EP4707446A1

EP4707446A1 - Fiber article manufacturing method

Info

Publication number: EP4707446A1
Application number: EP24800092.9A
Authority: EP
Inventors: Tatsuya HIGASHIGAKI; Hiroaki Shintani; Yuki TSUKAMOTO; Chihiro Tanaka
Original assignee: Daicel Corp
Current assignee: Daicel Corp
Priority date: 2023-05-02
Filing date: 2024-04-25
Publication date: 2026-03-11
Also published as: JPWO2024228361A1; WO2024228361A1; CN120981618A

Abstract

An object of the present invention is to make it possible to produce a fiber article capable of achieving weight reduction and improvement in strength and suppressing an increase in pressure loss with the lapse of used time, in a case of producing the fiber article including a first fiber and a second fiber having an outer diameter smaller than that of the first fiber. A method for producing a fiber article of the present invention includes a first step of affixing a plurality of resin particles containing a polymer that can be fiberized to a fiber sheet including a plurality of first fibers, the fiber sheet being conveyed in a predetermined conveyance direction, a second step of applying a first external force to the plurality of first fibers and the plurality of resin particles of the fiber sheet that is conveyed, to reduce fiber gaps between the first fibers, and a third step of applying a second external force to the fiber sheet in which the applied first external force is relaxed, the fiber sheet being conveyed in the conveyance direction, to enlarge the fiber gaps between the plurality of first fibers, with respect to at least a width direction of the fiber sheet, to form a plurality of second fibers from the plurality of resin particles, each of the plurality of second fibers being thinner than each of the first fibers, and forming a fiber composite containing the plurality of first fibers and the plurality of second fibers.

Description

Technical Field

The present disclosure relates to a production method for a fiber article.

Background Art

In the present specification, terms defined as described below are used.
TD: An abbreviation for total denier, which refers to the denier (the number of grams per 9000 m) of a band or of a plurality of filaments of one bundle.
FD: An abbreviation for filament denier, which refers to the denier (the number of grams per 9000 m) of a single fiber (one fiber). The filament denier may also be referred to as a single fiber denier.
Band: A product formed by combining yarns, which are assemblies of filaments (single fibers) extruded from each spinneret of a plurality of spinning cabinets, and assembling a plurality of yarns to form an end with the TD set to a predetermined value. This end is then crimped. The crimped end (assembly of filaments) is called a band. That is, the band has a TD and a crimp-index.
As a fiber article used for applications such as a filter of an air conditioner, for example, as disclosed in Patent Document 1, a method for producing a fiber article including a first fiber and a second fiber having an outer diameter smaller than that of the first fiber is known.

Citation List

Patent Document

Patent Document 1: WO 2021/039980

Summary of Invention

Technical Problem

In the fiber article described in Patent Document 1, performance of the fiber article is improved by supporting the second fibers with the first fibers and allowing the first fibers and the second fibers to exhibit their respective functions. Here, for example, it is more preferable to produce the fiber article that can achieve weight reduction and strength improvement and can suppress an increase in pressure loss with the lapse of used time.
An object of the present disclosure is to make it possible to produce a fiber article capable of achieving weight reduction and improvement in strength and suppressing an increase in pressure loss with the lapse of used time in a case of producing the fiber article including a first fiber and a second fiber having an outer diameter smaller than that of the first fiber.

Solution to Problem

To solve the above problem, a method for producing a fiber article according to one aspect of the present disclosure includes a first step of affixing a plurality of resin particles containing a polymer that can be fiberized to a fiber sheet including a plurality of first fibers, the fiber sheet being conveyed in a predetermined conveyance direction, a second step of applying a first external force to the plurality of first fibers and the plurality of resin particles of the fiber sheet to which the plurality of resin particles are affixed, the fiber sheet being conveyed, to reduce fiber gaps between the plurality of first fibers, and a third step of applying a second external force to the fiber sheet in which the applied first external force is relaxed, the fiber sheet being conveyed in the conveyance direction, to enlarge the fiber gaps between the plurality of first fibers, with respect to at least a width direction of the fiber sheet, to form a plurality of second fibers from the plurality of resin particles, each of the plurality of second fibers being thinner than each of the plurality of first fibers, and forming a fiber composite containing the plurality of first fibers and the plurality of second fibers.

Advantageous Effects of Invention

According to one aspect of the present disclosure, in the case of producing a fiber article including a first fiber and a second fiber having an outer diameter smaller than that of the first fiber, a fiber article that can achieve weight reduction and strength improvement and can suppress an increase in pressure loss with the lapse of used time can be produced.

Brief Description of Drawings

FIG. 1 is a schematic diagram of a fiber sheet production apparatus according to a first embodiment.
FIG. 2 is a schematic diagram of a fiber article production apparatus according to the first embodiment.
FIG. 3 is a schematic diagram of a fiber article production apparatus according to a second embodiment.
FIG. 4 is an enlarged photograph of a fiber sheet before application of a second external force in Example 1.
FIG. 5 is an enlarged photograph of the fiber sheet after the application of the second external force in Example 1.
FIG. 6 is a graph showing a relationship between a degree of elongation in a width direction and a pressure loss of each of fiber articles of Examples 2 and 3.
FIG. 7 is a graph showing a relationship between the degree of elongation in the width direction and a trapping efficiency of each of the fiber articles of Examples 2 and 3.
FIG. 8 is a graph showing a relationship between the degree of elongation in the width direction and a PF value of each of the fiber articles of Examples 2 and 3.
FIG. 9 is a graph showing a relationship between the degree of elongation in the width direction and a thickness change rate of each of the fiber articles of Examples 2 and 3.
FIG. 10 is a graph showing a relationship between the degree of elongation in the width direction and a basis weight of each of the fiber articles of Examples 2 and 3.
FIG. 11 is a graph showing a relationship between a degree of elongation in a width direction and a pressure loss of a fiber article of Example 4.
FIG. 12 is a graph showing a relationship between the degree of elongation in the width direction and a trapping efficiency of the fiber article of Example 4.
FIG. 13 is a graph showing a relationship between the degree of elongation in the width direction and a PF value of the fiber article of Example 4.
FIG. 14 is a graph showing a relationship between the degree of elongation in the width direction and a basis weight of the fiber article of Example 4.
FIG. 15 is a graph showing a relationship between the degree of elongation in the width direction and a thickness change rate of the fiber article of Example 4.
FIG. 16 is a graph showing a relationship between J-ePM1 trapping efficiency and the degree of elongation of each of the fiber articles of Examples 2 and 3.
FIG. 17 is a graph showing a relationship between J-ePM1 trapping efficiency and the degree of elongation of the fiber article of Example 4.

Description of Embodiments

Embodiments of the present disclosure will be described below with reference to the drawings. In the present specification, the term "trapping efficiency" refers to trapping efficiency determined from Equation 3 shown later.

First Embodiment

A method for producing a fiber article according to a first embodiment includes the following first to third steps. In the first step, a plurality of resin particles containing a polymer that can be fiberized are affixed to a fiber sheet containing a plurality of first fibers and conveyed in a predetermined conveyance direction. In the second step, a first external force is applied to the plurality of first fibers and the plurality of resin particles of the fiber sheet to which the plurality of resin particles are affixed, the fiber sheet being conveyed, to reduce fiber gaps between the plurality of first fibers. In the third step, a second external force is applied to the fiber sheet in which the applied first external force is relaxed, the fiber sheet being conveyed in the conveyance direction, to enlarge the fiber gaps between the plurality of first fibers, with respect to at least a width direction of the fiber sheet, to form a plurality of second fibers from the plurality of resin particles, each of the plurality of second fibers being thinner than each of the plurality of first fibers, and forming a fiber composite containing the plurality of first fibers and the plurality of second fibers. In the first step of the present embodiment, a nonwoven fabric is used as the fiber sheet. In the present embodiment, in addition to this method for producing the fiber article, a fiber sheet production apparatus 1 and a fiber article production apparatus 2 used in the method will also be described.

