Manufacturing method of meltblown nonwoven fabric

Abstract

To provide a method capable of producing a melt-blown nonwoven fabric of a small diameter with good productivity.SOLUTION: A method of producing a melt-blown nonwoven fabric uses a polypropylene-based resin as a fiber forming resin. Cooling air is blown to fibers at a position lower than an outlet part of a slit 28a, 28b from which hot air is blown. A spinning condition is set so that an atmospheric temperature T0 right under a spinning nozzle 23 becomes higher than a melting point of the polypropylene-based resin by 125°C or more, and a difference between T0 and an atmospheric temperature T35 at a discrete position from the spinning nozzle 23 by 35 mm becomes 120°C or more. An air quantity of the cooling air is set to 1.5 times or more and less than 4 times of an air quantity of the hot air.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] The melt-blowing method is a method suitable for producing nonwoven fabrics made of fine fibers. Taking advantage of these characteristics, melt-blown nonwoven fabrics are used in a variety of fields, including filters, sanitary products, clothing, packaging materials, and battery separators. In recent years, research has been conducted toward the mass production of melt-blown nonwoven fabrics made of nanofibers, which have even smaller fiber diameters.

[0003] In order to increase the productivity of melt-blown nonwoven fabrics, for example, it is possible to narrow the pitch of the spinning nozzle in the spinning die. However, if the pitch of the spinning nozzle is narrowed, the spun fibers will fuse together before they are completely solidified, which will prevent the production of fine-diameter fibers. Therefore, Patent Document 1 proposes forcibly cooling the spun fibers directly below the spinning nozzle to suppress the fusion of the fibers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2012 / 077638 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technique described in Patent Document 1 is still insufficient for increasing the productivity of melt-blown nonwoven fabrics because the pitch of the spinning nozzle in the spinning die is still wide and the discharge amount is still small. Therefore, an object of the present invention is to improve the method for producing a melt-blown nonwoven fabric, and more specifically, to provide a method capable of producing a small-diameter melt-blown nonwoven fabric with good productivity. [Means for solving the problem]

[0006] The present invention relates to a method for producing a melt-blown nonwoven fabric, comprising a spinning step in which a melt of a fiber-forming resin is discharged from a plurality of spinning nozzles arranged in series at intervals, and hot air is blown onto the melt from slits provided so as to sandwich the spinning nozzles, thereby stretching the melt to form fibers, A polypropylene resin is used as the fiber-forming resin, blowing cooling air onto the fibers at a position below the outlet of the slit from which the hot air is blown out to cool the fibers; The spinning conditions are set so that the ambient temperature immediately below the spinning nozzle is 125° C. or more higher than the melting point of the polypropylene-based resin, and the difference between the ambient temperature immediately below the spinning nozzle and the ambient temperature at a position 35 mm away from the spinning nozzle is 120° C. or more; The above problem is solved by providing a method for producing a melt-blown nonwoven fabric, in which the volume of the cooling air is set to 1.5 times or more and less than 4 times the volume of the hot air. Effect of the Invention

[0007] According to the method of the present invention, a small-diameter melt-blown nonwoven fabric can be produced with good productivity. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of an apparatus for carrying out the production method of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing the structure of the spinning head in FIG. [Diagram 3] FIG. 3 is an enlarged view of a main part in FIG. [Figure 4] FIG. 4 is a perspective view showing a spinning die which is one component of the spinning head in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described below based on preferred embodiments with reference to the drawings. Fig. 1 shows one embodiment of a meltblown nonwoven fabric device for carrying out the method of the present invention. The manufacturing device 1 shown in the figure is equipped with a spinning head 10. The spinning head 10 has a longitudinal direction X and a width direction Y perpendicular to the longitudinal direction X, and is installed so that the width direction Y coincides with the machine direction MD of the manufacturing device 1. The spinning head 10 is connected to an extruder 12 having a hopper 11. The hopper 11 is filled with pellets of a fiber-forming resin, which is a raw material for the melt-blown nonwoven fabric. The resin supplied from the hopper 11 is melt-kneaded in the extruder 12 to become a molten material, and the molten material is supplied to the spinning head 10.

