Nonwoven fabric manufacturing method

Abstract

To provide a production method of nonwoven fabric that has an extremely thin thickness and is not be broken in the production process.SOLUTION: A production method of nonwoven fabric includes: a fiber ejection step of ejecting fibers from a plurality of fiber ejection units; a sheet conveyance step of conveying a sheet-like fiber layer in a transport direction, while collecting, on a conveyance surface, bundles of fibers ejected from the fiber ejection units to make the sheet-like fiber layer; and a fusion step of applying, by heating rollers, heat and pressure to the sheet-like fiber layer to fuse it. The fiber ejection unit includes at least: a first fiber ejection unit for forming a first layer in a thickness direction on the conveyance surface; and a second fiber ejection unit for ejecting fibers of a material different from the material at the first fiber ejection unit so as to form a second layer in the thickness direction on the conveyance surface. The production method of nonwoven fabric peels off the first layer and the second layer from each other after the fusion step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventionally, a method for producing a nonwoven fabric has been known (Patent Document 1). [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] One method for providing highly usable nonwoven fabrics is to reduce their thickness. Thin nonwoven fabrics have high conformability and are suitable, for example, as sanitary materials. However, during the manufacturing process, heat and tension are applied when the accumulated fiber layer is pulled out from the conveyor and heated and pressurized. If an attempt is made to manufacture a very thin nonwoven fabric during the manufacturing process, the heat and tension may cause the nonwoven fabric to break during the manufacturing process.

[0005] An object of the present invention is to provide a method for producing a nonwoven fabric that is very thin and does not break during the manufacturing process. [Means for solving the problem]

[0006] In order to solve the above problems, in the present invention, resin layers made of different materials are stacked and accumulated, and then peeled off after being heated and pressed.

[0007] Specifically, the present invention is a method for manufacturing nonwoven fabric, which includes a fiber spraying process in which fibers are sprayed from a plurality of fiber spraying devices; a sheet conveying process in which bundles of fibers sprayed from the plurality of fiber spraying devices are collected on a conveying surface and conveyed in a transfer direction while being formed into a sheet-like fiber layer; and a fusion process in which heat and pressure are applied to the sheet-like fiber layer by a heat roller to fuse them together, wherein the plurality of fiber spraying devices include at least a first fiber spraying device that forms a first layer in the thickness direction on the conveying surface, and a second fiber spraying device that sprays fibers made of a different material from the first fiber spraying device to form a second layer in the thickness direction on the conveying surface, and after the fusion process, the first layer and the second layer are peeled off.

[0008] The fiber layer constituting the first layer and the fiber layer constituting the second layer may have low compatibility.

[0009] After the peeling, the first layer and the second layer may be obtained as separate nonwoven fabrics.

[0010] The second fiber spraying device may have a plurality of fiber discharge ports, and the fiber layer constituting the second layer may be composed of two or more layers in the thickness direction.

[0011] The fiber layer constituting the first layer may be a single layer.

[0012] The first layer may be formed of polylactic acid fibers, and the second layer may be formed of fibers made of any one of polypropylene, polyethylene, and polyethylene terephthalate.

[0013] The surface temperature of the heat roller may be 120° C. or higher.

[0014] The conveying speed of the sheet conveying step may be 40 m / min or more, and the fiber discharge rate of the first fiber spraying device may be 0.5 / hole / min or less.

[0015] The fiber discharge pressure of the first fiber spraying device may be 0.11 MPa or more, and the yarn diameter of the first layer conveyed in the sheet conveying step may be 15 μm or less. [Effects of the Invention]

[0016] According to the present invention, it is possible to produce a nonwoven fabric that is very thin and does not break during the manufacturing process. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a plan view of a nonwoven fabric according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view in the CD direction of the nonwoven fabric according to the embodiment. [Figure 3] FIG. 3 is a flowchart showing a method for producing a nonwoven fabric according to an embodiment. [Figure 4] FIG. 4 is a diagram showing a nonwoven fabric manufacturing apparatus for manufacturing the nonwoven fabric according to the embodiment. [Figure 5] FIG. 5 is a diagram showing an example of a step of peeling off the nonwoven fabric. [Figure 6] FIG. 6 is a diagram showing an example of yet another step of peeling off the nonwoven fabric. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a manufacturing process of a nonwoven fabric according to an embodiment of the present invention will be described with reference to the 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.

[0019] <Embodiment> Fig. 1 is a plan view of nonwoven fabric C according to this embodiment as seen from above. Fig. 2 is a cross-sectional view of nonwoven fabric C in the CD direction when cut along line AA shown in Fig. 1. Nonwoven fabric C is a sheet with the longitudinal direction in the MD direction, and is composed of multiple layers.

[0020] As shown in FIG. 2, nonwoven fabric C has a two-layer structure in which fiber layers C1 and C2 are laminated. Fiber layer C1 is formed from fibers made from a polylactic acid-based resin. Fiber layer C1 corresponds to the second layer in the present disclosure. Polylactic acid is used as a raw material for biodegradable nonwoven fabrics. Fiber layer C2 is formed from a resin selected from polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Fiber layer C2 corresponds to the first layer in the present disclosure. Note that nonwoven fabric C may have a three-layer or more structure, for example, in which a fiber layer made from polylactic acid is sandwiched between fiber layers made from polyethylene, polypropylene, or polyethylene terephthalate.

[0021] Polylactic acid (PLA) is a biodegradable resin made from lactic acid, which is produced by fermenting glucose. Polylactic acid is eventually decomposed into carbon dioxide and water by microorganisms, reducing the environmental impact. The fiber diameter of the fibers that make up the fiber layer C1 is 15 μm or less.

[0022] In nonwoven fabric C, each fiber layer is compressed and bonded to each other by embossing. The embossed area ratio is 5 to 25%. The basis weight of each fiber layer is 10 to 30 g / m 2 Such nonwoven fabric C is suitable as a material for absorbent articles and masks.

[0023] Next, a method for producing a nonwoven fabric according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a flow chart relating to the method for producing a nonwoven fabric according to this embodiment. First, in the production method according to this embodiment, molten thermoplastic resin is discharged vertically downward from a die, and the resin is melted by an air current. The grease is pulled vertically downward to form fibers (step S101, an example of the "fiber spraying process" herein). Next, the fibers are stacked and transported on a conveyor (step S102, an example of the "sheet transport process" herein). Next, the stacked fibers are passed through a heated roll to fuse the fibers in each layer (step S103, an example of the "fusing process" herein). Finally, each layer is peeled off to obtain a thin nonwoven fabric (step S104, an example of the "peeling process" herein).

[0024] Next, a method and apparatus for producing nonwoven fabric C according to this embodiment will be described with reference to FIG. 4. FIG. 4 is a diagram showing a nonwoven fabric production apparatus M for producing nonwoven fabric C according to this embodiment. In FIG. 4, the nonwoven fabric production apparatus M is equipped with two sets of fiber spraying devices (fiber spraying devices) 10, each of which (10A, 10B) is equipped with a spinning device 20, a cooling air device 30, and an injector 40. By including the spraying devices 10A and 10B, the nonwoven fabric production apparatus M can produce a two-layer nonwoven fabric C. The spraying device 10B is an example of a "first fiber spraying device" for forming fiber layer C2, and the spraying device 10A is an example of a "second fiber spraying device" for forming fiber layer C1. To increase the number of layers of nonwoven fabric C, the number of spraying devices may be increased.

[0025] In the nonwoven fabric manufacturing apparatus M, a collecting conveyor (sheet transport device) 50, an embossing device 60, and a winder 70 are arranged in series together with a spraying device 10 so that various processes can be performed. The spraying devices 10A and 10B are arranged in series in the transport direction relative to the transport surface above the collecting conveyor 50. The nonwoven fabric manufacturing apparatus M is constructed to continuously produce a nonwoven fabric C whose CD (cross direction) is the direction into the paper surface of FIG. 3, and produces the nonwoven fabric C by a so-called spunbond method in which spun fibers (filaments) are collected in a sheet form and embossed to appropriately bond the fibers together.

[0026] The spinning device 20 is configured to include an extruder 21 and a spinneret 23. The extruder 21 melts raw material resin R (R1, R2) 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")

[0027] Here, different types of materials R1 and R2 are used for each of the ejection devices 10A and 10B, and sheet-like filaments made of different materials are layered to form two or more layers. As described above, the raw resin R1 can be any of polyethylene, polypropylene, and polyethylene terephthalate, and the raw resin R2 can be a polylactic acid-based resin. Furthermore, the raw resins R1 and R2 may contain additives such as various stabilizers, including known heat and weather stabilizers, antistatic agents, slip agents, antiblocking agents, antifogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, and waxes.

[0028] The cooling air device 30 is equipped with a pair of open-type blowers 31, 32 arranged in opposing positions. This 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 cooling air Ac from each of the blowers 31, 32. Here, one of the cooling air devices 30, the blower 31, is installed as a large type that can be used as a main blower, and the other opposite blower 32 is installed as a small type that can be used as a secondary blower for supplementary use.

[0029] The injector 40 is configured to generate a low-pressure region on the inlet side of the body 41 by blowing downward high-pressure air as a driving fluid onto the filament aggregate F, which descends from above to below in the spinning direction, passing through the body 41. This injector 40 draws the descending filament aggregate F so as to draw it into a low-pressure region on the inlet side of the body 41, while also drawing it downward within the body 41 with high-pressure air, thereby stretching the filament aggregate F descending from above in the spinning direction downward via the cooling air device 30. The process of forming a fibrous structure and stretching the filament aggregate F is the process of step S101 (fiber spraying process) shown in Figure 3.

[0030] The collecting conveyor 50 is constructed to include a main conveyor 51, a sub-conveyor 52, 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-conveyor 52 is also installed so that a mesh-like collecting belt 152, 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 152r and driven to rotate in the opposite direction. Increasing the number of ejection devices 10 can be achieved by increasing the number of sub-conveyors.

[0031] 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 point below the spraying devices 10A and 10B, and is configured to receive and transport the filament aggregate Fa pulled down by the injector 40, thereby collecting it into a cloth (sheet). That is, the collecting belt 151 has a sufficient area to collect the sheet-like filament aggregate Fa by rotating from the upstream end (leading edge) to the downstream end (rear edge) in the circumferential movement direction (transport direction) of the upper surface 151a, thereby functioning as a collecting surface and a conveying surface. The filament aggregate Fa becomes the lower fiber layer C2 in the nonwoven fabric C.

[0032] The collecting belt 152 is wound around a group of rollers 152r with its upper surface 152a positioned at a spraying point below the spraying device 10B, which is located midway in the direction of rotation of the upper surface 151a of the collecting belt 151, and is configured to receive and transport the filament aggregate Fb pulled down by the injector 40, thereby collecting it in a sheet form. The filament aggregate Fb becomes the upper fiber layer C1 of the nonwoven fabric C.

[0033] The collecting belts 152 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 positioned between the upper surface 151a and the jetting device 10B and driven to rotate in the reverse direction, so that the upper surfaces 152a of the collecting belts 152 function as a collecting surface and a conveying surface for collecting the sheet-like filament aggregate Fb. The collecting belts 152 are driven to rotate between the lower parts facing the upper surface (upper part) 151a of the collecting belt 151 so as to sandwich the sheet-like filament aggregate Fb without peeling or turning up, thereby assisting in conveying it downstream.

[0034] 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, and 154b-2, each functioning as a decompression chamber. Suction ports (not shown) are arranged in these suction chambers 154a to 154b-2 so as to suck the upper sides, and suction fans 155a to 155b-2, which can be driven individually, are connected to enable suction.

[0035] The suction chambers 154a and 154b are installed so as to be located below the injectors 40 of the jetting devices 10A and 10B, respectively, and the suction chambers 154a-2 and 154b-2 are installed so as to be located downstream of the suction chambers 154a and 154b.

[0036] The suction chamber 154a 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 10A, and is driven by a suction fan 155a. As the pressure is reduced by moving the collecting belt 151, the air is sucked upward from directly below the collecting belt 151.

[0037] 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.

[0038] 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.

[0039] The suction chamber 154b 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 10B, and when the suction fan 155b is driven to reduce the pressure, it sucks in the area directly below the collection belt 151 and above the collection belt 152 of the sub-conveyor 52.

[0040] The suction chamber 154b-2 is installed adjacent to the downstream side of the suction chamber 154b, as described below, so as to be located immediately below the end of the collection belt 151 of the main conveyor 51, and when the suction fan 155b-2 is driven to reduce the pressure, it sucks in the area from directly below the collection belt 151 upward.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In short, the collecting conveyor 50 performs a lamination process in which the filament aggregates Fa and Fb spun by the spraying devices 10A and 10B are collected and held by the suction boxes 54 onto the upper surfaces 151a-152a of the collecting belts 151-152 in the form of a sheet of a predetermined thickness, and then stacked to form a filament aggregate Fab (nonwoven fabric C) before embossing. The stacked nonwoven fabric C is transported downstream and delivered to the embossing device 60, which performs the welding process. The process of stacking the sprayed filaments F on the collecting conveyor 50 and transporting the nonwoven fabric C to the embossing device 60 is the process (sheet conveying process) of step S102 shown in FIG. 3.

[0046] The embossing device 60 is equipped with a pair of embossing rolls 61, 62, which rotate relative to one another with their cylindrical outer peripheral surfaces 61a, 62a in pressure contact with each other. In this embossing device 60, embossing protrusions (not shown) arranged regularly or irregularly on the cylindrical outer peripheral surface 62a of the upper embossing roll 62 are pressed against the smooth cylindrical outer peripheral surface 61a of the lower embossing roll 61 with a desired pressure.

[0047] As a result, the embossing device 60 feeds the filament aggregate Fab sandwiched between the embossing rolls 61, 62 in the direction of relative rotation, and performs embossing at a plurality of embossing locations corresponding to the positions where the embossing protrusions are formed, thereby entangling and compressing and bonding the filaments f, thereby processing the filaments f into a nonwoven fabric C that maintains its sheet-like shape. Note that the embossing protrusions formed on the cylindrical outer peripheral surface 62a of the embossing roll 62 may be formed on the cylindrical outer peripheral surface 61a of the embossing roll 61, or may be formed on both of these cylindrical outer peripheral surfaces 61a, 62a. Furthermore, the embossing protrusions are not limited to being convex, and may be formed in a concave shape so that, for example, a continuous rib shape is pressed against the opposing cylindrical surface for compression bonding.

[0048] Furthermore, the cylindrical outer surfaces 61a and 62a of the embossing rolls 61 and 62 are heated. When the cylindrical outer surfaces 61a and 62a are heated, a portion of each fiber constituting the nonwoven fabric C fuses together, making it possible to produce a strong nonwoven fabric. For this reason, the embossing rolls 61 and 62 in this embodiment also function as heat rollers. The process of processing the filament aggregate Fab into the nonwoven fabric C using the embossing device 60 is step S103 (fusion process) shown in FIG. 3.

[0049] The winder 70 receives the nonwoven fabric C in which the filaments f of the filament aggregate Fab are intertwined and bonded by the embossing device 60 while adjusting the tension so as not to loosen, and continuously winds the nonwoven fabric C into a roll without wrinkles and with a desired winding hardness.

[0050] As a result, the winder 70 can prepare the nonwoven fabric C of a desired length, in which the filament aggregate Fab is formed into a sheet and wound into a roll, so that it can be supplied to the next processing step or the like.

[0051] As described above, in the collecting conveyor 50 of this embodiment, the suction chambers 154a to 154b-2 of the suction box 54 installed below the collecting belt 151 of the main conveyor 51 are partitioned and installed to correspond to the injectors 40 of the jetting devices 10A, 10B, and the suction fans 155a to 155b-2 connected to each of them are set to suction at an air speed (air volume) according to the partitioned range (area) of the suction chambers 154a to 154b-2 and the required suction pressure. Here, the partitioned range and suction pressure of the suction chambers 154a to 154b-2 may be set appropriately.

[0052] Specifically, the suction chamber 154a is pulled down from the outlet of the injector 40 of the ejection device 10A directly above the collecting belt 151 of the main conveyor 51 without the interposition of a sub-conveyor. The filament aggregate Fa that is being lowered is sucked from below the collecting belt 151 and collected in a sheet form and held.

[0053] 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.

[0054] The suction chamber 154b sucks the filament aggregate Fb, which is pulled down from the outlet of the injector 40 of the ejection device 10B directly above the collecting belt 151 of the sub-conveyor 52, from below the collecting belt 151 via the sub-conveyor 52, and collects and holds it in a sheet form. The sub-conveyor 52 sandwiches the sheet-like filament aggregate Fb collected and held on the collecting belt 152 between itself and the lower collecting belt 151, and sends it downstream as a filament aggregate Fab.

[0055] The suction chambers 154b are driven by suction fans 155b to create a negative pressure so as to generate a suction pressure Pb below the conveyance surface of the collecting belt 152 that is sufficient to stably hold the descending filament aggregate Fb. Similar to the suction chambers 154a, these suction chambers 154b are also suctioned by the suction fans 155b to create a negative pressure so as to generate the desired suction pressure Pb in a narrow, partitioned area approximately equal to the spray area in the conveyance direction of the descending filament aggregate Fb. At the same time, the suction chambers 154b apply suction to the collecting belt 152 of the sub-conveyor 52, with the filament aggregate Fab on the collecting belt 151 interposed therebetween. Therefore, the suction volume of these suction chambers 154b may be increased or decreased by adjusting the suction range in the conveyance direction below the collecting belt 151 so as to generate an optimal suction pressure Pb on the collecting belt 152. Similarly, the collecting belt 152 may also be partitioned so that the suction range is adjustable.

[0056] As a result, the suction chamber 154b can continuously suck and hold the filament aggregate Fab that is increased from the sheet-like filament aggregate Fa via the collection belt 151 of the main conveyor 51, similar to the suction chamber 154a.

[0057] The suction chambers 154a-2 and 154b-2 continuously suck and hold the sheet-like filament assemblies Fa and Fab on the collecting belt 151 of the main conveyor 51 downstream of the suction chambers 154a and 154b, respectively.

[0058] These suction chambers 154a-2, 154b-2 are driven by suction fans 155a-2 to generate negative pressures Pa-2, Pb-2, respectively, that continuously suck and hold the sheet-like filament assemblies Fa, Fab on the collecting belt 151. Note that suction chamber 154a-2 is interposed between suction chambers 154a, 154b, and is continuous so as to suck without gaps, and is therefore installed to suck a wider partitioned area so as to connect the separated collection positions of each jetting device 10. Note that suction chamber 154b-2 may be installed to suck a shorter partitioned area, as it simply delivers the sheet-like filament assemblies Fab received from suction chamber 154b to the adjacent embossing device 60 downstream.

[0059] As a result, the suction chambers 154a-2 and 154b-2 can respectively suck and hold the sheet-like filament assemblies Fa and Fab located on the upper surface 151a via the collecting belt 151 of the main conveyor 51, successively to the suction chambers 154a and 154b. At this time, the sheet-like filament assemblies Fa and Fab on the collecting belt 151 of the main conveyor 51 are respectively sucked and held by the suction chambers 154a-2 and 154b-2, and therefore do not float up, but are sandwiched between the collecting belts 152 of the sub-conveyor 52. The sheet-like filament aggregate Fa is collected and held by the collecting belt 152, and is then stacked with the sheet-like filament aggregate Fb, which is turned upside down, to form the sheet-like filament aggregate Fab, which is then transported downstream while being suction-held.

[0060] As described above, the collecting conveyor 50 is configured so that the individual suction fans 155a to 155b-2 suck at a required air speed so that 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 is generated in each of the suction chambers 154a to 154b-2 of the suction box 54. Note that the relative relationship (strength) of the suction pressure P on the collecting surface (transport surface) of the filament aggregate F in each of the suction chambers 154a to 154b-2, which will be described below, will be explained by calculating and substituting an air speed value corresponding to the separation space from the connecting point of the suction fans 155a to 155b-2 to the collecting surface.

[0061] For example, the suction box 54 is adjusted so that the suction pressures Pa and Pb of the suction chambers 154a and 154b located at the points on the collecting conveyor 50 where the spraying devices 10A and 10B spray the filament aggregate F are greater than the suction pressures Pa-2 and Pb-2 of the suction chambers 154a-2 and 154b-2 located downstream of the suction chambers 154a and 154b. The suction pressures Pa and Pb are adjusted according to the basis weight of the filament aggregate F on the conveying surface so as not to reduce the pressure inside the suction chambers 154a and 154b too much, thereby preventing the smooth relative movement of the collecting belt 151.

[0062] In detail, the suction chamber 154a is configured to set the suction pressure Pa in the collection belt 151 of the main conveyor 51, which collects and holds the filament aggregate Fa spun by the ejection device 10A in a sheet form, to a value, for example, of 10 to 30 g / m2 when the basis weight of the semi-finished product to be wound into a roll by the winder 70 is 10 to 30 g / m2. 2 When producing the nonwoven fabric C, the air speed Pa is set to 7.5. This suction pressure (air speed) Pa is set to a relatively strong value so that the filament aggregate Fa is attracted to the upper surface 151a of the collecting belt 151 regardless of its basis weight, because this is the point where the filament aggregate Fa is sucked in and begins to be collected and held in a sheet form.

[0063] The suction chamber 154a-2 is connected to the suction chamber 154a in the same manner as the suction chamber 154a, and is configured to have a suction pressure Pa-2 and a basis weight of 10 to 30 g / m. 2When producing the nonwoven fabric C, the air velocity Pa-2 is set to 3.8. Here, like the suction pressure Pa, the suction pressure (air velocity) Pa-2 is sufficient to maintain the shape of the filament aggregate Fa that is sucked and held in a sheet shape, regardless of the basis weight (grammage) of the filament aggregate Fa, and since the filament aggregate Fa is sandwiched as is between the collecting belts 151, 152 of the main conveyor 51 and the sub-conveyor 52, it is kept low at about half the suction pressure Pa.

[0064] The suction chamber 154b is configured to have a suction pressure Pb of, for example, 10 to 30 g / m 2 When producing the nonwoven fabric C, the wind speed Pb is set to 6.0. Like the suction pressure Pa, the suction pressure (wind speed) Pb is set to a strong value regardless of the basis weight because the filament aggregate Fb is collected and formed into a sheet on the collecting belt 152 of the sub-conveyor 52. However, because the filament aggregate Fab on the collecting belt 151 of the main conveyor 51 is sucked in between, the wind speed Pb is kept low so as not to restrict the movement of the collecting belt 151.

[0065] The suction chamber 154b-2 is connected to the suction chamber 154b and has a suction pressure Pc-2 and a basis weight of 10 to 30 g / m 2 When producing the nonwoven fabric C, the suction pressure (wind speed) Pb-2 is set to be 3.2 to 3.8. The suction pressure (wind speed) Pb-2 is set lower than the suction pressure Pa depending on the basis weight so that the filament aggregate Fab conveyed from the sub-conveyor 52 is reliably sucked and held by the collecting belt 151 of the main conveyor 51 and delivered to the embossing device 60.

[0066] In the nonwoven fabric manufacturing apparatus M, the line speed (conveying speed) of the collecting belts 151, 152 is 40 m / min or more. The fiber discharge rate of the ejection devices 10A, 10B is 0.5 / hole / min or less. In the nonwoven fabric C produced under these conditions, the fiber diameter in the fiber layer C1 is 15 μm or less.

[0067] In the fiber layer C2, it is necessary to adjust the fibers so that they are oriented almost straight in the MD. This adjustment can be achieved, for example, by installing an adjustment roller 162 that pulls the spunbond fibers at line speed on the upper surface 152a of the collecting belt 152 of the nonwoven fabric manufacturing apparatus M. The adjustment roller 162 may be equipped with a cooling function for cooling the fibers.

[0068] Even if the adjusting roller 162 is not installed, the fibers can be oriented straight in the MD direction by matching the spinning speed in the jetting device 10B with the line speed of the collecting belt 152. The spinning speed in the jetting device 10B can be adjusted by the jetting pressure of the jetting device 10B.

[0069] Resins are composed of entangled string-like polymers and are divided into crystalline resins, which have crystalline portions in which the molecules are regularly arranged in a solidified state, and amorphous resins, which have no crystalline portions. In this embodiment, the polylactic acid-based resin that is ejected from the ejection device 10B (first fiber ejection device) and forms the fiber layer C1, and the polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) that are ejected from the ejection device 10A (second fiber ejection device) and form the fiber layer C2 are both crystalline resins.

[0070] Although polylactic acid is a crystalline resin, its crystallization rate is slow. Without the addition of a nucleating agent, it takes several hours for crystallization to occur even after heating to the optimal temperature (near 110°C). Adding a nucleating agent to polylactic acid can achieve a practical crystallization rate, but adding a nucleating agent makes it difficult to apply tension during spraying, necessitating a thicker fiber diameter. This may cause discomfort to users when used in sanitary products that come into contact with the skin. For this reason, in this embodiment, the fiber diameter is reduced without the addition of a nucleating agent, and the fibers are layered on the conveying surface in an amorphous state. Specifically, the resin constituting the fiber layer C1 is ejected from the fiber spraying device at an ejection pressure (fiber discharge pressure) of 0.11 MPa or greater, stretched, and layered with a thread diameter of 15 μm or less. As described above, the manufacturing device M conveys the nonwoven fabric C at a high speed of 40 m / min or greater, but in an amorphous state, polylactic acid-based fibers have low tensile strength. Therefore, when polylactic acid resin is made into a thin nonwoven fabric using the above-mentioned manufacturing apparatus M, there is a risk that the fabric may break during the manufacturing process due to the tension applied thereto.

[0071] On the other hand, the thermoplastic resin discharged from the discharge device 10A (second fiber spray device) crystallizes within a few seconds of passing through the cooling air device 30. Therefore, by the time the resin is accumulated on the conveyor, it has already crystallized and has tensile strength. Therefore, by stacking and drawing out the fiber layer C1 discharged from the first fiber spray device and the fiber layer C2 discharged from the second fiber spray device, the fiber layer C1 is reinforced by the fiber layer C2 and is less likely to break in the line.

[0072] In this embodiment, the surface temperatures of the cylindrical outer circumferential surfaces 61a, 62a of the embossing rolls 61, 62 are at least 120°C, preferably 145°C or higher. The inventors have found that fibers made of polylactic acid-based resin generally do not stick to the embossing rolls 61, 62 if the temperature of the embossing rolls 61, 62 is 120°C or higher, and do not remain on the embossing rolls 61, 62 if the temperature is 145°C or higher. Near the glass transition temperature of the polylactic acid-based resin (60°C to 90°C), the polylactic acid-based resin softens, but the fibers do not fuse together sufficiently, so they stick to the embossing rolls 61, 62. However, when heated sufficiently as described above, the fibers fuse together more firmly, and the fibers do not remain on the embossing rolls 61, 62. It is thought that it will no longer adhere to 61 and 62.

[0073] The compatibility parameter (SP value) of the polylactic acid constituting the fiber layer C1 is 19.8, while that of the polyethylene constituting the fiber layer C2 is 16.4, that of polypropylene is 14, and that of polyethylene terephthalate is 21.8. Regardless of which material is used for the fiber layer C2, the difference with polylactic acid is 0.5 or more, indicating incompatibility. Therefore, even after passing through the embossing rolls 61 and 62, the fiber layers C1 and C2 adhere to each other but are not compatible with each other. Therefore, after producing the nonwoven fabric C, the fiber layers can be separated. Each of the separated nonwoven fabrics can be used as an unprecedentedly thin nonwoven fabric. In particular, the fiber layer C1 composed of a polylactic acid-based resin can be used as the nonwoven fabric D1, which is biodegradable yet soft to the touch and comfortable for use in sanitary products. By adding a new separation process, nonwoven fabrics with new properties can be obtained without making major modifications to existing manufacturing equipment. Specific examples are shown in FIGS. 5 and 6, and the process of peeling off each layer to obtain a thin nonwoven fabric is step S104 in FIG. 3 (peeling process).

[0074] FIG. 4 illustrates an example of a process for peeling a nonwoven fabric. As described above, the production line operates at a speed of 40 m / min or more. Attempting to separate nonwoven fabric C into a thin nonwoven fabric under these conditions could result in the separated nonwoven fabric breaking. Therefore, nonwoven fabric C is first wound around a winder 70 to form a rolled paper 80, which is then separated in a separate process. The nonwoven fabric C, which has been produced and wound by the above-described production apparatus M and is now in the form of rolled paper 80, is slowly pulled out at a separate location. The fibrous layer C2 separates from the fibrous layer C1 as it passes through a peeling roll 81. The fibrous layer C1 can be used as a thin biodegradable nonwoven fabric D1. The peeled fibrous layer C2 is also collected separately. By providing a separate line speed separation process, a nonwoven fabric with new properties can be obtained without breaking each fibrous layer.

[0075] 5 is a diagram showing an example of yet another process for peeling off a nonwoven fabric. Although not shown, the nonwoven fabric manufacturing apparatus M may be provided with a plurality of ejection devices 10A (second fiber ejection devices). The ejection device 10A may also be provided with a plurality of spinnerets 23 (a plurality of fiber discharge ports), and filaments f may be ejected from a plurality of locations. On the other hand, as shown in FIG. 3, the ejection device 10B (first fiber ejection device) is a single device, and the spinneret 23 is also a single device.

[0076] With the nonwoven fabric manufacturing apparatus M configured as described above, the fiber layer C2 can be made into a multilayer structure composed of the same type of resin fiber. Because the nonwoven fabric C is reinforced and the layers do not break even when separated at high speeds of 40 m / min or more, a separation process can be implemented within the production line. Figure 5 shows an example in which a separation process is implemented between the embossing device 60 and the winder 70. The fiber layer C2 constituting the nonwoven fabric C, which is thermocompressed by passing between embossing rolls 61 and 62, is separated from the fiber layer C1 by a peeling roll 63 installed in the production line. The fiber layer C1 is formed into a thin, biodegradable nonwoven fabric D1 by the winder and wound up. The peeled fiber layer C2 is also collected separately. Even with this configuration, the biodegradable nonwoven fabric D1 remains a single layer, and its thickness is the same as when a separate separation process is implemented. This enables more efficient in-line production of nonwoven fabrics with novel properties.

[0077] The fiber layer C2 can be used as a thin nonwoven fabric D2, which is not biodegradable, for purposes other than those of the nonwoven fabric D1. If it is desired to obtain only the biodegradable nonwoven fabric D1, the fiber layer C2 may be re-dissolved and reused in the manufacturing process.

[0078] The nonwoven fabric D1 according to this embodiment is manufactured by the manufacturing method described above. The nonwoven fabric D1 according to this embodiment is biodegradable and, because it is very thin, it feels good against the skin. For this reason, the nonwoven fabric D1 can be used in hygiene products that come into contact with the skin of the user.

[0079] Although the present embodiment has been described above, the present invention is not limited to the above embodiment. In the embodiment, the resins forming the fiber layers C1 and C2 have been described, but the type of resin is not limited to this. Any resin can be used for each fiber layer as long as the compatibility parameter (SP value) is sufficiently different from that of the solid layer. Furthermore, the nonwoven fabric C is not limited to two layers. By adding a spraying device, a sub-conveyor, and a suction box, it is possible to form three or more layers, and obtain three or more thin nonwoven fabrics in the peeling process.

[0080] The embodiments and application examples disclosed above can be combined with each other. [Explanation of symbols]

[0081] C··Non-woven fabric C1, C2: Fiber layer D1,D2...Nonwoven fabric M··Nonwoven fabric manufacturing equipment 10, 10A, 10B...Ejection device 20. Spinning equipment 30·Cold air device 40··Injector 50··Collection conveyor 51 Main conveyor 52 Sub-conveyor 54··Suction box 60··Embossing device 70··Winder 80 roll paper 81,63··Peeling roll 141, 142 Signboard 151, 152 Collection belt 154a, 154b Suction chamber 162 Adjustment roller f··filament fr··Rotation diameter F, Fa, Fab, Fb filament assembly Lc Intersection distance Ld...Open interval Lr Evacuation interval P, Pa, Pb, Pe, Ps... Suction pressure (wind speed)

Claims

1. a fiber spraying step of spraying fibers from a plurality of fiber spraying devices; a sheet conveying step of collecting the fiber bundles sprayed from the plurality of fiber spraying devices on a conveying surface to form a sheet-like fiber layer and conveying the layer in a transfer direction; a fusing step of fusing the sheet-like fiber layer by applying heat and pressure with a heat roller; To be equipped with A method for producing a nonwoven fabric, comprising: The plurality of fiber spraying devices include at least: a first fiber spraying device that forms a first layer in a thickness direction on the conveying surface; a second fiber spraying device that sprays fibers made of a different material from that of the first fiber spraying device to form a second layer in the thickness direction on the conveying surface; , and After the fusion step, the first layer and the second layer are peeled off. Method for manufacturing nonwoven fabric.

2. the fiber layer constituting the first layer and the fiber layer constituting the second layer have low compatibility; A method for producing the nonwoven fabric according to claim 1.

3. After the peeling, the first layer and the second layer are obtained as separate nonwoven fabrics. A method for producing the nonwoven fabric according to claim 1 or 2.

4. The second fiber spraying device has a plurality of fiber discharge ports, The fiber layer constituting the second layer is composed of two or more layers in the thickness direction. A method for producing the nonwoven fabric according to any one of claims 1 to 3.

5. The fiber layer constituting the first layer is a single layer. A method for producing the nonwoven fabric according to any one of claims 1 to 4.

6. The first layer is formed of polylactic acid-based fibers, The second layer is formed of fibers made of any one of polypropylene, polyethylene, and polyethylene terephthalate. A method for producing the nonwoven fabric according to any one of claims 1 to 5.

7. The surface temperature of the heat roller is 120°C or higher. A method for producing the nonwoven fabric according to any one of claims 1 to 6.

8. The conveying speed of the sheet conveying step is 40 m / min or more, The fiber discharge rate of the first fiber spraying device is 0.5 / hole / min or less; A method for producing the nonwoven fabric according to any one of claims 1 to 7.

9. The fiber discharge pressure of the first fiber spraying device is 0.11 MPa or more, The yarn diameter of the first layer conveyed in the sheet conveying step is 15 μm or less. A method for producing the nonwoven fabric according to claim 8.

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