JP2022130318A - polyphenylene sulfide fiber - Google Patents

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

The present invention relates to polyphenylene sulfide fibers suitable for wet-laid nonwoven applications.

Polyphenylene sulfide (hereinafter sometimes abbreviated as PPS) resin has high heat resistance, chemical resistance, electrical insulation, and flame retardancy. It is used in applications such as canvas, electrical insulation, and battery separators.

Among them, nonwoven fabrics, which require densification and thinning, are used for electrical insulating paper and battery separator applications. In recent years, the demand for electrical insulating materials and battery separators that can be used in high-temperature environments has increased, and PPS nonwoven fabrics, which are excellent in heat resistance and chemical resistance, have attracted attention. Furthermore, as battery materials and the like become smaller and lighter, there is an increasing demand for thinner films and lower basis weight.

However, although various studies have been made on how to make the PPS nonwoven fabric thinner and lower in basis weight, there have been problems such as a decrease in mechanical strength and a decrease in uniformity. In order to solve the above problems, various proposals have been made for PPS fibers.

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

Also, a melt-blown nonwoven fabric having an average fiber diameter of 8 to 35 μm has been proposed by the melt-blowing method. According to this proposal, a melt-blown nonwoven fabric having a thin film and excellent productivity is obtained. (See Patent Document 2.).

Furthermore, a method of electrospinning PPS with a specific Na content to obtain PPS fibers with fine fineness and excellent mechanical strength has been proposed. According to this proposal, it is true that fibers having an ultrafine fineness of 1 μm (approximately 0.01 dtex) or less and high strength fibers of 5.5 cN/dtex or more are obtained, and a thin PPS nonwoven fabric is obtained. (See Patent Document 3.).

JP-A-7-189169 JP-A-11-315462 JP 2015-67919 A

However, in Patent Document 1, since the fiber diameter of the PPS fiber is large, it is difficult to make the wet-laid nonwoven sheet thin, and the dispersibility of the cut fibers during papermaking is reduced, resulting in sufficient thinning and low basis weight. There is also the issue of not being able to convert

Moreover, in Patent Document 2, the nonwoven fabric is a melt-blown nonwoven fabric, and since the crystallinity of the constituent fibers is low, the heat resistance and dimensional stability are inferior, and the mechanical strength of the nonwoven fabric cannot be obtained.

Furthermore, in Patent Document 3, since a special spinning method called electrospinning is applied, fiber productivity is inferior to spinning methods such as melt spinning.

The problem to be solved by the present invention is to provide a PPS fiber that makes it possible to reduce the thickness of the nonwoven fabric and improve the mechanical strength without lowering the productivity of the fiber and the nonwoven fabric.

The inventors have found that the following are important in order to provide a PPS fiber that can be thinned and improved in mechanical strength without lowering fiber productivity and nonwoven fabric productivity.

That is, the present invention is as follows.
1. A polyphenylene sulfide fiber which is a drawn yarn having a polymer chain end of COOH end, 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 has a strength of 5.0 to 7.0 cN/dtex.
3. 3. The polyphenylene sulfide fiber according to 1 or 2 above, wherein the sum of the degree of crystallinity and the rigid amorphous of the drawn yarn is 50 to 100%.
4. A wet-laid nonwoven fabric containing at least 10% of the polyphenylene sulfide fiber according to any one of 1 to 3 above.
5. 5. The wet-laid nonwoven fabric according to 4 above, further comprising undrawn yarns of polyphenylene sulfide fibers as binder fibers, and the undrawn yarns having a single fiber fineness of 0.9 to 3.0 dtex.
6. 6. The wet-laid nonwoven fabric as described in 4 or 5 above, wherein the undrawn yarn has a dry heat shrinkage of 60% or less.
7. 7. The wet-laid nonwoven fabric according to any one of 4 to 6 above, wherein the crystallinity of the undrawn yarn is 20% or less.

The PPS fiber of the present invention enables thinning and improvement in mechanical strength without lowering fiber productivity and nonwoven fabric productivity.

