Method for producing recycled plastic materials derived from used absorbent articles and plastic materials derived from used absorbent articles

Abstract

The present invention provides a method for manufacturing recycled materials derived from used absorbent articles that is highly safe and has a high cleaning effect. [Solution] A method for producing recycled materials derived from used absorbent articles comprises a dewatering and washing step and a separation step. The dewatering and washing step involves stirring a mixture of a mixture containing the plastic material, superabsorbent polymer, and pulp fibers of the used absorbent article with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent and a hydrophilic organic solvent and water to dewater the superabsorbent polymer and pulp fibers. The separation step involves separating at least one of the plastic material, superabsorbent polymer, and pulp fibers from the mixture.

Description

Technical Field

[0001] The present invention relates to a method for producing a recycled plastic material derived from used absorbent articles and a recycled plastic material derived from used absorbent articles.

Background Art

[0002] Methods for producing recycled members 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 a water-absorbing resin derived from a used absorbent article, which comprises discharging an absorbed liquid from the water-absorbing resin containing the absorbed liquid and restoring the water absorption capacity of the water-absorbing resin. This method includes: (i) an immersion step of immersing a used absorbent article containing a water-absorbing resin that has absorbed an absorbed liquid in an immersion liquid containing a hydrophilic organic solvent; (ii) a crushing step of crushing the used absorbent article into a crushed product during or before the immersion step; and (iii) a separation step of separating the water-absorbing resin from the mixture of the immersion liquid and the crushed product. In Patent Document 1, in step (iii), one or more members selected from pulp, non-woven fabric, and adhesive may be further separated and recovered, and a sterilization / disinfection step of sterilizing and / or disinfecting the water-absorbing resin may be performed in parallel with or after the immersion step. The separated water-absorbing resin, pulp, and non-woven fabric can become a recycled superabsorbent polymer, recycled pulp fiber, and recycled plastic material, respectively. Examples of the used absorbent articles targeted for recovering constituent members include used sanitary materials that have absorbed liquids such as urine and blood (absorbed liquid).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] In Patent Document 1, used absorbent articles are immersed in an immersion solution containing a hydrophilic organic solvent to remove moisture such as urine (the absorbed liquid) from the superabsorbent polymer (superabsorbent resin) (dehydration), thereby restoring the superabsorbent polymer's water absorption capacity. On the other hand, plastic materials (e.g., nonwoven fabrics) are separated and recovered from the immersion solution containing a hydrophilic organic solvent using conventional solid-liquid separation means.

[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 addition, when using a hydrophilic organic solvent, it is difficult to remove lipophilic dirt because of its hydrophilic nature, and the cleaning effect is difficult to obtain. In that case, it may be considered to use a hydrophobic organic solvent instead of a hydrophilic organic solvent. However, when using a hydrophobic organic solvent, it is difficult to remove hydrophilic dirt, and the cleaning effect is difficult to obtain. Therefore, it is difficult to obtain high-quality recycled plastic material.

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

[0007] One aspect of the present invention is a method for producing recycled plastic material derived from used absorbent articles, comprising: a washing step of washing the plastic material by stirring a mixture obtained by mixing a mixture containing plastic material 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; and a separation step of separating the plastic material from the mixture.

[0008] Another aspect of the present invention is a recycled plastic material derived from used absorbent articles, wherein the polyolefin resin content is 80% by mass or more. [Effects of the Invention]

[0009] According to the present invention, a method for producing recycled plastic material 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 plastic material derived from used absorbent articles. [Brief explanation of the drawing]

[0010] [Figure 1] This is a flowchart illustrating an example of a method for manufacturing recycled materials 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 plastic material derived from used absorbent articles, comprising: a washing step of stirring a mixture of a mixture containing plastic material 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 wash the plastic material; and a separation step of separating the plastic material from the mixture.

[0013] In this method, first, in the washing step, a mixture containing plastic material and a predetermined treatment liquid is mixed and stirred to wash the plastic material. Examples of the mixture include used absorbent articles and aggregates of multiple components derived from used absorbent articles.

[0014] In the washing process, by adding a non-flammable hydrophobic organic solvent to the treated water 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 treated 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 non-flammable hydrophobic organic solvent in the treated water can break the bonds between plastic materials and other components in the mixture, as well as the bonds between plastic materials themselves, thus dispersing the plastic materials in the treatment solution. For example, the adhesive joining the plastic materials to other components can be dissolved by the non-flammable hydrophobic organic solvent, thus separating the bonds. Alternatively, the bonds between plastic materials can be broken by the non-flammable hydrophobic organic solvent. By stirring the mixture, the plastic materials can be separated from other components and dispersed freely in the liquid.

