METAL MEMBRANE FILTER AND ITS MANUFACTURING METHOD

Abstract

To provide a metal film piece formation filter capable of obtaining an excellent antibacterial effect such as a HEPA filter even when depositing a metal film on a base material having a thickness and simply manufactured at a low cost, and a method for manufacturing the same.SOLUTION: A metal film piece formation filter 1 is obtained by dipping a filter into a metal film piece formation composition including: a metal precursor liquid including a reaction product between at least one kind selected from a group consisting of a metal complex and metal salt and at least one kind selected from ammonia and amine; and an organic reductant; and drying the filter to form metal film pieces 3 on the surface of each filament of a filter paper constituting at least the filter 2 in a dispersion state. Electrical resistances between two points on a plane and between two points of the front and rear surfaces are 100 MΩ or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a metal film piece-formed filter in which metal is applied in a dispersed state to a filter, and to a method for producing the same. [Background technology]

[0002] In general, deodorizing fiber sheets and bactericidal filters are known that are designed to exhibit deodorizing or sterilizing effects by forming a film of a metal such as Cu on a fiber filter (see, for example, Patent Documents 1 to 3).

[0003] Conventionally, a method for forming a metal film on such sheets or filters has been to immerse them in a special solution and then dry them, so that the film has good electrical and thermal conductivity (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 52-44458 [Patent Document 2] Japanese Patent Application Publication No. 58-8530 [Patent Document 3] JP 2006-14965 A [Patent Document 4] Patent Publication No. 2021-70873 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as in the above-mentioned conventional film-forming method, when the film is formed so that the electrical conductivity and thermal conductivity are good, electrons can freely move in the metal film on the surface of the substrate. That is, in the metal film formed by the above-mentioned conventional film-forming method, electrons are released from the surface of the metal and metal oxide, react with oxygen in the air to generate superoxide, and the superoxide reacts with moisture in the air to generate active oxygen, which exerts antibacterial properties. However, since the entire bactericidal filter formed by the metal film is a conductor, if a potential difference occurs at a specific part of the metal film due to an external factor, the movement of free electrons is restricted, and the electron emission is easily biased, making it difficult for the entire metal film to exert an antibacterial effect evenly. In particular, when the substrate on which the metal film is formed has a thickness and the environment is completely different between the surface and the inside, such as a HEPA filter with a separator between bellows-shaped filter papers and fixed with a frame, the phenomenon becomes significant, and excellent antibacterial performance cannot be obtained.

[0006] In addition, when the bactericidal filter made of the metal film is used as a purification filter for various fluids, the bactericidal filter is used to capture dust in the fluid that has passed through the bactericidal filter to purify the fluid, but in this case, the dust is not captured evenly in the thickness direction of the bactericidal filter, but is usually captured from the upstream side surface through which the fluid passes. Therefore, even if the downstream side surface of the bactericidal filter is clean, the upstream side surface is clogged with dust, so a guideline for replacement is given for one to several months, and disposable types are usually used by replacing with a new one each time. Therefore, even if a dense metal film is formed to have good electrical conductivity, the bactericidal filter itself must be replaced with a new one before the antibacterial effect of the metal film is exhausted, and the manufacturing cost for forming a dense metal film that ensures electrical conductivity and the densely formed metal film itself are wasted.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a metal film piece-formed filter and a manufacturing method thereof that can obtain a good antibacterial effect even when a metal film is formed on a thick substrate, such as a HEPA filter, and that can be manufactured simply and inexpensively. [Means for solving the problem]

[0008] In order to solve the above problems, the metal film piece-forming filter of the present invention is obtained by immersing a filter in a composition for forming a metal film piece, the composition containing a metal precursor liquid having a reaction product of at least one selected from the group consisting of metal complexes and metal salts with at least one selected from ammonia and amines, and an organic reducing agent, and then drying the filter, whereby metal film pieces are formed in a dispersed state at least on the surface of each filament of the filter paper constituting the filter, and the electric resistance between two points on the flat surface and between two points on the front and back is 100 MΩ or more. The filter is cut into a size of 30 mm x 30 mm, sterilized, and then placed in a sterilized petri dish, and NBRC3972 Escherichia coli is inoculated with a phosphate buffer solution. 9×10 5 ~3×10 6 0.1 ml of test bacteria solution adjusted to a concentration of cfu / ml was dropped and incubated at 35±1°C for 90 minutes. After thorough washing using 9.9 ml of SCDLP medium, the solution was serially diluted up to 1:10,000 with water. Each diluted solution was incubated at 35±1°C for 48 hours using the agar plate culture method, resulting in a viable bacteria count of 0.

[0010] The metal of the metal film piece formed filter may be Cu.

[0011] In the above-mentioned metal film piece formed filter, the filter may be a HEPA filter.

