JP2000248424A - Production of low temperature water-soluble polyvinyl alcohol-based fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low temperature water-soluble fiber having <=20 deg.C water dissolving temperature in excellent processability, having extremely low maximum shrinkage of <=20% of the resultant fiber, having excellent dimensional stability under high humidity and high tensile strength. SOLUTION: A spinning raw solution having 25-37 wt.% of polyvinyl alcohol(PVA) concentration and obtained by dissolving a PVA-based polymer having 650-1,350 average polymerization degree and 195-210 deg.C is subjected to wet spinning or dry-wet spinning into a solidifying bath containing >=50 wt.% of an organic solvent having solidifying property to the polymer at from -20 deg.C to 20 deg.C and performing extraction, wet stretching, drying and dry stretching treatments to obtain the objective fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention uses a polyvinyl alcohol (hereinafter abbreviated as PVA) having an average degree of polymerization of 650 to 1350 as a spinning dope polymer, and increases the PVA concentration to increase the efficiency of recovering the stock solution solvent. Good solidification when the stock solution becomes thread-like, the extractability of the stock solution becomes good, the yarn cross section is less, the process stability is good, and the obtained fiber is dissolved in low-temperature water. The present invention relates to an industrial production method of a water-soluble PVA-based fiber which has low shrinkage at the time.

[0002]

2. Description of the Prior Art Conventionally, PVA has been used as a water-soluble fiber.
-Based fibers, cellulosic fibers such as carboxymethylcellulose, polyalginic acid-based fibers, polylactic acid-based fibers, polyalkylene oxide-based fibers, and the like are known, and are used for base cloth for chemical lace, for blend spinning with wool or hemp, and the like. Have been. Among them, PVA fibers are most often used because of their excellent tensile strength. As a method for producing a fiber satisfying the above performance, JP-A-7-90714 discloses a PVA polymer having a dissolution temperature in water of 100 ° C. or less.
Is dissolved in an organic solvent such as DMSO by wet or dry-wet spinning in a solidification bath having a solidifying ability such as methanol, and subjected to dry heat shrinkage treatment under multi-step heating conditions, so that shrinkage during dissolution in water is achieved. To obtain a water-soluble fiber having high dimensional shrinkage stability and high tensile strength even when left under high humidity, but the PVA polymer used has a saponification degree of 88 to 99.5. Mole% (195 at melting point)
225 ° C.), and no clear limitation of the spinning dope concentration. When the method described as an example in the publication was repeated, it was found that there was considerable unevenness in the yarn cross-section, which had a problem in terms of process stability.

[0003] Also, Japanese Patent Application Laid-Open No. 1-229805 discloses that
PVA having a low degree of saponification is converted to dimethyl sulfoxide (hereinafter referred to as DM).
It is described that a solution dissolved in an organic solvent such as SO) is dry-wet spinned in a solidification bath having a solidifying ability such as methanol and is highly oriented to obtain a water-soluble fiber having high tensile strength. However, the technology described in this publication has problems such as severe shrinkage when dissolving in low-temperature water, making the dissolution difficult, and causing the product form to be distorted due to the shrinkage.

[0004]

As a typical example of a conventional method for producing a fiber which can be dissolved in low-temperature water, an average degree of polymerization of 1 is used.
A method of spinning a low melting point PVA having a low saponification degree of around 700 is used. However, when spinning a low melting point PVA having a low degree of saponification or the like, generally, the solidification at the time of spinning from the undiluted solution becomes less sweet than the spinning of the high melting point PVA, and the extractability of the undiluted solvent from the solidified yarn is poor. There is a problem that it requires a long time. If the extraction time is long,
Generally, unevenness in the cross-section of the yarn is large, and a yarn breakage trouble occurs during the spinning process, which makes stable production difficult. Furthermore, in the prior art, when the obtained water-soluble PVA-based fiber is densified,
Even when immersed in water, PVA-based fibers also have a disadvantage that they are not easily dissolved.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a low-temperature water-soluble polymer, which has not been obtained by the prior art, and has a low cross-sectional unevenness, excellent process stability, and excellent leaching property in low-temperature water. And a method for producing a PVA-based fiber.

