JPH02277809A - Production of high-tenacity polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:To stably produce the subject fiber at a low cost by extruding a solution of a PVA having specific polymerization degree and saponification degree through a nozzle, coagulating in an alkaline aqueous solution by wet- spinning technique. subjecting the coagulated fiber to drawing, neutralization, wet-heat treatment, washing with water and drying, removing the solvent from the fiber and drawing under heating. CONSTITUTION:The objective high-tenacity fiber is produced by dissolving a polyvinyl alcohol polymer having an average polymerization degree of >=1,500 and a saponification degree of >=98mol% in a solvent containing >=10wt.% of an organic solvent (e.g. dimethyl sulfoxide), extruding the solution through a nozzle, coagulating the extrudate in an aqueous solution containing >=5g/l of an alkali (e.g. sodium hydroxide) by a wet-spinning technique, drawing at a draw ratio of >=1.5, subjecting the drawn fiber to neutralization, wet-heat treatment, water-washing treatment and drying while drawing at a total draw ratio of >=3, almost completely removing the solvent and drawing the fiber at >220 deg.C at a total draw ratio of >=17.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for obtaining high-strength polyvinyl alcohol (hereinafter abbreviated as PVA) fibers inexpensively and stably.

(Conventional technology) Conventional PVA fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile fibers, and have been used not only as fibers for industrial materials, which is their main use, but also as cement reinforcement materials, as substitute fibers for asbestos, etc. is also used.

Methods for obtaining PVA-based fibers with high strength and high modulus include gel spinning of high molecular weight polyethylene - organic solvent applying the concept of ultra-stretching - dry-wet spinning in JP-A-59-100710 and JP-A-61-108711. JP-A No. 62-2233L6 and JP-A No. 63-99315 on q-machine solvent-wet spinning are known.

All of these methods use methanol, which has a high solvent extraction rate, to extrude and stretch the solvent, but they have not yet achieved satisfactory strength.Moreover, they require a methanol recovery process and the installation of explosion-proof equipment, making the manufacturing cost very high. become high.

On the other hand, JP-A-62-149909, JP-A-62-1
As seen in Publication No. 49910, PV containing boric acid
A method of coagulating an aqueous solution into an alkaline aqueous solution by dry-wet spinning is also known, but in these cases, it is difficult to obtain a uniform gel because it does not gel by cooling alone, and it is difficult to obtain a stable gel because it tends to cause agglutination between single filaments due to water swelling. It is difficult to obtain high strength fibers.

The problems with adopting such dry-wet spinning and using methanol coagulation liquid include operational risks, the difficulty of creating a large number of holes because the thread gets stuck right under the spinning nozzle, and the hole pitch is increased. For example, the spinning dope may stick to the nozzle surface, making it difficult to separate the nozzle.

(Problems to be Solved by the Invention) Accordingly, the present invention aims to obtain PVA fibers with high strength and high elastic modulus industrially at low cost and stably.

(Means for Solving the Problems) That is, the present invention provides, ``After dissolving a PVA-based polymer having an average polymerization degree of 1500 or more and a saponification degree of 98 mol% or more in a solvent containing at least 10% by weight or more of an organic solvent, the solution is discharged from a nozzle, coagulated with an aqueous solution containing at least 5 g/Q or more of alkali by wet spinning, and then stretched by 1.5 times or more, followed by neutralization treatment, moist heat treatment, water washing treatment, and drying. High-strength PV characterized by stretching to a total stretching ratio of 3 times or more, removing almost all of the solvent, and then stretching at a temperature exceeding 220°C to a total stretching ratio of 17 times or more.
This relates to a method for producing A-series fibers.

The requirements of the present invention are as follows.

(1) Dissolve in a solvent containing at least 10% by weight of an organic solvent.

(2) At least 5g of alkali # by wet spinning! Solidify with an aqueous solution containing the above.

(3) Stretching 1.5 times or more after forming the spinning fiber, and further processes including neutralization treatment, moist heat treatment, water washing treatment, and drying, totaling 3
Stretch more than twice.

(4) Dry heat stretching at high temperature and high magnification in a state containing almost no solvent.

Next, the concept of the present invention will be described. First, it promotes gelation of PVA-based fibers and fixes them in a state with less entanglement of molecular chains, and at the same time enables stable multi-hole spinning with less yarn unevenness by wet spinning.

