JPH01298208A - Polyvinyl alcohol-based synthetic yarn and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title yarn having a flat section, a large ratio of length and width of crystal and excellent heat resistance by using an aqueous solution of PVA containing boric acid (borate) as spinning dope, extruding the dope into a coagulating bath with a specific temperature and drawing at a high draw ratio. CONSTITUTION:In using an aqueous solution of PVA containing preferably 0.5-5wt.% boric acid (borate) as a spinning solution as spinning dope, extruding the solution into an alkali coagulating bath containing a salt and spinning, the temperature of the coagulating bath is 55-95 deg.C, preferably 60-80 deg.C and the prepared undrawn yarn is drawn at >=17 times, preferably >=20 times draw ratio to give the aimed yarn having <=65%, preferably <=60% circularity of section, >=2.1, preferably >=2.3 ratio of length and width of crystal, 4,000-20,000 polymerization degree of polymer and >=120 deg.C dissolution temperature of yarn in water.

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 a large crystal length-to-width ratio; The present invention relates to a method of wet-spinning a PVA aqueous solution containing boric acid or a borate into a high-temperature alkaline coagulation bath containing salts having dehydrating ability.

<Conventional technology> PVA fibers have traditionally been used for organic molding materials such as plastics and rubber, hydraulic inorganic materials such as cement and gypsum, and others by taking advantage of the characteristics of having the highest strength and high elasticity among general-purpose fibers. It is used for reinforcing various materials.

The first performance required of reinforcing PVA fibers is high strength and
It is said to have high elasticity. If the fibers do not have sufficient strength and elasticity, the obtained fa fiber reinforced molded product will naturally not have toughness.The second performance required is that the reinforcing fibers are the matrix. It is said to have excellent adhesion to (the above-mentioned plastics, rubber, cement, plaster, etc.).

If the adhesion between the reinforcing fibers and the 1 trix is insufficient, the fiber-reinforced molded product will not be able to withstand external stress due to the strength of the reinforcing fibers.
Elasticity is not fully utilized and no reinforcing effect is obtained, leading to cracks and destruction. In order to improve the adhesion between the fibers and the matrix, it is effective to increase the surface area of the fibers, and specific methods include flattening the fiber cross section, making it irregularly shaped, making it finer in denier, etc. Various manufacturing methods have been proposed in the past for increasing the strength and elasticity of PVA fibers, and some of them have already been implemented.

The most typical method for producing PVA fibers is P
In this method, a VA aqueous solution is subjected to wet spinning in a coagulation bath at room temperature containing salts having dehydrating ability, then subjected to stretching heat treatment, and acetalization is performed as necessary. As is well known, the PVA fibers obtained by this method have a cocoon-shaped cross section with a two-layered skin and core structure and a relatively large surface area, but they can only be stretched to a total stretching ratio of about 8 times. However, the strength is only about 7 da/d, which is not at all satisfactory as a reinforcing 4S fiber from the strength point of view.

Among the attempts to obtain higher strength and higher elasticity using this method, the one that seems to be the most effective was the
This method is described in Japanese Patent Publication No. 4-14901 and Japanese Patent Publication No. 44-3513. These methods are characterized in that a relatively high concentration PVA aqueous solution is used as a spinning stock solution, the fibers are spun in a coagulation bath at a high temperature of 65° C. or higher and made of salts having dehydrating ability, and the fibers are rapidly cooled immediately after separation. This method aims to increase the strength by forming a homogeneous fiber without skin or core, and the total stretching ratio is 1.
The strength can be increased up to 44 times, which is an improvement over the conventional method, but the strength is only slightly over 10//d, and the cross section is nearly circular, which is still not satisfactory.

Furthermore, as a method for obtaining higher strength PVA fibers, there is a method proposed in Japanese Patent Publication No. 48-32623 and Japanese Patent Publication No. 1368-1983. These proposed methods are characterized by using a PVA aqueous solution containing boric acid or a borate as a spinning stock solution, and spinning into an alkaline coagulation bath at 20 to 50°C containing salts having dehydrating ability. The fibers are more homogenized than the method described in Publication No. 44-3513, and the cross section is approximately circular and the surface area is small. Furthermore, in the former case, the mechanical properties are considerably improved, with a total draw ratio of about 22 times and a strength of about 17 y/d, but these are still insufficient.Furthermore, the surface area of the fibers is small, and the reinforcing f! & I am not satisfied with it. In the latter, the length of the fiber crystal is disclosed, but the ratio of crystal length (L) to width (W) (hereinafter abbreviated as L/W) claimed in the present invention is not described. . However, it is not hard to imagine that the L/W is much smaller than the fiber of the present invention from the values of the example, which are a total draw ratio of 16 times and a strength of 129/d.

