JPS62117725A - Polyamide film and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a p-phenylene terephthalamide (PPTA) film with improved tear performance by a method wherein a crystal orientation angle by X-rays incident normal to the surface of the film and the ratio of minimum intensity to maximum intensity in the angular distribution of the intensity of fluorescent radiation by polarized parallel rays incident normal to the surface of the film are specified. CONSTITUTION:In a polyamide film, the logarithmic viscosity number of which is 3.5 or more and which substantially consists of PPTA, a crystal orientation angle with respect to the peak in case of 2theta 23 deg. by X-rays incident normal to the surface of the film is 70 deg. or more. If the crystal orientation angle in case of 2theta 23 deg. is smaller than 70 deg., the balance of the properties in longitudinal direction and in lateral direction of the film is lost. The ratio is minimum intensity to maximum intensity in the angular distribution of the intensity of fluorescent radiation by polarized parallel rays incident normal to the surface of the film lies within the range of 0.7-1.0. The solvent suitable for preparing the dope for forming a PPTA film is sulfuric acid with the concentration of 95wt% or more. The way to obtain a transparent film with excellent mechanical properties is to invert the dope from its optical anisotropic property to its optical isotropic property before its solidification after the dope is cast onto a supporting surface.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides poly(P-phenylene terephthalamide) (
Regarding a film made of PPTA (hereinafter referred to as PPTA) and its manufacturing method, more specifically, it is transparent and isotropically mechanical with excellent properties in both the longitudinal direction (hereinafter abbreviated as MD direction) and width direction (TD force direction). The present invention relates to a PPTA film exhibiting characteristics and excellent tear resistance, and a manufacturing method for obtaining the same.

(Prior art) PPTA has particularly excellent crystallinity and a high melting point, and due to its rigid molecular structure, it has heat resistance and high mechanical strength. It is a molecular material.

It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength modulus and strength, and have already been implemented industrially. There are few proposals, and there are still no known examples of practical use.

Problems with PPTA include that its useful high molecular weight polymer is poorly soluble in organic solvents, and strong inorganic acids such as concentrated sulfuric acid must be used as a solvent. , for example, Special Public Interest Publication 1986-45
Publication No. 421 discloses that a linearly coordinating aromatic polyamide with a halogen group introduced into its aromatic nucleus is copolymerized with an aromatic polyamide other than PPTA that has no substituents on its aromatic nucleus, thereby making it soluble in organic solvents. Attempts have been made to obtain films from it. However, since the monomer is expensive, this increases the cost and has the drawback of impairing the heat resistance and crystallinity of the linearly coordinated aromatic polyamide.

On the other hand, Japanese Patent Publication No. 59-14567 discloses a method of extruding an aromatic polyamide solution having optical anisotropy from a slit through a short air layer into a coagulation bath. The mechanical strength was strong only in the TD direction, but the mechanical strength in the TD direction perpendicular to this was extremely weak, and only a product that was easy to tear was obtained.

If the optically anisotropic dope of aromatic polyamide is simply extruded and solidified as it is, it will be excessively oriented in the extrusion direction and will easily become fibrillated, which is weak in the TD direction. Various methods of producing films have been studied in an attempt to improve them.

For example, Japanese Patent Publication No. 57-35088 discloses that an aromatic polyamide solution having optical anisotropy is extruded from a ring die, simultaneously cast in a doped state in two axes using an inflation method, and then wet coagulated. It is said that an isotropic film can be obtained by this method.However, this method has the disadvantage that it is difficult to obtain a transparent film with a uniform thickness and its mechanical strength, especially tear strength, is low.

Also, Japanese Patent Publication No. 59-5407, Japanese Patent Publication No. 54-132
No. 674 discloses that by mechanically applying a shearing force to an optically anisotropic or optically isotropic dope of a linear aromatic polyamide in a die in a direction perpendicular to the extrusion direction,
Although it has been proposed to orient the material in two axes, ie, in the extrusion direction and in a direction perpendicular to the extrusion direction during extrusion, the structure of the die is complicated and there are difficulties in industrial implementation.

Furthermore, J, Appl, Polym, Sci, vol. 2
7, No. 8.2965-2985 (1982)
For this purpose, two
It has been proposed to obtain an axially oriented film, but this film has isotropic but low mechanical strength;
When drafted, the mechanical strength in the MD direction is high, but the mechanical strength in the TD direction is extremely low.

Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linearly coordinated aromatic polyamide is heated until it becomes optically isotropic immediately before solidification, and then solidified to produce a transparent material with mechanical properties. It is described to obtain films that are isotropic. This method is an original method that goes against the conventional concept of achieving high performance by utilizing optically anisotropic doping. At the same time, it has been successfully avoided that the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded and solidifies as it is, resulting in an opaque film.

The film produced by the method described in Japanese Patent Publication No. 57-17886 has a tear resistance that is at a level that is suitable for general use in electrical applications, and is extremely superior in this respect. It was confirmed that this film is fundamentally different from the film disclosed in Japanese Patent Publication No. 14170/1983, which only cracks easily.

However, for special applications, such as applications where strong mechanical tension is applied intermittently,
The film produced by the method generally disclosed in the publication does not necessarily have satisfactory tear resistance.

(Problems to be Solved by the Invention) In view of the current state of the art, the present invention provides a PPTA film with significantly improved tear resistance and a method for producing the same, using PPTA whose industrial production has already begun. We aim to provide the following.

(Means for solving the problem) The present inventors have developed a method using high-quality PP with excellent tear resistance.
As a result of extensive research and improvement of the method disclosed in Japanese Patent Publication No. 57-17886 in order to obtain a TA film, the following knowledge was obtained.

That is, P according to the method of Japanese Patent Publication No. 57-17886.
When making a PTA film, it is important to adopt a method of casting an optically anisotropic dope onto the supporting surface and to allow a long and sufficient time from the time of optical isotropy to solidification to increase the durability of the resulting film. We discovered that this is surprisingly important in improving tear performance, and further discovered that the film made in this way has a unique planar orientation, especially in the amorphous part. It has been found that shrinkage generally occurs during the drying process, but if this is not limited, the flatness and transparency of the film will be slightly inferior. Based on these findings, the present inventors conducted further research and completed the present invention.

The spear 1 of the present invention is a polyamide film substantially made of poly(P-phenylene terephthalamide) having a logarithmic viscosity of 3.5 or more, in which X
The crystal orientation angle of 2θ≒23° by a line is 70° or more, and the ratio of the minimum intensity to the maximum intensity in the angular distribution of fluorescence intensity due to parallel polarized light incident at right angles to the film surface is 0.7 to 1. The second aspect of the present invention is a polyamide film characterized by having a logarithmic viscosity of 3.5.
Poly(P-phenylene terephthalamide) and 95
An optically anisotropic dope consisting essentially of sulfuric acid with a weight of % or more is cast onto a support surface while maintaining optical anisotropy, and the dope is converted to optically isotropic by moisture absorption and/or heating. In the method of manufacturing a polyamide film which is then solidified, the optically isotropic dope is held on the supporting surface for at least 5 minutes after conversion to optically isotropic until solidification, and the film is dried under conditions that limit shrinkage. This is a method for producing a polyamide film characterized by the following.

The PPTA used in the present invention is conveniently produced essentially from unilene diamine and terephthaloyl chloride by a low temperature solution polymerization method.

The degree of polymerization of the polymer of the present invention is 3.5 or more, since if it is too low, a film with good mechanical properties cannot be obtained.
Logarithmic viscosity Yinh (sulfuric acid ioo
A degree of polymerization is selected that gives a value measured at 30° C. by dissolving 0.5 g of mz-busy polymer.

The film of the present invention can achieve its purpose only if it satisfies the following two requirements.

First of all, as a film of the present invention, the following X
It must have plane orientation defined by the crystal orientation angle determined by line diffraction. That is, the crystal orientation angle with respect to the peak of 2θ≈23° in X-rays incident at right angles to the film surface is 70” or more.

There are two types of incident X-rays: when they are incident at right angles to the film surface (hereinafter referred to as the TV direction), and when they are incident parallel to the surface (hereinafter referred to as the TV direction).
(hereinafter referred to as the Sv direction).

The film of the present invention is 20 by X+11 from the TV direction.
It has a large diffraction peak at −23°, but this 2θζ23
The crystal orientation angle at ° should be greater than or equal to 70';
More preferably, it is 80" or more.

This is because if the crystal orientation angle of 2θζ23° is smaller than 70″, the vertical/curvature balance of the film properties will be lost.

The film of the present invention preferably has a crystal orientation angle of 60" or less with respect to the 2θζ18° peak in X-rays incident parallel to the film surface. This means that if this requirement is met, the film's mechanical This is because the physical properties, such as tensile strength and tensile modulus, become very large.

