Base material for filter

Abstract

To provide a substrate for a filter, which can provide a filter rich in trapping efficiency even after the filter is washed.SOLUTION: A fiber layer provided in a substrate for a filter includes fibers containing a homopolymer of polyvinylidene fluoride having excellent strength as constitutive fibers. Consequently, the fibers primarily constitute the fiber layer and therefore a shape of the fiber layer can be maintained during washing, so that the constitutive fibers are hardly cut off. In addition, an average fiber diameter of the fiber layer is larger than 130 nm, which further prevents the constitutive fibers from being cut off. Consequently, fracture and crack hardly occur in the fiber layer even after the layer is washed. Further, the fiber layer, whose average fiber diameter is less than 450 nm, has a close structure. This enables the substrate for a filter comprising the fiber layer to still have high trapping efficiency, even when fracture and crack occurring in the fiber layer during washing deteriorate the trapping efficiency of the substrate for a filter comprising the fiber layer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a filter base material provided with a fiber layer, which constitutes a filter that can be washed and reused.

Background Art

[0002] Conventionally, air filters and masks have been required to have performance such as low pressure loss, excellent air permeability, and excellent collection performance for dust such as airborne dust and PM2.5, as well as pollen. To meet such demands, the following conventional technologies have been studied.

[0003] In JP-A-2014-114521 (Patent Document 1), a nonwoven fabric base material for an air filter or mask provided with a nanofiber nonwoven fabric layer having an average fiber diameter of 50 to 400 nm has been studied in order to efficiently collect fine dust in the atmosphere. As specific embodiments, in Examples 1 to 2 and Examples 6 to 9, a nanofiber nonwoven fabric layer made of a homopolymer of polyvinylidene fluoride having an average fiber diameter of 110 nm or 126 nm is disclosed.

[0004] In JP-A-2017-166106 (Patent Document 2), in order to realize a filter that can capture fine particles and reduce pressure loss, a fiber aggregate such as a nonwoven fabric mainly composed of fluororesin fibers having a large surface area per unit volume has been studied. It is disclosed that polyvinylidene fluoride fibers can be employed as the fluororesin fibers, and further, the lower limit value of the average fiber diameter of the fiber aggregate is about 0.2 μm. In addition, since the fiber aggregate is composed of fluororesin fibers having excellent waterproof properties, it is disclosed that washing, sterilization by steam or boiling can be performed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In recent years, in order to extend the life of air filters provided in air conditioners and the like, it has been required that the dust attached to the air filters be removed so that they can be repeatedly used. In addition, a habit of wearing masks daily has emerged for infectious disease prevention and the like, and it has been required that masks can be hygienically reused. And in order to meet such demands and be able to remove the attached dust and hygienically reuse them, air filters and masks are required to be washable, such as by washing.

[0007] In order to provide an air filter and a mask that meet such demands, the applicant of the present application has considered preparing an air filter and a mask using a filter base material having a fiber layer according to the prior art as described above. However, the prepared air filters and masks had a problem that their collection efficiency deteriorated after washing.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The applicant of the present application aims to provide a filter base material capable of providing a filter rich in collection efficiency even after washing.

Means for Solving the Problems

[0009] The present invention is "A filter base material formed by laminating a fiber layer and core-sheath fibers for constituting a filter that can be washed and reused, A spunbond nonwoven fabric to which an oil agent consisting of wherein The constituent fibers of the fiber layer are only continuous fibers, the fiber layer contains fibers containing a homopolymer of polyvinylidene fluoride as constituent fibers, Continuous and the average fiber diameter of the fibers constituting the fiber layer Continuous is greater than 130 nm and less than 450 nm, The fiber layer and the Spunbond nonwoven fabric are melt-bonded by the sheath component of the core-sheath fiber, a base material for a filter (however, excluding those in which the constituent fibers of the fiber layer contain an ionic surfactant).” is.

Advantages of the Invention

[0010] In order to clarify the cause of the problem that the air filter or mask prepared using the base material for a filter according to the prior art has inferior collection efficiency after washing, the applicant of the present application confirmed the structure of the base material for a filter before and after washing. As a result, in the base material for a filter after washing, breaks and cracks occurred in the fiber layer constituting the base material for a filter, which was considered to be the cause of the decrease in the collection efficiency.

[0011] As a result of continuous studies by the applicant of the present application, it has been found that the problem can be solved by using a base material for a filter having a fiber layer that satisfies the configuration according to the present invention.

[0012] The fiber layer included in the base material for a filter according to the present invention contains fibers containing a homopolymer of polyvinylidene fluoride that is excellent in strength as constituent fibers. Therefore, the fibers serve as the skeleton of the fiber layer, and the shape of the fiber layer is maintained during washing and the constituent fibers are difficult to be cut. In addition, since the average fiber diameter of the fiber layer is larger than 130 nm, the constituent fibers are even more difficult to be cut. As a result, breaks and cracks are less likely to occur in the fiber layer even after washing.

[0013] Furthermore, since the average fiber diameter of the fiber layer is less than 450 nm, the fiber layer has a dense structure. Therefore, even if the collection efficiency of the base material for a filter having the fiber layer decreases due to breaks and cracks occurring in the fiber layer during washing, the base material for a filter having the fiber layer still has a high collection efficiency.

[0014] From the above, according to the present invention, it is possible to provide a base material for a filter that can provide a filter rich in collection efficiency even after washing.

