JPH046738B2 - - 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, 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, the present invention relates to a film made of poly(P-phenylene terephthalamide) (hereinafter referred to as PPTA) and a manufacturing method thereof. ) and in the radial direction (TD direction) and exhibits excellent mechanical properties and dimensional stability, and does not curl, 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. 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 has been introduced into the aromatic nucleus of a linearly coordinating aramid is copolymerized with an amide having no substituent on the aromatic nucleus other than PPTA. Attempts have been made to make it soluble and obtain films from it. However, this monomer is expensive, so
In addition to the increased cost and concerns about the corrosivity of halogen atoms to metals, they also have the disadvantage of impairing the heat resistance and crystallinity of linearly coordinated aramids. On the other hand, Japanese Patent Publication No. 59-14567 discloses a method in which an aramid solution having optical anisotropy is extruded from a slit through a short air space into a coagulation bath. The mechanical strength in the TD direction, which is perpendicular to this, was extremely weak and could only be easily torn. If aramid optically anisotropic dope is simply extruded and solidified as it is, it will easily become fibrillated due to excessive orientation in the extrusion direction.
Since the film is weak in the TD direction, various methods of manufacturing the film have been investigated in an attempt to improve this problem. For example, in Japanese Patent Publication No. 57-35088, an aramid solution having optical anisotropy is extruded from a ring die, simultaneously cast in a doped state in two axes using an inflation method, and then wet solidified. It is said that an isotropic film can be obtained by doing this. 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 Publication No. 54-132674
In this publication, an optically anisotropic or optically isotropic dope of a linearly coordinated aramid is mechanically applied with a shearing force in a direction perpendicular to the extrusion direction in a die, so that the optically anisotropic or optically isotropic dope is However, the structure of the die is complicated and there are difficulties in industrial implementation. Furthermore, J.Appl.Polym.Sci.vol.27, No.8, P.2965
2985 (1982), it was proposed to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated conical mandrel. teeth,
Although the mechanical strength is isotropic, it is small, and when drafted, the mechanical strength in the MD direction is high, but the mechanical strength in the TD direction is extremely low. Japanese Patent Publication No. 57-17886 discloses that by heating an optically anisotropic dope of linearly coordinated aramid until it becomes optically isotropic immediately before solidifying it, and then solidifying it, it is transparent and has mechanical properties. It is described to obtain films that are isotropic. This method is an original method that goes against the conventional concept of achieving high performance by utilizing optically anisotropic doping, and it allows us to overcome the extreme uniaxial orientation of optically anisotropic doping. At the same time as the relaxation, the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded, and it has been successfully avoided that it will solidify as it is and become an opaque film. However, nothing is specifically disclosed about a film having a high Young's modulus and excellent moisture absorption dimensional stability, and a method for manufacturing the same. Also, nothing is written about curls. On the other hand, Japanese Patent Publication No. 55-51248 discloses a polyamide or polyamide hydrazide film suitable for magnetic tapes. And in it
Although a PPTA film is also described, an example in which a film was formed from an optically isotropic solution is described, since optically anisotropic liquid crystal dope provides a high Young's modulus in the vertical direction but becomes brittle in the horizontal direction. ing. but,
The PPTA film obtained in this way has a Young's modulus of
In addition to being small at 900Kg/ ^mm2 , it is difficult to avoid the formation of voids, which are thought to be caused by large shrinkage during solidification, and as a result, a film with low light transmittance can only be obtained and the film is easily torn. It has been found that when used as a film, the film is unsatisfactory in terms of surface smoothness, which is important, and furthermore, it has the disadvantage of being prone to curling at high temperatures. The publication also discloses a film made of a polyamide hydrazide copolymer and having a high Young's modulus and excellent moisture absorption dimensional stability. However, such a film has a high thermal shrinkage rate and deformation due to heat becomes noticeable at temperatures above 180°C, making it inconvenient for applications such as evaporating ferromagnetic material onto the film and using it as a magnetic tape. . Further, Japanese Patent Publication No. 53-44957 discloses a method for improving mechanical strength and dimensional stability and reducing moisture absorption rate by heat treating a polyamide or polyamide hydrazide film. Especially Example 4
PPTA film is listed here. However, applicable
PPTA film has an insufficient Young's modulus of 850 Kg/mm ² , and because the dope preparation process takes 1.5 hours at a high temperature of 120°C, the degree of polymerization decreases significantly, resulting in extremely low strength and elongation, making it brittle. It was found that since the 17% optically anisotropic dope was solidified without being optically isotropic, it had drawbacks such as low light transmittance and poor surface properties. (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 has excellent mechanical performance, is useful as a base film for magnetic recording media, and has excellent thermal resistance. Excellent dimensional stability against moisture,
An object of the present invention is to provide a transparent film that does not cause curling 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 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. (obtaining), the washed film is biaxially stretched in a wet state, and shrinkage, which generally occurs in the drying process, is limited, and
By heat-treating at temperatures above ℃, it is possible to obtain a highly transparent film with excellent mechanical properties such as strength and Young's modulus, excellent moisture absorption dimensional stability, and excellent heating dimensional stability.
