Method for producing recycled pulp fibers derived from used absorbent articles and recycled pulp fibers derived from used absorbent articles

Abstract

The present invention provides a method for producing recycled pulp fibers derived from used absorbent articles that is highly safe and has a high cleaning effect. [Solution] A method for producing recycled pulp fibers from used absorbent articles comprises a dewatering and washing step and a separation step. In the dewatering and washing step S3, a mixture containing pulp fibers from used absorbent articles and a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water is stirred to dewater the pulp fibers. In the separation step, the pulp fibers are separated from the mixture.

Description

[Technical Field]

[0001] This invention relates to a method for producing recycled pulp fibers derived from used absorbent articles and to recycled pulp fibers derived from used absorbent articles. [Background technology]

[0002] Methods for producing recycled materials derived from used absorbent articles, such as recycled plastic materials, recycled superabsorbent polymers, and recycled pulp fibers, are known. For example, Patent Document 1 discloses a method for recycling superabsorbent resin derived from used absorbent articles, characterized by draining the absorbent liquid from the superabsorbent resin containing the absorbent liquid and restoring the water absorption capacity of the superabsorbent resin. This method includes (i) an immersion step of immersing a used absorbent article containing superabsorbent resin that has absorbed the absorbent liquid in an immersion solution containing a hydrophilic organic solvent; (ii) a crushing step of crushing the used absorbent article into crushed material in or before the immersion step; and (iii) a separation step of separating the superabsorbent resin from a mixture of the immersion solution and the crushed material. Patent Document 1 states that in step (iii), one or more materials selected from pulp, nonwoven fabric, and adhesive may be further separated and recovered. The separated superabsorbent resin, pulp, and nonwoven fabric can become recycled superabsorbent polymer, recycled pulp fibers, and recycled plastic materials, respectively. Examples of used absorbent materials whose components are subject to recovery include used sanitary materials that have absorbed liquids such as urine and blood (absorbent fluids). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2021 / 162082 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent Document 1 describes a method in which used absorbent articles are immersed in an immersion solution containing a hydrophilic organic solvent to remove moisture (absorbent liquid) such as urine from the superabsorbent polymer (absorbent resin), thereby restoring the superabsorbent polymer's water absorption capacity. It is also believed that the pulp fibers are dehydrated during this process.

[0005] However, according to the inventor's research, the following facts were discovered for the first time. Patent Document 1 uses a hydrophilic organic solvent. However, hydrophilic organic solvents are difficult to handle from a safety standpoint due to their high volatility and flammability. In that case, it is conceivable to use a hydrophobic organic solvent instead of a hydrophilic organic solvent. However, hydrophobic organic solvents do not sufficiently remove hydrophilic contaminants. Therefore, it is difficult to obtain high-quality recycled pulp fibers.

[0006] Therefore, the object of the present invention is to provide a method for producing recycled pulp fibers derived from used absorbent articles that is highly safe and has a high cleaning effect, and to provide high-quality recycled pulp fibers derived from used absorbent articles. [Means for solving the problem]

[0007] One aspect of the present invention is a method for producing recycled pulp fibers derived from used absorbent articles, comprising: a dewatering and washing step of stirring a mixture obtained by mixing a mixture containing pulp fibers from used absorbent articles with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water to dewater the pulp fibers; and a separation step of separating the pulp fibers from the mixture.

[0008] Another aspect of the present invention is recycled pulp fibers derived from used absorbent articles, wherein the bulk density of the recycled pulp fibers is 0.045 to 0.090 g / cm³. 3 It is recycled pulp fiber. [Effects of the Invention]

[0009] According to the present invention, a method for producing recycled pulp fibers derived from used absorbent articles can be provided that is highly safe and has a high cleaning effect, and can also provide high-quality recycled pulp fibers derived from used absorbent articles. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart illustrating an example of a method for producing recycled pulp fibers derived from used absorbent articles according to the embodiment. [Modes for carrying out the invention]

[0011] This embodiment relates to the following aspects.

[0012] [Aspect 1] A method for producing recycled pulp fibers derived from used absorbent articles, comprising: a dewatering and washing step of stirring a mixture of a mixture containing pulp fibers from used absorbent articles and a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water to dewater the pulp fibers; and a separation step of separating the pulp fibers from the mixture.

[0013] In this method, first, in the dewatering and washing step, a mixture containing pulp fibers and a predetermined processing liquid is mixed and stirred to dewater the pulp fibers. However, the mixture may include, for example, used absorbent articles or aggregates of multiple components derived from used absorbent articles.

[0014] In the dewatering and washing process, by adding a non-flammable hydrophobic organic solvent to the treatment solution in addition to a hydrophilic organic solvent, or by using water instead of the hydrophilic organic solvent and adding a non-flammable hydrophobic organic solvent, the volatility and flammability of the treatment solution can be reduced while maintaining the effect of the organic solvent (described later). This enhances the safety of this method. Note that the hydrophilic organic solvent and water may be used simultaneously.

[0015] Furthermore, the nonflammable hydrophobic organic solvent in the treatment liquid can break the bonds between pulp fibers and other members in the mixture and the bonds between pulp fibers themselves, and disperse the pulp fibers in the treatment liquid. For example, the adhesive bonding the pulp fibers and other members can be dissolved by the nonflammable hydrophobic organic solvent to break the bond. Alternatively, the hydrogen bonds connecting the pulp fibers can be severed by the nonflammable hydrophobic organic solvent. Then, by stirring the mixture, the pulp fibers can be detached from other members and the like and be in a state of being dispersed separately in the liquid.

[0016] Furthermore, the dirt in the mixture can be removed by at least one of the nonflammable hydrophobic organic solvent, the hydrophilic organic solvent, and water in the treatment liquid. That is, the lipophilic dirt on the pulp fibers can be eluted and removed by the nonflammable hydrophobic organic solvent, and the hydrophilic dirt can be eluted and removed by at least one of the hydrophilic organic solvent and water. Thereby, a high cleaning effect can be obtained.

[0017] Furthermore, at least the nonflammable hydrophobic organic solvent among the nonflammable hydrophobic organic solvent and the hydrophilic organic solvent in the treatment liquid can dehydrate the moisture absorbed by the pulp fibers in the mixture.

[0018] In this way, in the dehydration cleaning step, the dirt is removed in a highly safe situation, and hygienic pulp fibers can be obtained. Therefore, hygienic recycled pulp fibers can be obtained by separation in the separation step.

[0019] Therefore, in the method for producing recycled pulp fibers derived from used absorbent articles, a method with high safety and high cleaning effect can be provided. In this method, since an organic solvent is generally used for the treatment of the mixture, the amount of water used for the treatment can be significantly reduced.

[0020] [Aspect 2] The dewatering and washing step comprises a first stirring step of mixing the non-flammable hydrophobic organic solvent with at least one of the hydrophilic organic solvent and water to form the treatment liquid and stirring the treatment liquid, and a second stirring step of mixing the treatment liquid with the mixture to form the mixed liquid and stirring the mixed liquid, according to embodiment 1.

[0021] In this method, the dewatering and washing process comprises a first stirring step and a second stirring step. First, in the first stirring step, a non-flammable hydrophobic organic solvent is mixed with at least one of a hydrophilic organic solvent and water to form a treatment liquid, and this treatment liquid is stirred. Due to the relationship between hydrophobicity and hydrophilicity, the non-flammable hydrophobic organic solvent and at least one of the hydrophilic organic solvent and water tend to separate when simply mixed. Therefore, in this method, stirring the treatment liquid mixed with both can suppress the separation of the treatment liquid. Subsequently, in the second stirring step, the (stirred) treatment liquid is mixed with a mixture (containing pulp fibers) to form a mixed liquid, and this mixed liquid is stirred. The treatment liquid is also prone to separation even when mixed with the mixture. Therefore, in this method, stirring the mixed liquid, which is a mixture of the treatment liquid and the mixture, can suppress the separation of the treatment liquid. Furthermore, the volatility and flammability of the processing liquid are further reduced, safety is enhanced, multiple components can be more reliably dispersed in the processing liquid, dirt in the mixture can be more reliably removed, and pulp fibers can be more reliably dewatered.

[0022] [Aspect 3] The method according to embodiment 1 or 2, further comprising an oxidizing agent treatment step of treating the mixture in the mixture with an oxidizing agent while stirring the mixture before the separation step.

