JPH01192813A - Polyvinyl alcohol based fiber excellent in flexing fatigue property - Google Patents

Abstract

PURPOSE:To obtain the aimed high-tenacity fiber with a high polymerization degree, consisting of a polyvinyl alcohol based polymer with a specified value or above of average polymerization degree, further, having specified mechanical properties and suitable as industrial materials and reinforcing composite materials. CONSTITUTION:The aimed polyvinyl based fiber, consisting of a PVA based polymer having >=5000 viscometric average polymerization degree in an aqueous solution at 30 deg.C, >=98mol% saponification degree and having >=10 single fiber denier, <=18g/d single fiber tensile strength, <=4% single fiber tensile elongation, <=1.2 flatness of fiber cross section and >=6000 MIT number of flexing to break.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a highly polymerized polyvinyl alcohol fiber that has high strength and excellent bending fatigue resistance, and is particularly suitable for use in industrial materials and reinforcing composite materials. The following also relates to suitable polyvinyl alcohol fibers.

(Conventional technology) Conventional polyvinyl alcohol fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile fibers, and their main use is not only as fibers for industrial materials, but also recently as asbestos substitute fibers, cement reinforcement materials, etc. It is also used in In particular, rubber reinforcing fibers are required to be resistant to compression-stretching fatigue, but to date no satisfactory polyvinyl alcohol yarn fibers have been found.

Gel spinning of high molecular weight polyethylene is a method for obtaining polyvinyl alcohol yarn fibers with high strength and high modulus.
JP-A-59-100710, JP-A-59-130314, and %-A, which apply the concept of super-stretching
The method described in Japanese Patent No. 108711 and the like is known. However, even if high strength and high elasticity polyvinyl alcohol yarn fibers are obtained by these methods, it is difficult to obtain fibers with high elongation and excellent bending fatigue resistance. Regarding flatness, there is no literature that mentions the correlation between flatness (-2) and bending fatigue.

(Problem to be Solved by the Invention) Based on the above background, the present inventors aimed to obtain a highly polymerized polyvinyl alcohol fiber having high strength, high elongation, high number of MIT bending fatigue cuts, and low flatness. We adopted a spinning method that can maintain as uniform a cross-section as possible using highly polymerized polyvinyl alcohol-based polymers, and aimed to increase strength through high-strength stretching by lowering the crystallinity of the fibers before stretching and creating strong intermolecular hydrogen. We focused on reducing bonding and achieving a shrinkage of 10% or less after stretching in order to achieve high elongation, and we conducted extensive studies. As a result, after dissolving the polyvinyl alcohol fiber, it was discharged from a nozzle and rapidly cooled to obtain a uniform and transparent gel fiber with suppressed crystallization with less entanglement of the shiborimer molecular chains.Then, after removing the solvent, dry heat stretching was performed. It has been found that a high degree of polymerization and high strength polyvinyl alcohol fiber with excellent bending fatigue resistance can be produced by applying a shrinkage treatment.

(Means for Solving Problem 11) That is, the present invention is a polyvinyl alcohol-based fiber characterized by being made of a polyvinyl alcohol-based polymer having an average degree of polymerization of 5000 or more and satisfying the following conditions: ( b) Dr≦10 (Dr: single fiber denier) (o
) DT ≧18 fl/d (DT: Single fiber tensile strength [) (c) DE≧4% (DE: single fiber tensile elongation)) Flatness of fiber cut cross section is 12 or less (e) Number of MIT bending fatigue cuts ≧6000 times Preferably, the polyvinyl alcohol fiber is made of a polyvinyl alcohol polymer having an average degree of polymerization of 10,000 or more, and further has a degree of molecular orientation α of 0.89≦α≦0.94 based on the speed of sound.

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 500.
It is a linear polyvinyl alcohol with a degree of saponification of 0 or more, a degree of saponification of 98 molar or more, and a low degree of branching. Also included are those copolymerized with 2 moles or less of other vinyl compounds, and also those to which about 3 weight or less of each of pigments, antioxidants, ultraviolet absorbers, crystallization inhibitors, etc. are added. In particular, add boric acid or borate that causes intermolecular crosslinking with the OH group of polyvinyl alcohol by 0.5% to polyvinyl alcohol.
It is preferable to add up to 3% 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 easier it is to obtain high-strength fibers.From this point of view, it is necessary to have an average degree of polymerization of 5,000 or more, and more preferably 10,000 or more. The higher the degree of polymerization, the fewer the molecular chain ends that tend to break out in defects, and the more tie molecules that connect crystals, which is advantageous for high-strength stretching. Examples include polyhydric alcohols such as methylene glycol, diethylene glycol, and sodium glycerol, dimethyl sulfoxide, dimethyl formamide, diethylene triamine, water, mixtures of these with alcohols, and aqueous solutions of rhodan salts. In the present invention, non-aqueous solvents are preferred, particularly ethylene glycol, glycerin and dimethyl sulfoxide.

