JPS61244527A - Manufacture of biaxially oriented polyamide film - Google Patents

Abstract

PURPOSE:To make a formless and unoriented polyamide film into one superior in evenness by controlling a boiling phenomenon, by a method wherein after the formless and unoriented polyamide film has been cooled lower than the glass temperature by orienting the same in a longitudinal and lateral directions under specific terms and applying first stage heat treatment to the same at a specific temperature, second stage heat treatment is applied to the same at a lower temperature than the fusion point of polyamide. CONSTITUTION:After an unoriented polyamide film has been cooled lower than the glass temperature of raw materials, polyamide by orienting the same film 2.7-3.5 times in a longitudinal direction at the temperature within a range of 45-60 deg.C and deformation rate of more than 10,000%/minute, then molding at both side end parts, orienting 3-5 times in a lateral direction within a range of a mean deformation rate of 2,000-10,000%/minute by making a film temperature less than 100 deg.C, applying first stage heat treatment to the film at the temperature within a range of 100-170 deg.C continuously and cooling the film at the temperature lower than the glass temperature of the raw materials, the polyamide, second stage heat treatment is applied to the film under temperature terms wherein the temperature lower by 10 deg.C than the fusion point of the raw material, the polyamide is made into the upper limit. As for a biaxially oriented polyamide film manufactured in this manner, a boiling quantity of the same is small to such an extent of less than 5%, physical properties are uniform and evenness is favorable.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing a biaxially oriented polyamide film. More specifically, it relates to an improvement in the method of producing biaxially stretched polyamide films by first stretching in the longitudinal direction using a roll-type longitudinal stretching method, and then gripping with tenter clips and stretching in the transverse direction. The present invention relates to a method for producing a film having uniform physical properties in the width direction.

[Polyamide film axially stretched using conventional technology has excellent toughness, heat resistance,
Excellent cold resistance, transparency, printability, chemical resistance, etc., and
Because it has characteristics such as not easily forming pinholes,
It is widely used as a base film for food and other packaging. When biaxially stretched polyamide film is used for food packaging, printing, lamination, bag making, food filling, and heat sealing are usually performed. This has a significant impact on production speed, product yield, etc. in processing, bag-making processes, etc. For example, if a base film with poor flatness or uneven physical properties is used, problems such as misaligned printing pitch, wrinkles, curling, and meandering may occur during printing, laminating, bag making, etc. However, there are disadvantages in that good quality products cannot be obtained and production speed cannot be increased. In addition, the flatness and uniformity of the physical properties of the base film are
Regardless of the presence or absence of bowing distortion, a base film with improved bowing distortion has good flatness and uniform physical properties, so there is an extremely strong demand for improvement in bowing distortion.

“Boeing distortion 1 is caused by the Boeing phenomenon.

The bowing phenomenon is a phenomenon in which a straight line is marked perpendicular to the transport direction on an unstretched film, as explained in, for example, Japanese Patent Laid-Open No. 58-55221 and Japanese Patent Laid-open No. 58-147322. Then, after completing biaxial stretching in the longitudinal and transverse directions and heat setting, the straight line will be distorted into an arched shape,
This is a phenomenon in which the center of the film lags behind. Furthermore, if a large number of small circles are drawn instead of a straight line, the circle remains enlarged in diameter at the center of the film, but becomes a slanted ellipse at the edges in the width direction of the film.

As a method for suppressing the bowing phenomenon that occurs during the production of biaxially stretched films, techniques described in JP-A-54-13706 and JP-A-51-80372 have been proposed. The technique described above is a technique applied to a simultaneous biaxial stretching method, and is not effective when applied to a sequential biaxial stretching method such as the method of the present invention.

Furthermore, Japanese Patent Publication No. 43-5557 proposes a method of providing a buffer zone between the lateral stretching zone and the heat treatment zone; however, according to experiments conducted by the present inventors, It was found that applying this technique to polyamide film was ineffective.

Furthermore, JP-A-50-73978 proposes a method in which a group of nip rolls are provided in the transverse stretching zone and the heat treatment zone, but this method tends to cause scratches on the film surface due to the nip rolls, making it impractical for practical use. do not have.

