AU2018360432B2

AU2018360432B2 - Method and system for recovering pulp fibers and highly water-absorbent polymer from used absorbent articles

Info

Publication number: AU2018360432B2
Application number: AU2018360432A
Authority: AU
Inventors: Toshio HIRAOKA; Takashi Kato; Takayoshi Konishi; Noritomo Kurita
Original assignee: Unicharm Corp
Current assignee: Unicharm Corp
Priority date: 2017-11-01
Filing date: 2018-07-26
Publication date: 2022-10-20
Anticipated expiration: 2038-07-26
Also published as: KR20200076664A; CN111263670A; JP6843030B2; RU2020117217A; KR102559361B1; BR112020008506A2; AU2018360432A1; BR112020008506B1; CN111263670B; RU2020117217A3; PH12020550527A1; WO2019087485A1; JP2019084470A

Abstract

Provided is a method that, when pulp fibers and a highly water-absorbent polymer are to be recovered from used absorbent articles, makes it possible to highly efficiently separate the pulp fibers and the highly water-absorbent polymer. This method comprises: a deactivation step (S13) in which pulp fibers and a highly water-absorbent polymer that have been separated from used absorbent articles are mixed with an acidic aqueous solution and the highly water-absorbent polymer is deactivated, the acidic aqueous solution having been adjusted to a pH at which the respective differences between the specific gravity and size of the highly water-absorbent polymer and the specific gravity and size of the pulp fibers are within prescribed ranges; a size separation step (S15) in which, in the acidic aqueous solution that includes the pulp fibers and the highly water-absorbent polymer, while pH is maintained within a prescribed range, difference in size is used to separate the pulp fibers and the highly water-absorbent polymer from other materials; and a specific gravity separation step (S16) in which, in the acidic aqueous solution that includes the pulp fibers and the highly water-absorbent polymer, while pH is maintained within a prescribed range, difference in specific gravity is used to separate the pulp fibers and the highly water-absorbent polymer from the other materials.

Description

I DESCRIPTION TITLE METHOD AND SYSTEM FOR RECOVERING PULP FIBERS AND HIGHLY WATER ABSORBENT POLYMER FROM USED ABSORBENT ARTICLES FIELD

[0001] The present invention relates to a method and a system of recovering pulp fibers and superabsorbent polymers from a used absorbent article.

BACKGROUND

[0002] A method of recovering pulp fibers and superabsorbent polymers from a used absorbent article such as a disposable diaper, etc., is known. For example, Patent Literature 1 discloses a method of separating and recovering fibers and superabsorbent polymers from used diapers. In this method, first, used diapers are thrown into a pulper, are dispersed in water, so that slurry is produced. Subsequently, the slurry is processed by a screen and a cleaner, whereby the superabsorbent polymers are recovered. Subsequently, the dispersion solution which includes the fibers that are the remaining portion is processed by a washing machine / a dehydrating machine and a cleaner, whereby the fibers are recovered.

[CITATION LIST] [PATENT LITERATURE]

[0003]

[PTL 1] International Publication No. W02014 / 007105A1

SUMMARY [TECHNICAL PROBLEM]

[0004] According to the method of Patent Literature 1, from the mixture of the superabsorbent polymers, the fibers and the other materials of the used diapers, first, the superabsorbent polymers are separated and recovered, and then, the fibers are separated and recovered from the mixture of the fibers and the other materials. Accordingly, in both cases, the superabsorbent polymers / the pulp fibers are separated from the mixture in which the other materials are mixed. Accordingly, in order to obtain superabsorbent polymers and pulp fibers which hardly include the other materials, a precise separation needs to be performed for each of the separation of the superabsorbent polymers and the separation of the pulp fibers. In such a case, it takes longer for the separation process, and there is a risk that the efficiency of the separation process is lowered. Accordingly, when recovering the pulp fibers and the superabsorbent polymers from used absorbent articles, there is room for improvement from the viewpoint of improving the efficiency of the separation process. A technique which enables the separation of superabsorbent polymers and pulp fibers with a high processing efficiency when recovering pulp fibers and superabsorbent polymers from a used absorbent article is desired.

[0005] A potential advantage of the present invention is to provide a method and a system which can separate superabsorbent polymers and pulp fibers with a high processing efficiency when recovering pulp fibers and superabsorbent polymers from a used absorbent article.

[SOLUTION TO PROBLEM]

[0006] The method of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers according to the present invention is as follows. (1) A method of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the method comprising: an inactivation process of inactivating superabsorbent polymers by mixing pulp fibers and superabsorbent polymers which are separated from the used absorbent article, and an acidic aqueous solution which is adjusted with pH so that a difference between a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range and a difference between a size of the superabsorbent polymers and a size of the pulp fibers is within a predetermined range; a size separation process of, while maintaining the pH within a predetermined range in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from other materials by using a difference in a size; and a specific gravity separation process of, while maintaining the pH within the predetermined range in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from the other materials by using a difference in a specific gravity. Generally, the specific gravity of superabsorbent polymers is larger than that of water, and when the superabsorbent polymers absorb water, the specific gravity of superabsorbent polymers is approximated to that of water in accordance with the water absorption amount. Further, the size of each of the superabsorbent polymers is small, however, when the

-Y

superabsorbent polymers absorb water, the size thereof is enlarged in accordance with the water absorption amount. Still further, the amount of water which is absorbed and retained by the superabsorbent polymers is extremely large, however, by performing an inactivation treatment for the superabsorbent polymers, such an amount is limited to some extent. From the above, by the degree of the inactivation treatment of the superabsorbent polymers, the amount of water retained by the superabsorbent polymers is adjusted, whereby the size and the specific gravity of the superabsorbent polymers can be adjusted to the desired values. As the inactivation treatment of the superabsorbent polymers, the treatment of immersing the superabsorbent polymers in a predetermined solution (for example: an acidic aqueous solution), may be mentioned. According to the present method, in the inactivation process, the superabsorbent polymers are inactivated by the acidic aqueous solution in which pH is adjusted, the water absorption amount of the superabsorbent polymers is adjusted, whereby the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are set to be respectively within the predetermined range. In such a case, within the predetermined range is set, for example, so that one is within 0.2 to 5 times as much of the other. Accordingly, the difference between the pulp fibers and the superabsorbent polymers is set so that the specific gravity is within the predetermined range, and the size is within the predetermined range. As a result, the pulp fibers and the superabsorbent polymers are easily separated from the other materials (mainly the resin materials) except the pulp fibers and the superabsorbent polymers among the materials of the used absorbent articles by using the difference in the sizes, and from the materials with a large specific gravity (mainly the metallic materials) among the other materials by using the difference in the specific gravities. Further, thereafter, the pulp fibers and the superabsorbent polymers are separated from each other, whereby the pulp fibers and the superabsorbent polymers can be recovered from the used absorbent article. At this time, the number of processes of separating the pulp fibers and the superabsorbent polymers, and the other materials can be reduced. That is, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved. As the resin materials among the other materials of the used absorbent article except the pulp fibers and the superabsorbent polymers, films (such as the back sheet, etc.), nonwoven fabric (such as the top sheet, etc.), elastic bodies (such as rubbers for leakage prevention walls), etc., may be mentioned. As the materials of a large specific gravity among the other materials, for example, the metallic materials, clips and stapler needles, etc., which are not included in the original absorbent articles but are mixed when recovering the used absorbent articles, may be mentioned. Further, the size of the superabsorbent polymers is the particle diameter of each of the superabsorbent polymers, and in a case in which the superabsorbent polymers are spherical, the size is the diameter, and in a case in which the superabsorbent polymers are in a massive state,

_r

the size is the longest width. The size of the pulp fibers is the average fiber length of the pulp fibers. The predetermined range of pH is the range in which the variation of pH is within 1.0.

[0007] The present method may be (2) the method according to the above-mentioned (1), wherein the specific gravity separation process includes a process of separating the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method. According to the present method, the difference in the specific gravities of the pulp fibers and the superabsorbent polymers is within the predetermined range. Accordingly, by the centrifugal separation method, the pulp fibers and the superabsorbent polymers can be separated from the other materials (the materials with a large specific gravity, for example the metallic materials) more accurately. Therefore, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved.

[0008] The present method may be (3) the method according to the above-mentioned (1) or (2), wherein the size separation process includes a screen separation process of separating the pulp fibers and the superabsorbent polymers from the other materials by using a screen which includes a plurality of openings each with a predetermined size. According to the present method, the difference in the sizes of the pulp fibers and the superabsorbent polymers is within the predetermined range. Accordingly, by letting the materials pass through a screen which includes a plurality of openings each with a predetermined size, the pulp fibers and the superabsorbent polymers can be separated from the other materials (mainly the resin materials, for example, films such as the back sheet, etc., nonwoven fabric such as the top sheet, etc., rubbers for leakage prevention walls, etc.) more accurately. Therefore, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved.

[0009] The present method may be (4) the method according to any one of the above mentioned (1) to (3), further comprising, before the size separation process, a rough size separation process of, while maintaining the pH within the predetermined range in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from the other materials by letting the pulp fibers and the superabsorbent polymers pass through a screen which includes a plurality of openings each with a size larger than a size of each of a plurality of openings of a screen used in the size separation process. According to the present method, before the size separation process, by letting the materials pass through a screen which includes the openings each with a larger size, the other materials which are relatively larger can be removed. Accordingly, in the size separation process, a situation can be suppressed in which the screen is clogged by the other materials which are relatively larger and the processing efficiency of separation is lowered.

[0010] The present method may be (5) the method according to any one of the above mentioned (1) to (4), wherein a proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution which is formed in the inactivation process is 0.1 mass % or more and 10 mass % or less. According to the present method, the proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution is 0.1 mass % or more and 10 mass % or less, whereby the separation of the pulp fibers and the superabsorbent polymers from the other materials can be performed more reliably. Accordingly, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved. Note that when the proportion is set to less than 0.1 mass %, the amount of the superabsorbent polymers and the pulp fibers to be separated is too small, and the capacity of the separating process is wasted, and when the proportion is set to more than 10 mass %, the superabsorbent polymers and the pulp fibers cannot be completely separated so as to be discharged together with other materials, and thus the processing efficiency is lowered in both cases.

