JP2569488B2 - Biaxially oriented polyethylene terephthalate film for magnetic disks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic disk in which a magnetic layer is provided on one or both sides of a film substrate, for example, a floppy disk, a video floppy or a magnetic camera disk. It relates to a suitable biaxially oriented polyethylene terephthalate film.

[Prior art] Conventional magnetic disks based on a biaxially oriented polyethylene terephthalate film had no problem within a range where the recording density was not so high. The problem of tracking errors and increased dropouts is becoming more frequent. One solution to this problem is disclosed in Japanese Unexamined Patent Publication No. Sho 59-1953.
Japanese Patent Publication No. JP-A No. 22-26139 discloses a magnetic disk based on a laminated film obtained by laminating a polyester film and a polyolefin film.

[Problems to be solved by the invention]

However, such a disk also has various drawbacks because the base material is a laminated film, and at present, it has not yet completely solved tracking errors and dropouts.

The present invention provides a magnetic disk for high density recording (90 TPI or more,
The purpose of the present invention is to provide a biaxially oriented polyethylene terephthalate film, which is a suitable base material, for the purpose of significantly improving tracking errors and dropout problems (especially, 150 TPI or more).

[Means for solving the problem]

The present invention comprises polyethylene terephthalate having a COOH terminal group content of 30 equivalents / ton or less, a refractive index in the thickness direction of 1.492 or less, a surface scratch resistance index of 2% or less, and a humidity expansion coefficient of 4 in any direction in the plane. The main feature thereof is a biaxially oriented polyethylene terephthalate film for a magnetic disk, which is in the range of × 10 ⁻⁶ /% RH to 10 × 10 ⁻⁶ /% RH.

The polyethylene terephthalate referred to in the present invention is at least 80 mol%, preferably at least 90 mol%, more preferably
95 mol% or more has ethylene terephthalate as a repeating unit, but within this limited amount range, a part of the acid component and / or the glycol component may be replaced with the following third component.

Acid component: isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 4 , 4'-diphenyl ether dicarboxylic acid, P-β-hydroxyethoxybenzoic acid,
Adipic acid, azelaic acid, sebacic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, ε-oxycaproic acid, trimellitic acid, trimesic acid, pyromellitic acid, α, β-bisphenoxyethane-4,4′-dicarboxylic acid Acid, α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylic acid, 5-sodium sulfoisophthalic acid, etc. Glycol components: propylene glycol, butylene glycol, hexamethylene glycol, decamethylene glycol, neopentylene Glycol, 1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 2,2-bis (4
-Β-hydroxyethoxyphenyl) propane, bis (4-β-hydroxyethoxyphenyl) sulfone, diethylene glycol, triethylene glycol, pentaerythritol, trimethylolpropane, polyethylene glycol and the like.

In addition, known additives in this polyethylene terephthalate, for example, heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, A release agent, an antistatic agent, a nucleating agent and the like may be blended. The intrinsic viscosity (measured in orthochlorophenol at 25 ° C.) of this polyethylene terephthalate is in the range of 0.40 to 1.20, preferably 0.45 to 0.80, and more preferably 0.48 to 0.75 dl / g. Things.

The polyethylene terephthalate (hereinafter PE) used in the present invention
T), when it is formed into a film and formed into a film, the COOH terminal group content is 30 equivalents / ton or less,
Preferably 25 equivalents / ton or less, more preferably 20 equivalents / ton
Tons or less. If the COOH terminal group content is more than the above range, tracking errors of a magnetic disk using the COOH as a base material increase. The lower limit of the COOH terminal group content is not particularly limited, but it is practically difficult to set it to 0, and about 5 equivalents / ton can be regarded as the lower limit in the practical range. There are various methods for reducing the COOH terminal group content of the PET film, and the method is not particularly limited. However, broadly, there are a polymer decomposition suppressing method, a solid phase polymerization method, and a terminal group blocking method.
As a specific example of the polymer decomposition suppressing method, it is effective to reduce the heat history in the PET polymerization step, and in that sense, the continuous polymerization method is more preferable than the so-called batch polymerization method.

Also, in the step of melt-extruding PET to form a film, it is effective to melt-extrude PET at the lowest possible temperature in a short time. Further, it is not desirable to grind the film edge or the rejected film and reuse it as a so-called recovered raw material because the content of the COOH terminal group of the film is easily increased.