[0010] A hot air supply unit 13 is connected to the spinning head 10. The supply unit 13 is connected to a hot air supply source (not shown). Air heated to a predetermined temperature is supplied from the hot air supply source. The supplied hot air is supplied to the spinning head 10 after the flow rate is adjusted in the supply unit 13.

[0011] Furthermore, a cooling air supply unit 14 is connected to the spinning head 10. The supply unit 14 is connected to a cooling air supply source (not shown). Air at a predetermined temperature is supplied from the cooling air supply source. The supplied cooling air is supplied to the spinning head 10 after the flow rate is adjusted in the supply unit 14.

[0012] A fiber collecting section 15 is installed below the spinning head 10. The collecting section 15 is equipped with an endless belt 16 made of a breathable material. The endless belt 16 is stretched between a pair of rollers 17, 17 and rotates.

[0013] The collecting section 15 is equipped with a suction box 18. The suction box 18 is installed within the circulating orbit of the endless belt 16. The suction box 18 is installed at a position corresponding to the fiber spinning line in the spinning head 10. By operating the suction box 18, the hot air and the cooling air ejected from the spinning head 10 are sucked in, and the deposition of the fibers on the endless belt 16 is stabilized.

[0014] The collecting section 15 further includes a winder 19. The meltblown nonwoven fabric 2 formed by the fibers accumulated on the endless belt 16 is wound up by the winder 19 and transported to the next process.

[0015] 2 and 3 show a schematic cross-sectional structure of the spinning head 10 in the width direction Y. The spinning head 10 is equipped with two divided die bodies 20a and 20b. The die bodies 20a and 20b are connected by fastening means such as bolts (not shown).

[0016] The spinning head 10 has a resin supply port 21 at its top, through which the melt of the fiber-forming resin, which is the raw material of the melt-blown nonwoven fabric, is fed. The melt fed to the resin supply port 21 is fed to a spinning die 22, which will be described below. The melt is fed from the resin supply port 21 to the spinning die 22 via a coat hanger-shaped or tournament-shaped flow path 21a.

[0017] The spinning head 10 has a spinning die 22 at its bottom. As shown in FIG. 4, the spinning die 22 has a die nose 22a whose cross section in the width direction Y is an isosceles triangle. At the ridge of the die nose 22a, a plurality of spinning nozzles 23 are drilled and arranged in series along the longitudinal direction X of the spinning die 22. The resin melt is supplied to the spinning nozzle 23 via a die flow path 24 (see FIG. 3) connected to the above-mentioned flow path 21a. The number of spinning nozzles 23 depends on the dimensions of the spinning die 22, but is generally 1000 pieces / m or more and 4100 pieces / m or less.

[0018] The die bodies 20a and 20b are provided with first manifolds 25a and 25b. The first manifolds 25a and 25b are connected to the above-mentioned hot air supply unit 13 (see FIG. 1). The hot air supplied from the hot air supply unit 13 passes through the first manifolds 25a and 25b, the hot air flow paths 26a and 26b, and the buffer spaces 27a and 27b, and is ejected from a pair of opposing slits 28a and 28b. The hot air ejected from the slits 28a and 28b is blown onto the fibers discharged from the spinning nozzle 23.

[0019] As shown in Fig. 3, both slits 28a and 28b extend along the hypotenuse of die nose 22a of spinning die 22 and are directed toward the ridge of die nose 22a. The hot air jets ejected from slits 28a and 28b join at the ridge of die nose 22a. The buffer spaces 27a and 27b and the slits 28a and 28b are defined by the spinning die 22 and plates 29a and 29b.

[0020] Directly below the plates 29a, 29b, cooling air blowing nozzles 30a, 30b are installed. In FIG. 3, there is no gap between the plates 29a, 29b and the blowing nozzles 30a, 30b, and the blowing nozzles 30a, 30b are shown to be directly attached to the lower surfaces of the plates 29a, 29b. However, there is no need to prevent gaps from being present between the plates 29a, 29b and the blowing nozzles 30a, 30b. Alternatively, a heat insulating material (not shown) may be interposed between the plates 29a, 29b and the blowing nozzles 30a, 30b to make it difficult for the heat of the plates 29a, 29b, which are in a high temperature state, to be conducted to the blowing nozzles 30a, 30b, thereby suppressing an unintended temperature rise of the cooling air.

