JP6694181B2 - Fibrous web and method for forming the same, laminated sheet and method for producing the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a fibrous web in which nanofibers are integrated, a method for forming the fibrous web, a laminated sheet including the fibrous web, and a method for manufacturing the laminated sheet.

  The nanofiber is a fibrous substance having a diameter of 1 nm or more and 1,000 nm or less and a fiber length of 100 times or more the diameter. An electrostatic spinning method (also called an electrospinning method or an electrospinning method) is known as a spinning method for nanofibers. The electrospinning method is performed using, for example, the electrospinning apparatus 1 shown in FIG.

  The electrostatic spinning device 1 includes a syringe 3 that contains a resin solution 21 in which a resin is dissolved in a solvent. A plunger 11 is inserted into the syringe 3. A piston 13 is attached to the tip of the plunger 11. A capillary 5 is provided at the bottom of the syringe 3. An opening portion 15 is provided at the tip of the capillary 5, and a plate-shaped collecting portion 7 is arranged so as to face the opening portion 15. Further, the electrostatic spinning device 1 includes a high voltage power supply 9. The capillary 5 is connected to the positive electrode of the high-voltage power supply 9, and the collector 7 is connected to the negative electrode. The high voltage power supply 9 is also connected to the ground 17.

  When the piston 13 is pushed toward the bottom of the syringe 3, the resin solution 21 in the syringe 3 flows into the capillary 5 and is further pushed to flow out from the opening 15 provided at the tip of the capillary 5. The nanofibers 25 are spun by electrospinning the resin solution 21 flowing out from the opening 15. Specifically, the resin solution 21 flowing out from the opening 15 is applied with a positive high voltage, and the liquid surface is deformed into a conical shape due to the repulsion of the charges induced on the liquid surface. Further, when the repulsive force of the electric charge exceeds the surface tension of the liquid, the resin solution 21 flowing out from the opening 15 jumps out from the apex of the conical liquid surface toward the collecting portion 7, and the continuous fluid jet 23a. To form. The fluid jet 23 a is stretched, the contained solvent evaporates, and is attracted to the collection unit 7 with an unstable whipping motion, and becomes a nanofiber 25 when it is accumulated on the collection unit 7. A fiber web can be formed by accumulating the spun nanofibers 25 on the collection unit 7.

  By the way, in the electrospinning method, in general, when a resin solution is charged and electrospun as described above (hereinafter referred to as “solvent-type electrospinning method”), the molten resin is charged instead of the resin solution. And electrospinning is performed (hereinafter referred to as "melt type electrostatic spinning method"). As a solvent-type electrostatic spinning method, for example, Patent Document 1 discloses a method of spinning nanofibers from an ethylene-vinyl alcohol copolymer (hereinafter referred to as “EVOH”) solution. As a solvent for this EVOH solution, dimethyl sulfoxide (hereinafter referred to as "DMSO") or a mixture of lower alcohol and water is used.

  Further, as a melt-type electrostatic spinning method, for example, Patent Document 2 discloses a method of spinning nanofibers from at least two kinds of molten resins containing EVOH.

International Publication No. 2012/133631 JP, 2011-183254, A

  However, in the solvent-type electrostatic spinning method using an EVOH solution, a large amount of a component such as water (hereinafter referred to as “solvent component”) that can be generally used as a hydrophilic solvent is mixed in nanofibers immediately after spinning. There are cases. In this case, a large number of cavities may be formed inside the nanofibers after the mixed solvent components are evaporated. The fibrous web in which such nanofibers are accumulated easily breaks depending on the use condition.

  On the other hand, in the melt-type electrostatic spinning method using the molten EVOH, the solvent is not used, so that it is not necessary to consider the possibility that the solvent component is mixed in the nanofibers. Generally, the electrostatic spinning device used in this case includes a laser irradiation device for heating and melting the resin, a mechanism for controlling the heating temperature within a certain range, and the like. Such an electrospinning apparatus is complicated, large-scale, and expensive.

  Alternatively, even when the electrospinning method is performed using the electrospinning device 1 that does not include a laser irradiation device or the like, it is possible to spin nanofibers from EVOH that has been heated and melted in advance, instead of the resin solution 21. Is not impossible. However, in this case, there is an operation in which the EVOH is heated and melted to such an extent that the EVOH does not burn, the molten EVOH is quickly accommodated in the syringe 3, and the electrospinning method is performed quickly before the EVOH solidifies in the syringe 3. Desired. The method in this case is complicated for the operator because it is necessary to quickly perform the electrostatic spinning method while controlling the temperature of the EVOH. If the operator is not skilled, EVOH may be solidified in the syringe 3, and it is difficult to efficiently mass-produce the fiber web.

  Therefore, in view of the above-mentioned problems, the present invention uses a method similar to the solvent-type electrostatic spinning method using an EVOH solution, in which the mixing of solvent components is suppressed as compared with the case of spinning by the solvent-type electrostatic spinning method. A first object of the present invention is to provide a fibrous web in which nanofibers are integrated by spinning a fiber, and a method for forming the fibrous web.

  Moreover, this invention makes it the 2nd subject to provide the laminated sheet provided with the said fiber web, and its manufacturing method.

  The present inventor diligently studied to solve the above-mentioned first problem, and thought that the cause of mixing the solvent component in the nanofiber immediately after spinning was that EVOH was dissolved in the solvent component in the EVOH solution. .. Considering water, which is a typical example of the solvent component, as shown in FIG. 2A, each EVOH molecule 31 in the EVOH solution 21 attracts a large number of water molecules 33 to the surroundings by hydrogen bonding or the like. Further, in the fluid jet 23a shown in FIG. 2B formed from the EVOH solution 21, a large number of EVOH molecules 31 are entangled with each other to form fibrils 37a. The fibrils 37a here are fibrous structures having diameters and fiber lengths on the order of nanometers. When the fibrils 37a are formed, it is assumed that most of the water molecules 33 attracted to the EVOH molecule 31 are trapped in the gap 39 between the EVOH molecule 31 and the EVOH molecule 31. Further, since the water molecules 35 trapped in the gap 39 are surrounded by the EVOH molecules 31 having a gas barrier property, it is considered that the water molecules 35 are less likely to be volatilized in the air. Then, it is presumed that water is enclosed in the inside of the nanofibers due to a large number of fibrils 37a assembled to spin the nanofibers.

  Therefore, the inventors of the present invention have found that if the EVOH does not dissolve in the solvent component, the solvent component is less likely to be trapped in the gap between the EVOH molecule and the EVOH molecule in the fluid jet, and easily volatilizes into the air. I thought it would be hard to be enclosed in. Based on this idea, the electrospinning method was carried out experimentally using a resin emulsion in which the dispersoid contained EVOH. As a result, it was discovered that nanofibers can be stably spun from a resin emulsion whose dispersoid contains EVOH. Therefore, the present inventor has found that it is possible to provide a fibrous web at least composed of EVOH and a method for forming the same, in which mixing of a dispersion medium (solvent component) is suppressed.

  That is, in order to solve the above-mentioned first problem, the method for forming a fibrous web according to the present invention is to spin nanofibers from a resin emulsion by electrostatic spinning to collect the spun nanofibers. The resin emulsion has a dispersoid and a dispersion medium, and the dispersoid contains at least an ethylene-vinyl alcohol copolymer (EVOH). ..

  In the method for forming a fibrous web of the present invention, the dispersoid further contains one adhesive resin selected from the group consisting of polyurethane, an ethylene-butadiene copolymer, and a mixture thereof. obtain.

  In the method for forming a fibrous web, the content of the EVOH in the resin emulsion is 5% by weight or more and 16% by weight or less, and the content of the adhesive resin is 0.1% by weight or more and 35% by weight or less. Can be characterized by

  The method for forming the fibrous web can be characterized in that the weight ratio of the adhesive resin to the EVOH (adhesive resin / EVOH) in the resin emulsion is 0.5 or more and 2.0 or less.

  In order to solve the above-mentioned second problem, a method for manufacturing a laminated sheet according to the present invention includes a step of preparing a breathable sheet, a step of forming a fibrous web by the method of forming a fibrous web, and Laminating the breathable sheet on at least one side of the formed fibrous web.

  Further, the fibrous web according to the present invention is a fibrous web in which nanofibers are accumulated, and the nanofibers are at least EVOH, polyurethane, ethylene-butadiene copolymer, and a group consisting of a mixture thereof. It is characterized by being constituted by one kind of adhesive resin selected.

  The present fibrous web can be characterized in that the weight ratio of the adhesive resin to EVOH (adhesive resin / EVOH) in the nanofibers is 0.5 or more and 2.0 or less.

