Method of manufacturing filter material

Abstract

To provide a method of manufacturing a filter material that serves as a nonwoven fabric-made support which is flexible when laminated with a PTFE film and high in rigidity after the filter material is manufactured by lamination.SOLUTION: There is prepared a fiber web including division type composite fibers formed by joining a polyethylene component and a polypropylene component. A high-pressure water flow is supplied to the fiber web to split the division type composite fibers into polyethylene ultra fine fibers and polypropylene ultra fine fibers, which are confounded to obtain nonwoven fabric. The nonwoven fabric and a PTFE film are laminated, heat is applied to the nonwoven fabric to melt the polyethylene ultra fine fibers, and the polyethylene ultra fine fibers and polypropylene fibers are combined to obtain a high-rigidity nonwoven fabric-made support. Simultaneously, the nonwoven fabric-made support and PTFE film are bonded to obtain a filter material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a filter material comprising a porous membrane made of polytetrafluoroethylene (hereinafter referred to as "PTFE membrane") and a nonwoven fabric support laminated to the PTFE membrane, and in particular to a method that is less likely to cause damage to the PTFE membrane during production of the filter material. [Background technology]

[0002] PTFE membranes are well known as filter materials with high collection efficiency and high air permeability (low pressure loss), and are used as filter materials for gases such as air or liquids. PTFE membranes are thin and soft, so they are laminated with a highly rigid nonwoven fabric support and used as filter materials. However, when the PTFE membrane is in contact with the highly rigid nonwoven fabric support, the PTFE membrane may be damaged by the nonwoven fabric support. When the PTFE membrane is damaged, the collection efficiency of the filter material decreases, which is a drawback.

[0003] For this reason, there is a demand for a nonwoven fabric support that is flexible when laminated with a PTFE membrane, but becomes highly rigid after lamination to produce a filter material. Patent Document 1 describes the use of a nonwoven fabric with a low apparent density as such a nonwoven fabric support.

[0004] [Patent Document 1] JP 2002-66226 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for producing a filter material that is flexible when laminated with a PTFE membrane but becomes a highly rigid nonwoven fabric support after lamination to produce a filter material. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention adopts means different from those described in Patent Document 1. That is, the present invention includes a step of preparing a fiber web containing a split composite fiber in which a polyethylene component and a high melting point polymer component having a melting point higher than that of the polyethylene component are joined, splitting the split composite fiber contained in the fiber web to generate polyethylene ultrafine fibers and high melting point polymer ultrafine fibers to obtain a nonwoven fabric, and laminating the nonwoven fabric on at least one side of a PTFE membrane, and then applying heat to the nonwoven fabric to soften or melt the polyethylene ultrafine fibers, bond between the polyethylene ultrafine fibers and the high melting point polymer ultrafine fibers to obtain a nonwoven support, and bonding the nonwoven support to the porous membrane. The present invention relates to a method for manufacturing a filter material.

[0007] First, the step of preparing the fiber web will be described. The fiber web used in the present invention is formed by accumulating split composite fibers in which a polyethylene component and a high melting point polymer component having a melting point higher than that of the polyethylene component are joined. Generally, a fiber web containing 30 to 100% by mass of such split composite fibers is prepared. Commercially available split composite fibers can be adopted. For example, as shown in FIGS. 1 and 2, the cross section of the split composite fiber is formed by joining a wedge-shaped or trapezoidal polyethylene component and a polymer component having a melting point higher than that of the polyethylene component such as a polypropylene component or a polyethylene terephthalate component having the same shape. Note that FIG. 1 shows a solid split composite fiber, and FIG. 2 shows a hollow split composite fiber. The split composite fiber is split by a physical impact such as a high-pressure water stream to generate polyethylene ultrafine fibers and high melting point polymer ultrafine fibers. Generally, hollow split composite fibers are more easily split and are preferred for use in the present invention. Also, the split composite fiber may be a long fiber or a short fiber, but generally short fibers are used.

