JPH0245974B2 - NIJIKUENSHINSARETAHORIIIPUSHIRONNKAPUROAMIDOFUIRUMUNOSEIZOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing biaxially oriented poly-ε-caproamide film. More specifically, the present invention relates to a method for producing a biaxially stretched poly-ε-caproamide film using a sequential biaxial stretching method consisting of a combination of a roll longitudinal stretching method and a tenter transverse stretching method. Biaxially stretched poly-ε-caproamide is widely used as a packaging film because it has excellent strength, cold resistance, printability, chemical resistance, etc., and is resistant to pinholes. It's starting to get worse. When poly-ε-caproamide is stretched as a film, directional hydrogen bonds occur in the direction in which it is first stretched, and it is then impossible to stretch it in a direction perpendicular to the direction in which it is first stretched. There was a problem that
See Japanese Patent Application Laid-open No. 141372/1983. ). For this reason, the biaxially oriented polyamides currently manufactured and sold are
The ε-caproamide film is produced by a so-called simultaneous biaxial stretching method using a tenter method or a tubular method. Although these simultaneous biaxial stretching methods are excellent methods, they have the following drawbacks. (1) In the simultaneous biaxial stretching method using the tenter method, the stretching device is extremely complicated, and there are limitations in various aspects such as the width of the film that can be produced, the film production speed, and the variability of the stretching ratio. (2) In the simultaneous biaxial stretching method using the tubular method, there are limitations in various aspects such as adjustment of film thickness accuracy and film production speed. On the other hand, in the sequential biaxial stretching method, the equipment used is relatively simple and can have a robust structure, so the film width can be widened and the film manufacturing speed can be increased. It can be said that this is an industrially advantageous method because it is easy to control each step and the quality control of the product is easy. However, as mentioned above, it has been difficult to sequentially biaxially stretch poly-ε-caproamide. As one method for solving the above-mentioned difficulties, a method described, for example, in Japanese Patent Publication No. 37-2195 has been proposed. In this method, poly-ε-caproamide is blended with oligomers or monomers as plasticizers and formed into a film. in this way,
When the blending ratio of the plasticizer is large, for example, when it is 2% by weight or more, a film without uneven stretching can be obtained. However, the plasticizer blended into the film
This causes a decrease in the stiffness and dimensional stability of the film.Furthermore, during stretching, the plasticizer plates out onto the roll surface and adheres to the film surface again, causing the films to block together. This may cause Furthermore, considering that the poly-ε-caproamide film is mainly used for food packaging, it is not desirable to incorporate such a large amount of plasticizer. As another method to solve the above-mentioned difficulties,
A method of sequential stretching under relatively high temperature conditions has been proposed, as described in Japanese Patent Publication No. 3195, Japanese Patent Publication No. 49-13505, and the like. However, poly
In resins such as ε-caproamide, which have an extremely fast crystallization rate, the higher the temperature, the more rapid and strong hydrogen bonds tend to occur. In the above stretching, there are problems in that the film tends to have stretching unevenness and is prone to tearing. Even if the film does not tear, the stretching ratio in the second stage of stretching must be significantly higher than that in the first stage in order to prevent stretching unevenness in the film. For this reason, there are disadvantages in that the film is unbalanced in orientation in the vertical and horizontal directions, and that the desired orientation effect cannot be achieved due to the high temperature. Furthermore, JP-A-53-141372 describes a method for solving the above problem by stretching at a relatively low temperature. However, when using this method, since the film temperature is low, the film frequently breaks in the tenter, making it substantially difficult to produce the film. Under such circumstances, the present inventors have conducted extensive studies with the aim of providing a method for producing a biaxially stretched poly-ε-caproamide film using a sequential biaxial stretching method. This led to the completion of the invention. The gist of the present invention is to first stretch a substantially amorphous, non-oriented poly-ε-caproamide film in the machine direction and then in the transverse direction to obtain a biaxially stretched film. In producing the poly-ε-caproamide film, the substantially amorphous poly-ε-caproamide film is
2.7 to 3.5 by heating to a temperature range of ~65℃ and using a roll longitudinal stretching method at a deformation rate of 5000%/min or more.
