JPH01104815A - Polyvinyl alcohol fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the titled fiber with high strength and high modulus, outstanding in hot water resistance, by extruding through a spinneret a PVA-based polymer solution and hot-drawing of the resultant undrawn yarn at high draw ratio followed by treatment with an aqueous boric acid solution and hot-drawing again etc. CONSTITUTION:First, a PVA-based polymer with a polymerization degree of <=1,500 (pref. 1,500 to 4,500) is dissolved in a solvent and the resulting solution is extruded through a spinneret followed by cooling. Thence, the (pseude) gel-like undrawn yarn obtained is subjected to hot-drawing by a factor of >=7 followed by treatment with an aqueous boric acid solution and then performing either hot drawing again or heat treatment, thus obtaining the objective fiber having the following characteristics: 1. tenacity...>=15g/d 2. initial tensile modulus...>=300 g/d (pref.>=500g/d) 3. hot water dissolution temperature...>=115 deg.C (pref.>=120 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having high strength and high modulus and excellent hot water resistance, and a method for producing the same.

(Prior technology) Conventional PVA fibers have higher strength and higher modulus than nylon, polyester, and polyacrylonitrile fibers, and have recently been used not only as fibers for industrial materials but also as asbestos substitute fibers for concrete reinforcement. However, its use in applications such as tire cords and plastic reinforcing materials is severely limited because its strength in hot water or heat is significantly reduced, and the advantages of PVA-based fibers such as adhesiveness and weather resistance are limited. It's hardly utilized.

Such PVA-based fibers are usually manufactured by a method of wet spinning in a coagulable inorganic salt aqueous solution using a PVA aqueous solution as a spinning stock solution, and then subjected to treatments such as stretching, drying, and heat treatment. However, the strength of this PVA-based fiber is , various methods have been proposed to improve the elastic modulus.

For example, Japanese Patent Publication No. 48-9209 discloses a method in which a spinning dope is prepared and then subjected to highly dry heat stretching. (initial tensile resistance)
A type fiber is obtained.

Japanese Patent Publication No. 43-16675 discloses a method of wet spinning in a coagulation bath of methanol, ethanol, etc. using PVA dissolved in a good solvent such as dimethyl sulfoxide as a spinning stock solution, and using PVA with a polymerization degree of 1750. T!
10.7g/d (7) Tensile strength, 480g/d (
PVA-based fibers having a D elastic modulus (initial tensile resistance) have been obtained.

JP-A-60-126312 discloses a method of performing wet-dry spinning by introducing an air gap using the above-mentioned method.
9.2 g/d (7) PVA-based fibers with a tensile strength of 420 g/d (D elasticity modulus) have been obtained.

On the other hand, P
As for the method applied to VA fiber, Japanese Patent Application Laid-Open No. 59-130
As described in Publication No. 314, the molecular weight is 1.7 million (
Using ultra-high molecular weight PVA with a degree of polymerization of 38,000), it is dissolved in a poor solvent such as glycerin or ethylene glycol,
Tensile strength: 19.2g by rapid cooling in paraffin bath
/d and a high strength PVA fiber with an elastic modulus of 628 g/d. The results of achieving high strength and high elastic modulus of these PVA-based fibers are shown to be largely dependent on the degree of polymerization of the PVA used. It shows that it is advantageous. This is shown in Japanese Patent Publication No. 47-8186, which shows that the strength is 13.0 when the degree of polymerization ranges from 1000 to 3800.
18.28/d171 PVA-based fibers were obtained from 9 g/d. The relationships between strength, elastic modulus and degree of polymerization achieved by the prior art are shown in FIGS. 1 and 2, respectively.

PV with excellent hot water resistance, which is an important objective of the present invention
Conventionally, for A-type fibers, a method has been used in which the fibers after drawing are acetalized to make them water-insolubilized, but there is a problem in that mechanical properties such as strength and elastic modulus are significantly reduced due to acetalization.

