Air filter

Abstract

To provide an air filter which is hardly deformed by wind and has excellent strength. [Solution] The air filter of the present invention comprises a nonwoven fabric having a sheath-core composite fiber composed of a core component which is an organic resin and a sheath component which is an organic resin having a melting point lower than that of the core component, and another organic resin different from the core component, wherein the constituent fibers of the nonwoven fabric are mainly the sheath-core composite fiber, and the fibers constituting the nonwoven fabric are bonded together by the sheath component and the other organic resin. The mass of the sheath-core composite fiber is 50 mass% or more (in which case the mass of the other organic resin is 50 mass% or less) of the sum of the masses of the sheath-core composite fiber and the other organic resin in the nonwoven fabric, and the mass of the other organic resin is 5 mass% or more (in which case the mass of the sheath-core composite fiber is 95 mass% or less), thereby more firmly bonding the constituent fibers together.

Description

[Technical Field]

[0001] The present invention relates to an air filter. [Background technology]

[0002] Conventionally, air filters with nonwoven fabrics have been used to remove and purify dust in the air. For example, Patent Document 1 (JP 2017-159249 A) ​​discloses an air filter having a support containing drawn polyester fibers, undrawn polyester fibers, and core-sheath polyester composite fibers with a sheath portion made of a copolymer polyester having a glass transition point of 40 to 80°C, and an electrically charged nonwoven fabric layer. In this air filter, the fibers constituting the support are bonded to each other by the sheath portion and the undrawn polyester fibers, resulting in a strong filter medium that can be easily pleated.

[0003] Incidentally, Example 8 of Patent Document 1 discloses the production of an air filter having, as a support, a nonwoven fabric made by papermaking 15% by mass of unstretched polyester fiber, 40% by mass of stretched polyester fiber, and 45% by mass of core-sheath type polyester composite fiber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-159249 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the strength of the air filters having the nonwoven fabric as a support body disclosed in the prior art, such as that described in Patent Document 1, was insufficient, and therefore, when air was passed through the prepared air filter, the air filter was sometimes deformed by the wind.

[0006] The present invention has been made under these circumstances, and an object of the present invention is to provide an air filter having excellent strength. [Means for solving the problem]

[0007] The invention of claim 1 of the present invention is "an air filter comprising a nonwoven fabric having a sheath-core composite fiber composed of a core component which is an organic resin and a sheath component which is an organic resin having a melting point lower than that of the core component, and another organic resin different from the core component, wherein the constituent fibers of the nonwoven fabric are mainly the sheath-core composite fiber, and the fibers constituting the nonwoven fabric are bonded to each other by the sheath component and the other organic resin, and the mass percentage of the sheath-core composite fiber to the sum of the masses of the sheath-core composite fiber and the other organic resin in the nonwoven fabric is 50 mass% or more and 95 mass% or less, and the mass percentage of the other organic resin is 5 mass% or more and 50 mass% or less."

[0008] The invention according to claim 2 of the present invention is "the air filter according to claim 1, wherein the nonwoven fabric is composed only of the core-sheath type composite fiber and the other organic resin."

[0009] The invention according to claim 3 of the present invention is "an air filter comprising a tribo-electrically charged nonwoven fabric layer having two or more different types of constituent fibers mixed between layers of the nonwoven fabric according to claim 1."

[0010] The invention according to claim 4 of the present invention is "the air filter according to claim 3, characterized in that the nonwoven fabric is composed only of the core-sheath composite fiber, the other organic resin, and the constituent fibers of the tribo-electrically charged nonwoven fabric layer, and the constituent fibers of the tribo-electrically charged nonwoven fabric layer adjacent to the nonwoven fabric are embedded in the nonwoven fabric." [Effects of the Invention]

[0011] The air filter according to claim 1 of the present invention comprises a nonwoven fabric having a core-sheath composite fiber composed of a core component which is an organic resin and a sheath component which is an organic resin having a melting point lower than that of the core component, and another organic resin different from the core component, wherein the constituent fibers of the nonwoven fabric are mainly composed of the core-sheath composite fiber, and the fibers constituting the nonwoven fabric are bonded together by the sheath component and the other organic resin. Furthermore, by having the mass of the core-sheath composite fiber account for 50 mass% or more of the sum of the masses of the core-sheath composite fiber and the other organic resin contained in the nonwoven fabric (in this case, the mass of the other organic resin is 50 mass% or less), the parts where the fibers are close to each other, such as the fiber intersections of the nonwoven fabric, are sufficiently bonded by the sheath component of the core-sheath composite fiber, and the constituent fibers are firmly bonded to each other. Furthermore, by having the mass of the other organic resin account for 5 mass% or more of the sum of the masses of the core-sheath composite fiber and the other organic resin contained in the nonwoven fabric (in this case, the mass of the core-sheath composite fiber is 95 mass% or less), the constituent fibers are bonded more firmly to each other by the other organic resin in addition to the bond formed by the sheath component of the core-sheath composite fiber. As described above, the present invention can provide an air filter having excellent strength.

[0012] The air filter according to claim 2 of the present invention has a configuration in which the nonwoven fabric provided in the air filter is made of only the core-sheath type composite fiber and the other organic resin. As a result, the core-sheath type composite fiber and the other organic resin bond the constituent fibers together effectively, making it possible to provide an air filter with superior strength.

[0013] The air filter of claim 3 of the present invention comprises a tribo-electrically charged nonwoven fabric layer having two or more different types of constituent fibers mixed between the above-mentioned nonwoven fabrics which have excellent strength. With this configuration, it is possible to provide an air filter which has excellent strength due to the presence of the above-mentioned nonwoven fabric, and which also has excellent filtering efficiency due to the tribo-electrically charged nonwoven fabric layer.

