Manufacturing method of fibrous nonwoven fabric

Abstract

To provide a method of manufacturing a fiber non-woven fabric which can manufacture a filter which superior in the efficacy of capturing, without complicating the device configuration.SOLUTION: The method of manufacturing the fiber non-woven fabric according to the present invention comprising, by the melt blown method, the steps of: discharging the thermoplastic resin melted from the nozzle plate along with the heated gas and extending the thermoplastic resin by the heated gas to form the fiber-shaped resin; and capturing the fiber-shaped resin in the web-shape. The flow rate of the heated gas is 150 to 1000 Nm3 / hour / m. Upon supposing that the temperature of the heated gas is Ta (degree Celsius), the temperature of the thermoplastic resin melted is Tp (degree Celsius), the temperature for crystallization of the thermoplastic resin is Tc (degree Celsius) and the melting point of the thermoplastic resin is Tm (degree Celsius), the method is performed such that the discharging of the heated gas complies with the formula (1): Ta is larger than Tc and is identical to or smaller than Tm+150 and the formula (2): Tp-Pa is identical to or larger than 80 and is identical to or smaller than 190.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a fibrous nonwoven fabric. [Background technology]

[0002] Fibre nonwoven fabrics are widely used as air filters, sanitary materials, absorbent materials, packaging materials, etc. The smaller the fiber diameter of such fibrous nonwoven fabrics, the more excellent their various performances, such as separation performance, liquid retention function, wiping performance, concealment performance, and flexibility. Therefore, various methods for producing fibrous nonwoven fabrics with small fiber diameters have been proposed.

[0003] Among these, the meltblown method tends to produce a fibrous nonwoven fabric with a small fiber diameter because heated air (heated compressed air) is blown onto the extruded molten resin to stretch (or pull) the molten resin.

[0004] As a method for producing a fibrous nonwoven fabric by the meltblown method, for example, a method has been proposed which includes the steps of: 1) discharging molten resin from a die (spinneret) together with heated air and stretching the molten resin with the heated air to obtain ultrafine fibers; 2) collecting the obtained ultrafine fibers on a suction roll or suction belt; and 3) suctioning and removing floating fibers adhering to the collected ultrafine fibers using a suction hood arranged along the outer circumferential surface of the suction roll or suction belt (for example, Patent Document 1).

[0005] It is also shown that in step 1, the temperature of the heated air should be the same as or higher than the temperature of the die (temperature of the molten resin).It is also said that by setting the distance d1 between the die and the suction roll or suction belt within a range that does not cause vibration of the molten resin, it is possible to suppress thread breakage and fiber entanglement, and by setting the distance d2 between the suction roll or suction belt and the suction hood within a range that allows floating fibers to be sucked and removed, it is possible to reduce variation in fiber diameter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Republished Patent No. 2012 / 102398 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the manufacturing method of Patent Document 1 requires the placement of a suction hood and the control of the airflow caused by the suction hood, which has the problem of making the device configuration complex.

[0008] The present invention has been made in view of the above-mentioned problems, and has an object to provide a method for producing a fibrous nonwoven fabric that can produce a fibrous nonwoven fabric from which a filter having excellent collection efficiency can be manufactured without complicating the device configuration. [Means for solving the problem]

