Polyphenylene sulfide fiber

Abstract

To provide a PPS fiber capable of thinning a nonwoven fabric and improving mechanical strength of the nonwoven fabric without lowering fiber productivity and nonwoven fabric productivity.SOLUTION: A polyphenylene sulfide fiber is a drawn yarn that has a COOH-terminal polymer chain, a melt flow rate (MFR) of 300 to 800 g / 10 min at 315°C, and a single fiber fineness of 0.30 to 1.20 dtex.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyphenylene sulfide fibers suitable for wetlaid nonwoven fabric applications. [Background technology]

[0002] Polyphenylene sulfide (hereinafter sometimes abbreviated as PPS) resin has high heat resistance, chemical resistance, electrical insulation, and flame retardancy, and these properties are utilized in a variety of applications, such as bag filters, papermaking canvas, electrical insulation materials, and battery separators.

[0003] Among these, nonwoven fabrics that require high density and thin film are used for electrical insulating paper and battery separator applications. In recent years, there has been increasing demand for electrical insulating materials and battery separators that can be used in high-temperature environments, and PPS nonwoven fabrics with excellent heat and chemical resistance have attracted attention. Furthermore, with the trend toward smaller and lighter battery materials, there is an increasing demand for thinner films and lower basis weight.

[0004] However, although various attempts have been made to reduce the thickness and weight of PPS nonwoven fabrics, problems remain, such as reduced mechanical strength and reduced uniformity. Therefore, various proposals have been made regarding PPS fibers to solve these problems.

[0005] For example, a PPS wet-laid nonwoven fabric has been proposed that is composed of drawn PPS fibers and undrawn PPS fibers that serve as binder fibers for drawing and thermocompression bonding (see Patent Document 1).

[0006] Furthermore, a melt-blown nonwoven fabric having an average fiber diameter of 8 to 35 μm has been proposed using a melt-blowing method, which has produced a thin melt-blown nonwoven fabric with excellent productivity (see Patent Document 2).

[0007] Furthermore, a method has been proposed for obtaining PPS fibers with fineness and excellent mechanical strength by electrospinning PPS with a specific Na content. This proposal has indeed produced ultrafine fibers of 1 μm (approximately 0.01 dtex) or less and high strength fibers of 5.5 cN / dtex or more, and thin PPS nonwoven fabrics (see Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-189169 [Patent Document 2] Japanese Patent Application Publication No. 11-315462 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-67919 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in Patent Document 1, the fiber diameter of the PPS fiber is large, which makes it difficult to make the wetlaid nonwoven sheet thin. In addition, there are also issues such as poor dispersibility of the cut fibers during papermaking, making it impossible to make the sheet sufficiently thin or with a low basis weight.

[0010] Furthermore, Patent Document 2 discloses a melt-blown nonwoven fabric, and the crystallinity of the constituent fibers is low, resulting in poor heat resistance and dimensional stability, and also in the lack of mechanical strength of a nonwoven fabric.

[0011] Furthermore, in Patent Document 3, a special spinning method called electrospinning is applied, and therefore the fiber productivity is inferior to that of spinning methods such as melt spinning.

[0012] The problem to be solved by the present invention is to provide a PPS fiber that enables a nonwoven fabric to be made thinner and have improved mechanical strength without reducing the productivity of the fiber and the productivity of the nonwoven fabric. [Means for solving the problem]

[0013] The following points were found to be important in order to provide a PPS fiber that can be made thinner and has improved mechanical strength without sacrificing fiber productivity and nonwoven fabric productivity.

