Crosslinked-gelatin nanofiber filter and production method therefor

Abstract

A purpose of the present invention is to provide a crosslinked-gelatin nanofiber filter which has satisfactory flexibility, is less apt to break when in use, and can have controlled solubility under specific temperature conditions. The crosslinked-gelatin nanofiber filter comprises gelatin, a thickening polysaccharide, and a cyclic sugar, does not dissolve in 20°C pure water, has a dissolution time in 25°C pure water of 60 minutes or shorter, and has an average fiber diameter of 300-600 nm.

Description

Cross-linked gelatin nanofiber filter and method for manufacturing the same

[0001] This invention relates to a cross-linked gelatin nanofiber filter and a method for producing the same.

[0002] Gelatin filters play an important role in environmental monitoring in hospitals, research facilities, pharmaceutical plants, and cleanrooms due to their high efficiency in capturing airborne particles and their biocompatibility.

[0003] For example, Patent Document 1 discloses a method for producing polymer fibers obtained from a gelatin solution, a polymer fiber material formed from the polymer fibers, and gelatin nanofibers used in gelatin filters.

[0004] Furthermore, conventional techniques for crosslinking gelatin nanofibers and the like using methods such as ultraviolet irradiation, gamma ray irradiation, heat treatment, and microwave treatment are known. As an example of such a technique, Patent Document 2 discloses a method of crosslinking using a crosslinking agent.

[0005] Japanese Patent Publication No. 2022-032977, U.S. Patent Application Publication No. 2021 / 0155764

[0006] However, conventional gelatin filters have very high solubility in water and dissolve instantly upon contact with water. Furthermore, conventional gelatin filters are brittle and inflexible, making them easily bent and damaged. Additionally, while gelatin filters treated to be immobilized have improved water insolubility, it is not easy to remove only the immobilized filter when collecting the analyte. Therefore, if the solubility of the gelatin filter can be controlled under specific temperature conditions when analyzing the collected analyte, it will be possible to easily extract and / or collect only the fine particles and microorganisms from the gelatin filter for analysis without adversely affecting them.

[0007] Therefore, the present invention has been made in view of the above problems, and aims to provide a cross-linked gelatin nanofiber filter that has good flexibility, is less prone to damage during use, and can control solubility under specific temperature conditions.

[0008] As a result of diligent research to solve the above problems, the present inventors have found that the above problems can be solved by using a specific cross-linked gelatin nanofiber filter containing gelatin, a thickening polysaccharide, and a cyclic sugar, and have completed the present invention.

[0009] In other words, the present invention provides various specific embodiments as shown below: <1> A cross-linked gelatin nanofiber filter comprising gelatin, a thickening polysaccharide, and a cyclic sugar, wherein it does not dissolve in pure water at 20°C, its dissolution time in pure water at 25°C is 60 minutes or less, and its average fiber diameter is 300 to 600 nm. <2> The cross-linked gelatin nanofiber filter according to <1>, wherein, under conditions of a flow rate of 0.4 to 0.6 L / min and an airflow linear velocity of 0.60 to 0.80 cm / s, the collection efficiency of particles with a particle diameter of 0.3 to 10 μm is 90% or more, and the pressure loss is 50 to 150 Pa·s / cm. <3> The cross-linked gelatin nanofiber filter according to <1> or <2>, wherein the thickening polysaccharide comprises xanthan gum. <4> The cross-linked gelatin nanofiber filter according to any one of <1> to <3>, wherein the cyclic sugar comprises cyclodextrin. <5> Mass per unit area is 10 to 200 g / m ２A crosslinked gelatin nanofiber filter according to any one of items <1> to <4>. <6> A method for producing a crosslinked gelatin nanofiber filter, comprising: a preparation step of preparing a spinning aqueous solution containing gelatin, a thickening polysaccharide, and a cyclic sugar; a spinning step of obtaining gelatin nanofibers by fiberizing the obtained spinning aqueous solution; and a crosslinking step of obtaining a crosslinked gelatin nanofiber filter by crosslinking the obtained gelatin nanofibers. <7> A method for producing a crosslinked gelatin nanofiber filter according to <6>, further comprising a suction collection step of obtaining a gelatin nanofiber sheet by suction collecting the gelatin nanofibers in the spinning step. <8> A method for producing a crosslinked gelatin nanofiber filter according to <6> or <7>, wherein in the preparation step, the spinning aqueous solution further contains a pH adjusting solution, and the pH of the spinning aqueous solution is 6.0 to 10.0. <9> The method for producing a cross-linked gelatin nanofiber filter according to <8>, wherein the pH adjusting solution is a Tris buffer with a molar concentration of 0.1 to 1.0 mol / L. <10> The method for producing a cross-linked gelatin nanofiber filter according to any one of <6> to <9>, wherein in the preparation step, the gelatin content is 15 to 35% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution. <11> The method for producing a cross-linked gelatin nanofiber filter according to any one of <6> to <10>, wherein in the preparation step, the thickening polysaccharide contains xanthan gum, and the content of the thickening polysaccharide is 0.1 to 1.0% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution. <12> A method for producing a cross-linked gelatin nanofiber filter according to any one of <6> to <11>, wherein in the preparation step, the cyclic sugar contains cyclodextrin, and the content of the cyclic sugar is 2 to 10% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution. <13> A method for producing a cross-linked gelatin nanofiber filter according to any one of <6> to <12>, wherein in the spinning step, the fibers are formed so that the average fiber diameter is 300 to 600 nm.<14> A cross-linked gelatin nanofiber filter that does not dissolve in pure water at 20°C, has a dissolution time of 60 minutes or less in pure water at 25°C, and has an average fiber diameter of 300 to 600 nm. <15> The cross-linked gelatin nanofiber filter according to <14>, which, under conditions of a flow rate of 0.4 to 0.6 L / min and a permeable linear velocity of 0.60 to 0.80 cm / s, has a collection efficiency of 90% or more for particles with a particle diameter of 0.3 to 10 μm, and a pressure loss of 50 to 150 Pa·s / cm.

[0010] According to the present invention, it is possible to provide a cross-linked gelatin nanofiber filter that has good flexibility, is less prone to damage during use, and has controllable solubility under specific temperature conditions.

[0011] A flowchart illustrating a method for manufacturing a cross-linked gelatin nanofiber filter according to one embodiment. A cross-sectional view illustrating the configuration of the nozzle member of a fiber manufacturing apparatus according to one embodiment. An enlarged view of part A in Figure 2. Photographs of the appearance of the spinning aqueous solutions of Reference Example (Example 1) (left in the photograph) and Example 4 (right in the photograph). Scanning electron microscope image of the cross-linked gelatin nanofiber filter of Example 4. Photograph of the appearance of the cross-linked gelatin nanofiber filter of Example 1.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. Unless otherwise specified, positional relationships such as up, down, left, and right shall be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to those shown. However, the following embodiments are illustrative examples for explaining the present invention, and the present invention is not limited to these. In other words, the present invention can be implemented with arbitrary modifications without departing from its essence.

[0013] The cross-linked gelatin nanofiber filter of this embodiment contains gelatin, a thickening polysaccharide, and a cyclic sugar, does not dissolve in pure water at 20°C, has a dissolution time of 60 minutes or less in pure water at 25°C, and has an average fiber diameter of 300 to 600 nm.

[0014] The crosslinked gelatin nanofiber filter of this embodiment is obtained by crosslinking gelatin nanofibers or gelatin nanofiber sheets containing gelatin, a thickening polysaccharide, and a cyclic sugar.

[0015] First, the gelatin nanofibers, gelatin nanofiber sheets, and methods for manufacturing them according to this embodiment will be described, and then the crosslinked gelatin nanofiber filter and its manufacturing method will be described in detail.

[0016] [Gelatin Nanofibers and Gelatin Nanofiber Sheets] The gelatin nanofibers of this embodiment can be suitably obtained by the gelatin nanofiber manufacturing method described later. Gelatin nanofibers have a more uniform fiber diameter, with particulate fibers due to thread breakage and the like being more suppressed.

