JPH046736B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a film made of poly(p-phenylene terephthalamide) (hereinafter referred to as PPTA) and a method for producing the same, and more specifically, to a long film that is transparent and has very few voids. direction (hereinafter abbreviated as MD direction) and width direction (TD direction)
The present invention relates to a PPTA film that exhibits excellent mechanical properties and a manufacturing method for obtaining the same. (Prior Art) There are few proposals for applying PPTA to films, and no examples of its practical use are known yet. 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, a unit in which a halogen group is introduced into the aromatic nucleus of a linearly coordinating aromatic polyamide is copolymerized with an aromatic polyamide other than PPTA that does not have a substituent on 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 transparent film with a uniform thickness, and its mechanical strength, particularly its tear 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), it was proposed to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated conical mandrel. Although the film is isotropic, its mechanical strength is low, and when drafted, its mechanical strength in the MD direction is high, but its mechanical strength in the TD direction is extremely low. 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 reduces the extreme uniaxial orientation of the optically anisotropic dope, and at the same time prevents the liquid crystal domain structure of the optically anisotropic dope from remaining even after the dope is extruded and solidifying into an opaque film. succeeded in avoiding it. However, when this method is generally carried out, the obtained film often contains many voids of about 1 to 10 μm, and sometimes the degree of transparency is not sufficient. (Problems to be Solved by the Invention) An object of the present invention is to provide a film with little or no voids as described above, using PPTA, whose industrial production has already begun, and which also has transparency. The object of the present invention is to provide a highly improved PPTA film with high performance and excellent flatness, and an industrial method for producing the same. (Means for Solving the Problems) The present inventors have made the following findings as a result of intensive research to obtain a high-quality PPTA film that does not have the above-mentioned drawbacks. That is, according to the method of Japanese Patent Publication No. 57-17886
When making a PPTA film, it goes without saying that complete defoaming (deaeration) of the stock solution (dope) is necessary, but this is one of the prerequisites for making a void-free film. However, the generation of voids in the produced film is closely related to the coagulation bath temperature, and the lower the temperature, the less voids will generally occur.Also, shrinkage generally occurs during the drying process, but this is limited. It has been found that if this is not done, the flatness and transparency of the film will be slightly inferior. Based on these findings, the present inventors
After further research, the present invention was completed. The first aspect of the present invention is that the number of voids is 0.6/mm ² or less, and the light transmittance X (%) and the thickness Y (μm) satisfy the relationship X≧80−0.5Y. Poly(p-phenylene terephthalamide) film, which is a poly(p-phenylene terephthalamide) film according to the second aspect of the present invention.
An optically anisotropic dope consisting essentially of sulfuric acid at a concentration of % by weight or more is cast onto a support surface while maintaining optical anisotropy, and the dope is made optically isotropic by absorbing moisture and/or heating. Poly(p-phenylene terephthalamide) is a poly(p-phenylene terephthalamide), which is characterized in that the film is produced by coagulating after conversion, and the coagulation is carried out with a coagulating solution at 2°C or lower, and after coagulation and washing, the film is dried in a state in which shrinkage is limited. ) can be manufactured by a film manufacturing method. The PPTA used in the present invention is substantially It is a polymer represented by the formula, and is conveniently produced from conventionally known paraphenylene diamine and terephthaloyl chloride by a low-temperature solution polymerization method. If the degree of polymerization of the polymer of the present invention is too low, it will not be possible to obtain a film with good mechanical properties. A polymer with a degree of polymerization that gives a value measured at 30℃ when dissolved is selected. The film of the present invention can achieve its purpose only if it satisfies the following two requirements. First of all, the number of voids described below is 0.6/
Must be less than mm ² . The number of voids is measured as follows. A film piece of an appropriate size is examined using an ordinary optical microscope using transmitted light.
Observe at least 5 different fields of view at magnifications ranging from 100x to 400x, count the number of voids with a major axis of 1 μ or more, and calculate the number of voids per 1 mm ² of the film surface. A film having a void count of more than 0.6 voids/mm ² has poor mechanical properties, often with a decrease in transparency, and also affects the accuracy of the unevenness on the film surface. In order to reduce the number of voids in the film, it is extremely important to keep the temperature of the coagulation bath at 2° C. or lower, in addition to the so-called duty of care to sufficiently deaerate the dope. Second, the light transmittance X (%) of the film must satisfy the relationship X≧80−0.5Y, where the thickness of the film is Y (μm). Light transmittance is measured as follows. Attach a film to the liquid cell location of an ordinary photoelectric photometer (or spectrophotometer), select visible light with a wavelength of 600 nm, and measure its transparency. One of the important features of the film according to the invention is its transparency. The film of the present invention preferably has a light transmittance of 90% or more. It is believed that the excellent transparency of the film of the present invention is closely related to the special manufacturing method. In other words, first, an optically anisotropic dope is cast onto a support surface, and then the optically anisotropic dope is completely optically isotropically made by absorbing moisture and/or heating to form a so-called domain interface, which is unique to the optically anisotropic dope. The second step is to suppress the above-mentioned void formation, and the third step is to solidify it after eliminating the void.
