Separation method and method for producing recycled materials from used absorbent articles

Abstract

This invention provides a separation method that enables the separation of pulp fibers from superabsorbent polymers without significantly impairing the water absorption capacity of the superabsorbent polymers. [Solution] A separation method for separating a mixture containing pulp fibers and a superabsorbent resin that constitutes a used absorbent article into a residual component containing aggregates of pulp fibers and a passing component containing the superabsorbent resin, wherein the mixture provided to the separation member is in a state in which the superabsorbent resin has swollen and the pulp fibers have formed aggregates.

Description

Technical Field

[0001] The present invention relates to a method for separating pulp fibers and a superabsorbent polymer. The present invention also relates to a method for producing a recycled member such as a superabsorbent polymer from a used absorbent article.

Background Art

[0002] The usage amount and disposal amount of absorbent articles such as disposable diapers are increasing year by year with the aging of society. Although used absorbent articles contain moisture, most of them are incinerated. On the other hand, recycling of used absorbent articles has started in small amounts (for example, Patent Documents 1 to 4).

[0003] When recycling used absorbent articles, it is common to go through a process of stirring the absorbent articles in water to remove dirt, separating and washing the constituent materials of the absorbent articles, and recovering reusable materials. Among the pulp fibers, superabsorbent polymers, and plastics that make up absorbent articles, plastics can be separated using various separation devices. Regarding the separation of pulp fibers and superabsorbent polymers, separation from pulp fibers has been achieved by deactivating or reducing the water absorbency of the superabsorbent polymer using chemicals (sometimes called inactivation). Chemicals for deactivating or reducing the water absorbency of superabsorbent polymers include polyvalent metal salts, inorganic acids, organic acids, etc. Specifically, calcium chloride, calcium acetate, magnesium chloride, magnesium sulfate, aluminum sulfate, lime, sulfuric acid, nitric acid, hydrochloric acid, acetic acid, succinic acid, maleic acid, fumaric acid, citric acid, etc. have been used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] However, the method of using chemicals to inactivate the water absorption properties of superabsorbent polymers and separating them from pulp fibers incurs costs due to the use of chemicals, and requires the use of new chemicals to restore the water absorption performance of the superabsorbent polymer. Therefore, material recycling of superabsorbent polymers is difficult, and in reality, their use is limited to solid fuels and the like.

[0006] Under these circumstances, the objective is to provide a separation method that enables the separation of pulp fibers from superabsorbent polymers without significantly impairing the water absorption properties of the superabsorbent polymers. Furthermore, the objective is to provide a method for manufacturing recycled materials from used articles using the aforementioned separation method. [Means for solving the problem]

[0007] The inventors of this invention have conducted extensive research to solve the aforementioned problems and have found that the following invention is suitable for the aforementioned purpose, leading to the present invention. That is, the present invention relates to the following invention.

[0008] <1> A separation method comprising passing a mixture containing pulp fibers and a superabsorbent polymer through a separating member having an opening, thereby separating a residual component containing aggregates of pulp fibers from a passing component containing the superabsorbent polymer, wherein the mixture subjected to the separating member is in a state in which the superabsorbent polymer has swollen and the pulp fibers have formed aggregates. <2> In the above mixture, the amount of liquid containing water is 30 to 1000 parts by mass per 1 part by mass of the superabsorbent resin in a dry state. <1> The separation method described above. <3> When passing the mixture through the separating member, pressure or centrifugal force is applied. <1> or <2> The separation method described above.