[0012] In order to solve the above problems, the present invention provides a method for producing a metal film piece-formed filter, which comprises the steps of immersing a filter in a metal film piece-forming composition containing a metal precursor liquid having a reaction product of at least one selected from the group consisting of metal complexes and metal salts with at least one selected from ammonia and amines, and an organic reducing agent, and drying the filter after the immersion, thereby producing a metal film piece-formed filter on the surface of each filament constituting the filter. By adjusting the immersion time, immersion pressure, and number of immersion and drying cycles, the metal film pieces are formed in a dispersed state at least on the surface of each filament of the filter paper constituting the filter so that the electrical resistance between two points on the plane and between two points on the front and back is 100 MΩ or more.

[0013] The method for producing the metal film filter is as follows: cut the filter into pieces of 20 mm × 20 mm, sterilize the pieces, place them in a sterilized petri dish, and infuse NBRC3972 E. coli at 9 × 10 with phosphate buffer. 5 ~3×10 6 0.1 ml of a test bacteria solution adjusted to a concentration of cfu / ml is dropped and incubated at 35±1°C for 90 minutes. After thorough washing using 9.9 ml of SCDLP medium, the solution is serially diluted up to 1:10,000 diluted water, and each diluted solution is incubated at 35±1°C for 48 hours using the agar plate culture method. The immersion time, immersion pressure, and number of immersions and drying times may be adjusted so that the viable cell count obtained is 0.

[0014] The method for producing the metal film piece-formed filter may involve one cycle of immersion and drying under atmospheric pressure for one day.

[0015] [Metal precursor liquid] The metal precursor liquid is obtained by reacting at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine in a mixed liquid of at least one selected from the group consisting of a metal complex and a metal salt, at least one selected from ammonia and an amine, and a solvent.

[0016] [At least one selected from the group consisting of metal complexes and metal salts] The at least one selected from the group consisting of the above metal complexes and metal salts may be only one or more types of metal complexes, only one or more types of metal salts, or a mixture containing both one or more types of metal complexes and one or more types of metal salts.

[0017] The metal complex is preferably a reaction product of one or more compounds for forming a metal complex selected from compounds having a partial structure of a NH3 ligand, an RNH2 ligand (R represents an alkylene group), an OH2 ligand, and a ligand derived from a diamine such as ethylenediamine or hexamethylenediamine, which can generate a metal complex, and a metal ion. The metal complex may be a metal complex previously generated by the above reaction. As the metal in the metal complex, a metal according to the purpose of the metal film to be formed may be used. Examples of the metal include silver (Ag), copper (Cu), lithium (Li), nickel (Ni), manganese (Mn), zinc (Zn), and cobalt (Co). Specific examples of the metal complex include ethylenediaminetetraacetate copper, tetraammine copper, and the like, which contain copper (Cu) as a metal.

[0018] The metal salt is a metal compound having a function of dissociating in a solvent containing water to become metal ions and forming a metal complex. The metal salt refers to a metal salt that is soluble in water at 25°C. Soluble in water at 25°C means that the solubility in water at 25°C is 0.1% by mass or more, and the solubility is preferably 1% by mass or more. When the metal salt is soluble in water, the metal salt dissociates in a solvent containing water to become metal ions, and the metal ions react with amines contained in the solvent to obtain a metal complex. Furthermore, when a compound for forming a complex described later is optionally contained in the solvent, the metal ions may react with the compound for forming a complex to form a metal complex.

[0019] [At least one selected from ammonia and amines] The at least one selected from the above ammonia and amine may be only one or more types of ammonia, may be only one or more types of amine, or may be a mixture containing both one or more types of ammonia and one or more types of amine. These may be included as salt compounds. The amines include primary amines, secondary amines, and tertiary amines. Specific examples of amines include alkylamines. Instead of amines or in addition to amines, ammonia may be included. As ammonia, various substances having basicity similar to amines can be used.

[0020] [solvent] The solvent is not particularly limited as long as it can dissolve at least one selected from the group consisting of the above-mentioned metal complexes and metal salts, and at least one selected from the above-mentioned ammonia and amines, and for example, an aqueous solvent such as water or a mixture of water and alcohol can be used. It is preferable that the water contains a small amount of impurities, particularly ions other than metal ions, and from this viewpoint, it is preferable to use purified water, ion-exchanged water, pure water, etc. Examples of alcohol include monohydric alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, isopropanol, n-propanol, isobutanol, and n-butanol, and polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, and glycerin.

[0021] From the viewpoint of solubility and handling, the aqueous solvent is preferably water or a mixture of water and a monohydric alcohol having 1 to 5 carbon atoms, more preferably water or a mixture of water and an alcohol selected from methanol, ethanol and propanol, and even more preferably water. When using a mixture of water and alcohol as a solvent, the mixing ratio is appropriately selected depending on the purpose. When using a mixture of water and alcohol as a solvent, the content of alcohol in the total amount of the mixture of water and alcohol is preferably 1% by mass to 60% by mass.

