JPH0733604B2 - High-strength polyvinyl alcohol fiber with excellent knot strength - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength polyvinyl alcohol fiber having excellent knot strength.

[0002]

2. Description of the Related Art Conventionally, polyvinyl alcohol (hereinafter referred to as P
VA) type fibers are used for reinforcing materials such as rubber reinforcing materials and plastic reinforcing materials because they have high strength and elastic modulus and low heat shrinkage, but they have low knot strength, fatigue resistance and hot water resistance. Due to its poor quality, its use is limited at present. Therefore, various attempts have been proposed to improve these physical properties.

For example, in JP-B-47-8186 and JP-B-48-9209, boric acid is added to a spinning stock solution and coagulated in an alkaline coagulating bath to improve the drawability of an undrawn yarn. , As a result, PVA
Methods have been proposed to improve the tensile strength, fatigue resistance, and hot water resistance of base fibers.

However, the PVA-based fiber obtained by such a method does not have a skin-core structure,
The cross section is uniform in the sense that the cross section is round,
As a result, the drawability is improved and the tensile strength is improved, but it does not have fiber properties such as knot strength and fatigue resistance comparable to those of polyamide or polyester fibers. Moreover, there is a problem that an increase in the draw ratio reduces the knot strength.

On the other hand, recently, when a PVA-based polymer (polymer) having an extremely high degree of polymerization of tens to hundreds of thousands is used, PVA-based fibers having high tensile strength and high initial elastic modulus can be obtained. Although it has been found (for example, Japanese Patent Laid-Open No. 59-130314) and attracts attention, PV having such an ultra-high degree of polymerization is used.
A-type polymers are difficult to produce and obtain industrially or commercially, and it can be said that they are not industrially available at least at present.

Therefore, the inventors of the present invention have earnestly studied PVA-based fibers having high strength and good fatigue resistance, which are made of PVA-based polymers having a polymerization degree that are industrially or commercially produced and available. The present invention has been achieved.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The A-based polymer has a higher degree of polymerization than conventional PVA-based fibers, but has a degree of polymerization that is industrially or commercially manufactured and available, and has a knot strength comparable to that of the polyamide or polyester fibers. It is an object of the present invention to provide a PVA-based fiber having fiber physical properties such as fatigue resistance and having high knot strength in spite of a large draw ratio, and a method for producing the same.

[0008]

In order to solve such a problem, the present invention has the following constitution. That is, the degree of polymerization is 250
It is made of polyvinyl alcohol polymer of 0 to 6000 and has a tensile strength of 14 g / d or more and a knot strength of 5.0 g / d.
d or more and the difference in birefringence between the inner and outer layers of the fiber is −
It is a high-strength polyvinyl alcohol fiber excellent in knot strength, which satisfies 8 × 10 ⁻³ ≦ (Δn) s− (Δn) c <0.

However, in the above equation, (Δn) s represents the birefringence at a position 2μ from the surface of the fiber, and (Δn) c represents the birefringence at the center of the fiber.

The PVA-based polymer used in the present invention is a PVA-based polymer and a derivative thereof having a degree of polymerization which can be industrially or commercially produced and obtained, for example, a completely saponified or partially saponified PVA-based polymer, As a copolymerization component in the main chain, for example, a small amount of an olefinic monomer such as ethylene, propylene or butylene is copolymerized, and a chemically post-treated PVA-based polymer and a small amount of PVA-based polymer of 10% by weight or less. Examples thereof include blends with other polymers having miscibility.

The degree of polymerization of these PVA-based polymers is 2,500 or more and 6,000 or less. When the degree of polymerization is less than 2500, the knot strength targeted by the present invention is comparable to that of polyamide or polyester fibers, and PVA-based fibers excellent in fatigue resistance and hot water resistance cannot be formed. In addition, PVA with a degree of polymerization exceeding 6000
It is generally difficult to industrially obtain the system polymer.