[0009] <4> A method for producing a recycled material from a used absorbent article composed of components including pulp fibers, superabsorbent polymers, and plastics, comprising: preparing a mixture containing the pulp fibers and the superabsorbent polymers; and passing the mixture through a separating member having an opening to separate it into a residual component containing aggregates of pulp fibers and a passing component containing the superabsorbent polymers, wherein the mixture provided to the separating member is in a state in which the superabsorbent polymers have swollen and the pulp fibers have formed aggregates. <5> The superabsorbent resin swells and the pulp fibers are dispersed in the liquid. The liquid is then allowed to stand, allowing the superabsorbent resin and pulp fibers to settle. After the supernatant liquid is removed, the mixture is prepared. <4> Methods used. <6> The recycled member is a superabsorbent resin, and the method includes obtaining a superabsorbent resin without deactivating it. <4> or <5> Methods used. [Effects of the Invention]

[0010] The present invention provides a separation method that enables the separation of pulp fibers from superabsorbent polymer without significantly impairing the water absorption properties of the superabsorbent polymer. Furthermore, the invention provides a method for manufacturing recycled materials from used articles using the separation method. [Brief explanation of the drawing]

[0011] [Figure 1] This is a conceptual diagram of the separation method of the present invention. [Figure 2] This is a flowchart showing an example of the manufacturing method of the present invention. [Figure 3] This is a schematic diagram of the separation apparatus used in Example 1. [Figure 4] This is a schematic diagram of the separation apparatus used in Example 3. [Figure 5]This is a schematic diagram of the roller used to apply pressure in Example 3. [Figure 6] This is a schematic diagram of the pressurizing member with a handle used to apply pressure in Example 3. (a) is a plan view, and (b) is a left side view. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is just one example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following unless its gist is changed. In this specification, when the expression "~" is used, it is used to mean an expression that includes the numerical value or physical property value before and after it.

[0013] <Separation method> The present invention relates to a separation method (hereinafter sometimes referred to as "the separation method of the present invention") which separates a mixture containing pulp fibers and a superabsorbent polymer into a residual component containing aggregates of pulp fibers and a passing component containing the superabsorbent polymer by passing the mixture containing pulp fibers and passing it through a separation member having an opening, wherein the mixture provided to the separation member is in a state in which the superabsorbent polymer has swollen and the pulp fibers have formed aggregates.

[0014] The inventors have found that by optimizing the amount of water in a mixture containing pulp fibers, a superabsorbent resin, and water, the superabsorbent resin can be swollen in the mixture, and the pulp fibers can spontaneously aggregate into an aggregate state. Furthermore, the swollen superabsorbent resin and the aggregate of pulp fibers can be separated by a separating member. FIG. 1 is a conceptual diagram of the separation method of the present invention. As shown in (a) of FIG. 1, the pulp fibers 1 are in a dispersed state in a large amount of water, and the dispersion behaves like a liquid. On the other hand, as shown in (b) of FIG. 1, when the amount of water is optimized, the superabsorbent resin 2 is in a swollen state, and the pulp fibers 1 are in an aggregate state (pulp fiber aggregate 3). As shown in (c) of FIG. 1, the superabsorbent resin 2 in a swollen state can be freely deformed and behaves as a so-called liquid state, so it can easily pass through a separating member 4 such as a mesh-like object when receiving an external force. On the contrary, since the pulp fiber aggregate 3 behaves as a solid state, it is difficult to pass through a separating member 4 such as a mesh-like object even when receiving an external force. In the separation method of the present invention, by utilizing the difference in properties between the superabsorbent resin 2 in a swollen state and the pulp fiber aggregate 3 in this way, the superabsorbent resin 2 and the pulp fiber aggregate 3 can be separated without using chemicals. By recovering these respectively, recycled superabsorbent resin and recycled pulp fibers can be obtained as recycled members.

[0015] According to the separation method of the present invention, it is possible to separate pulp fibers and a superabsorbent resin from a mixture of pulp fibers and a superabsorbent resin without using chemicals or the like. Therefore, it is possible to significantly reduce the cost required for separation and the labor required for managing chemicals. Furthermore, since the water absorption of the superabsorbent resin is maintained to a certain extent, material recycling as a superabsorbent resin is possible.