[0011] The present method may be (6) the method according to any one of the above mentioned (1) to (5), wherein the pH of the acidic aqueous solution is 1 or higher and 4 or lower. According to the present method, the pH of the acidic aqueous solution is adjusted to 1 or higher and 4 or lower, whereby the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0012] The present method may be (7) the method according to any one of the above mentioned (1) to (6), wherein the acidic aqueous solution includes a citric acid. According to the present method, since the acidic aqueous solution includes the citric acid (for example: the concentration of 0.5 to 2.0 mass %), the superabsorbent polymers are reliably dehydrated, and the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Further, a negative influence to the workers by acid, and

V

corrosion of equipment in each process can be suppressed. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0013] The present method may be (8) the method according to any one of the above mentioned (1) or (7), further comprising a polymer separation process of separating the superabsorbent polymers from the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers separated by the specific gravity separation process. According to the present method, since the other materials are removed from the pulp fibers and the superabsorbent polymers, by separating the pulp fibers and the superabsorbent polymers from each other, the pulp fibers and the superabsorbent polymers can be easily recovered separately.

[0014] The system which is used for recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers according to the present invention is as follows. (9) A system of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the system comprising: a screen separating machine which separates, while maintaining a pH within a predetermined range in an acidic aqueous solution which includes pulp fibers and superabsorbent polymers and in which the superabsorbent polymers are inactivated by mixing pulp fibers and superabsorbent polymers which are separated from the used absorbent article, and the acidic aqueous solution which is adjusted with the pH so that a difference between a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range and a difference between a size of the superabsorbent polymers and a size of the pulp fibers is within a predetermined range, the pulp fibers and the superabsorbent polymers from other materials by using a screen which includes a plurality of openings each with a predetermined size; and a cyclone separating machine which separates, while maintaining the pH within the predetermined range in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method. According to the present system, the superabsorbent polymers are inactivated by the acidic aqueous solution in which pH is adjusted, the water absorption amount of the superabsorbent polymers is adjusted, whereby the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are set to be respectively within the predetermined range. Accordingly, the difference between the pulp fibers and the superabsorbent polymers is set so that the specific gravity is within the predetermined range, and the size is within the predetermined range. As a result, the pulp fibers and the superabsorbent polymers are easily separated from mainly the resin materials among the other materials of the used absorbent articles except the pulp fibers and the superabsorbent polymers by using the difference in the sizes, and from the materials with a large specific gravity among the other materials, for example, the metallic materials, by using the difference in the specific gravities. Further, thereafter, the pulp fibers and the superabsorbent polymers are separated from each other, whereby the pulp fibers and the superabsorbent polymers can be recovered from the used absorbent article. At this time, the superabsorbent polymers and the pulp fibers are not individually separated from a mixture in which the other materials are mixed, whereby the number of processes of separating the pulp fibers and the superabsorbent polymers, and the other materials can be reduced. That is, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0015] The present system may be (10) the system according to the above-mentioned (9), further comprising, before the screen separating machine, a rough screen separating machine which, while maintaining the pH within the predetermined range in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separates the pulp fibers and the superabsorbent polymers from the other materials by letting the pulp fibers and the superabsorbent polymers pass through a screen which includes a plurality of openings each with a size larger than the predetermined size of each of the plurality of openings. The present system includes the rough screen separating machine before the screen separating machine, whereby by letting the materials pass through a screen which includes the openings each with a larger size, the other materials which are relatively larger can be removed before the screen separating machine. Accordingly, before the screen separating machine, a situation can be suppressed in which the screen is clogged by the other materials which are relatively larger and the processing efficiency of separation is lowered.

[0016] The present system may be (11) the system according to the above-mentioned (9) or (10), wherein a proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution which includes the inactivated superabsorbent polymers is 0.1 mass % or more and 10 mass % or less. According to the present system, the proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution is 0.1 mass % or more and 10 mass % or less, whereby the separation of the pulp fibers and the superabsorbent polymers from the other materials can be performed more reliably. Accordingly, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved. Note that when the proportion is set to less than 0.1 mass %, the amount of the superabsorbent polymers and the pulp fibers to be separated is too small, and the capacity of the separating process is wasted, and when the proportion is set to more than 10 mass %, the superabsorbent polymers and the pulp fibers cannot be completely separated so as to be discharged together with other materials, and thus the processing efficiency is lowered in both cases.

[0017] The present system may be (12) the system according to any one of the above mentioned (9) to (11), wherein the pH of the acidic aqueous solution is 1 or higher and 4 or lower. According to the present system, the pH of the acidic aqueous solution is adjusted to 1 or higher and 4 or lower, whereby the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0018] The present system may be (13) the system according to any one of the above mentioned (9) to (12), wherein the acidic aqueous solution includes a citric acid. According to the present system, since the acidic aqueous solution includes the citric acid (for example: the concentration of 0.5 to 2.0 mass %), the superabsorbent polymers are reliably dehydrated, and the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Further, a negative influence to the workers by acid, and corrosion of equipment in each process can be suppressed. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0019] The present system may be (14) the system according to any one of the above mentioned (9) to (13), further comprising a drum screen separating machine which separates the superabsorbent polymers from the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers separated by the cyclone separating machine, by a drum screen. The present system includes the drum screen separating machine, whereby the pulp fibers and the superabsorbent polymers are separated from each other, after the other materials are removed from the pulp fibers and the superabsorbent polymers, and thus the pulp fibers and the superabsorbent polymers can be easily recovered separately.

[0019A] According to a further aspect, the present invention may provide a method of recovering

01-1

pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the method comprising: an inactivation process of inactivating superabsorbent polymers by mixing pulp fibers and superabsorbent polymers which are separated from the used absorbent article, and an acidic aqueous solution which is adjusted with pH so that one of a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other and one of a size of the superabsorbent polymers and a size of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other; a size separation process of, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from other materials by using a difference in a size; and a specific gravity separation process of, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from the other materials by using a difference in a specific gravity.

[0019B] According to another aspect, the invention may provide a system of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the system comprising: a screen separating machine which separates, while maintaining a pH within a predetermined range so that one of a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other and one of a size of the superabsorbent polymers and a size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in an acidic aqueous solution which includes pulp fibers and superabsorbent polymers and in which the superabsorbent polymers are inactivated by mixing pulp fibers and superabsorbent polymers which are separated from the used absorbent article, and the acidic aqueous solution which is adjusted with the pH so that one of a the specific gravity of the superabsorbent polymers and a the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of a the size of the superabsorbent polymers and a the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, the pulp fibers and the superabsorbent polymers from other materials by using a screen which includes a plurality of openings each with a predetermined size; and a cyclone separating machine which separates, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method.

[ADVANTAGEOUS EFFECTS OF INVENTION]

[0020] According to the method and the system of the present invention, when recovering pulp fibers and superabsorbent polymers from a used absorbent article, the superabsorbent polymers and the pulp fibers can be separated with a high processing efficiency.

BRIEF DESCRIPTION OF DRAWINGS

[0021]

[FIG. 1] FIG. 1 is a block diagram which shows one example of the system according to an embodiment.

[FIG. 2] FIG. 2 is a schematic view which shows a configurational example of the rupturing device and the crushing device of FIG. 1.

[FIG. 5] FIG. 5 is a flowchart which shows one example of the method according to an embodiment.

DESCRIPTION OF EMBODIMENTS

[0022] Hereinbelow, the method of recovering pulp fibers from a used absorbent article which includes pulp fibers and superabsorbent polymers, according to an embodiment is explained. It should be noted that a used absorbent article includes an absorbent article which has been used by a user and is in a state in which excrement of the user is absorbed and retained, and further includes an absorbent article which has been used and is in a state in which excrement is not absorbed or retained, and still further includes an absorbent article which has not been used and is discarded. As an absorbent article, for example, a diaper, a urine collection pad, a sanitary napkin, a bed sheet, a pet sheet, may be mentioned. Incidentally, the method of recovering pulp fibers from a used absorbent article according to the present embodiment produces recycled pulp fibers, thus may also be regarded as a method of producing recycled pulp fibers from a used absorbent article. Further, the method of recovering pulp fibers from a used absorbent article according to the present embodiment recovers superabsorbent polymers together with the pulp fibers during the process, and produces recycled superabsorbent polymers by separation, thus may also be regarded as a method of producing recycled superabsorbent polymers from a used absorbent article. Hereinbelow, a method of recovering pulp fibers from a used absorbent article is explained.

[0023] First, the configurational example of the absorbent article is explained. The absorbent article includes a top sheet, a back sheet, and an absorbent body which is arranged between the top sheet and the back sheet. As one example of the size of the absorbent article, a length of

IU

approximately 15 to 100 cm, and a width of 5 to 100 cm, may be mentioned. Incidentally, the absorbent article may include other members which are provided in general absorbent articles, for example, a diffusion sheet, a leakage prevention wall, etc.

[0024] As the configuration member of the top sheet, for example, a liquid permeable nonwoven fabric, synthetic resin film with liquid permeable holes, a composite sheet thereof, etc., may be mentioned. As the configuration member of the back sheet, for example, a liquid impermeable nonwoven fabric, a liquid impermeable synthetic resin film, a composite sheet thereof, etc., may be mentioned. As the configuration member of the diffusion sheet, for example, a liquid permeable nonwoven fabric, etc., may be mentioned. As the configuration member of the leakage prevention wall, for example, a liquid impermeable nonwoven fabric may be mentioned, and may include an elastic member such as rubber. The material of a nonwoven fabric or a synthetic resin film is not particularly limited as long as it can be used for an absorbent article, and for example, olefin-based resin such as polyethylene, polypropylene, etc., polyamide-based resin such as 6-nylon, 6,6-nylon, etc., polyester-based resin such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc., may be mentioned. In the present embodiment, an example of an absorbent article in which the configurational member of the back sheet is a film and the configurational member of the top sheet is a nonwoven fabric is explained.