It is necessary to combine this with methods such as fixing the edges of the film in order to limit the shrinkage that occurs during drying, rather than performing the drying process without tension. The film of the present invention typically has a density of 1.370
~1.405g/ ^cm3 . This density value was measured at 30°C by density gradient tube method using carbon tetrachloride-toluene. This density range is considerably smaller than that of known PPTA fibers, which range from 1.43 to 1.46. When the density is less than 1.370, mechanical properties deteriorate,
If it exceeds 1.405, the film will have poor planar orientation and isotropy in mechanical properties. In any case, this low density results in a light and high-strength film. The film of the present invention preferably has a plane orientation defined by the crystal orientation angle determined by X-ray diffraction as described below. In other words, the crystal orientation angle with respect to the 2Θ≒23° peak due to X-rays incident at right angles to the film surface is 30° or more, and the crystal orientation angle with respect to the 2Θ≒18° peak due to X-rays incident parallel to the film surface is 60°. It is preferable that it is less than . The incidence of X-rays can be divided into two cases: one is incident perpendicularly to the film surface (hereinafter referred to as the TV direction) and the other is incident parallel to the surface (hereinafter referred to as the SV direction). The film of the present invention is exposed to X-rays from the TV direction.
It has a large diffraction peak at 2Θ≒23°, but this 2Θ≒
The crystal orientation angle at 23° is preferably 30° or more, more preferably 50° or more. Further, when incident from the SV direction, a large diffraction peak of 2Θ≒18° appears on the equator line, but it is preferable that the crystal orientation angle at 2Θ≒18° is 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, and has high mechanical properties both in the direction in which the film is taken and in the direction perpendicular thereto. It is highly preferred because it has high tear strength. A known method can be used to measure the crystal orientation angle, and for example, the following method may be used. A diffraction intensity curve is obtained by placing the counter at a predetermined angle of 2Θ and rotating the film 180°. For TVs, rotate 90 degrees from front to back, centering on the highest intensity. The arc length in degrees in the diffraction photograph corresponding to the point where the maximum intensity of this curve is half the intensity of the baseline drawn between the lowest intensity points (i.e., 50% of the baseline of maximum intensity). (angle with respect to the point) and use it as the crystal orientation angle of the sample.
During measurement, the diffraction intensity can be measured by stacking several films if necessary. When the film of the present invention was cut with a microtome equipped with a diamond knife to prepare a thin section and observed with an interference microscope, it was found that the surface layer (thickness of
A part with a slightly higher refractive index (2 μm) was observed, suggesting that a dense layer was formed on the surface. Next, a method for obtaining such a PPTA film will be described. In the method of the present invention, it is first necessary to prepare an optically anisotropic dope of PPTA. A suitable solvent for preparing the dope used for forming the PPTA film of the present invention is sulfuric acid at a concentration of 95% by weight or more. If the sulfuric acid content is less than 95%, it will be difficult to dissolve the dope, and the dope will have an abnormally high viscosity after being dissolved. The dope of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, and the like. Sulfuric acid has a concentration of 100% by weight
The above concentration is also possible, but from the viewpoint of stability and solubility of the polymer, a concentration of 98 to 100% by weight is preferably used. 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°C to 30°C) or higher, and specifically, approximately 10% by weight. It is preferably used in an amount of about 12% by weight or more. At a polymer concentration below this range, that is, at a polymer concentration that does not exhibit optical anisotropy at room temperature or higher temperatures, the formed PPTA film often does not have desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20% by weight or less, particularly preferably 18% by weight or less for PPTA with particularly high ηinh, and more preferably 16% by weight or less. 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 an optically anisotropic dope and changing the conditions for optically isotropic doping. It goes without saying that the dope used in the present invention should be filtered to remove as much insoluble dust, foreign matter, etc. as possible before being molded and solidified.
It is important to remove gases such as air generated or entrained during melting. Degassing can be done once the dope has been prepared, or it can be carried out consistently under vacuum (reduced pressure) from the stage of preparing the raw materials for preparation.