[0016] (mixture) The mixture provided to the separating member contains at least water, a superabsorbent resin, and pulp fibers and is in a gel state. Also, in the mixture provided to the separating member, the superabsorbent resin is swollen and the pulp fibers are in a state of forming an aggregate.

[0017] Examples of such mixtures include materials containing pulp fibers and superabsorbent polymer obtained from used absorbent articles, with the amount of water adjusted, as will be described later. Conventional separation methods for separating pulp fibers and superabsorbent polymer constituting used absorbent articles typically separate the pulp fibers and superabsorbent polymer by floating the dispersed pulp fibers in water while allowing the inactivated and shrunk superabsorbent polymer to settle. On the other hand, the separation method of the present invention involves aggregating the pulp fibers without inactivating the superabsorbent polymer, and then feeding a mixture containing the swollen aggregate of superabsorbent polymer and pulp fibers to a separation member.

[0018] The mixture may contain components other than pulp fibers and superabsorbent polymers. When preparing the mixture from used absorbent articles, it may contain plastics that make up the used absorbent articles, or the plastics may be removed beforehand to make the mixture plastic-free.

[0019] The "water-containing liquid" used to swell the superabsorbent polymer refers to water or a liquid primarily composed of water. Typically, the water content in the water-containing liquid is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. In addition to tap water, well water, groundwater, industrial water, treated wastewater, water obtained from rivers, lakes, or ponds, rainwater, etc., can be used as the water-containing liquid. Furthermore, water that is recycled within the facility may also be used. For example, treated water treated by the company's own wastewater treatment or directly recycled water that is reused in a cascading manner from water used in other processes such as subsequent processes can be used. This reduces the amount of new water used, thereby reducing environmental impact and costs. High-purity purified water can also be used, but care must be taken as this may lead to increased costs. In addition, inorganic salts, organic substances, metal ions, acids, etc., may be included in the water-containing liquid to the extent that it does not hinder the implementation of the present invention. For example, using an aqueous sodium chloride solution such as seawater or its diluted solution can reduce the amount of water required for swelling because it lowers the water absorption performance of the superabsorbent polymer. However, caution is necessary because if the solution contains more than a certain amount of polyvalent metal ions or acid, it may lead to a decrease in the water absorption performance of the superabsorbent polymer. Specifically, it is preferable to use a liquid containing water in which the concentration of polyvalent metal ions is 2000 mg / L or less. It is also preferable to use a liquid in which the hydrogen ion concentration due to the acid is 0.001 mol / L or less.

[0020] For example, a mixture can be prepared by mixing and stirring used absorbent articles with a liquid such as water, rupturing the used absorbent articles, removing plastics as appropriate, and then adjusting the amount of water. The water added when rupturing the used absorbent articles can be used to swell the superabsorbent polymer.

[0021] During the pretreatment stage, such as when rupturing used absorbent articles, a liquid containing a large amount of water exceeding the water absorption capacity of the superabsorbent polymer is usually used. In such cases, in order to obtain a gel-like mixture containing aggregates of swollen superabsorbent polymer and pulp fibers, it is necessary to reduce the liquid volume by decantation or the like after rupture and aggregate the pulp fibers. In the mixture, it is preferable that the amount of liquid containing water be about four times or less the maximum water absorption capacity of the superabsorbent polymer.

[0022] Specifically, the amount of liquid containing water is preferably 30 to 1000 parts by mass per 1 part by mass of the superabsorbent resin in its dry state. If the amount is greater than 1000 parts by mass, it greatly exceeds the water absorption capacity of the superabsorbent resin, and because there is a large amount of excess water, some of the pulp fibers tend to disperse in the water as individual fibers, making it easier for pulp fibers to be mixed into the components that pass through the separation member. If the amount is less than 30 parts by mass, the superabsorbent resin does not swell sufficiently, making it difficult for the superabsorbent resin to deform, and thus making it difficult for it to pass through the separation member. The amount of liquid containing water may also be 50 to 900 parts by mass, 60 to 800 parts by mass, 70 to 700 parts by mass, 80 to 600 parts by mass, 90 to 500 parts by mass, 100 to 400 parts by mass, etc., per 1 part by mass of the superabsorbent resin in its dry state.

