JP2553129B2 - Polyvinyl alcohol fiber with good fatigue resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyvinyl alcohol fiber which is inexpensive and has good fatigue resistance, and particularly relates to a polyvinyl alcohol fiber suitable for industrial materials and for reinforcing composite materials. .

(Prior art) Conventional polyvinyl alcohol fibers have higher strength and elastic modulus than polyamide, polyester, and polyacrylonitrile fibers, and they are mainly used for industrial materials, which is their main application, and recently as cement replacements for asbestos replacement fibers. Is also used. In particular, as a rubber-reinforcing fiber, one that is inexpensive and can withstand repeated bending fatigue of compression and extension is required, but at present, no satisfactory polyvinyl alcohol fiber has been found.

As a method for obtaining polyvinyl alcohol fibers, it is customary to carry out wet spinning using a low polymerization polyvinyl alcohol polymer having an average polymerization degree of about 2000.
Japanese Patent Publication No. 422, Japanese Patent Publication No. 47186/1987, Japanese Patent Publication No. 48326/1988 are known. However, with the methods shown in these, it is difficult to obtain fibers having good fatigue resistance because the average degree of polymerization of the polymer is low.

On the other hand, as a method for obtaining a high-strength fiber by using a polyvinyl alcohol-based polymer having a high degree of polymerization, a concept of gel spinning-super-drawing of high-molecular-weight polyethylene was applied to JP-A-59-100710.
JP-A-59-130314, JP-A-61-108711 and the like are known. Further, JP-A-61-289112 describes a high strength polyvinyl alcohol fiber having an average degree of polymerization of 10,000 or more. These high-polymerization degree polyvinyl alcohol fibers have good fatigue resistance as compared with low-polymerization products, but yet satisfactory fatigue resistance cannot be obtained and the cost becomes high. The reason why the fatigue resistance is insufficient is that with 100% high-polymerization polymer, the growth of crystals is promoted by the stretching heat treatment, and the number of fine crystals that are considered to be effective for fatigue resistance decreases, resulting in brittleness against bending and compression. Things can be considered. On the other hand, the reasons for the high cost include the polymerization temperature of the polyvinyl alcohol-based polymer having a high degree of polymerization, the limitation of the polymerization reaction rate, and the reduction of the productivity due to the decrease of the concentration of polyvinyl alcohol in the spinning dope.

(Problems to be Solved by the Invention) Based on the above background, the present inventors have conducted earnest studies in order to obtain a polyvinyl alcohol fiber that is inexpensive and has excellent fatigue resistance.

In order to improve fatigue resistance, it was considered to maintain a high level of strength and elongation, and to increase the number of fine crystals. In order to obtain high strength and high elongation, it is necessary to use a high-polymerization degree polymer, orientate and crystallize the molecular chain to reduce the defective molecular chain end, and increase the number of tie molecules connecting the crystals. good. Further, in order to increase the number of microcrystals, it is preferable to mix a high-polymerization degree polymer and a low-polymerization degree polymer to appropriately prevent mutual crystal growth.

Based on the above idea, the present inventors have conducted various studies to obtain a polyvinyl alcohol fiber that is inexpensive and has good fatigue resistance. As a result, the polymer (A) having an average degree of polymerization of 5,000 or more is 10 to 10%.
90% by weight and 90 to 10% by weight of one or more polymers (B) having an average degree of polymerization of 1500 to 10000, and the degree of polymerization of (A) is 1.5 from the average degree of polymerization of (B). It has been found that using two or more polymers having a relationship that is more than double results in very good results.

After dissolving this mixture with a solvent, spinning and drawing are carried out by a conventional method to obtain a polyvinyl alcohol fiber satisfying the above-mentioned two points.

(Means for Solving the Problems) That is, the present invention provides “a polyvinyl alcohol-based polymer (A) having an average degree of polymerization of 5000 or more of 10 to 90% by weight and an average degree of polymerization of 1500 lower than the polymer (A). ~ 1000
0 or more polyvinyl alcohol type polymer (B) of 90 to 10% by weight, and the average polymerization degree of the (A) is 1.5 times or more than the average polymerization degree of the (B). And the polyvinyl alcohol-based fiber having good fatigue resistance, characterized in that the MIT flex fatigue cutting number is 5000 times or more.

 Hereinafter, the contents of the present invention will be described in more detail.

