JPH0742611B2 - Polyimide fiber - Google Patents

Description

Detailed Description of the Invention

(Field of Industrial Application) The present invention relates to a novel high modulus fiber made of polyimide which is useful in the fields of space and aviation, electronic materials and the like. (Prior art) Conventionally, polyimide has heat resistance, mechanical properties, electrical properties,
It is known to be useful as a raw material for fibers, films and other molded articles having excellent weather resistance. For example, 4,
A film having excellent heat resistance is obtained from a polyimide produced from 4'-diaminodiphenyl ether and pyromellitic dianhydride, and is widely used for electrical insulation applications. On the other hand, due to the sophistication of advanced technology, it has higher heat resistance and higher strength in fields such as space and aircraft applications and electronic material applications.
In recent years, fibers, films and the like having mechanical properties such as high elastic modulus have been required. Therefore, the importance of rigid skeleton polyimide is being recognized in order to improve the mechanical properties of polyimide having excellent heat resistance. By the way, as a general manufacturing method of polyimide, since polyimide is often insoluble and infusible, a molding dope composed of a polyamic acid which is a precursor thereof and a solvent is cyclically or wet molded, and in the molding process thereof. A method of closing a polyamic acid to obtain a polyimide molded body has been adopted. In this case, poly-p-phenylene (or 4,4 '
-A biphenylene) pyromellitimide, which forms a completely rigid skeleton, is inferior in heat stretchability because crystallization rapidly progresses in the process of imidization due to its rigidity, and as a result, high mechanical properties are not expressed. There is a problem.
For example, as described in Textile Society of Japan, Vo1.40, No. 12, T-480 to T-487, poly-4,4'-biphenylenepyromellitimide has an initial elastic modulus of 1,000 g / de or more. ,
Fibers with high elasticity and strength of 10 g / de or more cannot be obtained. In consideration of the above problems, by improving the moldability by lowering the crystallinity without significantly reducing the rigidity of the molecular chain, various copolyimides showing good mechanical properties have been proposed. (JP-A 61-188127, JP-A 6-188127
No. 2-79227), since these are copolymers, their potential, that is, the level of crystal elastic modulus, cannot be denied, and further improvement of physical properties due to improvement of molding method cannot be expected. (Object of the invention) An object of the present invention is to solve the above-mentioned problems and to form a polyimide having improved moldability without copolymerization, and without significantly impairing crystallinity, and having extremely excellent mechanical properties. To provide a fiber having. (Structure of the Invention) As a result of intensive studies conducted by the present inventors in order to achieve the above object, a homopolymer of a polyimide having a specific chemical structure has a rigid skeleton but is excellent in moldability and can be stretched at a high ratio. It was found that a polyimide fiber having a high mechanical property can be obtained, and the present invention has been completed. Thus, according to the present invention, there is provided a fiber composed of a polyimide having a unit represented by the following formula (I) as a main repeating unit, the fiber having an initial elastic modulus of 1,000 g / de or more and a tensile strength of 15 g / de. A polyimide fiber as described above is provided. The polyimide in the present invention is pyromellitic dianhydride, or 3,3 ′, 4,4′-diphenyltetracarboxylic acid dianhydride or its derivative and 2,2′-dimethylbenzidine and / or its hydrochloride. It is synthesized from and in an organic solvent. Here, "mainly" means that 90% or more, preferably 95% or more, of the repeating unit of the polyimide is the above (I), and other constituent components are included outside the range. In this case, the object of the present invention cannot be achieved due to the influence of deterioration of crystallinity. Examples of the derivative of the aromatic diacid anhydride used in the present invention include diester and diester diacid chloride. Incidentally, such diester diacid chloride is a tetracarboxylic acid diester synthesized from an aromatic diacid anhydride, an alcohol, and a phenol, which is synthesized by a usual acid chloride method using thionyl chloride or the like. In the above, it is preferable to use an aliphatic alcohol or an ether group-containing aliphatic alcohol in view of reactivity and solubility of the obtained polymer. Next, the following organic solvents are used in the present invention.

