JPH0260684B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a film made of poly(P-phenylene terephthalamide) (hereinafter referred to as PPTA), and more specifically, in the longitudinal direction of the film (hereinafter referred to as MD direction). A thin material that exhibits excellent mechanical properties in both the width direction (TD direction) and the width direction (TD direction).
This relates to a method for manufacturing PPTA film. (Prior art) PPTA has particularly excellent crystallinity and a high melting point, and due to its rigid molecular structure, it has heat resistance and high mechanical strength, and has been attracting particular attention in recent years as a polymer. It is the material. It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been implemented industrially, but there are few proposals for application to films. There are still no known examples of practical use. The problem with PPTA is that its useful high molecular weight polymer is poorly soluble in organic solvents, and strong inorganic acids such as concentrated sulfuric acid must be used as a solvent. For example, in Japanese Patent Publication No. 56-45421, 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. The mechanical strength was strong only in the TD direction, but the mechanical strength in the TD direction perpendicular to this was extremely weak and 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, especially its tear strength, is low. Also, Japanese Patent Publication No. 59-5407, Japanese Patent Application 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, it is difficult to obtain a film with high tear strength using a method in which orientation is performed using shear force. Furthermore, J.APPl.Polym.Sci.vol.27, No.8,
P.2965-2985 (1982) proposes to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated conical mandrel. This film has the disadvantage that although its mechanical strength is isotropic, it 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 with an optically anisotropic dope immediately before solidification.
It is described that a transparent film having isotropic mechanical properties can be obtained by heating until it becomes optically isotropic and then solidifying it. This method is an original method that goes against the conventional idea of achieving high performance by utilizing optically anisotropic doping.
At the same time as relaxing the axial orientation, the liquid crystal domain structure of the optically anisotropic dope remained even after the dope was extruded, and succeeded in preventing it from solidifying into an opaque film. However, this publication does not specifically disclose a transparent film that is extremely thin and has a high Young's modulus. (Problems to be Solved by the Invention) The object of the present invention is to use PPTA, which has already been industrially produced, to produce a film that can be used as a base film for video tapes that can be recorded for long periods of time and is lightweight. An object of the present invention is to provide an industrial method for producing a thin film having a high Young's modulus, high transparency, and excellent flatness. (Means for Solving the Problems) The present inventors have made the following findings as a result of extensive research to obtain a PPTA film that meets the above objectives. That is, by using the technology disclosed in Japanese Patent Publication No. 57-17886 (first making an optically anisotropic dope of PPTA, making it optically isotropic and solidifying it), a transparent PPTA film with excellent mechanical performance was produced. In this method, the ratio of the moving speed of the cast dope to the speed of discharging the dope from the die is set to a certain level or higher, the washed film is stretched in a wet state, and shrinkage, which generally occurs during the drying process, is limited. It was found that by carrying out this process, an ultra-thin film with a high Young's modulus and extremely high transparency and flatness could be obtained. Based on these findings, the present inventors conducted further research and completed the present invention. That is, the present invention provides poly(P-
An optically anisotropic dope consisting essentially of phenylene terephthalamide) and 95% by weight or more of sulfuric acid is cast onto a support surface that moves from a die while maintaining its optical anisotropy, and is subjected to moisture absorption and/or heating. In the method of producing a film in which the dope is converted into optically isotropic material and then solidified by the film in at least one direction
This is a method for producing a polyamide film, which is characterized by stretching the film by a factor of 1.05 or more and then drying the film while limiting shrinkage. 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, a film with good mechanical properties cannot be obtained.
Logarithmic viscosity ηinh of 3.5 or more preferably 4.5 or more (sulfuric acid
A degree of polymerization is selected that gives a value measured at 30°C by dissolving 0.5g of polymer in 100ml. The film obtained by the present invention has the following characteristics. First of all, the film obtained by the present invention preferably has a thickness of 8 μm or less. For example, when a film with a thickness of more than 8 μm is used as a videotape, the bulkiness per unit length becomes larger in proportion to the thickness, and the film does not meet the needs for compact size, light weight, and long recording time. There is no particular lower limit to the thickness of the film, but it is usually used at a thickness of 1 μm or more. This is because, in addition to the problem that handling becomes difficult if the film is too thin, the resistance to deformation as a videotape is determined by (Young's modulus) x (thickness), and therefore, tapes with deformation resistance This is because in order to realize this, it becomes necessary to significantly increase the Young's modulus, which becomes difficult. The film of the present invention more preferably has 2
It has a thickness of ~7μm. Note that the thickness as used in the present invention is defined as the average value of the thickness at 5 or more (preferably 10) measurement points arbitrarily selected from the film. The thickness of the film can be changed depending on the polymer concentration in the dope, die gap, draft rate, etc. Second, the film obtained by the present invention has a Young's modulus in at least one direction of 1000 Kg/mm ² or more. As mentioned above, this requirement is closely related to the film's resistance to denaturation. For example, it is related to jitter characteristics when used as a magnetic tape, and preferably the Young's modulus in at least one direction is 1300 Kg/mm ^{2 or more, more preferably 1500 Kg/mm 2} or more.
