Electrospinning solution

Abstract

To provide an electrospinning solution that can reduce environmental burden and enables stable and favorable electrospinning of fibers with a low irritating odor.SOLUTION: An electrospinning solution used for electrospinning comprises ethyl cellulose, ethanol, and water, wherein the content of the ethyl cellulose relative to the total mass of the solution is 4 mass% or more, the ratio of the content of the ethanol and the water relative to the total mass of the solution (water / ethanol) is more than 0.1 and less than 0.55, and the content of acetic acid relative to the total mass of the solution is 1 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a solution for electrospinning.

Background Art

[0002] As a method for producing a film or fiber, an electrospinning method (electrospinning method) is known. In this electrospinning method, a high voltage is applied to a raw material solution for spinning (a solution or melt of a resin) to spin ultrafine fibers (for example, fibers on the order of nanometers (also referred to as nanofibers)). These are deposited to form a film or fiber sheet. Several proposals have been made so far regarding techniques related to such an electrospinning method.

[0003] For example, Patent Document 1 describes a technique in which an aqueous solution of a bioadhesive substance is plasticized while stirring an alcohol solution of a fiber-forming hydrophilic polymer to form a uniform suspension, and the suspension is electrospun. The bioadhesive substance is more soluble in water than in alcohol and is dissolved in water in advance so as to form fibers in which the bioadhesive substance is uniformly distributed as particles. Therefore, sufficient water is required to dissolve the bioadhesive substance. For example, it is described that the content mass ratio of water and alcohol should be approximately equal. On the other hand, it is necessary to control the water swelling of the fiber-forming hydrophilic polymer, and it is intended to start the spinning process immediately after mixing a solution of ethanol and water (within 30 minutes to 1 hour).

[0004] Patent Document 2 describes a technique for producing a multilayer electrospun food packaging film in which an outer layer spinning solution, an intermediate layer spinning solution, and an outer layer spinning solution are stacked in three layers by an electrospinning method. The intermediate layer spinning solution is obtained by dissolving a natural polymer substance such as gelatin in a solvent A such as ethanol, and the outer layer spinning solution is obtained by dissolving a cellulose derivative such as ethyl cellulose in a solvent B containing ethanol, water, and acetic acid. Regarding the solvent B, it is described that the volume ratio of acetic acid:ethanol:water = 7:2:1 (v / v / v). Non-Patent Document 1 describes a technique for spinning composite nanofibers by electrospinning from a solution in which an ethylcellulose / gelatin blend is dissolved in a solvent of water / ethanol / acetic acid. Regarding the solvent, a volume ratio of water / ethanol / acetic acid = 2 / 2 / 6 (v / v / v) is described.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The fibers obtained by the above electrospinning method are applied to, for example, sheet masks for cosmetics, etc., due to their high liquid retention properties and high adhesion properties resulting from the fineness of the fiber diameter. On the other hand, fibers manufactured by the conventional electrospinning method were often made using a petroleum-derived polymer resin and an organic solvent with high skin irritation. However, as the above applications indicate, people have more opportunities to come into contact with these fibers in their daily lives, and from the perspective of environmental protection, which has been on the rise in recent years, there has been a strong demand for reducing the environmental impact. In this regard, although the technology described in Patent Document 1 states that it may contain an environmentally friendly raw material such as ethyl cellulose, no examples of spinning actually using the ethyl cellulose are shown. In the technologies described in Patent Document 2 and Non-Patent Document 1, a large amount of acetic acid is used with respect to ethyl cellulose. Therefore, the resulting fibers have a strong acetic acid odor, and it is difficult to use them as materials applied to human skin, such as mask sheets for cosmetics. In this regard, Patent Document 2 describes using them for food packaging films, and Non-Patent Document 1 describes using them for food packaging and filtration applications, etc., and there is no description regarding reducing the odor when applied to human skin.

[0008] In view of the above points, the present invention relates to providing an electrospinning solution that enables good and stable electrospinning of fibers that can reduce the environmental impact and have little irritating odor. Furthermore, the present invention relates to a method for manufacturing a film and a fiber sheet that can reduce the environmental impact, have little irritating odor, and are excellent in the integrity as a single film and have good continuous usability, using the above electrospinning solution.

Means for Solving the Problems

[0009] The present invention provides an electrospinning solution that is a solution used for electrospinning, contains ethyl cellulose, ethanol, and water, the content of the ethyl cellulose with respect to the total mass of the solution is 4% by mass or more, the ratio of the content of the ethanol and the water (water / ethanol) with respect to the total mass of the solution is more than 0.1 and less than 0.55, and the content of acetic acid with respect to the total mass of the solution is 1% by mass or less.

[0010] The present invention also provides a method for producing a film, which comprises performing electrospinning using the electrospinning solution and forming a film composed of a deposit containing fibers on the surface of an object to be film-formed. Furthermore, the present invention provides a method for producing a fiber sheet, which comprises depositing fibers generated from the raw material liquid by electrospinning using the electrospinning solution as a raw material liquid.

