JPH0658739B2 - How to make a magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a perpendicular magnetic recording medium having an easy axis of magnetization in a direction perpendicular to a magnetic recording surface on a polymer molding substrate.

[Prior Art] Conventionally, thin film manufacturing techniques such as vapor deposition and sputtering have been used as a method for manufacturing a perpendicular magnetic recording medium on a polymer molded product substrate. When manufacturing a perpendicular magnetic recording medium by vapor deposition / sputtering, the perpendicular magnetic recording medium having good magnetic characteristics was obtained by raising the substrate temperature as high as possible, and the adhesion strength of the magnetic film was improved. However, these vapor deposition / sputtering methods form a magnetic film by colliding high-energy metal atoms with a substrate in a vacuum, so that the temperature of the substrate becomes higher. That is, in the case of a polymer molded product substrate having a melting, sublimation, or decomposition temperature, the substrate temperature cannot be increased indefinitely, and the upper limit is usually about 100 ° C. lower than the melting, sublimation, or decomposition temperature.

However, since the polymer molded product substrate always contains unreacted monomers and low-polymerization degree polymers (hereinafter referred to as oligomers) in its composition, these oligomers are deposited on the substrate surface, the soft magnetic film (permalloy _{· C o T i · C o} T a · C o Z r Nb , etc.) or a perpendicular magnetization film formed thereon (C _o C _r, C
_o W, C _{o Mo} , C _o V, etc.), the bad influence of the oligomer on the substrate surface, that is, the unevenness also causes unevenness on the film itself, resulting in poor head touch between the media and the head and deterioration of the reproduction output. Occurs. Further, due to the unevenness, the soft magnetic film undergoes the pinning of the domain wall and the magnetic characteristics are deteriorated. Further, since the convex portion on the rotating medium creates a collision portion with the head, it causes scratches and film baldness on the medium, resulting in extremely deteriorated durability. The instability of the head touch due to the unevenness also becomes an unstable factor of the absorption of the magnetic flux from the medium into the head, and the envelope characteristics are remarkably deteriorated and the recording density characteristics D ₅₀ are deteriorated.

In the past, in order to eliminate irregularities due to oligomers after forming a film, buffing was used to scrape the protrusions to improve the smoothness, but the drawback is that not only the continuity of the film is impaired, but the film surface is further damaged by abrasion powder Had.

Therefore, before directly sputtering or vapor deposition on the polymer molded product substrate, the polymer molded product substrate is heat-treated at a temperature below the melting, sublimation or decomposition of the substrate, and the oligomer deposited on the substrate is washed with a solvent. After that, a magnetic layer was formed to produce a magnetic recording medium having very few irregularities. However, there is a problem in that oligomer-deposited traces are formed on the substrate obtained by washing the oligomer with a solvent, and the protrusions due to the oligomer are eliminated, but concavities due to the deposition traces are increased.

It should be noted that this oligomer is not only inevitable in the production method for producing a polymer molded article substrate, but is also intentionally included for imparting stretchability when it is processed into a film.

〔Purpose〕

In view of the above points, the present invention eliminates oligomers that adversely affect all surfaces before film formation, and provides excellent perpendicular magnetic recording such as smoothness, magnetic characteristics, durability, reproduction output, envelope characteristics, and recording density characteristics. The purpose is to obtain a medium.

〔Overview〕

According to the present invention, in a perpendicular magnetic recording medium, a polymer molded product substrate of the medium is immersed in a solvent, and then the substrate is subjected to heat treatment at a temperature not higher than melting, sublimation or decomposition of the substrate to deposit on the substrate surface. After removing the oligomer, a magnetic layer is formed to produce a magnetic recording medium having extremely few irregularities.

〔Example〕

 Examples of the present invention will be described below with reference to the drawings and tables.

In this example, PET (polyethylene terephthalate) was used for the polymer molded product substrate, and acetone was used as the solvent. Other than this, trichlene, xylene, etc. may be used. FIG. 1 is a flow chart of steps for producing a medium of the present invention. First, soak PET in acetone, then put the PET in a constant temperature bath at 180 ° C. for 1 hour to precipitate the remaining oligomers, soak the PET in acetone again, and to eliminate the evaporation residue of acetone on PET. Immerse in alcohol, then blow the alcohol remaining on the PET and blow it off with nitrogen, and put P in the sputter device.
And excisional the ET, C _o T _i as a soft magnetic film thereon, and the C _o C _r film sputtered at a substrate temperature of 0.99 ° C. as a vertical magnetization film.
Of FIG. 2 (a) is a perpendicular magnetic recording medium made by the present invention, 1 to the acetone treatment was precipitated oligomer PET, 2 is C _o T _i soft magnetic film 0.5 [mu] m, 3 is C _o The C _r perpendicular magnetization film is 0.5 μm. FIG. 2 (b) shows a conventional medium. That is, PET was heat-treated to precipitate oligomers, washed with acetone, and then sputtered. Four
Is PET, 2 is a _{Co Ti} film, 3 is a _{Co Cr} film, and 5 is a trace of oligomers removed by acetone washing. The substrate temperature of both the medium of the present invention and the medium of the conventional method is 150 ° C. Table 1 shows the surface roughness of the medium.