  In the present fibrous web, at least a part of the nanofibers is composed of a core part which is elongated in the fiber length direction and is composed of the EVOH, and the adhesive resin which is intermittently present on the surface of the core part. And a bonded portion that is formed.

  A laminated sheet according to the present invention is characterized by including the fiber web and a breathable sheet laminated on at least one surface of the fiber web.

  In the present laminated sheet, the breathable sheet can be characterized by being a non-woven fabric having a fiber layer in which a plurality of thermoplastic resin fibers are stretched and arranged in substantially one direction.

  The laminated sheet can be characterized in that it is used as a filter or a filter medium for an air filter.

  In the method for forming a fibrous web according to the present invention having the above structure, the electrospinning method is carried out using a resin emulsion in which the dispersoid contains EVOH. The EVOH contained in the dispersoid does not dissolve in the solvent component contained in the dispersion medium. In the fibrous web thus formed, the nanofibers are composed of at least EVOH, and furthermore, the mixture of solvent components is suppressed.

  In addition, since the present forming method uses a resin emulsion in which the dispersoid contains EVOH, it is the same method as the solvent-type electrostatic spinning method using an EVOH solution, for example, using the electrostatic spinning apparatus 1 shown in FIG. , Can be easily implemented.

The schematic diagram which shows an example of the electrospinning apparatus used when performing an electrospinning method. (A) is a schematic diagram illustrating that EVOH is mixed with water in an EVOH solution, and (b) is a schematic diagram illustrating that fibrils are formed in a fluid jet formed from the EVOH solution. is there. In (a) and (b), water molecules attracted to EVOH molecules are drawn as the molecules of the solvent component, but other molecules of the solvent component are omitted. (A) is a schematic diagram explaining that EVOH is dispersed in a resin emulsion containing EVOH as a dispersion medium without being dissolved in water, and (b) is a fluid jet formed from the resin emulsion. It is a schematic diagram explaining that a fibril is formed. In (a) and (b), molecules of solvent components other than water molecules attracted to EVOH molecules are omitted. (A) is a schematic diagram showing a part of laminated sheet concerning Example 6, and (b) is a schematic diagram showing a part of laminated sheet concerning Example 5.

[First Embodiment of Method for Forming Fibrous Web]
The method for forming a fibrous web according to the first embodiment includes a step of spinning nanofibers from a resin emulsion by an electrostatic spinning method and accumulating the spun nanofibers to form a fibrous web. Further, the resin emulsion has a dispersoid and a dispersion medium. This dispersoid contains at least EVOH.

  The electrospinning method in Embodiment 1 is performed in the same manner, for example, when a resin emulsion is used instead of the resin solution 21 in the method for forming a fiber web using the electrospinning apparatus 1 shown in FIG. 1 described above. You can That is, in the electrospinning method according to the first embodiment, a voltage is applied between the positive electrode (electrode on the side that supplies the resin emulsion) and the negative electrode (electrode on the side that collects nanofibers) to charge the resin emulsion. Then, the nanofibers are spun by stretching by applying electrospinning. Further, nanofibers spun from the resin emulsion by the electrospinning method are accumulated to form a fibrous web. For example, in the method for forming a fibrous web using the electrostatic spinning apparatus 1 shown in FIG. 1 described above, nanofibers immediately after spinning are piled up on the collecting unit 7 to form a fibrous web on the collecting unit 7. ..

  The electrostatic spinning device used in Embodiment 1 is not particularly limited. The electrospinning method according to the first embodiment can be performed by the electrospinning device 1 having a simple device configuration, and thus can be performed by another electrospinning device, for example, an electrospinning device including a laser irradiation device. .. Therefore, in the electrospinning method according to the first embodiment, various electrospinning apparatuses can be appropriately selected and used as necessary. The voltage applied to the resin emulsion by the electrospinning method is about 5 to 30 kV when the electrospinning apparatus 1 is used, but is within the range of about 5 to 60 kV when another electrospinning apparatus is used. Adjust accordingly if necessary.

  The resin emulsion in Embodiment 1 is an aqueous dispersion liquid in which the dispersion medium (continuous phase) is a solvent component and the dispersoid (disperse phase) is resin fine particles containing at least EVOH. Here, the resin contained in the dispersoid is a resin that becomes a constituent component of the nanofibers by carrying out the first embodiment. Further, the solvent component is a mixture of water and a lower alcohol and preferably does not contain DMSO from the viewpoint of avoiding various problems caused by the organic solvent. The problems caused by the organic solvent are explosion, corrosion of equipment and facilities, environmental pollution, adverse effects on health maintenance of workers, and equipment cost for dealing with these problems.

  The particle size of the fine particles of the resin that is the dispersoid in the first embodiment is, for example, 10 nm or more and 1,000 nm or less, preferably 50 nm or more and 800 nm or less. It is preferable that the resin fine particles have a small particle diameter because nanofibers having a small fiber diameter can be spun. However, when the particle size of the resin fine particles is too smaller than 10 nm, the number of EVOH molecules constituting each resin fine particle is small, so that when the resin fine particles are stretched in the fluid jet, the EVOH molecules are separated from each other. Since entanglement is unlikely to occur and fibrils are less likely to be formed, it is difficult to continuously stably spin nanofibers having approximately the same fiber diameter.

  EVOH is a resin having ethylene and polyvinyl alcohol (hereinafter referred to as “PVA”) as comonomers, and exhibits both moisture resistance and gas barrier properties. EVOH is preferably one in which ethylene as a constituent component accounts for 29 mol% or more and 47 mol% or less, because gas barrier properties and moisture resistance are easily compatible with each other. Examples of commercially available EVOH include Eval (registered trademark of Kuraray Co., Ltd.) and Soarnol (registered trademark of Nippon Synthetic Chemical Industry Co., Ltd.).

  The lower alcohol contained in the dispersion medium in Embodiment 1 is an alcohol having 4 or less carbon atoms. Examples of the lower alcohol include one or more compounds selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 2-methyl-2-propanol and the like. Further, the lower alcohol is preferably one or more compounds selected from the group consisting of ethanol, 1-propanol, and 2-propanol, from the viewpoint of suppressing adverse effects on the health maintenance of workers. The lower alcohol is more preferably ethanol from the viewpoint of suppressing environmental pollution and adverse effects on health maintenance, and more preferably 1-propanol from the viewpoint of cost reduction.

  In Embodiment 1, the method for preparing the resin emulsion in which the dispersoid contains EVOH is not particularly limited. A resin emulsion in which the dispersoid contains EVOH may be prepared or a commercially available product may be purchased. Examples of commercially available products include Eversolve # 10 (manufactured by Cima Japan Co., Ltd.). When a commercially available product is used, Embodiment 1 is preferable from the viewpoint that it can be carried out simply and quickly.

  According to the embodiment 1 including the above-mentioned constitution, the mixing of solvent components such as water and lower alcohol is suppressed in the nanofiber immediately after spinning and the fiber web immediately after formation. This is confirmed by the fact that when the fibrous web immediately after being formed is placed away from the electrospinning apparatus, almost no alcohol odor can be perceived from the fibrous web. In addition, when the fiber web was cut and the cross section of many nanofibers was observed with an electron microscope, it was difficult to find cavities in the cross section, that is, traces of water or lower alcohol being encapsulated inside the nanofibers were found. Confirmed because it is difficult.

  The mechanism by which the mixing of the dispersion medium (solvent component) is suppressed in the nanofibers and the fiber web is unknown, but it is presumed as follows. In the resin emulsion, the resin fine particles (dispersoid) containing EVOH are dispersed without being dissolved in the solvent component (dispersion medium). That is, as shown in FIG. 3A, a large number of EVOH molecules 31 in the resin emulsion 27 are aggregated to form spherical resin fine particles 41. Inside the resin fine particles 41, the water molecules 33 are not contained at all or are hardly contained therein. Therefore, the water molecules 33 attracted to the EVOH molecules 31 are almost limited to those existing near the interface between the resin fine particles 41 and the dispersion medium. Further, as shown in FIG. 3B, the spherical resin fine particles 41 are stretched in the fluid jet 23b to become substantially string-shaped resin fine particles (43a, 43b).

  In the fluid jet 23b, EVOH molecules 31 forming one resin particle 43a are entangled with EVOH molecules 31 forming another resin particle 43b one after another to form a fibril 37b. It is considered that a large number of 37b aggregate to form nanofibers. Here, the EVOH molecules 31 forming the resin fine particles (43a, 43b) and the attracted water molecules 33 are almost limited to those existing near the interface between the resin fine particles (43a, 43b) and the dispersion medium. There is. Therefore, it is considered that the number of water molecules 35 trapped in the gap 39 between the EVOH molecule 31 and the EVOH molecule 31 forming the fibril 23b can be suppressed to be small.

