Method for manufacturing recycled fiber from mixture of highly water-absorbing polymer and pulp fiber

Abstract

To provide a method capable of achieving both a processing speed and energy efficiency in ozone processing, in a method of manufacturing recycled fibers from a mixture of highly water-absorbing polymer and pulp fiber.SOLUTION: A method for manufacturing recycled fibers from a mixture of highly water-absorbing polymer and pulp fiber includes: a first processing step S6; and a second processing step S9. In the first processing step, the mixture of the highly water-absorbing polymer and the pulp fiber is processed with ozone in a first processing liquid 52-1 while ozone is supplied to the first processing liquid in a first processing tank 31-1, and at least a part of the highly water-absorbing polymer is removed. In the second processing step, the pulp fiber is processed with ozone in a second processing liquid 52-2 while ozone discharged from the first processing liquid in the first processing tank is supplied to the second processing liquid in a second processing tank 31-2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers.

Background Art

[0002] A method for producing a mixture of a superabsorbent polymer and pulp fibers is known. For example, Patent Document 1 discloses a method for producing recycled fibers from a mixture of fibers and a superabsorbent polymer. This method continuously supplies a mixed liquid containing fibers containing a superabsorbent polymer and water into a treatment tank having a treatment liquid capable of dissolving the superabsorbent polymer at a first flow rate, while dissolving the superabsorbent polymer and continuously discharging the treatment liquid containing the removed fibers out of the treatment tank at a second flow rate. The treatment liquid capable of dissolving the superabsorbent polymer may be an aqueous solution containing a gaseous substance that decomposes the superabsorbent polymer so as to be soluble, and the gaseous substance may contain ozone.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, a superabsorbent polymer is more easily decomposed when an aqueous solution in which ozone is dissolved at a high concentration is used as a treatment liquid. However, when attempting to dissolve a high concentration of ozone in an aqueous solution and injecting ozone into the aqueous solution at a high concentration and high flow rate, not only ozone that actually dissolves in the aqueous solution but also a large amount of ozone that passes through without dissolving is likely to be generated. Thus, when ozone passes through the aqueous solution and is released from the aqueous solution, the amount of ozone that does not contribute to the decomposition of the superabsorbent polymer increases, and there is a risk that the energy consumed for ozone generation will be wasted. As a result, the energy efficiency of ozone treatment may decrease.

[0005] On the other hand, if priority is given to the energy efficiency of ozone treatment and at least one of the concentration and flow rate of ozone injected into the aqueous solution is reduced, the ratio of ozone passing through the aqueous solution can be decreased, and the energy efficiency of ozone treatment can be improved. However, when it is desired to shorten the treatment time of ozone treatment, that is, when it is desired to increase the treatment speed, ultimately, as described above, a method of injecting ozone into the aqueous solution at a high concentration and high flow rate must be adopted.

[0006] An object of the present invention is to provide a method capable of achieving both a treatment speed and energy efficiency in ozone treatment in a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers.

Means for Solving the Problems

[0007] One aspect of the present invention is a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, comprising: a first treatment step of supplying ozone to a first treatment liquid in a first treatment tank and treating a mixture of a superabsorbent polymer and pulp fibers with the ozone in the first treatment liquid to remove at least a part of the superabsorbent polymer; and a second treatment step of supplying the ozone released from the first treatment liquid in the first treatment tank to a second treatment liquid in a second treatment tank and treating pulp fibers with the ozone in the second treatment liquid.

Effects of the Invention

[0008] According to the present invention, in a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, a method capable of achieving both a treatment rate and energy efficiency in ozonation can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0010] This embodiment relates to the following aspects. [Aspect 1] A method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, comprising: a first treatment step of treating a mixture of a superabsorbent polymer and pulp fibers with ozone in the first treatment liquid in a first treatment tank while supplying ozone to the first treatment liquid in the first treatment tank to remove at least a part of the superabsorbent polymer; and a second treatment step of treating pulp fibers with ozone in the second treatment liquid in a second treatment tank while supplying the ozone discharged from the first treatment liquid in the first treatment tank to the second treatment liquid in the second treatment tank.

[0011] In this method, for the ozone treatment of pulp fibers in the first treatment step, ozone is supplied to the first treatment liquid in the first treatment tank and the ozone released from (passed through) the first treatment liquid is supplied to the second treatment liquid in the second treatment tank and used for the ozone treatment of pulp fibers in the second treatment step. That is, in this method, in order to increase the treatment speed of the ozone treatment, even if a large amount of ozone is released (passed through) without dissolving in the first treatment liquid by supplying ozone to the first treatment liquid at a high concentration and high flow rate, the released ozone can be used in the second treatment step. In this way, by using the ozone supplied for the ozone treatment in the first treatment step also in the ozone treatment in the second treatment step, ozone can be effectively utilized. Therefore, the treatment speed in the ozone treatment in the first treatment step can be increased and the energy efficiency of the ozone treatment can be increased. Thus, in a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, it is possible to achieve both the treatment speed and the energy efficiency in the ozone treatment.

[0012] [Aspect 2] The method according to aspect 1, wherein the first treatment step includes a continuous treatment step of continuously supplying the pulp fibers and the first treatment liquid into the first treatment tank, treating the pulp fibers with the ozone while continuously sending out of the first treatment tank the first treatment liquid containing the pulp fibers treated with the ozone.

[0013] In this method, while continuously supplying pulp fibers and a first treatment liquid into a first treatment tank and subjecting the pulp fibers to ozone treatment (while the superabsorbent polymer is oxidatively decomposed, dissolved, and removed), the first treatment liquid containing the ozone-treated pulp fibers is continuously sent out of the first treatment tank. That is, the pulp fibers are continuously treated. Therefore, in the first treatment tank, a continuous and stable flow of the first treatment liquid can be generated from the supply port of the first treatment liquid toward the discharge port of the first treatment liquid. Thereby, ozone dissolved in the first treatment liquid and ozone passing through the first treatment liquid and the pulp fibers can be drawn into the flow and made to easily contact each other. That is, the pulp fibers can be continuously brought into contact with ozone. Therefore, more ozone contributing to the decomposition of the superabsorbent polymer can be obtained, and the treatment speed and energy efficiency in the ozone treatment can be increased.

[0014] [Aspect 3] The first treatment step includes a preparation step of preparing the first treatment liquid containing the pulp fibers in the first treatment tank, a batch treatment step of treating the pulp fibers with the ozone after the preparation step, and a discharge step of discharging the first treatment liquid containing the pulp fibers treated with the ozone out of the first treatment tank after the batch treatment step, according to the method described in Aspect 1.

[0015] In this method, first, a first treatment liquid containing pulp fibers is prepared in a first treatment tank, then the pulp fibers are subjected to ozone treatment (while the superabsorbent polymer is oxidatively decomposed, dissolved, and removed), and thereafter, the first treatment liquid containing the ozone-treated pulp fibers is discharged out of the first treatment tank. That is, the pulp fibers are batch-treated. Therefore, in the first treatment tank, the pulp fibers remaining in the first treatment liquid can be made to easily and continuously contact ozone dissolved in the first treatment liquid and ozone passing through the first treatment liquid. Thereby, the pulp fibers can be continuously treated with ozone. Therefore, more ozone contributing to the decomposition of the superabsorbent polymer can be obtained, and the treatment speed and energy efficiency in the ozone treatment can be increased.

[0016] [Aspect 4] The method according to any one of Aspects 1 to 3, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, wherein the separated pulp fibers are supplied to the second treatment tank.

[0017] The first treatment liquid after the first treatment step contains, in addition to the pulp fibers from which at least a part of the superabsorbent polymer has been removed, low-molecular-weight organic substances produced by oxidative decomposition of the superabsorbent polymer. Therefore, when the pulp fibers are supplied to the second treatment step together with the first treatment liquid, the second treatment liquid in the second treatment step will contain not only the pulp fibers but also low-molecular-weight organic substances. In that case, the ozone in the second treatment liquid will be supplied not only to the pulp fibers but also to the low-molecular-weight organic substances, and there is a risk that ozone cannot be effectively used for the treatment of the pulp fibers. Therefore, in this method, the pulp fibers treated in the first treatment step are separated from the first treatment liquid, and the separated pulp fibers are supplied to the second treatment tank. That is, since the pulp fibers are separated from the low-molecular-weight organic substances and then supplied to the second treatment tank, it is possible to suppress the inclusion of low-molecular-weight organic substances in the second treatment liquid in the second treatment step. As a result, the ozone in the second treatment liquid will be supplied generally only to the pulp fibers, and ozone can be effectively used for the treatment of the pulp fibers. Therefore, the treatment speed and energy efficiency of the ozone treatment in the second treatment step can be increased.

