A method for producing recycled pulp fibers from used absorbent articles.

Abstract

To provide a method for producing recycled pulp fibers from used absorbent articles, capable of producing recycled pulp fibers which exhibit high dispersibility, and from which foreign substances are easily detected and removed.SOLUTION: There is provided a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers, which includes dehydration step (S03) and loosening step (S04). In the dehydration step, pulp fibers which have been separated from the used absorbent articles and cleaned are subjected to dehydration. In the loosening step, each one of a plurality of lumps of the pulp fibers formed by the dehydration is loosened so as to form recycled pulp fibers.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing recycled pulp fibers from used absorbent articles.

Background Art

[0002] Methods for producing recycled pulp fibers from used absorbent articles are known. For example, Japanese Unexamined Patent Application Publication No. 2020-183585 discloses a method for producing recycled pulp fibers from a used absorbent article containing a superabsorbent polymer, pulp fibers and excreta. This method comprises: a separation step of separating an inactivating aqueous solution and pulp fibers, respectively, from a mixed liquid obtained by mixing the inactivating aqueous solution and the used absorbent article; a viscosity reduction step of mixing the separated inactivating aqueous solution and a first oxidizing agent, decomposing excreta contained in the inactivating aqueous solution, and lowering the viscosity of the inactivating aqueous solution; and a re-supply step of returning the inactivating aqueous solution to the separation step. The method may further comprise: a solubilization step of mixing the pulp fibers separated in the separation step and an oxidizing agent aqueous solution containing a second oxidizing agent, decomposing the superabsorbent polymer contained in the pulp fibers, and solubilizing the superabsorbent polymer in the oxidizing agent aqueous solution; and another separation step of separating the oxidizing agent aqueous solution and the pulp fibers.

Prior Art Literature

Patent Literature

[0003]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In the method described in Patent Document 1, the separated pulp fibers are washed with washing water, dewatered, and finally extracted as recycled pulp fibers. However, the dewatered pulp fibers will contain numerous clumps, for example, about the size of a sphere several centimeters in diameter. Since it is not easy to break apart each of these numerous clumps of pulp fibers, the dispersibility of the extracted recycled pulp fibers may be low. If this occurs, when the recycled pulp fibers are reused in various products, clumps and unevenness of the fibers are likely to occur in the products.

[0005] Furthermore, since it is not easy to break apart each of the numerous clumps of pulp fibers, detecting foreign matter within the clumps is not easy, and even if detected, removal becomes difficult. Therefore, there is a risk that the extracted recycled pulp fibers may contain a significant amount of foreign matter. In that case, products containing recycled pulp fibers are more likely to have reduced performance due to the influence of foreign matter.

[0006] In particular, when recycled pulp fibers are stored without drying, the dewatering process involves squeezing them tightly to remove as much moisture as possible in order to suppress the growth of mold, etc. This process results in very strong bonding and entanglement between the fibers, making it significantly more difficult to break apart clumps.

[0007] The object of the present invention is to provide a method for producing recycled pulp fibers from used absorbent articles, which allows for the production of recycled pulp fibers that are highly dispersible and easy to detect and remove foreign matter. [Means for solving the problem]

[0008] One aspect of the present invention is a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers, comprising: a dewatering step of dewatering pulp fibers separated from and washed from used absorbent articles; and a disintegration step of disintegrating each of the multiple clumps of pulp fibers formed by the dewatering to produce recycled pulp fibers. [Effects of the Invention]

[0009] The present invention provides a method for producing recycled pulp fibers from used absorbent articles, which are highly dispersible and allow for easy detection and removal of foreign matter. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart showing a method for producing recycled pulp fibers from used absorbent articles according to an embodiment. [Figure 2] This is a schematic diagram showing an apparatus for performing the dismantling process according to the embodiment. [Figure 3] This is a flowchart showing the decomposition process according to the embodiment. [Figure 4] This is a flowchart showing the cleaning process according to the embodiment. [Figure 5] This is a flowchart showing the pulp fiber separation process according to an embodiment. [Modes for carrying out the invention]

[0011] This embodiment relates to the following aspects. [Aspect 1] A method for producing recycled pulp fibers from used absorbent articles containing pulp fibers, comprising a dewatering step of dewatering pulp fibers separated and washed from used absorbent articles, A method comprising: a dewatering step of dewatering each of the multiple clumps of pulp fibers formed by dewatering to produce recycled pulp fibers.

[0012] This method includes a disintegration step to break down each of the multiple clumps of pulp fibers formed by dewatering, thereby generating recycled pulp fibers. By breaking down each of the multiple clumps of pulp fibers after dewatering, the pulp fibers, and consequently the recycled pulp fibers, can be made highly dispersible. This makes it less likely for clumps or inconsistencies to occur in the recycled pulp fibers when they are reused. Furthermore, the high dispersibility makes it easier to detect and remove fine foreign matter embedded in the recycled pulp fibers.

[0013] [Aspect 2] The method according to Aspect 1, wherein the disintegrating step comprises a step of disintegrating the agglomerates of the dehydrated pulp fibers while suppressing fragmentation of foreign matter present in the agglomerates of the dehydrated pulp fibers. In the present method, the disintegrating step comprises disintegrating the agglomerates of pulp fibers while suppressing fragmentation of foreign matter present in the agglomerates of pulp fibers. This makes it difficult for fine foreign matter that has entered the agglomerates of pulp fibers to be further fragmented, allowing the foreign matter to maintain a certain size. Therefore, detection and removal of fine foreign matter in recycled pulp fibers can be performed more easily.

