JP6978269B2 - Manufacturing method of fiber and fiber sheet - Google Patents

Description

The present invention relates to a method for producing a fiber and a fiber sheet.

The electrospinning method (electrospinning method) is attracting attention as a technology that can relatively easily manufacture fibers having a nano-sized diameter (hereinafter, also referred to as nanofibers) without using mechanical force or thermal force. In the electric field spinning method, a high voltage is applied to the resin solution or melt that is the raw material of the fiber to charge the resin solution or melt, and the charged resin solution or melt is stretched by Coulomb force. This is a method for forming fibers having a small fiber diameter. Among them, the electric field spinning method using a resin melt (hereinafter, also referred to as a molten electric field spinning method) has been attracting attention as a highly productive method, and has added functionality such as hydrophilicity to fibers. , Further reduction in the diameter of the fiber obtained by the melting method has been desired. Therefore, in recent years, various proposals have been made regarding spinning methods or resin fibers that solve these problems.

Patent Document 1 discloses a highly hydrophilic polyolefin-based fiber spun by containing an alkyl sulfonate sodium salt in a hydrophobic polyolefin resin. This polyolefin fiber is manufactured by a general melt spinning method.

Patent Document 2 discloses that a nonwoven fabric made of an olefin polymer containing a hydrophilic agent can be heat-treated for a predetermined time to improve the liquid permeability of the nonwoven fabric.

Patent Document 3 describes that 100 parts by mass of a thermoplastic resin is heated and melted by heating and melting the resin containing 0.001 to 5 parts by mass of a slimming agent such as a saturated fatty acid compound having 12 to 24 carbon atoms. Disclosed is a method of performing melt electrospinning.

Japanese Unexamined Patent Publication No. 5-272006 International Publication 2015/0451 14 Pamphlet Japanese Unexamined Patent Publication No. 2015-178692

However, since the polyolefin fibers of Patent Document 1 and Patent Document 2 are not produced by the melt electrospinning method, it is not possible to obtain desired fibers having a small fiber diameter. Further, in the method of Patent Document 3, the fiber density is increased due to the tearing and fusion of the fibers due to the thinning of the resin, and the texture and flexibility are deteriorated when the sheet is manufactured from the fibers.

In particular, when the techniques of Patent Documents 1 and 2 are used for molten electrospun fibers, the molten electrospun fibers have a small diameter, a large surface area of the fibers, and an extremely short cooling time after fiber formation. The hydrophilizing agent forms aggregates in the resin, making it impossible to bleed out to the surface of the resin. As a result, the surface of the molten electrospun fiber sheet becomes highly hydrophobic even though it contains a hydrophilic agent, and the sheet is impregnated with an aqueous solvent such as a face mask or a wet sheet. It becomes difficult to use it.

Therefore, an object of the present invention is to eliminate the drawbacks of the prior art and provide a method for producing a molten electrospun fiber having excellent hydrophilicity and a fiber sheet thereof.

The present invention comprises a spinning step of spinning a melt of a resin composition containing a thermoplastic resin and a surfactant by an electrospinning method to obtain fibers, and heating the fibers at a temperature equal to or lower than the melting point of the thermoplastic resin. It provides a method for producing a fiber having a heating step.

The present invention also has a spinning step of spinning a melt of a resin composition containing a surfactant and a thermoplastic resin by an electrospinning method to obtain fibers, and a molding step of pressing the fibers to obtain a fiber sheet. A method for producing a fiber sheet, which comprises a heating step of heating the fiber sheet at a temperature equal to or lower than the melting point of the thermoplastic resin, and the molding step and the heating step are performed in this order, in the reverse order, or at the same time. It is to provide.

According to the present invention, it is possible to produce a molten electrospun fiber having excellent hydrophilicity and a small diameter. In addition, it is possible to produce a fiber sheet having excellent hydrophilicity, which is made of molten electrospun fibers having a small diameter.

FIG. 1 is a schematic view showing a method of manufacturing a fiber and a fiber sheet using a molten electric field spinning device. FIG. 2A is a schematic diagram showing the behavior of the surfactant contained in the thermoplastic resin before the heating step, and FIG. 2B is a schematic diagram showing the behavior of the surfactant contained in the thermoplastic resin after the heating step. It is a schematic diagram which shows.

Hereinafter, a method for producing a fiber and a fiber sheet of the present invention will be described with reference to a preferred embodiment thereof with reference to the molten electric field spinning apparatus 10 shown in FIG. The molten electric field spinning device 10 shown in FIG. 1 is roughly classified into a molten composition supply unit 10A, an electrode unit 10B, a fluid injection unit 10C, a collection unit 10D, and a processing unit 10E.

The electric field spinning method used for spinning the fiber of the present invention is a method in which a molten resin liquid is discharged under a state where a high voltage is applied, so that the discharged molten liquid is elongated and has a small fiber diameter. It is a method that can form fibers. Hereinafter, this method is also referred to as a molten electric field spinning method.

The melt electric field spinning device 10 includes a melt composition supply unit 10A. The melt composition supply unit 10A has a discharge nozzle 12 for discharging the melt R of the resin composition containing a thermoplastic resin and a surfactant, which will be described later, and a hopper 19 for supplying the resin composition in the housing 11. I have.

In the housing 11, the resin composition supplied from the hopper 19 can be heated and melted in the housing 11 to obtain a melt R of the resin composition. The molten liquid R can be supplied with the molten liquid R in the direction of the discharge nozzle 12, which will be described later, by a screw (not shown) provided in the housing 11.

The discharge nozzle 12 is a member that discharges the molten liquid R of the resin composition into an electric field, and includes a nozzle base 13 and a discharge nozzle tip portion 14. The discharge nozzle 12 is made of a conductive material such as metal. The nozzle base 13 and the discharge nozzle tip 14 are electrically insulated by an insulating member (not shown). Therefore, even if a high voltage is applied to the tip portion 14 of the discharge nozzle, it is prevented that the voltage is directly applied to the housing 11. The housing 11 and the discharge nozzle 12 communicate with each other, and the molten liquid R in the housing 11 can be discharged from the discharge port of the discharge nozzle tip portion 14. The tip portion 14 of the discharge nozzle is grounded and grounded.