[0014] That is, the present invention is as follows. 1. A polyphenylene sulfide fiber in the form of a drawn yarn having a polymer chain end terminated with a COOH terminal, a melt flow rate (MFR) at 315°C of 300 to 800 g / 10 min, and a single fiber fineness of 0.30 to 1.20 dtex. Furthermore, preferred embodiments of the present invention are as follows. 2. The polyphenylene sulfide fiber according to 1 above, wherein the drawn yarn strength is 5.0 to 7.0 cN / dtex. 3. The polyphenylene sulfide fiber according to 1 or 2 above, wherein the sum of the crystallinity and rigid amorphous of the drawn yarn is 50 to 100%. 4. A wetlaid nonwoven fabric containing at least 10% or more of the polyphenylene sulfide fiber described in any one of 1 to 3 above. 5. The wetlaid nonwoven fabric according to 4 above, further comprising undrawn yarns of polyphenylene sulfide fibers as binder fibers, the undrawn yarns having a single fiber fineness of 0.9 to 3.0 dtex. 6. The wetlaid nonwoven fabric according to 4 or 5 above, characterized in that the dry heat shrinkage of the undrawn yarn is 60% or less. 7. The wetlaid nonwoven fabric according to any one of 4 to 6 above, wherein the crystallinity of the undrawn yarn is 20% or less. [Effects of the Invention]

[0015] The PPS fiber of the present invention enables a thinner fiber and improved mechanical strength without reducing the productivity of the fiber and nonwoven fabric. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below together with preferred embodiments.

[0017] The PPS used in the present invention means a polymer containing, as a repeating unit, a phenylene sulfide unit such as a p-phenylene sulfide unit represented by the following structural formula (I) or an m-phenylene sulfide unit.

[0018] [ka]

[0019] PPS may be a homopolymer of only p-phenylene sulfide units or m-phenylene sulfide units, or a copolymer having both p-phenylene sulfide units and m-phenylene sulfide units, and may also be a copolymer or mixture with other aromatic sulfides as long as the effects of the present invention are not impaired.

[0020] From the viewpoint of heat resistance and durability, the PPS resin used in the present invention is preferably a PPS containing preferably 70 mol or more, more preferably 90 mol or more, of p-phenylene sulfide units, which are repeating units represented by the structural formula (I) above. In this case, other copolymerization components in the PPS resin are preferably m-phenylene sulfide units or other aromatic sulfide units.

[0021] PPS typically contains metals such as Na, Ca, Mg, and Fe. The polymer chain ends contain these metals as well as end groups derived from the polymerization raw materials and catalysts, such as Cl groups when p-dichlorobenzene is used as the polymerization raw material, or N-alkylpyridine groups or pyridine groups, which are decomposition products of N-methylpyrrolidone when N-methylpyrrolidone is used as the polymerization catalyst. Because a sufficient degree of polymerization can be achieved even with low viscosity, the key to the present invention is to polymerize PPS with Na at the polymer chain ends, and then acid-wash the polymer with an inorganic acid such as hydrochloric acid or an organic acid such as acetic acid to obtain PPS with COOH chain ends. PPS with COOH chain ends has higher kinetics during melting than PPS with other ends, even at the same degree of polymerization. Therefore, controlling the solidification behavior during extrusion can improve spinning operability. Furthermore, PPS with COOH terminals as polymer chain ends has a faster crystallization rate than PPS with other terminals, requiring less energy for molding below the melting point and near the glass transition point, and can be stretched at a high magnification, enabling the resulting fibers to be made stronger and finer. In particular, the COOH-terminated PPS used in the present invention is preferably PPS that has been washed with a cleaning solution adjusted to a pH of 5.0 or less with acetic acid, and has a sodium content of 200 ppm or less and an ash content of 0.05 or less.

[0022] The Na content and ash content of the present invention were measured by the following method. Five grams of polymer was precisely weighed, calcined at 500°C, and then calcined at 530°C for six hours, and the ash content (g) was measured. The resulting ash was dissolved in hydrochloric acid, and the Na content was measured using an atomic absorption spectrophotometer, AA-6300 (Shimadzu Corporation).

