JPS63243316A - Production of high-tenacity polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:To obtain the titled fiber having high tenacity and suitable for industrial material and reinforcing agent for composite material, by spinning a PVA polymer having an average polymerization degree and an atacticity K falling within respective specific ranges and finally subjecting the spun fiber to dry hot drawing to increase the total draw ratio. CONSTITUTION:A straight-chain PVA polymer having low branching degree, an average polymerization degree of >=1,500 (preferably >=6,000), an atacticity K of <=0.25 (preferably <=0.23) and a saponification degree of preferably >=98mol.% is homogeneously dissolved in water, ethylene glycol, etc. The obtained dope is subjected to wet spinning into an aqueous solution containing e.g. sodium hydroxide and sodium sulfate and, if necessary, neutralized, washed with water and drawn in wet state. After drying, the obtained fiber is finally drawn in dried hot atmosphere at >=200 deg.C (preferably 225-235 deg.C) to a total draw ratio of >=15 (preferably >=25) to obtain the objective fiber having a single fiber strength of generally >=15g/d.

Description

[Detailed description of the invention] Industrial application field> The present invention uses polyvinyl alcohol (hereinafter abbreviated as PVA) with a relatively small amount of syndioic components, thereby increasing its solubility in solvents and achieving high magnification. This invention relates to a method for producing fibers characterized by the ability to be drawn to a single fiber strength of 15 Q/
The present invention relates to a method for obtaining a high tenacity PVA fiber having a strength of d or more.

<Prior Art> Conventional PVA fibers have a higher strength modulus than polyamide, polyester, and polyacrylonitrile fibers, and have been used not only as fibers for industrial materials, which are their main uses, but also as cement reinforcement materials recently as asbestos substitute fibers.

As a method for obtaining high-strength PVA fibers, high-strength fibers and their manufacturing methods applying the concept of gel spinning and ultra-stretching of high-molecular-weight polyethylene are disclosed in JP-A-59-100710, JP-A-59-130514, and JP-A-59-130514. Tokukai Showa 6
This method is known from Japanese Patent No. 1-108711.

-Koichi Todo-i Calyx However, when the present inventors examined these methods, they found that it was difficult to uniformly dissolve PVA in a solvent, especially when the degree of polymerization of PVA was high, and the number of molecules per molecule chain increased. It was found that the stretching ratio decreased probably due to an increase in the number of hydrogen bonds between the fibers, and as a result, satisfactory fiber strength could not be obtained.

Further, JP-A-61-108713 describes that a PVA fiber with high strength, high modulus, and high hot water resistance can be obtained when the proportion of syndiotact is 52% or more.

The present inventors also investigated syndiorich PVA and found that PVA fibers with hot water resistance were obtained, but the draw ratio was low, probably due to the good stereoregularity and strong intermolecular hydrogen bonds, and the single fiber strength was low. Only 159/d or less was obtained.

In addition, if a poor solvent with a high polymerization degree of P"v'A that causes gelation is used, the solubility of PVA will decrease, and if stirred for a long time at high temperature to uniformly dissolve, PVA will be colored and decomposed. In addition, the stretching ratio decreased, possibly because defects were created in the fiber structure due to uneven dissolution, or because low temperature conditions were required to create PVA with a high degree of polymerization, making syndio-rich PVA easy to produce. Satisfactory high-strength PVA fibers were not obtained.

<Problems to be Solved by the Invention> Based on the above background, the present inventors considered that the following two points should be satisfied as a method for obtaining high-strength PVA-based fibers.

The first is to uniformly dissolve it in a solvent, especially a poor solvent that causes gelation, to minimize the entanglement of molecular chains and defects in the fibers.

The second method is to weaken the intermolecular hydrogen bonds in the spun yarn before stretching, increase the stretching ratio, and highly orient the molecular chains.

As a result of intensive investigation into the above two points, we discovered that by spinning a PVA-based polymer with a relatively small amount of syndioic components and drawing it at a high magnification, it was possible to obtain a highly strong PVA-based fiber that had never been seen before.

<Means for Solving the Problems> That is, the present invention provides ``(1) average polymerization degree of 1500 or more and atacticity K
After dissolving a polyvinyl alcohol-based polymer with a diameter of 0.25 or less in a solvent and spinning it by a conventional method, it is finally spun at 200°.
A method for producing a high-strength polyvinyl alcohol fiber, characterized by stretching with dry heat of C or more to make the total stretching ratio 15 times or more (2) The average degree of polymerization is 3000 or more Claim 1 The present invention relates to gel spinning of the stock solution in a dry-wet process using the method for producing high-strength polyvinyl alcohol fibers described in 1.

