JPS6036943B2 - Polyparaphenylene terephthalamide composite film and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyparaphenylene terephthalamide film having a novel structure and a method for producing the same. The present invention relates to a heat-resistant polyparaphenylene terephthalamide composite film and a method for producing the same. In recent years, there has been active development and improvement of materials used as electrical insulating materials in order to improve the performance of electrical equipment and make it smaller and lighter. In particular, electrical insulating materials with excellent heat resistance are required to increase the speed of motors, such as those used in Shinkansen trains, and to coat ultra-high voltage cables. Polyethylene terephthalate film, which is widely used as a general electrical insulating material, has insufficient heat resistance, so the use of heat-resistant polymers, such as aromatic polyamide and aromatic polyimide films and paper, is being considered and has already been done. Some products are commercially available. however,
Commercially available aromatic polyimide films require very expensive raw materials and complicated manufacturing processes, and also have problems with adhesion, and similarly aromatic polyamide paper has lower strength and electrical properties than polyethylene terephthalate film. is also inferior. On the other hand, various studies have been made on aromatic poly-IJ amide films, which are expected to be used as high-performance electrical insulating materials, but nothing satisfactory has yet been obtained. For example, the production of aromatic polyamide films containing metaphenylene isophthalamide as a main constituent unit is described in JP-A-52-58754 and JP-A-52-6084. Films have problems in terms of heat resistance, as is readily apparent from the structure of their constituent polymers. On the other hand, the production of a film of polyparaphenylene terephthalamide, which is known to have excellent heat resistance among many aromatic polyamides and to provide fibers with high strength and high elastic modulus, is disclosed in Japanese Patent Application Laid-Open No. 47-1999. Publication No. 39458, Tokubatsu Showa 5
1-116363. As a result of faithful follow-up tests based on the techniques disclosed by the present inventors, the films obtained by these proposed methods have excellent heat resistance as expected, but have the following drawbacks. It was revealed that it has. In other words, the film obtained by the former method, in which an optically anisotropic dope is formed by a dry-wet process (a molding method in which it is once extruded into a non-coagulable gas and then solidified), has a tensile strength in the direction perpendicular to the extrusion direction. It has the serious disadvantage of being extremely low and easily fibrillated, and also has poor transparency, which is one of the important characteristics that determine commercial value. Furthermore, the film obtained by the latter method, in which an anisotropic dope is similarly extruded into a non-coagulable gas through an annular orifice, and then the gas is injected into the tubular film and stretched in the longitudinal and lateral directions at the same time as film formation, is as follows: The tensile strength in the transverse direction is high, and the fibrillation, which is a drawback of the former film, has been improved, but the tearing strength is low and it tears easily, and it is more demanding from the processing surface, such as adhesiveness and impregnation with insulating oil. It has the disadvantage of insufficient performance. Furthermore, due to the Chixon viscosity, which is a characteristic of the optically anisotropic dope, it is extremely difficult to industrially stably obtain a film without uneven thickness using this method. The present inventors also attempted to form a film from an optically isotropic dope according to a conventional method, but only an extremely brittle film was obtained. The present inventors have discovered the drawbacks of the conventional aromatic polyamide films, namely, insufficient heat resistance and poor transparency.
As a result of intensive research, we have identified a film that is useful as an electrical insulating material in fields that require high mechanical properties, electrical properties, and heat resistance, without the problems of easy tearing, poor adhesion, and impregnability. An optically anisotropic dolph of a polymer. Surprisingly, the inventors have discovered that the desired film can be easily obtained by solidifying a thin film made of a composite of optically isotropic dope and optically isotropic dope, and have completed the present invention. That is, the films of the present invention contain at least 85 repeating units.