Kg/ ^mm2 or more. There are two types of films obtained by the present invention; one is a balanced type in which the vertical and horizontal Young's moduli are approximately equal to 1000 Kg/mm ² or more; It is a tensilized type with a large Young's modulus of 1000 Kg/mm ² or more. Such a thin film having a large Young's modulus in at least one direction can only be obtained by following a specific method described below. Particularly high Young's modulus is associated with stretching in a wet state and limiting shrinkage during drying. The film obtained by the present invention preferably has extremely high transparency and smooth flatness.
High transparency means, for example, that the transmittance of visible light at a wavelength of 600 nm is preferably 55% or more, more preferably
70% or more. Furthermore, the film obtained according to the present invention is preferably substantially free of voids. Furthermore, the film obtained by the present invention usually has a density in the range of 1370 to 1405 g/cm ³ . This density value was measured at 30°C by density gradient tube method using carbon tetrachloride-toluene. This density range is similar to that of known PPTA fibers.
This value is considerably smaller than the range of 1.43g/cm ³ to 1.46g/cm ³ . When the density is less than 1,370 g/cm ³ , mechanical properties deteriorate, and when it exceeds 1,405 g/cm ³ , the film becomes a film with impaired planar orientation and isotropy of mechanical properties. In any case, this low density results in a light and high-strength film. The film obtained in 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 peak of Θ≒23° caused by X-rays incident at right angles to the film surface is 30° or more, and the crystal orientation angle with respect to the peak of 2Θ≒18° caused by 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 obtained by the present invention is
Although it has a large diffraction peak at 2Θ≒23° depending on the line,
The crystal orientation angle at 2Θ≒23° is 30° or more. The angle is preferably 50° or more, and more preferably 50° or more. Furthermore, due to incidence from the SV direction, 2Θ≒
A large diffraction peak of 18° appears on the equator line, but
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 obtained by the present invention has a so-called plane-oriented structure, and the film has high mechanical properties (e.g. strength , elongation, Young's modulus) and high tear strength. And in this respect,
It can be clearly distinguished from the "film" disclosed in Publication No. 14170. 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. Furthermore, the film obtained by the present invention preferably has a thermal expansion coefficient of −5× in at least one direction.
It is in the range of 10-5 to ⁰ /℃. 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 can be used in a concentration of 100% by weight or more, but from the viewpoint of stability and solubility of the polymer, a concentration of 98 to 100% by weight is preferably used. The 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. Used above. 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 in the dope is not particularly limited, but it is usually 20% by weight or less, especially at high ηinh.
For PPTA, it is preferably used in an amount of 18% by weight or less, 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. Before molding and solidifying the dope used in the present invention, insoluble dust and foreign matter should be removed as much as possible by filtration, etc., and gases such as air generated or entrained during melting should be removed. It is preferable to leave it there. Deaeration can be performed once the dope has been prepared, or can be achieved by performing it under vacuum (reduced pressure) from the stage of charging raw materials for preparation. Preparation of the dope can be carried out continuously or batchwise. The dope prepared in this way can be transferred from a die, for example, a slit die, while maintaining its optical anisotropy.
It is cast onto a moving support surface. In the present invention, casting and subsequent conversion to optical isotropy,
Steps such as coagulation, washing, stretching, and drying are preferably carried out continuously, but if necessary, all or part of them may be carried out intermittently, that is, batchwise. In the present invention, it is important that the moving speed of the support surface through which the dope is cast is at least twice the linear speed at which the dope is discharged from the die. This is because this ratio is 2
This is because if casting is carried out under conditions less than double the thickness, it is difficult to make the obtained film thin, and it often causes uneven thickness of the film. The moving speed of the support surface is preferably 2.5 to 8 times the linear discharge speed of the dove. 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. To change optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope cast on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the phase of the dope to optically isotropic, or simultaneously or sequentially absorb moisture and heat. This can be achieved by using it in combination with 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 isotropically 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, the temperature of the coagulation liquid is preferably
The temperature is 15°C or lower, more preferably 5°C or lower. This is because, in general, it has been found that the lower the temperature of the coagulating liquid, the less voids are included in the film. 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 neutralizing with an alkaline aqueous solution and then using water or the like. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The cleaned film then needs to be stretched in the wet state before being subjected to drying. The stretching is
Stretching is performed at a stretching ratio of about 1.05 times higher in one direction or two directions. At this time, it is often seen that the moisture contained within the film comes out like sweat. In the case of stretching in one direction, it may be either in the MD direction or in a direction perpendicular to the MD direction, and the stretching is preferably performed by about 1.1 to 1.7 times. The stretching in two directions may be simultaneous biaxial stretching or sequential stretching one axis at a time. In the case of bidirectional stretching, it is preferably carried out at a stretching ratio of about 1.07 to 1.5 times. Stretching allows the PPTA molecular chains to be oriented in the stretching direction, resulting in improved mechanical properties. Therefore,
At a stretching ratio smaller than 1.05 times, no improvement in mechanical properties, particularly Young's modulus, can be expected. Note that stretching must be performed in a wet state before drying, and stretching cannot be performed effectively to improve mechanical properties if a large amount of sulfuric acid remains or after drying. 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.