[0023] The melt mass flow rate (hereinafter also referred to as MFR) of the PPS used in the present invention is preferably 300 g / 10 min to 800 g / 10 min. By making the MFR preferably 300 g / 10 min or more, the fluidity during melting is increased, improving spinnability and resulting in fibers with improved operability even at finer fibers. It is preferably 350 g / 10 min or more. Furthermore, by making the MFR 800 g / 10 min or less, PPS fibers with good mechanical properties are obtained. It is preferably 600 g / 10 min or less, more preferably 500 g / 10 min or less.

[0024] The MFR of PPS in the present invention refers to a value measured under conditions of a load of 5.0 kg and a temperature of 315°C according to JIS K7210-1:2014 Chapter 8, Method A: Mass Measurement Method.

[0025] The PPS fiber of the present invention can be obtained by melt spinning. The PPS fiber discharged from the spinneret and taken up is called an undrawn yarn, and the PPS fiber that has been subjected to a drawing process in the subsequent drawing step is called a drawn yarn (details will be described later in the section on the manufacturing method).

[0026] The single fiber fineness of the drawn yarn of the PPS fiber of the present invention (drawn yarn single fiber fineness) is preferably 0.30 to 1.20 dtex. It is preferably 0.30 to 0.90 dtex, and more preferably 0.30 to 0.70 dtex. By making the drawn yarn single fiber fineness 0.30 dtex or more, stable operability can be maintained without yarn breakage during spinning. Furthermore, by making the drawn yarn single fiber fineness preferably 0.90 dtex or less, and more preferably 0.70 dtex or less, uniformity during wet-laid nonwoven fabric formation can be improved, enabling improved mechanical strength.

[0027] The single fiber fineness of the undrawn PPS fiber of the present invention is preferably 0.90 to 3.0 dtex. By making the single fiber fineness of the undrawn yarn 0.90 dtex or more, spinning operability becomes stable, and by making it 3.0 dtex or less, preferably 2.2 dtex or less, uniformity during wet-laid nonwoven fabric processing is improved, enabling improved mechanical strength.

[0028] The drawn yarn strength of the PPS fiber of the present invention is preferably 5.0 to 7.0 cN / dtex, and more preferably 5.5 to 6.5 cN / dtex. By setting the strength to 5.0 cN / dtex or more, the mechanical strength of the wetlaid nonwoven fabric can be improved, while by setting the strength to 7.0 cN / dtex or less, the fiber drawing operability can be improved and the ability to impart crimp to the fiber can be easily controlled, thereby improving dispersibility during wetlaid nonwoven fabric formation.

[0029] The dry heat shrinkage of the undrawn PPS fiber of the present invention is preferably 60% or less. By setting it to preferably 60% or less, and more preferably 50% or less, the occurrence of wrinkles during the drying process in wet-laid nonwoven fabric processing is suppressed, enabling improved basis weight uniformity. The dry heat shrinkage is calculated using the following formula from the fiber length (A) before treatment and the fiber length (B) after treatment when treated at 180°C for 20 minutes. Dry heat shrinkage rate [%]=((A)-(B)) / (A)×100 When measuring fiber length, a specified load (fineness [dtex] x 270 mg) is applied to a single fiber, and the length is calculated.

[0030] The drawn yarn of the PPS fiber of the present invention preferably has a sum of crystallinity and rigid amorphous content of 50 to 100%. By making the sum of crystallinity and rigid amorphous content 50% or more, high-strength fibers can be obtained. Rigid amorphous refers to a state intermediate between polymer crystals and complete amorphous content, and refers to the amount remaining after subtracting the crystallinity (%) and mobile amorphous content (%) from the total crystal and amorphous content (100%) that makes up the fiber, as shown in the following formula: Rigid amorphous amount [%] = 100 [%] - Crystallinity [%] - Movable amorphous amount [%] The mobile amorphous amount referred to in the present invention is determined by temperature-modulated DSC measurement as described later in the Examples. The crystallinity also refers to a value measured by the method described later.