A layer in which {a] optically anisotropic dope of a carbocyclic aromatic polyamide whose mol% is paraphenylene terephthalamide is coagulated;

[b} A composite film consisting of a number of layers in contact with a layer made of solidified optically isotropic dope. Another invention provides an optically anisotropic dope consisting essentially of a carbocyclic aromatic polyamide in which at least 85 mol% of the repeating units consist of paraphenylene terephthalamide and sulfuric acid at a concentration of at least 9% by weight. This is a method of manufacturing a film with the novel structure of the present invention by forming a plurality of thin films of a plurality of layers adjoining each other in the thickness direction, and solidifying the composite thin film. The polymer used in the present invention has at least 85 repeating units.
It is a carbocyclic aromatic polyamide comprising mol% of paraphenylene terephthalamide. Other useful units are -CO~, -CO-, -NH-
-2-NH-, -3-CO-. ~,,F2,~3 are divalent aromatic rings in which bond chains extend coaxially or parallelly, for example, (
Y is an extended chain bond having a structure that can resonate with an aromatic ring, and examples thereof include -CONH-, -N=N-, and the like, and they may be the same or different from each other. These aromatic rings may have substituents, but they must not cause undesirable reactions during polymerization and processing steps. Examples of such substituents include halogen groups (e.g., chloro, frome), lower alkyl groups (e.g., methyl, ethyl), lower alkoxy groups (e.g., methoxy, ethoxy), nitro groups, acetyl groups, and the like. It will be done. As shown above, the polymer used in the present invention consists of an amide bond with paraphenylene terephthalamide as a repeating unit and an aromatic ring (the bonded chains extend coaxially or in parallel), and the main chain is These polymers have a structure that is easy to extend straight (referred to as linear coordination polymers), but as long as the linear coordination is not impaired, polymers that do not meet the above conditions, such as those in which the amide bond is coaxially extended from the aromatic ring. Bonds other than amide bonds such as imide bonds, alkylene bonds, imidazole bonds, oxazole bonds, ester bonds, and urea bonds, and cyclohexyl Approximately 5 mol% of groups with extended chain bonds other than aromatic rings such as silene, pyridylene, and bicyclohexylene
Polymers containing the following may also be used. However, the use of a polymer in which paraphenylene terephthalamide units account for 85 mol % or less in all repeating units is not preferable because the resulting film will have poor heat resistance and mechanical properties. The intrinsic viscosity of the polymer is related to the mechanical properties of the film, and a higher one is preferable, but if it is too high, problems occur during film formation. It is generally preferred to use a polymer having an intrinsic viscosity of at least 2.0, preferably 3.5. Such polymers can be produced by a low-temperature solution polycondensation method of an aromatic dicarboxylic acid halide and an aromatic diamine, and a method using a hydrohafide salt of an aromatic aminocarboxylic acid halide.
It can be synthesized by a known method. The film of the present invention is produced by forming an optically anisotropic dope and an optically isotropic dope of the above polymer into a thin film of a plurality of layers adjoining each other in the thickness direction, and then coagulating, washing, drying, and as necessary. It can be made by a so-called wet method, which involves heat treatment. The optically anisotropic dope used in the present invention is obtained by mixing a polymer and a solvent in a certain concentration range. This dope exhibits birefringence, and when polarized light passes through the dope, a depolarization phenomenon occurs. Optical anisotropic doping is described in Samurai Publication No. 47-248, Japanese Patent Application Laid-Open No. 47-394, and the like. The solvent used for dope formation is essentially one that can dissolve the polymer used in the present invention, does not significantly increase the fraction of the polymer, and is capable of forming an optically anisotropic dope. Any type of sulfuric acid may be used, but sulfuric acid having a concentration of at least % by weight is preferred from the viewpoint of economy and film properties. for example,
Amide-based polar solvents such as N,N'-dimethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea, and hexamethylphosphoramide containing solubilizing agents such as lithium chloride, calcium chloride, and magnesium chloride are
There are restrictions on the polymers that can be dissolved, and it cannot be used for polymers with high intrinsic viscosity, which are desirable for making films with good physical properties, or polymers containing only paraphenylene terephthalamide, and it has a dissolving power comparable to that of sulfuric acid. chlorosulfuric acid, which can easily dissolve polymers with high solid viscosity and polymers containing only paraphenylene terphthalamide component.
