JPH0678442B2 - Method for producing polyparaphenylene terephthalamide film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a film made of polyparaphenylene terephthalamide (hereinafter, also referred to as PPTA), and more specifically, it is transparent and has a longitudinal direction of the film. The present invention relates to a method for producing a PPTA film having excellent mechanical properties, particularly tear resistance, in both the MD direction and the width direction (TD direction).

(Prior Art) PPTA has excellent crystallinity and high melting point, and because of its rigid molecular structure, it has high heat resistance and high mechanical strength. It is a material. In addition, it has been reported that fibers spun from a concentrated solution exhibiting its optical anisotropy exhibit high strength and modulus, and it has already been industrially implemented, but there are few proposals for application to films. , The practical application is not yet known.

The problem with PPTA is that its useful high molecular weight polymer is poorly soluble in organic solvents, and strong inorganic acids such as agricultural sulfuric acid must be used as a solvent, in order to avoid this. For example, Japanese Patent Publication No. 56-45421
In the publication, a unit in which a halogen group is introduced into the aromatic nucleus of a linear coordinating aromatic polyamide and an aromatic polyamide having no substituent in the aromatic nucleus other than PPTA are copolymerized to be soluble in an organic solvent. , Then an attempt is made to get a film. However, this is costly because the monomer is expensive, and also has the drawback of impairing the heat resistance and crystallinity of the straight-chain coordinating aromatic polyamide.

On the other hand, JP-B-59-14567 discloses a method of extruding an aromatic polyamide solution having optical anisotropy through a slit into a coagulation bath through a short air layer. Only the mechanical strength of
The mechanical strength in the direction was extremely weak, and only those that could be split with a small force were obtained.

In this way, if the optically anisotropic dope of aromatic polyamide is simply extruded and coagulated as it is, it is likely to be fibrillated because it is excessively oriented in the discharge direction, which is weak in the TD direction. Various methods for producing films have been studied.

For example, in Japanese Examined Patent Publication No. 57-35088, a direction group polyamide solution having optical anisotropy is extruded from a ring die and simultaneously cast in a dope state in a biaxial direction by an inflation method, followed by wet coagulation. By doing so, an isotropic film is said to be obtained. However, it is difficult to obtain a transparent film having a uniform thickness by this method, and there is a defect that mechanical strength, particularly tear strength, is low.

Further, in JP-B-59-5407 and JP-A-54-132674, an optically anisotropic or optically isotropic dope of a linear coordinating aromatic polyamide is introduced in a die in a direction perpendicular to the extrusion direction. It has been proposed to mechanically apply a shearing force to orient the resin in the biaxial directions of the extrusion direction and the direction perpendicular to the extrusion direction at the time of extrusion, but the structure of the die is complicated and there is a difficulty in industrial implementation. Furthermore, J.Appl.Polym.Sci.vol.27, No.8, P.2965
~ 2985 (1982), it is proposed to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated cone-shaped mandrel. Has a low mechanical strength although it is isotropic, and when drafted, the mechanical strength in the MD direction is high, but that in the TD direction is extremely low.

Japanese Examined Patent Publication (Kokoku) No. 57-17886 discloses that a linearly coordinated aromatic polyamide optically anisotropic dope is heated immediately before solidification until it becomes optically isotropic, and then solidified to obtain transparent and mechanical properties. It is described to obtain a film that is directional. This method is an original method that is contrary to most of the conventional concepts of achieving high performance by utilizing the optically anisotropic dope, and thereby relaxes the extreme uniaxial orientation of the optically anisotropic dope. At the same time, we succeeded in avoiding that the optically anisotropic doped liquid crystal domain structure remains even after the dope is extruded and solidifies as it is to become an opaque film.

However, starting from Japanese Examined Patent Publication No. 59-14567, the film obtained from the optically anisotropic dope is very fragile as described above, and in Japanese Examined Patent Publication No. 57-17886,
Although the fragile defect is improved by changing the optically anisotropic dope to an optically isotropic dope, it has certain uses, for example, some uses such as the work of winding it around an iron core such as a motor as an electrically insulating film. It turned out that it was not enough for.

(Problems to be solved by the invention) In view of the technical present situation, an object of the present invention is to use PPTA, which has already been industrially produced, to have excellent flatness and to have a remarkable tear strength. It is to provide an improved method of manufacturing a PPTA film.

(Means for Solving Problems) The inventors of the present invention have earnestly studied the improvement of the method of JP-B-570-17886 in order to obtain a high-quality PPTA film having excellent flatness and excellent tear strength. As a result, the following findings were obtained.

That is, PPTA according to the method of Japanese Examined Patent Publication No.
When forming a film, a method of casting an optically anisotropic dope on a supporting surface, optically isotroping this, and forming a film is adopted, and in this method, a specific sulfuric acid aqueous solution is used in a coagulation bath, and then It has been found that a film having excellent flatness and excellent tear strength can be obtained by drying the film after washing and shrinking it under a certain condition.

