JP2023142116A - Fiber sheet and manufacturing method thereof - Google Patents

Abstract

To provide a fiber sheet, which suppresses fuzz and delamination between fiber sheets without deteriorating inherent properties of a nanofiber and has excellent adhesion with other material, at high productivity and excellent operability.SOLUTION: A fiber sheet includes nanofibers having average fiber diameter of 20 to 1000 nm. The nanofiber includes mixture of vinylidene fluoride polymer and vinylidene fluoride-based copolymer having melting point of 150°C or less.SELECTED DRAWING: None

Description

The present invention relates to a fiber sheet containing nanofibers and a method for producing the same.

In recent years, ultrafine fibers having a diameter of several to several hundred nanometers (nm), so-called nanofibers, have attracted attention. Nanofibers have characteristics such as their large specific surface area, small interfiber voids, uniform pore size distribution, and high porosity in fiber sheets containing nanofibers, so they are used as filter media for filters. It is expected to be applied to sound-absorbing materials, masks, waterproof and moisture-permeable membranes, separators for secondary batteries, sensor materials, cell culture substrates, etc. Among them, nanofibers made of polyvinylidene fluoride polymers have excellent properties such as mechanical strength, heat resistance, chemical resistance, and processability into nanofibers, so they can be applied to a wide range of fields. .

Electrostatic spinning is known as a method for producing nanofibers. In the general electrostatic spinning method, a spinning solution in which a polymer is dissolved is charged with a high voltage together with a metal spinning nozzle, and the solution is discharged from the tip of the spinning nozzle toward the surface of a grounded collection electrode. Form droplets. The droplets are attracted to the collection electrode surface by a strong electrostatic force at the tip of the spinning nozzle, and the spinning solution flies as a jet, becoming thinner as the solvent evaporates, forming nanofibers with a diameter of several to several hundred nm. is collected to form a non-woven fibrous sheet. According to the electrostatic spinning method, a wide range of materials can be made into nanofibers, and fibers can be made extremely fine and uniform. However, because the diameter of the obtained nanofibers is small and the mechanical strength per fiber is low, the surface of the fiber sheet containing nanofibers is prone to single fiber breakage and In addition to causing tearing of the nonwoven fabric, there is a problem in that the nanofiber sheet has low rigidity, which reduces processability.

In order to solve these problems, a method has been proposed in which a nanofiber sheet is laminated and integrated with a porous layer having excellent strength and rigidity (for example, Patent Document 1). Patent Document 1 states, ``It is a laminate in which a nonwoven fabric manufactured by an electrostatic spinning method and a breathable sheet are bonded together with an adhesive, and in the thickness direction of the nonwoven fabric, from the surface of the nonwoven fabric piece of the adhesive. A laminate in which the penetration depth is 40% or less of the thickness of the nonwoven fabric is disclosed. However, although this type of laminate improves the adhesive strength between the layers, the adhesive seeps into the interfiber voids and blocks the pores, so the inherent properties of nanofibers cannot be fully demonstrated. . Further, there is a problem that the components of the adhesive not only affect the fiber material but also elute into the liquid or the atmosphere, polluting the environment. Furthermore, since it involves the process of integrating the nonwoven fabric produced by electrostatic spinning with the breathable sheet using an adhesive, there are problems in that stable operability and sufficient productivity cannot be achieved. .

In addition, the present applicant has previously described a ``fiber sheet obtained by spinning a polyvinylidene fluoride-based copolymer mainly composed of vinylidene fluoride by an electrospinning method and collecting the spun fibers, A fiber sheet in which the fibers constituting the fiber sheet have an average fiber diameter of 20 nm or more and less than 1000 nm, a melting temperature of the fiber sheet in DSC measurement of 155 ° C. or more, and a heat of fusion of 45 J/g or less. (Patent Document 2). According to this method, the fiber sheet can be well integrated with other materials without shrinking significantly due to changes over time or heating during molding into products. In some cases, a considerable amount of fluffing occurred, and the properties tended to deteriorate. Furthermore, in the mass production of electrostatic spinning, there have been attempts to improve productivity by arranging spinning nozzles in multiple rows in the flow direction of the production line (for example, Patent Document 3); The sheet becomes multi-layered depending on the number of rows of spinning nozzles, and delamination is likely to occur, and properties are likely to deteriorate during processing into products. As described above, in the methods of Patent Documents 2 and 3, there is room for improvement with respect to the problems of fluffing and delamination between fiber sheets.

Japanese Patent Application Publication No. 2007-30175 Japanese Patent Application Publication No. 2015-45114 Japanese Patent Application Publication No. 2007-224458

The present invention solves the above-mentioned problems, and provides a fiber sheet that suppresses fuzzing and delamination between fiber sheets without impairing the inherent properties of nanofibers, and has excellent adhesion to other materials. With the goal.

The present inventor has made extensive studies in order to solve the above problems. As a result, it has been found that the above problem can be solved by containing a mixture of a vinylidene fluoride polymer and a specific vinylidene fluoride copolymer in a fiber sheet containing nanofibers, and the present invention I was able to complete it.

That is, the present invention has the following configuration.
[1] A fiber sheet containing nanofibers having an average fiber diameter of 20 to 1000 nm, the nanofibers being a mixture of a vinylidene fluoride polymer and a vinylidene fluoride copolymer with a melting point of 150° C. or less. including fiber sheets.
[2] The fiber sheet according to [1], wherein the mixing ratio (weight ratio) of the vinylidene fluoride polymer and the vinylidene fluoride copolymer is 50:50 to 95:5.
[3] The fiber sheet according to [1] or [2], wherein the fiber sheet is a laminate of two or more layers.
[4] The fiber sheet according to any one of [1] to [3], wherein a spinning solution containing a vinylidene fluoride polymer and a vinylidene fluoride copolymer having a melting point of 150° C. or less is electrospun. Production method.
[5] A method for producing a fiber sheet, which further heat-treats the fiber sheet obtained by the method described in [4] with circulating hot air or radiant heat.
[6] A fiber sheet composite in which the fiber sheet according to any one of [1] to [3] and a porous layer are laminated.
[7] A filter medium comprising the fiber sheet composite according to [6].

The fiber sheet of the present invention does not impair the inherent properties of nanofibers, is less prone to fluffing and delamination between fiber sheets, and has excellent processing resistance. In addition, because the fiber sheet has excellent adhesion to other materials, it can be laminated with a porous layer to form a fiber sheet composite, achieving high productivity and good results without having to go through integration processes such as adhesion or calendaring. A fiber sheet composite can be provided with ease of operation.

The present invention will be explained in detail below.

The fiber sheet of the present invention is a fiber sheet containing nanofibers having an average fiber diameter of 20 to 1000 nm, the nanofibers comprising a vinylidene fluoride polymer and a vinylidene fluoride copolymer having a melting point of 150°C or less. It is characterized by containing a mixture with coalescence. This structure suppresses fuzzing and delamination between fiber sheets without impairing the original properties of nanofibers, and allows fiber sheets with excellent adhesion to other materials to be produced with high productivity and good performance. It becomes possible to obtain it through operability.