Furthermore, surprisingly, a previously unknown and surprising effect has been discovered in that the occurrence of curls is almost or completely eliminated. 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 3.5 or more, and having elongation and Young's modulus in all directions parallel to the film surface. at least 10% and 1000 Kg/mm ² , the light transmittance at a wavelength of 600 nm is 60% or more, it is mainly composed of type I crystal, the density is 1.405 to 1.425 g/cm ³ , and it is parallel to the film surface. The hygroscopic expansion coefficient in the direction is 3.5×
10 ^-5 mm/mm/%RH or less, and such a film is suitable for the second aspect of the present invention, that is, poly(P-phenylene terephthalate) having a logarithmic viscosity of 3.5 or more. An optically anisotropic dope consisting essentially of amide) and 95% by weight or more of sulfuric acid is cast onto a support surface while maintaining its optical anisotropy, and the dope is made optically isotropic by absorbing moisture and/or heating. In the film production method, the film is coagulated and then solidified. After coagulation and washing, the film is
It can be produced by an aramid film production method that is characterized by biaxially stretching the film by a factor of 1.1 or more, followed by drying and heat treatment at a temperature of 350° C. or higher while limiting shrinkage of the film. The PPTA used in the present invention is substantially It is a polymer represented by the following formula, and is conveniently produced from conventionally known parphenylene diamine and terephthaloyl chloride by a low-temperature solution polymerization method. Note that the meaning that the film of the present invention consists essentially of PPTA means that a polymer other than PPTA may be blended or copolymerized in a small amount within a range that does not impede the effects of the present invention. 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 polymer with a degree of polymerization (measured at 30°C by dissolving 0.5 g of polymer in 100 ml) is selected. The film of the present invention should have the following requirements. The films of the present invention should have an elongation of at least 10% in all directions parallel to the plane of the film, preferably at least 15%. Films with an elongation of less than 10% are brittle and difficult to handle. Elongation depends on the stretching ratio, heat treatment temperature, heat treatment time, degree of polymerization of PPTA, etc. during film production, but in general, setting the stretching and heat treatment conditions to reduce the hygroscopic expansion coefficient will increase the elongation. It is often contradictory to holding a large amount. For this reason, stretching and heat treatment should be carried out so as to satisfy the requirements for both elongation and hygroscopic expansion coefficient. The degree of elongation is also related to tear strength, and in order to improve the workability of film slitting and other processing, it is necessary to have an elongation of 10% or more in all directions. It is essential. In addition, the PPTA film produced by the method described in Japanese Patent Publication No. 14170/1970 has an elongation of 4 to 6% at most in the MD direction, and an elongation of 1% in the TD direction.
Extremely easy to tear under less than The high elongation of the film of the present invention is related to the process of casting an optically anisotropic dope onto a supporting surface and then making it optically isotropic. The film of the present invention should have a Young's modulus in all directions parallel to the film plane of at least 1000 Kg/mm ² , preferably at least 1200 Kg/mm ² . This requirement is closely related to the film's resistance to deformation against external forces. For example, when the film of the present invention is used as a base film for a magnetic tape, the Young's modulus in the longitudinal direction is large, so even if the film is made thinner, the tape has good running properties and has excellent jitter characteristics. Furthermore, when the Young's modulus in the width direction is large, wrinkles and folds are less likely to occur in the tape, resulting in improved workability during tape manufacture and ease of handling during use. The Young's modulus of the film of the present invention is at a high level due to the unique process of making the optically anisotropic dope optically isotropic, solidifying it, biaxially stretching it, drying it, and heat treating it. It also depends on the stretching ratio and heat treatment temperature. The film of the present invention also has extremely high transparency, and its high transparency is characterized by a light transmittance of 60% or more at a wavelength of 600 nm. Described in Special Publication No. 55-51248 and Special Publication No. 53-44957
It is clearly distinguished from PPTA film. Such high transparency reflects the process characteristics of first preparing an optically anisotropic dope and then making it optically isotropic before forming the film, and limiting shrinkage of the film during dry heat treatment. There is. The light transmittance is preferably 70% or more. The high transparency of the film of the present invention is believed to be evidence of the fact that it is substantially free of voids, free of defects such as wrinkles and dust, and free of non-uniformity in the aggregated structure. The film of the present invention further has a hygroscopic expansion coefficient of 3.5×10 ^-5 mm/in all directions parallel to the film surface.
