JPS6018822A - Thin film type magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium which can be formed at a high speed, has high productivity and is suitable for a floppy disc having excellent dimensional accuracy by constituting a flexible base plate of an arom. polyamide film having a specified initial Young's modulus and coefft. of linear thermal expansion. CONSTITUTION:A film consists of an arom. polyamide polymer contg. the repetitive structural unit expressed by the general formula independently or in the form of a copolymer in which at least 75mol% of the repetitive unit is a poly- m-phenylene isophthalic amide polymer film. Said film has 1.35-1.41 density and the main refractive index thereof is specified. The polymer is extruded onto a casting roller to obtain an unoriented hydrous film which is successively stretched. The stretched film is dried and heat-set, by which the film is obtd. Said film has >=150kg/mm<2> initial Young's modulus at 200 deg.C an <=2.5X10<-5>cm/cm/ deg.C coefft. of linear thermal expansion. The magnetic recording medium is formed of, for example, a single-layered double-sided medium having the vertically magnetized film consiting of a CoCr alloy film 2 on both sides of a base plate 1 and a two- layered double-sided medium laminated with a soft magnetic material consisting of an NiFe alloy film 3 and a CoCr alloy film 2.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to magnetic recording media, that is, flexible magnetic tapes and flexible disks. The present invention relates to a magnetic recording medium whose recording layer is a ferromagnetic continuous thin film such as a thin film, a CoNi obliquely deposited film, or a CoCr perpendicularly anisotropic film.

[Prior art]

In place of the conventional coated magnetic recording media K, which has a recording layer in which fine ferromagnetic powder is dispersed in a binder resin, in recent years, with the demand for high-density recording, γ-FelO thin films formed by sputtering or reactive vapor deposition, diagonal Co formed by vapor deposition
The recording layer is a ferromagnetic thin film with a thickness of 0.02 to 2.0/f111, such as a Ni alloy film or a perpendicularly anisotropic CoCr alloy film having an axis of easy magnetization perpendicular to the film surface formed by sputtering or vapor deposition. A thin film magnetic recording medium formed on a flexible substrate has been proposed. In particular, flexible disks in which perpendicular magnetic anisotropic films are formed on both sides of a flexible substrate are attracting attention as the next generation magnetic recording medium and are being actively researched. A polymer film such as a polyethylene terephthalate (PET) film is usually used as a flexible substrate for such a thin-film magnetic recording medium, as in the case of a coating-type magnetic recording medium, but there are the following problems.

In other words, the aforementioned thin film magnetic recording media are usually manufactured by vapor deposition or sputtering known as the PVD method, but in such methods, a large amount of heat is applied to the substrate during film formation, and internal stress remains in the formed thin film. Various troubles occur due to the fact that the substrate needs to be heated in order to obtain good magnetic properties. For example, when PET film is used as a substrate, it has poor heat resistance, and there are problems such as melting or deformation of the film during film production, deterioration of film properties after production, curling of the medium, or cracks in the film. There are many problems that arise. Furthermore, we succeeded in producing a membrane [
Even in those few cases, the yield is extremely low due to complicated manufacturing processes such as straightening curls in post-processing. On the other hand, even when the substrate is made of polyimide film, which has excellent heat resistance unlike PET film, there are problems such as curling of the medium and distortion of images due to the low Young's modulus when using magnetic tape for video. . Furthermore, it was found that in a double-sided flexible disk using a polyimide film as a substrate, the playback output level on the front and back sides was significantly different. As described above, PET films and polyimide films, which have been widely used in the past, still lack sufficient heat resistance, dimensional stability under heat, Young's wheel, and surface shape as substrates. Furthermore, polyimide films are expensive and have practical problems.

[Purpose of the invention]

In view of the above-mentioned current situation, the present invention provides a thin film magnetic recording medium that is practically usable, inexpensive, and has good placement and reproduction characteristics.In particular, it can be formed at high speed, has high productivity, and has excellent dimensional stability. The main purpose of this invention is to provide a thin film type magnetic recording medium suitable for excellent floppy disks.

[Structure and effects of the invention]

The present inventors developed a new film and produced a thin-film magnetic recording medium based on the limb film, and found that it had extremely good characteristics.

