JPH0353336B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a film consisting essentially of polyparaphenylene terephthalamide (hereinafter referred to as PPTA). More specifically, it relates to a manufacturing method for obtaining an ultra-thin PPTA film that is transparent and exhibits excellent mechanical properties in both the longitudinal direction (hereinafter referred to as the MD direction) and the width direction (hereinafter referred to as the TD direction). It is. (Prior art) Linearly coordinated aromatic polyamides, represented by PPTA, have particularly excellent crystallinity and a high melting point, and due to their rigid molecular structure, they have heat resistance and high mechanical strength. It is a polymer material that has received particular attention in recent years. In addition, it has been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been implemented industrially, but there are few proposals for application to films. . Japanese Patent Publication No. 57-17886 discloses a method in which an optically anisotropic dope of polyamide such as PPTA using concentrated sulfuric acid as a solvent is made optically isotropic by heating, and then coagulated, washed, and dried. Although we have succeeded in obtaining a transparent film that exhibits excellent mechanical properties in both directions, it is extremely difficult to obtain an ultra-thin film due to the relatively high concentration of the dope used. On the other hand, this publication discloses obtaining a transparent film from an isotropic dope, but simply casting the isotropic dope onto a supporting surface, coagulating and washing it will result in a large amount of Only unsatisfactory transparency and mechanical properties including voids can be obtained. In addition, Japanese Patent Publication No. 57-35088 discloses that an optically anisotropic dope of polyamide such as PPTA using concentrated sulfuric acid as a solvent is extruded into a non-coagulable gas through an annular orifice, and while it is in the non-coagulable gas. , it is stated that a transparent film is obtained by pressurizing gas into the inside of the tubular film, but the distance from the tubular orifice to the coagulation bath as described in these examples is 150 ~
At 200 mm, the optically anisotropic dope does not become isotropic, and only a thick film that is opaque and easy to avoid in one direction is obtained. (Problems to be Solved by the Invention) The purpose of the present invention is to provide a method for producing an ultra-thin PPTA film that eliminates these drawbacks, has excellent transparency, and exhibits excellent mechanical properties in both the MD and TD directions. There is a particular thing. (Means for Solving the Problems) That is, the present invention involves casting an isotropic dope consisting essentially of polyparaphenylene terephthalamide and concentrated sulfuric acid onto a supporting surface, and then coagulating and cleaning the film. The method of manufacturing a polyparaphenylene terephthalamide film is characterized by using a 20 to 70% by weight aqueous sulfuric acid solution at 10° C. or lower as a coagulation bath and drying while limiting shrinkage. In the production method of the present invention, it is first necessary to prepare an isotropic polymer dope consisting essentially of PPTA. The PPTA used in the present invention is substantially It is a polymer represented by the formula, and is conveniently produced from conventionally known paraphenylene diamine and terephthaloyl chloride by a low-temperature solution polymerization method. In addition, the polymer used in the present invention includes:
Even if a small amount of components other than PPTA are copolymerized or blended, it is permissible as long as the effects of the present invention are not impaired. Examples of such components include metaphenylene, 4,4-biphenylene,
1,5-naphthalene, 2,6-naphthalene, 4,
Examples include polyamides such as 4'-diphenylene ether and 3,4'-diphenylene ether, and PPTA whose nucleus is substituted with halogen, alkyl group, nitro group, etc. If the polymer has a low degree of polymerization, it will not be possible to obtain a film with good mechanical properties, which is the objective of the present invention. ℃
A polymer with a degree of polymerization that gives a value measured in ) is selected. A suitable solvent for preparing the dope for forming the PPTA film of the present invention is concentrated sulfuric acid, preferably at a concentration of about 95% by weight or more. The sulfuric acid may have a concentration of 100% by weight or more, that is, fuming sulfuric acid, and trihalogenated acetic acid or the like may be used in combination 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 (approximately 20 to 30°C), and is preferably used at a concentration that exhibits isotropy, specifically 1 to 10
% by weight, preferably 2-6% by weight is used.
At a polymer concentration of 10% by weight or more, the polymer exhibits anisotropy and the thickness of the formed film increases, making it difficult to form an ultra-thin film (for example, a thickness of 3 μm or less). On the other hand, it is difficult to obtain a film with practical mechanical performance from a dope with a too small polymer concentration. In the present invention, the dope may be mixed with common additives, such as fillers, anti-glare agents, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizing agents, etc. Whether a dope is anisotropic or isotropic can be determined by a known method, such as the optical method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, Since it depends on the polymer concentration, the degree of polymerization of the polymer, the content of non-solvent, etc., it is possible to prepare an isotropic dope by examining these relationships in advance. The feature of the method of the present invention is that after the isotropic dope is cast in the form of a film on the supporting surface, it is solidified at a low solidification rate.
