JPH07305222A - Method for producing polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:To provide a method for producing polyvinyl alcohol(PVA) fiber having a high strength and a high initial elastic modulus. CONSTITUTION:This method for producing the PVA fiber comprises dissolving PVA in a solvent, subjecting the prepared spinning raw solution to a dry.wet spinning process in a coagulating bath, and subsequently heating and drawing the formed undrawn fiber, after once wound up or continuously. The characteristics of the method comprise (a) using a spinning raw solution comprising the mixture of (A) a PVA having an average polymerization degree of 3000-5000 with (B) a PVA having an average polymerization degree of 4000-7000, the average polymerization degree being higher than that of the PVA (A), in an A/B weight ratio of 95:5 to 70:30, and further (b) using a spinneret having an extrusion hole with a hole diameter of <=1mm and an L/D ratio of >=3 between the length L and diameter D of the hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having high strength and high initial elastic modulus.

[0002]

2. Description of the Related Art PVA fiber has high strength and high initial elastic modulus among general-purpose fibers, and has rubber hose, conveyor belt, cement reinforcing fiber, material sewing thread, tatami thread, fishing net, land net, heavy cloth, Widely used as a fiber for industrial materials such as ropes.

In addition, various attempts have been made to increase the strength and initial elastic modulus of PVA-based fibers in response to the demands of the increasingly sophisticated market in recent years. For example, Japanese Examined Patent Publication No. 3-75644 discloses a weight average. A method is disclosed in which a glycerin solution of PVA having a molecular weight of 500,000 or more is gel-spun in a cooling bath to remove glycerin in the solidified yarn, and then hot drawing is performed. In Japanese Patent Publication No. 6-11927, a solution of PVA in dimethyl sulfoxide (hereinafter abbreviated as DMSO) having a degree of polymerization of 2600 or more is dry / wet spun in a methanol bath, and the obtained undrawn yarn is heated. A method of stretching is disclosed.

These methods reduce the entanglement of molecular chains by using a low-concentration solution of highly polymerized PVA as a spinning stock solution, and use this solution for gel spinning or dry / wet spinning to obtain an undrawn yarn. It is intended to obtain a high-strength fiber by improving the drawability and drawing a stretched chain structure by drawing at a high ratio in a hot drawing process.

Further, in Japanese Patent Laid-Open No. 3-33211, at least a PVA-based polymer having an average degree of polymerization of 3000 or more as a main component and an average degree of polymerization of 15000 or more is used.
A method for producing a PVA-based fiber having excellent hot water resistance by using a PVA-based polymer containing 10% by weight or more and having a difference in average degree of polymerization of both polymers of 5000 or more is disclosed.

However, the methods described in Japanese Examined Patent Publication No. 3-75644 and Japanese Patent Laid-Open No. 3-33211 are difficult to obtain commercially, and high-pricity PVA of high price is used. Since this is a disadvantageous method in terms of raw material cost and manufacturing cost, industrial implementation is difficult. The method described in Japanese Examined Patent Publication No. 6-11927 has the above-mentioned drawbacks, but is an object of the present invention.
It was not possible to obtain fibers having a high strength of 22 g / d or more.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Although various attempts have been made to increase the strength and initial elastic modulus of A-type fibers, they are disadvantageous in terms of cost, difficult to carry out industrially, and obtain fibers with a high strength of 22 g / d or more. I couldn't. Therefore, an object of the present invention is to provide a method for producing a PVA-based fiber having a high strength of 22 g / d or more and a high initial elastic modulus from a commercially available PVA with high productivity.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have surprisingly found that two kinds having different average degrees of polymerization (hereinafter abbreviated as polymerization degrees) are used. When a spinning dope containing PVA in which PVA of the above is mixed in a specific ratio is subjected to dry and wet spinning using a spinneret having a specific pore size, the molecular chains of the mixed PVA with a high polymerization degree are uniformly distributed in the PVA with a low polymerization degree. The non-stretched yarn with high stretchability is obtained without lowering the concentration of PVA in the spinning dope by dispersing PVA by dispersing it in a high-strength and high initial elastic modulus. The present invention has been achieved by finding that a PVA-based fiber having

