JP2002054024A - Method of producing polybenzazole fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing polybenzazole fiber of high strength with high productivity. SOLUTION: The polybenzazole dope comprising polybenzazole fiber and solvent is extruded through the orifices on the spinneret that has the ratio of the land length L to the orifice diameter D, L/D<=1, and the taper angle immediately before the land part is <=18 deg., under the conditions with the pressure drop of <=10 MPa from the orifice to the spinneret thereby forming the dope filament. The resultant dope filament is drawn >=10 times in non-coagulating fluid, the drawn dope filament is brought into contact with coagulating fluid whereby the solvent is removed from the filament. In this process, there happen no worsened operability and no deterioration in quality, even when the dope throughput is increased at an increased spinning speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for industrially producing high-strength and high-modulus polybenzoxazole, and more particularly to a process for spinning polybenzazole fiber without deteriorating its excellent strength properties. .

[0002]

2. Description of the Related Art Polybenzazole fiber is expected to be a next-generation super fiber because it has significantly higher strength and heat resistance than aramid fiber and polyarylate fiber, which are representatives of currently marketed super fibers. ing. Since the polybenzazole polymer has a very rigid molecular skeleton, its processability is lower than that of aramid or polyarylate, and the flow behavior of the spinneret in the spinning step greatly affects spinnability. JP-A-7-157918 discloses that by using a nozzle having a die angle of 30 degrees or less, a fiber can be produced without yarn breakage even at a high spinning speed of 150 m / min or more. However, when the spinning speed and the discharge amount from the spinning hole are increased in order to further increase the productivity of the spinning process, there has been a problem that the mechanical properties of the polybenzazole fiber deteriorate.

[0003]

SUMMARY OF THE INVENTION In a process for producing a fiber from a spin dope comprising a polybenzazole polymer and a solvent, the present invention relates to a technique for producing a high-quality polybenzazole fiber having high productivity and no strength reduction. is there.

[0004]

The present invention is characterized by comprising the following steps when producing a fiber from a spin dope comprising polybenzazole or a polybenzazole polymer which is a copolymer thereof and a solvent. This is a method for producing polybenzazole fibers. (1) A spin dope is extruded from a hole of a spinneret having a taper angle of 20 degrees or less immediately before a land under a pressure loss of 10 MPa or less to form a dope filament. Stretching the filament in a non-coagulating fluid, and (3) removing the solvent from the stretched dope filament while contacting the filament with the coagulating liquid. Desirably, the ratio L / D of the land length L to the discharge hole diameter D
Is 1 or less.

Hereinafter, the present invention will be described in detail. The polybenzazole fiber in the present invention refers to a fiber made of a polybenzazole polymer, and is a polybenzazole (PBZ)
Are polybenzoxazole (PBO) homopolymer, polybenzothiazole (PBT), polybenzimidazole (PBI) homopolymer and their PBO, PBO
BT, PBI random, sequential or block copolymer. Here, polybenzoxazole, polybenzothiazole and their random, sequential or block copolymers are described, for example, in "Liquid Crystalline Polymer Composite" by Wolfe et al.
ons, Process and Products "U.S. Pat.
No. 3 (October 27, 1987), "Liquid Crystalli
ne Polymer Compositions, Process and Products, US Pat. No. 4,533,692 (August 6, 1985);
quid Crystalline Poly (2,6-Benzothiazole) Compositi
on, Process and Products "U.S. Patent No. 4,533,724.
(August 6, 1985), "Liquid Crystalline Po
lymer Compositions, Process and Products "U.S. Pat. No. 4,533,693 (August 6, 1985), Ever
s' Thermooxidatively Stable Articulated p-Benzob
isoxazole and p-Benzobisthiazole Polymres, U.S. Pat.No. 4,539,567 (November 16, 1982), Ta
`` Method for making Heterocyclic Block Copol '' such as si
ymer, U.S. Pat. No. 4,578,432 (March 2, 1986)
5th), etc. The structural unit contained in the polybenzazole polymer is preferably selected from a lyotropic liquid crystal polymer. The monomer units consist of the monomer units described in structural formulas (a) to (h), and more preferably essentially consist of structural formulas (a) to
It consists of monomer units selected from (c).

[0006]

Embedded image

[0007]

Embedded image

Hereinafter, a production method for obtaining polybenzazole fibers will be described. Suitable solvents for forming the polybenzazole polymer dope include cresol and non-oxidizing acids that can dissolve the polymer. Examples of suitable acid solvents include mineral acids such as polyphosphoric acid, methanesulfonic acid and concentrated sulfuric acid, or mixtures thereof. Further suitable solvents are mixtures of polyphosphoric acid and methanesulfonic acid. The most suitable solvent of the present invention is polyphosphoric acid.

