JPS6385108A - Highly strong acrylic fiber and production thereof - Google Patents

Abstract

PURPOSE:To produce the titled fiber having a tensile strength, a knot strength and an elastic modulus of higher than specific respective levels and suitable for tire cords, FRP composite materials, etc., by wet-spinning or wet and dry- spinning a spinning dope of a polyacrylonitrile polymer having a specific molecular weight, coagulating the spun dope and drawing the produced fiber. CONSTITUTION:A spinning dope which is produced by dissolving 5-20wt% polyacrylonitrile polymer having a weight-average molecular weight of >=500,000 and satisfying a formula: 2.0<=(weight-average molecular weight/number-average molecular weight)<=3.5 (preferably a polymer comprising >=90wt% acrylonitrile and >=1wt% (meth)acrylic acid or itaconic acid) in an organic solvent (preferably DMF, dimethylacetamide, dimethyl sulfoxide or gamma-butyrolactone) is subjected to wet-spinning or wet and dry-spinning. The spun dope is coagulated and then drawn to provide the objective fiber having a tensile strength of >=15g/d, a knot strength of >=5g/d and an elastic modulus of >=200g/d.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a highly tenacious acrylic fiber useful as a reinforcing fiber for composite materials, a fiber for industrial materials such as tire cords, or as a precursor for carbon fiber production. and its manufacturing method.

[Conventional technology]

Acrylic fibers are known for their dyeing clarity, weather resistance, bulkiness,
Due to its unique texture, it is produced and sold in large quantities for clothing, interior decoration, etc.

On the other hand, in recent years, carbon fibers have been expanded into non-clothing fields, and carbon fibers obtained by firing acrylic fibers have excellent properties such as high strength and high elasticity, and are attracting attention as fibers for composite materials. The physical properties of carbon fibers are largely determined by the properties of the starting materials.

Furthermore, since carbon fibers are manufactured through various production processes such as flame-proofing and firing, they tend to become fluffed and cut when they come into contact with guides during the process, which can reduce quality and productivity.

From this point of view, efforts are being made to improve acrylic fibers as carbon-like miscellaneous precursors, but precursors produced on an industrial scale generally have a strength of 5.
~8 //d, and the nodule strength is about 2 to 3 //d.

Therefore, it is possible to use polyester fibers with improved properties such as tensile strength and knot strength, which can be used as precursors for manufacturing high-performance carbon fibers for the space and aircraft industries, which require reliability, or as reinforcing fibers themselves. The emergence of acrylonitrile-based fibers is desired, and many attempts have been announced.

For example, in the special bulletin No. 56-52125, complex salts (Na
It is stated that high strength acrylic fibers can be obtained by solution polymerizing acrylonitrile in a concentrated solution in the presence of formaldehyde and hydrogen peroxide under the action of ultraviolet light, and directly spinning the obtained polymer solution. There is. Further, JP-A-59199809 describes a high-strength acrylic fiber obtained by dissolving an acrylonitrile polymer having a molecular weight of 400,000 or more in an aqueous solution of Rodan salt and then spinning the resulting solution. However, in these methods, spinning is performed using a solution containing sawmill salt, and in such cases, it is essential to remove inorganic impurities that cause strength loss after spinning and drawing, and a cleaning process is required. This is complicated and undesirable from an industrial standpoint. Furthermore, when using acrylic fibers obtained by these methods as precursors for carbon fibers, inorganic impurities have a greater influence on the physical properties of carbon fibers than they do on the acrylic fibers themselves, so they cannot be used completely. It is necessary to remove inorganic impurities, which requires more cleaning steps.

