JPS62289606A - Production of polyvinyl alcohol fiber having high tenacity and elastic modulus - Google Patents

Abstract

PURPOSE:To produce the titled fiber preventing thermal decomposition and discoloration of a PVA-DMSO solution spinning dope having high polymerization degree, by adjusting pH of the PVA-DMSO spinning dope within a specific range. CONSTITUTION:A PVA polymer having a polymerization degree of >=1,500 is dissolved in dimethyl sulfoxide at a concentration of <=30wt%. The solution is maintained to a hydrogen ion concentration of 4-10, preferably 5-9 at 25 deg.C and subjected to dry and wet spinning. The pH adjustment is preferably carried out by using an acid having a dissociation constant (pKa) of <=2 in water at 25 deg.C at an amount of 1.0X10<-5>-1.0X10<-1>mol/l.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention and Field of Industrial Application] The present invention relates to a method for producing high-strength, high-modulus polyvinyl alcohol (hereinafter abbreviated as PVA)-based fiber, and in particular to a method for producing a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber, which is known in the art.
This invention relates to a method for producing PVA-based fibers that have high mechanical properties that are incomparable to A-based fibers and comparable to aramid fibers.

[Prior Art] Conventionally, PVA fibers have higher mechanical properties, especially strength and Young's modulus, than fibers such as nylon and polyester.
In addition to its main use as a fiber for industrial materials, it has recently been used as an asbestos substitute fiber, but compared to aromatic polyamide (aramid) fiber, which is known as high strength and high modulus Wi fiber. and strength,
Both Young's modulus was inferior, and could not even match that of aramid fiber.

Such PVA-based fibers are usually manufactured by using a PVA aqueous solution as a spinning stock solution, wet-spinning in a coagulable salt-free aqueous solution, and subjecting it to stretching, drying, heat treatment, etc. Various means have been proposed to improve physical properties, particularly strength and modulus of elasticity. For example, in Japanese Patent Publication No. 4B-9209, rflll is used as a spinning dope.
There is also a method using an aqueous solution containing HQ or a salt thereof, and Japanese Patent Publication No. 16675/1989 describes a method using a dimethyl sulfoxide (hereinafter abbreviated as DMSO) solution as a spinning stock solution in an aqueous solvent such as methanol, ethanol, bempine, or chloroform. A method of wet spinning, and further disclosed in JP-A-56-128
309@ gazette describes P obtained by wet or dry spinning.
After drawing VA fiber at least 10 times, 0-3%
Methods have been proposed in which heat treatment is carried out at a temperature higher than the drawing temperature while allowing for a constant length or shrinkage of PVA fibers. , maximum strength of 10 g/d,
It exhibits an elastic modulus of only about 400 q/d at maximum, and even if one of the above physical properties is improved, the other elastic modulus or strength is not substantially improved. is the actual situation.

Furthermore, in recent years, JP-A-60-126312 discloses that a DMSO solution of PVA with a degree of polymerization of 1,500 or higher is spun in a methanol coagulation bath using a dry-wet method, and is highly stretched and oriented to achieve high strength and high elasticity. A method for obtaining a PVA-based fiber has been proposed.

However, PVA-DMSO solutions inherently have very poor thermal stability, and if left at room temperature for a long time, the viscosity of the solution decreases, and furthermore, at high temperatures of 80°C or higher, the viscosity of the solution decreases rapidly. High strength/high elastic modulus PVA
Fibers could not be stably obtained. Additionally, there was a problem that the fibers were colored yellowish brown.

However, regarding the thermal stability of the PVA-DMSO solution, there is a report by Lumen et al. [Polymer Chemistry, Vol. 16.

Page 217 (1959) ] Nii%le J = Uni, PV
It is presumed that the carbonyl group present in the main chain of the A-based polymer is ionically cleaved by DMSO, which is an essentially basic solvent, in a reverse aldol reaction, and the PVA polymer chain is cleaved. It is thought that the molecular weight of PVA decreases, causing a decrease in viscosity, and that the generated aldehyde causes the polymer solution or fibers to turn yellowish brown.However, until now there has been no attempt to prevent the decomposition of PVA-based polymers caused by DMSO. This has not been studied, and the current situation is that the excellent solubility of DMSO in PVA-based polymers has not been effectively utilized.