  According to the mechanism described above, when the electrospinning method is performed using the resin emulsion 27 in which the dispersoid contains EVOH shown in FIG. 3, the solvent type electrospinning method is performed using the EVOH solution 21 shown in FIG. It is presumed that water (dispersion medium, solvent component) is less likely to be encapsulated inside the nanofibers immediately after spinning than in the case. Further, it is considered that solvent components (dispersion medium) other than water, such as lower alcohol and DMSO, are not easily enclosed in the nanofibers immediately after spinning due to the mechanism described above, like water. Since lower alcohols and DMSO have lower boiling points than water, they easily vaporize and volatilize into the air immediately before fibrils are formed in the fluid jet. It is thought that it is hard to be enclosed.

  According to the first embodiment, it is possible to form a fibrous web in which nanofibers composed of at least EVOH are integrated. This fibrous web has few cavities inside the nanofibers due to the inclusion of the dispersion medium (solvent component). Therefore, it is less likely to break as compared with a fiber web in which nanofibers have many voids inside. Further, since EVOH exhibits moisture resistance, it is possible to prevent the shape of the nanofiber or the fibrous web from collapsing due to moisture absorption, unlike the nanofiber composed of a water-soluble resin such as PVA.

  Conventionally, it is difficult to remove particulate matter such as PM2.5 from the air with a thin mask or air filter, and in order to remove it, it is necessary to thicken the filter material of the mask or air filter. On the other hand, in the fibrous web formed according to Embodiment 1, the average fiber diameter of the nanofibers is 10 nm or more and 1,000 nm or less, and the fiber length of the nanofibers is 100 times or more the average fiber diameter. The average fiber diameter of the nanofibers is preferably 50 nm or more and 800 nm or less. The average fiber diameter is the average value of the diameters of the nanofibers measured at 50 arbitrary points in the photograph by taking a photograph of the fiber web with a scanning electron microscope (hereinafter referred to as “SEM”). Since the fibrous web in which the nanofibers are integrated has a large total surface area (specific surface area) per unit weight, is lightweight and has a small thickness, it can be used as a material for a filter material of a thin mask or an air filter. Examples of the air filter here include, but are not particularly limited to, an air filter for an air cleaner, an air filter for an indoor air conditioner, and an air filter for an in-vehicle air conditioner.

  The thickness, basis weight, pore size, and pressure loss of the fibrous web can be appropriately adjusted by adjusting the amount of nanofibers accumulated during the electrospinning method. Since nanofibers are extremely fine, it seems that the thickness of the fibrous web or the laminated sheet described later does not change even if the amount of accumulation is increased to reduce the pore size. The pore diameter is a measured value obtained by a method according to JIS Z 8831-2 and JIS Z 8831-3. The pressure loss is a measured value obtained by a test based on JIS B 9908, type 2.

  When used as a filter medium for a mask or an air filter or as a material for the filter medium, the fiber web formed according to the first embodiment preferably has a pore size of 10 nm or more and 1,000 nm or less. For the same reason, it is preferable that the pressure loss of the fibrous web is 10 Pa or more and 500 Pa or less. In these cases, particulate matter such as PM2.5 particles and PM1.0 particles in the air can be efficiently removed.

  When the fibrous web is used as the filter material of the mask or the material of the filter material, the pressure loss of the fibrous web formed according to Embodiment 1 is more preferably from the viewpoint of avoiding that the user of the mask becomes stuffy and removes the mask. It is 10 Pa or more and 100 Pa or less. Note that the smaller the pressure loss, the less likely the user of the mask will feel suffocation, but the capture rate of the fine particulate matter by the fibrous web will decrease. On the other hand, when the fibrous web is used as the filter material of the air filter or the material of the filter material, the problem of breathing does not occur even if the pressure loss of the fibrous web is large.

  The fibrous web formed according to Embodiment 1 is used as a material for a mask or an air filter for trapping PM2.5 particles from the viewpoint that the trapping rate of PM2.5 particles is high even if the basis weight and pressure loss are small. Preferably. The fiber web formed according to Embodiment 1 is even more preferably a pressure loss of 10 Pa or more and 100 Pa or less, and is used as a filter medium of a mask for capturing PM2.5 particles or a material of the filter medium. ..

  The fibrous web formed according to the first embodiment is not used as a filter medium but as a filter medium for a mask or an air filter when the thickness is increased by increasing the amount of nanofibers accumulated to increase the rigidity. May be.

  Although the method for forming the fibrous web according to the first embodiment and the fibrous web formed according to the first embodiment have been described above, the present invention can be carried out in different modes. Since the contents described above are common to the embodiment described below and the fiber web, the same description is omitted. Hereinafter, different points from the first embodiment and the fibrous web formed according to the first embodiment will be described.

[Second Embodiment of Method for Forming Fibrous Web]
In the forming method according to the second embodiment, the dispersoid of the resin emulsion contains EVOH, and the content of EVOH in this resin emulsion is 5% by weight or more and 25% by weight or less. According to the second embodiment, it is possible to efficiently form a large amount of nanofibers and fiber webs. If the content of EVOH in the resin emulsion is less than 5% by weight, the fiber length of the spun nanofibers becomes short, and the fiber web becomes bulky and the nanofibers easily fall off from the fiber web. It may become. Further, when the content of EVOH in the resin emulsion is more than 25% by weight, the viscosity of the resin emulsion is large and it is difficult for the resin emulsion to flow. Therefore, the nozzle hole of the electrostatic spinning device (for example, the electrostatic spinning device shown in FIG. 1) is used. The opening 15) in No. 1 may be easily clogged, and it may be difficult to efficiently spin a large amount.

  In Embodiment 2, preferably, the dispersoid of the resin emulsion contains EVOH, the content of EVOH in this resin emulsion is 5% by weight or more and 25% by weight or less, and the content of lower alcohol is 20% by weight or more and It is 40% by weight or less, and the water content is 40% by weight or more and 60% by weight or less. Since the resin emulsion in this case contains a predetermined amount of lower alcohol, it is sterilized, is less likely to cause mold, and can be stored for a long time in a refrigerator or the like. Therefore, it is possible to prepare the resin emulsion in advance and perform the electrospinning method at a later date, which is easy for the operator to work. Further, in this case, since the resin emulsion does not contain too much lower alcohol because it contains a large amount of water, various problems caused by the organic solvent evaporated from the fluid jet are unlikely to occur. For the same reason, evaporation of the organic solvent released from the fibrous web immediately after formation into the air is also suppressed. Therefore, even if the fibrous web immediately after being formed is not distilled under reduced pressure, even if a large amount of the fibrous web is stored in the warehouse as it is, it is possible to avoid the above-mentioned problems in the warehouse.

[Third Embodiment of Method for Forming Fibrous Web]
In the forming method according to the third embodiment, the dispersoid of the resin emulsion contains EVOH and polyurethane. Polyurethane is a type of adhesive resin that exhibits adhesiveness at room temperature (5 ° C. or more and 35 ° C. or less), and is synthesized by condensation of a compound having an isocyanate group in the molecule with a compound having a hydroxyl group in the molecule. .. Polyurethane is more hydrophilic than EVOH, but is less soluble in water. In the resin emulsion, polyurethane is dispersed as resin fine particles. That is, polyurethane, like EVOH, is a constituent component of the dispersoid and is not dissolved in the dispersion medium (solvent component).

  Polyurethane is synthesized, for example, by condensation of polyol and polyisocyanate. Examples of the polyol that constitutes the polyurethane include one or more compounds selected from the group consisting of polyacrylic polyol, polyether polyol, polyester polyol, polycarbonate polyol, polycaprolactone polyol, and the like.

  As the polyacrylic polyol, one or more compounds selected from the group consisting of poly-2-hydroxyethyl acrylate, poly-2-hydroxybutyl acrylate, poly-2-hydroxyethyl methacrylate, poly-2-hydroxybutyl methacrylate and the like. Is mentioned. Examples of the polyether polyol include one or more compounds selected from the group consisting of polypropylene glycol, polytetramethylene glycol, poly-2-methyltetramethylene glycol and the like. Examples of the polyester polyol include one or more compounds selected from the group consisting of polybutanediol adipate, poly-3-methylpentanediol adipate, poly-1,6-hexanediol adipate, polyneopentyl glycol adipate, and the like. .. Examples of the polycarbonate polyol include at least one compound selected from the group consisting of poly-3-methylpentanediol carbonate and polynonanediol carbonate. Examples of the polycaprolactone polyol include poly-β-methylvalerolactone and the like.

  Examples of the polyisocyanate that constitutes polyurethane include diisocyanate. Examples of the diisocyanate include at least one compound selected from the group consisting of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-diphenylmethane diisocyanate, norbornene diisocyanate, xylene diisocyanate and lysine diisocyanate.