[0022] [Preparation of metal precursor liquid] The metal precursor liquid can be prepared by adding at least one selected from the group consisting of the above-mentioned metal complexes and metal salts, and at least one selected from the above-mentioned ammonia and amines in a solvent, and thoroughly stirring and mixing the mixture.

[0023] Mixing may be performed at room temperature, or for the purpose of promoting dissolution, the solvent may be heated to 40° C. to 60° C. The stirring method is not particularly limited, and any known stirring method can be used, such as a method of putting the mixed solution into a container and stirring it using a rotor such as a magnetic stirrer, a method of stirring with a stirring device equipped with a rotary stirring blade such as a paddle, a method of putting the solution into a sealable container and stirring by shaking the container, and a method of irradiating with ultrasound.

[0024] A simple method is to use a stirring device equipped with a stirring blade. The rotation speed of the rotor can be 300 rpm (revolutions / minute: the same below) to 800 rpm, and preferably 400 rpm to 600 rpm. The stirring is preferably performed until the reaction between at least one selected from the group consisting of the above-mentioned metal complexes and metal salts and at least one selected from the above-mentioned ammonia and amines proceeds sufficiently, and when stirring is performed at room temperature using the above-mentioned stirring device equipped with a rotor, stirring is preferably performed for about 30 minutes to 90 minutes, and more preferably for about 50 minutes to 80 minutes. For example, when preparing a metal precursor liquid containing a copper complex, the metal precursor liquid that has been thoroughly stirred exhibits a blue color due to copper ions.

[0025] The above-mentioned metal precursor liquid may be prepared by applying a known molecular precursor method. In addition, the preparation of the metal precursor liquid can be performed by applying a known precursor method as described above, but from the viewpoint of obtaining a metal precursor with higher purity, it is preferable to include the following electrolysis step. That is, this electrolysis step is a step of storing an amine-containing electrolytic solution in each of the pair of electrolytic solution tanks in a reaction apparatus equipped with a pair of electrolytic solution tanks connected via a flow path equipped with a filter that does not allow metal ions to pass through but can allow hydrogen ions to pass through, and arranging a pair of metal electrodes at a position where at least a part of the electrodes contacts the electrolytic solution, and connecting the pair of electrodes via a DC power source, and applying a voltage between the pair of electrodes by a DC power source, and reacting the metal ions derived from the metal that is the electrode with the electrolytic solution in the electrolytic solution tank in which the electrode that becomes the anode is immersed to obtain a metal precursor liquid.

[0026] [Organic reducing agents] The organic reducing agent preferably includes at least one selected from compounds having a carboxy group. The organic reducing agent is preferably appropriately selected from organic carboxylic acid compounds having a carboxy group in the molecule and functioning as a reducing agent.

[0027] Examples of the organic reducing agent include at least one selected from ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid, and from the viewpoint of better formability of the metal film pieces, at least one selected from ascorbic acid, citric acid, and 3,4,5-trihydroxybenzoic acid is preferable, and at least one selected from ascorbic acid and citric acid is more preferable. One of the preferred aspects of the composition for forming metal film pieces is to include ascorbic acid as the organic reducing agent.

[0028] The organic reducing agent is preferably used as an aqueous solution. The water used to prepare the aqueous solution does not contain metal ions or has a metal ion concentration as low as possible from the viewpoint of uniformity of the obtained metal film. Therefore, the water used to prepare the aqueous solution is preferably purified water, ion-exchanged water, pure water, etc., for example. When dissolving the organic reducing agent in water, the water as the solvent may be heated to 30°C to 60°C, preferably to 35°C to 45°C, for the purpose of improving solubility. The dissolution may be performed with stirring, and the stirring method mentioned in the above-mentioned section on the method for preparing the solution of the metal complex can be appropriately applied in the same manner. The content of the specific reducing agent in the aqueous solution of the organic reducing agent is preferably in the range of 10% by mass to 40% by mass, more preferably in the range of 10% by mass to 30% by mass. When the content of the organic reducing agent relative to the total amount of the aqueous solution is 10% by mass or more, the aqueous solution contains a sufficient amount of organic reducing agent for the reaction, and when the content is 40% by mass or less, the stability of the aqueous solution is better.

[0029] [Preparation of composition for forming metal film pieces] The metal film piece forming composition is obtained by mixing the metal precursor liquid and the organic reducing agent, and the mixing ratio of the metal precursor liquid and the organic reducing agent is not particularly limited and can be appropriately selected according to the target metal. The metal ion contained in the metal precursor liquid can be 50 parts by mass to 400 parts by mass relative to 100 parts by mass of the organic reducing agent contained in the metal film piece forming composition, and from the viewpoint of obtaining a better formability of the metal film piece of the metal film piece forming composition, it is preferable that the metal ion contained in the metal precursor liquid is 100 parts by mass to 350 parts by mass relative to 100 parts by mass of the organic reducing agent, and it is more preferable that the metal ion contained in the metal precursor liquid is 150 parts by mass to 350 parts by mass relative to 100 parts by mass of the organic reducing agent.

