JP2858923B2 - Manufacturing method of high strength polyvinyl alcohol fiber with excellent hot water resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a high-strength polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having excellent hot water resistance and useful in fields such as cement and rubber reinforcing materials. .

<Conventional technology> Conventionally, among general-purpose polymer fibers, PVA-based fibers have higher strength and elastic modulus than polyester, polyamide, polyacrylonitrile-based fibers, etc., and are 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 a high-strength high-modulus fiber can be obtained by gel-spinning and ultra-stretching a raw material having an ultra-high molecular weight in polyethylene which is a general-purpose polymer. However, polyethylene itself was insufficient in that it had a low melting point and insufficient heat resistance, and as a reinforcing fiber, adhesion to matrix was poor.

Therefore, attempts have been made to increase the strength and elasticity of other general-purpose polymers using gel spinning and ultra-drawing techniques. Among them, PVA has the same planar zigzag structure as polyethylene and has an active hydroxyl group, so it is easy to generate intermolecular hydrogen bonds, and it is possible to obtain fibers with high strength, high elastic modulus, high heat resistance, and high affinity. Yes, for example, JP-A-59-100710
And JP-A-59-130314 have been proposed. These p
VA fibers have higher strength and higher elastic modulus than commercially available PVA fibers, and also have better heat resistance than the above polyethylene fibers. On the other hand, there is a problem that the PVA fiber polymer itself is insoluble in water and thus is inferior in hot water resistance. The hot water resistance of the high strength, high modulus PVA fiber is improved as compared with the conventional PVA fiber, but is not sufficient.

Therefore, proposals have been made to improve the hot water resistance of high-strength PVA-based fibers. For example, in JP-A-63-120107, 15
It has been proposed to apply 5 to 15% acetalization to a drawn yarn drawn twice or more times. However, the effect of improving hot water resistance is not sufficient with only light acetalization, and an acetalization step must be added. In addition, JP-A-1-56517
No., spinning and drawing three times or more after spinning, drying and PV
It has been proposed that a crosslinking agent such as an organic peroxide, an isocyanate-based compound, or an epoxy-based compound is applied to the surface of the A-fiber and then crosslinked by drying and stretching. However, since the crosslinkable agent is mainly present on the surface and is mainly composed of surface crosslinks, 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 attention in terms of safety and health must be handled. Further, JP-A-2-84587 discloses that in order to improve the fatigue resistance of PVA fiber cords, PVA fibers having a strength of 15 g / d or more are treated with organic compounds such as aldehydes, isocyanates, organic peroxides, carboxylic acids and phosphorus. Treatment with a crosslinking agent such as an acid, hydrochloric acid, or an inorganic compound such as titanium has been proposed. However, in order to perform post-treatment on the high-strength fiber in which the orientation and crystallization of molecules are progressing, the treatment must be performed at a high concentration and / or at a high temperature and / or for a long time.
As the fiber strength decreases, the manufacturing process becomes complicated, and the manufacturing cost increases. Japanese Patent Application Laid-Open No. 2-133605 proposes that PVA and an acrylic acid-based polymer are blended and spun to form a cross-link between the two polymers or to further cross-link by adding a cross-linking agent such as an organic peroxide. Have been. However, it is not sufficient in strength because it contains about 2% or more other than PVA which does not contribute to strength. Further, there are various problems because a polymer other than PVA is added to the stock solution.

As described above, various methods of crosslinking to improve the hot water resistance and fatigue resistance of high-strength PVA fibers have been proposed, but there is no method that satisfies both performance and manufacturing cost.

<Problems to be Solved by the Invention> Accordingly, the present invention is to obtain PVA fiber having excellent hot water resistance and strength, which is useful as a reinforcing material for cement or rubber, in a thimble manufacturing process.

<Means for Solving the Problems> The present inventors have pursued the above-mentioned problems and contacted a high-temperature content salt with a salt serving as a dehydration catalyst at a high temperature before the dry heat drawing as described later. By uniformly infiltrating this into Shino and drying and performing dry heat drawing, it is possible to obtain a fiber having a crosslinked structure uniformly not only on the fiber surface but also inside the fiber by a simpler manufacturing process than known methods. Thus, the present invention was found to be excellent in both strength and hot water resistance, leading to the present invention.