According to the present invention, the average degree of polymerization is from 650 to 135.
0, a PVA concentration of 25 to 35% by weight obtained by dissolving a PVA-based polymer having a melting point of 195 to 210 ° C in an organic solvent.
The spinning stock solution is wet-spun or dry-wet spun into a solidification bath at -20 to 20 ° C. containing 50% by weight or more of an organic solvent having a solidifying property with respect to the polymer, and is subjected to extraction, wet stretching, drying, and dry heat stretching. This is a method for producing a low-temperature water-soluble PVA-based fiber having a low shrinkage upon melting, which is characterized by performing a treatment. The present invention, as described above, the average degree of polymerization and melting point using a specific PVA-based polymer and a solidification bath of a specific composition and a specific temperature, all of these conditions, in order to achieve the object of the present invention, It is indispensable, and the object of the present invention is achieved only when all of these conditions are satisfied.

Next, a method for producing the water-soluble fiber of the present invention will be described. The raw material polymer used in the present invention is PVA
Based polymer having an average degree of polymerization of 650 to 13
It is in the range of 50, preferably in the range of 700 to 1000, particularly preferably in the range of 750 to 900.
If the average degree of polymerization is lower than 650, the cross section of the yarn is highly uneven, and the yarn frequently breaks during the spinning process, making it impossible to produce the fiber stably. Is not low. In order to dissolve in water of 0 to 30 ° C with low shrinkage after fiberization, complete saponification P having a melting point of 225 ° C
In the case of VA, the crystallinity after fiberization is too high,
Fibers that dissolve in water at 0 ° C. cannot be obtained. 0-3
If one wants to obtain fibers that dissolve in water at 0 ° C.,
It is necessary to use a PVA-based polymer at 5 ° C to 210 ° C. In particular, when it is desired to obtain a fiber that dissolves in water at 0 to 20 ° C, a so-called partially saponified PVA having a melting point of 200 ° C or less and containing a unit other than a vinyl alcohol unit, for example, a vinyl acetate unit is used. However, in the partially saponified PVA having a melting point of less than 195 ° C., considerable sticking occurs between the obtained fibers, and the polymer in the obtained fibers has low crystallinity and dimensional stability under high humidity cannot be obtained.
Also, the fibers of the present invention shrink greatly when dissolved in water, and the fibers of the present invention cannot be obtained. On the other hand, when the melting point exceeds 210 ° C., a low-temperature water-soluble fiber having the performance intended by the present invention cannot be obtained.

A so-called modified PVA containing a unit other than a vinyl alcohol unit and a vinyl acetate unit.
When it is desired to obtain a fiber having a dissolution temperature in water of less than 30 ° C. using a polymer, if the modification unit is a unit having a large crystallization inhibiting effect, a PVA-based polymer having a modification amount of about 0.5 mol% is used. Although a polymer can be suitably used in the present invention in some cases, it is generally preferable to use a PVA-based polymer modified by 1 mol% or more, particularly 2 mol% or more.

Examples of the modified unit include ethylene, allyl alcohol, itaconic acid, acrylic acid, maleic anhydride and its ring-opened product, arylsulfonic acid, vinyl esters of fatty acids having 4 or more carbon atoms such as vinyl pivalate, and vinylpyrrolidone. And a compound in which a part or all of the ionic group is neutralized. The method of introducing the modified unit may be a method by copolymerization or a method by an after-reaction. The distribution of the modified unit in the polymer chain is not particularly limited, whether it is random, block or graft.
If the amount of modification exceeds 5 mol%, the crystallinity will be excessively reduced, the dimensional stability under high humidity cannot be obtained, and the water-soluble fiber aimed at by the present invention cannot be obtained.

A stock solution for spinning is prepared by dissolving the PVA-based polymer. The stock solvent used in the present invention is not particularly limited as long as it is an organic solvent capable of dissolving the polymer, and examples thereof include polar solvents such as DMSO, dimethylacetamide, dimethylformamide, and N-methylpyrrolidone, glycerin, and ethylene. Examples thereof include polyhydric alcohols such as glycol and these solvents, or a mixture of these solvents and water. In particular, DMSO is most preferable in terms of low-temperature solubility, low toxicity, low corrosion, and the like.