  Further, the polyurethane may have a chain extender incorporated in its constituent components. Examples of chain stretching include 1,3-butanediol, 1,4-butanediol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 3-methylpentanediol, nonanediol, octanediol, One or more compounds selected from the group consisting of dimethylolheptane, dimethylolpropionic acid, dimethylolbutanoic acid and the like can be mentioned. From the viewpoint of avoiding deterioration of the nanofibers and the fiber web, the polyurethane is preferably made of a material exhibiting water resistance and hydrolysis resistance.

  In Embodiment 3, the method for preparing the resin emulsion in which the dispersoid contains EVOH and polyurethane is not particularly limited. From the viewpoint of simple and quick preparation, the dispersoid is prepared by mixing the commercially available resin emulsion containing the polyurethane as the dispersoid and the commercially available resin emulsion containing the EVOH as the dispersoid as described above. It is preferable to prepare a resin emulsion containing polyurethane.

  Commercially available resin emulsions whose dispersoid contains polyurethane include, for example, Superflex (registered trademark of Dai-ichi Kogyo Seiyaku Co., Ltd.) series, Superflex E series, Superflex R series, Elastron (registered trademark of the same company) series. , Elastron BN series (all manufactured by the same company) and the like. Among these commercially available products, the Superflex series is preferred from the viewpoint that the resin emulsion is stable because it is a self-emulsifying type and that the nanofibers are easily spun because the molecular weight of polyurethane is large.

  According to the third embodiment, nanofibers composed of EVOH and polyurethane are accumulated by the same method as the solvent-type electrostatic spinning method using an EVOH solution, for example, by using the electrostatic spinning device 1 shown in FIG. The resulting fibrous web can be stably and easily formed. Further, similarly to Embodiments 1 and 2, in the nanofiber immediately after spinning and the fiber web immediately after formation, the mixing of the dispersion medium (solvent component) is suppressed.

  In the fibrous web formed according to Embodiment 3, the structure of the cross section of the nanofiber is not particularly limited. For example, EVOH and polyurethane may have a bilateral structure in which they are aligned in the longitudinal direction of the nanofibers and joined to each other. Alternatively, it may have a sea-island structure composed of islands made of EVOH and the sea made of polyurethane. It may have a core-sheath structure composed of a core made of EVOH and a sheath made of polyurethane. Since it is composed of a polymer alloy of EVOH and polyurethane, it may have a structure in which the part composed of EVOH and the part composed of polyurethane cannot be distinguished from each other. The cross-sectional outer shape of the nanofiber may be circular, polygonal, or the like. Almost no cavity is found inside the nanofiber.

  Incidentally, conventionally, in order to spin nanofibers having a sea-island structure or a core-sheath structure by the electrostatic spinning method, two kinds of resin solutions were respectively discharged from different nozzle holes to be compounded and spun. Alternatively, a resin fiber having a sea-island structure or a core-sheath structure is prepared in advance, the resin fiber is heated by laser irradiation or the like to be melted, and the melt is discharged from a hole and electrospun to spin nanofibers. Was there. In these conventional methods, the device configuration is complicated, large-scale, and expensive device is required.

  On the other hand, according to the third embodiment, even when the electrospinning apparatus having a simple device configuration such as the electrospinning apparatus 1 shown in FIG. EVOH is likely to be located inside the nanofibers, and polyurethane is likely to be located at the surface portion of the nanofibers. Although the mechanism by which such a positional relationship is formed is unknown, it is presumed as follows. Polyurethane is more hydrophilic than EVOH. Therefore, in the dispersed phase (dispersoid) of the resin emulsion, the polyurethane covers at least a part of the surface of the EVOH resin fine particles, thereby reducing the area of the interface between the EVOH resin fine particles and the continuous phase (dispersion medium). It is thought to have been done. Furthermore, in the fluid jet, the dispersed phase (dispersoid) including the resin particles of EVOH and the resin particles of polyurethane is stretched and the nanofibers are spun, so that the above-mentioned positional relationship is likely to occur in the nanofibers. Presumed.

  Polyurethane is generally used as an adhesive and exhibits flexibility and adhesiveness at room temperature. The fibrous web formed according to Embodiment 3 is self-adhered in a state where nanofibers are entangled with each other due to the adhesiveness of polyurethane, and further, since polyurethane exhibits flexibility, it is formed according to Embodiments 1 and 2. Less likely to break than fibrous webs.

  Further, conventionally, there has been a problem that a fibrous web formed by accumulating nanofibers composed of EVOH is likely to be peeled from a base material as it is. In order to suppress peeling, it was necessary to perform heat treatment such as thermocompression bonding of the fibrous web to the base material by calendering. On the other hand, in the fibrous web formed according to the third embodiment, since polyurethane exhibits adhesiveness at room temperature, the fibrous web adheres to the base material. The fibrous web formed according to Embodiment 3 is unlikely to peel from the substrate even if it has not been heat treated. Furthermore, the fibrous web formed in Embodiment 3 is not limited to hydrophilic substrates, but can be attached to non-hydrophilic substrates such as aluminum foil and polyethylene terephthalate.

  Since polyurethane exhibits adhesiveness at room temperature, dust, pollen, etc. floating in the air passing through the fibrous web formed in Embodiment 3 or in the exhaled air are efficiently removed by adsorbing to the polyurethane. Therefore, the fiber web formed according to the third embodiment is more suitable as the filter material of the mask or the air filter or the material of the filter material than the fiber web formed according to the first and second embodiments. Further, for the same reason as in the above-described Embodiment 1, the fibrous web formed according to Embodiment 3 is preferably used as a filter medium of a mask or an air filter for capturing PM2.5 particles or a material of the filter medium, and The pressure loss is preferably 10 Pa or more and 100 Pa or less and used as a filter medium for a mask for capturing PM2.5 particles or a material thereof. The fibrous web formed according to Embodiment 3 remains thin even if it is formed by accumulating nanofibers until the pore diameter becomes 2.5 μm or less. By using the fibrous web formed according to the third embodiment as a filter medium or a material thereof, a thin and lightweight mask or air filter can be manufactured.

[Fourth Embodiment of Method for Forming Fibrous Web]
In the forming method according to Embodiment 4, the dispersoid of the resin emulsion contains EVOH and polyurethane, and the content of EVOH in this resin emulsion is 5% by weight or more and 16% by weight or less, and the content of polyurethane is 0% or less. 1% by weight or more and 35% by weight or less.

  In Embodiment 4, the nozzle holes of the electrostatic spinning device are less likely to be clogged than when the EVOH content in the resin emulsion is more than 16% by weight, so that the fibrous web can be formed more efficiently and easily. In the fibrous web formed according to Embodiment 4, the weight ratio of polyurethane to EVOH (polyurethane / EVOH) in the nanofibers does not become extremely small. Therefore, as compared with the case where the content of polyurethane is extremely low, the fibrous web formed according to Embodiment 4 is less likely to be damaged due to the adhesiveness and flexibility of polyurethane, and adheres to the base material to be peeled off. Hateful.

  In Embodiment 4, more preferably, the dispersoid of the resin emulsion contains EVOH and polyurethane, and the content of EVOH in this resin emulsion is 8% by weight or more and 15% by weight or less, and the content of polyurethane is 5% by weight. Or more and 15% by weight or less, the content of lower alcohol is 20% by weight or more and 40% by weight or less, and the content of water is 40% by weight or more and 60% by weight or less. With such a composition, since the water content is large, various problems caused by the organic solvent are unlikely to occur. In addition, in the fibrous web formed in this case, at least a part of the nanofibers has a core portion extending in the fiber length direction (longitudinal direction) of the nanofiber, and an adhesive portion intermittently existing on the surface of the core portion. And a structure having The core portion here is made of EVOH, and the adhesive portion is made of polyurethane. In addition, when observing the cross section of the nanofiber in this case with the SEM, almost no polyurethane (adhesive part) is found inside the core part. In addition, since the adhesive part may be raised from the surface of the core part, the appearance of the nanofibers observed by SEM seems to have a sparsely raised part (adhesive part) on the surface of the core part. ..

  As described above, when the nanofiber has a structure having a core portion and an adhesive portion, an adhesive portion and a portion where the surface of the core portion is exposed appear on the surface of the nanofiber. The adhesive portion self-adheres the nanofibers to each other, adheres the fibrous web to the base material, makes it difficult to separate from the base material, and adsorbs dust, pollen, and the like. Further, when the exposed portion of the surface of the core portion is appropriately exposed, clogging of the fibrous web can be avoided and the pressure loss of the fibrous web does not become too high because the number of bonded portions is not too large. Therefore, when the nanofiber has a structure having a core portion and an adhesive portion, as compared with the case where the nanofiber has a core-sheath structure or a sea-island structure, the fibrous web is further used as a filter medium for a mask or an air filter or a material for the filter medium. Are suitable.

[Fifth Embodiment of Method for Forming Fibrous Web]
In the forming method according to Embodiment 5, the dispersoid of the resin emulsion contains EVOH and polyurethane, and the weight ratio of polyurethane to EVOH (polyurethane / EVOH) in this resin emulsion is 0.5 or more and 2.0 or less. .. According to the fifth embodiment, a fibrous web can be easily formed as in the first to fourth embodiments. Further, in the formed fibrous web, the nanofibers are likely to have the above-described structure having the core portion and the adhesive portion.

  In embodiment 5, preferably, the dispersoid of the resin emulsion contains EVOH and polyurethane, and the weight ratio of polyurethane to EVOH (polyurethane / EVOH) in this resin emulsion is 0.5 or more and 2.0 or less, EVOH content of 8 wt% or more and 15 wt% or less, polyurethane content of 5 wt% or more and 15 wt% or less, lower alcohol content of 20 wt% or more and 40 wt% or less, water content Is 40% by weight or more and 60% by weight or less. With such a composition, since the water content is large, various problems caused by the organic solvent are unlikely to occur. Further, the fibrous web formed in this case is likely to have a structure having the core portion and the adhesive portion described above, and the clogging of the fibrous web is suppressed because the amount of the adhesive portion with respect to the amount of the core portion is appropriate. Therefore, it is more suitable as the filter material of the mask or the air filter or the material of the filter material than the fiber web obtained in the fourth embodiment.

[Embodiment 6 of the method for forming a fibrous web]
In the forming method according to the sixth embodiment, the dispersoid of the resin emulsion contains EVOH and an ethylene-butadiene copolymer. The ethylene-butadiene copolymer is a kind of adhesive resin that exhibits adhesiveness at room temperature, and is a copolymer having ethylene and butadiene as comonomers. Further, the ethylene-butadiene copolymer is difficult to dissolve in water. In the resin emulsion, the ethylene-butadiene copolymer is dispersed as resin fine particles. That is, the ethylene-butadiene copolymer constitutes the dispersoid of the resin emulsion, like the EVOH, and does not dissolve in the dispersion medium (solvent component).

  In Embodiment 6, the method for preparing the resin emulsion in which the dispersoid contains EVOH and the ethylene-butadiene copolymer is not particularly limited. From the viewpoint of simple and quick preparation, the dispersoid is dispersed by a method of mixing a commercial product of a resin emulsion containing an ethylene-butadiene copolymer and the aforementioned commercial product of a resin emulsion in which the dispersoid contains EVOH. It is preferable to prepare a resin emulsion whose quality contains EVOH and an ethylene-butadiene copolymer. Examples of commercially available resin emulsions whose dispersoid contains an ethylene-butadiene copolymer include CB-1200 (manufactured by Unitika Ltd.).

  According to the sixth embodiment, the EVOH and the electrospinning apparatus having a simple structure such as the electrospinning apparatus 1 shown in FIG. A fibrous web in which nanofibers composed of an ethylene-butadiene copolymer are integrated can be stably and easily formed. Further, similarly to Embodiments 1 and 2, in the nanofiber immediately after spinning and the fiber web immediately after formation, the mixing of the dispersion medium (solvent component) is suppressed.

  In the fibrous web formed according to Embodiment 6, the structure of the cross section of the nanofiber is not particularly limited. For example, it may have a bilateral structure of EVOH and an ethylene-butadiene copolymer. Alternatively, it may have a sea-island structure composed of islands composed of EVOH and a sea composed of ethylene-butadiene copolymer. It may have a core-sheath structure consisting of a core made of EVOH and a sheath made of an ethylene-butadiene copolymer. It may have a structure composed of a polymer alloy of EVOH and an ethylene-butadiene copolymer. The cross-sectional outer shape of the nanofiber may be circular, polygonal, or the like. Almost no cavity is found inside the nanofiber.

  The ethylene-butadiene copolymer is generally used as an adhesive and exhibits flexibility and strong adhesiveness at room temperature. Therefore, the fibrous web formed according to Embodiment 6 is self-adhesive in a state where nanofibers are entangled with each other due to the adhesiveness of the ethylene-butadiene copolymer, and the ethylene-butadiene copolymer is flexible. Since it exhibits the property, it is less likely to be damaged than the fibrous web formed according to Embodiments 1 and 2.

  The fibrous web formed according to Embodiment 6 is less likely to adhere to the substrate and separate from the substrate for the same reason as the fibrous web formed according to Embodiment 3. It can be attached not only to hydrophilic substrates but also to non-hydrophilic substrates such as aluminum foil and polyethylene terephthalate. Further, the fiber web formed according to the sixth embodiment is suitable as a filter medium for a mask or an air filter or a material for the filter medium for the same reason as the fiber web formed according to the third embodiment. It should be noted that the mask or air filter here is preferably used to trap PM2.5 particles.

[Embodiment 7 of the method for forming a fibrous web]
In the forming method according to Embodiment 7, the dispersoid of the resin emulsion contains EVOH and an ethylene-butadiene copolymer, and in this resin emulsion, the content of EVOH is 5% by weight or more and 16% by weight or less, -The content of the butadiene copolymer is 0.1% by weight or more and 35% by weight or less. In this case, the fibrous web can be formed more efficiently than when the EVOH content is too high. In addition, the weight ratio (ethylene-butadiene copolymer / EVOH) of the ethylene-butadiene copolymer to the EVOH in the nanofibers of the fibrous web formed according to Embodiment 7 does not become extremely small. Therefore, as compared with the case where the content of the ethylene-butadiene copolymer is extremely low, the fibrous web formed according to the embodiment 7 is less likely to be damaged and is less likely to be attached to the base material and peeled off.

  In Embodiment 7, more preferably, the dispersoid of the resin emulsion contains EVOH and an ethylene-butadiene copolymer, and the content of EVOH in this resin emulsion is 8% by weight or more and 15% by weight or less, ethylene-butadiene The content of the copolymer is 5% by weight or more and 15% by weight or less, the content of the lower alcohol is 20% by weight or more and 40% by weight or less, and the content of water is 40% by weight or more and 60% by weight or less. With such a composition, various problems caused by the organic solvent are unlikely to occur. The fibrous web formed in this case has the same structure as the structure having the core portion and the adhesive portion described above, that is, the core portion is made of EVOH, and the adhesive portion is made of the ethylene-butadiene copolymer. It tends to have a structured structure. The fibrous web formed in this case is more suitable as a filter material of a mask or an air filter or a material of the filter material, as compared with the case where the nanofiber has a core-sheath structure or a sea-island structure.

  In Embodiment 7, even more preferably, the dispersoid of the resin emulsion contains EVOH and an ethylene-butadiene copolymer, and the weight ratio of the ethylene-butadiene copolymer to the EVOH in this resin emulsion (ethylene-butadiene copolymer Combined / EVOH) is 0.5 or more and 2.0 or less, the content of EVOH is 8% by weight or more and 15% by weight or less, and the content of the ethylene-butadiene copolymer is 5% by weight or more and 15% by weight. Hereinafter, the content of the lower alcohol is 20% by weight or more and 40% by weight or less, and the content of water is 40% by weight or more and 60% by weight or less. With such a composition, various problems caused by the organic solvent are unlikely to occur. Further, the fibrous web formed in this case is likely to have a structure having the above-mentioned core portion and the adhesive portion, and clogging of the fibrous web is suppressed because the amount of the adhesive portion with respect to the amount of the core portion is appropriate. Therefore, it is more suitable as the filter material of the mask or the air filter or the material of the filter material than the fiber web formed according to the sixth embodiment.

[Embodiment 8 of the method for forming a fibrous web]
In the forming method according to Embodiment 8, the dispersoid of the resin emulsion contains EVOH, polyurethane, and an ethylene-butadiene copolymer. According to the eighth embodiment, a mask or an air filter is formed by an electrostatic spinning apparatus having a simple apparatus configuration like the electrostatic spinning apparatus 1 shown in FIG. 1 by a method similar to the solvent-type electrostatic spinning method using an EVOH solution. The filter material or the fibrous web suitable as the material for the filter material can be stably formed. Further, similarly to Embodiments 1 and 2, in the nanofiber immediately after spinning and the fiber web immediately after formation, the mixing of the dispersion medium (solvent component) is suppressed. Hereinafter, in the present specification, any one selected from the group consisting of polyurethane, ethylene-butadiene copolymer, and a mixture thereof is referred to as “adhesive resin”.

