JPH0233314A - High-tenacity polyvinyl alcohol based fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title high-tenacity fiber suitable for industrial material and reinforcement of composite material by using a polyvinyl alcohol based polymer having high polymerization degree and specified content of 1,2-glycol bond as a raw material and simultaneously drawing the spun yarn at a high draw ratio. CONSTITUTION:A polyvinyl alcohol based polymer having <=12000 average polymerization degree and <=1.2mol% 1,2-glycol bond and used at an amount of 80% based a raw material is spun, preferably by a method discharging from a spinning nozzle and then quenching. Then the obtained yarn is subjected to wet drawing at a draw ratio of >=3 times and then subjected to heat drawing at >=200 deg.C at a total draw ratio of >=17 times to provide the aimed fiber having <=1.2mol% 1,2-glycol bond, <=100ppm polyene bond and >=18g/d dingle fiber tensile strength.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a high-strength polyvinyl alcohol fiber and a method for producing the same, and in particular to a polyvinyl alcohol fiber suitable for use in industrial materials and reinforcing composite materials. It is an attempt to obtain.

(Prior technology) Conventional polyvinyl alcohol fibers have higher strength than polyamide, polyester, and polyacrylonitrile fibers, and are used not only as fibers for industrial materials, which is their main use, but also as fibers for reinforcing cement as an asbestos substitute. is also used.

However, the polyvinyl alcohol fibers obtained so far have not had the high strength of aromatic polyamide (aramid) fibers or ultra-high molecular weight polyethylene fibers.

Polyvinyl alcohol fibers are usually produced by a method of wet spinning in a coagulable inorganic salt aqueous solution using a polyvinyl alcohol aqueous solution as a spinning stock solution, followed by stretching, dry heat treatment, etc. Various methods have been proposed to obtain strength.

For example, Japanese Patent Publication No. 43-16675 describes a method of wet spinning in a dimethyl sulfoxide solution of polyvinyl alcohol in an organic solvent such as methanol, ethanol, benzene, or chloroform as the entire spinning stock solution, and JP-A No. 56-128.
No. 309 proposes a method in which polyvinyl alcohol fibers obtained by wet or dry spinning are stretched at least 10 times or more and then heat-treated. Also, Japanese Patent Publication No. 37-14422 and Japanese Patent Publication No. 47-32142
The publication discloses that a polyvinyl alcohol aqueous solution containing boric acid or a borate salt is spun into an alkaline coagulation bath containing various salts, the boric acid is crosslinked to polyvinyl alcohol, and then the boric acid or its crosslinked product is then spun. Disclosed is a method for removing it through steps such as neutralization and washing with water. However, the fiber strength Fi12f/d obtained by these methods
It was below r.

On the other hand, JP-A-60-126312 discloses that a polyvinyl alcohol fiber having a degree of polymerization of polyvinyl alcohol of about 4000 and a nine-dry wet spinning method using dimethyl sulfoxide as a solvent is used to obtain a polyvinyl alfur fiber with a stretching ratio of about 30 times and a strength of 209/dr. This has been shown to be possible, but it is not easy.

Gel spinning of ultra-high molecular weight polyethylene - An example of applying the concept of ultra-stretching to polyvinyl alcohol fibers was published in JP-A-5
There is a publication No. 9-130314, but the degree of polymerization is about ao.
In this method, polyvinyl alcohol fibers of ooo are produced by cooling using glycerin or ethylene glycol as a solvent to obtain polyvinyl alcohol fibers with a maximum strength of 19 P/dr. However, unlike polyethylene fibers, polyvinyl alcohol-based fibers have hydrogen bonds between and within molecules, and are thought to be difficult to fold and retain their molecular weight. Even if the entanglement is reduced, it is still difficult to obtain polyvinyl alcohol fibers with a satisfactory high draw ratio and high strength.

To obtain high-strength fibers, it is necessary to highly orient the molecular weight, and for this purpose, it is necessary to draw at a high magnification. In the case of polyvinyl alcohol fibers, the following points can be considered for K since high strength is achieved by stretching at a high ratio.

(1) Highly polymerized polyvinyl alcohol is used.

(2) Use a low concentration polyvinyl alcohol solution.

(8) Perform gel spinning.

