JPH0648534B2 - 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 and an in-plane anisotropy of expansion coefficient at temperature and humidity. The present invention relates to a method for manufacturing a polyester film for a small magnetic recording flexible disk.

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 layer and providing a magnetic layer.

In recent years, magnetic recording / reproducing devices using discs have been advanced in high density and high reliability of magnetic recording, and along with this, flexible discs also have (a) mechanical strength that does not cause distortion in recording. , (B) Heat-resistant dimensional stability that does not cause dimensional changes due to unexpected heat during recording and reproduction, (c) Excellent surface flatness that does not deteriorate electromagnetic conversion characteristics due to thin magnetic layers, ) 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 are being increasingly demanded, and the development of a disk with improved characteristics is desired.

Among these characteristics, for example, to improve modulation,
It has been proposed to make the magnetic easy axis 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 film, 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 of reducing the heat shrinkage ratio and the dimensional change in the width direction (transverse direction) of the biaxially stretched polyester film, a method of giving a limited shrinkage in the heat setting process in the film manufacturing process is known. However, it is difficult to produce a film which shows only a slight 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 of 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 being subjected to a limited shrinkage of 1 to 10% in the width direction, and then a floating treatment method is used.
A method of performing relaxation heat treatment at a temperature of 120 to 160 ° C has been proposed. However, according to the study result of the present inventor, the polyester film obtained by this method is 60% at 80%.
When it is placed in an atmosphere of RH, it behaves in an extraordinary manner in that it expands in the width direction (lateral direction). As a result, the anisotropy of the in-plane dimensional change increases, and the desired dimensional stability is obtained. It became clear that I could not get it.

An object of the present invention is to solve this problem and to provide a magnetic recording flexible disk having a small dimensional change and a small in-plane anisotropy even when placed in a high humidity atmosphere from room temperature to about 60 ° C. It is to provide a method for producing a polyester film.

According to the present invention, the biaxially stretched heat-fixed polyester film is heat-treated at a temperature lower than the heat-setting temperature while stretching the film transversely with a stenter at 60 ° C., A heat-treated film having a longitudinal shrinkage of 0.05 to 0.2% and a transverse shrinkage of 0.02 to 0.2% greater than the longitudinal shrinkage when kept at 80% RH for 72 hours is used. The running tension of the film is 4.0 ~
While keeping the pressure at 10 kg / cm ² , by the floating treatment method by aerodynamic force, relaxation heat treatment is performed for 5 seconds or more at a temperature of 90 to 110 ° C in a non-contact state to reduce the shrinkage ratio to 0.03% or less in both directions. And a polyester film for a magnetic recording flexible disk.

The polyester in the present invention is an aromatic polyester represented by polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polycyclohexylene dimethylene terephthalate and the like, 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 stretched heat-fixed polyester film according to the present invention is obtained by extruding a polyester melt through a die, quenching and solidifying, and then 3.0 to 4.5 times in the longitudinal direction and then 3.0 to 4.5 in the transverse direction.
It can be produced by a method of stretching 4.5 times and then heat setting. More preferably, the stretching ratio is 3.0 to 3.7 times in the machine direction and 0.1 to 0.3 times higher in the cross direction than in the machine direction. The biaxially stretched polyester film is preferably a balanced type. The heat setting temperature is preferably 180 to 240 ° C. 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 apart from this temperature range, the coefficient of thermal expansion of the film may deviate from the value required for the flexible disk, which is not preferable.

In the present invention, a biaxially stretched and heat-fixed polyester film is first stretched in the width direction in a stenter, particularly 1 to
The longitudinal shrinkage when heat-treated at a temperature lower than the heat-setting temperature while giving 7% elongation and kept for 72 hours under the temperature and humidity conditions of 60 ° C. and 80% RH is 0.05 to 0.2% and the transverse direction. The heat-treated film has a directional shrinkage greater by 0.02 to 0.2% than the longitudinal shrinkage. This heat treatment can also be referred to as a second heat setting treatment. For example, if the tow-out process is performed in the latter half of the heat setting zone (area) of the stenter, it can be divided into the heat setting process before the toe out (the first half process) and the heat setting process after the toe out (the second half process), The former corresponds to the above heat setting, and the latter corresponds to the above heat treatment. The heat treatment while stretching in the width direction is performed at a temperature lower than the heat setting temperature, preferably 20 to 50 ° C. lower. 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 during the elongation process, which is not preferable. On the other hand, if the heat treatment temperature is too low, there is a problem that the film is likely to break 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 the floating heat treatment method. In this relaxation heat treatment, the film running tension is kept at 4.0 to 10 kg / cm ² and the film is heated at a temperature of 90 to 110 ° C. for 5 seconds or more. This temperature is
If it is lower than 90 ° C, it is difficult to reduce the heat shrinkage rate to a desired value within a practical time. On the other hand, if it is higher than 110 ° C, the film becomes wavy, which is not preferable. The preferred processing time is 10 seconds or more. This upper limit is not particularly limited, but the effect of the relaxation treatment tends to reach saturation within 60 seconds, so about 60 or less, practically about 20 seconds may be sufficient. On the other hand, if the film running tension is less than 4.0 kg / cm ² , the film running becomes unstable, whereas if it is more than 10 kg / cm ² , the effect of the relaxation treatment is not exhibited and the film is wavy, which is not preferable.