Furthermore, Japanese Patent Application Laid-open No. 57-87331 discloses that as a measure to suppress the bowing phenomenon in the sequential biaxial stretching method, a film that has been sequentially biaxially stretched in the longitudinal and transverse directions is immediately cooled to below the glass transition temperature. After that, the paper proposes a method of releasing the grip on the side edge of the film and then gripping the side edge of the film again to perform heat treatment. Although it is effective for films, it has no effect at all on films stretched at relatively low temperatures, such as polyamide, and it has been impossible to suppress the bowing phenomenon.

The present inventors have previously completed a method for manufacturing a sequentially biaxially stretched polyamide film (for example, in JP-A-59-1716
26, Japanese Patent Application No. 59-30101, etc.), it has been found that when a film is manufactured by this method, the bowing phenomenon of the film occurs during the process of heat-setting the film.

[Problem to be Solved by the Invention 1] The present invention suppresses the bowing phenomenon that occurs when heat-setting a biaxially stretched polyamide film according to the sequential biaxial stretching method, and has uniform physical properties in the width direction and a flat film. The purpose of the present invention is to provide a method for producing a film with excellent properties.

"Means for Solving the Problems 1" However, the gist of the present invention is to prepare a substantially amorphous, unoriented polyamide film at a temperature of 45 to 60°C.
Within the range of 0°C, the film was stretched in the longitudinal direction by 2.7 to 73.5 times at a deformation rate of 10,000%/min or more using a roll-type longitudinal stretching method, and then both ends of the film were held with tenter clips. The film was held at a temperature of 100°C or lower, and stretched 3 to 5 times in the transverse direction at an average deformation rate of 2.000 to 100%/min. While holding the film, perform the first step heat treatment within the temperature range of 100-170°C, and then cool the film to below the glass transition temperature of the raw material polyamide,
The grips on both sides of the film are released, and then the film is transferred to the next heat treatment zone.
The present invention resides in a method for producing a biaxially stretched polyamide film, characterized in that a second stage heat treatment is performed at a temperature that is 0° C. lower as an upper limit.

The present invention will be explained in detail below.

The polyamide used as a raw material in the present invention is
ε-caprolactam homopolymer, ε
- Copolymers containing caprolactam as the main component and up to 2.\210 mol% of other compounds copolymerizable with it, and polymers compatible with these homopolymers and/or copolymers. It refers to a mixture of 5 to 20% by weight of agglomerates.

Examples of compounds copolymerizable with ε-caprolactam include aliphatic or aromatic diamines and condensates with aliphatic or aromatic dicarboxylic acids.

Specific examples of diamines include ethylene diamine, tetramethylene diamine, pentamethylene diamine, hexamethylene diamine, octamethylene diamine, decamethylene diamine, metaxylene diamine, paraxylene diamine, and the like.

Examples of dicarboxylic acids include adipic acid, sebacic acid, corkic acid, geltaric acid, azelaic acid, β-methyladipic acid, terephthalic acid, isophthalic acid, decamethylene dicarboxylic acid, and pimelic acid.

Examples of polymers that are compatible with the homopolymer and/or copolymer include copolymers of the diamines listed under I and the dicarboxylic acids described above.

Various resin additives such as lubricants, antistatic agents, antiblocking agents, stabilizers, dyes, pigments, and inorganic fine particles can be added to these raw polyamides to the extent that they do not adversely affect the properties of the film.

When using the method of the present invention, a substantially amorphous and unoriented polyamide film (hereinafter referred to as "unstretched film 1") is used. An unstretched film can be produced, for example, by heating and melting polyamide in an extruder, extruding it into a film from a T-Guy, and then applying the air knife casting method, electrostatic application method,
By a known casting method such as the Bachium chamber method,
It can be produced by rapid cooling on a casting roll maintained at 40° C. or lower, more preferably 35° C. or lower, above 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 type longitudinal stretching method refers to a method of longitudinal stretching using a roll type longitudinal stretching machine, and 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 heated to 45 to 65°C using a temperature-controlled preheating roll.
It is best to adjust it to

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. In addition, directional hydrogen bonds occur in the direction of stretching, and during the next stretching in the horizontal direction (hereinafter simply referred to as "lateral stretching"),
This is not preferable because it causes transverse stretching unevenness or unstretched portions in the film, and the film tends to tear.

In the longitudinal stretching process, 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 is expressed by formula (I), and the stretching ratio is (It
) refers to the value calculated by the formula respectively expressed.

X=U, , / [, IL ・ ・ ・
・ ・(It)] (In formula II and formula (■), each symbol has the following meaning.

