JPH05117911A - Production of highly strong polyvinyl alcohol fiber having excellent high temperature performance - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having excellent high temperature performance and useful as a reinforcing material for automotive tires, etc., by spinning a specific spinning raw solution, adding the first crosslinking agent to the spun fiber, drying the fiber, imparting the second crosslinking agent to the surface of the fiber and subsequently dry-thermally drawing the fiber. CONSTITUTION:A spinning raw solution comprising polyvinyl alcohol having a polymerization degree of >=300 and dissolved in a solvent such as dimethyl sulfoxide is spun into an organic solvent bath or aqueous solidifying bath capable of coagulating or gelling the polyvinyl alcohol by a wet spinning method or by a dry-wet spinning method, treated with a small amount of the first crosslinking agent (preferably a long chain alkyl phosphate ester) compatible with the below-mentioned second crosslinking agent, extracted with a solvent and subsequently dried. The spun raw fiber is treated with the second crosslinking agent (preferably the same as the first one) in an amount larger than that of the first agent, drawn in a total draw ratio of >=14 times, and subsequently dry-thermally drawn at 230-265 deg.C to give the objective fiber.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a high strength material having excellent high temperature performance such as hot water resistance and high temperature fatigue resistance which is useful as a reinforcing material in the field of rubber materials used at high temperatures such as automobile tires and oil brake hoses. Polyvinyl alcohol (hereinafter P
Abbreviated as VA) -based fiber.

[0002]

2. Description of the Related Art Conventionally, among general-purpose polymer fibers, PVA-based production has higher strength and elastic modulus than polyester, polyamide, polyacrylonitrile-based fibers, etc., and it is reinforced not only for industrial materials but also for cement and rubber. It is practically used for materials. In recent years, it has been found that, in polyethylene, which is a general-purpose polymer, high strength and high modulus fibers can be obtained by gel spinning and ultra-stretching an ultra high molecular weight raw material. However, polyethylene itself is insufficient in that it has a low melting point and insufficient heat resistance, and that it has poor adhesion to the matrix as a reinforcing fiber.

Therefore, in other general-purpose polymers, attempts have been made to obtain high strength and high elastic modulus by using the technique of gel-spinning ultra-drawing. Among them, PVA has the same planar zigzag structure as polyethylene and has an active hydroxyl group,
There is a possibility of easily producing intermolecular hydrogen bonds and having high strength, high elastic modulus, high heat resistance and high affinity. For example, JP-A-59-100170 and JP-A-59-130314 have been proposed. ing. These PVA fibers are commercially available PVA
It has higher strength and higher elastic modulus than fibers, and is superior in heat resistance to the polyethylene fibers. On the other hand, PVA fiber has a problem that it is inferior in hot water resistance because the polymer itself is soluble in water. Although the hot water resistance of the PVA fiber having high strength and high elastic modulus is improved as compared with the conventional PVA fiber, it is not sufficient.

Therefore, proposals have been made to improve the hot water resistance of high-strength PVA fibers. For example, JP-A-63-120
In No. 107, a drawn yarn drawn 15 times or more has
It has been proposed to provide 15% acetalization.
However, the effect of improving hot water resistance is not sufficient when only light acetalization is performed, and the process is complicated. In addition, JP-A 1-1
No. 56517, a fiber is obtained by spin-drawing at least 3 times, applying a cross-linking agent such as an organic peroxide, an isocyanate compound, or an epoxy compound to the surface of the partially drawn yarn, and then performing dry heat drawing. It has been proposed to subject the surface to crosslinking. However, since the cross-linking agent is mainly present on the surface and mainly subject to surface cross-linking, the stretchability becomes insufficient and the elastic modulus is as low as 310 g / d at most. There is also a problem in that special organic compounds that require safety and health care must be handled. Furthermore, JP-A-2
In order to improve the fatigue resistance of PVA fiber cord, PVA fiber having a strength of 15 g / d or more is used as an organic compound such as aldehyde, isocyanate, organic peroxide, carboxylic acid, phosphoric acid or hydrochloric acid in order to improve fatigue resistance of PVA fiber cord. It has been proposed to treat with a crosslinking agent such as an inorganic compound such as titanium. However, since post-treatment is applied to the stretched high-strength fiber in which the orientation and crystallization of molecules are advanced, it is inevitable that high-concentration and / or high temperature and / or long-term treatment is required.
The fiber strength is reduced, and this is a problem in the manufacturing process, which in turn increases the manufacturing cost. Also, Japanese Patent Laid-Open No. 2-1336
No. 05 proposes that PVA and an acrylic acid-based polymer are blend-spun to form a cross-link between the two polymers, or a cross-linking agent such as an organic peroxide is added to perform cross-linking. However, P that is not related to strength
Since the content other than VA is about 2% or more, the strength is not sufficient. Furthermore, there are various problems because a polymer other than PVA is added to the stock solution.

