JPH046737B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a film made of polyparaphenylene terephthalamide (hereinafter referred to as PPTA) and a method for producing the same, and more specifically, the present invention relates to a film made of polyparaphenylene terephthalamide (hereinafter referred to as PPTA) and a method for producing the same. The ulnar direction (hereinafter referred to as MD direction) and the width direction (hereinafter referred to as
(referred to as TD direction) exhibits excellent mechanical properties.
The present invention relates to a PPTA film and a manufacturing method for obtaining the same. (Prior art) Linearly coordinated aromatic polyamides, represented by PPTA, have particularly excellent crystallinity and a high melting point, and due to their rigid molecular structure, they have heat resistance and high mechanical strength. It is a polymer material that has received particular attention in recent years. It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been implemented industrially, but there are few proposals for application to films. There are still no known examples of practical use. The problem with PPTA is 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, in Japanese Patent Publication No. 56-45421, by copolymerizing a unit in which a halogen group is introduced into the aromatic nucleus of a linearly coordinating aromatic polyamide and an aromatic polyamide other than PPTA that does not have a substituent in the aromatic nucleus. Attempts have been made to make it soluble in organic solvents and 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 in which an aromatic polyamide solution having optical anisotropy is extruded from a slit through a short air space into a coagulation bath. Only the mechanical strength was strong, but the mechanical strength in the TD direction perpendicular to the mechanical strength was extremely weak and could only be easily torn. In this way, simply extruding an optically anisotropic dope of aromatic polyamide and solidifying it as is,
Because the film is excessively oriented in the discharge direction, it tends to become fibrillated and becomes weak in the TD direction. Various film manufacturing methods have been studied to improve this problem. For example, in Japanese Patent Publication No. 57-35088, an aromatic polyamide solution having optical anisotropy is extruded from a ring die, and after being simultaneously cast in a doped state in two axes using an inflation method, It is said that an isotropic film can be obtained by wet coagulation. However, this method has the disadvantage that it is difficult to obtain a film with uniform thickness and its mechanical strength is low. Also, Japanese Patent Publication No. 59-5407, Japanese Patent Publication No. 54-132674
In the publication, an optically anisotropic or optically isotropic dope of a linearly coordinated aromatic polyamide is mechanically applied with a shearing force in a direction perpendicular to the extrusion direction in a die, so that the dope is aligned with the extrusion direction during extrusion. Although it has been proposed that the die be oriented in two axes perpendicular to that direction, the structure of the die is complicated and there are difficulties in industrial implementation. Furthermore, J.Appl.Polym.Sci.vol, 27, No. 8,
P.2965-2985 (1982) proposes that a biaxially oriented film can be obtained by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated conical mandrel. However, this film has low isotropic mechanical strength, and when drafted, although it has high mechanical strength in the MD direction,
It was significantly lower in the TD direction. Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linear aromatic polyamide is coated immediately before solidification,
It is described that a transparent film having isotropic mechanical properties can be obtained by heating until it becomes optically isotropic and then solidifying it. 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 as relaxing the axial orientation, the liquid crystal domain structure of the optically anisotropic dope remained even after the dope was extruded, and succeeded in preventing it from solidifying into an opaque film. However, as mentioned above, this method has no choice but to use concentrated sulfuric acid or other inorganic strong acids as a solvent, so the polymer decomposition occurs when the optically anisotropic dope is heated to a temperature at which it becomes optically isotropic. Unavoidably, there is a problem in obtaining a film with high elongation, and if the film is simply heated to form an optically isotropic dope and then extruded, the flow orientation during extrusion is lower than that of an optically anisotropic dope. Although it is relaxed, the viscosity becomes extremely high, making it difficult to extrude it in the first place. (Problems to be solved by the invention) As described above, since the optically anisotropic dope has a domain structure in which polymers are aggregated as liquid crystals,
Even when the dope is made into a film, the domain structure remains, and the resulting film becomes opaque. If an attempt is made to use an optically isotropic dope to avoid this, the useful high molecular weight PPTM polymer will have an extremely high viscosity, and it will not be possible to form a film unless the polymer concentration is approximately 5% by weight or less. Films made from oriented dopes tend to produce voids during solidification, and their mechanical properties are also completely inadequate. The purpose of the present invention is to use PPTA, whose fibers are already produced industrially, to have excellent transparency as described above, and to produce a film not only in the MD direction but also in the TD direction.
