JPH01292120A - Production of chemically cyclized polyimide fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having high heat-resistance, by wet-spinning an amide solvent solution of a (partially cyclized) polyamic acid, washing with water in such a manner as to give a specific polymer concentration in a dried fiber, drying the fiber and chemically cyclizing the compound. CONSTITUTION:The raw material for the objective fiber is a polyamic acid produced by the reaction of an aromatic diamine (e.g., 4,4'-diaminodiphenyl ether) with an aromatic tetracaboxylic acid dianhydride (e.g., pyromellitic anhydride) or a partially cyclized polyamic acid produced by chemically imidating a part of the amic acid unit of the above polymer. An amide solvent solution of the above raw material is subjected to wet-spinning into an aqueous coagulation bath composed of N-methyl-pyrrolidone, water, etc. The wet-spun fiber is washed with water in such a manner as to give a polymer concentration of 50-85wt.% in a dried (partially cyclized) polyamic acid fiber. The washed fiber is dried and then treated with a chemical cyclizing agent such as acetic anhydride to obtain the objective fiber suitable for tire cord, flame-proofing clothes, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing wholly aromatic polyimide fibers useful as heat-resistant fibers or high-strength/high-modulus fibers by chemical cyclization.

[Prior Art] Fully aromatic polyimide fibers are extremely useful as heat-resistant fibers, and fibers made of polymers with a specific rigid structure are extremely useful as high-strength, high-modulus fibers.

Fully aromatic polyimides are generally produced by spinning a soluble precursor polymer, polyamic acid, into fibers, and then imidizing them using thermal or chemical means. There is. As an imidization method, thermal cyclization is more cost-effective than chemical cyclization, but chemical cyclization is often superior in terms of 41 Fil properties.

There are two main methods used to obtain chemically cyclized polyimide fibers by wet spinning.

The first method is disclosed in Japanese Patent Publication No. 37-97 and is a method of wet spinning in a chemical cyclizing agent or a coagulation solution containing the same.

The second method is wet spinning in an aqueous coagulation system followed by chemical cyclization.

However, the first method has the following drawbacks. That is, acetic anhydride, which is commonly used as a chemical cyclization agent, and pyridine, which is a cyclization catalyst, are both chemicals with extremely strong odors, and the coagulation bath is usually used in an open system, which poses a problem in terms of the working environment. Moreover, it takes a long time, at least several minutes, for the chemical cyclization to proceed completely, and a coagulation bath with a long residence time is required, making the spinning apparatus abnormally large.

In the second method, the coagulated yarn that has been washed with water is chemically cyclized as it is, but in this case, the coagulated yarn contains about 3 to 4 times (by weight) water as the dry yarn. Therefore, all of that water reacts with acetic anhydride and turns into acetic acid. That is, the usage efficiency of the chemical cyclizing agent becomes extremely poor. On the other hand, there is a problem in that polyamic acid or partially cyclized polyamic acid fibers that have been thoroughly washed with water and dried are no longer cyclized even if treated with a chemical cyclizing agent.

[Problems to be Solved by the Invention] Therefore, a method for chemically cyclizing polyamic acid fibers or partially cyclized polyamic acid fibers wet-spun using an aqueous coagulation bath using a cyclizing agent efficiently is particularly desired.

The inventors of the present invention have conducted extensive studies with this goal in mind, and found that if the water washing conditions are controlled so that the amide catalyst remains in a specific proportion in the dried fibers, and then chemical cyclization is performed after drying, this purpose can be achieved. The present invention was achieved based on the discovery of the following.

[Means for Solving the Problems] That is, the present invention involves chemically imidizing a polyamic acid obtained by polymerizing an aromatic diamine and an aromatic tetracarboxylic dianhydride or a part of the amic acid units of the polymer. The amide solvent solution of partially cyclized polyamic acid is wet-spun in an aqueous coagulation system, and then chemically cyclized to obtain polyimide fibers. Density is 50-85%
This is a method for producing chemically cyclized polyimide fibers, which is characterized in that the wet-spun yarn is washed with water so that the yarn becomes cyclized, then dried, and then treated with a chemical cyclizing agent.

The present invention will be explained in more detail below.

The aromatic diamino acids constituting the polyimide fiber of the present invention include m-phenide diamine, p-phenide diamine, 4.4°-diaminodiphenyl ether, 3, 4
--diaminodiphenyl ether, benzidine, or a nuclear methyl or halogen substituted product thereof. In addition, the aromatic tetracarboxylic dianhydride is pyromellitic anhydride.

