Polyphenylene sulfide fiber nonwoven fabric and membrane containing same

Abstract

This polyphenylene sulfide fiber nonwoven fabric comprises a polyphenylene sulfide fiber (A), a copolymerized polyphenylene sulfide fiber (B), and a polyphenylene sulfide fusion-bonding portion (C). Among melt endotherm peaks of the nonwoven fabric obtained by increasing the temperature of same at 16°C / min from 50°C in a nitrogen atmosphere by using a differential scanning calorimeter (DSC), a melting point (Tm-L) which is defined as the peak top of a peak observed on the lowest temperature side is 240-270°C. Provided is a polyphenylene sulfide fiber nonwoven fabric that has both high tear strength and tensile strength even when having a low per-area-weight.

Description

[Technical Field]

[0001] The present invention relates to a polyphenylene sulfide fiber nonwoven fabric and a membrane comprising the same. [Background technology]

[0002] Polyphenylene sulfide (PS) has excellent heat resistance, chemical resistance, electrical insulation, and flame retardancy, as well as excellent mechanical properties and moldability, making it widely used as a metal replacement material and a material that can withstand extreme environments. Taking advantage of these properties, PS fibers are also used in applications such as bag filters, papermaking canvases, electrical insulating paper, battery separators, and various diaphragms. In particular, for hydrogen production equipment diaphragms and fuel cell diaphragms, which are attracting attention as clean energy sources, as well as for these diaphragm reinforcement materials, research is being conducted to combine the heat resistance and chemical resistance to high-concentration alkaline solutions of PS with the ion permeability and gas separation properties of nonwoven fabric materials.

[0003] A recent challenge is to make diaphragms thinner and lighter in order to make devices smaller, lighter, and more powerful. Thin, low-basis-weight nonwoven fabrics are prone to breakage due to minute fluctuations in tension during the manufacturing process, and they are also easily torn by contact with edges or burrs on other components during the modularization process. Therefore, there is a need for nonwoven fabrics that are thin and have low basis weight, yet have excellent mechanical strength and are resistant to tearing.

[0004] To address this issue, for example, a polyphenylene sulfide wetlaid nonwoven fabric composed of drawn polyphenylene sulfide fibers and undrawn polyphenylene sulfide fibers as binder fibers bonded by thermocompression has been proposed (see, for example, Patent Document 1). The undrawn polyphenylene sulfide fibers undergo plastic deformation by thermocompression bonding, bonding the drawn polyphenylene sulfide fibers together, resulting in a nonwoven fabric with excellent tensile strength.

[0005] In addition, a wet-laid nonwoven fabric made of fine binder fibers with excellent adhesiveness, which are obtained by stretching unstretched polyphenylene sulfide fibers in an ethylene glycol bath at 110°C, has also been proposed (see, for example, Patent Document 2). By including stretched polyphenylene sulfide fibers that do not increase the degree of orientation, a nonwoven fabric with excellent tensile strength can be obtained, even if it is thin.

[0006] On the other hand, undrawn fibers have the problem of being prone to thermal shrinkage. Therefore, wetlaid nonwoven fabrics using copolymerized polyphenylene sulfide fibers with low crystallinity as a papermaking binder have also been proposed (see, for example, Patent Document 3). The nonwoven fabric is made of copolymerized polyphenylene sulfide fibers and polyphenylene sulfide fibers, and contains copolymerized polyphenylene sulfide fibers with a small diameter and low thermal shrinkage rate as a binder, resulting in a thin nonwoven fabric with excellent thermal dimensional stability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-77494 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-146428 [Patent Document 3] International Publication No. 2020 / 066815 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the technology disclosed in Patent Document 1 has problems such as the tendency for the nonwoven fabric to tear due to contact with edges or burrs of other components during the modularization process. According to the inventors' research, the unstretched polyphenylene sulfide fibers used as binder fibers tend to fuse together during thermal calendering and not retain their fiber shape. This reduces the tear strength of the nonwoven fabric, resulting in the above-described tearing.

[0009] The technology disclosed in Patent Document 2 uses only small-diameter binder fibers stretched in an ethylene glycol bath at 110°C, which is advantageous for thinning nonwoven fabrics. However, like unstretched polyphenylene sulfide fibers, the fiber shape is not easily retained during thermal calendering due to fusion, and as mentioned above, the tear strength is insufficient. In addition, this method also has issues such as shrinkage of the nonwoven fabric during the papermaking drying process, which can lead to drying wrinkles and swelling.

[0010] On the other hand, in Patent Document 3, the fibers are made of copolymerized polyphenylene sulfide, which has a low melting point, and therefore the adhesive strength between the fibers is insufficient, and the tensile strength of the nonwoven fabric tends to decrease.

[0011] An object of the present invention is to provide a polyphenylene sulfide fiber nonwoven fabric that is suitable for reducing the thickness and the basis weight and that has both high tear strength and tensile strength, and a diaphragm containing the same. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention has the following configuration.

[0013] (1) A polyphenylene sulfide fiber nonwoven fabric comprising polyphenylene sulfide fibers (A), copolymerized polyphenylene sulfide fibers (B), and polyphenylene sulfide fused portions (C), the nonwoven fabric having a melting point (Tm-L) of 240 to 270°C, which is defined as the peak top of the lowest-temperature peak observed among the melting endothermic peaks obtained by heating the nonwoven fabric from 50°C at a rate of 16°C / min in a nitrogen atmosphere using a differential scanning calorimeter (DSC).

[0014] (2) The polyphenylene sulfide fiber nonwoven fabric according to (1), wherein the copolymerized polyphenylene sulfide fiber (B) is a copolymerized polyphenylene sulfide fiber composed of repeating units of p-phenylene sulfide units and m-phenylene sulfide units.

[0015] (3) The polyphenylene sulfide fiber nonwoven fabric according to (1) or (2), wherein the area ratio of the polyphenylene sulfide fused portions (C) is 5 to 50%.

[0016] (4) A polyphenylene sulfide fiber nonwoven fabric according to any one of (1) to (3), having a tear strength of 0.200 to 10.0 N.

[0017] (5) The polyphenylene sulfide fiber nonwoven fabric according to any one of (1) to (4), wherein the copolymerized polyphenylene sulfide fibers (B) contain 4.0 to 40.0 mol % of copolymerized units in p-phenylene sulfide.

[0018] (6) The polyphenylene sulfide fiber nonwoven fabric according to any one of (1) to (5), wherein the molar percentage of p-phenylene sulfide units in the polyphenylene sulfide fused portions (C) is 97.0 molar percent or more.

