JPS6366233A - Aramid film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a transparent aramid film, by biaxially drawing a coagulated and washed film in a wet state, drying and heat-treating the drawn film in a state of limited shrinkage, having improved mechanical performance as well as dimensional stability without causing curls. CONSTITUTION:A film, obtained by casting an optically anisotropic dope consisting of poly(p-phenylene terephthalamide) having >=3.5, preferably >=4.5 inherent viscosity and sulfuric acid in >=95wt% concentration on a support surface, converting the above-mentioned dope into an optical isotropic dope by moisture absorption and/or heating, coagulating the dope (preferably with dilute sulfuric acid in >=10wt% concentration at <=10 deg.C), washing the coagulated dope, biaxially drawing the coagulated film in a wet state at >=1.1 times, drying the film in a state of limited shrinkage of the film and heat-treating the dried film at >=350 deg.C and having at least 10% elongation and at least 1,000kg/mm<2> Young's modulus in all the directions parallel to the film surface, <=3.5X10<-5>mm/ mm/%RH moisture absorption expansion coefficient and >=60% light transmittance at 600nm wavelength.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to poly(P-phenylene terephthalamide) (
Regarding the film made of PPTA (hereinafter referred to as PPTA) and its manufacturing method, more specifically, the film exhibits excellent mechanical properties and dimensional stability in both the longitudinal direction (hereinafter abbreviated as MD direction) and the radial direction (TD direction), and has excellent curl No PPT
This relates to the A film and the manufacturing method for obtaining it.

(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 is a polymer material that has attracted particular attention in recent years. It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus.
Although it has already been implemented industrially, there are few proposals for its application to films, and no practical example is known yet.

Problems with PPTA include 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 order to
In Publication No. 45421, a unit in which a 7-rogen group is introduced into the aromatic nucleus of a linearly coordinating aramid is copolymerized with Ami-F, which has no substituent on the aromatic nucleus other than PP7, and can be used as an organic solvent. Attempts have been made to melt and obtain films from it.

However, since the monomer is expensive, there are concerns about the metal corrosiveness of the rogen atoms, and the heat resistance and crystallinity of the linearly coordinated aramyrus are impaired. There are some drawbacks.

On the other hand, Japanese Patent Publication No. 59-14567 discloses a method of extruding an aramid solution having optical anisotropy from a slit through a short air layer into a coagulation bath. Only the intensity is strong, and T is perpendicular to it.
D The mechanical strength in the force direction was extremely low, and only a product that was easily torn was obtained.

In this way, simply extrude the aramid optically anisotropic dope 7
If the film is simply solidified as it is, it will be excessively oriented in the discharge direction, making it prone to fibrillation and weak in the TD force direction. Various inspections were carried out.

For example, Japanese Patent Publication No. 557-35088 discloses that 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. Assume that an isotropic film is obtained by /').

However, this method has the drawback 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. 54-1.3
In Publication No. 2674, an optically anisotropic or optically isotropic dope of linearly coordinated arami F is mechanically applied with a shearing force in a direction perpendicular to the extrusion direction in a goo, so that it is aligned with the extrusion direction during extrusion. Although it has been proposed that the die be oriented in two axes perpendicular to that direction, the structure of the die is complicated and there are difficulties in industrial implementation.

Further J, Appl, Polym, Scf, v
ol, 27, A 8, P.

2965-2985 (1982), a biaxially oriented film was produced by extruding an optically anisotropic dope of PPTA onto a ring die and a conical mantle coated with oil. However, this film has the disadvantage that 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 significantly low. be.

Japanese Patent Publication No. 57-17886 discloses that by heating the optically anisotropic r-zo of linearly coordinated aramy P until it becomes optically isotropic immediately before solidification, and then solidifying it, transparent mechanical properties can be obtained. It is described that a film is obtained which is isotropic. Is this method suitable for conventional optical anisotropy? This is an original idea that goes against the big man's concept of achieving high performance by utilizing doping. This successfully avoids the liquid crystal main structure of the dope remaining even after the dope has been extruded and solidifying into 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 producing the same. ! ! Nothing is written about curls.

On the other hand, Japanese Patent Publication No. 55-51248 discloses a polyamide film or a polyamide film for magnetic tape. Among them, PPTA film is also described, but optically anisotropic liquid crystal-doped films can obtain a high Young's modulus in the vertical direction but become brittle in the horizontal direction, and are made from an optically isotropic solution. An example in which a film was used is described. The Young's modulus of the PPTA film obtained in this way is as small as 900/-2, and it is difficult to avoid the generation of zey P, which is thought to be caused by large shrinkage during solidification, and therefore, light transmission is difficult. The disadvantage is that only a film with a low ratio can be obtained and the film is easily torn;
When used as a magnetic tape, the film is unsatisfactory in terms of surface smoothness, which is important.
6 = It was found that the product had the disadvantage of being prone to curling under warm conditions. The publication also discloses a film made of polyamidehydra)P copolymer, which has a high Young's modulus and excellent moisture absorption dimensional stability. However, since Kotobuki has learned that such films have a large thermal shrinkage rate and deformation due to heat becomes noticeable at temperatures above 180°C, they are inconvenient for applications such as evaporating ferromagnetic material onto the film and using it as a magnetic tape. It is.

