JP2826182B2 - 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 high-strength, high-modulus fibers can be obtained by gel-spinning and ultra-drawing ultrahigh-molecular-weight raw materials in polyethylene, which is a general-purpose polymer. However, polyethylene itself is insufficient in that it has a low melting point and insufficient heat resistance, and as a reinforcing fiber, adhesiveness to matrix is poor.

Therefore, attempts have been made to increase the strength and elasticity of other general-purpose polymers by using a gel spinning super-drawing technique. Among them, PVA has the same planar zigzag structure as polyethylene and also 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. For example, JP-A-59-100710
And JP-A-59-130314 have been proposed. these
PVA fibers have higher strength and higher elastic modulus than commercially available PVA fibers, and also have better heat resistance than the above-mentioned polyethylene fibers. On the other hand, the PVA fiber has a problem that it is inferior in hot water resistance because the polymer itself is soluble in water. The hot water resistance of the high-strength, high-modulus PVA fibers is improved, but not sufficient, as compared with conventional PVA fibers.

Therefore, proposals have been made to improve the hot water resistance of high-strength PVA-based fibers. For example, in JP-A-63-120107,
It has been proposed to apply 5 to 15% acetalization to a drawn yarn drawn 15 times or more. However, the effect of improving hot water resistance is not sufficient only by light acetalization, and the process is complicated. In Japanese Patent Application Laid-Open No. 1-156517, spin drawing is performed three times or more, and an organic peroxide is applied to the surface of the partially drawn yarn.
By providing a crosslinking agent such as an isocyanate compound and an epoxy compound, and then performing dry heat drawing,
It has been proposed to crosslink the fiber surface. However, since the cross-linking agent is mainly present on the surface and is mainly made of surface cross-linking, the stretchability becomes insufficient, and the elastic modulus is at most 31.
Low at 0g / d. There is also a problem in that special organic compounds that require attention in terms of safety and health must be handled.
JP-A-2-84587 further discloses a PVA fiber having a strength of 15 g / d or more in order to improve the fatigue resistance of the PVA fiber cord.
It has been proposed to treat with a crosslinking agent such as an organic compound such as aldehyde, isocyanate, organic peroxide and carboxylic acid, and an inorganic compound such as phosphoric acid, hydrochloric acid and titanium. However, since post-treatment is performed on a drawn high-strength fiber in which the orientation and crystallization of molecules are progressing, a high-concentration and / or high-temperature and / or long-term treatment must be performed, and the fiber strength decreases. In addition, it is a problem in the manufacturing process, and the manufacturing cost is increased. 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 affect the strength. Further, there are various problems because a polymer other than PVA is added to the stock solution.

As described above, various cross-linking methods for improving 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 excellent strength, which is useful as a reinforcing material for cement or rubber, by a simple manufacturing process.

<Means for Solving the Problems> The present inventors have pursued the above-mentioned problems, and contact the acid with the high-liquid-content-state itoshino before dry-heat stretching, as described later, to uniformly disperse the acid inside the itoshino. By performing dry heat drawing after drying, 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 a known method. It was recognized that both the strength and the hot water resistance were excellent, which led to the present invention.

The present invention provides a cross-linking agent for improving the hot water resistance of a high-strength PVA fiber by applying a cross-linking agent to a drawn yarn in which molecular orientation and crystallization are progressing by dry heat drawing by a known method. Introducing crosslinking mainly on the surface, while penetrating the crosslinking agent into the interior of the fiber to achieve uniform crosslinking, the type of crosslinking agent used when the crosslinking agent is penetrated into the fiber By optimizing the applied amount and the liquid content of Itoshino, uniform penetration of the cross-linking agent inside the fiber is achieved, followed by dry heat stretching, orientation crystallization and dehydration cross-linking, thereby introducing uniform cross-linking. It was done. Also, this method is characterized in that it is obtained by a simpler manufacturing process than known methods. In other words, it is important to use an acid having essentially an affinity for PVA as a cross-linking agent, and to make contact with the product in a state where the liquid content of Itoshino is high and the acid easily penetrates.

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 both strength and hot water resistance are excellent. When improving the hot water resistance by uniformly stretching by dry stretching after acid adhesion as in the present invention, it was 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 of the aqueous solution 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 preferably 98 mol% or more,
More preferably, it is at least 9 mol%. It is particularly preferable that the content be 99.9 mol% or more in view of hot water resistance. The PVA used is a monomer having another vinyl group, for example, a monomer such as ethylene, itaconic acid, or vinylpyrrolidone.
It may be a PVA-based polymer copolymerized at a ratio of 10 mol% or less.