In the present invention, when a PVA-based polymer having a low degree of saponification having many vinyl acetate units is used, if the spinning solution is strongly alkaline or acidic, a saponification reaction occurs during dissolution and defoaming, and the dissolution temperature in water is 100 ° C. It is necessary to avoid adding excessively strong alkali substances such as caustic soda and strong acid substances such as sulfuric acid.However, weak alkalinity such as in DMSO solution or addition of sodium acetate should be avoided. No saponification reaction takes place under or under weakly acidic conditions. Therefore, an alkaline substance or an acidic substance may be added to the stock solution as long as the stock solution is maintained in the range of weak alkali to weak acid.
When a polymer having an ionic group such as carboxylic acid or sulfonic acid is used, the acidity of the spinning dope may be adjusted by adding caustic soda for neutralizing hydrogen ions.

The concentration of PVA in the stock solution for spinning varies depending on the composition, the degree of polymerization, and the solvent. However, in order to obtain the water-soluble fiber of the present invention, the concentration of PVA must be as high as 25 to 35% by weight. And preferably 28 to 32% by weight. If the PVA concentration is less than 25%, the PV used
Since the A-based polymer has a low degree of polymerization, there is little entanglement of the molecular chains, and even when the spinning solution is discharged from a nozzle into a solidification bath and extruded, the solidification is poor and it is difficult to form a thread. Conversely, the entanglement of the molecular chains increases, the viscosity increases, and the spinnability that can be spun is lost. Dissolution is carried out with stirring under reduced pressure after replacement with nitrogen.
It is preferable in terms of prevention of a crosslinking reaction and suppression of foaming. The liquid temperature at the time of discharging the spinning stock solution is preferably in a range of 50 to 150 ° C. and a range in which the stock solution does not gel.

The obtained spinning dope is subjected to wet or dry-wet spinning in a solidifying bath mainly composed of an organic solvent having a solidifying ability for the polymer, ie, a solidifying solvent. The solidification referred to in the present invention means that a liquid spinning dope changes to a non-fluid solid, and both solidification, which solidifies without changing the composition of the stock solution and solidification, which changes the composition of the stock solution. Is included.

The solidifying solvent having a solidifying ability used in the present invention includes alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and fatty acid esters such as methyl acetate and ethyl acetate. Kind,
Examples thereof include aromatics such as benzene and toluene, and mixtures of two or more thereof. It is also possible to mix an undiluted solvent with these solidifying solvents to form a solidifying bath. However, from the point of solidification speed, and from the viewpoint of preventing unevenness of the yarn cross section,
It is necessary that the solidification bath contains 50% by weight or more of the solidification solvent, and the mixing weight ratio of the solidification solvent / the stock solution solvent is preferably 95/5 to 50/50. 90 / 10-60 /
More preferably, it is 40 and most preferably 85/15 to 55/45. By mixing the undiluted solvent with the solidification bath, the solidification ability can be adjusted, and the cost of separating and recovering the undiluted solvent and the solidified solvent can be reduced. As a solidifying solvent, methanol is excellent in solidifying properties. Therefore, when a mixed solution of a solidifying solvent and a stock solution is used as a solidifying bath, a mixed solution of methanol and DMSO is preferable.

The temperature of the solidification bath is between -20 and + 20 ° C. The solidification bath temperature is preferably from -10 to + 15 ° C, more preferably from -5 to + 10 ° C, and most preferably from 0 to + 5 ° C from the viewpoints of homogenous solidification and energy saving. If the temperature of the solidification bath is above or below this temperature range, the performance of the resulting fibers as defined in the present invention is reduced. As described above, the spinning dope is heated to a considerably high temperature, and when such a spinning dope is introduced into the solidification bath, the temperature of the solidification bath is usually higher than 30 ° C. Therefore, it is necessary to cool the solidification bath in order to keep the solidification bath temperature at 20 ° C. or lower.

The spinning method of the present invention may be any of a wet spinning method and a dry-wet spinning method, and spinning conditions suitable for each spinning method may be set. However, when the spinning dope is discharged from multiple holes, the wet spinning method is more preferable than the dry-wet spinning method in order to prevent the fibers from sticking at the time of discharging. In addition, the wet spinning method is a method of directly discharging a spinning solution from a spinneret to a solidification bath, while the dry-wet spinning method is a method of temporarily spinning a spinning solution from the spinneret into air or an inert gas. It is a method of discharging and then introducing into a solidification bath.

