JPH0327112A - Production of high-tenacity polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:To easily produce the subject fiber at a low cost by extruding an aqueous solution containing polyvinyl alcohol and boric acid or its salt through a nozzle into a specific atmosphere, removing water from the obtained fibrous hydrogel and hot-drawing the fiber. CONSTITUTION:A spinning dope containing a polyvinyl alcohol having an average polymerization degree of >=2,000 (preferably 2,500-6,000) and 0.05-5.0wt.% (based on the polyvinyl alcohol) of boric acid or its salt (the pH of the solution is preferably adjusted to 3.0-5.0 in the case of using a boric acid salt) is extruded through a nozzle into an ammonia gas atmosphere to form a fibrous hydrogel, which is introduced into an aqueous solution of a dehydrating inorganic salt (e.g. boric acid) or a methanol bath to effect the dehydration and obtain an undrawn fiber. The objective fiber can be produced by hot-drawing the undrawn fiber at >=200 deg.C until the strength of the fiber reaches >=15.0g/d.

Description

[Detailed Description of the Invention] [Industry] Field of Application 1 The present invention relates to a method for producing polyvinyl alcohol C (hereinafter abbreviated as PVA) fibers, and the present invention relates to a method for producing polyvinyl alcohol C (hereinafter abbreviated as PVA) fiber, which is produced by ultra-high strength PVA using a new and improved spinning means. It concerns the method of manufacturing fibers. [Prior Art] PVA fiber has the highest strength among general-purpose fibers, ffj4! e
jI nature. PVA has a good balance of properties necessary for fibers such as chemical resistance and light resistance, and is much cheaper than other raw materials used for ultra-high strength fibers, so PVA is an ultra-high strength fiber made using this material. There is a lot of research and development going on. According to recent theories. In order to obtain PVA-based ultra-high strength fiber Ht, the key point is to use high polymerization degree PVA as a raw material, use a spinning stock solution prepared with a low concentration of PVA, and perform gel spinning by some method. Although this has been strongly suggested, the reality is that we are forced to compromise in the face of various constraints, and no definitive method has yet emerged. In other words, as a method for producing PVA-based ultra-high strength fiber, for example, l
) A method of introducing a mixed solvent solution of highly polar dimethyl sulfoxide (DMSO) and water into methanol and coagulating it into a gel-like state (JP-A-60-126312, JP-A-62-1)
62010, etc.), 2) Dry-wet spinning method using a spinning solution using an aqueous thiocyanic acid solution as a solvent into a low-temperature coagulation solution (Japanese Patent Application Laid-open No. 104912/1982), 3) Polymer melts at high temperatures such as ethylene glycol and forms a gel when cooled. A method of gel spinning using the properties of a solvent such as
No. 130314) have been proposed, but all of them are
Concentration control and recovery operations for organic solvents, inorganic salts, etc. increase costs and complicate processes, and at the same time, the negative effects of these components remaining in the fibers on stretchability cannot be ignored. In the midst of all this. 4) A method of dry/wet spinning a spinning dope containing gI acid using a neutral or alkaline aqueous solution containing dehydrating salts as a coagulating liquid (Japanese Patent Laid-Open No. 1499-1499)
10, etc.), and this method, ``wet spinning using a combination of a boric acid-containing stock solution and an alkaline coagulation bath,'' has already been established as an industrial manufacturing method for PVA fibers, and there is little resistance in terms of equipment. This seems to be the most effective method. However, this method cannot necessarily be said to be superior in fiber strength to the above-mentioned manufacturing methods 1) to 3, and improvements are still needed in terms of obtaining ultra-high strength. [Problems to be Solved by the Invention] From this perspective, the present inventors have developed a method of using a boric acid-containing stock solution, in particular a fibrous hydrogel produced by discharging this stock solution through pores into the atmosphere where ammonia vapor is present. As a result of intensive research, it was discovered that the undrawn yarn obtained by removing water from this yarn showed extremely good drawability and a fiber with extremely high strength was obtained.After further investigation into the details, , we have finally completed the present invention. [Means for Solving the Problems 1] That is, the gist of the present invention is that the average degree of polymerization is 2,000 or more (7) PVA and the PVA has an average degree of polymerization of 0.05 to 5. Owt%
An aqueous solution containing boric acid or a salt thereof is discharged from the pores into an ammonia gas atmosphere to form a uIi fibrous hydrogel, and the undrawn yarn obtained by removing water from the hydrogel is formed. l5. The present invention relates to a method for producing high-strength PVA fibers, which comprises hot-drawing the fibers to a strength of Og/d or higher. In the present invention, when removing water from the fibrous hydrogel, it is preferable to introduce it into a dehydrating inorganic salt aqueous solution or methanol bath to form undrawn threads. Further, it is preferable that the dehydrating inorganic salt aqueous solution or methanol contains ammonia, and the ammonia volatilized from the ammonia creates an ammonia gas atmosphere in the vicinity of the pores. It is also possible to form an undrawn yarn by stretching the fibrous hydrogel by a factor of 3.0 times or less and then removing water with a dry air stream. According to the present invention, high-strength fibers can be produced more rationally than the above-mentioned four methods using a spinning dope containing boric acid or a borate, as well as conventional methods such as 1) to 3]. This is something that can be obtained. The reason why such high-strength fibers can be obtained by the present invention is that the stock solution discharged from the nozzle immediately turns into ammonia gas. Upon contact, it immediately becomes a hydrogel-like fiber with a fixed molecular arrangement, and is then dehydrated, so that the molecular chains in the resulting undrawn yarn remain unentangled in the dilute stock solution, making it possible to use the gel spinning method. It is presumed that an undrawn yarn that can be drawn to a high degree in conditions close to the ideal can be obtained. On the other hand, in the conventional method using boric acid or borates, the spinning stock solution discharged from the nozzle comes into contact with an alkaline coagulating solution containing dehydrating salts, so coagulation and gelation proceed simultaneously, and especially during the coagulation process, molecular Since tangles are likely to occur, it is thought that the conditions for gel spinning are inevitably different from those for Fl. The present invention will be explained in detail below, but the gist of the present invention will be omitted. PL (This is not limited to the above description. PVA, which is the main raw material in the present invention, cannot have the desired high strength if the degree of polymerization is low, so the average degree of polymerization is 2, O
C) It must be 0 or more, and the upper limit is about 30,000. Of these, 2,500 to 6
,000 average degree of polymerization is most preferred. The saponification degree is preferably 99 mol% or more, but only when an alkaline bath liquid is used to dehydrate the fibrous hydrogel, saponification progresses due to the alkali of the bath liquid, so the saponification degree is 95 mol% or more. Boric acid or borate can be used if the mole % is less than 7. Boric acid or borate is 0.05 to 5. If the amount of boric acid or borate added is less than 0.05vvt%, the gelling effect will be weak and the gel spinning effect will be weak. The amount of hyammonia consumed exceeding 1.% of OW becomes large, and the remaining boric acid component also becomes relatively large, resulting in a tendency for the drawability to decrease, resulting in poor bf.