[0019] (7) A membrane comprising the polyphenylene sulfide fiber nonwoven fabric according to any one of (1) to (6). [Effects of the Invention]

[0020] The present invention can provide a polyphenylene sulfide fiber nonwoven fabric suitable for thinning and reducing the basis weight. The present invention can also provide a polyphenylene sulfide fiber nonwoven fabric excellent in tear strength and tensile strength. Furthermore, the present invention can provide a polyphenylene sulfide fiber nonwoven fabric that is less likely to break during the manufacturing process or in subsequent processes. This makes it possible to provide a diaphragm with a thinner fabric and a lower basis weight. DETAILED DESCRIPTION OF THE INVENTION

[0021] The polyphenylene sulfide fiber (A) of the present invention is composed of 97.0 mol % or more of repeating units that are p-phenylene sulfide units represented by the following general formula (1). The repeating units are preferably 98.0 mol %, more preferably 99.0 mol % or more. Since the polyphenylene sulfide fiber (A) exhibits high fiber strength, the polyphenylene sulfide fused portions (C) fuse the fibers together, thereby allowing stress to be borne, resulting in a nonwoven fabric with high tensile strength. Furthermore, from the viewpoint of improving tensile strength, the mass % of the polyphenylene sulfide fiber (A) in the polyphenylene sulfide fiber nonwoven fabric is preferably 1 mass % or more, more preferably 2 mass % or more. Furthermore, from the viewpoint of a balance with tear strength, it is preferably 80 mass % or less, more preferably 60 mass % or less. The presence of the polyphenylene sulfide fiber (A) of the present invention can be confirmed by microscopic infrared spectroscopy as described in the Examples.

[0022] [ka]

[0023] The copolymerized polyphenylene sulfide fiber (B) of the present invention contains at least one type of copolymerized unit other than p-phenylene sulfide in an amount of 4.0 mol % or more, preferably 5.0 mol % or more. In the present invention, the inclusion of the copolymerized polyphenylene sulfide fiber (B) can improve tear strength. Furthermore, in terms of mechanical properties, the copolymerized unit content is preferably 40.0 mol % or less, more preferably 30.0 mol % or less. Examples of copolymerized units other than p-phenylene sulfide include aromatic sulfides such as triphenylene sulfide and biphenylene sulfide, as well as alkyl- and halogen-substituted derivatives thereof. While not particularly limited, m-phenylene sulfide represented by the following general formula (2) is preferred. The inclusion of m-phenylene sulfide as a copolymerized unit reduces the melting point and / or crystallinity without impairing the heat resistance, chemical resistance, and other characteristics of polyphenylene sulfide, thereby more effectively suppressing crack propagation during tearing. The mass % of polyphenylene sulfide fiber (B) in the polyphenylene sulfide fiber nonwoven fabric is preferably 1 mass % or more, more preferably 2 mass % or more, from the viewpoint of improving tensile strength. Furthermore, from the viewpoint of a balance with tear strength, it is preferably 80 mass % or less, more preferably 60 mass % or less. The presence of copolymerized polyphenylene sulfide fiber (B) containing m-phenylene sulfide in the nonwoven fabric of the present invention can be confirmed by microscopic infrared spectroscopy as described in the Examples.

[0024] [ka]

[0025] In the present invention, the copolymerized polyphenylene sulfide fiber (B) preferably contains p-phenylene sulfide units in an amount of 60.0 mol% to 96.0 mol% of the repeating units. By controlling the repeating units of p-phenylene sulfide units to preferably 60.0 mol% or more, more preferably 70.0 mol% or more, the polyphenylene sulfide fiber has good spinnability and excellent heat resistance and mechanical properties. Furthermore, by controlling the p-phenylene sulfide units to preferably 96.0 mol% or less, more preferably 95.0 mol% or less, the crystallinity of the copolymerized polyphenylene sulfide is reduced, resulting in a copolymerized polyphenylene sulfide fiber that contributes to further improvement of tear strength. Furthermore, the m-phenylene sulfide units, a preferred copolymerization component, are preferably contained in an amount of 4.0 mol% to 40.0 mol% of the repeating units. By controlling the m-phenylene sulfide unit content to preferably 5.0 mol% or more, and even more preferably 6.0 mol% or more, the melting point and crystallinity of the copolymerized polyphenylene sulfide can be lowered, resulting in a copolymerized polyphenylene sulfide fiber (B) with excellent crack propagation suppression effect upon tearing. Furthermore, by controlling the m-phenylene sulfide unit content to preferably 40.0 mol% or less, and even more preferably 30.0 mol% or less, excessive decreases in melting point and crystallinity can be suppressed, resulting in a copolymerized polyphenylene sulfide fiber (B) with good heat resistance and mechanical properties. The mole percentages of p-phenylene sulfide units and m-phenylene sulfide units in the copolymerized polyphenylene sulfide fiber (B) of the present invention are values ​​determined by microscopic infrared spectroscopy as described in the Examples.

[0026] In the present invention, the presence of copolymerized polyphenylene sulfide fibers (B) in the nonwoven fabric allows easily deformed low-crystalline elements to be anisotropically scattered, which suppresses crack propagation due to tearing and results in a nonwoven fabric with high tear strength.

[0027] The cross-sectional shape of the polyphenylene sulfide fiber (A) and copolymer polyphenylene sulfide fiber (B) of the present invention is not limited in any way and may be any shape, such as a round cross section, a multi-lobal cross section such as a triangular cross section, a flat cross section, an S-shaped cross section, a cross cross section, a hollow cross section, etc. When a papermaking method, which is a preferred production method for the polyphenylene sulfide fiber nonwoven fabric of the present invention, is employed, a round cross section is preferred from the viewpoint of fiber dispersion during papermaking, etc.

[0028] In the polyphenylene sulfide fiber nonwoven fabric of the present invention, it is preferred that the copolymerized polyphenylene sulfide fibers (B) are partially fused to the extent that the effects of the present invention are not impaired. For example, if the surface is partially fused by heat calendering or the like, and fusion with surrounding fibers is exhibited while retaining the fibrous shape, the adhesion area between the constituent fibers increases, which can also contribute to reducing fiber slip-out.

[0029] Conventionally, copolymerized polyphenylene sulfide fiber (B) has been used as a binder fiber because of its low melting point. However, as mentioned above, this makes it difficult to obtain high tensile strength due to insufficient adhesive strength. In the present invention, polyphenylene sulfide fused portion (C) is used as a binder.

[0030] In the present invention, to form a strong bond, the polyphenylene sulfide fused portion (C) preferably contains p-phenylene sulfide units at 97.0 mol% or more, more preferably 98.0 mol% or more, and even more preferably 99.0 mol% or more. Increasing the p-phenylene sulfide units increases the strength of the polyphenylene sulfide fused portion (C), making it less susceptible to fracture when tensile stress is applied, and as a result, less likely to come loose from the bonded component fiber bundles. In the present invention, the mol% of p-phenylene sulfide units in the polyphenylene sulfide fused portion (C) is determined by microscopic infrared spectroscopy as described in the Examples.

[0031] The polyphenylene sulfide fused portion (C) in the present invention is preferably in the form of a film of at least a portion of the polyphenylene sulfide. Here, the fused portion refers to, for example, when a binder fiber is used as a precursor, a portion where the fiber loses its fibrous form and becomes amorphous, bonding the fibers that make up the nonwoven fabric. By having the polyphenylene sulfide fused portion (C) in the nonwoven fabric, the fibers contained in the nonwoven fabric of the present invention are bonded together by the polyphenylene sulfide, making it less likely for the fibers to come loose when tensile stress is applied to the nonwoven fabric.

