Laminated fiber sheet and method for producing same

Abstract

Provided is a fluorine-free laminated fiber sheet.　The fluorine-free laminated fiber sheet of the invention is formed by laminating a nanofiber layer composed of nanofibers having an average fiber diameter of 20 nm or more and less than 1,000 nm and a porous layer composed of fibers having an average fiber diameter of 1 μm or more. The fluorine-free laminated fiber sheet is characterized in that: for the porous layer, air suction is applied until the pressure reaches 125 Pa in accordance with JIS L 1096, and the Frazier air permeability calculated from the air flow rate at this time and the test area is in the range of 1-150 cm3 / cm2 / sec; the density of the porous layer is in the range of 0.1-1 g / cm3; and on the surface of the porous layer that is not in contact with the nanofibers, there is an oil-repellent film composed of an organosilicone comprising T units in its backbone.

Description

Laminated fiber sheet and method for producing same

[0001] The present invention relates to a fluorine-free laminated fiber sheet and a method for producing the same.

[0002] In recent years, ultrafine fibers with diameters of several to several hundred nanometers (nm), so-called nanofibers, have been attracting attention. Nanofibers have characteristics such as a large specific surface area, small interfiber voids in fiber sheets containing nanofibers, uniform void size distribution, and high porosity. Therefore, nanofibers are expected to be applied to filter media, sound-absorbing materials, masks, waterproof and breathable membranes, secondary battery separators, sensor materials, cell culture substrates, and the like. Nanofibers made from polyvinylidene fluoride polymers, among others, have excellent properties such as mechanical strength, heat resistance, chemical resistance, and processability into nanofibers, making them suitable for a wide range of applications.

[0003] Nanofibers are currently used in a variety of dust-collecting filters. Exhaust gas typically contains sulfuric acid mist, hydrochloric acid mist, oil mist, and other contaminants, and these filters are operated at high temperatures for long periods of time. For this reason, proposed fiber materials include heat- and chemical-resistant filters that use fluororesins, silicone resins, colloidal alumina, and other materials attached to a heat-resistant base fabric to improve the filter's heat resistance, chemical resistance, and durability. Other filters use fluorine materials to eliminate the effects of oil mist and improve antifouling properties.

[0004] The present applicant previously proposed a fiber sheet obtained by electrospinning a polyvinylidene fluoride copolymer primarily composed of vinylidene fluoride and collecting the spun fibers, the fiber sheet having an average fiber diameter of 20 nm or more and less than 1,000 nm, a melting temperature of 155°C or more, and a heat of fusion of 45 J / g or less as measured by DSC (Patent Document 1). Generally, nanofibers have a small diameter and low mechanical strength per fiber. Therefore, the surface of a fiber sheet containing nanofibers can break single fibers or tear the nonwoven fabric due to friction when the nanofibers come into contact with processing equipment, and the low rigidity of the nanofiber sheet can also reduce processability. For this reason, a method has been proposed in which the nanofiber sheet is laminated and integrated with a porous layer that has excellent strength and rigidity (e.g., Patent Document 2).

[0005] Fiber sheets using hydrophobic fluorine materials, such as those described in Patent Document 1, repel water from the surface of the fiber sheet, but allow oil to penetrate through the surface of the fiber sheet. Furthermore, since fluorine materials have a lower surface free energy than other materials, adhesion between laminates is reduced, making it difficult to laminate and integrate them with a porous layer. Furthermore, due to concerns about the environmental impact and waste disposal issues associated with fluorine materials, there is a growing social demand to avoid their use.

[0006] Patent Document 3 discloses a filter in which a silane-based coating agent is applied to a fiber filter material made of woven or nonwoven fabric to enhance chemical resistance. Patent Document 4 discloses an air filter in which an oil-repellent film made of a silica sol hydrolyzate containing the fluorine-containing functional group component is formed on the fiber surface of a nonwoven fabric.

[0007] JP 2015-45114 A JP 2007-30175 A JP 2005-220459 A JP 2021-098157 A

[0008] When using fiber sheets made from fluorine-containing compounds as raw materials, oil repellency and adhesion become issues. These issues are also required for fiber sheets that do not use fluorine materials. In terms of oil repellency, there have been no nanofiber materials (polymers) that are oil repellent without using fluorine. Regarding adhesion, for example, during pleating, this can affect the adhesion (peeling) of the laminate, and can also affect the processability of nonwoven fabrics with a large basis weight.

[0009] The present invention aims to solve the above-mentioned problems and to provide a fiber sheet that does not use a fluorine-containing compound and has excellent oil repellency and adhesion, high flexibility, and also high processability, such as pleating.

[0010] As a result of extensive research into solving the above problems, the inventors discovered that by adopting a specific structure, a fluorine-free laminated fiber sheet that solves the above problems can be obtained, and thus completed the present invention.

[0011] That is, the present invention has the following configuration: [1] A laminated fiber sheet comprising a nanofiber layer containing nanofibers having an average fiber diameter of 20 nm or more and less than 1000 nm and a porous layer made of fibers having an average fiber diameter of 1 μm or more, wherein the laminated fiber sheet has a Frazier air permeability of 1 to 150 cm when air is sucked to a pressure of 125 Pa in accordance with JIS L 1096 and calculated from the air flow rate and test area at that time. ３ / cm ２ / sec, and the density of the porous layer is 0.1 to 1 g / cm ３ [2] A fluorine-free laminated fiber sheet according to [1], characterized in that the main component of the oil-repellent film is an organosilicon obtained by curing a compound represented by formula (1). In formula (1), R １are independently hydrogen or an alkyl group having 1 to 2 carbon atoms, and n is an integer of 2 to 6. [3] The fluorine-free laminated fiber sheet according to [1] or [2], wherein the oil-repellent film contains the compound represented by formula (1) as a main component and further contains an organosilicon formed by curing the compound represented by formula (2). In formula (2), Me is a methyl group, and m is an integer of 5 to 100. [4] The fluorine-free laminated fiber sheet of [1] or [2], wherein the polymer constituting the nanofiber layer is a polymer that does not contain fluorine. [5] The fluorine-free laminated fiber sheet of [1] or [2], wherein the nanofiber layer is a laminate of two or more layers. [6] The fluorine-free laminated fiber sheet of [1] or [2], wherein a porous substrate for forming a nanofiber sheet is laminated on the nanofiber layer side. [7] The porous layer has a basis weight of 20 to 150 g / m ２ [8] A fluorine-free laminated fiber sheet according to [1], wherein the porous layer is made of a nanofiber layer containing nanofibers having an average fiber diameter of 20 nm or more and less than 1000 nm, and a porous layer is made of fibers having an average fiber diameter of 1 μm or more, and the density of the porous layer is 0.1 to 1 g / cm ３ a method for producing a fluorine-free laminated fiber sheet according to [8], which comprises a step of forming an oil-repellent film by the following steps: a step of applying an oil-repellent film-forming coating liquid containing an organosilicon to the surface of the porous layer, and a step of curing the coating film to form a porous layer having an oil-repellent film. [9] A method for producing a fluorine-free laminated fiber sheet according to [8], which comprises a step of laminating a nanofiber layer on the surface of the porous layer on which the oil-repellent film is not formed.

[0012] The laminated fiber sheet of the present invention is a laminated fiber sheet that does not use a fluorine-containing compound, has excellent oil repellency and adhesion, is highly flexible, and is also highly processable, such as for pleating. This laminated fiber sheet is resistant to interlayer delamination between the laminated fiber sheets, without impairing the inherent properties of the nanofibers. Furthermore, the fiber sheet for filters has an oil-repellent porous layer membrane on the outermost layer, and is excellent in water and oil repellency and stain resistance. Furthermore, since the present invention does not use a fluorine-containing material, it is a fiber sheet for filters that is environmentally friendly and easy to handle waste disposal.

[0013] Hereinafter, an embodiment of the fluorine-free laminated fiber sheet of the present invention will be described in detail.