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

The PVA-based polymer referred to in the present invention is a linear polyvinyl alcohol with a saponification degree of 98 mol or more and a low degree of branching, as long as the average degree of polymerization determined by the viscosity method in an aqueous solution at 30°C is 1500 or more. It is.

Copolymerized with 2 molar or less of other vinyl compounds, or 3% by weight or less of pigments, antioxidants, ultraviolet absorbers, or intermolecular crosslinks with the OH groups of PVA to improve stringiness during spinning. Also included are those to which boric acid or borate salts are added.

Gel spinning of ultra-high molecular weight polyethylene - Concept of ultra-stretching (
The concept of creating a dilute solution of a highly polymerized polymer, gelling or fixing it with less entanglement of the polymer molecular chains, stretching it to a high ratio, and increasing its strength) can also be applied to PVA-based polymers, and by gel spinning, PVA The higher the polymerization degree of the system polymer, the easier it is to obtain high strength fibers. The preferred degree of polymerization of the PVA-based polymer is 3000 or more, more preferably 600.
It is 0 or more.

The feature of the present invention is that the PV attacticity K is 0.25 or less.
The method is to use A-based polymers. For the value of this attacticity, see the 32nd Polymer Symposium GIC
16 (1983), 33rd Polymer Symposium GIC19
(1984), and is calculated based on the following formula.

K = (rrrr − mmmm) / (rrrr+
mmmm) where rrrr and mmmm are 13C-
Pentad tacticity of methine carbon in PVA observed in NMR
).

A chain consisting of two monomer units is called a diat (two-unit chain structure), and it is composed of H meso diato (m) and racemic diato (r).

In the five monomer one-unit chain structures (pentads), a total of 10 splittings due to pentad tacticity can be observed from four combinations of m and r, among which mmmm
and rrrr are the molar fractions of absorption intensity of methine carbon based on . There are no particular restrictions on the method for producing PVA with K of 0.25 or less, and any method can be used to produce it. For example, it can be produced by polymerizing and saponifying vinyl acetate in a solvent with a high dielectric constant (dimethyl sulfoxide, ethylene carbonate, sulfolane, etc.), or by polymerizing and saponifying vinyl acetate other than vinyl acetate, such as vinyl benzoate. Examples include methods to do so.

Atacticity K is 0.25 or less, preferably 0.23
The following is that in the PVA used in the present invention, intermolecular hydrogen bonds are weakened and solubility is improved;
This means improving stretchability.

Generally commercially available PVA6 or high polymerization degree PVA obtained by low temperature emulsion polymerization method or pearl polymerization method is K
is larger than 0.25, and the racemic (r) fraction is high, so intermolecular hydrogen bonds are strong, and the solubility and stretchability are inferior to PVA with K of 0.25 or less.

The present invention uses PVA with a relatively high degree of polymerization with K of 0.25 or less.
However, there is no problem in adding a small amount of PVA with KK greater than 0.25.

Solvents for PVA-based polymers include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, organic solvents such as dimethyl sulfoxide, dimethyl formamide, and diethylene triamine, water, and mixed solvents of two or more of these. Any solvent such as a mixed solvent with alcohol or an aqueous Rodan salt solution may be used.

In particular, the present invention is effective when obtaining high-strength fibers using high-polymerization degree PVA by gel spinning and high-strength stretching using a poor solvent such as polyhydric alcohol. The dissolving machine may be of any type as long as it can obtain a homogeneous solution of PVA, but the one that has a particularly strong stirring effect and minimizes the localization of the polymer is one that has a hook that rotates on its axis and revolves around the melting vessel wall, Examples include a closed container equipped with a scraper that contacts and revolves, a Banbury mixer, and a 12-screw kneading extruder. Note that when dissolving at high temperatures for a long period of time, coloring and decomposition of the polymer tends to occur, so it is preferable to dissolve under N2 atmosphere.

The spinning method may be any commonly used method such as wet, dry, dry-wet, etc., but wet-dry spinning is particularly preferred from the viewpoint of gel spinning-ultra-stretching.