Advantages of the Invention

[0011] The electrospinning solution of the present invention can reduce the environmental load and enables good and stable electrospinning of fibers with less irritating odor. In addition, according to the method for producing a film and a fiber sheet of the present invention, by using the electrospinning solution of the present invention, a film and a fiber sheet with reduced environmental load, less irritating odor, excellent integrity as a single film, and good continuous usability can be suitably produced.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] The electrospinning solution of the present invention (hereinafter, also simply referred to as a solution) will be described below. The electrospinning solution of the present invention is used in the electrospinning method as a raw material liquid to be sprayed. The electrospinning method is a method in which a positive or negative high voltage is applied to a raw material solution to charge the raw material solution, and the charged raw material solution is sprayed toward an object. The sprayed raw material solution spreads in space while being repeatedly refined by Coulomb repulsive force or the like. In this process, or after adhering to the object, the solvent, which is a volatile substance, dries to form fibers. In the electrospinning method, the fibers can be the aforementioned nanofibers. The nanofibers generally have a diameter equivalent to a circle of 10 nm or more and 3000 nm or less, and particularly preferably 10 nm or more and 1000 nm or less. The thickness of the nanofibers can be measured, for example, by observing with a scanning electron microscope (SEM) at a magnification of 10,000 times, selecting 10 fibers arbitrarily from the two-dimensional image excluding defects (aggregates of nanofibers, intersection parts of nanofibers, polymer droplets), drawing a line perpendicular to the longitudinal direction of the fibers, and directly reading the fiber diameter. In the electrospinning method, the formed fibers can be deposited to form a film or a fiber sheet.

[0014] The electrospinning solution of the present invention contains ethyl cellulose, ethanol, and water. Ethyl cellulose is a solute in the solution and is a main component of fibers produced by the electrospinning method. Ethyl cellulose is a plant-derived polysaccharide polymer in which the hydroxyl group of cellulose is substituted with an ethoxy group. When the ethoxyl group content is 33.1% by mass or more, it is soluble in ethanol and has extremely low solubility in water. The ethyl cellulose of the present invention preferably contains those having an ethoxyl group content of 33.1% by mass or more, and more preferably only those having an ethoxyl group content of 33.1% by mass or more. The ethoxyl group content can be calculated from the amount (%) of the ethoxy group described in the description of ethyl cellulose in the eighteenth revised Japanese Pharmacopoeia in the Ministry of Health, Labour and Welfare. Ethanol and water are solvents for ethyl cellulose, have a small pungent odor, and also have little irritation to the skin. Thus, the electrospinning solution of the present invention as a whole has a low environmental load and little pungent odor.

[0015] Water can be ionized and charged compared with non-ionizable ethanol, and thus can impart conductivity to the electrospinning solution of the present invention. Therefore, it can contribute to the stabilization of fiber formation by the electrospinning method. In addition, water contributes to the improvement of the adhesion of the film formed by the electrospinning method to the object to be film-formed, the improvement of durability, and the appearance.

[0016] In the above-mentioned electrospinning method, ethanol and water are dried after spraying, and fibers made of ethyl cellulose are formed. Since the spun fibers are formed of ethyl cellulose, they have a low environmental load. In addition, since the solvent is ethanol and water, the spun fibers are less likely to generate a pungent odor and are easy to apply to the skin. In addition, the fibers made of ethyl cellulose are hardly soluble in a cosmetic liquid or the like and have high high-temperature stability.

[0017] In the electrospinning solution of the present invention, the content of ethyl cellulose with respect to the total mass of the solution is 4% by mass or more. Thereby, entanglement of polymer chains is likely to occur, and the concentration becomes easy to fibrillate. From this viewpoint, it is preferable that ethyl cellulose is 8% by mass or more, and more preferably 10% by mass or more, based on the total mass of the solution. Also, from the viewpoint of making the viscosity such that the solution can be easily extruded from the nozzle, the content of ethyl cellulose with respect to the total mass of the solution is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less. The weight-average molecular weight of ethyl cellulose is preferably 130,000 g / mol or more from the viewpoint of facilitating fiber formation, and preferably 200,000 g / mol or less from the viewpoint of increasing the amount of fibers and facilitating efficient spinning.