The discharge nozzle tip 14 is heated by, for example, heat transfer from a heater (not shown) provided on the nozzle base 13 or heat transfer from the melt R in the housing 11. The heating temperature of the melt R at the tip portion 14 of the discharge nozzle depends on the type of the thermoplastic resin and the surfactant used, but is preferably 100 ° C. or higher, particularly 200 ° C. or higher, and 400 ° C. or lower, particularly 350 ° C. It is preferably ℃ or less.

The melt electric field spinning device 10 further includes an electrode portion 10B. The electrode portion 10B includes a charged electrode 21 arranged at a position facing the discharge nozzle 12 and a high voltage generator 22 connected to the charged electrode portion 21.

The charging electrode 21 is arranged at a position separated from the tip portion 14 of the discharge nozzle 12 by a predetermined distance so as to face the discharge nozzle 12. Further, the charging electrode 21 is connected to the high voltage generator 22. With these configurations, an electric field can be formed between the tip portion 14 of the discharge nozzle 12 and the charging electrode 21 to which a high voltage is applied by the high voltage generator 22, and the electric field is discharged from the discharge nozzle tip portion 14. The molten liquid R can be charged. It is preferable that the charged electrode 21 is made of a conductive material such as metal or is covered with a dielectric.

The distance between the discharge nozzle 12 and the charging electrode 21 depends on the desired fiber diameter (diameter) and the collectability on the collection electrode 27 described later, but is preferably 10 mm or more and 150 mm or less, and more preferably 30 mm or more and 75 mm or less. It is preferable to have. Within this range, the melt R is likely to be charged in an electric field. Further, sparks and corona discharges are less likely to occur between the discharge nozzle 12 and the charged electrode 21, and malfunction of the device 10 is less likely to occur. It does not matter whether the applied voltage is positive or negative.

The melt electric field spinning device 10 further includes a fluid injection unit 10C. The fluid injection unit 10C includes a fluid injection device 23 below the virtual straight line connecting the molten composition supply unit 10A and the electrode unit 10B. The fluid injection device 23 is provided between the molten composition supply unit 10A and the electrode unit 10B.

An air flow A flows between the tip of the discharge nozzle tip 14 and the charging electrode 21 in a direction intersecting the direction connecting the two. This air flow A is ejected from the fluid injection device 23. The molten liquid R discharged from the tip portion 14 of the discharge nozzle can form finer fibers by being conveyed to the air flow A. For this purpose, it is preferable to use air, which is a heating fluid, as the air flow A. The temperature of the heated air is preferably 100 ° C. or higher and 500 ° C. or lower, and more preferably 200 ° C. or higher and 400 ° C. or lower, although it depends on the type of the thermoplastic resin and the surfactant. For the same purpose, the flow rate of the air flow A at the discharge port of the fluid injection device 23 when the air flow A is ejected is preferably 50 L / min or more and 350 L / min or less, and 150 L / min or more and 250 L / min or less. It is more preferably min or less.

The molten electric field spinning device 10 includes a collecting unit 10D for collecting fibers F. The collection unit 10D includes a collection sheet 24, a conveyor 25, a high voltage generator 26, and a collection electrode 27. The collecting unit 10D is provided at a position on a straight line intersecting a virtual straight line connecting the molten composition supply unit 10A and the electrode unit 10B, and at a position facing the fluid injection unit 10C. The collection unit 10D is electrically connected to each other.

The collection sheet 24 collects the fibers F formed by being conveyed to the air flow A and stretched. The collection sheet 24 can be, for example, a long strip. The collection sheet 24 is unwound from the raw roll 24a and conveyed to the transfer conveyor 25. The collection sheet 24 can be made of a resin such as polypropylene.

The transport conveyor 25 transports the fibers F collected on the collection sheet 24 to a downstream process. A collection electrode 27 for collecting fibers F is arranged inside the conveyor 25. A high voltage generator 26 is connected to the collection electrode 27, and a high voltage is applied to the collection electrode 27 by the high voltage generator 26. When a high voltage is applied to the collection electrode 27, the fibers F are attracted to the negatively charged transfer conveyor 25 side and are deposited on the surface of the collection sheet 24. Further, the collection electrode 27 may be grounded to the ground instead of the high voltage generator 26.

The melt electric field spinning device 10 further includes a processing unit 10E downstream of the collection unit 10D. The processing unit 10E includes a pair of press rolls 31, 31 and a heating device 32.

The pair of press rolls 31 and 31 press the fibers F deposited on the surface of the collection sheet 24 to form the fiber sheet F'. As shown in FIG. 1, the pair of press rolls 31, 31 are arranged so as to face each other. The pair of press rolls 31, 31 can press the fiber F by introducing the fiber F between them. If the fiber F is not formed into a sheet, the pair of press rolls 31 and 31 may not be provided.

The heating device 32 is a device that heats the fiber F deposited on the surface of the collection sheet 24 or the fiber sheet F'processed and molded by the pair of press rolls 31 and 31. In FIG. 1, the heating device 32 is provided downstream of the pair of press rolls 31, 31. The heating device 32 is arranged so as to cover the entire upper and lower surfaces of the collection sheet 24 so that the fiber sheet F'can be heated. When the fibers F are not formed into a sheet using the pair of press rolls 31, 31, the fibers F deposited on the surface of the collection sheet 24 can be directly introduced into the heating device 32 and heated.

The above is the description of the molten electric field spinning apparatus 10 shown in FIG. 1, and the method of manufacturing the fiber and the fiber sheet using the molten electric field spinning apparatus 10 will be described below. The manufacturing method of the present invention is roughly classified into three steps: a spinning step, a molding step, and a heating step.

<Spinning process>
First, the hopper 19 is filled with a resin composition containing a thermoplastic resin and a surfactant, and the resin composition is heated and melted in the housing 11. The melt R of the resin composition after heating and melting is extruded toward the discharge nozzle 12 by the rotation of the screw and supplied to the discharge port of the tip portion 14 of the discharge nozzle.

Next, the melt R of the resin composition is discharged from the tip portion 14 of the discharge nozzle and spun by an electric field spinning method. Specifically, the tip portion 14 of the discharge nozzle 12 is grounded, and the charging electrode 21 is connected to the high voltage generator 22 to apply a voltage between the tip portion 14 of the discharge nozzle 12 and the charging electrode 21. Generates an electric field. By discharging the melt R from the discharge nozzle 12 into this electric field, the melt R is charged with a high electric charge. The charged melt R is attracted to the charged electrode 21 by an electric attractive force. At that time, it is spun so as to be made into ultrafine fibers by repeating stretching from the attractive force and the self-repulsive force.

