JPS61177229A - Manufacture of biaxially oriented polyamide film - Google Patents

Abstract

PURPOSE:To prevent bowing phenomenon from occurring and realize physical properties uniform in the width direction and at the same time favorable evenness of film by a method wherein substantially amorphous and un-oriented polyamide film is stretched longitudinally and laterally respectively under specified conditions such as specified temperatures, specified rates of deformation and specified draw ratios and, after that, kept at a specified temperature. CONSTITUTION:Firstly, substantially amorphous and un-oriented polyamide film is longitudinally stretched by a roll type longitudinally stretching method at a temperature ranging 45-65 deg.C and a rate of deformation of 10,000%/min or more by a draw ratio of 270-350%. Secondly, the film is laterally stretched with its ends held by the clips of a tenter at a temperature of 100 deg.C or less and a mean rate of deformation of 2,000-10,000%/min by a draw ratio of 300-500%. Thirdly, the film is heated with the passage of time up to 190 deg.C while satisfying the condition represented by the formula. Finally, the film is kept for 3sec or longer at a temperature ranging 190-210 deg.C in order to be thermoset. The resultant biaxially oriented polyamide film has the amount of bowing strain of 5% or less and uniform physical properties in the width direction of the film and further has enough high mean refractive index and is thermally set under fully crystallized state.

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to a method for producing a biaxially stretched polyamide film. More specifically, the present invention relates to an improvement in the method of producing biaxially stretched polyamide films by first stretching the film in the longitudinal direction using a roll-type longitudinal stretching method, then holding it with tenter clips and stretching it in the transverse direction. The present invention relates to a method for producing a film that has uniform physical properties in the width direction and is sufficiently heat-set. "Conventional technology" Biaxially stretched polyamide film has excellent toughness and
It is widely used as a base film for food and other packaging because it has excellent heat resistance, cold resistance, transparency, printability, chemical resistance, etc., and is resistant to cracks and pinholes. For example, to make food packaging bags, printing, lamination, bag making, food filling, and heat sealing are usually performed. In this case, the presence or absence of bowing distortion in the base film has a great effect on production speed, yield, etc. in printing, laminating, bag making processes, etc. In other words, if there is bowing distortion in the base film, problems such as misalignment of printing pitch, wrinkles, and meandering occur during printing, laminating, and bag making processes, making it impossible to obtain good products and making it difficult to increase production speed. I can't. Therefore, there is an extremely strong demand for improving the bowing distortion of the base film. [Boeing distortion -1 is caused by the Boeing phenomenon. The bowing phenomenon is a phenomenon in which a straight line is marked on an unstretched film perpendicular to the transport direction, as explained in, for example, JP-A-58-55221 and JP-A-58-147322. Then, after biaxial stretching is completed and heat setting is performed, the straight line is delayed and distorted into an arched shape at the center of the film. Also, if you draw many small circles instead of straight lines, after heat setting the film will remain a circle with an enlarged diameter at the center, but at the edges in the width direction of the film it will become an slanted ellipse. This is a phenomenon. As a method for preventing the bowing phenomenon that occurs during the production of biaxially stretched films, for example, Japanese Patent Publication No. 43-99
The techniques described in Japanese Patent Publication No. 19 and Japanese Patent Publication No. 55-2784.7 have been proposed. The techniques proposed in these publications are techniques applied to a simultaneous biaxial stretching method, and are not effective when applied to a sequential biaxial stretching method such as the method of the present invention. In addition, JP-A-51-80372, JP-A-5
A technique described in Japanese Patent No. 7-57629 and the like has also been proposed. The present inventors conducted tests applying these techniques to the method of the present invention, but were unable to improve the bowing phenomenon. The present inventors have completed a method for producing a biaxially stretched polyamide film (see, for example, Japanese Patent Application Laid-Open No. 59-171626, Japanese Patent Application No. 59-30101, etc.), but when producing a film according to this method, the film It was found that the bowing phenomenon occurs during the process of heat-setting the film. [Problems to be Solved by the Invention-1 31 The present invention prevents the bowing phenomenon that occurs when heat-setting a biaxially stretched polyamide film according to the sequential biaxial stretching method, and achieves uniform physical properties in the width direction. The purpose of the present invention is to provide a method for producing a film having excellent flatness.