[0018] In the electrospinning solution of the present invention, the ratio (water / ethanol) of the contents of ethanol and water with respect to the total mass of the solution is more than 0.1 and less than 0.55. Furthermore, in the electrospinning solution of the present invention, the content of acetic acid with respect to the total mass of the solution is 1% by mass or less. By reducing the acetic acid content as a solvent for ethyl cellulose to an extremely low level in this way, the pungent odor of the spun fibers can be significantly suppressed. On the other hand, when the acetic acid content as a solvent is extremely low, the dissolution state of ethyl cellulose becomes different from the conventional one. In this regard, it has been found that it is difficult to achieve good spinning simply by using ethanol as the main component of the solvent instead of acetic acid, even though acetic acid has been used as the main component of the solvent to improve spinning in the past. For example, in a solution obtained by dissolving ethyl cellulose, which is soluble in ethanol, in a solvent of ethanol alone, when sprayed in the electrospinning method, it does not form fibers but becomes particles. Also, even if partial fibrillation can occur, most of it becomes particles. The material deposited after spraying in this way has poor integrity as a single film. For example, when trying to lift the deposited material, it may collapse into pieces, and it may be difficult to have sufficient strength to be used as a film or fiber sheet. In contrast, in the electrospinning solution of the present invention, good spinning can be achieved by setting the ratio (water / ethanol) of the above content to be more than 0.1 and less than 0.55. That is, in the electrospinning using the electrospinning solution of the present invention, it is preferably prevented that the sprayed solution becomes particles, and the diameter reduction can be stably performed. This is considered to be due to appropriately changing the dissolution state of ethyl cellulose in the solvent by setting the composition ratio in the solvent as described above. More specifically, by making the solvent a "ethanol / water" mixed system with the content ratio in a specific range, it becomes moderately poor-solvent, the spread of the polymer chains of ethyl cellulose in the solution becomes smaller, and the entanglement between the polymer chains is appropriately increased, making fibrillation more likely to occur. As a result, the electrospinning solution of the present invention is preferably prevented from becoming particles during spraying in the electrospinning method, and fibrillation is promoted. Also, since the generation of particles can be preferably prevented, the deposited material after spraying (for example, the film and fiber sheet described above) has excellent integrity as a single film. For the preferred prevention of the generation of these particles, it is necessary that the water is neither too little nor too much as the composition ratio of the solvent, and the above-mentioned content ratio in the specific range is important.

[0019] By setting the solvent to an "ethanol / water" mixed system at a ratio within a specific range of the above content, the electrospinning solution of the present invention is less likely to precipitate and become a suspension. Thereby, spinning inhibition due to precipitation can be avoided. Furthermore, due to the prevention of precipitation, the electrospinning solution of the present invention maintains a certain dissolved state, is easy to handle, and enables stable and repeated production of fibers with a certain quality in the electrospinning method. In this regard, in the technique described in Patent Document 1 mentioned above, it is premised that spinning is carried out using a suspension. In the case of a suspension, precipitation and poor dispersion may occur over time, and there are problems such as time constraints from solution preparation to spinning and poor spinning stability. In addition, although a certain amount of water is required as a solvent, the water swelling of the hydrophilic polymer must be controlled, and in some cases, the experience of technicians is required. On the contrary, as described above, the electrospinning solution of the present invention is an environmentally friendly solution that is easy to handle and enables stable and repeated production of fibers with a certain quality by suppressing suspension and precipitation.

[0020] Thereby, the electrospinning solution of the present invention can reduce the environmental load and can stably electrospin fibers with less irritating odor well. By performing electrospinning using the electrospinning solution of the present invention, for example, nanofibers having an average fiber diameter of 50 nm or more and 3000 nm or less can be preferably produced. By depositing such nanofibers, an ultrathin film and a fiber sheet can be preferably produced with excellent integrity as a single film and strength sufficient for continuous use.

[0021] In the electrospinning solution of the present invention, from the viewpoint of more effectively preventing the generation of the above-mentioned particles and enhancing the spinning stability, the ratio (water / ethanol) of the above content to the total mass of the solution is preferably more than 0.25, and more preferably 0.285 or more. From the same viewpoint as above and the viewpoint of making it less likely to become a suspension, the ratio (water / ethanol) of the above content to the total mass of the solution is preferably 0.520 or less, and more preferably 0.420 or less.

[0022] From the viewpoint of more effectively suppressing the pungent odor, the content of acetic acid relative to the total mass of the solution is preferably 0.9% by mass or less, and more preferably 0 (zero) % by mass.

[0023] The fact that the electrospinning solution of the present invention is not a suspension can be indicated by turbidity. The electrospinning solution of the present invention can be said not to be a suspension if the turbidity is 500 NTU or less, and the turbidity is preferably 400 NTU or less.

[0024] (Method for measuring turbidity) Turbidity can be measured with a portable turbidimeter 2100Q (manufactured by TOA-DKK Corporation, trade name). For the measurement, the sample is poured into a measuring container, set in the instrument, and the result displayed digitally is read and confirmed.