[0023] (Separation member) In the separation method of the present invention, a mixture in which the superabsorbent polymer has swollen and the pulp fibers have formed aggregates is separated by passing it through a separation member. The separation member is a member having an opening of a size that allows the superabsorbent polymer to deform and pass through. The shape of the opening is not particularly limited, and squares, other polygons (triangles, pentagons, hexagons, etc.), circles, ovals, etc. can be used. Furthermore, the shapes of the multiple openings may be uniform or non-uniform.

[0024] The size of the opening is not particularly limited as long as it allows the swollen superabsorbent polymer to pass through selectively. The size of the opening can be selected as the length of the longest side if the opening is rectangular, the diameter if it is circular, the major axis if it is elliptical, or the length of the longest side of the smallest circumscribing quadrilateral if it is polygonal, and is usually around 0.5 mm to 10 mm. The size of the opening may also be 0.8 mm or more, 1 mm or more, 9 mm or less, 8 mm or less, 7 mm or less, 6 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2 mm or less, 1.5 mm or less, etc., and may be appropriately selected depending on how the external force is applied during separation.

[0025] The material of the separating member is not particularly limited, as long as it has sufficient strength and durability to carry out the present invention. Examples of metals include stainless steel, brass, iron, iron with improved corrosion resistance through plating, copper, titanium, aluminum, etc., but the invention is not limited to these. Examples of polymer materials include polyester, nylon, acrylic, aramid, carbon fiber, polyethylene, polypropylene, etc., but the invention is not limited to these.

[0026] Furthermore, while the separating member may consist of a single layer, it may also be made of multiple layers of materials, either identical or different, or of multiple layers of materials with identical or different opening sizes.

[0027] As the separating member, mesh-like materials such as wire mesh or mesh belts, or perforated materials such as punching plates can be used. When using mesh-like materials, plain weave is common, but it is not limited to this. Other weaves such as twill weave or satin weave, or even weaves where the warp and weft threads are not intertwined, such as knitted fabrics, can be preferably used as long as they have the effect of separating the pulp fibers from the swollen superabsorbent polymer. In other words, the separating member having an opening is a member having a mesh structure or a porous structure, and it is preferable that it is a roll-shaped or flat plate-shaped member including a mesh structure or a porous structure.

[0028] (separation) In the separation method of the present invention, an external force is applied to a mixture containing an aggregate of pulp fibers and a swollen superabsorbent polymer, thereby selectively allowing the swollen superabsorbent polymer to pass through, separating the mixture into a residual component containing the aggregate of pulp fibers and a passing component containing the superabsorbent polymer and a liquid component. As the external force, centrifugal force or pressure can be used, and in the separation method of the present invention, it is preferable to apply pressure or centrifugal force when passing the mixture through the separation member.

[0029] An example of a separation method utilizing centrifugal force is a device equipped with a cylindrical rotating tank (for example, a cage-like structure with a mesh-like material formed on its sides) with openings on its sides, into which a mixture is placed and rotated to generate centrifugal force and separate the components. As a result, components containing aggregates of pulp fibers remain inside the rotating tank, while components containing superabsorbent polymers and liquids are discharged to the outside of the rotating tank.

[0030] An example of a separation method utilizing pressure is a method in which pressure is generated by pressing a pressurizing member, such as a roller or a flat plate, against a separation member, thereby separating the materials. Furthermore, by combining a long, roll-shaped separation member with a pressurizing member such as a roller, the separation method of the present invention can be carried out continuously.

[0031] Furthermore, a method can be used in which negative pressure (suction force) is applied when the superabsorbent polymer passes through the opening of the separating member. The method of generating pressure is not particularly limited and may be any of the following methods: mechanical pressurization, pneumatic pressurization, or depressurization by suction force. These methods may be used simultaneously or in stages. Furthermore, pressure (positive or negative) and centrifugal force may be used simultaneously or in stages.