The vehicles of the present invention have been completed as the present invention through further research based on these findings. That is, according to the present invention, an optically anisotropic dope substantially consisting of polyparaphenylene terephthalamide (PPTA) having an inherent viscosity of 3.5 or more and sulfuric acid of 95% by weight or more is used as a support surface while maintaining the optical anisotropy. The dope was cast on the surface, converted into an optically isotropic material by absorbing moisture and / or heating, and then maintained at 10 ° C or lower.
Coagulate in a sulfuric acid aqueous solution of more than wt%, then wash,
Further, it is a method for producing a polyparaphenylene terephthalamide film which is dried while shrinking the film by 0.6 to 0.9 times.

The PPTA used in the present invention is substantially It is a polymer represented by the following formula, and it is convenient to produce it from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low temperature solution polymerization method.

Since the degree of polymerization of the polymer of the present invention is too low to obtain a film having good mechanical properties, a logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (dissolving 0.5 g of the polymer in 100 ml of sulfuric acid at 30 ° C. The degree of polymerization that gives a measured value) is selected.

A suitable solvent for preparing the dope for molding 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 dope after dissolution 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 or the like. 100% by weight of sulfuric acid
Although the above are possible, 98 to 100% by weight concentration is preferably used from the viewpoint of stability and solubility of the polymer.

The polymer concentration in the dope used in the present invention is preferably at least a concentration exhibiting optical anisotropy at room temperature (about 20 ° C. to 30 ° C.) or higher, and specifically about
It is used in an amount of 9.5% by weight or more, preferably about 12% by weight or more. At polymer concentrations below this level, that is, at polymer concentrations that do not exhibit optical anisotropy at room temperature or below, molded PPTA films often lack favorable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but usually 20% by weight or less,
For PPTA having a particularly high ηinh, 18% by weight or less is preferably used, and more preferably 16% by weight or less.

The dope of the present invention contains the usual additives such as extenders, delusterants, UV stabilizers, heat stabilizers, antioxidants, pigments,
A dissolution aid or the like may be mixed.

Whether the dope is optically anisotropic or optically isotropic can be examined by a known method, for example, the method described in JP-B-508474. The critical point is the kind of solvent, temperature, polymer. Since it depends on the concentration, the degree of polymerization of the polymer, the content of the non-solvent, etc., by investigating these relationships in advance, it is possible to create an optically anisotropic dope and change the conditions to make it an optically isotropic dope. It is possible to change from isotropic to optically isotropic.

It is preferable that the dope used in the present invention has as much as possible insoluble dust, foreign substances, and the like removed by filtration or the like prior to molding and coagulation, and gases such as air that are generated or caught during melting have been removed. . The degassing can be performed after the dope is once prepared, or can be achieved by continuously performing vacuum (reduced pressure) from the step of charging the raw materials for the preparation. The dope can be prepared continuously or batchwise.

The dope thus prepared is cast on the support surface while maintaining the optical anisotropy by, for example, a slit die. Also, in the laboratory, casting can be performed on a supporting surface with a doctor knife. As the support surface, glass, stainless steel,
It is selected from materials such as tantalum, hastelloy, and fluororesin, or drums, belts, plates, etc. coated with these or precious metals such as gold and platinum.

The method for obtaining a transparent film having excellent mechanical properties of the present invention is to cast a dope on a support surface and then convert the dope from optical anisotropy to optical isotropic prior to solidification.

In order to change the optical anisotropy from the optical anisotropy, specifically, the optically anisotropic dope cast on the support surface is solidified prior to the solidification to reduce the concentration of the solution material forming the dope and reducing the solvent. Optical anisotropy or transition is caused by a change in the dissolution capacity and polymer concentration, or the temperature of the dope is raised by heating to cause the phase of the dope to be optically isotropic, and further, moisture absorption and heating are performed. This can be achieved by using them simultaneously or sequentially. In particular, the method of utilizing moisture absorption is useful, including the method of using heating in combination, because optical anisotropy of optical anisotropy is efficiently performed without causing decomposition of PPTA.

Air having a normal temperature and humidity may be used for absorbing the dope, but it is preferable to use air that has been humidified or heated. The super-humidified air may contain water in a mist state over the saturated vapor pressure, or may be so-called steam. Moisture absorption is usually carried out in the range of room temperature to about 180 ° C., but supersaturated steam of about 45 ° C. or less often contains large granular condensed water, so that it is preferably carried out by humidified air at 50 ° C. to 150 ° C. .

In the case of a method by heating, the heating means is not particularly limited,
Examples of the method include applying humidified air to the casting dope, irradiating an infrared lamp, and dielectric heating.

