Method for producing filter material

Abstract

To obtain a filter material having collection efficiency and air permeability which can be used for a medium and high-performance air filter material to be used for building air conditioning even if static elimination processing is performed.SOLUTION: A non-woven fabric material that makes a polyester long fiber being an approximately Y4 shape whose cross section is shown in Fig. 2 is prepared. A staple fiber web composed of split short fibers in which polypropylene and polyethylene are joined in a divisible manner is prepared. A laminate is acquired by laminating the non-woven fabric material and the staple short web. a high pressure water flow treatment is performed from the staple short web side of the laminate, and a composite non-woven fabric obtained by laminating and joining the non-woven fabric material and the staple short web is acquired. A filter material is acquired by eliminating water from the composite non-woven fabric.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a filter material used for filtering gases such as air, and more particularly to a method for producing a medium to high performance air filter material used for air conditioning in buildings. [Background technology]

[0002] Conventionally, a composite nonwoven fabric in which an ultrafine fiber layer and a thick fiber layer are laminated and the ultrafine fibers and the thick fibers are entangled between the layers has been used as a filter material with high collection efficiency and low pressure loss (high air permeability) (Patent Document 1). Specifically, it is described that a high-pressure water flow is sprayed from the meltblown nonwoven fabric side to entangle the polypropylene ultrafine fibers and the polyethylene terephthalate thick fibers, and then a filter material is obtained by performing an electrification treatment by a hydrocharge method (Patent Document 1, Examples).

[0003] However, when the filter material obtained by this method is used for a long period of time, the charge on the surface of the ultrafine fibers disappears, causing a problem of reduced collection efficiency. For this reason, only filter materials with a certain level of collection efficiency after neutralization are used in medium- to high-performance air filter materials for building air conditioning, and the filter material described in Patent Document 1 cannot be used. In addition, the polyethylene terephthalate thick fiber used has a circular cross section, and the gaps between the thick fibers tend to be dense, making it difficult to achieve high breathability.

[0004] Therefore, in order to obtain a filter material that has a collection efficiency and air permeability that can be used as a medium- to high-performance air filter material for building air conditioning even after static electricity has been removed, the present inventors proposed the inventions described in Patent Documents 2 and 3.

[0005] [Patent Document 1] WO2020 / 137605 [Patent Document 2] Patent Application No. 2023-2779 [Patent Document 3] Patent Application No. 2023-9460 Specification Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is the same as that of the inventions described in Patent Documents 2 and 3, and is to more rationally produce a filter material that has a collection efficiency and air permeability sufficient for use as a medium- to high-performance air filter material for building air conditioning, even after static electricity has been removed. [Means for solving the problem]

[0007] That is, the present invention provides a structure in which the cross-sectional shape is substantially Y-shaped and the top, bottom, left and right are connected at the bottom. the polyester long fibers are entangled at the boundary between the nonwoven fabric substrate and the short fiber web to obtain a composite nonwoven fabric; and a dehydration and drying step for removing water derived from the high-pressure water stream treatment from the composite nonwoven fabric.

[0008] The present invention also relates to a method for producing a filter material, comprising the steps of: preparing a nonwoven fabric substrate having polyester long fibers having a substantially Y4-shaped cross section as constituent fibers; subjecting a short fiber web made of splittable short fibers in which polypropylene and polyethylene are bonded in a splittable manner to a high-pressure water stream treatment to split and split the splittable short fibers into polypropylene ultrafine short fibers and polyethylene ultrafine short fibers, thereby preparing an ultrafine short fiber web; laminating the nonwoven fabric substrate and the ultrafine short fiber web to obtain a laminate; applying a high-pressure water stream treatment from the ultrafine short fiber web side of the laminate to entangle the polyester long fibers, polypropylene ultrafine short fibers, and polyethylene ultrafine short fibers at the boundary between the nonwoven fabric substrate and the ultrafine short fiber web to obtain a composite nonwoven fabric; and a dehydration and drying step to remove water resulting from the high-pressure water stream treatment from the composite nonwoven fabric.