[0032] There are no particular restrictions on the surface material of pressurizing members such as rollers and flat plates. Materials such as stainless steel and other metals, polyethylene, polypropylene, polyethylene terephthalate, nylon, polyacetal, polycarbonate, and polyvinyl chloride, foams such as polyurethane foam and expanded styrene, rubbers such as natural rubber, synthetic rubber, and silicone rubber, polypropylene nonwoven fabrics, polyethylene terephthalate nonwoven fabrics, felts, etc., can be used.

[0033] The surface shape of pressurizing members such as rollers and flat plates is not particularly limited as long as it can allow the swollen superabsorbent resin to pass through. Smooth surfaces, surfaces with irregularities, or surfaces with voids such as nonwoven fabrics can be used.

[0034] (Residual component) The residual components are those that remain on the surface of the separating member and include aggregates of pulp fibers. The proportion of superabsorbent polymer in the residual components is usually 10% by mass or less, preferably 8% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0035] If plastics have been removed from used absorbent articles before preparing a gel-like mixture, the remaining components consist mainly of aggregates of pulp fibers, and the proportion of pulp fibers in the remaining components is usually 90% by mass or more, preferably 92% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0036] Residual components and components adhering to the surface of pressurizing components such as rollers can be removed by scraping with a flat-ended tool such as a scraper, or by detaching them through shaking, impact, or by supplying water at an appropriate pressure.

[0037] (passing component) The passing components are those that have passed through the separating member and include superabsorbent polymers and liquid components. The proportion of pulp fibers in the solid content (dry mass) of the passing components is usually 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0038] If plastics have been removed beforehand from used absorbent articles before preparing a gel-like mixture, the passing component mainly consists of superabsorbent polymer as solid matter, and the proportion of superabsorbent polymer in the solid matter (dry mass) of the passing component is usually 70% by mass or more, preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0039] The components that pass through are collected in a container placed below or outside the separating member. Furthermore, components adhering to the back or outside of the separating member can be efficiently removed by scraping with a flat-faced tool such as a scraper, or by supplying water at an appropriate pressure (for example, by applying downward impact).

[0040] <Method for manufacturing recycled materials> The present invention relates to a method for producing a recycled material by separating and recovering at least a portion of the constituent members from a used absorbent article composed of pulp fibers, superabsorbent polymers, and plastics, comprising: preparing a mixture containing the pulp fibers and the superabsorbent polymer; and passing the mixture through a separating member having an opening to separate a residual component containing aggregates of pulp fibers from a pass-through component containing the superabsorbent polymer, wherein the mixture subjected to the separating member is in a state in which the superabsorbent polymer has swollen and the pulp fibers have formed aggregates. (This method may be hereinafter referred to as "the manufacturing method of the present invention").

[0041] (Used absorbing materials) Used absorbent materials include absorbent materials used by users, as well as absorbent materials discarded during the manufacturing process for reasons such as not meeting specifications. There are no particular restrictions on what constitutes an absorbent material, but examples include disposable diapers (for children, adults, pets, etc.), incontinence pads, urine pads, sanitary napkins, and breast pads.

[0042] Most absorbent articles consist of a surface material, leak-proof three-dimensional gathers, absorbent material, waterproofing material, and other components. Nonwoven fabrics such as polypropylene and polyester are used for the surface material. Three-dimensional gathers that prevent leakage use elastic materials such as polyurethane and nonwoven fabrics such as polypropylene. Absorbent materials consist of pulp fibers (including absorbent paper), superabsorbent polymers, etc. Waterproofing materials use films such as polyethylene with micropores to ensure breathability. The materials that make up these absorbent articles can be broadly classified into three types of constituent materials: pulp fibers, superabsorbent polymers, and plastics (referring to components other than pulp fibers and superabsorbent polymers).

