JPH0448088B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a biaxially stretched polyamide film, and can be particularly used for stabilizing stretch molding. [Background Art and Problems] Conventionally, methods for producing polyamide biaxially stretched films include a multistage biaxial stretching method using a tenter;
A simultaneous biaxial stretching method using a tenter and a tube stretching method in which the inside of a tube-shaped film is pressurized and biaxially stretched at the same time are known. In this method, directional hydrogen bonding occurs in a direction perpendicular to the direction of initial stretching, and subsequent stretching in the perpendicular direction tends to result in neck stretching, making it extremely difficult to obtain a uniform stretched film. In addition, in the method (2), since the side edges of the raw film are gripped with grips, this part does not contribute to stretching, resulting in a large loss and a significant decrease in yield. The disadvantage is that the manufacturing cost is significantly higher. In addition, in the method, vertical and horizontal stretching occurs simultaneously,
It is easy to set and change the stretching ratio, it is possible to obtain a well-balanced film, and it has great features such as low equipment costs. On the other hand, in this method, it is most important to uniformly heat the tubular film in the heated stretching section to stabilize the stretching start point, but it is very difficult to ensure this. Therefore, in order to solve the problems in the above method, heated gas is sprayed at the starting point of stretching from a direction perpendicular to the feeding direction of the tubular film, and a gas at a lower temperature than the heated gas is blown in the feeding direction of the tubular film. A method in which the tube-shaped film is heated to 45 to 70°C by blowing from the upstream side of the
After heating to ~90℃, maintain the atmospheric temperature between the stretching start point and end point at 180~250℃ to reduce the difference in longitudinal and lateral stretching magnification.
Method of stretching while maintaining 0.2 to 0.6
15914) is proposed. However, the former method requires two air rings for blowing out gas, and
Equipment for heating the blown gas to 150℃ or higher,
Furthermore, it is not sufficient in terms of heating efficiency due to catalytic conduction heating of the heated gas and energy loss due to dripping of the heated gas. In addition, in the latter method, it is necessary to heat the raw film in advance, and the atmospheric temperature after the stretching start point is set to 180 to 250°C.
It is necessary to raise the temperature to a high temperature, and no efforts have been made to uniformly heat the film at the starting point of stretching or to stabilize the tubular film before and after stretching, and these problems have not yet been solved. [Object of the Invention] Here, the object of the present invention is to eliminate the drawbacks of these conventional techniques and to stabilize the stretching start point at a constant position, thereby achieving high stability during stretch forming and improving the stability of the resulting film. It is an object of the present invention to provide a method for producing a polyamide biaxially stretched film of good quality. [Means and effects for solving the problem] Therefore, in the present invention, after cooling the molten polyamide resin extruded into a tube shape from a die,
In a method for producing a biaxially stretched polyamide film, the tubular polyamide film is fed in one direction while being heated, and simultaneously stretched in the feeding direction and the width direction by tension and internal pressure in the feeding direction. Atmosphere temperature 80
~200°C, and blow air directly from the upstream side of the heated stretching zone to the vicinity of the stretching start point of the heated stretching zone at an angle of 20 to 60° to the film feeding direction. The stretching ratio is within 2 to 4.5, and the stretching ratio difference obtained by subtracting the stretching ratio in the feeding direction from the stretching ratio in the width direction is 0 to 4.5.
It is characterized by being stretched under conditions of 0.8. Therefore, the method of the present invention will be explained in more detail.
