JP2888496B2 - Method for producing high modulus polyvinyl alcohol fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drawing method for producing a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having a high elastic modulus, and more particularly to a PVA which is excellent as a reinforcing material for rubber, plastic and the like. The present invention relates to a method for obtaining a system fiber.

[0002]

2. Description of the Related Art Conventionally, PVA-based fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile-based fibers. It is also used for such purposes. PVA-based fibers have better weather resistance, alkali resistance, and adhesiveness than liquid crystal fibers such as aromatic polyamides and aromatic polyesters, but still have low strength and elastic modulus, and are particularly useful as reinforcing materials for plastics and tires. High modulus fibers have long been desired.

As a method for obtaining a PVA-based fiber having a high strength and a high elastic modulus, there is a concept of gel spinning and ultra-drawing of a high molecular weight polyethylene, for example, Japanese Patent Application Laid-Open No. Sho 59-100710, which is based on Japanese Patent Application Laid-Open No. Gazette, JP-A-59-
JP-A-130314 and JP-A-61-108711 are known. In these methods, high polymerization degree PVA is dissolved in a solvent, cooled and gelled or coagulated by a dry-wet method to form a yarn, and then the solvent is extracted and stretched at a high draw ratio by dry heat stretching. No satisfactory elastic modulus was obtained.

[0004] In order to obtain a PVA-based fiber having a high modulus of elasticity, it must be drawn at a high magnification to have a highly oriented crystal structure.
For that purpose, it is necessary to stretch near the melting point of PVA.
However, PVA has a melting point close to the decomposition temperature, and when stretched for a long time at a high temperature, the PVA is decomposed, and the fiber is colored yellow or brown, resulting in a decrease in the strength modulus. In addition, the higher the temperature near the melting point, the more the relaxation of the orientation during stretching and the loss of the PVA molecular chain occur, and the elastic modulus tends to decrease.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for highly orienting crystals involved in stretching and tie molecules connecting the crystals while suppressing the decomposition and orientation relaxation of PVA in the stretching step. It is something you want to do.

[0006]

Means for Solving the Problems The present invention provides a method of spinning a spun yarn obtained by spinning from a solution containing a polyvinyl alcohol-based polymer having a viscosity average polymerization degree of at least 1500 at a temperature of at least 220 ° C. After stretching so that the total stretching ratio becomes at least 17 times, further stretching is performed at a temperature lower than the maximum temperature in the stretching, and the stretching rate is 1% or more and the tension is 2 g / d or more. Characteristic method for producing high-modulus polyvinyl alcohol-based fiber ".

The PVA polymer referred to in the present invention is 30%
The average degree of polymerization determined by the viscosity method in an aqueous solution of
It is a straight chain having a degree of saponification of 95 mol% or more and a low degree of branching. The higher the average degree of polymerization of PVA, the greater the number of tie molecules penetrating between the crystals, and the easier it is to obtain high modulus fibers. The PVA polymerization degree is preferably 4,000 or more, more preferably 10,000 or more.

In addition, additives of 5% by weight or less, such as boric acid, polyacrylic acid, titanium sulfate, lithium chloride, ultraviolet absorber, antioxidant and surfactant, are added to PVA for the purpose of improving stretchability and suppressing decomposition. You can add it. In addition, another compound of 3 mol% or less may be copolymerized for the purpose of increasing the added value.

As the solvent for the PVA-based polymer, those used in a conventional method can be employed.
Polyhydric alcohols such as trimethylene glycol, diethylene glycol, and glycerin, and mixed solvents thereof with water, or dimethyl sulfoxide, dimethylformamide, diethylene triamine, and mixed solvents thereof with water, and further, propyl alcohol or rhodan salt with water And the like. Among these, a solvent which gels by quenching is convenient for forming a uniform gel and obtaining a high elasticity fiber by amorphization, fixation in view of molecular chains, delay of solvent extraction, and the like.

The spinning method can be a conventional spinning method, and any of a wet method, a dry method, and a dry-wet method can be used, but a dry-wet gel spinning method is preferred.

The coagulation bath may be any of those commonly used, such as alcohols such as methanol and ethanol, acetone and ether, alkaline aqueous solution, sodium sulfate aqueous solution and a mixture thereof.