[0008] The fineness of the conjugated fiber is an arbitrarily determinable matter, but is preferably 1.1 to 5.5 dtex. When the fineness of the conjugated fiber is less than 1.1 dtex, the fineness of each ultrafine fiber to be produced has to be made as fine as, for example, less than 0.055 dtex, making it difficult to actually manufacture the conjugated fiber. On the other hand, when the fineness exceeds 5.5 dtex, the fineness of each ultrafine fiber to be produced also becomes thick, resulting in a decrease in the collection efficiency of coarse dust and a tendency to become unsuitable as a nonwoven support that also functions as a prefilter. Note that the fineness of the ultrafine fiber produced by splitting is preferably about 0.055 to 0.242 dtex. When short fibers are employed as the conjugated fiber, the fiber length may be of the same degree as that of conventionally known short fibers, and is preferably, for example, about 5 to 120 mm.

[0009] The basis weight of the fiber web formed by accumulating the conjugated fiber is preferably 20 to 70 g / m 2 If this basis weight is less than 20 g / m 2 , there is a tendency that it becomes inappropriate to use it as a nonwoven support with a thin thickness and high rigidity. On the other hand, when the basis weight exceeds 70 g / m 2 , the thickness tends to increase and the air permeability of the nonwoven support decreases. The fiber web may contain different types of fibers such as other types of conjugated fibers and non-conjugated fibers. For example, it may contain other types of conjugated fibers formed by joining a polypropylene component and a polyethylene terephthalate component. Further, non-conjugated fibers having a fineness of about 0.5 to 1.0 dtex may be contained. When these different types of fibers are included, the content thereof is about 70% by mass or less in the fiber web. The fiber web may be simply an accumulation of conjugated short fibers, or may be one in which the conjugated fibers are intertwined by a pretreatment such as a water flow treatment.

[0010] The fiber web is subjected to high-pressure water flow treatment or the like, and the split-type composite fibers are split. Then, ultra-fine polyethylene fibers and ultra-fine high-melting-point polymer fibers such as ultra-fine polypropylene fibers or ultra-fine polyethylene terephthalate fibers are produced. When subjecting the fiber web to high-pressure water flow treatment or the like, it is preferable to laminate a base material. As the base material, a thin and flexible woven fabric base material or a non-woven fabric base material is used. Specifically, those with a basis weight of 5 to 20 g / m 2 are used. Laminating such a base material on the fiber web is preferable because it can prevent the ultra-fine fibers from getting entangled with the mesh-shaped conveyor or floating during the splitting of the fibers by high-pressure water flow treatment or the like. In particular, when the non-woven fabric base material is arranged on the conveyor side, the ultra-fine fibers generated by the splitting do not get entangled with the conveyor, and the splitting can be carried out efficiently. As the non-woven fabric base material, it is preferable to use a conventionally known long-fiber non-woven fabric base material. For example, a long-fiber non-woven fabric base material composed of polypropylene long fibers as constituent fibers, a long-fiber non-woven fabric base material composed of core-sheath type composite long fibers as constituent fibers, etc. are used. In particular, it is preferable to use a long-fiber non-woven fabric base material composed of core-sheath type composite long fibers in which the core component is polyethylene terephthalate and the sheath component is polyethylene, and the core-sheath type composite long fibers are partially bonded to each other by the fixing due to the softening or melting of the sheath component. Such a long-fiber non-woven fabric base material has good morphological stability due to the bonding between the core-sheath type composite long fibers, and because it is a partial bonding, it is difficult for the ultra-fine fibers generated at the non-bonded portions to get entangled with the conveyor.