A known method can be used to measure the crystal orientation angle.
For example, the following method is used. Predetermined 20
A diffraction intensity curve is obtained by placing the counter at an angle of and rotating the film 180°.

In addition, for TV, the maximum intensity is centered around 90
The arc length in degrees of the diffraction photograph corresponding to the point indicating half the intensity of the baseline drawn between the highest and lowest intensity points of this curve (i.e. , 50% of the highest intensity baseline
(with respect to the point) and use it as the crystal orientation angle of the sample. During the measurement, the diffraction intensity can be measured by stacking several films if necessary.

In the film of the present invention, the ratio of the minimum intensity to the maximum intensity in the angular distribution of fluorescence intensity due to parallel polarized light incident perpendicularly to the film surface is within the range of 0.7 to 1.0. This measurement is performed using a polarized fluorophotometer (for example, FOM-2 model manufactured by JASCO Corporation). The polarizer and analyzer are placed parallel to each other, and the film sample is set between them with the surface perpendicular to the incident light beam. Since PPTA itself emits fluorescence,
There are no 8 rods that contain fluorescent substances. polarizer (and therefore analyzer)
Alternatively, the intensity of fluorescence generated at each angle while rotating the film is recorded. Figure 1 shows this plotted on a pie chart.

In FIG. 1, S indicates the minimum intensity and L indicates the maximum intensity. Therefore, S/L=0.7 to 1.0 is a film of the present invention, and S/L<0.7 is a film outside the present invention. The direction in which fluorescence is generated is considered to be related to the direction of orientation of molecular chains, whether crystalline or amorphous, in the measurement of the present invention. For films that meet the requirements as
It is presumed that the molecular chains are oriented almost randomly within the plane of the film.On the other hand, in films other than the present invention as shown in (b) of Figure 1, it is thought that so-called biaxial orientation is remarkable. It will be done. It has been found that such special orientation characteristics of the film of the present invention are closely related to the retention time of the dope in an optically isotropic state during film production. It is believed that this is related to the high tear strength. The film of the present invention preferably has a polarized fluorescence intensity ratio of 068-10.

The film of the present invention is preferably one having the following characteristics.

The film of the present invention has the following void number of 1.
It is preferable that the number of particles per trend is 2 or less. The number of voids is measured as follows. A film piece of an appropriate size is magnified from 100x to 400x using an ordinary optical microscope using transmitted light.
Observe at least 5 different fields of view at a magnification range of 1.2 times, count the number of voids with a major axis of 1 μ or more,
Converted per film surface Z IIE2. 1 piece/m
A film having a void count of more than 2 has poor mechanical properties, often resulting in decreased transparency, and also affects the accuracy of the unevenness on the film surface.

The film of the present invention preferably has a light transmittance of 70% or more. The light transmittance is measured as follows. A film is lowered onto the liquid cell of an ordinary photoelectric photometer (or spectrophotometer), a visible light beam with a wavelength of 600 nm is selected, and its transmittance is measured. One of the important features of the film of the present invention is its transparency.

The film of the present invention usually has a density of 1.370 to 1.
．． 405fi/c! This density value was measured at 30°C by the density gradient tube method using carbon tetrachloride-toluene. That's 1.43 to 1.4
This value is quite small compared to the range of 6.

When the density is less than 1.370, mechanical properties deteriorate,
If it exceeds 1.405, the film will have poor planar orientation and thus poor isotropy in mechanical properties. In any case, this low density results in a light and high-strength film.

Next, a method for obtaining such a PPTA film will be explained.

In the method of the present invention, it is first necessary to prepare an optically anisotropic dope of PPTA.

A suitable solvent for preparing the dope used for molding the P P 1' A film of the present invention is sulfuric acid with a concentration of 95% or higher. The dope of the present invention, which is difficult to dissolve with less than 95% sulfuric acid or has an abnormally high viscosity after dissolution, includes chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide,
A small amount of trihalogenated acetic acid or the like may be mixed.

Sulfuric acid can be used in a concentration of 100% by weight or more, but from the viewpoint of stability and solubility of the polymer, a concentration of 98 to 100% by weight is preferably used.

The polymer concentration in the dope used in the present invention is at room temperature (
A concentration that exhibits optical anisotropy at a temperature of about 20° C. to 30° C. or higher is preferably used, and specifically, it is used at a concentration of about 10% by weight or more, preferably about 12% by weight or more. . At polymer concentrations below this, ie, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the formed PPTA film often does not have desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20ff.
If % or less, especially for PI'TA with high '/inh, 18 M% or less is preferably used, and more preferably 16 M% or less is used.