[0023] This method further includes an oxidizing agent treatment step, which involves treating the mixture (including pulp fibers) in the mixed liquid with an oxidizing agent while stirring the mixed liquid, prior to the separation step (including simultaneously with the dewatering and washing step). This oxidizing agent treatment step can bleach, sterilize, and deodorize the mixture. As a result, the mixture can be made more hygienic. At this time, the oxidizing agent treatment is performed in the presence of at least a non-flammable hydrophobic organic solvent among non-flammable hydrophobic organic solvents and hydrophilic organic solvents, so damage to the mixture by the oxidizing agent can be suppressed. In this way, bleaching, sterilization, and deodorization are performed in a highly safe environment while suppressing damage, thus enabling the production of more hygienic pulp fibers.

[0024] [Aspect 4] The method according to any one of embodiments 1 to 3, further comprising an oxidizing agent treatment step of treating the pulp fibers in the mixture with an oxidizing agent while stirring the mixture after the other components of the mixture have been separated from the mixture in the separation step.

[0025] This method further includes an oxidizing agent treatment step in which, after the other components of the mixture have been separated from the mixture in the separation step, the pulp fibers in the mixture are treated with an oxidizing agent while the mixture is being stirred. This oxidizing agent treatment step can bleach, sterilize, and deodorize the pulp fibers. As a result, the pulp fibers can be made more hygienic. At this time, the oxidizing agent treatment is performed in the presence of at least a non-flammable hydrophobic organic solvent, which is one of a non-flammable hydrophobic organic solvent and a hydrophilic organic solvent, so that damage to the pulp fibers by the oxidizing agent can be suppressed. In this way, bleaching, sterilization, and deodorization are performed in a safe environment with suppressed damage, so that more hygienic pulp fibers can be obtained. At this time, since the pulp fibers are oxidized after the other components of the mixture have been separated from the mixture, there is no influence from other components in the mixture, and the efficiency of oxidation can be increased.

[0026] [Aspect 5] The method according to any one of embodiments 1 to 4, further comprising an oxidizing agent treatment step of treating the pulp fibers separated from the mixed liquid in the separation step with an oxidizing agent.

[0027] This method further includes an oxidizing agent treatment step in which the pulp fibers separated from the mixture in the separation step are treated with an oxidizing agent. This oxidizing agent treatment step can bleach, sterilize, and deodorize the pulp fibers. As a result, the pulp fibers can be made more hygienic. At this time, since the pulp fibers separated from the mixture are oxidized, there is no influence from other impurities in the mixture, and the oxidation efficiency can be increased. In this way, bleaching, sterilization, and deodorization are carried out in a highly safe environment during the oxidizing agent treatment step, so more hygienic pulp fibers can be obtained.

[0028] [Aspect 6] The method according to any one of embodiments 1 to 5, further comprising a pretreatment step of reducing the moisture content of the mixture before the dewatering and washing step.

[0029] If the amount of moisture (e.g., urine) in a mixture containing pulp fibers is high, the amount of water used in subsequent processes will increase, potentially making it difficult to control the composition of the processing solution. Therefore, this method includes a pretreatment step to reduce the moisture content of the mixture before the dewatering and washing process. This allows for controlling the amount of moisture released from the mixture during the dewatering and washing process, thereby controlling the composition of the processing solution. Furthermore, if the amount of moisture in a mixture containing pulp fibers is high, the volume and mass of the mixture to be processed in subsequent processes may become too large, potentially reducing process efficiency. Therefore, by reducing the moisture content of the mixture through the pretreatment step, the volume and mass of the mixture in subsequent processes can be reduced, thereby suppressing a decrease in process efficiency.

[0030] [Aspect 7] The method according to any one of embodiments 1 to 6, further comprising a bag-breaking step of breaking the packaging bag containing the mixture before the dewatering and washing step.

[0031] Mixtures containing pulp fibers, such as used absorbent materials, are sometimes collected enclosed in packaging bags. Therefore, in order to process such mixtures, it is necessary to remove them from the packaging. In this method, a bag-breaking step is performed to break open the packaging bag containing the mixture before the dewatering and washing step. As a result, the mixture is removed from the packaging bag, making it possible to reliably carry out the subsequent steps on the mixture.

[0032] [Aspect 8] The method according to any one of embodiments 1 to 7, further comprising an organic solvent recovery step of separating and recovering at least the non-flammable hydrophobic organic solvent and / or the hydrophilic organic solvent from the mixed liquid after the separation step.

[0033] This method further includes an organic solvent recovery step in which at least a non-flammable hydrophobic organic solvent or a hydrophilic organic solvent, or both, are separated from the mixed liquid after the separation step and recovered. The recovered organic solvent can be reused, for example, by being supplied to a dehydration and washing step. As a result, this method allows for dehydration, washing, bleaching, sterilization, and dehydration of the mixture while suppressing the increase in the cost of organic solvents.

[0034] [Aspect 9] The method according to any one of embodiments 1 to 8, wherein the non-flammable hydrophobic organic solvent comprises at least one of a fluorinated organic solvent and an aromatic organic solvent.

[0035] In this method, since the non-flammable hydrophobic organic solvent contains at least one of a fluorinated organic solvent and an aromatic organic solvent, the pulp fibers can be more reliably dispersed in the treatment solution, becoming loose, and lipophilic stains can be removed more reliably.

[0036] [Aspect 10] The method according to any one of embodiments 1 to 9, wherein the hydrophilic organic solvent comprises at least one of a ketone-based organic solvent and an alcohol-based organic solvent.

[0037] In this method, since the hydrophilic organic solvent includes at least one of ketone-based organic solvents and alcohol-based organic solvents, the pulp fibers can be dewatered more reliably with the treatment solution while further suppressing damage to the pulp fibers, and hydrophilic contaminants can be removed more reliably.

[0038] [Aspect 11] The method according to any one of embodiments 1 to 10, wherein the water includes acidic water.

[0039] In this method, acidic water is used in the dewatering and washing process. This acidic water can be used to disinfect and adjust the pulp fibers, which have become alkaline due to excrement, to a neutral to weakly acidic state. This suppresses the odor of the pulp fibers.

[0040] [Aspect 12] The oxidizing agent includes at least one of ozone, hydrogen peroxide, and chlorine-based substances. The method according to any one of embodiments 3 to 5.

[0041] This method includes at least one of the following as an oxidizing agent: ozone, hydrogen peroxide, and chlorine-based substances (e.g., sodium hypochlorite), all of which have strong bleaching, sterilizing, and deodorizing effects. Therefore, plastic materials, superabsorbent polymers, and pulp fibers can be bleached, sterilized, and deodorized more reliably.

[0042] [Aspect 13] The method according to any one of embodiments 1 to 12, further comprising a drying step for drying the pulp fibers, wherein the drying step is performed after the dewatering and washing step and at least after the separation step.

[0043] In this method, the drying step for drying the pulp fibers is performed after the dewatering and washing step, and at least one of the steps after the separation step. Here, since the pulp fibers are dewatered in the dewatering and washing step beforehand and are easier to dry, the energy required for drying can be reduced, and the pulp fibers can be processed more easily in the next step or reused more easily.

[0044] [Aspect 14] Recycled pulp fibers derived from used absorbent articles, wherein the bulk density of the recycled pulp fibers is 0.045 to 0.090 g / cm³. 3 , is recycled pulp fiber.

[0045] This recycled pulp fiber contains pulp fibers derived from used absorbent materials, yet its bulk density is 0.045 to 0.090 g / cm³. 3 The values ​​are small, as shown above. Thus, recycled pulp fibers, despite being derived from used absorbent materials, have a very low bulk density and can therefore be considered to be of the same high quality as pulp fibers before use. As a result, these recycled pulp fibers can be used as a good absorbent material.

[0046] The following describes a method for producing recycled pulp fibers derived from used absorbent articles and recycled pulp fibers derived from used absorbent articles according to this embodiment.

[0047] However, used absorbent articles include absorbent articles that have been used, such as those containing excrement and those that do not contain excrement, as well as unused absorbent articles, such as those discarded during the production stage (production loss) and those discarded after storage. Absorbent articles include plastic materials (nonwoven fabric, etc.) and pulp fibers as constituent materials, and may include superabsorbent polymers. Examples include disposable diapers, incontinence pads, sanitary napkins, bed sheets, and pet sheets. Recycled plastic materials refer to plastic materials derived from used absorbent articles, specifically plastic materials recovered from used absorbent articles. Recycled superabsorbent polymers refer to superabsorbent polymers derived from used absorbent articles, specifically superabsorbent polymers recovered from used absorbent articles. Recycled pulp fibers refer to pulp fibers derived from used absorbent articles, specifically pulp fibers recovered from used absorbent articles. Used absorbent articles contain soiling substances. These contaminants include, for example, excrement, sebum, bacteria, odor-causing substances, and coloring substances derived from them, machine oil from manufacturing equipment, and various organic substances.

