阅读说明：本技术 聚苯硫醚短纤维、纤维结构体、过滤器用毡及袋式过滤器 (Polyphenylene sulfide short fiber, fiber structure, filter felt, and bag filter ) 是由 杉本武司 光永怜央 森达哉 小林祐真 于 2018-12-12 设计创作，主要内容包括：单纤维纤度为0.70～0.95dtex,强度为4.5～5.5cN/dtex,纤维长度为20～100mm,熔体流动速率(MFR)值为200～295g/10分钟的聚苯硫醚短纤维。提供不降低纤维生产性和毡生产性,而能够提高粉尘捕集性能和提高机械强度的聚苯硫醚短纤维。(A polyphenylene sulfide short fiber having a single fiber fineness of 0.70 to 0.95dtex, a strength of 4.5 to 5.5cN/dtex, a fiber length of 20 to 100mm, and a Melt Flow Rate (MFR) of 200 to 295g/10 min. A polyphenylene sulfide short fiber which can improve the dust trapping performance and the mechanical strength without lowering the fiber productivity and the felt productivity.)

1. A polyphenylene sulfide short fiber has a single fiber fineness of 0.70 to 0.95dtex, a strength of 4.5 to 5.5cN/dtex, a fiber length of 20 to 100mm, and a melt flow rate MFR value of 200 to 295g/10 min.

2. The polyphenylene sulfide staple fiber according to claim 1, wherein the degree of crystallinity is 30 to 40% and the amount of rigid amorphous content is 40 to 60%.

3. The polyphenylene sulfide staple fiber according to claim 1 or 2, having a birefringence Δ n of 0.25 to 0.30.

4. The polyphenylene sulfide staple fiber according to any one of claims 1 to 3, which has a crimp number of 10 to 16 peaks/25 mm and a crimp degree of 12 to 20%.

5. A fiber structure comprising 10% by mass or more of the polyphenylene sulfide short fiber according to any one of claims 1 to 4.

6. A filter mat comprising at least 1 or more layer composed of the fiber structure according to claim 5.

7. A bag filter obtained by sewing the filter felt according to claim 6 into a bag.

8. A method for producing the polyphenylene sulfide short fiber according to any one of claims 1 to 4, comprising the steps of producing an undrawn yarn by a melt spinning method using a polyphenylene sulfide resin having an MFR of 200 to 295g/10 min, drawing the undrawn yarn at a temperature of 80 to 170 ℃ at a magnification of 2 to 5 times, performing a fixed-length heat treatment at a temperature of 190 to 270 ℃ at a magnification of 1.05 to 1.15 times, crimping the undrawn yarn by a stuffer box, drying the crimped yarn, applying an oil, and cutting the crimped yarn to a predetermined length to obtain the polyphenylene sulfide short fiber.

9. A method for producing a fibrous structure comprising the polyphenylene sulfide short fiber, the fibrous structure being in the form of a nonwoven fabric, the method comprising passing the polyphenylene sulfide short fiber according to any one of claims 1 to 4 through a carding machine to produce the nonwoven fabric.

10. A method for manufacturing a felt for a filter having a 3-layer structure including a fiber web 31 forming a filter layer having an air inflow surface, an aggregate 32 serving as a woven fabric, and a fiber web 33 forming a non-filter layer having an air discharge surface, the method comprising: a net 31 is produced by the method of claim 9, a woven fabric or aggregate 32 is laminated on the net 31, a net 33 is produced, the net 31 and the woven fabric or aggregate are further laminated on the laminated body, and the laminated body is entangled to be integrated,

as a method of integrating the entangled net, a needle punching method and a spunlacing method are used.

11. A method for manufacturing a bag filter by sewing the filter felt according to claim 6 into a bag, wherein a thread made of a material such as polyarylene sulfide, a fluorinated resin, or a fluorinated resin copolymer is used as a thread used for the sewing.

Technical Field

The present invention relates to polyphenylene sulfide short fibers suitable for a bag filter, and a bag filter.

