JP2012012711A - Nanofiber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nanofiber sheet which has a nanofiber layer having a uniform distribution of nanofibers.SOLUTION: A nanofiber sheet of this invention comprises a substrate layer and a nanofiber layer which is laminated on the substrate layer and includes nanofibers. The substrate layer has air permeability and has an initial electrification voltage of 0.3 kV or less measured by the half-life measuring method according to JIS L1094. Preferably a large number of openings are formed in the substrate layer, and a mesh sheet is preferable for the substrate layer.

Description

  The present invention relates to a nanofiber sheet containing nanofibers.

  Nanofibers are applied to fields that require optical properties such as high transparency using the nanosize effect, for example. As an example, a transparent fabric can be realized by setting the diameter of the nanofiber to be equal to or less than the wavelength of visible light. Moreover, structural coloring can be expressed by making the diameter of the nanofiber the same as the wavelength of visible light. In addition, by utilizing the high specific surface area effect, fields that require high adsorption properties and high surface activity, and by utilizing the high molecular alignment effect, mechanical properties such as tensile strength and electrical properties such as high electrical conductivity are provided. Studies are also being conducted in fields where characteristics are required. Nanofibers having such characteristics are used, for example, as single fibers, as well as as aggregates (fabrics) and composite materials.

As an application example of nanofibers, a composite fiber structure composed of nanofibers spun by an electrospinning method and a fiber structure has been proposed (see Patent Document 1). This fiber structure is selected from non-woven fabrics, woven fabrics, and knitted fabrics having a surface resistivity of 10 ³ to 10 ¹² Ω as measured by the JISK6271 ring method. According to the description in this document, a low-weight nanofiber assembly (nanofiber layer), which has been difficult to handle in the past due to low strength and ultrafineness, can be brought into close contact with the fiber structure. In the composite fiber structure described in the literature, the nanofiber layer is difficult to peel off from the fiber structure, and the filter saddle material, the medical tissue culture support, the fuel cell electrolyte membrane support, the alkaline secondary battery, and the nonaqueous system It is said to be suitable as a secondary battery separator or the like.

JP 2008-303521 A

  In a nanofiber layer in which nanofibers are integrated, it is usually desirable that the nanofibers are uniformly distributed throughout the nanofiber layer, the nanofiber distribution is uniform, and the nanofiber layer has a uniform thickness. . If there is unevenness in the distribution of nanofibers in the nanofiber layer, for example, if the nanofiber contains a functional agent that exhibits a whitening effect (whitening component), the distribution of the functional agent also becomes uneven. Even if a nanofiber layer is used while adhering to the skin, the whitening effect may not be stably obtained. Also, in general, a nanofiber layer having no unevenness in the distribution of nanofibers has a better appearance than that having unevenness in the distribution.

  However, a technology that can stably supply a nanofiber layer that has no unevenness in the distribution of nanofibers has not been provided yet, and in particular, in order to prevent unevenness in the distribution of nanofibers in a nanofiber layer with a low weight. It was difficult. As described in Patent Document 1, even if the surface resistivity of the base material layer on which the nanofiber layer is laminated is set in a specific range, the nanofiber layer thus obtained has a particularly low weight. In addition, the distribution of nanofibers was uneven.

  The subject of this invention is providing the nanofiber sheet | seat provided with the nanofiber layer with uniform distribution of nanofiber.

  As a result of various studies on the distribution of nanofibers in the nanofiber layer formed on the base material layer by electrospinning, the present inventors measured the base material layer by the half-life measurement method defined in JIS L1094. It was found that the distribution of nanofibers becomes uniform by using a low-chargeable base material layer whose initial charged voltage is a specific value or less.

  The present invention has been made based on the above knowledge, and is a nanofiber sheet comprising a base material layer and a nanofiber layer including nanofibers laminated on the base material layer and formed by an electrospinning method. The present invention provides a nanofiber sheet having an initial charged voltage of 0.3 kV or less measured by a half-life measuring method defined in JIS L1094 of the base material layer.

  ADVANTAGE OF THE INVENTION According to this invention, the nanofiber sheet provided with the nanofiber layer with uniform nanofiber distribution is provided. Such a nanofiber sheet of the present invention has a good appearance due to the uniform distribution of nanofibers, and can be suitably used for various applications. For example, when nanofibers contain various functional agents. The effect of the functioning agent can be obtained stably.

