JP2833887B2 - Method for producing polyvinyl alcohol fiber with excellent strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet or dry-wet spinning method mainly used for producing polyvinyl alcohol (hereinafter abbreviated as PVA) fibers having excellent strength. It is about.

[0002]

2. Description of the Related Art Since PVA fiber has higher strength and elastic modulus than polyamide, polyester and polyacrylonitrile fibers, it is used not only as a fiber for industrial materials, which is its main use, but also as a reinforcing material such as cement and plastic in recent years. It is being used.

As a method for producing such a high-strength PVA-based fiber, Japanese Patent Application Laid-Open No. Sho 59-1303 applies the concept of gel spinning and ultra-drawing of ultra-high molecular weight polyethylene to PVA.
No. 14 is known, and coagulation spinning by wet or dry-wet spinning using a high polymerization degree PVA and an organic solvent instead of gel spinning is also disclosed in JP-A-59-10071.
0, Japanese Patent Application Laid-Open No. 60-12312 and Japanese Patent Application Laid-Open
It is known in, for example, JP-A-3-99315.

[0004] However, in the case of coagulation spinning employed in the prior art, a high degree of polymerization cannot always provide PVA fibers as high in strength as gel spinning. Accordingly, the present invention has sought to find out why high-strength PVA fibers cannot be obtained by the conventionally known coagulation spinning, and has found that one of the remarkable factors lies in the solidification extraction process of the spinning solution.

As described above, the conventional spinning method is based on the idea of gel spinning of ultra-high molecular weight polyethylene, and it has been considered that rapid solidification and delayed solvent extraction are important in the coagulation process for high strength.

The present inventors have analyzed the solidification extraction process in coagulation spinning in detail, and found that the dope temperature, coagulation bath temperature, coagulation bath composition, PVA concentration in dope, PVA, which were empirically obtained from spinning experiments. It has been found that the direction of increasing the strength of various conditions such as the degree of polymerization and the type of solvent does not always coincide with the direction of delayed solvent extraction, but coincides with the direction of higher solvent residual ratio in the solidified yarn.

[0007] The coagulation spinning method is lower in cost than the gel spinning method and is advantageous in industrialization. In other words, in the case of gel spinning, the spinning dope is higher in temperature than the coagulation spinning, and the solidification bath is lower in temperature, so that the equipment cost is higher. Therefore, the hole pitch of the nozzle becomes large to prevent sticking, and the size cannot be reduced. On the other hand, in the coagulation spinning, the spinning solution is low in temperature, the solidification bath is high in temperature, and it is compact and can be made into multiple holes. However, the conventional coagulation spinning has a problem that the strength tends to be lower than that of gel spinning particularly at a high degree of polymerization.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a PVA in which both the stock solution and the coagulation bath use an organic solvent system.
In the coagulation spinning method of the system fiber, it is sought to produce a PVA fiber having a high degree of polymerization and excellent strength comparable to the gel spinning method.

[0009] The coagulation spinning referred to herein means that PV is added to an organic solvent.
The undiluted solution in which A is dissolved is extruded from a nozzle into a coagulation bath of an organic solvent system having coagulability by a wet or dry-wet method, and the coagulation bath penetrates into the undiluted spinning solution and solidifies by changing the composition of the undiluted spinning solution. Gel spinning is a spinning method in which an undiluted solution in which PVA is dissolved in an organic solvent having the ability to solidify without changing the composition (gelling ability) is below the gelling temperature by a wet method or a dry-wet method from a nozzle. This is a spinning method in which the PVA is extruded into a solidification bath or a gas layer and a solidification bath and solidified without changing the composition of the PVA stock solution. The method of the present invention is directed to the former coagulation spinning method.

[0010]

Means for Solving the Problems The present invention relates to a method for preparing a spinning solution obtained by dissolving a polyvinyl alcohol polymer having a viscosity-average degree of polymerization of 3500 or more in an organic solvent by a wet method or a dry-wet method. Extruded into an organic solvent-based coagulation bath having a volume of less than 1 in the bath draft, in a coagulation spinning of a polyvinyl alcohol fiber, the residual ratio of the solvent contained in the coagulation yarn at the first godet roller portion Is a method for producing a polyvinyl alcohol-based fiber, which is spun so as to be 25 to 80% with respect to the amount of the undiluted solvent. "

The PVA used in the present invention is a PVA having an average degree of polymerization of 3500 or more as determined by a viscosity method in an aqueous solution at 30 ° C. If it is lower than 3500, a PVA fiber having a higher strength than gel spinning can be obtained even by the conventional coagulation spinning. Viscosity average degree of polymerization is 7000 or more, preferably 150
If it is at least 00, the effect of the spinning method of the present invention will be more remarkable.