[0009] The present invention also includes a process for preparing a nonwoven fabric substrate having polyester long fibers as constituent fibers and a cross section of approximately Y4 shape, a process for laminating a short fiber web made of splittable short fibers in which polypropylene and polyethylene are bonded in a splittable manner on one side of the long fiber nonwoven fabric having long fibers as constituent fibers, and then performing a high-pressure water flow treatment from the short fiber web side to split and split the splittable short fibers to generate polypropylene ultrafine short fibers and polyethylene ultrafine short fibers, and to entangle the long fibers and both ultrafine short fibers, thereby forming a long fiber nonwoven fabric and both ultrafine short fibers. the step of preparing an integrated web in which fibers are integrated; the step of laminating the nonwoven fabric substrate and the integrated web to obtain a laminate; the step of applying a high-pressure water jet treatment from the integrated web side of the laminate to entangle the polyester long fibers, the polypropylene ultrafine short fibers, and the polyethylene ultrafine short fibers at the boundary between the nonwoven fabric substrate and the integrated web to obtain a composite nonwoven fabric; and the dehydration and drying step of removing water resulting from the high-pressure water jet treatment from the composite nonwoven fabric.

[0010] The cross-sectional shape of the polyester long fiber, which is the constituent fiber of the nonwoven fabric substrate used in the present invention, will be described. This cross-sectional shape has four approximate Y shapes as shown in FIG. 1. The approximate Y shapes are connected vertically and horizontally at the lower end 1 to form an approximate Y4 shape as shown in FIG. 2. This approximate Y4 shape has four recesses 2, eight protrusions 3, and four small recesses 4. The four recesses 2 are deeply recessed between the protrusions 3. The polyester long fiber having such a cross-sectional shape has high rigidity due to the approximately +-shaped portion 5 in the center and the four approximately V-shaped portions 6 connected to each end of the approximately +-shaped portion 5. Therefore, the nonwoven fabric substrate used in the present invention functions as an aggregate for the filter material. In addition, because of such a cross-sectional shape, the gaps between the polyester long fibers are widened, resulting in an aggregate with high air permeability.

[0011] The fineness of the polyester long fibers is arbitrary, but is preferably about 6 to 30 decitex, and most preferably 8 to 16 decitex. If the fineness is low, the rigidity decreases and the fiber becomes unsuitable as an aggregate for a filter material. The polyester long fibers may be made of one type of polyester, but it is preferable to combine a low-melting polyester and a high-melting polyester. That is, it is preferable to use a composite type in which the approximately V-shaped portion 6 of the cross-sectional shape of the polyester long fibers is formed of a low-melting polyester and the approximately +-shaped portion 5 is formed of a high-melting polyester. This is because, after accumulating the composite type polyester long fibers, the low-melting polyester is softened or melted and then solidified to obtain a nonwoven fabric substrate in which the polyester long fibers are fused to each other by the low-melting polyester. The basis weight of the nonwoven fabric substrate is arbitrary, but is generally 50 g / m 2 More preferably, it is 50 to 100 g / m 2 If the basis weight is too low, the rigidity decreases, and the function of the filter material as an aggregate tends to decrease.

[0012] On the other hand, there are three types of webs prepared for lamination with the nonwoven fabric substrate. That is, a staple fiber web, an ultrafine staple fiber web, or an integrated web. The staple fiber web is formed by accumulating splittable staple fibers in which polypropylene and polyethylene are bonded in a splittable manner. In the present invention, splittable refers to splitting and generating ultrafine staple fibers by the physical impact of a high-pressure water stream colliding with the splittable staple fibers. The cross section of such splittable staple fibers has a shape, for example, as shown in FIG. 3. That is, the cross section of the splittable staple fiber is a solid circle, and the cross sections of the polypropylene and the polyethylene are each wedge-shaped and bonded alternately. It may also have a shape as shown in FIG. 4. That is, the cross section of the splittable staple fiber is a hollow circle, and the cross sections of the polypropylene and the polyethylene are each trapezoidal and bonded alternately. In the present invention, polypropylene and polyethylene are selected because when polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers generated by splitting are mixed, they are unlikely to become charged even if they are rubbed against each other by high-pressure water stream treatment. Although both are polyolefin-based ultrafine short fibers, it was unexpected that they would not become electrostatically charged due to friction between them, and the reason for this is presumed to be as follows: Short fiber webs are made by passing short fiber cotton through a carding machine to open it up, and to make it easier to open up, an oil is applied to the surface of the short fibers, in other words, the oil functions as an antistatic agent.