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 wet- or dry-wet spun through a nozzle into a coagulation bath of 20 ° C. or lower mainly composed of an organic solvent having a coagulation effect on PVA such as methanol, ethanol and acetone. 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.
It is one of the most important points that 5 to 10,000 ppm of acid is added to PVA with respect to PVA in the step before the dry heat drawing so that A undergoes dehydration crosslinking. Examples of the crosslinking agent for PVA include aldehydes, isocyanates, epoxies, methylols, organic peroxides, organic acids and inorganic acids. And inorganic acids. Examples of the acid of the present invention include carboxylic acids having 1 to 5 carbon atoms and sulfonic acids, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid and the like. 220-260 ° C
And those which decompose to produce an acid. Among them, sulfuric acid and phosphoric acid, which are non-volatile at the time of stretching under dry heat and have a strong action as a dehydration catalyst, are preferable. In some cases, it may be advantageous to use a catalyst that promotes the crosslinking reaction, such as urea when using phosphoric acid. It is necessary that the acid adhere to the yarn having a liquid content of 30% / PVA or more at 5 to 10,000 ppm / PVA in the step before the dry heat drawing. If the liquid content is less than 30%, the acid does not uniformly penetrate into the inside of the thread, which is not preferable. 80% / P liquid content
VA or more is more preferable in terms of uniformity.

In the present invention, the liquid content of itoshino is defined as the liquid content of itoshino during 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 removed. The weight% is measured (W ₂ ) by evaporating to a constant weight and dried under reduced pressure to a constant weight, and is a value (W) given by the following equation.

The amount of acid adhered varies depending on the acid strength, the temperature during hot drawing and the residence time, but if it is less than 5 ppm / PVA, the dehydration crosslinking during dry drawing becomes insufficient, so the target effect of improving hot water resistance is achieved. Can not be obtained. It is more preferably at least 15 ppm / PVA, most preferably at least 40 ppm. Especially when a strong acid such as phosphoric acid or sulfuric acid is used, the acid adhesion amount is 10,000pp.
If it exceeds m, the decomposition reaction has a higher priority than the dehydration crosslinking at the time of dry heat drawing, so that the yarn strength is disadvantageously reduced. An appropriate amount of acid to be deposited should be selected depending on the acid strength, the temperature at the time of dry heat drawing and the residence time.

The step of applying the acid 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, an acid may coexist in an oil bath immediately before drying, or an acid may be added to a solvent extraction bath before the oil bath. Further, an acid 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 acid is not added to the oil bath, the acid may be washed away, so it is preferable to add the acid to the entire bath.

The itoshino solidified in the coagulation bath is subjected to extraction washing, removal of the stock solution solvent and the like in the yarn with an extract of a coagulating organic solvent such as methanol, and drying. It is preferable to perform wet stretching in a single stage or more preferably in multiple stages before drying, so that hard adhesion during drying can be prevented. A more preferred wet stretching ratio is 2.5 to 5.5 times. If the wet stretching ratio exceeds 6 times, the single yarn breakage or cross-sectional deformation is liable to occur, so that it should be avoided. The drying temperature is preferably from 30C to 150C in terms of drying efficiency and performance. Five
It is more preferable that the temperature be 0 ° C to 120 ° C.

Then, at a temperature of 220 ° C. so that the total draw ratio becomes 15 times or more.
One of the important points of the present invention is to carry out the above dry heat stretching to carry out orientational crystallization of molecules and also to carry out dehydration crosslinking by acid. In the case of drawing the fiber after dry drying with acid, it was feared that the cross-linking of PVA significantly reduced the dry heat drawability and that the orientation and crystallization of molecules could not be performed sufficiently. The key point of the present invention was that it was surprisingly found that if the type, amount and state of adhesion of the cross-linking 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 acid selected in the present invention as a crosslinkable agent to be applied before the dry heat stretching has such a function and is excellent. The fiber strength and the degree of dehydration cross-linking differ depending on the type and amount of acid to be applied (acid strength) 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 acid is not applied are found, and at approximately the same stretching temperature and the same stretching time, the raw yarn to which the acid is applied is stretched, and the degree of crosslinking is 30 to 100%. What is necessary is just to determine the amount of application of a predetermined acid so that it may become. The degree of cross-linking referred to here is the undissolved after treatment for 1 hour at a bath ratio of 1: 1000 free in hot water at a temperature 5 ° C higher than the hot water temperature at which the drawn yarn of the PVA fiber that does not impart acid is completely dissolved. Measure the undissolved residual amount when the gel remaining on the wire mesh when the fiber is passed through a 300 mesh wire mesh is dried at 80 ° C. under reduced pressure until a constant weight is obtained, and 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.
The higher the degree of polymerization, the higher the temperature must be. 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 higher the total draw ratio, the better, but in consideration of the occurrence of fluff and breakage, the maximum draw ratio of 0.
Should be 75-0.95 times. 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 acid is brought into contact with the high-moisture content of itoshino to uniformly penetrate the acid into the inside, and then dried. Can be performed uniformly to the inside of the fiber,
This makes it possible to produce inexpensively PVA fibers having excellent fatigue resistance.

