JP2653682B2 - Polyvinyl alcohol-based synthetic fiber and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having a flat cross section and having a large ratio of crystal length to width, and the fiber. That is, a wet spinning of an aqueous PVA solution containing boric acid or borate into a high-temperature alkaline coagulation bath containing salts having a dehydrating ability.

<Conventional technology> Conventionally, PVA fibers have the highest strength among general-purpose fibers.
Utilizing the feature of high elasticity, it is used for reinforcing organic molding materials such as plastic and rubber, hydraulic inorganic materials such as cement and gypsum, and other various substances.

Performance required for reinforcing PVA fiber is firstly high strength
It is said to be highly elastic. If the fibers do not have sufficient strength and elasticity, the resulting fiber-reinforced molded article will, of course, have no toughness.

The second required performance is that the reinforcing fiber has excellent adhesiveness to matrix (the above-mentioned plastic, rubber, cement, gypsum, etc.). If the adhesion between the reinforcing fiber and the matrix is insufficient, the fiber-reinforced molded article may be cracked or destroyed against external stress, without sufficiently utilizing the strength and elasticity of the reinforcing fiber to obtain a reinforcing effect. Will be. To improve the adhesion between the fiber and the matrix, it is effective to increase the surface area of the fiber. Specifically, there are methods such as flattening, deforming, and fine denier of the fiber cross section. Conventionally, various production methods have been proposed for increasing the strength and elasticity of PVA-based fibers, and some of them have been implemented.

The most typical method for producing PVA-based fibers is PVA
This is a method in which an aqueous solution is wet-spun in a coagulation bath at room temperature containing salts having a dehydrating ability, subjected to a drawing heat treatment and, if necessary, converted into an acetal. The PVA-based fiber obtained by this method has a relatively large surface area in a cocoon-shaped cross section having a two-layer structure of a skin and a core, as is well known,
It can be stretched only to a total draw ratio of about 8 times and has a strength of only about 7 g / d, which is not at all satisfactory as a reinforcing fiber in terms of strength.

Among the attempts to obtain higher strength and higher elasticity by this method, the one that seems to be most effective is
This method is described in JP-A-44-14901 and JP-B-44-3513. These methods use relatively high concentrations of PV
A aqueous solution of spinning solution A
It is characterized by spinning in a coagulation bath at a high temperature of 5 ° C. or higher and quenching immediately after the bath is separated. Such a method is intended to achieve higher altitude by using a uniform fiber without a skin and a core, and the total draw ratio can be increased up to about 14 times, and the strength is improved as compared with a normal method. However, it is slightly more than 10 g / d, and the cross section is almost circular, which is not yet satisfactory.

As a method for obtaining a higher strength PVA fiber, there is a method proposed in Japanese Patent Publication No. 48-32623, Japanese Patent Publication No. 53-1368, or the like. These proposed methods are characterized in that an aqueous PVA solution containing boric acid or borate is used as a spinning solution and spun into an alkaline coagulation bath at 20 to 50 ° C. containing salts having a dehydrating ability. Kosho 44-3513
The cross section of the fiber is further homogenized as compared with the method described in Japanese Patent Application Laid-Open Publication No. H10-15095 or the like, and has a substantially circular shape and a small surface area. Furthermore, in the former, the total draw ratio is about 22 times, the strength is about 17 g / d, and the mechanical properties have been considerably improved but are still insufficient, and the surface area of the fiber is small, which is not satisfactory as a reinforcing fiber. . In the latter, the crystal length of the fiber is disclosed, but the crystal length (L) claimed in the present invention is used.
And the ratio of the width (W) (hereinafter abbreviated as L / W) is not described.
However, it is not difficult to imagine that the L / W is much smaller than the fiber of the present invention from the numerical values of the examples in which the total draw ratio is 16 times and the strength is 12 g / d. As will be described later, the reinforcing effect is improved only when L / W is increased instead of L. Further, since this fiber has a circular cross section and a small surface area, it is not preferable as a reinforcing fiber.

