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

Abstract

DEPCT67 This invention provides a method for producing recycled pulp fibers from used absorbent materials; a method. That leads to the achievement of recycled pulp fibers that exhibit high dispersibility, and which matter Foreign particles are easily detected and removed; this invention provides a method for producing pulp fibers. Recycled from used absorbent materials containing pulp fibers, a method that includes a dehydration step (S03). and the loosening step (S04) in the dehydration step, the membrane fibers are separated from the used adsorbent and Cleaned and introduced into dehydration during the loosening process, each piece of the fibrous mass is a pulp. A certain amount that was formed by dehydration is unleashed to produce recycled pulp fibers;

Description

Method for producing recycled pulp fibers from post-consumer absorbent articles

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

[0002] Methods for producing recycled pulp fibers from used absorbent articles are known. For example, Japanese Patent Application Laid-Open No. 2020-183585 discloses a method for producing recycled pulp fibers from used absorbent articles containing a superabsorbent polymer, pulp fibers, and excrement. This method includes a separation step of separating the inactivating aqueous solution and the pulp fibers from a mixture of the inactivating aqueous solution and the used absorbent article, a viscosity reduction step of mixing the separated inactivating aqueous solution with a first oxidizing agent to decompose the excrement contained in the inactivating aqueous solution and reduce the viscosity of the inactivating aqueous solution, and a resupply step of returning the inactivating aqueous solution to the separation step. The method may further include a solubilization step of mixing the pulp fibers separated in the separation step with an oxidizing aqueous solution containing a second oxidizing agent to decompose the superabsorbent polymer contained in the pulp fibers and solubilize them in the oxidizing aqueous solution, and another separation step of separating the oxidizing aqueous solution from the pulp fibers.

[0003] Japanese Patent Application Laid-Open No. 2020-183585

[0004] In the method of Patent Document 1, the separated pulp fibers are washed with wash water, dewatered, and finally extracted as recycled pulp fibers. However, the dewatered pulp fibers contain numerous agglomerates, each about the size of a sphere with a diameter of several centimeters. Because it is difficult to disentangle each of these numerous agglomerates of pulp fiber, the extracted recycled pulp fibers may have poor dispersibility. As a result, when the recycled pulp fibers are reused in various products, the products are likely to have clumps or unevenness of the fibers.

[0005] Furthermore, because it is not easy to separate the numerous clumps of pulp fiber, it is not easy to detect foreign matter in the clumps, and even if it is detected, it is difficult to remove it. Therefore, there is a risk that the extracted recycled pulp fiber contains a non-negligible amount of foreign matter. In such cases, the performance of products containing recycled pulp fiber is likely to be reduced due to the influence of the foreign matter.

[0006] In particular, if the extracted recycled pulp fibers are stored without drying, the pulp fibers are squeezed hard during the dehydration process to remove as much moisture as possible in order to prevent the growth of mold, etc., and as a result, the bonds and entanglements between the fibers become very strong, making it increasingly difficult to break up the clumps.

[0007] An object of the present invention is to provide a method for producing recycled pulp fibers from used absorbent articles, which can obtain recycled pulp fibers that are highly dispersible and from which foreign matter can be easily detected and removed.

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

[0009] According to the method of the present invention, it is possible to provide a method for producing recycled pulp fibers from used absorbent articles, which can obtain recycled pulp fibers that are highly dispersible and from which foreign matter can be easily detected and removed.

[0010] Fig. 1 is a flowchart showing a method for producing recycled pulp fibers from used absorbent articles according to an embodiment. Fig. 2 is a schematic diagram showing an apparatus for performing an unwinding process according to an embodiment. Fig. 3 is a flowchart showing an unwinding process according to an embodiment. Fig. 4 is a flowchart showing a cleaning process according to an embodiment. Fig. 5 is a flowchart showing a pulp fiber separation process according to an embodiment.

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

[0012] This method includes a defibrating step in which each of the multiple lumps of pulp fibers formed by dewatering is defibrated to produce recycled pulp fibers. By defibrating each of the multiple lumps of pulp fibers after dewatering, the pulp fibers, and ultimately the recycled pulp fibers, can be made highly dispersible. This makes it possible to reduce the occurrence of fiber clumps and unevenness when the produced recycled pulp fibers are reused. Furthermore, by making the fibers highly dispersible, it is possible to easily detect and remove small foreign objects that have become embedded in the recycled pulp fibers.

[0013] [Aspect 2] The method of Aspect 1, wherein the defibrating step includes a step of defibrating the dewatered pulp fiber clumps while suppressing fragmentation of foreign matter present in the pulp fiber clumps. In this method, the defibrating step includes a step of defibrating the pulp fiber clumps while suppressing fragmentation of foreign matter present in the pulp fiber clumps. This makes it difficult for fine foreign matter that has entered the pulp fiber clumps to be further fragmented, allowing it to maintain a certain size. This makes it easier to detect and remove fine foreign matter from recycled pulp fibers.