As a specific example of the solid-state polymerization method, there is a method in which PET pellets are heated to 200 ° C. or more in a vacuum or nitrogen to promote solid-state polymerization and reduce COOH end groups.

As specific examples of the terminal group blocking method, a known terminal blocking agent,
For example, there is a method of reducing the COOH terminal group content by adding orthophenyl phenoxyglycidyl ether, diphenyl carbonate, dimethyldiphenoxysilane, or the like to PET in a polymerization step or a film forming step.

Next, the thickness direction refractive index of the present invention the film (abbreviated as n _Z) is 1.492 or less, preferably should be 1.490 or less, more preferably 1.488 or less. When the value of n _Z becomes larger than the above, there is a tendency to increase the number of dropouts, and since the tracking errors also increases, and that does not conform to the present invention purposes. Although the lower limit of the value of n _Z is not necessarily limited, as the value of n _Z decreases, film strength in the thickness direction is weakened, a problem toughness in the thickness direction when the disc Therefore, around 1.470 can be regarded as a practical lower limit.

Next, the scratch resistance index of the surface of the film of the present invention must be 2% or less, preferably 1% or less, more preferably 0.5% or less. If the scratch resistance index is larger than the above value, the number of dropouts increases, and the object of the present invention is not met.

Naturally, the lower limit of the scratch resistance index is most preferably 0%, but it is extremely difficult to achieve this. Therefore, it is appropriate to consider the practical lower limit to be about 0.01%.

The method for keeping the scratch resistance index within the above range is not necessarily limited, but, for example, in a PET film, waxes such as carnauba wax, montanic acid wax, rice wax or synthetic wax, silicon-based surfactants , 0.01 to 0.2% by weight of fluorosurfactants
It is effective to contain a certain amount. Also, the density of coarse protrusions on the film surface, that is, the number of coarse protrusions having a height of 0.87 μm or more per unit area of 2 / cm ² or less,
More preferably 1 piece / cm ² or less, still more preferably 0.5 pieces / cm ²
By setting the average particle size to not more than cm ² , the scratch resistance index can be significantly reduced. The most effective method for keeping the coarse projection density within the above range is to precisely pass the molten PET in the melt extrusion process for producing an unstretched sheet. As the filter for overuse, a filter obtained by sintering metal fiber or metal powder is preferable, and the excess limit is 5 μm cut, preferably 3 μm cut, more preferably 2 μm.
It is desirable to use cut ones.

Next, the humidity expansion coefficient of the biaxially oriented PET film of the present invention is (4 to 10) × 10 ⁻⁶ /% RH, preferably (4 to 8) × 1.
It is required to be in the 0 ^-6 /% within the range of RH. If the value of the humidity expansion coefficient is larger than the above range, a tracking error is likely to occur at the time of recording / reproduction on a magnetic disk having a high recording density (for example, a floppy disk having a track density of 100 TPI or more), and it becomes difficult to accurately reproduce a signal. . On the other hand, if the value of the humidity expansion coefficient is smaller than the above range, when the disk is punched in the disk manufacturing process, the disk is broken, cracked, or the punched end face becomes jagged, which is not suitable for the purpose of the present invention. In addition,
The value of the humidity expansion coefficient must be within the above range in the film plane, that is, in any of the longitudinal direction, the width direction, and the oblique direction of the film. In a film in which the value in one direction falls within the range of the present invention and the value in the other direction does not, when a magnetic disk is used, the dimensional change due to humidity change differs depending on the circumferential direction of the disk. This also causes a tracking error.