In the present invention, a solution of a highly polymerized polyvinyl alcohol polymer is discharged through a spinning nozzle and immediately placed in a coagulation bath for rapid cooling. In this case, since the solution temperature and the coagulation bath temperature are greatly different, wet spinning is not possible and dry-wet spinning or gel spinning is required. As for the composition of the coagulation bath, a liquid with a slow extraction rate is preferred in order to cause uniform gelation and obtain gel fibers with a low degree of flatness and a nearly circular cross section. For example, non-aqueous solvents may be mixed with alcohol or water at a ratio of 20% or less by weight, and substances that are incompatible with solvents such as hexane, decalin, and petroleum-based solvents may be considered, but the present invention is not limited thereto. . For example, alcohol or a mixed system of alcohol and water at a temperature of 10° C. or lower may be used. The temperature of the coagulation bath is preferably 20°C or lower and Tf-IQ°C or higher (Tf is the coagulation temperature of the solvent) in order to obtain gel fibers that are transparent, suppress crystallization, and have a nearly circular shape.The obtained transparent gel fibers Possible ways to remove the solvent include extraction with C1-C6 lower alcohols, acetone, benzene, chloroform, etc., and/or scattering with hot air. It is preferable to remove it gradually to obtain a uniform circular cross section.Dry heat or wet heat stretching may be used in a state containing a solvent, but in the present invention, the final stretching must be performed at least at a dry heat temperature of 200°C or higher. .20
At temperatures below 0°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 is insufficiently crystallized, resulting in poor heat resistance and dimensional stability. I don't like it because it causes problems with sexuality etc. Therefore, in order to obtain high-strength polyvinyl alcohol fibers for industrial materials, the total stretching ratio must be increased to 12 times or more, preferably 15 times or more, using dry heat at 200° C. or higher. Note that polyvinyl alcohol-based polymers tend to discolor and decompose due to heat, so it is desirable to use an N2 atmosphere when dissolving in a solvent or dry-heat stretching. Furthermore, in the present invention, after stretching, the yield strength is preferably 10% or less. Apply 2 to 5% shrinkage to increase elongation while suppressing strength loss. When the shrinkage rate exceeds 10%, the strength decreases significantly, and the tensile strength of the single fiber according to the present invention is l8? /d or more cannot be maintained ○ Next, the degree of molecular orientation will be mentioned.

When measuring the speed of sound using a sound speed measuring device, if the angle between the propagation direction of the sound wave and the molecular chain is θ (here, 00≦θ≦900), then 0082θ= 1− (2Cu2/3C2) −−1
1) becomes.

Here, Cu: Sound speed of the same randomly oriented material C: Sound speed of fiber Since the sound speed does not depend on the degree of crystallinity below the glass transition temperature T2, the degree of molecular orientation α is α== (3cos2θ−1)/2 ・・...(
2) It becomes.

From the definitions (1) and (2), the relationship between the speed of sound C and the degree of molecular orientation α is (1″ 1−Cu2 /C2).

The degree of molecular orientation α of the obtained drawn yarn is 0.89≦α≦0.9
4 is preferable, and α=091 to 0.93 is more preferable. If α is less than 0.89, the single fiber tensile strength is 18
r/d or less, making it difficult to obtain high-strength fibers.

When α exceeds 0.94, fatigue of the fibers due to bending, buckling, etc. becomes severe. In other words, if the degree of molecular orientation in the amorphous portion that connects the crystals is large, the molecular chains will be in a fully extended state, resulting in poor bending fatigue properties. Therefore, a fiber with good bending fatigue resistance is obtained by performing a shrinkage treatment after stretching to disturb the molecular orientation of the amorphous part and increase the elongation of the fiber, but in order to maintain high strength, the shrinkage rate must be 10% or less. There is a need to.

The drawn yarn obtained in the above steps is further divided into single fibers by -h
(Dr)≦lO1 single fiber tensile strength (DT)≧18f
/d, single fiber tensile elongation (DE) ≧4%, flatness of fiber cut cross section (here, flatness is expressed as the ratio of major axis / minor axis of the cut cross section) 1.2 or less, MIT bending fatigue cutting number ≧600
It is a high-strength polyvinyl alcohol fiber that satisfies 0 cycles and has excellent bending fatigue resistance.

When Dr exceeds 10, the number of single fibers constituting the yarn decreases, resulting in a decrease in bending fatigue resistance.

Preferably Dr≦5. If the DT is less than 18 f/d, it will be easy to break due to bending fatigue.

