Method for producing polyphenylene sulfide composite fiber and wet nonwoven fabric

Abstract

To provide polyphenylene sulfide composite fibers having favorable heat resistance and chemical resistance, also having a fine fiber diameter, high adhesion and mechanical strength, and excellent dimensional stability; a method of manufacturing the same; and a nonwoven fabric.SOLUTION: There are provided polyphenylene sulfide composite fibers, the composite fibers are obtained as core-sheath type composite fibers in which a component A is arranged in a core and a component B is arranged in a sheath when polyphenylene sulfide, in which 97 mol% or more of repeating units are composed of p-phenylene sulfide units, is the component A, and a copolymerized polyphenylene sulfide, in which 60 to 97 mol% of repeating units are composed of p-phenylene sulfide units and 3 to 40 mol% of repeating units are composed of m-phenylene sulfide units, is the component B, and the composite fibers have an average fiber length of 1 to 100 mm; a method of manufacturing the same; and a nonwoven fabric.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to polyphenylene sulfide composite fibers, a method for producing the same, and nonwoven fabrics.

Background Art

[0002] Since polyphenylene sulfide has high heat resistance, chemical resistance, electrical insulation, and flame retardancy, it is used in various applications that take advantage of these properties, such as bag filters, papermaking canvases, electrical insulating papers, battery separators, and various diaphragms.

[0003] On the other hand, in recent years, equipment that can be used in extreme environments and aerospace applications has attracted attention, and high environmental resistance is also required for motors and batteries used therein. Under such circumstances, the demand for electrical insulating papers, battery separators, and various diaphragms that can be used in high-temperature environments has been increasing, and nonwoven fabrics containing polyphenylene sulfide fibers with excellent heat resistance and chemical resistance have attracted attention.

[0004] However, in the case of a nonwoven fabric composed only of stretched polyphenylene sulfide fibers, there is a problem that a nonwoven fabric having mechanical properties that can withstand practical use cannot be obtained because the adhesiveness between the fibers is low. Therefore, in order to solve the above problems, various proposals have been made regarding polyphenylene sulfide fibers and nonwoven fabrics containing them.

[0005] For example, a polyphenylene sulfide nonwoven fabric composed of stretched polyphenylene sulfide fibers and unstretched polyphenylene sulfide fibers has been proposed (see Patent Document 1). According to this technique, since the unstretched polyphenylene sulfide acts as a binder during thermal adhesion, a polyphenylene sulfide nonwoven fabric having high mechanical properties can be obtained.

[0006] In addition, low heat shrinkage binder fibers that suppress heat shrinkage in the drying process have been proposed by pre-heat-treating unstretched polyphenylene sulfide fibers at a temperature below the crystallization temperature (see Patent Document 2). According to this technique, in addition to reducing wrinkles and swelling of the nonwoven fabric generated in the drying process, the resulting nonwoven fabric has excellent thermal dimensional stability.

[0007] Furthermore, binder fibers with a fine fiber diameter and excellent adhesiveness have been proposed, which are obtained by stretching unstretched polyphenylene sulfide fibers in an ethylene glycol bath at 110 °C to reduce the fiber diameter (see Patent Document 3). According to this technique, the fiber diameter can be reduced while maintaining a low molecular chain orientation, and a homogeneous polyphenylene sulfide nonwoven fabric with a small CV value of the fiber diameter in the wet nonwoven fabric can be obtained even with a low basis weight.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in the technique disclosed in Patent Document 1, although the unstretched polyphenylene sulfide fibers used as binder fibers contribute to adhesion and result in a nonwoven fabric with high mechanical properties, the heat shrinkage rate of the unstretched polyphenylene sulfide fibers is extremely high, so the fibers shrink in the drying process, causing wrinkles and swelling in the nonwoven fabric. Furthermore, there is also a problem that the presence of unstretched polyphenylene sulfide fibers with a larger fiber diameter than the skeletal fibers in the stretched polyphenylene sulfide fibers serving as the skeletal fibers causes uneven basis weight in the nonwoven fabric and impairs the homogeneity of the nonwoven fabric.

[0010] In addition, in the technology disclosed in Patent Document 2, although heat shrinkage in the drying process can be suppressed by heat-treating the unstretched polyphenylene sulfide fiber, heat crystallization proceeds due to the heat treatment, and the adhesiveness as a binder fiber decreases, resulting in problems such as a decrease in the mechanical properties of the nonwoven fabric. Also, similar to Patent Document 1, since it is in an unstretched state, the fiber diameter is thick, which causes unevenness in the basis weight within the nonwoven fabric and impairs the uniformity of the nonwoven fabric.

[0011] In addition, in the technology disclosed in Patent Document 3, by stretching the unstretched polyphenylene sulfide fiber in an ethylene glycol bath at 110°C, fibers with a low degree of orientation and a fine fiber diameter can be obtained. However, since the above method involves stretching without orientation crystallization, the heat shrinkage rate of the obtained fibers is extremely high, and the fibers shrink in the drying process, causing wrinkles and bulges in the nonwoven fabric. Also, since the fibers obtained by the above method have low mechanical strength, when the fibers are used as binder fibers, there is also a problem that the mechanical properties of the nonwoven fabric deteriorate.

[0012] Thus, polyphenylene sulfide fibers and nonwoven fabrics containing the same, which are suitable fibers for constituting nonwoven fabrics, have a fine fiber diameter, high adhesiveness and mechanical strength, and excellent dimensional stability, have not been reported so far.

Means for Solving the Problems

[0013] As a result of the inventors' further study, when using a polyphenylene sulfide resin composed only of p-phenylene sulfide units, although the dimensional stability is improved by crystallizing the obtained fibers by heat treatment, at the same time, a problem occurs in that the heat adhesiveness decreases due to the reduction of the amorphous part, and it was confirmed that it is difficult to achieve both dimensional stability and heat adhesiveness.

[0014] Therefore, as a result of intensive studies by the present inventors, a core-sheath type composite cross-section is adopted in which a copolymerized polyphenylene sulfide resin with low crystallinity is used for the sheath part and a polyphenylene sulfide resin with excellent mechanical properties is used for the core part. After spinning, by performing stretching and heat setting under specific conditions, a polyphenylene sulfide composite fiber is obtained which not only has excellent heat resistance and chemical resistance, but also has a fine fiber diameter, high adhesiveness and mechanical strength, and excellent dimensional stability. It has been found that a nonwoven fabric containing the same has good mechanical properties.

[0015] That is, the present invention aims to solve the above-mentioned problems. The polyphenylene sulfide composite fiber of the present invention uses a polyphenylene sulfide in which 97 mol% or more of the repeating units are p-phenylene sulfide units as component A, and 60 to 97 mol% of the repeating units are p-phenylene sulfide units and 3 to 40 mol% are m-phenylene sulfide units. The copolymerized polyphenylene sulfide is used as component B, and it is a core-sheath type composite fiber in which component A is arranged in the core part and component B is arranged in the sheath part, and the average fiber length is 1 to 100 mm. For papermaking It is a polyphenylene sulfide composite fiber.