In the present invention, when introducing cross-linking for improving hot water resistance of high-strength PVA fiber, a known method is used to apply a cross-linking agent to a drawn yarn that has been subjected to dry heat drawing and molecular orientation and crystallization, and the fiber surface is obtained. In contrast to the introduction of cross-linking mainly, the type and amount of the cross-linking agent when penetrating the cross-linking agent into the fiber, and by adjusting the liquid content of Itoshino, the fiber of the cross-linking agent Internal uniform infiltration is measured, followed by dry heat stretching, orientation crystallization and dehydration crosslinking at the same time, thereby introducing uniform crosslinking. Also, this method is characterized in that it is obtained by a simpler manufacturing process than known methods.

Hereinafter, the present invention will be described more specifically. Used in the present invention
Although the degree of polymerization of PVA is not particularly limited, it is preferable to use a PVA having a higher degree of polymerization because strength and hot water resistance are excellent. In the case of improving the hot water resistance by applying a salt which becomes a dehydration catalyst at a high temperature and then drying and stretching the same to uniformly crosslink as in the present invention, it has been found that the higher the degree of polymerization, the greater the effect of improving the hot water resistance. The average degree of polymerization determined from the viscosity is preferably 3000 or more. Further, when the average degree of polymerization is at least 7000, the synergistic effect of improving the hot water resistance by uniform crosslinking is particularly large and is preferable. The saponification degree of PVA used is 9
It is preferably at least 8 mol%, more preferably at least 99 mol%, and particularly preferably at least 99.9 mol% in terms of hot water resistance. The PVA used is a PVA obtained by copolymerizing a monomer having a vinyl group, for example, a monomer such as ethylene, itaconic acid, or vinylpyrrolidone at a ratio of 10 mol% or more.
It may be a system polymer.

Solvents for PVA used in the present invention include dimethylsulfoxide (hereinafter abbreviated as DMSO), glycerin, ethylene glycol, dimethylformamide, dimethylimidazolidinone, water, and aqueous solutions of rodane salts, and a mixture of these solvents. . PVA is dissolved at a temperature suitable for each solvent and defoamed to obtain a spinning stock solution.

The obtained spinning dope is spin-dried through a nozzle into a coagulation bath of 20 ° C. or lower mainly comprising an organic solvent such as methanol, ethanol, acetone or the like which has a coagulation action on PVA. Of course, a mixed solvent of a coagulable organic solvent and a stock solution can also be used as the coagulation bath. If the temperature of the coagulation bath exceeds 20 ° C., the solidified yam becomes uneven and high-strength fibers cannot be obtained. It is preferable to set the coagulation bath temperature to 10 ° C. or lower because the solidified yam becomes more homogeneous. The so-called "gelling spinning" is a system that solidifies only by cooling, and is usually once extruded into the air. In the present invention, the "gelling spinning" is included in the dry-wet spinning referred to in the present specification. Things.

Itoshino solidified in the coagulation bath is subjected to wet stretching, solvent extraction, drying, and dry heat drawing.
In the step before dry heat drawing, so that A is dehydrated and crosslinked, 220
It is one of the important points to give a salt that functions as a dehydration catalyst at a high temperature of up to 270 ° C. to 20 to 20,000 ppm (vs. PVA) in Itoshino. Salts that function as dehydration catalysts at high temperatures of 220 to 270 ° C include, for example, acid salts of polyvalent strong acids such as sulfuric acid and phosphoric acid with alkali metals or alkaline earth metals, ammonium salts of strong acids with ammonia, and strong acids. And salts of transition metals. Specifically, primary potassium phosphate, secondary potassium phosphate, primary sodium phosphate, secondary sodium phosphate, acidic potassium sulfate, calcium acid phosphate, ammonium sulfate, ammonium phosphate, primary ammonium phosphate, phosphorus phosphate Examples thereof include ammonium secondary acid, potassium ammonium phosphate, copper sulfate, copper nitrate, cobalt nitrate, and manganese chloride. Crosslinking agents for PVA include aldehydes, isocyanates, epoxies, methylols, and organic peroxides.The cross-linking reaction between these and PVA is carried out at 200 ° C or lower. Is decomposed or, in the case of organic peroxides, decomposes too rapidly, so that it is not suitable as a dehydration crosslinking agent in the dry heat drawing step performed at 220 ° C. or higher. Catalysts that promote dehydration and crosslinking of PVA at high temperatures include inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, and organic sulfonic acids, all of which are strong acids at room temperature.
Careful handling is required.