[Organic solvent]

N, N, N ', N'-tetramethylurea (TMU), N, N-dimethylacetamide (DMAC), N, N-diethylacetamide (DEAC), N, N-dimethylpropionamide (DMPR),
N, N-Dimethylbutyramide (NMBA), N, N-Dimethylisobutyramide (NMIB), N-Methylpyrrolidone-2
(NMP), N-ethylpyrrolidone-2 (NEP), N-methylcaprolactam (NMC), N, N-dimethylmethoxyacetamide, N-acetylpyrrolidine (NAPR), N-acetylpiperidine, N-methylpiperidone-2 (NMPD) ),
N, N'-dimethylethyleneurea, N, N'-dimethylpropyleneurea, N, N, N ', N'-tetramethylmalonamide,
N-acetylpyrrolidone, dimethyl sulfoxide (DMS
O), hexamethylphosphoramide (HMPA). When 3,3 ', 4,4'-diphenyltetracarboxylic acid diacid anhydride is used as the aromatic diacid anhydride, a phenolic solvent can be used. The polyimide precursor of the present invention is synthesized by solution polymerization of the above monomers in the above solvent.

[Synthesis of polyimide precursor]

As a method for synthesizing the polyimide precursor, a method in which a monomer mainly composed of an aromatic diamine and an aromatic tetracarboxylic acid anhydride and / or a derivative thereof is combined and solution-polymerized is adopted. As shown in Example 1 below, while maintaining the NMP solution in which 2,2′-dimethylbenzidine was dissolved at −10 ° C., pyromellitic dianhydride was added in an approximately equivalent amount of the above diamine and vigorously stirred to form a solution. When the viscosity was gradually increased and agitation was continued, a highly viscous solution was obtained, and the intrinsic viscosity was measured.
It was 5.2, and it was confirmed that a polyamic acid with a high degree of polymerization was produced. Intrinsic viscosity (ηinh) is measured in NMP 35
1 / C [ln at a temperature of 0.5g / dl with an Ostwald viscometer
(T / t ₀ )]. In addition, tetracarboxylic acid diester diacid chloride, or
When 2,2'-dimethylbenzidine hydrochloride is used as well, solution polymerization may be carried out in the same manner, but it is also possible to add a dehydrochlorinating agent such as a tertiary amine at that time. In addition,
The 2,2'-dimethylbenzine constituting the polyimide of the present invention is a nucleus-substituted derivative of rigid diamine, but it is superior in reactivity as compared with the chlorine-substituted derivative and a polymer having a high degree of polymerization can be obtained. It is also advantageous in terms of price. As described above, the polyimide of the present invention is synthesized by imidizing the polyimide precursor obtained from the aromatic diacid anhydride and / or its derivative and 2,2′-dimethylbenzine and / or its hydrochloride. To be done. The imidization may be carried out by using a chemical cyclizing agent described later or by heating, and either one may be selected. Further, the copolymerization component may be introduced to the extent that it does not deviate from the object of the present invention, but the range is at most about 0.1 mol per 1 mol of polyimide. Polyimide of the present invention, in addition to the heat resistance of the original polyimide,
The molded article has good mechanical properties, and in this connection, the fiber made of the polyimide and the method for producing the fiber will be described in detail. The fiber of the present invention is produced by subjecting the solution containing the above-mentioned polyimide precursor to ordinary dry or wet molding, and imidizing the obtained yarn. The polyimide precursor solution is as follows. Adjusted.

[Preparation of polyimide precursor solution]

The polyimide precursor solution is adjusted by adjusting the polymer concentration so that the solution containing the polyimide precursor-containing solution has a viscosity suitable for molding, and the solution may be used as it is as a molding dope or as a non-solution. Alternatively, the polymer may be once isolated by, for example, mixing and re-dissolving in a suitable solvent to form a dope for molding. Although any method can be adopted in the present invention, the former method is industrially preferable. Molding into a filament is carried out by usual dry or wet spinning of the polyimide precursor solution. The yarn is subsequently imidized into a polyimide fiber. This fiber exhibits excellent mechanical properties with an initial elastic modulus of 1,000 g / de or more and a tensile strength of 15 g / de or more, and is expected to be highly useful in fields such as advanced composite materials (ACM). Now, the fiber production method of the present invention that brings out the latent performance of the polyimide will be described in detail.

[Fiber production method]

The polyimide precursor solution prepared as described above is extruded from the spinning nozzle and the molding or desolvation of the yarn is promoted by a ring or wet molding method. At this time, since a solvent having a high boiling point is often used as the solvent for the precursor, it is preferable to adopt a wet molding method. As the coagulant for promoting desolvation, a combination of a solvent and water used for preparing a precursor solution, or a combination of an aliphatic alcohol such as methanol and water and / or the solvent may be used. A combination of a solvent and water is preferable in terms of handling and process convenience. Incidentally, there is no problem in containing an appropriate inorganic compound in the system in order to make the solidified state of the yarn denser, and for the same purpose, the chemical cyclization agent described below is added to the precursor solution, A part of the precursor may be imidized. As described above, the filamentous body that has undergone desolvation proceeds as it is,
Alternatively, it is subjected to thermal stretching after imidization. It is effective to increase the strength of the yarn before the hot drawing in order to give high tension during the hot drawing and to promote the molecular blending to a high degree. For that purpose, the latter hot drawing after imidization is preferable. There are two types of imidization methods, a heating imidization method in which a polyamic acid is dehydrated and ring-closed by heating, but the latter is preferable in order to suppress crystallization before hot drawing. Hereinafter, the chemical imidization method will be described in detail.

[Chemical imidization method] This means to promote ring-closure imidization of polyamic acid with a dehydrating agent such as acetic anhydride, in which case a tertiary amine such as pyridine is used as a catalyst to increase the imidization rate. You can also In the imidization of the yarn, specifically, after winding the coagulated yarn on a bobbin, the bobbin is immersed in the above-mentioned chemical cyclizing agent, or the coagulated yarn is placed on the chemical cyclizing agent. The yarn and the chemical cyclizing agent may be brought into contact with each other by a method such as passing through a bath, and the method is not particularly limited. Further, at this time, by using the yarn imidization promoting method previously proposed by the present inventors in Japanese Patent Application No. 62-272342 (JP-A-1-113434),
The imidization can be progressed more effectively. The yarn obtained as described above is subjected to a hot drawing process and imparted with high mechanical properties, but it is essential that the yarn is stretched to 2 times or more. Therefore, the high-strength, high-modulus fiber of the present invention cannot be obtained. This is because liquid crystal spinning, which is the case with aramid fibers, cannot generally be applied to the molding of polyimide fibers, and therefore a high degree of molecular blending must be achieved by some other method. Here, the stretching temperature can be set broadly, but it is preferable to carry out at a boiling point of the solvent of −100 ° C. or higher and a boiling point of the solvent of + 100 ° C. or lower. Since the remaining molecular weight is large, the relaxation of the molecular chain is large, and efficient stretching is difficult,
Further, stretching at a temperature higher than the latter is accompanied by rapid evaporation of the solvent, which is one of the causes for producing a defective portion that prevents the development of excellent mechanical properties such as generation of voids. However, this is not the case when the temperature is raised stepwise and the stretching is advanced. After stretching, it is preferable to employ a high temperature heat treatment for accelerating crystallization, completion of imidization and removal of the solvent, and in the case of 450 ° C. or higher and 650 ° C. or lower, more preferably 50
Temperatures above 0 ° C and below 600 ° C are used. Thus, the fiber of the present invention having excellent mechanical properties such as an elastic modulus of 1,000 g / de or more and a tensile strength of 15 g / de or more is provided. (Operation / Effect of Invention) The greatest feature of the polyimide in the present invention is that it can be stretched at a high ratio even though it has a rigid skeleton and does not use a copolymerization component. It becomes possible to obtain a polyimide fiber having mechanical properties. Incidentally, British Patent No. 903,271 discloses that 3,3'-dimethylbenzidine, 3,3'-, as a component of polyimide.
Although benzidine derivatives such as dimethoxybenzidine have been described, the rigid polyimides using these are inferior in the heat drawability as compared with the polyimide of the present invention, and therefore the mechanical properties of the obtained fiber are also in the polyimide of the present invention. It does not reach. The fiber of the present invention exhibits excellent performance in the fields of advanced composite materials (ACM), electronic materials and the like. (Examples) Hereinafter, the present invention will be described with reference to Examples. Intrinsic viscosity (ηinh) in the examples was measured at 35 ° C by diluting the precursor solution with a solvent so that the polymer concentration was 0.5 g / dl. Tensileon manufactured by Toyo Sokki Co., Ltd. was used for tensile properties. A single yarn was measured at a length of 100 mm and a pulling speed of 50 mm / min. Example 1

[Synthesis of polyimide precursor]

