Method for manufacturing air filter media, air filter media, filter pack, and air filter unit

Abstract

To provide a production method of an air filter filtering medium which can inhibit deterioration of a function during joint, and to provide an air filter filtering medium, a filter pack, and an air filter unit.SOLUTION: A production method of an air filter filtering medium includes: a first step in which a porous membrane and an aeration membrane are prepared; and a second step in which the porous membrane and the aeration membrane are adhered to each other by using a hot melt adhesive in a melting state. In the second step, a temperature of the aeration membrane is lower than a temperature of the hot melt adhesive in the melting state.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an air filter medium, an air filter medium, a filter pack, and an air filter unit. [Background technology]

[0002] Conventionally, for example, porous membranes made of polytetrafluoroethylene (hereinafter sometimes referred to as PTFE) (hereinafter sometimes referred to as PTFE porous membranes) have been used as air filters. PTFE porous membranes have higher dust collection efficiency than glass fiber filter media when compared at the same pressure loss, and are therefore particularly suitable for use in HEPA filters (High Efficiency Particulate Air Filters) and ULPA filters (Ultra Low Penetration Air Filters).

[0003] As such a filter, for example, an air filter medium in which a PTFE porous film and an air-permeable support material are laminated, such as the air filter medium described in Patent Document 1 (JP-A-2009-297702), has been proposed. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0004] The air filter medium described in Patent Document 1 is produced by thermally laminating the entire PTFE porous membrane and the breathable support material using a pair of heated heat rolls.

[0005] However, in this type of thermal lamination process using a heated roll, there is a risk that the function of one of the layers constituting the filter medium may be deteriorated by heat, so it is desirable to minimize the deterioration of function during bonding. [Means for solving the problem]

[0006] A method for producing an air filter medium according to a first aspect includes a first step of preparing a porous membrane and a breathable membrane, and a second step of bonding the porous membrane and the breathable membrane with a molten hot-melt adhesive, wherein the temperature of the breathable membrane in the second step is lower than the temperature of the molten hot-melt adhesive.

[0007] The breathable film is not particularly limited and may be, for example, a nonwoven fabric.

[0008] According to this method for manufacturing an air filter medium, the porous membrane and the breathable membrane can be joined together while the temperature of the breathable membrane is lower than the temperature of the hot melt adhesive in a molten state, thereby suppressing deterioration of the function of the breathable membrane.

[0009] A manufacturing method of an air filter medium according to a second aspect is the manufacturing method of an air filter medium according to the first aspect, wherein either the porous membrane or the breathable membrane is a meltblown nonwoven fabric, a spunbonded nonwoven fabric, or a membrane containing one or more selected from the group consisting of antibodies, antibacterial agents, and antifungal agents.

[0010] Here, when either porous membrane or breathable membrane contains meltblown nonwoven fabric or spunbonded nonwoven fabric, when bonding porous membrane and breathable membrane, heat is likely to cause wrinkles, and it may be difficult to bond uniformly.On the other hand, according to the manufacturing method of this air filter medium, the heating of meltblown nonwoven fabric or spunbonded nonwoven fabric is suppressed, so that porous membrane and breathable membrane can be bonded uniformly.

[0011] Furthermore, when either the porous membrane or the breathable membrane contains an antibody such as a protein, the antibody such as the protein may be denatured by heat, resulting in a decrease or loss of antibody function. However, according to this method for producing an air filter medium, the denaturation of the antibody due to heat is suppressed, so that the decrease in antibody function is minimized.

[0012] In addition, when either the porous film or the breathable film contains an antibacterial agent or an antifungal agent, the antibacterial agent or the antifungal agent may be denatured by heat, and the function of the antibacterial agent or the antifungal agent may be reduced or lost.However, according to the manufacturing method of this air filter medium, the denaturation of the antibacterial agent or the antifungal agent by heat is suppressed, so the reduction of the function of the antibacterial agent or the antifungal agent can be suppressed.

[0013] A method for producing an air filter medium according to a third aspect is the method for producing an air filter medium according to the first or second aspect, wherein the porous film is a polytetrafluoroethylene porous film.

[0014] This method for producing an air filter medium can produce a high-performance air filter medium.

[0015] A manufacturing method of an air filter medium according to a fourth aspect is a manufacturing method of an air filter medium according to any one of the first aspect to the third aspect, in which the breathable film contains one or more selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), polyphenylene sulfide (PPS), polypropylene (PP), and polyamide (PA).

[0016] In addition, the air filter medium equipped with the breathable film has a TOC (Total Organic Carbon) content of 1000 μg / m2 per unit area, which is released from the air filter medium when an inert gas is passed through the air filter medium heated to 40°C for 60 minutes. 2 It is preferable that:

[0017] A fifth aspect of the invention relates to a method for producing an air filter medium according to any one of the first to fourth aspects, in which the porous membrane and the breathable membrane are bonded together with a fibrous hot melt adhesive.

[0018] In this method for producing an air filter medium, the pressure loss of the resulting air filter medium is kept small because the hot melt adhesive is fibrous.

[0019] A manufacturing method for an air filter medium according to a sixth aspect is the manufacturing method for an air filter medium according to the fifth aspect, and in the second step, the hot melt adhesive is extruded from a nozzle in a molten state, and the hot melt adhesive is stretched using an air flow having a speed faster than the extrusion speed of the hot melt adhesive from the nozzle, thereby fiberizing the hot melt adhesive.

[0020] This method of manufacturing an air filter medium makes it easy to form fibers from a hot melt adhesive.

[0021] A seventh aspect of the invention relates to a method for producing an air filter medium, which is the method for producing an air filter medium according to the fifth or sixth aspect, in which a plurality of fibrous hot melt adhesive strands are arranged so as to share a common longitudinal direction.

[0022] It is preferable that the plurality of fibers of the adhesive do not overlap each other, or that each fiber intersects at three or less locations.

[0023] This method of manufacturing an air filter medium prevents multiple fibers of the hot melt adhesive from overlapping with each other, which allows the porous membrane and the breathable membrane to be uniformly bonded together and prevents partial peeling.

[0024] When the air filter medium is pleated, the air-permeable film is prevented from peeling off from the porous film during pleating.

[0025] An eighth aspect of the invention relates to a method for producing an air filter medium according to any one of the first to seventh aspects, wherein the hot melt adhesive has a melt viscosity of 1000 mPa·s or more and 2500 mPa·s or less at 180°C.

[0026] This method of manufacturing the air filter medium makes it easy to apply it in a molten state.

[0027] A manufacturing method of an air filter medium according to a ninth aspect is a manufacturing method of an air filter medium according to any one of the first aspect to the eighth aspect, in which the hot melt adhesive is one or more types selected from the group consisting of polyolefin-based resins and polyamide-based resins.

[0028] Here, it is preferable that one or more hot melt adhesives selected from the group consisting of polyolefin-based resins and polyamide-based resins are used together with a fluororesin porous membrane, from the viewpoint of enhancing adhesiveness.

[0029] This method for producing an air filter medium makes it possible to bond the porous membrane and the breathable membrane well.

[0030] A tenth aspect of the invention relates to a method for producing an air filter medium, which is a method for producing an air filter medium according to any one of the first to ninth aspects, wherein the average fiber diameter of the porous membrane, the average fiber diameter of the adhesive, and the average fiber diameter of the breathable membrane are expressed as average fiber diameter of the porous membrane:average fiber diameter of the adhesive:average fiber diameter of the breathable membrane=1 / 2000 to 1 / 30:1 to 6:1.

[0031] The average fiber diameter of the porous membrane may be, for example, 30 nm or more and 150 nm or less. The average fiber diameter of the adhesive may be, for example, 20 μm or more and 60 μm or less. The average fiber diameter of the breathable membrane may be, for example, 5 μm or more and 30 μm or less.

[0032] This method for manufacturing an air filter medium can reduce the air resistance of the adhesive fibers in the resulting air filter medium, while preventing the adhesive fibers from getting between the fibers of the breathable membrane, preventing the adhesive fibers from being interposed between the porous membrane and the breathable membrane, resulting in areas where the adhesive function is not exerted.

[0033] An eleventh aspect of the invention relates to a method for producing an air filter medium according to any one of the first to tenth aspects, in which, after the second step, the sheet having the porous membrane, the hot-melt adhesive, and the breathable membrane is passed between a pair of rolls. When passing between the rolls, the sheet is subjected to a pressure of 0.3 Pa or more and 0.6 Pa or less.

[0034] According to this method for producing an air filter medium, the adhesion between the porous membrane and the breathable membrane is improved.

[0035] An air filter medium according to a twelfth aspect is an air filter medium manufactured by the manufacturing method according to any one of the first aspect to the eleventh aspect.