Background

Polyphenylene sulfide (hereinafter, abbreviated as PPS in some cases) resin has excellent properties suitable as engineering plastics, such as heat resistance, barrier properties, chemical resistance, electrical insulation properties, and moist heat resistance, and is mainly used for injection molding and extrusion molding in various electric parts, electronic parts, mechanical parts, automobile parts, films, fibers, and the like.

For example, PPS materials are widely used for filter cloths used in various industrial filters such as bag filters for collecting exhaust gas. As such a filter cloth, a filter cloth in which PPS staple fibers are laminated on a base cloth made of a staple yarn of the PPS staple fibers and the base cloth is integrated by needling is exemplified.

Such a filter cloth is used to collect dust in exhaust gas and discharge exhaust gas containing no dust to the outside. The properties required for the bag filter include dust trapping performance and mechanical strength.

In order to reduce the soot concentration in the exhaust gas, a bag filter having excellent dust trapping performance is required. In order to improve the dust-collecting performance of the bag filter, it is a common method to make the fiber used finer. By using fine fibers, the number of fibers constituting the filter cloth is increased, and dust is likely to be entangled.

In addition, in the bag filter, a pulse jet method is often used as a method for efficiently removing dust adhering to the filter cloth. The pulse jet method is a method in which dust adhering to the surface of the filter cloth is not accumulated while the dust is being attached, and the filter cloth is vibrated by periodically jetting a high-speed air flow to the filter cloth, thereby sweeping off the dust adhering to the surface of the filter cloth. In such a pulse jet method, dust can be brushed off, but it is a matter of course that the mechanical strength of the filter cloth tends to decrease with time by a high-speed air flow applied as an external force. When an external force is periodically applied, if the mechanical strength of the filter cloth and the dimensional stability of the filter cloth are insufficient, there is a problem that the filter cloth is broken and cannot function as a bag filter. That is, mechanical strength is important as a characteristic required for the bag filter. In addition, in order to improve the mechanical strength of the bag filter, it is particularly important to increase the tensile strength of the fibers used. From the above, it is important that the PPS fiber is fine in fineness and high in strength as the characteristics of the PPS fiber to be tested in the bag filter.

As a method for obtaining a fine PPS fiber, a special drawing method called flow drawing has been proposed (patent document 1). In this proposal, a fine fineness of 0.22dtex of raw cotton was surely obtained.

Further, a method of obtaining high-strength PPS fibers by drawing at a high ratio has been proposed (patent document 2). In this proposal, a high-strength fiber of 5cN/dtex or more is obtained. Further, in patent document 3, high-strength raw cotton of 5cN/dtex or more is obtained by setting the amount of rigid amorphous to a specific range.

Further, patent document 4 proposes a method for obtaining a polyarylene sulfide fiber which is extremely fine and has excellent mechanical strength by performing electric field spinning. This proposal does provide a high-strength fiber having an extremely fine fineness of 1 μm or less (about 0.01dtex) and a tenacity of 5.5cN/dtex or more.

Disclosure of Invention

Problems to be solved by the invention

However, in patent document 1, a special drawing method called flow drawing is used, and fiber productivity is lowered. Further, there is no description about a method for improving the strength, and the mechanical strength cannot be said to be sufficient.

The fibers actually obtained by the method described in patent document 2 have a fineness of 10dtex or more, and the fibers actually obtained by the method described in patent document 3 have a fineness of 2dtex or more, which cannot be said to be a sufficiently fine fineness for improving the dust collecting performance. In patent document 2, in order to achieve high rigidity and high strength, a large-fineness fiber of 10dtex or more is assumed, but no mention is made of a method for achieving high rigidity and high strength using a small-fineness fiber. Patent document 3 describes a method of using high molecular weight PPS, but the high molecular weight PPS is inferior in drawability and is disadvantageous for making the fineness finer.

In patent document 4, a fiber having a small fineness and high strength is obtained, but the productivity of the fiber is inferior to that of a spinning method such as melt spinning by using special spinning such as electric field spinning.