Second, wet stretching is carried out by 1.5 times or more with a large amount of solvent remaining,
It destroys the microcrystals formed at the initial stage of spinning to increase the number of amorphous parts and increase the degree of molecular orientation. Next, in the process up to drying, the fibers are stretched by a total of three times or more to suppress swelling in water and to reduce sticking between single filaments. Finally, high-strength, high-modulus fibers with advanced oriented crystallization are formed by high-temperature drawing. This makes it possible to obtain stable high-strength PVA fibers at low cost.

The contents of the present invention will be explained in more detail below.

The PVA-based polymer referred to in the present invention is one having an average degree of polymerization of 1,500 or more as determined by the viscosity method in an aqueous solution at 30°C, a linear polymer with a saponification degree of 98 mol% or more, and a low degree of branching. be. The higher the average degree of polymerization of PVA, the easier it is to obtain a high-strength, high-modulus fiber, preferably 4000 or more, more preferably too0 or more. The higher the degree of polymerization, the fewer molecular chain ends that tend to form defects, and the more tie molecules that connect crystals, the more likely it is to become a high-strength, high-modulus fiber.

The degree of saponification of PVA may be 98 mol% or more, and becomes 99 mol% or more when saponified in an alkaline coagulation bath.

Simplification of the polymer saponification process in this way leads to cost reduction. At the saponification degree h of the drawn yarn (99 mol% at the ends), the molecular chains are too disordered, and crystallization does not proceed, resulting in a lower melting point and lower heat resistance.

Solvents for PVA-based polymers include dimethyl sulfoxide, dimethyl formamide, or a mixture of these with water, a mixture of polyhydric alcohols such as glycerin or ethylene glycol with water, or methyl sulfoxide or dimethyl formamide, n-propyl alcohol and water. Examples include mixed systems with and others. The proportion of these organic solvents in the total solvent is 10% by weight or more. Organic solvent is 1
If it is less than 0% by weight, adhesion of the nozzle surface and agglutination of threads may occur, making spinning apt to become unstable and making it difficult to obtain a uniform gel. Preferably it is 30% by weight or more.

A wet spinning method is preferable. If a wet/dry method is adopted, the threads are stuck directly under the nozzle, making it necessary to increase the hole pitch, making it difficult to create a large number of holes.Additionally, the undiluted solution sticks to the nozzle surface, making it difficult to separate the nozzle. occurs.

Any additive may be used as long as it stabilizes spinning and drawing, such as boric acid, emulsifiers, pH adjusters, and antioxidants.

Coagulation is carried out in an aqueous solution containing 5 g IQ or more of alkali.

The alkali may be any of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, etc., but sodium hydroxide is preferable because it is inexpensive and highly soluble in water. If the alkali concentration is less than 5 g#, coagulation is weak and the threads are likely to swell and dissolve in water, resulting in sticking, cross-sectional deformation, and a decrease in strength. Also, the degree of saponification of PVA during spinning is 99 mol%.
There is a possibility that it will not be more than that. Preferably it is 30gIQ or more.

After solidification and before the neutralization process, the film is stretched at least 1.5 times or more, preferably 2 to 5 times, while containing a solvent.

If it is less than 1.5 times, the gel yarn containing the solvent is weak and the heat generated during neutralization causes fusing or single yarn breakage, or fiber damage due to water swelling is undesirable. In addition, the film is stretched by a total of 3 times or more, preferably 4 to 7 times, including the stretching up to the neutralization step and the steps of neutralization, heating, water washing, and drying. In particular, in order to prevent dissolution of 1III during washing with water, it is preferable to wet-roll the product by a total of 4 times or more before washing with water.

In order to prevent sticking between single filaments due to water swelling, it is preferable to perform a moist heat treatment at 60 to 95°C in an aqueous solution of a neutralized salt such as sodium sulfate, but it is more preferable to simultaneously stretch the yarn by a factor of 1.2 times or more. . Next, after removing the solvent and neutralized salt by washing with water, drying is performed at a temperature of 13 (1'c) or less to suppress crystallization and prevent sticking, thereby removing almost all of the solvent.

Thereafter, stretching is carried out at 220°C or higher, preferably 230-260°C. Any stretching method may be used, including one stage, two or more stages, dry heat, oil bath, and nitrogen gas zone stretching. If the stretching temperature is lower than 220° C., oriented crystallization will not proceed and the stretching ratio will become low, making it impossible to obtain a product with high strength. 260 again
If the temperature exceeds .degree. C., PVA decomposes rapidly and molecular chains flow, making it impossible to obtain high strength. Stretching is performed so that the total stretching ratio is 17 times or more. If it is less than 17 times, the orientation of the molecular chains will be insufficient and only low strength will be obtained.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited only to the Examples.

Example 1 and Comparative Example 1 Average degree of polymerization is 4100. PV with saponification degree of 99.5 mol%
Add A to dimethyl sulfoxide at 11% by weight, and at the same time add 0.8% by weight of boric acid/PVA and 0.0% of sulfuric acid.
05% by weight/solvent was added and dissolved at 90°C. The melting machine is a closed system, and after the pressure is reduced, nitrogen gas is passed through the system and the PV
Color decomposition of A was suppressed. The solution was then brought to 50°C and the pore size was 0.08ml11. Wet spinning was performed by discharging from a nozzle with 300 holes into a coagulation bath containing 200 g of NaOH and maintained at 15°C. After obtaining fiber in coagulation bath 4
Stretch in the air twice, then H*50411 at 80°C.
Neutralization was performed in a mixed aqueous solution of 0g/σ, ffa*504300g/l, and further Na, So, 350g/l at 90°C
Moist heat stretching was performed at 1.4@g/l in an aqueous solution (5.6 times in total). Subsequently, it was washed with water and dried with hot air at 100°C.

Through the above steps, PVA is completely saponified and the degree of saponification is 99.9.
It became mol%. Finally, stretching was carried out at a temperature of 238°C. The total stretching ratio was 20.5 times. The single yarn denier variation rate of the obtained single yarn was 3.4%, and the single yarn average strength was 20.
It was found that the fiber had a high strength of 9 g/d, and the fluctuation rate of single yarn strength was low at 4.2%, making it a relatively uniform yarn.

As a comparative example t, the stretching ratio before neutralization in Example 1 was 1.2.
We conducted a case where the amount was doubled. During neutralization, the gel fibers became devitrified, and although they were stretched at a wet heat stretching ratio of 2.5 times (3.0 times in total), they became more stuck. Although the final stretching was carried out at 238°C, the total stretching ratio was as low as 16.5 times, the average strength of the obtained units was as low as 17.1 g/d, and the rate of variation in strength was [
q was as large as 5%.

Example 2 Average polymerization 1 [7700, saponification & 98.8 mol% P
VA was added to a solvent of ethylene glycol/water at a weight ratio of 57.5 to 10% by weight and dissolved at 100°C. The solution was then brought to 70°C and the composition was 1lao[1
Wet spinning was performed by discharging the product into a coagulation bath of 150 g/f2 maintained at 25°C.

The obtained fibers were then stretched 3 times in the air, subsequently neutralized, and further subjected to a 1.7 times wet heat treatment (total of 5.1
times). Next, the film was washed with water, dried with hot air at 100°C, and finally stretched at a total stretching ratio of 19.8 times at a temperature of 246°C. The average strength of the obtained single yarn was 21.5 g/d, making it a highly strong fiber, and the rate of variation in strength was as low as 4.5%, making it a relatively uniform yarn.

Example 3 P with an average degree of polymerization of 17,700 and a degree of saponification of 99.9 mol%
Add VA to 7% by weight to a solvent with dimethyl sulfoxide/water = 6/4 weight ratio, and at the same time add 1.0% of boric acid.
Weight %/PVA was added and dissolved at 110°C. The solution was then heated to 60°C and the composition was NaOH30gIQ, N
Wet spinning was performed by discharging the coagulation bath containing 150 g of atSOa/I2 at 50° C. through a nozzle with a hole diameter of 0 and a number of 11 m5 holes, 250. The obtained fibers were stretched 4 times, and after neutralization, subjected to wet heat stretching 1.5 times (6.0 times in total).
.

The film was then washed with water, dried with hot air at 100°C, and finally stretched at 252°C with a total stretching ratio of 19.5 times.

The average strength of the obtained unit was as strong as 23.7 g/d, and the rate of variation in strength was as low as 3.8%.

Claims (1)

[Claims] After dissolving a polyvinyl alcohol-based polymer with an average degree of polymerization of 1500 or more and a degree of saponification of 98 mol% or more in a solvent containing at least 10% by weight or more of an organic solvent, the solution is discharged from a nozzle and wet-spun to produce at least 5 g of alkali.
After coagulating with an aqueous solution containing more than /l, then stretching 1.5 times or more, and stretching to a total of 3 times or more including the steps of neutralization treatment, moist heat treatment, water washing treatment, and drying, most of the solvent A method for producing high-strength polyvinyl alcohol fibers, which comprises stretching the fibers at a temperature exceeding 220° C. to a total stretching ratio of 17 times or more.