Embodiments for Carrying Out the Invention

[0015] In the present invention, various configurations can be appropriately selected, such as the following configurations. Note that, unless otherwise specified or defined, all various measurements described in the present invention were performed under the conditions of normal pressure of 25°C in the atmosphere. And, unless otherwise specified or defined, all various measurement results described in the present invention were measured up to a value one digit smaller than the required value, and the required value was calculated by rounding off the one-digit smaller value. As a specific example, when the value up to the first decimal place is the required value, the value up to the second decimal place is obtained by measurement, and the value up to the first decimal place is calculated by rounding off the obtained value of the second decimal place, and this value is taken as the required value. Also, each upper limit value and each lower limit value exemplified in the present invention can be arbitrarily combined.

[0016] The base material for a filter of the present invention includes a fiber layer. The fiber layer plays a role of collecting and holding particles in the base material for a filter, and also plays a role of forming the skeleton of the base material for a filter.

[0017] The fiber layer referred to in the present invention means a layer composed of fibers, and can be, for example, a layer derived from a fibrous web, a non-woven fabric, or a sheet-like fabric such as a woven fabric or a knitted fabric. In particular, when the fiber layer is a fiber layer in which fibers are randomly entangled, such as a fiber layer derived from a fibrous web or a non-woven fabric, the shape and size of the voids formed by the fibers become uniform, and a base material for a filter capable of providing a filter rich in filtration performance can be realized, which is preferable.

[0018] The base material for a filter of the present invention contains fibers containing a homopolymer of polyvinylidene fluoride as constituent fibers of the fiber layer (hereinafter, may be abbreviated as constituent fibers). The polyvinylidene fluoride referred to here means a polymer having a -(CH2CF2)- structure in its structure. Also, the homopolymer of polyvinylidene fluoride means that it has a molecular structure in which the structure is continuously formed.

[0019] The fiber layer included in the base material for a filter according to the present invention contains fibers containing a homopolymer of polyvinylidene fluoride, which is excellent in strength as a constituent fiber. Among polyvinylidene fluorides, it is known that homopolymers have higher strength compared to copolymers of polyvinylidene fluoride. Therefore, the fibers serve as the framework of the fiber layer, and the shape of the fiber layer is maintained even during washing, and the constituent fibers are hardly cut by washing.

[0020] Hereinafter, the homopolymer of polyvinylidene fluoride may be referred to as "PVDF homopolymer", and the fiber containing the homopolymer of polyvinylidene fluoride may be abbreviated as "PVDF homopolymer fiber".

[0021] The molecular weight of the PVDF homopolymer can be appropriately selected. The molecular weight may be 300,000 or more, 380,000 or more, 570,000 or more, 750,000 or more, or 780,000 or more. Further, PVDF homopolymer fibers formed by mixing PVDF homopolymers having different molecular weights may also be used. The "molecular weight" referred to in the present invention is a value measured based on gel permeation chromatography. When the molecular weight of the PVDF homopolymer adopted in a catalog, a paper, or the like is described, that molecular weight can be regarded as the molecular weight of the PVDF homopolymer.

[0022] The strength of the PVDF homopolymer can be appropriately selected. However, the higher the strength of the PVDF homopolymer, the more likely it is to realize a base material for a filter that can provide a filter rich in collection efficiency even after washing. Therefore, it is preferable to adopt a PVDF homopolymer capable of preparing a film having a breaking strength of 30 MPa or more, preferably a PVDF homopolymer capable of preparing a film having a breaking strength of 40 MPa or more, and more preferably a PVDF homopolymer capable of preparing a film having a breaking strength of 50 MPa or more, based on the standard method of ASTM D638 plastic tensile test method.

[0023] In addition to the PVDF homopolymer, the constituent fibers may contain other resins described below. The other resins can be appropriately selected. For example, polyether resins (such as polyethylene glycol, polypropylene glycol, polyether ether ketone, polyacetal, modified polyphenylene ether, aromatic polyether ketone, etc.), phenolic resins, epoxy resins, polyimide resins, polyamideimide resins, polyamide resins (such as aromatic polyamide resins such as aramid resins, aromatic polyetheramide resins, nylon resins, etc.), urethane resins, epoxy resins, polysulfone resins (such as polysulfone), polyethersulfone resins (such as polyethersulfone, sulfonated polyethersulfone, etc.), fluorine-based resins (such as polytetrafluoroethylene, copolymers of PVDF, perfluorosulfonic acid resins, etc.), vinyl alcohol-based resins (such as polyvinyl alcohol, polyvinyl acetate, etc.), polycaprolactone, polyglycolic acid, polyvinyl pyrrolidone, polybenzimidazole resin, acrylic resins (such as polyacrylonitrile-based resins copolymerized with acrylic esters or methacrylic esters, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.), etc. can be known resins, and it may be only one type of resin or a plurality of types of resins such as a mixed resin.

[0024] These resins may be composed of either linear polymers or branched polymers, and the resins may also be block copolymers or random copolymers. Also, the three-dimensional structure and the presence or absence of crystallinity of the resins may be any.

[0025] However, in order to realize a filter base material in which the shape of the fiber layer is prevented from changing even during washing and breakage and cracks are less likely to occur in the fiber layer due to the higher strength of the constituent fibers, it is preferable that the polymer constituting the constituent fibers is only the PVDF homopolymer.