The degree of saponification of the PVA used is not particularly limited, but is preferably 98.5 mol% or more, and more preferably 99.9 mol or more. The PVA used may be a polyvinyl alcohol-based polymer obtained by copolymerizing another monomer having a vinyl group, for example, a monomer such as ethylene, itaconic acid, or vinylpyrrolidone at a ratio of 10 mol% or less, preferably 2 mol% or less. Good.

The solvent used in the present invention is not particularly limited as long as it can dissolve PVA and can solidify this PVA stock solution by infiltration of an organic solvent having a solidifying ability such as methanol, and dimethyl sulfoxide ( Polar solvents such as DMSO), dimethylformamide and dimethylimidazolidinone. Also, a mixture of these solvents and the like can be used. Among many solvents, D
MSO can be dissolved at low temperatures below 80 ° C.
This is a preferable solvent because the decrease in the polymerization degree of A can be reduced.

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 a high-strength fiber. For this purpose, it is preferable to lower the PVA concentration within a range that does not cause breakage of single yarns, yarn spots, or sticking between single yarns during spinning.

In addition to the PVA and the solvent, various additives such as a coloring agent such as a pigment, etc.
A required amount of an antioxidant, a crosslinking agent, a UV absorber, a surfactant, a pH adjuster such as an acid, or the like may be added. Further DMS
For solvents with relatively high freezing temperatures, such as O,
It is sometimes preferable to add methanol or the like having a coagulating action within a range in which PVA does not coagulate, because the spinning solution does not freeze even when the coagulation bath is set at a temperature lower than the freezing temperature of the solvent.

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

There is no particular limitation on the spinning method of the present invention. The wet spinning method, in which the nozzle is in direct contact with the coagulation bath, or the dry-wet spinning method, in which an air layer is interposed between the nozzle and the coagulation bath, may be used, but the wet spinning method, in which the equipment can be made compact, is preferred. There is.

As the coagulation bath, a solvent having a coagulation 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 they have a solidifying ability in PVA. Among them, methanol is preferable in terms of solidification balance and cost. In the present invention, the coagulation bath preferably contains 5 to 70% of the stock solution. The content of the undiluted solvent varies depending on the type of the organic solvent having a solidifying ability, but if it is less than 5%, the difference from the undiluted solution composition is large, and uneven coagulation is likely to occur due to rapid aggregation of PVA. 7
If it exceeds 0%, the coagulation rate is low and fiber formation is not sufficiently performed, so that the obtained yarn tends to stick. The solvent content of the stock solution in the coagulation bath is more preferably from 10 to 50% by weight, and even more preferably from 15 to 45% by weight.

The temperature of the coagulation bath is not particularly limited, but if it exceeds 20 ° C., the coagulated yarn becomes opaque with many voids, and it is difficult to obtain high-strength fibers which are not homogeneous. The coagulation bath temperature is more preferably 15 ° C. or lower, and even more preferably 10 ° C. or lower in that a uniform coagulated yarn is obtained. However, if the temperature of the coagulation bath is too low, the spinning solution discharged from the nozzle may freeze and become unable to discharge, so this point should be considered.

Next, it is one of the most important points of the present invention to make the residual ratio of the solvent contained in the coagulated yarn in the first godet roller section 25 to 80%. The general idea of the present invention in this regard is that extraction in a coagulation bath is performed so that the amount of solvent extraction is suppressed in a range where a solidified yarn is formed, so that the structure of the solidified yarn is as uniform as possible. It focuses on the residual ratio of the solvent in the yarn at the time of leaving the coagulation bath as an index. The residual solvent ratio should be set by changing the residence time in the coagulation bath, that is, by changing the length of the spinning cylinder that forms the coagulation bath (coagulation bath length) and the take-up speed of the first godet roller on the coagulation bath. Can be. That is, the gist of the present invention is to reduce the residence time in the spinning cylinder so that the residual ratio of the solvent contained in the coagulated yarn falls within the above range, and more specifically, the spinning. This is achieved by shortening the cylinder and increasing the take-up speed. If the residual ratio of the solvent exceeds 80%, coagulation becomes insufficient, and the obtained yarn sticks or extremely difficult to spin normally. When the solvent remaining ratio is less than 25%, high-strength fibers comparable to gel spinning cannot be obtained. Solvent residual rate is 30-60%
Is preferable, and a high-strength fiber is easily obtained.