[0025] The electrospinning solution of the present invention preferably contains one or more selected from the group consisting of glycol solvents, specifically polyethylene glycol, glycerin, diglycerin, diethylene glycol monoethyl ether, propylene glycol, 1,3-butanediol, and 1,3-propanediol (hereinafter these are collectively referred to as plasticizer A). Thereby, in electrospinning using the electrospinning solution of the present invention, when the spun fibers are deposited, the adhesion at the fiber intersections is more easily promoted. As a result, the film and fiber sheet formed by depositing the fibers are more suppressed in fluffiness like fuzziness when touched, and have an excellent continuous use feeling such as skin compatibility. That is, the adhesion to the object to be applied such as the skin is further enhanced. From the viewpoint of more effectively suppressing fluffiness, the content of the glycol solvent relative to the total mass of the solution is preferably 4% by mass or more, and more preferably 6% by mass or more. From the viewpoint of making the fibers thinner, the content of the glycol solvent relative to the total mass of the solution is preferably 20% by mass or less, and more preferably 10% by mass or less. Also, from the viewpoint of more effectively suppressing fluffiness, the ratio of the content of ethyl cellulose to the glycol solvent (glycol solvent / ethyl cellulose) to the total mass of the solution is preferably 0.08 or more, and more preferably 0.42 or more. From the viewpoint of facilitating the maintenance of the fibrous form, the ratio of the content of ethyl cellulose to the glycol solvent (glycol solvent / ethyl cellulose) to the total mass of the solution is preferably 1 or less.

[0026] The electrospinning solution of the present invention may contain other components as long as the above-described component composition and its effects are not inhibited. Examples of other components include polyols, liquid oils, plasticizers for ethyl cellulose, conductivity control agents for electrospinning solutions, water-soluble polymers, coloring pigments, powders such as extender pigments, dyes, fragrances, repellents, antioxidants, stabilizers, preservatives, various vitamins, and the like. When other components are contained in the electrospinning solution, the content ratio of the other components is preferably 0.1% by mass or more and 30% by mass or less, and more preferably 0.5% by mass or more and 20% by mass or less.

[0027] The present invention can preferably implement a film manufacturing method in which electrospinning is performed using the electrospinning solution of the present invention to form a film composed of a deposit containing fibers on the surface of an object to be film-formed. According to the film manufacturing method of the present invention, using the electrospinning solution of the present invention, it is possible to reduce the environmental load, have less irritating odor, and preferably manufacture a film having excellent integrity as a single film and good continuous usability.

[0028] The object to be film-formed can be various objects capable of electrospinning on which a film is to be formed. For example, human skin, animal skin, the surface of plants, human nails, and the like can be mentioned. Among them, since the film obtained in the present invention is flexible and highly followable, the effect can be easily felt when it is attached to the skin and used. Such a method for producing a film is useful as various cosmetic methods that are not intended for surgical, therapeutic, or diagnostic methods of the human body. For example, the method for producing a film of the present invention can be applied for the purpose of beauty, such as skin whitening, concealing skin spots, concealing skin dullness and dark circles, concealing skin wrinkles, softening the skin, protecting the skin from ultraviolet rays, and moisturizing the skin. In addition, the method for producing a film of the present invention can also be applied to various acts for personal skin protection at home, such as protecting various wounds such as abrasions, incisions, lacerations, and puncture wounds, preventing bedsores, and the like.

[0029] The preferred embodiments of the method for producing a film of the present invention will be described below with reference to FIGS. 1 and 2. In the embodiments shown below, a nozzle is used for spinning the raw material liquid, but it is not limited thereto. Various methods that enable spinning in the electrospinning method can be employed. For example, a method such as spraying the solution from the surface of a roll immersed in a bath may be used.

[0030] In the method for producing a film of the present invention, the electrospinning solution of the present invention is directly sprayed onto the surface of the film-forming object. By direct spraying, a film composed of a deposit containing fibers is formed on the surface of the film-forming object. Examples of the electrospinning apparatus include those shown in FIG. 1. The electrospinning apparatus 10 for film formation shown in FIG. 1 includes a low-voltage power supply 11, a high-voltage power supply 12, an auxiliary electric circuit 13, a micro gear pump 14, a container 15 for the electrospinning solution, a nozzle 16, a pipeline 17, a flexible pipeline 18, a current limiting resistor 19, and a switch SW.

[0031] The low-voltage power supply 11 is capable of generating a voltage of several V to a dozen or so V. For the purpose of enhancing the portability of the electrospinning apparatus 10, the low-voltage power supply 11 preferably consists of one or more batteries. Also, using a battery as the low-voltage power supply 11 has the advantage that replacement can be easily performed as needed. Instead of a battery, an AC adapter or the like can also be used as the low-voltage power supply 11. The high-voltage power supply 12 is connected to the low-voltage power supply 11 and includes an electric circuit (not shown) that boosts the voltage generated by the low-voltage power supply 11 to a high voltage. The boosting electric circuit is generally composed of a transformer, a capacitor, a semiconductor element, and the like.