The polyvinyl polymer referred to in the present invention is an average degree of polymerization determined by a viscosity method in an aqueous solution at 30 ° C. of 1500 or more, and a chain-like polyvinyl alcohol having a saponification degree of 98 mol% or more and a low branching degree. is there. In addition, those obtained by copolymerizing 2 mol% or less of other vinyl compounds, and those obtained by adding 3 wt% or less of pigments, antioxidants, ultraviolet absorbers, crystallization inhibitors and the like are also included. In particular, boric acid or borate that causes intermolecular cross-linking with the OH group of polyvinyl alcohol is 0.
Addition of 5 to 3% by weight is preferable because it improves the spinnability of the polymer, reduces screw drop during spinning and breakage of single yarn, and suppresses crystallization of the fiber.

As the average degree of polymerization of polyvinyl alcohol is higher, the number of molecular chain ends that tend to become defective portions is small and there are many tie molecules that are continuous between crystals, so that a fiber having high strength and high elongation is easily obtained.

Here, referring to the degree of polymerization of the polyvinyl alcohol-based polymer, the average degree of polymerization of the polymer (A) (hereinafter, abbreviated as _{A in the} present invention) is 5,000 or more, because the strength and elongation decrease when it is less than 5,000, which is preferable. Is over 10,000. The maximum average degree of polymerization of the polymer (B) (hereinafter, abbreviated as _{B in the} present invention, when two or more kinds are referred to as _B1 and _B2 ---) is 1500 to 10,000 is that the number of molecular chain ends is large at 1500 or less. The strength and fatigue resistance are reduced due to the decrease in the number of molecules, and when it is 10,000 or more, the cost is increased. Therefore, it is preferably 2,000 to 5,000. The polymer (B) may be two or more kinds having different average polymerization degrees, compositions, mixing ratios of additives, and the like.

Further, _A ≧ 1.5 _B , and preferably _A ≧ 2 _B. However, when the polymer (B) is composed of two or more kinds, the value of the highest average degree of polymerization is used for _B. The mixing ratio of each of the polymers (A) and (B) is 10 to 90% by weight, and 90 to
The amount of 10% by weight causes a decrease in fatigue resistance and cost increase due to crystal growth when the mixing ratio of the polymer (A) is 90% by weight or more, and decreases the strength and the fatigue resistance at 10% by weight or less. The mixing ratio of the polymer (B) is preferably 70 to 20% by weight.

Solvents for polyvinyl alcohol polymers generally include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, dimethyl sulfoxide, dimethylformamide, diethylenetriamine, water, and mixtures of these with alcohols or rhodane salt aqueous solutions. The concentration of the polyvinyl alcohol polymer is preferably in the range of 5 to 25% by weight depending on the spin drawability. The preparation of such a thickened solution is generally carried out by stirring and heating, but in order to suppress the decomposition of the polymer, it is preferably under N ₂ atmosphere or in vacuum.

A solution in which polyvinyl alcohol is completely dissolved is spun as a spinning dope, and the spinning method is dry or wet.
Alternatively, a dry-wet method in which both are combined may be used. The stretching method may be any of a submerged stretching method, a dry heat stretching method, and a zone stretching method, but a stretching temperature of 200 ° C. or higher is preferable in order to promote oriented crystallization at a high stretching ratio. Further, in the present invention, it is preferable that after stretching, shrinkage is 10% or less, preferably 2 to 5% to increase the elongation while suppressing the decrease in strength, and the fatigue strength is better. When the shrinkage ratio is 10% or more, the strength is severely reduced, which is not preferable. It should be noted that the N ₂ atmosphere is preferable in order to suppress coloring and decomposition of the polymer during spinning and stretching.

The polyvinyl alcohol fibers having good fatigue properties obtained here are single fiber denier Dr ≦ 10, single fiber tensile strength DT ≧ 17 g /
d, Tensile elongation of single fiber DE ≧ 4% is preferable. More preferably, Dr ≦ 5, DT ≧ 20 g / d, and DE ≧ 5%. Dr
When the value exceeds 10, the yarn or cord becomes hard and compression fatigue easily occurs. If the DT is less than 17 g / d, it is easy to cut when fatigued. When the DE is less than 4%, the strain energy generated during compression and elongation of the fiber cannot be completely absorbed, and a kink band (crack) is likely to occur, which is not preferable in terms of fatigue resistance.

The flex fatigue test is based on JIS P8115 “MIT for paper and board.
"Folding strength test method using a shape tester" is applied to fibers, and sample yarn denier is 800 constant, load is 500 g, reciprocating speed is 175 times /
The number of times of reciprocal bending until the sample is cut under the condition of a bending angle of 135 ° is measured.