[0048] The method for producing recycled pulp fibers derived from used absorbent articles according to this embodiment comprises a dewatering and washing step and a separation step. The dewatering and washing step is a step of stirring a mixture obtained by mixing a mixture containing pulp fibers from used absorbent articles with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water to dewater the pulp fibers. The separation step is a step of separating the pulp fibers from the mixture. However, the mixture may be, for example, used absorbent articles (themselves) or an aggregate of multiple components derived from used absorbent articles.

[0049] The method described above can achieve the following effects. First, in the dewatering and washing step, the pulp fibers are dewatered by stirring the mixture of the mixture and the treatment solution. In this dewatering and washing step, by adding a non-flammable hydrophobic organic solvent to the treatment solution in addition to a hydrophilic organic solvent, or by using water instead of the hydrophilic organic solvent and adding a non-flammable hydrophobic organic solvent, the volatility and flammability of the treatment solution can be reduced while maintaining the effect of the organic solvent (described later). This enhances the safety of the method. Note that the hydrophilic organic solvent and water may be used simultaneously.

[0050] Furthermore, in the dewatering and washing process, the non-flammable hydrophobic organic solvent in the processing liquid can break the bonds between the pulp fibers in the mixture and other materials (e.g., plastic materials, superabsorbent polymers), as well as the bonds between the pulp fibers themselves, thereby dispersing the pulp fibers in the processing liquid. For example, adhesives that join pulp fibers to other materials can be dissolved with the non-flammable hydrophobic organic solvent to break the bonds. Alternatively, hydrogen bonds that connect pulp fibers to each other can be broken with the non-flammable hydrophobic organic solvent. Then, by stirring the mixture, the pulp fibers can be separated from other materials and dispersed freely in the liquid.

[0051] Furthermore, in the dewatering and washing process, contaminants in the mixture can be removed using at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water in the processing liquid. Specifically, lipophilic contaminants in the pulp fibers can be dissolved and removed using the non-flammable hydrophobic organic solvent, while hydrophilic contaminants can be dissolved and removed using at least one of a hydrophilic organic solvent and water. This allows for a high cleaning effect to be obtained.

[0052] Furthermore, in the dewatering and washing process, the water absorbed by the pulp fibers in the mixture can be dewatered by at least one non-flammable hydrophobic organic solvent among the non-flammable hydrophobic organic solvents and hydrophilic organic solvents in the treatment liquid. During dewatering, the majority of the treatment liquid consists of at least one non-flammable hydrophobic organic solvent among the non-flammable hydrophobic organic solvents and hydrophilic organic solvents. Therefore, even if a small amount of water remains, the reabsorption of water by the pulp fibers can be suppressed.

[0053] Therefore, in this method, the dewatering and washing process removes dirt under highly safe conditions, yielding hygienic pulp fibers, which can then be obtained through the subsequent separation process to acquire hygienic recycled pulp fibers.

[0054] Therefore, this method provides a highly safe and highly effective cleaning method for producing recycled pulp fibers derived from used absorbent materials. Furthermore, since this method generally uses organic solvents to treat the mixture in the dewatering and washing process, the amount of water used for treatment can be significantly reduced.

[0055] Next, a method for producing recycled pulp fibers derived from used absorbent articles according to this embodiment will be described in detail.

[0056] First, let's describe an example of the composition of an absorbent article. An absorbent article comprises a surface sheet, a backing sheet, and an absorbent material placed between the surface sheet and the backing sheet. An example of the size of an absorbent article is a length of approximately 15 to 100 cm and a width of 5 to 100 cm. In addition, an absorbent article may further include other components that are generally found in absorbent articles, such as a diffusion sheet to assist in the diffusion of liquids such as urine, a leak-proof wall to prevent lateral leakage of liquids, side sheets or outer sheets to hold the surface sheet, backing sheet, and absorbent material, and elastic members for waist gathers or three-dimensional gathers.

[0057] As for the material of the surface sheet, there are no particular restrictions as long as it can be used for absorbent articles, but examples include liquid-permeable nonwoven fabrics, synthetic resin films with liquid-permeable pores, and composite sheets thereof. As for the material of the back sheet, there are no particular restrictions as long as it can be used for absorbent articles, but examples include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, and composite sheets thereof. As for the material of the diffusion sheet, there are no particular restrictions as long as it can be used for absorbent articles, but examples include liquid-permeable nonwoven fabrics. As for the material of the leakproof wall, side sheet, and outer sheet, there are no particular restrictions as long as it can be used for absorbent articles, but examples include liquid-impermeable nonwoven fabrics. As for the material of the elastic member, there are no particular restrictions as long as it can be used for absorbent articles, but examples include elastic threads. As for the material of the nonwoven fabric and synthetic resin film, there are no particular restrictions as long as it can be used for absorbent articles, but examples include synthetic resins. Examples of synthetic resins include olefin resins such as polyethylene and polypropylene, polyamide resins such as 6-nylon and 6,6-nylon, and polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Natural fibers such as cotton and rayon may be used as the material for the nonwoven fabric. There are no particular restrictions on the material for the elastic thread as long as it can be used in absorbent articles, but examples include styrene-butadiene rubber and urethane rubber. In this embodiment, at least the nonwoven fabric and synthetic resin film described above are referred to as plastic materials, and may include the elastic thread.

[0058] Absorbent materials include absorbent materials, namely pulp fibers and superabsorbent polymers. While there are no particular restrictions on pulp fibers as long as they can be used in absorbent articles, examples include cellulose fibers. Examples of cellulose fibers include wood pulp, cross-linked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. The size of the pulp fibers is preferably such that the average length of the fiber is several tens of micrometers, with 20-40 micrometers being preferred, and the average length is preferably several millimeters, with 2-5 mm being preferred. Superabsorbent polymers (SAP) are not particularly limited as long as they can be used in absorbent articles and have acidic groups, but examples include those containing carboxyl groups, sulfo groups, etc., with those containing carboxyl groups being preferred. Examples include polyacrylate-based (containing carboxyl groups), polysulfonate-based (containing sulfo groups, etc.), and polymaleate-based (containing carboxyl groups) superabsorbent polymers. The size of the superabsorbent polymer (when dry) can be such that the average particle size is several hundred μm, with 200 to 500 μm being preferred. The absorbent body may also include a core wrap sheet that encloses the absorbent material, formed from a liquid-permeable sheet such as tissue paper.

[0059] One side and the other side of the absorbent are bonded to the surface sheet and the back sheet, respectively, via adhesive. In a plan view, the portion of the surface sheet that extends outward from the absorbent, surrounding it (peripheral portion), is bonded to the portion of the back sheet that extends outward from the absorbent, surrounding it (peripheral portion), via adhesive. Therefore, the absorbent is enclosed within the joint of the surface sheet and the back sheet. If the absorbent has a core wrap sheet, the absorbent material is bonded to the core wrap sheet via adhesive. Each of the diffusion sheets, leak-proof walls, side sheets, outer sheets, and elastic members are also bonded to other members with adhesive. There are no particular restrictions on the adhesive as long as it can be used for absorbent articles, but examples include hot-melt adhesives. Examples of hot-melt adhesives include pressure-sensitive or heat-sensitive adhesives mainly composed of rubber such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin such as polyethylene.

[0060] As described above, absorbent articles having the above configuration generally contain some or all of the aforementioned contaminating substances at the stage of used absorbent articles.

[0061] Next, a method for producing recycled pulp fibers derived from used absorbent articles according to this embodiment will be described. Figure 1 is a flowchart showing an example of a method for producing recycled pulp fibers derived from used absorbent articles according to this embodiment.

[0062] A method for producing recycled pulp fibers derived from used absorbent articles comprises a dewatering and washing step S3 and either a first separation step S5 or a second separation step S7. This method may further comprise at least one of the following: a bag breaking step S1, a pretreatment step S2, a first oxidizing agent treatment step S4, a second oxidizing agent treatment step S6, a drying step S8, a recovery step S9, a resupply step S10, and either the other of the first separation step S5 or the second separation step S7. Each step will be described in detail below.

