JP2912877B2 - Aromatic polyamide film and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film comprising a para-oriented aromatic polyamide and a method for producing the same, and more particularly, to a longitudinal direction of the film (referred to as an MD direction). The present invention relates to a thin and highly transparent para-oriented aromatic polyamide film exhibiting excellent mechanical properties in both a width direction and a width direction (referred to as a TD direction) and having a small thickness unevenness and high transparency. [0002] Poly (p-phenylene terephthalamide) (hereinafter referred to as P
PTA) is a polymer material which has particularly excellent crystallinity and a high melting point, and has a high heat resistance and a high mechanical strength because of its rigid molecular structure. . Further, it has been reported that fibers spun from a concentrated solution showing its optical anisotropy exhibit high strength and modulus, and have already been industrially implemented.
There are few proposals for application examples to films, and practical examples have not yet been known. [0003] Problems with PPTA include that useful high molecular weight polymers are poorly soluble in organic solvents, and that strong inorganic acids such as concentrated sulfuric acid must be used as solvents. For example, JP-B-56-45421 discloses a linear coordinating aromatic polyamide obtained by introducing a halogen group into the aromatic group,
Attempts have been made to copolymerize an aromatic polyamide having no substituent on an aromatic other than TA to make it soluble in an organic solvent and obtain a film therefrom. But,
This is disadvantageous in that the cost is high because the monomer is expensive, and the heat resistance and crystallinity of the linear coordinating aromatic polyamide are degraded. On the other hand, JP-B-59-14567 discloses a method in which an aromatic polyamide solution having optical anisotropy is extruded from a slit through a short air layer into a coagulation bath. Only the mechanical strength in the MD direction was strong, and the mechanical strength in the TD direction orthogonal thereto was extremely weak, and only those that were easy to avoid were obtained. In this way, simply extruding the optically anisotropic dope of the aromatic polyamide and coagulating it as it is is likely to be excessively oriented in the discharge direction and easily fibrillated and weak in the TD direction. Various film production methods have been studied. [0005] For example, Japanese Patent Publication No. 57-35088 discloses that an aromatic polyamide solution having optical anisotropy is extruded from a ring die and is simultaneously cast in a biaxial direction in a dope state by an inflation method. It is stated that an isotropic film can be obtained by wet solidification. However, in this method, it is difficult to obtain a transparent film having a uniform thickness, and there is a drawback that mechanical strength, particularly tear strength, is low. In Japanese Patent Publication No. Sho 59-5407 and Japanese Patent Laid-Open Publication No. Sho 54-132677, an optically anisotropic or optically isotropic dope of a linear coordinating aromatic polyamide is formed in a die in the direction of extrusion. It has been proposed to mechanically apply a shearing force in a right angle direction to orient the material in the biaxial direction of the extrusion direction and the right angle direction at the time of extrusion. However, the structure of the die is complicated and there is a problem in industrial implementation. . Further, it is difficult to obtain a film having a high tear strength by a method in which orientation is performed by a shearing force. [0007] Further, J.I. Appl. Polym. Sc
i. vokl. 27, no. 8. P. 2965-298
6 (1982) proposes to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto a conical mandrel coated with oil. The mechanical strength is low, though isotropic, and when drafting, the mechanical strength in the MD direction is high, but the mechanical strength in the TD direction is remarkably low. Difficult to reduce spots. Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linear coordinating aromatic polyamide is heated immediately before coagulation until it becomes optically isotropic, and then coagulated, whereby a transparent and mechanically doped dope is obtained. It is described that a film having isotropic physical properties is obtained. This method is an original one against the general concept of obtaining high performance by utilizing the conventional optically anisotropic doping, thereby relieving extreme uniaxial orientation of the optically anisotropic doping. At the same time, the optically anisotropic doped liquid crystal domain structure remains after extruding the dope and succeeds in avoiding solidification to form an opaque film. However, there is no specific disclosure of a transparent film that is extremely thin and has little unevenness in thickness. SUMMARY OF THE INVENTION An object of the present invention is to provide a film which is extremely thin, has little unevenness of thickness, has high transparency and is excellent in flatness, using a para-oriented aromatic polyamide. . Means for Solving the Problems The present inventors have conducted intensive studies to obtain a para-oriented aromatic polyamide film meeting the above object, and have obtained the following findings. That is,
A technique disclosed in Japanese Patent Publication No. 57-17886, ie, an optically anisotropic dope of PPTA is prepared, and then this is optically isotropic and solidified to obtain a transparent para-oriented aromatic material having excellent mechanical performance. In the method for producing an aromatic polyamide film, after the dope is separated from the die, adhered to a support surface as short as possible, solidified under specific conditions by optical isotropy, washed, and shrinkage occurring in a drying process It was found that a novel film having an extremely thin thickness and a small thickness unevenness can be obtained with extremely high transparency and flatness by conducting the above process, and as a result of further studies, the present invention was completed. The invention claimed in the present application to achieve the above object is as follows. (1) A film made of a substantially para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more, having a thickness of 8 μm or less, and having a thickness unevenness of the film of 10% or less (excluding 5% or less) A) an aromatic polyamide film; (2) An optically anisotropic dope consisting essentially of a para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is added to a die while maintaining the optical anisotropy. A method for producing a film in which the dope is cast on a moving supporting surface, and the dope is optically isotropically converted by moisture absorption and / or heating and then solidified, wherein the dope is 30 mm or less (excluding 8 mm or less) from a die. After making contact on the support surface at a distance, converted to optically isotropic, then 5 ° C.