The obtained itoshino is stretched by 1.5 to 4 times in a wet stretching bath comprising a solidifying solvent or a mixture of the solidifying solvent and a stock solution. It is preferable to increase the wet stretching ratio within a range in which fluff does not appear, in order to suppress sticking of the yarn. The wet stretching ratio is 1.5
If the ratio is less than twice, the fibers tend to stick together, and if it exceeds four times, fluff is likely to appear. In order to increase the wet stretching ratio, it is effective to raise the temperature of the wet stretching bath to near the boiling point. It is also effective to perform wet stretching in two or more stages. In addition, as the liquid used for the wet stretching bath, the same as the above-described solidification bath solvent can be used. Preferably, the wet stretching ratio is 2.0 to 3.5 times.

The wet-stretched Ishino is brought into contact with an extraction bath mainly comprising a solidifying solvent to extract and remove the undiluted solvent from the Itoshino.
In this extraction treatment, the residence time in the extraction bath can be shortened by continuously flowing the pure solidified solvent in the countercurrent direction to the traveling direction of Itoshino. By this extraction treatment, the amount of the spinning dope solvent contained in the yarn is reduced to 1% or less, preferably 0.1% or less of the weight of the yarn. The contact time is preferably 5 seconds or more, particularly preferably 15 seconds or more. In order to increase the extraction speed and improve the extraction, it is preferable to raise the temperature of the extraction bath solvent to near the boiling point. As in the present invention, in the case of a fiber made of a polymer that easily causes inter-fiber sticking,
By passing a ketone such as acetone, methyl ethyl ketone and methyl isobutyl ketone and methanol through a mixed bath having a mixing weight ratio of 80/20 to 20/80 in the final extraction bath (replacement bath), the solidification is further strengthened. Adhesion between fibers, which tends to occur during drying, can be prevented.

The extracted itoshino is dried in a gas bath at 150 ° C. or lower. Attachment of a hydrophobic oil such as a mineral oil, silicone, or fluorine before drying is more effective in preventing sticking during drying.

The dried raw yarn thus obtained is subjected to dry heat drawing at 1.1 to 5.0 times at 80 to 150 ° C. or heat treatment at a constant length at 80 to 150 if necessary for dissolving in water. Water-soluble fibers with low shrinkage can be obtained. Such dry heat stretching,
The reason that low-shrinkage water-soluble fibers can be produced without setting complicated conditions for constant-length heat treatment is that the low-polymerization degree PVA-based polymer has the property of potentially low shrinkage and shrinkage stress. Is due.

The most important feature of the production method of the present invention is that the use of PVA having a low degree of polymerization makes it possible to increase the concentration of the stock solution, which leads to an improvement in the solidification of the stock solution, The solvent extractability from the solvent is improved, and the process passability is also improved. Further, since the amount of the undiluted solvent used is small, the cost for solvent recovery is reduced.

Next, the fiber obtained by the production method of the present invention will be described. The water-soluble fiber (T ° C) of the water-soluble fiber obtained by the above production method is preferably 0 to 30 ° C. 30
Exceeding ° C. increases the operational risk of dissolution and increases the amount of energy required for dissolution, increasing dissolution costs. Also, it is difficult to completely dissolve and remove. When the water dissolution temperature is high, when the water-soluble fiber obtained by the present invention is dissolved and removed from the mixture of the water-soluble fiber obtained by the present invention and the other water-insoluble fiber, the other water-insoluble fiber shrinks or is damaged. And will deteriorate. From these points, the dissolution temperature in water is preferably 30 ° C or lower.

In addition, even when the web made of the water-soluble fiber obtained in the present invention is hot-embossed into a high-density nonwoven fabric, the water dissolution temperature (T ° C.) ) Is preferably 30 ° C. or less,
The temperature is more preferably 0 ° C or lower, and even more preferably 10 ° C or lower. In the present invention, the dissolution temperature in water (T
° C) is 0.01 mg / dtex for a fiber with a test length of 10 cm.
Is a temperature at which fibers are melted when the load is suspended, immersed in water at 0 ° C., and the water is heated at a rate of 2 ° C./min.