[0011] Next, the process of manufacturing the non-woven fabric will be described. To manufacture a non-woven fabric, a high-pressure water stream treatment, a needle punching treatment, or the like may be applied to the fiber web to split the conjugate fiber and generate ultrafine fibers. When the conjugate fiber has a cross-section as shown in FIG. 1 or FIG. 2, polyethylene ultrafine fibers and polypropylene ultrafine fibers are generated. Then, by the high-pressure water stream treatment or the needle punching treatment, ultrafine fibers are generated, and the generated ultrafine fibers are entangled with each other to form a non-woven fabric having a predetermined strength. At this time, even if there are different kinds of fibers in the fiber web, the different kinds of fibers and the ultrafine fibers are entangled with each other. Further, as described above, when a high-strength substrate such as a non-woven fabric base material is laminated on the fiber web, the generated ultrafine fibers and the constituent fibers of the non-woven fabric base material are entangled with each other to form a non-woven fabric having higher strength. Such a non-woven fabric is excellent in flexibility because the main constituent fibers are ultrafine fibers.

[0012] After manufacturing the non-woven fabric, this non-woven fabric is laminated on at least one side of the PTFE film. Then, heat is applied to the non-woven fabric by a conventionally known method. This heat is at a temperature at which the polyethylene ultrafine fibers are softened or melted and at which other ultrafine fibers or different kinds of fibers are not softened or melted. When the ultrafine fibers are polyethylene ultrafine fibers and polypropylene ultrafine fibers, generally, heating at a temperature of about 140 to 150°C may be sufficient. Thereby, only the polyethylene ultrafine fibers in the non-woven fabric are softened or melted, and the ultrafine fibers are fixed to each other to form a high-rigidity non-woven fabric support. At the same time, due to the softening or melting of the polyethylene ultrafine fibers, the non-woven fabric support and the PTFE film are adhered to obtain a filter material. Incidentally, when a long fiber non-woven fabric base material having a core-sheath type conjugate long fiber whose core component is polyethylene terephthalate and sheath component is polyethylene as the constituent fibers is used as the non-woven fabric base material, the polyethylene as the sheath component may be softened or melted and adhered to the PTFE film.

[0013] The obtained filter material is processed into a predetermined shape and used as a filter pack or a filter unit. The filter pack or the filter unit is applied to a clean room or a semiconductor manufacturing apparatus and used for air cleaning inside thereof.

Advantages of the Invention

[0014] In the method for manufacturing a filter medium according to the present invention, when laminating on the PTFE membrane, the nonwoven fabric is mainly composed of ultrafine fibers as constituent fibers and the ultrafine fibers are not bonded to each other, so it is flexible. On the other hand, when heat is applied to the nonwoven fabric after laminating it on the PTFE membrane, the polyethylene ultrafine fibers are softened or melted and fixed, and the ultrafine fibers are bonded to each other, so a filter medium having a nonwoven fabric support with high rigidity can be obtained. Therefore, according to the method for manufacturing a filter medium according to the present invention, when laminating on the PTFE membrane, since the nonwoven fabric is flexible, it is less likely to damage the PTFE membrane. Thus, there is an effect that a filter medium with high collection efficiency and high air permeability can be reasonably obtained.

Example

[0015] Example 1 [Preparation of fiber web] Segmented composite short fibers having a solid circular cross-section shown in FIG. 1 and a division number of 16 were prepared. This segmented composite short fiber is formed by joining a high-density polyethylene component and a polypropylene component, and the mass ratio of the high-density polyethylene component to the polypropylene component is high-density polyethylene component: polypropylene component = 40:60. When this segmented composite short fiber is split, high-density polyethylene ultrafine fibers of about 0.10 dtex and polypropylene ultrafine fibers of about 0.15 dtex are generated. The fineness of this segmented composite short fiber is 2.0 dtex, and the fiber length is 51 mm. A cotton mass made of this segmented composite short fiber was passed through a carding machine to create a fiber web with a basis weight of 50 g / m 2 ².

