JP2001084564A - Polyester film for high capacity magnetic recording disk and high capacity magnetic recording disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film excellent to prevent output characteristic from being deteriorated due to unstable traveling of a magnetic head owing to uneven contact with a disk and suitable for a high capacity and high efficiency disk by arranging a specified number of large projections each having a height and diameter at the bottom of specified value ranges on one surface of the biaxially oriented polyester film. SOLUTION: It is important as the polyester film for a magnetic recording disk to realize stable traveling of the head and secure excellent stable output characteristic and desirable to control the modulation showing the output stability to be 10% or lower. For this purpose, such large projections are arranged on at least one surface of the biaxially oriented polyester film, as have a height of >=100 nm and <300 nm, desirably >=110 nm and <229 nm, a bottom diameter of >=5 μm and <50 μm, desirably >=10 μm and <45 μm and the number of projections of >=4 pieces/cm2 and <20 pieces/cm2, desirably >=5 pieces/cm2 and <16 pieces/cm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording disk, and more particularly to a high-density, high-density polyester film which is excellent in uniformity in contact with a magnetic head for reading and which can ensure stable output characteristics. The present invention relates to a polyester film for a high-performance magnetic recording disk capable of increasing the capacity.

[0002]

2. Description of the Related Art With the spread of personal computers and the like in recent years, floppy (registered trademark) disk drive devices and floppy disks as storage devices have become widespread, and the capacity and density of floppy disks have been increasing. are doing. A floppy disk is generally manufactured by applying a magnetic layer to a biaxially stretched polyester film, performing a smoothing treatment, and punching the disk shape, and providing an easy-adhesion layer in advance when applying the magnetic layer. Often.

At present, a floppy disk having a storage capacity of 200 MB or more, which is almost the same size as a conventional 3.5-inch floppy disk, and which is 100 times or more the size of the conventional floppy disk has been developed. To increase the recording density of magnetic recording disks, it is important to reduce errors caused by the disk itself.
There is a biaxially stretched polyester film which is a support due to a film surface defect.

[0004] In order to cope with an increase in the capacity of a magnetic recording disk, the film surface is preferably smooth. By smoothing the film surface, stable output characteristics can be ensured well and high capacity can be achieved. It is said that the number of coarse projections must be reduced.

[0005] In order to cope with an increase in the capacity of a magnetic recording disk, the film surface has been smoothed to improve the output characteristics, and at the same time, the number of coarse projections has been reduced. However, when the number of the coarse protrusions becomes smaller than a certain number, unstable running occurs due to uneven contact with the disk, particularly in a magnetic head, and the output characteristics deteriorate. This is because the number of remaining portions (stumps) of the protrusions formed by surface polishing performed after applying the magnetic layer to the film surface was insufficient to secure the support and stable running of the magnetic head.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the deterioration of output characteristics due to unstable running caused by uneven contact of a magnetic head with a disk in view of the prior art and the current state. An object of the present invention is to provide an excellent polyester film for a magnetic recording disk suitable for a high capacity and high performance disk.

[0007]

The object of the present invention is to provide a biaxially oriented polyester film on at least one side with a height of 100 n.
300nm or more and less than m, can be achieved by a polyester film for a magnetic disk having less than 4 / cm ² or more 20 / cm ² the coarse projections of less than base diameter 5 [mu] m 50 [mu] m.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with preferred embodiments, but the present invention is not limited thereto.

The polyester resin constituting the polyester film for a magnetic recording disk of the present invention means a substantially linear polyester containing an aromatic dicarboxylic acid and an aliphatic glycol as main acidic components and glycol components, respectively. Acid, naphthalenedicarboxylic acid, isophthalic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid,
Diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid and the like can be used. Examples of the aliphatic glycol include those having 1 to 1 carbon atoms such as ethylene glycol, diethylene glycol, trimethylene glycol, tetramethylene glycol, and hexamethylene glycol.
For example, alicyclic glycols such as polymethylene glycol and cyclohexanedimethanol of No. 12 can be used. Of these polyesters, in particular, polyethylene terephthalate, polyethylene-2,6-naphthalate, or at least 80 mol% of all dicarboxylic acid components and all glycol components are terephthalic acid, 2,6-naphthalenedicarboxylic acid, and ethylene glycol. Copolyesters are preferred. The components which can be copolymerized in less than 20% of each of the acid component and the glycol component are, in addition to the above, as the acid component, for example, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, dimer acid and dodecadionic acid;
There are trifunctional carboxylic acids such as trimellitic acid, alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid, and the like, and glycol components include polyethylene glycol, polypropylene glycol, polyalkylene glycol such as polytetramethylene glycol, And aromatic diols such as hydroquinone.