[0063] This method produces recycled materials derived from used absorbent articles from a mixture containing pulp fibers from used absorbent articles. The mixture is not particularly limited as long as it contains pulp fibers from used absorbent articles. Examples of the mixture include used absorbent articles (themselves) and aggregates of multiple materials derived from used absorbent articles. Examples of such aggregates include collections of pulp fibers and other materials (e.g., plastic materials, superabsorbent polymers, etc.) extracted from used absorbent articles. Examples of such aggregates include those with a higher proportion of pulp fibers and a lower proportion of other materials (plastic materials, superabsorbent polymers) compared to absorbent articles (products).

[0064] (1) Bag breaking process S1 The bag-breaking step S1 is a step in which the packaging bag containing the mixture is broken open before the dewatering and washing step S3. The broken packaging bag is removed and the mixture is taken out. When used absorbent articles are used as the mixture, the used absorbent articles may be packed in a packaging bag to prevent, for example, excrement, bacteria, or odors from leaking out, or to facilitate transport. Alternatively, when an aggregate of multiple components derived from used absorbent articles is used as the mixture, for example, an aggregate of plastic material, superabsorbent polymer, and pulp fibers, the aggregate may be packed in a packaging bag to prevent it from falling apart. In order to process such a mixture, it is necessary to remove the mixture from the packaging bag. Therefore, in this method, the packaging bag is broken open to allow the mixture to be taken out. Then, the mixture is taken out of the packaging bag so that subsequent steps (for example, the pre-treatment step S2, the dewatering and washing step S3, etc.) can be carried out reliably. At this time, it is preferable not to crush or damage the mixture as much as possible. This is to avoid damaging the materials and components in the mixture, thereby making them easier to reuse. Furthermore, if the mixture is not enclosed in a packaging bag or if it is not necessary, the bag-breaking step S1 can be omitted.

[0065] An example of a device that performs the bag-breaking process S1 is a bag-breaking device that breaks open a packaging bag containing recyclable waste (e.g., PET bottles, cans, glass bottles, plastic containers and packaging) without damaging the recyclable waste.

[0066] (2) Pretreatment step S2 The pretreatment step S2 is a step to reduce the moisture content of the mixture before the dewatering and washing step S3. If the amount of moisture (e.g., urine) in the mixture is large, a large amount of moisture will be released into the processing solution during the dewatering and washing step S3. This may make it difficult to control the composition of the processing solution thereafter. Furthermore, if the amount of moisture contained in the mixture is large, the volume and mass of the mixture to be processed in the steps after the dewatering and washing step S3 may be too large, which may reduce the efficiency of the process. Therefore, in this method, the moisture content of the mixture is reduced (dewatered) in the pretreatment step S2 before the dewatering and washing step S3. For example, the moisture absorbed by the superabsorbent polymer or pulp fibers in the mixture is reduced. This makes it possible to keep the amount of moisture released from the mixture by dewatering in the dewatering and washing step S3 low, making it easier to control the composition of the processing solution. Furthermore, the volume and mass of the mixture in the steps after the dewatering and washing step S3 can be reduced, suppressing a decrease in process efficiency. However, since the pretreatment step S2 is performed before the dewatering and washing step S3, it is sufficient to dewater the mixture to a certain extent, and complete dewatering is not necessarily required. The moisture content of the mixture after dewatering can be, for example, 30 to 80% by mass. If the moisture content of the mixture is low or if it is not necessary, the pretreatment step S2 can be omitted.

[0067] The apparatus (method) for performing the pretreatment step S2 is not particularly limited as long as it can achieve the moisture content of the mixture described above, but for example, a drying apparatus for drying the mixture can be used. The drying conditions in the drying apparatus are not particularly limited as long as it can achieve the moisture content of the mixture described above, but for example, a temperature of 60 to 110°C can be used. If the temperature is too low, it will take too long, and if it is too high, the components, especially plastic materials, may melt. For example, the drying time can be 2 to 48 hours.

[0068] (3) Dehydration and washing process S3 The dewatering and washing step S3 is a step in which a mixture containing pulp fibers of used absorbent articles is mixed with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water, and the mixture is stirred to dewater the pulp fibers.

[0069] The mixture may also be an aggregate containing used absorbent articles or pulp fibers that have not undergone the bag-breaking step S1 and / or the pre-treatment step S2.

[0070] The treatment solution contains at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water. Therefore, the treatment solution may contain a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water; it may contain a non-flammable hydrophobic organic solvent and a hydrophilic organic solvent (without water); or it may contain a non-flammable hydrophobic organic solvent and water (without the hydrophilic organic solvent). Other solvents, chemicals, aqueous solutions, etc., may be included as long as they do not affect dehydration and washing. The total proportion of at least one of the non-flammable hydrophobic organic solvent, hydrophilic organic solvent, and water in the treatment solution is, for example, 50% by mass or more. From the viewpoint of the effect of dehydration and washing, a higher proportion is preferable, therefore, 70% by mass or more is preferable, 80% by mass or more is more preferable, and 90% by mass or more is even more preferable.

[0071] In the context of non-flammable hydrophobic organic solvents, "hydrophobic organic solvent" refers to an organic solvent that is miscible with water. There are no particular restrictions on the non-flammable hydrophobic organic solvent as long as it is a liquid and capable of dehydrating and washing the pulp fibers contained in the mixture. For example, a non-flammable hydrophobic organic solvent is thought to separate the water contained in the pulp fibers and transfer it to a hydrophilic organic solvent or water, while simultaneously dissolving and removing contaminants (mainly oily substances) from the pulp fibers. However, the mechanism is not limited to this.

[0072] Examples of non-flammable hydrophobic organic solvents include fluorinated organic solvents, aromatic organic solvents, and combinations of at least two of these. Examples of fluorinated organic solvents include hydrochlorofluoroolefin solvents, such as 1-chloro-2,3,3-trifluoropropene. Alternatively, examples of hydrofluoroolefin solvents include 1,1,1,3,3-pentafluorobutane and 1,3,3,3-tetrafluoropropene. Such non-flammable hydrophobic organic solvents can more reliably disperse pulp fibers in the treatment solution, making them loose, and more reliably remove lipophilic contaminants. Furthermore, fluorinated organic solvents, especially 1-chloro-2,3,3-trifluoropropene, 1,1,1,3,3-pentafluorobutane, and 1,3,3,3-tetrafluoropropene, have low volatility and flammability, making them easy to handle from a safety standpoint. Examples of the above-mentioned aromatic organic solvents include aromatic hydrocarbons, such as benzene-based aromatic hydrocarbons, such as toluene and xylene.

[0073] A hydrophilic solvent is a liquid that is miscible with water. A hydrophilic organic solvent is a liquid, and there are no particular restrictions as long as it can dehydrate and wash the pulp fibers contained in the mixture. For example, a hydrophilic organic solvent is thought to dehydrate the pulp fibers by dissolving the water contained within them, and also remove contaminants (mainly water-based) from the pulp fibers by dissolving them within itself. However, this mechanism is not the only possible mechanism.

[0074] Examples of hydrophilic organic solvents include ketone-based organic solvents, alcohol-based organic solvents, and combinations of at least two of these. Examples of ketone-based organic solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, and cyclohexanone. Examples of alcohol-based organic solvents include methanol, ethanol, propanol, butanol, and pentanol. Such hydrophilic organic solvents can dehydrate pulp fibers more reliably in the treatment solution while suppressing damage to the pulp fibers, and can more reliably remove hydrophilic contaminants. Furthermore, ketone-based organic solvents, in particular acetone, dissolve water well, are not easily oxidized by oxidizing agents, and have the property of protecting functional groups. Therefore, acetone can dehydrate pulp fibers while suppressing the decomposition (dissolution) of easily decomposed superabsorbent polymers (if present), especially when oxidizing agent treatment is performed simultaneously, and can remove some or all of the contaminants contained in these materials. Furthermore, by combining it with a non-flammable hydrophobic organic solvent and reducing the amount of hydrophilic organic solvent used, the safety of the treatment solution can be improved in terms of volatility and flammability.

[0075] Furthermore, non-flammable hydrophobic organic solvents and hydrophilic organic solvents, particularly non-flammable hydrophobic organic solvents, can dissolve the adhesives that join together the components of a used absorbent article (for example, at least two of the following: plastic material, superabsorbent polymer, and pulp fiber). This makes it easier to separate the components of the used absorbent article from each other. Therefore, if the mixture is the used absorbent article itself, it makes it easier to decompose the used absorbent article into its individual components.