[0016] The For papermaking According to a preferred embodiment of the polyphenylene sulfide composite fiber of the present invention, the area ratio of the core part in the cross-section of the core-sheath type composite fiber is 75 to 95%.

[0017] The For papermaking According to a preferred embodiment of the polyphenylene sulfide composite fiber of the present invention, the birefringence of the polyphenylene sulfide composite fiber is 0.18 to 0.40.

[0018] The For papermaking According to a preferred embodiment of the polyphenylene sulfide composite fiber of the present invention, the average fiber diameter of the polyphenylene sulfide composite fiber is 25 μm or less, the strength is 2.0 cN / dtex or more, and the elongation is 50% or less.

[0019] The polyphenylene sulfide composite fiber of the present invention is characterized in that the melt mass flow rate MFR(A) of the component A used as a raw material is 50 to 250 g / 10 min, and the melt mass flow rate MFR(B) of the component B is 10 g / 10 minutes or more greater than MFR(A). It is produced by a method characterized by this.

[0020] The nonwoven fabric of the present invention is characterized by containing any of the above polyphenylene sulfide composite fibers Wet type and is a nonwoven fabric.

Effects of the Invention

[0021] The polyphenylene sulfide composite fiber of the present invention is a core-sheath type composite fiber in which the core part is polyphenylene sulfide in which 97 mol% or more of the repeating units are p-phenylene sulfide units (hereinafter, may be abbreviated as polyphenylene sulfide (A)), and the sheath part is a copolymerized polyphenylene sulfide in which 60 to 97 mol% of the repeating units are p-phenylene sulfide units and 3 to 40 mol% are m-phenylene sulfide units (hereinafter, may be abbreviated as copolymerized polyphenylene sulfide (B)). By making it like this, it is possible to provide a polyphenylene sulfide composite fiber that not only has excellent heat resistance and chemical resistance, but also has a fine fiber diameter, high adhesiveness and mechanical strength, and excellent dimensional stability, and a nonwoven fabric having good mechanical properties.

Embodiments for Carrying Out the Invention

[0022] The polyphenylene sulfide composite fiber of the present invention is a core-sheath type composite fiber in which polyphenylene sulfide in which 97 mol% or more of the repeating units are p-phenylene sulfide units (hereinafter, may be abbreviated as polyphenylene sulfide (A)) is used as component A, and copolymerized polyphenylene sulfide in which 60 to 97 mol% of the repeating units are p-phenylene sulfide units and 3 to 40 mol% are m-phenylene sulfide units (hereinafter, may be abbreviated as copolymerized polyphenylene sulfide (B)) is used as component B, with component A in the core part and component B in the sheath part, and the average fiber length is 1 to 100 mm. The polyphenylene sulfide composite fiber will be described in detail below.

[0023] [Polyphenylene Sulfide (A)] The polyphenylene sulfide (A) used in the present invention is importantly composed of p-phenylene sulfide units represented by the structural formula (1) in an amount of 97 mol% or more of the repeating units. By setting the p-phenylene sulfide units to 97 mol% or more, preferably 98 mol% or more of the repeating units, not only excellent chemical resistance and heat resistance are obtained, but also fibers excellent in drawability and mechanical properties are obtained. Examples of the remaining repeating units other than the above p-phenylene sulfide units include aromatic sulfides such as triphenylene sulfide and biphenylene sulfide, or their alkyl-substituted products, halogen-substituted products, and the like.

[0024] [Chemical formula]

[0025] Other thermoplastic resins can be blended with the polyphenylene sulfide (A) used in the present invention as long as the effects of the present invention are not impaired. Examples of the thermoplastic resin include copolymerized polyphenylene sulfide copolymerized with m-phenylene sulfide units, polyetherimide, polyethersulfone, polysulfone, polyphenylene ether, polyester, polyarylate, polyamide, polyamideimide, polycarbonate, polyolefin, and polyetheretherketone. The mass ratio of the blendable thermoplastic resin is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less based on the blended composition in order to sufficiently exhibit the characteristics of the polyphenylene sulfide (A) of the present invention. Here, the blend refers to the melt mixing and kneading of two or more components of resin, which is different from the composite technology of arranging two or more components of resin at an arbitrary position in the fiber cross section during spinning.

[0026] In the polyphenylene sulfide (A) used in the present invention, various metal oxides, inorganic substances such as kaolin and silica, pigments for coloring, matting agents, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers, crystal nucleating agents, fluorescent brighteners, end group blocking agents, compatibilizers and other various additives can be added as long as the effects of the present invention are not impaired.

[0027] The polyphenylene sulfide (A) used in the present invention preferably has a melting point (hereinafter sometimes abbreviated as Tm(A)) of 260 to 300°C. By making Tm(A) preferably 260°C or higher, more preferably 270°C or higher, a polyphenylene sulfide composite fiber having excellent heat resistance can be obtained. Also, by making Tm(A) preferably 300°C or lower, more preferably 290°C or lower, it becomes easy to set the temperature conditions during fiber production. Note that Tm(A) refers to the value measured by the method described in item B of the Examples section.

[0028] [Copolymerized polyphenylene sulfide (B)] It is important that 60 to 97 mol% of the repeating units of the copolymerized polyphenylene sulfide (B) used in the present invention are composed of p-phenylene sulfide units represented by the structural formula (1). By making the p-phenylene sulfide units 60 mol% or more, preferably 70 mol% or more, a polyphenylene sulfide composite fiber having excellent heat resistance and chemical resistance can be obtained. Also, by making the p-phenylene sulfide units 97 mol% or less, preferably 95 mol% or less, the crystallinity of the copolymerized polyphenylene sulfide decreases, resulting in a polyphenylene sulfide composite fiber having excellent adhesiveness.

[0029] In addition, for the copolymerized polyphenylene sulfide (B) used in the present invention, it is important that 3 to 40 mol% of the repeating units consist of m-phenylene sulfide units represented by the structural formula (2). By setting the m-phenylene sulfide units to 3 mol% or more, preferably 5 mol% or more, the crystallinity of the copolymerized polyphenylene sulfide decreases, resulting in a polyphenylene sulfide composite fiber with excellent adhesiveness. Also, by setting the m-phenylene sulfide units to 40 mol% or less, preferably 30 mol% or less, a polyphenylene sulfide composite fiber having excellent heat resistance and chemical resistance is obtained.