Therefore, the present inventors are currently studying a PVA-DMSO solution that does not cause thermal decomposition or two-coloring even at high temperatures. We found that it is particularly effective to maintain the PV within the range, and we proposed it earlier;
The present invention was achieved as a result of extensive research into fiberizing means for A-DMSO solution.

[Problems to be Solved by the Invention] The purpose of the present invention is to eliminate the above-mentioned problems of the prior art, to prevent thermal decomposition and coloring of the PVA-DMSO solution, and to use conventional PVA-based fibers. The object of the present invention is to provide an industrial method for producing PVA-based fibers having excellent fiber physical properties, particularly high strength and high modulus of elasticity, which are clearly distinguishable from those of conventional PVA fibers.

[Means for Solving the Problems] The above object of the present invention is to dissolve a polyvinyl alcohol-based polymer having a degree of polymerization of at least 1500 in dimethyl sulfoxide so that the polymer concentration is 30% by weight or less, and Hydrogen ion concentration (1) H) at °C is 4 or more 1
This can be achieved by dry-wet spinning a spinning solution that has been adjusted to a range of 0 or less.

Below, in specifically explaining the structure of the present invention, two means for adjusting the PVA-DMSO spinning solution in the present invention will be described first.

The PVA polymer in the present invention has a degree of polymerization of 1500 or more, preferably 2000 or more.

Most preferably, it is a PVA type polymer with a high polymerization degree of 3000 or more. The PVA-based polymer is P that is soluble in DMSO.
There is no particular limitation as long as it is a VA-based polymer, for example, completely saponified P
VA, partially saponified PVA, syndiotactic PVA,
Low-temperature polymerized PVA, PV with a small amount of olefin monomers such as ethylene, propylene, butylene copolymerized in the main chain
Examples include A, but preferably saponification degree is 99.
Completely saponified PVA with a mole % or more is preferable.

Furthermore, the PVA-DMSO spinning solution used in the present invention should have a polymer concentration of 30% by weight or less, preferably 25% by weight or less, and if this polymer concentration exceeds 30% by weight, the solution viscosity may increase to tens of thousands of voids. It becomes extremely high and difficult to exhibit fluidity even at high temperatures, making it difficult to spin.

Furthermore, the most characteristic feature of the PVA-DMSO spinning solution in the present invention is the hydrogen ion concentration (D H
> is kept in the range of 4 to 10, preferably 5 to 9.

That is, as is well known in the art, DMSO is essentially a basic solvent, and its pH at 25° C. is usually 12 to 13, indicating strong basicity. PV of the present invention
Only when the pH of the A-DMSO spinning solution is adjusted within a specific range of 4 to 10 can
It has excellent thermal stability such that the PVA polymer does not undergo thermal decomposition or thermal coloration even at high temperatures, preferably 100° C. or higher, and more preferably 120° C. or higher. If the pH exceeds 10, the thermal stability of the spinning solution deteriorates, and if the pH falls below 4, it is strongly acidic, which may cause problems such as corrosion of the coating or the thermal stability of DMSO itself (DI- (if DMSO is 150 It is not preferable because it has the problem of rapid decomposition at temperatures above ℃.

As a means for adjusting the pH of the PVA-DMSO spinning solution, an acid having an acid dissociation constant (pKa) of 2 or less in water at 25° C. is added at a rate of 1.0 x 10-" to 1.0 x 10' mole/
It is desirable to use a range of amounts in g. At this time, pKa
In cases where the pH exceeds 2, it is difficult to dissociate in DMSO, and an extremely large amount of acid is required to maintain the pH of the PVA-DMSO solution below 10, which may cause problems with acid leakage during molding. , the thermal stability of the PVA-DMSO solution is adversely affected, which is not preferable.

Here, ff [dissociation constant (pK
a) Examples of acids of 2 or less include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, benzenesulfonic acid, toluenesulfonic acid,
Phenolsulfonic acid, sulfozalcylic acid, sulfobenzoic acid, aniline sulfonic acid.

Methane or ethanesulfone, lauryl sulfonic acid,
Cetyl sulfonic acid, styrene sulfonic acid.