As still another method, Japanese Patent Application Laid-Open No.
As proposed in JP-A-61-108712, there is a method of dissolving PVA in a solvent such as dimethyl sulfoxide or glycerin, performing a dry / wet or quenching gel spinning method, and removing the solvent to perform high stretching. Although the fiber obtained by this method has greatly improved mechanical properties, it is not suitable as a reinforcing fiber because it is very homogeneous and has a circular cross section and a small surface area.

As described above, all attempts to increase the strength and elasticity of PVA-based fibers have been directed to homogenization of the fiber structure, and the resulting fibers have been improved in terms of mechanical properties. However, none of them satisfy the two properties required for the reinforcing fiber at the same time in the direction of decreasing the surface area because they are almost circular in terms of the cross-sectional shape.

On the other hand, as a means for intentionally increasing the surface area, there is a method of spinning using a deformed nozzle to deform the cross section. However, in this method, it is necessary to increase the spinning draft in the case of PVA-based fiber, so that not only the drawability is significantly reduced and the strength is reduced as compared with the case of using a normal circular nozzle, but also the spinnability is deteriorated and the production is reduced. This is not preferred because the properties are also reduced.

As another method, it is possible to increase the surface area of the fiber per unit amount by reducing the denier of the fiber, but the direction of fine denier decreases the spinnability and productivity, and further increases the The dispersibility of the obtained fiber in the matrix is deteriorated, which is not preferable.

As described above, the conventional technology has high strength and high elasticity,
In addition, it was impossible to obtain a PVA-based fiber having a large surface area.

<Problems to be Solved by the Invention> Under such circumstances, the present inventors aimed at providing a PVA-based fiber having a high strength, a high elasticity, a flat cross section, and a large surface area suitable for a reinforcing fiber. As a result of intensive studies, the present invention has been reached.

<Means for Solving the Problems> The fiber of the present invention is an aqueous solution containing 3 to 30% by weight of PVA and containing boric acid or borate at a temperature of 85 to 125 ° C. and having a degree of polymerization of 1500. The above aqueous solution was used as a spinning dope and a temperature of 60 to 9 containing a caustic alkali in a range of 5 to 50 g / and a salt having a dehydrating ability of 100 g / to a saturation concentration from a round cross-section nozzle.
The spun yarn obtained by extruding into a 5 ° C alkaline coagulation bath is
It is a fiber obtained by drawing at least 7 times, a PVA-based fiber having a flat fiber cross section, a cross section solidity of 65% or less, and an L / W defined by the present invention of 2.3 or more.

The present inventors have studied the reinforcing performance of various PVA-based fibers, as a result, the reinforcing effect is not known why the strength and elastic modulus of the reinforcing fiber, but the L / W of the fiber is more closely related, It has been found that in order to obtain a sufficient reinforcing effect, it is necessary that L / W is 2.3 or more, and it is essential that the cross-sectional solidity is 65% or less, preferably 60% or less.
The crystal length L of the fiber has little correlation with the reinforcing performance and mechanical properties of the fiber, and a strong correlation appears only as L / W.

An effective method for producing the fiber of the present invention is to use PVA of 3%.
Temperature of up to 30% by weight and containing boric acid or borate
An aqueous solution of a PVA-based solution having a polymerization degree of 1500 or more at ~ 125 ° C was used as a spinning dope, and from a round cross-section nozzle, 5 to 50 g of caustic alkali and 100 g of a salt having a dehydrating ability were used.
When extruding and spinning in an alkaline coagulation bath containing in the range of a saturation concentration, the coagulation bath temperature is set to 60 to 95 ° C, and the obtained spun yarn is drawn at a draw ratio of 17 times or more at a draw ratio. is there.