[0012] Wet stretching in a state containing a solvent may or may not be carried out, but it is preferable to carry out stretching at a temperature of 70 ° C or less, preferably at least three times, in the process up to drying. 70 for wet stretching
The reason for making the temperature 3 times or more below ℃ is that the crystallinity is reduced,
The purpose is to weaken intermolecular hydrogen bonds to facilitate the movement of molecular chains so that dry heat drawing in the final step can be performed at a high magnification, and to reduce sticking between single yarns.

The solvent extraction of the PVA-based polymer may be carried out with any of alcohol, acetone, water and the like, but lower alcohols such as methanol and ethanol are preferred.

Thereafter, drying must be performed to remove the extractant and the like, and the temperature is 130 ° C. or less, preferably 70 to 100 ° C. If it exceeds 130 ° C., crystallization increases, and it is difficult to increase the magnification in subsequent stretching.

In the present invention, in order to increase the orientation of the PVA molecular chain, the film must be stretched at a high temperature at a high magnification. Examples of the heating device include a contact type or non-contact type heater, a hot blast stove, and a liquid bath such as silicon. The heating atmosphere includes air and an inert gas such as N ₂ and CO ₂ . In order to enable high-magnification stretching industrially, it is preferable to provide a temperature difference of two or more stages by using a non-contact type heater or hot blast stove in air.

[0016] The stretching temperature must ultimately be above 220 ° C. If the temperature is lower than 220 ° C., the draw ratio decreases, and orientation and crystallization do not proceed, so that it is difficult to obtain a high elastic modulus fiber. Here, the stretching temperature means the actually measured maximum temperature of the heater or hot blast stove. The optimum temperature varies depending on the degree of polymerization, solvent and spinning method, but is initially 150-150 to prevent fiber melting and high crystallization.
200 ° C. is preferable, and the higher the degree of polymerization in the second and subsequent stages, the higher the degree of polymerization.
In this case, the temperature is desirably set to 250 to 260 ° C. Where P
It is difficult to obtain a high modulus fiber when the temperature is raised to such a state that the drawing tension is reduced by coloring due to the decomposition of VA or flow phenomenon of the molecular chain due to partial melting.

In the present invention, the total stretching ratio needs to be 17 times or more, preferably 19 times or more. Here, the total stretching ratio means a value obtained by multiplying the wet stretching ratio by the dry stretching ratio.

In general, the modulus of elasticity increases in comparison with the total stretching ratio, and the stretching ratio increases in proportion to the temperature. On the other hand, when the temperature is increased to the extent that occurs, the elastic modulus decreases. Therefore, there is a limit in obtaining a higher elastic modulus only by high-temperature stretching.

The present inventors have conducted intensive studies on increasing the elastic modulus. As a result, additional stretching is performed at a temperature lower than the maximum stretching temperature and at an elongation of 1% or more so that the stretching tension becomes 2% or more. I found that. In other words, by orienting the molecular chains under high tension and causing crystallization, it was possible to obtain an unprecedented high modulus fiber. The feature of the present invention is to promote a high degree of orientation and crystallization while preventing the orientation of the molecular chains from relaxing, and
This is to suppress the decomposition of PVA.

The temperature at the time of additional stretching is correlated with the elongation rate and the tension at the time of additional stretching, and is equal to or higher than the temperature at which the elongation rate at the additional stretching becomes 1% or more, and the tension at the time of additional stretching is 2 g / d. It is necessary to set the temperature below the above. Specifically, the degree of polymerization differs depending on the degree of polymerization.
C. and a degree of polymerization of 16000, the temperature is 240 to 255 ° C. If these temperatures are exceeded, the stretching tension is lowered and coloring due to decomposition is not preferred.

The elongation is 1% or more, preferably 2% or more. If the elongation is less than 1%, it becomes difficult to promote high orientation at high tension. Further, the higher the elongation rate, the better, but it is not preferable to increase the elongation so that fluff and breakage occur to cause fiber defects due to molecular chain breakage.

The tension at the time of additional stretching also varies depending on the degree of polymerization.
It is at least 2 g / d, preferably at least 3 g / d.

It is not good that the fiber after additional drawing is colored from yellow to brown. In this case, it is necessary to increase the speed to shorten the residence time of the additional stretching.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples. Various physical property values and parameters in the examples are measured by the following methods.

[0025] (1) was calculated by the viscosity average polymerization degree of the PVA based polymer (referred to as bar P _A) the intrinsic viscosity of an aqueous solution of JISK-6726 in accordance 30 ° C. [eta] Equation 1 than the measured value of.