[0014] An air filter according to claim 4 of the present invention is an air filter that includes a tribo-electrically charged nonwoven fabric layer, and the nonwoven fabric that the air filter includes is constituted only by the core-sheath composite fiber, the other organic resin, and the constituent fibers of the tribo-electrically charged nonwoven fabric layer. By being composed only of the sheath-core composite fibers, the other organic resin, and the constituent fibers of the tribo-electrically charged nonwoven fabric layer, the constituent fibers are effectively bonded together by the sheath-core composite fibers and the other organic resin. Furthermore, the constituent fibers of the tribo-electrically charged nonwoven fabric layer adjacent to the nonwoven fabric penetrate into the nonwoven fabric. For this reason, the constituent fibers of the tribo-electrically charged nonwoven fabric layer that have penetrated into the nonwoven fabric from the tribo-electrically charged nonwoven fabric layer firmly bond the nonwoven fabric and the tribo-electrically charged nonwoven fabric layer, making it possible to provide an air filter with excellent strength. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an electron microscope photograph (magnification: 100x) of a part of the main surface (the surface with the largest area of ​​the air filter) of the air filter prepared in Example 1 of the present invention. [Figure 2] The symbols shown in the (Explanation of Symbols) column have been added to those in FIG. [Figure 3] 1 is an optical microscope photograph (magnification: 100x) of a part of the main surface (the surface with the largest area of ​​the air filter) of the air filter prepared in Example 5 of the present invention. [Figure 4] The symbols shown in the (Explanation of Symbols) column have been added to those in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The air filter of the present invention comprises a nonwoven fabric containing core-sheath type composite fibers made of a core component which is an organic resin and a sheath component which is an organic resin having a melting point lower than that of the core component.

[0017] The constituent fibers of the nonwoven fabric provided in the air filter of the present invention are mainly composed of the sheath-core composite fibers. This allows for strong bonding at portions of the nonwoven fabric where fibers are close to each other, such as fiber intersections. In the present invention, the phrase "the constituent fibers of the nonwoven fabric are mainly composed of the sheath-core composite fibers" means that the mass percentage of the sheath-core composite fibers in the mass of the constituent fibers of the nonwoven fabric is 50 mass% or more. The higher the mass percentage of the sheath-core composite fibers in the fiber mass of the constituent fibers of the nonwoven fabric provided in the air filter of the present invention, the stronger the bonding between the constituent fibers of the nonwoven fabric. Therefore, this percentage is preferably 80 mass% or more, more preferably 85 mass% or more, and even more preferably 100 mass% (i.e., all of the fibers constituting the nonwoven fabric provided in the air filter are sheath-core composite fibers). The sheath-core composite fiber constituting the air filter of the present invention may contain only one type of sheath-core composite fiber having the same constituent resin, fineness, and fiber length, or may contain two or more types of sheath-core composite fibers that differ from each other in at least one of the constituent resin, fineness, and fiber length.

[0018] As described above, the core-sheath type composite fiber contained in the nonwoven fabric provided in the air filter of the present invention is composed of two types of organic resins, a core component and a sheath component. The constituent resins of the core component and the sheath component include, for example, polyester-based resins (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polycarbonate, polyarylate, wholly aromatic polyester resins, unsaturated polyester resins, etc.), polyolefin-based resins (polyethylene, polypropylene, polymethylpentene, polyolefin-based resins in which a portion of hydrocarbons is substituted with a cyano group or a halogen such as fluorine or chlorine, etc.), styrene-based resins, polyether-based resins (polyether ether ketone, polyacetal, phenol-based resins, melamine-based resins, urea-based resins, epoxy-based resins, modified polyolefins, etc.), and the like. The resin may be made of a known organic resin, such as polyphenylene ether, aromatic polyether ketone, etc.), polyimide resin, polyamideimide resin, polyamide resin (for example, aromatic polyamide resin, aromatic polyetheramide resin, nylon resin, etc.), resin having a nitrile group (for example, polyacrylonitrile, etc.), urethane resin, epoxy resin, polysulfone resin (polysulfone, polyethersulfone, etc.), fluorine resin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose resin, polybenzimidazole resin, acrylic resin (for example, polyacrylonitrile resin copolymerized with acrylic acid ester or methacrylic acid ester, etc.), vinylon fiber, etc.

[0019] It is preferable that both the core component and the sheath component of the core-sheath composite fiber are polyester-based resins, as this provides excellent flame retardancy and also prevents harmful gases from being emitted when the air filter is incinerated, resulting in excellent environmental performance of the filter.

[0020] The sheath-core composite fibers contained in the nonwoven fabric of the air filter of the present invention may be concentric sheath-core composite fibers in which the core component is located at the center of the fiber when the cross section of the fiber is observed, or eccentric sheath-core composite fibers in which the core component is located elsewhere than at the center of the fiber. However, concentric sheath-core composite fibers tend to have superior fiber strength to eccentric sheath-core composite fibers, and are therefore preferred. The cross-sectional shape of the sheath-core composite fibers may be circular or non-circular, such as elliptical.

[0021] The volume ratio of the core component to the sheath component in the fiber cross section of the sheath-core composite fiber is not particularly limited, but so that there is a large amount of fusion component that can participate in fusion, which can contribute to the shape stability of the nonwoven fabric that constitutes the air filter, and so that the strength of the sheath-core composite fiber itself can be maintained, the ratio is preferably (core component):(sheath component)=15:85 to 85:15, more preferably (core component):(sheath component)=20:80 to 70:30, even more preferably (core component):(sheath component)=23:77 to 60:40, and even more preferably (core component):(sheath component)=25:75 to 55:45.

