Method for recycling multiple materials including superabsorbent polymers and pulp fibers from used absorbent articles

Abstract

Provided is a method for recycling materials of used absorbent articles that can reduce the wastewater treatment load of process liquid and reduce the sanitation load in equipment maintenance. This method is for recycling multiple materials, including a superabsorbent polymer and pulp fibers, from used absorbent articles that are soiled and have absorbed moisture. This method comprises a pretreatment step (S01) for removing dirt and moisture from the used absorbent article in an inactivating aqueous solution that inactivates the superabsorbent polymer and discharging the inactivating aqueous solution containing the dirt and moisture, and a main treatment step (S02) for pouring water into the used absorbent article from which the dirt and moisture have been removed, and separating and recovering at least one of the multiple materials from the used absorbent article.

Description

[Technical Field]

[0001] The present invention relates to a method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles. [Background technology]

[0002] Methods for recycling materials from used absorbent articles are known. For example, Patent Document 1 discloses a method for recovering pulp fibers from used absorbent articles containing pulp fibers and a superabsorbent polymer. This method includes a receiving step of placing a collection bag containing used absorbent articles into a container, a shredding step of transferring the collection bag from the container to a shredding device connected to the container and shredding the used absorbent articles in the collection bag together with the collection bag in an inactivating aqueous solution using the shredding device, and a separation step of separating the pulp fibers, superabsorbent polymer, and inactivating aqueous solution from the shredded material obtained in the shredding step and the inactivating aqueous solution using a separator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-85686 Summary of the Invention [Problem to be solved by the invention]

[0004] The method of Patent Document 1 can recover multiple materials, such as films, nonwoven fabrics, pulp fibers, and superabsorbent polymers, from used absorbent articles. In each step of the method, multiple materials are treated in treated water, which includes an acidic aqueous solution. The acidic aqueous solution is reused by circulating it through multiple devices that perform multiple consecutive steps.

[0005] However, in this method, it is necessary to partially or entirely replace the acidic aqueous solution at an appropriate timing in order to adjust the pH of the acidic aqueous solution and to remove the acidic aqueous solution in which impurities that could not be removed have accumulated. Therefore, a certain amount of acidic aqueous solution may be discharged, which may increase the burden of wastewater treatment, such as neutralization of the acidic aqueous solution.

[0006] Furthermore, in this method, although dirt such as excrement contained in used absorbent articles is eventually removed, the articles must pass through multiple devices. Therefore, when maintaining the multiple devices, it is necessary to prevent the dirt from adversely affecting the external environment and workers, which may increase the burden on hygiene.

[0007] An object of the present invention is to provide a method for recycling materials from used absorbent articles, which can reduce the burden of wastewater treatment of treatment liquid and reduce the hygienic burden of maintaining the equipment. [Means for solving the problem]

[0008] One aspect of the present invention is a method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles that have been soiled and have absorbed moisture, the method comprising: a pretreatment step in which dirt and moisture are removed from the used absorbent articles in an inactivating aqueous solution that inactivates the superabsorbent polymer, and a main treatment step in which water is poured into the used absorbent article from which the dirt and moisture have been removed, and at least one of the multiple materials is separated and recovered from the used absorbent article. [Effects of the Invention]

[0009] According to the method of the present invention, a method can be provided for recycling materials from used absorbent articles, which can reduce the burden of wastewater treatment of treatment liquid and reduce the hygienic burden of maintaining the equipment. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart illustrating a method for recycling materials from used absorbent articles according to an embodiment. [Figure 2] 10 is a flowchart showing a pre-treatment process according to an embodiment. [Figure 3] FIG. 2 is a schematic diagram showing an apparatus for carrying out a pretreatment step according to an embodiment. [Figure 4] 1 is a flowchart showing the main processing steps according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present embodiment relates to the following aspects. [Aspect 1] A method for recycling a plurality of materials, including superabsorbent polymers and pulp fibers, from used absorbent articles that have been soiled and have absorbed moisture, the method comprising: a pretreatment step of performing a pretreatment in which dirt and moisture are removed from the used absorbent article in an inactivating aqueous solution that inactivates the superabsorbent polymer, and the inactivating aqueous solution containing the dirt and moisture is discharged; and a main treatment step of pouring water into the used absorbent article from which the dirt and moisture have been removed, and separating and recovering at least one of the plurality of materials from the used absorbent article.

[0012] In this method, first, in a pretreatment step, dirt and moisture are removed from used absorbent articles by inactivating (dehydrating) the superabsorbent polymer with an inactivating aqueous solution (e.g., a strongly acidic aqueous solution) that inactivates the superabsorbent polymer. Then, in the main treatment step, water is poured into the used absorbent articles from which the dirt and moisture have been removed and which have become lighter and smaller in volume, and at least one of the materials is separated and recovered. Therefore, the pretreatment process, which involves fewer steps, is carried out in an inactivating aqueous solution, while the main treatment process, which involves many steps such as decomposition, separation, and recovery, is carried out in water rather than in an inactivating aqueous solution. This allows for a reduction in the amount of inactivating aqueous solution used, thereby reducing the amount of inactivating aqueous solution discharged. As a result, this method can reduce the burden of treating the discharged water when recycling materials from used absorbent articles. Furthermore, because this treatment process involves many steps, i.e., requires a large amount of equipment, water is used, which prevents contamination from adversely affecting the external environment and workers during equipment maintenance. Therefore, this method reduces the hygienic burden when recycling materials from used absorbent articles. Therefore, this method can reduce the burden of wastewater treatment of treatment liquids (such as inactivating aqueous solutions) while also reducing the hygienic burden of maintaining multiple devices. Furthermore, since the pretreatment process removes dirt and moisture from used absorbent articles, making them lighter and smaller in volume, the amount of water used in this treatment process can also be reduced. Therefore, this method can reduce the environmental burden when recycling materials from used absorbent articles.

[0013] [Aspect 2] 2. The method of claim 1, wherein the inactivating aqueous solution comprises a strongly acidic aqueous solution.

[0014] In this method, a strong acidic aqueous solution is used as the inactivating aqueous solution in the pretreatment step. The use of a strong acidic aqueous solution can further accelerate the inactivation (dehydration) of the superabsorbent polymer. This allows for more efficient removal of dirt and moisture from used absorbent articles. Additionally, the strong acidic aqueous solution can sterilize or disinfect the used absorbent articles through its sterilizing or disinfecting action. Then, in the subsequent treatment step, dirt and moisture are further removed, resulting in a lighter and smaller volume. Furthermore, since the sterilized or disinfected used absorbent articles are treated in water (rather than in an acidic aqueous solution), the amount of acidic aqueous solution discharged can be further reduced. Furthermore, because no other inactivating agents (e.g., lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc.) or chemicals such as bactericides, disinfectants, or disinfectants are used, their consumption can be reduced. This reduces the wastewater treatment burden. Therefore, this method can reduce the wastewater treatment burden of the treatment solution while also reducing the hygienic burden associated with maintaining multiple devices.

[0015] [Aspect 3] Aspect 3. The method of aspect 2, wherein the pretreatment step comprises a step of performing the pretreatment while maintaining the used absorbent article in the acidic aqueous solution in the state in which it was collected.

[0016] In this method, the pretreatment step maintains the state of used absorbent articles when collected, and dirt and moisture are removed without being broken down into multiple materials. Therefore, the pretreatment step is less likely to result in the materials being broken down into small pieces and remaining in large quantities in the equipment, allowing workers to maintain the equipment extremely easily and hygienically. Furthermore, because used absorbent articles are not broken down into multiple materials, it is less likely for materials to get into the wastewater treatment solution (such as an acidic aqueous solution). This reduces the hygienic burden of wastewater treatment of the treatment solution (such as an acidic aqueous solution). Therefore, this method makes it possible to reduce the hygienic burden of maintaining multiple devices while also reducing the burden of wastewater treatment of the treatment solution (such as an acidic aqueous solution).

[0017] [Aspect 4] The method according to aspect 2 or 3, wherein the pretreatment step includes: an introduction step of introducing the used absorbent articles and the acidic aqueous solution into a treatment tank, wherein the liquid level of the acidic aqueous solution is lower than the top of the used absorbent articles that are not floating; an inactivation step of impregnating the used absorbent articles with the acidic aqueous solution in the treatment tank by repeatedly applying and releasing pressure to the used absorbent articles in the acidic aqueous solution; and a removal step of removing dirt and moisture from the used absorbent articles.

[0018] In this method, in the pretreatment step, the level of the acidic aqueous solution is lower than the top of the multiple used absorbent articles, and therefore the amount of acidic aqueous solution is very small. This makes it possible to further reduce the amount of acidic aqueous solution discharged. At the same time, it is possible to prevent the used absorbent articles from being separated or disassembled by the force of the acidic aqueous solution's water flow, which can occur during the inactivation step, thereby improving hygiene during equipment maintenance by workers and preventing materials from being mixed into the discharged treatment liquid (acidic aqueous solution). Furthermore, in the inactivation process, during the initial operation, pressure is applied to release gas (e.g., air) inside the used absorbent article to the outside. Then, when the pressure is released, the suction force associated with the restoration of the shape of the used absorbent article causes the external liquid (e.g., acidic aqueous solution) to be absorbed inside. During subsequent operations, pressure is applied to release gas and liquid (e.g., moisture released by the inactivation of the superabsorbent polymer by the acidic aqueous solution) inside the used absorbent article to the outside. Then, when the pressure is released, the external liquid (e.g., acidic aqueous solution) is absorbed inside. As a result, even if the amount of acidic aqueous solution is small, the acidic aqueous solution can be efficiently impregnated into the interior of the used absorbent article. Furthermore, because a strong acidic aqueous solution is used as the acidic aqueous solution, even a small amount of the acidic aqueous solution can reliably inactivate the superabsorbent polymer inside the used absorbent article, allowing the moisture inside (e.g., urine) to be released to the outside and dehydrating the article. As a result, the weight of the used absorbent article can be reduced by finally removing the moisture from the used absorbent article in the removal step. Here, in the inactivation process, along with the gas and liquid released from the used absorbent article due to the application of pressure, it is possible to push out to the outside any excrement adhering to the used absorbent article, thereby making the used absorbent article even lighter. In this way, in the pretreatment step, this method makes it possible to reduce dirt and moisture in used absorbent articles using a small amount of acidic aqueous solution, thereby preventing dirt and moisture from being carried over to the main treatment step. Therefore, it is possible to reduce the burden of wastewater treatment of the treatment liquid (such as an acidic aqueous solution) and also reduce the burden from a sanitary standpoint in the maintenance of a plurality of devices.

[0019] [Aspect 5] A method according to aspect 4, wherein the inactivating step comprises applying and releasing the pressure by banging the used absorbent article against other used absorbent articles.

[0020] In this method, the inactivation step in the pretreatment step includes a step of applying and relaxing pressure by colliding a plurality of used absorbent articles against each other in the treatment tank, thereby easily and reliably applying and relaxing pressure to the used absorbent articles and impregnating them with the acidic aqueous solution in the inactivation step while preventing the used absorbent articles from being separated or disintegrated by the force of the water flow of the acidic aqueous solution.

[0021] [Aspect 6] A method as described in aspect 5, wherein the treatment tank is a horizontal rotating drum, and the inactivation step includes a step of slamming the used absorbent articles against other used absorbent articles by rotating the rotating drum.

[0022] In this method, since the treatment tank in the pretreatment step is a horizontal rotating drum, the rotation of the rotating drum can easily and reliably cause the multiple used absorbent articles in the rotating drum to collide with each other in the inactivation step. This makes it possible to more easily and reliably apply and release pressure to the used absorbent articles and impregnate them with the acidic aqueous solution while preventing the used absorbent articles from being separated or disintegrated by the force of the water flow of the acidic aqueous solution.

[0023] [Aspect 7] Aspect 7. The method according to any one of Aspects 4 to 6, wherein the liquid level of the acidic aqueous solution in the introducing step is at a position where 3 / 5 to 4 / 5 of the used absorbent articles in the treatment tank are immersed.

[0024] In this method, in the pretreatment step, the liquid level of the acidic aqueous solution in the introduction step is at a position where 3 / 5 to 4 / 5 (number) of the multiple used absorbent articles in the treatment tank are immersed. In other words, 1 / 5 to 2 / 5 of the multiple used absorbent articles do not need to be immersed. By using a smaller amount of acidic aqueous solution for multiple used absorbent articles in this way, the amount of wastewater can be further reduced. Furthermore, by using a smaller amount of acidic aqueous solution, it is possible to further prevent the used absorbent articles from being separated and disassembled from the state they were in when collected due to the force of the water flow of the acidic aqueous solution that may occur during the inactivation step.

[0025] [Aspect 8] Aspect 8. The method according to any one of aspects 4 to 7, wherein in the introducing step, the weight of the acidic aqueous solution is 2 to 3 times the weight of the used absorbent articles in the treatment tank.

[0026] In this method, in the pretreatment step, the weight of the acidic aqueous solution in the introduction step is 2 to 3 times the weight of the multiple used absorbent articles in the treatment tank. By using a small amount of acidic aqueous solution for multiple used absorbent articles in this way, the amount of wastewater can be reduced. Furthermore, by using a small amount of acidic aqueous solution, it is possible to prevent the used absorbent articles from being separated or disassembled from the state they were in when collected due to the force of the water flow of the acidic aqueous solution that may occur during the inactivation step.

[0027] [Aspect 9] Aspect 9. The method according to any one of aspects 4 to 8, wherein in the introducing step, the pH of the acidic aqueous solution is 2.0 or less.

[0028] In the present method, the pH of the acidic aqueous solution in the introduction step in the pretreatment step is 2.0 or less. Therefore, even if the amount of the acidic aqueous solution is small relative to the number of used absorbent articles, the inactivation step of the present method can more reliably inactivate and dehydrate the number of used absorbent articles while preventing them from being separated or disassembled.

[0029] [Aspect 10] 10. The method of any one of aspects 4 to 9, wherein in the introducing step, the acidic aqueous solution comprises sulfuric acid.

[0030] In the present method, the acidic aqueous solution used in the introduction step in the pretreatment step contains sulfuric acid. Therefore, even if the amount of the acidic aqueous solution is small relative to the number of used absorbent articles, the inactivation step of the present method can more reliably inactivate and dehydrate the number of used absorbent articles while preventing them from being separated or disassembled.

[0031] [Aspect 11] Aspect 11. The method of any one of aspects 4 to 10, wherein the dehydration rate of the used absorbent article after the removing step is 60% or more.

[0032] In this method, the dehydration rate of the multiple used absorbent articles after the removal step in the pretreatment step is 60% or more. Therefore, this method can effectively inactivate and dehydrate the multiple used absorbent articles while preventing them from being separated and disassembled, and can very effectively reduce their weight.

[0033] [Aspect 12] The method according to any one of aspects 1 to 11, wherein the treatment process includes a separation process for separating the water containing the used absorbent article from which dirt and moisture have been removed into superabsorbent polymer, pulp fibers, water, and other materials, and a recovery process for separating and recovering the superabsorbent polymer and pulp fibers from the separated superabsorbent polymer, pulp fibers, and water.

[0034] In this method, each step of the treatment process is carried out in water rather than in an acidic aqueous solution, so the amount of acidic aqueous solution used and, in turn, the amount of acidic aqueous solution discharged can be reduced, thereby reducing the burden of wastewater treatment. Furthermore, because water is used in this treatment process, which involves many steps, it is possible to prevent contamination from adversely affecting the external environment and workers during equipment maintenance, thereby reducing the burden on hygiene.

[0035] [Aspect 13] Aspect 13. The method of aspect 12, wherein the treating step further comprises a shredding step of shredding the used absorbent articles before the separating step.

[0036] In this method, the treatment step further includes a shredding step of shredding the used absorbent articles before the separation step. Therefore, the shredding step can facilitate disintegrating the constituent materials of the used absorbent articles from each other before the separation step. This allows the separation step to be carried out more efficiently, and makes it easier to recycle the materials (constituent materials) of the used absorbent articles.

[0037] [Aspect 14] The method according to aspect 1 or 2, wherein the pretreatment step includes a crushing step of crushing the used absorbent articles, and an inactivation step of immersing the crushed pieces of the used absorbent articles in the inactivating aqueous solution.

[0038] In this method, used absorbent articles are crushed in the crushing step of the pretreatment step before the inactivation step of the pretreatment step, which makes it easier for the inactivating aqueous solution to come into contact with the superabsorbent polymer in the used absorbent articles through the cross-sections of the crushed articles. Therefore, the superabsorbent polymer can be efficiently inactivated (dehydrated), which reduces the amount of inactivating aqueous solution or the concentration of the inactivating agent in the inactivating aqueous solution, thereby reducing the environmental impact.

[0039] [Aspect 15] Aspect 3. The method according to aspect 1 or 2, wherein the pretreatment step includes an inactivation / crushing step of crushing the used absorbent article together with the inactivating aqueous solution.

[0040] In this method, the pretreatment step involves an inactivation / crushing step in which used absorbent articles are crushed and the superabsorbent polymer in the used absorbent articles is inactivated almost simultaneously, making it easier for the inactivating aqueous solution to come into contact with the superabsorbent polymer through the cross-sections of the crushed material and shortening the processing time of the pretreatment step. Therefore, the superabsorbent polymer can be efficiently inactivated (dehydrated), reducing the amount of inactivating aqueous solution or the concentration of the inactivating agent in the inactivating aqueous solution and reducing the energy consumed in the process. This reduces the environmental impact.

[0041] [Aspect 16] The method according to aspect 1 or 2, wherein the pretreatment step includes an inactivation step of immersing the used absorbent article in the inactivating aqueous solution, and a crushing step of crushing the used absorbent article containing the inactivated superabsorbent polymer.

[0042] In this method, the superabsorbent polymer in used absorbent articles is inactivated (dehydrated) in the inactivation step of the pretreatment step before the crushing step, so the swollen superabsorbent polymer can be reduced in size before the crushing step. This makes it less likely that the superabsorbent polymer will be damaged during the crushing step, reducing the amount of superabsorbent polymer that is difficult to reuse as superabsorbent polymer. This therefore increases the recovery rate of the superabsorbent polymer and reduces the amount of inactivating solution required to recover the superabsorbent polymer or the concentration of the inactivating agent in the inactivating solution. This reduces the environmental impact.

[0043] [Aspect 17] 17. The method according to any one of aspects 1 to 16, wherein an amount of the aqueous inactivation solution used in the pretreatment step is less than an amount of water added in the main treatment step.

[0044] If a method for recycling multiple materials from used absorbent articles is to be carried out using only the main treatment step without performing the pretreatment step, the main treatment step must be carried out using an inactivating aqueous solution. In this case, the amount of inactivating aqueous solution is roughly the same as the amount of water injected in the main treatment step when both the pretreatment step and the main treatment step are carried out (described below). Therefore, compared to a method for recycling multiple materials from used absorbent articles using only the main treatment step without performing the pretreatment step, i.e., a method for carrying out the main treatment step using an inactivating aqueous solution instead of water, this method can reduce the amount of inactivating aqueous solution, thereby reducing the environmental impact.

[0045] (First embodiment) Hereinafter, a method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles according to the first embodiment will be described. Note that 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 absorbent articles that have been unused but discarded. Examples of absorbent articles include disposable diapers, urine absorption pads, sanitary napkins, bed sheets, and pet sheets.

[0046] First, an example of the configuration of an absorbent article will be described. The absorbent article comprises a topsheet, a backsheet, and an absorbent body disposed between the topsheet and the backsheet. 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 provided in absorbent articles, such as a diffusion sheet, a leak-proof wall, a side sheet, and an exterior sheet.

[0047] 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.

[0048] 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. The type of synthetic resin film is also 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 fabrics and synthetic resin films are made of synthetic resins and can be referred to as plastic materials. In this embodiment, an absorbent article in which the backsheet is made of a film and the topsheet is made of a nonwoven fabric will be described as an example.

[0049] 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. The size of pulp fibers includes an average fiber length of several tens of μm (20 to 40 μm) and an average fiber length of several mm (2 to 5 mm). Examples of superabsorbent polymers (SAPs) include polyacrylate-based, polysulfonate-based, and maleic anhydride-based superabsorbent polymers. The size of the superabsorbent polymer (when dry) includes an average particle size of several hundred μm (200 to 500 μm). The absorbent may be enclosed in a core wrap formed of a liquid-permeable sheet.

[0050] 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. Thus, the absorbent body is enclosed within the bonded body of the top sheet and the back sheet. The adhesive is not particularly limited, 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.

[0051] Next, a method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles that have been soiled and absorbed moisture, according to an embodiment, will be described in detail. Used absorbent articles that have been soiled and absorbed moisture are collected, for example, from outside (hospitals, nursing homes, private homes, etc.). Separating and recovering the superabsorbent polymers and pulp fibers from used absorbent articles to obtain reusable superabsorbent polymers and pulp fibers results in the production of reusable recycled superabsorbent polymers and recycled pulp fibers, and therefore this method can be considered a method for producing recycled superabsorbent polymers and recycled pulp fibers.

[0052] 1 is a flowchart showing a method for recycling materials from used absorbent articles according to an embodiment. The method includes a pre-treatment step S01 and a main treatment step S02.

[0053] The pretreatment step S01 is a step of performing a pretreatment to remove dirt and moisture from used absorbent articles in an inactivating aqueous solution (e.g., a strongly acidic aqueous solution) and then discharge the inactivating aqueous solution containing the dirt and moisture. For example, used absorbent articles with dirt and moisture adhering thereto are placed in a treatment tank storing the inactivating aqueous solution. The inactivating aqueous solution then inactivates and dehydrates the superabsorbent polymer, and the moisture released from the superabsorbent polymer by dehydration and the inactivating aqueous solution remove the dirt and moisture from the used absorbent article. As a result, used absorbent articles with very little dirt and moisture are obtained, which are lightweight and have a small volume.

[0054] The inactivating aqueous solution is an aqueous solution containing an inactivating agent that inactivates (dehydrates) the superabsorbent polymer. Examples of the inactivating aqueous solution include a strongly acidic aqueous solution. Note that the inactivating aqueous solution may also be an aqueous solution containing other known inactivating agents (e.g., lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc.). In this embodiment, a strongly acidic aqueous solution is used as the inactivating aqueous solution.

[0055] Here, the strongly acidic aqueous solution inactivates and dehydrates the superabsorbent polymer contained in used absorbent articles. The upper limit of the pH of the strongly acidic aqueous solution is preferably 2.0, and the lower limit is preferably 0.5. An acidic aqueous solution with a pH of 2.0 or less can sufficiently inactivate and dehydrate the superabsorbent polymer, even if the used absorbent articles are prevented from being separated or disassembled, or even if the amount of acidic aqueous solution is small, and can also have high sterilizing ability. In other words, even in situations where it is difficult to distribute the acidic aqueous solution, such as when handling a large number of used absorbent articles, the superabsorbent polymer can be sufficiently inactivated and dehydrated. An acidic aqueous solution with a pH of 0.5 or higher is less likely to corrode equipment and can reduce the amount of alkaline chemicals required for neutralization during wastewater treatment. Note that pH varies depending on water temperature, so the pH in this invention is measured at an aqueous solution temperature of 20°C.

[0056] Examples of types of acidic aqueous solutions include aqueous solutions of inorganic acids and organic acids. 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. 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 allows metal ions and the like in excrement to be trapped and removed, and the cleaning effect of citric acid is expected to be highly effective in removing soiling components. In this embodiment, sulfuric acid is an inorganic acid. Therefore, even if the amount of acidic aqueous solution is small relative to the number of used absorbent articles, the pretreatment step S01 (inactivation step S12: described below) can more reliably inactivate and dehydrate the multiple used absorbent articles while preventing them from being separated and disassembled.

[0057] The acid concentration of the acidic aqueous solution is not particularly limited as long as the above pH is satisfied. The acid concentration of the inorganic acidic aqueous solution is not particularly limited, but when the inorganic acid is sulfuric acid, it is preferably 0.1 to 2.0 mass%, more preferably 0.15 to 1.5 mass%. The acid concentration of the organic acidic aqueous solution is not particularly limited, but when the organic acid is citric acid, it is preferably 0.5 to 4 mass%, more preferably 0.8 to 3 mass%.

[0058] In this embodiment, in the pretreatment step S01, a strong acidic aqueous solution is used as an inactivating agent (dehydrating agent) for the water-absorbent polymer, so there is no need to use other inactivating agents (dehydrating agents) (e.g., lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc.), and they are not used in this embodiment. In addition, since the strong acidic aqueous solution has a bactericidal or disinfecting action, there is no need to use chemicals such as bactericides, disinfectants, or disinfectants in the pretreatment step S01, and they are not used in this embodiment.

[0059] In the pretreatment step S01, a physical force may be applied to a plurality of used absorbent articles. For example, the acidic aqueous solution may be stirred to create a flow, which facilitates the acidic aqueous solution reaching the superabsorbent polymer and also washes away dirt from the used absorbent articles. Alternatively, for example, the used absorbent articles may be agitated in the acidic aqueous solution to facilitate the acidic aqueous solution reaching the superabsorbent polymer and also wash away dirt from the used absorbent articles.

[0060] In this treatment step S02, water is poured onto the used absorbent articles from which dirt and moisture have been removed, and at least one of a plurality of materials is separated and recovered from the used absorbent articles. The water used here is not particularly limited as long as it has a pH of 5.8 or higher and 8.6 or lower, and examples thereof include industrial water, tap water, and groundwater. In this treatment step S02, the method for separating and recovering materials from the used absorbent articles is not particularly limited as long as it is carried out in water, and known methods can be used, for example. As a result, the materials from the used absorbent articles (e.g., films, nonwoven fabrics, superabsorbent polymers, pulp fibers) are recovered as recyclable materials.

[0061] However, in this treatment step S02, the superabsorbent polymer that has been inactivated and dehydrated in the strong acidic aqueous solution in the pretreatment step S01 does not absorb water again and swell. The reason is as follows: When a superabsorbent polymer (for example, a crosslinked sodium polyacrylate) for absorbent articles such as disposable diapers is immersed in a strong acidic aqueous solution with a high electrolyte concentration, Na is neutralized, the degree of substitution of Na decreases and approaches zero, and the [polyacrylic acid] - Na + is chemically transformed into [polyacrylic acid]-H. As a result, even if the superabsorbent polymer is subsequently immersed in water again, it will no longer exhibit high water absorption capacity. Note that other inactivating aqueous solutions containing other inactivating agents are similar to the acidic aqueous solution, except that the ions absorbed into the superabsorbent polymer are different.

[0062] In this method, as described above, first, in the pre-treatment step S01, dirt and moisture are removed from the used absorbent article by inactivating (dehydrating) the superabsorbent polymer with an inactivating aqueous solution (e.g., a strongly acidic aqueous solution) that inactivates the superabsorbent polymer. Then, in the main treatment step S02, water is poured into the used absorbent article from which the dirt and moisture have been removed and which has become lighter and smaller in volume, and at least one of the materials is separated and recovered. Therefore, the pretreatment step S01, which involves a small number of steps, is carried out in an inactivating aqueous solution, while the main treatment step S02, which involves a large number of steps such as decomposition, separation, and recovery, is carried out in water rather than in an inactivating aqueous solution. This allows for a reduction in the amount of inactivating aqueous solution used, thereby reducing the amount of inactivating aqueous solution discharged. As a result, this method can reduce the burden of treating such discharged water when recycling materials from used absorbent articles. Furthermore, since water is used in this treatment step S02, which involves many steps, i.e., many pieces of equipment, it is possible to prevent contamination from adversely affecting the external environment and workers during equipment maintenance. Therefore, this method can reduce the burden on hygiene when recycling materials from used absorbent articles. Therefore, this method can reduce the burden of wastewater treatment of treatment liquid (such as inactivation aqueous solution) while also reducing the hygienic burden of maintaining multiple devices. Furthermore, since the pretreatment step S01 removes dirt and moisture from used absorbent articles, making them lighter and smaller in volume, the amount of water used in the main treatment step S02 can also be reduced. Therefore, this method can reduce the environmental burden when recycling materials from used absorbent articles.

[0063] In this embodiment, in the pretreatment step S01, a strong acidic aqueous solution is used as the inactivating aqueous solution. The use of a strong acidic aqueous solution can further accelerate the inactivation (dehydration) of the superabsorbent polymer. This allows for more efficient removal of dirt and moisture from used absorbent articles. In addition, the strong acidic aqueous solution can sterilize or disinfect the used absorbent articles through its sterilizing or disinfecting action. Then, in the main treatment step S02, dirt and moisture are further removed, resulting in a lighter and smaller volume. Furthermore, since the sterilized or disinfected used absorbent articles are treated in water (rather than in an acidic aqueous solution), the amount of acidic aqueous solution discharged can be further reduced. Furthermore, because no other inactivating agents (e.g., lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, aluminum chloride, etc.) or chemicals such as bactericides, disinfectants, or disinfectants are used, the amount of these chemicals used can be reduced. This reduces the burden of wastewater treatment. Therefore, in this method, it is possible to reduce the burden of draining the treatment liquid and also reduce the sanitary burden of maintaining a plurality of devices.

[0064] Next, the pretreatment step S01 will be further described. In this embodiment, as described above, the pretreatment step S01 is a step of performing pretreatment to remove dirt and moisture from used absorbent articles in a strongly acidic aqueous solution as an inactivating aqueous solution and then discharge the inactivating aqueous solution containing the dirt and moisture. FIG. 2 is a flowchart showing the pretreatment step S01 according to an embodiment. In this embodiment, the pretreatment step S01 includes an introduction step S11, an inactivation step S12, and a removal step S13. The introduction step S11 is a step of introducing used absorbent articles and a strongly acidic aqueous solution into a treatment tank. However, the liquid level of the acidic aqueous solution is lower than the top of the non-floating used absorbent articles. Next, in the inactivation step S12, used absorbent articles are impregnated with the acidic aqueous solution by repeatedly applying and releasing pressure to the acidic aqueous solution in the treatment tank. Next, in the removal step S13, moisture is removed from multiple used absorbent articles.

[0065] In the introduction step S11, the amount of acidic aqueous solution introduced into the treatment tank should be such that the liquid level of the acidic aqueous solution is lower than the top of the multiple used absorbent articles that are not floating. The top of the multiple used absorbent articles refers to the topmost part of the multiple used absorbent articles that are not floating in the acidic aqueous solution in the treatment tank. The positions of the top of the multiple used absorbent articles and the liquid level are determined when the multiple used absorbent articles are arranged in a roughly horizontal line when viewed as a single unit. "Roughly horizontal" means that the unevenness of the top surface of the item is within ±2 of the number of used absorbent articles 2.

[0066] In the inactivation step S12, pressure is repeatedly applied and released to the used absorbent article. That is, in the initial operation, pressure is applied to release gas (e.g., air) inside the used absorbent article to the outside, and the released gas pushes out excrement adhering to the used absorbent article. Subsequently, pressure is released, and the suction force associated with the restoration of the shape of the used absorbent article causes external liquid (e.g., acidic aqueous solution) to be absorbed into the interior. Furthermore, in the subsequent operation, pressure is applied to release gas and liquid (e.g., moisture released by inactivation with an acidic aqueous solution) inside the used absorbent article to the outside, and the released gas and liquid pushes out excrement adhering to the used absorbent article. Subsequently, pressure is released, and the external liquid (e.g., acidic aqueous solution) is absorbed into the interior. This process allows the used absorbent article to be maintained in the same state as when it was collected, while the acidic aqueous solution is impregnated into the interior of the used absorbent article, allowing the excrement inside to be expelled to the outside. Here, the gas and liquid released from the used absorbent article due to the application of pressure also allows the excrement adhering to the used absorbent article to be pushed to the outside.

[0067] In the removal step S13, the acidic aqueous solution (including the water discharged from the used absorbent article) is discharged from the treatment tank, and the acidic aqueous solution (including the water discharged from the used absorbent article) contained in the nonwoven fabric and pulp fibers of the used absorbent article is also discharged using, for example, centrifugal force or pressure. At this time, it is possible to push out to the outside the excrement adhering to the used absorbent article along with the acidic aqueous solution (including the water discharged from the used absorbent article) discharged from the used absorbent article. Furthermore, a step of washing the used absorbent article in water and then removing the water from the used absorbent article may be performed at least once.

[0068] In this embodiment, in the pretreatment step S01, the liquid level of the acidic aqueous solution is lower than the top of the multiple used absorbent articles, and therefore the amount of acidic aqueous solution is very small. This further reduces the amount of acidic aqueous solution discharged. At the same time, it also prevents the used absorbent articles from being separated or disassembled by the force of the acidic aqueous solution's water flow, which can occur in the inactivation step S12. This improves hygiene during equipment maintenance by workers and prevents materials from being mixed into the discharged treatment liquid (acidic aqueous solution). Furthermore, in the inactivation step S12, during the initial operation, pressure is applied to release gas (e.g., air) inside the used absorbent article to the outside. Then, when the pressure is released, the suction force associated with the restoration of the shape of the used absorbent article causes the external liquid (e.g., acidic aqueous solution) to be absorbed inside. During subsequent operations, pressure is applied to release gas and liquid (e.g., moisture released by the inactivation of the superabsorbent polymer by the acidic aqueous solution) inside the used absorbent article to the outside. Then, when the pressure is released, the external liquid (e.g., acidic aqueous solution) is absorbed inside. As a result, even if the amount of acidic aqueous solution is small, the acidic aqueous solution can be efficiently impregnated into the interior of the used absorbent article. Furthermore, because a strong acidic aqueous solution is used as the acidic aqueous solution, even a small amount of the acidic aqueous solution can reliably inactivate the superabsorbent polymer inside the used absorbent article, allowing the moisture inside (e.g., urine) to be released to the outside and dehydrating the article. As a result, the weight of the used absorbent article can be reduced by finally removing the moisture from the used absorbent article in the removal step. Here, in the inactivation process S12, along with the gas and liquid released from the used absorbent article due to the application of pressure, it is possible to push out to the outside any excrement adhering to the used absorbent article, thereby making the used absorbent article even lighter. In this way, in the pretreatment step S01, the method makes it possible to reduce dirt and moisture in used absorbent articles using a small amount of acidic aqueous solution, thereby preventing dirt and moisture from being carried over to the main treatment step S02. Therefore, it is possible to reduce the burden of wastewater treatment of the treatment liquid (such as an acidic aqueous solution) and also reduce the burden from a sanitary standpoint in the maintenance of a plurality of devices.

[0069] In the present embodiment, as a preferred aspect, the pretreatment step S01 includes a step of pretreating a plurality of used absorbent articles in an acidic aqueous solution while maintaining them in the state in which they were collected. In other words, the introduction step S11, the inactivation step S12, and the removal step S13 are carried out while maintaining the plurality of used absorbent articles in the state in which they were collected.

[0070] Here, the term "used absorbent article in its collected state" refers to a state in which the shape of the used absorbent article has not changed since it was transported from the place of use (e.g., a hospital, a nursing home, a home, etc.) or collection site (e.g., a dedicated collection site, a local garbage collection site, etc.) to the location where the method is implemented. Specifically, this term refers to a state in which the used absorbent article and its components have not been damaged (e.g., broken, crushed, shredded), separated, disassembled, etc. since it was collected. Therefore, this does not include, for example, reduction, expansion, or deformation in size due to compression or the discharge (release) of attached or absorbed bodily waste. Note that the term "used absorbent article in its collected state" includes a "rolled state." A "rolled state" refers to a state in which the used absorbent article is rolled or folded in a roughly rolled state with the topsheet on which the bodily waste has been discharged facing inward in order to prevent the bodily waste from adhering to the surrounding area and the resulting odor from diffusing to the surrounding area. There are no particular restrictions on how the absorbent article is rolled up, such as how it is rolled or folded, and it is preferable that the tape attached to the absorbent article maintains that state in the rolled up state. Note that an absorbent article that is partially damaged when removed from the wearer is also considered to be in the "state when retrieved" if there is no subsequent damage. In addition, if the "rolled state" is simply unfolded (unfolded), it may also be considered to be in the "state when retrieved."

[0071] In this embodiment, in the pretreatment step S01, the state of the used absorbent articles at the time of collection is maintained, and dirt and moisture are removed without being broken down into multiple materials. Therefore, in the pretreatment step S01, it is unlikely that the materials will be broken down into small pieces and remain in large numbers in the equipment, allowing workers to maintain the equipment extremely easily and hygienically. Furthermore, because the used absorbent articles are not broken down into multiple materials, it is difficult for the materials to get into the wastewater of the treatment liquid (such as an acidic aqueous solution). This reduces the hygienic burden of wastewater treatment of the treatment liquid (such as an acidic aqueous solution). Therefore, in this method, it is possible to reduce the hygienic burden of maintaining multiple devices while also reducing the burden of wastewater treatment of the treatment liquid (such as an acidic aqueous solution).

[0072] In this case, it is not necessary that all of the multiple used absorbent articles are in the state they were collected. From the viewpoint of suppressing the influence of used absorbent articles that are not in the state they were collected on used absorbent articles in the state they were collected (for example, suppressing damage to the used absorbent articles), it is preferable that 90% or more of the multiple used absorbent articles are in the state they were collected, and more preferably 95% or more. In this embodiment, 100% are present. There is no particular restriction on the proportion of rolled-up used absorbent articles among the multiple used absorbent articles, but in this embodiment, 100% are present.

[0073] In the present embodiment, as a preferred aspect, in the inactivation step S12, as a method for repeatedly applying and relaxing pressure to each of a plurality of used absorbent articles, the pressure is applied and relaxed by banging each of the plurality of used absorbent articles against each other. That is, the used absorbent articles are banged against each other. The method for banging each of the plurality of used absorbent articles against each other is not particularly limited, and examples include a method of stirring the acidic aqueous solution in a treatment tank, or a method of shaking or rotating the treatment tank. This makes it possible to easily and reliably apply and relax pressure to the used absorbent articles in the inactivation step S12, while preventing the used absorbent articles from being separated or disintegrated by the force of the water flow of the acidic aqueous solution (preferably while maintaining the used absorbent articles in the state at the time of collection), and to impregnate the used absorbent articles with the acidic aqueous solution.

[0074] 3 is a schematic diagram showing an example of the configuration of a pretreatment device 1 according to an embodiment. There are no particular limitations on the means for realizing the pretreatment step S01 (introduction step S11, inactivation step S12, and removal step S13), but in this embodiment, the pretreatment device 1 shown in this figure is used.

[0075] The pretreatment device 1 is a washing device having a horizontal rotating drum (which may be inclined relative to the horizontal) as a treatment tank 10. The rotating drum (treatment tank 10) has a horizontal plane CH including its rotation axis X and a vertical plane CV including the rotation axis X, and is equipped with an outer tank 12 capable of retaining / discharging liquid, and an inner tank 11 arranged inside the outer tank 12 so as to be rotatable about the rotation axis X and having a number of holes (not shown) in the peripheral wall. An example of such a device is a fully automatic water-washing and dehydrating machine (inner diameter of inner tank 11: 1000 mmφ).

[0076] As described above, in the pretreatment step S01, the treatment tank 10 is a horizontal rotating drum, and therefore, in the inactivation step S12, the rotation of the rotating drum allows the multiple used absorbent articles to be easily and reliably bumped against each other. That is, the used absorbent articles can be bumped against each other. This makes it possible to more easily and reliably apply and release pressure to the used absorbent articles, while preventing the used absorbent articles from being separated or disintegrated by the force of the water flow of the acidic aqueous solution (preferably while maintaining the collected state), and to impregnate the used absorbent articles with the acidic aqueous solution.

[0077] In the introduction step S11 using the pretreatment device 1 in this embodiment, the acidic aqueous solution WA is introduced into the inner tank 11 and outer tank 12 of the treatment tank 10, and a plurality of used absorbent articles 2 are introduced into the inner tank 11.

[0078] There are no particular restrictions on the arrangement of the multiple used absorbent articles 2 in the inner tub 11, but as shown in Fig. 3, it is preferable that the multiple used absorbent articles that make up the upper surface of the used absorbent articles are arranged in a state where they are lined up along a plane that is roughly parallel to the horizontal plane CH when viewed as a single unit. "Roughly along the horizontal plane CH" means that the unevenness of the upper surface of the used absorbent articles is within ±2 of the number of used absorbent articles 2. This is from the viewpoint of applying and relaxing pressure in roughly the same way to the multiple used absorbent articles 2 in the inactivation step S12.

[0079] Furthermore, although there is no particular limit to the amount of used absorbent articles 2 in the inner tank 11, it is preferable that they are arranged in an amount that is positioned below the horizontal plane CH, as shown in Fig. 3. If a large number of used absorbent articles 2 are arranged in the inner tank 11 so that the amount exceeds the horizontal plane CH, it becomes difficult to apply and release pressure to the used absorbent articles 2 in a generally uniform manner in the inactivation step S12, and it also becomes difficult to distribute the acidic aqueous solution WA to the used absorbent articles 2 in a generally uniform manner.

[0080] The amount of acidic aqueous solution WA should be such that the liquid level WL of the acidic aqueous solution WA is at least lower than the uppermost part 2TE of the plurality of used absorbent articles 2 that are not floating. However, the uppermost part 2TE of the plurality of used absorbent articles 2 refers to the uppermost part of the used absorbent article 2T that is the uppermost of the plurality of used absorbent articles 2 that are not floating in the acidic aqueous solution WA in the inner tank 11. In other words, when the plurality of used absorbent articles 2 are viewed as a single entity, the uppermost part refers to the uppermost part of the used absorbent article 2T that is the uppermost of the plurality of used absorbent articles 2 that are not floating and that constitute the upper surface of the entity.

[0081] In the example of FIG. 3 , the top 2TE of the uppermost used absorbent article 2T is positioned at a height d1 from the deepest point of the inner tub 11. Meanwhile, the liquid level WL of the acidic aqueous solution WA is positioned at a height d2 from the deepest point of the inner tub 11. Therefore, d1 > d2, and the liquid level WL of the acidic aqueous solution WA is positioned lower than the top 2TE of the multiple used absorbent articles 2 that are not floating. By reducing the amount of acidic aqueous solution WA, it is possible to prevent the used absorbent articles 2 from being separated or disassembled from the state they were in when collected due to the force of the water flow of the acidic aqueous solution WA. Note that, with respect to the inner diameter D1 of the inner tub 11, the horizontal plane CH is positioned at a height D1 / 2 from the deepest point of the inner tub 11, and D1 / 2 > d1, i.e., the multiple used absorbent articles 2 are positioned below the horizontal plane CH. Pressure can be applied / relaxed to the multiple used absorbent articles 2 in a generally uniform manner, making it easier to distribute the acidic aqueous solution WA.

[0082] The liquid level WL of the acidic aqueous solution WA is preferably at a position where approximately 3 / 5 to 4 / 5 (number) of the plurality of used absorbent articles 2 are immersed (submerged). In other words, it is not necessary for 1 / 5 to 2 / 5 (number) of the plurality of used absorbent articles 2 to be immersed. By using a smaller amount of the acidic aqueous solution WA for the plurality of used absorbent articles 2 in this way, the amount of wastewater can be further reduced. Furthermore, by using a smaller amount of the acidic aqueous solution WA, it is possible to further prevent the used absorbent articles 2 from being separated or disassembled from the state at the time of collection due to the force of the water flow of the acidic aqueous solution WA that may occur during the inactivation step S12 (preferably, the collected state can be maintained). This allows the superabsorbent polymers of the plurality of used absorbent articles 2 to be inactivated and dehydrated while maintaining the state at the time of collection, thereby reducing the weight of the plurality of used absorbent articles 2.

[0083] If the liquid level WL of the acidic aqueous solution WA is too low, the acidic aqueous solution may not sufficiently reach the multiple used absorbent articles 2, and may not be able to sufficiently inactivate the multiple used absorbent articles 2. On the other hand, if the liquid level WL of the acidic aqueous solution WA is too high, the large amount of water flow from the aqueous solution may cause the rolled up state of the used absorbent articles 2 to collapse, causing them to separate and disintegrate.

[0084] In the example of Figure 3, if the used absorbent articles 2 are arranged at approximately the same number density (number per unit volume), the liquid level WL of the acidic aqueous solution WA is located at a position where approximately 2 / 3 (number) of the multiple used absorbent articles 2 are immersed (submerged).

[0085] The weight of the acidic aqueous solution WA is preferably 2 to 5 times, and more preferably 2 to 3 times, the weight of the multiple used absorbent articles 2 (including excrement). Using a relatively small amount of the acidic aqueous solution WA relative to the multiple used absorbent articles 2 in this manner reduces the amount of wastewater. Furthermore, using a small amount of the acidic aqueous solution WA can prevent the used absorbent articles 2 from being separated or disassembled from the state at the time of collection due to the force of the water flow of the acidic aqueous solution WA, which may occur during the inactivation step S12 (preferably, the collected state can be maintained). This reduces the weight of the multiple used absorbent articles 2. If the amount of the acidic aqueous solution WA is too small, the acidic aqueous solution WA may not be sufficiently distributed over the multiple used absorbent articles 2, and the multiple used absorbent articles 2 may not be sufficiently inactivated. On the other hand, if the amount of the acidic aqueous solution WA is too large, the multiple used absorbent articles 2 may be easily separated or disassembled by the water flow, resulting in an increase in the amount of alkaline chemicals required for neutralization during wastewater treatment.

[0086] The temperature of the acidic aqueous solution WA is not particularly limited as long as the inactivation reaction proceeds in the inactivation step S12. The temperature may be room temperature or higher, for example, 15 to 30° C. Furthermore, the time for treating the used absorbent article in the acidic aqueous solution in the inactivation step S12 is not particularly limited as long as the superabsorbent polymer is inactivated and dehydrated, but may be, for example, 1 to 60 minutes, with 5 to 30 minutes being preferred.

[0087] Next, the inactivation step S12 using the pretreatment device 1 of this embodiment will be described. In the inactivation step S12, the inner tub 11 is rotated at a predetermined speed in a forward direction (pauses are possible midway) or in a forward / reverse direction, thereby moving the used absorbent articles 2 within the inner tub 11. That is, the inactivation step S12 includes a step of colliding the used absorbent articles 2 against each other by rotating the rotating drum. In the example of FIG. 3, before operation, the liquid level WL of the acidic aqueous solution WA is positioned at a position where approximately two-thirds (in number) of the used absorbent articles 2 are immersed. During operation, the used absorbent articles 2 and the acidic aqueous solution WA move within the inner tub 11, so that each used absorbent article 2 is immersed in the acidic aqueous solution WA approximately periodically, although not simultaneously.

[0088] In this case, the inner tub 11 of the treatment tub 10 is divided vertically into three regions (each having the same vertical width): an upper region, a middle region, and a lower region. At this time, for example, at the beginning of operation, a plurality of used absorbent articles 2 are accumulated in a state generally in the lower region of the inner tub 11. Thereafter, as the inner tub 11 rotates, each used absorbent article 2 rolls along the inner wall of the inner tub 11 until it reaches a height near the middle region, and then rolls down onto a plurality of other used absorbent articles 2 located in the lower region, repeating this process. As a result, adjacent used absorbent articles 2 collide with each other while rolling along the inner wall of the inner tub 11 until it reaches a height near the middle region, and adjacent used absorbent articles 2 collide with each other as they roll down onto a plurality of used absorbent articles 2 located in the lower region. This collision and other effects repeatedly apply and release pressure to the used absorbent articles 2. At this time, the rotation speed of the inner tub 11 is adjusted appropriately to prevent the used absorbent articles 2 from reaching the upper region and then free falling (being slammed) to the lower region due to gravity. If the rotation speed is too fast and the used absorbent articles 2 are allowed to free fall, the pressure on the used absorbent articles 2 will be too great, making them more likely to separate and disintegrate.

[0089] Here, the cycle of repeated application and relaxation of pressure is not particularly limited as long as the used absorbent article 2 is difficult to separate or disassemble (preferably, can maintain the state it was in when collected). For example, when the inner tub 11 (inner diameter 1000 mmφ) is rotated in the forward direction, the rotation speed can be greater than 20 rpm and less than 35 rpm. In this case, the cycle of repeated application and relaxation of pressure on the used absorbent article 2 is not necessarily clear and is not particularly limited (it does not have to be constant). For example, if the cycle is considered to be the time it takes for the inner tub 11 to rotate roughly once, it can be considered to be approximately 1.7 to 2.4 seconds. Furthermore, when the inner tub 11 (inner diameter 1000 mmφ) is rotated back and forth in the forward and backward directions, the rotation speed can be greater than 20 rpm and less than 35 rpm, and the cycle of the forward and backward rotation of the inner tub 11 can be approximately 2 to 6 seconds. In this case, too, the cycle of repeated application and relaxation of pressure in the used absorbent article 2 is not necessarily clear and is not particularly limited (it does not have to be constant). For example, if the cycle is considered to be the time it takes for the inner tub 11 to rotate back and forth in the forward and reverse directions, it may be about 2 to 6 seconds. Note that, in one cycle of the reciprocating rotation of the inner tub 11, the time spent in the forward direction and the time spent in the reverse direction may be different. For example, the time spent in one direction may be about 1.2 to 2 times the time spent in the other direction.

[0090] In this way, by repeatedly applying and releasing pressure to each of the used absorbent articles 2 while maintaining the multiple used absorbent articles 2 in the acidic aqueous solution WA in the treatment tank 10 in the state they were in when collected, the acidic aqueous solution can be impregnated into the interior of each of the used absorbent articles 2. This allows the superabsorbent polymer in each of the used absorbent articles 2 to be dehydrated. Furthermore, as the superabsorbent polymer is dehydrated, excrement adhering to each of the used absorbent articles 2 can be discharged.

[0091] Next, the removal step S13 using the pretreatment device 1 in this embodiment will be further described. In the previous inactivation step S12, moisture (e.g., urine) contained in the superabsorbent polymer of each used absorbent article 2 is discharged, so the superabsorbent polymer is dehydrated. However, each used absorbent article 2 as a whole still contains moisture (e.g., acidic aqueous solution, moisture discharged from the superabsorbent polymer). For example, the pulp fibers and nonwoven fabric of each used absorbent article still contain moisture. Therefore, in the removal step S13, moisture contained in each used absorbent article 2 is removed.

[0092] Specifically, in the removal step S13, the acidic aqueous solution WA is discharged from the treatment tank 10 (outer tank 12), and then the treatment tank (inner tank 11) is rotated around the rotation axis X (for example, at 100 rpm), whereby the moisture contained in each used absorbent article 2 can be removed by centrifugal force via the outer tank 12. As a result, not only can the moisture from the superabsorbent polymer be dehydrated in the inactivation step S12, but the moisture from the multiple used absorbent articles 2 can also be removed overall in the removal step S13, and multiple lightweight used absorbent articles 2 can be obtained.

[0093] Here, the dehydration rate of the multiple used absorbent articles after the removing step S13 is preferably 40% or more, more preferably 60% or more, and even more preferably 65% ​​or more, where the dehydration rate is calculated using the following formula. Dehydration rate (%) = {1 - (mass of a plurality of used absorbent articles after the pretreatment process has been performed - mass of a plurality of absorbent articles before use) / (mass of a plurality of used absorbent articles before the pretreatment process has been performed - mass of a plurality of absorbent articles before use)} × 100 = {1-(mass of water in a plurality of used absorbent articles after the pretreatment process) / (mass of water in a plurality of used absorbent articles before the pretreatment process)} × 100, is.

[0094] As described above, in the pretreatment step S01, the dehydration rate of the multiple used absorbent articles 2 after the removal step S13 is 40% or more. Therefore, the pretreatment step S01 allows the multiple used absorbent articles 2 to be inactivated and dehydrated extremely well in the state they are collected, and can be very effectively reduced in weight. This allows the used absorbent articles 2 to be transported and stored hygienically before being transferred to the main treatment step S02. This also reduces the amount of wastewater and the spread of excrement, enabling a more hygienic recycling process with less environmental impact. Note that in the removal step S13, water may be added to the treatment tank containing the multiple used absorbent articles 2, and the treatment tank may be rotated around the rotation axis X to wash the multiple used absorbent articles 2 with water.

[0095] The plurality of lightweight used absorbent articles 2 obtained after the removal step S13 of the pre-treatment step S01 are transferred to the main treatment step S02.

[0096] In this embodiment, the method for performing the inactivation step S12 is not particularly limited as long as it is possible to repeatedly apply and release pressure to each of a plurality of used absorbent articles in an acidic aqueous solution. For example, the following method can be considered as such a method.

[0097] One example of such a method is to use a vertical rotating drum as a treatment tank. The treatment tank (rotating drum) comprises an outer tank capable of holding liquid and an inner tank rotatably arranged inside the outer tank and having a number of holes in its peripheral wall. The inner tank is rotated forward (with pauses) or forward and backward at a predetermined speed to move multiple used absorbent articles within the inner tank. In this case, it is not necessary for all of the multiple used absorbent articles to be immersed in the acidic aqueous solution before operation. Meanwhile, during operation, the multiple used absorbent articles or the acidic aqueous solution move within the treatment tank so that each used absorbent article is immersed in the acidic aqueous solution approximately periodically, although not simultaneously.

[0098] In this case, the treatment tank of the vertical rotating drum is divided into roughly an upper region, a middle region, and a lower region in the vertical direction. For example, at the beginning of operation, multiple used absorbent articles are accumulated in the lower region of the rotating drum. Subsequently, as the inner tank rotates, the centrifugal force generated by the rotation moves each used absorbent article toward the inner wall of the inner tank, and some further toward the middle or upper region. They are pressed against the inner wall or other used absorbent articles, applying pressure. During periods of rotation rest or reversal, the centrifugal force disappears, and the pressure is relieved. In this way, the application and relief of pressure to the used absorbent articles are repeated due to the action of the used absorbent articles colliding with the inner wall or other used absorbent articles. Note that the rotation speed of the rotating drum is appropriately adjusted so that the pressure applied to the used absorbent articles is not too great, preventing them from separating or breaking down (preferably so that the state in which they were collected is maintained).

[0099] Another example of such a method is to periodically apply pressure to multiple used absorbent articles placed in a treatment tank by pressing a flat member against them from above, and then release the pressure by lifting the flat member upward. In this case, it is not necessary for all of the multiple used absorbent articles to be immersed in the acidic aqueous solution before operation. During operation, the multiple used absorbent articles or the acidic aqueous solution move within the treatment tank, so that each used absorbent article is immersed in the acidic aqueous solution approximately periodically, though not simultaneously. In this way, the application and release of pressure to the used absorbent articles is repeated due to the action of the used absorbent articles colliding with the inner wall, the flat member, or other used absorbent articles. Note that the pressure applied by the flat member is appropriately adjusted to prevent the pressure applied to the used absorbent articles from being too great and causing them to separate or disintegrate (preferably so that the used absorbent articles can maintain their original state when collected).

[0100] Another example of this method involves horizontally reciprocating a treatment tank containing multiple used absorbent articles, pressing the multiple used absorbent articles against one or the other inner wall, thereby applying pressure, and then releasing the pressure between the inner wall and the other inner wall (during the reciprocating motion). In this case, it is not necessary for all of the multiple used absorbent articles to be immersed in the acidic aqueous solution before operation. During operation, while applying pressure, the multiple used absorbent articles or the acidic aqueous solution move within the treatment tank, so that each used absorbent article is immersed in the acidic aqueous solution approximately periodically, though not simultaneously. In this way, the application and release of pressure to the used absorbent articles is repeated due to the action of the used absorbent articles colliding with the inner wall and other used absorbent articles. Note that the speed of the reciprocating motion of the treatment tank is appropriately adjusted to prevent the pressure applied to the used absorbent articles from being too great, causing them to separate or disintegrate (preferably so that the used absorbent articles maintain the state they were in when collected).

[0101] There are no particular limitations on the method for removing moisture contained in each used absorbent article 2, as long as it is possible to remove the moisture.

[0102] For example, when a vertical rotating drum is used as the treatment tank, the acidic aqueous solution is discharged from the treatment tank (outer tank) and then the treatment tank (inner tank) is rotated, whereby the moisture contained in each used absorbent article can be removed via the outer tank by centrifugal force. When a treatment tank having a flat plate-shaped member is used as the treatment tank, the acidic aqueous solution can be discharged from the treatment tank and then multiple used absorbent articles can be pressed against the inner wall of the treatment tank with the flat plate-shaped member, thereby removing the moisture contained in each used absorbent article. For example, when a treatment tank that reciprocates horizontally is used, the acidic aqueous solution can be discharged from the treatment tank and then the treatment tank is reciprocated horizontally, thereby removing the moisture contained in each used absorbent article.

[0103] Next, the main processing step S02 will be further described. As described above, the main processing step S02 is a step of disassembling a plurality of used absorbent articles from which dirt and moisture have been removed in water, and separating and recovering at least one of a plurality of materials from the disassembled plurality of used absorbent articles. Figure 4 is a flowchart showing the main processing step S02 according to an embodiment. In this embodiment, the main processing step S02 includes a crushing step S21, a film / nonwoven fabric separation step S22, a foreign matter removal step S23, a SAP separation step S24, an ozone treatment step S25, and a rinsing / spin-drying step S26.

[0104] The shredding step S21 is a step of shredding used absorbent articles in water. In this embodiment, first, in the shredding step S21, a plurality of used absorbent articles from which dirt and moisture have been removed, obtained in the pretreatment step S01, are supplied to a solution tank containing water (or not containing water). Next, the water containing the used absorbent articles (or each of the used absorbent articles and water) 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 then shredded by the biaxial shredder. As a result, shredded material is generated from the shredded used absorbent articles. The shredded material is sent alone or together with water to the film / nonwoven fabric separation step S22. The biaxial shredder is, for example, located below the solution tank and connected to the solution tank. In this case, the used absorbent articles are transferred to the twin-shaft shredder by gravity or by being drawn into the twin-shaft shredder. In another embodiment, water is not stored in the solution tank, and the used absorbent articles are supplied to the twin-shaft shredder together with water, and the used absorbent articles are shredded together with the water.

[0105] Next, the film / nonwoven fabric separation step S22 is a step of separating plastic materials from a mixture of synthetic resin plastic materials (e.g., films, nonwoven fabrics, collection bags, etc.), superabsorbent polymers, and pulp fibers obtained by decomposing used absorbent articles in water. In this embodiment, first, the mixture of crushed material and water produced in the crushing step S21 is supplied to a pulper separator. Next, the crushed material and water mixture is separated by a screen in the pulper separator into plastic materials and a mixture of pulp fibers, superabsorbent polymers, and water. As a result, the pulp fibers, superabsorbent polymers, and water that pass through the screen are supplied to the foreign matter removal step S23. Meanwhile, the plastic materials that do not pass through the screen are then washed with wash water, dried, and recovered as recycled plastic materials (films, nonwoven fabrics, etc.).

[0106] Next, in the foreign matter removal step S23, 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 mixture supplied from the film / nonwoven fabric separation step S22. In this embodiment, a screen separator (with relatively large mesh), a screen separator (with relatively small mesh), and a cyclone separator are arranged in this order to sequentially separate the foreign matter from the mixture. This results in pulp fibers and superabsorbent polymer with minimal foreign matter. The mixture of pulp fibers and superabsorbent polymer with minimal foreign matter is then supplied to the SAP separation step S24.

[0107] In the SAP separation step S24, 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 polymer with little foreign matter) supplied from the foreign matter removal step S23. In this embodiment, the drum screen separator separates the mixed liquid into superabsorbent polymer and water, and pulp fibers (containing a small amount of superabsorbent polymer). The superabsorbent polymer and water that pass through the screen are then separated into superabsorbent polymer and an acidic aqueous solution by another separator (e.g., an inclined screen separator). The superabsorbent polymer is washed with wash water, dried, and recovered as recycled superabsorbent polymer. Meanwhile, the pulp fibers that do not pass through the screen are supplied to the ozone treatment step S25.

[0108] In the ozone treatment step S25, the pulp fibers separated from used absorbent articles are treated with a treatment liquid containing ozone (e.g., water containing ozone). This treatment allows the ozone to come into contact with superabsorbent polymers and organic impurities (e.g., lignin) that may be attached to the surface or inside of the pulp fibers derived from used absorbent articles. This oxidatively decomposes the superabsorbent polymers 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.

[0109] The configuration of the ozone treatment device in the ozone treatment step S25 is not particularly limited as long as it can bring 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, 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 are mixed and contacted with the ozone-containing gas in the treatment liquid in the treatment tank. Examples of ozone supply devices include the ED-OWX-2 Ozone Water Exposure Tester manufactured by Ecodesign Inc. and the OS-25V Ozone Generator manufactured by Mitsubishi Electric Corporation. Furthermore, the use of a treatment liquid containing ozone can sterilize and bleach pulp fibers.

[0110] In the ozone treatment step S25, the concentration of pulp fiber contained in the treatment liquid is, for example, 0.5 to 20% by mass, and preferably 1 to 10% by mass, relative to 100% by mass of the treatment liquid. If the concentration of pulp fiber is too low, the treatment efficiency will decrease, and if it is too high, it will be difficult to remove impurities from the pulp fiber.

[0111] In the ozone treatment step S25, the ozone concentration in the treatment liquid 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, the pulp fibers are likely to be damaged. The treatment time with ozone is shorter when the ozone concentration in the treatment liquid 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 liquid and the treatment time (minutes) (hereinafter also referred to as the "CT value") is preferably 100 to 6000 ppm·min. If the CT value is too low, it becomes difficult to remove impurities, and if the CT value is too high, the pulp fibers are likely to be damaged.

[0112] The treatment liquid is preferably water (pH 5.8 to 8.6) with a pH closer to acidic (pH 5.8 to 7.0), and more preferably even closer to acidic (pH 5.8 to 6.0). By making the water more acidic, the deactivation and gasification of ozone in the treatment liquid can be suppressed, and the superabsorbent polymer can 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, water with a more acidic pH can be added to the treatment liquid in an amount corresponding to the range of the fluctuation.

[0113] The ozone treatment in the ozone treatment step S25 can suppress the residue of superabsorbent polymers, lignin, and other impurities in the pulp fibers, as well as deodorizing, sterilizing, and bleaching the pulp fibers and promoting fibrillation, resulting in pulp fibers with fewer impurities, suppressed bacterial growth, and a larger surface area, making them suitable for a variety of uses.

[0114] Thereafter, the pulp fibers treated with ozone in the ozone treatment step S25 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 are supplied to the rinsing and dewatering step S26.

[0115] In the rinsing and spin-drying step S26, the ozone-treated pulp fibers are rinsed with wash water (e.g., industrial water, tap water, or groundwater), and then the wash water is removed. In this embodiment, the rinsing function of the washing tub / spin-drying tub, which has a rotating drum, uses wash water to wash away impurities and treatment liquid (including ozone) that were present on the surface of the pulp fibers, the spin-drying function dehydrates the pulp fibers to reduce the amount of wash water, and the drying function dries the pulp fibers. As a result, the pulp fibers are recovered as recycled pulp fibers.

[0116] In the above-mentioned main treatment step S02, the above-mentioned step S22 can be considered a separation step in which the water containing a plurality of used absorbent articles from which dirt and moisture have been removed is separated into superabsorbent polymer, pulp fibers, and water, and other materials. Furthermore, the above-mentioned steps S23 to S26 can be considered recovery steps in which the superabsorbent polymer and pulp fibers are respectively separated and recovered from the separated superabsorbent polymer, pulp fibers, and water.

[0117] In this method, each step of the main treatment step S02 is performed in water rather than in an acidic aqueous solution, which reduces the amount of acidic aqueous solution used and, consequently, the amount of acidic aqueous solution discharged, thereby reducing the burden of wastewater treatment. Furthermore, because water is used in the main treatment step S02, which involves many steps, it is possible to prevent contamination from adversely affecting the external environment and workers during equipment maintenance, thereby reducing the burden on hygiene. In addition, in this method, all or part of the water discharged in each step of the main treatment step S02 may be returned to another step for reuse (e.g., as replenishment water for another step performed before the current step, water for washing materials, etc.). Because each step of the main treatment step S02 is performed in water rather than in an acidic aqueous solution, it can be reused extremely easily (without any special treatment). This reduces the amount of wastewater and the burden on wastewater treatment. Furthermore, all or part of the water discharged in each step of the main treatment step S02 may be reused as water for use in the pretreatment step S01 (e.g., water for adjusting the concentration or pH of an acidic aqueous solution, water for washing materials, etc.). This reduces the amount of water used in the pretreatment step S01 and lowers the environmental impact.

[0118] In this method, the treatment step S02 includes a shredding step S01 in which used absorbent articles are shredded before the separation steps (S23 to S26). Therefore, the shredding step before the separation step makes it easier to disintegrate the constituent materials of the used absorbent articles from each other. This allows the separation step to be carried out more efficiently, making it easier to recycle the materials (constituent materials) of the used absorbent articles.

[0119] (Second embodiment) A method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles according to a second embodiment will be described. This embodiment differs from the first embodiment in part of the pretreatment step S01. The following mainly describes the differences from the first embodiment.

[0120] In this embodiment, the pre-treatment process S01 differs from the first embodiment in that, unlike the introduction process S11 and inactivation process S12 shown in Figure 2, it includes a crushing process for crushing used absorbent articles and an inactivation process for immersing the crushed pieces of used absorbent articles in an inactivating aqueous solution (not shown).

[0121] In this embodiment, the shredding process carried out in the pre-treatment process S01 first involves supplying a plurality of used absorbent articles that have been soiled and have absorbed moisture to a receiving container. The used absorbent articles are then sent from the receiving container to a biaxial shredder (e.g., a biaxial rotary shredder, a biaxial differential shredder, or a biaxial shear shredder). The used absorbent articles are then shredded by the biaxial shredder. As a result, shredded material is produced from the shredded used absorbent articles. The shredded material is sent to the next process, the inactivation process. The shredded material may also be sent to the next process, the inactivation process, together with water or an inactivating aqueous solution.

[0122] The twin-shaft shredder is, for example, located below the receiving container and is in communication with the receiving container. In this case, used absorbent articles are transferred from the receiving container to the twin-shaft shredder by gravity or by being caught in the twin-shaft shredder. In this shredding process, the used absorbent articles are shredded without water. Note that in this shredding process, the used absorbent articles may be shredded with water (for example, in water or while being sprayed with water).

[0123] In this embodiment, the inactivation step performed in the pretreatment step S01 involves first supplying the crushed pieces of used absorbent articles crushed in the crushing step to a solution tank storing an inactivating aqueous solution (e.g., an acidic aqueous solution). The crushed pieces are then immersed in the inactivating aqueous solution. This inactivates (dehydrates) the superabsorbent polymer in the crushed pieces. The crushed pieces containing the inactivated (dehydrated) superabsorbent polymer are transferred to the removal step S13 together with the inactivating aqueous solution.

[0124] In this embodiment, used absorbent articles are crushed in the crushing step of the pretreatment step S01 before the inactivation step of the pretreatment step S01, which makes it easier for the inactivating aqueous solution to come into contact with the superabsorbent polymer in the used absorbent articles. Therefore, the superabsorbent polymer can be efficiently inactivated (dehydrated), which reduces the amount of inactivating aqueous solution or the concentration of the inactivating agent in the inactivating aqueous solution. This reduces the environmental impact of recycling materials from used absorbent articles.

[0125] In this embodiment, since the crushing step is performed in the pre-treatment step S01, the crushing step S21 in the main treatment step S02 may be omitted.

[0126] (Third embodiment) A method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles according to a third embodiment will be described. This embodiment differs from the first embodiment in part of the pretreatment step S01. The following mainly describes the differences from the first embodiment.

[0127] This embodiment differs from the first embodiment in that the pre-treatment process S01 includes an inactivation and crushing process (not shown) in which used absorbent articles are crushed together with an inactivating aqueous solution, unlike the introduction process S11 and inactivation process S12 shown in Figure 2.

[0128] In this embodiment, the inactivation and crushing step performed in the pretreatment step S01 first involves supplying a plurality of used absorbent articles that have been soiled and have absorbed moisture to a receiving container. Next, the used absorbent articles are sent from the receiving container to a biaxial crusher (e.g., a biaxial rotary crusher, a biaxial differential crusher, or a biaxial shear crusher), and an inactivating aqueous solution (e.g., an acidic aqueous solution) is supplied to the biaxial crusher. The used absorbent articles are then crushed together with the inactivating aqueous solution by the biaxial crusher. This crushes the used absorbent articles, and generates crushed material in which the superabsorbent polymer in the used absorbent articles has been inactivated (dehydrated). The crushed material containing the inactivated (dehydrated) superabsorbent polymer is transferred to a removal step S13 together with the inactivating aqueous solution.

[0129] The twin-shaft shredder is, for example, located below the receiving container and is in communication with the receiving container. In this case, used absorbent articles are transferred from the receiving container to the twin-shaft shredder by gravity or by being caught in the twin-shaft shredder. The inactivated aqueous solution is then supplied from above the twin-shaft shredder so as to be sprayed onto the shredding blades of the twin-shaft shredder and / or the used absorbent articles being transferred to the twin-shaft shredder.

[0130] In this embodiment, in the pretreatment step S01, the crushing and inactivation step crushes used absorbent articles and inactivates the superabsorbent polymer in the used absorbent articles almost simultaneously, making it easier for the superabsorbent polymer to come into contact with the inactivating aqueous solution and shortening the treatment time for the pretreatment step S01. Therefore, since the superabsorbent polymer can be efficiently inactivated (dehydrated), the amount of the inactivating aqueous solution or the concentration of the inactivating agent in the inactivating aqueous solution can be reduced, and the energy consumed in the process can be reduced. Therefore, this embodiment can reduce the environmental impact when recycling materials from used absorbent articles.

[0131] In this embodiment, since the crushing step is performed in the pre-treatment step S01, the crushing step S21 in the main treatment step S02 may be omitted.

[0132] (Fourth embodiment) A method for recycling multiple materials, including superabsorbent polymers and pulp fibers, from used absorbent articles according to a fourth embodiment will be described. This embodiment differs from the first embodiment in part of the pretreatment step S01. The following mainly describes the differences from the first embodiment.

[0133] In this embodiment, the pre-treatment step S01 differs from the first embodiment in that, unlike the introduction step S11 and the inactivation step S12 shown in FIG. 2, the pre-treatment step S01 includes an inactivation step of immersing used absorbent articles in the inactivating aqueous solution, and a crushing step of crushing used absorbent articles containing the inactivated superabsorbent polymer (not shown).

[0134] In this embodiment, the inactivation step performed in the pretreatment step S01 involves first supplying a plurality of used absorbent articles that have been soiled and have absorbed moisture into a solution tank containing an inactivating aqueous solution (e.g., an acidic aqueous solution). The used absorbent articles are then immersed in the inactivating aqueous solution, thereby inactivating (dehydrating) the superabsorbent polymer in the used absorbent articles. The used absorbent articles containing the inactivated (dehydrated) superabsorbent polymer are sent to the next step, the crushing step, either alone or together with the inactivating aqueous solution. This inactivation step may be performed using an apparatus such as that shown in FIG. 3.

[0135] In this embodiment, the shredding process carried out in the pretreatment process S01 first supplies used absorbent materials containing superabsorbent polymers inactivated (dehydrated) in the inactivation process to a receiving container. Next, the used absorbent materials are sent from the receiving container to a biaxial shredder (e.g., a biaxial rotary shredder, a biaxial differential shredder, or a biaxial shear shredder). The used absorbent products are then shredded by the biaxial shredder. As a result, shredded material containing the inactivated (dehydrated) superabsorbent polymers is produced. The shredded material is transferred to the removal process S13.

[0136] When used absorbent articles are sent from the receiving container to the twin-shaft shredder, the inactivating aqueous solution may be supplied to the twin-shaft shredder at the same time. In this case, the used absorbent articles are shredded together with the inactivating aqueous solution, and the shredded material containing the inactivated (dehydrated) superabsorbent polymer is transferred to the removal step S13 together with the inactivating aqueous solution.

[0137] The twin-shaft shredder is, for example, located below the receiving container and is in communication with the receiving container. In this case, used absorbent articles are transferred from the receiving container to the twin-shaft shredder by gravity or by being caught up in the twin-shaft shredder. When used absorbent articles are shredded in the twin-shaft shredder, an inactivated aqueous solution or water may be supplied from above the twin-shaft shredder so as to be sprayed onto the shredding blades of the twin-shaft shredder and / or the used absorbent articles being transferred to the twin-shaft shredder.

[0138] In this embodiment, the superabsorbent polymer in used absorbent articles is inactivated (dehydrated) in the inactivation step of the pretreatment step S01 before the crushing step, so that the swollen superabsorbent polymer can be reduced in size before the crushing step. This makes it difficult to damage the superabsorbent polymer during the crushing step, thereby reducing the amount of superabsorbent polymer that is difficult to reuse as superabsorbent polymer. Therefore, the recovery rate of the superabsorbent polymer can be increased, and the amount of inactivating aqueous solution required to recover the superabsorbent polymer or the concentration of the inactivating agent in the inactivating aqueous solution can be reduced. As a result, this embodiment can reduce the environmental impact when recycling materials from used absorbent articles.

[0139] In this embodiment, since the crushing step is performed in the pre-treatment step S01, the crushing step S21 in the main treatment step S02 may be omitted.

[0140] In a preferred aspect of each embodiment, the amount of the inactivating aqueous solution used in the pretreatment step S01 is less than the amount of water injected in the main treatment step S02.

[0141] If a method for recycling multiple materials from used absorbent articles is to be carried out using only the main treatment step S02 without carrying out the pretreatment step S01, the main treatment step S02 must be carried out using an inactivating aqueous solution. In this case, the amount of the inactivating aqueous solution is roughly the same as the amount of water injected in the main treatment step S02 when both the pretreatment step S01 and the main treatment step S02 are carried out (as described above, even when the inactivating aqueous solution is strongly acidic, for example, the sulfuric acid concentration of a sulfuric acid aqueous solution is 0.1 to 2.0 mass % and the citric acid concentration of a citric acid aqueous solution is 0.5 to 4 mass %, and the majority (95 mass % or more) of the inactivating aqueous solution is water). Therefore, compared to a method for recycling multiple materials from used absorbent articles using only the main treatment step S02 without carrying out the pretreatment step S01, i.e., a method for carrying out only the main treatment step S02 using an inactivating aqueous solution instead of water, this method can reduce the amount of inactivating aqueous solution. This reduces the environmental impact. [Example]

[0142] EXAMPLES The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples.

[0143] A. Evaluation of pre-treatment process S01 + main treatment process S02 (1) Sample Five types of absorbent article samples were used: two types of unused disposable diapers for infants and three types of unused disposable diapers for adults. Five types of disposable diapers were prepared for each example and comparative example, with the same number of each type. The baby diapers contained approximately 50% of the absorbent material in the absorbent core, while the adult diapers contained approximately 30% of the absorbent material. To simulate a "used" state, each disposable diaper was allowed to absorb 300 g of saline solution, and the weight of the entire diaper was then measured, yielding 135 kg.

[0144] (2) Evaluation of the treatment In the examples, the above-mentioned pretreatment step S01 and main treatment step S02 were carried out on the above-mentioned (1) sample (all disposable diapers). A 1% sulfuric acid aqueous solution, which is a strongly acidic aqueous solution, was used as the inactivating aqueous solution in the pretreatment step S01. In the comparative examples, the above-mentioned (1) sample (all disposable diapers) was subjected to the crushing step S12 to the fourth separation step S20 in the treatment of Patent Document 1. A 0.1% sulfuric acid aqueous solution was used as the acidic aqueous solution in all steps. The amounts of water used and the amount of wastewater to be treated were then compared between the examples and the comparative examples.

[0145] (3) Results In the case of the example, the amount of wastewater to be treated was only 360 L, which was the amount of water used in the pretreatment step S01, and the amount of sulfuric acid in the wastewater was also small at 3.6 L. Furthermore, the amount of water used in the main treatment step S02 was 2700 L, and the total amount of water used was small at 3060 L. On the other hand, in the case of the comparative example, the amount of wastewater to be treated was 6750 L, which was very large, and the amount of sulfuric acid in the wastewater was also large, at 6.75 L. Furthermore, the amount of water used in the entire process was also large, at 6750 L. Therefore, it was confirmed that in the examples, the amount of wastewater to be treated was small, the amount of strong acid (sulfuric acid) contained therein was also small, and the overall amount of water used was also small.

[0146] [Table 1]

[0147] B. Evaluation of pretreatment process S01 (1) Sample A total of five types of absorbent article samples were used: two types of unused disposable diapers for infants and three types of unused disposable diapers for adults. The weight of each disposable diaper was measured (pre-use weight). Next, to simulate a "used" state, each disposable diaper was soaked in 300 g of saline and rolled up. The weight of each disposable diaper was then measured again (post-use, pre-treatment weight). For the multiple disposable diapers used in the Examples and Comparative Examples, five types of disposable diapers were prepared so that the same number of each type was used for each Example and Comparative Example. In the disposable diapers for infants, the proportion of superabsorbent polymer in the absorbent member in the absorbent core was approximately 50%, while in the disposable diapers for adults, the proportion of superabsorbent polymer in the absorbent member in the absorbent core was approximately 30%.

[0148] (2) Evaluation of pretreatment process S01 The pretreatment step S01 was carried out for each example and comparative example using a fully automatic water washing and dehydrating machine (inner tank inner diameter: 1000 mmφ). For the examples and comparative examples, the conditions for the acidic aqueous solution in the pretreatment step S01 and the inactivation step S12 described above were changed in various ways. However, examples were carried out according to the conditions for the pretreatment step S01 described above, and comparative examples were carried out under conditions that were partially different from those conditions.

[0149] (3) Results The results are shown in Table 1 below. In Table 1, "acidic aqueous solution" describes the conditions for the acidic aqueous solution, and "addition amount" indicates the amount of sulfuric acid aqueous solution used. "Sulfuric acid concentration" indicates the sulfuric acid concentration in the sulfuric acid aqueous solution. "pH" indicates the pH of the sulfuric acid aqueous solution. "Immersion ratio" indicates the ratio of disposable diapers immersed in the sulfuric acid aqueous solution (below the liquid surface) among multiple disposable diapers in the introduction step S11.

[0150] In Table 1, "inactivation step" describes the conditions for the inactivation step S12, and "rotation speed" indicates the rotation speed of the inner tub. "Treatment time" indicates the time for treating disposable diapers in the sulfuric acid aqueous solution. "Forward or forward-reverse time" indicates the cycles when the inner tub alternates between rotating forward and stopping, or when rotating forward and reverse alternately, during the treatment time.

[0151] Furthermore, in Table 1, "disposable diapers" indicates the results of the pretreatment process S01, etc., and "weight before use" indicates the weight of multiple disposable diapers before use, i.e., before absorbing saline solution. "weight after use before treatment" indicates the weight of multiple disposable diapers after use and before performing the pretreatment process S01. "weight after treatment" indicates the weight of multiple disposable diapers after performing the pretreatment process S01, and "moisture content before treatment" indicates the proportion of moisture contained in multiple disposable diapers after use and before performing the pretreatment process S01 (relative to the weight before use). "Dehydration rate" indicates the proportion of moisture contained in multiple disposable diapers after performing the pretreatment process S01 (relative to the moisture contained in multiple disposable diapers before performing the pretreatment process S01). For "rolled up state", a circle indicates that 90% or more of the disposable diapers (the state they were in when collected) remain rolled up after the pre-processing step S01 (less than 10% of the disposable diapers are in a partially damaged state), and an X indicates that less than 90% (same, 10% or more) remain rolled up. Note that an "X" in "weight after processing" indicates that part of the disposable diaper has ruptured, separated, or disintegrated, making it impossible to properly measure the weight after processing, and an "X" in "dehydration rate" indicates that the weight after processing could not be measured and therefore cannot be calculated.

[0152] [Table 2]

[0153] In Examples 2 to 5, of the multiple disposable diapers after the pretreatment step S01, 90% or more (actually 100%) remained rolled. Furthermore, a dehydration rate exceeding 40% was achieved. On the other hand, in Comparative Examples 2 and 3, of the multiple disposable diapers after the pretreatment step S01, less than 90% remained rolled. Furthermore, the dehydration rate was low, or many of the used absorbent articles were damaged, separated, or disassembled during the treatment, making it impossible to achieve the desired dehydration rate. Specifically, in Comparative Example 2, the sulfuric acid concentration of the acidic aqueous solution was low (the pH was high), so the superabsorbent polymer in the disposable diaper was not completely inactivated. As a result, the superabsorbent polymer absorbed the acidic aqueous solution diluted with saline solution discharged from the disposable diaper. In Comparative Example 3, the dilution of the acidic aqueous solution was suppressed by reducing the amount of disposable diapers, but the rolled-up disposable diapers were hardly dehydrated, resulting in a low dehydration rate. Although not shown in the examples and comparative examples, when the liquid level of the acidic aqueous solution is above the top of the disposable diapers, i.e., when the amount of acidic aqueous solution is too large, many disposable diapers float on the liquid surface, making it difficult to carry out the pretreatment step S01.

[0154] 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. [Explanation of symbols]

[0155] S01 Pretreatment process S02 Main treatment process

Claims

1. A method for recycling a plurality of materials, including a superabsorbent polymer and pulp fibers, from a used absorbent article that has absorbed soiling and moisture, comprising: a pretreatment step of removing dirt and moisture from the used absorbent article in an inactivating aqueous solution that inactivates the superabsorbent polymer, and discharging the inactivating aqueous solution containing the dirt and moisture; a main treatment step of pouring water into the used absorbent article from which the dirt and moisture have been removed, and separating and recovering at least one of the plurality of materials from the used absorbent article; Equipped with The inactivation aqueous solution contains a strongly acidic aqueous solution, The pretreatment step includes: carrying out the pretreatment in the acidic aqueous solution while maintaining the used absorbent article in the state at the time of collection, method.

2. The pretreatment step includes: an introducing step of introducing the used absorbent articles and the acidic aqueous solution into a treatment tank, wherein the liquid level of the acidic aqueous solution is lower than the top of the used absorbent articles that are not floating; an inactivation step of impregnating the used absorbent article with the acidic aqueous solution by repeatedly applying and releasing pressure to the used absorbent article in the treatment tank; a removing step of removing dirt and moisture from the used absorbent article; Including, The method of claim 1.

3. The inactivation step includes a step of applying and relaxing the pressure by banging the used absorbent article against other used absorbent articles. The method of claim 2.

4. The treatment tank is a horizontal rotary drum, The inactivation step includes a step of colliding the used absorbent articles with the other used absorbent articles by rotating the rotating drum. The method of claim 3.

5. the liquid level of the acidic aqueous solution in the introducing step is at a position where 3 / 5 to 4 / 5 of the used absorbent articles in the treatment tank are immersed; The method of claim 2.

6. In the introducing step, the weight of the acidic aqueous solution is 2 to 3 times the weight of the used absorbent articles in the treatment tank. The method of claim 2.

7. In the introducing step, the pH of the acidic aqueous solution is 2.0 or less. The method of claim 2.

8. In the introducing step, the acidic aqueous solution contains sulfuric acid. The method of claim 2.

9. The dehydration rate of the used absorbent article after the removing step is 60% or more. The method of claim 2.

10. The main treatment step includes: a separation step of separating the water containing the used absorbent article from which dirt and moisture have been removed into a superabsorbent polymer, pulp fibers, and water, and other materials; a recovery step of separating and recovering the superabsorbent polymer and the pulp fibers from the separated superabsorbent polymer, pulp fibers, and water; Including, The method of claim 1.

11. The present processing step further includes a crushing step of crushing the used absorbent articles before the separating step. The method of claim 10.

12. The pretreatment step includes: a crushing step of crushing the used absorbent article; an inactivation step of immersing the crushed pieces of the used absorbent article in the inactivating aqueous solution; Including, The method of claim 1.

13. The pretreatment step includes: The used absorbent article is crushed together with the inactivating aqueous solution. The method of claim 1.

14. The pretreatment step includes: an inactivation step of immersing the used absorbent article in the inactivating aqueous solution; a crushing step of crushing the used absorbent article containing the inactivated superabsorbent polymer; Including, The method of claim 1.

15. The amount of the inactivation aqueous solution used in the pretreatment step is less than the amount of water added in the main treatment step. The method of claim 1.

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