Below, the present invention will be described in detail together with preferred embodiments.

The PPS used in the present invention means a polymer containing phenylene sulfide units such as p-phenylene sulfide units represented by the following structural formula (I) and m-phenylene sulfide units as repeating units.

PPS may be a homopolymer containing only p-phenylene sulfide units or m-phenylene sulfide units, or a copolymer containing both p-phenylene sulfide units and m-phenylene sulfide units, without impairing the effects of the present invention. As long as it is a copolymer or mixture with other aromatic sulfides, it may be used.

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

In general, PPS has metals such as Na, Ca, Mg, and Fe, and polymer chain ends include these metals, as well as terminal groups derived from polymerization raw materials and catalysts, for example, p-dichlorobenzene as a polymerization raw material. is used as a Cl group, and when N-methylpyrrolidone is used as a polymerization catalyst, it is a N-alkylpyridine group or a pyridine group which is a decomposition product thereof. In the present invention, since a sufficient degree of polymerization can be obtained even at low viscosity, after PPS having Na as a polymer chain terminal is polymerized, the polymer is polymerized with an inorganic acid such as hydrochloric acid, an organic acid such as acetic acid, or the like. It is important to use PPS that has been acid washed and the polymer chain ends are COOH terminated. PPS having a polymer chain end as a COOH end has high mobility when melted compared to PPS having the same degree of polymerization as PPS having other ends, and spinning performance can be improved by controlling solidification behavior during ejection. In addition, PPS with a polymer chain end as a COOH end has a faster crystallization rate than PPS with other ends, and the amount of energy required for the molding operation below the melting point and near the glass transition point is reduced, and stretching at a high magnification is possible. As a result, it becomes possible to increase the strength and fineness of the resulting fiber. In particular, the COOH-terminated PPS used in the present invention is preferably washed with a washing solution adjusted to pH 5.0 or less with acetic acid, and preferably has a Na content of 200 ppm or less and an ash content of 0.05 or less.

The Na content and ash content according to the present invention were measured by the following methods. That is, 5 g of the polymer was precisely weighed, calcined at 500° C., then calcined at 530° C. for 6 hours, and the ash content (g) was measured. Also, the obtained ash was dissolved in hydrochloric acid, and the Na content was measured with an atomic absorption photometer: AA-6300 (Shimadzu Corporation).

The melt mass flow rate (hereinafter also referred to as MFR) of PPS used in the present invention is preferably 300 g/10 minutes to 800 g/10 minutes. By setting the MFR to preferably 300 g/10 minutes or more, the fluidity at the time of melting is increased, so the spinnability is improved, and even with a fine fineness, the fiber has improved workability. It is preferably 350 g/10 minutes or more. Also, by setting the MFR to 800 g/10 minutes or less, the PPS fiber has good mechanical properties. It is preferably 600 g/10 minutes or less, more preferably 500 g/10 minutes or less.

The MFR of PPS in the present invention refers to a value measured by JIS K7210-1:2014 Chapter 8 A method: mass measurement method under conditions of a load of 5.0 kg and a temperature of 315 ° C.

The PPS fibers of the present invention can be obtained by melt spinning. The PPS fiber discharged from the spinneret and taken off is called undrawn yarn, and the yarn that has been drawn in the subsequent drawing step is called drawn yarn. (Details will be described later in the manufacturing method section).

The single fiber fineness of the drawn yarn of the PPS fiber of the present invention (drawn single fiber fineness) is preferably 0.30 to 1.20 dtex. It is preferably 0.30 to 0.90 dtex, more preferably 0.30 to 0.70 dtex. By setting the single fiber fineness of the drawn yarn to 0.30 dtex or more, stable workability can be maintained without yarn breakage during spinning. Further, by setting the single fiber fineness of the drawn yarn to preferably 0.90 dtex or less, more preferably 0.70 dtex or less, uniformity is improved during wet-laid nonwoven production, and mechanical strength can be improved.