[0013] The ultrafine short fiber web is produced by subjecting the above-mentioned short fiber web to a high-pressure water stream treatment to split and split the splittable short fibers into polypropylene ultrafine short fibers and polyethylene ultrafine short fibers. The high-pressure water stream treatment is a treatment in which a high-pressure water stream is made to impinge on the short fiber web, and specifically, it is preferably carried out by making a water stream with a pressure of 1 to 12 MPa impinge on the short fiber web. If the water stream pressure is less than 1 MPa, it tends to be difficult to split and split the splittable short fibers. On the other hand, if the water stream pressure exceeds 12 MPa, the ultrafine short fibers are too strongly entangled with each other, making it difficult to entangle the nonwoven fabric substrate and the ultrafine short fibers in a subsequent process.

[0014] The integrated web is obtained by laminating the above-mentioned short fiber web on one side of a long fiber nonwoven fabric having long fibers as constituent fibers, and then subjecting the short fiber web side to high-pressure water flow treatment to split and split the split type short fibers to generate polypropylene ultrafine short fibers and polyethylene ultrafine short fibers, and entangle the long fibers and both ultrafine short fibers, thereby integrating the long fiber nonwoven fabric and both ultrafine short fibers. The long fiber nonwoven fabric used to obtain the integrated web is composed of long fibers such as polypropylene long fibers and polyester long fibers, and the long fibers are bonded to each other by means such as partial heat fusion. Long fibers such as polypropylene long fibers are different from the polyester long fibers that constitute the nonwoven fabric substrate, and their cross section is generally circular. The fineness of long fibers such as polypropylene long fibers is 1 to 5 decitex. It is difficult to produce long fibers with a fineness of less than 1 decitex by the melt spinning method. If the fineness exceeds 5 decitex, the fineness difference with the resulting ultrafine short fibers becomes large, making it difficult for the long fiber nonwoven fabric and the ultrafine short fibers to be integrated. This long fiber nonwoven fabric is relatively thin, with a basis weight of 5 to 20 g / m 2 The weight is about 5g / m 2 If the weight is less than 20 g / m, it tends to be difficult to produce a long-fiber nonwoven fabric. 2 If the water pressure exceeds this range, the resulting ultrafine short fibers will be less likely to penetrate the long-fiber nonwoven fabric when a high-pressure water stream is applied, and the long-fiber nonwoven fabric and the ultrafine short fibers will be less likely to be integrated together.

[0015] The integrated web is formed by laminating a staple fiber web on one side of a long fiber nonwoven fabric and subjecting the staple fiber web to high-pressure water flow treatment. If high-pressure water flow treatment is applied from the long fiber nonwoven fabric side, the fibers in the staple fiber web are entangled with the transport conveyor, making it difficult to peel the integrated web from the transport conveyor. However, if high-pressure water flow treatment is applied from the long fiber nonwoven fabric side after high-pressure water flow treatment from the short fiber web side. In this case, the fibers in the staple fiber web are entangled with the long fiber nonwoven fabric to some extent, so that the fibers in the staple fiber web are unlikely to be entangled with the transport conveyor. As described above, this high-pressure water flow treatment is preferably performed by colliding a water flow with a pressure of 1 to 12 MPa against the staple fiber web. If the water flow pressure is less than 1 MPa, it tends to be difficult to split the splittable staple fibers. Furthermore, if the water flow pressure exceeds 12 MPa, the intertwining of the long fiber nonwoven fabric and the ultrafine short fibers becomes too strong, making it difficult for the nonwoven fabric substrate and the ultrafine short fibers to be intertwined in a later process. This high-pressure water flow treatment splits and splits the split type short fibers, producing polypropylene ultrafine short fibers and polyethylene ultrafine short fibers. In addition, the long fibers of the long fiber nonwoven fabric are intertwined with the produced polypropylene ultrafine short fibers and polyethylene ultrafine short fibers. As a result, an integrated web is obtained in which the long fiber nonwoven fabric and both ultrafine short fibers are integrated. In this integrated web, the surface on which the short fiber web is laminated generally has a greater amount of ultrafine short fibers. That is, the surface to which the high-pressure water flow is applied has a greater amount of ultrafine short fibers, and the surface from which the high-pressure water flow is discharged has a smaller amount of ultrafine short fibers.

