JPS618324A - Heat treatment of film - Google Patents

Abstract

PURPOSE:To perform a tenter type heat treatment of a film without causing bowing phenomenon, by accomplishing a heat treatment at a specified temperature rising rate after the temperature of the film prior to the processing is brought under the secondary transition temperature of the polymer. CONSTITUTION:To prevent bowing phenomenon of a film, it is heated at a temperature rising rate Y( deg.C/sec) in the heat treatment, provided that Y must meet the requirement of Y>2X+50, wherein X is represented by the distance (cm) between constrains of both end rim sections of a film 1 to be treated. So to speak, the film 1 being treated leaving a stretching zone 4 is introduced to a heat treating zone 3 with both end rim sections 1a constrained. The clearance C between the stretching zone and the heat treating zone is so formed that the temperature of the film being treated becomes under the secondary transition temperature Tg of the polymer while the temperature under the value Tg is kept for a proper time and a heated air shut down device 3a is provided at the inlet of the heat treating zone to enable immediate heating at the above-mentioned temperature rising rate. The heat treating zone is controlled with a heater 2 and a blower 6.

Description

[Detailed description of the invention] Industrial applications The present invention is a continuous crystalline thermoplastic polymer film.

The present invention relates to a heat treatment method for a film that can be carried out without causing a gluing phenomenon (delay in the center of the film) during running.

Conventional technology Industrial heat treatment methods for crystalline thermoplastic polymer films are broadly divided into roll-type heat treatment methods in which the film is brought into contact with heated rolls, and tenter methods in which both edges of the film are restrained and heated with hot air. There is a complete set of heat treatment methods. With the roll heat treatment method, scratches on the roll may be transferred or temperature unevenness in the width direction of the roll may occur! 7) The quality of the film becomes non-uniform in the width direction, which is particularly common when using Tuzoroll on wrinkled edges. In addition, the tenter set heat treatment method does not cause wrinkles or scratches, but compared to the roll heat treatment method, there is a maing phenomenon, that is, the physical properties of the film are delayed in the width direction compared to the side edges, and the center part of the film is arched. This tends to result in uneven molecular orientation in the width direction, resulting in unevenness in dimensional stability (heat shrinkage), mechanical strength, elongation, etc. Post-processing such as coating, laminating, slitting, printing, and bag-making, which caused distortion, often causes problems and also impairs the commercial value of the finished product, so post-processing is not acceptable. Since only products with uniformity within the specified range are commercialized, the product yield is reduced.

Various methods have been tried in the past to prevent such drawbacks, but all of them have drawbacks. For example, a heat treatment method in which the film is brought into contact with a heating roll with nip rolls (
Japanese Patent Publication No. 39-29214) has the above-mentioned disadvantages of the roll heat treatment method as well as the disadvantage of neck-down due to not restraining both sides.

In addition, the heat treatment method that applies a temperature difference in the width direction (% Publication No. 42-9273) has the disadvantages mentioned above in the case of a roll type, and the complexity of the equipment and the time it takes to adjust the conditions in the case of a set of tenters. There are disadvantages such as a decrease in the effective operating rate due to In addition, a heat treatment method (Japanese Unexamined Patent Application Publication No. 51-119) that attempts to make the physical properties uniform in the width direction by increasing the wind speed on both side line portions of the film is also available.
-91973) has the same drawbacks as the tenku complete set in Japanese Patent Publication No. 42-9273. In addition, in the method of heat-treating the film after horizontal stretching using a horizontal stretching roll in a tenter (%Kaikai No. 50-73978), scratches on the roll were likely to be transferred because the film came into contact with the roll in a heated state. However, there are drawbacks such as wrinkles occurring due to the temperature difference between the surrounding atmosphere and the roll, and simply cutting the film tension between the stretching process and the heat treatment process is insufficient to prevent the occurrence of the bowing phenomenon. I can't. Furthermore, as a method to overcome the drawbacks of these methods, a method has been proposed (%Kaikai No. 58-215318) in which hot air is applied to the film to heat it without flowing upstream in the running direction of the film in tenter set heat treatment. There is.

Problems to be Solved by the Invention The present inventors have developed a tenter set for the purpose of providing a tenter set heat treatment method that takes advantage of the advantages of a tenter set and can perform film heat treatment without causing the bowing phenomenon. As a result of intensive investigation into the occurrence of the lag phenomenon, focusing on the temperature increase rate during heating and the state of the film immediately before heat treatment, we found that after the film temperature before heat treatment was set to the second-order transition temperature (Tg) of the polymer, 1:A. They discovered that the bowing phenomenon can be highly prevented by heat treatment at a specific temperature increase rate, leading to the present invention.