It can also be achieved by going below. Preparation of the dope can be carried out continuously or batchwise. The dope thus prepared is cast onto a support surface using, for example, a slit die while maintaining optical anisotropy. In addition, in the laboratory, it can be cast onto a support surface using a doctor knife. As the supporting surface, a drum, belt, plate-shaped object, etc. made of a material such as glass, stainless steel, tantalum, Hastelloy, or fluororesin, or coated with these materials or a noble metal such as gold or platinum, is selected. The method of obtaining a transparent film with excellent mechanical properties according to the present invention is to cast a dope onto a support surface and then convert the dope from optically anisotropic to optically isotropic prior to solidification. In order to change optical anisotropy to optical isotropy, the optically anisotropic dope cast on the supporting surface is made to absorb moisture to lower the concentration of the solvent forming the dope before solidifying. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the dope phase to optically isotropic, or absorb moisture and heat simultaneously or sequentially. This can be achieved by using them together. In particular, methods using moisture absorption, including methods that use heating in combination, are useful because optical anisotropy can be made optically isotropic efficiently and without causing decomposition of PPTA. To make the dope absorb moisture, air at normal temperature and humidity may be used, but humidified or heated and humidified air is preferably used. The humidified air may contain mist-like moisture exceeding the saturated vapor pressure, and may be so-called water vapor. However, supersaturated steam at a temperature of about 45° C. or lower is not preferable because it often contains large particles of condensed water. Moisture absorption is usually from room temperature to about 180
C., preferably 50.degree. C. to 150.degree. C. with humidified air. In the case of a heating method, the heating means is not particularly limited, and examples include a method of applying humidified air to the casting dope as described above, a method of irradiating with an infrared lamp, and a method of dielectric heating. The optically isotropic cast dope on the support surface is then solidified. In the present invention, the dope coagulation liquid that can be used is, for example, dilute sulfuric acid containing about 70% by weight or less of water, aqueous sodium hydroxide and aqueous ammonia containing about 20% by weight or less, sodium sulfate or sodium chloride containing about 10% by weight or less. These include aqueous solutions and calcium chloride aqueous solutions. In the present invention, it is extremely important to maintain the temperature of the coagulating liquid at 2° C. or lower during coagulation. This is because when the temperature of the coagulating liquid exceeds 2°C, many voids are observed in the resulting film. In addition,
The lower limit of the coagulation bath temperature is not particularly limited, and is up to the melting point (freezing point) determined by the composition of the coagulation bath. 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 the acid content 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 after neutralization with an alkaline aqueous solution and then with water. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The washed film is then dried, but if desired, by stretching the wet film before drying by about 1.01 to 1.4 times in one or two directions,
The mechanical properties of the film can be improved. Drying must be carried out under tension, at a constant length, or with slight stretching to limit shrinkage of the film.
If a film that has a tendency to shrink upon removal of the cleaning liquid (e.g., water) is dried without any restriction on shrinkage, it may be difficult to obtain a film due to the formation of microscopically non-uniform structures (crystallization, etc.). The light transmittance of the film will be reduced.
Furthermore, the flatness of the film may be impaired or the film may curl. To dry while limiting shrinkage, for example, a tenter dryer or drying by sandwiching between metal frames can be used. Other conditions related to drying are not particularly limited, and methods such as methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods such as using radiant heat such as electric heaters and infrared lamps, dielectric heating method, etc. The drying temperature is not particularly limited, as long as it is at room temperature or above. However, in order to increase the mechanical strength, a high temperature is preferable, 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 in consideration of drying energy and decomposability of the polymer, it is preferably 500° C. or lower. 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. In addition, oil agent,
It is also possible to add dyes for identification to the film. In addition, in order to obtain the film of the present invention with excellent transparency, that is, extremely high light transmittance, it is necessary to use not only the dope but also a moisture absorbing gas, a heating gas, a supporting surface, a coagulating liquid, a cleaning liquid, a drying gas, etc. It is preferable to reduce the content of dust and dirt in the film as much as possible, and in this respect, it is one of the preferred embodiments to manufacture the film of the present invention in a so-called clean room or clean water. (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%
0.5 g of polymer was dissolved in 100 ml of sulfuric acid and measured at 30°C in a conventional manner. The viscosity of the dope is measured using a B-type viscometer.
Measurements were taken at a rotation speed of 1 rpm. The thickness of the film was measured using a dial gauge with a measuring surface of 2 mm in diameter. Strength elongation and modulus are
Film samples are measured using a constant speed elongation type strength and elongation measuring machine.
