JP3139689B2 - Polyvinyl alcohol-based synthetic fiber and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a synthetic material of polyvinyl alcohol (hereinafter abbreviated as PVA) useful as a fiber for reinforcing (hereinafter abbreviated as FRC) fibers of industrial materials requiring hot water resistance, especially cement products for autoclave curing. The present invention relates to a fiber and a method for producing the fiber.

[0002]

2. Description of the Related Art In recent years, health disorders due to asbestos have been clarified, and their use has been regulated. PVA-based synthetic fibers have the highest strength and elasticity among general-purpose fibers, and have good adhesiveness to cement and good alkali resistance. Therefore, the demand for PVA-based synthetic fibers is rapidly increasing as a substitute for asbestos in the FRC field. However, PVA-based synthetic fibers are inherently poor in heat and humidity resistance and dissolve under a heat and humidity condition of about 130 ° C., so that autoclave curing is impossible and has been used exclusively for room temperature curing. Currently, carbon fiber is partially used as an asbestos substitute material in autoclave curing,
In addition to poor adhesion to the cement matrix and poor reinforcing effect, it is very expensive compared to asbestos and PVA-based synthetic fibers.

[0003] On the other hand, attempts have been made to improve the wet heat resistance of PVA-based synthetic fibers. For example, Japanese Unexamined Patent Publication
No. 133605 discloses a method of blending an acrylic acid polymer or crosslinking the fiber surface with an organic peroxide, an isocyanate compound, a blocked isocyanate compound, a urethane compound, an epoxy compound, or the like. It has been disclosed. However, even when the acrylic acid-based polymer is blended, the acrylic acid-based polymer is eluted in the solvent extraction process at the time of spinning of PVA, and the effect is lost. Even if the elution residue is cross-linked, the cross-linking is an ester bond, so that it is easily hydrolyzed by the alkali of the cement and cannot withstand autoclaving at all. Even when only the fiber surface is crosslinked, swelling and dissolution occur from the center of the fiber during autoclave curing, and satisfactory wet heat resistance cannot be obtained.

[0004] The idea of this surface cross-linking treatment is that if the cross-linked structure extends to the inside of the fiber, it becomes difficult to perform high-magnification drawing, and as a result, it becomes impossible to obtain a high-strength fiber. The reason for this is to keep the crosslinked structure on the fiber surface in view of the balance between the heat resistance and the wet heat resistance. However, in the PVA fiber obtained by this treatment, the crosslinked structure to be formed is mainly unevenly distributed on the fiber surface. Therefore, as described above, when the fiber comes into contact with hot water, it swells from the central portion thereof. It dissolves and the wet heat resistance becomes insufficient.

[0005] This phenomenon is particularly remarkable when the fiber is used for FRC. That is, the fibers for FRC are generally mixed into the cement as cut fibers, and the cut surface is directly exposed to the steam containing the cement component and the alkali, and swells or dissolves from the center of the cross section where the crosslinked structure is not formed. It will be. Therefore, even if only the surface portion of the fiber is crosslinked, the wet heat resistance of the FRC fiber is not improved. In fact, it has been confirmed that this type of crosslinked fiber loses its reinforcing effect by autoclaving at 140 ° C.

Japanese Patent Application Laid-Open No. 2-249705 discloses a PVA used as a reinforcing cord for a pneumatic tire.
It is disclosed that a system fiber is subjected to a crosslinking treatment for the purpose of improving fatigue resistance. As a means for this, in addition to the case where a cross-linking agent is post-processed to a PVA-based fiber cord to form a cross-linked structure on the fiber surface, the cross-linking agent is added to a spinning solution or a coagulation bath, and this is added to the inside of the fiber. The idea of infiltrating and cross-linking is also disclosed. However, in the process of adding a cross-linking agent to a spinning solution or a coagulation bath,
In the former case, the crosslinking agent elutes into the coagulation bath, and in the latter case,
Since the coagulation bath removes the solvent exclusively from the spinning solution and does not diffuse to the center of the fiber, it does not lead to the formation of a crosslinked structure up to the center of the fiber, and neither of them has the effect of improving the moist heat resistance of the present invention.

Japanese Patent Application Laid-Open No. 63-120107 discloses a method of formalizing PVA-based synthetic fiber drawn 15 times or more so that the degree of formalization is 5 to 15 mol%. However, with such a degree of formalization, only a very small part of the amorphous region is rendered hydrophobic, and it cannot withstand autoclave curing. As will be described in detail later, the gel elastic modulus defined by the present invention of such a fiber is at most only 1 to 2 × 10 ↑ -3 g / cm · d, and is clearly distinguished from the fiber of the present invention.