Examples of tlif2 include vinylsulfonic acid, allylsulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, and 2-acrylamido-2-methylpropanesulfonic acid, among which sulfuric acid, nitric acid, and benzenesulfonic acid.

It is preferable to use one kind or a combination of two or more kinds of l-luenesulfonic acid.

In addition, the PVA-DMSO spinning solution in the present invention may contain a small amount of a solvent that is compatible with DMSO in order to improve the viscosity of the solution, and in order to further improve the thermal stability of the solution. , hydroquinone, hindered phenolic compounds.

A small amount of an antioxidant such as a hindered amine compound can also be included.

Next, a method for forming fibers from the above thermally stable PVA-DMSO spinning solution will be described.

The PVA-DMSO spinning solution in the present invention is made into fibers by a so-called dry-wet spinning method. That is, the spinning solution is extruded from the spinneret through an air layer or an inert gas atmosphere layer into a coagulation bath. At this time, the distance between the spinneret and the liquid surface of the coagulation bath (inert gas atmosphere) is not particularly limited, but is suitably 2 to 100 m, preferably 3 to 20 m, and if it is shorter than 2 m, the dry/wet It becomes difficult to stably carry out spinning, and if the length is longer than 100 m, it becomes difficult for the fibrous solution extruded from the spinneret to run stably, and slight yarn sway can cause stagnation between single yarns in this gas atmosphere. This will cause problems such as.

In addition, the linear velocity (Vo) of the spinning solution discharged from the spinneret hole
and the yarn take-up speed (■1) in the coagulation bath are set in conjunction with each other, and the spinning draft calculated by Vo/V1 is 0.05.
~1.0, preferably 0°07~0.75. If the spinning draft is less than 0.05, the yarn may become loose/V in the coagulation bath or the fineness variation between single yarns will increase, making it difficult to perform stable spinning. Furthermore, if the spinning draft exceeds 1.0, the denseness and drawability of the coagulated yarn will decrease, making it particularly difficult to increase the strength of the fiber.

Further, in the coagulation bath during dry-wet spinning, a solvent that is miscible with DMS O, which is a solvent for PVA, is used as a coagulant, such as alcohols such as methanol, ethanol, and butanol, acetone, and benzene.

Toluene etc. or one or more of these and DMSO
Mixed solvents with and aqueous solutions (saturated) of inorganic salts such as caustic soda are used, but methanol, ethanol, and acetone are particularly preferred.

The coagulation bath temperature also depends on the density of the coagulated thread.

It is desirable to use a low temperature of 30° C. or lower, preferably 20° C. or lower, from the viewpoint of fusion between single yarns.

The coagulated yarn obtained by dry-wet spinning is then subjected to processes such as desolvation, stretching (secondary stretching), drying, and stretching (secondary stretching) to become a high-strength, high-elasticity yarn. During,
Particular consideration should be given to the drawing process.

That is, after the coagulated yarn is desolvated, it is usually cold rolled,
The film is stretched approximately 2.0 to 7.0 times (-second stretching) by cold stretching using cold pins or the like, or heating stretching using a heating tube, hot plate, heating roll, heating pin, heated liquid, etc. This drawn yarn is further heated at a temperature of 20°C in a heated atmosphere, such as air or an inert gas such as nitrogen, argon, helium, etc.
0°C or higher, lower than the fiber melting temperature, preferably about 200°C or higher
Hot stretching (secondary stretching) is carried out through a heating tube set at 270°C so that the stretching ratio throughout the entire stretching process, that is, the unstretching ratio is at least 10 times, preferably 15 times or more. ) is tM. For this reason, the stretching ratio limited to secondary stretching varies depending on the stretching temperature, but is usually 2.
It is desirable to set the magnification as high as possible, such as 0 times or more, especially 3 to 7 times.

The present invention is no exception to the use of oil treatment during drying or hot drawing of fiber yarns, and in order to prevent adhesion between single yarns during the drying process, etc.
It is a more desirable embodiment to employ a fiber opening means.