Further, some of the inventors of the present invention have also proposed to uniformly crosslink the inside of the fiber by contacting the crosslinker solution with a high liquid content during the spinning process of PVA. On the other hand, it was found that the level was not sufficiently satisfactory.

As described above, various crosslinking methods have been proposed for improving high temperature performance such as hot water resistance and fatigue resistance of the high strength PVA fiber, but there is no method satisfying both performance and manufacturing cost.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention provides a high-strength PVA fiber having excellent high-temperature performance, which is useful in a field requiring excellent high-temperature performance (particularly fatigue resistance and hot water resistance) of tires and hoses. Is obtained by a simple manufacturing process.

[0008]

Means for Solving the Problems The present inventors have pursued the above-mentioned problems, and as described below, in the first step, the liquid content in the spinning process is high and it is easy to uniformly apply the crosslinking agent to the inside of the fiber. A small amount of the cross-linking agent is uniformly applied, then once dried to reduce the liquid content, and the cross-linking agent hardly penetrates into the inside of the fiber and is therefore likely to be unevenly distributed on the fiber surface. By adding a large amount of a cross-linking agent having good compatibility (the same cross-linking agent as in the first step is possible), a stretched raw yarn that is uniformly unevenly distributed on the fiber surface is produced, and this is dry-heat stretched at 230 ° C or higher. The fibers are oriented and crystallized, and the cross-linking inside the fiber is mild, and the fiber surface is stronger and more uniform than the inside of the fiber. We found that fatigue was excellent Which has led to the present invention.

That is, according to the present invention, "a spinning dope obtained by dissolving PVA in a solvent is wet- or dry-wet spun in an organic solvent system or an aqueous solidification bath having a coagulating action or a gelling action on PVA, and then the solvent is added. (1) When PVA having a degree of polymerization of 3,000 or more is used for producing a PVA-based fiber by performing dry heat drawing so that the total draw ratio is 14 times or more (2) A first cross-linking agent having a cross-linking ability with respect to PVA and having compatibility with a second cross-linking agent to be applied in a post-step in the inside and the surface of the fiber in the step before the spin drying. Applying a small amount, (3) applying the second cross-linking agent unevenly on the fiber surface after spin drying, (4) hot drawing 230 to 2
A method for producing a PVA fiber, which is performed at 65 ° C. It is.

The present invention will be described in more detail below. The degree of polymerization of PVA used in the present invention should be 3000 or more. When the degree of polymerization is less than 3000, it is difficult to obtain a high strength of 16 g / d or more, and the effect of improving the high temperature performance by crosslinking is not sufficient. A degree of polymerization of 7,000 or more is preferable because high strength is easily obtained and the effect of improving high temperature performance by crosslinking is remarkable. The saponification degree of the PVA used is preferably 98 mol% or more, more preferably 99 mol% or more, and particularly preferably 99.9 mol% or more because hot water resistance is excellent.
The PVA used may be a PVA-based polymer obtained by copolymerizing another vinyl group-containing monomer, for example, a monomer such as ethylene, itaconic acid, or vinylpyrrolidone at a ratio of 10 mol% or less.