The undrawn yarn of the PPS fiber of the present invention preferably has a single fiber fineness of 0.90 to 3.0 dtex. By setting the undrawn yarn single fiber fineness to 0.90 dtex or more, the spinning operability is stabilized. It is possible to improve the physical strength.

The drawn yarn strength of the PPS fiber of the present invention is preferably 5.0 to 7.0 cN/dtex. It is preferably 5.5 to 6.5 cN/dtex. By setting the strength to 5.0 cN/dtex or more, the mechanical strength of the wet-laid nonwoven fabric can be improved, and by setting the strength to 7.0 cN/dtex or less, the fiber drawing runnability can be improved. In addition, since the crimpability of the fibers can be easily controlled, the dispersibility is improved when the wet-laid nonwoven fabric is formed.

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

The drawn yarn of the PPS fiber of the present invention preferably has a crystallinity and a rigid amorphous sum of 50 to 100%. A high-strength fiber can be obtained by setting the sum of the degree of crystallinity and the rigid amorphous to 50% or more. Rigid amorphous refers to an intermediate state between crystalline and completely amorphous polymers. It refers to the remaining amount after subtracting the movable amorphous amount (%).
Rigid amorphous amount [%] = 100 [%] - crystallinity [%] - movable amorphous amount [%]
Here, the movable amorphous content referred to in the present invention is obtained from measurement by temperature-modulated DSC as described later in Examples. Also, the degree of crystallinity is a value measured by a method described later.

The undrawn yarn of the PPS fiber of the present invention preferably has a degree of crystallinity of 20% or less. By setting the crystallinity of the undrawn yarn to 20% or less, the undrawn yarn acts as an adhesion point between fibers in the drying process during wet nonwoven fabric processing, making it possible to improve the paper strength of the nonwoven fabric.

It is important that the weight ratio of drawn yarns and undrawn yarns (raw cotton weight ratio) in the wet-laid nonwoven fabric made of PPS fibers of the present invention is 20 to 80%, and preferably the weight ratio of drawn yarns is 30 to 70%. be. If the weight ratio of the drawn yarn is less than 20%, the film will be formed and the tensile strength will decrease, which is not preferable. If the weight ratio of the drawn yarn exceeds 80%, the bonding points between the fibers are reduced, and the tensile strength of the wet-laid nonwoven fabric is lowered, which is not preferable.

Next, the method for producing the PPS fiber of the present invention will be explained.

The PPS fiber of the present invention can be obtained by a melt spinning method using a PPS resin whose polymer chain ends are COOH ends. First, after polymerizing PPS having Na as a polymer chain end by a known method, the polymer is acid-washed with an inorganic acid such as hydrochloric acid, an organic acid such as acetic acid, or the like to remove the COOH end of the polymer chain. to obtain a PPS resin. The PPS resin powder or pellets are melted and the melted resin is spun from a spinneret.

Since the PPS resin whose polymer chain ends are COOH ends has high molecular mobility, it is important to control the solidification behavior during spinning and the ejection stability during melt molding processing into a fiber shape. Regarding the control of solidification behavior, the spinning temperature normally selected from the resin melting point to the upper part of the pack housing is sufficient during melt spinning, but only the temperature of the lower part of the pack housing and the mouthpiece part is compared with the upper part of the pack housing. However, it is important to lower the temperature preferably by 5 to 15°C, more preferably by 9 to 11°C. The preferred temperature for the spin block and the upper portion of the pack housing is 315-330°C, and the preferred temperature for the lower portion of the spin block and the mouthpiece portion is 305-315°C.

In the conventional production of PPS fibers, L/D defined as the quotient obtained by dividing the land length L of the spinneret ejection hole (the length of the straight pipe portion that is the same as the diameter of the ejection hole of the spinneret) by the diameter D of the ejection hole of the spinneret is 1.0. It was usually set between 0 and 4.0. 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 ejection stability. By setting L/D to 5.0 or more and 10.0 or less, the back pressure when spinning PPS with high molecular mobility at 290 ° C to 360 ° C is optimized, and the ejection stability is improved. It is possible to make the claimed scope of the invention finer.