[0043] Examples of pulp fibers that make up absorbent articles include, but are not limited to, wood pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose.

[0044] Examples of superabsorbent resins that make up absorbent articles include, but are not limited to, polyacrylate-based, polysulfonic acid-based, polyamino acid-based, cellulose-based, and starch-based resins.

[0045] The flow chart shown in Figure 2 is an example of the manufacturing method of the present invention. The manufacturing method shown in Figure 2 includes a first separation step of separating used absorbent articles into plastics and a first mixture containing pulp fibers, superabsorbent polymer, and water; a preparation step of adjusting the liquid volume of the first mixture to prepare a second mixture containing swollen superabsorbent polymer, aggregates of pulp fibers, and water; and a second separation step of passing the second mixture through a separation member having an opening to separate it into a residual component containing the aggregates of pulp fibers and a passing component containing the superabsorbent polymer.

[0046] (First separation step) In the first separation step, the used absorbent material is separated into plastics and a first mixture containing pulp fibers, superabsorbent polymer, and water. Known methods can be used for separating the plastics from the mixture of pulp fibers and superabsorbent polymer. For example, methods include separating the used absorbent material by utilizing the difference in specific gravity after crushing, using a screen, using a cyclone, separating by cutting into strips, separating by forming numerous holes on the surface of the absorbent material without crushing or cutting, and separating by absorbing water to pressurize the inside and then rupturing it with an impact, but these are not limited to these. The separated plastics can be recovered by known methods and used as recycled material.

[0047] (Preparation process) In the preparation step, the volume of the first mixture is adjusted to prepare a second mixture containing a swollen superabsorbent polymer, a collection of pulp fibers, and water. The second mixture corresponds to the mixture in the separation method of the present invention described above. Washing and sterilization can also be performed at this stage.

[0048] In the first separation step, a large amount of water is usually used, so the first mixture is a liquid in which the superabsorbent polymer is swollen and the pulp fibers are dispersed. After allowing this liquid to stand and the pulp fibers to settle, the supernatant liquid is removed to prepare the second mixture.

[0049] In the preparation process, it is preferable to adjust the amount of liquid containing water to 30 to 1000 parts by mass per 1 part by mass of dry superabsorbent resin. Even if the amount of liquid exceeds 1000 parts by mass per 1 part by mass of dry superabsorbent resin, if left to stand for a while, the pulp fibers and superabsorbent resin will eventually settle because both have a specific gravity greater than 1. By removing the supernatant, if the amount of water falls below 1000 times, it can be made suitable for passing through the separation member.

[0050] (Second separation step) In the second separation step, the second mixture is passed through a separation member having an opening to separate it into a residual component containing the pulp fiber aggregate and a pass-through component containing the superabsorbent resin. The second separation step corresponds to the separation step in the separation method of the present invention described above, and the preferred embodiment is the same as described above.

[0051] The solid components of the passing material mainly consist of superabsorbent polymers, and by recovering the superabsorbent polymers from the passing material, they can be obtained as recycled material. The method for recovering the superabsorbent polymers is not particularly limited, but for example, the passing material can be washed and sterilized, then dried (dehydrated) to recover the superabsorbent polymers. Alternatively, the passing material can be dried and then washed and sterilized. Furthermore, in order to increase the superabsorbent polymer content in the solid components recovered from the passing material, the preparation step and the second separation step may be repeatedly performed using the recovered solid components. By mixing the recovered solid components with water to prepare a mixture equivalent to the second mixture, and then repeatedly passing it through a separation member having an opening, the proportion of superabsorbent polymers in the solid components of the passing material can be increased.