``Means for Solving the Problems'' However, the gist of the present invention is to prepare a substantially amorphous, unoriented polyamide film at a temperature of 45 to 6
Within the range of 5°C, the film was stretched 2.7 to 3.5 times in the longitudinal direction using a roll longitudinal stretching method at a deformation rate of 1-o, ooo%/min or more, and then the edges of the film were stretched. Hold the film with tenter clips and keep the film temperature below 100°C.
After stretching in the transverse direction 3A-5 times at an average deformation rate of 2.000 to 1 (1,000%/min), the film temperature was changed over time according to the general formula % formula %, where θ = film temperature ( "C) t - Elapsed time after completion of stretching in the transverse direction (seconds)" Raise the temperature to 190 ° C.
The present invention relates to a method for producing a biaxially stretched polyamide film, characterized by heat setting by holding the film in a temperature range of 210° C. for 3 seconds or more. The present invention will be explained in detail below. In the present invention, polyamide refers to a homopolymer of ε-caprolactam, a copolymer containing ε-caprolactam as a main component, and 2 to 10 mol% of other compounds copolymerizable with it. ), and these homopolymers and/or copolymers mixed with 5 to 20% by weight of a polymer compatible with these homopolymers and/or copolymers. Compounds that can be copolymerized with ε-caprolactam include warm mixtures with condensation. Specific examples of diamines include ethylenesoamine, tetramethylene diamine, pentamethylene diamine, hexamethylene diamine, octamethylene di-amine, decamethylene diamine, metaxylene diamine, paraxylene diamine, and the like. Examples of nocarboxylic acids include adipic acid, sebacic acid, corkic acid, geltaric acid, azelaic acid, β-methyladipic acid, terephthalic acid, isophthalic acid, decamethylene dicarboxylic acid, dodecamethylene dicarboxylic acid, and Vimeri. , antistatic agents, antiblocking agents, stabilizers, dyes, pigments, undefeated fine particles, and other various resin additives can be added within the range that does not adversely affect the properties of the film. When the method of the present invention is used, the polyamide film is substantially amorphous (hereinafter referred to as 1-unstretched film).
Use. An unstretched film can be obtained, for example, by heating and melting polyamide in an extruder, extruding it into a film from a T-Guy, and casting it at 40°C or lower using a known casting method such as an air knife casting method, an electrostatic application method, or a vacuum chamber method. It can be produced by quenching with a casting roll kept at a temperature of 35° C. or lower, more preferably below the dew condensation temperature. When using the method of the present invention, an unstretched film is first stretched in the longitudinal direction (hereinafter simply [
This is called longitudinal stretching-1. )do. 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 R stretching method can be used. To longitudinally stretch an unstretched film, first, the unstretched film is heated to 45 to 65°C using a temperature-controlled preheating roll.
It is best to adjust the heating temperature accordingly. If the temperature of the unstretched film is lower than 45°C, longitudinal stretching unevenness is likely to occur in the film after longitudinal stretching, and if it is higher than 65°C, the film tends to stick to the roll surface -1]; The film tends to have longitudinal stretching unevenness, and furthermore, directional hydrogen bonds occur in the stretched direction, and during the next stretching in the horizontal direction (hereinafter simply referred to as "transverse stretching 1"), the film tends to develop unevenness in the horizontal direction. This is undesirable because stretching unevenness or unstretched portions may occur, and the film may be easily torn. In the longitudinal stretching step, it is necessary to adopt stretching conditions such that the deformation rate is 10.000%/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 (1). Ru. ■F/I+): Vertical deformation speed of film (%/min)
: Film stretching ratio (times), UH/lJ. More sought after. L: Length of stretching section in R direction (, n) U: Linear speed of low speed roll (

07 minutes) UH: Linear speed of high-speed roll (
1o/min)] Deformation speed (V14D) is 10,00
If it is lower than 0%/min, even if the longitudinal stretching is performed well, the film tends to become uneven in the transverse stretching during the subsequent transverse stretching, which is not preferable. It is preferable that the ratio is greater than i, o, o o o%/min because longitudinal stretching is performed well and no transverse stretching unevenness occurs in the film during the subsequent transverse stretching. The first limit of the deformation speed is the structure and performance of the device used.