Therefore, when high strength and high elastic modulus PV^-based woven fibers are desired, the hot water resistance that improves with high-magnification stretching is simply utilized.
In order to reduce entanglements between molecules in solution A and perform high-magnification stretching, boric acid is added to the PVA/ethylene glycol (or glycerin) solution to moderately stretch PVA. Low concentration solution spinning ~ ultra-stretching. A law is proposed. By this method, using PVA with a polymerization degree of 3400, the strength was 18.4 g.
/d and elastic modulus of 470 g/d, but when the present inventors retested this method, the temperature of dissolution in hot water specified in the present invention was less than 115"C, and after spinning, If unreacted boron remained in the undrawn yarn, high-magnification hot drawing was difficult.

As mentioned above, in order to obtain high strength and high elastic modulus PVA fibers, ultra-high polymerization degree P described in JP-A-59-130314 is used.
Although it is advantageous to use VA, it is difficult to obtain it commercially because it is obtained by a very special polymerization method, and such ultra-high polymerization degree PVA has low solubility in solvents. There is a problem that it is difficult to produce silk industrially.

On the other hand, commercially available polymerization degrees (1500 to 4500
As shown in Figures 1 and 2, when using PVA with a strength of 20 g/d and an elastic modulus of 480 g/d, an OPVA fiber with a strength of 20 g/d and an elastic modulus of 480 g/d was obtained, but an elastic modulus of 500 g/d or higher was not achieved. The problem is that it doesn't. Furthermore, an essential problem with PVA-based fibers is that they have low heat resistance in the presence of water, that is, low hot water resistance and moist heat resistance.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional drawbacks of high-strength, high-modulus PVA-based fibers and methods for producing the same, namely, the following: PVA has a commercially acceptable degree of polymerization (approximately 1,500 to 4,500).
This method solves all of the following problems at the same time: PVA fibers with an initial modulus of elasticity of 500 g/d or higher have not been obtained from PVA fibers, and ■ The essential problem of pv^ fibers is that they have low hot water resistance. The object of the present invention is to provide a PVA fiber having particularly high strength, high modulus of elasticity, and excellent hot water resistance. That is, the object of the present invention is to provide a novel PVA-based fiber that maintains high strength and high elastic modulus comparable to aramid fibers and has significantly improved hot water resistance. Still another object is to provide an industrial manufacturing method for such novel Pv^-based fibers. .

(Means for solving the problems) That is, the present invention provides: (1) a polymer with a degree of polymerization of 1500 or more and a tensile strength of 15 g/
polyvinyl alcohol fiber having an initial tensile resistance of 300 g/d or more, and a hot water dissolution temperature as defined in the text of 115° C. or more; (2) Polymerization A polyvinyl alcohol-based polymer having a polyvinyl alcohol-based polymer having a polyvinyl alcohol content of 1,500 or more is dissolved in a solvent for the polyvinyl alcohol-based polymer, the solution is extruded from a spinneret, and the solution is cooled and returned to (a) gel-like unstretched fibers or (or) pseudo-gel-like unstretched fibers. This method of producing polyvinyl alcohol fibers is characterized in that the fibers are hot-stretched to a stretching ratio of 7 times or more, then treated with a boric acid aqueous solution, and then hot-stretched or heat-treated.

The present invention will be explained in detail below.

The PVA polymer constituting the fiber of the present invention is at least 1,500 or more, and the upper limit is not particularly limited, but it is about 10,000 or less,
More preferably, it is a completely saponified or partially saponified PVA-based polymer having a degree of polymerization of 1,500 to 4,500.
If the degree of polymerization is less than 1,500, fibers with high strength, high elastic modulus, and excellent hot water resistance, which are the objectives of the present invention, cannot be obtained, and the above-mentioned birch has fibers with a degree of polymerization of 10,000 or more. Only by this method can the high-performance PVA-based fiber defined in the present invention be obtained.