[0036] This air filter medium is prevented from deteriorating in function.

[0037] A filter pack according to a thirteenth aspect is the air filter medium of the twelfth aspect, which is folded so as to create mountain folds and valley folds.

[0038] An air filter unit according to a fourteenth aspect includes an air filter medium manufactured by the manufacturing method according to any one of the first to twelfth aspects, or a pleated air filter medium manufactured by the manufacturing method according to any one of the first to twelfth aspects and folded so as to create mountain folds and valley folds, and a frame. The frame holds the air filter medium or the pleated filter medium.

[0039] An air filter medium according to a fifteenth aspect includes a porous membrane, a breathable membrane, and a hot-melt adhesive. The hot-melt adhesive bonds the porous membrane to the breathable membrane. The breathable membrane has a portion of the fiber opposite the porous membrane side that is less deformed by heat than a portion of the fiber on the porous membrane side of the breathable membrane.

[0040] This air filter medium is prevented from functionally deteriorating due to heat in the fiber at the portion of the breathable membrane opposite to the porous membrane side. [Brief explanation of the drawings]

[0041] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the layer structure of an air filter medium (No. 1). [Figure 2] FIG. 2 is a schematic cross-sectional view showing the layer structure of the air filter medium (No. 2). [Figure 3] FIG. 2 is a schematic cross-sectional view showing the layer structure of the air filter medium (No. 3). [Figure 4] FIG. 2 is a schematic perspective view of the appearance of the filter pack. [Figure 5] FIG. 2 is a schematic perspective view of the appearance of the air filter unit. [Figure 6] FIG. 10 is a schematic diagram illustrating an adhesive application step. [Figure 7] FIG. 10 is a diagram showing an example of the shape of adhesive fibers applied. [Figure 8] FIG. 10 is a diagram showing another example of the shape of adhesive fibers applied. DETAILED DESCRIPTION OF THE INVENTION

[0042] The air filter medium, filter pack, air filter unit, and manufacturing methods thereof will be described below with reference to examples.

[0043] (1) Air filter media The air filter medium includes a porous membrane, a breathable membrane, and a fibrous adhesive that bonds the porous membrane and the breathable membrane together.

[0044] The average fiber diameter of the porous membrane, the average fiber diameter of the adhesive, and the average fiber diameter of the breathable membrane preferably satisfy the relationship of average fiber diameter of the porous membrane: average fiber diameter of the adhesive: average fiber diameter of the breathable membrane = 1 / 2000 to 1 / 30:1 to 6:1.

[0045] By using an adhesive having an average fiber diameter at least 1 time the average fiber diameter of the breathable membrane, the fibers of the adhesive are prevented from penetrating between the fibers of the breathable membrane. It is more preferable that the average fiber diameter of the adhesive is at least 2.0 times the average fiber diameter of the breathable membrane. By using an adhesive having an average fiber diameter no greater than 6 times the average fiber diameter of the breathable membrane, the rate of increase in pressure loss caused by the adhesive fibers themselves can be kept low. It is preferable that the weight ratio of the number of adhesive fibers with a fiber diameter larger than the average fiber diameter of the breathable membrane to the total number of fibers in the adhesive is 90% by weight or more.

[0046] In addition, by using adhesive that has average fiber diameter that is 30 times or more than the average fiber diameter of porous membrane, can minimize the influence that adhesive fiber has on the filter performance of porous membrane.In addition, by using adhesive that has average fiber diameter that is for example 2000 times or less than the average fiber diameter of porous membrane, can easily minimize the increase rate of the pressure loss that adhesive fiber itself causes.

[0047] Furthermore, by using a breathable membrane whose average fiber diameter is 30 times or more the average fiber diameter of the adhesive, even if the porous membrane is thin and therefore difficult to stand on its own, the breathable membrane can easily support the porous membrane, thereby increasing the rigidity of the air filter medium.

[0048] The average fiber diameter of the porous membrane may be calculated as the number-average fiber diameter by randomly selecting 50 fibers from a scanning electron microscope image. The average fiber diameter of the adhesive and the average fiber diameter of the breathable membrane can be evaluated based on fibers present within a predetermined range of an image observed using a microscope or the like, and may be calculated as the number-average fiber diameter of, for example, 200 fibers.

[0049] The adhesive preferably has an average fiber diameter of 20 μm or more, more preferably 30 μm or more, from the viewpoint of preventing the fibers of the adhesive from getting between the fibers of the breathable film. When the adhesive is used to bond a porous film having an average fiber diameter of 30 nm or more and 150 nm or less, the average fiber diameter is preferably 60 μm or less, and may be 55 μm or less, from the viewpoint of preventing the rate of increase in pressure loss due to the presence of the fibers of the adhesive.

[0050] The average length of the fibers of the adhesive is not particularly limited, but may be, for example, 100 times or more the average fiber diameter of the adhesive, and preferably 500 times or more the average fiber diameter of the adhesive.

[0051] When a 1 cm long imaginary line is drawn in a direction perpendicular to the longitudinal direction of any one of the plurality of adhesive fibers, the average number of adhesive fibers intersecting the imaginary line is preferably 2 to 3. This average number can be, for example, the average value counted for 200 random adhesive fibers. By arranging the plurality of adhesive fibers side by side, overlapping of the adhesive fibers is suppressed, enabling the adhesion points between the porous membrane and the breathable membrane to be evenly arranged. Furthermore, since the average number of adhesive fibers intersecting the 1 cm long imaginary line is 2 or more, stress concentration at specific adhesion points when force is applied to the porous membrane or breathable membrane is suppressed, making it easier to maintain a good adhesive state. For example, when a bonded porous membrane and breathable membrane is pleated, peeling between the porous membrane and the breathable membrane during pleating can be suppressed. By having the average number of adhesive fibers intersecting the 1 cm long imaginary line be 3 or less, an increase in pressure loss of the air filter medium is suppressed.

[0052] In addition, when the number of adhesive fibers is about the same, such as when the average number of adhesive fibers intersecting an imaginary line of 1 cm in length is about the same, the adhesive with a larger average fiber diameter will have a higher application amount per unit area (g / m 2) tends to increase. However, as will be described later, it has become clear that the rate of increase in pressure loss due to the fibers of the adhesive covering the porous membrane tends to be significantly larger than the rate of increase in the amount of adhesive applied per unit area. Therefore, from the viewpoint of sufficiently suppressing the rate of increase in pressure loss, it is more preferable that the average fiber diameter of the adhesive is 1000 times or less than the average fiber diameter of the porous membrane.

[0053] It is preferable that the adhesive fibers do not overlap each other when viewed in the thickness direction of the air filter medium, or that there are three or fewer intersections between each fiber. The intersections between adhesive fibers refer to the average number of intersections between each adhesive fiber and its own fiber and other adhesive fibers per fiber. It is not particularly limited, but may be calculated as the average of the intersections between 100 adhesive fibers in any region. It is also more preferable that there are two or fewer intersections between adhesive fibers per adhesive fiber. Although the overlapping adhesive fibers can bond the porous membrane and the breathable membrane at the overlapping adhesive fiber locations, the gap between the porous membrane and the breathable membrane widens at the overlapping adhesive fiber locations, making it difficult to sufficiently bond the porous membrane and the breathable membrane around the overlapping adhesive fiber locations. Therefore, there are locations where the porous membrane floats relative to the breathable membrane, making it difficult to ensure a uniform adhesion state throughout the membrane. Therefore, it is preferable to have as few overlapping adhesive fibers as possible. Furthermore, even if overlapping of adhesive fibers occurs in some places, it is possible to improve the adhesion by disposing sufficient adhesive fibers around the overlapping places. However, in this case, the amount of adhesive required to bond the porous membrane and the breathable membrane increases, which increases the pressure loss of the air filter medium.

[0054] The plurality of adhesive fibers are preferably arranged such that the longitudinal directions of the plurality of adhesive fibers are parallel to each other in a predetermined direction when viewed in the thickness direction of the air filter medium, thereby making it possible to prevent the adhesive fibers from overlapping with each other.

[0055] The adhesive fibers preferably have a wavy shape with peaks and valleys when viewed in the thickness direction of the air filter medium. Preferably, more than half of the adhesive fibers have a wavy shape with peaks and valleys, and more preferably, 90% or more of the adhesive fibers have a wavy shape with peaks and valleys.

[0056] The shape of the adhesive is preferably a shape other than a shape that causes overlapping of fiber portions in a single adhesive when viewed in the thickness direction of the air filter medium, and for example, it is preferably not a spiral shape or a randomly applied shape.

