JPH0273832A - Production of para oriented aromatic polyamide flame-retardant film - Google Patents

Abstract

PURPOSE:To improve mechanical characteristics, etc., of a flame-retardant film by using a flame-retardant-containing liquid of a specific concentration when optically anisotropic dope consisting of para-oriented aromatic polyamide and concentrated sulfuric acid, etc., is formed into a film and the resultant film is brought into contact with the flame-retardant-containing liquid to provide the flame-retardant film. CONSTITUTION:An optically anisotropic dope consisting of a para-oriented aromatic polyamide having >=2.5 inherent viscosity and solvent consisting of one or more kind of concentrated sulfuric acid having >=95wt.% concentration, chlorosulfuric acid and fluorosulfuric acid is formed into a film and coagulated and the solvent is removed and then the film is brought into contact with a flame-retardant-containing liquid having the concentration C expressed by the formula 5/T<=C<=25/T in the relationship between the concentration C (wt.%) of the flame-retardant and thickness T (mum) of the film after drying and dried while limiting contraction to provide para-oriented aromatic polyamide flame- retardant film having high strength and modulus and excellent long-term heat resistance and suitable for an insulator for condenser.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a flame-retardant film made of para-oriented aromatic polyamide, and more specifically, the present invention relates to a method for producing a flame-retardant film made of para-oriented aromatic polyamide, and more particularly, the present invention relates to a method for producing a flame-retardant film made of para-oriented aromatic polyamide. ) and width direction (hereinafter referred to as T
A rose-oriented aromatic polyamide flame retardant that exhibits excellent mechanical properties in both the D force direction (omitted), has flame retardancy with a limiting oxygen index (L, 0.1) of 30 or more, and has excellent long-term heat resistance. The present invention relates to a film manufacturing method.

(Prior art) Polyparaphenylene terephthalamide (hereinafter referred to as PPTA)
Aromatic polyamides of the disorganized type, such as those exemplified by the above, have particularly excellent crystallinity and a high melting point, and because of their WM-direct molecular structure, they have heat resistance and high mechanical strength.
It is a polymer material that has received particular attention in recent years.

It has also been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been put into industrial use. Also, PPTA
Some examples of molding into films have been proposed (for example, Japanese Patent Publication No. 56-45421, Japanese Patent Publication No. 57-178).
Publication No. 86, etc.).

It is very difficult to impregnate flame retardant into these para-oriented aromatic polyamide molded products due to their high crystallinity and dense structure. Until now, as a method for making aromatic polyamide flame retardant, impregnation of undried fibers swollen in water with additives such as flame retardants has been proposed, as disclosed in JP-A-50-12322 and JP-A-49-75824. , No. 5335020 and Japanese Patent Publication No. 56-33487. However, for the disjointed aromatic polyamide fibers, only a technology has been disclosed in which a spinning dope with a low polymer concentration is used and wet spinning is performed in a high-temperature coagulation bath, and the yarn obtained by this method is void-free. It has a large amount of carbon, a low density, and a significantly low strength. This is because the premise is to create porous fibers with many voids and a density of about 1.35 g/d or less, which is easy to impregnate.

In addition, since the porous fibers with many voids are impregnated with flame retardants, their strength and modulus are low, sacrificing the high strength and high modulus that are the main characteristics of para-oriented aromatic polyamide fibers. It has become.

On the other hand, Japanese Patent Application Laid-Open No. 63-152641 discloses a technique for impregnating a dense film with high plane orientation with a flame retardant. They have the disadvantage that they tend to become brittle and often lack long-term heat resistance.

(Problems to be Solved by the Invention) An object of the present invention is to produce a para-oriented aromatic polyamide flame-retardant film that has high strength, high modulus, is flame-retardant, and has excellent long-term heat resistance. It is about providing law.