The above polyester can be produced by various methods, and as a polymerization catalyst, typically, an antimony-based compound such as antimony trioxide, various titanium compounds and the like can be used. The intrinsic viscosity of the polymer is not particularly limited, but is preferably 0.4 to 1.9 as a solution measured in orthochlorophenol at 25 ° C.

The polyester film for a magnetic recording disk according to the present invention is preferably made of a biaxially oriented polyester film, particularly from the viewpoint of mechanical properties and isotropy required for the magnetic recording disk.

The biaxially oriented polyester film of the present invention has a dimensional change of from -0.3% to 0.12%, more preferably from -0.2% to 0.1% at 80 ° C. for 30 minutes.
At 10% or less, the in-plane anisotropy at this time is 0.0% to 0.1%.
It is preferably at most 05%. 80 ° C, 80 ° C
The dimensional change rate for 30 minutes under% RH is -0.3% or more and 0.2% or less, more preferably -0.2% or more and 0.1% or less.
8% or less, and the in-plane anisotropy at this time is 0.0% or more and 0.1% or more.
% Is preferable. For slow changes over time such as track shift and deterioration of flatness during long-term use, the characteristics at high temperature of 80 ° C. and under both dry and humid conditions are within the above range,
This is practically preferable because the amount of change with time is small. Since it was found that it was necessary to specify, it was specified in this way.

The biaxially oriented polyester film according to the present invention
Lum has a thermal expansion coefficient of 8 × 10^-6~ 25 × 10^-6(1 /
° C), more preferably 10 x 10^-6~ 23x
10 ^-6(1 / ° C.). Thermal expansion coefficient is 8 × 10^-6Less than
Or 25 × 10^-6(1 / ° C)
And a floppy disk drive such as a read head
The difference from the coefficient of thermal expansion of the metal parts of the equipment increases,
Tracking failure depending on temperature difference during recording / reading
Is not preferred. The anisotropy of the coefficient of thermal expansion is 0
-10 × 10^-6(1 / ° C.). Anisotropy of thermal expansion coefficient
Increases, the recording track becomes elliptical due to temperature changes.
And mechanical position tracking becomes difficult.
This is not desirable because of the
Care must be taken with P-disks.

In the polyester film of the present invention, it is important to secure good and stable output characteristics by realizing stable head running. For example, the modulation showing output stability is suppressed to 10% or less. It is desirable. For this reason, at least one side of the biaxially oriented polyester film has a height of 100 nm or more and less than 300 nm,
Preferably 110 nm or more and less than 229 nm, bottom diameter 5
μm or more and less than 50 μm, preferably 10 μm or more and 45 μm
It is necessary that the number of coarse projections less than m is 4 / cm ² or more and less than 20 / cm ² , preferably 5 / cm ² or more and less than 16 / cm ² .

The polyester film of the present invention has a center line average surface roughness (Ra) of the film surface of not less than 1 nm and not more than 2 nm.
It is preferably less than 5 nm, more preferably 4 to
It is 21 nm, particularly preferably 5 to 20 nm. The maximum projection height (SRmax) on both sides of the film is 200 nm.
Or less, preferably 170 nm or less. These satisfy the requirements of the high-density recording method. In addition, about the center line surface roughness, when the smooth layer described below is laminated on the film surface, it means a value measured on the surface of the smooth layer.

The polyester film of the present invention contains 0.2% by weight of particles having an average particle size of not less than 0.04 μm and less than 0.4 μm in order to realize the formation of the coarse projections and the surface roughness described above.
It is preferable to add at least 0.4% by weight. Examples of the particles to be added include colloidal silica, calcium carbonate, and alumina. Among them, it is preferable that colloidal silica is contained as main particles. Also,
Particles having different particle diameters and shapes may be further combined and added, for example, a surface-treated average particle diameter of 0.4 μm
Calcium carbonate of not less than 1.0 μm and less than 1.0 μm may be further added so as to be 0.001% by weight or more and 0.1% by weight or less.

The polyester film of the present invention preferably has a thickness of 25 to 70 μm, more preferably 25 to 65 μm.

The biaxially oriented polyester film of the present invention preferably has a static friction coefficient of 0.4 to 0.6, more preferably 0.45 to 0.55, and a dynamic friction coefficient of 0.3 to 0.5. Preferably, more preferably 0.35-
0.45.