It is an object of the present invention to provide a film that is sufficiently oriented in both the longitudinal and lateral directions, has excellent flatness, has high strength and elongation and modulus in both the longitudinal and lateral directions, and an industrial method for producing the same. (Means for solving the problem) The concept of the above-mentioned Japanese Patent Publication No. 17886-1986 is as follows.
While using a dope with a high polymer concentration, which is preferable for improving the mechanical properties of the film, we also applied the low viscosity of the dope due to the liquid crystal phenomenon naturally formed by PPTA to make it easier to dissolve, transport, and form the polymer. , the dope is heated for a short time just before final solidification to make it optically isotropic and to obtain a transparent film. The inventors of the present invention have diligently studied the application of this idea and overcome its shortcomings, and as a result of the incidentally discovered phenomenon and elucidation of its mechanism, the following novel film and its manufacturing method have been developed to solve the above-mentioned problems. This discovery led to the completion of the present invention. The polyparaphenylene terephthalamide film of the present invention is a film consisting essentially of polyparaphenylene terephthalamide having a logarithmic viscosity ηinh of 2.5 or more, and having a density of 1.365 g/cm ³ to 1.405
g/cm ³ and the number of voids is 5/mm ² or less,
The light transmittance is 55% or more, the crystal orientation angle of the (200) plane is 70° or more when X-rays are incident perpendicular to the film surface, and the crystal orientation angle of the (010) plane when X-rays are incident parallel to the film surface. is 60° or less and the elongation at break is 19% or more. In the film manufacturing method of the present invention, the logarithmic viscosity ηinh is
2.5 or more and at least one solvent selected from the group consisting of sulfuric acid, chlorosulfuric acid, and fluorosulfuric acid at a concentration of 98% by weight or more. Formed into a film on the supporting surface while maintaining anisotropy, absolute humidity 1g (water)/Kg (dry air)
or more and in an atmosphere with a relative humidity of 99% or less, after leaving the dope until it is substantially converted into an optically isotropic dope by absorbing moisture, or after absorbing moisture to the extent that it loses its optical anisotropy, or after absorbing moisture. After heating and converting the optically anisotropic dope that has absorbed moisture to a temperature at which it substantially changes into an optically isotropic dope while
It is characterized by solidifying, then washing and drying with limited shrinkage. The PPTA used in the present invention is substantially It is a polymer represented by, and is conveniently produced from conventionally known paraphenylene diamine and terephthaloyl chloride by a low-temperature solution polymerization method. The degree of polymerization of the polymer of the present invention is usually 2.5 or more, preferably 2.5 or more, because if it is too low, a film with good mechanical properties, which is the object of the present invention, cannot be obtained.
Logarithmic viscosity ηinh of 3.5 or higher (polymer 0.2 in 100 ml of sulfuric acid
A degree of polymerization is selected that gives a value measured at 30°C after dissolving g. The film of the present invention can achieve its purpose only if it satisfies the following four requirements. First of all, the density of the film must be in the range of 1.365 g/cm ³ to 1.405 g/cm ³ . This density value was measured at 30° C. using a density gradient tube method using carbon tetrachloride-toluene. This density range is 1.43 compared to that of known PPTA fibers.
This value is considerably smaller than the range of g/cm ³ to 1.46 g/cm ³ . The reason for this is not clear, but it is probably due to the plane orientation described later.