[0057] The amount of adhesive is 1 g / m between one porous membrane and one breathable membrane when viewed in the thickness direction of the air filter medium, from the viewpoint of improving the adhesion between the porous membrane and the breathable membrane. 2 It is preferable that the content is 2 g / m or more. 2 In order to minimize the increase in pressure loss due to the presence of adhesive fibers, the amount of adhesive is preferably 5 g / m or more between one porous membrane and one breathable membrane as viewed in the thickness direction of the air filter medium. 2 Preferably, it is 4 g / m or less. 2 More preferably, it is:

[0058] From the viewpoint of minimizing the total organic carbon (TOC) of the air filter medium, the adhesive preferably contains at least one of a polyolefin resin and a polyamide resin, and preferably is composed primarily of a polyolefin resin. Furthermore, it is preferable that the adhesive is not a rubber-based adhesive or an acrylic-based adhesive. The weight ratio of the polyolefin resin in the adhesive is, for example, 70% or more, preferably 90% or more. Furthermore, from the viewpoint of suppressing an increase in pressure loss due to the adhesive fiber diameter becoming too large, the adhesive preferably has a melt viscosity of 2500 mPa·s or less at 180°C, more preferably 2200 mPa·s or less. Furthermore, from the viewpoint of suppressing the extruded fibers from being cut midway, making it easy to obtain continuously extending fibers and to easily control the application position, the adhesive preferably has a melt viscosity of 1000 mPa·s or more, more preferably 1500 mPa·s or more at 180°C. From the viewpoint of preventing deterioration of the adhesive, the heating temperature when melting the adhesive is preferably 250°C or lower, and more preferably 200°C or lower.

[0059] In addition, when adhesive is applied so that the peel strength of porous membrane and breathable membrane in air filter material is ensured to be more than 0.1N / 35mm, the pressure loss of the laminated product that porous membrane and breathable membrane are laminated without using adhesive and the pressure loss of the air filter material that is obtained by bonding porous membrane and breathable membrane with adhesive are preferably less than 10%, more preferably less than 7%, and even more preferably less than 6%.Here, the increase rate of pressure loss is calculated by the following formula: Pressure loss increase rate (%) = (pressure loss of air filter media / pressure loss of laminate) x 100 - 100

[0060] The porous membrane preferably has an average fiber diameter of, for example, 30 nm or more and 150 nm or less, which makes it possible to increase the collection efficiency of the air filter medium.

[0061] The porous membrane is not particularly limited, and may be a meltblown nonwoven fabric, a spunbonded nonwoven fabric, a membrane containing an antibody, etc., but is preferably a fluororesin porous membrane mainly composed of a fluororesin and having a porous membrane structure with fibrils (fibers) and nodes (nodes) connected to the fibrils. Here, "mainly" means that when a plurality of types of components are contained, the fluororesin porous membrane is contained in the largest amount. For example, the fluororesin porous membrane may contain 50% by weight or more of fluororesin relative to the weight of the fluororesin porous membrane, preferably 80% by weight or more of fluororesin, more preferably 95% by weight or more of fluororesin, or may be composed only of fluororesin. This allows an air filter medium with sufficient performance to be obtained. In addition, when the porous membrane is a fluororesin porous membrane, even when it is used for applications requiring high performance as an air filter medium, the amount of TOC generated can be suppressed.

[0062] The component different from the fluororesin contained in the fluororesin porous membrane may be, for example, an inorganic filler, which is a non-melt-processable component that does not cause fibrosis.

[0063] The fluororesin used in the fluororesin porous membrane may consist of one type of component or two or more types of components. Examples of fluororesins include those containing fibrous PTFE. Examples of fluororesins include mixtures of three components: fibrous PTFE, a non-fibrous non-thermal melt processable component, and a non-fibrous non-thermal melt processable component with a melting point of less than 320°C. The melting point can generally be measured by DSC (differential scanning calorimetry) and appears as an endothermic peak. For amorphous structures that do not have a clear melting point, the softening point can be used instead. The softening point can be determined by differential thermal analysis (DTA) as the temperature at which the slope of the DTA graph first changes.

[0064] Fiberizable PTFE is high-molecular-weight PTFE obtained by emulsion polymerization or suspension polymerization of tetrafluoroethylene (TFE). The term "high molecular weight" here refers to a material that is easily fiberized during stretching to produce porous membranes, yielding long fibrils. Its standard specific gravity (SSG) is 2.130 to 2.230, and its melt viscosity is so high that it does not substantially melt flow. Fiberizable PTFE can be determined by whether paste extrusion, a typical method for molding high-molecular-weight PTFE powder made from TFE polymers, is possible. If the unsintered molded product obtained by paste extrusion has substantially no strength or elongation, for example, if the elongation is 0% and it breaks when pulled, it can be considered to have no fiberizable properties. The high-molecular-weight PTFE may be modified polytetrafluoroethylene, homopolytetrafluoroethylene, or a mixture of modified PTFE and homoPTFE.

[0065] Examples of non-thermal melt processable components that do not cause fibrosis include thermoplastic components such as low-molecular-weight PTFE, thermosetting resins, inorganic fillers, and mixtures thereof. Low-molecular-weight PTFE has a number-average molecular weight of 600,000 or less, a melting point of 320°C or more and 335°C or less, and a melt viscosity at 380°C of 100 Pa·s to 7.0×10 5 It is PTFE with a Pa·s.

[0066] The non-fibrous hot melt processable component with a melting point of less than 320 ° C preferably has a melt viscosity of less than 10,000 Pa·s at 380 ° C. The melting point of the non-fibrous hot melt processable component is determined by the differential scanning calorimeter (DSC) at a heating rate of 10 ° C / min to the melting point or higher, completely melting once, cooling to the melting point or lower at 10 ° C / min, and then heating again at 10 ° C / min, and the peak top of the heat of fusion curve obtained.

[0067] These fibrous PTFE, non-fibrous non-thermal melt processable components, and non-fibrous non-thermal melt processable components having a melting point of less than 320 ° C. can be those described in detail in, for example, International Publication No. 2020 / 067182.

[0068] In addition, in the manufacturing method of fluororesin porous membrane, the fine powder obtained by coagulation and co-coagulation from emulsion polymerization of TFE is used, and after dehydration and drying, liquid lubricant (extrusion aid) is mixed, and paste extrusion is carried out to obtain sheet-like extrudate.Then, the sheet-like extrudate is rolled by calendar roll or the like to obtain the unsintered film, and the liquid lubricant is removed from the unsintered film, and then stretched to obtain fluororesin porous membrane.

[0069] The fluororesin porous membrane thus obtained preferably has a pressure loss of 300 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec. The pressure loss of the fluororesin porous membrane is not particularly limited, but may be 50 Pa or more.

[0070] The fluororesin porous membrane may have a particle collection efficiency of 99.00% or more, preferably 99.99% or more, when air containing NaCl particles with a particle diameter of 0.1 μm is passed through it at a flow rate of 5.3 cm / sec.

[0071] The PF value of the fluororesin porous membrane is preferably not less than 20. The PF value is determined by the following formula using the pressure loss and collection efficiency determined using NaCl particles with a particle diameter of 0.1 μm: PF value={−log((100−collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0072] The thickness of the fluororesin porous film can be, for example, 1.0 μm or more, and preferably 3.0 μm or more. Increasing the film thickness of the fluororesin porous film makes it possible to increase the dust-holding capacity. The film thickness of the fluororesin porous film is, for example, 300 μm or less, and preferably 200 μm or less. The thickness of the fluororesin porous film can be determined, for example, by using a film thickness meter (Model 1D-110MH, manufactured by Mitutoyo Corporation) to measure the total film thickness of five layers of the film, and dividing this value by 5 to obtain the film thickness of one layer.

[0073] In addition, when the porous membrane is a fluororesin porous membrane, the adhesive preferably contains at least one of a polyolefin resin and a polyamide resin, from the viewpoint of having good adhesion to the fluororesin porous membrane and being able to reduce the amount of total organic carbon (TOC) of the air filter medium.

[0074] The breathable film is preferably, for example, a meltblown nonwoven fabric, a spunbond nonwoven fabric, or a film containing one or more substances selected from the group consisting of antibodies, antibacterial agents, and antifungal agents.