In the polyester film of the present invention, a slippery layer containing monodisperse particles may be laminated on the film surface in order to control the coefficient of friction. The monodispersed particles preferably have an average particle size of 0.03 to 0.3 μm, and the content is preferably 1 × 10 ⁵ to 1 × 10 ⁸ particles / mm ² . When trying to obtain the required coefficient of friction with only the particles added to the polyester resin, many of the particles are buried inside the film, so the average particle size is large and the amount of addition is large, and unnecessarily large projections are formed. On the other hand, the particles added to the slippery layer are arranged on the polyester resin interface, so that even if the average particle size is small, it is effective in slipperiness. However, the monodisperse particles are less than 1 × 10 ⁵ particles / mm ^2, in the interval between the monodisperse particles is too large, not preferable for practical antiblocking effect fades, 1 × 10 ⁸ pieces / mm If the number is more than ² , the particles are likely to be aggregated, causing the particles to fall off and forming unnecessarily large projections, which is not preferable. Examples of the monodispersed particles include calcium carbonate, colloidal silica, alumina, and organic particles, and it is preferable that colloidal silica and organic particles are contained as main particles. Further, the particles preferably have a spherical ratio of 1.0 to 1.3. Further, particles having different particle diameters and types may be added in combination (for example, colloidal silica and calcium carbonate, organic particles and alumina). Examples of the organic particles include cross-linked divinylbenzene particles and silicone particles.

As the resin used for the slippery layer, resins of various types such as polyester, acrylic, urethane, nylon and the like and a mixture thereof can be used, but when a magnetic layer is laminated on the slippery layer. Therefore, it is preferable that the polyester resin has an easy adhesive property, and a polyester resin, particularly a water-soluble or water-dispersible polyester resin is preferably used.
As the water-soluble polyester, a sulfonate-containing polyester is typical, and 5-Na sulfoisophthalic acid,
It is a polyester resin in which a sulfonate group is introduced into a molecule by a component such as 5-ammonium sulfoisophthalic acid, 5-K sulfoisophthalic acid, or 4-Na sulfoisophthalic acid. The content of the polyvalent carboxylic acid component having a sulfonic acid salt group is preferably from 3 to 50 mol%, more preferably from 5 to 25 mol% of the total polyvalent carboxylic acid component. Other polycarboxylic acid components include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, adipic acid, sebacic acid,
There are trimellitic acid and pyromellitic acid. Examples of the glycol component include ethylene glycol, 1,4-butanediol, diethylene glycol, dipropylene glycol, hexamethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. The polyester resin used for the slippery layer preferably has a glass transition point of 40 ° C. or higher. Since the film is heated in both the film forming step and the magnetic layer coating step, in the case of a resin having a low glass transition point, the slippery layer is stuck to the roll in the step, which may cause wrinkles. It is preferable that such an easy lubricating layer is laminated with a thickness (dry) of 0.01 to 0.03 μm after drying.

The magnetic recording disk according to the present invention is manufactured using such a polyester film for a magnetic recording disk, can have a capacity of 100 MB or more, and has excellent uniformity in contact with a magnetic head. , Stable head running and output characteristics can be realized. Although the disk size is not particularly limited, the most general-purpose 3.5 is used.
Inches are preferred. The track density is 200
A high density of 0 tracks / inch or more is possible, and is suitably used for such an application.

The biaxially oriented polyester film of the present invention can be produced from the above polyester by a known method. The polyester melted by the extruder is extruded from the die in a sheet form, cooled and solidified on a cooling drum, then successively biaxially stretched or simultaneously biaxially stretched, heat-set, and then wound up as a biaxially oriented film Can be In these production steps, the physical properties of the film are adjusted by appropriately selecting conditions such as a stretching ratio in the longitudinal and transverse directions, a stretching temperature and a heat setting temperature, and a relaxing operation in the longitudinal and transverse directions.

The method for laminating the lubricious layer in the present invention includes a method of preparing an aqueous coating and applying it in a film forming process, a method of co-extrusion, and a method of preparing an organic solvent-based coating to form a film. There are other methods such as off-line coating, but the thickness of the lubricating layer, resin properties, addition of monodisperse particles,
From the viewpoint of productivity and the like, a method based on application of an aqueous coating agent is most preferable. Examples of the method of preparing the aqueous coating composition include a method of completely dissolving the resin in water, and a method of forming an emulsion or suspension using an emulsifier, a dispersant, or the like. At this time, it is preferable to add monodisperse particles, and therefore, it is preferable that the monodisperse particles are also prepared as an aqueous dispersion. A surfactant (anionic or nonionic) may be added to the aqueous coating composition in order to improve the wettability to the film during application. It is necessary to apply the aqueous coating before the orientation and crystallization of the polyester film are completed.
For example, in the sequential biaxial stretching film-forming process, a method is generally used in which the film is applied to the film after longitudinal stretching, and the adhesion between the slippery layer and the film body is improved during the transverse stretching and the heat setting. As a coating method, a gravure coating method, a roll coating method, a Meyer bar method, or the like is used. In some cases, a method of improving the wettability by corona treatment or the like on the film surface before coating may be employed.

