JPH0121170B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a film with good film formability and high toughness from a solution containing an aromatic polyamide. Aromatic polyamides have excellent heat resistance and mechanical properties, and are therefore supplied as high-strength, heat-resistant fibers. By the way, among aromatic polyamides, such as polyparaphenylene terephthalamide, the position of the bond of the divalent aromatic group constituting the polymer makes the polymer molecule a linear, rod-like, rigid structure, i.e. It is known that so-called para-oriented aromatic polyamides exhibit optical anisotropy, that is, a liquid crystal structure, in a concentrated polymer solution, and that the polymers form a partially aligned domain structure and are dispersed therein. It is well known that when fibers are formed from such a solution, polymer molecules are highly oriented in one dimension due to the flow of the solution inside the discharge nozzle, resulting in the formation of high-strength fibers. (Japanese Unexamined Patent Publication No. 47-39458). In this case, it is said that the domain structure in the solution is once broken by the flow of the solution in the nozzle or the elongated flow of the solution in the non-coagulating bath, and the polymer molecular chains are arranged uniformly in one direction. On the other hand, when such an optically anisotropic solution is used for film forming, a high degree of orientation similar to the above occurs in the discharge direction when the solution passes through the slit of the die, and this orientation is almost completed in the next solidification process. . Since the film thus formed is highly oriented only in the ejection direction, the film has a high modulus in the ejection direction, but its strength in the direction perpendicular to the ejection direction (width direction) is weak and it is brittle and easily fibrillated. It is something. In order to increase the strength in the width direction, even if so-called sequential biaxial orientation is attempted by further stretching the above film in the width direction, a preferable biaxial orientation cannot be achieved due to the high softening point of the aromatic polyamide. It is difficult. Therefore, a method for forming a biaxially oriented film that takes advantage of the characteristic of an optically anisotropic solution that a remarkable orientation is achieved under flowing conditions and that does not have the above-mentioned drawbacks was investigated. For example, the invention described in Japanese Patent Publication No. 57-35088 simultaneously generates two-dimensional flow in the vertical and horizontal directions by applying the so-called inflation method to an aromatic polyamide solution having optical anisotropy. It is reported that a well-balanced film can be obtained by stretching and orienting the film. However, the film obtained by this method actually had large unevenness and low tear strength. As the present inventors continued to study the flow characteristics of solutions with optical anisotropy, it was discovered that the domain structure in which polymers are partially arranged in the solution is not possible under one-dimensional flow. Understand that when broken, the polymer can be oriented uniformly in one direction, whereas under two-dimensional flow, the domain structure is maintained and each domain simply flows in a random direction. It came to this.
Therefore, the present inventors conducted intensive research on a method for producing a film with balanced strength in two axes by utilizing the flow characteristics of the above-mentioned domains under two-dimensional flow. The inventors have discovered that the formation of the domain can be achieved by controlling the temperature conditions, and that the formation of the domain can proceed from the optical pseudo-anisotropic temperature region. We have arrived at the present invention. Therefore, the present invention provides a semi-dry, semi-wet process for producing an aromatic polyamide film, which consists of extruding an aromatic polyamide solution from a die into a non-coagulating gas, then introducing it into a coagulating bath, and then taking it off continuously. In the method, the aromatic polyamide solution has at least a temperature range exhibiting optical isotropy and a temperature range exhibiting optical pseudo-anisotropy, and the temperature of the die is such that the aromatic polyamide solution exhibits optical isotropy. The temperature of the non-coagulable gas and/or coagulation bath is maintained within a temperature range where the aromatic polyamide solution exhibits optical pseudo-anisotropy. This is a method for producing an aromatic polyamide film. In the present invention, aromatic polyamide means, in the broadest sense, a unit of the following formula:

【formula】

[Formula] and [However, in the above formula, when the unit is present in the polymer, it is present in substantially equimolar amounts, and the groups R, R' and R'' may be the same or different, and represents a divalent group, n is 0 or 1, and at least about 95 mol% of all groups R, R' and R'' in the polymer are hard groups having extended chain bonds or It thus consists of a series of such hard groups directly bonded to each other, provided that the hard cyclic groups may be bonded with azo or azoxy groups. ] A polymer consisting essentially of repeating units selected from the group consisting of
It is also described in detail in Japanese Patent No. 47-39458. Among these, R, R' and R'' are 1,4-
Typical examples include polymers selected from phenylene, 4,4'-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene, particularly polyparabenzamide and polyparaphenylene. Preferred examples include terephthalamide. Examples of the solvent for forming the aromatic polyamide solution include concentrated sulfuric acid, 100% by weight concentrated sulfuric acid, and fuming sulfuric acid.