[0030] By setting the content of metal ions relative to the organic reducing agent within the above preferred range, metal film pieces can be formed more efficiently on the surface of each filament constituting the filter. If the mixing ratio of the metal precursor liquid to 100 parts by mass of the organic reducing agent is less than 50 parts by mass, the metal is difficult to precipitate quickly, and if it exceeds 400 parts by mass, the reducing power of the metal ions becomes insufficient. The content of the metal precursor liquid in the preparation of the composition for forming metal film pieces can be controlled by adjusting the type and content of the metal complex when preparing the metal precursor liquid, or the type of electrolyte, the concentration of the electrolyte, the applied energy of the direct current, the application time, etc. in the electrolysis process when preparing the above-mentioned metal precursor liquid.

[0031] In general, it is difficult to measure the content of a specific metal compound relative to the total amount of the composition for forming metal film pieces. However, the physical properties of the metal film pieces formed by the composition for forming metal film pieces depend on the metal content in the composition for forming metal film pieces. From the viewpoint of forming stable metal film pieces, the metal content relative to the total amount of the composition for forming metal film pieces is preferably in the range of 0.5% by mass to 10% by mass, and more preferably in the range of 1% by mass to 8% by mass. When the metal content is in the above range, the structure of the metal film pieces formed by the composition for forming metal film pieces becomes more uniform, and stable metal film pieces can be formed.

[0032] The metal content in the composition for forming metal film pieces can be measured, for example, by the method described in "Basics of Coordination Chemistry: Werner Complexes and Organometallic Complexes" (KS Chemistry Specialist Book: Kodansha, 1989).

[0033] The content of the specific reducing agent in the composition for forming metal film pieces can be measured, for example, by the following method. First, the composition for forming metal film pieces is dried to prepare a powder. The obtained powder is analyzed using a thermogravimeter-differential thermal analyzer (TG-DTA) to measure the content of the specific reducing agent.

[0034] The pH of the composition for forming metal film pieces at room temperature (25° C.) is preferably 6 to 8, and more preferably in the neutral range of about pH 7.5. The pH can be measured with a known pH meter.

[0035] [filter] As the filter, various air filters that can be used for the purpose of removing dirt, dust, etc. from the air and making the air clean can be used. Specific examples of the filter include a HEPA filter that has a particle collection rate of 99.97% or more for particles with a particle size of 0.3 μm at a rated air volume and an initial pressure loss of 245 Pa or less. However, in addition to this HEPA filter, a quasi-HLPA filter that has a particle collection rate of 95 to 99% for particles with a particle size of 0.3 μm at a rated air volume and an initial pressure loss of 245 Pa or less may be used, or a MEPA filter that has a particle collection rate of 50 to 95% or more for particles of 0.4 and 0.7 μm, or even a low-grade coarse dust filter may be used. These filters can collect dust and other particles by blocking the flow line of the particles with the filter paper that constitutes the filter. The fiber filaments that make up this filter paper may be inorganic fibers such as glass fibers, or organic fibers such as polyethylenes such as PET, low-density polyethylene (LDPE), and high-density polyethylene (HDPE), polycarbonate (PC), polyvinyl chloride (PVC), polystyrene, acrylic resins such as polymethyl methacrylate (PMMA), polyamides such as nylon 6, phenolic resins, melamine resins, urethane resins, and carbon fibers, or natural fibers such as silk, cotton, cellulose, and hemp.

[0036] [Manufacturing of metal film filters] The above-mentioned metal film piece-forming filter is manufactured by immersing the filter in the above-mentioned metal film piece-forming composition and drying it, so that metal film pieces are dispersed and formed on at least the surface of each filament of the filter paper constituting the filter. In this case, the immersion time, immersion pressure, and number of immersions and drying are not particularly limited as long as they are conditions that can form metal film pieces in a dispersed state on at least the surface of each filament of the filter paper constituting the filter so that the electrical resistance between two points on the plane of the completed metal film piece-forming filter and between two points on the front and back is 100 MΩ or more. The immersion time, immersion pressure, and number of immersions and drying are each subjected to a batch test, and the immersion time, immersion pressure, and number of immersions and drying that satisfy the corresponding conditions can be adopted. The immersion time is, for example, preferably 6 hours or more at room temperature (25°C), and more preferably 12 hours or more. When it is desired to increase the membrane thickness, the immersion time or storage time can be 24 hours or more. In the case of a filter such as a HEPA filter, which is constructed by folding a continuous filter paper into an accordion shape and placing a separator between each accordion and then fitting it into a frame, the entire filter may be immersed in a composition for forming metal film pieces to form metal film pieces on the entire filter, or in a manufacturing process, one or more of the filter paper, separator, and frame, including at least the filter paper, may be immersed in a composition for forming metal film pieces to form metal film pieces on at least one of the filter paper, separator, and frame, including at least the filter paper, and then the filter may be manufactured in a subsequent process.