(4) Suppress intermolecular hydrogen bonds.

(5) Providing appropriate voids between molecules.

(6) Suppressing color decomposition of fibers during stretching.

Conventionally, no method has been found that satisfies the above (1) to (6) and obtains high-strength polyvinyl alcohol fibers by high-strength stretching.

(Problems to be Solved by the Invention) Based on the above background, the present inventors conducted extensive studies in order to obtain a high-strength polyvinyl alcohol fiber. Generally, to increase fiber strength, it is necessary to use a polymer with a high degree of polymerization to increase the number of tie molecules that connect crystals, and at the same time to increase the orientation and crystallization of molecular chains, it is necessary to draw at a high magnification.

On the other hand, suppressing color decomposition when fibers are drawn at high temperatures is also a way to increase strength. The present inventors focused on and studied the 1,2-glycol bond within the polymer molecule, and found that
If the number of 1,2-glycol bonds exceeds 1.2 molar, oriented crystallization may be inhibited, or cypolyene bonds may be formed by condensation of 1,2-glycol bonds, resulting in decomposition and easy discoloration. It has been found that it is difficult to obtain high strength fibers.

In other words, the present invention was achieved by discovering that polyvinyl alcohol with a high degree of polymerization having a 1,2-glycol bond of 1.2 molar or less is effective for obtaining high-strength fibers.

(Means for Solving the Problems) The present invention consists of a polyvinyl alcohol polymer having an r(1) average degree of polymerization of 12,000 or less, with a 1.2-glycol bond of 1.2 mol or less and a polyene bond of 100 ppm. The following is a high-strength polyvinyl alcohol fiber having a single fiber tensile strength of 117d or more.

(2) The average degree of polymerization is 12,000 or less, and 1.2-
At least 80 or more polyvinyl alcohol-based polymers having glycol bonds of 1.2 mol or less are used, wet stretching is carried out at a stretching ratio of 3 times or more, and then heated stretching is carried out at a temperature of 200° C. or higher at a total stretching ratio of 17 times or more. conduct, 1, 2
- Glycol bond is 1.2 molar or less, polyene bond is IO ppm or less, single fiber tensile strength is 18 f/
A method for producing polyvinyl alcohol fibers, characterized by obtaining fibers with a particle size of d or more. ”.

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

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 12,
000 or less, preferably it, <' is 3000 or less
8000. Although the average degree of polymerization may be 12,000 or more, it requires an operation to lower the polymerization temperature, which increases costs. Saponification degree is 99.5 molti or more, 1
, 2-glycol bond is 162 or less, preferably 1
．． It is 0 molti or less.

A method for obtaining the polymer includes, for example, polymerizing a vinyl ester, most preferably vinyl acetate, at a polymerization temperature of 10° C. or lower, removing unreacted vinyl ester by distillation, and performing alcoholysis by adding an alkali. .

The polymerization can be carried out by methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. When polymerizing at a polymerization temperature of 0°C or lower, suspension polymerization using water as a medium;
In emulsion polymerization, polymerization can be carried out by dissolving alcohol, glycol, glycerin, dimethyl sulfoxide, or an inorganic salt in an aqueous medium as a freezing point depressant. In order to obtain polyvinyl alcohol with the required polymerization degree, polymerization is carried out by setting the polymerization temperature, polymerization rate, monomer concentration, etc. If necessary, polymerization degree regulators such as disulfide, mercaptan, diazothioether, etc.
Logenides and the like can also be used.

The degree of polymerization of polyvinyl alcohol in the present invention is determined according to JIS
Based on K 6726, the degree of polymerization PA is measured from the limiting viscosity [η] of the aqueous solution at 30°C as described above using the following formula, and defined as nine values: PA=((η)X10',/8.29)"-613 However, the unit of [η]: g7t In the case of the present invention, the average degree of polymerization is 1 in addition to the case of a single system.
．． A mixed system may be used in which the polyvinyl alcohol polymer having 2-glycol bonds of 1.2 molar or less accounts for at least 80% by weight or more, preferably 90% by weight or more. 80% by weight unclarified has a large amount of 1゜2-glycol bonds, and as mentioned above, coloring and decomposition of the polymer is promoted,
As oriented crystallization is reduced, it becomes difficult to obtain high-strength fibers.