It is necessary to attach the salt to the shinoshi having a liquid content of 30% / PVA or more in a step before the dry heat drawing at 10 to 20,000 ppm / PVA. If the liquid content is less than 30%, the salt does not uniformly penetrate into the inside of the shinoshino, which is not preferable. It is more preferable that the liquid content is 80% / PVA or more in terms of uniformity. In the present invention, the liquid content of Itoshino is defined as the liquid content of the Itoshino in the process, which is shaken vigorously three times by hand to drain the liquid, quickly measure its weight (W ₁ ), and then the coagulation bath and the undiluted solvent are completely It is dried under reduced pressure until it evaporates to a constant weight, the weight is measured (W ₂ ), and the value is given by the following formula (W).

The amount of salt attached varies depending on the strength of the function as a cross-linking catalyst, the temperature during hot drawing and the residence time, but if it is less than 10 ppm / PVA, dehydration cross-linking during hot drawing becomes insufficient. The desired hot water resistance improvement effect cannot be obtained. It is more preferably at least 30 ppm / PVA, most preferably at least 80 ppm. If the amount of salt attached exceeds 20,000 ppm, the decomposition reaction takes precedence over the dehydration crosslinking at the time of dry heat drawing, so that the yarn strength is disadvantageously reduced. An appropriate amount of acid should be selected depending on the type of salt, the temperature at the time of dry heat drawing and the residence time.

The step of applying the salt must be performed before the hot drawing, but is not particularly limited as long as the liquid content of the yarn is 30% / PVA or more before the hot drawing. For example, a salt may coexist in an oil bath immediately before drying, or a salt may be added to a solvent extraction bath before the oil bath. Further, a salt may be added to one bath in which the undiluted solution is discharged from the nozzle and solidified. In this case, the uniformity inside the fiber is excellent, but after the first bath (wet stretching bath, extraction bath,
If the same concentration of salt is not added to an oil bath, the salt may be washed away. Therefore, it is preferable to add the salt to all baths.

After the solidification in the coagulation bath, the undiluted solvent in the yarn is extracted, washed and removed with an extract of a coagulable organic solvent such as methanol, and dried. It is preferable to perform wet stretching in a single stage or more preferably in multiple stages before drying, so that sticking during drying can be prevented. A more preferred wet stretch ratio is 2.5 times to 5.5 times. If the wet stretching ratio exceeds 6 times, breakage of single yarn and cross-sectional deformation are likely to occur, so that it should be avoided. The drying temperature is preferably from 30C to 150C in terms of drying efficiency and performance. More preferably, it is 50 to 120 ° C.

Then, it is important to carry out the dry heat stretching so that the temperature is 220 ° C. or more and the total stretching ratio is 15 times or more so that the molecules are oriented and crystallized and the salt is also subjected to dehydration crosslinking by salt. One of the points. In the case where the raw yarn is dry-drawn after the addition of the salt, it is feared that the dry-heat drawability is significantly reduced due to the cross-linking of the PVA, and that the orientation and crystallization of the molecule may not be sufficiently performed. The key point of the present invention was that it was found that if the type, amount and state of adhesion of the crosslinkable agent and the dry heat stretching temperature were selected, the dry heat stretchability was unexpectedly hardly reduced.
The reason for this is unknown, but it is presumed that the dry heat drawing first gives rise to a change in the physical structure of oriented crystallization of molecules, followed by a change in the chemical structure of dehydration crosslinking. It is considered that the salt selected in the present invention as a crosslinkable agent to be applied before the dry heat drawing has such a function and thus is excellent. The fiber strength and the degree of dehydration crosslinking depend on the type and amount of the salt to be provided and the balance between the dry heat drawing temperature and the residence time, and should be appropriately selected. As an example, the stretching temperature and the residence time at which the strength is the highest in the state where the salt is not applied are found, and the raw yarn to which the salt is applied is stretched at substantially the same stretching temperature and the stretching time so that the degree of crosslinking is 30 to 100%. What is necessary is just to determine the application amount of the predetermined salt. The degree of crosslinking referred to here is the undissolved fiber after being treated at a bath ratio of 1000 for 1 hour in hot water at a temperature 5 ° C higher than the hot water temperature at which the drawn yarn of the PVA fiber without salt is completely dissolved. Is passed through a 300 mesh wire gauze, the remaining amount of undissolved gel when dried under reduced pressure at 80 ° C. to a constant weight at 80 ° C. is measured, and is calculated from the residual ratio with respect to the initially used amount.