First, the polyamide resins used in the present invention include nylon 6, nylon 8, nylon 11, nylon 12, nylon 6-12, nylon 66, nylon
610 etc. Note that the polyamide resin used in the present invention may be blended with other thermoplastic resins without departing from the gist of the present invention, or may be blended with heat stabilizers,
Additives such as plasticizers, antistatic agents, and colorants may also be added. Furthermore, it may be a multilayer film with other crystalline thermoplastic resins or non-crystalline thermoplastic resins. These resins are first extruded into a tube shape from a die and cooled to form a tube-shaped film, and then this tube-shaped polyamide resin film is held, for example, by a pair of upper and lower nip rolls, and fed in one direction while being heated between them. Due to the tension and internal pressure in the feeding direction, it is simultaneously stretched in the feeding direction and the width direction. The stretching conditions at this time include an ambient temperature of 80 to 200°C in the heated stretching zone of the tubular film;
It is necessary to maintain the temperature preferably at 100-170°C. Here, if the ambient temperature is less than 80°C, the tubular film will not be heated sufficiently, making it impossible to increase the forming speed, and in some cases, the stretching start point will occur below the stretching heating section, causing bubbles to form. This is not desirable because it causes instability. On the other hand, if the ambient temperature exceeds 200° C., it is difficult to maintain the stretching start point at a constant position, resulting in a gourd-like shape, making it impossible to obtain a fixed stretching bubble diameter, which is not preferable. In addition, the stretching ratio during stretching is 2 to 4.5.
It is within. Specifically, the width direction is 2.2 to 4.5, preferably 2.4 to 3.4, and the feeding direction is 2 to 4, preferably
The conditions are that the stretching ratio is 2.2 to 3.2, and the stretching ratio difference (stretching ratio in the width direction - stretching ratio in the feeding direction) is 0 to 0.8. In this case, the stretching ratio difference is 0.1
-0.8 is preferable, and 0.1-0.5 is more preferable. Here, if the stretching ratio is less than 2, the strength of the film will be low, while if it exceeds 4.5, stretching will become difficult and may cause tube rupture. Furthermore, if the difference in stretching ratio is outside the above range, the stretching start point will not be constant and a gourd-like stretching bubble will result, which will not only result in unstable quality but also make production itself difficult. On the other hand, near the stretching start point of the heated stretching zone, from the upstream side thereof, the angle is set at a predetermined angle with respect to the film feeding direction, preferably 20 to 60 degrees, more preferably 30 to
Directly blow air at an angle of 50°. If the air blowing angle is within the above range, the air blown to the stretching start point of the tubular film will flow along the outer surface of the tubular film, creating a flowing air film on the film surface, and as a result, stretching will begin. Temperature distribution at points can be made uniform. Therefore, the stretching start point can be stabilized at a constant position, and the film can be prevented from shaking after stretching. In this case, the blown air is usually at room temperature, but heated air may also be used. [Example] The figure shows an example of a manufacturing apparatus used in the manufacturing method of the present invention. In the figure, compressed air is supplied to the inside of a molten polyamide resin extruded downward from an annular die 2 into a tube shape by an extruder 1. Polyamide resin supplied with compressed air is
After being cooled through an air ring 3 and a cooling tank 4, it is taken up by a nip roll 5 and sent to the next process. The air ring 3 is connected to the die 2
The outer surface of the molten polyamide resin extruded into a tube shape from the die 2 is cooled by air. The cooling tank 4 is disposed below the air ring 3, and has a hole in the center through which the molten polyamide resin extruded from the die 2 passes, and is filled with water. This results in
The molten polyamide resin extruded from die 2 is
First, it is air-cooled in the air ring 3, and then further cooled and solidified by the water-cooling effect of the cooling tank 4. The tubular polyamide resin film sent out from the Nippuro roll 5 passes through two guide rolls 6 and 7, and then passes through an upper Nippuro roll 8 and a lower Nippuro roll 9, and is then wound onto a winder (not shown), for example. . At this time, the circumferential speed of the lower nip roll 9 is higher than the circumferential speed of the upper nip roll 8, and compressed air is injected into the tube-shaped film between the upper nip roll 8 and the lower nip roll 9, so the tube-shaped film is When heated to a temperature at which stretching is possible, the tubular film is simultaneously stretched in the feeding direction and the width direction by the effects of both, namely, the expansion force of the compressed air and the tension in the feeding direction. In this case, the stretching ratio during stretching may be appropriately determined depending on the type of polyamide resin, for example, 2 to 4 in the feeding direction, preferably 2.2 to 3.2, and 2.2 to 3.2 in the width direction.
4.5, preferably 2.4 to 3.4, and the stretching ratio difference (stretching ratio in the width direction - stretching ratio in the feed direction) is 0 to 0.8. The difference in stretching ratio is
It is preferably from 0.1 to 0.7, more preferably from 0.1 to 0.5. A stretching heating section 10 is provided between the upper nip roll 8 and the lower nip roll 9 to heat the tubular film to a temperature at which it can be stretched.