Fiber Sheet Production Apparatus

FIG. 1 is a schematic diagram of a fiber sheet production apparatus 1 (hereinafter, also referred to as a production apparatus 1) according to the first embodiment. As illustrated in FIG. 1, a container box B in which a baled original fabric 50 is compressed and packed in a folded manner is supplied to the production apparatus 1. The original fabric 50 includes first fibers 51 that are a plurality of long fibers. The production apparatus 1 continuously feeds the original fabric 50 from the container box B. The production apparatus 1 produces a fiber sheet 60 by using a plurality of short fibers 52 formed from the plurality of first fibers 51. The production apparatus 1 of the present embodiment also serves as a nonwoven fabric production apparatus. The fiber sheet 60 of the present embodiment is a nonwoven fabric. The nonwoven fabric referred to herein is a nonwoven fabric in accordance with JIS L 0222:2001. As an example, in the present embodiment, the fiber sheet 60, which is the nonwoven fabric, is produced based on a needle punching method. A method for producing the nonwoven fabric is not limited to the needle punching method, and it may be other known methods such as a spunlace method. The fiber sheet 60 is conveyed in a predetermined conveyance direction P. The fiber sheet 60 has a long shape in which the conveyance direction P is a longitudinal direction and a direction orthogonal to the conveyance direction P among directions perpendicular to a thickness direction is a width direction. The conveyance direction P is also referred to as an MD direction. The direction orthogonal to the conveyance direction P is also referred to as a TD direction.
Material of the plurality of first fibers 51 can be selected as appropriate. As an example, the plurality of first fibers 51 include at least one of rayon, polypropylene, polyethylene terephthalate, polyethylene, or cellulose acetate. As an example, the plurality of first fibers 51 are crimped. Thus, the original fabric 50 has stretchability. In the original fabric 50 immediately after being fed out from the container box B, the plurality of first fibers 51 are interlaced. The original fabric 50 of the present embodiment is a band including crimped cellulose acetate fibers (hereinafter, also referred to as CA fibers) as the plurality of first fibers 51. As an example, the CA fibers are spun by dry spinning. The spinning is not limited to the dry spinning. The CA fibers are crimped with a primary crimp which is a minimum crimp unit, while being crimped with a secondary crimp which is a crimp unit larger than the primary crimp. The CA fibers may be further crimped with a higher-order crimp which is a crimp unit larger than the secondary crimp. Cross-sectional shape of the first fiber 51 can be set as appropriate. The cross-sectional shape of the first fiber 51 can be set to any of, for example, a circular shape, a Y-shape, or an irregular shape.
TD and FD of the original fabric 50 may be set as appropriate. As an example, TD of the original fabric 50 may have a value of millions, hundreds of thousands, tens of thousands, or thousands of units. In another example, TD of the original fabric 50 preferably has a value in a range of 3 million or more and 5 million or less, and more preferably has a value in a range of 1 million or more and 2 million or less. In another example, TD of the original fabric 50 preferably has a value in a range of 100,000 or more and 700,000 or less, and more preferably has a value in a range of 100,000 or more and 300,000 or less. In another example, TD of the original fabric 50 preferably has a value in a range of 5000 or more and 100,000 or less, and more preferably has a value in a range of 10,000 or more and 50,000 or less.
As an example, FD of the original fabric 50 has a value in a range of 20 or less. In another example, FD of the original fabric 50 preferably has a value in a range of 1 or more and 15 or less, more preferably has a value in a range of 1 or more and 10 or less, and still more preferably has a value in a range of 1 or more and 8 or less. When the production apparatus 1 of the present embodiment is driven, the original fabric 50 is conveyed while being applied with a relatively weak tension (load) having a value in a range of 2 mgf or more and 50 mgf or less per denier in the conveyance direction P.
As a specific example, the production apparatus 1 includes a feed roll pair 3 that guides the original fabric 50 fed out from the container box B, a plurality of guide members G1 to G3, and a cutter 10 that forms the plurality of short fibers 52 from the plurality of first fibers 51 of the original fabric 50. The feed roll pair 3 includes a pair of feed rolls 4 and 5. The guide members G1 to G3 include a plurality of guide rolls as an example. The production apparatus 1 also includes a conveyance device 11 that conveys the plurality of short fibers 52 emitted from the cutter 10, and a packaging device 12 that compresses and packs the plurality of short fibers 52 conveyed by the conveyance device 11. The packaging device 12 forms a fiber block 53 in which the plurality of short fibers 52 are compressed and packed in a predetermined shape. The fiber block 53 is used in the next step. The feed roll pair 3 is not essential and may be omitted.
The production apparatus 1 further includes a blowing and scutching machine 13 that removes impurities in the fiber block 53 and arranges the plurality of short fibers 52, a blower BL that conveys the plurality of short fibers 52 passed through the blowing and scutching machine 13 in the conveyance direction P, a weighing feeder 14 that weighs the plurality of short fibers 52 conveyed by the blower BL and supplies the plurality of short fibers 52 to a carding machine 15 by a predetermined amount, and at least one carding machine 15 that performs a carding process on the plurality of short fibers 52. The carding machine 15 forms a nonwoven fabric intermediate 54 including the plurality of short fibers 52.
A length dimension of each of the short fibers 52 can be set as appropriate. The length dimension of each of the short fibers 52 has a value in a range of 10 mm or more and 100 mm or less, as an example. In another example, the length dimension of each of the short fibers 52 has a value in a range of 30 mm or more and 100 mm or less. For example, when the length dimension of each of the short fibers 52 has a value of 100 mm or less, unnecessary entanglement of the short fibers 52 with respect to the carding machine 15 can be suppressed. For example, when the length dimension of each of the short fibers 52 has a value of 10 mm or more, the plurality of short fibers 52 which are crimped can be easily entangled with each other. This provides the fiber sheet 60, which is a bulky nonwoven fabric having abundant fiber gaps. In addition, a fiber article 62 (see FIG. 2) having a reduced fiber density as compared with a case where a plurality of uncrimped short fibers are used is obtained.
The production apparatus 1 further includes an interlacer 19 that interlaces the plurality of short fibers 52 of the nonwoven fabric intermediate 54 emitted from the carding machine 15 and forms the fiber sheet 60 which is the nonwoven fabric, a dryer 20 that dries the fiber sheet 60 emitted from the interlacer 19, and a winder 21 that winds the fiber sheet 60 passed through the dryer 20. The interlacer 19 includes, for example, a plurality of needles that interlace the plurality of short fibers 52 in the nonwoven fabric intermediate 54 by reciprocating in a predetermined direction.
The production apparatus 1 further includes a supply device 18. The supply device 18 supplies a second intermediate 59, which is a nonwoven fabric intermediate including a plurality of fibers, to a first intermediate 56, which is the nonwoven fabric intermediate 54 emitted from the carding machine 15. The second intermediate 59 includes the short fibers 52 or fibers each of which is different from each of the short fibers 52. As an example, the second intermediate 59 includes, for example, pulp fibers or synthetic fibers. The second intermediate 59 is fed from a supply roll R1 in the supply device 18 and is disposed to overlap with the first intermediate 56. The intermediates 56 and 59 are conveyed in a state of being overlapped with each other and introduced into the interlacer 19. The interlacer 19 interlaces the plurality of fibers of the intermediates 56 and 59. The fiber sheet 60, which is a composite sheet and a nonwoven fabric, is thus formed. In the fiber sheet 60, the intermediates 56 and 59 are disposed to overlap with each other.
The fiber sheet 60 may include the plurality of first intermediates 56 and at least one second intermediate 59. In this case, the second intermediate 59 may be disposed between the plurality of first intermediates 56. The second intermediate 59 may be further disposed to overlap with a stacked body including the plurality of first intermediates 56. The plurality of first intermediates 56 and the at least one second intermediate 59 may be integrally interlaced. In the production apparatus 1, the supply device 18 may be omitted. In this case, the fiber sheet 60 is constituted only by the first intermediate 56.
The fiber sheet 60 emitted from the interlacer 19 is dried by the dryer 20. The dried fiber sheet 60 is wound around a winding roll R2 provided with the winder 21. The winding roll R2 is used in the next step.