[0014] <Laminated fiber sheet> The fluorine-free laminated fiber sheet of the present invention is a laminated fiber sheet comprising a nanofiber layer containing nanofibers having an average fiber diameter of 20 nm or more and less than 1000 nm and a porous layer made of fibers having an average fiber diameter of 1 μm or more, laminated together, and the laminated fiber sheet has a Frazier air permeability of 1 to 150 (cm), calculated from the air flow rate and test area when air is sucked to a pressure of 125 Pa in accordance with JIS L 1096. ３ / cm ２ / sec), and the density of the porous layer constituting the porous layer is 0.1 to 1 g / cm ３ and further characterized in that the porous layer surface has an oil-repellent film made of an organic silicone containing T units in its skeleton.

[0015] The average fiber diameter of the nanofibers constituting the nanofiber layer is 20 nm or more but less than 1000 nm, preferably 30 to 600 nm, and more preferably 50 to 300 nm. If the average fiber diameter of the nanofibers is less than 1000 nm, the specific surface area is increased, making it easier to exhibit the characteristics inherent to nanofibers, such as excellent filtering performance. If the average fiber diameter of the nanofibers is 20 nm or more, satisfactory single fiber strength is achieved, and breakage and fluffing of the nanofibers during processing into products can be suppressed. Note that the average fiber diameter of the nanofibers is smaller than the average fiber diameter of the nonwoven fabric constituting the porous layer.

[0016] Examples of materials constituting the nanofibers include fluorine-free polymeric materials such as polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyamide, polyurethane, polystyrene, polysulfone, polyethersulfone, polyacrylonitrile, polymethyl methacrylate, polyglycolic acid, polycaprolactone, polyvinyl acetate, polycarbonate, polyimide, polyetherimide, polyetherimide siloxane copolymer, polyurea, cellulose, cellulose derivatives, chitin, chitosan, collagen, gelatin, and copolymers thereof. The weight-average molecular weight of the resin is not particularly limited, but is preferably in the range of 10,000 to 10,000,000, more preferably in the range of 50,000 to 5,000,000, and even more preferably in the range of 100,000 to 1,000,000. A weight-average molecular weight of 10,000 or more is preferred because of its excellent fiber-forming properties, while a weight-average molecular weight of 10,000,000 or less is preferred because of its excellent solubility and thermoplasticity and ease of processing. Among these, polyetherimide siloxane copolymers and polyurethanes are preferred.

[0017] The nanofibers may contain, but are not limited to, a conductive agent. The inclusion of a conductive agent in the nanofibers results in ultrafine nanofibers, suppressing the generation of beaded structures known as "beads," resulting in homogeneous nanofibers and allowing the nanofibers to more easily exhibit their inherent properties. Furthermore, the high voltage applied during the electrospinning process described below strongly attracts the nanofibers toward the collector and densely collects them, improving adhesion between the nanofibers themselves and between the nanofibers and other materials, thereby suppressing fuzzing and delamination. Examples of conductive agents include anionic surfactants such as sodium dodecyl sulfate, cationic surfactants such as tetrabutylammonium bromide, or organic or inorganic salts. A concentration of the conductive agent of 0.02 to 10% by mass relative to the weight of the nanofibers provides a suitable effect.

[0018] The nanofibers may contain other components as long as the effects of the present invention are not impaired. For example, polymer components 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, polyethersulfone, polyacrylonitrile, polymethyl methacrylate, cellulose, cellulose acetate, collagen, glucomannan derivatives, chitin, chitosan, polylysine, polyamic acid, polyimide, polyetherimide, polyetherimide siloxane copolymer, or polyvinyl formal; metal oxide components such as silica, alumina, titania, zirconia, yttrium-stabilized zirconia, barium titanate, or hydroxyapatite; hydrophilic materials; weathering agents; stabilizers; and the like. These may be used alone or in combination of two or more. The concentration of the other components is not particularly limited, and may be 0.1 to 20% by mass relative to the nanofibers.

[0019] The nanofibers may be single-component fibers or composite fibers containing multiple components. The composite form is not particularly limited, and may be a blend of multiple components, a side-by-side composite, or a sheath-core composite. The nanofiber layer may also contain additives such as antibacterial agents, deodorants, antistatic agents, conductive materials, fluorescent materials, smoothing agents, hydrophilic agents, water repellents, hydrophilic and oil repellents, antioxidants, weathering agents, surfactants, and charge stabilizers, as needed, provided the effects of the present invention are not impaired.

[0020] The melting point or glass transition point of the nanofiber is not particularly limited, but is preferably 50° C. or higher, more preferably 80° C. or higher, and even more preferably 100° C. or higher. A melting point or glass transition point of 50° C. or higher is preferred because the nanofiber layer is less likely to melt even when processed under high-temperature conditions during processing into products, and the inherent properties of the nanofiber are more likely to be exhibited.

[0021] The nanofibers may be crystalline or amorphous. If the nanofibers are crystalline, the degree of crystallinity is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. A crystallinity of 10% or more is preferable because the mechanical strength of the fibers is high and the nanofiber layer is less likely to break during processing into products.

[0022] The surface shape of the nanofiber is not particularly limited and may be smooth or uneven. A smooth surface can increase the strength of the fiber, while an uneven surface can increase the specific surface area of ​​the fiber. The cross-sectional shape of the nanofiber may be circular, elliptical, or flat, and can be controlled by the type and viscosity of the solvent used in the spinning solution, the humidity of the spinning space, the electrostatic spinning conditions, etc.

[0023] The nanofiber layer is not particularly limited, and may be formed by laminating or blending a plurality of different fibers. Examples include laminating or blending a plurality of fibers with different fiber diameters, non-elastomeric fibers and elastomeric fibers, high-melting point fibers and low-melting point fibers, high-crystalline fibers and low-crystalline fibers, and hydrophilic fibers and water-repellent fibers. When two types of fibers with different fiber diameters or properties are laminated or blended, the fiber blending ratio is not particularly limited, but may be, for example, a weight ratio of 1:10 to 10:1.

[0024] In the nanofiber layer, the nanofibers may be arranged randomly or one- or two-dimensionally. When they are arranged randomly, properties such as mechanical strength are expressed isotropically, while when they are arranged one- or two-dimensionally, various properties are expressed anisotropically. Furthermore, the nanofibers are not particularly limited, but are preferably continuous fibers from the viewpoint of preventing fluffing, etc.

[0025] The nanofiber layer may contain the above-described nanofibers, and the basis weight is not limited. However, in order to easily exhibit the properties of the nanofibers, it is preferable that the basis weight is 0.01 to 20 g / m ２ It is preferable that the density is 0.1 to 5 g / m ２More preferably, it is 0.2 to 3 g / m ２ The thickness of the nanofiber layer is not particularly limited, but is preferably 0.5 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 30 μm.

[0026] The nanofiber layer may be a single layer, or two or more layers may be laminated. The nanofiber layer has the effect of preventing delamination between fiber layers, so even if two or more layers are laminated, delamination is unlikely to occur during processing into a product, and the properties are unlikely to deteriorate. When two or more fiber sheets are laminated, there are no particular limitations as long as each layer contains the above-mentioned nanofibers. Each layer may contain the same nanofibers, or may contain nanofibers with different average fiber diameters or constituent components. The nanofiber layer may be provided on a protective fiber sheet, and the protective fiber sheet may be the same as or different from the nanofiber layer. The method for forming the protective fiber sheet is the same as the method for forming the nanofiber layer.

[0027] Alternatively, the nanofiber layer can be formed using a nanofiber sheet in which the desired nanofiber layer is laminated on the surface of a porous substrate (a porous substrate for nanofiber sheet formation, to distinguish it from the material constituting the porous layer described below). Examples of porous substrates for nanofiber sheets include nonwoven fabrics that constitute the porous layer described below. Therefore, the density and air permeability of these porous substrates for nanofiber sheets are the same as those that constitute the porous layer described below. The porous substrate for nanofiber sheets may be the same as or different from the material that constitutes the porous layer described below.

[0028] The air permeability of the nanofiber sheet is not particularly limited, but is preferably 1.0 to 400 cm ３ / cm ２ / sec, and 1 to 200 cm ３ / cm ２ / sec, and more preferably 2 to 150 cm ３ / cm ２ / sec. In this specification, the term "air permeability" refers to the Frazier air permeability.