3.3-. 4.4--Biphenyltetracarboxylic dianhydride, 3.3-. Examples include 4.4-benzophenonete 1-racarboxylic dianhydride and 3.3-4,4°-diphenyl ether tetracarboxylic dianhydride. When these monomers are used alone, homopolymers are produced. In addition, a random copolymer made by combining several monomers may also be used.

The amide solvent used in the present invention includes N-methylpyrrolidone (NMP), N,N-dimethylpolamide, N,
Examples include N-dimethylacetamide.

The wet spinning stock solution may be the polyamic acid solution itself obtained by polymerization, but the present inventors have previously
The method proposed in Publication No. 416, that is, the use of a partially cyclized polyamic acid solution in which some of the amic acid units are partially imidized, provides a coagulated yarn with good transparency and fewer voids. More preferred.

As the coagulation bath, an aqueous solution of the same amide solvent used for polymerization is used. The coagulated thread is then washed with water, and it is important to wash with water so that an appropriate amount of the amide solvent remains in the system. That is, it is necessary to control the water washing process so that the polymer concentration is 50 to 85% by weight at the stage of drying and evaporating water. If the polymer concentration of the dry yarn is less than 50%, it is undesirable because sticking occurs between single yarns and even between yarns. Further, if the polymer concentration of the dried yarn exceeds 85%, it is disadvantageous that cyclization does not proceed at all or proceeds only very slowly even when treated with a chemical cyclizing agent. Factors for controlling the polymer concentration of the dry yarn within the above range include the column length and concentration of the washing bath.

The washed coagulated thread is then dried to evaporate the moisture.

In this case, any of air drying, batch drying using an oven, or continuous drying using a hot air roller or a hot roller may be used. The dry concentration is preferably 100'C or less because the amide solvent is not distilled off at the same time.

The dried polyamic acid fibers or partially cyclized polyamic acid fibers are treated with a chemical cyclizing agent to form a polyimide ring. As the chemical cyclizing agent, aliphatic acid anhydrides such as acetic anhydride and propionic anhydride are usually used. Moreover, an organic base such as pyridine, 3-methylpyridine, 3,5-lutidine, etc. may be used simultaneously as a cyclization catalyst. It is also possible to use other active hydrogen-free organic solvents as diluents during this chemical cyclization. Such diluents include dioxane, benzene, toluene, chloroform, and the like. The treatment conditions for chemical cyclization are a concentration of 15 to 50°C.

Further, the processing time is 10 minutes to 1 day.

The chemically cyclized fibers are then dried and finally subjected to hot stretching or heat treatment at high temperatures to improve their mechanical properties.

[Example] Intrinsic viscosity (η1nh) of polyamic acid in the following examples
So that the ratio is 0.5 g of polymer/100 ml of solvent,
Dilute the polymerization solution with NMI) and measure at 25°C.

The polymer concentration of the dry yarn was calculated by determining the polymer weight before thermal cyclization based on the weight of the Voimide fiber obtained by heating it in an oven at 280°C for 30 minutes to proceed with solvent removal and thermal cyclization. It is.

In addition, the tensile properties of the fibers were measured using Tensilon manufactured by Toyo Baldwin ■ on the yarns.

Arms 100th order, tensile speed 50mm/m! n.

Example 1 This example describes the production of poly(4°4°-oxydiphenylene pyromellitimide) fibers obtained by batch drying spun partially cyclized polyamic acid fibers and then chemically cyclizing them, and their characteristics. shows.

4,4-monodiaminodiphenyl ether (D
0.25 equivalents of amic acid units of acetic anhydride and pyridine were added to a polyamic acid solution of η1nh1.56 obtained by reacting A) with pyromellitic anhydride (PMDA) to obtain a polymer concentration of 12% and a solution viscosity of 190. Boyz (25
A partially cyclized polymer solution was obtained.

This solution was prepared using a 0,08 mm J2 (20 mm J2) solution consisting of NMP/water (volume ratio 25/75) using a 20-hole cap.
Wet spinning during coagulation at ℃, spinning speed 10 m/m1n)
Then, it was stretched 1° to 4 times in a water bath (20° C.) with a tower length of 1 m, washed with water, wound up on a glass bobbin, and air-dried at room temperature for 1 hour. The polymer concentration of the partially cyclized polyamic acid fiber after drying was 69%.

This dried thread was dried using acetic anhydride/pyridine (volume ratio 70/30).
After being chemically imidized by immersion in water at room temperature overnight, the cyclizing agent was extracted by immersion in toluene for 1 hour, and then dried. In figure 3 shows that chemical cyclization was completed under these conditions.
This was confirmed because the absorption of 1μ amic acid completely disappeared.