Examples include N-alkyl-substituted amide solvents such as dimethylacetamide and N-methylpyrrolidone (addition of inorganic salts such as lithium chloride and calcium chloride is also possible). Examples of the non-coagulable gas include air, nitrogen gas, and the like. The composition of the coagulating liquid is not particularly limited, and may be a composition used in normal wet molding. A typical coagulation liquid composition is a mixture of the solvent used to form the polymer solution and water, to which inorganic salts are optionally added. The temperature range showing optical isotropy and the temperature range showing optical anisotropy or optical pseudo-anisotropy vary depending on the type and concentration of the polymer as well as the type of solvent, but the following It can be determined by the following measurement method. That is, preparing a predetermined aromatic polyamide solution,
Spread it thinly on a glass slide and place it.
I'll cover it with a prepared slide. The thus prepared sample is placed under observation using a polarizing microscope with crossed Nicols. Regarding the case where there is an optically anisotropic temperature region on the low temperature side, first, the temperature of the sample is sufficiently lowered to bring the aromatic polyamide solution on the slide glass into a state exhibiting optical anisotropy. When the temperature of the sample is gradually increased while being observed with a polarizing microscope, it is observed that the field of view becomes dark at a certain temperature and changes to an optically isotropic state. A temperature region lower than this temperature is defined as a temperature region exhibiting optical anisotropy. On the other hand, if the sample temperature is kept slightly higher than the temperature range that exhibits optical anisotropy and the sample is moved slightly, the aromatic polyamide solution on the slide glass will exhibit optical anisotropy. is observed.
However, this optical anisotropy disappears over time when the static state is restored, and the optical isotropy returns again. The time from when this optical anisotropy is developed until it returns to optical isotropy (hereinafter referred to as reduction time) varies depending on the temperature of the sample.
The closer the sample temperature is to the temperature region exhibiting optical anisotropy, the longer it becomes. A temperature range in which this reduction time is 2 seconds or more is defined as a temperature range exhibiting optical pseudo-anisotropy. Note that, where the polymer concentration is low to a certain extent, optical anisotropy is not exhibited even in a low temperature region, and only optical pseudo-anisotropy is exhibited. In the method of the present invention, once the type of aromatic polyamide, the solvent system, and the concentration of the aromatic polyamide are determined, optical isotropy, optical pseudoanisotropy, and optical anisotropy are determined according to the above measurement method. The temperature of the die is measured in the optically isotropic temperature region, and the temperature of the non-coagulating gas and/or coagulation bath is measured in the optically anisotropic temperature region or the optically pseudo-anisotropic temperature region. The aromatic polyamide solution is extruded from a die according to a known method, introduced into a coagulation bath via a non-coagulable gas, and continuously withdrawn to produce a film. At this time, the aromatic polyamide solution extruded from the die is rapidly cooled in a non-coagulating gas and/or coagulating bath and rapidly reaches a temperature that exhibits optical anisotropy, resulting in the formation of extremely small domains. It will be done. At this time, some shearing is inevitably applied, which further promotes the formation of domains. Note that a change in optical anisotropy may also occur due to a change in the concentration of the aromatic polyamide solution due to evaporation or moisture absorption of the solvent in a non-coagulating gas, or diffusion of the solvent in a coagulating bath. However, in the present invention, since the nuclei of many microdomains are first formed by a temperature change accompanied by a rapid state change, it is possible for the domains to remain in a microscopic state even if anisotropy due to other factors such as those mentioned above is added. Can be done. As a result, a film is formed that is uniform and free from unevenness, and therefore has high elongation and toughness despite its relatively high modulus. The type of die for forming the film may be a ring die for producing a cylindrical film, or a fish tail die, T-die or coat hanger die for producing a flat film or sheet. A manifold die may also be used. Alternatively, stretching may be carried out immediately at the point where optical anisotropy is beginning to appear. For example, it may be extruded from a ring die, inflated by inflation, and two-dimensional flow may be generated, or T