\'MD: Film longitudinal deformation speed (%/min)
: Longitudinal stretching ratio of film L: [length of direction stretching section (1n) UL : Linear speed of low speed roll (+n/min) Ul, :
Linear speed of high-speed roll (1o/min) 1 Deformation speed (V
If the Mn) force is 10.000%/min J:'), even if the longitudinal stretching is performed well, the film tends to become uneven in the lateral stretching during the next lateral stretching, which is not preferable. The deformation speed can be varied depending on the structure and performance of the apparatus used, the film temperature 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 reduced within the range 1-, and when the film temperature is high, it is preferably increased within the range 1-h.

When the longitudinal stretching ratio of the film is smaller than 2.7 times, the desired orientation effect cannot be imparted to the final film, and when the film is stretched at a magnification of more than 3.5 times, the next horizontal stretching ratio is less than 3.5 times. This is undesirable because it tends to sometimes cause lateral stretching unevenness or unstretched residues, and also tends to tear.

When using the method of the present invention, the film longitudinally stretched under the conditions described in -H is immediately adjusted to a temperature range of 45 to 60°C, and the film is stretched for a period of time expressed by the following formula (ITI), that is, = e
(3,9-0,53T,) , , , , , ,
, (■) [In the formula (■), t means the time (seconds) from the end of R stretching to the start of lateral stretching, and T1 is the temperature ('C) of the film during this time, which is 45~ Selected from the range of 60°C. It is preferable to transport the tenter rail to the next lateral stretching start position (the position where the tenter rail starts widening) within a time period of 1, where e means the base of the natural logarithm.

After finishing the longitudinal stretching, this film was 45-11= The reason for adjusting the temperature to -60°C is as follows.

That is, 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 easily tear when performing transverse stretching, and if it is higher than 60°C, it will be difficult to transport the film to the transverse stretching start position after the longitudinal stretching is completed. This is because the time becomes extremely short, which causes problems in the design, arrangement, and operability of the device, which is undesirable.

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, at the lowest possible temperature that allows for lateral stretching,
It is preferable to transfer within a short period of time. If the time calculated by the above formula (II) is exceeded, the film tends to have lateral stretching unevenness during lateral stretching, or unstretched residues tend to occur at the edges of the film in the width direction. Undesirable.

When using the method of the present invention, when horizontal stretching is performed using a tenter set horizontal stretching method, until the mechanically set magnification between the tenter clips reaches 1.4 times the original value, 12- is applied to the center line in the film width direction. It is preferable to widen the tenter clip at an angle of 6 degrees or less, and keep the temperature of the tenter clip lower than the temperature of the film during this time.

The conditions immediately after the start of lateral stretching at the lateral stretching start position are set as above by suppressing the occurrence of necks near the tenter clips and by randomizing the neck stretching generation device at the center in the width direction of the film. This is to avoid breakage of the film and to make the physical properties uniform along the width direction of the film.

When performing transverse stretching using a tenter, the film temperature is raised stepwise from the transverse stretching position, and at the transverse stretching end position, the temperature is 100°C or less, preferably within the range of 70 to 100°C, particularly preferably 75°C. The temperature conditions must be within the range of ~90°C.

When using the method of the present invention, the temperature of the film after finishing the longitudinal stretching and being transferred to the starting position of the lateral stretching is 4
5% and 60° C. is too low as a temperature for transversely stretching the film, and if transversely stretching is performed at this temperature, the film is likely to break at the tenter clips, making it more difficult than stable transversely stretching 1.

In order to perform stable transverse stretching, and furthermore to obtain a film with relatively balanced orientation in the longitudinal direction, as mentioned above, by setting the widening angle of the tenter clip at a specific stage in the initial stage of the transverse stretching process. In addition to randomizing the starting point of the neck stretching, which occurs in the direction of the width Jj direction, it is necessary to transversely stretch the film while raising the temperature in stages.

If the temperature is rapidly raised when transversely stretching a film, the portions of the film where neck stretching has not yet started, that is, the portions of the film that have not yet been transversely stretched, receive intense heat, resulting in the direction f' generated in the longitudinal stretching process. Hydrogen bonds with l: become strong, and when this is stretched laterally, uneven stretching or unstretched portions occur, resulting in a film whose orientation in the longitudinal Jj direction and the transverse force direction is not clearly balanced, which is not preferable.

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 100'C or less. Preferably 70·y l O(1"
Within the range of C, particularly preferably 75・＼, 9 (1'C
If the temperature conditions are within the range of It was confirmed that a film with good precision could be produced stably.