(Means for Solving the Problems) As a result of intensive research into methods for obtaining such films, the present inventors have discovered that optically anisotropic dopes of para-oriented aromatic polyamides are coated on supporting surfaces in the form of films. After that,
In a method in which an undried film with a moisture content of 50% by weight or more obtained by coagulating, then coagulating and removing the solvent is brought into contact with a liquid containing a flame retardant, and then dried, the film thickness is It was discovered that by specifically limiting the concentration of the flame-containing liquid, it was possible to obtain a film that exhibited excellent mechanical properties, as well as excellent flame retardancy and long-term heat resistance.After further research, the present invention was completed. It has arrived.

That is, the present invention comprises a para-oriented aromatic polyamide having a logarithmic viscosity ηinh of 2.5 or more and at least one solvent selected from the group consisting of concentrated sulfuric acid, chlorosulfuric acid, and fluorosulfuric acid at a concentration of 96% by weight or more. After the optically anisotropic dope containing the flame retardant is formed into a film, it is coagulated, the solvent is substantially removed, the resulting film is brought into contact with a liquid containing a flame retardant, and then dried while limiting shrinkage. In the method for producing a dispersion type aromatic polyamide flame retardant film, the concentration C [wt%] of the flame retardant in the flame retardant-containing liquid is 5/T.
This manufacturing method is characterized in that ≦C≦25/T (where T is the thickness of the film after drying [μml)].

The flame retardant contained in the aromatic polyamide flame retardant film of the present invention is preferably selected from aliphatic phosphoric esters, aliphatic cyclic phosphoric esters, and aromatic phosphoric esters.

These typical flame retardants are (HsCzO)+ P=O, (H2CO)3 P=0,
etc., and some of the hydrogen atoms of these aliphatic substituents and aromatic substituents may be substituted with halogen. Flame retardancy is usually achieved by selecting one of these compounds and diffusing it into the film, but it is also possible to diffuse and impregnate two or more compounds.

In general, non-esterified phosphoric acid compounds such as phenylphosphonic acid are also effective as flame retardants, but these compounds are highly acidic and para-oriented aromatic polyamide films themselves may be used during impregnation or in various applications. may deteriorate during use.

Flame retardancy, which is the object of the present invention (for example, L, 0.1. is 3
0 or more), the flame retardant must be contained so as to provide 0.1% by weight or more and 1.0% by weight or less of phosphorus based on the total weight of the film. Further, in order to ensure high flame retardant fastness, it is preferable that the flame retardant is sufficiently impregnated not only in the surface layer of the film but also in the center.

It has been found that if the flame retardant is localized only in the surface layer, for example, long-term heat resistance will not be sufficient.

The film produced by the method of the present invention can satisfactorily meet the flame retardant standard UL-94-v0.

The para-configured aromatic polyamide used in the present invention is substantially composed of units selected from the group consisting of the following structural units.

N11-Ar, -Nll----(1)Co-Arz-
CO---(II)Nll-Ar:+-CO----
-(I[l) where Ar, , Ar2 and Ar3 are each divalent aromatic groups, and (I) and (n) are substantially equimolar when present in the polymer.

In the polyamide film of the present invention, in order to ensure good mechanical performance, ^rl+Δr2 and Ar3 are each so-called para-configurational groups.

Here, the term "isomorphic" means that the bonds that grow the molecular chain are coaxially or parallelly located in opposite directions of the aromatic nucleus. Specific examples of such divalent aromatic groups include paraphenylene, 4,4'-biphenylene, 4-naphthylene, 1,5-naphthylene, 2,6-
Examples include naphthylene and 25-pyridylene. They may be substituted one or more with non-reactive groups such as halogen, lower alkyl, nitro, methoxy, sulfonic acid, cyano groups, etc. Ar, , Ar, and Ar= may each be two or more types, and may be the same or different.

The polymer used in the present invention can be produced from diamines, dicarboxylic acids, and aminocarboxylic acids corresponding to each unit by a method known so far. Specifically, a method is used in which a carboxylic acid group is first induced into an acid halide, acid imidabride, ester, etc. and then reacted with an amino group, or a method in which an amino group is induced into an isocyanate group and then reacted with a carboxylic acid group. As for the polymerization method, so-called low-temperature solution polymerization method, interfacial polymerization method, melt polymerization method, solid phase polymerization method, etc. can be used.