[0018] [Aspect 5] The method according to any one of Aspects 1 to 3, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, and an adjustment step of adjusting the solid content ratio of the second treatment liquid with the separated pulp fibers, wherein the second treatment liquid containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment tank.

[0019] In this method, the pulp fibers processed in the first treatment step are separated from the first treatment liquid, and the second treatment liquid with the solid content ratio adjusted by the separated pulp fibers is supplied to the second treatment tank. That is, the pulp fibers are separated from the low-molecular-weight organic substances, mixed with the new second treatment liquid to have an appropriate solid content ratio, and then supplied to the second treatment tank. Therefore, it is possible to suppress the inclusion of low-molecular-weight organic substances in the second treatment liquid of the second treatment step, and to appropriately adjust the ratio of ozone to pulp fibers during the ozone treatment. As a result, the ozone in the second treatment liquid is supplied mainly to the pulp fibers only, and the concentration of the pulp is appropriate, so that the ozone can be effectively used for the treatment of the pulp fibers. Therefore, the treatment speed and energy efficiency of the ozone treatment in the second treatment step can be increased.

[0020] [Aspect 6] The second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the treatment liquid in the second treatment tank to perform at least one of deodorization, bleaching, and sterilization, according to the method according to any one of aspects 1 to 5.

[0021] In this method, the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the treatment liquid in the second treatment tank to perform at least one of deodorization, bleaching, and sterilization. In this way, by using the ozone supplied for the ozone treatment in the first treatment step in the ozone treatment for performing at least one of deodorization, bleaching, and sterilization in the second treatment step, the ozone can be effectively utilized. And in this method, it is possible to produce pulp fibers in which deodorization, bleaching, and sterilization have further progressed from the first treatment step.

[0022] [Aspect 7] The second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the treatment liquid in the second treatment tank to remove at least a part of the superabsorbent polymer, according to the method according to any one of aspects 1 to 6.

[0023] In this method, the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the treatment liquid in the second treatment tank to remove at least a part of the superabsorbent polymer. In this way, by using the ozone supplied for the ozone treatment in the first treatment step in the ozone treatment for removing at least a part of the superabsorbent polymer in the second treatment step, the ozone can be effectively utilized. And in this method, pulp fibers with further removal of the superabsorbent polymer can be produced from the first treatment step.

[0024] [Aspect 8] The method according to any one of Aspects 1 to 3, further comprising a step of preparing the mixture of the superabsorbent polymer and the pulp fibers taken out from the used absorbent article as the mixture of the superabsorbent polymer and the pulp fibers used in the first treatment step.

[0025] In this method, in the first treatment step, a mixture of a superabsorbent polymer and pulp fibers taken out from a used absorbent article is used. Therefore, for used absorbent articles with a large amount to be discarded, their constituent materials can be recycled. Thereby, the environmental load can be reduced.

[0026] Hereinafter, a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to this embodiment will be described.

[0027] Here, regarding the mixture of a superabsorbent polymer and pulp fibers, which is the raw material for the recycled fibers to be produced, there are no particular restrictions as long as the pulp fibers and the superabsorbent polymer are mixed. Examples of the origin of the mixture include, for example, a mixture of pulp fibers and a superabsorbent polymer contained in an absorber that absorbs some liquid. Examples of the absorber include an absorber provided in a sanitary product such as an absorbent article capable of absorbing body fluids (exemplified: excreta, blood). Examples of the state of the mixture include, for example, simply a mixture of pulp fibers and a superabsorbent polymer, a pulp fiber aggregate containing a superabsorbent polymer, a pulp fiber aggregate in which a superabsorbent polymer is attached to part or all of the surface of the pulp fibers.

[0028] In this embodiment, an example in which the mixture of the superabsorbent polymer and pulp fibers is pulp fibers containing a superabsorbent polymer obtained from a used absorbent article will be described. However, the present invention is not limited to this embodiment, and appropriate changes and the like are possible within the scope not departing from the gist of the present invention. However, a used absorbent article means an absorbent article that has been transferred (for example, sold), has been used to absorb excreta (exemplified: urine, feces, menstrual blood), has been used but has not absorbed excreta, and an unused one, as well as an absorbent article that has not been transferred due to production loss or the like. Examples of absorbent articles include disposable diapers, urine pads, incontinence pads, sanitary napkins, disposable underwear, bed sheets, and pet sheets.

[0029] First, a configuration example of the absorbent article will be described. The absorbent article includes a surface sheet, a back sheet, and an absorber disposed between the surface sheet and the back sheet. Examples of the size of the absorbent article include, for example, a length of about 15 to 100 cm and a width of 5 to 100 cm, but it is not limited to this example. Note that the absorbent article may further include other members provided in a general absorbent article, for example, a diffusion sheet, a leak-proof wall, a side sheet, an outer packaging sheet, a filamentous or sheet-like elastic member disposed on the leak-proof wall or the outer packaging sheet.

[0030] Examples of the constituent members of the surface sheet include a liquid-permeable nonwoven fabric, a synthetic resin film having liquid-permeable pores, and a composite sheet thereof. Examples of the constituent members of the back sheet include a liquid-impermeable nonwoven fabric, a liquid-impermeable synthetic resin film, and a composite sheet thereof. Examples of the constituent members of the diffusion sheet include a liquid-permeable nonwoven fabric. Examples of the constituent members of the leak-proof wall and the side sheet include a water-repellent nonwoven fabric. Examples of the constituent members of the exterior sheet include a liquid-impermeable and breathable nonwoven fabric, a liquid-impermeable and breathable synthetic resin film, and a composite sheet thereof. Examples of the constituent members of the elastic member include a rubber-based synthetic resin. There is no particular limitation on the type of nonwoven fabric, and examples include a meltblown nonwoven fabric, a spunbond nonwoven fabric, an airlaid nonwoven fabric, and an air-through nonwoven fabric. There is no particular limitation on the type of synthetic resin film, and known film materials can be used. There is no particular limitation on the materials of the nonwoven fabric and the synthetic resin film as long as they can be used for absorbent articles. Examples include olefin-based resins such as polyethylene and polypropylene, polyamide-based resins such as 6-nylon and 6,6-nylon, and polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate. Examples of the material of the nonwoven fabric further include cellulose-based fibers. In order to impart breathability, the synthetic resin film may contain inorganic particles such as calcium carbonate. There is no particular limitation on the material of the rubber-based synthetic resin as long as it can be used for absorbent articles. Examples include styrene-butadiene rubber and urethane rubber. These materials such as nonwoven fabrics, synthetic resin films, and elastic members are synthetic resins and can be referred to as plastic materials.

[0031] As constituent members of the absorber, there may be mentioned an absorber material, for example, pulp fibers which are fibrous substances and superabsorbent polymers which are particulate substances. Examples of the pulp fibers which are fibrous substances include, for example, cellulose-based fibers. Examples of the cellulose-based fibers include, for example, wood pulp fibers, crosslinked pulp fibers, non-wood pulp fibers, regenerated cellulose fibers, and semi-synthetic cellulose fibers. As for the size of the pulp fibers, the average major axis of the fibers is, for example, several tens of μm, preferably 20 to 40 μm, and the average fiber length is, for example, several mm, preferably 2 to 5 mm. Examples of the superabsorbent polymer (SuperAbsorbent Polymer: SAP) which is a particulate substance include, for example, polyacrylate-based, polysulfonate-based, and maleic anhydride-based water-absorbent polymers. As for the size (when dry) of the superabsorbent polymer, the average particle diameter is, for example, several hundreds of μm, preferably 200 to 500 μm. The absorber may include a core wrap formed of a liquid-permeable sheet.

[0032] One surface and the other surface of the absorber are each joined to the surface sheet and the back sheet via an adhesive. In plan view, the portion (peripheral portion) of the surface sheet that extends outside the absorber so as to surround the absorber is joined to the portion (peripheral portion) of the back sheet that extends outside the absorber so as to surround the absorber via an adhesive. Therefore, the absorber is wrapped inside the joined body of the surface sheet and the back sheet. The adhesive is not particularly limited, and examples thereof include hot melt adhesives. Examples of the hot melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives mainly composed of rubber such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, styrene-isoprene-styrene, and polyurethane, or mainly composed of olefins such as polyethylene.

[0033] Next, a method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to the embodiment will be described. In this embodiment, the mixture of the superabsorbent polymer and pulp fibers is derived from a used absorbent article as described above.

