JPH076087B2 - High strength and high modulus PVA fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-strength and high-modulus polyvinyl alcohol (abbreviated as PVA in the present specification and the same hereinafter) fiber and a method for producing the same. In particular, it is intended to obtain a PVA fiber suitable for industrial materials and reinforcing composite materials.

<Prior art> Conventional PVA fibers have higher strength and modulus than polyamide, polyester, and polyacrylonitrile fibers,
Not only as a fiber for industrial materials, which is its main application, but recently, it is about to be used as a reinforcing material for cement as an asbestos alternative fiber.

However, the PVA fibers obtained so far do not have high strength and module like aromatic polyamide (aramid) fibers and ultra high molecular weight polyethylene fibers.

PVA fibers are usually produced by wet spinning in a coagulating inorganic salt aqueous solution using a PVA aqueous solution as a spinning dope, and then subjecting it to treatments such as stretching, drying, and heat treatment.The strength and elastic modulus of this PVA fiber are improved. Various methods have been proposed to achieve this.

For example, JP-B-43-16675 discloses a method of wet spinning a dimethyl sulfoxide (hereinafter abbreviated as DMSO) solution of PVA as an original spinning solution in an organic solvent such as methanol, ethanol, benzene or chloroform, and JP-A-56-128309. The publication proposes a method in which PVA fibers obtained by a wet or dry spinning method are stretched at least 10 times and then heat treated. Also, Japanese Patent Publication No. 37-14422 and Japanese Patent Publication No. 47-32142.
In the publication, a PVA aqueous solution containing boric acid or a borate is spun in an alkaline coagulation bath containing various salts to cross-link boric acid with PVA, and then boric acid or its cross-linked product is added again in the following. A method of removing in a process such as Japanese-style and washing with water is disclosed. However, the draw ratio of the PVA fiber obtained by these methods is 15 times or less, and the strength of the obtained fiber is
It was less than 12g / dr and Modulus was less than 400g / dr.

On the other hand, in JP-A-60-126312, the degree of polymerization of PVA is about 4000.
Draw ratio of about 30 by dry-wet spinning method using DMSO as solvent
It has been shown that a PVA fiber having a strength of 20 g / dr and a modulus of 450 g / dr can be obtained, but it is difficult to easily break the strength of 20 g / dr or more and the modulus of 500 g / dr or more as in the present invention.

Ultra high molecular weight polyethylene gel spinning
As an example of application to PVA fiber, there is JP-A-59-130314, which uses PVA with a degree of polymerization of about 30,000 to make gel fiber by cooling with glycerin or ethylene glycol as a solvent, and has a maximum strength of 19 g / dr, Module 500-600g / dr
Is a method of obtaining PVA fiber. However, unlike polyethylene fibers, PVA fibers have intermolecular and intramolecular hydrogen bonds, and it is believed that folding molecular chains are difficult to remove.
It was difficult to obtain a PVA fiber with a high draw ratio and high strength and high modularity, which is still satisfactory, even if the concentration of the polymerized PVA was lowered and the entanglement of the molecular chain was reduced.

In order to obtain a high-strength, high-modulus fiber, it is necessary to highly orient the molecular chains, and therefore it is necessary to draw at a high ratio. In the case of PVA fiber, the following points can be considered in order to achieve high strength and high modulus by high-stretch drawing.

(1) Using a high degree of polymerization PVA ... Decreasing defects by lowering the molecular chain ends Maintaining a high stretching tension Increasing the strength contribution rate by linking between crystalline and amorphous (2) Using a low concentration PVA solution ... Reduces entanglement and increases draw ratio (3) Performs gel spinning ... Fixes molecular chain morphology and suppresses entanglement of molecular chains (4) Suppresses hydrogen bonding between molecules ... Between molecular chain and lamella during drawing (5) Giving moderate voids between molecular chains ... Improves slippage between molecular chains and lamellas during stretching (6) Suppresses whitening (voids) and color decomposition of fibers during stretching ... Strength and Modulus Prevention of Degradation Conventionally, a method of satisfying the above (1) to (5) and obtaining a high-strength and high-modulus PVA fiber by high-stretch drawing has not been found.