FIG. 1 is a schematic diagram showing an apparatus for performing an electrospinning method.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The nanofiber sheet of the present invention includes a base material layer and a nanofiber layer laminated on the base material layer and including nanofibers.

  The nanofiber layer is preferably composed only of nanofibers. However, it is not prevented that the nanofiber layer includes other components in addition to the nanofiber. Nanofibers are generally 10-3000 nm, particularly 10-1000 nm, when the thickness is expressed in terms of equivalent circle diameter. The thickness of the nanofiber is observed by magnifying it 10,000 times by, for example, scanning electron microscope (SEM) observation, and defects (nanofiber lump, nanofiber intersection, polymer droplet) are excluded from the two-dimensional image. Measurement can be made by selecting 10 fibers (nanofibers) arbitrarily, drawing a line perpendicular to the longitudinal direction of the fibers, and directly reading the fiber diameter.

  The length of the nanofiber is not critical in the present invention, and a length corresponding to the method for producing the nanofiber can be used. In addition, the nanofiber may exist in a state of being oriented in one direction in the nanofiber layer, or may be oriented in a random direction.

  The thickness of the nanofiber layer is set to an appropriate range depending on the specific application. When the nanofiber sheet is used, for example, to adhere to human skin, the thickness of the nanofiber layer is preferably set to 50 nm to 1 mm, particularly 500 nm to 500 μm. The thickness of the nanofiber layer can be measured using a contact-type film thickness meter, Mitsutyo Lightmatic VL-50A (R5 mm carbide spherical surface probe). The load applied to the sheet during measurement is 0.01N.

An appropriate range of the basis weight (weight per unit area) of the nanofiber layer is set according to the specific application. When the nanofiber sheet is used for adhering to human skin, for example, the basis weight of the nanofiber layer is preferably set to 0.01 to 100 g / m ² , particularly 0.1 to 50 g / m ^2. .

In general, if the nanofiber layer has a low basis weight (for example, a basis weight of 0.1 g / m ² , particularly 0.05 to 3.0 g / m ² ), the nanofibers are not uniformly distributed and unevenness occurs. In the present invention, as will be described later, in the present invention, as a base material layer on which the nanofiber layer is laminated, low chargeability with an initial charged voltage measured by a half-life measuring method specified in JIS L1094 is a specific value or less By using the base material layer, even if the nanofiber layer has a low basis weight, the distribution of the nanofiber is made uniform and unevenness is hardly caused.

  In the nanofiber layer, the nanofibers are joined at their intersection or the nanofibers are intertwined. As a result, the nanofiber layer can maintain a sheet-like form by itself. Whether the nanofibers are bonded or intertwined depends on the method of manufacturing the nanofiber layer (nanofiber sheet).

  Nanofibers are made from a polymer compound as a raw material. As the polymer compound, any of natural polymers and synthetic polymers can be used. The polymer compound may be a water-soluble polymer compound or a water-insoluble polymer compound.

  In the present specification, “water-soluble polymer compound” means that 1 g of a polymer compound is weighed in an environment of 1 atm and 23 ° C., then immersed in 10 g of ion-exchanged water, and immersed after 24 hours. A high molecular compound having a property of dissolving 0.5 g or more of the high molecular compound.

  Further, in this specification, the “water-insoluble polymer compound” means that 1 g of a polymer compound is weighed in an environment of 1 atm and 23 ° C., then immersed in 10 g of ion-exchanged water, and after 24 hours, This refers to a polymer compound having a property that 0.8 g or more of the immersed polymer compound does not dissolve.