[0009] The present invention relates to the following method for producing a fibrous nonwoven fabric. <1> A process of discharging a molten thermoplastic resin together with a heated gas from a spinneret by a melt-blown method, and stretching the thermoplastic resin with the heated gas to form a fibrous resin; and a process of collecting the fibrous resin in a web form. Including, The flow rate of the heating gas is set to 150 to 1000 Nm 3 / hour / m, When the temperature of the heated gas is Ta (°C), the temperature of the molten thermoplastic resin is Tp (°C), the crystallization temperature of the thermoplastic resin is Tc (°C), and the melting point of the thermoplastic resin is Tm (°C), the heated gas is discharged so as to satisfy the following formulas (1) and (2): Method for manufacturing fibrous nonwoven fabric. Formula (1) Tc <Ta≦Tm+150 Formula (2) 80≦Tp-Ta≦190 <2> does not include a step of blowing a cooling gas of 30°C or less onto the discharged thermoplastic resin, <1> A method for producing the fibrous nonwoven fabric described in <3> The heated gas is discharged so as to further satisfy the following formula (1)': <1> or <2> A method for producing the fibrous nonwoven fabric described in Formula (1)' Tm-30≦Ta≦Tm+150 <4> The flow rate of the heating gas is set to 250 to 850 Nm 3 / h / m, <1> ~ <3> 10. A method for producing the fibrous nonwoven fabric according to claim 9. <5> The thermoplastic resin is a propylene-based polymer. <1> ~ <4> 10. A method for producing the fibrous nonwoven fabric according to claim 9. <6> The fibrous nonwoven fabric has an average fiber diameter of 2.0 μm or less and a coefficient of variation of fiber diameter of 1.0 or less. <1> ~ <5> 10. A method for producing the fibrous nonwoven fabric according to claim 9. [Effects of the Invention]

[0010] According to the present invention, a method for producing a fibrous nonwoven fabric can be provided, which can produce a fibrous nonwoven fabric capable of producing a filter having excellent collection efficiency without complicating the device configuration. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a fibrous nonwoven fabric manufacturing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0012] As described above, conventionally, the temperature of the heated gas (Ta) is generally set to be equal to or higher than the temperature of the molten thermoplastic resin (the temperature of the spinneret) (Tp). In contrast, the present inventors have discovered that by setting the temperature of the heated gas (Ta) lower than the temperature of the molten thermoplastic resin (Tp) by a certain amount or more and controlling the flow rate of the heated gas within a predetermined range, it is possible to maintain a small fiber diameter while reducing the variation in fiber diameter, thereby achieving excellent collection efficiency when used as a filter.

[0013] Specifically, the heated gas is sprayed so as to satisfy the following formulas (1) and (2), and the flow rate of the heated gas is set to 150 to 1000 Nm 3 It is effective to keep it within the range of / hour / m. Formula (1) Tc <Ta≦Tm+150 Formula (2) 80≦Tp-Ta≦190

[0014] The reason for this is not clear, but is presumed to be as follows. That is, when Tp - Ta (ΔT) is 80°C or higher, the resin extruded from the spinneret is cooled moderately rapidly and therefore tends to solidify moderately. As a result, the resin extruded in the form of fibers is less likely to fuse together, thereby reducing the variation in fiber diameter. On the other hand, when ΔT is 190°C or lower and the temperature (Ta) of the heated gas satisfies the range of formula (1), the resin extruded from the spinneret is not cooled too rapidly, and the drawing (pulling) effect of the heated gas is less likely to be impaired. As a result, insufficient drawing by the heated gas can be suppressed, and an increase in fiber diameter can be suppressed. On the other hand, if the flow rate of the heated gas is not controlled in order to rapidly cool the fibers, the drawing effect may not be fully exerted, resulting in an increase in fiber diameter, or the fibers may fuse with adjacent fibers immediately after discharge, resulting in large variations in fiber diameter. In other words, by spraying heated gas at a predetermined flow rate so as to satisfy formulas (1) and (2), a fibrous nonwoven fabric with small fiber diameters and little variation in fiber diameter can be obtained. Furthermore, when such a fibrous nonwoven fabric is used as a filter, it has excellent collection efficiency.

[0015] Therefore, in the method for producing a fibrous nonwoven fabric of the present invention, there is no need to perform an additional step of spraying a cooling gas of 30°C or less onto the discharged resin to achieve a rapid cooling effect. In other words, there is no need to spray gas in multiple stages, but rather it can be done in one stage. Furthermore, there is no need to control the airflow using a suction hood as in Patent Document 1. Therefore, the method for producing a fibrous nonwoven fabric of the present invention can be realized with a relatively simple device configuration.

[0016] 1. Manufacturing method of fibrous nonwoven fabric The method for producing a fibrous nonwoven fabric of the present invention includes: 1) a step of discharging a molten thermoplastic resin together with heated gas from a spinneret by a melt-blown method to form a fibrous resin; and 2) a step of collecting the fibrous resin in the form of a web.