[0026] Since the average fiber diameter of the PVDF homopolymer fibers contained in the constituent fibers is small, it can contribute to realizing a filter base material capable of providing a filter rich in filtration performance. From this perspective, the average fiber diameter of the PVDF homopolymer fibers contained in the constituent fibers is less than 450 nm, preferably 400 nm or less. On the other hand, if the average fiber diameter of the PVDF homopolymer fibers contained in the constituent fibers is too small, the constituent fibers of the fiber layer are likely to be cut during washing, and many breaks and cracks occur, making it difficult to realize a filter base material capable of providing a filter rich in filtration performance. From this perspective, the average fiber diameter of the PVDF homopolymer fibers contained in the constituent fibers is greater than 130 nm, preferably 150 nm or more. The "average fiber diameter" referred to in the present invention means the arithmetic average value of the fiber diameters of 50 fibers measured based on an electron micrograph at 5000 times magnification taken of the cross-section, surface, etc. of the measurement object. Also, when the fiber diameter is too small to be measured, it can be measured based on an electron micrograph at a magnification higher than 5000 times. When the cross-sectional shape of the fiber is non-circular, the diameter of a circle having the same area as the cross-sectional area is regarded as the fiber diameter.

[0027] The percentage of the mass of the PVDF homopolymer fibers in the mass of the constituent fibers can be adjusted as appropriate. The constituent fibers may contain fibers made of other resins described above in addition to the PVDF homopolymer fibers. However, the higher the percentage of the mass of the PVDF homopolymer fibers in the mass of the constituent fibers, the more the shape of the fiber layer can be maintained even during washing and the less likely the constituent fibers are to be cut by washing, so that a filter base material can be realized. Therefore, the percentage is preferably 10% by mass or more, preferably 20% by mass or more, preferably 30% by mass or more, preferably 40% by mass or more, preferably 50% by mass or more, preferably 60% by mass or more, preferably 70% by mass or more, preferably 80% by mass or more, preferably 90% by mass or more, and most preferably the constituent fibers of the fiber layer are only PVDF homopolymer fibers.

[0028] The fiber length of the constituent fibers can be appropriately selected, and can be short fibers or long fibers having a specific length, or continuous fibers having a fiber length such that it is substantially difficult to measure the fiber length. Since the small number of fiber ends in the fiber layer results in a smooth surface, uniform thickness, and excellent various physical properties such as mechanical strength, a filter base material capable of providing a filter richer in filtration performance can be realized. Therefore, it is preferable that the constituent fibers include fibers having a continuous length, and it is more preferable that the constituent fibers are only continuous fibers. The "fiber length" as used in the present invention can be measured based on an electron micrograph at 5000 times magnification that photographs the cross-section, surface, etc. of the object to be measured. When the fiber length of the fiber is too long and difficult to measure, it can be measured based on an electron micrograph at a magnification lower than 5000 times.

[0029] In addition to single fibers, the constituent fibers may also be fibril-like fibers or composite fibers. As the composite fibers, for example, core-sheath type, sea-island type, side-by-side type, orange type, bimetal type, etc. of fibers can be used. The cross-sectional shape of the constituent fibers may be a fiber with a cross-sectional shape other than a substantially circular fiber or an elliptical fiber, i.e., a fiber with a cross-sectional shape such as a hollow shape, a polygonal shape such as a triangular shape, an alphabetic character type shape such as a Y shape, an irregular shape, a multi-leaf shape, a symbol type shape such as an asterisk shape, or a shape in which a plurality of these shapes are combined.

[0030] The method for preparing the constituent fibers can be appropriately selected. For example, melt spinning method, dry spinning method, wet spinning method, direct spinning method (melt blowing method, spunbond method, electrospinning method which is a method of applying an electric field to a spinning solution to spin, a method of spinning using centrifugal force, a method of spinning using an accompanying air flow described in JP-A-2011-012372, etc., neutralization spinning method which is a kind of electrospinning method described in JP-A-2005-264374, etc.), a method of extracting fibers with a fine fiber diameter by removing one or more resin components from composite fibers, etc., known methods can be used.

[0031] The fibers prepared using the above-described method can be used to prepare a fiber web by subjecting them to, for example, a dry method or a wet method, and a nonwoven fabric can be prepared by entangling and / or integrating the constituent fibers of the prepared fiber web. Examples of methods for entangling and / or integrating the constituent fibers include a method of entangling them by a needle, a water stream, or a fluid stream such as water vapor / gas, and a method of adhesively integrating or melt-integrating the constituent fibers with a binder or adhesive fibers by subjecting the fiber web to a heat treatment. The heat treatment method can be appropriately selected, and for example, a method of heating and pressing with a calendar roll, a method of heating with a hot air dryer, a method of irradiating infrared rays under no pressure to heat the contained polymer, etc. can be used.

[0032] In addition to the fiber web, the nonwoven fabric may also be subjected to the above-described method of entangling and / or integrating the constituent fibers.

[0033] Also, by collecting the fibers spun using a direct spinning method (particularly, an electrospinning method), a fiber web or nonwoven fabric composed only of continuous fibers can be prepared. Note that, depending on the spinning conditions, a film-like or granular non-fibrous material called a shot may adhere to the main surface of the fiber web or nonwoven fabric prepared using the direct spinning method. Whether or not a non-fibrous material exists on the main surface of the fiber layer can be appropriately adjusted, and a filter base material having a fiber layer with a non-fibrous material on the main surface or a filter base material having a fiber layer without a non-fibrous material on the main surface may be prepared.