The cast dope which is optically isotropic on the supporting surface is then subjected to solidification, and the temperature and the solid-liquid concentration of the coagulating liquid are very important in the present invention. That is, in the present invention,
The temperature of the coagulating liquid is selected to be 10 ° C or lower, preferably 5 ° C or lower. If the temperature exceeds 10 ° C, the solidification rate may be too fast to cause uneven solidification, resulting in uneven thickness and partial drying shrinkage during drying, making it difficult to maintain flatness. Further, the lower the coagulation bath temperature, the smaller the amount of voids generated in the film, the higher the transparency (light transmittance), and the higher the mechanical performance such as strength. The lower limit of the coagulation bath temperature is not limited to a certain time and is up to the melting point (freezing point) determined by the composition of the coagulation bath.

As the coagulating liquid of the present invention, a 10% by weight or more aqueous sulfuric acid solution is used. The concentration of sulfuric acid in the coagulating liquid is also important.If the concentration is too low, the same phenomenon as the coagulating liquid temperature will occur, and if it is less than 10% by weight, the film will become thick and partial drying shrinkage will occur during drying, resulting in a film with poor flatness. Disappear.

The upper limit of the sulfuric acid concentration is not particularly limited, but it may be lower than the concentration at which the film is solidified, and usually about 70% by weight or less is preferably used.

Since the coagulated film contains acid as it is, it is necessary to wash and remove the acid component as much as possible in order to produce a film in which mechanical properties are hardly deteriorated by heating. Specifically, it is desirable to remove the scatter up to about 500 ppm or less. Water is usually used as the cleaning liquid, but if necessary, it may be carried out with warm water, or may be neutralized with an alkaline aqueous solution and then washed with water or the like. The cleaning is performed, for example, by running the film in the cleaning liquid or spraying the cleaning liquid.

The washed film is then dried, but in the present invention, it is very important to dry while shrinking in a specific range. By drying while shrinking, a tear strength several times as high as the tear strength of a conventional general film can be exhibited. The shrinking method can be easily performed by utilizing the shrinking force of the film itself, and the shrinkage ratio is selected to be 0.6 to 0.9 times.
If the shrinkage ratio does not reach 0.6 times, the shrinkage force becomes extremely weak, and the partial shrinkage force inside the film partially causes wrinkles in the film, impairing the flatness and curling. Further, if the temperature of the coagulating liquid is high or the concentration of sulfuric acid in the coagulating liquid is not appropriate, wrinkles are particularly generated, which is not practical at all. If the shrinkage ratio exceeds 0.9 times,
It is not possible to obtain the particularly high tear strength films aimed at by the invention.

Immediately before this drying, remove the water adhering to the film,
It is also preferred to use it after uniformly sucking it up and then drying it, because partial drying shrinkage (uneven shrinkage) of the film can be eliminated and good flatness can be obtained.

For shrinking and drying, it is possible to use, for example, setting a tenter dryer in the shrinking direction, or using a stretching type tenter from the opposite direction.

Other conditions relating to drying are not particularly limited,
You can freely choose from heating gas (air, nitrogen, argon, etc.) and room temperature gas, radiant heat using electric heaters and infrared lamps, and dielectric heating.
The drying temperature is also not particularly limited, but may be room temperature or higher.

The maximum temperature for drying is not particularly limited, but if considering the drying energy and the degradability of the polymer, it is 500 ° C.
The following are preferred.

In producing a film by the method of the present invention, any of the above steps may be carried out batchwise or continuously, and it is also possible to produce while continuously running the film throughout all the steps. This is one of the preferred embodiments.
Further, an oil agent, a dye for identification, or the like may be applied to the film in any process.

(Examples) Hereinafter, examples and reference examples (production examples of PPTA) of the present invention will be shown, but these are for illustrating the present invention and not for limiting the present invention. In the examples, unless otherwise specified, parts by weight or% by weight is shown.

The logarithmic viscosity ηinh in the examples and reference examples is 98% sulfuric acid 100 ml.
0.5 g of the polymer was dissolved in and measured at 30 ° C. by a conventional method.

The viscosity of the dope was measured with a B-type viscometer at a rotation speed of 1 rpm.

The thickness of the film was measured with a dial gauge having a measuring surface with a diameter of 2 mm.

Tear strength is cut into a rectangle of 20 mm × 100 mm, width 20 mm
A cut was made in the middle of the two, two ends were grabbed, the sample was torn at a tensile speed of 30 mm / min with a constant-speed elongation type strong elongation measuring machine, a load curve was drawn three times, and the average value was calculated.

For strength and modulus, a constant-speed elongation type strength and elongation measuring machine cuts a film sample into a rectangle of 100 mm x 10 mm, and draws the load-stretch curve 5 times at the initial gripping length of 30 mm and pulling speed of 30 mm / min. , Calculated from this.