[0075] The meltblown or spunbond nonwoven fabric can support the porous membrane or function as a pre-collection layer by being placed upstream of the porous membrane. The antibody-containing membrane may be, for example, a membrane carrying an antibody. The antibody is preferably one that captures at least one harmful substance selected from bacteria, fungi, viruses, and allergens. Examples of bacteria include gram-positive bacteria such as Staphylococcus (Staphylococcus aureus and Staphylococcus epidermidis), Micrococcus, Bacillus anthracis, Bacillus cereus, Bacillus subtilis, and Propionibacterium acnes, as well as gram-negative bacteria such as Pseudomonas aeruginosa, Serratia marcescens, Burkholderia cepacia, Streptococcus pneumoniae, Legionella pneumoniae, and Mycobacterium tuberculosis. Examples of fungi include Aspergillus, Penicillius, Cladosporium, Fusarium, and Alternaria. Examples of viruses include influenza virus, coronavirus (SARS virus), adenovirus, and rhinovirus. Examples of allergens include pollen, mite allergens, and cat allergens. The film containing an antibacterial agent may be, for example, a film carrying an antibacterial agent. Examples of antibacterial agents include organic antibacterial agents, such as surfactant-based antibacterial agents, alcohol-based antibacterial agents, imidazole-based antibacterial agents, and antibacterial agents using the naturally-derived substance hinokitiol. The film containing an antifungal agent may be, for example, a film carrying an antifungal agent. Examples of antifungal agents include organic antifungal agents, such as surfactant-based antifungal agents, alcohol-based antifungal agents, imidazole-based antifungal agents, and antifungal agents using the naturally-derived substance hinokitiol.

[0076] In addition, meltblown nonwoven fabrics or spunbonded nonwoven fabrics are prone to wrinkles due to heat shrinkage when bonding a porous membrane and a breathable membrane, which may make it difficult to achieve uniform bonding. Particularly, when bonding a porous membrane and a breathable membrane by heating to a temperature exceeding the softening point of the resin constituting at least a part of the breathable membrane, shrinkage and wrinkles due to heat are significant. On the other hand, according to this air filter medium manufacturing method, the heating of the meltblown nonwoven fabric or spunbonded nonwoven fabric is suppressed, so that the porous membrane and the breathable membrane can be uniformly bonded. For example, even when using a breathable membrane whose area shrinks to 95% or less when heated at a temperature above its softening point, this air filter medium manufacturing method makes it possible to achieve uniform bonding. In addition, when wrinkles are generated due to heat when bonding a porous membrane and a breathable membrane, when the bonded porous membrane and the breathable membrane are further processed into a pleated shape, it may be difficult to achieve a uniform pleated shape. In contrast, according to this method for manufacturing an air filter medium, the decrease in uniformity during pleating is suppressed.

[0077] When a meltblown or spunbond nonwoven fabric is thermally laminated, its density changes due to shrinkage caused by heat, which may result in an increase in pressure loss. In contrast, a manufacturing method that does not actively heat the meltblown or spunbond nonwoven fabric itself can suppress the increase in pressure loss.

[0078] Furthermore, membranes containing antibodies such as proteins generally denature at temperatures above 80°C, which may result in a decrease or loss of antibody function. However, a manufacturing method that does not actively heat the membrane containing antibodies such as proteins itself minimizes the decrease in antibody function.

[0079] Furthermore, films containing antibacterial or antifungal agents, particularly organic antibacterial or antifungal agents, may be denatured in high-temperature environments such as 80°C, resulting in a decrease or loss of the function of the antibacterial or antifungal agent. However, a production method that does not actively heat the film itself minimizes the decrease in the function of the antibacterial or antifungal agent. The antibacterial or antifungal agent may be a known agent whose function is decreased or lost when heated to 100°C or higher, or a known agent whose function is decreased or lost when heated to 120°C or higher.

[0080] When the breathable membrane is used as a support layer for supporting a porous membrane, for example, the average fiber diameter is preferably 5 μm or more and 30 μm or less, more preferably 10 μm or more and 25 μm or less, thereby sufficiently supporting the porous membrane and suppressing an increase in pressure loss caused by an excessively large fiber diameter of the breathable membrane.

[0081] When the breathable membrane is used as a pre-collection layer by being disposed upstream of the porous membrane in the airflow, for example, the average fiber diameter is preferably 0.5 μm or more and 10.0 μm or less, which makes it possible to distribute the dust collection load on the porous membrane and suppress early clogging of the porous membrane.

[0082] The breathable film may contain one or more selected from the group consisting of polyethylene terephthalate (PET), polyethylene (PE), polyphenylene sulfide (PPS), polypropylene (PP), and polyamide (PA). Such breathable film may be a meltblown nonwoven fabric, a spunbond nonwoven fabric, or the like. The air filter medium using this breathable film has a total organic carbon (TOC) per unit area of ​​the air filter medium that is released from the air filter medium when an inert gas is passed through the air filter medium heated to 40°C for 60 minutes, and the amount of TOC is 1000 μg / m. 2 Preferably, it is 500 μg / m or less. 2Even if the breathable film contains a component that can generate organic gas in a high-temperature environment, the porous film and the breathable film are joined using an adhesive, and there is no need to heat the breathable film until it is in a molten state, so that an increase in the amount of total organic carbon due to heating of the breathable film is suppressed.

[0083] The breathable membrane is preferably composed of fibers that are not core-sheath structure fibers that include a core and a sheath having a melting point lower than that of the core, and that have a uniform cross-sectional structure.

[0084] Preferably, breathable film is flame retardant.Specifically, breathable film is preferably flame retardant that corresponds to HF-1 in UL94-HF method.In addition, air filter material is obtained by bonding porous film and breathable film with adhesive, and there is no need to bond breathable film in molten state, so it is easy to select the breathable film of air filter material that shows flame retardancy.

[0085] The breathable film preferably has a pressure loss of, for example, 10 Pa or less when air is passed through it at a flow rate of 5.3 cm / sec.

[0086] The breathable membrane may have a particle collection efficiency of 10% or less, preferably 5% or less, when air containing NaCl particles with a particle diameter of 0.1 μm is passed through it at a flow rate of 5.3 cm / sec.

[0087] In addition, even when a plurality of breathable films are used, the preferable physical properties of the breathable film are the same for each film.

[0088] In addition, as described above, since the porous membrane and the breathable membrane are bonded by an adhesive, there is no need to partially melt either layer to bond them, and there is little restriction in the selection of the material of the porous membrane and the breathable membrane.

[0089] (2) Layer structure of air filter media The layer structure of the air filter medium is not particularly limited.

[0090] For example, as shown in Fig. 1, the air filter medium 30 may be configured such that a porous membrane 31 and a first breathable membrane 32 are stacked in the air flow direction, and an adhesive 38 is located between the porous membrane 31 and the first breathable membrane 32. As shown in Fig. 1, the first breathable membrane 32 may be provided on the downwind side of the porous membrane 31, or as shown in Fig. 2, it may be provided on the upwind side of the porous membrane 31. In addition, as shown in Fig. 3, the air filter medium may include a first breathable membrane 32 that is stacked on the porous membrane 31 in the air flow direction, and a second breathable membrane 33 that is stacked on the opposite side of the first breathable membrane 32 side of the porous membrane 31, and the porous membrane 31 is supported from both the downwind side and the upwind side. In this case, it is preferable that the adhesive 38 is located between the porous membrane 31 and the first breathable membrane 32, and the adhesive 38 is located between the porous membrane 31 and the second breathable membrane 33.

[0091] Air filter material can also be laminated with air permeable membrane on the leeward side of porous membrane, and laminated with pre-collection layer as another example of air permeable membrane on the windward side of porous membrane.In this case, by making the dust collection load that porous membrane bears on the pre-collection layer at more upstream side, can prevent porous membrane from clogging early.

[0092] (3) Physical properties of air filter media The pressure loss of the air filter medium may be, for example, 400 Pa or less, preferably 300 Pa or less. The pressure loss of the air filter medium is not particularly limited, but may be 50 Pa or more. The pressure loss of the air filter medium can be measured as the pressure loss when air is passed through at a flow rate of 5.3 cm / sec.

[0093] The air filter medium may have a particle collection efficiency of 99.00% or more, preferably 99.99% or more, when air containing NaCl particles with a particle diameter of 0.1 μm is passed through it at a flow rate of 5.3 cm / sec.

[0094] As an air filter medium, it is preferable that the PF value, determined using the pressure loss and collection efficiency determined using NaCl particles with a particle diameter of 0.1 μm, be 20 or more, for example, as determined by the following formula: PF value = {-log((100-collection efficiency (%)) / 100)} / (pressure loss (Pa) / 1000).

[0095] The thickness of air filter material is preferably 350 μ m or more for example.In addition, when air filter material is used in the state of having folded part, the thickness of air filter material is preferably 1000 μ m or less, more preferably 750 μ m or less, from the viewpoint of preventing the thickness of folded part from becoming too large.The thickness of air filter material is the thickness value when a load of 0.3 N is applied to the measurement object in a specific measuring device.

[0096] In the air filter medium, it is preferable that the porous membrane has an average fiber diameter of 30 nm or more and 150 nm or less, the adhesive has an average fiber diameter of 20 μm or more and 60 μm or less, and the breathable membrane has an average fiber diameter of 5 μm or more and 30 μm or less.

