JPH0257816B2 - - 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 film that has selective light transmittance and excellent surface properties. Due to orientation,
The present invention relates to a PPTA film that exhibits excellent mechanical properties in both the longitudinal direction (hereinafter abbreviated as MD direction) and the width direction (TD direction) of the film, and a manufacturing method for obtaining the same. (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. In addition, it has 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. 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 is 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 that the mechanical strength, especially the 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, Journal of Abright Polymer Science, Volume 27 (No. 8), Nos. 2965-2985
Page (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; ,
If mechanical strength is low and draft is applied, MD
Although its mechanical strength in the TD direction is high, it has the disadvantage of being extremely low in the TD direction. Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linear aromatic polyamide is coated immediately before solidification,
It is described that a transparent film having isotropic mechanical properties can be obtained by heating until it becomes optically isotropic and then solidifying it. This method is an original method that goes against the conventional concept of achieving high performance by utilizing optically anisotropic doping.
At the same time as relaxing the axial orientation, the liquid crystal domain structure of the optically anisotropic dope remained even after the dope was extruded, and succeeded in preventing it from solidifying into an opaque film. However, there is no specific disclosure of a transparent film that has very good light transmittance and even selective light transmittance. (Problems to be Solved by the Invention) The purpose of the present invention is to use PPTA, which has already been industrially produced, to have extremely high light transmittance in the visible region and to be difficult to transmit in the ultraviolet region. The purpose of the present invention is to provide a film with excellent flatness that can be used as a base film for computer display (hereinafter referred to as CRT) filters, 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 extensive research to obtain a PPTA film that meets the above objectives. That is, by the technique disclosed in Japanese Patent Publication No. 57-17886 (a method of first making an optically anisotropic dope of PPTA, making it optically isotropic and solidifying it,
In order to obtain a transparent PPTA film with excellent mechanical performance, optical isotropy is achieved by humidification after casting on the support surface, and an alkaline aqueous solution is applied to strengthen the deoxidation of the film after solidification. After treatment, it is washed with water and the shrinkage that generally occurs during the drying process is limited, and furthermore, because the polymer has high heat resistance, it can be dried at temperatures exceeding 350°C, but by performing this at a temperature below 350°C,
It has been found that a film with excellent flatness can be obtained that has extremely high transparency in visible light but does not pass through ultraviolet light. Based on these findings, the present inventors conducted further research and completed the present invention. That is, the first aspect of the present invention is a film substantially made of poly(p-phenylene terephthalamide) having a logarithmic viscosity of 4.5 or more, which has a peak of 2θ≒23° caused by X-rays incident at right angles to the film surface. The crystal orientation angle with respect to the peak of 2θ≒18° due to X-rays incident parallel to the film surface is 60° or less, and the crystal orientation angle is 1.370 to 1.405.
It has a density in the range of g/cm ² and a wavelength from 430 nm.
An aromatic polyamide film characterized by having a light transmittance of 60% or more at 750 nm and a light transmittance of 1% or less at a wavelength of 410 nm or less,
Such a film uses the second aspect of the present invention, that is, an optically anisotropic dope consisting essentially of poly(p-phenylene terephthalamide) having a logarithmic viscosity of 4.5 or more and 95% by weight or more of sulfuric acid. A method for producing an aromatic polyamide film in which the dope is cast from a die onto a supporting surface while maintaining its anisotropy, the dope is converted to optical isotropy by moisture absorption, and then solidified, and the film after solidification is treated with an alkaline aqueous solution. After washing with water,
Moreover, it can be produced by an aromatic polyamide film production method characterized by drying at a temperature of 350° C. or lower while limiting shrinkage of the film. 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 mechanically practical and it will be impossible to obtain a film with good flatness.
A polymer with a degree of polymerization (measured at 30°C by dissolving 0.2 g of polymer in 100 ml) is selected. The film of the present invention is selected to have a light transmittance of 60% or more in the wavelength range of visible light from 430 nm to 750 nm. Light transmittance is measured as follows. A film is pasted on the liquid cell of an ordinary photoelectric photometer (for example, a self-recording spectrophotometer), and the transmittance at each wavelength is measured. This light transmittance is 60%
For example, when the following film is used as a CRT filter, the brightness of the CRT screen is insufficient.
This is not desirable as it makes color identification difficult. Furthermore, there is no particular upper limit to the light transmittance, and the closer it is to 100%, the higher the transparency, but as a CRT filter, it is preferable to keep it at about 90% in order to increase the contrast ratio with external light. Furthermore, the film of the present invention does not transmit ultraviolet light, that is, light having a wavelength of 410 nm or less, and has a transmittance of 1% or less, so it is possible to prevent eye strain that occurs with CRTs and the like. The film of the present invention also has extremely high mechanical properties, such as strength, elongation, and Young's modulus, respectively.
15Kg/mm ² , 25%, 400Kg/mm ² or more. The films of the present invention are also preferably substantially free of voids. Furthermore, the film of the present invention has a density of 1.370
~1.405g/ ^cm2 . This density value was measured at 30°C by density gradient tube method using carbon tetrachloride-toluene. This density range is from 1.43 g/cm ² to that of known PPTA fibers.
This value is considerably smaller than the range of 1.46 g/cm ² . If the density is less than 1.370 g/cm ² , the mechanical properties will deteriorate, and if it exceeds 1.405 g/cm ² , 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 must have plane orientation defined by the crystal orientation angle determined by X-ray diffraction as described below. In other words, the crystal orientation angle with respect to the peak at 2θ≒23° caused by X-rays incident at right angles to the film surface is 30° or more, and the crystal orientation angle related to the peak at 2θ≒18° caused by X-rays incident parallel to the film surface is 60°. It must be 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° must be 30° or more, and more preferably 50° or more. Furthermore, due to incidence from the SV direction, a large diffraction peak at 2θ≒18° appears on the equator line, but the crystal orientation angle at this 2θ≒18° needs to be 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. Place the counter at the specified 2θ angle and insert the film.