Examples of borates that can be used include alkano metal salts of boric acid such as monolithium borate, potassium borate, and lithium borate, and ammonium borate. When these borates are used, the spinning stock solution is It is preferable to adjust the pH to 3.0-5.Q using a strong acid such as hydrochloric acid or sulfuric acid.
This dotted boric acid does not require substantially any pH adjustment, and is also preferable. In the method of the present invention, an aqueous solution containing PVA and boric acid or its salt as solutes that satisfies the above conditions is prepared and used as a spinning stock solution.
When the stock solution is discharged from the nozzle, it is immediately subjected to a strong gelling action by ammonia, so the viscosity (or concentration) of the spinning stock solution may be considerably lower than in other methods, and the stock solution concentration is typically 1 to 15 wt%. , more preferably 1.5-10
Within this range, if PVA with a higher degree of polymerization than 6 is used as a raw material, or if boric acid or ζj
In applications where a large amount of salt is used, better results can be obtained with a lower concentration of the stock solution.

The temperature of the stock solution should generally be in the range of 0 to 150°C. Preferably, the temperature is 0 to 70°C. The spinning stock solution discharged from the nozzle undergoes the action of gaseous ammonia and immediately becomes a fibrous hydrogel like Harusame or Shirataki. This gelation phenomenon is caused by the PVA Although it is influenced by the concentration, degree of fusion, concentration of boric acid or borate, and concentration of ammonia, it is almost instantaneous, so the contact zone with ammonia gas can be short, usually preferably between 2 mm and 1,000 mm. However, this method increases the residence length of ammonia gas in the air, including the contact zone, and increases the draft increasing effect due to the presence of fibrous hydrogel, but this effect can be avoided by setting the discharge direction upward. The obtained fibrous hydrogel has a water content exceeding 90 wt% and is cross-linked, so it has low strength and has considerable rubber-like elasticity. An undrawn yarn can be obtained by the so-called dry 7 yarn method, in which the fiber is introduced into methanol or a dehydrating non-11 fl saline solution and dehydrated.
It is also possible to obtain an undrawn yarn by the so-called dry spinning method by drawing it to the following low magnification and introducing it into dry air using J2, which has increased the strength to some extent.