It is thought that compared to the axially oriented one, there are micro-gaps between molecules, resulting in a lower density. The density is
If it is less than 1.365g/ ^cm3 , the mechanical properties will deteriorate,
If it exceeds 1.405 g/cm ³ , the film will have poor planar orientation. In any case, this low density results in a light and high-strength film. Second, the number of voids described below must be 5/mm ² or less. The number of voids is measured as follows. A film piece of an appropriate size is observed in at least 5 different fields of view at a magnification ranging from 100x to 400x using a normal optical microscope using transmitted light, and the number of voids with a major axis of 30μ or more is determined. Count and convert it to 1 mm ² of the film surface. A film having more than 5 voids/mm ² has poor mechanical properties, lowers transparency, and in extreme cases, the film appears cloudy. Incidentally, in a film made from a normal optically isotropic dope, the number of voids of 50/mm ² or more is usually observed. Third, the film must have a light transmittance of 55% or more. Light transmittance is measured as follows. Attach a film to the place where the liquid cell of a normal photoelectric photometer (or spectrophotometer) is set,
Select visible light with a wavelength of 600 nm and measure its transmittance. One of the important features of the film according to the invention is its transparency. As mentioned above, the film obtained by directly extruding an optically anisotropic dope into a coagulation bath through a slight air gap is devitrified and usually has a light transmittance of 10% or less.
Although this light transmittance naturally decreases as the film thickness increases, the film according to the present invention has a transparency well above 55% up to the commonly used thickness of about 200 μm. Fourthly, the film of the present invention must have plane orientation defined by the crystal orientation angle determined by X-ray diffraction as described below. In other words, the crystal orientation angle of the (200) plane due to X-rays incident at right angles to the film surface is
70° or more, and the crystal orientation angle of the (010) plane measured by X-rays incident parallel to the film surface must be 60° or less. As shown in FIG. 1, the incidence of X-rays can be divided into two cases: one incident perpendicular to the film surface (hereinafter referred to as the TV direction) and the other incident parallel to the surface (hereinafter referred to as the SV direction). The crystal structure of PPTA has been widely discussed; for example, there is a study by Takayanagi et al. (J. Appl. Polym. Sci., Vol. 23, p. 915 (1979)). The film of the present invention has a large diffraction peak at 2θ≒23°, which is the reflection of the (200) plane by X-rays from the TV direction, but the crystal orientation angle at 2θ≒23° is
It must be at least 70°. That is, this orientation angle appears almost as a Debye ring in the diffraction photograph.
Furthermore, a large diffraction peak at 2θ≒18°, which is a reflection of the (010) plane due to incidence from the SV direction, appears on the equator line, but the crystal orientation angle at this 2θ≒18° needs to be 60° or less. It can be said that the film of the present invention has a planar orientation structure only when both of these crystal orientation angles are satisfied, and a film with a crystal orientation angle outside of this range cannot be said to have planar orientation. Therefore, the object of the present invention is to
A film with high mechanical properties in the MD and TD directions cannot be obtained. A known method can be used to measure the crystal orientation angle, for example, the following method. Place the counter at the specified 2θ angle and insert the film.
Obtain the diffraction intensity curve by rotating 180°.
For TVs, rotate 90 degrees from front to back, centering on the highest intensity. The highest intensity of this curve,
Measure the arc length in degrees in the diffraction photograph corresponding to the point showing half the intensity with respect to the baseline drawn between the lowest intensity points (i.e., the angle with respect to the 50% point with respect to the highest intensity baseline). , which is taken as the crystal orientation angle of the sample. During measurement, the diffraction intensity can be measured by overlapping the films if necessary. When a cross-section of the film of the present invention was torn and observed with a scanning electron microscope, a parallel layered structure was observed on the surface of the film, and this is considered to be one of the facts supporting the planar orientation structure of the film of the present invention. Ru. Furthermore, the film of the present invention has an elongation at break of 19% or more. Next, a simple method for obtaining such a PPTA film will be described. Specifically, one method is to hold an optically anisotropic dope in the form of a film on a support surface, and in that state, the optically anisotropic dope is converted into an optically isotropic dope by absorbing moisture. After the optically anisotropic dope on the surface absorbs moisture, or while absorbing moisture, it is converted by heating to a temperature at which it changes to an optically isotropic dope. Suitable solvents for preparing the dope for forming the PPTA film of the present invention include sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, or mixtures thereof at a concentration of 98% by weight or more. Sulfuric acid of 100% or more, ie, fuming sulfuric acid, trihalogenated acetic acid, etc., may be mixed and used within a range that does not impair the effects of the present invention. The concentration of the polymer in the dope used in the present invention is preferably at least a concentration that exhibits optical anisotropy at room temperature (approximately 20 to 30°C) or higher, and specifically, approximately 10% by weight or more. , preferably about
Used at 12% by weight or more. At polymer concentrations below this, that is, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the molded
PPTA films often no longer have favorable mechanical properties. The upper limit of the polymer concentration in the dope is not particularly limited, but is usually 25% by weight.