[0097] (4) Filter pack Next, the filter pack (pleated filter medium) of this embodiment will be described with reference to FIG.

[0098] FIG. 4 is a perspective view of the appearance of the filter pack 20 of this embodiment.

[0099] The filter pack 20 includes the air filter medium described above (e.g., air filter medium 30). The air filter medium of the filter pack 20 is a processed filter medium that has been pleated into a zigzag shape with alternating mountain folds and valley folds. Pleating can be performed, for example, using a rotary folding machine. The folded width of the air filter medium is not particularly limited, but is, for example, 25 mm or more and 280 mm or less. The pleating of the filter pack 20 increases the folded area of ​​the air filter medium when used in an air filter unit, thereby providing an air filter unit with high collection efficiency.

[0100] In addition to the air filter medium, the filter pack 20 may further include spacers (not shown) for maintaining the pleat spacing when used in an air filter unit. The material of the spacers is not particularly limited, but a hot-melt resin is preferably used. Furthermore, the air filter medium 30 may have a plurality of embossed protrusions, which maintain the pleat spacing.

[0101] (5) Air filter unit Next, the air filter unit 1 will be described with reference to FIG.

[0102] FIG. 5 is a perspective view showing the appearance of the air filter unit 1 of this embodiment.

[0103] The air filter unit 1 includes the air filter medium or filter pack described above and a frame 25 that holds the air filter medium or filter pack (pleated filter medium). The air filter unit 1 may be fabricated so that an air filter medium that is not folded in a mountain or valley manner is held in the frame, or so that the filter pack 20 is held in the frame 25. The air filter unit 1 shown in FIG. 5 is fabricated using the filter pack 20 and the frame 25.

[0104] Frame 25 is made, for example, by combining plate materials or molding resin, and the gap between filter pack 20 and frame 25 is preferably sealed with a sealant. The sealant is used to prevent leakage between filter pack 20 and frame 25, and is made of, for example, epoxy, acrylic, or urethane resin.

[0105] The air filter unit 1, which includes a filter pack 20 and a frame 25, may be a mini-pleat type air filter unit in which one flat filter pack 20 is held and stored inside the frame 25, or may be a V-bank type air filter unit or a single-header type air filter unit in which multiple flat filter packs are arranged and held in a frame.

[0106] (6) Examples of uses The air filter medium, filter pack, and air filter unit according to the present embodiment are used, for example, in the following applications.

[0107] ULPA filters (Ultra low Penetration Air Filters) (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN (registered trademark) filters (for industrial use), catalytic filters (for exhaust gas treatment), adsorbent filters (for HDD integration), adsorbent vent filters (for HDD integration), vent filters (for HDD integration, etc.), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt materials, gas turbine cartridge filters (for gas turbine compatible products), cooling filters (for electronic equipment housings), etc.

[0108] Freeze-drying materials such as freeze-drying containers, automotive ventilation materials for electronic circuits and lamps, container applications such as container caps, protective ventilation applications for electronic devices, ventilation / internal pressure adjustment applications such as medical ventilation applications.

[0109] Flat, pleated, three-dimensional masks (which prevent dust, oily smoke, bacteria, viruses, etc. from entering the body through the human mouth and nose).

[0110] (7) Manufacturing method of air filter media The method for manufacturing an air filter medium includes a first step of preparing a porous membrane and a breathable membrane, and a second step of bonding the porous membrane and the breathable membrane using a molten hot melt adhesive, and in the second step, the temperature of the breathable membrane is lower than the temperature of the molten hot melt adhesive.

[0111] In this way, in the second step, the porous membrane and the breathable membrane can be bonded together in a state where the temperature of the breathable membrane is lower than the temperature of the hot melt adhesive in a molten state. Therefore, the breathable membrane is prevented from being exposed to high temperatures, which prevents deformation of the breathable membrane and deterioration of its function.

[0112] For example, one bonding method involves bonding a porous membrane and a breathable membrane together, sandwiching them between heat rolls from the outside in the thickness direction, and melting the breathable membrane. However, this bonding method requires melting the surface of the breathable membrane facing the porous membrane. Therefore, when the breathable membrane is heated by a heat roll pressed against the surface of the breathable membrane opposite the porous membrane, the surface of the breathable membrane pressed against the heat roll becomes even more melted when heated until the surface facing the porous membrane melts. This can result in the loss of the functionality of the breathable membrane prior to the bonding process. Specifically, the fiber diameter of the breathable membrane can change significantly, increasing pressure loss. Furthermore, the fiber diameter of the breathable membrane can change significantly, reducing the support function of the porous membrane. Furthermore, for breathable membranes containing antibodies or other substances that lose their functionality at high temperatures, the functionality of the antibodies or other substances can be degraded or lost.

[0113] In contrast, in the manufacturing method of the air filter medium, in the second step, the temperature of the breathable film is maintained lower than the temperature of the molten hot melt adhesive, making it possible to suppress deterioration of the function of the breathable film.

[0114] Although the application of a molten hot melt adhesive at a higher temperature than the breathable film may cause some deformation of the fibers in the area of ​​the breathable film where the hot melt adhesive is applied due to the heat of the hot melt adhesive, this deformation occurs only near the surface of the breathable film where the adhesive is applied, and deformation of the fibers is suppressed inside the breathable film and near the surface opposite to the surface where the adhesive is applied. This makes it possible to suppress deformation of the fibers over most of the thickness of the breathable film.

[0115] The same is true for a porous membrane, which may be deformed due to contact with the molten hot melt adhesive only in the vicinity of the surface to be joined by the adhesive, but deformation is suppressed in areas away from the adhesive. Note that when the porous membrane is made of, for example, a fluororesin porous membrane or the like having a melting point higher than that of the adhesive, the influence of deformation of the fibers of the porous membrane is suppressed.

[0116] The bonding of the porous membrane and the breathable membrane may be performed using a porous membrane roll 61 wound into a roll, as shown in Fig. 6. Here, an example will be described in which breathable membranes 32 and 33 are bonded to both sides of the porous membrane 31 via an adhesive 38. The porous membrane 31 may be a fluororesin porous membrane stretched in the longitudinal and transverse directions.

[0117] In the apparatus shown in FIG. 6 , the porous membrane 31 sequentially delivered from the porous membrane roll 61 is supplied to the silicone rubber nip roll 64 via roll 74. The first breathable membrane 32 sequentially delivered from the first breathable membrane roll 62 is supplied to the temperature-controlled roll 65 via rolls 71, 72, and 73. After passing through roll 73 and before reaching the temperature-controlled roll 65, an adhesive 38 dispensed from a hot melt gun 68 is applied to the surface of the first breathable membrane 32 to be bonded to the porous membrane 31. The temperature-controlled roll 65 adjusts the temperature so that the adhesive 38 applied to the first breathable membrane 32 maintains its adhesive strength. The first breathable membrane 32 and the porous membrane 31 are bonded by passing between the temperature-controlled roll 65 and the silicone rubber nip roll 64 with the adhesive 38 interposed therebetween. The sheet-like product formed by bonding the first breathable membrane 32 and the porous membrane 31 is then supplied to the silicone rubber nip roll 67 via rolls 75, 76, and 77. The second breathable membrane 33, sequentially fed from the second breathable membrane roll 63, is supplied to the temperature-controlled roll 66 via rolls 78, 79, and 80. After passing through the roll 80 and before reaching the temperature-controlled roll 66, an adhesive 38 is applied from a hot melt gun 68 to the surface of the second breathable membrane 33 that will be bonded to the porous membrane 31. The temperature-controlled roll 66 adjusts the temperature so that the adhesive 38 applied to the second breathable membrane 33 maintains its adhesive strength. The second breathable membrane 33 and the porous membrane 31 are bonded by passing between the temperature-controlled roll 66 and a silicone rubber nip roll 67 with the adhesive 38 interposed therebetween. The sheet-like material formed by bonding the first breathable membrane 32, the porous membrane 31, and the second breathable membrane 33 in this manner is turned into a product via rolls 81, 82, 83, 84, 85, 86, and 87, and wound up onto the product roll 69.

[0118] The adhesive is preferably applied in a molten state. Here, it is preferable to warm the breathable film in order to prevent the adhesive from hardening in the breathable film. Even in this case, the breathable film is not heated above its melting point, and is preferably heated using temperature-controlled rolls 65, 66 at, for example, 35°C to 70°C, more preferably 40°C to 60°C. This prevents the breathable film from melting and prevents deformation of the fibers of the breathable film. Furthermore, even if the breathable film contains a component that can release organic gases due to heat, suppressing melting of the breathable film also prevents the release of organic gases from the breathable film. From the same perspective, it is preferable that the breathable film is bonded to the porous film without becoming molten even when heated by the temperature-controlled rolls 65, 66.

