JP4863894B2 - Nonwoven fabric and method for producing the same - Google Patents

Description

  The present invention relates to a nonwoven fabric and a method for producing the same.

  Nonwoven fabrics can be imparted with various functions by appropriately combining constituent fibers, fiber web forming methods, or fiber web bonding methods, and are therefore applied to various uses. For example, a nonwoven fabric containing ultrafine fibers having an average fiber diameter of 4 μm or less is excellent in filtration performance, and can be suitably used as a filter for liquids and gases, and also has excellent liquid retention performance. It can also be suitably used as a battery separator.

  As one method for producing a nonwoven fabric containing ultrafine fibers having an average fiber diameter of 4 μm or less, a resin component (sea component) that can be dissolved and removed in a certain solvent is difficult to dissolve and remove in this solvent. Using fiber (so-called sea-island type fiber) in which components (island components) are dispersed, a fiber web is formed by the card method or air-lay method, and then the fibers are entangled by the action of a needle or water flow. There is a method of generating ultrafine fibers made of island components by dissolving and removing the sea components of the sea-island type fibers with a solvent after forming the web. According to this method, it is possible to produce a nonwoven fabric containing ultrafine fibers having an average fiber diameter of 4 μm or less, but the ultrafine fibers are in a bundle and there is not much difference from thick fibers. The liquid retention performance was insufficient.

  For this reason, the applicant of the present application has proposed an “ultrafine fiber-dispersed non-woven fabric in which ultrafine fibers having a fiber diameter of 4 μm or less and a fiber length of 3 mm or less are dispersed, and the adhesion rate of deposits is 0.5 mass% or less” Patent Document 1). When manufacturing this ultra-fine fiber-dispersed non-woven fabric, it is actually an ultra-fine mixture of high-density polyethylene and polypropylene that is manufactured by removing the sea component of sea-island fibers with island components made of high-density polyethylene and polypropylene. It was manufactured by fusing with fibers. Like this ultra-fine mixed fiber, manufacturing an ultra-fine fiber in which two or more types of resins are present is complicated and expensive because it requires advanced technology. Therefore, an inexpensive nonwoven fabric in which ultrafine fibers are dispersed has been awaited.

JP 2002-155458 A (Claim 1, Examples, etc.)

  In view of the present situation as described above, the present invention provides a non-woven fabric excellent in various properties such as filterability and liquid retention performance inherent to the non-woven fabric, in which ultra-fine fibers are dispersed without using ultra-fine mixed fibers, and It aims at providing the manufacturing method.

  The invention according to claim 1 of the present invention is as follows: “An ultrafine single fiber mainly composed of ultrafine single fibers having an average fiber diameter of 4 μm or less and composed of a single resin component, and the ultrafine single fibers are fused with a film-like resin. A nonwoven fabric in which the fibers are not in a bundled state and in which individual ultrafine fibers are dispersed. The nonwoven fabric has a porosity of 50 to 95% and a tensile strength per unit weight of 1.5 N / g or more. "Non-woven fabric."

  The invention according to claim 2 of the present invention is “the nonwoven fabric according to claim 1, wherein the ultrafine single fiber is made of a polyolefin-based resin”.

  The invention according to claim 3 of the present invention is “the nonwoven fabric according to claim 1 or 2, wherein the film-like resin is made of a polyolefin resin”.

  The invention according to claim 4 of the present invention is, “A fiber assembly group mainly composed of an assembly of ultrafine single fibers comprising an average fiber diameter of 4 μm or less and a single resin component, together with a fusible resin powder, A process of dispersing the fusible resin powder while dividing the fiber aggregate group into individual ultrafine single fibers by being ejected into the gas from the nozzle by the action of the compressed gas, and the dispersed ultrafine single fibers and A step of accumulating fusible resin powder to form a powder-containing fiber web, and a step of fusing the fusible resin powder to fuse ultrafine single fibers with the fusible resin powder. And a step of pressing the fused powder-containing fiber web at a temperature lower than the melting point of the fusible resin powder by 50 ° C. or more, and having a porosity of 50 to 95% and a unit weight per unit weight Nonwoven fabric with a strength of 1.5 N / g or more Production method. "Is.

  The invention according to claim 5 of the present invention is “the method for producing a nonwoven fabric according to claim 4, wherein the ultrafine fibers are made of a polyolefin resin”.

  The invention according to claim 6 of the present invention is “the method for producing a nonwoven fabric according to claim 4 or 5, wherein the fusible resin powder is made of a polyolefin resin”.

  The invention according to claim 7 of the present invention is as follows: "The nonwoven fabric according to any one of claims 4 to 6, wherein the average particle size of the fusible resin powder is 0.5 to 50 µm." Manufacturing method. "

  The invention according to claim 8 of the present invention is as described in any one of claims 4 to 7, wherein the melt flow index of the fusible resin powder is 20 to 100 g / 10 min. Manufacturing method of nonwoven fabric. "

  The invention according to claim 9 of the present invention is as follows: “The mass ratio of the fiber assembly group to the fusible resin powder is 1: 0.5 to 2,” The manufacturing method of the nonwoven fabric in any one of 8. ".

  The invention according to claim 10 of the present invention is characterized in that "the heat-resisting resin powder is melted by heat treatment at a temperature 10 ° C or higher than the melting point of the fusible resin powder. It is the manufacturing method of the nonwoven fabric in any one of 4-9.

  In the invention according to claim 1 of the present invention, the ultrafine single fibers are not in a bundle state, and the individually dispersed ultrafine single fibers are fused together by a film-like resin. Excellent characteristics.

  The invention according to claim 2 of the present invention is excellent in chemical resistance because the ultrafine single fiber is made of a polyolefin resin, and can be applied to various applications. For example, it can be suitably used even for alkaline battery separator applications that require alkali resistance.

  The invention according to claim 3 of the present invention is excellent in chemical resistance because the film-like resin is made of a polyolefin resin, and can be applied to various applications. For example, it can be suitably used even for alkaline battery separator applications that require alkali resistance.

  Since the invention according to claim 4 of the present invention is fused with the fusible resin powder and does not use the conventional ultrafine mixed fiber, the nonwoven fabric excellent in various characteristics such as filterability and liquid holding performance can be inexpensively produced. It is a method that can be manufactured.

  In the invention according to claim 5 of the present invention, since the ultrafine fibers are made of a polyolefin resin, it is possible to produce a nonwoven fabric that is excellent in chemical resistance and applicable to various uses.

  In the invention according to claim 6 of the present invention, since the fusible resin powder is made of a polyolefin-based resin, it is possible to produce a nonwoven fabric having excellent chemical resistance and applicable to various uses.

  In the invention according to claim 7 of the present invention, since the average particle diameter of the fusible resin powder is 0.5 to 50 μm, the fusible resin powder is uniformly dispersed and held in the powder-containing fiber web. A nonwoven fabric having a high tensile strength per unit basis weight can be produced. In addition, the wide surface area of the ultrafine single fiber can be effectively utilized.