The problem with fluorosulfuric acid is that it is very expensive. A sulfuric acid content of 9% by weight or less lacks the dissolving power. Although so-called fuming sulfuric acid may be used in a concentration of 10% by weight or more, it is particularly preferable to use sulfuric acid in a concentration range of about 99 to 10% by weight because it tends to cause a decrease in the intrinsic viscosity of the polymer. In the sulfuric acid solvent, as long as the effects of the present invention are not impaired,
Other additives such as chlorosulfuric acid, fluorosulfuric acid, hydrofluoric acid, halogenated alkylsulfonic acid, halogenated alkylsulfonic acid, halogenated aromatic sulfonic acid, halogenated lower alkyl alcohol, ketone, and aldehyde may be mixed. forgiven. Preparation of the dope does not require any special equipment or methods as long as attention is paid to temperature. For example, a solvent is charged into a dissolution tank equipped with a water absorber, and then the polymer is added all at once or gradually, and the polymer is dissolved while stirring. The viscosity of the dope increases as it dissolves, and in particular, the higher the intrinsic viscosity of the polymer and the greater the amount of polymer, the higher the viscosity of the dope. In such cases, it is necessary to maintain the dissolution temperature high, but increasing it higher than necessary increases the decomposition of the polymer, so this must be avoided. The melting temperature is the intrinsic viscosity of the polymer,
Although it differs depending on the concentration of the polymer, it is generally best to carry out at a concentration of 10% or less. The optically anisotropic dope is obtained in a range above a certain critical polymer concentration which is higher than the optically isotropic dope. The critical polymer concentration at which the dope exhibits optical anisotropy varies depending on the intrinsic viscosity of the polymer used and the concentration of the solvent, and can be easily determined experimentally. For example, when using sulfuric acid with a concentration of IQ% by weight as a solvent, a polymer having an intrinsic viscosity of 2.5 or more becomes an anisotropic dope at a polymer concentration of 9 to IQ% by weight or more. In addition, in the case of 99.5% sulfuric acid solvent,
When the amount is about 8 to 9% by weight or more, it becomes an anisotropic dope. In carrying out the present invention, the concentration of each dope polymer may be arbitrarily selected within the range of anisotropy and isotropy.
Generally, optically isotropic dolphs have a polymer concentration in the range of 2 to 8% by weight. and 10 to 25% by weight, preferably 14
An optically anisotropic dope in the range of ~22% by weight is used. The viscosity of the dope is an important item in film formation, and is generally 10,000 ml.
It is preferable to select the polymer concentration, the intrinsic viscosity of the polymer, the concentration of the solvent, and the doping temperature so that it is 5000 poise or less. In addition, the viscosities of the dopes of both components do not need to be completely equal, but care should be taken so that they are not extremely different. Furthermore, if necessary, conventional additives such as fillers, ultraviolet stabilizers, antioxidants, etc. may be mixed into the dope.