<Effect of the Invention> In contrast to the conventional crosslinking treatment method for high-strength PVA fibers, which mainly involves surface crosslinking, in the present invention, acid is applied to a high liquid content yarn, dried and then stretched by dry heat. In order to improve the hot water resistance, the cross-linking PVA has high strength and high heat resistance without adding new equipment and manufacturing process.
Since the fibers can be obtained, it is possible to manufacture the fibers at low cost. Therefore, the obtained high strength, hot water resistance
PVA fiber is superior in cost performance to other super fibers such as conventional PVA fiber and para-aramid, and is used in the field of rubber materials 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 PVA having a viscosity average degree of polymerization of 4100 and a saponification degree of 99.8 mol% was added to DMSO at a concentration of 9.5% by weight, and dissolved at 70 ° C. in a nitrogen atmosphere. The obtained spinning dope was used with a pore size of 0.12 mm and the number of pores.
Wet spinning from a nozzle of 300 into a coagulation bath (first bath) consisting of methanol / DMSO = 7/3 (weight ratio) at 3 ° C., and the obtained coagulated yarn was subjected to the same methanol / DMSO bath (first bath) as the first bath. 2 baths)
Was further immersed. Next, it was immersed in a methanol bath containing 50 ppm of phosphoric acid (third bath) to extract DMSO, and at the same time, phosphoric acid was allowed to permeate into the shinoshino. The liquid content of Itoshino after the second bath is
It was 290%. Then, it is dipped in a methanol bath (fourth bath) at 40 ° C. containing 50 ppm of phosphoric acid and wet stretched to make the total wet stretching ratio 5 times, and then DMSO is passed through a methanol bath containing 50 ppm of phosphoric acid (fifth bath). It was further extracted and dried with hot air at 100 ° C. In this way, a dried yarn having phosphoric acid of 120 ppm / PVA was obtained. Next, when the film was stretched in a hot-air furnace having a temperature gradient of 200 ° C. in the first furnace and 236 ° C. in the second furnace, the total stretching ratio was possible up to 21 times. The residence time in the furnace during the 21-fold stretching was 79 seconds in total.

This 21-fold drawn yarn was colored black-purple, and it was presumed that a dehydration crosslinking reaction had occurred. The yarn strength was 18.7 g / d. The yarn was immersed in hot water at 150 ° C. for 1 hour in an oak clave at a constant length, taken out and dried, and the strong residual ratio was measured. As a result, the strength was hardly reduced to 92%, indicating excellent hot water resistance.

Comparative Example 1 Spinning and stretching were performed in the same manner as in Example 1 except that phosphoric acid was not added to baths 1 to 5. The total draw ratio was possible up to 21.5 times.

The drawn yarn obtained was colored to a very slight yellow color. The yarn strength was 19.6 g / d. The yarn was immersed in hot water of various temperatures in an autoclave at a constant length for 1 hour, taken out, and the dissolution state was observed. 135 ° C as a result
Most of the above hot water dissolved, and the shape of the yarn was not maintained.

Comparative Example 2 The drawn yarn obtained in Comparative Example 1 contains 10% of phosphoric acid and 25% of urea
It was immersed in an aqueous solution at 60 ° C. for 30 minutes, washed with water at room temperature for 5 minutes, dried at 80 ° C., and then heat-treated at 190 ° C. for 6 minutes. The obtained fiber was colored deep purple, and the same tendency as in Example 1 was observed. The hot water resistance was excellent at 145 ° C, but the yarn strength was 15.
3 g / d, which was lower than that of Example 1 and Comparative Example 1, was unsatisfactory as a high-strength PVA fiber having a degree of polymerization of 4100.

Example 2 DMS was applied to PVA having a viscosity average degree of polymerization of 8000 and a saponification degree of 99.8 mol%.
Add O and heat and dissolve at 70 ℃ in nitrogen atmosphere to make 7% PVA
A solution was obtained. This spinning stock solution was wet-spun from a nozzle having a pore diameter of 0.15 mm and a number of holes of 500 into a coagulation bath (first bath) composed of 7/3 methanol / DMSO = 7/3, and the obtained coagulated yarn was methanol / DMSO = Perform wet stretching in a wet stretching bath (second bath) on 9/1,
The total wet stretching ratio was set to 4 times, and then a methanol bath (3rd
DMSO was extracted through a bath) and dried with hot air at 70 ° C. 60 ppm and 1 ppm of phosphoric acid and urea in all of the first to third baths
It was added so as to be 00 ppm. In this example, since the phosphoric acid is added to the first bath, the liquid content of Itoshino upon contact with the acid is 500%.
That was all. After drying, the attached amount of phosphoric acid on the yarn was 150 ppm.

