JP2856837B2 - Polyvinyl alcohol fiber and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having excellent strength, modulus of elasticity and hot water resistance, and a method for producing the same, particularly for industrial materials. And a PVA fiber suitable for reinforcing a composite material.

<Conventional technology> Conventional PVA fiber has higher strength and higher modulus than polyamide, polyester, and polyacrylonitrile fibers, and is used not only as a fiber for industrial materials, which is its main application, but also as a substitute fiber for asbestos in recent years. Is about to be used.

However, the PVA fibers obtained so far do not have the high strength and the jurass like aromatic polyamide (aramid) fibers and ultrahigh molecular weight polyethylene fibers.

PVA fiber is usually manufactured by wet spinning in a coagulable inorganic salt aqueous solution using a PVA aqueous solution as a spinning solution and subjecting it to stretching, drying, heat treatment, etc., to improve the strength and elastic modulus of this PVA fiber. Various methods have been proposed to achieve this.

For example, Japanese Patent Publication No. Sho 43-16675 discloses a method in which a solution of PVA in dimethyl sulfoxide (hereinafter abbreviated as DMSO) is wet-spun as an undiluted spinning solution in an organic solvent such as methanol, ethanol, benzene or chloroform. The gazette proposes a method in which PVA fibers obtained by a wet or dry spinning method are stretched at least 10 times or more and then heat-treated. Also, Japanese Patent Publication No. 37-14422 and Japanese Patent Publication No. 47-3
No. 2142 discloses that a PVA aqueous solution containing boric acid or borate is spun into an alkaline coagulation bath containing various salts to crosslink boric acid to PVA, and then boric acid or a crosslinked product thereof is again A method of removing in a process such as neutralization and washing with water is disclosed. However, the PV obtained by these methods
The draw ratio of the A fiber was 15 times or less, the strength of the obtained fiber was 12 g / dr or less, and the modulus was 350 g / dr or less.

On the other hand, Japanese Unexamined Patent Publication No. 62-85013 discloses a method of applying a high degree of polymerization and low concentration spinning-super drawing to dissolve PVA having a degree of polymerization of 12000 in ethylene glycol so that spinning can be performed at a low concentration. Gel spinning with the addition of an acid or borate, followed by stretching, gives a strength of 21.9 g / d and a modulus of 6
It has been shown to obtain a monofilament of 28 g / d.
However, in this case, the added boric acid or borate remained in the fiber, and the draw ratio was reduced, whereby the strength and the elastic modulus were reduced, and the hot water resistance was insufficient. In addition, there were problems such as a decrease in rubber fatigue resistance.

<Problems to be solved by the invention> Based on the above background, the present invention provides a PVA having excellent hot water resistance and rubber fatigue resistance while maintaining high strength and high elastic modulus.
It is intended to provide a system fiber.

<Means for Solving the Problems> As a result of intensive studies for solving the above problems, the present inventors have found that spinning properties can be improved by adding boric acid or borate in low concentration spinning of high polymerization degree PVA. To improve the drawability, hot water resistance and rubber fatigue resistance by adding a surfactant while stabilizing spinning.
This has led to the present invention.

That is, the present invention relates to "(1) a PVA-based fiber obtained from a spinning stock solution obtained by adding boric acid or a borate and a surfactant to a PVA-based polymer having a viscosity-average degree of polymerization of 1500 or more; During PV 0.
A fiber in which boron equivalent to boric acid or borate in an amount of 6% by weight or less is present and a surfactant in an amount of 5% by weight or less coexists. The tensile strength of a single fiber is 16 g / d or more, and the initial elastic modulus is PVA-based fiber that satisfies the following formula and has a hot water-breaking temperature of 125 ° C or more under a load of 200 mg / d: YM ≧ 224 × ( _A ) ^0.11 (YM: initial elastic modulus of single fiber (g / d) _A : Viscosity average degree of polymerization of PVA polymer) (2) When a PVA polymer having a viscosity average degree of polymerization of 1500 or more is dissolved in a solvent containing at least an organic chemical, boric acid or borate is added to the polymer. 0.1 to 5% by weight, a surfactant is added to the polymer in an amount of 0.3 to 15% by weight to the spinning solution, and the stock solution is discharged from a nozzle to form a gel yarn,
Thereafter, the solvent is removed from the gel yarn, and boric acid or borate is removed from the polymer so as to be 0.6% by weight or less and the surfactant is 5% by weight or less. A method for producing PVA-based fibers, wherein the drawing is performed so that the magnification is 17 times or more. It is about.

