JPH0245976B2 - NIJIKUENSHINHORIIIPUSHIRONNKAPUROAMIDOFUIRUMUNOSEIZOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a biaxially oriented poly-ε-caproamide film. More specifically, the biaxially stretched poly-ε-
This invention relates to an improvement in the method for producing a caproamide film, and relates to a method for producing a film with excellent flatness. Biaxially oriented poly-ε-caproamide has excellent toughness, heat resistance, cold resistance, transparency, printability, chemical resistance, etc., and is less likely to cause pinholes, so it is used for food products. It is widely used as a base film for other packaging. For example, to make food packaging bags, printing, lamination, bag making, food filling, and heat sealing are usually performed. In this case, the quality of the flatness of the base film has a great influence on the production speed, yield, etc. in printing, laminating, bag making processes, etc. That is, if there is slack in the base film, pitch deviations occur during printing, wrinkles occur during lamination processing and bag making processes, and production speed cannot be increased. Therefore, there is an extremely strong demand for improving the flatness of the base film, especially the "edge sagging phenomenon." The "edge sagging phenomenon" is caused by the phenomenon that the edges of the film are longer than the center in the longitudinal direction of the film. This phenomenon is observed and confirmed by the difference in the way the film stretches when a constant tension is applied to the biaxially stretched film and the load is removed. For example, the "edge sagging phenomenon" will be explained with reference to FIG. In FIG. 1, 1 is a flat table, 2 and 3 are base lines drawn on the table, 4 is an adhesive tape, 5 is a cutting line, and 6 is a marked line on the film. A film (for example, 3 meters) cut in a length direction longer than the distance between base lines 2 and 3 (for example, 2 meters) is placed on a flat table 1, and one end of the film is fixed on the table with an adhesive tape 4. At the other end of the film, apply a constant load, e.g. 20 per cm width.
The film is tensed by applying a load of gram, and a marked line 6 is drawn on the film corresponding to the base line 3. Next, when a load is applied and the film is cut along the lengthwise cutting line 5 into strips each having a constant width (for example, 3 cm), the marked line 6 shifts for each strip, so the film It is observed that the edge is longer than the center in the width direction. The difference in length between the center and the edge of the film in the width direction is thought to be due to the bowing phenomenon that occurs during the heat setting process performed after the biaxial stretching process of the film. That is, while the two ends of the biaxially stretched film in the width direction are held and restrained by tenter clips, the central portion in the width direction of the film is not restrained at all, and the influence of the tenter clips is extremely weak. Therefore, when the film is exposed to high temperatures in the heat setting process after the biaxial stretching process, the center portion in the width direction is However, the temperature of the film is not yet sufficiently heated to the heat-setting temperature, and the temperature is set in the transverse stretching zone where there are parts that are more difficult to deform, that is, on the upstream side of the film, which lags behind the edges in the width direction. Even in the film cooling process that follows the above heat setting process, the center part in the width direction of the film still lags, and as a result, the length in the center part in the width direction of the film becomes short and the edges become long, and this length It is thought that the ``edge sagging phenomenon'' occurs due to the difference in . "Edge sagging phenomenon" of stretched film as shown above
Many proposals have been made regarding methods for improving film thickness and producing films with excellent flatness. For example, Japanese Patent Publication No. 44-20000 proposes a method of gradually cooling a biaxially stretched film while making the temperature uniform in the width direction when the film is heat-set and cooled. According to experiments conducted by the present inventors, this method has an improvement effect on sagging caused by localized temperature unevenness on the film or abnormal distortion that occurs when the film is cooled.
It was found that no improvement effect was observed in the sagging caused by the Boeing phenomenon. In addition, Japanese Patent Application Laid-open No. 49-99676 discloses that when cooling a heat-set film after biaxial stretching, the temperature at the center in the width direction of the film is maintained within a specific range. A method has been proposed to improve the sagging of a part.