The solvent for PVA used in the present invention is dimethyl sulfoxide (hereinafter abbreviated as DMSO), glycerin,
Examples thereof include solvents such as ethylene glycol, dimethylformamide, dimethylimidazolidinone, water, and an aqueous solution of rhodanate, and mixed solvents of these solvents. PVA is dissolved at a temperature suitable for each solvent and defoamed to obtain a spinning dope.

The spinning solution thus obtained is passed through a nozzle to form a PV.
Wet or dry-wet spinning is carried out in an organic solvent-based or water-based solidifying bath having a coagulating action or gelling action on A. The bath temperature is set to 20 ° C. or lower in a solidification bath mainly composed of an organic solvent having a coagulating action on PVA such as methanol, ethanol, and acetone. Of course, a mixed solvent of a coagulating organic solvent and a stock solution solvent can be used as the solidifying bath. If the temperature of the solidifying bath exceeds 20 ° C., the solidified filaments become non-uniform, and high strength fibers cannot be obtained. When the temperature of the solidifying bath is 10 ° C. or lower, the solidified yarn becomes more homogeneous, which is preferable. The so-called "gelling spinning" is a system that solidifies only by cooling and is usually extruded into the air. Therefore, the description of dry-wet spinning in the specification is used to include the "gelling spinning".

The thread that has been solidified in the solidifying bath is then wet-drawn, solvent-extracted and dried by a conventional method, and the obtained raw thread is dry-heated drawn so that the total draw ratio is 14 times or more.

The present inventors have found that in order to obtain PVA fibers having excellent high-temperature performance, it is important that crosslinks are made mild inside the fibers and strong on the fiber surface, and each is even. I found it. However, in order to obtain such a cross-linked structure, even if a cross-linking agent is added to the fiber before extraction and drying as in the conventional case, since it penetrates into the fiber at a high liquid content, the fiber surface cannot be strongly cross-linked. It was found that when the cross-linking agent was applied once after drying, it could be unevenly distributed on the surface, but the adhesion unevenness of the cross-linking agent was large, and neither was satisfactory.

As a result of various examinations, it was found that it is important to apply the crosslinking agent in two stages before spinning drying and after spinning drying, and the present invention was accomplished. That is, in the present invention, the content of the stock solution solvent, the solidification extraction bath, etc. is large relative to PVA, and the crosslinking agent is easily applied uniformly to the inside and the surface of the fiber.
A small amount of the first cross-linking agent of VA is applied and dried at 50 ° C. or higher (preferably 100 ° C. or higher), and the liquid content is lowered by the drying, and the cross-linking agent hardly penetrates into the inside and is easily unevenly distributed on the fiber surface By providing a second cross-linking agent having good compatibility with the first cross-linking agent in a later step, the second cross-linking agent is unevenly distributed on the fiber surface, and the first cross-linking agent having good compatibility in advance is provided. Since the agent is uniformly applied to the surface, the unevenness of application of the second crosslinking agent can be suppressed as much as possible. Therefore, a small amount of the cross-linking agent inside the fiber and a large amount of the cross-linking agent on the fiber surface can be evenly distributed. In the present invention, the second crosslinking agent is the first
It is preferable to add more than the above-mentioned crosslinking. It is more preferable to give it at 2 times equivalent or more. The first cross-linking agent having good compatibility with the second cross-linking agent referred to in the present invention may be any as long as it has an affinity for the second cross-linking agent and can uniformly disperse the second cross-linking agent, Furthermore, it is meant to include a mixture with a surfactant having the dispersibility of the second cross-linking agent even when it has no ability to disperse the second cross-linking agent. Of course the first
And the second cross-linking agent may be the same.

