JPH10266016A - Spinning of polyvinyl alcohol fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject fiber improved in a spinning property, less in adhesion among fibers or cutting of single fibers industrially advantageously by spinning a spinning stock solution of an aqueous solution of a polyvinyl alcohol containing a small amount of boric acid (salt) according to a wet spinning method. SOLUTION: This polyvinyl alcohol fiber is obtained by spinning a spinning stock solution of an aqueous solution of a polyvinyl alcohol containing 0.005-0.1 wt.%, preferably 0.01-0.05 wt.% boric acid (salt) based on the polyvinyl alcohol into a coagulation bath consisting of an aqueous sulfate solution such as sodium sulfate, ammonium sulfate, etc., according to a wet spinning method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for wet spinning polyvinyl alcohol (hereinafter abbreviated as PVA) fibers.

[0002]

2. Description of the Related Art In general, PVA fibers are produced by P
A method is known in which a VA aqueous solution is used as a spinning solution and wet spinning is performed in a coagulable inorganic salt aqueous solution, followed by stretching, heat treatment, and acetalization treatment for improving water resistance. In the spinning process by wet spinning, the PVA spinning solution is extruded from a spinneret into a coagulation bath, solidified and hardened mainly by the dehydration effect of the inorganic salt, formed into PVA fibers, and wound up at a predetermined speed. For the coagulation bath, a saturated solution such as an aqueous solution of sodium sulfate or an aqueous solution of ammonium sulfate is generally used to enhance the coagulation ability. However, in the above spinning method, since the coagulation state is insufficient, single yarn breakage due to bath resistance in the coagulation bath is apt to occur, and the spinnability has been reduced. In particular, there has been a problem that fibers cut in the vicinity of the spinneret form a lump without being wound up and are mixed into the product as abnormal fibers. This is remarkably observed when the spinning speed is increased, and also causes a problem that the improvement in productivity is hindered.

On the other hand, in spinning PVA fiber, a method utilizing boric acid or borate is disclosed in Japanese Patent Laid-Open No. 62-1499.
No. 09, Japanese Patent Publication No. 07-6087 and the like. Japanese Patent Application Laid-Open No. 62-149909 discloses that when obtaining PVA fibers having high strength and high
PVA aqueous solution containing 0.1 to 5% by weight of boric acid or borate with respect to VA and having a pH of 3.5 to 5 is used as a spinning solution and wet-spun in a neutral or alkaline coagulation bath to form PVA. A method is disclosed in which boric acid or borate undergoes a cross-linking reaction to form PVA gel fibers, and then boric acid or cross-linked boric acid is removed by steps such as neutralization and washing with water. However, the spinning method requires that the amount of boric acid or borate added is large, that the pH of the spinning solution and the coagulation bath be adjusted, and that boric acid or cross-linked boric acid be removed after spinning. There is a problem.

Japanese Patent Publication No. 7-6087 discloses a high strength
In order to obtain a high modulus PVA fiber, 0.05 to 10% by weight of boric acid or borate is added to PVA based on PVA.
A spinning solution (pH 5 to 9) using ethylene glycol or the like as a solvent, which has been cross-linked, is cooled with a gas or / and a liquid to form a fiber by gelation, and the remaining amount of the solvent with respect to the PVA fiber, and boric acid or boric acid There is disclosed a method of performing a step such as washing with water to adjust the remaining amount of the acid salt and the like. In addition, the amount of boric acid or borate added is 0.1%.
If the content is less than 05% by weight, effects such as a decrease in PVA concentration due to a thickening effect are hardly observed, and it is described that a target PVA fiber is difficult to obtain. However, in the spinning method,
A large amount of boric acid or borate added,
There is a problem that the pH adjustment of the spinning stock solution is essential and that the residual amount of boric acid or borate after spinning is essential.