The longitudinally stretched film is immediately adjusted to a temperature range of 45 to 60°C for a period of time expressed by the following formula (), i.e., t=e ^(5-0.07T ₁ ^). ...() [In the formula (), e is the base of the natural logarithm, t means the time (seconds) from the end of stretching in the vertical direction to the start of stretching in the horizontal direction, and T ₁ is the length of the film during this period. The temperature is selected from the range of 45 to 60°C. ] within the time period, the material is transferred to the next lateral stretching start position, and immediately before reaching the lateral stretching start position, the temperature range expressed by the following equation (), that is, T ₁ +3≦T ₂ ≦T ₁ +10...() [In formula (), T ₁ has the same meaning as in formula (), and T ₂ means the film temperature at the local heating point. ] Local heating is performed within 1 second within a temperature range _of
The temperature condition is T ₃ < T ₁ , and the film temperature is increased stepwise from the starting position of lateral stretching until the film temperature reaches 70 to 100 at the end position of lateral stretching.
The temperature conditions are within the range of ℃, and the deformation rate is
The present invention relates to a method for producing a biaxially stretched poly-ε-caproamide film, characterized in that the film is stretched 2.7 to 4.5 times in the transverse direction at a rate of 2000 to 10000%/min. The present invention will be explained in detail below. In the present invention, poly-ε-caproamide refers to a homopolymer of ε-caprolactam generally referred to as nylon 6, and does not include a copolymer. This polymer may contain various resin additives such as lubricants, antistatic agents, antiblocking agents, stabilizers, dyes, pigments, and inorganic fine particles. In the method of the present invention, a substantially amorphous poly-ε-caproamide film (hereinafter referred to as "unstretched film") is used. An unstretched film can be produced by, for example, heating and melting poly-ε-caproamide in an extruder, extruding it into a film from a T-die, and applying the air knife casting method, electrostatic application method,
Produced by quenching on a casting roll maintained at a temperature below the glass transition temperature of poly-ε-caproamide, preferably below 30°C, and above the dew condensation temperature using a known casting method such as the vacuum chamber method. be able to. When using the method of the present invention, the unstretched film is
First, the film is stretched in the longitudinal direction (hereinafter simply referred to as "longitudinal stretching") by a roll longitudinal stretching method. Stretching by a roll longitudinal stretching method refers to a method of longitudinal stretching using a roll longitudinal stretching machine. In the present invention, a conventionally known roll-type high-speed longitudinal stretching machine can be used. To longitudinally stretch an unstretched film, first the unstretched film is
Heat to ~60℃ and adjust temperature. If the temperature of the unstretched film is lower than 45°C, it is preferable because it tends to cause longitudinal stretching unevenness in the film after longitudinal stretching.If it is higher than 65°C, the film tends to stick to the roll surface, which is also preferable. Longitudinal stretching spots are likely to occur on the film,
Furthermore, directional hydrogen bonds occur in the direction of stretching, which may cause lateral stretching unevenness or tearing of the film during the next lateral stretching (hereinafter simply referred to as ``lateral stretching''). This is not desirable because it makes it easier to do so. In the longitudinal stretching process, it is necessary to adopt stretching conditions such that the deformation rate is 5000%/min or more and the stretching ratio is in the range of 2.7 to 3.5 times. Here, the deformation speed refers to a value calculated by the following equation (). V _MD = (X-1)/L x ( _UL + U _H /2 x 100...() [In formula (), each symbol has the following meaning. V _MD : Film longitudinal deformation rate (%/ _{( minutes ) _} Linear speed of roll (m/min)] If the deformation speed (V _MD ) is lower than 5000%/min, even if longitudinal stretching is performed well, the film is likely to have transverse stretching irregularities during the next transverse stretching. If the deformation rate is higher than 5000%/min, the longitudinal stretching will be performed well and no transverse stretching unevenness will occur in the film during the next transverse stretching, which is preferable.The upper limit of the deformation speed is the Various choices can be made depending on the structure and performance of the device, the temperature of the film at the start of stretching, etc., but it is best to set it to 30000%/min or less.In addition, when the film temperature at the start of stretching is low, It is preferable to keep the deformation speed low within the above range, and to increase it within the above range when the film temperature is high.When the longitudinal stretching ratio of the film is less than 2.7 times, the desired orientation is achieved in the final film. If it is larger than 3.5 times, the film tends to tear during stretching, and furthermore, it tends to cause horizontal stretching unevenness during the next horizontal stretching, which is not preferable. Various changes can be made by changing the linear speed of the high-speed roll and low-speed roll in the longitudinal stretching machine. According to the present invention, the film longitudinally stretched under the above conditions is immediately adjusted to a temperature range of 45 to 60°C. Then, the time expressed by the following formula (), t=e ^(5-0.07T ₁ ⁾ ...() [In formula (), e is the base of the natural logarithm, t is the time after the end of stretching in the vertical direction, It means the time (seconds) until the start of stretching in the transverse direction, and _T1 is the temperature of the film during this time, which is selected from the range of 45 to 60°C. Transfer the film to the starting position (the position where the tenter rail starts widening). After completing the longitudinal stretching, the film is
The reason for adjusting the temperature to 60°C is as follows. In other words, if the temperature of the film is lower than 45°C, it is undesirable because the temperature will be too low and the film will be easily torn when performing horizontal stretching. Since the time is extremely short, the distance between the longitudinal stretcher and the transverse stretcher must be extremely shortened, and the introduction section of the transverse stretcher (the part where the film is bitten) must be extremely shortened, making it difficult to design the equipment. This poses problems in terms of placement and operability, making it undesirable. If the deformation rate in the longitudinal stretching process is 5000%/min or more, heat will be generated during stretching, and the film temperature will drop slightly (10 to 20%).