The production of thin films from two types of dopes (which is a feature of the present invention) does not require any special equipment and can be carried out using conventional methods and equipment. For example, after extruding each dope into a thin film through a slit-shaped die, the dopes may be stacked on a drum or net, or two dopes may be side- or wedged together through a slit-shaped or ring-shaped die. A method of extruding into a thin film from a mold (extrusion from a ring-shaped die in the latter case,
A so-called inflation method may be used in which film formation and stretching are performed simultaneously by gas injection or the like. ), or by casting one dope in the form of a thin film on a slope and then casting the other dope on top of it, to create a composite thin film of two types of dopes. Dofu. When making thinner films, the film forming draft is selected based on the properties of the dope, slit width, coagulation ratio composition, target film thickness, etc., and taking into account productivity as long as stable film formation can be achieved. It will be done. In the conventional method, the larger the draft, the greater the molecular orientation in that direction (vertical direction), the lower the strength in the direction perpendicular to it (lateral direction), and the film becomes more likely to fibrillate. The method is characterized in that even if the draft is increased, the strength of the resulting film in the transverse direction is high, and therefore a good film can be produced with high productivity. The ratio of the two types of dopes used varies depending on the polymer concentration of the dope used, but
Usually, the ratio of the volume of the optically anisotropic dope to the volume of the optically isotropic dope is preferably in the range of 4 to 0.25. When the volume ratio is 4 or more, the resulting film becomes less tearable and has lower transparency. On the other hand, 0.2
If it is less than 5, the resulting film will have poor mechanical properties. Particularly suitable films are obtained when the above-mentioned volume ratio is in the range of 2 to 0.5. In addition, during film formation, the film thickness from the optically anisotropic dope affects the transparency of the final film, and it is preferably set to 150 or less when obtaining a film with particularly good transparency. . The film forming temperature is selected depending on the polymer concentration of the dope, the intrinsic viscosity of the polymer, and the solvent so that the viscosity of the dope is suitable for film formation. However, excessive heating is undesirable from the viewpoint of polymer decomposition. It is usually 100 oo or less, preferably 85 qC or less. The dope formed into a thin film is introduced into a coagulation bath to remove the solvent. Prior to contacting the coagulant, the thin film may be briefly contacted with a gas such as air or nitrogen, or with a non-coagulable liquid layer such as toluene or heptane. The temperature of the gas layer does not necessarily have to be room temperature, and the film of the present invention can be obtained even in a heated atmosphere or in a cold atmosphere. It may also be a gas layer with high humidity. Various techniques can be used for coagulation. Useful systems include water, aqueous solutions of dope-forming solvents, and those systems containing salts such as common salt, calcium chloride, sulfur, and the like. Also included are organic solvents miscible with water, such as aqueous solutions such as methanol, ethanol, and ethylene glycol. From an economical point of view, water or an aqueous sulfuric acid solution is preferred. If the heating temperature is too high, rapid desolvation will occur and voids will be likely to occur, so a lower temperature is generally preferred. The suitable range varies depending on the bath composition; for example, in the case of a rich composition with a high coagulation ability, it is better to keep the normal temperature low, and in the case of a high composition with a small coagulation ability,
Even if the bath temperature is high, for example, from 80 to 10,000, the formation of voids is small, and generally it is 10,000 or less, preferably in the range of -25 to 5,000. The membrane pulled up from the coagulation process is then brought into contact with water or a dilute aqueous solution in order to complete the coagulation and remove the adhering solvent. At this time, it is preferable to apply tension to the membrane in the lateral direction as well. If necessary, washing may be performed under no tension (allowing contraction). In particular, when it is desired to obtain a film with high tensile strength, it is preferable to carry out stretching in the machine direction and/or the transverse direction.
In this case, it is effective to stretch a film that is not completely solidified and has large swelling. Another method involves stretching in a coagulation bath. Even a small amount of sulfuric acid remaining in the membrane can cause deterioration, so the membrane must be thoroughly cleaned.
Neutralize with sodium hydroxide, etc. if necessary. In addition,
The presence of metal ions in the material may cause a decrease in electrical properties and heat resistance, so even if a neutralizing agent is used, it is necessary to remove the neutralizing agent and neutralizing salt as much as possible. In addition, it is preferable to use soft water with a low content of metal ions. After washing, remove as much adhering water as possible with a squeezing roll or the like, or without actively removing the water, place the waist in contact with a heating roll, a heating plate, or a heating atmosphere under tension, or Dry under no tension (allowing shrinkage). Alternatively, a method may be used in which the membrane is actively densified and then dried under pressure, such as by passing it between heated press rolls. Drying during stretching is also permissible. If necessary, the membrane is heat-treated under no tension (allowing shrinkage), under tension, under pressure, or under stretching in order to impart dimensional stability and fix the structure. The treatment temperature is arbitrarily selected within a range that does not cause decomposition of the polymer, but a range of 50 to 5000C is usually practical.
