JPH04289216A - Production of high-tenacity polyvinyl alcoholic fiber excellent in strength - Google Patents

Abstract

PURPOSE:To produce polyvinyl alcoholic fiber excellent in tenacity stably for a long period with excellent reproducibility. CONSTITUTION:A polyvinyl alcoholic polymer having >=1500 viscosity-average polymerization degree is dissolved in an organic solvent and the resultant spinning solution is then spun into a coagulation bath composed of an organic solvent. In the process, the bath temperature is regulated to <=20 deg.C and the solvent in the spinning solution in an amount of 5-70% is contained in the coagulation bath. The moisture content in the coagulation bath is further regulated to <=0.8% to carry out the spinning.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably obtaining polyvinyl alcohol (hereinafter abbreviated as PVA) fibers with excellent strength over a long period of time.

0002

[Prior Art] Conventional PVA fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile fibers, and are used not only as fibers for industrial materials, which is their main use, but also as cement reinforcement materials as an asbestos substitute. It is being used as a reinforcing material for plastics. Furthermore, as technology advances, the need for PVA-based fibers with increasingly superior strength is increasing.

On the other hand, the concept of obtaining high-strength fibers by gel-spinning and ultra-stretching a dilute solution of ultra-high molecular weight polyethylene was applied to PVA, and PVA was dissolved in an organic solvent to coagulate the organic solvent system with coagulation ability. It is disclosed in JP-A-59-130314 and JP-A-59-10 that high-strength PVA fibers can be obtained by wet-spinning or dry-wet spinning in a bath.
This method has been proposed in JP-A No. 0710, JP-A-61-108711, JP-A-63-99315, and the like.

However, with the methods employed in these inventions, it is not possible to stably obtain PVA fibers with excellent strength over a long period of time. Therefore, we focused on the coagulation bath to find out why it is not possible to obtain PVA fibers with excellent strength over a long period of time using conventionally known methods, and we have found a significant reason why this is not possible.

[0005] In the conventional spinning method, methanol and
A hydrophilic organic solvent such as ethanol or acetone is used, and this absorbs moisture from the atmosphere, resulting in a coagulation bath containing 1% or more of moisture. It has been found that it is difficult to stably obtain high strength PVA fibers when a coagulation bath containing 1% or more water is used. It has been found that this is particularly noticeable when the coagulation bath composition contains a stock solvent and the temperature is 20°C or lower.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention provides a PVA solution in which both the stock solvent and the coagulation bath are organic solvent systems.
In the spinning method of PVA-based fibers, we investigated how to stably produce PVA-based fibers with excellent strength over a long period of time.

[0007]

[Means for Solving the Problems] That is, the present invention aims to dissolve a PVA-based polymer having a viscosity average degree of polymerization of 1,500 or more in an organic solvent, and use the resulting spinning stock solution as an organic solvent having a coagulability with respect to the polymer. When performing wet or dry-wet spinning in a coagulation bath containing a solvent, the coagulation bath must meet the following (1)
A method for producing PVA-based fibers with excellent strength, characterized by satisfying conditions (3) to (3). (1) Set the coagulation bath temperature to 20℃ or less. (2) Contain 5 to 70% of the same organic solvent as the stock solvent in the coagulation bath.
(3) The water content in the coagulation bath should be 0.8% or less.

The PVA used in the present invention must have an average degree of polymerization of 1500 or more as determined by the viscosity method in an aqueous solution at 30°C. Lower than 1500 indicates high strength P
VA fibers cannot be obtained. When the viscosity average degree of polymerization is 3,000 or more, preferably 4,000 or more, high strength PVA fibers can be easily obtained. When the degree of polymerization is 7,000 or more, the number of molecular terminals that are prone to defects is further reduced, making it easier to obtain high-strength fibers.

There is no particular limitation on the degree of saponification of the PVA used, but it is preferably 98.5 mol% or more, and 99.9 mol%
It is more preferable that it is above because the hot water resistance is particularly excellent. The PVA used may also be a polyvinyl alcohol polymer copolymerized with other vinyl group-containing monomers, such as ethylene, itaconic acid, vinylpyrrolidone, etc., at a ratio of 10 mol or less, preferably 2 mol% or less. .