[0032] The area ratio of polyphenylene sulfide fused portions (C) in the polyphenylene sulfide fiber nonwoven fabric of the present invention is preferably 5 to 50%. By setting the area ratio of polyphenylene sulfide fused portions (C) to preferably 5% or more, more preferably 10% or more, the adhesion area between the constituent fibers is increased, thereby improving strength. This makes it less likely for the constituent fibers to come loose even when tensile stress is applied to the nonwoven fabric during processing. Furthermore, by setting the area ratio to preferably 50% or less, more preferably 40% or less, sufficient polyphenylene sulfide fibers (A) and copolymerized polyphenylene sulfide fibers (B) are present in the nonwoven fabric, which provide excellent tensile strength, resulting in a nonwoven fabric with high tensile strength. Furthermore, the softness and breathability characteristic of nonwoven fabrics can be maintained. The area ratio of polyphenylene sulfide fused portions (C) in the present invention is a value measured by microscopic infrared spectroscopy of the nonwoven fabric surface using the method described in the Examples.

[0033] In the polyphenylene sulfide fiber nonwoven fabric of the present invention, the type of nonwoven fabric is not particularly limited, and examples thereof include spunbond nonwoven fabrics, meltblown nonwoven fabrics, spunlace nonwoven fabrics, needlepunched nonwoven fabrics, and papermaking nonwoven fabrics. Among these, papermaking nonwoven fabrics are preferred because they can be easily made into a low basis weight and thin fabric.

[0034] The polyphenylene sulfide fiber nonwoven fabric of the present invention has a melting point (Tm-L) of 240 to 270°C, which is defined as the peak top of the lowest-temperature peak observed among the melting endothermic peaks obtained by heating from 50°C at a rate of 16°C / min under a nitrogen atmosphere using a differential scanning calorimeter (DSC). By setting the melting point (Tm-L) to 270°C or less, preferably 265°C or less, and more preferably 260°C or less, the copolymerized polyphenylene sulfide fibers (B) are not completely fused within the nonwoven fabric during thermal calendering, thereby suppressing a decrease in tear strength. Furthermore, by setting the melting point (Tm-L) to 240°C or more, preferably 243°C or more, and more preferably 245°C or more, the copolymerized polyphenylene sulfide fibers are partially fused, thereby suppressing fiber separation and improving heat resistance. Furthermore, complete fusion during thermal calendering prevents damage to the fiber morphology. The melting point (Tm-L) of the polyphenylene sulfide fiber nonwoven fabric is a value measured by the method described in the examples.

[0035] The basis weight of the polyphenylene sulfide fiber nonwoven fabric of the present invention is 1.00 to 100 g / m 2 The basis weight is preferably 1.00 g / m 2 More preferably, 3.00 g / m 2 More preferably, 5.00 g / m 2 By setting the weight to 100 g / m or more, breakage during the manufacturing process is less likely to occur, and the processability is improved. 2 or less, more preferably 80.0 g / m 2 or less, more preferably 60.0 g / m 2 By satisfying the following conditions, a lightweight nonwoven fabric with excellent flexibility can be obtained. In addition, a thin diaphragm with a low basis weight can be obtained. The basis weight of the nonwoven fabric in the present invention refers to a value measured by the method described in the Examples.

[0036] The thickness of the polyphenylene sulfide fiber nonwoven fabric of the present invention is preferably 5.00 to 300.00 μm. By setting the thickness to preferably 5.00 μm or more, more preferably 8.00 μm or more, and even more preferably 10.00 μm or more, breakage during the manufacturing process is less likely to occur, improving processability. Furthermore, by setting the thickness to preferably 300.00 μm or less, more preferably 250.00 μm or less, and even more preferably 200.00 μm or less, the permeability of ions and the like when used as a diaphragm or the like is improved. Furthermore, when used as a diaphragm or the like in a device, the volume occupied by the nonwoven fabric is reduced, allowing for the device to be made smaller and lighter. The thickness of the nonwoven fabric in the present invention refers to a value measured by the method described in the Examples.

[0037] The tear strength of the polyphenylene sulfide fiber nonwoven fabric of the present invention is preferably 0.200 to 10.0 N. By setting the tear strength to preferably 0.200 N or more, more preferably 0.250 N or more, and even more preferably 0.350 N or more, even if a crack occurs in the nonwoven fabric during processing, the crack is less likely to propagate throughout the nonwoven fabric, resulting in a nonwoven fabric that is less likely to tear. Furthermore, by setting the tear strength to preferably 10.0 N or less, more preferably 7.50 N or less, and even more preferably 5.00 N or less, problems are less likely to occur when cutting the nonwoven fabric. The tear strength can be improved by, for example, increasing the proportion of copolymerized polyphenylene sulfide fiber (B). The tear strength of the nonwoven fabric in the present invention refers to a value measured by the method described in the Examples.

[0038] The tensile strength of the polyphenylene sulfide fiber nonwoven fabric of the present invention is preferably 2.5 to 300.0 N / 15 mm. By setting the tensile strength to preferably 2.5 N / 15 mm or more, more preferably 3.5 N / 15 mm or more, and even more preferably 5.0 N / 15 mm or more, breakage during the manufacturing process is reduced. Furthermore, the nonwoven fabric is less likely to break even when tensile stress is applied during subsequent processes or during use. Furthermore, by setting the tensile strength to preferably 300.0 N / 15 mm or less, more preferably 250.0 N / 15 mm or less, and even more preferably 200.0 N / 15 mm or less, the flexibility of the nonwoven fabric can be maintained, resulting in a nonwoven fabric with excellent assembly properties when used as a diaphragm or the like. The polyphenylene sulfide fibers (A) having high fiber strength are firmly bonded by the polyphenylene sulfide fused portions (C), resulting in improved tensile strength. That is, by having polyphenylene sulfide fibers (A) and polyphenylene sulfide fused portions (C), fiber slippage is less likely to occur, and the polyphenylene sulfide fibers (A) bear stress, etc., resulting in a nonwoven fabric with high tensile strength. The tensile strength of the nonwoven fabric in the present invention refers to a value measured by the method described in the examples.

[0039] In the polyphenylene sulfide fiber nonwoven fabric of the present invention, the square root of the product (√XY), where X (N) is the tear strength and Y (N / 15 mm) is preferably 1.4 or more. By making √XY 1.4 or more, more preferably 1.5 or more, and even more preferably 1.6 or more, breakage and the like during the manufacturing process can be suppressed. Furthermore, satisfying the above-mentioned preferred ranges of tear strength and tensile strength at the same time is more preferable because it results in a nonwoven fabric that is less likely to break even when pressed against a module with tensile stress applied when mounted in an apparatus as a diaphragm or the like.

[0040] In the present invention, unlike a combination of only polyphenylene sulfide fiber (A) and polyphenylene sulfide fused portions (C), or only polyphenylene sulfide fiber (A) and copolymer polyphenylene sulfide fiber (B), the preferred tensile strength and tear strength can be achieved by including all of polyphenylene sulfide fiber (A), copolymer polyphenylene sulfide fiber (B), and polyphenylene sulfide fused portions (C). To achieve a better balance, the mass ratio (A / B) of polyphenylene sulfide fiber (A) to copolymer polyphenylene sulfide fiber (B) is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.5 or more. It is also preferably 50 or less, more preferably 25 or less, and even more preferably 2 or less.

[0041] The air permeability of the polyphenylene sulfide fiber nonwoven fabric of the present invention is 1 to 150 cc / cm 2 / s. The air permeability is preferably 1 cc / cm 2 / s or more, preferably 3cc / cm 2 / s or more, more preferably 5cc / cm 2 By setting the air permeability to 150 cc / cm or more, the permeability of ions and the like when used in a diaphragm or the like is improved. 2 / s or less, more preferably 120cc / cm 2 / s or less, more preferably 100cc / cm 2 / s or less, the nonwoven fabric has sufficient mechanical strength, is less likely to break during the manufacturing process, and improves processability. Furthermore, when used in diaphragms and the like, the nonwoven fabric is less likely to break or crack during assembly. The breathability of the nonwoven fabric in the present invention refers to a value measured by the method described in the Examples.

[0042] The diaphragm of the present invention comprises the polyphenylene sulfide fiber nonwoven fabric of the present invention described above. Here, the diaphragm is not particularly limited, but it is used for ion permeation and gas separation in, for example, hydrogen production equipment, fuel cells, etc. The polyphenylene sulfide fiber nonwoven fabric of the present invention has excellent mechanical strength even when thin and has a low basis weight, and therefore serves as a diaphragm with excellent ion permeation efficiency and resistance to tearing during packaging and use. Another example of the diaphragm of the present invention is a diaphragm formed by laminating the polyphenylene sulfide fiber nonwoven fabric of the present invention with another material such as a porous film. The polyphenylene sulfide fiber nonwoven fabric of the present invention contains copolymerized polyphenylene sulfide fiber (B) with a low melting point, and therefore has excellent thermal adhesion to other materials, and is a high-performance diaphragm with little delamination or loss of ion permeation efficiency between layers.

[0043] A preferred example of a method for producing the polyphenylene sulfide fiber nonwoven fabric of the present invention and a diaphragm containing the same is as follows. First, polyphenylene sulfide fibers (A), copolymerized polyphenylene sulfide fibers (B), and a precursor of the polyphenylene sulfide fused portion (C) are dispersed in water to prepare a papermaking solution, which is then made into paper and dried. Next, the precursor of the polyphenylene sulfide fused portion (C) is heat-fused between the fibers using a thermal calendar or the like to form the fused polyphenylene sulfide portion (C). In the present invention, the fused polyphenylene sulfide portion (C) can be formed by using unstretched polyphenylene sulfide fibers as its precursor and fusing them using a thermal calendar or the like.

[0044] Hereinafter, the methods for producing polyphenylene sulfide fiber nonwoven fabrics and diaphragms using polyphenylene sulfide fibers (A), copolymerized polyphenylene sulfide fibers (B), and unstretched polyphenylene sulfide fibers, which are preferably used in the present invention, will be specifically described using a papermaking nonwoven fabric as an example.

[0045] [Method for producing polyphenylene sulfide fiber (A)] The polyphenylene sulfide to be used is preferably dried before being subjected to melt spinning in order to prevent water contamination and remove oligomers, in order to improve spinnability. Drying conditions usually include vacuum drying at 100 to 200°C for 1 to 24 hours.

[0046] In melt spinning, a melt spinning technique using an extruder such as a pressure melter, single-screw extruder, or twin-screw extruder can be applied. The extruded polyphenylene sulfide passes through a pipe, is metered by a metering device such as a gear pump, passes through a filter to remove foreign matter, and is then introduced to a spinneret. At this time, the temperature from the polymer pipe to the spinneret (spinning temperature) is preferably 280°C or higher to increase fluidity, and preferably 380°C or lower to suppress thermal decomposition of the polymer.

[0047] When the polyphenylene sulfide fiber used in the present invention is a composite fiber, the polyphenylene sulfide and other component resins are melted separately, then passed through polymer piping, metered by a known metering device such as a gear pump, and passed through a filter to remove foreign matter, and then each is introduced into a spinneret. The respective polymers introduced into the spinneret are shaped into an arbitrary composite form within the spinneret, merged, and extruded from the spinneret holes as a composite fiber.

[0048] The spinneret used for extrusion preferably has a nozzle hole diameter D of 0.1 mm or more and 0.6 mm or less, and L / D, defined as the quotient obtained by dividing the land length L of the nozzle hole (the length of the straight tube portion having the same diameter as the nozzle hole) by the hole diameter D, is preferably 1 or more and 10 or less.

[0049] The polyphenylene sulfide fibers extruded from the spinneret holes are cooled and solidified by blowing cooling air (air). The temperature of the cooling air can be determined in consideration of the balance with the cooling air speed from the viewpoint of cooling efficiency, but a preferred embodiment is 30°C or less. By setting the temperature of the cooling air to preferably 30°C or less, the solidification behavior due to cooling is stabilized, resulting in polyphenylene sulfide fibers with a highly uniform fiber diameter.

[0050] The cooling air is preferably blown in a direction substantially perpendicular to the undrawn fibers discharged from the spinneret, and the speed of the cooling air is preferably 10 m / min or more from the viewpoints of cooling efficiency and uniformity of fineness, and is preferably 100 m / min or less from the viewpoint of spinning stability.

[0051] The cooled and solidified undrawn fibers are taken up by a roller (godet roller) rotating at a constant speed. The take-up speed is preferably 300 m / min or more to improve linear uniformity and productivity, and 2000 m / min or less to prevent yarn breakage.

[0052] The undrawn fiber thus obtained is once wound up or taken up and then continuously subjected to a drawing step. Drawing is carried out by running the fiber over a heated first roller or a heating device provided between the first roller and the second roller, for example, in a heating bath or on a hot plate. The drawing conditions are determined by the mechanical properties of the undrawn fiber obtained, but the drawing temperature is determined by the temperature of the heated first roller or the heating device provided between the first roller and the second roller, and the draw ratio is determined by the ratio of the peripheral speeds of the first roller and the second roller.

[0053] The temperature of the heated first roller or heating device in the drawing step is preferably 80° C. or higher and 130° C. or lower. A temperature of 80° C. or higher fixes the drawing point, enabling stable drawing, while a temperature of 130° C. or lower can prevent yarn breakage and improve processability. Furthermore, from the viewpoint of fixing the drawing point, the temperature of the second roller is preferably 20° C. or lower higher than the temperature of the heated first roller or heating device.