[0030]

Chemical formula

[0031] Note that the molar fractions of the p-phenylene sulfide units and m-phenylene sulfide units in the copolymerized polyphenylene sulfide (B) used in the present invention can be measured by infrared spectroscopic analysis.

[0032] Examples of the copolymerization mode of the copolymerized polyphenylene sulfide (B) used in the present invention include random copolymerization and block copolymerization. From the viewpoint of easy control of the melting point, random copolymerization is preferably used.

[0033] The copolymerized polyphenylene sulfide (B) used in the present invention can contain other copolymerization components as long as the effects of the present invention are not impaired. Examples of other copolymerization components include aromatic sulfides such as triphenylene sulfide and biphenylene sulfide, or their alkyl-substituted products and halogen-substituted products. The mass ratio of other copolymerization components is preferably 5% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less in order to sufficiently exhibit the characteristics of the copolymerized polyphenylene sulfide (B) of the present invention.

[0034] In the copolymerized polyphenylene sulfide (B) used in the present invention, a thermoplastic resin can be blended within a range that does not impair the effects of the present invention. Examples of the thermoplastic resin include various thermoplastic resins such as polyphenylene sulfide consisting only of p-phenylene sulfide units as repeating units, polyetherimide, polyethersulfone, polysulfone, polyphenylene ether, polyester, polyarylate, polyamide, polyamideimide, polycarbonate, polyolefin, and polyetheretherketone. The mass ratio of the blendable thermoplastic resin is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less based on the blended composition in order to sufficiently exhibit the characteristics of the copolymerized polyphenylene sulfide (B) of the present invention. Here, the blend refers to the melt mixing and kneading of two or more resins, which is different from the composite technology of arranging two or more resins at arbitrary positions in the fiber cross-section during spinning.

[0035] In the copolymerized polyphenylene sulfide (B) used in the present invention, various additives such as various metal oxides, kaolin, silica and other inorganic substances, pigments for coloring, matting agents, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers, crystal nucleating agents, fluorescent brighteners, end group blocking agents, compatibilizers, etc. can be added within a range that does not impair the effects of the present invention.

[0036] The copolymerized polyphenylene sulfide (B) used in the present invention preferably has a melting point (hereinafter sometimes abbreviated as Tm(B)) of 200 to 270°C. By setting Tm(B) preferably at 200°C or higher, more preferably 210°C or higher, a polyphenylene sulfide composite fiber excellent in heat resistance can be obtained. Also, by setting Tm(B) preferably at 270°C or lower, more preferably 260°C or lower, and even more preferably 255°C or lower, a polyphenylene sulfide composite fiber having high adhesiveness can be obtained. Here, Tm(B) refers to the value measured by the method described in item B of the Examples section.

[0037] [Polyphenylene Sulfide Composite Fiber] The polyphenylene sulfide composite fiber of the present invention is preferably a core-sheath type composite fiber in which polyphenylene sulfide (A) forms the core part and copolymerized polyphenylene sulfide (B) forms the sheath part. By using a core-sheath type composite fiber, the polyphenylene sulfide (A) in the core part serves as the skeleton part, thereby exhibiting excellent mechanical strength, and the copolymerized polyphenylene sulfide (B) in the sheath part serves as the thermal adhesion part, resulting in a polyphenylene sulfide composite fiber having high adhesiveness.

[0038] The cross-sectional shape of the polyphenylene sulfide composite fiber of the present invention is not particularly limited and can be any shape such as a circular cross-section, a multi-lobed cross-section such as a triangular cross-section, a flat cross-section, an S-shaped cross-section, a cross-section at ten o'clock, or a hollow cross-section. However, when it is necessary to disperse short fibers in a medium for papermaking applications, resin reinforcement applications, etc., a circular cross-section is preferred from the viewpoint of fiber dispersibility.

[0039] The polyphenylene sulfide composite fiber of the present invention is a short fiber, and it is important that the average fiber length is 1 to 100 mm. By setting the average fiber length to 1 mm or more, preferably 3 mm or more, more preferably 4 mm or more, the fibers are moderately entangled during nonwoven processing, and the resulting nonwoven fabric has excellent mechanical strength. Also, by setting the average fiber length to 100 mm or less, preferably 60 mm or less, more preferably 30 mm or less, unevenness in basis weight due to excessive entanglement during nonwoven processing can be prevented, and a nonwoven fabric with few wrinkles and uniform quality can be obtained. The average fiber length in the present invention refers to the value measured by the method described in column C of the Examples section.

[0040] In the cross-section of the polyphenylene sulfide composite fiber of the present invention, the area ratio of the core part to the total cross-sectional area is preferably 75 to 95%. By making the area ratio of the core part preferably 75% or more, more preferably 85% or more, the ratio of the core part serving as the skeleton part becomes high, resulting in a polyphenylene sulfide composite fiber excellent in dimensional stability. Further, by making the area ratio of the core part preferably 95% or less, more preferably 92% or less, exposure of the core component to the fiber surface can be prevented, and a polyphenylene sulfide composite fiber having high adhesiveness can be obtained. The area ratio of the core part in the present invention refers to the value measured by the method described in item E of the Examples section.

[0041] The birefringence of the polyphenylene sulfide composite fiber of the present invention is preferably 0.18 to 0.40. By making the birefringence preferably 0.18 or more, more preferably 0.22 or more, the fiber becomes a fiber in which the molecular chains are highly oriented, resulting in a polyphenylene sulfide composite fiber excellent in mechanical properties. Further, by making the birefringence preferably 0.40 or less, more preferably 0.30 or less, excessive orientation crystallization of the copolymerized polyphenylene sulfide (B) in the sheath part can be prevented, and a polyphenylene sulfide composite fiber having high adhesiveness can be obtained. The birefringence of the fiber in the present invention refers to the value measured by the method described in item F of the Examples section.

[0042] The average fiber diameter of the polyphenylene sulfide composite fiber of the present invention is preferably 25 μm or less. By making the average fiber diameter preferably 25 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less, uneven cooling during melt spinning is less likely to occur, resulting in excellent spinnability and a polyphenylene sulfide composite fiber having good fiber diameter uniformity. The average fiber diameter in the present invention refers to the value measured by the method described in item D of the Examples section.

[0043] The polyphenylene sulfide fiber of the present invention preferably has a strength of 2.0 cN / dtex or more. By setting the strength preferably at 2.0 cN / dtex or more, more preferably 3.0 cN / dtex or more, the handleability during nonwoven processing is improved, and the mechanical strength of the obtained nonwoven fabric is improved. Further, the upper limit of the strength is not particularly limited, but the industrially achievable upper limit is about 7.0 cN / dtex.

