JPH0222038A - Manufacture of polyester film for magnetic recording flexible disc - Google Patents

Abstract

PURPOSE:To obtain a film having small dimensional change and inner face anisotropy even at high humidity by feeding a heated air having a temp. higher than the second order transition temp. of a polyester to only one side of a film in a definite zone of floating heat treatment and transferring the film so as to draw a curved face. CONSTITUTION:A biaxially oriented polyester film having a dimensional changing ratio in the longitudinal direction of 0.05-0.3% and a dimensional changing ratio in the width direction of 0.02-0.2% larger than the dimensional changing ratio in the longitudinal direction when the film is kept under a condition of 60 deg.C and 80%RH for 72hr is prepd. In this instance, a heat-treated film is taken off and the heat treatment under relaxed condition thereof is performed under a noncontacting condition by means of a floating heat treatment method. This is performed by feeding a heated air having a temp. 40-80 deg.C higher than the second order transition temp. of the polyester to only one side of the film to float the film and transferring the film in such a way that the transferring stress is kept at 13kg/cm<2> or smaller than the film draws a curved face. A polyester film having small dimensional change and inner face anisotropy even in a high humidity atmosphere and good flatness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a polyester film for magnetic recording flexible disks, and more specifically, it is possible to produce a polyester film for a magnetic recording flexible disk in a short period of time, with small dimensional changes due to temperature and humidity, and within the plane of the expansion coefficient depending on temperature and humidity. The present invention relates to a method for manufacturing a polyester film for magnetic recording flexible disks that has low anisotropy and excellent flatness.

Prior art and its problems Magnetic recording flexible disks are usually based on a biaxially oriented polyester film, the surface of which is coated with magnetic fine particles together with a binder, or coated with magnetic metal by vacuum deposition, sputtering, plating, etc. It is manufactured by forming a thin film layer and applying a magnetic layer.

In recent years, magnetic recording and reproducing devices using disks have become more dense and reliable, and along with this, flexible disks also have (a) mechanical strength that does not cause distortion in recording. , (0) heat-resistant dimensional stability that does not cause dimensional changes due to unexpected heat during recording and reproduction, (c) excellent surface flatness so that electromagnetic conversion characteristics do not deteriorate due to thinning of the magnetic layer, (ni) ) Characteristics such as in-plane isotropy with small fluctuations in input/output voltage during one track revolution, in other words, excellent modulation, are increasingly required, and there is a demand for the development of disks with improved these characteristics.

Among these characteristics, for example, improving modulation,
It has been proposed to make the axis of easy magnetization of the magnetic material of the magnetic layer isotropic using a randomizer during the disk manufacturing process (Japanese Patent Laid-Open No. 60193137).

However, the modulation may be worsened by distortion of the base film, etc., and even if the unsolidified magnetic layer is made non-oriented using a randomizer as proposed above, the effect is small. The deterioration of modulation caused by Bethfilm becomes a particular problem when the flexible disk is used in an atmosphere with changes in temperature and humidity, or in an atmosphere with high or low temperatures. The reason for this deterioration is that axially oriented polyester films generally undergo dimensional changes (expansion and contraction) with changes in temperature and humidity, and dimensional changes do not occur in the same direction. It is mentioned that there is anisotropy in fat swelling ratio.

In addition, flexible disks have this upper limit operating temperature of 51
．． It is required to expand the temperature from 5°C to about 60°C, and it is desired to have dimensional stability, electromagnetic conversion characteristics, etc. that can withstand use at this 60°C. This increase in the operating temperature increases the dimensional change (expansion and contraction) of the base film and also increases the anisotropy.

As a means of obtaining flexible disks with small thermal shrinkage rates and dimensional changes, a method has been proposed in the past in which a base film or disk is cut, and a plurality of these sheets are stacked and subjected to relaxation heat treatment (Japanese Patent Laid-Open No. 1983-1999). No. 127233). Although this heat treatment is ideal in that it is carried out under no tension at all, it cannot process webs with continuous magnetic layers formed thereon, resulting in another problem of low workability and production efficiency. .

Further, as a method of reducing the heat shrinkage rate and dimensional change in the width direction (lateral direction) of a biaxially oriented polyester film, a method of applying limited shrinkage during the heat setting process in the film manufacturing process is known. However, it is difficult to produce a film that exhibits only slight deformation in the longitudinal direction (longitudinal direction) using the normal biaxial stretching heat setting method.