[0017] Regarding step 1) In step 1), a fibrous resin is obtained by discharging a molten thermoplastic resin together with heated gas from a spinneret using the melt-blown method.

[0018] The thermoplastic resin to be used is not particularly limited, and examples thereof include homo- or copolymers of α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene (e.g., high-pressure low-density polyethylene, linear low-density polyethylene (LLDPE), high-density polyethylene, polypropylene (propylene homopolymer), polypropylene random copolymer, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene random copolymer, ethylene-1-butene random copolymer, propylene-1-butene random copolymer, etc.), polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyamides (nylon-6, nylon-66, polymethaxylene adipamide, etc.), polyvinyl chloride, polyimide, ethylene-vinyl acetate copolymer, polyacrylonitrile, polycarbonate, polystyrene, ionomers, and mixtures thereof.

[0019] Among these, high-pressure low-density polyethylene, linear low-density polyethylene (LLDPE), high-density polyethylene, propylene-based polymers (such as polypropylene and polypropylene random copolymers), polyethylene terephthalate, and polyamide are preferred, and propylene-based polymers are preferred from the viewpoints of excellent spinnability, mechanical strength, and chemical resistance.

[0020] The melting point (Tm) of the propylene polymer is 155°C or higher, preferably in the range of 157 to 165°C. The propylene polymer may be a propylene homopolymer or a copolymer of propylene with a very small amount of one or more α-olefins. The α-olefin to be copolymerized is one or more α-olefins having 2 or more carbon atoms, preferably 2 to 8 carbon atoms, and specific examples include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene. Among these, a propylene homopolymer is particularly preferred.

[0021] The melt flow rate (MFR: ASTM D-1238, 230°C, load 2160 g) of the propylene polymer may be such that it is melt spinnable, and is usually preferably 500 to 3000 g / 10 min, more preferably 1000 to 2500 g / 10 min. When the MFR of the propylene polymer is in the above range, it is easy to obtain a nonwoven fabric having good spinnability and good mechanical strength such as tensile strength.

[0022] The melt-blown method is a method in which, when a molten thermoplastic resin is extruded from a spinneret in the form of fibers, heated gas is applied to both sides of the molten extruded material (the extruded thermoplastic resin), and the diameter of the extruded material is reduced by accompanying the heated gas. Specifically, for example, a raw material thermoplastic resin (e.g., a propylene homopolymer) is melted using an extruder or the like. The molten thermoplastic resin is introduced into a spinneret connected to the tip of the extruder and extruded in the form of fibers from the spinning nozzle of the spinneret. The extruded thermoplastic resin in the form of fibers is exposed to heated gas ejected from the gas nozzle of the spinneret, and the resin is stretched by the heated gas, thereby thinning the resin. The heated gas is not particularly limited, but may be, for example, air.

[0023] As described above, from the viewpoint of reducing the diameter of the fibers constituting the fibrous nonwoven fabric and reducing the variation in fiber diameter (narrowing the fiber diameter distribution), when the crystallization temperature of the thermoplastic resin is Tc (°C) and the melting point of the thermoplastic resin is Tm (°C), the heated gas is blown so as to satisfy the following formulas (1) and (2): Formula (1) Tc <Ta≦Tm+150 Formula (2) 80≦Tp-Ta≦190

[0024] As shown in formula (1), when the temperature (Ta) of the heated gas is higher than the crystallization temperature (Tc), poor drawing due to solidification of the discharged thermoplastic resin can be suppressed, and an increase in fiber diameter can be suppressed. When the temperature (Ta) of the heated gas is Tm+150°C or less, not only is it easy to adjust ΔT (Tp-Ta) within the above range, but also it is possible to suppress fiber breakage due to a decrease in the melt viscosity of the discharged thermoplastic resin. In particular, from the viewpoint of sufficiently stretching the discharged thermoplastic resin and making it easier to obtain fibers with a smaller fiber diameter, it is more preferable that the temperature (Ta) of the heated gas satisfies the following formula (1)'. Formula (1)' Tm-30≦Ta≦Tm+150