In addition, JP-A-61-152811, JP-A-61-
No. 160415 discloses that dimethyl sulfoxide (DM
High-strength acrylic fibers are produced by solution polymerization of acrylonitrile using an azobis-based initiator in SO) solution and dry-wet spinning at °C using a solution of a polyacrylonitrile polymer with a higher molecular weight than that normally used for acrylic fibers. It is stated that fibers can be obtained. However, it is well known that radical polymerization using a solution polymerization system has a significantly slower polymerization rate than that of a suspension polymerization system, and therefore, when producing it industrially, the equipment becomes extremely large and costs increase. Not efficient. Furthermore, DMSO is a solvent that tends to cause chain transfer (
Fiber Handbook Raw Material Hato P767 (1963, Maruzen)) and is not suitable for obtaining polyacrylonitrile polymers with a high degree of polymerization.

In the claims of JP-A-61-160415, the intrinsic viscosity is at least 2.5, but according to the examples, the weight average molecular weight is at most 450,000 (intrinsic viscosity 3.9).
It has only been considered so far. In addition, the molecular weight distribution curve is determined by GPC.
It was measured according to the law. Furthermore, JP-A-61-1
In 52゛811 publication, although the limiting viscosity is limited to 2.5 or more and less than 3.6 (weight average molecular weight 240,000 or more and less than 400,000) in the claims, it is a solution using DMSO. The polymerization method cannot produce a polymer with a weight average molecular weight of 500,000 or more and is not suitable for producing high-strength acrylic fibers.

[Solution of problems and structure of the present invention]

Therefore, in order to solve these problems, the present inventors
By using an acrylonitrile polymer with a specific molecular weight synthesized by a spinning method using an organic solvent and a polymerization method using a polymerization solvent and initiator with a specific composition, it has high strength and does not contain inorganic impurities. The present invention was completed by discovering that polyacrylonitrile fibers can be obtained.

The gist of the present invention is that the tensile strength of
51/d or more, knot strength 6, P/d or more, elastic modulus 20
After wet or dry-wet spinning a spinning dope in which a high-strength acrylic fiber with a P/r of 1 or more and a specific acrylonitrile polymer are dissolved in an organic solvent in an amount of 5 to 20% by weight, the spinning solution is preferably heated at a temperature of 50 to 100°C. 1 stage stretching, then 100°C
The tensile strength is increased to 1 by performing two-step stretching for 2+s at a temperature exceeding 150°C and below the decomposition temperature of the polyacrylonitrile polymer.
5 t/a or more, knot strength 6 J'/d or more, elastic modulus 2
The objective is to produce high-strength acrylic fibers with a strength of 00 J'/a or more.

In order to produce the polyacrylonitrile fiber of the present invention, the weight average molecular weight is 500,000 or more, preferably 600,000 or more, and the monodispersity of the polymer is required.The weight average molecular weight/number average molecular weight (Mw/Mn) is 2. ．． It is necessary to use a polyacrylonitrile polymer having a molecular weight of 0 to 3.5. In addition, the number average molecular weight (Mn) is a value measured by an osmotic pressure method, and the weight average molecule i (My) is a value calculated by measuring the intrinsic viscosity [η] (dimethylformamide solution, 30 ° C.) using the following formula. be.

[η)=3.35×10 CMv]0°” The high molecular weight polyacrylonitrile polymer of the present invention can also be produced by ordinary suspension polymerization, emulsion polymerization, and solution polymerization, but My/Mn Since the polymer has a large molecular weight and contains many low molecular weight substances, it tends to be difficult to improve the strength etc. of the obtained fiber.Therefore, it is important to obtain a polymer with a small Mw/Mn.For example: JP-A-61-1
11310, i.e. at least 70 m
10 to 70% by weight of a polymerizable unsaturated monomer containing 1% or more of acrylonitrile, 15 to 60% by weight of an organic solvent,
After polymerizing a mixture of 15 to 60% by weight of water with a radical initiator, 1 to 10% of water and/or an organic solvent is added to 1 part by weight of the monomer. A method of polymerizing by adding a certain amount is preferable, but in order to obtain a polymer having a higher molecular weight, 10 to 50% by weight of unsaturated monomer, 15 to 50% by weight of organic solvent, and 25 to 70% by weight of water. It is preferable to initiate polymerization at a composition within the range of .