The dope of the present invention may also contain conventional additives, such as fillers, anti-glare agents, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizers, etc.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, such as the method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, polymer It depends on the concentration, degree of polymerization of the polymer, content of non-solvent, etc., so by investigating these relationships in advance, optical anisotropic doping can be achieved by changing the conditions to optically anisotropic doping or optically isotropic doping. It is possible to change from tropic to optically isotropic.

Before molding and solidifying the dope used in the present invention, insoluble dust, foreign matter, etc. should be removed as much as possible by filtration, etc., and gases such as air generated or drawn in during melting should be removed. is preferred. Deaeration can be performed once the dope has been prepared, or can be achieved by performing it under vacuum (reduced pressure) from the stage of charging raw materials for preparation. Dawg preparation can be carried out continuously or batchwise.

The dope thus prepared is cast onto a support surface using, for example, a slit die while maintaining optical anisotropy. In addition, in the laboratory, it can be cast onto a support surface using a doctor knife. As the supporting surface, a drum, belt, plate-shaped object, etc. made of a material such as glass, stainless steel, mental, hastelloy, or fluorine resin, or coated with these materials or a noble metal such as gold or platinum, is selected.

The method of obtaining a transparent film with excellent mechanical properties according to the present invention is to cast a dope onto a support surface and then convert the optical anisotropy of the dope to optical isotropy prior to solidification.

To change optical anisotropy to optical isotropy, specifically, prior to coagulation of the optically anisotropic dope cast on the support surface, the concentration of the solvent that forms the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the dope phase to optically isotropic, or absorb moisture and heat simultaneously or sequentially. This can be achieved by using them together.

In particular, methods that utilize moisture absorption, including methods that use heating in combination, are effective in improving the optical isopower ratio of optical anisotropy and
It is useful because it can be done without causing decomposition.

To make the dope absorb moisture, air at normal temperature and humidity may be used, but preferably, humidified or heated and humidified air is used. Does humidified air have saturated vapor pressure? It may also contain water in the form of mist, or may be so-called water vapor. However, supersaturated steam at a temperature of about 45° C. or lower is not preferable because it often contains large particles of condensed water. Moisture absorption is usually carried out using humidified air at room temperature to about 180°C, preferably 50°C to 150°C.

In the case of a heating method, the heating means is not particularly limited;
A method of applying humidified air as described above to the casting dope,
Methods include irradiation with an infrared lamp and dielectric heating.

The cast dope is optically isotropic on the support surface, and its state is
After holding for at least 5 minutes, solidify.

Holding the dope in an optically isotropic state for more than 5 minutes is important to ensure that the PPTA molecules in the obtained film have a random planar orientation rather than a biaxial orientation, and this also improves the tear resistance of the film. The time period for which the optical force ratio can be maintained on the support surface is preferably 8 minutes or more.

In the present invention, the dope coagulating liquid that can be used is, for example, dilute sulfuric acid containing about 70% by weight or less of water, aqueous sodium hydroxide solution containing about 20% by weight or less, aqueous ammonia, about 1% by weight or less
These include 0% by weight or less of sodium sulfate, sodium chloride aqueous solution, and calcium chloride aqueous solution.

In the present invention, the temperature of the coagulating liquid is preferably as low as possible, preferably 15°C or lower, more preferably 5°C or lower. This is because the lower the coagulation bath temperature, the smaller the amount of voids generated within the film, the higher the transparency (light transmission''4), and the higher the mechanical performance such as strength.

Note that the lower limit of the coagulation bath temperature A is not particularly limited, and is up to the melting point (freezing point) determined by the composition of the coagulation bath.

Since the coagulated film as it is contains acid, it is necessary to wash and remove the acid as much as possible in order to produce a film whose mechanical properties are less likely to deteriorate due to heating. Specifically, it is desirable to remove the acid content to about 500 ppm or less.

Water is usually used as the cleaning liquid, but if necessary, hot water may be used, or washing may be performed by neutralizing with an alkaline aqueous solution and then using water or the like. Cleaning is carried out, for example, by running a film in a cleaning liquid or by spraying a cleaning liquid.

The washed film is then dried, if desired, by rolling the wet film in one or two directions before drying.
By stretching the film by a factor of about 0.01 to 1.4, the mechanical properties of the film can be improved.