The purpose of autoclaving is to stabilize the dimensions of cement products. The mechanism is that calcium oxide and silica react with each other to generate crystals called tobermorite, and this reaction proceeds under a moist heat of 140 ° C. or more. However, it is desirable to set the temperature to 160 ° C. or higher because the curing time can be relatively shortened. Therefore, although the practical curing humidity is 160 ° C. or higher, as described above,
With the conventional technology, it has been impossible to stably produce PVA-based synthetic fibers that can withstand such severe curing.

[0009]

Accordingly, the present invention relates to a PV
The highly heat- and moisture-resistant PV which can withstand the autoclave curing at 140 ° C., preferably 160 ° C. or more, where the wet heat resistance of the A-based synthetic fiber cannot be realized by the conventional technology.
It is intended to provide A type synthetic fibers.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies and found that the gel elasticity, which indicates the degree of cross-linking, is very closely correlated with autoclave resistance. This led to the invention.

That is, the fiber of the present invention has a strength of 11 g / d.
As described above, the gel elastic modulus is 6.0 × 10 ↑ −3 g / cm ·
It is a PVA-based synthetic fiber characterized by having an elution ratio of d or more and 40% or less.

As a fiber for FRC having a satisfactory reinforcing effect, its strength needs to be 11 g / d or more. Furthermore, 1
To withstand autoclave curing at 40 ° C., the gel elasticity must be 6.0 × 10 3 −3 g / cm · d or more and the elution rate must be 40% or less. In order to withstand the preferred autoclave curing temperature of 160 ° C., it is particularly desirable that the gel elasticity be 8.0 × 10 3 −3 g / cm · d or more.

In order to impart wet heat resistance to PVA-based synthetic fibers, it is necessary to introduce crosslinks between PVA molecules. The gel elastic modulus specified in the present invention is a numerical value of the degree of crosslinking, and the larger the value, the more crosslinking is introduced. The method for measuring the gel elastic modulus will be described later, but is roughly as follows. Since aqueous zinc chloride is a strong solvent for PVA,
It can melt synthetic fibers. However, when the PVA molecules are cross-linked, the PVA crystals are dissolved in the aqueous zinc chloride solution, but because of the cross-linking network, the fiber as a whole does not dissolve, but shrinks to a gel-like state. The elongation behavior of this gel with respect to tensile stress follows the Hooke's law, and the gel elastic modulus defined in the present invention corresponds to the spring constant.

The elution rate referred to in the present invention, which will be described later in detail, is a weight reduction rate of the fiber when the fiber is cut into 6 mm and immersed in an artificial cement solution at 160 ° C. It is a measure of how uniformly the direction is introduced. If the value is not more than 40%, the reinforcing effect cannot be obtained by autoclave curing at 140 ° C. or more. However, in general, the dissolution of the fiber proceeds from the cut end, and if the cut length is different, the dissolution rate is different. In the present invention, what is measured at 6 mm is tentatively specified, but a fiber having an elution rate of 40% at 6 mm is 3 m.
In m, it corresponds to about 50%. The aforementioned gel modulus indicates the degree of crosslinking, but does not necessarily reflect the uniformity of crosslinking in the fiber. Therefore, in the present invention, the gel elastic modulus is a so-called necessary condition for withstanding autoclaving at 140 ° C., whereas the elution rate reflecting uniformity is a sufficient condition, and it is necessary to satisfy both at the same time. .

The present inventors studied various fibers having different gel elastic moduli, and found that the damage of the fibers after the autoclave curing was smaller for the larger gel elastic moduli.
In order to enable autoclave curing at 40 ° C., a value of 6.0 × 10 3 −3 g / cm · d or more is required, and an elution rate is 40% or less, preferably a gel elasticity of 8.0 × 10 ↑ -3g / cm · d or more and elution rate 30%
If it is below, it was found that it has sufficient wet heat resistance.

By the way, in the conventionally known crosslinking treatment, it was necessary to extremely increase the drug concentration and the stretching / heat treatment temperature in order to obtain the above gel elastic modulus. However, this is accompanied by a drastic decrease in strength, and it has been difficult to maintain the required strength of 11 g / d as a fiber for FRC. Also, it was difficult to penetrate the cross-linking agent into the center of the fiber, and an elution rate of 40% or less could not be obtained.