As will be explained later, the reinforcing effect is improved only when the L/W ratio increases, and furthermore, this fiber has a circular cross section and a small surface area, so it is not good for reinforcing fibers. .

As another method, as proposed in JP-A-60-126312 and JP-A-61-108712, PVA is dissolved in a solvent such as dimethyl sulfoxide or glycerin, and then dry/wet or rapidly cooled gel is produced. There is a method in which a conversion spinning method is carried out, followed by high stretching after removing the solvent. Although the fibers obtained by this method have significantly improved mechanical properties,
Since it is very homogeneous, its cross section is circular and its surface area is small, so it cannot be said to be suitable as a reinforcing fiber.

As mentioned above, conventional attempts to increase the strength and elasticity of PVA fibers have all aimed at homogenizing the fiber structure, and the resulting fibers have improved mechanical properties. However, in terms of cross-sectional shape, it is almost circular, and there is no one that exhibits the two properties required of reinforcing fibers at the same time in the direction of decreasing surface area.

On the other hand, as a means of increasing the surface area diagrammatically, there is a method of spinning using an irregularly shaped nozzle to make the cross section irregularly shaped. ! ,
However, with this method, it is necessary to increase the spinning draft in the case of PVA-based fibers, and therefore the drawability is significantly lower than when using a normal circular nozzle (7) Not only is the strength lower, but also the spinning draft is poor. This is not preferable because it also reduces productivity.

Alternatively, the surface area of the fiber per unit area can be increased by reducing the denier of the fiber, but the direction of decreasing the denier causes a decrease in spinnability and productivity, and the resulting This is undesirable because it worsens the dispersibility of fibers in the matrix.As described above, it has been impossible to obtain PVA-based fibers that have high strength, high elasticity, and a large surface area using conventional techniques. .

(Problems to be Solved by the Invention) Under these circumstances, the present inventors aimed to provide a PVA-based fiber with high strength, high elasticity, flat cross section, and large surface area, suitable for reinforcing fibers. As a result of intensive studies, we have arrived at the present invention. (Means for solving the problems) The FA and fiber of the present invention have a cross-sectional solidity of 65- or less,
and PVA whose L/W as defined in the present invention is 2.1 or more
It is a type fiber.

As a result of studying the reinforcing performance of various PVA-based fibers, the present inventors found that the reinforcing effect is more closely related to the L/W of the fiber than to the strength and elastic modulus of the reinforcing fiber, although it is unclear why. , in order to obtain a sufficient reinforcing effect, L, /W should be 2,
It was found that it is essential that 1 or more, preferably (, < is 2.3 or more, and that the cross-sectional solidity is 65% or less and the striking mechanism is 60 inches or less. f!! The length L of the crystal has little correlation with the reinforcing performance and mechanical properties of the fiber (a strong correlation only appears as L/W).

Furthermore, an effective method for producing the fibers of the present invention involves wet spinning using a PVA aqueous solution containing boric acid or a borate as a spinning stock solution, and applying a spinning solution to an alkaline coagulation bath at 55 to 95°C containing salts having dehydrating ability [717 times or more stretching]. This is a method of stretching at different magnifications.

The most significant feature of this method is that, whereas conventional methods are carried out at a coagulation bath temperature of 20 to 50°C, the method of the present invention raises the temperature to a high temperature of 55 to 95°C. Despite the fact that the fibers are devitrified and have a flat cross section, their drawability is greatly improved17, the L/W of the fibers is increased, the reinforcing effect is dramatically improved, and the mechanical properties of the fibers are further improved. We found that the physical properties were also significantly improved. Even in the case of PVA with a high degree of polymerization, which had the problem of extremely low drawability and mechanical properties not necessarily improved when conventionally known relatively low-temperature coagulation baths were used, the method of the present invention can be used. It was also found (7) that it became possible to stretch to a high degree, and that the effect of the degree of polymerization of PVA could be fully brought out, resulting in a large L/W and a fl [7] having a flat cross section.