[0119] Furthermore, it is preferable that the hot melt adhesive is heated to a molten state when applied, but is not reheated after application. By minimizing the heating history of the hot melt adhesive in this way, it is possible to suppress the generation of organic gases, even if the hot melt adhesive contains components that can generate organic gases when heated.

[0120] The adhesive is preferably applied using an applicator. The applicator preferably has a plurality of discharge nozzles arranged in a row, and the molten resin discharged from each discharge nozzle is stretched by an air flow sent around each nozzle in the discharge direction at a speed faster than the discharge speed, thereby forming a desired fiber diameter for application. Here, by reducing the melt viscosity of the molten resin, the adhesive becomes more easily stretched, thereby enabling the fiber diameter to be made thinner. Furthermore, by increasing the speed of the air flow, the adhesive becomes more easily stretched, thereby enabling the fiber diameter to be made thinner.

[0121] The shape of the adhesive application is not particularly limited, but it is preferable to apply the adhesive so that multiple adhesive fibers are arranged side by side, with the direction perpendicular to the conveyance direction of the breathable membrane 32 being the longitudinal direction of the adhesive fibers, as shown in Figures 7 and 8. The adhesive application shape may be a wave shape in which peaks protruding in a direction intersecting the longitudinal direction of the adhesive fibers and valleys protruding on the opposite side to the peaks in a direction intersecting the longitudinal direction of the adhesive fibers are arranged alternately, as shown in Figure 7. Alternatively, the adhesive may be a wave shape in which peaks and valleys are arranged alternately so as to have a portion extending in a direction intersecting the longitudinal direction of the adhesive fibers, as shown in Figure 8.

[0122] The breathable membranes 32, 33 coated with the adhesive as described above are overlapped with the porous membrane 31, and pressure is applied by the nip rolls 64, 67. At this time, the breathable membranes 32, 33 and the porous membrane 31 are pressed against each other to obtain the air filter medium 30. Here, the pressure applied by the nip rolls 64, 67 to the laminate of the porous membrane and the breathable membrane bonded with the adhesive is preferably, for example, 0.6 MPa or less, from the viewpoint of suppressing the increase in the rate of pressure loss due to the pressure during lamination. Furthermore, the pressure applied by the nip rolls 64, 67 to the laminate of the porous membrane and the breathable membrane bonded with the adhesive is preferably, for example, 0.3 MPa or more, from the viewpoint of easily ensuring a good bonding state. The pressure can be measured, for example, using a pressure measurement film (Prescale manufactured by Fujifilm Corporation) as the instantaneous pressure when passing between the rolls. It is also preferable that the temperature of the nip rolls 64, 67 is not heated to a temperature higher than the melting point of the breathable membranes 32, 33.

[0123] In addition, for example, in the case of the manufacturing method that the porous membrane obtained by stretching is not wound up in roll form, is conveyed as it is, and is transferred to the process of bonding air permeable membrane, the thick air filter material that contains air permeable membrane must be rolled up and stored, so it will require space.On the other hand, as mentioned above, if the porous membrane that is not bonded with air permeable membrane is wound up in roll form and stored, and when the filter material that is bonded with air permeable membrane needs, carry out bonding process to obtain and ship the filter material, it can save space.

[0124] In addition, when the breathable film is melted and bonded to the porous film, it takes a long time to heat the fiber of the breathable film by heating roller until it is melted, so when the breathable film is bonded to the porous film by applying adhesive, the bonding process can be carried out in a shorter time.Here, when the porous film is produced, if the porous film is obtained by stretching for a certain time, the time required for the bonding of the porous film and the breathable film may be shorter than the time required for the stretching of the porous film.Therefore, if the porous film obtained by stretching is transported as it is without being wound into a roll, and the manufacturing method is transferred to the process of bonding the breathable film, the stretching process of the porous film is the rate-limiting step.On the other hand, if the manufacturing method is carried out by preparing a large number of porous film rolls that can be stored in a small space in advance, and the bonding process with the breathable film is carried out while sending out the porous film that is wound into a roll, it can save space and quickly obtain air filter material. [Example]

[0125] Hereinafter, the contents of the present disclosure will be specifically described with reference to examples and comparative examples.

[0126] In Example 1, a fluororesin porous membrane obtained as follows was bonded to an air-permeable membrane using an adhesive to obtain an air filter medium.

[0127] First, 300 g of hydrocarbon oil (IP Solvent 2028, manufactured by Idemitsu Kosan Co., Ltd.) was added as an extrusion liquid lubricant to 1 kg of PTFE fine powder (Polyflon Fine Powder F106, manufactured by Daikin Industries, Ltd.) with an average molecular weight of 6.5 million and mixed at 20°C. The resulting mixture was then extruded using a paste extrusion device to obtain a rod-shaped compact. This rod-shaped compact was then formed into a sheet using a calendar roll heated to 70°C to obtain a fluororesin sheet. This fluororesin sheet was then passed through a hot air drying oven at 250°C to evaporate and remove the hydrocarbon oil, yielding a strip-shaped unsintered fluororesin sheet with an average thickness of 200 μm and an average width of 150 mm.

[0128] Next, the unsintered fluororesin sheet was stretched in the longitudinal direction at a stretch ratio of 5. The stretching temperature in the longitudinal direction was 250°C, and the stretching rate (% / s) in the longitudinal direction was 150 (% / s).

[0129] Next, the stretched unsintered fluororesin sheet was stretched in the width direction at a stretching temperature of 350°C and a stretching ratio of 30 times using a tenter capable of continuous clipping, to obtain a fluororesin porous membrane. The fluororesin porous membrane was wound around a porous membrane roll. The average fiber diameter of the obtained fluororesin porous membrane was 69 nm.

[0130] Then, while the fluororesin porous membrane is sent out from the porous membrane roll, the breathable membrane coated with adhesive is stacked on the downwind side of the fluororesin porous membrane in the direction of air flow, and the breathable membrane is bonded to the fluororesin porous membrane through the nip roll, thereby obtaining the air filter material of embodiment 1.

[0131] The breathable film used in Example 1 was a spunbond nonwoven fabric (average fiber diameter 11 μm, basis weight 40 g / m) made of PET. 2 , thickness 230 μm).

[0132] The adhesive used in Example 1 was an olefin-based hot melt resin (manufactured by Asahi Chemical Synthetic Co., Ltd., product number: Asahi Melt FR921) having a melt viscosity of 1600 (mPa·s) at 180°C.

[0133] The adhesive was applied to the breathable membrane by spraying at a line speed of 30 m / min using an ITW Dynatec applicator. The applicator used was equipped with multiple nozzles whose adhesive ejection directions were parallel to each other. During application, the air flow speed was controlled to be faster than the adhesive ejection speed, so that the adhesive fibers stretched against the breathable membrane were applied in a wavy pattern. The opening size at the tip of the applicator's nozzle was 0.43 μm. 2 The size of the air outlet is 0.64 μm 2 The pump speed for pumping the adhesive in a molten state heated to 180°C was set to 6.4%, and air heated to 190°C was pumped at a flow rate of 3000 cm3 to stretch the adhesive fibers after the molten adhesive was discharged from the nozzle. 3 The adhesive applied in this manner had an average fiber diameter of 48.7 μm and an adhesive application rate of 3.2 g / m 2 It was.

[0134] In Example 1, there were no locations where multiple adhesive fibers substantially overlapped each other. Furthermore, in Example 1, when a 1 cm long imaginary line was drawn in a direction perpendicular to the longitudinal direction of any one of the multiple adhesive fibers, the average number of adhesive fibers intersecting the imaginary line was 2.5. In Example 1, the nip pressure when bonding the breathable membrane to the fluororesin porous membrane using nip rolls was 0.40 Pa.

[0135] In Example 1, in order to prevent the adhesive from curing in the breathable film before bonding with the fluororesin porous film, the breathable film to which the adhesive was applied was heated to 40°C using a temperature-control roll.

[0136] In Example 1, the peel strength (N / 35 mm) of the bonded porous membrane and breathable membrane was measured and found to be 0.15 (N / 35 mm). The peel strength was measured using a precision universal testing machine manufactured by Shimadzu Corporation, based on the JIS Z 0237:2009 180-degree peel test method, with a test piece width of 35 mm and a pulling speed of 100 mm / min (the same applies below). The increase in pressure loss due to the bonding of the porous membrane and breathable membrane was also determined and found to be 5.7% in Example 1.

[0137] In Example 2, a hot melt resin (Asahi Chemical Synthetic Co., Ltd., product number: Asahi Melt FR530) with a melt viscosity of 2050 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 42.6 μm, and the applied amount of adhesive was 3.0 g / m 2 The same as in Example 1 above, except that the nip pressure was 0.55 Pa. In Example 2 above, the peel strength (N / 35 mm) of the joined porous membrane and breathable membrane was measured and found to be 0.15 (N / 35 mm). In addition, the increase rate of pressure loss in Example 2 was 1.5%.