After that, by further spraying the air flow A from the fluid injection device 23 toward the discharged molten liquid R, finer fibers are generated from the molten liquid R and conveyed to the collection unit 10D side. The melt R is conveyed to the air flow A before reaching the charged electrode 21, so that its flight direction changes. Further, the air flow A stretches the melt R and solidifies it while further making it ultrafine, thereby producing fibers F having a smaller diameter. The fibers F generated from the melt R are conveyed by the air flow A, and are attracted and collected by the electric attractive force generated in the collection electrode 27, and are deposited on the surface of the collection sheet 24.

The fiber F thus produced is considered to be one continuous fiber between the discharge nozzle 12 and the collection sheet 24. Even if the fibers are temporarily cut due to manufacturing conditions, the surrounding environment, etc., the cut fibers come into contact with each other immediately, and as a result, the fibers F are transferred from the discharge nozzle 12 to the collection sheet 24. It is considered as if it were a continuous fiber between them. This fiber is spun from a resin composition containing a thermoplastic resin and a surfactant, which will be described later, as a raw material, and is substantially not deteriorated by molten electrospinning. , The composition of the fiber F, which is a product produced by the spinning process, is substantially the same.

From the viewpoint of effectively stretching the melt R, the fluidity index (MFR) of the resin composition to be discharged is set to 10 g / min or more, particularly 100 g / min or more, at the discharge port of the discharge nozzle tip 14. It is preferable to do so. The fluidity index (MFR) is measured according to JIS K7210-1999 using a die having a pore size of 2.095 mm and a length of 8 mm under a load of 230 ° C. and 2.16 kg, for example, when polypropylene is used as a raw material resin. Will be done.

In the production method of the present invention, the melt R of the resin composition discharged from the discharge nozzle 12 is highly charged due to being discharged into the electric field. The amount of charge of the resin composition on the melt R is preferably 2000 nC / g or more, more preferably 3000 nC / g or more, and more preferably 5000 nC / g or more, from the viewpoint of ultrafine fibers by electrospinning. It is more preferable to do so. The amount of charge to the melt R is, for example, a melt R discharged into a metal container placed in a Faraday cage (KQ1400, manufactured by Kasuga Electric Co., Ltd.) under the same conditions as the fiber manufacturing method of the present invention for 1 minute. It can be collected and measured by a Coulomb meter (NK-1002A, manufactured by Kasuga Electric Co., Ltd.) connected to the Faraday cage.

From the viewpoint of sufficiently charging the melt R, the applied voltage applied between the discharge nozzle 12 and the charging electrode 21 or the collection electrode 27 is preferably 5 kV or more and 100 kV or less, and more preferably 10 kV or more and 80 kV or less. When the applied voltage is in this range, the melt R is easily charged satisfactorily, and the production efficiency of fine-diameter fibers can be further improved. Further, sparks and corona discharges are less likely to occur between the discharge nozzle 12 and the charging electrode 21 or the collection electrode 27, and malfunction of the device is less likely to occur. It does not matter whether the applied voltage is positive or negative.

<Molding process>
Since this step is a step adopted in the method for manufacturing a fiber sheet of the present invention, when the fiber sheet is not manufactured, the heating step described later may be carried out without carrying out this step.

The molding step is a step of pressing the fiber F obtained by the above-mentioned <spinning step> to obtain a fiber sheet F'. The fibers F deposited on the surface of the collection sheet 24 are introduced between the pair of press rolls 31 and 31 arranged downstream in the traveling direction by the traveling of the collecting sheet 24. The fiber F is pressed by the press pressure of the pair of press rolls 31 and 31, and is formed into a fiber sheet F'.

The press pressure (linear pressure) applied to the fibers F by the pair of press rolls 31, 31 is preferably 1 N / mm or more and 40 N / mm or less, preferably 1 N / mm or more and 15 N, from the viewpoint of maintaining the flexibility of the fiber sheet. It is more preferably / mm or less.

<Heating process>
Finally, the fiber F obtained by the above-mentioned <spinning step> or the fiber sheet F'obtained in the <molding step> is passed through the heating device 32 to heat the fiber F or the fiber sheet F'. By going through this heating step, the fiber or fiber sheet of the present invention in which hydrophilicity is developed in the fiber F or the fiber sheet F'can be produced. The heating method is not particularly limited, but for example, a method of blowing hot air for treatment, a method of irradiating infrared rays, a method of immersing in a heating liquid such as hot water, a method of passing between a pair of heated rolls, a constant temperature bath, etc. Examples thereof include a method of holding in a heated space and a method of sandwiching and pressing with a heated metal plate.

The term "hydrophilic" in the present invention means that the dispersibility of the fibers in water or an aqueous liquid is high, and that the retention of water or water liquid between the fibers is high. The hydrophilicity can be evaluated using, for example, the wetting time and the impregnation rate as an index. These evaluation methods will be described in detail in Examples described later.

By the way, both the fiber F and the fiber sheet F'use a thermoplastic resin as one of the raw materials. However, when the fiber F or the fiber sheet F'is heated at a temperature equal to or higher than the melting point of the thermoplastic resin, the constituent fibers become the constituent fibers. It melts and fuses with each other. As a result, the fiber diameter and fiber density become large, and it becomes impossible to manufacture fibers or fiber sheets that maintain flexibility and liquid retention. For this reason, in the heating step, it is preferable to heat the fiber F or the fiber sheet F'at a temperature equal to or lower than the melting point of the thermoplastic resin. By heating the fiber F or the fiber sheet F'at a temperature equal to or lower than the melting point of the thermoplastic resin, the fiber or the fiber sheet having good hydrophilicity can be produced.

The heating temperature in the heating step is more preferably (MP-100) ° C. or higher (MP-10) ° C. or lower, and (MP-80) ° C. or higher, when the melting point of the thermoplastic resin is MP (° C.). It is more preferably (MP-10) ° C. or lower, further preferably (MP-60) ° C. or higher and (MP-10) ° C. or lower, and (MP-40) ° C. or higher and (MP-10) ° C. or lower. It is even more preferable to have. From the same viewpoint, for example, when the heating method in the heating step is a method of holding in a heated space such as a constant temperature bath, the heating time is preferably 5 minutes or more and 30 minutes or less, and 5 minutes or more and 20 minutes or less. Is more preferable. By heating in this temperature range, the rigidity of the fiber can be improved in addition to the higher hydrophilicity of the fiber and the fiber sheet of the present invention.