[0032] The auxiliary electric circuit 13 is interposed between the low-voltage power supply 11 and the high-voltage power supply 12 and has a function of adjusting the voltage of the low-voltage power supply 11 to stably operate the high-voltage power supply 12. Further, the auxiliary electric circuit 13 has a function of controlling the rotational speed of a motor provided in the micro gear pump 14 described later. By controlling the rotational speed of the motor, the supply amount of the spraying composition from the container 15 of the electrospinning solution to the micro gear pump 14 is controlled. A switch SW is attached between the auxiliary electric circuit 13 and the low-voltage power supply 11, and the electrospinning solution device 10 can be operated / stopped by turning the switch SW on and off.

[0033] The nozzle 16 is made of various conductors including metal and non-conductors such as plastic, rubber, and ceramic, and has a shape that allows the spraying composition to be discharged from its tip. A minute space through which the spraying composition flows is formed along the longitudinal direction of the nozzle 16. The diameter of the tip of the nozzle 16 (the size of the cross-section of the minute space) can be appropriately set according to the fiber diameter of the fiber to be spun (for example, on the order of nanometers). For example, it is preferably 100 μm or more and 1000 μm or less in terms of diameter. The nozzle 16 communicates with the micro gear pump 14 via a pipe 17. The pipe 17 may be a conductor or a non-conductor. The nozzle 16 is electrically connected to the high-voltage power supply 12. This makes it possible to apply a high voltage to the nozzle 16. In this case, in order to prevent an excessive current from flowing when a human body directly touches the nozzle 16, the nozzle 16 and the high-voltage power supply 12 are electrically connected via a current-limiting resistor 19.

[0034] The micro gear pump 14 communicates with the nozzle 16 via the pipeline 17 and functions as a device for supplying the electrospinning solution contained in the container 15 to the nozzle 16. The micro gear pump 14 operates by receiving power supply from the low-voltage power supply 11. Further, the micro gear pump 14 is configured to supply a predetermined amount of the spraying composition to the nozzle 16 under the control of the auxiliary electric circuit 13.

[0035] The container 15 is connected to the micro gear pump 14 via the flexible pipeline 18. The electrospinning solution is contained in the container 15. The container 15 preferably has a cartridge-type replaceable form.

[0036] The electrospinning device 10 for film formation having the above configuration can be used, for example, as shown in FIG. 2. FIG. 2 shows a state in which a handy-type electrospinning device 10A having dimensions that can be held with one hand is sprayed toward the skin of a person's arm to form a film. In the electrospinning device 10A shown in the figure, all of the members of the configuration diagram shown in FIG. 1 are housed in a cylindrical housing 10H. A nozzle (not shown) is arranged at one end 10E in the longitudinal direction of the housing 10H. The nozzle is arranged on the housing 10H so that the blowing direction of the electrospinning solution coincides with the longitudinal direction of the housing 10H and protrudes toward the skin side. By arranging the nozzle tip to protrude toward the skin in the longitudinal direction of the housing 10H, it becomes difficult for the spraying composition to adhere to the housing, and a film can be formed stably.

[0037] When operating the electrospinning device 10A for film formation shown in Fig. 2, the user himself / herself holds the device 10A by hand and directs one end 10E of the device 10 where a nozzle (not shown) is disposed toward the film formation target site. In Fig. 2, a state where one end 10E of the electrospinning device 10A is directed toward the inner side of the user's forearm is shown. Under this state, the switch of the electrospinning device 10A is turned on to perform the electrospinning method. When power is supplied to the electrospinning device 10A, an electric field is generated between the nozzle and the skin. In the embodiment shown in Fig. 2, a positive high voltage is applied to the nozzle and the skin becomes the negative electrode. When an electric field is generated between the nozzle and the skin, at the tip of the nozzle, the electrospinning solution of the present invention is polarized by electrostatic induction and its tip portion becomes conical, and droplets of the electrospinning solution of the present invention charged from the cone tip are discharged into the air along the electric field toward the skin. As the solvent evaporates from the electrospinning solution of the present invention discharged into the space and charged, the charge density on the surface of the electrospinning solution of the present invention becomes excessive, and it spreads into the space while being repeatedly refined by the Coulomb repulsive force and reaches the skin. In this way, the refined fibers are deposited on the film to be formed. As a result, a film composed of a deposit containing fibers is formed on the surface of the skin, which is the film formation target. At that time, by using the electrospinning solution of the present invention, fiber formation can be performed well, and a film excellent in integrality as a single film and having good continuous usability can be formed well. Since the electrospinning solution of the present invention is used, the produced film can reduce the environmental load and has less irritating odor. Moreover, since the electrospinning solution of the present invention is unlikely to become a suspension, in the method for producing the film of the present invention using the solution, a film of a certain quality can be stably and repeatedly produced at any time without requiring special liquid adjustment.

[0038] The present invention can preferably implement a method for producing a fiber sheet in which the electrospinning solution of the present invention is discharged from a nozzle by an electrospinning method using the electrospinning solution of the present invention as a raw material liquid and fibers generated from the raw material liquid are deposited. According to the method for producing a fiber sheet of the present invention, using the electrospinning solution of the present invention, a fiber sheet with reduced environmental load, less irritating odor, excellent integrality as a single film, and good continuous usability can be preferably produced. According to the method for manufacturing a fiber sheet of the present invention, a fiber sheet having good performance as described above can be continuously produced on a production line using the electrospinning solution of the present invention.