<Problems to be solved by the invention> Based on the above background, the present invention uses a high polymerization degree PVA,
By adding boric acid or borate to increase the solution viscosity by cross-linking, stable gel spinning of low-concentration PVA solution, and by partially removing cross-linked boron, the draw ratio can be increased easily and easily. Stable high strength High modular PVA
The purpose is to obtain fibers.

<Means for Solving Problems> That is, the present invention, as a method for obtaining a high-strength, high-modulus PVA fiber, has a polymerization degree of at least 1500 or more, and preferably boric acid or a low-concentration solution of PVA polymer of 3000 or more. Add borate to crosslink PVA, and after stable gel spinning of a low-concentration solution with less entanglement of molecular chains, remove some of the crosslinked boron to moderate hydrogen bond inhibition and between intermolecular chains. The purpose of this is to provide a suitable gap between the lamellas so as to enable easy and stable high-magnification stretching.

More specifically, the present invention has an average degree of polymerization of 1500 or more.
A PVA fiber obtained by gel-spinning a spinning solution prepared by adding boric acid or a borate to PVA, which is 0.05 to 0.8% by weight of boric acid or borate based on PVA in the fiber. With high tensile strength of 15 g / dr or more and tensile modulus of 400 g / dr or more.
The fiber is preferably PVA having an average degree of polymerization of 6000 or more, a single fiber strength of 20 g / dr or more, and a tensile modulus.
It is a high-strength, high-modulus PVA fiber that is 500g / dr or more,
And as a method for producing such fibers, the average degree of polymerization is
When dissolving 1500 or more PVA polymers in a solvent capable of gel spinning, adjust the pH to 5 to 9 and add boric acid or borate to the polymer, discharge the resulting solution from a nozzle, and cool. After gelation, all or most of the solvent is removed, and 0.05 to 0.8 wt% of boric acid or borate corresponding to borate is left with respect to the polymer, followed by stretching at a high magnification. High strength and high modulus PV
A method for producing A fiber, preferably in the production method, PVA
And a solvent for the PVA polymer is ethylene glycol or glycerin, and the total draw ratio is at least 20 times.

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

The PVA referred to in the present invention has an average degree of polymerization of 1500 or more as determined by a viscosity method in an aqueous solution at 30 ° C. and a saponification degree of 98.
% Means a linear PVA polymer having a low degree of branching. The higher the average degree of polymerization, the greater the possibility of obtaining high-strength fibers, but in that case, unless the PVA concentration is lowered, the viscosity becomes too high and the solubility in the solvent and the spinnability deteriorate. The average degree of polymerization of PVA is more preferably 6000 or more, further preferably 1000.
It is 0 or more, and it is desirable that the PVA concentration is 15% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less to reduce the entanglement of the molecular chain.

The solvent is preferably a poor solvent which easily gels by cooling in order to fix the entanglement of the molecular chain in a small state, and which dissolves PVA uniformly. As such a solvent,
Polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, glycerin, etc., and a mixed solvent of water and DMSO, or a mixed solvent of water and an inorganic salt such as rhodan salt or calcium chloride, the present invention is not limited to this. It is not something that will be done. However, since dissolution and spinning at 200 ° C. or higher are likely to cause PVA coloring and decomposition, a solvent that dissolves PVA at a temperature lower than that is desirable.

In the present invention, 1 to 15% by weight of boric acid or borate may be added to a mixed solution of PVA and a solvent, and an alkali or an acid may be added to adjust the pH to 5 to 9.

The boric acid or borate is preferably added in the state of a dispersion liquid of PVA and a solvent, and when PVA is added after being dissolved in the solvent, crosslinking is locally caused to cause viscosity unevenness of the spinning dope.

One of the features of the present invention is that boric acid or borate is cross-linked with PVA in the state of the stock solution for spinning, and the concentration of PVA is decreased by increasing the viscosity to carry out spinning. As a result, it is possible to obtain a spinning base yarn which has a small number of entangled molecular chains and which can be drawn at a high ratio.

To crosslink boric acid or borate with PVA, adjust the pH to 5
It is necessary to adjust the pH to above, but it is not preferable that the pH is 9 or more because the PVA polymer is likely to be colored and decomposed. A particularly preferred range of pH is 5.5-7.5.