[0025] As the configurational member of the absorbent body, absorbent materials, that is, pulp fibers and superabsorbent polymers may be mentioned. The pulp fibers are not particularly limited as long as they can be used for an absorbent article, and for example, cellulose-based fibers may be mentioned. As the cellulose-based fibers, for example, wood pulp, cross-linked pulp, non-wood pulp, regenerated cellulose, semi-synthetic cellulose, etc., may be mentioned. As the size of pulp fibers, the average value of a major axis of fibers of, for example, several tens of m may be mentioned, and 20 to 40 m is preferable, and the average value offiber lengths of, for example, several mm may be mentioned, and 2 to 5 mm is preferable. The superabsorbent polymers (SAP) are not particularly limited as long as they can be used for an absorbent article, and for example, absorbent polymers of polyacrylate-based, polysulfonate-based, and maleic anhydride-based, may be mentioned. As the size of superabsorbent polymers (when dry), the average value of particle diameters of, for example, several hundreds of m may be mentioned, and 200 to 500 m is preferable.

[0026] One surface and the other surface of the absorbent body are joined to the top sheet and the back sheet, respectively, through an adhesive agent. In a plan view, the portion which

II

extends toward the outer side of the absorbent body so as to surround the absorbent body among the top sheet (the peripheral portion) is joined to the portion which extends toward the outer side of the absorbent body so as to surround the absorbent body among the back sheet (the peripheral portion), through an adhesive agent. Accordingly, the absorbent body is wrapped inside the joined body of the top sheet and the back sheet. The adhesive agent is not particularly limited as long as it can be used for an absorbent article and is reduced with joining force by softening, etc., by later-described hot water, etc., and for example, a hot melt-type adhesive agent may be mentioned. As a hot melt-type adhesive agent, for example, a pressure-sensitive or heat-sensitive adhesive agent of a rubber-based such as styrene - ethylene - butadiene - styrene, styrene butadiene - styrene, styrene - isoprene - styrene, etc., or of olefin-based such as polyethylene, etc., may be mentioned.

[0027] Next, the method of recovering pulp fibers from a used absorbent article which includes pulp fibers and superabsorbent polymers, according to the present embodiment is explained. In the present embodiment, used absorbent articles are recovered and obtained from outside for the purpose of reusing (recycling). At this time, the used absorbent articles are encapsulated in a plurality of bags for collection (hereinbelow, which are referred to as "collection bags") so that dirt (such as excrement, etc.), fungi and odor do not leak outside. Each of the used absorbent articles inside the collection bag is recovered, etc., in a state of being mainly rolled or folded with the top sheet in which excrement is excreted placed on the inner side, so that excrement is not exposed to the top sheet side and odor is not spread to the surroundings.

[0028] First, the system 1 which is used for the method of recovering pulp fibers from a used absorbent article is explained. The system 1 is a system which recovers pulp fibers and superabsorbent polymers from a used absorbent article, and thus is a system which produces recycled pulp fibers and recycled superabsorbent polymers. FIG. 1 is a block diagram which shows one example of the system 1 according to the present embodiment. The system 1 includes the second dust removal device 15 and the third dust removal device 16, and preferably further includes the rupturing device 11, the crushing device 12, the first separation device 13, the first dust removal device 14, the second separation device 17, the third separation device 18, the oxidizing agent treatment device 19, and the fourth separation device 20. Hereinbelow, explanations are given in detail.

[0029] First, the rupturing device 11 and the crushing device 12 are explained. The rupturing device 11 punches a hole in a collection bag which includes used absorbent articles within the inactivation aqueous solution. The crushing device 12 crushes the used absorbent articles

IZ/

together with the collection bag within the inactivation aqueous solution which are sunk under the water surface of the inactivation aqueous solution. Note that the inactivation aqueous solution is an aqueous solution which inactivates superabsorbent polymers, and the absorption performance of the superabsorbent polymers is reduced by the inactivation. Accordingly, in a case in which the superabsorbent polymers have absorbed more water than the reduced absorption performance, the superabsorbent polymers release water to the amount acceptable for the absorption performance. That is, the superabsorbent polymers are dehydrated. Hereinbelow, an example of a case in which acidic aqueous solution is used as the inactivation aqueous solution is explained.

[0030] FIG. 2 is a schematic view which shows the configurational example of the rupturing device 11 and the crushing device 12 of FIG. 1. The rupturing device 11 stores the acidic aqueous solution B which is supplied for example through a pipe which includes a valve, and punches a hole in the collection bag A which is placed inside the acidic aqueous solution B. The rupturing device 11 includes the solution tank V and the hole punching portion 50. The solution tank V stores the acidic aqueous solution B. The hole punching portion 50 is provided inside the solution tank V, and when the collection bag A is placed inside the solution tank V, punches a hole in the surface of the collection bag A which comes into contact with the acidic aqueous solution B. The hole punching portion 50 includes the delivery portion 30 and the rupturing portion 40. The delivery portion 30 delivers (withdraws) the collection bag A into the acidic aqueous solution B inside the solution tank V (physically and forcibly). As the delivery portion 30, for example, a stirring machine may be mentioned, and includes the stirring blade 33, the supporting axis (the rotation axis) 32 which supports the stirring blade 33, and the driving device 31 which rotates along the axis of the supporting axis 32. The stirring blade 33 rotates around the rotation axis (the supporting axis 32) by the driving device 31, whereby causes a swirling flow in the acidic aqueous solution B. The delivery portion 30 withdraws the collection bag A to the bottom portion direction of the acidic aqueous solution B (the solution tank V) by the swirling flow. The rupturing portion 40 is arranged at the lower portion (preferably the bottom portion) of the solution tank V, and includes the rupturing blade 41, the supporting axis (the rotation axis) 42 which supports the rupturing blade 41, and the driving device 43 which rotates along the axis of the supporting axis 42. The rupturing blade 41 rotates around the rotation axis (the supporting axis 42) by the driving device 43, whereby punches a hole in the collection bag A which has moved to the lower portion of the acidic aqueous solution B (the solution tank V). Note that the lower portion of the solution tank V indicates the portion on the lower side than half the position in the height direction of the solution tank V.

I -Y

Incidentally, the rupturing blade 41 of the hole punching portion 50 in the rupturing device 11 may be movable upward and downward in the solution tank V while rotating around the rotation axis (the supporting axis 42). In such a case, the rupturing blade 41 moves upward, whereby a hole can be punched in the collection bag A without having to let the collection bag A move to the lower portion of the acidic aqueous solution B (the solution tank V).

[0031] The crushing device 12 crushes the used absorbent articles inside the collection bag A together with the collection bag A which has sunk under the water surface of the acidic aqueous solution B. The crushing device 12 includes the crushing portion 60 and the pump 63. The crushing portion 60 is connected to the solution tank V through the pipe 61, and the used absorbent articles inside the collection bag A which have been delivered together with the acidic aqueous solution B (the mixed solution 91) from the solution tank V are crushed within the acidic aqueous solution B together with the collection bag A. As the crushing portion 60, a biaxial crushing device (for example: a biaxial rotation-type crushing machine, a biaxial differential-type crushing machine, a biaxial shear-type crushing machine) may be mentioned, and for example, a SUMICUTTER (manufactured by Sumitomo Heavy Industries Environment Co., Ltd.) may be mentioned. The pump 63 is connected to the crushing portion 60 through a pipe 62, and withdraws the crushed matter which is obtained by the crushing portion 60 together with the acidic aqueous solution B (the mixed solution 92) from the crushing portion 60, and delivers the same to the subsequent process. Note that the crushed matter includes the pulp fibers, the superabsorbent polymers, and other materials (the materials of the collection bag A, films, nonwoven fabric, elastic bodies, etc.). The rupturing device 11 and the crushing device 12 are preferably different devices.

[0032] By referring to FIG. 1, the first separation device 13 stirs the mixed solution 92 which includes the crushed matter obtained by the crushing device 12 and the acidic aqueous solution, and while performing the washing so as to remove the dirt (the excrement, etc.) from the crushed matter, the pulp fibers, the superabsorbent polymers and the acidic aqueous solution are separated from the mixed solution 92 (the mixed solution 93), and delivers the same to the first dust removal device 14. As the first separation device 13, for example, a washing machine including a washing and dehydrating tank and a water tank surrounding the washing and dehydrating tank, may be mentioned. However, the washing and dehydrating tank (a rotating drum) is used as a washing and sieving tank (separating tank). The size of the plurality of penetrating holes provided in the peripheral surface of the washing tank is set to be a size so that it is easy for the pulp fibers and the superabsorbent polymers among the crushed matter to pass therethrough and it is difficult for the other materials to pass therethrough. As the washing machine, for example, a horizontal-type washing machine ECO-22B (manufactured by Inamoto Co., Ltd.) may be mentioned.

[0033] Incidentally, the used absorbent articles may not be crushed together with the collection bag within the inactivation aqueous solution (for example: an acidic aqueous solution) and may be crushed together with the collection bag within gas (for example: air). In such a case, the rupturing device 11 is not necessary, and the crushing device 12 performs the crushing in the air in a state in which the inactivation aqueous solution is not present. Thereafter, the crushed matter of the crushing device 12 and the inactivation aqueous solution are supplied to thefirst separation device 13.

[0034] Incidentally, in a case in which the acidic aqueous solution as the inactivation aqueous solution is not used in the rupturing device 11 to the first separation device 13, the acidic aqueous solution may be added from the first dust removal device 14, and the inactivation aqueous solution which includes the pulp fibers and the superabsorbent polymers to be supplied to the first dust removal device 14 may be made to be substantially the acidic aqueous solution.