[0076] The lower limit of the proportion of the non-flammable hydrophobic organic solvent in the treatment solution is, for example, 20% by mass, preferably 30% by mass, and more preferably 40% by mass. The upper limit is, for example, 95% by mass, preferably 85% by mass, and more preferably 75% by mass. A proportion of 20% by mass or more makes it easier to remove lipophilic contaminants and adhesives, and when used in combination with a hydrophilic organic solvent, it enhances the safety of the treatment solution in terms of volatility and flammability. A proportion of 95% by mass or less allows it to be used in combination with a hydrophilic organic solvent or water, making it easier to remove hydrophilic contaminants.

[0077] On the other hand, the lower limit of the ratio of at least one of the hydrophilic organic solvent and water in the treatment solution is, for example, 5% by mass, preferably 10% by mass, and more preferably 15% by mass. The upper limit is, for example, 80% by mass, preferably 70% by mass, and more preferably 60% by mass. A ratio of 5% by mass or more makes it easier to remove hydrophilic contaminants. A ratio of 80% by mass or less allows for use in combination with a non-flammable hydrophobic organic solvent, which enhances the safety of the treatment solution in terms of volatility and flammability, and also makes it easier to remove lipophilic contaminants. The mass ratio of the hydrophilic organic solvent to water in the treatment solution depends on the mass ratio of the non-flammable hydrophobic organic solvent to the hydrophilic organic solvent and water, but is generally between 0:100 and 100:0.

[0078] The treatment solution is mainly composed of a hydrophobic agent (non-flammable hydrophobic organic solvent) and a hydrophilic agent (hydrophilic organic solvent, water), so the hydrophobic agent and the hydrophilic agent tend to separate from each other. Therefore, in this method, in the dewatering and washing step S3, the superabsorbent polymer and pulp fibers are dewatered and washed while stirring the mixture of the mixture and the treatment solution, thereby suppressing the separation of the treatment solution during dewatering and washing.

[0079] The preferred state of agitation is one in which the hydrophobic agent and the hydrophilic agent are dispersed almost uniformly, i.e., an emulsified state. If the treatment tank containing the treatment liquid is rotating, the agitation conditions can be, for example, 20 to 200 rpm, with 40 to 100 rpm being preferred. If agitation is performed within the treatment tank using an agitator blade, for example, 100 to 2000 rpm can be used, with 200 to 1000 rpm being preferred.

[0080] The proportion of the mixture (including pulp fibers) in the mixed liquid is not particularly limited, as long as the dewatering and washing step S3 can be carried out. For example, the proportion can be 0.1 to 20% by mass, and is preferably 1 to 10% by mass. A proportion of 0.1% by mass or more allows for efficient processing. A proportion of 20% by mass or less facilitates dewatering and washing.

[0081] In the dehydration and washing step S3, there are no particular restrictions on the temperature of the dehydration and washing as long as the dehydration and washing can be performed, but it should be at least lower than the boiling point of any of the non-flammable hydrophobic organic solvents, hydrophilic organic solvents, or water. Examples of dehydration and washing temperatures include room temperature (example: 25°C) to 50°C, with 30 to 40°C being preferred. A temperature above room temperature makes it easier to shorten the time required for dehydration and washing. A temperature below 50°C makes it easier to suppress the evaporation (boiling) of organic solvents. There are no particular restrictions on the duration of the dehydration and washing as long as the dehydration and washing can be performed, but examples include 1 to 200 minutes.

[0082] The apparatus for performing the dewatering and washing process S3 is not particularly limited in its specific configuration, as long as it can store the processing liquid, immerse the mixture in the processing liquid, and stir the processing liquid containing the mixture. Examples of such apparatus include one having a tank in which the mixture can be placed and the processing liquid can be stored, a supply means for supplying the processing liquid into the tank, and a stirring means for stirring the processing liquid in the tank.

[0083] Here, the dewatering and washing step S3 preferably comprises a first stirring step S31 and a second stirring step S32. However, the first stirring step S31 is a step of mixing a non-flammable hydrophobic organic solvent with at least one of a hydrophilic organic solvent and water to form a treatment liquid, and stirring the treatment liquid. The second stirring step S32 is a step of mixing the treatment liquid stirred in the first stirring step S31 with a mixture to form a mixed liquid, and stirring the mixed liquid.

[0084] Non-flammable hydrophobic organic solvents and at least one of hydrophilic organic solvents and water are easily separated when simply mixed, and also easily separated when mixed with a mixture, due to the relationship between hydrophobicity and hydrophilicity. In other words, the treatment liquid is easily separated into non-flammable hydrophobic organic solvents and at least one of hydrophilic organic solvents and water. Therefore, in this method, in the dewatering and washing step S3, first, the treatment liquid is stirred in the first stirring step S31 to suppress the separation of the treatment liquid. Then, in the second stirring step S32, the treatment liquid containing the mixture is stirred to suppress the separation of the treatment liquid while dewatering and washing the pulp fibers. As a result, the hydrophilic organic solvent can be mixed more reliably with the non-flammable hydrophobic organic solvent (and water), the volatility and flammability of the treatment liquid can be further reduced, and its safety can be further enhanced. At the same time, multiple components can be dispersed more reliably in the treatment liquid, dirt in the mixture can be removed more reliably, and the pulp fibers can be dewatered more reliably.

[0085] Furthermore, in the dewatering and washing process S3, if a large amount of water is used (for example, 50% by mass or more), it is preferable to use acidic water (acidic aqueous solution). Pulp fibers that have become alkaline due to excrement, etc., can be adjusted to neutral to weakly acidic by using acidic water. This suppresses the odor of the pulp fibers. Acidic water can also disinfect the mixture.

[0086] The acid in acidic water (acidic aqueous solution) is not particularly limited, and examples include acidic substances such as inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferred from the viewpoint of not containing chlorine and from the viewpoint of cost. Examples of organic acids include carboxylic acids having multiple carboxyl groups (example: citric acid), carboxylic acids having one carboxyl group (example: acetic acid), sulfonic acids (example: methanesulfonic acid), etc. As for organic acids, it is preferable to have multiple carboxyl groups from the viewpoint of readily forming chelate complexes with divalent or higher metals contained in excrement, etc. (example: calcium) and less likely to leave ash residue in pulp fibers, and citric acid is more preferable. The acid concentration of the acidic aqueous solution is not particularly limited as long as the dehydration function is achieved, and examples include 0.1 to 30% by mass. Furthermore, if other components include a superabsorbent polymer and an acid is used to inactivate the superabsorbent polymer in order to suppress its water absorption, it is preferable that the acid has an acid dissociation constant (pKa, in water) that is smaller than the acid dissociation constant (pKa, in water) of the acid group in the superabsorbent polymer.

[0087] The acidic water (acidic aqueous solution) preferably has a pH within a predetermined range. The upper limit of the pH is preferably 6.0, more preferably 5.0. A pH of 6.0 or lower facilitates the dehydration of the superabsorbent polymer. The lower limit of the pH is preferably 0.5, more preferably 1.0. A pH of 0.5 or higher makes it less likely to damage the pulp fibers. However, the pH is measured at 25°C, for example, using a twin pH meter AS-711 manufactured by Horiba, Ltd.

[0088] (4) First oxidizing agent treatment step S4 The first oxidizing agent treatment step S4 (oxidizing agent treatment step) is a step in which the mixture in the mixed liquid is treated with an oxidizing agent while stirring the mixed liquid, before the separation step (first separation step S5 or second separation step S7). However, the first oxidizing agent treatment step S4 may be performed simultaneously with the dewatering and washing step S3, or after the dewatering and washing step S3. The first oxidizing agent treatment step S4 bleaches, sterilizes or disinfects, and deodorizes the mixture in the mixed liquid with an oxidizing agent.

[0089] When the first oxidizing agent treatment step S4 is performed simultaneously with the dehydration and washing step S3, the oxidizing agent is added to the treatment solution before the mixture is dehydrated and washed, or while it is being dehydrated and washed. The mixture is then treated with the oxidizing agent while being dehydrated and washed in the treatment solution. On the other hand, when the first oxidizing agent treatment step S4 is performed after the dehydration and washing step S3, the oxidizing agent is added to the treatment solution after the mixture has been dehydrated and washed in the treatment solution. The mixture is then treated with the oxidizing agent after being dehydrated and washed in the treatment solution.