[0031] The undrawn yarn of the PPS fiber of the present invention preferably has a crystallinity of 20% or less. By setting the crystallinity of the undrawn yarn to 20% or less, the undrawn yarn acts as an adhesive point between fibers during the drying step in wet-laid nonwoven fabric processing, enabling the paper strength of the nonwoven fabric to be improved.

[0032] It is important that the weight ratio of stretched yarn to unstretched yarn (raw cotton weight ratio) in a wetlaid nonwoven fabric made of PPS fiber of the present invention is 20 to 80%, and preferably the weight ratio of stretched yarn is 30 to 70%. If the weight ratio of stretched yarn is less than 20%, it will become film-like and the tensile strength will decrease, which is not preferable. If the weight ratio of stretched yarn is more than 80%, the number of bonding points between fibers will decrease and the tensile strength of the wetlaid nonwoven fabric will decrease, which is not preferable.

[0033] Next, the method for producing the PPS fiber of the present invention will be described.

[0034] The PPS fiber of the present invention can be obtained by melt spinning a PPS resin whose polymer chain ends are COOH terminals. First, PPS having Na at the polymer chain ends is polymerized by a known method, and then the polymer is acid-washed with an inorganic acid such as hydrochloric acid or an organic acid such as acetic acid to obtain a PPS resin whose polymer chain ends are COOH terminals. Powder or pellets of this PPS resin are melted, and the molten resin is spun from a spinneret.

[0035] Furthermore, because PPS resin, whose polymer chain ends in COOH, has high molecular mobility, controlling the solidification behavior and extrusion stability during spinning is important when melt-molding into fiber form. To control the solidification behavior, during melt spinning, the section from the resin melt point to the top of the pack housing can be at the spinning temperature normally selected, but it is essential that the temperature of only the lower pack housing and spinneret section be lowered, preferably by 5 to 15°C, more preferably by 9 to 11°C, compared to the temperature of the upper pack housing. The preferred temperature for the spin block and upper pack housing is 315 to 330°C, and the preferred temperature for the lower spin block and spinneret section is 305 to 315°C.

[0036] In conventional PPS fiber production, the ratio L / D, defined as the quotient obtained by dividing the land length L of the spinneret discharge hole (the length of the straight tube portion having the same diameter as the spinneret discharge hole) by the spinneret discharge hole diameter D, has usually been set to 1.0 or more and 4.0 or less. However, in the present invention, it is important to set L / D to 5.0 or more and 10.0 or less in order to improve discharge stability. By setting L / D to 5.0 or more and 10.0 or less, the back pressure is optimized when spinning PPS, which has high molecular mobility, at 290°C to 360°C, improving discharge stability and enabling the fine fiber size within the claimed range of the present invention.

[0037] As the melt spinning machine, a pressure melter spinning machine or a single-screw or twin-screw extruder spinning machine is generally used. To prevent gelation due to thickening during the spinning process, the heating temperature is preferably as low as possible while still being sufficient to melt the polymer, specifically in the range of 290 to 360°C. Also to prevent gelation, a nitrogen atmosphere is preferably used during melting. The molten polymer is then extruded from the spinneret and cooled and solidified by blowing cooling air. The cooling air speed is typically 5 to 100 m / min, and the temperature may be room temperature or lower. After cooling and solidification, the PPS fiber is given an appropriate amount of oil as a sizing agent and then taken up by a predetermined take-up device. The take-up speed is typically in the range of 500 to 7,000 m / min.

[0038] The resulting undrawn yarn is then subjected to a drawing step to obtain a drawn yarn. In the drawing step, the yarn is preferably drawn in a heating bath, in heated steam, on a hot plate, or on a hot roller at a drawing temperature of about 90 to 170°C and a draw ratio of 2 to 5. The drawing may be one-stage or two-stage drawing.

[0039] A fixed length heat treatment may be carried out after the hot drawing. It is important to carry out the fixed length heat treatment while keeping the length of the yarn constant or to relax it by a few percent.