The disjoint aromatic polyamide used in the present invention includes:
Groups other than those mentioned above are copolymerized with about 10 mol% or less,
Other polymers may also be blended.

The most typical para-configured aromatic polyamide of the present invention is poly-p-phenylene terephthalamide (P
PT^) and poly-P-benzamide.

The degree of polymerization of the aromatic polyamide of the present invention is usually 2.5 or higher, preferably 3.5 or higher, because if it is too low, a film with good mechanical properties, which is the object of the present invention, cannot be obtained. A polymer having a degree of polymerization that gives a logarithmic viscosity η1nh (value measured at 30° C. by dissolving 0.5 g of polymer in 100 rd sulfuric acid) is selected.

Next, a method for obtaining a loosely oriented aromatic polyamide film impregnated with a flame retardant will be described.

Suitable solvents for preparing the optically anisotropic dope used in forming the film of the present invention include sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, or mixtures thereof at a concentration of 96% by weight or more. The sulfuric acid may be 100% or more, that is, fuming sulfuric acid, or trihalogenated acetic acid or the like may be mixed and used as long as the effects of the present invention are not impaired.

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, specifically about 9% by weight or more, preferably about 10% by weight or more. . At polymer concentrations below this range, ie, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the formed 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,
Particularly for PPTA with high ηinh, a weight of 16 weight or less is preferably used.

The dope used in the present invention may contain additives such as extenders, anti-glare agents, ultraviolet stabilizers, heat stabilizers, antioxidants, solubilizing agents, etc., as long as they do not significantly impair the solubility of the polymer in the dope. may be mixed.

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, you can create an optically anisotropic dope and change the conditions to make it an optically isotropic dope. It is possible to change from tropic to optically isotropic.

To obtain the film of the present invention, the optically anisotropic dope is preferably formed into a film on a support surface, and then the dope is converted from optically anisotropic to optically isotropic prior to solidification.

In order to convert optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope formed into a film on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. The dope can be transformed into an optically isotropic region by changing the solubility of the solvent and the polymer concentration, or the dope can be heated to transform it into an optically isotropic region simultaneously or sequentially, or the dope can be transformed into an optically isotropic region by heating and moisture absorption. This can be achieved by using them together.

The dope can be made to absorb moisture, for example, by leaving it in the air for a certain period of time or more.

The air in this case preferably has a relative humidity of 50% or more.

Further, actively applying humidification to a normal humid atmosphere is a desirable embodiment because it shortens the time until optical isotropy is achieved, and when heating is used in combination, the heating temperature can be lowered. If the relative humidity exceeds 99%, water will condense on the dope at low temperatures, leading to polymer precipitation.
Relative humidity of 100% or more can be used at temperatures above 45° C., although the flatness of the film may be lost.

In addition, in a method that uses heating simultaneously with moisture absorption or after moisture absorption, for example, when sulfuric acid is used as a solvent, the temperature at which optical anisotropy substantially disappears and the dope converts to optical isotropy is: Polymer concentration, degree of polymerization, sulfuric acid concentration,
Although it varies depending on the thickness of the dope and the degree of moisture absorption,
Generally, the temperature is preferably about 45°C or higher, and the upper limit is, when considering the decomposability of the polymer, it is desirable that the temperature is not too high for boat fishing, and the temperature of the film dope is 20°C.
It is desirable to select a value that does not exceed .

Although the mechanism of optical isotropy caused by this moisture absorption is not necessarily clear, it is probably because the liquid crystal region of the PPTA solvent system is considerably reduced due to the decrease in polymer concentration and solvent concentration due to moisture absorption. This moisture absorption alone is enough to make the film optically isotropic, but if this is further accompanied by heating, isotropy can be achieved in a short period of time. This method is particularly effective when the dope is thick.

In the present invention, the dope coagulating liquid that can be used is, for example, dilute sulfuric acid containing about 70% by weight or less of water, aqueous sodium hydroxide solution containing about 20% by weight or less, aqueous ammonia, about 5% by weight or less
These include 0% by weight or less sodium chloride aqueous solution and calcium chloride aqueous solution. The temperature of the coagulation bath is not particularly limited, and is usually in the range of -5°C to 50°C.