[0017] Gelatin nanofiber sheets can be obtained, for example, by forming sheets from the obtained gelatin nanofibers by suction collection on a breathable conveyor.

[0018] Gelatin nanofibers and gelatin nanofiber sheets can be used as filter materials for capturing fine particles, microorganisms, bacteria, viruses, etc., as well as in medical biomaterials and sanitary masks.

[0019] The average fiber diameter of the gelatin nanofiber or gelatin nanofiber sheet in this embodiment can be appropriately set according to the required performance and is not particularly limited, but is preferably 300 to 600 nm, more preferably 350 to 550 nm, and even more preferably 400 to 500 nm. When the average fiber diameter of the gelatin nanofiber is within the above range, the gelatin nanofiber sheet tends to have better collection efficiency of the target material. The average fiber diameter of the gelatin nanofiber can be measured from images taken with a scanning electron microscope (SEM) (Hitachi High-Tech Corporation, SU3500 (product name)). The average fiber diameter of the gelatin nanofiber may also be calculated as the average value of 100 measurements.

[0020] [Method for producing gelatin nanofibers and gelatin nanofiber sheets] Figure 1 is a flowchart showing the method for producing a crosslinked gelatin nanofiber filter according to this embodiment. As shown in Figure 1, the method for producing gelatin nanofibers according to this embodiment includes a preparation step (S1) of preparing a spinning aqueous solution containing gelatin, a thickening polysaccharide and a cyclic sugar, and a spinning step (S2) of fiberizing this spinning aqueous solution to obtain predetermined gelatin nanofibers.

[0021] In addition to the above steps, the method for producing gelatin nanofibers may include a defoaming step of the spinning aqueous solution, etc., after the above preparation step (S1), which is not shown.

[0022] The spinning process (S2) described above may further include a suction collection process to obtain a gelatin nanofiber sheet by forming the obtained gelatin nanofibers into a sheet by suction collection on a breathable conveyor.

[0023] The presence of gelatin, thickening polysaccharides, and cyclic sugars in the spinning aqueous solution tends to improve the miscibility between the gelatin and thickening polysaccharides via the cyclic sugars. Improved miscibility effectively suppresses clumping and fiber breakage during fiber formation, allowing for the desirable acquisition of gelatin nanofibers with more uniform fiber diameters.

[0024] <Preparation Step (S1)> In Preparation Step (S1), a spinning aqueous solution containing gelatin, thickening polysaccharides, and cyclic sugars is prepared.

[0025] [Gelatin] The spinning solution contains gelatin.

[0026] The type of gelatin is not particularly limited and can be appropriately selected from known types. Examples of such gelatin include gelatin derived from animals such as cattle, pigs, chickens, and fish. The gelatin may also be acid-treated gelatin (so-called type A) or alkali-treated gelatin (so-called type B). Among these, alkali-treated gelatin is preferred from the viewpoint of the pH of the solution when the gelatin is dissolved. Alkali-treated gelatin is also preferred because it can suitably suppress the turbidity of the spinning aqueous solution. In the spinning aqueous solution of this embodiment, one type of gelatin can be used alone, or two or more types can be used in any combination and ratio.

[0027] Gelatin is typically water-soluble, readily dissolving in water at 25-35°C and solidifying upon drying. After solidification, gelatin is resistant to shrinkage and deliquescent properties, making it highly biocompatible. Because gelatin is biologically inert, it has little effect on microorganisms, bacteria, viruses, etc., making it suitable for their collection. Therefore, gelatin is suitable as a substrate for gelatin nanofibers, gelatin nanofiber sheets, cross-linked gelatin nanofiber filters, etc., according to this embodiment.

[0028] As described later, by cross-linking gelatin, it is possible to create a gelatin that does not become insoluble in pure water at 20°C but dissolves in pure water at 25-35°C within a predetermined time. One method for cross-linking gelatin is to heat-denature the proteins in the gelatin by heat treatment. With such a method, the gelatin dissolves under certain conditions as described above. By appropriately controlling the heating time and heating temperature, it is also possible to create a gelatin that does not dissolve in water.

[0029] Acid-treated gelatin can be obtained by immersing animal-derived gelatin, such as that from cattle, pigs, chickens, or fish, or gelatin obtained from these sources, in a dilute acid solution, such as hydrochloric acid, sulfuric acid, sulfurous acid, or phosphoric acid, or a mixture thereof.

[0030] Alkali-treated gelatin is obtained by immersing animal-derived gelatin, such as that from cattle, pigs, chickens, or fish, or gelatin obtained from these sources, in an alkaline solution such as potassium hydroxide, sodium hydroxide, calcium hydroxide, or a mixture thereof.

[0031] For specific methods of producing acid-treated and alkali-treated gelatin, see, for example, Arthur Weiss's "The Macromolecular Chemistry of Gelatin" (Academic Press, 1964).

[0032] The gelatin content in the spinning aqueous solution is not particularly limited, but is preferably 15 to 35% by mass, more preferably 20 to 33% by mass, and even more preferably 25 to 30% by mass, based on the total amount (100% by mass) of the spinning aqueous solution in terms of solid content. When the gelatin content in the spinning aqueous solution is within the above range, it is more effectively possible to suppress the change from fibrous to granular form due to thread breakage during fiber formation, and it is possible to obtain gelatin nanofibers that are easier to stretch and have a more uniform fiber diameter.

[0033] [Thickening polysaccharides] The spinning solution contains thickening polysaccharides.

[0034] The thickening polysaccharides are not particularly limited as long as they can bind to the cyclic sugars described later and gel, and known thickening polysaccharides can be used depending on the type of cyclic sugar.

[0035] As for the thickening polysaccharide, water solubility is preferred, and a thickening polysaccharide that dissolves easily when in contact with water at 25-35°C is more preferred.

[0036] The type of the thickening polysaccharide is not particularly limited, and it can be appropriately selected from known ones and used. Examples of the thickening polysaccharide include, for example, guar gum; xanthan gum; carrageenans such as κ-carrageenan, ι-carrageenan, and λ-carrageenan; alginic acids such as alginic acid and alginates; gellan gums such as deacylated gellan gum and native gellan gum; pectins such as LM pectin and HM pectin; galactomannans such as tara gum and locust bean gum; tamarind seed gum; psyllium seed gum; sabaku yomogi seed gum; glucomannan; ramzan gum; welan gum; curdlan; pullulan; karaya gum; tragacanth gum; gatti gum; gum arabic; cassia gum; macrohomopsis gum; agar; soybean polysaccharides and the like. The spinning aqueous solution of the present embodiment can use the thickening polysaccharide alone or in any combination and ratio of two or more kinds.

[0037] From the viewpoint of cold water solubility, it is preferable to contain xanthan gum as the thickening polysaccharide. Xanthan gum tends to dissolve easily when contacted with water at 25 to 35 °C. Xanthan gum is a gum produced by fermenting starch such as corn with Xanthomonas campestris, and is composed of repeating units of two molecules of glucose, two molecules of mannose, and glucuronic acid. Xanthan gum can also be said to be a chain polysaccharide. In the present embodiment, by using xanthan gum as the thickening polysaccharide together with gelatin and cyclic sugar, the miscibility between gelatin and xanthan gum in the spinning aqueous solution tends to be further improved.

[0038] The content of the thickening polysaccharide in the spinning aqueous solution is not particularly limited, but in terms of solid content conversion, it is preferably 0.1 to 1.0% by mass, more preferably 0.2 to 0.8% by mass, and still more preferably 0.3 to 0.7% by mass with respect to the total amount (100% by mass) of the spinning aqueous solution. When the content of the thickening polysaccharide in the spinning aqueous solution is within the above range, the viscosity suitable for fiberizing the spinning aqueous solution can be obtained.