[0040] The fixed length heat treatment temperature is preferably 130°C or higher, more preferably 150°C or higher, to suppress shrinkage of the raw cotton and improve processability during drying. In addition, by setting the temperature to 200°C or lower, more preferably 180°C or lower, pseudo-adhesion between fibers can be suppressed.

[0041] The step of drawing the undrawn yarn may be a continuous step in which drawing is carried out following spinning, or a discontinuous step in which the undrawn yarn is taken up at a predetermined speed, temporarily stored in a can or wound up, and then subjected to the drawing step. The resulting PPS fiber may be in the form of a multifilament, a monofilament, or a staple fiber, but in the present invention, staple fiber is particularly preferred. This is because staple fiber is generally produced on a larger scale on an industrial scale than filaments, and therefore has cost advantages.

[0042] A papermaking dispersant is preferably applied to the PPS fibers to be used as a raw material for fiber structures such as papermaking. The application of the papermaking dispersant to the obtained PPS fibers is usually performed using a kiss roller in the tow state. The papermaking dispersant deposition rate is preferably 0.2% by mass or more and 0.8% by mass or less based on the fiber weight. By setting the dispersant deposition rate to preferably 0.1% by mass or more, and more preferably 0.3% by mass or more, fiber dispersibility is improved, resulting in a wetlaid nonwoven fabric with excellent film thickness uniformity and basis weight CV value. Furthermore, by setting the dispersant deposition rate to preferably 0.8% by mass or less, and more preferably 0.5% by mass or less, processability is improved.

[0043] After the dispersant has been applied in this way, the fabric may be crimped using a crimper. By crimping the fabric, the fibers become entangled with each other, resulting in a wetlaid nonwoven fabric with excellent mechanical properties.

[0044] The crimp number is preferably 2 crimps / 25mm or more and 15 crimps / 25mm or less. By setting the crimp number to 2 crimps / 25mm or more, and more preferably 5 crimps / 25mm or more, the fibers become entangled, resulting in a wetlaid nonwoven fabric with excellent mechanical properties. Furthermore, by setting the crimp number to 15 crimps / 25mm or less, and more preferably 12 crimps / 25mm or less, the dispersion of fibers during papermaking is improved, resulting in a wetlaid nonwoven fabric with good thickness uniformity and basis weight CV value.

[0045] The PPS fibers obtained as described above can be dried using a setter and then cut with a cutter to obtain cut fibers. The cut length of the cut fibers is preferably 1 mm or more and 20 mm or less. By setting the cut length to preferably 1 mm or more, and more preferably 3 mm or more, the fibers can be entangled to form a wetlaid nonwoven fabric with excellent mechanical properties. Furthermore, by setting the cut length to preferably 20 mm or less, and more preferably 10 mm or less, the dispersibility of the fibers during dispersion is improved, resulting in a wetlaid nonwoven fabric with good film thickness uniformity and basis weight CV value.

[0046] A dispersion can be prepared by mixing the drawn cut fibers obtained by the above method and the undrawn cut fibers obtained by the above method except for the drawing in any desired ratio and dispersing them in water.

[0047] If the dispersant was not added to the tow, the dispersant may be added to the cut fibers at this stage.

[0048] The dispersion liquid is fed to a paper machine to obtain a wetlaid nonwoven fabric. The basis weight and thickness of the obtained wetlaid nonwoven fabric can be changed by adjusting the fiber concentration of the dispersion liquid to be fed.

[0049] The wetlaid nonwoven fabric obtained as described above is preferably dried to remove moisture. The drying temperature is preferably 90°C or higher and 150°C or lower so as to prevent a decrease in fusibility due to crystallization of the amorphous portion.