According to experiments conducted by the present inventors, even when this method for preventing sagging in the inside was applied to improve edge sagging, the improvement effect was not significant. Furthermore, Japanese Patent Application Laid-Open No. 58-55221 discloses that in order to improve the flatness of a heat-set film after biaxial stretching, a certain tension is applied to the film in steam at a temperature range of 90 to 150°C. A method of processing has been proposed. However, this method requires an apparatus for steam-treating the film and a step of drying the film after the steam treatment, resulting in high costs. Furthermore, Japanese Patent Application Laid-Open No. 126476/1984 discloses that a high tension is applied to the film while the film is stretched in the longitudinal direction and the transverse direction, or after a heat setting step following the stretching in the transverse direction. Methods have been proposed to improve the flatness of films. However, if you follow this method and simply apply a high tension to the film,
The effect of improving flatness is not sufficient, and the improvement effect can only be achieved by combining it with a heat relaxation process after applying tension, and a device for heat relaxation is required, so it is not economical. do not have. Under such circumstances, the present inventors conducted extensive studies with the aim of providing an industrially advantageous method for producing a biaxially oriented poly-ε-caproamide film with excellent flatness. As a result, the present invention has been completed. However, the gist of the present invention is to
When producing a biaxially stretched poly-ε-caproamide film by first stretching the ε-caproamide film in the longitudinal direction, then holding it with tenter clips and stretching it laterally, the temperature of the film after completing the lateral stretching is as follows: 150 ~ from the heat setting temperature while keeping the temperature uniform in the film width direction.
The first step is to slowly cool the film to a temperature of 165°C.Then, the film temperature is set to a profile that gradually decreases from the edge to the center in the film width direction, and the temperature difference between the edge and the center is set to 10 to 30°C. While keeping the film width within the range of 45~
The second step is to slowly cool the film to a temperature of 50℃, and then the film temperature is increased over the entire width of the film.
After rapidly cooling the film to below 45°C, the film is cut at both edges immediately before it is released from the tenter clips, and the product film is taken off while applying a taking tension of 45 to 145 kg/ ^cm2 . A method for producing a biaxially oriented poly-ε-caproamide film with improved flatness, the method comprising: 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 other compounds containing ε-caprolactam as a main component and copolymerizable with it. A copolymer with This polymer may contain various resin additives such as lubricants, antistatic agents, antiblocking agents, stabilizers, dyes, pigments, and inorganic fine particles. When using the method of the present invention, a poly-ε-caproamide film is first stretched in the longitudinal direction, and then held at both ends of the film with tenter clips and stretched in the transverse direction. The film is biaxially stretched. In order to stretch the film in the longitudinal direction, it is preferable to use a roll longitudinal stretching method using a roll longitudinal stretching machine. Tenter clips are preferably used to stretch the film in the transverse direction. (Poly-ε-
For details of the method of sequentially biaxially stretching a caproamide film, see Japanese Patent Application No. 1983-45368. ) A poly-ε-caproamide film that has been stretched in the transverse direction using tenter clips is usually heated to 190°C or higher while holding both ends with tenter clips in order to impart dimensional stability to the poly-ε-caproamide film. It is heat-set at a temperature below the melting point of. This heat setting process often gives the film a relaxation of 3% or more in the width direction. It is an object of the present invention to provide a film manufacturing method that allows the final film to have excellent flatness even after such a heat-setting step. When using the method of the present invention, in the first step, the temperature of the film after the transverse stretching step is kept uniform in the width direction of the film, and is kept at 150 to 165°C from the heat setting temperature.