As the melt spinning machine, a pressure melter type spinning machine or a single- or twin-screw extruder type spinning machine is generally used. In order to prevent gelation due to thickening in the spinning step, the heating temperature is preferably as low as possible and sufficiently high enough to melt, specifically in the range of 290 to 360°C. Similarly, from the viewpoint of preventing gelation, it is preferable to use a nitrogen atmosphere during melting. Then, the molten polymer is discharged from the die and cooled and solidified by blowing cooling air. The velocity of the cooling air is usually 5 to 100 m/min, and the temperature may be room temperature or lower. After being cooled and solidified, the PPS fibers are applied with an appropriate amount of oil as a sizing agent, and then taken up by a predetermined take-up device. Take-off speeds are typically in the range of 500-7000 m/min.

The obtained undrawn yarn is then subjected to a drawing step to obtain drawn yarn. In the stretching step, the film is preferably stretched at a stretching temperature of about 90 to 170° C. and at a stretching ratio of 2 to 5 times by running in a heating bath, heating steam, hot plate, or hot roller. Further, the drawing may be one-step drawing or two-step drawing.

A fixed-length heat treatment may be performed after the hot drawing. In the fixed-length heat treatment, it is important to perform the heat treatment while keeping the length of the yarn constant, or to relax it by several percent.

The fixed-length heat treatment temperature is preferably 130° C. or higher, more preferably 150° C. or higher, so that the shrinkage of the raw cotton can be suppressed and the process passability during drying is improved. Further, by setting the temperature to preferably 200° C. or lower, more preferably 180° C. or lower, pseudo adhesion between fibers can be suppressed.

Further, the step of drawing the undrawn yarn may be a continuous step of drawing followed by spinning, or the undrawn yarn taken at a predetermined speed is once stored in a can or wound up, and then subjected to the drawing step. It may be a discontinuous process of providing. The obtained PPS fibers may be multifilaments, monofilaments, or staple fibers, but staple fibers are particularly preferred in the present invention. This is because staple fibers are generally produced in a larger scale industrially than filaments, and thus cost advantages can be obtained.

A papermaking dispersant is preferably added to the PPS fibers in order to serve as a raw material for fiber structures such as papermaking. Application of the papermaking dispersant to the obtained PPS fibers is usually carried out in a tow state using a kiss roller. The papermaking dispersant adhesion rate is preferably 0.2% by mass or more and 0.8% by mass or less with respect to the fiber weight. By setting the dispersant adhesion rate to preferably 0.1% by mass or more, more preferably 0.3% by mass or more, the dispersibility of the fibers is improved, and the wet-laid nonwoven fabric is excellent in film thickness uniformity and basis weight CV value. Become. Further, by setting the dispersant adhesion rate to preferably 0.8% by mass or less, more preferably 0.5% by mass or less, process passability is improved.

After applying the dispersant in this manner, crimping may be applied using a crimper. By imparting crimps, the fibers are entangled with each other, resulting in a wet-laid nonwoven fabric having excellent mechanical properties.

The number of crimps is preferably 2 crimps/25 mm or more and 15 crimps/25 mm or less. By setting the number of crimps to 2 crimps/25 mm or more, more preferably 5 crimps/25 mm or more, the fibers are entangled to form a wet-laid nonwoven fabric having excellent mechanical properties. In addition, by setting the number of crimps to 15 crests/25 mm or less, more preferably 12 crests/25 mm or less, the dispersibility of fibers during papermaking is improved, and the wet-laid nonwoven fabric has good film thickness uniformity and basis weight CV value. Become.