When heat-treating under pressure, the pressure varies depending on the treatment temperature, but at 15,000 yen it is 5 m/h/or more, and at 200 ohm/lm
It is preferable to select it within a range of h/ or more. It is not necessary to heat-treat the film after drying, and the film characteristic of the present invention can also be obtained by drying the film before drying. In the former case, it is effective to heat the film after drying at a temperature higher than the drying temperature. The processing atmosphere may be the atmosphere when the processing temperature is low, but preferably an inert gas such as nitrogen when the processing temperature is high. When a wet film is heated, the film shrinks, and the film made only from the optically anisotropic dope has a large shrinkage in the width direction of the film, but compared to this, the film made from the two types of dopes of the present invention has a small shrinkage. The composite film of the present invention obtained by such a method has structural features such as a layer of dense tissue in the thickness direction, and
In comparison, it has a layer of coarse structure. The degree of organization can be observed using an electron microscope, but it can also be easily evaluated indirectly by measuring the apparent density. A large porosity (%) calculated from this apparent density generally suggests that aggregation of the polymer is incomplete or that micropores are present. On the other hand, the smaller the porosity, the more dense the structure is. When the optically anisotropic dope is solidified, a film with low porosity is obtained. On the other hand, optically isotropic doping provides a film with a relatively large porosity. For example, the porosity of a film made by coagulating optically anisotropic dope (optically isotropic dope) is 70-80% (80-80%) in a wet state before drying.
90%) and 10-30% (30-50%) after drying. The composite film of the present invention, which is composed of a layer formed by solidifying the optically anisotropic dope and a layer formed by solidifying the optically isotropic dope, has a small porosity, most of which is 30% or less, and has voids in the thickness direction. They have different porosity, and are roughly divided into layers with a small porosity (about 30% or less) and layers with a large porosity (about 50% or less). A preferred film is one in which the ratio of the densely textured layer to the coarsely textured layer is between 0.9 and 0.4 when the overall thickness of the film is 1. in range. Films with a dense layer of 0.9 or more have tear o strength,
Adhesion and other properties deteriorate, and films below 0.4 have poor mechanical and electrical properties. By changing the coagulation conditions on both sides of the film, a film with an asymmetrical cross-sectional structure of a dense structure and a coarse structure can be obtained (for example, as described in Japanese Patent Application Laid-Open No. 51-16363). The film with an asymmetric cross-sectional structure obtained by this method has the same degree of molecular orientation in both layers, whereas the composite film of the present invention has a different degree of molecular orientation in each layer. , is structurally different from the composite film cone of the present invention. The fact that the degree of molecular orientation in the composite film of the present invention differs between the two eyebrows is supported by the fact that a molded product with better molecular orientation can be obtained from an optically anisotropic dope than an optically isotropic dope. Furthermore, there are obvious physical differences between these films; for example, films with an asymmetric structure with a rough structure obtained by changing coagulation conditions have poor transparency, whereas the composite film of the present invention has poor transparency. Although the films have layers with a rough structure, they have excellent transparency as described below, and also have different electrical and mechanical properties. The film of the present invention is structurally characterized as described above as a composite film consisting of a plurality of adjoining layers, a layer made of a coagulated optically anisotropic dope and a layer made of a coagulated optically isotropic dope. However, it is further characterized by having the following unexpected physical properties. That is, the composite film of the present invention has excellent transparency even though it has a layer with a rough structure, and has a light transmittance (%) of 60% or more at a wavelength of 50 m. Films with good transparency have great commercial value. On the other hand, a film obtained only from an anisotropic dope has poor transparency, with a light transmittance of 10% or less in an unstretched film and 40% or less in a stretched film. Films made from optically isotropic dopes have relatively good transparency, but the transparency is less than 70% for films with a thickness of 50 mm, and less than 20% for films with a thickness of 150 mm.