[0037] There is no particular limit to the upper limit of the immersion time, but from the viewpoint of productivity, it can be 120 hours or less, and preferably 90 hours or less. In this case, by setting the temperature of the composition for forming metal film pieces to room temperature or higher, for example, 30°C or higher, preferably 40°C or higher, the reaction rate increases and metal film pieces can be formed in a shorter storage time. From the viewpoint of not affecting the composition for forming metal film pieces, the temperature is preferably 80°C or less. For example, when the atmospheric temperature is 35°C, the storage time is preferably 4 hours or more, and more preferably 8 hours or more. The upper limit of the storage time is the same as that at room temperature.

[0038] The immersion pressure may be normal atmospheric pressure, or may be reduced pressure or increased pressure. The filter may be immersed without degassing the air bubbles trapped between the filaments of the filter paper constituting the filter, or may be immersed after degassing. When degassing, the nonwoven fabric surface may be physically pressed, or the immersion pressure may be changed.

[0039] Drying can be performed by a conventional method such as natural drying, heat drying, and blow drying, which are generally performed. In the case of natural drying, it is sufficient to leave it at room temperature for 60 minutes to 5 hours. In the case of heat drying, a known heating means can be appropriately selected and applied. Examples of the heating method include a method of contacting a heating means such as a plate-shaped heater or a heat roll from the back side of the substrate, a method of passing through a heating zone such as an electric furnace, a method of irradiating energy rays such as infrared rays or microwaves, and a method of blowing hot air. There is no particular limit to the heating temperature during heat drying. Considering the drying efficiency and suppression of the influence on the substrate, the heating temperature can be in the range of 30°C or more and less than 100°C, and is preferably in the range of 30°C to 60°C. From the viewpoint of productivity, the drying time during heat drying is preferably in the range of 10 seconds to 20 minutes. In the case of blow drying, it may be blown with air under the environmental atmosphere, or it may be blown with hot air as described above.

[0040] The amount of metal constituting the metal film piece by the metal film piece forming composition is not particularly limited, but in fact, when the metal film piece forming filter is used as a filter for fluid filtration, it has a lifespan set for its original purpose as a filter, so it generally has a replacement period of one to several months or one to several years. Therefore, even if a dense metal film having a conductivity of less than 100 MΩ is formed, the filter itself has a lifespan, so the metal constituting the metal film is often wasted to the extent that it is formed densely. In addition, if a large amount of metal constituting the metal film piece is attached, the pressure loss at the rated air volume of the metal film piece attached filter to which the metal film piece is attached increases, and the initial performance is greatly changed. Therefore, it is most efficient for a metal film piece forming filter to form a metal film with as little metal attachment as possible that can efficiently obtain an antibacterial effect during the lifespan of the filter. Specifically, this condition (electrical resistance of 100 MΩ or more between two points on the flat surface of the metal film piece-forming filter and between two points on the front and back) can be easily met if the immersion time is short, the immersion pressure is close to normal pressure, and the number of immersions and dryings is small; therefore, in the case of the composition for forming metal film pieces according to the examples described below, this can be achieved by simply immersing and drying once.

[0041] The dispersion state of the metal film pieces formed in the metal film piece-forming filter can be confirmed by the electric resistance between two points on the plane of the metal film piece-forming filter, between two points on the front and back of the filter being non-conductive at 100MΩ or more, but ideally, it is preferable that the metal film pieces are formed in a uniformly dispersed state at least on each filament of the filter paper that constitutes the filter from the surface to the inside of the filter.When the filter is immersed in the composition for forming metal film pieces, the composition for forming metal film pieces can be uniformly contacted with the entire surface of each filament of the filter paper that constitutes the filter from the surface to the inside of the filter, so that the uniformly dispersed state described above can be easily obtained.