The PVA-based polymer used in the present invention, especially the above-mentioned high polymerization degree P
What is fundamentally important when solution spinning a VA polymer to form a gel-like undrawn fiber is to gel it while preventing the solvent from evaporating as much as possible. There is no structural difference between the inner and outer layers of the fiber, a stable and homogeneous gel-like undrawn fiber is obtained, and the total draw ratio in the subsequent drawing step is improved. If the fibers drawn at a specific draw ratio are subjected to boric acid treatment and then heat treated, the result is a tensile strength of 15 g/d or more.
High-strength, high-modulus PVA-based fibers with an initial tensile resistance of 300 g/d or more, especially high-modulus PVA-based SaW with an elastic modulus of over 500 g/d, and an unprecedented hot water dissolution temperature of 115°C or higher It has been discovered that this can be obtained even if the degree of polymerization is 3500. The details are described below.

The hot water dissolution temperature referred to in the present invention is as described below in detail, but 5 cm of PVA fiber and 10 cm of water were sealed in a sample container at a heating rate of 20"07 min using a differential scanning calorimeter. The peak temperature of the melting curve when the temperature is raised is not particularly limited as long as the PVA polymer can be gelled. Preferably, a spinning stock solution is prepared by sufficiently dissolving the PVA polymer in these solvents (until it becomes transparent), but the concentration of the solution is determined depending on the degree of polymerization of the PVA polymer used in order to minimize the entanglement of the PVA molecular chains. Depending on the situation, it is desirable to keep the concentration as low as possible for spinning. For example, in a PVA/ethylene glycol solution with a polymerization degree of 3500, the concentration is 10
A concentration of ~20% by weight is preferred.

In order to turn the spinning dope prepared in this way into gel spinning, it is important to set the spinning temperature and cooling temperature in relation to the gelation rate of the spinning dope. The spinning temperature is desirably set at a temperature approximately 10 to 15° C. higher than the gelation temperature of the spinning dope, and the longer the time maintained at that temperature, the higher the cooling temperature can be set. Furthermore, it is desirable to use a refrigerant (e.g., decalin, n-paraffin, etc.) that does not displace the solvent of the spinning dope for cooling. This is because a refrigerant that does not replace the solvent of the spinning dope (e.g., methanol, ethanol, etc.) When using spinning fibers, the solvent in the fibers is extracted before the gelation of the spun fibers has fully progressed, resulting in a difference in structure between the inner and outer layers of the undrawn fibers, as seen in wet spinning, resulting in a homogeneous structure. This is because undrawn fibers are difficult to form.
Next, the gel-like undrawn fibers thus formed may be hot-stretched to as high a magnification as possible, but it is preferable to extract the solvent in advance to form pseudo-gel-like undrawn fibers and then heat-draw them. Preferably, before extracting the solvent, the gelled undrawn fibers are allowed to stand at room temperature for at least one hour to allow sufficient syneresis to occur, so that free solvent not bound to the gelled fibers naturally flows out of the fibers. After that, the solvent in the fibers is removed by extraction with methanol etc. or heat drying to make pseudo gel-like unstretched fibers and hot stretching increases the rate of increase in strength and elastic modulus with the stretching ratio. This is because the strength and modulus of elasticity that can be achieved also increase as the strength increases.

The pseudogel-like undrawn fiber thus obtained is stretched at a temperature in the range of 100°C to 220″C, preferably
Stretching is carried out in three stages at a temperature range of 150''C to 210''C.

The distribution of the stretching ratio at each temperature does not need to be particularly limited, but the first stage is 3 to 5 times, the second stage is 2 to 4 times, and the third stage is about 3 times or less, so that the total stretching ratio is as high as possible. The stretching temperature and the stretching ratio may be set so that the stretching temperature and the stretching ratio can be set so that the stretching temperature and the stretching ratio can be set as follows. Although a non-contact type heating plate is used as the stretching device in the present invention, the present invention is not limited to this. In addition, the "pseudo gel-like undrawn fiber" referred to in the present invention refers to an undrawn fiber made only of a polymer from which the solvent contained in the gel-like undrawn fiber obtained by spinning has been completely removed. be.