[0054] Furthermore, after passing through the second roller, the drawn fibers may be heated and heat-set by a heated third roller or a heating device provided between the second and third rollers. The heat-setting temperature for heat-setting is preferably 180 to 240°C. A heat-setting temperature of 180°C or higher can reduce shrinkage through thermal crystallization. This can suppress width reduction during the nonwoven fabric production process and produce a nonwoven fabric with excellent dimensional stability. Furthermore, a heat-setting temperature of 240°C or lower can suppress fusion of the fibers to the rollers and prevent deterioration of processability.

[0055] It is preferable to apply a papermaking dispersant or the like to the obtained fibers as needed. The application of the dispersant is usually carried out in a tow state using a kiss roller or guide oiling. The papermaking dispersant adhesion rate is preferably 1 to 6 mass% relative to the mass of the fibers. By setting the dispersant adhesion rate to preferably 1 mass% or more, more preferably 2 mass% or more, the dispersibility of the fibers in the dispersion liquid that serves as the precursor of the nonwoven fabric is improved, resulting in a homogeneous nonwoven fabric. Furthermore, by setting the dispersant adhesion rate to preferably 6 mass% or less, more preferably 5 mass% or less, the processability during nonwoven fabric processing is improved.

[0056] The resulting fibers may then be crimped using a crimper and heat-set using a setter. By crimping the fibers, the fibers become entangled, increasing the adhesive area between the fibers, and a nonwoven fabric with excellent mechanical strength can be obtained.

[0057] The number of crimps in the crimping is preferably 2 to 15 crimps per 25 mm. By setting the number of crimps to 2 crimps or more, the fibers are more easily entangled, resulting in a nonwoven fabric with excellent mechanical strength. Furthermore, by setting the number of crimps to 15 crimps or less, the dispersibility of the fibers in the dispersion liquid is improved, resulting in a homogeneous nonwoven fabric.

[0058] The heat setting temperature by the setter is preferably 80 to 100° C. By setting the heat setting temperature to preferably 80° C. or higher, it is possible to fix the crimped form, and by setting the heat setting temperature to preferably 100° C. or lower, it is possible to suppress shrinkage of the fibers.

[0059] The resulting fibers are then cut to a predetermined length with a cutter to obtain cut fibers. The fiber length of the cut fibers is preferably 0.5 to 15 mm. By setting the fiber length to preferably 0.5 mm or more, the fibers are more likely to entangle with each other, resulting in a nonwoven fabric with excellent mechanical strength. Furthermore, by setting the fiber length to preferably 15 mm or less, it is possible to prevent the fibers from entangling with each other in the dispersion, causing clumps and other irregularities.

[0060] [Method for producing copolymerized polyphenylene sulfide fiber (B)] The undrawn fibers can be obtained in the same manner as in the polyphenylene sulfide fibers (A), except that copolymerized polyphenylene sulfide is used as the raw polymer.

[0061] After drawing the obtained undrawn fiber, it is not necessary to subject it to heat setting in order to develop high adhesiveness, but if heat setting is performed, it is preferable to set the heat setting temperature to 210° C. or less. By setting the heat setting temperature to preferably 210° C. or less, more preferably 190° C. or less, and even more preferably 150° C. or less, excessive thermal crystallization can be suppressed, and a copolymerized polyphenylene sulfide fiber having high adhesiveness can be obtained.

[0062] The cut fibers of the obtained fibers can be obtained in the same manner as the polyphenylene sulfide fibers (A).

[0063] [Method for producing unstretched polyphenylene sulfide fibers] Cut fibers of undrawn fibers can be obtained in the same manner as in the production method of polyphenylene sulfide fiber (A), except that drawing and heat setting are not performed. The raw material polymer may be the same as described above as long as it is within the component ranges described above.

[0064] [Manufacturing method of polyphenylene sulfide fiber nonwoven fabric] The three types of cut fibers obtained by the above method are each dispersed in water. These dispersions are then mixed in the desired ratio to obtain a papermaking dispersion. The melting point (Tm-L) in the present invention can be adjusted by the melting point of the copolymerized polyphenylene sulfide fiber (B) that constitutes the nonwoven fabric. The melting point of the copolymerized polyphenylene sulfide fiber (B) can generally be lowered by increasing the copolymerization ratio, and can be improved by decreasing the copolymerization ratio.

[0065] The total amount of the three types of cut fibers relative to the total mass of the papermaking dispersion is preferably 0.05 to 5% by mass. By making the total amount 0.05% by mass or more, production efficiency can be improved and the load on the dewatering process can be reduced. Furthermore, by making it 5% by mass or less, the dispersion state can be improved and a uniform wetlaid nonwoven fabric can be obtained.

[0066] The dispersions may be prepared by first preparing three types of dispersions of cut fibers separately and then mixing them, or by directly preparing a dispersion containing the three types of cut fibers. The method of preparing a dispersion of each fiber separately and then mixing them is preferred because the stirring time can be controlled separately in accordance with the shape and properties of each fiber, while the method of directly preparing a dispersion containing the three types of cut fibers is preferred because it simplifies the process.

[0067] The papermaking dispersion may contain dispersants and oils such as cationic, anionic, and nonionic surfactants to improve water dispersibility, thickeners to increase the viscosity of the dispersion and prevent aggregation of the papermaking dispersion, and antifoaming agents to suppress foam generation.

[0068] The papermaking dispersion prepared as described above is made into paper using a cylinder, fourdrinier, or tilted wire papermaking machine or a hand-made papermaking machine, and the paper is dried using a Yankee dryer, rotary dryer, or the like to form a dry web. This is then subjected to a heat and pressure treatment to obtain a nonwoven fabric. In this invention, the simultaneous application of heat and pressure is referred to as a heat and pressure treatment, and is distinguished from treatments such as drying that involve only heating without pressure. A dry web refers to a wet-formed nonwoven fabric that has not been subjected to this heat and pressure treatment.

[0069] In a preferred method for producing the polyphenylene sulfide fiber nonwoven fabric of the present invention, the polyphenylene sulfide fused portions (C) are preferably produced by subjecting the unstretched polyphenylene sulfide fibers to heat and pressure treatment, etc., in terms of simplicity and low cost. In this case, it is preferable to suppress crystallization as much as possible during the dry web production process. To achieve this, the drying temperature in the papermaking process is preferably 80 to 150°C, and more preferably 90 to 140°C. It is also preferable to suppress crystallization by shortening the drying process time. Insufficient drying not only reduces the paper strength of the dry web, but also causes rapid thermal shrinkage during the subsequent heat and pressure treatment, making the paper more likely to break. Conversely, excessive drying promotes crystallization of the dry web, making it difficult for the unstretched polyphenylene sulfide fibers to undergo plastic deformation during the subsequent heat and pressure treatment. As a result, the polyphenylene sulfide fused portions (C) are not formed in sufficient amounts, and the mechanical properties of the resulting nonwoven fabric are reduced. Here, the drying temperature in the papermaking process refers to the maximum temperature of the processing temperature (ambient temperature) during drying in the papermaking process.