In both of the above publications, a large amount of boric acid or borate is added to the spinning dope, so that the viscosity (spinning pressure) of the spinning dope tends to increase with time.
As a result, it is difficult to spin the PVA fiber stably. In the latter (Japanese Patent Publication No. 7-6087), it is described that the lower limit of the amount of boric acid added is 0.05% by weight.
The lower limit at which the effect of lowering the VA concentration can be expected is shown. This corresponds to a numerical value exceeding the range of “the viscosity of the spinning dope does not increase due to pH” which is the reason for the upper limit of the amount of boric acid added in the present invention. Although the latter and the present invention cannot be directly compared with each other because of the difference in the basic configuration, they can be said to be clearly distinguishable without overlapping the scope of the present invention.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for spinning a PVA fiber in which an undiluted spinning solution of a PVA aqueous solution is wet-spun into a coagulation bath of an inorganic salt. It is intended to be relatively inexpensive and easily manufactured.

[0007]

Means for Solving the Problems The present inventors have found that the object of the present invention can be achieved by adding a small amount of boric acid and a borate to a spinning dope, and have accomplished the present invention. Although the purpose and basic constitution are different from those of the present invention, a method utilizing boric acid or a borate (Japanese Patent Laid-Open No. 62-1499).
No. 09, Japanese Patent Publication No. 07-6087).
That the spinning pressure is constant with respect to the spinning time, that the pH adjustment of the spinning solution and the coagulation bath is not essential, that a boric acid or borate removal step is not required after spinning,
Effect was found.

That is, the present invention provides a method of spinning a spinning solution of a polyvinyl alcohol aqueous solution containing 0.005 to 0.1% by weight of boric acid or borate with respect to polyvinyl alcohol by wet spinning. Spinning method of alcohol fiber. (2) The method for spinning polyvinyl alcohol fiber as described in (1) above, wherein the coagulation bath is a sulfate aqueous solution. It is.

Hereinafter, the present invention will be described in detail. The PVA used in the present invention preferably has a saponification degree of 90% or more, and below this, no sufficient effect is observed. The degree of polymerization is not particularly limited, but is preferably 500 or more which is usually used. The spinning solution can be adjusted by adding boric acid or borate to the above PVA aqueous solution. As the borate, for example, sodium borate, potassium borate, ammonium borate and the like are suitably used. Boric acid or borate is used in an amount of 0.005 to PVA in the spinning dope.
It is preferably added in an amount of 5 to 0.1% by weight, particularly 0.01% by weight.
~ 0.05% by weight is preferred. When the amount is less than 0.005% by weight, a sufficient effect is not recognized.
When the amount exceeds the above range, the gelling ability of the PVA aqueous solution becomes large, and the pH causes an increase in the viscosity of the spinning solution and a sharp increase in the spinning pressure during spinning. Unless a special boric acid removing step or a super-stretching step is carried out in the subsequent step, boric acid becomes P
It remains in a large amount in the VA fiber and inhibits crystallization of PVA.
The method of adding boric acid and borate is not particularly limited,
Addition by batch or addition by injection can be performed.

The stock solution for spinning of the present invention has no problem in the stability of the stock solution for spinning as compared with the case where boric acid is not added.
Handling is easy. The stability of the spinning dope of the present invention means that no gelling or a sharp increase in viscosity of the spinning dope is observed over time. PH of spinning solution
Is not particularly limited, but is preferably adjusted within a range that does not cause corrosion of the apparatus, that is, it is preferably adjusted at pH 3 to 11. Usually, PVA and boron have a pH of about 5.
It is known that gelation occurs at 5 or more, but the ability to gel at the amount of boric acid added according to the present invention is extremely low, and even if the pH is 5.5 or more, it can be used without any problem.

The P of the spinning dope adjusted as described above
The VA concentration is preferably from 5 to 35% by weight, and additives such as an antioxidant, an ultraviolet absorber and a pigment can be added to the spinning dope if necessary.

In the present invention, dehydrating inorganic salts such as sodium sulfate and ammonium sulfate are used as a coagulation bath. An improvement in spinnability is observed at any pH,
The pH range is not particularly limited, and conventionally known coagulation bath conditions are sufficient.