5,2 g of 2,2'-dimethylbenzidine in 100 ml of dehydrated NMP
After dissolving (26.3 mmol), the solution was cooled to -10 ° C, and 5.74 g (2 mg of pyromellitic dianhydride (PMDA) was stirred vigorously.
6.3 mmol) was added. Polymerization was continued, NMP was added in sequence as the viscosity of the solution increased, and finally a high-viscosity solution having a polymer concentration of 4.5 wt% was obtained (I). The polymerization time required during this period was about 3 hours, and the intrinsic viscosity reached 5.2.
Similarly, by changing the acid component, a precursor solution containing a polymer composed of 3,3 ′, 4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) and 2,2′-dimethylbenzidine ( II) was obtained. Next, the diamine component was changed to the hydrochloride of 2,2'-dimethylbenzidine and the polymerization with PMDA was performed. At this time, pyridine as a dehydrochlorinating agent was added in advance in an amount of twice the number of moles of diamine, and a high-viscosity solution similar to (I) was obtained (III). In addition, these intrinsic viscosities are
Shown in 1.

[Wet spinning]

Using the precursor solution obtained above as a spinning dope as it is, after degassing under reduced pressure, in a coagulation bath at room temperature consisting of water 95 / NMP5 (volume ratio) through a nozzle having a pore diameter of 0.3 mm and a pore number of 12,
Wet spinning was performed at a discharge rate of 5 m / min, 3 m was passed through the coagulation bath, and then stretching and desolvation were performed in a stretching bath composed of water at room temperature. Further, the obtained yarn was hot-drawn by the following two methods. (Method A) The obtained yarn was continuously dried on a drying drum, and further heated stepwise from 150 ° C to 550 ° C to perform hot drawing. (Method B) The obtained yarn was once wound on a glass bobbin for 10 minutes, and acetic anhydride / pyridine (volume ratio 70
/ 30) was immersed in a chemical cyclization bath for 1 hour to promote imidization, the yarn was washed with water, dried, hot-drawn at 250 ° C, and further treated at 550 ° C under tension. The draft, the draw ratio, the hot draw ratio, and the tensile properties of the obtained polyimide fiber single yarn during spinning are shown in Table-I. Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that the diamine component and the acid component were variously changed, and then wet spinning was performed as described above, and the obtained yarn was hot-stretched by the (method B). The results are shown in Table-II. It was The polyimide using 3,3′-dimethylbenzidine and 3,3′-dimethoxybenzidine as the diamine component is the same as in Example 1, 2.
The heat drawability was inferior to the polyimide using 2'-dimethylbenzidine, and the fiber properties were also the same. Comparative Example 2 Copolyimides having various diamine components and acid components were polymerized, wet-spun in the same manner as in Example 1, and further heat-stretched by (Method B). The results are shown in Table-III. The elastic modulus was lower than that of the homopolymer. Example 2 When the wet spinning of the precursor solution (I) obtained by polymerizing PMDA and 2,2′-dimethylbenzidine obtained in Example 1 was hot-stretched by (method B), The results of changing the draw ratio are shown in Table IV. A strength of 15 g / de and an elastic modulus of 1,000 g / de were achieved by a heat draw ratio of 2 times or more. Example 3 The solution (I) obtained by polymerizing PMDA and 2,2′-dimethylbenzidine of Example 1 was wet-spun, and the wound yarn was dipped in a bath containing methanol with bobbins for 10 minutes for swelling treatment. After that, chemical cyclization and hot stretching were performed according to (Method B). The swelling treatment promoted imidization and obtained good fiber properties. The results are shown below. Thermal draw ratio: 2.4 Fiber physical properties (D / T / E / M): 2.3 / 20.5 / 1.8 / 1,330 Example 4 Acetic anhydride was added to the precursor solution (I) of Example 3 in an amount of 0.4 equivalent based on the polyamic acid unit, and pyridine. Was mixed with acetic anhydride in an equimolar amount and allowed to stand overnight to partially promote imidization, which was used as a dope (IV) for spinning. Hereinafter, Example 3
As described above, wet spinning and swelling treatment were performed, and hot stretching was performed by (method B). The results are shown below. The coagulability of the dope was improved and the physical properties of the fiber were further improved. Thermal draw ratio: 2.7 Fiber physical properties (D / T / E / M): 2.2 / 20.8 / 1.8 / 1,380

Claims (1)

[Claims] 1. A fiber comprising a polyimide whose main repeating unit is a unit represented by the following formula (I), wherein the fiber has an initial elastic modulus of 1000 g / de or more and a tensile strength of 15 g / de.
The above is a polyimide fiber.