[0035] The first dust removal device 14, while maintaining the pH within the predetermined range, separates the acidic aqueous solution (the mixed solution 93) which includes the pulp fibers and the superabsorbent polymers delivered from the first separation device 13 into the pulp fibers and the superabsorbent polymers within the acidic aqueous solution (the mixed solution 94) and the other materials (the foreign matter) by a screen which has a plurality of openings. In order to maintain the pH within the predetermined range, for example, liquid which changes the pH (for example: water) is not added during the procedure, or in a case in which liquid is added, liquid with approximately the same pH (for example: acidic aqueous solution) is added. The predetermined range is the range in which the variation of pH is within 1.0. As the first dust removal device 14, for example, a screen separating machine (a rough screen separating machine) may be mentioned. Note that the openings of the screen (the sieve) are not particularly limited, and for example, slits, round holes, rectangular holes, a mesh, may be mentioned, and in this embodiment, round holes are used. The size of the openings, that is, the size of the round holes (the diameter) is set so that it is possible for the pulp fibers and the superabsorbent polymers to pass through and it is difficult for the other materials which could not be removed by the first separation device 13 (foreign matter) to pass through, and further, so as to be larger than the size of the openings of the screen of the second dust removal device 15. The size of the round holes is, for example, 2 to 5 mmp in diameter, and by such a size, the other materials (the foreign matter) of approximately 10 mm square or larger can at least be removed.

I -)

In a case of slits, the size of the slits (the width) is, for example, 2 to 5 mm. Incidentally, from the viewpoint of improving the efficiency of foreign matter removal, while applying pressure to the mixed solution 93 which is delivered from thefirst separation device 13 (for example : 0.5 to 1 kgf / cm 2 ), such a mixed solution 93 may be supplied to the first dust removal device 14. As the first dust removal device 14, a Pack Pulper (manufactured by Satomi Corporation), may be mentioned.

[0036] The second dust removal device 15, while maintaining the pH within the predetermined range, separates the acidic aqueous solution (the mixed solution 94) which includes the pulp fibers and the superabsorbent polymers delivered from the first dust removal device 14 into the pulp fibers and the superabsorbent polymers within the acidic aqueous solution (the mixed solution 95) and the other materials (the foreign matter) by a screen which has a plurality of openings. As the second dust removal device 15, for example, a screen separating machine may be mentioned. Note that the openings of the screen (the sieve) are not particularly limited, and for example, slits, round holes, rectangular holes, a mesh, may be mentioned, and in this embodiment, slits are used. The size of the slits (the width) is set so that it is possible for the pulp fibers and the superabsorbent polymers to pass through and it is difficult for the other materials which could not be removed by the first dust removal device 14 (foreign matter) to pass through. The size of the slits is, for example, 0.2 to 0.5 mm in width, and by such a size, the other materials (the foreign matter) of approximately 3 mm square or larger can at least be removed. In a case of round holes, the size of the round holes (the diameter) is, for example, 0.2 to 0.5 mmp. Incidentally, from the viewpoint of improving the efficiency of foreign matter removal, while applying pressure to the mixed solution 94 which is delivered from the first dust removal device 14 (for example : 0.5 to 2 kgf / cm 2 ), such a mixed solution 94 may be supplied to the second dust removal device 15. The pressure is, from the viewpoint of removing relatively smaller foreign matter, preferably higher than the pressure of the first dust removal device 14. As the second dust removal device 15, for example, Ramoscreen (manufactured by Aikawa Iron Works Co., Ltd.), may be mentioned.

[0037] The third dust removal device 16, while maintaining the pH within the predetermined range, performs centrifugal separation for the acidic aqueous solution (the mixed solution 95) which includes the pulp fibers and the superabsorbent polymers delivered from the second dust removal device 15, and separates the pulp fibers and the superabsorbent polymers within the acidic aqueous solution (the mixed solution 96) and the other materials (the foreign matter with a larger weight).

IV

As the third dust removal device 16, for example, a cyclone separating machine may be mentioned. In order that the pulp fibers and the superabsorbent polymers within the acidic aqueous solution which have relatively smaller specific gravity is raised, and foreign matter which has larger specific gravity (such as metal, etc.) is let to descend, the acidic aqueous solution (the mixed solution 95) which includes the pulp fibers and the superabsorbent polymers is supplied into a conical housing placed in an up-side down manner of the third dust removal device 16 (which is not shown) in a predetermined flow rate. As the third dust removal device 16, for example, an ACT low concentration cleaner (manufactured by Aikawa Iron Works Co., Ltd.), may be mentioned.

[0038] The second separation device 17 separates the acidic aqueous solution (the mixed solution 96) which includes the pulp fibers and the superabsorbent polymers delivered from the third dust removal device 16 into the pulp fibers within the acidic aqueous solution (the mixed solution 97) and the superabsorbent polymers within the acidic aqueous solution by a screen which has a plurality of openings. Accordingly, the second separation device 17 may also be regarded as a dehydrating machine which removes the acidic aqueous solution together with the superabsorbent polymers from the mixed solution 96. As the second separation device 17, for example, a drum screen separating machine may be mentioned. Note that the openings of the drum screen (the sieve) are not particularly limited, and for example, slits, round holes, rectangular holes, a mesh, may be mentioned, and in this embodiment, slits are used. The size of the slits (the width) is set so that it is possible for the superabsorbent polymers to pass through and it is difficult for the pulp fibers to pass through. In a case of slits, the size of the slits is, for example, 0.2 to 0.8 mm in width, and by such a size, a large number of superabsorbent polymers can at least be removed. In a case of round holes, the size of the round holes is, for example, 0.2 to 0.8 mmp in diameter. As the second separation device 17, for example, a drum screen dehydrator (manufactured by Toyo Screen Co., Ltd.), may be mentioned.

[0039] The third separation device 18, while separating the pulp fibers delivered from the second separation device 17, the superabsorbent polymers which have remained without being separated and the acidic aqueous solution (the mixed solution 97) into solid (the mixed matter 98) which includes the pulp fibers and the superabsorbent polymers and liquid which includes the superabsorbent polymers and the acidic aqueous solution by a screen which has a plurality of openings, applies pressure to the solid so as to crush the superabsorbent polymers in the solid. Accordingly, the third separation device 18 may also be regarded as a dehydrating machine of a pressure dehydration type which removes the acidic aqueous solution together with the

I

/ superabsorbent polymers from the mixed solution 97. Note that the solid (the mixed matter 98) includes a slight amount of the acidic aqueous solution. As the third separation device 18, for example, a screw press dehydrating machine may be mentioned. Such a screw press dehydrating machine includes a cylindrical drum screen, a screw axis which extends along the cylindrical axis of the drum screen, and a screw blade which is provided on the outer side of the screw axis and rotates along the inner peripheral surface of the drum screen. Note that the openings of the drum screen (the sieve) are not particularly limited, and for example, slits, round holes, rectangular holes, a mesh, may be mentioned, and in this embodiment, slits are used. The size of the slits (the width) is set so that it is possible for the superabsorbent polymers to pass through and it is difficult for the pulp fibers to pass through. In a case of slits, the size of the slits is, for example, 0.1 to 0.5 mm in width, and by such a size, the remaining superabsorbent polymers can at least be removed. The third separation device 18, while delivering the liquid which includes the superabsorbent polymers and the acidic aqueous solution from the slits on the side surface of the drum screen, crushes and delivers the solid which includes the pulp fibers and the superabsorbent polymers from the gap of the lid body at the tip of the drum screen in which the pressure is adjusted. As the pressure which is applied to the lid body, for example, 0.01 MPa or more and 1 MPa or less, may be mentioned. As the third separation device 18, a screw press dehydrator (manufactured by Kawaguchi Seiki Co., Ltd.), may be mentioned.

[0040] The oxidizing agent treatment device 19 treats the pulp fibers which include the crushed superabsorbent polymers in the solid delivered from the third separation device 18 (the mixed matter 98) with an aqueous solution (the treatment solution) which includes an oxidizing agent. Accordingly, the oxidizing agent treatment device 19 performs oxidative decomposition for the superabsorbent polymers so as to be removed from the pulp fibers, and delivers the pulp fibers which do not include the superabsorbent polymers together with the treatment solution (the mixed solution 99). The oxidizing agent treatment device, in a case in which ozone is used as the oxidizing agent, for example, includes a treatment tank and an ozone supplying device. The treatment tank stores the acidic aqueous solution as the treatment solution. The ozone supplying device supplies ozone containing gas which is a gaseous substance to the treatment tank. As the ozone generating device of the ozone supplying device, for example, ozone water exposure tester ED OWX-2 manufactured by EcoDesign, Inc., and ozone generator OS-25V manufactured by Mitsubishi Electric Corporation, may be mentioned. The nozzle of the ozone supplying device is arranged at the lower portion of the treatment tank and has, for example, a tube-like or a plate like shape. The nozzle supplies the ozone containing gas Z into the treatment solution as a plurality of fine bubbles. As the treatment solution, from the viewpoint of suppressing the deactivation of ozone and of the inactivation of the superabsorbent polymers, an acidic aqueous solution is preferable. Further, in a case in which the acidic aqueous solution is used in the crushing process and in the dust removal process, since there is a continuity between each of the processes, there is no risk that any inconvenience occurs by the aqueous solution in each of the processes being different, whereby the treatment can be performed stably and reliably. Still further, from the viewpoint of reducing influence to the workers and to the device by acid, an organic acid is preferable, and among the organic acid, citric acid is preferable from the viewpoint of removing metal. Incidentally, ozone gas is used as the oxidizing agent, however, the present embodiment is not limited to this example, and other oxidizing agents may be used, and other than gaseous oxidizing agent, a liquid oxidizing agent or the one in which a solid oxidizing agent is melt in a solution may also be used. As the oxidizing agent, for example, chlorine dioxide, peracetic acid, sodium hypochlorite, hydrogen peroxide, may be mentioned.