Means for Solving the Problems In other words, the present invention provides a heat treatment process in which an at least uniaxially stretched film of a crystalline thermoplastic polymer is continuously run with both edges constrained. the film from a temperature below the second order transition temperature (Tg) of the polymer;
The temperature that immediately leads to the temperature at which the heat treatment is to be performed and the rate of temperature increase up to that temperature is expressed by the formula Y〉2X+50 (where Y is the average temperature increase rate from the Tg of the film to be treated to the heat treatment temperature (
℃/sec) %X is a film heat treatment method characterized by satisfying the distance (minor) between both end edge restraints of the film to be processed.

By making the treated film less than the Tt of the polymer prior to the heat treatment, it is possible to prevent the occurrence of heat shrinkage, which causes the bowing phenomenon, before the heat treatment. In order to make the temperature lower than Tg, it is industrially preferable to pass the film from the stretching zone through a cooling zone rather than directly to the heat treatment zone. When providing a cooling zone, the cooling temperature and cooling time must be carefully controlled to obtain a specific temperature increase rate in the next heat treatment zone, and to avoid overcooling. It is preferable that the film to be treated is cooled down to a Tt droplet and immediately heated to heat treatment. Examples of the cooling zone that can be used include a method in which a zone for blowing cold air is provided between the stretching zone and the heat treatment zone, and a method in which a barrier is provided at the entrance to the heat treatment zone. When installing a blocker, it is preferable that the gap to the film surface be 5 mm or less. In any case, it is necessary that the film surface temperature be lowered to below the Tg of the film to be processed.

It is also advantageous to provide a sufficient gap to allow cooling below Tg when the sheet is continuously led from the drawing sheet to the heat treatment zone. Particularly preferred conditions are that the film to be processed is cooled from the stretching temperature to a temperature below the Tg of the polymer and 30°C below the Tg, and this temperature is about 0.01 seconds to about 1 second.
The goal is to control the heat treatment to a certain degree and guide it to the next heat treatment zone.

This operation is preferably carried out when the film to be treated is a film stretched by the tubular method or the transverse-longitudinal stretching method.

In order to prevent the bowing phenomenon, this step alone is insufficient, and it is necessary to heat at a specific temperature increase rate in the subsequent heat treatment.

According to studies by the present inventors, the bowing phenomenon cannot be prevented even if the film to be processed is directly heat-treated at the temperature increase rate of the present invention without being cooled to below the temperature T from the stretching zone.

The heating rate of the present invention is expressed as a function of the width of the film being treated. That is, the temperature increase rate (Y:° C./sec) must satisfy Y>2X+50. Here, X is the distance 111 m (α) between both end edge restraints of the film to be processed.

If heat treatment is performed at a temperature increase rate that does not satisfy this equation, the bowing phenomenon cannot be prevented. A more preferable heating rate satisfies Y>2X+100.

This formula was discovered by the present inventors based on the fact that the lower limit of the temperature increase rate changes depending on the film width. In other words, when the film width is narrow, the restraining force of the clips at both ends extends to the center of the film, making it difficult for zapping to occur. Regulation of the temperature increase rate according to the film width is an important requirement of the present invention.

The temperature increase rate (Y) is measured by bringing a thermocouple into contact with the film surface, running it through the heating zone, and recording it with a temperature recorder for one hour. The distance oO between the two end edge restraints of the film to be processed is the width of the film to be processed during heat treatment, and is measured from one end of the chuck of the tenter to the other end using a normal measuring means.

The rate of temperature increase in the present invention is adjusted by carefully controlling the running speed of the film to be processed, heating temperature, heating capacity (amount of energy), etc.

The heat treatment method of the present invention can be performed using any apparatus that can adjust the temperature increase rate as appropriate. For example, when hot air is used, this can be achieved by carefully controlling the rotational speed of the hot air sorber, but a blowing air velocity of less than sm/sec or more than 30 m/sec is not preferred from the viewpoint of uniform heating.

In addition, further infrared heater (millimeter unit heater)
A method of local irradiation using irradiation is also preferably used. In this case, this can be achieved by installing an infrared heater parallel to the film surface and as close as possible, and controlling the output according to the film running speed by changing the voltage.

In the present invention, it is also possible to combine a plurality of heating means. For example, it is preferable to combine a hot air blower and an infrared heater.

The width (3) of the film to be processed used in the method of the present invention varies depending on the tenter device, but is 5 mm or less, preferably 11 to 13,000 tr or less. Furthermore, the thickness of the film that can be applied to the method of the present invention is not particularly limited. Usually, films with a thickness of about 1 to 300 μm are targeted.