[0039] [Cyclic saccharides] The spinning aqueous solution contains cyclic saccharides.

[0040] The type of cyclic sugar is not particularly limited and can be appropriately selected from known ones for use. Such cyclic sugars include, for example, cyclic oligosaccharides. Examples of cyclic oligosaccharides include cyclodextrin, cyclic isomaltooligosaccharide, cyclic tetrasaccharide, and cyclic pentasaccharide. Examples of cyclic tetrasaccharides include those mainly containing cyclonigerosyl nigerose. Cyclonigerosyl nigerose is a compound in which four glucose molecules are connected cyclically. Examples of cyclic pentasaccharides include those in which five glucose molecules are connected cyclically. In the spinning aqueous solution of the present embodiment, a cyclic sugar can be used alone or in any combination and ratio of two or more kinds.

[0041] Among these, as the cyclic sugar, it is preferable to contain cyclodextrin from the viewpoints of the dispersibility and miscibility of gelatin and thickening polysaccharides. The type of cyclodextrin is not particularly limited and can be appropriately selected from known ones for use. Examples of cyclodextrin include α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, δ-cyclodextrin, and ε-cyclodextrin.

[0042] The cyclic sugar preferably contains at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, more preferably contains at least one selected from the group consisting of α-cyclodextrin and γ-cyclodextrin, and still more preferably contains γ-cyclodextrin. By including at least one selected from the group consisting of α-cyclodextrin and γ-cyclodextrin as the cyclic sugar, the miscibility of the spinning aqueous solution, the sheet stability after spinning, and the solubility can be further improved.

[0043] In this embodiment, cyclic sugars are typically water-soluble and tend to dissolve easily when in contact with water at 25-35°C. Because cyclic sugars have the property of retaining moisture, when they are included in a spinning solution, the viscosity of the spinning solution increases, and the dispersibility and miscibility of gelatin and thickening polysaccharides tend to improve. Furthermore, when xanthan gum is used as the thickening polysaccharide, the dispersibility and miscibility of gelatin and xanthan gum in the spinning solution tend to improve even further.

[0044] Spinning solutions can become cloudy depending on the combination of materials. Even in such solutions, improving the dispersibility and miscibility between gelatin and thickening polysaccharides tends to more effectively suppress this clouding and enable more efficient production of gelatin nanofibers. This effect tends to be more favorably obtained when xanthan gum is used as the thickening polysaccharide.

[0045] Furthermore, when the spinning aqueous solution contains cyclic sugars, the dispersibility and miscibility between gelatin and thickening polysaccharides are improved, which effectively suppresses the formation of clumps during fiber formation and tends to result in the desirable acquisition of gelatin nanofibers with a more uniform fiber diameter. This is thought to be because, due to the structure of cyclic sugars, they contribute to the interaction between both gelatin and thickening polysaccharides, and because cyclic sugars, gelatin, and thickening polysaccharides each play a complementary role. Possible interactions between cyclic sugars and gelatin include, for example, "hydrogen bonding," "hydrophobic interaction," "hydrophobic effect," and "electrostatic interaction." Possible interactions between cyclic sugars and thickening polysaccharides include, for example, "inclusion," "hydration," and "intermolecular interaction." These mechanisms are not limited to these.

[0046] Using cyclodextrin as a cyclic sugar further improves the dispersibility and miscibility between gelatin and thickening polysaccharides. In addition, the resulting gelatin nanofibers, gelatin nanofiber sheets, and cross-linked gelatin nanofiber filters tend to exhibit more favorable suppression of shrinkage, hygroscopicity, and deliquescence. This is because cyclodextrin can only bind to water molecules through its outer hydroxyl group, and among cyclic sugars, it has relatively low solubility in water. Therefore, it is presumed that the inclusion of cyclodextrin effectively suppresses its hygroscopicity and deliquescence, thereby effectively inhibiting shrinkage due to moisture absorption after fiber formation.

[0047] Furthermore, when xanthan gum is used as a thickening polysaccharide and cyclodextrin as a cyclic sugar, the turbidity of the spinning aqueous solution can be more effectively suppressed, and gelatin nanofibers tend to be produced more efficiently. In addition, the formation of clumps during fiberization tends to be more effectively suppressed. As a result, gelatin nanofibers with a more uniform fiber diameter tend to be obtained.

[0048] The content of cyclic sugars in the spinning aqueous solution is not particularly limited, but is preferably 2 to 10% by mass, more preferably 3 to 10% by mass, and even more preferably 5 to 10% by mass, based on the total amount (100% by mass) of the spinning aqueous solution in terms of solid content. When the content of cyclic sugars in the spinning aqueous solution is within the above range, the viscosity of the spinning aqueous solution tends to increase, and the dispersibility and miscibility between gelatin and thickening polysaccharides tend to improve. In addition, shrinkage due to moisture absorption of gelatin nanofibers, gelatin nanofiber sheets, and crosslinked gelatin nanofiber filters tends to be suppressed.

[0049] [pH adjusting solution] The spinning aqueous solution may further contain a pH adjusting solution.

[0050] In conventional gelatin fiber manufacturing, the gelatin solution contains gelatin and cyclic sugars, but the solution may become cloudy during preparation. When gelatin nanofibers are spun using this cloudy gelatin solution, the gelatin may not be fully stretched and may be blown away by the spinning air as droplets. In addition, there is a tendency for gelatin nanofibers to change from fibrous to granular due to thread breakage. Thus, the efficiency of gelatin nanofiber manufacturing is reduced when using a cloudy gelatin solution.

[0051] The mechanism of clouding is presumed to be as follows: The pH of the gelatin solution is usually lower than the isoionic point, and the added cyclic sugars have a negative charge in the solution. Therefore, it is presumed that they aggregate and cause clouding. The mechanism of clouding is not limited to the above.

[0052] By including a pH adjusting solution in the spinning aqueous solution, the turbidity of the spinning aqueous solution can be more effectively suppressed, and gelatin nanofibers tend to be obtained more efficiently.

[0053] The type of pH adjusting solution is not particularly limited and can be appropriately selected from known solutions. Examples of such pH adjusting solutions include buffers such as Tris (tris(hydroxymethyl)aminomethane) buffer, phosphate buffer, citrate buffer, EDTA (ethylenediaminetetraacetic acid) buffer, HEPES (2-[4-(2-hydroxyethyl)piperazine-1-yl]ethanesulfonic acid) buffer, and acetate buffer; and alkaline aqueous solutions such as sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, ammonia water, a mixed solution of sodium dihydrogen phosphate and disodium hydrogen phosphate, and basic amino acid solution. In the spinning aqueous solution of this embodiment, one pH adjusting solution can be used alone, or two or more can be used in any combination and ratio.

[0054] Among these, Tris buffer is preferred as the pH adjusting solution because it has low impact on living organisms, is not easily volatile and has excellent stability, and does not easily produce residue after spinning. Using Tris buffer improves the stability of the spinning aqueous solution and more effectively suppresses turbidity, which tends to allow for more uniform fiber formation of gelatin nanofibers. Furthermore, because Tris buffer has high biological stability, even if Tris is contained in the gelatin nanofilter and gelatin nanofilter sheet, it tends to allow for analysis without adversely affecting the target organisms such as bacteria and viruses.

[0055] Furthermore, by using Tris buffer, the amount of amine in the spinning aqueous solution increases due to the amine contained in trishydroxymethylaminomethane in the Tris buffer. Therefore, when crosslinking gelatin nanofibers or gelatin nanofiber sheets in the crosslinking process described later, the formation of crosslinks within and between gelatin molecules is further promoted. As a result, the heat treatment time can be further shortened, and production efficiency tends to improve. Note that the heat treatment time is the time required to obtain the crosslinked gelatin nanofiber filter described later, which does not dissolve in water at 20°C but dissolves in water at 25-35°C within a predetermined time.