[0050] By subjecting the above-mentioned wetlaid nonwoven fabric to thermocompression bonding using a flat-plate heating press or a calender roll, fusion bonding occurs with the undrawn cut fibers of the present invention, resulting in a wetlaid nonwoven fabric with excellent mechanical properties. The thermocompression temperature is preferably 170°C or higher and 250°C or lower, and the compression time is preferably 1 minute or higher and 10 minutes or lower. By setting the thermocompression temperature to 170°C or higher, fusion bonding of the PPS fibers of the present invention results in a wetlaid nonwoven fabric with excellent mechanical properties. By setting the thermocompression temperature to 250°C or lower, thermal shrinkage of the wetlaid nonwoven fabric during thermocompression bonding can be suppressed. Furthermore, by setting the compression time to 1 minute or longer, the entire wetlaid nonwoven fabric can be heated uniformly, resulting in a homogeneous wetlaid nonwoven fabric. By setting the compression time to 10 minutes or shorter, deterioration of the mechanical properties of the wetlaid nonwoven fabric due to excessive crystallization can be suppressed. [Example]

[0051] The PPS fiber of the present invention will be described in more detail below with reference to examples. The physical properties in the examples were determined by the following methods.

[0052] [Measurement method] A. Melt flow rate (MFR) The melt mass flow rate of PPS was measured using a melt indexer (F-F01 manufactured by Toyo Seiki Seisaku-sho, Ltd.) according to the above-mentioned method (JIS K7210-1 (2014) Chapter 8, Method A: Mass measurement method, load 5.0 kg, temperature 315°C).

[0053] B. Fineness The fineness was measured in accordance with JIS L1015 (2010).

[0054] C. Strength Using a tensile tester (Orientec "Tensilon"), a stress-strain curve was obtained under the conditions of a sample length of 2 cm and a pulling speed of 2 cm / min according to the method described in JIS L1015 (2010), and the strength at break was calculated from the curve. The tensile strength was calculated by dividing this value by the fineness calculated in B above.

[0055] D. Crystallinity Differential scanning calorimetry was performed under nitrogen using a differential scanning calorimeter (TA Instruments DSCQ1000) at a heating rate of 10°C / min. The heat of crystallization at the temperature of the observed exothermic peak was taken as ΔHc (J / g). The heat of fusion at the temperature of the endothermic peak (melting point) observed at temperatures above 200°C was taken as ΔHm (J / g). The difference between ΔHm and ΔHc was divided by the heat of fusion of fully crystalline PPS (146.2 J / g) to calculate the degree of crystallinity, Xc (%) (Equation 1 below). Xc={(ΔHm-ΔHc) / 146.2}×100 (1) <dsc> Atmosphere: Nitrogen flow (50 mL / min) Temperature and heat calibration: High purity indium Specific heat calibration: sapphire Temperature range: 0~350℃ Heating rate: 10℃ / min Sample size: 5 mg · Sample container: Standard aluminum container.

[0056] E. Rigid amorphous amount Temperature-modulated DSC measurements were performed under nitrogen using the same differential scanning calorimeter as in D above, under conditions of a heating rate of 2°C / min, a temperature amplitude of 1°C, and a temperature modulation period of 60 seconds. Auxiliary lines were drawn on the baseline of the resulting chart around the glass transition temperature (Tg), and the difference was taken as the specific heat difference (ΔCp). This was divided by the specific heat difference around the Tg of completely amorphous PPS (ΔCp0: 0.2699 J / g°C) to determine the mobile amorphous amount (Xma) using the following equation (2). Furthermore, the rigid amorphous amount (Xra) was calculated from the difference between the overall crystallinity (Xc) and the mobile amorphous amount (Xma) using the following equation (3). Xma(%)=ΔCp / ΔCp0×100 (2) Xra(%)=100-(Xc+Xma) (3) <Temperature Modulated DSC> Atmosphere: Nitrogen flow (50 mL / min) Temperature and heat calibration: High purity indium Specific heat calibration: sapphire Temperature range: 0~250℃ Heating rate: 2°C / min Sample size: 5 mg · Sample container: Standard aluminum container.