[0024]

[Method for measuring physical properties] The method for measuring characteristic values and the method for evaluating the effects of the present invention are as follows.

(1) Number of coarse projections, height, and bottom diameter Using a two-beam microscope, coarse projections existing on a 1 cm square of the film surface were extracted by marking, and the height and bottom diameter of each were determined by ZYGO. . Thus, the number of coarse projections having a height and a bottom diameter within the range specified in the present invention was determined.

(2) Film Surface Roughness (Central Surface Average Surface Roughness SRa) Using a three-dimensional roughness meter manufactured by Kosaka Laboratory Co., Ltd., stylus weight 6 mg, measuring length 500 μm, cutoff 0.25 mm It measured on condition of.

(3) Average particle size and content of particles in the film The average particle size of the particles is determined by observing a cross section of the film with a transmission electron microscope (TEM) at a magnification of 100,000 or more. T
The section thickness of the EM was about 100 nm, and
Measure over 0 visual fields. Aggregated particles were the average value of the equivalent circle equivalent diameters for the aggregates, and the particle size of the monodispersed particles was for the monodispersed particles.

The content of the particles is such that the polyester dissolves,
A solvent in which the particles were not dissolved was selected, the particles were centrifuged from the polyester, and the weight was measured and calculated. The ratio of the weight of the particles to the total weight (% by weight) was defined as the particle content. In some cases, the combined use of infrared spectroscopy is also effective.

(4) Particle Size, Content, and Spherical Ratio of Monodisperse Particles in Smooth Layer The scanning surface of the easy-smooth layer of the film is scanned with a scanning electron microscope (SEM).
The maximum and minimum diameters were measured for each particle, and the particle diameter of each particle was determined as the average of the maximum and minimum diameters. In addition, the number of particles was counted from the SEM photograph and the number of particles per unit area was calculated and defined as the content. The maximum diameter / minimum diameter ratio of each particle is determined for 100 or more particles,
The average of them was defined as the spherical ratio.

(5) Dimensional change rate The sample is treated in a hot air oven or a constant temperature and high humidity bath at 80 ° C. for 30 minutes or at 80 ° C. and 80% RH for 30 minutes. Was measured. For the dimension measurement, a universal photographer equipped with a reader having a resolution of 1 μm can be used.

Dimensional change rate = (length before processing−length after processing) / length before processing × 100 (%) (6) Output Characteristics The stability of the output characteristics can be evaluated by modulation. The modulation indicates the stability of the reproduction output during one rotation of the floppy disk, and is defined by a measured value. The modulation is represented by the following equation using the maximum output value A and the minimum output value B during one rotation. The smaller the value, the better.

Modulation = (AB) / (A +
B) × 100 (%) A: Approximately 200 including the maximum output voltage in one round of the track
0 Average output voltage of flux reversal B: About 200 including minimum output voltage in one round of track
Average output voltage of zero magnetic flux reversal In an actual measurement circuit, the reproduced output is envelope-detected, and the maximum output value A and the minimum output value are measured based on the maximum output voltage and the minimum output voltage of the output waveform. If the value of the modulation is 10% or less, it can be said that the output characteristics are stable. If the contact between the disk and the head becomes uneven and the running of the head becomes unstable, the modulation becomes worse.

[0033]

Next, embodiments of the present invention will be described based on examples.

Example 1 For a film base, polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.1 g) was used.
1% by weight, 0.03% by weight of antimony oxide, 0.35% by weight of dimethylphenylphosphonate as a phosphorus compound), 0.2% by weight of colloidal silica having an average particle size of 0.13 μm, and 0.3 μm of average particle size The raw material pellets obtained by adding and mixing 0.05% by weight of colloidal silica were vacuum-dried (5 Torr) at 180 ° C. for 3 hours, and then supplied to an extruder and melted at 285 ° C.

