Methods for recycling plastic materials from used nonwoven fabrics containing used absorbent materials.

Abstract

A method for recovering plastic materials from used nonwoven fabric products is provided, wherein impurities in the recovered plastic materials are suppressed. The method includes: a primary separation step (S2), in which the superabsorbent polymer and pulp fibers are separated from a mixture of plastic materials obtained by decomposing used nonwoven fabric products in an inactivating aqueous solution, the superabsorbent polymer, and pulp fibers; and a secondary separation step (S3), in which an oxidant aqueous solution is dispersed into the mixture in the air and a physical impact is applied, thereby separating the superabsorbent polymer and pulp fibers that were not separated in the primary separation step from the plastic materials, thus recovering the plastic materials.

Description

Technical Field

[0001] This invention relates to a method for recovering plastic materials from used nonwoven fabric articles containing used absorbent materials. Background Technology

[0002] Techniques for recovering plastic materials from used nonwoven fabric articles containing used absorbent articles are known. For example, Patent Document 1 (Japanese Patent Application Publication No. 2018-171589) discloses a method for recovering constituent components from used absorbent articles. This method recovers membrane and absorbent materials, which are constituent components, from used absorbent articles. The method includes: a pretreatment step in which the used absorbent article is swollen with water; a decomposition step in which the swollen used absorbent article is subjected to physical impact to decompose the used absorbent article into at least membrane and absorbent materials; and a separation step in which the decomposed membrane and absorbent materials are separated.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-171589 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In Patent Document 1, during the separation process, plastic materials such as membranes and nonwoven fabrics are separated from absorbent materials such as superabsorbent polymers and pulp fibers. However, it is difficult to completely separate the absorbent material from the plastic material, and it is unavoidable that a certain amount of absorbent material remains in the separated plastic material; that is, the plastic material contains a certain amount of impurities. Therefore, the reuse of such plastic materials is limited to applications such as solid fuels, which may also contain a certain amount of impurities.

[0008] This also applies to situations where used medical gowns, caps, masks, and other nonwoven fabric products are collected together with used absorbent items, and plastic materials are recovered from these used nonwoven fabric products.

[0009] The object of the present invention is to provide a method for suppressing impurities in the recycled plastic material in a method for recycling plastic material from a used nonwoven fabric article containing used absorbent articles, and a plastic material in which impurities are suppressed.

[0010] Solution for solving the problem

[0011] One technical solution of the present invention is a method for recovering plastic materials from used nonwoven fabric products containing used absorbent articles, wherein the used nonwoven fabric products contain plastic materials, and the used absorbent articles also contain superabsorbent polymers and pulp fibers. The method includes: a primary separation step, in which the superabsorbent polymer and the pulp fibers are separated from a mixture of the plastic materials, the superabsorbent polymers, and the pulp fibers obtained by decomposing the used nonwoven fabric products in an inactivated aqueous solution; and a secondary separation step, in which an oxidant aqueous solution is dispersed into the mixture in the air and a physical impact is applied, thereby separating the superabsorbent polymers and the pulp fibers that were not separated in the primary separation step from the plastic materials, and recovering the plastic materials.

[0012] Another technical solution of the present invention is a plastic material derived from a used nonwoven fabric product containing used absorbent articles, wherein the proportion of pulp fiber and superabsorbent polymer contained in the plastic material is less than 5% by mass, and the proportion of ash contained in the plastic material is less than 10% by mass.

[0013] The effects of the invention

[0014] According to the method of the present invention, a method for suppressing impurities in the recycled plastic material can be provided in a method for recycling plastic material from a used nonwoven fabric article containing used absorbent articles, and the plastic material in which the impurities are suppressed is also provided. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating a method for recovering plastic materials from used nonwoven fabric articles containing used absorbent materials, according to an embodiment. Detailed Implementation

[0016] This embodiment relates to the following technical solutions.

[0017] [Technical Solution 1]

[0018] A method for recovering plastic material from a used nonwoven fabric containing a used absorbent article, wherein the used nonwoven fabric contains plastic material, and the used absorbent article also contains a superabsorbent polymer and pulp fibers, the method comprising: a primary separation step in which the superabsorbent polymer and pulp fibers are separated from a mixture of the plastic material, the superabsorbent polymer, and the pulp fibers obtained by decomposing the used nonwoven fabric in an inactivated aqueous solution; and a secondary separation step in which an oxidant aqueous solution is dispersed into the mixture in the air and a physical impact is applied to separate the superabsorbent polymer and pulp fibers that were not separated in the primary separation step from the plastic material, thereby recovering the plastic material.

[0019] In this method, firstly, in a primary separation step, the superabsorbent polymer (SAP) is dehydrated by inactivating an aqueous solution, thereby inhibiting swelling and separating most of the SAP and pulp fibers from the mixture of plastic material, SAP, and pulp fibers. Then, in a secondary separation step, physical impact is applied to the mixture in air while dispersing an aqueous oxidant solution, separating the remaining SAP and pulp fibers from the plastic material, thus recovering the plastic material.

[0020] In this way, during the secondary separation process, an aqueous oxidant solution is dispersed into the mixture, thereby decomposing at least a portion of the superabsorbent polymer remaining on the surface of the mixture. Therefore, the superabsorbent polymer adhering to the plastic material, and the pulp fibers adhering with the superabsorbent polymer, can be easily removed from the plastic material. Simultaneously, the mixture can be washed with the aqueous oxidant solution for sterilization, disinfection, and deodorization. Furthermore, physical impact is applied to the mixture in air, not in water (solution), thus directly applying this physical impact to the plastic material, the superabsorbent polymer, and the pulp fibers. Therefore, the superabsorbent polymer and pulp fibers adhering to the plastic material can be easily removed from the plastic material. Thus, through these synergistic effects, the superabsorbent polymer and pulp fibers can be easily separated from the mixture (plastic material), and impurities in the resulting plastic material can be suppressed. Therefore, the reuse applications of this plastic material can be expanded.