℃), so it may be necessary to cool the film to adjust it to a temperature range of 45-60°C. The film that has been subjected to longitudinal stretching is transferred to the next transverse stretching step, but this transfer needs to be carried out in a short period of time. According to experiments conducted by the present inventors, the time it takes to transfer a film that has been longitudinally stretched to the next transverse stretching process is as follows:
It has been found that it is better to set the time within the time calculated by the above formula (). Specifically, when the film temperature adjusted after the end of longitudinal stretching is 45°C, t is within 6.4 seconds, and when it is 50°C, t is within 4.5 seconds.
It was found that when the temperature is 60°C, t needs to be within 2.2 seconds. If the time calculated by the above equation () is exceeded, the film is likely to have lateral stretching irregularities when stretched in the next lateral stretching step, which is not preferable. When using the method of the present invention, the longitudinally stretched film is transferred to the transverse stretching process, and immediately before the transverse stretching start position, the temperature falls within the temperature range expressed by the following equation (), that is, T ₁ +3≦T ₂ ≦T ₁ +10 ...() [In formula (), T ₁ has the same meaning as in formula (), and T ₂ means the film temperature at the local heating point. ] Perform local heating within 1 second within the temperature range. The reason why the film is locally heated immediately before the lateral stretching start position is to keep the neck occurrence position constant. That is, stretching of a poly-ε-caproamide film is achieved by neck stretching, and this tendency is more pronounced in transverse stretching than in longitudinal stretching. When the film is laterally stretched, both ends of the film are gripped with tenter clips, and the tenter clips are moved along the tenter rail and spread out in a fan shape, thereby stretching the film laterally. The problem is that the film is prone to scratches starting near the clip, and the scratches that occur near the clip quickly reach the claws of the clip, causing the film to become extremely thin in that area, causing the film to break. In order to prevent the film from breaking near the clip when the film is laterally stretched, there are methods such as thickening the ends (edges) in the width direction of the film, or locally thinning the film at specific points other than the vicinity of the film clip. . However, the former method has problems such as adversely affecting the thickness accuracy of the final film and reducing product yield, while the latter method has problems with the thickness accuracy of the final film. Both methods are undesirable as they adversely affect accuracy. According to experiments conducted by the present inventors, when local heating is performed by arranging a heater corresponding to the position where the film is desired to generate a neck immediately before the lateral stretching start position, starting from the locally heated part, It was found that the lateral stretching could be carried out smoothly without causing any netting. The heater for local heating may be of any type as long as it can heat the film to a temperature sufficient to generate a neck, but it is particularly suitable for a rod-shaped heater placed on the top or bottom of the film in parallel to the film transport direction. It is better to do so. As for the type of heater, an infrared rod-shaped heater with an elliptical reflective shade is preferred, but ceramic heaters, aluminum cast heaters, etc. may also be used. The size of the heater that locally heats the film is
Various choices can be made depending on the capacity of the heater, the distance between the film and the heater, etc., but it is best to use one that is as thin and long as possible, with a width of 10 mm or less, particularly preferably 5 mm or less. If it is difficult to manufacture a heater of this size, you can place a shielding member between the general heater and the sheet, or wrap the rod-shaped heater with a material that reflects infrared rays to reduce the width.