[0034] FIG. 1 is a flowchart showing an example of a method for manufacturing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers according to an embodiment. This will be described in detail below.

[0035] As shown in FIG. 1, this method includes a first treatment step S6 and a second treatment step S9. This method may further include a fourth separation step S7, a supply step S8, and a fifth separation step S10. This method may further include a crushing step S1, a first separation step S2, a dust removal step S3, a second separation step S4, and a third separation step S5. Among these, the crushing step S1 to the third separation step S5 can also be said to be steps for preparing pulp fibers containing a superabsorbent polymer (a mixture of a superabsorbent polymer and pulp fibers), which are raw materials for the recycled fibers produced by this method. Also, the crushing step S1 to the fifth separation step S10 can also be said to be a method for producing each of a recycled plastic material, a superabsorbent polymer (SAP), and pulp fibers using used absorbent articles. This will be specifically described below.

[0036] In this embodiment, used absorbent articles are collected from the outside and used for reuse (recycling). At that time, by enclosing a plurality of used absorbent articles in a collection bag, leakage of excrement, fungi, and odors to the outside is suppressed. Each used absorbent article in the collection bag is collected in a rolled or folded state with the surface sheet on which excrement is excreted facing inward so that, for example, excrement and fungi are not exposed on the front side and odors do not diffuse to the surroundings. Note that the used absorbent articles do not necessarily have to be enclosed in a collection bag or rolled up.

[0037] The crushing step S1 is a step of crushing a used absorbent article together with an inactivating aqueous solution containing an inactivator that inactivates the superabsorbent polymer. The crushing step S1 is carried out by a crushing device such as a twin-shaft crusher. Crushing together with the inactivating aqueous solution means supplying the used absorbent article to the crushing device together with the inactivating aqueous solution and crushing it, putting the used absorbent article into the inactivating aqueous solution stored in the crushing device and crushing it, and combinations thereof. In the present embodiment, the used absorbent article is crushed while being supplied to the crushing device together with the inactivating aqueous solution. In this method, when the inactivating aqueous solution is used after the first separation step S2, if the inactivating aqueous solution is insufficient, it is appropriately replenished.

[0038] In the present embodiment, a collection bag containing a used absorbent article is supplied to a receiving device and moves to a crushing device communicating with the lower side of the receiving device. At the same time, an inactivating aqueous solution (exemplified: acidic aqueous solution) is supplied to the crushing device via the receiving device. At this time, the inactivating aqueous solution may be supplied so as to fall on the used absorbent article from above the used absorbent article. This is from the viewpoint of suppressing the scattering of crushed materials (including substances derived from excrement such as bacteria and odor-causing substances) during crushing. The collection bag is crushed together with the inactivating aqueous solution by the crushing device. Thereby, the used absorbent article in the collection bag is crushed in the inactivating aqueous solution together with the collection bag, and crushed materials having a size of, for example, 1 to 150 mm are generated. At this time, the superabsorbent polymer is inactivated and dehydrated by the inactivating aqueous solution to become small in particle size. The crushed materials are sent to the first separation step S2 together with the inactivating aqueous solution.

[0039] As the inactivating aqueous solution, it is preferable to use an aqueous solution of an inorganic acid and an organic acid, that is, an acidic aqueous solution. When using an acidic aqueous solution, it is difficult for ash and chlorine to remain in plastic materials, superabsorbent polymers, pulp fibers, etc., compared with the case of using an aqueous solution such as lime or calcium chloride, and the degree of inactivation (particle size and specific gravity) can be easily adjusted with pH. As the organic acid, citric acid having a chelating effect and a cleaning effect is preferable, and as the inorganic acid, sulfuric acid which does not contain chlorine and has a low cost is preferable. Note that as the inactivating aqueous solution, it may be inactivated with an aqueous solution containing a polyvalent metal ion source capable of supplying known polyvalent metal ions.

[0040] The pH of the acidic aqueous solution is preferably 1.0 to 4.0. When the pH is 1.0 or more, the equipment is difficult to corrode, and the alkaline chemicals required for the neutralization treatment during wastewater treatment can also be reduced. When the pH is 4.0 or less, the superabsorbent polymer can be made sufficiently small, and the sterilization ability can also be enhanced. Since the pH changes depending on the water temperature, the pH in the present invention refers to the pH measured at an aqueous solution temperature of 20°C. The concentration of the acidic aqueous solution is not particularly limited, but in the case of citric acid, it is preferably 0.5 to 4% by mass, and in the case of sulfuric acid, it is preferably 0.1 to 2.0% by mass.

[0041] During the crushing step S1, due to the heat generated during crushing and / or the heat of the acidic aqueous solution, etc., the bonding strength of the adhesive (for example, hot melt adhesive) between the respective components can be reduced, and the respective components can be easily separated from each other. Alternatively, by heating the acidic aqueous solution (temperature: 70 to 95°C), the adhesive (for example, hot melt adhesive) used for bonding between the components of the used absorbent article can be softened, and the bonding strength of the adhesive can be reduced. Thereby, the components can be easily separated from each other naturally or with a small impact. It is also possible to further sterilize (disinfect) the used absorbent article.

[0042] Next, the first separation step S2 separates the mixture of the plastic material, the inactivated superabsorbent polymer, the pulp fiber, the excrement, and the inactivated aqueous solution supplied from the crushing step S1 into a first fraction containing the plastic material and a second fraction containing the inactivated superabsorbent polymer, the pulp fiber, the excrement, and the inactivated aqueous solution. The first separation step S2 is carried out by a separation device such as a screen separator, a pulper separator, or a combination thereof.

[0043] In this embodiment, in the pulper separator, while the acidic aqueous solution containing the crushed material generated in the crushing step S1 is being stored and stirred, the crushed material is dissociated into constituent materials. Then, the acidic aqueous solution containing the crushed material (dissociated constituent materials) is separated by a screen, and the second fraction containing the inactivated superabsorbent polymer, the pulp fiber, the excrement, and the acidic aqueous solution becomes the accept and is sent to the dust removal step S3. On the other hand, the first fraction such as a collection bag, a film, and a non-woven fabric becomes the reject and is taken out. The taken-out collection bag, film, non-woven fabric, etc. are sterilized, washed, dried, etc. as necessary and recovered as a plastic material. Note that in the first separation step S2, another acidic aqueous solution not used in the crushing step S1 may be supplied as the acidic aqueous solution. At this time, a part of the pulp fiber, the superabsorbent polymer, and the excrement may not pass through the screen and remain on the screen together with the first fraction. On the other hand, a part of the collection bag, film, and non-woven fabric may pass through the screen together with the second fraction.

[0044] Note that when, as in this embodiment, the superabsorbent polymer is inactivated in advance, granulated, and its water absorption capacity is suppressed before the first separation step S2 (in the crushing step S1 or the like), after the first separation step S2, an inactivated aqueous solution (acidic aqueous solution) may not be used, and after substantially removing the inactivated aqueous solution, water (aqueous solution) not containing an inactivating agent may be used. In that case, water (aqueous solution) not containing an inactivating agent may be used from any step after the first separation step S2. Thereby, the usage amount of the inactivated aqueous solution (and the inactivating agent) can be reduced, and the burden of wastewater treatment can be reduced.

[0045] In this embodiment, in the first separation step S2, the pH of the acidic aqueous solution may be adjusted so as to be maintained within a predetermined range. The predetermined range of pH is such that the fluctuation of pH is within ±1.0. Thereby, the difference between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber can be made within a predetermined range. In this case, the difference being within the predetermined range means, for example, that one is within the range of 0.2 to 5 times that of the other. Thereby, the difference between the pulp fiber and the superabsorbent polymer is that the specific gravity is within a predetermined range and the size is within a predetermined range. As a result, the pulp fiber and the superabsorbent polymer can be easily separated from other materials (mainly plastic materials) excluding the pulp fiber and the superabsorbent polymer among the materials of the used absorbent article by utilizing the difference in size and specific gravity. The adjustment of pH can be performed using an acidic aqueous solution or an alkaline aqueous solution from a pH adjusting device installed in the separation device based on the pH value measured by a pH sensor installed in the separation device. Note that the pH may be similarly adjusted in at least one of the dust removal step S3, the second separation step S4, and the third separation step S5 described later.

[0046] Next, the dust removal step S3 is a step of removing (dusting) foreign matters from the mixed liquid containing the pulp fiber, the superabsorbent polymer, excrement, and the acidic aqueous solution separated in the first separation step S2. The dust removal step S3 is carried out by a dust removal device (examples: screen separator, cyclone separator, combination thereof).