Examples of the coagulant include alcohols such as methanol, ethanol, and butanol, acetone, benzene, toluene, etc., or mixtures thereof with solvents, as well as saturated inorganic salt aqueous solutions and caustic soda aqueous solutions, but the present invention is not limited thereto. It's not something you can do.

Solvent removal is generally performed by extraction with chemicals and/or drying. In the present invention, there is no problem with stretching in a hydrogen or organic solvent bath before or after the solvent has been completely removed;
It is necessary to draw with dry heat at 00° C. or higher, and make the total stretching ratio 15 times or higher. If the temperature is less than 200°C, the movement of the molecular chains required for stretching is insufficient, making it impossible to draw at a high magnification, and the degree of crystallinity decreases, resulting in insufficient fixation of the molecular chains, making it difficult to obtain high-strength fibers.

The stretching temperature is preferably 225 to 235°C. 245“C
If this is the case, the molecular chains will be missing, resulting in a decrease in the stretching ratio, and one-color decomposition, resulting in a decrease in strength. There is no problem even if the fiber is stretched in an oil bath at 200° C. or higher, but a step is required to remove the oil attached to the fibers. Although the dry heat stretching may be carried out in one stage or in multiple stages of two or more stages in an atmosphere of air or inert gas, it is preferable to use a non-contact type hollow heater in view of fiber damage.

The total stretching ratio is 15 times or more, preferably 20 times or more, more preferably 25 times or more, but high polymerization degree PVA#!
However, the stretching ratio decreases. If it is less than 15 times, it will be difficult to obtain high-strength m-fibers with the desired single fiber strength of 15 f/d or more. By using PVA with weak intermolecular hydrogen bonds of the present invention, solubility in solvents is improved, fiber defects are reduced, fluff breakage during spinning and drawing is reduced, and it is possible to draw at a high magnification. It has become easier to stably produce tensile PVA fibers.

The present invention will be specifically explained below using Examples.

Examples 1 and 2 and Comparative Example 1.2 PVA polymerized in a dimethyl sulfoxide (DMSO) solvent and having an average degree of polymerization of 1700 and 3700 was used in Examples 1 and 2, respectively.

The attack according to the present invention was 0.19 and 0.20, respectively, and the degree of saponification was 99.0 mol. Two PVA in water 18 and 10 respectively
At the same time, 2% by weight of boric acid was added to each PVA and dissolved with stirring at 98°C for 3 hours. The obtained solution was wet-spun into an aqueous solution containing caustic soda and Glauber's salt by a conventional method, neutralized, washed with water, and then wet-stretched 5 times. Next, the solvent water was completely evaporated by hot air drying, and then heated from 180°C to 230°C.
It was stretched in a hot air oven with a temperature gradient up to C.

As Comparative Example 1, the average degree of polymerization obtained from a normal methanol solution was 3700% = 0.30. Spinning and drawing was performed in the same manner as in Example 2 using PVA with a saponification degree of 92.2 mol.

Further, as Comparative Example 2, the same PVA as in Example 1 was spun and then stretched at a constant stretching temperature of 190°C.

The results of spinnability, drawability and fiber performance are summarized in Table 1.

The following margin Example 1 is PVA with an average degree of polymerization of 1700 and K=0.19.
was used, but it dissolved uniformly in water at 98°C for 3 hours to form a nearly transparent solution. The solution was discharged from a 300-hole nozzle and spun continuously for 2 days, but there were few tension irregularities between single yarns and no single yarn breakage occurred. The raw yarn that has been wet-stretched 5 times is heated to 5.3℃ using a heater with a temperature gradient of 180 to 230℃.
Although it was stretched twice, there was no single yarn breakage in 5 days. The total draw ratio of 26.5 times corresponds to 80% of the maximum cutting draw ratio, but the fact that there was no single filament breakage for a long time confirmed that the fibers had few defects and shape irregularities. The resulting drawn yarn had a single fiber strength of 1 B and 1 f/d, making it a high-strength PVA fiber.

Example 2 had an average degree of polymerization of 5700. PV of fc=0.20
A, but the spinning drawability was good as in Example 1. Single fiber strength jJi20.7 vd%%'): L lath 426
g/d, unprecedented high strength and high modulus PV
It was A fiber.