Cut fibers can be obtained by cutting the PPS fibers obtained as described above with a cutter after drying with a setter. The cut length of the cut fiber is preferably 1 mm or more and 20 mm or less. By setting the cut length to preferably 1 mm or more, more preferably 3 mm or more, a wet-laid nonwoven fabric having excellent mechanical properties can be obtained by entangling the fibers. Further, by setting the cut length to preferably 20 mm or less, more preferably 10 mm or less, the dispersibility of the fibers during dispersion is improved, resulting in a wet-laid nonwoven fabric with excellent film thickness uniformity and basis weight CV value.

Dispersion liquid is prepared by mixing drawn yarn cut fiber obtained by the above method and undrawn yarn cut fiber obtained by the method except for drawing in the above method at an arbitrary ratio and dispersing it in water. can be done.

If the dispersant is not applied in the tow state, the dispersant may be applied to the cut fibers at this stage.

A wet-laid nonwoven fabric can be obtained by supplying the above dispersion to a paper machine. The basis weight and thickness of the obtained wet-laid nonwoven fabric can be changed by adjusting the fiber concentration of the dispersion to be supplied.

The wet-laid nonwoven fabric obtained as described above is preferably dried in order to remove moisture. The drying temperature is preferably 90° C. or higher and 150° C. or lower so as not to cause deterioration of fusion bondability due to crystallization of the amorphous portion.

By thermocompression bonding the wet-laid nonwoven fabric with a flat plate heating press or calender rolls, the non-stretched yarn-cut fibers of the present invention cause fusion bonding, resulting in a wet-laid nonwoven fabric having excellent mechanical properties. The thermocompression bonding temperature is preferably 170° C. or more and 250° C. or less, and the compression bonding time is preferably 1 minute or more and 10 minutes or less. By setting the thermocompression bonding temperature to preferably 170° C. or higher, the fusion bonding of the PPS fibers of the present invention provides a wet-laid nonwoven fabric having excellent mechanical properties. By setting the thermocompression bonding temperature to 250° C. or lower, thermal shrinkage of the wet-laid nonwoven fabric during thermocompression bonding can be suppressed. Moreover, by setting the pressing time to 1 minute or longer, the entire wet-laid nonwoven fabric can be uniformly heated, resulting in a homogeneous wet-laid nonwoven fabric. By setting the crimping time to 10 minutes or less, deterioration of the mechanical properties of the wet-laid nonwoven fabric due to excessive crystallization can be suppressed.

The PPS fiber of the present invention will be described in more detail below with reference to examples. In addition, each physical property value in the examples was obtained by the following method.

[Measuring method]
A. Melt flow rate (MFR)
The melt mass flow rate of PPS was measured using a melt indexer (Toyo Seiki Seisakusho Co., Ltd. F- F01) was used.

B. Fineness Fineness was measured according to JIS L1015 (2010).

C. Strength Using a tensile tester ("Tensilon" manufactured by Orientec), according to the method described in JIS L1015 (2010), the stress-strain curve was obtained under the conditions of a sample length of 2 cm and a tensile speed of 2 cm / min, and cut from these. Seek the power of time. The tensile strength was determined by dividing the value by the fineness determined in B above.

D. Crystallinity Differential scanning calorimetry is performed under nitrogen with a differential scanning calorimeter (DSCQ1000 manufactured by TA Instruments) at a temperature increase rate of 10 ° C./min, and the temperature of the observed exothermic peak is measured at the crystallization temperature. The amount of heat was ΔHc (J/g). The heat of fusion at the endothermic peak temperature (melting point) observed at a temperature of 200° C. or higher was defined as ΔHm (J/g). The crystallinity Xc (%) was obtained by dividing the difference between ΔHm and ΔHc by the heat of fusion (146.2 J/g) of the completely crystalline PPS (equation 1 below).
Xc = {(ΔHm−ΔHc)/146.2}×100 (1)
<DSC>
- Atmosphere: Nitrogen flow (50 mL/min)
・Temperature/calorific value calibration: high-purity indium ・Specific heat calibration: sapphire ・Temperature range: 0 to 350℃
・Temperature increase rate: 10°C/min ・Sample amount: 5 mg
・Sample container: Aluminum standard container.