[0041] The fourth separation device 20 separates the pulp fibers from the treatment solution which includes the pulp fibers treated by the oxidizing agent treatment device 19 (the mixed solution 99) by a screen which has a plurality of openings, whereby the pulp fibers are recovered and the recycled pulp fibers are produced. As the fourth separation device 20, for example, a screen separating machine may be mentioned. Note that the openings of the screen (the sieve) are not particularly limited, and for example, slits, round holes, rectangular holes, a mesh, may be mentioned, and in this embodiment, slits are used. The size of the slits (the width) is set so that it is difficult for the pulp fibers to pass through. In a case of slits, the size of the slits is, for example, 0.2 to 0.8 mm in width. In a case of round holes, the size of the round holes is, for example, 0.2 to 0.8 mmp in diameter.

[0042] Incidentally, the system 1 includes, preferably, the ozone treatment device 22, the pH adjustment device 23, and the water storage tank 24. These devices are for regenerating and reusing the acidic aqueous solution which is used in the system 1. By reusing the acidic aqueous solution, the cost of the acidic aqueous solution can be reduced. The ozone treatment device 22 performs the sterilization treatment for the acidic aqueous solution 101 in which the superabsorbent polymers are further separated from the superabsorbent polymers and the acidic aqueous solution which are separated by the second separation device 17, by an ozone containing aqueous solution. The pH adjustment device 23 adjusts pH of the acidic aqueous solution 102 which has been performed with the sterilization treatment by the ozone containing aqueous solution, so as to produce the regenerated acidic aqueous solution 103. The water storage tank 24 stores the surplus among the regenerated acidic aqueous solution 103.

[0043] Next, the method of recovering the pulp fibers from a used absorbent article is explained. This method is a method which recovers pulp fibers (and preferably further recovers superabsorbent polymers) from a used absorbent article, and thus is a method which produces recycled pulp fibers (and preferably further produces recycled superabsorbent polymers). FIG. 3 is a flow chart which shows one example of the method according to the present embodiment. This method includes the second dust removal process S15 and the third dust removal process S16, and preferably includes the hole punching process S11 the crushing process S12, the first separation process S13, the first dust removal process S14, the third separation process S18, the oxidizing agent treatment process S19, the second separation process S17, and the fourth separation process S20. Hereinbelow, explanations are given in detail.

[0044] The hole punching process S11 is performed by the rupturing device 11. The collection bag A in which the used absorbent articles are encapsulated are thrown into the solution tank V in which the acidic aqueous solution B are stored, and a hole is punched in the surface of the collection bag A which comes into contact with the acidic aqueous solution B. When the hole is punched in the collection bag A, the acidic aqueous solution B surrounds and seals the collection bag A so that the dirt, fungi and odor of the used absorbent articles inside the collection bag A are not released outside. When the acidic aqueous solution enters inside the collection bag A from the hole, the gas inside the collection bag A exits to the outside of the collection bag A, the specific gravity of the collection bag A is to be larger than that of the acidic aqueous solution B, and the collection bag A sinks inside the acidic aqueous solution B. Further, the acidic aqueous solution B inactivates the superabsorbent polymers inside the used absorbent articles inside the collection bag A.

[0045] The superabsorbent polymers inside the used absorbent articles are inactivated and the absorption performance thereof is reduced, whereby the superabsorbent polymers are dehydrated and the particle diameter is decreased, so that the handling at each of the subsequent processes becomes easier and the processing efficiency is improved. The reason why the acidic aqueous solution, that is, an aqueous solution of inorganic acid or organic acid is used as the inactivation aqueous solution is that, in comparison with an aqueous solution of lime or calcium chloride, ash content is less likely to remain in the pulp fibers, and further, it is easier to adjust the degree of inactivation (the particle diameter and the degree of specific gravity) by pH. As the pH of the acidic aqueous solution, 1.0 or higher and 4.0 or lower is preferable, and 1.2 or higher and 2.5 or

/- V

lower is more preferable. When the pH is too high, the absorption performance of the superabsorbent polymers cannot be sufficiently lowered. Further, the sterilization performance may be lowered. When the pH is too low, there is a risk of corrosion in the equipment, and a large amount of alkaline chemicals are to be required for neutralization treatment during wastewater treatment. Especially, in order to separate the pulp fibers and the superabsorbent polymers from the other materials, it is preferable that the size and the specific gravity of the pulp fibers and those of the superabsorbent polymers are relatively similar to each other. Accordingly, by setting the pH of the acidic aqueous solution to 1.0 or higher and 4.0 or lower, the superabsorbent polymers can be made to be even smaller by the inactivation, whereby the size and the specific gravity of the pulp fibers and those of the superabsorbent polymers can be made to be relatively similar to each other. As the organic acid, for example, citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, ascorbic acid, etc., may be mentioned, and hydroxycarbonate-based organic acid such as citric acid, tartaric acid, gluconic acid, etc., is especially preferable. By the chelating effect of citric acid, metal ions, etc., in the excrement can be trapped and removed, and further, by the washing effect of citric acid, high level of dirt component removal effect can be expected. On the other hand, as the inorganic acid, for example, sulfuric acid, hydrochloric acid, and nitric acid, may be mentioned, and from the viewpoint of not including chlorine, and the cost, etc., sulfuric acid is preferable. Since pH varies depending on the water temperature, the pH in the present invention is referred to as the pH when measured at an aqueous solution temperature at 20 °C. The organic acid concentration of the organic acid aqueous solution is not particularly limited, and in a case in which the organic acid is citric acid, 0.5 mass % or higher and 4 mass % or lower is preferable. The inorganic acid concentration of the inorganic acid aqueous solution is not particularly limited, and in a case in which the inorganic acid is sulfuric acid, 0.1 mass % or higher and 0.5 mass % or lower is preferable.

[0046] In the rupturing device 11 shown in FIG. 2, for example, first, by the rotation of the stirring blade 33 around the rotation axis (the supporting axis 32), a swirling flow is caused in the acidic aqueous solution B, and the collection bag A is withdrawn to the bottom portion of the acidic aqueous solution B (the solution tank V) physically and forcibly. Then, the collection bag A which has been moved to the bottom portion comes into contact with the rupturing blade 41 by the rotation of the rupturing blade 41 around the rotation axis (the supporting axis 42), whereby a hole is punched. Incidentally, in a case in which the rupturing blade 41 is movable upward and downward in the solution tank V, the rupturing blade 41 may move upward, whereby a hole can be punched in the collection bag A without having to let the collection bag A be withdrawn to the bottom portion direction of the acidic aqueous solution B (the solution tank V) by the swirling flow.

[0047] The crushing process S12 is performed by the crushing device 12. While the acidic aqueous solution B which includes the collection bag A in which a hole is punched and is sunk under the water surface of the acidic aqueous solution B, that is the mixed solution 91, is being discharged from the solution tank V, the used absorbent articles inside the collection bag A are crushed together with the collection bag A within the acidic aqueous solution B. For example, in the crushing device 12 shown in FIG. 2, first, the used absorbent articles inside the collection bag A which have been delivered together with the acidic aqueous solution B from the solution tank V are crushed within the acidic aqueous solution B together with the collection bag A by the crushing portion 60 (the in-solution crushing process). At this time, in the crushing portion 60, the mixed solution 91 is supplied between the rotation blade which rotates toward the inner side in a state of being engaged with each other and the spacer of the biaxial crushing device, whereby the collection bag A is crushed together with the bag. Further, the acidic aqueous solution B (the mixed solution 92) which includes the crushed matter obtained by the crushing portion 60 (the in-solution crushing process) is withdrawn from the crushing portion 60 by the pump 63 (the withdrawal process), and is delivered to the subsequent process.

[0048] The crushing process S12, preferably includes a process of crushing the used absorbent articles together with the collection bag A so that the average value of the size of the crushed matter is 50 mm or larger and 100 mm or smaller. As the absorbent article, a length of approximately 150 mm to 1000 mm and a width of 100 mm to 1000 mm is assumed. By crushing the crushed matter so that the average value of the size of the crushed matter is to be 50 mm or larger and 100 mm or smaller, a slit can be reliably provided in the back sheet and / or the top sheet of each of the used absorbent articles. Accordingly, substantially all pulp fibers can be extracted from the slit in each of the used absorbent articles, whereby the recovery rate of the pulp fibers (the total amount of pulp fibers to be regenerated / the total amount of pulp fibers in the supplied used absorbent articles) can be improved. When the average value of the size is set to less than 50 mm, materials other than the pulp fibers (for example: films (such as the material of the collection bag A, the back sheet, etc.), nonwoven fabric (such as the top sheet, etc.), elastic bodies (such as rubbers for leakage prevention walls)) are cut into too small sizes, whereby it is difficult for such materials to be separated from the pulp fibers in the subsequent processes. As a result, foreign matter (other materials) to be mixed into the regenerated pulp fibers is increased, and the recovery rate of the pulp fibers is to be reduced. On the other hand, when the average value of the size is set to be larger than 100 mm, it is difficult to apply a slit in the used absorbent articles. As a result, used absorbent articles from which pulp fibers cannot be extracted occur, and the recovery rate of the pulp fibers is to be reduced.

[0049] The first separation process S13 is performed by the first separation device 13. The mixed solution 92 which includes the crushed matter and the acidic aqueous solution obtained by the crushing device 12 is stirred, and while the washing to remove dirt from the crushed matter is performed, the mixed solution 92 is separated into the pulpfibers, the superabsorbent polymers and the acidic aqueous solution, and other materials. At this time, in order to improve the washing effect, and / or to adjust pH, an acidic aqueous solution may be separately added. As a result, the pulp fibers, the superabsorbent polymers and the acidic aqueous solution (partially including the other materials, etc.) among the mixed solution 92 is separated by passing through the penetration hole, so as to be delivered from the first separation device 13 (the mixed solution 93). On the other hand, the other materials except the pulpfibers, the superabsorbent polymers and the acidic aqueous solution among the mixed solution 92 cannot pass through the penetration hole, and remain inside the first separation device 13 or is delivered through another route. Note that a portion of the other materials cannot be completely separated and is delivered together with the mixed solution 93. When a washing machine is used as the first separation device 13, as the size of the penetration hole of the washing machine which functions as a sieve, 5 mm to 20 mmp in a case of round holes may be mentioned, and in a case of holes with other shapes, a size with substantially the same area as the round hole may be mentioned.