In the present invention, the residual ratio of the solvent contained in the coagulated yarn at the first godet roller was measured as follows. First, the coagulated yarn in the first godet roller section is wiped off the liquid adhering to the surface, and two samples are sampled for the same time.
One is PVA by Soxhlet extraction and absolute drying.
Determine the weight (A). The other is dissolved in water and decomposed by gas chromatography to determine the weight (B) of the undiluted solvent. Assuming that the weight ratio of the solvent to PVA in the spinning dope is (C), the residual ratio of the solvent contained in the coagulated yarn at the first godet roller can be determined at 100 B / AC.

The coagulated yarn drawn by the first godet roller in the coagulation bath or on the coagulation bath is converted into a fiber according to the following steps. That is, the undiluted solvent and the like in the coagulated yarn are extracted, washed and removed by an extraction bath made of an organic solvent having a coagulation ability, and dried. It is preferable to perform wet stretching of one step or more preferably two or more steps in total in any step from immediately after the first roller to before drying, because it is possible to prevent sticking during drying. A more preferable wet stretching ratio is 2.5 to 5.5. Drying temperature is 4
0 to 150 ° C. is preferred in terms of drying efficiency and performance. Further, it is preferable to increase the drying temperature in multiple stages.

Next, hot drawing is performed at a high temperature to orient and crystallize the PVA fiber to obtain a high-strength fiber. The hot stretching temperature is preferably 210 ° C. or higher, more preferably 220 to 255 ° C.
It is better to do it. At this time, the total draw ratio is 16 in the conventional method.
The stretching is performed at a magnification of at least 18 times, more preferably at least 18 times. A feature of the method of the present invention is that sufficient strength can be obtained by stretching at a relatively low magnification of 12 to 18 times. The hot stretching may be dry heat, heat medium such as silicon, or wet heat such as in high-temperature steam. By controlling the temperature in multiple stages, 2
You may heat-stretch in steps or more. Further, heat treatment and heat shrinkage may be performed as necessary.

It is unknown why the solvent remaining rate of the coagulated yarn in the first godet roller section has a great effect on the fiber performance, but the coagulated yarn in the first godet roller section is extracted at a fixed length. Since the absolute value of the small-angle X-ray scattering intensity of the dried sample is lower than that of the conventional method, the junction points are more uniformly distributed than that of the conventional method. It is considered that the orientation becomes high and the strength is increased.

The reason why the sampling portion of the coagulated yarn for measuring the residual solvent ratio in the present invention is the first godet roller is based on the following reason. Since the yarn discharged from the nozzle is back-drafted (in a state where the bath draft is less than 1) in a coagulation bath up to the first godet roller, solvent extraction is performed under very low tension. On the other hand, in a multiple-stage extraction bath after the first godet roller, there is a difference that the solvent extraction is performed under a high tension due to the contraction of the yarn and the wet drawing accompanying the solvent extraction. If the extraction baths in the multiple stages after the first godet roller are exactly the same and only the spinning cylinder length is changed, even if the solvent remaining ratio of the sampling yarn at the same part of the extraction bath is the same, the small angle of the sampling yarn When the X-ray scattering intensity was measured, the absolute value of the shorter spinning cylinder length decreased. From this, it was found that the solvent extraction behavior under low tension where the backdraft works was important for the formation of the structure of the coagulated yarn, and attention was paid to the solvent remaining ratio of the coagulated yarn in the first godet roller portion.

As described above, by controlling the solvent remaining ratio of the coagulated yarn in the first godet roller section of the coagulated yarn to a specific range, a uniform raw yarn can be obtained, and the total draw ratio is 12 to 10. Powerful and excellent PV equivalent to gel spinning even at 16 times
It is possible to stably produce the A fiber with good reproducibility.

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 PVA having a viscosity average degree of polymerization of 7800 and a saponification degree of 99.9 mol% was added to DMSO so as to be 6.5% by weight, and further, 2.0% by weight of methanol was added as an antifreezing agent. Then, the mixture was dissolved at 80 ° C. for 8 hours in a nitrogen atmosphere.
In a coagulation bath having a methanol / DMSO weight ratio of 75/25 ° C., wet spinning was performed at a spinning cylinder length of 0.6 m and a first godet roller speed of 8 m / min. At this time, the residual ratio of the solvent was 45%.