[0029] The airflow resistance of the nanofiber sheet is not particularly limited, but is preferably 0.1 × 10 ８ ~100 x 10 ８ N·sec / m ３ is preferably 0.2 × 10 ８ ~50 x 10 ８ N·sec / m ３ More preferably, it is 0.5 × 10 ８ ~30 x 10 ８ N·sec / m ３ It is more preferable that:

[0030] Porous Layer The porous layer is formed from fibers having an average fiber diameter of 1 μm or more. The average fiber diameter of the fibers constituting the porous layer is preferably 1 to 100 μm, more preferably 3 to 50 μm, and even more preferably 5 to 30 μm. An average fiber diameter of 1 μm or more is preferable because it compensates for the lack of strength and rigidity of the nanofiber layer and results in a laminate that is excellent in processability into products. Note that an average fiber diameter of 100 μm or less increases the contact area between the porous layer and the nanofiber layer, thereby improving peel resistance.

[0031] The fiber components constituting the porous layer are not particularly limited, and examples 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, polyurethane resins, 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 laminate and improving processability into products, the fiber components constituting the base layer preferably contain 30% by mass or more, and more preferably 50% by mass or more, of polyester resin or cellulose material. Furthermore, from the viewpoint of processability and availability, polyethylene terephthalate is preferred as the polyester resin, and cellulose is preferred as the cellulose material.

[0032] The fibers constituting the porous layer may be single-component or composite fibers. Furthermore, composite fibers may be blends of multiple components, or may have composite configurations such as concentric sheath-core, eccentric sheath-core, side-by-side, sea-island, or radial. Composite fibers may also be made from two or more materials with different melting points. Examples of high-melting-point components include polypropylene, polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, nylon 6, nylon 6,6, and poly-L-lactic acid. Examples of 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 difference in melting point between the high-melting-point component and the low-melting-point component of the composite fiber is not particularly limited, but is preferably 15°C or higher, more preferably 30°C or higher, in order to widen the processing temperature range for heat fusion.

[0033] The fibers constituting the porous layer may contain additives such as antibacterial agents, deodorants, antistatic agents, conductive materials, fluorescent materials, smoothing agents, hydrophilic agents, water repellents, antioxidants, weather resistance agents, surfactants, charge stabilizers, etc., as needed, provided that the effects of the present invention are not impaired. Furthermore, the surfaces of the fibers may be treated with a fiber finishing agent, which can impart functions such as hydrophilicity, water repellency, antistatic properties, surface smoothness, and abrasion resistance, as provided that the effects of the present invention are not impaired.

[0034] The cross-sectional shape of the fibers constituting the porous layer is not particularly limited, and examples include circular, elliptical, flat, semicircular, star-shaped, triangular, rectangular, pentagonal, multi-lobed, array-shaped, T-shaped, and horseshoe-shaped. From the viewpoint of improving the peel resistance between the nanofiber layer and the porous layer, an elliptical, flat, or semicircular cross-sectional shape is preferable. A porous layer containing fibers having an elliptical, flat, or semicircular cross-sectional shape can be obtained, for example, by forming fibers having an elliptical, flat, or semicircular cross-sectional shape into a web and then bonding the web using heat or an adhesive, or by thermally calendering a nonwoven fabric composed of fibers having a circular cross-sectional shape.

[0035] A nonwoven fabric is used as such a porous layer. The nonwoven fabric is not particularly limited, and examples include thermally bonded nonwoven fabrics, thermally calendered nonwoven fabrics, through-air nonwoven fabrics, air-laid nonwoven fabrics, spunlace nonwoven fabrics, needle-punched nonwoven fabrics, wet-laid nonwoven fabrics, spunbonded nonwoven fabrics, meltblown nonwoven fabrics, chemically bonded nonwoven fabrics, flash-spun nonwoven fabrics, and electrospun nonwoven fabrics. In order to easily achieve specific ranges of specific volume and surface resistivity, a thermally calendered nonwoven fabric, spunlace nonwoven fabric, chemically bonded nonwoven fabric, or wet-laid nonwoven fabric is preferred, and a thermally calendered nonwoven fabric or wet-laid nonwoven fabric is more preferred. Furthermore, the porous layer is not particularly limited, but from the viewpoint of improving the peel resistance between the nanofiber layer and the porous layer, it is preferable that the porous layer does not have an uneven shape such as embossed points or shaped portions. Furthermore, the porous layer may be formed by laminating or mixing multiple fibers having different fiber diameters and properties, as long as the effects of the present invention are not impaired.

[0036] The basis weight of the porous layer is not particularly limited, but is preferably 5 to 150 g / m ２ It is preferable that the density is 10 to 105 g / m ２ More preferably, it is 15 to 85 g / m ２ It is more preferable that the basis weight of the porous layer is 5 g / m ２ If the density is 150 g / m or more, the rigidity of the laminate can be increased and the processability into products can be improved, which is preferable. ２ If it is less than this, the breathability and liquid permeability of the laminate can be improved, which is preferable.

[0037] The thickness of the porous layer is not particularly limited, but is preferably 0.01 to 1 mm, and more preferably 0.05 to 0.8 mm. A thickness of 0.01 mm or more is preferable because it increases the rigidity of the laminate and improves processability into products, while a thickness of 1 mm or less is preferable because it increases the breathability and liquid permeability of the laminate.

[0038] The specific volume of the porous layer is 1 to 10 cm ３ / g, and 2 to 8 cm ３ / g, and 3 to 6 cm ３ / g. As the specific volume of the porous layer is made smaller, the fibers constituting the porous layer become denser, the surface irregularities and pore size of the porous layer become smaller, the contact area with the nanofiber layer increases, and the peel resistance between the nanofiber layer and the porous layer can be improved. From this perspective, it is preferable that the specific volume of the porous layer is 10 cm ３ / g or less, satisfactory peel resistance is obtained, and ３ / g or less, good peel resistance is obtained, and ３ / g or less, sufficient peel resistance can be obtained. On the other hand, the larger the specific volume of the porous layer, the sparser the fibers constituting the porous layer become, and the better the breathability and liquid permeability of the laminate. From this viewpoint, the specific volume of the porous layer is set to 1 cm ３ / g or more, satisfactory breathability and liquid permeability can be obtained, ３ / g or more, good air permeability and liquid permeability can be obtained. ３ If the tensile strength is 1 / g or more, sufficient air permeability and liquid permeability can be obtained.

[0039] The density of the porous layer is 0.1 to 1 g / cm ３ is preferably 0.13 to 0.5 g / cm ３ More preferably, it is 0.17 to 0.33 g / cm ３ It is more preferable that the density of the porous layer is 0.1 g / cm ３ If it is more than 1 g / cm, the breathability and liquid permeability of the laminate can be improved, which is preferable. ３ The density of the porous layer can be obtained, for example, by dividing the basis weight of the porous layer by the thickness.

[0040] The breaking strength of the porous layer is not particularly limited, but the average breaking strength in the longitudinal and transverse directions is preferably 30 N / 50 mm or more, more preferably 60 N / 50 mm or more. If the average breaking strength in the longitudinal and transverse directions is 30 N / 50 mm or more, the strength and rigidity of the laminate are improved, and the processability into products can be improved.

[0041] The air permeability of the porous layer is not particularly limited, but is preferably 1 cm３ / cm ２ / sec or more is sufficient, and 50 cm ３ / cm ２ / sec or more is more preferable, and 100 cm ３ / cm ２ It is more preferable that the air permeability of the porous layer is 1 cm / sec or more. ３ / cm ２ / sec or more is preferable because the breathability and liquid permeability of the laminate can be increased. It is more preferable that it is 3 to 80 μm, even more preferable that it is 5 to 60 μm, and particularly preferable that it is 10 to 50 μm. If the average pore size of the porous layer is 1 μm or more, it is preferable because the breathability and liquid permeability of the laminate can be improved, and if it is 100 μm or less, it is preferable because a uniform laminate can be obtained.

[0042] The porous layer may be subjected to antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorbing treatment, near-infrared absorbing treatment, electret treatment, or the like depending on the purpose, as long as the effects of the present invention are not significantly impaired.