On the other hand, the composite film of the present invention exhibits a transmittance of 80% or more at a thickness of 50 mm, and a transmittance of 60% or higher even at a thickness of 150 mm. This is an unpredictable compound effect. Furthermore, the composite film of the present invention is characterized by having mechanical properties not found in conventional polyparaphenylene phthalamide films. 3. In other words, conventional films are weak in tearing in the extrusion direction, and this tendency is particularly noticeable when films are heat-treated or stretched to improve dimensional stability. The film of the invention has high tear strength even when it is heat treated or stretched. The film of the present invention also has excellent tensile strength in the direction perpendicular (lateral direction) to the extrusion direction (longitudinal direction). For example, in conventional films, the ratio of tensile strength in the transverse direction/tensile strength in the longitudinal direction is 0.3 or less when there is no transverse stretching, and 0.3 when stretching is performed.
．． 6-0. In contrast, the composite film of the present invention has a temperature of 0.6 to 0.8 even when there is no stretching in the transverse direction.
It also has excellent tensile strength in the transverse direction. The film of the present invention has good crystallinity and a high melting point (approximately 550
It is made from a polymer whose main component is poly(paraphenylene terphthalamide). Therefore, the film retains excellent mechanical and electrical properties up to high temperatures. In addition, hydrophilic -CO-NH-
Although it has bonds, it is highly crystalline, so there is little dimensional change or deterioration of electrical insulation properties due to moisture absorption. If desired, the ZO film may contain conventional additives such as UV stabilizers, antioxidants, etc., as long as they do not impair the characteristics of the film of the present invention. In addition, the presence of inorganic salts, such as salt, in the film may lead to a decrease in heat resistance and a decrease in electrical properties. The amount of residual inorganic salt in the film is preferably 0.1 to 0.5% or less. The film of the present invention is structurally characterized by being composed of a plurality of adjoining layers, a layer made of an optically anisotropic dope and a layer made of an optically isotropic dope, and has transparency. It has mechanical properties such as high tear resistance in the longitudinal direction, high tensile strength in the transverse direction, and good mechanical and electrical properties at high temperatures. It also has excellent impregnation properties. Therefore, electrical insulation materials in fields that require high heat resistance, electrical properties, and mechanical properties, such as insulation of heat-resistant electric wires and cables, electrical insulation of motor magnet wires, insulation of heaters, and interlayer insulation of transformers. It is extremely useful for insulation, other printed wiring boards, household VTR tape, zero adhesive tape, etc. The method for measuring each characteristic in the present invention is as follows. Intrinsic viscosity: Approximately 98.5% concentrated sulfuric acid and 0 polymer
．． The relative viscosity of a solution containing the following is measured at 35o0 using a conventional method, and calculated using the following formula. Intrinsic viscosity = ln (relative viscosity) 0.2 Porosity (%): The apparent density (g/
Flow) and calculate it using the following formula. Porosity = (1 seemingly feeding density 1.44) x. 〇Light transmittance (%): Set the film in close contact with the wall of a quartz cell filled with pure water, adjust it so that the transmittance is 100% when using only pure water, and then apply it to a colorimeter. Measure the transmittance at a wavelength of 50 h#. Tensile strength and elongation: A film cut into a strip of 1 length x 10 lengths was tested using a tensile tester at a sample length of 5 lengths and a tensile speed of 2.
The tensile strength (k9/side 2) and tensile elongation (%) are calculated from the stress-strain curve. Tear strength: Measured using an Elmendorf tear tester according to JIS-P-8116. Dielectric breakdown voltage: Measured according to JIS-C-2318. Examples will be shown below, and the percentages shown in the examples are percentages by weight unless otherwise specified. Example 1 Polyvalent phenylene terephthalamide having an intrinsic viscosity of 5.2 was dissolved in 99.5% sulfuric acid to give a polymer concentration of 4.0%. The resulting dope had a viscosity of about 3900 poise (about 5000) as measured by a rotational viscometer and was optically isotropic. On the other hand, polyparaphenylene terephthalamide having an intrinsic viscosity of 4.1 was dissolved in sulfuric acid of the same concentration to give a polymer concentration of 18%. The obtained dope had a viscosity of approximately 500 poise (approximately 7000 poise) and was optically heterotropic as a result of observation using a polarizing microscope. An optically isotropic dope was cast to a thickness of 50 mm on a glass plate preheated to about 70 qo, and then an optically anisotropic dope was cast thereon to a thickness of 50 mm.
