selection of gravure roll and its rotation speed, usage conditions such as blade pressure, coating speed, and control of drying temperature. Therefore, in the present invention, by optimizing the process of coating conditions, it was possible to find a uniform and smooth coating over a large area.

It goes without saying that the process conditions for the present back coat are applicable 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 back coat layer having the following composition was formed on a polyimide film having a thickness of 9 μm and a width of 150 mm.

(Composition)
Polyurethane (Mw50,000); 34
．． 0 parts by weight Nitrocellulose low molecular weight (1/16sec);
24.5 〃High molecular weight (1/2sec)
; 11.6 〃(JI
Molecular weight measurement based on SK6721) Carbon black 0.023 μm;
85.0〃0.3μm
; 0.5 Abrasive material (CoAl2O3);
4.2 Isocyanate curing agent
; 14.4 Stearic acid
; 1
．． 0 〃Methyl ethyl ketone;
65.0 〃Toluene
; 105.2 〃
Cyclohexane;
13.3 Various coating conditions were prepared using the process conditions shown in Table 1. The equipment used at this time was a test coater manufactured by Yasui Seiki Co., Ltd. The gravure roll was a precision roll diagonal type, the drying temperature was kept constant at 120°C, and the blade pressure was a spring balance (within 5gf). (Sample numbers 1 to 8 from top to bottom)
).

[0015]

[Table 1]

The thickness of the sample surface prepared above was measured using a length measuring device, and the surface roughness was measured using a non-contact three-dimensional surface roughness meter (manufactured by WYKO, TO
PO-3D) Ra, Rms, PV values, and stereoscopic diagrams were also added, as well as observations using an optical microscope. These (Table 2)
and (FIG. 2) (Sample No. 1) to (FIG. 9) (Sample No. 8).

[0017]

[Table 2]

Then, (Table 2) and (FIG. 2) to (FIG. 9)
), the roll depth is 450 μm or less and the tape speed is 4.
Sample No. 5 was prepared under conditions of 5 to 5 m/min and a roll rotation speed of 65 to 105 rpm. It was found that in samples Nos. 1, 4, 6 and 8, there was no roll transfer or uneven coating on the back-coated surface, and a relatively uniform and good finish was obtained.

Further detailed comparison of Ra, Rms, and PV values shows that sample No. 1 was prepared under the conditions of roll depth of 450 μm or less, tape speed of 4.5 m/min, and roll rotation speed of 70 rpm. ．． No. 6 showed the smallest value, and photographic observation (x1000) showed that no fine particles were observed, indicating excellent smoothness.

Therefore, it can be seen that if a back coat is prepared under these conditions, a good magnetic medium without shape transfer to the surface of the magnetic recording layer can be realized.

(Example 2) Next, under the conditions for producing the back coat, the drying temperature was controlled stepwise as shown in FIG. 10 and compared (Samples Nos. 9 to 11). This 3D diagram (
11) to (FIG. 13). Note that other manufacturing conditions and evaluation are the same as in (Example 1).

[0022] The drying temperature should be adjusted from around 60°C to 15°C.
When the temperature was controlled stepwise to near 0°C, the compactness increased more than when it was not controlled.

This is considered to be because the solvent scattering rate was moderated by controlling the drying temperature.

(Example 3) A magnetic recording layer was formed by continuous vacuum deposition on a 9 μm polyimide film as an example of CoC.
r and CoO were sequentially formed under the conditions shown in Table 3. C
o-Cr (composition ratio of Co:Cr=8:2 in Wt%)
has a film thickness of 1000 Å (SEM observation), and CoO has a film thickness of 6
This is a magnetic recording medium equipped with a magnetic recording layer of 0.00 Å (SEM observation).

[0025]

[Table 3]

This was coated with a back coat to a thickness of 0.6 μm under the optimal conditions found in (Example 1) and (Example 2).
The electrical properties were investigated. This is shown in (FIG. 14) (the present invention).

It can be seen that compared to the comparative example in which coating was not carried out under the optimum conditions, a flatter shape was obtained at the edge of the envelope, and a practically usable medium without transfer to the magnetic recording layer could be realized.

From the above, the back code described in the present invention
It can be seen that by having a magnetic recording medium, it is possible to obtain a magnetic recording medium having a large area, uniformity, and excellent characteristics without any shape transfer to the magnetic recording layer.

[0029]

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. By applying a coating treatment using a solution containing as a main component under optimized coating conditions, a good magnetic recording medium with excellent smoothness and no shape transfer to the magnetic recording layer can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the magnetic recording medium of the present invention.

FIG. 2: Sample No. 1 in (Example 1) of the present invention. A perspective view of the surface of 1 measured at 200x magnification.

FIG. 3: Sample No. 1 in (Example 1) of the present invention. 2 surface at magnification 2
Perspective view measured at 00x

FIG. 4 (Example 1) of the present invention
Sample No. A perspective view of the surface of No. 3 measured at 200x magnification.

FIG. 5: Sample No. 1 in (Example 1) of the present invention. Perspective view of the surface of 4 measured at 200x magnification

[
FIG. 6: Sample No. 1 in (Example 1) of the present invention. 5
A perspective view of the surface measured at 200x magnification.

FIG. 7: Sample No. 1 in (Example 1) of the present invention. A perspective view of the surface of No. 6 measured at 200x magnification.

FIG. 8 (Example 1 of the present invention)
) Sample No. A perspective view of the surface of No. 7 measured at 200x magnification.

FIG. 9 shows sample No. 1 in (Example 1) of the present invention. A perspective view of the surface of No. 8 measured at 200x magnification.

FIG. 10 Characteristic diagram of (Example 2) of the present invention

[Figure 1
1] Sample No. 1 showing the temperature control described in (Example 2) of the present invention. A perspective view of the surface of No. 9 measured at 20x magnification.

FIG. 12 shows sample No. 1 showing the temperature control described in (Example 2) of the present invention. A perspective view of the surface of No. 10 measured at 20x magnification.

FIG. 13 shows sample No. 1 showing the temperature control described in (Example 2) of the present invention. A perspective view of the surface of No. 11 measured at 20x magnification.

FIG. 14(a) shows the envelope in the deck running test in (Example 3) of the present invention; FIG. 14(b) shows the envelope in the deck running test in the conventional example;
diagram showing the

[Explanation of symbols]

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

Claims (3)

[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 point transition layer is provided on the opposite surface of the non-magnetic substrate from the magnetic recording layer. Using a solution containing a mixture of polyurethane, nitrocellulose, isocyanate curing agent, carbon powder of large and fine particle sizes, alumina, and powder having a temperature of around 10°C, a blade pressure of 0. 5g or less, roll depth 450
1. A method for manufacturing a magnetic recording medium, characterized in that processing is carried out using a tape of 4.5 to 5 m/min and a roll rotation speed of 65 to 105 rpm. 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the processing is performed at a roll depth of 450 μm or less, a tape speed of 4.5 m/min, and a roll rotation speed of 70 rpm. 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the manufacturing method is performed by setting the drying temperature in stages from 60 to 150°C.