Various choices can be made depending on the temperature of the film at the start of stretching, etc., but it is preferably 50,000%/min or less. Note that when the film temperature at the start of stretching is low, the deformation rate is preferably low in the range 7L, and when the film temperature is high, it is preferably increased within the above range. When the longitudinal stretching ratio of the film is less than 2.7 times, it is necessary to impart the desired orientation effect to the final film, and when it is greater than 3.5 times, the next horizontal stretching This is undesirable because it tends to sometimes cause transverse stretching unevenness and unstretched residues, and also tends to tear. The longitudinal stretching ratio of the film can be varied in various ways by changing the linear speed of the high-speed roll and the low-speed roll in the roll-type longitudinal stretching machine. When using the method of the present invention, the film longitudinally stretched under the above conditions is immediately adjusted to a temperature range of 45 to 60°C, and the time expressed by the following formula (IT), i.e., ゛(3°9-0° 053T,) ・・・・・・(I
)t - θ [In formula (■), 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
, is the temperature of the film during this period, and is selected from the range of 45 to 60°C. It is preferable to transport it to the next lateral stretching start position (the position where the tenter rail starts expanding IJ) during the first opening. After finishing the longitudinal stretching, the film was heated to 45-60°C.
The reason for adjusting the temperature range is as follows. In other words, if the temperature of the film is lower than 45°C, the temperature will be too low during transverse stretching and the film will easily tear, which is undesirable. Since the transfer time of the film becomes extremely short, it is necessary to extremely shorten the distance between the longitudinal stretcher and the transverse stretcher, or to shorten the film introduction section (the part where the film is bitten) of the transverse stretcher. First, this is because problems arise in terms of the design, arrangement, or operability of the device, which is undesirable. If the deformation rate in the stretching process is ζ'000%/min or more, the film temperature will rise slightly (10 to 20°C) by -1- due to heat generation during stretching.
In some cases, it may be necessary to cool the film in order to adjust it to a temperature range of 60°C. After the longitudinal stretching, the film is transferred to the next transverse stretching step, but since polyamide has a fast crystallization rate, the hydrogen bonds in the longitudinally stretched film become stronger over time. For this reason, it is difficult to adopt a method of rapidly cooling the film after longitudinal stretching and then heating it again to the temperature at which it can be stretched in the pre-heating zone of a transverse stretching machine. It is preferable to transfer at a temperature as low as possible in a short period of time. According to the experiments conducted by the present inventors, it was found that the time for transferring the film that has been longitudinally stretched to the next horizontally stretching step is preferably within the time calculated by the above formula (n). . Specifically, when the film temperature adjusted after longitudinal stretching is 45°C, t' is within 4.5 seconds, when it is 50°C, t' is within 3.5 seconds, and at 60°C. In this case, it was found that 1゛ needs to be within 2.1 seconds. Said (1
) If the time calculated by formula □ is exceeded, the film is likely to have horizontal stretching irregularities when stretched in the next horizontal stretching process. This is likely to occur and is not desirable. When using the method of the present invention, the longitudinally stretched film is transferred to a transverse stretching step, and the film thickness profile at the transverse stretching start position is gradually decreased from the middle direction edge to the center in the IJ direction, and,
It is preferable that the thickness of the central part of the film in the middle direction is in the range of 75-90% of the thickness of the end part in the l] direction (tenter clip gripping part). Setting the film thickness profile at the horizontal stretching start position as shown above suppresses neck occurrence near the tenter clip (to avoid film breakage), and reduces the neck stretching light wheel position at the center of the film direction. This is to make the neck stretch random (to prevent the occurrence of a specific fixed thickness profile in the stretched film by not fixing the neck stretching occurrence position). When using the method of the present invention, when transversely stretching using a tenter set transversely stretching method, the film must be It is preferable that the tenter clip is expanded at an angle of 6 degrees or less, and the temperature (T2) of the tenter clip during this time is set to a temperature condition such that T2<TI. Setting the conditions to -1- immediately after the start of lateral stretching suppresses the occurrence of necks near the tenter clips (to avoid film breakage), and randomizes the position of neck stretching at the center of