A slit-like opening of 10 mm or less may be provided facing the film. The number of heaters can be varied from one to several depending on the width of the film after longitudinal stretching. If there is one, it should be placed in the center of the width of the film parallel to the film transport direction, and if there are more than one, the location should be chosen so as not to be too close to the film tenter clip. FIGS. 1 and 2 show schematic diagrams of the situation in which the film is locally heated and the film is neck-stretched. FIG. 1 shows a case in which the heater is arranged approximately at the center in the width direction of the film, and FIG. 2 shows a state in which two heaters are arranged. In the figure, 1 and 21 are longitudinally stretched films, 2 and 22 are infrared slit heaters, 3 and 23 are neck generation points, and 4,
24 are parts that are not laterally stretched, 5, 2
Reference numerals 5 and 26 indicate the neck-stretched portions, 6 and 26 the locations where the non-lateral stretching begins to be uniformly stretched, A the lateral stretching start position, and B the lateral stretching end position. The temperature (T ₂ ) at which the film is heated by the heater for local heating is within the temperature range expressed by the above equation (). When T ₂ is lower than T ₁ +3 (°C), no net occurs in the heated part of the film, and when T ₂ is higher than T ₁ +10 (°C), the heated part of the film is extremely It is not preferable because it becomes thin. The time to locally heat the film using the heater for local heating shall be within 1 second. If the local heating time is too long, the locally heated portion of the film becomes extremely thin, which is not preferable. When using the method of the present invention, a longitudinally stretched film is locally heated by the above method and then laterally stretched by a tenter type lateral stretching method. In the present invention, a conventionally known tenter-type high-speed lateral stretching machine can be used. At this time, the temperature (T ₃ ) of the tenter clips of the tenter type lateral stretching machine is adjusted so as to satisfy the condition T ₃ <T ₁ . The tenter clip temperature T ₃ is
If the temperature is higher than T ₁ (the temperature (°C) from when the film finishes stretching in the longitudinal direction until it starts stretching in the lateral direction), necking will occur near the clip during lateral stretching of the film, and this area will This is because the film is likely to break. When performing transverse stretching using a tenter, the temperature of the film must be raised stepwise from the transverse stretching start position, and the temperature conditions must be such that the film temperature falls within the range of 70 to 100°C at the transverse stretching end position. There is. In the film longitudinally stretched by the above method, the hydrogen bonds oriented in the direction of stretching become stronger over time, so that the film is transported to the transverse stretching start position in a very short time and the transverse stretching is started. The film temperature at this time, that is, 45 to 60°C, is too low for transversely stretching the film, and if transversely stretching is carried out at this temperature, breakage at the clips is likely to occur, making stable transversely stretching difficult. In order to perform stable transverse stretching, as described above, in addition to locally heating the film to keep the neck stretching start position constant, the film is laterally stretched while gradually increasing its temperature. If the temperature is rapidly raised during horizontal stretching of a film, the portions of the film where net stretching has not yet started, that is, the portions of the film that have not yet been horizontally stretched, will be exposed to strong heat, and as a result, the directionality that occurred during the longitudinal stretching process will be reduced. The hydrogen bonds with the . According to experiments conducted by the present inventors, when a film is laterally stretched using a tenter, the film temperature is raised stepwise from the lateral stretching start position, and at the lateral stretching end position, the film temperature is 70 to 100. It was found that when the temperature conditions are within the range of 0.degree. C., the portions that have not yet been laterally stretched disappear in an extremely short period of time, as if they were "clearing a fog." To heat the film in stages in the transverse stretching zone, divide the top or bottom of the film into several sections perpendicular to the film transport direction, and install an infrared heater or hot air in each section. All you have to do is blow it in. The film temperature at the end of horizontal stretching is 70 to 100.
