JPH0322650B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to flexible magnetic disks. [Prior Art] Flexible magnetic disks (typically known as ``floppy disks'', hereinafter simply referred to as floppy disks) are often used as auxiliary storage devices in small computers. .
Information is normally recorded on floppy disks by concentrically distributing a large number of narrow annular recording areas called "tracks."Recently, in order to increase the recording capacity, track density (disk There is a strong need to increase the number of tracks per unit length in the radial direction. However, an increase in track density necessarily involves a decrease in track width, so increasing the track density of a floppy disk requires a change in the disk's radial dimension (recording/playback) in response to changes in temperature and humidity during use. (change in relative position with respect to the head) is required to be small. This is because such dimensional changes shift the relative positions of the head and track in the radial direction, making it impossible to reproduce signals recorded on the track (causing so-called "off-track"). Therefore, to achieve high track density,
The following characteristics are required. That is, (1) the dimensional change due to changes in relative humidity, that is, the humidity expansion coefficient, is small in all directions within the disk surface. (2) The anisotropy of the coefficient of thermal expansion within the disk plane is small, and its average value is close to the effective coefficient of thermal expansion of the drive head support system (determined by the material and structure of the head support system). (3) Permanent deformation is small when placed in a high temperature and high humidity atmosphere for a long period of time (the upper limit of temperature and humidity for use or storage). Conventionally, floppy disks have been widely used in which a biaxially oriented polyethylene terephthalate film (hereinafter referred to as PET film) is used as a base film and a magnetic layer is provided on one or both surfaces of the film. So,
The humidity expansion coefficient of PET film is approximately 10×10 ^-6 1/%
Since the RH is extremely large and the anisotropy of the thermal expansion coefficient within the film plane is also not small, it is almost impossible to increase the track density. Furthermore, for devices intended for outdoor use such as magnetic cameras that use floppy disks as recording media, they are required to be able to be stored under high temperature and high humidity conditions of approximately 70°C and 90% RH. When stored under such high temperature and high humidity conditions, floppy disks using PET film undergo significant permanent deformation due to heat shrinkage, and it is even necessary to significantly reduce the track density compared to those used exclusively indoors. On the other hand, it has been proposed to use a biaxially oriented polyP-phenylene sulfide film as a base film for magnetic recording media (for example,
38613), these conventional biaxially oriented polyP-phenylene sulfide films have extremely desirable properties in that they have a lower humidity expansion coefficient than PET films and a lower thermal shrinkage rate even under high temperature and high humidity conditions. However, it could not be used as a base film for floppy disks for the reasons described below. That is, (1) the anisotropy of the coefficient of thermal expansion within the film plane is extremely large; therefore, when this film is used as a base film for a floppy disk,
Even with a track density comparable to that of conventional PET-based floppy disks, off-track easily occurs. (2) Since the average in-plane coefficient of thermal expansion of the film is larger than that of general metal materials, floppy disks based on such films have a large difference from the effective coefficient of thermal expansion of the head support system of the disk drive. This can easily cause off-track. (3) The thickness, degree of orientation, thermal shrinkage rate, etc. are non-uniform, and as a result, the magnetic layer curls or waves due to the thermal history it receives when forming it. [Object of the Invention] The object of the present invention is to satisfy all of the above-mentioned required characteristics that could not be met with the prior art, to be able to record at a significantly higher track density than conventional floppy disks, and as a result, to provide a disk with a large recording capacity. An object of the present invention is to provide a flexible magnetic disk. [Structure of the Invention] In the present invention, 70 mol% or more of the repeating units have the structural formula

A biaxially oriented polyP-phenylene sulfide film consisting of [Formula] is the main constituent layer of the base film, and on at least one surface thereof,
In a flexible magnetic disk provided with a magnetic recording layer, the isotropy F of the base film is 0.1 or less, and the coefficient of thermal expansion α ₀ at 25°C in the direction of the main orientation axis is 1.5×
It is characterized by a flexible magnetic disk having a temperature of 10 ^-5 1/°C or more and 3.0×10 ^-5 1/°C or less. Polyp-phenylene sulfide (hereinafter referred to as "PPS") in the present invention has the structural formula

Refers to a compound containing 70 mol% or more, preferably 90 mol% or more of repeating units represented by the formula. If the content of para-bonded phenylene sulfide units is less than 70 mol%, the crystallinity of the polymer will decrease. This is undesirable because it tends to cause permanent deformation due to heat shrinkage during storage. The remaining 30 mol% or less of repeating units in the polymer are metaphenylene sulfide units.

