JPH0228222A - Production of aramid film - Google Patents

Abstract

PURPOSE:To obtain the title film having planar property, readily slidable property and mechanical characteristics in the width direction by casting sulfuric acid dope of para-oriented aromatic polyamide and then bring the cast material into contact with roughed surface having a specific roughed surface degree under pressure after moisture absorption treatment and drying the cast material. CONSTITUTION:(A) para-oriented aromatic polyamide (e.g., expressed by the formula having >=3.5 logarithmic viscosity is dissolved in (B) >=95wt.% sulfuric acid to give an optically anisotropic dope and the dope is cast on the supporting surface of belt, drum, etc., from a slit die. Then the dope is transformed to optically isotropic dope by moisture absorption or/and heating and then solidified e.g., by passing through an aqueous solution of alkali to afford a humid film being 0.8-5.0 in total amount of sulfuric acid and water based on the polymer, which is brought into contact with a roughened surface having 10S-50S roughened surface degree, e.g., roller and dried to provide the aimed film.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a film made of para-oriented aromatic polyamide, and more specifically, the present invention relates to a method for producing a film made of para-oriented aromatic polyamide, and more specifically,
The present invention relates to a method for producing an aramid film that exhibits excellent mechanical properties in both the MD force direction (abbreviated) and width direction (TD force direction), and has excellent flatness and slipperiness.

(Prior art) Para-oriented aromatic polyamides have particularly excellent crystallinity and high melting points, and due to their rigid molecular structure, they have heat resistance and high mechanical strength, and have received particular attention in recent years. It is a polymer material that has been used for many years. 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 examples of their application to films. However, there are still no known examples of practical use.

The problem with para-oriented aromatic polyamides is that their useful high molecular weight polymers are poorly soluble in organic solvents, and strong inorganic acids such as concentrated sulfuric acid must be used as solvents. .

Japanese Patent Publication No. 59-14567 discloses a method of extruding an aromatic polyamine solution having optical anisotropy from a slit through a short air space into a coagulation bath.
In this method, only the mechanical strength in the MD force direction was strong, but the mechanical strength in the TD force direction perpendicular to it was extremely weak, and only a product that could be easily torn was obtained.

If the optically anisotropic dope of aromatic polyamide is simply extruded and solidified as it is, it will be excessively oriented in the extrusion direction, making it easy to fibrillate and weak in the TD force direction. Various methods of producing films have been studied in an attempt to improve them.

For example, in Japanese Patent Publication No. 54-35088, after extruding an aromatic polyamide mortar liquid having optical anisotropy from a ring die and simultaneously casting it in a doped state in two axes using an inflation method, It is said that an isotropic film can be obtained by wet coagulation. However, this method has the 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. 54-132
No. 674 discloses that by mechanically applying a shearing force to an optically anisotropic or optically isotropic dope of a linear aromatic polyamide in a goo in a direction perpendicular to the extrusion direction,
Although it has been proposed to orient the material in two axes, ie, in the extrusion direction and in a direction perpendicular to the extrusion direction during extrusion, the structure of the die is complicated and there are difficulties in industrial implementation.

Furthermore, J, Appl, Polym, Sci, vo
l, 27, Nα8, P, 2965-2985 (19
82) 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; Although the mechanical strength is isodirectional, it is low, and when a draft is applied, the mechanical strength in the MD force direction is high, but the mechanical strength in the TD force direction is extremely low.

Japanese Patent Publication No. 57-17886 discloses that an optically anisotropic dope of a linearly coordinated aromatic polyamide is heated until it becomes optically isotropic immediately before solidification, and then solidified to produce a transparent material with mechanical properties. It is described to obtain films that are isodirectional. This method is an original method that goes against the conventional concept of achieving high performance by utilizing optically anisotropic doping. At the same time, it has been successfully avoided that the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded and solidifies as it is, resulting in an opaque film.

The aramid film produced by this method has excellent mechanical properties, heat resistance, chemical resistance, dimensional stability, etc.
magnetic tape, photographic film, capacitor film,
It is expected to be used as a material for electrical insulation films, ink ribbons for thermal printers, films for flexible printed wiring boards, etc.

However, in order to smoothly produce polyamide films and apply them to the above uses, it is necessary to improve the slipperiness of polyamide films.