℃ is preferable, but if the deformation rate and stretching ratio of the film are high, the film temperature should be set higher within the above range, and if the deformation temperature and stretching ratio are low, the film temperature should be set within the above range. It is preferable to choose a lower one. In the lateral stretching process, the deformation speed is set at 2000~
It is necessary to adopt stretching conditions in the range of 10000%/min and the stretching ratio in the range of 2.7 to 4.5 times. Here, the deformation speed refers to a value calculated by the following equation (). V _TD = (Y-1)/L _T ×U _T ×100...() [In formula (), each symbol has the following meaning. V _TD : Film lateral deformation rate (%/min) Y: Film stretching ratio (times), determined from y ₂ /y ₁ . y ₁ means the width of the film at the lateral stretching start position (position shown in FIG. 1A), and y ₂ means the film width at the lateral stretching end position (position shown in FIG. 1B). U _T : Speed of tenter (m/min) L _T : Length of the lateral stretching section (length from position A to position B in Figure 1) (m), ] Deformation speed (V _TD ) is 2000 If it is lower than %/min,
Lateral stretching unevenness tends to occur in the film, and if the stretching rate is greater than 10,000%/min, the film tends to break, which is not preferable. When the transverse stretching ratio of the film is smaller than 2.7 times, it is not preferable because the physical properties of the final film will not be excellent. When it exceeds 4.5 times, the transversely stretched film tends to break, which is not preferable. The biaxially stretched poly-ε-caproamide film produced by the above method is preferably heat-treated by a conventional method in order to impart dimensional stability. The heat treatment is preferably carried out at a temperature of, for example, 130°C or higher and lower than the melting point for 5 minutes or less, preferably 1 minute or less. The heat treatment may be performed with the film in either a tensioned state, a relaxed state, or a combination of both. The present invention has been described in detail above, and according to the present invention, a sequential biaxial stretching method consisting of a combination of a roll-type longitudinal stretching method and a tenter-type lateral stretching method has excellent thickness accuracy and an excellent appearance. It is possible to efficiently produce a biaxially stretched poly-ε-caproamide film, and the industrial utility value of the present invention is extremely large. Next, the present invention will be explained in more detail based on examples, but the present invention will not exceed the gist thereof.
It is not limited to the following examples. Example 1 Poly-ε-caproamide (manufactured by Mitsubishi Chemical Corporation, Novamitsu 1020J) with a relative viscosity of 3.5 was heated to 65 mmφ.
The mixture was kneaded in an extruder with a cylinder temperature of 260°C, extruded into a film using a T-die, and rapidly cooled on a 600mmφ casting roll cooled to 30°C to form a film with a thickness of approximately 150 microns and a width of approximately 350 mm. A substantially amorphous (unstretched) film was obtained. The above unstretched film is guided into a longitudinal stretching machine consisting of multiple rolls of 150 mmφ and width 700 mm at a transfer speed of 8 m/min, heated and adjusted to 45°C, and then deformed between rolls with different circumferential speeds. Longitudinal stretching was carried out at a speed of 6000%/min and a stretching ratio of 3.1 times. The temperature of the longitudinally stretched film is immediately adjusted to 45°C by a group of rolls following the longitudinal stretching zone, and while maintaining this temperature, it is stretched to a width of 1.5 m and a length of 12 m in 6 seconds.
The film was transferred to the horizontal stretching start position of a tenter-type horizontal stretching machine having a size of m. Immediately before the lateral stretching start position of the tenter-type lateral stretching machine, in order to locally heat the film from the bottom surface, an infrared slit heater with a slit gap of 5 mm is installed parallel to the film transport direction at the center of the film in the width direction. It was established in With this heater,
The corresponding film part temperature was locally heated to 50°C. The tenter clip of the tenter-type horizontal stretching machine attaches to the water-cooled pipe that is cast and embedded in the tenter rail.
It is designed to be cooled by passing cooling water through it, and the horizontally extending section (zone) is divided into three equally spaced zones, each zone is equipped with an infrared heater, and each zone can be independently controlled at temperature. A possible structure was created. Both ends of the longitudinally stretched film were held with tenter clips cooled to 40°C, and transversely stretched using a transversely stretched machine at a deformation rate of 2400%/min and a stretching ratio of 3.3 times. The film temperature in the transversely stretched portion was 60°C at the exit of the first section, 70°C at the exit of the second section, and 75°C at the exit of the third section (the end position of the transverse stretching). The horizontally stretched film is held at a constant width with tenter clips for 1 hour at a temperature of 200°C.
Heat treatment was carried out three times in total: at a temperature of 200° C. for 2 seconds with the clip interval narrowed by 5% to provide relaxation, and then at a constant width of 200° C. for 2 seconds. After heat treatment, the film is cut off at both ends and wound up using a winder to a thickness of 15 mm.