[0034] In addition, a filter base material having a laminated structure may be prepared by collecting the fibers spun using a direct spinning method (particularly, an electrospinning method) on another base material such as a spunbond nonwoven fabric. At this time, if the other base material (particularly, a spunbond nonwoven fabric) contains an oil agent (particularly, a nonionic surfactant), it is preferable because a filter base material with excellent collection efficiency in which the fibers spun by direct spinning (particularly, electrospinning) are uniformly dispersed can be prepared. Regarding the other base material provided with the oil agent used at this time, the surface resistance of its main surface is 5.0×10 13It is preferable to adjust the type of the oil agent and the amount of the oil agent present so that it becomes Ω or less. Further, the surface resistance is preferably 5.0×10 13 Ω or less, preferably 1.0×10 13 Ω, and more preferably 5.0×10 12 Ω or less. By directly spinning (particularly, electrospinning) on another base material having such a surface resistance of the main surface, the spun fibers can be uniformly dispersed and deposited on the other base material. As a result, it is preferable that a base material for a filter excellent in collection efficiency can be prepared.

[0035] The fiber layer included in the base material for a filter according to the present invention is characterized in that its average fiber diameter is larger than 130 nm and less than 450 nm.

[0036] Since the average fiber diameter of the fiber layer is larger than 130 nm, the constituent fibers are hardly cut by washing. As a result, breakage and cracks are hardly generated in the fiber layer even by washing. Since the larger the average fiber diameter of the fiber layer, the easier the effect is effectively exhibited, the average fiber diameter of the fiber layer is preferably 140 nm or more, and preferably 150 nm or more.

[0037] And since the average fiber diameter of the fiber layer is less than 450 nm, the fiber layer has a dense structure. Therefore, even if the collection efficiency of the base material for a filter including the fiber layer decreases due to breakage or cracks generated in the fiber layer during washing, the base material for a filter including the fiber layer still has a high collection efficiency. Since the smaller the average fiber diameter of the fiber layer, the easier the effect is effectively exhibited, the average fiber diameter of the fiber layer is preferably 440 nm or less, preferably 430 nm or less, preferably 420 nm or less, preferably 410 nm or less, and preferably 400 nm or less.

[0038] Various physical properties such as the basis weight and thickness of the fiber layer can be appropriately selected.

[0039] First, when a layer (such as a fiber layer) constituting the filter base material can be easily obtained (for example, when the layer can be easily peeled off from the filter base material and obtained), among the obtained layers, a layer composed of fibers such as a fiber web or a non-woven fabric layer is defined as the fiber layer, and the thickness and basis weight of the fiber layer are directly measured to obtain the thickness and basis weight of the fiber layer constituting the filter base material. For example, the thickness can be 0.1 μm to 200 μm, can be 0.2 μm to 150 μm, can be 0.2 μm to 100 μm, and can be 0.2 μm to 50 μm. Note that the "thickness" referred to in the present invention means the average value of 10 points randomly selected and measured by the measurement method of JIS C2111 5.1(1) using an outside micrometer (0 to 25 mm) defined in JIS B7502:1994. For example, the basis weight can be 0.05 to 50 g / m 2 and can be 0.1 to 30 g / m 2 and can be 0.1 to 20 g / m 2 and can be 0.1 to 10 g / m 2 and can be. Note that the "basis weight" of the present invention means a value measured as 10 cm × 10 cm in accordance with JIS L1085.

[0040] On the other hand, when each layer (such as a fiber layer) constituting the filter base material cannot be easily obtained (for example, when the layer cannot be easily peeled off from the filter base material), the thickness of the fiber layer can be obtained by the following method. (1) Take an electron micrograph (magnification: 2000 times) of the cross-section obtained by cutting the filter base material in the thickness direction. (2) Visually check the taken electron micrograph and measure the thickness of each layer constituting the filter base material. Note that the thickness referred to here means the length of the shortest distance between the line segment connecting the two main surfaces of the filter base material shown in the taken electron micrograph at the shortest distance and the intersection point (A) of one main surface in each layer and the other main surface to the intersection point (B). (3) Among the respective layers, a layer composed of fibers such as a fiber web or a nonwoven fabric layer is defined as a fiber layer. Using the method of the above-described step (2), the length of the shortest distance between intersection point (A) and intersection point (B) of the fiber layer is obtained, and this is defined as the thickness of the fiber layer.

[0041] Also, when each layer (such as a fiber layer) constituting the base material for the filter cannot be easily obtained, the basis weight of the fiber layer can be obtained by the following method. (1) Take an electron micrograph (magnification: 2000 times) of the cross-section obtained by cutting the base material for the filter in the thickness direction. (2) Visually check the taken electron micrograph to confirm whether the base material for the filter has a fiber layer. (3) When the base material for the filter has a fiber layer, confirm the components constituting the fiber layer and other layers. Note that the components constituting the fiber layer (for example, the type of the constituent resin of the fibers constituting the fiber layer and the type of the binder bonding the constituent fibers to each other) and the components constituting other layers can be obtained by subjecting the fiber layer and other layers collected from the base material for the filter to various known analytical apparatuses and analytical methods such as IR, DSC, NMR, MS, Raman spectroscopy, elemental analysis, and combustion test. (4) Select a solvent (for example, DMF, DMAc, NMP, etc., which are polar solvents) capable of dissolving layers other than the fiber layer without dissolving the fiber layer, and immerse the base material for the filter in the solvent to dissolve layers other than the fiber layer in the solvent. Take out the residue from the solvent, and define the basis weight of the residue after solvent removal as the basis weight of the fiber layer. Note that when there is no solvent capable of dissolving layers other than the fiber layer without dissolving the fiber layer, select a solvent capable of dissolving only the fiber layer, immerse the base material for the filter in the solvent to dissolve only the fiber layer in the solvent. Take out the residue from the solvent, subtract the basis weight of the residue after solvent removal from the basis weight of the base material for the filter, and define the calculated value as the basis weight of the fiber layer.