The film-forming polymer to which the method of the present invention is applied is as follows.

Polyethylene terephthalate% Polyethylene-2゜6
-su7talate, polynato2 methylene terephthalate,
Polyhexamethyleneazide semir%f:v capramide,
Film 1 made of thermoplastic polymers such as polyethylene, polypropylene, polyvinyl chloride, polyvinyl fluoride, copolymers containing these as main components, or mixtures thereof
In particular, it can be suitably applied to l-axis stretched films and biaxially stretched films (including lance films and tensilized films).

Function The present invention will be explained in detail below with reference to the drawings showing the main parts of the embodiments.

FIGS. 1, 2, and 3 separately show wall portions of embodiments of the present invention, and in each figure, (a) is an explanatory cross-sectional view, and (middle) is a perspective view.

In FIG. 1, the film l to be processed that has left the stretching zone is forced to run continuously with both edges (la) restrained (not shown) and guided to a heat treatment zone 3 installed downstream in the running direction X. . At this time, the distance between the stretching zone and the heat treatment sheet/O is determined so that the temperature of the film to be processed becomes less than 12 of the polymer and is maintained at a temperature less than Tg for an appropriate period of time, forming a cooling sheet 77. . A hot air blocker 3b is installed at the entrance of the heat treatment zone to ensure proper cooling and immediate heating at a specific temperature increase rate. The heat treatment zone is controlled by a heating heater 2 and a blower 6. An infrared heater 5 is installed immediately after the entrance of the heat treatment zone to stabilize heating at the initial stage of temperature rise, which tends to be unstable and uneven heating. Further, the temperature increase rate can also be finely adjusted using this infrared heater.

In the device shown in FIG. 2, cold air pipes 3b are installed at both ends of the gap between the blocking device 3b and the film 1, with their openings 3b' facing each other, and the film 1 is opened from the opening of one of the cold air pipes. By sucking the cold air blown out in the width direction (arrow Z) from the opening of the other cold air pipe, the cold air moves near the gap between the blocking device 3b and the film 1, and the upstream side in the running direction of the film 1 is drawn. This eliminates the effect of hot air on the air. The cold air pipe 3b may be installed so as to blow out cold air into the gap between the blocking device 3a and the film l, but it may also be installed immediately before the upstream side of the blocking device. Furthermore, in order to carry out the temperature increase rate of the method of the present invention, as only the essential parts are shown in FIG. For hot air blowing, which blows hot air onto the film 1, one or more rows of devices 2 are installed on one side or both sides of the film 1, and the blown hot air is substantially directed to the upstream side in the running direction of the film 10. At least in the most upstream row, the hot air is blown from the device 2 so that the hot air is blown in the direction of the arrow y/) from diagonally above the upstream side in the running direction of the film 10 to the downstream side with respect to the surface of the film 1. It is also possible to use a film heat treatment apparatus provided so as to be inclined diagonally downward. If the direction of the hot air blowing is inclined as above, that is, the hot air blowing will be carried out at an angle formed by the direction (arrow y/) and the running direction of the film 1 (arrow
The present invention has an effect when θ>90°, but the effect is even greater when preferably 135°>θ>105°.

According to the method of the present invention, unlike the conventional tenter set, the thermal shrinkage of the film 1 on the upstream side of the heat treatment zone does not occur or is negligibly small, and as a result, the zawing phenomenon hardly occurs. For example, fft[! Even after heat treatment, the center part was hardly deformed into a delayed arched shape. Depending on the conditions, it is also possible to modify the final ink generated by the lateral stretching of the tenter. In addition, since there is no need to create a temperature difference or a wind speed difference in the width direction, the equipment is simple, and therefore operation is easy and stable operation is possible. In addition, unlike the conventional roll method that uses a heating roll, in the present invention, nothing comes into contact with the film 1, so there are no scratches or wrinkles. Therefore, the heat-treated film obtained by the method of the present invention has uneven quality in the width direction. There is almost no breakage and the quality is very stable.

