JPH01266212A - Production of high-tenacity polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having high tenacity and modulus at a low cost, by dissolving a PVA polymer in a specific solvent, spinning the obtained spinning dope using a coagulation bath composed of a low-temperature aqueous solution containing an inorganic salt and drawing the obtained fiber using a specific method. CONSTITUTION:A PVA polymer having an average polymerization degree of >=3,000 is dissolved in a solvent (e.g. ethylene glycol) capable of giving a gelled PVA by cooling. The obtained spinning dope is extruded through a spinning nozzle, cooled with air and immersed in an aqueous solution of an inorganic salt at <=25 deg.C to effect the gel spinning of the dope. The produced fiber is drawn at a draw ratio of >=5 in a state containing 30-300wt.% of the solvent based on the PVA. The drawn fiber is washed with water, dried and then drawn at >=200 deg.C at a total draw ratio of >=18 to obtain the objective fiber. The inorganic salt to be used in the gel spinning process is e.g. Na2SO4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for inexpensively producing polyvinyl alcohol fibers having high strength and high modulus of elasticity.

(Conventional technology) Conventional polyvinyl alcohol fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile fibers, and are used not only as fibers for industrial materials, which is their main use, but also as cement reinforcement fibers recently as asbestos substitute fibers. It is also used for materials etc.

As a method for obtaining polyhinyl alcohol-based fibers with high strength and high elastic modulus, the concept of gel spinning and ultra-stretching of high molecular weight polyethylene is applied, as disclosed in JP-A-59-100710, JP-A-59-130314, and JP-A-59-130314. Kaisho 61-1087
No. 11 and the like are publicly known. All of these methods use methanol, which has a high solvent extraction rate, to extract the solvent and then stretch, but they have not yet achieved satisfactory strength, and furthermore, they require a methanol recovery process and the installation of explosion-proof equipment, resulting in extremely high production costs. become high. Therefore, there are still many problems to be solved in order to industrially produce polyvinyl alcohol fibers with high strength and high modulus at low cost.

(Problems to be Solved by the Invention) Based on the above background, the present inventors have conducted extensive studies to obtain polyvinyl alcohol-based fibers with high strength and high modulus at low cost.

As a result, it was found that the following five conditions must be met. That is, (1) use a solvent that gels when cooled (2)
Using a low-temperature inorganic salt aqueous solution as a coagulation bath (3) Stretching to a high magnification in a state containing a large amount of solvent (4) Extracting the solvent with water (5) Using a low-temperature inorganic salt aqueous solution to stretch at a high magnification at a high temperature Gelation is caused and the molecular chains are fixed in a state with little entanglement, and at the same time a skin layer is formed to the extent that the single filaments do not stick together.

Next, wet stretching is carried out at a high magnification with a large amount of remaining solvent to destroy the microcrystals formed at the initial stage of spinning, increase the amorphous portion, and increase the degree of molecular orientation. In this state, there is little swelling due to water and solvent extraction is possible by washing with water. Finally, high-strength, high-modulus fibers with advanced oriented crystallization are formed by high-temperature drawing.

(Means for Solving the Problems) That is, the present invention provides the following features: ``A polyvinyl alcohol-based polymer having an average degree of polymerization of 3000 or more is dissolved in a solvent that gels when cooled to create a spinning stock solution, and then the stock solution is passed through a spinning nozzle. is discharged, cooled with air, and then immersed in an aqueous solution containing at least an inorganic salt at a temperature of 25° C. or less to perform gel spinning.
Stretched by 5 times or more in a state containing a solvent of ``Method for producing characteristic high-strength polyvinyl alcohol fibers.''

The contents of the present invention will be explained in more detail below.

Generally, in order to increase fiber strength, it is necessary to increase the orientation and crystallization of molecular chains, which requires high-magnification stretching. On the other hand, uniform fiber cross-sections and reduced adhesion between fibers also reduce defects and fibrillation, leading to higher strength.