[0016] The fineness of the splittable staple fibers used to prepare the staple fiber web, ultrafine staple fiber web, or integrated web can be determined arbitrarily, but is preferably 1 to 5 denier. If the fineness of the splittable staple fibers is less than 1 denier, the fineness of each ultrafine staple fiber produced must be reduced to, for example, less than 0.05 denier, which makes it difficult to actually produce the splittable staple fibers. If the fineness exceeds 5 denier, the fineness of each ultrafine staple fiber produced also becomes thick, the collection efficiency decreases, and the material is unsuitable as a medium to high performance air filter material for building air conditioning. The fineness of the ultrafine staple fibers produced by splitting is preferably about 0.05 to 0.3 denier. The fiber length of the splittable staple fibers may be approximately the same as the fiber length of conventionally known staple fibers, and is preferably, for example, about 5 to 120 mm.

[0017] The basis weight of the short fiber web formed by accumulating splittable short fibers is 20 to 70 g / m 2 It is preferable that the basis weight is 20 g / m 2 If the fiber density of the layer made of the resulting ultrafine short fibers is low, the collection efficiency is low, and the material is unsuitable as a medium- to high-performance air filter material for building air conditioning. 2 If the fiber density exceeds 100%, the fiber density becomes too high, and the air permeability tends to decrease. For the same reason, the short fiber web used to obtain the ultrafine short fiber web or the integrated web preferably has a similar basis weight. The short fiber web may contain other split short fibers. Specifically, the split short fibers disclosed in Patent Document 3, in which polyethylene terephthalate and polyolefin are bonded in a splittable manner, may be contained. Polyethylene terephthalate has a higher hydrophilicity than polyolefin, and therefore can be entangled with less unevenness when subjected to high-pressure water flow treatment.

[0018] A nonwoven fabric substrate and a staple fiber web are laminated to obtain a laminate. Then, this laminate is subjected to a high-pressure water stream treatment from the staple fiber web side. The high-pressure water stream treatment is a treatment in which a high-pressure water stream is collided with the staple fiber web, and specifically, it is preferably performed by colliding a water stream with a pressure of 1 to 12 MPa with the staple fiber web. The nonwoven fabric substrate used in the method according to the present invention is made of polyester long fibers having a cross section of approximately Y4 shape, and therefore has an advantage that the gaps between the polyester long fibers are wide and the high-pressure water stream can easily pass through. Therefore, the water stream is unlikely to remain between the nonwoven fabric substrate and the staple fiber web, and the splitting and inter-fiber entanglement of the splittable staple fibers by the high-pressure water stream are promoted. If the pressure of the water stream is less than 1 MPa, the splittable staple fibers tend to be difficult to split. Also, if the pressure of the water stream exceeds 12 MPa, the ultrafine short fibers generated by splitting tend to flow out from the opposite side of the nonwoven fabric substrate (the side on which the staple fiber web is not laminated). This high-pressure water jet treatment splits and splits the splittable staple fibers into polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers. In addition, the polyester long fibers, polypropylene ultrafine staple fibers, and polyethylene ultrafine staple fibers are entangled at the boundary between the nonwoven fabric substrate and the staple fiber web. As a result, a composite nonwoven fabric is obtained in which the nonwoven fabric substrate and the ultrafine staple fiber layer are laminated together.

[0019] Alternatively, a laminate may be obtained by laminating an ultrafine fiber web instead of the staple fiber web on the nonwoven fabric substrate. In this case, the high-pressure water jet treatment is also performed from the ultrafine fiber web side. The high-pressure water jet treatment entangles the polyester long fibers, polypropylene ultrafine fibers, and polyethylene ultrafine fibers at the boundary between the nonwoven fabric substrate and the ultrafine fiber web, thereby obtaining a composite nonwoven fabric.