After coagulating in the following coagulating liquid, washing and stretching
320 with limited shrinkage of the film without
A method for producing an aromatic polyamide film, characterized by drying at a temperature of at least ℃. The para-oriented aromatic polyamide used in the present invention, PPTA as its representative polymer, is substantially: It is a polymer represented by the following formula, and is conveniently produced from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low-temperature solution polymerization method.
If the polymerization degree of the polymer of the present invention is too low, a film having good mechanical properties cannot be obtained, so that the logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (100 ml of sulfuric acid)
Of a polymer having a degree of polymerization which gives 0.3 g of a polymer dissolved in water at 30 ° C.). The upper limit of the degree of polymerization of the polymer is not limited as long as it can be produced industrially. The film of the present invention can achieve the object only when the following requirements are satisfied. First,
Next, a film having a thickness of 8 μm or less is selected as the film of the present invention. Films with a thickness exceeding 8 μm
For example, when used as a capacitor film, in order to make a capacitor with the same capacity as a thin film, it is generally necessary to increase the electrode area in proportion to the square of the thickness. Lightweight and large capacitance cannot be obtained. Although there is no particular lower limit on the thickness of the film, handling is difficult if the film is too thin. When the film of the present invention is used for a capacitor, for example, the thickness is preferably 5 μm or less. Second, the film of the present invention has a thickness unevenness of 10% or less (however,
Excluding 5% or less) . This requirement is indispensable for producing a capacitor having the same capacitance, for example, in the case of a capacitor film as described above. If a capacitor with a large unevenness in film thickness is used as a capacitor, not only will the yield be high and productivity will deteriorate,
Since a space is generated in the capacitor, vibration of the film is generated by applying an AC electrode, and a sound corresponding to a frequency may be generated. The thickness and thickness unevenness referred to in the present invention can be measured, for example, by using a capacitance-type contact thickness meter (type CL-23 manufactured by Ono Sokki Co., Ltd.).
0), the average value of the thickness at 10 measurement points arbitrarily selected from the film, and (maximum value−minimum value)
/ Average value × 100. The film of the present invention,
It has high transparency and smooth flatness. Also, the film of the present invention is preferably substantially free of voids. Further, the film of the present invention generally has a density in the range of 1370 to 1420 g / cm ³ . This density value was measured at 30 ° C. by a density gradient tube method using carbon tetrachloride-toluene. Scope of this density is considerably smaller compared to that of known PPTA fiber is in the range of 1.43 g / cm ² of 1.46 g / cm ^2. If the density is less than 1370 g / cm ² , the mechanical properties deteriorate, and if it exceeds 1420 g / cm ² , the film loses the isotropy of the mechanical properties according to the plane orientation. In any case, since the density is so small,
A light and high strength film will be obtained. The film of the present invention preferably has a plane orientation defined by a crystal orientation angle by X-ray diffraction described below. That is, the crystal orientation angle related to the peak at 2θ ≒ 23 ° due to X-rays incident perpendicular to the film surface is 30 ° or more, and the crystal orientation angle related to the peak at 2θ ≒ 18 ° due to the X-rays incident parallel to the film surface. 60
° or less. The incidence of X-rays is classified into a case where the X-ray is incident on the film surface at a right angle (hereinafter referred to as TV direction) and a case where the X-ray is incident on the surface in parallel (hereinafter referred to as SV direction). Of the film was exposed to X-rays from the TV direction.