Cool slowly to a temperature range of . Here, "uniformly" means that the temperature difference in the width direction of the film is at least 5°C.
means to be kept within the range. If this condition is not met, not only edge sagging may occur in the final film, but also local sagging may occur in the width direction of the film, which is undesirable. Further, if the film temperature is not gradually cooled to a range of 150 to 165° C. and the film is moved to the next second stage, the desired effect of improving edge sag will not be observed. When using the method of the present invention, next, in the second step,
The film temperature has a profile that gradually decreases from the edge to the center in the width direction of the film, and
While maintaining the temperature difference between the edges and the center within the range of 10 to 30°C, the center in the width direction of the film is slowly cooled to a temperature of 45 to 50°C. The temperature profile at this stage is
It is determined by the shape and degree of the edge sag that is finally obtained, and is often selected from curved profiles that approximate a parabola, inverted trapezoid, etc. In order to create a profile in which the film temperature gradually decreases from the edge to the center in the film width direction, (a) multiple long infrared heaters are arranged in a row parallel to the film transport direction, and generally perpendicular to the film transport direction; (b) A cold air blowing nozzle installed along the film width direction and at an angle close to parallel to the film surface selectively cools the center part of the film width direction. (c) A method using a plurality of hot air nozzles blowing out controlled hot air, which are arranged in a row in the direction of film transport and generally perpendicular to the film transport direction; (d) It is possible to select and adopt methods such as combining methods (a) to (c). Among these, the method of using (a) and (b) in combination is preferred. In the process of cooling the film temperature, the film temperature profile can be appropriately selected as necessary so that the temperature difference between the edge and the center in the width direction of the film is within the range of 10 to 30°C. However, if the temperature difference is outside this range, e.g. less than 10°C,
The effect of improving the edge sag of the final film is small, and if the temperature is higher than 30°C, the so-called "curling" phenomenon in which the edges in the width direction of the film curl toward the center occurs, which is not preferable. In this second stage, the center portion in the width direction of the film is further cooled to a temperature of 45 to 50° C. while maintaining the film temperature at the profile as described above. Unless the temperature at the center in the width direction of the film is cooled to a range of 45 to 50°C, the flatness of the final product film will not be improved even if the film is subjected to an appropriate tension as described below. Undesirable. The cooling rate of each of the first stage and second stage is not particularly limited, but is in the range of 20°C/sec to 55°C/sec, particularly preferably 20°C/sec to 35°C/sec.
It is best to choose within the range of °C/sec. According to the present invention, in the third step, the film temperature is rapidly cooled to 45°C or less over the entire width of the film, and then just before the film is released from the tenter clips, both edges of the film are cut, and the product film is It is taken up while applying a taking-off tension of 145Kg/ ^cm2 . If the above-mentioned pulling tension is applied to the product film without cooling it to below 45℃ at this stage, the effect of improving the edge sag will be small and the accuracy of the thickness of the final product film will be easily impaired. Undesirable. After rapidly cooling the film temperature to below 45℃,
Before releasing the film from the tenter clips, cut both edges of the film and attach it to the finished film.
Apply a pulling tension of 45 to 145 Kg/ ^cm2 . It is not preferable to cut both edges of the film while holding both edges of the film with tenter clips, otherwise wrinkles will occur in the finished film. If the above tension is applied to a film that does not have both edges cut, the tension will not be effectively transmitted to the entire product film because the thickness of both edges is much larger than the thickness of the product film. Also, wrinkles are likely to occur on the recycled linitsprol, which is undesirable. When the film take-up tension is less than 45Kg/cm ² , the effect of improving the edge sag of the final product film is small; when it is more than 145Kg/cm ² , the final film has uneven thickness and The thermal shrinkage rate in the length direction increases, which tends to impair dimensional stability, which is not preferable. The take-up tension applied to the film can be adjusted by adjusting the number of rotations of the nip roll, movement of the dancer roll, etc. The present invention is as described in detail above,
According to the present invention, a film that has been biaxially stretched and then heat-set can be processed using a conventional film post-processing device without the need for a special thermal relaxation device, steam treatment, drying device, etc. It is possible to improve the film to have excellent flatness, 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. Examples 1-2 Poly-ε-caproamide with a relative viscosity of 3.5,
Knead with a 65mmφ extruder at a cylinder temperature of 260℃, extrude into a film with a T-die, and heat at 30℃.
The film was rapidly cooled on a 600 mm diameter casting roll to obtain an unstretched film with a thickness of about 150 microns and a width of about 350 mm. This film was stretched 3.0 times in the longitudinal direction using a longitudinal stretching machine composed of a plurality of rolls each having a diameter of 150 mm and a width of 700 mm. Subsequently, the film was stretched 3.2 times in the transverse direction using a tenter type transverse stretching machine. After the transverse stretching, the film is held in the heat-setting furnace 21 shown in Fig. 2 with tenter clips at both ends of the film, held under tension at a temperature of 196°C for 2 seconds, and then held at the tenter clip interval. The film was narrowed by 5% to give the film some relaxation in the width direction, and heat-setting treatment was performed at a temperature of 196° C. for 2 seconds. After the heat-setting process, the film was introduced into the apparatus shown schematically in FIG. 2 and subjected to post-processing operations. In FIG. 2, 20 is the film immediately after heat setting, 21 is a heat setting furnace, 22, 23, and 24 are infrared panel heaters, 25 is a cold air nozzle for cooling the center of the film, 26 is a cold air nozzle for cooling the entire width of the film, 27 is a tenter rail, 28 is a selvage cutting blade, 29 is a film selvage portion, 30 is a product film, 31 is a dancer roll for detecting take-up tension, 32
indicates the nip roll, and the arrow indicates the film transport direction. The film was transferred at a speed of 24 meters per minute through the apparatus shown in Figure 2 under the temperature profile conditions shown in Table 1 and Figure 3 (the horizontal axis is the film width direction, and the vertical axis is the film temperature). (Means the setting value.)
After the film is cooled, just before the film is released from the tenter clip, the edge is cut with an edge cutting blade 28 to separate the product film 30 from the film edge.
The product film was wound into a product with a thickness of about 15 microns and a width of 800 mm by a take-up winder (not shown) while applying the take-up tension shown in Table 1. The properties of the obtained product film were evaluated using the methods described below. The results are shown in Table 1. (1) Flatness of the film As shown in Figure 1, draw straight lines 2 and 3 parallel to each other 2 meters apart on a flat table 1.
Attach one end of the 3 meter length (product film cut lengthwise) to table 1 with adhesive tape 4.
Fix it on top. A load of 20 grams per cm in the width direction is applied to the other end of the film to tension the film, and a marked line 6 is drawn on the film corresponding to the base line 3. Next, the load is removed and the film is cut into strips at 3 cm intervals along the length of the film. Then, a load of 60 grams was applied to the free end of each strip,
The deviation between the base line 3 on the table and the marked line 6 on the strip is sequentially measured. The difference between the maximum value and the minimum value among the measured values is used as an index of flatness. If this index is 2 mm or less, there is no practical problem with the product film, but it is more preferably 1.5 mm or less. (2) Film thickness unevenness (%) This refers to the value calculated using the following formula after measuring the thickness of a product film at 3 cm intervals in the width direction. Thickness unevenness=maximum thickness-minimum thickness/average thickness×100 This thickness unevenness is preferably 10% or less. (3) Hot water shrinkage rate (%) A square sample with a side length of 100 mm is prepared from the product film, and this sample is heated at 25℃ and relative humidity 40%.
The temperature was controlled in an atmosphere of , and gauge lines were marked at intervals of 80 mm. This sample was immersed in hot water for 5 minutes and taken out, and then left in an atmosphere of 25° C. and 40% relative humidity for 24 hours, and the change (Δl ₁ ) between the marked lines was measured and calculated using the following formula. Hot water shrinkage rate = Δl ₁ /80×100 Examples 3 to 4 Using the same type of poly-ε-caproamide as used in Example 1, an unstretched film was prepared in the same manner as in Example 1, and then, Using the same equipment used in the same example, the film was first stretched 2.9 times in the machine direction, and then stretched 3.2 times in the cross direction. After the transverse stretching, the film is held in a heat setting furnace 21 with tenter clips held at both ends of the film, held under tension at a temperature of 193°C for 2 seconds, and the interval between the tenter clips is further narrowed by 3%. 2 at a temperature of 193℃ with relaxation in the width direction.
Heat setting treatment was performed for seconds. While transporting the film at a speed of 24 meters per minute through the apparatus shown in Figure 2, After cooling under the same temperature profile conditions, the film was wound up with a winder while applying the take-up tension shown in Table 1 to obtain a product film with a thickness of about 15 microns and a width of 800 mm. Various properties of the obtained product film were evaluated according to the method described in Example 1. The results are shown in Table 1.

【table】

[Table] Comparative Examples 1 to 9 Using the same type of poly-ε-caproamide as used in Example 1, unstretched films were prepared in the same manner as in the same example, and then in the same equipment as used in the same example. , first stretched 3.0 times in the longitudinal direction,
Subsequently, it was stretched 3.2 times in the transverse direction. After the transverse stretching, the film is held in a heat setting furnace 21 with tenter clips held at both ends of the film, held under tension at a temperature of 196°C for 2 seconds, and further narrowed by 5% between the tenter clips in the film width direction. Heat setting treatment was performed at a temperature of 196° C. for 2 seconds in a relaxed state. While transporting the film at a speed of 24 meters per minute through the apparatus shown in Figure 2, the film was wound up with a winder while applying the temperature profile and take-up tension listed in Table 2 to a thickness of approximately 15 microns. A product film with a width of 800 mm was obtained. Various properties of the obtained product film were evaluated according to the method described in Example 1. The results are shown in Table 2.

[Table] Note: *1 to *4 have the same meaning as the annotations in Table 1.
From Tables 1 and 2, the following is clear. (1) When the method of the present invention was used, a film was obtained that had little edge sagging, had excellent flatness, had little thickness unevenness, and had a low hot water shrinkage rate. (2) On the other hand, in the case of a comparative example that did not meet the requirements of the present invention, the film had large edge sag and poor flatness, resulting in a film that was problematic in practice.

[Brief explanation of drawings]

FIG. 1 is a perspective view for explaining the edge sagging phenomenon, FIG. 2 is a schematic plan view of the main parts of the apparatus used in the method of the present invention, and FIG. 3 is a temperature profile of the films of Examples 1 and 2. , FIG. 4 shows the temperature profile of the films of Examples 3-4. In the figure, 1 is a table, 2 and 3 are base lines, 4 is an adhesive tape, 5 is a cutting line, 6 is a marked line,
20 is a film immediately after heat setting, 21 is a heat setting furnace,
22, 23, and 24 are infrared panel heaters, 25 is a cold air nozzle for cooling the center of the film, and 2
6 is a cold air nozzle for cooling the entire width of the film, 27 is a tenter rail, 28 is an edge cutting blade, 29 is a film edge, 30 is a product film, 31 is a dancer roll for detecting take-up tension, 32 is a nip roll, and the arrow is a film transfer Show direction.

Claims (1)

[Claims] 1. In producing a biaxially stretched poly-ε-caproamide film by first stretching the poly-ε-caproamide film in the longitudinal direction, then holding it with tenter clips and stretching it laterally. , the first step is to gradually cool the film from the heat setting temperature to a range of 150 to 165°C while keeping the film temperature uniform in the film width direction after the completion of the transverse stretching process; The first step is to gradually cool the central part in the width direction of the film to a temperature of 45 to 50°C while keeping the temperature difference between the edge and the central part in the range of 10 to 30°C. In two steps, the film temperature is rapidly cooled to below 45℃ over the entire width of the film, and then just before the film is released from the tenter clips, both edges of the film are cut, and a take-up tension of 45 to 145 kg/cm ² is applied to the finished film. A method for producing a biaxially oriented poly-ε-caproamide film with improved flatness, the method comprising the steps of: a third step of taking off while applying a load;