Further, Japanese Patent Publication No. 53-44957 discloses an improvement method for improving mechanical strength and dimensional stability and reducing moisture absorption rate by heat treating a polyamide P or polyamide P film. In particular, Example 4 describes a PPT human film. However, the PPTA film has an insufficient Young's modulus of 850 K4/lri'', and since the dope is prepared at a high temperature of 120°C for 1.5 hours, the degree of polymerization is significantly reduced and the strength and elongation are extremely low. It has been found that it has disadvantages such as being small and brittle, and having a low light transmittance and poor surface properties because it is solidified from an optically anisotropic dope of about 17% without being optically isotropic.

(Problems to be Solved by the Invention) The purpose of the present invention is to
The object of the present invention is to provide a manufacturing method using PTA, especially for magnetic recording media.

(Means for Solving the Problems) The present inventors have made the following findings as a result of intensive research to obtain a PPTA film that meets the above objectives.

That is, by the technique disclosed in Japanese Patent Publication No. 57-17886 (first doping PPTA with optical anisotropy, making it optically isotropic and solidifying it), it is possible to obtain a transparent material with excellent mechanical properties. PPTA film can be obtained)
In the step, the washed film was biaxially stretched in a wet state,
In addition, shrinkage, which generally occurs during the drying process, is limited, and by heat treatment at a temperature of 350°C or higher, a highly transparent film with excellent mechanical properties such as strength and Young's modulus, and excellent moisture absorption and dimensional stability can be produced. In addition to this, it has been found that it has excellent heating dimensional stability, and surprisingly, it has been found that there is little or no curling, a previously unknown and surprising effect.

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 terephthalamyl) having a logarithmic viscosity of 3.5 or more, and having elongation and Young's modulus in all directions parallel to the film surface. are respectively at least 10% and 1000Kg/
F12, light transmittance at wavelength of 600℃m is 60%
An aramid film having the above properties and a hygroscopic expansion coefficient in the blood formation direction parallel to the film surface of 3.5 x 10-5 /wn/XRH or less, and such a film. The second aspect of the present invention, i.e., the BoIJ having a logarithmic viscosity of 3.5 or more (P-phenylene terephthalamine P
) and 95% or more of sulfuric acid is cast onto a supporting surface while maintaining its optical anisotropy, and the P-plate is heated by absorbing moisture and/or heating. In the method of producing a film in which the film is converted to optically isotropic and then solidified, after solidification and washing, the film is biaxially stretched to 1.1 times or more in a wet state, and then dried and It can be manufactured by an aramid film manufacturing method characterized by performing heat treatment at a temperature of 350° C. or higher.

The PPTA used in the present invention is a polymer substantially represented by the following formula, and is conveniently produced from conventionally known norahenylene diamine and teroyl chloride by a low-temperature solution polymerization method.

If the degree of polymerization of the polymer of the present invention is too low, it will be difficult to obtain a film with good mechanical properties. A polymer having a degree of polymerization that gives a value measured at 30° C. after dissolving 59 is selected.

The film of the present invention should have the following requirements.

The films of the present invention should have an elongation in all directions parallel to the film plane of at least 10%, 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 the tear strength, and in order to improve the workability of film slitting and other processing, it is necessary to increase the elongation by 10% in all directions.
It is important to have a degree of elongation higher than that.

Note that the PPTA film made by the method described in Japanese Patent Publication No. 55-14170 has an elongation of 4 at most in the MD direction.
~6%, and the elongation in the TD direction is less than 1%, making it extremely easy to tear. The high elongation of the film of the present invention is related to the process of casting an optically anisotropic dope onto a support surface and then making it optically isotropic.

The film of the invention should have a Young's modulus in all directions parallel to the film plane of at least 1000 Kq/rum2, preferably at least 1200 Kq/rum2.

This requirement is closely related to the film's resistance to deformation to 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 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, which improves workability during tape manufacture and ease of handling during use. The Young's modulus of the film of the present invention depends on the stretching ratio and heat treatment temperature during production.

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.
It is clearly distinguished from the PPTA films described in Japanese Patent Publication No. 14170, Japanese Patent Publication No. 55-51248, and Japanese Patent Publication No. 53-44957. This high degree of transparency
This reflects the process characteristics of first preparing an optically anisotropic dope and then making it optically isotropic to form a film, and limiting shrinkage of the film during dry heat treatment.