Furthermore, as a polymerization degree effect, it has been found that in addition to improving the surficial properties and reinforcing effect of fibers, which are related to L/W and cross-sectional fullness, water resistance is also improved.

In other words, increasing the degree of polymerization of PVA improves water resistance.
A has a dissolution temperature in water of only about 115°C i 75(x
When the polymerization degree is 1f40,000 PVA, the H is about 120 to 125°C, and when the degree of polymerization is 7,000 or more, the temperature increases to 130°C or more.

In terms of heat, this effect cannot be brought out by spinning using a conventional coagulation bath at a temperature of 20 to 50°C, and can only be achieved by spinning at a higher coagulation bath temperature and drawing at a high degree.

As mentioned above, increasing the coagulation bath temperature is accompanied by devitrification of the yarn and a decrease in cross-sectional solidity, but it improves the drawability, increases the L/W of the fiber, and reduces the degree of polymerization effect. Pull it out,
In addition to L/WK, it also has the effect of improving water resistance. The reason for this is not well understood, but it is thought that the coagulation mechanism is completely different from that of conventional spinning methods.

An example of the method for producing fibers of the present invention will be described in detail below.

The degree of polymerization of PvA used is 1500 or more, preferably 20
00 or more, more preferably 3000 or more.

If the degree of polymerization of PVA is less than 1500, crystal growth in the fiber axis direction will be insufficient, L/W will not be 2.1 or more, and mechanical properties will not be improved.

Also, if you want higher water resistance in addition to L, /W + mechanical properties, you can further increase the degree of polymerization of PVA <, 40
00 or more, more preferably 7000 or more.

The spinning stock solution is an aqueous solution of the PVA with a concentration of 3 to 30% by weight, and contains boric acid or borate in an amount of 70.5 to 5% by weight based on the PVA.The concentration of PVA is determined by its degree of polymerization. It is necessary to adjust the concentration accordingly, but if the concentration is too low, even if the stretchability is good, crystals will grow in the fiber axis direction (
(If L and /W do not become large or are too high, the stretchability will decrease.

The temperature of the spinning dope is 85-125°C, preferably 95-12°C.
0°C; if it is too low, the stretchability will be inhibited [2, if it is too high, the stock solution will boil. Further, in order to stabilize the spinning condition, an appropriate amount of an organic acid such as acetic acid or an inorganic acid such as nitric acid may be added to the spinning dope.

The temperature of the coagulation bath is 55-95°C, preferably 60-80°C
If the temperature is 55° C. or lower, the cross section of the fiber will not become very flat, and the drawability will be low, so the L/W will not become large. On the other hand, temperatures above 95°C are undesirable because the coagulation bath boils and adhesion occurs between single image fibers.As the alkali component of the coagulation bath, caustic alkalis such as sodium hydroxide and potassium hydroxide are used, and the concentration is between 2 and 30°C. 200 f/J, preferably 5 to 50 f/l.

Further, as the salt component of the coagulation bath, a salt having a dehydrating ability such as sodium sulfate or sodium carbonate is used, and the concentration is 1009/J to saturated concentration, preferably close to saturated concentration. As the spinning nozzle, a normal circular nozzle or a nozzle having a similar shape is used.

The fibers after spinning may be subjected to alkali neutralization, wet heat stretching, water washing, dry stretching, and heat treatment according to conventional methods. The stretching ratio in a wet state is 3 times or more, preferably 5 times or more.

It is necessary to carry out the stretching so that the total stretching ratio of wet and dry stretching is 17 times or more, preferably 20 times or more. The larger the total stretching ratio, the larger the L/W, and when it is less than 17 times, the L/W reaches 2.1 and is not present.

(Effects of the Invention) The fibers of the present invention have excellent mechanical properties with a large L/W ratio, and have a flat cross section with a cross-sectional solidity of 65 inches or less and a large surface area, so they can be used in cement, plastics, etc. It is well suited for use as a reinforcing fiber for rubber and other materials, but due to its excellent mechanical properties, it can also be used for general industrial materials such as ropes and cables.

In addition, fibers obtained from PVA with a polymerization degree of 4000 or higher have excellent water resistance, making it possible to autoclave FRC, which was previously impossible due to lack of water resistance. However, it can also be used in applications that require water resistance, such as robes for ships or large-scale prayers, fishing nets, and fire hoses.

The present invention will be explained below with reference to Examples. Note that the degree of fullness of the cross section (the degree of flatness of the cross section) is defined in the present invention.

