Nonwoven fabric manufacturing method and nonwoven fabric manufacturing apparatus

Abstract

An object of the present invention is to provide a nonwoven fabric manufacturing method and a nonwoven fabric manufacturing apparatus in which fibers are welded to each other by a method other than embossing.SOLUTION: A method for producing a nonwoven fabric includes a spinning step of discharging a molten resin from a spinneret and drawing the resin by an air stream to form fibers, and an ultrasonic welding step of transmitting ultrasonic vibration to the fibers of the resin formed into fibers to weld the fibers to each other.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Conventionally, methods for producing nonwoven fabrics containing multiple fiber layers have been known. For example, Patent Document 1 discloses a nonwoven fabric production device that entangles filaments (fibers) with each other by embossing and then compresses and bonds them. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-70875 Summary of the Invention [Problem to be solved by the invention]

[0004] Embossing can cause fibers to become stiff and uncomfortable against the skin, and some fibers can stick to the embossing roll.

[0005] An object of the present invention is to provide a method and apparatus for manufacturing a nonwoven fabric in which fibers are fused together by a method other than embossing. [Means for solving the problem]

[0006] A method for producing a nonwoven fabric according to one aspect of the present invention includes: a spinning step in which the molten resin is discharged from a die and stretched by an air current to form fibers; and an ultrasonic welding step of transmitting ultrasonic vibrations to the fibrous resin fibers to weld the fibers together. [Effects of the Invention]

[0007] According to the present invention, the fibers can be fused together by a method other than embossing. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view of a nonwoven fabric produced by a nonwoven fabric production method according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a nonwoven fabric produced by the nonwoven fabric production method according to the embodiment. [Figure 3] FIG. 3 is a diagram showing classification of bonding methods between fibers. [Figure 4] FIG. 4 is a flowchart illustrating the method for producing a nonwoven fabric according to the embodiment. [Figure 5] FIG. 5 is a diagram showing a nonwoven fabric manufacturing apparatus according to an embodiment. [Figure 6] FIG. 6 is a perspective view of an ultrasonic welding device provided in the nonwoven fabric manufacturing apparatus according to the embodiment. [Figure 7] FIG. 7 is a diagram showing an oscillator provided in an ultrasonic welding device. [Figure 8] FIG. 8 is a diagram showing how a vertically vibrating horn transmits ultrasonic vibrations to a filament assembly. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the configurations of the following embodiments are merely examples, and the present invention is not limited to the configurations of these embodiments.

[0010] <Embodiment> Fig. 1 is a plan view of nonwoven fabric C produced by the nonwoven fabric production method according to this embodiment, as viewed from above. Fig. 2 is a cross-sectional view of nonwoven fabric C in the CD direction, taken along line AA in Fig. 1. Nonwoven fabric C is a sheet with its longitudinal direction in the MD direction, and is composed of multiple layers.

[0011] As shown in Figure 2, nonwoven fabric C has a layered structure in which three fiber layers C1 are laminated. In nonwoven fabric C, each fiber layer C1 is welded to one another by ultrasonic welding. Ultrasonic welding is performed by passing the laminated fiber layers C1 through a horn that transmits ultrasonic vibrations, causing the fibers to melt and weld together. Nonwoven fabric C according to this embodiment is a thermally bonded nonwoven fabric formed by heating the interior of the nonwoven fabric using ultrasonic vibrations transmitted by the horn, thereby welding the fibers together.

[0012] FIG. 3 shows a classification of methods for bonding fibers together. As shown in FIG. 3, there are two methods for bonding fibers together: one that uses a solvent and one that uses heat to melt and bond the fibers together. Thermal bond nonwoven fabrics are hygienic because they do not use a solvent and instead bond the fibers in the fiber layer C1 by welding. This type of nonwoven fabric C is suitable for use in absorbent articles such as diapers and as a material for masks.

[0013] There are two methods for joining fibers by melting them together using heat: applying heat from the outside and generating heat inside the resin. Methods for applying heat from the outside include embossing the nonwoven fabric C to fuse the fibers together. Methods for generating heat inside the resin include ultrasonic welding to fuse the fibers of the fiber layer C1 together.

[0014] In the embossing method, the laminated fiber layer C1 passes through a pair of upper and lower heated rolls heated to a predetermined temperature, thereby fusing the fibers together. When embossing, the laminated fiber layer C1 is pressed against the heated rolls from above and below (in the thickness direction of the nonwoven fabric C), which can harden the fibers and make them uncomfortable against the skin. Furthermore, when attempting to fuse fibers with low heat resistance using heated rolls, there is a risk that the fibers will stick to the heated rolls.

[0015] In this embodiment, the nonwoven fabric C uses ultrasonic welding to weld the fibers in the laminated fiber layers C1. When ultrasonic waves are transmitted to the laminated fiber layers C1, heat is generated within the laminated fiber layers C1, welding the fibers within the laminated fiber layers C1. This prevents the exterior (surface) of the laminated fiber layers C1 from being pressed against the fabric and becoming hard, improving the feel against the skin. Furthermore, because the laminated fiber layers C1 are not pressed against the fabric by a heated roll, embossing prevents the fibers from sticking to the heated roll.