[0020] Alternatively, an integrated web may be laminated on a nonwoven fabric substrate instead of a staple web to obtain a laminate. In this case, the high-pressure water stream treatment is also applied from the integrated web side. The high-pressure water stream treatment causes the polyester long fibers, polypropylene ultrafine short fibers, and polyethylene ultrafine short fibers to be entangled at the boundary between the integrated web and the nonwoven fabric substrate. As a result, a composite nonwoven fabric is obtained in which the integrated web and the nonwoven fabric substrate are laminated and joined. Furthermore, when the integrated web has a surface with a large amount of ultrafine short fibers and a back surface with a small amount of ultrafine short fibers, it is preferable to obtain a composite nonwoven fabric as follows. That is, when laminating the integrated web and the nonwoven fabric substrate, the surface of the integrated web with a large amount of ultrafine short fibers is laminated so as to abut against the nonwoven fabric substrate to obtain a laminate. Then, a high-pressure water stream is applied from the back surface side of the integrated web with a small amount of ultrafine short fibers to entangle the polyester long fibers, polypropylene ultrafine short fibers, and polyethylene ultrafine short fibers. This is because this method results in more entanglement of the polyester long fibers and the ultrafine short fibers, resulting in higher bonding strength. Also, the back surface, which contains a smaller amount of ultrafine short fibers, becomes the filtering surface of the composite nonwoven fabric, so the filtering surface is less prone to fluffing and roughness, and dust that has accumulated on the filtering surface is easier to brush off.

[0021] The composite nonwoven fabric described above contains water due to the high-pressure water flow treatment, and this water is removed through a dehydration and drying process to obtain a filter material. The dehydration and drying process can be performed by a conventional method, for example, by squeezing the composite nonwoven fabric with a mangle or the like and then passing it through a dryer. This filter material is almost uncharged, so it can be used as it is as a medium- to high-performance air filter material for building air conditioning. However, in reality, it is often used as a medium- to high-performance air filter material for building air conditioning after being destaticized and measuring the collection efficiency and air permeability. If the collection efficiency and air permeability are measured without going through the destaticization process, the collection efficiency due to charging may be measured. Note that destaticization can be performed by a known method, for example, by passing the filter material through a static eliminator. Effect of the Invention

[0022] The filter material obtained by the method according to the present invention is obtained by high-pressure water jet treatment using a specific nonwoven fabric substrate and a specific web (short fiber web, ultrafine staple fiber web, or integrated web). Therefore, the polyester long fibers, polypropylene ultrafine staple fibers, and polyethylene ultrafine staple fibers in the nonwoven fabric substrate are less likely to become electrically charged, and the filter efficiency is less likely to decrease even when static electricity is removed.

[0023] Furthermore, when an integrated web is used as the specific web and has a surface with a large amount of ultrafine short fibers and a back surface with a small amount of ultrafine short fibers, and the laminate is laminated so that the surface with a large amount of ultrafine short fibers abuts the nonwoven fabric substrate, and a high-pressure water flow is applied to the back surface with the small amount of ultrafine short fibers to obtain a filter material, the relatively smooth back surface with a small amount of ultrafine short fibers becomes the filtering surface, making it easy to brush off collected dust and making it easy to wash or regenerate the filter material. EXAMPLES

[0024] Example 1 As a nonwoven fabric substrate, polyester spunbond (product name: Dilla, thick fiber type) manufactured by Unitika Ltd. was prepared. This nonwoven fabric substrate is made of polyester long fibers (fineness 16 decitex) with a cross-sectional shape shown in FIG. 2, and has a basis weight of 90 g / m 2 The polyester long fiber is a composite polyester long fiber in which the approximately V-shaped portions 6 in Fig. 2 are made of a low melting point polyester and the approximately +-shaped portions 5 are made of a high melting point polyester. The nonwoven fabric substrate is formed by bonding the composite polyester long fibers together at the approximately V-shaped portions 6.

[0025] On the other hand, splittable staple fibers were prepared with a hollow circular cross-sectional shape as shown in Figure 4, a fineness of 2.2 dtex, and a fiber length of 51 mm. This splittable staple fiber has approximately the same mass ratio of polypropylene and polyethylene, and the fineness of the polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers generated after splitting is approximately 0.14 dtex. The splittable staple fibers were passed through a carding machine to obtain a basis weight of 50 g / m. 2A staple fiber web was prepared.