  The invention according to claim 8 of the present invention is such that the melt flow index of the fusible resin powder is 20 to 100 g / 10 min., And moves to the intersection of the ultrafine single fibers when melted, and a film is formed between the ultrafine single fibers. In order to show the viscosity and fluidity suitable for forming, a non-woven fabric having a high tensile strength per unit weight can be produced.

  In the invention according to claim 9 of the present invention, since the mass ratio of the fiber assembly group and the fusible resin powder is 1: 0.5 to 2, practically sufficient tensile strength per unit basis weight is obtained. And a nonwoven fabric having a high porosity of 50% or more.

  In the invention according to claim 10 of the present invention, since the fusible resin powder is melted by heat treatment at a temperature 10 ° C. higher than the melting point of the fusible resin powder, Viscosity and fluidity suitable for forming a film between the ultrafine fibers can be obtained, and a nonwoven fabric having a high tensile strength per unit basis weight can be produced.

  The non-woven fabric of the present invention has an average fiber diameter of 4 μm or less so that it is excellent in various properties such as filterability and liquid retention performance, and is easy to manufacture and inexpensive, so that it is an ultrafine single fiber composed of a single resin component. Is the subject. The smaller the average fiber diameter of this ultrafine single fiber, the better the various properties such as filterability and liquid retention performance. Therefore, the average fiber diameter of the ultrafine single fiber is preferably 3 μm or less, and preferably 2 μm or less. Is more preferable. On the other hand, the lower limit of the average fiber diameter of the ultrafine fibers is not particularly limited, but about 0.01 μm is appropriate. “Fiber diameter” in this specification refers to the diameter when the cross-sectional shape of the fiber is circular, and when the cross-sectional shape of the fiber is non-circular, the diameter of the circle having the same cross-sectional area and area is used. “Average fiber diameter” means the number average value of the fiber diameters of 500 randomly selected fibers.

  The ultrafine single fiber of the present invention preferably has a fiber length of 3 mm or less so as to be excellent in dispersibility. A more preferable fiber length is 2 mm or less. In addition, although the minimum of the fiber length of an ultrafine single fiber is not specifically limited, about 0.1 mm is suitable. Moreover, it is preferable that it is the ultrafine single fiber cut | disconnected by the length of 3 mm or less so that fiber length may be uniform.

  The single resin component constituting the ultrafine fiber of the present invention can be composed of any component (for example, an organic component or an inorganic component), such as a polyamide-based resin, a polyvinyl alcohol-based resin, a polyvinylidene chloride-based resin, Polyvinyl chloride resin, polyester resin, polyacrylonitrile resin, polyolefin resin (eg, polyethylene resin, polypropylene resin, etc.), polystyrene resin (eg, crystalline polystyrene, amorphous polystyrene, etc.), aromatic An organic component such as a polyamide-based resin or a polyurethane-based resin, or an inorganic component such as glass, carbon, potassium titanate, silicon carbide, silicon nitride, zinc oxide, aluminum borate, or wollastonite can be used. Among these, it is preferable that the ultrafine single fiber is made of a polyolefin-based resin because it is excellent in chemical resistance and can be applied to various uses. For example, even for separators for alkaline batteries that require alkali resistance. It can be preferably used. Examples of the polyolefin resin include high density polyethylene, low density polyethylene, polypropylene, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. Further, when the ultrafine single fiber is made of a polyamide-based resin, it is excellent in hydrophilicity, and can be applied to uses that require hydrophilicity. For example, it can be suitably used for battery separator applications that require high electrolyte solution retention.

  As for the ultrafine single fiber of the present invention, the diameter of each ultrafine single fiber does not substantially change in the fiber axis direction (that is, has substantially the same diameter) so that the texture of the nonwoven fabric is excellent. Is preferred. In this way, the ultrafine single fibers whose diameters are substantially the same in the fiber axis direction in the individual ultrafine single fibers and are not changed, for example, are compounded by extruding the island component by regulating the die into the sea component at the spinneret portion. It can be obtained by removing the sea component of the sea-island fiber produced by the composite spinning method. In general, the sea component of the sea-island fiber produced by the mixed spinning method is removed, or the diameter of the individual ultrafine single fiber is substantially the same in the fiber axis direction and does not change depending on the melt blow method. It is difficult to obtain fibers.

  The ultrafine single fiber of the present invention can be unstretched, but is preferably stretched so as to be excellent in strength. This “stretching” means that the film is stretched by a stretching process different from the spinning process (for example, a stretching process by a stretching yarn threading machine). For example, a fiber obtained by spraying hot air against a melt-extruded resin as in the melt blow method is not stretched because the spinning process and the stretching process are the same. In addition, when the sea-island fiber is drawn, the ultrafine single fiber made of the island component obtained by removing the sea component of the sea-island fiber is in a drawn state.

  Since the nonwoven fabric of the present invention is mainly composed of the above-mentioned ultrafine single fibers (50 mass% or more of the nonwoven fabric constituting fibers), it is excellent in filtration performance and liquid retention performance. The larger the amount of the ultrafine single fiber as described above, the better the performance. Therefore, the ultrafine single fiber preferably accounts for 70 mass% or more of the nonwoven fabric constituting fiber, and accounts for 90 mass% or more. More preferably, it is a 100 mass% extra fine monofilament.

  As the fiber other than the ultrafine single fiber, a thick fiber having an average fiber diameter exceeding 4 μm can be used. When using this thick fiber, the upper limit of the average fiber diameter is not particularly limited, but if the difference in the average fiber diameter from the ultrafine fiber is too large, the texture of the thick fiber tends to be impaired. The upper limit of the average fiber diameter is preferably about 50 μm. The fiber length of the thick fibers is preferably 3 mm or less, and more preferably 2 mm or less so that the dispersibility is excellent. The lower limit of the fiber length of the thick fiber is not particularly limited, but about 0.1 mm is appropriate. Moreover, it is preferable that the thick fiber is cut into a length of 3 mm or less so that it has a uniform length. In addition, a thick fiber can be comprised from the organic component similar to an ultrafine single fiber, or the inorganic component 1 type, or 2 or more types. The thick fiber may be unstretched, but is preferably stretched so as to be excellent in strength.

  The nonwoven fabric of the present invention is a nonwoven fabric in which the individual ultrafine fibers are not dispersed in the bundle state as described above, and therefore has various characteristics such as filtration performance and liquid retention performance mainly composed of the ultrafine fibers. It can be demonstrated. For example, at the stage where the sea component of the sea-island fiber is removed, the ultrafine single fibers composed of the island components are in a bundle state oriented in a certain direction, but the nonwoven fabric of the present invention is divided into individual ultrafine single fibers, They are separated, not in a bundle state, but in a state where the ultrafine fibers cross each other and are dispersed.