Fiber Article Production Apparatus

FIG. 2 is a schematic diagram of a fiber article production apparatus 2 (hereinafter, also referred to as production apparatus 2) according to the first embodiment. FIG. 2 also shows an enlarged view of the first fibers 51 (short fibers 52), resin particles 91, and second fibers 92 included in a produced fiber composite 61 and a fiber article 62. The fiber sheet 60 including the plurality of first fibers 51 (here, the short fibers 52) is supplied from the winding roll R2 to the production apparatus 2. As will be described in detail later, in the production apparatus 2 of the present embodiment, a predetermined first external force and a predetermined second external force are applied to the fiber sheet 60 to which a plurality of resin particles 91 are affixed, the fiber sheet being conveyed, and thus, the second fibers 92 are abundantly formed from the resin particles 91. Thereby, the fiber composite 61 containing the first fibers 51 and the second fibers 92 is formed.
As a specific example, the production apparatus 2 includes a plurality of guide members G4 to G7 that guide the fiber sheet 60 in the conveyance direction P, an affixing device 25 that affixes an affix liquid 90 containing the plurality of resin particles 91 to the fiber sheet 60, and a dryer 26 that dries the fiber sheet 60 to which the affix liquid 90 is affixed. As an example, the guide members G4 to G7 include a plurality of guide rolls. The production apparatus 2 includes a pressure-bonding roll pair 27 that pressure-bonds the dried fiber sheet 60, and a stretching device 30 that stretches the plurality of first fibers 51 (short fibers 52) included in the fiber sheet 60 passed through the pressure-bonding roll pair 27 in a predetermined direction. The pressure-bonding roll pair 27 includes a pair of pressure-bonding rolls 28 and 29. The production apparatus 2 also includes a winder 31 that winds the fiber composite 61 emitted from the stretching device 30.
As an example, the affixing device 25 includes a reservoir 32 that reserves the affix liquid 90, and an affixing roll 33 that affixes the affix liquid 90 in the reservoir 32 to the short fibers 52 (first fibers 51) of the fiber sheet 60 via a circumferential surface. The affixing device 25 includes a liquid collection unit 34 that collects the affix liquid 90 emitted from the reservoir 32 and a pump 35 that circulates the collected affix liquid 90 to the reservoir 32 again. A configuration of the affixing device 25 is not limited. For example, the affixing device 25 may include one or more nozzles for spraying the affix liquid 90 onto the fiber sheet 60, and a housing that accommodates the nozzles. As an example, the affix liquid 90 is a water affix liquid. The use of the water affix liquid makes it possible to produce the affix liquid 90 at a relatively low cost. In addition, the affix liquid 90 can be easily handled by using the water affix liquid. The affix liquid 90 may contain a liquid other than water.
As an example, the resin particles 91 have a lamellar structure in which polymer chains are linked and folded. Specifically, this lamellar structure is formed of a fine fiber in which the polymer chains are linked in millions and formed into a ribbon shape. The fine fiber is folded and stored in each of the resin particles 91.
The resin particles 91 are primary particles. The plurality of resin particles 91 are bound to each other and thereby, secondary particles are formed. When an external force is applied to two resin particles 91 bound to each other in a direction in which the two resin particles 91 are separated from each other, the fine fiber in the resin particles 91 is drawn out exteriorly, and then, the second fibers 92 are formed. When the affix liquid 90 is affixed to the first fibers 51, the plurality of resin particles 91 are dispersed and affixed to a surface of the plurality of first fibers 51. As an example, the secondary particles of the plurality of resin particles 91 are affixed to the surface of the first fibers 51.
The resin particles 91 are formed by a polymerization reaction and contain a lamellar structure, for example. The resin particles 91 contain, for example, at least one of polytetrafluoroethylene (PTFE), polypropylene, polyethylene, or polyamide. The resin particles 91 of the present embodiment include PTFE.
PTFE contained in the resin particles 91 is, for example, high molecular weight PTFE obtained from emulsion polymerization or suspension polymerization of TFE. The high molecular weight PTFE may be at least any of modified PTFE or homo PTFE. The modified PTFE includes, for example, TFE and a monomer other than TFE such as a modified monomer. Typically, the modified PTFE is uniformly modified by the modified monomer or is modified at an early or end stage of the polymerization reaction, but the modified PTFE is not particularly limited. The modified PTFE includes a TFE unit based on TFE and a modified monomer unit based on the modified monomer. The "modified monomer unit" referred to herein is a part of a molecular structure of the modified PTFE, and is a part derived from the modified monomer. As long as the modified monomer can be copolymerized with TFE, the modified monomer is not particularly limited.
The "high molecular weight" of the high molecular weight PTFE referred to herein is a molecular weight at which PTFE is easily fiberized at the time of producing the fiber article 62 and at which a fibril having a long fiber length is provided. The high molecular weight has a value of a standard specific gravity (SSG) in a range of 2.130 or more and 2.230 or less, and indicates a molecular weight at which melt flow substantially does not occur because of high viscosity. For the information regarding PTFE that can be fiberized, for example, the description in WO 2013/157647 can be referred to.
Here, the resin particles 91 are set to have a mean particle size of a value in a range of from 100 nm to 100 µm, for example. As an example, the value of the mean particle size is further preferably in a range of from 200 nm to 700 nm, and is still further preferably in a range of from 250 nm to 400 nm. Note that the mean particle size herein refers to a median diameter (cumulative 50% diameter (D50)) calculated from a measurement result of dynamic light scattering. The resin particles 91 are formed by paste extrusion, for example.
The pressure-bonding roll pair 27 applies the first external force to the plurality of first fibers 51 and the plurality of resin particles 91 in the fiber sheet 60 to which the plurality of resin particles 91 are affixed, the fiber sheet being conveyed, thereby narrowing the fiber gaps between the first fibers 51. As an example, the pressure-bonding roll pair 27 of the present embodiment is a thermocompression-bonding roll pair that thermocompression-bonds the fiber sheet 60. A heating temperature of the plurality of first fibers 51 and the plurality of resin particles 91 in being heated with the thermocompression-bonding roll pair can be adjusted as appropriate. The heating temperature can be set to a temperature in a range of, for example, more than 25°C and 200°C or less. The heating temperature is preferably a temperature, for example, in a range of from 50°C to 200°C, more preferably a temperature in a range of from 70°C to 200°C, and still more preferably a temperature in a range of from 90°C to 200°C. In another example, the heating temperature is preferably a temperature in a range of 110°C or more and 200°C or less, and more preferably a temperature in a range of 150°C or more and 200°C or less. The heating temperature may be, for example, below a melting point of each material of the first fibers 51 and the resin particles 91, or may be below a decomposition temperature of each material of the first fibers 51 and the resin particles 91.
The stretching device 30 applies the second external force to the fiber sheet 60 in which the first external force is applied and then relaxed, the fiber sheet being conveyed, to enlarge the fiber gaps between the plurality of first fibers 51, with respect to at least a width direction W of the fiber sheet 60 (a direction perpendicular to a paper surface in FIG. 2). As an example, the stretching device 30 of the present embodiment applies the second external force in the conveyance direction P and the width direction W to the conveyed fiber sheet 60. As an example, the stretching device 30 is a known simultaneous biaxial stretching device. For a configuration of the simultaneous biaxial stretching device, for example, a description of JP 4224241 B can be referred to.
When the production apparatus 2 is driven, the fiber sheet 60 to which the affix liquid 90 is affixed by the affixing device 25 is sent to the dryer 26. The fiber sheet 60 is dried through volatilization of a solvent component of the affix liquid 90. The dried fiber sheet 60 is introduced into the pressure-bonding roll pair 27. When the fiber sheet 60 passes through a nip point of the pressure-bonding roll pair 27, the first external force is applied to the plurality of first fibers 51 and the plurality of resin particles 91 of the fiber sheet 60. In the present embodiment, the plurality of first fibers 51 and the plurality of resin particles 91 are heated by the pressure-bonding roll pair 27 when the first external force is applied. The first fibers 51 are plasticized by being heated. Thus, the fiber gaps are easily narrowed by the first external force. After the fiber sheet 60 passes through the nip point of the pressure-bonding roll pair 27, the first external force applied to the plurality of first fibers 51 and the plurality of resin particles 91 is relaxed.
The first external force may be applied to the plurality of first fibers 51 and the plurality of resin particles 91 by a configuration other than the pressure-bonding roll pair. The first external force may be applied to the plurality of first fibers 51 and the plurality of resin particles 91 by a configuration other than the thermocompression-bonding roll pair. In this case, for example, the production apparatus 2 may include a pressure-bonding roll pair having no heating function.