A 70% by weight aqueous sulfuric acid solution is used. More preferably, it is a coagulation bath of 0° C. or lower. By using such a coagulation bath, the coagulation rate of the film is reduced, thereby relaxing the formation of a so-called skin solidified layer on the film surface, and reducing the difference from the internal solidified layer. It is presumed that uniform coagulation and shrinkage of the entire film is promoted, and the generation of voids due to large coagulation and shrinkage due to the low polymer concentration can be suppressed. Since the solidified film as it is contains acid, it is necessary to wash and remove the acid content as much as possible in order to produce a film whose mechanical properties are less likely to deteriorate due to heating. Specifically, it is desirable to remove the acid content to about 500 ppm or less, more preferably 200 ppm or less.
Water is usually used as the cleaning liquid, but if necessary, warm water may be used, or washing may be performed after neutralization with an alkaline aqueous solution and then with water. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. In the method of the present invention, the thickness and surface dimensions of the film change significantly before and after drying, and in this respect, special care must be taken during drying in order to obtain a high quality film. In other words, to avoid wrinkles,
It is necessary to limit the contraction of the film under tension. Here, under tension includes three modes: under constant length, contracted to an extent that wrinkles do not form, and slightly stretched. It is also possible to make the film thinner by stretching during drying or before and after drying. In the present invention, drying means drying in air, nitrogen,
It is heating in an inert gas atmosphere such as argon, and can be dried on a heating roll, in a tenter, in a heated atmosphere, in silicone oil, fixed to a metal frame, etc. good. The drying temperature is not particularly limited, but
A temperature higher than normal temperature or a high temperature is preferred in order to effectively improve the mechanical strength, and a temperature higher than 100°C, more preferably higher than 200°C is used. The maximum temperature for drying is not particularly limited, but considering the drying energy and decomposability of the polymer, the maximum temperature is 500°C.
℃ or less is preferable. In producing a film by the method of the present invention,
All of the above steps may be carried out batchwise or continuously, and one preferred embodiment is to manufacture the film while running it continuously throughout the entire process. In addition, oil agent,
It is also possible to add dyes for identification to the film. (Example) Below are examples and reference examples (manufacturing example of PPTA)
However, these reference examples and examples do not limit the present invention in any way. In the examples, parts by weight or weight % are shown unless otherwise specified. Logarithmic viscosity ηinh is 0.2 of polymer in 100ml of 98% sulfuric acid
g was dissolved and measured 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 mm in diameter. The strength and elongation and modulus were determined by cutting the film sample into a rectangle of 100 mm x 10 mm using a constant speed extension type strength and elongation measuring machine, with an initial grip length of 30 mm and a tensile speed of 30 mm.
The load-elongation curve was drawn five times in mm/min, and the calculation was made based on this. Next, the number of voids is measured as follows. A piece of film of an appropriate size is magnified from 100x using an ordinary optical microscope using transmitted light.
Observe at least 5 different fields of view at a magnification of 400x, count the number of voids with a major axis of 1 μ or more, and calculate the number of voids per 1 mm ² of the film surface. Reference Example (Production of PPTA) PPTA was obtained as follows by a low temperature solution polymerization method. In a polymerization apparatus shown in Japanese Patent Publication No. 53-43986, 65 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine were dissolved therein. After cooling to 8° C., 91.4 parts of terephthalic acid dichloride was added all at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese-like shape, so the polymerization reaction product was discharged from the polymerization apparatus according to the method described in Japanese Patent Publication No. 53-43986, and immediately transferred to a twin-screw closed kneader. The polymerization reaction product was finely pulverized. Next, the fine powder was transferred to a Hexiel mixer, and approximately the same amount of water was added thereto for further pulverization, followed by filtration, washing in hot water several times, and drying in hot air at 110°C. 95 parts of pale yellow PPTA polymer with ηinh of 5.0 was obtained. Note that polymers with different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and monomers (paraphenylenediamine and terephthalic acid dichloride) and/or the ratio between polymers. Example 1 PPTA having an ηinh of 5.0 was dissolved in 99.7% by weight sulfuric acid at a polymer concentration of 3% to obtain an isotropic dope at room temperature (30°C). The viscosity of this dope at room temperature is
It was 8000 poise. This dope was degassed under reduced pressure and applied onto a glass plate at 30° C. with an applicator having a step of 0.01 mm. After application, 0℃, 50
% sulfuric acid aqueous solution, in a 30 wt % sulfuric acid aqueous solution at -10°C,
and -5°C in a 40% by weight sulfuric acid aqueous solution, neutralized and washed with water, fixed in a metal frame in an air oven at 250°C, and dried.
Table 1 shows the properties of the films obtained under the above three coagulation conditions. Note that MD is the direction in which the applicator is drawn, and TD is the direction perpendicular to it.