[Effect of the invention] As mentioned above, the present invention has a high degree of polymerization (1500 or more) P
A feature of the invention is that the hydrogen ion concentration (pH) is controlled within a predetermined range as a means for thermally stabilizing the VA-DMSO-based spinning solution. By employing such a spinning solution of highly polymerized PVA, it was possible to achieve a strength of 15 o/d or higher and an elastic modulus of 2 for the first time.
PVA-based fibers with high strength and high elastic modulus of 50 g/d or more can now be produced industrially and stably to an extent that could never be predicted with conventional technology, and this has led to the use of PVA-based fibers as general industrial materials. It has a remarkable effect in the field of PVA-based fibers, making it possible to use it in a wide range of applications.

[Example] Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.

In this example, the degree of polymerization and mechanical performance of PVA were determined according to the following measurement method.

a. Degree of polymerization of PVA Based on JIS K6726, the degree of polymerization (Po) was calculated from the intrinsic viscosity ([η]) of the aqueous solution at 30° C. using the following formula.

Log(Pn)=1.613xLoc+ ([η]X1
04/8.29> However, [η]: <ml/9> b9 Mechanical performance fibers were conditioned in advance at 20°C and 65% relative humidity for 24 hours, and the sample length of the single yarn constituting the fibers was 2OIII111. ．． Single yarn strength and initial elastic modulus were measured using a tensile tester at a take-up speed of 100 mm/min.

Example 1 Vinyl acetate was subjected to bulk polymerization at a temperature of 50°C using azobisisobutyronitrile as an initiator. The obtained polyvinyl acetate was completely saponified (saponification degree: 99.5 mol%) to obtain PVA with a polymerization degree of 5000 (polymerization rate: 18%).

Next, 5.09 (1.0
The mixture was heated and dissolved at 0°C for 2.5 hours. The P obtained at this time
The DH of the VA-DMSO solution was 6.8, and the solution viscosity at 45°C was 2400 voices. Using this spinning stock solution at 125°C, the pore diameter was 0°12mmφ and the number of holes was 100.
It was discharged into the air at a discharge rate of 50 c/min from the nozzle of No. 1, and after traveling through a space of 1 Q mm (distance between the nozzle surface and the liquid level of the coagulation bath), the temperature 15 containing 3% by weight of DMSO was discharged. °C
It was introduced into a methanol coagulation bath for coagulation, and was taken off at a speed of 12 m/min so that the spinning draft was 0.27.

The obtained undrawn yarn was washed with methanol, drawn four times in a two-way drawer, and dried with a heating roller at 80°C.

The dried yarn was stretched 4.5 times through a heating tube with a nitrogen stream at 245° C. and wound up with a winder. The total drawing ratio of the obtained drawn yarn was 18.0 times, and the single yarn fineness was 3.
．． 3d, single yarn strength is 21. (1+/d, elastic modulus is 39
0 o/d, and elongation was 5.5%. Further, the obtained coagulated thread was washed with methanol and dried, and its degree of polymerization was measured and found to be 4800, and almost no decrease in the molecular weight of PVA during the thread spinning step was observed.

Example 2 Wet-dry spinning was performed in exactly the same manner as in Example 1, except that the amount of toluenesulfonic acid in the PVA-DMSO solution was changed as shown in Table 1.

Table 1 summarizes the hue, degree of polymerization, and physical properties of the stretching system.

In Table 1, in No. 5.6, the pH of the spinning stock solution is outside the supination range of the present invention, and the physical properties of the resulting yarn are also poor.

(Explanation below) Example 3 Wet-dry spinning was carried out in exactly the same manner as in Example 1, except that the diameter of the spinneret hole used was changed and the spinning draft was changed as shown in Table 2.

The physical properties of the obtained drawn yarn are summarized in Table 2.

(Hereinafter, blank space) Example 4 The same procedure as in Example 1 was carried out, except that the total stretching ratio of the dry yarn at 245°C in a heating tube with a nitrogen stream was changed as shown in Table 3. Wet-dry spinning was performed.

The physical properties of the obtained drawn yarn are summarized in Table 3.

Table 3

Claims (1)

[Claims] A polyvinyl alcohol polymer having a degree of polymerization of at least 1500 is dissolved in dimethyl sulfoxide so that the polymer concentration is 30% by weight or less, and the hydrogen ion concentration (pH) at 25°C is in the range of 4 to 10. A method for producing high-strength, high-modulus polyvinyl alcohol fibers, which comprises dry-wet spinning a spinning solution prepared as described above.