[0047] In this embodiment, foreign matters such as other materials (collection bags, films, nonwoven fabrics, elastic members, etc.) that could not be completely separated from the mixed liquid supplied from the first separation step S2 are separated by the dust removal device. As the dust removal device, for example, a screen separator (relatively large mesh size), a screen separator (relatively small mesh size), and a cyclone separator are arranged in this order, and foreign matters are sequentially separated from the mixed liquid. Thereby, a mixed liquid containing pulp fiber, superabsorbent polymer, excrement, and acidic aqueous solution with few foreign matters is obtained. The mixed liquid is supplied to the second separation step S4. Note that when it is not necessary to separate foreign matters in the mixed liquid (examples: few foreign matters are contained, foreign matters are separated in other subsequent steps), the dust removal step S3 can be omitted.

[0048] Next, the second separation step S4 is a step of separating the superabsorbent polymer from the mixed solution containing pulp fibers with few foreign substances, the superabsorbent polymer, excrement, and an acidic aqueous solution, which is supplied from the dust removal step S3 (or the first separation step S2). The second separation step S4 is carried out by a separation device such as a screen separator, a drum screen separator, or a combination thereof.

[0049] In the present embodiment, by means of a drum screen separator, the superabsorbent polymer, excrement, and acidic aqueous solution, and pulp fibers, excrement, and acidic aqueous solution remaining on the surface or the like of the superabsorbent polymer are separated from the mixed solution supplied from the dust removal step S3 (or step S2). The pulp fibers remaining on the surface or the like of the superabsorbent polymer can be referred to as pulp fibers containing the superabsorbent polymer (a mixture of the superabsorbent polymer and pulp fibers). Thereby, a mixed solution containing the superabsorbent polymer, excrement, and acidic aqueous solution, and a mixed solution containing pulp fibers containing the superabsorbent polymer, excrement, and acidic aqueous solution are obtained. Then, the mixed solution containing the superabsorbent polymer, excrement, and acidic aqueous solution is removed of excrement and acidic aqueous solution, and is sterilized, washed, dried, etc. as necessary, and recovered as the superabsorbent polymer. The superabsorbent polymer separated and recovered in this way is reactivated as necessary to become a so-called recycled superabsorbent polymer (SAP in FIG. 1). On the other hand, the mixed solution containing pulp fibers containing the superabsorbent polymer, excrement, and acidic aqueous solution is supplied to the third separation step S5.

[0050] Next, the third separation step S5 is a step of separating the pulp fibers containing the superabsorbent polymer from the mixed solution containing pulp fibers containing the superabsorbent polymer, excrement, and acidic aqueous solution, which is supplied from the second separation step S4. The third separation step S5 is carried out by a separation device such as a screen separator, a drum screen separator, a screw press separator, or a combination thereof.

[0051] In this embodiment, a pulp fiber containing a superabsorbent polymer, excrement, and an acidic aqueous solution are separated from the mixed solution supplied from the second separation step S4 by a screen separator and / or a drum screen device. As a result, the pulp fiber containing the superabsorbent polymer, the excrement, and the acidic aqueous solution are taken out respectively. The pulp fiber containing the superabsorbent polymer is mixed with, for example, the first treatment liquid used in the first treatment step S6 and supplied to the first treatment step S6.

[0052] Thus, the crushing step S1 to the third separation step S5 can be said to be steps for preparing a pulp fiber containing a superabsorbent polymer (a mixture of a superabsorbent polymer and pulp fiber), which is a raw material for recycled fiber produced by this method, using a used absorbent article.

[0053] Next, the first treatment step S6 to the second treatment step S9 according to the embodiment will be described. First, the apparatus for executing the first treatment step S6 to the second treatment step S9 will be described.

[0054] FIG. 2 is a schematic view showing a configuration example of an apparatus 2 for carrying out the first treatment step S6 to the second treatment step S9. In the figure, the white arrows indicate the movement of pulp fibers, the thick arrows indicate the movement of ozone, and the thin arrows indicate the movement of the treatment liquid.

[0055] The apparatus 2 includes a first treatment device 4-1 that ozone-treats the pulp fiber separated in the third separation step S5 in the first treatment liquid 52-1, and a second treatment device 4-2 that ozone-treats the pulp fiber ozone-treated by the first treatment device 4-1 in the second treatment liquid 52-2. The apparatus 2 may further include a storage unit 3 that temporarily stores the pulp fiber separated in the third separation step S5, a separation device 14 that separates the pulp fiber ozone-treated in the first treatment liquid 52-1 from the first treatment liquid 52-1, and an adjustment device 15 that adjusts the solid content ratio of the second treatment liquid 52-2 with the separated pulp fiber.

[0056] The storage unit 3 includes a mixed liquid tank 12 and a stirrer 13. The mixed liquid tank 12 stores the mixed liquid 51 containing pulp fibers at a certain ratio in the first treatment liquid, which is supplied through the pipe 61. The stirrer 13 stirs the mixed liquid 51 in the mixed liquid tank 12 so that the pulp fibers in the mixed liquid 51 do not sink to the lower part of the mixed liquid 51.

[0057] The first treatment device 4-1 includes a supply pump P1, a first treatment tank 31-1, an ozone supply device 41 having an ozone generator 42 and a nozzle 43, and an ozone delivery device 44-1. The supply pump P1 is provided in the middle of the pipe 62 connecting the mixed liquid tank 12 and the first treatment tank 31-1, and supplies the mixed liquid 51 in the mixed liquid tank 12 into the first treatment tank 31-1. The first treatment tank 31-1 has the first treatment liquid 52-1. The first treatment liquid 52-1 is not particularly limited as long as it does not affect the ozone treatment. For example, water, acidic aqueous solutions (exemplified: sulfuric acid aqueous solution, citric acid aqueous solution), organic solvents (exemplified: methanol, acetone) can be mentioned.

[0058] The ozone supply device 41 supplies the ozone-containing gas 53, which is a gaseous substance, into the first treatment tank 31-1. Examples of the ozone generator 42 of the ozone supply device 41 include the ozone water exposure tester ED-OWX-2 manufactured by Eco Design Co., Ltd., and the ozone generator OS-25V manufactured by Mitsubishi Electric Corporation. The ozone-containing gas 53 is another type of gas containing ozone. For example, oxygen gas containing ozone can be mentioned. The ozone-containing gas 53 is supplied into the first treatment tank 31-1 through the pipe 71 connecting the ozone generator 42 and the first treatment tank 31-1. The nozzle 43 for delivering the ozone-containing gas 53 into the first treatment tank 31-1 is arranged at the lower part (preferably the bottom) of the first treatment tank 31-1. The nozzle 43 supplies the ozone-containing gas 53 as a plurality of fine bubbles into the first treatment liquid 52-1 from the lower part to the upper part of the first treatment tank 31-1.

[0059] The ozone delivery device 44-1 is provided in the middle of a pipe 72 that connects the upper part of the first treatment tank 31-1 and the nozzle 43 (described later) of the second treatment device 4-2. The ozone delivery device 44-1 is supplied to the first treatment liquid 52-1, passes through the first treatment liquid 52-1, and the ozone-containing gas 53 released from the first treatment liquid 52-1 is supplied to the second treatment device 4-2 via the pipe 72 while adjusting the flow rate as necessary (the unnecessary part is branched off to other uses (not shown)).

[0060] Note that the first treatment liquid 52-1 in the first treatment tank 31-1 is only the first treatment liquid 52-1 before the start of the first treatment step S6, and becomes a liquid in which the first treatment liquid 52-1 and the mixed liquid 51 are mixed after the start. Usually, the same treatment liquid is used for the first treatment liquid 52-1 and the mixed liquid 51. In this embodiment, including the liquid in which the first treatment liquid 52-1 and the mixed liquid 51 are mixed, the liquid in the first treatment tank 31-1 is referred to as the first treatment liquid 52-1.

[0061] The separation device 14 is provided in the middle of a pipe 63 that connects the lower part of the first treatment tank 31-1 and the upper part of the second treatment tank 31-2 (described later) of the second treatment device 4-2. The separation device 14 separates the pulp fibers ozone-treated with the first treatment liquid 52-1 in the first treatment tank 31-1 from the first treatment liquid 52-1. This is because the first treatment liquid 52-1 contains decomposition products of SAP, which are unnecessary substances. The separated pulp fibers are supplied to the adjustment device 15 via the pipe 63. Alternatively, the separated pulp fibers are directly supplied to the second treatment device 4-2 via the pipe 63 (without passing through the adjustment device 15). The separated first treatment liquid 52-1 is discharged to the first treatment tank 31-1 or to the outside (exemplified: a drainage treatment device) via the pipe 81. Examples of the separation device 14 include a screen separator, a drum screen separator, a screw press separator, or a combination thereof.