[0010] The solvent used in the present invention is not particularly limited as long as it is an organic solvent that dissolves PVA, and includes polar solvents such as dimethyl sulfoxide (DMSO), dimethyl formamide, and dimethyl imidazolidine, and polyhydric alcohols such as glycerin and ethylene glycol. can give. A mixture of these solvents may also be used. As will be described later, an important point of the present invention is to reduce the water content in the coagulation bath, so the stock solution should not contain more than 2% water. The water content in the stock solution is preferably 0.5% or less, and 0.2
% or less is more preferable. Among the many solvents, D
MSO can be dissolved at low temperatures below 80°C, and PV
It is a preferable solvent since it can reduce the decrease in the degree of polymerization of A.

[0011] The PVA concentration of the spinning dope varies depending on the degree of polymerization of PVA and the type of solvent, but is usually 2 to 30% by weight, preferably 3 to 20% by weight. In particular, the purpose of the present invention is to obtain high-strength fibers, and for this purpose, it is better to lower the PVA concentration within a range that does not cause single filament breakage, yarn unevenness, or sticking between single filaments during spinning to prevent molecular chain entanglement. This is preferable because it allows for high-magnification stretching with less.

[0012] In addition to PVA and the solvent, the spinning dope may also contain various additives depending on the purpose, such as coloring agents such as pigments,
PH of antioxidants, ultraviolet absorbers, surfactants, acids, etc.
Conditioners, gelling promoters such as boric acid, etc. may be added in required amounts. Furthermore, for a solvent with a relatively high freezing temperature such as DMSO, if a substance with a coagulating effect such as methanol is added within a range that does not coagulate PVA, the spinning dope will freeze even if the coagulation bath is below the freezing temperature of the solvent. This may be preferable because it does not.

[0013] As the coagulating bath, an organic solvent having a coagulating ability for PVA is used. For example, alcohols such as methanol and ethanol, and ketones such as acetone and methyl ethyl ketone are not particularly limited as long as PVA has a coagulability, but methanol is preferred from the viewpoint of coagulability balance and cost. In order to obtain high strength fibers, the present invention also contains a neat solvent in the coagulation bath. The content of the solvent in the stock solution varies depending on the type of organic solvent having coagulation ability, but is 5 to 70% by weight. When it is less than 5%, there is a large difference in composition from the stock solution composition, and rapid aggregation of PVA results in non-uniform coagulation. On the other hand, if it exceeds 70%, the coagulation rate will be slow and fiber formation will not be sufficient, resulting in the resulting yarns becoming stuck or, in extreme cases, normal spinning becoming difficult. The raw solvent content in the coagulation bath is preferably 10 to 50% by weight, more preferably 15 to 45% by weight.

Next, one of the important points of the present invention is to maintain the moisture content in the coagulation bath at a low level. As mentioned above, many methods have been proposed for obtaining high-strength fibers using organic solvents for both the stock solution solvent and the coagulation bath. It is true that PVA fibers with excellent strength can be obtained by adopting suitable spinning conditions in spinning tests on a relatively small scale and over a short period of time (for example, continuous spinning time of one day or less).
It has been observed that spinning on a large scale for a long period of time may reduce the strength of the resulting PVA fibers.

When we investigated the cause of this problem, we unexpectedly found that it is related to the fact that the coagulation bath absorbs moisture from the atmosphere and that the moisture content of the coagulation bath exceeds 1%. Even if water is not actively added to the coagulation bath, when the water content in the coagulation bath is analyzed by gas chromatography described below, for example, in the case of a DMSO-methanol coagulation bath,
It was found that moisture absorption from the atmosphere reaches as much as 5% by weight. Particularly, as in the present invention, when the coagulation bath contains a considerable amount of a stock solvent with high hygroscopicity and is maintained at a low temperature as described below, the water content of the coagulation bath increases, and its effects are likely to become apparent.