Preferably it is 20y/, d or more. Furthermore, with regard to DE, if it is less than 4%, the movement of the amorphous portion is poor and the yarn becomes brittle against fatigue. Preferably, the degree of flatness is 6% or more.If the degree of flatness exceeds 1.2, fibrillation will occur, and fatigue properties will deteriorate. Furthermore, resistance to external forces also deteriorates. Further, if the number of MIT bending fatigue cuts is lower than 6000 times, the use of industrial materials will be limited.

The bending fatigue test method was applied to fibers using JIS P8115 1 "Test method for folding strength using an MIT tester for paper and paperboard", and the sample yarn denier was 5oo-H1 under a load of 500.
The number of reciprocating bends of the sample in the cutting casing is measured under the conditions of f, reciprocating speed of 175 times/min, and bending angle of 135°.

The present invention will be specifically explained below using examples.

Example 1 Completely saponified polyvinyl alcohol with an average degree of polymerization of 16,000 was mixed with dimethyl sulfoxide (D
MSO) at 95° C. under N2 atmosphere with stirring. The solution was then brought to 80°C and the pore size was 0.1.5 rrrm.
CD was discharged using a nozzle with 10 holes, dropped into a coagulation bath 20 mm below, and then withdrawn at a speed of 5 m/min. The coagulation bath composition was DMSO/methanol-85/15 (weight ratio), and the temperature was set at io<0>C. There were no single fiber breakages during spinning or tension unevenness due to gel point fluctuations, and the gel fibers were transparent and uniform. After stretching this gel fiber 5 times with DMSO/methanol-50150, 100% methanol
The sample was immersed in a water 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 3.8 times with a hollow heater at 230°C, and then subjected to 2% shrinkage at 235°C, resulting in a single fiber denier of 3.5, a single fiber tensile strength of 20 f/d, and a single fiber tensile elongation of 5.5. % of polyvinyl alcohol fibers were obtained. In addition, the flatness of the fiber cut cross section determined from electron micrographs was 1.
It was 05. In addition, when the number of MIT bending fatigue cuts was measured using an MIT type tester, it was 12,000 times. Further, the degree of molecular orientation α determined based on the speed of sound was 0.93.

Example 2 and Comparative Examples Y, 2 Completely saponified polyvinyl alcohol having an average degree of polymerization of 7000 was dissolved in glycerin at 170° C. to a concentration of 9% by weight, and at the same time, 1% by weight of boric acid was added. The dissolver was a closed system, and N2 gas was flowed into the system after reducing the pressure to suppress the coloring and decomposition of polyvinyl alcohol. Then the solution was heated to 170°C.
A nozzle with a hole diameter of 0.2 mm and a number of holes of 20 is used to discharge 2
It was dropped into a bath under 5 haze. 1 bath composition is 1 part methanol
The temperature was 5°C. After obtaining gel fibers by cooling, the solvent was extracted with a bath of 100% methanol, and then the methanol was removed with hot air at 60°C.

The film was stretched 5 times with a hollow heater at 170°C, stretched 35 times with a hollow heater at 235°C, and then subjected to heat treatment at 238°C for 5% shrinkage. A uniform solution was discharged without single filament breakage, yarn disorder, or filter clogging during spinning, and the gel fiber was highly transparent. The single fiber denier of the obtained fiber is 2
．． 5. Tensile strength of single fiber is l 9 d/l, tensile elongation of single fiber is 4.8%, flatness of fiber cut cross section is l, l, MIT
The number of bending fatigue cuts was 8,700 times, and the degree of molecular orientation α determined by the sound velocity was 0.92.

As Comparative Example 1, the total draw ratio was increased to 19.5 times, the single fiber denier was 2.2, the single fiber tensile strength was 2.18 f/d,
A fiber with a single fiber tensile elongation of 3.2% and a degree of molecular orientation α of 0.95 was obtained. The number of MIT bending fatigue cuts of this fiber is 4600.
It was one of the lowest times.

As Comparative Example 2, the gel fibers obtained in Example 2 were nipped to obtain fibers with a cut cross section of 1.8 in flatness.
Fibrillation occurred during the bending fatigue cutting test and the number of cuts was reduced to 4200.

Patent applicant RiRashi Co., Ltd.

Claims (1)

[Claims] (1) A high-strength polyvinyl alcohol-based fiber with a high degree of polymerization and excellent bending fatigue resistance, which is made of a polyvinyl alcohol-based polymer with an average degree of polymerization of 5,000 or more and satisfies the following conditions. (a) Dr≦10 (Dr: single fiber denier) (b) DT≧18g/d (DT: single fiber tensile strength) (c) DE≧4% (DE: single fiber tensile elongation) (d) Fiber cutting Cross-sectional flatness 1.2 or less (e) MIT bending fatigue cutting number ≧ 6000 times