[0025] Furthermore, as shown in formula (2), the temperature (Ta) of the heated gas is set to be lower than the temperature (Tp) of the molten thermoplastic resin by a certain amount. Specifically, by setting Tp - Ta (ΔT) to 80°C or higher, a moderate quenching effect can be achieved, that is, the discharged fibrous thermoplastic resin can be appropriately solidified. This can suppress fusion between the discharged fibrous thermoplastic resins, thereby reducing the variation in fiber diameter. On the other hand, by setting ΔT to 190°C or lower, poor drawing due to excessive solidification of the discharged fibrous thermoplastic resin due to excessive quenching can be suppressed, and an increase in fiber diameter can be suppressed. ΔT is preferably 80 to 150°C, and more preferably 90 to 140°C.

[0026] The temperature (Ta) of the heating gas may be selected depending on the resin so as to satisfy the above-mentioned formula (1), and preferably so as to further satisfy formula (1)'. When the thermoplastic resin is a propylene-based polymer, the temperature (Ta) of the heating gas is, for example, preferably 130 to 310°C, more preferably 140 to 240°C, and even more preferably 150 to 220°C.

[0027] The temperature (Tp) of the molten thermoplastic resin may be selected depending on the resin so as to satisfy the above-mentioned formula (2). When the thermoplastic resin is a propylene-based polymer, the temperature (Tp) of the molten thermoplastic resin is, for example, preferably 210 to 400°C, and more preferably 220 to 350°C.

[0028] The temperature (Tp) of the molten thermoplastic resin can be measured as the set temperature of the spinneret (die). The temperature (Ta) of the heated gas can be measured as the temperature of the heated gas immediately after it is discharged from the spinneret (die). Specifically, the temperature (Ta) of the heated gas can be measured as the temperature of the heated gas at the opening of the gas nozzle of the spinneret (die). The temperature (Ta) of the heated gas can be adjusted, for example, by measuring the temperature (Ta) of the heated gas at the opening of the gas nozzle of the spinneret (die) and adjusting the supply temperature of the heated gas so that the temperature (Ta) of the heated gas at the opening of the gas nozzle is a predetermined temperature; or by preparing data (a calibration curve) showing the relationship between the temperature (Ta) of the heated gas at the opening of the gas nozzle and the supply temperature of the heated gas under predetermined conditions (e.g., die temperature, heated gas flow rate), and adjusting the supply temperature of the heated gas based on the data so that the temperature (Ta) of the heated gas at the opening of the gas nozzle is a predetermined temperature.

[0029] The crystallization temperature (Tc) and melting point (Tm) of a thermoplastic resin can be measured using DSC (differential scanning calorimetry). Specifically, using a PerkinElmer DSC Pyris1 or SII NanoTechnology DSC7020 differential scanning calorimeter (DSC), under a nitrogen atmosphere (20 mL / min), a sample (approximately 5 mg) was heated to a temperature set for each resin (230 °C for propylene-based polymers), held at that temperature for 3 min, then cooled to 30 °C at 10 °C / min, held at 30 °C for 1 min, and then heated to the target temperature at 10 °C / min. The melting point (Tm) was calculated from the apex of the crystalline melting peak during the heating process, and the crystallization temperature (Tc) was calculated from the apex of the crystallization peak during the cooling process. Note that if multiple crystalline melting peaks are observed, the higher peak is taken as the melting point (Tm).

[0030] The discharge rate of the thermoplastic resin per spinning nozzle of the spinneret is usually 0.05 to 3.0 g / min, preferably 0.1 to 2.0 g / min. If the discharge rate is 0.05 g / min or more, not only is productivity less likely to be impaired, but fiber breakage is also easily suppressed. If the discharge rate is 3.0 g / min or less, the diameter of the resulting fiber is easily made sufficiently small.