  Examples of the water-soluble polymer compound constituting the nanofiber include, for example, pullulan, hyaluronic acid, chondroitin sulfate, poly-γ-glutamic acid, modified corn starch, β-glucan, glucooligosaccharide, heparin, keratosulfuric mucopolysaccharide, cellulose, pectin, etc. , Xylan, lignin, glucomannan, galacturon, psyllium seed gum, tamarind seed gum, gum arabic, tragacanth gum, soy water soluble polysaccharide, alginic acid, carrageenan, laminaran, agar (agarose), fucoidan, methylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose Natural polymers such as partially saponified polyvinyl alcohol (when not used in combination with a crosslinking agent described later), low saponified polyvinyl alcohol, polyvinyl pyrrolidone (PVP), polyethylene Examples thereof include synthetic polymers such as oxide and sodium polyacrylate. These water-soluble polymer compounds can be used alone or in combination of two or more. Of these water-soluble polymer compounds, from the viewpoint of easy preparation of nanofibers, pullulan and synthetic polymers such as partially saponified polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene oxide having a saponification degree of 80 to 96 mol% may be used. preferable.

  Examples of the water-insoluble polymer compound constituting the nanofiber include, for example, polyvinyl alcohol (fully saponified polyvinyl alcohol that can be insolubilized after formation of the nanofiber, partially saponified polyvinyl alcohol that can be crosslinked after formation of the nanofiber by using in combination with a crosslinking agent described later) , Oxazoline-modified silicone such as poly (N-propanoylethyleneimine) graft-dimethylsiloxane / γ-aminopropylmethylsiloxane copolymer, zein (main component of corn protein), polyester, polylactic acid (PLA), polyacrylonitrile resin , Acrylic resin such as polymethacrylic acid resin, polystyrene resin, polyvinyl butyral resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyurethane resin, polyamide resin, Polyimide resins, polyamide-imide resins. These water-insoluble polymer compounds can be used alone or in combination of two or more. Of these water-insoluble polymer compounds, fully saponified polyvinyl alcohol that can be insolubilized after nanofiber formation from the viewpoint of being highly safe and readily available, soluble in solvents such as ethyl alcohol and isopropyl alcohol, etc. It is preferable to use partially saponified polyvinyl alcohol, oxazoline-modified silicone such as γ-aminopropylmethylsiloxane copolymer, water-soluble polyester, twein and the like that can be crosslinked after nanofiber formation by using in combination with a crosslinking agent.

  The nanofiber may be composed of only the above-described polymer compound, or may contain other components in addition to the polymer compound. Examples of such other components include a crosslinking agent, a pigment, an additive, a surfactant, an antistatic agent, and a foaming agent. The crosslinking agent is used, for example, for the purpose of crosslinking the above partially saponified polyvinyl alcohol to insolubilize it. The pigment is used for the purpose of coloring the nanofiber. Each of these other components is preferably contained in the nanofiber by 0.01 to 70% by mass.

  In the nanofiber sheet of the present invention, the nanofiber layer is directly laminated on the base material layer. The base material layer is preferably laminated so as to be peelable from the nanofiber layer. With this configuration, after the nanofiber layer is attached to, for example, human skin, the substrate layer can be peeled off from the nanofiber layer to leave the nanofiber layer on the human skin. There is an advantage of becoming. Therefore, it is preferable that no layer including an adhesive means is provided between the nanofiber layer and the base material layer. From the viewpoint of enhancing the peelability of the base material layer from the nanofiber layer, if necessary, the nanofiber layer laminated surface of the base material layer may be subjected to a release treatment such as application of silicone resin or corona discharge treatment. Good.

  The base material layer preferably has air permeability. When the base material layer has air permeability, the peelability of the base material layer from the nanofiber layer is improved. For example, when the nanofiber layer is attached to human skin as described above, the base layer is used. The material layer is easily peeled from the nanofiber layer. In addition, since the nanofiber layer itself also has air permeability, when the base material layer has air permeability, the nanofiber sheet of the present invention comprising the base material layer and the nanofiber layer is The entire sheet also has air permeability.

Whether the base material layer has air permeability can be determined by, for example, the air permeability measured according to JIS P8117 (conforming to ISO5636 / 5-Part5). The air permeability is a value defined by the time taken for 100 ml of air to pass through an area of 6.42 cm ² . High air permeability means that it takes time to pass air, that is, low air permeability, and conversely, low air permeability means high air permeability. Thus, the magnitude of the air permeability is opposite to the air permeability. The air permeability of the base material layer having air permeability is preferably 30 seconds or less, more preferably 20 seconds or less. A base material layer having an air permeability exceeding 30 seconds cannot be said to have air permeability.