For high-magnification stretching, the present inventors fixed molecular chain entanglement in a state with less entanglement through gelation, lowered the crystallinity of the fiber before stretching, and contained a solvent in order to suppress strong intermolecular hydrogen bonds. The idea was to destroy the microcrystals in the early stage of spinning by stretching at a high magnification in the still state. In addition, in order to make the fiber cross section uniform and prevent fibers from sticking together, we gelled them with a low-temperature inorganic salt aqueous solution to form a surface layer that does not cause sticking and an inner layer that contains a large amount of solvent, and then wet-stretched the fibers at a high magnification. The idea was to create fibers that would be less likely to swell or stick to water.

The polyvinyl alcohol-based polymer referred to in the present invention is 3
The average degree of polymerization determined by the viscosity method in an aqueous solution at 0°C is 300.
0 or more, the degree of saponification is 98 mol% or more, and it is a straight chain with a low degree of branching. Note that it also includes those copolymerized with 2 mol% or less of other vinyl compounds, and further includes those to which 3% by weight or less of pigments, antioxidants, ultraviolet absorbers, crystallization inhibitors, etc. are added. In particular, adding 0.5 to 5% by weight of boric acid or borate, which causes intermolecular crosslinking with the OH groups of polyvinyl alcohol, improves the spinnability of the polymer and reduces screw dropout and single fiber breakage during spinning. This is preferable because it also suppresses crystallization of gel fibers.

The higher the average degree of polymerization of polyvinyl alcohol, the easier it is to obtain a fiber with high strength and high elastic modulus, and preferably it is too high or higher. The higher the degree of polymerization, the fewer the molecular chain ends that tend to become defective parts, and the more tie molecules that connect crystals, making it easier to form a high-strength, high-modulus fiber.

As a solvent for polyvinyl alcohol-based polymers, it is preferable to use a solvent that causes polyvinyl alcohol to gel when cooled, such as polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, mixed solvents of these and water, or dimethyl sulfoxide. , dimethylformamide, diethylenetriamine, and mixed solvents of these and water.

In the present invention, a solution of a polyvinyl alcohol polymer is discharged from a spinning nozzle and immediately immersed in an aqueous solution containing at least an inorganic salt at a low temperature in which extraction of the solvent is small, so that the fiber cross section is uniform and there is no agglutination between single filaments. is obtained, and wet stretching at high magnification is possible. In this case Hara! Wet spinning is not possible due to the large difference between jL temperature and coagulation bath temperature.
Either dry-wet spinning or gel spinning that gels only by cooling is achieved, or the distance from the nozzle to the coagulation bath is shortened and the spun yarn is immersed in the coagulation bath in order to rapidly cool the spun yarn as uniformly as possible. The coagulation bath composition is known to be methanol or a mixture of methanol and a solvent, but in this case, although there is no problem with uniform cross sections and non-sticking, the solvent is extracted quickly, so the amount of remaining solvent is small and it is difficult to control the amount of remaining solvent. , high-strength low-humidity stretching cannot be performed stably. On the other hand, if a non-extractable liquid such as decalin or hexane is used, high-strength, low-moisture stretching is possible, but since the residual amount of solvent far exceeds 300% by weight, a large amount of solvent is squeezed out during wet stretching, resulting in aggregation between single filaments. It happens easily. In addition, all of the known techniques require complicated drug recovery and require a drug recovery process and explosion-proof equipment, making them industrially unprofitable.

In the present invention, an aqueous solution coagulation bath containing at least an inorganic salt was employed as described above from the viewpoint of manufacturing high strength, high modulus polyvinyl alcohol fibers at low cost. Inorganic salts include, for example, NatSO4, K, SO, CaCQ*, Zn, for the purpose of preventing adhesion between single filaments and maintaining a uniform cross section.
Examples include 5O*, ZnCQt, etc., but the present invention is not limited thereto. In addition to inorganic salts, there are acids and alkalis for adjusting pHII, and the same solvent as the polymer solution, but other organic solvents and alcohols are not preferred because they complicate the recovery process and increase costs. The concentration of the inorganic salt aqueous solution is preferably close to the saturated solubility. The temperature of the coagulation bath is 25° C. or lower, preferably 10° C. or lower, in order to obtain transparent gel fibers with low crystallinity. However, spinning is not possible below the freezing temperature of the inorganic salt aqueous solution or the precipitation temperature of the inorganic salt. 2
If the temperature exceeds 5°C, crystallization tends to occur, resulting in an opaque gel, and the solvent extraction rate increases, which is not preferable.