[0016] Unlike crushing a mixture, this method allows various components of different types and sizes to be separated from other components and dispersed in the liquid while maintaining their original state. For example, if the mixture is a used absorbent article, each component can be separated from other components and dispersed in the liquid while maintaining the same state in which it was used in the absorbent article. In the case of plastic materials, for example, polyolefin-based plastic materials, rubber-based plastic materials, and polyethylene terephthalate-based plastic materials can be separated from other components and dispersed in the liquid while maintaining their original state.

[0017] Furthermore, the treated water can be used to remove contaminants from the mixture using at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water. Specifically, lipophilic contaminants on plastic materials 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. In other words, a high cleaning effect can be obtained.

[0018] Thus, in the washing process, dirt is removed in a highly safe environment, resulting in hygienic plastic material. Therefore, hygienic recycled plastic material can be obtained through separation in the separation process. The obtained plastic material can then be separated into polyolefin-based plastic material, rubber-based plastic material, and polyethylene terephthalate-based plastic material by known separation methods, such as the water-based specific gravity separation method. In other words, the plastic material can be separated according to its material (composition).

[0019] Therefore, this method provides a highly safe and effective cleaning method for producing recycled plastic materials derived from used absorbent articles. Furthermore, since this method generally uses organic solvents for processing the mixture, the amount of water used for processing can be significantly reduced.

[0020] [Aspect 2] The method according to embodiment 1, wherein the cleaning 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.

[0021] In this method, the cleaning process includes a first stirring process and a second stirring process. First, in the first stirring process, a mixture, a nonflammable hydrophobic organic solvent, and at least one of a hydrophilic organic solvent and water are mixed to form a treatment liquid, and the treatment liquid is stirred. The nonflammable hydrophobic organic solvent and at least one of the hydrophilic organic solvent and water are likely to separate in a simply mixed state due to the relationship between hydrophobicity and hydrophilicity. Therefore, in this method, by stirring the treatment liquid in which both are mixed, separation of the treatment liquid can be suppressed. Then, in the second stirring process, the (stirred) treatment liquid and the mixture (including the plastic material) are mixed to form a mixed liquid, and the mixed liquid is stirred. The treatment liquid is likely to separate even when mixed with the mixture. Therefore, in this method, by stirring the mixed liquid in which the treatment liquid and the mixture are mixed, separation of the treatment liquid can be suppressed. And the volatility and flammability are further reduced to enhance safety, multiple members can be more reliably dispersed in the treatment liquid, dirt in the mixture can be more reliably removed, and the highly water-absorbent polymer and pulp fibers can be more reliably dehydrated.

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

[0023] In this method, before the separation step (including simultaneously with the dehydration cleaning step), it further comprises an oxidizing agent treatment step of treating the mixture (including the plastic material) in the mixed liquid with an oxidizing agent while stirring the mixed liquid. By this oxidizing agent treatment step, the mixture can be bleached, sterilized, and deodorized. At this time, since the treatment with the oxidizing agent is performed in the presence of at least the nonflammable hydrophobic organic solvent among the nonflammable hydrophobic organic solvent and the hydrophilic organic solvent, damage to the plastic material by the oxidizing agent can be suppressed. Thus, in the oxidizing agent treatment step, bleaching, sterilization, and deodorization are performed while suppressing damage in a highly safe situation, so that a more hygienic plastic material can be obtained.

[0024] [Aspect 4] The method according to any one of embodiments 1 to 3, further comprising an oxidizing agent treatment step of treating the plastic material 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 plastic material in the mixture is treated with an oxidizing agent while the mixture is being stirred. This oxidizing agent treatment step can bleach, sterilize, and deodorize the plastic material. As a result, the plastic material 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 plastic material by the oxidizing agent can be suppressed. In this way, bleaching, sterilization, and deodorization are performed in a safe environment with suppressed damage, so a more hygienic plastic material can be obtained. At this time, since the pulp fibers are oxidized after the other components 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 a sanitary treatment step of subjecting the plastic material separated from the mixed liquid in the separation step to sanitary treatment.

[0027] This method further includes a sanitary treatment step in which the plastic material separated from the mixture in the separation step is subjected to sanitary treatment. Examples of such sanitary treatments include treatment with an oxidizing agent, treatment with steam, treatment with ultraviolet light, and treatment with high-pressure water jets. This sanitary treatment step, that is, treatment to enhance hygiene, can remove bacteria and odor-causing organic matter present in the plastic material. This makes the plastic material more hygienic. At this time, since the sanitary treatment is applied to the plastic material 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 step removes bacteria and odor-causing organic matter in a highly safe environment, so a more hygienic plastic material can be obtained.

[0028] [Aspect 6] The method according to embodiment 5, wherein the sanitary treatment step includes an oxidizing agent treatment step of treating the plastic material separated from the mixed liquid with an oxidizing agent.