[0056] Examples of Tris buffers include Tris-HCl buffer, Tris-Base buffer, Tris-EDTA(TE) buffer, Tris-Borate-EDTA(TBE) buffer, Tris-Acetate-EDTA(TAE) buffer, Tris-Glycine buffer, and Tris-Phosphatate buffer. Among these, Tris-Base buffer is more preferable from the viewpoint of eliminating concerns such as structural changes in gelatin, as it does not contain any extraneous substances. Examples of extraneous substances include chelating agents, metal ions, other buffering components, sugars, and surfactants.

[0057] The molar concentration of the solute contained in the pH adjusting solution is not particularly limited, but is preferably 0.1 to 1.0 mol / L, more preferably 0.2 to 0.9 mol / L, and even more preferably 0.3 to 0.7 mol / L. When the molar concentration of the buffer solution is within the above range, the turbidity of the spinning aqueous solution is further suppressed, and gelatin nanofibers with a more uniform fiber diameter tend to be obtained.

[0058] The pH adjusting solution is not particularly limited, but it is preferably a Tris buffer with a solute molar concentration of 0.1 to 1.0 mol / L, more preferably a Tris buffer with a solute molar concentration of 0.2 to 0.9 mol / L, and even more preferably a Tris buffer with a solute molar concentration of 0.3 to 0.7 mol / L. When the above Tris buffer is used as the pH adjusting solution, the turbidity of the spinning aqueous solution is further suppressed, and gelatin nanofibers with a more uniform fiber diameter tend to be obtained.

[0059] The content of the pH adjusting solution in the spinning aqueous solution is not particularly limited, but is preferably 60 to 80% by mass, more preferably 63 to 77% by mass, and even more preferably 65 to 75% by mass, relative to the total amount (100% by mass) of the spinning aqueous solution. When the content of the pH adjusting solution in the spinning aqueous solution is within the above range, the turbidity of the spinning aqueous solution can be suppressed more effectively, and gelatin nanofibers tend to be produced more efficiently. As a result, gelatin nanofibers with a more uniform fiber diameter tend to be obtained more effectively.

[0060] [Spinning solution]

[0061] The pH of the spinning aqueous solution in this embodiment is not particularly limited and can be appropriately selected depending on the type of raw material used, spinning conditions, etc. The pH of the spinning aqueous solution may be adjusted to 6.0 to 10.0. Preferably, the pH of the spinning aqueous solution is 7.0 to 9.9, more preferably 8.0 to 9.7, and even more preferably 8.5 to 9.5. When the pH of the spinning aqueous solution is within the above range, the turbidity of the spinning aqueous solution can be more effectively suppressed, and gelatin nanofibers tend to be produced more efficiently. Therefore, gelatin nanofibers with more uniform fiber diameters tend to be obtained. In the preparation step (S1) of this embodiment, for example, the pH of the spinning aqueous solution can be adjusted by adjusting the amount of each component and the molar concentration of the pH adjusting solution.

[0062] The temperature of the spinning aqueous solution is not particularly limited and can be appropriately selected depending on the type of raw materials used and the spinning conditions. The temperature of the spinning aqueous solution is preferably 30 to 80°C, more preferably 40 to 75°C, and even more preferably 50 to 70°C. When the temperature of the spinning aqueous solution is within the above range, materials such as gelatin dissolve more uniformly, which further suppresses turbidity of the spinning aqueous solution and tends to allow for more efficient production of gelatin nanofibers. As a result, gelatin nanofibers with more uniform fiber diameters tend to be obtained.

[0063] The spinning aqueous solution of this embodiment may contain other additives as needed. Examples of other additives include crosslinking agents, antibacterial agents, antifungal agents, dispersants, defoaming agents, spinning stabilizers, and antiviral agents.

[0064] The spinning aqueous solution of this embodiment is preferably free of sulfate ions. If the spinning aqueous solution contains sulfate ions, it tends to be difficult to obtain the desired gelatin nanofiber or gelatin nanofiber sheet. In this specification, "free of sulfate ions" means that the sulfate ions in the spinning aqueous solution are measured by ion chromatography (Dionex ICS-2100 (product name) manufactured by Thermo Scientific) and the measured value is, for example, 1.0 ppm or less. The lower limit is above the detection limit, for example, 0.1 ppm or more.

[0065] <Spinning Process (S2)> In the spinning process (S2), the above-mentioned spinning aqueous solution is converted into fibers using, for example, the fiberization apparatus shown in Figure 2 to obtain gelatin nanofibers. In this specification, the "fiberization apparatus" may also be referred to as the "microfiber manufacturing apparatus" or "fiber manufacturing apparatus".

[0066] The method of fiberization is not limited to the method using the fiberization apparatus shown in Figure 2; for example, conventionally known methods such as the meltblown method or the electrospinning method may also be employed. In this embodiment, it is preferable to fiberize the gelatin nanofibers using the fiberization apparatus shown in Figure 2. The configuration of the fiberization apparatus in this embodiment will be described below.

[0067] Figure 2 is a cross-sectional view illustrating the configuration of the nozzle member of the microfiber manufacturing apparatus according to this embodiment. Figure 3 is an enlarged view of part A in Figure 2.

[0068] As shown in Figure 2, the microfiber manufacturing apparatus 1 according to this embodiment includes a nozzle member 10. The nozzle member 10 includes a first nozzle 11, a second nozzle 12, and a discharge nozzle 13. Furthermore, the spinning aqueous solution, which is the raw material supplied from the discharge nozzle 13, is stretched by the airflow from low-pressure and high-pressure air sprayed from the first nozzle 11 and the second nozzle 12. The microfiber manufacturing apparatus 1 also includes a collection device (not shown) for collecting the stretched microfibers.

[0069] As shown in Figure 3, in the microfiber manufacturing apparatus 1 according to this embodiment, a high-speed airflow F is formed by the high-pressure air injected from the first nozzle 11.Ｈ Then, a low-speed airflow F is formed by the low-pressure air injected from the second nozzle 12. Ｌ And is formed. Then, the spinning aqueous solution supplied from the discharge nozzle 13 is subjected to a low-speed airflow F Ｌ This is first extended, and the high-speed airflow F Ｈ This will result in a second extension, meaning it will be extended in two stages.

[0070] As shown in Figure 2, the nozzle member 10 includes a first nozzle 11 that injects high-pressure air via a high-pressure manifold 14 connected to a high-pressure air supply source, a second nozzle 12 that injects low-pressure air via a low-pressure manifold 15 connected to a low-pressure air supply source, and a discharge nozzle 13 that supplies a spinning aqueous solution from a spinning aqueous solution stock tank 17 via a gear pump 16. In addition, a heating device 30, such as a heater, is attached to the outer circumference of the nozzle member 10 near the discharge nozzle 13.

[0071] The following describes a microfiber manufacturing apparatus 1 in which the nozzle member 10 of this embodiment consists of a first nozzle 11 which is a flat nozzle, a second nozzle 12 which is a straight nozzle, and a discharge nozzle 13 which is a nozzle pitch, with the length of each nozzle set to 10 mm or more and formed in a comb shape.

[0072] Preferably, the high-pressure air injected from the first nozzle 11 is supplied at 0.2 MPa for a nozzle diameter of 1.0 mm x 50 mm, and the low-pressure air injected from the second nozzle 12 is supplied at 0.03 MPa for a nozzle diameter of 1.5 mm. Preferably, the flow velocity ratio of the high-pressure air to the low-pressure air is set to approximately 2:1 to 3:1. Specifically, the flow velocity of the low-pressure air is set to 200 to 300 m / sec, and the flow velocity of the high-pressure air is set to 600 to 700 m / sec.

[0073] In this way, the first nozzle 11 injects high-pressure or low-pressure air via the high-pressure manifold 14, and the second nozzle 12 injects high-pressure or low-pressure air via the low-pressure manifold 15. Therefore, even if the first nozzle 11 or the second nozzle 12 is configured as a flat nozzle, it is possible to inject air at a uniform pressure.