−5= That is, the present invention provides a thin film magnetic recording medium having a ferromagnetic thin film as a recording layer on a flexible substrate, in which the flexible substrate has an initial Young's height of 1 sokg/m at 200°C.
Coefficient of linear thermal expansion 2.5 x 1'rs/cm above nP,
This is a thin film type magnetic recording medium characterized by being an aromatic polyamide film at a temperature of 7° C. or lower.

The present invention described above is based on various studies on the causes of curling in conventional substrates, and it has been found that the curling is caused by the lack of high-temperature dimensional stability of the substrate, and the above-mentioned structure reduces curling during film formation. As a result, stable and high-speed film formation is possible, and curling as a medium is also reduced to the point where it does not pose a practical problem. Moreover, the material of the present invention does not have the problem of electromagnetic conversion characteristics differing between the front and back sides of the substrate as seen in conventional polyimide films, and is also cheaper than polyimide films, which has a great practical advantage.

The aromatic polyamide film referred to herein is a film consisting of an aromatic polyamide-based polymer containing repeating structural units represented by the general formula in the form of monopoly or copolymerization,
Preferably, it is an aromatic polyamide polymer film containing 75 or more moles of the structural unit.

Here, Arl, Art, and Ar may be the same or different, and a typical one has the following structural formula.

Rn Rn Rn Rn Here, R is lower alkyl, borrowed alkoxy, halogen, or nitro group, and n is θ including 0 and 4.
is an integer of ~4, and is one selected from the following, where KY represents hydrogen or a lower alkyl group.

Among the aromatic polyamide films, in the case of poly-m-phenylene isophthalamide-based polymer films in which at least 75 molar units of repeating units are composed of m-phenylene diamine and isophthalic acid halide such as isophthalic acid chloride. is the density of the film d(g/c!ri is 1.35
to 1.41, and the D line of Na (sodium) (
Principal refraction height nα, nβ and n for wavelength ss9nm)&C
γ (However, in the order of increasing principal refractive index values lCf1α, nβ
, nγ) satisfy the following formula, and the relationship between the principal refractive indexes nα and nβ is Knα−nβ≦0. 4ISF&C is preferably a polymetaphenylene isophthalamide film that satisfies the relationship: OB.

A polymetaphenylene isophthalamide film that satisfies the above conditions has excellent mechanical properties, two-dimensional stability, 9 surface properties, and is suitable for the aromatic polyamide film of the present invention. Furthermore, a patent application filed earlier by one of the present inventors in 1982-217
As described in the specification of No. 691, 55tin has a moisture absorption dimensional change rate of 0.6 coefficient or less, small in-plane anisotropy, and a Young's modulus of 450 #/m or more, which has excellent mechanical and dimensional stability against temperature and humidity. Therefore, it is particularly suitable for floppy disks, where such dimensional stability is said to be essential for increasing density.

Incidentally, as a method for manufacturing the above-mentioned aromatic polyamide film used in the present invention, a method such as that disclosed in Japanese Patent Application Laid-Open No. 56-28242 can be applied.

Furthermore, the above-described poly-m-7 enylene iso phthalamide film is disclosed in a patent application filed in 1973 by one of the present inventors.
It can be obtained by the method described in the specification of No. 7-60293.57-89848゜-〇-57-96265 and Japanese Patent Application No. 57-217691. Typical manufacturing methods are shown below. Namely, polymetaphenylene isophthalamide (al), N-methylpyrrolidone-2(b) as an amide solvent, calcium chloride (as a solubilization aid),
A composition having the following composition is prepared using cl.

The above composition was processed using a 30m/m extruder to give a size of 0.1mm.
, extruded onto a casting roller at 110°C from a T-die with a width of 400 srs, introduced into a 43T calcium chloride aqueous solution at 100°C, and then washed in cold water below 10°C. Get the film. This unstretched water-containing film was stretched 2.6 times in the machine direction (MD) K in a 30% N-methylpyrrolidone-2 aqueous solution at 50°C.
Further, the film is successively stretched in the width direction (TD) &ct perpendicular to the MD at a stretching ratio of o times. This film is dried at 10° C. in a hot air dryer at 60° C. and further heat-set at 290° C. to obtain a polymetaphenylene isophthalamide film.

The thin film magnetic recording medium referred to here refers to a γ-Felon thin film formed on a flexible substrate by sputtering, reactive sputtering, or reactive vapor deposition, and a CoN thin film formed by oblique vapor deposition.
1 alloy thin film and CoC formed by sputtering or evaporation
1. A ferromagnetic thin film formed by PVD or CVD, such as an r-alloy thin film, is used as a magnetic recording layer. There may be a different organic or inorganic layer between the substrate and the magnetic recording layer to improve adhesion, and there may also be a protective/lubricant layer on the magnetic recording layer. .