Below, 20% by weight especially for PPTA with high ηinh
The following are preferably used. The dope of the present invention contains conventional additives, such as fillers, anti-glare agents, UV stabilizers, heat stabilizers,
Antioxidants, pigments, solubilizing agents, etc. may be mixed. Whether the dope is optically anisotropic or optically isotropic is
It can be investigated by known methods, such as the method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, polymer concentration, degree of polymerization of the polymer, content of non-solvent, etc. Therefore, by examining these relationships in advance, optical anisotropy can be changed to optical isotropy by creating optically anisotropic dope and changing the conditions to optically isotropic dope. The method of obtaining a transparent film with excellent mechanical properties according to the present invention is to form a dope into a film on a supporting surface, and then convert the dope from optically anisotropic to optically isotropic prior to solidification. In order to change optical anisotropy to optical isotropy, the optically anisotropic dope formed into a film on the supporting surface is made to absorb moisture to lower the concentration of the solvent forming the dope before solidifying. The dope can be changed to an optically isotropic region by changing the solubility and polymer concentration, or the dope can be heated to increase its temperature by heating in addition to changing the optically anisotropic region of the dope due to moisture absorption. This can be achieved by transitioning the phase to optical isotropy. Absolute humidity 1 is the method for making dope absorb moisture.
g (water)/Kg (dry air) or more, and relative humidity
This can be achieved by passing through an atmosphere of 99% or less. If the absolute humidity is less than 1g (water)/Kg (dry air), the rate of moisture absorption is slow and it is not practical, especially when converting an optically anisotropic dope to an optically isotropic dope only by absorbing moisture near room temperature.
(water)/Kg (dry air) or more, more preferably 10 g (water)/Kg (dry air) or more, particularly preferably 20 g (water)/Kg (dry air). Further, actively applying humidification to a normal humid atmosphere is a desirable embodiment because it shortens the time until optical isotropy is achieved, and when heating is used in combination, the heating temperature can be lowered. If the relative humidity exceeds 99%, water condenses on the dope at low temperatures, leading to polymer precipitation and loss of flatness of the film, which is undesirable. In addition, in a method that uses both moisture absorption and heating after moisture absorption, for example, when sulfuric acid is used as a solvent, the optical anisotropy substantially disappears, and the temperature at which the dope converts to optical isotropy is the temperature at which the polymer concentration, degree of polymerization of the polymer,
The sulfuric acid concentration varies depending on the thickness of the dope and the degree of moisture absorption, but it is usually preferably about 45°C or higher, and the upper limit is when considering the degradability of the polymer.
Generally, it is preferable that the temperature is not too high, and it is preferable that the temperature of the film-like dope is selected so as not to exceed 200°C. An important feature of the production method of the present invention is that PPTA absorbs moisture when making the optically anisotropic dope optically isotropic. As a result, a film with excellent transparency and high strength and elongation can be produced industrially and easily without impairing the physical properties of the film. Although the mechanism of optical isotropy caused by this moisture absorption is not necessarily clear, it is probably because the liquid crystal region of the PPTA-solvent system is considerably reduced due to the decrease in polymer concentration and solvent concentration due to moisture absorption. This moisture absorption alone is sufficient to achieve optical isotropy, but if this is further accompanied by heating, isotropy can be achieved in a short period of time. This method is particularly effective when the dope is thick. If this optical isotropy is achieved only by heating without moisture absorption, heating at high temperatures and for a long time will be required, and the resulting film will also have poor physical properties due to partial decomposition of the polymer. Cheap. In the present invention, the dope coagulating liquid can be used, for example, water, dilute sulfuric acid of about 70% by weight or less,
Examples include aqueous sodium hydroxide solutions and aqueous ammonia of up to about 20% by weight, aqueous sodium chloride solutions and aqueous calcium chloride solutions of up to about 50% by weight.