Although there is a large diffraction peak at θ ≒ 23 °, this 2θ ≒ 2
The crystal orientation angle at 3 ° is preferably 30 ° or more. More preferably, it is 60 ° or more. Further, a large diffraction peak of 2θ ≒ 18 ° appears on the equator line due to incidence from the SV direction, and the crystal orientation angle at 2θ ≒ 18 ° is preferably 60 ° or less. When both of these crystal orientation angles are satisfied, it can be said that the film of the present invention has a so-called plane-oriented structure,
It is highly preferred because it has high mechanical properties (eg, strength, elongation, Young's modulus) in both the film-drawing direction and the direction perpendicular thereto, and also has high tear strength. In this respect, it can be clearly distinguished from the film disclosed in Japanese Patent Publication No. 55-14170. As a method for measuring the crystal orientation angle, a known method can be employed, for example, the following method.
Place the counter tube at the specified 2θ angle and set the film at 180 °
By rotating, a diffraction intensity curve is obtained. In the case of a TV, the maximum strength is used as the center, and the TV is rotated by 90 ° before and after. The arc length in the diffractogram, in degrees, corresponding to the point at which the highest intensity of the curve is half the intensity relative to the baseline drawn between the lowest intensity points (ie, 50% of the maximum intensity baseline). Angle to point)
Is measured, and this is defined as the crystal orientation angle of the sample. In the measurement, the diffraction intensity can be measured by stacking several films as necessary. Such a thin film having a small thickness unevenness can be produced according to the following method.
In addition, the fact that the unevenness of the film is small is related to the fact that shrinkage during drying is limited as described later. In the method of the present invention, first, it is necessary to adjust the optically anisotropic doping of PPTA. A suitable solvent for adjusting the dope used for forming the PPTA film of the present invention is sulfuric acid having a concentration of 95% by weight or more. With less than 95% sulfuric acid, dissolution is difficult or the dope after dissolution becomes abnormally high in viscosity. Chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, and the like may be slightly mixed in the dope of the present invention. Sulfuric acid may be used in an amount of 100% by weight or more, but a concentration of 98 to 100% by weight is preferably used from the viewpoint of stability and solubility of the polymer. The concentration of the polymer in the dope used in the present invention is preferably not less than a concentration exhibiting optical isotropy at room temperature (about 20 to 30 ° C.) or higher.
0% by weight or more is preferred. At polymer concentrations that do not exhibit optical anisotropy at room temperature or higher, molded PPTA films often do not have favorable mechanical properties. Although the upper limit of the polymer concentration of the dope is not particularly limited, it is usually preferably 20% by weight or less, particularly preferably 18% by weight or less, particularly preferably 16% by weight or less for PPTA having a high ηinh. . The dope of the present invention may contain ordinary additives, for example, extenders, delusterants, ultraviolet stabilizers, heat stabilizers, antioxidants, pigments, and solubilizers. Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, for example, a method described in Japanese Patent Publication No. 50-8474. The critical point is determined by the type of solvent, temperature, polymer concentration, It depends on the degree of polymerization of the polymer, the content of non-solvent, etc.Therefore, by examining these relationships in advance, an optically anisotropic dope is created, and by changing the condition to become an optically isotropic dope, It can be changed to optical isotropic. In the dope used in the present invention, insoluble dust and foreign matters are removed as much as possible prior to molding and solidification by filtration or the like, and a base such as air generated or entrained during melting is removed. It is preferable to remove them.
Degassing can be performed after adjusting the dope,
It can also be achieved by performing the process under vacuum (reduced pressure) from the stage of charging the raw materials for adjustment. Adjustment of the dope can be performed continuously or batchwise. The dope adjusted in this way is cast on a supporting surface moving from a die, for example, a slit die, while maintaining optical anisotropy. The distance until the dope contacts the support surface is important, and is 30 mm or less (excluding 8 mm or less).
) . If the distance is too large, the reason is not clear, but not only is a granular material generated, resulting in uneven thickness, but also breakage and the like. This phenomenon is particularly noticeable when the film is made thinner.