A micron biaxially stretched film was obtained. Film production using the above method was carried out continuously for 5 hours, and the film was successfully produced without any breakage during the process. Table 1 shows the various conditions during film production and the conditions during film stretching. The physical properties of the obtained film were evaluated by the method described below. The results are shown in Table 2. (1) Film thickness (microns) Measure the thickness at 30 points in the width direction of the film and show the average value. (2) Film thickness unevenness (%) Means the value calculated from the following formula. Thickness unevenness=Maximum thickness in the width direction−Minimum thickness in the width direction/Average thickness in the width direction×100 It can be said that the thickness accuracy is good when the thickness unevenness is 15% or less. (3) Balance degree, in-plane orientation index, refractive index (x) in the longitudinal direction (longitudinal direction) of the film, refractive index (y) in the width direction (horizontal direction), and refractive index in the thickness direction ( It means the value calculated by the following formula after measuring each of z). Balance degree = | , using a Shimadzu autograph (DSS-2000 model), check the chuck interval.
50mm, tensile speed 50mm/min, measurement atmosphere 25℃, relative humidity 40%. (5) Boiling water shrinkage rate (%) Prepare a square sample with a side length of 100mm from the film, control the temperature of this sample in an atmosphere of 25℃ and 40% relative humidity, and mark marked lines at intervals of 80mm. did.
This sample was immersed in hot water for 5 minutes and taken out.
Leave it in an atmosphere of 25℃ and 40% relative humidity for 24 hours.
It means the value calculated by measuring the change (△l ₁ ) between the gauge lines and using the formula below. Boiling water shrinkage rate = △l ₁ /80×100 (6) Dry heat shrinkage rate (%) The sample prepared by the method described in (5) above was heated at 160°C.
The sample was left in an oven whose temperature was adjusted _to means value. Dry heat shrinkage rate = △l ₂ /80×100 (7) Pinhole resistance strength (g) A circular formwork with an inner diameter of 100mmφ is attached to the crosshead of an autograph (DSS-2000 type), and the sample film is placed in this formwork. A needle with a spherical tip with a diameter of 0.5 mm was attached to the load cell, which was fixed under tension and attached to one autograph head, through a round metal rod.
By moving at an ascending speed of mm/min, the strength (g) at which the punctured film breaks was measured. (8) Haze (%) Measured in accordance with JIS K6714. Examples 2 and 3 Using poly-ε-caproamide with a relative viscosity of 3.5 (manufactured by Mitsubishi Chemical Corporation, Novamitsu 1020CA),
An unstretched film was produced in the same manner as described in Example 1. This unstretched film was longitudinally stretched using the same longitudinal stretching machine as used in Example 1 under the conditions listed in Table 1. The longitudinally stretched film was transferred to the transverse stretching start position under the conditions described in the first element, and was laterally stretched under the conditions described in Table 1 using the same tenter type transverse stretching machine as used in Example 1. In Example 2, a laterally stretched film was
Subsequently, it was heat-treated at a temperature of 200° C. for 4 seconds while being held with tenter clips and under tension without being relaxed. In Example 3, the laterally stretched film was
At a constant width, for 1 second at a temperature of 200°C, and then for 2 seconds at a temperature of 200°C with the clip interval narrowed by 8% to provide relaxation.
Heat treatment was carried out at a temperature of 200° C. for 2 seconds at a constant width. After the heat treatment, both edges of the film were cut off and wound up using a winder. Various physical properties of the obtained film were evaluated in the same manner as described in Example 1. The results,
Shown in Table 2. Examples 4-6 Unstretched films were prepared using the same materials as used in Example 1 and in the same manner as described in that Example. For the unstretched film, a stretched film was produced using the same stretching apparatus as used in Example 1 and under the conditions listed in Table 1. In each example, the film was manufactured by the above method.
Although the process was carried out continuously for several hours, the film was not cut during the process, and the process went smoothly. Examples 7 and 8 Using the same kind of material as used in Example 1, 90mmφ
The mixture was kneaded in an extruder at a cylinder temperature of 260℃, extruded into a film using a T-die, and rapidly cooled on a 600mmφ casting roll cooled to 30℃ to form a film with a thickness of about 150 microns and a width of about 50mm. A substantially amorphous (unstretched) film was obtained. Regarding the above unstretched film, a stretched film was produced using the same stretching apparatus as used in Example 1 and under the conditions listed in Table 1. In these examples, the tenter-type stretching machine is divided into two sections, and an infrared heater is placed in each section.