[0009] The concentration of the polymer in the solvent is preferably at least 7% by weight, more preferably at least 10% by weight, most preferably at least 12 to 18% by weight. The maximum concentration is limited by practical handling properties such as, for example, polymer solubility and dope viscosity. Due to their limiting factors, the polymer concentration is usually 30
It does not exceed weight%.

[0010] Suitable polymers, copolymers or dopes are synthesized by known techniques. See, eg, Wolfe et al., US Pat. No. 4,533,693 (August 6, 1985), Sy.
U.S. Pat. No. 4,772,678 to S. bert et al. (September 2, 1988)
0) Harris U.S. Pat. No. 4,847,350 (198).
(July 11, 2009). Polybenzazole polymers are disclosed in US Pat.
According to 899591 (February 18, 1992), it is possible to increase the molecular weight at a high reaction rate under a relatively high temperature and high shear condition in a dehydrating acid solvent.

The dope polymerized in this way exhibits liquid crystallinity. Generally, a rigid polymer solution has a heterogeneous microstructure called a polydomain structure in a specific concentration range. Within each polydomain, the direction of rigid molecular chains is almost aligned. As a parameter quantitatively representing a liquid crystalline solution, a director vector u representing a direction of a molecular chain is used.
And an order parameter S representing the distribution of the orientation with respect to the vector. It is said that the polydomain structure of a solution composed of polybenzazole and polyphosphoric acid has a large deformation under flow so that the directions of the individual directors u are aligned, the domain boundaries of the domains disappear, and the domain changes to a monodomain structure.

As a feature of the flow of the polybenzazole solution in the spinneret, as the discharge rate is increased, unstable flow called melt fracture is very likely to occur in the portion where the cross-sectional area of the narrow tube is reduced. The capillary inlet of the spinneret is generally processed into a tapered shape, and is designed so that the cross-sectional area changes or becomes gentle. JP-A-7-15791
Japanese Patent Publication No. 8 describes that the shape of the spinneret governs the stable maximum discharge amount and thus greatly contributes to productivity. However, when the discharge amount is extremely high, the shape needs to be further devised. First, as shown in FIG. 1, an elongated flow portion is formed near the axis of symmetry of the thin tube at the thin tube inflow portion, and the flow is stagnant at the tapered tube wall. Cogswell (Journal of Polymer Engineeri
ng and Science, Vol. 12, p. 64, 1972) flows into the capillary at a free flow angle.
This free inflow angle becomes smaller as the flow rate increases and becomes less than 10 degrees. Melt fracture is less likely to occur as the taper angle 2θ in FIG. 2 is closer to the free inflow angle, but the cost of precision processing of the spinneret is increased.
It is difficult to make it below the degree. The apparent shear rate is defined by the following equation. In the equation, Q is a volume flow rate [cc / sec], and D is a capillary diameter [cm].

[0013]

(Equation 1)

When the apparent shear rate is about 5000 [1 /
Sec], the taper angle 2θ is not preferred to be not more than 20 degrees, which is not preferable because the melt fracture becomes more unstable. The more preferable taper angle is 18 degrees or less, and the most preferable taper angle is 16 degrees or less. In addition, even if a spinneret having a preferable shape is used, unstable flow is unavoidable in a system in which excessive shear stress is generated at the time of discharge, and the fiber strength is reduced. The pressure loss at the spinneret portion is preferably 10 MPa or less. This pressure loss does not include the viscous resistance when passing through pores such as a filter mesh and a sand, but means the viscous resistance of elongation and shear generated mainly at the capillary inlet and the capillary part. More preferably 9MP
It is preferable that it is not more than a. As a means for reducing the viscous resistance while maintaining the discharge amount of the dope, there are a method of increasing the diameter D of the thin tube portion and a method of increasing the spinning temperature.

As a result of further study on the shape of the spinneret, it is important that the ratio L / D between the land length L and the discharge hole diameter D is 1 or less. As L becomes longer, the strength tends to decrease. This is because, as L becomes longer, the dope receives friction on the wall surface and the velocity distribution develops. In the developed velocity distribution, it is presumed that the difference between the shear velocity histories near the axis of symmetry and the wall of the tube widens, causing a structural difference inside the fiber.