[0090] The oxidizing agent is not particularly limited as long as it can remove contaminants contained in the mixture while minimizing the impact on each component (e.g., damage to pulp fibers). The oxidizing agent may be, for example, a liquid or a gas mixed with a liquid, and is thought to reduce contaminants by oxidative decomposition, lowering their molecular weight and making them more soluble in the solution, but is not limited to this mechanism.

[0091] Examples of oxidizing agents include ozone, hydrogen peroxide, and chlorine-based substances (e.g., sodium hypochlorite), or combinations of two or more of these. Because these oxidizing agents have relatively high oxidizing power, they effectively reduce contaminants contained in each component of used absorbent articles, such as pulp fibers. This allows for the removal of bacteria and the reduction of odor and coloring substances, enabling more reliable sterilization, disinfection, deodorization, and decolorization of each component. Note that when using acetone as the hydrophilic organic solvent, hydrogen peroxide should not be used as the oxidizing agent.

[0092] The oxidizing agent may be mixed into the treatment solution, or it may be mixed with another solvent (e.g., an organic solvent, acidic water, or water) before being mixed into the treatment solution.

[0093] When using gaseous ozone as an oxidizing agent and supplying gaseous ozone to the treatment solution to form a treatment solution containing the oxidizing agent, the ozone concentration in the treatment solution is not particularly limited, as long as it is a concentration that can reduce the contaminants contained in each component. The ozone concentration is, for example, 0.2 to 2 ppm by mass, preferably 0.4 to 1.5 ppm by mass. A concentration of 0.2 ppm by mass or higher facilitates the reduction of contaminants, and a concentration of 2 ppm by mass or lower can suppress damage to pulp fibers. The contact time between the ozone-containing treatment solution and each component is not particularly limited, as long as it is a time that can reduce the contaminants contained in each component. Generally, the contact time is shorter when the ozone concentration is high and longer when the ozone concentration is low. The contact time is, for example, 1 to 200 minutes, preferably 2 to 60 minutes. The product of ozone concentration (ppm by mass) and contact time (minutes) (hereinafter also referred to as the "CT value") is preferably 0.2 to 40 ppm by mass·minute, more preferably 0.5 to 20 ppm by mass·minute. A CT value of 0.2 ppm·min or higher facilitates the reduction of contaminants, while a CT value of 40 ppm·min or lower suppresses the oxidative decomposition of each component. Ozone treatment reduces contaminants contained in each component, for example, by removing bacteria, odor-causing substances, and color-causing substances, and can sterilize, disinfect, deodorize, and decolorize (bleach) each component. Examples of ozone generators that supply gaseous ozone into the treatment machine include the ED-OWX-2 ozone water exposure tester manufactured by Eco Design Co., Ltd., the OS-25V ozone generator manufactured by Mitsubishi Electric Corporation, and the REX MC ozonizer MC-985S manufactured by a subsidiary of Rex Industries Co., Ltd.

[0094] When using a gas (e.g., ozone) as an oxidizing agent, the oxidizing agent may be supplied to the treatment liquid by, for example, the following method. This method involves generating a predetermined amount of oxidizing agent in an oxidizing agent generator, continuously supplying the oxidizing agent to the treatment liquid in the treatment tank at a predetermined airflow rate, while continuously disposing of (discharging) the same amount of waste oxidizing agent (used oxidizing agent) outside the treatment tank. In this case, a flow of oxidizing agent is easily generated, new oxidizing agent is easily continuously supplied to the surface of each component, and reactants are easily continuously discharged from that surface. Therefore, the oxidation reaction on the surface of each component can be carried out more reliably.

[0095] The proportion of the mixture in the above-mentioned treatment solution is not particularly limited, as long as the above-mentioned oxidizing agent treatment can be carried out. For example, the proportion can be 0.1 to 20% by mass, and 1 to 10% by mass is preferred. A proportion of 0.1% by mass or more allows the treatment to proceed efficiently. A proportion of 20% by mass or less facilitates the treatment with the oxidizing agent.

[0096] Dirt, such as excrement, sebum, bacteria, odor-causing substances, and coloring agents derived from them, machine oil from manufacturing equipment, and various organic substances, is expected to be reduced as follows: Dehydration primarily releases dirt absorbed inside each component along with water to the outside. At the same time, dirt attached to each component is also released to the outside along with the released water. Simultaneously, oxidation primarily decomposes dirt attached to each component (including that released from the inside and attached), reducing its molecular weight, solubilizing it, and removing it. This also makes sterilization, disinfection, deodorization, and bleaching of each component possible. However, the reduction of dirt on each component is not limited to this mechanism.

[0097] In the first oxidizing agent treatment step S4, there are no particular restrictions on the temperature of the oxidizing agent treatment as long as the above-described oxidizing agent treatment can be performed, but it should be at least lower than the boiling point of the treatment solution. Examples of oxidizing agent treatment temperatures include room temperature (example: 25°C) to 50°C, with 30 to 40°C being preferred. A temperature above room temperature makes it easier to shorten the time required for the oxidizing agent treatment. A temperature below 50°C makes it easier to suppress the evaporation (boiling) of the organic solvent, thereby suppressing the dehydration condensation of the acid groups of the superabsorbent polymer and thus suppressing the decrease in its water absorption.

[0098] This method includes a first oxidizing agent treatment step S4, which is performed before the separation step (first separation step S5 or second separation step S7) (or simultaneously with the dewatering and washing step S3), in which the mixture (including pulp fibers) in the mixture is treated with an oxidizing agent while the mixture is being stirred. This first oxidizing agent treatment step S4 can bleach, sterilize or disinfect and deodorize the mixture. This makes the mixture more hygienic. At this time, the oxidizing agent treatment is performed in the presence of at least a non-flammable hydrophobic organic solvent among the non-flammable hydrophobic organic solvent and hydrophilic organic solvent, so that damage to the mixture by the oxidizing agent can be suppressed. In this way, in the first oxidizing agent treatment step S4, bleaching, sterilization or disinfection and deodorization are performed in a highly safe environment while suppressing damage, so that more hygienic pulp fibers can be obtained.

[0099] The first oxidizing agent treatment step S4 may be omitted if it is not necessary, such as when the mixture is sufficiently hygienic due to the dewatering and washing step S3, or when oxidizing agent treatment is performed separately in the second oxidizing agent treatment step S6, which will be described later.

[0100] (5) First separation step S5 The first separation step S5 (separation step) is a step of separating pulp fibers and at least one of other materials (e.g., plastic material, superabsorbent polymer) from the mixed liquid. However, the mixed liquid may be the liquid immediately after the dewatering and washing step S3 (omitting the first oxidizing agent treatment step S4), or it may be the liquid after both the dewatering and washing step S3 and the first oxidizing agent treatment step S4. Since the separated pulp fibers and at least one of the other materials are removed from the mixed liquid containing contaminants and other materials, they can be said to be recycled materials that have been dewatered and washed, and contaminants and other materials have been reduced.

[0101] In the first separation step S5, for example, one of the pulp fibers or other components is separated from the mixture of the pulp fibers and other components and the processing liquid. If, for example, pulp fibers are separated as the one component, the separated material can be recycled pulp fibers. If a plastic material, which is one of the other components, is separated, the separated material can be recycled plastic material. If a superabsorbent polymer, which is one of the other components, is separated, the separated material can be recycled superabsorbent polymer.

[0102] Alternatively, in the first separation step S5, for example, two of the pulp fibers and other components are separated from the mixture of the pulp fibers and other components and the processing liquid. If, for example, a plastic material and a superabsorbent polymer are separated as the two components, the separated materials can be recycled in a mixed state. The two components may be further separated into individual recycled components (recycled plastic material, recycled superabsorbent polymer).

[0103] The apparatus for performing the first separation step S5 is not limited in its specific configuration, as long as it is capable of separating one or two components from the mixed liquid. Examples of separation methods include using one screen or a combination of multiple screens, using specific gravity, using centrifugal force, or a combination thereof.

[0104] (6) Second oxidizing agent treatment step S6 The second oxidizing agent treatment step S6 (oxidizing agent treatment step) is a step in which, after the predetermined components have been separated from the mixture in the first separation step S5, the remaining components in the mixture are treated with an oxidizing agent while stirring the mixture. The second oxidizing agent treatment step S6 bleaches, sterilizes or disinfects, and deodorizes the remaining components in the mixture. The method and conditions for the oxidizing agent treatment are as described in the first oxidizing agent treatment step S4, but they do not have to be the same as those for the first oxidizing agent treatment step S4.