The fiber of the present invention is not limited to any particular method, but an extremely effective method is a fiber having a strength of 13 g / g.
The acetalization treatment is performed on PVA-based synthetic fibers of d or more under special conditions, and the present invention proposes two methods. One is to apply an aqueous solution or emulsion containing monoaldehyde or dialdehyde or its acetalized compound or both to the fiber in the first stage, and thereafter,
In the second step, a treatment is performed with a mixed solution of a monoaldehyde and an acid. In addition, the aldehyde is used as the emulsion.
In the case of hydrophobicity, it is for emulsification using a suitable emulsifier. The other is formaldehyde 100-250g
/ L, sulfuric acid 30-80 g / l in a 70-100 ° C bath containing acetal.

First, the two-stage processing will be described. In the first stage, without using an acid as a reaction catalyst, monoaldehyde or dialdehyde and / or an acetalized product thereof are permeated without crosslinking to the fiber center,
Subsequently, in the second stage, treatment with a mixed bath of monoaldehyde and acid causes an intermolecular cross-linking reaction between the aldehydes provided in the first stage and PVA, and at the same time, the formation of PVA with the monoaldehyde. It produces intramolecular crosslinks.

That is, in the method of the present invention, a step of permeating a monoaldehyde or a dialdehyde and / or an acetalized product thereof into the fiber center (first step)
This is characterized in that it is separated from a process (second stage) in which a crosslinking reaction is caused by an acid serving as a reaction catalyst.

When aldehydes are added to a PVA-based synthetic fiber simultaneously with an acid, crosslinking is first generated from the fiber surface.
This cross-linking is very strong and dense and significantly impedes the subsequent penetration of the cross-linking agent into the fiber core. In addition, when dialdehyde or its acetal is used, it is extremely unstable in the presence of an acid, and has a fatal drawback that it tends to deactivate its ability as a crosslinking agent for PVA. The two-stage treatment of the present invention can solve such a problem at once, and is a very preferable embodiment from the viewpoint of both physical properties and productivity.

The first step is, as described above, a step of infiltrating aldehydes into the central portion of the fiber.
Dialdehyde or its acetalized product can be used alone or in combination. Monoaldehyde generally has a swelling ability with respect to PVA-based fibers, easily penetrates into the center of the fiber, and forms crosslinks in the center of the fiber by the second-stage acid. Known types of monoaldehyde can be used, such as formaldehyde and benzaldehyde, but formaldehyde is suitable from the viewpoint of permeability and minimizing a decrease in strength of PVA-based fiber as a raw yarn. The conditions to be applied, that is, the concentration and the humidity may be appropriately adjusted so as not to cause excessive swelling, but the concentration is approximately 5 to 100 g / l, preferably 20 to 70 g / l, and 50 to 95 ° C., preferably 70 to 70 g / l. ９０90 ° C.

In the first stage, the use of dialdehyde or an acetalized product thereof is also effective in increasing or increasing the gel modulus, but care must be taken because the strength tends to decrease. 0.3 to 25 g / l, preferably 0.5 to 15 g / l, more preferably 1.0 to 10 g / l
g / l is desirable. The dialdehyde that can be used in the present invention is a linear compound such as glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexane 1,6 dial, or orthophthalaldehyde, isophthalaldehyde, terephthalaldehyde, phenylmalondialdehyde. There are aromatic compounds such as aldehydes, and one or two or more kinds may be mixed, but glutaraldehyde, malondialdehyde, succinaldehyde or an acetalized product thereof from the viewpoint of permeability and reactivity into the fiber. Glutaraldehyde is particularly preferred. Among these, compounds which are highly reactive and polymerize even when they do not coexist with an acid, such as malondialdehyde, can be acetalized with an alcohol and used as an acetalized product. A typical example is tetramethoxypropane obtained by acetalizing malondialdehyde with methanol, which is stable if no acid coexists, but can be converted back to dialdehyde by the acid to react with PVA.

Further, when such a dialdehyde or an acetalized product thereof is used, an auxiliary agent for accelerating the permeation into the central portion of the fiber can be used. The auxiliary agent is not particularly limited as long as it mainly has a swelling ability with respect to PVA-based fibers, but monoaldehyde, which can react with PVA by itself, among which formaldehyde is preferred. Also,
Thus, the concentration when monoaldehyde and dialdehyde or an acetalized product thereof are used in combination is not substantially different from that when each is used alone (described above). This first step is a step for infiltrating the aldehydes to the center of the fiber, so that the aldehydes are PVA in the first step.
It is necessary to prevent the acetalization reaction from occurring,
For that purpose, it is important that the aldehyde-containing liquid used in the first stage does not substantially contain an acid or the like which serves as an acetalization catalyst.