[Formula] Ether unit

[Formula] Sulfone unit

[Formula] Biphenyl Uni Tsuto

[Formula] Naphthyl Uni Tsuto

[Formula] Substituted phenyl sulfur sulfide unit

[Formula] (where R represents an alkyl group having 1 to 10 carbon atoms, a nitro group, a phenyl group, or an alkoxy group having 1 to 10 carbon atoms),
Trifunctional phenyl sulfide unit

[Operation and effect of the invention]

The floppy disk of the present invention has the above-described structure, so that (1) the displacement of the track due to thermal expansion is approximately equal in all directions of the disk, and the magnitude thereof is equal to that of the head support system of the disk drive. Since it is approximately equal to the effective coefficient of thermal expansion, deviations in the relative positions of the head and track due to temperature changes are extremely small, and off-track will not occur even if the track width is narrowed. (2) Since the displacement of the track position due to changes in humidity is extremely small in all directions within the disk surface, the displacement of the relative position of the head and track due to humidity changes is extremely small (generally, the head support system is made of metal). (The effective humidity expansion coefficient of the head is almost 0), and off-track does not occur even if the track width is narrowed. (3) Even if the disk is left in a high temperature and high humidity atmosphere for a long time, permanent deformation of the disk is small, so off-track will not occur even if the track width is narrowed. In terms of track position stability, the disks now exhibit superior characteristics unimaginable for conventional floppy disks, making it possible for the first time to record at significantly higher track densities than before, resulting in significantly larger recording capacities. It became Flotspy disk. Next, a method for manufacturing the floppy disk of the present invention will be described. First, as a method for polymerizing PPS used in the present invention, a method is used in which alkali sulfide and P dihalobenzene are reacted in a polar solvent at high temperature and high pressure. In particular, it is preferable to react sodium sulfide and P-dichlorobenzene in an amide-based high-boiling polar solvent such as N-methyl-pyrrolidone. In this case, in order to adjust the degree of polymerization, a so-called polymerization aid such as a caustic alkali or an alkali metal carboxylic acid salt is added.
Most preferably, the reaction is carried out at 230°C to 280°C. The pressure within the polymerization system and the polymerization time are appropriately determined depending on the type and amount of the auxiliary agent used, the desired degree of polymerization, and the like. The PPS thus obtained is supplied to a well-known melt extrusion device such as an extruder and melted. The molten resin is continuously extruded from a so-called T-die, cast onto a cooled metal drum, and rapidly solidified to form an unoriented amorphous sheet. Next, the sheet thus obtained is biaxially stretched. Conventionally, various methods such as sequential biaxial stretching and simultaneous biaxial stretching are known as methods for stretching plastic films, but in order to stably obtain the PPS film used as the main constituent layer of the base film of the present invention, In this method, a so-called vertical and horizontal sequential biaxial stretching method is used, in which the sheet is rapidly stretched in the longitudinal direction by a group of rolls, and then stretched in the width direction by a tenter.
Like the simultaneous biaxial stretching method and the horizontal and vertical sequential biaxial stretching method,
In the first stretching method using a tenter, not only the physical properties of the film become different and non-uniform between the center and the edges, but even in the center, the above-mentioned characteristics required of the PPS filler used in the product of the present invention are not achieved. I can't satisfy you. Stretching in the longitudinal direction (longitudinal stretching) is performed by rapid stretching between rolls with different circumferential speeds, and the temperature of the film immediately before stretching is in the range of 95 to 105°C.
In addition, the temperature difference in the width direction (difference between the highest temperature and the lowest temperature in the portion that will later be effectively stretched transversely) is set to be 3° C. or less. Further, the stretching speed is set to be 30000%/min or more. If the temperature difference in the width direction is large or the stretching speed is slow, not only will the obtained biaxially stretched film lack uniformity in thickness, but also in-plane isotropy of the coefficient of thermal expansion will not be obtained. The stretching ratio is determined as follows. In other words, the degree of optical orientation immediately before lateral stretching is
The magnification is chosen to be in the range of 0.145 to 0.165. The term "immediately before transverse stretching" as used herein does not necessarily mean immediately after the end of longitudinal stretching. For example, if the tenter has a preheating section for lateral stretching, this means immediately after the preheating is completed. In any case, it refers to the state immediately before the film is stretched in the width direction.