The stretching temperature depends on the degree of polymerization of the PVA, but must be at least 220 ° C. or higher. The higher the polymerization, the higher the temperature, the higher the temperature. If the total draw ratio of the wet draw and the dry heat draw is less than 15 times, the fiber strength is low, so it must be 15 times or more. The total draw ratio is preferably higher, but should be 0.75 to 0.95 times the maximum draw ratio in consideration of the occurrence of fluff and breakage. After the dry heat stretching, a constant-length heat treatment or dry heat shrinkage may be further performed to promote crystallization and promote dehydration crosslinking.

As described above, a predetermined amount of salt is brought into contact with a high liquid content of Ishino to allow the salt to uniformly penetrate into the inside, and then dried. It is possible to produce PVA fiber which is excellent in hot water resistance and fatigue resistance because it can be uniformly performed to the inside and is inexpensive.

(Effect of the Invention) Whereas the conventional crosslinking treatment method for high-strength PVA fibers mainly involves surface crosslinking, the present invention employs a method in which a salt is brought into contact with a high-moisture-content Ishino, dried and then stretched by dry heat. Cross-linking is uniformly applied to the inside of the fiber at the same time as molecular orientation and crystallization, thereby improving hot water resistance and adding high strength and high heat water resistance without adding new equipment and manufacturing process.
A fiber can be obtained, so that it can be manufactured at low cost. High strength and high heat resistance obtained
PVA fiber is superior in cost performance to other super fibers such as conventional PVA fiber and para-amide, and is used in rubber material fields such as hoses and tires, FRC and FRC.
It can be widely used in the field of reinforcing materials such as RP.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 1 7.5 of PVA having a viscosity average degree of polymerization of 4000 and a saponification degree of 99.9 mol% was used.
It was added to DMSO so as to be a weight% and dissolved at 70 ° C. under a nitrogen atmosphere. The obtained spinning dope was wet-spun from a nozzle having a pore size of 0.15 mm and a number of holes of 500 into a coagulation bath (first bath) at 5 ° C. and methanol / DMSO = 7/3 (weight ratio). The obtained coagulated yarn is further immersed in the same methanol / DMSO bath as the first bath (second bath), and then methanol / DMSO at 90 ° C. = 90/10
4 times wet stretching was performed through a wet stretching bath (third bath). Thereafter, the first extraction bath (methanol / DMSO = 98/2)
DMSO was further extracted by passing through a second extraction bath (fifth bath) of 99.9 / 0.1 methanol / DMSO containing 100 ppm of phosphorus tertiary ammonium, and 150 ppm (vs. PVA). ) Was added to Itoshino and dried at 80 ° C. The liquid content of Itoshino after the fourth bath is 15
It was 0%. Next, the obtained spun yarn was stretched in a hot air furnace having a first furnace of 180 ° C. and a second furnace of 236 ° C. at a total draw ratio of 20.5 times. The residence time in the drawing furnace was 75 seconds.

The obtained drawn yarn was deeply colored in a purple system, and it was presumed that a dehydration crosslinking reaction had occurred. The yarn strength was 18.3 g / d. The yarn was immersed in hot water at 150 ° C. for 1 hour in an autoclave at a constant length, and then taken out and dried. When the strong residual ratio was measured, it hardly decreased to 94%, indicating excellent hot water resistance.

Comparative Example 1 Spin drawing was performed in the same manner as in Example 1 except that phosphoric acid was not added to the second bath, and a total draw ratio of 21 was possible.

No coloring was observed in the obtained drawn yarn. The yarn strength was 19.6 g / d. The drawn yarn was immersed in hot water of various temperatures in an autoclave at a constant length for 1 hour, taken out, and the dissolved state was observed. As a result, almost no water was dissolved in hot water at 135 ° C. or higher, and the yarn shape was not maintained.

Comparative Example 2 The drawn yarn obtained in Comparative Example 1 contains 8% of phosphoric acid and 20% of urea
Immerse in an aqueous solution at 60 ° C for 30 minutes, wash with running water at room temperature for 15 minutes, then 80 ° C
It was dried and then heat-treated at 192 ° C. for 6 minutes. This treated yarn was colored in the same manner as in Example 1. The hot water resistance of this treated yarn was excellent at 148 ° C, but the yarn strength was 14.8 g / d, which was lower than that of Example 1 and Comparative Example 1, and the high-strength PV having a degree of polymerization of 4000.
The A fiber was unsatisfactory.

Example 2 PVA having a viscosity average degree of polymerization of 7800 and a saponification degree of 99.8 mol% was added to 6
It was added to DMSO so as to be a weight% and dissolved at 70 ° C. under a nitrogen atmosphere. This was spun, wet drawn, extracted and dried in the same manner as in Example 1. However, monobasic sodium phosphate (120 ppm) was added to the fifth bath instead of ammonium phosphate. After the fourth bath, the liquid content of Itoshino was 160%, and the adhesion rate of monosodium phosphate was 190 ppm (vs. PVA). Next, the obtained spun yarn is heated in a hot stove at 160 ° C. in the first furnace and 245 ° C. in the second furnace, and the total draw ratio is
The film was dried and stretched to 20 times.

The obtained drawn yarn was colored as in Example 1, and the yarn strength was 19.6 g / d. In addition, this thread is
After being immersed in hot water at 65 ° C. for 1 hour at a constant length and taken out and dried, the strong residual ratio was determined to be 92%. The heat-resistant water of the yarn prepared without adding sodium phosphate monobasic was 140 ° C. It can be seen that the use of PVA having a high degree of polymerization increases the hot water resistance improving effect of the present invention.

Example 3 PVA having a viscosity average degree of polymerization of 18000 and a saponification degree of 99.8 mol%
Glycerin to a concentration of 180 wt.
It melted by heating at ° C. The obtained spinning dope is 0.17 mmφ in pore size,
Dry-wet spinning was performed from a nozzle having 100 holes with an air gap of 1 cm in a first bath of methanol / glycerin = 8/2 at -5 ° C. The obtained gel shinoshi was wet-drawn, glycerin was extracted, and copper sulfate was added to a methanol bath immediately before drying.
Copper sulfate was adhered to Itoshino by a roller touch method and then dried. The liquid content of the yarn upon contact with copper sulfate was 80%, and the adhesion rate of copper sulfate after drying was 280 ppm (vs. PVA). The obtained spun yarn was dried and drawn in a hot air furnace at a first furnace of 160 ° C. and a second furnace of 259 ° C. to obtain a drawn yarn having a total draw ratio of 18 times.

Although the coloring of the obtained drawn yarn was less than in Examples 1 and 2, the hot water resistance was extremely excellent at 180 ° C. or higher.
The yarn strength was also excellent at 20.8 g / d.

It is well known that a very small amount of copper sulfate is effective in preventing the coloration of PVA, but it has been found that a large amount of copper sulfate is effective in improving hot water resistance when it is attached to a large amount and hot stretched.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirofumi Sano 1621 Sazu, Kurashiki-shi, Okayama Pref. -213510 (JP, A) JP-A-1-156517 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) D01F 6/14

Claims (1)

(57) [Claims] 1. A method for producing a polyvinyl alcohol-based fiber by spin-drying a spinning stock solution in which polyvinyl alcohol is dissolved in an organic solvent-based coagulation bath at 20 ° C. or lower after wet- or dry-wet spinning to produce polyvinyl alcohol-based fiber. A salt serving as a dehydration catalyst for polyvinyl alcohol is brought into contact with a yarn having a liquid content of 30% or more with respect to polyvinyl alcohol at 220 to 270 ° C., and the salt is attached to polyvinyl alcohol at 10 to 20,000 ppm and dried. A method for producing a high-strength polyvinyl alcohol-based fiber having excellent hot water resistance, which is followed by performing dry heat drawing at a temperature of 220 ° C or higher and 270 ° C or lower and a total draw ratio of 15 times or higher.