[0052] By recovering the superabsorbent polymer from the passing components without inactivating it, the recovered superabsorbent polymer retains a certain degree of water absorption. Therefore, it is possible to obtain a superabsorbent polymer with a certain degree of water absorption without performing any treatment to restore its water absorption. For example, the manufacturing method of the present invention can produce a superabsorbent polymer having a water absorption capacity of 70% or more, 80% or more, or 90% or more of the absorbency of an unused superabsorbent polymer, or a superabsorbent polymer with a water absorption capacity of 100 to 500 times, 150 to 400 times, or 200 to 300 times its own weight.

[0053] Furthermore, it is preferable not to perform a step to deactivate the superabsorbent polymer before the second separation step, and when obtaining a superabsorbent polymer as a regenerated material using the manufacturing method of the present invention, it is preferable to obtain the superabsorbent polymer without deactivation.

[0054] The residual components mainly consist of aggregates of pulp fibers, and by recovering the pulp fibers from the residual components, recycled pulp fibers can be obtained. The method for recovering the pulp fibers is not particularly limited, but since the aggregates of pulp fibers easily break down when in contact with water, it is preferable to bring the residual components into contact with water and disperse the pulp fibers. For example, by adding water to the residual components remaining on the surface of the separation member and applying appropriate shaking or agitation, the aggregates of pulp fibers break down, and the pulp fibers pass through the separation member together with the water. Since the pulp fibers that have passed through the separation member are dispersed in water, the pulp fibers can be recovered by separating them from the water and drying them. Alternatively, washing and sterilization may be performed before or after separating the pulp fibers from the water.

[0055] Furthermore, since residual components may include superabsorbent polymers in addition to pulp fibers, the pulp fibers may be recovered after removing the superabsorbent polymers using known methods. For example, the pulp fibers may be recovered after deactivating or reducing the water absorption capacity of the superabsorbent polymers using chemicals.

[0056] Furthermore, the manufacturing method shown in Figure 2 may include washing or sterilization steps after the first separation step, after the preparation step, or after the second separation step. For example, sterilization can be performed on the material to be separated using a disinfectant such as sodium hypochlorite, or by ultraviolet light or ozone treatment.

[0057] The manufacturing method shown in Figure 2 is an example in which a mixture containing pulp fiber aggregates and swollen superabsorbent resin is prepared after removing plastics. However, the manufacturing method of the present invention is not limited to removing plastics before preparing the mixture containing pulp fiber aggregates and swollen superabsorbent resin.

[0058] In the manufacturing method of the present invention, the superabsorbent resin obtained as a recycled material can be used as a component of absorbent articles such as disposable diapers, incontinence pads, urine pads, sanitary napkins, and breast pads; for agricultural and horticultural applications such as soil water retention agents, seedling sheets, seed coatings, and fertilizer release agents; for distribution and transportation applications such as coolants and condensation prevention sheets; for electrical and electronic applications such as waterproofing materials for communication cables; for civil engineering and construction applications such as sealing materials and concrete curing materials; for cosmetic applications such as moisturizers; for medical applications such as wound dressings and fabric softeners; and for daily necessities applications such as disposable hand warmers, cat litter, and pet sheets. In the manufacturing method of the present invention, the pulp fibers obtained as recycled material can be used as a component of various absorbent articles, including disposable diapers, as well as in building materials, recycled paper, cardboard, solid fuel, and the like. In the manufacturing method of the present invention, the plastics obtained as recycled materials can be used as components of various absorbent articles, including disposable diapers, as well as various molded articles, various films, solid fuels, and the like. [Examples]

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless its essence is changed.

[0060] • Used absorbent materials used in the experiment A commercially available infant diaper (pants type, size M, unused) was disassembled, and a mixture of pulp fibers and superabsorbent polymer (referred to as Sample A) was extracted. The dry weight of Sample A was approximately 14.7 g, consisting of 7.1 g of pulp fibers (48% by weight) and 7.6 g of superabsorbent polymer (52% by weight). Sample A was added to 3 L of tap water and stirred to obtain a mixture of aggregates of pulp fibers and swollen superabsorbent polymer (referred to as Sample B).