[0021] [Technical Solution 2]

[0022] According to the method described in technical solution 1, the oxidant aqueous solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide.

[0023] In this method, the oxidant aqueous solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. Therefore, it is possible to more effectively decompose the surface of the superabsorbent polymer remaining in the mixture, and to more easily remove the superabsorbent polymer remaining in the mixture and the pulp fibers with superabsorbent polymer adhering to them from the plastic material. At the same time, it is possible to more effectively sterilize, disinfect, and deodorize the mixture.

[0024] [Technical Solution 3]

[0025] The method according to technical solution 1 or 2 further includes: a crushing step of crushing the used nonwoven fabric in the inactivated aqueous solution, wherein the primary separation step includes: a step of separating the superabsorbent polymer and the pulp fiber from the mixture of the used nonwoven fabric crushed in the crushing step.

[0026] In this method, prior to the first separation step, the used nonwoven fabric in the inactivation aqueous solution is broken into predetermined sizes, thereby breaking the plastic material, superabsorbent polymer, and pulp fibers into predetermined sizes. That is, the superabsorbent polymer can be inactivated and dehydrated with the inactivation aqueous solution, suppressing swelling while making the plastic material, superabsorbent polymer, and pulp fibers into sizes easily separable in the first and second separation steps. Therefore, it is easier to separate the superabsorbent polymer and pulp fibers from the mixture (plastic material).

[0027] [Technical Solution 4]

[0028] According to any one of technical solutions 1 to 3, in the primary separation step, the inactivation aqueous solution is an acidic aqueous solution, the pH of the acidic aqueous solution is maintained within a predetermined range, and the superabsorbent polymer and the pulp fiber are separated from the mixture.

[0029] In this method, in the primary separation step, the inactivation aqueous solution is an acidic aqueous solution, the pH of which is maintained within a predetermined range, and the superabsorbent polymer and pulp fiber are separated from the mixture. Therefore, the superabsorbent polymer can be reliably inactivated and dehydrated using the inactivation aqueous solution in the primary separation step, while inhibiting swelling and separating most of the superabsorbent polymer and pulp fiber from the mixture. Consequently, the amount of superabsorbent polymer and pulp fiber that would be separated in the secondary separation step is reduced, and the superabsorbent polymer and pulp fiber can be more easily separated from the mixture (plastic material).

[0030] [Technical Solution 5]

[0031] According to any one of technical solutions 1 to 4, the physical impact is applied to the mixture by the collision of the rotating blades of an impeller that agitates the mixture in the air.

[0032] In this method, physical impact is applied to the mixture by the collision of the rotating blades of an impeller agitating the mixture in air. This allows for more reliable physical impact on the mixture in air. Consequently, it makes it easier to remove superabsorbent polymer residues and pulp fibers coated with superabsorbent polymer from the plastic material.

[0033] [Technical Solution 6]

[0034] According to any one of technical solutions 1 to 5, the primary separation process is performed by one of two primary separation devices connected in parallel.

[0035] The primary separation unit, which performs the initial separation process, is prone to material blockage and other issues. Therefore, in this method, the primary separation process is performed by one of two primary separation units connected in parallel. This allows the method to be executed continuously without temporary interruptions, for example, if one of the primary separation units requires maintenance, by stopping that unit and operating the other, the method can be run continuously. Thus, it enables the efficient recovery of plastic materials with few impurities.

[0036] [Technical Solution 7]

[0037] According to any one of technical solutions 1 to 6, the used nonwoven fabric article, in addition to the used absorbent article, also includes at least one of a medical gown, a medical cap, and a mask made of nonwoven fabric.

[0038] This method can be applied not only to used absorbent items such as disposable diapers, but also to used nonwoven fabric products including medical gowns, medical caps, and masks made of nonwoven fabric. In this case, impurities in the resulting plastic material can be suppressed, expanding the applications for recycling the plastic material.

[0039] [Technical Solution 8]

[0040] According to any one of technical solutions 1 to 7, the plastic material recovered in the secondary separation process is for oiling purposes.

[0041] In this method, the plastic material recovered in the secondary separation process can be used for oil refining. That is, the plastic material obtained by this method is a plastic material with suppressed impurities, so the reuse application can be extended to oil refining (a technique of using heat or a catalyst to decompose used plastic material to produce liquid products).

[0042] [Technical Solution 9]

[0043] A plastic material derived from a used nonwoven fabric containing used absorbent articles, wherein the proportion of pulp fiber and superabsorbent polymer contained in the plastic material is less than 5% by mass, and the proportion of ash contained in the plastic material is less than 10% by mass.

[0044] Although this plastic material is derived from used nonwoven fabric products containing used absorbent materials, the proportion of pulp fiber and superabsorbent polymer is less than 5% by mass, and the proportion of ash is less than 10% by mass. That is, this plastic material is a plastic material with suppressed impurities, and therefore its reuse can be extended to a wide variety of applications (e.g., oiling).

[0045] The following describes a method for recovering plastic materials from used nonwoven fabric products containing used absorbent articles, according to an embodiment. Used absorbent articles include absorbent articles used by a user and absorbent articles that have been discarded but not used. Examples of absorbent articles include disposable diapers, diaper pads, sanitary napkins, bed sheets, and pet pads. Used absorbent articles include those that have absorbed / retained the user's excrement. Used nonwoven fabric products include nonwoven fabric products used by a user and nonwoven fabric products that have been discarded but not used. Nonwoven fabric products are articles composed of multiple components containing nonwoven fabric, and at least include nonwoven fabric made of synthetic resin, i.e., plastic material. Examples of nonwoven fabric products, in addition to the aforementioned absorbent articles, include medical gowns, medical caps, masks, and wiping cloths. It should be noted that the nonwoven fabric product contains at least 50% by weight of nonwoven fabric in the article.