The fiber sheet 60 in which the first external force is relaxed is introduced into the stretching device 30. In the stretching device 30, with respect to the conveyance direction P and the width direction W, the second external force is applied to the fiber sheet 60 to enlarge the fiber gaps between the plurality of first fibers 51 . At this time, the second external force is applied to the plurality of first fibers 51 and the plurality of resin particles 91 to separate the resin particles 91 adhering to each other between the plurality of first fibers 51. Thereby, the fine fiber of the resin particles 91 is extended exteriorly and the second fibers 92 bridging the plurality of first fibers 51 are formed. As a result, the fiber composite 61 containing abundantly the plurality of second fibers 92 together with the plurality of first fibers 51 is formed. Here, the second fibers 92 of the present embodiment contain PTFE as a main component. In other words, the second fibers 92 include PTFE in an amount of more than 50 wt.% of the total weight of the second fibers 92. The plurality of second fibers 92 are fixed to the plurality of first fibers 51 in a state of being dispersed each other. Thus, according to the present embodiment, there can be produced the fiber article 62 in which a network structure constituted by the plurality of first fibers 51 and the plurality of second fibers 92 is hardly broken and strength is improved.
Here, the first external force applied to the fiber sheet 60 is relaxed, the fiber gaps between the plurality of first fibers 51 are widened, and thereby the second fibers 92 are formed. However, in the present embodiment, by actively applying the second external force to the plurality of first fibers 51 and the plurality of resin particles 91, the fiber gaps between the plurality of first fibers 51 can be enlarged in a desired direction. This makes it possible to form the second fibers 92 furthermore abundantly. For example, thickness, number, or the like of the second fibers 92 to be formed can be adjusted by adjusting at least one of strength of the second external force or temperature at the time of applying the second external force. This can adjust the properties of the fiber article 62 to be produced within a certain range.
In the fiber sheet 60 of the present embodiment, after the relaxation of the first external force applied to the plurality of first fibers 51 and the plurality of resin particles 91, the fiber gaps between the plurality of first fibers 51 in the thickness direction are naturally enlarged by restoring force. On the other hand, in the fiber sheet 60, the fiber gaps between the plurality of first fibers 51 are enlarged through the application of the second external force, with respect to both the conveyance direction P and the width direction W. As a result, in the fiber sheet 60, as an example, each of the fiber gaps in two directions perpendicular to the thickness direction and orthogonal to each other is formed to be wider than any one of the gaps in the thickness direction. The "fiber gaps in two directions" referred to herein correspond to the conveyance direction P and the width direction W.
The fiber composite 61 is wound around a winding roll R3 included in the winder 31. The fiber article 62 is produced by cutting the fiber composite 61 into a predetermined size. The fiber article 62 is thus produced in which unevenness of the fiber gaps between the plurality of first fibers 51 and the plurality of second fibers 92 is suppressed in the fiber gaps in the two directions. The fiber article 62 of the present embodiment has a configuration in which the fiber gaps in the two directions are formed to be wider than the fiber gaps in the thickness direction. Thus, for example, the fiber article 62 having a relatively small basis weight and capable of suppressing an increase in pressure loss with the lapse of used time is produced.
As an example, the fiber article 62 produced by the production method of the present embodiment is a filter member that is disposed in a flow path through which a predetermined fluid flows and filters impurities mixed in the fluid. The fluid passing through the inside of the fiber article 62 may be either gas or liquid. The gas is, for example, air. The fiber article 62 has a sheet shape. As illustrated in the enlarged view in FIG. 2, for example, some resin particles 91 may remain in the produced fiber article 62.
As described above, the method for producing the fiber article 62 of the present embodiment includes the first step of affixing the plurality of resin particles 91 containing the polymer that can be fiberized to the fiber sheet 60 containing the plurality of first fibers 51, the fiber sheet being conveyed in the predetermined conveyance direction P. The method also includes the second step of applying the first external force to the plurality of first fibers 51 and the plurality of resin particles 91 in the fiber sheet 60 to which the plurality of resin particles 91 are affixed, the fiber sheet being conveyed, thereby narrowing the fiber gaps between the first fibers 51.
The production method also includes the third step of applying the second external force to the fiber sheet 60 in which the first external force is applied and then relaxed, the fiber sheet being conveyed, to enlarge the fiber gaps between the plurality of first fibers 51, with respect to at least the width direction W of the fiber sheet 60, to form the second fibers 92 from the plurality of resin particles 91, each of the second fibers 92 having an outer diameter smaller than that of each of the first fibers 51, and forming the fiber composite 61 containing the first fibers 51 and the second fibers 92.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60 in a plurality of directions including the width direction W. As an example, in the third step, the second external force is applied to the fiber sheet 60 simultaneously in a plurality of directions including the width direction W.
For example, by adjusting at least one of the strength of the second external force or the temperature at the time of applying the second external force, the fiber gap between the plurality of first fibers 51 and the plurality of second fibers 92 of the fiber article 62, the number of second fibers 92, and a length dimension of the second fibers 92 can be adjusted. This allows for the production of the fiber articles 62 having properties different from each other. Specifically, by increasing the second external force within a certain range, the basis weight and the thickness in a natural state of the fiber article 62 are reduced. By reducing the second external force within a certain range, the basis weight and the thickness in the natural state of the fiber article 62 are increased. By increasing the second external force within a certain range, the second fibers 92 are abundantly formed. For example, when the number of the second fibers 92 is increased, a tensile elongation rate with respect to the natural state of the fiber article 62 is reduced. For example, when the number of the second fibers 92 is increased, tensile strength of the fiber article 62 is increased.
For example, an outer diameter D2 of the second fiber 92 can be adjusted by adjusting at least one of the strength of the second external force or the temperature at the time of applying the second external force. By increasing the second external force in a certain range, the outer diameter D2 can be set small. By reducing the second external force within a certain range, the outer diameter D2 can be set large.
In the production method of the present embodiment, the outer diameter D2 of the second fiber 92 is set to be smaller than an outer diameter D1 of the first fiber 51. Thus, the produced fiber article 62 has a fiber composite structure with fibers having different diameters. As an example, by adjusting at least one of the strength of the second external force or the temperature at the time of applying the second external force, a ratio D1/D2 of the outer diameter D1 to the outer diameter D2 can be set to a value in a range of 15.0 or more and 1666.7 or less. The ratio D1/D2 is, for example, preferably in a range of 15.0 or more and 1300.0 or less, more preferably in a range of 15.0 or more and 714.3 or less, and still more preferably in a range of 15.0 or more and 300.0 or less. In another example, the ratio D1/D2 is, for example, preferably in a range of 60.0 or more and 1666.7 or less, more preferably in a range of 60.0 or more and 1300.0 or less, still more preferably in a range of 60.0 or more and 714.3 or less, and still more preferably in a range of 60.0 or more and 300.0 or less.
When the ratio D1/D2 is 15.0 or more, for example, the fiber article 62 in which the respective functions of the first fibers 51 and the second fibers 92 having outer diameters different from each other are easily exhibited can be produced. When the value of the ratio D1/D2 is 1666.7 or less, for example, the fiber article 62 in which the second fibers 92 are easily stretched around the first fibers 51 while suppressing an increase in the outer diameter D1 of the first fibers 51 can be produced. The second fibers 92 can be easily formed by maintaining the outer diameter D2 at a relatively large value. In addition, by setting the ratio D1/D2 to a value in a range of 60.0 or more and 1666.7 or less, an amount of use of the second fibers 92 can be reduced and a production cost of the fiber article 62 can be suppressed, while maintaining a filter performance of the fiber article 62 to be produced.
As the outer diameter D1, for example, a value in a range of 5.0 µm or more and 50.0 µm or less is preferable, and a value in a range of 20.0 µm or more and 30.0 µm or less is more preferable. As a result, the plurality of second fibers 92 can be easily disposed abundantly around the first fibers 51 while the second fibers 92 are stably supported by the first fibers 51.
As the outer diameter D2, for example, a value in a range of 30.0 nm or more and 1.0 µm or less is preferable, a value in a range of 30.0 nm or more and 800 nm or less is more preferable, and a value in a range of 30.0 nm or more and 166.7 nm or less is still more preferable. In another example, the outer diameter D2 preferably has a value in a range of 50.0 nm or more and 800.0 nm or less, for example. This makes it possible to increase the ratio D1/D2 while avoiding an excessive decrease in the outer diameter D2 of the second fibers 92. As a result, the fiber article 62 abundantly containing the second fibers 92 can be stably produced.
In the fiber article 62 produced by the production method of the present embodiment, as an example, a ratio V1/V2 of a total volume V1 of the first fibers 51 to a total volume V2 of the second fibers 92 and the resin particles 91 is set to a value in a range of 1.9 or more and 124.0 or less. The ratio V1/V2 is further preferably set to a value in a range of 20.0 or greater to 124.0 or less. This makes it possible to produce the fiber article 62 in which the outer diameter D1 of the first fibers 51 and the outer diameter D2 of the second fibers 92 are made differently each other and the respective functions of the first fibers 51 and the second fibers 92 are easily exhibited.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 in which the basis weight has a value in a range of 60 g/m² or more and 300 g/m² or less, and the tensile strength in a minimum strength direction in which the tensile strength is minimized among the directions perpendicular to the thickness direction has a value in a range of 0.8 N/10 mm or more and 100 N/10 mm or less. The unit "N/10 mm" indicates how much N of a load the fiber sheet can withstand per a measurement width of 10 mm. The "minimum strength direction" referred to herein corresponds to the width direction W of the fiber sheet 60. The tensile strength in the minimum strength direction can be adjusted by, for example, the second external force to be applied in the width direction W to the conveyed fiber sheet 60. This makes it possible to produce the fiber article 62 in which the basis weight and the tensile strength in the minimum strength direction are set to values in the above-described ranges.