[0022] The difference between the melting point of the core component of the sheath-core composite fiber contained in the nonwoven fabric provided in the air filter of the present invention and the melting point of the sheath component of the sheath-core composite fiber {(melting point of the core component of the sheath-core composite fiber) - (melting point of the sheath component of the sheath-core composite fiber)} is preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher, so that the core component does not melt or soften at the temperature at which the sheath component melts and the fiber shape of the sheath-core composite fiber is maintained. Note that the "melting point" in the present invention refers to the value obtained by Method A specified in JIS L 1015:2010 "Test methods for synthetic fiber staples," 8.16.1 (melting point).

[0023] The fineness of the core-sheath composite fiber contained in the nonwoven fabric provided in the air filter of the present invention is not particularly limited, but is preferably 1 to 70 dtex, more preferably 3 to 40 dtex, and even more preferably 6 to 20 dtex. Note that the "fineness" in the present invention refers to the value obtained by Method A specified in JIS L 1015:2010 "Testing methods for synthetic fiber staples," 8.5.1 (corrected fineness).

[0024] The fiber length of the core-sheath composite fibers contained in the nonwoven fabric provided in the air filter of the present invention is not particularly limited, but is preferably 10 to 130 mm, more preferably 20 to 110 mm, and even more preferably 35 to 80 mm. Note that the "fiber length" in the present invention refers to the average fiber length measured by Method C specified in JIS L 1015:2010 "Testing methods for synthetic fiber staples," 8.4.1 (direct method).

[0025] The air filter according to the present invention includes a nonwoven fabric having a core-sheath composite fiber and another organic resin. The constituent fibers of the nonwoven fabric are bonded together by both the sheath component of the core-sheath composite fiber and the other organic resin. This results in stronger bonds between the constituent fibers than in a nonwoven fabric in which the constituent fibers are bonded together only by the sheath component.

[0026] The percentage by mass of the other organic resin relative to the sum of the masses of the sheath-core composite fibers and the other organic resin in the nonwoven fabric provided in the air filter of the present invention is 5 mass% or more, more preferably 10 mass% or more, and even more preferably 20 mass% or more, so that the constituent fibers can be firmly bonded to each other. On the other hand, if the mass percentage of the other organic resin is too high, the percentage by mass of the sheath-core composite fibers relative to the mass of the nonwoven fabric will be small. In other words, the content of the sheath-core composite fibers, which form the skeleton of the nonwoven fabric, will be low, which may reduce the strength of the nonwoven fabric. Therefore, this percentage is 50 mass% or less, preferably 40 mass% or less, and even more preferably 30 mass% or less.

[0027] The shape of the other organic resin contained in the nonwoven fabric of the air filter of the present invention will be explained using Figures 1 and 2, which are electron microscope photographs of a portion of the air filter prepared in Example 1, and Figures 3 and 4, which are optical microscope photographs of a portion of the air filter prepared in Example 5. The shape of the other organic resin is not particularly limited, but may be, for example, a fiber portion shape (A1 and A2) in which the other organic resin surrounds the constituent fibers (1) of the nonwoven fabric (100), as shown in the portions (A1 and A2) in the electron microscope photograph of Figure 2, which appear to have a larger fiber diameter than the other constituent fibers, and in which the other organic resin is present covering the constituent fibers (1) of the nonwoven fabric (100), and the other organic resin has a plurality of bonded portions (A1) at portions where the fibers are close to each other, such as fiber intersections of the nonwoven fabric, and the bonded portions (A1) are connected between each other by another organic resin (A2). Alternatively, the organic resin may be in the form of particles that bond fibers together at the intersections of the constituent fibers of the nonwoven fabric with shapes similar to spheres (B in Figure 4), or in the form of webs that form membranes between the constituent fibers of the nonwoven fabric, or may be a mixture of these shapes. The shape of the other organic resin can be confirmed using, for example, an optical microscope or an electron microscope. Among these, nonwoven fabrics having the above-mentioned fiber part shapes are preferred because they efficiently reinforce the bonds between fibers in areas where the fibers are close to each other, such as the fiber intersections of the nonwoven fabric, thereby enabling the realization of nonwoven fabrics and air filters with excellent strength.

[0028] Regarding the positional relationship between the sheath-core composite fiber and the other organic resin contained in the nonwoven fabric of the air filter of the present invention, if the other organic resin is present surrounding the sheath-core composite fiber as in the fiber portion shapes (A1 and A2) described above in Figure 2, the size of the bonding points between the fibers is larger due to the other organic resin surrounding the sheath-core composite fiber, and the bonding points between the fibers are less likely to come loose, making it possible to realize an air filter with excellent strength, which is preferable.

[0029] The other organic resin contained in the nonwoven fabric of the air filter of the present invention is preferably derived from a single fiber, which is obtained by melting a single fiber during the manufacturing process of the air filter (nonwoven fabric). In nonwoven fabrics manufactured in this manner, the other organic resin tends to be distributed throughout the thickness of the nonwoven fabric. This is preferable because the constituent fibers of the nonwoven fabric of the air filter can be uniformly bonded together, resulting in excellent air filter strength. When the other organic resin is derived from a single fiber, the larger the single fiber fineness, the more widely the constituent fibers of the nonwoven fabric constituting the air filter can be bonded together. Therefore, the single fiber fineness is preferably 1 dtex or more, more preferably 5 dtex or more, even more preferably 10 dtex or more, and even more preferably 20 dtex or more. On the other hand, if the single fiber fineness is too large, the other organic resin may aggregate too many fibers when bonding the constituent fibers of the nonwoven fabric, resulting in localized organic resin derived from the single fiber in the nonwoven fabric and potentially failing to impart an overall effect of increasing rigidity. Therefore, a fineness of 50 dtex or less is preferable. Furthermore, the fiber length of the monofilaments is not particularly limited, but having a certain fiber length makes it possible to bind together the constituent fibers of the nonwoven fabric that constitutes a wider range of air filters. On the other hand, if the fiber length of the monofilaments is too long, when another organic resin binds the constituent fibers of the nonwoven fabric, too many fibers may be bound together, causing the organic resin derived from the monofilaments to be localized in the nonwoven fabric, and preventing the effect of increasing rigidity as a whole from being imparted. Therefore, the fiber length is preferably 10 to 130 mm, more preferably 20 to 110 mm, and even more preferably 35 to 80 mm.

