JPS6039408A - Preparation of precursor yarn for carbon yarn - Google Patents

Abstract

PURPOSE:To obtain precursor yarn having improved quality and high strength free from occurrence of fluff, by setting void between the face of nozzle hole and the liquid level of coagulating bath, subjecting an acrylonitrile polymer to set spinning at a specific flow velocity. CONSTITUTION:Acrylonitrile is polymerized in an aqueous solution consisting essentially of zinc chloride, to give a spinning stock solution. The spinning stock solution is heated, the flow velocity of it in the nozzle hole is made >=20m/min, and extruded into a coagulating bath equipped with void between the face of the nozzle hole and the liquid level of the coagulating bath. The gelatinized yarn is drawn from the coagulating bath at a flow velocity 0.8 as fast as the flow velocity in the nozzle hole, orientated, and dried to give the desired precursor yarn.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for spinning acrylic polymer IIa #1' useful as a carbon fiber precursor.

Currently, high-strength or high-elasticity carbon fibers can only be obtained practically from acrylic polymer fibers. Generally, in order to obtain carbon fiber from acrylic polymer fiber,
The fibers undergo a flameproofing step in which the yarn is heated at 00 to 300°C, and a carbonization process in which the flameproofed fiber is heated at 800 to 1500°C in a non-oxidizing atmosphere. In the flameproofing process, a cyclization reaction occurs within or between molecules within the acrylic polymer fiber, and the fiber is oxidized, reaching a softening point that can withstand the carbonization process and changing into a structure that is easily carbonized. The thread generates heat during the flameproofing process, but it is known that if temperature control is poor, the temperature will rise before the softening point rises and the filaments will fuse together. In addition, it is known that the diffusion of oxygen into the filament is rate-limiting in this reaction, and if the flame-retardant process is attempted to be completed in a short time, the flame-retardant center of the filament will be inadequate. Deteriorates the quality of carbon fiber. In order to prevent these drawbacks, it is conceivable to reduce the single fiber diameter of the precursor fiber.

In wet spinning of acrylic fibers, the spinning stock solution is generally
It is extruded into a coagulation bath through a nozzle hole of ~200μ to form a gel-like thread, and the strength of the thread is increased by orienting the molecules in the direction of the fiber axis by cold drawing and hot drawing. Although the filament becomes smaller through cold stretching and hot stretching, the stretching ratio cannot be increased indefinitely, and stretching beyond the point at which sufficient molecular orientation is obtained will not only result in a large number of fluffs but also cause the filament to be perpendicular to the fiber axis. An abnormal structure occurs in the direction, and the strength of the resulting φ carbon fiber becomes low. Furthermore, if the molecular orientation within the system is increased, the elongation of the fibers will be reduced, which will increase the occurrence of fuzz in subsequent steps, reducing the quality of the carbon fibers.

As a result of various studies to avoid the above-mentioned problems and reduce the single yarn diameter, the present inventor found that the goal could be achieved by so-called air gap spinning, and arrived at the present invention.

That is, in the present invention, when spinning an acrylonitrile polymer using an aqueous solution mainly containing zinc chloride as a solvent, a gap is provided between the nozzle hole surface and the liquid surface of the coagulation bath, and the flow rate of the spinning dope in the nozzle hole is set to 20 m/min. In the present invention, the acrylonitrile polymer is Use one containing 85% or more of acrylonitrile. Copolymerization components are not particularly required, but when used, acrylic acid, methyl acrylate, itaconic acid, etc. are preferred.

As the solvent, an aqueous solution containing zinc chloride as a main ingredient is used. The concentration of zinc chloride is preferably 55 to 65% from the viewpoint of solubility.

Although the concentration of zinc chloride may be lowered further and other salts such as sodium chloride may be added, if the amount added is increased, the spinnability of the spinning dope will deteriorate, making it impossible to fully enjoy the effects of the present invention.

In that case, the lower limit of zinc chloride concentration is 50%.