Next, a method for producing the film of the present invention will be described. High-purity PET pellets containing substantially no particles (25 ° C O
-Intrinsic viscosity measured in chlorophenol 0.49 dl / g)
Into a rotary vacuum polymerization apparatus to perform solid phase polymerization.
To the solid phase polymerized pellets, carnauba wax, methylphenyl polysiloxane, O-phenyl phenoxyglycidyl ether as a terminal blocking agent and colloidal silica as fine particles were added in the form of a master pellet, and the mixture was added to an extruder. Feed and melt extrude at as low a temperature as possible, for example 275 ° C. (the temperature of the molten polymer). The inside of the melt extrusion system is maintained at the highest degree of vacuum, for example, 10 mmHg, and the residence time of the polymer in the melt extrusion system (after the raw material is caught in the extruder from the base of the extruder hopper, comes out of the die) The average time until is as short as possible, for example within 15 minutes. In addition, it is important to insert a precision filtration device between the extruder and the die, and it is important to remove coarse particles and foreign substances in the molten polymer by this device.
Good results are likely to be obtained when using a filter with a cut of μm, more desirably a filter with a cut of 3 μm. The molten polymer thus passed is guided to a die, formed into a sheet, and the molten sheet is wound around a cooling drum and cooled and solidified to form an unstretched film. In this cooling and solidification, in order to improve the adhesion between the molten sheet and the cooling drum, a so-called electrostatic casting method in which a high-voltage electrode is set on the molten sheet side and an electrostatic charge that is excited may be used. . The unstretched film thus obtained is heated to a temperature of 80 to 130 ° C., and is biaxially 2.5 to 3.
5 times primary biaxial stretching. This primary biaxial stretching may be either simultaneous biaxial stretching or sequential biaxial stretching. The primary biaxially stretched film is 5 ° C. or more higher than the highest temperature among the temperatures used during the primary biaxial stretching, and a secondary biaxial stretching temperature described later. Heat treatment is performed at a lower temperature range for about 0.5 to 5 seconds, and then the sheet is simultaneously biaxially stretched 1.5 to 2.5 times in the biaxial direction again. The temperature at this time is higher than the heat treatment temperature described above, and
Temperatures in the range below ℃ are desirable. Thus, the second biaxially stretched film is brought to a temperature of 5
Heat-treat at a temperature higher than ℃ and lower than 230 ℃ for 0.5 to 30 seconds. During this heat treatment, each of the two
It is highly desirable to provide 1-5% relaxation. Intermediate cooling of the heat-treated film in a temperature range of 100 to 150 ° C,
Then, by gradually cooling to room temperature, the biaxial orientation of the present invention
A PET film is obtained.

A magnetic layer, for example, a floppy disk can be manufactured by providing a magnetic layer on one side or both sides of the film of the present invention prepared by the method described above by a known method and punching out a disk. Of course, the surface of the film of the present invention may be subjected to a known surface treatment such as a corona discharge treatment or a plasma treatment, or a known anchor coating agent may be applied to improve the adhesion to the magnetic layer. As the magnetic layer, a ferromagnetic metal or its oxide fine particles are dispersed in a binder, and a coating-type magnetic layer or a ferromagnetic metal or its oxide is applied by vapor deposition, sputtering, ionization. Any of thin film type magnetic layers formed by thinning by a technique such as plating or plating can be used. The recording method using magnetism may be either horizontal recording or vertical recording.

The surface of the film of the present invention is activated by corona discharge treatment, flame treatment, oxidation treatment with an oxidizing agent, or low-temperature plasma treatment to increase the surface wetting tension (or reduce the contact angle of the surface with water droplets). The thing is
The adhesive layer between the film surface and the magnetic layer is improved, and thus the quality of the magnetic disk is improved. In the same sense, providing various coating layers or undercoat layers on one or both surfaces of the film of the present invention is effective not only for improving the adhesion to the magnetic layer but also for preventing electrostatic noise. is there.

[Action]

Since the film of the present invention has a small coefficient of humidity expansion in any direction in the film plane and a small difference in the value of the coefficient of humidity expansion in each direction, the magnetic disk made using this film as a base material is affected by changes in environmental humidity. There is an advantage that errors in recording and reproduction (tracking errors) are small. Conversely, the recording density can be increased by increasing the track density of the magnetic disk. Further, since the surface of the film of the present invention is characterized in that it is hardly scratched and the surface layer is hardly scraped off, making a magnetic disk using this film as a base material has the advantage of reducing the number of dropouts. .

[Measurement and evaluation methods]

The measurement and evaluation methods used in the present invention are summarized below.

Humidity expansion coefficient (β): A sample with a length of 100 mm and a width of 10 mm is cut out from a film sample with the direction to be measured as the length, and this is placed in a constant temperature and humidity chamber with a constant tension micro-displacement meter (Japan Automatic Control ( to set the initial length l ₀ stretch instrument incorporating Ltd.)). The tension is
Leave the tank constant at 10 g / mm ² and the atmosphere in the bath at 20 ° C. and 35% RH, and leave it for tens of minutes to several hours until the output of the displacement meter becomes stable. The output at this time a stable and X _1. Next, the tension and the temperature are kept constant, the humidity is increased to 85% RH, and the output is left for several ten minutes to several hours until the output is stabilized again. The output at this time a stable and X _2. (X ₂ −X ₁ )
Is converted to a change in the length of the test piece, and Δl is given by the following equation.

