JPS62162010A - Production of polyvinyl alcohol fiber of high tenacity and elasticity - Google Patents

Abstract

PURPOSE:A specific polyvinyl alcohol (PVA) is dissolved in a solvent mainly consisting of dimethyl sulfoxide and subjected to dry-wet spinning to form gel fiber, then, the gel fiber is drawn to give the titled fiber of high strength and elasticity. CONSTITUTION:PVA of more than 1,500 polymerization degree is dissolved in a solvent mainly consisting of dimethyl sulfoxide to prepare a spinning dope. The dope is subjected to dry-wet spinning into a coagulation bath mainly containing methanol at a temperature lower than 25 deg.C to form gel fiber. The gel fiber is drawn by means of heaters and other devices to give the objective fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to high-strength, high-elasticity polyvinyl alcohol (hereinafter referred to as P
The present invention relates to a method for producing fibers based on VA.

(Prior Art) It is known that high-strength, high-modulus fibers can be obtained by dissolving ultra-high molecular weight polyethylene in a solvent, gel spinning, and then ultra-stretching. However, although this high-strength, high-modulus fiber has the advantage of being able to be produced relatively cheaply, it has the major disadvantage of a low melting point, which makes it easier to use a relatively inexpensive high-strength, high-modulus fiber with a higher melting point polymer. The emergence of fibers is expected.

Regarding high-strength and high-modulus fibers, it has been found in several patents that PVA may exist even if it is not an ultra-high molecular weight polymer such as polyethylene.
3-16675fidPVA with dimethyl sulfoxide (
This paper shows that highly elastic fibers can be obtained by dissolving DMSO (hereinafter referred to as DMSO) or a solvent containing DMSO as a main component and performing wet spinning. It is also a high-strength fiber. Also, JP-A-60-12
6311 and JP-A-60-126312 disclose that high strength and high modulus fibers can be obtained by dissolving PVA in DMSO and performing dry/wet spinning. However, these patents contain no description or even any suggestion of gel spinning. Especially JP-A-60-126
When comparing No. 312 with Comparative Example, it is reasonable to consider that dry/wet spinning is performed with the spinnerets taken out of the coagulation bath under wet spinning conditions, and these conditions can hardly be called gel spinning. The reason for this is that gel spinning is generally performed by dry and wet spinning, but under gel spinning conditions, wet spinning causes the boria solution to gel near the spinneret, making spinning impossible. Problems to be Solved) As described above, DMSO is a solvent for PVA that produces high-strength, high-modulus fibers, but gel spinning may provide more desirable conditions for producing high-strength, high-modulus fibers. Since there is no mention in the literature regarding this point, fiDMs
It was considered that conditions for gel spinning could not exist at o.

As a result of research on gel spinning when DMSO is used as a solvent, the present inventor found that gel spinning conditions exist and that high strength and high modulus fibers can be obtained, leading to the present invention.

The first object of the present invention is to dissolve PVA with a degree of polymerization of 1,500 or more in a solvent mainly composed of DMSO, and then gel-spun the PVA solution into a gel fiber by dry/wet spinning in a coagulation bath at 25°C or lower. A second object of the present invention is to provide a method for producing high-strength, high-modulus PVA-based fibers, which is characterized in that the gel fibers are substantially transparent in the above-mentioned manner. It is an object of the present invention to provide a method for producing a high-strength, high-modulus PVA-based fiber.

(Means for Solving the Problems) When trying to make a high-strength, high-modulus fiber as in the present invention, the strength should generally be 15 to 2024 or more, and the elastic modulus should be 300 to 400 P/d or more. It is expected that either one person or both of them will be satisfied.

When trying to make such high-strength, high-modulus fibers,
As a result of research, it has been found that it is preferable to use a solvent with good solubility in PVA and perform gel spinning. Wet spinning has the advantage of being able to spin at a low concentration with less entanglement of PVA molecules, but when it comes to fiber formation in a coagulation bath, PVA is rapidly concentrated and then gelled and coagulated, resulting in increased entanglement. In contrast, in gel spinning, the concentration of the PVA solution before gelation is virtually zero or small, resulting in a favorable structure with small or homogeneous molecular entanglements, or both. I guess it's possible.