As described above, the spinnability is improved, and PVA fibers with few single yarn breaks can be obtained. INDUSTRIAL APPLICABILITY The present invention can be applied without any problem in the production of wet PVA fibers containing no boric acid in the spinning solution, and does not affect the fiber properties.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the present invention, the measurement of abnormal fiber and fiber properties caused by spinnability and single yarn breakage was carried out by the following methods. Single yarn break: By observing the vicinity of the spinneret, 1
The number of the fibrous materials cut in 0 minutes floating in the coagulation bath was measured. Abnormal fiber: The obtained PVA fiber is cut into about 5 mm,
500 g of the fibers were dispersed in water, and a mass of abnormal fibers was selected by a flat screen having a width of 0.5 mm, and the number thereof was measured. Water swelling degree: The obtained PVA fiber was swollen in a large amount of water at 20 ° C. for 1 hour, and after taking out the swollen fiber and removing excess water, it was centrifugally dehydrated at 11 cm and 3000 rpm from the center to determine its weight. The sample was dried at 100 ° C. for 3 hours and its weight was determined. The degree of water swelling of the PVA fiber at this time is given by Equation 1.

[0015]

(Equation 1) The degree of water swelling is a measure of the compatibility with water and the PVA molecular network structure. It can be understood that the higher the crystallization of PVA fibers, the lower the degree of water swelling.

Examples 1 and 2 and Comparative Examples 1 and 2 PVA having a polymerization degree of 1600 and a saponification degree of 99.0 mol%, and boric acid having a concentration of 0.05% based on PVA were dissolved in hot water at 90 ° C. Thus, a spinning solution having a PVA concentration of 14% was prepared. This spinning dope was kept at 70 ° C. and extruded from a spinneret having 500 holes into a coagulation bath of saturated sodium sulfate having a pH of 7 at 40 ° C. and spun. The spinning pressure at this time was 2.1 kg /
cm ² , and there was no change in the spinning pressure 5 hours after spinning. The winding speed was 40 m / min. This undrawn yarn was drawn 5 times in a saturated aqueous solution of sodium sulfate at 90 ° C. in order to impart water resistance, and a PVA fiber was obtained. In addition, the polymerization degree was changed to 4800 PVA, and PVA
The concentration was 11%, and the amount of boric acid added was 0.0
3% was added and a PVA fiber was obtained in the same manner as in Example 1. For comparison, spinning was performed in the same manner as in Example 1 when boric acid was not added and when boric acid was added at 3% to PVA.
The spinning pressure in Comparative Example 3 in which 3% of boric acid was added to PVA increased to 4.8 kg / cm ² after 5 hours, indicating an increase in the viscosity of the spinning stock solution. Table 1 shows the results of measuring the single fiber breakage, the abnormal fiber content and the water swelling degree of the obtained fiber. In Examples 1 and 2 to which the boric acid of the present invention was added, single yarn breakage was not observed and a good spinning state was obtained. Single yarn breakage was clearly observed in the vicinity, and stable spinning was difficult. As in Comparative Examples 1 and 2, the spinning pressure in Examples 1 and 2 did not show a sharp rise even after 5 hours from the spinning. Five hours after the spinning, the spinning pressure increased greatly and spinning was no longer possible. Furthermore, the PVA obtained in Example 1, which is the spinning conditions of the present invention,
Although the water swelling degree of the fiber showed the same value as that of Comparative Example 1 in which boric acid was not added, the water swelling degree of the PVA fiber obtained in Comparative Example 3 was higher than that of Example 1 and Comparative Example 2, The result was a change in fiber properties.

[0017]

[Table 1] * 1 Boric acid concentration:% by weight (vs. PVA). * 2 Single yarn break: individual / 10 minutes. * 3 Abnormal lumpy fiber: individual / 500 g. * 4 Spinning pressure: kg / cm ² .

[0018]

According to the present invention, it is possible to produce a PVA fiber having a very good spinnability and a very small amount of agglutinated fibers and single-thread broken fibers as compared with the conventional PVA wet spinning method. Also, there is no problem in the stability of the spinning solution,
This is an industrially advantageous production method that does not affect the physical properties of PVA fibers and can be easily applied to conventional spinning methods.

Claims (2)

[Claims] 1. A method for spinning a polyvinyl alcohol fiber, comprising spinning a spinning solution of a polyvinyl alcohol aqueous solution containing 0.005 to 0.1% by weight of boric acid or borate based on polyvinyl alcohol by wet spinning. Law. 2. The method according to claim 1, wherein the coagulation bath is a sulfate aqueous solution.