In general, for example, when the fiber sheet is continuously produced by a wet papermaking method, a large number of the short fibers contained in the affix liquid as a fiber sheet material are oriented to extend in the conveyance direction of the fiber sheet in a production line. For example, when the plurality of first fibers included in the fiber sheet are continuously spun by dry spinning, the first fibers of long fibers emitted from the spinning cabinet are oriented to extend in the conveyance direction. Thus, the fiber article usually has a structure in which the plurality of fibers are extended in a direction orthogonal to the minimum strength direction among directions perpendicular to the thickness direction (in other words, a direction corresponding to the conveyance direction of the fiber sheet in the production line, hereinafter, also referred to as a "second direction"). In the fiber article, typically, entanglement of the plurality of fibers is relatively small in the minimum strength direction. Thus, in the direction, the strength of the fiber article is minimized among the plurality of directions perpendicular to the thickness direction.
On the other hand, the fiber article 62 of the present embodiment is formed such that an abundance of the second fibers 92 extend in the width direction W of the fiber sheet at the time of production. As a result, in the fiber article 62, the entanglement of the first fibers 51 and the second fibers 92 in the minimum strength direction is increased. As a result, in the fiber article 62, the tensile strength in the minimum strength direction is set to a value in a range of at least 0.8 N/10 mm or more because of an abundance of the first fibers 51 and the second fibers 92.
The tensile strength of the fiber article 62 in the minimum strength direction has a value in a range of 100 N/10 mm or less. This prevents the tensile strength of the fiber article 62 from increasing excessively and facilitates the production of the fiber article 62. The tensile strength of the fiber article 62 of the present embodiment in the minimum strength direction has a value in a range of 0.8 N/10 mm or more and 100 N/10 mm or less. The range of the tensile strength in the minimum strength direction preferably has a value in a range of 1 N/10 mm or more and 100 N/10 mm or less, and more preferably has a value in a range of 5 N/10 mm or more and 100 N/10 mm or less, for example. In another example, the range of the tensile strength in the minimum strength direction preferably has a value in a range of 8 N/10 mm or more and 100 N/10 mm or less, and more preferably has a value in a range of 10 N/10 mm or more and 100 N/10 mm or less, for example.
The value of the basis weight set in the third step is, for example, preferably a value in a range of 60 g/m² or more and 300 g/m² or less, and more preferably a value in a range of 60 g/m² or more and 250 g/m² or less. In another example, the value of the basis weight is, for example, preferably a value in a range of 60 g/m² or more and 200 g/m² or less, more preferably a value in a range of 80 g/m² or more and 200 g/m² or less, and still more preferably a value in a range of 100 g/m² or more and 200 g/m² or less. This makes it easy to reduce the weight of the fiber article 62.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 having the tensile elongation rate in the minimum strength direction with respect to a natural state in a value in a range of 5% or more and 250% or less. This makes it possible to produce the fiber article 62 in which the tensile elongation rate is set to a value within such a range. The tensile elongation rate preferably has a value in a range of 10% or more and 250% or less, and more preferably has a value in a range of 20% or more and 250% or less, for example. In another example, the tensile elongation rate preferably has a value in a range of 30% or more and 250% or less, and more preferably has a value in a range of 40% or more and 250% or less, for example.
Here, the tensile strength is measured using, for example, a Tensilon universal material testing machine which is a tensile testing machine in compliance with JIS B 7721:2018. In this case, a test piece formed in a width of 10 mm and a length of 60 mm is used. The tensile strength is measured under setting conditions of a distance between chucks of 40 mm and a tensile speed of 200 mm/min. The tensile elongation rate is calculated based on Equation 1 shown below under the same conditions as in the measurement of the tensile strength. $Tensile elongation rate (%) = elongation (mm) / distance between chucks (mm) \times 100$
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 having a PF value in a range of 16 or more and 84 or less. The PF value referred to herein refers to a value calculated based on Equations 2, 3, and 4 shown below. In the calculation of a transmittance (%) described in Equation 2, NaCl particles having a particle size of 0.4 µm generated according to a method described in JIS B9928:1998, Annex 5 (stipulation), Method for Generating NaCl Aerosol (Pressure Spray Method) are used. The number of NaCl particles before and after passing of the fiber article 62 when air containing the NaCl particles is caused to pass through the fiber article 62 in the thickness direction at a flow rate of 5.3 cm/sec is measured with a particle counter. The transmittance (%) is calculated based on the measured value. $Transmittance (%) = (CO / CI) \times 100$
In this regard, CO is the number of NaCl particles after passing of the fiber article 62. CI is the number of NaCl particles before passing of the fiber article 62. $Trapping efficiency (%) = 100 - transmittance (%)$ $PF value = \{- \log (100 - trapping efficiency (%)) / 100\} / (pressure loss (Pa) / 1000)$
The PF value is, for example, preferably a value in a range of 16 or more and 70 or less, and more preferably a value in a range of 16 or more and 60 or less. In another example, for example, the value is preferably in a range of 20 or more and 84 or less, and more preferably in a range of 25 or more and 84 or less.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 having the thickness in the natural state within a range of less than 3.0 mm. This allows for the production of the fiber article 62 in which the thickness in the natural state is set to a value in the range of less than 3.0 mm. Thus, the fiber article 62 that can be easily reduced in size can be produced. The thickness of the fiber composite 61 in the natural state set in the third step preferably has a value in a range of 0.1 mm or more and less than 3.0 mm, more preferably has a value in a range of 0.1 mm or more and 2.5 mm or less, and still more preferably has a value in a range of 0.1 mm or more and 2.0 mm or less, for example. In another example, the thickness preferably has a value in a range of 0.5 mm or more and 2.5 mm or less, and more preferably has a value in a range of 1.0 mm or more and 2.5 mm or less, for example.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 in which a pressure loss when air is caused to pass in the thickness direction at a flow rate of 5.3 cm/sec is a value in a range of 3 Pa or more and 35 Pa or less. This allows for the production of the fiber article 62 in which the pressure loss is set to the value within the range. The pressure loss of the fiber composite 61 set in the third step preferably has a value in a range of 3 Pa or more and 25 Pa or less, and more preferably has a value in a range of 3 Pa or more and 15 Pa or less, for example. In another example, the pressure loss preferably has a value in a range of 6 Pa or more and 35 Pa or less, and more preferably has a value in a range of 9 Pa or more and 35 Pa or less, for example.
The pressure loss is measured by, for example, the following procedure. Set a measurement sample in a holder having an inner diameter of 113 mm (an effective area of 100 cm² as a filter medium). Adjust a flow rate of air flowing through the measurement sample to 5.3 cm/sec with a flow meter. At this time, the pressure loss generated between an upstream side and a downstream side in an air flowing direction of the measurement sample is measured by a manometer.
In the third step of the present embodiment, as an example, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 having a trapping efficiency of a value in a range of 35% or more and 95% or less. The trapping efficiency is calculated by Equation 3. This allows for the production of the fiber article 62 in which the trapping efficiency is set within the range. As the trapping efficiency set in the third step, for example, a value in a range of 35% or more and 85% or less is preferable, and a value in a range of 35% or more and 75% or less is more preferable. In another example, as the trapping efficiency, for example, a value in a range of 40% or more and 90% or less is preferable, and a value in a range of 45% or more and 90% or less is more preferable.
When at least one of the basis weight, the tensile strength, the tensile elongation rate, the PF value, the thickness in the natural state, the pressure loss, or the trapping efficiency of the fiber composite 61 is set, a desired set value can be easily set by using a single first intermediate 56, for example.
In the third step of the present embodiment, the second external force is applied to the fiber sheet 60, to form the fiber composite 61 classified into a filter group of JIS-ePM1 in Classification described in item 7.3 of JIS B 9908-1:2019. This allows for the production of the fiber article 62 that can be used for a high-quality filter classified into the filter group of "JIS-ePM1".
As described above, according to the method for producing the fiber article 62 of the present embodiment, in the case of producing the fiber article 62 including the first fiber 51 and the second fiber 92 having an outer diameter smaller than that of the first fiber 51, the fiber article 62 that can achieve weight reduction and strength improvement and suppress an increase in pressure loss with the lapse of used time can be produced. Hereinafter, a second embodiment will be described focusing on differences from the first embodiment.