[0042] For the antibacterial effect, it is important that the free electrons of the metal molecules that make up the formed metal film pieces can move freely. However, if the metal film b becomes a single conductor as in the case of metal film-formed filter a in which electrical conductivity is ensured and the metal film b is formed over the entire filter c as shown in Figure 2(a), when part of the metal film-formed filter a is placed in an environment that generates a potential difference as shown in Figure 2(b), there is a concern that the movement of the free electrons e around the metal molecules d that make up the metal film b will be hindered, and the antibacterial effect will not be achieved. However, if the metal film pieces 3 are formed in a dispersed state on the filter 2 as in the metal film piece-formed filter 1 shown in Figure 1(a), the electrical conductivity is independent in the formation area of ​​each dispersed metal film piece 3, so the movement of the free electrons 32 around the metal molecules 31 that make up each metal film piece 3 is ensured. Therefore, as shown in Fig. 1(b), even if a part of the area where the metal film pieces 3 of the filter 1 formed with the metal film pieces 3 is placed in an environment where the movement of the free electrons 32 is inhibited by the potential difference, the movement of the free electrons 32 around the metal molecules 31 constituting the metal film pieces 3 is not inhibited in the other areas where the metal film pieces 3 are formed, and the antibacterial effect can be exhibited. Therefore, if the metal film pieces 3 can be formed in a dispersed state in the filter 2, excellent antibacterial properties can be obtained. An example of an environment where a part of the area of ​​the filter 1 formed with the metal film pieces is subjected to a potential difference is when the housing to which the filter 1 formed with the metal film pieces 1 is attached or the screws fixing the housing are made of an electric conductor having a different potential from the filter 1 formed with the metal film pieces and are in contact with a part of the filter 1 formed with the metal film pieces.

[0043] Regarding the antibacterial effect, it has been confirmed that, in the case of the metal film piece forming composition according to the embodiment described later, a metal film piece-formed nonwoven fabric having a viable bacteria count of 0 in a specified antibacterial activity test can be formed even by performing a minimum treatment of ordinary immersion and drying once. Regarding the performance of this metal film piece-formed nonwoven fabric, a batch test is performed to determine the immersion time, immersion pressure, and number of immersion and drying cycles so that the viable bacteria count is 0 in the specified antibacterial activity test, and the manufacturing conditions for the metal film piece-formed nonwoven fabric having a viable bacteria count of 0 in the specified antibacterial activity test can be found. Therefore, from the immersion time, immersion pressure, number of immersion and drying cycles, etc. obtained from this batch test, a metal film piece-formed nonwoven fabric having a viable bacteria count of 0 in the specified antibacterial activity test can be manufactured.

[0044] The metal film piece-formed filter of the present invention constructed in this manner simply has metal film pieces formed in a dispersed state on at least the surface of each filament of the filter paper that constitutes the filter so that the electrical resistance between two points on the plane of the metal film piece-formed filter and between two points on the front and back is 100 MΩ or more. Therefore, the filter can be manufactured by a simple method, for example, by immersing the filter once in a composition for forming metal film pieces and drying it. Moreover, since only a single immersion and drying is required and the amount of metal used to form the metal film pieces is small, the filter can be manufactured inexpensively.

[0045] In addition, in the metal film-formed filter, metal film pieces are formed in a dispersed state at least on the surface of each filament of the filter paper that constitutes the filter, thereby ensuring the movement of free electrons of metal molecules in the formation area of ​​each metal film piece, thereby achieving excellent antibacterial properties.

[0046] Furthermore, since the metal film piece-formed filter has metal film pieces formed in a dispersed state at least on the surface of each filament of the filter paper that constitutes the filter, it can be used without impairing the inherent properties of the filter material, such as flexibility and suppleness.

[0047] In the above description, the filter is immersed in the composition for forming metal film pieces, but the method for attaching the composition for forming metal film pieces to the filter is not limited to the immersion method, and the composition may be applied by roll coating, flow coating, spray coating, etc. However, in the case of these application methods, the composition is easily applied to the surface of the filter, but is difficult to apply to the inside, so there is a concern that it will be difficult to form metal film pieces in a dispersed state on the surface of each filament of the filter paper constituting the filter on both the surface and the inside of the filter. However, even if this happens, if it is confirmed that the electrical resistance between two points on the plane of the metal film piece-formed filter and between two points on the front and back is 100 MΩ or more, and a metal film piece-formed nonwoven fabric with a viable bacteria count of 0 is obtained in a predetermined antibacterial activity test, it can be determined that the metal film pieces are formed in a required dispersed state. Effect of the Invention

[0048] As described above, according to the present invention, a metal film piece forming composition containing a metal precursor liquid having a reaction product of at least one selected from the group consisting of metal complexes and metal salts with at least one selected from ammonia and amines, and an organic reducing agent is immersed in the filter and then dried, forming metal film pieces in a dispersed state on each filament of the filter paper constituting the filter, so that it is possible to prevent the metal molecules attached to each filament of the filter paper constituting the filter from forming a single film electrically conducting. Therefore, each metal molecule attached to each filament of the filter paper constituting the filter can exchange electrons individually in units of metal film pieces, so that the entire filter formed with the metal film pieces can exhibit an excellent antibacterial effect evenly at any part of the filter formed with the metal film pieces. Moreover, the metal film pieces formed on the filter formed with the metal film pieces are not dense metal films that ensure electrical conductivity, so they can be manufactured easily and at low cost. [Brief description of the drawings]