[0062] The adjusting device 15 is provided at a position closer to the second treatment device 4-2 (the second treatment tank 31-2 thereof) than the separation device 14 in the middle of the pipe 63. The adjusting device 15 uses the separated pulp fibers to adjust the solid content ratio of the second treatment liquid supplied through the pipe 82. The second treatment liquid containing pulp fibers with the adjusted solid content ratio is supplied to the second treatment device 4-2 (the second treatment tank 31-2 thereof) through the pipe 63 by a supply pump P2 (described later).

[0063] Note that the pulp fibers separated in the third separation step S5 may be directly supplied to the first treatment device 4-1. In that case, the storage unit 3 can be omitted. Also, the pulp fibers ozonated in the first treatment device 4-1 may be directly supplied to the second treatment device 4-2 without being separated from the first treatment liquid 52-1. In that case, the separation device 14 and the adjusting device 15 can be omitted.

[0064] The second treatment device 4-2 includes a supply pump P2, a second treatment tank 31-2, a nozzle 43 for ozone supply, and an ozone delivery device 44-2. The supply pump P2 is provided in the middle of the pipe 63 and supplies the first treatment liquid 52-1 containing pulp fibers or the second treatment liquid containing pulp fibers with the solid content ratio adjusted by the adjusting device 15 into the second treatment tank 31-2. The second treatment tank 31-2 contains the second treatment liquid 52-2. The second treatment liquid 52-2 is not particularly limited as long as it does not affect the ozone treatment, and examples include water, acidic aqueous solutions, and organic solvents. Also, usually, the second treatment liquid 52-2 is the same as the first treatment liquid 52-1, but it does not necessarily have to be the same as the first treatment liquid 52-1.

[0065] The nozzle 43 for ozone supply is arranged at the lower part (preferably the bottom) of the second treatment tank 31-2 and is connected to the ozone delivery device 44-1 through the pipe 72. Therefore, the nozzle 43 supplies the ozone-containing gas 53 supplied from the ozone delivery device 44-1 into the second treatment liquid 52-2 as a plurality of fine bubbles from the lower part to the upper part of the second treatment tank 31-2. Note that the second treatment device 4-2 may further have an ozone supply device 41 for assisting the ozone-containing gas 53 supplied from the ozone delivery device 44-1.

[0066] The ozone delivery device 44-2 is provided in the middle of a pipe 73 that connects the upper part of the second treatment tank 31-2 and a device (not shown) to which other ozone-containing gas is to be supplied. The ozone delivery device 44-2 passes through the second treatment liquid 52-2 and supplies the ozone-containing gas 53 released from the second treatment liquid 52-2 to a device to which other ozone-containing gas is to be supplied via the pipe 73.

[0067] Note that the second treatment liquid 52-2 in the second treatment tank 31-2 is only the second treatment liquid 52-2 before the start of the second treatment step S9, and after the start, it becomes a mixed liquid of the first treatment liquid 52-1 from the first treatment tank 31-1 and the second treatment liquid 52-2, or a mixed liquid of the second treatment liquid 52-2 of the adjustment device 15 and the second treatment liquid 52-2 of the second treatment tank 31-2. Usually, the same treatment liquid is used for the first treatment liquid 52-1 and the second treatment liquid 52-2. In this embodiment, including these, the liquid in the second treatment tank 31-2 is referred to as the second treatment liquid 52-2. Also, the first treatment liquid 52-1 and the second treatment liquid 52-2 may be the same.

[0068] Next, the first treatment step S6 to the second treatment step S9 will be described.

[0069] The first treatment step S6 is a step of treating pulp fibers containing a superabsorbent polymer with ozone in the first treatment liquid 52-1 while supplying ozone to the first treatment liquid 52-1 in the first treatment tank 31-1 to remove at least a part of the superabsorbent polymer. In this step, as an ozone treatment, a treatment is carried out to oxidatively decompose the superabsorbent polymer contained in the pulp with ozone in the first treatment liquid 52-1, reduce its molecular weight, and turn it into a decomposition product of the superabsorbent polymer. Since the decomposition product is a low-molecular-weight organic substance soluble in the first treatment liquid 52-1, it dissolves in the first treatment liquid 52-1 and is removed from the pulp fibers. Thereby, impurities such as superabsorbent polymers contained in the pulp fibers can be removed, and high-purity pulp fibers can be produced. In the first treatment step S6, sterilization, bleaching, and deodorization of the pulp fibers can also be performed by ozone treatment.

[0070] In this embodiment, first, the pulp fibers separated in the third separation step S5 (mainly with superabsorbent polymers remaining on the surface) are mixed with an acidic aqueous solution to form a mixed solution 51 so as to reach a preset concentration. The concentration of the pulp fibers in the mixed solution 51 is set to reach a preset concentration in a state where it is put into the first treatment tank 31-1 and mixed with the first treatment liquid 52-1. The mixed solution 51 is supplied to the mixed solution tank 12 via the pipe 61 and stored. Since the specific gravity of the pulp fibers is greater than 1, the mixed solution 51 is stirred by the stirrer 13 in the mixed solution tank 12 so that the pulp fibers and water do not separate.

[0071] Then, the mixed solution 51 in the mixed solution tank 12 is continuously or intermittently supplied to the first treatment tank 31-1 according to the opening and closing control of the valve V1 of the pipe 62 and the flow rate control of the supply pump P1. Thereby, the pulp fibers are supplied into the first treatment liquid 52-1 from the first supply port 32-1 provided at the upper part of the first treatment tank 31-1. The first treatment liquid 52-1 is an acidic aqueous solution and has a specific gravity of approximately 1. Therefore, the pulp fibers settle from the upper part to the lower part of the first treatment liquid 52-1.

[0072] On the other hand, the ozone-containing gas 53 generated by the ozone generator 42 is supplied to the first treatment tank 31-1 via the pipe 71 and is discharged from the nozzle 43 of the first treatment tank 31-1 into the first treatment liquid 52-1 in the state of fine bubbles (example: microbubbles or nanobubbles). The ozone-containing gas 53 rises from the lower part to the upper part of the first treatment liquid 52-1.

[0073] Then, in the first treatment liquid 52-1, pulp fibers that sediment from the upper part to the lower part and ozone-containing gas 53 that rises from the lower part to the upper part collide with each other while advancing in opposite directions. Then, the ozone-containing gas 53 adheres to the surface of the pulp fibers so as to wrap the pulp fibers. At this time, ozone in the ozone-containing gas 53 reacts with the superabsorbent polymer in the pulp fibers, oxidatively decomposes the superabsorbent polymer, reduces its molecular weight, and dissolves it in the first treatment liquid 52-1. Thereby, the superabsorbent polymer on the pulp fibers is removed from the pulp fibers. Then, the pulp fibers sediment to the bottom of the first treatment tank 31-1, and the ozone-containing gas 53 escapes to the upper space of the first treatment tank 31-1.

[0074] Thereafter, the first treatment liquid 52-1 (including pulp fibers) at the bottom of the first treatment tank 31-1 is supplied from the first outlet 33-1 of the first treatment tank 31-1 through the open valve V2 to the separation device 14 via the pipe 63.

[0075] Next, the fourth separation step (separation step) S7 is a step of separating the pulp fibers treated in the first treatment step S6 from the first treatment liquid 52-1. The separated pulp fibers are supplied to the adjustment device 15 or to the second treatment device 4-2. The method of separating the pulp fibers from the first treatment liquid 52-1 is not particularly limited, and examples include a method of passing the first treatment liquid 52-1 containing pulp fibers through a screen mesh having an aperture of 0.15 to 2 mm, for example. When the first treatment liquid 52-1 containing pulp fibers is passed through a screen mesh having an aperture of 0.15 to 2 mm, the waste water containing the products of oxidative decomposition of the superabsorbent polymer passes through the screen, but the pulp fibers do not pass through and remain on the screen mesh.

[0076] In this embodiment, by controlling the opening and closing of the valve V2 of the pipe 63, the separation device 14 (screen separator) is supplied with the first treatment liquid 52-1 containing ozone-treated pulp fibers from the first discharge port 33-1 of the first treatment tank 31-1 through the pipe 63. In the separation device 14, pulp fibers are separated from the first treatment liquid 52-1 containing pulp fibers. The pulp fibers separated from the first treatment liquid 52-1 are supplied to the adjustment device 15 through the pipe 63. The remaining first treatment liquid 52-1 from which the pulp fibers have been separated is sent, for example, to the first treatment tank 31-1 or the like through the pipe 81 and reused, or discharged to the outside (example: wastewater treatment device).