In the present invention, the water content of the coagulation bath must be 0.8% by weight or less. If it exceeds 0.8%,
It is not possible to obtain PVA fibers that are stable, reproducible, and strong over a long period of time. More preferably, the water content in the coagulation bath is 0.4% or less. As mentioned above, when using polar organic solvents or polyhydric alcohols as the solvent for the stock solution, or alcohols or ketones as the organic solvent with coagulation ability, the coagulation bath absorbs moisture when left in the atmosphere because both are highly hydrophilic. 1% or more.

Therefore, in the present invention, in order to prevent the coagulation bath from absorbing moisture, the water content of the coagulation bath is reduced to 0.8% by sealing it with dry air or dry nitrogen, or by dehumidifying the coagulation liquid with a dehumidifying agent such as molecular sieve. Must be maintained below. Sealing with dry nitrogen is preferable because it also serves as an explosion-proof measure for the highly flammable coagulation bath. Further, it is preferable to use a combination of sealing with dry nitrogen and dehumidification with a dehumidifying agent, since the water content in the coagulation bath can be further reduced.

Although it is unclear why a small amount of water in the coagulation bath has a large effect on fiber performance, it is
This is thought to be because A selectively adsorbs water in the coagulation bath and has a large effect on the subsequent coagulation and solidification form of PVA. For example, when a PVA spinning dope using DMSO as a solvent is coagulated in a coagulation bath with a weight ratio of methanol/DMSO/water of 70/27/3, the coagulated yarn is sufficiently immersed in the coagulation bath to reach equilibrium. When we achieved this and analyzed the composition of itoshino, we found that the methanol/DMSO ratio in itoshino almost matched the methanol/DMSO ratio in the coagulation bath of 70/27, whereas the methanol/water ratio in itoshino was 70/27. The ratio of methanol/water in the coagulation bath was 70/10, which was significantly higher than the methanol/water ratio in the coagulation bath of 70/3, indicating that water was selectively adsorbed by the thread.

In the present invention, the composition of the coagulation bath is TC
Measurement was performed using D-method gas chromatography using diglyme as an internal standard under the following conditions. Column initial temperature and holding time 70
Column heating rate for 5 minutes at °C
... 10℃/min Column final temperature and holding time
・・・・・・ 7 minutes at 200℃ Vaporization chamber temperature and detector temperature ・・・・・・ 250℃ and 200℃ Retention time ・・・・・・
Methanol: about 2.8 minutes, water: about 6.7 minutes, diglyme: about 14 minutes, DMSO: about 18 minutes The coagulation bath composition was determined from the area of each peak.

[0020] The coagulation bath temperature must be below 20°C. When the temperature exceeds 20° C., the coagulated thread becomes opaque with many voids, and is not homogeneous, making it impossible to obtain high-strength fibers. It is more preferable that the coagulation bath temperature is 15° C. or lower, and even more preferable that it is 10° C. or lower in terms of obtaining a uniformly coagulated thread. However, if the coagulation bath temperature is too low, the spinning stock solution discharged from the nozzle may freeze and become impossible to discharge, so this point should be taken into consideration.

[0021] There are no particular limitations on the spinning method of the present invention. It may be a wet spinning method in which the nozzle is in direct contact with the coagulation bath, or a wet-dry spinning method in which an air layer is interposed between the nozzle and the coagulation bath. Another way to classify spinning methods is to classify them into gel spinning and coagulation spinning depending on the solidification form, but in the present invention, even in gel spinning, if there is an air layer between the nozzle and the coagulation bath, the dry-wet method is used. This is called spinning. Wet spinning solidifies immediately after the nozzle is discharged, so it is easy to create pores without sticking even if the nozzle hole pitch is reduced.On the other hand, wet spinning has the characteristic that the air layer acts as a heat insulating layer, making it easy to create pores. Since the temperature of the coagulation bath and coagulation bath can be controlled independently, uniform discharge is achieved, and unevenness on the cross section of the fibers is small, so that it can be selected as appropriate depending on the purpose.

[0022] Bath draft (ratio of the first godet roller speed to the discharge linear velocity when the stock solution passes through the nozzle)
is preferably 0.1 to 0.5. The nozzle hole diameter is selected so that the bath draft falls within this range. A more preferable bath draft is 0.15 to 0.3.

[0023] The coagulated filament taken up by the first roller in or above the coagulation bath is made into fibers according to the following steps. That is, the undiluted solvent in the coagulation thread is extracted and washed using an extraction bath made of an organic solvent having coagulation ability, and then dried. It is preferable to carry out wet stretching in one stage or more preferably in multiple stages in any step from immediately after the first roller to before drying, in order to prevent sticking during drying. A more preferable wet stretching ratio is 2.5 times to 5.5 times. The extraction bath also absorbs moisture, but in terms of adhesion and performance, it is preferable for the extraction bath to have a low moisture content. Therefore, as a countermeasure against moisture reduction, it is preferable to seal with dry nitrogen and/or dehumidify with a dehumidifier as in the case of a coagulation bath. The drying temperature is preferably 40 to 150°C in terms of drying efficiency and performance. Furthermore, it is preferable to increase the drying temperature in multiple steps. In the present invention, since the thread contains less water, it is easy to dry, and troubles such as sticking do not occur due to severe drying.

[0024] Next, hot stretching is carried out at high temperature and high magnification, and the PV
The A molecules are oriented and crystallized to form high-strength fibers. Hot stretching is preferably carried out at 210°C or higher, more preferably at 220°C to 220°C.
The total stretching ratio at 55°C is 16 times or more, more preferably 18
Implement this to more than double the amount. The hot stretching may be carried out by dry heat, in a heat medium bath such as silicone, or by moist heat such as in high-temperature steam. Further, by controlling the temperature in multiple stages, hot stretching may be performed in two or more stages. Further, heat treatment or heat shrinkage may be performed as necessary.

As described above, uniform coagulation is achieved by controlling the concentration of the stock solvent in the coagulation bath and the temperature of the coagulation bath within a specific range, and furthermore, the coagulation of PVA is achieved by controlling the water content of the coagulation bath below a specific concentration. By suppressing the subtle effects of water at the moment, a homogeneous yarn is obtained, and by further drawing it at a high draw ratio of 16 times or more, it is possible to make PVA fibers with excellent strength and stability over a long period of time. It was possible to manufacture the product with good reproducibility.

[0026]

[Examples] The present invention will be explained in detail below using Examples, but the present invention is not limited to these Examples.

Example 1: Viscosity average degree of polymerization is 4050
, PVA with a saponification degree of 99.9 mol% was added to DMSO to give a concentration of 8.5% by weight, and the mixture was heated at 70°C for 1 hour under a nitrogen atmosphere.
Dissolved for 0 hours. The obtained spinning stock solution was heated to 50°C, and passed through a nozzle with a hole diameter of 0.14 mm and 500 holes into a coagulation bath at 3°C with a weight ratio of methanol/DMSO/water = 70.0/29.8/0.2. The coagulated yarn was then taken to a first godet roller. At this time, the coagulation bath and godet roller chamber are all sealed except for the passage through which the yarn passes and the atmosphere-opening pipe of the coagulation bath circulation tank, and dry nitrogen is blown inside to create a slight positive pressure relative to the atmosphere. Efforts were made to maintain the moisture content at 0.2%.

The obtained coagulated yarn was immersed in a methanol bath to extract DMSO, subjected to wet stretching of a total of 4 times in two stages, and dried with hot air at 100°C. then 180
It was hot-stretched in a hot air oven having a temperature gradient of -200-235°C so that the total stretching ratio was 22.5 times.

[0029] This spinning was carried out continuously for one week, and the spinning was stable throughout the entire process and period without any troubles such as roller sticking. The strength of the yarn obtained was 20.5 g/d both at the beginning and at the end, exceeding 20 g/d.

After spinning for one week, the spinning was stopped, the nozzle was reattached, and spinning was carried out in the same manner. There were no troubles, and the yarn strength was 20.3 g/d, which was more than 20 g/d, and the reproducibility was good.