The temperature of the coagulation bath is not particularly limited, and is usually in the range of about -5 to 50°C. Since the solidified film as it is contains acid, it is necessary to wash and remove the acid content 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 oxidation to about 500 ppm or less.
Water is usually used as the cleaning liquid, but if necessary, warm water may be used, or washing may be performed with water after neutralization with an alkaline aqueous solution. Cleaning is carried out, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The washed film is then dried. Drying here refers to the operation of removing cleaning liquid etc. adhering to the film. Any method may be used as long as the cleaning liquid etc. can be removed, such as air drying at room temperature,
Any method may be used, such as drying under a heated inert gas atmosphere, such as air, nitrogen, or argon, drying on a heated roll, or drying under a heated atmosphere using a tenter. Further, in order to prevent the film from wrinkling or to improve the film's flatness, drying must be carried out under tension or at a constant length, with the shrinkage of the film being restricted. The drying temperature is not particularly limited, but
In order to effectively improve the mechanical strength, a high temperature is preferred, and a temperature of 100° C. or higher, more preferably 200° C. or higher, is used. The maximum temperature for drying is not particularly limited, but considering the drying energy and degradability of the polymer, the maximum temperature is 500
℃ or less is preferable. In producing a film by the method of the present invention,
All of the above steps may be carried out batchwise or continuously, and one preferred embodiment is to manufacture the film while running it continuously throughout the entire process. Further, an oil agent, an identification dye, etc. may be added to the film in any step. (Example) Below are examples and reference examples (manufacturing example of PPTA)
However, these reference examples and examples are for explaining the present invention, and are not intended to limit the present invention. In the examples, parts by weight or weight % are shown unless otherwise specified. Logarithmic viscosity ηinh is 98%
0.2 g of polymer was dissolved in 100 ml of sulfuric acid and measured at room temperature at 30°C. The viscosity of the dope is measured using a B-type viscometer.
Measurements were made at a rotation speed of 1 rpm. The thickness of the film is
Measurements were made using a dial gauge with a measuring surface of 2 mm in diameter. Strength and elongation and modulus are measured using a constant speed extension type strength and elongation measuring machine.
Cut out a rectangle, draw a load-extension curve 5 times with an initial grip length of 30 mm and a pulling speed of 30 mm/min.
It was calculated from this. Note that when the films of all Examples were observed under a polarizing microscope, no dense striped pattern was observed in any of the films having a light transmittance of 55% or more. Reference Example (Production of PPTA) PPTA was obtained as follows by a low temperature solution polymerization method. In a polymerization apparatus shown in Japanese Patent Publication No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine were dissolved therein. After cooling to 8° C., 91.4 parts of terephthalic acid dichloride was added all 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 Publication No. 53-43986, and immediately transferred to a twin-screw closed kneader. The polymerization reaction product was finely pulverized. Next, the finely pulverized product was transferred to a Heshisiel mixer, and approximately the same amount of water was added thereto for further pulverization, followed by filtration, washing in hot water several times, and drying in hot air at 110°C. 95 parts of pale yellow PPTA polymer with ηinh of 6.5 was obtained. Note that polymers with different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and monomers (paraphenylenediamine and terephthalic acid dichloride), and/or the ratio between monomers. Example 1 PPTA having an ηinh of 5.0 was dissolved in 99.7% sulfuric acid at a polymer concentration of 13.0% to obtain a dope with optical anisotropy at 50°C. The viscosity of this dope at room temperature is
It was 14,000 poise. In order to make film formation easier,
This dope was placed in a beaker and kept at approximately 70°C. At that time as well, the dope exhibited optical anisotropy and a viscosity of 4000 poise. This dope was applied onto a glass plate at 30° C. with an applicator having a step of 0.1 mm. Immediately after application, a 15 cm diameter glass shear was placed over a portion of the dope to block moisture from the air. The absolute humidity of this glass plate is 8.7g.
(water)/Kg (dry air) at 60℃ in the atmosphere.
