JP7619786B2 - Manufacturing method of meltblown nonwoven fabric - Google Patents

Description

The present invention relates to a method for producing meltblown nonwoven fabric.

The melt-blowing method is suitable for producing nonwoven fabrics made of fine-diameter 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 that use nanofibers, which have even smaller fiber diameters, as their constituent fibers.

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, narrowing the pitch of the spinning nozzle causes fusion between the spun fibers before they completely solidify, which prevents the production of fine-diameter fibers. Therefore, Patent Document 1 proposes forcibly cooling the spun fibers directly below the spinning nozzle to suppress fusion between the fibers.

International Publication No. 2012/077638

However, in the technology described in Patent Document 1, the pitch of the spinning nozzle in the spinning die is still wide and the discharge amount is small, so that it is still insufficient to increase the productivity of melt-blown nonwoven fabrics.
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.

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.

The method of the present invention allows for the production of small-diameter melt-blown nonwoven fabrics with good productivity.

FIG. 1 is a schematic diagram showing one embodiment of an apparatus for carrying out the production method of the present invention. FIG. 2 is a cross-sectional view showing the structure of the spinning head in FIG. FIG. 3 is an enlarged view of a main portion in FIG. FIG. 4 is a perspective view showing a spinning die which is one component of the spinning head in FIG.

The present invention will be described below based on preferred embodiments with reference to the drawings. Fig. 1 shows one embodiment of a melt-blown 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.

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.

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.

A fiber collection section 15 is installed below the spinning head 10. The collection 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.

The collection section 15 is equipped with a suction box 18. The suction box 18 is installed within the 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, stabilizing the deposition of the fibers on the endless belt 16.

The collection section 15 further includes a winder 19. The meltblown nonwoven fabric 2, which is made up of fibers accumulated on the endless belt 16, is wound up by the winder 19 and transported to the next process.

Figures 2 and 3 show a schematic cross-sectional structure of the spinning head 10 in the width direction Y. The spinning head 10 has two separate die bodies 20a and 20b. The die bodies 20a and 20b are connected by fastening means such as bolts (not shown).

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

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 molten resin is supplied to the spinning nozzle 23 via the 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 or more/m and 4100 or less/m.

The die bodies 20a and 20b are provided with first manifolds 25a and 25b. The first manifolds 25a and 25b are connected to the hot air supply section 13 (see FIG. 1) described above. The hot air supplied from the hot air supply section 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.

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

Directly below the plates 29a, 29b are installed cooling air blowing nozzles 30a, 30b. 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 attached directly to the undersides 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 unintended temperature increases in the cooling air.

The blow nozzles 30a, 30b are installed so as to be perpendicular to the fiber spinning line L. Therefore, the cooling air is blown perpendicularly 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.
As shown in Fig. 2, the rear end of each blowing nozzle 30a, 30b is connected to a second manifold 33a, 33b provided inside the manifold block 32a, 32b via a cooling air flow path 31a, 31b. The manifold block 32a, 32b is attached to the side of the die body 20a, 20b. The second manifold 33a, 33b is connected to the above-mentioned cooling air supply unit 14 (see Fig. 1).

To manufacture a melt-blown nonwoven fabric using the manufacturing apparatus 1 having the above configuration, first, the raw resin is supplied from the hopper 11 shown in FIG. 1 to the extruder 12, and the resin is melted and kneaded in the extruder 12. The resin that has become molten in the extruder is sent to the 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 to prevent spinning defects caused by a decrease in the temperature of the molten material or the hot air.

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, solidifying them to a state where they are less likely to fuse together even if they come into contact with each other.

As mentioned above in the Background Art section, in a method for producing meltblown nonwoven fabric, a technique for blowing cooling air onto spun fibers to cool the fibers is described in Patent Document 1. However, the method described in this document does not allow for high productivity production of small diameter meltblown nonwoven fabric. In contrast, in the present invention, by making ingenious efforts in the production conditions of meltblown nonwoven fabric, it has become possible to improve the productivity of small diameter meltblown nonwoven fabric, which has been considered difficult to achieve until now.

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

The polypropylene-based resin that can be used in the present invention includes a propylene homopolymer 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.

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, from the viewpoint of achieving finer fiber diameters. 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 created using standard polystyrene.

Although it depends on the molecular weight, the melting point of the polypropylene resin is preferably 50°C or more and 180°C or less, more preferably 70°C or more and 170°C or less, and even more preferably 90°C or more and 165°C or less. 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.

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 while 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. In addition, 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 resins can also be measured by remelting the produced melt-blown nonwoven fabric and measuring it in the same manner as above.

Various additives may be added to the polypropylene resin 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. Examples of such additives include ultraviolet absorbers, crystal nucleating agents, antibacterial agents, antifungal agents, flame retardants, hydrophilic agents, water repellents, and pigments.

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.

From the viewpoint of reducing the diameter of the spun fibers and effectively suppressing the increase in the 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, when the ambient temperature directly below the spinning nozzle 23 is T ₀ and the ambient temperature at a position 35 mm away from the spinning nozzle 23 is T ₃₅ , the temperature difference between T ₀ and T ₃₅ , i.e., (T ₀ -T ₃₅ ), is preferably 120 ° C. or more, more preferably 130 ° C. or more, and even more preferably 150 ° C. or more. It is advantageous to set the spinning conditions so that the diameter of the spun fiber is thinned and the diameter of the fiber is prevented from increasing due to contact between the fibers. The ambient temperature can be measured by installing a thermocouple on the spinning line (on the dashed line indicated by the symbol L in FIG. 3) at the hot air blowing section where the resin is not discharged. In order to minimize the influence of the outside air, it is preferable to install the thermocouple at a location closer to the resin blowing section of the hot air blowing section, to the extent that the spun fibers are not entangled.

To adjust the ambient temperature directly below the spinning nozzle 23 and (T ₀ -T ₃₅ ), the spinning conditions such as the temperature of the molten material, the discharge rate of the molten material, 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 position at which the cooling air is blown may be controlled.

Regarding the temperature of the molten material, 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 molten material is set to the higher of the temperature inside the barrel of the extruder 12 or the heating temperature of the spinning head 10.

The amount of molten material discharged is preferably set to 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 fiber breakage and sufficient cooling of the fibers. Also, from the viewpoint of improving the productivity of the meltblown nonwoven fabric, it is preferably set to 3 kg/hr/m or more, more preferably 4 kg/hr/m or more, and even more preferably 5 kg/hr/m or more.

The discharge rate for one spinning nozzle 23 is preferably set to 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 preferably set to 0.05 g/min/hole or more, more preferably 0.06 g/min/hole or more.

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 it may be different. The temperature of the hot air is the set temperature of the device that generates the hot air.

From the viewpoint of thinning the fibers, the flow rate of the hot air is preferably set to 500 ^Nm3 /hr/m or more, more preferably 600 ^Nm3 /hr/m or more, and even more preferably 700 ^Nm3 /hr/m or more. From the viewpoint of preventing fiber breakage and sufficient cooling of the fibers, the flow rate is preferably set to 1000 ^Nm3 /hr/m or less, more preferably 950 ^Nm3 /hr/m or less, and even more preferably 900 ^Nm3 /hr/m or less. The flow rate of the hot air is measured by an air flow meter installed in the supply air piping.

From the viewpoint of sufficient cooling of the fibers, the temperature of the cooling air is preferably set to 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.

From the viewpoint of sufficient cooling of the fibers, the flow rate of the cooling air is preferably set to 1000 ^Nm3 /hr/m or more, more preferably 1500 ^Nm3 /hr/m or more, and even more preferably 2000 ^Nm3 /hr/m or more. From the viewpoint of thinning of the fibers, the flow rate is preferably set to 4000 ^Nm3 /hr/m or less, more preferably 3500 ^Nm3 /hr/m or less, and even more preferably 3000 ^Nm3 /hr/m or less. The flow rate of the cooling air can be determined by inserting a Pitot tube into the cooling air flow path to measure the air speed and multiplying it by the cross-sectional area of the cooling air flow path.

The degree of cooling of the spun fibers is also affected by the ratio of the volume of hot air to the volume of cooling air. From this perspective, it is preferable to set the volume of cooling air to 1.5 times or more the volume of hot air in order to sufficiently cool the fibers, more preferably 2 times or more, and even more preferably 3 times or more. Also, from the perspective of thinning the fibers, it is preferable to set the volume of cooling air to less than 4 times the volume of hot air, more preferably 3.8 times or less, and even more preferably 3.5 times or less.

Regarding the position where the cooling air is blown, 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 sufficient cooling of the fibers. 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.

As shown in Figures 2 and 3, it is preferable to blow the cooling air onto the fiber spinning line from both sides in order to ensure stable spinning and sufficient cooling of the fiber.

In addition to the above manufacturing conditions, other manufacturing conditions that can be set for the melt-blown nonwoven fabric 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 reducing the diameter of 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.

By adopting the above conditions, spinning can be performed 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.
In addition, by adopting the above conditions, spinning can be performed so as to obtain a meltblown nonwoven fabric having 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 criterion 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 formation index value is preferably satisfied when the basis weight of the nonwoven fabric is 5 g/ ^m2 .

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 production 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 a three-dimensional guard disposed at the front, rear, or sides.
(a) The excellent filtering property has an advantage that when the melt-blown nonwoven fabric obtained by the present production method is used as various separation membranes, sanitary masks, etc., it can efficiently capture foreign matter to be removed.

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. When 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 value of the fiber diameter 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.

The formation index is determined 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 a transmission 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 - V ₀ )] x 100...(1)
In the formula, _V is the amount of transmitted light when the light is on (with a sample piece), _V is the amount of transmitted light when the light is off (with a sample piece), _V is the amount of transmitted light when the light is on (without a sample piece), and _V is the amount of transmitted light when the light is off (without a 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 absorbance obtained according to the following formula (3).
Formation index = coefficient of variation of absorbance E × 10
= [standard deviation of absorbance (σ)] / [average value of 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 as to be smaller than the size of the sample piece and as large an area as possible, and then the formation index of the sample piece can be obtained.

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 sheet constituting the back sheet or leak-proof cuff, which are components of absorbent articles such as sanitary napkins and disposable diapers. It also has excellent filtering properties, making it useful as a filter material for various separation membranes and sanitary masks.

The use of the melt-blown nonwoven fabric obtained by the present production method is not particularly limited, and it can be used for various purposes 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.

Absorbent articles are primarily used to absorb and retain liquids excreted from the body, such as urine and menstrual blood. Absorbent articles typically include a top sheet, a back sheet, and a liquid-retentive absorbent disposed between the two sheets. Absorbent articles may further include various components according to the specific use of the absorbent article. Such components are well 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 disposed on both sides in the longitudinal direction along the front-to-rear direction of the wearer. The leak-proof cuffs have a fixed end and a free end, and preferably an elastic member is disposed near the free end.

The meltblown nonwoven fabric obtained by this manufacturing method is desirably in the form of an SMS from the viewpoint of improving the strength and transportability of the sheet, and can be used as a constituent member of an absorbent article, such as a back sheet or a constituent sheet of a leak-proof cuff that requires water resistance, or a top sheet that requires concealment of the color of menstrual blood, urine, etc. When the back sheet of an absorbent article is formed from a laminated sheet of a resin film and an exterior nonwoven fabric that covers the non-skin-facing side, this may be used in place of the resin film or the exterior nonwoven fabric. Or 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.

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.

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."

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°C, MFR: 1200g/min)
(2) Manufacturing equipment Spinning nozzle hole diameter: 0.15 mm
Spinning nozzle pitch: 0.25 mm
Length of spinning nozzle row: 250 mm
Resin temperature: 270°C
・Single hole discharge amount: 0.06g/min/hole
・Resin discharge amount: 14.4kg/hr/m
Hot air temperature: 345℃
Hot air volume: ⁷⁵⁰ Nm3/hr/m
Ambient temperature directly below the spinning nozzle T ₀ : 322° C.
Endless belt speed: 48 m/min
(3) Cooling air ・Temperature: 5℃
Area where cooling air is blown: Entire area from directly below the spinning nozzle to 38 mm away Air volume: ²⁵⁰⁰ Nm3/hr/m
Ambient temperature T ₃₅ at a position 35 mm away from the spinning nozzle: 185° C.
・Temperature difference T ₀ - _{T 35} : 137℃
(4) Nonwoven fabric: Weight: 5 g/ ^m2
Average fiber diameter: 662 nm
・Condition index: 258

[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 Table 1 below. In addition, the volume of the cooling air was changed as shown in Table 1 below. A melt-blown nonwoven fabric having a basis weight of 5 g/ ^m2 was obtained in the same manner as in Example 1 except for the above. The average fiber diameter and formation index measured for the obtained melt-blown nonwoven fabric are shown in the same table.

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).

REFERENCE SIGNS LIST 10 Spinning head 20a, 20b Die body 22 Spinning die 22a Die nose 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 (7)

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. The manufacturing method according to claim 1, in which the cooling air is blown from both sides onto the fiber spinning line within a range from directly below the spinning nozzle to a position at least 35 mm away from the spinning nozzle. The manufacturing 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. The manufacturing method according to any one of claims 1 to 3, in which the melt discharge rate is set to 20 kg/hr/m or less and spinning is performed. The manufacturing 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. The manufacturing 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. A method for manufacturing an absorbent article, comprising the steps of: manufacturing a melt-blown nonwoven fabric by the method according to any one of claims 1 to 6; and laminating the manufactured melt-blown nonwoven fabric and an absorbent body.

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