Comparative Example 1: Spinning was carried out in the same manner as in Example 1, except that the coagulation bath was opened to the atmosphere and allowed to freely absorb moisture. There were no troubles at the start of spinning, and the yarn strength was good at 20.3 g/d, but after 2 days after starting spinning, the yarn strength decreased to 19.6 g/d. The water content in the coagulation bath at this time was 1.2%.

Comparative Example 2: After preparing a coagulation bath by mixing methanol and DMSO, the temperature was 25°C and the relative humidity was 80%.
When the coagulation bath was left in the atmosphere for more than one week, the weight ratio of methanol/DMSO/water in the coagulation bath was 68/28/4. When spinning was carried out in the same manner as in Example 1 using this coagulation bath,
Yarn strength was 19.2 g/d.

Example 2: Viscosity average degree of polymerization is 8100
, PVA with saponification degree of 99.8 mol%, methanol, DM
The weight ratio of SO to PVA/methanol/DMSO is 8/1.
/91, and heated under nitrogen atmosphere at 80℃ for 12 hours.
Dissolved for hours. The obtained spinning stock solution was heated to 60°C and the pore size was 0.
．． Wet-dry spinning was carried out through a 15 mm nozzle with 150 holes into a coagulation bath at 5° C. with a weight ratio of methanol/DMSO/water of 71.0/28.9/0.1 with an air layer of 5 mm in between. . At this time, the coagulation bath and godet roller chamber were sealed with dry nitrogen as in Example 1, and a column packed with molecular sieve 4A was installed in the middle of the piping of the coagulation bath circulation line to bring the coagulation bath into contact with the molecular sieve. The coagulation bath was dehumidified and the water content in the coagulation bath was maintained at 0.1% or less.

[0034] The obtained coagulated yarn was immersed in a methanol bath to extract DMSO, subjected to wet stretching of a total of 4.5 times in three stages, and dried with hot air at 100°C. then 17
Hot stretching was carried out in a hot air oven having a temperature gradient of 0-190-240°C so that the total stretching ratio was 23 times. It was possible to operate stably without any problems such as roller wrapping, and the yarn strength was excellent at 22.2 g/d.

[0035]

[Effect of the invention] In the conventional method for producing high-strength PVA fibers, the moisture in the coagulation bath had a subtle effect on the coagulation behavior of PVA, so the strength, long-term process stability, and reproducibility had not reached the level of industrial technology. In contrast, in the present invention, the strength, long-term process stability, and reproducibility are improved by specifying the coagulation bath water content, stock solvent concentration, and coagulation bath temperature. This makes it possible to provide stable supplies. Therefore, compared to other high-strength fibers such as the strong PVA fibers and para-aramid fibers obtained by the present invention, and conventional high-strength PVA fibers, it has excellent cost performance, and is used in rubber materials such as automobile tires and hoses. It can be widely and effectively used in the field of reinforcing materials such as FRC and FRP.

Claims (1)

[Scope of Claims] [Claim 1] A polyvinyl alcohol-based polymer having a viscosity average degree of polymerization of 1,500 or more is dissolved in an organic solvent, and the resulting spinning stock solution contains an organic solvent that has a coagulating ability for the polymer. A method for producing polyvinyl alcohol fibers with excellent strength, characterized in that the coagulation bath satisfies the following conditions (1) to (3) during wet or dry-wet spinning in a coagulation bath. (1) Set the coagulation bath temperature to 20℃ or less. (2) Contain 5 to 70% of the same organic solvent as the stock solvent in the coagulation bath.
(3) The water content in the coagulation bath is 0.8% or less [Claim 2]
10. The method for producing polyvinyl alcohol fibers according to claim 1, wherein the moisture content in the coagulation bath is maintained at 0.8% or less by controlling the moisture content of the gas in contact with the coagulation bath to be 0.1% or less. [Claim 3] The water content of the coagulation bath is maintained at 0.8% or less by bringing the coagulation bath into contact with a dehumidifier.
manufacturing method of polyvinyl alcohol fiber.