  As a base material layer having air permeability, for example, a mesh sheet (made by weaving fibers, made by knitting fibers, or made by extrusion molding), perforated sheet (sheet) In addition, a sheet in which a large number of apertures penetrating the sheet in the thickness direction are formed), paper, non-woven fabric, and the like can be used, and a laminated sheet obtained by bonding two or more of these can also be used. As an apertured sheet, for example, a sheet made of resin formed with a large number of holes by mechanical means; a mixed sheet of resin and inorganic filler is peeled off by stretching, and micropores are formed in the mixed sheet And those in which micropores are communicated using open cells by foam molding. Moreover, as resin used as the formation material of a mesh sheet | seat and an apertured sheet, polyolefin, such as polyethylene (PE) and polypropylene (PP), polyester, polyamide, polyurethane, polystyrene, a polyethylene-vinyl acetate copolymer, etc. are mentioned.

  However, as will be described later, in the present invention, the initial charged voltage measured by the half-life measuring method specified in JIS L1094 of the base material layer must be 0.3 kV or less. It is necessary to select one that can satisfy a specific range of such initial charging voltage. From this point of view, the base material layer preferably has a large number of apertures formed, and in particular, a large number of apertures (openings) that penetrate the base material layer in the thickness direction (the laminating direction of the nanofiber layer). ) And a large number of the apertures are formed with a predetermined regularity. Specifically, a mesh sheet and an aperture sheet may be mentioned, and a mesh sheet is particularly preferable. When a large number of holes are formed in the base material layer with a predetermined regularity, the initial withstand voltage of the base material layer can be reduced, for example, by increasing the area of each hole. It is easy to obtain a low initial charging voltage. Here, “a large number of openings are formed with a predetermined regularity” means that 5 to 400, preferably 10 to 200, openings are formed per inch. It means that the holes are formed in at least one direction continuously or at a predetermined interval. For example, in the case where a large number of 5 to 400 holes per inch are formed in a lattice shape or a staggered pattern on the laminated surface of the nanofiber layer in the base material layer, “a large number of openings have a predetermined regularity. It is said that it is formed with.

  One of the main characteristics of the nanofiber sheet of the present invention is that the initial charged voltage measured by the half-life measuring method defined in JIS L1094 of the base material layer is 0.3 kV or less. Such a low-charge base layer having a low initial withstand voltage is difficult to be charged. Therefore, when a nanofiber layer is formed on a low-charge base layer according to a conventional method by electrospinning, the nanofibers are low-charge. Therefore, the nanofibers can be accurately deposited at a desired position on the low-chargeable substrate layer. Therefore, by forming the nanofiber layer using the low-chargeable base material layer, even when the nanofiber layer having a low basis weight is formed, the nanofiber layer having a uniform nanofiber distribution and no unevenness is obtained. can get. The initial charged voltage measured by the half-life measuring method prescribed | regulated to JISL1094 of a base material layer becomes like this. Preferably it is 0.01-0.3 kV. The initial charging voltage is measured as follows.

<Initial voltage measurement method>
The initial charged voltage of the base material layer is 23 ° C. and 50% RH using an Honest meter (model number H-0110, manufactured by Sisid Electrostatic Co., Ltd.) according to the half-life measuring method specified in the charging test method of JIS L1094. Measure under the environment. The initial charged voltage is measured on the laminated surface of the nanofiber layer in the base material layer. The measurement conditions are as follows. Applied voltage: 10 kV, distance between applied electrode and sample: 15 mm, distance between voltage receiving portion and sample: 15 mm.

  Examples of a method for setting the initial charged voltage measured by the half-life measuring method defined in JIS L1094 of the base material layer to 0.3 kV or less include 1) reducing the surface resistivity of the base material layer, 2) group 3) When the material layer contains an antistatic agent and / or a conductive material, and 3) when the substrate layer has openings formed therein, in particular, a large number of openings (openings) that penetrate the substrate layer in the thickness direction ) Is formed with a predetermined regularity (for example, when a mesh sheet is used), a method of adjusting (enlarging) the area of the opening is exemplified. The methods 1) to 3) may be combined.