The invention provides a polyphenylene sulfide short fiber which can improve dust collection performance and mechanical strength without reducing fiber productivity and felt productivity.

Means for solving the problems

The following conditions were found to be important in order to provide a polyphenylene sulfide short fiber which can improve the dust trapping performance and improve the mechanical strength without lowering the fiber productivity and the felt productivity. Namely, the present invention is as follows.

1. A polyphenylene sulfide short fiber has a single fiber fineness of 0.70 to 0.95dtex, a strength of 4.5 to 5.5cN/dtex, a fiber length of 20 to 100mm, and a Melt Flow Rate (MFR) of 200 to 295g/10 min.

Further, preferred embodiments of the present invention are as follows.

2. The crystallinity is 30-40%, and the rigid amorphous content is 40-60%.

3. The birefringence (Deltan) is 0.25 to 0.30.

4. The number of crimps is 10 to 16 peaks/25 mm, and the degree of crimps is 12 to 20%.

5. A fiber structure comprising 10 mass% or more of the polyphenylene sulfide short fiber of the present invention.

6. A filter mat comprising at least 1 or more layer composed of the above fiber structure.

7. A bag filter is obtained by sewing the filter into a bag shape with a felt.

8. A method for producing a polyphenylene sulfide short fiber, which comprises producing an undrawn yarn by a melt spinning method using a polyphenylene sulfide resin having an MFR of 200 to 295g/10 min, drawing the undrawn yarn at a temperature of 80 to 170 ℃ at a magnification of 2 to 5 times, subjecting the drawn undrawn yarn to a fixed-length heat treatment at a temperature of 190 to 270 ℃ at a magnification of 1.05 to 1.15 times, crimping the drawn undrawn yarn by a stuffer box, drying the crimped yarn, applying an oil, and cutting the crimped yarn to a predetermined length.

9. A method for producing a fibrous structure comprising polyphenylene sulfide short fibers, wherein the fibrous structure is in the form of a nonwoven fabric, the method comprising passing the polyphenylene sulfide short fibers described in any one of 1 to 4 through a carding machine to produce a nonwoven fabric.

10. A method for manufacturing a felt for a filter having a 3-layer structure of a fiber web 31 forming a filter layer of an air inflow surface, a woven fabric (aggregate) 32, and a fiber web 33 forming a non-filter layer of an air discharge surface, the method comprising: the method of producing the net 31 by the method described in the above 9, laminating the net 31 and the woven fabric (aggregate) 32, then producing the net 33, further laminating the net 31 and the woven fabric (aggregate) on the laminate, and then interlacing and integrating them, and as a method of interlacing and integrating the net, a needle punching method or a spunlacing method is used.

11. A method for manufacturing a bag filter by sewing the filter felt according to the above 6 in a bag shape, wherein a thread made of a material such as polyarylene sulfide, a fluorinated resin, or a fluorinated resin copolymer is used as a thread used for the sewing.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a polyphenylene sulfide short fiber which can improve dust collection performance and mechanical strength without lowering fiber productivity and felt productivity.

Drawings

Fig. 1 is an exploded cross-sectional view of a filter material (filter cloth) using a nonwoven fabric containing polyphenylene sulfide short fibers of the present invention.

Detailed Description

Hereinafter, the present invention will be described in detail together with the desired embodiments.

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

The PPS may be a homopolymer having 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 be a copolymer or a mixture with other aromatic sulfides, as long as the effects of the present invention are not impaired.

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

The weight average molecular weight of the PPS resin in the invention is preferably 30000-90000. When melt-spinning is performed using a PPS resin having a weight average molecular weight of less than 30000, the spinning tension is low, and yarn breakage often occurs during spinning, and if a PPS resin having a weight average molecular weight of more than 90000 is used, the viscosity during melting becomes too high, and the spinning equipment must be made to have a special high pressure resistance standard, which is disadvantageous because the equipment cost becomes high. More preferably, the weight average molecular weight is 40000-60000.