In the present invention, the solvent for dissolving the PVA polymer is dimethyl sulfoxide (hereinafter referred to as DMS).
O), ethylene glycol, glycerin, propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, and other polyhydric alcohol solvents, resorcinol, formamide, amine solvents such as saturated aqueous urea solutions, or lithium bromide, lithium chloride, etc. An aqueous solution of an inorganic salt such as lithium halide, zinc chloride, aluminum chloride, magnesium chloride, or a mixed solvent thereof can be used.

As a spinning method of a spinning dope obtained by dissolving a PVA polymer in the above-mentioned solvent, a dry-wet spinning method in which the spinning nozzle is first discharged into air or an inert atmosphere and then introduced into a coagulation bath to complete coagulation The law is adopted.

In this case, examples of the coagulating bath liquid include methanol, ethanol, acetone, toluene and the like, mixed solvents of these with a polymer solvent, inorganic salt aqueous solutions and the like.

The unstretched yarn obtained by such a spinning method is desolvated and stretched. The stretching means in the middle includes a heating tube, a heating plate, a heating roll, a heating pin, a heating liquid,
Various stretching means using a fluidized bed or the like can be applied alone or in combination. Further, these may be stretched in one stage or in multiple stages.

However, to obtain the fiber of the present invention,
Although not particularly limited to the above-mentioned drawing and other steps such as heat treatment in the middle thereof, as the final step of the drawing, a drawing step is adopted in which a heating tube is used and a drawn fiber yarn having an overall draw ratio of at least 15 times is obtained. It is essential.

More specifically, in the above heating tube drawing of the present invention, a yarn which has been drawn to some extent in advance is heated in an atmosphere such as air or an inert atmosphere gas such as nitrogen, helium or argon at a temperature of 230 ° C. or higher, The fiber is passed through a heating tube set at a temperature not higher than the fusing temperature of the fiber, and heat-stretched so that the stretching ratio during the entire stretching step, that is, the total stretching ratio is at least 15 times, preferably 18 times or more.
The higher the total draw ratio, the higher the tensile strength of the obtained fiber, but the characteristics such as knot strength and fatigue resistance do not necessarily improve. Considering the spinning stability and the like, 25 times or less is preferable.

That is, although the draw ratio of the heating tube differs depending on the draw ratio up to that point, it is more preferable to set the conditions of the heat tube drawing so as to form the birefringence difference described below including the draw ratio. Good to set.

The heating tube is preferably blown with nitrogen gas in order to suppress thermal oxidative decomposition of the polymer.

In the above heating tube drawing, if the atmospheric temperature is 230 ° C. or lower, the total draw ratio of at least 15 times required for producing the high strength PVA-based fiber cannot be obtained, while if the temperature is higher than the fusing temperature of the fiber. However, the fiber yarn is cut during the drawing process, which is not preferable.

Here, the melting temperature of the fiber tends to be higher than the melting point of the yarn measured by the differential thermal analysis (DSC), which is usually measured, because the yarn is in a drawing tension state in the heating tube.

In the PVA-based fiber of the present invention obtained by such a drawing method, the conventional fiber has a higher degree of orientation in the surface layer portion than that in the center. On the contrary, the degree of orientation of the surface layer portion is lower than that of the center portion.

That is, the difference in birefringence between the inner and outer layers of the fiber of the present invention is −8 × 10 ⁻³ ≦ (Δn) s− (Δn) c <0.
Is satisfied.

However, in the above equation, (Δn) s is the birefringence at a position 2 μ from the surface of the fiber, and (Δn) c is the birefringence at the center of the fiber.

The fiber of the present invention having such an orientation degree distribution has higher tensile strength and knot strength than conventional PVA fibers, and in particular has a knot strength of 5.0 g / d or more, which is a physical property not seen in the past. In addition, the fatigue resistance and heat resistance are greatly improved.

When the difference in the birefringence is out of the range represented by the above formula, the object of the present invention is not achieved, and particularly in the case of the fiber having the difference in the birefringence larger than 0, the present invention is obtained. It is difficult to obtain a fiber having high strength and high elastic modulus, which are the characteristics of the PVA-based fiber, and improved water resistance, heat resistance, and knot strength.