Subsequently, in the second stage, treatment is carried out in a mixed bath of monoaldehyde and acid. Here, the purpose of using the monoaldehyde is to prevent the aldehydes permeated into the fiber in the first stage from reverse osmosis into the bath in the second stage and to diffuse, and to increase the acetalization degree as described later. It is in.

The monoaldehyde used in the second stage includes
Known substances such as formaldehyde and benzaldehyde can be mentioned, but formaldehyde is most preferred. Its concentration is 10 to 150 g / l, preferably 30 to 150 g / l.
It is 120 g / l, more preferably 50 to 100 g / l. The acid used as the reaction catalyst is not particularly limited, but the most common sulfuric acid is 10 to 200 g / l,
Preferably it is 30 to 150 g / l. The temperature of the bath may be appropriately adjusted based on the reaction rate, the swelling state of the fibers, and the like.
It is approximately 60-95 ° C, preferably 70-90 ° C. Glauber's salt can also be used in the bath to suppress swelling. The degree of acetalization as a guide is 15 mol%
As described above, the content is preferably 20 to 35 mol%.

On the other hand, in addition to the two-stage treatment, the fiber of the present invention is obtained by adding a PVA-based synthetic fiber having a strength of 13 g / d or more to 100 to 2 g / d.
It can also be obtained by treating in a 70-100 ° C. bath containing 50 g / l formaldehyde and 30-80 g / l sulfuric acid.

Usually, the formalization of polyvinyl alcohol-based synthetic fibers is carried out in a bath of about 20 to 50 g / l of formaldehyde and about 200 to 270 g / l of sulfuric acid. However, the method of the present invention employs extremely high formaldehyde and low sulfuric acid conditions. You can say that. Formaldehyde is unlikely to cause intermolecular cross-linking reflecting PVA and gel elasticity, but by adopting such conditions of high formaldehyde and low sulfuric acid, intermolecular cross-linking can be introduced to the center of the fiber.

The method of the present invention can be used for a P having a strength of 13 g / d or more.
The present invention is applied to VA-based synthetic fibers, but the spinning method of such fibers is not particularly limited as long as required strength can be ensured. For example, (1) PV
A method in which a solution obtained by adding boric acid or a salt thereof to an aqueous solution A is used as a spinning solution, and the solution is spun into a relatively high-temperature alkaline coagulation bath,
(2) Known methods such as a method of dissolving PVA in an organic solvent such as dimethyl sulfoxide or glycerin as a spinning dope and spinning into a methanol coagulation bath can be employed.
(3) Addition of 1 to 20% by weight of a surfactant to PVA to the spinning dope promotes penetration of a crosslinking agent and aldehydes and enhances stretchability. Therefore, it is preferable. The surfactant is preferably a nonionic surfactant.

Although the degree of polymerization of the PVA used is not particularly limited, it is naturally preferable that the strength is higher because it is a reinforcing fiber, and the gel elastic modulus is more than 1500 because it is somewhat affected by the degree of polymerization. Is more than 2000,
More preferably, it is 3000 or more. Degree of saponification is 98
Mol%, preferably 99.5 mol% or more, and a higher one is more advantageous. In particular, when performing a two-stage treatment without using dialdehyde, it is relatively difficult to obtain a gel elastic modulus. Therefore, PVA obtained by adding a nonionic surfactant to a spinning dope with PVA having a degree of polymerization of 2,000 or more. It is preferable to use synthetic fibers.

In the method of the present invention, the above-described two-step treatment or treatment with high formaldehyde and low sulfuric acid is used as a basic skeleton, but it is also possible to use another crosslinking agent in combination. For example, an organic substance such as a methylol-based compound or a melamine-based compound, or an inorganic substance such as an acid such as phosphoric acid or sulfuric acid, or a salt thereof may be applied, crosslinked, and then subjected to an acetalization treatment. However, it is necessary to adjust the crosslinking by such a crosslinking agent so as not to hinder the penetration of the aldehyde into the central part of the fiber during the subsequent acetalization treatment.