In the case of using the PPS resin in the present invention, commercially available PPS resins include "トレリナ" (registered trademark) manufactured by imperial レ (strain) and "フォートロン" (registered trademark) manufactured by "strain) クレハ.

The PPS staple fiber in the invention has a fiber length of 20-100 mm, preferably 40-80 mm. When the fiber length is in this range, the felt processability in the subsequent step can be improved.

The single fiber fineness of the PPS staple fiber used in the invention is 0.70-0.95 dtex, preferably 0.75-0.85 dtex. By setting the single fiber fineness to 0.70dtex or more, spinning workability can be improved, and fly (fly) or the like at the time of felt processing can be suppressed to improve card passing property. Further, the single fiber fineness is 0.95dtex or less, whereby the dust collecting performance can be improved.

The PPS staple fiber used in the invention has the strength of 4.5-5.5 cN/dtex, preferably 4.7-5.1 cN/dtex. By setting the strength to 4.5cN/dtex or more, the mechanical strength of the felt can be improved, and by setting the strength to 5.5cN/dtex or less, the stretch workability can be improved, and in addition, the crimp application property of the short fiber can be improved, and fly etc. at the time of felt processing can be suppressed, and the card passing property can be improved.

The PPS resin used as a raw material in the production of the PPS staple fiber of the present invention has a Melt Flow Rate (MFR) value of 200 to 295g/10 min, preferably 210 to 270g/10 min, and more preferably 220 to 250g/10 min. By setting the MFR value to 200g/10 min or more, the fluidity at the time of melting can be secured, and a fine-denier PPS short fiber can be obtained. Further, by setting the MFR value to 295g/10 min or less, a sufficient molecular weight of the polymer can be obtained, and a high-strength PPS short fiber can be obtained.

Further, since PPS is a resin which is not deteriorated by hydrolysis or the like, the MFR of the PPS staple fiber of the invention itself is, similarly to the PPS resin as a raw material thereof, 200 to 295g/10 min, preferably 210 to 270g/10 min, and more preferably 220 to 250g/10 min.

In the PPS staple fiber of the invention, it is extremely important that the single fiber fineness is 0.70-0.95 dtex and the strength is 4.5-5.5 cN/dtex. When a fine-denier PPS staple fiber is produced by a conventional melt spinning method, a resin having a high MFR value and good drawability is generally used, but such a resin tends to have a low molecular weight and it is difficult to increase the strength. On the other hand, when high-strength PPS staple fibers are produced by a conventional melt spinning method, a resin having a low MFR value and a high molecular weight is generally used, but in this case, the drawability is poor, the spinning workability is inferior, and it is difficult to make the fineness fine. If it is high in strength and coarse in fineness, the dust trapping performance becomes inferior, and if it is fine in fineness and low in strength, the mechanical strength as a felt becomes inferior. Accordingly, the present inventors have conducted extensive studies and found that a fine fineness and a high strength can be simultaneously achieved by using a resin having a specific MFR in a range of 200 to 295g/10 min.

The elongation of the PPS staple fiber of the present invention is preferably 50.0% or less, and more preferably 40.0% or less. The lower the elongation, the more highly oriented the molecular chain is in the fiber axial direction, and is preferable in improving the strength physical properties. The lower limit of the elongation is preferably 5.0% or more in order to ensure good workability and process passability.

The PPS staple fiber of the present invention preferably has a dry heat shrinkage at 180 ℃ of 20% or less, more preferably 10% or less, and still more preferably 5% or less. The lower the dry heat shrinkage ratio, the more the shrinkage at the time of producing a felt or at the time of actual use as a filter can be suppressed, and therefore, the lower the dry heat shrinkage ratio, the more preferable. The lower limit of the dry heat shrinkage is not particularly limited, and may be 1% or more as a practically possible range.