[0074] Since the spinning solution is supplied via the gear pump 16, it is possible to supply the spinning solution continuously and stably without the occurrence of pulsation or other issues. The supply of the spinning solution is not limited to via the gear pump 16, and various supply methods can be applied. For example, one such supply method is to supply the spinning solution by extrusion using pressurized air.

[0075] Furthermore, since the nozzle member 10 is equipped with a heating device 30, the temperature of the spinning solution can be raised even when, for example, the ambient temperature at the manufacturing site drops. As a result, the viscosity of the spinning solution can be stabilized. The heating device 30 may be an electric heating wire or hot water. The heating temperature is usually 160 to 200°C.

[0076] The first nozzle 11 is positioned to inject high-pressure air in a substantially horizontal direction. The discharge nozzle 13 is positioned facing downward in the vertical direction to supply the spinning aqueous solution vertically downward. In this way, the first nozzle 11 and the discharge nozzle 13 are positioned at approximately right angles to each other. The second nozzle 12 is positioned between the angle between the first nozzle 11 and the discharge nozzle 13, and is positioned to inject low-pressure air toward the high-pressure air injected by the first nozzle 11. The second nozzle 12 is preferably positioned at an angle of 20 to 60° relative to the first nozzle 11, and more preferably at an angle of about 40° relative to the first nozzle 11. When the second nozzle 12 is positioned at an angle greater than 20° relative to the first nozzle 11, particles are less likely to be generated in the fine fibers, and the collection rate tends to be good. When the second nozzle 12 is positioned at an angle less than 60° relative to the first nozzle 11, the high-speed airflow F Ｈ Furthermore, the spinning aqueous solution supplied from the discharge nozzle 13 tends to be suitably entrained.

[0077] As shown in Figure 3, the tip of the discharge nozzle 13 is positioned above the nozzle opening of the second nozzle 12. This results in a flow of low-pressure air F being ejected from the second nozzle 12. ＬThe spinning aqueous solution is suitably carried along with it. Furthermore, using a position adjustment mechanism (not shown), the position in which the spinning aqueous solution is supplied from the discharge nozzle 13 can be appropriately adjusted so as to be carried along with the gentle airflow ejected from the second nozzle 12.

[0078] With the microfiber manufacturing apparatus 1 configured in this way, the spinning aqueous solution supplied from the discharge nozzle 13 is first stretched by low-pressure air, resulting in an average fiber diameter of 500 to 800 nm. Then, it is secondarily stretched by high-pressure air, resulting in an average fiber diameter of 100 to 600 nm. This stretching process makes it possible to manufacture nano-level microfibers with minimal variation. Furthermore, the microfiber manufacturing apparatus 1 according to this embodiment is equipped with a nozzle member 10 that integrates various nozzles, enabling more stable fiber production and further improving productivity.

[0079] In the spinning process, it is preferable to spin the gelatin nanofibers so that the average fiber diameter is 300 to 600 nm. It is more preferable to spin the fibers so that the average fiber diameter is 350 to 550 nm, and even more preferable to spin them so that the average fiber diameter is 400 to 500 nm.

[0080] The average fiber diameter of the gelatin nanofibers can be appropriately set according to the required performance. When the average fiber diameter is within the above range, the gelatin nanofiber sheet tends to have superior collection efficiency for the target material. Furthermore, it tends to make the gelatin nanofibers easier to insolubilize, resulting in a more suitable cross-linked gelatin nanofiber filter.

[0081] The average fiber diameter of gelatin nanofibers can be controlled, for example, by using the fiberization apparatus according to this embodiment. The average fiber diameter can be measured from images captured by a scanning electron microscope (SEM) (Hitachi High-Tech Corporation, SU3500 (product name)). The fiber diameter may also be calculated as the average value of 100 measurements.

[0082] In this embodiment, after the spinning process, a suction collection step may be further included in which the obtained gelatin nanofibers are collected on a breathable conveyor to form a sheet, thereby obtaining a gelatin nanofiber sheet. In this specification, the shape of the gelatin nanofiber sheet is not particularly limited.

[0083] [Cross-linked gelatin nanofiber filter]

[0084] The cross-linked gelatin nanofiber filter of this embodiment does not dissolve in pure water at 20°C, has a dissolution time of 60 minutes or less in pure water at 25°C, and has an average fiber diameter of 300 to 600 nm. The cross-linked gelatin nanofiber filter of this embodiment contains gelatin, a thickening polysaccharide, and a cyclic sugar, and does not dissolve in pure water at 20°C, has a dissolution time of 60 minutes or less in pure water at 25°C, and has an average fiber diameter of 300 to 600 nm.

[0085] The crosslinked gelatin nanofiber filter of this embodiment is preferably obtained by crosslinking gelatin nanofibers or gelatin nanofiber sheets containing gelatin, a thickening polysaccharide, and a cyclic sugar.

[0086] A crosslinked gelatin nanofiber filter can be obtained by crosslinking gelatin nanofibers or gelatin nanofiber sheets using a crosslinking process described later.

[0087] Cross-linked gelatin nanofiber filters can be used as filter materials for capturing fine particles, microorganisms, bacteria, viruses, etc., as well as in medical biomaterials and sanitary masks.

[0088] In this embodiment, by using a cross-linked gelatin nanofiber filter, it is possible to obtain more reliable data when collecting fine particles, microorganisms, bacteria, viruses, etc., under various environmental conditions. Therefore, these are more suitable as filter materials. Since the cross-linked gelatin nanofiber filter dissolves easily at a predetermined water temperature, it does not adversely affect fine particles or microorganisms, and they can be easily extracted and / or collected for analysis. Therefore, these can be applied, for example, to elucidating the mechanisms of harmful effects caused by fine particles or microorganisms.

[0089] Cross-linked gelatin nanofiber filters have a uniform average fiber diameter and are therefore useful as filter materials for capturing, for example, fine particles, microorganisms, bacteria, and viruses. The cross-linked gelatin nanofiber filter of this embodiment can efficiently capture minute particles (i.e., fine particles) in the air. Therefore, cross-linked gelatin nanofiber filters are more suitably used in the fields of microbiology and environmental monitoring.

[0090] The average fiber diameter of the cross-linked gelatin nanofiber filter in this embodiment is 300 to 600 nm. More preferably, it is 350 to 550 nm, and even more preferably, 400 to 500 nm. When the average fiber diameter of the cross-linked gelatin nanofiber filter is within the above range, the collection efficiency of the target material tends to be better when it is made into a gelatin nanofiber sheet. Because the average fiber diameter is within the above range, the fibers intertwine with each other, for example, as shown in Figure 5. Therefore, the filter has good flexibility and tends to be less prone to damage during use.

[0091] The average fiber diameter of a cross-linked gelatin nanofiber filter can be measured from images captured using a scanning electron microscope (SEM) (Hitachi High-Tech Corporation, SU3500 (product name)). The average fiber diameter of the gelatin nanofibers may also be calculated, for example, as the average value of 100 measurements.

[0092] The cross-linked gelatin nanofiber filter does not dissolve in pure water at 20°C, and its dissolution time in pure water at 25°C is 60 minutes or less. Preferably, the dissolution time in pure water at 25°C is 1 minute or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. The cross-linked gelatin nanofiber filter may dissolve instantaneously in pure water at 25°C. The fact that the cross-linked gelatin nanofiber filter dissolves within the above range makes it useful for collecting and analyzing fine particles, microorganisms, bacteria, viruses, etc.

[0093] The cross-linked gelatin nanofiber filter preferably does not dissolve in pure water at 20°C, and its dissolution time in pure water at 35°C is preferably 60 minutes or less. Alternatively, the cross-linked gelatin nanofiber filter may dissolve in pure water at 35°C for 1 minute or more. The cross-linked gelatin nanofiber filter may also dissolve instantaneously in pure water at 35°C. The dissolution of the gelatin nanofibers within the above range makes it useful for the collection and analysis of fine particles, microorganisms, bacteria, viruses, etc.