On the other hand, the amount of boric acid or borate added is 0.05 to 1 relative to PVA.
0% by weight is preferred. If it is less than 0.05% by weight, the decrease in PVA concentration due to the thickening effect and the hydrogen bond suppressing effect, which are the features of the present invention, are difficult to be seen, and finally it becomes difficult to obtain a high-strength and high-modulus PVA fiber. If the addition amount of boric acid or borate exceeds 10% by weight, PV will increase due to thickening.
A decrease in A concentration can be expected, but it causes cost increase due to uncrosslinked boric acid and borate, and it becomes difficult to remove most of the crosslinked boron. .

The degree of polymerization and concentration of PVA and the amount of boric acid or borate added have contradictory relations in order to adjust the viscosity of the undiluted solution to 500 to 5000 poise, which is preferable for spinning. That is, when the PVA polymerization degree is low and the PVA concentration is low, it is necessary to increase the amount of boric acid or borate added.

In the present invention, after completely dissolving the boron-crosslinked PVA in the solvent,
The spinning solution is discharged from a nozzle and simultaneously cooled with a gas and / or a liquid to be gelated to form fibers. The obtained gel fiber contains a large amount of boron which is cross-linked with a solvent, and it is necessary to remove them with an extracting agent such as water, methanol, ethanol or acetone. The extractant is not limited to this. The cross-linked boron can be removed by washing with water or a dilute aqueous solution of an inorganic acid, but PVA swells and extends in the presence of water, so it is preferable to perform it while giving a little tension. If the PVA fiber contains water, the fibers tend to stick to each other after being wound onto the bobbin, so it is desirable to remove the water by washing with water or alcohol or acetone, or by drying.

Another feature of the present invention is to regulate the residual amount of the solvent and the crosslinked boron within a certain range. If the residual amount of the solvent is large, the fibers are likely to stick together or the fibers may be colored and decomposed during stretching.
It is necessary to remove the solvent to less than or equal to wt%, more preferably less than or equal to 2 wt%. On the other hand, when the residual amount of the crosslinked boron is large, the slip between the molecular chains of the fibers or between the lamellas is reduced during the stretching, so that high-stretching cannot be performed. When the cross-linked boron is completely removed, hydrogen bonds are suppressed and moderate voids between molecular chains and lamellas are reduced, which is a negative factor for increasing the draw ratio. Therefore, the amount of residual boron is
The amount of boric acid or borate as PVA fiber is preferably 0.05 to 0.8% by weight, more preferably 0.05 to 0.5% by weight.

From the above, spinning atoms capable of high-magnification stretching can be obtained,
The final stretching is 200-240 considering the improvement of physical properties by crystallization.
Dry heat stretching at ℃ is preferred. The draw ratio varies depending on the degree of polymerization of PVA, the concentration of PVA, the spinning draft and the drawing conditions (temperature, speed, heater length), etc., but the fiber obtained by spinning a stock solution with a high degree of polymerization of PVA and a low concentration at a low draft is It can be stretched to a high ratio. The higher the draw ratio, the higher the orientation of the molecular chains of the fibers, and it is easy to obtain a high-strength and high-modulus fiber, but the total draw ratio is 15 times or more, preferably 20 times or more. However, since a fiber whitening (void) is likely to occur near the maximum draw ratio and the strength is lowered, a draw ratio slightly lower than the maximum draw ratio is desirable. When the stretching temperature was 240 ° C. or higher, the PVA was likely to be colored and decomposed, but the phenomenon that the strength was low was observed although the stretching ratio was high.

The PVA fiber obtained by the present invention contains a small amount of boron, the tensile strength of the single fiber is 15 g / dr or more, and the tensile modulus is 400 g.
/ dr or more, especially when the average degree of polymerization of PVA was 6000 or more, the tensile strength was 20 g / dr or more and the tensile modulus was 500 g / dr or more.

According to the present invention, it becomes possible to inexpensively and stably produce PVA fiber having strength and module comparable to aramid fiber, and it is considered to be applied not only to general industrial material applications but also to reinforcing materials for composite materials. It can be said that its usefulness is extremely large. The present invention will be specifically described below with reference to examples.