The actual magnification varies depending on the stretching temperature and the degree of polymerization of the polymer, but is approximately in the range of 3.9 to 4.9 times.
(Of course, it goes without saying that this magnification range is not important, but the control of the degree of optical orientation mentioned above is important.) Even if this degree of optical orientation is too large or too small, the in-plane isotropic You can't get a good film. In addition, the density of the film just before horizontal stretching was 1.317
The longitudinal stretching temperature, magnification, and preheating conditions for transverse stretching are selected to be in the range of ~1.330. If the density is too small, uniform stretching will be difficult, and if it is too large, the film will have poor isotropy. The longitudinally uniaxially stretched film whose degree of orientation has been accurately controlled in this way is laterally stretched using a tenter. The stretching temperature is 95 to 110°C, and the stretching speed V is
When the stretching temperature is T°C, at least V=40T
-3200 (unit: %/min) or higher is required.
If the stretching temperature is too low or too high, the film will tear during stretching. The same applies when the stretching speed is slow. The stretching ratio is selected in the range of 3.5 to 3.9 times. Next, the stretched film thus obtained is subjected to fixed length heat treatment. Such heat treatment is usually carried out by providing a heat treatment chamber after the stretching chamber in the same tenter as that used for stretching.
A separate tenter or heated roll may be used. In either case, the heat treatment must be performed with a constant length in both the longitudinal and width directions. The constant length mentioned here means that the change in width and length during heat treatment is 1% or less. Heat treatment temperature is 200~250℃
(more preferably 210 to 240℃), and
Do this for ~50 seconds. After fixed length heat treatment, at a temperature below the heat treatment temperature,
It is permissible to perform relaxation of a few percent or less in the longitudinal direction and/or width direction. The biaxially oriented PPS film obtained as described above may be used as it is as a base film, or at least 50% of the thickness of the base film may be used as a base film.
It may also be used as a base film by laminating it with other suitable films such as PPS film. As already mentioned, in the present invention, the magnetic recording layer formed on the base film is of a coating type,
Although any type of metal thin film type may be used, a method for manufacturing a coated type disk will be explained here as an example. Coating type discs use magnetic paint, which is made by dispersing magnetic powder in a polymer binder solution.
It is manufactured by applying it to a base film and drying it, then punching it out into a disc shape. The composition of the binder used is not particularly limited, but a thermosetting type such as a urethane type binder is preferable. Such a binder is dissolved in an organic solvent such as methyl isobutyl ketone, ethyl acetate, toluene, or the like. Furthermore, magnetic powder is added to the solution and mixed and dispersed. The type of magnetic powder is not limited, but generally, γ-Fe ₂ O ₃ , CrO ₂ ,
Fine powder of Fe, Ni, Co, etc. is used. Also suitable is a composite magnetic powder in which cobalt is epitaxially grown on the surface of fine iron powder. The composition of the paint is approximately 30 to 70 parts by weight of magnetic powder and 15 to 40 parts by weight of binder to 100 parts by weight of solvent. Also,
It is also effective to add a lubricant such as stearic acid, a hardness modifier such as fine alumina powder, etc. to the paint. The paint thus obtained is applied to one or both sides of the base film and dried to a thickness of 0.3 to 5 μm.
m (preferably 1 to 3.0 μm) of the magnetic recording layer is formed. Thereafter, if necessary, the surface is smoothed by calendering, polishing, etc., and then heated to crosslink the coating. Next, the sheet-like product thus obtained is punched out into a disk shape, and polished as necessary to give a mirror finish to the surface. Furthermore, if necessary, the above-mentioned disk is inserted into a protective case called a jacket to obtain a floppy disk. [Methods for Measuring Characteristics, Evaluation Criteria, etc.] Next, the definitions, measuring methods, and evaluation methods of the characteristic values of the polymer, film, and floppy disk used in the description of the present invention will be explained. (1) Characteristic melt viscosity (μ) Using a Koka type float tester with a capillary die of length L and radius R, the pressure P at temperature T was measured.
When the volumetric discharge amount when extruding the polymer is Q, the apparent shear stress τ, the apparent shear rate γ〓, and the apparent viscosity μ are defined as follows. τ = (RP) / (2L) γ = (4Q) / (πR ³ ) μ = τ / γ At this time, the curve μ = f obtained by plotting μ at that time for various γ = (γ〓), γ〓=
Characteristic melt viscosity μ ₀ with value at 200 (s) ^-1