I left it there while keeping it warm. After 2 minutes, the area other than the area surrounded by the shear became transparent, so the shear was removed and the entire glass plate was
immersed in a water bath at °C. The film thus solidified remained opaque in the area surrounded by the shear, but the rest remained transparent as a result of conversion from optical anisotropy to isotropy during the doping step. The periphery of this coagulated film was fixed to a metal frame and heated to 120°C.
dried in an air oven. During drying, the film tore along the circumference where the shear dish was placed, so I re-formed the film again, and after solidifying, it was difficult to cut the opaque part inside the shear dish and the other transparent parts, so I fixed the metal frame separately. Drying was carried out in the same manner. The properties of both films are shown in Table 1.

[Table] Comparative Example 1 In order to make the opaque area surrounded by the shear in Example 1 transparent by the method disclosed in Japanese Patent Publication No. 57-17886, the glass plate was covered with the shear immediately after applying the dope, and then the glass plate was covered with the shear. When heated in an air oven at 130°C, it finally became transparent after 7 minutes. Table 2 shows the properties of the film that was coagulated, washed, and dried in the same manner as in Example 1. It can be seen that ηinh has decreased, and as a result of partial decomposition of the polymer, the strength has also decreased. That is, in Example 1, the area that absorbed moisture became transparent in 60℃ x 2 minutes, whereas the area that was covered with shear film and did not absorb moisture took 130℃ x 7 minutes to become transparent, and the obtained film also had poor physical properties. It was inferior. In order to repeat the method disclosed in Japanese Patent Publication No. 57-17886, an optically anisotropic dope prepared by dissolving PPTA with ηinh=4.3 in 99.0% sulfuric acid was applied to a glass plate in the same manner as in Example 1. Immediately covered with shear glass and kept at 95°C to make it transparent. After about 2 minutes, the dope in the area covered with the shear became transparent, so the shear was removed and the dope was placed in water at about 10°C to coagulate. A dry film was obtained in the same manner as in Example 1. The part of the film that was covered with a shear coat and made transparent only by heating was not covered with a shear coat (therefore, some transparency was also done by humidification)
Transparency was slightly lower than that of the film, with a light transmittance of 43%. Other properties of the film from the part covered with shear are: ηinh = 4.2, strength 25
Kg/mm ² (MD) and 23Kg/mm ² (TD), elongation
They were 4.7% (MD) and 4.8% (TD).

[Table] Example 2 A PPTA polymer of ηinh or 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 13.0% to obtain a dope with optical anisotropy at 60°C. When the viscosity of this dope was measured at room temperature, it was 14,500 voids. To make it easier to form a film, put this dope in a tank and heat it for about 70 minutes.
It was kept at ℃. This case also had the same optical anisotropy as above, and the viscosity was 4200 poise. Approximately 70 1.5m bent pipes from the tank to the die via the gear pump
℃ and cast from a die with a 0.2 mm x 300 mm slit onto a mirror-polished Hastelloy belt, with an absolute humidity of 15.4 g (water)/Kg (dry air).
The dope was exposed to air at 25° C. for 200 seconds, and after the dope became transparent, it was coagulated in 3% sulfuric acid at 8° C. The coagulated film was washed overnight with water at room temperature and then dried at a fixed length with hot air at 200°C.
The properties of this film are shown in Table 3.

[Table] Comparative Example 2 In Example 2, instead of casting the dope onto the belt, the dope was poured at 8°C through a 1cm air layer at 3°C.