[0042] Also, among the respective materials used for preparing the base material for the filter, when other materials other than the materials used for forming the fiber layer are identified, the thickness and basis weight of the other materials are directly measured in the same manner as in the case of "when each layer (such as a fiber layer) constituting the base material for the filter can be easily peeled off and obtained", and the thickness and basis weight of the materials used for forming the fiber layer are calculated by subtracting the values obtained by measurement from the thickness and basis weight of the base material for the filter. And the calculated values may be regarded as the thickness and basis weight of the fiber layer constituting the base material for the filter.

[0043] The fiber layer according to the present invention can be used alone as a base material for the filter, but if necessary, a separately prepared base material (for example, a sheet-like fabric such as a spunbond nonwoven fabric, a porous film, etc.) can be laminated on the fiber layer to prepare a base material for the filter.

[0044] The lamination method of the fiber layer and the base material can be appropriately selected, but methods such as simply overlapping, partially melt-bonding the constituent components of the fiber layer and / or the base material, or laminating and integrating with a binder, and a method of preparing a laminate by accumulating fibers spun on the main surface of the base material to form a fiber layer on the base material can be adopted.

[0045] In particular, when the base material contains core-sheath type fibers, it is preferable because the sheath component of the core-sheath type fibers can firmly melt-bond the fiber layer and the base material. And since it is difficult for the base material to fall off from the base material for the filter provided with the fiber layer and the base material, the fiber layer can be effectively protected by the base material. As a result, it is preferable that a filter rich in collection efficiency even after washing can be provided by effectively preventing breakage and cracks from occurring in the fiber layer. Examples of such a base material include a spunbond nonwoven fabric made of core-sheath type fibers, a dry nonwoven fabric, and a wet nonwoven fabric.

[0046] Also, it is preferable that the strength of the base material is high so that the fiber layer can be effectively protected by the base material. The "strength" of the present invention can be measured by subjecting the fiber aggregate to the method described below. Specifically, it is preferable that the base material has a strength of 2 N / 50 mm or more in both the MD direction and the CD direction so as to improve the washing resistance, preferably a base material of 3 N / 50 mm or more, preferably a base material of 10 N / 50 mm or more, and preferably a base material of 15 N / 50 mm or more. On the other hand, the upper limit value can be adjusted as appropriate, but when a base material having too high strength is provided, the air permeability of the mask may decrease. Therefore, it is preferable to adopt a base material having a strength of less than 500 N / 50 mm.

[0047] Note that the strength in the MD direction and the CD direction of the base material can be determined by the following method. (Method for measuring strength) (1) A rectangular sample (short side: 50 mm, long side: 200 mm) was taken from the measurement object. At this time, when the production direction of the measurement object is known, the sample was taken so that the production direction and the long side direction of the measurement object are parallel. When the production direction of the measurement object is not known, a plurality of samples were taken from various directions of the measurement object so that the main surface of the measurement object and the long side of the sample are parallel, and then each sample was subjected to the measurement of the maximum stress described below. The direction of the measurement object parallel to the long side of the sample showing the highest maximum stress was defined as the production direction of the measurement object. (2) Using a tensile testing machine (manufactured by Orientec Co., Ltd., trade name: Tensilon (registered trademark), TM-111-100), the sample was pulled in the long side direction until breakage occurred under the conditions of a grip interval of 100 mm and a tensile speed of 50 mm / min. (3) The maximum stress measured until the sample breaks was defined as the "strength". In this way, the strength (N / 50 mm) in the direction (MD direction) parallel to the long side of the sample in the measurement object was measured. (4) A new rectangular sample (short side: 50 mm, long side: 200 mm) was taken from the measurement object such that the short side direction was parallel to the direction parallel to the long side direction of the sample in the measurement object. At this time, when the production direction of the measurement object was known, the sample was taken such that the production direction was parallel to the short side direction of the measurement object. (5) By subjecting the sample taken in the step (4) described above to the steps (2) to (3), the strength (N / 50 mm) in the direction (CD direction) parallel to the long side direction of the sample in the measurement object was measured.

[0048] The fiber layer or laminate of fiber layers manufactured as described above may be subjected to various secondary processes such as a pressing process such as a resilient press process to adjust the thickness according to its use and usage mode, a hydrophilization process such as a sulfonation process, a plasma process, or a fluorine gas process, punching out the shape, or molding.

[0049] Next, a manufacturing example of the method for manufacturing the substrate for a filter according to the present invention will be given and explained. Note that the explanation will be omitted for the points having the same items and configurations as described above. (1) A step of preparing a spinning solution prepared by dissolving a PVDF homopolymer in a solvent or a spinning solution prepared by dispersing a PVDF homopolymer in a dispersion medium. (2) A step of spinning by subjecting the spinning solution to an electrospinning device to make it thinner and collecting it to prepare a fiber web. (3) A step of removing the solvent or dispersion medium remaining in the fiber web to prepare a fiber layer containing PVDF homopolymer fibers with an average fiber diameter greater than 130 nm and less than 450 nm. The manufacturing method of the substrate for a filter comprising these steps can be used.