Second Embodiment

FIG. 3 is a schematic diagram of a fiber article production apparatus 102 (hereinafter, also referred to as a production apparatus 102) according to the second embodiment. The production apparatus 102 is different from the production apparatus 2 in that the production apparatus 102 includes a known sequential biaxial stretching device. The production apparatus 102 includes a first stretching device 87 configured by the following components 65 to 69 to stretch the fiber sheet 60 in the conveyance direction (longitudinal direction) P. The production apparatus 102 also includes a second stretching device 88 configured by the following components 82 to 83 to stretch the fiber sheet 60 in the width direction (lateral direction) W. A winding roll R4 obtained by winding up the fiber sheet 60 immediately after passing through the pressure-bonding roll pair 27 in FIG. 2 (in other words, immediately after the first external force is applied) is supplied to the production apparatus 102. The fiber sheet 60 includes the plurality of first fibers 51 (short fibers 52 as an example) to which the plurality of resin particles 91 are affixed.
Specifically, the first stretching device 87 includes a feeding roll 65 that feeds the fiber sheet 60 from the winding roll R4, and a preheating roll group 70 that preheats the fiber sheet 60. The preheating roll group 70 includes a plurality of preheating rolls 71 to 74. The production apparatus 102 also includes a heating furnace 66 that heats the preheated fiber sheet 60, and two stretching roll pairs 67 and 68 that stretch the fiber sheet 60 passing through the heating furnace 66 in the conveyance direction P. The heating furnace 66 is a hot-air furnace, as an example. The stretching roll pair 67 includes a pair of stretching rolls 75 and 76. The stretching roll pair 68 includes a pair of stretching rolls 77 and 78. The production apparatus 102 also includes a cooling roll group 69 that cools the fiber sheet 60 passing through the stretching roll pairs 67 and 68. The cooling roll group 69 includes a plurality of cooling rolls 79 to 81.
The second stretching device 88 includes a heating furnace 84 that heats the fiber sheet 60 conveyed in the conveyance direction P, and a stretching mechanism 85 that holds both ends in the width direction W of the fiber sheet 60 conveyed while being heated for a certain period of time and thereby stretches the fiber sheet 60 in the width direction W. The heating furnace 84 is a hot-air furnace, as an example. The second stretching device 88 includes a cooling and cutting unit 83 that cools the fiber composite 61 obtained by passing through the stretching mechanism 85 and cuts the fiber composite into a predetermined width. The cooling and cutting unit 83 includes a pair of cooling rolls 95 and 96. For the configuration of the sequential biaxial stretching device, for example, a description of JP 2006-096801 A can be referred to.
When the production apparatus 102 is driven, the fiber sheet 60 in which the first external force is applied and relaxed is heated in the heating furnace 66 and conveyed, and passes through each of the nip points of the stretching roll pairs 67 and 68, in the first stretching device 87. When the fiber sheet 60 is stretched in the conveyance direction P by the stretching roll pairs 67 and 68, the second external force is applied to the fiber sheet 60 in the conveyance direction P. In the second stretching device 88, when the fiber sheet 60 passes through the heating furnace 84, the stretching mechanism 85 applies the second external force to the fiber sheet 60 in the width direction W. This applies the second external force to the fiber sheet 60 in a plurality of directions including the width direction W. With the application of the second external force, the plurality of second fibers 92 are formed from the plurality of resin particles 91 of the fiber sheet 60. As a result, the fiber composite 61 including the plurality of first fibers 51 and the plurality of second fibers 92 is produced. As described above, in the third step of the method for producing the fiber article 62 of the present embodiment, the second external force is applied to the fiber sheet 60 sequentially in one direction and the other direction of the width direction W and the conveyance direction P.
The fiber composite 61 is cooled by the cooling and cutting unit 83 and cut into a predetermined width. Thereafter, the fiber composite 61 is wound around the winding roll R3 of the winder 31. The wound fiber composite 61 is further cut into a predetermined size, whereby the fiber article 62 is produced. In the second embodiment described above, the effects of the first to third steps are also exhibited in the same manner as in the first embodiment.
As illustrated in FIG. 3, in the second embodiment, for example, the fiber sheet 60 passing through the first stretching device 87 may be temporarily wound, thereby forming a winding roll R5, and then the winding roll R5 may be supplied to the second stretching device 88. This makes it easy to adjust timing of applying the second external force to the fiber sheet 60 sequentially in the conveyance direction P and the width direction W, for example.

Confirmation Test

Next, a confirmation test for the present disclosure and results thereof will be described below. The present disclosure is not limited to the Examples described below.

Test 1

A fiber sheet 60 containing a plurality of first fibers 51 (short fibers 52) which are crimped CA fibers was prepared. In addition, a plurality of resin particles 91 containing PTFE were prepared. A fiber article 62 according to Example 1 was produced by performing the first to third steps. In Example 1, in a first step, the plurality of resin particles 91 were affixed to the plurality of first fibers 51 (short fibers 52) based on an impregnation method. As the fiber sheet 60, a nonwoven fabric produced by a needle punching method was used. In a second step, a heating temperature of the pressure-bonding roll pair 27 was set to 170°C. A nip pressure as the first external force of the pressure-bonding roll pair 27 was set to 10 MPa. FIG. 4 is an enlarged photograph of the fiber sheet 60 of Example 1 before application of the second external force. FIG. 5 is an enlarged photograph of the fiber sheet 60 of Example 1 after the application of the second external force. In FIG. 5, silica powder is affixed to the second fibers 92 to improve visibility.
As shown in FIGS. 4 and 5, in Example 1, it was confirmed that fiber gaps between the plurality of first fibers 51 included in the fiber sheet 60 before the application of the second external force were enlarged by applying the second external force. It was also confirmed that by applying the second external force to the fiber sheet 60, the plurality of second fibers 92 bridging the plurality of first fibers 51 different from each other were formed from the resin particles 91.

Test 2

A fiber sheet 60 containing a plurality of first fibers 51 (short fibers 52) which are crimped CA fibers was prepared. In addition, a plurality of resin particles 91 containing PTFE were prepared. A fiber article 62 of Example 2 containing 44 mass% of the second fibers 92 and a fiber article 62 of Example 3 containing 8 mass% of the second fibers 92 were produced by performing the first to third steps in the same manner as that in Example 1. Sizes of the fiber articles 62 of Examples 2 and 3 were set to 15 cm in length × 15 cm in width × 0.5 cm in thickness. In the third step, a simultaneous biaxial stretching device corresponding to the stretching device in the production apparatus 2 of the first embodiment was used to apply the second external force to the fiber sheet 60.
Each of the length dimension in the width direction (direction corresponding to the width direction W of the fiber sheet 60) of each of the produced Examples 2 and 3 was elongated such that each of degrees of elongation represented by the following Equation 5 had a plurality of values in a range of 30% or more and 90% or less. At this time, each of the pressure losses (Pa), PF values, and trapping efficiencies (%) with respect to each of the degrees of elongation (%) in Examples 2 and Example 3 was measured based on each method shown in the first embodiment. Also, each of the thickness change rates (%) with respect to each of the degrees of elongation (%) in Example 2 and Example 3 at this time was measured. Also, each of the basis weights (g/m²) with respect to each of the degrees of elongation (%) in Example 2 and Example 3 at this time was measured. $Degree of elongation (%) = (length after elongation L / natural length L 0) \times 100 - 100$
FIG. 6 is a graph showing a relationship between the degree of elongation in the width direction and the pressure loss of each of the fiber articles 62 of Examples 2 and 3. In the results shown in FIG. 6, it was confirmed that in both Examples 2 and 3, the pressure loss was reduced as the degree of elongation was increased. The content of the second fibers 92 in Example 3 is larger than that in Example 2. Thus, it was confirmed that the pressure loss in Example 3 was higher than that in Example 2 in the entire range of the test.
FIG. 7 is a graph showing a relationship between the degree of elongation in the width direction and the trapping efficiency of each of the fiber articles 62 of Examples 2 and 3. In the results shown in FIG. 7, it was confirmed that in both of Examples 2 and 3, the trapping efficiency was mostly maintained even when the degree of elongation was increased. The content of the second fibers 92 in Example 3 is larger than that in Example 2. Thus, it was confirmed that the trapping efficiency of Example 3 was higher than that of Example 2 in the entire range of the test.
FIG. 8 is a graph showing a relationship between the degree of elongation in the width direction and the PF value of each of the fiber articles 62 of Examples 2 and 3. From the results shown in FIG. 8, it was confirmed that in Example 3, the PF value was increased as the degree of elongation was increased from 30% to 50%, and thereafter, the PF value was mostly maintained even when the degree of elongation was increased. A similar tendency was also confirmed for the PF value of Example 2.
FIG. 9 is a graph showing a relationship between the degree of elongation in the width direction and a thickness change rate of each of the fiber articles 62 of Examples 2 and 3. In the results shown in FIG. 9, it was confirmed that the thickness did not change significantly even when the degree of elongation was increased in both Examples 2 and 3. From these tested results, it is considered that even when the content of the second fibers in the fiber article 62 changes to some extent in the production process, the fiber article 62 in which the change in thickness due to the change in degree of elongation is suppressed can be produced.
FIG. 10 is a graph showing a relationship between the degree of elongation in the width direction and the basis weight of each of the fiber articles 62 of Examples 2 and 3. In the results shown in FIG. 10, in both of Examples 2 and 3, it was confirmed that the basis weight was gradually decreased as the degree of elongation was increased.