[0094] In this specification, "not dissolving" means that, in the dissolution time measurement described below, the cross-linked gelatin nanofiber filter remains visible to the naked eye in pure water for at least 10 minutes, preferably 30 minutes, more preferably 60 minutes, and even more preferably more than 120 minutes from the start of the test. The upper limit of the time the cross-linked gelatin nanofiber filter remains undissolved in pure water at 20°C is not particularly limited, but from a practical standpoint, it is preferable that it remains undissolved for, for example, 24 hours. Examples of pure water include ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, and ultrapure water, which have had ionic impurities removed as much as possible.

[0095] The dissolution time of a cross-linked gelatin nanofiber filter in pure water at 20°C can be measured by the following method. Specifically, in an environment with a temperature of 20°C and a humidity of 50%, a cross-linked gelatin nanofiber filter cut into 1 cm squares is placed into a screw-top tube containing 50 cc of pure water adjusted to 20°C. The degree of dissolution is then visually checked, and the time when all of the cross-linked gelatin nanofiber filter has dissolved from the time of placement is defined as the dissolution time. At this time, the pure water in the screw-top tube is stirred at 200 rpm using a stirrer.

[0096] Furthermore, the dissolution time of a cross-linked gelatin nanofiber filter in pure water at 25°C can be measured by the following method. Specifically, in an environment with a temperature of 25°C and a humidity of 50%, a cross-linked gelatin nanofiber filter cut into 1 cm squares is placed in a screw-top tube containing 50 cc of pure water adjusted to 25°C. The degree of dissolution is then visually checked, and the time when all of the cross-linked gelatin nanofiber filter has dissolved from the time of placement is defined as the dissolution time. At this time, the pure water in the screw-top tube is stirred at 200 rpm using a stirrer. The dissolution time in pure water at 35°C can be measured in the same manner as the measurement at 25°C, except that the temperature of the pure water is changed from 25°C to 35°C.

[0097] In this specification, in the measurement of the dissolution time described above, "dissolved" means that the cross-linked gelatin nanofiber filter is no longer visible to the naked eye in pure water.

[0098] The cross-linked gelatin nanofiber filter possesses good flexibility and handling properties. Furthermore, the cross-linked gelatin nanofiber filter is resistant to crumbling and exhibits suitable bending strength (durability) during use, making it resistant to damage. For example, the cross-linked gelatin nanofiber filter dissolves easily when immersed in water at 25°C to 35°C. Conventional gelatin filters or sheets are prone to crumbling and lack flexibility and handling properties. They are also presumed to have low durability in capturing fine particles. Observing the shape of conventional filters or sheets reveals they are aggregates of particles and fibers, and compared to aggregates of fibers alone, they are particularly inferior in handling properties under certain temperature conditions. The cross-linked gelatin nanofiber filter of this embodiment does not dissolve in pure water at 20°C. On the other hand, it dissolves within 60 minutes in pure water at 25-35°C. As a result, for example, under high temperature and high humidity conditions, it does not dissolve while being used for collection or analysis, and can be used continuously by dissolving it directly into a culture medium after collection or analysis.

[0099] Furthermore, the cross-linked gelatin nanofiber filter is thought to possess solubility at a predetermined temperature. This is presumed to be because the filter, by containing the aforementioned cyclic sugars, affects the physical properties of the solution. Specifically, this is thought to be due to multiple factors, including the stabilization of the molecular structure by the encapsulation of the hydrophobic parts of gelatin by the cyclic sugars, changes in the gelation temperature of gelatin and the viscosity properties of the thickening polysaccharides, and changes in the encapsulation efficiency with temperature. The mechanism is not limited to these.

[0100] Furthermore, the inclusion of cyclic sugars in the cross-linked gelatin nanofiber filter results in uniform fibers having the above-mentioned average fiber diameter. In addition, due to the entanglement of the fibers, the cross-linked gelatin nanofiber filter exhibits good flexibility, making it less prone to damage during use and resulting in good handling properties.

[0101] The thickness of the cross-linked gelatin nanofiber filter is not particularly limited, but is, for example, 50 to 500 μm, preferably 100 to 400 μm. A sheet thickness within this range tends to allow the sheet to dissolve more favorably within the desired time. In this specification, the thickness can be measured, for example, using a micrometer.

[0102] The cross-linked gelatin nanofiber filter is not particularly limited, but under conditions of a flow rate of 0.4 to 0.6 L / min and a linear airflow velocity of 0.60 to 0.80 cm / s, the collection efficiency of particles with a particle size of 0.3 to 10 μm is preferably 85% or more, more preferably 90% or more, and even more preferably 94% or more. The cross-linked gelatin nanofiber filter is not particularly limited, but under conditions of a flow rate of 0.4 to 0.6 L / min and a linear airflow velocity of 0.60 to 0.80 cm / s, the collection efficiency of particles with a particle size of 0.3 to 1.0 μm is preferably 85% or more, more preferably 90% or more, and even more preferably 94% or more. The cross-linked gelatin nanofiber filter is not particularly limited, but under conditions of a flow rate of 0.4 to 0.6 L / min and a linear airflow velocity of 0.60 to 0.80 cm / s, it preferably has a particle collection efficiency of 85% or more, more preferably 90% or more, and even more preferably 94% or more for particles with a particle size of 1.0 to 10 μm.

[0103] Collection efficiency is, for example, based on an effective area of ​​12.88 cm². ２ The particle size can be measured using a cross-linked gelatin nanofiber filter (40.5 mmφ) and a light scattering particle counter (manufactured by RION, KC-01E (product name)). More specifically, it can be measured by the method shown in the examples described later.

[0104] The pressure loss of the cross-linked gelatin nanofiber filter is not particularly limited, but is preferably 50 to 150 Pa·s / cm, more preferably 60 to 100 Pa·s / cm, and even more preferably 65 to 80 Pa·s / cm, under conditions of a flow rate of 0.4 to 0.6 L / min and a permeable linear velocity of 0.60 to 0.80 cm / s.

[0105] The pressure loss can be measured using a differential pressure gauge (manufactured by Yamamoto Electric Works, model number Manostar WO81FN50DH) to measure the pressure difference with the atmosphere during the measurement of the collection efficiency described above. More specifically, it can be measured by the method shown in the examples described later.

[0106] The mass per unit area of the crosslinked gelatin nanofiber filter (hereinafter also referred to as basis weight) can be appropriately set according to the required performance, but is preferably 10 to 200 g / m ２ and more preferably 30 to 150 g / m ２ and even more preferably 50 to 100 g / m ２ When the mass per unit area of the crosslinked gelatin nanofiber filter is within the above range, the collection efficiency of the object to be collected tends to be more excellent. The mass per unit area of the crosslinked gelatin nanofiber filter can be calculated by cutting the obtained crosslinked gelatin nanofiber filter into a predetermined area and measuring its mass.

[0107] The crosslinked gelatin nanofiber filter of the present embodiment preferably does not contain sulfate ions. In this specification, "not containing" means that the crosslinked gelatin nanofiber filter is dispersed in pure water, and the sulfate ions are measured in the dispersion liquid by ion chromatography (manufactured by Thermo Scientific, Dionex ICS-2100 (trade name)), and the measured value is 1.0 ppm or less. The lower limit is above the measurement limit, for example, 0.1 ppm or more. Sulfate ions become impurities when analyzing the analysis target collected by the crosslinked gelatin nanofiber filter, and affect the accuracy of the analysis.

[0108] 〔Method for producing crosslinked gelatin nanofiber filter〕 The method for producing the crosslinked gelatin nanofiber filter of the present embodiment includes a preparation step of preparing a spinning aqueous solution containing the above-described gelatin, a thickening polysaccharide, and a cyclic sugar, as shown in FIG. 1, and the above-described obtained spinning aqueous solution. A spinning step of obtaining gelatin nanofibers by fiberizing, and a crosslinking step of obtaining a crosslinked gelatin nanofiber filter by crosslinking the obtained gelatin nanofibers. In the crosslinking step, the gelatin nanofibers may be crosslinked, or the gelatin nanofiber sheet may be crosslinked.