The crystallinity of the PPS staple fiber of the present invention is preferably 30 to 40%. By setting the crystallinity to 30% or more, a high-strength fiber can be obtained. Further, by setting the crystallinity to 40% or less, the crimp application property of the short fibers can be improved, fly at the time of felt processing can be suppressed, and the card passing property can be improved.

The PPS staple fiber of the invention has a rigidity amorphous content of preferably 40 to 60%, more preferably 43 to 55%, and still more preferably 45 to 50%. The term "rigid amorphous" means a state between a crystalline state and a completely amorphous state of a polymer, and means a remaining amount obtained by subtracting a crystallinity (%) and a mobile amorphous amount (%) from the whole (100%) of crystalline/amorphous bodies forming a fiber, as shown in the following formula.

The rigid amorphous content [% ] -crystallinity [% ] -movable amorphous content [% ].

Here, the movable amorphous content in the present invention is obtained by measurement using a temperature-modulated DSC as described later in examples. By setting the amount of rigid amorphous to 40% or more, a high-strength fiber can be obtained. Further, by setting the rigid amorphous content to 60% or less, the crimp application property of the short fibers can be improved, fly-over at the time of felt processing can be suppressed, and the card passing property can be improved.

The birefringence (Δ n) of the PPS staple fiber of the invention is preferably 0.25 to 0.30. By setting the birefringence to 0.25 or more, a fiber having high strength can be obtained. Further, by setting the birefringence to 0.30 or less, the curl imparting property of the short fibers can be improved, fly at the time of felt processing can be suppressed, and the card passing property can be improved.

The number of crimps of the PPS staple fiber of the invention is preferably 10 to 16 peaks/25 mm, more preferably 12 to 16 peaks/25 mm. Further, the degree of curling is important to be 12 to 20%, and preferably 15 to 20%. By setting the number of crimps to 10 peaks/25 mm or more and the degree of crimpness to 12% or more, the crosslinkability between fibers becomes high, and fly or the like at the time of felt processing can be suppressed, and the card passing property can be improved. Further, by setting the number of crimps to 16 peaks/25 mm or less and setting the degree of crimps to 20% or less, the occurrence of nodules during felt processing can be suppressed, and felt processability can be improved.

In the case of producing high-strength PPS staple fibers by a conventional melt spinning method, a resin having a low MFR value and a high molecular weight is generally used, but in this case, the stiffness is high, and therefore it is difficult to increase the number (degree) of crimp. If it is high strength and low curl number (degree), the felt processability becomes inferior, and if it is low strength and high curl number (degree), the mechanical strength of the felt becomes inferior. The present inventors have conducted extensive studies and as a result have found that the use of a PPS resin having a specific MFR range of 200 to 295g/10 min can achieve both high strength and high crimp number (degree), that is, both mechanical strength and felt processability of a felt. That is, it has been found that the use of a PPS resin having a specific MFR in the range of 200 to 295g/10 min makes it possible to achieve a fine fineness, a high strength, and a high number (degree) of crimp at the same time, and to improve the dust collecting performance and the mechanical strength at the same time without lowering the fiber productivity and the felt productivity.

The PPS staple fiber of the present invention can be used as a fiber structure containing the same. Such a fiber structure preferably contains the PPS staple fiber of the present invention in an amount of 10 mass% or more, more preferably 25 mass% or more, and still more preferably 40 mass% or more, relative to the fiber structure. The effect of improving the dust-trapping performance can be obtained by including 10 mass% or more of the PPS staple fiber of the present invention.

In the above-mentioned fiber structure, cotton-like materials using the PPS staple fibers of the present invention, cotton-like materials further mixed with other fibers, staple yarns, nonwoven fabrics, woven fabrics, knitted fabrics, and other fabrics can be cited, but a nonwoven fabric is suitably selected, and particularly a dry nonwoven fabric having a mesh shape is suitably selected.