[0026] After laminating a staple fiber web on one side of the nonwoven fabric substrate, a high-pressure water stream was applied twice to the staple fiber web from a nozzle with a hole diameter of 0.12 mm at a pressure of 2.8 MPa, and then a high-pressure water stream was applied twice to the staple fiber web at a pressure of 8.3 MPa. This high-pressure water stream treatment split and split the split type staple fibers, producing polypropylene ultrafine short fibers and polyethylene ultrafine short fibers of about 0.14 decitex. At the same time, the polypropylene ultrafine short fibers, polyethylene ultrafine short fibers, and polyester long fibers were entangled to obtain a composite nonwoven fabric in which the nonwoven fabric substrate and the staple fiber web were integrated. This composite nonwoven fabric was squeezed with a mangle and then introduced into a dryer to remove the water in the composite nonwoven fabric, thereby obtaining a filter material.

[0027] Example 2 The same nonwoven fabric substrate as used in Example 1 was prepared.

[0028] An integrated web was prepared by the following method. First, a long-fiber nonwoven fabric (basis weight 9 g / m2) was prepared by accumulating polypropylene long fibers having a fineness of about 3 dtex and a circular cross section and partially heat-pressing the fibers. 2 ) was prepared. Then, the same short fiber web as used in Example 1 was laminated on one side of this long fiber nonwoven fabric, and then a high-pressure water stream was applied twice from the short fiber web side from a nozzle having a hole diameter of 0.12 mm at a pressure of 2.8 MPa, and then a high-pressure water stream was applied four more times from the short fiber web side from a nozzle having a hole diameter of 0.12 mm at a pressure of 8.3 MPa. This high-pressure water stream treatment split and split the split type short fibers, producing polypropylene ultrafine short fibers and polyethylene ultrafine short fibers of about 0.14 decitex. At the same time, the polypropylene ultrafine short fibers, polyethylene ultrafine short fibers, and polypropylene long fibers in the long fiber nonwoven fabric were entangled, and an integrated web was obtained.

[0029] After laminating the integrated web on one side of the nonwoven fabric substrate, a high-pressure water stream was applied twice to the integrated web from a 0.12 mm nozzle at a pressure of 2.8 MPa, and then a high-pressure water stream was applied twice to the integrated web at a pressure of 8.3 MPa. This high-pressure water stream treatment entangled the polypropylene ultrafine short fibers, polyethylene ultrafine short fibers, and polyester long fibers, resulting in a composite nonwoven fabric in which the nonwoven fabric substrate and the integrated web were integrated. This composite nonwoven fabric was squeezed with a mangle and then introduced into a dryer to remove the water from the composite nonwoven fabric, resulting in a filter material.

[0030] Example 3 The same nonwoven fabric substrate as used in Example 1 was prepared.

[0031] An integrated web was prepared by the following method. First, splittable staple fibers were prepared that had a solid circular cross-sectional shape as shown in Figure 3, a fineness of 2.0 dtex, and a fiber length of 51 mm. This splittable staple fiber had approximately the same mass ratio of polypropylene and polyethylene, and the fineness of the polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers generated after splitting was approximately 0.13 dtex. The splittable staple fibers were passed through a carding machine to obtain a basis weight of 50 g / m2. 2 A short fiber web of the above was prepared. Next, the long fiber nonwoven fabric used in Example 2 was prepared, and the short fiber web prepared was laminated on one side of the long fiber nonwoven fabric. After that, a high-pressure water stream was applied twice from the short fiber web side, which was ejected from an ejection hole having a hole diameter of 0.12 mm at a pressure of 2.8 MPa, and then a high-pressure water stream was applied four times from the short fiber web side, which was ejected from an ejection hole having a hole diameter of 0.12 mm at a pressure of 8.3 MPa. This high-pressure water stream treatment split and split the split type short fibers, producing polypropylene ultrafine short fibers and polyethylene ultrafine short fibers of about 0.13 decitex. At the same time, the polypropylene ultrafine short fibers, the polyethylene ultrafine short fibers, and the polypropylene long fibers in the long fiber nonwoven fabric were entangled, and an integrated web was obtained.

[0032] After laminating the integrated web on one side of the nonwoven fabric substrate, a high-pressure water jet treatment was performed under the same conditions as in Example 2 to entangle the polypropylene ultrafine short fibers, polyethylene ultrafine short fibers, and polyester long fibers, thereby obtaining a composite nonwoven fabric in which the nonwoven fabric substrate and the integrated web were integrated. This composite nonwoven fabric was squeezed with a mangle and then introduced into a dryer to remove the water from the composite nonwoven fabric, thereby obtaining a filter material.