[0029] In this method, the sanitary treatment step includes an oxidizing agent treatment step in which the plastic material separated from the mixture is treated with an oxidizing agent. This oxidizing agent treatment step can bleach, sterilize, and deodorize the plastic material, thereby making it more hygienic. Since the plastic material separated from the mixture is oxidized at this time, it is not affected by other impurities in the mixture, and the oxidation efficiency can be increased. Thus, in the oxidizing agent treatment step, bleaching, sterilization, and deodorization are performed under highly safe conditions, making it possible to obtain a more hygienic plastic material.

[0030] [Aspect 7] The method according to any one of embodiments 1 to 6, further comprising a specific gravity separation step of separating the plastic material separated from the mixed liquid in the separation step into at least an olefin-based plastic material and other plastic materials in water.

[0031] This method further comprises a specific gravity separation step in which the plastic material separated from the mixed liquid in the separation step is separated by specific gravity into at least olefin-based plastic material and other components in water. In other words, at least olefin-based plastic material can be extracted from the plastic material. This allows the plastic material to be reused according to its material.

[0032] [Aspect 8] The method according to any one of embodiments 1 to 7, further comprising a pretreatment step of reducing the moisture content of the mixture before the washing step.

[0033] If a mixture containing plastic materials contains a large amount of water (e.g., urine), the amount of water used in subsequent processes may increase, making it difficult to control the composition of the treatment solution. Therefore, this method includes a pretreatment step to reduce the water content of the mixture before the washing step. This allows for controlling the amount of water released from the mixture during the washing step, thereby controlling the composition of the treatment solution. Furthermore, if a mixture containing plastic materials contains a large amount of water, the volume and mass of the mixture to be treated in subsequent processes may become too large, potentially reducing the efficiency of the process. Therefore, by reducing the water 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.

[0034] [Aspect 9] The method according to any one of embodiments 1 to 8, further comprising a bag-breaking step of breaking a packaging bag containing the mixture before the washing step.

[0035] Mixtures containing plastic materials, such as used absorbent articles, 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 before the washing step to break open the packaging bag containing the mixture. This removes the mixture from the packaging bag, ensuring that the washing step and subsequent steps can be carried out reliably on the mixture.

[0036] [Aspect 10] The method according to any one of embodiments 1 to 9, further comprising a recovery step of separating and recovering at least one of the non-flammable hydrophobic organic solvent, the hydrophilic organic solvent, and the adhesive from the mixed liquid after the separation step.

[0037] This method further includes a recovery step in which at least one of the non-flammable hydrophobic organic solvent, hydrophilic organic solvent, and adhesive from the mixed liquid after the separation step is separated and recovered. The recovered organic solvent can be reused, for example, by being supplied to a washing step, and the recovered adhesive can be reused, for example, in absorbent articles. As a result, this method allows for the dispersion and washing of the mixture while suppressing the increase in the cost of organic solvents.

[0038] [Aspect 11] The method according to any one of embodiments 1 to 10, wherein the non-flammable hydrophobic organic solvent comprises at least one of a fluorinated organic solvent and an aromatic organic solvent.

[0039] 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 plastic material can be more reliably dispersed in the treatment solution, becoming loose, and lipophilic stains can be removed more reliably.

[0040] [Aspect 12] The method according to any one of embodiments 1 to 11, wherein the hydrophilic organic solvent comprises at least one of a ketone-based organic solvent and an alcohol-based organic solvent.

[0041] In this method, since the hydrophilic organic solvent contains at least one of ketone-based organic solvents and alcohol-based organic solvents, hydrophilic stains can be more reliably removed from plastic materials using the treatment solution.

[0042] [Aspect 13] The method according to any one of embodiments 3, 4, or 6, wherein the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a chlorine-based substance.

[0043] This method includes at least one of the following as an oxidizing agent: ozone, hydrogen peroxide, and a chlorine-based substance (e.g., sodium hypochlorite), all of which have strong bleaching, sterilizing, and deodorizing effects. Therefore, plastic materials can be bleached, sterilized, and deodorized more reliably.

[0044] [Aspect 14] The method according to any one of embodiments 1 to 13, further comprising a drying step for drying the plastic material, wherein the drying step is performed after the washing step and at least after the separation step.

[0045] In this method, the drying process for the plastic material is performed after the washing process and at least after the separation process. Here, the plastic material is reduced to a state with extremely low moisture content by a non-flammable hydrophobic organic solvent and a hydrophilic organic solvent, making it easy to dry. This reduces the energy required for drying and makes the plastic material easier to process in the next step or easier to reuse.