The PVA crosslinking agent used in the present invention includes:
Aldechts, diisocyanates, epoxies, methylols, organic peroxides, organic acids or inorganic acids,
There is no particular limitation as long as it is a compound that reacts with the above-mentioned cross-linking agent at a hot drawing temperature of 250 ° C. or less, but a compound that cross-links PVA during hot drawing in the subsequent step can produce cross-linked fibers in a simple step. preferable. Therefore, a suitable crosslinking agent is an organic acid or an inorganic acid, a compound which forms an acidic substance at 250 ° C. or lower, and the like. In the present invention, the point is that the cross-linking agent is knitted uniformly on the fiber surface,
For this purpose, the crosslinking agent is preferably a compound having a low affinity with PVA and a large molecular weight. Therefore, the most preferable cross-linking agent in the present invention is a long-chain alkyl phosphoric acid (mono, di, tri) ester, a sulfuric acid ester, a nitric acid ester, a phosphoric acid condensate or a phosphate amine compound, a phosphate compound of an amine or an amide, or Examples thereof include sulfonate compounds, thio compounds, and ammonium compounds having an amide bond or a urea bond. Further, organic peroxides that generate radicals at the hot stretching temperature can also be used. Further, the first cross-linking agent and the second cross-linking agent are not limited as long as they have good compatibility, but the exact same ones are most preferable in terms of compatibility and process simplicity.

The amount of the cross-linking agent applied varies greatly depending on the kind of the cross-linking agent and is in the range of 10 to 10,000 ppm. It is necessary to optimize the applied amount depending on the molecular weight of the cross-linking agent, the acid strength, the equivalent amount per molecule, the amount of radicals generated, and the heat stretching and / or heat treatment conditions (temperature and residence time) in the subsequent step. As described above, the feature of the present invention is that the cross-linking agent is unevenly distributed on the surface in order to strengthen the surface cross-linking of the fiber. Therefore, it is preferable to add the second cross-linking agent in a larger amount than the first cross-linking agent. It is more preferable that the amount of the second cross-linking agent applied to the first cross-linking agent is at least twice the equivalent amount.
Most preferably, it is a double equivalent or more.

Although the reason why the strength of the surface crosslinks is stronger and the fatigue strength at high temperature is superior to the internal crosslinks is not clear, the crosslinking reaction essentially inhibits the oriented crystallization, so that the fiber strength decreases with the degree of crosslinking. , If the degree of cross-linking is the same, cross-linking concentrates on the surface and less cross-linking in the interior gives higher strength because oriented crystallization proceeds more than in the case of uniform cross-linking, and high temperature fatigue resistance is conversely surface cross-linking is strong. Therefore, it is presumed that excellent results can be obtained because the fibers do not fuse together even at a higher temperature than in the case of uniform crosslinking.

The method of re-applying the crosslinking agent after once drying is as follows:
The cross-linking agent itself or the solvent dilution solution of the cross-linking agent can be applied by a dip nip method, a roller touch method, or a constant amount discharge method with a pump, but the cross-linking agent is diluted in terms of uniformity and control of the applied amount. It seems that the method of delivering a certain amount of liquid by a pump and applying it is optimal. In this case, it is necessary to re-dry. Before applying the cross-linking agent, for example, when the cross-linking agent is applied in a solidifying bath, the cross-linking agent may be washed out in the subsequent steps such as a wet drawing bath, an extraction bath, and an oil agent bath. It is preferable to add the crosslinking agent to all the baths in the same concentration.

As described above, the stretched raw yarn in which a small amount of the cross-linking agent is evenly penetrated into the inside of the fiber, and which is evenly distributed on the surface of the fiber, has a total draw ratio (hereinafter abbreviated as TD) of 14 times or more. Hot stretching must be done at ~ 265 ° C. One of the important points of the present invention is to perform oriented crystallization of PVA molecules by performing hot stretching and to crosslink PVA with a crosslinking agent. It is a feature of the present invention that the strength reduction is slight and strong surface cross-linking that significantly improves hot water resistance and high temperature fatigue resistance is generated without adding a new step. Hot stretching temperature is 230
In the case of the present invention using PVA having a degree of polymerization of 3000 or more at a temperature of less than 0 ° C, neither oriented crystallization nor crosslinking of PVA is sufficient. Two
Above the melting point of PVA crystals at temperatures above 65 ° C,
Not only oriented crystallization does not occur, but PVA decomposition becomes a priority rather than crosslinking.