[0016] [Preparation of nonwoven fabric base material] Polyethylene terephthalate with a melting point of 256 °C and high-density polyethylene with a melting point of 134 °C were introduced into a composite melt spinning apparatus, and core-sheath type composite long fibers with polyethylene terephthalate as the core component and high-density polyethylene as the sheath component were melt spun, and accumulated on a conveyor to obtain a long fiber web. This long fiber web was introduced into an embossing apparatus composed of a heated embossed roll and a smooth roll, and only the high-density polyethylene as the sheath component was melted and solidified to obtain a nonwoven fabric base material in which the core-sheath type composite long fibers were partially bonded at positions corresponding to the convex portions of the heated embossed roll. The fiber diameter of the core-sheath type composite long fiber was 3.6 dtex (fiber diameter 20 μm), and the mass ratio of the core component to the sheath component was 1:1. The basis weight of the nonwoven fabric base material was 15 g / m 2 It was.

[0017] [Manufacture of nonwoven fabric] After laminating a fiber web on one side of the nonwoven fabric base material, high-pressure water jets ejected from ejection holes with a pore diameter of 0.12 mm at a pressure of 2.8 MPa were applied twice from the fiber web side, and then high-pressure water jets ejected at a pressure of 8.3 MPa were applied twice each alternately from the fiber web side and the nonwoven fabric base material side. By this high-pressure water jet treatment, the split-type composite short fibers were split and cut, and high-density polyethylene ultra-fine fibers of about 0.10 decitex and polypropylene ultra-fine fibers of about 0.15 decitex were generated. At the same time, the high-density polyethylene ultra-fine fibers, polypropylene ultra-fine fibers, and the core-sheath type composite long fibers in the nonwoven fabric base material were entangled with each other, and the fiber web and the nonwoven fabric base material were compositely integrated. Then, after lightly squeezing with a mangle, it was introduced into a dryer to evaporate the water derived from the high-pressure water jet to obtain a nonwoven fabric.

[0018] Example 2 [Preparation of fiber web] A split-type composite staple fiber with a hollow circular cross-section shown in Fig. 2 and a division number of 16 was prepared. This split-type composite staple fiber is formed by joining a high-density polyethylene component and a polypropylene component, and the mass ratio of the high-density polyethylene component to the polypropylene component is high-density polyethylene component: polypropylene component = 40:60. When this split-type composite staple fiber is split, high-density polyethylene ultrafine fibers of about 0.11 dtex and polypropylene ultrafine fibers of about 0.17 dtex are generated. Also, the fineness of this split-type composite staple fiber is 2.2 dtex, and the fiber length is 51 mm. A tuft made of this split-type composite staple fiber was passed through a carding machine to obtain a fiber web with a basis weight of 50 g / m 2 of the fiber web was created.

[0019] [Manufacture of non-woven fabric] After laminating this fiber web on one side of the non-woven fabric substrate used in Example 1, high-pressure water stream treatment was performed in the same manner as in Example 1 and dried to obtain a non-woven fabric.

[0020] Example 3 [Preparation of fiber web] The hollow split-type composite staple fiber used in Example 2 and the following solid split-type composite staple fiber were prepared. The solid split-type composite staple fiber is formed by joining a polypropylene component and a polyethylene terephthalate component in the manner shown in Fig. 1, and the mass ratio of the polypropylene component to the polyethylene terephthalate component is polypropylene component: polyethylene terephthalate component = 35:65. When this split-type composite staple fiber is split, polypropylene ultrafine fibers of about 0.12 dtex and polyethylene terephthalate ultrafine fibers of about 0.22 dtex are generated. Also, the fineness of this split-type composite staple fiber is 2.75 dtex, and the fiber length is 51 mm. A mixed tuft obtained by mixing the above hollow split-type composite staple fiber and solid split-type composite staple fiber in a mass ratio of 1:1 was passed through a carding machine to obtain a fiber web with a basis weight of 50 g / m 2 of the fiber web was created.