[0046] First, an example of the composition of an absorbent article will be described. An absorbent article comprises a surface sheet, a back sheet, and an absorbent body disposed between the surface sheet and the back sheet. As an example of the size of an absorbent article, a length of approximately 15cm to 100cm and a width of 5cm to 100cm can be listed. It should be noted that absorbent articles may also include other components commonly found in absorbent articles, such as diffuser sheets, leak-proof walls, side sheets, and outer sheaths.

[0047] Examples of components for the surface sheet include, for example, liquid-permeable nonwoven fabrics, synthetic resin membranes with liquid-permeable pores, and composite sheets thereof. Examples of components for the back sheet include, for example, liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin membranes, and composite sheets thereof. Examples of components for the diffuser sheet include, for example, liquid-permeable nonwoven fabrics. Examples of components for leak-proof walls and side sheets include, for example, water-repellent nonwoven fabrics; leak-proof walls may also include elastic components such as rubber. Examples of components for the outer sheet include, for example, liquid-impermeable and air-permeable nonwoven fabrics, liquid-impermeable and air-permeable synthetic resin membranes, and composite sheets thereof. There are no particular limitations on the type of nonwoven fabric; examples include, for example, meltblown nonwoven fabrics, spunbond nonwoven fabrics, air-laid nonwoven fabrics, and hot-air nonwoven fabrics. Furthermore, there are no particular limitations on the type of synthetic resin membrane; known membrane materials can be used. Here, the materials used for nonwoven fabrics and synthetic resin films are not particularly limited as long as they can be used as absorbent articles. Examples 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). These nonwoven fabrics and synthetic resin films are synthetic resins and can be called plastic materials. In this embodiment, an absorbent article in which the back sheet is a film and the surface sheet is a nonwoven fabric will be described as an example.

[0048] Examples of absorbent materials include absorbent materials such as pulp fibers and superabsorbent polymers. Examples of pulp fibers include cellulose fibers. Examples of cellulose fibers include wood pulp, cross-linked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. Regarding the size of the pulp fibers, the average long diameter can be, for example, tens of μm, preferably 20 μm to 40 μm, and the average fiber length can be, for example, several mm, preferably 2 mm to 5 mm. Examples of superabsorbent polymers (SAP) include polyacrylate-based, polysulfonate-based, and maleic anhydride-based superabsorbent polymers. Regarding the size (when dry) of the superabsorbent polymer, the average particle size can be, for example, several hundred μm, preferably 200 μm to 500 μm. The absorbent may also include a core-cladding layer formed of a liquid-permeable sheet.

[0049] One side and the other side of the absorbent are bonded to the surface sheet and the back sheet respectively by means of an adhesive. Viewed from above, the portion of the surface sheet that extends outwards from the absorbent (peripheral portion) in a manner surrounding the absorbent is bonded to the portion of the back sheet that extends outwards from the absorbent (peripheral portion) in a manner surrounding the absorbent by means of an adhesive. Thus, the absorbent is incorporated into the interior of the bonded surface sheet and the back sheet. There are no particular limitations on the adhesive; for example, hot-melt adhesives can be cited. Examples of hot-melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives with rubber-based substrates such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefin-based substrates such as polyethylene.

[0050] Furthermore, the composition of medical gowns, medical caps, masks, and wiping cloths is as follows. Medical gowns are not particularly limited as long as they contain nonwoven fabric, and may include, for example, a body portion made of nonwoven fabric to cover the wearer's body, sleeves made of nonwoven fabric to cover the wearer's arms, and straps made of nonwoven fabric to secure the body portion to the wearer's body. Similarly, medical caps are not particularly limited as long as they contain nonwoven fabric, and may include, for example, a crown portion made of nonwoven fabric to cover the wearer's head, and may also include jaw straps made of nonwoven fabric to secure the crown portion to the head. Masks are not particularly limited as long as they contain nonwoven fabric, and may include, for example, a mask body portion made of nonwoven fabric to cover at least the wearer's nose and mouth, and a pair of ear loops made of nonwoven fabric to secure the mask body portion to the front of the wearer's face. Wiping cloths consist of one or more sheets made of nonwoven fabric. The nonwoven fabrics (and synthetic resin films) used in these products can be any of the aforementioned nonwoven fabrics (and synthetic resin films).

[0051] Next, a method for recovering plastic materials from used nonwoven fabric products containing used absorbent articles will be specifically described according to the embodiments. In this embodiment, absorbent articles (e.g., disposable diapers) will be used as an example of nonwoven fabric products for explanation.

[0052] Figure 1 This is a flowchart illustrating a method for recovering plastic materials from used nonwoven fabric products containing used absorbent materials, according to an embodiment. This method, as a process for recovering plastic materials from used nonwoven fabric products, includes a primary separation step S2 and a secondary separation step S3. In this embodiment, it also includes a crushing step S1 and a dewatering and drying step S4. It should be noted that, in this embodiment, in conjunction with this method, a dust removal step S5 to a pulp fiber separation step S8 are also included. Each step will be described below.

[0053] In this embodiment, used absorbent materials (non-woven fabric products) are collected from the outside for reuse (recycling). At this time, multiple used absorbent materials are sealed into a collection bag to prevent leakage of excrement, bacteria, and odors to the outside. The used absorbent materials inside the collection bag are collected primarily in a rolled-up or folded state, such as so that excrement and bacteria are not exposed on the surface and odors do not spread to the surrounding area. It should be noted that used absorbent materials may also be left unsealed in the collection bag and not rolled up.

[0054] The crushing step S1 is a process of crushing used absorbent materials (non-woven fabric products) in an inactivating aqueous solution. In this embodiment, in the crushing step S1, a collection bag containing the used absorbent materials is supplied to a solution tank storing an acidic aqueous solution, which serves as the inactivating aqueous solution. The acidic aqueous solution containing the collection bag is fed from the solution tank to a twin-shaft crusher (e.g., a twin-shaft rotary crusher, a twin-shaft differential crusher, or a twin-shaft shear crusher). The collection bag is crushed along with the collection bag by the twin-shaft crusher. Thus, the used absorbent materials inside the collection bag are crushed together with the collection bag in the acidic aqueous solution, generating crushed material. The crushed material is conveyed, alone or together with the acidic aqueous solution, to a primary separation step S2.