Comparative Example 1 is a case of PVA with an average degree of polymerization of 3,700 and a high content of syndioic components (=0.50), but it had poor solubility in water and exhibited a slightly opaque solution. The liquid-resistant material was spun in the same manner as in Example 2, but single yarn breakage occurred five times in two days. The dry heat stretching ratio is as low as 2.82 times (total stretching ratio 14.2 times);
There were 8 single yarn breakages during one day of drawing. The denier and strength of single fibers are highly uneven, with an average strength of 13.9 f/
It became as low as d.

In Comparative Example 2, the stretching heater temperature was 190°C in Example 1.
However, the single fiber at the center of the 300 filament was easily broken, and the total stretching ratio decreased to 19.8 times, probably because sufficient temperature was not provided for the molecular chains to stretch.

Therefore, the strength was as low as 15.21, and the degree of crystallinity as determined by X-ray scanning was as low as 48 degrees, resulting in poor dimensional stability against heat and a decline in commercial value as a fiber for industrial materials.

Example 3 and Comparative Example 3 The average degree of polymerization obtained from the DMSO solution was 6800, K=0.
25. Using cDPVA with saponification degree of 99.9 mol%, P
VA concentration was added at one time. Next, the mixture was stirred and mixed at 180° C. under an N atmosphere for 4 hours to obtain a homogeneous solution. The solution was discharged into the air through a 20-hole nozzle, and then placed in a 7/3 methanol/glycerin bath to cool and gel. Next, glycerin was completely extracted with methanol, and methanol was blown off with hot air at 80°C. The spun filament was almost circular in shape and had slight denier irregularities. The obtained spun yarn is 1
It was drawn in two dry heat stages at 70°C and 255°C with a hollow heater to obtain a high-strength PVA fiber with a total draw ratio of 18.3 times and a single fiber strength of 22.897 d.

As Comparative Example 3, the average degree of polymerization was 7000 obtained by the bar polymerization method.
, K = 0.29, K/degree of 99.9 molti PVA was dissolved in glycerin and gel spinning was performed in the same manner as in Example 3, but there was fluff breakage during spinning, and tension unevenness caused The denier spots have become larger. The obtained spun yarn was subjected to two-step dry heat stretching as in Example 3, but the total stretching ratio was 11.
．． The single fiber strength was 18.59/d, which was lower than that of Example 3.

Example 4 Average degree of polymerization obtained from sulfolane solution: 3200, K=0.
18.Saponification degree? ? ．． 9 moy% (7) PVA? 5 parts by weight and an average degree of polymerization of 12,000 obtained by low-temperature pearl polymerization.
, K=0.31, PVA with a saponification degree of 99.9 mol 5 parts by weight of mixed PVA were added to the water to give a concentration of 30% by weight, and the mixture was stirred at 98° C. for 8 hours to uniformly dissolve. then 1
It was spun for one day using a dry method using a 00 hole nozzle.
During that time, there was never a single thread breakage. After removing water by hot air drying, one-stage stretching was performed in a hot air oven with a temperature gradient of 200 to 235°C, but the total stretching ratio was as high as 19.5 times, and the single fiber strength was 2 L4 9/d. Indicated.

Example 5 Example? Using DPVA, add it to a mixed solution of DMSO/water = 8/2 so that the PVA concentration is 12% by weight, and heat at 95°C.
The mixture was stirred for 6 hours to obtain a homogeneous transparent liquid. The solution was discharged into the air from a 20-hole nozzle, and immediately immersed in a methanol/DMSO = s/s bath at 5°C to form a transparent gel fiber, which was then extracted with methanol and vacuum dried at 40°C. . Then, 2
Stage stretching, total stretching ratio 23.7 times, single fiber strength 2L59
/d was obtained.

Claims (3)

[Claims] (1) A polyvinyl alcohol-based polymer with an average degree of polymerization of 1500 or more and an atacticity K of 0.25 or less is dissolved in a solvent and spun using a conventional method, and then finally heated to 200°C.
A method for producing high-strength polyvinyl alcohol-based fibers, which comprises stretching with dry heat to achieve a total stretching ratio of 15 times or more. (2) The method for producing high-strength polyvinyl alcohol fibers according to claim 1, wherein the average degree of polymerization is 3,000 or more. (3) Claims 1 or 2, characterized in that the solvent for dissolving the polyvinyl alcohol polymer is one that causes polyvinyl alcohol to gel when cooled, and the stock solution is subjected to gel spinning using a dry-wet process. A method for producing high-strength polyvinyl alcohol fibers as described in .