[0031]

The present invention will be described below with reference to examples. In the examples,% is a value based on weight unless otherwise specified. Further, in the examples, the strength, the gel elastic modulus, the dissolution rate, the acetalization degree, and the bending strength of the slate are measured by the following methods. (1) Strength: Measured with an Instron tensile tester according to JIS L-1015. In addition, fiber is short, 20mm
If the test length cannot be obtained, measure with a test length of 1 mm. (2) Gel elastic modulus: A multifilament yarn having a denier of 1000 to 2000 is fixed at the upper end so as to have a length of 20 cm, and a 1-gram load is applied to the lower end.
When this is immersed in a 50% by weight aqueous solution of zinc chloride at 50 ° C., the fibers shrink. The sample length when the contraction completely stops is measured, and this is defined as Acm. Next, load 1
Similarly, the sample length is measured in an aqueous zinc chloride solution, changing the sample length from 30 g to 30 g, and this is defined as Bcm. Note that the load used is one having a specific gravity of 8, and A and B are each read to the order of 0.1 mm. Gel modulus = 29 / (BA) · D (g / cm ·
d). However, D before immersion in the aqueous zinc chloride solution,
Denier of the sample. When the sample is cut to several mm, first fix the upper end of the single fiber, apply a load of C milligram to the lower end so that the test length becomes 2 mm, and shrink by the above method to read the sample length ( L ↓ 1cm). Next, the load is changed to E
Change to milligrams (however, C <E) and read the sample length in the same manner (L ↓ 2 cm). Gel modulus = (EC) / 10 ／ 5 · (L ↓ 2-L ↓ 1)
D (g / cm · d) (3) Elution rate: The fiber was cut into 6 mm, and about 0.5 g of the fiber was weighed (referred to as Ag).
It is placed in a 4.5 mm-thick stainless steel autoclave together with 00 cc of the artificial cement solution, and immersed in a 160 ° C. oil bath for 2 hours. Thereafter, the fiber is pulled up from an oil bath and cooled, the fiber is taken out and dried, and then weighed (Bg). Elution rate = (AB) / A × 100 (%). In addition, artificial cement liquid is 3.5 g of potassium hydroxide /
1, sodium hydroxide 0.9 g / l, calcium hydroxide 0.4 g / l. (4) Degree of acetalization: Measured according to the vinyl formal analysis method of JIS K-6729. (5) Flexural strength of slate; 6 mm PVA-based synthetic fiber
And 2 parts of the pulp, 3 parts of pulp and 95 parts of Portland cement are wet-processed by a Hatschek machine, primary cured at 50 ° C for 24 hours, and then cured at 160 ° C for 10 hours.
Time autoclave curing to obtain a slate plate, JI
The bending strength was measured according to SK6911. When the bending strength is 240 kg / cm @ 2 or more, it is determined that the reinforcing effect is obtained.

Example 1 Completely saponified PVA having a degree of polymerization of 1800 was dissolved in water at a concentration of 15%, and 1.5 moles each of boric acid and a nonylphenol ethylene oxide adduct of 1.5 mol were added to PVA.
% And 3.0% to obtain a spinning stock solution. The spinning stock solution is wet-spun into a coagulation bath at 60 ° C. comprising 15 g / l of sodium hydroxide and 350 g / l of sodium sulfate, and subjected to roller stretching, neutralization, wet heat stretching, washing with water and a 3 g / l phosphoric acid bath according to a conventional method. And dried. Subsequently, at 230 ° C., the total stretching ratio is 23
The film was stretched by dry heat so as to be twice as large. The resulting fiber is
Strength 15.3 g / d, gel elasticity 0.5 × 10 ↑ -3 g /
cm · d, and the elution rate was 93%. Subsequently, the fiber was immersed in a mussel-like shape in a 70 ° C. water bath containing 2 g / l of glutaraldehyde and 50 g / l of formaldehyde, and was appropriately squeezed, followed by 100 g / l of formaldehyde and 70 g / sulfuric acid.
l, Glauber's salt 30 g / l, 80 ° C bath treatment. Table 1 shows the physical properties of the obtained fibers and the performance of the slate plate.

Comparative Example 1 Winding was performed in exactly the same manner as in Example 1 except that the film was stretched by dry heat so that the total stretching ratio was 13 times, and the strength was 11.2 g.
/ D of fiber was obtained. Subsequently, Table 1 shows the physical properties and slate plate performance of the fibers subjected to the two-stage treatment in the same manner as in Example 1.