Since the coagulated film as it is contains acid, it is necessary to wash and remove the acid as much as possible in order to produce a film whose mechanical properties are less likely to deteriorate due to heating. Specifically, it is desirable to remove the acid content to about 500 pp+m or less. 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 washing with water.

Cleaning is carried out, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid.

The film produced in this way must be kept in a moisture content of at least 50% by weight or more, preferably 80% by weight or more, without being dried, and must be brought into contact with a liquid containing a flame retardant. . When the water content is less than 50% by weight, the product is in a so-called half-dried or dried state, and the diffusion rate of the flame retardant from the liquid containing the flame retardant is significantly reduced, making it impossible to impregnate the flame retardant to a practical level.

The flame retardant impregnation treatment is performed by connecting the film to a flame retardant-containing liquid, and in the present invention, the flame retardant concentration C [wt%] of the flame retardant-containing liquid is 5/T≦C≦25/T.
(However, T is limited to the film thickness after drying [μm]). When C is less than 5/T, the impregnation rate of the flame retardant becomes low and no flame retardant effect is exhibited (for example, O,
1 becomes less than 30). When C exceeds 25/T, the impregnation rate of the flame retardant becomes high and the mechanical properties after a long-term heat resistance test deteriorate significantly.

The contact time between the film and the flame retardant-containing liquid was 0.
It is preferable to set the time in the range of 1 to 3 minutes.

If the contact time between the fill and the flame retardant-containing liquid is less than 0.1 [minute], the flame retardancy is insufficient, probably because the flame retardant is localized only in the surface layer (for example, if 0.1. less than 30).

If the contact time exceeds 3 [minutes], the impregnation rate of the flame retardant will increase, and the mechanical properties after the long-term heat resistance test will deteriorate significantly.

The flame retardant impregnation treatment is carried out by bringing the film into contact with the flame retardant-containing liquid. Preferably, aqueous solutions are most preferred. Even non-water-soluble flame retardants can be impregnated in the form of an emulsion, dispersion, or colloid, but from the viewpoint of easy impregnation to the inside of the film, the particle size is 0.1μ or less, preferably 0.01μ or less. It is preferable that the particles are dispersed. Additives such as surfactants may be added to stabilize these emulsions, dispersions, etc. and to improve flame retardancy. If a flame retardant is unnecessary or poorly soluble in water, use a water-soluble compound such as acetone, methanol, dimethylformamide, N-methylpyrrolidone, dimethylacetamide, etc. The flame retardant can also be used by dissolving or dispersing it in a solvent or a mixed solution of these and water.

Impregnation can be carried out by immersing the film in a liquid containing an impregnating agent, or by spraying or showering. The impregnation temperature can be set arbitrarily between room temperature and the boiling point of the impregnating agent-containing liquid, but a high temperature is preferable.

The film rendered flame retardant in this way is dried, if necessary, after washing off the flame retardant adhering to the surface, but it can also be stretched prior to drying if desired. That is,
1.01 in one or two directions of wet film before drying
By stretching the film by about 1.4 times, the mechanical properties of the film can be improved.

The film must be dried under tension, at a constant length, or slightly stretched while limiting 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, microscopically nonuniform structural formation (crystallization, etc.) may occur. The resulting film may lose its flatness or 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.
Any method can be selected from methods using heated gas (air, nitrogen, argon, etc.) or room temperature gas, methods using radiant heat such as electric heaters or infrared lamps, and dielectric heating methods.

In the present invention, it is important that the drying temperature of the film is 50°C or higher. This is because drying at less than 50'C will result in insufficient densification of the film structure (low density). Drying temperature is preferably 100-300
It is °C.

The heat treatment of the film may be carried out as necessary, but in that case, it is necessary to limit shrinkage of the film while under tension, under constant length, or slightly stretched. if,
When a film that has a tendency to shrink with the removal of a cleaning solution (e.g., water) is heat-treated without any restriction on shrinkage, the resulting film becomes The flatness of the film may be impaired or it may curl. In order to perform heat treatment while limiting shrinkage, a method such as a tenter dryer or sandwiching between metal frames can be used. Other conditions related to heat treatment are not particularly limited, and heating gas (
Any method can be selected from methods such as air, nitrogen, argon, etc.), a method using room temperature gas, a method using radiant heat such as an electric heater or an infrared lamp, and a dielectric heating method. The heat treatment temperature is preferably 300 to 1I50'c.

(Example) Examples and reference examples (manufacturing examples of PPTA) of the present invention are shown below, but these reference examples and examples explain embodiments of the present invention, and do not limit the present invention. It's not a thing. In addition, % in an example shows weight %.

In the examples, the logarithmic viscosity ηinh was measured by dissolving 0.2 g of the polymer in 100% 98% sulfuric acid at 30°C by a conventional method. 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 2 on diameter measuring surface. To determine the strength and elongation, a film sample was cut into a rectangle of 100 nn x 10 mm using a constant speed extension type strength and elongation measuring machine, and the load-elongation curve was run 5 times at an initial grip length of 30mm and a tensile speed of 30mm/min. This is what we drew and calculated from this. Density was measured at 30°C by density gradient tube method using carbon tetrachloride-toluene.

[Measurement of phosphorus content in film]

Approximately 50 to 100 μg of the film containing the flame retardant is accurately weighed and placed in a platinum basket. This is combusted in an oxygen stream, and the gas produced by the combustion is introduced into a mixed solution of 0.01N caustic soda IClIn1 and water 10-1 and absorbed. Water is added to the above solution that has absorbed the combustion gas, and the volume is adjusted to exactly 50 d. This solution was passed through an ion chromatogram (Guionex Model 10, manufactured by Guionex Co., Ltd.) to measure the phosphorus content. At that time, the separation column used was a column packed with TSK Gel-Anion PW (manufactured by Toyo Soda Co., Ltd.), and the eluent was a 1:1 solution of 0.0015 mol/l sodium bicarbonate aqueous solution and 0.0012 mol/l sodium carbonate aqueous solution. 1 mixed solution was used. Alternatively, the quantification of phosphorus was performed based on a phosphorus-containing calibration curve prepared by performing the above operation in advance using a known amount of potassium dihydrogen phosphate.

[Measurement of critical oxygen index]

The limit oxygen index (L, O, I), which is an indicator of flame retardancy, was determined based on Japanese Industrial Standard (JIS) K 7201 using a flame retardant test device (manufactured by Suga Test Instruments Co., Ltd., Model 0N-1). The film itself was used as a test piece for measurement. The minimum oxygen flow rate at which the test piece can burn continuously for 3 minutes or more or 5 cm or more is A (f/min), and the nitrogen flow rate at this time is 8.
(= 11.4-A) (f/sin), then
L, O, I are values expressed by L, O, I=(A/(A+B))X100.

Example 1 r) 99.7% PPTA polymer with inh 5.5
The polymer was dissolved in sulfuric acid at a polymer concentration of 12.0%, and a dope with optical anisotropy was obtained at 60°C. The viscosity of this dope was measured at room temperature and was found to be 14,500 voids.

To facilitate film formation, the dope was kept at about 70°C and degassed under vacuum. This case also had optical anisotropy as described above, and the viscosity was 4200 voids. This dope is passed through a filter from the tank, passed through a gear pump, kept at about 70°C, and then passed through a 1.5 m curved pipe to the die, and then passed through a gou with a slit of 0.3 mg++ x 300 mm into a mirror-polished Hastelloy tube. Cast onto a belt and heat the cast dope to about 90°C at a relative humidity of 95%.
After blowing air of
It was introduced into an aqueous sulfuric acid solution and solidified. The coagulated film is then peeled off from the belt and passed through a rotating roller for approximately 20 minutes.
Clean by running in a water tank at °C (retention time approximately 3 minutes),
A film with a moisture content (based on dry film weight) of approximately 400% by weight was obtained.