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 blemishes, and free of non-uniformity in its aggregated structure.

The film of the present invention further has a hygroscopic expansion coefficient of 3.5X10-50/throat/%RH in all directions parallel to the film surface.
Should be less than or equal to, preferably 2.5X10~5 go/r
an/%RH or less. Hygroscopic expansion coefficient is 3.5X10
A film exceeding "rrm/van/%RII" means that the film lacks dimensional stability against changes in humidity. This has the disadvantage that the length changes, which causes so-called skew in the reproduced image.The excellent dimensional stability against moisture absorption of the film of the present invention is due to its excellent dimensional stability in the swollen glue state after water washing is substantially completed. This is essentially accomplished by a combination of biaxial stretching of , followed by limited shrinkage drying and limited shrinkage heat treatment at 350°C μ.

Surprisingly, it was discovered that the PPTA film of the present invention, which satisfies all the requirements of logarithmic viscosity, elongation, Young's modulus, light transmittance, and hygroscopic expansion coefficient, exhibits little or no curling. . Although the detailed mechanism is still unknown, the subtle differences in the agglomerated structure on both sides of the film formed during solidification are resolved by biaxial stretching in the swollen gel state, and then the structure is fixed by high temperature heat treatment. It can be estimated that curling is least likely to occur when the properties of the produced film satisfy all of the above requirements. Note that curling here refers to a phenomenon in which when a 3 cTn square film is placed on a smooth surface, the center or both ends of the sample float up by 2° C. or more in a normal temperature and humidity atmosphere.

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 weight of 35 Kg/rran.
It has a strength of 2 or more, more preferably 45Kg/
It has an intensity of ran2 or higher. Such high strength in 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 an excellent surface smoothness with a center line average roughness (Ra) of at least one surface of 0.05 μm or less.

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 makes it possible to make it optically isotropic in gas after casting, to limit shrinkage of the film during biaxial stretching of the wet film after water washing, and during drying and heat treatment steps. It was also discovered that Ra can be further reduced by using a specific coagulation bath to reduce the coagulation rate. Center line average roughness (Ra) is JIS B-
0601 and JIS B-0651. For example, the all-purpose surface shape measuring instrument Surfcom 3B manufactured by Tokyo Seimitsu Co., Ltd. can be used.

The film of the present invention is approximately 10μ? A thin film of n or less is preferred. Particularly preferably, the thickness is 8 μm or less.

This is because, for example, when used as a videotape, the bulkiness of a tape of the same length increases in proportion to its thickness, which meets the needs for compact size, weight, 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 large Young's modulus, this feature is particularly utilized when the film is thin. For example, the stiffness of a videotape is (Young's modulus) x (thickness) 3). Therefore, if the Young's modulus is large, even if the thickness is made thinner, the characteristics and handling properties of the film for each purpose will be affected. This is because it can be maintained. The film of the present invention is preferably
It has a thickness of 7 μm. Note that the thickness as referred to in the present invention is defined as the average value of the thickness at 5 or more (preferably 10) measurement points arbitrarily selected from the film.

The thickness of the film can be changed and set depending on the polymer concentration in the dope, the gap between the gooses, the draft rate, the stretching ratio, etc.

Further, the film of the present invention typically has a density of 1.40.
It is in the range of 5 to 1.42517 cm3. This density value was measured at 30° C. by density gradient tube method using carbon tetrachloride-toluene. This density ranges from 1.43 f/3 to 1.43 f/3 for known PPTA fibers.
This is a small value compared to the range of 4617 cm3. Density generally increases with increasing heat treatment temperatures in film production to increase crystallinity.

The film of the present invention preferably has a temperature of 25° C. and 65% RH.
The moisture absorption rate is 2% or less, more preferably 1,
5z or less. In order to reduce the moisture absorption rate of the film by /J, it is effective to increase the heat treatment temperature.
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 with a hydrophobic comonomer or end-capping agent to further reduce the moisture absorption rate.

The film of the present invention is glossy and glossy. Further, the film of the present invention preferably has a coefficient of dynamic friction of at least 0.4 or less. 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 0.1jX or less. Such favorable features are the result of the
Copolyamide P hydrazide films disclosed in Japanese Patent Publication No. 1248 and Japanese Patent Publication No. 53-44957;
This is something that the Arami P copolymer film of Publication No. 168655 cannot possess. 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 in applications such as capacitors that undergo a solder bath immersion process.

A preferable aspect of the film of the present invention, which has a low heat shrinkage rate, is PPT, which has high crystallinity, high orientation, and rigidity.
The original properties of the A molecule are made dense by a combination of optically isotropic solidification from optically anisotropic P-p, biaxial stretching in a wet state, and limited shrinkage heat treatment at 350°C or higher. Is the highly oriented and highly crystalline structure distorted? It is believed that this is a fully realized result because it was formed without leaving anything behind.

It has been revealed that the film of the present invention mainly consists of a so-called I-type PPTA crystal structure in which the crystal a-axis is oriented in a direction substantially perpendicular to the film plane. Takayanagi et al. (J.
, Appl, Polym, SCj,, Volume 23,
915 (1,979)), and the distinction can be easily made by X-ray diffraction method: type 1 has a diffraction peak at 2θξ21°, and type 1 has a diffraction peak at 20-18°. You can make things into ■ shapes.

If both crystal forms are mixed, 20#18° and 2θ-21°
Both quirks appear. Since the film of the present invention mainly has a type I crystal structure, it has a diffraction peak at 20-21'. However, for a film with an oriented component, the incidence of X-rays is divided into two cases: when the X-rays are incident at right angles to the film surface (hereinafter referred to as the TV force direction) and when they are incident parallel to the surface (hereinafter referred to as the SV force direction). I need to swim. However, depending on the incident direction of the X-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 almost perpendicular to the film plane, so in TV X-ray diffraction, for example, (200
) peak (2θ to 23°) is not observed. On the other hand, since the crystal 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 is the so-called peak in the X-ray diffraction diagram of the TV. , observed as an s-ring. When the drying temperature or heat treatment temperature is increased in the production of the film of the present invention, in general, the crystallinity increases and the I-type crystal structure in which the crystal a-axis is oriented perpendicular to the film plane increases, and conversely, the crystal bl1
1] was found to reduce the ■-type crystal structure oriented perpendicular to the film plane. It has also been found that biaxial stretching of a wet film 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 necessary to prepare an optically anisotropic dope of PPTA.

A suitable solvent for preparing the PP used to form the PPTA film of the present invention is sulfuric acid at a concentration of 95 wt 2 or higher. If the sulfuric acid content is less than 95%, dissolution may be difficult or the dope will have an abnormally high viscosity after dissolution.

The dope of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, and the like. Although it is possible to use sulfuric acid with a concentration of 100% by weight or more, from the viewpoint of stability and solubility of the polymer, the concentration should be 98 to 100% by weight.
Weight % concentrations are 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 It is used in an amount of 10% by weight or more. If the polymer concentration is lower than this, i.e., a low Hf lj polymer that does not exhibit optical anisotropy at room temperature or higher temperatures, the molded PPTA film will easily contain dir2 and will not have desirable transparency or mechanical properties. Totoga evening. The upper limit of the polymer concentration of the dope is not particularly limited, but it is usually 18% by weight or less, particularly for PPTA with high ηinh, 16% by weight or less, and more preferably 14% by weight or less. .

The dope of the present invention may also contain conventional additives such as fillers, deglapers, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizers, lubricants, etc.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, such as the method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, polymer It depends on the concentration, degree of polymerization of the polymer, content of non-solvent, etc., so by investigating these relationships in advance, it is possible to change the optically anisotropic dope to the conditions that make it an optically isotropic dope. It is possible to change from anisotropy to optical isotropy.

Prior to molding and solidification, the P-ZO used in the present invention removes as much cine-soluble dust, foreign matter, etc. as possible by filtration, etc.
It is preferable to remove gases such as air generated or trapped during melting. Deaeration is performed once at P-
This can be carried out after the preparation of the liquid, or it can be achieved by carrying out the process under vacuum (reduced pressure) from the stage of charging the raw materials for preparation. The dope can be prepared continuously or in batches.

The dope thus prepared is cast onto a support surface from a die, for example a slit die, while maintaining its optical anisotropy. In addition, in the laboratory, it can be cast onto a glass plate using a doctor knife. In the present invention, even if steps such as casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, and dry heat treatment are performed continuously, all or part of these steps may be performed intermittently in batches. You can go to the ceremony. Preferably, the casting process is carried out continuously, and moreover, at a moving speed of 12 times or more of the linear speed at which the dope is discharged from the supporting surface on which the P-poly is cast. This is because not only can a thin film be easily obtained, but also the unevenness in film thickness can be reduced. The moving speed of the support surface is preferably 2.5 to 8 times the linear speed of dope discharge.

The method of obtaining the transparent film 2 having excellent mechanical properties according to the present invention is to cast the dope on the supporting surface and then, prior to solidification, P-
This converts the optical anisotropy to optical isotropy.

To change optical anisotropy to optical isotropy, specifically, before solidifying the optically anisotropic r-zo cast on the support surface, the concentration of the solvent that forms the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility of the solvent and polymer concentration, or increase the temperature of the dope by heating to transform the phase of the dope to optically isotropic, or absorb moisture and heat simultaneously or sequentially. This can be achieved by using both in combination.

In particular, methods using moisture absorption, including methods that use heating in combination, are effective in achieving optical equalization of optical anisotropy and in PPTA.
It is useful because it can be done without causing decomposition.

To make the P-pu absorb moisture, air at normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain mist-like moisture exceeding the saturated vapor pressure, and may be so-called water vapor. However, supersaturated steam at a temperature of about 45° C. or lower is not preferred because it often contains large particles of condensed water. Moisture absorption is usually carried out with humidified air at room temperature to about 180°C, preferably 50°C to 150°C.

In the case of a heating method, the heating means is not particularly limited;
A method of applying heated air to the casting dope as described above,
Methods include irradiation with an infrared lamp and dielectric heating.

The optically isotropically cast dope on the supporting surface is then solidified t
box office. In the present invention, examples of the dope coagulating liquid that can be used include water, about 10% 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, Examples include aqueous sodium chloride solution and aqueous calcium chloride solution, but in order to obtain a film with excellent surface smoothness and low Ra, dilute sulfuric acid preferably has a concentration of 10% by weight or more, and more preferably 30% by weight. % or more dilute sulfuric acid.

In accordance with 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 less diide to be included in the film, thus improving the surface properties of the film.

The coagulation bath temperature is preferably 5°C or less, 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 deteriorated by heating. Specifically, it is desirable to remove the acid content at a concentration of about 500 ppm or less. Water is usually used as the cleaning liquid 7, but if necessary, hot water may be used, or washing may be performed by neutralizing with an alkaline aqueous solution and then washing with water. Cleaning is carried out, for example, by running the film in a cleaning liquid, spraying the cleaning liquid, or the like.

The washed 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 stretched by 1.1 times or more in each of the MD force direction and the direction J perpendicular thereto. There is a need. Simultaneous biaxial stretching can be carried out, for example, with a tenter, and sequential biaxial stretching can be carried out, for example, with MD stretching in a mouth-roll and TD stretching, for example, in a tenter, and the MD stretching and TD stretching can be carried out in either order. When stretching is performed, it is often observed that water contained within the film comes out like sweat.

Biaxial stretching smoothes the clay surface and densifies the structure of the PPTA molecular chain orientation, increasing mechanical properties (Young's modulus and strength) and improving dimensional stability (moisture absorption, temperature). It has effects such as an increase in gloss and light transmittance, a decrease in Ra, and a decrease in curl. If the stretching ratio is less than 12.1 times, both of these functions and effects will be insufficient. Although the upper limit of the stretching ratio is not particularly specified, it is difficult to stretch the film to a stretching ratio of 1.5 times or more. The stretching ratio is preferably 1.1.5 to 1.3.
It is 5 times more. The stretching may be carried out in two or more parts.

Note that stretching must be performed in a wet state (gel state) before drying, and effective stretching for improving mechanical properties etc. cannot be performed in a state where a large amount of sulfuric acid, which is a solvent, remains or after drying.

Preferably, the water content in the wet state is about 50-300% by weight.

In the present invention, it is preferable that the MD and TT stretching ratios in biaxial stretching are approximately the same.

However, 1 to 1 is that in the state of the wet film after washing with water, the orientation of the molecular chains in the MD is often prioritized, 2 although slightly, and especially in the direction that has not been stretched in sequential biaxial stretching. Slight shrinkage may occur, orientation relaxation and associated shrinkage may occur in trenches whose shape is fixed by drying, orientation of the entangled product (film) and Z-lance selection (for example, slight orientation in MD or TD). (e.g., the design of a tensilized r film that gives priority to

Drying must be carried out while the biaxially stretched film is under tension, under constant length, or slightly stretched while limiting shrinkage of the film. If drying is performed without any restriction on shrinkage, the light transmittance of the resulting film will not only decrease, but also due to the formation of microscopically non-uniform structures (crystallization, etc.). The effect of biaxial stretching is diminished and I7 increases. To dry while limiting shrinkage,
For example, a tenter dryer or drying by sandwiching between metal frames can be used. Drying is usually carried out at a temperature of 50 to 450°C, 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 may decompose.
The temperature is preferably 450° C. or lower because of the extreme decrease in elongation and the difficulty of securing sufficient time for heat setting. 350℃
The reason for this lower limit temperature is that below this temperature, it is difficult to obtain a film having a hygroscopic expansion coefficient of 3.5×10 −51/1 rvn/%RH or less and an elongation of 10 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 the shrinkage of the film during heat treatment, and the heat treatment 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. As a special case, biaxially stretched wet films'! It is also possible to introduce the product into a zone maintained at 11-350° C. or less while limiting the yield, and to carry out drying and heat treatment simultaneously or one after another without knowing the boundary. However, in a preferred embodiment iZi: the biaxially stretched wet film is subsequently dried without orientation relaxation, for example in a tenter at a relatively low temperature of 100-300°C;
This process is followed by heat treatment at 350°C or higher. Alternatively, roll up the once dried film as described above,
It is also possible to consider a method of applying heat treatment again. In any case, once drying is performed at a relatively low temperature, it is preferable to obtain a film with less uneven internal structure and defects.

In the film manufacturing method of the present invention, when drying and/or heat treatment is performed at a low temperature, a PPTA film with a ■-shaped crystal structure in which the crystal axis is oriented almost perpendicular to the film surface is produced; When the temperature is high, there are many ■-type crystals with the crystal a-axis oriented almost perpendicular to the film surface.
It has been found that at high temperatures of 350°C or higher, most or all of the crystals become type I crystals, and the dimensional stability against temperature and humidity is also related to the conversion between these two crystal types and the conversion of orientation. It is assumed that

When heat treated at 350°C or above while limiting shrinkage, in addition to converting to an I-type crystal structure, the crystal C axis orientation becomes perfectly parallel to the film surface, and the film surface is Phenomena such as a smooth and dense aggregate structure (preferably density of 1.4052/α3 or more) and heat setting without distortion were observed, and these effects lead to improved strength. increase (preferably 35 KGJ/wn2 or more), increase in Young's modulus (1 in all directions within the film plane)
000Kf/scream) reduction in hygroscopic expansion coefficient (3.5 x 10' wn in all directions parallel to the film surface)
/ran/%1'LH or less), increase in surface smoothness (Ra
), heat shrinkage rate, and curling.

The means of heating in drying or heat treatment is not particularly limited, and may include methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters or infrared lamps, dielectric heating methods, etc. You can freely choose from the following methods.

In one embodiment of the method of the present invention, it is preferable to manufacture the film while continuously running it throughout the entire process.
However, if desired, it may be done partially batchwise. -ti It is possible to apply an oil agent, an identification dye, etc. to the film in any step.

In the present invention, in order to obtain a film with excellent transparency, that is, extremely high light transmittance, the dope is a thermal dope, a moisture absorption gas, a heating gas, a supporting surface, a coagulating liquid, a cleaning liquid, and a drying gas. It is preferable to minimize the content of dirt and dust in the heat treatment gas, etc. In this respect, it is also preferable to manufacture the film of the present invention in a so-called screen room or with clean water. This is one of the aspects.

(Example) Examples and reference examples (manufacturing examples of PPTA) are shown below, but these reference examples and examples explain the present invention, and do not limit the present invention. In the examples, parts by weight or weight % are shown unless otherwise specified. The logarithmic viscosity ηinh was measured by dissolving 0.5f of the polymer in 100 mA' of 98% sulfuric acid at 30°C in a conventional manner. The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm. The thickness of the film was measured using a dial gauge with a measuring surface of 2 m in diameter. The strength and elongation and Young's modulus were determined by cutting the film sample into a 100cm x 10mm rectangle using a constant speed extension type strength and elongation measuring machine, using an initial gripping length of 30m and a tensile speed of 30g/min. The load-extension curve was drawn five times and calculated accordingly.

The light transmittance was measured using a UV-visible absorption photometer using a light beam with a wavelength of 600 nm. The hygroscopic expansion coefficient is determined by grasping a 2-width sample into a thermomechanical analyzer, with a length of 8 trrm,
Set with a load of 0.15Kp/m, and set the humidity to 0 at 25℃.
The ratio of the increment to the initial length of the sample when changing from % to 90% is determined with respect to the change in relative humidity. Curl centerline average roughness (Ra) and density were determined or measured by the methods described above.

Moisture absorption rate is determined by drying the sample at 25℃ and 65%RH.
The ratio of the increase to the initial weight of the sample when left in the atmosphere is expressed as a percentage.

The heating shrinkage rate is 25 mm when the sample is approximately 10 on long.
After precisely measuring the length at ℃ and 65% RH, it was heated to 250℃.
Put it in the oven for 2 hours, take it out and heat it at 25℃, 65%
The length was measured after being left in an RH atmosphere for 2 hours, and the ratio of the decrease to the initial length of the sample was expressed as a percentage.

Examples 1 to 3 and Comparative Examples 1 to 2 Prepare small clean pliers and carry out this example inside them.

PPTA having y+inh of 5.8 was dissolved in 99.5% sulfuric acid at a polymer concentration of 12.5% to obtain a dope having optical anisotropy at 60°C. This P-p exhibited 9900 voids at about 30°C. The dope was degassed under vacuum at about 65-70°C for 5 hours.

I kept this P-pu at 65℃ or higher! Well, it was cast onto a glass plate with a carefully finished surface, and then cast into a film using a doctor knife. The cast optically anisotropic dope was heated together with the glass plate on a hot plate at 120°C, and was converted into a transparent optically isotropic P-dope by absorbing moisture from 80% humidity air at 32°C.

Next, the glass plate on which P-zo was cast was heated to -10°C at 25°C.
% sulfuric acid aqueous solution to solidify it. After being immersed for about 10 minutes, the formed film was removed 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 biaxially stretched at room temperature using a film stretcher.

The stretching ratios are shown in Table 1 (stretching ratios are the same both vertically and horizontally.

). Next, with the film 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 21 rIIn from both sides and held in that state for about 15 minutes to perform drying and heat treatment. Ta. 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. Table 1
Describe it in The light transmittances of all the films were within the range of 78 to 91%, and the films of Examples had clearly higher surface gloss than the films of Comparative Examples.

Additionally, as a result of X-ray diffraction, the film of Comparative Example 2 contained type I crystals and type ■ crystals, whereas the film of Example 2 had substantially all type I crystals, and the other films had type I crystals. There are only a few type crystals, and most of it consists of type I crystals. Furthermore, it was found that the film of the example was superior to the film of the comparative example in terms of plane orientation of the crystal C axis, and while in the case of type I crystal, the crystal a axis was perpendicular to the film plane, It was also found that the crystal axis of type (2) crystals was perpendicular to the film plane. Also, for all films, one line is 5.0
It was in the range of ~5.3.

Margin Comparative Example 3 A follow-up test of Example 4 of Japanese Patent Publication No. 53-44957 was conducted.

Prepare PPTA with ηinh = 5.8, and
' was dissolved in 98% concentrated sulfuric acid 501 at 120°C over 1.5 hours.

P-pu was slightly darkened. This optically anisotropic dope was cast onto a glass plate heated to about 135°C and immediately placed in water at about 2°C. Because the decomposition of PPTA had progressed, when I tried to remove the film from the water after 5 minutes, it was torn and I could not remove it.

For reference, I measured ηinh and found it to be 1.4.

Therefore, once again, PPTA 10 F with η1nh=5.3
98% concentrated sulfuric acid 50'? The dope was then heated to 120°C, cast onto a glass plate heated to 135°C, and immediately placed in water at 2°C.

P-P immediately before being immersed in water maintained its optical anisotropy. After being immersed in water for 5 minutes, it was peeled off from the glass plate and washed in running water at 25°C for 24 hours. This film was sandwiched between stainless steel frames and dried at 300° C. for 5 minutes. This opaque film was then heated at 400°C for 1.
An attempt was made to uniaxially stretch the film to 1x, but it was difficult to stretch both in the casting direction and in 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 830/! !
II+2, but the strength was 9 Ky/mm2 and the elongation was 1
．． The light transmittance was as low as 8%, and the light transmittance was only 11%.

Comparative Example 4 The results of a follow-up 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 η1nh=5.6 and 99% concentrated sulfuric acid. After this was cast onto a glass plate, it was directly immersed in water at 5°C to solidify, fixed on a stainless steel frame, and dried with hot air at 100°C.

This film has a strength of 11 KIi/myr2 and an elongation of 1
Although it had almost isotropic properties with a Young's modulus of 860 Ky/2 and a light transmittance of 32%, many small Hz ids were observed. It was also easily torn by hand.

Next, this film was placed between the frames again and subjected to constant heat treatment at 320° C. for 30 seconds. Although the light transmittance increased slightly to 37%, the light transmittance disappeared and was poor. '-1: Significant curling was observed both before and after heat treatment.

Examples 4 to 7, Comparative Example 5 17 fnh is 5.50 PPTA polymer 99.7%
The polymer was dissolved in sulfuric acid at a polymer concentration of 11.5% to obtain an optically anisotropic P-polymer at 60°C. The viscosity of this dope was measured at room temperature and was found to be 10,600 poise. To make it easier to form a film, while keeping this P-pu at about 70°C,
Makoto also deflated below. This case also had optical anisotropy as in Example 2, and the viscosity was 4400 poise. Pass through the filter from the tank, go through the gear pump, and reach the die 1, 5
Keep the curved pipe of m at about 70℃, 0.15 m x 300 m+
A mirror-polished tantalum bell) (moving at 12 m/min) was cast at a discharge linear velocity of 3.5 m/min from a die with a slit of Then, the cast dope was made optically isotropic, and together with the belt, it was introduced into a 15% by weight aqueous sulfuric acid solution at -5°C and coagulated.

The coagulated film is then peeled off from the belt and heated to approximately 40°C.
in a 1% aqueous solution of soda carbonate, then at -25°C.
It was washed by running it under water.

After washing, the film with a water content of approximately 280% is first stretched at room temperature in the longitudinal direction (MD) using the peripheral speed difference of the rolls, then placed in a tenter and stretched in the width direction (MD) near the entrance. TD) and the temperature near the center of the tenter is 150℃.
After drying by heating for a fixed length, an infrared lamp was attached near the exit of the tenter for heat treatment, and then the film was rolled up.

The obtained films all had a rating of 465-5. It has a thickness of Q pm, and X-ray diffraction shows that most of the crystals are ■-type crystals, the a-axis of the crystal is perpendicular to the film plane, and the light transmittance is 83-92%.
ηinh = 4.7-5.1, moisture absorption rate 1.2-1.9
It was within the range of %.

Other properties, along with stretching conditions and heat treatment temperature, are shown in Table 2.
It was shown to.

In Comparative Example 5, the wet stretching ratio was small, so the improvement in the film properties was insufficient.

The following margin (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,
In addition to pressure resistance, chemical resistance other than strong acids, and dense structure, it has the following characteristics.

■ It has a very large Young's modulus and has excellent deformation resistance against external forces.

■ Don't be young.

■ Low hygroscopic expansion coefficient and small dimensional changes due to changes in humidity. Moisture absorption rate should also be low.

−■ Excellent transparency.

■ It has a low heating shrinkage rate and excellent dimensional stability against heating.

■ High strength.

■ Be tough with appropriate elongation.

■ Excellent surface properties.

A feature of the film manufacturing method of the present invention is that it is possible to industrially produce an aramid film having both of these characteristics, and also that it is particularly easy to manufacture a thin film.

The film of the present invention is particularly useful as a base film for magnetic recording compensatory holidays such as magnetic tapes and magnetic disks by taking advantage of the above-mentioned characteristics.
In addition, we also sell dielectric materials for capacitors, PACE FILNO tape for thermal transfer printers, and transparent 4! It is also useful for films, flexible printed wiring boards, adhesive tapes, and insulation materials for electrical equipment.

In particular, when the thin film of the present invention is used as a magnetic tape for a videotape recorder, either in the non-ingu type or in the non-ingu type, it is lightweight and allows long-time recording.
This results in a high-quality tape with excellent image clarity and stability.

Patent applicant Asahi Kasei Kogyo Co., Ltd. Procedural amendment (voluntary) July 7, 1960 Commissioner of the Patent Office Kuro 1) Akio Yu 1, Indication of the case Showa Otsu/Year Patent No. 27θ Otsu 70
2. Name of the invention Aramid film and its manufacturing method 3. Relationship with the person making the amendment Patent applicant 1-chome Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture] No. 2-6 Contents of the amendment (1) Specification No. 3 Page number/line ``Correct ND force direction to ``MD direction''.

(2) On page 6, line 7, ``accompanied by contraction'' is corrected to ``due to contraction.''

(3) Insert the following sentence between line 70 and // on page 10.

"The fact that the film of the present invention consists essentially of PPTA means that a small amount of polymer other than PPTA may be blended or copolymerized within the range that does not impede the effects of the present invention. (4) On page 1, line 77, "to make it isotropic" is corrected to "to make it isotropic."

(5) On the same page, line 70, "weight" is corrected to "lightweight."

(6) Same No. 9, page 9, ``Revealed,'' is corrected to ``Revealed,''.

(7) On page 32, line 1, ``byyoyo,'' is corrected to ``by''.

-ノ= (8) On page 33, line 70, "screen room" is corrected to "in the clean room."

(9) On page 3, line 73, "Curl center line" is corrected to "Curl, center line."

aO ditto 4t, page 2, line 7, “X-ray circuit mae yoyoto” is changed to “
"According to the previous X-ray episode," he corrected.

αp Table 2 "Young's modulus (exposure)" on page 3 of the same page is corrected to "Young's modulus (Kq/ltA)".

(c) Do not be young. ]of"
Do not curl. ” he corrected.

03 In the same Google page, No. 7, line O, "Surface quality" is corrected to "Surface smoothness (2)."

that's all

Claims (2)

[Claims] (1) A film substantially consisting of poly(p-phenylene terephthalamide) having a logarithmic viscosity of 3.5 or more,
The elongation and Young's modulus in all directions parallel to the film plane are at least 10% and 1000 Kg/mm^2, respectively;
The light transmittance at a wavelength of 600 nm is 60% or more, and the hygroscopic expansion coefficient in the direction parallel to the film surface is 3.5 × 1.
An aramid film characterized by having a RH of 0^-^5mm/mm/%RH or less (2) An optically anisotropic dope consisting essentially of poly(P-phenylene terephthalamide) with a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is placed on a support surface while maintaining optical anisotropy. In the method of producing a film, the dope is cast into a dope, converted to optically isotropic by moisture absorption and/or heating, and then solidified. After coagulation and washing, the film is biaxially stretched to 1.1 times or more in a wet state. , a method for producing an aramid film characterized by drying and heat treatment at a temperature of 350°C or higher while limiting shrinkage of the film.