E. Rigid amorphous content Temperature-modulated DSC measurement is performed using the same differential scanning calorimeter as in D above, under nitrogen, under the conditions of a temperature increase rate of 2 ° C./min, a temperature amplitude of 1 ° C., and a temperature modulation period of 60 seconds. An auxiliary line is drawn on the baseline around the glass transition temperature (Tg) of the chart, and the difference is defined as the specific heat difference (ΔCp), and the specific heat difference (ΔCp0: 0.2699 J / g ° C.) before and after the Tg of the completely amorphous PPS. , and the movable amorphous amount (Xma) was obtained from the following formula (2). Furthermore, the rigid amorphous amount (Xra) was calculated from the difference between the crystallinity (Xc) from the whole and the movable amorphous amount (Xma) according to the following equation (3).
Xma (%)=ΔCp/ΔCp0×100 (2)
Xra (%) = 100 - (Xc + Xma) (3)
<Temperature modulation DSC>
- Atmosphere: Nitrogen flow (50 mL/min)
・Temperature/calorific value calibration: high-purity indium ・Specific heat calibration: sapphire ・Temperature range: 0 to 250℃
・Temperature increase rate: 2°C/min ・Sample amount: 5 mg
・Sample container: Aluminum standard container.

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

G. Spinnability In each example and comparative example, 24 spindles were spun, and the number of yarn breakages per spindle was counted at spinning times of 0 to 12 hours and 12 to 24 hours. There are various possible causes of thread breakage, but the number of thread breakages in 12 to 24 hours is higher than that in 0 to 12 hours because of thread breakage due to contamination of the spinneret. The spinnability was rated as ◯ when the number of times of thread breakage per spindle was less than 2 times in a spinning time of 12 hours, Δ when 2 to 3 times, and x when 4 times or more.

H. Drying process passability PPS fibers with a cut length of 6 mm obtained in Examples or Comparative Examples were mixed with an aqueous dispersion having a fiber concentration of 1% by weight, and then passed through a hand-made paper machine (square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd.). A wet-laid nonwoven fabric having a basis weight of 20 g/m 2 was obtained using an automatic couching machine, and subjected to a couching treatment. The undried nonwoven fabric is put into a KRK rotary dryer (standard type) manufactured by Kumagai Riki Kogyo Co., Ltd., and treated at a temperature of 120 ° C. for a treatment time of about 2.5 minutes per time to wrinkle the wet nonwoven fabric ( Drying process passability) was confirmed. Regarding the wrinkles during drying in the drying process, ◯ (excellent) indicates that almost no shrinkage wrinkles occur and continuous papermaking is possible. When it was assumed that continuous papermaking was impossible due to peeling, it was evaluated as x (defective).
I. Paper strength The wet-laid nonwoven fabric obtained by the above method G was subjected to thermocompression bonding at a pressing pressure of 1.5 MPa for 3 minutes using a flat plate heating press at 230°C. The resulting wet-laid nonwoven fabric was measured using 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. Arithmetic average value of is taken as tensile strength (N / 25 mm), ○ (excellent) when the average value of tensile strength is 15 N / 25 mm or more, △ (normal) when it is 10 to 15 N / 25 mm, less than that It was set as x (defective).

J. Comprehensive judgment In the above spinnability (0 to 12 hours, 12 to 24 hours) and papermaking evaluation (drying process passability, paper strength), if there is even one judgment of × (bad) among the 6 items, the overall Judgment was given as × (poor), and if only ◯ (excellent) or △ (normal) was judged among the 6 items, overall judgment was given as ◯ (excellent), and ◯ (excellent) was given as a pass.

<Examples 1 to 6, Comparative Examples 1 to 3>
After polymerizing PPS having Na as a polymer chain end by a known method so as to obtain the MFR shown in Table 1, the polymer was washed with a washing solution adjusted to pH 5.0 or less with acetic acid. After confirming that the Na content was 200 ppm or less and the ash content was 0.05 or less, it was judged to be a 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 melt spinning, the resin was melt extruded by a pressure melter, fed PPS to a spin pack while being metered by a gear pump, and spun through a spinneret with an L/D of 6.25.