Here, the so-called draught defined by the ratio of the velocity (V.) when the fibrous hydrogel first contacts with the mouth roller or guide to the linear velocity (Vo) of the stock solution discharged from the nozzle]・(Vo/V+ ) is influenced by the composition of the stock solution, concentration, temperature, etc., but it is approximately 0.
．． 1 to 3.0, and the spinning draw ratio (
V2/V. ), there is a tendency for the total draw ratio to decrease as the ratio increases.
In the case of dry spinning, it is important that the coagulation bath liquid for the purpose of dehydration from the fibrous hydrogel does not exceed 30 times the organic solvent. Methanol can be used as an inorganic salt, and as an inorganic salt, sulfur sulfate, ammonium sulfate, a mixture of sulfur sulfate and ammonium sulfate, or an inorganic salt containing 50% or more of any of these can be used. Here, ammonia is coexisted in these coagulation bath liquids, and the more volatile ammonia can create an ammonia gas atmosphere near the nozzle, and the gas concentration can be controlled by the ammonia concentration of the pseudo-solid bath liquid.
This is the most preferable method for controlling the ammonia gas atmosphere, which is the key point of the method of the present invention. Boric acid or boric acid chloride remaining in undrawn yarn impairs drawability, so it is necessary to remove it or limit the amount used as much as possible. In the case of dry spinning, where it is virtually impossible to remove boric acid,
Addition of boric acid or its moiety to the stock solution results in 0.0% of PVA.
The content is preferably 5 wt% or less, preferably 0.05 to 0.
．． It is in the range of 3wt%. On the other hand, in the case of the dry-wet spinning method, most of the boric acid or its salts cannot be eluted out of the fiber through the dehydration (or coagulation) process, neutralization process, thermal treatment process, washing process, etc. By finally drying, the desired undrawn yarn can be obtained. The undrawn yarn thus obtained by the dry spinning method or wet/dry spinning method is either wound up once or drawn continuously. The stretching method can be performed by a conventionally known method.
In other words, one stage may be 6 stages, or a method such as zone stretching may be used, but the stretching temperature is 200°C.
Above, regarding the draw ratio, the total draw ratio (spinning draw ratio ×
A hot stretching ratio of 15 times or more is required. The present invention will be further clarified with the following examples. [Example 1] Average degree of polymerization: 3,300. PVA with M degree of 99.9 mol%
700g. Add 25g of boric acid and deionized water to it,
A spinning stock solution of 10I2 was prepared by raising the maximum temperature to 120° C. and completely dissolving it using a 21 Goo-type dissolving machine. This spinning stock solution was taken out from the bottom of a tank kept at 90°C in 1FA, passed through a gar bomb and a filter, and passed through a pore size of 250 μm.
, was discharged into an ammonia gas atmosphere from five large nozzles. Here, the undiluted solution in the nozzle is evacuated by the piping system on the way and has a temperature of 22°C, and the area around the nozzle is warmer than the 25% ammonia water placed in the Petri dish at the bottom of the nozzle because there are many polyethylene sheets surrounding the nozzle. The ammonia gas atmosphere was maintained by the volatilizing ammonia gas, and the ambient temperature was 22°C. The discharged stock solution immediately turned into a gel and became colorless, transparent, and sticky.
There is no stringiness, and the result is a fibrous, bound drogel with a shirataki-like appearance. This 6 is introduced into a methanol bath where the liquid level is 5 cm below the nozzle surface, the direction is changed using a rotating guide installed 80 cm below the liquid level, the material is wound up into a skein removal machine, and it is further immersed in methanol for a day and night to remove water and methanol. Proceed with the replacement and solidification of
Finally, it was air-dried to obtain an undrawn yarn. Drumt during this time is 0
．． 65, the spinning draw ratio was 1.0, and the boron content contained in the undrawn yarn was reduced to 0.23 wt% as boric acid. After this, it will be 240℃! l! ! The total stretching ratio is 18 in the wind furnace.
．． It was stretched to 5 times its size to obtain a high-strength PVA fiber with a strength of 19.8 g/d. [Example 2] Average degree of polymerization: 4,600. Saponification degree 99.9 mol% (7)P
Dissolve 500 g of VA and 15.0 g of boric acid in water and make 10
A spinning stock solution of I2 was prepared, and this was discharged into an ammonia gas atmosphere through a 5-sized nozzle with a pore size of 30 μm to form a fibrous hydrogel, which was then introduced into a dehydration bath. Here, the stock solution is inside the nozzle just before being discharged.
℃, and the dehydration bath contained ammonium sulfate at 40.5 wt% and 5.2 mol/g. The nozzle was installed 1.0 cm above the liquid level, and an ammonia atmosphere was maintained near the nozzle by the ammonia gas vaporized from the dehydration bath.