<Nano fiber>
The average fiber diameter of the nanofibers constituting the fiber sheet of the present invention is 20 to 1000 nm, preferably 30 to 600 nm, and more preferably 50 to 300 nm. If the average fiber diameter of nanofibers is 1000 nm or less, the specific surface area becomes large and the characteristics derived from nanofibers, such as excellent filter performance, are more likely to be exhibited. It can suppress breakage and fuzzing of nanofibers during processing.

The nanofibers constituting the fiber sheet of the present invention contain a mixture of a vinylidene fluoride polymer and a vinylidene fluoride copolymer having a melting point of 150° C. or less. By having this structure, vinylidene fluoride polymer has excellent durability such as chemical resistance and heat resistance, and can form thin and uniform fibers, and is flexible and has no fuzz or interlayer between fiber sheets. It is thought that it will be possible to combine the characteristics of vinylidene fluoride-based copolymers, such as suppressing peeling and having excellent adhesion to other materials. Here, the vinylidene fluoride polymer means a homopolymer polymerized substantially only from vinylidene fluoride monomers. Vinylidene fluoride copolymer means a copolymer of vinylidene fluoride and another monomer, and vinylidene fluoride and a fluorine-based monomer such as trifluoroethylene, tetrafluoroethylene, or hexafluoropropylene. An example is a copolymer with Among these, a copolymer of vinylidene fluoride and hexafluoropropylene is preferred from the viewpoint of suppressing fuzzing and delamination between fiber sheets and improving adhesion to other materials. The copolymer may be a random copolymer or a block copolymer, but random copolymers are preferred from the viewpoint of suppressing fuzzing and delamination between fiber sheets and improving adhesion with other materials. Preferably, it is a polymer.

The melting point of the vinylidene fluoride copolymer in the present invention is 150°C or lower, preferably 135°C or lower, and more preferably 125°C or lower. By using a vinylidene fluoride copolymer having a melting point of 150° C. or lower, it is possible to suppress fluffing and delamination between fiber sheets and improve adhesion to other materials. Vinylidene fluoride copolymers, which have a melting point of 150°C or lower, have high softening and solubility against heat and solvents, so when accumulating nanofibers in the fiber sheet manufacturing process, they can be used in a soft state that is not completely solidified. Since nanofibers or nanofibers and other materials come into contact and form a strong bond, it is thought that it is possible to suppress fuzzing and delamination between fiber sheets and improve adhesion with other materials. The lower limit of the melting point of the vinylidene fluoride copolymer is not particularly limited, but is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. If the melting point is 60° C. or higher, the nanofibers will be difficult to melt even if processed at high temperatures during processing into products, and the original properties of the nanofibers will be easily maintained.

The mixing ratio (weight ratio) of vinylidene fluoride polymer and vinylidene fluoride copolymer in the nanofibers constituting the fiber sheet of the present invention is not particularly limited, but is 50:50 to 95:5. The ratio is preferably 60:40 to 93:7, even more preferably 75:25 to 92.5:7.5. If the mixing ratio (weight ratio) of vinylidene fluoride polymer and vinylidene fluoride copolymer in the nanofiber is 50:50 or more, it will have excellent durability such as chemical resistance and heat resistance, and will be thin and uniform. It is easy to obtain fibers, and when it is 95:5 or less, it suppresses fluffing and interlayer peeling, and has excellent adhesion to other materials.

The weight average molecular weight of the vinylidene fluoride polymer and vinylidene fluoride copolymer that are the constituent components of the nanofibers is not particularly limited, but is preferably from 100,000 to 1,000,000, and preferably from 200,000 to More preferably, it is 800,000. If the weight average molecular weight is 100,000 or more, nanofiber formation is excellent, and if it is 1,000,000 or less, it is excellent in solubility and thermoplasticity, and processing becomes easy.

The melt viscosity of the vinylidene fluoride polymer, which is a component of the nanofibers, is not particularly limited, but it should be 2 to 60 kpoise at a melting temperature of 232 ° C. and a shear rate of 100 sec ^-1 , as measured in accordance with ASTM D3835. is preferable, 10 to 50 kpoise is more preferable, and even more preferably 20 to 40 kpoise. Furthermore, the melt viscosity of the vinylidene fluoride copolymer is not particularly limited, but is preferably 0.5 to 35 kpoise at a melting temperature of 232°C and a shear rate of 100 sec ^-1 , as measured in accordance with ASTM D3835. It is preferably 2 to 30 kpoise, more preferably 5 to 20 kpoise.

The nanofibers may include, but are not limited to, a conductivity imparting agent. When the nanofibers contain a conductivity imparting agent, the nanofibers become extremely fine and the generation of bead-like objects is suppressed, making it possible to obtain homogeneous nanofibers and making it easier to exhibit the original properties of the nanofibers. Furthermore, because the high voltage during the electrostatic spinning process (described later) causes the nanofibers to be strongly attracted toward the collector and collected tightly, the adhesion between nanofibers or between nanofibers and other materials improves, preventing fuzzing and delamination. Can be suppressed. Examples of the conductivity imparting agent include anionic surfactants such as sodium dodecyl sulfate, cationic surfactants such as tetrabutylammonium bromide, and organic or inorganic salts. If the concentration of the conductivity imparting agent is 0.1 to 10% by weight based on the weight of the nanofibers, an effect commensurate with its use can be obtained.

Nanofibers are not particularly limited, but may be provided with a water repellent. By adding a water repellent, the water repellency of the nanofibers is improved, the deterioration of properties due to water absorption and moisture absorption is suppressed, and the properties derived from the nanofibers can be maintained for a long period of time. Normally, when a water repellent is applied to nanofibers, fluffing and delamination tend to occur, and adhesion with other materials decreases, but the nanofibers used in the present invention are made of vinylidene fluoride polymer, Since it contains a mixture of vinylidene fluoride copolymers with a melting point of 150° C. or less, it can provide good fuzz resistance and peeling resistance even if a water repellent is applied. The water repellent is not particularly limited as long as it can impart water repellency to nanofibers, and examples include fluorine group-containing oligomers, fluorine group-containing polymers, fluorine-based surfactants having perfluoroalkyl groups, and perfluoroalkenyl groups. Examples include fluorine-based surfactants, silicone oligomers, silicone polymers, silicone-based silane compounds, fluorine-based silane compounds, fluorine-containing cage-type silsesquioxanes, fluorine-modified polyurethanes, and silicone-modified polyurethanes. Among these, it is preferable to use a water repellent containing fluorine, such as a fluorine group-containing polymer, a fluorine-containing cage-type silsesquioxane, or a fluorine-modified polyurethane, from the viewpoints of water repellency, workability, and cost. The concentration of the water repellent is not particularly limited, but is preferably 0.1 to 20% by weight, more preferably 1 to 15% by weight, based on the nanofibers. If the concentration of the water repellent is 0.1% by weight or more, water repellency can be imparted to the nanofibers, and if it is 20% by weight or less, an improvement in effect commensurate with the amount used can be obtained. The state in which the water repellent is applied is not particularly limited, and may be mixed into the nanofibers or coated on the surface of the nanofibers. The method of applying the water repellent agent is not particularly limited, and even if it is a method of dispersing or dissolving the water repellent agent in a spinning solution and spinning it, dipping method or spray coating method can be used after obtaining the nanofibers. It may be applied using a known device/method such as.