 Hereinafter, the present invention will be described in detail.

The viscosity average polymerization degree obtained from the intrinsic viscosity of the PVA-based polymer and the aqueous solution at 30 ° C. used in the present invention is 1,500 or more, preferably 4,000 or more, more preferably 10,000 or more, and the saponification degree is 98 mol%. As described above, a linear PVA having a low degree of branching is preferable. It should be noted that a copolymer of 2 mol% or less of another vinyl compound, an antioxidant of 3 wt% or less,
It is also possible to add additives such as ultraviolet absorbers.

It was already known that as the degree of PVA polymerization increases, the strength, elastic modulus, and hot water resistance increase.However, in the present invention, it is necessary to provide a fiber that exhibits higher performance when compared with PVA fiber having the same degree of polymerization. Is what you do.

Examples of the solvent for the PVA polymer used in the present invention include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, and organic chemicals such as dimethyl sulfoxide (DMSO), dimethylformamide, and diethylene triamine, and two or more of these. Or a mixed system of these and water, a propanol aqueous solution, and the like. In particular, in order to obtain a transparent and uniform gel fiber among these, polyhydric alcohol and
DMSO and a mixed solvent thereof with water are preferred. In the present invention, a solvent containing at least an organic chemical is most suitable because a uniform gel yarn is obtained and strength and hot water resistance are enhanced.

In the present invention, high polymerization degree PVA is spun at a low concentration, and gelation (coagulation) is performed in a state where the molecular chain is small, thereby improving the performance. In this case, the lower the PVA concentration, the less spinnability, Thread breakage easily occurs. To solve this,
In the present invention, boric acid or borate is added to the spinning dope,
The spinnability is maintained by partial crosslinking. However, if a large amount is added or the residual amount is large, it is not preferable because drawing becomes difficult during spinning or hot drawing and rubber fatigue resistance is deteriorated.

In the present invention, the amount of boric acid or borate added is preferably 0.1 to 5% by weight based on the PVA polymer, more preferably 0.3 to 5% by weight.
３3% by weight. There is no problem in adding an acid to soften the crosslinking (thickening) by adjusting the pH. The residual amount of boron corresponding to boric acid or borate is 0.6% by weight or less, preferably 0.03 to 0.3% by weight. If the content exceeds 0.6% by weight, the draw ratio decreases, and the strength, the elastic modulus, and the rubber fatigue resistance decrease.

Another feature of the present invention is that a surfactant is added to the spinning solution together with boric acid.

The following three are considered as effects of the addition of the surfactant.
The first helps to remove the boric acid or borate added for stabilization of the low density spinning with the solvent. This is to suppress a decrease in the draw ratio and a decrease in rubber fatigue resistance, which are problems when a large amount of residual boric acid is present. Also the second
The reason is that the surfactant itself acts as a smoothing agent and increases the draw ratio to obtain fibers having high strength and high elastic modulus. Also the third
The reason for this is that the addition of a surfactant improves the hot water resistance, for which the change in microstructure during gel formation is considered to be one factor, although the reason is not clear.

The addition amount of the surfactant is 0.3 to 15% by weight, preferably 1 to 8% by weight based on the PVA polymer. When the amount is less than 0.3% by weight, the above-mentioned effects are small, and when the amount exceeds 15% by weight, spinning becomes unstable or troublesome to remove.

The residual amount of the surfactant in the fiber is 5% by weight or less, preferably 0.05 to 2% by weight. If it exceeds 5% by weight, the affinity for water is increased, and the penetration of water into the interior of the fiber is promoted.

The surfactant is preferably dispersed or dissolved in the PVA solution in a size of 100 μm or less. 500
If there is a large aggregate exceeding μ, the fiber may be broken at the time of spinning, the molecular orientation may be disturbed, or a defect may be easily formed due to a void at the time of removal, resulting in a decrease in fiber performance.

The surfactant is finely dispersed or dissolved in the PVA solution, and as long as it has little decomposition or coloring, it may be any of commercially available nonionic, anionic, cationic and amphoteric surfactants, and There is no problem with two or more types.