To heat the film stepwise to 41-degrees in the transverse stretching process,
On the top and/or bottom surface of the film, in a direction perpendicular to the direction of film travel, at least two sections 1: Jl-
The method may include a method of blowing hot air into each section, a method of installing an infrared heater, or a method of combining these methods.

The film temperature at the end of lateral stretching is 70 to 100°C.
However, when the deformation rate and stretching ratio of the film are high, the film temperature should be set higher within the range 1-, and when the deformation speed and stretching ratio are low, the film temperature should be within the range 1-. I prefer to choose the lower one within 1. stomach.

In the horizontally stretched -L culm, the average deformation speed is 2, +1
(It is necessary to adopt a stretched strip fl in the range of 111.0+10%/min and the stretching ratio of 3 to 5 times, more preferably in the range of 3.5 to 4.5 times.

Here, the average deformation speed refers to a value calculated by the following equation (TV).

Ru.

VTD near (average deformation rate of lume (%/min) Y:
Mechanically set stretching ratio (times) of the film, calculated by dividing the width between tenters at the end position of lateral stretching by the width between tenters at the start position of lateral stretching: Speed of tenter (1 n/min) LT: Length of transverse stretching section (, o) 1 When the average deformation rate (■, 1,) is lower than 2.000%/min, transverse stretching unevenness is likely to occur in the film, and in, 000%/min, L If it is too large, the film is likely to break, which is not preferable.

When the transverse stretching ratio of the film is less than 3 times, unstretched portions tend to occur, and when it exceeds 5 times, the transversely stretched film tends to break, which is not preferable.

A polyamide film stretched in the longitudinal direction and then in the transverse direction at a relatively low temperature while suppressing crystallization according to the above method shows almost no bowing phenomenon at the stage when the transverse stretching is completed. However, if the film that has been horizontally stretched is used for various purposes as it is, it suffers from shrinkage and has a drawback of poor dimensional stability. In order to impart dimensional stability to the biaxially stretched film, a method of heat treating the biaxially stretched film is employed. It has been found that when a biaxially stretched film produced according to the method of the present invention is heat treated in the same tenter after transverse stretching, a large bowing phenomenon occurs in the final film. .

In order to suppress the bowing phenomenon that occurs in this heat treatment process, the present inventors conducted studies and experiments by changing the temperature riser during heat treatment, the rail pattern of the tenter, etc. As far as heat treatment is concerned, there is a limit to suppressing the bowing phenomenon that occurs in the final film, and it has been found that it is extremely difficult to reduce the bowing distortion within the target range.

As a result of further experiments, it was found that the bowing phenomenon that occurs in the final film can be significantly suppressed by performing the heat treatment in two stages. The two-step heat treatment method involves heating both ends of the transversely stretched film to temperatures of 100 and 170 while holding both ends with tenter clips.
The first stage of heat treatment is carried out at a temperature of 110°C, preferably 150°C, and then the film is cooled to below the glass transition temperature of the raw material polyamide. Transfer to the next heat treatment zone,
This is a method in which a second stage heat treatment is carried out at a temperature 10° C. or more lower than the melting point of the raw material polyamide, while holding and transporting both ends of the film with separate tenter clips. In this case, as will be described later, by selecting the temperature conditions for the second stage heat treatment within a range that satisfies the requirements listed in 1. Any heat-shrinkable film can be obtained.

In the M1 stage heat treatment, if the heat treatment temperature is higher than 170"C, a large bowing phenomenon will occur in the film during the heat treatment stage under this condition, which is undesirable. Also, if the heat treatment temperature is lower than 100"C, both side edges will be damaged after cooling. This is not preferable because the film released from the partial grip may undergo severe shrinkage in the transport direction and width direction, or irregular shrinkage may occur, impairing the flatness of the final film.

In addition, when performing the first stage heat treatment, the interval between the tenter clips may be the same as that at the end of the lateral stretching, and the tenter clips may be maintained in a tensioned state, or the interval may be narrowed and the interval may be performed in a relaxed state.

After the first heat treatment, it is necessary to cool the film to a temperature below the glass transition temperature of the raw material polyamide while holding both ends of the film with tenter clips. If the grips on both ends of the film are immediately released after the first Pi heat treatment without cooling it below the glass transition temperature of the raw material polyamide, the film will experience irregular shrinkage while being transferred to the next heat treatment zone. Also, since the film comes into contact with the guide rolls etc. in a hot state, the film may stick to the guide rolls etc. or be cooled unevenly.
This impairs the flatness of the final film.