[0057] F.Dry heat shrinkage rate The dry heat shrinkage is calculated using the following formula from the fiber length before treatment (A) and the fiber length after treatment (B) when treated at 180°C for 20 minutes. Dry heat shrinkage rate [%]=((A)-(B)) / (A)×100 When measuring fiber length, a specified load (fineness [dtex] x 270 mg) is applied to a single fiber, and the length is calculated.

[0058] G. Spinnability In each example and comparative example, spinning was carried out using 24 spindles, and the number of thread breakages per spindle was counted for spinning times of 0 to 12 hours and 12 to 24 hours. There are various possible causes of thread breakage, but the reason the number of thread breakages is higher for 12 to 24 hours compared to 0 to 12 hours is that thread breakages are caused by dirty spinnerets. Spinnability was evaluated as ○ if the number of thread breakages per spindle during a 12-hour spinning time was less than 2, △ if it was 2 to 3, and × if it was 4 or more.

[0059] H.Drying process passability A 1% by weight aqueous dispersion of 6 mm cut PPS fibers obtained in the Examples or Comparative Examples was prepared, and a wet-laid nonwoven fabric with a basis weight of 20 g / m was obtained using a hand-made papermaking machine (a square sheet machine with automatic couching, manufactured by Kumagaya Riki Kogyo Co., Ltd.). This nonwoven fabric was then couched. The wet nonwoven fabric was placed in a standard KRK rotary dryer manufactured by Kumagaya Riki Kogyo Co., Ltd., at 120°C for approximately 2.5 minutes per cycle, and the wrinkling of the wet-laid nonwoven fabric (ability to pass through the drying process) was checked. Regarding wrinkling during drying, those with almost no shrinkage wrinkling and capable of continuous papermaking were rated as ○ (excellent); those with shrinkage wrinkling but sufficient to enable continuous papermaking were rated as △ (fair); and those with shrinkage wrinkling or peeling that presumably precluded continuous papermaking were rated × (poor). I. Paper Strength The wet-laid nonwoven fabric obtained by method G above was subjected to thermocompression bonding for 3 minutes at a pressure of 1.5 MPa using a flat-plate heating press at 230°C. The maximum point load of the obtained wet-laid nonwoven fabric was measured using a Tensilon (UTM-III-100, manufactured by Orientec Co., Ltd.) with a sample width of 25 mm, an initial length of 30 mm, and a tensile speed of 20 mm / min. The arithmetic mean value of five measurements was taken as the tensile strength (N / 25 mm). Average tensile strength values ​​of 15 N / 25 mm or more were rated as ○ (excellent), 10 to 15 N / 25 mm as △ (fair), and values ​​below that were rated × (poor).

[0060] J. Overall Judgment In the above spinnability (0-12 hours, 12-24 hours) and papermaking evaluation (drying process passability, paper strength), if there was even one × (bad) judgement among the six items, the overall judgement was × (bad), and if there were only ○ (excellent) or △ (average) judgements among the six items, the overall judgement was ○ (excellent), and ○ (excellent) was considered a pass.

[0061] <Examples 1 to 6, Comparative Examples 1 to 3> PPS having sodium at the polymer chain end was polymerized by a known method to achieve the MFR listed in Table 1, and then washed with a cleaning solution adjusted to pH 5.0 or less with acetic acid. The sodium content was confirmed to be 200 ppm or less and the ash content was 0.05 or less, and the resin was determined to be COOH-terminated PPS resin. This PPS resin was vacuum dried at 150°C for 6 hours and then melt-spun at a spinning temperature of 330°C. In the melt spinning, the resin was melt-extruded using a pressure melter, and the PPS was fed into a spinning pack while being metered using a gear pump, and spun through a spinneret with an L / D of 6.25.