[0031] As mentioned above, the flow rate of the heated gas is set to 150 to 1000 Nm3 in order to reduce the diameter of the fibers constituting the fibrous nonwoven fabric and to reduce the variation in the diameter of the fibers (to narrow the fiber diameter distribution). 3 / hour / m. The flow rate of the heating gas is 150Nm 3 When the flow rate of the heated gas is 1000 Nm / hr / m or more, the extruded thermoplastic resin can be sufficiently stretched and the fiber diameter can be sufficiently reduced. 3 / hr / m or less, it is easy to suppress the increase in the variation in fiber diameter due to the turbulence of the air flow. From the same point of view, the flow rate of the heating gas is 250 to 850 Nm 3 / h / m is preferred.

[0032] The type of heating gas is not particularly limited, and examples thereof include gases inert to the molten resin, such as air, carbon dioxide gas, nitrogen gas, etc. Among these, air is preferred from the viewpoint of economy.

[0033] The extruded thermoplastic resin is stretched by heated gas to obtain a fibrous resin thinned to preferably 2.0 μm or less, more preferably 0.1 μm to 2.0 μm.

[0034] In the method for producing a fibrous nonwoven fabric of the present invention, there is no need to perform an additional step of spraying a cooling gas at 30°C or less onto the discharged resin to achieve a rapid cooling effect. In other words, there is no need to spray gas in multiple stages, but it can be done in one stage. Therefore, according to the method for producing a fibrous nonwoven fabric of the present invention, an attachment for spraying cooling gas can be omitted.

[0035] Furthermore, in the method for producing a fibrous nonwoven fabric of the present invention, it is not necessary to control the airflow with a suction hood in order to obtain a fibrous nonwoven fabric having a small fiber diameter and little variation in fiber diameter, and therefore, the method for producing a fibrous nonwoven fabric of the present invention can omit an attachment called a suction hood.

[0036] Regarding step 2) In step 2), the resulting fibrous resin is collected in the form of a web on a collector.

[0037] Examples of the collector include a perforated belt and a perforated drum. The collection of the fibrous resin may be promoted by, for example, sucking air from the back side of the collector.

[0038] Alternatively, the finely divided fibers may be collected on a desired substrate pre-installed on a collector. Examples of the substrate include other nonwoven fabrics such as meltblown nonwoven fabrics, spunbond nonwoven fabrics, needle-punched and spunlace nonwoven fabrics, woven fabrics, knitted fabrics, and paper. This process can also produce ultrafine fiber nonwoven fabric laminates for use in high-performance filters, wipers, and the like.

[0039] 2. Fiber nonwoven fabric manufacturing equipment The fibrous nonwoven fabric manufacturing apparatus used in the method for manufacturing the fibrous nonwoven fabric of the present invention will be described with reference to the drawings.

[0040] 1 is a schematic diagram showing an example of the configuration of a fibrous nonwoven fabric manufacturing apparatus 10. As shown in FIG. 1, the fibrous nonwoven fabric manufacturing apparatus 10 has an extruder 20, a die (spinneret) 30, and a collection mechanism 40.

[0041] The extruder 20 has a hopper 21 and a compression section 22. The extruder 20 melts the solid thermoplastic resin introduced into the hopper 21 in the compression section 22. The extruder 20 may be a single-screw extruder or a multi-screw extruder.

[0042] The die (spinneret) 30 is disposed at the tip of the extruder 20. The die 30 has a plurality of spinning nozzles 31 and a plurality of air nozzles 32.

[0043] The spinning nozzles 31 are usually arranged in a row. The spinning nozzles 31 introduce the molten thermoplastic resin conveyed from the extruder 20 and extrude the resin in the form of fibers from the nozzle openings. The diameter of the spinning nozzle may be, for example, 0.05 to 0.80 mm. The temperature (Tp) of the molten thermoplastic resin can be adjusted by the temperature setting of the die 30.

[0044] The gas nozzles (air nozzles) 32 are arranged near the nozzle openings of the spinning nozzles 31, specifically, on both sides of the row of the spinning nozzles 31. The gas nozzles 32 inject heated gas (heated compressed gas) near the openings of the spinning nozzles 31. As shown in Fig. 1, the gas nozzles 32 inject heated gas onto the thermoplastic resin immediately after it has been discharged from the openings of the spinning nozzles 31.