As a method for producing the spinning dope, so-called solution polymerization in which monomers are polymerized in the above-mentioned solvent is preferred, and when the granular or powdered polymer obtained by polymerization in water is dissolved in the above-mentioned solvent, non-uniform portions are not created. Solution polymerization is difficult in other inorganic salt aqueous solutions.If sufficient care is not taken, the stringiness will deteriorate and the effects of the present invention will not be obtained.Solution polymerization is difficult in other inorganic salt aqueous solutions. The polymer concentration in the stock solution is preferably as high as possible, preferably 6% or more. The molecular weight of the polymer is preferably 50,000 or more, more preferably 90,000 or more, and the viscosity of the stock solution at 45° C. is preferably 150 voids or more in order to obtain good spinnability and yarn strength. Although there is no upper limit to the viscosity, the nozzle back pressure can be suppressed by the pressure limits of the piping, nozzle holder, and nozzle, and even if the temperature of the stock solution is raised to lower the spinning viscosity, the amidation of the nitrile group of the polymer It cannot be set too high because it will reduce the strength of the fibers, but it depends on the solvent composition, but it is preferably 1.
Since the temperature is preferably 20° C. or lower, more preferably 60° C. or lower, the temperature is limited depending on the device. When the stock solution temperature is 100°C, there is no particular difficulty as long as it is 20,000 poise or less. However, from the above-mentioned amidation point of view, it is necessary that the allowable time for maintaining the temperature at 100° C. be within 3 minutes.

The hole diameter of the nozzle is preferably 200 μm or less. If this is large, the filamentous stock solution just coming out of the nozzle hole will become thicker, which is contrary to the purpose of the present invention. If it is less than 50μ, the nozzle back pressure becomes high, and spinning becomes difficult with a high viscosity stock solution. Nozzle hole length/
The ratio of the hole diameters is preferably 1 or more in order to prevent the so-called ballast effect, which occurs when the stock solution tries to spread along the nozzle hole surface immediately after being discharged from the nozzle hole, but if it is too large, the nozzle back pressure will increase, so it should be up to 15. Will.

The coagulating solution is preferably an aqueous solution having a zinc chloride concentration of 15% or more in order to maintain a circular cross section of the yarn and prevent the generation of microvoids in the final fiber, and 35% or less in terms of coagulation properties. Some other salts may also be present. The temperature of the coagulating liquid is preferably 20° C. or lower, more preferably 10° C. or lower, from the viewpoint of the strength of the thread.

In the present invention, the raw solution is discharged from above the surface of the coagulation bath to below, and the first feature is that at this time, a gap is provided between the nozzle hole surface and the surface of the coagulation bath to perform so-called air gap spinning. do. For this purpose, it is necessary to increase the flow rate of the spinning dope in the nozzle hole. If this is small, the coagulating liquid will rise between the threads of the undiluted solution discharged from the nozzle due to surface tension, and the air gap will be filled with the coagulating liquid. The minimum flow rate to maintain the air gap varies depending on the distance between the nozzle holes, but the number of filaments of the precursor fiber for carbon fiber is generally 3,
000-12,000 pieces requested, 3,000-12
．． In order to uniformly discharge the spinning dope from the 000 nozzle holes, the area on the nozzle hole surface cannot be made too large, and therefore it is difficult to set the distance between the nozzle holes to 1+m or more. Therefore, the flow rate needs to be 20 m/1/1 inch or more. The upper limit of the flow rate is limited by the viscosity of the stock solution and the pressure resistance of the device.

The distance between the nozzle hole surface and the coagulation bath liquid level, the thickness of the so-called air gap, is not particularly limited;
Alternatively, the distance is preferably 2rMn or more to prevent the air gap from disappearing due to swelling of the nozzle hole surface due to nozzle back pressure, etc., and the larger this distance is, the ratio of the flow rate of the spinning dope in the nozzle hole to the speed of drawing out the gel thread from the coagulation bath. Although it is possible to increase the so-called nozzle draft, it is preferable to use a number of 20 or less since there is almost no change if the number of drafts exceeds 20, and if the spinnability of the spinning dope is not sufficient, yarn breakage will only increase.

The nozzle draft can be set depending on the spinnability of the spinning dope, and the second feature of the present invention is to set it to 0.8 times or more. In normal spinning, when the nozzle hole surface is in the coagulation liquid, the gel thread can be pulled out of the coagulation bath at only 1/3 of the flow rate of the stock solution in the nozzle hole, but in the system of the present invention, this can be pulled out by 0. The size can be increased by 8 times or more depending on the stringiness of the stock solution. Even if the nozzle draft is increased, the yarn will only become thinner, without lowering the maximum draw ratio in subsequent drawings.

The filament diameter of the final fiber can be reduced.

The gel yarn pulled out from the coagulation bath is thoroughly washed with water (cold stretching is performed before or during washing if necessary) to thoroughly remove the solvent, and then subjected to hot water stretching and steam stretching.