Boric acid or borate thus obtained,
A low-concentration PVA solution containing a surfactant is extruded from a nozzle and formed into a fibrous form. The method is a commonly used wet method or dry-wet method (including the gel spinning method).
There is. In the dry method, the PVA concentration must be increased, and high strength and high elasticity yarn is difficult to obtain. In addition, dry-wet spinning is preferable from the viewpoint of obtaining a uniform gel yarn.

The coagulation bath may be any of alcohols such as methanol and ethanol, acetone and a mixed system thereof with a solvent or water, or an aqueous solution of an inorganic salt such as alkali or sodium sulfate. In order to obtain a uniform and transparent gel yarn, the coagulation bath temperature is preferably set to 20 ° C. or lower.

Almost all of the solvent is removed from the gel yarn (coagulated yarn) thus obtained using alcohol, water or a mixture thereof, and at this time, a part of boric acid or borate or a surfactant is removed. There is no problem if removed. When a large amount is added, it is necessary to actively remove it to make the residual amount referred to in the present invention.

Then, an extractant such as alcohol or water is evaporated by drying to obtain a spun yarn, which is then hot-drawn at a high magnification by a conventional method to enhance the orientation and crystallization of the PVA molecular chain. In the spinning step, it is preferable to perform 2 to 6 times wet stretching in a state containing a solvent in terms of promoting orientation, but the total stretching ratio including the wet stretching ratio is 17 times or more, and preferably 19 times or more. Dry heat stretching is performed as follows.

The initial elastic modulus of the single fiber increases with the draw ratio. In particular, in the present invention, a fiber satisfying YM ≧ 224 × ( _A ) ^0.11 can be obtained as described above. It shows a value higher by 50 g / d or more than the fiber produced without adding the agent.

The temperature of the dry heat stretching is 200 ° C. or higher, preferably 220 ° C. or higher. High temperature, high magnification stretching involves high orientation and high crystallization,
It is desirable to improve the hot water resistance as well as the strength elastic modulus, but it is necessary to pay attention to prevent the PVA from decomposing due to an excessively high temperature.

<Effect of the Invention> PVA containing boron and surfactant obtained as described above
The system fiber has a single fiber tensile strength of 16 g / d or more, an initial elastic modulus of YM ≧ 224 × ( _A ) ^0.11 , and 200 mg / d.
The hot water break temperature under load is 125 ° C or higher. Particularly when the degree of polymerization is 10,000 or more, the strength is 22 g / d or more, and the elastic modulus is 600 g / d.
It is a high performance PVA fiber with a hot water break temperature of 140 ° C or higher, which is not seen in the past, and has excellent rubber fatigue resistance despite boron-containing fiber, and industrial materials, rubber, plastic, It is expected to be used for new applications such as reinforcing materials such as segments, and its usefulness is extremely large.

Hereinafter, the present invention will be described more specifically with reference to examples.
Various physical properties in the examples described below were measured by the following methods.

1) Viscosity average degree of polymerization of PVA ( _A ) Calculated from the measured value of intrinsic viscosity [η] of an aqueous solution at 30 ° C. according to JIS K-6726 according to the following equation.

log _A = 1.63 log ([η] × 10 ⁴ /8.29) 2) Tensile strength and elongation and elastic modulus of single fiber Single fiber conditioned in advance according to JIS L-1013, test length 10 cm
The tensile elongation at break and the initial elastic modulus were determined at an initial load of 0.25 g / d and a tensile strength of 100% / min, and an average value of 10 points or more was adopted. Denier was measured by the Denicon method.

3) Hot water resistance (WTb) A load of 200 mg per denier is applied to 25 single fibers, suspended in the middle of a watertight glass cylindrical sealed container, and water is heated from the surroundings at a rate of 1 to 2 ° C / min. As the temperature was raised, the temperature at which the fiber was melted was read.

4) Residual amount of boron The dried spinning yarn was dissolved in water at 95 ° C., and mannite (manufactured by Kanto Chemical Co., Ltd.), which easily reacts with boron, was added, and the amount was calculated by titration of NaOH.

5) Residual amount of surfactant The dried spun yarn was dissolved in water at 100 ° C under vacuum, and the residual amount was determined from the ratio of the peak area of boron or the surfactant to the peak area of PVA itself by NMR measurement.