[0077] Next, the adjustment step S8 is a step of adjusting the solid content ratio of the second treatment liquid with the separated pulp fibers. The second treatment liquid containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment tank 31-2. However, the second treatment liquid used for adjusting the solid content ratio is a treatment liquid different from the second treatment liquid 52-2 stored in the second treatment tank 31-2.

[0078] In this embodiment, the separated pulp fibers are supplied from the separation device 14 to the adjustment device 15 through the pipe 63. In the adjustment device 15, the separated pulp fibers are adjusted so that the solid content ratio of the second treatment liquid supplied through the pipe 82 is at a desired value. The second treatment liquid containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment device 4-2 (the second treatment tank 31-2 thereof) through the pipe 63 by a supply pump P2 (described later).

[0079] The solid content ratio of the second treatment liquid 52-2 is the content ratio of pulp fibers in the second treatment liquid, and examples thereof include 0.5 to 20% by mass, and preferably 1 to 15% by mass. If the solid content ratio is too small, the efficiency of supply and ozone treatment will decrease too much, and if it is too large, supply will be difficult and ozone treatment may not be evenly performed.

[0080] Note that the fourth separation step S7 (separation device 14) and the adjustment step S8 (adjustment device 15) may not be performed when, for example, the decomposition products of the superabsorbent polymer in the first treatment liquid 52-1 after the first treatment step S6 are few. In that case, the treatment efficiency can be increased and the cost can be suppressed.

[0081] Next, in the second treatment step S9, ozone discharged from the first treatment liquid 52-1 in the first treatment tank 31-1 is supplied to the second treatment liquid 52-2 in the second treatment tank 31-2, and in the second treatment liquid 52-2, the pulp fibers are treated with ozone. However, as the ozone, at least a part of the ozone discharged from the first treatment liquid 52-1 in the first treatment tank 31-1 may be used, and it is preferable to use as much as possible. If there is any remaining ozone discharged from the first treatment liquid 52-1 in the first treatment tank 31-1, that ozone may be used for other purposes. Further, if necessary, another ozone may be added in the second treatment step S9. The ozone treatment performed in the second treatment step S9 is not particularly limited, and examples thereof include at least one of the following treatment steps.

[0082] That is, as the second treatment step S9, there may be a step of treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to perform at least one of deodorization, bleaching, and sterilization. This can be performed, for example, when the superabsorbent polymer of the pulp fibers is sufficiently removed in the first treatment step S6. In this case, the ozone concentration (mass ppm), the treatment time in the treatment tank (minutes), or the product thereof (hereinafter also referred to as "CT value (ppm·min)") can be very small as compared with the case of the first treatment step S6. Therefore, whether ozone is injected into the first treatment liquid 52-1 at a high concentration and high flow rate or not, it can be sufficiently covered by the ozone discharged from the first treatment liquid 52-1 in the first treatment tank 31-1.

[0083] Alternatively, as the second treatment step S9, there may be a step of treating the pulp fibers treated in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to remove at least a part of the superabsorbent polymer. This can be carried out, for example, when the superabsorbent polymer of the pulp fibers has not been sufficiently removed in the first treatment step S6. In this case, the ozone concentration (mass ppm), the treatment time (minutes) in the treatment tank, or the CT value (ppm·min) can be of the same level or slightly lower compared to the case of the first treatment step S6. Therefore, when ozone is injected into the first treatment liquid 52-1 at a high concentration and high flow rate, it can be sufficiently covered by the ozone released from the first treatment liquid 52-1 in the first treatment tank 31-1.

[0084] In this embodiment, first, the first treatment liquid 52-1 containing the pulp fibers treated in the first treatment step S6, the pulp fibers separated in the fourth separation step S7, or the second treatment liquid whose solid content ratio of the pulp fibers has been adjusted in the adjustment step S8 is continuously or intermittently supplied to the second treatment tank 31-2 according to the opening and closing control of the valves V2 and / or V3 of the pipe 63 and the flow rate control of the supply pump P2. Thereby, the pulp fibers are supplied into the second treatment liquid 52-2 from the second supply port 32-2 provided at the upper part of the second treatment tank 31-2. The second treatment liquid 52-2 is an acidic aqueous solution and has a specific gravity of approximately 1. Therefore, the pulp fibers settle from the upper part to the lower part of the second treatment liquid 52-2.

[0085] On the other hand, the ozone-containing gas 53 released from the first treatment liquid 52-1 in the first treatment tank 31-1 is supplied to the second treatment tank 31-2 through the pipe 72 and is released from the nozzle 43 of the second treatment tank 31-2 into the second treatment liquid 52-2 in the state of fine bubbles (example: microbubbles or nanobubbles). The ozone-containing gas 53 rises from the lower part to the upper part of the second treatment liquid 52-2.

[0086] Then, inside the second treatment liquid 52-2, pulp fibers that sediment from the upper part to the lower part and ozone-containing gas 53 that rises from the lower part to the upper part collide with each other while advancing in opposite directions. Then, the ozone-containing gas 53 adheres to the surface of the pulp fibers so as to wrap around the pulp fibers. At this time, ozone in the ozone-containing gas 53 reacts with the superabsorbent polymer in the pulp fibers, oxidatively decomposes the superabsorbent polymer, reduces its molecular weight, and dissolves it in the second treatment liquid 52-2. Thereby, the superabsorbent polymer on the pulp fibers is removed from the pulp fibers. Then, the pulp fibers sediment to the bottom of the second treatment tank 31-2, and the ozone-containing gas 53 escapes to the upper space of the second treatment tank 31-2.

[0087] Thereafter, the second treatment liquid 52-2 (including pulp fibers) at the bottom of the second treatment tank 31-2 is supplied from the second outlet 33-2 of the second treatment tank 31-2 through the open valve V4 to the fifth separation step S10 via the pipe 64.

[0088] Next, the fifth separation step S10 is a step of separating the pulp fibers treated in the second treatment step S9 from the second treatment liquid 52-2. The separated pulp fibers are taken out as recycled pulp fibers. The method of separating the pulp fibers from the second treatment liquid 52-2 is not particularly limited, and examples include passing the second treatment liquid 52-2 containing pulp fibers through a screen mesh having an aperture of, for example, 0.15 to 2 mm. Thereby, the wastewater containing the products of oxidative decomposition of the superabsorbent polymer passes through the screen. On the other hand, the pulp fibers remain on the screen and are taken out as high-quality pulp fibers (recycled pulp fibers).

[0089] In this embodiment, the pulp fibers processed in the second treatment step S9 are supplied from the second outlet 33-2 of the second treatment tank 31-2 to the separation device (screen separator: not shown) according to the opening / closing control of the valve V4 of the pipe 64 and the flow rate control of the supply pump P3. In the separation device, the pulp fibers are separated from the second treatment liquid 52-2 containing the pulp fibers and taken out. The remaining second treatment liquid 52-2 from which the pulp fibers have been separated is sent to the second treatment tank 31-2 or the like via a pipe, for example, and reused, or discharged to the outside. The taken-out pulp fibers are sterilized, washed, dried, etc. as necessary, and recovered as pulp fibers. The pulp fibers separated and recovered in this way become so-called recycled pulp fibers.

[0090] In addition, in the above embodiment, as the second treatment step, the pulp fibers ozone-treated in the first treatment step S6 are further ozone-treated. However, the second treatment step is not limited to this example. For example, as the second treatment step, in the second treatment liquid 52-2 in the second treatment tank 31-2, the pulp fibers containing a superabsorbent polymer newly supplied separately from the pulp fibers ozone-treated in the first treatment step S6 are ozone-treated to remove at least a part of the superabsorbent polymer. This can be carried out, for example, when it is desired to remove the superabsorbent polymer from pulp fibers different from the pulp fibers treated in the first treatment step S6.

[0091] Alternatively, as the second treatment step, in the second treatment liquid 52-2 in the second treatment tank 31-2, the pulp fibers newly supplied separately from the pulp fibers ozone-treated in the first treatment step S6 are ozone-treated to perform at least one of deodorization, bleaching, and sterilization. This can be carried out, for example, when at least one of deodorization, bleaching, and sterilization is required for pulp fibers different from the pulp fibers treated in the first treatment step S6.