[0021] When the dry yarn drawn with a crosslinking agent after drying is subjected to dry heat drawing, it is feared that the cross-linking of PVA significantly reduces the dry heat drawability, and the oriented crystallization of molecules cannot be sufficiently performed. However, the key to the present invention was to find that unexpectedly, the dry heat drawability is hardly reduced by selecting an appropriate type of cross-linking agent, the amount and state of attachment, and the dry heat stretch temperature. It became a point. The reason for this is unknown, but it is presumed that during dry heat drawing, the physical structure change due to oriented crystallization of the molecules is prioritized, and then the chemical structure change such as the crosslinking reaction occurs. The crosslinking agent applied before the dry heat drawing is considered to be excellent because it has such a function. As described above, the strength and the degree of crosslinking of the fiber should be properly selected because they depend on the type and amount of the crosslinking agent to be applied, the balance between the dry heat drawing temperature and the residence time. As an example, a stretching temperature and a residence time that give the highest strength without a cross-linking agent are found, and the cross-linking agent-provided original yarn is stretched at a stretching temperature and a stretching time that are substantially the same as those to obtain a predetermined degree of cross-linking. The amount of the cross-linking agent to be used may be determined.

The total draw ratio including wet drawing and dry heat drawing is 1
If it is less than 4 times, the fiber strength is low, so it must be 14 times or more. It is preferable that the total draw ratio is high, but in consideration of the occurrence of fuzz and yarn breakage, the maximum draw ratio is 0.75 to 0.95.
Should be doubled. After the dry heat drawing, a fixed length heat treatment or a dry heat shrinkage may be further applied to accelerate crystallization and accelerate crosslinking.

In summary, it was found that in order to obtain a high-strength PVA fiber having excellent high-temperature performance, it is important to uniformly and strongly crosslink the fiber surface as compared with the inside of the fiber.
For this purpose, the PVA crosslinking agent is first applied in a small amount in a state where the liquid content in the spinning step is high and the crosslinking agent can easily permeate uniformly, and then it is dried once, and the liquid content is low, and it penetrates into the inside of the fiber. By re-adding more cross-linking agent that is compatible with the above-mentioned cross-linking agent in a state where it is difficult to unevenly distribute on the surface, the cross-linking agent is evenly unevenly distributed on the surface, and if necessary re-drying, Then, hot drawing is performed to allow the PVA molecules to be oriented and crystallized, and at the same time, to make the surface stronger and more uniform than the inside of the fiber.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 PVA having a viscosity average degree of polymerization of 4000 and a saponification degree of 99.8 mol% was added to DMSO so as to have a concentration of 9.5% by weight and dissolved at 80 ° C. in a nitrogen atmosphere. The spinning solution thus obtained was used to have a pore diameter of 0.13 mm and a pore number of 50.
Nozzle from 0 to 3 ° C methanol / DMSO = 7/3
Wet spinning is carried out in a solidifying bath consisting of (weight ratio), and the solidified yarn obtained is subjected to a 4-fold wet drawing in a bath of methanol / DMSO = 9/1 at 40 ° C., and then shown by the following chemical formula 1. The long-chain alkyl phosphate amine neutralized product used as a cross-linking agent was added to the DMS in a methanol bath containing 0.3% thereof.
O was extracted and dried at 100 ° C.

[0026]

[Chemical 1]

In this way, 0.5% of the above-mentioned cross-linking agent /
A spun raw yarn containing PVA was obtained. In addition to the above 3
% Contact methanol solution by roller touch method,
Immediately after drying with a hot roller of 80 ° C., it was drawn 5.5 times in a hot air drawing furnace having a temperature gradient of 180 ° C. in the first furnace, 200 ° C. in the second furnace, and 243 ° C. in the third furnace to obtain a sample of 22 times TD. .. The sample was dried with a hot roller, sampled, and the amount of the cross-linking agent attached was measured by Soxhlet extraction.
% / PVA, and the amount of the cross-linking agent attached is 0.5 before spinning and drying.
% / PVA and 2.5% / PVA after spinning and drying. T
The total residence time in the furnace during hot drawing of D22 times was 55 seconds.