  As described above, the non-woven fabric of the present invention is in a state where the individual ultrafine fibers are dispersed, but the ultrafine single fibers in this state are fused with a film-like resin. As described above, since it is fused with a film-like resin, it is excellent in various properties such as filterability and liquid holding performance, and is inexpensive because a conventional ultrafine mixed fiber is not used. As can be seen from FIG. 1 which is an electron micrograph on the surface of the nonwoven fabric of the present invention, this “film-like” means that the resin is in a state of spreading wider than the diameter of the ultrafine single fiber. It is preferable from the viewpoint of strength, filterability, or liquid holding performance that the fusion with the resin is present not only at the intersection of the ultrafine single fibers but also at locations other than the intersection. It is preferable that the fusion with the film-like resin is not on the entire surface of the nonwoven fabric but partially so that voids formed by the ultrafine single fibers can be used effectively. In addition, when the ultrafine single fibers are fused to each other by the fusion of conventional ultrafine mixed fibers, most of the fusion points are at the intersections of the ultrafine single fibers, and the fusion point is determined by the diameter of the ultrafine single fibers. Is not widely spread and is not in the form of a film.

  The film-like resin is not particularly limited as long as the ultrafine fibers can be fused, but is preferably made of a polyolefin resin or a polyamide resin. The former polyolefin resin is excellent in chemical resistance and can be applied to various uses, and the latter polyamide resin is excellent in hydrophilicity and applicable to uses requiring hydrophilicity. More specifically, examples of the polyolefin resin include high density polyethylene, low density polyethylene, polypropylene, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. A nylon 6-nylon 12 copolymer can be mentioned as a polyamide-type resin. In particular, it is preferable that the constituent component of the ultrafine single fiber and the film-like resin component are the same system because they can be a nonwoven fabric having excellent affinity, strong fusing power, and high tensile strength. For example, it is preferable that both the ultrafine single fiber and the film-like resin are made of a polyolefin resin, or that both the ultrafine single fiber and the film-like resin are made of a polyamide resin.

In the nonwoven fabric of the present invention, the ultrafine single fibers as described above are fused with a film-like resin, and the porosity is 50 to 95%. When the porosity is less than 50%, the amount of film-like resin is large, the film-like resin is filled in the void formed by the ultrafine single fibers, and the filterability due to being mainly composed of ultrafine single fibers This is because the characteristics deteriorate. On the other hand, if it exceeds 95%, the shape stability as a nonwoven fabric is poor and difficult to handle, so it is more preferably 92% or less, still more preferably 90% or less, and 85% or less. More preferred is 80% or less. In addition, the porosity of a nonwoven fabric says the value obtained by the following formula.
Porosity = {1-W / (T × d)} × 100
Here, W means the basis weight (g / m ² ), T means the thickness (μm) of the nonwoven fabric, d is the density (g / cm ³ ) of the ultrafine single fiber constituent resin and the film-like resin. It refers to the mass average value of density (g / cm ³ ). For example, when the ultrafine monofilament having a density d ₁ contains a (mass%) in the nonwoven fabric and the film-like resin having a density d ₂ contains b (mass%) in the nonwoven fabric, A value calculated from an equation.
Density (d) = d ₁ × a / 100 + d ₂ × b / 100

  The nonwoven fabric of the present invention is firmly fused with the above-described film-like resin, and the tensile strength per unit basis weight is 1.5 N / g or more so that the nonwoven fabric is easy to handle. Preferably it is 1.8 N / g or more, More preferably, it is 2.0 N / g or more. In addition, “tensile strength” is obtained by collecting a rectangular sample (width: 50 mm, length: 200 mm) from the nonwoven fabric in the warp direction and the transverse direction of the nonwoven fabric, respectively, according to JIS P-8113. Using a tensile tester (UCT-500, manufactured by Orientec Co., Ltd.), the average value in the vertical direction and the horizontal direction, which was measured at a gripping interval of 100 mm and arithmetically averaged the measured values, “Tensile strength per unit basis weight” means a quotient obtained by dividing the tensile strength by basis weight. The basis weight refers to the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard—basis weight measurement method). In addition, the warp direction of the nonwoven fabric means the longitudinal direction, and the weft direction means a direction orthogonal to the warp direction.

Basis weight of the nonwoven fabric of the present invention is not particularly limited in thickness, weight per unit area is preferably a 15~70g / ^{m 2,} and more preferably 20 to 50 g / ^{m 2.} Moreover, it is preferable that it is 0.03-1.6 mm in thickness, and it is more preferable that it is 0.04-1.1 mm. In addition, when the thickness at the time of no load is less than 1 mm, the thickness means a value measured by the method specified in JIS B 7502, that is, a value measured by an outer micrometer at the time of 18 N / cm ² load, Is 1 mm or more, it is a value measured under a pressure of 20 gf / cm ² according to JIS L 1096-8.5.1 (woven fabric thickness).

  The nonwoven fabric of the present invention preferably has an adhesion rate of deposits such as surfactants and pastes of 0.5 mass% or less so that the intended use is not limited. Thus, when the adhesion rate of a deposit | attachment is low, the danger that a deposit | attachment will detach | desorb from a nonwoven fabric is low during use of a nonwoven fabric, and brings about various favorable effects. For example, when a nonwoven fabric is used as a filter, if the filter (nonwoven fabric) itself generates contaminants, the role as a filter is halved. However, if the amount of deposit is small, the possibility that the deposit will be detached is low. Can be suitably used. In addition, when using a nonwoven fabric as a battery separator, deposits may elute during use and adversely affect the chemical reaction, but if the amount of deposits is small, there is a low possibility that the deposits will elute, It can be suitably used as a battery separator. The smaller the adhesion rate of this deposit, the better the effect, so the adhesion rate is preferably 0.3 mass% or less, more preferably 0.1 mass% or less, and 0.08 mass%. More preferably, it is 0.06 mass% or less, more preferably 0.04 mass% or less, and further preferably 0.02 mass% or less.