% sulfuric acid for direct coagulation. Table 3 shows the properties of the film that was processed in the same manner as in Example 2. The film was completely opaque with the liquid crystal domains remaining, and the strength in the TD direction was very weak. It was easily fibrillated. Example 3 Polymer concentration of PPTA with ηinh of 6.2 at 60℃
Dissolved in 99.6% sulfuric acid to a concentration of 14.0%. This dope exhibits optical anisotropy at 80℃ and has a viscosity of 3300
It was poise. This dope was applied onto a glass plate at 25° C. using an applicator with a 0.1 mm step. After that, absolute humidity 7.5g (water)/Kg
When the dope was collected and analyzed after being left in air at 18°C (dry air) for one minute, it was found that it had absorbed moisture to the extent that the sulfuric acid concentration had dropped to 94.4%. However, the dope was still opaque at this point, and when it was then heated to 120° C. for 90 seconds in a dry nitrogen oven, it became optically isotropic and became transparent. After coagulating this with 15°C water, it was neutralized with a 5% casein soda aqueous solution, and then further washed with water to bring the acid concentration to 400 ppm. 250% of this wet film
Table 3 shows the properties of the film after constant length drying at ℃ for 30 minutes. Comparative Example 3 After applying the optically anisotropic dope of Example 3 to a glass plate in the same manner, it was immediately placed in a dry nitrogen oven at 120°C and kept for 90 seconds. Although this dope was not optically isotropic, it was coagulated, neutralized, washed with water, and dried in the same manner as in Example 3. The properties of this film are shown in Table 3. When the surface of this opaque film was observed using a scanning electron microscope, numerous irregularities measuring 10 to 20 microns were observed. This is thought to correspond to one unit of a liquid crystal domain, and was not observed at all in the transparent film in which the domains were dissolved. Example 4 PPTA having an ηinh of 3.4 was dissolved in 99.5% sulfuric acid so that the polymer concentration was 15.0%. This dope exhibited optical anisotropy at 60°C and had a viscosity of 2400 poise. From the tank to the die via the gear pump
A 1.5 m bent pipe was kept at 60°C and the optical fiber was placed on a rotating drum with a mirror-polished tantalum lining and a mirror-polished tantalum lining, about 1/3 of which was immersed in water from a die with a 0.1 mm x 800 mm slit. Cast anisotropic dope, absolute humidity 6.6g (water)/Kg (dry air) 15
After keeping it in air at ℃ for 40 seconds, it was passed through a zone blowing hot air at 140℃ for 4 seconds, resulting in an optically isotropic transparent dope. however
It did not become transparent with hot air at 120℃. The resulting transparent dope was further heated at 5°C on a rotating drum.
coagulated in water. After that, it was treated in a continuous process consisting of water washing, neutralization, and water washing steps, and the acid concentration was adjusted to 450 ppm. This wet film was heated to 300℃.
Table 3 shows the properties of the film dried for 20 minutes at a constant length. Example 5 Using the same dope as in Example 4, after casting on the same rotating drum from the same slit die, when running in the same atmosphere of air, the absolute humidity was reduced to about 10 g (water)/Kg using a commercially available humidifier. (dry air)
A box adjusted to 70°C was set up in the middle, and while running through the zone for 20 seconds, it took 40 seconds from the casting point to the hot air zone, as in Example 4, and then a zone where hot air at 70°C was blown. When the dope was passed through the dope for 4 seconds, an optically isotropic transparent dope was obtained. Subsequent coagulation, washing with water,
The drying process was carried out in exactly the same manner as in Example 4. The properties of the obtained film are shown in Table 3. Comparative Example 4 PPTA having an ηinh of 4.6 was dissolved in 99.8% sulfuric acid so that the polymer concentration was 4.0%. This dope is
It was optically isotropic at 50°C and had a viscosity of 7100 poise. This dope was cast onto a belt from a die in the same manner as in Example 2, exposed to the same humidity-controlled air, and then coagulated, washed and dried in exactly the same manner to obtain a film. Table 4 shows the properties of this slightly cloudy-looking transparent film.

[Table] Example 6 A PPTA polymer having an ηinh of 6.5 dl/g was dissolved in 99.7% sulfuric acid at a polymer concentration of 12.0% to obtain a dope with optical anisotropy at 60°C. When the viscosity of this dope was measured at room temperature, it was 16,300 poise. To facilitate film formation, this dope was degassed under vacuum while being maintained at approximately 80°C. This case also had optical anisotropy as above, and the viscosity was 6400 poise. The 1.5m curved pipe from the tank through the filter to the gear pump to the die is maintained at approximately 75℃.