Test 3

A fiber sheet 60 including synthetic fibers "SS-100" manufactured by Daiwabo Co., Ltd. as a plurality of crimped first fibers 51 (short fibers 52) was prepared. In addition, a plurality of resin particles 91 containing PTFE were prepared. A fiber article 62 of Example 4 containing about 10 mass% of the second fibers 92 was produced by sequentially performing the first to third steps. In the first step, the plurality of resin particles 91 were affixed to the plurality of first fibers 51 (short fibers 52) based on a gravure coating method. In the second step, a heating temperature of the pressure-bonding roll pair 27 was set to 110°C. A nip pressure as the first external force of the stretching roll pairs 67 and 68 was set to 5 MPa. A size of the fiber article 62 of Example 4 was set to 15 cm in length × 15 cm in width × 0.2 cm in thickness. By using a sequential biaxial stretching device corresponding to the stretching device in the production apparatus 102 of the second embodiment, the second external force to the fiber sheet 60 was applied.
A length dimension of the produced Example 4 in the width direction (direction corresponding to the width direction W of the fiber sheet 60) was elongated within a range of 40% or more and 100% or less from a natural length L0. At this time, pressure loss (Pa), a PF value, and a trapping efficiency (%) (using NaCl particles having a particle size of 0.4 µm) with respect to a degree of elongation (%) in Example 4 were measured according to the methods described in the first embodiment. Also, a basis weight (g/m²) with respect to the degree of elongation (%) in Example 4 at this time was measured.
FIG. 11 is a graph showing a relationship between the degree of elongation in the width direction and the pressure loss of the fiber article 62 of Example 4. From the results shown in FIG. 11, it was confirmed that in Example 4, as in Examples 2 and 3, the pressure loss was decreased as the degree of elongation was increased.
FIG. 12 is a graph showing a relationship between the degree of elongation in the width direction and the trapping efficiency of the fiber article 62 of Example 4. In the results shown in FIG. 12, as in Examples 2 and 3, it was confirmed that the trapping efficiency was mostly maintained even when the degree of elongation was increased.
FIG. 13 is a graph showing a relationship between the degree of elongation in the width direction and the PF value of the fiber article 62 of Example 4. From the results shown in FIG. 13, it was confirmed that the PF value of Example 4 was increased substantially linearly as the degree of elongation was increased.
FIG. 14 is a graph showing a relationship between the degree of elongation in the width direction and the basis weight of the fiber article 62 of Example 4. In the results shown in FIG. 14, it was confirmed that the basis weight of Example 4 was gradually decreased as the degree of elongation was increased. As a result, it was confirmed that even when the fiber article 62 is produced using a sequential secondary stretching device, the basis weight of the fiber article 62 can be adjusted by adjusting the strength of the second external force to be applied to the fiber sheet 60 and varying the degree of elongation.
FIG. 15 is a graph showing a relationship between the degree of elongation in the width direction and the thickness change rate of the fiber article 62 of Example 4. In the results shown in FIG. 15, it was confirmed that the thickness change rate was increased as the degree of elongation was increased.
In addition, in Examples 2 to 4, a J-ePM1 trapping efficiency (%) was measured based on a method in accordance with an item 7.2 "Calculation of particulate matter trapping rate (J-eMPx)" in a general ventilation filter test (JIS B 9908-1:2019). In this measurement, a particulate matter (at least one of solid or liquid particles suspended in the atmosphere) obtained by reducing the particulate matter by 50% with a classifying device at an aerodynamic particle size of 1 µm was used as a particulate matter (PM1) for testing.
FIG. 16 is a graph showing a relationship between the J-ePM1 trapping efficiency (%) and the degree of elongation of each of the fiber articles of Examples 2 and 3. FIG. 17 is a graph showing a relationship between the J-ePM1 trapping efficiency (%) and the degree of elongation of the fiber article of Example 4. In FIGS. 16 and 17, the J-ePM1 trapping efficiency is denoted as "ePM1". FIG. 17 shows a plurality of prepared data of Example 4.
According to the measurement results shown in FIG. 16, in Examples 2 and 3, the J-ePM1 trapping efficiency (%) had a value of 50% or more with the degree of elongation in a range of 30% or more and 100% or less. Also, according to the measurement results shown in FIG. 17, in Example 4, the J-ePM1 trapping efficiency (%) had a value of 50% or more with the degree of elongation in a range of 50% or more and 100% or less.
As described above, in any of Examples 2 to 4, the J-ePM1 trapping efficiency (%) was a value of 50% or more. Thus, it was confirmed that all of Examples 1 to 4 correspond to a filter group classified as "JIS-ePM1" in the item 7.3 "Classification" of JIS B 9908-1:2019. Thus, the fiber article produced by the production method of the present disclosure can be said to be a filter having a high-quality filter function classified as "JIS-ePM1".

Disclosed Items

Each of the following items discloses a preferred embodiment.

Aspect 1

A method for producing a fiber article, the method including a first step of affixing a plurality of resin particles containing a polymer that can be fiberized to a fiber sheet including a plurality of first fibers, the fiber sheet being conveyed in a predetermined conveyance direction, a second step of applying a first external force to the plurality of first fibers and the plurality of resin particles of the fiber sheet to which the plurality of resin particles are affixed, the fiber sheet being conveyed, to reduce fiber gaps between the plurality of first fibers, and a third step of applying a second external force to the fiber sheet in which the applied first external force is relaxed, the fiber sheet being conveyed in the conveyance direction, to enlarge the fiber gaps between the plurality of first fibers, with respect to at least a width direction of the fiber sheet, to form a plurality of second fibers from the plurality of resin particles, each of the plurality of second fibers being thinner than each of the plurality of first fibers, and forming a fiber composite containing the plurality of first fibers and the plurality of second fibers.
According to the above production method, in the third step, the fiber gaps between the plurality of first fibers can be actively enlarged in a direction in which the second external force is applied. With this configuration, the second external force is applied to the resin particles affixed to the plurality of first fibers, and the second fibers can be abundantly formed from the plurality of resin particles such that the second fibers extend in a direction in which the second external force is applied. Thus, entanglement of the first fibers and the second fibers at least in the width direction in the fiber sheet can be increased. Therefore, a tensile strength at least in the width direction in the fiber sheet can be improved by the first fibers and the second fibers. Therefore, in the case of producing the fiber article using the fiber composite containing the plurality of first fibers and the plurality of second fibers, the strength of the fiber article can be improved.
In addition, in the fiber sheet conveyed in the conveyance direction, any one of the fiber gaps at least in the direction in which the second external force is applied is widened. This makes it possible to reduce a basis weight of the fiber article. Therefore, the weight of the fiber article can be reduced.

Aspect 2

The method for producing a fiber article according to item 1, wherein in the third step, the second external force is applied to the fiber sheet in a state where the fiber sheet is heated.
According to the above production method, in the third step, by heating the plurality of resin particles affixed to the plurality of first fibers, for example, fine fibers folded and accommodated in the resin particles can be easily drawn out to the outside by the second external force, and the second fibers can be easily formed abundantly.

Aspect 3

The method for producing a fiber article according to item 1 or 2, wherein in the third step, the second external force is applied to the fiber sheet also in the conveyance direction of the fiber sheet.
According to the above production method, in the third step, by additionally applying the second external force to the plurality of resin particles in the conveyance direction, for example, the fine fibers can be drawn out from the resin particles to the outside and the second fibers can be formed even more easily and abundantly.

Aspect 4

The method for producing a fiber article according to item 3, wherein in the third step, the second external force is applied to the fiber sheet sequentially in one direction and the other direction, among the width direction and the conveyance direction.
According to the above production method, the second fibers can be abundantly formed by shifting each of timings of applying the second external force in one direction and the other direction, among the width direction and the conveyance direction. Thus, a degree of freedom in setting of the production method can be improved.