The adhesion rate of this deposit refers to the percentage of the mass of the deposit relative to the mass of the nonwoven fabric. That is, the value calculated from the following equation.
A = {(ms ₁ + ms ₂ ) / mf} × 100 (1)
[Where A is the adhesion rate (%) of the deposit, ms ₁ is the mass (g) of the hot water extract, ms ₂ is the mass (g) of the hot methanol extract, and mf is the mass (g) of the nonwoven fabric. Meaning each)

The mass of the hot water extract (ms ₁ ) and the mass of the hot methanol extract (ms ₂ ) are values obtained by the following procedure.
(Hot water extract)
1. About 5 g of a nonwoven fabric test piece is taken and the absolute dry mass (g) is obtained.
2. Prepare a water bath, round bottom flask, and Liebig condenser.
3. After putting 100 mL of ultrapure water into the round bottom flask, a Liebig condenser is attached to the top of the round bottom flask. Thereafter, the round bottom flask is immersed in a water bath, the water bath is heated to 100 ° C., the ultrapure water is refluxed, and the temperature of the ultrapure water is set to a temperature of 98 to 100 ° C.
4). After putting a nonwoven fabric test piece in a round bottom flask, the operation which recirculate | refluxs the water vapor | steam which generate | occur | produces is performed for 15 minutes in the state which maintained the temperature of the ultrapure water at 98-100 degreeC, and an extract is extracted.
5. The extracted reflux water is transferred to an evaporating dish whose absolute dry mass (g) has been obtained in advance.
6). After adding 100 mL of ultrapure water to the used round bottom flask, a Liebig condenser is attached to the top of the round bottom flask. Thereafter, the round bottom flask is immersed in a water bath, the water bath is heated to 100 ° C., the ultrapure water is refluxed, and the temperature of the ultrapure water is set to a temperature of 98 to 100 ° C.
7). After the extracted non-woven fabric test piece is put in the round bottom flask again, the operation of refluxing the generated water vapor is carried out for 15 minutes while maintaining the temperature of ultrapure water at 98-100 ° C. Extract.
8). The re-extracted reflux water is transferred to the used evaporating dish, and then evaporated to about 10 mL on a water bath heated to 100 ° C.
9. The evaporating dish is placed in an oven at 150 ° C. to evaporate to dryness, and the absolute dry mass (g) of the extracted matter is measured. Then, the mass (unit: g) of the hot water extract is calculated from the difference between the absolute dry mass of the extraction and the absolute dry mass of the evaporating dish.
10. The operations from 1 to 9 are repeated, and the mass (unit: g) of the hot water extract of another nonwoven fabric test piece is calculated.
11. The arithmetic average value of the mass (unit: g) of the hot water extract of the two nonwoven fabric test pieces is defined as the mass (ms ₁ ) of the hot water extract used in the formula (1).
(Thermal methanol extract)
1. After putting 100 mL of methanol (special grade) into the round bottom flask, a Liebig condenser is attached to the top of the round bottom flask. Then, a round bottom flask is immersed in a water bath, a water bath is heated at 65 degreeC, methanol is refluxed, and the temperature of methanol is made into the temperature 62-64 degreeC.
2. After putting the non-woven fabric test piece used for the measurement of the amount of hot water extract into the round bottom flask, the operation of refluxing the generated steam was carried out for 15 minutes with the temperature of methanol maintained at 62-64 ° C. Then, deposits are extracted.
3. The extracted refluxing methanol is transferred to an evaporating dish whose absolute dry mass (g) has been obtained in advance.
4). After putting 100 mL of methanol (special grade) into the used round bottom flask, a Liebig condenser is attached to the top of the round bottom flask. Then, a round bottom flask is immersed in a water bath, a water bath is heated at 65 degreeC, methanol is refluxed, and the temperature of methanol is made into the temperature 62-64 degreeC.
5. After the extracted non-woven fabric test piece is put in the round bottom flask again, the operation of refluxing the generated steam is performed for 15 minutes in a state where the temperature of methanol is maintained at 62 to 64 ° C., and the deposit is extracted again. To do.
6). The re-extracted refluxing methanol is transferred to the used evaporating dish, and then evaporated to about 10 mL on a water bath heated to 66 ° C.
7). The evaporating dish is placed in an oven at 150 ° C. to evaporate to dryness, and the absolute dry mass (g) of the extracted matter is measured. Then, the mass (unit: g) of the hot methanol extract is calculated from the difference between the extraction absolute dry mass and the absolute dry mass of the evaporating dish.
8). The operations (1) to (7) are repeated, and the mass (unit: g) of the hot methanol extract of the nonwoven fabric test piece after being used for measuring another hot water extract amount is calculated.
9. The arithmetic average value of the mass (unit: g) of the hot methanol extract of the two nonwoven fabric test pieces is defined as the mass (ms ₂ ) of the hot methanol extract used in the formula (1).

  As this hot water extract, there are pastes (for example, acrylamide, sodium polyacrylate, sodium polyalginate, polyethylene oxide, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, polyvinyl alcohol, etc.). There are activators (compounds having both hydrophilic and lipophilic groups, such as nonionic surfactants).

  The nonwoven fabric of the present invention does not need to be a single layer, and can contain two or more layers in which ultrafine fibers are dispersed. When two or more layers in which ultrafine fibers are dispersed are provided, various characteristics can be imparted. For example, filtration performance can be improved by providing two or more layers in which ultrafine single fibers having different abundances of ultrafine single fibers are dispersed. Moreover, the layer (For example, the nonwoven fabric which consists of a fiber in which a fiber diameter exceeds 4 micrometers, such as a net | network, a textile fabric, a knitted fabric, etc.) which does not contain an ultrafine single fiber can also be included.

  The nonwoven fabric of the present invention is excellent in various properties (for example, filtration performance, insulation, liquid retention performance, wiping performance, and / or concealment) due to the inclusion of ultrafine single fibers, and various strengths. Can be used for applications. For example, gas or liquid filters (hepa filters, bag filters, cartridge filters, etc.), deodorizing filter substrates, deodorizing filter substrates, mask substrates (surgical, industrial, etc.), filter presses, surgical drapes It can be used for various applications such as surgical gowns, diaper coverings, battery separators, water absorbent sheets (for humidifiers, etc.).

  The nonwoven fabric of the present invention has, for example, a fiber assembly group mainly composed of an assembly of ultrafine single fibers composed of a single resin component having an average fiber diameter of 4 μm or less, and a function of compressed gas together with a fusible resin powder. The fiber assembly group is divided into individual ultrafine single fibers and dispersed, and the fusible resin powder is dispersed, and the dispersed ultrafine single fibers and the fusible resin. A step of accumulating powder to form a powder-containing fiber web, and a step of fusing the fusible resin powder to fuse the ultrafine single fibers with the fusible resin powder. The powder-containing fiber web can be produced by a step of pressing at a temperature lower by 50 ° C. or more than the melting point of the fusible resin powder.

  More specifically, first, a fiber assembly group mainly composed of an assembly of ultrafine single fibers composed of a single resin component having an average fiber diameter of 4 μm or less as described above, and a fusible resin powder. prepare. In addition, the state of the aggregate of the ultrafine single fibers may be a bundle state in which the ultrafine single fibers are oriented in a certain direction, or may be in a randomly oriented state, but the former is in the bundle state. This is suitable because it is easy to make a nonwoven fabric in which ultrafine single fibers are uniformly dispersed. As described above, this ultrafine single fiber is preferably composed of a polyolefin resin. In addition, the fiber assembly group is a collection of ultrafine single fibers, and the ultrafine single fibers occupy 50 mass% or more of the fiber assembly group, preferably 70 mass% or more, so as to be excellent in various performances. More preferably, it occupies 90 mass% or more, and most preferably occupies 100 mass%. In addition, you may use together the aggregate | assembly of two or more types of very fine single fibers which differ in the point of an average fiber diameter.