The water-soluble fiber obtained by the production method of the present invention has a small maximum shrinkage in water of preferably 20% or less, and is excellent in dimensional stability when dissolved in water. The maximum shrinkage ratio in water is the maximum shrinkage ratio of the length shrunk to complete dissolution / test length. When the maximum shrinkage exceeds 20%, only the water-soluble fiber obtained by the production method of the present invention is converted from a fiber product comprising a mixture of the water-soluble fiber obtained by the production method of the present invention and another water-insoluble fiber. When dissolving and removing with water, in addition to the problem that the dimensional change of the fiber product is large and the shape and physical properties of the fiber product are impaired, the water-soluble fiber of the present invention absorbs water and shrinks into a gel, resulting in a specific surface area. And it takes a long time to completely dissolve it. In particular, when a water-soluble fiber having a high maximum shrinkage rate when dissolved in water is used for a delicately designed base cloth for a chemical lace, the shape of the lace tends to be deformed when dissolved.
When the maximum shrinkage of the water-soluble fiber used for the base fabric is 20% or less, the shrinkage upon dissolution of the base fabric becomes almost 0%, which is extremely industrial because it can be used for a lace of a delicate design. High value. When water-soluble fiber is used for wool blending or hemp blending, the maximum shrinkage of the water-soluble fiber is 20%.
When the content is below, since the mixed spun yarn hardly shrinks when the mixed spun yarn is subjected to the dissolution treatment, the water-soluble fiber can be easily completely dissolved and removed, and a soft and bulky mixed spun yarn can be obtained.

The maximum shrinkage in water is more preferably 15% or less, and even more preferably 10% or less.
Conventionally, in a fiber stretched and oriented at a high magnification, since the oriented molecules are relaxed and become non-oriented before melting, the maximum shrinkage reaches 70% and the water solubility is deteriorated. In the water-soluble fiber obtained in the above, orientation relaxation during dissolution is suppressed and low shrinkage is achieved by well combining orientation and relaxation in the fiber production process.

Next, one of the preferred features of the present invention is that the water-soluble fiber obtained by the production method of the present invention has a tensile strength of 2.5 cN / dtex or more. 1. Tensile strength
When it is less than 5 cN / dtex, not only tends to cause troubles in a post-process such as a knitting process or a non-woven fabric process, or it tends to be inferior in high-speed productivity, but also the physical properties of the obtained knitted fabric or non-woven fabric are poor. It is inferior and cannot be used for a wide range of applications. Note that the tensile strength in the present invention is determined by JIS L after moisture conditioning a fiber at 20 ° C. × 65% RH.
A tensile test is performed in accordance with No. 1015, and the dry strength is measured, and is expressed in cN / dtex.

The fiber obtained by the production method of the present invention also has a property that fibers are firmly adhered to each other by thermocompression bonding. Utilizing this property, the fiber can be formed into a web and then hot-embossed to fix the shape of the web and immediately form a non-woven fabric. For example, the single fiber obtained in the present invention can be formed into a web by a roller card method. The nonwoven fabric obtained by heat-embossing is suitable for use as a chemical lace base fabric because it is water-soluble, has excellent dimensional stability when absorbing moisture and dissolving in water, and has excellent tensile strength. Further, since the fibers can be bonded to each other by hot embossing, by utilizing this property, two or more woven or knitted fabrics or nonwoven fabrics made of the fiber obtained by the present invention are stacked and hot-pressed to further improve the heat bonding property. It can be joined by superimposing it on a film and hot-pressing it, and a wide object, bag-like object or laminate can be easily made.

As described above, the present invention has an average degree of polymerization of 650 to 1100 and a melting point of 195 to 210 ° C. (saponification degree of 8
8 to 92 mol%) of a PVA-based polymer dissolved in an organic solvent, and a spinning dope having a PVA concentration of 25 to 37% by weight,
Wet spinning or dry-wet spinning in a solidification bath at -20 to 20 ° C. containing 50% by weight or more of an organic solvent having solidifying property with respect to the polymer, followed by extraction, wet stretching, drying, and dry heat stretching. Thus, low-temperature water-soluble PVA-based fibers, which cannot be obtained by the conventional technology, have less cross-sectional unevenness, have excellent process stability, and have excellent leaching properties in low-temperature water, can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples,% is a value based on weight unless otherwise specified. The polymerization degree of PVA is JIS K-6726.
Viscosity ηs of PVA dilute aqueous solution at 30 ° C based on
p was measured at five points, the intrinsic viscosity [η] was determined from the following equation 1,
Further, the average degree of polymerization is determined by the following equation (2). [Η] = lim η _sp / C (C → 0) ‥‥ 1 Average polymerization degree = ([η] × 10 ⁴ /8.29) ^1.613 ‥‥ 2

