JPH0457769B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is directed to highly polymerized polyvinyl alcohol (hereinafter referred to as
This method aims to obtain high-strength, high-modulus PVA-based fibers by dissolving PVA (abbreviated as PVA) in a mixed solvent to obtain uniform, transparent gel fibers, and then drawing them at a high magnification. <Conventional technology> Conventional PVA fibers are made of polyamide, polyester,
It has a higher strength modulus than polyacrylonitrile fibers, and has been used not only as a fiber for industrial materials, which is its main use, but also as a substitute for asbestos in cement reinforcement materials. As a method for obtaining high-strength, high-modulus PVA fibers, methods of gel spinning of high molecular weight polyethylene applying the concept of ultra-stretching are disclosed in JP-A-59-100710, JP-A-59-130314, and JP-A-61-108711. It is publicly known, such as the publication No. However, with these methods, it is difficult to uniformly dissolve PVA with a high degree of polymerization or uniformly gel it with low crystallinity, and as a result, it is difficult to stretch at a high magnification, or single filament breaks (feathers) occur during stretching, resulting in unsatisfactory results. There are still issues to be solved in order to industrially manufacture highly strong and highly modular PVA functions. <Problems to be Solved by the Invention> Based on the above background, the present inventors have determined that in order to obtain a PVA-based fiber with high strength and high modulus, a high degree of polymerization is required.
It is necessary to use a solvent that can uniformly dissolve the PVA polymer, to minimize spots and defects between single filaments, and to draw at a high drawing ratio, the crystallinity of the fiber before drawing must be low, and strong intermolecular hydrogen We focused our efforts on suppressing the bonding. As a result, by adding water to a non-aqueous solvent, a high degree of polymerization can be achieved.
By improving the solubility of PVA, causing gelation without solvent extraction by rapid cooling, and suppressing crystallization with less entanglement of polymer molecular chains, it is possible to obtain uniform and transparent gel fibers. I found that it shows. <Means for solving the problem> That is, the present invention provides a polyvinyl alcohol-based polymer having an average degree of polymerization of 3000 or more in a non-aqueous solvent/water weight ratio of 30/70 to 30/70.
After dissolving in a mixed solvent that satisfies the 90/10 range, it is discharged from a spinning nozzle, and then at a temperature of 10°C or lower to Tf - 10°C or higher (where Tf is the coagulation temperature of the mixed solvent) at which the mixed solvent is hardly extracted. to obtain uniform and transparent gel fibers, then remove part or all of the solvent, and finally draw with dry heat at 200°C or higher so that the total stretching ratio is 10 times or more. A method for producing high-strength polyvinyl alcohol fibers characterized by: It is related to. The content of the present invention will be explained in more detail below. The PVA-based polymer referred to in the present invention has an average degree of polymerization of 3000 or more as determined by the viscosity method in an aqueous solution at 30°C, and a saponification degree of 98 mol% or more. It is a linear polyvinyl alcohol with a low degree of branching. It also includes those copolymerized with 2 mol % or less of other vinyl compounds, and further includes those added with 3 wt % or less of pigments, antioxidants, ultraviolet absorbers, crystallization inhibitors, and the like. In particular, 0.5 to 5 wt% of boric acid or borate, which causes intermolecular crosslinking with the OH group of PVA.
Adding it is preferable because it improves the spinnability of the polymer, reduces screw dropout and single fiber breakage during spinning, and suppresses crystallization of gel fibers. Almost high-strength, high-modulus fibers with a high average polymerization degree of PVA are easily obtained, preferably 6,000 or more, and more preferably 10,000 or more. The higher the degree of polymerization, the fewer the molecular chain terminals that are prone to defects, and the more tie molecules that connect crystals, which is advantageous for high-magnification stretching, but it does not dissolve uniformly in poor solvents, especially polyhydric alcohols. lie. Solvents for PVA-based polymers generally include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, dimethyl sulfoxide, dimethyl formamide, diethylene triamine, water, a mixture of these with alcohol, and an aqueous solution of Rodan salt. In the present invention, the weight ratio of non-aqueous solvent and water is 30/70 to 30/70 in terms of polymer solubility and uniform gelation.