[0105] For example, the second oxidizing agent treatment step S6 is a step in which, after one of the other components, such as a plastic material, has been separated from the mixture in the first separation step S5, the remaining components in the mixture, such as pulp fibers and the remaining other components, are treated with an oxidizing agent while stirring the mixture. In this case, the second oxidizing agent treatment step S6 can bleach, sterilize or disinfect and deodorize the pulp fibers and the remaining other components. This makes the pulp fibers and the remaining other components more hygienic. At this time, since the oxidizing agent treatment is performed in the presence of at least a non-flammable hydrophobic organic solvent, damage to the pulp fibers and the remaining other components by the oxidizing agent can be suppressed. The remaining other components are, for example, a superabsorbent polymer.

[0106] Alternatively, for example, the second oxidizing agent treatment step S6 is a step in which, after other components, such as plastic materials and superabsorbent polymers, have been separated from the mixture in the first separation step S5, the remaining components in the mixture, such as pulp fibers, are treated with an oxidizing agent while stirring the mixture. In this case, the second oxidizing agent treatment step S6 can bleach, sterilize or disinfect, and deodorize the pulp fibers. This makes the pulp fibers more hygienic. At this time, since the oxidizing agent treatment is carried out in the presence of at least a non-flammable hydrophobic organic solvent, damage to the pulp fibers by the oxidizing agent can be suppressed.

[0107] Thus, in the second oxidizing agent treatment step S6, bleaching, sterilization or disinfection, and deodorization are performed in a highly safe environment while suppressing damage, making it possible to obtain more hygienic pulp fibers and other remaining materials.

[0108] Furthermore, the second oxidizing agent treatment step S6 may be omitted if it is not necessary, such as when the mixture is in a sufficiently hygienic state or when oxidizing agent treatment has already been performed in the first oxidizing agent treatment step S4 or elsewhere.

[0109] In another embodiment, the method may further include an oxidizing agent treatment step in which one or two of the pulp fibers and other components (e.g., plastic materials, superabsorbent polymers) separated from the mixture in the first separation step S5 are treated with an oxidizing agent (for example, when the first oxidizing agent treatment step S4 is not performed). In this additional oxidizing agent treatment step, the one or two components are immersed in acidic water (acidic aqueous solution) and then treated with an oxidizing agent in the acidic water. The acidic water, oxidizing agent, and conditions for the oxidizing agent treatment are as described above. In addition, known reactivation treatments may be performed on the superabsorbent polymer as needed.

[0110] This separate oxidizing agent treatment step allows for bleaching, sterilization, disinfection, and deodorization of one or both of the components. This makes the components more hygienic. Since the components separated from the mixture are treated with an oxidizing agent in separate acidic water, there is no influence from other impurities in the mixture, and the efficiency of the oxidizing agent treatment can be increased. Thus, in this separate oxidizing agent treatment step, bleaching, sterilization, disinfection, and deodorization are performed under highly safe conditions, resulting in more hygienic components, such as pulp fibers.

[0111] In another embodiment, the method may further include a sanitary treatment step in which one or two of the pulp fibers and other components separated from the mixed liquid in the first separation step S5 are subjected to sanitary treatment (for example, when the first oxidizing agent treatment step S4 is not performed). The sanitary treatment step is a treatment that enhances the sanitary properties of each component, and examples include high-pressure steam treatment and ultraviolet (UV) treatment in addition to the other oxidizing agent treatment step described above.

[0112] High-pressure steam treatment is a process in which high-pressure steam is brought into contact with each component separated from the mixed liquid. This high-pressure steam can decompose at least a portion of the fouling substances (organic matter). The temperature of the high-pressure steam can be, for example, 110 to 180°C, the treatment time can be, for example, 1 to 120 minutes, and the steam pressure can be, for example, 0.2 to 1.2 MPa.

[0113] Ultraviolet (UV) treatment is a process in which each component separated from the mixed solution is immersed in an aqueous solution containing water or a predetermined oxidizing agent, and then irradiated with a predetermined amount of UV light. When water or the aqueous solution containing the predetermined oxidizing agent is irradiated with UV light, active species are generated. For example, when the wavelength of UV light is 253.7 nm, hydroxyl radicals are generated as active species through the reaction of UV light with the predetermined oxidizing agent (ozone + water, hydrogen peroxide). Also, when the wavelength of UV light is 184.9 nm, hydroxyl radicals are generated as active species through the reaction of UV light with water. These hydroxyl radicals can decompose at least a portion of the contaminants (organic matter). However, the concentration of each component in the aqueous solution during UV treatment is appropriately adjusted so that the UV light is not blocked by each component.

[0114] This sanitary treatment process removes bacteria, odor-causing organic matter, and other contaminants present in one or both of the components. This makes the components more hygienic. Since the sanitary treatment is applied to the components separated from the mixture, there is no influence from other contaminants in the mixture, and the efficiency of the treatment can be increased. In this way, the sanitary treatment process removes bacteria, odor-causing organic matter, and other contaminants in a highly safe environment, resulting in more hygienic components.

[0115] (7) Second separation step S7 The second separation step S7 (separation step) is a step in which the mixture (pulp fibers and other components that were not separated in the first separation step S5) is separated from the mixed liquid. However, the mixed liquid may be the liquid immediately after the first separation step S5 (omitting the second oxidizing agent treatment step S6), or it may be the liquid that has gone through both the first separation step S5 and the second oxidizing agent treatment step S6. The separated mixture (components) is removed from the mixed liquid containing contaminants and other components, and can be said to be recycled components that have been dewatered and washed, and contaminants and other components have been reduced.

[0116] In the second separation step S7, at least one component is separated from the mixture of the treatment liquid and the mixture containing, for example, pulp fibers and other components. If one component is separated, for example, if pulp fibers are separated, the separated material can be recycled pulp fibers. If plastic material is separated, the separated material can be recycled plastic material. If superabsorbent polymer is separated, the separated material can be recycled superabsorbent polymer.

[0117] Alternatively, if the two components are separated, for example, plastic material and pulp fibers, or superabsorbent polymer and pulp fibers, the separated components can be mixed together to form a recycled component. The two separated components may then be further separated to form individual recycled components (recycled plastic material, recycled superabsorbent polymer, recycled pulp fibers), for example.

[0118] The apparatus for performing the second separation step S7 is not particularly limited in its specific configuration, as long as it is capable of separating one or two components from the mixed liquid. Examples of separation methods include using one screen or a combination of multiple screens, using specific gravity, using centrifugal force, or a combination thereof.

[0119] (8) Drying process S8 The drying step S8 is a step of drying the pulp fibers and at least one of the other components. However, the drying step S8 may be performed after the second separation step S7, or after the dewatering and washing step S3, and at least one of the other separation steps, the first separation step S5. In addition, the drying step S8 may be omitted if it is unnecessary, such as when the components dry easily by using a large amount of organic solvent in the dewatering and washing step S3.

[0120] Drying step S8 is performed by placing each component in a drying atmosphere at a temperature higher than room temperature, or by blowing dry air at a temperature higher than room temperature onto each component. The drying temperature can be, for example, 40 to 110°C, with 50 to 100°C being preferred. A drying temperature of 40°C or higher can shorten the drying time. A drying temperature of 110°C or lower can suppress the components from sticking together and the components from deteriorating due to heat. The drying time can be, for example, 30 to 300 minutes. Drying step S8 may also be performed under reduced pressure, for example, 0.1 to 100 kPa, from the viewpoint of accelerating drying.

[0121] In this method, a drying step S8, in which at least one of the pulp fibers and other components (e.g., plastic material, superabsorbent polymer) is dried, is performed at least once after the dewatering and washing step S3 and after the separation steps (first separation step S5, second separation step S7). Here, since at least one of the pulp fibers and other components is dewatered in advance in the dewatering and washing step S3 and is therefore easier to dry, the energy required for drying can be reduced, and at least one of the pulp fibers and other components can be processed more easily in the next step or reused more easily.

[0122] (9) Recovery process S9 The recovery step S9 is a step in which, after the separation step (first separation step S5 or second separation step S7), at least one of the non-flammable hydrophobic organic solvent, hydrophilic organic solvent, and adhesive from the mixed liquid from which the pulp fibers and other components have been removed is separated and recovered.