Reference Example (Production of PPTA) PPTA was obtained by the low temperature solution polymerization method as follows. Tokusho
In a polymerization apparatus disclosed in Japanese Patent Laid-Open No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine was dissolved. 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, so the polymerization reaction product was discharged from the polymerization apparatus according to the method described in JP-B-53-43986, immediately transferred to a biaxial closed type kneader, and polymerization was carried out in the kneader. The reaction was finely ground. Next, the fine pulverization was transferred into a Hexiel mixer, and after adding approximately the same amount of water to further pulverize, it was filtered, washed several times in warm water, and dried in hot air at 110 ° C. 95 parts of a pale yellow PPTA polymer having an ηinh of 5.0 was obtained. Polymers having different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and the monomers (paraphenylenediamine and terephthalic acid dichloride), and / or the ratio between the monomers.

Examples 1-2 A PPTA polymer having ηinh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 12.0% to obtain a dope having optical anisotropy at 60 ° C. When the viscosity of this dope was measured at room temperature, it was 14500
It was a poise. The dope was kept at about 70 ° C. to facilitate film formation. It was also degassed under vacuum. Also in this case, the optical anisotropy was the same as above, and the viscosity was 4200 poise. Pass the filter from the tank, keep the 1.5 m curved pipe reaching the die through the gear pump at about 70 ° C, cast from a die with a slit of 0.3 mm × 300 mm to a mirror-polished Hastelloy belt, Air is blown at about 90 ° C with humidity of about 95% to make the casting dope optically isotropic, and then held on the belt for about 1 minute.
It was introduced into a weight% sulfuric acid aqueous solution and solidified. Then, the coagulated film is peeled off from the belt and washed by running in a water tank at about 20 ° C via a rotating roller (residence time about 3 minutes)
Then, the mixture was passed through a 1.5% caustic soda aqueous solution (about 20 ° C.) tank (retention time of about 1.5 minutes), and then into a 20 ° C. water tank (retention time of about 6 minutes).

The film taken out from the water tank is set in a biaxial stretching device (manufactured by Iwamoto Seisakusho), and MD and T are applied while applying hot air at 150 ° C
D It was dried while shrinking in both directions. The physical property results are summarized in Table 1. When the tear strength of the commercially available polyethylene terephthalate film and the polyimide film was measured, they were respectively 340 g / mm and 230 g / mm, and the tear strength of the film obtained by the present invention was several times better than that. .

Comparative Example 1 When the film was washed with the same method and conditions as in Example 1 and taken out from the cattle tank, it was dried at 150 ° C. while shrinking 0.48 times with the same apparatus as in Example 1, and wrinkles were generated on the entire surface. I could not measure the thickness.

Comparative Example 2 A film was formed and washed in the same manner as in Example 1 except that 22 ° C. water was used in the coagulation bath, and dried at 150 ° C. while shrinking 0.8 times with the same apparatus as in Example 1, and a partial 15 μm to 32
The thickness unevenness of μm occurred, and the tear strength could not be calculated.

Comparative Example 3 The film formed by the same method and conditions as in Example 1 and washed with water was fixed to a 100 mm × 200 mm metal frame and dried at 150 ° C. The physical properties of the obtained film are shown in Table 1.

(Effect of the invention) The film of the present invention has high tear strength not found in commercially available films, as shown in the examples, and
Since PPTA itself has excellent heat resistance and mechanical properties, it is particularly useful for heavy electric motors and the like.

Further, the film of the present invention has not only these properties but also excellent weather resistance, dimensional stability, oil resistance, pressure resistance, chemical resistance other than strong acid, and structural denseness. For this reason, the film of the present invention is used as an insulating material or magnetic tape (various magnetic cards, floppy disks, video tapes, audio tapes, computer tapes, etc.) for high-speed electrical crisis, flexible printed wiring boards, electronic white boards, thermal transfer printer bases. It can be suitably used for films, electric wire coatings, filtration membranes, etc., and because of its excellent transparency, which is another feature, it is also useful for packaging materials, plate-making materials, photographic films, etc. .

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Claims (1)

[Claims] 1. An optically anisotropic dope consisting essentially of polyparaphenylene terephthalamide having an inherent viscosity of 3.5 or more and sulfuric acid of 95% by weight or more is cast on a supporting surface while maintaining the optical anisotropy. Then, after the dope is converted to optical isotropicity by moisture absorption and / or heating, the dope is coagulated in a 10 wt% or more sulfuric acid aqueous solution kept at 10 ° C. or lower, and then washed, and the film is further increased to 0.6 to 0.9 times. A method for producing a polyparaphenylene terephthalamide film, which shrinks while drying.