Nanofibers may contain other components as long as they do not impair the effects of the present invention, such as polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylic acid, polyvinylpyrrolidone, polyethylene, polypropylene, cyclic Polyolefin, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polyglycolic acid, polycaprolactone, polybutylene succinate, nylon 6, nylon 6,6, aromatic polyamide, polyurethane, polycarbonate, polystyrene, polysulfone, polyether sulfone, polyacrylonitrile , polymethyl methacrylate, cellulose, cellulose acetate, collagen, glucomannan derivatives, chitin, chitosan, polylysine, polyamic acid, polyimide, or polymeric components such as polyvinyl formal, silica, alumina, titania, zirconia, yttrium-stabilized zirconia, It may contain a metal oxide component such as barium titanate or hydroxyapatite, a hydrophilic material, a weathering agent, a stabilizer, and the like. These may be used alone or in combination of two or more. The concentration of other components is not particularly limited, and may be 0.1 to 20% by weight based on the nanofibers.

<Fiber sheet>
Since the fiber sheet of the present invention contains the above-mentioned nanofibers, fluffing and delamination between the fiber sheets are suppressed, and the fiber sheet has excellent adhesion to other materials.

The fiber sheet only needs to contain the above-mentioned nanofibers, and its basis weight is not limited, but it is preferably 0.01 to 20 g/m ² in order to easily exhibit the characteristics of nanofibers. The amount is preferably 0.1 to 5 g/m ² , more preferably 0.2 to 3 g/m ² . The thickness of the nanofiber sheet is also not particularly limited, and is preferably 0.5 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 30 μm.

The fiber sheet may be laminated or mixed with fibers other than the above-mentioned nanofibers as long as the effects of the present invention are not impaired. For example, it includes fibers made only of vinylidene fluoride polymer with an average fiber diameter of 10 nm to 10 μm, and a mixture of vinylidene fluoride polymer and vinylidene fluoride copolymer with a melting point of 150°C or less. Examples include fiber sheets in which nanofibers of 20 to 1000 nm are laminated or mixed at a weight ratio of 1:10 to 10:1.

The fiber sheet of the present invention may be a single layer or may be a stack of two or more layers of fiber sheets. The fiber sheet of the present invention has the effect that delamination between the fiber sheets is difficult to occur, so even if two or more layers are laminated, delamination is unlikely to occur during processing into a product, and properties are less likely to deteriorate. When two or more layers of fiber sheets are laminated, there is no particular limitation as long as each layer contains the above-mentioned nanofibers, and each layer may contain the same nanofibers, and the average fiber diameter and constituent components (for example, fluorine Nanofibers having different mixing ratios of vinylidene chloride polymer and vinylidene fluoride copolymer, types and contents of various additives, etc.) may be included.

The fiber sheet of the present invention can be laminated with a porous layer to form a fiber sheet composite. The fiber sheet composite can impart various properties such as mechanical strength, abrasion resistance, processability, and pleat properties to the fiber sheet by the porous layer. In addition, since the fiber sheet of the present invention has excellent adhesion with other materials, it can be integrated with the porous layer without going through integration processes such as adhesion or calendering, simplifying the manufacturing process. can do.

<Porous layer>
The porous layer used in the fiber sheet composite of the present invention is not particularly limited as long as it does not contain the above-mentioned nanofibers, and examples thereof include woven fabrics, knitted fabrics, nonwoven fabrics, papermaking, felt, nets, and microporous films. From the viewpoint of processability and availability, nonwoven fabric is preferred. Examples of nonwoven fabrics include, but are not limited to, thermal bond nonwoven fabrics, thermal calendar nonwoven fabrics, through-air nonwoven fabrics, airlaid nonwoven fabrics, spunlace nonwoven fabrics, needle punched nonwoven fabrics, wet-laid nonwoven fabrics, spunbond nonwoven fabrics, melt blown nonwoven fabrics, chemical bond nonwoven fabrics, flash spun nonwoven fabrics, Alternatively, electrospun nonwoven fabric can be exemplified. In general, nanofibers have a small fiber diameter, so the strength per single yarn is low.Also, in order to express sufficient functionality with a small fabric weight, the fabric weight of the fiber sheet used for product processing is low, and the sheet strength is low. It has the characteristic of being small, which leads to a decrease in workability when processing it into products. From this point of view, it is preferable to compensate for the low mechanical strength of the fiber sheet with the mechanical strength of the porous layer, and the average fiber diameter of the fibers constituting the porous layer is 1 to 100 μm, preferably 3 to 50 μm. , more preferably 5 to 40 μm. If the average fiber diameter is 1 μm or more, it will compensate for the lack of strength and rigidity of the fiber sheet, and a laminate with excellent processability into products will be obtained, and if it is 100 μm or less, the contact area between the porous layer and the fiber sheet will increase. By doing so, peeling resistance is improved.

The components constituting the porous layer are not particularly limited, and include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate and polylactic acid, polyamide resins such as nylon 6 and nylon 6,6, and polyurethane resins. Examples include fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polysulfone, polyethersulfone, and cellulose materials such as cellulose and cellulose acetate. These may be used alone or in combination of two or more. Among these, from the viewpoint of imparting mechanical properties and rigidity to the fiber sheet composite and improving processability into products, polyolefin resins, polyester resins, or cellulose materials are used as components constituting the porous layer. It is preferably contained in an amount of 50% by weight or more, more preferably 50% by weight or more. Further, from the viewpoint of processability and availability, the polyolefin resin is preferably polyethylene or polypropylene, the polyester resin is preferably polyethylene terephthalate, and the cellulose material is preferably cellulose.

When the porous layer is a nonwoven fabric, the fibers constituting the nonwoven fabric may be monocomponent fibers or composite fibers, but when composite fibers are used, the adhesion to the fiber sheet can be improved by post-processing such as heat treatment. This is preferable because it can improve the The composite fiber may be a blend of multiple components, or may have a composite form such as a concentric sheath-core type, an eccentric sheath-core type, a parallel type, an island-in-the-sea type, or a radial type. It may also be a composite fiber made of two or more materials with different melting points, and high melting point components include polypropylene, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, nylon 6, nylon 6,6, poly-L - Lactic acid is an example, and low-melting point components include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polyethylene terephthalate copolymer, poly-DL-lactic acid, polypropylene copolymer, and polypropylene. The melting point difference between the high melting point component and the low melting point component of the composite fiber is not particularly limited, but in order to widen the processing temperature range of heat treatment, it is preferably 15 ° C. or higher, and more preferably 30 ° C. or higher. .

The cross-sectional shape of the fibers constituting the nonwoven fabric is not particularly limited, and examples include circular, oval, flat, semicircular, star, triangular, quadrilateral, pentagonal, multilobal, array, T-shape, and horseshoe shape. However, from the viewpoint of improving adhesion with the fiber sheet, it is preferable that the shape be oval, flat, or semicircular. A nonwoven fabric containing fibers having an elliptical, flat, or semicircular cross-sectional shape is obtained by, for example, forming fibers having an oval, flat, or semicircular cross-sectional shape into a web shape, and then bonding the fibers with heat or adhesive. It can be obtained by a method in which a nonwoven fabric composed of fibers having a circular cross-sectional shape is thermally calendered. Furthermore, the surface of the fibers may be treated with a fiber finishing agent to the extent that the effects of the present invention are not impaired. can be granted. Moreover, a plurality of fibers having different fiber diameters and properties may be laminated or mixed within a range that does not impair the effects of the present invention.