[0026]

(Equation 1)

(2) Degree of polymerization degree reduction After the drawn yarn or the additional drawn yarn is dissolved in hot water at 130 to 140 ° C. under oxygen-free condition, the viscosity average polymerization of the drawn yarn or the additional drawn yarn is performed in the same manner as in (1). seeking degrees (shown as bar P _a dash) to calculate the reduction rate with respect to the bar P _a of the polymer by the following equation 2.

[0028]

(Equation 2)

(3) Tensile strength and elongation and initial modulus According to JIS L-1013, a yarn conditioned in advance was tested for a test length of 20 cm, an initial load of 0.25 g / d, and a tensile speed of 100.
% / Min, the breaking elongation at break and the initial elastic modulus were determined, and n = 1
An average value of 0 was adopted. Denier was measured by the gravimetric method.

(4) Orientation coefficient α Direct reading viscoelasticity measuring instrument DD manufactured by Orientec Co., Ltd.
Using a V-5-B type, the velocity C of a sound wave of 10 KHz applied to the fiber axis was measured, and compared with the sound velocity Cu (2.2 km / sec) of a non-oriented sample obtained from a cast film of PVA, The molecular orientation coefficient α was calculated from the following Mosley equation (3).

[0031]

(Equation 3)

(5) Crystallinity Xc A wide angle X-ray diffractometer RAD-rc manufactured by Rigaku Corporation was used, a 40 Kv 100 mA CuKα ray was used as a radiation source, and a graphite monochromator and a scintillation counter were used. The scanning speed was 1.0 degree / min for 2θ = 5 to 35 degrees and was calculated from the crystal peak area ratio to the total area.

[0033]

Example 1 Viscosity average polymerization degree 8,000, saponification degree 9
9.8 mol% of dry PVA was dissolved at 80 ° C. in dimethyl sulfoxide to form a 7% by weight solution. Note dissolver system in a closed system flowing after depressurization, N ₂ gas PV
The coloring decomposition of A was suppressed. Then, the solution was poured to a pore size of 0.15 m.
m, and discharged from a nozzle having 300 holes, and solidified by a wet method. The coagulation bath composition was methanol / dimethyl sulfoxide = 7/3 weight ratio, and the temperature was 5 ° C.

Thereafter, the film was stretched 4 times in methanol at 40 ° C., and dimethyl sulfoxide was almost completely extracted with methanol, dried with hot air at 90 ° C. and wound around a bobbin. The obtained spun yarn is 170-20 at a speed of 2 m / min.
It was passed through three sections at 0 to 246 ° C. in hot air stoves having different temperatures, and stretched at a total stretching ratio of 19.5 times. The stretching tension was 2.7 g / d.

The drawn yarn had a tensile strength of 19.1 g / d, an elongation of 4.3%, and an initial elastic modulus of 440 g / d. The orientation coefficient α determined from the sound velocity was 0.89, and the crystallinity Xc determined from the X-ray was 74%, indicating that the fiber was a highly oriented and highly crystalline fiber.

Next, the drawn yarn was additionally drawn in a hot air oven at a temperature of 240 ° C., a residence time of 15 seconds, an elongation of 2.1%, and a tension of 3.4 g / d. The additionally drawn yarn obtained was not colored, and the degree of polymerization decrease was 16.8%, which was almost the same as 15.9% of the drawn yarn before the additional drawing. The tensile strength of the additional stretched yarn was 20.5 g / d, the elongation was 3.6%, and the initial elastic modulus was 495 g / d, and the strength and elastic modulus were improved by additional stretch. Especially elastic modulus is higher than ever before, rubber,
It had excellent properties as a reinforcing material such as plastic. Α was 0.93 and Xc was 82%, and the degree of orientation and the degree of crystallinity were clearly increased by additional stretching.

[0037]

[Comparative Example 1] This example shows that even if an attempt is made to increase the stretching temperature to increase the stretching ratio, if the stretching temperature is too high, the performance will be reduced rather. And the stretching temperature in the third step was 252
This is an example in which stretching was performed in a hot blast stove instead of C. In this example, since the temperature was as high as 252 ° C., the total draw ratio was increased to 20.3 times, but the tension at the time of drawing was reduced to 2.1 g / d, and the obtained drawn yarn was slightly yellowish. became. The degree of polymerization decrease was as high as 24.6%, and the yarn strength was 17.2 g / d.
The elastic modulus is as low as 431 g / d, and the performance of the yarn before additional drawing is lower than that of the yarn of Example 1.