That is, according to the present invention, a spinning stock solution prepared by dissolving PVA in a solvent is dry / wet spun in a coagulation bath to form an undrawn yarn, and the undrawn yarn is once wound,
Or, when producing a PVA fiber by continuous hot drawing, (a) PVA having an average degree of polymerization of 3,000 or more and 5,000 or less.
(A) and the average degree of polymerization is 4,000 or more and 7,000 or less, and
Using a spinning dope prepared by mixing PVA (B) having a higher degree of polymerization than PVA (A) so that the weight ratio of A and B is 95: 5 to 70:30, and (b) the pore diameter D is A method for producing a PVA-based fiber is characterized by using a spinneret having a discharge hole of 1 mm or less and a ratio (L / D) of a hole length L to a hole diameter D of 3 or more. It is a thing.

[0010] Incidentally, the degree of polymerization P _a in the present invention, JI
PV measured by the PVA test method described in S-K6726
It is calculated from the intrinsic viscosity [η] of the aqueous solution A by the following formula. log P _a = 1.613 × log ([η] × 10 ⁴ /8.29)

The present invention will be described in detail below.

The degree of polymerization of the low degree of polymerization PVA (A) used in the present invention must be 3000 or more, preferably 3500 or more. When the degree of polymerization of PVA (A) is lower than 3000, the strength of the obtained fiber becomes low and the object of the present invention cannot be achieved. The upper limit of the degree of polymerization of PVA (A) is 5000 from the viewpoint of polymer cost.

On the other hand, the degree of polymerization of high degree of polymerization PVA (B) is
In order to improve the strength of the obtained fiber, it must be higher than the polymerization degree of PVA (A) and not less than 4000. The upper limit of the degree of polymerization of PVA (B) is 7,000 in terms of polymer cost and manufacturing cost. These PVA
The saponification degree of (A) and (B) is preferably 99 mol% or more.

The present inventors have made a detailed study on the mixing ratio of these PVAs, and as a result, have found that the low polymerization degree PVA (A)
It has been found that it is important to mix PVA (B) having a high degree of polymerization with a weight ratio of 95: 5 to 70:30. When the mixing ratio of the high polymerization degree PVA (B) is smaller than the above range, the effect of mixing the high polymerization degree PVA (B) becomes small, and the strength and initial elastic modulus of the obtained fiber are not improved. I cannot achieve my purpose. On the other hand, high degree of polymerization PV
If the mixing ratio of A (B) is larger than the above range, the entanglement of the molecular chains having a high degree of polymerization PVA (B) will increase and the drawability of the undrawn yarn obtained will decrease, so the concentration of PVA in the spinning solution will be low. This is not preferable because it leads to an increase in manufacturing cost.

In the present invention, these PVA are dissolved in a solvent to prepare a spinning dope. As the solvent, DMS
O, glycerin, ethylene glycol, 1,3-dimethyl-2
-Imidazolidinone, water, etc. or a mixed solvent thereof can be mentioned, but DMSO is particularly preferably used.

As a method of mixing two types of PVA having different degrees of polymerization, a method of mixing each PVA in a solid state before dissolving it in a solvent, or a method of dissolving each PVA individually in a solvent Examples thereof include a method of mixing in a solid state, but a method of mixing in a solid state is simple and preferable.

The concentration of PVA in the spinning dope is
The content of both (A) and (B) is preferably 5 to 35% by weight, more preferably 10 to 30% by weight. Dissolution is preferably carried out at 80 to 120 ° C. in a nitrogen atmosphere because decomposition and deterioration of the polymer can be prevented.

Further, a cross-linking agent, a heat-resistant agent, a pigment, etc. may be mixed in the spinning dope solution to the extent that the drawability of the undrawn yarn is not lowered, in order to increase the saponification degree of the final fiber and enhance the hot water resistance. You may mix an alkaline component with. Also, PV
A small amount of the third PVA having a polymerization degree different from those of A (A) and (B) may be mixed.

In the present invention, the stock solution for spinning prepared as described above is subjected to dry / wet spinning in a coagulation bath through an air gap, in which case the pore diameter D is 1 mm or less and the pore length is It is extremely important to perform spinning using a spinneret having a discharge hole having a ratio of L to the hole diameter D (L / D) of 3 or more.