[0050] First, step (1) will be explained. The type of solvent or dispersion medium is appropriately selected, and examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, acetonitrile, dimethyl sulfoxide, 1,4-dioxane, pyridine, formic acid, toluene, benzene, cyclohexane, cyclohexanone, carbon tetrachloride, methylene chloride, chloroform, trichloroethane, ethylene carbonate, diethyl carbonate, propylene carbonate, and the like. Note that the solvent or dispersion medium may be a single type or a mixed solvent or mixed dispersion medium formed by mixing a plurality of types.

[0051] The concentration and type of the PVDF homopolymer contained in the spinning solution are appropriately adjusted so that the substrate for the filter according to the present invention can be prepared.

[0052] The temperature and viscosity of the spinning solution are appropriately selected so that the desired fiber layer can be prepared. The temperature of the spinning solution can be 5 to 40°C, can be 10 to 35°C, and can be 15 to 30°C. Also, the viscosity of the spinning solution can be 0.05 to 8 Pa·s, can be 0.1 to 6 Pa·s, and can be 0.2 to 5 Pa·s. Note that this "viscosity" refers to the value at a shear rate of 100 s-1 measured at a temperature of 25°C using a viscosity measuring device.

[0053] Next, step (2) will be described. The method of spinning by thinning the spinning solution is appropriately selected so that the required fiber layer can be prepared. For example, a direct spinning method can be adopted. When the electrospinning method is adopted, a voltage is applied to the spinning solution, and at the same time, a voltage opposite to the said voltage is applied to a counter electrode such as a metal plate provided at a distance from the discharge part of the spinning solution, so that the spinning solution flies toward the counter electrode and is thinned. Then, by collecting the thinned spinning solution on a collector, a fiber web is formed on the collector. Note that the counter electrode such as the above-mentioned metal plate may be used as the collector, but a laminate of the substrate and the fiber web can be prepared by forming a fiber web on a substrate such as a spunbond nonwoven fabric laid on the counter electrode. By feeding the laminate of the substrate and the fiber web prepared in this way to the next process, it is preferable that a filter substrate composed of a laminate of the substrate and the fiber layer can be easily prepared.

[0054] Then, step (3) will be described. The method for removing the solvent or dispersion medium remaining in the fiber web can be appropriately selected. As an example, a method of feeding the fiber web to a heating device can be adopted. Note that the type of the heating device can be appropriately selected. For example, a method using a device that heats or heats and presses with rolls, an oven dryer, an infrared heater, a hot air dryer, a device that can irradiate infrared rays and heat, etc. can be adopted. The heating temperature by the heating device is appropriately selected, but it is adjusted so that the remaining solvent or dispersion medium can be volatilized and removed, and the temperature is such that the constituent components such as the constituent fibers are not decomposed or denatured unintentionally.

[0055] In addition, when an adhesive component or a crosslinkable resin is present in the constituent fibers of the fiber web, fiber adhesion by the adhesive component or crosslinking of the crosslinkable resin may be performed by feeding it to a heating device.

[0056] In addition, in the method for manufacturing the base material for a filter described above, by adjusting the molecular weight of the PVDF homopolymer used, the blending of the PVDF homopolymer (for example, using a spinning solution obtained by mixing a PVDF homopolymer with a large molecular weight and a PVDF homopolymer with a small molecular weight), the composition and viscosity of the spinning solution, the solid content concentration of the PVDF homopolymer contained in the spinning solution, the spinning conditions, the method and conditions for removing the solvent or dispersion medium, etc., it is possible to adjust the average fiber diameter of the fibers constituting the fiber layer, and a base material for a filter that satisfies the configuration according to the present invention can be manufactured.

[0057] The prepared fiber layer can be used alone as a base material for a filter, but if necessary, a separately prepared base material (for example, a sheet-like fabric such as a spunbond nonwoven fabric, a porous film, etc.) can be laminated on the fiber layer to prepare a base material for a filter.

[0058] The method for laminating the fiber layer and the base material can be appropriately selected, but methods such as simply overlapping, partially melt-bonding the constituent components of the fiber layer and / or the base material, or laminating and integrating with a binder, and a method of preparing a laminate by accumulating the fibers spun on the main surface of the base material to form a fiber layer on the base material can be adopted.

[0059] Note that by laminating the base material on both main surfaces of the fiber layer, it is possible to prepare a base material for a filter that can provide a filter rich in collection efficiency even after washing, which is preferable.

[0060] The fiber layer or the laminate of the fiber layer manufactured as described above can be subjected to various secondary processes such as a pressurizing process such as a resilient press treatment to adjust the thickness according to its use and usage mode, a hydrophilization treatment such as a sulfonation treatment, a plasma treatment, or a fluorine gas treatment, punching out the shape, and molding.

[0061] Using the filter base material manufactured as described above, a filter that can be washed and reused can be prepared. Specifically, a three-layer filter in which the filter base material is provided between woven fabrics or knitted fabrics can be prepared, and a mask adopting the three-layer filter on a face can be prepared. Alternatively, an air filter can be prepared using a filter provided with a filter base material.