- When entering the coagulation bath with the die, even if one-dimensional flow is caused by stretching with a slight stretch, it will eventually show good mechanical properties in both the tension direction and the width direction, and will become fibrillated in the width direction. There isn't. In addition, as a special form of coagulation, an optically isotropic polymer solution discharged from a die as a flat thin film may be placed on a rotating roll, and then brought into contact with a coagulating liquid on the roll and coagulated. . The solidified film is then washed to remove the solvent, dried, and, if necessary, subjected to stretching and/or heat treatment. The film obtained by the method of the present invention often becomes tough even if it is not particularly stretched by constant length heat treatment. The aromatic polyamide film obtained by the method of the present invention can be used alone as it is, but it can also be used as a molded product laminated by suitable means. The effects of the present invention will be illustrated below with examples, and the percentages in the examples are expressed on a weight basis unless otherwise specified. The intrinsic viscosity (ηinh.) used as a measure of the degree of polymerization of a polymer is 100 c.c. of 98% by weight concentrated sulfuric acid.
0.5g of polymer was dissolved in the solution and measured at 30°C using a conventional method. The mechanical properties of the film were tested using a constant speed elongation strength tester using a 5 mm x 20 mm test piece at 100% per minute.
It was measured at an elongation speed of . Further, as the toughness amount, the product of modulus (GPa) and elongation (%) was used. Example 1 Poly-P-phenylene terephthalamide (hereinafter referred to as PPTA) of ηinh.5,2 and 100.0% sulfuric acid were
A planetary stirring bath was charged so that PPTA was 8 wt%, and the mixture was stirred for about 1.5 hours. The obtained polymer solution was glutinous at room temperature, but showed fluidity when heated to 120°C, making it possible to form a film. According to the measurement method described in the text, this polymer solution was optically isotropic at 120°C, and even when shear force was applied with the preparation, it became a dark field as soon as the shear force was stopped. On the other hand, at 10°C, it exhibited optical pseudo-anisotropy. The polymer solution was kept at 120℃ in diameter of 50mm.
A cylindrical thin film was extruded through a φ ring die into an air layer at a temperature of 10°C, and at the same time air was blown into the cylindrical thin film from the center of the ring die to inflate the cylindrical thin film, and then introduced into water at a temperature of 10°C. One part of the cylindrical film in the coagulation bath was cut open to form a flat film, which was washed with water for one day and night, fixed in a frame of fixed length, and dried at 100°C. Film is transparent when wet,
Thickness: 7μm, transverse modulus, elongation, and strength: 14.0GPa, 16%, and 31.5Kg/mm ² , longitudinal modulus; elongation and strength: 8.0GPa, 60%, and 25.0, respectively.
It was Kg/ ^mm2 . When the toughness was evaluated using modulus x elongation, the toughness in the horizontal and vertical directions was 224 and 480 GPa%, respectively, which were good. Example 2 The PPTA used in Example 1 was similarly added to 100.0% sulfuric acid to create a solution with a PPTA concentration of 7.9%. The resulting polymer solution was glutinous at room temperature, but became isotropic when heated to 120°C. On the other hand, at 5°C, optical pseudo-anisotropy was exhibited. This polymer solution was kept at 120℃ for a length of 100 minutes.
It was extruded into a flat film using a mm x 100 μm T-die into an air layer at a temperature of 10°C, and then coagulated in water at a temperature of 5°C. After washing with water, it was further stretched 1.2 times in the longitudinal direction with a constant width in warm water (80°C). further 10 at 90℃
Drying or heat treatment was carried out under constant conditions for 15 minutes at 200°C and 15 minutes at 350°C. obtained thickness
Modulus elongation in longitudinal direction of 11.5μm film,
The strength is 11.2GPa, 28%, and 35.0Kg/mm ² respectively, and the lateral modulus, elongation, and strength are respectively
It was 9.0GPa, 55%, and 32.3Kg/ ^mm2 . Furthermore, the toughness is 313GPa・% in both the vertical and horizontal directions.