It is said that PVA is not blessed with a solvent that has good solubility and that gels in a short period of time when cooled in a coagulation bath. As a result of various research and research, we discovered DMSO. DMSO solution dissolves PVA almost completely at 60 to 80°C, and gels in a short time at temperatures below 25°C, preferably around 0°C, and satisfies dissolution and gelation. can do.

In the present invention, PVA is dissolved with DMSO,
DMSO alone or DMSO as a main component, which means methanol, ethanol, n-propertool, water, dimethylformamide, dimethylacetamide, ethylene glycol, etc., which have the ability to dissolve in DMSO or dissolve PVA, can be blended. can.

The main feature of the present invention is that PVA is dissolved using DMSO, which has relatively good solubility, and then rapidly cooled and gelled by dry/wet spinning. Gelation occurs in a short period of time by cooling, and gel fibers can be obtained by dry spinning or dry/wet spinning, but when a solvent with relatively good solubility is used as in the present invention, rapid cooling causes gelation in a short period of time (e.g. It is not known particularly in the case of PVA or DMSO that gel fibers can be obtained within a short period of about 10 seconds, preferably within several seconds, and this was discovered as a result of intensive research.

Although the fibers spun in the present invention are in a liquid column state, they can be made into gel fibers by cooling them in a low-temperature coagulation bath. In this case, if wet spinning is performed using the same PVA solution and coagulation bath (composition and temperature), gelation will occur near the spinneret, making spinning impossible. In this case, a temperature difference is required between the spinneret and the coagulation bath, so the present invention requires dry and wet spinning.

In the present invention, gelation is achieved in a relatively short time by cooling in a coagulation bath. Gelation is mainly controlled by the temperature of the coagulation bath, the composition of the coagulation bath, and the degree of PVA (rQ), and the gel fibers vary from completely milky white to They vary from translucent to particularly preferred transparent ones.

It is easy to think that polymer and solvent are uniformly dispersed microscopically in gelled fibers, but this is not actually the case.
It is thought that high-concentration PVA is separated into networks at low concentrations due to spinodal decomposition, etc.
Depending on the degree of uniformity and the size of the network, the gel fibers can vary from milky white to transparent.In order to accelerate gelation, the thinner the fibers or the faster the cooling, the slower the solvent is applied. The more it is removed, the more transparent the gel fiber becomes, which is highly desirable for producing high-strength, high-modulus fibers.

In gel spinning, it is believed that the faster the spun fibers (liquid column) are cooled to the lowest possible temperature, the more transparent they become, in other words, the more uniform the gel fibers can be obtained, but the present invention This is not necessarily the case with DMSO, which is a solvent for DMSO. It appears that the freezing state of a solution of PVA in DMSO varies depending on the PVA concentration, but 100%
When the temperature is about -5 to 0°C, the fibers are milky white.

In this frozen state, the fibers are hard, which makes them less easy to handle, and because they are milky white, they are less uniform than gel fibers, which are virtually transparent, and because they are frozen, they are considered to be inferior in terms of DMSO removal. .

In the case of DMSO, this freezing temperature is relatively high, about -5 to 0 degrees Celsius above, but this is because DMSO has a relatively high melting point of 18.5 degrees Celsius, and has a low melting point and freezing temperature. This freezing temperature can be lowered by adding dimethylsulfamide or alcohol.

There is a region where good gel fibers can be obtained at the tube temperature above the freezing temperature. In gel spinning, it is a necessary condition that there is no significant extraction of the solvent DMSO by the coagulation bath before gelation occurs, so the spun fibers (liquid column) enter the coagulation bath for a short period of time, for example, about 10 seconds. It is preferable that gel fibers can be formed within a relatively short period of time. As a result, it becomes virtually impossible to perform wet spinning using the same PVA bath solution under the same coagulation bath (composition and temperature) with the spinneret set to the actual coagulation bath temperature. Dry/wet spinning under these conditions is the scope of the present invention in which gel fibers are produced by gel spinning.

