Method for recovering plastic materials from used nonwoven products, including used absorbent articles

Abstract

To provide a method for recovery of a plastic material from a used nonwoven fabric product, capable of suppressing impurities in recovered plastic material.SOLUTION: A method includes: a primary separation process S2 of, in an inert aqueous solution and from a blend of a plastic material obtained by decomposing a used nonwoven fabric product, a high water absorbing polymer and pulp fibers, separating the high water absorbing polymer and the pulp fibers; and a secondary separation process S3 of recovering the plastic material by adding physical impact to the blend in an air while spraying an oxidizer aqueous solution to separate the high water absorbing polymer and the pulp fibers that remained unseparated in the primary separation process from the plastic material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recovering plastic materials from post-consumer nonwoven products, including post-consumer absorbent articles. [Background technology]

[0002] There is known a technique for recovering plastic materials from used nonwoven fabric products including used absorbent articles. For example, Patent Document 1 (JP 2018-171589 A) discloses a method for recovering components from used absorbent articles. This method is a method for recovering the components, film and absorbent material, from used absorbent articles. This method includes a pretreatment step of swelling the used absorbent article with water, a decomposition step of applying a physical impact to the swollen used absorbent article to decompose the used absorbent article into at least a film and absorbent material, and a separation step of separating the decomposed film and absorbent material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-171589 A Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, in the separation process, plastic materials such as films and nonwoven fabrics and absorbent materials such as superabsorbent polymers and pulp fibers are separated from each other. However, it is difficult to completely separate the absorbent materials from the plastic materials, and it is unavoidable that some absorbent materials remain in the separated plastic materials, that is, the plastic materials contain some impurities. Therefore, the only applications for recycling such plastic materials are those that can tolerate some impurities, such as solid fuel.

[0005] This also applies when other nonwoven products, such as used medical gowns, medical caps and masks, are collected together with used absorbent articles and the plastic materials are recovered from those used nonwoven products.

[0006] The object of the present invention is to provide a method for recovering plastic materials from used nonwoven products, including used absorbent articles, which is capable of suppressing impurities in the recovered plastic material, and to provide a plastic material with suppressed impurities. [Means for solving the problem]

[0007] One aspect of the present invention is a method for recovering plastic materials from used nonwoven products including used absorbent articles, wherein the used nonwoven products contain a plastic material, and the used absorbent articles further contain a superabsorbent polymer and pulp fibers, the method comprising: a primary separation step in which the superabsorbent polymer and the pulp fibers are separated from a mixture of the plastic material, the superabsorbent polymer, and the pulp fibers obtained by decomposing the used nonwoven product in an inactivating aqueous solution, and a secondary separation step in which an oxidizing agent aqueous solution is sprayed on the mixture in air while applying a physical impact to separate the superabsorbent polymer and the pulp fibers that remained without being separated in the primary separation step from the plastic material, and the plastic material is recovered.

[0008] Another aspect of the present invention is a plastic material derived from used nonwoven products, including used absorbent articles, wherein the proportion of pulp fibers and superabsorbent polymer contained in the plastic material is 5% by mass or less, and the proportion of ash contained in the plastic material is less than 10% by mass. Effect of the Invention

[0009] According to the method of the present invention, it is possible to provide a method for recovering plastic materials from used nonwoven products, including used absorbent articles, which is capable of suppressing impurities in the recovered plastic material, and a plastic material with suppressed impurities. [Brief description of the drawings]

[0010] [Figure 1] 1 is a flowchart showing a method for recovering plastic materials from used nonwoven products, including used absorbent articles, according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present embodiment relates to the following aspects. [Aspect 1] A method for recovering plastic materials from used nonwoven products including used absorbent articles, wherein the used nonwoven products contain a plastic material, and the used absorbent articles further contain a superabsorbent polymer and pulp fibers, the method comprising: a primary separation step of separating the superabsorbent polymer and the pulp fibers from a mixture of the plastic material, the superabsorbent polymer, and the pulp fibers obtained by decomposing the used nonwoven product in an inactivating aqueous solution; and a secondary separation step of spraying an aqueous oxidizing agent solution on the mixture in air while applying physical impact to separate the superabsorbent polymer and the pulp fibers that remained in the primary separation step from the plastic material, and recovering the plastic material.

[0012] In this method, first, in a primary separation step, the superabsorbent polymer is inactivated and dehydrated with an inactivating aqueous solution to suppress swelling, and most of the superabsorbent polymer and pulp fibers are separated from a mixture of the plastic material, the superabsorbent polymer, and the pulp fibers. Then, in a secondary separation step, the mixture is sprayed with an oxidizing aqueous solution in air while being subjected to physical impact, and the remaining superabsorbent polymer and pulp fibers are separated from the plastic material, thereby recovering the plastic material. In this way, since the mixture is sprayed with the oxidizing agent solution in the secondary separation step, at least a part of the surface of the superabsorbent polymer remaining in the mixture can be decomposed. Therefore, the superabsorbent polymer attached to the plastic material and the pulp fibers attached via the superabsorbent polymer can be easily removed from the plastic material. At the same time, the mixture can be washed with the oxidizing agent solution to perform sterilization, disinfection, and deodorization. In addition, since the mixture is subjected to a physical impact not in water (solution) but in air, the physical impact can be directly applied to the plastic material, the superabsorbent polymer, and the pulp fibers. Therefore, the superabsorbent polymer and the pulp fibers attached to the plastic material can be easily removed from the plastic material. Therefore, due to the synergistic effect of these, the superabsorbent polymer and the pulp fibers can be easily separated from the mixture (plastic material), and impurities in the obtained plastic material can be suppressed. Therefore, it becomes possible to expand the applications of the reuse of the plastic material.

[0013] [Aspect 2] 2. The method of claim 1, wherein the aqueous oxidant solution is an aqueous solution comprising at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. In this method, the oxidizing agent aqueous solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. Therefore, the surface of the superabsorbent polymer remaining in the mixture can be more appropriately decomposed, making it easier to remove the superabsorbent polymer remaining in the mixture and the pulp fibers to which the superabsorbent polymer is attached from the plastic material. At the same time, the mixture can be more appropriately sterilized, disinfected, and deodorized.

