JPH0284504A - Polyvinyl alcohol fiber suitable for reinforcement material - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention reduces the weight by generating a large number of microvoids while maintaining high strength and high elastic modulus, and also creates pleats on the surface of the fiber. This relates to polyvinyl alcohol-based fibers that have excellent reinforcing effects and have improved adhesion to the matrix.

(Prior art) Compared to polyamide, polyester, or polyacrylic fibers, conventional polyvinyl alcohol fibers have mechanical properties, especially high modulus of elasticity, and are excellent in weather resistance and hydrophilicity. It is widely used as an industrial and industrial fiber material, such as for tire hoods or cement reinforcement.

This method of producing polyvinyl alcohol fibers differs from the melt spinning method used for polyester fibers, etc., in that the polymer is dissolved in a solvent to form a spinning stock solution, which is then discharged from a spinning nozzle to form a filament. A method of removing and hot stretching is used.

However, after dissolving ultra-high polymerization degree polyethylene with a solvent,
Since it was confirmed that high-strength, high-modulus fibers can be obtained by gel spinning followed by ultra-stretching, numerous patents have been disclosed that apply this method to polyvinyl alcohol fibers as well. For example, JP-A-59-1303
In Publication No. 14, high polymerization degree polyvinyl alcohol is dissolved in ethylene glycol or glycerin, which is a polyhydric alcohol, to prepare a spinning dope, and after gel spinning, the solvent is removed and hot stretched, which is not seen in conventional polyvinyl alcohol fibers. It has high performance like that. Also, JP-A-610040
In Publication No. 60, highly polymerized polyvinyl alcohol is dissolved in dimethyl sulfoxide, transparent gel spinning is performed, the solvent is slowly removed, and the solvent removal is strengthened by drying under reduced pressure, followed by hot stretching. High-performance fibers that are not found in conventional fibers have been obtained. In any case, it seems that the production of high-strength, high-modulus polyvinyl alcohol fibers will not be possible without an approach based on increasing the degree of polymerization of polyvinyl alcohol polymers and gel spinning.

Whitening is observed when polyvinyl alcohol fibers are hot-stretched at high magnification, but this is thought to be due to the generation of voids or horizontal stripes due to stress relaxation during hot-stretching.

In conventional polyvinyl alcohol fibers having an average degree of polymerization of about 2000, the degree of crystal orientation and tensile strength tended to decrease due to this whitening phenomenon. Therefore, conventional hot drawing of polyvinyl alcohol fibers was carried out at a draw ratio lower than the drawing ratio at which the fibers whitened, and the resulting fiber surface had fewer horizontal stripes and voids and was nearly transparent. On the other hand, when the average degree of polymerization is 3000 or more, the strength and elastic modulus increase even if there is whitening, but satisfactory performance cannot be obtained because of the large number of macrovoids. As in the present invention, it contains many micro voids and has few large voids, so it is light and maintains high strength and high elastic modulus.
In addition, polyvinyl alcohol fibers that have good adhesion to a matrix due to the large amount of brightness on the fiber surface have not yet been reported.

Currently, it is desired that reinforcing fibers for industrial materials such as cement, plastics, and rubber have high strength, high modulus of elasticity, light weight, and good adhesion to the matrix, but it is still difficult to satisfy all three requirements at the same time. Fiber is not available.

Aramid fibers, arylate fibers, and carbon fibers are being considered as highly strong fibers, but although these fibers themselves have high strength, they have poor adhesion to cement and plastics and lack reinforcing properties. Acrylic fibers have also been studied; for example, in JP-A-51-20222, wet-spun acrylic fibers have many folds on the surface, so they have excellent adhesion to cement and have a reinforcing effect against breakage. However, since the m-fiber strength itself is low, a particularly large reinforcing effect cannot be expected. Furthermore, many studies have been made on polyvinyl alcohol fibers, taking advantage of their inherent good adhesive properties. For example, JP-A-61-16701
In Publication No. 1, ultra-fine denifre polyvinyl alcohol fibers are made by wet spinning to increase the adhesion surface area to the matrix (thus increasing the reinforcing effect. However, in this case as well, the strength of the fibers themselves is currently low, so reinforcing The effect is weak.

(Problems to be solved by the invention) As mentioned above (lightweight, high strength and high modulus of reinforcing fibers,
It is necessary to improve adhesion, and the present inventors have intensively studied polyvinyl alcohol-based fibers that can satisfy these requirements at the same time.

As a result, the transparent and uniform gel-spun fibers are stretched under conditions that do not cause crystallization to destroy the initial microcrystals, and then stretched at a high magnification under conditions that cause crystal orientation, and then subjected to constant length heat treatment. The present invention was achieved by discovering a polyvinyl alcohol fiber that has a large number of microvoids and stripes and has high strength and high modulus of elasticity.

(Means for Solving the Problems) In other words, the present invention has a specific gravity of 1.300 or less, an average degree of polymerization of 3000 or more, and an X-ray small-angle scattering intensity of (IEo, t
+ I Eo, 3) / (I Mo, t+ I, 4
o, ) ≧ 5 (where ■ 8: scattering intensity on the equator line (CP
S), scattering intensity on IH two meridians (cps), 0,2
．． There are many microvoids satisfying the scattering angle ε (degrees) of 0.3, and there are at least 5 horizontal stripes per 10μ length on the fiber surface in the direction perpendicular to the fiber axis. The present invention relates to a polyvinyl alcohol-based m-fiber suitable for reinforcing materials, characterized by having a tensile strength of 18 g/d or more and an elastic modulus of 450 g/d or more.

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

The polyvinyl alcohol fiber of the present invention has many microvoids of 101μ or less in size on the surface, is light, has good adhesion to the matrix, and has excellent tensile strength and elastic modulus. The reason why such polyvinyl alcohol-based fibers have high tensile strength and elastic modulus even if they have horizontal stripes and voids on the surface is that they use a highly polymerized polyvinyl alcohol-based polymer and a special spinning method. This is because there are fewer macro voids.

In other words, the conventionally used polyvinyl alcohol with an average degree of polymerization of about 2000 has a low degree of polymerization, resulting in a decrease in strength due to an increase in defective parts due to a large number of molecular chain ends and a small number of tie molecules connecting crystals. .

What is the polyvinyl alcohol-based polymer referred to in the present invention?30
The average degree of polymerization determined by the viscosity method in an aqueous solution of 'C is 30.
It is a linear polyvinyl alcohol with a saponification degree of 98 mol% or more and a low degree of branching. Copolymerized with 2 mol% or less of Ike's vinyl compound, as well as 3% or less of pigments, antioxidants, ultraviolet absorbers,
It also includes those to which crystallization inhibitors and the like are added. In particular, adding 0.5 to 5% by weight of boric acid or borate, which causes intermolecular crosslinking with the OH groups of polyvinyl alcohol, improves the spinnability of the polymer and reduces screw dropout and single fiber breakage during spinning. This is preferable because it also suppresses crystallization of gel fibers. The higher the average degree of polymerization of polyvinyl alcohol, the easier it is to obtain high-strength fibers.The degree of polymerization is 3000 or more, preferably 6.
000 or more, more preferably 10,000 or more. Solvents for polyvinyl alcohol polymers generally include polyhydric alcohols such as ethylene glycol, trimethylene glycol, diethylene glycol, and glycerin, dimethyl sulfoxide, dimethyl formamide, diethylene triamine, water, mixtures of these with alcohols, and aqueous solutions of Rodan salt. In the present invention, ethylene glycol, glycerin and dimethyl sulfoxide are preferred as non-aqueous solvents.

The feature of the present invention is a fiber having microvoids and grooves on the surface and having high strength and high elastic modulus, but the following four conditions are necessary to obtain this fiber.

The first is to obtain uniform and transparent gel fibers.

After the polymer is dissolved in a solvent to form a solution with as few molecular chain entanglements as possible, it is discharged from a spinning nozzle and immediately quenched. In this case, wet spinning is difficult because the solution temperature and coagulation temperature are different, and dry-wet spinning or gel spinning is required. For the coagulation bath composition, a liquid with a slow extraction rate is desirable in order to cause uniform gelation. For example, non-aqueous solvents mixed with 70% by weight or less of alcohol or water, 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 to these. . For example, alcohol at 10°C or lower or a mixture of alcohol and water may be used. The temperature of the coagulation bath is preferably 20°C or lower and Tr-10°C or higher (TI 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 second method is to stretch the film at a high magnification while containing a solvent. In this case, it is desirable to cause only molecular orientation without causing crystallization, for example by stretching the film by at least 3 times, preferably at least 5 times, in an aqueous sodium sulfate solution, an alcohol bath, or an air bath at 80° C. or lower.

Next, most of the solvent is extracted with methanol, water, etc.

Thirdly, the wet drawn fiber containing almost no solvent is heated to 200°C.
As mentioned above, it is preferable to stretch at a high magnification at a temperature of 220° C. or higher. That is, by sufficiently causing crystallization at 200° C. or higher and by increasing the total stretching ratio to 15 times or higher, the oriented crystallization of molecular chains is promoted.

The stretching may be carried out by any method such as dry heat stretching using air or inert gas, oil bath stretching, or zone stretching, and stretching may be carried out in one or more stages.

The fourth method is to subject the high-magnification drawn yarn to constant length heat treatment. This causes partial orientation relaxation and crystal growth, resulting in fibers having microvoids and horizontal stripes according to the present invention. The heat treatment temperature is t±10°C (t
≦205°C), color decomposition of PVA does not occur,
In addition, a temperature that causes partial orientation relaxation and crystal growth is preferable. In addition, it is not preferable to actively induce shrinkage during heat treatment because the strength and elastic modulus decrease.

In order to obtain the polyvinyl alcohol fibers of the present invention, which are lightweight, have good adhesive properties, and have high strength and high elastic modulus, homogeneous and transparent gel fibers are stretched to a certain length and heat treated to orient and crystallize the molecular chains. , promotes orientation relaxation and crystal growth to the extent that the elastic modulus is not reduced. As a result, there are few macrovoids larger than 1μ, and microvoids smaller than lO@μ, l! -l There are many stripes, and the specific gravity is 1. : 1oo or less and becomes a fiber with high strength and high elastic modulus. The specific gravity was determined by the density gradient tube method at 25°C, and if it is 1300 or more, the weight of the reinforcing material becomes large, which limits its use and reduces its commercial value.

Macro voids of 1μ or more can be removed by splitting the drawn fibers vertically or
It was judged by cutting into slices and observing with an electron microscope.

Macrovoids of 10 mμ or less were determined using small-angle X-ray scattering intensity. The measurement was carried out using a small-angle X-ray scattering device and a scintillation counter at a scattering angle of ε=0.15° to 1.
06 at a speed of 1'/15 minutes, the scattering intensity in the equator direction and the meridian direction was measured, and the value obtained by subtracting the intensity when there was no sample (air scattering) was calculated. It was set as 4. (r to, * + I go, a) / (I engineering. If the value of t + Exo, J is less than 5, the specific gravity will be 1.300 or more, or if the specific gravity is less than IJOO, there will be many macro voids, This is not preferable because strength and elastic modulus decrease.

The reason for the occurrence of horizontal stripes on the fiber surface is not clear, but it is thought that they occur due to orientation relaxation of some of the highly oriented fibers. FIG. 1 shows an electron micrograph of a fiber with horizontal stripes obtained according to the present invention. In the present invention, there must be at least five horizontal stripes per length of IOμ. If there are fewer than 5 reinforcing materials, the adhesion to the matrix of plastic, cement, rubber, etc. will be reduced, and the strength and fatigue resistance of the composite material will be deteriorated.

The strength of the single fibers obtained in the present invention is igg/d or more, and the elastic modulus is 450 g/d or more. If the strength is less than 18 g/d, the strength and fatigue resistance of the composite material decreases, and the elastic modulus is 450 g/d.
If it is less than that, problems tend to occur in impact resistance, strain recovery, etc.

It has been found that the present invention provides polyvinyl alcohol-based W4 fibers that are unprecedented in weight, have good adhesive properties, and have high strength and high modulus of elasticity, and exhibit excellent effects as reinforcing materials.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited only to the Examples.

Examples and Comparative Examples Examples 1 and 2 have polyvinyl alcohol polymerization degree of 330.
0 and 4800, solvent dimethyl sulfonate, bobbinyl alcohol concentration 10% and 9% by weight
After purging with nitrogen, the mixture was dissolved at 65 to 70°C under reduced pressure to obtain a spinning stock solution. The composition of the coagulation bath was a 7/3 mixture of methanol/dimethylsulfokind at a temperature of 8° C. for transparent gel spinning. Then, after wet stretching 5 times in methanol at 40°C,
It was thoroughly extracted with methanol, dried with hot air at 100°C, and wound up to give a fiber before being stretched. Stretching was carried out in an air bath at 230°C, and the total stretching ratio was 20.1i and 20.8 times, respectively. This fiber was further heat treated at 235°C. The specific gravity of the fiber is 1.298, ■, 292, and the small-angle X-ray scattering intensity ratio (I to, x+ I!.,)/(rs.*
+I, lo, s) were 7.8.8.8, respectively. In addition, some macrovoids of 0.1 to 10μ were observed by electron microscopy, but no voids of 10μ or more were observed. There are as many as 10 horizontal stripes per 10μ length, and the tensile strength is 19.0120.5g/d and the elastic modulus is 491 and 54, respectively.
It was 3g/d.

Examples 3 to 6 used high polymerization products with an average degree of polymerization of 6,800 to 18,500, the solvent was ethylene glycol and glycerin, and the polyvinyl alcohol concentration was 6 to 8% by weight.
After purging with nitrogen, the pressure was reduced to 170°C and 185°C, respectively.
The solution was dissolved at 190°C for 16 hours using an automatic, revolving pot to obtain a stock solution. The coagulation bath composition is methanol ethylene glycol = 7/3 and methanol/glycerin - 6/4 mixed liquid, the temperature is 10 to 15°C, and the spinning draft is approximately 0.5.
Transparent gel was spun with the nozzle 30+ am away from the coagulation bath liquid level. After spinning, wet stretching is carried out for 3 to 30 minutes while containing the solvent.
After 6 times, it was extracted with methanol, dried at 70°C, and then stretched at 240°C, with a total stretching ratio of 17.8 to t9.
．． sr=. Continue to stretch at 238° at the same speed as the drawing speed.
It was heat-treated for 10 seconds and rolled up. The specific gravity of the fiber is 1.29
0 to 1.292, and the small-angle X-ray scattering intensity ratio is 9.4 to
It became 20.7. As far as I could see with an electron microscope, there were many wide stripes, 15 to 20 per 10μ length, and few macrovoids. Tensile strength 21-25g/a, elastic modulus 550-64ag/
In d, the tensile strength and elastic modulus also increased as the repolymer was highly polymerized.

In Example 7, a highly polymerized product having an average degree of polymerization of 12,000 was dissolved in trimethyl sulfoxide by adding 20% water, and spinning was carried out at a coagulation bath temperature of -20°C. The effect in this case is at the same level as that shown in Example 3.

The same experiment as Example 5 was conducted in Comparative Example 1 at a coagulation bath temperature of 30° C., in Comparative Example 2 without wet stretching, and in Comparative Example 3 without constant length heat treatment. That is, in Comparative Example 1, since the coagulation bath temperature was as high as 30° C., crystallization occurred during spinning, the total stretching ratio decreased, and many macrovoids of 1 μ or more were observed in the stretching system. As a result, the tensile strength and elastic modulus were each 17.4 g/d.

It was as low as 442 g/d.

In Comparative Example 2, wet stretching was not performed, so the total stretching ratio was low, and the tensile strength decreased, whitening occurred, and there were fewer horizontal stripes and microvoids (the specific gravity was as high as 1,315). Comparative example 2 because fixed length heat treatment was not applied
The results were similar.

Margin below Next, the results of evaluation of practical physical properties are shown.

A slate board was made by mixing the fibers obtained in Example 2 with cement using a paper making machine, and its bending strength was measured to be 350.
Kg/cg+', conventional product is 250Kg/ca
The results were better compared to those showing “+”.

The fiber obtained in Example 5 was made into a twisted yarn hood of 1500 d/IX2 and resorcinol formalin latex (RFL).
After the treatment, the cord was placed in rubber to make a belt, and the strength retention rate of the cord after being bent 100,000 times was measured and found to be 65%. The fiber obtained in Comparative Example 2 was similarly subjected to a belt bending fatigue test, but the strength retention rate after 100,000 cycles was as low as 50%.

Finally, the fibers obtained in Example 5 and Comparative Example 3 were
Rubber adhesive strength was evaluated using a code of IX2. In this case, similarly to the above, three cords were placed in rubber after RFL treatment, and the pull-out strength of the three cords after vulcanization was examined. As a result, the adhesive force (pulling resistance) in Example 5 was as high as 1I kg, but in Comparative Example 3, which had fewer horizontal stripes, it was 9 kg.

[Brief explanation of the drawing]

FIG. 1 shows a whitened polyvinyl alcohol fiber containing many wide stripes obtained by the present invention.

Claims (1)

[Claims] The specific gravity is 1.300 or less, the average degree of polymerization is 3000 or more, and the small-angle X-ray scattering intensity is (I_E_O_._2+I_E_
O_. _3)/(I_M_O_._2+I_M_O_.
_3) ≧5 (where I_E: scattering intensity on the equator line (CP
S), I_M: Meridian scattering intensity (CPS), 0.2
, 0.3: There are many microvoids that satisfy the scattering angle ε (degrees), and there are at least 5 horizontal stripes per 10μ length on the fiber surface in the direction perpendicular to the fiber axis. A polyvinyl alcohol fiber suitable for reinforcing materials, characterized by having a fiber tensile strength of 18 g/d or more and an elastic modulus of 45 g/d or more.