[0044] The polyphenylene sulfide composite fiber of the present invention preferably has an elongation of 50% or less. By setting the elongation preferably at 50% or less, more preferably 40% or less, the fiber has a sufficiently high molecular orientation degree, becomes less likely to undergo plastic deformation (drawing), and the handleability during nonwoven processing is improved. Further, the lower limit of the elongation is not particularly limited, but the industrially achievable lower limit is about 8%. In addition, the strength and elongation in the present invention refer to the values measured by the method described in Item G of the Examples section.

[0045] The polyphenylene sulfide composite fiber of the present invention not only has excellent heat resistance and chemical resistance, but also has a fine fiber diameter, high adhesiveness and mechanical strength, and excellent dimensional stability. Taking advantage of these characteristics, it can be suitably used for various applications such as filter applications such as bag filters, chemical liquid filters, food filters, chemical filters, oil filters, engine oil filters, air purification filters, paper applications such as electrical insulating paper, heat-resistant work clothing applications such as fire-fighting suits, safety clothing, laboratory work clothes, thermal insulation clothing, flame-retardant clothing, highly visible textiles, felts for papermaking, sewing threads, heat-resistant felts, release materials, dryer canvases for papermaking, separators for batteries, separators for electrodes, various diaphragms, heart patches, artificial blood vessels, artificial skin, substrates for printed circuit boards, copy rolling cleaners, ion exchange substrates, oil retaining materials, heat insulating materials, cushioning materials, brushes, net conveyors, motor binding threads, motor binder tapes, etc. However, it is particularly preferably used in the form of a nonwoven fabric, and is suitably used for paper applications such as electrical insulating paper, separator applications for batteries, and various diaphragm applications.

[0046] [Nonwoven fabric] The nonwoven fabric of the present invention is a nonwoven fabric containing the polyphenylene sulfide composite fiber of the present invention. By containing the polyphenylene sulfide composite fiber of the present invention, a nonwoven fabric having good heat resistance and chemical resistance can be obtained. Further, since it has a structure in which a binder portion having excellent adhesiveness is uniformly arranged around a skeleton portion having excellent mechanical strength, a nonwoven fabric with less unevenness in basis weight and uniform can be obtained. Furthermore, by reducing the unevenness in adhesion between fibers, a nonwoven fabric having good mechanical properties can be obtained.

[0047] The nonwoven fabric of the present invention preferably has a basis weight of 3 to 100 g / m 2 . By setting the basis weight to preferably 3 g / m 2 or more, more preferably 5 g / m 2 or more, and even more preferably 10 g / m 2 or more, it becomes difficult for paper breakage to occur during the papermaking process, and the process passability is improved. Further, by setting the basis weight to preferably 100 g / m 2 or less, more preferably 80 g / m 2 or less, and even more preferably 60 g / m 2 or less, a lightweight and flexible nonwoven fabric can be obtained. Note that the basis weight of the nonwoven fabric in the present invention refers to the value measured by the method described in Item H of the Examples section.

[0048] The nonwoven fabric of the present invention preferably has a tensile strength of 5 to 300 N / 15 mm. By setting the tensile strength to preferably 5 N / 15 mm or more, more preferably 10 N / 15 mm or more, and even more preferably 15 N / 15 mm or more, it becomes difficult for paper breakage to occur during the papermaking process. Further, even when tensile stress is applied during subsequent processes or in use, the nonwoven fabric is less likely to tear. Also, by setting the tensile strength to preferably 300 N / 15 mm or less, more preferably 250 N / 15 mm or less, and even more preferably 200 N / 15 mm or less, the flexibility of the nonwoven fabric can be maintained, and a nonwoven fabric with excellent assemblability when used for diaphragms or the like can be obtained. Note that the tensile strength of the nonwoven fabric in the present invention refers to the value measured by the method described in Item J of the Examples section.

[0049] The non-woven fabric of the present invention preferably has a tear strength of 20 to 1000 gf. By setting the tear strength to preferably 20 gf or more, more preferably 50 gf or more, and even more preferably 100 gf or more, even when cracks occur in the non-woven fabric during the process, the cracks are less likely to propagate throughout the non-woven fabric, resulting in a non-woven fabric that is less likely to tear. Also, by setting the tear strength to preferably 1000 gf or less, more preferably 900 gf or less, and even more preferably 800 gf or less, problems are less likely to occur during the cutting of the non-woven fabric. Note that the tear strength of the non-woven fabric in the present invention refers to the value measured by the method described in Item K of the Examples section.

[0050] The non-woven fabric of the present invention has an air permeability of 0.01 cc / cm 2 / s to 300 cc / cm 2 / s, which is preferable. By setting the air permeability to preferably 0.01 cc / cm 2 / s or more, more preferably 0.10 cc / cm 2 / s or more, even more preferably 1.0 cc / cm 2 / s or more, the permeability of ions and the like when used in a separator or the like is improved. Also, by setting the air permeability to preferably 300 cc / cm 2 / s or less, more preferably 250 cc / cm 2 / s or less, even more preferably 200 cc / cm 2 / s or less, the non-woven fabric will have sufficient mechanical strength, making it less likely for paper breakage to occur during the papermaking process and improving the process passability. Also, when used in a separator or the like, tearing and cracking during assembly are less likely to occur. Note that the air permeability of the non-woven fabric in the present invention refers to the value measured by the method described in Item L of the Examples section.

[0051] The non-woven fabric of the present invention preferably has a thickness of 5 μm to 300 μm. By setting the thickness to preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, paper breakage during the papermaking process is less likely to occur, and the process throughput is improved. Further, by setting the thickness to preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less, the permeability of ions and the like when used for a separator or the like is improved. Further, when mounted on a device as a separator or the like, the occupied volume of the non-woven fabric is reduced, so that the device can be miniaturized and lightened. Note that the thickness of the non-woven fabric in the present invention refers to the value measured by the method described in item M of the Examples section.

[0052] [Method for Producing Polyphenylene Sulfide Composite Fiber] The method for producing a polyphenylene sulfide composite fiber of the present invention is characterized in that, with respect to the polyphenylene sulfide (A) and the copolymerized polyphenylene sulfide (B) used as raw materials, the melt mass flow rate of the polyphenylene sulfide (A) (hereinafter, may be abbreviated as MFR(A)) is 50 to 250 g / 10 min, and the melt mass flow rate of the copolymerized polyphenylene sulfide (B) (hereinafter, may be abbreviated as MFR(B)) is larger than MFR(A). Hereinafter, the method for producing a polyphenylene sulfide composite fiber of the present invention will be described in detail.

[0053] As the method for producing a polyphenylene sulfide composite fiber of the present invention, it is preferable to use polyphenylene sulfide (A) having an MFR(A) of 50 to 250 g / 10 min. By setting MFR(A) to 50 g / 10 min or more, preferably 80 g / 10 min or more, and more preferably 100 g / 10 min or more, the fluidity during melting increases, so that the spinnability is improved, and a polyphenylene sulfide composite fiber excellent in fiber diameter uniformity is obtained. Further, by setting MFR(A) to 250 g / 10 min or less, preferably 230 g / 10 min or less, and more preferably 200 g / 10 min or less, a polyphenylene sulfide composite fiber having good mechanical strength is obtained. Note that the melt mass flow rate in the present invention refers to the value measured by the method described in item A of the Examples section.