The most significant feature of such a method is that the method of the present invention is conventionally carried out at a coagulation bath temperature of 20 to 50 ° C., whereas the method of the present invention raises the temperature to 60 to 95 ° C. Fiber is devitrified and the cross section becomes flat,
They have found that the stretchability is greatly improved, the L / W of the fiber is increased, the reinforcing effect is dramatically improved, and the mechanical properties of the fiber are also significantly improved. In addition, when a conventionally known relatively low-temperature coagulation bath is used, even in the case of a PVA having a high degree of polymerization, which has a problem that the stretchability is remarkably low and the mechanical properties are not necessarily improved, according to the method of the present invention, It has also been found that the fiber can be drawn at a high degree, the effect of the degree of polymerization of PVA can be sufficiently brought out, and as a result, a fiber having a large L / W and a flat cross section can be obtained. Furthermore, as a polymerization degree effect, it has been found that the water resistance is improved in addition to the improvement of the mechanical properties and the reinforcing effect of the fibers related to the L / W and the cross-sectional integrity.

That is, when the degree of polymerization of PVA is increased, the water resistance is improved, and in the case of PVA having a degree of polymerization of about 1700 which is usually used industrially, the PVA having a degree of polymerization of about 4000 in water is only about 115 ° C.
About 120-125 ° C and 130 ° C when the degree of polymerization is 7000 or more
It improves to the above.

Needless to say, spinning using a conventional coagulation bath at a temperature of 20 to 50 ° C. cannot achieve this effect, and the spinning can be carried out by increasing the coagulation bath temperature and drawing only after high stretching.

As described above, raising the coagulation bath temperature involves devitrification of the yarn and lowering of the cross-sectional solidity, but improves the drawability, increases the L / W of the fiber, and reduces the polymerization degree effect. Pull out, L
In addition to / W, it has the effect of improving the water resistance. Although the reason is not well understood, it is considered that the solidification mechanism is completely different from the conventional spinning method.

Hereinafter, an example of the method for producing a fiber of the present invention will be described in detail.

The degree of polymerization of the PVA used is 1500 or more, preferably 2000 or more, and more preferably 3000 or more. PVA polymerization degree is 150
If it is less than 0, crystal growth in the fiber axis direction is insufficient and L / W is 2.
It is not more than 1, and the mechanical properties are not improved.

If higher water resistance is required in addition to L / W and mechanical properties, the degree of polymerization of PVA may be further increased, and it is 4,000 or more, more preferably 7000 or more.

The spinning solution is an aqueous solution having a concentration of 3 to 30% by weight of the PVA, and contains boric acid or borate in an amount of 0.5 to 5% by weight based on the PVA. The concentration of PVA needs to be appropriately adjusted according to the degree of polymerization. If the concentration is too low, crystals do not easily grow in the fiber axis direction even if the stretchability is good, and L / W does not increase. Conversely, if it is too high, the stretchability decreases.

The temperature of the spinning dope is 85 to 125 ° C., preferably 95 to 120 ° C. If it is too low, the drawability is impaired, and if it is too high, the stock does boil. To stabilize the spinning condition, an appropriate amount of an organic acid such as acetic acid or an inorganic acid such as nitric acid can be added to the spinning solution.

The temperature of the coagulation bath is between 60 and 95C, preferably between 60 and 80C. If the temperature is lower than 60 ° C., the cross section of the fiber is not very flat, and the drawability is low, so that the L / W does not increase. On the other hand, if the temperature is 95 ° C. or more, it is not preferable because boiling of the coagulation bath and sticking between the single fibers occur.

Sodium hydroxide, as an alkaline component of the coagulation bath,
Caustic alkali such as potassium hydroxide is used, and its concentration is 5 to 50 g /. As the salt component of the coagulation bath,
Salts having a dehydrating ability such as sodium sulfate and sodium carbonate are used, and the concentration is 100 g / -saturated concentration, and it is preferable that the concentration is close to saturation. As the spinning nozzle, a normal circular nozzle or a nozzle having a shape similar to that is used.