(lower number indicates flatness), crystal length-to-width ratio (L/W) and mechanical properties (dry breaking strength and elongation and initial elastic modulus) measured by the method below Vi. be.

○ Cross-sectional solidity The cross-sectional photograph of the fiber is enlarged to about 100 yj and its cross-sectional area F is determined.

Next, a wide width B of the cross-sectional middle shell was determined and calculated using the following formula.

In addition, take out arbitrarily from one multifilament yarn.
This is determined for 7 and 20 single fibers, and the average value is defined as the cross-sectional fullness of the fibers constituting the multifilament yarn.

Length and width ratio of O crystal It was measured by a known wide-angle X-ray diffraction method under the following conditions.

Wide-angle X-ray (1) Rigaku Denki Co., Ltd. 15 rotation anticathode X-ray diffraction device (
Type RA D-rA) 40kV, 100m
ACuKα (graphite monochromator) using non-tyrene counter (2) Goniometer slit system: DS+/,°, 5SV2°, R8O, 1
5□ Scanning speed: 20 = % (3) Sample (125□ fiber with length 2.50,
(lined up in parallel with a width of 1.5 degrees) was attached to a fiber sample stage, and the diffraction curves of plane indices (020) and (100) were measured using the transmission method, and the half-width B (hkl) of each curve was determined. Obtained.

Crystal size ratio (L/W) Plane index (020"l) obtained by the above transmission method.

(100) From the value of the half-width B (hkl) of the peak, 5c
Each crystal size was calculated using Herrer's formula.

D(hkl)=λ/ Bo(hkl)CO3θ(
hkl) However, K = 0.9 λ = 1.5418 (in) B o: Width of diffraction curve after slit correction by Janes' method (radian) θ (hkl) Nibragg angle (deg,) L/W, = D
(020), /'D(100),! : L-te-seeking meta.

0 Dry breaking strength, elongation, initial elastic modulus (1) Trial H...Multifilament yarn (2
) Dry breaking strength and elongation, initial elastic modulus...Temperature 20℃,
Compliant with JIS-1017 in atmosphere F with relative humidity 65%1
7. Measured with an Instron tester at a test length of 20 and a tensile rate of 10 F/min, and the initial elastic modulus was determined from the elongation-load curve.

(3) Number of measurements: Measurements were performed 10 times, and the average value was calculated.

Dissolution temperature in O water 25 single fibers were arbitrarily taken out from the multifilament yarn, bundled, and a load of 115009/'d was suspended from one end. Fix the other end with a jig, and immerse it with the loaded side down in a glass tube containing water at 30°C along with a thermometer.

Next, the glass tube was sealed and the temperature was raised at a rate of 2°C per minute to determine the fJ of the sample. The temperature at which fibers melt and break is defined as the water dissolution temperature. Note that the number n of measurements is 2 and 1, and the average value is taken.

Examples 1 to 3, Comparative Example 1.2 Completely saponified PVA with a degree of polymerization of 3500 was dissolved in water to a concentration of 9% by weight, and boric acid was added to this at 3.5% by weight based on PVAK.
In addition, a spinning stock solution was obtained. Next, this spinning stock solution was heated to 105°C, and the solution was heated to 60°C (Example 1), 70°C (Example 2), and 90°C (Example 3), 40°C (Comparative Example 1),
Spinning was carried out through a spinneret having a circular nozzle with 1000 holes in a coagulation bath at each temperature of 100°C (Comparative Example 2), and 6 m/min.
Let's take a bath at the speed of a minute, Mena. Subsequently, roller stretching, neutralization, 1.5 times wet heat stretching, water washing and drying were carried out in accordance with conventional methods, and the stretching ratio in the wet state was increased to 6 times, and then 230
Dry heat stretching was carried out at °C and the film was wound onto a bobbin.

At a coagulation bath temperature of 40° C., the spun yarn was relatively transparent and had a high cross-sectional solidity, but as the temperature increased, the yarn became severely devitrified and the cross-sectional solidity decreased. Table 1 shows the quality of the obtained filaments. All yarn compositions are 1800 d/1
000 f.

Table 1 As described above, by increasing the coagulation bath temperature beyond the range of the examples, the cross-sectional solidity decreases, and even for PVA with a relatively high degree of polymerization, the stretchability improves dramatically, and L/ A fiber with a large W and excellent mechanical properties and relatively good water resistance was obtained. In addition, the cement reinforcing properties of the fibers of the examples were far superior to those of the comparative examples.

