JPH0667601B2 - Manufacturing method of polyester film for magnetic recording flexible disk. - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyester film for a magnetic recording flexible disk, and more specifically, it has a small dimensional change due to temperature and humidity within a short time and an expansion coefficient of temperature and humidity within the plane. The present invention relates to a method for producing a polyester film for a magnetic recording flexible disk, which has a small irregularity and an excellent flatness.

Conventional technology and its problems Magnetic recording flexible disks are usually based on a biaxially oriented polyester film, on the surface of which magnetic fine particles are coated with a binder, or by a method such as vacuum deposition, sputtering or plating. It is manufactured by forming a thin film layer and providing a magnetic layer.

In recent years, the magnetic recording / reproducing apparatus using a disk has been advanced in high density and high reliability of magnetic recording, and along with this, (a) the mechanical strength of a flexible disk without distortion in recording. , (B) Heat-resistant dimensional stability that does not cause dimensional changes due to unexpected heat during recording / reproduction, (c) Excellent surface flatness that electromagnetic conversion characteristics do not deteriorate due to thinning of the magnetic layer, (d) ) There is an increasing demand for in-plane isotropy in which the fluctuation of the input / output voltage per track is small, in other words, excellent modulation and other characteristics, and there is a demand for the development of disks with improved characteristics.

Among these characteristics, for example, to improve modulation,
It has been proposed to make the axis of easy magnetization of the magnetic material of the magnetic layer isotropic using a randomizer in the process of manufacturing the disk (Japanese Patent Laid-Open No. 60-193137).

However, the modulation may be aggravated by the distortion of the base filter, and even if the magnetic layer in the unsolidified state is made non-oriented by the randomizer as in the above proposal, the effect is small. Deterioration of modulation due to the base film is particularly problematic when the flexible disk is used in an atmosphere accompanied by changes in temperature and humidity, or in an atmosphere of high temperature or low temperature. The reason for this deterioration is
Biaxially oriented polyester film generally undergoes dimensional change (expansion and contraction) with changes in temperature and humidity, and the dimensional change does not occur isotropically. In other words, the biaxially oriented polyester film has a temperature and humidity expansion rate. It is mentioned that there is anisotropy.

In addition, the flexible disk has a maximum operating temperature of 51.5
It is required to expand from ℃ to 60 ℃, and it is required to have dimensional stability, electromagnetic conversion characteristics, etc. that can withstand use at 60 ℃. The expansion of the operating temperature increases the above-mentioned dimensional change (expansion and contraction) of the base film and causes the above-mentioned anisotropy to increase.

As a means for obtaining a flexible disk having a small heat shrinkage ratio and a small dimensional change, a method of cutting a base film or a disk and subjecting a plurality of these sheets to a relaxation heat treatment in a state of being superposed has been proposed (Japanese Patent Laid-Open No. 59-59- No. 127233). Although this heat treatment is ideal in that it is carried out without any tension, it cannot process a web on which a magnetic layer is continuously formed,
Therefore, it has another problem that workability and production efficiency are low.

Further, as a method for reducing the heat shrinkage rate and the dimensional change of the biaxially oriented polyester film in the axial direction (transverse direction), a method of giving limited shrinkage in the heat setting process in the film manufacturing process is known. However, it is difficult to manufacture a film which shows only a subtle deformation of the film in the longitudinal direction (longitudinal direction) of the film by a usual biaxially stretched heat setting method.

Therefore, as a method for improving the dimensional stability in the longitudinal direction of the film, a method of relaxing and heat treating the film after heat fixing has been proposed. For example, in JP-A-53-96072, a biaxially stretched polyester film is heat-set while giving a restricted shrinkage of 1 to 10% in the width direction, and then a floating treatment method is used.
A method of relaxation heat treatment at a temperature of 120 to 160 ° C has been proposed. However, according to the research results of the present inventor, the polyester film obtained by this method is 60 ° C, 80% RH.
Unexpectedly, it behaves in such a way that it expands in the width direction (transverse direction) in the atmosphere, and as a result, the anisotropy of the in-plane dimensional change becomes large, and the desired dimensional stability cannot be achieved. Moreover, it was revealed that the film was wavy and the flatness was deteriorated.

OBJECT OF THE INVENTION The present inventor has solved this problem and has a very small dimensional change and a small in-plane anisotropy even when placed in a high humidity atmosphere from room temperature to a temperature of about 60 ° C. As a result of research to produce a polyester film for a magnetic recording flexible disk excellent in heat resistance, in order to obtain a satisfactory result in the aerodynamic floating heat treatment, the film to be treated is 60 ° C, 8
A biaxially oriented polyester having a longitudinal dimensional change rate of 0.05 to 0.3% and a widthwise dimensional change rate of 0.02 to 0.2% greater than the longitudinal dimensional change rate when kept at 0% RH for 72 hours. It was revealed that the film is a film, but if the processing temperature of this film is too high, the film corrugates and the flatness is impaired. Therefore, it is necessary to lower the processing temperature and prolong the processing time. The present inventor has arrived at the present invention as a result of further research to solve this problem.