[0049] [Figure 1] FIG. 2A is a partial cross-sectional view showing an outline of the overall configuration of a filter having metal film pieces, and FIG. 2B is a partially enlarged view explaining the movement of electrons in the filter having metal film pieces. [Diagram 2] FIG. 1A is a partial cross-sectional view showing an outline of the overall configuration of a conventional metal film-formed filter, and FIG. 1B is a partially enlarged view explaining the movement of electrons in the metal film-formed filter. [Diagram 3] 1 shows X-ray diffraction data showing the state of formation of metal film flakes in the metal film flake-formed filter of Example 1 and the filter of Comparative Example 1. [Figure 4] (a) and (b) are electron microscope photographs at 60x and 500x magnification of the metal film piece-formed filter of Example 1, and (c) and (d) are electron microscope photographs at 60x and 500x magnification of the filter of Comparative Example 1. [Diagram 5] 1 is a graph showing the relationship between the absorption coefficient measured by a photoelectric colorimeter and the bacterial concentration of NBRC3972 (Escherchia coli). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] [Example 1, Comparative Example 1] (1. Preparation of copper complex aqueous solution) 2.54 parts by mass of copper formate tetrahydrate (metal salt) and 4.56 parts by mass of 25% by mass ammonia water were added to 25 parts by mass of pure water, and the mixture was stirred at room temperature at 500 rpm for 1 hour to obtain a metal precursor liquid. The obtained metal precursor solution was deep blue when observed with the naked eye.

[0051] (2. Preparation of Aqueous Ascorbic Acid Solution) 72 parts by mass of pure water was mixed with 18 parts by mass of ascorbic acid as an organic reducing agent, and the mixture was stirred at a liquid temperature of 40° C. for 10 minutes to obtain a colorless and transparent aqueous solution of ascorbic acid.

[0052] (3. Preparation of composition for forming metal film pieces) The metal precursor liquid obtained in (1.) and the ascorbic acid aqueous solution obtained in (2.) were mixed in a ratio of 100 parts by mass of ascorbic acid to 300 parts by mass of copper in the metal precursor solution, and the mixture was stirred and mixed at room temperature for 20 minutes to obtain a composition for forming metal film pieces. Immediately after mixing, the mixture was dark green, but when mixing was continued, the obtained composition for forming metal film changed to yellow after 20 minutes. The pH of the obtained composition for forming metal film pieces was measured using a pH meter (PICCOLO+, manufactured by HANNA Instruments), and the pH of the composition for forming metal film pieces at 25°C was 7.5.

[0053] (4. Application of the composition for forming metal film pieces to a substrate) A HEPA filter (Iris Ohyama KPMMS-DC50) was cut to a size of 12 cm wide, 3 cm high, and 7.5 cm long so that it could fit into a polypropylene plastic case (13.5 cm x 9.5 cm x 5.1 cm) and placed in the case. 353 g of the metal film piece forming composition obtained above was poured into this plastic case to immerse the HEPA filter, and then the case was covered with a lid, sealed with parafilm, and left to stand at 24.0°C for 24 hours. After 24 hours, the filter was removed from the plastic dish, washed five times with pure water, and then dried at room temperature to obtain a metal film piece-formed filter in which copper was attached to the surface of each filament constituting the filter.

[0054] [Copper evaluation] (1. Regarding adhesion status) As shown in FIG. 3, the metal film piece-formed filter according to Example 1 obtained above and the filter according to Comparative Example 1 before copper was attached were confirmed by X-ray diffraction, and a copper diffraction peak was confirmed for the metal film piece-formed filter according to Example 1. The metal film piece-formed filter obtained above was cut, and the cut surface was observed with an electron microscope equipped with elemental analysis. For comparison, the filter according to Comparative Example 1 before copper was attached was used and observed with the same electron microscope. The results are shown in FIG. 4. The electron microscope was a tabletop microscope (Hitachi Corporation, Miniscope TM3030), and the cross section was analyzed by normal SEM mode at 60x and 500x magnification, and copper was qualitatively detected. It was also confirmed from the electron microscope photograph that the amount of copper metal film pieces attached to the filter was not so large that it would affect the pressure loss of the filter or the air volume in the environment in which the filter was used.

[0055] (2. Conductivity Evaluation) Using a digital multimeter (Keysight Technologies 34401A), we measured the resistance between two points on the flat surface of the metal film filter, and between two points on the front and back surfaces. As a result, it was found that the resistance exceeded the measurement limit of 100 MΩ, indicating that no conductivity was obtained.