  In Embodiment 8, preferably, the dispersoid of the resin emulsion contains EVOH, polyurethane, and an ethylene-butadiene copolymer, and the content of EVOH in the resin emulsion is 5% by weight or more and 16% by weight or less. The content of the adhesive resin (total of polyurethane and ethylene-butadiene copolymer) is 0.1% by weight or more and 35% by weight or less. In this case, the fibrous web can be formed more efficiently than when the EVOH content is too high. Further, the fiber web formed in this case has an extremely small weight ratio (adhesive resin / EVOH) of the adhesive resin (total of polyurethane and ethylene-butadiene copolymer) to EVOH in the nanofiber. Not too much. The fibrous web formed in this case is less likely to be damaged and less likely to adhere to the base material and be peeled off, as compared with a fibrous web having an extremely low content of the mixture.

  In Embodiment 8, more preferably, the dispersoid of the resin emulsion contains EVOH, polyurethane, and an ethylene-butadiene copolymer, and the content of EVOH in this resin emulsion is 8% by weight or more and 15% by weight or less, Content of adhesive resin (total of polyurethane and ethylene-butadiene copolymer) is 5 wt% or more and 15 wt% or less, content of lower alcohol is 20 wt% or more and 40 wt% or less, water content Is 40% by weight or more and 60% by weight or less. In this case, various problems caused by the organic solvent are unlikely to occur. Further, the fibrous web formed in this case has the same structure as the structure having the core portion and the adhesive portion described above, that is, the core portion is made of EVOH, and the adhesive portion is made of the mixture described above. It tends to have a structure. The fibrous web formed in this case is more suitable as a filter material of a mask or an air filter or a material of the filter material, as compared with the case where the nanofiber has a core-sheath structure or a sea-island structure.

  In Embodiment 8, even more preferably, the dispersoid of the resin emulsion contains EVOH, polyurethane, and an ethylene-butadiene copolymer, and the adhesive resin (polyurethane and ethylene-butadiene copolymer The weight ratio of (total) to EVOH (adhesive resin / EVOH) is 0.5 or more and 2.0 or less, the content of EVOH is 8% by weight or more and 15% by weight or less, and the adhesive resin (polyurethane and ethylene- The content of butadiene copolymer) is 5 wt% or more and 15 wt% or less, the content of lower alcohol is 20 wt% or more and 40 wt% or less, and the water content is 40 wt% or more and 60 wt% or less. % Or less. In this case, various problems caused by the organic solvent are unlikely to occur. Further, the fibrous web formed in this case is likely to have a structure having the core portion and the adhesive portion described above, and since the amount of the adhesive portion relative to the amount of the core portion is appropriate, the filter material of the mask or the air filter. Alternatively, it is suitable as a material for the filter medium.

[Other Embodiments of Method for Forming Fibrous Web]
When nanofibers are accumulated by the electrospinning method in Embodiments 1 to 8, nanofibers may be accumulated on a metal foil or a mount to form a fibrous web. An aluminum foil is illustrated as a metal foil. For example, when the electrospinning apparatus 1 is used, the electrospinning method is performed after placing the metal foil or the mount on the collecting unit 7 in advance. Until the fibrous web is peeled off from the metal foil or the mount, the fibrous web can be easily carried or stored together with the metal foil or the mount.

  The resin emulsions in Embodiments 1 to 8 may further contain additives and auxiliaries, if necessary, as long as the effects of the invention are not impaired. In order to contain the additive or the auxiliary agent, the additive or the auxiliary agent is mixed at the time of preparing the resin emulsion or in the commercially available resin emulsion prepared. As the additive, one or more kinds selected from the group consisting of a lubricant, a plasticizer, a crystallization rate retarder, an antioxidant, an ultraviolet absorber, an antistatic agent, an anti-coloring agent, a flame retardant, a light stabilizer and the like. Agents. Examples of the auxiliaries include one or more agents selected from the group consisting of pigments, fungicides, antibacterial agents and the like.

  The nanofibers spun according to any one of Embodiments 1 to 8 and the formed fiber web may optionally contain the above-mentioned additives and auxiliaries as long as they do not impair the effects of the invention. Is also good.

  From the viewpoint of removing fine particulate matter such as PM2.5 particles and PM1.0 particles, the fibrous web obtained by any of Embodiments 1 to 8 has a pore size of 600 to 1,000 nm. Is preferred. From the viewpoint of removing ultrafine particles such as PM0.1 particles and bacteria, the pore size is preferably 300 nm or more and less than 600 nm. From the viewpoint of removing influenza virus, the pore size is preferably 38 nm or more and less than 300 nm. From the viewpoint of removing norovirus, the pore size is preferably 10 to 38 nm. If the pore size is too large for the particles to be removed, it will be difficult to remove the particles. If the pore size is too small, clogging is likely to occur, and the mask user becomes uncomfortable.

  The nanofiber forming the fibrous web obtained in any of Embodiments 1 to 8 preferably has a fiber length of 20 cm or more. Since the fibrous web in this case does not easily become bulky, a thin mask or an air filter can be manufactured by using it as a filter medium or a material of the filter medium. Further, in this case, since the nanofibers are hard to drop from the fibrous web, it is possible to avoid the deterioration of the fibrous web due to the falling.

[Laminated sheet and manufacturing method thereof]
The method for producing a laminated sheet according to the present invention comprises a step of preparing a breathable sheet, and an electrospinning method to spin nanofibers from a resin emulsion and to accumulate the spun nanofibers to form a fibrous web. And a step of laminating a breathable sheet on at least one side of the formed fibrous web. In addition, a step of spinning nanofibers from a resin emulsion by an electrospinning method to form a fibrous web by accumulating the spun nanofibers, and a fibrous web obtained by this step, Embodiments 1 to 8 and other embodiments are as described above.

  The breathable sheet is a member that has breathability and supports the fiber web to protect it from damage, and is laminated on at least one surface of the fiber web. The breathable sheet includes, for example, a breathable cloth such as a non-woven fabric and a woven fabric, and a mesh having fine meshes, but is not particularly limited and is appropriately selected as necessary. The material of the breathable sheet may be hydrophilic, hydrophobic, or metal. In addition, when a breathable sheet is laminated on the fibrous web formed in Embodiments 3 to 8, since the fibrous web exhibits adhesiveness, the fibrous web is peeled from the breathable sheet regardless of the material of the breathable sheet. Hateful.

  It is also preferable to laminate a breathable sheet on both sides of the fibrous web. In this case, separate breathable sheets may be laminated on one surface and the other surface of the fibrous web. Alternatively, by laminating one surface of the fibrous web on one end of the air-permeable sheet and then bending the air-permeable sheet to sandwich the fibrous web, the other end of the air-permeable sheet is attached to the other surface of the fibrous web. You may laminate. It is possible to manufacture a laminated sheet in which the fibrous web is less likely to break during use.

  When the fibrous web is formed on the metal foil or the mount as described above, the present manufacturing method can be carried out by peeling the fibrous web from the metal foil or the mount and attaching it to the breathable sheet. In this case, since the fibrous web can be carried or stored together with the metal foil or the mount, the forming of the fibrous web and the step of laminating the breathable sheet on the fibrous web are performed at different places or different days. It is preferable from the viewpoint that it can be carried out.

  From the viewpoint of simplification of the working process, the present manufacturing method spins nanofibers from a resin emulsion by an electrostatic spinning method, accumulates the spun nanofibers to form a fiber web, and forms the formed fiber. It is preferable to stack the breathable sheet on one side of the web all at once. To this end, when performing the electrospinning method, the nanofibers immediately after being spun are accumulated on the breathable sheet to form a fibrous web. For example, when forming a fibrous web using the apparatus 1 shown in FIG. 1, an air-permeable sheet is placed on the collection unit 7, and then the electrospinning method is performed. Further, since the fiber web is charged by the electrostatic spinning method, the fibrous web immediately after formation is easily attached to the breathable sheet, and further, the nanofibers are easily attached to each other. The laminated sheet produced in this case is more difficult to peel the fibrous web from the breathable sheet and more unlikely to be damaged than the case where the fibrous web is peeled from the metal foil or the mount and attached to the breathable sheet. Therefore, it is further suitable as a filter medium for a mask or an air filter.

  When the fibrous web formed according to Embodiment 1 or 2 is used in the present production method, it is preferable that the laminated sheet is subjected to heat treatment after the step of laminating the breathable sheet on the fibrous web. Further, the heat treatment allows the nanofibers to be thermally shrunk or partially fused to obtain a laminated sheet having a small pore size. Furthermore, the heat treatment makes it possible to obtain a laminated sheet in which the nanofibers are fused to each other, and further, the fiber web is fused to the breathable sheet. Therefore, in the heat-treated laminated sheet, the fibrous web is less likely to be peeled from the breathable sheet and is less likely to be damaged than in the case where the heat-treated laminated sheet is not subjected. The heat-treated laminated sheet tends to be suitable as a filter medium for a mask or an air filter.