Further, when the final stage of the drawing step is not a heating tube but another drawing means such as a hot plate or a heating roll is adopted, the surface layer of the fibers, which is a feature of the present invention, is lower than the birefringence index of the central part. PVA-based fibers having a fiber structure cannot be obtained, and there is a problem that the fibers are fused.

Although it is not clear why good results can be obtained by using a heating tube in the final step of drawing, the drawn yarn is heated and drawn in a gas without directly contacting with a heated metal. It is presumed that this is because the heating efficiency is gentle, the temperature range that can be set just below the melting point is relatively wide, and the molecular orientation of the surface layer of the fiber can be relaxed preferentially.

The total draw ratio defined in the present invention is such that the fiber properties of the obtained PVA-based fibers are as good as or better than those of polyamide or polyester fibers, especially the tensile strength is 15.0 g / d or more and the elastic modulus is The amount is 200 g / d or more, which is important for making the fiber excellent in water resistance and bending resistance.

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

[0031]

EXAMPLES In this example, the fiber physical properties and birefringence are
The measurement was performed under the following conditions.

(1) Fiber strength (tensile strength and knot strength) Measurement sample; Single yarn measurement yarn length; 100 mm Tensile speed during measurement; 100 mm / min Measurement atmosphere; 20 ° C, 65% relative humidity (2) Birefringence Rate equipment; Carl Zeiss Jena's transmission interference microscope method; Du Pont method Calculation method: According to the following formula.

[0033]

[Equation 1] Example 1 A completely saponified PVA-based polymer having a degree of polymerization of 3900 was added to DMS.
It was dissolved in O to prepare a 9% solution, which was used as a spinning stock solution.
The spinning solution hole diameter 0.12 mm ^phi, extruded from a nozzle hole number 27, was coagulated in a coagulation bath consisting of methanol once through the space portion of 7 mm.

The obtained coagulated yarn was taken out at 5 m / min, further washed with methanol to remove DMSO, and then at room temperature for 4 minutes.
It is stretched twice, and then the inside air temperature is 230 ℃ and 235 ℃.
It heat-stretched with one heating tube so that the total stretch ratio might be 18 times.

As a result, fibers having physical properties of tensile strength of 18.4 g / d and knot strength of 7.6 g / d were obtained. The birefringence distribution of this fiber in the cross-sectional direction is shown as A in FIG.

The distribution of orientation in the cross-sectional direction of the single yarn of this fiber was lower in the surface layer than in the central portion. (Δn) s− (Δn) c = −2.9 × 10 ^{−3 Further} , 20 fibers obtained (single fiber fineness of 2.8 denier, number of filaments of 27) were combined into a yarn of about 1500 denier. , This is 33 turns for 10 cm of lower twist,
The tire cord was formed by twisting 33 turns per 10 cm of the upper twist.

Further, a Mallory tube fatigue test was conducted by applying an adhesive treatment, and the tube bending angle was 90 °.
It had a life of 250 minutes. It can be seen that the fatigue resistance of the conventional tire cord made of PVA fiber is remarkably improved as compared with the tire cord having a life of 10 to 20 minutes at a tube bending angle of 90 °.

Example 2 A completely saponified PVA polymer having a degree of polymerization of 3100 was added to DMS.
It was dissolved in O to prepare a 15% solution, which was used as a spinning dope. The spinning dope hole diameter 0.12 mm ^phi, extruded from a nozzle hole number 27, was coagulated in a coagulation bath consisting of methanol once through the space portion of 5 mm.

The coagulated filaments thus obtained were taken out at 5 m / min, further washed with methanol to remove DMSO, and then 4 at room temperature.
Stretching was performed twice, and then hot stretching was performed using a heating tube having an inside air temperature of 230 ° C. so that the total stretching ratio was 17.4 times.

As a result, fibers having high physical properties such as a tensile strength of 16.4 g / d and a knot strength of 5.2 g / d were obtained.