[0030] In addition, the term "single fiber" in the present invention refers to a fiber made of a single resin.

[0031] The other organic resin contained in the nonwoven fabric of the air filter of the present invention can be the same organic resin as the constituent resin of the core-sheath composite fiber. If the other organic resin is a polyester-based resin, it is preferable because it has excellent flame retardancy and does not emit harmful gases when the air filter is incinerated, thereby improving the environmental performance of the filter. Furthermore, the other organic resin may be the same resin as the sheath component of the core-sheath composite fiber, or a different resin. If the other organic resin is the same resin as the sheath component of the core-sheath composite fiber, it is preferable because it has a high affinity with the sheath component and can firmly bond the core-sheath composite fiber.

[0032] The melting point of the other organic resin is preferably 70 to 220°C, more preferably 80 to 170°C, and even more preferably 90 to 130°C, so that the air filter has excellent heat resistance, and because if the melting point of the other organic resin is too high, it will need to be melted at a high temperature during the air filter manufacturing process, which will require a lot of energy to manufacture the air filter.

[0033] The difference between the melting point of the sheath component of the core-sheath composite fiber and the melting point of the other organic resin contained in the nonwoven fabric provided in the air filter of the present invention {(melting point of the sheath component of the core-sheath composite fiber) - (melting point of the other organic resin)} is preferably 30°C or less, more preferably 10°C or less, even more preferably 5°C or less, and most preferably 0°C (the melting point of the sheath component of the core-sheath composite fiber and the melting point of the other organic resin are the same), because a smaller difference tends to result in a nonwoven fabric and air filter with excellent strength, and a nonwoven fabric and air filter having the above-mentioned fiber portion shape.

[0034] The mass percentage of the core-sheath type composite fibers in the nonwoven fabric of the air filter of the present invention, relative to the sum of the masses of the core-sheath type composite fibers and the other organic resin, is 50 mass% or more, so that the parts of the nonwoven fabric where the fibers are in close proximity, such as the fiber intersections, are sufficiently bonded by the sheath component of the core-sheath type composite fibers, and the constituent fibers are strongly bonded to each other. The higher the mass percentage of the core-sheath type composite fibers, the stronger the bonds between the constituent fibers of the nonwoven fabric become. Therefore, a mass percentage of 60 mass% or more is more preferable, and 70 mass% or more is even more preferable. The upper limit of the mass percentage of the core-sheath type composite fibers is 95 mass% or less, so that the nonwoven fabric constituting the air filter is efficiently reinforced by the bonding by the other organic resin in addition to the bonding by the sheath component of the core-sheath type composite fibers, and the constituent fibers of the nonwoven fabric are more strongly bonded to each other. Furthermore, in order to firmly bond the constituent fibers of the nonwoven fabric, the upper limit of the mass percentage of the core-sheath type composite fibers is more preferably 93 mass % or less, and even more preferably 90 mass % or less.

[0035] The nonwoven fabric of the air filter of the present invention may contain fibers other than core-sheath type composite fibers, such as single fibers composed of a resin different from the aforementioned organic resin, fibers containing functional particles as described later, and constituent fibers of the triboelectric nonwoven fabric layer as described later. Furthermore, the fibers other than core-sheath type composite fibers may be fibers with irregular cross-sections, such as polygonal shapes like elliptical, hollow, or triangular shapes, alphabetic shapes like Y-shapes, irregular shapes, multi-lobed shapes, symbolic shapes like asterisk shapes, or shapes formed by combining multiple such shapes, or they may be hollow fibers with a hollow interior.

[0036] The fineness of the fibers other than the core-sheath type composite fibers is not particularly limited, but is preferably 5 to 70 dtex, more preferably 10 to 40 dtex, and even more preferably 15 to 20 dtex. The fiber length of the fibers other than the core-sheath type composite fibers is not particularly limited, but is preferably 10 to 130 mm, more preferably 20 to 110 mm, and even more preferably 35 to 80 mm.

[0037] If the nonwoven fabric provided in the air filter of the present invention is composed only of sheath / core composite fibers and another organic resin, this is preferable because the bonding between the constituent fibers by the sheath / core composite fibers and the other organic resin is effectively exerted, making it possible to provide an air filter with even greater strength.If the air filter of the present invention is provided with a tribo-electrically charged nonwoven fabric layer, which will be described later, it is preferable that the fibers that make up the nonwoven fabric provided in the air filter of the present invention are composed only of sheath / core composite fibers and the fibers that make up the tribo-electrically charged nonwoven fabric layer.

[0038] The nonwoven fabric provided in the air filter of the present invention is preferably made entirely of fibers made of organic resin, since organic resin is easy to handle and dispose of.

[0039] The basis weight of the nonwoven fabric of the present invention is 10 to 1000 g / m so that the nonwoven fabric constituting the air filter has an excellent dust collection capacity and is easy to handle. 2 is preferable, and 30 to 500 g / m 2 More preferably, 45 to 200 g / m 2 In the present invention, the "weight per unit area" refers to the area per square meter of the largest surface (main surface) of the nonwoven fabric or air filter. 2 This refers to the mass per unit mass.