[0043] The oil-repellent porous layer has an oil-repellent film on its surface, which is made of an organic silicone containing a trifunctional silicone (T unit) skeleton. The main component of the oil-repellent film is preferably an organic silicone obtained by curing a compound represented by formula (1). By including such a structure, it is possible to improve the oil repellency and adhesion of the fiber sheet.

[0044] In this specification, the term "main component" refers to the component that is contained in the largest amount by mass of all the components that make up the oil-repellent film, i.e., the component that is contained in a proportion of 50 mass% or more of the entire oil-repellent film. Other components and subcomponents may also be present, but as long as the above proportions are met, the compound of formula (1) is considered to be the main component.

[0045] In formula (1), R １ are independently hydrogen or an alkyl group having 1 to 2 carbon atoms, and n is an integer of 2 to 6.

[0046] Specific examples of the organosilicon represented by formula 1 include condensates of methyltrimethoxysilane, methyltripropoxysilane, and the like. The compound of formula 1 may be a condensation product of only one of such monomers, or a condensation product of two or more of the above-mentioned monomers. Including the silicone of formula (1) imparts oil repellency.

[0047] The organic silicone preferably contains a bifunctional silicone (D unit) in addition to the T unit. Specifically, the oil-repellent film is preferably an organic silicone that contains the compound represented by formula (1) as a main component and further contains a compound represented by formula (2) as a D unit and is cured.

[0048] Here, "containing" means that the structural unit derived from the compound represented by formula (2) is present in the oil-repellent film in a range of 30 to 5 mass %, preferably 20 to 10 mass %, based on the solid content of the entire film. However, even if the amount is slightly above or below the above range, it is considered to be "containing" as long as it is within a range that does not significantly impair the effects of the present invention.

[0049] In formula (2), Me is a methyl group, and m is an integer of 5 to 100. Examples of the silicone compound of formula (2) include condensates of dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, methylvinyldimethoxysilane, and methylvinyldiethoxysilane. Adding both compounds of formula 3 to a coating agent further improves the organic properties of the coating film, and as a result, further improves the water repellency and other properties of the coating film.

[0050] The organic silicone preferably contains 70 to 95% by mass, and more preferably 80 to 90% by mass, of the compound represented by formula (1). The organic silicone preferably contains 30 to 5% by mass, and more preferably 20 to 10% by mass of the compound represented by formula (2). Furthermore, the organic silicone may contain compounds corresponding to Q and M units in an amount of 10% by mass or less.

[0051] The amount of oil-repellent film formed is usually 10 to 50 g / m2 in terms of solid content. ２ , preferably 15 to 35 g / m ２ The density of the porous layer after the oil-repellent film formation is 0.1 to 1 g / cm, depending on the material and basis weight of the oil-repellent film. ３ is preferably 0.13 to 0.5 g / cm ３ More preferably, it is 0.17 to 0.33 g / cm ３ When the thickness is in this range, a sheet having excellent oil repellency and breathability can be obtained.

[0052] The basis weight of the porous layer after the oil-repellent film is formed is 5 to 150 g / m ２ It is preferable that the density is 10 to 105 g / m ２ More preferably, it is 15 to 85 g / m ２ When the thickness is in this range, the rigidity of the laminate can be increased, the processability into products can be improved, and the breathability and liquid permeability of the laminate can be increased, which is preferable.

[0053] The basis weight of the porous layer after the oil-repellent film is formed is not particularly limited, and is ３ / cm ２ / sec or more is sufficient, and 50 cm ３ / cm ２ / sec or more is more preferable, and 100 cm ３ / cm ２ If the air permeability is in this range, the breathability and liquid permeability of the laminate can be improved.

[0054] Laminate Structure: The laminated fiber sheet of the present invention is a laminate of the porous layer and nanofiber layer. The laminated fiber sheet of the present invention is suppressed from fuzzing and delamination between fiber sheets, and has excellent mechanical strength and rigidity, making it easy to process into products. Furthermore, excellent adhesion between the nanofiber sheet and the porous layer is achieved without the need for integration processes such as adhesive processing or calendaring, enabling the laminated fiber sheet to be produced with high productivity and good operability. The laminate structure is not particularly limited; as long as the nanofiber layer, the porous layer, and the porous layer surface have an oil-repellent film, the oil-repellent film may or may not be in direct contact with the nanofiber layer. Furthermore, when a nanofiber sheet is used, the porous substrate constituting the nanofiber sheet need only be laminated with the porous layer.

[0055] The Frazier air permeability of the laminated fiber sheet is 1 to 150 cm ３ / cm ２ / sec. Furthermore, it is in the range of 1 to 50 cm ３ / cm ２ / sec. When the Frazier air permeability of the porous layer is in the above range, a laminated fiber sheet having stain resistance and high oil repellency can be obtained. In this specification, the Frazier air permeability is calculated from the air flow rate and test area at that time when air is sucked to a pressure of 125 Pa in accordance with JIS L 1096.

[0056] The basis weight of the laminated fiber sheet is not particularly limited, but is preferably 5 to 200 g / m ２ It is preferable that the density is 10 to 150 g / m ２ More preferably, it is 15 to 120 g / m ２ It is more preferable that the basis weight of the laminated fiber sheet is 5 g / m ２ If the laminated fiber sheet has a thickness of 200 g / m or more, the rigidity of the laminated fiber sheet is increased, and the processability into products can be improved. ２If the thickness is 0.01 mm or less, it can be made lighter when used as, for example, a filter medium, a mask, a sound-absorbing material, etc. Furthermore, the thickness of the laminated fiber sheet 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. If the thickness of the laminated fiber sheet is 0.01 mm or more, the rigidity of the laminated fiber sheet is increased and the processability into products can be improved, and if the thickness is 2 mm or less, it can be made space-saving when used as, for example, a filter medium, a mask, a sound-absorbing material, etc.

[0057] The laminated fiber sheet may be subjected to antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorption treatment, near-infrared absorption treatment, electret treatment, etc. depending on the purpose, as long as the effects of the present invention are not significantly impaired. The laminated fiber sheet of the present invention has sufficient mechanical strength and appropriate rigidity, and also exhibits the effect of excellent secondary processability such as antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorption treatment, near-infrared absorption treatment, or electret treatment.

[0058] The laminated fiber sheet of the present invention suppresses fluffing and delamination between fiber sheets, has excellent adhesion and mechanical strength between the nanofiber sheet and the porous layer, and contains few adhesives and other components, so it can be suitably used as a high-performance filter medium, although not limited thereto. The object of filtration is not particularly limited, and it may be an air filter medium used in air conditioners and clean rooms, or a liquid filter medium used to filter wastewater, paint, abrasive particles, etc. The type of filter is also not particularly limited, and it may be a flat membrane filter, a pleated filter, or a cylindrically rolled depth filter.

[0059] When the laminated fiber sheet is used as a filter material 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 even more preferably 50 to 200 Pa. If the pressure loss is 10 Pa or more, sufficient collection efficiency is obtained, and if it is 1500 Pa or less, the breathability of the gas filter is improved, resulting in effects such as reduced power consumption and reduced load on the fan. Furthermore, when air containing particles with a particle diameter of approximately 0.1 to 0.3 μm is passed through at 5.3 cm / sec, the particle collection efficiency is preferably 80% or more, more preferably 90% or more. 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 collection performance of an air filter, and a higher QF value means higher performance.

[0060] <Method for manufacturing laminated fiber sheet> The method for manufacturing a fluorine-free laminated fiber sheet of the present invention is a laminated fiber sheet in which a nanofiber layer made of nanofibers having an average fiber diameter of 20 nm or more and less than 1000 nm and a porous layer made of fibers having an average fiber diameter of 1 μm or more are laminated, and the method includes the step of forming an oil-repellent film by the following steps: ３ a step of applying an oil-repellent film-forming coating liquid containing an organic silicone to the surface of the porous layer; and a step of curing the coating to form a porous layer having an oil-repellent film.