When polypropylene (melting point: about 150 ° C.) is contained as the thermoplastic resin, the heating temperature in the heating step is more preferably 50 ° C. or higher and 140 ° C. or lower, and further preferably 70 ° C. or higher and 140 ° C. or lower. It is more preferably 90 ° C. or higher and 140 ° C. or lower, and even more preferably 110 ° C. or higher and 140 ° C. or lower. From the same viewpoint, for example, when the heating method in the heating step is a method of holding in a heated space such as a constant temperature bath, the heating time is preferably 5 minutes or more and 30 minutes or less, and 5 minutes or more and 20 minutes or less. Is more preferable. By heating in this temperature range, the rigidity of the fiber can be improved in addition to the higher hydrophilicity of the fiber and the fiber sheet of the present invention.

In the embodiment shown in FIG. 1, since the heating device 32 is separately provided downstream of the pair of press rolls 31 and 31, the fiber sheet is manufactured by performing the forming step and the heating step in this order after the spinning step. However, the fiber sheet may be manufactured by simultaneously performing the molding step and the heating step. When the molding step and the heating step are performed at the same time, for example, instead of providing the heating device 32, a heating means such as a heater can be provided on the pair of press rolls 31 and 31. Alternatively, the heating device 32 may be provided upstream of the pair of press rolls 31 and 31, and the fiber sheet may be manufactured by performing the heating step and the molding step in this order after the spinning step. That is, the fiber sheet may be manufactured by performing the molding step and the heating step in the reverse order of the embodiment shown in FIG. Regardless of which manufacturing method is adopted, high hydrophilicity can be exhibited in the fiber sheet.

The fiber and fiber sheet of the present invention obtained through the heating step are hydrophilic due to the inclusion of the thermoplastic resin and the surfactant. The reason why the hydrophilicity is developed by heating the fiber and the fiber sheet is not clear, but the present inventor speculates as follows.

As shown in FIGS. 2A and 2B, the surfactant 5 has a hydrophilic group 5a and a hydrophobic group 5b, and is mixed with the thermoplastic resin 6. As shown in FIG. 2A, the fiber F and the fiber sheet F'before the heating step are mixed with the thermoplastic resin 6 because they contain a hydrophobic thermoplastic resin as a main raw material. The surfactant 5 is free from the inside of the resin 6, is present at the interface 6S between the resin 6 and the outside air so that the hydrophilic group 5a faces the outside air, or is the surfactant in the resin 6. 5 exists so that the hydrophobic group 5b faces the resin 6 side, that is, forms a W / O type micelle 5M. As shown in FIG. 2B, by heating the fiber F or the fiber sheet F', the molecular motion of the surfactant 5 and the resin 6 is promoted, and the surfactant 5 is the interface 6S between the resin 6 and the outside air. It will be more prominent (bleed out). The surfactant 5 bleeding out to the interface 6S between the resin 6 and the outside air has the hydrophilic group 5a of the surfactant 5 directed outward and hydrophobic due to the affinity between the surfactant 5 and the resin 6. The base 5b is present toward the resin 6 side. The fibers and fiber sheets of the present invention exhibit hydrophilicity by allowing water to interact with the hydrophilic groups 5a existing outside the interface 6S of the resin 6.

As described above, according to the production method of the present invention, fibers having various fiber diameters can be produced depending on the conditions for carrying out the molten electric field spinning method. In particular, it is possible to produce a fiber called nanofiber, which has an extremely fine fiber diameter. When the fiber diameter of the fiber of the present invention is expressed as a circle-equivalent diameter, it is preferably 100 nm or more and 3000 nm or less, more preferably 300 nm or more and 2000 nm or less, and 500 nm or more and 1500 nm or less. It is more preferably 600 nm or more and 1200 nm or less. By having a fiber diameter in this range, the hydrophilic effect after the heating step can be more exhibited.

From the same viewpoint, the fiber diameter of the fiber in the fiber sheet is preferably 100 nm or more and 3000 nm or less, more preferably 300 nm or more and 2000 nm or less, and more preferably 500 nm or more when the fiber diameter is expressed as a circle-equivalent diameter. It is more preferably 1500 nm or less, and further preferably 600 nm or more and 1200 nm or less. By having a fiber diameter in this range, the hydrophilic effect can be more exhibited in the fiber sheet after the heating step.

The fiber diameter of the molten electrospun fiber can be arbitrarily selected from a two-dimensional image observed by a scanning electron microscope (SEM), excluding defects such as a mass of the molten electrospun fiber, an intersection of the fused electrospun fibers, and polymer droplets. It can be measured by selecting 10 fibers and directly reading the length when a line orthogonal to the longitudinal direction of the fiber is drawn as the fiber diameter.

The impregnation rate of water in the fiber sheet is preferably 500% by mass or more, more preferably 700% by mass or more, and more preferably 1000% by mass or more, provided that the fiber diameter of the above-mentioned fiber is satisfied. Is more preferable. The method for measuring the impregnation rate of water will be described later.

The fiber sheet obtained by the production method of the present invention preferably has a basis weight of 1 g / m ² or more and 100 g / m ² or less from the viewpoint of improving the flexibility and hydrophilicity of the fiber sheet, and is preferably 10 g / m ^2. More preferably, it is 50 g / m ^{2 or less.}

The above has been described with respect to the method for producing a fiber and the method for producing a fiber sheet of the present invention, and the resin composition used in the method for producing a fiber sheet of the present invention will be described below.

The resin composition used in the method for producing a fiber of the present invention contains a thermoplastic resin and a surfactant. As the thermoplastic resin, it is preferable to use a resin having fiber-forming property in molten electric field spinning. Further, it is preferable to use a resin having a melting point. A resin having a melting point is a heat absorption peak caused by a phase change from a solid to a liquid before the resin is thermally decomposed when the resin is heated by the differential scanning calorimetry method (DSC method). It is the resin shown.