That is, as a result of a detailed study by the present inventors on the spinneret for dry and wet spinning, the diameter D of the discharge hole was 1 mm.
Below, preferably below 0.7mm, more preferably below 0.5mm
Below, when dry / wet spinning is performed using a spinneret having a discharge hole having a ratio (L / D) of the hole length L and the hole diameter D of 3 or more, preferably 5 to 10, the pressure applied to the discharge hole is It has been found that the so-called nozzle pressure can be increased and the unstretched yarn in which the molecular chains of PVA are uniformly oriented by the shear stress in the discharge holes and the degree of molecular orientation of the molecular chains is improved.

On the other hand, when the diameter D of the discharge hole is larger than 1 mm or the L / D of the discharge hole is smaller than 3, the nozzle pressure cannot be increased and the shear stress is small, so that the molecular chain Since the degree of orientation is low, the strength and initial elastic modulus of the obtained fiber cannot be improved.

The size of the air gap in dry / wet spinning is not particularly limited, but is preferably 20 to 100 mm.

As the coagulation bath, alcohols such as methanol and ethanol, acetone and a mixture of these and a solvent of PVA can be used, but methanol is preferably used.

After removing the solvent (for example, DMSO) in the solidified yarn obtained by dry and wet spinning with a solvent such as methanol, an oil agent is added and dried to obtain an undrawn yarn.
At this time, if desired, a catalyst for promoting a dehydration reaction such as phosphoric acid or p-toluenesulfonic acid is added to the oil agent, and a dehydration reaction is performed in a subsequent hot drawing step to enhance the hot water resistance. May be.

The unstretched yarn obtained above is once wound or continuously supplied to the hot stretching step and subjected to hot stretching. The draw ratio during hot drawing is not particularly limited, but in order to improve the strength and initial elastic modulus of the obtained fiber,
It is preferably 15 times or more, more preferably 17 times or more. Further, the stretching speed is preferably 20 m / min or more.

The hot stretching can be performed by various methods.
For example, there are a method of drawing while contacting an undrawn yarn with a heating body such as a heat plate, a method of drawing in a heating medium, a method of drawing in a hot air heating bath, and a method of drawing by a dielectric heating method. A hot air heating bath is preferably used. The temperature during hot stretching is not particularly limited,
For example, when drawing in a hot air heating bath, it is preferable to set the yarn inlet temperature to 200 ° C or higher and the outlet temperature to 270 ° C or lower.

According to the present invention, PVA fibers having a high strength of 22 g / d or more and a high initial elastic modulus are produced at low cost and with good productivity by using commercially available PVA having a polymerization degree. It is possible.

[0028]

In the present invention, the PVA fiber having a high strength and a high initial elastic modulus of 22 g / d or more can be obtained by mixing the spinning solution prepared by mixing the low polymerization degree PVA and the high polymerization degree PVA with the pore size Of 1 mm or less and L / D of 3 or more, when dry and wet spinning is performed using a spinneret having discharge holes, the molecular chains of the high degree of polymerization PVA are dispersed uniformly in the low degree of polymerization PVA and are low. It is considered that the polymerization degree PVA is connected, and the degree of molecular orientation is improved by the shear stress in the discharge hole, resulting in an undrawn yarn structure in which the entanglement of PVA molecular chains is suppressed, and high-magnification drawing is possible. .

[0029]

EXAMPLES Next, the present invention will be specifically described by way of examples.

Examples 1-2 and Comparative Examples 1-2 As shown in Table 1, PVA having a polymerization degree of 4000 and PVA having a polymerization degree of 5500 were mixed at a weight mixing ratio of 100: 0 (Comparative Example 1, polymerization degree of 40).
00 PVA only), 85:15 (Example 1), 75:25 (Example 2), and 60:40 (Comparative Example 2) so that the concentration of PVA was 14.5% by weight. To be 100 ℃
Was dissolved in DMSO to prepare a spinning dope.

This spinning solution was prepared by using a stainless steel spinneret having 150 discharge holes each having a hole diameter D of 0.5 mm and a hole length L of 2.5 mm (that is, L / D = 5). , Discharge linear velocity 6.0 m / min, dry / wet spinning into methanol coagulation bath through 30 mm air gap, then D with methanol
After removing MSO, 1.3% by weight of an oil agent containing polyoxyethylene sorbitan trioleate as a main component was added,
Further, it was dried at 90 ° C. to obtain an undrawn yarn.