[0046] [Aspect 15] A recycled plastic material derived from used absorbent articles, wherein the polyolefin resin content is 80% by mass or more.

[0047] This recycled plastic material, derived from used absorbent materials, may contain various types of plastic materials, but it has the characteristic of containing 80% or more by mass of a specific type of resin: polyolefin resin. Therefore, it can be used as a high-quality recycled plastic material with a high purity of this specific type of resin.

[0048] The following describes a method for producing recycled plastic material derived from used absorbent articles according to this embodiment, and the recycled plastic material derived from used absorbent articles.

[0049] 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 superabsorbent polymers and / or pulp fibers as constituent materials, and 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.

[0050] The method for producing recycled plastic material derived from used absorbent articles according to this embodiment comprises a washing step and a separation step. The washing step is a step of washing the plastic material by stirring a mixture obtained by mixing a mixture containing the plastic material of used absorbent articles with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water. The separation step is a step of separating the plastic material from the mixture. However, the mixture may be, for example, used absorbent articles (themselves) or an assembly of multiple components derived from used absorbent articles.

[0051] The method described above can achieve the following effects. First, in the washing step, the plastic material is washed by stirring a mixture of a mixture containing plastic material and a predetermined treatment solution. In this washing step, by adding a non-flammable hydrophobic organic solvent to the treatment water 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.

[0052] Furthermore, the non-flammable hydrophobic organic solvent in the treated water can break the bonds between plastic materials and other components in the mixture, as well as the bonds between plastic materials themselves, thus dispersing the plastic materials in the treatment solution. For example, the adhesive joining the plastic materials to other components can be dissolved by the non-flammable hydrophobic organic solvent, thus separating the bonds. Alternatively, the bonds between plastic materials can be broken by the non-flammable hydrophobic organic solvent. By stirring the mixture, the plastic materials can be separated from other components and dispersed freely in the liquid.

[0053] Unlike crushing a mixture, this method allows various components of different types and sizes to be separated from other components and dispersed in the liquid while maintaining their original state. For example, if the mixture is a used absorbent article, each component can be separated from other components and dispersed in the liquid while maintaining the same state in which it was used in the absorbent article. In the case of plastic materials, for example, polyolefin-based plastic materials, rubber-based plastic materials, and polyethylene terephthalate-based plastic materials can be separated from other components and dispersed in the liquid while maintaining their original state.

[0054] Furthermore, the treated water can be used to remove contaminants from the mixture using at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water. Specifically, lipophilic contaminants on plastic materials 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. In other words, a high cleaning effect can be obtained.

[0055] Thus, in the washing process, dirt is removed in a highly safe environment, resulting in hygienic plastic material. Therefore, hygienic recycled plastic material can be obtained through separation in the separation process. The obtained plastic material can then be separated into polyolefin-based plastic material, rubber-based plastic material, and polyethylene terephthalate-based plastic material by known separation methods, such as the water-based specific gravity separation method. In other words, the plastic material can be separated according to its material (composition).

[0056] Therefore, this method provides a highly safe and effective cleaning method for producing recycled plastic materials derived from used absorbent articles. Furthermore, since this method generally uses organic solvents for processing the mixture, the amount of water used for processing can be significantly reduced.

[0057] Next, a method for producing recycled plastic material derived from used absorbent articles according to this embodiment will be described in detail.

[0058] 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. An absorbent article may further include other components that are typically found in absorbent articles, such as a diffusion sheet to assist in the diffusion of liquid, a leak-proof wall to prevent lateral leakage of liquid, 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Next, a method for producing recycled plastic material 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 plastic material derived from used absorbent articles according to this embodiment.

[0064] A method for producing recycled plastic material derived from used absorbent articles comprises a 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 second separation step S7, 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.

[0065] This method produces recycled plastic material derived from used absorbent articles from a mixture containing plastic material from used absorbent articles. The mixture is not particularly limited as long as it contains plastic material from used absorbent articles. Examples of the mixture include used absorbent articles (themselves) and assemblies of multiple components derived from used absorbent articles. Examples of such assemblies include collections of plastic material and other materials (e.g., superabsorbent polymers and pulp fibers) extracted from used absorbent articles. Examples of such assemblies include those with a higher proportion of plastic material and a lower proportion of other materials (e.g., superabsorbent polymers and pulp fibers) compared to absorbent articles (products).

[0066] (1) Bag breaking process S1 The bag-breaking step S1 is a step that takes place before the washing step S3 and involves breaking open the packaging bag containing the mixture. The broken packaging bag is removed, and the mixture is taken out. When used absorbent materials are used as the mixture, the used absorbent materials may be packed into a packaging bag to prevent, for example, excrement, bacteria, or odors from leaking out, or to facilitate transport. When an aggregate of multiple components derived from used absorbent materials is used as the mixture, for example, an aggregate of plastic material, superabsorbent polymer, and pulp fibers, the aggregate may be packed into 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, and subsequent steps (for example, the pre-treatment step S2, the washing step S3, etc.) can be reliably carried out on the mixture. 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 otherwise unnecessary, the bag-breaking step S1 can be omitted.