Examples of the thermoplastic resin include polyolefin resins such as polyethylene, polypropylene and ethylene-α-olefin copolymers; polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polylactic acid and liquid crystal polymers; nylon 6 and nylon 66 and the like. Polypolymer resin; Vinyl-based polymers such as polyvinyl chloride, polyvinylidene chloride and polystyrene; Acrylic polymers such as polyacrylic acid, polyacrylic acid ester, polymethacrylic acid and polymethacrylic acid ester; polyvinyl acetate, polyvinylacetate- Ethylene copolymer; and the like. These resins may be used alone or in combination of two or more.

Among these thermoplastic resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-α-olefin copolymers should be used from the viewpoint of easy spinning due to their properties such as low melting point, high fluidity, and high ductility. Is preferable. In particular, the resin composition used in the present invention is advantageous in that it can suitably perform electric field spinning with a resin melt even when it contains a polyolefin resin that cannot be electrospun with a solution containing the resin.

The resin composition used in the present invention contains a surfactant in addition to the thermoplastic resin. The surfactant in the present invention is used to modify a thermoplastic resin, which is generally hydrophobic, to develop hydrophilicity. Surfactants are roughly classified into nonionic surfactants and ionic surfactants. Examples of the ionic surfactant include anionic surfactant and cationic surfactant. From the viewpoint of imparting a high charge to the melt liquid during melt electric field spinning and improving the spinnability, it is preferable to use an ionic surfactant having an ionizable structure as the surfactant.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether, sorbitan fatty acid ester, glycerin fatty acid ester and the like. These surfactants can be used alone or in combination of two or more.

Examples of the anionic surfactant include fatty acid salts, alkyl sulfonates, alkyl sulfates, alkyl phosphates and the like. Examples of these salts include metal salts such as Na, K, Li, Zn and Ca, ammonium salts, amine salts and the like. These surfactants can be used alone or in combination of two or more.

Examples of the cationic surfactant include an alkylamine salt, a quaternary ammonium salt, an alkylbetaine and the like. Examples of these salts include halogenated salts such as Cl and Br, acetylated salts and the like. These surfactants can be used alone or in combination of two or more.

In the present invention, among these surfactants, it is preferable to contain an ionic surfactant, and it is more preferable to contain an alkyl sulfonate. By containing the alkyl sulfonate, the spinnability can be improved by increasing the chargeability of the melt during electrospinning by the melt electrospinning method, and fibers having a smaller diameter can be produced. Further, the bleed-out of the surfactant to the fiber surface in the heating step can be satisfactorily performed, and the hydrophilicity of the fiber and the fiber sheet can be suitably developed. That is, it is advantageous in that the improvement of spinnability and the development of hydrophilicity in the molten electric field spinning method can be achieved at the same time.

The "alkyl sulfonate" in the present invention has an alkyl group at the terminal in the molecular structure, or has an alkylene group in a part of the molecular structure, and has a salt structure at an arbitrary position in the molecular structure. It refers to an organic sulfonate having a sulfonic acid group. Examples of the alkyl sulfonate include an alkylbenzene sulfonate (R-Ph-SO ₃ M), a higher alcohol sulfate ester salt (RO-SO ₃ M), and a polyoxyethylene alkyl ether sulfate (RO- (RO-). CH ₂ CH ₂ O) _n- SO ₃ M), Alkyl Sulfonate (RO-CO-C-C (-SO ₃ M) -O-CO-M), Dialkyl Sulfonate (R-) O-CO-C-C (-SO ₃ M) -O-CO-R), α-sulfo fatty acid ester (R-CH (-SO ₃ M) -COOCH ₃ ), α-olefin sulfonate (R- CH = CH- (CH ₂ ) _n- SO ₃ M, R-CH (-OH) (CH ₂ ) _n- SO ₃ M), acyl taurine salt (R-CO- NH- (CH ₂ ) _2- SO ₃ M), acylalkyl taurine salt (R-CO- N (-R')-(CH ₂ ) _2- SO ₃ M), alkane sulfonate (R-SO ₃ M), acyl acetylionate (R-CO) -O- (CH ₂ CH ₂ ) -SO ₃ M) and the like can be mentioned.

In these alkyl sulfonates, R represents an alkyl group or an alkylene group, and the number of carbon atoms thereof is preferably 8 or more and 22 or less, more preferably 10 or more and 20 or less, and further preferably 12 or more and 18 or less. R'also represents an alkyl group, the number of carbon atoms of which is preferably 5 or less. Ph represents a optionally substituted phenyl group. M represents a monovalent cation such as metal, ammonium, quaternary amine, quaternary ammonium, imidazolium, phosphonium, piperidinium, pyridinium, pyrrolidinium, sulfonium, morpholinium, etc., and is preferably a metal ion, and further. It is preferably a sodium ion. n represents a number of preferably 6 or more and 24 or less, more preferably 8 or more and 22 or less, and further preferably 10 or more and 20 or less. These alkyl sulfonates may be used alone or as a mixture of two or more.

Of these alkyl sulfonates, alkane sulfonate (R-SO ₃ M), alkylbenzene sulfonate (R-Ph-SO ₃ M), acyl acetylionate (R-CO-O- (CH ₂ CH ₂₎₎ ) -SO ₃ M), acylalkyl taurine salt (R-CO- N (-R')-(CH ₂ ) _2- SO ₃ M), preferably alcan sulfonate (R-SO ₃ M). Is more preferred, and sodium alkanesulfonate (R-SO ₃ Na) is even more preferred. In particular, by using alkane sulfonate (R-SO ₃ M) or a sodium salt thereof (R-SO ₃ Na), in addition to being able to improve the spinnability even when the amount of the surfactant added is small, in addition to being able to improve the spinnability. Further, it is possible to satisfactorily bleed out the surfactant to the fiber surface in the heating step, and it is possible to more preferably develop the hydrophilicity of the fiber and the fiber sheet.

From the same viewpoint, it is also preferable to use a mixture of two or more alkane sulfonates having different numbers of carbon atoms in the alkyl group (R-SO 3 _M). Alcan sulfonate (R-SO ₃ M) has a primary alkane sulfonate having a sulfonic acid base bonded to the end of the structure and a secondary sulfonic acid base having a sulfonic acid base bonded to the middle of the structure. Where the alkane sulfonate is present, it is preferable to use the secondary alcan sulfonate from the viewpoint that the resin composition can be charged more stably, and two or more kinds of second or more secondary having different alkyl groups having different carbon atoms are preferable. It is more preferred to use a mixture of graded alkane sulfonates. When using a mixture of two or more alkane sulfonates (R-SO ₃ M) having different alkyl groups and different carbon atoms, it is more preferable to use sodium alkane sulfonate (R-SO _{3 Na) as at least one of them.} ..