  Note that the heat treatment is performed in the air, oxygen, nitrogen, or a rare gas. Examples of rare gases include helium, neon, argon, krypton, and xenon. Further, the temperature of the heat treatment is 50 to 180 ° C., the treatment time is in the range of 1 second to 1 hour, and the laminate sheet is appropriately adjusted so as to exhibit the desired pore size. As an example of the heat treatment, a laminated sheet comprising a fibrous web and a breathable sheet laminated on both sides of this fibrous web is calendered for 1 to several seconds to perform thermocompression bonding of the fibrous web to the breathable sheet. Can be mentioned.

  When the fibrous web formed according to any of Embodiments 3 to 8 is used in this production method, the laminated sheet may not be subjected to heat treatment. The fibrous web formed by any of Embodiments 3 to 8 exhibits adhesiveness at room temperature due to polyurethane and ethylene-butadiene copolymer, so that the fibrous web is difficult to be peeled from the breathable sheet without heat treatment, The fibrous web is less likely to break. Even with a laminated sheet including the fibrous web formed according to any one of Embodiments 3 to 8, it is possible to adjust the pore diameter and the pressure loss of the laminated sheet by performing heat treatment. It is preferable to carry out.

  The laminated sheet produced by the present production method is suitable as a filter material for a mask or an air filter because the fibrous web exhibits the effects described above in Embodiments 1 to 8 and the breathable sheet protects the fibrous web. There is. Since the present laminated sheet has a high PM2.5 particle trapping rate, it is preferably used as a mask for trapping PM2.5 particles or a filter medium for an air filter, and more preferably a mask for trapping PM2.5 particles. Used as a filter medium. It is possible to manufacture a mask and an air filter that are easy to use by reducing the weight of the mask and the air filter and reducing the thickness thereof as compared with the conventional filter material. In addition, the laminated sheet has a pore diameter of 10 nm or more and 1,000 nm or less by adjusting the amount of nanofibers accumulated during production or by partially fusing the fibers of the nanofibers by a heat treatment described later. Therefore, the size of the pore diameter can be appropriately adjusted according to the standard so that the pressure loss becomes 10 Pa or more and 500 Pa or less.

  The breathable sheet is preferably a non-woven fabric provided with a fiber layer formed of a plurality of thermoplastic resin fibers that are stretched and arranged in substantially one direction. The thermoplastic resin fiber forming this fiber layer is, for example, a stretched polyester fiber having an average fiber diameter of about 10 μm. The nonwoven fabric provided with this fiber layer has a small thickness of the thermoplastic resin fibers and is thin. Further, it exhibits strong tensile strength in the direction in which the thermoplastic resin fiber is stretched. The present laminated sheet having a nonwoven fabric provided with this fiber layer has a small overall thickness, and the fibrous web is less likely to be damaged even when pulled in the direction in which the thermoplastic resin fibers are stretched. The non-woven fabric provided with this fiber layer may have a single-layer structure composed of a single fiber layer.

  When the breathable sheet is a nonwoven fabric provided with a fiber layer formed by a plurality of thermoplastic resin fibers arranged by stretching in substantially one direction, the present laminated sheet is used when the fiber web has a small basis weight. Even if it exists, the particulate matter can be efficiently captured. The laminated sheet in this case is more suitable for use as a mask or an air filter than a laminated sheet including a breathable sheet made of fibers that are not stretched in substantially one direction.

The breathable sheet is more preferably a non-woven fabric having a multi-layer structure in which a plurality of fiber layers formed of a plurality of thermoplastic resin fibers that are stretched and arranged in substantially one direction are provided. In the nonwoven fabric having this multilayer structure, the alignment axis of the thermoplastic resin fibers in one fiber layer and the alignment axis of the thermoplastic resin fibers in the other fiber layer intersect. Although such a non-woven fabric has a multi-layer structure, the thermoplastic resin fibers do not overlap each other so much and the thickness thereof is thin. Furthermore, since it exhibits strong tensile strength in a plurality of directions, it has excellent dimensional stability. The nonwoven fabric having this multilayer structure can be appropriately adjusted at the time of production so that the basis weight is about 5 to 60 (g / m ² ) and the thickness is about 50 to 170 μm. Examples of the non-woven fabric having this multilayer structure include various non-woven fabrics (manufactured by JX ANCI Co., Ltd.) commercially available as Milife (registered trademark of New Japan Oil Co., Ltd.) series. The present laminated sheet including the nonwoven fabric having the multilayer structure has a small overall thickness, and the fibrous web is less likely to be damaged even when pulled in a plurality of directions. Since the laminated sheet does not tear even if pulled by a force equivalent to a human grip, the laminated sheet is not easily broken even when used as a filter medium for a mask.

  The breathable sheet is even more preferably a cross-woven cloth. The cross-latitude orthogonal non-woven fabric is a non-woven fabric having the above-mentioned multilayer structure and being laminated so that the above-mentioned array axis in one fiber layer and the above-mentioned array axis in the other fiber layer are orthogonal to each other. .. As the non-woven fabric orthogonal to the background, for example, the non-woven fabrics commercially available as Milife series can be mentioned. The cross-latitude orthogonal nonwoven fabric has further improved tensile strength in all directions and dimensional stability as compared with a nonwoven fabric in which the array axes intersect but are not orthogonal. In the case of the present laminated sheet including the cross-woven cloth, the fibrous web is less likely to be damaged, and is less likely to be broken as a filter material for a mask.

[Raw materials, electrostatic spinning equipment]
Eversolve # 10 (manufactured by Nippon Cima Co., Ltd.) was prepared as a commercially available resin emulsion having a dispersoid of EVOH. The composition of this resin emulsion is about 10 wt% EVOH, about 40 wt% n-propanol, and about 50 wt% water.

  As a commercial product of a resin emulsion having a dispersoid containing polyurethane, Superflex 460 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), which is a kind of Superflex series, was prepared. The composition of this resin emulsion is about 30% by weight of solid content (polyurethane) and about 70% by weight of water. A polycarbonate polyol is used as the polyurethane.

  CB-1200 (manufactured by Unitika Ltd.) was prepared as a commercial product of a resin emulsion whose dispersoid contained an ethylene-butadiene copolymer. The composition of this resin emulsion is about 20% by weight of solid content (ethylene-butadiene copolymer), about 20% by weight of 2-propanol and about 60% by weight of water.

  As a commercially available powder of PVA, PVA-117 (manufactured by the same company) of Kuraray Poval (registered trademark of Kuraray Co., Ltd.) series was prepared.

Two types of commercially available nonwoven fabrics were prepared as breathable sheets. Nonwoven fabric A is a non-woven fabric of polypropylene fiber (model number: 6640-1C, manufactured by Shinwa Co., Ltd.) and has a basis weight of 40 g / m ² . The non-woven fabric B is a non-woven fabric (model number: TY0505FE, manufactured by JX ANCI Co., Ltd.) commercially available as a type of Milife (registered trademark of New Japan Petroleum Co., Ltd.) and has a basis weight of 10 g / m ² . The non-woven fabric B is a non-woven fabric having a multi-layered structure. The multi-layered structure is formed by laminating fiber layers in which polyester fibers are stretched and arranged in substantially one direction, and the alignment axis of one fiber layer and other fibers are arranged. The axis of arrangement of the fiber layers intersects.

  As an electrostatic spinning device, a NEU nanofiber electrospinning unit (manufactured by Kato Tech Co., Ltd.) was prepared. This electrostatic spinning device has the same configuration as the electrostatic spinning device 1 shown in FIG. Further, this electrostatic spinning device can form nanofibers having an average fiber diameter of 50 nm or more and 800 nm or less and a fiber length of 100 times or more the average fiber diameter, or a fiber web in which the nanofibers are integrated. ..

[Example 1]
2 parts by weight of the resin emulsion in which the dispersoid contained EVOH and 1 part by weight of the resin emulsion in which the dispersoid contained polyurethane were mixed to prepare a resin emulsion in which the dispersoid contained EVOH and polyurethane. The composition of the prepared resin emulsion was 6.8 wt% EVOH, 12.5 wt% polyurethane, 30.0 wt% lower alcohol (n-propanol), and 50.7 wt% water. In the prepared resin emulsion, the weight ratio of the adhesive resin (polyurethane) to EVOH (adhesive resin / EVOH) was 1.8.

Then, by using the prepared electrospinning apparatus, a voltage of 10 kV was applied to the prepared resin emulsion to spin nanofibers by the electrospinning method, and the nanofibers immediately after spinning were placed on the nonwoven fabric A (breathable sheet). By stacking, a breathable sheet was laminated on one side while forming a fibrous web, and a laminated sheet according to Example 1 was produced as a prototype. When the nanofiber according to Example 1 was prototyped, the fiber web had a basis weight of 0.2 g / m ² .