Examples Example 1 Polyethylene terephthalate was extruded from a die having a circular slit, rapidly cooled, heated, and stretched in a tube shape by 3.3 times in the machine direction (longitudinal direction) and 3.5 times in the circumferential direction (horizontal direction). A biaxially stretched film with a thickness of 20 μm was obtained. Next, using a tenter set heat treatment equipment, the stretched film was
Width 1.300 in stacked sheets. While running at a speed of 30 m/min, the temperature was heated to 65°C, and then immediately heated to 230°C.
Hot air was blown onto the stretched film at a speed of 15 m/min, and the stretched film was heated for 15 seconds while adjusting the temperature increase rate to 350° C./sec using an infrared auxiliary heater to obtain a heat-treated film. The temperature of the hot air is a value measured on the surface of the film being blown onto it (the same applies to the following Examples and Comparative Examples). A straight line was drawn in the width direction of the film surface before heat treatment, and the delay at the center of the width of the film was actually measured as an indicator of the amount of deformation (seeing phenomenon) after heat treatment. Furthermore, the deviation of the main axis of orientation from the reference value at each position a predetermined distance apart from one side edge in the width direction of the film was measured using a polarizing microscope. However, the standard orientation main axis is the horizontal direction, and the misalignment of the orientation main axis when viewed from above the film in the running direction of the film is when it deviates from the true lateral direction to the counterclockwise direction. The case was set to one direction. In addition, a density gradient tube of n-hebutane-carbon tetrachloride was used for density.
Measured at 5°C.

The above results are shown in Table 1.

Example 2 Polyethylene terephthalate was extruded from a die having linear slits and rapidly cooled. The original fabric was then sequentially biaxially stretched vertically and horizontally using a tenter stretching machine to increase the length by 3.3 times in the longitudinal direction and 3.5 times in the transverse direction. It was stretched to a thickness of 20 μm and a width of 1300 m+. This stretched film to be treated was led to a heat treatment apparatus in the same manner as in FIG. 2, with both end edges restrained. The gap between the stretching zone and the heat treatment zone was a cooling zone of 50 cln, in which the film to be treated was cooled to about 60°C. In the heat treatment zone, hot air at 230℃ flows at a speed of 30m.
/min, and the heating rate was adjusted to 330°C/sec using an infrared auxiliary heater. At this time, the film running speed was 1-160 m/min, and the heat treatment time was 7.5 seconds. The results of the heat-treated film are shown in Table 1.

Actual Winding Examples 3 to 6, Comparative Example 1.2 Heat treatment was performed using the same apparatus as in Example 2 while changing the film width and heating rate shown in Table 2. The results are shown in Table 2.

Example 7 Polyhexamethylene azinamide was extruded from a die having a circular slit, rapidly cooled, and then heated to form a biaxially stretched film having a thickness of 14μ by stretching 3.1 times in the longitudinal direction and 3.2 times in the transverse direction in the form of a tube. The resulting film was cooled to 25° C. and heat treated using the same apparatus as in Example 1 under the conditions shown in Table 3. The results are shown in Table 3.

From the comparison of the above examples and comparative examples, it can be seen that the film heat-treated by the method 1 of the present invention and the apparatus of the present invention has extremely excellent uniformity of quality in the width direction. Furthermore, because there is extremely little unevenness in the width direction of properties related to mechanical properties such as dimensional stability (heat shrinkage rate), thickness, and density, subsequent processing steps such as coating, laminating, slitting, printing, and bag making are possible. There will be no problems, and the finished processed product will be of excellent quality. Therefore, according to the present invention, applications requiring high precision, such as floppy disks for computers, magnetic tapes for video and audio, etc.
We can manufacture optimal films for aerial photography base films and electrical applications such as capacitors. Moreover, since the quality is excellent in uniformity in the width direction, the entire width of the film can be effectively manufactured into products, resulting in a high product yield and extremely high industrial value.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are explanatory diagrams showing embodiments of the method of the present invention, in which (a) is an explanatory cross-sectional view and (b) is a perspective view. DESCRIPTION OF SYMBOLS 1... Film, la... Edge part, 2... Heating device, 3... Heat treatment device, 3a... Heat shield, 3b...
・Cold air pipe, 3b'... opening, 4... stretching zone,
5...Infrared auxiliary heater, 6-Zorower, 7...
- Cooling zone, 8... Hot air deflection plate, h... Gap between film and barrier, C... Gap between stretching zone and heat treatment zone, X... Film running direction, Y... Flow direction of hot air, 2... Width direction of film Patent applicant Asahi Kasei Industries, Ltd. Figure 1 (a) (b)

Claims (1)

[Scope of Claims] In a heat treatment process in which a film of a crystalline polymer that has been uniaxially stretched is continuously run with both edges constrained, the film to be treated is heated to T
g) from a temperature below to the temperature at which it is to be immediately heat treated;
A film heat treatment method characterized in that the temperature increase rate to reach the temperature satisfies the following formula Y>2X+50 Y: Average temperature increase rate from Tg of the film to be heated to the heat treatment temperature (℃/sec ) X: Distance between both edge restraints of the film to be processed (cm)