JPH0697498B2 - Thin film type magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film magnetic recording medium in which dimensional changes due to storage environment are stabilized.

2. Description of the Related Art With the development of high-density magnetic recording, thin-film magnetic recording media are being put to practical use, but they are roughly classified into hard disks using aluminum as a substrate and floppy disks and magnetic tapes using a polymer material as a substrate. It When a polymer material is used as the substrate, the thin film magnetic recording medium may be deformed due to the shrinkage characteristics of the polymer material. The most problematic one of them is the problem of curling, and a dimensional error occurs between the thin film layer and the polymer material that is the substrate due to hot flashes and the like when forming the thin film layer, and this dimensional difference causes curling. When such a curl occurs, stable contact between the magnetic recording medium and the magnetic head becomes difficult, and stable recording / reproducing characteristics cannot be obtained.

The problem of curl due to dimensional difference involves two factors,
One is irreversible change and the other is reversible change. Of these, irreversible changes can be considered as curls near room temperature and normal humidity, and irreversible changes can be flattened by adjusting the manufacturing conditions of the thin film layer and the heat shrinkage characteristics of the polymer substrate. However, the other reversible change is the change due to the bimetal effect due to the change in the temperature / humidity environment of the polymer material serving as the substrate.

This bimetal effect is a very important problem as long as a polymer material is used. To avoid this problem, a thin film layer on both sides of the polymer material substrate was proposed as shown in FIG. Is a method of forming.

FIG. 3 is a sectional view showing a conventional example, 6 is a polymer substrate formed of a polymer material, 7 is a magnetic thin film layer, and 8 is a thin film layer. Since the magnetic thin film layer 7 and the thin film layer 8 are present on both sides of the polymer substrate 6 as shown in FIG. 3, even if the polymer substrate 6 expands or contracts, the curl of the entire magnetic recording medium does not occur. It became a structure.

Problems to be Solved by the Invention However, due to the shrinkage property of the polymer material, a skew distortion caused by the expansion and contraction of the entire magnetic recording medium is an important problem along with the curl. This skew distortion is slightly different from the case of curling, and even if a polymer material is used, if the polymer material is provided with sufficient heat-shrinking characteristics, the polymer material does not deform. Therefore, ideally, it can be said that the problem can be solved by adequately controlling the heat-creep characteristics of the polymer material. However, in reality, even if the polymer material is once subjected to heat rubble such that skew distortion does not occur, a large skew strain will be generated by subsequently receiving another heat rubble when forming the thin film layer. Specifically, in the case of a magnetic recording medium having thin film layers on both sides of a polymer substrate material as shown in FIG.
In particular, when thin film layers are formed on both sides, a large amount of heat leakage occurs when the thin film layers are formed, and as a result, it is difficult to stabilize a large skew strain. Because when forming a thin film layer when forming a thin film layer on one side, the thin film layer is formed on only one side of the substrate made of a polymeric material, so the surface on the other side is a polymeric material and is cooled. When brought into contact with metal, etc., (1) the true contact area increases due to the deformation of the polymeric material, and (2) the polymeric material and the cooled metal are extremely strong due to the electrostatic force due to the electrical insulation of the polymeric material. It is possible to closely adhere and (3) the polymer material to be directly and sufficiently cooled. On the other hand, when forming a thin film layer when forming thin film layers on both sides, a thin film layer has already been formed on the opposite side of the thin film layer that is being formed, and when cooling through the already formed thin film layer, (1 ) Since the thin film layer is difficult to deform, the real contact area is small. (2) Since the thin film layer does not have high electrical insulation like polymer materials, it does not adhere due to electrostatic force, and (3) polymer material Since it is indirectly cooled through the thin film layer, it often receives a larger amount of heat speck than that when forming a thin film layer on one side.

Since such a large amount of hot dust must be received during the manufacturing process of the magnetic recording medium, skew distortion is generally a problem in the thin film magnetic recording medium, but as shown in FIG. 3, the curl stabilization is taken into consideration. In the case of the configuration, it is difficult to stabilize the skew distortion by receiving even greater heat dust.

The present invention solves the problem that, in a thin film magnetic recording medium using a polymer material as a substrate, it has been extremely difficult to stabilize the skew distortion due to hot rippling during the manufacturing process, and is likely to cause a dimensional change. It is what

Means for Solving the Problems In order to solve the above problems in the present invention, in a thin film magnetic recording medium having a thin film layer on both sides of a substrate made of a polymer material, the tensile strength against the total thickness is The tensile strength of the thin film layer is 30% or more.