[0054] As a method for producing the polyphenylene sulfide composite fiber of the present invention, it is preferable to use a copolymerized polyphenylene sulfide (B) having an MFR (B) larger than MFR (A). As a result of further study by the present inventors, it was confirmed that by using a copolymerized polyphenylene sulfide (B) having an MFR (B) larger than MFR (A), a polyphenylene sulfide composite fiber having excellent mechanical strength can be obtained. This is because, since MFR (B) is larger than MFR (A), it is possible to suppress the generation of an inner / outer layer orientation difference due to the high orientation of molecular chains on the fiber surface that occurs during the cooling process during spinning, and uniform drawing becomes possible in the subsequent drawing process. Furthermore, as a result of intensive study by the present inventors, it was found that by using a copolymerized polyphenylene sulfide (B) having an MFR (B) larger than MFR (A), a fiber excellent in adhesiveness can be obtained. This is because, in the fiber manufacturing process such as spinning and drawing, excessive orientation crystallization can be suppressed by reducing the spinning stress burden on the copolymerized polyphenylene sulfide (B) that becomes the sheath portion. As a result, the ratio of the amorphous portion contributing to thermal adhesion can be increased, resulting in a fiber excellent in adhesiveness. Note that MFR (B) is preferably 5 g / 10 min or more larger than MFR (A), and more preferably 10 g / 10 min or more larger.

[0055] In the method for producing the polyphenylene sulfide composite fiber of the present invention, it is preferable to use a copolymerized polyphenylene sulfide (B) having an MFR (B) of 60 to 350 g / 10 min. By setting MFR (B) to preferably 60 g / 10 min or more, more preferably 80 g / 10 min or more, and even more preferably 100 g / 10 min or more, the fluidity during melting increases, so the spinnability is improved, and a polyphenylene sulfide composite fiber excellent in fiber diameter uniformity is obtained. Also, by setting MFR (B) to preferably 350 g / 10 min or less, more preferably 300 g / 10 min or less, and even more preferably 280 g / 10 min or less, a polyphenylene sulfide composite fiber having good mechanical strength is obtained.

[0056] As a method for producing the polyphenylene sulfide (A) used in the present invention, for example, a method of reacting an alkali metal sulfide such as sodium sulfide with p-dichlorobenzene in an organic amide solvent such as N-methyl-2-pyrrolidone to obtain a polyphenylene sulfide can be mentioned.

[0057] As a method for producing the copolymerized polyphenylene sulfide (B) used in the present invention, for example, a method of reacting an alkali metal sulfide such as sodium sulfide with p-dichlorobenzene and m-dichlorobenzene in an organic amide solvent such as N-methyl-2-pyrrolidone to obtain a polyphenylene sulfide can be mentioned.

[0058] The polyphenylene sulfide (A) and the copolymerized polyphenylene sulfide (B) used in the present invention are preferably dried before being subjected to melt spinning for the purpose of preventing moisture from mixing in and removing oligomers, which is preferable for improving the yarn manufacturing property. As the drying conditions, vacuum drying at 100 to 200°C for 1 to 24 hours is usually used.

[0059] In melt spinning, a melt spinning method using an extruder such as a pressure melt type, a single-screw or twin-screw extruder type can be applied. The extruded polyphenylene sulfide passes through a pipe, is metered by a metering device such as a gear pump, and after passing through a filter for removing foreign matters, it is led to each spinneret. Each polymer led to the spinneret is shape-regulated so that the polyphenylene sulfide (A) is arranged in the core part and the copolymerized polyphenylene sulfide (B) is arranged in the sheath part in the spinneret and is merged, and is discharged from the die hole as a core-sheath type composite fiber. At this time, the temperature from the polymer pipe to the spinneret (spinning temperature) is preferably 280°C or higher in order to enhance fluidity, and preferably 380°C or lower in order to suppress thermal decomposition of the polymer.

[0060] The spinneret used for extrusion preferably has a pore diameter D of the die hole of 0.1 to 0.6 mm, and the L / D defined as the quotient of the land length L of the die hole (the length of the straight pipe part having the same diameter as the pore diameter of the die hole) divided by the pore diameter is preferably 1 to 10.

[0061] The polyphenylene sulfide composite fibers discharged from the spinneret holes are cooled and solidified by blowing cooling air (air). The temperature of the cooling air can be determined in balance with the cooling air velocity from the viewpoint of cooling efficiency, but a preferred embodiment is that it is 30°C or lower. By preferably setting the temperature of the cooling air to 30°C or lower, the solidification behavior due to cooling becomes stable, and polyphenylene sulfide composite fibers with high fiber diameter uniformity are obtained.

[0062] Also, the cooling air is preferably flowed in a direction substantially perpendicular to the undrawn fibers discharged from the spinneret. At this time, the velocity of the cooling air is preferably 10 m / min or more from the viewpoints of cooling efficiency and fiber diameter uniformity, and preferably 100 m / min or less from the viewpoint of spinning stability.

[0063] 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 for improving fiber diameter uniformity and productivity, and preferably 2000 m / min or less to avoid thread breakage.

[0064] The undrawn fibers thus obtained are once wound up, or continuously after being taken up, and are subjected to a drawing process. Drawing is performed by running the fibers through 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 obtained undrawn fibers. 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.

[0065] The draw ratio in the drawing process is preferably 2.0 times or more. By setting the draw ratio preferably at 2.0 times or more, more preferably 2.5 times or more, fibers with highly oriented molecular chains are obtained, resulting in polyphenylene sulfide composite fibers with excellent mechanical properties. Although the upper limit of the draw ratio is not particularly limited, the industrially achievable upper limit is about 8.0 times.

[0066] The temperature of the heated first roller or heating device in the drawing process is preferably 80 to 130°C. By setting the temperature of the first roller or heating device at 80°C or more, the drawing point is fixed and stable drawing becomes possible. Also, by setting the temperature of the first roller or heating device at 130°C or less, thread breakage during the process can be suppressed and the process throughput is improved. Further, from the viewpoint of fixing the drawing point, the temperature of the second roller is preferably set at +20°C or less than the temperature of the heated first roller or heating device.

[0067] Furthermore, after passing through the second roller, the drawn fiber may be heated by a heated third roller or a heating device provided between the second roller and the third roller to perform heat setting. When performing heat setting, the heat setting temperature is preferably 210°C or less. By setting the heat setting temperature preferably at 210°C or less, more preferably 190°C or less, and even more preferably 150°C or less, excessive heat crystallization is suppressed, resulting in polyphenylene sulfide composite fibers having high adhesiveness.