  In addition, when the aggregate of ultrafine single fibers is in an entangled state, it becomes difficult to uniformly disperse the ultrafine single fibers even by the action of a compressed gas as described later. It is preferable not to be in a state. For example, ultrafine single fiber aggregates beaten by a beater or the like, which are mechanically splittable fibers, beaten by a beater, or ultrafine single fiber aggregates obtained by flash spinning, etc. It is preferable not to use it because it is in a tangled state.

  On the other hand, since the fusible resin powder is the basis of the above-mentioned non-woven fabric film-like resin, it is preferably made of a polyolefin resin or a polyamide resin as described above. In particular, a fusible resin powder of the same system as the constituent components of the ultrafine fiber is used. As described above, since the ultrafine single fiber is preferably made of a polyolefin resin, the fusible resin powder is also preferably made of a polyolefin resin.

  The average particle size of the fusible resin powder is not particularly limited. However, if the average particle size is too large, the fusible resin powder is melted and solidified to form one film-like resin. The average particle size is 50 μm or less because the area around the wafer becomes wider, it becomes difficult to effectively utilize the large surface area of the ultrafine single fiber, and it becomes difficult to uniformly disperse the fusible resin powder. Preferably, it is 30 μm or less, and more preferably 20 μm or less. On the other hand, if the average particle size of the fusible resin powder is too small, the number of fusing points of the fusible resin powder increases, but the fusible resin powder is melted and solidified. Since the area per fused film-like resin is too small, the force to bond between ultrafine fibers is weak, and it tends to be difficult to obtain sufficient tensile strength, so the average particle size is 0. It is preferably 5 μm or more, and more preferably 1 μm or more. The “average particle diameter” refers to the value of the weight distribution average particle diameter measured by a laser diffraction / scattering particle size distribution analyzer (manufactured by Seishin Enterprise Co., Ltd.).

  Also, if the melt flow index of the fusible resin powder is too low, the melt viscosity and fluidity are poor, it is difficult to move to the intersection of the ultrafine single fibers at the time of melting, and the fusible resin powder melts, When solidifying and fusing, it tends to be difficult to fuse between ultrafine single fibers in the film state, and the tensile strength when bonded under the same temperature condition decreases, so the fusible resin powder The melt flow index of the body is preferably 20 g / 10 min. Or more, and more preferably 30 g / 10 min. Or more. On the other hand, if the melt flow index is too high, the melt viscosity and fluidity are too high, and when the fusible resin powder is fused, it moves to the bottom of the powder-containing fiber web, and the powder-containing fiber web. The upper part of the fiber is not so fused, and the number of fusion points between the ultrafine fibers is reduced, so that the tensile strength is reduced. In extreme cases, a film is formed at the bottom of the nonwoven fabric. Therefore, it is preferably 100 g / 10 min. Or less, and more preferably 90 g / 10 min. The “melt flow index” refers to a value obtained according to JIS K7210 (condition 4, test temperature 190 ° C., test load 21.18 N).

  Such a fiber assembly group and the fusible resin powder are preferably blended so that the mass ratio of the fiber assembly group and the fusible resin powder is 1: 0.5 to 2. . If the amount of the fusible resin powder is less than this, the strength of the nonwoven fabric tends to be insufficient. On the other hand, if the amount of the fusible resin powder is larger than this, the voids formed by ultrafine single fibers or the like It is because it tends to be difficult to sufficiently exhibit the performance of the nonwoven fabric due to being porous, and is more preferably 1: 0.7 to 1.5.

  In addition, it is preferable to use a material having a low adhesion rate of the adhered material as the above-described fiber assembly group and the fusible resin powder because a nonwoven fabric having a low adhesion rate of the adhered material can be produced. The fiber aggregate group and the fusible resin powder having a low adhesion rate of the deposit can be obtained by washing with a solvent such as acetone. In addition, the ultrafine single fiber assembly manufactured by extracting and removing the sea component of the sea-island fiber has a low adhesion rate. Even in this case, the amount of deposits can be further reduced by further washing with a solvent such as acetone after extraction and removal.

  Next, the fiber assembly group and the fusible resin powder as described above are supplied to the nozzle and ejected from the nozzle into the gas by the action of the compressed gas, whereby the fiber assembly group is separated into individual ultrafine fibers. Are divided and dispersed, and the fusible resin powder is dispersed. The flow of compressed gas passing through the nozzle is preferably substantially laminar. In the case of laminar flow, entanglement between the ultrafine single fibers hardly occurs, and the ultrafine single fibers are easily dispersed. In general, when the average fiber diameter of the fibers supplied to the nozzle is as thin as 4 μm or less (especially 2 μm or less) and the rigidity is low (soft), in the case of a bundle of ultrafine single fiber aggregates, or ultrafine single fibers When it is made of an organic component and has low rigidity (soft), it becomes easy to get entangled. However, even in such a case, the entanglement can be suppressed by making the flow of the compressed gas supplied to the nozzle substantially laminar. Note that by using a Venturi tube as the nozzle, the flow of the compressed gas passing through the nozzle can be made substantially laminar.

  The fusible resin powder and the fiber assembly group ejected from the nozzle outlet are collided with a collision member provided in front of the nozzle outlet, so that the ultrafine single fiber and the fusible resin powder Dispersibility can be increased. In particular, when the flow of the compressed gas passing through the nozzle is a laminar flow, it is preferable to provide a collision member so that the fusible resin powder and the ultrafine fibers are easily dispersed.

Any gas can be used as the compressed gas, but it is preferable in terms of work to use air. Further, the compressed gas is divided and dispersed into individual ultrafine single fibers, and the gas passage speed at the nozzle outlet is 100 m / sec or more so that the fusible resin powder can be dispersed. preferable. The “gas passage speed” refers to a value obtained by dividing the flow rate (m ³ / sec) of the gas ejected from the nozzle at 1 atm by the transverse area (m ² ) at the nozzle ejection port. The pressure of the compressed gas is preferably ² kg / cm ² or more so that it can be divided and dispersed into individual ultrafine single fibers and the fusible resin powder can be dispersed.

  Subsequently, the dispersed ultrafine single fibers and the fusible resin powder are accumulated to form a powder-containing fiber web. The accumulation of the ultrafine single fibers and the fusible resin powder can be performed using a collecting member such as a porous roll or a net, for example. Note that the ultrafine single fibers and the fusible resin powder can be naturally dropped and accumulated, or can be accumulated by sucking gas from below the collecting member.