[0040] The thickness of the nonwoven fabric of the present invention is preferably 0.1 to 50 mm, more preferably 0.5 to 25 mm, and even more preferably 1 to 5 mm, so that the nonwoven fabric constituting the air filter has a high dust collection capacity and is easy to handle. The "thickness" in the present invention refers to the length between two main surfaces of the air filter when a load of 98 Pa is applied from one main surface to the other main surface, as measured using a high-precision digital length measuring device.

[0041] The air filter of the present invention may be composed of just one layer of nonwoven fabric, or may be composed of two or more layers of multiple nonwoven fabrics of the same or different types. An example of an air filter composed of multiple nonwoven fabrics is an air filter that has two or more layers of nonwoven fabric that satisfy the configuration of the present invention, and that is provided with a tribo-electrically charged nonwoven fabric layer between the two layers, with two or more different types of fiber constituents mixed. The two or more types of fiber constituents will become tribo-electrically charged if the constituent resins are different, but it is preferable that there is a mixture of fibers made of fiber constituents that are easily charged by friction, so as to ensure a sufficient amount of charge. Examples of combinations of fiber constituents that are easily charged by friction include acrylic fiber and polyolefin fiber, and fluorine fiber and polyamide fiber. Furthermore, when the air filter of the present invention is provided with a tribo-electrically charged nonwoven fabric layer, it is preferable that the fiber constituents of the nonwoven fabric be embedded in the tribo-electrically charged nonwoven fabric layer and / or the fiber constituents of the tribo-electrically charged nonwoven fabric layer be embedded in the nonwoven fabric by needle punching or the like, in order to improve the strength of the air filter and to make the air filter less susceptible to delamination.

[0042] The air filter of the present invention may also include other materials than nonwoven fabric, such as porous materials other than nonwoven fabric.

[0043] The air filter of the present invention may contain functional particles. Examples of functional particles include activated carbon, radioactive material adsorbents (e.g., zeolite, Prussian blue, etc.), antifungal agents, catalysts (e.g., titanium oxide, manganese dioxide, platinum-supported alumina, etc.), humidity conditioners (e.g., silica gel, etc.), deodorizers (e.g., activated carbon, carbon black, etc.), flame retardants (e.g., phosphate-based agents, aluminum hydroxide), deodorants, insect repellents, disinfectants, fragrances, cation exchange resins, anion exchange resins, dyes, pigments, etc. The functional particles may be present, for example, supported inside the fibers constituting the air filter, on the surface of the fibers constituting the air filter, on the surface of the nonwoven fabric constituting the air filter, or in the internal voids of the nonwoven fabric.

[0044] The basis weight of the air filter of the present invention is 15 to 1000 g / m so that the dust collection capacity of the air filter is excellent and the handling is excellent. 2 is preferable, and 35 to 600 g / m 2 More preferably, 50 to 250 g / m 2 is more preferred.

[0045] The thickness of the air filter of the present invention is preferably 0.1 to 50 mm, more preferably 0.5 to 30 mm, and even more preferably 1 to 6 mm, so as to provide an excellent dust collection capacity and ease of handling.

[0046] The air filter of the present invention may be in the form of a flat plate without any particular processing, or may be pleated. When the air filter is pleated, the pleat height is preferably 1 to 50 mm, more preferably 3 to 45 mm, and even more preferably 5 to 30 mm. When the air filter is pleated, the pleat spacing is preferably 2 to 20 mm, more preferably 3 to 15 mm, and even more preferably 3 to 10 mm.

[0047] Furthermore, the air filter of the present invention may be subjected to processing other than pleating. Examples of processed air filters include a net composite filter in which a net is added to the air filter for the purpose of reinforcement, and a roll filter for a roll filter device in which the air filter is processed so as to be rolled up and then unwound for use.

[0048] Next, an example of a method for manufacturing the air filter of the present invention will be described.

[0049] First, a fiber web is prepared in which core-sheath type composite fibers, each having a core component made of an organic resin and a sheath component made of an organic resin having a melting point lower than that of the core component, are blended with single fibers made of another organic resin different from that of the core component. In this case, the sheath component and the other organic resin may be the same resin or different resins, but as mentioned above, they are preferably the same resin.

[0050] In this case, the difference between the melting point of the sheath component of the core-sheath composite fiber and the melting point of the other organic resin that constitutes the single fiber {(melting point of the sheath component of the core-sheath composite fiber) - (melting point of the other organic resin that constitutes the single fiber)} is preferably 30°C or less, more preferably 10°C or less, even more preferably 5°C or less, and most preferably 0°C (the melting point of the sheath component of the core-sheath composite fiber is the same as the melting point of the other organic resin that constitutes the single fiber) because a small difference tends to result in a nonwoven fabric and air filter with excellent strength, and a nonwoven fabric and air filter having the above-mentioned fiber portion shape.

[0051] The fiber web can be produced, for example, by a dry method in which the above-mentioned fibers are fed into a carding device or an air-laying device to entangle the fibers, or by a wet method in which the above-mentioned fibers are dispersed in a solvent and formed into a sheet, and the fibers are entangled. However, since a certain degree of bulk is preferred to ensure excellent dust collection capacity, it is preferable to employ a dry method in which the fibers are entangled by feeding them into a carding device or an air-laying device.

[0052] The fiber web formed as described above may be entangled with a water jet or needles for ease of handling. When the fiber web is entangled with needles, the suitable needle entanglement conditions are not particularly limited, but a needle density of 30 to 1000 needles / cm is preferred. 2 It is preferable for them to intertwine at a rate of 50-600 strands / cm 2 When entangling the fiber webs, it is possible to entangle only a single layer of the fiber web, or, for example, it is possible to prepare two of the fiber webs and, between them, prepare another fiber web that is a precursor to the tribo-electrically charged nonwoven fabric layer and that contains a mixture of two or more different types of constituent fibers, and then overlay the two fiber webs so that the other fiber web is sandwiched between them, and then entangle them using a water jet or needles.