[0039] A preferred embodiment of the method for manufacturing a fiber sheet of the present invention will be described below with reference to FIG. 3.

[0040] In the method for manufacturing a fiber sheet of the present invention, examples of the electrospinning apparatus used include those shown in FIG. 3. The electrospinning apparatus 20 for forming a fiber sheet shown in FIG. 3 includes a nozzle 21 that discharges the electrospinning solution L of the present invention, which is a raw material liquid, and a counter electrode 22 that is arranged to face the nozzle 21 while being separated from it, and generates an electric field between the nozzle 21 and the counter electrode 22. Further, the electrospinning apparatus 20 has means (voltage application device) 23 for applying a voltage so as to make the polarities of the nozzle 21 and the counter electrode 22 different from each other, and includes a space 25 into which a base material layer 24 can be introduced between the nozzle 21 and the counter electrode 22.

[0041] The nozzle 21 and the counter electrode 22 are made of a conductive material such as metal. The nozzle 1 can be of various structures and shapes that can be normally obtained, and the diameter of the tip of the nozzle 1 can be appropriately set according to the fiber diameter (for example, on the order of nanometers) of the fiber to be spun as the discharge port of the electrospinning solution L of the present invention. The counter electrode 22 can also be of various structures that can be normally obtained. The voltage application device 23 has a voltage application unit 31 such as a DC high-voltage power source and an electric wire 32, and electrically connects the voltage application unit 31 to the nozzle 21 and the counter electrode 22 by the electric wire 32. In addition, the counter electrode 22 is grounded. Thereby, the polarities of the nozzle 21 and the counter electrode 22 can be made different from each other by applying a voltage. Making the polarities different from each other means that, for example, when the polarity of the voltage applied to one is positive, the polarity of the voltage applied to the other is negative, or a zero polarity without positive or negative.

[0042] In the electrospinning apparatus 20 shown in FIG. 3, a positive voltage is applied to the nozzle 21 and a negative voltage is applied to the counter electrode 22. However, the method for manufacturing the fiber sheet of the present invention is not limited to this, and various application forms can be adopted as described above. For example, a negative voltage may be applied to the nozzle 21 and a positive voltage may be applied to the counter electrode 22. Further, a positive or negative voltage may be applied to the nozzle 21 and the counter electrode 22 may be set to zero polarity, or vice versa. The zero polarity is achieved, for example, by grounding the nozzle 21 to the counter electrode 22 in the electrospinning apparatus 20 of FIG. 3.

[0043] In the electrospinning apparatus 20, the voltage application device 23 applies a voltage to make the polarities of the nozzle 21 and the counter electrode 22 different from each other, and forms an electric field in the space 25 between the nozzle 21 and the counter electrode 22. This space 25 is a region where the base material layer 24 can be introduced, and is a region where the raw material liquid L discharged from the nozzle 21 is spun into fibers.

[0044] In the space 25 where the electric field is formed, a potential difference is generated between the nozzle 21 and the counter electrode 22. At the tip of the nozzle 21, charges gather on the surface of the droplet of the electrospinning solution L of the present invention and become charged. The charged electrospinning solution L of the present invention is discharged toward the space 25 in the same manner as the method for manufacturing the film of the present invention described above, spreads in the space while repeating miniaturization, and reaches the base material layer 24. The fibers refined in this way are deposited on the base material layer 24. As a result, a fiber sheet 26 is formed on the surface of the base material layer 24. At that time, by using the electrospinning solution of the present invention, fiber formation can be performed well, and a fiber sheet excellent in integrality as a single film and having good continuous usability can be formed well. Since the electrospinning solution of the present invention is used, the manufactured fiber sheet can reduce the environmental load and has less irritating odor. Moreover, since the electrospinning solution of the present invention is less likely to become a suspension, in the method for manufacturing the fiber sheet of the present invention using the solution, a fiber sheet of a certain quality can be stably and repeatedly continuously produced without any special liquid adjustment at any time.

Example

[0045] Hereinafter, the present invention will be described in more detail based on examples, but the present invention should not be construed as being limited thereto. In the present examples, "parts" and "%" are both based on mass unless otherwise specified. "-" means that there is no corresponding value or the like in that item.