Define. In the present invention, a die with L=10 mm and R=0.5 mm was used, and values measured at T=300° C. were used. (2) Optical orientation n〓−n〓 Set the sample film in a polarizing microscope equipped with crossed Nicols so that the film surface is perpendicular to the optical axis, and then set the compensator at an azimuth angle of 45° with respect to the analyzer axis. Insert it so that it has.
Next, the sample is rotated around the optical axis and placed at a phase reduction position (a position where the phase difference produced by the sample is reduced by the compensator) in the direction of plus or minus 45° from the extinction position. At this time, the optical path difference Γ ₀ caused by the birefringence of the sample
is obtained from the compensation value of the compensator, and the degree of optical orientation n〓−n〓 is defined by Γ ₀ /d ₀ . (Here d ₀ represents the thickness of the sample). At this time, on the sample, the direction perpendicular to the rotation axis of the compensator is the γ direction of the sample, and the parallel direction is the β direction.
It is the direction. In the present invention, measurements were performed using a polarizing microscope POH type manufactured by Nippon Kogaku, a universal stage manufactured by Leitz, and a compensator manufactured by Leitz, using monochromatic light of the sodium D line (wavelength 0.5893 μm). (3) Film density (ρ) Measured at 20°C using a density gradient tube using a lithium breath aqueous solution. (4) Polymer glass transition point (T _g ), melting point (T _n )
and melting point (T _nf ) of the film after biaxial stretching DSC
It was measured by the method. (5) Main orientation axis The base film is measured in the same way as for the degree of optical orientation in (2) above, and the γ direction is defined as the main orientation axis of the film. (6) Tensile elastic modulus A section of 150 mm in length and 10 mm in width was cut in a direction tilted by θ degrees from the main orientation axis of the sample film, and tested using an Instron type tensile tester with a grip gap of 100 mm and a tensile speed of 50 mm/min. With the initial slope of the S-S curve when pulled at θ
Let it be the tensile elastic modulus in the direction. (7) Coefficient of thermal expansion at 25°C Cut a section 70 to 200 mm long and 10 mm wide in the direction to be measured, place it in a constant temperature and humidity chamber without any load, and heat it at 18°C to 35°C at a constant humidity of 35% RH. After raising the temperature to
min). Next, the tension was set at 10 g/mm ² and the initial length l ₀ in an expansion/contraction measuring device equipped with a constant tension minute displacement meter (manufactured by Japan Automatic Control Co., Ltd.) in a constant temperature and humidity chamber, and the tension was kept constant.
The temperature is raised from 18℃ to 35℃ with a constant humidity of 35%RH. At this time, read the displacement meter outputs x ₁ and x ₂ at 20°C and 30°C, convert (x ₂ - x ₁ ) into the change in sample length, and let Δlα be α = Δl〓/(10 ×l ₀ ) defines the coefficient of thermal expansion at 25°C in the longitudinal direction of the sample. (8) Humidity expansion coefficient β Same as thermal expansion coefficient, temperature is constant at 20℃, humidity is increased from 35%RH to 85%RH ΔRH=50
When changing %RH, read the displacement meter outputs x ₃ and x ₄ at 35% RH and 85% RH, and convert the difference (x ₄ − x ₃ ) into a change in length as Δl〓 β = Δl Calculate as 〓/(50×l ₀ ). (9) Permanent deformation γ (θ) under high temperature and high humidity As in (7) above, the sample cut in the θ direction was
℃, 50% RH for 24 hours, then measure the dimensions in that atmosphere, then 70℃, 90% RH.
After leaving it for 2 hours at 23℃ and 50% temperature for 24 hours, measure the dimensions again and calculate the amount of permanent deformation from the difference between before and after. (10) Playback characteristics of floppy disk A commercially available 8-inch standard disk drive (48 tracks/inch, track width approximately 320 μm) was used. Test R: Characteristics against humidity changes Insert the floppy disk to be tested into a disk drive placed in a constant temperature and humidity chamber at 25℃ and 20℃.
After leaving it at %RH for 24 hours, place it on the outermost track (track 00) at 25℃ and 20%RH for 125K.
Let R ₀ be the minimum signal amplitude when a Hz sine wave signal is recorded and immediately played back. Then, change the atmosphere to 25℃, 70%, and set the minimum signal amplitude to _R1 when playing again after 24 hours.
Then, R ₁ /R ₀ is calculated and used as an index of humidity change resistance (the closer the value is to 1, the better). Test S: Permanent deformation characteristics under high temperature and high humidity Insert the floppy disk to be tested into the drive, leave it for 24 hours at 23℃ and 50%RH, and record a 125KHz sine signal on the outermost track under the same atmosphere. , let S ₀ be the minimum signal amplitude when immediately reproduced. Next, take out only the disk, place it under 70℃ and 90%RH for 2 hours, and then put it again.
The minimum signal amplitude when inserted into a drive at 23°C and 50% RH and played back 24 hours later is _S1 . S ₁ /S ₀ is used as an index of permanent deformation characteristics.
(The closer the value is to 1, the better). (11) Dimensional stability test of floppy disk T: Isotropy of thermal expansion Using method (7) above, azimuth angle θ = 0 ~