A 90/10 mixed solvent is good. Ethylene glycol, glycerin and dimethyl sulfoxide are preferred as the non-aqueous solvent. If the water content is more than 70% by weight, gelation will not occur and it will be difficult to obtain uniform gel fibers. High degree of polymerization when water is less than 10% by weight
PVA is not sufficiently dissolved and it is difficult to form a uniform gel. In the present invention, it is necessary to discharge a solution of a highly polymerized PVA polymer from a spinning nozzle and immediately immerse it in a liquid (one bath) from which most of the mixed solvent is to be extracted. In this case, wet spinning is not possible because the solution temperature and the first bath temperature are significantly different, and dry-wet spinning is required. Shorten the distance and immerse in one bath. 1 Bath composition is a liquid that hardly extracts the mixed solvent in order to cause uniform gelation, for example, a liquid with the same or similar composition to the mixed solvent, or a mixed solvent, water or non-aqueous solvent with 20% alcohol by weight. Possible materials include mixtures of the following, and materials that are incompatible with solvents such as hexane, decalin, and petroleum solvents. Note that a water-soluble liquid is preferable in terms of recovery and removal from the fibers, and in particular, a water-soluble liquid having the same composition as the mixed solvent is preferable. The temperature of the first bath must be below 10°C and above Tf - 10°C (Tf is the coagulation temperature of the mixed solvent) in order to obtain transparent gel fibers with suppressed crystallization. If it exceeds 10°C, crystallization tends to occur and become an opaque gel, and if it is below Tf -10°C, spinning becomes impossible due to freezing, both of which are not preferred. To remove the solvent from the transparent gel fibers obtained, extraction with _C1 to _C6 lower alcohols, acetone, benzene, chloroform, etc.
Methods such as scattering with hot air or the like can be considered, but it is desirable to remove the solvent as gradually as possible and dry at a low temperature to suppress crystallization. Although drying or wet heat stretching may be carried out in a state containing a solvent, the present invention
It must be stretched with dry heat above ℃. 200℃
If it is less than that, the fiber molecular chains are insufficiently softened, making it difficult to draw at a high magnification, making it difficult to obtain high-strength fibers, and the resulting drawn yarn is insufficiently crystallized, causing problems in heat resistance, dimensional stability, etc. It occurs and is not desirable. Therefore, in order to obtain high-strength PVA fibers for industrial use, it is necessary to draw the fibers by dry heat at 200°C or higher by at least 2 times, preferably at least 3 times, and at a total stretching ratio of at least 10 times, preferably at least 15 times. Must be. In addition, dry heat stretching may be performed in two or more stages at a temperature of 200°C or less,
Finally, it is necessary to stretch at 200°C or higher. Note that PVA-based polymers tend to discolor and decompose due to heat, and N ₂
It is desirable to use it under an atmosphere. Hereinafter, the present invention will be specifically explained with reference to Examples. Examples 1 and 2 and Comparative Examples 1 and 2 Complete saponification with an average degree of polymerization of 7000 and 14000
PVA was dissolved in a mixed solvent of 60/40 weight ratio of glycerin/water at 150° C. to give a concentration of 10% by weight and 7% by weight, respectively. The dissolving machine was a closed system, and after reducing the pressure inside the system, N ₂ gas was flowed to suppress the discoloration and decomposition of PVA. Next, the solution was heated to 120° C. and discharged from a nozzle with a hole diameter of 0.2 mm and 20 holes, and dropped into a bath 25 mm below. The composition of the first bath was the same as the solvent: glycerin/water = 60/40, and the temperature was 0°C. As Comparative Example 1, when the bath composition was 100% methanol,
Comparative Example 2 was also conducted in which the temperature of one bath was 20°C. After obtaining gel fibers by cooling in one bath, they are immersed in methanol/glycerin = 30/70 and 20/30 baths to gradually extract the solvent, and finally methanol
Glycerin and water were removed by placing in a 100% bath. Then, after removing methanol with hot air at 60°C, it was stretched 5 times with a hollow heater at 170°C, and finally at 230°C.
The film was stretched using a hollow heater at a maximum stretching ratio of 90%. Table 1 shows the morphology and crystallinity of the gel fibers after one bath and the dry gel fibers after removing the solvent, as well as the performance of the drawn fibers obtained.

【table】

[Table] In the case of Examples 1 and 2, a uniform solution was discharged without single fiber breakage, yarn disorder, or filter clogging during spinning, and the gel fibers were highly transparent. The cross section of the dried gel fibers was a perfect circle, and the crystallinity determined from X-rays was as low as 26% in Example 1 and 28% in Example 2, and the total stretching ratio was 16.0 times and 12.5 times, respectively. In addition
Although it was stretched for 24 hours, there was no breakage of the feather threads. The strengths of the obtained yarns are 19 g/d and 21 g/d, respectively.
d, the modulus is 495 g/d and 530 g/d,
It has become a high-strength, high-modulus fiber. Comparative Example 1 is a case in which methanol was used as the bath composition in Example 2, but the cross section of the dried gel fiber was slightly oval and wrinkles were observed on the surface, probably due to the high extraction rate of the solvent, and the stretching ratio and performance were low. It became. Comparative Example 2 is a case where the bath temperature was set to 20°C in Example 1, but the gel fiber becomes opaque and the crystallinity of the dry gel fiber is as high as 38%, resulting in a fiber with a low draw ratio and low strength modulus. It was hot. Example 3 Completely saponified PVA with an average degree of polymerization of 12,000 was heated to 7% by weight in a mixed solvent of dimethyl sulfoxide (DMSO)/water = 80/20 weight ratio at 95°C.