Examples of the organic solvent include dimethylformamide, dimethylacetamide, dimethylsulfoxide, and r-butyrolactone.

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-, iso- or t-butyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, acrylic acid, methacrylic acid , itaconic acid, α-chloroacrylonitrile, 2-hydroxyethyl acrylate, hydroxyalkyl acrylate or methacrylate, acrylamide, diacetone acrylamide, methacrylamide, vinyl chloride, vinylidene chloride, vinyl bromide, vinyl acetate, etc. Can be mentioned. These polymerizable unsaturated monomers can be copolymerized with acrylonitrile alone or in combination. The copolymerization ratio is 20% by weight as mentioned above, and 1% when the obtained acrylic fiber is used as a carbon fiber precursor.
It is preferably 0% by weight or less.

Unsaturated monomers for copolymerization include acrylic acid, methacrylic acid,
Itaconic acid is particularly preferred, and when it is used, it becomes possible to greatly shorten the flame-proofing time when flame-proofing the precursor.

In producing the polyacrylonitrile fiber of the present invention, first, the acrylonitrile polymer described above is dissolved in an organic solvent to prepare a spinning dope. In order to obtain high-strength twill fibers, it is necessary to bring the entire molecular chains that make up the fibers close to the so-called unstretched chain state, which extends in the direction of the fiber axis. In order to facilitate spinning, it is important to prepare a polymer solution (spinning stock solution) in which the molecular chains are sufficiently loosened. Examples of the organic solvent include solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide, and r-butyl dichton. Further, the polymer concentration varies depending on the molecular weight of the polymer, the viscosity of the spinning dope, etc., but it is usually preferably set in the range of 5 to 20%, particularly 5 to 15%.

The spinning dope thus obtained is shaped into a fiber by wet spinning or dry-wet spinning.

In particular, when producing precursors for carbon fibers, a dry-wet spinning method is used, in which the cross-section of the obtained fibers is closer to a perfect circle.In other words, the spinning stock solution is discharged into the air through a nozzle, and then immersed in a coagulation bath. It is preferable to use the method of

Next, a first stage stretching is performed at a temperature of 50 to 100"C, a second stage stretching is performed at a temperature exceeding 100"C and 150"C or less, and then a temperature exceeding 150"C, which is the decomposition temperature of the acrylonitrile polymer. Third stage stretching is performed at the following temperature.

The stretching process is the most important process for realizing the high strength fiber performance of polyacrylonitrile fibers. As the stretching means, it is necessary to carry out three-stage stretching under high temperature conditions in the post-step (subsequent stretching step). The first stage stretching is preferably carried out using a heat medium such as hot water. Further, it is preferable that the second and third stage stretching be carried out in a high boiling point heat medium. The second and third stage stretching may be performed in steam or dry heat stretching, but voids are likely to be generated when stretched in steam, and the stretchability is poor in dry heat stretching.

Examples of high boiling point media include water-soluble polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, 3-methylpentane-1,
3,5-)riol, etc., especially ethylene glycol and glycerin are preferred.

Next, the drawn yarn is washed with water if necessary and then dried to obtain the desired fiber. Note that if polyhydric alcohol remains in the final fiber, it acts as a plasticizer and causes a decrease in strength, so it is necessary to wash the final fiber until the polyhydric alcohol content is 0.12% or less.

〔Effect of the invention〕

The polyacrylonitrile fiber of the present invention thus obtained has physical properties such as a strength of 15 J'/d or more, particularly 17 J/d or more, an elastic modulus of 200 // d or more, and a knot strength of 6 J/d or more. Since such polyacrylonitrile fibers have excellent strength, they can be used as tire cords, reinforcing fibers for fiber-reinforced composite materials, precursors for carbon fibers, and the like.

