JPS63249714A - Production of high-strength acrylic fiber - Google Patents

Abstract

PURPOSE:To obtain the title fibers of markedly improved fiber physical properties such as tensile strength or tensile modulus with industrial advantage by drawing the yarn formed by coagulation of an acrylonitrile polymer of high polymerization degree at a high ratio through a specific process. CONSTITUTION:An acrylonitrile polymer of over 80wt.% acrylonitrile content and over 500,000mol.wt. is subjected to dry-wet spinning process to prepare a coagulated yarn. The yarn is drawn through a multi-stage process in hot water having a temperature gradient. The drawn yarn is dried with hot rollers heated at 50-100 deg.C, until the liquid fraction in the drawn yarn is lowered less than 150wt.% based on the fiber weight. Then, the yarn is drawn again in a heat medium at 150-230 deg.C so that the total draw ratio reaches over 15 times to give the subject fiber of over 15g/d strength and over 200g/d elastic modulus. As a heat medium, for examples, steam is used.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for producing acrylic fibers that are significantly superior in tensile strength, elastic modulus, and other physical properties compared to conventional acrylic fibers. .

[Conventional technology]

Conventional acrylic fibers have excellent properties not found in other synthetic fibers, such as weather resistance and dyeability, but they have low mechanical strength (and are used for clothing and interior decoration such as carpets and curtains). Acrylic fibers are mainly used for general purposes, and are not used for so-called reinforcing purposes.Therefore, many attempts have been made to produce acrylic fibers with mechanical properties that can be used as reinforcing fibers.

For example, Japanese Patent Application Laid-Open No. 57-51810 discloses that fibers obtained by wet or wet-dry spinning are wet-stretched, dried under no tension, and then contact-stretched on a heating plate to achieve effective total stretching. It has been proposed to obtain acrylic fibers with high elastic modulus by increasing the magnification from 9 times to 25 times.

JP-A-57-161117 discloses that the relative viscosity is 2.
There is a method of dry or wet spinning an acrylonitrile polymer of 5 to 6.0, washing or wet stretching after cleaning, drying on a heated roll under tension, stretching under dry heat, and further heat treatment under dry heat. Proposed.

JP-A No. 59-199809 discloses that an acrylic polymer with a molecular weight of 400,000 is dissolved in the solvent under reduced pressure and defoamed, and the resulting spinning stock solution is spun, solidified, and then processed in subsequent steps. Multi-stage stretching under high temperature conditions, then 13
20 J'/ by drying under tension at 0°C or less
It has been described that acrylic fibers with a diameter of d or more are produced.

[Problems to be Solved by the Invention] The gist of all of these known techniques is to improve tensile strength, and such improvement in tensile strength depends on other mechanical properties, such as tensile modulus and knots. It often reduces the strength and does not comprehensively improve or improve other mechanical properties such as tensile strength and elastic modulus. Unlike fully aromatic polyamide fibers, it does not satisfy the fiber physical properties required for reinforcing fibers in composite materials.

Therefore, the present inventors have conducted extensive studies on a method for manufacturing high-strength acrylic fibers that have well-balanced mechanical properties such as strength and elastic modulus, using polyacrylonitrile-based polymers with a high degree of polymerization and a weight average molecular weight of 500,000 or more. As a result, we have arrived at the present invention, which has significantly improved and improved fiber properties compared to conventional acrylic fibers, and provides an industrially advantageous method for producing such high-strength acrylic fibers. There is a particular thing.

[Means for solving problems]

The gist of the present invention is to use a coagulated thread obtained by dry-wet spinning an acrylonitrile polymer having a weight average molecular weight of 500,000 or more.
The drawn yarn is drawn in multiple stages in warm water with a temperature gradient, and the resulting drawn yarn is heated using hot rolls set at 50 to 100°C to reduce the liquid fraction of the drawn yarn to 150% or less of the fiber weight, preferably 100%.
Dry until below, then use a high temperature heating medium to
The purpose is to produce high-strength acrylic fibers by re-stretching at 0 to 230°C so that the total stretching ratio is 15 times or more.

The acrylonitrile polymer used in the present invention needs to have a weight average molecular weight of 500,000 or more, preferably 700,000 or more. In order to produce the high-strength acrylic fiber of the present invention, it is important to carry out stretching at a high stretching ratio of 15 times or more. It is impossible to perform such high-strength stretching, and the high-strength acrylic fiber of the present invention cannot be obtained.

The acrylonitrile polymer used in the present invention can be produced by a conventional suspension polymerization method, emulsion polymerization method, or solution polymerization method.
The method described in the above publication, i.e. at least 70 mol% of acrylonitrile, containing 10 to 70% by weight of a polymerizable unsaturated monomer, 15 to 60% by weight of an organic solvent, and 15 to 60% by weight of water. After polymerizing the mixture with a radical initiator, add 1 part of water and/or an organic solvent to 1 part by weight of the monomer.
The method of adding ~10 parts by weight and carrying out the 11 reaction is preferred in that a high molecular weight polymer can be stably obtained.

Note that the organic solvents used here include DMF (dimethylformamide), DMAc (dimethylacetamide),
Examples include γ-butyrolactone and DMSO (dimethyl sulfoxide).