The optimal amount of solvent remaining in the obtained transparent gel fiber is 30 to 300% by weight based on the polyvinyl alcohol.

If it is less than 30% by weight, it is difficult to reduce the wet stretching ratio of the fiber to 5 times or more as defined in the present invention. If it exceeds 300% by weight, a large amount of solvent is squeezed out during wet stretching, which is undesirable because it tends to cause sticking between the filaments. The transparent gel fiber is then wet-stretched in a hot inorganic salt aqueous solution, for example, a saturated NatSOa aqueous solution at 80°C. On the other hand, wet stretching may be carried out in a methanol bath, but this is disadvantageous from both safety and profitability points of view. Dry heat stretching at 100°C or lower may also be used, but it tends to cause sticking between the single filaments. The need for a wet stretching ratio of 5 times or more is to lower the degree of crystallinity, weaken intermolecular hydrogen bonds, and facilitate the movement of molecular chains, so that dry heat stretching can be performed at a high ratio, and The goal is to reduce the sticking of single yarns due to swelling during the water washing process.

After wet stretching, the film must be thoroughly washed with water and dried, but it is desirable to remove water as gradually as possible and dry at a low temperature to suppress crystallization.

Further, the residual amount of the solvent is 5% by weight or less, preferably 1% by weight or less. If the residual amount of solvent is large, coloring and decomposition of the fibers is likely to occur during subsequent dry heat stretching. Note that it is desirable to shrink the film during drying for the purpose of preventing sticking and increasing the total stretching ratio.

In the present invention, at least the final drawing must be done with dry heat at 200°C or higher, preferably 220°C or higher. 2
At temperatures below 00°C, the fiber molecular chains are insufficiently softened, making it difficult to draw at high magnification, making it difficult to obtain high-strength fibers, and the resulting drawn yarn has low crystallinity, causing problems in heat resistance, dimensional stability, etc. I don't like it.

In order to obtain a high-strength, high-modulus polyvinyl alcohol fiber, it must be drawn with dry heat at 200° C. or higher and the total stretching ratio should be 18 times or more, preferably 20 times or more.

If the total stretching ratio is less than 18 times, the molecular orientation is insufficient, making it difficult to obtain a high-strength, high-modulus fiber, and the heat resistance also decreases, which is not preferable.

Note that polyvinyl alcohol-based polymers tend to discolor and decompose due to heat, so it is desirable to use a nitrogen atmosphere during dissolution in a solvent or dry heat stretching.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited only to the Examples.

Example 1.2 and Comparative Examples 1 and 2 Completely saponified polyvinyl alcohol having an average degree of polymerization of 7,000 and 14,000 was dissolved in glycerin at IH° C. to a concentration of 10% by weight and 7% by weight, respectively.

The melting machine is a closed system, and the inside of the system is filled with N after being depressurized.

Gas was passed to suppress the color decomposition of polyvinyl alcohol.

The solution was then heated to 170° C. and discharged through a nozzle with a hole diameter of 0.2 mm and 20 holes, and dropped into a coagulation bath below 25a+a+. Coagulation bath composition is NatSOa/water = 8
g/100g and the temperature was 10°C. After cooling in a coagulation bath to obtain a gel fiber, it was stretched 6 times in a NatsO+ aqueous solution at 80°C, then washed with water and dried with hot air at 100°C. Finally, it was stretched in a hot air oven at 235° C. at a maximum stretching ratio of 90%. Table 1 shows the total stretching ratio. The physical properties of the gel fibers after passing through the coagulation bath and the dried gel fibers after removing the solvent, the amount of remaining solvent, and the performance of the obtained drawn fibers are also shown in Table 1.
It was shown to.