〔Example〕

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

Example 1 Synthesized by suspension polymerization according to the method described in the examples of JP-A-61-111310, the composition was 98% by weight acrylonitrile and 2% by weight methacrylic acid, weight average molecular weight 790,000, MW/ A polyacrylonitrile polymer having Mf1=3.4 was dissolved in dimethylformamide (DMF) to prepare a stock solution having a concentration of 10.5% by weight. This spinning solution was transferred from a spin tank kept at 50°C with a pore diameter of 150 μm.
DMF 9 degrees 79.5% by weight using a nozzle with 500 holes
Wet-dry spinning was performed under coagulation bath conditions at a temperature of -4°C. still,
The distance between the nozzle and the coagulation bath was 5 mm.

Using the thus obtained coagulated thread, it was first stretched 2.5 times in hot water (95°C), then 2 times in ethylene glycol at 140°C, and finally 3 times in glycerin at 170°C.
A stretching ratio of 5 times was achieved.

This drawn yarn was washed and dried to obtain acrylic fibers having the yarn quality shown in Table 1.

Example 2 Weight average molecular weight 530,000, MY/Mn==3. Spinning was performed in the same manner as in Example 1 using a polyacrylonitrile polymer (acrylonitrile/methacrylic acid 98/2 ratio).The concentration of the spinning dope was 15.0% by weight.
The temperature of the stock solution was 80°C. The coagulation bath concentration (dimethylformamide) was 81.3% by weight and the temperature was -0.9°C in the same manner as in Example 1. [Table 1 shows the yarn quality of the obtained fibers after stretching, washing and drying.

Comparative Example 1 Spinning was performed in the same manner as in Example 1 using a polyacrylonitrile polymer having a weight average molecular weight of 420,000 and My/Mn = 2-8 (acrylonitrile/methacrylic acid = 98/211 rfi ratio). In addition, the concentration of the spinning stock solution was 15.0.
Weight %, stock solution temperature 80' C1 coagulation bath concentration (dimethylformamide) 78,411 i weight %, temperature -4.2°C. Stretching was carried out in the same manner as in Example 1, but fluffing became noticeable during the stretching in the third-stage glycerin bath, and stable sampling was not possible. The fiber quality after washing and drying is shown in Table 1.

Table 1

Claims (1)

[Claims] 1. Tensile strength of 15 g/dry obtained by wet or dry-wet spinning of a polyacrylonitrile polymer having a weight average molecular weight of 500,000 or more and 2.0≦weight average molecular weight/number average molecular weight≦3.5. d or more, knot strength 6g/
d or more, high strength acrylic fiber with an elastic modulus of 200 g/d or more 2, a polyacrylonitrile polymer with a weight average molecular weight of 500,000 or more, 2.0≦weight average molecular weight/number average molecular weight≦3.5 in an organic solvent 5 ~20
A high-strength acrylic fiber having a tensile strength of 15 g/d or more, a knot strength of 6 g/d or more, and an elastic modulus of 200 g/d or more, which is produced by wet or dry-wet spinning a spinning dope dissolved in weight%, coagulating, and then stretching. Production method 3, the production method 4 according to claim 2, wherein the polyacrylonitrile polymer contains 90% by weight or more of acrylonitrile and 1% by weight or more of methacrylic acid, acrylic acid or itaconic acid. A patent claim characterized in that the polyacrylonitrile polymer is obtained by a suspension polymerization method using a mixed solvent of water and an organic solvent as a polymerization solvent and an azo radical initiator as a polymerization catalyst. A manufacturing method 5 according to claim 2, a manufacturing method 6 according to claim 4, characterized in that the organic solvent is dimethylformamide, dimethylacetamide, dimethyl sulfoxide, or γ-butyrolactone. The first stage drawing is carried out at a temperature of 100°C and below 150°C, and the third stage drawing is carried out at a temperature exceeding 150°C and below the decomposition temperature of the acrylic fiber.
The manufacturing method according to claim 2, characterized in that stage stretching is performed.