[0016] Each fiber layer C1 may be formed from fibers made from a polylactic acid-based resin. Polylactic acid (PLA) is a biodegradable resin that is hydrolyzed by water in the natural environment to lower its molecular weight, and is eventually decomposed into carbon dioxide and water by microorganisms. The nonwoven fabric C according to this embodiment is a biodegradable nonwoven fabric made from a polylactic acid-based material. However, the nonwoven fabric C is not limited to biodegradable nonwoven fabrics made from a polylactic acid-based material, and can be modified as appropriate.

[0017] The crystallization rate of polylactic acid is slower than that of thermoplastic resins such as polypropylene (PP). When nonwoven fabric made from polylactic acid is produced by the spunbond method, under the conditions for producing nonwoven fabric made from polypropylene, the polylactic acid fibers discharged from the nozzle (discharge outlet, spinneret 23 shown in Figure 5) in the spinning process do not crystallize on the conveyor. Furthermore, since polylactic acid has low heat resistance when the crystallization degree is low, when fiber layers of polylactic acid with low crystallization degree are fused together by embossing, the fibers with low heat resistance will stick to the heated roll. Furthermore, polylactic acid However, if the crystallinity is insufficient, thermal shrinkage occurs when heated. Therefore, passing low-crystallinity polylactic acid fibers through a heated roll can result in thermal shrinkage and an uneven surface. Furthermore, the glass transition temperature of polylactic acid is approximately 60°C. Generally, when uncrystallized or low-crystallinity thermoplastic resins are heated above the glass transition temperature of the fibers by a heated roll, the fibers stick to the heated roll. To solve these problems, a nucleating agent (nucleating agent) can be added to the raw material polylactic acid to increase the resin's crystallinity. However, this creates another problem: the nucleating agent remains after biodegradation of the biodegradable nonwoven fabric. Furthermore, adding a nucleating agent to the raw resin of nonwoven fabrics makes it difficult to pull the fibers tightly during the spinning process, resulting in a larger fiber diameter. As the fiber diameter increases, nonwoven fabrics become stiffer and less comfortable against the skin. Nonwoven fabrics that are less comfortable against the skin are unsuitable for use in absorbent articles or masks.

[0018] The nonwoven fabric manufacturing method according to this embodiment does not involve welding the stacked fiber layers C1 by embossing. Therefore, even when fiber layers made of polylactic acid with low crystallinity are welded together, the fibers are prevented from sticking to the heated roll. Furthermore, since the fibers welded by ultrasonic welding are inside the stacked fiber layers C1 in the area where the ultrasonic waves are transmitted, the outer surface (surface) of the fiber layer is prevented from becoming uneven, improving the feel against the skin. Furthermore, since there is no need to add a crystal nucleating agent (nucleating agent) to the raw material polylactic acid, the fiber diameter is prevented from increasing, improving the feel against the skin. Therefore, according to this embodiment, the feel against the skin of the nonwoven fabric C made from polylactic acid as the raw material can be improved.

[0019] In this embodiment, no nucleating agent is added to the raw material polylactic acid. As a result, the nonwoven fabric C produced by the manufacturing method of this embodiment does not contain a nucleating agent. As a result, the nonwoven fabric C produced by the manufacturing method of this embodiment does not leave behind any nucleating agent after decomposing in nature. Furthermore, if the raw resin contains a nucleating agent, the resin cannot be pulled strongly during the spinning process, resulting in thicker fibers. Furthermore, the use of a nucleating agent increases the manufacturing cost of the nonwoven fabric C. However, since the nonwoven fabric C produced by the manufacturing method of this embodiment does not contain a nucleating agent, these problems do not occur. Furthermore, the nonwoven fabric C produced by the manufacturing method of this embodiment does not contain a crystallization accelerator.

[0020] Next, a method for producing nonwoven fabric C according to this embodiment will be described with reference to FIG. 4. FIG. 4 is a flowchart illustrating the method for producing nonwoven fabric C according to this embodiment. First, in the method for producing nonwoven fabric C according to this embodiment, in the spinning step, molten polylactic acid resin is discharged vertically downward from a spinneret, and the resin is pulled vertically downward by an airflow to form fibers (step S101, an example of the "spinning step" in this application). In the conveying step S102 following step S101, the fibers are piled up on a conveyor and conveyed. In the welding step S103 following step S102, the fibers stacked in three layers are passed through a horn and ultrasonic vibrations are transmitted to weld the fibers together (an example of the "ultrasonic welding step" in this application).

[0021] Next, a method and apparatus for producing the nonwoven fabric C according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram showing a nonwoven fabric production apparatus M for producing the nonwoven fabric C according to this embodiment. In Fig. 5, the nonwoven fabric production apparatus M is equipped with three sets of spraying devices (fiber spraying devices) 10, and each of the spraying devices 10 (10A, 10B, 10C) is constructed with a spinning device 20, a cooling air device 30, and an injector 40. By being equipped with the spraying devices 10A, 10B, 10C, the nonwoven fabric production apparatus M can produce a three-layer nonwoven fabric C.

[0022] In the nonwoven fabric manufacturing apparatus M, together with the ejection device 10, a collection conveyor 50, an ultrasonic welding device 60, and a winder 70 are arranged in series so that various processes can be performed. 10A, 10B, and 10C are arranged in series in the conveying direction on the conveying surface above the collecting conveyor 50. The direction toward the paper surface of Figure 5 is the CD (cross direction) of the nonwoven fabric manufacturing apparatus M. The nonwoven fabric manufacturing apparatus M is constructed to continuously manufacture nonwoven fabric C, and produces nonwoven fabric C by a so-called spunbond method in which spun fibers (filaments) are collected in a sheet form and ultrasonic welding is performed to appropriately bond the fibers together.

[0023] The spinning device 20 is configured to include an extruder 21 and a spinneret 23. The extruder 21 melts raw material resins R (R1, R2, R3) supplied to a hopper 22, and sends a predetermined flow rate of the melt to the spinneret 23 by rotating a spiral rotor 21r. The spinneret 23 has multiple composite spinning nozzles (not shown) configured to discharge the melt while forming a desired fibrous structure, and spins (discharges) the melt from the extruder 21 in the direction of gravity as a bundle F of multiple filaments (fibers) f (hereinafter referred to as a "filament aggregate"). As described above, a polylactic acid-based resin is used as the raw material resin R.

[0024] The cooling air device 30 is equipped with a pair of open-type air blowers 31, 32 arranged in opposing positions. When viewed from the spinning direction (gravity direction), the cooling air device 30 is arranged between the spinning device 20 and the injector 40. The cooling air device 30 cools the filament aggregate F that is discharged from the spinning device 20 and passes from above to below by blowing cooled air Ac from each of the air blowers 31, 32. Here, one of the air blowers 31 is installed as a large type that can be used as a main blower, and the other opposite air blower 32 is installed as a small type that can be used as a sub blower and auxiliary. In the open-type nonwoven fabric manufacturing apparatus M, air can flow in from outside the air blower 30 when cooling with the air blower 30.

[0025] The injector 40 has a structure that generates a low-pressure region on the inlet side of the body 41 by blowing downward-flowing high-pressure air as a driving fluid onto the filament aggregate F that descends through the body 41 from above in the spinning direction. The injector 40 draws the descending filament aggregate F so as to draw it into the low-pressure region on the inlet side of the body 41, and also draws it downward within the body 41 with high-pressure air, thereby stretching the filament aggregate F that descends from above in the spinning direction via the cooling air device 30. The process from when the polylactic acid-based resin is discharged from the spinneret 23 of the spinning device 20 until the filament aggregate F is deposited on the collection conveyor 50 is step S101 (spinning process) shown in FIG. 4.

[0026] The collecting conveyor 50 is constructed to include a main conveyor 51, sub-conveyors 52 and 53, and a suction box (suction means) 54. The main conveyor 51 is installed so that a mesh-like collecting belt 151, which is formed wider than the width of the filament aggregate F and is breathable on both sides, is wound around a group of rollers 151r and driven to rotate. The sub-conveyors 52 and 53 are also installed so that mesh-like collecting belts 152 and 153, which are formed wider than the width of the filament aggregate F and are breathable on both sides, are wound around a group of rollers 152r and a group of rollers 153r, respectively, and driven to rotate in opposite directions.

[0027] The collecting belt 151 is wound around a group of rollers 151r with a length that ensures that the upper surface 151a is positioned at the spraying points below the spraying devices 10A, 10B, and 10C. The collecting belt 151 receives and transports the filament aggregate Fa that is pulled down by the injector 40 and stretched by the injector 40, thereby collecting the filament aggregate Fa into a cloth (sheet). That is, the collecting belt 151 has a sufficient area to collect the sheet-like filament aggregate Fa and functions as a collecting surface and a conveying surface by rotating from the upstream end (leading edge) to the downstream end (rear edge) in the rotating direction (transport direction) of the upper surface 151a. The filament aggregate Fa forms the lower fiber layer C1 in the nonwoven fabric C shown in FIG. 2.

[0028] The collecting belt 152 is wound around a group of rollers 152r with its upper surface 152a positioned at a spraying point below the jetting device 10B, which is located midway in the circumferential movement direction of the upper surface 151a of the collecting belt 151. The collecting belt 152 receives and transports the filament aggregate Fb that is pulled down by the injector 40, thereby collecting it in sheet form. The collecting belt 153 is wound around a group of rollers 153r with its upper surface 153a positioned at a spraying point below the jetting device 10C, which is located at the downstream end (rearmost rear) of the circumferential movement direction of the upper surface 151a of the collecting belt 151. The collecting belt 153 receives and transports the filament aggregate Fc that is pulled down by the injector 40, thereby collecting it in sheet form. The filament aggregate Fb becomes the middle fiber layer C1 in the nonwoven fabric C shown in FIG. 2.

[0029] These collecting belts 152, 153 are installed downstream from below the jetting device 10A, which is located at the upstream end (head) of the circulating direction of the upper surface 151a of the collecting belt 151, and are driven to rotate in the reverse direction while positioned between the upper surface 151a and the jetting devices 10B, 10C, so that their upper surfaces 152a, 153a function as a collecting surface and a conveying surface for collecting the sheet-like filament assemblies Fb, Fc. The collecting belts 152, 153 are driven to rotate between their lower parts facing the upper surface (upper part) 151a of the collecting belt 151 so as to sandwich the sheet-like filament assemblies Fb, Fc without peeling or turning over, thereby assisting in the conveyance downstream.

[0030] The suction box 54 is housed within the collecting belt 151 of the main conveyor 51 and is divided into suction chambers 154a, 154a-2, 154b, 154b-2, 154c, and 154c-2, each functioning as a decompression chamber. Suction ports (not shown) are arranged in the suction chambers 154a to 154c-2 so as to suck the upper sides, and suction fans 155a to 155c-2, which can be driven individually, are connected to enable suction.

[0031] The suction chambers 154a, 154b, and 154c are installed so as to be located below the injectors 40 of the ejection devices 10A, 10B, and 10C, respectively, and the suction chambers 154a-2, 154b-2, and 154c-2 are installed so as to be located downstream of these suction chambers 154a, 154b, and 154c.

[0032] The suction chamber 154a is installed so as to be located directly below the collection belt 151 of the main conveyor 51 below the injector 40 of the ejection device 10A, and when the suction fan 155a is driven to reduce the pressure, it sucks in the area from directly below the collection belt 151 upward.

[0033] The suction chamber 154a-2 is located adjacent to the downstream side of the suction chamber 154a and is positioned directly below the collection belt 151 of the main conveyor 51 between it and the suction chamber 154b located below the ejection device 10B, as described below.The suction fan 155a-2 is driven to reduce the pressure, thereby sucking in the area above the collection belt 151.

[0034] As a result, the filament aggregate Fa spun by the jetting device 10A is sucked by the suction chamber 154a below the collecting belt 151 of the main conveyor 51 so as to be collected on the upper surface 151a. As the collecting belt 151 moves around in the length direction, the filament aggregate Fa is collected in a sheet-like form on the upper surface 151a and held thereon for transport. Thereafter, as the collecting belt 151 moves around in the length direction, the filament aggregate Fa is passed from the suction chamber 154a to the adjacent suction chamber 154a-2, where it is sucked and held thereon so as to maintain its sheet shape and is transported.

[0035] The suction chamber 154b is installed so as to be located directly below the collecting belt 151 of the main conveyor 51 below the injector 40 of the ejection device 10B, and is driven by a suction fan 155b. As the pressure is reduced by moving the conveyor 52, the area directly below the collecting belt 151 and above the collecting belt 152 of the sub-conveyor 52 is sucked.

[0036] The suction chamber 154b-2 is located adjacent to the downstream side of the suction chamber 154b and is positioned directly below the collection belt 151 of the main conveyor 51 between it and the suction chamber 154c located below the ejection device 10C, as described below.The suction fan 155b-2 is driven to reduce the pressure, thereby sucking in the area above the collection belt 151.

[0037] As a result, the filament aggregate Fa spun by the ejection device 10A is transported by the suction chambers 154a and 154a-2 described above, followed by the suction chambers 154b and 154b-2 below the collecting belt 151 of the main conveyor 51, where it is suctioned and held in sheet form on the upper surface 151a.

[0038] Furthermore, the filament aggregate Fb spun by the jetting device 10B is sucked by the suction chamber 154b below the collecting belt 151 of the main conveyor 51 so as to be collected on the upper surface 152a of the collecting belt 152 of the sub-conveyor 52 on the upper surface 151a. Therefore, the filament aggregate Fb is collected and held in a sheet-like form on the upper surface 152a as the collecting belt 152 moves around in the longitudinal direction.

[0039] Incidentally, the collecting belt 152 of the sub-conveyor 52 rotates in the opposite direction to the collecting belt 151 of the main conveyor 51, and therefore the upper surface 152a of the collecting belt 152 moves in the opposite direction, and then is turned upside down and moves in the same direction facing the upper surface 151a of the collecting belt 151 of the main conveyor 51. Therefore, the filament aggregate Fb spun by the jetting device 10B is collected and held in a sheet-like form on the upper surface 152a of the collecting belt 152 of the sub-conveyor 52 and transferred, and then overlaps the sheet-like filament aggregate Fa on the upper surface 151a of the collecting belt 151 of the main conveyor 51, and is suction-held in the sheet-like form by the suction chamber 154b below the collecting belt 151 of the main conveyor 51 and transferred.

[0040] As a result, the filament aggregate Fab (Fa, Fb) that is collected, held, and stacked in a sheet form below the ejection device 10B is transferred from the suction chamber 154b to the adjacent suction chamber 154b-2 as the collection belt 151 moves around in the longitudinal direction, where it is suction-held and transported so as to maintain its sheet shape.

[0041] The suction chamber 154c is installed so as to be located directly below the collection belt 151 of the main conveyor 51 below the injector 40 of the ejection device 10C, and when the suction fan 155c is driven to reduce the pressure, it sucks in the area directly below the collection belt 151 and above the collection belt 153 of the sub-conveyor 53.

[0042] The suction chamber 154c-2 is installed adjacent to the downstream side of the suction chamber 154c, as described below, so as to be located just below the end of the collection belt 151 of the main conveyor 51, and when the suction fan 155c-2 is driven to reduce the pressure, it sucks in the area from just below the collection belt 151 upward.

[0043] As a result, the filament aggregates Fab spun by the ejection devices 10A and 10B are transported by the suction chambers 154a to 154b-2 described above, followed by the suction chambers 154c and 154c-2 below the collecting belt 151 of the main conveyor 51, where they are suction-held in sheet form overlapping on the upper surface 151a.

[0044] The filament aggregate Fc spun by the ejection device 10C is caught by the main conveyor 51. The filament aggregate Fc is sucked by the suction chamber 154c below the collecting belt 151 so as to be collected on the upper surface 153a of the collecting belt 153 of the sub-conveyor 53 on the upper surface 151a. As a result, the filament aggregate Fc is collected in a sheet-like form on the upper surface 153a and held and transported as the collecting belt 153 moves around in the longitudinal direction. The filament aggregate Fc becomes the upper fiber layer C1 of the nonwoven fabric C shown in FIG. 2.

[0045] Incidentally, the collecting belt 153 of the sub-conveyor 53 also rotates in the opposite direction to the collecting belt 151 of the main conveyor 51, and therefore the upper surface 153a of the collecting belt 153 moves in the opposite direction, and then is turned upside down and moves in the same direction facing the upper surface 151a of the collecting belt 151 of the main conveyor 51. Therefore, the filament aggregate Fc spun by the jetting device 10C is collected and held in a sheet-like form on the upper surface 153a of the collecting belt 153 of the sub-conveyor 53 and transferred, and then further overlaps the sheet-like filament aggregate Fab on the upper surface 151a of the collecting belt 151 of the main conveyor 51, and is suction-held in the sheet-like form by the suction chamber 154c below the collecting belt 151 of the main conveyor 51 and transferred.

[0046] As a result, the filament aggregate Fabc (Fa, Fb, Fc) that is collected, held, and stacked in a sheet form below the ejection device 10C is transferred from the suction chamber 154c to the adjacent suction chamber 154c-2 as the collection belt 151 moves around in the longitudinal direction, where it is suction-held and transported so as to maintain its sheet shape.

[0047] In short, the collecting conveyor 50 collects and holds the filament assemblies Fa, Fb, and Fc spun by the spraying devices 10A, 10B, and 10C on the upper surfaces 151a to 153a of the collecting belts 151 to 153 by suction using suction boxes 54 in the form of a sheet of a predetermined thickness, and then stacks them to form a filament assembly FaC (nonwoven fabric C) before ultrasonic welding, which is transported downstream and handed over to the ultrasonic welding device 60. The process in which the filament assemblies Fa, Fb, and Fc are piled up on the collecting conveyor and transported is step S102 shown in FIG.

[0048] In the process of step S103 shown in FIG. 4, ultrasonic vibrations are transmitted to the filament assembly FABC that has been transported to the ultrasonic welding device 60, and welding is performed.

[0049] FIG. 6 is a perspective view of an ultrasonic welding apparatus 60 according to this embodiment. The ultrasonic welding apparatus 60 includes a transducer 60A, an ultrasonic generator 60B, and a cable 60K connecting each transducer 60A and the ultrasonic generator 60B above a filament assembly Fbc. The ultrasonic generator 60B converts commercial power into ultrasonic power, and supplies the ultrasonic power converted by the ultrasonic generator 60B to the transducer 60A via the cable 60K. The transducer 60A generates ultrasonic vibrations using the supplied ultrasonic power and transmits the ultrasonic vibrations to the filament assembly Fbc transported below the transducer 60A. The transmitted ultrasonic vibrations heat the interior of the filament assembly Fbc, causing the filaments f to weld together. The ultrasonic generator 60B may be integrated with the transducer 60A.

[0050] Furthermore, a roll-shaped rotating body 60R may be disposed below the ultrasonic welding device 60. When the filament assembly Fabc passes between the rotating body 60R and the ultrasonic welding device 60, the filaments f in the filament assembly Fabc can be fused together while the filament assembly Fabc is being transported by the rotating body 60R.

[0051] 7 is a diagram showing an extracted portion of a vibrator 60A provided in the ultrasonic welding apparatus 60. The vibrator 60A includes an ultrasonic generator 60S that generates ultrasonic vibrations, and a filter 60B that is disposed below the ultrasonic generator 60S and amplifies the amplitude of the ultrasonic vibrations generated by the ultrasonic generator 60S. The ultrasonic vibration amplifier 60A includes an amplitude amplifier 60E and a horn 60F disposed below the amplitude amplifier 60E for transmitting ultrasonic vibrations whose amplitude has been amplified by the amplitude amplifier 60E to the filament assembly Fbc. The oscillator 60A vibrates in the vertical direction (up and down) and brings the horn 60F into contact with the filament assembly Fbc transported below the horn 60F. When the ultrasonic vibrations are transmitted to the filament assembly Fbc from the contact surface of the horn 60F, the filaments f are fused together inside the filament assembly Fbc below the contact surface.

[0052] FIG. 8 illustrates how the vertically vibrating horn 60F transmits ultrasonic vibrations to the filament assembly FBC. FIG. 8(A) illustrates a state in which the horn 60F is positioned above the filament assembly FBC. The horn 60F vibrates vertically, changing from the state shown in FIG. 8(A) to a state in which it contacts the filament assembly FBC as shown in FIG. 8(B). When the filament assembly FBC and the horn 60F are in contact as shown in FIG. 8(B), ultrasonic vibrations are transmitted to the filament assembly FBC. Then, when the horn 60F is separated from the filament assembly FBC as shown in FIG. 8(C), the filaments f within the filament assembly FBC are welded together. The horn 60F may be a rotating body having a roll shape, and ultrasonic vibrations may be transmitted to the filament assembly FBC from the side of the roll. The vertically vibrating horn 60F applies pressure vertically for a shorter period of time than a rotating body, thereby preventing the surface of the filament assembly FBC from hardening.

[0053] Normally, when filaments are welded together, the filaments f become hard at the welded portions, resulting in a poor feel against the skin. In this embodiment, ultrasonic vibration generates heat inside the filament aggregate Fbc, causing the filaments f inside the filament aggregate Fbc to weld together, thereby preventing the filaments f on the exterior (surface) of the filament aggregate Fbc from welding together. This prevents the filaments f from hardening outside the filament aggregate Fbc, improving the feel against the skin.

[0054] As a result, the ultrasonic welding device 60 comes into contact with the horn 60F, and welds the filaments f together inside the filament assembly Fbc to which the ultrasonic vibrations are transmitted, thereby processing the nonwoven fabric C into one that maintains its sheet-like shape. The ultrasonic welding device 60 may also apply pressure in the vertical direction while transmitting the ultrasonic vibrations. By applying pressure, the filaments f become entangled, and the ultrasonic welding device 60 can weld the filaments f while entangling them.

[0055] The pressure with which the horn 60F presses the filament aggregate FBC may be varied depending on the raw material of the filaments f. For example, applying a higher pressure to less meltable filaments f than to more meltable filaments f increases the welding strength between the filaments f. When pressing a filament aggregate FBC made of easily meltable filaments f, lowering the pressure prevents the filaments f from hardening on the outer surface (surface) of the filament aggregate FBC, thereby improving the feel against the skin. Therefore, by varying the pressure with which the horn 60F presses the filament aggregate FBC depending on the raw material of the filaments f, it is possible to produce a nonwoven fabric C with a feel that is suited to the skin for each raw material of the filaments f. It is also possible to produce nonwoven fabrics C with different feel against the skin by varying the pressure with which multiple filament aggregates FBC made from the same raw material are pressed.

[0056] The amplitude of the ultrasonic vibration transmitted to the filament assembly Fbc may be changed depending on the material of the filaments f. The amplitude refers to the amplitude of the vibration at the tip of the horn 60F. For example, for filaments f that are difficult to melt, the amplitude of the ultrasonic vibration is made larger than for filaments f that are easy to melt, which increases the amplitude of the vibration at the tip of the horn 60F and increases the welding strength between the filaments f. In addition, for a filament assembly Fbc that is made up of filaments f that are easy to melt, When transmitting ultrasonic vibrations to abc, the amplitude of the ultrasonic vibrations is reduced and the amplitude of the vibration at the tip of the horn 60F is reduced to prevent filaments f from welding together on the exterior (surface) of the filament aggregate Fbc. This prevents the filaments f from hardening on the exterior (surface) of the filament aggregate Fbc, improving the feel against the skin. The feel against the skin can also be improved by changing the frequency of the ultrasonic vibrations transmitted to the filament aggregate Fbc. A low frequency increases the amplitude, and a high frequency decreases the amplitude. Nonwoven fabrics C with different feel against the skin can also be produced by varying the amplitude or frequency of the ultrasonic vibrations transmitted to multiple filament aggregates Fbc made from the same raw material.

[0057] In this embodiment, the fiber layers C1 constituting the nonwoven fabric C are made of polylactic acid-based resin. However, different resins may be used as long as they can be stretched during the spinning process (step S101). For example, the middle fiber layer C1 may be made of a resin that melts easily, while the upper and lower fiber layers C1 constituting the outer (surface) portions of the nonwoven fabric C may be made of a resin that melts less easily. The middle fiber layer C1, made of a resin that melts easily, melts more easily with ultrasonic vibrations than the resins constituting the upper and lower fiber layers C1. Therefore, when ultrasonic vibrations are transmitted to melt the resins constituting the upper and lower fiber layers C1, the resin constituting the middle fiber layer C1 sandwiched between the upper and lower fiber layers C1 melts more than the resins constituting the upper and lower fiber layers C1, thereby increasing the welding strength within the nonwoven fabric C. On the other hand, the outer (surface) portions of the nonwoven fabric C are made of the upper and lower fiber layers C1, and therefore have weaker welding strength than the inner portions of the nonwoven fabric C. This prevents the filaments f from becoming hard and improves the feel against the skin. In this case, the filaments f constituting either the upper or lower fiber layer C1 that forms the exterior (surface) of the nonwoven fabric C may be made to be easily melted. By hardening the surface of the nonwoven fabric C that faces away from the wearer's skin when the nonwoven fabric C is processed into an absorbent article, a mask, or the like, it is possible to produce a nonwoven fabric C that can withstand stimuli such as friction applied to the face away from the skin when worn by a wearer.

[0058] 4, a pressing step may be provided in which the filament aggregate FBC passes between a pair of upper and lower rolls to uniformize the thickness of the filament aggregate FBC. Uniform thickness of the filament aggregate FBC prevents uneven transmission of ultrasonic vibrations in step S103. Therefore, in the nonwoven fabric C, uneven welding between the filaments f is eliminated, and the formation of unbonded or weakly bonded portions between the fiber layers C1 is suppressed.

[0059] The winder 70 receives the nonwoven fabric C in which the filaments f of the filament aggregate Fbc are joined together by the ultrasonic welding device 60 while adjusting the tension so as not to slacken, and continuously winds the nonwoven fabric C into a roll without wrinkles and with the desired winding hardness.

[0060] As a result, the winder 70 can prepare the nonwoven fabric C of a desired length, in which the filament aggregate Fbc is formed into a sheet and wound into a roll, so that it can be supplied to the next processing step or the like.

[0061] In this way, by welding the filaments f together inside the filament aggregate Fbc by ultrasonic welding, it is possible to produce a nonwoven fabric C that feels good against the skin. Also, it is possible to produce a nonwoven fabric C made from a polylactic acid-based resin.

[0062] As described above, in the collecting conveyor 50 of this embodiment, the suction chambers 154a to 154c-2 of the suction box 54 installed under the collecting belt 151 of the main conveyor 51 are partitioned and installed to correspond to the injectors 40 of the jetting devices 10A to 10C, and the suction fans 155a to 155c-2 connected to each of the suction chambers 154a to 154c-2 are also configured to have a wind speed (air volume) according to the partition range (area) of the suction chambers 154a to 154c-2 and the required suction pressure. Here, the suction chambers 154a to 154c-2 are set to suck in a range of compartments to be sucked and a suction pressure can be set appropriately.

[0063] Specifically, the suction chamber 154a sucks the filament aggregate Fa, which is pulled down from the outlet of the injector 40 of the ejection device 10A directly above the collection belt 151 of the main conveyor 51, from below the collection belt 151 without the need for a sub-conveyor, and collects and holds it in a sheet form.

[0064] This suction chamber 154a is partitioned so that a suction pressure Pa capable of stably holding the descending filament aggregate Fa is generated under the conveying surface of the collection belt 151 in a narrow range approximately equal to the spray area in the transport direction, and the interior of this partitioned range is suctioned by a suction fan 155a to create a negative pressure.

[0065] The suction chambers 154b and 154c respectively suck the filament assemblies Fb and Fc that are pulled down from the outlets of the injectors 40 of the ejection devices 10B and 10C directly above the collecting belts 152 and 153 of the sub-conveyors 52 and 53 from below the collecting belt 151, and collect and hold them in a sheet form. These sub-conveyors 52 and 53 sandwich the sheet-like filament assemblies Fb and Fc that are collected and held on the collecting belts 152 and 153 between themselves and the lower collecting belt 151, and send them downstream as filament assemblies Fab and Fabc.

[0066] These suction chambers 154b, 154c are driven by suction fans 155b, 155c to create negative pressure so as to generate suction pressures Pb, Pc below the conveying surfaces of the collecting belts 152, 153, sufficient to stably hold the descending filament assemblies Fb, Fc. Similar to the suction chamber 154a, these suction chambers 154b, 154c are also suctioned and created negative pressure by the suction fans 155b, 155c so as to generate the desired suction pressures Pb, Pc in a narrow, compartmented range approximately equal to the spray area in the conveying direction of the descending filament assemblies Fb, Fc. At the same time, these suction chambers 154b, 154c apply suction to the collecting belts 152, 153 of the sub-conveyors 52, 53, with the filament assemblies Fab, Fabc on the collecting belt 151 interposed therebetween. For this reason, these suction chambers 154b, 154c may increase or decrease the suction volume by adjusting the suction range in the transport direction below the collection belt 151 so that optimal suction pressures Pb, Pc are generated on the collection belts 152, 153, and the suction range within the collection belts 152, 153 may also be similarly divided into adjustable sections.

[0067] As a result, the suction chambers 154b and 154c, like the suction chamber 154a, can continuously suck and hold the filament assemblies Fab and Fabc that are increased from the sheet-like filament assembly Fa via the collection belt 151 of the main conveyor 51.

[0068] The suction chambers 154a-2, 154b-2, and 154c-2 continuously suck and hold the sheet-like filament assemblies Fa, Fab, and Fabc on the collection belt 151 of the main conveyor 51 downstream of the suction chambers 154a, 154b, and 154c, respectively.

[0069] These suction chambers 154a-2, 154b-2, and 154c-2 are driven by suction fans 155a-2, 155b-2, and 155c-2 to generate suction pressures Pa-2, Pb-2, and Pc-2, respectively, that continuously suck and hold the sheet-like filament aggregates Fa, Fab, and Fabc on the collection belt 151. The suction chambers 154a-2 and 154b-2 are interposed between the suction chambers 154a, 154b, and 154c, and are continuous to suck without gaps. Therefore, they are installed to suck a wide partitioned area so as to connect the separate collection positions of each ejection device 10. The suction chamber 154c-2 receives the sheet-like filament aggregates Fa, Fab, and Fabc from the suction chamber 154c. Since the device simply delivers the liquid to the adjacent ultrasonic welding device 60 downstream, it is installed so as to suck in a relatively short section range.

[0070] As a result, the suction chambers 154a-2, 154b-2, and 154c-2 can suck and hold the sheet-like filament assemblies Fa, Fab, and Fabc located on the upper surface 151a via the collecting belt 151 of the main conveyor 51, successively to the suction chambers 154a, 154b, and 154c, respectively. At this time, the sheet-like filament assemblies Fa and Fab on the collecting belt 151 of the main conveyor 51 are sucked and held by the suction chambers 154a-2 and 154b-2, respectively, and therefore do not float up, but are sandwiched between the collecting belts 152 and 153 of the sub-conveyors 52 and 53. Furthermore, the sheet-like filament assemblies Fa and Fab are superimposed on the sheet-like filament assemblies Fb and Fc that are collected and held by the collecting belts 152 and 153 and are turned upside down, forming sheet-like filament assemblies Fab and Fabc, which are then transported downstream while being sucked and held.

[0071] As described above, the collecting conveyor 50 is configured so that each suction fan 155a to 155c-2 of the suction box 54 generates a suction pressure P sufficient to collect and hold the sheet-like filament aggregate F on the collecting belt 151 of the main conveyor 51, and the individual suction fans 155a to 155c-2 are configured to suck at the required wind speed.

[0072] For example, the suction box 54 is adjusted so that the suction pressures Pa, Pb, and Pc of the suction chambers 154a, 154b, and 154c located at the points where the filament aggregate F is sprayed by the spraying devices 10A, 10B, and 10C on the collection conveyor 50 are greater than the suction pressures Pa-2, Pb-2, and Pc-2 of the suction chambers 154a-2, 154b-2, and 154c-2 located downstream of each other. Furthermore, among these, the suction pressures Ps (Pa, Pa-2) of the leading suction chambers 154a, 154a-2 in the transport direction of the filament aggregate F, Pm (Pb, Pb-2) of the intermediate suction chambers 154b, 154b-2, and Pe (Pc, Pc-2) of the rearmost suction chambers 154c, 154c-2 are suction-held on both the upstream and downstream sides, so the suction pressure Pm at the intermediate position can be adjusted to be smaller than the leading suction pressure Ps and the rearmost suction pressure Pe (Ps > Pm and Pe > Pm). Furthermore, the suction pressures Pa, Pb, and Pc are adjusted according to the weight of the filament aggregate F on the transport surface so as not to excessively reduce the pressure inside the suction chambers 154a, 154b, and 154c, thereby preventing smooth relative movement of the collecting belt 151.

[0073] <Other embodiments> Although the embodiments of the present invention have been described above, the various embodiments described above can be combined as much as possible. [Explanation of symbols]

[0074] C··Non-woven fabric C1 Fiber layer M··Nonwoven fabric manufacturing equipment 10, 10A, 10B, 10C...Ejection device 20. Spinning equipment 30·Cold air device 40··Injector 50··Collection conveyor 51 Main conveyor 52, 53 Sub-conveyor 54··Suction box 60··Embossing device 70··Winder 141, 142 Signboard 151, 152, 153 Collection belt 154a, 154b, 154c··Suction chamber 162 Adjustment roller f··filament fr··Rotation diameter F, Fa, Fab, Fabc, Fb, Fc filament assembly Lc Intersection distance Ld...Open interval Lr Evacuation interval P, Pa, Pb, Pc, Pe, Pm, Ps... Suction pressure (wind speed) 60...Ultrasonic welding equipment 60A vibrator 60B··Ultrasonic oscillator 60S··Ultrasonic Generator 60E Amplitude Enlargement Device 60F Horn 60R Rotating body

Claims

1. a spinning step in which the molten resin is discharged from a die and stretched by an air current to form fibers; an ultrasonic welding process of transmitting ultrasonic vibrations to the fibrous resin fibers to weld the fibers together, Nonwoven fabric manufacturing method.

2. The resin is made from a biodegradable material. The method for producing a nonwoven fabric according to claim 1.

3. The resin is a polylactic acid resin. The method for producing a nonwoven fabric according to claim 2.

4. a spinning device that discharges a molten resin from a nozzle and stretches the resin using an airflow to form fibers; an ultrasonic welding device that transmits ultrasonic vibrations to the fibrous resin fibers to weld the fibers together, Nonwoven fabric manufacturing equipment.

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