[0138] In Example 3, the breathable film material was a PET material copolymerized with a phosphorus-based flame retardant (average fiber diameter 12 μm, basis weight 50 g / m 2 The average fiber diameter of the adhesive was 45.8 μm, and the adhesive application amount was 3.1 g / m 2 The same as in Example 2 except that the nip pressure was 0.45 Pa. In Example 3, the peel strength (N / 35 mm) of the joined porous membrane and breathable membrane was measured and found to be 0.15 (N / 35 mm). In addition, the increase rate of pressure loss in Example 3 was 2.7%.

[0139] In Example 4, the hot melt resin of the adhesive was changed to Tomide 1310 manufactured by Fuji Chemical Industry Co., Ltd., which has a melt viscosity of 2500 mPa·s at 180°C, the average fiber diameter of the adhesive was 54.3 μm, and the amount of adhesive applied was 3.4 g / m 2The same as in Example 1 except that the nip pressure was 0.45 Pa. In Example 4, the peel strength (N / 35 mm) of the joined porous membrane and breathable membrane was measured and found to be 0.17 (N / 35 mm). In addition, the increase rate of pressure loss in Example 4 was 7.7%.

[0140] In Example 5, a hot melt resin (manufactured by Henkel, product number: TECHNOMELT MP801) with a melt viscosity of 4000 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 71.6 μm, and the coating amount of the adhesive was 4.2 g / m 2 The same as in Example 1 above, except that the nip pressure was 0.55 Pa. In Example 5 above, the peel strength (N / 35 mm) of the joined porous membrane and breathable membrane was measured and found to be 0.2 (N / 35 mm). In addition, the increase rate of pressure loss in Example 5 was 15.8%.

[0141] In Example 6, a hot melt resin (Asahi Chemical Synthetic Co., Ltd., product number: Asahi Melt FR561) with a melt viscosity of 4100 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 98.3 μm, and the applied amount of adhesive was 4.8 g / m 2 The same as in Example 1 above, except that the nip pressure was 0.50 Pa. In Example 6 above, the peel strength (N / 35 mm) of the joined porous membrane and breathable membrane was measured and found to be 0.25 (N / 35 mm). In addition, the increase rate of pressure loss in Example 6 was 17.2%.

[0142] According to the above examples, it was confirmed that when the average fiber diameter of the adhesive is increased, the rate of increase in pressure loss due to the adhesive fibers covering the porous membrane increases significantly. In particular, when Example 2 and Example 5, which have the same nip pressure, are compared, it can be seen that the rate of increase in pressure loss increases significantly as the average fiber diameter of the adhesive increases.

[0143] In Example 7, a synthetic rubber-based hot melt resin (Sanyo Life Material 939S) with a melt viscosity of 2300 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 102.2 μm, and the applied amount of adhesive was 4.7 g / m 2 A filter medium similar to that of Example 1 was obtained, except that the nip pressure was 0.55 Pa. In the filter medium of Example 7, the increase rate of pressure loss was 43.1%.

[0144] In Example 8, a hot melt resin (Asahi Chemical Synthetic Co., Ltd., product number: Asahi Melt FR921) with a melt viscosity of 1600 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 45.3 μm, and the applied amount of adhesive was 3.1 g / m 2 The filter medium of Example 8 was the same as Example 1 except that the nip pressure was 0.75 Pa. In the filter medium of Example 8, the increase rate of pressure loss was 23.1%.

[0145] In Example 9, a hot melt resin (Asahi Chemical Synthetic Co., Ltd., product number: Asahi Melt FR530) with a melt viscosity of 2050 mPa·s at 180°C was used, the average fiber diameter of the adhesive was 43.7 μm, and the applied amount of the adhesive was 3.0 g / m 2 The filter medium of Example 9 was the same as Example 1 except that the nip pressure was 0.90 Pa. In the filter medium of Example 9, the increase rate of pressure loss was 50.8%.

[0146] In Example 10, a PP-based hot melt adhesive was used as the adhesive, and the adhesive was spray-applied using an applicator equipped with a plurality of nozzles whose discharge directions for discharging the adhesive were randomly oriented. The average fiber diameter of the adhesive was 116 μm, and the applied amount of adhesive was 5 g / m. 2 The support layer is made of PET material copolymerized with a phosphorus-based flame retardant (average fiber diameter 12 μm, basis weight 50 g / m 2An air filter medium was obtained in the same manner as in Example 1 above, except that a porous membrane and a breathable membrane (thickness 260 μm) were used. In the above Example 10, the peel strength (N / 35 mm) of the bonded porous membrane and breathable membrane was measured, and the porous membrane was broken without being able to be peeled off from the breathable membrane. In the above Example 10, the adhesive fibers were randomly applied, so there was a large amount of overlap between the adhesive fibers. Specifically, in Example 10, an average of five overlapping points between the adhesive fibers per adhesive fiber were confirmed. In Example 10, the peel strength was confirmed to be strong enough to cause membrane rupture, but the increase rate of pressure loss was 39.2%.

[0147] According to Examples 1-10, when the porous fluororesin membrane and the nonwoven fabric are bonded together, the porous fluororesin membrane and the nonwoven fabric are prevented from being directly heated by the rolls. Therefore, when the porous fluororesin membrane and the nonwoven fabric have predetermined functions, the functions are prevented from being deteriorated by heat.

[0148] The increasing rate of above-mentioned pressure loss is measured by the pressure loss of the laminated product that only overlaps porous membrane and breathable membrane and is not bonded to each other, and the pressure loss of the air filter material that porous membrane and breathable membrane are bonded to each other with adhesive, and the increasing rate of pressure loss that accompanies bonding is calculated as follows:

[0149] (Pressure loss of laminate before bonding) The measurement sample, which was simply a porous membrane with an air-permeable membrane laminated on it but not bonded to it, was set in a filter holder with a diameter of 100 mm, and the inlet side was pressurized with a compressor, and the air flow rate was adjusted to 5.3 cm / sec using a flow meter. The pressure loss at this time was measured with a manometer.

[0150] (Pressure loss of the air filter media after bonding) A measurement sample of an air filter medium, in which a porous membrane and a breathable membrane were bonded with an adhesive, was set in a filter holder with a diameter of 100 mm, and the inlet side was pressurized with a compressor, and the air flow rate was adjusted to 5.3 cm / sec using a flow meter. The pressure loss at this time was measured with a manometer.

[0151] (Increase in pressure loss) From the pressure loss of the laminate and the pressure loss of the air filter medium measured as described above, the rate of increase in pressure loss was calculated according to the following formula. Pressure loss increase rate (%) = (pressure loss of air filter media / pressure loss of laminate) x 100 - 100

[0152] In addition, as Comparative Example 1, an air filter medium was obtained by thermally laminating the same fluororesin porous membrane as in Example 1 and a core-sheath nonwoven fabric (spunbond nonwoven fabric manufactured by PT MULTI SPUNINDO JAYA) with PE as the core and PET as the sheath.

[0153] In addition, as Comparative Example 2, an air filter medium was obtained by thermally laminating the same fluororesin porous membrane as in Example 1 and a core-sheath nonwoven fabric (manufactured by Unitika, product number: Elbes) with PE as the core and PET as the sheath.

[0154] In the air filter media of Comparative Example 1 and Comparative Example 2, the opposite side of the bonded surface of the fluororesin porous membrane with the nonwoven fabric and the opposite side of the bonded surface of the nonwoven fabric with the fluororesin porous membrane are pressed against a roll that is heated to 200 ° C, which is the temperature that exceeds the melting point of the resin that constitutes the sheath of the nonwoven fabric, to carry out thermal lamination.In such Comparative Examples 1 and 2, the opposite side of the bonded surface is heated the most, so the shape change degree of the surface opposite to the bonded surface of the nonwoven fabric is large.In addition, in the air filter media of Comparative Example 1 and Comparative Example 2, the nonwoven fabric and the fluororesin porous membrane are exposed to high temperature, so even if the nonwoven fabric and the fluororesin porous membrane have a predetermined function, the function will be deteriorated by heat.