the film in the 11 direction. (This is to prevent the occurrence of a specific fixed thickness profile in the film without fixing the neck stretch occurrence position). When performing transverse stretching using a tenter, the film temperature is raised stepwise from the i-stretching start position, and at the transverse stretching end position, the film temperature is in the range of 70 to 100°C, more preferably 75 to 90°C. Humidity conditions need to be such that it can enter the room. In the film R-stretched by the above method, the hydrogen bonds that are oriented in the direction of stretching become stronger over time, so the film is transported to the lateral stretching start position in a very short time and the lateral stretching is started. The film temperature at this time, i.e., 45 to 60°C, is too low for transversely stretching the film, and if transversely stretching is carried out at this temperature, the film is likely to break at the tenter clips, making stable transverse stretching difficult. be. In order to perform stable transverse stretching, and furthermore to obtain a film with relatively balanced orientation in the longitudinal direction, the thickness profile of the film to be subjected to the transverse stretching process must be specified, and the By setting the tenter clip at a specific angle at the initial stage, in addition to randomizing the neck stretching start point that occurs in the center of the film, it is possible to Transverse stretching.If the temperature is raised rapidly when horizontally stretching the film, the parts of the film where neck stretching has not yet started,
In other words, as a result of being exposed to strong heat, the directional hydrogen bonds generated in the longitudinal stretching process become stronger in the parts of the film that have not yet been stretched horizontally. Otherwise, the lateral stretching ratio must be increased. As a result, the film becomes a film in which the longitudinal and transverse orientations are poorly balanced, which is not preferable. According to experiments 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°C. More preferably 75 to 90°C
If the temperature conditions are within the range of , it is possible to suppress the hydrogen bonds from becoming strong, and to make the N/N stretching vanishing point occur at the peak of the lateral stretching process, resulting in a good orientation balance. It was found that a film with good thickness accuracy could be stably produced. To raise the temperature of the film stepwise in the transverse stretching process = 15-, at least two or more compartments are provided on the soil surface and/or the bottom surface of the film in a direction perpendicular to the direction in which the film travels; Any method such as blowing hot air into each compartment, installing an infrared heater, or a combination of these methods may be used. The film temperature at the end position of transverse stretching is preferably in the range of 70 to 100°C, but if the deformation rate and stretching ratio of the film are high, the film temperature should be selected to be higher within the above range. When the magnification is low, it is preferable to select a lower film temperature within the above range. In the transverse stretching process, the average deformation rate is set at 2.000 to 1.
It is necessary to adopt stretching conditions in the range of 0,000%/min and the stretching ratio of 3 to 5 times, more preferably in the range of 3, 5'', 4.5 times.Here, the deformation speed is It refers to the value calculated by the formula expressed by the following formula (III). [In the formula (■), each symbol has the following meaning. ■: Lateral deformation rate of the film (%/min) D Y: At the mechanically set stretching ratio (times) of the film, S'
Determined from 2/yl. yl means the width between the tenters at the lateral stretching start position (position ``-'' in Figure 6), and y means the width between the tenters at the lateral stretching end position (positions B and B'' in Figure 6). 0: Speed of tenter (1o/min) LT: Length of horizontal stretching section (,,) ]
When the average deformation rate (V, p) is less than 2,000%/min, transverse stretching unevenness is likely to occur in the film,
If it is larger than %/min, the film is likely to break, which is not preferable. When the transverse stretching ratio of the film is less than 3 times, unstretched residue tends to occur, and when it exceeds 5 times, the transversely stretched film tends to break, which is not preferable. When using the method of the present invention, the temperature (θ) of the sequentially biaxially stretched film is raised over time to 190°C under conditions that satisfy the above general formula as explained in 11 below, and then
It is heat-set by holding it in the temperature range of -210°C for 3 seconds or more. The present inventors performed the following on the film after completing the lateral stretching process:
When we conducted an experiment on heat setting conditions and the magnitude of bowing strain, we found that the temperature (θ) of the film after the transverse stretching process was
over time, the condition that satisfies the above general formula, i.e.,
19 along the area surrounded by curve A and curve C in Figure 1.