The fiber after spinning may be subjected to alkali neutralization, wet heat stretching, washing with water, dry stretching, and heat treatment according to a conventional method. The stretching ratio in the wet state is 3 times or more, preferably 5 times or more. It is necessary to perform stretching so that the total stretching ratio including wet and dry becomes 17 times or more, preferably 20 times or more. L / W increases as the total draw ratio increases, and L
/ W does not reach 2.1.

<Effects of the Invention> The fiber of the present invention has a large L / W and excellent mechanical properties, and has a flat cross-section and a large surface area such that the cross-sectional solidity is 65% or less. Although it is preferably used as a reinforcing fiber such as rubber, it can also be used for general industrial materials such as ropes and cables due to its excellent mechanical properties.

In addition, the fibers obtained from PVA having a degree of polymerization of 4000 or more have excellent water resistance, and cannot be carried out because of the lack of the conventional water resistance. Instead, it can be applied to applications requiring water resistance, such as ropes for ships or fisheries, fishing nets, fire hoses, and the like.

Hereinafter, the present invention will be described with reference to examples. It should be noted that the cross-sectional solidity (the degree of flatness of the cross section; the smaller the numerical value indicates the flatter), the ratio of the length to the width of the crystal (L /
W) and mechanical properties (dry breaking strength and elongation and initial elastic modulus)
Is measured by the following method.

○ enlarged depict cross-sectional photograph of a cross section adequacy fibers about 100 mm ² cross-sectional area F
Ask for.

Next, the widest width B in the cross section was calculated by the following equation.

In addition, this is obtained for 20 single fibers arbitrarily taken out of one multifilament yarn, and the average value thereof is defined as the cross-sectional fulfillment of the fibers constituting the multifilament yarn.

○ Ratio of crystal length to width Measured by a known wide-angle X-ray diffraction method under the following conditions.

Wide-angle X-ray (1) 40 kV, 100 mA CuKα (Graphite Monochromator) scintillation counter using a rotating anti-cathode X-ray diffractometer (Type RAD-rA) manufactured by Rigaku Corporation (2) Goniometer Slit system: DS1 / 2 ゜, SS1 / 2 ゜, RS0.15mm Scanning speed: 2θ = 1/2 ゜ / min (3) Fiber sample of 125mg fiber (2.5cm length and 1.5cm width arranged in parallel) Attached to the table, surface index (02
0) and (100) were measured, and the half width B of each curve was measured.
(Hkl).

Crystal size ratio (L / W) Calculate each crystal size using the Scherrer equation from the half-value width B (hkl) of the peaks of plane indices (020) and (100) obtained by the transmission method described above. did.

D (hkl) = Kλ / Bo (hkl) COSθ (hkl) where K = 0.9 λ = 1.5418 (Å) Spread of diffraction curve after slit correction by Bo: Jones method (radian) θ (hkl): Bragg angle (Deg.) L / W = D (020) / D (100).

○ Dry rupture strength and elongation, initial elastic modulus (1) Sample: Multifilament yarn (2) Dry rupture strength and elongation, initial elasticity: Compliant with JIS-1017 in an atmosphere at a temperature of 20 ° C and a relative humidity of 65% The initial elastic modulus was determined from its elongation to load curve using an Instron tester at a test length of 20 cm and a tensile speed of 10 cm / min.

(A) Number of measurements: 10 measurements were made, and the average was determined.

○ Dissolution temperature in water Arbitrary 25 single fibers are taken out from the multifilament yarn and bundled, and a load of 1/500 g / d is suspended at one end.
The other end is fixed with a jig, and immersed together with a thermometer in a glass tube filled with water at 30 ° C. with the loaded side down.

Next, the glass tube is sealed and the temperature is raised at a rate of 2 ° C. per minute.
The temperature at which the sample fibers dissolve and cut is defined as the dissolution temperature in water. Note that the number n of measurements is 2, and the average value is taken.