By the way, in the production of perpendicular magnetic recording media, which has been actively developed in recent years due to the high possibility of ultra-high density deployment, a high substrate temperature of 160°C or higher, and in some cases 200°C or higher, is required in order to obtain good characteristics. ing. Therefore, the present invention, which uses an aromatic polyamide film as a substrate which has excellent dimensional stability and strength at high temperatures, is particularly effective.

The above-mentioned perpendicular magnetic recording medium is as known from Japanese Patent Publication No. 58-91, Japanese Patent Publication No. 58-10764, etc.
A perpendicular magnetic anisotropic film is formed on one or both sides (front and back) of the base film, and a NiFe alloy (f
) A soft magnetic film having a coercive force of about 20 Oe or less and a thickness of about 0.5 μm is usually used. In addition, the perpendicular magnetic anisotropy film usually contains 10 to 2 Cr.
C containing 3 wt% in hexagonal system with the C axis oriented to the film normal.
A polycrystalline film of oCr alloy is used, and the vertical orientation of the C axis (
It is evaluated using the half width Δ050 of the rocking curve of X-ray diffraction. ), and the perpendicular coercive force He(v) measured by applying a magnetic field in the direction perpendicular to the film surface must be appropriate.

[Example 1] A perpendicular magnetic recording medium was fabricated as described below using the aforementioned polymetaphenylene isophthalamide film having a thickness of 50 μm as a substrate. For comparison, the substrate is a polyimide film, specifically a 50 μm thick Kapton film (Du
A perpendicular magnetic recording medium was produced in the same manner using a magnetic recording medium (trade name, manufactured by Pont Co., Ltd.). Table 1 below shows typical physical properties of both substrates. It can be seen from the same table that the polymetaphenylene isophthalamide film according to the present invention has extremely excellent physical properties at high temperatures.

Table 1: A perpendicular magnetic recording medium is manufactured by using a facing target sputtering method known in Japanese Unexamined Patent Publication No. 57-158380, etc., and has a first perpendicular magnetization film made of a KCoCr alloy film on both sides of the substrate.
A single-layer double-sided medium shown in Figure (al K, 13-) and a double-layer double-sided medium shown in Figure 1 (bl) in which a soft magnetic film made of a NiFe alloy film and a perpendicular magnetization film made of a CoCr alloy film were laminated were fabricated. did.

That is, the NiFe alloy film is a NiFe alloy target (Ni: 81wt9G, 150mmX100mm)
Using a facing target type sputtering device with two targets facing each other at an interval of 120 mm, one sputtering target was placed on the side of both targets.
While feeding the substrate film onto a rotating drum with a diameter of 250 mm kept at 40°C, the argon gas pressure was 1, OPa.
, sputtering was carried out at an average deposition rate of 0.9 pm/min to form a 0.64 μm NiFe alloy film with double-sided pressure.

Then, the CoCr alloy film is coated with a CoCr alloy target (C
r: 17 wt%) using the same apparatus as above.
Film or NiFe was placed on a rotating drum kept at 10°C.
While the film with the alloy film formed thereon was fed, sputtering was performed at an average deposition rate of 1.0 μm/min to sequentially form 0.4 μm CoCr alloy films on both sides, producing a single-layer double-sided medium and a two-layer double-sided medium, respectively. .

14- Also, for comparison, a film was prepared in the same way as in 4. Polymetaphenylene isophthalamide filament/
In the example using the l-me, if the alloy film is formed only on one side during manufacturing, the outer side of the alloy film side is about 1
The medium had a curl [5] with a radius of curvature of about 00 mmR, but the medium with the same composition of alloy films formed on both sides became a completely flat medium. 1- In a comparative example using a Kapton film, a NiFe alloy film was formed only on one side during manufacturing, and at the stage when the NiFe alloy film was removed, curling occurred on the outside of the film surface with a radius of curvature of 15 mmH, and further NiFe alloy film was formed on both sides. At the stage where the CoCr alloy film was formed only on one side of the structure on which the film was formed, curling occurred with a radius of curvature of 20 mmH, making handling extremely inconvenient. Furthermore, even when alloy films with the same composition were formed on both sides, curls of about 60 wR remained.