For example, the degree of polymerization is 3600 and the degree of polymerization is 10000. Alternatively, it may be a polyvinyl alcohol polymer mixture with a degree of polymerization of 3,000 and 5,000.

Polyvinyl alcohol poly! - also includes those to which 3 weight or less of pigments, antioxidants, ultraviolet absorbers, crystallization inhibitors, etc. are added. Especially the O of polyvinyl alcohol
Boric acid or borate that causes intermolecular crosslinking with H groups is added to 0.
It is preferable to add 5 to 5% by weight because it improves the spinnability of the polymer, reduces screw dropout and single fiber breakage during spinning, and suppresses crystallization of gel fibers. The higher the average degree of polymerization of polyvinyl alcohol, the fewer molecular terminal ends that tend to become defects, and the more tie molecules that connect crystals, making it easier to form into a high-strength, high-modulus fiber.

Any solvent may be used for polyvinyl alcohol-based polymers, but solvents that cause polyvinyl alcohol to gel when cooled are preferred, such as polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, and mixtures thereof with water. There are solvents, dimethyl sulfoxide, dimethyl formamide, diethylene triamine, and mixed solvents of these and water.

Any spinning method may be used, but in the present invention, a polyvinyl alcohol polymer solution is discharged from a spinning nozzle and immediately immersed in a low-temperature alcohol such as methanol or ethanol, or a mixture of these and the solvent, or an aqueous solution containing an inorganic salt. A method of obtaining transparent gel horizontal writing is preferable to rapid cooling. In this case, wet spinning is not possible because the temperature of the stock solution and the coagulation bath temperature are greatly different, and dry-wet spinning results in gel spinning that gels only by cooling, but the spun yarn that is discharged is rapidly cooled as uniformly as possible. Therefore, the distance from the nozzle to the coagulation bath is shortened and the product is immersed in the coagulation bath. The coagulated spun yarn is preferably wet-stretched three times or more while still containing the solvent. If the wet stretching is less than 3 times, the microcrystals generated during spinning will be less likely to be broken, and the subsequent stretching ratio will be low, making it difficult to increase the strength. In the present invention, after wet stretching, the solvent is almost completely removed, and then the film is heated and stretched at 200° C. or higher, preferably 220° C. or higher, to a total stretching ratio of 17 times or higher.

A temperature lower than 200° C. is not preferable because the stretching ratio is low and oriented crystallization is not sufficient. Further, if the total stretching ratio is 17 times or less, the molecular orientation will be insufficient and high strength will not be obtained.

Since the present invention aims to obtain highly strong fibers, the above-mentioned stretching at high temperature and high magnification is essential. However, here the 1.2-
If the number of glyfur bonds exceeds 1.2 moles, coloring and decomposition of the fibers will occur if the above-mentioned high-temperature stretching treatment is carried out. On the other hand, if the stretching temperature is lowered to a temperature that does not cause this color decomposition, it becomes impossible to achieve a high degree of stretching, and as a result, it becomes impossible to obtain high-strength fibers. Therefore, in the present invention, the 1,2-glycol bond is suppressed to 1.2 mole or less in order to obtain a high-strength fiber without discoloration and decomposition even during high-strength, high-magnification stretching treatment.

In addition, in order to suppress the color decomposition of polyvinyl alcohol as much as possible, it is preferable to use a KN2 gas bath, a silicone oil bath, etc. other than a bath or air bath in which the heating temperature and residence time at that temperature are adjusted. The high-strength polyvinyl alcohol fiber referred to in the present invention has a sample length of 10 cIL and a tensile speed of 5 m/m.
The single fiber strength measured by a tensile tester was 1897.
It means 6 or more, preferably 20 f/d or more.

As mentioned above, when the number of <1.2-glycol bonds increases, it decomposes during the heating process, and double bonds are likely to be formed due to dehydration, resulting in the formation of polyene bonds. Polyene bonds may be formed up to 1,100 pp, but if the amount exceeds 1,100 pp, the resulting yarn will have a yellowish tinge and its strength will decrease, which is not preferable.

Next K 1. The method for measuring 2-glycol bond/content and polyene bond gold content will be explained.