Example 4 Completely saponified PVA with a degree of polymerization of 1700 was dissolved in water at a concentration of 14%, and boric acid was added in an amount of 1.5% by weight based on the PVA.
This was added to prepare a spinning stock solution. Next, this was heated to 100°C, and sodium hydroxide 30 f/j, sodium sulfate 34
0? The coagulation bath was discharged through a nozzle having a circular nozzle with 1000 holes into a coagulation bath at 80° C./l, and was ablated at a speed of 8 m/min.

Subsequently, roller stretching, neutralization, 2x wet heat stretching, water washing, and drying were carried out in accordance with conventional methods to increase the stretching ratio in the wet state to 7 times, followed by dry heat stretching at 225°C and winding onto a bobbin. .

The spun yarn was severely devitrified and its cross-sectional solidity was as low as 50%. The stretching ratio is 25 times, and the L/W is 2.
．． 4, and the water dissolution temperature was 118°C, which was relatively good. The reinforcing properties of this UL and fiber cement were extremely excellent.

Comparative Example 3 The process up to drying was exactly the same as in Example 2, but the dry heat stretching ratio was reduced to make the total stretching ratio 16 times.

The cross-sectional solidity of the obtained fiber was 36%, which was the same as in Example 2, but the L/W and water dissolution temperature were 2 and 3, respectively.
It has a low temperature of 0.114℃ and has a reinforcing effect.

It was far inferior to the fiber of Example 2.

Examples 5 to 7 Degree of polymerization 4500% (Example 5)% 7500 (Example 6)
, 18,000 (Example 7) were dissolved in water at a concentration of 8.5, 7.0, 4.5 tungsten, respectively, and boric acid was added to the solution at a concentration of 4M tungsten to PVA. The mixture was added to prepare a spinning dope, which was then spun in the same manner as in Example 4, and wound onto a bobbin at a stretching ratio of 25, 24, and 5.22 times, respectively. The quality of the obtained fibers is shown together with the quality of the fibers obtained in Comparative Example 4, which will be described later, and a portion of the above-mentioned Examples and Comparative Examples.

Comparative Example 4 The same treatment as in Example 6 was performed except that the coagulation bath temperature was 35° C., and the film was stretched to the verge of breakage in dry heat stretching. The quality of the flL fibers is also shown in Table 2.

This table shows that the method of the present invention reduces the cross-sectional solidity and L
/W, and it is clear that it is extremely effective in bringing out the degree of polymerization effect that extends to the dissolution temperature in water.

Furthermore, the fibers of Examples 5 to 7 showed amazing cement reinforcing properties, and the higher the degree of PVA polymerization, 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 wt.
Dry and wet spinning was performed in a methanol coagulation bath at ℃. The distance between the nozzle surface and the coagulation bath liquid level was 15 square meters. The obtained spun yarn was wet-stretched 6 times while removing the solvent and dried.

Next, dry heat stretching was carried out at 240° C. to give a total stretching ratio of 24 times.

The cross-sectional fullness of the obtained fiber was very high, 92%, and was almost circular. Also, the L/W was 2.6, which showed excellent mechanical properties.

When the cement reinforcing properties of this fiber were investigated, Example 1
It was considerably inferior to the fibers of No. 3 to 3. In addition, when the fractured surface of the cement was observed with an electron microscope, it was found that Example 1
When fibers with a flat cross section with low cross-sectional solidity of ~3 were used for reinforcement, there was almost no shedding;
It was observed that many dropouts occurred when fibers having this circular cross section were used.

Patent applicant: RiRashi Co., Ltd.

Claims (3)

[Claims] (1) A polyvinyl alcohol-based synthetic fiber having a cross-sectional solidity of 65% or less and a crystal length-to-width ratio of 2.1 or more. (2) The degree of polymerization of the polymer constituting the fiber is 4000-2
0000, and the fiber has a dissolution temperature in water of 120°C or higher. (3) When spinning a polyvinyl alcohol aqueous solution containing boric acid or a borate as a spinning stock solution and extruding it into an alkaline coagulation bath containing salts, the coagulation bath temperature is 55 to 95.
A method for producing polyvinyl alcohol-based synthetic fibers, which comprises stretching the obtained spun yarn at a stretching ratio of 17 times or more.