Examples 1 to 3 and Comparative Examples 1 and 2 Completely saponified PVA having a degree of polymerization of 3500 was dissolved in water at a concentration of 9% by weight, and boric acid was added at 3.5% by weight to PVA to obtain a spinning stock solution. Next, this undiluted spinning solution was heated to 105 ° C., and was composed of 15 g / sodium hydroxide and 350 g / sodium sulfate.
A 1000-hole coagulation bath at a temperature of 0 ° C. (Example 1), 70 ° C. (Example 2), 90 ° C. (Example 3), 40 ° C. (Comparative Example 1), and 100 ° C. (Comparative Example 2) The fiber was spun through a die having a circular nozzle and allowed to take a bath at a speed of 6 m / min. Roll stretching, neutralization, 1.5 times wet heat stretching, washing with water and drying are performed according to a conventional method, and the stretch ratio in the wet state is set to 6 times. Then, dry heat stretching is performed at 230 ° C. and wound on a bobbin. I took it.

At a coagulation bath temperature of 40 ° C., the spun yarn was relatively transparent and had a high degree of cross-sectional solidity. The fiber quality of the obtained fiber is
It is shown in the table. The yarn configuration is all 1800d / 1000f.

By increasing the coagulation bath temperature in the range of the examples in this way, the cross-sectional solidity is reduced, and even with a PVA having a relatively high degree of polymerization, the stretchability is dramatically improved, and the L / W is large and Fibers having excellent mechanical properties and relatively good water resistance were obtained. Also, the reinforcing properties of the cement were much better for the fibers of the examples than for the comparative examples.

Example 4 Completely saponified PVA having a degree of polymerization of 1700 was dissolved in water at a concentration of 14% by weight, and boric acid was added to the PVA at 1.5% by weight to prepare a spinning solution. Next, this was heated to 100 ° C., discharged into a coagulation bath of sodium hydroxide 30 g / and sodium sulfate 340 g / at 80 ° C. through a die having a 1000-hole circular nozzle, and allowed to separate at a speed of 8 m / min. . Subsequently, roller stretching, neutralization, 2 times wet heat stretching, washing with water and drying were performed according to a conventional method, and the stretching ratio in a wet state was increased to 7 times.
The film was stretched by dry heat at a temperature of ° C. and wound on a bobbin.

The spun yarn was severely devitrified, and the cross-sectional solidity was as low as 50%. The stretching ratio was 25 times, the L / W was as large as 2.4, and the dissolution temperature in water was 118 ° C, which was relatively good. The reinforcing property of the cement of this fiber was extremely excellent.

Comparative Example 3 The procedure was the same as in Example 2 until drying, except that the dry heat stretching ratio was reduced to make the total stretching ratio 16 times.

The cross-sectional degree of the obtained fiber was 36%, which was the same as that of Example 2. However, the L / W and the dissolution temperature in water were low at 2.0 and 114 ° C., respectively. compared to,
It was much worse.

Examples 5 to 7 Degree of polymerization: 4500 (Example 5), 7500 (Example 6), 18000
The fully saponified PVA of Example 7 was added to water in 8.5 and 7.
0, 4.5% by weight, dissolved in boric acid
A stock solution for spinning was prepared by adding 4% by weight to PVA, then spun in the same manner as in Example 4, and wound around a bobbin with a draw ratio of 25, 24.5, and 22 times, respectively. The yarn quality of the obtained fiber is shown together with the fiber quality of the fiber obtained in Comparative Example 4 to be described later and a part of the above Examples and Comparative Examples.

Comparative Example 4 The same treatment as in Example 6 was carried out except that the coagulation bath temperature was changed to 35 ° C., and the film was stretched to just before breaking in dry heat stretching. The yarn quality of this fiber is also shown in Table 2.