Next, the glass plate was immersed in about 25 quarts of water to solidify. The membrane separated from the glass plate was thoroughly washed with running water, then attached to a frame and dried in a 12,000° hot air dryer. The film thus obtained with a thickness of 24 cm had the properties shown in Table 1. As is clear from Table 1, the film of the present invention has extremely high tensile strength in the transverse direction and high tear strength in the longitudinal direction, compared to the film obtained only from the optically anisotropic dope (Comparative Example 1). , it was also highly transparent. Furthermore, compared to the film obtained only from optically isotropic dope (Comparative Example 2), both tensile strength (mechanical properties) and dielectric breakdown voltage (electrical properties) were superior. Comparative Example 1 The optical film used in Example 1 The anisotropic dope was cast onto a glass plate to a thickness of 100 mm, and the same treatment as in Example 1 was carried out to produce a film.The resulting film with a thickness of 31 mm was opaque, and
It was easy to tear in the vertical direction. Comparative Example 2 The optically anisotropic dope used in Example 1 was cast onto a glass plate to a thickness of 100 mm, and the same treatment as in Example 1 was performed to produce a film. The resulting 9 mm thick film was transparent but had low tensile strength and was brittle. Table 1 Example 2 Using the dopes used in Example 1, each dope was cast onto a glass plate using the proportions of the optically anisotropic dope and the isotropic dope shown in Table 2. 1 in water at about 5℃
It was soaked day and night. After washing with pure water, the adhering water was wiped off with a sponge, and heat treatment was performed under tension at 30,000 for about 1 minute. Each of the obtained films had the characteristics shown in Table 2. Table 2 OA: Optically anisotropic dope 01: Optically isotropic dope As a result of observation of the cross section of the film using an electron microscope, the film of the present invention has a two-layer structure consisting of a layer with no voids and a layer with visible voids. It was getting better. The ratio of the thickness of the layer without voids/thickness of the layer with voids is optically anisotropic doping/optical isotropic doping = 80
In the case of a film obtained by forming a film of /70, the ratio was about 36/1. On the other hand, films obtained only from optically anisotropic doping,
Almost no voids were observed throughout the cross section, and the cross-sectional structure was almost uniform. Example 3 An optically anisotropic dope in which polyparaphenylene terephthalamide with an intrinsic viscosity of 4.1 was dissolved in 99.5% sulfuric acid at a concentration of 20%, and an optically isotropic dope dissolved in the same concentration at 4%. - are combined into a composite thin film through a slit with a width of 0.15 x 10 ribs (the optically anisotropic doped layer is approximately 100 mm thick and the optically isotropic doped layer is approximately 50 mm thick). So that
The amount of extrusion of each dope and the gap between the channels of each dope were adjusted. ) extruded into the atmosphere. After running 20 times in the atmosphere, it was then introduced into a coagulation chamber consisting of a 30% aqueous sulfuric acid solution at about 0°C. The solidified bath was run for 1 hour, then pulled up, and then introduced into rolls and stretched 1.2 times in the tensile direction. After stretching, the film was washed to remove residual solvent, and then passed through a group of hot rolls with a surface temperature of 15,000°C for tension drying. The film thus obtained has a thickness of 39
France, porosity 25%, transmittance 82%, tensile strength in the stretching direction 18.9k9/side 2, tensile strength in the right angle direction 11.5k9
The film had a dielectric breakdown voltage of 20V/leg, and was a transparent film with excellent mechanical and electrical properties. Further, the rough layer side surfaces of this film were adhered to each other with a silicone adhesive, and the adhesive force was measured by pulling in a direction perpendicular to the adhesive surface, and the result was 540 g/25 skin. On the other hand,
In the film of Comparative Example 1, the adhesive strength measured by the same method was 310 g/25 willow, and the film of the present invention also had good adhesive strength. Example 4 Various polymers having the compositions shown in Table 3 were mixed at a concentration of 99.4.