Next, the raw yarn was dry-heat drawn by a dry-heat drawing machine having furnace temperatures of 150 ° C., 180 ° C., and 246 ° C. so that the total draw ratio was 20.5 times. The residence time at this time is 38 seconds at 150 ° C, 29 seconds at 180 ° C, 24
20 seconds at 6 ° C.

The drawn yarn obtained is colored deep purple and the yarn strength is 2
It was 0.1 g / d. In addition, this yarn is placed in an autoclave at 165 ° C.
After being immersed in hot water at a constant length for 1 hour, the sample was taken out, and the residual strength after drying was measured to be 90%.

The hot water resistance of a control uncrosslinked yarn similarly prepared without the addition of phosphoric acid was 140 ° C. Incidentally, the effect of improving the hot water resistance by crosslinking at a degree of polymerization of 4100 is 15 ° C., whereas the effect of this example at a degree of polymerization of 8000 is 25 ° C. from Example 1 and Comparative Example 1; Great improvement effect.

Example 3 DMS was applied to PVA having a viscosity average degree of polymerization of 6000 and a saponification degree of 99.2 mol%.
Add O and heat and dissolve at 70 ° C in a nitrogen atmosphere to obtain a P concentration of 8%.
A VA solution was obtained. The spinning stock solution was spin-dry-spun from a nozzle having a hole diameter of 0.18 mm and a number of holes of 100 into a first bath of methanol / DMSO = 80/20 at −5 ° C. as an air gap of 1 cm.

The obtained coagulated Ishino was subjected to wet stretching and DMSO extraction in the same manner as in Example 2, sulfuric acid was added to the final methanol bath immediately before drying, and sulfuric acid was adhered to the Ishino by a roller touch method, followed by drying. The liquid content of Itoshino upon contact with sulfuric acid was 190%. The amount of sulfuric acid adhering to the dried itoshino was 80 ppm.
Next, the raw yarn was dry-heat drawn by a drawing machine at a first furnace of 180 ° C. and a second furnace of 239 ° C. so that the total drawing ratio was 20 times.

The yarn strength of the obtained drawn yarn was 19.1 g / d, and the hot water resistance was 155 ° C., all of which were excellent.

Example 4 Glycerin was added to PVA having a viscosity average degree of polymerization of 3500 and a saponification degree of 99.9 mol%, and was dissolved by heating at 180 ° C. in a nitrogen atmosphere to obtain a 14% concentration PVA solution. This spinning stock solution has a pore size of 0.16 mm,
From a nozzle having 150 holes, dry and wet spinning was performed as a 5 mm air gap in a first bath of methanol / glycerin = 85/15 at −10 ° C. The obtained coagulated yarn is treated with methanol /
Glycerin is subjected to 4.5 times wet stretching in a 95/5 wet stretching bath, and then in a methanol extraction bath containing 200 ppm of phosphoric acid.
DMSO was dried after washing. The liquid content of itoshino after wet stretching is 150
%. The amount of phosphoric acid attached was 300 ppm. Next, this raw yarn was dry-heat drawn by a drawing machine at a first furnace of 180 ° C. and a second furnace of 232 ° C. so that the total drawing ratio was 22 times.

The yarn strength of the obtained drawn yarn is 16.3 g / d, hot water resistance 141.
° C, which was very excellent for use of PVA having a polymerization degree of 3500.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirofumi Sano 1621 Sazu, Kurashiki-shi, Okayama Prefecture Kuraray Co., Ltd. Examiner Shigemi Sawamura (56) References JP-A-3-213510 (JP, A) JP-A-3 -287812 (JP, A) JP-A-1-156517 (JP, A) JP-B-44-2509 (JP, B1) JP-B-31-9893 (JP, B1) (58) Fields investigated (Int. . ^6, DB name) D01F 11/06 D01F 6/14 D06M 11/00 - 11/84

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. An acid is brought into contact with a yarn having a liquid content of 30% / polyvinyl alcohol or more, and the acid is adhered to polyvinyl alcohol at 5 to 10,000 ppm and dried. Then, the temperature is 220 ° C. or more, and the total draw ratio is 15 times or more. A method for producing a high-strength polyvinyl alcohol-based fiber excellent in hot water resistance, characterized by performing dry heat drawing.