The content of the surfactant in the resin composition is preferably 0.5% by mass or more, more preferably 1% by mass or more, still more preferably 3% by mass, from the viewpoint of imparting hydrophilicity to the fibers and fiber sheets of the present invention. % Or more, and even more preferably 5% by mass or more. From the same viewpoint, it is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, still more preferably 20% by mass or less. The content of the surfactant in the resin composition is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and further preferably 3% by mass or more and 30% by mass or less. Even more preferably, it is 5% by mass or more and 20% by mass or less. That is, the resin composition used in the above-mentioned spinning process is mainly composed of a thermoplastic resin.

By including the surfactant in this range, the bleed-out of the surfactant to the fiber surface in the heating step can be satisfactorily performed, and the hydrophilicity of the fiber and the fiber sheet can be satisfactorily exhibited. On the other hand, when the surfactant is contained in the resin composition in an amount of more than 50% by mass, the ratio of the resin to the thermoplastic resin is small, so that the ultrafine fibers spun by the molten electric field spinning can be stably produced. It becomes difficult to obtain.

In addition to the surfactant, the resin composition used in the above-mentioned spinning step can also be used by blending various other additives with the resin as long as the effects of the present invention are not impaired. Examples of other additives include antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents, metal deactivators and the like. Examples of the antioxidant include a phenol-based antioxidant, a phosphite-based antioxidant, and a thio-based antioxidant. Examples of the neutralizing agent include higher fatty acid salts such as calcium stearate and zinc stearate. Examples of the light stabilizer and the ultraviolet absorber include hindered amines, nickel complex compounds, benzotriazoles, benzophenones and the like. Examples of the lubricant include higher fatty acid amides such as stearic acid amide. Examples of the antistatic agent include fatty acid partial esters such as glycerin fatty acid monoester. Examples of the metal deactivator include phosphons, epoxies, triazoles, hydrazides, oxamides and the like.

The method for producing the resin composition is not particularly limited. For example, a surfactant is added to a thermoplastic resin melted by heating, and if necessary, other additives are further added and kneaded. Can be manufactured by. Such a resin composition may be produced as a masterbatch by adding a surfactant to a previously melted thermoplastic resin and kneading it, and as in the above-mentioned spinning step, the thermoplastic resin and the surfactant may be produced. The agent may be individually supplied to the molten electrospinning apparatus 10 and manufactured by heating, melting and kneading in the apparatus 10. When the resin composition of the present invention is produced as a masterbatch, it can be cooled, molded into a pellet shape or the like, and stored as a solid substance.

The fiber obtained by the production method of the present invention can be used for various purposes as a molded body of the fiber in which it is integrated. Examples of the shape of the molded body include a cotton-like body and a thread-like body in addition to the sheet. The fiber obtained by the production method of the present invention is suitably used as a soundproofing material, a heat insulating material, or the like as a cotton-like body, for example. The molded body of the fiber may be used by laminating it with another sheet or by containing various liquids, fine particles, fibers and the like. In particular, since the fiber obtained by the production method of the present invention has high hydrophilicity, it can be more preferably used for impregnating an aqueous solution such as a cosmetic solution, a cleaning solution, or a disinfectant solution.

Further, the fiber sheet obtained by the production method of the present invention can be used as a long fiber or a short fiber as a textile product such as a woven fabric or a non-woven fabric, for example, for medical purposes such as gauze, or for cosmetic purposes such as face masks and decorative sheets. , Human skin, teeth, gums, hair, non-human mammalian skin, teeth, gums, plant surfaces such as branches and leaves, floors, etc. for non-medical purposes such as cleaning of wiping sheets and wet wipes, and decorative purposes. It is also suitably used as a sheet attached to an object such as a wall or furniture. Since the fiber sheet obtained by the production method of the present invention is also highly hydrophilic, it can be more preferably used for impregnating an aqueous solution such as a cosmetic solution, a cleaning solution, or a disinfectant solution. It is also suitably used as a high-performance filter having high dust collection and low pressure loss, a battery separator that can be used at a high current density, a cell culture substrate having a high pore structure, and the like. In addition to the above-mentioned applications, it can also be used for electromagnetic wave shielding materials, bioartificial equipment, IC chips, organic EL, solar cells, electrochromic display elements, photoelectric conversion elements and the like.

Although the present invention has been described above based on the preferred embodiment thereof, the present invention is not limited to the above embodiment. For example, in the above embodiment, the spinning step, the molding step and the heating step are carried out as a series of steps, but these steps do not have to be carried out as a series of steps. Specifically, the fiber F spun in the above-mentioned spinning step may be recovered as it is, and then a molding step and a heating step may be performed separately. Even with the fiber or fiber sheet produced in this way, the effect of the present invention is sufficiently exhibited.

With respect to the above-described embodiment, the present invention further discloses the following method for producing a fiber and a method for producing a fiber sheet.
<1>
A spinning process in which a melt of a resin composition containing a thermoplastic resin and a surfactant is spun by an electrospinning method to obtain fibers.
A method for producing a fiber, which comprises a heating step of heating the fiber at a temperature equal to or lower than the melting point of the thermoplastic resin.

<2>
The method for producing a fiber according to <1>, wherein the thermoplastic resin is a polyolefin resin.
<3>
The method for producing a fiber according to <1> or <2>, wherein the surfactant is an ionic surfactant.
<4>
The method for producing a fiber according to any one of <1> to <3>, wherein the surfactant is an alkyl sulfonate.
<5>
The method for producing a fiber according to any one of <1> to <4>, wherein the surfactant is an alkane sulfonate.
<6>
The method for producing a fiber according to any one of <1> to <5>, wherein the content of the surfactant in the resin composition is 0.5% by mass or more and 50% by mass or less.