[0046] (Examples 1 to 21) (1) Preparation of electrospinning solution An electrospinning solution was prepared with the component ratios of the solute (ethyl cellulose) and the solvent shown in Tables 1 and 2, or the component ratios of the solute (ethyl cellulose), the solvent, and the glycol solvent shown in Tables 1 and 2. The contents in the table are based on the total mass of the solution. All of the ethyl cellulose as the solute used Ethocel STD4 (weight average molecular weight 44,000 g / mol), Ethocel STD45 (weight average molecular weight 13.5 g / mol), Ethocel STD100 (weight average molecular weight 180,000 g / mol), and Ethocel STD200 (weight average molecular weight 188,000 g / mol) manufactured by The Dow Chemical Company. The ethoxyl group content of the ethyl cellulose was 48% by mass or more and 49.5% by mass or less in all cases. For ethanol as the solvent, ethanol 99.5 manufactured by Fujifilm Wako Pure Chemical Corporation was used, and for water, deionized water was used. For polyethylene glycol as the glycol solvent, Wako Grade 1 polyethylene glycol 400 manufactured by Fujifilm Wako Pure Chemical Corporation was used, for diglycerin, diglycerin 801 manufactured by Sakamoto Pharmaceutical Co., Ltd. was used, for propylene glycol, reagent grade propylene glycol manufactured by Fujifilm Wako Pure Chemical Corporation was used, for 1,3-butanediol, 1,3-butylene glycol manufactured by KH Neochem Co., Ltd. was used, for 1,3-propanediol, Wako special grade 1,3-propanediol manufactured by Fujifilm Wako Pure Chemical Corporation was used, for glycerin, reagent grade glycerin manufactured by Fujifilm Wako Pure Chemical Corporation was used, and for diethylene glycol monoethyl ether, CARBITOL Solvent JSQI Personal Care Grrade manufactured by The Dow Chemical Company Japan was used. (2) Conducting electrospinning Using the prepared electrospinning solution as the raw material solution and a 100% rayon spunlace nonwoven fabric (manufactured by Shinwa Co., Ltd.) as the object to be spun (substrate layer), electrospinning was carried out using the electrospinning apparatus shown in Fig. 3. As a result, fiber sheet samples of each example were obtained. The electrospinning conditions at that time were as follows. (Electrospinning requirements) Voltage 28 kV Distance between nozzle and electrode 180 mm Discharge rate 1 mL / h Temperature and humidity 24°C 50% RH Inner diameter of nozzle tip 0.25 mm

[0047] (Comparative Examples 1 to 3) Electrospinning was carried out in the same manner as in Example 1, except that an electrospinning solution containing no water as a solvent was prepared at the component ratios shown in Table 3.

[0048] (Comparative Example 4) Using acetic acid (reagent special grade manufactured by Fujifilm Wako Pure Chemical Corporation) as a solvent, and containing 3 times the content of ethanol and water respectively with respect to the total mass of the solution, electrospinning was carried out in the same manner as in Example 1 except that an electrospinning solution was prepared at the component ratios shown in Table 3, and a fiber sheet sample of Comparative Example 4 was obtained.

[0049] (Comparative Examples 5 to 14) Electrospinning was carried out in the same manner as in Example 1, except that an electrospinning solution was prepared at the component ratios of the solute (ethyl cellulose) and solvent shown in Table 3.

[0050] For the products obtained by the electrospinning method in each example and each comparative example, the following tests (1) to (5) were carried out. (1) Spinning quality (spinning stability) The evaluation was carried out by magnifying the deposit deposited on the substrate by electrospinning 5,000 times or 1,000 times with a scanning electron microscope (SEM). The observation was carried out by selecting random positions. From the SEM image at 5,000 times magnification, if all the deposits are fibrous and there is intersection adhesion between the fibers, it is rated as "5"; if all the deposits are fibrous and there is no intersection adhesion between the fibers from the SEM image at 5,000 times magnification, it is rated as "4"; if 5 or more particulate matters are observed in the SEM image at 1,000 times magnification, it is rated as "3"; if 5 or more particulate matters are observed from the SEM image at 5,000 times magnification, it is rated as "2"; if all the deposits are particulate (no fibers) from the SEM image at 5,000 times magnification, it is rated as "1". (2) Sheet feel (fluffiness) When each fiber sheet sample was obtained, the surface was gently tapped up and down with a finger 3 times. For those without fiber sheet samples, the evaluation results were set as 1 or 2 as follows. If fluffiness was observed on the surface of the fiber sheet, it was evaluated as "fluffiness present"; if there was no fluffiness, it was evaluated as "fluffiness absent". "Slightly fluffiness present" was evaluated as the case where fluffiness was not observed with 3 taps up and down but was observed with 10 taps. These evaluations were performed by visually observing the tapped surface of each fiber sheet. 1: Not a sheet (polymer precipitation) 2: Not formed into a single film 3: Fluffiness present 4: Slightly fluffiness present 5: Fluffiness absent (3) Odor (acetic acid odor) For each example and comparative example, 0.005 g of the fiber sheet immediately after production was prepared, and the odor of the sheet was directly smelled for evaluation. The evaluation was carried out by 1 male and 2 females in their 30s. They rated 100% deionized water (without acetic acid odor) as "2" and 1% aqueous acetic acid solution as "0", and evaluated the degree of acetic acid odor, and used the average value. (4) Median fiber diameter The fiber thickness was observed under SEM at magnifications of 10,000 to 5,000 times. From the two-dimensional image, all the fibers shown in the two-dimensional image were selected, excluding defects (aggregates of nanofibers, intersections of nanofibers, polymer droplets, fibers with unclear focus in the depth direction). The median fiber diameter was measured by drawing a line perpendicular to the longitudinal direction of the fiber from the two-dimensional image and directly reading the fiber diameter. (5) Turbidity It was measured based on the above (method for measuring turbidity). For the evaluation, if the turbidity was 400 NTU or less, it was rated as "2", if it was more than 400 NTU and 500 NTU or less, it was rated as "1", and if it was more than 500 NTU, it was rated as "0" to evaluate the degree of turbidity.