[0070] In producing the nonwoven fabric of the present invention, it is preferable to subject a dry web containing a mixture of three types of cut fibers to a heat and pressure treatment. By subjecting the dry web to a heat and pressure treatment, the unstretched polyphenylene sulfide fibers are melted and softened, as described above, and polyphenylene sulfide fused portions (C) can be formed. Any means for applying heat and pressure can be used, including, for example, a hot press using a flat plate or a hot calender. Of these, a hot calender, which allows continuous processing, is preferred. Examples of rolls that can be used for the hot calender include a metal-metal roll, a metal-paper roll, and a metal-rubber roll.

[0071] The temperature conditions for the heat and pressure treatment are preferably a temperature equal to or higher than the glass transition temperature of the unstretched polyphenylene sulfide fiber and equal to or lower than the melting point of the copolymerized polyphenylene sulfide fiber (B). To this end, the heating temperature is preferably set to 150 to 240°C. By setting the heating temperature at 150°C or higher, the unstretched polyphenylene sulfide fiber melts and softens, forming fused polyphenylene sulfide portions (C), resulting in a nonwoven fabric with excellent mechanical properties. By setting the heating temperature at 240°C or lower, the copolymerized polyphenylene sulfide fiber (B), which has a low melting point, is completely fused, preventing damage to the fiber shape. Furthermore, fusion to a heating device such as a thermal calender can be prevented, preventing deterioration of processability.

[0072] When calendering is used as the heat and pressure treatment, the pressure is preferably 98 to 7000 N / cm. A pressure of 98 N / cm or more is preferable, allowing the formation of polyphenylene sulfide fused portions (C) and resulting in a nonwoven fabric with excellent mechanical properties. On the other hand, a pressure of 7000 N / cm or less is preferable, preventing tearing of the nonwoven fabric during the heat and pressure treatment step and allowing for stable treatment. The process speed is preferably 1 to 30 m / min. A speed of preferably 1 m / min or more, more preferably 2 m / min, allows for good work efficiency. On the other hand, a speed of preferably 30 m / min or less, more preferably 20 m / min or less, allows heat to be conducted to the fibers inside the nonwoven fabric, allowing for effective thermal fusion of the fibers.

[0073] The diaphragm of the present invention can be produced by using the polyphenylene sulfide fiber nonwoven fabric of the present invention as described above, or by laminating other materials such as porous films, as necessary. When laminating, it is preferable to perform heat fusion bonding using a thermal calendar or the like. By setting the heating temperature during thermal calendaring to 220°C or less, the fiber morphology of the polyphenylene sulfide fibers (A) and copolymerized polyphenylene sulfide fibers (B) in the polyphenylene sulfide fiber nonwoven fabric of the present invention is not damaged, and a diaphragm having both high tear strength and tensile strength is obtained. [Example]

[0074] The polyphenylene sulfide fiber nonwoven fabric of the present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. Various modifications and alterations are possible within the scope of the present invention. The respective property values ​​in the examples were determined by the following methods.

[0075] [Measurement and evaluation method] (1) Measurement of area ratio of polyphenylene sulfide fused portion (C) and mole % of repeating unit: The surface of the nonwoven fabric sheet after heat and pressure treatment was photographed at 150x magnification using a microscopic infrared spectrophotometer (Agilent Technologies, Inc., "Cary 660") in imaging mode. The obtained image was processed using the image processing software "ImageJ" to calculate the area percentage of the polyphenylene sulfide region where the fibrous shape had been lost and the region had become a film. The region where the fibrous shape had been lost and the region had become a film was manually selected using the active contour extraction processing mode. This was performed at three arbitrary locations on the nonwoven fabric surface, and the average value obtained was used as the area percentage of the polyphenylene sulfide fused region (C). The mole percentage of the repeating unit of the polyphenylene sulfide fused region (C) was determined from the infrared absorption spectrum of the region where the fibrous shape had been lost and the region had become a film, obtained at 150x magnification. -1The peak intensity was calculated from the peak intensity due to the out-of-plane bending angle of the para-substituted benzene CH in the vicinity, using a calibration curve obtained from the peak intensities of standard samples with known mole percentages.

[0076] (2) Melting point of copolymer polyphenylene sulfide fiber (B): The melting point of the copolymerized polyphenylene sulfide fiber (B) was measured by heating a cut fiber of the obtained copolymerized polyphenylene sulfide fiber (B) from 50°C to 320°C at a rate of 16°C / min using a DSC ("Q1000" manufactured by TA Instruments Inc.), and measuring the peak-top temperature of the melting peak (endothermic peak) observed at a temperature of 200°C or higher in the obtained DSC curve. Three measurements were made per level, and the arithmetic average was calculated.

[0077] (3) Melting point of polyphenylene sulfide fiber nonwoven fabric (Tm-L): The melting point of the polyphenylene sulfide fiber nonwoven fabric was measured by heating the nonwoven fabric from 50°C to 320°C at a rate of 16°C / min using a DSC ("Q1000" manufactured by TA Instruments Inc.), and measuring the temperature of the lowest melting peak (endothermic peak) observed at temperatures of 200°C or higher on the DSC curve obtained. Three measurements were taken per level, and the arithmetic mean value was calculated.

[0078] (4) Weight: According to JISL1913 (2010) mass per unit area, three 10cm x 10cm sample pieces are taken, and the mass (g) of each is measured under standard conditions. The average value is calculated as 1m. 2 Mass per unit (g / m 2 ) is expressed as

[0079] (5) Thickness: According to JISP8118 (2014) Thickness: Method A, 20 test pieces of 10 cm x 10 cm were taken, and the thickness of each test piece was measured using a micrometer (Mitutoyo Corporation). The arithmetic mean value was taken as the thickness (μm) of the nonwoven fabric.

[0080] (6) Tear strength: According to JIS L1096 (2010) tear strength: Method D (pendulum method), 63mm x 100mm test pieces were measured in both the warp (direction of progress in the nonwoven fabric manufacturing process) and weft (width direction in the nonwoven fabric manufacturing process) directions of the nonwoven fabric. Using an Elmendorf-type tear tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.), a 20mm slit was made perpendicularly at the center of both grips of the test piece, and the strength when the remaining 43mm was torn in both the warp and weft directions was measured. Five measurements were taken in each warp and weft direction for each level, and the arithmetic mean was calculated to determine the tear strength (N) of the nonwoven fabric.

[0081] (7) Tensile strength: In accordance with JIS L1913 (2010) Tensile Strength and Elongation (Standard Time), tensile strength was measured in both the warp (direction of progress in the nonwoven fabric manufacturing process) and weft (cross direction in the nonwoven fabric manufacturing process) directions of the nonwoven fabric. Using a Tensilon (Orientec Co., Ltd. "UTM-III-100"), the maximum point load was measured under the conditions of a sample width of 15 mm, initial length of 20 mm, and a pulling speed of 20 mm / min. Five measurements were taken in each warp and weft direction for each level, and the arithmetic average was calculated to determine the tensile strength (N / 15 mm) of the nonwoven fabric.