[0053] Next, the fiber web is heated at a temperature equal to or higher than the temperature at which the other organic resin constituting the sheath component and the single filaments can be melted, but lower than the temperature of the core component, to melt the other organic resin constituting the sheath component and the single filaments of the core-sheath composite fiber.The fiber web is then cooled to produce a nonwoven fabric.

[0054] The heating time of the fiber web is not particularly limited, but is preferably 1 to 30 minutes, more preferably 3 to 20 minutes, and even more preferably 5 to 10 minutes, so that the other organic resin contained in the single fibers constituting the fiber web can be melted evenly and so that the fiber web is less likely to lose its shape.

[0055] Methods for heating the fiber web include, for example, a method of heating and pressurizing with a calendar roll, a method of heating with a hot air dryer, and a method of irradiating with infrared rays under no pressure. Among these methods, a method of heating with a hot air dryer is preferred because the fiber web is heated to its interior by applying hot air from the dryer to the fiber web, and the sheath component and the other organic resin located inside the fiber web can also be sufficiently melted. This is preferable because it allows for the realization of an air filter with excellent strength.

[0056] Examples of methods for cooling the fiber web include a method of cooling by leaving it in a so-called normal temperature environment of 40°C or less, and a method of cooling by blowing air at 40°C or less onto the fiber web.

[0057] The nonwoven fabric described above may be used as an air filter as it is, or may be used as an air filter in combination with other members such as a net. [Example]

[0058] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0059] (Preparing the fiber) The following fibers were prepared: Polyester-based core-sheath composite fiber A: (Core component: polyester resin (melting point: 250°C), sheath component: polyester copolymer resin (melting point: 110°C), core / sheath volume ratio = 50:50, cross-sectional shape: circular, core component located at the center of fiber cross section, fineness: 15 dtex, fiber length: 51 mm) Polyester-based core-sheath composite fiber B: (Core component: polyester resin (melting point: 250°C), sheath component: polyester copolymer resin (melting point: 110°C), core / sheath volume ratio = 50:50, cross-sectional shape: circular, core component located at the center of fiber cross section, fineness: 6 dtex, fiber length: 51 mm) Polyester-based core-sheath composite fiber C: (Core component: polyester resin (melting point: 250°C), sheath component: polyester copolymer resin (melting point: 210°C), core / sheath volume ratio = 50:50, cross-sectional shape: circular, core component located at the center of fiber cross section, fineness: 17 dtex, fiber length: 76 mm) Polyester copolymer monofilament: (melting point: 110°C, fineness: 22 dtex, fiber length: 38 mm)

[0060] Example 1 72 mass% of polyester-based sheath-core composite fiber A, 18 mass% of polyester-based sheath-core composite fiber B, and 10 mass% of polyester copolymer monofilament were blended and opened by a carding machine to form fiber web A. The fiber web A has a needle density of 50 needles / cm 2 The fibers were entangled by needle punching. Next, the fiber web A after the fibers were entangled was placed in a dryer at a temperature of 150° C. for 3 minutes. Finally, the fiber web A was taken out of the dryer and left to cool at 25° C. for 5 minutes to produce a nonwoven fabric. The nonwoven fabric produced in this manner was designated as air filter A.

[0061] (Examples 2 to 4, Comparative Example 1) Air filters B to E were produced in the same manner as in Example 1, except that various fibers were mixed in the compositions shown in Table 1 and the basis weight of the prepared fiber web was changed.

[0062] (Comparative Example 2) An attempt was made to manufacture air filter F in the same manner as in Example 1, except that various fibers were blended according to the composition shown in Table 1, the basis weight of the prepared fiber web was changed, and the temperature of the dryer was changed to 230°C. However, the produced nonwoven fabric had severe unevenness in the thickness direction and was unusable as an air filter, so it was not possible to produce an air filter (Air Filter F). The reason for this is thought to be that the mass percentage of the sheath-core conjugate fibers, which form the skeleton of the nonwoven fabric and are contained in the fiber web, was only 45 mass% of the sum of the masses of the polyester copolymer monofilaments that melt upon heating at a low melting point, and therefore the fiber web shrunk severely inside the dryer, causing a biased fiber distribution, resulting in severe unevenness in the thickness direction of the nonwoven fabric.

[0063] (Examples 5 to 6, Comparative Example 3) Air filters G to I were produced in the same manner as in Example 1, except that various fibers were blended according to the composition shown in Table 1, the basis weight of the prepared fiber web was changed, and the temperature of the dryer was changed to 230°C.

[0064] As described above, in all of the air filters prepared in Examples 1 to 6, the sheath component of the polyester-based core-sheath composite fibers was melted, and the fibers constituting the air filter were bonded to each other throughout the entire thickness of the air filter. Furthermore, the bonded portions had portions that were further bonded by a polyester copolymer (another organic resin) derived from polyester copolymer monofilaments throughout the entire thickness direction of the air filter.

[0065] The shape of the polyester copolymer (another organic resin) in Examples 1 to 4 at this time was, as shown by A1 and A2 in Figures 1 to 3, such that the polyester copolymer (another organic resin) was present covering the constituent fibers of the nonwoven fabric, and the other organic resin had multiple bonded portions at parts where the fibers were close to each other, such as fiber intersections of the nonwoven fabric, and the other organic resin was connected between the bonded portions, forming a fibrous portion shape, and this fibrous portion shape was thicker than the constituent fibers of the nonwoven fabric provided in the air filter.

[0066] In addition, the shape of the polyester copolymer (another organic resin) in Examples 5 and 6 was granular as shown in B of Figure 4, and the granular polyester copolymer was present in the areas where the polyester-based core-sheath composite fibers C were close to each other.