[0067] 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.

[0068] (2) Pretreatment step S2 The pretreatment step S2 is a step to reduce the moisture content of the mixture before the washing step S3. If the mixture contains a large amount of moisture (e.g., urine), the amount of water in the washing step S3 and subsequent steps may increase, making it difficult to control the composition of the treatment solution. Therefore, in this method, the moisture content of the mixture is reduced by the pretreatment step S2 before the washing step S3. This makes it possible to keep the amount of moisture released from the mixture in the washing step S3 low, making it easier to control the composition of the treatment solution. Furthermore, if the mixture contains a large amount of moisture, the volume and mass of the mixture to be treated in the washing step S3 and subsequent steps may be too large, potentially reducing the efficiency of the process. Therefore, by reducing the moisture content of the mixture in the pretreatment step S2, the volume and mass of the mixture in the washing step S3 and subsequent steps can be reduced, thereby suppressing a decrease in process efficiency. The moisture content of the mixture after the pretreatment step S2 can be, for example, 30 to 80% by mass. Note that the pretreatment step S2 can be omitted if it is not necessary, such as when the moisture content of the mixture is low.

[0069] 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.

[0070] (3) Washing process S3 The washing step S3 is a step of washing the plastic material by stirring a mixture obtained by mixing a mixture containing the plastic material of the used absorbent article with a treatment liquid containing at least one of a non-flammable hydrophobic organic solvent, a hydrophilic organic solvent, and water.

[0071] The mixture may also be an aggregate containing used absorbent articles or plastic materials that have not undergone the bag-breaking step S1 and / or the pre-treatment step S2.

[0072] 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 the cleaning effect. 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 cleaning effectiveness, 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.

[0073] In the context of non-flammable hydrophobic organic solvents, "hydrophobic organic solvent" refers to an organic solvent that is miscible with water. As long as the non-flammable hydrophobic organic solvent is a liquid and capable of cleaning the plastic material contained in the mixture, there are no particular restrictions. Non-flammable hydrophobic organic solvents are thought to remove contaminants (mainly lipophilic substances) from plastic materials by dissolving them in the solvent itself. However, this mechanism is not the only possible mechanism.

[0074] 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 plastic materials 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.

[0075] 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 clean the plastic material contained in the mixture. Hydrophilic organic solvents are thought to remove contaminants (mainly hydrophilic) from plastic materials by dissolving them in themselves, for example. However, this mechanism is not the only one that works.

[0076] 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 more reliably remove hydrophilic contaminants. Furthermore, ketone-based organic solvents, particularly acetone, dissolve water well, are difficult to oxidize with oxidizing agents, and have the property of protecting functional groups. Therefore, acetone, especially when oxidizing agent treatment is performed simultaneously, can remove some or all of the contaminants contained in the material while suppressing the decomposition (dissolution) of easily decomposable plastic materials. In addition, 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.

[0077] 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.

[0078] 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.

[0079] 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 90% 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.

[0080] The treatment solution is mainly composed of a hydrophobic agent (non-flammable hydrophobic organic solvent) and a hydrophilic agent (hydrophilic organic solvent, water), and the hydrophobic agent and the hydrophilic agent tend to separate from each other. Therefore, in this method, in the washing step S3, the plastic material is washed while stirring the mixture of the mixture and the treatment solution, thereby suppressing the separation of the treatment solution during washing.

[0081] 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.

[0082] The proportion of the mixture (including plastic material) in the mixed liquid is not particularly limited, as long as the washing step S3 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 for efficient processing. A proportion of 20% by mass or less facilitates dewatering and washing.

[0083] In the washing process S3, there are no particular restrictions on the washing temperature as long as the washing process 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 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 washing time as long as the washing process can be performed, but examples include 1 to 200 minutes.

[0084] The apparatus for performing the 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.

[0085] Here, the 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 make 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 make a mixed liquid, and stirring the mixed liquid.

[0086] 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 solvent and at least one of hydrophilic organic solvents and water. Therefore, in this method, in the 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 wash the plastic material while suppressing the separation of the treatment liquid. 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 plastic material can be washed more reliably.

[0087] (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 washing step S3 or after the 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.