  Regarding the method for reducing the initial voltage of 1), examples of the method for reducing the surface resistivity of the base material layer include a method of applying antistatic processing to the base material layer. The antistatic processing method generally includes processing that prevents the generation of static electricity and the charging of the fiber by adding an antistatic processing agent such as a surfactant to the fiber and imparting hydrophilicity to the fiber. It is done. Specific examples include a method using an antistatic agent, a method using corona discharge, and a method using plasma. Examples of the antistatic processing agent include an anionic surfactant, a cationic surfactant, a nonionic surfactant, carbon black, and the like. The desired surface resistivity can be adjusted by applying or impregnating a predetermined amount onto the fiber layer lamination surface.

The surface resistivity of the base material layer (laminated surface of the nanofiber layers) is preferably 10 ¹² Ω or less, more preferably 10 ⁶ to 10 ¹⁰ Ω. The surface resistivity is measured as follows.

<Measurement method of surface resistivity>
In order to stabilize the sample in the measurement environment, the sample is allowed to stand for 4 hours in an environment of 23 ° C. and 50% RH, and then the surface low efficiency of the sample is measured. It is measured at a voltage of 500 V by the double ring method defined in item 6 of JIS K6271. A surface resistance meter R8340 manufactured by ADVANTEST can be used for measurement of low surface efficiency.

  Regarding the method for reducing the initial voltage of 2) above, examples of the antistatic agent include an electrostripper manufactured by Kao Corporation, and examples of the conductive substance include carbon black and the like. It can be contained in the base material layer.

Regarding the method for reducing the initial voltage of 3), the base material layer (for example, mesh sheet) in which a large number of openings (openings) are formed with a predetermined regularity has the following configuration. preferable.
The area of each opening in the base material layer is preferably 0.001 mm ² or more, more preferably 0.002 to ⁵ mm ² .
The hole area ratio (space area per square inch / 1 square inch) of the base material layer is preferably 30% or more, and more preferably 50 to 90%.
The number of holes in the base material layer is 5 to 400 per inch, preferably 10 to 200. The area of each individual aperture, the aperture ratio, and the number of apertures can be determined by observing with a microscope and reading directly from the image.
The shape of the opening in plan view is not particularly limited, and can be, for example, a circle, an ellipse, a quadrangle, a rhombus, or the like.

  The nanofiber sheet of the present invention can be suitably manufactured by forming nanofiber layers by depositing nanofibers on the surface of a smooth substrate using, for example, an electrospinning method. FIG. 1 shows an apparatus 30 for performing the electrospinning method. In order to perform the electrospinning method, an apparatus 30 including a syringe 31, a high voltage source 32, and a conductive collector 33 is used. The syringe 31 includes a cylinder 31a, a piston 31b, and a capillary 31c. The inner diameter of the capillary 31c is about 10 to 1000 μm. The cylinder 31a is filled with a solution of a polymer compound that is a raw material for the nanofiber. The solvent of this solution is water or an organic solvent, or a mixed solvent of water and an organic solvent compatible with water, depending on the type of polymer compound. The high voltage source 32 is a DC voltage source of 10 to 30 kV, for example. The positive electrode of the high voltage source 32 is in conduction with the polymer solution in the syringe 31. The negative electrode of the high voltage source 32 is grounded. The conductive collector 33 is a metal plate, for example, and is grounded. The distance between the tip of the needle 31c in the syringe 31 and the conductive collector 33 is set to about 30 to 300 mm, for example. The apparatus 30 shown in FIG. 1 can be operated in the atmosphere. There is no restriction | limiting in particular in an operating environment, It can be set as the temperature of 20-40 degreeC, and humidity 10-50% RH.

  Under a state where a voltage is applied between the syringe 31 and the conductive collector 33, the piston 31b of the syringe 31 is gradually pushed in to push out the polymer compound solution from the tip of the capillary 31c. In the extruded solution, the solvent is volatilized, the polymer compound as a solute is solidified, and nanofibers are formed while being stretched and deformed by a potential difference, and are drawn to the conductive collector 33. At this time, by placing a sheet (for example, a mesh sheet) to be a base material layer (not shown) on the surface of the conductive collector 33, nanofibers can be deposited on the surface of the base material layer. . The nanofibers thus formed are continuous fibers of infinite length on the principle of production. In order to obtain a hollow nanofiber, for example, a capillary 31c is used as a double tube, and a solution that is incompatible with the core and the sheath may be flowed.