[0061] Formation of Oil-Repellent Film This method includes a step of applying an oil-repellent film-forming coating liquid containing an organic silicone to the surface of the porous layer, and a step of curing the coating to form an oil-repellent film on the surface of the porous layer.

[0062] The porous layer is as described above. A solution containing the compound represented by formula (1) and, if necessary, formula (2) is used as the coating liquid for forming the oil-repellent film. The use of such compounds leaves unhydrolyzed substituents, contributing to oil repellency and flexibility of the coated product. The coating liquid contains a reaction catalyst and a solvent. Any known catalyst that promotes the hydrolysis of the silicone compound can be used without any particular restrictions. Examples of acid catalysts include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and acetic acid. Examples of base catalysts include ammonia, tetramethylammonium hydroxide, 2-hydroxyethyltrimethylammonium hydroxide, ethanolamine, diethanolamine, and triethanolamine. When using these conventional catalysts, reaction water is allowed to coexist.

[0063] An organometallic compound may also be used as a catalyst. When applied, the organometallic compound absorbs moisture on the fiber or moisture (humidity) in the air, and the organometallic compound undergoes hydrolysis itself. Examples of organometallic compounds preferably used in the present invention include those containing titanium, zirconium, aluminum, or tin. More specifically, examples include tetrapropoxy titanate, tetrabutoxy titanate, tetrapropoxy zirconate, tetrabutoxy zirconate, tripropoxy aluminate, aluminum acetylacetonate, dibutyltin diacetate, and dibutyltin dilaurate.

[0064] The amount of the catalyst (acid catalyst, base catalyst, or organometallic compound) used is usually 0.1 to 20 parts by mass, preferably 0.5 to 10 parts by mass, per 100 parts by mass of the compounds represented by formulas (1) and (2).

[0065] In addition, an organic solvent can be added to the coating solution to uniformly mix the organic silicone compound, catalyst, and optionally required water. Examples of organic solvents used for this purpose include alcohols. More specifically, examples include methanol, ethanol, propanol, isopropanol, butanol, pentanol, and hexanol. In order to adjust the viscosity and drying speed of the coating solution, organic solvents with high viscosity and boiling point, such as glycols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, dipropylene glycol, and polypropylene glycol, and cellosolves such as methoxyethanol, propoxyethanol, butoxyethanol, methoxypropanol, ethoxypropanol, propoxypropanol, and butoxypropanol, may be used alone or in combination of two or more.

[0066] The amount of the organic solvent used is such that the concentration of the silicone compound in the coating liquid used in the present invention is generally 10 to 80% by mass, preferably 20 to 60% by mass.

[0067] The coating liquid may contain additives such as pigments, flame retardants, ultraviolet absorbers, plasticizers, lubricants, stabilizers, fillers, lubricants, curing agents, antifoaming agents, and antifungal agents. These additives may be used alone or in combination of two or more.

[0068] In the present invention, the coating liquid is applied to the surface of the porous layer constituting the laminated fiber sheet. The coating method is not particularly limited, and examples thereof include coating using a dispenser, spin coating, roll coating, curtain coating, flow coating, printing, microgravure coating, gravure coating, wire bar coating, dip coating, spray coating, meniscus coating, and inkjet coating.

[0069] After the coating liquid is applied, the coating film is dried and heat-treated to harden and solidify. The drying and heat-treatment conditions for hardening and solidifying are usually a temperature of 30 to 150°C, preferably 50 to 120°C, and more preferably 60 to 80°C, and a time of 1 to 30 minutes, preferably 1 to 10 minutes. The amount of coating liquid applied to the porous layer is usually 2 to 150 g / m2 in terms of basis weight converted to solid content. ２ , preferably 15 to 75 g / m ２ is.

[0070] As described above, when the coating liquid is applied to the porous layer, the organosilicon compound is hydrolyzed to form siloxane bonds (Si-O-Si). The coating liquid may be applied after the formation of the laminate or to the porous layer before the nanofiber layer is laminated thereon.

[0071] Formation of Nanofiber Layer The method may further include a step of laminating a nanofiber layer on the surface of the porous layer on which the oil-repellent film is not formed. Alternatively, a nanofiber sheet having a nanofiber layer formed on the surface of a porous substrate may be laminated on the porous layer.

[0072] The nanofiber layer used in the present invention is preferably formed by a method for producing a nanofiber sheet. The method for producing a nanofiber sheet is not particularly limited, and examples include a spinning method using air, centrifugal force, or electrostatic force from a spinning solution containing the polymer material that constitutes the nanofiber sheet, and using a porous substrate such as a nonwoven fabric as needed. Among these, electrospinning using electrostatic force is preferred because it can produce nanofibers with small and uniform diameters.

[0073] The electrostatic spinning method is a method in which a spinning solution is discharged and an electric field is applied to the discharged spinning solution to form fibers with a very small fiber diameter on a collector. Examples of the electrostatic spinning method include a method in which a spinning solution is extruded from a nozzle and an electric field is applied to the spinning solution, a method in which a spinning solution is foamed and an electric field is applied to the spinning solution, and a method in which a spinning solution is introduced onto the surface of a cylindrical electrode and an electric field is applied to the spinning solution.

[0074] The spinning solution is not particularly limited as long as it has spinnability. For example, a solution in which the polymer material constituting the nanofiber sheet is dispersed or dissolved in a solvent, or a solution in which the polymer material constituting the nanofiber sheet is melt-kneaded by heat or laser irradiation, etc., can be used. However, from the viewpoint of making the average fiber diameter of the nanofibers constituting the fiber sheet of the present invention small and uniform, it is preferable to use a spinning solution in which a polymer is dissolved in a solvent.

[0075] The solvent for dispersing or dissolving the polymer material is not particularly limited, and examples thereof include 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, Examples of solvents include acetic acid, tetrahydrofuran, dichloromethane, chloroform, and 1,1,1,3,3,3-hexafluoroisopropanol, but from the viewpoint of the solubility of the vinylidene fluoride polymer and the vinylidene fluoride copolymer, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, triethyl phosphate, acetone, methyl ethyl ketone, tetrahydrofuran, cyclohexanone, and γ-butyrolactone are preferred. These solvents may be used alone or in combination of two or more in any desired ratio.

[0076] The additives, such as the conductivity-imparting agent and water-repellent agent, described above, are not particularly limited, but are preferably contained in the spinning solution. By including them in the spinning solution, the additives can be uniformly imparted to the nanofibers, and various functions can be imparted without an additive imparting step, which is preferable. The content of the additive may be appropriately selected depending on the type and the desired effect, and an amount of 0.001 to 5% by mass of the spinning solution is preferable because an effect commensurate with the use can be obtained.

[0077] The method for preparing the spinning solution is not particularly limited, and examples thereof include stirring and ultrasonic treatment. The order of mixing is also not particularly limited, and the components may be mixed simultaneously or sequentially. When preparing the spinning solution by stirring, the stirring temperature and stirring time are not particularly limited as long as the polymers can be sufficiently mixed. For example, stirring may be performed at 40 to 120°C for about 1 to 24 hours.

[0078] The viscosity of the spinning solution is not particularly limited, but is preferably 10 to 10,000 cP, more preferably 50 to 8,000 cP, and even more preferably 200 to 5,000 cP. If the viscosity of the spinning solution is 10 cP or higher, good spinnability and spinning stability can be obtained, and if it is 10,000 cP or lower, preparation of the spinning solution and discharge during electrospinning are easy. The viscosity of the spinning solution can be adjusted by appropriately changing the molecular weight and concentration of the polymer, and the type and mixing ratio of the solvent.

[0079] The temperature of the spinning solution may be room temperature, or may be increased to, for example, 0 to 200°C while heating or cooling. The spinning solution may be discharged from a nozzle using a pump after being filled in a syringe or tank. The inner diameter of the nozzle is not particularly limited, and may be 0.1 to 1.5 mm, for example. The flow rate of the spinning solution per hole is not particularly limited, and may be 0.1 to 20 mL / hr, for example.