In order to obtain PVA-based fibers with high strength, high elastic modulus, and excellent hot water resistance, which is the ultimate goal of the present invention, we investigated a method of crosslinking PVA molecules constituting the fibers with boric acid.

That is, the aforementioned pseudogel-like undrawn fibers and drawn fibers having different draw ratios were treated in an aqueous boric acid solution having a concentration of about 1% by weight for 30 minutes, and then hot-stretched or heat-treated. As a result, if the stretching ratio is 7 times or less, the fiber becomes cloudy due to the subsequent hot stretching, making it difficult to stretch at a high stretching ratio, resulting in high strength and
It has been found that the object of the present invention cannot be achieved in terms of high elastic modulus. On the other hand, it has been found that when a drawn fiber with a draw ratio of 7 times or more is treated with an aqueous boric acid solution, the object of the present invention can be achieved by subsequent hot drawing or heat treatment.

Note that it was more effective to obtain the high-performance PVA-based fiber, which is the object of the present invention, by immersing the drawn yarn after three-stage drawing in an aqueous boric acid solution and then heat-treating it under tension. Therefore, it is believed that the method of the present invention, which imparts hot water resistance to PVA fibers by treating them with an aqueous boric acid solution, will be equally effective for high-strength, high-modulus PVA fibers obtained by methods different from the present invention. It will be done.

The PVA fiber thus obtained has a degree of polymerization of 1500 or more, preferably 1500 to 4500, a tensile strength of 15 g/d or more, and an initial tensile resistance of 300 g/d.
As mentioned above, it preferably has the characteristics of 500 g/d or more and a hot water dissolution temperature of 115° C. or more, preferably 120° C. or more.

In addition, one of the characteristics is that the fiber contains boron.

(Function) As shown in Comparative Example 3, which will be described later, when a pseudogel-like undrawn fiber is impregnated with a boric acid aqueous solution and hot-stretched, the fiber becomes cloudy and cannot be stretched sufficiently.This is because water evaporates during hot-stretching. This is not due to the formation of voids during hot stretching (it is thought that boron crosslinks between PVA molecules during hot stretching, resulting in a significant increase in internal strain due to stretching. Similarly, as shown in Comparative Example 4.5 below) Similarly, in a method in which boric acid is added to the spinning dope in advance, excess boric acid is removed from undrawn fibers in which pv^ molecules are moderately crosslinked with boron, and the fibers are then hot stretched, clouding occurs and insufficient stretching is performed. As a result, PVA fibers with high strength, high elastic modulus, and excellent hot water resistance, which are the objectives of the present invention, have not been obtained. The object of the present invention is achieved by stretching to a certain extent to advance oriented crystallization, then impregnating the amorphous part with a boric acid aqueous solution and hot stretching or heat treatment to crosslink the PVA molecules in the amorphous part with boron. As a result of conducting research based on this, we have found that novel PVA fibers, which are the object of the present invention, can be produced even if the boron content is relatively small, as shown in the examples below. is obtained.

Next, a method for testing and measuring characteristic values used in the present invention will be explained.

<Hot water resistance test method> Using a high-performance differential scanning calorimeter (DSC-10^) manufactured by Rigaku Denki, 5 cm of sample PVA-based fiber and 10 cm of water were sealed in the same sample container, and the temperature was increased at a heating rate of 20゛C/ The peak temperature of the melting curve of the PVA-based fiber obtained when the temperature was raised in minutes was determined, and this was defined as the "temperature at which it dissolves in hot water" as specified in the present invention. Becomes pressurized water
The temperature at which it dissolves in hot water can be measured even at temperatures above 100°C. Furthermore, in the present invention, "excellent hot water resistance" means that the temperature is high.