Perform drying, oiling, relaxing, etc. as necessary. Relaxation may be omitted in the spinning process and performed at the beginning of the flameproofing process. In order to obtain fibers with small filament diameters, it is preferable to carry out the drawing in two or more stages in order to increase the total drawing ratio. A preferred example of stretching is cold stretching by 1.5 to 3 times in an aqueous solution at 25°C with approximately the same composition as the coagulation bath;
After washing with water, it is heated 2 to 5 times in hot water at 50 to 100°C, and 2 to 5 times in pressurized steam at 1 atmosphere or more, and the ratio of the yarn speed after steam drawing to the speed at which the gel yarn is drawn out from the coagulation bath is By drawing the filament to a diameter of 20 or less, fibers with a fine filament diameter without being excessively oriented can be obtained.

This is made flame resistant under tension by a conventional method under temperature and speed conditions such that the 02 absorption amount is 3 to 12%.
Strong carbon fibers can be obtained by carbonizing at 1,500°C.

The effects of the present invention will be shown below using Examples and Comparative Examples, but the invention is not limited thereto.

Example 6 Polymerizing acrylonitrile in a 0% zinc chloride aqueous solution,
A spinning stock solution was obtained. The molecular weight of polyacrylonitrile was determined by Staudinger's formula to be 122,000. The polymer concentration was 8.2%, and the solution viscosity measured by a B-type viscometer at 45° C. was 1,050 voids. This stock solution was heated to 60°C.
The diameter of the hole is 0.12nwn, the circular pitch of the hole is 0.8awn, and the length of the straight part of the hole is 0.6, excluding the part where the hole expands into a funnel shape at the inlet where the stock solution enters the hole.
Flow rate of 50 m/mi from a nozzle with 3,000 holes
Extruded with n. The coagulation liquid was a 28% zinc chloride aqueous solution at 5°C, and the air gap between the nozzle hole surface and the coagulation bath liquid level was 10+nm. Gel thread from coagulation bath at 70m/min
The film was drawn out at a speed of After drying, a fluff-free fiber with a single yarn diameter of 9.4 microns was obtained. The highest steam stretching ratio that allowed continuous operation was 3.6 times. This fiber is placed in the air at 240°C in the first half and 270°C in the latter half.
J, TS R-7, which was made flame resistant under a tension of 300 g for 30 minutes and then carbonized at 1,250°C in pure nitrogen.
Strand strength measured by 601 is 382 kg/
It was mm'. The increase in oxygen in the flame-resistant yarn was 7.2%.

Comparative Example 1 When the nozzle was immersed in the coagulation solution in the example, thread breakage occurred directly below the nozzle when the speed at which the gel thread was drawn out from the coagulation bath was set at 36 m/min or higher.

The same speed was set to 30 m/min, and fibers with a single yarn diameter of 14.5 microns were obtained in the same manner as in the examples. The highest steam stretching ratio that allowed continuous operation was 3.3 times. This fiber was made flame resistant under a tension of 300 g at 220° C. in the first half and 260° C. in the latter half for 6 minutes to give an oxygen increase of 7.9%, and carbonized at 1.250° C. in pure nitrogen. Strand strength is 213
kg/mm2.

Comparative Example 2 In the example, the flow rate of the stock solution in the nozzle hole was set to 10 m/mi.
The coagulation liquid blocks the air gap of 0nyn, and the speed at which the gel thread is pulled out from the coagulation bath is 5n.
+/mj, it was not possible to make it more than n.

Procedural Amendment (Voluntary) 1985, 10 Katana S, Commissioner of the Patent Office Kazuo Wakasugi, 1988 Patent Application No. 145289 3, Name of the person making the amendment Name: Nikkiso Co., Ltd. Representative Oto Katsura 2 Department 4, Agent Postal code 150-91 Address 3-43-2 Ebisu, Shibuya-ku, Tokyo Nikkiso Co., Ltd.]! 6. Contents of amendment (1) As stated in the attached sheet.

Amendment 1: The claims on page 1, line 4 of the specification to page 2, line 9 are amended as follows.

2. Claims (1) When performing koto spinning of an acrylonitrile polymer using an aqueous solution mainly containing zinc chloride as a solvent, a gap is provided between the nozzle hole surface and the coagulation bath liquid surface, and a gap is provided within the nozzle hole. (2) A method for producing precursor fibers for carbon fibers, characterized in that the flow rate of the spinning dope is 20 m/min or more, and the speed of drawing out the Kel yarn from the coagulation bath is higher than 0.8 times the flow rate. A method for producing a precursor fiber for carbon fiber according to claim 1, wherein the solvent is an aqueous solution with a zinc chloride concentration of 55% or more and 65% or less (3) An acrylonitrile polymer is solution polymerized in a solvent. (4) A method for producing a precursor fiber for carbon fiber according to claim 1, wherein the gap between the nozzle hole surface and the coagulation liquid level is 2 to 20+ m. Method for producing precursor fibers for carbon fibers (5) The method for producing precursor fibers for carbon fibers according to claim 1, wherein the coagulating liquid is an aqueous solution with a zinc chloride concentration of 35% or less. ) The method for producing a precursor fiber for carbon fiber according to claim 1, wherein the polyacrylonitrile polymer has a molecular weight of 50,000 or more and a spinning solution viscosity (45° C.) of 150 or more. 2. Insert "," next to "To obtain" on page 2, line 16 of the specification.