Example 1 A mixture of PVA and DMSO having a degree of polymerization of 800 and a melting point of 205 ° C. (partially saponified PVA having a saponification degree of 91 mol%) was replaced with nitrogen, and dissolved by stirring at 90 ° C. for 8 hours under a reduced pressure of 110 Torr. Thereafter, defoaming was performed at 90 ° C. for 8 hours under the same 110 Torr to obtain a DMSO solution containing 32% PVA. This spinning solution is kept at 90 ° C., the number of holes is 3000, and the hole diameter is 0.06 mmφ.
Was wet-spun into a solidification bath consisting of a mixture of methanol / DMSO at a mixing weight ratio of 70/30 at 0 ° C. The obtained Itoshino is methanol / DMSO = 96 /
2.5 times wet stretching in a 50 ° C. wet stretching bath consisting of
DMSO was extracted and removed by countercurrent contact with heated methanol, and a mineral oil-based oil agent was added at 1% / polymer, and dried with a hot air drier at 120 ° C. to obtain a multifilament spun yarn of 16000 dr / 3000f. The content of DMSO in the obtained spun yarn was measured by gas chromatography and was not detected. The spun yarn is then heated to 80 ° C.
In a hot air furnace consisting of three sections at −100 ° C. to 120 ° C., a three-stage heating / dry heat stretching process was performed, and a total stretching ratio of 6 times was performed. The dissolution temperature (T) of the obtained fiber in water is 15 ° C.
It was low. Further, the tensile strength was 3.5 cN / dtex, and the maximum shrinkage upon dissolution in water was 7%. The cross-sectional shape of the obtained fiber was observed with a microscope and the diameter was measured.
If the fiber diameter deviated by more than 40% from the average diameter in the book is 3
It was a book, and there was very little unevenness in the yarn cross section. The spinning was performed continuously for 12 hours, but there was no process trouble such as thread breakage, and the process stability was excellent.

Comparative Example 1 Fibers were obtained in the same manner as in Example 1 except that a polymerization degree of 1700 and a melting point of 195 ° C. (partially saponified PVA having a saponification degree of 88 mol%) were used and the stock solution concentration was 21%. As a result of measuring the content of DMSO in the obtained spun yarn by gas chromatography, it was found that it contained 0.1%, indicating that the solvent extractability was poor. Although the dissolution temperature in water was as low as 15 ° C., the maximum shrinkage upon dissolution in water was as large as 30%. The cross-sectional shape of the obtained fiber was observed with a microscope, and the diameter was measured. As a result, there were 30 fibers having a fiber diameter deviating by 40% or more from the average diameter of 100 fibers, and the yarn cross-section was highly uneven. In addition, when the above-mentioned spinning was performed continuously for 12 hours, process troubles such as thread breakage frequently occurred.

Comparative Example 2 Polymerization degree 1700, melting point 210 ° C. (Saponification degree 93.5 mol%
Example 1 except that a partially saponified PVA) was used, the PVA concentration was 22%, and the wet stretching ratio was 3.0 times.
In the same manner as in the above, a spun yarn of 16000d / 3000f was obtained.
Then, dry heat stretching of 2.0 times was performed in a hot blast stove consisting of two sections at 140 ° C to 170 ° C. Although the dissolution temperature (T) in water of the obtained fiber was as low as 20 ° C. or less, the maximum shrinkage upon dissolution in water was as large as 40%.