In other words, if the slipperiness of the film is insufficient, especially in the case of a thin polyamide film, it will cause serious problems such as winding, rewinding, coating, slitting, etc., and will cause process problems such as the occurrence of winding wrinkles and the attraction of dust due to static electricity. becomes an obstacle.

On the other hand, especially in magnetic tapes for high-density recording such as video tapes and floppy disks, unevenness on the tape surface causes smoothness loss during contact with the head, resulting in dropouts, recording errors, color noise, etc.
The base film is required to be extremely smooth without any rough protrusions.

In order to improve the slipperiness of the film, for boat fishing, for example, inorganic fine powder is mixed with a polymer solution or melt to provide minute protrusions on the surface. It is difficult to use as an industrial production method due to the complicated purification techniques and management techniques for uniformly dispersing the particles.

(Problems to be Solved by the Invention) An object of the present invention is to easily produce a high-performance film using a para-coordinating aromatic polyamide, particularly an aramid film with excellent smoothness and ease of slipping. The purpose is to provide a method.

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

That is, by the technique disclosed in Japanese Patent Publication No. 57-17886 (in which an optically anisotropic dope of para-isotropic aromatic polyamide is first prepared and then solidified by optical isopotency ratio), a transparent mechanical (obtaining a polyamide film with reduced performance), the slippage of the shrinkage-limited dried film is suppressed by sandwiching the coagulated film or the wet film after water washing between certain roughened surfaces and applying pressure. I found that it improved dramatically.

Based on these findings, the present inventors conducted further research and completed the present invention.

That is, in the present invention, an optically anisotropic dope consisting essentially of a para-isotropic aromatic polyamide with a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is applied onto 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 coagulated, in which the weight ratio of the total amount of sulfuric acid and water to the para-isotropic aromatic polyamide is 0 after coagulation. This method of producing a film is characterized in that a rough surface having a roughness of 103 to 50S is pressed against at least one surface of a wet film having a roughness of .8 to 5.0 and drying is carried out while limiting shrinkage of the film.

The para-coordinating aromatic polyamide used in the present invention is ■ A polyamide consisting essentially of a component in which an amide group is bonded to the para position of a Hensen ring forming the main chain, such as S--5-1-CH,-), is used.

Among these, aromatic polyamide films containing halogen atoms may cause corrosion of the metal layer of the conductor after long-term use, so aromatic polyamide films that do not substantially contain halogen atoms are preferably used. . Particularly preferably used is poly-p-phenylene terephthalamide (abbreviated as PPTA).

If the degree of polymerization of the polymer of the present invention is too low, it will not be possible to obtain a film with good mechanical properties.
A degree of polymerization is selected that gives a value (measured at 30°C with 0.2 g of polymer dissolved in 1 ml).

In the method of the present invention, it is first necessary to prepare an optically anisotropic dope of a disorientating aromatic polyamide.

A suitable solvent for preparing the dope for forming the PPTA film of the present invention is sulfuric acid at a concentration of 95% by weight or more. It is difficult to dissolve with less than 95% sulfuric acid,
The dope becomes extremely viscous after being dissolved. 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 in a concentration of 100% by weight or more, from the viewpoint of stability and solubility of the polymer, a concentration of 98 to 100% by weight is preferably used.

The polymer concentration in the dope used in the present invention is at room temperature (
A concentration that exhibits optical anisotropy at a temperature of about 20° C. to 30° C. or higher is preferably used, and specifically, it is used at a concentration of 10% by weight or more, preferably about 11% by weight or more. At polymer concentrations below this, ie, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the molded polyamide film often does not have desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20
% by weight or less, especially for PPTA with high ηinh.
It is preferably used in an amount of 8% by weight or less, more preferably 16% by weight or less.

The dope of the present invention contains conventional additives, such as fillers, light removers, UV stabilizers, heat stabilizers, antioxidants, pigments,
A solubilizing agent or the like may be mixed.

Whether a 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, you can create an optically anisotropic dope, and by changing the conditions to create an optically anisotropic dope, you can increase the optical anisotropy. It is possible to change from tropic to optically isotropic.