The molten polymer was filtered with a filtration accuracy of 0.5 μm (9
After filtering with a high precision filter with 5% cut diameter)
The sheet was extruded from a die into a sheet, wound around a casting drum having a surface temperature of 25 ° C. using an electrostatic application casting method, and cooled and solidified to form an unstretched film. This unstretched film was stretched 3.5 times in the longitudinal direction at 85 ° C. Next, both surfaces of the film are subjected to corona discharge treatment, and an aqueous coating agent obtained by adding colloidal silica having an average particle size of 0.08 μm to a water-soluble sulfonic acid-containing polyester resin is applied to both surfaces by the Meyer bar coating method to have the same application amount. Was applied as follows. Subsequently, the film is stretched 3.76 times in the width direction at 105 ° C. using a stenter,
Further, heat fixation is performed at 220 ° C. for 10 seconds under a constant length.
It was subjected to a 6.0% relaxation treatment in the width direction at ℃. The film that came out of the stenter is 0.05% in the longitudinal direction at an ambient temperature of 25 ° C.
After relaxation, a biaxially oriented polyester film having a thickness of 62 μm was obtained. The resulting film had a height of 100 on one side.
nm to less than 300 nm, bottom diameter 5 μm to 50 μm
Less than 6 coarse protrusions / cm ² . Further, SRa was 18.8 nm. When the characteristics of the obtained film as a floppy disk after the application of the magnetic layer were evaluated, it was found that the magnetic head had excellent stability and reliability in running properties and output characteristics.

Example 2 For a film base, polyethylene terephthalate polymerized by an ordinary method (polymerization catalyst: magnesium acetate 0.1 g) was used.
1% by weight, 0.03% by weight of antimony oxide, 0.35% by weight of dimethylphenylphosphonate as a phosphorus compound), 0.2% by weight of colloidal silica having an average particle diameter of 0.13 μm, surface-treated, cubic shape 0.002% by weight of calcium carbonate having an average particle size of 0.78 μm
A biaxially oriented polyester film having a thickness of 62 μm was obtained in the same manner as in Example 1, except that the raw material pellets added and mixed so as to be as follows were used. The obtained film has a height of 100 nm or more and less than 300 nm and a bottom diameter of 5 μm on one side.
It had 6 / cm ² of coarse protrusions having a size of not less than m and less than 50 μm.
Further, SRa was 10.2 nm. When the characteristics of the obtained film as a floppy disk after the application of the magnetic layer were evaluated, it was found that the magnetic head had excellent stability and reliability in running properties and output characteristics.

Comparative Example 1 When filtering a molten polymer, a filtration accuracy of 0.3 μm (9
A biaxially oriented polyester film having a thickness of 62 μm was obtained in the same manner as in Example 1, except that a high-precision filter having a 5% cut diameter) was used. The obtained film has a height of 100 nm or more and less than 300 nm and a bottom diameter of 5 μm on one side.
It had ² / cm ² of coarse protrusions having a size of not less than m and less than 50 μm.
Further, SRa was 18.0 nm. When the characteristics of the obtained film as a floppy disk after the application of the magnetic layer were evaluated, the remaining portions of the protrusions formed by polishing the film surface during the application of the magnetic layer (stumps)
Insufficient number of magnetic heads prevent uniform contact of the magnetic head with the disk, causing unstable running of the magnetic head.
Stable output characteristics could not be obtained.

[0038]

[Table 1]

[0039]

According to the present invention, the contact between the magnetic head and the film magnetic layer can be made uniform by limiting the height, bottom diameter and number of the coarse projections on the film surface to specific ranges. A high-capacity, high-performance magnetic recording disk that prevents deterioration of output characteristics due to unstable running of the magnetic head can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4F100 AA20H AK41A AK41B AK41C AL06 BA02 BA03 BA06 BA10B BA10C CC10 DD07B DD07C DE01B DE01C EH17 EH172 EH46 EH462 EJ372 EJ373 EJ38 EJ38A EJ38B EJ38C00B05 EJ38C EJ55 EJ38C EJ55 CB07 DA02 FA09

Claims (3)

[Claims] 1. A biaxially oriented polyester film having, on at least one surface thereof, coarse projections having a height of 100 nm or more and less than 300 nm and a bottom diameter of 5 μm or more and less than 50 μm in a number of 4 / cm ² or more and less than 20 / cm ^2. Polyester film for high capacity magnetic recording disks. 2. A film comprising a resin containing particles having an average particle diameter of 0.04 μm or more and less than 0.4 μm in an amount of 0.2% by weight or more and less than 0.4% by weight, and having a center line average surface roughness (SR
a) is 1 nm or more and less than 25 nm, and the thickness is 25 to 70 μm
2. The polyester film for a high-capacity magnetic recording disk according to claim 1, wherein: 3. A high-capacity magnetic recording disk having a track density of 2000 tracks / inch or more, manufactured using the polyester film for a magnetic recording disk according to claim 1.