The fibrous l:'rr+ gel was changed direction by a fiI pole drive roll installed directly below the nozzle and 50 cm below the water surface, passed through a dehydration bath for a further 1.5 cm, and then punched with a diameter of 60 cm. The fibers were wound at a constant speed on a perforated metal drum.The lower part of this drum was immersed in a dehydration/neutralization bath containing 35wt% ammonium sulfate and 0.5N of sulfuric acid. Dehydration and neutralization were performed by continuous rotation for several hours. Next, the drum was soaked in saturated ammonium sulfate solution, subjected to a wet heat treatment at 130°C, and finally washed with water and air-dried. The drum in this case is o. 23, and the spinning draw ratio was 1.7{9.

The undrawn yarn thus obtained contains 0.12 wt% of VA acid, but is completely stretched at 240°C {8% maximum of 24
[Comparative Example 1] In Example 2, the same amount of ammonium sulfate was used, but no ammonia was added. I tried to conduct a test under the same conditions as in Example 2 except for using a dehydration bath that did not contain water, but the water was discharged from the nozzle! “The stock solution showed no signs of gluing in the air.
First, continuous thread formation was impossible due to the low concentration and viscosity of crude oil4).

[Comparative Example 21 An undrawn yarn was produced under the same conditions as in Example 2, except that the spinning stock solution was directly discharged into the mixed aqueous solution of ammonium sulfate/ammonia by dipping the nozzle in a dehydration bath. I got it.

The maximum total stretching ratio that could be drawn at 240°C was 15.8 times, and the elasticity of the drawn yarn was 16.2 g/d. [Example 31 450 g of PVA with an average degree of polymerization of 6,500 and a degree of saponification of 99.9 and 1% A. t; and 20.0 g of boric acid with water.
An undrawn yarn was obtained under the same conditions as in Example 2 except that a spinning dope dissolved in R was used.

This yarn No. 6 was drawn at 240° C. to a maximum total draw ratio of 23.9 times, and the strength of this drawn yarn was 25.2 g/d.

C Example 41 Average degree of polymerization 3,300, degree of saponification 99 PV of E-nore
A spinning stock solution containing 850 gF of A and log boric acid dissolved in ios with water was discharged into an ammonia gas atmosphere under the following conditions using a 20-hole nozzle with a hole diameter of 160 μm. That is, the nozzle is installed obliquely near the bottom of a plastic cylindrical container with an inner diameter of 10 cm, and concentrated ammonia water is stored directly below the nozzle to maintain an ammonia gas atmosphere inside the container. The discharged stock solution immediately gels with ammonia gas and becomes a colorless and transparent fibrous hydrogel.
The draft 1 is placed on a rotating roll installed diagonally above. l
The fibers were continuously taken out while maintaining the temperature at 2, and then stretched with the next rotating roll. After R, the fibers were introduced into a drying zone at 50 to 80° C. to obtain a dry undrawn yarn. At this time, the spinning drawing f
8 ratio is 25 {gt:, this material contains boric acid, but it is difficult to stretch, and the strength of the fiber stretched at 235°C with a total stretching ratio of 16.2 times is 17.0 g/ d
Deakno: .

[Effect 1 of the invention 6 As is clear from the above results, the present invention involves discharging a stock solution containing a specific amount of boric acid or its salt into an ammonia gas atmosphere to form a fibrous hydrogel, and removing water from the hydrogel. By removing the undrawn yarn to obtain an undrawn yarn with high drawability, and then drawing it, it is possible to produce PVA fiber with high strength and a wide range of uses in a simple process. It also has the advantage that it can be provided at a lower cost than conventional methods, making it extremely useful industrially.

Claims (1)

[Claims] 1. Polyvinyl alcohol with an average degree of polymerization of 2,000 or more and 0.05 to 5.0 wt relative to the polyvinyl alcohol.
% of boric acid or its salt is discharged into an ammonia gas atmosphere through the pores to form a fibrous hydrogel, and the undrawn yarn obtained by removing water from the hydrogel is 15.0 g/d. A method for producing a high-strength polyvinyl alcohol fiber, which comprises hot-stretching the fiber to a strength of 2. The method according to claim 1, wherein the fibrous hydrogel is introduced into a dehydrating inorganic salt aqueous solution or a methanol bath to form an undrawn thread. 3. Claim 1, wherein the dehydrating inorganic salt aqueous solution or methanol contains ammonia, and the ammonia volatilized from the ammonia creates an ammonia gas atmosphere in the vicinity of the pores.
and the method described in 2. 4. The method according to claim 1, wherein after stretching the fibrous hydrogel by a factor of 3.0 times or less, water is removed by a dry air stream to form an undrawn yarn.