Next, these undrawn yarns were set to have a yarn inlet temperature of 200.degree. C. and an outlet temperature of 240.degree.
m hot air heating bath at a drawing speed of 30 m / min and hot drawing at a draw ratio of 90% of the maximum draw ratio. Table 1 shows the production conditions and the performance of the obtained fiber.

[0033]

[Table 1]

As is clear from Table 1, the fibers obtained in Examples 1 and 2 have high tensile strength and high initial elastic modulus,
It had excellent performance. On the other hand, in Comparative Example 1 in which only PVA having a low degree of polymerization was used, the draw ratio could be increased, but only fibers having low strength were obtained, and P
In Comparative Example 2 in which the mixing ratio of VA was large, the draw ratio was not high, and high-strength fiber was not obtained.

Example 3, Comparative Example 3 As shown in Table 2, PVA having a degree of polymerization of 4500 and 2100 were mixed with PVA having a degree of polymerization of 6200 at a weight mixing ratio of 90:10. Each PVA has a concentration of 12.0
A stock solution for spinning was prepared by dissolving it in DMSO so that the concentration was 19.0% by weight.

These spinning stock solutions were discharged using a stainless spinneret having 300 discharge holes each having a hole diameter of 0.3 mm and a hole length of 3.0 mm (L / D = 10). 10m /
Dry and wet spinning was performed in a methanol coagulation bath through a 30 mm air gap in minutes.

Then, after removing DMSO in the fiber with methanol, the dehydration reaction was promoted by mixing phosphoric acid in an oil agent containing polyoxyethylene sorbitan trioleyl ether as a main component so that the concentration became 0.5 N. Add the catalyst solution to 1.
An unstretched yarn was obtained by applying 0% by weight and further drying at 90 ° C. This undrawn yarn was hot-drawn in the same manner as in Example 1 to obtain a drawn yarn. Table 2 shows the production conditions and the performance of the obtained fiber.

[0038]

[Table 2]

As is clear from Table 2, the fiber obtained in Example 3 had both high tensile strength and initial elastic modulus and excellent performance. On the other hand, in Comparative Example 3 mainly composed of PVA having a degree of polymerization of 2100, the draw ratio could be increased, but the strength of the obtained fiber was low.

Comparative Example 4 Same as Example 1 except that a spinneret made of stainless steel having 150 discharge holes each having a hole diameter of 1.5 mm and a hole length of 5 mm (L / D = 3.33) was used. The PVA fiber was manufactured as follows, but only the hot drawing of 15.1 times was possible, and the strength of the obtained fiber was
Only 13.2 g / d.

Comparative Example 5 Same as Example 1 except that a stainless steel spinneret having 150 discharge holes each having a hole diameter of 0.5 mm and a hole length of 1 mm (L / D = 2) was used. The PVA fiber was manufactured as follows, but only the 16.3 times hot drawing was possible, and the strength of the obtained fiber was
Only 14.1 g / d.

[0042]

According to the present invention, a PVA fiber having a high strength of 22 g / d or more and a high initial elastic modulus is produced from a commercially available PVA having a polymerization degree at a low cost with high productivity. It becomes possible.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoji Ichise, 23 Uji Kozakura, Uji City, Kyoto Prefecture, Unitika Stock Company Central Research Laboratory (72) Inventor Yoshihiro Akiyama, 23 Uji Kozakura, Uji City, Kyoto Unitika Stock Company Central In the laboratory

Claims (1)

[Claims] 1. A spinning stock solution prepared by dissolving polyvinyl alcohol in a solvent is dry / wet spun in a coagulation bath to form an unstretched yarn, and the unstretched yarn is once wound or continuously heated. When a polyvinyl alcohol fiber is produced by stretching, (a) polyvinyl alcohol (A) having an average degree of polymerization of 3000 or more and 5000 or less, and polyvinyl alcohol (A) having an average degree of polymerization of 4000 or more and 7,000 or less Polyvinyl alcohol (B) having a higher degree of polymerization than that of (1) is used in such a manner that the weight ratio of A and B is 95: 5 to 70:30. (B) Pore diameter D is 1 mm or less. And a spinneret having a discharge hole having a ratio (L / D) of the hole length L to the hole diameter D of 3 or more is used.