Example

[0062] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0063] (Spinning solution) The following polymers were dissolved in dimethylformamide (boiling point: 153°C) to prepare spinning solutions A to B with a solid content concentration of 14% by mass. The types of polymers contained in each spinning solution are as follows. Note that the vinylidene fluoride - hexafluoropropylene copolymer is not a PVDF homopolymer. · Spinning solution A: Vinylidene fluoride - hexafluoropropylene copolymer (a resin capable of preparing a film with a breaking strength of 25 MPa measured based on the standard method of ASTM D638 plastic tensile test method) · Spinning solution B: PVDF homopolymer (a resin capable of preparing a film with a breaking strength of 45 MPa measured based on the standard method of ASTM D638 plastic tensile test method)

[0064] (Comparative Example 1) The spinning solution A was electrospun by subjecting it to the following spinning conditions and collecting it on a substrate to prepare a laminated web in which a fiber web made of continuous fibers and the substrate were laminated. · Shape of the spinning solution discharge part in the metal nozzle (spinning solution discharge part): circular shape with an inner diameter of 0.44 mm · Distance between the tip of the metal nozzle and the collector (metal plate): 10 cm · Voltage applied to the spinning solution: 15 kV · Spinning solution discharged from the metal nozzle: 1 g / hour · Atmosphere of the electrospinning environment: temperature 25°C, humidity 30%RH ·Base material: A spunbond nonwoven fabric (basis weight: 15 g / m) made of core-sheath type fibers with a polyester core (melting point: 260 °C) and a polyethylene sheath (melting point: 130 °C). 2 Strength in the MD direction: 38 N / 50 mm, strength in the CD direction: 16 N / 50 mm, an oil agent is applied, and the surface resistance on the main surface on the fiber collection surface side is 3.5×10 12 Ω Then, the prepared laminated web was brought into contact with a heating roll whose surface temperature was adjusted to 130 °C to remove the solvent remaining in the laminated web and to melt the sheath component of the core-sheath type fibers in the spunbond nonwoven fabric, thereby adhesively integrating the fiber web and the base material to prepare a nonwoven fabric.

[0065] (Example 1) A nonwoven fabric was prepared in the same manner as in Comparative Example 1, except that spinning solution B was used instead of spinning solution A.

[0066] Regarding each of the prepared nonwoven fabrics as a base material for a filter, its configuration, and the initial pressure loss and collection efficiency before and after washing were summarized in Table 1. In the table, regarding the type of polymer forming the constituent fibers of the portion derived from the fiber web in the base material for the filter (hereinafter sometimes referred to as the fiber layer), poly(vinylidene fluoride - hexafluoropropylene) copolymer is described as "copolymer", and PVDF homopolymer is described as "homo".

[0067] In addition, the initial pressure loss and collection efficiency before and after washing were determined using the following measurement methods.

[0068] (Measurement method for collection efficiency and initial pressure loss before washing) A test piece was taken from the base material for the filter. Then, the taken test piece was attached to a measuring device "AP-9000" manufactured by Shibata Kagaku Co., Ltd. The test piece was attached to the measuring device such that the main surface on the fiber layer side of the base material for the filter faced the upstream side. First, the test flow rate was adjusted to 40 liters per minute per 44 cm 2 of the effective filtration area of the test piece (for example, when the effective filtration area is 4.4 cm 2The test flow rate supplied to the test piece was 4 liters per minute, the differential pressure between the upstream and downstream of the test piece was measured, and the initial pressure loss (unit: Pa) of the test piece was determined from the measured differential pressure. Note that the lower the value of the initial pressure loss of the filter base material, the better the air permeability of the filter or mask that can be provided. Next, the effective filtration area of the test piece was 44 cm 2 The test flow rate was adjusted so that it would be 30 liters per minute per 4.4 cm (for example, if the effective filtration area was 4.4 cm 2 The test flow rate supplied to the test piece was 3 liters per minute, and a test air flow containing sodium chloride particles (median particle size distribution: 0.06 to 0.10 μm, geometric standard deviation: 1.8 or less) at a concentration of 50 mg / m 3 or less (concentration fluctuation: ±15% or less) was supplied to the upstream side of the test piece. After supplying the test air flow for 1 minute, the concentrations of the sodium chloride particles present on the upstream and downstream sides of the test piece were measured using a light scattering type dust concentration meter, and the concentration of the sodium chloride particles collected on the test piece was calculated from the measured concentrations on both sides. Then, the percentage of the concentration of the sodium chloride particles collected on the test piece in the concentration of the sodium chloride particles supplied to the upstream side of the test piece was calculated, and the value was taken as the collection efficiency (unit: %) of the test piece. Note that the higher the value of the collection efficiency of the filter base material, the better the dust collection performance of the filter or mask that can be provided. The initial pressure loss and collection efficiency measured as described above were taken as the initial pressure loss and collection efficiency before washing of the filter base material.

[0069] (Method for Measuring Collection Efficiency and Initial Pressure Loss after Washing) Another test piece was taken from the filter base material. Then, the taken another test piece was sandwiched between polyester water-absorbing and quick-drying knits, and the periphery was welded to prepare a mask with a three-layer structure. The prepared mask was put into a household washing machine together with a commercially available laundry detergent for washing and then dehydrated. In this way, the washing of the mask was repeated 10 times, and finally the dehydrated mask was naturally dried. The other test piece was taken out from the mask after natural drying and subjected to the above-mentioned (measurement method of collection efficiency and initial pressure loss before washing), and in the same manner, the initial pressure loss (unit: Pa) and the collection efficiency (unit: %) were obtained.