Should be less than mm/%RH, preferably 2.5×
10 ^-5 mm/mm/%RH or less. The coefficient of hygroscopic expansion is
A film that exceeds 3.5×10 ^-5 mm/mm/%RH means that it lacks dimensional stability against changes in humidity. As a result, the length of the magnetic tape changes, resulting in a so-called skew in the reproduced image. The excellent dimensional stability against moisture absorption of the film of the present invention is due to biaxial stretching in a swollen gel state after water washing is substantially completed, followed by limited shrinkage drying and limited shrinkage heat treatment at 350°C or higher. This is basically achieved through a combination. The present invention satisfies all the requirements of logarithmic viscosity, elongation, Young's modulus, light transmittance, and hygroscopic expansion coefficient.
PPTA films were surprisingly found to exhibit little or no curling. Although the detailed expression mechanism is unknown, subtle differences in the aggregate structure on both sides of the film formed during coagulation are
It can be assumed that curl is least likely to occur when the curl is resolved by biaxial stretching in a swollen gel state, and then the structure is heat-fixed by high-temperature heat treatment, and the properties of the resulting film satisfy all of the above requirements. can. Note that curling here refers to a phenomenon in which when a film cut into a 3 cm square is placed on a smooth surface, the center or both ends of the sample float up by 2 mm or more in an atmosphere of normal temperature and humidity. In addition to the above requirements, the film of the present invention preferably has the following aspects. The film of the present invention preferably has a strength of 35 kg/mm ² or more, more preferably 45 kg/mm ^{2 or} more. The high strength of PPTA films is inherent to a unique process in which an optically anisotropic dope with a relatively high polymer concentration is optically isotropic and then solidified into a film. Further, the film of the present invention preferably has a center line average roughness (Ra) of 0.05 μm on at least one surface thereof.
It is a film with excellent surface smoothness as shown below. More preferably, Ra is 0.02 μm or less. Because of such surface smoothness, the film of the present invention can be particularly preferably used for magnetic tapes such as video tapes. The excellent surface smoothness of the film of the present invention can be achieved by making it optically isotropic in a gas after casting and by cleaning the wet film after washing with water.
It was discovered that Ra can be lowered by reducing the coagulation rate using a specific coagulation bath. I also understood. Center line average roughness (Ra) is
It can be measured according to JIS B-0601 and JIS B-0651. For example, the all-purpose surface profile measuring device Surfcom 3B manufactured by Tokyo Seimitsu Co., Ltd. can be used. The film of the present invention is preferably a thin film of about 10 μm or less. Particularly preferably, the thickness is 8 μm or less. This is because, for example, when used as a videotape, the bulkiness per length increases in proportion to the thickness, which meets the needs for compactness, lightness, and long recording time. Although there is no particular lower limit to the thickness of the film, it is usually used at a thickness of 1 μm or more. Since the film of the present invention has a significantly high Young's modulus, this feature is particularly utilized when the film is thin. This means, for example, that the strength of the waist as a videotape is (Young's modulus) x
(Thickness) is determined by ³ , and therefore, if the Young's modulus is large, even if the thickness is reduced, the properties and handling properties for various uses as a film can be maintained. The film of the present invention more preferably has a thickness of 2 to 7 μm. Note that the thickness referred to in the present invention is 5 or more points (preferably 10 points) arbitrarily selected from the film concerned.
Defined as the average thickness at measurement points. The thickness of the film can be changed and set by changing the polymer concentration in the dope, the die gap, the draft rate, the stretching ratio, etc. Furthermore, the film of the present invention usually has a density of
It is in the range of 1.405 to 1.425 g/cm ³ . This density value was measured at 30°C by density gradient tube method using carbon tetrachloride-toluene. This density range is smaller than that of known PPTA fibers, which range from 1.43 g/cm ³ to 1.46 g/cm ³ . Density generally increases as the heat treatment temperature during film manufacturing increases to increase crystallinity. The film of the present invention is preferably 25°C, 65%
The moisture absorption rate at RH is 2% or less, more preferably 1.5% or less. In order to reduce the moisture absorption rate of the film, it is effective to increase the heat treatment temperature, but it also depends a little on the stretching ratio of the swollen gel after washing with water. As a special method, it is also a preferred embodiment to use PPTA containing a hydrophobic comonomer or end-capping agent to further reduce the moisture absorption rate. The film of the present invention is highly glossy and has a luster. Further, the film of the present invention preferably has a dynamic friction coefficient of 0.4 or less on at least one surface thereof. A film with a small coefficient of friction not only has excellent processability, but also improves tape running properties when used as a magnetic tape, for example. The film of the present invention preferably has a heat shrinkage rate of 0.2% or less at 250°C, more preferably
It is 0.15% or less. Such favorable characteristics are
This is something that the copolyamide hydrazide films disclosed in Japanese Patent Publication Nos. 51248-1982 and 44957-1982 and the aramid copolymer films disclosed in 168655-1982 cannot have. A film with a low heat shrinkage rate would be useful, for example, as a base film for vapor-deposited magnetic tapes, as well as for applications such as capacitors that undergo a solder bath immersion process.
A preferred aspect of the film of the present invention, which has a low heat shrinkage rate, is that the inherent properties of PPTA molecules, such as high crystallinity, high orientation, and rigidity, cause the optically anisotropic dope to become optically isotropic and solidify. The combination of biaxial stretching in the same state and limited shrinkage heat treatment at 350°C or above resulted in the formation of a dense, highly oriented, highly crystalline structure without any distortion, resulting in more than enough results. I believe that it is. It has been revealed that the film of the present invention mainly consists of a so-called type PPTA crystal structure in which the crystal a-axis is oriented in a direction substantially perpendicular to the film surface. Takayanagi et al. (J.Appl.Polym.Sci., 23rd
Vol. 915 (1979),
The distinction can be easily made using X-ray diffraction method: 2θ≒
The one with a diffraction peak at 21° can be considered a mold, and the one with a diffraction peak at 2θ≒18° can be considered a mold.
When both crystal forms coexist, peaks at both 2θ≒18° and 2θ≒21° appear. Since the film of the present invention mainly has a type crystal structure, it has a diffraction peak at 2θ≈21°. However, for oriented films, the incidence of X-rays is divided into two cases: one incident perpendicular to the film surface (hereinafter referred to as the TV direction) and the other incident parallel to the surface (hereinafter referred to as the SV direction). I need to think about it. In other words, X
Depending on the direction of incidence of the rays, it is possible that no diffraction peaks will be observed. In the case of the film of the present invention, the crystal a-axis is oriented in a direction substantially perpendicular to the film surface, so that, for example, a (200) peak (2θ≈23°) is not observed in TV X-ray diffraction. on the other hand,
Since the crystal b-axis and the crystal c-axis exist almost parallel to the film plane, for example, in a preferred embodiment of the film of the present invention, the (004) peak appears as a so-called Debye ring in the TV X-ray diffraction diagram. Observed. When the drying temperature or heat treatment temperature is increased in the production of the film of the present invention, in general, as the crystallinity increases, the type crystal structure in which the crystal a-axis is oriented perpendicular to the film surface increases, and conversely, the crystal b-axis is perpendicular to the film surface. It was found that the type crystal structure oriented in In addition, 2 parts of the film in a wet state
It has also been found that axial stretching increases the in-plane orientation of the crystal c-axis. These phenomena are considered to be closely related to the increase in the Young's modulus and the decrease in the hygroscopic expansion coefficient of the film by the method of the present invention. 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%, dissolution may be difficult, and 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, 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 polymer concentrations below this range, i.e., at low polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the formed PPTA film tends to contain voids and often lacks desirable transparency and mechanical properties. . The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 18% by weight or less, particularly preferably 16% by weight or less for PPTA with a particularly high ηinh, and more preferably 14% 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, lubricants, 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, it is possible to change from optical anisotropy 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 thus prepared is cast from a die, for example a slit die, onto a support surface while maintaining optical anisotropy. In addition, in the laboratory, it can be cast onto a glass plate using a doctor knife. In the present invention, casting and subsequent conversion to optical isotropy,
The steps of coagulation, washing, stretching, dry heat treatment, etc. may be performed continuously, or all or part of these steps may be performed intermittently, that is, batchwise. Preferably, the casting process is carried out continuously, and moreover, the moving speed of the support surface on which the dope is cast is at least twice the linear speed at which the dope is discharged from the die. In this way,
This is because not only can a thin film be easily obtained, but also the thickness unevenness of the film can be reduced. More preferably, the moving speed of the supporting surface is equal to the linear velocity of dope discharge.
It is 2.5 to 8 times. 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 before solidifying. 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 concentration of the polymer, or increase the temperature of the dope by heating to transform the phase of the dope into an optically isotropic region, 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 saturation pressure, or 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℃,
It is preferably carried out using humidified air at 50°C to 150°C. In the case of a heating method, the heating means is not particularly limited, and examples include a method of applying heated air to the casting dope as described above, a method of irradiating with an infrared lamp, and a method of using dielectric heating. The optically isotropically cast dope on the support surface is then solidified. In the present invention, examples of the dope coagulating liquid that can be used include water, about 70% by weight or less of dilute sulfuric acid, about 20% by weight or less of aqueous sodium hydroxide and aqueous ammonia, about 10% by weight or less of sodium sulfate, In order to obtain a film with excellent surface smoothness, i.e., a small Ra, an aqueous solution of sodium chloride, calcium chloride, etc. is preferably 10% by weight or more of dilute sulfuric acid, more preferably 30% by weight or more. dilute sulfuric acid. In the present invention, the temperature of the coagulating liquid is preferably 10°C or lower. This is because it has been found that the lower the temperature, the lower the solidification rate and the tendency for fewer voids to be included in the film, thus improving the surface properties of the film. The coagulation bath temperature is more preferably 5°C or lower, and even more preferably 0°C to 40°C. Since the coagulated film as it is contains a large amount of 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. Removal of acid content is
Specifically, it is desirable to reduce the concentration 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 by neutralizing with an alkaline aqueous solution and then washing with water. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The cleaned film needs to be biaxially stretched in the wet state before being subjected to drying. The biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching, but in either case, it is necessary to stretch the film by at least 1.1 times in the MD direction and the direction perpendicular thereto (TD direction). There is. Simultaneous biaxial stretching can be performed, for example, with a tenter, and sequential biaxial stretching can be performed with MD stretching, for example, with a roll, and TD stretching, with, for example, a tenter, and the MD stretching and TD stretching may be performed in either order. When stretching is performed, it is often observed that the moisture contained within the film comes out like sweat. Biaxial stretching improves the degree of orientation of PPTA molecular chains, smoothes the surface, and densifies the structure, resulting in an increase in mechanical properties (Young's modulus and strength) and dimensional stability (resistance to moisture absorption, It has effects such as improving temperature), increasing gloss and light transmittance, reducing Ra, and reducing curl. If the stretching ratio is less than 1.1 times, all of these functions and effects will be insufficient. Although the upper limit of the stretching ratio is not particularly limited, it is quite difficult to stretch the stretching ratio to 1.5 times or more. The stretching ratio is preferably 1.15 to 1.35 times. The stretching may be carried out in two or more parts. Note that stretching must be carried out in a wet state (gel state) before drying, and stretching that is effective for improving mechanical properties etc. cannot be performed in a state where a large amount of sulfuric acid remains in a solvent or after drying. Water content in wet state is approximately 50
Preferably it is ~300% by weight. In the present invention, the MD and TD stretching ratios in biaxial stretching are preferably approximately the same. However, in the wet film state after washing with water, the orientation of the molecular chains in the MD often takes priority, albeit slightly, and in particular, in sequential biaxial stretching, a slight shrinkage occurs in the direction that has not been stretched. However, until the shape is fixed by drying, the orientation will be relaxed and shrinkage will occur, and the orientation balance of the final product (film) should be selected (e.g., the orientation may be slightly prioritized for MD or TD). Taking into account factors such as the design of the raised film, etc.
The MD and TD stretching ratios may be set to slightly different values. For drying, the biaxially stretched film is placed under tension.
It is necessary to limit shrinkage of the film by stretching it to a constant length or slightly stretching it. If drying is performed without any restriction on shrinkage, the light transmittance of the resulting film will not only decrease, but also due to microscopic non-uniform structure formation (crystallization, etc.). The effect of biaxial stretching is diminished. To dry while limiting shrinkage, for example, a tenter dryer or drying by sandwiching between metal frames can be used. Drying is usually 50-450℃
The temperature is preferably 100 to 300°C. In the present invention, it is very important to carry out heat treatment following drying, and it should be carried out at a temperature of 350°C or higher. The upper limit of the heat treatment temperature should be determined in relation to the heat treatment time, but if the temperature is too high, the polymer will decompose, the elongation will drastically decrease, and it will be difficult to secure enough time for heat setting. Therefore, the temperature is preferably 450°C or less. The lower temperature limit of 350°C means that below this temperature, the coefficient of hygroscopic expansion is 3.5×
This is because it is difficult to obtain a film with elongation of 10% or more at 10 ^-5 mm/mm/%RH or less. The heat treatment temperature is preferably 350 to 430°C. The heat treatment time is usually selected from 5 seconds to 30 minutes. It is important to limit shrinkage of the film during heat treatment as well, and can be carried out by, for example, holding the film in a tenter or a metal frame. Drying and heat treatment in the present invention are not strictly classified. In special cases, a biaxially stretched wet film can be introduced into a zone maintained at 350° C. or higher with limited shrinkage, and drying and heat treatment can be carried out simultaneously or one after another without any clear boundaries. However, in a preferred embodiment, the biaxially stretched wet film is continuously heated at 100 to 300° C. in a tenter, for example, without relaxing the orientation.
Drying at a relatively low temperature of 350℃
The above is the process to be processed. Alternatively, a method may be considered in which the film once dried as described above is rolled up and heat treated again. In any case, it is preferable to dry the film once at a relatively low temperature because it is possible to obtain a film with less uneven internal structure and defects. In the method for producing the film of the present invention, drying or/
When heat treatment is performed at low temperature, the film has a crystal structure in which the crystal b-axis is oriented almost perpendicular to the film surface.
When a PPTA film is produced and the drying and/or heat treatment is increased, there will be more I-type crystals with the crystal a-axis oriented almost perpendicular to the film surface, and at high temperatures of 350°C or higher, most or all of the crystals will become type-type crystals. It is assumed that the dimensional stability against temperature and humidity is also related to the conversion between the two crystal forms and the conversion of orientation. Heat treatment at 350°C or above while limiting shrinkage not only converts it into a type crystal structure, but also makes the crystal c-axis more perfectly parallel to the film surface, making the film surface smoother. The agglomerated structure becomes more dense (density is 1.405g/ ^cm3 or more).
Phenomena such as heat fixation without distortion were observed.
These actions result in an increase in strength (preferably
35Kg/mm2 or ^more ), increase in Young's modulus (1000Kg/mm2 ^or more in all directions within the film plane), decrease in hygroscopic expansion coefficient (3.5 in all directions parallel to the film plane)
×10 ^-5 mm/mm/%RH or less), increased surface smoothness (reduced Ra), decreased heat shrinkage rate, and reduced curling. The means of heating in drying or heat treatment is not particularly limited, and methods include methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters and infrared lamps, dielectric heating methods, etc. You can freely choose from. 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 in the heat treatment gas as much as possible, and from this point of view, it is also a preferred embodiment to manufacture the film of the present invention in a so-called clean room or with clean water. It is. (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.
This was measured 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 and elongation and Young's modulus are determined by measuring the film sample using a constant speed extension type strength and elongation measuring machine.
It was calculated by cutting a rectangle of 100 mm x 10 mm, 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 is measured using a light beam with a wavelength of 600 nm.
It was measured using an ultraviolet-visible absorption photometer. The hygroscopic expansion coefficient is the initial length of the sample when a 2 mm wide sample is set in a thermomechanical analyzer with a grasping length of 8 mm and a load of 0.15 Kg/ ^mm2 , and the humidity is changed from 0% to 90% at 25°C. The ratio of the increment to the change in relative humidity is calculated. The curl centerline average roughness (Ra) and density were determined or measured by the methods described above. The moisture absorption rate is 65% at 25℃ from the sample in an absolutely dry state.
The ratio of the increase to the initial weight of the sample when left in an RH atmosphere is expressed as a percentage. To determine the heating shrinkage rate, take a sample approximately 10cm long,
After precisely measuring the length at 25℃ and 65%RH,
Put it in the oven at 250℃ for 2 hours, take it out and bake it for 25 minutes.
The length of the sample was measured after being left in an atmosphere of 65% RH for 2 hours, and the ratio of the decrease to the initial length of the sample is expressed as a percentage. Examples 1 to 3 and Comparative Examples 1 to 2 A small clean bench was prepared, and the present examples were conducted therein. PPTA with ηinh of 5.8 was dissolved in 99.5% sulfuric acid at a polymer concentration of 12.5% to obtain a dope with optical anisotropy at 60°C. This dope exhibited 9900 poise at about 30°C. The dope was degassed under vacuum at about 65-70°C for 5 hours. This dope was cast onto a carefully finished glass plate while maintaining the temperature above 65°C, and then sulfur-rolled into a film using a doctor knife. The cast optically anisotropic dope is heated together with the glass plate on a hot plate at 120°C, and heated to 32°C.
Moisture was absorbed from air at 80% humidity and converted into a transparent optically isotropic dope. Next, the glass plate on which the dope was cast was heated to -10°C.
It was immersed in a 25% aqueous solution of sulfuric acid to solidify it. about 10
After being immersed for a minute, the formed film was taken out from the sulfuric acid aqueous solution, left standing in water at about 25° C. for 2 days and nights (however, the water was changed a total of 7 times), and washed. The resulting wet film (approximately 230% water content) was simultaneously stretched at room temperature using a film stretcher.
Axially stretched. The stretching ratios are shown in Table 1 (the stretching ratios are the same both vertically and horizontally). Next, while the film is attached to the film stretcher, a hot plate heated to a high temperature is brought close to the film at a distance of about 1 to 2 mm from both sides of the film and held in that state for about 15 minutes to perform drying and heat treatment. Ivy. Table 1 shows the temperature of the hot plate. For comparison, a film obtained by drying a wet film to a fixed length without stretching (Comparative Example 1) and a film obtained by drying and heat treatment at a low hot plate temperature (Comparative Example 2) were combined. It is described in Table 1. The light transmittances of all the films were in the range of 78 to 91%, and the films of Examples clearly had higher surface gloss than the films of Comparative Examples. In addition, as a result of X-ray diffraction, the film of Comparative Example 2 contained a mixture of pattern crystals and pattern crystals, whereas the film of Example 2 had substantially all pattern crystals, and the other films had only a small amount of pattern crystals. The only ones that existed were mostly made up of type crystals. Furthermore, it was found that the film of the example was better in plane orientation of the crystal c-axis than the film of the comparative example. It was also found that the crystal b-axis of the crystal was perpendicular to the film plane. Also, the ηinh of all films is 5.0 to 5.3
It was within the range of

【table】

[Table] Comparative Example 3 A supplementary test of Example 4 of Japanese Patent Publication No. 53-44957 was carried out. Prepare PPTA with ηinh=5.8 and 10g of it at 98%
It was dissolved in 50 g of concentrated sulfuric acid at 120°C over 1.5 hours. The dope was quite dark. This optically anisotropic dope is cast onto a glass plate heated to about 135°C.
It was immediately placed in water at approximately 2°C. Perhaps because the decomposition of PPTA had progressed, when I tried to remove the film from the water after 5 minutes, it tore and I could not take it out. For reference, when we measured ηinh, it was 1.4. Therefore, once again, 10g of PPTA with ηinh = 5.3 was added to 98%
The dope was dissolved in 50 g of concentrated sulfuric acid at 75°C over 2 hours, then heated to 120°C, cast onto a glass plate heated to 135°C, and immediately placed in water at 2°C.
The dope immediately before being immersed in water maintained its optical anisotropy. After being immersed in water for 5 minutes, it was removed from the glass plate and washed in running water at 25°C for 24 hours. Place this film in a stainless steel frame.
It was dried at 300°C for 5 minutes. Next, an attempt was made to uniaxially stretch this opaque film to 1.1 times at 400°C, but stretching was difficult in both the casting direction and the direction perpendicular to it, and there were many places where the film would break. When we sampled the unbroken part of the film stretched only in the casting direction, the Young's modulus was 830Kg/ ^mm2 .