[0021] [Manufacture of non-woven fabric] After laminating this fiber web on one side of the nonwoven fabric base material used in Example 1, high-pressure water flow treatment was performed in the same manner as in Example 1, followed by drying to obtain a nonwoven fabric.

[0022] Example 4 [Manufacture of Nonwoven Fabric] As the nonwoven fabric base material, a polypropylene long fiber nonwoven fabric with a fineness of 2.9 dtex (fiber diameter 20 μm) was integrated, and the polypropylene long fibers were partially thermally crimped to each other, with a basis weight of 9 g / m 2 was prepared. After laminating the fiber web used in Example 2 on one side of this nonwoven fabric base material, high-pressure water flow treatment was performed in the same manner as in Example 1, followed by drying to obtain a nonwoven fabric.

[0023] Comparative Example 1 [Manufacture of Nonwoven Fabric] Polyethylene terephthalate with a melting point of 256 °C and high-density polyethylene with a melting point of 134 °C were introduced into a composite melt spinning apparatus, and a core-sheath type composite long fiber with polyethylene terephthalate as the core component and high-density polyethylene as the sheath component was melt spun, and accumulated on a conveyor to obtain a long fiber web. This long fiber web was introduced into an embossing apparatus composed of a heated embossed roll and a smooth roll, and only the high-density polyethylene as the sheath component was melted and solidified, so that a nonwoven fabric was obtained in which the core-sheath type composite long fibers were partially joined at the locations corresponding to the convex portions of the heated embossed roll. The fiber diameter of the core-sheath type composite long fiber was 3.3 dtex (fiber diameter 20 μm), and the mass ratio of the core component to the sheath component was 1:1. Also, the basis weight of the nonwoven fabric was 40 g / m 2 was.

[0024] Comparative Example 2 [Manufacture of Nonwoven Fabric] A cotton mass composed only of the solid split type composite short fibers used in Example 3 was passed through a carding machine to create a fiber web with a basis weight of 50 g / m 2 After laminating this fiber web on one side of the nonwoven fabric base material used in Example 1, high-pressure water flow treatment was performed in the same manner as in Example 1, followed by drying to obtain a nonwoven fabric.

[0025] Since many of the constituent fibers of the nonwoven fabrics obtained by the methods according to Examples 1 to 4 and Comparative Example 2 were ultrafine fibers, they were flexible and did not damage the PTFE film even when laminated with the film. On the other hand, the nonwoven fabric according to Comparative Example 1 was highly rigid because the constituent fibers were made of high-denier long fibers.

[0026] 〈Flexibility and air permeability of nonwoven fabric support〉 The nonwoven fabrics obtained by the methods according to Examples 1 to 4 and Comparative Example 2 were heated at the temperature (145 °C) at which only the polyethylene ultrafine fibers melt for 5 minutes to obtain nonwoven fabric supports. The flexibility (mN) of the nonwoven fabric supports was measured according to 6.7.4 (Gurley method) of JIS L1913:2010 "General Test Methods for Nonwoven Fabrics". Also, the air permeability (cc / cm 2 / s) of the nonwoven fabric supports was measured according to Method A (Frazer type method) of 8.26.1 of JIS L1096:2010 "Test Methods for Fabrics of Woven and Knitted Fabrics". The results are as shown in Table 1. [Table 1] ━━━━━━━━━━━━━━━━━━━━━ Flexibility Air permeability ━━━━━━━━━━━━━━━━━━━━━ Example 1 3.5 72 Example 2 3.1 67 Example 3 2.5 48 Example 4 3.0 64 Comparative Example 2 1.3 34 ━━━━━━━━━━━━━━━━━━━━━

[0027] As is clear from the results in Table 1, when the nonwoven fabrics obtained by the methods according to Examples 1 to 4 are heated, their flexibility increases, making them suitable as nonwoven fabric supports for PTFE films. Also, due to the melting of the polyethylene ultrafine fibers, the air permeability also improves slightly, making them suitable as pre-filter materials. Note that the nonwoven fabric obtained by the method according to Comparative Example 2 had the same flexibility and air permeability as the original nonwoven fabric because there were no polyethylene ultrafine fibers that melted when heated.