The porous layer may contain antibacterial agents, deodorants, antistatic agents, conductive materials, fluorescent materials, smoothing agents, hydrophilic agents, water repellents, antioxidants, weathering agents, and surfactants within the range that does not impede the effects of the present invention. If necessary, additives such as a charge stabilizer and a charge stabilizer may be contained.

The porous layer is not particularly limited, but may have an uneven shape such as embossed points or shaping. Generally, a porous layer with uneven shapes such as embossed points or shaping has a small contact area with the fiber sheet, so it easily peels off, but the fiber sheet of the present invention can be easily peeled off from other materials. Because of its excellent adhesion, even if it has uneven shapes such as embossed points or shapes, it can be easily integrated.

The basis weight of the porous layer is not particularly limited, but is preferably from 5 to 150 g/m ² , more preferably from 10 to 105 g/m ² , even more preferably from 15 to 85 g/m ² . If the basis weight of the porous layer is 5 g/m2 or ^more , it can increase the rigidity of the fiber sheet composite and improve the processability into products, and if it is 150 g/ ^m2 or less, the properties derived from nanofibers can be improved. It becomes difficult to obstruct.

The thickness of the porous layer is not particularly limited, but is preferably 0.01 to 1 mm, more preferably 0.05 to 0.8 mm. Within the above range, the rigidity of the fiber sheet composite can be increased and the processability into products can be improved.

The specific volume of the porous layer is not particularly limited, but is preferably 1 to 10 cm ³ /g, preferably 2 to 8 cm ³ /g, and more preferably 3 to 6 cm ³ /g. If the specific volume of the porous layer is 10 cm ³ /g or less, satisfactory peeling resistance can be obtained, and if it is 1 cm ³ /g or more, the properties derived from nanofibers will not be easily disturbed.

<Fiber sheet composite>
Since the fiber sheet composite of the present invention has the above-mentioned fiber sheet and porous layer laminated, fluffing and delamination between the fiber sheets are suppressed, and it has excellent mechanical strength and rigidity, so it is easy to process into products. It has good properties. In addition, the fiber sheet and porous layer have excellent adhesion without having to undergo integration processes such as adhesion or calendering, making it possible to manufacture fiber sheet composites with high productivity and good operability. becomes possible.

The basis weight of the fiber sheet composite is not particularly limited, but is preferably from 5 to 200 g/m ² , more preferably from 10 to 150 g/m ² , even more preferably from 15 to 120 g/m ² . If the basis weight of the fiber sheet composite is 5 g/m ² or more, the rigidity of the fiber sheet composite increases and the processability into products can be improved, and if it is 200 g/m ² or less, it can be used as a filter material, for example. When used as a mask, sound absorbing material, etc., the weight can be reduced. The thickness of the fiber sheet composite is not particularly limited, but is preferably 0.01 to 2 mm, more preferably 0.05 to 1.5 mm, and even more preferably 0.06 to 1 mm. preferable. If the thickness of the fiber sheet composite is 0.01 mm or more, the rigidity of the fiber sheet composite increases and the processability into products can be improved, and if it is 2 mm or less, it can be used as a material for filters, masks, sound absorbers, etc. When used as a material, space can be saved.

The fiber sheet composite may be subjected to antistatic finishing, water repellent finishing, hydrophilic finishing, antibacterial finishing, ultraviolet absorption finishing, near-infrared absorption finishing, or electret finishing, depending on the purpose, as long as the effects of the present invention are not significantly impaired. It may also be applied. The fiber sheet composite of the present invention has sufficient mechanical strength and appropriate rigidity, and has been subjected to electrostatic processing, water-repellent processing, hydrophilic processing, antibacterial processing, ultraviolet absorption processing, near-infrared absorption processing, or electret processing. It also has the effect of being excellent in secondary processability, such as.

The fiber sheet composite of the present invention suppresses fluffing and delamination between the fiber sheets, has excellent adhesion between the fiber sheet and the porous layer and mechanical strength, and contains few components such as adhesives, so it is not particularly limited, but It can be suitably used as a filter medium for high-performance filters. The object to be filtered is not particularly limited, and may be a filter medium for air filters used in air conditioners or clean rooms, or a filter medium for liquid filters used for filtering wastewater, paint, abrasive particles, etc. It's okay. The type of filter is not particularly limited, and may be a flat membrane filter, a pleated filter, or a depth filter rolled up into a cylindrical shape.

When the fiber sheet composite is used as a filter medium for an air filter, the pressure loss when air is passed through at a flow rate of 5.3 cm/sec is preferably 10 to 1500 Pa, more preferably 20 to 300 Pa, and 50 More preferably, the pressure is between 200 Pa and 200 Pa. If the pressure loss is 10 Pa or more, sufficient collection efficiency can be obtained, and if the pressure loss is 1500 Pa or less, the air permeability of the gas filter increases, resulting in effects such as reducing power consumption and reducing the load on the fan. Furthermore, when air containing particles with a particle size of about 0.1 to 0.3 μm is passed through at a speed of 5.3 cm/sec, the collection efficiency of the particles is preferably 80% or more, and 90% or more. It is more preferable that there be. Furthermore, the QF value (=log(1-collection efficiency/100)/pressure loss×1000) is preferably 12 or more, more preferably 15 or more. The QF value is a value used as an index indicating the level of collection performance of an air filter, and the larger the QF value, the higher the performance.

<Method for manufacturing fiber sheet>
The method for producing the fiber sheet of the present invention is not particularly limited, and a spinning method using air, centrifugal force, electrostatic force, etc. is performed from a spinning solution containing a vinylidene fluoride polymer and a vinylidene fluoride copolymer. For example, it is preferable to use an electrospinning method using electrostatic force because the diameter of the nanofibers can be made small and uniform.

The electrostatic spinning method is a method in which a spinning solution is discharged and an electric field is applied to turn the discharged spinning solution into fibers, thereby obtaining fibers with a very small fiber diameter on a collector. For example, methods include spinning by extruding the spinning solution from a nozzle and applying an electric field, spinning by foaming the spinning solution and applying an electric field, and spinning by introducing the spinning solution to the surface of a cylindrical electrode and applying an electric field. Here are some ways to do it.

The spinning solution is not particularly limited as long as it has spinnability, but for example, a solution prepared by dispersing or dissolving vinylidene fluoride polymer and vinylidene fluoride copolymer in a solvent, or vinylidene fluoride copolymer dispersed or dissolved in a solvent, or vinylidene fluoride Although a polymer and a vinylidene fluoride copolymer melt-kneaded by heat or laser irradiation can be used, the average fiber diameter of the nanofibers constituting the fiber sheet of the present invention can be made small and uniform. From this point of view, it is preferable to use a spinning solution in which a vinylidene fluoride polymer and a vinylidene fluoride copolymer are dissolved in a solvent.