As is apparent from FIG. 2 and Table 1, the surface properties of the medium according to the present invention are very smooth as compared with the conventional method. Table 2 shows the magnetic characteristics.

As can be seen from the above, the medium according to the present invention exhibits good characteristics as a perpendicular magnetization film. Next, FIGS. 3 and 4 show reproduction output, recording density characteristics, and envelope. All of these were measured at a medium rotation speed of 300 rpm and a linear velocity of 2 m / s and a head main magnetic pole film thickness of 0.5 μm. FIG. 3 shows recording density characteristics, (a) shows the medium according to the present invention, and (b) shows the medium according to the conventional method. The data in FIG. 3 are summarized in Table 3.

As can be seen from FIG. 3 and Table 3, the reproduction output of the medium of the present invention is doubled, and the recording density D ₅₀ at which the output is halved is also increased by nearly 40%. FIG. 4 shows the envelope characteristic. (a) is the medium of the present invention, and (b) is the conventional method medium. This envelope has a recording density of 5 KBPI. The medium according to the invention exhibits very good envelope characteristics. On the other hand, the envelope of the medium according to the conventional method has variations in reproduction output.

〔effect〕

As described above, the perpendicular magnetic recording medium according to the present invention has various effects as compared with the conventional method. The effects are summarized below.

◎ Improvement of reproduction output ◎ Improvement of recording density characteristic ◎ Improvement of envelope characteristic ◎ Improvement of magnetic characteristic In this example, PET was used as the polymer molded article substrate, but a heat resistant polymer molded article such as aramid or polyimide was used. The present invention is effective even in the case of a substrate. Further, the solvent used in this example is acetone, trichlene, xylene and the like, but the present invention is effective even if these are diluted with alcohols. Furthermore, even if the above solvent is used for steam cleaning, the present invention has further effects. Further, in this embodiment, the _Co T _i film was used as the soft magnetic film, and the _Co C _r film was used as the perpendicular magnetization film.
Other soft magnetic films (permalloy, supermalloy,
_{C o T a, C o Z} r Nb , etc.), a perpendicular magnetic film (C _o W, C _o V, etc.) even present invention is effective. Furthermore, in addition to two-layer film medium is also effective in C _o C _r monolayer is made also effective in B _a -F _e rrite coating type perpendicular magnetic film. Further, although the present embodiment is prepared as a medium for floppy disk, the same effect can be obtained as a 16 mm VTR tape, 8 mm VTR tape, and audio tape.

In this embodiment, PET is held in a constant temperature bath at 180 ° C. for 1 hour, but the temperature may be any temperature as long as it is below the melting / sublimation / decomposition temperature, and the time is the holding temperature and the type of PET.
This cannot be generally stated because it depends on the thickness of PET.

Further, in this embodiment, the oligomer is precipitated by heat-treating PET in a constant temperature bath, but heat treatment in vacuum shortens the oligomer precipitation time. Further, in this example, the solvent is used for removing the precipitated oligomer, but ultrasonic waves, ultraviolet rays irradiation, charged particle irradiation, and oxidation by ozone are also effective.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram for producing a perpendicular magnetic recording medium according to the present invention. 2 (a) and 2 (b) are cross-sectional views of the medium of the present invention and the medium of the conventional method, respectively. FIG. 3 shows the recording density characteristic, and FIG. 4 shows the envelope. 1 ... PET which was soaked in acetone before heat treatment and then heat treated to precipitate oligomers, and then treated with acetone. 2 …… C _o T _i spatter film 3 …… C _o C _r sputter film 4 …… PET (those obtained by precipitating an oligomer and then treated with acetone) 5 …… A trace of the oligomer after the oligomer is treated with acetone . (a) ... medium according to the present invention (b) ... medium according to conventional method

Claims (1)

[Claims] 1. In a perpendicular magnetic recording medium having an easy axis of magnetization perpendicular to the magnetic recording surface, a polymer molded product substrate of the medium is immersed in a solvent capable of removing oligomers precipitated from the substrate, Magnetic recording characterized in that the substrate is heat-treated at a temperature below melting, sublimation or decomposition of the substrate to form a magnetic layer on the polymer molded product substrate from which oligomers precipitated on the substrate surface are removed. How to make media.