  The nanofiber sheet thus obtained can be used by attaching it to, for example, human skin, non-human mammalian skin, teeth, branches, leaves or other plant surfaces. In this case, prior to attaching the nanofiber layer to the surface of the object, the surface is preferably wetted with a liquid material. By doing so, the nanofiber layer can be successfully attached to the surface of the object using the action of surface tension. Instead of making the surface of the object wet, the surface of the nanofiber layer may be wet with a liquid material.

  In order to make the surface of the object wet, for example, various liquid materials may be applied or sprayed on the surface. The liquid material to be applied or sprayed includes a liquid component at the temperature at which the nanofiber layer is adhered, and has a viscosity at that temperature (viscosity measured using an E-type viscometer) of about 5000 mPa · s or less. The substance it has is used. Examples of such a liquid material include water-based liquids such as water, aqueous solutions and aqueous dispersions, and non-aqueous solvents, aqueous solutions thereof and dispersions thereof. Further, emulsions such as O / W emulsions and W / O emulsions, liquids thickened with various thickeners such as thickening polysaccharides, and the like are also included. Specifically, when a nanofiber layer (nanofiber sheet) is used as, for example, a cosmetic and is attached to human skin, a lotion or a cosmetic cream is used as a liquid for moistening the surface of the target skin. Can be used.

  The nanofiber sheet of the present invention is a laminated sheet in which a nanofiber layer and a base material layer are laminated. In use, the nanofiber sheet is made such that the surface on the nanofiber layer side faces the surface of the object. Is brought into contact with the surface. Then, only the nanofiber layer can be transferred and adhered to the surface of the object by peeling and removing the base material layer from the nanofiber layer. According to this method, it is possible to successfully attach a nanofiber layer having low rigidity and not good handleability to the surface of an object.

  The nanofiber sheet of the present invention has a good appearance because the nanofibers constituting the nanofiber layer are uniformly distributed on the base material layer, and can be suitably used for various applications. When a functional agent is contained, the effect by the action of the functional agent can be stably obtained. Examples of the functional agent include a whitening component such as vitamin C, a moisturizing component such as glycerin, and the like, and these can be used alone or in combination of two or more.

  The nanofiber sheet of the present invention is suitably used for various cosmetics such as a skin whitening sheet for beauty purposes, a stain / wrinkle concealed sheet, a sheet-like foundation, and a point makeup sheet.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, in the electrospinning method shown in FIG. 1, the formed nanofibers are deposited on a plate-like conductive collector 33, but instead of this, a conductive rotating drum is used, and the periphery of the rotating drum is rotated. Nanofibers may be deposited on the surface.

  The nanofiber layer may be a single layer structure or a multilayer structure of two or more layers. The nanofiber layer having a two-layer structure includes, for example, a water-soluble layer containing water-soluble nanofibers of the water-soluble polymer compound and a water-insoluble layer containing water-insoluble nanofibers of the water-insoluble polymer compound. Can do.

  Further, an adhesion layer may be formed on the surface of the nanofiber layer to further improve the adhesion between the nanofiber layer and the surface of the object. That is, the nanofiber sheet of the present invention may have a multilayer structure in which a base material layer, a nanofiber layer, and an adhesive layer are sequentially laminated. Examples of the adhesive constituting the adhesive layer include oxazoline-modified silicone, acrylic resin-based, olefin resin-based, and synthetic rubber-based pressure-sensitive adhesives. In addition, the adhesive layer may be applied continuously over the entire surface of the nanofiber layer (that is, in a solid state), but from the viewpoint of maximizing the characteristics of the nanofiber layer, the adhesive layer is the minimum necessary. It is preferable that it is applied in the amount of. For this purpose, the adhesive layer is preferably formed discontinuously on one surface of the nanofiber layer. As an aspect of discontinuously forming the adhesive layer, for example, (i) an aspect in which an adhesive is dispersedly arranged on the nanofiber layer to form an adhesive layer, or (ii) a nanofiber on the nanofiber layer. For example, an adhesive layer may be formed by depositing a shaped adhesive.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”.