[0014] [Aspect 3] The method according to claim 1 or 2, further comprising a crushing step of crushing the used nonwoven product in the inactivation aqueous solution, and the primary separation step includes a step of separating the superabsorbent polymer and the pulp fibers from the mixture in the used nonwoven product crushed in the crushing step. In this method, prior to the primary separation step, the used nonwoven fabric product in the inactivating aqueous solution is crushed to a predetermined size, thereby crushing the plastic material, the superabsorbent polymer, and the pulp fibers to a predetermined size. That is, the superabsorbent polymer is inactivated and dehydrated in the inactivating aqueous solution, suppressing swelling, while allowing the plastic material, the superabsorbent polymer, and the pulp fibers to be crushed to a size that is easy to separate in the primary separation step and the secondary separation step. Therefore, the superabsorbent polymer and the pulp fibers can be more easily separated from the mixture (plastic material).

[0015] [Aspect 4] A method according to any one of aspects 1 to 3, wherein in the primary separation step, the inactivation aqueous solution is an acidic aqueous solution, and the superabsorbent polymer and the pulp fibers are separated from the mixture while maintaining the pH of the acidic aqueous solution within a predetermined range. In this method, in the primary separation step, the inactivating aqueous solution is an acidic aqueous solution, and the superabsorbent polymer and pulp fibers are separated from the mixture while the pH of the acidic aqueous solution is maintained within a predetermined range. Therefore, in the primary separation step, the superabsorbent polymer is more reliably inactivated and dehydrated by the inactivating aqueous solution, and most of the superabsorbent polymer and pulp fibers can be separated from the mixture while suppressing swelling. This makes it possible to reduce the amount of superabsorbent polymer and pulp fibers to be separated in the secondary separation step, and to more easily separate the superabsorbent polymer and pulp fibers from the mixture (plastic material).

[0016] [Aspect 5] 5. The method of any one of the preceding claims, wherein the physical impact is applied to the mixture by impact of rotating blades on an impeller that agitates the mixture in air. In this method, a physical impact is applied to the mixture by the collision of rotating blades in an impeller that stirs the mixture in air. This makes it possible to apply a physical impact to the mixture more reliably in air. Therefore, the superabsorbent polymer remaining in the mixture and the pulp fibers to which the superabsorbent polymer is attached can be more easily removed from the plastic material.

[0017] [Aspect 6] 6. The method of any one of the preceding aspects, wherein the primary separation step is carried out in one of two primary separation devices connected in parallel. The primary separation device that performs the primary separation process is the first separation, and therefore is prone to situations such as clogging with the materials to be separated. Therefore, in this method, the primary separation process is performed in one of the two primary separation devices connected in parallel. As a result, for example, if one of the primary separation devices in operation requires maintenance, the one primary separation device can be stopped while the other primary separation device is operated, thereby allowing the method to be performed continuously without pausing. Therefore, plastic materials with fewer impurities can be efficiently recovered.

[0018] [Aspect 7] The method according to any one of aspects 1 to 6, wherein the used nonwoven fabric product includes, in addition to the used absorbent article, at least one of a medical gown, a medical cap, and a mask having a nonwoven fabric as a material. The present method can be applied to used nonwoven fabric products including at least one of medical gowns, medical caps, and masks, which contain nonwoven fabric as a material, in addition to used absorbent articles such as disposable diapers. In such cases, impurities in the obtained plastic material can be suppressed, and the applications of the reuse of plastic materials can be expanded.

[0019] [Aspect 8] 8. The method of any one of the preceding aspects, wherein the plastic material recovered in the secondary separation step is for oilification. In this method, the plastic material recovered in the secondary separation process can be used for oilification. In other words, since the plastic material obtained by this method is a plastic material with reduced impurities, it is possible to expand the use of the reuse to oilification (a technology in which used plastic materials are decomposed using heat or a catalyst to produce a liquid product).

[0020] [Aspect 9] A plastic material derived from used nonwoven fabric products, including used absorbent articles, wherein the proportion of pulp fiber and superabsorbent polymer contained in the plastic material is 5% by mass or less, and the proportion of ash contained in the plastic material is less than 10% by mass. Although this plastic material is derived from used nonwoven fabric products, including used absorbent articles, the proportion of pulp fiber and superabsorbent polymer is 5% by mass or less, and the proportion of ash is less than 10% by mass. In other words, since this plastic material is a plastic material with reduced impurities, it is possible to expand the uses of its reuse to various applications (e.g., oil production).

[0021] Hereinafter, a method for recovering plastic materials from used nonwoven fabric products including used absorbent articles according to an embodiment will be described. However, the used absorbent articles include absorbent articles that have been used by users and absorbent articles that have been unused but discarded. Examples of absorbent articles include disposable diapers, urine pads, sanitary napkins, bed sheets, and pet sheets. The used absorbent articles include absorbent articles that have absorbed and retained the excrement of users. In addition, the used nonwoven fabric products include nonwoven fabric products that have been used by users and nonwoven fabric products that have been unused but discarded. The nonwoven fabric products are products composed of multiple members including nonwoven fabric, and include at least a nonwoven fabric made of synthetic resin, that is, a plastic material. Examples of nonwoven fabric products include medical gowns, medical caps, masks, and wipes in addition to the above-mentioned absorbent articles. It should be noted that the nonwoven fabric products include at least 50% by mass or more of nonwoven fabric in the product.

[0022] First, a configuration example of an absorbent article will be described. The absorbent article includes a top sheet, a back sheet, and an absorbent disposed between the top sheet and the back sheet. An example of the size of the absorbent article is a length of about 15 to 100 cm and a width of 5 to 100 cm. The absorbent article may further include other members that are included in general absorbent articles, such as a diffusion sheet, a leak-proof wall, a side sheet, and an exterior sheet.