[0028] 〈Dust collection efficiency of nonwoven fabric support〉 The collection efficiency (%) of dust with particle sizes of 0.3 to 0.4 μm, 1.0 to 1.3 μm, 1.6 to 2.2 μm, and 3.0 to 4.0 μm was measured under the conditions of a test area: 100 cm 2 , a test flow rate: 32 L / min, a test wind speed: 5.3 cm / s, a test temperature: 24 °C, and a particle size and particle type: JIS 11 types. The results are shown in Table 2. [Table 2] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Collection Efficiency (%) ───────────────────────────────── 0.3 - 0.4 1.0 - 1.3 1.6 - 2.2 3.0 - 4.0 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example 1 40.1% 42.6% 45.6% 54.7% Example 2 31.0% 31.1% 36.4% 51.1% Example 3 25.1% 31.5% 40.0% 62.6% Example 4 40.4% 43.8% 47.6% 60.9% Comparative Example 2 48.8% 52.5% 59.2% 76.8% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

[0029] As is clear from the results in Table 2, the nonwoven support obtained by heating the nonwoven fabric obtained by the methods according to Examples 1 to 4 has a relatively high collection efficiency for dust with a large particle size and is suitable as a pre-filter material.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Claims

1. A step of preparing a fibrous web containing a split-type composite fiber in which a polyethylene component and a high melting point polymer component having a melting point higher than that of the polyethylene component are joined together, a step of splitting the split-type composite fiber contained in the fibrous web to produce polyethylene ultrafine fibers and high melting point polymer ultrafine fibers to manufacture a non-woven fabric, and a method for manufacturing a filter material, characterized in that after laminating the non-woven fabric on at least one side of a porous membrane made of polytetrafluoroethylene, heat is applied to the non-woven fabric to soften or melt the polyethylene ultrafine fibers, and the polyethylene ultrafine fibers and the high melting point polymer ultrafine fibers are bonded to obtain a non-woven fabric support, and the non-woven fabric support is adhered to the porous membrane.

2. The method for manufacturing a filter material according to claim 1, wherein the split-type composite fiber is formed by joining a polyethylene component and a polypropylene component.

3. The method for manufacturing a filter material according to claim 1, wherein the split-type composite fiber is split by high-pressure water jet treatment.

4. The method for manufacturing a filter material according to claim 1, wherein a base material is laminated on the fibrous web.

5. The method for manufacturing a filter material according to claim 4, wherein the base material is a non-woven fabric base material.

6. The method for manufacturing a filter material according to claim 5, wherein the non-woven fabric base material uses core-sheath type composite long fibers as constituent fibers, the core component is polyethylene terephthalate, and the sheath component is polyethylene.

7. A method for manufacturing a non-woven fabric used in the method for manufacturing a filter material according to claim 1, wherein a fibrous web containing a split-type composite fiber in which a polyethylene component and a high melting point polymer component having a melting point higher than that of the polyethylene component are joined together and a base material are laminated to obtain a laminate, and then the laminate is subjected to high-pressure water jet treatment to split the split-type composite fiber to generate polyethylene ultrafine fibers and high melting point polymer ultrafine fibers, and the two ultrafine fibers are entangled with each other.

8. The method for manufacturing a non-woven fabric according to claim 7, wherein the base material is a non-woven fabric base material, and the non-woven fabric base material uses core-sheath type composite long fibers in which the core component is polyethylene terephthalate and the sheath component is polyethylene as constituent fibers.

9. The method for manufacturing a non-woven fabric according to claim 8, wherein the core-sheath type composite long fibers as constituent fibers are partially bonded by being fixed by softening or melting of the sheath component.

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