Action In the present invention, in a thin film magnetic recording medium having thin film layers on both sides of a polymer substrate, the tensile strength of the thin film layer is 30% or more with respect to the tensile strength of the entire thickness, and the tensile strength of the polymer material is 70% or more. % Or less, even if internal stress occurs in the substrate made of the polymer material, the deformation of the substrate made by the polymer material is suppressed by the strength of the thin film layer, and the dimensional change of the magnetic recording medium as a whole is improved and the skew distortion is improved. To do.

Example FIG. 1 is a sectional view showing an example of the structure of a thin film magnetic recording medium according to the present invention. In FIG. 1, 1 is a polymer substrate made of a polymer material, 2 is a magnetic layer side underlayer, 3 is a magnetic thin film layer, 4 is a first thin film layer, and 5 is a second thin film layer.

In FIG. 1, the thin film layer on the magnetic surface side is the underlayer 2 on the magnetic layer side.
And the magnetic thin film layer 3 on the opposite side to the magnetic surface. Two thin film layers 4 and 5 are formed on the side opposite to the magnetic surface. Only one example is shown, and the skew distortion can be easily improved by further increasing the number of layers to 3 or 4, or conversely, even if only 1 layer, the manufacturing conditions of the substrate and the thin film layer are sufficient. The significance of the present invention can be achieved by examining the above.

In FIG. 2, the substrate 4 made of a polymer material is appropriately selected from conventionally known polymer materials such as polyethylene, polystyrene, polyamide, polyimide and vinyl chloride, and the magnetic thin film layer is made of CoCr, CoNiO, CoO, CoP, γ-Fe ₂ O ₃ , Fe ₃ O ₄
The magnetic layer-side underlayer 2, the thin film layers 4 and 5 are selected from various conventionally known magnetic materials as appropriate, and various metals and their oxides, nitrides, etc. can be widely selected from materials that generally form a thin film. You can The magnetic thin film layer 3, the magnetic layer side underlayer 2, and the thin film layers 4 and 5 are formed by various conventionally known thin film manufacturing methods such as a vacuum deposition method, a sputtering method, an ion plating method and a plating method. is there.

The effect of the present invention will be described below with respect to some specific examples.

(Example 1) 12 μm thick polyethylene terephthalate was used as a substrate, CoNi (20 wt%) was used in an oxygen atmosphere of 5 × 10 ⁻³ Torr.
It was vapor-deposited to a thickness of 00Å. Next, 8 × 10 on the side opposite to the magnetic surface
^In the oxygen atmosphere of ^-3 Torr, Mg was vapor-deposited at a rate of 1,000Å each time, and sample A was not vapor-deposited, sample B was deposited once, sample C was deposited twice, sample D was deposited three times,
Obtained sample E that was vapor-deposited twice and sample F that was vapor-deposited 5 times,
Based on these, an 8 mm wide magnetic tape was prepared. Skew distortion of this magnetic tape at 60 ℃, 90%, 100H storage was evaluated using NTSC signal by a rotary head video tape recorder (VTR). The tensile strength of the magnetic tape is 0.2% at a pulling speed of 0.05% / sec using a tensile tester.
The tensile strength of the thin film layer was calculated from the tensile strength of the entire thickness and the difference between the tensile strength of each substrate after the thin film layer was removed by etching. The results of these evaluations are summarized in Table 1.

In Table 1, the skew distortion is indicated by the shift time of the reproduction signal of the NTSC signal, and the negative sign indicates that the NTSC signal is contracted in the longitudinal direction of the magnetic tape. When the skew distortion during VTR playback is 30 μsec or more, it affects the image, and when it is 10 μsec or more, it affects the audio signal multiplexed by FM modulation and NTSC signal. As is clear from Table 1, skew strain gradually begins to improve by setting the tensile strength of the thin film layer to 20% or more with respect to the tensile strength of the entire thickness, and the image is no longer affected. Skew distortion was further improved by setting the tensile strength of to 30% or more, and the influence on the FM-modulated audio signal was eliminated. Regarding the change in curl, sample A having a thin film layer only on the magnetic surface side showed a large change in curl and a stable reproduction signal could not be obtained, but samples B to F having thin film layers on both sides of the substrate were obtained. With respect to, the change in curl was small and a stable reproduction signal could be obtained. In Table 1, the skew strain of sample A is larger than the skew strain of sample B because sample A has a thin film layer on only one side, while sample B has a thin film layer on both sides. It seems that it was because I received a reminder.