[0109] <Crosslinking Process (S3)> In the crosslinking process, the gelatin nanofibers or gelatin nanofiber sheets are crosslinked, so that the gelatin contained in the gelatin nanofibers or gelatin nanofiber sheets forms crosslinks within and between gelatin molecules.

[0110] The method of crosslinking is not particularly limited and can be carried out by conventionally known methods. Examples of such methods include ultraviolet irradiation, gamma ray irradiation, heat treatment, microwave treatment, chemical modification with inorganic compounds, and chemical modification with organic compounds.

[0111] As a method for crosslinking, heat treatment is preferred. Heat treatment is useful because it has a short treatment time, allows for partial insolubilization of gelatin nanofibers or gelatin nanofiber sheets by controlling the heating temperature and time, and is a simple treatment method.

[0112] When gelatin is heated to high temperatures, the secondary structure of the protein (such as α-helices and β-sheets) breaks down, transforming into a disordered, coiled, random coil structure. As a result, the solubility of gelatin decreases. Furthermore, heating causes cross-linking within and between gelatin molecules, causing them to bond tightly together and form a network structure. This network makes it difficult for water molecules to be trapped, so gelatin becomes less soluble in water, and insolubilization progresses.

[0113] In this specification, "insolubilization" does not mean complete insolubilization, but rather a state of "partial insolubilization." That is, "insolubilization" in this specification means that a substance that dissolves immediately upon contact with water will, after undergoing a predetermined treatment, remain insoluble for a certain period of time, but then dissolve.

[0114] Such "insolubilization" can be achieved, for example, by controlling the degree of crosslinking within and between gelatin molecules by controlling the time and / or temperature of the heat treatment in the crosslinking process. In other words, it can be achieved by adjusting the degree of insolubilization through heat treatment.

[0115] The heat treatment temperature is not particularly limited, but is preferably 60 to 150°C, more preferably 100 to 145°C, and even more preferably 130 to 140°C. When the heat treatment temperature is within the above range, the insolubilization of gelatin nanofibers or gelatin nanofiber sheets tends to proceed in a shorter time, thereby improving production efficiency.

[0116] The heating time is not particularly limited, but is usually 1 minute or more, preferably 10 to 60 minutes, more preferably 15 to 40 minutes, even more preferably 20 to 35 minutes, and even more preferably 25 to 30 minutes. By heating the time within the above range, the insolubilization of the gelatin nanofiber or gelatin nanofiber sheet progresses further, and it tends to dissolve more readily at the desired dissolution time.

[0117] The features of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0118] The materials used in the examples and comparative examples are as follows: Gelatin: Reagent (Wako Grade 1, Fujifilm Wako Pure Chemical Industries, Ltd.) Thickening polysaccharides: Xanthan gum (Tokyo Chemical Industries, Ltd.) Cyclic sugar: γ-cyclodextrin (Tokyo Chemical Industries, Ltd.) pH adjusting solution: Aqueous solution of Tris-BASE (Tokyo Chemical Industries, Ltd.) prepared to have a molar concentration of 0.5 mol / L (Tris-BASE buffer solution)

[0119] (Example 1) [Preparation of Spinning Solution] To pure water at 60°C, γ-cyclodextrin, xanthan gum, and gelatin were added in that order and stirred until uniformly dissolved to prepare a spinning solution. The amount of pure water added was such that the total of gelatin, cyclodextrin, xanthan gum, and pure water was 100% by mass. The mixing ratios of each material are as shown in Table 1. The pH of the obtained spinning solution was as shown in Tables 1 and 3.

[0120] [Spinning and Sheet Formation of Gelatin Nanofibers] The obtained spun aqueous solution was introduced into a solution tank, and gelatin nanofibers were obtained using a liquid-phase pump and the microfiber manufacturing apparatus shown in Figure 2. The manufacturing conditions for the microfiber manufacturing apparatus were as follows. The average fiber diameter of the obtained gelatin nanofibers is shown in Table 1. The average fiber diameter of the gelatin nanofibers was measured by the method shown below. The obtained gelatin nanofibers were sucked onto a mesh conveyor, and the fibers were deposited and collected to obtain a gelatin nanofiber sheet. [Manufacturing Conditions] First nozzle: Nozzle diameter 1.0 mm × Nozzle length 50 mm High-pressure air pressure of the first nozzle: 0.2 MPa Flow velocity of high-pressure air: 600 m / sec Second nozzle: Nozzle diameter 1.5 mm Low-pressure air pressure of the second nozzle: 0.03 MPa Secondary stretching air temperature: 180°C Flow velocity of low-pressure air: 250 m / sec Flow velocity ratio of high-pressure air to low-pressure air: 2.5:1

[0121] [Crosslinking Treatment] The gelatin nanofiber sheet was heat-treated for 30 minutes in a constant temperature bath (manufactured by AS ONE, model ON-450S (product name)) set to 140°C. After the heat treatment, it was removed from the constant temperature bath and allowed to cool naturally. The crosslinked gelatin nanofiber filter of Example 1 was obtained.

[0122] (Examples 2 and 3) Examples 2 and 3 were obtained in the same manner as in Example 1, except that the heating temperature (temperature of the constant temperature bath) was changed to 100°C and 60°C during the crosslinking process.

[0123] (Comparative Example 1) Comparative Example 2 was obtained using the same method as in Example 1, except that the cross-linking treatment was omitted (the constant temperature bath was not heated).

[0124] The performance of the obtained gelatin nanofibers and crosslinked gelatin nanofiber filters was evaluated as follows. The results are shown in Tables 1 and 3.

[0125] (Average fiber diameter of gelatin nanofibers and cross-linked gelatin nanofiber filters) The average fiber diameter (nm) of the obtained gelatin nanofibers and cross-linked gelatin nanofiber filters was calculated by taking images with a scanning electron microscope (SEM) (Hitachi High-Tech Corporation, SU3500 (product name)), measuring 100 points from the images, and averaging the results.

[0126] (Basis value of cross-linked gelatin nanofiber filter) The mass per unit area of ​​the obtained cross-linked gelatin nanofiber filter is calculated by weighing the obtained sheet over 100 cm². ２ The material was cut to a size of (10 cm x 10 cm) and its mass was measured. From these values, the mass per unit area (g / m²) was calculated. ２ It was converted as follows:

[0127] (Thickness of the cross-linked gelatin nanofiber filter) The thickness (μm) of the obtained cross-linked gelatin nanofiber filter was measured using a micrometer (Mitutoyo Corporation, OMV-25MX (product name)).

[0128] (Solubility Test 1) The dissolution time of the cross-linked gelatin nanofiber filter was measured as follows: Under conditions of 20°C and 50% humidity, a 1 cm square piece of cross-linked gelatin nanofiber filter was placed in a screw-cap tube containing 50 cc of pure water adjusted to 20°C. The time from the time of placement until the entire filter dissolved was measured and defined as the dissolution time. The degree of dissolution was confirmed visually. The pure water in the screw-cap tube was stirred at 200 rpm using a stirrer. Solubility was evaluated using the dissolution time according to the following criteria: AA: Did not dissolve even after more than 120 minutes. CC: Dissolved within 120 minutes.

[0129] (Solubility Test 2) The dissolution time of the cross-linked gelatin nanofiber filter was measured as follows: Under conditions of 25°C and 50% humidity, a 1 cm square piece of cross-linked gelatin nanofiber filter was placed in a screw-cap tube containing 50 cc of pure water adjusted to 25°C. The time from the time of placement until the entire filter dissolved was measured and defined as the dissolution time. The degree of dissolution was confirmed visually. The pure water in the screw-cap tube was stirred at 200 rpm using a stirrer. Solubility was evaluated using the dissolution time according to the following evaluation criteria. Tables 1 and 3 show the dissolution times. AA: Dissolved within 60 minutes. CC: Did not dissolve even after 60 minutes.