[0067] On the other hand, in both the air filters prepared in Comparative Examples 1 and 3 as described above, the fibers constituting the air filter were bonded to each other throughout the entire thickness of the air filter simply because the sheath component of the polyester-based core-sheath composite fiber had melted.

[0068] The fiber compositions, basis weights, and thicknesses of the air filters of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1 below. Note that for Comparative Example 2, air filter F could not be manufactured, so a "-" is entered next to each item indicating the filter configuration.

[0069] [Table 1]

[0070] Next, the physical properties of the air filters of the examples and comparative examples were evaluated by the following methods.

[0071] (Pressure loss measurement) The prepared air filter has an effective opening area of ​​0.0625 m 2 The filter was attached to a test duct holder. Air was then passed through at a surface velocity of 10 cm / s, and the pressure difference between the upstream and downstream sides of the air filter was measured using a Cosmo Instruments DM-3500 digital manometer differential pressure gauge. Measurements were taken at five randomly selected locations on one air filter, and the average value was taken as the pressure loss of the air filter (unit: Pa).

[0072] (bending resistance measurement) The bending resistance (mN) of the air filters of the examples and comparative examples was measured according to 6.7.4 "Gurley method" of JIS L1913:2010 "Testing methods for general nonwoven fabrics." Note that the higher the bending resistance value, the more resistant the air filter is to deformation by external forces such as wind, and the stronger the air filter is.

[0073] The physical properties of the air filters of the examples and comparative examples are shown in Table 2. Note that for comparative example 2, since it was not possible to manufacture an air filter, a "-" mark is entered next to each item representing the physical properties of the air filter.

[0074] [Table 2]

[0075] The following was revealed by comparing air filters (air filters prepared in the comparative examples and air filters prepared in the examples) that have nonwoven fabrics whose constituent fibers are mainly core-sheath type composite fibers.

[0076] The results of comparing Examples 1 to 4 with Comparative Example 1, and the results of comparing Examples 5 and 6 with Comparative Example 3, reveal that in an air filter comprising a nonwoven fabric in which the fibers constituting the nonwoven fabric are bonded together by the sheath component of the core-sheath composite fiber and another organic resin, an air filter with excellent strength can be realized by ensuring that the mass percentage of the other organic resin in the sum of the masses of the core-sheath composite fiber and the other organic resin is 5 mass% or more (and at the same time, by ensuring that the mass percentage of the core-sheath composite fiber is 95 mass% or less).

[0077] Furthermore, the results of comparing Examples 5 and 6 with Comparative Example 2 revealed that in the nonwoven fabric constituting the air filter, unless the mass percentage of the other organic resin in the sum of the masses of the core-sheath composite fiber and the other organic resin is 50 mass% or less (and at the same time, the mass percentage of the core-sheath composite fiber is 50 mass% or more), an air filter with excellent strength cannot be realized.

[0078] Furthermore, the results of comparing Example 4 and Example 6 revealed that when the shape of the other organic resin in the nonwoven fabric constituting the air filter is fibrous, it is possible to realize a nonwoven fabric and an air filter having superior strength compared to when the shape of the other organic resin is granular.

[0079] From the above, it has been found that by satisfying the configuration of the present invention, an air filter having excellent strength can be realized.

[0080] Example 7 A fiber web J (basis weight: 65 g / m) was prepared in the same manner as the fiber web A in Example 1, except that the basis weight was different. 2 ) was formed. Next, 50 mass% of acrylic fiber (melting point: 160°C, fineness: 1.7 dtex, fiber length: 51 mm) and 50 mass% of polypropylene fiber (melting point: 160°C, fineness: 1.7 dtex, fiber length: 51 mm) were mixed and opened by a carding machine to obtain an electrostatic fiber web (basis weight: 20 g / m 2 ) was formed. The two fiber webs J were stacked in the order of fiber web J-charged fiber web j-fiber web J, with the charged fiber web j sandwiched between them. Then, from one main surface side, the needle density was 50 needles / cm 2 By performing the needle punching process at step 1, some of the fibers constituting the charged fiber web j penetrated into the fiber web J, thereby entangling the fibers constituting each fiber web with each other. As a result, a fiber web laminate was formed in which each fiber web was integrated. Thereafter, this fiber web laminate was placed in a dryer at 150°C for 3 minutes to melt the sheath components of the polyester sheath-core composite fiber A and the polyester sheath-core composite fiber B, and the polyester copolymer monofilaments. Next, the fibrous web laminate was removed from the dryer and left to cool at 25°C for 5 minutes, producing a nonwoven fabric. This nonwoven fabric had a tribo-electrically charged nonwoven fabric layer in which acrylic fibers and polypropylene fibers were mixed, between layers of nonwoven fabric derived from fibrous web J. Furthermore, in the nonwoven fabric derived from fibrous web J, the constituent fibers were bonded together by fusion of the sheath components of the polyester-based core-sheath composite fibers A and B, and the fibers were also bonded together at their intersections by a polyester copolymer (another organic resin) derived from molten polyester copolymer monofilaments. Next, the nonwoven fabric was washed with warm water at 60°C for 10 minutes, and then air-dried to remove the oil. After that, air was blown onto the nonwoven fabric to rub the constituent fibers, thereby causing frictional electrification, and the nonwoven fabric was further electrified. The nonwoven fabric produced in this way was designated as air filter J.