[0092] Alternatively, in the above-described embodiment, as the second treatment step, an ozone treatment step for pulp fibers using the second treatment apparatus 4-2 is exemplified. However, the second treatment step is not limited to this example. As the second treatment step, in another second treatment liquid in another second treatment tank, ozone treatment is performed on a component other than the pulp fibers in the first treatment step S6, for example, a plastic material or a superabsorbent polymer, to perform at least one of deodorization, bleaching, and sterilization. This can be carried out, for example, when at least one of deodorization, bleaching, and sterilization is required for a component other than the pulp fibers treated in the first treatment step S6. For example, a treatment for performing at least one of deodorization, bleaching, and sterilization on the plastic material recovered in the first separation step or the superabsorbent polymer recovered in the second separation step S4 can be mentioned. In that case, this method can also be said to be a method for treating a plastic material or a superabsorbent polymer.

[0093] In the ozone treatment for oxidatively decomposing the superabsorbent polymer in the first treatment step S6 and the second treatment step S9, the ozone concentration in the treatment liquid is not particularly limited as long as it can decompose the superabsorbent polymer. Examples of the ozone concentration in the treatment liquid include 10 to 50 mass ppm. By the concentration not being too low, the superabsorbent polymer can be completely solubilized, and by the concentration not being too high, the pulp fibers are not damaged. The treatment time in the treatment liquid is not particularly limited as long as it can decompose the superabsorbent polymer, but it is shorter when the ozone concentration of the treatment liquid is high and longer when the ozone concentration is low. The contact time is typically 5 to 300 minutes. The CT value (ppm·min), which is the product of the ozone concentration (ppm) of the treatment liquid and the treatment time (min) of the treatment step, includes, for example, 100 to 15000 ppm·min. If the CT value is too small, there is a risk that the superabsorbent polymer cannot be completely solubilized and the superabsorbent polymer remains in the pulp fibers, and if the CT value is too large, there is a risk of damaging the pulp fibers.

[0094] In the ozone treatment for performing at least one of deodorization, bleaching, and sterilization of the constituent members (examples: pulp fibers, superabsorbent polymers, plastic materials) in the second treatment step S9, the ozone concentration in the treatment liquid is not particularly limited as long as it is a concentration at which at least one of deodorization, bleaching, and sterilization of the constituent members can be performed. Examples of the ozone concentration in the treatment liquid include 0.3 to 2 mass ppm. If the concentration is too low, it becomes difficult to remove bacteria and the like, and if the concentration is too high, there is a risk that adverse effects will begin to occur on the constituent members. The contact time between the ozone water and the constituent members is not particularly limited as long as it is a time capable of removing bacteria and other organic substances adhering to the surface of the constituent members, but it is shorter when the ozone concentration in the treatment liquid is high and longer when the ozone concentration is low. The contact time is typically 0.3 seconds to 15 minutes. Examples of the CT value (ppm·min), which is the product of the ozone concentration (ppm) and the contact time (min) in the treatment liquid, include 0.05 to 20 ppm·min. If the CT value is too small, it becomes difficult to perform sterilization and the like, and if the CT value is too large, there is a risk that adverse effects will begin to occur on the constituent members.

[0095] As described above, in this method, for the ozone treatment of the pulp fibers in the first treatment step S6, it is supplied to the first treatment liquid 52-1 in the first treatment tank 31-1, and the ozone discharged (passed through) from the first treatment liquid 52-1 is supplied to the second treatment liquid 52-2 in the second treatment tank 31-2 and used for the ozone treatment of the pulp fibers in the second treatment step S9. That is, in this method, in order to increase the treatment speed of the ozone treatment, by supplying ozone to the first treatment liquid 52-1 at a high concentration and high flow rate, even if a large amount of ozone is discharged (passed through) without dissolving in the first treatment liquid 52-1, the discharged ozone can be used in the second treatment step S9. In this way, by using the ozone supplied for the ozone treatment in the first treatment step S6 also in the ozone treatment in the second treatment step S9, ozone can be effectively utilized. Therefore, the treatment speed in the ozone treatment in the first treatment step S6 can be increased, and the energy efficiency of the ozone treatment can be increased. Thus, in the method for producing recycled fibers from pulp fibers containing a superabsorbent polymer, it is possible to achieve both the treatment speed and the energy efficiency in the ozone treatment.

[0096] In a preferred embodiment of the present method, the first treatment step S6 may include a continuous treatment step of continuously supplying pulp fibers and a first treatment liquid 52-1 into the first treatment tank 31-1, treating the pulp fibers with ozone, and continuously discharging the first treatment liquid 52-1 containing the pulp fibers treated with ozone out of the first treatment tank 31-1. In other words, this first treatment step S6 is a continuous treatment that continuously executes the first treatment step S6 without interruption. Accordingly, the second treatment step S9 may also include a similar continuous treatment.

[0097] For example, in the first treatment device 4-1, by opening valves V1 and V2 and controlling the flow rates by supply pumps P1 and P2 so that the first treatment liquid (mixed liquid 51) is continuously supplied to the first treatment tank 31-1 and the first treatment liquid 52-1 is continuously discharged from the first treatment tank 31-1, a continuous treatment can be realized. It is preferable that the flow rate of the first treatment liquid supplied to the first treatment tank 31-1 is equal to the flow rate of the first treatment liquid 52-1 discharged from the first treatment tank 31-1. Accordingly, in the second treatment device 4-2, by opening valves V3 and V4 and similarly controlling the flow rates of the first treatment liquid 52-1 or the second treatment liquid 52-2 supplied to the second treatment tank 31-2 and the second treatment liquid 52-2 discharged from the second treatment tank 31-2 by supply pumps P2 and P3, a similar continuous treatment can be realized. However, in this case, the first treatment liquid 52-1 remains the second treatment liquid 52-2 as it is.

[0098] Thus, in a preferred embodiment of the present method, while continuously supplying pulp fibers and the first treatment liquid (mixed liquid 51) into the first treatment tank 31-1, the pulp fibers are subjected to ozone treatment (while the superabsorbent polymer is oxidatively decomposed, dissolved, and removed), and the first treatment liquid 52-1 containing the ozone-treated pulp fibers is continuously sent out of the first treatment tank 31-1. That is, the pulp fibers are continuously treated. Therefore, in the first treatment tank 31-1, a continuous and stable flow of the first treatment liquid 52-1 can be generated from the first supply port 32-1 toward the first discharge port 33-1. Thereby, ozone dissolved in the first treatment liquid 52-1 and ozone passing through the first treatment liquid 52-1 and the pulp fibers can be drawn into the flow and made to easily come into contact with each other. That is, the pulp fibers can be continuously brought into contact with ozone. Therefore, a large amount of ozone contributing to the decomposition of the superabsorbent polymer can be obtained, and the treatment speed and energy efficiency in the ozone treatment can be increased.

[0099] In a preferred embodiment of the present method, the first treatment step S6 may include a preparation step, a batch treatment step, and a sending-out step. However, the preparation step is a step of preparing the first treatment liquid 52-1 containing pulp fibers in the first treatment tank 31-1. The batch treatment step is a step of treating the pulp fibers with ozone after the preparation step. The sending-out step is a step of sending out the first treatment liquid 52-1 containing the pulp fibers treated with ozone out of the first treatment tank 31-1 after the batch treatment step. In other words, this first treatment step S6 is a batch treatment in which the pulp fibers and the first treatment liquid 52-1 are put into the first treatment tank 31-1 and then the first treatment step S6 is carried out in a closed state. Accordingly, the second treatment step S9 may also include a similar batch treatment.

[0100] For example, in the first processing device 4-1, the valve V1 is opened and the valve V2 is closed, and the supply pump P1 controls the flow rate so that a predetermined amount of the first processing liquid (mixed liquid 51) is supplied to the first processing tank 31-1. After that, the supply pump P1 is stopped, the valve V1 is closed, and ozone treatment of the pulp fibers is performed in the first processing tank 31-1 containing a predetermined amount of the first processing liquid 52-1 (containing the mixed liquid 51), whereby batch processing can be realized. Thereafter, accordingly, in the second processing device 4-2, the valves V2 and V3 are opened and the valve V4 is closed, and the supply pump P2 controls the flow rate so that the first processing liquid 52-1 is supplied to the second processing tank 31-2 in a predetermined amount. After that, the supply pump P2 is stopped, the valves V2 and V3 are closed, and ozone treatment of the pulp fibers is performed in the second processing tank 31-2 containing a predetermined amount of the first processing liquid 52-1, whereby batch processing can be realized in the same manner. However, in this case, the first processing liquid 52-1 remains the second processing liquid 52-2 as it is.