[Table] Comparative Example 1 The dope of Example 1 after being degassed under reduced pressure was applied onto glass at 30°C using an applicator with a step of 0.01 mm, and then heated in 15°C water, 30°C water, 5°C, 10 wt. % aqueous sulfuric acid solution, neutralized and washed with water, fixed in a metal frame in an air oven at 250°C, and dried. Table 2 shows the properties of the film obtained under the above conditions.

[Table] Example 2 PPTA having an ηinh of 4.0 was dissolved in 99.7% by weight sulfuric acid at a polymer concentration of 5% to obtain an isotropic dope at room temperature. The viscosity of this dope at room temperature was 12,000 poise. To facilitate film formation, it was placed in a beaker and kept at 60°C. At that time, the dope also showed isotropy and had a value of 7000 poise. This dope was degassed under reduced pressure and applied onto a glass plate at 30° C. with an applicator having a step of 0.01 mm. After application, -
It was coagulated in a 40% by weight aqueous sulfuric acid solution at 5°C, neutralized and washed with water, and dried in an air oven at 250°C while being biaxially stretched. Table 3 shows the properties of the film obtained under the above conditions.

[Table] (Effects of the invention) The film obtained by the method of the present invention is an ultra-thin PPTA film with very few voids, which has high strength and high modulus, and also has high heat resistance, high transparency, and high dielectric strength. Since it has a rate of
Taking advantage of its characteristics, it is particularly useful for insulators for capacitors, base films for magnetic tapes, tapes for thermal transfer printers, etc. It can also be used as packaging materials, lightweight surface materials for model airplanes, wire covering materials, transparent films, etc. can.

Claims (1)

[Claims] 1. In a film production method in which an isotropic dope consisting essentially of polyparaphenylene terephthalamide and concentrated sulfuric acid is cast onto a supporting surface, then coagulated and washed, a 20 to 70% by weight bath at 10°C or lower is used as a coagulation bath. 1. A method for producing a polyparaphenylene terephthalamide film, which uses an aqueous solution of 1.5% sulfuric acid and is dried while limiting shrinkage.