The dope extruded from the thin tube of the spinneret into a non-coagulable fluid such as air is stretched by a take-off device such as a roller. The zone where the dope filament contacts the coagulating liquid and is solidified is called a draw zone. In this draw zone, the molecules of the polybenzazole polymer and the solvent can be oriented more highly than the orientation at the mouth of the die. In order to obtain high strength fiber,
It is preferable to stretch at a high magnification, but if it is stretched at a too high magnification, the spinning tension becomes excessive and the frequency of yarn breakage increases, which is not preferable. In a preferred draw zone, the draw ratio is 10 times or more and 200 times or less, more preferably 20 times or more and 100 times or less, and most preferably 25 times or more and 80 times or less. The dope filament processed in this manner has a base in which a fiber structure in which the polymer is densely aggregated is formed in a subsequent coagulation / washing step.

In the draw zone, it is particularly preferable to control the cooling rate of the dope filament by flowing a non-coagulating fluid whose temperature has been adjusted for stable drawing. From the viewpoint of industrial implementation, the non-coagulable fluid is preferably a gas, and particularly preferably air. When cooling with air, the air temperature is preferably in the range of room temperature to 90 ° C. When the draw ratio of the draw zone is high, it is necessary to moderately increase the viscosity of the dope. Is preferred.

After the polybenzazole fiber is cooled and solidified, it is brought into contact with a coagulating liquid and coagulated and / or solvent-extracted. The solidification described here means that the fluidity is exhibited even when the molded body is again heated to a temperature at which the dope flows by reducing the solvent fraction in the molded body or increasing the moisture percentage in the solvent. Indicates that it will be gone. The extraction means an operation for lowering the solvent concentration in the molded body. The coagulation solution is preferably a phosphoric acid aqueous solution, and the phosphoric acid aqueous solution has a concentration of 75% or less and a temperature of 60 ° C.
It is more preferred that: In the water washing after coagulation, it is preferable to extract the concentration of the phosphorus element to 0.7% or less based on the weight of the polymer. At this time, the solvent concentration in the polymer is 2% or less in terms of phosphoric acid. It is particularly preferable to carry out the neutralization step in the water washing step to maintain the strength during the post-processing of the fiber, but this is not essential. It is preferable that an alkali metal base is used as the neutralizing agent, and that the molar ratio of the alkali metal to P remaining in the fiber be 0.2 or more and 1.5 or less.

The inside of the polybenzazole fiber from which the solvent in the fiber has been sufficiently extracted contains the non-solvent which has entered the inside of the fiber by mutual diffusion with the solvent. In the polybenzazole fiber containing a large amount of non-solvent, organic solvent molecules and metal ions can be injected into the fiber. It is possible to impregnate the fibers with pigments, dyes, lubricants, ultraviolet absorbers, antioxidants, light stabilizers and the like.

Through these steps, it is desirable that the water present in the polybenzazole formed body sufficiently extracted with the solvent is dried. Moisture in the molded article can be evaporated to room temperature and dried to 3% or less based on the weight of the polymer at normal temperature.
It is equal to or less than the equilibrium moisture content of the polybenzazole molded article.
The equilibrium moisture content varies depending on the environment in which it is used, but is approximately 2%. In an industrial process, a method of drying in a short time using a high temperature is more advantageous from the viewpoint of productivity. In particular, the polybenzazole polymer has extremely excellent heat resistance, and does not decrease in strength even when dried at a temperature of 230 ° C. or higher. The higher the drying temperature, the shorter the time required for drying, so that the cycle time of the production equipment or the drying batch can be shortened.

It is known that drying at an elevated temperature improves the Young's modulus of the fiber. Conversely, it is preferable to dry at a low temperature in order to increase the elongation of the polybenzazole fiber. It is also known that the Young's modulus is improved when dried under high tension. However, in a state where a high tension is applied, the speed at which the coagulant diffuses inside the fiber and dissipates to the outside of the yarn decreases, and the time required for drying increases.

Heat treatment can be performed at a temperature of 400 ° C. or more for the purpose of further increasing the degree of orientation of the molded body and further increasing the packing between molecular chains. The heat treatment is preferably performed under tension in order to prevent a decrease in strength due to the heat treatment.

Tensioning a fiber containing a large amount of a coagulant before drying has the effect of improving the elastic modulus in heat treatment. The higher the tension in the heat treatment, the higher the elastic modulus can be improved. However, if an excessive tension is applied, defects such as thread breakage are likely to occur. Since the fiber obtained by the method with improved spinneret conditions of the present invention has a high fiber strength before heat treatment, the tension in heat treatment can be set high. Therefore, a high elastic modulus polybenzazole fiber can be stably manufactured.

[0024]

EXAMPLES Examples are shown below, but the present invention is not limited to these examples. All amounts and percentages are by weight unless otherwise indicated. <Measurement Method of Strength and Elastic Modulus> Measurement was performed by attaching a capstan-type gripper having a capacity of 5 kN to an autograph manufactured by Shimadzu Corporation in accordance with ASTM D885-98.

(Examples 1 to 4 and Comparative Examples 1 to 3) A polyphosphoric acid solution in which 14% of a polybenzoxazole polymer having an intrinsic viscosity of 29.3 dl / g was dissolved was subjected to various spinnerets under the conditions shown in Table 1. More extruded. The extruded dope filament was passed through a 350 mm long cross-flow type quench zone, introduced into a funnel-type coagulation bath provided at a position of 1650 mm from the spinneret, solidified, and then sufficiently washed with three Nelson-type washing tanks. After washing with water, the yarn was passed through a 0.1% aqueous solution of caustic soda, and the washed yarn was dried through a Nelson-type drying oven. Table 1 shows the spinning status and the mechanical properties of the fiber.

[0026]

[Table 1]

In Table 1, the spinneret taper angle represents the angle immediately before the thin tube (2θ in FIG. 2). The pressure loss of the spinneret was a value read by a pressure gauge at the entrance of the spin pack after removing the filter medium and the wire mesh filter of the spin pack. The actual spinning was performed with a 7 mm filter layer of Sinter Morundum # 24 and a set filter (# 100 mesh + # 800 mesh + # 50 mesh are all made of SUS316).

From Examples 1 and 2 and Comparative Example 1, when the taper angle immediately before the spinneret exceeds 20 degrees, the jet discharged from the capillary is disturbed, so that yarn breakage during spinning is liable to occur and at the same time the fiber strength is increased. It can be seen that is decreased.

The effects of L / D will be described in Examples 1, 3 and Comparative Example 2. When L / D exceeds 1, the strength of the fiber tends to decrease. This is presumed to be due to the fact that the velocity profile of the elongational flow of the tapered portion develops into a parabolic shape while passing through a long capillary, and then, at the outlet of the spinneret, the molecular orientation unevenness of the inner and outer layers occurs during the elongation and elongation. I have.

Examples 1 and 4 and Comparative Example 3 clarify the effect of excessive shear resistance at the spinneret. Pressure loss at the spinneret (the sum of the shear resistance generated at the tube wall with the spinneret and the elongation resistance generated at the tapered portion) is 10MP.
When it exceeds a, the jet discharged from the capillary is disturbed, and yarn breakage during spinning is likely to occur, and at the same time, the fiber strength is reduced.

(Examples 5 and 6) Intrinsic viscosity number 28.7
Polyphosphoric acid solutions containing 14% of dl / g polybenzoxazole polymer were extruded from various spinnerets under the conditions shown in Table-2. The extruded dope filament was passed through a 350 mm long cross-flow quench zone, introduced into a funnel-type coagulation bath provided at a position of 1650 mm from the spinneret, solidified, and then washed with three Nelson-type washing tanks. After that, the yarn was further passed through a 0.1% aqueous solution of caustic soda, washed with water, wound up with a winder, immersed in ion-exchanged water for 8 hours, washed with water, and dried in an oven at 80 ° C. for 3 hours. Table 2 shows the spinning state and the mechanical properties of the fiber.

[0032]

[Table 2]

Under the conditions satisfying the taper angle just before the introduction hole, the pressure loss, and the land length according to the present invention, even at a high spinning speed such as a spinning speed of 720 m / min and a spinning speed of 800 m / min, the occurrence of yarn breakage does not increase and the strength decreases. And stable spinning.

[0034]

As described above, even if the production is performed at a high spinning speed and a high dope discharge rate, no deterioration in operability and quality occurs.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a flow state of a dope in a spinneret.

FIG. 2 is an explanatory view of a shape of a spinneret pore portion.

[Explanation of symbols]

 2θ: Introducing angle of tapered portion D: Pore diameter L: Land length

Claims (2)

[Claims] 1. A method for producing a polybenzazole fiber, comprising the steps of producing a fiber from a spin dope comprising a polybenzazole or a polybenzazole polymer as a copolymer thereof and a solvent. (1) A spin dope is extruded from a hole of a spinneret having a taper angle of 20 degrees or less immediately before a land under a pressure loss of 10 MPa or less to form a dope filament. Stretching the filament in a non-coagulating fluid, and (3) removing the solvent from the stretched dope filament while contacting the filament with the coagulating liquid. 2. The ratio L / D of the land length L to the discharge hole diameter D is 1
The method for producing a polybenzazole fiber according to claim 1, which is as follows.