[0021] The blow nozzles 30a, 30b are installed so as to be perpendicular to the fiber spinning line L. Therefore, the cooling air is blown at a right angle to the spun fibers. Alternatively, the installation angle of the blow nozzles 30a, 30b may be set so that the cooling air is blown obliquely downward in FIG. The rear ends of the blowing nozzles 30a, 30b are connected to second manifolds 33a, 33b provided inside the manifold blocks 32a, 32b via cooling air flow paths 31a, 31b as shown in Fig. 2. The manifold blocks 32a, 32b are attached to the side surfaces of the die bodies 20a, 20b. The second manifolds 33a, 33b are connected to the above-mentioned cooling air supply unit 14 (see Fig. 1).

[0022] To manufacture a melt-blown nonwoven fabric using the manufacturing apparatus 1 having the above configuration, first, a raw resin is supplied from a hopper 11 shown in FIG. 1 to an extruder 12, and the resin is melt-kneaded in the extruder 12. The resin that has become molten in the extruder is sent to a spinning head 10. In the spinning head 10, the molten material is discharged from a plurality of spinning nozzles 23 (see FIG. 4) that are arranged in series at intervals. At the same time, hot air is ejected from a pair of slits 28a, 28b that are provided opposite to each other so as to sandwich the spinning nozzle 23, and the hot air is blown onto the molten material. The molten material is stretched by the blowing of the hot air and formed into fibers. The spinning head 10 may be heated in order to prevent poor spinning caused by a decrease in the temperature of the molten material or the hot air.

[0023] In the above spinning process, cooling air is blown from cooling air blowing nozzles 30a, 30b installed at a position lower than the outlet of slits 28a, 28b from which hot air is blown, and the cooling air is blown onto the spun fibers to cool the fibers. This cooling lowers the temperature of the semi-molten fibers, and solidifies the fibers to a state where they are unlikely to fuse together even if they come into contact with each other.

[0024] In the manufacturing method of meltblown nonwoven fabric, a technique of blowing cooling air onto spun fibers to cool the fibers is described in Patent Document 1, as mentioned above in the Background Art section. However, the method described in the same document cannot produce small-diameter meltblown nonwoven fabrics with high productivity. In contrast, in the present invention, by making ingenious efforts in the manufacturing conditions of meltblown nonwoven fabrics, it has become possible to improve the productivity of small-diameter meltblown nonwoven fabrics, which has been considered difficult to achieve until now.

[0025] In order to improve the productivity of small-diameter melt-blown nonwoven fabrics, in the present invention, a polypropylene-based resin is used as a fiber-forming resin that is a raw material for melt-blown nonwoven fabrics. By using a polypropylene-based resin and adopting the spinning conditions described below, even if the pitch of the spinning nozzle 23 is narrowed to increase the productivity of the melt-blown nonwoven fabrics, it is possible to effectively suppress the increase in the diameter of the fibers caused by the fusion of the spun fibers.

[0026] The polypropylene-based resin that can be used in the present invention includes a homopolymer of propylene and a copolymer of propylene and an α-olefin. There is no particular limitation on the type of homopolymer, and any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene may be used. On the other hand, when a copolymer is used, the copolymer may be a random copolymer or a block copolymer. In either case, the α-olefin to be used preferably has a carbon number of 2 or more, more preferably 2 to 8. Examples of such α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene. Among polypropylene-based resins, it is preferable to use a propylene homopolymer from the viewpoint of achieving a fine fiber diameter and a good balance between price and performance.

[0027] From the viewpoint of achieving a finer fiber diameter, the weight average molecular weight of the polypropylene resin is preferably 25,000 or more, more preferably 35,000 or more, and is preferably 100,000 or less, more preferably 60,000 or less. The weight average molecular weight can be measured by high-temperature gel permeation chromatography (GPC). The weight average molecular weight is calculated based on a calibration curve prepared using standard polystyrene.

[0028] The polypropylene resin preferably has a melting point of 50°C to 180°C, more preferably 70°C to 170°C, and even more preferably 90°C to 165°C, depending on its molecular weight. By using a polypropylene resin having a melting point in this range as a raw material, it becomes possible to perform spinning successfully. The melting point of the resin is measured using a differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.). Thermal analysis of the resin sample is performed at a heating rate of 10°C / min, and the melting peak temperature is taken as the melting point of the resin.