β = △ l / (50 × ₁₀ ) Scratch resistance index: A 250 mm long, 12.5 mm wide tape-shaped sample is cut out from the target film. At this time, the longitudinal direction of the film is aligned with the longitudinal direction of the tape. Fix both ends of this tape-shaped sample, apply tension of 4 kg / mm ² and stretch tightly.
Push a single-edged leather blade against the center. At this time, the blade is oriented in a direction perpendicular to the longitudinal direction of the sample so as to face directly below. The pressing force is such that the film bends 5 mm by the blade. The leather blade is then moved at a speed of 4 m / min, rubbing the film surface 10 times. Next, this film sample is removed, and aluminum is vapor-deposited on the rubbed film surface using a bell jar type vapor deposition machine.

Next, observe the deposition surface with a differential interference microscope and observe the magnification.
Take a photo of 50 fields of view for any part at 1000x. For each of the 50 photos, mark the scratched area, add the area of the scratched area on all 50 photos, divide this total area by the total area of the total area of the 50 photos, The value obtained by multiplying by the above is defined as the scratch resistance index (%). A film having a smaller value of the scratch resistance index is less likely to be scratched on the surface in the practical process of the film, and it can be said that the film is superior.

Coarse protrusion density: Of protrusions on the film surface, the height is 0.87 μm
It is indicated by the number of the above (per 1 cm ² ). The measurement method is as follows: when the film is pressed against a smooth glass surface to make it adhere to it, and when the film surface is irradiated with monochromatic light (sodium D line), the Newton rings generated around the protrusions are observed with a microscope, and triple or more Newton rings are generated. The number of projections is counted over a film area of 10 cm ² , and this number is calculated by converting the number per 1 cm ² .

Thickness direction refractive index: Measured with an Atsube refractometer according to the method described in ASTM D542-50. Note that methylene iodide was used as the contact liquid, and a sodium lamp was used as the light source.

COOH terminal group content: Andre 'Conix: Makromol. Chem. Vol. 26,226-235 (195
8) Measured by the method described (dissolving a PET sample in benzyl alcohol and titrating it with an aqueous sodium hydroxide solution).

Production and Characteristic Evaluation of Floppy Disk: The following magnetic paint is applied to both sides of a film having a thickness of 75 μm and dried to make the thickness of the magnetic layer 1 μm. I made an inch floppy disk.

Co-containing γ-Fe ₂ O ₃ powder: 45 parts by weight Vinyl chloride / vinyl acetate copolymer: 17 parts by weight Acrylonitrile / butadiene: 3 parts by weight Copolymer polyisocyanate: 1 part by weight Methyl isobutyl ketone: 50 parts by weight Toluene: 50 Parts by weight Carbon black: 4 parts by weight After loading this disk in a 96 TPI mini floppy disk drive and recording it in an environment of 20 ° C and 20% RH,
Reproduction was performed in an environment of 80% RH at ℃, and the magnitude of the tracking error was determined based on the magnitude of the output decrease at that time. Using a drop-in / out counter, the number of drop-outs was measured for 10 discs of the same type, and this was converted to the number of drop-outs per disc.

〔Example〕

Next, embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 PE having an intrinsic viscosity of 0.48 dl / g and substantially no particles inside
The T-chip was subjected to solid-state polymerization at 220 ° C. for 15 hours under a vacuum of 1 mmHg. This was mixed with 2 mol% of orthophenylphenoxyglycidyl ether, 10 ppm of methylphenylorganopolysiloxane, 0.1 wt% of carnauba wax and 0.1% by weight of fine silica ( 0.3% by weight (particle size: 20 millimicrons) was added, fed to an extruder, and melt-extruded at a polymer temperature of 273 ° C. At this time, the inside of the extrusion system was maintained at a vacuum of 20 mmHg, and the average residence time of the polymer in the melt extrusion system was 10 minutes.