In the DMSO solution of PVA of the present invention, gelation does not easily occur even if it is cooled with a solution that is incompatible with the PVA solution, such as hexane.
In the coagulation bath containing O, gelation was observed in a short time as described above. From this, it is thought that methanol penetrates into the spun fibers (liquid column) in a short period of time, and for this reason, the effect toward coagulation and cooling combine to cause gelation in a short period of time, resulting in gel spinning. Considering the above, it is necessary for the coagulation bath to have PVA as a non-solvent as the main component or as one of the main components, and that it is a component that moves DMSO in the direction of becoming a non-solvent. That's what I would say. In addition, in gel spinning, it is generally desirable that the coagulation bath into which the spun fibers (liquid column) are placed has a composition that allows for gelation and extraction of the solvent from the fibers.

Solvent extraction in a coagulation bath should be carried out at a temperature below the melting temperature of the gel fibers, and increasing the extraction rate tends to make them opaque, so it is better to avoid conditions that would make the gel fibers milky white. It is best to use transparent gel fibers. This extraction rate is slow when the temperature of the coagulation bath is lowered, and the extraction rate is reduced by adding a solvent component to the coagulation bath.

If it is desired to produce uniform transparent gel fibers, the temperature of the coagulation bath may be kept low within a range that does not freeze, and the solvent components in the coagulation bath may be appropriately blended. In this case, care must be taken because if the amount of the solvent component is excessive, the gel fibers may remain too soft and the processability may deteriorate. As a result of experiments, when methanol is the main component of the coagulation bath, DMSO is 10 to 70%, preferably 20 to 50%.
It seems to be particularly preferable to mix about 30 to 50 pieces.

Also, it is desirable that the bath agent components in the coagulation bath be properly mixed. The first reason is that as the solvent is extracted, the solvent components infiltrate and are kept constant and controlled, and the other reason is that when stretching in a wet gel state containing coagulation bath components, the solvent component polymer and When stretching a wet gel with a compatible liquid, it is possible to maintain transparency during stretching under wet conditions; It appears that the process of deterioration is progressing more rapidly.

This stretching of the wet gel will be referred to as wet stretching. When carrying out this wet stretching, it is desirable that the affinity components such as bath additives are evenly distributed in the inner and outer layers of the fibers before wet stretching. It appears to have a leveling effect. However, D
When MSO is used, the effect of wet stretching is not very large;
It is not a necessary condition for making high-strength, high-modulus fibers,
As one example, a high-strength side modulus fiber can be produced by one-step dry heat stretching of a dried PVA gel fiber from which DMSO has been removed as much as possible. Of course, multi-stage stretching in which the stretching temperature is increased sequentially may be used, and from an industrial perspective, 2 to 3 stages of stretching would be preferable.

In order to extract the solvent easily and efficiently, it may be possible to start at a low temperature at which gelation occurs and then increase the temperature in several steps or continuously over time.

In any case, it seems impossible to adequately extract high-strength, high-modulus fibers in a few minutes, and ideally it would take several hours to several days.

For this reason, extraction is carried out by winding the gel fiber onto a perforated bobbin, passing a coagulation bath or methanol, which is a solvent for DMSO, through the fiber layer of the bobbin and flowing it from the inside of the bobbin to the outside for solvent extraction. do it.

In this way, the coagulation bath may be formed in multiple stages instead of one stage, and the final stage may use methanol to extract as much solvent as possible.

In this case, good wet stretching can be performed near room temperature. Although methanol does not seem to have a great affinity for PVA, it is effective because methanol generally contains water and some bath agent components such as DMSO remain.

For PVA, final stretching is accomplished by dry heat stretching.