  Next, the fusible resin powder contained in the powder-containing fiber web is melted to fuse the ultrafine single fibers with the fusible resin powder. This step is not particularly limited as long as the fusible resin powder can be melted and fused, but the fusible resin powder melts and loses its powder shape. 10 ° C. or higher than the melting point of the fusible resin powder so that the fusible resin can be agglomerated between the ultrafine single fibers (particularly at the intersection of the ultrafine single fibers) and solidified to be fused in a film state. It is preferable that the fusible resin powder is melted by heat treatment at a high temperature (preferably 20 ° C. or more) and below the melting point of the ultrafine fibers.

  When the fusible resin powder is melted, solidified and fused, if an excessive pressure is applied to the powder-containing fiber web, the fusible resin is formed by ultrafine single fibers or the like. In other words, the void ratio is low, and the effect of having a porous structure cannot be obtained. Therefore, even when melted or pressurized, the fusible resin is not filled into the void. It is preferable to melt under a slight pressure. Examples of the apparatus that can be melted under such conditions include a suction drum dryer, a suction conveyor dryer, and a fusing oven. The “melting point” refers to a melting point obtained by a differential scanning calorimetry (DSC) method defined in JIS K 7121-1987.

  Then, the fused powder-containing fiber web is pressed at a temperature lower by 50 ° C. or more than the melting point of the fusible resin powder, and the nonwoven fabric of the present invention, that is, the porosity is 50 to 95%, and the unit A nonwoven fabric having a tensile strength per unit weight of 1.5 N / g or more can be obtained. By applying pressure in this manner, a desired porosity can be obtained.

  Note that when the fusible resin fused at the time of pressurization is melted again, the fusible resin is filled in the voids formed by ultrafine fibers, etc., so that the melting point of the fusible resin powder And pressurizing at a temperature lower by 50 ° C. or more. Further, the pressure is not particularly limited as long as it is a non-woven fabric having the above-described porosity and tensile strength, and when the pressure is applied between the calender rolls, the linear pressure is 1 to 50 kg / cm. Is preferable, and it is more preferable that it is 2-40 Kg / cm.

  The above is the basic method for producing the nonwoven fabric of the present invention. The fusible resin powder and the fiber assembly group are used as a nozzle so that the fusible resin powder and the ultrafine fibers are easily dispersed uniformly. Before feeding, it is preferable to mix using a mixer or the like.

  In addition, after the powder-containing fiber web is formed and before the fusible resin powder is fused, the powder-containing fiber web is supplied again to the same or different nozzle, so that the fusible resin powder and the ultrafine single fiber are supplied. Can be ejected from a nozzle into a gas and redispersed to form a powder-containing fiber web repeatedly.

  In addition, you may supply a fiber assembly group to a nozzle so that the quantity of the aggregate | assembly of an ultrafine single fiber which differs in the point of an average fiber diameter may change continuously or discontinuously. If it changes in this way, the nonwoven fabric which has the layer or area | region from which an apparent density differs in the thickness direction by the difference in an average fiber diameter can be manufactured. Moreover, it can also supply to a nozzle, changing the compounding quantity of two or more types of fusible resin powders which differ in the point of an average particle diameter and / or a composition continuously or discontinuously.

  In addition, when the dispersed ultrafine single fibers and the fusible resin powder are accumulated to form a powder-containing fiber web, the dispersed ultrafine single fibers and the fusible resin powder are made of materials that do not contain the ultrafine single fibers. For example, a laminate can be formed by accumulating on a net, a woven fabric, a knitted fabric, a non-woven fabric made of fibers having a fiber diameter exceeding 4 μm, and the like. In addition, after forming a nonwoven fabric, the nonwoven fabric can also be integrated with the material which does not contain the above ultrafine single fibers.

  Next, a manufacturing apparatus that can be used for manufacturing the nonwoven fabric of the present invention will be described with reference to FIG. 2, which is a schematic explanatory view of one embodiment of the nonwoven fabric manufacturing apparatus. In addition, the case where the fiber assembly group which consists only of the assembly of an ultrafine single fiber is used is demonstrated.

  First, the fiber aggregate group of the fusible resin powder and the ultrafine single fiber is inserted into a mixing device 10 such as a mixer, and the aggregate group of the ultrafine single fiber is divided into smaller aggregate groups, Split, break or mix into single fibers.

  Next, the assembly group of ultrafine single fibers mixed with the melted resin powder is supplied from the mixing device 10 to the nozzle 30 via the supply pipe 11. For the transfer, an appropriate carrier gas supplied from a carrier gas supply device (not shown) provided in the mixing device 10 can be used. A compressed gas is introduced into the nozzle 30 from the compressed gas inlet 20. Due to the action of the compressed gas, the group of ultrafine single fibers mixed with the fusible resin powder surely moves to the nozzle 30, and vigorously ejects from the nozzle 30 into the gas 40 a in the dispersion chamber 40. Is done. When the gas 40a is ejected, an ultrafine single fiber 70a is generated from the ultrafine single fiber assembly group due to a pressure difference between the nozzle 30 and the gas 40a, and together with the fusible resin powder 70b, Disperse with. Further, by colliding the ultrafine single fibers 70a and the fusible resin powder 70b ejected from the nozzle 30 with the collision member 45, the division of the ultrafine single fiber aggregate group and the dispersion of the ultrafine single fibers 70a are promoted and fused. The dispersion of the conductive resin powder 70b is promoted. The distance between the jet port of the nozzle 30 and the flat part (collision part) of the collision member 45 is preferably 1 to 100 mm, more preferably 5 to 40 mm, still more preferably 5 to 30 mm, still more preferably 10 to 30 mm, and most preferably. Is 10-20 mm.

  The ultrafine single fibers 70a and the fusible resin powder 70b dispersed in the gas 40a in the dispersion chamber 40 descend in the dispersion chamber 40 and are placed on the collecting member 50 made of a net provided at the bottom of the dispersion chamber 40. Accumulation forms a powder-containing fiber web 80. In the manufacturing apparatus used in the present invention, as shown in FIG. 2, a gas suction device 60 can be provided below the collecting member 50 at the bottom of the dispersion chamber 40, and the gas in the dispersion chamber 40 can be provided by the gas suction device 60. It is possible to suck 40a and promote the accumulation of the ultrafine single fibers 70a and the fusible resin powder 70b.

  Next, the endless belt-shaped collecting member 50 conveys the powder-containing fiber web 80 to the heat-sealing device 90, and the heat-bonding device 90 melts the fusible resin powder 70b. By doing so, the ultrafine fibers are fused. Thereafter, the nonwoven fabric 83 of the present invention can be manufactured by applying pressure with a pair of rolls 95a and 95b set at a temperature lower by 50 ° C. or more than the melting point of the fusible resin powder. And this nonwoven fabric 83 is wound up by the winding apparatus 100. FIG.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention.