The fiber structure of the present invention described above can be made into a filter felt including the fiber structure. Such a filter mat preferably contains at least 1 or more layer composed of the fiber structure of the present invention. The fiber structure of the present invention containing 1 or more layers can provide an effect of improving the dust trapping performance. The form of the fibrous structure of the present invention is not particularly limited, and cotton-like materials, nonwoven fabrics, woven fabrics, knitted fabrics, and the like can be mentioned, but nonwoven fabrics are suitably selected, and particularly, dry nonwoven fabrics in a mesh form are suitably selected. The form of the layer other than the layer composed of the fiber structure of the present invention is not particularly limited, and cotton, nonwoven fabric, woven fabric, knitted fabric, and the like can be mentioned. The material used for the layers other than the layer composed of the fiber structure of the present invention preferably has heat resistance and chemical resistance, and therefore polyarylene sulfide, fluorinated resin copolymer, and the like are preferably used, and polyarylene sulfide, Particularly Polyphenylene Sulfide (PPS), is particularly preferably used.

The structure of the filter felt of the present invention is not particularly limited, but a preferable example is shown in fig. 1 by an exploded cross-sectional view. Fig. 1 is an exploded cross-sectional view of a filter material (filter cloth) using a nonwoven fabric containing PPS staple fibers of the present invention. In fig. 1, the fiber web 31 forming the filter layer of the air inflow surface indicates, for example, a surface of the filter material for surface filtration, a surface on which air containing dust first comes into contact with the filter material. That is, the surface is a surface on which dust is collected on the surface of the filter material to form a dust layer. The fibrous structure of the present invention is used for the web 31, and contains the PPS staple fibers of the present invention in an amount of 10 mass% or more. The opposite side surface is formed of the fiber web 33 which is a non-filter layer forming the air discharge surface, and indicates a surface from which the dust-removed air is discharged. Further, a woven fabric (aggregate) 32 is sandwiched between the fiber webs 31 and 33, and a felt is produced by a needle punching process. The felt thus produced can provide a felt for a filter excellent in mechanical strength such as dimensional stability, tensile strength and abrasion resistance, and also excellent in dust trapping property.

The filter of the present invention is sewn into a bag shape with a felt, and is suitably used as a bag filter for collecting exhaust gas from a garbage incinerator, a coal boiler, a metal melting furnace, or the like, which requires heat resistance. As the sewing thread used for sewing, a thread made of a material having heat resistance and chemical resistance is preferably used, and therefore, polyarylene sulfide, fluorinated resin, and fluorinated resin copolymer are preferably used, and polyarylene sulfide is particularly preferably used.

Next, an example of a method for producing the PPS staple fiber of the present invention will be described.

The PPS resin can be obtained by melt spinning using the PPS resin having an MFR of 200 to 295g/10 min as described above. The PPS resin is melted in powder or pellet form, and the melted resin is spun from a spinneret. As the melt spinning machine, a pressure-melt type spinning machine or a single-screw or twin-screw extrusion type spinning machine is generally used. The molten polymer is then discharged from the die, and cooled and solidified by blowing cooling air. The cooled and solidified fibers are subjected to drawing by a predetermined drawing device after being applied with an appropriate amount of finish as a sizing agent. The specific melting temperature is usually 305 to 340 ℃, the wind speed of the cooling wind is usually 35 to 100 m/min, the temperature of the cooling wind is usually room temperature or below, and the traction speed is usually 400 to 3000 m/min.

The drawn fiber is then usually subjected to a drawing process. In the stretching step, it is preferable to stretch the sheet at a stretching temperature of about 80 to 170 ℃ by moving the sheet in a heating bath, on a hot plate, or on a hot roll. The stretching ratio is preferably 2 to 5 times, and more preferably 3 to 4 times. The number of stretching steps may be 1-step stretching, but 2-step stretching is preferable.

By performing the fixed-length heat treatment after the hot drawing, crystallization of the fiber progresses further, and the amount of rigid amorphous increases. In the conventional fixed-length heat treatment, the heat treatment is usually performed while the length of the yarn is substantially constant, or the yarn is loosened by several percent. However, in the production of the present invention, it is important to apply a slight stretching, i.e., a magnification of 1.05 to 1.15 times, during the fixed-length heat treatment.