Regarding the amount of 1,2-glycol bond in polyvinyl alcohol, add about 5% trifluoroacetic acid to a DMSO-ds bath solution of polyvinyl alcohol, and
”Measure H-NMR. δ of the spectrum is 3.
Let A be the area of the peak that appears around 25 ppm, and δ=
If the peak area of 1.2 to 1.8 ppm is B, then the following formula (
1) The amount of 1.2-glycol bond can be determined.

Further, the amount of polyene in polyvinyl alcohol is determined by 1H-island. Let A be the total area of the peaks present at δ = 5.8 to 7.4 ppm, and δ = 1.2 to 1,
Letting the peak area of gppm be B, the amount of polyene can be determined using the following formula 2).

The present invention will be specifically explained below using examples, but the present invention is not limited only to the examples.

Example 1 and Comparative Example 1 Completely saponified polyvinyl alcohol with an average degree of polymerization of 4500 and 1.2-glycol bonds of 0.9 mol was dissolved in glycerin at 170° C. to a concentration of 9% by weight. The solution was then heated to 170° C. to a pore size of 0.2 u+.

It was discharged through a nozzle with 20 holes and dropped into a coagulation bath under 25W. Coagulation bath composition is methanol/glycerin =
In 9/1, the temperature was 0°C. After dry-wet gel spinning, wet stretching was carried out at a stretching ratio of 4 times, and then the solvent was extracted with methanol and the methanol was removed with hot air at 60"C.

Next, dry heat stretching was performed at 248° C. to give a total stretching ratio of 19 to 23 times. The single fiber strength of the obtained drawn yarn was 22
f/d at nine. In addition, 1,2-glycol bond Fio
, 9 molti and the polyene bond was 50 ppm.

In Comparative Example 1, polyvinyl alcohol having a 1,2-glycol bond of 1,5 molt was used, but the single fiber strength of the resulting drawn yarn was reduced to 17 f/d, and color decomposition occurred.

Example 2 Completely saponified polyvinyl alcohol with an average degree of polymerization of 7000.1,2-glycol bonds of 0.8 mol was dissolved in dimethyl sulfoxide at 95°C to a concentration of 5% by weight. The solution was then wet-dry gel spun at 80°C. The coagulation bath composition was methanol/dimethyl sulfoxide = 6/4, and the temperature was 10°C.

After spinning, wet stretching was performed at a stretching ratio of 5 times. Thereafter, it was treated in the same manner as in Example 1, and dry-heat stretched at 248° C. to a total stretching ratio of 20 to 23 times. The single fiber strength of the obtained drawn yarn was 21 f/d. Further, the amount of 1,2-glycol bond was 0.8 mol, and the polyene bond was 75 ppm.

Example 3 Average degree of polymerization: 2700. Completely saponified polyvinyl alcohol with 1.4 moles of 1,2-glycol bonds/average degree of polymerization: 9
000,1.2-Glycol bond A mixture of 0.7 mol of completely saponified polyvinyl alcohol = 1/9 was dissolved in glycerin, treated in the same manner as in Example 1, and finally 2
Dry heat stretching was performed at 35°C.

The single fiber strength of the obtained drawn yarn was 23 f/d.

Furthermore, the amount of 1,2-glycol bond was 0.75 ppm, and the amount of polyene bond was 45 ppm.

Claims (2)

[Claims] (1) Made of polyvinyl alcohol polymer with an average degree of polymerization of 12,000 or less, with 1,2-glycol bond
．． A high-strength polyvinyl alcohol fiber having a polyene bond of 2 mol% or less, a polyene bond of 100 ppm or less, and a single fiber tensile strength of 18 g/d or more. (2) The average degree of polymerization is 12,000 or less, and 1,2-
Use at least 80% or more of a polyvinyl alcohol polymer with glycol bonds of 1.2 mol% or less, perform wet stretching at a stretching ratio of 3 times or more, and then heat stretching at a total stretching ratio of 17 times or more at 200°C or higher. conduct, 1, 2
- A method for producing polyvinyl alcohol fibers, characterized by obtaining fibers having a glycol bond of 1.2 mol % or less, a polyene bond of 100 ppm or less, and a single fiber tensile strength of 18 g/d or more.