[0014] [Aspect 3] The method according to Aspect 1 or 2, wherein the defibrating step includes a quantification step of quantifying the pulp fiber agglomerates formed by the dewatering, the number of the pulp fiber agglomerates corresponding to a predetermined mass or volume range, and a defibrating step of defibrating the quantified pulp fiber agglomerates. In this method, the defibrating step defibrates the pulp fiber agglomerates for each of several pulp fiber agglomerates corresponding to a predetermined mass or volume range. In other words, the amount of pulp fiber agglomerates defibrated at one time is limited. This ensures reliable defibration of the pulp fiber agglomerates. This makes it easier to detect and remove small foreign matter from recycled pulp fibers.

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

[0016] [Aspect 5] The method according to Aspect 4, wherein the foreign matter detection step includes a step of detecting metallic foreign matter using a metal detection device. In this method, by detecting metallic foreign matter using a metal detection device, metallic foreign matter contained in used absorbent articles that could not be removed during separation of pulp fibers can be easily detected and thereby 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 using a foreign matter detection device. In this method, by detecting non-metallic foreign matter using the foreign matter detection device, non-metallic foreign matter contained in used absorbent articles that could not be removed during pulp fiber separation can be easily detected and thereby easily removed.

[0018] [Aspect 7] The method according to any one of Aspects 1 to 6, further comprising an ozone treatment step of ozone-treating the pulp fibers separated from the used absorbent article before the dewatering step. The ozone treatment step can suppress the residual lignin and other impurities in the pulp fibers, deodorize, sterilize, and bleach the pulp fibers, and promote fibrillation. As a result, the pulp fibers have fewer impurities, suppress bacterial growth, and have a larger surface area, making them suitable for a variety of applications. However, highly fibrillated pulp fibers have a stronger bond between pulp fibers, resulting in a lower dispersibility. Therefore, this method includes a disintegration step of disintegrating clumps formed from pulp fibers in such a state. This allows the highly fibrillated pulp fibers to be highly dispersible. Therefore, when the recycled pulp fibers are reused, it is possible to reduce the occurrence of clumps and unevenness in the fibers and facilitate the detection and removal of small foreign matter that has become embedded in the recycled pulp fibers.

[0019] [Aspect 8] The method according to any one of Aspects 1 to 7, further comprising a storage step of storing the recycled pulp fibers produced after the disintegration step in a wet state. In this method, the recycled pulp fibers produced after the disintegration step are stored in a wet state. In this case, storing the fine recycled pulp fibers without drying them has the advantage of reducing the equipment required for drying and the equipment required for storage and transportation. However, storing the recycled pulp fibers in a wet state may cause the growth and proliferation of various bacteria such as mold on the recycled pulp fibers. Even in such cases, this method uses ozone treatment to sterilize the fibers, thereby suppressing the growth and proliferation of such bacteria. As a result, products containing recycled pulp fibers can be prevented from having poor properties due to the effects of various bacteria.

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

[0021] [Aspect 10] The method according to any one of Aspects 1 to 9, wherein the loosening step and subsequent steps are carried out in a closed space. In this method, the loosening step and subsequent steps are carried out in a closed space, which can further prevent the intrusion of foreign matter and various bacteria into the recycled pulp fibers.

[0022] Hereinafter, a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to an embodiment will be described. The 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, urine absorption pads, sanitary napkins, bed sheets, and pet sheets.

[0023] First, an example of the configuration of an absorbent article will be described. The absorbent article comprises a top sheet, a back sheet, and an absorbent body disposed between the top sheet and the back sheet. An example of the size of the absorbent article is a length of approximately 15 to 100 cm and a width of 5 to 100 cm. The absorbent article may further comprise other components that are typically included in absorbent articles, such as a diffusion sheet, a leak-proof wall, side sheets, and an exterior sheet.

[0024] The material for the top sheet is not particularly limited, and known top sheet materials can be used. Examples include liquid-permeable nonwoven fabrics, synthetic resin films with liquid-permeable holes, and composite sheets of these. The material for the back sheet is not particularly limited, and known back sheet materials can be used. Examples include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets of these. The material for the diffusion sheet is not particularly limited, and known diffusion sheet materials can be used. Examples include liquid-permeable nonwoven fabrics. The materials for the leak barrier and side sheets are not particularly limited, and known leak barrier and side sheet materials can be used. Examples include water-repellent nonwoven fabrics, and the leak barrier may further include an elastic member such as rubber thread. The material for the exterior sheet is not particularly limited, and known exterior sheet materials can be used. Examples include liquid-impermeable yet breathable nonwoven fabrics, liquid-impermeable yet breathable synthetic resin films, and composite sheets of these.

[0025] The type of nonwoven fabric mentioned above is not particularly limited, and examples thereof include meltblown nonwoven fabric, spunbond nonwoven fabric, thermalbond nonwoven fabric, airlaid nonwoven fabric, and air-through nonwoven fabric. Furthermore, the type of synthetic resin film is not particularly limited, and known film materials can be used. Here, the material for the nonwoven fabric or synthetic resin film is not particularly limited as long as it can be used for absorbent articles, and examples include olefin-based resins such as polyethylene and polypropylene, polyamide-based resins such as 6-nylon and 6,6-nylon, and polyester-based resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). These nonwoven fabric and synthetic resin film materials are synthetic resins and can be referred to as plastic materials. In this embodiment, an absorbent article in which the backsheet is a film and the topsheet is a nonwoven fabric will be described as an example.