[0055] Here, in the crushing step S1, it is preferable to crush the used absorbent material to a size of approximately 25mm to 150mm. If the size is 25mm or larger, materials other than pulp fibers and superabsorbent polymers (e.g., membranes, nonwoven fabrics, elastomers, etc.) are cut to a greater extent, making it easier to separate these materials from the pulp fibers and superabsorbent polymers in subsequent processes. If the size is less than 150mm, the materials in the used absorbent material are less likely to entangle with each other. If the size exceeds 150mm, the materials tend to entangle with each other, and if entangled, they are difficult to separate.

[0056] If used absorbent materials are treated in an inactivating aqueous solution, the superabsorbent polymers contained in or contained in the used absorbent materials are inactivated, dehydrated, and reduced to small particle size. Therefore, the treatment of superabsorbent polymers in subsequent processes becomes easier and the treatment efficiency is improved. An acidic aqueous solution, i.e., an aqueous solution of inorganic and organic acids, is used as the inactivating aqueous solution because, compared to aqueous solutions of lime, calcium chloride, etc., it leaves no ash residue in plastic materials and pulp fibers, and also because the degree of inactivation (particle size, specific gravity) can be easily adjusted by pH. The pH of the acidic aqueous solution is preferably 1.0 to 4.0. If the pH is set above 1.0, the equipment is less likely to corrode, and the amount of alkaline chemical reagents required for neutralization treatment during wastewater treatment can be reduced. If the pH is set below 4.0, the superabsorbent polymers can be sufficiently reduced, and the bactericidal ability is also improved. Examples of organic acids include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, ascorbic acid, etc., with citric acid being preferred. Citric acid's chelating effect allows for the capture and removal of metal ions and other contaminants from excrement, and its cleaning effect also enables the removal of high levels of dirt. On the other hand, examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid; sulfuric acid is preferred from the viewpoints of being chlorine-free and cost-effective. Since pH varies with water temperature, the pH in this invention refers to the pH measured at an aqueous solution temperature of 20°C. The concentration of the organic acid in the aqueous solution is not particularly limited, but when the organic acid is citric acid, it is preferably 0.5% by mass or more and 4% by mass or less. The concentration of the inorganic acid in the aqueous solution is not particularly limited, but when the inorganic acid is sulfuric acid, it is preferably 0.1% by mass or more and 0.5% by mass or less. In this embodiment, citric acid, an organic acid, is used as the inactivation aqueous solution.

[0057] It should be noted that used absorbent material fed into the twin-shaft crusher may not need to be placed in a collection bag. Furthermore, used absorbent material, whether sealed in a collection bag or not, may be fed into the twin-shaft crusher without passing through a solution tank. Additionally, the crushing process using the twin-shaft crusher may not be carried out in the inactivation aqueous solution; for example, it may be carried out in air. In this case, a separation step S2 is performed in the inactivation aqueous solution as a subsequent process.

[0058] It should be noted that by increasing the temperature of the inactivating aqueous solution (temperature: 70℃~95℃), the adhesive used to bond the components of the used absorbent article (e.g., hot melt adhesive) can be softened, reducing the adhesive's bonding strength. This allows the components to easily separate naturally or with a small impact. Furthermore, the used absorbent article can also be sterilized (disinfected).

[0059] In this way, during the crushing process S1, each component of the used absorbent article is crushed to approximately a predetermined size. Furthermore, due to the reduced bonding strength of the adhesive between the components during crushing and / or the heat from the inactivating aqueous solution, the components tend to move away from each other.

[0060] Next, the primary separation step S2 is a process of separating the superabsorbent polymer and pulp fibers from a mixture of plastic material, superabsorbent polymer, and pulp fibers obtained by decomposing used absorbent articles (non-woven fabric products) in an inactivating aqueous solution. In this embodiment, in the primary separation step S2, the mixture of crushed material generated in the crushing step S1 and the acidic aqueous solution, which is the inactivating aqueous solution, is supplied to a pulp separator (primary separation device). The pulp separator has a stirring separation tank that functions as a washing tank and a screening tank. In the pulp separator, the mixture of crushed material and acidic aqueous solution is stirred to remove dirt from the crushed material, while pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution are separated (removed) through the screen. That is, pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution are separated from the mixture by passing through the screen and discharged from the pulp separator. On the other hand, the remaining mixture, i.e., other materials (collection bags, membranes, non-woven fabrics, etc.), cannot pass through the screen and remain in the pulp separator. Subsequently, other materials are conveyed quantitatively to the secondary separation process S3 per unit time via a screw conveyor. It should be noted that some of the other materials may pass through a screen.

[0061] However, pulp fibers, superabsorbent polymers, excrement, and a portion of the acidic aqueous solution may remain in the mixture. Furthermore, other materials in the mixture, such as collection bags, membranes, and nonwoven fabrics, are made of synthetic resins and can be considered plastic materials. Therefore, in the first separation step S2, the plastic materials in the mixture, along with small amounts of residue (pulp fibers, superabsorbent polymers, excrement, and acidic aqueous solution), become residue on the screen, while the pulp fibers, superabsorbent polymers, excrement, and acidic aqueous solution separated from the mixture become the material that passes through the screen.

[0062] In this embodiment, the primary separation process S2 is performed by one of two primary separation devices connected in parallel. For example, two pulp separators are connected in parallel, one pulp separator is operated, and when maintenance or other necessitates its operation, it is stopped, and the other pulp separator is put into operation. Thus, the primary separation process S2 can be performed continuously. It should be noted that three or more primary separation devices can also be connected in parallel.