The coefficient of thermal expansion α (θ) is measured every 22.5 degrees up to 155.5 degrees, and the difference Δα between the maximum and minimum values is determined and used as an index of isotropy of thermal expansion. Test U: Magnitude of thermal expansion Also, find the arithmetic mean of the maximum and minimum values,
It is used as an index of the magnitude of thermal expansion. Test P: Magnitude of hygroscopic expansion Using method (8) above, azimuth θ = 0 ~
Humidity expansion coefficient β every 22.5 degrees up to 155.5 degrees
(θ) and use their maximum value β _n as an index of the magnitude of hygroscopic expansion. Test Q: Magnitude of permanent deformation By the method (9) above, azimuth θ = 0 ~
Permanent deformation γ (θ) is measured every 22.5 degrees up to 155.5 degrees, and the maximum value γ _n is used as an index of the magnitude of permanent deformation. [Example] Next, the present invention will be described in further detail with reference to Examples. Example 1 (1) Preparation of PPS polymer 32.6 kg of sodium sulfide in an autoclave
(250 mol, including 40 wt% crystallization water), 100 g of sodium hydroxide, 36.1 kg of sodium benzoate (250
mol) and 79.2 kg of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) were charged and the temperature was gradually raised to 205° C. while stirring, and 7.0 kg of distillate containing 6.9 kg of water was removed. To the residual mixture, add 1,
4-dichlorobenzene (hereinafter abbreviated as DCB)
Add 37.5Kg (255mol) and 20.0Kg of NMP,
Heated at 265°C for 4 hours. The reaction product was washed 8 times with boiling water and dried at 80℃ for 24 hours using a vacuum dryer to obtain μ, 2900 poise, N1.17, Tg91℃,
High polymerization degree PPS with Tm285℃21.1Kg (yield 78
%) was obtained (referred to as PPS-A). (2) Melt molding 0.1wt% of calcium stearate powder is added as a lubricant to the composition obtained in (1) above, and after stirring and mixing with a mixer, it is poured into the hopper of a 40mmφ extruder, and the mixture is poured into the hopper of a 40mmφ extruder. Replace the air with nitrogen gas. The composition melted at 310°C was filtered through a filter (metal fiber material, maximum pore diameter 10 μm) attached to the tip of the extruder.
φ), extruded through a T-die having a linear lip with a length of 250 mm and a gap of 0.8 mm, and was cast onto a metal drum whose surface temperature was maintained at 30° C. and solidified by cooling. At this time, from the point where the extruded melt contacts the drum, about 5
Parallel to the drum axis at a distance of mm, thickness 0.1 mm
A stainless steel wire with a diameter of φ was stretched, and casting was performed while applying a DC voltage of about 5 kV between the wire and the drum (electrostatic casting). The obtained film has a width of 230 mm, a thickness of 800 μm, and a density of
1.315 was an unstretched film (film A
). (3) Biaxial stretching and heat treatment Film A was stretched 4.3 times in the longitudinal direction of the film at a stretching temperature of 97°C and a stretching speed of 110,000%/min using a longitudinal stretching device consisting of a group of rolls, so that the degree of optical orientation was 0.156. A uniaxially stretched film was obtained. Next, the film was fed into a tenter and stretched in the width direction at a stretching temperature of 99°C and a stretching speed of 1000%/min.
The film was stretched 3.75 times and further heat treated at 220°C for 10 seconds in a subsequent heat treatment chamber in the same tenter to obtain a PPS biaxially stretched film with a thickness of 50 μm (referred to as base film A). (4) Characteristics of the base film The characteristics of the base film obtained in this way were measured as follows: Isotropy F=0.030 α ₀ =2.3×10 ^-5 (1/℃) It met the required characteristics. (5) Creation of floppy disc γ-Fe ₂ O ₃ magnetic powder 45 parts by weight VAGH (vinyl chloride-vinyl acetate copolymer manufactured by UCC) 17 parts by weight N1432J (acrylonitrile-butadiene copolymer manufactured by Nippon Zeon) 3.5 Parts by weight Coronate L (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd.) 1.5 parts by weight Methyl isobutyl ketone 50 parts by weight Toluene 50 parts by weight Carbon black 4 parts by weight A magnetic paint consisting of the above composition was prepared and applied on the above base film. , coated on both sides to a thickness of 3.0 μm (after drying) and dried, punched out into a disk shape with a diameter of 8 inches, and inserted into the jacket of a commercially available standard floppy disk to make a floppy disk (Disc A). ). (6) Evaluation Table 1 shows the evaluation results of the prepared floppy disk in comparison with a commercially available floppy disk (8″ single-sided single-density type, designated as disk B) whose base film is polyethylene terephthalate film. From Table 1, it can be seen that the floppy disk of the present invention (1) has excellent in-plane isotropy of the coefficient of thermal expansion, (2) has small dimensional stability change due to changes in humidity, and (3) can withstand high temperatures and high humidity. Therefore, it can be seen that the product of the present invention is suitable for high track density recording, systems intended for outdoor use, etc.