Therefore, as a method of improving the dimensional stability of the film in the longitudinal direction, a method of subjecting the film after heat setting to a relaxation heat treatment has been proposed. For example, in Japanese Patent Application Laid-Open No. 5396072, a biaxially stretched polyester film is
A method has been proposed in which heat setting is performed while giving a limited shrinkage of 50%, and then relaxation heat treatment is performed at a temperature of 120 to 160° C. using a floating treatment method.

However, according to the research results of the present inventors, the polyester film obtained by this method has a temperature of 60°C.

When placed in an atmosphere of 80% RH, the width direction (
As a result, the anisotropy of in-plane dimensional changes becomes large, and the desired dimensional stability cannot be achieved.Furthermore, the film becomes wavy and its flatness deteriorates. It became clear that

Purpose of the Invention The inventor of the present invention has solved this problem, and has achieved an extremely small dimensional change even when placed in a high humidity atmosphere from room temperature to about 60 degrees Celsius, small in-plane anisotropy, and flatness. As a result of research to produce a polyester film for magnetic recording flexible disks with excellent properties, it was found that in order to obtain satisfactory results with aerodynamic floating heat treatment, the film subjected to the treatment must be 60%
The dimensional change rate in the longitudinal direction is 0.05 to 0.3% when kept under the temperature and humidity conditions of ℃ and 80% RH for 72 hours, and the dimensional change rate in the width direction is 0.02% higher than the longitudinal dimensional change rate. ~0
．． It is a biaxially oriented polyester film that is 2% larger. However, even with this film, if the processing temperature is too high, the film will become wavy and its flatness will be impaired. Therefore, it is necessary to lower the processing temperature and increase the processing time. became clear. The present inventor conducted further research to solve this problem, and as a result, arrived at the present invention.

Therefore, an object of the present invention is to provide a flexible magnetic recording medium that exhibits extremely small dimensional changes, small in-plane anisotropy, and excellent planarity even when placed in a high humidity atmosphere from room temperature to about 60°C. An object of the present invention is to provide a method for efficiently producing a polyester film for discs in a short time.

Structure/Effects of the Invention According to the present invention, the longitudinal dimensional change rate is 0.05 to 0.3% when kept under temperature and humidity conditions of 60°C and 980% Rli for 72 hours. And the width direction dimensional change rate is 0.
0.02 to 0.2% larger biaxially oriented polyester film is traveling and subjected to relaxation heat treatment using an aerodynamic floating treatment method to produce a film in which the dimensional change rate is 0.02% or less in both cases, the floating heat treatment Air heated to a temperature 40 to 80 °C higher than the second-order transition point of the polyester is sent to only one side of the film in at least a certain section of the film to levitate the film, and the running stress 13'j/cm
This is achieved by a method for producing a polyester film for a magnetic recording flexible disk, which is characterized in that the polyester film for magnetic recording flexible disks is subjected to relaxation heat treatment in a treatment time of less than 5 seconds while running in a curved manner while maintaining the following conditions.

The polyester in the present invention is an aromatic polyester represented by polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polycyclohexylene dimethylene terephthalate, etc. These may be homopolymers or copolymers (the copolymer components are 2
(preferably 0 mol% or less). The molecular weight of the polyester may be a normal one and is not particularly limited. Moreover, the polyester may contain arbitrary additives.

In the present invention, the biaxially oriented polyester film subjected to floating heat treatment is heated at 72°C under temperature and humidity conditions of 60°C and 80% RH.
The longitudinal dimensional change rate when maintained for a period of time is 0.05 to 0.
3%, and the dimensional change rate in the width direction is 0.02 to 0.2% larger than the longitudinal dimensional change rate. Such an axially oriented polyester film is produced by extruding a polyester melt through a die, rapidly cooling and solidifying it, and then increasing the size by 3.0 to 4.5 times in the machine direction and then by 3.0 times in the width direction.
It can be manufactured by a method of stretching to ~4.5 times, heat setting, and further heat treatment. A normal stretching temperature can be used as the stretching temperature. The stretching ratio is 3.0 to 3.7 in the longitudinal direction.
It is more preferable to increase the height by 0.1 to 0.3 times higher in the horizontal direction than in the vertical direction. This biaxially oriented polyester film is preferably a balanced type.