[0033] Comparative Example A melt-blown nonwoven fabric made of polypropylene was prepared. This melt-blown nonwoven fabric was made of ultrafine polypropylene fibers with a fiber diameter of 3 μm and had a basis weight of 20 g / m. 2 This melt-blown nonwoven fabric was laminated on the surface of the nonwoven fabric substrate used in Example 1, and a high-pressure water stream was applied to the melt-blown nonwoven fabric from a nozzle hole having a diameter of 0.12 mm at a pressure of 2.8 MPa, and then a high-pressure water stream was applied to the melt-blown nonwoven fabric from a nozzle hole having a diameter of 0.12 mm three times at a pressure of 4.1 MPa, thereby entangling the polypropylene ultrafine fibers and the polyester long fibers to obtain a composite nonwoven fabric. After squeezing the composite nonwoven fabric with a mangle, the composite nonwoven fabric was introduced into a dryer to remove the water from the composite nonwoven fabric, and a filter material was obtained.

[0034] The filter materials obtained in Examples 1 to 3 and the Comparative Example were destaticized in accordance with the method described in JIS B 9908-4(2019) 9 (Test Method), and then the collection efficiency and air permeability were measured by the following method. The results are shown in Table 1.

[0035] [Collection efficiency (%)] The collection efficiency was measured in accordance with the method described in ASTM F 2299 (with the exception that the particles were neutralized). The detailed measurement conditions were as follows: Test area: 49.0 cm 2 , Test flow rate: 28.3 L / min, Particle size: 0.3 μm (0.303 ± 0.006 μm), Particle type: NANOSPHERE SIZE STANDARDS 3300A (Thermo Fisher Scientific) Spherical polystyrene standard particles In addition, only in Example 3, the detailed measurement conditions were different as follows: Test area: 100 cm 2, Test flow rate: 32L / min, Test air speed: 5.3cm / s, Test temperature: 24℃, Particle size and type: JIS type 11

[0036] [Air permeability (cc / cm 2 / s)] The air permeability was measured according to the method described in JIS L 1096 (2010) 8.26.1A (Fragile type method).

[0037] [Table 1] ━━━━━━━━━━━━━━━━━━━━━━ Collection efficiency Air permeability ━━━━━━━━━━━━━━━━━━━━━━ Example 1 21.2 45.3 Example 2 37.6 25.9 Example 3 95.6 25.2 Comparative Example 16.1 44.4 ━━━━━━━━━━━━━━━━━━━━━━

[0038] As is clear from a comparison between Examples 1 to 3 and the Comparative Example, after the static electricity is removed from the filter material, the filter material obtained by the methods of Examples 1 to 3 has a higher collection efficiency than the filter material obtained by the method of the Comparative Example. [Brief description of the drawings]

[0039] [Figure 1] FIG. 2 is a diagram showing an approximate Y shape of a cross-sectional shape of a polyester long fiber, which is an approximate Y4 shape. [Diagram 2] FIG. 2 is a diagram showing a cross-sectional shape of a polyester long fiber, which is approximately a Y4 shape. [Diagram 3] FIG. 2 is a diagram showing an example of a cross-sectional shape of a splittable short fiber used in the present invention. [Figure 4] FIG. 2 is a diagram showing another example of the cross-sectional shape of the splittable short fiber used in the present invention. [Explanation of symbols]

[0040] 1. The lower end of one of the approximately Y shapes of the cross section of the polyester filament is approximately Y4 shape. 2. A recess formed in an approximately Y4 shape 3. A protruding portion formed in an approximately Y4 shape 4. Small recess formed in approximately Y4 shape 5 Approximate + shape in approximate Y4 shape 6. Approximate V-shaped portion of approximate Y4 shape

Claims

1. The cross-sectional shape is roughly Y-shaped, with the top, bottom, left and right sides connected at the bottom. A step of preparing a nonwoven fabric substrate having polyester long fibers as constituent fibers, A step of preparing a staple fiber web composed of splittable staple fibers in which polypropylene and polyethylene are bonded in a splittable manner; A step of laminating the nonwoven fabric substrate and the staple fiber web to obtain a laminate; a step of subjecting the laminate to a high-pressure water jet treatment from the staple fiber web side to split and split the splittable staple fibers to generate polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers, and entangling the polyester long fibers, the polypropylene ultrafine staple fibers, and the polyethylene ultrafine staple fibers at the boundary between the nonwoven fabric substrate and the staple fiber web to obtain a composite nonwoven fabric; A method for producing a filter material, comprising a dehydration and drying step for removing water resulting from the high-pressure water jet treatment from the composite nonwoven fabric.