[0050] The present method (the system) includes, as described above, in the crushing process which crushes the used absorbent articles (the hole punching process S11 (the rupturing device 1) to the first separation process S13 (the first separation device 13)), at least the hole punching process S11 (the rupturing device 1) and the crushing process S12 (the crushing device 12). Accordingly, the used absorbent articles in a state of being placed in the collection bag are crushed together with the collection bag within the inactivation aqueous solution, whereby dirt and fungi are hardly mixed into the inactivation aqueous solution and odor is hardly produced at least until the initiation of the crushing. Further, even if dirt and fungi are mixed into the inactivation aqueous solution and odor is produced when the used absorbent articles are crushed, at almost the same time as the crushing, the inactivation aqueous solution into which the dirt and fungi are mixed is delivered from the solution tank together with the crushed matter, whereby the inactivation aqueous solution can be washed away with the dirt and fungi hardly remaining in the solution tank. In addition, since odor can be sealed by the inactivation aqueous solution, the production of odor can also be suppressed to a lower degree. Accordingly, when crushing used absorbent articles, dirt and fungi can be suppressed from being scattered and odor accompanied therewith can be suppressed from being released.

[0051] Incidentally, the used absorbent articles may not be crushed together with the collection bag within the inactivation aqueous solution (for example: an acidic aqueous solution) and may be crushed together with the collection bag within gas (for example: air). In such a case, the hole punching process S1 is not necessary, and the crushing process S12 performs the crushing in the air in a state in which the inactivation aqueous solution is not present. Thereafter, the inactivation aqueous solution is supplied to the first separation process S13 together with the crushed matter of the crushing process S12. Note that in a case in which the acidic aqueous solution as the inactivation aqueous solution is not used, the acidic aqueous solution may be added from the first dust removal process S14, and the inactivation aqueous solution which includes the pulp fibers and the superabsorbent polymers to be supplied to the first dust removal process S14 may be made to be substantially the acidic aqueous solution.

[0052] The first dust removal process S14 is performed by the first dust removal device 14. While the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers delivered from the first separation device 13, that is, the mixed solution 93 maintains pH within the predetermined range, the mixed solution 93 is separated into the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers and the other materials (the foreign matter) by a screen. As a result, the pulpfibers, the superabsorbent polymers and the acidic aqueous solution (partially including the other materials, etc.) among the mixed solution 93 is separated by passing through the screen, and is delivered from the first dust removal device 14 (the mixed solution 94). On the other hand, the other materials except the pulp fibers, the superabsorbent polymers and the acidic aqueous solution among the mixed solution 93 cannot pass through the screen, and remain inside the first dust removal device 14 or is delivered through another route. Note that a portion of the other materials cannot be completely separated and is delivered together with the mixed solution 94.

[0053] Incidentally, it is preferable that the acidic aqueous solution is adjusted with pH at least until the first dust removal process S14, so that the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are within a predetermined range. In such a case, the predetermined range is, for example, a range in which one is within 0.2 to 5 times as much as the other. The size is for performing the separation by the difference in the sizes, and the specific gravity is for performing the separation by the difference in the specific gravities. Accordingly, the processes before the first dust removal process S14 can be regarded as an inactivation process of inactivating the superabsorbent polymers by mixing the pulp fibers and the superabsorbent polymers, and the acidic aqueous solution which is adjusted with pH so that the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are within a predetermined range.

[0054] Further, as the concentration of the total of the pulp fibers and the superabsorbent polymers within the acidic solution in the first dust removal process S14, for example, 0.1 mass % or more and 10 mass % or less may be mentioned, and 0.1 mass % or more and 5 mass % or less is preferable. Still further, as the ratio of the pulp fibers to the superabsorbent polymers within the acidic solution, for example, 50 to 90 mass %: 50 to 10 mass % may be mentioned.

[0055] The second dust removal process S15 is performed by the second dust removal device 15. While the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers delivered from the first dust removal device 14, that is, the mixed solution 94 maintains pH within the predetermined range, the mixed solution 94 is separated into the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers and the other materials (the foreign matter) by a screen. As a result, the pulp fibers, the superabsorbent polymers and the acidic aqueous solution (partially including the other materials, etc.) among the mixed solution 94 are separated by passing through the screen, and are delivered from the second dust removal device 15 (the mixed solution 95). On the other hand, the other materials except the pulp fibers, the superabsorbent polymers and the acidic aqueous solution among the mixed solution 94 cannot pass through the screen, and remain inside the second dust removal device 15 or is delivered through another route. Note that a portion of the other materials cannot be completely separated and is delivered together with the mixed solution 95. Incidentally, the acidic aqueous solution is adjusted with pH so that the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are within a predetermined range.

[0056] The third dust removal process S16 is performed by the third dust removal device 16. While the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers delivered from the second dust removal device 15, that is, the mixed solution 95 maintains pH within the predetermined range, the mixed solution 95 is subjected to a centrifugal separation by a conical housing placed in an up-side down manner and is separated into the pulp fibers and the superabsorbent polymers within the acidic aqueous solution and the other materials (the foreign matter with a larger weight). As a result, the pulp fibers, the superabsorbent polymers and the acidic aqueous solution among the mixed solution 95 are delivered from the upper portion of the third dust removal device 16 (a cyclone separating machine) (the mixed solution 96). On the other hand, the other materials except the pulp fibers, the superabsorbent polymers and the acidic aqueous solution among the mixed solution 95, such as metal, are delivered from the lower portion of third dust removal device 16 (a cyclone separating machine). Incidentally, the acidic aqueous solution is adjusted with pH so that the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are within a predetermined range.

[0057] The present method (the system) includes, as described above, in the dust removal process of removing foreign matter (other materials) (the first dust removal process S14 (the first dust removal device 14) to the third dust removal process S16 (the third dust removal device 16)), at least the second dust removal process S15 (the second dust removal device 15) and the third dust removal process S16 (the third dust removal device 16).

[0058] The second separation process S17 is performed by the second separation device 17. The acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers delivered from the third dust removal device 16, that is, the mixed solution 96, is separated into the pulp fibers within the acidic aqueous solution and the superabsorbent polymers within the acidic aqueous solution by a drum screen. As a result, the acidic aqueous solution which includes the superabsorbent polymers is separated from the mixed solution 96 by passing through the drum screen and is delivered from the second separation device 17. On the other hand, the acidic aqueous solution which includes the pulp fibers among the mixed solution 96 cannot pass through the drum screen, and is delivered from the second separation device 17 through another route (the mixed solution 97). Incidentally, thereafter, the superabsorbent polymers can be separated from the separated superabsorbent polymers and the acidic aqueous solution by a screen separating machine, etc. Accordingly, the aforementioned processes can be regarded as a process of separating and recovering the superabsorbent polymers, and thus a process of producing recycled superabsorbent polymers.

[0059] The third separation process S18 is performed by the third separation device 18. The pulp fibers, the remaining superabsorbent polymers which could not be separated and the acidic aqueous solution delivered from the second separation device 17, that is the mixed solution 97, is separated into a solid which includes the pulp fibers and the superabsorbent polymers and a liquid which includes the superabsorbent polymers and the acidic aqueous solution by a drum screen. Further, together with the separation, the superabsorbent polymers within the solid are applied with pressure and are crushed. The crushing may be exemplified by crushing the

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superabsorbent polymers in a gel state with a pressure which is or greater than the gel strength. As a result, the acidic aqueous solution which includes the superabsorbent polymers is separated from the mixed solution 97 by passing through the drum screen and is delivered from the third separation device 18. On the other hand, the pulp fibers in which the superabsorbent polymers are crushed among the mixed solution 97 cannot pass through the drum screen, and are delivered to the outside of the third separation device 18 from the gap of the lid body at the tip portion of the drum screen (the mixed matter 98). The pressure which is applied to the lid body is, for example, 0.01 MPa or more and 1 MPa or less, and is preferably 0.02 MPa or more and 0.5 MPa or less. When the pressure is set to less than 0.02 MPa, it is difficult to crush the superabsorbent polymers, whereby the time for the oxidizing agent treatment cannot be shortened so much, and when the pressure is set to more than 0.5 MPa, although the superabsorbent polymers can be sufficiently crushed, there is a risk of damaging the pulp fibers.