The heat setting temperature is preferably 40°C or more higher than the stretching temperature and 20°C lower than the melting point, for example, in the case of polyethylene terephthalate film, it is preferably 180 to 240°C. Here, the heat setting temperature refers to the maximum temperature during heat setting treatment or in the heat setting treatment zone. Even if the film is heat-set at a temperature significantly outside this temperature range, the coefficient of thermal expansion of the film may deviate from the value desired for a flexible disk, which is not preferable. In addition, the heat treatment after heat setting is performed under the biaxially stretched heat set polyester film while giving a low elongation in the width direction, especially 0 to 4% elongation.
or heat-treated at a temperature lower than the heat-setting temperature while giving limited shrinkage, especially less than 1% shrinkage, at 60° C., 80% RH.
The longitudinal dimensional change rate when held for 72 hours under the temperature and humidity conditions of 0.05 to 0.3%, and the width direction dimensional change rate is 0.02 to 0.2% higher than the longitudinal dimensional change rate. Make it a large film.

This heat treatment can also be called a second-stage heat setting treatment. For example, if tow-out or tow-in treatment is performed in the latter half of the under heat-setting zone (area), the heat-setting treatment before tow-out or tow-in (first-half treatment) and the heat-setting treatment after tow-out or tow-in (second-half treatment) The former corresponds to the above-mentioned heat fixation, and the latter corresponds to the above-mentioned heat treatment. The heat treatment while giving a specific proportion of elongation or limited shrinkage in the width direction is carried out at a temperature lower than the heat setting temperature, preferably at a temperature as low as 20 to 50°C. If the heat treatment temperature is not lower than the heat setting temperature, the anisotropy of the coefficient of thermal expansion will expand, possibly because the higher-order structure is destroyed during the process of elongation or limited contraction, which is not preferable. On the other hand, if the heat treatment temperature is too low, the effect will not be sufficient and the film will be more likely to break during stretching.

In the present invention, next, the film heat-treated as described above is removed from the underclip, and relaxation heat treatment is performed in a non-contact state using a floating heat treatment method. In this relaxation heat treatment, air heated to a temperature 40 to 80 °C higher than the secondary transition point of polyester is sent to only one side of the film in at least a certain section to levitate the film, and the running stress is 13 kg/cm or less. , especially 2-13K
g/cti, and run in a curved manner (in other words, not to create a flat surface). When a heated and relatively softened film is run, if it is run so as to create a flat surface (for example, horizontally), it is likely to be undulated and the flatness of the film will deteriorate. In order to avoid this problem, it is effective to lower the processing temperature, but this increases the processing time. However, by running the film in a curved manner, the above problem can be solved, the flatness of the film can be maintained even at relatively high processing temperatures, and the processing time can be shortened. This curved surface has a radius of 500 mm or more 1 oo
It is preferable that it is below os. Running stress is 13Kg/
If it is larger than cm, the reduction in dimensional stability will not be sufficient or will not be uniform.

An example of an apparatus that levitates a film using heated air and causes it to travel along a curved surface is the apparatus shown in FIG.

Any other device may be used as long as it satisfies the above conditions.

In FIG. 1, 1 is a biaxially oriented polyester film;
2 is an entrance guide roll, 2' is an entrance presser, 3 is an entrance guide roll, 4 is an air tank, 5 is an air nozzle, and 6 is an exit guide roll.

7 is a cooling roll, 7' is an exit presser roll, 8 is a heat insulation booth, 9 is an air exhaust port, 10 is a heater, 11 is a blower, and 12 is an air supply port. The air nozzles 5 are arranged at predetermined intervals along the outer periphery of the air tank 4 in a substantially arc shape. Air heated by heater 10 is sent to blower 1
1, the air is sent from the air supply port 12 to the air tank 4, and further from the air tank to the individual air nozzles 5. The heated air blown out from the air nozzle 5 hits one side of the running film 1 and causes the film to float.