【table】

[Table] Example 2 (1) Preparation of PPS polymer In the same manner as in Example 1, μ ₀ 3500 poise,
High polymerization degree with N1.25, Tg91℃, _Tn 285℃
Assume that PPS is obtained (PPS-C). (2) Melt molding Same as Example 1, width 240mm, thickness
An unstretched film of 1200 μm was obtained (film-
C). (3) Biaxial stretching and heat treatment Six types of biaxially stretched PPS films with thicknesses (approximately 75 μm) were obtained under the same conditions as in Example 1 (3), except for the combination of longitudinal and horizontal stretching ratios (base film C-1 to C-6). (4) Properties of base film The properties of the obtained film are shown in Table 2. (5) Preparation of floppy disks Floppy disks were prepared in the same manner as in (5) of Example 1 (disks C-1 to C-6). (6) Evaluation results Table 2 shows the evaluation results of the created floppy disk. From this result, it can be seen that the floppy disks of the present invention all show excellent dimensional stability, while
Similarly, even if a PPS film is used as the base film, it is found that a film that does not satisfy the constituent requirements of the present invention lacks dimensional stability (especially isotropy of thermal expansion).

【table】

Claims (1)

[Scope of Claims] 1 A biaxially oriented polyP-phenylene sulfide film in which 70 mol% or more of the repeating units have the structural formula [Formula] is the main constituent layer of the base film, and at least one surface of the biaxially oriented polyP-phenylene sulfide film is composed of: In a flexible magnetic disk provided with a magnetic recording layer, the isotropy F of the base film is 0.1 or less, and the coefficient of thermal expansion α ₀ at 25°C in the direction of the main orientation axis is 1.5×
10 ^-5 ~3.0×10 ^-5 1/°C. A flexible magnetic disk.