A rectangle of 100 mm x 10 mm was cut out, and a load-elongation curve was drawn five times at an initial grip length of 30 mm and a pulling speed of 30 mm/min, and the calculation was made from this. 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 in powder form all at once. 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 Hexiel 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 5.0 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 and Comparative Example 1 PPTA having an ηinh of 5.0 was dissolved in 99.7% sulfuric acid at a polymer concentration of 13.0% under vacuum to obtain a dope with optical anisotropy at 50°C. The viscosity of this dope at room temperature was 14,000 voids. In order to facilitate film formation, this dope was filtered through a stainless steel non-woven filter and placed in a beaker and kept at about 70°C. Even at that time, the dope exhibits optical anisotropy and the viscosity is
It was 4000 voices. This dope was cast onto a glass plate at 30° C. using a doctor knife having a step of 0.1 mm. The glass plate was placed in a desiccator and evacuated for about 20 minutes to degas the casting dope, and then air at about 70° C. and about 90% relative humidity was introduced into the desiccator. It was found that the cast dope became transparent and became isotropic in about 40 seconds. The glass plate was then placed in water maintained at 1°C. After about 20 seconds, the film peeled off from the glass plate. Put the film in water at about 15-20℃ for about 2 hours,
Next, soak in 2% NaOH aqueous solution for 30 minutes, and then again for 15~15 minutes.
It was washed by soaking it in a water bath at 20°C overnight. The next day, take out the film from the aquarium and put it in a 10cm x
It was sandwiched between two 15 cm stainless steel frames and dried for a fixed length in an air oven maintained at 250°C. The same experiment was repeated using water at 5°C and water at 10°C as coagulation baths. The results are summarized and shown in Table 1. Note that the logarithmic viscosity ηinh of all the films was in the range of 4.5 to 4.7. In Table 1, MD means the direction of the doctor knife, and TD means the direction perpendicular to it.

[Table] Example 2 A PPTA polymer having an ηinh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 12.0% to obtain a dope with optical anisotropy at 60°C. When the viscosity of this dope was measured at room temperature, it was 14,500 voids. To facilitate film formation, this dope was degassed under vacuum while being maintained at approximately 70°C. This case also had optical anisotropy as above, and the viscosity was 4200 voids.
The 1.5m curved pipe from the tank through the filter to the gear pump to the die is maintained at approximately 70°C and is 0.2mm x
The dope is cast from a die with a 300 mm slit onto a mirror-polished Hastelloy belt (moving at 2 m/min), and air at about 90°C with a relative humidity of about 95% is blown to make the cast dope optically isotropic. It was then introduced together with the belt into a 20% by weight aqueous sulfuric acid solution at -8°C to coagulate. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. The washed film was placed in a tenter dryer, stretched by 5% in the width direction and at a constant length in the length direction, and dried first with hot air at 120°C and then with hot air at 220°C. The properties of the obtained film are shown in Table 2. Example 3 The coagulation bath was changed to a 10% by weight sulfuric acid aqueous solution at -3°C,
Roll the washed film lengthwise before drying.
Example 2 was repeated except that the film was stretched 1.2 times and tenter drying was carried out at a constant length in both the width and length directions. The results are shown in Table 2. Both the film of Example 2 and the film of this example were tough films that were extremely difficult to tear.

[Table] (Effects of the Invention) As shown in the Examples, the film of the present invention has good mechanical properties as shown by high strength and high modulus, which are not found in commercially available films. 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. For this reason,
The film of the present invention can be suitably used as an insulating material for electrical equipment that rotates at high speed, magnetic tape, flexible printed wiring boards, wire coating materials, filtration membranes, etc., and has another feature of excellent transparency. Because of this, it is also useful for packaging materials, plate-making materials, photographic films, etc. In particular, the film of the present invention has very few voids and has excellent transparency, so when it is used as an electrical insulation film, magnetic tape, or flexible printed wiring board, the quality of these products (e.g. insulation, Image clarity, stability, etc.) are further improved.

Claims (1)

[Claims] 1. A polyester characterized in that the number of voids is 0.6/mm2 ^or less, and the light transmittance X% and the thickness Y (μm) satisfy the relationship X≧80−0.5Y. (p-phenylene terephthalamide) film. 2 Poly(p-phenylene terephthalamide) and
An optically anisotropic dope consisting essentially of sulfuric acid with a concentration of 95% by weight or more is cast onto a support surface while maintaining its optical anisotropy, and the dope is made optically isotropic by absorbing moisture and/or heating. A process for producing a film in which poly(p-phenylene terephthalate) is coagulated after being converted into poly(p-phenylene terephthalate), which is characterized by coagulating with a coagulating solution at 2° C. or lower, and drying the film after coagulating and washing with limited shrinkage. amide) film manufacturing method.