[0045] The heating gas supplied to the gas nozzle 32 is supplied from a gas heating device 50. The temperature (Ta) of the heating gas can be adjusted by a heating temperature adjusting means (not shown) attached to the gas heating device 50.

[0046] The collecting mechanism 40 has a perforated belt (collector) 41, rollers 42 and 42 that support and transport the perforated belt 41, and an air suction unit 43 that is arranged on the back side of the collecting surface of the perforated belt 41. The air suction unit 43 is connected to a blower 44. The collecting mechanism 40 then collects the obtained fibrous resin on the moving perforated belt 41.

[0047] According to this configuration, the resin melted in the extruder 20 is introduced into the spinning nozzle 31 of the die (spinneret) 30 and discharged from the opening of the spinning nozzle 31. Meanwhile, heated gas is sprayed from the gas nozzle 32 toward the vicinity of the opening of the spinning nozzle 31. The discharged resin is then stretched and thinned by the heated gas to become a fibrous resin.

[0048] The temperature (Ta) of the heated gas is adjusted to satisfy the above-mentioned formulas (1) and (2). As a result, the molten resin is appropriately quenched and stretched. The flow rate of the heated gas is adjusted to satisfy the above-mentioned range. As a result, the molten resin can be sufficiently stretched even if it is quenched. Therefore, the fiber diameter can be reduced while the variation in fiber diameter can be reduced. The discharged fibrous resin is collected on the perforated belt 41 and becomes a fibrous nonwoven fabric.

[0049] 3. Fiber nonwoven fabric As described above, the fibrous nonwoven fabric obtained by the method for producing a fibrous nonwoven fabric of the present invention is characterized by 1) a small average fiber diameter and 2) little variation in fiber diameter (small coefficient of variation (CV value) of fiber diameter).

[0050] The average fiber diameter of the fibers constituting the fibrous nonwoven fabric is usually preferably 2.0 μm or less, and more preferably 0.1 to 2.0 μm. The average fiber diameter of the fibers constituting the fibrous nonwoven fabric can be measured by arbitrarily selecting 1000 nonwoven fabric fibers from an electron microscope photograph (magnification 1000x) of the fibrous nonwoven fabric, measuring the diameters of the selected fibers, and calculating the average.

[0051] The coefficient of variation (CV value) of the fiber diameter of the fibers constituting the fibrous nonwoven fabric is preferably 1.0 or less, more preferably 0.85 or less. The CV value can be calculated by dividing the standard deviation (Dp) of the measurement results of the average fiber diameter by the average fiber diameter (Da) (see the following formula). CV value = standard deviation (Dp) / average fiber diameter (Da)

[0052] To reduce the average fiber diameter of the fibers constituting the fibrous nonwoven fabric as described above, it is preferable to set the flow rate of the heated gas at a certain level or higher, it is preferable to reduce the amount of molten thermoplastic resin discharged, it is preferable to keep the temperature (Tp) of the molten thermoplastic resin high, and it is preferable to keep the temperature (Ta) of the heated gas not too low, as described above. To reduce the coefficient of variation (CV value) of the fibers constituting the fibrous nonwoven fabric as described above, it is preferable to set the difference ΔT (=Tp-Ta) between the temperature (Tp) of the molten thermoplastic resin and the temperature (Ta) of the heated gas at a certain level or higher, as described above, it is preferable to keep the flow rate of the heated gas not too high.

[0053] Fiber nonwoven fabric hole weight 10g / m 2 The average pore size measured by the method is preferably 0.01 to 10.0 μm, and more preferably 0.1 to 3.0 μm. If the average pore size is 0.01 μm or more, when the fibrous nonwoven fabric is used as a filter, the pressure loss will not be too high and a decrease in flow rate will be easily suppressed. The average pore size of the fibrous nonwoven fabric can be measured by the bubble point method. Specifically, a test piece of the fibrous nonwoven fabric is impregnated with a fluorine-based inert liquid, and the pore size is measured using a capillary flow porometer.