The causes of curl are 1) the bimetal effect due to the difference in thermal contraction rate between the metal film and the base film when the film is prepared at high temperature and the medium is taken out to room temperature, that is, the difference in reversible thermal expansion coefficient, and 2) the bimetallic effect due to the difference in reversible thermal expansion coefficient and 2) sputtering. This is thought to be because the metal film is attached to the base film in a stretched state due to the tension applied to the base film in the film, and when the tension is released, the base film contracts. In order to prevent such una curl, it is necessary to satisfy both the dimensional stability of the film at high temperatures, that is, the low coefficient of thermal expansion, and the high Young's modulus at high temperatures. As shown in Table 1, the film of the example had much better high-temperature dimensional stability than the film of the comparative example, which is why the curl of the medium was small. In order to have the above effects, the coefficient of thermal expansion is preferably in the range of 1.0 to 2.0 x 101α/cm/°C, and the Young's modulus at about 200°C is 200 to 97W.
It is desirable that the coefficient of thermal expansion is 2.5X1.
Even if it is about 0-'', the high-temperature Young's modulus may be a sufficiently large value, or the opposite relationship may be used.Furthermore, the required Young's modulus value may vary depending on the film tension during sputter film formation. However, the coefficient of thermal expansion is approximately 2.5 × 10-l
The effects of the present invention are exhibited if the initial Young's modulus at 200° C. is 150 kg/Inrf or more at 1Cm/Crn/°C or less.

Furthermore, when the base film is polymetaphenylene inphthalate S, the density d(9/cJI) is 1.35.
~1.41 and the principal refraction na, nβ.

When nγ satisfies the following formula %, the high temperature dimensional stability and the surface properties described below are excellent, and the effects of the present invention are significantly exhibited.

Further, a perpendicular magnetic recording medium was prepared using a 750 μm thick PET film as a substrate under the same conditions as described above. In this case, cracks and cloudiness occurred in the produced alloy film due to insufficient heat resistance of the film and oligomer precipitation. Furthermore, although it was possible to fabricate an Nlce alloy film when fabricating a 2N medium, CoC
When laminating the r-alloy film, the NiFe alloy film cracked and a good medium could not be obtained t'1. It was ic. by the way,
When the deposition rate of the alloy film was lowered to about 0.3 μm/min and the temperature of the rotating drum for transporting the film was lowered to about 110°C during the production of the CoCr alloy film, the appearance remained although some curling remained. A good medium could be obtained. As described above, it is possible to use PET film for the substrate, but the productivity is greatly reduced, and the reproduction output (described later) of the obtained medium is about 50% lower than that of the example for both the front and back sides. It was something.

Table 2 below shows the crystal properties and magnetic properties of the perpendicular magnetic recording media of Examples and Comparative Examples.

In Table 2, He(h) is the coercive force measured in the plane parallel to the film surface, and Hk is the anisotropic magnetic field measured from the in-plane MH curve.

Table 2 18- From the above table, it can be seen that in the Examples, both the front and back sides of the film have exactly the same characteristics, but in the Comparative Example, there is a difference in characteristics between the front and back sides. The reason for this is thought to be that the surface properties, that is, the surface roughness, the orientation of the polymer chains of the film, and the degree of crystallinity are different between the front and back sides of the comparative Kapton film. In this respect, the surface roughness of the substrate film is approximately the same in the example as 0.006 pm on the front side and 0.007 pm on the back side in terms of center line average roughness, but in the comparative example, wheat is o, o o sμm, back side is 0.
This is also supported by the large difference of 0.04 μm.

Next, the obtained media of Examples and Comparative Examples were slit into 0.5 inch widths, used in a tape drive snowmaking machine, and the recording density characteristics of digital signals were investigated. The head is an auxiliary pole excitation type vertical head known from Japanese Patent Publication No. 58-91, etc., and the main pole is a permalloy film with an effective thickness of 1.4 μm and a trunk width of 2 am.

The auxiliary magnetic pole is made of SOOμm thick ferrite for recording purposes.
A wire with a diameter of 1.7 and a 500-turn winding for playback was used. The tape speed was 4.76σ/8ec during recording.
NRZI-Al at IH/sec at 9,52 when regenerated
l-1 saturation recordings were made.