[0023] Examples of the constituent members of the surface sheet include liquid-permeable nonwoven fabric, synthetic resin film having liquid-permeable holes, composite sheets thereof, etc. Examples of the constituent members of the back sheet include liquid-impermeable nonwoven fabric, liquid-impermeable synthetic resin film, composite sheets thereof. Examples of the constituent members of the diffusion sheet include liquid-permeable nonwoven fabric. Examples of the constituent members of the leakage barrier and side sheet include water-repellent nonwoven fabric, and the leakage barrier may include an elastic material such as rubber. Examples of the constituent members of the exterior sheet include liquid-impermeable and breathable nonwoven fabric, liquid-impermeable and breathable synthetic resin film, composite sheets thereof. There are no particular limitations on the type of nonwoven fabric, and examples thereof include meltblown nonwoven fabric, spunbond nonwoven fabric, airlaid nonwoven fabric, and air-through nonwoven fabric. There are also no particular limitations on the type of synthetic resin film, and known film materials can be used. Here, the material of the nonwoven fabric or synthetic resin film is not particularly limited as long as it can be used for absorbent articles, and examples thereof 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). The material of these nonwoven fabrics and synthetic resin films is synthetic resin, and can be called a plastic material. In this embodiment, an absorbent article in which the constituent member of the back sheet is a film and the constituent member of the top sheet is a nonwoven fabric will be described as an example.

[0024] The constituent members of the absorbent body include absorbent body materials, that is, pulp fibers and superabsorbent polymers. Examples of pulp fibers include cellulosic fibers. Examples of cellulosic fibers include wood pulp, crosslinked pulp, non-wood pulp, regenerated cellulose, semi-synthetic cellulose, etc. The size of the pulp fibers includes an average value of the long diameter of the fibers of, for example, several tens of μm, preferably 20 to 40 μm, and an average value of the fiber length of, for example, several mm, preferably 2 to 5 mm. Examples of the superabsorbent polymer (SAP) include water-absorbing polymers of, for example, polyacrylates, polysulfonates, and maleic anhydrides. The size of the superabsorbent polymer (when dry) includes an average value of the particle diameter of, for example, several hundred μm, preferably 200 to 500 μm. The absorbent body may include a core wrap formed of a liquid-permeable sheet.

[0025] One side and the other side of the absorbent are respectively bonded to the top sheet and the back sheet via an adhesive. In plan view, the portion (peripheral portion) of the top sheet that extends outside the absorbent so as to surround the absorbent is bonded to the portion (peripheral portion) of the back sheet that extends outside the absorbent so as to surround the absorbent via an adhesive. Therefore, the absorbent is enclosed inside the bonded body of the top sheet and the back sheet. There is no particular limit to the adhesive, but examples of the adhesive include hot melt adhesives. Examples of hot melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives that are mainly made of rubber such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefins such as polyethylene.

[0026] Examples of the configurations of medical gowns, medical caps, masks, and wipes are as follows. The medical gown is not particularly limited as long as it contains a nonwoven fabric, and for example, it has a body part made of nonwoven fabric to cover the wearer's body, sleeve parts made of nonwoven fabric to cover both arms of the wearer, and a string part made of nonwoven fabric or the like to fix the body part to the wearer's body. The medical cap is not particularly limited as long as it contains a nonwoven fabric, and for example, it has a crown part made of nonwoven fabric to cover the wearer's head, and may further have a chin strap part made of nonwoven fabric or the like to fix the crown part to the head. The mask is not particularly limited as long as it contains a nonwoven fabric, and for example, it has a mask main body part made of nonwoven fabric to cover at least the nose and mouth of the wearer, and a pair of ear loops made of nonwoven fabric or the like to fix the mask main body part to the front of the wearer's face. The wipes are provided with a sheet made of a single layer or multiple layers of nonwoven fabric. The nonwoven fabrics (and synthetic resin films) used in these products can be any of the nonwoven fabrics (and synthetic resin films) described above.

[0027] Next, a method for recovering plastic materials from used nonwoven fabric products including used absorbent articles according to an embodiment will be specifically described. In this embodiment, an absorbent article (e.g., a disposable diaper) will be taken as an example of the nonwoven fabric product.

[0028] Fig. 1 is a flow chart showing a method for recovering plastic materials from used nonwoven fabric products including used absorbent articles according to an embodiment. This method includes a primary separation step S2 and a secondary separation step S3 as steps for recovering plastic materials from used nonwoven fabric products, and further includes a crushing step S1 and a dewatering / drying step S4 in this embodiment. Note that in this embodiment, the method further includes a dust removal step S5 to a pulp fiber separation step S8. Each step will be described below.

[0029] In this embodiment, used absorbent articles (nonwoven fabric products) are collected from outside for reuse (recycling). At that time, a plurality of used absorbent articles are sealed in a collection bag to prevent excrement, bacteria, and odor from leaking to the outside. Each used absorbent article in the collection bag is collected, for example, mainly in a rolled or folded state with the top sheet, through which excrement is excreted, facing inward so that excrement and bacteria are not exposed to the surface and odor is not diffused to the surroundings. Note that the used absorbent articles do not have to be sealed in a collection bag or rolled up.

[0030] The crushing step S1 is a step of crushing used absorbent articles (nonwoven fabric products) in an inactivating aqueous solution. In this embodiment, in the crushing step S1, a collection bag containing used absorbent articles is supplied to a solution tank that stores an acidic aqueous solution, which is an inactivating aqueous solution. The acidic aqueous solution containing the collection bag is sent from the solution tank to a biaxial crusher (e.g., a biaxial rotary crusher, a biaxial differential crusher, a biaxial shear crusher). The collection bag is crushed together with the collection bag by the biaxial crusher. As a result, the used absorbent articles in the collection bag are crushed together with the collection bag in the acidic aqueous solution to generate crushed material. The crushed material is sent to the primary separation step S2 alone or together with the acidic aqueous solution.