After cooling the film, which has been cooled to below the glass transition temperature of the raw material polyamide, it is necessary to immediately release both ends of the film from the tenter clips. By this release, stress fields in the transport direction that cause the bowing phenomenon, such as relaxation stress due to longitudinal stretching and machine direction stress based on Poisson's ratio during lateral stretching, are released, and these stress fields are released in the subsequent heat treatment zone. The occurrence of bowing distortion due to stress can be avoided.

The cooled film released from the grip of the tenter clips is transferred to the succeeding second stage tenter for heat treatment, and both ends of the film are gripped again. To transfer between the first stage heat treatment tenter and the second stage heat treatment tenter, use one selected from guide rolls, expanders, dancer rolls for tension control, tension pickup rolls, nip rolls, etc. It can be installed and used as needed.

To carry out the second stage heat treatment, the film is transferred to the second stage heat treatment tenter while gripping both sides of the film and transferring the film to -I at a temperature 10°C lower than the melting point of the raw material polyamide.
- Perform the second stage heat treatment under eye temperature conditions. If the heat treatment is performed at a temperature higher than this upper limit temperature, the surface of the film may become white or the film may break, which is not preferable.

When using the method of the present invention, the temperature conditions for the second stage heat treatment can be freely selected from the following conditions depending on the properties to be imparted to the film to be finally obtained.

In other words, the shrinkage rate when immersed in boiling water for 5 minutes is 4.
% or less, the heat treatment temperature is within a temperature range of 190°C as the lower limit and -1° as the temperature 10°C lower than the melting point of the raw material polyamide, preferably 195°C, ．． It shall be selected within the temperature range of 205°C. If the heat treatment is performed at a temperature lower than 190° C., the shrinkage rate of the final film will increase, and a non-heat-shrinkable film with a small shrinkage rate will not be obtained.

Further, in order to obtain a heat-shrinkable film for use in shrink packaging that has a shrinkage rate of 15% or more when immersed in boiling water for 5 minutes, the heat treatment temperature is 100-170°C, preferably 120-170°C. It shall be selected within a temperature range of 150°C. Films that have been heat-treated at temperatures below 100°C will naturally shrink during storage indoors due to insufficient heat treatment.
If the temperature is 170° C. or higher, the heat shrinkage rate will be low and a heat-shrinkable film with a high shrinkage rate will not be obtained.

In addition, when performing the second Pi heat treatment, the stretching balance can be adjusted by making the rail spacing between the left and right tenters a little narrower, making it a constant width, or making it a little wider, if necessary. . Particularly when obtaining a non-heat-shrinkable film, it is effective to suppress the bowing phenomenon by narrowing the tenter rail spacing at the initial stage to give relaxation in the width direction, and then making it a constant width. When obtaining a film, it is more effective to suppress the bowing phenomenon if the width is constant throughout.

The film that has undergone the second stage heat treatment is cooled and rolled up according to a conventional method.

The biaxially stretched polyamide film produced in this manner has a low bowing amount (defined later) of 5% or less, has uniform physical properties in the width direction of the film, and has good flatness.

[Effects of the Invention-1 The method of the present invention is capable of suppressing the bowing phenomenon that occurs when heat-setting a polyamide film that has been biaxially stretched using a sequential stretching method. It is possible to easily produce a non-shrinkable film or a heat-shrinkable film that has the following properties, has excellent flatness, and is sufficiently heat-set.

"Example" = 23- 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 it exceeds the gist thereof.

In the example below, the physical properties of the resulting film are:
Evaluation was made by the method described below.

(1) Film thickness μ+n) Measurements were made at 30 points along the width direction of the film, and the average value was used.

(2) Film thickness unevenness (%) It was calculated using the following formula.

Here, d5: Maximum thickness in the width direction 812 Minimum thickness in the width direction dad = Average thickness in the width direction 3) Amount of bowing (%) Place a magic marker on the surface of the unstretched film at right angles to the film transport (flow) direction. A straight line drawn with ink is the rate at which the straight line is deformed on the product film obtained through a series of processes such as longitudinal stretching, transverse stretching, and heat treatment.The length of the straight line is the length at which the center of the film lags behind the side edges of the film. The value obtained by dividing the width by the film width and ending with 100 was adopted.