[0014] [Aspect 3] The method according to Aspect 1 or 2, wherein the disintegrating step comprises: a quantifying step of quantifying agglomerates of pulp fibers corresponding to a preset mass or volume range among the plurality of agglomerates of pulp fibers formed by the dewatering; and an agglomerate disintegrating step of disintegrating the quantified agglomerates of pulp fibers. In the present method, in the disintegrating step, among a plurality of agglomerates of pulp fibers, each of the agglomerates of pulp fibers corresponding to a predetermined mass or volume range is disintegrated. That is, the amount of pulp fiber agglomerates disintegrated at one time is limited. This enables reliable disintegration of the agglomerates of pulp fibers. Therefore, detection and removal of fine foreign matter in recycled pulp fibers can be performed more easily.

[0015] [Aspect 4] The method according to any one of Aspects 1 to 3, wherein the disintegrating step comprises a foreign matter detection step of detecting foreign matter in the disintegrated pulp fibers and removing the foreign matter when foreign matter is detected. The present method comprises a step of detecting and removing foreign matter in the disintegrated pulp fibers. Since fine foreign matter is detected from the disintegrated pulp fibers, any foreign matter can be easily detected and easily removed.

[0016] [Aspect 5] The method according to aspect 4, wherein the foreign matter detection step includes a step of detecting metallic foreign matter with a metal detector. In the present method, by detecting metallic foreign matter with a metal detector, metallic foreign matter contained in a used absorbent article that has not been removed during separation of pulp fibers can be easily detected, and thereby can be easily removed.

[0017] [Aspect 6] The method according to aspect 4 or 5, wherein the foreign matter detection step includes a step of detecting non-metallic foreign matter with a foreign matter detector. In the present method, by detecting non-metallic foreign matter with a foreign matter detector, non-metallic foreign matter contained in a used absorbent article that has not been removed during separation of pulp fibers can be easily detected, and thereby can be easily removed.

[0018] [Aspect 7] The method according to any one of aspects 1 to 6, further comprising an ozone treatment step of performing ozone treatment on pulp fibers separated from the used absorbent article before the dewatering step. The ozone treatment in the ozone treatment step can suppress the residual of lignin and other impurities in the pulp fibers, achieve deodorization, sterilization and bleaching of the pulp fibers, and further promote fibrillation. Therefore, the obtained pulp fibers have few impurities, suppressed bacterial growth and increased specific surface area, making them suitable for various applications. However, pulp fibers with advanced fibrillation have strong binding force between the fibers, resulting in lower dispersibility. Therefore, in the present method, a defibering step of disintegrating lumps formed by the pulp fibers in such a state is performed. Thereby, the pulp fibers with advanced fibrillation can be brought into a state of high dispersibility. Therefore, when the recycled pulp fibers are reused, clumping and unevenness of the fibers can be made less likely to occur, and the detection and removal of fine foreign matter entrapped in the recycled pulp fibers can be facilitated.

[0019] [Aspect 8] The method according to any one of embodiments 1 to 7, further comprising a storage step of storing the recycled pulp fibers generated after the disintegration step in a wet state. In this method, the recycled pulp fibers generated after the disintegration process are stored in a moist state. This has the advantage of reducing the equipment required for drying, as well as the equipment required for storage and transportation, by storing the fine recycled pulp fibers without drying them. However, storing recycled pulp fibers in a moist state may lead to the growth and proliferation of mold and other fungi. In such cases, this method uses ozone treatment to sterilize the fibers, thereby suppressing their growth and proliferation. As a result, products containing recycled pulp fibers can be prevented from having their properties reduced due to the influence of various fungi.

[0020] [Aspect 9] The method according to embodiment 8, further comprising an antimicrobial treatment step of treating the pulp fibers separated from the used absorbent article with an antimicrobial agent before the dewatering step. In this method, pulp fibers separated from used absorbent materials are treated with an antibacterial agent, thereby suppressing the growth and proliferation of various bacteria.

[0021] [Aspect 10] The method according to any one of embodiments 1 to 9, wherein the steps after the disassembly step are carried out in a closed space. In this method, the processes from the disintegration stage onward are carried out in a closed space, which further suppresses the contamination of recycled pulp fibers with foreign matter and the invasion of various bacteria.

[0022] The following describes a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to an embodiment. However, used absorbent articles include not only absorbent articles that have been used by a user, i.e., absorbed and retained the user's excrement, but also unused but discarded absorbent articles. Examples of absorbent articles include disposable diapers, incontinence pads, sanitary napkins, bed sheets, and pet sheets.

[0023] First, let's describe an example of the composition of an absorbent article. An absorbent article comprises a surface sheet, a backing sheet, and an absorbent material placed between the surface sheet and the backing sheet. An example of the size of an absorbent article is a length of approximately 15 to 100 cm and a width of 5 to 100 cm. In addition, an absorbent article may further include other components that are generally found in absorbent articles, such as a diffusion sheet, a leak-proof wall, a side sheet, and an outer sheet.

[0024] There are no particular restrictions on the material of the surface sheet, and known surface sheet materials can be used. Examples include liquid-permeable nonwoven fabrics, synthetic resin films with liquid-permeable pores, and composite sheets thereof. There are no particular restrictions on the material of the back sheet, and known back sheet materials can be used. Examples include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets thereof. There are no particular restrictions on the material of the diffusion sheet, and known diffusion sheet materials can be used. An example is a liquid-permeable nonwoven fabric. There are no particular restrictions on the material of the leak-proof wall and side sheet, and known leak-proof wall and side sheet materials can be used. An example is a water-repellent nonwoven fabric, and the leak-proof wall may further include an elastic member such as rubber thread. There are no particular restrictions on the material of the outer sheet, and known outer sheet materials can be used. Examples include liquid-impermeable and breathable nonwoven fabrics, liquid-impermeable and breathable synthetic resin films, and composite sheets thereof.

[0025] The types of nonwoven fabrics mentioned above are not particularly limited, and examples include meltblown nonwoven fabrics, spunbond nonwoven fabrics, thermalbond nonwoven fabrics, airlaid nonwoven fabrics, and air-through nonwoven fabrics. Similarly, there are no particular limitations on the type of synthetic resin film, and known film materials can be used. Here, the materials for the nonwoven fabrics and synthetic resin films are not particularly limited as long as they can be used for absorbent articles, but examples include olefin resins such as polyethylene and polypropylene, polyamide resins such as 6-nylon and 6,6-nylon, and polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). These materials for nonwoven fabrics and synthetic resin films are synthetic resins and can be called plastic materials. In this embodiment, an absorbent article in which the back sheet is made of film and the front sheet is made of nonwoven fabric will be described as an example.

[0026] Absorbent materials include pulp fibers and superabsorbent polymers. Examples of pulp fibers include cellulosic fibers. Examples of cellulosic fibers include wood pulp, cross-linked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. The average size of the pulp fibers is, for example, several tens of μm in the major axis (20-40 μm), and the average fiber length is, for example, several millimeters (2-5 mm). Examples of superabsorbent polymers (SAP) include polyacrylate-based, polysulfonate-based, and maleate anhydride-based superabsorbent polymers. The average particle size of the superabsorbent polymer (when dry) is, for example, several hundred μm (200-500 μm). The absorbent material may be enclosed in a core wrap formed from a liquid-permeable sheet.

[0027] One side and the other side of the absorbent are joined to the surface sheet and the back sheet, respectively, via adhesive. In a plan view, the portion of the surface sheet that extends outward from the absorbent, surrounding it (peripheral portion), is joined to the portion of the back sheet that extends outward from the absorbent, surrounding it (peripheral portion), via adhesive. Therefore, the absorbent is enclosed within the joint of the surface sheet and the back sheet. There are no particular restrictions on the adhesive, but examples include hot-melt adhesives. Examples of hot-melt adhesives include rubber-based adhesives such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin-based adhesives such as polyethylene, which are pressure-sensitive or heat-sensitive adhesives.

[0028] Next, a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to the embodiment will be described in detail. Separating and recovering pulp fibers from used absorbent articles to obtain reusable pulp fibers can be said to be the production of recycled pulp fibers, as this generates reusable recycled pulp fibers.

[0029] Figure 1 is a flowchart illustrating a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to an embodiment. This method comprises a dewatering step S03 and a loosening step S04, and in this embodiment, it further comprises a pulp fiber separation step S01, a washing step S02, and a storage step S05.

[0030] The pulp fiber separation step S01 is a step in which pulp fibers are separated from used absorbent material. The washing step S02 is a step in which the pulp fibers obtained in the pulp fiber separation step S01 are washed.

[0031] The dewatering process S03 is a process for dewatering pulp fibers that have been separated from used absorbent materials and washed. After being washed, the pulp fibers are rinsed, i.e., washed and cleaned with water, and then dewatered to remove as much water as possible. In dewatering, the pulp fibers are squeezed (compressed) tightly to remove moisture. As a result, the fibers bind together and intertwine, forming multiple clumps of pulp fibers. The shape of each clump varies, but considering the size of the sphere containing the clump, for example, they can be as large as a few centimeters to 10 centimeters in diameter.

[0032] In this embodiment, the pulp fibers used in the dewatering step S03 are those obtained through the pulp fiber separation step S01 and the washing step S02. However, the present invention is not limited to this example, and other pulp fibers may also be used, for example, pulp fibers recovered from another facility that separates pulp fibers from used absorbent articles, and pulp fibers obtained by washing those pulp fibers in the washing step S02.

[0033] The disintegration step S04 is a step in which each of the multiple clumps of pulp fibers formed by dewatering is disintegrated to produce recycled pulp fibers. Here, "disintegrating" means reducing the size of the pulp fiber clumps to a size smaller than the original size. In this embodiment, the size of the clumps, when considered as the size of the sphere containing the clumps, is set to a diameter of 2 cm or less, preferably 1 cm or less, and more preferably 0.5 cm or less. It is not necessary to disintegrate all of the multiple clumps of pulp fibers, but it is preferable to disintegrate at least 95% of the clumps, and more preferably 98% or more. However, the size of the pulp fiber clumps is measured by the following method.

[0034] <Size of pulp fiber clumps> (1) Place the pulp fiber aggregate containing multiple clumps to be evaluated onto the scanner. Ensure that the clumps do not overlap or touch each other. However, if only the individual dispersed fibers are in contact, it is considered that they are not in contact. (2) Capture a scanned image of the pulp fibers. (3) The software is used to binarize the scanned image, and contiguous regions are treated as a single block. The diameter of the circle containing each block is then calculated. However, regions connected only by dispersed individual fibers are treated as separate blocks.

[0035] Storage process S05 is the process of storing the generated recycled pulp fibers while they are still wet.

[0036] As described above, this method may include, before the dewatering step S03, a pulp fiber separation step S01, which is a step to prepare pulp fibers, for separating pulp fibers from used absorbent articles, and a washing step S02, for washing the separated pulp fibers. It may also include a storage step S05, for storing the recycled pulp fibers generated in the disintegration step S04 in a wet state. Details of the pulp fiber separation step S01, washing step S02, and storage step S05 will be described later.

[0037] In this method, in the dewatering step S03, pulp fibers are dewatered to form multiple clumps of pulp fibers, and in the loosening step S04, each of the multiple clumps of dewatered pulp fibers is loosened to produce recycled pulp fibers. By loosening each of the multiple clumps of pulp fibers after dewatering, the loosened pulp fibers, and consequently the generated recycled pulp fibers, can be made highly dispersible. As a result, when the generated recycled pulp fibers are reused in various products, it is possible to reduce the occurrence of clumps and unevenness of fibers in those products. Furthermore, by making the recycled pulp fibers highly dispersible, it is possible to easily detect and remove fine foreign matter that has entered the recycled pulp fibers after the clumps have been loosened. In other words, this method makes it possible to produce recycled pulp fibers from used absorbent articles that have high dispersibility and are easy to detect and remove foreign matter from.

[0038] The following provides further explanation of each of the processes mentioned above.

[0039] As described above, the dewatering step S03 dewaters the pulp fibers that have been separated from the used absorbent material and washed. There are no particular restrictions on the dewatering device used to perform the dewatering step S03, as long as it is capable of dewatering, but examples include a screw press dewatering machine, a belt press dewatering machine, and a washing tub / dewatering tub with a rotating drum. When dewatering is completed, some or all of the pulp fibers have formed multiple clumps due to the pressure applied during dewatering. The pulp fibers containing the multiple clumps are then discharged from the dewatering device and transferred to the loosening step S04.

[0040] Next, the loosening step S04, as described above, loosens each of the multiple clumps of pulp fibers formed by dewatering to produce recycled pulp fibers. Here, there are no particular restrictions on the loosening device used to carry out the loosening step S04, as long as it can loosen the clumps of pulp fibers, but for example, a pin mill grinder can be used. A pin mill grinder is equipped with a disc and a number of pins arranged perpendicular to the surface of the disc (parallel to the axis of rotation of the disc), and the rotation of the disc applies impact force and shear force to the clumps by the pins, thereby loosening the clumps. When the loosening is complete, the multiple clumps of pulp fibers have been loosened and reduced by the impact force and shear force, and preferably have disappeared. Then, the pulp fibers that contain almost no clumps (preferably none at all) are sent out of the loosening device and moved to the next step.

[0041] Here, the loosening process S04 will be described in detail. Figure 2 is a schematic diagram showing the apparatus for performing the loosening process S04, and Figure 3 is a flowchart of the loosening process S04. The loosening process S04 includes a clumping process S32, and in this embodiment, it further includes a quantitative process S31 and an inspection process S33, the inspection process S33 including a metal inspection process S34 and a foreign matter inspection process S35. The apparatus for performing the clumping process S32, the quantitative process S31, and the metal inspection process S34 and foreign matter inspection process S35 of the inspection process S33 are a loosening apparatus 15, a quantitative apparatus 13, a metal detection apparatus 17 and a foreign matter detection apparatus 19, and conveying apparatuses 21 to 25, respectively. However, the conveying apparatus 21 may be a conveyor such as a belt conveyor or a driven roller conveyor. Also, in the loosening process S04, the pulp fibers are in a wet state.

[0042] In this embodiment, the pulp fibers P0 that have passed through the pulp fiber separation step S01 and the washing step S02 are supplied via the conveying device 20 to the dewatering device 11 (example: screw press dewatering machine) that performs the dewatering step S03 described above. The pulp fibers P0 dewatered by the dewatering device 11 are supplied as pulp fibers P1 containing multiple clumps via the conveying device 21 to the quantification device 13 of the loosening step S04.

[0043] First, the quantitative process S31 is carried out by the quantitative device 13. The quantitative process S31 is a process of quantifying the amount of pulp fiber clumps that correspond to a predetermined range of mass or volume from among the multiple clumps of pulp fibers formed by the dewatering process S03.

[0044] Specifically, the quantitative device 13 receives pulp fibers P1, which are in the form of multiple clumps, continuously or intermittently supplied from the dewatering device 11 via the conveying device 21, and measures the mass or volume of the pulp fibers P1. When measuring mass, it measures whether the mass of the pulp fibers P1 reaches a predetermined mass range (example: 50g to 100g). When measuring volume, it measures whether the volume of the pulp fibers P1 reaches a predetermined volume range (example: 500cm³). 3 ~1000cm 3 The device measures whether or not the mass or volume reaches a predetermined range. When the mass or volume reaches that predetermined range, the conveying device 21 is temporarily stopped, and the pulp fibers P1, which are multiple lumps within that predetermined range, are sent to the disintegrating device 15 via the conveying device 22 as pulp fibers P2 for disintegration.

[0045] One method for measuring mass within a predetermined range is to prepare a container to temporarily hold the supplied lumps and measure whether the mass of multiple lumps in the container reaches the predetermined range using an electronic balance. Another method for measuring volume within a predetermined range is to prepare a container with a volume equivalent to the maximum value of the predetermined volume range to temporarily hold the supplied lumps and measure whether the multiple lumps fill, for example, 80% or more of the container using an image sensor.

[0046] In another embodiment, the conveying device 21 is a screw conveyor, and the pulp fibers P1 sent from the dewatering device 11 are directly supplied to the loosening device 15 without using the metering device 13 and the conveying device 21. In this case, the screw on the screw conveyor rotates at a constant speed, and when viewed from the lower side in the conveying direction, the distance between the screw blades is equal (the pitch of the screw blades is constant). Therefore, as the pulp fibers P1 containing multiple clumps enter between the screw blades, a nearly constant mass or volume of pulp fibers P1 is supplied to the loosening device 15 (loosening process S32). In this case, the screw conveyor is a conveying device, but it can also be viewed as a metering device (metering process S31).

[0047] Next, the agglomeration process S32 is carried out by the agglomeration device 15. The agglomeration process S32 is a process of agglomerating pulp fiber clumps that have been quantified in the quantification process S31 and fall within a predetermined mass or volume range.

[0048] Specifically, the pulp fiber disintegrator 15 (example: pin mill grinder) receives pulp fibers P2, which are multiple clumps supplied from the quantitative device 13 via the conveying device 22, in predetermined mass or volume ranges, and disintegrates the pulp fibers P2. In this case, the pulp fiber disintegrator 15 is a batch type. The disintegrated pulp fibers P2 are then sent to the metal detection device 17 via the conveying device 23 as pulp fibers P3 for metal detection.

[0049] However, the quantitative step S31 (quantifying device 13) may be omitted. In that case, for example, the dewatering device 11 intermittently supplies the pulp fibers P0, which are multiple clumps, to the loosening device 15, and the loosening device 15 intermittently performs the clumping step S32 (batch type). Alternatively, the dewatering device 11 may continuously supply the pulp fibers P0 to the loosening device 15, and the loosening device 15 may continuously perform the clumping step S32 (continuous type).

[0050] In this method, in the disintegration step S04, several pulp fiber lumps P2, which are pulp fiber lumps P1 that correspond to a predetermined mass or volume range determined in the quantification step S31, are disintegrated in the clump disintegration step S32. In other words, the amount of pulp fiber lumps disintegrated at one time is limited to a predetermined mass or volume range. This ensures that the pulp fiber lumps are reliably disintegrated. Therefore, in subsequent steps, the detection and removal of fine foreign matter in the recycled pulp fibers can be made easier.

[0051] Next, inspection step S33 is carried out using various inspection devices. In this embodiment, these are a metal detection device 17 and a foreign matter detection device 19. Inspection step S33 is a step of detecting foreign matter in the pulped pulp fibers P3 and removing the foreign matter if it is detected. In a preferred embodiment, this method includes such an inspection step S33, which allows for the detection of fine foreign matter from the pulped pulp fibers P3, making it easy to detect and remove any foreign matter present. In this embodiment, inspection step S33 includes a metal inspection step S34 and a foreign matter inspection step S35.

[0052] First, the metal inspection process S34 is performed by the metal detection device 17. The metal inspection process S34 is a process in which the metal detection device detects metal foreign matter contained in the disassembled pulp fibers P3.

[0053] Specifically, the metal detection device 17 is positioned in the middle of the conveying device 23 and detects whether or not metallic foreign matter is present in the pulp fibers P3 passing through the conveying device 23. Examples of the metal detection device 17 include proximity sensors (electromagnetic induction type, capacitive type, magnetic type) that are positioned one or more times around the passage of the pulp fibers P3 in the conveying device 23.

[0054] After the metal detection process S34, the pulp fibers P4 are transferred from the conveyor 23 to the conveyor 24. Pulp fibers P4 in which metal is detected by the metal detection device 17 are removed by the conveyor 24 as metal-containing pulp fibers P5. They are then passed to a metal foreign matter removal device (not shown in Figure 5) where the metal foreign matter is removed. After that, they may be returned to the conveyor 23 and undergo the metal detection process S34 again. On the other hand, pulp fibers P4 in which no metal is detected by the metal detection device 17 are supplied by the conveyor 24 as metal-free pulp fibers P6 to the next foreign matter detection device 19.

[0055] This method, by including such a metal inspection step S34, makes it possible to easily detect metallic foreign matter contained in used absorbent articles that could not be removed during the separation of pulp fibers, and thereby easily remove it.

[0056] Next, the foreign matter inspection process S35 is carried out by the foreign matter detection device 19. The foreign matter inspection process S35 is a process in which the foreign matter detection device detects non-metallic foreign matter contained in the pulp fibers P6 that have passed through the metal inspection process S34.

[0057] Specifically, the foreign object detection device 19 is positioned in the middle of the conveying device 24 and detects whether or not non-metallic foreign objects are present in the pulp fibers P6 passing through the conveying device 24. An example of a metal detection device 17 is a device combining one or more image sensors or a digital camera with an image processing system, positioned around the passage of the pulp fibers P6 in the conveying device 24.

[0058] After the foreign matter inspection process S35, the pulp fibers P6 are transferred from the conveying device 24 to the conveying device 25. Pulp fibers P6 in which non-metallic foreign matter is detected by the foreign matter detection device 19 are removed by the conveying device 25 as pulp fibers P7 containing foreign matter. They are then passed to a foreign matter removal device (not shown in Figure 5) where non-metallic foreign matter is removed. After that, they may be returned to the conveying device 24 and undergo the foreign matter inspection process S35 again. On the other hand, pulp fibers P6 in which no foreign matter is detected by the foreign matter detection device 19 are supplied by the conveying device 25 as pulp fibers P8 that do not contain foreign matter to a storage container for pulp fibers.

[0059] This method, by having such a foreign matter inspection step S35, makes it possible to easily detect non-metallic foreign matter contained in used absorbent articles that could not be removed during the separation of pulp fibers, and thereby easily remove it.

[0060] In this embodiment, in a preferred configuration, the loosening step S04 may include a step of loosening the pulp fiber clumps while suppressing the further fragmentation of foreign matter present in the dewatered pulp fiber clumps. This makes it more difficult for fine foreign matter embedded in the pulp fiber clumps to be further fragmented, allowing them to maintain a certain size. Therefore, detection and removal of fine foreign matter in recycled pulp fibers (inspection step S33 (metal inspection step S34, foreign matter inspection step S35)) can be made easier. However, as a method to make it more difficult for foreign matter in the clumps to be fragmented, when the loosening step S04 (clump loosening step S32) is performed with a pin mill grinder, for example, the fragmentation of foreign matter can be suppressed by adjusting the shape of the pins. For example, the shape of the pins can be adjusted by making the entire pin cylindrical, making the tip hemispherical, making the diameter of the cylinder relatively thicker, or relatively reducing the number of pins.

[0061] Furthermore, in this embodiment, in a preferred manner, the processes from the disintegration process S04 onward are carried out in a closed space. That is, at least the quantitative device 13, the disintegration device 15, the metal detection device 17, the foreign matter detection device 19, and the conveying devices 21-25 are arranged in a closed space. Preferably, the device for removing detected foreign matter and the device for storing the pulp fibers after each inspection in a storage container are also arranged in a closed space. This makes it possible to further suppress the contamination of at least the disintegrated recycled pulp fibers with foreign matter and the invasion of various bacteria.

[0062] Next, in this embodiment, as shown in Figure 1, a storage process S05 is carried out as a process following the disintegration process S04. Here, an example of a storage device for carrying out the storage process S05 is a device that stores the generated recycled pulp fibers in a sealed state, for example, in a storage container, without drying them, and then transports the storage container to a storage facility. By storing the recycled pulp fibers without drying them, the equipment required for drying can be reduced, and the volume of the recycled pulp fibers is reduced, so the capacity of the storage container, the size of the storage facility that stores the storage container, and the equipment required to transport the storage container can be reduced.

[0063] However, if recycled pulp fibers are stored in a wet state, there is a risk of mold and other fungi growing and multiplying on the recycled pulp fibers. To address this, the pulp fibers are strongly squeezed in the dewatering step S03 to reduce the moisture content as much as possible. However, in this case, because the fibers are squeezed so strongly, the bonds and entanglement between the fibers become very strong, and the tendency for the clumps of pulp fibers to become difficult to separate becomes significant. Therefore, this method includes a loosening step S04 before the storage step S05. This makes it possible to suppress the growth and multiplication of mold and other fungi while also preventing the clumps of pulp fibers from becoming difficult to separate.

[0064] In the present invention, the washed pulp fibers supplied to the dewatering step S03 are not particularly limited, but examples include pulp fibers washed by the washing step S02 described below. The washing step S02 will now be described in detail. Figure 4 is a flowchart of the washing step S02 according to an embodiment. In this embodiment, the washing step S02 comprises an ozone treatment step S21, a rinsing step S22, and an antibacterial treatment step S23. However, the washing step S02 does not need to include the other steps as long as it includes the rinsing step S22.

[0065] The ozone treatment process S21 is performed before the dewatering process S03 and involves ozone treatment of pulp fibers separated from used absorbent articles.

[0066] The ozone treatment process S21 involves treating the pulp fibers with a treatment solution containing ozone (e.g., water containing ozone). This treatment allows superabsorbent polymers and organic impurities (e.g., lignin, excrement residue, bacteria, mold, etc.) that may be adhering to the surface or interior of the pulp fibers derived from used absorbent articles to come into contact with ozone. As a result, the superabsorbent polymers and organic impurities are oxidized and decomposed by the ozone, solubilized in the treatment solution, and easily removed from the pulp fibers, thus obtaining pulp fibers with fewer impurities. Furthermore, depending on the strength of the ozone treatment (the magnitude of the CT value ((ozone concentration) × (treatment time))), fibrillation of the pulp fibers can be promoted, thereby obtaining pulp fibers with further fibrillation and an even larger specific surface area.

[0067] The ozone treatment apparatus in the ozone treatment process S21 is not particularly limited in its configuration, as long as it can bring the pulp fibers into contact with ozone. The ozone treatment apparatus includes, for example, a treatment tank for storing the treatment liquid and an ozone supply device for supplying ozone-containing gas into the treatment tank. In the ozone treatment apparatus, for example, pulp fibers are introduced into the treatment liquid from the top or bottom of the treatment tank, ozone-containing gas is supplied into the treatment liquid from the bottom of the treatment tank, and the pulp fibers and the ozone-containing gas in the treatment liquid are mixed and brought into contact within the treatment tank. Examples of ozone supply devices include the ED-OWX-2 ozone water exposure tester manufactured by Eco Design Co., Ltd. and the OS-25V ozone generator manufactured by Mitsubishi Electric Corporation. Furthermore, by using a treatment liquid containing ozone, the pulp fibers can be sterilized and bleached.

[0068] In the ozone treatment process S21, the concentration of pulp fibers in the treatment solution can be, for example, 0.5 to 20% by mass, and preferably 1 to 10% by mass, based on 100% by mass of the treatment solution. If the concentration of pulp fibers is too low, the treatment efficiency will be poor, and if it is too high, it will be difficult to remove impurities from the pulp fibers.

[0069] In the ozone treatment step S21, the ozone concentration in the treatment solution is preferably 1 to 200 ppm by mass. If the concentration is too low, it becomes difficult to remove impurities from the pulp fibers, and if the concentration is too high, it becomes easy to damage the pulp fibers. The ozone treatment time is shortened when the ozone concentration in the treatment solution is high and lengthened when the ozone concentration is low, and is typically 5 to 120 minutes. The product of the ozone concentration in the treatment solution (ppm) and the treatment time (minutes) (hereinafter also referred to as the "CT value") is preferably 100 to 6000 ppm·minute. If the CT value is too low, it becomes difficult to remove impurities, and if the CT value is too high, it becomes easy to damage the pulp fibers.

[0070] The treatment solution is not particularly limited as long as it contains or can contain ozone, for example, water itself or an acidic aqueous solution. The treatment solution is preferably acidic (pH 2.0 to 6.0) to neutral (pH 6.0 to 8.0). More preferably, the pH of the treatment solution is 2.0 to 7.0 or lower, and even more preferably 2.5 to 6.0. By treating in an acidic state, the deactivation and gasification of ozone in the treatment solution can be suppressed, and the superabsorbent polymer can be oxidized and decomposed in a short time. To maintain the pH of the treatment solution, for example, the pH of the treatment solution may be monitored with a pH sensor, and when the pH fluctuates towards the neutral side, a predetermined acidic solution may be added to the treatment solution in an amount corresponding to the fluctuation range.

[0071] Ozone treatment in the ozone treatment process S21 suppresses the residue of superabsorbent polymers, lignin, and other impurities in the pulp fibers, while also deodorizing, sterilizing, and bleaching the pulp fibers, and further promoting fibrillation. As a result, the pulp fibers become suitable for a variety of applications due to their low impurity content, suppressed bacterial growth, and increased surface area. However, pulp fibers that have undergone advanced fibrillation have stronger bonding forces between the fibers, resulting in reduced dispersibility. Therefore, this method includes a disintegration process to break down clumps formed by such pulp fibers. This makes it possible to achieve a highly dispersible state for the fibrillated pulp fibers. Consequently, when reusing recycled pulp fibers, it is less likely to cause clumps or unevenness in the fibers, and it becomes easier to detect and remove fine foreign matter embedded in the recycled pulp fibers.

[0072] Subsequently, the pulp fibers treated with ozone in the ozone treatment process S21 are separated from the treatment liquid (solid-liquid separation) by a separation device having a sieve (or mesh) that is provided separately from the ozone treatment device, and then proceed to the rinsing process S22.

[0073] The rinsing process S22 is carried out using a general rinsing device. This process involves rinsing the ozone-treated pulp fibers with washing water (examples: pure water, tap water, industrial water). This washes away impurities and treatment liquid (including ozone) that were present on the surface of the pulp fibers. After rinsing in the rinsing process S22, the pulp fibers proceed to the antibacterial treatment process S23.

[0074] The antimicrobial treatment process S23 is carried out using a general antimicrobial agent spraying device. This process is performed before the dewatering process S03 and involves treating the pulp fibers separated from the used absorbent material with an antimicrobial agent. For example, the pulp fibers, from which impurities have been reduced by rinsing, are agitated while an antimicrobial agent or a liquid containing an antimicrobial agent is sprayed onto the pulp fibers.

[0075] In this method, since the pulp fibers separated from used absorbent articles are treated with an antibacterial agent, the generation and proliferation of various bacteria can be suppressed in subsequent processes, such as the storage process S05.

[0076] Furthermore, in this embodiment, an ozone treatment step S21 is performed as a step prior to the disintegration step S04. The ozone treatment of the pulp fibers sterilizes the pulp fibers and removes impurities. As a result, even if the recycled pulp fibers are stored in a wet state during the storage step S05, the occurrence and proliferation of mold and other fungi can be suppressed. This prevents the deterioration of properties in products containing recycled pulp fibers due to the influence of various fungi.

[0077] In the present invention, the separated pulp fibers supplied to the washing step S02 are not particularly limited, but examples include pulp fibers separated by the pulp fiber separation step S01 described below. The pulp fiber separation step S01 will now be described in detail. Figure 5 is a flowchart of the pulp fiber separation step S01 according to an embodiment. In this embodiment, the pulp fiber separation step S01 comprises a crushing step S11, a plastic separation step S12, a foreign matter removal step S13, and an SAP separation step S14.

[0078] The crushing step S11 is a step in which used absorbent articles (nonwoven fabric products) are crushed in an inactivated aqueous solution. In this embodiment, in the crushing step S11, a plurality of used absorbent articles, or collection bags containing them (hereinafter also simply referred to as "used absorbent articles"), are supplied to a solution tank containing an acidic aqueous solution, which is an inactivated aqueous solution. The acidic aqueous solution containing the used absorbent articles is sent from the solution tank to a twin-shaft shredder (examples: twin-shaft rotary shredder, twin-shaft differential shredder, twin-shaft shear shredder). The used absorbent articles are crushed by the twin-shaft shredder. As a result, crushed material is produced from the crushed used absorbent articles. The crushed material is sent to the plastic separation step S12, either alone or together with the acidic aqueous solution.

[0079] When used absorbent articles are treated in an inactivating aqueous solution, the superabsorbent polymers contained in or that were contained in the used absorbent articles are inactivated, dehydrated, and reduced in particle size. This makes it easier to handle the superabsorbent polymers in subsequent processes and improves the efficiency of the treatment. Acidic aqueous solutions, i.e., aqueous solutions of inorganic and organic acids, are used as the inactivating aqueous solution because, compared to aqueous solutions of lime or calcium chloride, no ash remains on the plastic material or pulp fibers, and the degree of inactivation (particle size and specific gravity) can be easily adjusted by pH. The pH of the acidic aqueous solution is preferably 1.0 to 4.0. Setting the pH above 1.0 reduces corrosion of equipment and reduces the amount of alkaline chemicals required for neutralization during wastewater treatment. Setting the pH below 4.0 allows the superabsorbent polymers to be sufficiently reduced in size and enhances the bactericidal capacity. Examples of organic acids include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, and ascorbic acid, with citric acid being preferred. Due to the chelating effect of citric acid, metal ions and other substances in excrement can be trapped and removed, and the cleaning effect of citric acid allows for a high level of dirt removal. On the other hand, examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferred from the viewpoint of not containing chlorine and cost. Since pH changes with water temperature, the pH in this invention refers to the pH measured at an aqueous solution temperature of 20°C. The concentration of organic acid in the organic acid aqueous solution is not particularly limited, but when the organic acid is citric acid, it is preferably 0.5% by mass or more and 4% by mass or less. The concentration of inorganic acid in the inorganic acid aqueous solution is not particularly limited, but when the inorganic acid is sulfuric acid, it is preferably 0.1% by mass or more and 0.5% by mass or less. In this embodiment, sulfuric acid is used as the inactivating aqueous solution.

[0080] Next, the plastic separation step S12 is a step of separating plastic material from a mixture of synthetic resin plastic material (examples: film, nonwoven fabric, collection bag, etc.), superabsorbent polymer, pulp fibers, and excrement obtained by decomposing used absorbent articles in an acidic aqueous solution. In this embodiment, the mixture of crushed material produced in the crushing step S11 and the acidic aqueous solution (including excrement) is supplied to the pulper separator. The pulper separator has an agitated separation tank that functions as a washing tank and a sieving tank. In the pulper separator, the mixture of crushed material and the acidic aqueous solution is agitated and washed to remove dirt from the crushed material, and then separated by a screen into a mixture of plastic material, pulp fibers, superabsorbent polymer, and acidic aqueous solution. The pulp fibers, superabsorbent polymer, and acidic aqueous solution that pass through the screen are supplied to the foreign matter removal step S13. Meanwhile, the plastic material that does not pass through the screen is then washed with washing water, dried, and recovered. Disinfection or sterilization may be performed with a disinfectant or sterilizing agent at the same time as, or before or after, the cleaning process.

[0081] Next, in the foreign matter removal step S13, at least one separator (example: screen separator, cyclone separator) separates any foreign matter such as film, nonwoven fabric, and collection bags that could not be removed from the mixture supplied from the plastic separation step S12. In this embodiment, a screen separator (with a relatively large mesh opening), a screen separator (with a relatively small mesh opening), and a cyclone separator are arranged in this order, and foreign matter is sequentially separated from the mixture. As a result, pulp fibers and superabsorbent polymers with fewer foreign matter are obtained. The mixture of pulp fibers and superabsorbent polymers with fewer foreign matter and an acidic aqueous solution (containing excrement) is supplied to the SAP separation step S14.

[0082] In the SAP separation step S14, the superabsorbent polymer is separated from the mixed liquid (containing pulp fibers with few foreign matter and the superabsorbent polymer) supplied from the foreign matter removal step S13 by at least one separator (example: drum screen separator). In this embodiment, the drum screen separator separates the mixed liquid into the superabsorbent polymer and acidic aqueous solution (including excrement) and pulp fibers (containing a small amount of superabsorbent polymer). The superabsorbent polymer and acidic aqueous solution that have passed through the screen are then separated into the superabsorbent polymer and acidic aqueous solution by another separator (example: inclined screen separator), the superabsorbent polymer is washed with washing water, dried, and recovered. Disinfection or sterilization may be performed with disinfectants or sterilizers at the same time as or before / after washing. Meanwhile, the pulp fibers that did not pass through the screen are supplied to the washing step S02.

[0083] The absorbent articles of the present invention are not limited to the embodiments described above, and can be appropriately combined or modified without departing from the purpose and spirit of the present invention. [Explanation of Symbols]

[0084] S03 Dehydration process S04 Disassembly Process

Claims

1. A method for producing recycled pulp fibers from used absorbent articles containing pulp fibers, A dewatering process for dewatering pulp fibers that have been separated from and washed used absorbent materials, A disintegration step in which each of the multiple clumps of pulp fibers formed by dewatering is disintegrated to produce recycled pulp fibers, Equipped with, A method further comprising a storage step of storing the recycled pulp fibers generated after the disintegration step in a moist state, which is not dried after the dewatering step.

2. A method for producing recycled pulp fibers from used absorbent articles containing pulp fibers, A dewatering process for dewatering pulp fibers that have been separated from and washed used absorbent materials, A disintegration step in which each of the multiple clumps of pulp fibers formed by dewatering is disintegrated to produce recycled pulp fibers, Equipped with, The disintegration step includes a step of disintegrating the pulp fiber mass while suppressing the fragmentation of foreign matter present in the dehydrated pulp fiber mass so that it is less likely to be fragmented than before the disintegration step. method.

3. The disintegration step includes a quantitative step of quantifying the portion of the pulp fiber mass that corresponds to a predetermined mass or volume range from among the multiple masses of pulp fiber formed by the dewatering, A process of breaking down the quantified pulp fiber clumps, including, The method according to claim 1 or 2.

4. The aforementioned disintegration step includes a foreign matter detection step in which foreign matter is detected within the disintegrated pulp fibers and removed if foreign matter is detected. The method according to any one of claims 1 to 3.

5. The aforementioned foreign object detection step includes a step of detecting metallic foreign objects using a metal detection device. The method according to claim 4.

6. The aforementioned foreign object detection step includes a step of detecting foreign objects other than metal using a foreign object detection device. The method according to claim 4 or 5.

7. The method further comprises an ozone treatment step, in which the pulp fibers separated from the used absorbent article are treated with ozone before the dewatering step. The method according to any one of claims 1 to 6.

8. The method further comprises an antimicrobial treatment step, prior to the dewatering step, in which the pulp fibers separated from the used absorbent article are treated with an antimicrobial agent. The method according to any one of claims 1 to 7.

9. The processes following the aforementioned disassembly are carried out in a closed space. The method according to any one of claims 1 to 8.

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