[0070] The initial pressure loss and collection efficiency measured as described above were taken as the initial pressure loss and collection efficiency after washing in the base material for the filter.

[0071]

Table 1

[0072] The base material for the filter of Example 1 was superior in collection efficiency after washing to the base material for the filter of Comparative Example 1. In the base material for the filter of Comparative Example 1, the collection efficiency decreased significantly after washing. This was considered to be because the constituent fibers (fibers composed of a vinylidene fluoride - hexafluoropropylene copolymer) were cut during washing, and breakage and cracks occurred in the fiber layer. In contrast, in the base material for the filter of Example 1, the collection efficiency did not decrease so much after washing. This was considered to be because it contained PVDF homopolymer fibers with excellent strength as constituent fibers, and these fibers formed the framework of the fiber layer, maintaining the shape of the fiber layer during washing and making it difficult for the constituent fibers to be cut, thus preventing breakage and cracks from occurring in the fiber layer.

[0073] (Comparative Example 2, Examples 2 - 3) Nonwoven fabrics were prepared in the same manner as in Example 1, except that the solid content concentration of the PVDF homopolymer in Spinning Solution B was changed to 8% by mass in Comparative Example 2, 15% by mass in Example 2, and 17% by mass in Example 3.

[0074] (Comparative Examples 3 - 4) Nonwoven fabrics were prepared in the same manner as in Example 1, except that the solid content concentration of the PVDF homopolymer in Spinning Solution B was changed to 17.5% by mass in Comparative Examples 3 - 4 and the amount of fibers collected on the base material was changed.

[0075] Using the prepared nonwoven fabrics as the base material for the filter, their configurations, initial pressure losses, and collection efficiencies before and after washing were summarized in Table 2. In the table, for the types of polymers that make up the constituent fibers of the portion derived from the fiber web in the base material for the filter (hereinafter sometimes referred to as the fiber layer), the PVDF homopolymer is described as "homo".

[0076]

Table 2

[0077] The base material for the filter of Comparative Example 3, in which the average fiber diameter of the fiber layer was 450 nm and the basis weight was 0.5 g / m 2 was 64.9% in terms of collection efficiency after washing. Also, the base material for the filter of Comparative Example 4, in which the average fiber diameter of the fiber layer was 450 nm and the basis weight was 0.9 g / m 2 was 72.0% in terms of collection efficiency after washing. From the results of Comparative Example 3 and Comparative Example 4, if a base material for a filter having a fiber layer with an average fiber diameter of 450 nm and a basis weight of 0.8 g / m 2 was prepared, it was considered that the collection efficiency after washing had a performance between 64.9% and 72.0%. That is, it was speculated that the collection efficiency after washing could not exceed 72.0%. This was considered to be because the average fiber diameter of the fiber layer was as large as 450 nm and the fiber layer could not have a dense structure.

[0078] Also, in order to provide a base material for a filter with excellent collection performance, it is desirable that the fiber layer has a dense structure. Therefore, it was considered that by reducing the average fiber diameter of the fiber layer constituting the base material for the filter, a base material for the filter with excellent collection efficiency after washing could be provided. However, the base material for the filter of Comparative Example 2, with a basis weight of 0.8 g / m 2 and an average fiber diameter of 130 nm, did not exceed 72.0% in terms of collection efficiency after washing. This was considered to be because the average fiber diameter of the fiber layer was as small as 130 nm and the constituent fibers were difficult to cut.

[0079] On the one hand, the basis weight is 0.8 g / m 2 All of the filter base materials of Examples 1 to 3, which have a basis weight of 0.8 g / m and an average fiber diameter greater than 130 nm and less than 450 nm, had a collection efficiency after washing exceeding 72.0%.

[0080] From the above, it has been found that a filter base material including PVDF homopolymer fibers excellent in strength as constituent fibers and having a fiber layer with an average fiber diameter greater than 130 nm and less than 450 nm can provide a filter rich in collection efficiency even after washing.

Industrial Applicability

[0081] The present invention relates to a filter base material provided with a fiber layer, which constitutes a filter that can be washed and reused. By using the filter base material, masks that can be washed and reused (for example, two-dimensional sheet-shaped masks, three-dimensional corrugated-shaped or pleated-shaped masks, folded-in-half-shaped masks, cup-shaped masks), and air filters for air purification or air conditioners that can be washed and used (for example, two-dimensional sheet-shaped filters, three-dimensional corrugated-shaped or pleated-shaped filters, depth-type filters) can be provided. In addition, a liquid filter may be prepared using the filter base material according to the present invention.

Claims

Claim 1 A filter base material formed by laminating a fiber layer and a spunbond nonwoven fabric provided with an oil agent composed of core-sheath type fibers for constituting a filter that can be washed and reused, wherein the constituent fibers of the fiber layer are only continuous fibers, the fiber layer contains continuous fibers containing a homopolymer of polyvinylidene fluoride as constituent fibers, the average fiber diameter of the continuous fibers constituting the fiber layer is greater than 130 nm and less than 450 nm, the fiber layer and the spunbond nonwoven fabric are melt-bonded by the sheath component of the core-sheath type fibers, a filter base material (however, excluding those in which the constituent fibers of the fiber layer contain an ionic surfactant).

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