[0026] Examples of absorbent materials include absorbent materials, namely pulp fibers and superabsorbent polymers. Examples of pulp fibers include cellulosic fibers. Examples of cellulosic fibers include wood pulp, crosslinked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. Pulp fiber sizes include an average fiber length of several tens of microns (20 to 40 μm) and an average fiber length of several millimeters (2 to 5 mm). Examples of superabsorbent polymers (SAPs) include polyacrylate-based, polysulfonate-based, and maleic anhydride-based water-absorbing polymers. Examples of the size of the superabsorbent polymer (when dry) include an average particle size of several hundred microns (200 to 500 μm). The absorbent may be enclosed in a core wrap formed of a liquid-permeable sheet.

[0027] One side and the other side of the absorbent body are bonded to the top sheet and the back sheet, respectively, via an adhesive. In plan view, the portion (peripheral portion) of the top sheet that extends outward from the absorbent body so as to surround the absorbent body is bonded via an adhesive to the portion (peripheral portion) of the back sheet that extends outward from the absorbent body so as to surround the absorbent body. Therefore, the absorbent body is enclosed within the bonded body of the top sheet and the back sheet. There are no particular limitations on the adhesive, but examples include hot melt adhesives. Examples of hot melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives that are primarily rubber-based, such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin-based, such as polyethylene.

[0028] Next, a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to an embodiment will be specifically described. Note that separating and recovering pulp fibers from used absorbent articles to obtain reusable pulp fibers results in the production of reusable recycled pulp fibers, and can therefore be considered as the production of recycled pulp fibers.

[0029] 1 is a flowchart showing a method for producing recycled pulp fibers from used absorbent articles containing pulp fibers according to an embodiment. The method includes a dewatering step S03 and a loosening step S04, and in this embodiment, further includes a pulp fiber separating step S01, a washing step S02, and a storage step S05.

[0030] The pulp fiber separating step S01 is a step of separating pulp fibers from a used absorbent article. The washing step S02 is a step of washing the pulp fibers obtained in the pulp fiber separating step S01.

[0031] The dewatering step S03 is a step of dewatering the pulp fibers that have been separated from the used absorbent article and washed. After being washed, the pulp fibers separated from the used absorbent article are rinsed, i.e., washed with water, and then dewatered to remove as much water as possible. In the dewatering step, the pulp fibers are squeezed (compressed) strongly to remove the water. This causes the fibers to bond and entangle with each other, forming multiple clumps of pulp fiber. The shapes of the individual clumps vary, but their size, when considered in terms of the size of a sphere containing the clumps, can be, for example, several centimeters to 10 cm in diameter.

[0032] In this embodiment, the pulp fibers used in the dewatering step S03 are pulp fibers 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 be used, for example, pulp fibers obtained by obtaining pulp fibers collected from used absorbent articles at a separate facility that separates pulp fibers, and washing the pulp fibers in the washing step S02.

[0033] The disintegrating step S04 is a step of disintegrating each of the multiple pulp fiber agglomerates formed by dehydration to produce recycled pulp fibers. Here, "disintegrating" refers to reducing the size of the pulp fiber agglomerates to be smaller than their original size. In this embodiment, the size of the agglomerates, when considered as the size of a sphere containing the agglomerates, is set to a diameter of 2 cm or less, preferably 1 cm or less, and more preferably 0.5 cm or less. While it is not necessary to disintegrate all of the multiple pulp fiber agglomerates, it is preferable to disintegrate at least 95% of the agglomerates, and more preferably 98% or more of the agglomerates. The size of the pulp fiber agglomerates is measured by the following method.

[0034] <Size of pulp fiber clumps> (1) Place a collection of pulp fibers containing multiple clumps to be evaluated on a scanner. At this time, ensure that the clumps do not overlap each other and do not touch each other. However, if only individual dispersed fibers are in contact, they are considered not in contact. (2) Import a scanned image of the pulp fibers. (3) Use software to binarize the scanned image, treating continuous areas as a single clump, and calculate the diameter of the circle containing the clump for each clump. However, areas connected only by individual dispersed fibers are considered to be separate clumps.

[0035] The storage step S05 is a step of storing the produced recycled pulp fibers in a wet state.

[0036] As described above, this method may include a pulp fiber separating step S01, which is a step of preparing pulp fibers, of separating pulp fibers from used absorbent articles, and a washing step S02, which is a step of washing the separated pulp fibers, before the dewatering step S03. The method may also include a storage step S05, which stores the recycled pulp fibers generated in the disentangling step S04 in a wet state. The pulp fiber separating step S01, the washing step S02, and the storage step S05 will be described in detail below.

[0037] In this method, in the dewatering step S03, pulp fibers are dewatered to form a plurality of pulp fiber agglomerates, and in the disintegrating step S04, each of the dewatered pulp fiber agglomerates is disintegrated to produce recycled pulp fibers. By disintegrating each of the dewatered pulp fiber agglomerates in this manner, the disintegrated pulp fibers, and ultimately the produced recycled pulp fibers, can be made highly dispersible. This makes it possible to reduce the occurrence of fiber clumps or unevenness in the products when the produced recycled pulp fibers are reused in various products. Furthermore, by making the recycled pulp fibers highly dispersible, it is possible to easily detect and remove small foreign matter that has become embedded in the recycled pulp fibers after disintegrating the agglomerates. In other words, this method can produce recycled pulp fibers from used absorbent articles, which can produce recycled pulp fibers that are highly dispersible and from which foreign matter can be easily detected and removed.

[0038] Each of the above steps will be further explained below.

[0039] As described above, the dewatering step S03 involves dewatering the pulp fibers separated from the used absorbent article and washed. The dewatering device used in the dewatering step S03 is not particularly limited as long as it is capable of dewatering, and examples include a screw press dewatering machine, a belt press dewatering machine, and a washing / dewatering tub having a rotating drum. When dewatering is complete, 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 sent out of the dewatering device and transferred to the disentangling step S04.

[0040] Next, in the defibrating step S04, as described above, each of the multiple pulp fiber agglomerates formed by dewatering is defibrated to produce recycled pulp fibers. The defibrating device used in the defibrating step S04 is not particularly limited as long as it can defibrate the pulp fiber agglomerates, and examples thereof include a pin mill crusher. A pin mill crusher includes a disk and multiple pins arranged perpendicular to the disk surface (parallel to the disk's rotation axis). The rotation of the disk applies impact and shear forces to the agglomerates, thereby defibrating them. When defibration is complete, the impact and shear forces have defibrated the multiple pulp fiber agglomerates, reducing them and preferably eliminating them. The pulp fibers, which contain almost no agglomerates (preferably no agglomerates at all), are then sent out from the defibrating device and transferred to the next step.

[0041] The deflocculating step S04 will now be described in detail. FIG. 2 is a schematic diagram showing an apparatus for performing the deflocculating step S04, and FIG. 3 is a flowchart showing the deflocculating step S04. The deflocculating step S04 includes a deflocculating step S32, and in this embodiment, further includes a quantification step S31 and an inspection step S33. The inspection step S33 includes a metal inspection step S34 and a foreign matter inspection step S35. The deflocculating step S32, the quantification step S31, and the metal inspection step S34 and foreign matter inspection step S35 of the inspection step S33 are performed by the deflocculating device 15, the quantification device 13, the metal detection device 17, the foreign matter detection device 19, and the conveying devices 21 to 25, respectively. The conveying device 21 may be, for example, a conveyor such as a belt conveyor or a drive roller conveyor. Furthermore, in the deflocculating step 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 to a dewatering device 11 (e.g., a screw press dewatering machine) that performs the above-mentioned dewatering step S03 via a conveying device 20. The pulp fibers P0 dewatered by the dewatering device 11 are supplied as pulp fibers P1 containing multiple clumps via a conveying device 21 to a quantification device 13 in the loosening step S04.

[0043] First, the quantification step S31 is performed by the quantification device 13. The quantification step S31 is a step of quantifying the number of pulp fiber agglomerates that correspond to a predetermined range of mass or volume, from among the multiple pulp fiber agglomerates formed by dehydration in the dehydration step S03.

[0044] Specifically, the quantification device 13 receives a plurality of clumps of pulp fibers P1 supplied continuously or intermittently from the dewatering device 11 via the conveying device 21, and measures the mass or volume of the pulp fibers P1. When measuring the mass, it measures whether the mass of the pulp fibers P1 reaches a predetermined mass range (e.g., 50 g to 100 g). When measuring the volume, it measures whether the volume of the pulp fibers P1 reaches a predetermined volume range (e.g., 500 cm). ３ ~1000cm ３ When the mass or volume reaches the predetermined range, the conveying device 21 is temporarily stopped, and the pulp fibers P1, which are a plurality of clumps within the predetermined range of mass or volume, are sent to the untangling device 15 via the conveying device 22 as pulp fibers P2 to be untangled.

[0045] A method for measuring the mass of a predetermined range includes preparing a container for temporarily storing the supplied lumps and measuring with an electronic balance whether the mass of the multiple lumps in the container reaches a predetermined range.A method for measuring the volume of a predetermined range includes preparing a container for temporarily storing the supplied lumps and having a volume equivalent to the maximum value of the predetermined volume range, and measuring with an image sensor whether the multiple lumps fill, for example, 80% or more of the container.

[0046] In another embodiment, the conveying device 21 is a screw conveyor, and the pulp fibers P1 delivered from the dewatering device 11 are supplied directly to the defibrating device 15 without using the metering device 13 and the conveying device 21. In this case, the screws of the screw conveyor rotate at a constant speed, and when viewed from the lower surface in the conveying direction, the distance between the screw blades is equal (the screw blade pitch is constant). Therefore, the pulp fibers P1 containing multiple clumps enter between the screw blades, and a substantially constant mass or volume of pulp fibers P1 is supplied to the defibrating device 15 (defibrating step S32). In this case, the screw conveyor is a conveying device, but can also be seen as a metering device (quantitative step S31).

[0047] Next, the deflocculating step S32 is carried out by the deflocculating device 15. The deflocculating step S32 is a step of deflocculating the pulp fiber agglomerates that have been determined in the determining step S31 and fall within the predetermined mass or volume range.

[0048] Specifically, the untangling device 15 (e.g., a pin mill crusher) receives a plurality of clumps of pulp fibers P2 supplied from the quantification device 13 via a conveying device 22 in units of a predetermined mass or volume range, and untangles the pulp fibers P2. In this case, the untangling device 15 is a batch type. The untangled pulp fibers P2 are then sent to the metal detection device 17 via a conveying device 23 as pulp fibers P3 for metal inspection.

[0049] However, the quantification step S31 (quantification device 13) may be omitted. In that case, for example, the dewatering device 11 may intermittently supply the pulp fibers P0, which are a plurality of clumps, to the defibrating device 15, and the defibrating device 15 may intermittently perform the defibrating step S32 (batch type). Alternatively, the dewatering device 11 may continuously supply the pulp fibers P0 to the defibrating device 15, and the defibrating device 15 may continuously perform the defibrating step S32 (continuous type).

[0050] In this method, in the deflocculating step S04, among the multiple clumps of pulp fibers P1, a number of clumps of pulp fibers P2 corresponding to a predetermined mass or volume range, which are quantified in the quantification step S31, are deflocculated in the deflocculating step S32. In other words, the amount of pulp fiber clumps deflocculated at one time is limited to a predetermined mass or volume range. This ensures that the pulp fiber clumps can be reliably deflocculated. Therefore, in subsequent steps, it is easier to detect and remove small foreign matter from the recycled pulp fibers.

[0051] Next, the inspection process S33 is performed using various types of inspection devices. In this embodiment, these are a metal detection device 17 and a foreign matter detection device 19. The inspection process S33 is a process of detecting foreign matter in the disintegrated pulp fibers P3 and removing the foreign matter if detected. By including such an inspection process S33 as a preferred aspect, the method can easily detect fine foreign matter from the disintegrated pulp fibers P3, and any foreign matter present can be easily detected and removed. In this embodiment, the inspection process S33 includes a metal inspection process S34 and a foreign matter inspection process S35.

[0052] First, the metal inspection step S34 is performed by the metal detector 17. The metal inspection step S34 is a step in which the metal detector detects metallic foreign matter contained in the disintegrated pulp fibers P3.

[0053] Specifically, the metal detector 17 is disposed midway along the conveying device 23 and detects whether or not metal foreign matter is present in the pulp fibers P3 passing through the conveying device 23. Examples of the metal detector 17 include one or more proximity sensors (electromagnetic induction type, capacitance type, magnetic type) disposed around the path of the pulp fibers P3 in the conveying device 23.

[0054] After the metal inspection step S34, the pulp fibers P4 are transferred from the conveying device 23 to the conveying device 24. Pulp fibers P4 in which metal is detected by the metal detection device 17 are removed by the conveying device 24 as metal-containing pulp fibers P5. The pulp fibers are then transferred to a metal foreign matter removal device (not shown in FIG. 5 ) to remove the metal foreign matter. The pulp fibers may then be returned to the conveying device 23 and subjected to the metal inspection step S34 again. Meanwhile, pulp fibers P4 in which no metal is detected by the metal detection device 17 are supplied by the conveying device 24 to the next foreign matter detection device 19 as metal-free pulp fibers P6.

[0055] By including this metal inspection step S34, the present method can easily detect metallic foreign matter contained in used absorbent articles that could not be removed during separation of the pulp fibers, thereby making it easy to remove them.

[0056] Next, a foreign matter inspection step S35 is performed by the foreign matter detector 19. The foreign matter inspection step S35 is a step in which the foreign matter detector detects foreign matters other than metals contained in the pulp fibers P6 that have passed through the metal inspection step S34.

[0057] Specifically, the foreign matter detector 19 is disposed midway along the conveying device 24 and detects whether or not foreign matter other than metal is present in the pulp fibers P6 passing through the conveying device 24. The metal detector 17 may be, for example, a device that combines one or more image sensors or digital cameras with an image processing system, disposed around the path of the pulp fibers P6 in the conveying device 24.

[0058] After the foreign matter inspection step S35, the pulp fibers P6 are transferred from the conveying device 24 to the conveying device 25. Pulp fibers P6 in which foreign matter other than metals has been detected by the foreign matter detection device 19 are removed by the conveying device 25 as foreign matter-containing pulp fibers P7. The pulp fibers P6 are then transferred to a foreign matter removal device (not shown in FIG. 5 ), where foreign matter other than metals is removed. The pulp fibers P6 may then be returned to the conveying device 24 and subjected to the foreign matter inspection step S35 again. On the other hand, pulp fibers P6 in which no foreign matter has been detected by the foreign matter detection device 19 are supplied by the conveying device 25 to a storage container for storing pulp fibers as foreign matter-free pulp fibers P8.

[0059] By including this foreign matter inspection step S35, the present method can easily detect foreign matter other than metals that is contained in used absorbent articles and that could not be removed during separation of the pulp fibers, thereby making it easy to remove them.

[0060] In this embodiment, as a preferred aspect, the loosening step S04 may include a step of loosening the pulp fiber agglomerates while suppressing fragmentation of foreign matter present in the dewatered pulp fiber agglomerates. This makes it difficult for fine foreign matter that has entered the pulp fiber agglomerates to be further fragmented, allowing the particles to maintain a certain size. This makes it easier to detect and remove fine foreign matter from the recycled pulp fibers (inspection step S33 (metal inspection step S34, foreign matter inspection step S35)). However, when the loosening step S04 (agglomeration step S32) is performed using a pin mill, for example, adjusting the shape of the pins can suppress fragmentation of foreign matter. For example, possible adjustments to the shape of the pins include making the entire pin cylindrical, making the tip hemispherical, increasing the cylindrical diameter relatively, or reducing the number of pins relatively.

[0061] In addition, in this embodiment, as a preferred aspect, the processes from the loosening step S04 onwards are carried out in a closed space. That is, at least the quantification device 13, the loosening device 15, the metal detection device 17, the foreign matter detection device 19, and the conveying devices 21 to 25 are arranged in a closed space. Preferably, the device for removing any detected foreign matter and the device for storing the pulp fibers in a storage container after each inspection are also arranged in a closed space. This makes it possible to further prevent the intrusion of foreign matter and various bacteria into at least the loosened recycled pulp fibers.

[0062] Next, in this embodiment, as shown in Fig. 1 , a storage step S05 is carried out as a step following the loosening step S04. Here, an example of a storage device for carrying out the storage step S05 is a device that stores the produced recycled pulp fibers in a wet state without drying them, for example, in a sealed storage container, and transports the storage container to storage equipment. Storing the recycled pulp fibers without drying them can reduce the equipment required for drying, and the volume of the recycled pulp fibers is reduced, so that the capacity of the storage container, the size of the storage equipment for storing the storage container, and the equipment required for transporting the storage container can be reduced.

[0063] However, if recycled pulp fibers are stored in a wet state, there is a risk that various bacteria, such as mold, may develop and grow on the recycled pulp fibers. To address this, the pulp fibers are squeezed hard in the dehydration step S03 to reduce the moisture content as much as possible. However, in this case, the fibers are squeezed hard, which causes the fibers to bond and entangle very strongly, making it more difficult to disentangle the pulp fiber clumps. Therefore, the present method includes a loosening step S04 before the storage step S05. This prevents the pulp fiber clumps from becoming difficult to disentangle while also suppressing the development and growth of various bacteria, such as mold.

[0064] In the present invention, the washed pulp fibers supplied to the dewatering step S03 are not particularly limited, but may be, for example, pulp fibers washed in the washing step S02 described below. The washing step S02 will now be described in detail. FIG. 4 is a flowchart showing the washing step S02 according to an embodiment. In this embodiment, the washing step S02 includes 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 any other steps as long as it includes the rinsing step S22.

[0065] The ozone treatment step S21 is a step performed before the dewatering step S03, in which the pulp fibers separated from the used absorbent article are treated with ozone.

[0066] In the ozone treatment step S21, pulp fibers are treated with a treatment liquid containing ozone (e.g., water containing ozone). This treatment allows the ozone to contact the superabsorbent polymer and organic impurities (e.g., lignin, excrement residue, bacteria, mold, etc.) that may be attached to the surface or interior of the pulp fibers derived from used absorbent articles. This oxidatively decomposes the superabsorbent polymer and organic impurities with the ozone, solubilizes them in the treatment liquid, and allows them to be easily removed from the pulp fibers, resulting in 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 further advancing fibrillation and producing pulp fibers with an increased specific surface area.

[0067] The configuration of the ozone treatment device in the ozone treatment step S21 is not particularly limited as long as it can bring the pulp fibers into contact with ozone. The ozone treatment device may, for example, include a treatment tank that stores a treatment liquid and an ozone supply device that supplies an ozone-containing gas into the treatment tank. In the ozone treatment device, for example, the pulp fibers are introduced into the treatment liquid from the top or bottom of the treatment tank, and the 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 contacted in the treatment tank. Examples of ozone supply devices include an ozone water exposure tester ED-OWX-2 manufactured by Ecodesign Inc. and an ozone generator OS-25V manufactured by Mitsubishi Electric Corporation. Furthermore, the use of a treatment liquid containing ozone can sterilize and bleach the pulp fibers.

[0068] In the ozone treatment step S21, the concentration of pulp fibers contained in the treatment solution is, for example, 0.5 to 20% by mass, and preferably 1 to 10% by mass, relative to 100% by mass of the treatment solution. If the concentration of pulp fibers is too low, the treatment efficiency will be reduced, 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 treatment time with ozone is shorter when the ozone concentration in the treatment solution is high and longer when the ozone concentration is low, and is typically 5 to 120 minutes. The product of the ozone concentration (ppm) in the treatment solution and the treatment time (minutes) (hereinafter also referred to as the "CT value") is preferably 100 to 6000 ppm·minutes. 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 liquid is not particularly limited as long as it contains ozone or is capable of containing ozone, and examples thereof include water itself and an acidic aqueous solution. The treatment liquid is preferably acidic (pH 2.0 to 6.0) to neutral (pH 6.0 to 8.0). More preferably, the pH of the treatment liquid is 2.0 to 7.0 or less, and even more preferably 2.5 to 6.0. Treatment under an acidic condition can suppress deactivation and gasification of ozone in the treatment liquid, allowing the superabsorbent polymer to be oxidatively decomposed in a short period of time. To maintain the pH of the treatment liquid, for example, the pH of the treatment liquid can be monitored with a pH sensor, and when the pH fluctuates toward the neutral side, a predetermined acidic solution can be added to the treatment liquid in an amount corresponding to the fluctuation range.

[0071] The ozone treatment in the ozone treatment step S21 can suppress the residual superabsorbent polymer, lignin, and other impurities in the pulp fibers, deodorize, sterilize, and bleach the pulp fibers, and further promote fibrillation. Therefore, the pulp fibers have fewer impurities, suppress bacterial growth, and have a larger surface area, making them suitable for a variety of applications. However, fibrillated pulp fibers have a stronger bond between the pulp fibers, resulting in a lower dispersibility. Therefore, the present method includes a disintegration step to disintegrate clumps formed from pulp fibers in such a state. This allows the fibrillated pulp fibers to be highly dispersible. Therefore, when the recycled pulp fibers are reused, clumps and unevenness of the fibers can be reduced, and it is easier to detect and remove small foreign matter that has become embedded in the recycled pulp fibers.

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

[0073] The rinsing step S22 is carried out using a general rinsing device. This is a step in which the ozone-treated pulp fibers are rinsed with cleaning water (e.g., purified water, city water, or industrial water). This washes away impurities and treatment liquid (including ozone) that were present on the surface of the pulp fibers. The pulp fibers rinsed in the rinsing step S22 are then transferred to the antibacterial treatment step S23.

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

[0075] In this method, the pulp fibers separated from used absorbent articles are treated with an antibacterial agent, which makes it possible to suppress the occurrence and proliferation of various bacteria in subsequent processes, such as the storage process S05.

[0076] Furthermore, in this embodiment, an ozone treatment step S21 is carried out as a step prior to the loosening step S04. The ozone treatment of the pulp fibers sterilizes the pulp fibers and removes impurities. This prevents the occurrence and proliferation of various bacteria, such as mold, on the recycled pulp fibers, even if the recycled pulp fibers are stored in a moist state in the storage step S05. This prevents the properties of products containing recycled pulp fibers from being degraded due to the influence of various bacteria.

[0077] In the present invention, the separated pulp fibers supplied to the washing step S02 are not particularly limited, but may be, for example, pulp fibers separated in 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 showing the pulp fiber separation step S01 according to an embodiment. In this embodiment, the pulp fiber separation step S01 includes a crushing step S11, a plastic separation step S12, a foreign matter removal step S13, and an SAP separation step S14.

[0078] The shredding process S11 is a process of shredding used absorbent articles (nonwoven fabric products) in an inactivating aqueous solution. In this embodiment, in the shredding process S11, a plurality of used absorbent articles or a collection bag containing them (hereinafter simply referred to as "used absorbent articles") are supplied to a solution tank containing an acidic aqueous solution, which is an inactivating aqueous solution. The acidic aqueous solution containing the used absorbent articles is sent from the solution tank to a biaxial shredder (e.g., a biaxial rotary shredder, a biaxial differential shredder, or a biaxial shear shredder). The used absorbent articles are shredded by the biaxial shredder. As a result, shredded material is generated from the shredded used absorbent articles. The shredded material is sent to the plastic separation process S12, either alone or together with the acidic aqueous solution.

[0079] When used absorbent articles are treated in an inactivating aqueous solution, the superabsorbent polymer contained or previously contained in the used absorbent articles is inactivated, dehydrated, and reduced to small particle sizes. This facilitates handling of the superabsorbent polymer in subsequent processes and improves processing efficiency. The reason for using an acidic aqueous solution, i.e., an aqueous solution of an inorganic or organic acid, as the inactivating aqueous solution is that, compared to aqueous solutions such as lime or calcium chloride, no ash remains in plastic materials 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. A pH of 1.0 or higher reduces equipment corrosion and reduces the amount of alkaline chemicals required for neutralization during wastewater treatment. A pH of 4.0 or lower allows the superabsorbent polymer to be sufficiently small and enhances sterilization ability. 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. The chelating effect of citric acid traps and removes metal ions and the like in excrement, and the cleaning effect of citric acid is expected to provide a high degree of dirt removal. Examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, with sulfuric acid being preferred due to its chlorine-free nature and cost advantages. Because pH varies with water temperature, the pH in the present invention refers to the pH measured at an aqueous solution temperature of 20°C. The organic acid concentration of 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 inorganic acid concentration of 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, an inorganic acid, is used as the inactivating aqueous solution.

[0080] Next, in the plastic separation step S12, plastic materials are separated from a mixture of synthetic resin plastic materials (e.g., films, nonwoven fabrics, collection bags, etc.) obtained by decomposing used absorbent articles in an acidic aqueous solution, superabsorbent polymers, pulp fibers, and excrement. In this embodiment, the mixture of crushed material and acidic aqueous solution (including excrement) produced in the crushing step S11 is supplied to a pulper separator. The pulper separator has an agitation separation tank that functions as a washing tank and a sieve tank. In the pulper separator, the mixture of crushed material and acidic aqueous solution is agitated and washed to remove dirt from the crushed material, and then separated by a screen into plastic materials and a mixture of pulp fibers, superabsorbent polymers, and acidic aqueous solution. The pulp fibers, superabsorbent polymers, and acidic aqueous solution that pass through the screen are then supplied to the foreign matter removal step S13. Meanwhile, the plastic materials that do not pass through the screen are subsequently washed with wash water, dried, and recovered. Simultaneously with cleaning, or before or after cleaning, disinfection or sterilization may be carried out using a disinfectant or a germicide.

[0081] Next, in the foreign matter removal step S13, at least one separator (e.g., a screen separator or a cyclone separator) is used to separate any remaining foreign matter, such as film, nonwoven fabric, or collection bags, from the mixed liquid supplied from the plastic separation step S12. In this embodiment, a screen separator (with a relatively large mesh size), a screen separator (with a relatively small mesh size), and a cyclone separator are arranged in this order, and the foreign matter is sequentially separated from the mixed liquid. This results in pulp fibers and superabsorbent polymer with minimal foreign matter. The mixed liquid of the pulp fibers and superabsorbent polymer with minimal foreign matter and the acidic aqueous solution (containing excrement) is supplied to the SAP separation step S14.

[0082] In the SAP separation step S14, at least one separator (e.g., a drum screen separator) is used to separate the superabsorbent polymer from the mixed liquid (containing pulp fibers and superabsorbent polymers with little foreign matter) supplied from the foreign matter removal step S13. In this embodiment, the drum screen separator separates the mixed liquid into the superabsorbent polymer and acidic aqueous solution (containing excrement) and the pulp fibers (containing a small amount of superabsorbent polymer). The superabsorbent polymer and acidic aqueous solution that passed through the screen are then separated into the superabsorbent polymer and the acidic aqueous solution by another separator (e.g., an inclined screen separator), and the superabsorbent polymer is washed with wash water, dried, and recovered. The superabsorbent polymer may be disinfected or sterilized with a disinfectant or bactericide simultaneously with, before, or after the washing. Meanwhile, the pulp fibers that did not pass through the screen are supplied to the washing step S02.

[0083] The absorbent article of the present invention is not limited to the above-described embodiments, and suitable combinations and modifications can be made without departing from the object and spirit of the present invention.

[0084] S03 Dehydration process S04 Loosening process

Claims

DEPCT671. A method for the production of recycled pulp fibers from used absorbents, including pulp fibers, comprising: a dehydration step for dehydrating the washed pulp fibers separated from the used absorbents; and a loosening step for loosening each pulp ball of a certain number of pulp fibers formed by dehydration to produce recycled pulp fibers.

2. A method according to claim 1, where the loosening step includes the loosening of pulp fiber ball lumps while suspending the separation of impurities present in the dehydrated pulp fiber ball lumps.

3. A method according to claim 1 or 2, where the loosening step includes: a quantification step for determining the quantity of pulp fiber ball lumps corresponding to a predetermined range of mass or volume among a certain number of pulp fiber ball lumps formed by dehydration; and a loosening step of the quantified pulp fiber ball lumps. 4.

5. A method under claim 1 through 3, whereby the decomposition procedure includes a foreign object detection procedure for the decomposition of the pulp fibers and the removal of any foreign objects if detected.

6. A method under claim 4, whereby the foreign object detection procedure includes a procedure for the detection of metallic foreign objects using a metal detector.

7. A method under claim 4 or 5, whereby the foreign object detection procedure includes a procedure for the detection of non-metallic foreign objects using a foreign object detector.

8. A method under claim 1 through 6, which also includes: an ozone treatment procedure for the decomposition of the pulp fibers separated from the used adsorbent with ozone, prior to the dehydration step.

9. A method under claim 1 through 7, which also includes: a storage procedure for the storage of the recycled pulp fibers produced in a wet state, after the decomposition step.The method under claim 8, which also includes: the antimicrobial treatment procedure of the membrane fibers separated from the used adsorbent with an antimicrobial agent, prior to the dehydration step; 10. Any one of the methods under claims 1 through 9, in which the loosening and subsequent steps are performed in a closed space;

Images