The solvent for dispersing or dissolving the vinylidene fluoride polymer and the vinylidene fluoride copolymer is not particularly limited, and includes water, methanol, ethanol, propanol, acetone, methyl ethyl ketone, tetrahydrofuran, cyclohexanone, γ-butyrolactone, N,N -Dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, triethyl phosphate, propylene glycol monomethyl ether, diethylene glycol ethyl methyl ether, toluene, xylene, pyridine, formic acid , acetic acid, tetrahydrofuran, dichloromethane, chloroform, and 1,1,1,3,3,3-hexafluoroisopropanol. , N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, triethyl phosphate, acetone, methyl ethyl ketone, tetrahydrofuran, cyclohexanone, or γ-butyrolactone. is preferred. These solvents may be used alone or in a mixture of two or more in any proportion.

Although additives such as the conductivity imparting agent and water repellent agent described above are not particularly limited, it is preferable to include them in the spinning solution. By including it in the spinning solution, the additive can be uniformly applied to the nanofibers, and various functions can be imparted without going through an additive application process, which is preferable. The content of the additive may be appropriately selected depending on the type and desired effect, and a content of 0.001 to 5% by weight based on the spinning solution is preferable because an effect commensurate with the use can be obtained.

The method for preparing the spinning solution is not particularly limited, and examples include methods such as stirring and ultrasonication. Further, the order of mixing is not particularly limited, and each component may be mixed simultaneously or sequentially. The stirring temperature and stirring time when preparing a spinning solution by stirring are not particularly limited as long as the vinylidene fluoride polymer and the vinylidene fluoride copolymer can be sufficiently mixed, and are, for example, 40 to 120°C. The mixture may be stirred for about 1 to 24 hours.

The viscosity of the spinning solution is not particularly limited, but is preferably from 10 to 10,000 cP, more preferably from 50 to 8,000 cP, even more preferably from 200 to 5,000 cP. If the viscosity of the spinning solution is 10 cP or more, good spinnability and spinning stability can be obtained, and if the viscosity is 10,000 cP or less, the spinning solution can be easily prepared and discharged during electrostatic spinning. The viscosity of the spinning solution can be adjusted by appropriately changing the molecular weight and concentration of the vinylidene fluoride polymer or vinylidene fluoride copolymer, and the type and mixing ratio of the solvent.

The spinning solution may be spun at room temperature, or may be heated or cooled to, for example, 0 to 200°C. Examples of the method for discharging the spinning solution include a method of discharging the spinning solution filled in a syringe or tank from a nozzle using a pump. The inner diameter of the nozzle is not particularly limited, and can be 0.1 to 1.5 mm, for example. Further, the amount of the spinning solution fed through a single hole is not particularly limited, and can be exemplified from 0.1 to 20 mL/hr.

The method of applying the electric field is not particularly limited as long as it allows stable electrostatic spinning, and for example, a high voltage may be applied to the nozzle or the spinning solution and the collector may be grounded. The voltage to be applied is not particularly limited as long as it can form fibers and stably spin the fibers, and may be 5 to 100 kV, for example. Further, the distance between the nozzle and the collector (spinning distance) is not particularly limited as long as the solvent is sufficiently volatilized, and may be 50 to 1000 mm, for example. Further, the electric field strength is not particularly limited, but is preferably 1 to 10 kV/cm, more preferably 2 to 5 kV/cm. If the electric field strength is 1 kV/cm or more, the peeling resistance between the fiber sheets or between the fiber sheet and the porous layer can be improved, and if the electric field strength is 10 kV/cm or less, the porosity of the fiber sheet can be increased. This makes it easier to achieve both high specific surface area and high air permeability. The material of the collector is not particularly limited as long as it can collect electrospun nanofibers, but conductive materials such as metals can be suitably used. Although the shape of the collector is not particularly limited, it is preferable to use a conveyor-shaped collector to continuously produce the fiber sheet.

It is preferable that the temperature and humidity of the atmosphere during electrospinning be controlled, and the range is not particularly limited, and examples thereof include 20 to 30° C. and 25 to 45 RH%. This temperature and humidity range can be controlled relatively easily throughout the year, and changes in spinning behavior and physical properties of the resulting fiber sheet due to changes in atmospheric temperature and humidity are less likely to occur.

When the fiber sheet is a laminate of two or more layers, an example of a method is to use a conveyor-like collector, arrange two or more rows of nozzles in the direction of travel of the conveyor, and perform electrostatic spinning. At this time, from the viewpoint of uniformity of the fiber sheet, it is preferable to perform electrostatic spinning while traversing the nozzle in a direction perpendicular to the conveyor traveling direction (width direction of the fiber sheet). Furthermore, the spinning solutions discharged from each row may be the same or different. When the spinning solutions are the same, a laminate of fiber sheets with the same physical properties is obtained, and when the spinning solutions are different, a laminate of fiber sheets with different physical properties is obtained. For example, the content of additives such as conductivity imparting agents and water repellents, the concentration of vinylidene fluoride polymers and vinylidene fluoride copolymers, and the type of solvent can be changed as appropriate to suit the desired physical properties. can.

<Method for manufacturing fiber sheet composite>
The method for producing the fiber sheet composite of the present invention is not particularly limited, and includes a method of electrostatically spinning a fiber sheet on a porous layer, a method of preparing a fiber sheet and a porous layer, and thermocompression bonding with a heated flat roll or embossing roll. Examples include a method of adhesive treatment using a hot melt agent or a chemical adhesive, but from the viewpoint of simplifying the manufacturing process, a method of electrospinning a fiber sheet on a porous layer is preferable. Since the fiber sheet of the present invention is characterized by excellent adhesion to other materials, it is possible to obtain a fiber sheet composite in which the fiber sheet and the porous layer are fully adhered without performing thermocompression bonding or adhesive treatment. It is possible.

The fiber sheet composite of the present invention may be subjected to heat treatment using circulating hot air or radiant heat for the purpose of further increasing the peel resistance between the fiber sheets and between the fiber sheet and the porous layer. In the case of thermocompression bonding using flat rolls or embossing rolls, the fiber sheet may be melted and formed into a film, or the area around the embossing points may be torn, resulting in considerable damage. For example, when a fiber sheet composite is used as a gas filter medium, damage tends to cause performance deterioration, such as a decrease in air permeability due to formation of a melted film or a decrease in collection properties due to tearing. . Furthermore, in the case of adhesion using a hot melt agent or a chemical adhesive, the voids between the fibers of the fiber sheet are filled by the component, which also tends to cause performance deterioration. On the other hand, heat treatment using circulating hot air or radiant heat is preferable because there is little damage to the fiber sheet and sufficient peeling resistance can be imparted.

When heat treatment is performed using circulating hot air or radiant heat, the fibers constituting the porous layer preferably include thermally bondable conjugate fibers, although there are no particular limitations thereon. The melting point of the low melting point component of the heat-adhesive composite fiber is not particularly limited, but from the viewpoint of expanding the range of heat treatment processing conditions, it is preferably 20°C or more lower than the melting point of the vinylidene fluoride polymer used in the present invention, and 30°C or more. It is more preferable that the temperature is lower than ℃. Furthermore, the heat treatment temperature using circulating hot air or radiant heat is not particularly limited, but can be set within a range below the melting point of the vinylidene fluoride polymer used in the present invention while checking the balance between peeling resistance and desired properties. .

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto. In addition, the measurement methods or definitions of the physical property values shown in the examples are shown below.

<Melting point of vinylidene fluoride polymer and vinylidene fluoride copolymer>
Using a PerkinElmer DSC measuring device (DSC8500), the temperature was measured in the temperature range from room temperature to 230°C, at a temperature increase/decrease rate of 10°C/min, under nitrogen atmosphere, and the temperature at the top of the melting peak in the 2nd run was measured. was defined as the melting point (°C).
<Average fiber diameter of nanofibers and fibers constituting the porous layer>
Using a scanning electron microscope (SU-8000) manufactured by Hitachi, Ltd., the fiber sheet and porous layer were observed at 500 to 30,000 times magnification, and the fiber diameters of 50 or more fibers were measured using image analysis software. The average value was taken as the average fiber diameter.
<Filter performance>
Using a filter efficiency automatic detection device (Model 8130) manufactured by TSI, sample sodium chloride (particle size: 0.07 μm (number median diameter), particle concentration: 20 mg/m ³ ) at a flow rate of 5.3 cm/sec. The pressure drop and collection efficiency were measured.
<Workability>
When the fiber sheet composite is passed through the processing line, the fuzziness, the degree of delamination between the fiber sheets, and the degree of adhesion between the fiber sheet and the porous layer are visually judged and marked as ◎, ○, or × as follows. Workability was evaluated in three stages.
◎: When passed through the processing line, no fluffing, no interlayer peeling between the fiber sheets, and no peeling between the fiber sheet and the porous layer occurred, which was at a satisfactory level.
○: Slight fluffing occurs when passing through the processing line, but no delamination between the fiber sheets or delamination between the fiber sheet and the porous layer is observed, which is at an acceptable level.
×: When passed through the processing line, the properties deteriorate due to fuzzing, delamination between the fiber sheets, or delamination between the fiber sheet and the porous layer, and the product cannot be processed into a product.

[Example 1]
19 parts by weight of vinylidene fluoride polymer manufactured by Solvay Specialty Polymers (trade name: Solef 6010; melting point: 170°C), vinylidene fluoride copolymer manufactured by Arkema (trade name: Kynar 2500; vinylidene fluoride and hexafluoropropylene) 1 part by weight of N,N-dimethylacetamide, 0.05 part by weight of sodium dodecyl sulfate as a conductivity imparting agent, and fluorooctylsilsesquioxane (as a water repellent). 1 part by weight (manufactured by NVD Nanotechnologies, Inc.) was mixed to prepare a spinning solution.
A conveyor-like collector is used as the collecting part, and the collector surface is made of a nonwoven fabric (thickness: about 0.3 mm, basis weight: about 0.3 mm, basis weight: approximately 80 g/m ² ) was applied as a porous layer. Next, three nozzles with an inner diameter of 0.3 mm and 12 holes were installed in the conveyor traveling direction with an interval of 380 mm between them. Electrostatic spinning was performed on the layers to produce a fiber sheet composite in which three layers of fiber sheets and a porous layer were laminated. The spinning conditions of this example were: the amount of liquid sent to each nozzle through a single hole using a pump was 2.4 mL/hr, the applied voltage was 45 kV, the spinning distance was 100 mm, the nozzle traverse width was 170 mm, and the traverse speed was 150 mm/hr. Electrospinning was carried out at a temperature of 25° C. and a humidity of 30 RH% in the spinning space, adjusting the feeding speed of the porous layer by a conveyor-like collector so that the basis weight of the fiber sheet was 1.7 g/m ² .
The average fiber diameter of the nanofibers constituting the fiber sheet was 110 nm, and the filter performance of the fiber sheet composite was a pressure loss of 140.0 Pa and a collection efficiency of 99.99%. In addition, although a slight amount of fuzz occurred when passing through the processing line, no delamination between the fiber sheets or delamination between the fiber sheet and the porous layer was observed, indicating acceptable processability and filter performance after processing. The pressure loss was 142.5 Pa and the collection efficiency was 99.94%.

[Example 2]
Same as Example 1 except that the vinylidene fluoride polymer (trade name: Solef6010) was changed to 18.5 parts by weight and the vinylidene fluoride copolymer (trade name: Kynar2500) was changed to 1.5 parts by weight. A spinning solution was prepared. Next, the spinning conditions were the same as in Example 1, except that the amount of liquid sent through each nozzle using a pump was changed to 0.8 mL/hr, and the fiber sheet was made to have a fabric weight of 0.8 g/ ^m2 . The feeding speed of the porous layer by the conveyor-like collector was adjusted to produce a fiber sheet composite in which three layers of fiber sheets and the porous layer were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 110 nm, and the filter performance of the fiber sheet composite was a pressure loss of 114.6 Pa and a collection efficiency of 99.98%. In addition, when passed through the processing line, there was no occurrence of fuzz, delamination between the fiber sheets, or delamination between the fiber sheet and the porous layer, and the processability was satisfactory, and the filter performance after processing was determined by the pressure loss was 117.2 Pa, and the collection efficiency was 99.96%.

[Example 3]
Same as Example 1 except that the vinylidene fluoride polymer (trade name: Solef 6010) was changed to 16.5 parts by weight and the vinylidene fluoride copolymer (trade name: Kynar 2500) was changed to 3.5 parts by weight. A spinning solution was prepared. Next, the spinning conditions were the same as in Example 1 except that the traverse speed of the nozzle was changed to 220 mm/sec, and the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the basis weight of the fiber sheet was 0.7 g/ ^m2 . A fibrous sheet composite in which three layers of fibrous sheets and a porous layer were laminated was produced by adjusting the amount. The average fiber diameter of the nanofibers constituting the fiber sheet was 110 nm, and the filter performance of the fiber sheet composite was a pressure loss of 44.3 Pa and a collection efficiency of 98.0%. In addition, when passed through the processing line, there was no occurrence of fuzz, delamination between the fiber sheets, or delamination between the fiber sheet and the porous layer, and the processability was satisfactory, and the filter performance after processing was determined by the pressure loss was 42.1 Pa, and the collection efficiency was 96.0%.

[Example 4]
The spinning solution was prepared in the same manner as in Example 1, except that the vinylidene fluoride polymer (trade name: Solef6010) was changed to 15 parts by weight, and the vinylidene fluoride copolymer (trade name: Kynar 2500) was changed to 5 parts by weight. Prepared. Next, under the same spinning conditions as in Example 3, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fabric weight of the fiber sheet was 0.4 g/ ^m2 , and the three layers of fiber sheets and the porous layer were combined. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 130 nm, and the filter performance of the fiber sheet composite was a pressure loss of 46.5 Pa and a collection efficiency of 98.3%. In addition, when passed through the processing line, there was no occurrence of fuzz, delamination between the fiber sheets, or delamination between the fiber sheet and the porous layer, and the processability was satisfactory, and the filter performance after processing was determined by the pressure loss was 42.1 Pa, and the collection efficiency was 95.2%.

[Example 5]
The spinning solution was prepared in the same manner as in Example 1, except that the vinylidene fluoride polymer (trade name: Solef 6010) was changed to 10 parts by weight and the vinylidene fluoride copolymer (trade name: Kynar 2500) was changed to 10 parts by weight. Prepared. Next, the spinning conditions were the same as in Example 3, except that the amount of liquid sent through each nozzle using a pump was changed to 3.2 mL/hr, and the fiber sheet was made to have a fabric weight of 0.3 g/ ^m2 . The feeding speed of the porous layer by the conveyor-like collector was adjusted to produce a fiber sheet composite in which three layers of fiber sheets and the porous layer were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 120 nm, and the filter performance of the fiber sheet composite was a pressure loss of 38.3 Pa and a collection efficiency of 96.7%. In addition, due to the increased proportion of vinylidene fluoride copolymer with a melting point of 150°C or lower, the durability of the nanofibers was slightly lowered, and slight fuzz was observed when passed through the processing line. No peeling was observed and the processability was acceptable, and the filter performance after processing was a pressure loss of 35.0 Pa and a collection efficiency of 93.7%.

[Example 6]
The spinning solution was prepared in the same manner as in Example 1, except that the vinylidene fluoride polymer (trade name: Solef6010) was changed to 18 parts by weight, and the vinylidene fluoride copolymer (trade name: Kynar 2500) was changed to 2 parts by weight. Prepared.
A conveyor-like collector is used as the collection part, and the collector surface is made of a nonwoven fabric (thickness: about 0.3 μm, basis weight: about 0.3 μm, basis weight: approximately 80 g/m ² ) was applied as a porous layer. Next, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and electrostatic spinning was performed on the porous layer while traversing the nozzle in a direction perpendicular to the traveling direction of the conveyor to form a single-layer fiber sheet. A fiber sheet composite in which porous layers were laminated was produced. The spinning conditions of this example were as follows: The amount of liquid sent through a single hole to each nozzle using a pump was 1.6 mL/hr, the applied voltage was 45 kV, the spinning distance was 100 mm, the nozzle traverse width was 110 mm, and the traverse speed was 150 mm/hr. Electrospinning was carried out at a temperature of 25° C. and a humidity of 30 RH% in the spinning space, adjusting the feeding speed of the porous layer by a conveyor-like collector so that the fabric weight of the fiber sheet was 0.6 g/m ² .
The average fiber diameter of the nanofibers constituting the fiber sheet was 100 nm, and the filter performance of the fiber sheet composite was a pressure loss of 102.0 Pa and a collection efficiency of 99.93%. In addition, when passed through the processing line, no fluffing or separation of the fiber sheet and the porous layer occurred, and the processability was satisfactory.The filter performance after processing was as follows: pressure loss was 101.4 Pa, collection The efficiency was 99.87%.

[Example 7]
The same procedure as in Example 6 was carried out, except that the vinylidene fluoride copolymer was changed to KynarADS2 (trade name: KynarADS2, a random copolymer of vinylidene fluoride and hexafluoropropylene, melting point: 115°C) manufactured by Arkema. A spinning solution was prepared. Next, under the same spinning conditions as in Example 6, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fiber sheet had a basis weight of 0.5 g/ ^m2 , and the single-layer fiber sheet and the porous layer were separated. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 100 nm, and the filter performance of the fiber sheet composite was a pressure loss of 105.0 Pa and a collection efficiency of 99.92%. In addition, when it was passed through the processing line, no fluffing or separation of the fiber sheet and the porous layer occurred, and the processability was satisfactory.

[Example 8]
The same procedure as in Example 6 was carried out, except that the vinylidene fluoride copolymer was changed to KynarUltraFlexB (random copolymer of vinylidene fluoride and hexafluoropropylene, melting point: 105°C) manufactured by Arkema. A spinning solution was prepared. Next, under the same spinning conditions as in Example 6, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fiber sheet had a basis weight of 0.6 g/ ^m2 , and the single-layer fiber sheet and the porous layer were separated. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 100 nm, and the filter performance of the fiber sheet composite was a pressure loss of 103.0 Pa and a collection efficiency of 99.92%. In addition, when it was passed through the processing line, no fluffing or separation of the fiber sheet and the porous layer occurred, and the processability was satisfactory.

[Example 9]
The same procedure as in Example 6 was carried out, except that the vinylidene fluoride copolymer was changed to Kynar 2800 (trade name, manufactured by Arkema) (random copolymer of vinylidene fluoride and hexafluoropropylene, melting point: 145°C). A spinning solution was prepared. Next, under the same spinning conditions as in Example 6, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fiber sheet had a basis weight of 0.6 g/ ^m2 , and the single-layer fiber sheet and the porous layer were separated. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 100 nm, and the filter performance of the fiber sheet composite was a pressure loss of 98.0 Pa and a collection efficiency of 99.89%. Further, when the fiber sheet was passed through the processing line, a slight amount of fluffing occurred, but no peeling between the fiber sheet and the porous layer was observed, and the processability was acceptable.

[Example 10]
The fiber sheet composite produced in Example 1 was further heat-treated with circulating hot air at 100°C. The filter performance of the fiber sheet composite after heat treatment was that the pressure loss was 160.0 Pa and the collection efficiency was 99.99%. In addition, when passed through the processing line, there was no occurrence of fuzz, delamination between the fiber sheets, or delamination between the fiber sheet and the porous layer, and the processability was satisfactory, and the filter performance after processing was determined by the pressure loss was 160.0 Pa, and the collection efficiency was 99.91%.

[Comparative example 1]
20 parts by weight of vinylidene fluoride polymer (trade name: Solef6010) manufactured by Solvay Specialty Polymers, 80 parts by weight of N,N-dimethylacetamide, 0.05 parts by weight of sodium dodecyl sulfate as a conductivity imparting agent, and fluorooctyl as a water repellent. A spinning solution was prepared by mixing 1 part by weight of silsesquioxane. Next, under the same spinning conditions as in Example 1, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fabric weight of the fiber sheet was 0.8 g/ ^m2 , and the three layers of the fiber sheet and the porous layer were combined. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 110 nm. In addition, the filter performance of the fiber sheet composite was 123.4 Pa in pressure loss and 99.97% in collection efficiency, but peeling of the top layer of the fiber sheet was confirmed when passing through the processing line. could not be processed.

[Comparative example 2]
A spinning solution was prepared in the same manner as in Comparative Example 1. Next, under the same spinning conditions as in Example 6, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fiber sheet had a basis weight of 0.5 g/ ^m2 , and the single-layer fiber sheet and the porous layer were separated. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 120 nm. In addition, the filter performance of the fiber sheet composite was that the pressure loss was 96.0 Pa and the collection efficiency was 99.82%, but when it was passed through the processing line, the pressure loss was 93.2 Pa, and the collection efficiency was 99.82%. The efficiency was 95.3%, and the filter performance was significantly degraded.

[Comparative example 3]
20 parts by weight of vinylidene fluoride copolymer (trade name: Kynar 2800), 80 parts by weight of N,N-dimethylacetamide, 0.05 parts by weight of sodium dodecyl sulfate as a conductive agent, fluorooctylsilsesquioxane as a water repellent. 1 part by weight was mixed to prepare a spinning solution. Next, under the same spinning conditions as in Example 1, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fabric weight of the fiber sheet was 0.9 g/ ^m2 , and the three layers of the fiber sheet and the porous layer were combined. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 120 nm, the pressure loss of the fiber sheet composite was 160.0 Pa, and the collection efficiency was 99.99%. However, because the nanofibers are made of a vinylidene fluoride copolymer with a melting point of 150°C or lower, they lack durability, and when passed through a processing line, the pressure loss is 134.9 Pa and the collection efficiency is 99.77. %, and the filter performance has significantly decreased.

[Comparative example 4]
A spinning solution was prepared by mixing 20 parts by weight of vinylidene fluoride copolymer (trade name: Kynar 2500), 56 parts by weight of N,N-dimethylacetamide, and 24 parts by weight of tetrahydrofuran. Next, the spinning conditions were the same as in Example 1 except that the spinning distance was changed to 180 mm, and the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the basis weight of the fiber sheet was 2.4 g/ ^m2 . A fiber sheet composite was produced in which three layers of fiber sheets and a porous layer were laminated. The average fiber diameter of the nanofibers constituting the fiber sheet was 260 nm, the pressure loss of the fiber sheet composite was 140.0 Pa, and the collection efficiency was 99.63%. However, because the nanofibers are made of a vinylidene fluoride copolymer with a melting point of 150°C or lower, they lack durability, and when passed through a processing line, the pressure loss is 104.9 Pa and the collection efficiency is 96.3. %, and the filter performance deteriorated significantly.

[Comparative example 5]
16 parts by weight of vinylidene fluoride copolymer manufactured by Arkema (trade name: Kynar 3120; block copolymer of vinylidene fluoride and hexafluoropropylene, melting point: 165°C), 58.8 parts by weight of N,N-dimethylformamide , 25.2 parts by weight of acetone, and 0.02 parts by weight of sodium dodecyl sulfate as a conductivity imparting agent were mixed to prepare a spinning solution. Next, the spinning conditions were the same as in Example 1 except that the amount of liquid fed through each nozzle using a pump was changed to 3.0 mL/hr and the spinning distance was changed to 125 mm, and the fabric weight of the fiber sheet was 1.0 g/hr. A fiber sheet composite in which three layers of fiber sheets and a porous layer were laminated was produced by adjusting the feeding speed of the porous layer by a conveyor-like collector so that the porous layer had a thickness of m ² . The average fiber diameter of the nanofibers constituting the fiber sheet was 120 nm. In addition, regarding the filter performance of the fiber sheet composite, the pressure loss was 125.0 Pa and the collection efficiency was 99.85%, but when the fiber sheet composite was passed through the processing line, peeling of the top layer of the fiber sheet was confirmed. could not be processed.

[Comparative example 6]
The same procedure as in Example 6 was carried out, except that the vinylidene fluoride copolymer was changed to Kynar 2850 (trade name: Kynar 2850, a random copolymer of vinylidene fluoride and hexafluoropropylene, melting point: 155°C) manufactured by Arkema. A spinning solution was prepared. Next, under the same spinning conditions as in Example 1, the feeding speed of the porous layer by the conveyor-like collector was adjusted so that the fiber sheet had a basis weight of 0.6 g/ ^m2 , and the three layers of the fiber sheet and the porous layer were combined. A fiber sheet composite was produced in which the fiber sheets were laminated. The average fiber diameter of the nanofibers constituting the sheet was 100 nm. In addition, regarding the filter performance of the fiber sheet composite, the pressure loss was 110.0 Pa and the collection efficiency was 99.92%, but peeling of the top layer of the fiber sheet was confirmed when passing it through the processing line, and the product could not be processed.

[Comparative Example 7]
The fiber sheet composite produced in Comparative Example 6 was further heat-treated with circulating hot air at 100°C. The filter performance of the three-layer fiber sheet composite after heat treatment was a pressure loss of 120.0 Pa and a collection efficiency of 99.5%, but the top layer of the fiber sheet peeled off when passed through the processing line. It was confirmed that the product could not be processed.

The results of the above examples and comparative examples are summarized in Tables 1 to 3.

As can be seen from the results in Tables 1 to 3, when the nanofibers constituting the fiber sheet are made of vinylidene fluoride polymer (Comparative Examples 1 and 2), and when they are made of vinylidene fluoride copolymer (Comparative Examples 3 to 3), 5) In the case of a mixture of a vinylidene fluoride polymer and a vinylidene fluoride copolymer with a melting point exceeding 150°C (Comparative Examples 6 and 7), during product processing, fluffing, delamination between fiber sheets, Although performance is degraded due to durability issues, Examples 1 to 10 containing a mixture of vinylidene fluoride polymer and vinylidene fluoride copolymer with a melting point of 150°C or lower have good processability. This means that the performance deterioration during product processing is small. Further, in the comparison of Examples 6 to 9, it can be seen that processability tends to be improved when a vinylidene fluoride copolymer having a lower melting point is used. In addition, in the comparison of Examples 1 to 5, when the mixing ratio (weight ratio) of vinylidene fluoride polymer and vinylidene fluoride copolymer was 75:25 to 92.5:7.5, processing It can be seen that there is a tendency for the performance to improve. Furthermore, it can be seen that in Example 10, which was further heat-treated with circulating hot air compared to Example 1, the workability tended to be improved. On the other hand, in Comparative Example 7, since it does not contain a vinylidene fluoride copolymer having a melting point of 150° C. or less, it can be seen that the processability is not improved even if it is further heat-treated with circulating hot air.

The fiber sheet of the present invention does not impair the inherent properties of nanofibers, is less prone to fluffing or delamination between fiber sheets, and has excellent adhesion to other materials. In addition, the fiber sheet composite of the present invention is less likely to cause fuzzing or delamination between the fiber sheets, and has excellent adhesion between the fiber sheet and the porous layer without going through an integration process such as adhesion or calendering. Since fiber sheet composites can be provided with high productivity and good operability, they can be used as filter media, sound-absorbing materials, masks, waterproof and moisture-permeable membranes, separators for secondary batteries, sensor materials, cell culture substrates, etc. It can be used suitably.

Claims (7)

A fiber sheet containing nanofibers having an average fiber diameter of 20 to 1000 nm, the nanofibers comprising a mixture of a vinylidene fluoride polymer and a vinylidene fluoride copolymer with a melting point of 150 ° C. or less. fiber sheet. The fiber sheet according to claim 1, wherein a mixing ratio (weight ratio) of the vinylidene fluoride polymer and the vinylidene fluoride copolymer is 50:50 to 95:5. The fiber sheet according to claim 1 or 2, wherein the fiber sheet is a laminate of two or more layers. The method for producing a fiber sheet according to any one of claims 1 to 3, wherein a spinning solution containing a vinylidene fluoride polymer and a vinylidene fluoride copolymer having a melting point of 150° C. or less is electrospun. A method for producing a fiber sheet, comprising further heat-treating the fiber sheet obtained by the method according to claim 4 with circulating hot air or radiant heat. A fiber sheet composite in which the fiber sheet according to any one of claims 1 to 3 and a porous layer are laminated. A filter medium comprising the fiber sheet composite according to claim 6.