This 22 times stretched yarn is purple and colored,
It was presumed that the dehydration cross-linkage had occurred. The strength of the yarn is 18.3 g / d, the hot water disconnection temperature under load of 200 mg / d in the autoclave is 155 ° C., and the degree of polymerization is 4000.
The hot water resistance of PVA was extremely excellent. The yarn was twisted and dipped in an RFL liquid to obtain a dip cord, which was embedded in the belt. The obtained belt was bent and fatigued 30,000 times at 100 ° C., and the strength of the cord taken out from the belt was measured before the fatigue. It was excellent as 70% when measured as a retention rate with respect to the cord strength. This drawn yarn was dissolved in 50% zinc chloride aqueous solution at 50 ° C. to dissolve PVA crystals, and the elastic modulus of the obtained gel (useful as a measure of the degree of crosslinking of the whole fiber) was measured. It was ^-2 g / d. In addition, the drawn yarn end was immersed in a 20% hydrochloric acid aqueous solution at 20 ° C.
When the swelling state of the yarn end was observed while it was soaked for a minute and washed with water while it was still wet, surface wrinkles were clearly observed, showing that a highly crosslinked material that is difficult to swell in hydrochloric acid is present on the fiber surface, It was observed that was almost dissolved and cross-linking was not so advanced.

Comparative Example 1 An uncrosslinked 22 times stretched yarn was obtained in the same manner as in Example 1 except that the crosslinking agent in Example 1 was not added before and after spinning and drying. The hue was almost white, the yarn strength was 18.9 g / d, and the hot water disconnection temperature in the autoclave was 130 ° C. 100 ° C. as in Example 1, 3
The strength retention rate after ten thousand belt bending fatigue is 55%,
It was inferior to Example 1. Further, in the same manner as in Example 1, measurement of gel elastic modulus in a zinc chloride aqueous solution and observation of a swollen state in hydrochloric acid showed that the yarn was dissolved and no cross-linking was formed.

Comparative Example 2 Same as Example 1 except that the concentration of the cross-linking agent in the extraction bath before spin-drying was increased to 0.9% and the adhesion treatment of the cross-linking agent after spin-drying and before hot drawing was omitted. As a result, a 22 times stretched yarn was obtained. The adhesion amount of the cross-linking agent was 1.4% / PVA based on the result of Soxhlet extraction. The obtained drawn yarn has a purple hue and a yarn strength of 17.5 g /
d, which is lower than that of Example 1, and the hot water cutoff temperature in the autoclave was 156 ° C., which was equivalent to that of Example 1, but 100
65% strength retention after belt bending fatigue at 30,000 cycles
Was better than Comparative Example 1, but lower than Example 1. The gel elastic modulus in the zinc chloride aqueous solution was 0.3 × 10 ^-2 g / d, which was about the same as in Example 1, but the swelling state in hydrochloric acid showed slight wrinkles on the surface and the inside of the fiber became gel beads. It was confirmed that the number of surface cross-links was small, but the number of internal cross-links was more than that in Example 1.
That is, although there was no difference in the overall degree of cross-linking between Example 1 and Comparative Example 2, it was found that the cross-linking distribution was that Example 1 was the surface cross-linking type, whereas Comparative Example 2 was the uniform cross-linking type.

Example 2 DMSO was added to PVA having a viscosity average degree of polymerization of 8500 and a saponification degree of 99.9 mol% and was heated and dissolved at 80 ° C. in a nitrogen atmosphere to obtain a PVA solution having a concentration of 7.5%. This spinning dope was prepared with a hole diameter of 0.16 mm and a hole number of 400.
From the nozzle of No. 1 through the air gap of 10 mm, dry-wet spinning was performed at 4 ° C. in a solidification bath consisting of methanol / DMSO = 7/3. The solidified yarn obtained is treated with methanol / DMS at 40 ° C.
After performing wet stretching 4 times at O = 9/1, DMSO was extracted with a methanol bath. Next, a long-chain alkylphosphoric acid represented by the following chemical formula 2 was used as a cross-linking agent in a hexane bath containing 0.8% of the cross-linking agent by a roller touch method, and dried with hot air at 120 ° C.