Examples 1 to 4 and Comparative Examples 1 and 2 In dissolving fully saponified PVA having an average degree of polymerization of 1700, 3400, 7000, and 12000 in ethylene glycol, boric acid was added in an amount of 4% by weight based on PVA, and A small amount of sodium hydroxide was added to adjust the pH to 6 to 7, and the mixture was dissolved at 160 ° C. for 3 hours with stirring. As shown in Table 1, the PVA concentrations were 26, 14, and 7.5% by weight, respectively, in the order of polymerization degree.

After defoaming the dissolved stock solution, the denier of the spinning raw yarn is 200d
The undiluted solution was discharged from a single-hole nozzle with a hole diameter of 0.8 mm by a gear pump so as to be r, and was cooled and gelled with air. The spinning draft at this time was 1.5 to 2. Continue to the gel fiber first
The solvent and adsorbed water were extracted in the second bath of methanol while the solution was passed through the water of the bath, and when the solvent and part of boron were removed, the elongation was 1.3 times. After that, methanol and water were evaporated from the spun yarn by hot air at 70 ° C. and wound on a bobbin.

The obtained spun raw yarn is drawn by a hollow heater at 225 ° C.
Although the results shown in the table were obtained, the results of Comparative Example 1 in which no boric acid was added and Comparative Example 2 in the case where a large amount of boric acid remained were also shown.

In each of Examples 1 to 4, all spinning stock solutions were slightly colored, but PVA was completely dissolved and an increase in viscosity was observed.
In the comparison between both Example 3 and Comparative Example 1, when the PVA concentration was not added without adding boric acid, the same stable viscosity of spinning could not be obtained, and the viscosity increase was observed only with boric acid and ethylene glycol. It was considered that PVA and boric acid were crosslinked due to the absence of such factors. In Example 3, when the pH of the stock solution was set to 4.1, a highly viscous product was not obtained, and it was found that cross-linking of boric acid hardly occurred. In addition, since boric acid cross-links with PVA, the spinnability during spinning was very good, and no breakage was observed during spinning.

Most of the solvent and cross-linking boron were removed with water in the first bath and methanol in the second bath, but the remaining amount of boron was almost determined by the residence time in the first bath, and most of the boron was removed in the methanol in the second bath. Nakatsuta. 70 in Examples 1-4
Residual amount of ethylene glycol after hot air drying at ℃ is 1.0 to 3.2
Each of them was as low as wt% and the residual amount of boric acid was 0.21 to 0.33 wt%, which was within the scope of the present invention. The remaining amount of water is 1 wt%
It was as follows. The residual amount of ethylene glycol was determined from the weight loss after the ethylene glycol was scattered with high temperature hot air, and the residual amount of boric acid was determined by converting the boron content obtained by atomic absorption into boric acid.

Next, the obtained spun raw yarn was dry-heat drawn at 225 ° C., but almost no coloring of the fiber was observed, and the total draw ratio was 18.5 to 23.0.
It was twice as high as never before. The higher the degree of polymerization of PVA and the lower the concentration of PVA, the higher the draw ratio, and the tensile strength and modulus of the single fiber increased correspondingly. Boric acid was added to PVA with an average degree of polymerization of 12000
%, And by adjusting the residual amount of boric acid to 0.27 wt%, PVA fiber having a strength of 21.9 g / dr and a modulus of 628 g / dr was obtained, and the performance was almost comparable to that of aramid fiber.

On the other hand, Comparative Example 1 is a case where boric acid is not added, but it is necessary to increase the PVA concentration by about 2 times as compared with Example 3 using PVA of the same degree of polymerization, and the spinning tone tends to be slightly worse. It was The residual amount of boric acid in the obtained spun raw yarn was 0.15 wt%, and the residual amount of water was 4.2 wt%. The draw ratio is 12.
The strength was as low as 8 times, and the strength of 12.6 g / dr and the modulus of 303 g / dr were inferior to those of Example 3 in which 4% of boric acid was added.

Comparative Example 2 is a case in which the residual amount of boric acid was increased to 1.5 wt% in Example 2, but the draw ratio was 14.0 times lower than 18.5 times in Example 2 and the strength and module were low.