[0031] Here, in the crushing step S1, it is preferable that the used absorbent articles are crushed so that the size of the crushed pieces is approximately 25 to 150 mm. If the size is 25 mm or more, materials other than the pulp fibers and the superabsorbent polymer (e.g., film, nonwoven fabric, elastomer, etc.) are cut largely, making it easier to separate these materials from the pulp fibers and the superabsorbent polymer in the subsequent steps. If the size is 150 mm or less, the materials of the used absorbent articles are less likely to become entangled with each other. If the size exceeds 150 mm, the materials are more likely to become entangled with each other, and once entangled, they are more difficult to disaggregate.

[0032] When used absorbent articles are treated in an inactivating aqueous solution, the superabsorbent polymer contained or contained in the used absorbent articles is inactivated and dehydrated to become small particle size. Therefore, the superabsorbent polymer can be easily handled in the subsequent process, and the efficiency of the treatment is improved. The reason why an acidic aqueous solution, i.e., an aqueous solution of an inorganic acid and an organic acid is used as the inactivating aqueous solution is that, compared with an aqueous solution of lime or calcium chloride, no ash remains in the plastic material or pulp fiber, and the degree of inactivation (particle size and 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 1.0 or more, the equipment is less likely to corrode, and the amount of alkaline chemicals required for neutralization treatment during wastewater treatment can be reduced. If the pH is 4.0 or less, the superabsorbent polymer can be made sufficiently small, and the sterilization ability can be enhanced. Examples of organic acids include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, ascorbic acid, etc., and citric acid is preferable. The chelating effect of citric acid can trap and remove metal ions in excrement, and the cleaning effect of citric acid can be expected to achieve a high dirt component removal effect. On the other hand, examples of inorganic acids include sulfuric acid, hydrochloric acid, and nitric acid, but sulfuric acid is preferred from the viewpoints of not containing chlorine and cost. Since pH varies depending on water temperature, the pH in the present invention refers to the pH measured at an aqueous solution temperature of 20°C. The organic acid concentration of the organic acid 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 inorganic acid concentration of the inorganic acid 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, the organic acid citric acid is used as the inactivation aqueous solution.

[0033] The used absorbent articles fed into the biaxial crusher do not have to be in a collection bag. Also, a collection bag containing used absorbent articles or used absorbent articles not in a collection bag may be fed into the biaxial crusher without passing through a solution tank. Also, crushing in the biaxial crusher does not have to be performed in an inactivating aqueous solution, and may be performed in air, for example. In this case, the subsequent step, the primary separation step S2, is performed in an inactivating aqueous solution.

[0034] In addition, by increasing the temperature of the inactivating aqueous solution (temperature: 70 to 95°C), the adhesive (e.g., hot melt adhesive) used to bond the components of the used absorbent article can be softened and the bonding strength of the adhesive can be reduced. This allows the components to be easily dissociated from each other naturally or by a small impact. It also becomes possible to sterilize (disinfect) the used absorbent article.

[0035] In this way, in the crushing step S1, each component of the used absorbent article is crushed to approximately a predetermined size. Furthermore, when the adhesive strength between each component is reduced due to the heat generated during crushing and / or the heat of the inactivating aqueous solution, each component is easily separated from each other.

[0036] Next, the primary separation step S2 is a step of separating the superabsorbent polymer and the pulp fiber from the mixture of the plastic material, the superabsorbent polymer, and the pulp fiber obtained by decomposing the used absorbent article (nonwoven fabric product) in the inactivating aqueous solution. In this embodiment, in the primary separation step S2, the mixture of the crushed material generated in the crushing step S1 and the acidic aqueous solution, which is the inactivating aqueous solution, is supplied to a pulper separator (primary separation device). The pulper separator has an agitation separation tank that functions as a washing tank and a sieve tank. In the pulper separator, the mixture of the crushed material and the acidic aqueous solution is agitated and washed to remove dirt from the crushed material, while the pulp fiber, the superabsorbent polymer, the excrement, and the acidic aqueous solution are separated (removed) by a screen. That is, the pulp fiber, the superabsorbent polymer, the excrement, and the acidic aqueous solution pass through the screen to be separated from the mixture, and are sent out from the pulper separator. On the other hand, the remaining mixture, i.e., other materials (collection bags, films, nonwoven fabrics, etc.), cannot pass through the screen and remain in the pulper separator. The other materials are then sent to the secondary separation process S3 by a screw conveyor at a fixed amount per unit time. Note that some of the other materials may pass through the screen.

[0037] However, some of the pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution may remain in the mixture. In addition, other materials in the mixture, such as the collection bag, film, and nonwoven fabric, are made of synthetic resin and can be called plastic materials. Therefore, in the primary separation step S2, the plastic materials and a small amount of remaining materials (pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution) that are the mixture become the residue on the screen, and the pulp fibers, superabsorbent polymer, excrement, and acidic aqueous solution that are separated from the mixture become the pass-through materials that have passed through the screen.

[0038] In this embodiment, the primary separation step S2 is performed in one of two primary separation devices connected in parallel. For example, two pulper separators are connected in parallel, and one pulper separator is operated. When the pulper separator requires maintenance or the like, the pulper separator is stopped and the other pulper separator is operated. This allows the primary separation step S2 to be performed continuously. Note that three or more primary separation devices may be connected in parallel.

[0039] In this embodiment, in the primary separation step S2, the pH of the acidic aqueous solution is adjusted to be maintained within a predetermined range. The predetermined pH range is a range in which the pH fluctuates within ±1.0. As a result, the difference between the specific gravity and size of the superabsorbent polymer and the specific gravity and size of the pulp fiber can be within a predetermined range. In this case, the difference within the predetermined range is, for example, within a range of 0.2 to 5 times that of the other. As a result, the difference between the pulp fiber and the superabsorbent polymer is that the specific gravity is within a predetermined range and the size is within a predetermined range. As a result, the pulp fiber and the superabsorbent polymer can be easily separated from other materials (mainly plastic materials) of the used absorbent article other than the pulp fiber and the superabsorbent polymer by utilizing the difference in size and specific gravity. The pH can be adjusted using an acidic aqueous solution or an alkaline aqueous solution based on the pH value measured by the pH sensor. In the secondary separation step S3, the pH may also be adjusted in the same manner as in the primary separation step S2.

[0040] Furthermore, when an inactivating aqueous solution (acidic aqueous solution) is used in the disruption step S1, the pH of the acidic aqueous solution may be adjusted in the same manner as in the primary separation step S2.

[0041] Next, in the secondary separation process S3, an aqueous oxidizing agent solution is sprayed onto the mixture in the air while physical impact is applied to separate the remaining superabsorbent polymer and pulp fibers that were not separated in the primary separation process from the plastic material, thereby recovering the plastic material.

[0042] In this embodiment, in the secondary separation step S3, the mixture (residue: plastic material and remaining matter) from which the pulp fibers, superabsorbent polymer, etc. have been separated in the primary separation step S2 is supplied to a separation device. The separation device includes a cylindrical section installed sideways, a plurality of impellers provided in the cylindrical section, a plurality of oxidizing agent aqueous solution supply units provided on the upper outer peripheral surface of the cylindrical section, and a screen (sieve) provided on the lower outer peripheral surface of the cylindrical section. A mixture supply port is provided on one end of the cylindrical section, and a discharge port is provided on the other end. The plurality of impellers are arranged along the axial direction of the cylindrical section so that air flows from one end of the cylindrical section to the other end while rotating around the axis of the cylindrical section. The plurality of oxidizing agent aqueous solution supply units are aligned along the axial direction. The size of each opening of the screen (sieve) is large enough to allow the pulp fibers and superabsorbent polymer to pass through, but large enough to prevent the plastic material from passing through.

[0043] The mixture is stirred by the blades of the impeller rotating in the cylindrical section while the aqueous oxidant solution is sprayed from the aqueous oxidant solution supply section in the air inside the cylindrical section, and moves from one end side to the other end side of the cylindrical section while being subjected to physical impact by the collision of the blades of the impeller. Meanwhile, the mixture is washed (including sterilization and bleaching) to remove dirt by the aqueous oxidant solution sprayed while moving (flowing) in the air. At the same time, the pulp fibers and superabsorbent polymers in the mixture are removed from the plastic material in the mixture by physical impact and oxidative decomposition of the superabsorbent polymer by the oxidant, and pass through the screen at the bottom of the cylindrical section to be separated (removed) together with the aqueous oxidant solution. On the other hand, the plastic material in the mixture from which the pulp fibers and superabsorbent polymers have been removed is discharged from the outlet at the other end side of the cylindrical section without passing through the screen. That is, the superabsorbent polymers and pulp fibers that were not separated in the primary separation step S2 and remained are separated from the plastic material, and a plastic material with reduced impurities is generated and recovered. In addition, since the secondary separation step S3 is carried out in air, the dehydration of the plastic material progresses. Also, the separated oxidizing agent aqueous solution may be reused in the oxidizing agent treatment step S7 (described later).

[0044] Here, the oxidizing agent aqueous solution is an aqueous solution containing an oxidizing agent. The oxidizing agent contains at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. In this embodiment, ozone is used as the oxidizing agent from the viewpoint of oxidizing power, sterilizing power, and bleaching power. In this case, the oxidizing agent aqueous solution is preferably acidic. The reason is from the viewpoint of suppressing the deactivation of ozone and maintaining the inactivation of the superabsorbent polymer. Furthermore, when an acidic aqueous solution such as a citric acid aqueous solution is used as the inactivating aqueous solution in the crushing step S1 or the primary separation step S2, it is also from the viewpoint of the continuity of each step and the viewpoint of being able to reuse the aqueous solution without waste. Note that, when the application of the plastic material finally obtained by this method is an application in which residual chlorine is undesirable, sodium hypochlorite is not used as the oxidizing agent. In addition, when the oxidizing agent aqueous solution separated in the secondary separation step S3 is reused in the oxidizing agent treatment step S7 (described later), when the pulp fiber or the superabsorbent polymer is used for a sanitary material application, sodium hypochlorite is not used as the oxidizing agent in order to suppress residual chlorine in the pulp fiber.

[0045] The ozone concentration in the oxidizing aqueous solution is not particularly limited as long as it is a concentration that can realize the desired function, i.e., oxidizing power, sterilizing power, and bleaching power, but for example, 0.2 to 10 mass ppm can be mentioned, and 0.5 to 5 mass ppm is preferable. When the concentration is not too low, the desired function can be exhibited, and when the concentration is not too high, corrosion of the equipment can be suppressed. The treatment time with the oxidizing aqueous solution is not particularly limited as long as it can exhibit the desired function, but it is shorter when the ozone concentration in the oxidizing aqueous solution is high, and longer when the ozone concentration is low, and is typically 1 to 10 minutes. The product of the ozone concentration (ppm) in the oxidizing aqueous solution and the treatment time (minutes) of the treatment step (hereinafter also referred to as "CT value") is, for example, 0.5 to 10 ppm·min, and 1 to 5 ppm·min is preferable. When the CT value is not too small, the desired function can be exhibited, and when the CT value is not too large, corrosion of the equipment can be suppressed. As the oxidizing agent aqueous solution, the oxidizing agent aqueous solution used in the oxidizing agent treatment step S7 described below may be reused in this step with its concentration reduced.

[0046] Regarding sterilization or disinfection, for example, there are more than 1 billion / ml of general bacteria in used paper diapers, but it cannot be said that the acidic aqueous solution used in the primary separation step S2 can completely sterilize them. Therefore, a certain amount of general bacteria exists in the plastic material (with a small amount of pulp fiber or superabsorbent polymer attached) separated in the primary separation step S2 (for example, 3,400 general bacteria / ml). The same is true when the secondary separation step S3 is performed without using an oxidizing aqueous solution. In that case, there may be concerns about adverse effects on the safety of workers and the occurrence of decay and mold in the extracted plastic material. In addition, there is a strong excrement odor that is thought to be caused by general bacteria. However, by performing the secondary separation step S3 using an oxidizing aqueous solution, general bacteria in the plastic material can be removed below the detection limit, just like E. coli, and the excrement odor can be reduced to a level that is almost unnoticeable.

[0047] Next, a dehydration / drying step S4 may be performed. The dehydration / drying step S4 is a step of dehydrating and / or drying the separated plastic material. In this embodiment, a step of drying the plastic material is performed in a high-temperature atmosphere in a thermostatic chamber or with hot air or the like. The drying temperature may be, for example, 80 to 120°C. The drying time may vary depending on the drying temperature, but may be, for example, 10 to 120 minutes, and is preferably 15 to 100 minutes. This not only evaporates and removes the moisture remaining in the plastic material, but also sterilizes the plastic material. This makes it possible to achieve the effect of sterilization (disinfection) while removing the moisture.

[0048] In this way, in this method, since the superabsorbent polymer and pulp fiber are separated and removed from the plastic material mainly by the secondary separation step S3, it is possible to recover a plastic material with reduced impurities. Among the impurities contained in the plastic material, the ratio of pulp fiber and superabsorbent polymer is 5 mass% or less, preferably 3 mass% or less, and the ratio of ash is less than 10 mass%, preferably 5 mass% or less, more preferably 3 mass% or less. Furthermore, since sterilization is performed with an oxidizing agent, there are almost no bacteria. Such a low-impurity plastic material can be reused for a wide variety of purposes. One such use is, for example, oilification, a technology in which used plastic materials are decomposed using heat or a catalyst to produce a liquid product.

[0049] In this method, first, in the primary separation step S2, the superabsorbent polymer is inactivated and dehydrated with an inactivating aqueous solution (e.g., an acidic aqueous solution) to suppress swelling, and most of the superabsorbent polymer and pulp fibers are separated from a mixture of plastic material (film, nonwoven fabric, etc.), superabsorbent polymer, and pulp fibers. Then, in the secondary separation step S3, the mixture is sprayed with an oxidizing aqueous solution (e.g., an ozone aqueous solution) in the air while being subjected to physical impact, and the remaining superabsorbent polymer and pulp fibers are separated from the plastic material, thereby recovering the plastic material. In this way, since the mixture is sprayed with the oxidizing agent aqueous solution in the secondary separation step S3, at least a part of the surface of the superabsorbent polymer remaining in the mixture can be oxidatively decomposed and solubilized. Therefore, the superabsorbent polymer attached to the plastic material and the pulp fibers attached via the superabsorbent polymer can be easily removed from the plastic material. At the same time, the mixture can be washed with the oxidizing agent aqueous solution to perform sterilization, disinfection, and deodorization. In addition, since the mixture is subjected to a physical impact not in water (solution) but in air, the physical impact can be directly applied to the plastic material, the superabsorbent polymer, and the pulp fibers. Therefore, the superabsorbent polymer and the pulp fibers attached to the plastic material can be easily removed from the plastic material. Therefore, due to the synergistic effect of these, the superabsorbent polymer and the pulp fibers can be easily separated from the mixture (plastic material), and impurities in the obtained plastic material can be suppressed. Therefore, it becomes possible to expand the applications of the reuse of the plastic material.

[0050] In a preferred embodiment of the method, the aqueous oxidizing agent solution is an aqueous solution containing at least one of ozone, chlorine dioxide, peracetic acid, sodium hypochlorite, and hydrogen peroxide. This allows the surface of the superabsorbent polymer remaining in the mixture to be more appropriately decomposed, making it easier to remove the superabsorbent polymer remaining in the mixture and the pulp fibers to which the superabsorbent polymer is attached from the plastic material. At the same time, the mixture can be more appropriately sterilized, disinfected, and deodorized. In particular, ozone is preferred because of its high effects.

[0051] In a preferred embodiment of the present method, the used nonwoven fabric product in the inactivating aqueous solution is crushed to a predetermined size prior to the primary separation step S2, thereby crushing the plastic material, the superabsorbent polymer, and the pulp fibers to a predetermined size (crushing step S1). That is, the superabsorbent polymer is inactivated and dehydrated in the inactivating aqueous solution, suppressing swelling, while allowing the plastic material, the superabsorbent polymer, and the pulp fibers to be made to a size that is easy to separate in the primary separation step and the secondary separation step. Therefore, the superabsorbent polymer and the pulp fibers can be more easily separated from the mixture (plastic material).

[0052] In a preferred embodiment of this method, in the primary separation step S2, the inactivating aqueous solution is an acidic aqueous solution, and the superabsorbent polymer and pulp fibers are separated from the mixture while the pH of the acidic aqueous solution is maintained within a predetermined range. Therefore, in the primary separation step, the superabsorbent polymer is more reliably inactivated and dehydrated with the inactivating aqueous solution, and most of the superabsorbent polymer and pulp fibers can be separated from the mixture while suppressing swelling. This makes it possible to reduce the amount of superabsorbent polymer and pulp fibers to be separated in the secondary separation step, and to more easily separate the superabsorbent polymer and pulp fibers from the mixture (plastic material).

[0053] In the present method, in a preferred embodiment, the physical impact is applied to the mixture by the collision of rotating blades of an impeller that stirs the mixture in air. This makes it possible to more reliably apply physical impact to the mixture in air. Therefore, it is possible to more easily remove the superabsorbent polymer remaining in the mixture and the pulp fibers to which the superabsorbent polymer is attached from the plastic material.

[0054] Since the primary separation device performing the primary separation step S2 is the first separation, it is easy for situations such as clogging with the materials to be separated to occur. Therefore, in a preferred embodiment of the present method, the primary separation step S2 is performed in one of two primary separation devices connected in parallel. As a result, for example, when one of the primary separation devices in operation requires maintenance, the one primary separation device can be stopped while the other primary separation device is operated, thereby making it possible to continuously perform the present method without pausing the operation. Therefore, plastic materials with fewer impurities can be efficiently recovered.

[0055] In a preferred embodiment, the method can be applied to used nonwoven fabric products including at least one of medical gowns, medical caps, and masks, which contain nonwoven fabric as a material, in addition to used absorbent articles such as disposable diapers. In this case, too, impurities in the resulting plastic material can be suppressed, and the applications for recycling plastic materials can be expanded.

[0056] In a preferred embodiment of the present method, the plastic material recovered in the secondary separation step S3 can be used for oilification. In other words, since the plastic material obtained by the present method is a plastic material with reduced impurities, it is possible to expand the use of the reuse of the plastic material to oilification (a technology for decomposing used plastic materials using heat or a catalyst to produce a liquid product).

[0057] Although this plastic material is derived from used nonwoven fabric products, including used absorbent articles, the proportion of pulp fiber and superabsorbent polymer contained in the plastic material is 5% by mass or less, and the proportion of ash contained in the plastic material is less than 10% by mass. In other words, since this plastic material is a plastic material with reduced impurities, its reuse applications can be expanded to various applications (e.g., oil production).

[0058] In addition, in this embodiment, as shown in FIG. 1, the method further includes a dust removal step S5, a SAP separation step S6, an oxidizing agent treatment step S7, and a pulp fiber separation step S8, which are steps for separately recovering pulp fibers and superabsorbent polymer (SAP) from used nonwoven fabric products.

[0059] In this embodiment, the mixture containing the pulp fibers, the superabsorbent polymer, the excrement, and the acidic aqueous solution separated in the primary separation step S2 is treated in the dust removal step S5. The pulp fibers and the superabsorbent polymer separated in the secondary separation step S3 may also be mixed with the mixture and treated in the dust removal step S5.

[0060] In the dust removal step S5, at least one separator (e.g., a screen separator or a cyclone separator) is used to separate foreign matter such as other materials (collection bags, films, nonwoven fabrics, elastic bodies, etc.) from the mixed liquid supplied from the primary separation step S2 (and the secondary separation step S3). In this embodiment, in the dust removal step S5, a screen separator (with a relatively large mesh size), a screen separator (with a relatively small mesh size), and a cyclone separator are arranged in this order, and foreign matter is successively separated from the mixed liquid. As a result, pulp fibers and superabsorbent polymers containing less foreign matter are obtained. The mixed liquid of the pulp fibers and superabsorbent polymers containing less foreign matter and the acidic aqueous solution (containing excrement) is supplied to the SAP separation step S6.

[0061] In the SAP separation step S6, at least one separator (e.g., drum screen separator) is used to separate the superabsorbent polymer from the mixed liquid (containing pulp fibers and superabsorbent polymer with little foreign matter) supplied from the dust removal step S5. In this embodiment, in the SAP separation step S6, the drum screen separator separates the superabsorbent polymer and the acidic aqueous solution (containing excrement) from the mixed liquid. This results in the superabsorbent polymer and the acidic aqueous solution with little foreign matter. The superabsorbent polymer is separated from the acidic aqueous solution (liquid) by another separator (e.g., inclined screen separator) and taken out. Meanwhile, the pulp fibers with little foreign matter (but containing a small amount of superabsorbent polymer) are supplied to the oxidizing agent treatment step S7.

[0062] In the oxidizing agent treatment step S7, the aqueous oxidizing agent solution is used to oxidize and decompose the superabsorbent polymer in the pulp fibers containing little foreign matter (but containing a small amount of superabsorbent polymer) supplied from the SAP separation step S6, solubilizing and removing it from the pulp fibers. In this embodiment, in the oxidizing agent treatment step S7, the pulp fibers are fed into a treatment tank that stores an aqueous oxidizing agent solution containing ozone as an oxidizing agent, and the superabsorbent polymer in the pulp fibers is oxidized and decomposed to be solubilized, resulting in pulp fibers with extremely few impurities. The pulp fibers with few impurities (including superabsorbent polymer) are supplied to the pulp fiber separation step S8 together with the aqueous oxidizing agent solution.

[0063] The type of oxidizing agent in the oxidizing agent treatment step S7 is the same as that in the secondary separation step S3. In this embodiment, ozone is used as the oxidizing agent from the viewpoint of oxidizing power, sterilizing power, and bleaching power. The ozone concentration in the oxidizing agent aqueous solution is not particularly limited as long as it is a concentration that can decompose the superabsorbent polymer, and can be, for example, 10 to 50 mass ppm. If the concentration is not too low, the superabsorbent polymer can be completely solubilized, and if the concentration is not too high, the pulp fibers are not damaged. The treatment time with the oxidizing agent aqueous solution is not particularly limited as long as it is a time that can decompose the superabsorbent polymer, but is shorter if the ozone concentration in the oxidizing agent aqueous solution is high, and is longer if the ozone concentration is low, and is typically 5 to 120 minutes. The product of the ozone concentration (ppm) in the oxidizing agent aqueous solution and the treatment time (minutes) of the treatment step (hereinafter also referred to as the "CT value") is preferably 100 to 6000 ppm·min. If the CT value is too small, the superabsorbent polymer may not be completely solubilized and may remain in the pulp fibers, whereas if the CT value is too large, the pulp fibers may be damaged.

[0064] In the pulp fiber separation step S8, a separator (e.g., a screen separator) is used to separate the pulp fibers from the pulp fibers and the aqueous oxidizing agent solution supplied from the oxidizing agent treatment step S7. The pulp fibers thus separated and collected become so-called recycled pulp fibers. The recycled pulp fibers are washed with wash water and taken out. EXAMPLES

[0065] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0066] (1) Sample Using unused used disposable diapers as the raw material, plastic materials were recovered after the primary separation step S2 and after the secondary separation step S3 by carrying out the method shown in Fig. 1. However, the ozone concentration and treatment time (CT value) in the secondary separation step S3 were set to 1 ppm × 2 min (2 ppm min).

[0067] (2) Evaluation method For each of the primary separation process S2 and the secondary separation process S3 (including the case where ozone is not used), the amount of residual pulp fiber (mass %) remaining on the plastic, the amount of residual superabsorbent polymer (mass %) remaining on the plastic, and the amount of residual ash (mass %) were evaluated. However, the calculation methods for each are as follows: (a) Residual amount of pulp fiber (mass%), residual amount of superabsorbent polymer (mass%) <Method for measuring residual amount after primary separation process> In the primary separation process, the plastic material after separation of the pulp fiber and the superabsorbent polymer is dried (120°C x 60 minutes) and weighed at about 1 kg (measured value A) to obtain sample α1. Next, the sample α1 is adjusted to an aqueous solution with a solid concentration of 1%, and ozone gas is blown in while stirring to perform ozone treatment. However, the ozone concentration in the aqueous solution and the treatment time are 50 ppm x 30 minutes (CT value 1500) (the superabsorbent polymer is decomposed, solubilized, and removed). Next, the sample α2 obtained by solid-liquid separation of the ozone aqueous solution is dried (120°C x 60 minutes) and weighed (measured value A'). As a result, |A'-A| is the residual mass D of the remaining superabsorbent polymer. Meanwhile, the sample α2 is immersed in toluene to dissolve the adhesive (HMA) and separate it into pulp fiber and plastic material. Next, the pulp fiber is air-dried in a draft (60 minutes), and the result of weighing it is the residual mass C of the pulp fiber. The mass B of the plastic material itself is calculated using ADC. therefore, Plastic material (mass%) = B / A x 100 Pulp fiber (mass%) = C / A x 100 Superabsorbent polymer (mass%) = D / A × 100; <Method for measuring residual amount after secondary separation process> The residual amount after the secondary separation step is measured in the same manner as the residual amount after the primary separation step. (b) Residual ash content (mass%) Ash content refers to the amount of inorganic or non-combustible residue remaining after organic matter has been incinerated, and the amount of remaining ash (mass%), i.e., the ash content ratio, refers to the ratio (mass ratio) of ash contained in the sample to be measured. The ash content ratio is measured according to "5. Ash content test method" in "2. General test methods" of the Sanitary Treatment Product Material Standards. Specifically, the ash content ratio is measured as follows. (i) A platinum, quartz or porcelain crucible (with lid) is heated vigorously at 500 to 550°C for 1 hour, allowed to cool, and then its mass is accurately measured. (ii) Take 2 to 4 g of plastic material that has been dried at 120°C for 60 minutes, place it in a crucible, and accurately measure its mass. (iii) Remove the lid of the crucible or move it aside if necessary, and heat it gently at first, then gradually increase the temperature and ignite it at 500-550°C for at least 4 hours until no charcoal remains, and ash it. (iv) After cooling, accurately weigh the mass of the crucible. The residue is again incinerated until it reaches a constant weight, and after cooling, accurately weigh the mass of the crucible. The ash content (mass%) is calculated based on the measurements in (1), (2), and (4).

[0068] (3) Evaluation results Among the plastic materials separated after the primary separation step S2, the proportion (residual amount) of pulp fiber was about 25% by mass, the proportion (residual amount) of superabsorbent polymer was about 10% by mass, and the proportion (residual amount) of ash was 12.3% by mass, and the proportion (residual amount) was more than 10% by mass. Among the plastic materials separated after the secondary separation step S3, the pulp fiber content was about 3% by mass, the superabsorbent polymer content was about 1% by mass, and the ash content was about 7% by mass, and the ash content was about 10% by mass. Therefore, by adding the secondary separation step S3, the pulp fibers, superabsorbent polymer and ash, i.e., impurities, contained in the plastic material could be significantly reduced.

[0069] The absorbent article of the present invention is not limited to the above-described embodiments, and appropriate combinations and modifications can be made without departing from the scope and spirit of the present invention.

Description of Symbols

[0070] S2 Primary Separation Process S3 Secondary Separation Process

Claims

1. 1. A method for recovering plastic materials from a used nonwoven product, including a used absorbent article, wherein the used nonwoven product comprises a plastic material, and the used absorbent article further comprises a superabsorbent polymer and pulp fibers; a primary separation step of separating the superabsorbent polymer and the pulp fibers from a mixture of the plastic material, the superabsorbent polymer, and the pulp fibers obtained by decomposing the used nonwoven fabric product in an inactivating aqueous solution; a secondary separation step in which an aqueous oxidizing agent solution is sprayed on the mixture obtained after the separation of the superabsorbent polymer and the pulp fibers in the primary separation step in air while a physical impact is applied to the mixture, thereby separating the superabsorbent polymer and the pulp fibers that were not separated in the primary separation step from the plastic material, and recovering the plastic material; Equipped with method.

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

3. The method further includes a crushing step of crushing the used nonwoven fabric products in the inactivating aqueous solution, The primary separation step includes a step of separating the superabsorbent polymer and the pulp fibers from the mixture in the used nonwoven fabric product crushed in the crushing step. The method according to claim 1 or 2.

4. In the primary separation step, The inactivation aqueous solution is an acidic aqueous solution, The superabsorbent polymer and the pulp fibers are separated from the mixture while the pH of the acidic aqueous solution is maintained within a predetermined range.

4. The method according to claim 1 .

5. The physical impact is applied to the mixture by the impact of rotating blades on an impeller that agitates the mixture in air.

5. The method according to any one of claims 1 to 4.

6. The primary separation step is carried out in one of two primary separation devices connected in parallel; 6. The method according to any one of claims 1 to 5.

7. The used nonwoven fabric product includes at least one of a medical gown, a medical cap, and a mask, which have a nonwoven fabric as a material, in addition to the used absorbent article.

7. The method according to any one of claims 1 to 6.

8. The plastic material recovered in the secondary separation step is for use in oilification.

8. The method according to any one of claims 1 to 7.

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