% Or less (excluding 5% or less) , which is an essential requirement for obtaining a thin film with extremely small thickness unevenness. In addition,
It is preferable that the distance until the film-shaped dope coming out of the die comes into contact with the support surface is as short as possible. In the present invention, the steps of casting and subsequent conversion to optical isotropic, coagulation, washing, stretching, drying and the like are preferably carried out continuously, but if necessary, all or some of them. May be performed intermittently, that is, in a batch manner. In order to obtain a transparent film having excellent mechanical properties according to the present invention, it is necessary to convert the dope from optically anisotropic to optically isotropic prior to solidification after casting the dope on the support surface. In order to make the optically isotropic from the optical anisotropy, specifically, the optically anisotropic dope cast on the support surface is absorbed prior to solidification to reduce the concentration of the solvent forming the dope. , The dope is transferred to the optically isotropic region by changing the solvent dissolving capacity and the polymer concentration, or the dope is heated by heating, and the dope phase is transferred to the optically isotropic, or the moisture absorption and heating are performed simultaneously. Alternatively, it can be achieved by using them sequentially. Among them, the method utilizing moisture absorption is useful because the optical anisotropy, including the method using heating, is efficiently performed without causing decomposition of PPTA. To dope the dope, air at normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain water in the form of mist exceeding the saturated vapor pressure, or may be so-called steam. However, saturated steam at about 45 ° C. or lower often contains large granular condensed water, which is not preferable in some cases. Usually, normal temperature to about 180 ° C, preferably 50 to 1
It is performed by humidified air at 50 ° C. In the case of the heating method, the heating means is not particularly limited, and examples thereof include a method of applying the humidified air to the casting dope, a method of irradiating an infrared lamp, and a method of dielectric heating. The casting dope optically isotropic on the support surface is then subjected to coagulation by contact with a coagulation liquid. In the present invention, the coagulating liquid of the dope can be, for example, diluted sulfuric acid of about 70% by weight or less, aqueous sodium hydroxide solution and ammonia water of about 20% by weight or less,
Sodium sulfate, sodium chloride aqueous solution and calcium chloride aqueous solution of about 10% by weight or less. In the present invention, the temperature of the coagulating liquid is preferably 5 ° C. or less. In general, it has been found that the lower the concentration of the coagulating liquid, the smaller the void containing the film. Since the solidified film containing that or until the acid, to produce a small film of reduction in mechanical properties by heating wash acid content, it is necessary to perform as much as possible removed. It is desirable that the removal of the acid content is specifically performed to about 500 ppm or less. Water is usually used as a washing liquid, but if necessary, washing may be performed with warm water, or after neutralizing and washing with an aqueous alkaline solution, washing with water or the like. The cleaning is performed by, for example, running the film in the cleaning liquid or spraying the cleaning liquid. The washed film can be stretched.
Dried without bets, but drying should be carried out to limit the contraction of full <br/> Irumu under tension or under a constant length. If a film having a tendency to shrink with the removal of a washing liquid (eg, water) is dried without any limitation on shrinkage, a non-uniform structure formation (e.g., crystallization) may occur on a microscopic basis. The light transmittance of the obtained film is reduced. In addition, in the case of the thin film of the present invention, not only a film having poor mechanical properties is often obtained, but also partial unevenness or the like occurs, resulting in uneven thickness, or further impairing the flatness of the film, It may curl. In order to dry while limiting shrinkage, for example, a tenter drier or drying by sandwiching between metal frames can be used. Other conditions relating to drying are not particularly limited, and include methods using a heating gas (air, nitrogen, argon, etc.) or a normal temperature gas, a method using radiant heat such as an electric heater or an infrared lamp, and a method using a dielectric heating method. The drying temperature can be freely selected, but the drying temperature is preferably high.
A temperature of at least 20 ° C. is particularly preferred. The maximum drying temperature is not particularly limited, but is preferably 500 ° C. or lower in consideration of drying energy and decomposability of the polymer. In the method of the present invention, it is one of the preferred embodiments that the film is produced by continuously running the film throughout the entire process. However, if desired, the film may be partially batchwise operated. Further, an oil agent, a dye for identification, or the like may be applied to the film in an optional step. In addition, in order to obtain a film having excellent transparency in the present invention, that is, an extremely large light transmittance, the dope is, of course, a gas for absorbing moisture, a gas for heating, a supporting body, a coagulating liquid, a cleaning liquid, a drying gas, and the like. It is preferable to reduce the content of dust and dirt as much as possible. In this regard, producing the film of the present invention in a so-called clean room or clean water is also one of the preferred embodiments. EXAMPLES Examples of the present invention and production examples of reference examples (PPTA) will be shown below, but these reference examples and examples explain the present invention. This does not limit the present invention. In the examples, unless otherwise specified, parts by weight or% by weight are indicated. Logarithmic viscosity ηinh is 98% sulfuric acid 100ml
0.2 g of the polymer was dissolved in the solution and measured at 30 ° C. by a conventional method. The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm. The thickness of the film is measured by a capacitance type non-contact thickness gauge (type CL-23, manufactured by Ono Sokki Co., Ltd.).
(Type 0), the thickness was determined from the average value of the thickness at 10 measurement points arbitrarily selected from the film, and the thickness unevenness was calculated from (maximum value−minimum value) / average value × 100.