[Example 1]
Pullulan (water-soluble polymer compound, Hayashibara Shoji Co., Ltd.) was used as the polymer compound, which was dissolved in ion-exchanged water to obtain an electrospinning (ES) solution having a concentration of 15%. A mesh sheet (polyethylene terephthalate mesh manufactured by Tokyo Screen Co., Ltd., trade name: Bolting Cross Tetron T-No. 120T) to be a breathable base material layer using the ES solution with the apparatus shown in FIG. A nanofiber layer was formed on the surface of the substrate, and a nanofiber sheet having a two-layer structure of a nanofiber layer and a base material layer was obtained. The manufacturing conditions of the nanofiber are as follows. Applied voltage: 27 kV, capillary-collector distance: 185 mm, aqueous solution discharge rate: 1 ml / h, production environment: 28 ° C., 36% RH. Thus, in the nanofiber sheet of Example 1 obtained, the thickness of the nanofiber layer was 30 μm, and the thickness of the nanofiber was 300 to 600 nm.

[Example 2 and Comparative Examples 1-3]
In Example 1, a nanofiber sheet was obtained in the same manner as in Example 1 except that the base material layer shown in Table 1 was used. The thickness of the nanofiber layer in the nanofiber sheet obtained in each Example and Comparative Example was 30 μm, and the thickness of the nanofiber was 300 to 600 nm.

The base material layers used in each example and comparative example are as follows.
Example 1 (mesh sheet): Polyethylene terephthalate mesh (trade name: Bolting Cross Tetron T-No. 120T) manufactured by Tokyo Screen Co., Ltd. Opening rate is 52%, and the number of openings is 120 per inch.
Example 2 (mesh sheet): Polyethylene terephthalate mesh (trade name: Bolting Cross Tetron T-No.80T) manufactured by Tokyo Screen Co., Ltd., and the shape of the opening (opening) in plan view is square. The hole area ratio is 47%, and the number of holes is 80 per inch.
Comparative Example 1 (spunbond nonwoven fabric): Constituent fibers are polyethylene terephthalate fibers, basis weight 16 g / m ² .
Comparative Example 2 (OA paper): Constituent fiber is pulp, thickness is 100 μm.
Comparative Example 3 (polyethylene terephthalate film): thickness 25 μm.

[Evaluation]
About the nanofiber sheet obtained by the Example and the comparative example, the following method evaluated the uniformity of the nanofiber in a nanofiber layer. The results are shown in Table 1 below.

[Uniformity of nanofibers]
The surface of the nanofiber layer in the nanofiber sheet is visually observed and evaluated according to the following evaluation criteria.
○: There is no unevenness in the distribution of the nanofibers, and the nanofibers are uniformly attached on the laminated surface of the nanofiber layers in the base material layer.
X: Nanofibers adhere to the entire laminated surface of the nanofiber layers in the base material layer, but fine unevenness is seen in the distribution of nanofibers.
XX: On the laminated surface of the nanofiber layer in the base material layer, there are a portion where the nanofiber is attached and a portion where the nanofiber is not attached, and a large unevenness is seen in the distribution of the nanofiber.

  As is clear from the results shown in Table 1, the nanofiber sheet obtained in each example had a good appearance in which the nanofibers were uniformly distributed in the nanofiber layer and there was no unevenness. On the other hand, the nanofiber sheet of each comparative example has uneven distribution of nanofibers because the initial charged voltage measured by the half-life measuring method specified in JIS L1094 of the base material layer exceeds 0.3 kV. As a result, the appearance was inferior to the nanofiber sheet of each Example.

30 Device 31 Syringe 32 High voltage source 33 Conductive collector

Claims (3)

A nanofiber sheet comprising a base material layer and a nanofiber layer including nanofibers laminated on the base material layer and formed by an electrospinning method,
The nanofiber sheet whose initial charged voltage measured by the half-life measuring method prescribed | regulated to JISL1094 of the said base material layer is 0.3 kV or less.   The nanofiber sheet according to claim 1, wherein a large number of apertures are formed in the base material layer.   The nanofiber sheet according to claim 1 or 2, wherein the base material layer is a mesh sheet.

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