After that, the total fineness is set to about 100,000 dtex, and it is drawn at a specific drawing ratio and a drawing temperature of 98 ° C. so that the fineness and fiber characteristics shown in Table 1 are obtained, and after applying a dispersant with a kiss roller and drying. It was cut to 6 mm to obtain drawn yarn cut fibers. Furthermore, an undrawn yarn-cut fiber was obtained by a method in which only the drawing was removed from the above method. The resulting PPS cut fiber was mixed with an aqueous dispersion having a fiber concentration of 1% by weight, and was wet-processed with a basis weight of 20 g/m ² using a hand-made paper machine (square sheet machine with automatic couching manufactured by Kumagai Riki Kogyo Co., Ltd.). The nonwoven fabric was subjected to a couching treatment. The undried nonwoven fabric was placed in a KRK rotary dryer (standard type) manufactured by Kumagai Riki Kogyo Co., Ltd. and treated at a temperature of 120 ° C. for a treatment time of about 2.5 minutes to obtain a wet nonwoven fabric. . Further, the wet-laid nonwoven fabric was subjected to thermocompression bonding for 3 minutes at a press pressure of 1.5 MPa using a flat plate heating press at 230°C.

The above evaluation was performed on the obtained PPS cut fiber and wet-laid nonwoven fabric. The results are shown in the table below.

In Examples 1 to 4, a PPS for papermaking having good spinnability and good water dispersibility can be obtained. The paper strength of was also strong enough. In Example 5, the fineness of the drawn yarn was thin, while the fineness of the undrawn yarn was thick. Therefore, the basis weight of papermaking varied greatly, and the paper strength was inferior to the wet nonwoven fabric using fine undrawn yarn. In Example 6, an undrawn yarn was used which was collected under the condition that polymer orientation progressed during spinning. In this case, the dry heat shrinkage rate of the undrawn yarn was high and wrinkles were likely to occur in the drying process.

On the other hand, in Comparative Example 1, wrinkles occurred during drying due to the large fineness and the large variation in basis weight. Furthermore, sufficient paper strength could not be obtained because the number of constituent sheets was reduced. In Comparative Example 2, due to the Ca terminal, the degree of polymerization of the resin decreased when the MFR was increased, and sufficient strength of the fiber was not obtained. Therefore, sufficient paper strength was not obtained in the obtained wet-laid nonwoven fabric. In Comparative Example 3, due to Ca terminal and low MFR, spinnability deteriorated in spinning fine fineness product, fiber strength was low, and sufficient paper strength could not be obtained. In Comparative Example 4, due to Na terminal, fiber strength was not obtained, and sufficient paper strength was not obtained.

Claims (7)

A polyphenylene sulfide fiber which is a drawn yarn having a polymer chain end of COOH end, 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. The polyphenylene sulfide fiber according to claim 1, wherein the drawn yarn has a strength of 5.0 to 7.0 cN/dtex. 3. The polyphenylene sulfide fiber according to claim 1, wherein the sum of the degree of crystallinity and rigid amorphousness of the drawn yarn is 50 to 100%. A wet laid nonwoven fabric containing at least 10% of the polyphenylene sulfide fiber according to any one of claims 1 to 3. 5. The wet-laid nonwoven fabric according to claim 4, further comprising undrawn yarns of polyphenylene sulfide fibers as binder fibers, wherein the undrawn yarns have a single fiber fineness of 0.9 to 3.0 dtex. 6. The wet-laid nonwoven fabric according to claim 4 or 5, wherein the dry heat shrinkage of the undrawn yarn is 60% or less. The wet-laid nonwoven fabric according to any one of claims 4 to 6, wherein the crystallinity of the undrawn yarn is 20% or less.