[0060] The oxidizing agent treatment process S19 is performed by the oxidizing agent treatment device 19. The pulp fibers and the crushed superabsorbent polymers in the solid delivered from the third separation device 18 are treated by an aqueous solution which includes an oxidizing agent. Accordingly, the superabsorbent polymers are subjected to an oxidative decomposition so as to be removed from the pulp fibers. As a result, the superabsorbent polymers which have been attached to the pulp fibers in the mixed matter 98 (for example: which have been remained on the surface of the pulp fibers) are subjected to the oxidative decomposition by an aqueous solution (the treatment solution) which includes an oxidizing agent (for example: ozone), and change into an organic matter with low molecular weight which is soluble in an aqueous solution, whereby are removed from the pulp fibers. The state in which the superabsorbent polymers are subjected to an oxidative decomposition and are changed into an organic matter with low molecular weight which is soluble in an aqueous solution is referred to a state in which the superabsorbent polymers pass through a screen of 2 mm. Accordingly, impurities such as the superabsorbent polymers, etc., included in the pulp fibers are removed, pulp fibers with high purity can be produced, and sterilization, bleaching, and deodorization of the pulp fibers can be performed by the oxidizing agent treatment. For example, in the oxidizing agent treatment device 19, the mixed matter 98 is thrown from the upper portion of the treatment tank and the treatment solution, that is, the aqueous solution which includes the oxidizing agent sinks from the upper portion toward the lower portion. On the other hand, the ozone containing gas is continuously released from the nozzle of the treatment tank into the treatment solution in a state of fine bubbles (for example: microbubbles or nanobubbles). That is, the ozone containing gas rises from the lower portion to the upper portion of the treatment solution. Inside the treatment solution, the sinking pulp fibers z I and the rising ozone containing gas collide while traveling with facing each other. Further, the ozone containing gas is attached to the surface of the pulp fibers so as to wrap the pulp fibers. At this time, the ozone in the ozone containing gas reacts with the superabsorbent polymers in the pulp fibers, performs oxidative decomposition for the superabsorbent polymers, and let the superabsorbent polymers dissolve in the treatment solution. Accordingly, the superabsorbent polymers which are included in the pulp fibers in the mixed matter 98 are subjected to the oxidative decomposition, so as to be removed from the pulp fibers.

[0061] The present method (the system) includes, as described above, in the recovery process of recovering the pulp fibers, etc. (the second separation process S17 (the second separation device 17) to the fourth separation process S20 (the fourth separation device 20)), at least the third separation process S18 (the third separation device 18) and the oxidizing agent treatment process S19 (the oxidizing agent treatment device 19). Accordingly, by crushing the superabsorbent polymers in a substantially spherical or a massive state, the surface area of the superabsorbent polymers can be largely enlarged, and the exposed portion of the superabsorbent polymers can be increased, by for example the inner side portion of the superabsorbent polymers being exposed to the outer side. Accordingly, in the oxidizing agent treatment process S19 (the oxidizing agent treatment device 19), the contact area in the superabsorbent polymers with the oxidizing agent can be increased, by for example letting the inner side portion of the superabsorbent polymers which has been difficult to come into contact with the oxidizing agent in a case of the superabsorbent polymers in a substantially spherical or a massive state, come into contact with the oxidizing agent. Therefore, the oxidative decomposition of the superabsorbent polymers can be even more efficiently proceeded, and the time for oxidizing agent treatment can be shortened. Thus, the efficiency of the treatment of removing the superabsorbent polymers from the pulp fibers can be improved.

[0062] The fourth separation process S20 is performed by the fourth separation device 20, and the treatment solution which includes the pulp fibers that have been treated by the oxidizing agent treatment device 19, that is, the mixed solution 99, passes through a screen with a plurality of openings, whereby the pulp fibers and the treatment solution are separated from the mixed solution 99. As a result, the treatment solution 104 passes through the screen so as to be separated from the mixed solution 99, and is delivered from the fourth separation device 20. The separated treatment solution 104, that is, the oxidizing agent treatment solution, may be returned to the oxidizing agent treatment device 19 and may be reused. Accordingly, the cost of the oxidizing agent treatment solution can be reduced. On the other hand, the pulp fibers among the mixed solution 99 cannot pass through the screen and remain in the fourth separation device 20 or is delivered through another route. The aforementioned processes can be regarded as a process of separating and recovering the pulp fibers, and thus a process of producing recycled pulp fibers.

[0063] Note that the specific gravity of the superabsorbent polymers was measured by the specific gravity bottle method of the measurement method of the density and the specific gravity of chemical products according to JIS K 0061. As a result, the specific gravity of the superabsorbent polymers before absorption was 1.32 g / ml. The specific gravity when inactivated by a citric acid aqueous solution (pH 2) was 1.04 g / ml, and the specific gravity when inactivated by a citric acid aqueous solution (pH 4) was 1.01 g / ml. On the other hand, since the actual measurement of the size of the superabsorbent polymers (after absorption) was difficult, it was assumed that the superabsorbent polymers were spheres, and the size (the diameter) thereof was calculated as follows. That is, the average diameter of the superabsorbent polymers before absorption was assumed to be 200 [m, and the size (the diameter) of the superabsorbent polymers after absorption was estimated by a volume expansion calculation based on the water amount of the aqueous solution absorbed by the superabsorbent polymers. The volume expansion calculation was performed in the following manner. First, the amount of water absorbed by the superabsorbent polymers (per 1 particle) was measured. Next, it was assumed that the volume of water which corresponds to such water amount is the volume V of the superabsorbent polymers after absorption, and based on V = 4/ 37ur3 , the radius r of the superabsorbent polymers after absorption was obtained. Further, the diameter which is twice the radius r is regarded as the size of the superabsorbent polymers (after absorption). As a result, the gel diameter when activated by a citric acid aqueous solution (pH 2) was approximately 420 [m, and the gel diameter when activated by a citric acid aqueous solution (pH 4) was approximately 540 [m.

[0064] Note that the proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution was measured in the following manner. First, a portion of the acidic aqueous solution was taken as a sample, the sample is put into in afilter of 200 mesh and the sample weight WO was measured. Next, the sample on the filter is hung for 5 minutes to be drained, is subjected to an absolute drying by a predetermined absolute drying method (a method of heating and drying a sample at 120 °C for 10 minutes), and the absolute dry weight W1 of the obtained absolutely dried matter was measured. Next, the absolutely dried matter was immersed in an aqueous solution which includes ozone, the obtained matter is absolutely dried by the above mentioned absolute drying method, and the absolute dry weight W2 as the pulp fibers was measured. Further, the weight obtained by subtracting the absolute dry weight W2 from the absolute dry weight WI was regarded as the weight of the superabsorbent polymers, and the proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution was calculated by the following formula. That is, (the proportion of the pulp fibers)= (the absolute dry weight W2) / (the sample weight WO), and (the proportion of the superabsorbent polymers)= (the absolute dry weight WI - the absolute dry weight W2) / (the sample weight WO). From the viewpoint of weight proportion, the solid weight of dirt is extremely small, thus can be ignored.

[0065] Incidentally, this method preferably includes the ozone treatment process S22 and the pH adjustment process S23. These processes are for the purpose of regenerating and reusing the acidic aqueous solution which is used in this method. By reusing the acidic aqueous solution, the cost of the acidic aqueous solution can be reduced. The ozone treatment process S22 performs the sterilization treatment for the acidic aqueous solution 101 in which the superabsorbent polymers are further separated from the superabsorbent polymers and the acidic aqueous solution which are separated by the second separation process S17, by an ozone containing aqueous solution. The pH adjustment process S23 adjusts pH of the acidic aqueous solution 102 which has been performed with the sterilization treatment by the ozone containing aqueous solution, so as to produce the regenerated acidic aqueous solution 103. The acidic aqueous solution 103 is, for example, supplied to the rupturing device 11. Alternatively, in a case in which the hole punching process S11 is not present, and the crushing is performed without using an inactivation aqueous solution in the crushing device 12, the acidic aqueous solution 103 is supplied to the first separation process S13. Alternatively, the acidic aqueous solution 103 may be supplied to other processes (devices) if necessary. The surplus of the acidic aqueous solution 103 is stored in the water storage tank 24.

[0066] Generally, the specific gravity of superabsorbent polymers is larger than that of water, and when the superabsorbent polymers absorb water, the specific gravity of superabsorbent polymers is approximated to that of water in accordance with the water absorption amount. Further, the size of each of the superabsorbent polymers is small, however, when the superabsorbent polymers absorb water, the size thereof is enlarged in accordance with the water absorption amount. Still further, the amount of water which is absorbed and retained by the superabsorbent polymers is extremely large, however, by performing an inactivation treatment for the superabsorbent polymers, such an amount is limited to some extent. From the above, by the degree of the inactivation treatment of the superabsorbent polymers, the amount of water retained by the superabsorbent polymers is adjusted, whereby the size and the specific gravity of the superabsorbent polymers can be adjusted to the desired values. As the inactivation treatment of the superabsorbent polymers, the treatment of immersing the superabsorbent polymers in a predetermined solution (for example: an acidic aqueous solution), may be mentioned.

[0067] Accordingly, the above-mentioned method (the system) of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers includes, in the dust removal process of removing foreign matter (other materials) (the first dust removal process Si4 (the first dust removal device 14) to the third dust removal process S16 (the third dust removal device 16)), at least the second dust removal process S15 (the second dust removal device 15) and the third dust removal process S16 (the third dust removal device 16). The second dust removal process S15 is also a size separation process, and the third dust removal process S16 is also a specific gravity separation process. The second dust removal device 15 is also a screen separating machine, and the third dust removal device 16 is also a cyclone separating machine (a centrifugal separating machine). Further, the superabsorbent polymers are inactivated by the acidic aqueous solution in which pH is adjusted in advance, the water absorption amount of the superabsorbent polymers is adjusted, whereby the differences between the specific gravity and the size of the superabsorbent polymers and the specific gravity and the size of the pulp fibers are set to be respectively within the predetermined range (the inactivation process). In such a case, within the predetermined range is set, for example, so that one is within 0.2 to 5 times as much of the other. Accordingly, the difference between the pulp fibers and the superabsorbent polymers is set so that the specific gravity is within the predetermined range, and the size is within the predetermined range. As a result, the pulp fibers and the superabsorbent polymers are easily separated from the other materials (mainly the resin materials) except the pulp fibers and the superabsorbent polymers among the materials of the used absorbent articles by using the difference in the sizes (the second dust removal process S15 (the second dust removal device 15)), and from the materials with a large specific gravity (mainly the metallic materials) among the other materials by using the difference in the specific gravities (the third dust removal process S16 (the third dust removal device 16)). Further, thereafter, the pulp fibers and the superabsorbent polymers are separated from each other (the second and the third separation processes S17 and S18 (the second and the third separation devices 17 and 18), whereby the pulp fibers and the superabsorbent polymers can be recovered from the used absorbent article. At this time, the number of processes of separating the pulp fibers and the superabsorbent polymers, and the other materials can be reduced. That is, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved. As the resin materials among the other materials of the used absorbent article except the pulp fibers and the superabsorbent polymers, films (such as the back sheet, etc.), nonwoven fabric (such as the top sheet, etc.), elastic bodies (such as rubbers for leakage prevention walls), etc., may be mentioned. As the materials of a large specific gravity among the other materials,

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for example, the metallic materials, clips and stapler needles, etc., which are not included in the original absorbent articles but are mixed when recovering the used absorbent articles, may be mentioned. Further, the size of the superabsorbent polymers is the particle diameter of each of the superabsorbent polymers, and in a case in which the superabsorbent polymers are spherical, the size is the diameter, and in a case in which the superabsorbent polymers are in a massive state, the size is the longest width. The size of the pulp fibers is the average fiber length of the pulp fibers.