3. Delete the ``,'' next to ``Flame retardant process'' on page 2, line 17, ζ.

4. On the second page, second line from the bottom, after “In the flame-retardant process”, “
," is inserted.

5. On page 3, line 1, ``oxidized'' is corrected to ``oxidized''.

6. On page 3, line 8, insert "," next to "rate-limiting".

7, page 3, lines 8-9, “When I try to finish,” [
"If you increase the yarn speed when you are about to finish the process," correct this.

8. On page 3, line 10, change the ``,'' in ``known,'' to ``
. ” is corrected.

9. Page 3, line 14 r, insert ``,'' after ``in general''.

10. On the 4th page, lines 4-5, next to ``If you make it bigger'', ``,
” is inserted.

11. On the 4th page, 2nd line from the bottom, "acrylic" is corrected to "acrylo".

12. On the 4th page, first line from the bottom, "acrylic" is corrected to "acrylo".

13. Delete "," from "other salts" on page 5, line 8.

14. On page 5, lines 8-9, insert "," after "yoiga".

15. On the 5th page, line 6 from the bottom, "In case" is followed by ","
Insert.

16, page 6, lines 3 to 11, "Limited to upper limit to viscosity" is corrected as follows.

“There is no particular upper limit for viscosity from the viewpoint of yarn quality.However,
The nozzle back pressure, which increases with viscosity, can be suppressed by the pressure limits of piping, nozzles, etc., and in order to increase the viscosity of the raw solution and lower the spinning viscosity, there is a method of increasing the temperature of the raw solution of the spinning material, but the nitrile group in the polymer Amidation of carbon fiber reduces the strength of the carbon fiber, so the temperature cannot be raised too high, and depending on the solvent composition, the stock solution temperature should be at most 120°C, preferably 60"C or less, so raise the stock solution temperature and increase the nozzle height. The effect of lowering the pressure cannot be expected to be large, so the upper limit of the viscosity is determined depending on the pressure resistance of the equipment used.'' 17, page 7, line 6, insert ``r'' after ``for the coagulating liquid.'' do.

18. On page 7, line 6, delete the ``,'' in ``koku,''.

19. On page 8, line 2, ``Different but'' is corrected to ``Different.''.

20, page 8, line 8 [It is difficult. Insert the following sentence after J.

``The smaller the distance between the nozzle holes, that is, the distance between the filaments, the easier it is for the coagulated liquid to rise between the filaments due to capillary action, so it is necessary to increase the yarn speed in order to maintain the air gap. 21, page 10, line 2, insert ``shi'' next to ``Example of stretching''.

22, page 10, line 3, “The same composition replaces “ga” in J with “J in
Correct.

23, page 10, line 8, “No excessive orientation”
Next to [and therefore less fluff] Patent applicant Nikkiso Co., Ltd.

Claims (1)

[Scope of Claims] (1) When wet spinning an acrylonitrile polymer using an aqueous solution mainly containing zinc chloride as a solvent, a gap is provided between the nozzle hole surface and the liquid surface of the coagulation bath, and the spinning inside the nozzle hole is performed. The flow rate of the stock solution is set to 20 m/min or more,
The gel thread withdrawal rate from the coagulation bath is 0.8 of the flow rate.
Precursor fiber manufacturing method for carbon JIi textiles, characterized in that the solvent is an aqueous solution with a zinc chloride concentration of 55% or more and 65% or less Method for producing precursor fibers (3) Method for producing precursor fibers for carbon fibers according to claim 1, in which an acrylonitrile polymer is solution polymerized in a solvent (4) Nozzle hole surface and coagulation liquid The gap between the surface and the surface is 2 to 20 m.
(5) A method for producing carbon fiber precursor &ll#1' according to claim 1, wherein the coagulation liquid is an aqueous solution with a zinc chloride concentration of 35% or less. (6) The carbon according to claim 1, wherein the polyacrylonitrile polymer has a molecular weight of 50,000 or more and a spinning dope viscosity (45° C.) of 150 voids or less. Method for producing precursor fiber for fibers