[0068] It is preferable to apply a papermaking dispersant or the like to the polyphenylene sulfide composite fiber of the present invention as needed. The application of the dispersant is usually carried out in a tow state using a kiss roller or guide oiling. The above-mentioned papermaking dispersant adhesion rate is preferably 1 to 6% by mass based on the fiber mass. By setting the dispersant adhesion rate preferably at 1% by mass or more, more preferably 2% by mass or more, the dispersibility of the fibers in the dispersion liquid, which is the precursor of the non-woven fabric, is improved, resulting in a homogeneous non-woven fabric. Also, by setting the dispersant adhesion rate preferably at 6% by mass or less, more preferably 5% by mass or less, the process throughput during non-woven fabric processing is improved.

[0069] Next, the polyphenylene sulfide composite fiber of the present invention may be crimped by a crimper and heat-fixed by a setter. By imparting crimps, the fibers are entangled with each other, increasing the adhesion area between the fibers and resulting in a non-woven fabric with excellent mechanical strength.

[0070] The number of crimps in the above crimping is preferably 2 to 15 crests / 25 mm. By preferably setting the number of crimps to 2 crests / 25 mm or more, the fibers are easily entangled with each other, resulting in a non-woven fabric with excellent mechanical strength. Also, by preferably setting the number of crimps to 15 crests / 25 mm or less, the dispersibility of the fibers in the dispersion liquid is improved, resulting in a homogeneous non-woven fabric.

[0071] Also, the heat-fixing temperature by the setter is preferably 80°C or higher and 100°C or lower. By preferably setting the heat-fixing temperature to 80°C or higher, the crimped form can be fixed, and by preferably setting the heat-fixing temperature to 100°C or lower, it is possible to prevent the adhesiveness from being impaired due to excessive heat crystallization.

[0072] Next, the obtained polyphenylene sulfide composite fiber is cut to a predetermined length by a cutter to obtain cut fibers.

[0073] [Method for manufacturing non-woven fabric] The method for manufacturing the non-woven fabric of the present invention will be described in detail below.

[0074] The papermaking liquid for manufacturing the non-woven fabric of the present invention is obtained by dispersing the cut fibers obtained as described above alone or mixed with cut fibers of other fibers at an arbitrary ratio in water. Here, the cut fibers of other fibers are preferably cut fibers of heat-resistant fibers such as polyphenylene sulfone fibers, meta-aramid fibers, and fluorine fibers from the viewpoint of obtaining a paper with excellent heat resistance. By supplying this papermaking liquid to a paper machine, a non-woven fabric can be obtained.

[0075] The fiber concentration of the papermaking liquid is preferably 0.05 to 5% by mass. When the fiber concentration is less than 0.05% by mass, the production efficiency decreases and the load on the dehydration process increases. Conversely, when it exceeds 5% by mass, the dispersion state of the fibers deteriorates and it becomes difficult to obtain a uniform nonwoven fabric.

[0076] To the papermaking liquid, a dispersant composed of surfactants such as cationic, anionic, and nonionic surfactants to improve water dispersibility, an oil agent, a binder to increase the viscosity of the dispersion liquid to prevent aggregation of the papermaking liquid, and an antifoaming agent to suppress the generation of foam may be added.

[0077] The papermaking liquid prepared as described above is used to make paper using a papermaking machine such as a cylinder-type, fourdrinier-type, inclined wire-type papermaking machine or a hand papermaking machine, and this is dried using a Yankee dryer, a rotary dryer, etc., to remove moisture and temporarily bond the fibers together to obtain a dry web.

[0078] The drying temperature is preferably 80 to 150°C. Preferably, when it is 80°C or higher, the temporary bonding between the fibers proceeds sufficiently and a dry web having sufficient mechanical properties is obtained. Also, by setting the drying temperature to 150°C or lower, excessive crystallization proceeds and the adhesiveness in the subsequent thermocompression bonding process is lost, and as a result, the mechanical properties of the obtained nonwoven fabric deteriorate. Here, the drying temperature refers to the highest temperature at the treatment temperature (ambient temperature) during drying in the above papermaking process.

[0079] By thermocompression bonding the dry web obtained as described above, adhesion occurs between the polyphenylene sulfide composite fibers of the present invention, resulting in a nonwoven fabric having excellent mechanical strength. As the means for thermocompression bonding, any means may be used, but for example, hot pressing with a flat plate or the like, a calendar, etc. can be adopted. Among them, a calendar that can be processed continuously is preferable. As the calendar roll, a metal-metal roll, a metal-paper roll, a metal-rubber roll, etc. can be used.

[0080] The thermocompression bonding temperature is preferably 170 to 250 °C. By preferably setting the thermocompression bonding temperature to 170 °C or higher, the fibers are joined by the adhesion of the copolymerized polyphenylene sulfide (B) in the sheath part, resulting in a wet nonwoven fabric with excellent mechanical strength. Also, by preferably setting the thermocompression bonding temperature to 250 °C or lower, heat shrinkage of the nonwoven fabric during thermocompression bonding can be suppressed.

[0081] As the thermocompression bonding means, when calendar processing is adopted, the linear pressure is preferably 98 to 7000 N / cm. By preferably setting the linear pressure to 98 N / cm or higher, the fibers are firmly pressed together through the copolymerized polyphenylene sulfide (B) in the sheath part, resulting in a wet nonwoven fabric with excellent mechanical strength. Also, by preferably setting the linear pressure to 7000 N / cm or lower, a decrease in tear strength and air permeability due to excessive crushing of the constituent fibers and formation of a film can be suppressed. The process speed is preferably 1 to 30 m / min. By preferably setting the process speed to 1 m / min or higher, in addition to suppressing a decrease in the mechanical strength of the nonwoven fabric due to excessive thermal crystallization, good working efficiency can be obtained. Also, by preferably setting the process speed to 30 m / min or lower, heat can be conducted to the fibers inside the nonwoven fabric, and the effect of thermal fusion bonding of the fibers can be obtained.

Examples

[0082] Hereinafter, the polyphenylene sulfide composite fiber of the present invention and the nonwoven fabric containing the same will be described more specifically with reference to examples. Each characteristic value in the examples was determined by the following method.

[0083] A. Melt mass flow rate: The melt mass flow rate MFR(A) of polyphenylene sulfide (A) and the melt mass flow rate MFR(B) of the copolymerized polyphenylene sulfide (B) were measured three times for each level at a temperature of 315°C and a load of 5.0 kg in accordance with "Chapter 8 Method A: Mass Measurement Method" of JIS K7210-1:2014 using a melt indexer (F-F01 manufactured by Toyo Seiki Seisaku-sho, Ltd.). The arithmetic mean value was determined and used as MFR(A) (g / 10 min) and MFR(B) (g / 10 min).