[0082] (8) Breathability: JISL1913 (2010) Air permeability: According to the Frazier method, three 15cm x 15cm specimens were taken, and the air permeability of the three specimens was measured at a test pressure of 125Pa using an air permeability tester ("FX3300" manufactured by TEXTEST AG). The arithmetic mean value was calculated as the air permeability (cm 3 / cm 2 / s).

[0083] (9) Confirmation of the presence of polyphenylene sulfide fiber (A) and copolymer polyphenylene sulfide fiber (B) in nonwoven fabric, and measurement of the mole percentage of repeating units The surface of the nonwoven fabric sheet after the heat and pressure treatment was imaged at 150x magnification using a micro-infrared spectrophotometer (Agilent Technologies, Inc., "Cary 660"), and the remaining fiber shape was manually selected and processed using the active contour extraction processing mode. The processed image was subjected to infrared absorption spectroscopy at each pixel, and the 810cm -1 The presence of polyphenylene sulfide fiber (A) and copolymer polyphenylene sulfide fiber (B) in the nonwoven fabric was confirmed by the peak intensity derived from the out-of-plane bending vibration of the benzene para-substituted CH fiber, which appears near 810 cm. The mole percentage of the repeating units of polyphenylene sulfide fiber (A) and copolymer polyphenylene sulfide fiber (B) was determined from the infrared absorption spectrum in each region obtained at 150x magnification as described above. -1 The peak intensity due to the out-of-plane bending angle of the para-substituted benzene CH near 780cm -1 The peak intensity was calculated from the peak intensity due to the out-of-plane bending angle of the meta-substituted benzene CH in the vicinity, using a calibration curve obtained from the peak intensities of standard samples with known mole percentages.

[0084] [Reference example 1] (Polyphenylene sulfide fiber (A)) Polyphenylene sulfide consisting solely of p-phenylene sulfide units was vacuum dried at 150°C for 12 hours and then melt-spun at a spinning temperature of 330°C. In the melt spinning, polyphenylene sulfide was melt-extruded using a twin-screw extruder and metered using a gear pump while being fed into a spinning pack. Polyphenylene sulfide was then extruded from a spinneret with 36 holes, each with a hole diameter D of 0.23 mm and a land length L of 0.3 mm, at a single-hole throughput rate of 0.5 g / min. The spinneret used had straight inlet holes located directly above the nozzle holes, and the connection between the inlet holes and the nozzle holes was tapered. The polyphenylene sulfide extruded from the spinneret passed through a 50 mm heat-retaining zone and then air-cooled over 1.0 m using a uniflow cooling device at 25°C and an air velocity of 18 m / min. Thereafter, an oil was applied, and the 36 filaments were passed through a first godet roller and a second godet roller at 1000 m / min and wound up on a winder to obtain undrawn fibers.

[0085] The resulting undrawn fibers were taken up using a feed roller equipped with a nip roller. After tension was applied between the undrawn fibers and the first roller, they were heated and drawn six times around the first and second rollers heated to 90°C and 100°C, respectively. They were then heat-set by passing six times around the third roller heated to 230°C. The draw ratio was 3.85x. After the third roller, the fibers were taken up using an unheated roller at a peripheral speed of 400 m / min. Using a guide oiler, 2% by mass of dispersant was applied to the fibers. Subsequently, the fibers were crimped to 8 crimps / 25 mm and heat-set at 70°C for 1 minute using a setter. The resulting fibers were then cut with a cutter to obtain cut fibers with an average fiber length of 6 mm. The p-phenylene sulfide units in the polyphenylene sulfide fibers (A) thus obtained were 100.0% by mole as determined by a microinfrared spectrophotometer.

[0086] [Reference example 2] (Copolymer polyphenylene sulfide fiber (B)) Undrawn fibers were obtained in the same manner as in Reference Example 1, except that a copolymerized polyphenylene sulfide consisting of 90 mol% p-phenylene sulfide units and 10 mol% m-phenylene sulfide units was used. The obtained undrawn fibers were taken up using a feed roller equipped with a nip roller. After tension was applied between the undrawn fibers and the first roller, the fibers were heated and drawn six times around the first and second rollers heated to 90°C and 100°C, respectively. The fibers were then heat-set by passing them six times around a third roller heated to 150°C. The draw ratio was 3.85 times. After the third roller, the fibers were taken up using an unheated roller at a peripheral speed of 400 m / min. Using a guide oil supply, 2% by mass of a dispersant was applied to the fiber mass. Subsequently, the fibers were crimped to 8 peaks / 25 mm using a crimper, and then heat-set using a setter at 70°C for 1 minute. The obtained fibers were then cut with a cutter to obtain cut fibers with an average fiber length of 6 mm. The content of m-phenylene sulfide units in the polyphenylene sulfide fiber (B) thus obtained was 10.0% by mole as determined by a micro-infrared spectrophotometer.

[0087] [Reference example 3] (Unstretched polyphenylene sulfide fiber) Undrawn fibers were obtained in the same manner as in Reference Example 1. Using guide oiling, 2% by mass of a dispersant was applied to the obtained undrawn fibers, based on the fiber mass. Subsequently, after imparting 8 crimps / 25 mm using a crimper, the fibers were heat-set at 70°C for 1 minute using a setter. The obtained fibers were then cut with a cutter to obtain cut fibers with an average fiber length of 6 mm. The p-phenylene sulfide units of the undrawn polyphenylene sulfide fibers obtained in this manner were 100.0% by mole, as determined by a microscopic infrared spectrophotometer.

[0088] [Reference example 4] (Undrawn polyphenylene sulfide fibers with low mole percent of p-phenylene sulfide units) Undrawn fibers were obtained in the same manner as in Reference Example 1, except that polyphenylene sulfide containing 96 mol% p-phenylene sulfide units was used. A dispersant was applied to the obtained undrawn fibers using guide oiling in an amount of 2 mass% based on the fiber mass. Subsequently, the fibers were crimped to 8 crimps / 25 mm using a crimper, and then heat-set at 70°C for 1 minute using a setter. The obtained fibers were then cut with a cutter to obtain cut fibers with an average fiber length of 6 mm. The p-phenylene sulfide units of the undrawn polyphenylene sulfide fibers obtained in this manner were found to be 96.0% by mole% using a microscopic infrared spectrophotometer.

[0089] [Reference example 5] (Undrawn copolymer polyphenylene sulfide fiber) Undrawn fibers were obtained in the same manner as in Reference Example 2. The obtained undrawn fibers were treated in the same manner as in Reference Example 3 to obtain cut fibers of undrawn copolymerized polyphenylene sulfide fibers.