[0051]

Table 1

[0052]

Table 2

[0053]

Table 3

[0054] As shown in Tables 1 to 3, in the evaluation of the spinning quality, all the fiber sheet samples prepared using the electrospinning solution of each example were rated "3" or higher, and most of them were composed of fibers (median fiber diameter of 400 nm or less). Therefore, when the fiber sheet was peeled off from the base sheet and picked up by hand, it could be lifted as a single film, and it had excellent integrity and good continuous usability. In contrast, in the electrospinning solutions of Comparative Examples 5 to 10 and 14, ethyl cellulose did not dissolve, and the transparent solvent and solid were separated. Polymer precipitation occurred in the solution (turbidity "-"). When electrospinning was carried out using this, all of the deposits were in a particulate state (fibers were not present), and spinning could not be performed (evaluation of spinning quality and sheet usability "1"). In the electrospinning solutions of Comparative Examples 1 to 3 and 11 to 13, the ratio of the contents of ethanol and water (water / ethanol) to the total mass of the solution did not meet the requirement of "more than 0.1 and less than 0.55", the evaluation of spinning quality was "1" or "2", and the evaluation of sheet usability was "2". That is, most of the deposits obtained by electrospinning were particles, and when trying to peel them off from the base sheet, they crumbled and it was difficult to peel them off from the base sheet in the first place, and they could not be used as a fiber sheet. Also, in the evaluation of odor (acetic acid odor), compared with Comparative Example 4 in which a large amount of acetic acid was used as a solvent, the fiber sheets prepared by electrospinning in each Example were "2: The sensory evaluation of odor is equivalent to that of water". From the above, it was found that the electrospinning solution of the present invention can reduce the environmental load by using a plant-derived polysaccharide polymer such as ethyl cellulose as a solute, and can stably electrospin fibers with less irritating odor well. Further, it was found that by the electrospinning method using the electrospinning solution of the present invention, a film and a fiber sheet with reduced environmental load, less irritating odor, excellent integrity as a single film, and good continuous usability can be suitably produced.

[0055] In Examples 5, 6, 11 - 17, 19, and 20, since an electrospinning solution containing a glycol solvent was used, the adhesion at the fiber intersections was further promoted, and the fluffiness of the obtained fiber sheet samples was suppressed. Therefore, the continuous usability such as skin compatibility of the fiber sheet samples was further improved. Therefore, it was found that by including the aforementioned glycol solvent in the electrospinning solution of the present invention, in the electrospinning method, a fiber sheet with suppressed fluffiness and further improved continuous usability such as skin compatibility can be produced.

Explanation of Signs

[0056] 10, 10A Electrospinning apparatus for forming a film 20 Electrospinning apparatus for forming a fiber sheet

Claims

1. A solution for electrospinning, comprising: ethyl cellulose, ethanol and water, wherein the content of ethyl cellulose in the total mass of the solution is 4% by mass or more, the ratio of the content of ethanol to the content of water (water / ethanol) in the total mass of the solution is more than 0.1 and less than 0.55, and the content of acetic acid in the total mass of the solution is 1% by mass or less. A solution for electrospinning.

2. The electrospinning solution according to claim 1, wherein the ratio of the content of ethanol to the content of water (water / ethanol) in the total mass of the solution is more than 0.

25.

3. The electrospinning solution according to claim 1 or 2, further comprising a glycol solvent.

4. The electrospinning solution according to claim 3, wherein the glycol solvent comprises one or more selected from polyethylene glycol, glycerin, diglycerin, diethylene glycol monoethyl ether, propylene glycol, 1,3-butanediol, and 1,3-propanediol.

5. The electrospinning solution according to claim 1 or 2, wherein the content of ethyl cellulose in the total mass of the solution is 8% by mass or more.

6. A method for producing a film, comprising performing electrospinning using the electrospinning solution according to claim 1 or 2 to form a film composed of a deposit containing fibers on the surface of an object to be film-formed.

7. The method for producing a film according to claim 5, wherein the object to be film-formed is skin.

8. A method for producing a fiber sheet, comprising depositing fibers generated from the raw material liquid by electrospinning using the electrospinning solution according to claim 1 or 2 as a raw material liquid.

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