[0063] In this embodiment, in the primary separation step S2, the pH of the acidic aqueous solution is adjusted to maintain within a predetermined range. The predetermined pH range is set to a pH variation within ±1.0. This allows the difference in specific gravity and size between the superabsorbent polymer and the pulp fiber to be within a predetermined range. In this case, the difference within the predetermined range is, for example, set to one being 0.2 to 5 times that of the other. Thus, the difference between the pulp fiber and the superabsorbent polymer is that both their specific gravity and size are within a predetermined range. As a result, the pulp fiber and superabsorbent polymer can be easily separated from other materials (mainly plastic materials) in the used absorbent article material, except for the pulp fiber and superabsorbent polymer, by utilizing the differences in size and specific gravity. pH adjustment can be performed using acidic or alkaline aqueous solutions based on the pH value measured by a pH sensor. It should be noted that the pH can also be adjusted in the same way as in the primary separation step S2 in the secondary separation step S3.

[0064] In addition, in the crushing process S1, when using an inactivating aqueous solution (acidic aqueous solution), the pH of the acidic aqueous solution can be adjusted in the same way as in the primary separation process S2.

[0065] Next, the secondary separation process S3 separates the superabsorbent polymers and pulp fibers that were not separated in the primary separation process from the plastic material by dispersing an aqueous oxidant solution into the mixture in the air and applying physical impact, thereby recovering the plastic material.

[0066] In this embodiment, in the secondary separation step S3, a mixture (residue: plastic material and residue) of pulp fibers, superabsorbent polymers, etc., separated by the primary separation step S2, is supplied to the separation device. This separation device includes a horizontally inverted cylindrical section, multiple impellers disposed within the cylindrical section, multiple oxidant aqueous solution supply sections disposed on the upper outer circumferential surface of the cylindrical section, and a screen (sieve) disposed on the lower outer circumferential surface of the cylindrical section. A mixture supply port is located at one end of the cylindrical section, and a discharge port is located at the other end. The multiple impellers rotate around the axis of the cylindrical section and are arranged axially along the cylindrical section in a manner that generates airflow from one end to the other. The multiple oxidant aqueous solution supply sections are arranged axially. The size of each opening in the screen (sieve) is such that pulp fibers and superabsorbent polymers can pass through, but is too small for plastic materials to pass through.

[0067] Furthermore, the mixture is agitated by the blades of an impeller rotating within the cylindrical section while being dispersed with an oxidant aqueous solution from the oxidant aqueous solution supply section in the air. It is subjected to physical impact through the collision of the impeller blades and moves from one end of the cylindrical section to the other. During this process, the mixture moves (flows) in the air and is cleaned (including sterilization and bleaching) by the dispersed oxidant aqueous solution to remove dirt. Simultaneously, pulp fibers, superabsorbent polymers, etc., in the mixture are removed from the plastic material through physical impact and oxidative decomposition of the superabsorbent polymers by the oxidant, and are separated (removed) along with the oxidant aqueous solution through a screen on the lower side of the cylindrical section. On the other hand, the plastic material in the mixture after the removal of pulp fibers, superabsorbent polymers, etc., does not pass through the screen and is discharged from the outlet on the other end of the cylindrical section. In other words, the superabsorbent polymers and pulp fibers that were not separated in the first separation step S2 are separated from the plastic material, generating and recovering plastic material with suppressed impurities. It should be noted that the secondary separation process S3 is carried out in air, thus improving the dehydration of the plastic material. Additionally, the separated oxidant aqueous solution can be reused in the oxidant treatment process S7 (described later).

[0068] Here, the oxidant aqueous solution is an aqueous solution containing an oxidant. Oxidants include at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. In this embodiment, ozone is used as the oxidant from the viewpoints of oxidizing power, bactericidal power, and bleaching power. In this case, the oxidant aqueous solution is preferably acidic. The reasons are to suppress ozone deactivation and to maintain the inactivation of the highly absorbent polymer. Furthermore, when an acidic aqueous solution such as citric acid aqueous solution is used as the inactivation aqueous solution in the crushing step S1 and the primary separation step S2, it is also from the viewpoints of continuity of each step and the ability to reuse the aqueous solution without waste. It should be noted that if the final plastic material obtained in this method is intended for a purpose where chlorine residue is undesirable, sodium hypochlorite is not used as the oxidant. Furthermore, when the aqueous solution of the oxidant separated in the secondary separation step S3 is reused in the oxidant treatment step S7 (described later), and when pulp fibers or superabsorbent polymers are used in sanitary applications, sodium hypochlorite is not used as an oxidant in order to suppress the residue of chlorine in the pulp fibers.

[0069] The ozone concentration in the oxidant aqueous solution is not particularly limited, as long as it achieves the desired function, namely oxidizing power, bactericidal power, and bleaching power. Examples include 0.2 ppm to 10 ppm, preferably 0.5 ppm to 5 ppm. Maintaining a concentration that is not too low ensures the desired function is achieved, while maintaining a concentration that is not too high inhibits equipment corrosion. The treatment time in the oxidant aqueous solution is not particularly limited, as long as it achieves the desired function. A higher ozone concentration results in a shorter treatment time, and a lower ozone concentration results in a longer treatment time; typically, it is 1 to 10 minutes. The product of the ozone concentration (ppm) in the oxidant aqueous solution and the treatment time (minutes) (hereinafter also referred to as the "CT value") is, for example, 0.5 ppm·min to 10 ppm·min, preferably 1 ppm·min to 5 ppm·min. Maintaining a CT value that is not too low ensures the desired function is achieved, while maintaining a CT value that is not too high inhibits equipment corrosion. It should be noted that, as an aqueous oxidant solution, the concentration can be reduced and the aqueous oxidant solution used in the oxidant treatment step S7 described later can be reused in this process.