% of sulfuric acid to produce an optically anisotropic dope with a polymer concentration of 20% and an optically isotropic dope with a polymer concentration of 3%. The optically isotropic dope and the optically anisotropic dope were cast on a glass plate to a thickness of about 50 mm and about 100 mm, respectively, and then solidified with water at room temperature. After washing and drying, it was heat-treated at 300oC under about 3 inkstone sand tension. The obtained film is shown in Table 3.
It had the properties shown below. Table 3 Note: P-T' Paraphenylennaref Lua Kodo Note 2)
The tensile strength in the longitudinal direction of the film after exposure to IRr hot air at 300°C was measured, and the strength retention rate (multi) was expressed as the strength after x and oo.
From the results in Strength Table 3 above, we can see that strong, heat-resistant films can be obtained from polymers that contain a small amount of units with rigid linear coordination in addition to paraphenylene terephthalamide. It can be seen that when the amount is 15 mol % or more, the strength and heat resistance are significantly lowered. Example 5 - Polyparaphenylene terephthalamide copolymer containing 5 mol% units and 99
．． An optically anisotropic dope with a polymer concentration of 21% consisting of 8% sulfuric acid and an isotropic dope with a polymer concentration of 4% consisting of polyparaphenylene terephthalamide and the same solvent were placed in a diameter of 1.
They were extruded together into the air in a tube shape through a ring-shaped orifice with a slit width of 0.2 ribs, passed through the air for about 15 ribs, and then introduced into a coagulation chamber at about 5°C. Air was forced into the extruded tubular thin film to expand it to about twice the diameter of the orifice. In addition, a coagulating liquid having the same composition as the outside was made to exist inside the tubular thin film. The fully solidified thin film is lifted from the solidified layer,
Then washed and dried. The obtained film has a longitudinal tensile strength of 19.5 k9/side 2, an elongation of 23%, a transverse tensile strength of 16.6 k9/2 ribs, an elongation of 20%, and a longitudinal tear strength of 0.54 k9/ It was a transparent and strong film. Note that the porosity was 23% and the light transmittance was 89%. For comparison, a film was made using the same method using only the same optically anisotropic dope. However, uniform stretching was not possible and the orifice diameter was approximately 1
．． Expanded 5 times. The obtained film had a relatively high longitudinal tensile strength of 15.5k9/Yanagi2, but a longitudinal tear strength of 0.21k9/side, which was lower than the film of the present invention. In addition, to solidify the inside of the tubular film, a film was made using the same method except that it expanded approximately 1.5 times the orifice diameter from only the optically anisotropic dope at a temperature of 40 oo using an aqueous solution containing 15% sodium bicarbonate. Ta.

Claims (1)

[Scope of Claims] 1. A layer of (a) a coagulated optically anisotropic dope of a carbocyclic aromatic polyamide in which at least 85 mol% of the repeating structural units are composed of paraphenylene terephthalamide;
(b) A polyparaphenylene terephthalamide-based composite film consisting of a plurality of layers in contact with a layer formed by coagulating an optically isotropic dope. 2. (a) an optically anisotropic dope consisting essentially of a carbocyclic aromatic polyamide in which at least 85 mol% of the repeating units consist of paraphenylene terephthalamide and sulfuric acid at a concentration of at least 98% by weight; ) A method for producing a polyparaphenylene terephthalamide composite film, which comprises forming a plurality of thin films with an optically isotropic dope in contact with each other in the thickness direction, and solidifying the composite thin film.