[0029] The polypropylene resin preferably has a melt flow rate (hereinafter also referred to as "MFR") of 500 g / min or more from the viewpoint of reducing the amount of hot air used and reducing the fiber diameter of the resulting nonwoven fabric. From this viewpoint, the MFR is more preferably 800 g / min or more, and even more preferably 1000 g / min or more. From the viewpoint of preventing thread breakage, the MFR is preferably 2500 g / min or less, and even more preferably 2000 g / min or less. The MFR is measured in accordance with JIS K 7210 at a temperature of 230°C, a load of 2160 g, an orifice diameter of 2.095 mm, and an orifice length of 8.000 mm. The MFR of the constituent resin can also be measured by remelting the produced melt-blown nonwoven fabric and measuring it in the same manner as above.

[0030] The polypropylene resin may contain various additives for the purpose of thinning the fibers or crystallizing them, or for the purpose of imparting various properties to the target melt-blown nonwoven fabric, such as ultraviolet absorbers, crystal nucleating agents, antibacterial agents, antifungal agents, flame retardants, hydrophilic agents, water repellents, and pigments.

[0031] In order to manufacture a fine-diameter melt-blown nonwoven fabric using the polypropylene-based resin described above, it is desirable to sufficiently elongate the melt by raising the temperature of the discharged molten material. From this viewpoint, the spinning conditions are set so that the ambient temperature directly below the spinning nozzle 23 is preferably 125°C or higher than the melting point of the polypropylene-based resin. From the viewpoint of further thinning of the fiber, the ambient temperature is preferably (Mp+160)°C or higher, more preferably (Mp+190)°C or higher, where Mp is the melting point of the polypropylene-based resin. In addition, from the viewpoint of preventing the fiber from breaking and sufficiently cooling the fiber, the ambient temperature is preferably (Mp+230)°C or lower, and more preferably (Mp+210)°C or lower. The polypropylene-based resin may be a single resin or a mixture of multiple resins. When multiple polypropylene-based resins with different melting points are mixed, Mp means the melting point of the polypropylene-based resin with the highest melting point.

[0032] From the viewpoint of reducing the diameter of the spun fibers and effectively suppressing the increase in diameter of the fibers due to contact between the fibers, it is desirable to rapidly cool the fibers by increasing the difference between the ambient temperature directly below the spinning nozzle 23 and the ambient temperature at a position a predetermined distance away from the spinning nozzle 23. From this viewpoint, the present inventors have furthered their investigations and found that it is effective to use the ambient temperature at a position 35 mm away from the spinning nozzle 23 as an index. In detail, the ambient temperature immediately below the spinning nozzle 23 is defined as T0, and the ambient temperature at a position 35 mm away from the spinning nozzle 23 is defined as T 35 Then, T0 and T 35 The temperature difference between 35It is advantageous to set the spinning conditions so that the temperature of the fiber spun from the nozzle is preferably 120°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher, from the viewpoints of reducing the diameter of the spun fibers and suppressing the increase in the diameter of the fibers due to contact between the fibers. The atmospheric temperature can be measured by installing a thermocouple on the spinning line (on the dashed line indicated by symbol L in FIG. 3) at the hot air outlet where no resin is being discharged. In order to minimize the influence of the outside air, it is preferable to install the thermocouple at a location on the hot air outlet closer to the resin outlet, to the extent that the spun fibers do not become entangled.

[0033] The ambient temperature immediately below the spinning nozzle 23, and (T 35 ) can be adjusted by controlling the spinning conditions such as the temperature of the melt, the discharge rate of the melt, the temperature of the hot air, the volume of the hot air, the temperature of the cooling air, the volume of the cooling air, and the blowing position of the cooling air.

[0034] With regard to the temperature of the melt, assuming that the melting point of the polypropylene resin is Mp, it is preferably set to (Mp+90)° C. or higher, more preferably (Mp+100)° C. or higher, and even more preferably (Mp+110)° C. or higher. It is also set to (Mp+140)° C. or lower, more preferably (Mp+130)° C. or lower, and even more preferably (Mp+120)° C. or lower. The temperature of the melt is set to the higher of the temperature inside the barrel of the extruder 12 or the heating temperature of the spinning head 10.

[0035] The discharge rate of the molten material is set to preferably 20 kg / hr / m or less, more preferably 17 kg / hr / m or less, and even more preferably 15 kg / hr / m or less from the viewpoint of preventing breakage of the fibers and sufficient cooling of the fibers, and is set to preferably 3 kg / hr / m or more, more preferably 4 kg / hr / m or more, and even more preferably 5 kg / hr / m or more from the viewpoint of improving the productivity of the meltblown nonwoven fabric.

[0036] The discharge rate for one spinning nozzle 23 is set to preferably 0.08 g / min / hole or less, more preferably 0.07 g / min / hole or less, from the viewpoint of preventing fiber breakage and sufficient cooling of the fibers. Also, from the viewpoint of improving the productivity of the melt-blown nonwoven fabric, it is set to preferably 0.05 g / min / hole or more, more preferably 0.06 g / min / hole or more.

[0037] Regarding the temperature of the hot air, from the viewpoint of thinning the fiber, the melting point of the polypropylene resin is preferably set to (Mp+125)°C or higher, more preferably (Mp+160)°C or higher, and even more preferably (Mp+190)°C or higher, where Mp is the melting point of the polypropylene resin. Also, from the viewpoint of preventing the fiber from breaking and sufficiently cooling the fiber, the temperature is preferably set to (Mp+220)°C or lower, more preferably (Mp+205)°C or lower, and even more preferably (Mp+200)°C or lower. Depending on the structure of the manufacturing apparatus 1, the temperature of the hot air may be substantially the same as the atmospheric temperature directly below the spinning nozzle 23, or may be different. The temperature of the hot air is the set temperature of the device that generates the hot air.

[0038] The hot air volume is preferably 500 Nm from the viewpoint of thinning the fibers. 3 / hr / m or more, more preferably 600Nm 3 / hr / m or more, more preferably 700Nm 3 / hr / m or more. From the viewpoint of preventing fiber breakage and sufficient cooling of the fiber, it is preferable to set the speed at 1000 Nm 3 / hr / m or less, more preferably 950Nm 3 / hr / m or less, more preferably 900Nm 3 The volume of hot air is measured by an air flow meter installed in the supply air piping.

[0039] From the viewpoint of sufficient cooling of the fibers, the temperature of the cooling air is set to preferably 20° C. or less, more preferably 10° C. or less, and even more preferably 5° C. or less. The temperature of the cooling air is adjusted by a cold air generator, and the temperature of the cooling air is measured by installing a thermocouple at the position of the outlet of the cooling air blowing nozzle.

[0040] The volume of the cooling air is preferably 1000 Nm from the viewpoint of sufficient cooling of the fibers. 3 / hr / m or more, more preferably 1500Nm 3 / hr / m or more, more preferably 2000Nm 3 From the viewpoint of reducing the diameter of the fibers, it is preferable to set the fiber speed to 4000 Nm / hr / m or more. 3 / hr / m or less, more preferably 3500Nm 3 / hr / m or less, more preferably 3000Nm 3 The volume of cooling air can be calculated by inserting a Pitot tube into the cooling air flow path to measure the air speed, and multiplying this by the cross-sectional area of ​​the cooling air flow path.

[0041] The degree of cooling of the spun fibers is also affected by the ratio of the hot air volume to the cooling air volume. From this viewpoint, it is preferable to set the cooling air volume to 1.5 times or more of the hot air volume from the viewpoint of sufficient cooling of the fibers, more preferably 2 times or more, and even more preferably 3 times or more. It is also preferable to set the cooling air volume to less than 4 times the hot air volume from the viewpoint of thinning the fibers, more preferably 3.8 times or less, and even more preferably 3.5 times or less.

[0042] Regarding the position at which the cooling air is blown, from the viewpoint of sufficient cooling of the fibers, it is preferable to blow the cooling air within the range from directly below the spinning nozzle 23 to a position at least 35 mm away from the spinning nozzle 23. From the viewpoint of cooling efficiency, it is desirable to blow the cooling air over the entire area from directly below the spinning nozzle 23 to a position at least 35 mm away.

[0043] As shown in Figs. 2 and 3, it is preferable to blow the cooling air onto the fiber spinning line from both sides from the viewpoint of stable spinning and sufficient cooling of the fiber.

[0044] In addition to the above-mentioned production conditions, the production conditions of the melt-blown nonwoven fabric that can be set include the hole diameter and pitch of the spinning nozzle 23. The hole diameter of the spinning nozzle 23 is preferably set to 0.2 mm or less, more preferably 0.19 mm or less, and even more preferably 0.18 mm or less, from the viewpoint of thinning the fibers. Also, from the viewpoint of improving the productivity of the melt-blown nonwoven fabric, it is preferably set to 0.13 mm or more, more preferably 0.14 mm or more, and even more preferably 0.15 mm or more. The pitch P of the spinning nozzle 23 (see FIG. 4) is preferably set to 0.9 mm or less, more preferably 0.6 mm or less, and even more preferably 0.3 mm or less, from the viewpoint of improving the productivity of the melt-blown nonwoven fabric. Also, from the viewpoint of stable spinning and sufficient cooling of the fibers, it is preferably set to 0.20 mm or more, more preferably 0.22 mm or more, and even more preferably 0.24 mm or more.

[0045] By adopting the above conditions, spinning can be carried out so as to obtain fine fibers having an average fiber diameter of preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 550 nm or less in the resulting meltblown nonwoven fabric. Moreover, by adopting the above-mentioned various conditions, spinning can be carried out so as to obtain a meltblown nonwoven fabric with a good formation index of preferably 350 or less, more preferably 300 or less, and even more preferably 280 or less. The formation index is a standard for evaluating the quality of the formation of a nonwoven fabric, and the smaller the value, the better the formation of the nonwoven fabric. The above-mentioned formation index value is determined when the basis weight of the nonwoven fabric is 5 g / m 2 It is preferable to be satisfied when

[0046] When the average fiber diameter of the melt-blown nonwoven fabric is 1000 nm or less, the melt-blown nonwoven fabric has excellent (a) water resistance (water pressure resistance) and (b) filtering properties. (a) Excellent water resistance has the advantage of enhancing leak prevention when the meltblown nonwoven fabric obtained by this manufacturing method is used, for example, as a back sheet of absorbent articles such as sanitary napkins and disposable diapers, or as a constituent sheet of three-dimensional guards placed at the front, rear, or sides. (a) The excellent filtering properties have the advantage that when the melt-blown nonwoven fabric obtained by this production method is used as various separation membranes, sanitary masks, etc., it can efficiently capture foreign matter that needs to be removed.

[0047] The average fiber diameter of the constituent fibers of the meltblown nonwoven fabric can be determined by the following method. When obtaining a nonwoven fabric to be measured from a diaper or the like, the hot melt adhesive is deactivated with a cold spray or an organic solvent, and the nonwoven fabric to be measured is carefully peeled off and isolated. This process is common to all measurements in this specification unless otherwise specified. The average fiber diameter is measured by first randomly collecting five small samples from the nonwoven fabric. If the nonwoven fabric is in the form of an SMS (spunbond / meltblown / spunbond three-layered nonwoven fabric), the nonwoven fabric is observed from the top surface to measure the fine fibers derived from meltblown. Next, a photograph is taken with a scanning electron microscope at a magnification of 1000 to 10000 times so that 20 to 60 fibers are reflected in the field of view. The fiber diameter is measured so that all fibers in the field of view are counted once, and the average fiber diameter value for 100 or more fibers is calculated in nanometer order and rounded off to the first decimal place. The value obtained in this manner is the average fiber diameter.

[0048] The formation index is calculated using a formation tester (FMT-MIII) manufactured by Nomura Shoji Co., Ltd. Specifically, a sample piece taken from a melt-blown nonwoven fabric is placed on a sample stage, and the transmitted image when light is irradiated from one side of the sample piece is captured by a two-dimensional CCD camera. The effective size of the sample piece, 10 cm x 10 cm, is divided into 320 x 230 pixels, the intensity of light received by each pixel is measured, and the transmittance for each pixel is calculated using the following formula. Transmittance T(%)=[(V T -V R ) / (V 100 -V0) × 100 (1) In the formula, V T is the amount of light transmitted when the light is on (with the sample), V R is the amount of light transmitted when the light is off (with the sample piece present), and V100 is the amount of light transmitted when the light is on (without sample piece), and V0 is the amount of light transmitted when the light is off (without sample piece). The absorbance is calculated from the obtained transmittance T according to the following formula (2). Absorbance E=2-logT ···(2) The formation index is calculated from the obtained absorbance according to the following formula (3). Formation index = Coefficient of variation of absorbance E × 10 = [Standard deviation of absorbance (σ)] / [Average absorbance (Eave.)] × 10 (3) The measurement is carried out on 10 sample pieces, and the average value is regarded as the formation index of the meltblown nonwoven fabric. When the size of the sample piece is small and an effective size of 10 cm × 10 cm cannot be obtained, the sample piece is placed in the center of the sample stage and the effective size is appropriately specified so that it is smaller than the size of the sample piece and is as large as possible, and the formation index of the sample piece can be obtained by performing the measurement.

[0049] The meltblown nonwoven fabric obtained by this manufacturing method has excellent water pressure resistance due to its fine fiber diameter, and is useful, for example, in the form of SMS, as a back sheet or a sheet constituting a leakproof cuff, which is a constituent material of absorbent articles such as sanitary napkins and disposable diapers. In addition, it has excellent filtering properties and is useful as a filter material for various separation membranes and sanitary masks.

[0050] The applications of the melt-blown nonwoven fabric obtained by the present production method are not particularly limited, and the fabric can be used in a variety of applications by taking advantage of its properties. For example, the present manufacturing method can produce a melt-blown nonwoven fabric used as a component of an absorbent article. The melt-blown nonwoven fabric obtained by the present manufacturing method is used, for example, by laminating it on an absorbent body of an absorbent article. Specifically, an absorbent article can be manufactured by a method including a step of manufacturing the melt-blown nonwoven fabric by the above-mentioned method and a step of laminating the manufactured melt-blown nonwoven fabric and an absorbent body.

[0051] Absorbent articles are primarily used to absorb and retain liquids discharged from the body, such as urine and menstrual blood. Absorbent articles typically include a top sheet, a back sheet, and a liquid-retentive absorbent interposed between the two sheets. The absorbent article may further include various components according to the specific use of the absorbent article. Such components are known to those skilled in the art. For example, when the absorbent article is a disposable diaper, sanitary napkin, or incontinence pad, one or more pairs of leak-proof cuffs can be arranged on both sides in the longitudinal direction along the front-rear direction of the wearer. The leak-proof cuff has a fixed end and a free end, and preferably an elastic member is arranged near the free end.

[0052] The meltblown nonwoven fabric obtained by this manufacturing method is preferably in the form of an SMS from the viewpoint of improving the strength and transportability of the sheet, and can be used as a back sheet or a leak-proof cuff component sheet that is required to be water-resistant, or a top sheet that is required to conceal the color of menstrual blood, urine, etc., among the components of absorbent articles. When the back sheet of an absorbent article is formed from a laminated sheet of a resin film and an exterior nonwoven fabric covering the non-skin-facing side thereof, the meltblown nonwoven fabric may be used in place of the resin film or the exterior nonwoven fabric. Alternatively, it may be used in place of the entire conventional back sheet. The meltblown nonwoven fabric obtained by this manufacturing method can also be used as a filter material for a sanitary mask.

[0053] Although the present invention has been described above based on its preferred embodiment, the present invention is not limited to the above embodiment. For example, in the above-mentioned manufacturing method, the conditions related to the manufacturing method of the conventional melt-blown nonwoven fabric are appropriately applied to the points not specifically described. Furthermore, the structure of the spinning head 10 for carrying out the manufacturing method of the present invention is not limited to that shown in the figure, and the spinning head 10 may have another structure as long as it is capable of carrying out the manufacturing method of the present invention. EXAMPLES

[0054] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass".

[0055] Example 1 A melt-blown nonwoven fabric was produced using the production apparatus shown in Figures 1 to 4. The production conditions are as follows. (1) Resin Polypropylene homopolymer (Mp: 160℃, MFR: 1200g / min) (2) Manufacturing equipment Spinning nozzle hole diameter: 0.15mm Spinning nozzle pitch: 0.25mm Length of spinning nozzle row: 250mm Resin temperature: 270℃ ·Single hole discharge amount: 0.06g / min / hole ·Resin discharge amount: 14.4kg / hr / m Hot air temperature: 345℃ Hot air volume: 750Nm 3 / hr / m Ambient temperature directly below the spinning nozzle T0: 322℃ Endless belt speed: 48m / min (3) Cooling air ·Temperature: 5℃ Cooling air blowing area: All areas within 38 mm from directly below the spinning nozzle ·Air volume: 2500Nm 3 / hr / m Ambient temperature T at a position 35 mm away from the spinning nozzle 35 : 185℃ ·Temperature difference T0-T 35 : 137℃ (4) Nonwoven fabric Weight: 5g / m 2 Average fiber diameter: 662nm ·Conformation index: 258

[0056] [Examples 2 to 4 and Comparative Examples 1 and 2] In Example 1, the temperature of the hot air was changed so that the atmospheric temperature T0 immediately below the spinning nozzle became the value shown in the following Table 1. In addition, the flow rate of the cooling air was changed as shown in the following Table 1. Other than these, the same procedure as in Example 1 was used to produce a fiber with a basis weight of 5 g / m. 2 The average fiber diameter and formation index of the obtained melt-blown nonwoven fabric were measured and are shown in the same table.

[0057] [Table 1]

[0058] As is clear from the results shown in Table 1, in each example, the melt-blown nonwoven fabric was produced under conditions in which the pitch of the spinning nozzle was narrowed to increase productivity, but the constituent fibers of the melt-blown nonwoven fabric were small, with an average fiber diameter of less than 1000 nm, and the melt-blown nonwoven fabric had good texture. In contrast, the melt-blown nonwoven fabrics obtained in the comparative examples had an average fiber diameter of more than 1000 nm due to insufficient cooling of the fibers (Comparative Example 1) and an insufficient hot air temperature (Comparative Example 2). [Explanation of symbols]

[0059] 10 Spinning head 20a, 20b Die body 22 Spinning die 22a Dynos 23 Spinning nozzle 25a, 25b First manifold 27a,27b Buffer space 28a,28b Slit 29a, 29b Plate 30a, 30b Cooling air blowing nozzle 31a, 31b Cooling air flow path 32a, 32b Manifold block 33a, 33b Second manifold

Claims

1. A method for producing a melt-blown nonwoven fabric, comprising a spinning step in which a molten fiber-forming resin is discharged from a plurality of spinning nozzles arranged in series at intervals, and hot air is blown onto the molten resin from slits provided so as to sandwich the spinning nozzles, thereby stretching the molten resin into fibers, A polypropylene resin is used as the fiber-forming resin, blowing cooling air onto the fibers at a position below the outlet of the slit from which the hot air is blown out to cool the fibers; The spinning conditions are set so that the ambient temperature immediately below the spinning nozzle is 125° C. or more higher than the melting point of the polypropylene-based resin, and the difference between the ambient temperature immediately below the spinning nozzle and the ambient temperature at a position 35 mm away from the spinning nozzle is 120° C. or more; The volume of the cooling air is set to 1.5 times or more and less than 4 times the volume of the hot air, The atmospheric temperature immediately below the spinning nozzle and the atmospheric temperature at a position 35 mm away from the spinning nozzle are measured on the spinning line by installing a thermocouple at the hot air blowing section where the polypropylene-based resin is not discharged. A method for producing a melt-blown nonwoven fabric.

2. The method according to claim 1, wherein the cooling air is blown onto the fiber spinning line from both sides within a range from directly below the spinning nozzle to a position at least 35 mm away from the spinning nozzle.

3. The method according to claim 1 or 2, wherein the hole diameter of the spinning nozzle is 0.2 mm or less, and the pitch of the spinning nozzle is 0.3 mm or less.

4. The method according to any one of claims 1 to 3, wherein spinning is carried out with a discharge rate of the molten material set to 20 kg / hr / m or less.

5. The method according to any one of claims 1 to 4, wherein spinning is carried out so that the average fiber diameter is 1000 nm or less and the formation index is 350 or less.

6. The method according to any one of claims 1 to 5, which produces a meltblown nonwoven fabric to be used as a constituent material of an absorbent article.

7. A method for producing an absorbent article, comprising the steps of: producing a melt-blown nonwoven fabric by the method according to any one of claims 1 to 6; and laminating the produced melt-blown nonwoven fabric and an absorbent body.

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