The film flying height is preferably 5 to 15#. The air that floated the running film 1 is sent from both ends of the film to the heat insulation booth 8.
Then, the air is exhausted from an air exhaust port 9 provided on the side wall of the heat insulation booth, and then sent to a reheating heater 10. The mixing ratio of fresh air supplied to the heater 10 and air from the exhaust port 9 can be arbitrarily selected. On the other hand, the running film 1 is guided by entrance guide rolls 2 and 3,
Air nozzles 5 arranged in a substantially arc shape inside the heat insulation booth 8
It travels on a curved surface while being floated by the heated air from the air nozzle 5, during which time it undergoes relaxation heat treatment. The film after the relaxation heat treatment is passed through the exit guide roll 6 and cooled down by the cooling roll 7. The temperature of the heated air blown out from the air nozzle 5 is 4° below the secondary transition point of polyester.
The temperature is 0 to 80°C higher, for example, in the case of polyethylene terephthalate film, it is preferably 110 to 140°C.

In this way, sufficient relaxation heat treatment can be performed even with a treatment time of less than 5 seconds, and the resulting film has a dimensional change rate of 0.02% or less in both axial directions and excellent flatness. When this dimensional change rate of 0.02% or less is expressed in terms of heat shrinkage rate, it is -0.02% to 0.02%.

In the present invention, the short treatment time increases the speed of the relaxation heat treatment, which is industrially advantageous. In addition, it is also possible to remove the heat-treated film from the underclip, cool it first, cut off both ends, wind it up into a roll, unwind it from the roll, and subject it to floating relaxation treatment in the same manner as above. However, it is more efficient to process them sequentially.

The polyester film obtained by the present invention can be made into a long web by providing a magnetic layer thereon. This web can be manufactured using conventional methods, such as a method using magnetic paint. Any known magnetic paint can be used. For example, γ-Fe 20a
powder, cellulose acetate butyrate, epoxy resin, lecithin, silicone oil, etc., methyl isobutyl ketone.

Those dissolved and dispersed in a solvent such as toluene can be applied. Also known methods and conditions can be applied to drying the magnetic paint.

Furthermore, known means and known treatment conditions can be applied to the calender treatment to smooth the magnetic layer.

For winding up the magnetic recording medium on which the magnetic layer is formed, known winding equipment can be used as is.

The polyester film obtained by the present invention has the following advantages.

It is possible to manufacture a magnetic recording flexible disk that does not cause deterioration of modulation due to thermal history up to 1.60°C.

In the case of a 2.degree. 5.25 inch disc, if the disc has 96 TPI (tracks/inch), no missing pulses will occur due to tracking deviation even without a servo mechanism.

3. Since there is virtually no dimensional change caused by repeated use or thermal history of the flexible disk, there will be no clamping abnormalities due to distortion of the central hole and no damage to the disk due to this.

Example Next, the present invention will be explained in more detail with reference to Examples.

Note that the symbol MD in the examples indicates the longitudinal direction (vertical direction) of the film, and TD indicates the width (horizontal) direction. In addition, film properties were measured using the following method.

evaluated.

(1) Heat shrinkage rate Width 10 in the measurement direction of heat shrinkage rate, length 3501B
Cut a 1B film into a length of about 300 m.
Attach gauge points at m intervals. This sample was heated to 25℃ and 50%
After keeping it in a constant temperature and humidity chamber at RH for 24 hours, read the length between gauge marks using a reading microscope. Next, this sample was heated to 60°C.
It was kept in a constant temperature and humidity chamber maintained at 80% RH for 3 days, then taken out and placed in the above temperature and humidity chamber at 25°C and 50% RH for 2 days.
Hold for 4 hours and measure the length between the gauge points again. The rate of change in dimensions (thermal acid) is calculated by dividing the amount of shrinkage by the original length between the gauge points and calculating 1.
It is expressed as a percentage of 0.00.

In addition, in order to determine the in-plane dimensional change rate of the film treated under various conditions, samples were cut out at every 30 degrees in the plane of the film as described above and the heat shrinkage rate was measured. The maximum and minimum heat shrinkage rates also matched the MD or TD of the original film. Therefore, the values in the table are indicated by MD and TD.

(2) Flatness of the film A sample with a width of about 1 TrL and a length of 3 m is spread on a flat table surface, and the waviness of the film is evaluated.

A film with large undulations is considered bad, and a film with no undulations that is the same as an untreated film (not subjected to relaxation heat treatment) is considered good.

Examples 1 to 4 and Comparative Examples 1 to 3 Polyethylene terephthalate was melted and extruded through a die slit, cooled and solidified, and then stretched 3.6 times in the longitudinal direction.
Subsequently, it was stretched 3.7 times in the transverse direction using a sunder, and further heat-set at a maximum temperature of 215°C in the first half of the heat-setting zone of the under, and limited shrinkage of 0.8% in the width direction in the second half of the zone. It was heat-treated at a temperature of 180° C. while giving. The thickness of the obtained film was 75μ. Thermal shrinkage rate of this film (60°C.

80%RH, 72 hours) was 0.090% in the vertical direction and 0.120% in the horizontal direction. Next, this heat-treated film was subjected to relaxation treatment at the temperature shown in Table 1 at a running tension of 5 to 9/cd and a heat treatment time of 3 seconds 1 in an aerodynamic floating relaxation heat treatment apparatus shown in FIG. 1 connected to the heat-setting zone. was applied.

The shrinkage rates of these films after being held at 60° C., 80% RH for 3 days (72 hours) are shown in Table 1. The smaller the shrinkage rate value, the better the dimensional stability is, and the smaller the difference in shrinkage rate between the MD and TD values, the smaller the anisotropy. In the table, a negative thermal acid value means expansion, and a value close to 0 indicates excellent dimensional stability.

Table 1 As is clear from Table 1, at a treatment temperature of 100° C. or lower, the thermal shrinkage rate (60° C., 80% RH, 3 days) is not much different from untreated and has no effect.

Example 5 The same procedure as Example 3 was carried out except that the relaxation heat treatment time was changed to 1 second. The results are shown in Table 2. Note that the results of Comparative Example 1 and Example 3 are also listed in Table 2 for reference.

Table 2 9 - Examples 6 to 9 and Comparative Example 4 The same procedure as in Example 3 was carried out except that the film running tension during the relaxation heat treatment was changed as shown in Table 3.

The results are shown in Table 3.

Table 3 The table has a high thermal acid value.

Examples 10 to 13 and Comparative Example 5.6 The same procedure as in Example 3 was carried out except that elongation was applied during the heat treatment in the latter half of the under heat setting zone. The results are shown in Table 4.

For comparison, the same procedure as above was carried out except that during the heat treatment, a more limited shrinkage than that of the present invention was given.

The results are also listed in Table 4 as Comparative Examples 9 and 10.

Table 4 As is clear from Table 3, the processing stress ranged from 2 to 13 by 9/
If the crA is within the range, both thermal acidity and running behavior will be satisfactory.

On the other hand, as shown in Comparative Example 4, where the treatment stress is too high, as is clear from Table 4, when a film subjected to floating heat treatment that has been given more limited shrinkage than necessary, the thermal shrinkage rate becomes smaller in the machine direction (MD). is rather elongated in the transverse direction (TD), increasing anisotropy. On the other hand, a film that has undergone some limited shrinkage or elongation has a small thermal shrinkage and is excellent in its anisotropy.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of the floating heat treatment apparatus. 1 is a biaxially oriented polyester film, 4 is an air tank, 5 is an air nozzle, 10 is a heater, 11 is a blower, and 12 is an air supply port. Patent applicant Teijin Ltd.

Claims (1)

[Scope of Claims] 1. When kept under temperature and humidity conditions of 60°C and 80% RH for 72 hours, the dimensional change rate in the longitudinal direction is 0.05 to 0.3% and the dimensional change rate in the width direction is within the range of 0.05 to 0.3%. 0 from the vertical dimension change rate.
0.02 to 0.2% larger biaxially oriented polyester film is traveling and subjected to relaxation heat treatment using an aerodynamic floating treatment method to produce a film in which the dimensional change rate is 0.02% or less in both cases, the floating heat treatment In at least a certain section of the film, air heated to a temperature 40 to 80°C higher than the secondary transition point of polyester is sent to only one side of the film to levitate the film, and the running stress is maintained at 13 kg/cm^2 or less. A method for producing a polyester film for a magnetic recording flexible disk, which comprises running the polyester film on a curved surface and subjecting it to relaxation heat treatment in a treatment time of less than 5 seconds. 2. The biaxially oriented polyester film to be subjected to floating heat treatment is obtained by heat-treating a biaxially stretched and heat-set polyester film at a temperature lower than the heat-setting temperature while giving low elongation in the width direction or limited shrinkage in the width direction. 2. The method according to claim 1, wherein the film is a film produced by 3.Claim 2, wherein the film is heat treated while giving the film an elongation of 0 to 4% in the width direction or a limited shrinkage of less than 1%.
Manufacturing method described.