Example 2 PVA having a degree of polymerization of 1000 and a melting point of 195 ° C. (partially saponified PVA having a degree of saponification of 88 mol%) and DMSO were mixed, the atmosphere was replaced with nitrogen, and the mixture was stirred and dissolved at 90 ° C. under a reduced pressure of 110 Torr for 8 hours. Thereafter, degassing was performed at 90 ° C. for 8 hours under the same 110 Torr, to obtain a DMSO solution containing 28% PVA. This spinning dope was kept at 90 ° C., and was wet-spun through a nozzle having 400 holes and a hole diameter of 0.10 mmφ into a solidification bath consisting of a mixed solution of methanol / DMSO at a mixing weight ratio of 70/30 at 5 ° C. The obtained Itoshino is methanol / DMSO = 95/5
And then subjected to 3.0-fold wet stretching in a 45 ° C. wet stretching bath, and brought into countercurrent contact with heated methanol to extract and remove DMSO.
Dry at 120 ° C hot air dryer, 1670dr / 400f
Was obtained. The content of DMSO in the obtained spun yarn was measured by gas chromatography and was not detected. The spun yarn is then passed through a hot-air stove consisting of two sections at 80 ° C. to 120 ° C. for 2 hours.
A dry heat stretching process was performed at the stage, and a total stretching ratio of 6 times was applied. The dissolution temperature (T) in water of the obtained fiber was 20 ° C. or less, and the maximum shrinkage in water was 15%. The tensile strength is 5.5 cN / dtex, the elongation at break is 20%,
Toughness was 120 cN / dtex ×%. The cross-sectional shape of the obtained fiber was observed with a microscope, and the diameter was measured. As a result, there were two fibers having a fiber diameter deviated by 40% or more from the average diameter in 100 fibers, and the unevenness in the yarn cross section was extremely small.
The spinning was performed continuously for 12 hours, but there was no process trouble such as thread breakage, and the process stability was excellent.

Comparative Example 3 Polymerization degree 1750, melting point 225 ° C. (saponification degree 99.9 mol%
Of completely saponified PVA) and a PVA concentration of 21
% And 1670 dte in the same manner as in Example 2.
An x / 400f spun yarn was obtained. Then 170-230
Dry heat stretching was performed at 15 ° C. to a total stretching ratio of 15 times.
The obtained fiber did not dissolve in water at 100 ° C.

Example 3 The spun yarn obtained in Example 1 was subjected to a constant-length heat treatment in a hot-air oven at 120 ° C. to 150 ° C. under a two-stage heating condition. The obtained fiber has a dissolution temperature (T) in water of 20 ° C. or less, a maximum shrinkage in water as small as 6%, and a tensile strength of 2.6.
cN / dtex, elongation at break was 10%, and toughness was 26 cN / dtex ×%. Also RH93
% Was as low as 0.8%, indicating excellent dimensional stability.

Example 4 A spun yarn was obtained in the same manner as in Example 1, except that PVA having a degree of polymerization of 750 and a melting point of 200 ° C. (a degree of saponification of 90 mol%) was used. This spun yarn is kept at 100 ° C.-120 ° C.-15
In a hot blast stove consisting of three sections at 0 ° C., a total stretching ratio of 5.5 times was performed under three-stage heating conditions. The obtained fiber has a water dissolution temperature (T) of 12 ° C., a maximum shrinkage in water as small as 6%, and a tensile strength of 3.6 cN / dte.
x, elongation at break is 8%, toughness is 29 cN / dtex
Met. The dimensional change at RH 93% was as low as 1.7%, and the dimensional stability was excellent. When the cross-sectional shape of the obtained fiber was observed with a microscope, the cross-sectional shape of the obtained fiber was observed with a microscope, and the diameter was measured. And the unevenness of the yarn cross section was extremely small. In addition, the above spinning is
The test was carried out continuously for 2 hours, but there was no process trouble such as thread breakage, and the process stability was excellent.

Example 5 A fiber obtained in exactly the same manner as in Example 4 except that the constant-length heat treatment was changed to 120 ° C. had a water dissolution temperature (T) of 10 ° C. and a maximum shrinkage in water of 9%. %, The tensile strength was 2.5 cN / dtex, the elongation at break was 10%, and the toughness was 25 cN / dtex ×%. Also RH9
The dimensional change at 3% was as low as 2.5%, and the dimensional stability was excellent.

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Claims (1)

[Claims] An average degree of polymerization of 650 to 1350 and a melting point of 1
Polyvinyl alcohol concentration of 25 to 210 ° C. obtained by dissolving a polyvinyl alcohol polymer in an organic solvent at 25 to 210 ° C.
35% by weight of a spinning dope containing 50% by weight or more of an organic solvent having a solidifying property with respect to the polymer;
Wet spinning or dry-wet spinning in a solidification bath, extraction, wet drawing,
A method for producing a low-temperature water-soluble polyvinyl alcohol-based fiber, which comprises performing a dry heat drawing treatment after drying.