6) Rubber fatigue resistance 1500 in accordance with JIS L-1017 method A (Firestone method)
Twist the denier yarn at 22T / inch and twist them together to form a cord with three twists of 22T / inch, then apply RFL (resorcinol formalin resin solution) dipping, and make 15 cords each. Put in two layers and vulcanize in rubber. Put the obtained belt on a 25 mmφ pulley and set it at 25 ° C for 42
After repeating bending and compression 100,000 times under a load of kg, the cord is pulled out of the rubber and the tensile strength is measured.

Rubber fatigue resistance was evaluated based on the strength retention rate against cord strength after dipping and before fatigue.

Examples 1 and 2 and Comparative Examples 1 and 2 Viscosity average degree of polymerization was 7,000 (Example 1) and 18,000
The fully gelled PVA of (Example 2) was mixed with glycerin so as to be 7.5% by weight and 4% by weight, respectively. 1% by weight
It was dissolved at 80 ° C.

In both cases of Examples 1 and 2, a transparent solution was obtained. Then, the solution was discharged into the air from a nozzle having 300 holes and a hole diameter of 0.18 mm, and dropped into a coagulation bath 20 mm below. The composition of the coagulation bath was methanol / glycerin = 7/3 (weight ratio), and the temperature was kept at -10 ° C. At this stage, in each case, a transparent gel fiber which was almost a perfect circle was obtained. Then 40 ℃
And the solvent was extracted almost completely in a subsequent methanol bath. Most of boric acid and surfactant were removed during the period from the coagulation bath to the extraction, and the amount of boric acid and surfactant remaining in the spun yarn after drying at 90 ° C. in hot air was 0.25% by weight in Example 1. and
0.87 wt%, Example 2 was 0.17 wt% and 0.59 wt%, respectively.
% By weight.

Next, when the raw yarn had a degree of polymerization of 7000 (Example 1, Comparative Example 2), the total draw ratio was 20.4 times in a hot air oven at 251 ° C., and the degree of polymerization was 18,
In the case of 000 (Example 2, Comparative Example 1), the film was stretched in a hot air oven at 258 ° C. so that the total stretching ratio was 19.6 times.

Comparative Example 1 was obtained by adding boric acid to 0.05% by weight in Example 2 but was not spinnable at a PVA concentration of 4% by weight.
Single yarn breakage occurred and spinning was impossible. Therefore, in Comparative Example 1, the spinning and drawing was carried out in the same manner as in Example 1 by using a PVA concentration of 5.5% by weight capable of spinning. However, because of the high PVA concentration, the total stretching ratio was low at 18.1 times.

In Comparative Example 2, the surfactant was added to 0.1% by weight in Example 1, but the boric acid was hardly removed, and the residual amount of boric acid increased to 0.65% by weight. Therefore, the total draw ratio is
It decreased by 18.5 times.

Table 1 shows the performance evaluation results of the obtained drawn yarns.

In Example 1, the single fiber strength was as high as 22.9%, the elastic modulus was as high as 617 g / d, and the hot water temperature (WTb) was 145 ° C., which was excellent in hot water resistance. In addition, the rubber has a high level of rubber fatigue resistance and can be used for industrial materials and reinforcing materials.

Example 2 was a fiber having a degree of polymerization of 18,000, but had a single fiber strength of 24.8 g / d and an elastic modulus of 672 g / d, which was comparable to aramid or polyarylate. WTb is also 153 ℃
The result was higher than the area of the normal PVA fiber. Further, the rubber fatigue resistance was good, and a fiber having a high commercial value was obtained.

Comparative Example 1 was the same as Example 2 except that the amount of boric acid added was reduced.
The A concentration was increased and a surfactant was added at 5% by weight. However, since the PVA concentration was as high as 5.5%, the draw ratio was lowered, and the strength, elastic modulus and hot water resistance were lowered.

Comparative Example 2 is the same as Example 1 except that the amount of the surfactant added was reduced and boric acid was added at 10% by weight. However, the amount of boric acid remaining was large, the draw ratio was reduced, and the strength and WTb were low. However, the rubber fatigue resistance was not satisfactory.