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

Advantageous Effects of Invention According to the present invention, the object of the present invention is to have a longitudinal dimensional change rate of 0.05 to 0.3% and a width direction when held for 72 hours under a temperature and humidity condition of 60 ° C and 80% RH. The dimensional change rate is 0.02 to 0.2% larger than the longitudinal dimensional change rate, while the biaxially oriented polyester film is run, and the dimensional change rate is 0.
A method for producing a film of 02% or less, in which air heated to a temperature 40 to 80 ° C. higher than the second-order transition point of polyester is sent to only one side of the film during at least a certain section of the floating heat treatment, Levitated and running stress 13
Keep below kg / cm ² and run along curved surface 5
This is achieved by a method for producing a polyester film for a magnetic recording flexible disk, which is characterized by performing a relaxation heat treatment for a processing time of less than a second.

The polyester in the present invention is an aromatic polyester represented by polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polycyclohexylene dimethyl terephthalate, etc., which may be a homopolymer or a copolymer (copolymerization component is 20 Mol% or less is preferable). The molecular weight of the polyester may be an ordinary one and is not particularly limited. Further, the polyester may contain any additive.

The biaxially oriented polyester film to be subjected to the floating heat treatment in the present invention has a longitudinal dimensional change rate of 0.05 to 0.3% and a widthwise dimensional change rate when kept for 72 hours under the temperature and humidity conditions of 60 ° C. and 80% RH. 0.02 to 0.2 from the vertical dimensional change rate
% Of biaxially oriented polyester film. Such a biaxially oriented polyester film is produced by extruding a polyester melt through a die, quenching and solidifying, and then 3.0% in the longitudinal direction.
It can be produced by a method in which it is stretched by ˜4.5 times, then by 3.0 to 4.5 times in the width direction, heat set, and further heat treated. As the stretching temperature, a normal stretching temperature can be adopted. The draw ratio is 3.0 to 3.7 times in the machine direction, and the transverse direction is more than the machine direction.
It is more preferable to increase it by 0.1 to 0.3 times. The biaxially oriented polyester film is preferably a balanced type. Heat setting temperature is 40 ° C higher than stretching temperature and 20 ° C higher than melting point
Lower temperatures are preferred, for example 180 to 240 ° C. for polyethylene terephthalate film. Here, this heat setting temperature refers to the maximum temperature in the heat setting process or in the heat setting process zone. Even if the film is heat-set at a temperature far away from this temperature range, the thermal expansion coefficient of the film may deviate from the value required for the flexible disk, which is not preferable. Further, the heat treatment after heat setting is carried out by imparting a biaxially stretched heat set polyester film with a low elongation in the width direction in the tenter, particularly while giving 0 to 4% elongation, or while giving a limited shrinkage, especially less than 1% shrinkage. Heat treatment at a temperature lower than the fixed temperature, and heat and humidity conditions of 60 ° C, 80% RH 7
The vertical dimensional change rate when held for 2 hours is 0.05 to 0.3%, and the widthwise dimensional change rate is 0.02 from the vertical dimensional change rate.
~ 0.2% larger film.

This heat treatment can also be referred to as a second heat setting treatment. For example, if the tow-out treatment or tow-in treatment is performed in the latter half of the heat setting zone (area) of the tenter, the heat setting treatment before the toe-out or to-in (the first half treatment) and the heat setting treatment after the toe-out or toe-in (the latter half treatment) The former corresponds to the above heat setting, and the latter corresponds to the above heat treatment. The heat treatment while imparting a specific proportion of elongation or limiting shrinkage in the width direction is performed at a temperature lower than the heat setting temperature, preferably at a low temperature of 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 is expanded, probably because the higher order structure is destroyed in the process of elongation or limited shrinkage, which is not preferable. On the other hand, if the heat treatment temperature is too low, the effect is not sufficient, and the film is likely to be broken during stretching.

In the present invention, next, the film heat-treated as described above is removed from the tenter clip, and relaxation heat treatment is performed in a non-contact state by a floating heat treatment method. In this relaxation heat treatment, air heated to a temperature 40 to 80 ° C. higher than the second-order transition point of polyester in at least a certain section is sent to only one side of the film to levitate the film, and a running stress of 13 kg / cm ² Hereafter, it is necessary to run the vehicle so as to draw a curved surface (in other words, not to form a flat surface) while keeping it at ² to 13 kg / cm ² . When a heated and relatively soft film is run, if it is run so as to form a flat surface (for example, horizontally), waviness is likely to occur and the flatness of the film is deteriorated. To avoid this problem, it is effective to lower the processing temperature, but this results in a longer processing time. However, the above problem can be solved by traveling along a curved surface, the flatness of the film can be maintained even at a relatively high processing temperature, and the processing time can be shortened.
This curved surface preferably has a radius of 500 mm or more and 100 mm or less. If the running stress is more than 13 kg / cm ² , the dimensional stability is not sufficiently reduced or a uniform reduction cannot be obtained.

The treatment shown in FIG. 1 can be cited as an apparatus for floating the film with heated air and running it so as to draw a curved surface.
Other devices may be used as long as they satisfy the above conditions.

In FIG. 1, 1 is a biaxially oriented polyester film, 2
Is an inlet guide roll, 2'is an inlet press roll, 3 is an inlet guide roll, 4 is an air tank, 5 is an air nozzle, 6 is an outlet guide roll, 7 is a cooling roll, 7'is an outlet press roll, and 8 is a warm 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 a predetermined interval along the outer circumference of the air tank 4 in a substantially arc shape. The air heated by the heater 10 is sent from the air supply port 12 to the air tank 4 by the blower 11, and further sent from the air tank to the individual air nozzles 5.
The heated air blown out from the air nozzle 5 hits one surface of the traveling film 1 and raises the film. The film floating amount is preferably 5 to 15 mm. The air from which the traveling film 1 is floated moves to the heat insulation booth 8 from both side edges of the film, is exhausted from the air exhaust port 9 provided on the side wall of the heat insulation booth, and is then sent to the heater 10 again. heater
The mixing ratio of fresh air supplied to 10 and air from the exhaust port 9 can be arbitrarily selected. On the other hand, the running film 1 is guided by the inlet guide rolls 2 and 3 and sent to the air nozzles 5 arranged in a substantially arcuate shape in the heat insulating booth 8 while being floated by the heated air from the air nozzles 5 and curved. While running, during which it is subjected to a relaxation heat treatment. The film after the relaxation heat treatment is cooled by the cooling roll 7 through the exit guide roll 6. The temperature of the heated air blown out from the air nozzle 5 is 40 to 80 ° C. higher than the second-order transition point of polyester, and for example, in the case of polyethylene terephthalate film, it is preferably 110 to 140 ° C. By doing so, sufficient relaxation heat treatment can be performed even if the treatment time is less than 5 seconds, and the obtained film has a dimensional change rate in both axial directions of 0.02% or less and is excellent in flatness. If this dimensional change rate of 0.02% or less is expressed by the heat shrinkage rate, it is −0.
It becomes 02-0.02%.

In the present invention, the short treatment time increases the speed of the relaxation heat treatment, which is industrially advantageous. Also, after removing the heat-treated film from the tenter clip, it is possible to cool it once and cut off both end portions to wind it into a roll, unwind it from the roll and perform floating relaxation treatment in the same manner as above. It is more efficient to process continuously.

The polyester film obtained by the present invention can be made into a long web by providing a magnetic layer thereon. As a method for producing this web, a conventional method, for example, a method using a magnetic paint can be used. Known magnetic paints can be used. For example, γ-Fe ₂ O ₃ powder, cellulose acetate butyrate, epoxy resin,
Lecithin, silicone oil, etc.
Those dissolved and dispersed in a solvent such as toluene can be applied. Known means and conditions can be applied to the drying of the magnetic paint.
Further, known means and known processing conditions can be applied to the calendering treatment for smoothing the magnetic layer.
For winding the magnetic recording medium on which the magnetic layer is formed, known winding equipment can be used as it is.

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

1. It is possible to manufacture a magnetic recording flexible disk that does not cause deterioration of modulation due to heat history up to 60 ° C.

2. 96 TPI when using a 5.25 inch disc
In the case of (track / inch), a missing pulse due to tracking deviation does not occur without a servo mechanism.

3. Repeated use of the flexible disk and virtually no dimensional change caused by thermal history eliminates clamp failure due to distortion of the central hole and damage to the disk.

EXAMPLES Next, the present invention will be described more specifically by way of examples.
The symbol MD in the example is the longitudinal direction of the film (vertical direction).
, And TD indicates the width (width) direction. The film characteristics were measured and evaluated by the following methods.

(1) Heat shrinkage rate A film with a width of 10 mm and a length of 350 mm is cut out in a zigzag pattern in the measurement direction of heat shrinkage rate, and marking points at intervals of about 300 mm are attached. After holding this sample in a constant temperature and humidity room at 25 ° C and 50% RH for 24 hours, read the length between gauge marks using a reading microscope. Then, this sample was kept in a constant temperature and humidity chamber kept at 60 ° C and 80% RH for 3 days and then taken out, and then kept in the above constant temperature and humidity chamber at 25 ° C and 50% RH for 24 hours, and then marked again. Measure the length between. The rate of dimensional change (heat yield) is the amount of shrinkage divided by the length between the original gauge points and expressed as a percentage.