Method for measuring the strength and elastic modulus of drawn fibers〉JIS-L
-1017. That is, the sample PVA fiber was heated to 20°C165%R.
After leaving it in the H atmosphere for 24 hours, "Tensilon" U
It was measured using a TM-4L type tensile tester at a sample length of 3C11 and a tensile rate of 3C1/min. The load obtained here~
The elastic modulus was measured from the elongation rate curve according to the definition of JIS-L-1017.

<Measurement method of boron content> It was determined by gravimetric method. That is, the weight of the fiber before immersion in the boric acid aqueous solution (-〇) and the weight (W) of the fiber after being immersed in the boric acid aqueous solution and after thoroughly drying and removing the water contained in the fiber at room temperature. , was calculated using the following formula.

10 (Example) Examples will be shown below, but the present invention is not limited to these examples.

(Examples 1-2) Completely saponified PV with a degree of polymerization of 2000 and 3500 (degree of saponification of 99% or more), A in ethylene glycol
The mixture was dissolved at 60°C to prepare a spinning dope having a PVA concentration of 20.15% by weight. After defoaming, these solutions were held at a temperature of 115°C and 1110°C and extruded into the air through a spinneret with a hole of 0.2 mm, and 50III
Cooled by passing through a 0° C. decalin bath under Il. After leaving the gel-like undrawn fiber obtained by cooling at room temperature for 1 hour,
The ethylene glycol contained in the gel-like fibers is extracted with methanol, and the resulting pseudo-gel-like undrawn fibers are heated at 150° C. by 3 times and heated to 200° C. using a non-contact heating plate.
It was stretched 3.4 times at ℃ and 1.8 times at 210℃.

The thus obtained drawn fibers were immersed in a 1% by weight boric acid aqueous solution for 30 minutes, and then subjected to tension heat treatment at 210°C. As a result, PVA fibers with high strength, high elastic modulus, and excellent hot water resistance as shown in Table 1 were obtained.

(Comparative Examples 1 and 2) In Examples 1 and 2, the results of the drawn fibers before being immersed in the boric acid aqueous solution are shown in Table 1 as Comparative Example 1.2. In either example, the temperature at which it dissolves in hot water is low, and its hot water resistance is extremely poor.

(Example 3) The pseudogel-like undrawn fibers obtained in Example 2 (PVA with a degree of polymerization of 3500) were stretched 3 times at 150°C and 3 times at 200°C. After being immersed in an aqueous solution for 10 minutes, it was stretched 1.8 times at 210''C.As a result, as shown in Table 1, PVA fibers targeted by the present invention were obtained.

(Comparative Example 3) After immersing the pseudogel-like undrawn fibers of Example 3 in a 1% by weight boric acid aqueous solution for 10 minutes,
When the fibers were stretched 3.4 times at 200°C, the fibers became cloudy and three-stage stretching at 210°C could not be performed.

As a result, in terms of strength and elastic modulus, P
VA fiber was not obtained. Note that similar results were obtained even when the boric acid aqueous solution concentration was set to 0.5% by weight.

(Example 4) Gel-like undrawn fiber obtained in Example 2 (polymerization degree 3500
') at room temperature for 1 hour, the gel-like fibers were
3 times at 'C, 4 times at 150℃, 1.8 at 200℃
The ethylene glycol solvent was removed by stretching the film twice. The drawn fibers were immersed in a boric acid aqueous solution (1% by weight) for 30 minutes, and then subjected to tension heat treatment again at 200°C. As shown in Table 1, the PVA fibers targeted by the present invention were obtained.

(Comparative Example 4) When dissolving PVA with a degree of polymerization of 3400 in ethylene glycol, 4% by weight of boric acid was added to I'VA and further p
To make H-6 to 7, a small amount of sodium hydroxide was added and dissolved at 160°C. The PVA degree was 15% by weight. This spinning stock solution is discharged from a 0.2- spinneret,
It was cooled in air to form a gel. Subsequently, the film was passed through a first bath of water, and when a portion of boron was removed, the solvent was extracted in a second bath of methanol while stretching the film approximately 1.3 times.