Further, in the case of the thin film obtained by the present invention, only a film with poor mechanical properties is often obtained, and 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 may include methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters or infrared lamps, dielectric heating methods, etc. It can be freely selected, and the drying temperature is not particularly limited as long as it is room temperature or higher. 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 the method of the present invention, it is one of the preferred embodiments to manufacture the film while running it continuously throughout the entire process, but if desired, it may be carried out partially in a batch manner. In addition, oil agent,
It is also possible to add dyes for identification to the film. In the present invention, in order to obtain a film with excellent transparency, that is, extremely high light transmittance, in addition to the dope, a moisture absorbing gas, a heating gas, a supporting surface, a coagulating liquid, a cleaning liquid, and a drying gas are used. It is preferable to reduce the content of dirt and dust 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 all at once in powder form. After a few minutes, the polymerization reaction 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 was immediately transferred to a twin-screw closed kneader. The polymerization reaction product was ground. 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 5.5 was obtained. Note that polymers with different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and monomers (paraphenylenediamine and terephthalic acid dichloride), and/or the ratio between monomers. Examples 1 to 5 A PP polymer having ηinh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain an optically anisotropic dope at 60°C. When the viscosity of this dope was measured at room temperature, it was 10,600 poise. To make it easier to form a film, the dope was kept at about 70°C.
Degassed under vacuum. This case also had optical anisotropy as above, and the viscosity was 4400 poise. A 1.5m curved pipe from the tank, through the filter, through the gear pump, to the die is maintained at approximately 70℃ and is 0.1mm x 300mm.
The cast dope is cast from a die with a slit onto a mirror-polished tantalum belt (moving at 12 m/min), and air at about 90°C with a relative humidity of about 85% is blown to make the cast dope optically isotropic. , and the belt were introduced into water at 5° C. to solidify. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. The washed film was stretched in a tenter without drying, and then dried with hot air at 240° C. under a fixed length using another tenter. Table 1 summarizes the results of sampling while varying the linear velocity of discharge from the die and the stretching ratio.

[Table] Example 6 PPTA having an ηinh of 4.8 was dissolved at 10% in 99.5% sulfuric acid to obtain a dope of 8400 poise with optical anisotropy at 45°C. After degassing and filtration, the dope was cast onto a tantalum belt through a die with a 0.08 mm x 300 mm slit. At this time, the linear velocity of dope discharge from the die was set to 3.5 m/min, and the moving speed of the belt was set to 10 m/min. Relative humidity about 80%
The sulfurized dope was converted into a transparent optically isotropic dope by blowing air at 75°C, and then coagulated with a 10% aqueous sulfuric acid solution at 0°C. After the coagulated film was peeled off from the belt, it was washed successively with water at room temperature, a 2% aqueous solution of caustic soda, and water at about 30 to 40°C. The washed wet film containing about 250-350% water is stretched 1.3 times in MD and 1.1 times in TD in a tenter, and then stretched 1.05 times in TD only in another tenter with hot air at 180℃. The film was dried while being stretched. The obtained film has a thickness of 3.0μmηinh4.4,
Light transmittance 93%, density 1.389g/cm ³ , number of poids 0.9
ke/mm ² , MD strength 31Kg/mm ² , TD strength 24Kg/mm ² ,
MD elongation 13%, TD elongation 17%, MD Young's modulus 1670
Kg/mm ² and TD Young's modulus was 1100 Kg/mm. (Effects of the Invention) As shown in the Examples, the film obtained by the present invention has good mechanical properties as expressed by high strength and high Young's 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. Therefore, the film obtained by the present invention can be suitably used as an insulating material for high-speed rotating electrical equipment, magnetic tape, flexible printed circuit boards, wire coating materials, filtration membranes, etc. Due to its excellent transparency, packaging materials,
It is also useful as a plate-making material, photographic film, etc. In particular, the film obtained by the present invention is extremely thin and has a high Young's modulus, so when used as a videotape or a magnetic tape, it is lightweight and can be used for long recording times, improving the clarity and stability of images. It is also useful as a high quality tape.

Claims (1)

[Claims] 1 A support for moving an optically anisotropic dope consisting essentially of poly(P-phenylenetephthalamide) having a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid from a die while maintaining its optical anisotropy. In a method for manufacturing a film in which the dope is cast onto a surface, converted to optically isotropic by moisture absorption and/or heating, and then solidified, the moving speed of the supporting surface is set to be at least twice the linear velocity of discharging the dope from the die. A method for producing a polyamide film, which comprises: stretching the film in a wet state by a factor of 1.05 or more in at least one direction after coagulating and washing the film, and then drying the film in a state where shrinkage of the film is limited.