The strength, crystallinity, rigidity amorphous content, and birefringence as described above can be suitably applied to the PPS staple fiber by setting the temperature of the constant length heat treatment to 190 ℃ or higher, more preferably 200 ℃ or higher, and still more preferably 210 ℃ or higher. Further, by setting the temperature of the constant-length heat treatment to 270 ℃ or lower, more preferably 240 ℃ or lower, the pseudo-adhesion between the fibers can be suitably suppressed.

By setting the fixed length heat treatment time to 5 seconds or more, the above-described strength, crystallinity, rigidity amorphous content, and birefringence can be suitably applied to the PPS staple fiber. On the other hand, even if the constant length heat treatment time is too long, the strength, crystallinity, rigidity amorphous content, and birefringence are merely saturated, and the upper limit value of the constant length heat treatment time is preferably about 12 seconds.

The present inventors have found that the fineness and strength can be adjusted by subjecting fibers made of a PPS resin having a specific MFR to a fixed-length heat treatment under specific conditions as described above. That is, by controlling the molecular orientation and the heat-setting property at the time of the fixed-length heat treatment in stretching, even a PPS resin that can achieve a high MFR such as a small fineness can be made to have high strength.

Subsequently, the yarn subjected to the fixed-length heat treatment is crimped by a stuffer box type crimper box. Further, at this time, the curl may be heat-set by steam or the like. When the yarn of the PPS fiber crystallized by the fixed length heat treatment is fixed in a crimped state, it is important to use a temperature equal to or higher than the fixed length heat treatment temperature as the temperature at the time of crimping, but if the steam temperature is too high, fusion between the fibers may occur.

Then, the finish oil is preferably applied by 0.01 to 3.0% by mass with respect to the amount of the fiber, and the relaxation heat treatment is preferably performed at 50 to 150 ℃ for 5 to 60 minutes, as required. Further, the fibers were cut into a predetermined length to obtain a PPS staple fiber. The order of these steps can be changed as necessary.

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

Examples of the form of the fibrous structure of the present invention include fabrics such as mixed cotton, nonwoven fabric, woven fabric, and knitted fabric, and the nonwoven fabric is preferably selected, and particularly, dry nonwoven fabric is preferably selected. As a method for producing a nonwoven fabric, a method of passing the PPS staple fiber of the present invention through a carding machine to produce a nonwoven fabric can be suitably used. Here, the fibrous structure of the present invention may contain the PPS staple fiber of the present invention in an amount of 10 mass% or more, and may be mixed with other fibers before passing through a carding machine.

Next, a method for producing the filter felt of the present invention will be explained.

The filter felt of the present invention has a 3-layer structure of a fiber web 31 forming a filter layer of an air inflow surface, a woven fabric (aggregate) 32, and a fiber web 33 forming a non-filter layer of an air discharge surface. The following methods may be suitably used: first, a net 31 is produced by the above-described method, a net 31 and a cloth (aggregate) 32 are laminated, a net 33 is produced, the laminated body of the net 31 and the cloth (aggregate) is further laminated, and then they are entangled and integrated. Further, as a method of interlacing and integrating the web, a needle punching method and a spunlacing method are preferable.

The PPS staple fibers of the invention are used for the web 31. The material used for the reinforcing cloth and the net of the 2 nd net layer is preferably heat-resistant and chemical-resistant, and therefore polyarylene sulfide, fluorinated resin and fluorinated resin copolymer are preferably used, and polyarylene sulfide, particularly polyphenylene sulfide, is preferably used.

Next, a method for manufacturing the bag filter of the present invention will be explained.

The filter of the present invention may be sewn into a bag shape with a felt to make a bag filter. As the sewing thread used for sewing, a thread made of a material having heat resistance and chemical resistance is preferably used, and polyarylene sulfide, fluorinated resin copolymer, and the like are preferably used, and polyarylene sulfide, particularly polyphenylene sulfide, is preferably used.