The distribution of orientation in the cross-sectional direction of the single yarn of this fiber was lower in the surface layer than in the central portion. (Δn) s− (Δn) c = −1.6 × 10 ^{−3 In the} same manner as in Example 1, about 150
A yarn was twisted to make a yarn of 0 denier, and then these two yarns were twisted together by applying the same number of twists to form a tire cord. A tube fatigue test was conducted at a tube bending angle of 90 °, and the life was 180. This is also the same as the conventional P
The fatigue resistance was significantly improved as compared with the tire cord made of VA fiber.

Comparative Example 1 After removing DMSO in Example 1, the film was stretched 4 times at room temperature, and subsequently a hot plate at the same temperature was used instead of the heating tube at 230 ° C., and the total stretching ratio was 17 times. Was hot-stretched.

As a result, fibers having physical properties of tensile strength of 13.2 g / d and knot strength of 3.8 g / d were obtained.

The orientation distribution in the cross-sectional direction of the single yarn of this fiber was remarkably higher in the surface layer than in the central portion.

(Δn) s− (Δn) c = 8.4 × 10 ^{−3 The} obtained fiber was subjected to a tube fatigue test of tire cords in the same manner as in Examples 1 and 2, and the life was 58.
It was a minute.

Comparative Example 2 In Example 1, the total draw ratio was changed and the change in the physical properties of the fiber was examined. As a result, as shown in Table 1, it is possible to obtain a tensile strength of 14 g / d or more for the first time by stretching 15 times or more. It was found that a fiber having a strength and a knot strength of 5.0 g / d or more was obtained.

[0047]

[Table 1] Comparative Example 3 The procedure of Comparative Example 1 was repeated except that stretching was performed in a heating tube instead of the hot plate, DMSO was removed, and stretching was performed 4 times at room temperature, and then the inside air temperature of the heating tube was changed. As a result of the stretching, as shown in Table 2, at a temperature lower than 230 ° C., the distribution of the orientation degree of the fiber becomes out of the range defined by the present invention as the stretching ratio becomes lower, and the knot exceeding 4 g / d is obtained. No fibers with strength were obtained.

[0048]

[Table 2]

[0049]

EFFECTS OF THE INVENTION The PVA-based fiber of the present invention has water resistance and heat resistance satisfying good practical performance without water insolubilization treatment such as acetalization, and has a knot strength of 5. It has excellent performance as a PVA-based fiber of 0 g / d or more. Particularly, it is considered that the fiber having a high draw ratio of more than 15 times and having a high knot strength is related to the peculiar difference in birefringence of the PVA-based fiber of the present invention. Of course, in the present invention, PV having a polymerization degree of 1500 or more together with the above birefringence difference
Needless to say, the fact that the fiber is composed of the A-based polymer has a close relationship in order to form a high-strength PVA-based fiber having excellent fiber physical properties such as knot strength, fatigue resistance, and hot water resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing birefringence distributions in a cross-sectional direction of a fiber obtained in Example 1 and a conventional fiber (vinylon [registered trademark], T5501).

[Explanation of symbols]

 A: Fiber obtained in Example 1 B: Conventional fiber (Vinylon [registered trademark], T 5501)

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-60-126312 (JP, A) JP-A-55-107506 (JP, A) JP-A-59-130314 (JP, A) JP-B-48- 32623 (JP, B1)

Claims (1)

[Claims] 1. A polyvinyl alcohol-based polymer having a degree of polymerization of 2,500 or more and 6,000 or less and a tensile strength of 14 g / d.
As described above, the knot strength is 5.0 g / d or more, and the difference in birefringence between the inner and outer layers of the fiber is −8 × 10 ⁻³ ≦ (Δn) s−.
A high-strength polyvinyl alcohol fiber having excellent knot strength, which satisfies (Δn) c <0. (However, in the above formula, (Δn) s represents the birefringence at a position 2 μ from the surface of the fiber, and (Δn) c represents the birefringence at the center of the fiber.)