The strength was 9 Kg/mm ² , the elongation was as low as 1.8%, and the light transmittance was only 11%. Comparative Example 4 The results of a supplementary test of Reference Production Example 4 of Japanese Patent Publication No. 55-51248 are shown. An optically isotropic solution with a polymer concentration of 5% was prepared from PPTA with ηinh = 5.6 and 99% concentrated sulfuric acid. After casting this on a glass plate, it was directly immersed in water at 5℃ to solidify, and then fixed on a stainless steel frame for 100℃.
Dry with hot air at ℃. This film had almost isotropic properties with a strength of 11 Kg/mm ² , an elongation of 14%, a Young's modulus of 860 Kg/mm ² , and a light transmittance of 32%, but many small voids were observed. It was also easily torn by hand. Next, put this film between the frames again and heat it at 320℃.
A fixed length heat treatment was performed for 30 seconds. Although the light transmittance increased slightly to 37%, the voids did not disappear. Further, curling was significant both before and after the heat treatment. Examples 4 to 7, Comparative Example 5 A PPTA polymer having an ηinh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain a dope with optical anisotropy at 60°C. When the viscosity of this dope was measured at room temperature, it was 10,600 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 above, and the viscosity was 4400 poise.
The 1.5m bent pipe from the tank, through the filter, to the gear pump, to the die is maintained at approximately 70℃, and the temperature is 0.15mm.
It was cast onto a mirror-polished tantalum belt (moving at 12 m/min) at a linear discharge speed of 3.5 m/min from a die with a 300 mm slit, and the relative humidity was approximately 85.
The cast dope is made optically isotropic by blowing air at about 90℃, and then the dope is heated to 15% by weight at -5℃ along with the belt.
It was introduced into an aqueous sulfuric acid solution and solidified. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C, in a 1% aqueous solution of sodium carbonate, and then in -25°C water. The washed film with a water content of approximately 280% is first uniaxially stretched at room temperature in the longitudinal direction (MD) using the difference in circumferential speed of the rolls, then placed in a tenter and stretched in the transverse direction (TD) near the entrance. The film was stretched and dried by heating at a constant temperature of 150°C near the center of the tenter, and an infrared lamp was attached near the exit of the tenter for heat treatment, and then the film was wound up. The obtained films all had a thickness of 4.5 to 5.0 μm, and according to X-ray diffraction, most of the films were type crystals, the crystal a-axis was perpendicular to the film surface, and the light transmittance was 83.
~92%, ηinh = 4.7 to 5.1, and moisture absorption rate was in the range of 1.2 to 1.9%. Other properties are shown in Table 2 along with the stretching conditions and heat treatment temperature. In Comparative Example 5, the wet stretching ratio was small, and therefore the various properties of the film were not sufficiently improved.

【table】

[Table] (Effects of the invention) The film of the present invention has the original properties of PPTA film, such as excellent electrical insulation, heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and a dense structure. In addition to gender, it also has the following characteristics: It has a very large Young's modulus and has excellent deformation resistance against external forces. Do not curl. Low hygroscopic expansion coefficient and small dimensional changes due to changes in humidity. Moisture absorption rate should also be low. Excellent transparency. Low heating shrinkage rate and excellent dimensional stability against heating. Must have great strength. Must have appropriate elongation and be tough. Excellent surface smoothness. The film manufacturing method of the present invention is characterized in that an aramid film having both of these characteristics can be produced industrially, and in addition, it is particularly easy to produce a thin film. Taking advantage of the above characteristics, the film of the present invention is particularly useful as a base film for magnetic recording media such as magnetic tapes and magnetic disks. It is also useful for base films for printer tapes, transparent conductive films, flexible printed circuit boards, adhesive tapes, and insulating materials for electrical equipment. In particular, when the thin film of the present invention is used as a magnetic tape for a video tape recorder, either in a binder type or in a non-binder type, it is lightweight, enables long-time recording, and has excellent image clarity and stability. The tape will be of high quality.

Claims (1)

[Claims] 1 A film consisting essentially of poly(P-phenylene terephthalamide) having a logarithmic viscosity of 3.5 or more, and having elongation and Young's modulus in all directions parallel to the film surface of at least 10% and 1000 Kg/mm, respectively. ² , the light transmittance at a wavelength of 600 nm is 60% or more, it is mainly composed of type crystals, and the density is 1.405 ~
An aramid film having a weight of 1.425 g/cm ³ and a hygroscopic expansion coefficient in a direction parallel to the film surface of 3.5×10 ^-5 mm/mm/%RH or less.