The stretching heating section 10 includes a heating source such as an infrared heater arranged in an annular shape along the inner peripheral surface of a cylindrical body whose upper and lower ends are open. The atmospheric temperature of the heated stretching zone due to this is 80 to 200℃, preferably 100 to 170℃.
It is kept at ℃. As a result, the tubular film is heated to at least the temperature at which it can be stretched, mainly by radiant heat from the heating source. The temperature of the film at the end of stretching is 130°C or less, preferably 110°C.
temperature is below ℃. On the upstream side of the stretching/heating section 10, that is, on the nip roll 8 side, there is an air ring device 11 that directly blows air at a predetermined angle with respect to the film feeding direction near the stretching start point of the heating stretching zone of the tubular film. It is provided. Air ring device 11
In this case, an air outlet such as a slit or a plurality of pores is provided along the inner peripheral surface of the annular ring body. Therefore, air is blown uniformly in the circumferential direction of the tubular film. In addition, the blowing angle α from these air blowing ports is the angular range in which the air blown from there can smoothly flow from the film stretching start point along the outer surface of the film in the feeding direction, that is, in the film feeding direction. The angle is set within the range of 20 to 60 degrees, more preferably 30 to 50 degrees. Further, although room temperature air is usually used as the blown air, heated air may also be used. Further, a preheating section 12 is provided upstream of the air ring device 11, that is, on the nip roll 8 side, if necessary. The preheating section 12 has the same configuration as the stretching heating section 10, and includes an infrared heater and the like arranged along the inner peripheral surface of the cylindrical body. On the other hand, on the downstream side of the stretching/heating section 10, that is, on the lower nip roll 9 side, guide rollers 13 are provided for sequentially flattening the tube-shaped film after stretching and introducing it into the lower nip roll 9. The guide rollers 13 are arranged in a V-shape such that the width of the plurality of guide rollers becomes gradually narrower as they go downward. As a result, the tube-like film after stretching is moved to the guide roller 13.
After being guided to the lower nip roll 9 while being successively folded into a flat shape, the sheet is heat-fixed if necessary, and then wound onto a winder (not shown), for example. Next, the operation of this embodiment will be explained. First, molten polyamide resin extruded into a tube shape from a die 2 by an extruder 1 is expanded into a tube shape by compressed air injected inside, and is sequentially cooled by an air ring 3 and a cooling tank 4. After being solidified into a tube shape, it passes from the nip roll 5 through guide rolls 6 and 7 to the upper nip roll 8.
sent to. The tube-shaped film sent to the upper nip roll 8 is heated in a stretching heating section 10 to a temperature at which it can be stretched. Then, the compressed air injected into the polyamide resin film between the upper nip roll 8 and the lower nip roll 9 and the nip roll 8,
The tube-shaped film is simultaneously stretched in the feeding direction and the width direction due to the difference in circumferential speed between the tubes. Incidentally, the stretching ratio is within the above range. At this time, since air is blown from the air ring device 11 near the stretching start point of the stretching zone of the tube-shaped film, the air ring device 11
The air blown from the tubular film is blown to the stretching start point of the tubular film and then flows along the outer surface of the tubular film in the film feeding direction, so that the film surface is surrounded by a fluidized air film. As a result, the temperature distribution at the stretching start point becomes uniform in the circumferential direction of the tubular film, so that the stretching start point is stabilized at a constant position and the film is prevented from shaking after being stretched. After that, the tube-shaped film after stretching is
After being folded flat by the guide roller 13,
It is taken up by the lower nip roll 9. The tubular film taken up by the lower nip roll 9 is heat-set if necessary and then wound up. Therefore, according to this example, air is blown near the stretching start point of the heated stretching zone of a tubular polyamide resin film at an angle of 20 to 60 degrees with respect to the film feeding direction, and the stretching in the feeding direction is performed. Increase the magnification to 2