[0088] When the first oxidizing agent treatment step S4 is performed simultaneously with the washing step S3, the oxidizing agent is added to the treatment solution before or during the washing of the mixture. The mixture is then treated with the oxidizing agent while being washed with the treatment solution. On the other hand, when the first oxidizing agent treatment step S4 is performed after the washing step S3, the oxidizing agent is added to the treatment solution after the mixture has been washed with the treatment solution. The mixture is then treated with the oxidizing agent after being washed with the treatment solution.

[0089] The oxidizing agent is not particularly limited as long as it can remove the contaminants in the mixture while minimizing the impact on each component (e.g., damage to the components). The oxidizing agent may be, for example, a liquid or a gas mixed with a liquid, and is thought to reduce the contaminants by oxidizing and decomposing them, reducing their molecular weight, and making them more soluble in the solution, but is not limited to this mechanism.

[0090] 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 are effective in reducing contaminants contained in various components of used absorbent articles, such as plastic materials. 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.

[0091] 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.

[0092] 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 amount of 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 each component. 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 amount of 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 oxidative decomposition of each component, especially easily decomposed components. 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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 washing step S3), in which the mixture (including plastic material) in the mixed liquid is treated with an oxidizing agent while the mixed liquid is being stirred. This first oxidizing agent treatment step S4 can bleach, sterilize or disinfect, and deodorize the mixture. As a result, the mixture can be made more hygienic. At this time, since 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, damage to the plastic material by the oxidizing agent can be suppressed. Thus, 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 a more hygienic plastic material can be obtained.

[0098] Furthermore, 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 washing step S3 or when oxidizing agent treatment is performed separately in the second oxidizing agent treatment step S6 or later described below.

[0099] (5) First separation step S5 The first separation step S5 (separation step) is a step of separating at least one of the plastic material and other components (superabsorbent polymer and pulp fiber) from the mixed liquid. However, the mixed liquid may be the liquid immediately after the washing step S3 (omitting the first oxidizing agent treatment step S4), or it may be the liquid after both the washing step S3 and the first oxidizing agent treatment step S4. Since at least one of the separated plastic material and other components is taken out of the mixed liquid containing contaminants and other components, it can be said to be a recycled component that has been dewatered and washed, and the amount of contaminants and other components has been reduced.

[0100] In the first separation step S5, for example, one of the plastic material and the other component is separated from the mixture of the plastic material and the other component and the processing liquid. If the plastic material is separated as the one component, the separated material can be recycled plastic material. If the superabsorbent polymer of the other component is separated, the separated material can be recycled superabsorbent polymer. If the pulp fibers of the other component are separated, the separated material can be recycled pulp fibers.

[0101] Alternatively, in the first separation step S5, for example, two of the plastic material and other components are separated from the mixture of the plastic material and other components and the processing liquid. If, for example, a superabsorbent polymer and pulp fibers 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 superabsorbent polymer, recycled pulp fibers).

[0102] 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.

[0103] (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.

[0104] For example, the second oxidizing agent treatment step S6 is a step in which, after one of the other components, such as pulp fibers, has been separated from the mixture in the first separation step S5, the remaining components in the mixture, such as plastic material 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 plastic material and the remaining other components. This makes the plastic material 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 plastic material and the remaining other components by the oxidizing agent can be suppressed.

[0105] Alternatively, for example, the second oxidizing agent treatment step S6 is a step in which, after other components, such as the superabsorbent polymer and pulp fibers, have been separated from the mixture in the first separation step S5, the remaining components in the mixture, such as the plastic material, 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 plastic material. This makes the plastic material 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 plastic material by the oxidizing agent can be suppressed.

[0106] 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 a more hygienic plastic material.

[0107] 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.

[0108] In another embodiment, the method may further include a sanitary treatment step in which one or two of the plastic material, superabsorbent polymer, and pulp fiber components separated from the mixture 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, ultraviolet (UV) treatment, and another oxidizing agent treatment.

[0109] 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.

[0110] Ultraviolet (UV) treatment is a process in which each component separated from the mixed solution is immersed in water or an aqueous solution containing a predetermined oxidizing agent, and then irradiated with a predetermined amount of UV light. When water or an aqueous solution containing a predetermined oxidizing agent is irradiated with UV light, it generates active species. For example, when the wavelength of UV light is 253.7 nm, the reaction between UV light and a predetermined oxidizing agent (ozone + water, hydrogen peroxide) generates hydroxyl radicals as active species. Also, when the wavelength of UV light is 184.9 nm, the reaction between UV light and water generates hydroxyl radicals as active species. These hydroxyl radicals can decompose at least a portion of the contaminants (organic matter).

[0111] Another oxidizing agent treatment step involves treating each component separated from the mixture with an oxidizing agent. This treatment may be carried out in an acidic solution such as sulfuric acid or citric acid. The oxidizing agent, treatment method, and conditions are as described above.