[0123] The separated mixture contains a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and an adhesive, as well as pollutants such as excrement. Therefore, by heating and / or reducing the pressure of the mixture, at least one of the non-flammable hydrophobic organic solvent and the hydrophilic organic solvent contained in the mixture is boiled and evaporated. Then, by cooling the vapor, at least one of the non-flammable hydrophobic organic solvent and the hydrophilic organic solvent is recovered. In other words, at least one of the non-flammable hydrophobic organic solvent and the hydrophilic organic solvent is distilled. The adhesive, on the other hand, is removed as a residue after distillation of the mixture. As a result, the recovered non-flammable hydrophobic organic solvent, hydrophilic organic solvent, and adhesive can be reused because the amount of pollutants and other agents has been reduced. Note that since the non-flammable hydrophobic organic solvent and the hydrophilic organic solvent have different boiling points, they can be recovered separately by fractional distillation.

[0124] The recovery process S9 includes the organic solvent recovery process S91 and the adhesive recovery process S92.

[0125] The organic solvent recovery step S91 is a step in which, after the separation step (first separation step S5 or second separation step S7), the organic solvent (non-flammable hydrophobic organic solvent and / or hydrophilic organic solvent) from the mixed liquid is separated and recovered. When the non-flammable hydrophobic organic solvent and the hydrophilic organic solvent are recovered separately, they are recovered by fractional distillation. The recovered organic solvent can be reused, for example, by supplying it to the dehydration and washing step or by using it for other purposes. As a result, in this method, the increase in the cost of organic solvents is suppressed, and the mixture can be dehydrated, washed, bleached, sterilized, and dehydrated while contributing to the reduction of environmental impact.

[0126] The adhesive recovery step S92 is a step in which the adhesive dissolved in the mixed liquid (processing liquid) is separated from the mixed liquid (processing liquid) and recovered after the separation step (first separation step S5 or second separation step S7). The adhesive is recovered, for example, as the residue obtained by distilling the processing liquid in the organic solvent recovery step S91. The recovered adhesive can be reused, for example, in the manufacture of absorbent articles. This contributes to reducing the environmental impact of this method.

[0127] (10) Resupply process S10 The resupply process S10 is a process in which at least one of the non-flammable hydrophobic organic solvent and hydrophilic organic solvent recovered in the recovery process S9 (organic solvent recovery process S91) is supplied to the dewatering and washing process S3 for use as a processing liquid. This helps to reduce the environmental burden while suppressing the increase in the cost of organic solvents.

[0128] As described above, the method for producing recycled pulp fibers derived from used absorbent articles according to the embodiment is carried out.

[0129] Next, recycled pulp fibers derived from used absorbent articles according to the embodiment will be described. The recycled pulp fibers according to this embodiment are produced by the method for producing recycled pulp fibers derived from used absorbent articles according to the above embodiment.

[0130] In the recycled pulp fibers derived from used absorbent articles according to this embodiment, the bulk density is 0.045 to 0.090 g / cm³. 3 The bulk density of the recycled pulp fibers is preferably 0.045 to 0.085 g / cm³. 3 , that is.

[0131] This recycled pulp fiber contains pulp fibers derived from used absorbent materials, yet its bulk density is 0.045 to 0.090 g / cm³. 3 The values ​​are small, as shown above. Thus, although this recycled pulp fiber is derived from used absorbent materials, it has a very low bulk density and therefore can be said to contain high-quality pulp fibers. As a result, this recycled pulp fiber can be used as a good absorbent material. [Examples]

[0132] The present invention will be described below based on examples, but the present invention is not limited to these examples. In the following examples, the dewatering and washing step S3 was examined.

[0133] (1) Sample Example 1: Recycled pulp fibers produced by the method for producing recycled pulp fibers derived from used absorbent articles according to the above embodiment were prepared. Specifically, for used absorbent articles, pretreatment steps S2 to drying step S8 excluding the first oxidant treatment step S4 were carried out. However, the plastic material was separated from the mixed solution in the first separation step S5, and the superabsorbent polymer and pulp fibers were separated from the mixed solution in the second separation step S7. From the separated superabsorbent polymer and pulp fibers, the pulp fibers were sieved and separated to obtain recycled pulp fibers. Comparative Example 1: Unused pulp fibers for absorbent articles were prepared. Comparative Example 2: Used absorbent articles were crushed in advance, water was used as the treatment liquid (without using non-volatile hydrophobic organic solvents and hydrophilic solvents), and recycled pulp fibers were prepared in the same manner as in Example 1 except that acidic water was used for the dehydration treatment of the superabsorbent polymer. For each example and each comparative example, five absorbent articles were prepared.

[0134] (2) Evaluation A plurality of samples were taken from each pulp fiber, and for each sample, the bulk density of each pulp fiber was measured by the following method. First, a transparent container that can measure 100 cc (or cm 3 ) was prepared, and its mass A (g) was measured. Next, the sample was put into the transparent container up to 100 cc (or cm 3 ), and the mass B was measured. Then, B - A = C is the mass (g) of the sample, and C / 100 = bulk density (g / cm 3 ).

[0135] (3) Results In Example 1, the bulk density of the recycled pulp fibers was 0.045 - 0.090 g / cm 3 . In Comparative Example 1, the bulk density of the pulp fibers was 0.034 g / cm 3 . In Comparative Example 2, the bulk density of the pulp fibers was 0.15 - 0.20 g / cm 3 .

[0136] Thus, the recycled pulp fibers of Example 1, while containing pulp fibers derived from used absorbent articles, have a bulk density of 0.045 to 0.090 g / cm³. 3 The bulk density of the recycled pulp fibers in Example 1 was found to be very low compared to that of the pulp fibers in Comparative Example 2, and was about the same as that of the pulp fibers in Comparative Example 1. Therefore, it was found that the recycled pulp fibers in Example 1 contain high-quality pulp fibers. As a result, it was found that these recycled pulp fibers can be used, for example, as a good absorbent material.

[0137] The abduction method of the present invention is not limited to the embodiments described above, and can be appropriately combined or modified without departing from the purpose and spirit of the present invention. [Explanation of symbols]

[0138] S3 Dehydration and washing process S5 Separation process

Claims

1. A method for producing recycled pulp fibers derived from used absorbent articles, A dewatering and washing step involves stirring a mixture of a mixture containing pulp fibers from used absorbent articles and a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water to dewater the pulp fibers. A separation step of separating the pulp fibers from the mixture, A method that includes [a certain feature].

2. The aforementioned dewatering and washing step is A first stirring step involves mixing the non-flammable hydrophobic organic solvent with at least one of the hydrophilic organic solvent and water to form the treatment solution, and then stirring the treatment solution. A second stirring step involves mixing the aforementioned processing liquid and the aforementioned mixture to form the aforementioned mixed liquid, and stirring the aforementioned mixed liquid. Equipped with, The method according to claim 1.

3. Prior to the separation step, the method further comprises an oxidizing agent treatment step in which the mixture in the mixture is treated with an oxidizing agent while the mixture is being stirred. The method according to claim 1.

4. The method further comprises an oxidizing agent treatment step, in which, after the other components of the mixture have been separated from the mixture in the separation step, the mixture is stirred while the pulp fibers in the mixture are treated with an oxidizing agent. The method according to claim 1.

5. The system further comprises an oxidizing agent treatment step in which the pulp fibers separated from the mixture in the separation step are treated with an oxidizing agent. The method according to claim 1.

6. The process further includes a pretreatment step to reduce the moisture content of the mixture before the dewatering and washing step. The method according to claim 1 or 2.

7. Prior to the dewatering and washing step, the process further includes a bag-breaking step in which the packaging bag containing the mixture is broken open. The method according to claim 1 or 2.

8. The method further comprises an organic solvent recovery step, after the separation step, in which at least the non-flammable hydrophobic organic solvent and / or the hydrophilic organic solvent from the mixed liquid are separated and recovered. The method according to claim 1 or 2.

9. The non-flammable hydrophobic organic solvent comprises at least one of a fluorinated organic solvent and an aromatic organic solvent. The method according to claim 1 or 2.

10. The hydrophilic organic solvent comprises at least one of a ketone-based organic solvent and an alcohol-based organic solvent. The method according to claim 1 or 2.

11. The water includes acidic water. The method according to claim 1 or 2.

12. The oxidizing agent includes at least one of ozone, hydrogen peroxide, and chlorine-based substances. The method according to any one of claims 3 to 5.

13. The process further comprises a drying step for drying the pulp fibers, The drying step is performed after the dewatering and washing step and at least one of the separation steps. The method according to claim 1 or 2.

14. Recycled pulp fibers derived from used absorbent articles, The bulk density of the recycled pulp fibers is 0.045 to 0.090 g / cm³. ３ , Recycled pulp fibers.

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