The obtained coagulated yarn was immersed in a methanol bath, DMSO was extracted, wet-stretched 4.0 times, and dried with hot air at 100 ° C. Next, the first furnace at 170 ° C.
The second furnace was hot stretched in a hot air oven at 245 ° C. so that the total stretching ratio became 15 times. The yarn strength obtained is 21.5 g / d
r.

Comparative Example 1 The spinning solution used in Example 1 was wet-spun in the same manner as in Example 1 at a spinning cylinder length of 2.5 m and a first godet roller speed of 4 m / min. At this time, the residual ratio of the solvent was 20%. Thereafter, the same operation as in Example 1 was carried out, and the total stretching ratio could be 24 times, but the yarn strength was 19.5 g / dr.

Example 2 Viscosity average degree of polymerization 17000
A PVA having a saponification degree of 99.9 mol% was added to DMSO so as to have a weight of 4.0 wt%, and methanol of 3.0 wt% was further added as an antifreezing agent.
Melted for 3 hours, and the weight ratio of methanol / DMSO at −3 ° C. was 80/2 from a nozzle having a hole diameter of 0.16 mm and 300 holes.
In a coagulation bath consisting of 0, the spinning was performed at a spinning cylinder length of 0.6 m and a first godet roller speed of 6 m / min. At this time, the residual ratio of the solvent was 55%.

The obtained coagulated yarn was immersed in a methanol bath, DMSO was extracted, wet-stretched 4.0 times, and dried with hot air at 100 ° C. Next, the first furnace at 160 ° C.
The second furnace was hot-stretched in a hot-air oven at 250 ° C. so that the total stretching ratio was 16.0 times. The obtained yarn strength is 22.5 g
/ Dr. Higher polymerization degree PVA was used than in Example 1 and the strength was high.

Comparative Example 2: The spinning stock solution used in Example 2 was wet-spun in the same manner as in Example 2 at a spinning cylinder length of 2.5 m and a first godet roller speed of 4 m / min. At this time, the residual ratio of the solvent was 23%. Thereafter, the same operation as in Example 2 was performed, and the total draw ratio was 23 times, but the yarn strength was 2 times.
0.0 g / dr.

[0034]

According to the conventional method for producing high-strength PVA fibers by coagulation spinning, rapid solidification in a coagulation bath and delayed solvent extraction have been considered important, so that the residence time in the coagulation bath is long,
The solvent remaining ratio of the coagulated yarn in the first godet roller was too low, and it was difficult to produce high-strength fibers comparable to gel spinning at a high degree of polymerization. On the other hand, in the present invention, by changing the length of the spinning cylinder and the speed of the first godet roller, shortening the residence time of the coagulation bath under the back draft, and setting the solvent residual ratio of the coagulated yarn to be high, the high-strength fiber is set. Is made possible. Therefore, the PVA fiber having excellent strength obtained according to the present invention is more excellent in cost performance than other high-strength fibers such as para-aramid fiber and conventional PVA fiber, and is used in the field of rubber materials such as automobile tires and hoses. , FRC and FRP can be widely and effectively used.

────────────────────────────────────────────────── ─── front page of the continuation (72) inventor Omori Kurashiki, Okayama Prefecture Akio Sakazu 1621 address, Ltd. Kuraray the examiner true s field Tadahiro (58) investigated the field (Int.Cl. ^6, DB name) D01D 5/06 D01F 6/14

Claims (2)

(57) [Claims] 1. A spinning dope obtained by dissolving a polyvinyl alcohol polymer having a viscosity average degree of polymerization of 3500 or more in an organic solvent, in a coagulation bath of an organic solvent system having coagulation ability by a wet method or a dry-wet method. In the coagulation and spinning of the polyvinyl alcohol-based fiber, which is extruded and forms a yarn in a state of less than 1 bath draft, the residual ratio of the solvent contained in the coagulated yarn at the first godet roller portion is 25 to the amount of the undiluted solvent.
A method for producing a polyvinyl alcohol-based fiber, wherein the fiber is spun so as to be 80% or less. 2. The method according to claim 1, wherein the total draw ratio is 12 to 18 times.