[0112] This sanitary treatment process removes bacteria and odor-causing organic matter from one or two components, such as plastic materials. This makes the components (plastic materials, etc.) more hygienic. Since the sanitary treatment is applied to the components separated from the mixture, there is no influence from other impurities in the mixture, and the efficiency of the treatment can be increased. In this way, the sanitary treatment process removes bacteria and odor-causing organic matter in a highly safe environment, resulting in more hygienic components.

[0113] In the case of a separate oxidizing agent treatment process, one or both of the components, such as plastic materials, can be bleached, sterilized, disinfected, and deodorized. This makes the components more hygienic. In this case, since the components separated from the mixture are treated with the oxidizing agent, there is no influence from other impurities in the mixture, and the efficiency of the oxidizing agent treatment can be increased. Thus, in this oxidizing agent treatment process, bleaching, sterilization, disinfection, and deodorization are carried out under highly safe conditions, so more hygienic components can be obtained.

[0114] (7) Second separation step S7 The second separation step S7 (separation step) is a step in which the mixture (plastic material 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, so it can be said to be a recycled component that has been cleaned and has reduced contaminants and other components.

[0115] 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, a plastic material and other components. If one component is separated, for example, if a plastic material is separated, the separated material can be recycled plastic material. If a superabsorbent polymer is separated, the separated material can be recycled superabsorbent polymer. If pulp fibers are separated, the separated material can be recycled pulp fibers.

[0116] Alternatively, if the two components are separated, for example, a plastic material and a superabsorbent polymer, or a plastic material 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).

[0117] 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.

[0118] In addition, as another embodiment, this method may further include a specific gravity separation step. The specific gravity separation step is a step of separating the plastic material separated from the mixed liquid in the separation step (first separation step S5 or second separation step S7) in water by specific gravity into at least olefin-based plastic material and other plastic material.

[0119] In this method, during the washing step S3, the plastic material can be disintegrated and dispersed into polyolefin-based plastic material, rubber-based plastic material, polyethylene terephthalate-based plastic material, etc. Therefore, the various types of plastic materials separated from the mixture in the separation step (first separation step S5 or second separation step S7) can be separated by specific gravity in water into at least olefin-based plastic material and other components. In other words, at least olefin-based plastic material can be extracted from the plastic material. This allows for the effective reuse of olefin-based plastic material.

[0120] Furthermore, the underwater specific gravity separation method can be used not only to separate polyolefin-based plastic materials, but also to separate rubber-based plastic materials and polyethylene terephthalate-based plastic materials, respectively. This allows for the effective reuse of rubber-based plastic materials and polyethylene terephthalate-based plastic materials, respectively.

[0121] (8) Drying process S8 The drying step S8 is a step of drying the plastic material 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 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 due to the use of a large amount of organic solvent in the washing step S3.

[0122] 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.

[0123] In this method, a drying step S8 for drying at least one of the plastic material and other components (e.g., superabsorbent polymer, pulp fiber) is performed after the washing step S3 and at least one of the separation steps (first separation step S5, second separation step S7). Here, since at least one of the plastic material and other components is washed in advance in the washing step S3 and is easier to dry, the energy required for drying can be reduced, and at least one of the plastic material and other components can be processed in the next step or easily reused.

[0124] (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 is separated from the mixed liquid from which the plastic material, superabsorbent polymer, and pulp fibers have been removed, and recovered.

[0125] 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.

[0126] The recovery process S9 includes the organic solvent recovery process S91 and the adhesive recovery process S92.

[0127] 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 washing step or 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.

[0128] 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.

[0129] (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 washing process S3 for use as a treatment liquid. This helps to reduce the environmental burden while suppressing the increase in the cost of organic solvents.

[0130] As described above, the method for producing recycled plastic material derived from used absorbent articles according to the embodiment is carried out.

[0131] Next, a recycled plastic material derived from used absorbent articles according to the embodiment will be described. The recycled plastic material according to this embodiment is manufactured by the method for manufacturing recycled components derived from used absorbent articles according to the above embodiment, and the mass ratio of a specific material is increased by a known separation method, for example, the water specific gravity separation method.

[0132] The recycled plastic material derived from used absorbent articles according to this embodiment has a polyolefin resin content of 80% by mass or more. Preferably, the polyolefin resin content of the plastic material is 90% by mass or more, and more preferably 95% by mass or more.

[0133] The plastic material composition in recycled plastic materials can be analyzed using Fourier transform infrared spectroscopy (FT-IR) or gas chromatography-mass spectrometry (GC-MS).

[0134] This recycled plastic material, being derived from used absorbent materials, may contain various types of plastic materials, but it has the characteristic of containing 80% or more by mass of a specific type of resin: polyolefin resin. Therefore, it can be reused as a high-quality recycled plastic material with a high purity of this specific type of resin.