The acrylonitrile polymer preferably contains 80% by weight or more, particularly 90% by weight or more of acrylonitrile. Monomers to be copolymerized with acrylonitrile include methyl acrylate or methacrylate, ethyl acrylate or methacrylate, n + , in- or t-butyl acrylate or methacrylate, 2-ethylhexyl acrylate or methafrylate, acrylic acid, methacrylic acid, itacon unsaturated monomers such as acid, α-chloroacrylonitrile, 2-hydroxyethyl acrylate, hydroxyalkyl acrylate or methacrylate, acrylamide, diacetone acrylamide, methacrylamide, vinyl chloride, vinylidene chloride, vinyl bromide, vinyl acetate, etc. . These polymerizable unsaturated monomers can be copolymerized with acrylonitrile alone or in combination. The copolymerization ratio is preferably 20% by weight as described above, and further preferably 10% by weight or less when the obtained acrylic fiber is used as a carbon fiber precursor.

Such acrylonitrile polymers can be prepared using solvents such as DMF, DMAc, γ-butyrolactone, DM
The polymer solution obtained by dissolving in an organic solvent such as SO is used as a spinning stock solution.

The obtained spinning stock solution is spun using a dry-wet spinning method, and the obtained coagulated yarn is drawn in multiple stages using hot water with a temperature gradient.However, the process up to obtaining the drawn yarn drawn with this warm water is not particularly limited. It is not something that can be done.

It is necessary to dry the drawn yarn thus obtained using hot rolls maintained at 50 to 100°C. In this case 5
At temperatures below 0°C, it becomes difficult to dry until the liquid fraction reaches 150% or less; on the other hand, when drying at temperatures above 100°C, the water contained in the drawn yarn rapidly evaporates, causing voids, etc. This increases the damage to the yarn, making it difficult to produce high-strength acrylic fibers. Subsequently, it is necessary to re-draw the obtained drawn yarn with a liquid fraction of 150% or less using a high-temperature heating medium, but the heating medium used here is
Examples include high temperature steam and water-soluble polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, and glycerin.

Further, the main high temperature stretching needs to be carried out in the range of 150 to 230'C. At temperatures below 150°C, it is impossible to perform high stretching to produce high-strength acrylic fibers, while at temperatures above 230°C, polyacrylonitrile begins to decompose and the drawability decreases. The drawn yarn thus obtained is washed again if necessary, treated with an oil agent, then dried and burned at a temperature of 100 to 150°C, and more preferably at a temperature of 150 to 200°C. By performing dry heat stretching of 1.05 to 1.20 times, a total stretching ratio of 15 times or more is achieved.

The acrylic fiber of the present invention thus obtained has physical properties such as a single fiber strength of 15 V'd or more, especially 17 //d or more, and an elastic modulus of 200 P/d or more, especially 240 J7d or more, and is suitable for industrial or industrial use. Widely used for industrial purposes and fiber reinforcement (
Specifically, it can be used in industrial applications such as canvas, asbestos substitutes, sewing thread, hoses, and heavy fabrics, and as a reinforcing fiber for composite materials.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

In addition, the strong elongation in the examples was calculated from the SS curve, and the liquid fraction was calculated using the following formula.

(W... Wai thread weight W'... absolute dry weight) Weight average molecular weight (My) is determined by measuring the intrinsic viscosity [η] of the polymer at 25°C using dimethylformamide as a solvent. , is a value calculated using the following formula.

[η) = 3.35 x 10 [Mw:]0°?
5 Example 1 Weight average molecular weights obtained by suspension polymerization method: 470,000, 520,000 and 710,000, composition AN/MAA (methacrylic acid) = 99/
A spinning dope having a composition of polymer/DMF=10/90 (wt%) was obtained using 1 (wt%) of an acrylonitrile-based polymer. This spinning stock solution was transferred from a spin tank maintained at 50°C to a nozzle with a hole diameter of 200 μm and a number of holes of 500 to 82.5% DMF and 17% water at -25°C.
It was spun into a coagulation bath consisting of 5% by weight using a dry-wet spinning method. Note that the distance between the nozzle surface and the coagulation bath was arranged in five orders. The coagulated thread thus obtained was stretched twice in hot water at 70°C and twice in purified water, dried with a heated roller at 90°C until the liquid fraction reached 5070, and then stretched at 180°C.
After stretching 3.7 times in glycerin, washing and oil treatment, drying at 140°C, and further stretching at 200°C for 1.
Dry heat stretching of 1x was performed to achieve a total stretching ratio of 16.3x. Table 1 shows the physical properties of the acrylic fiber thus obtained.

Table 1 Example 2 A water drawn yarn was obtained in the same manner as in Example 1, the liquid fraction was adjusted as shown in Table 2 by changing the drying conditions, and high temperature stretching and further dry heat stretching were carried out in the same manner as in Example 1. I did it. The results are shown in Table 2.

Table 2

Claims (1)

[Claims] 1. A coagulated thread obtained by wet-dry spinning an acrylonitrile polymer containing 80% by weight or more and having a weight average molecular weight of 500,000 or more in warm water with a temperature gradient in multiple stages. Then, the drawn yarn was heated to a temperature of 50 to 100°C using a hot roll to reduce the liquid fraction of the drawn yarn to 15% of the fiber weight.
A strength of 15 g/d or more, characterized by drying until it becomes 0% or less, and then re-stretching at 150 to 230 ° C. using a high temperature heating medium, so that the total stretching ratio is 15 times or more, A method for producing high-strength acrylic fibers with an elastic modulus of 200 g/d or more. 2. The manufacturing method according to claim 1, characterized in that the drawn yarn is dried until the liquid fraction becomes 100% or less.