FIG. 2 shows the recording density characteristics on the front side of an example having a two-layer film structure. The horizontal axis is the recording density (KBPI), the vertical axis is the reproduction output (mho-p), and both axes are on a logarithmic scale. 2KB
PI and 45KBPI (second peak) and 90KBPI
(Third peak) output is shown in Table 3.

The comparative Kapton film that has been used in the past has a large output difference between the front and back sides and cannot be used for double-sided flexible discs, but the example of the present invention shows good electromagnetic cost conversion characteristics that are almost the same on both the front and back sides. There are no problems like the comparative example.

Table 3 [Example 2] Using a 12 μm thick polymetaphenylene isophthalamide film having the same physical properties as Example 1, a semi-continuous vacuum evaporation apparatus was used as disclosed in the Institute of Electronics and Communication Engineers Technical Research Report MR81-2. A magnetic thin film made of a CoNi alloy film was formed on only one side by oblique evaporation. In other words, the film was placed on a rotating cylindrical can with a diameter of 300 m and maintained at 85°.
Maximum incident angle of 90° while traveling at n, 35m/win
A CoNi alloy film was deposited at a minimum incidence angle (critical incidence angle) of 55°C. The vapor deposition was carried out using a CoNi alloy rod (Ni: 20w) placed in a crucible placed at 221ff+ below the can.
t%) with a 270° deflection type 6 kW electron gun,
Flow 208 CCM of oxygen gas and vacuum degree I X 1 o-'
I went with Torr. The thickness of the obtained CoNi alloy film was 2500A, and the coercive force He measured in the tape running direction was 3.
80 Qe.

The squareness ratio was 0.88.

Furthermore, for comparison, a similar CoNi alloy film was deposited on the front side of a 12 μm Kapton film with the same characteristics as in Example 1, to obtain a magnetic film with similar characteristics.

21- The magnetic tape prepared as above was slit into O, S inch width and commercially available TDK-T-6 manufactured by Tokyo Denki Kagaku Kogyo ■.
Insert it into the 0 cassette, and use the HR-6700 made by Japan Victor
Evaluation was made using 8 VH machines. The evaluation was performed by visually judging the stability of the reproduced image, and also by checking the dropout (15 μsec, 20 dB).
(decrease) was measured.

The results are shown in Table 41C.

Table 4 As described above, the stability and dropout of the reproduced images in the comparative examples are inferior to those in the examples, but this is thought to be due to the poor surface properties of the Kapton film in the examples and the low Young's force.

Further, when an αNi alloy film was similarly prepared using a PET film as a substrate, the film often melted due to heat loss. Further, even when film formation was possible, the curling of the medium was severe and post-heat treatment had to be performed, resulting in extremely low yields.

As described above, the magnetic recording medium based on the aromatic polyamide film according to the present invention can easily and inexpensively provide extremely good characteristics both in flexible discs and magnetic tapes. The base film of the present invention is effective when heat resistance is required during medium production, and when heat resistance is required as an FC medium, for example when used in a flight recorder.

[Brief explanation of drawings]

Figure 1 shows the media configuration in Example-1, where (a) is a single-layer double-sided medium, (bl is a two-layer double-sided medium). Figure 2 shows the two-layer configuration of Example 4-1. Indicates the recording density characteristics of [
, is something. 1: Substrate 2: CoCr alloy film 3: N5Fe alloy film 23 times

Claims (1)

[Claims] 1. A thin film magnetic recording medium in which a ferromagnetic thin film is formed as a recording layer on a flexible substrate, wherein the flexible substrate is
1. A thin film type magnetic recording medium characterized in that it is an aromatic polyamide film having an initial Young's modulus at 0°C of 150 Yu/m♂ or more and a linear thermal expansion coefficient of 2.5×10-'cFrL/crrL/°C or less. λ The thin film magnetic recording medium according to claim 1, wherein the aromatic polyamide film is a polymetaphenylene isophthalamide film that satisfies the following two-stripe property. a Film density d (,!i'/c/) 1.3s
~1.41 b The principal refractive indexes nα, nβ, and nγ (however, na, nβ+nr are set in descending order of the principal refractive index values) for the D-line (wavelength ss 9 nm) Ic of Na are expressed by the following two equations. 3. The thin film magnetic recording medium according to claim 1, wherein the ferromagnetic thin film is a perpendicularly anisotropic film. 4. The thin film magnetic recording medium according to claim 2 or 3, wherein the flexible substrate is a disk.