The mixture was stirred and dissolved. Before dissolution, 1% by weight of boric acid was added to PVA. The solution was then heated to 80° C. and discharged from a nozzle with a hole diameter of 0.3 mm and 10 hoses, dropped into a bath 20 mm below, and withdrawn at a speed of 5 m/min. 1 bath composition is
DMSO/methanol = 85/15 and the temperature is -
The temperature was set at 25°C. There were no single filament breakages during spinning or tension unevenness due to gel point fluctuations, and the gel fibers were transparent and uniform. This gel fiber is DMSO/methanol = 50/50
After stretching the film twice, it was immersed in a 100% methanol bath to extract most of the solvent, and then dried at 40°C under reduced pressure for one day and night. The obtained fibers were stretched 7.3 times with a hollow heater at 234°C, and the strength was 2 g/d, the elongation was 4.8%, and the modulus was 510 g/d.
d PVA fiber was obtained. Examples 4 and 5 Completely saponified PVA with an average degree of polymerization of 3400 as Example 4 and 18000 as Example 5 was used, and 25
% and 6% by weight in a mixed solvent of ethylene glycol (EG)/water = 45/55 weight ratio.
It was dissolved at 130°C. A twin-screw kneading extruder was used as the dissolver, and the residence time was set to about 5 minutes, but in all cases, a uniform and uncolored solution was obtained. Both solutions were heated to 110°C, pore diameter 0.15 mm, number of holes 48.
1 of n-hexane at -5°C.
It was quenched by immersion in a bath. Both gel fibers were transparent and had perfectly circular cross sections. Both gel fibers were immersed in a bath of EG/methanol = 60/40 and then 100% methanol, and then dried with hot air at 100°C to obtain dry gel fibers with an EG residual rate of about 3%. Next, in the case of Example 4, it was stretched 2 times at 180°C, 4 times at 210°C, and 1.8 times at 232°C to obtain a fiber with a strength of 18.6 g/d and a modulus of 440 g/d. In Example 5
By stretching 2 times at 180°C, 3.5 times at 210°C, and 1.6 times at 235°C, an unprecedented high-strength, high-modulus PVA fiber with a strength of 23.4 g/d and a modulus of 542 g/d was obtained. Comparative Example 3 The same procedure as Example 2 was carried out using a mixed solvent of glycerin/water = 95/5, but at 150°C, the degree of polymerization was 14,000.
PVA was not completely dissolved and the spinning filter pressure increased dramatically, making spinning difficult. Furthermore, although it was almost completely dissolved at 180°C, the gelation temperature was high due to the small amount of water, and even though the spinning temperature was set to 175°C, water evaporated rapidly just below the nozzle, causing bubbles to form in the yarn. The obtained spun yarn was stretched in the same manner as in Example 2, but the total stretching ratio was as low as 5.5 times, and the fiber strength was also drastically reduced. Comparative Example 4 In Example 3, the mixed solvent was DMSO/water =
Although the ratio was set to 20/80, gelation was difficult to occur and it was difficult to obtain uniform gel fibers. The obtained spun yarn was stretched in the same manner as in Example 3, but the total stretching ratio was
It was as low as 9.4 times, and did not become a high-strength, high-modulus PVA fiber.

Claims (1)

[Claims] 1. A polyvinyl alcohol polymer having an average degree of polymerization of 3000 or more in a non-aqueous solvent/water weight ratio of 30/70.
After dissolving in a mixed solvent that satisfies the range of ~90/10, it is discharged from a spinning nozzle, and then the mixed solvent is extracted from below 10°C to above Tf -10°C (where Tf is the coagulation temperature of the mixed solvent). Obtain uniform and transparent gel fibers by immersing them in a liquid at a high temperature, then remove part or all of the solvent, and finally draw with dry heat at 200℃ or higher so that the total stretching ratio is 10 times or more. A method for producing strong polyvinyl alcohol fibers characterized by: 2. The method for producing a high-strength polyvinyl alcohol fiber according to claim 1, which is a polyvinyl alcohol polymer having an average degree of polymerization of 10,000 or more. 3. The method for producing high-strength polyvinyl alcohol fibers according to claim 1 or 2, which comprises adding 0.5 to 5 wt% of boric acid or a boric acid salt to the polyvinyl alcohol polymer. 4. The method for producing high-strength polyvinyl alcohol fibers according to any one of items 1 to 3, wherein the non-aqueous solvent is any one or more of glycerin, ethylene glycol, and dimethyl sulfoxide.