[0101] Thus, in a preferred embodiment of this method, first, the first processing liquid 52-1 containing pulp fibers is prepared in the first processing tank 31-1, and then the pulp fibers are ozone-treated (the superabsorbent polymer is oxidized, decomposed, dissolved, and removed), and thereafter, the first processing liquid 52-1 containing the ozone-treated pulp fibers is sent out of the first processing tank 31-1. That is, the pulp fibers are batch-processed. Therefore, in the first processing tank 31-1, the pulp fibers remaining in the first processing liquid 52-1 can be made to easily and continuously contact the ozone dissolved in the first processing liquid 52-1 or the ozone passing through the first processing liquid 52-1. Thereby, it becomes possible to continuously treat the pulp fibers with ozone. Therefore, more ozone contributing to the decomposition of the superabsorbent polymer can be obtained, and the processing speed and energy efficiency in the ozone treatment can be increased.

[0102] In a preferred embodiment of this method, it further includes a separation step (fourth separation step S7) of separating the pulp fibers treated in the first processing step S1 from the first processing liquid 52-1. And the separated pulp fibers are supplied to the second processing tank 31-2.

[0103] After the first treatment step S6, the first treatment liquid 52-1 contains, in addition to pulp fibers from which at least a part of the superabsorbent polymer has been removed, low-molecular-weight organic substances produced by oxidative decomposition of the superabsorbent polymer. Therefore, when the pulp fibers are supplied to the second treatment step S9 together with the first treatment liquid 52-1, the second treatment liquid 52-2 in the second treatment step S9 will contain not only the pulp fibers but also low-molecular-weight organic substances. Then, the ozone in the second treatment liquid 52-2 will be supplied not only to the pulp fibers but also to the low-molecular-weight organic substances, and there is a risk that the ozone cannot be effectively used for the treatment of the pulp fibers.

[0104] Therefore, in this method, the pulp fibers treated in the first treatment step S6 are separated from the first treatment liquid 52-1 (fourth separation step S7), and the separated pulp fibers are supplied to the second treatment tank 31-2. That is, since the pulp fibers are separated from the low-molecular-weight organic substances and then supplied to the second treatment tank 31-2, it is possible to suppress the inclusion of low-molecular-weight organic substances in the second treatment liquid 52-2 in the second treatment step S9. As a result, the ozone in the second treatment liquid 52-2 will be supplied mainly to the pulp fibers only, and the ozone can be effectively used for the treatment of the pulp fibers. Therefore, the treatment speed and energy efficiency of the ozone treatment in the second treatment step S9 can be increased.

[0105] In a preferred embodiment of this method, it further includes a separation step (fourth separation step S7) of separating the pulp fibers treated in the first treatment step S6 from the first treatment liquid 52-1, and an adjustment step S8 of adjusting the solid content ratio of the second treatment liquid 52-2 with the separated pulp fibers. The second treatment liquid 52-2 containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment tank 31-2.

[0106] Thus, in a preferred embodiment of the present method, the pulp fibers processed in the first treatment step S6 are separated from the first treatment liquid 52-1 (the fourth separation step S7), and the second treatment liquid 52-2 with the solid content ratio adjusted by the separated pulp fibers is supplied to the second treatment tank 31-2 (the adjustment step S8). That is, the pulp fibers are separated from the low-molecular-weight organic substances, mixed with the new second treatment liquid 52-2 to have an appropriate solid content ratio, and supplied to the second treatment tank 31-2. Therefore, it is possible to suppress the inclusion of low-molecular-weight organic substances in the second treatment liquid 52-2 in the second treatment step S9, and to make the ratio of ozone to pulp fibers during the ozone treatment appropriate. Thereby, the ozone in the second treatment liquid 52-2 is supplied mainly to the pulp fibers only, and the concentration of the pulp is appropriate, so that the ozone can be effectively used for the treatment of the pulp fibers. Therefore, the treatment speed and energy efficiency of the ozone treatment in the second treatment step S9 can be increased.

[0107] In a preferred embodiment of the present method, the second treatment step S9 includes a step of treating the pulp fibers processed in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to perform at least one of deodorization, bleaching, and sterilization. In this way, by using the ozone supplied for the ozone treatment in the first treatment step S6 in the ozone treatment for performing at least one of deodorization, bleaching, and sterilization in the second treatment step S9, the ozone can be effectively utilized. And in the present method, it is possible to produce pulp fibers in which deodorization, bleaching, and sterilization have further progressed from the first treatment step S6.

[0108] In a preferred embodiment of the present method, the second treatment step S9 includes a step of treating the pulp fibers processed in the first treatment step S6 with ozone in the second treatment liquid 52-2 in the second treatment tank 31-2 to remove at least a part of the superabsorbent polymer. In this way, by using the ozone supplied for the ozone treatment in the first treatment step S6 in the ozone treatment for removing at least a part of the superabsorbent polymer in the second treatment step S9, the ozone can be effectively utilized. And in the present method, it is possible to produce pulp fibers in which the removal of the superabsorbent polymer has further progressed from the first treatment step S6.

[0109] In this embodiment, pulp fibers containing a superabsorbent polymer (a mixture of a superabsorbent polymer and pulp fibers) are treated in two steps (the first treatment step S6 and the second treatment step S9) using ozone in the first treatment step S6, but they may be treated in three or more steps using the ozone.

[0110] In this embodiment, for the ozone treatment of the pulp fibers in the first treatment step S6, it is supplied to the first treatment liquid 52-1, and the ozone that has passed through (been discharged from) the first treatment liquid 52-1 is reused in another step such as the ozone treatment of the pulp fibers in the second treatment step S9. Thus, since this method is a method of reusing ozone that is discharged (passes through) without being utilized and is discarded, it can also be called a method of reusing waste ozone (an ozone recycling method). Also, the first treatment step S6 to the second treatment step S9 can also be said to be a method of removing the superabsorbent polymer from pulp fibers containing a superabsorbent polymer (a mixture of a superabsorbent polymer and pulp fibers).

[0111] The absorbent article of the present invention is not limited to the above-described embodiments, and appropriate combinations, changes, etc. are possible within the scope not departing from the object and gist of the present invention.

Explanation of Reference Numerals

[0112] S6 First treatment step S9 Second treatment step 31-1 First treatment tank 31-2 Second treatment tank 52-1 First treatment liquid 52-2 Second treatment liquid

Claims

1. A method for producing recycled fibers from a mixture of a superabsorbent polymer and pulp fibers, comprising: a first treatment step of treating a mixture of a superabsorbent polymer and pulp fibers with ozone in a first treatment liquid in a first treatment tank while supplying ozone to the first treatment liquid in the first treatment tank to remove at least a part of the superabsorbent polymer; a second treatment step of treating pulp fibers with ozone in a second treatment liquid in a second treatment tank while supplying the ozone released from the first treatment liquid in the first treatment tank to the second treatment liquid in the second treatment tank; and comprising: a method.

2. The method according to claim 1, wherein the first treatment step includes a continuous treatment step of continuously supplying the pulp fibers and the first treatment liquid into the first treatment tank, treating the pulp fibers with ozone, and continuously sending out the first treatment liquid containing the pulp fibers treated with ozone outside the first treatment tank. The method according to claim 1.

3. The first treatment step includes: a preparation step of preparing the first treatment liquid containing the pulp fibers in the first treatment tank; a batch treatment step of treating the pulp fibers with ozone after the preparation step; and a sending step of sending out the first treatment liquid containing the pulp fibers treated with ozone outside the first treatment tank after the batch treatment step. and comprising: The method according to claim 1.

4. The method according to any one of claims 1 to 3, further comprising a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid, wherein the separated pulp fibers are supplied to the second treatment tank. The separated pulp fibers are supplied to the second treatment tank. The method according to any one of claims 1 to 3.

5. a separation step of separating the pulp fibers treated in the first treatment step from the first treatment liquid; an adjustment step of adjusting the solid content ratio of the second treatment liquid with the separated pulp fibers; and further comprising: The method according to any one of claims 1 to 3, wherein the second treatment liquid containing the pulp fibers with the adjusted solid content ratio is supplied to the second treatment tank. The method according to any one of claims 1 to 3.

6. The method according to any one of claims 1 to 3, wherein the second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the second treatment liquid in the second treatment tank to perform at least one of deodorization, bleaching, and sterilization. The method according to any one of claims 1 to 3.

7. The second treatment step includes a step of treating the pulp fibers treated in the first treatment step with ozone in the second treatment liquid in the second treatment tank to remove at least a part of the superabsorbent polymer. The method according to any one of claims 1 to 3.

8. The method further includes a step of preparing a mixture of the superabsorbent polymer and pulp fibers taken out from a used absorbent article as the mixture of the superabsorbent polymer and pulp fibers used in the first treatment step. The method according to any one of claims 1 to 3.

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