This film was impregnated with the flame retardant by contacting it with a 2% aqueous solution of Ni-19A (manufactured by Meisei Chemical Industry Co., Ltd., registered trademark, chemical structure is) for 0.5 minutes at 25°C. , Wash the obtained flame retardant film with water, about 10 cm x 25
It was sandwiched between two stainless steel frames with a diameter of 1.5 cm and dried for a fixed length in an air oven maintained at 200°C. Further, the obtained film was subjected to constant length heat treatment for 0.5 minutes in an air oven maintained at 350°C. Table 1 shows the measurement results of the obtained film.

Examples 2 to 7 A film containing 400% water was prepared in the same manner as in Example 1, and the film thickness and flame retardant concentration were varied as shown in Table 1, and the film was diluted with a flame retardant containing liquid by 0.5%. After being brought into contact with the impregnation for a minute, the film was sandwiched between two frames made of stainless steel containing about 1010 Cl x 25, and the film was dried and heat treated under the same conditions as in Example 1. The results are shown in Table 1.

Comparative Examples 1 and 2 A 400% water-containing film (thickness: 5 μl) obtained in the same manner as in Example 1 was coated with 0.5% of the flame retardant shown in Example 1 at a concentration of 0.5.7% aqueous solution. After contacting with impregnation for a minute, the obtained film was sandwiched between two stainless steel frames of about 10 marks x 25 CII, and the film was dried and heat treated under the same conditions as in Example 1. The results are shown in Table 1.

Comparative Examples 3 and 4 The flame retardant shown in Example 1 was added to a 400% water-containing film (thickness 25 μm) obtained in the same manner as in Example 1 at concentrations of o, i, and a% aqueous solutions of 0.5 After being brought into contact with the impregnation for a minute, the obtained film was sandwiched between two stainless steel frames of about 10 CIRX 25 cm, and the film was dried and heat treated under the same conditions as in Example 1. The result is the first
Shown in the table.

Comparative Example 5 A 400% water-containing film (thickness 25μ11) obtained in the same manner as in Example 1 was impregnated with the flame retardant shown in Example 1 in an aqueous solution with a concentration of 10% for 5 minutes. The film was placed in a stainless steel container measuring approximately 10cm x 251cm.
The film was dried and heat treated under the same conditions as in Example 1. The results are shown in Table 1.

Comparative Example 6 A 400% water-containing film (thickness 25μI) obtained in the same manner as in Example 1 was soaked for about 10 minutes without impregnating it with anything.
The film was placed between two stainless steel frames measuring cm x 25 cm, and dried and heat treated under the same conditions as in Example 1. The results are shown in Table 1.

(Left below) Example 8 Examples 1, 2, 3, 4, 5, 6.7 and Comparative Example 1.2
, 3, 4, and 5.6.
A long-term heat resistance test was conducted in an air oven maintained at 0'C for 19.5 hours (the results are shown in Table 2). The results showed that the film of the present invention maintained excellent physical properties even after the long-term heat resistance test.

(Margins below) (Effects of the invention) The film of the invention has good mechanical properties represented by high strength and high modulus, has a value of 0.1 exceeding 30, and satisfies UL-94 Vo. This is a new film that has both excellent flame retardancy and even better long-term heat resistance. The film of the present invention also has heat resistance and high breakdown voltage.

Taking advantage of these performance characteristics, the film of the present invention is useful as a base material for FPCs, TABs, etc., and is also useful as an insulator for capacitors, a coating material for electric wires and optical fibers, etc. It is particularly useful as a flame retardant for these electrical and mechanical applications.

Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Scope of Claims] A para-oriented aromatic polyamide having a logarithmic viscosity ηinh of 2.5 or more, and at least one solvent selected from the group consisting of concentrated sulfuric acid, chlorosulfuric acid, and fluorosulfuric acid with a concentration of 96% by weight or more. After forming an optically anisotropic dope comprising In the method for producing a para-oriented aromatic polyamide flame-retardant film to be dried, the concentration C [wt%] of the flame retardant in the flame retardant-containing liquid is 5/T≦C≦25/T (
However, a manufacturing method characterized in that T is within the range of the film thickness after drying [μm]