It was found that when the temperature was raised to 0°C, the bowing strain during the heat setting process could be significantly reduced. ! @1 In the figure, curve A is θ=135X(1,-1
,0-0・17")+70, and the curve C is derived from θ=97(1,-10-'・"'f:)+100
This is a curve derived from . Curve B is a preferable temperature increase curve of the film temperature, and curve D and curve E are examples of undesirable temperature increase curves. According to experiments conducted by the present inventors, it was further found that the temperature at which the film is heat-set is preferably in the range of 190° to 210°C, and the heat-setting time is preferably 3 seconds or more. This temperature is 1
If it is lower than 90°C, it will take too much time to heat-set the film sufficiently, which is undesirable. If it exceeds 210°C, the temperature will be too high, and the film will be on the verge of melting, making it easy to whiten and devitrify, which is undesirable. Moreover, when the heating time is less than 3 seconds, the film cannot be sufficiently heat-set, and a film of good quality cannot be obtained. When heat setting the film under the above conditions, narrow the gap between the holders that hold both ends of the film, and reduce the gap by 3 to 15%.
It is preferable to provide relaxation in the range of . In order to raise the temperature of the film so that it satisfies Ichihi's general formula during heat fixing, a large number of infrared panel heaters are installed along the film transport (flow) direction and the temperature is raised sequentially. For example, a method may be used in which a large number of partitions are provided by installing partition walls in a direction perpendicular to the direction in which the film is transported, and the temperature is sequentially raised using hot air. "Effects of the Invention" According to the method of the present invention, it is possible to suppress the bowing phenomenon that occurs when heat-setting a polyamide film that has been biaxially stretched by the sequential stretching method, and therefore to create a uniform physical shape in the width direction of the film. It is possible to easily produce a film that has excellent flatness and is sufficiently heat-set. "Examples" Next, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 Poly-ε-caproamide (manufactured by Mitsubishi Chemical Industries, Ltd., Tsubamitsudo 102OCA) having a relative viscosity of 3.5 was heated to 90 m+
The mixture was kneaded using an nφ extruder at a cylinder temperature of 260°C, extruded into a film using a T-die, and rapidly cooled using a 600 vnφ casting roll cooled to 35°C to a thickness of about 150 microns. A substantially amorphous (unstretched) film of approximately 350+ om width was obtained. With a red felt-tip pen, write on the surface of this unstretched film.
A straight line was drawn in a direction perpendicular to the film transport direction. This unstretched film has a diameter of 1501φ and a width of 700 m+
8+n/
After heating and adjusting the temperature to 50°C, the deformation rate was 14.5 min between rolls with different circumferential speeds. ．． 700%/
Longitudinal stretching was carried out at a stretching ratio of 3.1 times. The longitudinally stretched film is immediately heated to 45°C by a group of rolls following the longitudinal stretching zone, and while maintaining this temperature, the film is stretched in widths of 1,5+n and lengths of 20+ for 3.5 seconds.
The tenter set was transferred to the horizontal stretching start position of a horizontal stretching rack having a size of n. The thickness of the film transferred to this position is 80 microns at the clip gripping part and 68 microns at the center in the film width direction, and the thickness at the center is 85% of the thickness at the clip gripping part. Ta. The tenter clips of the tenter set horizontally extending Iso are cast into the tenter rail and have a structure that allows cooling water to pass through the buried water cooling pipe.
The building is divided into sections, each section is equipped with an infrared heater, and the temperature of each section can be adjusted independently. Grip both ends of the longitudinally stretched film with tenter clips that have been cooled to 40°C, and expand the tenter rail at an angle of 5 degrees to the center line of the film until the mechanically set magnification is 2.0x. Transverse stretching was performed at an average deformation rate of 3.000%/min and a stretching ratio of 3.5 times. The film temperature in the transverse stretching zone was 60°C in the first section;
The temperature was 70°C in the second compartment and 80°C in the third compartment. After completing the transverse stretching, the film was subsequently transferred to a heat setting zone and heat set under the following conditions. The heat fixation zone was divided into eight sections at approximately equal intervals, and an infrared heater was placed in each section, so that the temperature of each section could be adjusted independently. A gap was provided between each section, so that the film temperature could be detected with a scanning infrared thermometer. The time it takes for the film to pass through each compartment is approximately 1.4 seconds, and the film temperature at the two-way entrance of the first section is 135°C.The temperature of the film is 165°C at the exit of the second section, 180°C at the dual-use entrance of the third section, and the exit of the fourth section. de1
The temperature was raised to 90°C. 1 This temperature increase pattern is shown in curve B in Figure 1.