Obtain the diffraction intensity curve by rotating 180°.
For TVs, rotate 90 degrees from front to back, centering on the highest intensity. The highest intensity of this curve,
It corresponds to a point showing half the intensity with respect to the baseline drawn between the lowest intensity points. The value of the arc length in degrees in the diffraction photograph (that is, the angle with respect to the 50% point with respect to the baseline of the highest intensity) is measured, and this is taken as the crystal orientation angle of the sample. During measurement, the diffraction intensity can be measured by stacking several films if necessary. Next, a method for obtaining such a PPTA film will be described. In the method of the present invention, it is first necessary to adjust the optical anisotropic doping 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 or the soluble dope will have an abnormally high viscosity. 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. 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, 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. Before molding and solidifying the dope used in the present invention, insoluble dust, foreign matter, etc. should be removed as much as possible by sieving, 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 adjusted, 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. 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. Transition to the optically isotropic region can be achieved by changing the solubility and polymer concentration, or by simultaneously or sequentially using moisture absorption and heating. 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. When a heating method is used in combination, the heating means is not particularly limited, such as a method of applying heated air to the casting dope as described above, a method of irradiating with an infrared lamp,
Examples include methods using dielectric heating. The optically isotropically cast dope on the support surface is then solidified. In the present invention, the dope coagulating liquid that can be used is, for example, dilute sulfuric acid containing water of about 70% by weight or less, sodium hydroxide aqueous solution and aqueous ammonia containing about 20% by weight or less, sodium sulfate or sodium chloride aqueous solution of about 10% by weight or less. and calcium chloride aqueous solution. 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 coagulated film contains acid as it is, in order to produce a highly transparent film that is less likely to be colored by heating, it is essential to neutralize and wash it with an aqueous alkaline solution, and washing with water alone will take several days. However, it is not possible to obtain a film with high transparency, and it is difficult to produce it industrially. Specifically, it is desirable to remove the acid content to about 500 ppm or less. Water is usually used as the cleaning solution after neutralization, but warm water may be used as necessary. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The washed film may be stretched in a wet state before drying, which is a preferred embodiment to obtain high mechanical properties. 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.). Not only does the light transmittance of the resulting film become low, but the transmitted image appears to be unstable, making it unsuitable for use with, for example, a CRT filter. 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. In order to obtain the film of the present invention, it is necessary to dry the film at a temperature below 350°C; if it is dried at a temperature higher than that, coloring etc. will occur and only a film with low light transmittance will be obtained. You can't get a film of invention. The drying temperature is preferably 300°C or lower. The drying method is not particularly limited and can be freely selected from methods such as heating or using room temperature gas (air, nitrogen, argon, etc.), radiant heating methods such as electric heaters and infrared lamps, dielectric heating methods, etc. can. 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%
0.2 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.
It was calculated by cutting a rectangle of 100 mm x 10 mm and drawing a load-elongation curve five times at an initial grip length of 30 mm and a pulling speed of 30 mm/min. The light transmittance curve was measured using Shimadzu UV-200. Reference Example (Production of PPTA) PPTA was obtained as follows by a low temperature solution polymerization method. In a polymerization apparatus shown in Japanese Patent Publication No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine were dissolved therein. After cooling to 8° C., 91.4 parts of terephthalic acid dichloride was added all at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese-like shape, so the polymerization reaction product was discharged from the polymerization apparatus according to the method described in Japanese Patent Publication No. 53-43986, and immediately transferred to a twin-screw closed kneader. The polymerization reaction product was finely pulverized. Next, the finely pulverized product was transferred to a Henschel mixer, and approximately the same amount of water was added thereto for further pulverization, followed by washing in warm water several times and drying in hot air at 110°C. 95 parts of pale yellow PPTA polymer with ηinh of 5.7 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 1-2 A PPTA polymer with ηinh or 5.7 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 10,200 poise. To facilitate film formation, this dope was degassed under vacuum while being maintained at approximately 70°C. This case also had optical anisotropy as described above, and the viscosity was 4800 poise.
The 1.5m curved pipe from the tank passes through a filter, gets a gear pump, and reaches the die, keeping it at about 70℃, 0.2mm
A mirror-polished tantalum belt (Example 1 was 5 m/min,
In Example 2, the cast dope was cast at a speed of 4 m/min) and air at about 70°C with a relative humidity of about 85% was blown to make the cast dope optically isotropic, and the dope was introduced into water at 5°C together with the belt. and solidified. The coagulated film was then peeled off from the belt, wound up once in water, and left in water. 1% of wet film
Soak in NaOH bath for 1 hour, then overnight.
Washed with running water. 10cm of washed film
I sandwiched it between the gold corners and dried it in a hot air dryer for 30 minutes to prevent shrinkage. Table 1 shows the hot air temperature at that time and the results of the obtained film. The density of the film is 1.391g/cm ² (Example 1) and 1.399g/cm 2
cm ² (Example 2), and the crystal orientation angle at 2θ≒23° with respect to the TV direction is 70 to 75°, and with respect to the SV direction.
Crystal orientation angle at 2θ≒18° is 45 to 50° (both examples)
It was hot. In addition, the transmittance of the obtained film at each wavelength is shown in FIG. Comparative Example 1 A film was formed in the same manner as in Example 2, washed with running water for one day and night without neutralization treatment, and dried in the same manner as in Example 2. The results of the obtained film are shown in Table 1 and FIG. Comparative Example 2 Films cleaned in the same manner as in Example 1 except that the belt speed was 3 m/min were shown in Table 1.
Constant length drying was performed for 10 minutes at a drying temperature of . The results of the obtained film are shown in Table 1 and FIG.