Table 1 shows the composition of the resin emulsion prepared in Example 1, Examples 2 to 7 described later, and Comparative Example 1.

[Example 2]
The fiber web had a basis weight of 0.5 g / m ^2, and the nonwoven fabric A was used as a breathable sheet. Other than that, the laminated sheet according to Example 2 was prototyped under the same conditions as in Example 1.

[Example 3]
The fiber web had a basis weight of 1.0 g / m ^2, and the nonwoven fabric A was used as the breathable sheet. Other than that, the laminated sheet according to Example 3 was prototyped under the same conditions as in Example 1.

[Example 4]
The fiber web had a basis weight of 0.5 g / m ^2, and the nonwoven fabric B was used as a breathable sheet. Other than that, the laminated sheet according to Example 4 was manufactured under the same conditions as in Example 1.

[Example 5]
The fiber web had a basis weight of 1.5 g / m ^2, and the nonwoven fabric B was used as a breathable sheet. Other than that, the laminated sheet according to Example 5 was prototyped under the same conditions as in Example 1.

[Example 6]
The fiber web had a basis weight of 1.5 g / m ^2, and the nonwoven fabric A was used as a breathable sheet. About the others, the laminated sheet according to Example 6 was manufactured under the same conditions as in Example 1.

[Example 7]
2 parts by weight of the resin emulsion in which the dispersoid contains EVOH and 1 part by weight of the resin emulsion in which the dispersoid contains the ethylene-butadiene copolymer are mixed so that the dispersoid contains EVOH and the ethylene-butadiene copolymer. A containing resin emulsion was prepared. The composition of the prepared resin emulsion was 6.8 wt% EVOH, 10.0 wt% ethylene-butadiene copolymer, 30.0 wt% lower alcohol (n-propanol), and 53.2 wt% water. In the prepared resin emulsion, the weight ratio of the adhesive resin (ethylene-butadiene copolymer) to EVOH (adhesive resin / EVOH) was 1.5. Further, the basis weight of the fibrous web was set to 0.5 g / m ^2, and the nonwoven fabric A was used as the breathable sheet. Other than that, the laminated sheet according to Example 7 was manufactured under the same conditions as in Example 1.

[Comparative Example 1]
The prepared PVA powder was dissolved in water to prepare a PVA solution. The composition of this PVA solution was 10% by weight of PVA and 90% by weight of water. Further, 2 parts by weight of this PVA solution and 1 part by weight of a resin emulsion whose dispersoid contains an ethylene-butadiene copolymer were mixed to prepare a resin solution for electrostatic spinning. The composition of this resin solution was 6.8 wt% PVA, 6.8 wt% ethylene-butadiene copolymer, and 86.4 wt% water.

Then, using the prepared electrospinning apparatus, a voltage of 10 kV was applied to the prepared resin solution to spin nanofibers by the electrospinning method, and the nanofibers immediately after spinning were placed on the nonwoven fabric A (breathable sheet). By stacking, a breathable sheet was laminated on one surface while forming a fibrous web, and a laminated sheet according to Comparative Example 1 was produced as a prototype. When the nanofiber according to Comparative Example 1 was prototyped, the fiber web had a basis weight of 0.5 g / m ² .

[Test method]
Using the filter performance evaluation tester (model number: DFT-4, manufactured by Tokyo Direc Co., Ltd.), the test method according to JIS B 9908: 2011 format 2 was used to laminate the laminates according to Examples 1 to 7 and Comparative Example 1. With respect to each of the sheets, the initial filtration performance for 11 kinds of the test powder 1 defined in JIS Z 8901 was evaluated.

[Test results]
Table 2 shows measured values of pressure loss, PM0.3 particle capture rate, and PM2.5 particle capture rate as initial filtration performances of the laminated sheets according to Examples 1 to 7 and Comparative Examples 1 and 2. Shown in.

  As shown in Table 2, the laminated sheets according to Examples 2 and 7 were superior to the laminated sheet according to Comparative Example 1 in the trapping rate of PM2.5 particles. In Examples 2 and 7, since the fibrous web was formed from the resin emulsion, an adhesive part composed of polyurethane or ethylene-butadiene copolymer was apt to appear on the surface of the nanofiber, and PM2.5 particles were formed by the adhesive part. It is considered that the capture rate of the was increased. On the other hand, in Comparative Example 1, since the fibrous web was formed from the resin solution, there were many ethylene-butadiene copolymers that were encapsulated inside the nanofibers, and it is considered that the capture rate of PM2.5 particles was suppressed. Be done.

  Regarding the breathable sheet, although the basis weight of the non-woven fabric B is smaller than that of the non-woven fabric A, Example 5 using the non-woven fabric B has a capture rate of PM0.3 particles in comparison with Example 6 using the non-woven fabric A. And PM2.5 particle capture rate were both excellent.

  Regarding the difference between the experimental results of Example 5 and Example 6 described above, the mechanism is unknown, but it is presumed as follows. In the laminated sheet 61 according to Example 6 shown in FIG. 4A, the fibers 63 forming the non-woven fabric A are irregularly entangled with each other, and thus the irregular surface of the non-woven fabric A has irregularities. .. The nanofibers 25 accumulated on the nonwoven fabric A have irregular arrangement. Therefore, in the fibrous web accumulated on the non-woven fabric A, there are a portion 65 where the nanofibers 25 are densely gathered and a portion where pores 67 having a large diameter are formed because the nanofibers 25 are scarcely accumulated. It is assumed that there is. That is, it is considered that in the laminated sheet 61 according to Example 6, the number of pores 67 having a large diameter is large and thus the trapping rate of PM2.5 particles and the trapping rate of PM0.3 particles are suppressed.

  On the other hand, in the laminated sheet 51 according to Example 5 shown in FIG. 4B, since the thermoplastic resin fibers 53 forming the nonwoven fabric B are stretched and arranged in substantially one direction, the nonwoven fabric B is formed. The cloth surface is flat. The nanofibers 25 accumulated on the non-woven fabric B are arranged in a line. Therefore, in the fibrous web accumulated on the non-woven fabric B, it is assumed that the accumulation amount of the nanofibers 25 is less uneven in each part. That is, in the laminated sheet 51 according to the example 5, as compared with the laminated sheet 61 according to the example 6, since the number of pores having a large diameter is small, the capture rate of PM2.5 particles and the capture rate of PM0.3 particles are high. It is thought that

1 Electrospinning device 21 Resin solution 27 Dispersoid resin emulsion containing EVOH

Claims (11)

By the electrospinning method, spinning the nanofibers from the resin emulsion, including the step of forming a fiber web by accumulating the spun nanofibers,
The resin emulsion has a dispersoid and a dispersion medium,
The method for forming a fibrous web, wherein the dispersoid contains at least an ethylene-vinyl alcohol copolymer (EVOH).   The fiber according to claim 1, wherein the dispersoid further contains one kind of adhesive resin selected from the group consisting of polyurethane, ethylene-butadiene copolymer, and a mixture thereof. How to form a web.   The content of the EVOH in the resin emulsion is 5% by weight or more and 16% by weight or less, and the content of the adhesive resin is 0.1% by weight or more and 35% by weight or less. Item 3. A method for forming a fibrous web according to item 2.   The weight ratio (adhesive resin / EVOH) of the adhesive resin to the EVOH in the resin emulsion is 0.5 or more and 2.0 or less, wherein the fiber web according to claim 2 or 3. Forming method. A step of preparing a breathable sheet,
A step of forming a fibrous web by the method for forming a fibrous web according to any one of claims 1 to 4,
Laminating the breathable sheet on at least one side of the formed fibrous web,
A method for producing a laminated sheet, comprising: A fibrous web comprising electrospun nanofibers integrated,
The nanofiber is at least
EVOH,
One adhesive resin selected from the group consisting of polyurethane, ethylene-butadiene copolymer, and mixtures thereof;
A fibrous web comprising:   The fiber web according to claim 6, wherein a weight ratio (adhesive resin / EVOH) of the adhesive resin to EVOH in the nanofibers is 0.5 or more and 2.0 or less. At least a portion of the nanofibers,
A core portion formed of the EVOH, which extends in the fiber length direction,
Intermittently present on the surface of the core portion, an adhesive portion made of the adhesive resin,
Fibrous web according to claim 6 or 7, characterized in that it has a. A fiber web according to any one of claims 6 to 8,
A breathable sheet laminated on at least one side of the fibrous web,
A laminated sheet comprising:   The laminated sheet according to claim 9, wherein the breathable sheet is a nonwoven fabric having a fiber layer in which a plurality of thermoplastic resin fibers are stretched and arranged in substantially one direction.   The laminated sheet according to claim 9 or 10, which is used as a filter or a filter medium for an air filter.

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