[0084] B. Melting Point The melting points Tm(A) of polyphenylene sulfide (A) and Tm(B) of the copolymerized polyphenylene sulfide (B) were measured three times for each level by heating from 25°C to 320°C at a rate of 10°C / min using a differential scanning calorimeter (DSC Q2000 manufactured by TA Instruments). The arithmetic mean value of the peak top temperatures of the largest endothermic peaks in the obtained DSC curves was determined and used as Tm(A) (°C) and Tm(B) (°C).

[0085] C. Average Fiber Length: One hundred polyphenylene sulfide composite fibers were randomly extracted and stretched to such an extent that plastic deformation did not occur under the conditions of a 10-fold objective lens and a 10-fold eyepiece lens using an optical microscope (BX53M manufactured by Olympus Corporation). The distance between both ends of the fiber was measured, and the arithmetic mean value was determined and used as the average fiber length (mm).

[0086] D. Average Fiber Diameter: One hundred polyphenylene sulfide composite fibers were randomly extracted, and the fiber diameter (μm) was measured from the side of the fiber under the conditions of a 40-fold objective lens and a 10-fold eyepiece lens using an optical microscope (BX53M manufactured by Olympus Corporation). The arithmetic mean value was determined and used as the average fiber diameter (μm).

[0087] E. Area Ratio of the Core Part: 100 randomly selected polyphenylene sulfide composite fibers were extracted, and photographs of the cross-sections of the fibers were taken at 1000 times magnification using a scanning electron microscope (VE-7800 type manufactured by Keyence Corporation). The total cross-sectional area and the area of the core part of each fiber were measured, and the arithmetic mean value of each was obtained. The area ratio of the core part was calculated by dividing the area of the core part by the total cross-sectional area.

[0088] F. Birefringence of fibers: 10 randomly selected polyphenylene sulfide composite fibers were extracted, and the birefringence was determined by measuring the retardation and the optical path length of single fibers using an optical microscope (BX53M manufactured by Olympus Corporation). The arithmetic mean value was obtained and used as the birefringence.

[0089] G. Strength and elongation: The strength and elongation of the polyphenylene sulfide composite fibers were measured using a tensilon (UTM-III-100 manufactured by Orientec Co., Ltd.) under the conditions of a sample length of 200 mm and a tensile speed of 200 mm / min according to "8.5 Tensile strength and elongation rate" of JIS L1013:2010. Five measurements were taken for each level, and the arithmetic mean value was obtained and used as the strength (cN / dtex) and elongation (%).

[0090] H. Areal density of nonwoven fabric: Three 5 cm × 5 cm sample pieces were collected from the nonwoven fabric obtained in the examples, and the mass (g) of each was measured in the standard state. The average value was expressed as the mass per 1 m 2 (g / m 2 ).

[0091] I. Number of wrinkles in nonwoven fabric: Using an optical microscope (BX53M manufactured by Olympus Corporation), the number of wrinkles ( / 100 cm 2 ) in the dry web obtained in the examples was confirmed under the conditions of an objective lens magnification of 40 times and an eyepiece lens magnification of 10 times. Here, the wrinkles in the dry web refer to linear wrinkles generated at locations where the thermal dimensional change rate in the dry web is locally different due to poor fiber dispersion, etc. The number of wrinkles with a total length of 0.1 cm or more was confirmed by measuring three samples for each level, and the arithmetic mean value was obtained and used as the number of wrinkles (pieces) in the dry web.

[0092] J. Tensile strength of non-woven fabric: Measurements were taken in the longitudinal (the direction of progress of the non-woven fabric manufacturing process) and transverse (the width direction of the non-woven fabric manufacturing process) directions of the non-woven fabric obtained in the examples. Using a tensilon (UTM-III-100 manufactured by Orientec), the maximum point load was measured under the conditions of a sample width of 15 mm, an initial length of 20 mm, and a tensile speed of 20 mm / min. For each longitudinal and transverse direction per level, measurements were taken 5 times, and the arithmetic mean value was determined as the tensile strength (N / 15 mm) of the non-woven fabric.

[0093] K. Tear strength of non-woven fabric: From the non-woven fabric obtained in the examples, test pieces of 63 mm × 100 mm were measured in the longitudinal (the direction of progress of the non-woven fabric manufacturing process) and transverse (the width direction of the non-woven fabric manufacturing process) directions of the non-woven fabric. Using an Elmendorf type tear tester (manufactured by Yasuda Seiki Seisakusho), a 20-mm cut was made at right angles in the center of both grips of the test piece, and the strength shown when the remaining 43 mm was torn in the longitudinal and transverse directions was measured. For each longitudinal and transverse direction per level, measurements were taken 5 times, and the arithmetic mean value was determined as the tear strength (gf) of the non-woven fabric.

[0094] L. Air permeability of non-woven fabric: In accordance with JIS L1913 (2010) Frazier method, 10 sample pieces of 5 cm × 5 cm were collected from the non-woven fabric obtained in the examples, and using an air permeability tester (FX3300 manufactured by Textest), the air permeability of 10 test pieces was measured at a test pressure of 125 Pa, and the arithmetic mean value was taken as the air permeability (cc / cm 2 / s).

[0095] M. Thickness of non-woven fabric: In accordance with JIS P8118 (2014), 10 sample pieces of 5 cm × 5 cm were collected from the non-woven fabric obtained in the examples, and the thickness of 10 test pieces was measured one by one using a micrometer (manufactured by Mitutoyo), and the arithmetic mean value was taken as the thickness (μm) of the non-woven fabric.

[0096] 〔Example 1〕 Polyphenylene sulfide (A) with a repeating unit of 100 mol% of p-phenylene sulfide units, an MFR (A) of 160 g / 10 min, and a Tm (A) of 284 °C, and a copolymerized polyphenylene sulfide (B) with a repeating unit of 75 mol% of p-phenylene sulfide units and 25 mol% of m-phenylene sulfide units, an MFR (B) of 200 g / 10 min, and a Tm (B) of 243 °C were vacuum dried at 150 °C for 12 hours and then melt-spun at a spinning temperature of 320 °C. In the melt spinning, polyphenylene sulfide (A) and copolymerized polyphenylene sulfide (B) were melt-extruded by a twin-screw extruder respectively, and supplied to a spin pack while being metered by a gear pump. Thereafter, polyphenylene sulfide (A) was arranged in the core part and copolymerized polyphenylene sulfide (B) was arranged in the sheath part within a spinneret, and the shape was regulated so that the area ratio of the core part in the cross section of the composite fiber was 75%, and they were made to merge and spun through a spinneret having 36 discharge holes of round holes.