Before molding and solidifying the dope used in the present invention, insoluble dust, foreign matter, etc. should be removed as much as possible by filtration, etc., and gases such as air generated or drawn in during melting should be removed. is preferred. Deaeration can be performed after the dope is 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 onto a support surface from a slit die, for example, 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 drying are performed continuously, all or part of these steps may be performed intermittently, that is, batchwise. You may go. 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.

The support surface used in the present invention is in the shape of a heald or drum, or is used as a plate. The material is not particularly limited as long as at least the surface in contact with the dope is acid resistant; for example, glass, Hastelloy, tantalum, metal fluororesin plated with gold, platinum, titanium nitride, etc. are preferably used. Preferably, these materials have a so-called mirror finish, in which case the flatness of the film obtained by the method of the present invention is further improved.

The method for obtaining the film of the present invention is to cast the dope onto a support surface and then convert the dope from optically anisotropic to optically isotropic prior to solidification.

To change optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope cast on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the dope phase into an optically isotropic region, or use moisture absorption and heating simultaneously or sequentially. This can be achieved by

In particular, methods using moisture absorption, including methods that use heating in combination, are useful because the optical isopotency ratio of optical anisotropy can be achieved efficiently and without causing decomposition of the polymer.

To make the dope absorb moisture, air at normal temperature and humidity may be used, but humidified or heated and humidified air is preferably used. The humidified air may contain mist-like moisture exceeding the saturated vapor pressure, and may be so-called water vapor. just,
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
Room temperature to about 180°C1 preferably 50°C-150°C
This is done by humidifying the air.

In the case of a heating method, the heating means is not particularly limited;
A method of applying humidified air as described above to the casting dope,
There are methods such as irradiation with an infrared lamp and methods using dielectric heating.

The optically isotropically cast dope on the support surface is then solidified. In the present invention, water, an aqueous sulfuric acid solution of about 70% by weight or less, an aqueous alkaline solution such as caustic soda, etc. can be used as the coagulating liquid for the dope.

The coagulation bath is preferably a 10-50% by weight aqueous sulfuric acid solution.

In the present invention, the temperature of the coagulating liquid is preferably 30°C or lower, more preferably 10"C or lower. This is because the lower the temperature, the lower the solidification rate and the fewer voids included in the film. This is because the surface area of the film is improved.

It is necessary to press a certain rough surface onto at least one surface of the solidified film, either as it is or after first completing the cleaning described below.

When pressure treated, the film has a zero
．． It is important to contain a weight ratio of 8 to 5.0 of water and optionally sulfuric acid. If the weight ratio is less than 0.8, the effect of contact pressure is small and improvement in film slippage is expected, but if it exceeds 5.0, uneven scratches may occur on the roll etc. after contact pressure treatment. It is undesirable because it has disadvantages such as Desirably, the weight ratio is 1.5 to 4.0.

The contact pressure treatment generally squeezes out water and sulfuric acid contained in the wet or coagulated film. The pressure during the contact pressure treatment is usually in the range of 0.1 to 100 kg/c-.

It is important that the surface to be subjected to contact pressure treatment is roughened. The rough surface is preferably 105 to 50S expressed as the surface roughness of machining (hereinafter abbreviated as RMAX).

If RMAX is less than 103, the film will have poor slippage after drying while limiting shrinkage (if RMAX is more than 50S, the slipperiness will improve, but the surface irregularities will be too large, making it undesirable for, for example, magnetic tape). .

The roughness of the surface to be pressure treated can also be varied on both sides of the film, in which case it is possible to adjust the surface properties of both sides of the film.

Contact pressure treatment can be carried out in the solidified state, in the partially washed state, or in the completely washed state, but in general, from the viewpoint of the contact pressure effect, the less washed state is preferable. Preferably, from the viewpoint of the wide selection of rough surface materials, the cleaned state is preferred.

The material for the rough surface may be made of acid-resistant stainless steel, Hastelloy, glass, etc. using a matte finish commonly used.

Contact pressure treatment can be carried out in a laboratory, for example, by sandwiching a wet or coagulated film between plates with roughened surfaces, and applying pressure with a static load or press machine as necessary.
When applying it continuously to a running film, there are two methods: applying tension to the running film through a rough-surfaced roll, and applying pressure by sandwiching the film between a pair of rolls, one of which has a roughened surface. It is done by methods etc.