[0068] As a preferred aspect of the present embodiment, the specific gravity separation process, that is, the third dust removal process S16 (the specific gravity separation process) may include a process of separating the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method. According to the present method, the difference in the specific gravities of the pulp fibers and the superabsorbent polymers is within the predetermined range, whereby by the centrifugal separation method, the pulp fibers and the superabsorbent polymers can be separated from the other materials (the materials with a large specific gravity, for example the metallic materials) more accurately. Therefore, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved.

[0069] As a preferred aspect of the present embodiment, the second dust removal process S15 (the size separation process) may include a screen separation process of separating the pulp fibers and the superabsorbent polymers from the other materials by using a screen which includes a plurality of openings each with a predetermined size. According to the present method, the difference in the sizes of the pulp fibers and the superabsorbent polymers is within the predetermined range, whereby by letting the materials pass through a screen which includes a plurality of openings each with a predetermined size, the pulp fibers and the superabsorbent polymers can be separated from the other materials (mainly the resin materials, for example, films such as the back sheet, etc., nonwoven fabric such as the top sheet, etc., rubbers for leakage prevention walls, etc.) more accurately. Therefore, the processing efficiency of separating the pulp fibers and the superabsorbent polymers can be improved.

[0070] The preferred aspect of the present embodiment may further comprise, before the second dust removal process S15 or the size separation process (the second dust removal device or the screen separating machine), the first dust removal process S14 or the rough size separation process (the first dust removal device 14 or the rough screen separating machine).

The present system includes, before the second dust removal process S15 (the second dust removal device 15), the pulp fibers and the superabsorbent polymers materials and the other materials are let to pass through a screen which includes the plurality of openings each with a larger size. Accordingly, the other materials which are relatively larger can be removed in advance. Therefore, in the second dust removal process S15 (the second dust removal device 15), a situation can be suppressed in which the screen is clogged by the other materials which are relatively larger and the processing efficiency of separation is lowered.

[0071] As a preferred aspect of the present embodiment, a proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution which includes the inactivated superabsorbent polymers may be 0.1 mass % or more and 10 mass % or less. According to the present method (system), the proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution is 0.1 mass % or more and 10 mass % or less, whereby the separation of the pulp fibers and the superabsorbent polymers from the other materials can be performed more reliably. Accordingly, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved. Note that when the proportion is set to less than 0.1 mass %, the amount of the superabsorbent polymers and the pulp fibers to be separated is too small, and the capacity of the separating process is wasted, and when the proportion is set to more than 10 mass %, the superabsorbent polymers and the pulp fibers cannot be completely separated so as to be discharged together with other materials, and thus the processing efficiency is lowered in both cases.

[0072] As a preferred aspect of the present embodiment, the pH of the acidic aqueous solution may be 1 or higher and 4 or lower. According to the present method (system), the pH of the acidic aqueous solution is adjusted to 1 or higher and 4 or lower, whereby the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0073] As a preferred aspect of the present embodiment, the acidic aqueous solution may include a citric acid. According to the present method (system), since the acidic aqueous solution includes the citric acid (for example : the concentration of 0.5 to 2.0 mass %), the superabsorbent polymers are reliably dehydrated, and the specific gravity and the size of the superabsorbent polymers can be approximated to the specific gravity and the size of the pulp fibers in a greater degree, respectively. Accordingly, the pulp fibers and the superabsorbent polymers can be separated from the other materials more reliably. Further, a negative influence to the workers by acid, and corrosion of equipment in each process can be suppressed. Therefore, the processing efficiency of separating the superabsorbent polymers and the pulp fibers can be improved.

[0074] The preferred aspect of the present embodiment may further comprise, the second separation process S17 or the polymer separation process (the second separation device 17 or Ramoscreen separating machine) of separating the superabsorbent polymers from the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers separated by the third dust removal process S16 or the specific gravity separation process (the third dust removal device 16 or the cyclone separating machine). According to the present method (system), since the other materials are removed from the pulp fibers and the superabsorbent polymers, by separating the pulp fibers and the superabsorbent polymers from each other, the pulp fibers and the superabsorbent polymers can be easily recovered separately.

[0075] The above-mentioned embodiment explains a case in which the configurational member of the back sheet is a film, and the configurational member of the top sheet is a nonwoven fabric. However, an embodiment in a case in which the configurational member of the back sheet is a nonwoven fabric, and the configurational member of the top sheet is a film, or a case in which both of the configurational members of the back sheet and the top sheet are films, can also be realized by the similar method as the above-mentioned embodiment, and can exhibit the similar effect.

[0076] The absorbent article of the present invention is not limited to the above-described each of the embodiments, and combination or variation, etc., is possible as appropriate, within a range which does not deviate from the purpose and the spirit of the present invention.

REFERENCE SIGNS LIST

[0077] S13 first separation process (inactivation process) S15 second dust removal process (size separation process) S16 third dust removal process (specific gravity separation process)

[0078] Any reference to or discussion of any document, act or item ofknowledge in this specification is included solely for the purpose of providing a context for the present invention. It is not suggested or represented that any of these matters or any combination thereof formed at the priority date part of the common general knowledge, or was known to be relevant to an attempt to solve any problem with which this specification is concerned.

[0079] In this specification, the terms 'comprises', 'comprising', 'includes', 'including', or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.

Claims

The claims defining the invention are as follows:

1. A method of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the method comprising: an inactivation process of inactivating superabsorbent polymers by mixing pulp fibers and superabsorbent polymers which are separated from the used absorbent article, and an acidic aqueous solution which is adjusted with pH so that one of a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other and one of a size of the superabsorbent polymers and a size of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other; a size separation process of, while maintaining the pH within a predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from other materials by using a difference in a size; and a specific gravity separation process of, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from the other materials by using a difference in a specific gravity.

2. The method according to claim 1, wherein the specific gravity separation process includes a process of separating the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method.

3. The method according to claim 1 or 2, wherein the size separation process includes a screen separation process of separating the pulp fibers and the superabsorbent polymers from the other materials by using a screen which includes a plurality of openings each with a predetermined size.

4. The method according to any one of claims I to 3, further comprising, before the size separation process, a rough size separation process of, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separating the pulp fibers and the superabsorbent polymers from the other materials by letting the pulp fibers and the superabsorbent polymers pass through a screen which includes a plurality of openings each with a size larger than a size of each of a plurality of openings of a screen used in the size separation process.

5. The method according to any one of claims 1 to 4, wherein a proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution which is formed in the inactivation process is 0.1 mass % or more and 10 mass % or less.

6. The method according to any one of claims I to 5, wherein the pH of the acidic aqueous solution is 1 or higher and 4 or lower.

7. The method according to any one of claims 1 to 6, wherein the acidic aqueous solution includes a citric acid.

8. The method according to any one of claims I to 7, further comprising a polymer separation process of separating the superabsorbent polymers from the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers separated by the specific gravity separation process.

9. A system of recovering pulp fibers and superabsorbent polymers from a used absorbent article which includes pulp fibers and superabsorbent polymers, the system comprising: a screen separating machine which separates, while maintaining a pH within a predetermined range so that one of a specific gravity of the superabsorbent polymers and a specific gravity of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other and one of a size of the superabsorbent polymers and a size of the pulp fibers is within a predetermined range of 0.2 to 5 times as much as the other, in an acidic aqueous solution which includes pulp fibers and superabsorbent polymers and in which the superabsorbent polymers are inactivated by mixing pulp fibers and superabsorbent polymers which are separated from the

JY

/ used absorbent article, and the acidic aqueous solution which is adjusted with the pH so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, the pulpfibers and the superabsorbent polymers from other materials by using a screen which includes a plurality of openings each with a predetermined size; and a cyclone separating machine which separates, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, the pulp fibers and the superabsorbent polymers from the other materials by a centrifugal separation method.

10. The system according to claim 9, further comprising, before the screen separating machine, a rough screen separating machine which, while maintaining the pH within the predetermined range so that one of the specific gravity of the superabsorbent polymers and the specific gravity of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other and one of the size of the superabsorbent polymers and the size of the pulp fibers is within the predetermined range of 0.2 to 5 times as much as the other, in the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers, separates the pulp fibers and the superabsorbent polymers from the other materials by letting the pulp fibers and the superabsorbent polymers pass through a screen which includes a plurality of openings each with a size larger than the predetermined size of each of the plurality of openings.

11. The system according to claim 9 or 10, wherein a proportion of the pulp fibers and the superabsorbent polymers to the acidic aqueous solution which includes the inactivated superabsorbent polymers is 0.1 mass % or more and 10 mass % or less.

12. The system according to any one of claims 9 to 11, wherein the pH of the acidic aqueous solution is 1 or higher and 4 or lower.

13. The system according to any one of claims 9 to 12, wherein the acidic aqueous solution includes a citric acid.

14. The system according to any one of claims 9 to 13, further comprising a drum screen separating machine which separates the superabsorbent polymers from the acidic aqueous solution which includes the pulp fibers and the superabsorbent polymers separated by the cyclone separating machine, by a drum screen.