The melt coming out of the extruder is passed through a metal fiber sintered filter having a performance of 3 micron cut, then formed into a sheet with a T-type die, which is wound around a cooling drum having a surface temperature of 50 ° C. Cool and solidify, about 2.4m thick
m unstretched sheets were made. In order to improve the adhesion between the cooling drum and the melt, a wire electrode was placed on the melt side, and a direct current of 10,000 V was applied thereto to maintain uniformity during cooling. After preheating this unstretched sheet to 90 ° C, stretched 3.3 times in the longitudinal direction while heating with an infrared heater,
Immediately cooled to 20 ° C. Next, this was preheated with hot air of 100 ° C., and then stretched 3.3 times in the width direction in hot air of 105 ° C. Next, after heat-treating this film in hot air of 140 ° C. for 2 seconds, it was sent to a simultaneous biaxial stretching type stenter,
While heating with hot air at ℃
After stretching by 1.7 times, and then heat-setting for 10 seconds in hot air at 200 ° C while giving 1% relaxation in biaxial directions,
, And then slowly rolled up to room temperature to obtain a biaxially oriented PET film having a thickness of 75 microns. Table 1 shows the characteristics of this film and a floppy disk produced using the film.

Example 2 PE having an intrinsic viscosity of 0.46 dl / g and substantially no particles inside
The T chip was heat-treated at 230 ° C. for 5 hours in a vacuum of 1 mmHg, and then heat-treated at 195 ° C. for 8 hours at the same degree of vacuum to perform solid phase polymerization. To this chip were added 0.5% by weight of diphenyl carbonate, 15 ppm of dimethylpolysiloxane, 0.1% by weight of montanic acid wax and 0.4% by weight of colloidal titanium oxide (particle diameter 160 mm) in the form of a master pellet. In the same manner as in Example 1, a biaxially oriented PET film having a thickness of 75 microns was obtained. Table 1 shows the characteristics of this film and a floppy disk produced using the film.

Comparative Example 1 A commercially available biaxially oriented PET film (thickness 75
Micron) and the characteristics of the floppy disk produced therefrom are shown in Table 1 for comparison. The outline of the method for producing this film is as follows.

A PET chip with an intrinsic viscosity of 0.62 (containing about 0.25% by weight of Ca / Li / P-based precipitated particles) was placed in a vacuum of 50 mmHg at 180 ° C for 6 hours.
Let dry for hours. The chips are fed to an extruder and melt extruded at a polymer temperature of 290. The degree of vacuum in the extrusion system is 100mmH
g, the average residence time of the polymer in the melt extrusion system is 20 minutes. The molten polymer was passed through a 15-micron cut filter, then formed into a sheet with a T-type die, wrapped around a cooling drum having a surface temperature of 60 ° C, and cooled and solidified. Stretched sheet. Heat this sheet to about 90 ° C, stretch it 3.4 times in the longitudinal direction,
Next, it is heated to 100 ° C., stretched 3.8 times in the width direction, and subsequently heated to 220 ° C. to perform a heat treatment for about 5 seconds.
During this heat treatment, a relaxation of about 5% is provided in the width direction of the film. Then, by gradually cooling to room temperature, a normal biaxially oriented PET film is obtained.

From the above results, the film of the present invention is
It can be seen that the coefficient of humidity expansion in each direction is smaller than that of the PET film, and the difference between the directions is smaller. Also,
Since both the scratch resistance index and the coarse projection density are excellent, it is clear that a disk with few tracking errors and dropouts can be obtained when used as a substrate for a floppy disk.

〔The invention's effect〕

Since the film of the present invention has a small coefficient of humidity expansion in each direction in the film plane and a small difference in direction, a disk with few tracking errors can be obtained when used as a substrate for a magnetic disk. Further, since there are few tracking errors, the recording density of the disk can be increased. Further, since the film of the present invention has a good surface with a small scratch resistance index, it is also effective in reducing the dropout of a disk.

As described above, the PET film of the present invention is suitable for a substrate for a magnetic disk, but is particularly useful as a substrate for a floppy disk. In addition, high recording density (for example,
(100 TPI or more) As a substrate for a floppy disk, it is particularly excellent. The film of the present invention is also useful as a substrate for video floppy disks or a substrate for magnetic camera disks.

Claims (1)

(57) [Claims] 1. A polyethylene terephthalate having a COOH terminal group content of 30 equivalents / ton or less, a refractive index in the thickness direction of 1.492 or less, a scratch resistance index of 2% or less, and a coefficient of humidity expansion in any direction in the plane. A biaxially oriented polyethylene terephthalate film for a magnetic disk in the range of 4 × 10 ⁻⁶ /% RH or more and 10 × 10 ⁻⁶ /% RH or less.