[0080] The method for applying an electric field is not particularly limited as long as it enables stable electrospinning. For example, a high voltage may be applied to the nozzle or spinning solution and the collector grounded. The applied voltage is not particularly limited as long as it allows fibers to be formed and stable spinning is possible, and examples include 5 to 100 kV. The distance between the nozzle and the collector (spinning distance) is not particularly limited as long as it allows sufficient solvent volatilization, and examples include 50 to 1,000 mm. The electric field strength is not particularly limited, but is preferably 1 to 10 kV / cm, and more preferably 2 to 5 kV / cm. An electric field strength of 1 kV / cm or higher can improve the peel resistance between fiber sheets and between the fiber sheet and the porous layer. An electric field strength of 10 kV / cm or lower can increase the porosity of the fiber sheet, making it easier to achieve both a high specific surface area and high air permeability. The collector material is not particularly limited as long as it can collect electrospun nanofibers, and conductive materials such as metals are suitable. The shape of the collector is not particularly limited, but it is preferable to use a conveyor-shaped collector to continuously produce a fiber sheet.

[0081] The atmospheric temperature and humidity during electrospinning are preferably controlled, and the ranges are not particularly limited, but examples include 20 to 30°C and 25 to 45% RH. This temperature and humidity range allows for relatively easy control throughout the year, and changes in the spinning behavior and the physical properties of the resulting fiber sheet due to changes in the atmospheric temperature and humidity are unlikely to occur.

[0082] For a laminate having two or more nanofiber layers, an example method is electrospinning using a conveyor-like collector with two or more rows of nozzles arranged in the conveyor's traveling direction. In this case, from the viewpoint of uniformity of the fiber sheet, electrospinning is preferably performed while the nozzles traverse perpendicular to the conveyor's traveling direction (the width direction of the fiber sheet). The spinning solutions ejected 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; 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 a conductive agent or a water repellent, the type and concentration of the polymer material, the type of solvent, etc. can be appropriately changed according to the desired physical properties.

[0083] In a method for electrospinning two or more nanofiber layers onto a porous substrate, the nanofiber layers are preferably laminated by the following steps: electrospinning a protective fiber layer onto the porous layer, and electrospinning a nanofiber layer onto the protective fiber sheet. The protective fiber sheet may be the same as or different from the nanofiber layer. The method for forming the protective fiber sheet is the same as the method for forming the nanofiber layer.

[0084] In the present invention, a heat treatment using circulating hot air or radiant heat may be performed to further enhance the peel resistance between the nanofiber layer and the porous substrate of the obtained laminated fiber sheet, or between the nanofiber layers in the case of two or more layers. Heat treatment using circulating hot air or radiant heat is preferred because it causes almost no damage to the laminated fiber sheet and can impart sufficient peel resistance.

[0085] When heat treatment is performed using circulating hot air or radiant heat, the temperature is not particularly limited, but can be set within a range below the melting point of the polymer material constituting the porous layer or nanofiber layer while maintaining a balance between peel resistance and the desired properties.

[0086] The method for producing the laminated fiber sheet of the present invention is not particularly limited other than the formation of the oil-repellent film, and examples thereof include a method of electrospinning a nanofiber layer onto a porous layer on which no oil-repellent film is formed, and a method of preparing a nanofiber sheet having a nanofiber layer spun onto a porous substrate and another porous layer, and then subjecting them to thermocompression bonding using a heated flat roll or embossing roll, or to bonding using a hot melt agent or chemical adhesive. Specifically, a porous layer on which an oil-repellent film is formed is laminated on the nanofiber layer side of a nanofiber sheet having a nanofiber layer previously formed on the surface of a porous substrate.

[0087] The fiber sheet of the present invention has the characteristic of excellent adhesion to other materials, and it is possible to obtain a laminated fiber sheet in which the nanofiber layer and the porous layer are sufficiently adhered to each other without performing thermocompression or adhesive treatments.

[0088] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0089] The basis weight and average fiber diameter of the fibers of the porous layer used in the examples were measured as follows. <Measurement of basis weight> The weight of a fiber sheet cut into a square of 100 mm square was measured, and the weight of the fiber sheet cut into a square of 100 mm square was measured. ２ The value converted into the weight per unit area is the basis weight of the nonwoven fabric (g / m ２ )

[0090] <Measurement of Average Fiber Diameter> Using a scanning electron microscope (SU-8020) manufactured by Hitachi, Ltd., the fiber diameters of 50 fibers were measured using image analysis software (Scion Image 4.0.3.2), and the average value was taken as the average fiber diameter.

[0091] Production Example 1 10 g of methyltrimethoxysilane (MTMS) oligomer (a 50 mass % solution in a mixed solvent of toluene and methanol in a mass ratio of 1:1 (manufactured by Colcoat Co., Ltd., product name: SS-101)) as the methyltrimethoxysilane represented by Formula 1, and 1 g of an organic titanium catalyst (manufactured by Matsumoto Fine Chemical Co., Ltd., TC-401, titanium tetraacetylacetonate) were mixed and stirred at 24° C. for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0092] [Production Examples 2 and 3] As in Production Example 1, 10 g of a methyltrimethoxysilane (MTMS) oligomer (manufactured by Colcoat Co., Ltd., product name: SS-101) was mixed with the organotitanium catalyst, except that in Production Example 2 it was changed to AL-3100 (aluminum tris(acetylacetonate)) manufactured by Matsumoto Fine Chemical Co., Ltd., and in Production Example 3 it was changed to TC-750 (titanium diisopropoxybis(ethylacetoacetate)), and the mixture was stirred at 24°C for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0093] [Production Example 4] 10 g of the methyltrimethoxysilane oligomer used in Production Example 1, 1.25 g of polydimethylsiloxane having a reactive functional group represented by Formula 2 (FM-9915 manufactured by JNC Corporation), and 0.5 g of an organic titanium catalyst (TC-750 manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 24°C for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0094] [Production Example 5] 12 g of the methyltrimethoxysilane oligomer used in Production Example 1, 1 g of methyltrimethoxysilane (MTMS), and 1.4 g of an organic titanium catalyst (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 4°C for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0095] [Production Example 6] 12 g of the methyltrimethoxysilane oligomer used in Production Example 1, 1 g of triethoxymethylsilane (TEMS), and 1.4 g of an organic titanium catalyst (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 24°C for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0096] Comparative Production Example 1 12 g of the methyltrimethoxysilane oligomer used in Production Example 1, 4 g of trimethoxyphenylsilane (TMPS), and 2 g of an organic titanium catalyst (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 24° C. for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0097] Comparative Production Examples 2 and 3 Coating solutions for forming oil-repellent films of Comparative Production Examples 2 and 3 were prepared in the same manner as in Comparative Production Example 1, except that trimethoxyphenylsilane (TMPS) used in Comparative Production Example 1 was replaced with trimethoxypropylsilane (TMPrS) and dimethyldimethoxysilane (DMDM), respectively.

[0098] Comparative Production Example 4 10 g of the methyltrimethoxysilane oligomer used in Production Example 1, 0.5 g of tetraethoxysilane (TEOS), and 1.1 g of an organic titanium catalyst (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 4° C. for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0099] Comparative Production Example 5 10 g of the methyltrimethoxysilane oligomer used in Production Example 1, 1.0 g of tetraethoxysilane (TEOS), and 1.2 g of an organic titanium catalyst (TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) were mixed and stirred at 24° C. for 3 hours to prepare a coating liquid for forming an oil-repellent film.

[0100]

[0101]

[0102] [Production Examples 1 to 6, Comparative Production Examples 1 to 5] Formation of oil-repellent film The coating liquids for forming oil-repellent films prepared in Production Examples 1 to 6 and Comparative Production Examples 1 to 5 were coated with a porous film containing 180 cm@-125 Pa as a base material for forming a porous layer. ３ / cm ２ / sec. ２ , density 0.194g / cm ３ A nonwoven fabric (PET30W manufactured by Uma Paper Co., Ltd.) was dipped in the coating solution for 10 seconds. The nonwoven fabric was pulled out of the coating solution, spread on a horizontal wire mesh, and left at room temperature for 10 minutes. Thereafter, the single layer nonwoven fabric was placed in a dryer maintained at 60°C for 30 minutes to dry, thereby obtaining an oil-repellent film-coated porous layer.

[0103] <Evaluation of oil repellency> 50 μL of n-hexadecane solution was dropped onto the obtained oil-repellent film-coated porous layer (nonwoven fabric) at five locations, and if the solution did not penetrate into three or more locations, the oil repellency was rated as ◯, if the solution did not penetrate into one or two locations, the oil repellency was rated as Δ, and if the solution penetrated into all five locations, the oil repellency was rated ×. The compositions of the coating solutions and the evaluation results are shown in Tables 1 and 2.

[0104] The diluent is a solvent for MTMS, and the amount of MTMS is the total amount of the oligomer and the solvent in terms of solution amount.

[0105] The diluent is a solvent for MTMS, and the amount of MTMS is the total amount of the oligomer and the solvent in terms of solution amount.

[0106] Example 7 Production of Nanofiber Layer A spinning dope was prepared by mixing 15 parts by mass of an ester-based polyurethane (product name: Elastollan (registered trademark) C80A) manufactured by BASF Japan Ltd., 85 parts by mass of N,N-dimethylacetamide, and 0.025 parts by mass of sodium dodecyl sulfate as a conductivity-imparting agent.

[0107] A conveyor-type collector was used as the collection section, and a nonwoven fabric (thickness: 0.234 mm, basis weight: 80 g / m) made of heat-bondable composite fiber (average fiber diameter: 40 μm) containing polyethylene terephthalate copolymer and polyethylene terephthalate was attached to the collector surface. ２ ) was attached as a nanofiber sheet-forming porous substrate. Next, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the direction of travel of the conveyor, electrospinning was performed on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby producing a nanofiber sheet.

[0108] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed speed of the porous substrate for nanofiber sheet formation: 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0109] The pressure loss was measured as follows. The pressure loss in the following examples and comparative examples was also measured in the same manner as in Example 7. <Pressure loss measurement> A handy air permeability meter (FX3360 PORTAIR) manufactured by TEXTEST Co., Ltd. was used, and the measurement range was 20 cm. ２ The pressure loss was measured under the condition of a wind speed of 5.3 cm / sec.

[0110] Formation of an oil-repellent film The coating solution prepared in Production Example 1 was applied to a PET nonwoven fabric (density: 0.194 g / cm) by a dipping method. ３ , breathability: 180 cm ３ / cm ２ / sec, average fiber diameter: 20 μm, thickness: 0.155 mm, basis weight: 30 g / m ２ ) to prepare a porous layer with an oil-repellent film. A porous layer with an oil-repellent film formed on the surface was laminated on the nanofiber layer of the nanofiber sheet to prepare a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the above-mentioned method. As a result of the evaluation, the oil repellency was evaluated as ○, and the air permeability of the laminated fiber sheet was evaluated as 15.6 cm ３ / cm ２ The air permeability was evaluated as follows: The air permeability in the following examples and comparative examples was evaluated in the same manner as in Example 7.

[0111] <Measurement of air permeability> A handy air permeability measuring device (FX3360 PORTAIR) manufactured by TEXTEST was used, and the measurement range was 20 cm. ２ The air permeability was measured under the condition of a differential pressure of 125 Pa.

[0112] Example 8 A spinning dope was prepared by mixing 15 parts by mass of an ester-based polyurethane (trade name: PANDEX (registered trademark) T1190) manufactured by DIC Covestro Polymer Co., Ltd., 85 parts by mass of N,N-dimethylacetamide, and 0.025 parts by mass of sodium dodecyl sulfate as a conductivity-imparting agent.

[0113] Using the same nanofiber sheet-forming porous substrate as in Example 7, three rows of a single nozzle, each with an inner diameter of 0.3 mm and 12 holes, were installed in the direction of conveyor travel, and the nozzle was caused to traverse in a direction perpendicular to the direction of conveyor travel, while electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby producing a nanofiber sheet.

[0114] The spinning conditions were as follows: single-hole liquid feed rate to each nozzle using a pump: 1.0 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30 RH%; and conveyor-like collector feed rate: 5 mm / sec. The nanofiber layer had an average fiber diameter of 200 nm, and the pressure loss of the nanofiber sheet was 270 Pa.

[0115] Formation of Oil-Repellent Film Using the coating liquid prepared in Production Example 1, an oil-repellent film was formed on the surface of the porous layer in the same manner as in Example 7. The obtained porous layer with the oil-repellent film was laminated on the nanofiber sheet in the same manner as in Example 7 to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the method described above. As a result of the evaluation, the oil repellency was evaluated as ○, and the air permeability of the laminated fiber sheet was 2.59 cm ３ / cm ２ / sec.

[0116] [Example 9] Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby producing a nanofiber sheet.

[0117] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed speed of the porous substrate for nanofiber sheet formation: 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0118] Formation of an oil-repellent film The coating solution prepared in Production Example 1 was used, and the density was 0.342 g / cm ３ , breathability 243 cm ３ / cm ２ / sec, average fiber diameter 40 μm, thickness 0.234 mm, basis weight 80 g / m ２ An oil-repellent film was formed on the surface of the porous layer using a PET nonwoven fabric of this type as the porous layer in the same manner as in Example 7. The obtained porous layer with the oil-repellent film was laminated on a nanofiber sheet to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated using the method described above. As a result of the evaluation, the oil repellency was evaluated as ○, and the air permeability of the laminated fiber sheet was evaluated as 16.2 cm ３ / cm ２ / sec.

[0119] [Example 10] Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate layer to form a nanofiber layer, thereby producing a nanofiber sheet.

[0120] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed speed of the porous substrate for nanofiber sheet formation: 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0121] Formation of Oil-Repellent Film Using the coating liquid prepared in Production Example 2, an oil-repellent film was formed on the surface of the porous layer in the same manner as in Example 7. The resulting porous layer with the oil-repellent film was laminated on the nanofiber sheet in the same manner as in Example 7 to produce a laminated fiber sheet. As a result of the evaluation, the oil repellency was good, and the air permeability of the laminated fiber sheet was 14.1 cm ３ / cm ２ / sec.

[0122] [Example 11] Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby producing a nanofiber sheet.

[0123] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed rate for the nanofiber sheet-forming porous layer: 7 mm / sec. The nanofiber layer had an average fiber diameter of 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0124] Formation of an oil-repellent film The coating solution prepared in Production Example 1 was used, and the density was 0.196 g / cm ３ , ventilation rate 270 cm ３ / cm ２ / sec, average fiber diameter 20 μm, thickness 0.092 mm, basis weight 30 g / m ２ An oil-repellent film was formed on the surface of the porous layer using a PET nonwoven fabric of this type in the same manner as in Example 7. The resulting porous layer with the oil-repellent film was laminated on a nanofiber sheet to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the method described above. As a result of the evaluation, the oil repellency was evaluated as ○, and the air permeability of the laminated fiber sheet was evaluated as 16.4 cm ３ / cm ２ / sec.

[0125] Example 12 Production of Nanofiber Layer A spinning dope was prepared by mixing 18 parts by mass of polyetherimide siloxane copolymer (product name: SILTEM STM1500) manufactured by SABIC Corporation, 82 parts by mass of N,N-dimethylacetamide, and 0.025 parts by mass of sodium dodecyl sulfate as a conductivity-imparting agent.

[0126] A conveyor-type collector was used as the collection unit, and a PET nonwoven fabric (average fiber diameter: 20 μm, thickness: 0.1 mm, basis weight: 30 g / m) was applied to the collector surface as a porous substrate for forming a nanofiber sheet. ２ Next, a nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the direction of travel of the conveyor, electrospinning was performed on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby producing a nanofiber sheet.

[0127] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 3.0 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 190 mm; traverse speed: 200 mm / sec; spinning space temperature: 25°C; humidity: 30 RH%; and conveyor-like collector feed rate of the porous substrate for nanofiber sheet formation: 4.5 mm / sec. The average fiber diameter of the nanofiber layer was 250 nm, and the pressure loss of the nanofiber sheet was 69 Pa.

[0128] Formation of Oil-Repellent Film Using the coating liquid prepared in Production Example 1, an oil-repellent film was formed on the surface of a porous layer in the same manner as in Example 7. The resulting porous layer with an oil-repellent film was laminated on a nanofiber sheet to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the method described above. As a result of the evaluation, the oil repellency was evaluated as ○, and the air permeability of the laminated fiber sheet was 11.3 cm ３ / cm ２ / sec.

[0129] Comparative Example 6 Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and while the nozzle was traversing in a direction perpendicular to the conveyor traveling direction, electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate to form a nanofiber layer, thereby obtaining a nanofiber sheet.

[0130] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed speed of the porous substrate for nanofiber sheet formation: 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0131] Formation of an oil-repellent film: Using the coating solution prepared in Production Example 1, a nonwoven fabric containing polypropylene and polyethylene (average fiber diameter: 30 μm, basis weight: 40 g / m) was used instead of the porous layer used in Example 7. ２ , Thickness: 0.890 mm, Density: 0.045 g / cm ３ , breathability 359 cm ３ / cm ２ / sec) to form an oil-repellent film on the surface of the porous layer. The obtained porous layer with the oil-repellent film was laminated on the nanofiber sheet in the same manner as in Example 7 to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the above-mentioned method. As a result of the evaluation, the oil repellency was ×, and the air permeability of the laminated fiber sheet was 18.3 cm ３ / cm ２ / sec.

[0132] Comparative Example 7 Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, to form a nanofiber layer, thereby obtaining a nanofiber sheet.

[0133] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and conveyor-like collector feed speed of the porous substrate for nanofiber sheet formation: 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa.

[0134] Formation of Oil-Repellent Film: Using the coating solution prepared in Production Example 1, a PET nonwoven fabric (average fiber diameter: 20 μm, basis weight: 43 g / m) was used instead of the porous layer used in Example 7. ２ , Thickness: 0.386 mm, Density: 0.111 g / cm ３ , breathability 164 cm ３ / cm ２ An oil-repellent film was formed on the surface of the porous layer using a pressure of 1000 kJ / sec. The obtained porous layer with the oil-repellent film was laminated on the nanofiber sheet in the same manner as in Example 7 to produce a laminated fiber sheet. The oil repellency of the obtained laminated fiber sheet was evaluated by the method described above. As a result of the evaluation, the oil repellency was ×, and the air permeability of the laminated fiber sheet was 15.2 cm ３ / cm ２ / sec.

[0135] Comparative Example 8 Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 7, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, forming a nanofiber layer and obtaining a nanofiber sheet.

[0136] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 1.2 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 170 mm; traverse speed: 150 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and electrostatic spinning was performed with the conveyor-like collector feeding the porous substrate for nanofiber sheet formation at a speed of 7 mm / sec. The average fiber diameter of this nanofiber layer was 200 nm, and the pressure loss of the nanofiber sheet was 40 Pa. In Comparative Example 8, the oil repellency was evaluated by the above method without laminating an oil-repellent film-coated porous layer. The evaluation result showed that the oil repellency was poor.

[0137] Comparative Example 9 Using the same nanofiber sheet-forming porous substrate and spinning solution as in Example 12, one nozzle with an inner diameter of 0.3 mm and 12 holes was installed, and electrostatic spinning was performed from the spinning solution on the nanofiber sheet-forming porous substrate while the nozzle was traversing in a direction perpendicular to the conveyor's traveling direction, to form a nanofiber layer, thereby obtaining a nanofiber sheet.

[0138] The spinning conditions for this example were: single-hole liquid feed rate to each nozzle using a pump: 3.0 mL / hr; applied voltage: 45 kV; spinning distance: 100 mm; nozzle traverse width: 190 mm; traverse speed: 200 mm / sec; spinning space temperature: 25°C; humidity: 30% RH; and electrostatic spinning was performed with a conveyor-like collector at a feed rate of 4.5 mm / sec for the porous substrate for forming a nanofiber sheet. The average fiber diameter of this nanofiber layer was 250 nm, and the pressure loss of the nanofiber sheet was 69 Pa. In Comparative Example 9, the oil repellency was evaluated by the above method without laminating an oil-repellent film-coated porous layer. The evaluation result showed that the oil repellency was poor.

[0139] <Pleating Processability and Filter Processability> The laminated fiber sheets obtained in Examples 7 to 12 and Comparative Examples 6 to 9 were pleated to form pleated filters. Pleating was performed using a high-speed multi-reciprocating folding machine manufactured by Hoptec Co., Ltd., where 400 pleats were continuously pleated at a pleating speed of 20 pleats / min with a pleat height of 10 mm. The pleats were then pressed for 20 minutes at 0.08 MPa on a table set to 50°C. The pleated laminated fiber sheet was observed for its pleat shape and pitch when released, and pleating processability was evaluated based on whether the peak shape and pitch were stable. Pleating without disturbance in the peak shape and pitch was deemed to have good pleating processability.

[0140] Filter processability was evaluated based on a comprehensive assessment of the processing speed, trouble occurrence rate, yield, and non-defective product rate when processing various filters, and a satisfactory level was deemed good. The laminated fiber sheets obtained in Examples 7 to 12 had good pleating and filter processability, and no defects such as tearing were observed in the resulting pleated filters. On the other hand, the laminated fiber sheet obtained in Comparative Example 6 had irregularities in the peak shape and pitch of the pleats, resulting in poor pleating processability. The laminated fiber sheet obtained in Comparative Example 7 showed no defects in pleating processability. The laminated fiber sheets obtained in Comparative Examples 8 to 9 experienced tearing in the nanofiber layer after pleating, confirming a decrease in filter performance.

[0141]

[0142]

Claims

1. A laminated fiber sheet comprising a nanofiber layer containing nanofibers with an average fiber diameter of 20 nm or more but less than 1000 nm and a porous layer made of fibers with an average fiber diameter of 1 μm or more, wherein the laminated fiber sheet has a Frazier air permeability of 1 to 150 cm when air is sucked to a pressure of 125 Pa in accordance with JIS L 1096 and calculated from the air flow rate and test area at that time. ３ / cm ２ / sec, and the density of the porous layer is 0.1 to 1 g / cm ３ and further comprising an oil-repellent film on the surface of the porous layer, the oil-repellent film being made of an organic silicone having a T unit in its skeleton.

2. The fluorine-free laminated fiber sheet according to claim 1, wherein the main component of the oil-repellent film is an organic silicone obtained by curing a compound represented by formula (1). In formula (1), R １ are independently hydrogen or an alkyl group having 1 to 2 carbon atoms, and n is an integer of 2 to 6.

3. The fluorine-free laminated fiber sheet according to claim 1 or 2, wherein the oil-repellent film contains the compound represented by formula (1) as a main component and further contains an organic silicone formed by curing the compound represented by formula (2). In formula (2), Me is a methyl group, and m is an integer of 5 to 100.

4. The fluorine-free laminated fiber sheet according to claim 1 or 2, wherein the polymer constituting the nanofiber layer is a polymer that does not contain fluorine.

5. The fluorine-free laminated fiber sheet according to claim 1 or 2, wherein the nanofiber layer is a laminate of two or more layers.

6. The fluorine-free laminated fiber sheet according to claim 1 or 2, wherein a porous substrate for forming a nanofiber sheet is laminated on the nanofiber layer side of the laminated fiber sheet.

7. The basis weight of the porous layer is 20 to 150 g / m ２ 2. The fluorine-free laminated fiber sheet according to claim 1, wherein the fluorine content is in the range of 0.1 to 1.0%.

8. A nanofiber layer containing nanofibers having an average fiber diameter of 20 nm or more and less than 1000 nm, and a porous layer consisting of fibers having an average fiber diameter of 1 μm or more, the density of which is 0.1 to 1 g / cm ３ and a method for producing a fluorine-free laminated fiber sheet, the method comprising the steps of: applying an oil-repellent film-forming coating liquid containing an organic silicone to the surface of the porous layer; and curing the coating to form a porous layer having an oil-repellent film.

9. A method for producing the fluorine-free laminated fiber sheet according to claim 8, comprising the step of laminating a nanofiber layer on the surface of the porous layer on which the oil-repellent film is not formed.

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