Aspect 5

The method for producing a fiber article according to item 1 or 2, wherein in the third step, the second external force is applied to the fiber sheet simultaneously in a plurality of directions including the width direction.
According to the above production method, by applying the second external force to the fiber sheet simultaneously in the plurality of directions including the width direction, the second fibers extending in the plurality of directions can be abundantly formed in a short time. Thus, production efficiency of the fiber article can be improved.

Aspect 6

The method for producing a fiber article according to any one of items 1 to 5, wherein in the first step, a nonwoven fabric is used as the fiber sheet.
According to the above production method, when producing the fiber article including the first fiber and the second fiber having an outer diameter smaller than that of the first fiber, the fiber article having a nonwoven fabric structure, a fiber article that is reduced in weight and improved in strength can be produced.

Aspect 7

The method for producing a fiber article according to any one of items 1 to 6, wherein in the first step, the plurality of resin particles having a lamellar structure are used.
According to the above production method, the second fibers can be efficiently formed from the resin particles through the third step using the plurality of resin particles having the lamellar structure.

Aspect 8

The method for producing a fiber article according to any one of items 1 to 7, wherein in the first step, the plurality of first fibers which are crimped are used.
According to the above production method, the first fibers can be configured to be bulkier as compared with the first fibers not crimped. Thus, the fiber gaps formed by the plurality of first fibers can be abundantly disposed in the fiber article. Thus, a basis weight of the fiber article can be reduced. Therefore, the fiber article further reduced in weight can be produced.

Aspect 9

The method for producing a fiber article according to any one of items 1 to 8, wherein in the first step, the plurality of first fibers including at least one of rayon, polypropylene, polyethylene terephthalate, polyethylene, or cellulose acetate are used.
According to the above production method, a selection range of a material of the first fibers can be expanded. Thus, a degree of freedom in designing the fiber article can be improved.

Aspect 10

The method for producing a fiber article according to any one of items 1 to 9, wherein the polymer that can be fiberized includes at least one of polytetrafluoroethylene, polypropylene, polyethylene, or polyamide.
According to the above production method, a selection range of the material of the second fibers can be expanded. Therefore, this production method also allows for further improvement of the degree of freedom in designing the fiber article.

Aspect 11

The method for producing a fiber article according to any one of items 1 to 10, wherein in the third step, the second external force is applied to the fiber sheet and thereby forming the fiber composite in which the basis weight has a value in a range of 60 g/m² or more and 300 g/m² or less, and a tensile strength in a minimum strength direction in which the tensile strength is minimized among the directions perpendicular to a thickness direction has a value in a range of 0.8 N/10 mm or more and 100 N/10 mm or less.
According to the above production method, the basis weight of the fiber article can be reduced, and a fiber article abundantly including the fiber gaps formed by the first fibers and the second fibers can be produced. Therefore, the weight of the fiber article can be easily reduced. Also, according to the above production method, it is possible to improve the strength of the fiber article to be produced, while reducing the weight of the fiber article to be produced. Thus, for example, the fiber article with improved durability can be produced. In addition, for example, the tensile strength of the plurality of first fibers in the fiber article is improved. Thus, for example, by increasing the second external force applied to the plurality of first fibers, the fiber gaps can be more abundantly provided in the produced fiber article. In addition, because the tensile strength of the first fibers is improved, when the strength of the second external force to be applied to the plurality of resin particles is adjusted in the third step, the adjustment of the strength can be prevented from being restricted by the tensile strength of the first fibers. This makes it easy to form the second fibers abundantly.

Aspect 12

The method for producing a fiber article according to item 11, wherein in the third step, the second external force is applied to the fiber sheet to form the fiber composite in which the tensile elongation rate in the minimum strength direction with respect to a natural state is a value in a range of 5% or more and 250% or less.
According to the above production method, the tensile elongation rate of the first fibers is improved, and therefore, when the strength of the second external force to be applied to the plurality of resin particles is adjusted in the third step, the adjustment of the strength can be prevented from being restricted by the tensile elongation rate of the first fibers. This enables the second fibers to be abundantly formed more easily.

Aspect 13

The method for producing a fiber article according to any one of items 1 to 12, wherein in the third step, the second external force is applied to the fiber sheet to form the fiber composite having the thickness in the natural state within a range of less than 3.0 mm.
According to the above production method, the fiber article to be produced can be made thin. Thus, weight reduction and reduction in size can be achieved, and the fiber article with improved strength can be easily produced.

Aspect 14

The method for producing a fiber article according to any one of items 1 to 13, wherein in the third step, the second external force is applied to the fiber sheet to form the fiber composite in which a pressure loss when air is caused to pass in the thickness direction at a flow rate of 5.3 cm/sec is a value in a range of 3 Pa or more and 35 Pa or less.
According to the above production method, there can be produced the fiber article that can be reduced in weight and improved in strength, can prevent clogging during use, and can efficiently flow a fluid to be filtered inside.

Aspect 15

The method for producing a fiber article according to any one of items 1 to 14, wherein in the third step, the second external force is applied to the fiber sheet to form the fiber composite having a trapping efficiency of a value in a range of 35% or more and 95% or less.
According to the above production method, because the trapping efficiency of the fiber article to be produced is set to a value in the above range, there can be produced the fiber article that is reduced in weight and improved in strength and has stable filter performance.

Aspect 16

The method for producing a fiber article according to any one of items 1 to 15, wherein in the third step, the second external force is applied to the fiber sheet to form the fiber composite classified into a filter group of JIS-ePM1 in Classification described in item 7.3 of JIS B 9908-1:2019.
According to the above production method, the fiber article usable for a high-quality filter classified into the filter group of "JIS-ePM1" can be produced.
The configurations in the embodiments and combinations thereof are examples. Addition, omission, substitution, and other changes of the configurations can be appropriately made without departing from the gist of the present disclosure. The present disclosure is not limited by the embodiments but is limited only by the claims. The aspects disclosed in the present specification can be combined with any other feature disclosed herein. Size of the fiber article 62 is not limited. The fiber article 62 may be used in a state of combining a plurality of fiber articles 62 or other configurations.

Reference Signs List

51 First fiber
60 Fiber sheet
61 Fiber composite
62 Fiber article
91 Resin particle
92 Second fiber

Claims

A method for producing a fiber article, the method comprising:
a first step of affixing a plurality of resin particles containing a polymer that can be fiberized to a fiber sheet including a plurality of first fibers, the fiber sheet being conveyed in a predetermined conveyance direction;

a second step of applying a first external force to the plurality of first fibers and the plurality of resin particles of the fiber sheet to which the plurality of resin particles are affixed, the fiber sheet being conveyed, to reduce fiber gaps between the plurality of first fibers; and

a third step of applying a second external force to the fiber sheet in which the applied first external force is relaxed, the fiber sheet being conveyed in the conveyance direction, to enlarge the fiber gaps between the plurality of first fibers, with respect to at least a width direction of the fiber sheet, to form a plurality of second fibers from the plurality of resin particles, each of the plurality of second fibers being thinner than each of the plurality of first fibers, and forming a fiber composite containing the plurality of first fibers and the plurality of second fibers.
The method for producing a fiber article according to claim 1, wherein in the third step, the second external force is applied to the fiber sheet in a state where the fiber sheet is heated.
The method for producing a fiber article according to claim 1, wherein in the third step, the second external force is applied to the fiber sheet also in the conveyance direction of the fiber sheet.
The method for producing a fiber article according to claim 3, wherein in the third step, the second external force is applied to the fiber sheet sequentially in one direction and the other direction, among the width direction and the conveyance direction.
The method for producing a fiber article according to claim 1, wherein in the third step, the second external force is applied to the fiber sheet simultaneously in a plurality of directions including the width direction.
The method for producing a fiber article according to any one of claims 1 to 5, wherein in the first step, a nonwoven fabric is used as the fiber sheet.
The method for producing a fiber article according to any one of claims 1 to 5, wherein in the first step, the plurality of resin particles having a lamellar structure are used.
The method for producing a fiber article according to any one of claims 1 to 5, wherein in the first step, the plurality of first fibers which are crimped are used.
The method for producing a fiber article according to any one of claims 1 to 5, wherein in the first step, the plurality of first fibers including at least one of rayon, polypropylene, polyethylene terephthalate, polyethylene, or cellulose acetate are used.
The method for producing a fiber article according to any one of claims 1 to 5, wherein the polymer that can be fiberized includes at least one of polytetrafluoroethylene, polypropylene, polyethylene, or polyamide.