[0056] (3. Antibacterial Evaluation) The metal film piece-formed filter obtained in Example 1 was subjected to the following antibacterial activity test. As a control, the same antibacterial activity test was carried out using the filter before copper was attached (Comparative Example 1). The test bacteria used in the antibacterial test were NBRC3972 (Escherchia coli) obtained from the National Institute of Technology and Evaluation. The concentration of the bacteria in the solution was 9 x 10 5 ~3×10 6The concentration of bacteria was adjusted to 0.065 and 0.170 (9×10 7 ~3×10 8 cfu / ml), which is reduced to 1 / 100, resulting in 9 x 10 5 ~3×10 6 A bacterial solution containing cfu / ml was prepared. The filter paper portion of the metal film piece-formed filter was cut into a size of 20 mm x 20 mm, and both sides were sterilized by ultraviolet irradiation. The sterilized test piece was placed in a sterilized petri dish, and the above 9 x 10 5 ~3×10 6 A test bacterial solution adjusted to a concentration of cfu / ml was dropped in 0.05 ml portions twice, a total of 0.1 ml. After culturing at 35±1° C. for 24 hours, the test specimen was placed in a sterilized stomacher bag and thoroughly washed out with 9.9 ml of SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.). The viable cell count was confirmed by agar plate culture method, and serial dilution was performed up to 1:10000 diluted water. 1 ml of each diluted bacterial solution was taken out into a 90 mm sterilized petri dish, and a standard agar medium (manufactured by Nippon Pharmaceutical Co., Ltd.) prepared at about 48°C was poured over it, stirred, solidified, and then cultured in an incubator at a temperature of 35°C ± 1°C for 48 hours. From each dilution ratio, a petri dish suitable for measurement (with the number of grown colonies being approximately 30 to 300 cfu) was selected, and the number of colonies was measured. The results are shown in Table 1.

[0057] [Table 1]

[0058] In Table 1, the viable cell count was calculated according to the following formula. [Viable bacteria count] N=C×D×V N: number of live bacteria, C: number of colonies in the petri dish, D: dilution ratio, V: volume of SCDLP medium

[0059] From the above results, the filter having the copper-adhered metal film pieces according to Example 1 was able to obtain an extremely excellent antibacterial effect, with the viable bacteria count being 0 after 90 minutes.

[0060] The present invention can be embodied in various other forms without departing from its spirit or main features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as being limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0061] 1 Metal film forming filter 2. Filters 3 Metal film piece 31 Metal molecules 32 free electron

Claims

1. A filter is immersed in a composition for forming metal film pieces, the composition comprising a metal precursor liquid having a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and an organic reducing agent, and then dried, whereby metal film pieces are formed in a dispersed state at least on the surface of each filament of the filter paper constituting the filter, The electrical resistance between two points on the flat surface and between two points on the front and back is 100 MΩ or more. A metal membrane filter characterized in that the filter is cut into a size of 30 mm x 30 mm, sterilized, placed in a sterilized petri dish, and 0.1 ml of a test bacterial solution prepared by adjusting NBRC3972 Escherichia coli to a concentration of 9 x 105 to 3 x 106 cfu / ml with phosphate buffer is dropped onto the filter. The filter is then cultured at 35±1°C for 90 minutes, thoroughly washed out with 9.9 ml of SCDLP medium, and then serially diluted to 1:10,000 with diluted water. Each diluted bacterial solution is cultured at 35±1°C for 48 hours using an agar plate culture method, resulting in a viable bacterial count of 0.

2. 2. The filter according to claim 1, wherein the metal is Cu.

3. 3. The filter according to claim 1, wherein the filter is a HEPA filter.

4. A step of immersing a filter in a composition for forming a metal film piece, the composition comprising a metal precursor liquid having a reaction product of at least one selected from the group consisting of a metal complex and a metal salt with at least one selected from ammonia and an amine, and an organic reducing agent; drying the filter after immersion; A method for producing a metal film-formed filter, in which metal film pieces are formed in a dispersed state on at least the surface of each filament of a filter paper constituting a filter, comprising: A method for manufacturing a metal film-formed filter, characterized in that metal film pieces are formed in a dispersed state at least on the surface of each filament of the filter paper that constitutes the filter, so that the electrical resistance between two points on a flat surface and between two points on the front and back is 100 MΩ or more by adjusting the immersion time, immersion pressure, and number of immersion and drying times.

5. The filter is cut into a size of 20 mm x 20 mm, sterilized, and then placed in a sterilized petri dish. 0.1 ml of a test bacterial solution prepared by adjusting NBRC3972 Escherichia coli to a concentration of 9 x 105 to 3 x 106 cfu / ml with phosphate buffer is dropped onto the test bacterial solution. After culturing at 35±1°C for 90 minutes, the test bacterial solution is thoroughly washed out using 9.9 ml of SCDLP medium, and then diluted stepwise to 1:10,000 diluted water. Each diluted bacterial solution is cultured by agar plate culture at 35±1°C for 48 hours, and the immersion time, immersion pressure, and number of immersion and drying steps are adjusted so that the resulting viable bacterial count is 0.

6. 6. The method for producing a filter having metal film pieces according to claim 5, wherein the immersion and drying are performed once for one day under atmospheric pressure.

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