Example 1
Twenty-five island components made of polypropylene were present in the sea component made of copolymerized polyester, and sea-island fibers (fineness = 1.7 dtex, cut fiber length = 1 mm) obtained by a composite spinning method were prepared. This sea-island type fiber is immersed in a 10 mass% sodium hydroxide aqueous solution to extract and remove the copolymer polyester, which is a sea component, and then air-dried to produce a polypropylene ultrafine fiber (average fiber diameter = 2 μm, cut fiber length = 1 mm). , Melting point: 160 ° C., non-fibrillated, stretched, having substantially the same diameter in the fiber axis direction, and the adhesion rate of deposits is less than 0.02 mass%). A collection was obtained.

  On the other hand, low-density polyethylene resin powder (melting point = 107 ° C., average particle size = 6 μm, melt flow index = 75 g / 10 min.) Was prepared as the fusible resin powder.

Subsequently, the nonwoven fabric was manufactured using the apparatus similar to the nonwoven fabric manufacturing apparatus shown in FIG. That is, a bundle of bundles of ultrafine single fibers and low-density polyethylene resin powder are supplied to a mixer, and after they are unwound and mixed, the cross-sectional shape at the outlet is circular (diameter = 8.5 mm) To the venturi pipe and laminar compressed air (pressure = 5 kg / cm ² ) is introduced from the compressed gas inlet of the venturi pipe, and the mixture is ejected from the venturi pipe into the air (injection of the venturi pipe). The gas passing speed at the outlet = 118 m / s) was made to collide with a collision member provided in front of the jet outlet of the Venturi tube to disperse the polypropylene ultrafine single fiber and the low density polyethylene resin powder. The distance between the outlet of the venturi tube and the collision member was 15 mm.

Next, a base material (wet nonwoven fabric made of polyester fiber having a basis weight of 8 g / m ² ) on which the dispersed polypropylene ultrafine single fiber and the low density polyethylene resin powder are placed on a collection member made of a net. The powder-containing fiber web was formed by accumulating on it. When accumulating, air was sucked (3 m ³ / min) by a suction box installed under the collecting member. In this powder-containing fiber web, the mass ratio of the ultrafine polypropylene fiber and the low-density polyethylene resin powder was 1: 1.

  Next, the wet nonwoven fabric substrate carrying the powder-containing fiber web was heat-treated with a continuous bonding machine (Asahi Textile Machine Industry Co., Ltd., JR series, model JR-600) set at a temperature of 132 ° C. and having a nip opened. And fused with a low density polyethylene resin powder to form a fused fiber web-wet nonwoven fabric composite.

Then, after peeling the fused fiber web from the fused fiber web-wet nonwoven fabric composite, the fused fiber web is a calender roll comprising a steel roll and a cotton roll (temperature: 50 ° C., linear pressure: 25 kg / cm). , A nonwoven fabric having a basis weight of 40 g / m ² , a thickness of 90 μm (using a micrometer), a porosity of 51.7%, and a tensile strength per unit basis weight of 2.2 N / g was produced. In addition, the adhesion rate of the deposit of this nonwoven fabric was less than 0.02 mass%. Moreover, when the electron micrograph on this nonwoven fabric surface was observed (refer FIG. 3), a polypropylene ultrafine fiber is not in a bundle state, it exists in the state in which each individual ultrafine fiber was disperse | distributed, and it is partially coat-like resin. It was fused.

The nonwoven fabric was hydrophilized with a hydrophilization treatment apparatus as shown in FIG. That is, a pair of plate-like stainless steel electrodes 1a, 1b (supporting a polytetrafluoroethylene film (substantially non-porous, thickness: 0.1 mm, size: 200 mm × 250 mm)) as the dielectrics 2a, 2b ( The non-woven fabric 3 is sandwiched between the dielectric plates 2a and 2b of the discharge treatment apparatus arranged so that the dielectrics face each other by utilizing the weight of one flat plate-like stainless steel electrode 1a. . Next, a bipolar sine wave voltage (high frequency power supply 4: AGI-020 (manufactured by Kasuga Denki), output: 800 W, output per unit area: 1.6 W / cm ² , per unit area in air under atmospheric pressure (Energy: 12.7 J / cm ² , frequency: 20 kHz) was applied to both electrodes 1a, 1b for 10 seconds to generate a discharge in the internal voids of the nonwoven fabric 3 and to make it hydrophilic, thereby producing a hydrophilic nonwoven fabric. .

The air permeability, potassium hydroxide retention rate, and potassium hydroxide retention rate of this hydrophilic nonwoven fabric were measured by the following methods. As a result, the air permeability was 2.5 cm ³ / cm ² · sec. The potassium hydroxide retention rate was 270%, and the potassium hydroxide retention rate under pressure was 5.7%. Thus, since it had air permeability and was excellent in the holding | maintenance property of a potassium hydroxide solution, it could be used conveniently as a separator for sealed nickel-hydrogen secondary batteries.
1. Air permeability;
The hydrophilized non-woven fabric was cut, three test pieces of 15 cm × 15 cm were collected, and measured according to JIS L 1096-8.27.1 A method (Fragile method) except that the arithmetic average value was calculated. .
2. Potassium hydroxide retention rate;
(1) After cutting the hydrophilized nonwoven fabric and collecting 3 pieces of 10 cm × 10 cm test pieces, each test piece is left in an environment of temperature 20 ± 2 ° C. and relative humidity 65 ± 5% for 2 hours or more, After reaching the water balance, the mass (M, unit: g) of each test piece was measured (up to the third digit of the decimal point).
(2) Each test piece was immersed in a bath of an aqueous potassium hydroxide solution having a specific gravity of 1.3 (20 ° C.) for 60 minutes to be sufficiently absorbed.
(3) After pulling out each test piece from the bath and suspending each test piece for 10 minutes to remove the unretained potassium hydroxide aqueous solution, the mass (M1, unit: g) of each test piece was measured. (Up to 3 decimal places).
(4) After calculating the potassium hydroxide liquid retention rate (R, unit:%) for each test piece by the following formula, the arithmetic average value of each test piece was calculated to obtain the potassium hydroxide liquid retention rate.
R = {(M1-M) / M} × 100
3. Liquid retention ratio under pressure of potassium hydroxide;
(1) After collecting three round test pieces with a diameter of 30 mm in the width direction of the hydrophilized nonwoven fabric, leave the test pieces in an environment of temperature 20 ± 2 ° C. and relative humidity 65 ± 5% for 2 hours or more. Then, after reaching the water balance, the mass (M2, unit: g) of each test piece was measured (up to the fourth digit of the decimal point).
(2) Each test piece was sufficiently absorbed by being immersed in a potassium hydroxide aqueous solution having a specific gravity of 1.3 (20 ° C.) under a reduced pressure of −750 mmHg or less for 10 minutes.
(3) Each test piece was pulled up from the bath, and both sides of each test piece were sandwiched between three filter papers (ADVANTEC, TYPE2), and then a pressure of 4.52 MPa was applied for 30 seconds with a pressurizer.
(4) After pressurization, each test piece was quickly taken out, and the mass (M3, unit: g) of each test piece was measured (up to the fourth decimal place).
(5) After calculating the liquid retention ratio (Rp, unit:%) of potassium hydroxide under the following formula for each test piece, calculate the arithmetic average value of each test piece (up to the first digit of the decimal point), It was set as the liquid retention rate under pressure of potassium hydroxide.
Rp = {(M3-M2) / M2} × 100