is shown as In the subsequent 5th to 8th sections, the film temperature was set to 198. In the section from the 6th section to the 8th section, the rail gap of the clip holding the end of the film was narrowed by 5%, and relaxation heat fixation was performed. After the heat-setting process was completed, the film was slowly cooled, released from the tenter clips, and wound up with a winder without cutting off both ends of the film. The average thickness of the rolled film excluding both ears is:
It was about 15 microns. The amount of bowing distortion of the film thus obtained was measured in the following manner. The red line drawn on the surface of the unstretched film is the finally obtained film 1-, which has a slightly arched shape as shown in FIG. This bow-shaped situation is expressed by the following formula: B = amount of bowing strain (%) L, = gap between tenter clips (IIfl) 1 - maximum bulge amount of the red line (IIllo) Therefore, the amount of bowing strain was calculated. The results are shown in Table 1 along with the temperature conditions after the lateral stretching step. In FIG. 2, 1 indicates a film, and 2 indicates an arrow indicating the direction of transport of the film. The amount of bowing distortion of the film obtained in this example is 4.7
%, which was smaller than 5%, which is said to be free from practical-L problems. Further, the refractive index of the film obtained in this example in the width direction and transport (length) direction was measured using an Ab13e refractometer. The average of these measurements is 1. ．． 5433, and was judged to be sufficiently crystallized and preferably heat-set. When used as a packaging base film, it is said that there are no practical problems if the average refractive index is 1.542 or more. Examples 2-3 Unstretched films of the same type as used in Example 1 were biaxially stretched in a similar manner to that described in that example. The film that had been horizontally stretched was heated and heat-set using the same heating and heat-setting apparatus used in Example 1 under the conditions listed in Table 1. The amount of bowing strain and refractive index of the obtained film were measured according to the method described in Example 1. The results are shown in Table 1. Comparative Examples 1-3 Unstretched films of the same type as used in Example 1 were stretched biaxially in the same manner as described in that Example. The film that had been horizontally stretched was heated and heat-set using the same heating and heat-setting apparatus used in Example 1 under the conditions listed in Table 1. The amount of bowing distortion and the refractive index of the obtained film were measured according to the method described in Example 1. The results are shown in Table 1. From Table 1, the following becomes clear. (1) The biaxially stretched polyamide film obtained by the method of the present invention has a bowing strain of 5% or less and has uniform physical properties in the width direction of the film. still,
It has a sufficiently high average refractive index and is heat-set in a sufficiently crystallized state. (2) The biaxially stretched polyamide film obtained in Comparative Example had an excessive amount of bowing strain (Comparative Example 1).
2) Problems tend to occur during practical use due to insufficient heat fixation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the change in film temperature over time during heating and heat-setting of a sheet according to the method of the present invention. This indicates that an increase in temperature is favorable. FIG. 2 is a diagram showing the calculation method for the amount of bowing distortion, where 1 is the film, 2 is the film transport direction, 3 is the red line,
L indicates the gap between tenter clips, and 1 indicates the maximum bulge of the red line. Applicant Tamabishi Monsanto Kasei Co., Ltd. Agent Patent Attorney Atsutani - (1 idiot) Fig. 1 Lateral direction, -2 IminamiwinteryoiLj') Light TeL BimP
Af: C rare ν) Section 2 Nagi

Claims (1)

[Claims] (1) A substantially amorphous and unoriented polyamide film is stretched at a temperature of 45 to 65°C using a roll longitudinal stretching method at a deformation rate of 10,000%/min or more.
．． Stretch the film 7 to 3.5 times in the machine direction, then hold the edges of the film with tenter clips and lower the film temperature to 1.
00℃ or less, average deformation rate 2,000 to 10,00
After stretching in the transverse direction 3 to 5 times at a rate of 0%/min,
The film temperature is changed over time using the general formula 135 x (1-10^-^0^.^1^7^t)+70
<θ<97×(1-10^-^0^.^2^1t)+1
00 However, the temperature is raised to 190 °C under conditions that satisfy θ = film temperature (°C), t = elapsed time after completion of stretching in the lateral direction (seconds), and then 190~
A method for producing a biaxially oriented polyamide film, which comprises heat setting by holding in a temperature range of 210° C. for 3 seconds or more.