[0070] Regarding sterilization or disinfection, for example, used diapers may contain more than 1 billion bacteria / ml of common bacteria, but these cannot be completely sterilized in the acidic aqueous solution up to the first separation step S2. Therefore, the plastic material separated in the first separation step S2 (with a small amount of attached pulp fibers and superabsorbent polymers) contains a certain level of common bacteria (e.g., 3400 common bacteria / ml). The same applies when performing the second separation step S3 without using an oxidizing aqueous solution. This could potentially lead to adverse effects on operator safety and concerns about the deterioration or mold growth of the extracted plastic material. Additionally, there is the possibility of a strong fecal odor, believed to be caused by common bacteria. However, by performing the second separation step S3 using an oxidizing aqueous solution, common bacteria in the plastic material can be removed to below the detection limit, similar to E. coli, and the fecal odor can be reduced to an almost imperceptible level.

[0071] Next, a dehydration and drying step S4 can be performed. The dehydration and drying step S4 is a process of dehydrating and / or drying the separated plastic material. In this embodiment, the plastic material is dried using a high-temperature atmosphere or hot air in a constant-temperature bath. Examples of drying temperatures include 80°C to 120°C. The drying time depends on the drying temperature and is, for example, 10 minutes to 120 minutes, preferably 15 minutes to 100 minutes. This not only evaporates and removes residual moisture from the plastic material but also sterilizes it. Thus, a sterilization (disinfection) effect is achieved while removing moisture.

[0072] In this method, the superabsorbent polymer and pulp fibers are further separated and removed from the plastic material primarily through a secondary separation step S3, thus enabling the recovery of plastic material with reduced impurities. The proportion of pulp fibers and superabsorbent polymers among the impurities contained in this plastic material is 5% by mass or less, preferably 3% by mass or less, and the ash content is less than 10% by mass, preferably 5% by mass, more preferably 3% by mass or less. Furthermore, sterilization is performed using an oxidant, so bacteria are virtually non-existent. Such low-impurity plastic material allows for a wide range of applications for its reuse. Examples of such applications include techniques for decomposing used plastic material using heat or a catalyst to produce liquid products, i.e., oleochemicals.

[0073] In this method, firstly, in a primary separation step S2, the superabsorbent polymer is dehydrated by inactivating an aqueous solution (e.g., an acidic aqueous solution), thereby inhibiting swelling and separating most of the superabsorbent polymer and pulp fibers from the mixture of plastic materials (membranes, nonwoven fabrics, etc.), superabsorbent polymer, and pulp fibers. Then, in a secondary separation step S3, a physical impact is applied to the mixture by dispersing an oxidant aqueous solution (e.g., an ozone aqueous solution) into the air, and the remaining superabsorbent polymer and pulp fibers are separated from the plastic materials, thereby recovering the plastic materials.

[0074] In this way, in the secondary separation step S3, an aqueous oxidant solution is dispersed into the mixture, thereby oxidizing and decomposing at least a portion of the superabsorbent polymer remaining on the surface of the mixture and solubilizing it. Therefore, the superabsorbent polymer adhering to the plastic material and the pulp fibers adhering via the superabsorbent polymer can be easily removed from the plastic material. Simultaneously, the mixture can be washed with the aqueous oxidant solution for sterilization, disinfection, and deodorization. Furthermore, physical impact is applied to the mixture in air, not in water (solution), thus directly applying this physical impact to the plastic material, the superabsorbent polymer, and the pulp fibers. Therefore, the superabsorbent polymer and pulp fibers adhering to the plastic material can be easily removed from the plastic material. Thus, through these synergistic effects, the superabsorbent polymer and pulp fibers can be easily separated from the mixture (plastic material), and impurities in the resulting plastic material can be suppressed. Therefore, the reuse applications of this plastic material can be expanded.

[0075] In this method, preferably, the oxidant aqueous solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. Therefore, it is possible to more effectively decompose the surface of the superabsorbent polymer remaining in the mixture, and to more easily remove the superabsorbent polymer remaining in the mixture and the pulp fibers with superabsorbent polymer adhering to them from the plastic material. At the same time, it is possible to more effectively sterilize, disinfect, and deodorize the mixture. In particular, ozone has high effects in these aspects and is therefore preferred.

[0076] In this method, preferably, before the primary separation step S2, the used nonwoven fabric in the inactivation aqueous solution is broken into a predetermined size, thereby breaking the plastic material, superabsorbent polymer, and pulp fiber into a predetermined size (breaking step S1). That is, the superabsorbent polymer can be inactivated and dehydrated with the inactivation aqueous solution, suppressing swelling while making the plastic material, superabsorbent polymer, and pulp fiber into sizes that are easy to separate in the primary and secondary separation steps. Therefore, it is easier to separate the superabsorbent polymer and pulp fiber from the mixture (plastic material).

[0077] In this method, preferably, in the primary separation step S2, the inactivation aqueous solution is an acidic aqueous solution, the pH of which is maintained within a predetermined range, and the superabsorbent polymer and pulp fiber are separated from the mixture. Therefore, the superabsorbent polymer can be more reliably inactivated and dehydrated using the inactivation aqueous solution in the primary separation step, while suppressing swelling and separating most of the superabsorbent polymer and pulp fiber from the mixture. This reduces the amount of superabsorbent polymer and pulp fiber that would be separated in the secondary separation step, making it easier to separate the superabsorbent polymer and pulp fiber from the mixture (plastic material).

[0078] In this method, as a preferred approach, physical impact is applied to the mixture by the collision of the rotating blades of an impeller agitating the mixture in air. This allows for more reliable physical impact on the mixture in air. Consequently, it makes it easier to remove superabsorbent polymer residues and pulp fibers coated with superabsorbent polymer from the plastic material.

[0079] The primary separation unit performing the primary separation step S2 is the initial separation unit, and therefore, it is prone to problems such as material blockage. Therefore, in this method, as a preferred embodiment, the primary separation step S2 is performed by one of two primary separation units connected in parallel. Thus, for example, if one of the operating primary separation units requires maintenance, by stopping that unit and operating the other, the method can be continuously executed without temporary interruptions. Therefore, it is possible to efficiently recover plastic materials with few impurities.

[0080] As a preferred embodiment, this method can be applied not only to used absorbent articles such as disposable diapers, but also to cases where at least one of medical gowns, medical caps, and masks made of nonwoven fabric is used as a nonwoven fabric product. In this case, impurities in the resulting plastic material can be suppressed, expanding the applications for recycling the plastic material.

[0081] In this method, as a preferred embodiment, the plastic material recovered in the secondary separation step S3 can be used for oil refining. That is, the plastic material obtained by this method is a plastic material with suppressed impurities, so the reuse application can be extended to oil refining (a technique of using heat or a catalyst to decompose used plastic material and produce liquid products).

[0082] Although this plastic material is derived from used nonwoven fabric products containing used absorbent materials, the proportion of pulp fibers and superabsorbent polymers contained in the plastic material is less than 5% by mass, and the proportion of ash contained in the plastic material is less than 10% by mass. That is, this plastic material is a plastic material with suppressed impurities, and therefore its reuse can be extended to a wide variety of applications (e.g., oiling).

[0083] In addition, in this embodiment, such as Figure 1 As shown, this method also includes a dust removal step S5, a SAP separation step S6, an oxidant treatment step S7, and a pulp fiber separation step S8, as steps to recover pulp fibers and super absorbent polymer (SAP) from used nonwoven products.

[0084] In this embodiment, the mixture of pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution separated in the primary separation step S2 is processed in the dust removal step S5. It should be noted that, alternatively, the pulp fibers and superabsorbent polymer separated in the secondary separation step S3 may also be mixed in the aforementioned mixture and processed in the dust removal step S5.

[0085] The dust removal process S5 utilizes at least one separator (e.g., a screen separator or a cyclone separator) to separate foreign matter such as collection bags, membranes, nonwoven fabrics, elastomers, etc., from the mixture supplied from the primary separation process S2 (and the secondary separation process S3). In this embodiment, in the dust removal process S5, a screen separator (with relatively large mesh), a screen separator (with relatively small mesh), and a cyclone separator are arranged sequentially to separate foreign matter from the mixture in sequence. This yields pulp fibers and superabsorbent polymers with fewer foreign matter. The mixture of pulp fibers with fewer foreign matter, superabsorbent polymers, and an acidic aqueous solution (containing excrement) is then supplied to the SAP separation process S6.

[0086] SAP separation step S6 uses at least one separator (e.g., a drum screen separator) to separate the superabsorbent polymer from the mixture (containing pulp fibers with few foreign matter and superabsorbent polymer) supplied by the self-dust removal step S5. In this embodiment, in SAP separation step S6, the superabsorbent polymer and acidic aqueous solution (including excrement) are separated from the mixture using a drum screen separator. This yields a superabsorbent polymer with few foreign matter and an acidic aqueous solution. The superabsorbent polymer is then separated from the acidic aqueous solution (liquid) using another separator (e.g., an inclined screen separator) and removed. Meanwhile, the pulp fibers with few foreign matter (containing a small amount of superabsorbent polymer) are supplied to the oxidant treatment step S7.

[0087] In the oxidant treatment step S7, an aqueous oxidant solution is used to oxidize and decompose the superabsorbent polymer (which includes a small amount of superabsorbent polymer) in the pulp fibers supplied from the SAP separation step S6, removing it from the pulp fibers. In this embodiment, in the oxidant treatment step S7, pulp fibers are fed into a treatment tank containing an aqueous oxidant solution with ozone as the oxidant, oxidizing and decomposing the superabsorbent polymer in the pulp fibers, thus solubilizing it and obtaining pulp fibers with very few impurities. The pulp fibers with few impurities (including superabsorbent polymer) are then supplied to the pulp fiber separation step S8 together with the aqueous oxidant solution.

[0088] The type of oxidant used in the oxidant treatment step S7 is the same as that used in the secondary separation step S3. In this embodiment, ozone is used as the oxidant from the viewpoints of oxidizing power, bactericidal power, and bleaching power. The ozone concentration in the oxidant aqueous solution is not particularly limited as long as it is sufficient to decompose the superabsorbent polymer; for example, it can be 10 ppm to 50 ppm by mass. By keeping the concentration not too low, the superabsorbent polymer can be completely solubilized; by keeping the concentration not too high, damage to the pulp fibers will not be caused. The treatment time in the oxidant aqueous solution is not particularly limited as long as it is sufficient to decompose the superabsorbent polymer; a higher ozone concentration in the oxidant aqueous solution results in a shorter time, and a lower ozone concentration results in a longer time, typically 5 minutes to 120 minutes. The product of the ozone concentration (ppm) in the oxidant aqueous solution and the treatment time (minutes) of the treatment step (hereinafter also referred to as the "CT value") is preferably 100 ppm·min to 6000 ppm·min. If the CT value is too small, the superabsorbent polymer cannot be completely solubilized, and superabsorbent polymer may remain in the pulp fiber. If the CT value is too large, it may damage the pulp fiber.

[0089] In the pulp fiber separation process S8, a separator (e.g., a screen separator) is used to separate the pulp fibers from the oxidant aqueous solution supplied in the self-oxidant treatment process S7. The separated and recycled pulp fibers become so-called recycled pulp fibers. The recycled pulp fibers are washed with washing water and removed.

[0090] Example

[0091] The present invention will be described below based on embodiments, but the present invention is not limited to the embodiments.

[0092] (1) Sample

[0093] Using unused, used disposable diapers as raw materials, the process is carried out... Figure 1 The method shown recycles plastic materials after the first separation step S2 and the second separation step S3. The ozone concentration and treatment time (CT value) in the second separation step S3 are set to 1 ppm × 2 minutes (2 ppm·min).

[0094] (2) Evaluation Methods

[0095] For the primary separation process S2 and the secondary separation process S3 (including the case where ozone is not used), the residual amount of pulp fiber adhering to the plastic (mass%), the residual amount of superabsorbent polymer adhering to the plastic (mass%), and the residual amount of ash (mass%) were evaluated respectively.

[0096] The calculation methods for each are as follows.

[0097] (a) Residual pulp fiber content (mass%), residual superabsorbent polymer content (mass%)

[0098] <Method for determining residual content after a single separation process>

[0099] In one separation process, the plastic material after separating pulp fibers and superabsorbent polymer was dried (120°C × 60 minutes) and weighed (measurement value A), as sample α1. Next, sample α1 was adjusted to a 1% solids concentration aqueous solution, and ozone gas was blown in while stirring for ozone treatment. The ozone concentration in the aqueous solution and the treatment time were set to 50 ppm × 30 minutes (CT value 1500) (the superabsorbent polymer was decomposed, solubilized, and removed). Next, sample α2 obtained from the solid-liquid separation of the ozone aqueous solution was dried (120°C × 60 minutes) and weighed (measurement value A'). The result, |A'-A|, became the residual mass D of the remaining superabsorbent polymer. On the other hand, sample α2 was immersed in toluene to dissolve the adhesive (HMA), separating it into pulp fibers and plastic material. Next, the pulp fibers were air-dried in a fume hood (60 minutes), and the result was weighed as the residual mass C of the pulp fibers. The mass B of the plastic material itself is calculated using ADC.

[0100] thus

[0101] Plastic material (mass%) = B / A × 100

[0102] Pulp fiber (mass%) = C / A × 100

[0103] Superabsorbent polymer (mass%) = D / A × 100;

[0104] <Method for determining residual content after secondary separation process>

[0105] The method for determining the residual amount after the secondary separation process is the same as that for determining the residual amount after the primary separation process.

[0106] (b) Ash residue (mass%)

[0107] Ash content refers to the amount of inorganic or non-flammable residue remaining after organic matter has been ashed. The residual ash content (mass %), or ash rate, refers to the ratio (mass ratio) of ash contained in the sample to be tested. The ash rate mentioned above is determined according to "2. General Test Methods" and "5. Ash Test Method" of the material standard for physiological treatment products. Specifically, the ash rate is determined as follows.

[0108] (i) Preheat a platinum, quartz or magnetic crucible (with lid) to 500°C to 550°C for 1 hour, let it cool, and then weigh it precisely.

[0109] (ii) Collect 2g to 4g of plastic material that has been dried at 120℃ for 60 minutes, put it into a crucible, and weigh it precisely.

[0110] (iii) First, lightly heat the crucible. If necessary, cover or move it. Gradually increase the temperature and heat it at 500℃~550℃ for more than 4 hours to ashed it until there are no carbide residues.

[0111] (iv) After cooling, accurately weigh the crucible. Ash the residue again to constant weight, and after cooling, accurately weigh the crucible. Calculate the ash content (mass%) based on these measurements (1), (2), and (4).

[0112] (3) Evaluation Results

[0113] In the material separated as a plastic material after the first separation process S2, the proportion (residual amount) of pulp fiber is approximately 25% by mass, the proportion (residual amount) of superabsorbent polymer is approximately 10% by mass, exceeding 5% by mass. The proportion (residual amount) of ash is 12.3% by mass, exceeding 10% by mass.

[0114] In the material separated as a plastic material after the secondary separation process S3, the proportion of pulp fiber is approximately 3% by mass, the proportion of superabsorbent polymer is approximately 1% by mass, and the proportion is less than 5% by mass. The proportion of ash is approximately 7% by mass, and the proportion is less than 10% by mass.

[0115] Therefore, by adding a secondary separation process S3, the amount of pulp fibers, superabsorbent polymers, and ash, i.e. impurities, contained in plastic materials can be significantly reduced.

[0116] The absorbent articles of the present invention are not limited to the embodiments described above, and can be appropriately combined and modified without departing from the purpose and spirit of the present invention.

[0117] Explanation of reference numerals in the attached figures

[0118] S2 Primary Separation Process

[0119] S3 Secondary Separation Process

Claims

1. A method for recycling plastic materials from used nonwoven fabric articles containing used absorbent materials, wherein, The used nonwoven fabric contains plastic materials, and the used absorbent article also contains superabsorbent polymers and pulp fibers. The method includes: A primary separation process, in which the superabsorbent polymer and the pulp fibers are separated from a mixture of the plastic material obtained by decomposing the used nonwoven fabric in an inactivating aqueous solution, the superabsorbent polymer, and the pulp fibers; and In a secondary separation process, an aqueous solution of an oxidant is dispersed in air into the mixture after the primary separation process has separated the superabsorbent polymer and the pulp fiber, and a physical impact is applied to separate the superabsorbent polymer and the pulp fiber that were not separated in the primary separation process from the plastic material, thereby recovering the plastic material.

2. The method according to claim 1, wherein, The oxidant aqueous solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide.

3. The method according to claim 1 or 2, further comprising: The crushing process involves breaking down the used nonwoven fabric products in the inactivation aqueous solution. The primary separation process includes the process of separating the superabsorbent polymer and the pulp fibers from the mixture of the used nonwoven fabric products that have been crushed in the crushing process.

4. The method according to claim 1 or 2, wherein, In the aforementioned separation process, The inactivation solution is an acidic aqueous solution. The pH of the acidic aqueous solution is maintained within a predetermined range, and the superabsorbent polymer and the pulp fiber are separated from the mixture.

5. The method according to claim 1 or 2, wherein, The physical impact is applied to the mixture by the collision of the rotating blades of an impeller that agitates the mixture in the air.

6. The method according to claim 1 or 2, wherein, The primary separation process is performed by one of two primary separation devices connected in parallel.

7. The method according to claim 1 or 2, wherein, The used nonwoven fabric articles, in addition to the used absorbent articles, also include at least one of medical gowns, medical caps, and masks made of nonwoven fabric.

8. The method according to claim 1 or 2, wherein, The plastic material recovered in the secondary separation process is for use in oil refining.

9. A plastic material derived from a used nonwoven fabric containing a used absorbent article, said plastic material being a plastic material recycled according to any one of claims 1 to 8, wherein, The plastic material contains less than 5% by mass of pulp fiber and superabsorbent polymer. The plastic material contains less than 10% ash by mass.

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