<7>
The method for producing a fiber according to any one of <1> to <6>, wherein the heating temperature in the heating step is 50 ° C. or higher and 140 ° C. or lower.
<8>
The method for producing a fiber according to any one of <1> to <7>, wherein the fiber diameter is 100 nm or more and 3000 nm or less.
<9>
In the spinning step, an electric field is formed between a discharge nozzle for discharging the molten liquid and a charged electrode arranged apart from the discharge nozzle, and the molten liquid is supplied into the electric field from the discharge nozzle. The method for producing a fiber according to any one of <1> to <8>, wherein the fiber is obtained by spinning by an electric field spinning method.
<10>
The discharge nozzle for discharging the molten liquid is grounded, and the charging electrode arranged apart from the discharge nozzle is connected to the high voltage generator to generate the electric field between the discharge nozzle and the charging electrode. The method for producing a fiber according to <9> above.
<11>
Separately from the discharge nozzle and the charged electrode, a collecting unit for collecting fibers generated from the molten liquid is used, and the fibers are collected in the collecting unit in a state where the collecting unit is electrically connected. The method for producing a fiber according to <9> or <10>.

<12>
The method for producing fibers according to any one of <9> to <11>, wherein the heating fluid is sprayed toward the molten liquid discharged from the discharge nozzle to convey the fibers generated from the molten liquid.
<13>
A spinning process in which a melt of a resin composition containing a surfactant and a thermoplastic resin is spun by an electrospinning method to obtain fibers.
The molding process of pressing the fiber to obtain a fiber sheet and
It has a heating step of heating the fiber sheet at a temperature equal to or lower than the melting point of the thermoplastic resin.
A method for producing a fiber sheet, in which the molding step and the heating step are performed in this order, in the reverse order, or at the same time.
<14>
The method for producing a fiber sheet according to <13>, wherein the molding step and the heating step are performed at the same time.
<15>
The method for producing a fiber sheet according to <13> or <14>, wherein the fiber diameter of the fiber in the fiber sheet is 100 nm or more and 3000 nm or less, and the impregnation rate of water is 500% by mass or more.

Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the invention is not limited to such examples.

<1. Fiber>
[Examples 1 to 3]
Using the molten electrospinning apparatus 10 shown in FIG. 1, polypropylene (PP; PolyMirae, MF650Y) as a thermoplastic resin and sodium alkanesulfonate (Bayer, Melsolate H95, alkyl group carbon number) as a surfactant 10 to 18) were supplied into the housing 11 in the amounts shown in Table 1, and these were heated and melted in the housing 11 and kneaded, and then the melt R made of the resin composition was spun by an electrospinning method. .. The fiber F obtained by electrospinning was recovered as a cotton-like fiber without being pressed by the press roll 31 and heated by the heating device 32. The cotton-like fiber F was held in a constant temperature bath heated to 130 ° C. for 20 minutes to obtain the desired fiber. No press processing was performed. The spinning conditions of the electric field spinning method were as follows.

-Manufacturing environment: 27 ° C, 50% RH
-Heating temperature inside the housing 11: 220 ° C
Discharge amount of melt R: 1 g / min
-Voltage applied to the discharge nozzle tip 14 (stainless steel): 0 kV (grounded to ground)
-Voltage applied to the charged electrode 21 (80 mm x 80 mm, thickness 10 mm, made of stainless steel): -20 kV
Distance between the tip of the discharge nozzle 14 and the charged electrode 21: 35 mm
-Temperature of the air flow ejected from the fluid injection device 23: 340 ° C.
-Flow rate of air flow ejected from the fluid injection device 23: 200 L / min
-Voltage applied to the collection electrode 27 :: -20 kV

[Reference Examples 1 to 3]
Electric field spinning was performed under the same conditions as in Examples 1 to 3. The fibers obtained by electrospinning were not heated.

[Comparative Example 1]
Electric field spinning was performed in the same manner as in Example 1 except that no surfactant was used.

[Comparative Example 2]
Electrospinning was carried out in the same manner as in Example 1 except that the polypropylene content in the resin composition was 99.9% by mass and the content of sodium alkylsulfonate was 0.1% by mass.

[Evaluation 1-1: Spinnability]
The quality of the continuous charging operation by the molten electric field spinning device, that is, the spinnability was evaluated. In the continuous charging operation, spinning was performed by continuously operating for 5 minutes under the same conditions as in Example 1. The evaluation was performed according to the following criteria. The results are shown in Table 1.
A: The molten electric field spinning with the molten liquid of the resin composition was continuously formed.
B: The molten electric field spinning of the resin composition with the molten liquid could not be performed.

[Evaluation 1-2: Measurement of average fiber diameter]
The average fiber diameter of the electrospun fibers was measured. Specifically, 10 fibers are arbitrarily selected from the two-dimensional image observed by a scanning electron microscope (SEM) excluding defects such as fiber lumps, fiber intersections, and polymer droplets, and are orthogonal to the longitudinal direction of the fibers. The length when the line was drawn was directly read as the fiber diameter, and the average value of these was taken as the average fiber diameter (nm). The results are shown in Table 1 below.

[Evaluation 1-3: Hydrophilicity]
0.25 g of each of the fibers of Examples 1 to 3, Reference Examples 1 to 3, and Comparative Examples 1 and 2 was immersed in 50 mL of ion-exchanged water for 1 minute to evaluate the hydrophilicity. The evaluation was performed visually according to the following criteria.
A: Fibers settle or disperse in water.
B: Fibers float on the surface of the water.

In Examples 1 to 3 and Reference Examples 1 to 3, cotton-like fine-diameter fibers could be produced as shown in Table 1. In particular, it can be seen that Examples 1 to 3 in which the fibers after electrospinning are heated are superior in hydrophilicity as compared with Reference Examples 1 to 3. On the other hand, in Comparative Examples 1 and 2, electrospinning could not be performed and fibers could not be produced.

<2. Fiber sheet>
[Examples 4 to 7]
The fibers F having an average fiber diameter of 550 nm were obtained by electrospinning under the same spinning conditions as in Example 1. The collected fibers are collected in 210 mm x 297 mm (JIS A4 size), and then the collected fibers are used in a hand press machine (Toyo Seiki Seisakusho Co., Ltd., Minitest Press MP-WCL) at room temperature for 10 MPa for 10 seconds. A sheet was produced by pressing under the conditions of. The desired fiber sheet was obtained by holding the fiber sheet in a constant temperature bath heated to 130 ° C. for 20 minutes. The basis weight of this fiber sheet was 20 g / m ² .