Drying must be carried out under tension, at a constant length, or with slight stretching to limit shrinkage of the film.

If a film that has a tendency to shrink upon removal of the cleaning liquid (e.g., water) is dried without any restriction on shrinkage, it may not be profitable due to the formation of microscopically non-uniform structures (crystallization, etc.). The light transmission force of the film becomes smaller.

Furthermore, the flatness of the film may be impaired or the film may curl. To dry while limiting shrinkage, for example, a tenter dryer or drying between metal frames can be used. Other conditions related to drying are not particularly limited, such as heated gas (air, nitrogen, argon, etc.)
The drying temperature can be freely selected from methods such as drying, using room temperature gas, using radiant heat such as electric heaters and infrared lamps, and dielectric heating.The drying temperature is also not particularly limited, but as long as it is above room temperature. good. However, in order to increase the mechanical strength, a high temperature is preferable, and a temperature of 100° C. or more, more preferably 200'C or more is used. The maximum temperature for drying is not particularly limited, but considering drying energy and decomposability of the polymer, it is 500°C.
The following are preferred.

In producing the film by the method of the present invention, all of the above steps may be carried out batchwise or continuously, and the film may be produced while running continuously throughout the entire process. This is one of the preferred embodiments. Further, an oil agent, an identification dye, etc. may be added to the film in any step.

(Example) Examples and reference examples (manufacturing examples of PPTA) are shown below, but these reference examples and examples explain the present invention, and do not limit the present invention. In the examples, parts by weight or weight % are shown unless otherwise specified. Logarithmic viscosity ηinh is 98% sulfuric acid 100% polymer 0
．． 5g was dissolved and measured at 30°C in a conventional manner. The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm.

The thickness of the film was measured using a diamond gauge with a measuring surface of 21 m in diameter. Strength and elongation and modulus were measured using a constant speed elongation type strength and elongation measuring machine.
Cut into a rectangle of 10 mm, the initial grip length is 30 mm,
Draw a load-extension curve 5 times at a tensile speed of 30 m x 1 minute,
This is an upward calculation. To evaluate tear resistance performance, tear propagation resistance and end tear resistance were measured. The tear propagation resistance was measured according to J I SP 81.16-73, and the end tear resistance was measured according to J I S 02318-72, and the average value was recorded.

Reference Example (Production of PPTA) The following PPTA was obtained by a low temperature solution polymerization method. In the polymerization apparatus shown in Japanese Patent Publication No. 53-43986, N
-70 parts of anhydrous lithium chloride in 1000 parts of methylpyrrolidone
1 part, and then 48.6 parts of para-phenylene diamine. After cooling to 8°C, 91.4 parts of terephthalic acid dichloride was added at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese-like shape, so
The polymerization reaction product was discharged from the polymerization apparatus according to the method described in Japanese Patent No. 86, and immediately transferred to a two-screw closed kneader, and the polymerization reaction product was pulverized in the same kneader. Next, the finely pulverized product was transferred to a hexyl mixer, an approximately equal amount of water was added, and the mixture was further pulverized, filtered, washed several times in hot water, and dried in hot air at 110°C. '2inh is 50 light yellow PPTA
95 parts of polymer were obtained.

Note that polymers with different clusters can be easily obtained by changing the ratio of N-methylpyrrolidone and monomers (halaphenylene diamine and terephthalic acid dichloride), and/or the ratio between monomers.

Example 1 and Comparative Example 1 1 inh is 5.00P P '1'' A is 99.7%
of sulfuric acid at a polymer concentration of 13.0% under vacuum.
A dope with optical anisotropy was obtained at 0°C. The viscosity of this dope at room temperature was 14,000 voids. In order to facilitate film formation, this dope was filtered through a stainless steel non-woven fabric filter, placed in a beaker, and maintained at about 70°C.

At that time as well, the dope exhibited optical anisotropy and a viscosity of 4000 voids. This dope was placed on a glass plate at 30°C.
Casting was carried out using a doctor knife with a step of 1 mm.

The glass plate was placed in a desiccator and evacuated for about 20 minutes to degas the cast dope, and then air at about 70° C. and a relative temperature of about 90% was introduced into the desiccator. 40
It was found that the cast dope became transparent and isotropic within seconds.