Comparative Example 2 The two-stage treatment in Example 1 was repeated using 2 g of glutaraldehyde.
/ L, formaldehyde 100g / l, sulfuric acid 70g /
l, Glauber's salt 30 g / l, one-stage treatment in a bath at 80 ° C. Table 1 shows the physical properties and slate board performance of the fiber thus obtained.

[0035]

[Table 1]

From Table 1, it is clear that fibers having the desired properties can be obtained only by the method of the present invention, and such fibers have excellent slate plate bending strength. In Comparative Example 1, the wet heat resistance was satisfied, but the strength was low, but in Comparative Example 2, cross-linking was not able to be introduced to the fiber central part because of the single-stage treatment, and the elution rate was large. During autoclave curing, wet heat deterioration has progressed from the center.

Examples 2 and 3, Comparative Examples 3 and 4 Completely saponified PVA having a degree of polymerization of 3000 was dissolved in dimethyl sulfoxide at a concentration of 12%, and the solution was dried and wet-spun into a methanol bath. Subsequently, extraction, wet stretching, and drying were performed according to a conventional method, and the film was stretched at 235 ° C. so as to have a total stretching ratio of 21 times. The resulting fiber had a strength of 19.1 g / d. The fibers were subjected to a crosslinking treatment under different conditions. Table 2 shows the processing conditions, fiber properties, and slate plate performance.

[0038]

[Table 2]

As shown in Table 2, when the concentration of the dialdehyde glutaraldehyde is low and the intermolecular crosslinking is insufficient, a satisfactory gel modulus cannot be obtained and the reinforcing effect of the slate plate is low. Also. Even if the acetalization treatment is carried out under the conditions of high formaldehyde and low sulfuric acid without performing the two-step treatment, the desired fiber can be obtained. Rate and dissolution rate are insufficient.

Example 4 A completely saponified PVA having a degree of polymerization of 3000 was dissolved in water at a concentration of 11%, and boric acid and a 40 mol adduct of nonylphenolethylene oxide were added to 1.8% and 7% of PVA, respectively, for spinning. The stock solution was used. The spinning stock solution was spun in the same manner as in Example 1, and subjected to roller stretching, neutralization and
It was wet-heat stretched, washed with water and dried. Subsequently, drawing was performed at 235 ° C. so that the total drawing ratio became 27 times, to obtain a fiber having a strength of 20 g / d. Subsequently, the first stage: formaldehyde 50 g /
1, second stage at 80 ° C .; two-stage treatment in a bath of formaldehyde 100 g / l, sulfuric acid 70 g / l, sodium sulfate 100 g / l, 85 ° C. The fiber thus obtained has a strength of 1
8.1 g / d, gel elastic modulus, degree of acetalization, and elution rate are 13.8 × 10 3 g / cm · d and 18.1 m, respectively.
ol%, 13%, the bending strength of the slate is 350kg / c
m ↑ 2, which was extremely high.

Industrial Applicability The fiber of the present invention is not only suitable as an FRC fiber for autoclave curing, but also because of its excellent strength and water resistance, steam which has been impossible due to insufficient water resistance conventionally. Vulcanization is possible, making it easy to deploy in the field of rubber materials such as tire cords, belts and hoses, as well as fishery materials such as ropes, waterproof fabrics, tarpaulins, curing sheets, sewing threads, FRP, fishing nets and cold gauze etc. It is useful as a general industrial material. Further, the production method of the present invention is extremely effective for obtaining such excellent fibers.

Claims (3)

(57) [Claims] 1. A gel having a strength of 11 g / d or more and a gel elasticity of 6.0.
× 10 ↑ -3 g / cm · d or more and the elution rate is 4
A polyvinyl alcohol-based synthetic fiber having a content of 0% or less. 2. In a first stage, an aqueous solution or emulsion containing monoaldehyde or dialdehyde and / or an acetalized product thereof is applied to a polyvinyl alcohol-based synthetic fiber having a strength of 13 g / d or more, and then in a second stage. A method for producing a polyvinyl alcohol-based synthetic fiber which is treated with a mixed solution of a monoaldehyde and an acid to form an acetal. 3. A polyvinyl alcohol-based synthetic fiber having a strength of 13 g / d or more is mixed with formaldehyde in an amount of 100 to 250.
g-100 and 30-100 g / l containing sulfuric acid 30-80 g / l
A method for producing a polyvinyl alcohol-based synthetic fiber, which is subjected to an acetalization treatment in a bath at ℃.