From this table, the method of the present invention reduces the cross-sectional solidity,
It is clear that it is very effective in eliciting the degree of polymerization effect, which extends to L / W and the dissolution temperature in water.

In addition, the fibers of Examples 5 to 7 exhibited remarkable cement reinforcement, and the higher the degree of polymerization of PVA, the better the autoclave resistance.

Comparative Example 5 The same PVA used in Examples 1 to 3 was dissolved in dimethyl sulfoxide at a concentration of 10% by weight to prepare a spinning stock solution, which was heated to 70 ° C, and methanol was heated at 10 ° C through a 50-hole circular nozzle. Dry and wet spinning was performed in a coagulation bath. The distance between the nozzle surface and the liquid surface of the coagulation bath was 15 mm. The obtained spun yarn was subjected to 6-fold wet stretching while removing the solvent, and dried. Then 240
Dry heat stretching was performed at ℃, and the total stretching ratio was set to 24 times.

The cross-sectional fulfillment of the obtained fiber was as high as 92% and almost circular. In addition, L / W was as large as 2.6 and excellent in mechanical properties.

When the reinforcing property of the cement of this fiber was examined, it was considerably inferior to the fibers of Examples 1 to 3. In addition, when the fracture surface of the cement was observed with an electron microscope, when the fibers having a flat cross section with low cross-sectional solidity of Examples 1 to 3 were used for reinforcement, almost no dropout occurred, whereas the circular shape It was recognized that a lot of dropouts occurred when fibers having a cross section were used.

Continuing from the front page (72) Inventor Shoji Akiyama 1-2-1 Kaigandori, Okayama-shi, Okayama Pref. JP-A-59-43112 (JP, A) JP-A-61-167011 (JP, A) JP-A-62-85013 (JP, A) JP-A-62-149910 (JP, A) JP-B-47-50330 (JP, A) , B1) Japanese Patent Publication No. 42-23976 (JP, B1) Japanese Patent Publication No. 31-2370 (JP, B1) Japanese Patent Publication No. 46-11457 (JP, B1) Japanese Patent Publication No. 41-12939 (JP, B1) 47-8186 (JP, B1)

Claims (3)

(57) [Claims] 1. An aqueous solution containing 3 to 30% by weight of polyvinyl alcohol and containing boric acid or borate at a temperature of 85 to 125 ° C., wherein the degree of polymerization of the polyvinyl alcohol is 1500 or more. Stretching the obtained spun yarn 17 times or more from a cross-sectional nozzle extruded into an alkaline coagulation bath at a temperature of 60 to 95 ° C containing caustic alkali in an amount of 5 to 50 g / and a salt having a dehydrating ability of 100 g / to a saturation concentration in a range of saturation concentration Wherein the fiber cross-section is flat and the cross-section solidity is 65% or less, and the ratio of the crystal length to the width is 2.3.
A polyvinyl alcohol-based synthetic fiber as described above. 2. The polymerization degree of the polymer constituting the fiber is 4000 to 4000.
The fiber according to claim 1, wherein the fiber has a dissolution temperature in water of 120 ° C or more. 3. Spinning an aqueous solution of polyvinyl alcohol containing 3 to 30% by weight of polyvinyl alcohol and containing boric acid or borate at a temperature of 85 to 125 ° C., wherein the degree of polymerization of the polyvinyl alcohol is 1500 or more. Undiluted solution,
When extruding from a round cross-section nozzle into an alkaline coagulation bath containing caustic alkali in an amount of 5 to 50 g / and a salt having a dehydrating ability of 100 g / to a saturation concentration and spinning, the coagulation bath temperature was set to 60 to 95 ° C. The obtained spun yarn is drawn at a draw ratio of 17 times or more, and the polyvinyl alcohol-based synthetic fiber having a flat fiber cross section, a cross section fullness of 65% or less, and a ratio of crystal length to width of 2.3 or more. A method for producing a polyvinyl alcohol-based synthetic fiber, comprising: