Method and apparatus for pretreatment of used absorbent articles

Abstract

To provide a pretreatment method for absorbent articles which have been used, with which weight of absorbent articles which have been used, can be reduced while they still maintain a recovered condition, by using a small amount of a water solution.SOLUTION: A pretreatment method removes contamination adhered to absorbent articles which have been used containing a high water-absorbing polymer, and an absorbed water content. The pretreatment method includes an introduction step S1, an inactivation step S2 and a removal step S3. In the introduction step S1, a plurality of absorbent articles which has been used in a recovered condition, and an acidic aqueous solution of strong acidity are introduced to a treatment tank. A liquid level of the acidic aqueous solution is located at a lower position than the uppermost part of the plurality of absorbent articles which has been used that is not floating. In the inactivation step S2, each of absorbent articles which have been used is impregnated with the acidic aqueous solution by repeating application and easing of a pressure in the acidic aqueous solution, while the plurality of used absorbent articles maintains the recovered condition, in the treatment tank. In the removal step S3, a water content is removed from the plurality of absorbent articles which has been used.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pretreatment method and a pretreatment apparatus for used absorbent articles.

Background Art

[0002] Before carrying out a treatment process for recycling used absorbent articles, a pretreatment method for removing dirt and absorbed moisture etc. previously attached to the used absorbent articles is known. For example, in Patent Document 1, there is disclosed a method for treating used paper diapers, characterized by washing used paper diapers while sequentially moving them from a water washing tank in the front stage to a water washing tank in the rear stage using a continuous washing machine having a plurality of groups of water washing tanks arranged in series. In this method, the used paper diapers are prewashed in a prewashing tank and mainwashed in a mainwashing tank, and at that time, quicklime (CaO) is mixed with water to dehydrate the superabsorbent polymer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method of Patent Document 1, the used paper diaper, that is, the used absorbent article, is immersed in an aqueous solution stored in a treatment tank such as a prewashing tank or a mainwashing tank, and treatment such as removing dirt attached to the used absorbent article and dehydrating the superabsorbent polymer is carried out. At that time, since an amount of aqueous solution sufficient to immerse the used absorbent article is used, there is a possibility that the amount of drainage of the aqueous solution after treatment increases.

[0005] Furthermore, absorbent materials, even after use, typically have a lower specific gravity than aqueous solutions and contain air in the voids between materials (e.g., voids between sheets or between constituent fibers), making them prone to floating on the surface when placed in an aqueous solution in a treatment tank. Therefore, even when used absorbent materials are placed in an aqueous solution, they are difficult to immerse in the solution. In other words, the aqueous solution has difficulty penetrating the interior of the used absorbent materials. Consequently, there is a risk that inactivating agents such as quicklime (CaO) in the aqueous solution may not be able to reach the superabsorbent polymer inside the used absorbent materials. This makes it difficult to dewater the superabsorbent polymer and remove dirt attached to the used absorbent materials. In other words, it becomes difficult to lighten the weight of used absorbent materials, and when they are moved to subsequent recycling processes, they may be heavy, bulky, difficult to handle, and difficult to temporarily store or transport.

[0006] In particular, used absorbent articles are often rolled up or folded with the surface sheet containing the excrement facing inward, in order to prevent the excrement from being exposed to the outside and to prevent the odor from spreading to the surroundings. In such cases, the liquid-impermeable back sheet or outer sheet is on the outside, so there is a significant tendency for aqueous solutions to have difficulty penetrating the inside of the used absorbent article.

[0007] However, if used absorbent materials are immersed in an aqueous solution and the agitation speed of the solution in a continuous washing machine is increased to facilitate penetration of the solution into the material, the used absorbent materials may break, causing components to leak out or separate into components and disintegrate, making it impossible to maintain the used absorbent materials in the same condition as when they were collected. In that case, when the used absorbent materials are moved to the subsequent recycling process, there will be many small components and scraps, making them difficult to handle and potentially hindering hygienic temporary storage and transportation.

[0008] Therefore, the object of the present invention is to provide a method for pre-treating used absorbent articles that can reduce their weight while maintaining them in the same condition as when they were recovered, using a small amount of aqueous solution. [Means for solving the problem]

[0009] The present invention relates to a pretreatment method for removing dirt and absorbed moisture adhering to used absorbent articles containing a superabsorbent polymer, comprising: a preparation step of preparing a plurality of used absorbent articles and a strongly acidic aqueous solution in a treatment tank, wherein each of the plurality of used absorbent articles is in the state as it was when recovered, and the liquid level of the acidic aqueous solution is lower than the uppermost of the plurality of used absorbent articles that are not floating; an inactivation step of impregnating each of the plurality of used absorbent articles with the acidic aqueous solution by repeatedly applying and releasing pressure in the acidic aqueous solution while maintaining the plurality of used absorbent articles in the state as it was when recovered in the treatment tank; and a removal step of removing moisture from the plurality of used absorbent articles. [Effects of the Invention]

[0010] The present invention provides a method for pre-treating used absorbent articles, which allows for weight reduction while maintaining the condition of the used absorbent articles at the time of recovery, using a small amount of aqueous solution. [Brief explanation of the drawing]

[0011] [Figure 1] This flowchart shows an example of a pretreatment method according to the embodiment. [Figure 2] This is a schematic diagram showing an example of the configuration of a preprocessing apparatus according to the embodiment. [Modes for carrying out the invention]

[0012] This embodiment relates to the following aspects. [Aspect 1] A pretreatment method for removing dirt and absorbed moisture attached to used absorbent articles containing a superabsorbent polymer, comprising: an introduction step of introducing a plurality of used absorbent articles and a strongly acidic aqueous solution into a treatment tank, wherein each of the plurality of used absorbent articles is in the state as it was when recovered, and the liquid level of the acidic aqueous solution is lower than the uppermost of the plurality of used absorbent articles that are not floating; an inactivation step of impregnating each of the plurality of used absorbent articles with the acidic aqueous solution by repeatedly applying and releasing pressure in the acidic aqueous solution while maintaining the plurality of used absorbent articles in the state as it was when recovered in the treatment tank; and a removal step of removing moisture from the plurality of used absorbent articles.

[0013] In this pretreatment method, 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 small. This reduces the amount of wastewater generated in this pretreatment method. At the same time, the small amount of acidic aqueous solution helps to suppress the phenomenon that can occur during the inactivation process, such as the used absorbent articles being separated and dismantled by the force of the water flow of the acidic aqueous solution, which would prevent the used absorbent articles from being maintained in the same condition as when they were recovered. In the inactivation process, during the initial operation, pressure is applied to release gas (e.g., air) from inside the used absorbent material. Then, as the pressure is released, the external liquid (e.g., acidic aqueous solution) is absorbed into the material by the suction force that occurs as the used absorbent material returns to its original shape. During subsequent operations, pressure is applied to release gas and liquid (e.g., water released by the inactivation of the superabsorbent polymer with the acidic aqueous solution) from inside the used absorbent material. Then, as the pressure is released, the external liquid (e.g., acidic aqueous solution) is absorbed into the material. As a result, even with a small amount of acidic aqueous solution, and even if the used absorbent material is in the state it was in when it was recovered, or even if it is rolled up, the acidic aqueous solution can be efficiently impregnated into the inside of the used absorbent material. Furthermore, since a strongly acidic aqueous solution is used as the acidic solution, even a small amount of the acidic solution can reliably inactivate the superabsorbent polymer inside the used absorbent article, allowing the internal moisture (e.g., urine) to be released to the outside and dehydrated. As a result, by removing moisture from the used absorbent article in the removal process, the used absorbent article can be made lighter while maintaining its condition as when it was recovered. In the inactivation process, the gases and liquids released from the used absorbent material by applying pressure can also push out any excrement attached to the used absorbent material. In this case, the used absorbent material can be made lighter while maintaining its condition as when it was recovered. Thus, in this pretreatment method for used absorbent articles, it is possible to lighten the weight of the used absorbent articles while maintaining them in the same condition as when they were recovered, using a small amount of acidic aqueous solution (treatment solution). This makes the used absorbent articles easier to handle, and allows for hygienic transport and storage for the recycling process. Furthermore, it reduces the amount of wastewater and the diffusion of excrement, resulting in a more hygienic and environmentally friendly recycling process.

[0014] [Aspect 2] The pretreatment method according to aspect 1, wherein the inactivation step includes a step of applying and releasing pressure by bringing each of the plurality of used absorbent articles into contact with one another. In this pretreatment method, the inactivation step includes a step of applying and releasing pressure by bumping multiple used absorbent articles against each other. This allows for easy and reliable application and release of pressure to the used absorbent articles in the inactivation step, while maintaining them in the same condition as when they were recovered, and enabling impregnation with an acidic aqueous solution.

[0015] [Aspect 3] The pretreatment method according to aspect 2, wherein the treatment tank is a horizontal rotating drum, and the inactivation step includes a step of causing each of the plurality of used absorbent articles to collide with each other by the rotation of the rotating drum. In this pretreatment method, since the treatment tank is a horizontal rotating drum, the rotation of the drum in the inactivation process allows multiple used absorbent materials to collide with each other easily and reliably. This makes it easier and more reliable to apply and release pressure to the used absorbent materials while maintaining them in the same condition as when they were recovered, and to impregnate them with an acidic aqueous solution.

[0016] [Aspect 4] The pretreatment method according to any one of aspects 1 to 3, wherein the liquid level of the acidic aqueous solution in the introduction step is at a position where 3 / 5 to 4 / 5 of the plurality of used absorbent articles are immersed. In this pretreatment method, the liquid level of the acidic aqueous solution in the introduction step is positioned so that 3 / 5 to 4 / 5 (number) of the multiple used absorbent articles 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, phenomena such as the separation and disintegration of used absorbent articles from their recovered state due to the force of the water flow of the acidic aqueous solution that may occur during the inactivation step can be further suppressed. As a result, multiple used absorbent articles can be inactivated and dewatered in the recovered state, and their weight can be reduced.

[0017] [Aspect 5] The pretreatment method according to any one of aspects 1 to 4, wherein in the introduction step, the weight of the acidic aqueous solution is 2 to 3 times the weight of the plurality of used absorbent articles in the treatment tank. In this pretreatment method, the weight of the acidic aqueous solution in the introduction step is 2 to 3 times the weight of a plurality of used absorbent articles in the treatment tank. By using a small amount of the acidic aqueous solution for the plurality of used absorbent articles in this way, the amount of drainage can be suppressed. Furthermore, by using a small amount of the acidic aqueous solution, events such as the used absorbent articles being separated and disassembled from the state when they are recovered by the force of the water flow of the acidic aqueous solution that may occur during the inactivation step can be more effectively suppressed. Thereby, a plurality of used absorbent articles can be inactivated and dehydrated in the state when they are recovered, and the weight can be reduced.

[0018] [Aspect 6] In the introduction step, the pH of the acidic aqueous solution is 2.0 or less. The pretreatment method according to any one of Aspects 1 to 5. In this pretreatment method, the pH of the acidic aqueous solution in the introduction step is 2.0 or less. Therefore, even if the acidic aqueous solution is in a small amount relative to a plurality of used absorbent articles, the inactivation step of this pretreatment method can more reliably inactivate and dehydrate a plurality of used absorbent articles in the state when they are recovered, and the weight can be reduced.

[0019] [Aspect 7] In the introduction step, the acidic aqueous solution contains sulfuric acid. The pretreatment method according to any one of Aspects 1 to 6. In this pretreatment method, the acidic aqueous solution in the introduction step contains sulfuric acid. Therefore, even if the acidic aqueous solution is in a small amount relative to a plurality of used absorbent articles, the inactivation step of this pretreatment method can more reliably inactivate and dehydrate a plurality of used absorbent articles in the state when they are recovered, and the weight can be reduced.

[0020] [Aspect 8] The dehydration rate of the plurality of used absorbent articles after the removal step is 40% or more. The pretreatment method according to any one of Aspects 1 to 7. In this pretreatment method, the dehydration rate of the plurality of used absorbent articles after the removal step is 40% or more. Therefore, by this pretreatment method, a plurality of used absorbent articles can be very well inactivated and dehydrated in the state when they are recovered, and the weight can be very effectively reduced.

[0021] The following describes the pretreatment method according to the embodiment.

[0022] However, used absorbent articles are absorbent articles that have been used by a user, and include unused articles that have been discarded. An absorbent article comprises a surface sheet, a backing sheet, and an absorbent material sandwiched between the two sheets, the absorbent material containing a superabsorbent polymer and may further contain pulp fibers. Examples of absorbent articles include disposable diapers, incontinence pads, sanitary napkins, bed sheets, and pet sheets.

[0023] Figure 1 is a flowchart illustrating an example of a pretreatment method according to this embodiment. The pretreatment method is a method of pretreatment in which moisture absorbed by the used absorbent article (preferably including any attached dirt) is removed from the used absorbent article before it is introduced into the recycling process. However, the recycling process is a process in which the used absorbent article is subjected to a process for recycling the materials that make up the used absorbent article. There are no particular restrictions on the recycling process, but for example, a method described in Japanese Patent Application Publication No. 2020-183585, which separates and recovers film, superabsorbent polymer, and pulp fibers from a used absorbent article, can be cited. Note that if this method is used as the recycling process, the perforation process is not necessary.

[0024] The pretreatment method comprises an introduction step S1, an inactivation step S2, and a removal step S3. The introduction step S1 is a step of introducing a plurality of used absorbent articles and a strongly acidic aqueous solution into a treatment tank. However, each of the plurality of used absorbent articles is in the state it was in when it was recovered, and the liquid level of the acidic aqueous solution is lower than the top of the plurality of used absorbent articles that are not floating. Next, in the inactivation step S2, while maintaining the plurality of used absorbent articles in the treatment tank in the state it was in when it was recovered, the acidic aqueous solution is impregnated into each of the plurality of used absorbent articles by repeatedly applying and releasing pressure in the acidic aqueous solution. Next, the removal step S3 removes water from the plurality of used absorbent articles.

[0025] Here, "the state in which used absorbent material was collected" means that the used absorbent material has not changed in shape since it was transported from the place of use (e.g., hospital, nursing home, home, etc.) or collection place (e.g., a dedicated collection point, a town garbage collection point, etc.) to the place where the pre-treatment method is carried out. Specifically, this means that the used absorbent material and its components have not been damaged (e.g., broken, crushed, shredded), separated, or dismantled since they were collected. Therefore, this excludes, for example, reduction in size, expansion, or deformation due to compression or discharge (release) of attached and absorbed excrement. Note that "the state in which used absorbent material was collected" includes "a rolled-up state." "A rolled-up state" means that the used absorbent material is generally rolled up, either by rolling or folding, with the surface sheet on which the excrement was excreted facing inward, in order to suppress the excrement from adhering to the surroundings or the odor from spreading to the surroundings. There are no particular restrictions on how the material is rolled up or folded, but it is preferable that the tape attached to the absorbent material maintains its rolled state.

[0026] In the introduction step S1, the strongly acidic aqueous solution introduced inactivates and dehydrates the superabsorbent polymer contained in the used absorbent article. The pH of the strongly acidic aqueous solution is preferably 2.0 as the upper limit and 0.5 as the lower limit. An acidic aqueous solution with a pH of 2.0 or lower can sufficiently inactivate and dehydrate the superabsorbent polymer even when the used absorbent article is recovered, especially in a rolled-up state, and even with a small amount of acidic aqueous solution, and can also have high sterilization capacity. In other words, even in situations where it is difficult for the acidic aqueous solution to spread, 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 treatment during wastewater treatment. Note that pH changes with water temperature, so the pH in this invention is the pH measured at an aqueous solution temperature of 20°C.

[0027] The amount of acidic aqueous solution 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. However, the top of the multiple used absorbent articles refers to the uppermost part of the uppermost used absorbent article among the multiple used absorbent articles that are not floating in the acidic aqueous solution in the treatment tank. The position of the top of the multiple used absorbent articles and the liquid level shall be determined by considering the multiple used absorbent articles as a single unit, and arranging the multiple used absorbent articles that make up its upper surface so that they are roughly horizontal. Roughly horizontal means that the unevenness of its upper surface is within ±2 units of the number of used absorbent articles 2.

[0028] Examples 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, but sulfuric acid is preferred from the viewpoint of not containing chlorine and cost. Examples of organic acids include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, ascorbic acid, etc., but citric acid is preferred. Due to the chelating effect of citric acid, metal ions and other substances in excrement can be trapped and removed, and due to the cleaning effect of citric acid, a high level of dirt removal effect can be expected. In this embodiment, sulfuric acid is used as the inorganic acid.

[0029] The acid concentration of an acidic aqueous solution is not particularly limited as long as it satisfies the above pH. The acid concentration of an acidic aqueous solution of an inorganic acid is not particularly limited, but when the inorganic acid is sulfuric acid, it is preferably 0.1 to 2.0% by mass or less, and more preferably 0.15 to 1.5% by mass. The acid concentration of an acidic aqueous solution of an organic acid is not particularly limited, but when the organic acid is citric acid, it is preferably 0.5 to 4% by mass, and more preferably 0.8 to 3% by mass.

[0030] In the inactivation process S2, pressure is repeatedly applied to and released from the used absorbent article. Specifically, in the initial operation, the application of pressure releases gas (e.g., air) from inside the used absorbent article to the outside, and along with the released gas, the excrement attached to the used absorbent article is pushed out. Subsequently, the release of pressure causes the external liquid (e.g., acidic aqueous solution) to be absorbed into the inside by the suction force that occurs as the used absorbent article returns to its original shape. Furthermore, in the subsequent operation, the application of pressure releases gas and liquid (e.g., water released by inactivation with an acidic aqueous solution) from inside the used absorbent article to the outside, and along with the released gas and liquid, the excrement attached to the used absorbent article is pushed out. Subsequently, the release of pressure causes the external liquid (e.g., acidic aqueous solution) to be absorbed into the inside. This process allows used absorbent materials to be maintained in the same condition as when they were collected, while simultaneously impregnating them with an acidic aqueous solution, thereby expelling the waste inside. Furthermore, the gases and liquids released from the used absorbent materials by applying pressure can also push out any waste attached to them.

[0031] In removal step S3, the acidic aqueous solution (including water discharged from the used absorbent material) inside the treatment tank is discharged, and acidic aqueous solution (including water discharged from the used absorbent material) contained in the nonwoven fabric and pulp fibers of the used absorbent material is discharged using, for example, centrifugal force or pressure. At this time, along with the acidic aqueous solution (including water discharged from the used absorbent material) discharged from the used absorbent material, it is also possible to push out any excrement attached to the used absorbent material. Furthermore, the used absorbent material may be washed in water while maintaining its condition as when it was recovered, and then the water may be removed from the used absorbent material at least once.

[0032] In this embodiment of the pretreatment method, in the introduction step S1, the liquid level of the acidic aqueous solution is lower than the top of the multiple used absorbent articles placed in the treatment tank. Therefore, considering the amount of used absorbent articles, the amount of acidic aqueous solution is relatively small. This suppresses the amount of wastewater generated in this pretreatment method. At the same time, the small amount of acidic aqueous solution suppresses the occurrence of issues that may arise during the inactivation step S2, such as the used absorbent articles being separated and dismantled by the force of the water flow of the acidic aqueous solution, which would prevent the used absorbent articles from being maintained in the same condition as when they were recovered. Furthermore, in the inactivation step S2, by repeatedly applying and releasing pressure to the used absorbent article, the inside of the used absorbent article can be impregnated with an acidic aqueous solution. Since a strongly acidic aqueous solution is used, even with a small amount of acidic aqueous solution, the superabsorbent polymer inside the used absorbent article can be reliably inactivated, and the moisture inside (e.g., urine) can be released to the outside, thus dehydrating the article. As a result, by finally removing the moisture from the used absorbent article in the removal step S3, the used absorbent article can be made lighter while maintaining its condition as when it was recovered. Furthermore, in the inactivation process S2, when the moisture inside the superabsorbent polymer is released to the outside, it can push out and discharge the excrement attached to the inside and surface (including the surface of the surface sheet, etc.) of the used absorbent article in the state it was in when it was recovered. In this case, the used absorbent article can be made lighter while maintaining its state in the state it was in when it was recovered. Thus, in the pretreatment method for used absorbent articles (comprising S1 to S3), it is possible to lighten the used absorbent articles while maintaining their condition as when they were recovered, using a small amount of acidic aqueous solution. This makes the used absorbent articles easier to handle, and allows for hygienic transport and storage for the recycling process. Furthermore, it reduces the amount of wastewater and the diffusion of excrement, enabling a more hygienic and environmentally friendly recycling process.

[0033] It is not necessary for all of the multiple used absorbent articles to be in the same condition as when they were collected. From the viewpoint of suppressing the impact of used absorbent articles that are not in the same condition as when they were collected on used absorbent articles that are in the same condition as when they were collected (for example, suppressing damage to used absorbent articles), it is preferable that 90% or more of the multiple used absorbent articles are in the same condition as when they were collected, and more preferably 95% or more. In this embodiment, 100% are in the same condition. There are no particular restrictions on the proportion of the multiple used absorbent articles that are in a rolled-up state, but for example, it is preferable that 90% or more are in the same condition as when they were collected, and more preferably 95% or more. In this embodiment, 100% are in the same condition.

[0034] In the inactivation step S2, pressure may be repeatedly applied and released to each of the multiple used absorbent articles by bumping the multiple used absorbent articles against each other. There are no particular restrictions on the method of bumping the multiple used absorbent articles against each other; for example, this could be done by stirring an acidic aqueous solution in the treatment tank or by oscillating or rotating the treatment tank. This makes it possible to easily and reliably apply and release pressure to the used absorbent articles and impregnate them with the acidic aqueous solution in the inactivation step S2 while maintaining them in the state they were in when they were recovered.

[0035] Figure 2 is a schematic diagram showing an example of the configuration of a pretreatment apparatus according to the embodiment. There are no particular limitations on the means for realizing the pretreatment method (introduction step S1, inactivation step S2, and removal step S3), but in this embodiment, the pretreatment apparatus 1 shown in the figure is used.

[0036] The pretreatment device 1 is a washing device having a horizontal (or inclined with respect to the horizontal) rotating drum as a processing tank 10. The rotating drum (processing tank 10) has a horizontal surface CH including its rotation axis X and a vertical surface CV including its rotation axis X, and comprises an outer tank 12 capable of holding / discharging liquid, and an inner tank 11 rotatably arranged inside the outer tank around the rotation axis X and having numerous holes (not shown) in its peripheral wall. An example of such a device is a fully automatic water washing and dewatering machine.

[0037] The introduction step S1 using the pretreatment device 1 in this embodiment will now be described. In the introduction step S1, an 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.

[0038] While there are no particular restrictions on the arrangement of the multiple used absorbent articles 2 within the inner tank 11, as shown in Figure 2, it is preferable that, when viewed as a single unit, the multiple used absorbent articles constituting the upper surface of the unit are arranged along a plane that is roughly parallel to the horizontal plane CH. "Roughly parallel to the horizontal plane CH" means that the irregularities on the upper surface of the unit are within ±2 units of the number of used absorbent articles 2. This is from the viewpoint of ensuring that the pressure applied and relieved to the multiple used absorbent articles 2 are roughly the same during the inactivation process S2.

[0039] Furthermore, although there are no particular restrictions on the amount of multiple used absorbent articles 2 in the inner tank 11, it is preferable to arrange them so that they are located below the horizontal plane CH, as shown in Figure 2. If a large amount of multiple used absorbent articles 2 is placed in the inner tank 11, exceeding the horizontal plane CH, it becomes difficult to apply and relieve pressure to the multiple used absorbent articles 2 in roughly the same way during the inactivation step S2, and it also becomes difficult to distribute the acidic aqueous solution WA to the multiple used absorbent articles 2 in roughly the same way.

[0040] The amount of acidic aqueous solution WA is such that the liquid level WL of the acidic aqueous solution WA is at least lower than the uppermost part 2TE of the multiple used absorbent articles 2 that are not suspended. However, the uppermost part 2TE of the multiple used absorbent articles 2 refers to the uppermost part of the uppermost used absorbent article 2T among the multiple used absorbent articles 2 that are not suspended in the acidic aqueous solution WA within the inner tank 11. In other words, the uppermost part refers to the uppermost part of the uppermost used absorbent article 2T among the multiple used absorbent articles 2 that are not suspended and constitute the upper surface of the multiple used absorbent articles 2 when viewed as a single unit.

[0041] In the example shown in Figure 2, the uppermost used absorbent article 2T, 2TE, is positioned at a height d1 from the deepest point of the inner tank 11. On the other hand, the liquid level WL of the acidic aqueous solution WA is positioned at a height d2 from the deepest point of the inner tank 11. Therefore, d1 > d2, and the liquid level WL of the acidic aqueous solution WA is lower than the uppermost 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 suppress the separation and disintegration of the used absorbent articles 2 from their recovered state due to the force of the water flow of the acidic aqueous solution WA. Note that the horizontal plane CH is positioned at a height D1 / 2 from the deepest point of the inner tank 11 relative to the inner diameter D1 of the inner tank 11, and D1 / 2 > d1, meaning that the multiple used absorbent articles 2 are located below the horizontal plane CH. Pressure can be applied / released in roughly the same way to the multiple used absorbent articles 2, making it easier to distribute the acidic aqueous solution WA.

[0042] Preferably, the liquid level WL of the acidic aqueous solution WA is positioned so that approximately 3 / 5 to 4 / 5 (number) of the multiple used absorbent articles 2 are immersed (submerged). That is, 1 / 5 to 2 / 5 (number) of the multiple used absorbent articles 2 do not need to be immersed. By using a smaller amount of acidic aqueous solution WA for multiple used absorbent articles 2 in this way, the amount of wastewater can be further reduced. Furthermore, by using a smaller amount of acidic aqueous solution WA, phenomena such as the used absorbent articles 2 being separated and disintegrated from their recovered state by the force of the water flow of the acidic aqueous solution WA that may occur during the inactivation process S2 can be further suppressed. As a result, the superabsorbent polymers of the multiple used absorbent articles 2 can be inactivated and dewatered while maintaining the recovered state, and thus the weight of the multiple used absorbent articles 2 can be reduced. Note that 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 there is a risk that the multiple used absorbent articles 2 cannot be sufficiently inactivated. On the other hand, if the liquid level WL of the acidic aqueous solution WA is too high, the large volume of aqueous solution may cause the rolled-up state of the used absorbent material 2 to break down, potentially leading to separation and disintegration.

[0043] In the example shown in Figure 2, assuming that the used absorbent articles 2 are arranged at approximately the same number density (number of items 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 submerged.

[0044] The weight of the acidic aqueous solution WA is preferably 2 to 5 times the weight of the multiple used absorbent articles 2 (including excrement), and more preferably 2 to 3 times. By using a relatively small amount of acidic aqueous solution WA relative to the multiple used absorbent articles 2, the amount of wastewater can be reduced. Furthermore, by using a small amount of acidic aqueous solution WA, it is possible to suppress phenomena such as the used absorbent articles 2 being separated and disintegrated from their recovered state by the force of the water flow of the acidic aqueous solution WA that may occur during the inactivation process S2. As a result, the multiple used absorbent articles 2 can be maintained in their recovered state while their superabsorbent polymers are inactivated and dewatered, and thus the weight of the multiple used absorbent articles 2 can be reduced. If the amount of acidic aqueous solution WA is too small, the acidic aqueous solution WA may not sufficiently reach the multiple used absorbent articles 2, and there is a risk that the multiple used absorbent articles 2 cannot be sufficiently inactivated. On the other hand, if the amount of acidic aqueous solution WA is too large, separation and disintegration by the water flow will occur more easily, and the amount of alkaline chemicals required for neutralization treatment during wastewater treatment will increase.

[0045] The temperature of the acidic aqueous solution WA is not particularly limited as long as the inactivation reaction proceeds in the inactivation step S2. The temperature may be at room temperature or higher than room temperature, for example, 15 to 30°C. Also, the time for treating the used absorbent article in the acidic aqueous solution in the inactivation step S2 is not particularly limited as long as the superabsorbent polymer is inactivated and dehydrated, for example, 1 to 60 minutes, and preferably 5 to 30 minutes.

[0046] Next, the inactivation step S2 using the pretreatment device 1 in this embodiment will be further described. In the inactivation step S2, the multiple used absorbent articles 2 placed in the inner tank 11 are moved within the inner tank 11 by rotating the inner tank 11 at a predetermined speed in the forward direction (with pauses possible) or in the forward and reverse directions. In the example in Figure 2, before operation, the liquid level WL of the acidic aqueous solution WA is at a position where approximately 2 / 3 (number) of the multiple used absorbent articles 2 are submerged. During operation, the multiple used absorbent articles 2 and the acidic aqueous solution WA move within the inner tank 11, so that each used absorbent article 2 is submerged in the acidic aqueous solution WA not simultaneously, but generally periodically.

[0047] In this case, the inner tank 11 of the processing tank 10 is divided vertically into three regions (with the same vertical width) roughly: an upper region, an intermediate region, and a lower region. At that time, for example, at the beginning of the operation, multiple used absorbent articles 2 are accumulated roughly in the lower region of the inner tank 11. Subsequently, each used absorbent article 2, due to the rotation of the inner tank 11, rolls along the inner wall of the inner tank 11, reaches a height near the intermediate region, and then rolls down onto other multiple used absorbent articles 2 located in the lower region, and this process is repeated. As a result, while rolling along the inner wall of the inner tank 11 and reaching a height near the intermediate region, adjacent used absorbent articles 2 collide with each other, and when rolling down onto multiple used absorbent articles 2 located in the lower region, adjacent used absorbent articles collide with each other. Due to these collisions and other actions, pressure is repeatedly applied to and released from the used absorbent articles 2. Furthermore, the rotation speed of the inner tank 11 is adjusted appropriately to prevent the used absorbent material 2 from reaching the upper region and then free-falling (slamming) down to the lower region due to gravity. If the rotation speed is too fast and the material starts free-falling, the pressure on the used absorbent material 2 will be too great, causing it to separate and break down.

[0048] Here, there are no particular restrictions on the cycle of repeated pressure application and release, as long as the used absorbent material 2 maintains the state it was in when it was recovered. For example, when the inner tank 11 (inner diameter 1000 mmφ) is rotated in the forward direction, the rotational speed can be greater than 20 rpm and less than 35 rpm. In this case, the cycle of repeated pressure application and release in the used absorbent material 2 is not necessarily clear and is not particularly restricted (it does not have to be constant). For example, if we consider the cycle to be roughly the time it takes for the inner tank 11 to complete one rotation, it can be considered to be about 1.7 to 2.4 seconds. Also, for example, when the inner tank 11 (inner diameter 1000 mmφ) is rotated back and forth in the forward and reverse directions, the rotational speed can be greater than 20 rpm and less than 35 rpm, and the cycle of the reciprocating rotational motion of the inner tank 11 in the forward and reverse directions can be about 2 to 6 seconds. In this case as well, the cycle of repeated pressure application and release in the used absorbent material 2 is not necessarily clear and is not particularly restricted (it does not have to be constant). For example, if we consider the period to be the time required for the inner tank 11 to perform reciprocating rotational motion in both forward and reverse directions, it can be estimated to be approximately 2 to 6 seconds. Note that the time in the forward direction and the time in the reverse direction may differ within one period of the reciprocating rotational motion of the inner tank 11. For example, the time in one direction may be approximately 1.2 to 2 times longer than the time in the other direction.

[0049] In this way, by repeatedly applying and releasing pressure to each used absorbent article 2 in the acidic aqueous solution WA in the treatment tank 10, while maintaining the multiple used absorbent articles 2 in the same state as when they were recovered, the acidic aqueous solution can be impregnated into the interior of each used absorbent article 2. This allows the superabsorbent polymer of each used absorbent article 2 to be dehydrated. In addition, the excrement attached to each used absorbent article 2 can be discharged along with the dehydration of the superabsorbent polymer.

[0050] Next, the removal step S3 using the pretreatment device 1 in this embodiment will be further explained. In the preceding inactivation step S2, the water (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 water (e.g., acidic aqueous solution, water discharged from the superabsorbent polymer). For example, the pulp fibers and nonwoven fabrics of each used absorbent article contain water. Therefore, in the removal step S3, the water contained in each used absorbent article 2 is removed.

[0051] In the removal step S3, specifically, 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, 100 rpm). By centrifugal force, the moisture contained in each used absorbent article 2 can be removed via the outer tank 12. As a result, not only is the moisture of the superabsorbent polymer dehydrated in the inactivation step S2, but the moisture of multiple used absorbent articles 2 can be removed overall in the removal step S3, resulting in multiple lighter used absorbent articles 2.

[0052] Here, the dewatering rate of the multiple used absorbent articles after the removal process S3 is preferably 40% or more, more preferably 60% or more, and even more preferably 65% ​​or more. However, the dewatering rate is calculated using the following formula. Dehydration rate (%) ={1-(mass of multiple used absorbent materials after pretreatment - mass of multiple unused absorbent materials) / (mass of multiple used absorbent materials before pretreatment - mass of multiple unused absorbent materials)}×100 = {1 - (Mass of moisture in multiple used absorbent articles after pretreatment) / (Mass of moisture in multiple used absorbent articles before pretreatment)} × 100 That is the case.

[0053] Thus, in this pretreatment method, the dewatering rate of the multiple used absorbent articles 2 after the removal step S3 is 40% or more. Therefore, this pretreatment method allows for extremely effective inactivation and dewatering of the multiple used absorbent articles 2 in the same condition as when they were recovered, and for very effective weight reduction. This enables hygienic transport and storage of the used absorbent articles 2 for the recycling process. Furthermore, it reduces the amount of wastewater and the diffusion of excrement, resulting in a more hygienic and environmentally friendly recycling process. In addition, in the removal step S3, water (which may also contain cleaning agents or disinfectants) 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.

[0054] The multiple lightweight used absorbent articles 2 obtained after the removal step S3 of this pretreatment method are transferred to the recycling process.

[0055] In this embodiment, there are no particular restrictions on the method for carrying out the inactivation step S2, as long as it is possible to repeatedly apply and release pressure in an acidic aqueous solution to each of the multiple used absorbent articles. For example, the following method can be considered.

[0056] One example of this method is to use a vertical rotating drum as the processing tank. The processing tank (rotating drum) comprises an outer tank capable of holding liquid and an inner tank rotatably positioned inside the outer tank and having numerous holes in its peripheral wall. Multiple used absorbent articles are placed in the inner tank, and the inner tank is rotated at a predetermined speed in the forward direction (with pauses in between) or in the forward and reverse directions, thereby moving the 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. On the other hand, during operation, as the multiple used absorbent articles or the acidic aqueous solution move within the processing tank, each used absorbent article is immersed in the acidic aqueous solution not simultaneously, but generally periodically.

[0057] In this case, the processing tank of the vertical rotating drum is divided vertically into roughly upper, middle, and lower regions. At that time, for example, in the initial stages of operation, multiple used absorbent materials accumulate in the lower region of the rotating drum. Subsequently, as the inner tank rotates, each used absorbent material is moved toward the inner wall of the inner tank by centrifugal force due to the rotation, and some are further moved toward the middle and upper regions, where they are pressed against the inner wall or other used absorbent materials, applying pressure. During periods of rotation pause or reversal, the centrifugal force disappears and the pressure is relieved. In this way, the used absorbent materials are repeatedly subjected to pressure application and release due to the collision action between the used absorbent materials, the inner wall, and other used absorbent materials. At that time, the rotation speed of the rotating drum is adjusted as appropriate to prevent the pressure applied to the used absorbent materials from becoming too high and causing them to separate or break down.

[0058] Another example of this method involves periodically applying pressure to multiple used absorbent materials placed in a treatment tank by pressing a flat plate-shaped member against them from above, and then releasing the pressure by pulling the flat plate-shaped member upwards. In this case, it is not necessary for all of the multiple used absorbent materials to be submerged in the acidic solution before the operation. During the operation, the multiple used absorbent materials or the acidic solution move within the treatment tank so that each used absorbent material is submerged in the acidic solution, not simultaneously, but generally periodically. In this way, the used absorbent materials are repeatedly subjected to pressure application and release through the action of collisions between the used absorbent materials and the inner wall, the flat plate-shaped member, and other used absorbent materials. At that time, the pressure applied to the flat plate-shaped member is adjusted as appropriate to prevent the pressure applied to the used absorbent materials from being too high and causing them to separate or disintegrate.

[0059] Another example of this method involves moving a treatment tank containing multiple used absorbent materials back and forth horizontally. This applies pressure by pressing the materials against one or the other inner wall, and then releasing the pressure between the inner walls (during the reciprocating motion). In this case, it is not necessary for all of the used absorbent materials to be immersed in the acidic solution before operation. During operation, when pressure is applied, the multiple used absorbent materials or the acidic solution move within the treatment tank, so that each used absorbent material is immersed in the acidic solution not simultaneously, but generally periodically. In this way, the pressure on the used absorbent materials is repeatedly applied and released due to the collision between the used absorbent materials, the inner wall, and other used absorbent materials. At that time, the speed of the reciprocating motion of the treatment tank is adjusted as appropriate to prevent the pressure applied to the used absorbent materials from becoming too high and causing them to separate or disintegrate.

[0060] There are no particular restrictions on the method for removing moisture contained in each used absorbent article 2, as long as the moisture can be removed.

[0061] For example, when using a vertical rotating drum as the processing tank, the acidic aqueous solution is discharged from the processing tank (outer tank), and then the processing tank (inner tank) is rotated, allowing the moisture contained in each used absorbent article to be removed via the outer tank by centrifugal force. When using a processing tank with a flat plate-shaped member, the acidic aqueous solution is discharged from the processing tank, and then the flat plate-shaped member presses multiple used absorbent articles against the inner wall of the processing tank, thereby removing the moisture contained in each used absorbent article. For example, when using a processing tank that reciprocates horizontally, the acidic aqueous solution is discharged from the processing tank, and then the processing tank is moved horizontally back and forth, thereby removing the moisture contained in each used absorbent article. [Examples]

[0062] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0063] (1) Sample As samples of absorbent materials, a total of five types were used: two types of unused infant diapers and three types of unused adult diapers. The weight of each diaper was measured (weight before use). Next, to simulate "used" conditions, 300g of 0.9% physiological saline solution was absorbed into each diaper, and they were rolled up. After that, the weight of each diaper was measured again (weight after use, before processing). For the multiple disposable diapers used in the examples and comparative examples, five types of disposable diapers were prepared for each example and comparative example, with an equal number of each type (for example, 30 diapers x 5 types, pre-use weight: approximately 8.6 kg). In infant disposable diapers, the proportion of superabsorbent polymer in the absorbent material was approximately 50%, while in adult disposable diapers, the proportion of superabsorbent polymer in the absorbent material was approximately 30%.

[0064] (2) Pretreatment The pretreatment method was carried out for each example and comparative example using a fully automatic water-washing and dewatering machine (inner diameter: 1000 mmφ). For the examples and comparative examples, the conditions for the acidic aqueous solution and inactivation step of the pretreatment method described above were varied. However, those carried out according to the conditions of the pretreatment method described above were designated as examples, and those carried out under conditions that differed in some respects were designated as comparative examples.

[0065] (3) Results The results are shown in Table 1 below. However, in Table 1, "acidic aqueous solution" refers to the conditions related to the acidic aqueous solution, and "amount added" 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 percentage of disposable diapers that are immersed in the sulfuric acid aqueous solution (below the liquid surface) out of multiple disposable diapers during the introduction process.

[0066] In Table 1, the "Inactivation Process" section lists the conditions for the inactivation process, with "Rotation Speed" indicating the rotation speed of the inner tank. "Processing Time" indicates the time for processing disposable diapers in the sulfuric acid solution. "Forward or Forward-Reverse Time" indicates the periods when the inner tank alternates between forward rotation and stopping, or when it alternates between forward and reverse rotation, within the processing time.

[0067] In Table 1, the results for "disposable diapers" include information on pretreatment methods, with "weight before use" indicating 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 before use and before the pretreatment method is performed. "Weight after treatment" indicates the weight of multiple disposable diapers after the pretreatment method is performed, and "moisture content before treatment" indicates the percentage of moisture contained in multiple disposable diapers before use and before the pretreatment method is performed (relative to the weight before use). "Dehydration rate" indicates the percentage of moisture contained in multiple disposable diapers after the pretreatment method is performed (relative to the moisture contained in multiple disposable diapers before the pretreatment method is performed). "Rolled state" indicates that of the multiple disposable diapers after the pretreatment method, if 90% or more of the diapers remained in a rolled state (the state when collected) (less than 10% of the diapers were partially damaged), it is indicated with "○", and if it is less than 90% (10% or more), it is indicated with "X". The "X" in "Post-processing weight" indicates that part of the diaper burst, separated, and fell apart, making it impossible to properly measure the post-processing weight. The "X" in "Dehydration rate" indicates that, due to the inability to measure the post-processing weight, the dehydration rate could not be calculated.

[0068] [Table 1]

[0069] In Examples 1-3, more than 90% (actually 100%) of the diapers remained rolled up after the pretreatment method was applied. Furthermore, a dewatering rate exceeding 40% was achieved. On the other hand, in Comparative Examples 1-4, less than 90% of the diapers remained rolled up after the pretreatment method was applied. Furthermore, the dewatering rate was low, or many of the used absorbent materials were damaged, separated, and disintegrated during the treatment process, preventing the achievement of the desired dewatering rate. Specifically, in Comparative Example 1, the sulfuric acid concentration in the acidic aqueous solution was low (high pH), which failed to completely inactivate the superabsorbent polymer in the diaper. As a result, the superabsorbent polymer absorbed the acidic aqueous solution diluted with saline solution discharged from the diaper. In Comparative Example 2, reducing the amount of diapers suppressed the dilution of the acidic aqueous solution, but the rolled-up diapers were hardly dewatered, resulting in a low dewatering rate. In Comparative Example 3, the sulfuric acid concentration was increased (pH was lowered) to the same level as in Example 1, and the treatment time was doubled to 20 minutes. As a result, the diapers were partially damaged, and pulp fibers and superabsorbent polymers were released into the treatment tank. In Comparative Example 4, the amount of diapers was increased, the sulfuric acid concentration was further increased (pH was further increased), and the amount of sulfuric acid solution was increased. As a result, the amount of solid matter in the treatment tank was large, and the load on the lower diapers during the inactivation process became too great, causing the diapers to be partially damaged, and pulp fibers and superabsorbent polymers to be released into the treatment tank. Although not shown in the Examples and Comparative Examples, if the liquid level of the acidic solution was above the top of the diapers, i.e., if the amount of acidic solution was too large, many diapers would float on the liquid surface, making it difficult to carry out the pretreatment method.

[0070] The pretreatment method of the present invention is not limited to the embodiments described above, and can be modified or combined with prior art as appropriate without departing from the purpose and spirit of the present invention. [Explanation of Symbols]

[0071] S1 introduction process S2 inactivation process S3 removal process

Claims

1. A pretreatment method for removing dirt and absorbed moisture attached to used absorbent articles containing a superabsorbent polymer, An introduction step in which multiple used absorbent articles and a strongly acidic aqueous solution are introduced into a treatment tank, wherein each of the multiple used absorbent articles is in the state it was in when it was recovered, and the liquid level of the acidic aqueous solution is lower than the top of the multiple used absorbent articles that are not floating. Within the treatment tank, the plurality of used absorbent articles are maintained in the state they were in when recovered, and an inactivation step is performed in which each of the plurality of used absorbent articles is impregnated with the acidic aqueous solution by repeatedly applying and releasing pressure in the acidic aqueous solution. A removal step of removing moisture from the plurality of used absorbent articles, It is equipped with, The aforementioned processing tank is a horizontal rotating drum, The inactivation step includes a step of applying and releasing pressure by causing each of the multiple used absorbent articles to collide with each other, while adjusting the rotation speed of the rotating drum so that each of the multiple used absorbent articles does not reach the upper region when the rotating drum is divided vertically into an upper region, an intermediate region, and a lower region, and alternating between forward rotation and stopping of the rotating drum, or by alternating between forward rotation and reverse rotation. Pre-treatment method.

2. In the introduction step, the liquid level of the acidic aqueous solution is at a position where 3 / 5 to 4 / 5 of the plurality of used absorbent articles are immersed. The pretreatment method according to claim 1.

3. In the introduction step, the weight of the acidic aqueous solution is two to three times the weight of the multiple used absorbent articles in the treatment tank. The pretreatment method according to claim 1 or 2.

4. In the aforementioned introduction step, the pH of the acidic aqueous solution is 2.0 or less. The pretreatment method according to any one of claims 1 to 3.

5. In the aforementioned introduction step, the acidic aqueous solution contains sulfuric acid. The pretreatment method according to any one of claims 1 to 4.

6. The dewatering rate of the plurality of used absorbent articles after the removal step, relative to the plurality of used absorbent articles before performing the aforementioned pretreatment method, is 40% or more. The pretreatment method according to any one of claims 1 to 5.

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