[0038]

Example 2 Viscosity average degree of polymerization 18000, saponification degree 9
9.2 mol% of PVA was dissolved in glycerin at 180 ° C. so as to be 5% by weight. The solution is then
C. and discharged from a nozzle having a hole diameter of 0.18 mm and 150 holes and dropped into a coagulation bath 20 mm below.

The coagulation bath composition was methanol / glycerin = 7
/ 3 weight ratio and the temperature was 0 ° C. The film was stretched 4 times in methanol at 40 ° C., extracted with a solvent, dried with hot air at 100 ° C., and wound around a bobbin. The obtained spun yarn is 1
The film was supplied to a radiant furnace at 70 ° C. to 258 ° C. at a speed of 1.5 m / min, and stretched at a stretching tension of 3.6 g / d and a total stretching ratio of 18.8. The drawn yarn had a strength of 21.5 g / d and an elastic modulus of 610 g / d.

Subsequently, additional stretching was performed with an elongation rate of 3.2% and a tension of 4.4 g / d in a radiant furnace at 250 ° C. at an input speed of 6.5 m / min. The additional drawn yarn had a strength of 22.6 g / d and an elastic modulus of 670 g / d, making it an unprecedented high elastic modulus fiber.

[0041]

Comparative Example 2 As Comparative Example 2, the additional stretching temperature in Example 2 was set to 261 ° C., and the stretching was performed at an elongation of 4.5%.
The tension dropped to 2.9 g / d. The strength of the additionally drawn yarn obtained was reduced to 19.5 g / d, and the elastic modulus was reduced to 582 g / d. The degree of polymerization decrease was 37.8%, which was about 2
It increased relatively, suggesting the breakage of the PVA molecular chain. Further, α obtained from the sound velocity was 0.91, which was lower than 0.95 in Example 2, and it was found that the orientation was relaxed by high temperature.

[0042]

Example 3 Viscosity average degree of polymerization 4000, saponification degree 99.
5 mol% of dry PVA was dissolved in water to 10 wt%. At that time, boric acid was added so as to be 3.5% by weight based on PVA. Then, the temperature of the solution was raised to 110 ° C., and a NaOH composition having a composition of 6 g / l and N
A ₂ SO ₄ was discharged into a coagulation bath maintained at 50 ° C. at 300 g / l to perform wet spinning.

Next, the resultant was neutralized with a dilute H ₂ SO ₄ aqueous solution and then washed with water. During this period, a total of 5.0 times wet stretching was performed. 12
Dry with hot air at 0 ° C. and continuously, 180-200-24
It was supplied to a hot air oven at 3 ° C. at a speed of 15 m / min and stretched. The stretching tension was 2.0 g / d, and the total stretching ratio was 25.7 times. The drawn yarn has a tensile strength of 17.8 g / d and an elongation of 5.8.
%, And the initial elastic modulus was 360 g / d.

Next, the drawn yarn was additionally drawn at a feed speed of 20 m / min, a hot air oven temperature of 235 ° C., an elongation of 1.5%, and a tension of 2.9 g / d. The tensile strength of the additional drawn yarn was 18.5 g /
d, elongation was 4.5%, initial elastic modulus was 415 g / d, and the effect of additional stretching was observed.

[0045]

Comparative Example 3 As Comparative Example 3, when the elongation rate of the additional stretching in Example 3 was set to 0.5%, the tension was 1.8 g / d.
And the initial elastic modulus was as low as 354 g / d.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-85310 (JP, A) JP-A-2-251608 (JP, A) JP-A-2-154008 (JP, A) JP-A-2- 169709 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) D01F 6/14 D02J 1/22

Claims (1)

(57) [Claims] 1. A spun yarn obtained by spinning a solution containing a polyvinyl alcohol-based polymer having a viscosity average polymerization degree of 1500 or more by a conventional method so that the total draw ratio becomes at least 17 times at a temperature of 220 ° C. or more. Characterized by being stretched further at a temperature lower than the maximum temperature in the stretching, at an elongation of 1% or more, and at a tension of 2 g / d or more. Manufacturing method.