(Example 2) Using an aromatic polyamide having a thickness of 30 µm as a substrate, FeNi (20 wt%) was sputtered as a magnetic layer side underlayer to a thickness of 2,000 Å, and further 2,000 Å CoCr (20 wt%) was sputtered thereon. did. Next, on the side opposite to the magnetic surface, of 1 × 10 ^-2 Torr
Si was sputtered at a rate of 2,000Å each time in an N ₂ atmosphere to form a plasma polymerized film on the magnetic surface side, and then a magnetic tape having a width of 8 mm was prepared. The prepared samples are 7 samples of G, H, I, J, K, L and M corresponding to the number of Si sputter layers of 1 to 7. The skew distortion of these tapes at 60 ℃, 90% and 100H storage was evaluated by NTV signal by a rotary head VTR. Also, the tensile strength of the magnetic tape was calculated based on the force at the time of 0.2% deformation at a tensile speed of 0.05% / sec by a tensile tester. The results of these evaluations are shown in FIG. As is clear from FIG. 2, the effect of improving skew distortion begins to appear when the tensile strength of the thin film layer with respect to the tensile strength of the entire thickness is 20% or more, and the tensile strength of the thin film layer with respect to the tensile strength of the full thickness is 30%. By setting the ratio to be at least%, the skew distortion is significantly improved.

Example 3 A thin film layer was formed by using polyethylene terephthalate having a thickness of 10 μm as a substrate. The thin film layer formed will be described with reference to FIG. 2. Only the magnetic thin film layer is formed ... Sample N, magnetic thin film layer and thin film layer 1 ... Sample O, magnetic thin film layer and thin film layer 1 and thin film layer 2 ... Sample P, magnetic layer side underlayer, magnetic thin film layer, thin film layer 1, thin film layer 2 ... Sample Q.
The magnetic thin film layer is formed with a thickness of 4 × 10 ^-3 Torr in an oxygen atmosphere.
1,000 Å of Co was vapor-deposited, and 1,000 Å of copper was vapor-deposited as a thin film layer 1, a thin film layer 2, and a magnetic layer side underlayer. Create these samples on magnetic tape and rotate at 60 ℃, 90%, 100H
Skew distortion of NTSC signal by VTR and tensile strength required for 0.2% deformation were evaluated. The results are summarized in Table 2.

As is clear from Table 2, when the tensile strength of the thin film is 20% or more with respect to the tensile strength of the entire thickness, the skew strain begins to show an improvement effect, and the tensile strength of the thin film layer is 30% with respect to the tensile strength of the entire thickness. Due to the above, the skew distortion is significantly improved.

(Example 4) As a substrate, polyethylene naphthalate having a thickness of 7 μm was used, and CoNi (20 wt%) was added in an oxygen atmosphere of 8 × 10 ⁻³ Torr to 2,
It was deposited to a thickness of 000Å. After that, a back coat layer was formed by a coating method, and a lubricant was applied to the magnetic surface side to obtain a sample R as an 8 mm wide magnetic tape. On the other hand, CoNi (20wt
%) After forming a magnetic thin film layer, Al was vapor-deposited on the side opposite to the magnetic surface in an oxygen atmosphere of 5 × 10 ^-3 Torr, and the sample was vapor-deposited to a thickness of 2,000Å. I got T. Applying a lubricant to the magnetic side of both samples S and T 8
It was a magnetic tape of millimeter width. Apply these tapes at 60 ℃, 90
%, Skew distortion at 100H storage NT by rotating head VTR
It was evaluated using the SC signal.

Also, the tensile strength of the magnetic tape was calculated based on the force at the time of 0.2% deformation at a tensile speed of 0.05% / sec by a tensile tester. These results are summarized in Table 3.

As is clear from Table 3, skew strain is improved by setting the tensile strength of the thin film to 20% or more with respect to the tensile strength of the entire thickness, and further, the tensile strength of the thin film layer to 30% or more with respect to the tensile strength of the entire thickness. By doing so, skew distortion is significantly improved.

Although the effects of the present invention have been described above with reference to four specific examples, the present invention is not limited to these specific examples and extends to all magnetic recording media satisfying the spirit of the present invention. In each of the embodiments, the magnetic tape is taken as an example in order to accurately measure the skew distortion, but the effect is also great in improving the dimensional stability of a magnetic recording medium having another form such as a floppy disk. There is.

As described above, according to the present invention, in the thin film magnetic recording medium having the thin film layers on both sides of the polymer substrate, the tensile strength of the thin film layer is 30% or more with respect to the tensile strength of the entire thickness. As a result, the excellent effect of improving the dimensional stability of the magnetic recording medium and improving the skew distortion can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between skew strain and tensile strength in the same embodiment, and FIG. 3 is a sectional view of a conventional example. 1 ... Substrate made of polymer material, 2 ... Underlayer on magnetic layer side,
3 ... Magnetic thin film layer, 4,5 ... Thin film layer.

Claims (1)

[Claims] 1. A thin film magnetic recording medium having thin film layers on both sides of a polymer substrate, wherein the tensile strength of the thin film layer is 30% or more of the tensile strength of the entire thickness. Type magnetic recording medium.