[Example 8]
Fiber F having an average fiber diameter of 1000 nm was obtained by electrospinning under the same spinning conditions as in Example 1 except that the discharge rate of the melt R was changed to 1.2 g / min. The fiber F was pressed and heated under the same conditions as in Example 4 to obtain a desired fiber sheet.

[Example 9]
Fiber F having an average fiber diameter of 1500 nm was obtained by electrospinning under the same spinning conditions as in Example 1 except that the discharge rate of the melt R was changed to 1.5 g / min. The fiber F was pressed and heated under the same conditions as in Example 4 to obtain a desired fiber sheet.

[Example 10]
Fiber F having an average fiber diameter of 5000 nm was obtained by electrospinning under the same spinning conditions as in Example 1 except that the temperature of the air flow ejected from the fluid injection device 23 was changed to the condition of 25 ° C. The fiber F was pressed and heated under the same conditions as in Example 4 to obtain a desired fiber sheet.

[Reference Example 4]
A fiber sheet was obtained by electrospinning and pressing under the same conditions as in Example 4. The fiber sheet was not heated.

[Reference Example 5]
A fiber sheet was obtained by electrospinning and pressing under the same conditions as in Example 8. The fiber sheet was not heated.

[Reference Example 6]
A fiber sheet was obtained by electrospinning and pressing under the same conditions as in Example 9. The fiber sheet was not heated.

[Reference Example 7]
A fiber sheet was obtained by electrospinning and pressing under the same conditions as in Example 10. The fiber sheet was not heated.

[Evaluation 2-1: Measurement of average fiber diameter]
The measurement of the average fiber diameter in the fiber sheets of Examples 4 to 10 and Reference Examples 4 to 7 was carried out in the same manner as in the above-mentioned [Evaluation 1-2: Measurement of average fiber diameter]. The results are shown in Table 2 below.

[Evaluation 2-2: Measurement of wetting time]
The fiber sheets of Examples 4 to 10 and Reference Examples 4 to 7 were cut into 5 cm squares and immersed in an impregnating solution (ion-exchanged water). The time required for water to spread over the entire surface of the fiber sheet was measured, and this was defined as the wetting time (sec). The results are shown in Table 2 below.

[Evaluation 2-3: Measurement of impregnation rate]
The water impregnation rate (%) at the wetting time (sec) measured in the above [Evaluation 2-2: Measurement of wetting time] was calculated from the following formula. The results are shown in Table 2 below.
Impregnation rate (%) = 100 × (mass of fiber sheet at wetting time (g) -mass of fiber sheet before immersion (g)) / mass of fiber sheet before immersion (g)
The mass (g) of the fiber sheet at the wetting time means the mass measured after 1 minute by pulling up the fiber sheet from the impregnating solution with tweezers after the measurement of [Evaluation 2-2: Measurement of wetting time]. When water did not spread over the entire surface of the fiber sheet even after being immersed for 1 hour or more, the mass of the fiber sheet after 1 hour was taken as the mass of the fiber sheet at the wetting time.

As shown in Table 2, Examples 4 to 10 in which the fiber sheet is heated have a shorter wetting time than Reference Examples 4 to 7 even when the fiber obtained by melt electrospinning is molded into the sheet. Alternatively, it can be seen that a fiber sheet having a high water content, that is, a high hydrophilicity can be produced. In particular, Examples 4 to 8 in which the fiber sheet having a fiber diameter of 1200 nm or less was heated had an extremely high impregnation rate as compared with Reference Examples 4 and 5. Since the fiber diameter of Example 10 and Reference Example 7 was large, it was difficult to get wet with water, and water did not spread over the entire surface of the fiber sheet within 1 hour. However, the impregnation rate in the fiber sheet of Example 10 is reference. It was higher than that of Example 7.

10 Melt electric field spinning device 11 Housing 12 Discharge nozzle 13 Nozzle base 14 Discharge nozzle tip 19 Hopper 21 Charging electrode 22 High voltage generator 23 Fluid injection device 24 Collection sheet 25 Conveyance conveyor 26 High voltage generator 27 Collection electrode 31 Press roll 32 Heating device A Air flow F Fiber F'Fiber sheet R Melted liquid of resin composition

Claims (11)

A spinning process in which a melt of a resin composition containing a polyolefin resin and a surfactant is spun by an electrospinning method to obtain a fiber having a fiber diameter of 1210 nm or less.
A method for producing a fiber, comprising a heating step of heating the fiber at a temperature equal to or lower than the melting point of the polyolefin resin and at 120 ° C. or higher and 140 ° C. or lower. The method for producing a fiber according to claim 1, wherein the polyolefin resin contains polypropylene. The method for producing a fiber according to claim 1 or 2, wherein the heating time in the heating step is 5 minutes or more and 30 minutes or less. The method for producing a fiber according to any one of claims 1 to 3, wherein the surfactant is an ionic surfactant. The surfactant is an organic sulfonate and
The organic sulfonate has an alkyl group at the terminal in the molecular structure, or has an alkylene group in a part of the molecular structure and has a sulfonic acid group having a salt structure at an arbitrary position in the molecular structure. The method for producing a fiber according to any one of claims 1 to 4, wherein the fiber is produced. The method for producing a fiber according to any one of claims 1 to 5 , wherein the surfactant is an alkane sulfonate. The method for producing a fiber according to any one of claims 1 to 6 , wherein the content of the surfactant in the resin composition is 0.5% by mass or more and 50% by mass or less. The method for producing a fiber according to any one of claims 1 to 7 , wherein the fiber diameter is 100 nm or more and 1200 nm or less. A method for producing a fiber sheet containing fibers obtained by the production method according to any one of claims 1 to 8.
A spinning process in which a melt of a resin composition containing a surfactant and a thermoplastic resin is spun by an electrospinning method to obtain fibers.
The molding process of pressing the fiber to obtain a fiber sheet and
It has a heating step of heating the fiber sheet at a temperature equal to or lower than the melting point of the thermoplastic resin.
A method for producing a fiber sheet, in which the molding step and the heating step are performed in this order, in the reverse order, or at the same time. The method for producing a fiber sheet according to claim 9, wherein the molding step and the heating step are performed at the same time. The impregnation ratio of put that water to the fiber sheet is more than 500 mass%, the production method of the fiber sheet according to claim 9 or 10.

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