[0054] The basis weight of the fibrous nonwoven fabric can be determined appropriately depending on the application, but is usually 1 to 200 g / m 2 It is preferable that the density is 2 to 150 g / m 2 It is more preferable that:

[0055] The porosity of the fibrous nonwoven fabric is generally preferably 40% or more, more preferably 60 to 95%. Furthermore, it is preferable that the volume of parts of the fibrous nonwoven fabric having a porosity of 40% or more occupies 90% or more, and it is more preferable that almost all parts have a porosity of 40% or more.

[0056] The fibrous nonwoven fabric may be used as a single layer nonwoven fabric or may be used as a nonwoven fabric constituting at least one layer of a laminate. Examples of other layers constituting the laminate nonwoven fabric include other nonwoven fabrics such as conventional meltblown nonwoven fabrics, spunbond nonwoven fabrics, needlepunched and spunlaced nonwoven fabrics, as well as woven fabrics, knitted fabrics, paper, etc.

[0057] The fibrous nonwoven fabric can be preferably used as a filter such as a gas filter (air filter) or a liquid filter. As described above, the fibrous nonwoven fabric of the present invention has a small fiber diameter and little variation in fiber diameter, so that relatively large pores (defective portions) are unlikely to form between the fibers. As a result, the filtration performance is high and the fabric is preferably used as a high-performance filter. [Example]

[0058] The present invention will be described below with reference to examples, which should not be construed as limiting the scope of the present invention.

[0059] [Example 1] A fibrous nonwoven fabric was produced using the production apparatus shown in Figure 1. Specifically, molten propylene homopolymer (crystallization temperature Tc: 130°C, melting point Tm: 160°C, MFR: 1500 g / 10 min) was supplied to a die, and heated air (temperature Ta: 200°C, flow rate: 600 Nm) was blown from both sides of the spinning nozzle at a discharge rate of 0.2 g / min from the die set temperature of 320°C (temperature Tp of the molten propylene homopolymer). 3 The diameter of the spinning nozzle of the die was 0.20 mm. The fibrous propylene homopolymer was extruded at a basis weight of 15 g / m. 2The propylene homopolymer was collected on a perforated belt as a collector so that the crystallization temperature (Tc) and melting point (Tm) of the propylene homopolymer were measured by the above-mentioned method.

[0060] [Examples 2 to 7, Comparative Examples 1 to 5] A fibrous nonwoven fabric was obtained in the same manner as in Example 1, except that the temperature (Ta) and flow rate of the heated air were changed as shown in Table 1.

[0061] The physical properties (basis weight, average fiber diameter, CV value, filter accuracy, and pressure loss) of the obtained nonwoven fabric laminate were measured by the following methods.

[0062] (1) Weight (g / m 2 ) Three samples measuring 50 cm in length and 50 cm in width were taken and the weight of each sample was measured. The average value obtained was converted to the weight per unit area and rounded off to the nearest tenth to obtain the weight per unit area (g / m 2 ) was decided.

[0063] (2) Average fiber diameter (μm) and coefficient of variation (CV value) of fibers in fibrous nonwoven fabric Using an electron microscope (Hitachi S-3500N), a photograph of the fibrous nonwoven fabric was taken at a magnification of 1000 times. 100 fibers were randomly selected from the fibers constituting the fibrous nonwoven fabric, and the width (diameter) of the selected fibers was measured. The average of the measurement results was taken as the average fiber diameter.