[0062] The fibers were then drawn at a specific draw ratio and drawing temperature of 98°C to achieve a total fineness of approximately 100,000 dtex and the fineness and fiber properties shown in Table 1, and a dispersant was applied using a kiss roller. After drying, the fibers were cut to 6 mm to obtain drawn cut fibers. Furthermore, undrawn cut fibers were obtained by a method other than the above-mentioned method, omitting only the drawing. The obtained PPS cut fibers were mixed with an aqueous dispersion of 1% by weight of fiber and spun using a hand-made papermaking machine (a square sheet machine with automatic couching, manufactured by Kumagai Riki Kogyo Co., Ltd.) to a basis weight of 20 g / m. 2 The wet-laid nonwoven fabric was subjected to a couching treatment. The nonwoven fabric was placed in a KRK rotary dryer (standard type) manufactured by Kumagai Riki Kogyo Co., Ltd. without being dried, and treated at a temperature of 120°C for a treatment time of approximately 2.5 minutes per cycle to obtain a wet-laid nonwoven fabric. The wet-laid nonwoven fabric was then subjected to thermocompression bonding for 3 minutes at a pressure of 1.5 MPa using a flat-plate heating press at 230°C.

[0063] The obtained PPS cut fibers and wet-laid nonwoven fabric were evaluated as described above, and the results are shown in the table below.

[0064] [Table 1]

[0065] In Examples 1 to 4, PPS for papermaking was obtained that had good spinnability and water dispersibility. The resulting wetlaid nonwoven fabrics also had improved wrinkles during the drying process and sufficient paper strength. In Example 5, the fineness of the drawn yarn was small, while the fineness of the undrawn yarn was large, resulting in large variations in paper weight and inferior paper strength compared to wetlaid nonwoven fabrics made with finer undrawn yarn. In Example 6, undrawn yarn was used, which was collected under conditions that promoted polymer orientation during spinning. In this case, the dry heat shrinkage of the undrawn yarn was high, making it prone to wrinkles during the drying process. Furthermore, the high crystallinity of the undrawn yarn meant that the adhesive strength of the binder fiber was low, resulting in inferior paper strength compared to Example 1.

[0066] On the other hand, in Comparative Example 1, wrinkles occurred during drying due to the large fineness and large variations in basis weight. Furthermore, sufficient paper strength was not obtained due to the small number of constituent fibers. In Comparative Example 2, because of the Ca termination, increasing the MFR reduced the degree of polymerization of the resin, and sufficient fiber strength was not obtained. As a result, the resulting wetlaid nonwoven fabric also did not have sufficient paper strength. In Comparative Example 3, because of the Ca termination and low MFR, spinning of a fine-fineness product was impaired, and fiber strength was low, so sufficient paper strength was not obtained. In Comparative Example 4, because of the Na termination, fiber strength was not obtained, and sufficient paper strength was not obtained.< / dsc>

Claims

1. A polyphenylene sulfide fiber in the form of a drawn yarn, in which the polymer chain ends are COOH terminals, the melt flow rate (MFR) at 315°C is 300 to 800 g / 10 min, and the single fiber fineness is 0.30 to 1.20 dtex.

2. 2. The polyphenylene sulfide fiber according to claim 1, wherein the drawn yarn has a strength of 5.0 to 7.0 cN / dtex.

3. 3. The polyphenylene sulfide fiber according to claim 1, wherein the sum of the crystallinity and rigid amorphous content of the drawn yarn is 50 to 100%.

4. A wetlaid nonwoven fabric containing at least 10% of the polyphenylene sulfide fiber according to any one of claims 1 to 3.

5. 5. The wetlaid nonwoven fabric according to claim 4, further comprising undrawn yarns of polyphenylene sulfide fibers as binder fibers, the undrawn yarns having a single fiber fineness of 0.9 to 3.0 dtex.

6. 6. The wetlaid nonwoven fabric according to claim 4, wherein the dry heat shrinkage of the undrawn yarn is 60% or less.

7. 7. The wetlaid nonwoven fabric according to claim 4, wherein the undrawn yarn has a crystallinity of 20% or less.

Images