~ 4, the stretching ratio in the width direction was within 2.2 to 4.5, and the stretching ratio in the width direction was either equal to the stretching ratio in the feeding direction or was stretched by a difference in ratio of 0.8. , the stability of stretch molding can be improved. In other words, the air blown to the starting point of stretching of the tubular film flows along the outer surface of the tubular film in the film feeding direction, creating a fluidized air film on the film surface, which results in the temperature distribution at the starting point of stretching. can be made uniform. Therefore, if the stretching ratio is within the above range, the stretching start point can be stabilized at a constant position, and the film can be prevented from shaking after stretching. Incidentally, if the blowing angle α from the air blowing port is outside the above range, the air blown to the stretching start point will not flow smoothly along the outer surface of the tubular film, and the flowing air will not flow uniformly over the film surface. It is difficult to make a membrane. As a result, it is possible to obtain a biaxially stretched film that has excellent physical properties such as good orientation balance and high thickness unevenness accuracy. In addition, as a manufacturing device, it is sufficient to install one air ring device 11 that blows air at a predetermined angle with respect to the film feeding direction near the stretching start point, so two air ring devices can be installed as in the conventional method. Compared to what is required, equipment costs and manufacturing costs are lower, and operation control can be performed extremely easily. Another major feature is that the air blown out from the air ring does not require particularly heated air. Therefore, the above-mentioned points will be clarified based on Examples 1 to 3 in which biaxially stretched films were manufactured under the following conditions. This is made by extruding polyamide (nylon 6) resin with an average molecular weight of 24,000 through an annular die 2 with a diameter of 50 mm, and cooling and solidifying it in a 40°C water bath in a cooling tank 4, resulting in a substantially amorphous material with a thickness of 100 μm and a diameter of 60 mm.
Molding speed of mmφ tube-like film 6m/min
The film was formed using The obtained unstretched tubular film was stretched using the drawing device shown in the figure, and the peripheral speed of the nip roll 8 for delivery was changed to 6 m/min, and the peripheral speed of the nip roll 9 for take-up was varied, and pressurized air was introduced into the tube. was encapsulated and biaxially stretched at a blow ratio of 3.2 to obtain a film that was stable for a long time and had excellent transparency. Note that the heating conditions are as follows. *Stretch heating section (infrared heater)...Diameter 350mm, height 250mm, temperature 340℃, ambient temperature 130℃ *Air ring...Inner diameter 270mmφ, slit gap 2mm, blowing angle 45°, 20℃ Air volume 10 ³ m/min, blowing Direction: Starting point of stretching *Film temperature after stretching...90℃ The film thus obtained was heated to 180℃ for 10
The physical properties of the film heat-set for 2 seconds are shown in the table below along with its stretchability.

[Table] In the table, the conditions of Comparative Examples 1 and 2 are the same as those of Example 1 except that the stretching ratio was changed. Further, the conditions of Comparative Example 3 were the same as those of Example 1 except that no air ring was used. [Effects of the Invention] As described above, according to the present invention, since the stretching start point can be stabilized at a constant position, a polyamide film with high stability during stretch molding and good quality of the resulting film can be produced. A method for producing an axially stretched film can be provided.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing an apparatus for producing a polyamide biaxially stretched film that implements the method of the present invention. 8... Upper nip roll, 9... Lower nip roll, 10... Stretching heating section, 11... Air ring device.

Claims (1)

[Claims] 1. After cooling the molten polyamide resin extruded into a tube shape from a die, the tube-shaped polyamide film is fed in one direction while being heated to a temperature at which it can be stretched in a heating stretching zone, and the tension and internal pressure in the feeding direction are Therefore, in the method for producing a polyamide biaxially stretched film that is simultaneously stretched in the feeding direction and the width direction, the atmospheric temperature of the heated stretching zone is set to 80 to 200°C, and the stretching of the heated stretching zone is performed from the upstream side of the heated stretching zone. Air is directly blown near the starting point at an angle of 20 to 60 degrees to the film feeding direction, and the stretching ratio in the feeding direction and width direction is within 2 to 4.5, and the stretching ratio in the width direction is 1. A method for producing a biaxially stretched polyamide film, characterized in that the film is stretched under conditions where the difference in stretching ratio obtained by subtracting the stretching ratio is 0 to 0.8.