The film temperature at the exit of the first section is 75℃, and the film temperature at the exit of the second section (lateral stretching end position) is 75℃.
The temperature was 95℃. After the transverse stretching, heat treatment was performed under the same conditions as described in Example 1. Film production using the above method was carried out continuously for 5 hours, and the film was successfully produced without any breakage during the process. Comparative Examples 1-9 Unstretched films were prepared using the same materials as used in Example 1 and in the same manner as described in the same example. For the unstretched film, a stretched film was produced using the same stretching apparatus as used in Example 1 and under the conditions listed in Table 1. Table 1 shows the conditions during film stretching. In the above Examples and Comparative Examples, the deformation speed, transfer time, etc. were determined by changing or combining the number of longitudinal stretching rolls, the distance between the longitudinal stretching machine and the tenter clip, the pattern of the tenter rail, etc. .

【table】

[Table] From Tables 1 and 2, the following is clear. (1) When the method of the present invention is used, the film does not break during film stretching, and the film can be manufactured continuously for a long time. (2) When the method of the present invention is used, the resulting biaxially stretched film has no stretching unevenness and has a good appearance. (3) When using the method of the present invention, there are fewer thickness irregularities;
A film with balanced physical properties in the vertical and horizontal directions can be obtained. (4) On the other hand, when the method of the present invention is not used, the film may break during stretching and cannot be stretched, or even if it can be stretched, the film will have stretching unevenness and will only have an inferior appearance. No (see Comparative Examples 1 to 9).

[Brief explanation of drawings]

FIGS. 1 and 2 show schematic diagrams of a situation in which a film is locally heated and a situation in which the film is neck-stretched. In the figure, 1 and 21 are longitudinally stretched films, 2 and 22 are infrared slit heaters, 3 and 23 are neck stretching points, respectively.
4 and 24 are parts that are not laterally stretched, respectively;
5 and 25 are the net-stretched parts, 6,
Reference numeral 26 indicates a location where the portion that has not been laterally stretched begins to be uniformly stretched, A indicates the transverse stretching start position, and B indicates the transverse stretching end position.

Claims (1)

[Claims] 1. Substantially amorphous and unoriented poly-ε-
The caproamide film is first stretched in the longitudinal direction,
The biaxially stretched polyester is then stretched in the transverse direction.
In producing ε-caproamide film,
The substantially amorphous poly-ε-caproamide film is heated to a temperature range of 45 to 65°C and stretched by 2.7 to 3.5 times at a deformation rate of 5000%/min or more using a roll longitudinal stretching method. The longitudinally stretched film is immediately adjusted to a temperature range of 45 to 60°C for a period of time expressed by the following equation (), i.e., t=e ^(5-0.07T ₁ ⁾ ... () [In the formula (), e is the base of the natural logarithm, t is the time (seconds) from the end of stretching in the vertical direction to the start of stretching in the horizontal direction, and T ₁ is the length of the film during this period. The temperature is selected from the range of 45 to 60°C. ] Within the time, the material is transferred to the next lateral stretching start position, and immediately before reaching the lateral stretching start position, the temperature range expressed by the following formula (), that is, T ₁ + 3 ≦ T ₂ ≦T ₁ +10...() [In formula (), T ₁ has the same meaning as in formula (), and T ₂ means the film temperature at the local heating point. ] Local heating is performed within 1 second in the temperature range _of
The temperature condition is T ₃ < T ₁ , and the film temperature is increased stepwise from the lateral stretching start position until the film temperature reaches 70 to 100 at the lateral stretching end position.
The temperature conditions are within the range of ℃, and the deformation rate is
A method for producing a biaxially stretched poly-ε-caproamide film, which comprises stretching 2.7 to 4.5 times in the transverse direction at a rate of 2000 to 10000%/min. 2. The method according to claim 1, wherein the local heating of the film is performed by one to several rod-shaped heaters arranged on the upper or lower surface of the film in parallel to the film transport direction. A method for producing an axially stretched poly-ε-caproamide film.