2. The cross-sectional shape is roughly Y-shaped, with the top, bottom, left and right sides connected at the bottom. A step of preparing a nonwoven fabric substrate having polyester long fibers as constituent fibers, a step of subjecting a staple fiber web made of splittable staple fibers in which polypropylene and polyethylene are bonded in a splittable manner to a high-pressure water jet treatment to split and split the splittable staple fibers into polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers, thereby preparing an ultrafine staple fiber web; A step of laminating the nonwoven fabric substrate and the ultrafine short fiber web to obtain a laminate; a step of subjecting the laminate to a high-pressure water jet treatment from the ultrafine fiber web side to entangle the polyester long fibers, the polypropylene ultrafine fibers, and the polyethylene ultrafine fibers at the boundary between the nonwoven fabric substrate and the ultrafine fiber web to obtain a composite nonwoven fabric; A method for producing a filter material, comprising a dehydration and drying step for removing water resulting from the high-pressure water jet treatment from the composite nonwoven fabric.

3. The cross-sectional shape is roughly Y-shaped, with the top, bottom, left and right sides connected at the bottom. A step of preparing a nonwoven fabric substrate having polyester long fibers as constituent fibers, a step of laminating a staple fiber web made of splittable staple fibers in which polypropylene and polyethylene are bonded in a splittable manner on one side of a long-fiber nonwoven fabric having long fibers as constituent fibers, and then subjecting the short-fiber web side to a high-pressure water jet treatment to split and split the splittable staple fibers to generate polypropylene ultrafine staple fibers and polyethylene ultrafine staple fibers, and entangling the long fibers and both ultrafine staple fibers to prepare an integrated web in which the long-fiber nonwoven fabric and both ultrafine staple fibers are integrated; laminating the nonwoven substrate and the integrated web to obtain a laminate; a step of subjecting the laminate to a high-pressure water jet treatment from the integrated web side to entangle the polyester long fibers, the polypropylene ultrafine short fibers, and the polyethylene ultrafine short fibers at the boundary between the nonwoven fabric substrate and the integrated web to obtain a composite nonwoven fabric; A method for producing a filter material, comprising a dehydration and drying step for removing water resulting from the high-pressure water jet treatment from the composite nonwoven fabric.

4. The method for producing a filter material according to any one of claims 1 to 3, further comprising a static elimination step added after the dehydration and drying step.

5. 3. The method for producing a filter material according to claim 1, wherein the polyester long fibers have a fineness of 6 to 30 dtex, and the resulting polypropylene ultrafine short fibers and polyethylene ultrafine short fibers have a fineness of 0.05 to 0.3 dtex.

6. The method for producing a filter material according to claim 3, wherein the polyester long fibers constituting the nonwoven fabric substrate have a fineness of 6 to 30 decitex, the long fibers constituting the long-fiber nonwoven fabric have a fineness of 1 to 5 decitex, and the resulting polypropylene ultrafine short fibers and polyethylene ultrafine short fibers have finenesses of 0.05 to 0.3 decitex.

7. 4. The method for producing a filter material according to claim 1, wherein the splittable staple fibers have a cross section in the shape of a solid circle, and the polypropylene and ethylene fibers each have a cross section in the shape of a wedge and are bonded alternately.

8. 4. The method for producing a filter material according to claim 1, wherein the splittable staple fibers have a hollow circular cross section, and the polypropylene and ethylene fibers each have a trapezoidal cross section and are joined alternately.

9. 4. The method for producing a filter material according to claim 3, wherein the integrated web has a surface having a larger amount of the ultrafine short fibers and a back surface having a smaller amount of the ultrafine short fibers, and the integrated web is laminated so that the surface of the integrated web and the nonwoven fabric substrate are in contact with each other to obtain a laminate, and then a high-pressure water jet treatment is applied from the back surface side of the integrated web.

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