In addition, in order to obtain the dimensional change rate in the plane of the film under various condition treatments, samples were cut out as described above at every 30 degrees in the plane of the film, and the heat shrinkage rate was measured. The maximum and minimum values of heat shrinkage are M of the original film
Matched D or TD. Therefore, the value in the table is M
Denote by D and TD.

(2) Film flatness A sample with a width of about 1 m and a length of 3 m is spread on a flat table surface and evaluated from the wavy state of the film.

A film with a large waviness is rated as bad, and a film without waviness that does not change from that of an untreated film (which does not undergo relaxation heat treatment) is considered good.

Examples 1 to 4 and Comparative Examples 1 to 3 Polyethylene terephthalate was melted, extruded through a die slit, cooled and solidified, and then stretched 3.6 times in the longitudinal direction, and then stretched 3.7 times in the transverse direction with a stenter, and further In the first half of the heat setting zone of the tenter, heat treatment was performed at a maximum temperature of 215 ° C., and in the latter half of the zone, heat treatment was performed at a temperature of 180 ° C. while giving 0.8% limiting shrinkage in the width direction. The thickness of the obtained film was 75μ. Thermal shrinkage of this film (60 ℃, 8
(0% 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 a relaxation treatment at a running tension of 5 kg / cm ² , a heat treatment time of 3 seconds, and a temperature shown in Table 1 by an aerodynamic floating relaxation heat treatment apparatus shown in FIG. 1 connected to the heat fixing zone. gave.

Table 1 shows the shrinkage rates of these films after being held at 60 ° C., 80% RH for 3 days (72 hours). The smaller the shrinkage value, the better the dimensional stability, and the smaller the difference in shrinkage between MD and TD values, the smaller the anisotropy. In the table, the negative heat flux value means expansion, and 0
The closer to the value, the better the dimensional stability.

As is clear from Table 1, at the treatment temperature of 100 ° C. or lower, the heat shrinkage rate (60 ° C., 80% RH, 3 days) is almost the same as that of the untreated and has no effect.

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

Examples 6 to 9 and Comparative Example 4 The procedure of Example 3 was repeated except that the film running tension during relaxation heat treatment was changed as shown in Table 3. The results are shown in Table 3.
Shown in.

As is clear from Table 3, when the treatment stress is in the range of ² to 13 kg / cm ² , both heat absorption and running behavior can be satisfied.

On the other hand, when the treatment stress shown in Comparative Example 4 is too high, the heat absorption value is high.

Examples 10 to 13 and Comparative Examples 5 and 6 The same procedure as in Example 3 was performed except that elongation was applied during the heat treatment in the latter half of the tenter heat setting zone. The results are shown in Table 4.

On the other hand, for comparison, the same process as above was performed except that the above-mentioned heat treatment gives a limiting shrinkage more than that of the present invention. The results are also shown in Table 4 as Comparative Examples 9 and 10.

As is clear from Table 4, when the film subjected to excessive shrinkage is subjected to floating heat treatment, the heat shrinkage ratio becomes smaller in the machine direction (MD) but rather stretches in the transverse direction (TD). Sex increases. On the other hand, a film to which a slight amount of limited shrinkage or elongation is applied has a small thermal shrinkage and an excellent anisotropy.

[Brief description of drawings]

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

Claims (3)

[Claims] 1. A vertical dimensional change rate of 0.05 to 0.3% when kept at 60 ° C. and 80% RH temperature and humidity conditions for 72 hours, and a widthwise dimensional change rate of 0.02 from the vertical dimensional change rate. ~ 0.2
% Is a method of producing a film having a dimensional change rate of 0.02% or less by performing relaxation heat treatment by an aerodynamic floating treatment method while running a biaxially oriented polyester film having a large size. The air heated to a temperature 40 to 80 ° C higher than the second-order transition point is sent to only one side of the film to levitate the film, and the running stress is kept at 13 kg / cm ² or less to run along a curved surface. A method for producing a polyester film for a magnetic recording flexible disk, wherein the relaxation heat treatment is performed for less than 5 seconds. 2. A biaxially oriented polyester film to be subjected to a floating heat treatment, wherein the polyester film biaxially stretched and heat-set is heat-treated at a temperature lower than the heat-setting temperature while giving a low elongation in the width direction or a limited shrinkage by a tenter. The production method according to claim 1, which is a film obtained by 3. The method according to claim 2, wherein the film is heat-treated while being stretched in the width direction by 0 to 4% or while being subjected to a restricted shrinkage of less than 1%.