It is desirable that the solvent component containing DMSO as a main component be removed as much as possible before this. Therefore, the residual amount of the solvent component containing DMSO as a main component is preferably 5% or less, more preferably 2% or less, and particularly preferably 0%. If this residual amount is large, coloring during dry heat stretching will be large, and the stretching temperature cannot be raised sufficiently, causing the problem that the possible stretching ratio will be small.

For this reason, it is necessary to perform solvent extraction strongly.As mentioned earlier, when dyeing yarn wound on a perforated bobbin with a bobbin dyeing machine, the extraction solution may be passed through the wound layer, which is the fiber layer, or Repeating extraction and drying, replacing the extract each time with a fresh one, will further strengthen the extract. Drying can be done by stopping the liquid flow and passing compressed air, which will enhance the extraction.

Solvent extraction is most effectively strengthened by drying under reduced pressure, and is most effective when heated within a range that does not impede the drawability or fiber properties of the drawn fibers. For PVA, it seems best to treat it at around 120°C for several hours to about a day. When drying under reduced pressure in a bobbin shape, it is possible that spots may appear.
To prevent this, it would be best to use a perforated bobbin and use a decompression pump (vacuum pump) to suction and discharge from the inside, or vice versa, to discharge from the outside of the bobbin. It would be preferable to actively flow a small amount of gas such as air.

The reason why vacuum drying is most effective is because the PVA solvent is volatile like DMSO, as in the present invention.
When an aqueous solution of sodium thiocyanate is used as a solvent, it is also effective in improving the physical properties of the fibers. Since water is also a solvent in the case of PVA, its removal will affect the drawing, which will affect the filigree properties of the drawn fibers.

Dry heat stretching is generally carried out by passing it through a heater, but it is generally done in an air atmosphere and the
℃, preferably about 200 to 240℃.

At high temperatures of 200°C or higher, crosslinking due to oxygen in the air or thermal decomposition under oxygen may occur, which may inhibit stretching. It is desirable to carry out the stretching under an active liquid. Since these materials have virtually no wetting effect on PVA, they are collectively referred to as dry heat stretching in the present invention.

The present invention is characterized by the use of PVA with a polymerization degree of 1500 or more.
This is because A-type fibers can be obtained. However, it is desirable to have a higher degree of polymerization, preferably 300 degrees of polymerization.
0 to 7000 or more.

Generally, completely saponified PVA is used for PVA, but when trying to make high-strength, high-modulus fibers with better extensibility, the toughness of PVA and the molecular structure of PVA need to be improved. By selecting the best point for improving crystallinity through modification (for example, post-partial acetylation of PVA) or taking countermeasures against deterioration, it will be possible to further improve performance.

Furthermore, the second claim of the present invention stipulates that the gel fiber is substantially transparent, which means that it is in a transparent state that is more than translucent in a wet state before drying.

(Applications of the present invention) The present invention relates to PVA dissolved in DMSO alone or in a solvent mainly composed of DMSO. It may also be applicable to making high-strength, high-modulus fibers from polyacrylonitrile (hereinafter referred to as PAN).

Although it has not been clarified how coagulation occurs during spinning of a PAN solution dissolved in a solvent mainly composed of DMSO, PAN can also be dry-spun and wet-spun in the same way as PVA to produce virtually transparent gel fibers. It is believed that the conditions for creating this can be determined by selecting the temperature and composition of the coagulation bath, and in some cases, the composition of a solvent mainly composed of DMSO to lower the freezing temperature.In this case, heat drying or vacuum drying This would be desirable since it would allow for more complete solvent removal.

In PAN, when the spun gel fibers are stripped of the solvent and dried, the fibers are generally very brittle and difficult to handle afterwards, but this problem can be avoided if the molecules are oriented to a certain degree. One method is that the spinning draft is about 1.1 or more and the denier of the dry gel fiber is 3.
When the size is relatively small, about 0 to 60 denier, it is necessary to spin and orient the fiber so that the dry elongation is about 1 oLs or more. Stretching (about 2 to 7 times) would be better.