[0032]

[Chemical 2]

Then, the obtained raw yarn was brought into contact with a hexane solution containing 2.4% of the above-mentioned cross-linking agent by a roller touch method, dried with hot air, and the first furnace 150 ° C, the second furnace 170 ° C and the third furnace The sample was drawn 5 times in a hot air drawing furnace having a temperature gradient of 245 ° C. to obtain a sample with 20 times TD. At this time, the total residence time in the drawing furnace was 62 seconds. The amount of the cross-linking agent attached was measured by Soxhlet extraction and found to be 0.4 after spin drying.
% / PVA and 2.3% / PVA immediately before hot drawing.

This drawn yarn was colored a bluish purple,
It was estimated that dehydration cross-linking of PVA had occurred. The strength of the yarn was 19.6 g / d, and the hot water disconnection temperatures in the autoclave were 165 ° C., 100 ° C., and the strength retention after belt bending fatigue at 30,000 cycles was 81%, which was excellent. The gel elastic modulus in a zinc chloride aqueous solution was 0.8 × 10 ^-2 g / d, and it was found by microscopic observation of the swollen state in hydrochloric acid that the surface cross-linking was stronger than in Example 1. Further, the inside of the fiber was in the form of gel beads, and it was found that the internal cross-linking was more advanced than in Example 1.

Comparative Example 3 Spin-drawing was carried out in the same manner as in Example 2 except that the application of Example 2 was omitted before the spin-drying.
A drawn yarn with a TD of 20 times was obtained. Purple to ultra-violet color spots are clearly observed on this drawn yarn, the hot water cutoff temperature in the autoclave is 140 to 162 ° C, and the gel elastic modulus is 0.0.
The degree of cross-linking greatly fluctuated to about 0.7 × 10 ^-2 g / d, and a satisfactory yarn could not be obtained.

COMPARATIVE EXAMPLE 4 Instead of applying a 0.8% hexane solution of the crosslinker of Example 2 before spin drying, phosphoric acid 10
Spin-drawing was carried out in the same manner as in Example 2 except that 0 ppm methanol solution was applied to obtain a TD 20-fold drawing system.
The obtained drawn yarn has a clear blue-purple to light purple color spot, and the hot water disconnection temperature in the autoclave is 155-1.
Although the change was relatively small at 62 ° C., the gel elastic modulus was greatly changed to 0.2 to 0.7 × 10 ⁻² g / d, and cross-linking unevenness of the single fiber was recognized. It is presumed that this is because the compatibility between the phosphoric acid used as the first cross-linking agent and the second cross-linking agent was poor, and the second cross-linking agent became adhesion spots.

[0037]

According to the present invention, the fiber surface can be strongly and uniformly crosslinked from the inside of the fiber, and the high temperature performance, especially the high temperature fatigue resistance and the fusion resistance under high temperature and high pressure are improved. Therefore, it is useful as a rubber material for brake hoses for automobile tires and other industrial materials that require high-temperature performance. Further, since the method of the present invention can carry out the crosslinking treatment within a process in a short time with almost no addition to the conventional spinning / drawing equipment, it is also useful in that it is industrially inexpensive.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Kobayashi 1621 Sakata, Kurashiki City, Okayama Prefecture Kuraray Co., Ltd.

Claims (1)

[Claims] 1. A spinning stock solution obtained by dissolving polyvinyl alcohol in a solvent is wet or dry-wet spun in an organic solvent system or an aqueous solidifying bath having a coagulating action or a gelling action for polyvinyl alcohol, and then the solvent. When a polyvinyl alcohol fiber is produced by dry-drawing the obtained spun raw yarn so that the total draw ratio is 14 times or more, (1) the degree of polymerization is 3000.
Using the above polyvinyl alcohol, (2) in the step before the spin drying, the inside and the surface of the fiber have a crosslinking ability with respect to the polyvinyl alcohol and are compatible with the second crosslinking agent to be applied in the subsequent step. A small amount of a certain first cross-linking agent is applied, (3) a second cross-linking agent is unevenly distributed on the fiber surface after spin-drying, and (4) hot stretching is performed at 230 ° C or higher.
A method for producing a polyvinyl alcohol fiber, which is performed at 265 ° C.