(Examples 2-7 and Comparative Examples 1-6)
The same polypropylene ultrafine fiber as in Example 1 (average fiber diameter = 2 μm, cut fiber length = 1 mm, melting point: 160 ° C., unfibrillated, stretched, having substantially the same diameter in the fiber axis direction. Using an aggregate of ultrafine single fibers in the form of bundles (attachment rate of kimono = less than 0.02 mass%) and low density polyethylene resin powder as shown in Table 1, the same operation as in Example 1 was performed. A powder-containing fiber web containing ultrafine single fibers and low-density polyethylene resin powder was formed at a mass ratio as shown in Table 1.

  Next, the wet nonwoven fabric substrate carrying the powder-containing fiber web is heat-treated under the temperature conditions as shown in Table 2, and is fused with a low density polyethylene resin powder to form a fused fiber web-wet nonwoven fabric composite. A material was formed. In addition, the same apparatus as Example 1 was used for the heat processing of Example 2-Comparative Example 4, and oven was used for the heat processing of Comparative Examples 5 and 6.

  Then, after the fused fiber web is peeled from the fused fiber web-wet nonwoven fabric composite, the fused fiber web is added under the conditions shown in Table 2 using a calender roll comprising a steel roll and a cotton roll. The nonwoven fabric which has the fabric weight as shown in Table 2, the thickness (all use micrometer), the porosity, and the tensile strength per unit basis weight as shown in Table 2 was manufactured. In addition, the adhesion rate of the deposit | attachment of any nonwoven fabric was also less than 0.02 mass%.

  When the electron micrographs on the nonwoven fabric surfaces of Examples 2 to 7 were observed, the polypropylene ultrafine fibers were not in a bundle state, but the individual ultrafine fibers were in a dispersed state, and were partially coated with a film-like resin. It was fused. In addition, in the nonwoven fabric of Example 7, the film-like resin is in a state exposed on the nonwoven fabric surface, and the area per one film-like resin is the film-like resin 1 of the nonwoven fabric of Examples 1 to 6. The area was wider than the area per piece.

  Moreover, when the electron micrograph in the nonwoven fabric surface of Comparative Examples 1 to 4 was observed, the polypropylene ultrafine fibers were not in a bundle state, but the individual ultrafine fibers were in a dispersed state, and were partially film-like. Although it was fused by the resin, the tensile strength did not reach 1.5 N / g, and the strength was weak.

  When an electron micrograph on the nonwoven fabric surface of Comparative Example 5 was observed, the polypropylene ultrafine single fibers were not in a bundled state, and the individual ultrafine single fibers were in a dispersed state, but the low density polyethylene resin powder was in a particle shape. There was almost no fusion due to the film-like resin, and the tensile strength was extremely weak.

  When the electron micrograph on the nonwoven fabric surface of Comparative Example 6 was observed, the polypropylene ultrafine fibers were not in a bundled state, and the individual ultrafine single fibers were in a dispersed state, but the low density polyethylene resin powder was fused. However, in some places, a continuous film with holes was formed to fill the voids formed by the ultrafine single fibers, the porosity was low, and the large surface area of the ultrafine single fibers could not be used effectively.

Electron micrograph on the surface of the nonwoven fabric of the present invention Schematic explanatory view of one embodiment of the nonwoven fabric manufacturing apparatus The electron micrograph in the surface of the nonwoven fabric of Example 1 of this invention Schematic cross-sectional view of the hydrophilic treatment apparatus used in Example 1

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Electrode 2a, 2b Dielectric material 3 Nonwoven fabric 4 High frequency power supply 10 Mixing device 11 Supply pipe 20 Compressed gas inlet 30 Nozzle 40 Dispersion chamber 45 Colliding member 50 Collection member 60 Gas suction device 70a Extra fine single fiber 70b Fusible resin Powder 80 Powder-containing fiber web 83 Non-woven fabric 90 Heat fusion device 95a, 95b Roll 100 Winding device

Claims (10)

An ultrafine single fiber composed mainly of ultrafine single fibers composed of a single resin component with an average fiber diameter of 4 μm or less, and the ultrafine single fibers fused together by a film-like resin. Is a nonwoven fabric in which the porosity of the nonwoven fabric is 50 to 95%, and the tensile strength per unit weight is 1.5 N / g or more. The nonwoven fabric according to claim 1, wherein the ultrafine single fiber is made of a polyolefin resin. The nonwoven fabric according to claim 1 or 2, wherein the film-like resin is made of a polyolefin resin. A fiber assembly group mainly composed of an assembly of ultrafine single fibers composed of a single resin component having an average fiber diameter of 4 μm or less is jetted into a gas from a nozzle together with a fusible resin powder by the action of a compressed gas. And dividing the fiber assembly group into individual ultrafine fibers and dispersing them, and dispersing the fusible resin powder,
A step of accumulating dispersed ultrafine single fibers and fusible resin powder to form a powder-containing fiber web;
And fusing the fusible resin powder to fuse the ultrafine single fibers with the fusible resin powder,
Pressurizing the fused powder-containing fiber web at a temperature lower by 50 ° C. or more than the melting point of the fusible resin powder;
And a method for producing a nonwoven fabric having a porosity of 50 to 95% and a tensile strength per unit weight of 1.5 N / g or more. The method for producing a nonwoven fabric according to claim 4, wherein the ultrafine fibers are made of a polyolefin resin. The method for producing a nonwoven fabric according to claim 4 or 5, wherein the fusible resin powder is made of a polyolefin resin. The method for producing a nonwoven fabric according to any one of claims 4 to 6, wherein an average particle diameter of the fusible resin powder is 0.5 to 50 µm. The method for producing a nonwoven fabric according to any one of claims 4 to 7, wherein the melt flow index of the fusible resin powder is 20 to 100 g / 10 min. The method for producing a nonwoven fabric according to any one of claims 4 to 8, wherein a mass ratio of the fiber assembly group and the fusible resin powder is 1: 0.5 to 2. The non-woven fabric according to any one of claims 4 to 9, wherein the fusible resin powder is melted by heat treatment at a temperature 10 ° C or higher than the melting point of the fusible resin powder. Manufacturing method.

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