 The present invention will be specifically described below with reference to examples.

Examples 1 and 2 and Comparative Example 1 Polyvinyl alcohol (A) having an average degree of polymerization of 15,000 / polyvinyl alcohol (B) having an average degree of polymerization of 1700 are respectively
As a comparative example 1, the two-type mixed polyvinyl alcohol mixed in the ratio of 10/90 and 50/50% by weight was dissolved in glycerin at 180 ° C. so as to be 18% by weight and 7% by weight. ), (B) polymer mixing ratio 5/95% by weight
And the polymer concentration was adjusted to 20% by weight, and the same operation was performed. The dissolver was a closed system, and the inside of the system was decompressed and then filled with N ₂ gas to suppress the coloring and decomposition of polyvinyl alcohol.

Next, the solution was heated to 170 ° C. and discharged from a nozzle having a hole diameter of 0.2 mm and a number of holes of 20 and dropped into a coagulation bath 25 mm below.
The coagulation bath composition was methanol / glycerin = 5/5 and the temperature was 0 ° C.

The gel fiber obtained by cooling in the coagulation bath was wet-stretched 5 times in a bath of methanol / glycerin = 9/1, and then the solvent was extracted with methanol.

Then, after removing methanol with hot air at 60 ° C, each was stretched 4 times with a hollow heater at 240 ° C.

In the case of Examples 1 and 2, a uniform solution was discharged without single yarn breakage during yarn spinning and yarn clutter filter clogging, and the gel fiber was rich in transparency. The denier of the obtained monofilament is 3.
5, each single fiber strength 19g / d and 22g / d, elongation 5.8%
And 4.9%. The number of MIT flex fatigue cuts measured with the MIT tester was 5900 and 7200, respectively. In Comparative Example 1, the above numerical values were 16 g / d, 5.0%, 4200 times, and the fatigue resistance was poor.

Example 3 and Comparative Example 2 9% by weight of a two-type mixed polyvinyl alcohol in which polyvinyl alcohol (A) having an average degree of polymerization of 12000 / polyvinyl alcohol (B) having an average degree of polymerization of 4500 was mixed at a ratio of 30/70% by weight. Dimethyl sulfoxide to 95 ° C
It was dissolved with stirring.

Next, the solution was heated to 60 ° C. and discharged from a nozzle having a hole diameter of 0.12 mm and 10 holes, and dropped into a coagulation bath 20 mm below. The coagulation bath composition was dimethyl sulfoxide / methanol = 4/6, and the temperature was set to 10 ° C. There was no single yarn breakage during spinning, and the gel fiber was transparent and uniform.

This gel fiber is dimethyl sulfoxide / methanol =
After being stretched twice in 5/5, it was immersed in a bath of 100% methanol to extract most of the solvent and dried at 40 ° C. under reduced pressure for one day.

The resulting fiber was drawn 9.2 times with a hollow heater at 238 ° C,
Furthermore, 5% shrinkage is applied at 245 ° C, and the single fiber denier is 2.1,
Strength is 21 g / d, elongation is 6.2%, MIT flex fatigue cuts 115
00 times of polyvinyl alcohol fiber was obtained.

As Comparative Example 2, only polyvinyl alcohol having an average degree of polymerization of 12000 was used, and the polyvinyl alcohol concentration was 6% by weight.
Then, the same operation as in Example 3 was performed. The number of MIT flexural fatigue cuts of the obtained fiber was 8,800, which was lower than that in Example 3.

Example 4 A polyvinyl alcohol having an average degree of polymerization of 15,000 / a polyvinyl alcohol having an average degree of polymerization of 4500 / a polyvinyl alcohol having an average degree of polymerization of 1700 were mixed at a ratio of 40/30/30% by weight to prepare a three-component mixed type polyvinyl alcohol. Fiberized by the same operation as. The resulting fiber has a single fiber denier of 4.
8, strength 20g / d, elongation 5.8%, MIT flex fatigue cut
It was 9,600 times and had good fatigue resistance.

Claims (1)

(57) [Claims] 1. A polyvinyl alcohol-based polymer (A) having an average degree of polymerization of 5000 or more in an amount of 10 to 90% by weight, and the polymer (A).
One or more polyvinyl alcohol-based polymers (B) having a lower average degree of polymerization of 1500 to 10,000
The average degree of polymerization of (A) has a relationship of 1.5 times or more than the average degree of polymerization of (B), and the MIT flex fatigue cutting number is 5000 times or more. Characteristic polyvinyl alcohol fiber with good fatigue resistance.