[0097] The polymer discharged from the spinneret passed through a heat-insulating region of 50 mm and then was air-cooled over 1.0 m under the conditions of a temperature of 25 °C and a wind speed of 18 m / min using a uniflow type cooling device. Thereafter, an oil agent was applied, and all 36 filaments were wound up by a winder via a first godet roller and a second godet roller at 1000 m / min to obtain undrawn fibers.

[0098] The above-mentioned undrawn fibers were taken up by a feed roller equipped with nip rollers, tension was applied to the undrawn fibers between them and the undrawn fibers were then passed around a first roller and a second roller heated to 90 °C and 100 °C respectively for 6 turns to perform heat drawing. Further, they were passed around a third roller heated to 120 °C for 6 turns to perform heat setting. The draw ratio was 3.85 times, and after being taken up by an unheated roller having a peripheral speed of 400 m / min after the third roller, 2 mass% of a dispersant was applied to the fibers by using guide oiling. Subsequently, after imparting crimps of 8 peaks / 25 mm by a crimper, heat setting at 70 °C for 1 minute was performed by a setter. Thereafter, the obtained fibers were cut by a cutter to obtain polyphenylene sulfide composite fibers having an average fiber length of 6 mm.

[0099] The obtained polyphenylene sulfide composite fiber was dispersed in water to prepare an aqueous dispersion with a fiber concentration of 1% by mass. After that, using a hand-made paper machine (a square sheet machine with automatic cutting, manufactured by Kumagai Riki Kogyo Co., Ltd.), a wet paper (10 cm square) with a basis weight of 50 g / m 2 was obtained. The web obtained by dehydration with a roller was put into a dryer (a standard type KRK rotary dryer manufactured by Kumagai Riki Kogyo Co., Ltd.) and treated at a temperature of 140 °C for a treatment time of about 2.5 minutes per cycle to obtain a dry web. Subsequently, the other side was thermocompression bonded 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.

[0100] [Examples 2 to 4, Comparative Example 1] Polyphenylene sulfide composite fibers and nonwoven fabrics were obtained in the same manner as in Example 1, except that the copolymerization ratio of the copolymerized polyphenylene sulfide (B) arranged in the sheath portion was changed, and the draw ratio in the drawing step was 3.61 times. The evaluation results of the obtained polyphenylene sulfide composite fibers and nonwoven fabrics are shown in Table 1.

[0101] [Example 5, Example 6, Comparative Example 2] Polyphenylene sulfide composite fibers and nonwoven fabrics were obtained in the same manner as in Example 1, except that the average fiber length of the polyphenylene sulfide composite fibers was changed. The evaluation results of the obtained polyphenylene sulfide composite fibers and nonwoven fabrics are shown in Table 1.

[0102] [Example 7] Polyphenylene sulfide composite fibers and nonwoven fabrics were obtained in the same manner as in Example 1, except that the area ratio of the polyphenylene sulfide (A) arranged in the core portion was changed. The evaluation results of the obtained polyphenylene sulfide composite fibers and nonwoven fabrics are shown in Table 1.

[0103] [Example 8] In the stretching step, the stretching ratio was 3.31 times, and polyphenylene sulfide composite fibers and nonwoven fabrics were obtained in the same manner as in Example 1, except that they were taken up by a non-heated roller without heat setting. The evaluation results of the obtained polyphenylene sulfide composite fibers and nonwoven fabrics are shown in Table 1.

[0104]

Table 1

[0105] The polyphenylene sulfide composite fibers obtained in Examples 1 to 7 are polyphenylene sulfide fibers suitable as fibers constituting a nonwoven fabric having excellent mechanical properties because the nonwoven fabric has a small number of wrinkles and the tensile strength and tear strength of the nonwoven fabric also show good values.

[0106] On the other hand, in the polyphenylene sulfide composite fiber obtained in Comparative Example 1, since the copolymerization ratio of the sheath portion was low and the adhesiveness was poor, fiber slippage occurred between the fibers, and the tensile strength and tear strength of the nonwoven fabric decreased. Further, in the polyphenylene sulfide composite fiber obtained in Comparative Example 2, since the average fiber length was large, unevenness in basis weight due to excessive entanglement of the fibers during nonwoven fabric processing occurred frequently, and the number of wrinkles of the obtained dry web increased. As described above, neither was suitable as a fiber constituting a nonwoven fabric.

Industrial Applicability

[0107] The polyphenylene sulfide composite fiber of the present invention is a polyphenylene sulfide composite fiber that is not only excellent in heat resistance and chemical resistance, but also has a fine fiber diameter, high adhesiveness and mechanical strength, and excellent dimensional stability. By using the polyphenylene sulfide composite fiber of the present invention in the form of a nonwoven fabric, a nonwoven fabric having few dry wrinkles and good mechanical properties is obtained, which is suitably used for paper applications such as electrical insulating paper, separator applications for batteries, and various diaphragm applications.

Claims

1. A wet nonwoven fabric comprising a core-sheath type composite fiber in which polyphenylene sulfide with 97 mol% or more of the repeating units consisting of p-phenylene sulfide units is used as component A, and a copolymerized polyphenylene sulfide in which 60 to 97 mol% of the repeating units consist of p-phenylene sulfide units and 3 to 40 mol% consist of m-phenylene sulfide units is used as component B, with component A in the core part and component B in the sheath part, and the average fiber length is 1 to 100 mm, and the tearing strength is 100 gf or more and 1000 gf or less.

2. The wet nonwoven fabric according to Claim 1, wherein the area ratio of the core part in the cross section of the polyphenylene sulfide composite fiber is 75 to 95%.

3. The wet nonwoven fabric according to any one of Claims 1 to 2, wherein the birefringence of the polyphenylene sulfide composite fiber is 0.18 to 0.

40.

4. The wet nonwoven fabric according to any one of Claims 1 to 3, wherein the average fiber diameter of the polyphenylene sulfide composite fiber is 25 μm or less, the strength is 2.0 cN / dtex or more, and the elongation is 50% or less.

5. A method for producing a polyphenylene sulfide composite fiber for papermaking, which is a core-sheath type composite fiber in which polyphenylene sulfide with 97 mol% or more of the repeating units consisting of p-phenylene sulfide units is used as component A, and a copolymerized polyphenylene sulfide in which 60 to 97 mol% of the repeating units consist of p-phenylene sulfide units and 3 to 40 mol% consist of m-phenylene sulfide units is used as component B, with component A in the core part and component B in the sheath part, and the average fiber length is 1 to 100 mm, characterized in that the melt mass flow rate MFR(A) of component A used as a raw material is 50 to 250 g / 10 min, and the melt mass flow rate MFR(B) of component B is 10 g / 10 min or more greater than MFR(A).

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