Example 3 PVA having a viscosity average degree of polymerization of 4,200 and a saponification degree of 99.6 mol%
Was mixed with DMSO to a concentration of 7% by weight, and
8% by weight, 10% by weight of POE (40) nonylphenol ether, and 0.1% by weight / dope of acetic acid were added for pH adjustment, and the mixture was stirred and dissolved under N _{2 at} 70 ° C. for 4 hours. Next, the solution was discharged from a nozzle having 500 holes and a hole diameter of 0.12 mm, and dropped into a coagulation bath of methanol / DMSO = 6/4, 5 ° C. by a dry / wet method. The obtained gel yarn was transparent in a circular cross section, and no trouble occurred during spinning. Subsequently, the film was stretched 5 times in a methanol bath, and then the solvent and additives were further extracted in a methanol bath and dried at 100 ° C. The residual amount of boric acid in the obtained spun yarn is 0.09% by weight, and the residual amount of surfactant is 1.
23% by weight, and this was subjected to a total draw ratio of 21.
Stretched at 7 times.

The single fiber strength of the obtained drawn yarn is 21.5 g / d and the elastic modulus is 581 g / d.
d, WTb was 139 ° C., resulting in a PVA fiber having excellent strength, elastic modulus and hot water resistance. When the above surfactant was not added, boric acid in the fiber was difficult to remove, the residual amount was 0.68% by weight, and the total draw ratio was reduced to 17.8 times. The single fiber strength of the obtained fiber is 18.9 g / d, and the elastic modulus is 490.
The value was as low as g / d.

Example 4 PVA having a viscosity average degree of polymerization of 1750 and a saponification degree of 99.9 mol%
To 14% by weight of water / ethylene glycol = 8/2
Mix with solvent in weight ratio, and at the same time boric acid 2.8 weight POE (30)
10% by adding 3% by weight of laurylsulfonic acid sodium salt
It was dissolved at 0 ° C. × 8 hours.

The obtained solution was heated to 80 ° C., the number of holes was 1000, and the hole diameter was 0.08 mm.
Of 250 g / NaOH aqueous solution by the wet method from the nozzle of 2
The fiber was spun into a coagulation bath at 0 ° C. and gelled. Then after neutralization 90
The film was wet-drawn in a 300 g / sodium sulfate aqueous solution at a temperature of 5 ° C. and stretched 5 times, and then sufficiently washed with water to remove the solvent and additives. At 110 ° C., the dried raw yarn was drawn at 230 ° C. so that the total draw ratio was 20.3 times. The residual amount of boric acid in the spun yarn was 0.39% by weight, and the residual amount of the surfactant was 2.9% by weight.

The obtained drawn yarn had a low PVA polymerization degree, but had a single fiber strength of 18.0 g / d and an elastic modulus of 524 g / d WTb of 130 ° C., and was a fiber excellent in strength and hot water resistance. Also in this case, when no surfactant is added, the residual amount of boric acid is 1.
At 2% by weight, the total draw ratio was 16.9 times, and the single fiber strength was 15.
It was as low as 4 g / d and the elastic modulus was 410 g / d.

Claims (2)

(57) [Claims] 1. A polyvinyl alcohol-based fiber obtained from a spinning solution obtained by adding boric acid or a borate and a surfactant to a polyvinyl alcohol-based polymer having a viscosity average degree of polymerization of 1500 or more, wherein 0.6% by weight or less of boric acid or boron equivalent to borate based on polyvinyl alcohol, and 5% by weight or less of a surfactant coexisting fiber, the tensile strength of a single fiber is 16g / d or more, A polyvinyl alcohol-based fiber having an initial modulus of elasticity satisfying the following formula and having a hot water-breaking temperature of 125 ° C or more under a load of 200 mg / d. YM ≧ 224 × (P _A ) ^0.11 (YM: Initial elastic modulus (g / d) of single fiber, P _A : Viscosity average degree of polymerization of polyvinyl alcohol polymer) 2. When a polyvinyl alcohol polymer having a viscosity average polymerization degree of 1500 or more is dissolved in a solvent containing at least an organic chemical, boric acid or a borate is added to the polymer in an amount of 0.1 to 1.0.
1 to 5% by weight and a surfactant are added to the polymer in an amount of 0.3 to 15% by weight to obtain a spinning dope, and the stock solution is discharged from a nozzle to form a gel yarn. Is removed, and boric acid or borate is removed to the polymer in an amount of 0.6% by weight or less, and the surfactant is removed in an amount of 5% by weight or less. Thereafter, the total draw ratio becomes 17 times or more. A method for producing a polyvinyl alcohol-based fiber, comprising: