JP7843678B2 - Polyethersulfone fibers, fiber packaging, nonwoven fabrics, and methods for producing polyethersulfone fibers - Google Patents

Description

This invention relates to polyethersulfone fibers, fiber packaging, nonwoven fabrics, and methods for producing polyethersulfone fibers.

Polyethersulfone (hereinafter also referred to as PES) has excellent heat resistance, creep resistance, dimensional stability, flame retardancy, and hot water resistance, and is being considered for use in a wide range of fields, including automotive parts, electronic components, printer and copier parts, medical device parts requiring sterilization, and dental equipment.
For example, Patent Document 1 (Japanese Unexamined Patent Publication No. 7-11134) describes an invention relating to a resin composition in which polyethersulfone is used as component (A) from an aromatic polysulfone resin, polysulfone as component (B) from an aromatic polysulfone resin, and polycarbonate resin as component (C), wherein the respective ratios of the composition are (A) 80 to 40% by weight, (B) 1 to 40% by weight, and (C) 1 to 40% by weight.

Furthermore, Patent Document 2 (Japanese Patent Publication No. 2020-20053) describes an invention for producing polyethersulfone fibers by dissolving a polyethersulfone, which consists of repeating units of a structure represented by a predetermined chemical formula and has an average weight molecular weight of 80,000 to 130,000, in an organic solvent; discharging a spinning stock solution with a concentration of 10 to 30% by mass of the polyethersulfone from an discharge port into a spinning bath containing the organic solvent; and humid heat stretching at a rate of 1.05 to 4 times.

Furthermore, Patent Document 3 (Japanese Patent Publication No. 3-185025) describes an invention relating to a method for producing aromatic polyethersulfone fibers, characterized by melting a polymer consisting of repeating units of predetermined chemical formulas I and II, where repeating units I and II are approximately equimolar, and having a reduced viscosity of 0.3 or higher as measured at a concentration of 0.5 g/dl in an NMP solvent at 30°C, and melt-spinning it into fibers at a draw speed of 50 m/min or higher through a spinneret having multiple spinning holes with pore diameters of 0.1 to 2.0 mm.

Patent Document 4 (Chinese Patent Application Publication No. 1763278) describes a polyethersulfone fiber and a method for producing the same, describing an invention relating to a method for producing polyethersulfone fibers in which the fineness of the monofiber is 0.3 to 30 dt, the limiting oxygen index of the fiber is 30 or higher, the fineness of the monofiber is 1.5 to 10 dt, and the polyethersulfone resin is heated and melted in a twin-screw extruder, then flows out in the form of a solution stream through a high-temperature resistant spinning pack, and is cooled and cured to form the fiber.
Furthermore, Patent Document 5 (Chinese Patent Application Publication No. 103361748) describes a high-temperature resistant polyethersulfone fiber and a method for producing the same, describing an invention relating to a method for producing a high-temperature resistant polyethersulfone fiber in which the moisture content is set to 50 PPM, melt-spinned at 330 to 380°C using twin-screw extrusion, and then cooled and hardened to form the fiber.

Japanese Patent Application Publication No. 7-11134 Japanese Patent Publication No. 2020-20053 Japanese Patent Application Publication No. 3-185025 Chinese Patent Application Publication No. 1763278 Specification Chinese Patent Application Publication No. 103361748

Although polyethersulfone resins possess excellent physical properties such as heat resistance, dimensional stability, and flame retardancy, they have a problem in that their high viscosity during melting makes it difficult to mold them into fibers. In particular, it has been difficult to obtain high-speed and high-purity fibers using the melt spinning method.
Patent Document 1 discloses a technique for improving moldability by mixing polyethersulfone with polycarbonate and melt-molding it. However, Patent Document 1 does not mention the manufacturing of fibers.

Patent Document 2 describes the process of fiberizing polyethersulfone resin, but since Patent Document 2 describes the production of polyethersulfone fibers by wet spinning or dry spinning using a solvent, there is a problem that a solvent is required in the production of the fibers, and therefore the solvent must be treated.
Patent Document 3 describes a method for fiberizing polyethersulfone resin by melt spinning. However, Patent Document 3 also describes that fiberization by melt spinning is possible by using aromatic polyethersulfone resin having a specific structure.
In this case, a solvent is not required, but it is necessary to use copolymerized polyethersulfone containing special repeating units, which presents the problem of difficulty in obtaining the raw materials.

Patent Document 4 describes that by devising the temperature setting of the extruder when melt-extruding polyethersulfone resin, polyethersulfone monofilaments can be provided by performing a stretching treatment after melt-spinning. In this case, since the fibers are obtained by stretching with a strong stretching force, there is a problem that the resulting fibers have a high thermal shrinkage rate, limiting their applications.
Furthermore, the high-temperature resistant polyethersulfone fiber described in Patent Document 5 also uses a modified masterbatch as a raw material and undergoes a stretching treatment of 2.3 to 6 times its original length. Therefore, the raw material is special, and it has a high thermal shrinkage rate, resulting in problems with dimensional stability.

In the field of industrial materials, heat resistance and dimensional stability are often required. Achieving both heat resistance and dimensional stability requires minimizing dry heat shrinkage. However, the polyethersulfone fibers obtained using the methods described in Patent Documents 4 or 5 have a problem of high heat shrinkage, although neither document mentions dry heat shrinkage.

Furthermore, because polyethersulfone resin is an amorphous thermoplastic resin, it has a high melt viscosity and is prone to melt fracture (roughness of the fiber surface), making it difficult to stably produce polyethersulfone fibers. Even if production was possible, the fiber quality or physical properties were insufficient, resulting in problems with process passability in subsequent processes such as fiber processing.

The present invention aims to solve the above-mentioned problems and provide a polyethersulfone fiber and a method for producing the same, which have a low thermal shrinkage rate and excellent heat resistance, low coefficient of linear expansion, mechanical strength, flame retardancy, chemical resistance, and dimensional stability, by melt spinning.
Another object of the present invention is to provide polyethersulfone fibers and methods for producing the same that can be melt-spun using a polyethersulfone resin with a simple structure, are excellent in terms of environment and cost, and have high purity.
Another object of the present invention is to provide a polyethersulfone fiber having high strength, low strength variation, and excellent tensile elongation, as well as a method for producing the same.
Another object of the present invention is to provide a polyethersulfone fiber that has excellent dimensional stability, good passability through subsequent processes, and excellent processability.

(1)
The polyethersulfone fiber conforming to a single plane consists of a polyethersulfone resin containing repeating units shown in the following formula (1), and has a dry heat shrinkage rate of 5% or less at 200°C.

According to the present invention, polyethersulfone, which has excellent heat resistance, low coefficient of thermal expansion, mechanical strength, flame retardancy, chemical resistance, and dimensional stability, can be used to create fibers. In particular, even when using the melt spinning method, the fibers do not need to be stretched, so polyethersulfone fibers with almost no thermal shrinkage can be obtained.
In other words, the reason why thermal shrinkage occurred in conventional PES fibers is thought to be that PES resin is an amorphous resin, making it difficult to mold, and when the fibers are stretched, the molecules become elongated, causing entropy shrinkage in high-temperature environments exceeding 100°C, resulting in fiber contraction. On the other hand, since the PES fibers of the present invention are unstretched PES fibers, the dry heat shrinkage rate can be kept extremely low, resulting in fibers that have excellent dimensional stability even in high-temperature environments, maintain high strength, and have little variation in strength. Furthermore, because they have excellent dimensional stability and tensile elongation, they have good passability through subsequent processes and excellent processability as fibers, making them suitable for use in high-performance textile products.
Furthermore, since it can be spun using a polyethersulfone resin with a simple structure and can be fiberized at relatively low temperatures using a melt spinning method that does not require solvent recovery, it does not require special spinning equipment, resulting in a polyethersulfone fiber that is superior from an environmental and cost standpoint. In addition, since no solvent is used in spinning, the impurity content can be significantly reduced, resulting in a high-performance fiber.
In this invention, the polyethersulfone fiber made of polyethersulfone resin may contain additives or mixtures in an amount that does not impair its physical properties.

(2)
The polyethersulfone fiber according to the second invention is a polyethersulfone fiber conforming to one plane, in which the polyethersulfone resin may contain 95 mol% or more of the repeating units represented by formula (1). More preferably, the polyethersulfone resin contains 98 mol% or more of the repeating units represented by formula (1), and most preferably 100 mol%.

This allows for the production of polyethersulfone resins with a simple structure and readily available materials, eliminating the need for specialized spinning equipment and resulting in superior polyethersulfone fibers from an environmental and cost perspective.

(3)
The polyethersulfone fiber according to the third invention is a single-faced polyethersulfone fiber according to the second invention, wherein the glass transition temperature (Tg) of the polyethersulfone resin is 200°C or higher, and the reduced viscosity may be 0.30 dl/g or more and 0.47 dl/g or less.

This allows for the production of polyethersulfone fibers with excellent winding properties after spinning and superior post-processing capabilities.

(4)
The polyethersulfone fiber according to the fourth invention is a polyethersulfone fiber according to any of the third inventions, and may have at least one physical property selected from the group consisting of the following physical properties (A), (B), and (C).
Physical property (A): The tensile strength of the polyethersulfone fiber is 0.6 cN/dtex or greater. Physical property (B): The variation in tensile strength of the polyethersulfone fiber is within ±0.3 cN/dtex. Physical property (C): The elongation of the polyethersulfone fiber is 10% or more and less than 200%.

This allows for the production of polyethersulfone fibers that are even stronger, exhibit superior strength uniformity, and possess excellent properties such as dimensional stability and thermal stability. Furthermore, the improved tensile elongation results in superior processability, making the fibers easier to use in high-performance textile products.

(5)
The polyethersulfone fiber according to the fifth invention is the polyethersulfone fiber according to the fourth invention, wherein, in physical property (A), the tensile strength of the polyethersulfone fiber may be 1.0 cN/dtex or greater.

This allows for the production of polyethersulfone fibers that are even stronger and possess excellent properties such as dimensional stability and thermal stability. Furthermore, despite their high strength, they exhibit excellent tensile elongation and virtually no strength variation, resulting in polyethersulfone fibers with excellent post-processing capabilities. For example, processes such as filament cutting can be easily carried out when processing them into nonwoven fabrics.

(6)
The fiber package according to the sixth invention may have polyethersulfone fibers according to any of the fifth inventions wound around a tube from one perspective.

This makes handling polyethersulfone fibers easier and improves their processability as textile products.

(7)
The nonwoven fabric according to the seventh invention may contain, in one aspect, polyethersulfone fibers according to any of the fifth inventions.

This makes it possible to obtain a high-performance, low-cost nonwoven fabric with excellent heat resistance, dimensional stability, low dry heat shrinkage, and strength.

(8)
A method for producing polyethersulfone fibers according to other aspects includes a drying step of drying a polyethersulfone resin to obtain a dried polyethersulfone resin, a melting step of heating and melting the dried polyethersulfone resin to obtain a molten product, a spinning step of extruding the molten product from a die to form a spindle, a bundling step of bundling the spindle to obtain a filament, and a winding step of winding the filament, and satisfies the following conditions.
Condition (a): The moisture content of the dry polyethersulfone resin is less than 50 ppm. Condition (b): The linear discharge speed is 5.0 m/min or more and 50.0 m/min or less. Condition (c): The shear rate during spinning is 300 ^s⁻¹ or more and 90,000 ^s⁻¹ or less. Condition (d): The spinning temperature is 340°C or more and 410°C or less. Condition (e): The winding speed is 550 m/min or more.

According to the present invention, polyethersulfone resin, which has excellent heat resistance, low coefficient of thermal expansion, mechanical strength, flame retardancy, chemical resistance, and dimensional stability, can be used to create fibers. In particular, even when using the melt spinning method, the fibers do not need to be stretched, so polyethersulfone fibers with almost no thermal shrinkage can be obtained.
In other words, the reason why thermal shrinkage occurred in conventional PES fibers is thought to be that PES resin is an amorphous resin, making it difficult to mold, and when the fibers are stretched, the molecules become elongated, causing entropy shrinkage in high-temperature environments exceeding 100°C, resulting in fiber contraction. On the other hand, the manufacturing method of the present invention is characterized by not performing a subsequent stretching process in which the bundled filaments are heated and stretched. As a result, the dry heat shrinkage rate can be kept extremely low, and therefore, even in high-temperature environments, it is possible to produce fibers with excellent dimensional stability and low strength variation while maintaining high strength. Furthermore, because it has excellent dimensional stability and tensile elongation, it has good passability through subsequent processes and excellent processability as a fiber, so it can be used as a fiber for high-performance textile products.
Furthermore, because it can be synthesized into fibers at relatively low temperatures using a melt spinning method that does not require solvent recovery, it does not require special spinning equipment, resulting in polyethersulfone fibers that are superior from an environmental and cost perspective. In addition, since no solvent is used in spinning, the impurity content can be significantly reduced, resulting in high-performance fibers.

(9)
The method for producing polyethersulfone fibers according to the ninth invention is the method for producing polyethersulfone fibers according to the eighth invention, wherein the glass transition temperature (Tg) of the polyethersulfone resin is 200°C or higher, and the reduced viscosity is 0.30 dl/g or higher and 0.47 dl/g or lower.

This reduces the likelihood of thread breakage and prevents excessive filtration pressure, resulting in excellent spinning performance and reliable fiber winding.

(10)
The method for producing polyethersulfone fibers according to the tenth invention is the method for producing polyethersulfone fibers according to the eighth or ninth invention, wherein in condition (d), the spinning temperature may be 340°C or higher and 385°C or lower.

This allows for the production of polyethersulfone fibers that are even stronger and possess excellent properties such as dimensional stability and thermal stability. Furthermore, despite their high strength, they exhibit excellent tensile elongation and virtually no strength variation, resulting in polyethersulfone fibers with excellent post-processing capabilities. For example, processes such as filament cutting can be easily carried out when processing them into nonwoven fabrics.

This is a schematic diagram illustrating an example of a method for producing polyethersulfone fibers by melt-extruding and melt-spinning polyethersulfone resin.

The present invention will be described in detail below.
In this invention, a polyethersulfone resin having a specific chemical structure is used as a raw material, and by appropriately selecting the melt-spinning conditions, it is possible to create fibers without stretching during the manufacturing process. As a result, polyethersulfone fibers can be produced that have a very low thermal shrinkage rate and excellent heat resistance, low coefficient of linear expansion, mechanical strength, flame retardancy, chemical resistance, and dimensional stability.
In particular, because PES resin is an amorphous resin, it has high viscosity when melted and is prone to melt fracture (roughness of the fiber surface), resulting in poor moldability. For this reason, it has been difficult to manufacture PES fibers from PES resin using the melt spinning method. Specifically, when PES resin is converted into fibers by the melt spinning method, stable production is difficult, and the resulting fibers have a high thermal shrinkage rate and poor dimensional stability. This is thought to be because the fibers' molecules stretch during the stretching process after spinning, and when PES fibers are exposed to high-temperature environments exceeding 100°C, entropy shrinkage occurs, causing the fibers to shrink due to heat.
Since the PES fiber of the present invention is an undrawn PES fiber, its dry heat shrinkage rate can be kept extremely low. As a result, it is possible to produce a fiber that has excellent dimensional stability even in high-temperature environments, maintains high strength, and has little variation in strength. Furthermore, because it has excellent tensile elongation, it has good passability through subsequent processes and excellent processability as a fiber, making it a fiber that can be used in high-performance textile products.
Furthermore, the PES fibers of the present invention can be spun using a polyethersulfone resin with a simple structure and can be produced by a melt spinning method that does not require solvent recovery, thus eliminating the need for special spinning equipment and resulting in PES fibers that are superior from the standpoint of the environment and cost. In addition, since no solvent is used in spinning, the content of impurities can be significantly reduced, resulting in high-performance fibers.

[Polyethersulfone resin]
The polyethersulfone resin used in this invention contains specific polyethersulfone constituent units and satisfies predetermined properties, thus offering a good balance between moldability, heat resistance, and low thermal shrinkage.
The polyethersulfone fiber of the present invention consists of the following polyethersulfone resin, the polyethersulfone resin mainly contains repeating units represented by the following formula (1).

(Constituent units of polyethersulfone resin)
The repeating units of equation (1) are described in detail below.
The molar percentage of the repeating unit of formula (1) relative to the total repeating units constituting the polyethersulfone resin is preferably 95 mol% or more.
From the viewpoint of improving heat resistance, the aforementioned mol% is preferably 98 mol% or more, more preferably 99 mol% or more, and most preferably 100 mol%.

There are no particular restrictions on the terminal structure of the polyethersulfone resin, but it is preferable that it has a chain-like aliphatic group having 5 to 14 carbon atoms at the end.
The chain-like aliphatic group may be saturated or unsaturated, and may be linear or branched.

The polyethersulfone resin of the present invention possesses characteristics such as high heat resistance, robust mechanical properties, chemical resistance, and hydrolysis resistance. Furthermore, because it does not contain easily hydrolyzable bonds such as esters, it exhibits excellent resistance to hot water and can be used even in high-temperature steam atmospheres. In addition, it has a low coefficient of linear expansion and low temperature dependence, resulting in excellent dimensional stability.

(Conditions for polyethersulfone resin)
The polyethersulfone resin used in the present invention preferably satisfies the following characteristics (a) and (b).
Characteristics (a): Glass transition temperature (Tg) of 200°C or higher. Characteristics (b): Reducing viscosity of 0.30 dl/g or higher and 0.47 dl/g or lower.

Polyethersulfone resins, by satisfying the above properties (a) and (b), exhibit a good balance between spinnability and heat resistance. Since polyethersulfone resins are prone to shear heat generation during molding, properties (a) and (b) affect the spinning conditions. Therefore, polyethersulfone resins that satisfy both properties (a) and (b) also possess good spinnability.

Regarding characteristic (a), the glass transition temperature (Tg) of the polyethersulfone resin is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher, from the viewpoint of exhibiting high spinnability, and preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 230°C or lower.
Polyethersulfone resins with a glass transition temperature (Tg) below 200°C tend to have low and insufficient heat resistance.
The glass transition temperature (Tg) of polyethersulfone resin can be measured by the following method: Using differential scanning calorimetry (DSC), the temperature is increased from 30°C to at least 30°C higher than the predicted glass transition temperature at a heating rate of 10°C/min, held for 1 minute, then cooled to 0°C at a cooling rate of 20°C/min, held for 1 minute, and the glass transition temperature (Tg) observed when the temperature is measured again at a heating rate of 10°C/min is used.

Regarding characteristic (b), the reduced viscosity of the polyethersulfone resin used in the fibers of the present invention is preferably 0.30 dl/g or more, more preferably 0.33 dl/g or more, and most preferably 0.35 dl/g or more. Furthermore, it is preferably 0.47 dl/g or less, more preferably 0.45 dl/g or less, and most preferably 0.44 dl/g or less.
When the reducing viscosity exceeds the upper limit, the spinning process in melt spinning tends to result in poor spinnability.

The reduced viscosity in this invention is a value calculated by measuring it using an Ubbelohde viscous tube in dimethylformamide (DMF) at 25°C and a concentration of 1 g/dl, with reference to the method described in JIS K7367-1 (2002).
The reduced viscosity (η _sp /c, in units of dl/g) is calculated based on the following formula, and the average of five measured values is used.
η _sp /c=(t−t ₀ )/t ₀ /c (dl/g)
t; Transit time between markings in a polymer solution viscometer (seconds)
t ₀ ; Transit time between markings on a viscometer of pure solvent (seconds)
c; Concentration of polymer solution (g/dl)

The polyethersulfone resin used in the present invention may contain, as needed, any components such as matting agents, plasticizers, antistatic agents, color inhibitors, gelling inhibitors, and resin modifiers, provided that their properties are not impaired.
Furthermore, the polyethersulfone resin may be blended with at least one additive selected from fillers, flame retardants, colorants, lubrication improvers, antioxidants, and conductive agents, in order to utilize the inherent properties of the polyethersulfone resin while imparting desired performance.

The polyethersulfone resin used in the present invention preferably has a glass transition temperature (Tg) of 200°C to 250°C and a reduced viscosity of 0.30 dl/g to 0.47 dl/g, and is melt-spun accordingly. This allows for the easy and stable production of polyethersulfone fibers without stretching treatment. The melt-spinning temperature is preferably 340°C to 410°C.
Polyethersulfone resins have a relatively high melt viscosity, which makes them prone to shear heating during molding and affects spinning conditions. Therefore, a good balance between spinnability, heat resistance, and thermal shrinkage is achieved when the glass transition temperature and reduced viscosity are within the above range.

[Melting spinning of polyethersulfone resin]
Next, we will explain the melt spinning method for polyethersulfone resin.
The polyethersulfone resin obtained above, having a glass transition temperature (Tg) of 200°C or higher and a reduced viscosity of 0.30 dl/g or higher and 0.47 dl/g or lower, is thoroughly dried to obtain a dried polyethersulfone resin under the following conditions (a) (drying step).
Subsequently, the dried polyethersulfone resin is heated and melted to obtain a molten product (melting step).
Then, the molten material is extruded from the die to form a spindle (spinning process).
Furthermore, the spun yarn extruded from the die is bundled together to obtain a filament (bundling process).
Finally, the filament is wound onto a tube (winding process).
In this way, the polyethersulfone fibers of the present invention can be manufactured according to the following conditions (a) to (e).
Condition (a): Moisture content of the dry polyethersulfone resin is less than 50 ppm. Condition (b): Linear velocity of extrusion is 5.0 m/min or more and 50.0 m/min or less. Condition (c): Shear velocity during spinning is 300 ^s⁻¹ or more and 90,000 ^s⁻¹ or less. Condition (d): Spinning temperature is 340°C or more and 410°C or less. Condition (e): Winding speed is 550 m/min or more. The manufacturing method of the present invention is characterized in that it substantially does not involve a subsequent drawing process in which the bundled filaments are heated and drawn.
Furthermore, as a subsequent step, the bundled filaments may be heated to a temperature of 150°C to 300°C to perform a heat treatment process.
The following provides a detailed explanation of each step.

(drying process)
The polyethersulfone resin obtained above is stored in a vacuum dryer and dried at a temperature of 100°C to 200°C for 10 to 30 hours. Since polyethersulfone resin is hygroscopic, it is preferable to dry it thoroughly.
The moisture content of the polyethersulfone resin is preferably less than 50 ppm through the drying process. More preferably, the moisture content of the polyethersulfone resin is 30 ppm or less, and even more preferably 25 ppm or less. This prevents the generation of air bubbles during spinning.
The dried polyethersulfone resin may be in pellet or powder form. Drying may be carried out under nitrogen flow or under fluid flow using a tumbler or the like.
By keeping the water content of the dry polyethersulfone resin below 50 ppm, it is possible to prevent the generation of gas due to moisture during melting, thereby effectively preventing problems such as the inclusion of voids in the spun yarn or the formation of gel-like insoluble matter that would prevent stable spinning.
From the drying process to the spinning process, it is preferable to maintain an environment of 30°C or higher, and more preferably 40°C or higher, to prevent an increase in the moisture content of the polyethersulfone resin. The upper limit is preferably 80°C or lower. Furthermore, nitrogen flow is even more preferable.

(Spinning process)
The melt extrusion of the polyethersulfone resin in the present invention can be any known method, as long as it is suitable for melt spinning. For example, the polyethersulfone resin may be pelletized and then melt-extruded using an extruder-type extruder 1.
Figure 1 shows an example of a method for producing polyethersulfone fibers by melt-extruding polyethersulfone resin from an extruder 1 and melt-spinning it.
The molten resin extruded from the extruder 1 passes through piping and is sent to the spinning head, where it is measured by a known metering device such as a gear pump 2, passes through a filter in the spinning pack 3, and then enters the spinning die 3a.

In condition (d), the spinning temperature is the temperature of the molten resin from the gear pump 2 to the spinneret 3a, and it is preferable that the polyethersulfone resin is between 340°C and 410°C. If the spinning temperature is lower than the lower limit, problems such as increased filtration pressure or overloading of the extruder may occur, and if it exceeds the upper limit, the quality of the fibers may deteriorate due to the effects of thermal decomposition. A more preferable spinning temperature in the present invention is between 340°C and 390°C, with 345°C and 375°C being the most preferable.
Because polyethersulfone resin has a high melt viscosity, the resin temperature tends to be higher than the cylinder temperature setting due to shear heating. Therefore, it is preferable to perform molding while monitoring the resin temperature. If the melt viscosity exceeds the upper limit, the spinnability during melt spinning deteriorates, and if the melt viscosity exceeds the lower limit, stable spinning becomes difficult.

In condition (c), the shear rate γ in the spinneret hole is preferably 300 ^s⁻¹ or more and 90,000 ^s⁻¹ or less, more preferably 340 ^s⁻¹ or more and 60,000 ^s⁻¹ or less, and even more preferably 5,000 ^s⁻¹ or more and 60,000 ^s⁻¹ or less.
The shear rate γ is calculated using the following formula.
γ = 4Q/πr ³
(where r is the radius of the spinneret hole (cm), and Q is the polymer discharge rate per single hole ( ^cm³ /sec))
When the shear rate γ is within the above range, the fiber orientation is sufficient, making it easier to obtain fine-denier fibers and thus easier to obtain the desired physical properties.
Furthermore, it is preferable to set a short residence time for the polyethersulfone resin. If the residence time is too long, thermal decomposition may increase the melt viscosity, cause bubbles to form, degrade the quality of the fibers, or lead to yarn breakage.

The hole diameter D of the spinneret 3a is preferably 0.09 mm or more and 0.70 mm or less, and more preferably 0.12 mm or more and 0.45 mm or less.
Furthermore, by installing a heater and a heat-retaining cylinder directly below the spinneret 3a, the diameter of the extruded fibers is stabilized, and changes in the surface temperature of the spinneret and the ambient temperature below the spinneret are suppressed by the outside air. This results in uniform finening due to the draft, and stable spinning without yarn breakage or fluffing.

In condition (b), the linear velocity of the spinning fiber discharge at the spinneret 3a is preferably 5.0 m/min or more and 50.0 m/min or less, and more preferably 10.0 m/min or more and 40.0 m/min or less.
In condition (c), the shear rate in the spinneret hole is preferably 300 ^s⁻¹ or more and 90,000 ^s⁻¹ or less, more preferably 340 ^s⁻¹ or more and 60,000 ^s⁻¹ or less, and even more preferably 5,000 ^s⁻¹ or more and 60,000 ^s⁻¹ or less.
Furthermore, the winding speed (spinning speed) in condition (e) is preferably 550 m/min or more, more preferably 600 m/min or more, and even more preferably 650 m/min or more. In this case, the upper limit of the winding speed is preferably 5,000 m/min or less, and more preferably 4,000 m/min or less.
Furthermore, the ratio of the winding speed to the linear speed is preferably between 40 and 1,600 times.
This makes it possible to produce high-quality polyethersulfone fibers using the melt spinning method.

The bundling process, winding process, and subsequent heating processes will be explained in more detail.
(Focusing process)
The spun yarn, extruded from the spinneret 3a, is coated with a predetermined oil by an oil application device and bundled into a single filament.
The polyethersulfone fiber of the present invention is a filament, and may be either a monofilament or a multifilament. In the case of a multifilament, it is preferable that the number of single filaments be six or more. If the number of single filaments is less than six, the strength of the multifilament itself will be weaker, making it difficult to wind it smoothly through the process, which may lead to yarn breakage and a decrease in productivity.
Furthermore, the cross-sectional shape of each single filament is not particularly limited; it may be a round cross-section, or an irregular cross-section depending on the purpose and application.

(winding process)
The polyethersulfone fibers, which have become filaments after the bundling process, are then taken up by the first godet roll 4 and the second godet roll 5 and wound onto the winding bobbin 6. The winding speed is preferably 550 m/min or more. It is more preferably 600 m/min or more, and even more preferably 650 m/min or more. The upper limit of the winding speed is preferably 5,000 m/min or less, and more preferably 4,000 m/min or less.
The spinning tension measured between the second godet roll 5 and the winding bobbin 6 is preferably between 4.7 cN and 47 cN. If the tension is less than 4.7 cN, the fibers may slacken, causing the yarn to wrap around the second godet roll 5 or resulting in a defective shape of the winding bobbin 6. In this invention, the spinning tension refers to the tension measured when the yarn is wound onto the winding bobbin 6.

(Post-processing: heat treatment)
The polyethersulfone fibers obtained as described above may be subjected to heat treatment for a certain period of time. This heat treatment may be carried out under an inert atmosphere such as nitrogen gas.

As described above, the polyethersulfone fibers of the present invention do not include a stretching process (stretching step) as a post-spinning step. By using non-stretchable PES fibers, entropy shrinkage does not occur even in high-temperature environments exceeding 100°C, and fiber shrinkage can be effectively prevented. In particular, since polyethersulfone resin is an amorphous thermoplastic resin, orientation crystals do not occur even when stretched or heat-treated. On the other hand, stretching treatment increases the dry heat shrinkage rate and worsens dimensional stability.
In this context, "stretching" refers to the process of stretching fibers to 1.2 times or more their original length. Operations that apply appropriate tension to the fibers during processes such as winding, as described above, do not constitute a stretching process.

(Physical properties of polyethersulfone fibers)
The polyethersulfone fibers obtained as described above are preferably given the following physical properties by adjusting the shear rate γ, pore size D, winding speed ratio, etc.
In other words, the fineness of the polyethersulfone fiber obtained by melt spinning is preferably 30 dtex or more as a total fineness, and more preferably 50 dtex or more. As a single filament fineness, it is preferably 1 dtex or more and about 12 dtex.
Furthermore, the polyethersulfone fiber may be monofilament or multifilament. In the case of multifilament, the number of filaments is preferably six or more.
Furthermore, the tensile strength of the polyethersulfone fiber is preferably 1.0 cN/dtex or higher, more preferably 1.2 cN/dtex or higher, and even more preferably 1.5 cN/dtex or higher.
Furthermore, the variation in the tensile strength of the polyethersulfone fibers is preferably less than ±0.3 cN/dtex, and more preferably within ±0.2 cN/dtex.
Furthermore, the elongation at break of the polyethersulfone fiber is preferably 10% to 200%, more preferably 20% to 180%, and even more preferably 30% to 170%.
This makes it possible to produce polyethersulfone fibers that are high in strength and also have excellent properties such as dimensional stability and thermal stability.

Furthermore, the dry heat shrinkage rate of the polyethersulfone fiber of the present invention at 200°C is 5% or less, preferably 4% or less, more preferably 3% or less, even more preferably 2% or less, and most preferably 1% or less.
A dry heat shrinkage rate of 5% or less allows for use in a variety of industrial materials. In particular, its excellent dimensional stability even in high-temperature environments makes it suitable for use in precision parts or products manufactured or used in harsh environments.
For example, when used as a heat-adhesive composite fiber to fix fibers in a nonwoven fabric form by heat fusion, heat-adhesive composite fibers have a problem in that, due to differences in the properties of the composite resin components, large thermal shrinkage occurs during the heat treatment process, causing the densely packed areas of the fibers to harden. By keeping the dry heat shrinkage rate below the above upper limit, it is possible to prevent the nonwoven fabric from shrinking and hardening, improve dimensional stability, and obtain a high-quality nonwoven fabric.
Furthermore, the reduced viscosity of the resin constituting the polyethersulfone fiber is preferably 0.30 dl/g or higher. This results in good processability and allows for the production of high-quality fibers without the occurrence of thread breakage.

[Uses of polyethersulfone fibers]
Applications of the polyethersulfone fibers of the present invention include nonwoven fabrics, filters, ropes, and the like. For example, they can be used as long fibers, or woven into fabrics, or as short fibers into nonwoven fabrics, and are useful as materials for heat-resistant clothing, heat insulation materials, heat-resistant filters, and insulating paper stocks. Furthermore, they have excellent electrical properties and can be used as electronic circuit boards.
The polyethersulfone fibers of the present invention can be precisely processed due to their dimensional stability and can be used in the fields of electrical and electronic components, automobiles, and medicine. Because they do not emit endocrine disruptors, they can also be used in the fields of medicine and food.

Furthermore, the polyethersulfone fibers of the present invention have excellent processability, allowing them to be blended with multiple types of fibers to form commingled fibers or processed into fiber-reinforced plastics. Additionally, the polyethersulfone fibers of the present invention can be used as short fibers to form nonwoven fabrics, nonwoven laminates, or fiber-reinforced plastics. Processed polyethersulfone fibers obtained in this way are lightweight due to their excellent strength and can withstand harsh environments, making them suitable for applications in aerospace, automotive, and other fields (structures, engine parts, etc.).
Furthermore, the polyethersulfone resin of the present invention exhibits excellent rigidity and dimensional stability over a wide temperature range, as well as superior creep resistance, gasoline, gasohol, and engine oil resistance at high temperatures, and excellent sliding properties, making it suitable for applications in the mechanical field.

The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto.

<Method for measuring polyethersulfone resin>
The characteristic values in the examples were measured using the following method.
1. Reduced viscosity (η _sp /c)
The reduced viscosity was measured using an Ubbelohde viscosity tube in dimethylformamide (DMF) at 25°C and a viscosity of 1 g/dl, referring to the description in JIS K7367-1 (2002). The reduced viscosity (η _sp /c, in units of dl/g) was calculated based on the following, and the average value of five measurements was used.
η _sp /c=(t−t ₀ )/t ₀ /c(dl/g)
t; Transit time between markings in a polymer solution on a viscometer (seconds)
t ₀ ; Transit time between markings on a viscometer of pure solvent (seconds)
c; Concentration of polymer solution (g/dl)

2. Moisture content (ppm)
The measurement was performed using a Karl Fischer type moisture meter (Mitsubishi Chemical Corporation, VA-200 model).

3. Strength, Elongation, and Strength Variation In accordance with the standard time test of JIS L1013 (2010), a Shimadzu AGS-500NX tensile testing machine was used to determine the breaking strength, elongation, and modulus of elasticity (initial tensile resistance) of a sample length of 200 mm at a tensile speed of 200 mm/min. The average value of 10 points was used to measure the strength, elongation, and strength variation.

4. Glass transition temperature (Tg)
Measurements were taken using a differential scanning calorimeter (DSC-6220, manufactured by SII Nanotechnology Co., Ltd.). A thermal history was subjected to polyethersulfone resin under a nitrogen atmosphere. The thermal history conditions were as follows: first heating (heating rate 10°C/min), followed by cooling (cooling rate 20°C/min), and then a second heating (heating rate 10°C/min).

<Evaluation Method for Polyethersulfone Fibers>
5. Evaluation of Spinning Status The spinning status after spinning for more than two hours was evaluated as follows.
○: Spinning was successful and stable without any thread breakage.
△: The yarn broke during the 2-hour spinning process.
(Air bubbles: While it is possible to wrap the material, air bubbles, likely due to resin degradation, form directly beneath the nozzle, causing thread breakage and uneven strength.)
Unable to wind: Frequent thread breakage prevented winding (either due to resin degradation causing thread breakage or increased filtration pressure making winding impossible).
Spinning impossible: It was simply impossible to wind the yarn.

6. Dry Heat Shrinkage Rate The dry heat dimensional change rate (%) under conditions of 200°C was determined by JIS L1013 (2010) 8.18.2 b) Filament Dimensional Change Rate (Method B).

(Example 1)
<Melting spinning process of polyethersulfone resin>
Sumika Excel® 3600G (manufactured by Sumitomo Chemical Co., Ltd.) was used as the polyethersulfone resin.
This polyethersulfone resin had a glass transition temperature of 225°C and a reducing viscosity of 0.36 dl/g.

These chips were dried in a vacuum dryer at 160°C for 20 hours. The moisture content was 20 ppm or less (drying process).
The obtained dried chips were melted and extruded using an extruder 1 while being heated, and the melted and extruded resin was metered by a gear pump 2 and supplied to a spinning pack 3 (melting process).
The spinning temperature was set to 360°C, and the material was extruded from the spinneret 3a to form fibers. The spinneret had 24 holes, the linear velocity during extrusion from the spinneret 3a was 11.2 m/min, and the shear rate γ was 5931 ^s⁻¹ (spinning process).

The spun yarn extruded from the spinneret 3a was lubricated once it had solidified, and was bundled into a single multifilament 30 cm directly below the spinneret (bundling step). Then, it was wound onto a paper tube using a winder at a winding speed (spinning speed) of 650 m/min to obtain a polyethersulfone fiber of 260 dtex/24 f (winding step).
The obtained physical properties and spinnability evaluation results are shown in Table 1.

(Example 2)
Polyethersulfone fibers were obtained in the same manner as in Example 1, except that a chip of Sumika Excel® 4100G (manufactured by Sumitomo Chemical Co., Ltd.) was used as the polyethersulfone resin, and the spinning conditions were as shown in Table 1.
The polyethersulfone resin in Example 2 had a glass transition temperature of 225°C and a reduced viscosity of 0.43 dl/g.
(Example 3)
Polyethersulfone fibers were obtained in the same manner as in Example 1, except that the spinning conditions were as shown in Table 1.

(Example 4)
Polyethersulfone fibers were obtained in the same manner as in Example 1, except that the spinning conditions were as shown in Table 1.
(Example 5)
Polyethersulfone fibers were obtained in the same manner as in Example 1, except that the spinning conditions were as shown in Table 1.

(Comparative Example 1)
Spinning was carried out in the same manner as in Example 1, except that a chip of Sumika Excel® 4800G (manufactured by Sumitomo Chemical Co., Ltd.) was used as the polyethersulfone resin, and the spinning conditions were as shown in Table 1.
The polyethersulfone resin of Comparative Example 1 had a glass transition temperature of 225°C and a reduced viscosity of 0.48 dl/g.
In Comparative Example 1, although spinning was possible, the fiber quality was poor, resulting in numerous breaks and making it impossible to wind the yarn.

(Comparative Example 2)
The procedure was the same as in Example 1, except that the spinning conditions were as shown in Table 1.
In Comparative Example 2, the resin viscosity was high due to the low spinning temperature, causing the gear pump 2 (GP) to become overloaded and malfunction, making spinning impossible.

(Comparative Example 3)
Spinning was carried out in the same manner as in Example 1, except that the moisture content of the polyethersulfone resin chip was set to 60 ppm and the spinning conditions were as shown in Table 1.
In Comparative Example 3, although spinning was possible, the moisture content was not appropriate, resulting in the formation of numerous air bubbles within the fibers, which led to poor fiber condition and made it impossible to wind the fibers.

(Comparative Example 4)
After spinning in the same manner as in Example 1, the following stretching treatment was performed.
In other words, the polyethersulfone fibers wound in the winding process were placed on rollers and unwound, then guided to a roll heater heated to 150°C, stretched to a stretching ratio of 1.7 times, and then wound up.

(Comparative Example 5)
After spinning in the same manner as in Example 1, the following stretching treatment was performed.
In other words, the polyethersulfone fibers wound in the winding process were placed on rollers and unwound, then guided to a roll heater heated to 150°C, stretched to a stretching ratio of 2.0, and then wound up.

(Comparative Example 6)
Spinning was carried out in the same manner as in Example 1, except that a tip of Ultrazone® E1010 (manufactured by BASF) was used as the polyethersulfone resin, and the spinning conditions were as shown in Table 1.
The polyethersulfone resin of Comparative Example 6 had a glass transition temperature of 222°C and a reduced viscosity of 0.48 dl/g.
In Comparative Example 6, although spinning was possible, the fiber quality was poor, resulting in numerous breaks and making it impossible to wind the yarn.

(Comparative Example 7)
Spinning was carried out in the same manner as in Example 1, except that a tip of Ultrazone® E2010 (manufactured by BASF) was used as the polyethersulfone resin, and the spinning conditions were as shown in Table 1.
The polyethersulfone resin of Comparative Example 7 had a glass transition temperature of 225°C and a reduced viscosity of 0.56 dl/g.
In Comparative Example 7, although spinning was possible, the fiber quality was poor, resulting in numerous breaks and making it impossible to wind the yarn.

From the results in Tables 1 and 2, it was confirmed that the polyethersulfone fibers of Examples 1 to 5 had a dry heat shrinkage rate of 5% or less, a breaking strength of 0.6 cN/dtex or more, a breaking strength variation of ±0.3 cN/dtex or less, and an elongation of 10% or more and less than 200%.
The obtained fibers were then bundled, cut, and passed through a papermaking process, followed by calendering to produce a nonwoven fabric. The polyethersulfone fibers obtained from Examples 1 to 5 exhibited good process passability, and the resulting nonwoven fabrics had good dimensional stability.

Furthermore, the polyethersulfone fibers of Examples 1 to 3 were very excellent fibers with high tensile strength of 1.0 cN/dtex or higher and little variation in strength.
Furthermore, it was confirmed that the polyethersulfone fibers obtained from Examples 1 to 3 exhibited superior passability to subsequent processes and dimensional stability. In addition, the fibers obtained from Examples 1 and 2 showed particularly excellent process passability and dimensional stability.

On the other hand, in Comparative Examples 1 to 7, spinning was either not possible, or even if spinning was possible, the fiber quality was poor and winding was not possible.
Furthermore, even if winding was possible in Comparative Examples 4 and 5, the dry heat shrinkage rate was poor, resulting in problems with post-processing and dimensional stability. When the fibers obtained from Comparative Examples 4 and 5 were calendered, they exhibited poor process passability and poor dimensional stability of the nonwoven fabric.

1. Extruder 2. Gear pump 3. Spinning pack 3a. Spinning die 4. First godet roll 5. Second godet roll 6. Winding bobbin

Claims (6)

The material contains a polyethersulfone resin comprising repeating units shown in the following formula (1):
The aforementioned polyethersulfone resin has a glass transition temperature (Tg) of 200°C or higher and 250°C or lower, and a reduced viscosity of 0.30 dl/g or higher and 0.47 dl/g or lower.
Unstretched polyethersulfone fiber having a dry heat shrinkage rate of 5% or less at 200°C.
The polyethersulfone fiber according to claim 1, wherein the polyethersulfone resin contains 95 mol% or more of the repeating units represented by formula (1). A fiber package in which polyethersulfone fibers according to claim 1 or 2 are wound around a tube. A nonwoven fabric comprising polyethersulfone fibers according to claim 1 or 2. A drying process to obtain dried polyethersulfone resin by drying polyethersulfone resin,
A melting step in which the dry polyethersulfone resin is heated and melted to obtain a molten product,
A spinning process in which the molten material is extruded from the die to form a spindle,
A bundling step of gathering the aforementioned spun yarn to obtain a filament, and a winding step of winding the aforementioned filament.
A method for producing unstretched polyethersulfone fibers containing,
The polyethersulfone resin has a glass transition temperature (Tg) of 200°C or higher and 250°C or lower, and a reduced viscosity of 0.30 dl/g or higher and 0.47 dl/g or lower.
A method for producing unstretched polyethersulfone fibers that satisfies the following conditions.
Condition (a): The moisture content of the dry polyethersulfone resin is less than 50 ppm. Condition (b): The linear discharge speed is 5.0 m/min or more and 50.0 m/min or less. Condition (c): The shear rate during spinning is 300 ^s⁻¹ or more and 90,000 ^s⁻¹ or less. Condition (d): The spinning temperature is 340°C or more and 410°C or less. Condition (e): The winding speed is 550 m/min or more. The method for producing polyethersulfone fibers according to claim 5, wherein in condition (d) above, the spinning temperature is 340°C or higher and 385°C or lower.