For the elongation and modulus, a film sample was cut into a rectangle of 100 mm x 10 mm using a constant-speed elongation type elongation meter, and a load-elongation curve was drawn five times with an initial gripping length of 30 mm and a pulling speed of 30 mm / min. , Calculated from this. Reference Example (Production of PPTA) PPTA was obtained by a low-temperature solution polymerization method as follows. In a polymerization apparatus disclosed in JP-B-53-43986, N
-Anhydrous lithium chloride 70 in 1000 parts methylpyrrolidone
Were dissolved, followed by 48.6 parts of paraphenylenediamine. After cooling to 8 ° C., 91.4 parts of terephthalic acid dichloride were added at once in powder form. After a few minutes, the polymerization reaction product solidified in the form of cheese.
The polymerization reaction product was discharged from the polymerization apparatus according to the method described in JP-A-86-86, and was immediately transferred to a twin-screw closed kneader, and the polymerization reaction product was finely pulverized in the kneader. Next, the finely pulverized product was transferred into a Hexiel mixer, to which an approximately equal amount of water was added, further pulverized, filtered, washed several times in warm water, and dried in hot air at 110 ° C. 95 parts of a pale yellow PPTA polymer having an η inh of 5.5 were obtained. The polymers having different ηinh are the ratio of N-methylpyrrolidone to a monomer (paraphenylenediamine and terephthalic acid dichloride),
Alternatively, it can be easily obtained by changing the ratio between monomers and the like. Example 1, Comparative Example 1 A PPTA polymer having a η inh of 5.3 was dissolved in 99.6% sulfuric acid at a polymer concentration of 12.0% to obtain a dope having optical anisotropy at 60 ° C. The viscosity of this dope measured at room temperature was 10,200 poise. In order to facilitate film formation, the dope was degassed under vacuum while keeping the dope at about 60 ° C. Also in this case, it had the same optical anisotropy as above, and the viscosity was 4000 poise. A 1.5 mm curved tube extending from the tank to the die through the gear pump to the die is kept at about 60 ° C., and a die having a slit of 0.2 mm × 250 mm is passed through a mirror-polished tantalum belt (3 to 5 mm).
At a distance of 8 m / min) and cast on a belt at a distance between the die and the support surface shown in Table 1 (Example 1: 21 mm, Comparative Example 1: 34 mm), and a relative humidity of about 15%, about 90 ° C. (73 g absolute humidity) (Water) / kg (dry air)), and the casting dope was optically isotropic, and was introduced into water at 5 ° C. with a belt to solidify. Next, the coagulated film was peeled off from the belt and washed by running in water at about 20 ° C. The washed film was sandwiched between metal frames and dried at 320 ° C. under a fixed length. Table 1 summarizes the results of sampling films having different thicknesses obtained by changing the belt speed. The film of Comparative Example 1 had granular irregularities on one surface. COMPARATIVE EXAMPLE 2 With the same apparatus and method as in Example 1, when the belt-shaped dope coming out of the die was brought into contact with the belt at a distance of 40 mm at a belt speed of 4 m / min and tried to cast, the dope was cut and could not be cast. . [Table 1] As shown in the examples, the film of the present invention is extremely thin and has a small thickness unevenness, has a high light transmittance, is not found in a commercially available film, and has a long direction and width. One
On the other hand , it has good mechanical properties represented by high strength and high Young's modulus. In addition to these mechanical properties, it has excellent electrical insulation, heat resistance, pressure resistance, chemical resistance other than strong acid, and dense structure. For this reason, the film of the present invention can be suitably used as an insulating material or a magnetic tape for high-speed rotating electric equipment, a flexible printed wiring board, a wire covering material, a filtration membrane, and the like. It is useful for packaging materials, plate making materials, photographic films and the like. Further, the film of the present invention is extremely thin, has little unevenness in thickness, has high transparency, and is excellent in heat resistance. It can be a capacitor that can be put directly into a solder bath and soldered. For this reason, it is useful as a film for a capacitor which is not seen in an organic film.

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Claims (1)

(57) [Claims] A film made of a substantially para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more, having a thickness of 8 μm or less, and having a thickness unevenness of 10% or less (5% or less).
% Or less). 2. An optically anisotropic dope consisting essentially of a para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is placed on a support surface that moves from a die while maintaining optical anisotropy. In a method for producing a film in which the dope is cast by optical absorption and / or heat absorption and / or heating and then solidified, the dope is placed on the supporting surface at a distance of 30 mm or less (excluding 8 mm or less) from a die. And then converted to optically isotropic, then coagulated in a coagulating liquid at 5 ° C or less, washed, and then without stretching
A method for producing an aromatic polyamide film, characterized in that the film is dried at a temperature of 320 ° C. or more while restricting shrinkage of the film.