[0155] In addition, for each of the air filter media of Examples 1-9 and Comparative Examples 1-2, the amount of outgassing was measured according to the dynamic headspace method as follows. In the measurement of the amount of outgassing, a 120mm x 40mm test piece was placed in a thermostatic chamber at 40°C for 60 minutes, and organic matter was desorbed from the test piece. A high-purity helium gas of 99.9999% was passed through the thermostatic chamber, and the gas that had passed through was sent to an adsorption tube to capture the generated organic matter. The captured organic matter was analyzed by gas chromatography mass spectrometry (GC-MS). The amount of outgassing was 52 μg / m for Example 1, 52 μg / m for Example 2, and 52 μg / m for Comparative Example 3. 2 , and Example 2 is 112 μg / m 2 , and Example 3 is 454 μg / m 2 , and Example 4 is 150 μg / m 2 , and Example 5 is 114 μg / m 2 , and Example 6 is 68 μg / m 2 , and Example 7 is 850 μg / m 2 , and Example 8 is 60 μg / m 2 , and Example 9 is 105 μg / m 2 , and Comparative Example 1 is 550 μg / m 2 , and Comparative Example 2 is 814 μg / m 2 It was confirmed that the amount of outgassing was particularly increased in Example 7, which used a synthetic rubber hot melt adhesive.

[0156] Furthermore, a flammability test was conducted using the UL94-HF method on each of the filter media of Examples 1-6 and Comparative Examples 1 and 2 above, and it was found that Example 1 was equivalent to HF-1, Example 2 was equivalent to HF-1, Example 3 was equivalent to HF-1, Example 4 was equivalent to HF-1, Comparative Example 5 was equivalent to HF-1, Comparative Example 6 was equivalent to HF-1, Comparative Example 1 was equivalent to HBF, and Comparative Example 2 was equivalent to HBF.

[0157] In Example 11, an air filter medium was obtained in the same manner as in Example 2, except that a core-sheath nonwoven fabric (spunbond nonwoven fabric manufactured by PT MULTI SPUNINDO JAYA) with a PE core and a PET sheath was used as the breathable membrane, coated with an antifungal agent. An organic synthetic antifungal agent (pyridine-based) was used as the antifungal agent.

[0158] Furthermore, as Comparative Example 3, use the same fluororesin porous membrane and breathable membrane as in Example 11, but do not use adhesive to bond the fluororesin porous membrane and breathable membrane, but bond by thermal lamination to obtain an air filter material similar to Example 11. In Comparative Example 3, similar to above Comparative Example 1 and Comparative Example 2, the heat lamination is carried out by pressing a roll that is heated to 200 ° C, which is the temperature that exceeds the melting point of the resin that constitutes the sheath of nonwoven fabric, against the opposite side of the bonded surface of the fluororesin porous membrane and the opposite side of the bonded surface of the nonwoven fabric and the fluororesin porous membrane, respectively.

[0159] A simple antifungal test was conducted on the above-mentioned Example 11 and Comparative Example 3, as a test conforming to the mold resistance test (JIS Z2911). In the simple antifungal test, a sample was cut into 20 mm x 20 mm pieces, and the Cladosporium fungus was used as the fungus species. The sample was placed on a potato dextrose agar medium, and a suspension with a spore suspension concentration of approximately 1000 RLU (ATP was measured using a Lumitester Smart manufactured by Kikkoman Biochemifa Corporation and used as a guide for the suspension concentration) was inoculated. The inoculation volume of the turbid liquid was 0.1 mL. The sample was left at room temperature for 8 days, and the condition of mold growth on the sample surface was observed with the naked eye.

[0160] In the simple antifungal test of Example 11, mold growth in the inoculated area was not visible to the naked eye. In the simple antifungal test of Comparative Example 3, mold growth in the inoculated area was clearly visible to the naked eye. When a similar antifungal test was carried out using only the breathable film coated with the antifungal agent (without the fluororesin porous film bonded thereto) as a sample, mold growth in the inoculated area was also not visible to the naked eye.

[0161] In addition, as Example 12, an air filter medium similar to Example 2 was obtained, except that a melt-blown nonwoven fabric (MPPW025 manufactured by HEIGEN) made of polypropylene (PP) was used as the breathable film.

[0162] Furthermore, as Comparative Example 4, use the same fluororesin porous film and breathable film as in Example 12, but do not use adhesive to bond the fluororesin porous film and breathable film, but bond by thermal lamination, obtain an air filter material similar to Example 12. In Comparative Example 4, the thermal lamination is carried out by pressing a roll that is heated to 150 ° C, which is the temperature that exceeds the melting point of the resin that constitutes the sheath of nonwoven fabric, against only one side of the surface that is opposite to the surface that is bonded with the fluororesin porous film in nonwoven fabric.

[0163] In Example 12, in which the breathable membrane was heated to 40°C by the temperature-regulating rolls, and in Comparative Example 4, in which the breathable membrane was heated to 150°C by thermal lamination, changes in size were measured for a sample of a predetermined area before and after bonding of the fluororesin porous membrane and the breathable membrane. No change was observed in Example 12, whereas in Comparative Example 4, the area had shrunk to about 95%, and wrinkles were formed in the resulting air filter medium in Comparative Example 4.

[0164] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure as defined in the claims. [Explanation of symbols]

[0165] 1 Air filter unit 20 Filter packs, pleated filter media 25 Frame 30 Air filter media 31 Porous membrane 32 First breathable membrane (breathable membrane) 33 Second breathable membrane (breathable membrane) 38 Hot melt adhesive [Prior art documents] [Patent documents]

[0166] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-297702

Claims

1. A first step of preparing a porous membrane (31) and breathable membranes (32, 33); A second step of bonding the porous membrane and the breathable membrane using a molten hot melt adhesive (38); A method for manufacturing an air filter medium, comprising: The breathable membrane is provided on the windward side or the leeward side of the porous membrane in the direction of air flow through the air filter medium, In the second step, the temperature of the breathable film is lower than the temperature of the molten hot melt adhesive. A method for manufacturing an air filter medium (30).

2. Either the porous film or the breathable film is a meltblown nonwoven fabric, a spunbond nonwoven fabric, or a film containing one or more selected from the group consisting of antibodies, antibacterial agents, and antifungal agents. A method for producing the air filter medium according to claim 1.

3. The porous membrane is a polytetrafluoroethylene porous membrane. The method for producing the air filter medium according to claim 1 or 2.

4. The breathable film contains one or more materials selected from the group consisting of polyethylene terephthalate, polyethylene, polyphenylene sulfide, polypropylene, and polyamide. The method for producing the air filter medium according to claim 1 or 2.

5. The porous membrane and the breathable membrane are bonded together using the fibrous hot melt adhesive. The method for producing the air filter medium according to claim 1 or 2.

6. In the second step, the hot melt adhesive in the molten state is discharged from a nozzle, and the hot melt adhesive is stretched using an air flow having a speed faster than the discharge speed of the hot melt adhesive from the nozzle, thereby fiberizing the hot melt adhesive. The method for producing the air filter medium according to claim 5.

7. A plurality of fibrous hot melt adhesives are arranged so as to share a common longitudinal direction. The method for producing the air filter medium according to claim 5.

8. The hot melt adhesive has a melt viscosity at 180°C of 1000 mPa·s or more and 2500 mPa·s or less. The method for producing the air filter medium according to claim 1 or 2.

9. The hot melt adhesive is one or more types selected from the group consisting of polyolefin-based resins and polyamide-based resins. The method for producing the air filter medium according to claim 1 or 2.

10. the average fiber diameter of the porous membrane, the average fiber diameter of the adhesive, and the average fiber diameter of the breathable membrane are expressed as average fiber diameter of the porous membrane: average fiber diameter of the adhesive: average fiber diameter of the breathable membrane = 1 / 2000 to 1 / 30: 1 to 6: 1, The method for producing the air filter medium according to claim 1 or 2.

11. A first step of preparing a porous membrane (31) and breathable membranes (32, 33); A second step of bonding the porous membrane and the breathable membrane using a molten hot melt adhesive (38); Equipped with In the second step, the temperature of the breathable film is lower than the temperature of the molten hot melt adhesive, After the second step, the sheet having the porous membrane, the hot melt adhesive, and the breathable membrane is passed between a pair of rolls, When passing between the rolls, the sheet is subjected to a pressure of 0.3 Pa or more and 0.6 Pa or less. A manufacturing method for air filter media.

12. A porous membrane (31); a breathable membrane (32, 33); a hot melt adhesive (38) for bonding the porous membrane and the breathable membrane; An air filter medium comprising: The breathable membrane is provided on the windward side or the leeward side of the porous membrane in the direction of air flow through the air filter medium, the degree of thermal deformation of the fibers in the portion of the breathable membrane opposite to the porous membrane side is smaller than the degree of thermal deformation of the fibers in the portion of the breathable membrane on the porous membrane side; Air filter media (30).

13. 13. The air filter medium according to claim 12, wherein the filter pack (20) is folded so as to create mountain folds and valley folds.

14. An air filter medium according to claim 12 or a filter pack (20) according to claim 13; A frame (25) for holding the air filter medium or the filter pack; An air filter unit (1) comprising:

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