[0130] (Bending Test) Under conditions of 25°C and 50% humidity, the obtained cross-linked gelatin nanofiber filter was simply bent using the method shown in Figure 6, and its condition was visually inspected. The bending test was evaluated according to the following criteria: AA: The filter did not break or crumble when bent. CC: The filter broke or crumbled when bent.

[0131] (Collection Efficiency and Pressure Loss) The collection efficiency of the obtained cross-linked gelatin nanofiber filter was measured for particles with diameters of 0.3–1.0 μm and 1.0–10 μm under conditions of a flow rate of 0.57 L / min and a linear velocity of 0.74 cm / s. First, the instrument difference between two light scattering particle counters (RION Corporation, KC-01E) was measured three times. Next, the effective area was 12.88 cm². ２ A cross-linked gelatin nanofiber filter (40.5 mmφ) was set in a filter holder, and the flow rate and differential pressure at the inlet were measured using a differential pressure gauge (Manostar WO81FN50DH, manufactured by Yamamoto Electric Works). This measurement was repeated three times. Then, a light scattering particle counter was started, and the measurement for 20 seconds was recorded. The measurement with the light scattering particle counter was repeated three times, and the collection efficiency (%) was calculated from the average of the three measured values. In addition, the pressure loss (Pa·s / cm) was calculated from the measurement value obtained by the differential pressure gauge during the above collection efficiency measurement.

[0132]

[0133] Table 2 shows the results of plotting the heating temperature during filter fabrication (°C) on the horizontal axis and the dissolution time (min) in solubility test 2 on the vertical axis for Examples 1 to 3.

[0134]

[0135] (Example 4) Example 4 was obtained in the same manner as in Example 1, except that the solvent was changed to Tris-BASE buffer.

[0136] For Example 4 and Reference Example (Example 1), the turbidity of the spinning aqueous solution was evaluated using the following method.

[0137] (Evaluation of turbidity of spinning solution) The obtained spinning solution was visually inspected, and turbidity was evaluated according to the following evaluation criteria. As an example, Figure 4 shows a spinning solution that is not turbid (Example 4) and a spinning solution that is turbid (Reference Example (Example 1)). In the non-turbid solution, the black line in the background is visible, whereas in the turbid solution, it is not visible. AA: The spinning solution is not turbid. CC: The spinning solution is turbid.

[0138] The evaluation results of the turbidity in Example 4 and Reference Example (Example 1), and the performance evaluation of the obtained gelatin nanofibers and crosslinked gelatin nanofiber filters were performed as described above. The results are shown in Table 3.

[0139]

[0140] As shown in Table 1, the cross-linked gelatin nanofiber filter of this embodiment (see Figure 6) did not dissolve in pure water at 20°C for more than 120 minutes, and its dissolution time in pure water at 25°C was within 60 minutes. Furthermore, as shown in Figure 6, a comparison between the example and the comparative example showed improvements in bending strength (durability) and collection efficiency.

[0141] Table 2 shows that the dissolution time of the cross-linked gelatin nanofiber filter differs depending on the heating temperature. This suggests that the degree of cross-linking within and between gelatin molecules changes depending on the heating temperature, and that this also affects solubility. Furthermore, it was found that various cross-linked gelatin nanofiber filters with different solubility can be obtained, indicating that cross-linked gelatin nanofiber filters can be applied to a wide range of uses.

[0142] Furthermore, as shown in Table 3, the spinning aqueous solution did not become cloudy when a pH adjusting solution was added to it (see Figure 4). In addition, the cross-linked gelatin nanofiber filter of Example 4 was shown to have a more uniform fiber diameter, as shown in the scanning electron microscope images (see Figure 5).

[0143] The disclosure of Japanese Patent Application No. 2024-156893, filed on 10 September 2024, is incorporated herein by reference in its entirety. Furthermore, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated as being incorporated by reference.

[0144] S1... Preparation of spinning aqueous solution S2... Spinning process of spinning aqueous solution S3... Crosslinking process of gelatin nanofibers 1... Microfiber manufacturing apparatus 10... Nozzle component 11... First nozzle 12... Second nozzle 13... Discharge nozzle 14... High-pressure manifold 15... Low-pressure manifold 16... Gear pump 17... Solution tank (spinning aqueous solution stock tank) 30... Heating device.

Claims

1. A cross-linked gelatin nanofiber filter containing gelatin, thickening polysaccharides, and cyclic sugars, which does not dissolve in pure water at 20°C, has a dissolution time of 60 minutes or less in pure water at 25°C, and has an average fiber diameter of 300 to 600 nm.

2. The cross-linked gelatin nanofiber filter according to claim 1, wherein, under conditions of a flow rate of 0.4 to 0.6 L / min and a linear airflow velocity of 0.60 to 0.80 cm / s, the collection efficiency of particles with a particle size of 0.3 to 10 μm is 90% or more, and the pressure loss is 50 to 150 Pa·s / cm.

3. The cross-linked gelatin nanofiber filter according to claim 1, wherein the thickening polysaccharide comprises xanthan gum.

4. The cross-linked gelatin nanofiber filter according to claim 1, wherein the cyclic sugar comprises cyclodextrin.

5. Mass per unit area is 10 to 200 g / m² ２ The crosslinked gelatin nanofiber filter according to claim 1.

6. A method for producing a crosslinked gelatin nanofiber filter, comprising: a preparation step of preparing a spinning aqueous solution containing gelatin, a thickening polysaccharide, and a cyclic sugar; a spinning step of obtaining gelatin nanofibers by fiberizing the obtained spinning aqueous solution; and a crosslinking step of obtaining a crosslinked gelatin nanofiber filter by crosslinking the obtained gelatin nanofibers.

7. A method for producing a crosslinked gelatin nanofiber filter according to claim 6, comprising a suction collection step in which the gelatin nanofibers are collected by suction in the spinning step to obtain a gelatin nanofiber sheet.

8. The method for producing a cross-linked gelatin nanofiber filter according to claim 6, wherein in the preparation step, the spinning aqueous solution further contains a pH adjusting solution, and the pH of the spinning aqueous solution is 6.0 to 10.

0.

9. The method for producing a cross-linked gelatin nanofiber filter according to claim 8, wherein the pH adjusting solution is a Tris buffer with a molar concentration of 0.1 to 1.0 mol / L.

10. The method for producing a crosslinked gelatin nanofiber filter according to claim 6, wherein in the preparation step, the gelatin content is 15 to 35% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution.

11. The method for producing a cross-linked gelatin nanofiber filter according to claim 6, wherein in the preparation step, the thickening polysaccharide contains xanthan gum, and the content of the thickening polysaccharide is 0.1 to 1.0% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution.

12. The method for producing a crosslinked gelatin nanofiber filter according to claim 6, wherein in the preparation step, the cyclic sugar contains cyclodextrin, and the content of the cyclic sugar is 2 to 10% by mass on a solid content basis with respect to the total amount of the spinning aqueous solution.

13. The method for producing a cross-linked gelatin nanofiber filter according to claim 6, wherein in the spinning step, the fibers are formed so that the average fiber diameter is 300 to 600 nm.

14. A cross-linked gelatin nanofiber filter that does not dissolve in pure water at 20°C, dissolves in pure water at 25°C in 60 minutes or less, and has an average fiber diameter of 300 to 600 nm.

15. The cross-linked gelatin nanofiber filter according to claim 14, wherein, under conditions of a flow rate of 0.4 to 0.6 L / min and a linear airflow velocity of 0.60 to 0.80 cm / s, the collection efficiency of particles with a particle size of 0.3 to 10 μm is 90% or more, and the pressure loss is 50 to 150 Pa·s / cm.

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