[0064] The standard deviation (Dp) of the measurement results was divided by the average fiber diameter (Da) to obtain the coefficient of variation (CV value) of the fiber diameter. CV value = standard deviation (Dp) / average fiber diameter (Da)

[0065] (3) Collection efficiency (%) The dust collection efficiency was measured using the following method. Three 15 cm x 15 cm samples were taken from any part of the fibrous nonwoven fabric (laminate), and the collection efficiency of each sample was measured using a collection performance measuring device (Model 8130, manufactured by Tokyo Dylec Co., Ltd.). To measure the collection efficiency, NaCl particle dust with a median particle diameter of 0.07 μm was generated using an atomizer, and the sample was then placed in a holder. The air flow rate was adjusted using a flow control valve so that the filter passage speed was 5.3 cm / sec, and the dust concentration was adjusted to 15 to 20 mg / m. 3 The number of dust particles upstream of the sample, D2, and the number of dust particles downstream, D1, were detected using a laser particle detector, and the value obtained using the following formula was rounded to one decimal place to determine the collection efficiency (%). Collection efficiency (%) = [1-(D1 / D2)] x 100 (D1: number of dust particles downstream, D2: number of dust particles upstream)

[0066] Table 1 shows the preparation conditions and evaluation results for Examples 1 to 7 and Comparative Examples 1 to 5.

[0067] [Table 1]

[0068] As shown in Table 1, when both formulas (1) and (2) are satisfied and the flow rate of the heating gas is 150 to 1000 Nm 3 The fibrous nonwoven fabrics of Examples 1 to 7, which were produced under conditions in which the flow rate of the heated gas was in the range of 0.05 / hr / m, had superior collection efficiency compared to the fibrous nonwoven fabrics of Comparative Examples 1, 2, and 5, which were produced under conditions that did not satisfy formula (2), and the fibrous nonwoven fabrics of Comparative Examples 3 and 4, which were produced under conditions in which the flow rate of the heated gas was outside the above range. This is thought to be because the fibrous nonwoven fabrics of Examples 1 to 7 had smaller average fiber diameters and lower CV values ​​than the fibrous nonwoven fabrics of Comparative Examples 1 to 5. [Industrial Applicability]

[0069] According to the present invention, it is possible to provide a method for producing a fibrous nonwoven fabric that can produce a fibrous nonwoven fabric having a small fiber diameter and little variation in fiber diameter without complicating the device configuration. [Explanation of symbols]

[0070] 10. Fiber nonwoven fabric manufacturing equipment 20 Extruder 21 Hopper 22 Compression section 30 Die (spinneret) 31 Spinning nozzle 32 Gas nozzle 40 Collection mechanism 41 Perforated Belt 42 Laura 43 Air suction part 44 Blower 50 Gas heating equipment P Molten thermoplastic resin G Heating gas

Claims

1. A method for producing a fibrous nonwoven fabric having an average fiber diameter of 2.0 μm or less, comprising: A step of discharging a molten thermoplastic resin together with a heated gas from a spinneret by a melt-blown method and stretching the thermoplastic resin with the heated gas to form a fibrous resin; collecting the fibrous resin in the form of a web; Including, The flow rate of the heating gas is set to 150 to 1000 Nm ３ / hour / m, When the temperature of the heated gas is Ta (°C), the temperature of the molten thermoplastic resin is Tp (°C), the crystallization temperature of the thermoplastic resin is Tc (°C), and the melting point of the thermoplastic resin is Tm (°C), the heated gas is discharged so as to satisfy the following formulas (1) and (2): Method for manufacturing fibrous nonwoven fabric. Formula (1) Tc<Ta≦Tm+150 Formula (2) 80≦Tp-Ta≦190

2. The method does not include a step of blowing a cooling gas of 30°C or less onto the discharged thermoplastic resin. A method for producing the fibrous nonwoven fabric according to claim 1.

3. The heated gas is discharged so as to further satisfy the following formula (1)': A method for producing the fibrous nonwoven fabric according to claim 1 or 2. Formula (1)' Tm-30≦Ta≦Tm+150

4. The flow rate of the heating gas is set to 250 to 850 Nm ３ / hour / m, A method for producing the fibrous nonwoven fabric according to any one of claims 1 to 3.

5. The thermoplastic resin is a propylene-based polymer. A method for producing the fibrous nonwoven fabric according to any one of claims 1 to 4.

6. The fibrous nonwoven fabric has a coefficient of variation of fiber diameter of 1.0 or less. A method for producing the fibrous nonwoven fabric according to any one of claims 1 to 5.

Images