As Comparative Example 1, methanol was used for the coagulation bath composition, wet stretching, and extraction in Example 1, and as Comparative Example 2, the coagulation bath temperature in Example 2 was changed to 30°C.

In the case of Examples 1 and 2, the gel fibers were highly transparent, and the residual amount of solvent was 43% in implementation % JI and 69% in Example 2. There was no adhesion between single filaments in the dried gel fibers, and the crystallinity determined by X-ray was 25% in Example 1 and <21% in Example 2h. The total stretching ratios at 235°C were 21.0 times and 19.5 times, respectively. The strengths of the obtained yarns were 19.8 g/d and 22.1 g/d, respectively, and the elastic modulus was 510 g/d.
and 545 g/d, making it a high-strength, high-modulus fiber.

In Comparative Example 1, since methanol was used in the coagulation bath composition, the residual amount of solvent in the gel fiber was as low as 8% by weight, and the wet stretching ratio in the 40° C. methanol bath was 4 times.

Therefore, the total stretching ratio was 17.2 times, and both the strength and elastic modulus were lower than in Example 1.

In Comparative Example 2, the coagulation bath temperature was set at 30° C., but the solvent extraction became faster and the gel fibers turned white and crystallization progressed. The wet stretching ratio was 4.5 times, and the fibers swelled when washed with water, and the single yarns stuck together when dried. The total stretching ratio is 17
．． 5 times, fibrillation was observed due to peeling of adhesive during stretching, and the strength and elastic modulus decreased.

In fact, Foam Example 3 Polyvinyl alcohol having an average degree of polymerization of 4,500 and a degree of saponification of 99 mol% was dissolved at 110° C. to a concentration of 7% by weight in a mixed solvent having an ethylene glycol/water ratio of 575% by weight. During dissolution, 2% by weight of boric acid was added to polyvinyl alcohol.

The solution was heated to 100° C. and the pore size Q was 12 mn+,
It was discharged from a nozzle with 80 holes and dropped into a coagulation bath under 2oalIII. The coagulation bath composition is (Na5O+
3g + NaOHIg)/100g of water and the temperature was 5°C. After obtaining gel fibers by cooling in a coagulation bath, 80°C (NatSO425g + NaOH0,5
g) Wet stretching was carried out 65 times in a bath containing 100 g of water. In the above steps, polyvinyl alcohol was completely saponified to a degree of saponification of 99.9 mol%.

Furthermore, a neutralization tower (HISO4Log + Na
Neutralize in 100 g of 2SO2)/100 g of water, then 30 g
It was washed with water at 110°C and dried with 3% shrinkage using hot air at 110°C, but no sticking between the single yarns was observed. The remaining amount of ethylene glycol solvent was 51% for gel fibers and 0.7% for dry gel fibers. Finally, dry heat stretching was performed in two stages in a hot air oven at 210 to 240°C. The total stretching ratio was 215 times. The obtained drawn fiber had a drier of 216 dr, a strength of 13.5 g/d, and a modulus of elasticity of 492 g/d.

Patent applicant RiRashi Co., Ltd.

Claims (1)

[Claims] After preparing a spinning stock solution by dissolving a polyvinyl alcohol-based polymer having an average degree of polymerization of 3000 or more in a solvent that gels when cooled, the stock solution is discharged from a spinning nozzle,
Following air cooling, gel spinning is performed by immersing in an aqueous solution containing at least an inorganic salt at a temperature of 25° C. or lower, and stretching is performed at least 5 times in a state containing 30 to 300% by weight of a solvent relative to polyvinyl alcohol. A method for producing a high-strength polyvinyl alcohol fiber, which comprises removing all or part of the solvent by washing with water and drying, and further stretching the fiber at a temperature of 200° C. or higher to a total stretching ratio of 18 times or higher.