[0135] Furthermore, the plastic materials obtained by the above method can be further separated by known separation methods, such as the water specific gravity separation method, according to their material (composition), such as polyolefin-based plastic materials, rubber-based plastic materials, and polyethylene terephthalate-based plastic materials. In this case, polyolefin-based plastic materials tend to float in water, polyethylene terephthalate-based plastic materials tend to sink, and rubber-based plastic materials are somewhere in between. [Examples]

[0136] 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 cleaning process S3 was examined.

[0137] (1) Sample Example 1: A recycled plastic material was prepared using the method for producing recycled components derived from used absorbent articles according to the above embodiment. Specifically, the used absorbent article was subjected to pretreatment steps S2 to drying step S8, excluding the first oxidizing agent treatment step S4. The plastic material was separated from the mixed liquid in the first separation step S5. The separated plastic material was then separated by a water specific gravity separation method to remove the material that floated in water, and the removed plastic material was used as recycled plastic material. However, the underwater specific gravity separation method used a "Water Flow Type Heavy-Density Separator: Naruto Ocean Type" manufactured by Nippon Seam Co., Ltd. to separate the low-density polyolefin-based plastic material (floating material) from other high-density plastic materials (sediment). Comparative Example 1: Used absorbent articles were crushed beforehand, water was used as the processing liquid (without using non-volatile hydrophobic organic solvents or hydrophilic solvents), and acidic water was used for dehydrating the superabsorbent polymer. The recycled plastic material was prepared in the same manner as in Example 1.

[0138] (2) Evaluation Multiple samples were taken from recycled plastic materials, and the mass ratio of the materials in each sample was analyzed using Fourier transform infrared spectroscopy (FT-IR) or gas chromatography-mass spectrometry (GC-MS).

[0139] (3) Results In Example 1, the polyolefin resin content in the recycled plastic material was 80% by mass or more. In Comparative Example 1, the polyolefin resin content in the recycled plastic material was 63% by mass, and it contained a large amount of other types of plastic materials and impurities (e.g., superabsorbent polymers, pulp fibers).

[0140] Thus, the recycled plastic material of Example 1, being derived from used absorbent articles, may contain various types of plastic materials, but it contains 80% or more by mass of a specific type of resin, polyolefin resin, which is higher than the polyolefin resin content of the plastic material of Comparative Example 1. Therefore, it was found that the recycled plastic material of Example 1 is an easy-to-handle recycled plastic material that is easy to separate before separation by the water specific gravity separation method, and after separation, it contains a high-quality recycled plastic material with high purity of a specific type of resin. As a result, it was found that this recycled plastic material can be used for various applications, for example, as a good plastic raw material.

[0141] 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]

[0142] S3 Cleaning process S5, S7 separation process

Claims

1. A method for producing recycled plastic materials derived from used absorbent articles, A washing step involves mixing a mixture containing plastic material 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, and stirring the mixture to wash the plastic material. A separation step of separating the plastic material from the mixture, A method that includes [a certain feature].

2. The aforementioned cleaning process is The 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 liquid, and then stirring the treatment liquid. 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. The process 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, prior to the separation step. 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 plastic material in the mixture is treated with an oxidizing agent. The method according to claim 1.

5. The system further comprises a sanitary treatment step of subjecting the plastic material separated from the mixed liquid in the separation step to sanitary treatment. The method according to claim 1.

6. The aforementioned sanitary treatment step includes an oxidizing agent treatment step in which the plastic material separated from the mixture is treated with an oxidizing agent. The method according to claim 5.

7. The separation step further comprises a specific gravity separation step in which the plastic material separated from the mixture in the separation step is separated in water into at least an olefin-based plastic material and other plastic materials by specific gravity. The method according to claim 1 or 2.

8. The washing step further comprises a pretreatment step to reduce the moisture content of the mixture. The method according to claim 1 or 2.

9. The process further includes a bag-breaking step, in which the packaging bag containing the mixture is broken before the washing step. The method according to claim 1 or 2.

10. The method further comprises a recovery step in which, after the separation step, at least one of the non-flammable hydrophobic organic solvent, the hydrophilic organic solvent, and the adhesive from the mixed liquid is separated and recovered. The method according to claim 1 or 2.

11. 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.

12. 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.

13. The oxidizing agent includes at least one of ozone, hydrogen peroxide, and chlorine-based substances. The method according to any one of claims 3, 4, or 6.

14. The process further comprises a drying step for drying the aforementioned plastic material, The drying step is performed after the washing step and at least one of the separation steps. The method according to claim 1 or 2.

15. Recycled plastic material derived from used absorbent articles, The polyolefin resin content is 80% by mass or more. Recycled plastic materials.

Images