The polyimide fiber obtained from the above formulation was hot-stretched to 1.4 times using a hot plate at 290°C. The resulting drawn yarn had a fineness of 55 denier and a strength of 3.3 g/d.

The elongation was 10.0%1 and the elastic modulus was 68 E/d. Also,
After processing this fiber in an air oven at 290°C for 64 hours, the strength was 3.2 g/d (retention rate 96%) and the elongation was 10.
．． The heat resistance life was extremely excellent at 2% (retention rate 102%).

Comparative Example 1 The spun yarn wound up on a glass bobbin in Example 1 was immediately placed in running water, washed with water for 10 minutes, and then soaked at room temperature for 1 hour.
The polymer concentration of the dried yarn, which was air dried for an hour, was 95%. This dried thread was dried using acetic anhydride/pyridine (volume ratio 70/30).
The IR diagram of the yarn soaked overnight at room temperature was exactly the same as that before the cyclization treatment, indicating that chemical cyclization had not progressed at all.

Example 2 This example describes the production of poly(4,1-oxydiphenylene pyromellitimide) fiber obtained by chemically cyclizing spun partially cyclized polyamic acid fiber after drying in a continuous system. Show characteristics.

η1nh2 obtained by reacting DA and PMDA in NMP
．． From the polyamic acid solution of No. 94, the formulation of Example 1 was used to obtain a polymer concentration of 9.8% and a degree of partial cyclization of 25%.

A partially cyclized polyamic acid solution having a solution viscosity of 1440 poise (25° C.) was obtained.

0.08 mmg of this solution was passed through a 30-hole nozzle into a coagulation bath (25°C) of NMP/water (volume ratio 25/75).
The material was wet-spun at a spinning speed of 13 m/m1n), stretched to 1°4 times using a water bath (23°C) with a tower length of 1 TrL, and washed with water.
Roll it up, dry it, and roll it up into an octagonal case-shaped processing frame. The polymer concentration of this dried yarn was 60%. This dried yarn was chemically cyclized using the same recipe as in Example 1, dried quickly, and stretched to 1.6 times using a 290°C hot plate, resulting in a fiber with a fineness of 57 denier.

The strength is 4.69/d, the elongation is 7.8%, the elastic modulus is 759/d, and the strength retention rate of Shun when treated in an air oven at 290'C for 64 hours is 96% and the elongation retention rate is 109%. %Met.

Example 3 In this example, p-phenylenediamine (P) and 3゜3'',
4.4--Biphenyltetracarboxylic dianhydride (BP
An example of manufacturing a chemically cyclized polyimide fiber consisting of DA) and its characteristics are shown below.

η1nh2. obtained by reacting P and BPDA in NMP.
From a polyamic acid solution of No. 74, a polymer concentration of 9.052, a degree of partial cyclization of 25%, and a solution viscosity of 66 were obtained using the recipe according to Example 1.
A partially cyclized polymer solution of 0 poise (25° C.) was obtained.

This solution was wet-spun using exactly the same equipment and recipe as in Example 1, and air-dried to form partially cyclized polyamic acid fibers with a polymer concentration of 61%. Cyclization, drying, under nitrogen flow, 4.2 at 450℃
It was stretched twice and subjected to rough tension heat treatment at 575°C. The obtained fiber has a fineness of 15 denier and a strength of 14.29/d.
, the elongation was 1°89%, and the elastic modulus was 870 y/d (very high strength and high elastic modulus).

After this Ili fiber was treated in air at 400°C for 1 hour, the fiber had a strength of 13.09/d (retention rate of 92%), an elongation of 1.62% (retention rate of 86%), and excellent heat resistance. was.

[Effects of the Invention] Chemically cyclized polyimide fibers obtained by the method of the present invention generally have extremely high heat resistance, and in the case of polymer species having a rigid structure, they have high strength and high modulus.

Therefore, electrical insulation materials, flame-retardant clothing, tire cords, F
It can be widely used for various industrial material applications such as RP.

Claims (1)

[Claims] (1) Amide system of polyamic acid obtained by polymerizing aromatic diamine and aromatic tetracarboxylic dianhydride, or partially cyclized polyamic acid obtained by chemically imidizing a part of the amic acid units of the polymer When wet-spinning a solvent solution in an aqueous coagulation bath and then chemically cyclizing it to obtain polyimide fibers, the polymer concentration of the polyamic acid fibers or partially cyclized polyamic acid fibers after drying should be 50 to 85% by weight. A method for producing chemically cyclized polyimide fiber, which comprises wet spinning, washing with water, drying, and treatment with a chemical cyclizing agent.