(4) Heat shrinkage rate and heat shrinkage rate difference (%) First, the product film was conditioned in an atmosphere of 25°C and 45% relative humidity, and a square marked line with a side length of 80m+++ was marked on the film surface. The square was drawn so that each side was parallel to the vertical and horizontal directions of the film. Next, this sample was immersed in boiling water for 5 minutes, taken out, and left again in an atmosphere at a temperature of 25° C. and a relative humidity of 45% for 24 hours. The dimensions of the square before and after immersion in boiling water were measured and calculated using the following formula.

Here, 1°11° is the length of the side along the longitudinal direction of the film before and after immersion, and l7. l,' is the length of the side along the lateral direction of the film before and after dipping; 1. .

13゛ means the quality of the diagonal of the strain force shape before and after immersion, and 14111゛ means the length of the other diagonal of the rectangle before and after immersion.

Note that the longitudinal shrinkage rate and the lateral ego 16 rate are preferably 3% or less, and the difference in lunar force direction shrinkage rate is preferably 1% or less.

(5) ILZ flatness of film (+am) As shown in Figure 1, straight line 2.3 is connected to 1- of flat table 1.
One end of a 3 meter length (product film cut in the width direction) is fixed to a table 11- with an adhesive tape 4 in parallel outside the premises with a distance of 1 meter. A load of 20 grams per 1 cm in the medial 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 base M3. Next, a load is applied and the film is cut into 111 books at 3 am intervals along the length direction I of the film. Next, a load of 60 grams was applied to the free end of each strip, and table 1
The deviation between the base line 3 of - and the marked line 6 of strip 1- is sequentially measured. The difference between the maximum value and the minimum value among the measured values is used as an index of modality.

If this index is 2nun or less, there is no practical problem with the product film, but more preferably 1.5 m
m or less is better.

Example 1 Poly-ε-caproamide (manufactured by Mitsubishi Chemical Industries, Ltd., Tsubamitsudo 102 OCA) having a relative viscosity of 3.5 was
With m+nφ extruder, cylinder temperature 27i ()”C
It was melted and kneaded under the conditions of 60 ('1111111φ
140μ thick.
A substantially amorphous, unoriented (unstretched) film having a width of about 3501111111 was obtained.

In order to measure the amount of bowing, a straight line was drawn on the surface of this unstretched film in a direction perpendicular to the direction of the film's transport force using a red 7-ertoven marker.

This unstretched film has a width of 150+na+φ and a width of 700V.
It was introduced into a longitudinal stretching machine consisting of multiple 1 m rolls at a transfer speed of 8IO/min, heated and adjusted to 50°C, and then deformed at a deformation rate of 14,700%/min between rolls with different circumferential speeds.
Longitudinal stretching was carried out under the conditions of a stretching ratio of 3.1 times, and the temperature of the longitudinally stretched film was adjusted to 45° C. by a group of rolls following the longitudinal stretching zone, and the width was 1.5 fn and the length was 201 mm.
The set of tenters No. o was transported to the horizontal stretching start position of the horizontal stretching rock. Next, both ends of the film were held with tenter clips, and while the temperature was raised from 60°C to 80°C, the deformation rate was 3.0°C.
Lateral stretching was carried out under the conditions of 0.00%/min and a stretching ratio of 4.5 times.

The film that has been stretched is then subjected to the first heat treatment at 130°C for 2 seconds while holding both ends, then cooled to 30°C, and gripping the edges on the side of the film.
I released it.

The released film passes through a guide roll and an expander roll and is guided to another tenter with a width of 1.5+++S and a length of 151n, where both ends of the film are gripped again with tenter clips and a 10% reduction in the width direction is carried out. After the second heat treatment was performed at 200°C for 10 seconds in the relaxed state, the film was cooled to 30°C, released from the tenter clip, trimmed on both sides, and determined the thickness. A film of approximately 15 μm and width of 1 μm was wound up.

The properties of the thus obtained film were measured based on the method described above. The measurement results are shown in Table 1.

The obtained film had a very small bowing amount of 2.5%, and its physical properties were uniform along the width direction.

Comparative Example 1 An unstretched film of the same type as used in Example 1 was stretched biaxially in the same manner as described on the same side. The film that has been horizontally stretched is then stretched in the same tenter for 200
After heat treatment at .degree. C. for 10 seconds, the film was cooled to 30.degree. C., released from the tenter crimp, trimmed at both ends, and then wound up.