Example 5 A fully saponified PVA having an average degree of polymerization of 7,000 was dispersed in glycerin to a concentration of 9 wt%, and borax (sodium borate) was added at 2 wt% to PVA while adjusting pH to 7.3, It was dissolved by stirring at 180 ° C. Gelation was carried out under the same spinning conditions as in Example 1 except that a 12-hole nozzle was used, and the obtained spinning raw yarn was drawn 20 times with a heater at 215 ° C.

The spinning solution was slightly colored, but PVA was completely dissolved and 9 wt% PV
Spinnability is good even at A concentration, and about 40% PVA compared to boric acid not added.
The concentration could be reduced.

The residual amount of glycerin in the spun yarn is 15 wt% and the residual amount of boric acid is
It was 0.11 wt%, and no sticking between single yarns and yarns was observed.

The drawn yarn has a single fiber denier of 4.2 dr and a tensile strength of 1
9.4 g / dr, tensile module 520 g / dr, and high strength and high modulus PVA fiber, which was unprecedented, was obtained.

Example 6 and Comparative Example 3 Fully saponified PVA having an average degree of polymerization of 3400 was dispersed in a mixed solvent of water / DMSO = 1/1 at a concentration of 12 wt%, and pH = 5.
While adjusting to 8, boric acid was added to PVA in an amount of 8 wt%, and dissolved by stirring at 80 ° C. The obtained undiluted solution had spinnability and was discharged into the air from a single hole nozzle, and cooled and gelled in a 0 ° C. methanol bath 20 cm below the nozzle. Then, the mixture was passed through a second bath, stretched 3 times in water at room temperature, passed through room temperature methanol in a third bath, dried with hot air at 80 ° C., and wound on a bobbin. The DMSO residual amount of the spun raw yarn immediately after drying was 0.9 wt%, and no water remained and boric acid residual amount was 0.56 wt%.

The obtained spun raw yarn was drawn in two stages by dry heat at 230 ° C, but the total draw ratio was very high at 24.1 times, and the tensile strength of single fiber was 20.7.
The g / dr and tensile modulus were 554 g / dr.

As Comparative Example 3, the solvent water / DMSO = 1/1 in Example 6 was replaced with water only, and coagulation was carried out in an alkaline bath to carry out wet spinning. Then, the mixture was neutralized-washed with water-dried at 60 ° C through a methanol bath, wound on a bobbin, and stretched under the same conditions as in Example 6, but the total stretching ratio was 15 and the tensile strength of the degraded fiber was 11.4 g / dr. The modulus was 321 g / dr, which was inferior to the PVA fiber obtained by the present invention.

Claims (6)

[Claims] 1. Obtained by gel spinning a spinning dope prepared by adding boric acid or borate to PVA having an average degree of polymerization of 1500 or more.
PVA fibers, wherein the fiber has 0.05 to 0.8% by weight of boric acid or boron corresponding to borate, based on PVA,
Single fiber tensile strength of 15g / dr or more, tensile modulus of 400g
High strength and high modulus PVA fiber that is more than / dr. 2. A high-strength, high-modulus PVA according to claim 1, wherein the average degree of polymerization is 6000 or more, the tensile strength of the single fiber is 20 g / dr or more, and the tensile modulus is 500 g / dr or more.
fiber. 3. A PVA polymer having an average degree of polymerization of 1500 or more is dissolved in a solvent capable of gel spinning to adjust the pH to 5 to 9 and boric acid or borate is added to the polymer to obtain a PVA polymer. The solution was discharged from a nozzle and gelled by cooling, and then the solvent was removed in whole or in large part, and the amount of the solvent was 0.05%.
A method for producing a high-strength, high-modulus PVA fiber, which comprises: leaving 0.8% by weight of boric acid or boron corresponding to a borate salt, and then drawing at a high ratio. 4. The production method according to claim 3, wherein the average degree of polymerization is 6000 or more. 5. The method according to claim 3 or 4, wherein the solvent of the PVA polymer is ethylene glycol and / or glycerin. 6. The production method according to claim 3, wherein the total draw ratio is at least 20 times.