[0081] (Example 8, Comparative Examples 4 to 5) Air filters K to M were produced in the same manner as in Example 7, except that various fibers were mixed in the compositions shown in Table 3 and the basis weight of the prepared fiber web was changed. As described above, in all of the air filters prepared in Examples 7 and 8, the fibers constituting the air filter were bonded to each other throughout the entire thickness of the air filter due to melting of the sheath component of the polyester-based core-sheath composite fibers. Furthermore, throughout the entire thickness of the air filter, the bonded portions contained portions further bonded by a polyester copolymer (another organic resin) derived from polyester copolymer monofilaments. The shape of the polyester copolymer (another organic resin) in the polyester nonwoven fabric constituting the air filters of Examples 7 and 8 was a monofilament shape in which the polyester copolymer (another organic resin) had multiple portions where it was bonded to the constituent fibers of the nonwoven fabric as shown in Figures 1 to 3, and the bonded portions were bound together by the other organic resin, and this monofilament shape was thicker than the constituent fibers of the nonwoven fabric provided in the air filter. On the other hand, in the air filters prepared in Comparative Examples 4 and 5, the fibers constituting the air filter were bonded together throughout the entire thickness of the air filter simply because the sheath component of the polyester-based core-sheath composite fiber had melted.

[0082] The fiber compositions, basis weights, and thicknesses of the air filters of Examples 7 and 8 and Comparative Examples 4 and 5 are shown in Table 3 below.

[0083] [Table 3]

[0084] Table 4 shows the physical properties of the air filters prepared in Examples 7 and 8 and Comparative Examples 4 and 5. The collection efficiency of the air filters was measured by the following method, and the collection efficiency (unit: %) was calculated.

[0085] (Collection efficiency measurement) The prepared air filter has an effective opening area of ​​0.0625 m 2 The filter was attached to a holder in a test duct. Then, airborne dust particles with particle diameters of 0.3 to 0.5 μm (airborne dust particle count: U) were supplied to the upstream side of the air filter, and air was passed through at a surface velocity of 10 cm / s. The airborne dust particle count (D) with particle diameters of 0.3 to 0.5 μm on the downstream side was measured using a particle counter (RION Corporation: Model KC-01E). Both measured values ​​were substituted into the following equation, and the calculated value was taken as the filtering efficiency (%). The filtering efficiency of the air filter was measured when the needle-punched side was positioned upstream, and when the needle-punched side was positioned downstream, and the average value was taken as the filtering efficiency of the examples and comparative examples. Collection efficiency (%) = [1-(D / U)] x 100

[0086] [Table 4]

[0087] The results of comparing Example 7 with Comparative Example 4, and the results of comparing Example 8 with Comparative Example 5, reveal that by satisfying the configuration of the present invention, an air filter with excellent strength can be realized.

[0088] Examples 9 to 12 Various fibers were blended in the compositions shown in Table 5, and the basis weight of the prepared fiber webs was changed, to form two of each fiber web in the same manner as fiber web J in Example 7. For ease of understanding, Table 5 also lists the filter configuration of Comparative Example 5. In addition, various types of charged fiber webs were formed in the same manner as charged fiber web j of Example 7 by blending various fibers in the compositions shown in Table 5 and changing the basis weight of the prepared fiber web. The two same types of fiber webs prepared in this way were stacked so as to sandwich the charged fiber web. Then, needles were placed on one of the main surfaces at a needle density of 50 needles / cm. 2 By performing a needle punching process at , some of the fibers constituting the charged fiber web penetrated into the fiber web, thereby entangling the fibers constituting each fiber web with each other. As a result, a fiber web laminate was formed in which each fiber web was integrated. Except for using the various fiber web laminates prepared in this manner, air filters N to Q were produced in the same manner as in Example 7. For ease of understanding, Tables 5 and 6 also show the physical properties of the air filter prepared in Comparative Example 5.

[0089] [Table 5]

[0090] Table 6 shows the physical properties of the air filters prepared in Examples 9 to 12.

[0091] [Table 6]

[0092] As a result of comparing Examples 9 to 12 with Comparative Example 5, it was found that an air filter having excellent strength can be realized by satisfying the configuration of the present invention. [Industrial Applicability]

[0093] The air filter of the present invention can be used by incorporating flat or pleated filters, and roll-type filters that are unwound and wound up by air conditioning equipment, into air conditioning equipment installed in buildings, factories, ordinary homes, mobile vehicles, etc. [Explanation of symbols]

[0094] 100: Nonwoven fabric 1: Nonwoven fabric constituent fibers A1: A part of the fiber that is derived from melted single fibers and is bonded at a point where fibers are close to each other, such as the fiber intersection of a nonwoven fabric (part of the fiber part). A2: The part that connects the constituent fibers of the nonwoven fabric, derived from melted single fibers (part of the fiber part) B: Granular organic resin

Claims

1. An air filter comprising a core-sheath type composite fiber made of a core component which is an organic resin and a sheath component which is an organic resin having a melting point lower than that of the core component, and a nonwoven fabric having another organic resin different from the core component, The constituent fibers of the nonwoven fabric are mainly the core-sheath type composite fibers, the fibers constituting the nonwoven fabric are bonded to each other by the sheath component and the other organic resin, an air filter in which the mass percentage of the core-sheath type composite fiber is 50 mass% or more and 95 mass% or less, and the mass percentage of the other organic resin is 5 mass% or more and 50 mass% or less, based on the sum of the masses of the core-sheath type composite fiber and the other organic resin contained in the nonwoven fabric.

2. the nonwoven fabric is composed only of the core-sheath type composite fiber and the other organic resin; 2. The air filter of claim 1.

3. An air filter comprising a tribo-electrically charged nonwoven fabric layer having two or more different types of constituent fibers mixed between layers of the nonwoven fabric according to claim 1.

4. the nonwoven fabric is composed only of the core-sheath composite fiber, the other organic resin, and the constituent fibers of the tribo-electrically charged nonwoven fabric layer, 4. The air filter according to claim 3, wherein constituent fibers of the tribo-electrically charged nonwoven fabric layer adjacent to the nonwoven fabric are embedded in the nonwoven fabric.

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