And the dry strength is 1.5 to 10 f/d preferably 2.5
It is considered that dry heat stretching should be carried out at a p/d or higher. Dry heat stretching of PAN requires a strength of 190 to 220, based on experience when using Thioqua/Sodium Acid as a solvent.
It has good heat resistance at °C and can be stretched under an inert gas or inert liquid.

The high strength, high modulus fibers of the present invention can be used as carbonized fibers, activated carbon fibers, and precursor fibers for carbon fibers. Although the present invention has been described as a method for producing fibers, this technique can also be applied to the production of molded products such as films.

(Example) Next, an example of the present invention will be described. All composition percentages are expressed herein in weight percent.

Example 1 Completely saponified PvA was dissolved in DMSO by stirring at 65 to 70°C for 16 hours to prepare a PVA solution, which was wet or dry-wet spun in a coagulation bath to investigate spinnability and the state of coagulated fibers. . The results are shown in Table 1.

According to Table 1, in Experiment A3, the concentration was low and the viscosity was too low to make dry/wet spinning stable, but wet spinning could be made stable. As seen in Experiments 44.11, 12, and 15, freezing occurs at temperatures below 5 to 0°C, although it varies depending on the PVA concentration. Experiment AI, 5, 7. and 10, a transparent gel is obtained, and at higher coagulation bath temperatures the transparency deteriorates and becomes translucent. It was also found that the transparency was better when a suitable amount of DMSO was added to the coagulation bath (comparison of Experiments A10 and 14).

In addition, in Experiment A2, both wet and dry spinning are possible.
When the coagulation bath temperature is lowered, wet spinning becomes virtually impossible as seen in Experiment A1, and only dry and wet spinning becomes possible, which is the area of the present invention where gel fibers are produced by gel spinning. Become. When the temperature of the coagulation bath is further lowered, the area becomes frozen, and only dry/wet spinning becomes possible.

Example 2 The gel fibers spun in Example 1 were extracted with DMSO as a solvent, and then dried under reduced pressure depending on the experimental points, and then subjected to dry heat stretching, and their physical properties were measured. The results are shown in Table 2.

From the second coat, in experiments A20 to A26, when dried under reduced pressure after solvent extraction, the stretching ratio was improved at about 120°C, and both strength and Young's modulus were improved.

Looking at the second part as a whole, the transparent gel fiber was extracted with DMSO solvent and then dried under reduced pressure.
) The best physical properties were shown in Experiments A21-26 and Experiment A34 with a PVA polymerization degree of 6600. This is Example 1
The spinning conditions make wet spinning virtually impossible.

Next, the dry/wet spinning of Experiment Point 32 of this example was carried out under spinning conditions in which wet spinning was virtually impossible, resulting in translucent gel fibers.

The fibers with the poorest physical properties were wet-spun or those with spinning conditions that allowed both wet and dry/wet spinning, and those in Experiments A27-31 of this example. This is from experimental point 35.

The detailed conditions for these steps are as follows.

Spinning drum 7) 0.97-1.03 Spinning coagulation bath passing time 10-20 minutes Methanol drying Winding at 40-50℃ for 10 minutes
4 to 6 ml + then drying under reduced pressure 210°C In both cases, the initial fiber length is 7.5 times/min at the beginning of stretching, and 6 times/min at the end of stretching.

Claims (1)

[Claims] 1. Polyvinyl alcohol with a degree of polymerization of 1500 or more is dissolved in a solvent containing dimethyl sulfoxide as a main component, and then the polyvinyl alcohol solution is gel-spun by dry/wet spinning in a coagulation bath at 25°C or lower. 1. A method for producing high-strength, high-modulus polyvinyl alcohol fibers, which comprises producing gel fibers and then drawing them. 2. A method for producing a high-strength, high-modulus polyvinyl alcohol fiber according to claim 1, wherein the gel fiber is substantially transparent.