Before and/or after the contact pressure treatment, it is necessary to wash and remove acid content from the film as much as possible. Specifically, the removal of acid content is approximately 500 ppn! It is desirable to do the following. Water is usually used as the cleaning liquid, but if necessary, hot water may be used, or washing may be performed by neutralizing with an alkaline aqueous solution and then using water or the like. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid.

The washed film is preferably stretched in a wet state before drying, and the stretching is carried out in one or two directions at a stretching ratio of 1.01 times or more. At this time, it is often seen that the moisture contained within the film comes out like sweat. In the case of stretching in one direction, it may be in the MD force direction or in a direction perpendicular to the MD force direction.

The stretching in two directions may be simultaneous biaxial stretching or sequential uniaxial stretching. PPT in the stretching direction by stretching
Since the molecular chains of A can be oriented, mechanical properties are improved. Note that stretching must be performed in a wet state before drying, and stretching cannot be performed effectively to improve mechanical properties if a large amount of sulfuric acid remains or after drying.

Drying must be carried out under tension, at a constant length, or with slight stretching to limit shrinkage of the film.

If a film that has a tendency to shrink upon removal of the cleaning liquid (e.g., water) is dried without any restriction on shrinkage, it may not be profitable due to the formation of microscopically non-uniform structures (crystallization, etc.). The light transmittance of the film will be reduced.

Furthermore, the flatness of the film may be impaired or the film may curl. To dry while limiting shrinkage, for example, a tenter dryer or drying between metal frames can be used. Other conditions related to drying are not particularly limited; heated gas (air, nitrogen, argon, etc.)
You can freely choose from methods such as drying, room temperature gas, use of radiant heat such as electric heaters and infrared lamps, and dielectric heating.The drying temperature is also not particularly limited, but as long as it is above room temperature. good. However, in order to increase the mechanical strength, a high temperature is preferable, and a temperature of 100°C or higher, more preferably 200"C or higher is used. The maximum drying temperature is not particularly limited, but Considering drying energy and polymer decomposition, 500°C
The following are preferred.

In the present invention, in order to obtain a film having excellent transparency, that is, extremely high light transmittance, 9. Not only dope, but also moisture absorption gas, heating gas, supporting facepiece,
It is preferable to keep the content of dirt and dust in the coagulation liquid, cleaning liquid, dry gas, etc. as low as possible;
It is also a preferred embodiment to produce the film of the present invention in a so-called clean room or with clean water.

The film obtained by the method of the present invention has a Young's modulus in at least one direction of 700 kg/rI112 or more. This requirement is closely related to the film's resistance to deformation. In particular, a preferred embodiment of the film produced by stretching in a wet state after washing has a weight of about 1000 kg/m
``It has a significantly high Young's modulus.

The film obtained by the method of the invention also has a tensile elongation of 8% or more in all directions. Films with an elongation less than 8% tend to tear easily and are not practical. The tensile elongation is preferably 10% or more.

On the other hand, the polyamide film made by the method described in Japanese Patent Publication No. 55-14170 has an elongation in the MD force direction of 4 to 6% at most, and an extremely low elongation in the TD force direction of less than 1%. Easy to tear.

(Example) Examples are shown below, but these Examples are intended to explain the present invention, and are not intended to limit the present invention. In addition, unless otherwise specified in the examples, weight parts or weight %
shows. The logarithmic viscosity ηinh was measured by dissolving 0.2 g of the polymer in 98% sulfuric acid 100 and 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 is 2 m in diameter.
Measurements were made using a dial gauge with a measuring surface of m. Strength and elongation and modulus are measured using a constant speed elongation type strength and elongation measuring machine.
Cut the film sample into a rectangle of 1'OOmm x 10mm, initial grip length 30mm, and pulling speed 30mm.
The load-extension curve was drawn five times in Z minutes, and the calculation was made from this. Surface roughness (RMAX) is measured using a surface roughness meter (
It was determined using Surfcom 550 (manufactured by Tokyo Seimitsu Co., Ltd.).

The coefficient of friction is 1 weight made of 5US304 on the film surface.
The stress was determined from the stress when a 95 g rectangular parallelepiped was placed on it and pulled horizontally at a speed of 100 s/min using a constant speed extension type strength and elongation measuring machine.

Examples 1-3 PPTA polymer with rl inh of 5.2 and 99.6
% sulfuric acid at a polymer concentration of 12% to obtain an optically anisotropic dope at 60°C. The viscosity of this dope was measured at room temperature and was found to be 9100 poise. To facilitate film formation, the dope was degassed under vacuum while being maintained at about 60°C. This case also had optical anisotropy as described above, and the viscosity was 4000 poise. Pass through the filter from the tank, go through the gear pump, and reach the die 1, 5
m bent pipe is kept at 60°C, 0.15mm x 250
From a die with a slit of M, a mirror surface (approximately 0.088
3) It is cast onto a polished tantalum endless belt, and air at about 100°C with a relative humidity of about 23% is blown to make the cast dope optically isotropic. Together with the belt, -
It was introduced into a 20% by weight aqueous sulfuric acid solution at 2°C and coagulated.

The coagulated film was then peeled off from the belt and washed by running it in warm water at about 20°C. Cleaned film (contains approximately 460 ppm sulfate and 380% water)
Approximately 2.5 kg between a pair of stainless steel rolls finished with RMAX shown in Table 1 without drying
The film was passed through the film under a pressure of g/ci, and then wet-stretched 1.1 times in MD and 1.2 times in TD using a tenter, and then dried with hot air at 200'C under constant length. Table 1 shows the friction coefficient and tensile properties of the obtained film.

Comparative Example 1 The same washed film obtained in Example 1 was dried in the same manner as in Example 1 between a pair of stainless steel rolls finished with an RMAX of 53 without drying. When the coefficient of friction of the obtained film was measured, it was 0.88, indicating that it was extremely difficult to slip.

Example 4 77inh 4.9 PPTA in 99.5% sulfuric acid 12
．． A dope having optical anisotropy of 7900 poise was obtained by dissolving at 5% and heating at 45°C. After deaeration and filtration, 0.2 m
The gutter was cast onto a tantalum belt from a die with m x 250 mm slits. relative? ! Approximately 31 degrees
Convert the cast dove into a transparent optically isotropic dope by blowing air at about 90 °C at 1'C, then 20 wt% at 1'C.
It was coagulated with an aqueous sulfuric acid solution. The coagulated film was peeled off from the belt and taken out from the coagulation bath, and one side of a pair of Hastelloy rolls placed close to the coagulation bath so as to press against each other was placed between the RMAX-finished rolls shown in Table 1. After passing through a coagulated film, the sample was washed with water at room temperature, a 1% aqueous solution of caustic soda, and water at room temperature in this order. When the film taken out from the coagulation bath was sampled separately, PPT
It was found that it contained 0.82 sulfuric acid and 2.67 water with respect to A.

The washed wet film containing about 310-390% water was stretched 1.05 times in MD and 1.10 times in TD in a tenter and then dried in hot air at 250'C under constant length.

The obtained physical properties are shown in Table 1.

Margin below (Effects of the Invention) As shown in the examples, the film obtained by the method of the present invention has good mechanical properties expressed by high strength and high Young's modulus, which are not found in commercially available films. Furthermore, the smoothness is very good. In addition to these properties, it also has excellent electrical insulation, heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and dense structure. Therefore, the film of the present invention can be suitably used for insulating materials for capacitors, insulating materials for high-speed rotating electrical equipment, magnetic tapes, flexible printed wiring boards, wire coating materials, filtration membranes, etc. Because of its excellent properties, it is also useful for packaging materials, plate-setting materials, photographic films, etc.

In particular, the film of the present invention has a high Young's modulus, strong tear resistance, and high surface precision, so it is useful as magnetic tape such as video tape, computer tape, audio tape, etc. It is useful as a high-quality videotape with excellent stability.

Claims (1)

[Claims] An optically anisotropic dope consisting essentially of a para-oriented aromatic polyamide with a logarithmic viscosity of 3.5 or more and 95% by weight or more of sulfuric acid is cast onto a support surface while maintaining optical anisotropy,
In a method for producing a film in which the dope is converted to optically isotropic by moisture absorption and/or heating and then solidified, after solidification,
A rough surface with a roughness of 10S to 50S is pressed against at least one side of a wet film in which the weight ratio of the total amount of sulfuric acid and water to the para-oriented aromatic polyamide is 0.8 to 5.0, while limiting shrinkage of the film. Manufacturing method of aramid film characterized by drying