[Table] (Effects of the Invention) As shown in the examples, the film of the present invention has permselectivity that is advantageous for base films for CRT filters, which is not found in commercially available films, and has been a problem in recent years. It can reduce eye strain caused by CRT work. Furthermore, it has good mechanical properties such as high strength and high modulus that are not found in commercially available films, and it also has good mechanical properties in the MD direction.
Exhibits extremely well-balanced physical properties in the TD direction.
In addition to these properties, it also has excellent electrical insulation, heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and dense structure. Therefore, the film of the present invention can be suitably used as an insulating material for high-speed rotating electrical equipment, magnetic tape, flexible printed circuit boards, wire coating material, film, etc. Furthermore, it has another characteristic of being transparent. Because of its excellent properties, it is also useful for packaging materials, plate-making materials, photographic films, etc.

[Brief explanation of drawings]

FIG. 1 shows the light transmittance of PPTA films at each wavelength. In the figure, the film of Example 1, the film of Example 2, the film of Comparative Example 1,
indicates the light transmittance of the film of Comparative Example 2.

Claims (1)

[Scope of Claims] 1. A film substantially made of poly(p-phenylene terephthalamide) having a logarithmic viscosity of 4.5 or more, which crystals exhibit a peak at 2θ≒23° when X-rays are incident at right angles to the film surface. The orientation angle is 30° or more, the crystal orientation angle with respect to the peak of 2θ≒18° due to X-rays incident parallel to the film surface is 60° or less, and has a density in the range of 1.370 to 1.405 g/cm ³ , Light transmittance for wavelengths from 430nm to 750nm is 60%
An aromatic polyamide film having the above properties and having a light transmittance of 1% or less at a wavelength of 410 nm or less. 2. An optically anisotropic dope consisting essentially of poly(p-phenylene terephthalamide) with a logarithmic viscosity of 4.5 or more and 95% by weight or more of sulfuric acid is transferred from a die onto a supporting surface while maintaining its optical anisotropy. In a method for producing an aromatic polyamide film, in which the dope is cast, the dope is converted to optical isotropy by moisture absorption, and then solidified, the film after solidification is treated with an alkaline aqueous solution and washed with water, and the shrinkage of the film is restricted. ,
A method for producing an aromatic polyamide film, characterized by drying at a temperature of 350°C or lower.