[0090] [Example 1] A dispersion with a fiber concentration of 0.07% by mass was prepared by dispersing 40% by mass of cut fibers of the polyphenylene sulfide fiber (A) obtained in Reference Example 1, 40% by mass of cut fibers of the copolymerized polyphenylene sulfide fiber (B) with a copolymerization molar ratio of 10% obtained in Reference Example 2, and 20% by mass of cut fibers of the unstretched polyphenylene sulfide fiber obtained in Reference Example 3 in water. This dispersion was used to prepare wet paper on a hand-made paper machine. The web obtained by dewatering with a roller was dried in a rotary dryer at 110°C for 70 seconds to obtain a dry web. Subsequently, one side of the web was heated and pressed at an iron roll surface temperature of 220°C, a linear pressure of 490 N / cm, and a roll rotation speed of 3 m / min. The other side was heated and pressed at an iron roll surface temperature of 220°C, a linear pressure of 490 N / cm, and a roll rotation speed of 3 m / min to obtain a nonwoven fabric. The evaluation results of the nonwoven fabric are shown in Table 1.

[0091] [Examples 2 to 7] A nonwoven fabric was obtained in the same manner as in Example 1, except that the mass ratio of the polyphenylene sulfide fiber (A), the copolymerized polyphenylene sulfide fiber (B), and the unstretched polyphenylene sulfide fiber was changed. The evaluation results of the nonwoven fabric are shown in Table 1.

[0092] [Comparative Example 1] A nonwoven fabric was obtained in the same manner as in Example 1, except that no unstretched polyphenylene sulfide fiber was used and the mixture was made of 50 mass% polyphenylene sulfide fiber (A) and 50 mass% copolymer polyphenylene sulfide fiber (B), although some breakage occurred during the drying step. The evaluation results of the nonwoven fabric are shown in Table 2.

[0093] Comparative Example 2 A nonwoven fabric was obtained in the same manner as in Example 1, except that copolymerized polyphenylene sulfide fiber (B) was not used and the polyphenylene sulfide fiber (A) was 50 mass % and unstretched polyphenylene sulfide fiber was 50 mass %. The evaluation results of the nonwoven fabric are shown in Table 2.

[0094] Comparative Example 3 A nonwoven fabric was obtained in the same manner as in Example 1, except that no polyphenylene sulfide fiber (A) was used and the mixture consisted of 50 mass% copolymerized polyphenylene sulfide fiber (B) and 50 mass% unstretched polyphenylene sulfide fiber. The evaluation results of the nonwoven fabric are shown in Table 2.

[0095] Comparative Example 4 Except for using only unstretched polyphenylene sulfide fibers, a nonwoven fabric was obtained in the same manner as in Example 1. The evaluation results of the nonwoven fabric are shown in Table 2.

[0096] [Examples 8 to 9, Comparative Examples 5 to 6] A nonwoven fabric was obtained in the same manner as in Example 1, except that the melting point was changed by changing the copolymerization mol % of the copolymerized polyphenylene sulfide fiber (B). The evaluation results of the nonwoven fabric are shown in Table 3.

[0097] [Example 10] A nonwoven fabric was obtained in the same manner as in Example 1, except that the unstretched polyphenylene sulfide fiber was changed to the unstretched polyphenylene sulfide fiber having a low molar percentage of p-phenylene sulfide units obtained in Reference Example 4. The evaluation results of the nonwoven fabric are shown in Table 3.

[0098] Comparative Example 7 A nonwoven fabric was obtained in the same manner as in Example 1, except that the unstretched polyphenylene sulfide fiber was changed to the unstretched copolymerized polyphenylene sulfide fiber obtained in Reference Example 5. The evaluation results of the nonwoven fabric are shown in Table 3.

[0099] [Table 1]

[0100] [Table 2]

[0101] [Table 3]

[0102] The polyphenylene sulfide fiber nonwoven fabrics obtained in Examples 1 to 10 contained polyphenylene sulfide fiber (A) and copolymerized polyphenylene sulfide fiber (B), and had polyphenylene sulfide fused portions (C), and nonwoven fabrics with high tear strength and tensile strength were obtained.

[0103] On the other hand, the polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 1 did not have polyphenylene sulfide fused portions (C) and had high tear strength, but a nonwoven fabric having sufficient tensile strength could not be obtained.

[0104] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 2 did not contain copolymerized polyphenylene sulfide fiber (B) and exhibited high tensile strength, but a nonwoven fabric having sufficient tear strength could not be obtained.

[0105] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 3 did not contain polyphenylene sulfide fibers (A) and had high tear strength, but a nonwoven fabric having sufficient tensile strength could not be obtained.

[0106] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 4 did not contain polyphenylene sulfide fiber (A) or copolymer polyphenylene sulfide fiber (B), and the tear strength of the obtained nonwoven fabric was insufficient. In addition, the tensile strength was lower than that of Comparative Example 2, which also had a weak tear strength.

[0107] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 5 had a low copolymerization molar ratio and contained copolymerized polyphenylene sulfide fiber (B) with a high melting point, and therefore had a high melting point (Tm-L). Although the nonwoven fabric exhibited high tensile strength, it was not possible to obtain a nonwoven fabric with sufficient tear strength.

[0108] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 6 contained copolymerized polyphenylene sulfide fiber (B) with a high copolymerization molar ratio and a low melting point, and therefore had a low melting point (Tm-L). Although the obtained nonwoven fabric exhibited high tensile strength, it was not possible to obtain a nonwoven fabric with sufficient tear strength.

[0109] The polyphenylene sulfide fiber nonwoven fabric obtained in Comparative Example 7 did not contain unstretched polyphenylene sulfide fibers that form the polyphenylene sulfide fused portions (C), and although it had high tear strength, it was not possible to obtain a nonwoven fabric with sufficient tensile strength.

Claims

1. A polyphenylene sulfide fiber nonwoven fabric comprising polyphenylene sulfide fibers (A), copolymerized polyphenylene sulfide fibers (B), and polyphenylene sulfide fusion-bonded portions (C), the nonwoven fabric having a melting point (Tm-L) of 240 to 270°C, the Tm-L being defined as the peak top of the lowest-temperature peak observed among the melting endothermic peaks obtained by heating the nonwoven fabric from 50°C at a rate of 16°C / min in a nitrogen atmosphere using a differential scanning calorimeter (DSC), and the polyphenylene sulfide fusion-bonded portions (C) having a molar percentage of p-phenylene sulfide units of 97.0 mol% or more.

2. 2. The polyphenylene sulfide fiber nonwoven fabric according to claim 1, wherein the copolymerized polyphenylene sulfide fibers (B) are copolymerized polyphenylene sulfide fibers comprising repeating units of p-phenylene sulfide units and m-phenylene sulfide units.

3. 3. The polyphenylene sulfide fiber nonwoven fabric according to claim 1, wherein the area ratio of the polyphenylene sulfide fused portions (C) is 5 to 50%.

4. The polyphenylene sulfide fiber nonwoven fabric according to any one of claims 1 to 3, having a tear strength of 0.200 to 10.0 N.

5. 5. The polyphenylene sulfide fiber nonwoven fabric according to claim 1, wherein the copolymerized polyphenylene sulfide fibers (B) contain 4.0 to 40.0 mol % of copolymerized units in p-phenylene sulfide.

6. A membrane comprising the polyphenylene sulfide fiber nonwoven fabric according to any one of claims 1 to 5.

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