The cast dope is cast from a die with a 0.2 mm x 300 mm slit onto a mirror-polished Hastelloy belt (moving at 2 m/min) and blown with air at about 85°C and a relative humidity of about 90%. It was made optically isotropic (retention time of about 12 seconds), and then introduced together with the belt into 10% by weight aqueous sulfuric acid 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 30°C. Put the washed film into a tenter dryer and dry it at a fixed length at 150℃ for the first time.
It was then dried with hot air at 220°C. The properties of the obtained film are shown in Table 5.

[Table] Examples 7 to 10 A PPTA polymer having an ηinh of 5.7 dl/g was dissolved in 99.3% sulfuric acid at a polymer concentration of 12.3% to obtain a dope with optical anisotropy at 60°C. This dope at about 80℃
It was degassed under vacuum while maintaining the temperature. This case also had optical anisotropy and a viscosity of 5800 poise. The 1.5m bent pipe that passes from the tank through the filter to the die via the gear pump is maintained at approximately 75℃, and is heated to 0.3mm x
Cast from a die with slits of 300 mm (Examples 7 and 8) and 0.2 mm x 300 mm (Examples 9 and 10) onto a mirror-polished tantalum belt (distance between the bottom edge of the die and the belt surface is approximately 1 cm). Then, the cast dope is made optically isotropic by blowing high temperature and high humidity air.
Together with the belt, it was introduced into water at 10°C to solidify. The temperature and humidity conditions of the air used to make the dope optically isotropic, and the time period during which the cast dope was exposed to high-temperature, high-humidity air to make the dope optically isotropic are summarized in Table 6 together with the results. Note that the time was adjusted by changing the moving speed of the belt. The coagulated film was then peeled off from the belt and washed with warm water at about 30°C, a 3% aqueous solution of caustic soda at room temperature, and water at room temperature in this order. The washed film was placed in a tenter dryer and dried at a fixed length, first with hot air at 150°C and then with hot air at 220°C. The properties of the obtained film are shown in Table 6.

【table】

[Table] (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 also has good mechanical properties in the MD direction. Exhibits extremely well-balanced physical properties in the TD direction. In addition to these mechanical properties, it also has excellent electrical insulation, heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and dense structure. Therefore, the film of the present invention can be suitably used for high-speed rotating electrical equipment, insulating materials for capacitors, magnetic tapes, flexible printed circuit boards, wire coating materials, filtration membranes, etc. Due to its excellent transparency, it is also useful for packaging materials, plate-making materials, photographic films, etc. A PPTA film with such excellent properties can be produced by a method that is extremely easy to implement industrially and does not require the use of a biaxial stretching machine.
One of the important effects of the present invention is that it can be manufactured.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the incident direction of X-rays when determining the crystal orientation angle.

Claims (1)

[Claims] 1. A film substantially consisting of polyparaphenylene terephthalamide having a logarithmic viscosity ηinh of 2.5 or more, the density of which is in the range of 1.365 g/cm ³ to 1.405 g/cm ³ , The number of voids is less than 5/ ^mm2 , the light transmittance is more than 55%, and the X incident perpendicularly to the film surface
The crystal orientation angle of the (200) plane measured by X-rays is 70° or more, the crystal orientation angle of the (010) plane measured by X-rays incident parallel to the film surface is 60° or less, and the elongation at break is 19%.
A polyparaphenylene terephthalamide film characterized by the above. 2. Optical anisotropy comprising polyparaphenylene terephthalamide having a logarithmic viscosity ηinh of 2.5 or more and at least one solvent selected from the group consisting of sulfuric acid, chlorosulfuric acid, and fluorosulfuric acid with a concentration of 98% by weight or more. The dope was formed into a film on the supporting surface while maintaining its optical anisotropy, and the absolute humidity was 1 g.
(water)/Kg (dry air) or more and relative humidity 99%
After leaving the dope in the following atmosphere until the dope is substantially converted into an optically isotropic dope by moisture absorption,
Alternatively, after absorbing moisture to the extent that it loses optical anisotropy, or after absorbing moisture and heating to a temperature at which the optically anisotropic dope that has absorbed moisture is converted into an optically isotropic dope, solidifying the dope. , followed by washing and drying while limiting shrinkage.