Next, the glass plates were placed in water maintained at 2°C for varying times after isotropy. After about 20 seconds, the film peeled off from the glass plate. Place the film in water at about 15-20°C for about 2 hours, then put it in 2% NaOH aqueous solution for 30 minutes.
The sample was immersed for 1 minute, and then immersed again in a water tank at 15 to 20°C overnight for washing.

The next day, the film taken out from the aquarium was approximately 10crrL×
15Cr! Sandwiched between two L stainless steel frames, 250
The legs were dried in an air oven kept at ℃.

The results are summarized and shown in Table 1. In addition, for all films, the logarithmic viscosity '7 inh is 4.4 to 4.8, the light transmittance is 75 to 91%, the density is 1.38 to l, 409/
CIrl5, thickness 10-15 μm, 2θ? 1
The SV crystal orientation angle of so was in the range of 35-45°.

Also,? , 1, MD means the direction of the doctor knife, and TD means the direction perpendicular to it.

(hereinafter referred to as gold) Example 2 A PPTA polymer having a RI inh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 12.0% to obtain a dope with optical anisotropy at 60°C. The viscosity of this dope was measured at room temperature and was found to be 14,500 voids.

The dope was kept at about 70°C to facilitate film formation. It was also degassed under vacuum. This case also had optical anisotropy as described above, and the viscosity was 4200 voids.

A 1.5 m long curved pipe from the tank, through the filter, to the gear pump, to the die is kept at about 70°C, and 0.2 mm x 3
A die with a 00ml slit was cast onto a mirror-polished Hastelloy cracked belt (moving at 2m/min), and air at about 90°C, which is about 95% of the relative temperature, was blown to give the dope an optical uniformity. After comparison, the sample was held on the belt for about 7 minutes, and then introduced together with the belt into a 20Mk% sulfuric acid aqueous solution at 0°C to solidify. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. The washed film was placed in a tenter dryer and stretched by 5% in each of the width and length directions and dried first with hot air at 120°C and then with hot air at 220°C.The resulting 8.5 μm film was Table 2 shows the properties of a film with a thickness of .

Example 3 Example 2 was repeated, except that the coagulation bath was changed to a 10% sulfuric acid aqueous solution at -3° C., and tenter drying was carried out in both the width and length directions.

The results are shown in Table 2. The thickness of the film was 4 μm.

(hereinafter referred to as "Kinpaku") (Effects of the Invention) As shown in the examples, the film of the present invention has good mechanical properties such as high strength and high modulus that are not found in commercially available films, and moreover, It shows well-balanced physical properties in both the direction and the TD direction. In addition to these mechanical properties, it also has excellent electrical insulation, heat resistance, oil resistance,
It has pressure resistance, resistance to chemicals other than strong acids, and a dense structure.

Therefore, the film of the present invention can be suitably used for insulating materials, magnetic tapes, flexible printed wiring boards, side wave covering materials, filtration membranes, etc. of electrical equipment that rotates at high speed, and has another feature. Due to its excellent transparency, it is also useful for packaging materials, plate-making materials, photographic films, etc.

In particular, the film of the present invention not only has excellent transparency but also excellent tear resistance, so it is useful as electrical insulation films, magnetic tapes, and flexible printed wiring boards, and its tough properties are preferably utilized.

[Brief explanation of drawings]

Figure 1 shows the angular distribution of fluorescent light intensity due to parallel polarized light incident on the film surface at right angles, and the vertical direction is the MD direction of the film. In Figure 1, (a) is a film of the present invention, and (b) is a film other than the present invention. L...Maximum strength S...Minimum strength

Claims (2)

[Claims] (1) A polyamide film consisting essentially of poly(P-phenylene terephthalamide) with a logarithmic viscosity of 3.5 or more, which is 2
The crystal orientation angle of θ≈23° is 70° or more, and the ratio of the minimum intensity to the maximum intensity in the angular distribution of fluorescence intensity due to parallel polarized light incident at right angles to the film surface is 0.
A polyamide film characterized in that it has a molecular weight of 7 to 1.0. (2) An optically anisotropic dope consisting essentially of poly(P-phenylene terephthalamide) with a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is applied to the support surface while maintaining the optical anisotropy. In a method for producing a polyamide film, the dope is cast onto a support surface, converted to optically isotropic by moisture absorption and/or heating, and then solidified, in which the dope is cast on a support surface for at least 5 minutes from the time of conversion to optical isotropy until solidification. A method for producing a polyamide film, which is characterized by drying while retaining an optically isotropic dope and limiting shrinkage of the film.