It was 495 GPa・%, which was good. Example 3 The PPTA used in Example 1 was similarly dissolved in 100.0% sulfuric acid to create a solution with a PPTA concentration of 7.5%. The obtained polymer solution exhibited isotropy at a temperature of 120°C. At a temperature of 1°C, even if shearing force was applied under crossed Nicols and then released, optical pseudo-anisotropy remained bright for more than 10 seconds. The polymer solution was kept at 120℃ with a length of 100mm.
The temperature is
After extruding into an air layer at 20°C, it was coagulated with water at 1°C. After washing with water, at 90℃ for 10 minutes and at 250℃ for 15 minutes,
It was dried or heat treated at 350°C for 10 minutes. The longitudinal modulus, elongation, and strength of the obtained film were 9.3GPa, 33%, and 34.5Kg/ ^mm2, respectively.
and the lateral modulus, elongation, and strength are
It was 9.0GPa, 41%, 28.6Kg/ ^mm2 . The amount of toughness of the film is determined in both the vertical and horizontal directions.
They were good at 307GPa・% and 369GPa・%. Comparative Example 1 The PPTA used in Example 1 was dissolved in 100.0% sulfuric acid to create a solution with a polymer concentration of 20 wt%. The polymer solution exhibited fluid optical anisotropy at 90°C, and solid optical anisotropy at 1°C. The polymer solution was kept at 90℃ with a diameter of 50 mm.
A cylindrical thin film was extruded into air at a depth of about 5 cm using a mm cylinder die, and at the same time, air was blown into the cylindrical thin film from the center of a ring die to inflate it, and then solidified in water at a temperature of 1°C. One part of the cylindrical film in the hard bath was cut open to form a single flat film, which was then washed with water for one day and night, fixed in a frame, and dried at a fixed length (100°C). The film had large local unevenness and low tear strength. The unidirectional modulus, elongation, and strength of the sample are 12 GPa, 3.8%, and 29.8, respectively.
Kg/mm ² , and the toughness was small at 45GPa%. Comparative example 2 PPTA with ηinh.5.5 and 100% sulfuric acid
It was charged into a planetary stirring bath so that the concentration was 10 wt%, and stirred for about 1.0 hour. The resulting polymer solution exhibited optical anisotropy at 20°C, but became isotropic when heated to 120°C. 120% of the polymer solution
It was extruded into a flat film into an air layer at a temperature of 20°C using a slit die with a length of 100 mm x 100 μm kept at a temperature of 20°C, and then coagulated with water at a temperature of 20°C. After washing with water, it was dried or heat treated at a constant temperature of 90°C for 10 minutes, 250°C for 15 minutes, and 350°C for 10 minutes. The longitudinal modulus, elongation, and strength of the obtained film were 5.0GPa, 33%, and 19Kg/ ^mm2, respectively.
The modulus, elongation, and strength in the lateral direction were 6.5 GPa, 26%, and 15 Kg/mm ² . The amount of toughness of the film is determined in both the vertical and horizontal directions.
It was inferior to the example at 165GPa・% and 169GPa・%.

Claims (1)

[Claims] 1. In a semi-dry, semi-wet manufacturing method for aromatic polyamide film, which consists of extruding an aromatic polyamide solution from a die into a non-coagulating gas, then introducing it into a coagulation bath, and then taking it off continuously, the aromatic The aromatic polyamide solution has at least a temperature range in which it exhibits optical isotropy and a temperature range in which it exhibits optical pseudo-anisotropy, and the temperature of the die is a temperature at which the aromatic polyamide solution exhibits optical isotropy. and the temperature of the non-coagulable gas and/or coagulation bath is maintained within a temperature range in which the aromatic polyamide solution exhibits optical pseudo-anisotropy. A semi-dry and semi-wet manufacturing method for aromatic polyamide film.