Next, methanol and water in the spun yarn were evaporated with hot air at 70'C, and the yarn was wound onto a bobbin. The obtained spun yarn was
Although drawn fibers were obtained by hot drawing at 5° C. about 10 times, as shown in Table 1, the PVA-based fibers targeted by the present invention were not obtained.

(Comparative Example 5) A spinning stock solution prepared by adding 2% by weight of boric acid to the PVA to a 16-fold aqueous solution of PVA with a degree of polymerization of 1750 was spun into a sodium hydroxide alkaline aqueous solution of Glauber's sulfate, and after hot stretching, it was washed with water to form PVA. After drying, leaving 0.3% by weight of boric acid, it was hot-stretched at 240'C by about 15 times. The physical properties of the drawn fiber thus obtained are shown in Table 1, indicating that the PVA fiber targeted by the present invention could not be obtained.

(Effect of the invention) PVA-based fibers have relatively high strength and high modulus among general-purpose polymer fibers such as nylon, polyester, and polyacrylonitrile fibers, but their strength decreases significantly in hot water or at high temperatures. Therefore, its use in applications such as tire cords and plastic reinforcing materials is severely restricted. Currently, commercially available high-strength, high-modulus PVA fibers have a strength of about 13 g/d, an elastic modulus of about 300 g/d, and a melting temperature in hot water of 114°C or lower (corresponding to Comparative Example 5). be. - The strength of the strength is 15 g/d or more, the elastic modulus is 300 g/d or more, and the temperature at which it dissolves in hot water is 115°C.
Since the new PVA fiber has been obtained, it can now be used as a material for tire cord belts, and has the effect of significantly expanding the scope of use in plastic reinforcing materials, lobes, cables, etc.

In addition, according to the present invention, the adhesive properties, which are the advantages of PVA-based fibers,
Since it takes advantage of its weather resistance, it can be expected that its fields of use will further expand. From the above, the industrial significance of the present invention is great.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between molecular weight (or degree of polymerization) and strength of the fibers of the present invention and the fibers described in known prior patents. FIG. 2, like FIG. 1, is a diagram showing the relationship between molecular weight (or degree of polymerization) and elastic modulus (initial tensile resistance). Note that the symbols in the figure indicate the following fibers. ■ Fiber of the present invention ◎ Fiber described in JP-A-60-126311 ■
JP 61-108711 MU JP 43-16675 〃8 JP 59-130314 ◇ JP 48-9209 ・ JP 47-8186 ◎14 Yaku 6O-126311 A gal 59-130314 Mu$' 1g43-16675 ■ stop invention

Claims (6)

[Claims] (1) Polyvinyl alcohol fibers with a degree of polymerization of 1500 or higher, a tensile strength of 15 g/d or higher, and an initial tensile resistance of 300 g/d or higher, and a hot water dissolution temperature of 115°C or higher as defined in the text. A polyvinyl alcohol fiber characterized by: (2) The polyvinyl alcohol fiber according to claim 1, which has a hot water dissolution temperature of 120° C. or higher. (3) The polyvinyl alcohol fiber according to claim 1 or 2, wherein the polyvinyl alcohol fiber contains boron in the fiber. (4) The polyvinyl alcohol fiber according to any one of claims 1 to 3, which has a degree of polymerization of 1,500 to 4,500. (5) A polyvinyl alcohol-based polymer having a degree of polymerization of 1500 or more is dissolved in a solvent for the polyvinyl alcohol-based polymer, the solution is extruded from a spinneret, and the resulting (a) gel-like undrawn fiber or ( b) A method for producing polyvinyl alcohol fibers, which comprises hot-stretching pseudogel-like unstretched fibers until the stretching ratio becomes 7 times or more, then treating the fibers with an aqueous boric acid solution, and subsequently hot-stretching or heat-treating the fibers. (6) The degree of polymerization of the polyvinyl alcohol polymer is 150
0 to 4,500, the method for producing polyvinyl alcohol fibers according to claim 5.