Regarding the thus obtained film, various characteristics +11 were tested in the same manner as in Example 1. The results are shown in Table 1.

The obtained film had a very high concentration of boing acid at 3 (6%), and the center part of the film was tighter than the edges and had poor flatness. The physical properties of the film were also better than that of the film obtained in Example 1.
Met. The Jj method described in Comparative Example 1 omits the heat treatment in the first stage 11 in the example described in Example 1, cooling and releasing the grip of the film from the tenter clip after cooling, but it does not produce non-defective products. In order to obtain the 5-L culm, it is necessary to omit the culm.

Example 2.3 In the example described in Example 1, the first stage and the second f father]
A biaxially stretched and heat-treated film was obtained in the same manner as in the same example except that the heat treatment temperature in Example 1 was changed as shown in Table 1.

Table 1 shows the results of measuring the bowing speed of the obtained film. All of the obtained films had a small amount of boing acid and were good.

Comparative Example 2/24 In the example described in Example 1, the first stage 11 and the second stage 1
A knee-axis stretched and heat-treated film was obtained by the same procedure as in the same example except that the heat treatment τ opening degree of Example 1 was changed as shown in Table 1.

Table 1 shows the measurement results of the Boeing acid of the obtained film and the observation results of the film appearance. The obtained film had poor appearance, film breakage during the second heat treatment, and a high amount of bowing, so it was not possible to produce a good product. A similar unstretched film was biaxially stretched in the same manner as described in the same example. After completing the transverse stretching, the film was then heat treated in the first stage 11 at 100°C for 2 seconds in the same tenter with 5% relaxation in the width direction. The film was cooled to C and the grips on both sides of the film were released.

The film released from the grip is passed through an idle roll and an expander roll, and has a width of 1.5+n and a length of 1.
Guide the film to another tenter of 0+n, hold both ends of the film again with tenter clips, and heat it at 120°C with a constant width.
The second stage of heat for 2 seconds at 11! This was done by cooling the film to 30°C, releasing the film from a tenter crimp, trimming both edges, and winding up the film to have a thickness of about 15μ and a width of 1+n.

Various physical properties of the thus obtained film were measured based on the methods described above. The measurement results are shown in Table 1.

The obtained film had a very small bowing amount of 2.4%, and its physical properties were uniform along the width direction.

Further, the heat shrinkage rate was approximately 29%, which is suitable for a heat-shrinkable film, and the difference in heat shrinkage rate in the diagonal direction was sufficiently small.

Example 5.6 In the example described in Example 4, the first stage and the first: (2
A biaxially stretched and heat-treated film was obtained by the same procedure as in the same example, except that the heat treatment temperature of [2-stage 1] was changed as shown in Table 1.

Table 1 shows the heat of 1st f father 1] and 2nd f father] 1 + l
The results of measuring the amount of bowing of the obtained film are shown together with the temperature. All of the obtained films had low boing acid content and were good films.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a method for evaluating the flatness of a film obtained by the method of the present invention. In the figure, 1 is a table, 2.3 is a base line, 4 is an adhesive tape for fixing the film, 5 is a cutting line of the sample, and 6 is a marked line.

Claims (3)

[Claims] (1) A substantially amorphous, unoriented polyamide film is stretched at a temperature of 45 to 65°C by a roll-type longitudinal stretching method at a deformation rate of 10,000%/min or more, with a deformation rate of 2.7 The film was stretched by ~3.5 times in the longitudinal direction, and then both ends of the film were held with tenter clips, the film temperature was kept below 100°C, and the average deformation rate was in the range of 2,000 to 10,000%/min. ,
The film is stretched 3 to 5 times in the transverse direction, and then a first heat treatment is performed at a temperature of 100 to 170°C while holding both edges of the film. After cooling the film to below temperature, the grips on both sides of the film are released, and then the film is transferred to the next heat treatment zone. A method for producing a biaxially oriented polyamide film, characterized in that a second stage heat treatment is performed under temperature conditions with an upper limit of a temperature lower than 0.9°C. (2) The second stage heat treatment is carried out in a temperature range with a lower limit of 190°C and an upper limit of a temperature 10°C lower than the melting point of the raw material polyamide, as set forth in claim (1). A method for producing a biaxially stretched polyamide film. (3) The method for producing a biaxially stretched polyamide film according to claim (1), characterized in that the second stage heat treatment is carried out within a temperature range of 100°C to 170°C.