After removing the heat-treated film from the stenter clip, it is possible to cool it once and cut off both side ends to wind it into a roll, unwind it from the roll and perform a floating relaxation treatment in the same manner as above. It is more efficient to process continuously.

As the relaxation heat treatment method, a conventionally known one such as a floating method using air pressure and a floating method can be used. This method is disclosed in
It is described in detail in Japanese Patent Publication No. 53-96072.

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 an acid 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 and the like dissolved and dispersed in a solvent such as methyl isobutyl kent and toluene can be used. 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 with reference to Examples. The symbol MD in the examples means the longitudinal direction of the film (longitudinal 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 into pieces in the direction of measurement of heat shrinkage rate, and marking points at intervals of about 300 mm are attached. This sample is placed in a constant temperature and humidity chamber at 25 ° C and 50% RH for 24 hours.
After holding the time, read the length between the marks with a reading microscope. Next, this sample was kept in a thermo-hygrostat kept at 60 ° C and 80% RH for 3 days and then taken out, and the above-mentioned 25 ° C and 50% was taken.
Hold in the constant temperature and humidity room of RH for 24 hours, and measure the length between gauge marks again. 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 the original film M
It was in agreement with D or TD. Therefore, the values in the table are shown as MD and TD.

(2) Film surface property 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 3 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 machine direction, and subsequently stretched 3.7 times in the cross direction with a stenter, and further While heat-setting at the maximum temperature of 215 ℃ in the first half of the heat setting zone of the tenter, while giving 3% extension in the width direction in the second half of the zone
Heat treatment was performed at a temperature of 180 ° C. The thickness of the obtained film is
It was 75μ. Thermal shrinkage of this film (60 ℃, 80% R
(H, 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 a temperature shown in Table 1 with a running tension of 6.8 kg / cm ² , a heat treatment time of 20 seconds, using an aerodynamic levitation relaxation heat treatment device connected to the heat fixing zone.

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 value of this shrinkage, the better the dimensional stability, and the MD
It is shown that the smaller the difference in shrinkage between the TD and TD values, the smaller the anisotropy.

As is clear from Table 1, at the treatment temperature of 80 ° C. or lower, the heat shrinkage ratio (60 ° C., 80% RH, 3 days) is not much different from that of the untreated and has no effect. In addition, the heat shrinkage is extremely small in the treatment at 130 ° C, but the flatness is deteriorated. From these results, it is understood that the temperature condition for the relaxation heat treatment requires 90 to 110 ° C.

Examples 4 to 8 and Comparative Example 4 The same procedure as in Example 3 was carried out except that the relaxation heat treatment time was changed as shown in Table 2. The results are shown in Table 2.

From these results, it can be seen that the relaxation heat treatment requires 5 seconds or more.

Examples 9 to 11 and Comparative Example 5 The procedure of Example 7 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 running tension is as low as 2.0 kg / cm ² , the heat shrinkage is small (in this case, the film stretches without shrinking. A minus in front of the value indicates that the film stretches. The stable film could not be run, and the film meandered and wrinkled.

Example 12 and Comparative Examples 6-8 The same procedure as in Example 7 was performed except that the heat treatment in the latter half of the stenter heat setting zone gave 7% elongation. The results are shown in Table 4 together with the results of Example 7.

On the other hand, for comparison, the same procedure as above was carried out except that elongation was not given or limited shrinkage was given during the heat treatment. The results are also shown in Table 3.

As is clear from Table 4, when the film subjected to the restriction shrinkage is subjected to relaxation heat treatment, the heat shrinkage rate after holding for 3 days at 60 ° C. and 80% RH becomes smaller in the machine direction (MD) but in the transverse direction (T).
Rather, it is elongated in D) and the anisotropy increases.

On the other hand, the stretched film is excellent in that the heat shrinkage is small and the anisotropy is small.

Claims (1)

[Claims] 1. A biaxially stretched heat-fixed polyester film is heat-treated at a temperature lower than the heat-fixing temperature for 72 hours under a temperature and humidity condition of 60 ° C. and 80% RH while stretching the film laterally with a stenter. When the vertical shrinkage is 0.05 ~
0.2% and the shrinkage in the transverse direction is less than the shrinkage in the longitudinal direction.
02-0.2% larger heat-treated film, then the non-contact state by the floating treatment method by aerodynamic force while keeping the running tension of the heat-treated film at 4.0-10 kg / cm ^2.
A method for producing a polyester film for a magnetic recording flexible disk, which comprises subjecting the film to a relaxation heat treatment at a temperature of 90 to 110 ° C. for 5 seconds or more to reduce the shrinkage ratio to 0.03% or less in both directions.