[0061] • Method for calculating the mass ratio of pulp fibers to superabsorbent polymers The mass ratio of pulp fibers to superabsorbent polymer was determined by the following method. A large amount of water was added to the sample, and the superabsorbent polymer was shrunk with an appropriate amount of calcium chloride and colored red with an appropriate amount of cobalt chloride. After stirring this liquid, only the pulp fibers floating in the water were selectively recovered by decantation. Meanwhile, the shrunk and colored superabsorbent polymer was left at the bottom of the container. By repeating this process many times, the pulp fibers and superabsorbent polymer were separated. Each was precipitated in a large amount of methanol and dehydrated by holding overnight, after which the liquid was removed and the samples were vacuum dried. Using these samples, the dry mass of the pulp fibers and superabsorbent polymer was determined.

[0062] • Method for evaluating water absorption properties The components that passed through the mesh were added to a large amount of methanol and dehydrated by holding overnight. The precipitate was recovered by filtration and vacuum dried. The water absorption properties of the recovered product obtained in this way were evaluated by the method specified in JIS K 7223 (Test method for water absorption of superabsorbent polymers), i.e., the so-called tea bag method. The water absorption properties of the superabsorbent polymer contained in infant diapers, as determined by the above method, are typically around 300-310 g / g.

[0063] (Example 1) Figure 3 shows a schematic diagram of the separation device used in Example 1. The separation device 5 shown in Figure 3 consists of a round cage container 6 with mesh sides placed inside a 35L plastic bucket (not shown). The round cage container 6 is made of stainless steel SUS304, has a diameter of 15cm and a height of 15cm, with a mesh wire diameter of 0.8mm and a mesh opening of 5.5mm. A support column 7 is installed in the center of the round cage container 6 and connected to a motor 8.

[0064] The round basket container 6 was tilted at approximately 45°, and approximately 200g of the aforementioned sample B (a mixture of pulp fiber aggregates and swollen superabsorbent polymer) was added to its side while it was slowly rotated. The round basket container 6 was then placed upright in a 35L plastic bucket and rotated at 800rpm for 30 seconds using motor 8. The superabsorbent polymer, which had swollen due to the rotation, passed through the mesh of the round basket container 6 and was collected in the plastic bucket. When the rotation was stopped, it was observed that most of the pulp fibers remained on the mesh of the round basket container 6. On the other hand, a small amount of pulp fiber aggregates were also observed in the superabsorbent polymer collected in the plastic bucket.

[0065] The water absorption properties were evaluated using the evaluation method described above, with the components dispensed into a plastic bucket. First, the components discharged into a plastic bucket were added directly to a large amount of methanol and dehydrated by holding overnight. The precipitate was recovered by filtration, vacuum dried, and its water absorption characteristics in pure water were evaluated according to the method specified in JIS K 7223 (Test method for water absorption of superabsorbent polymers). As a result, it showed good water absorption characteristics of 230 g / g.

[0066] Using the components remaining in the round basket container 6 or the components discharged into the poly bucket as samples, the mass ratio of pulp fibers to superabsorbent polymer in each component was calculated using the calculation method described above. The dried mass ratios of pulp fibers and superabsorbent polymer for each component were as follows. • Residual material in the round basket container 6: Pulp fiber: 96%, Superabsorbent polymer: 4% • Dispensed into a plastic bucket. Pulp fiber: 24%, Superabsorbent polymer: 76%

[0067] (Example 2) The procedure was the same as in Example 1, except that a round cage container (15 cm in diameter) was used as the round cage container 6, with sides made of galvanized iron wire mesh, a wire diameter of 0.7 mm, and a mesh opening of 4.4 mm.

[0068] When the water absorption characteristics in pure water were evaluated using the evaluation method described above with the component discharged into a plastic bucket, it showed good water absorption characteristics of 250 g / g.

[0069] Using the components remaining in the round basket container 6 and the components discharged into the poly bucket, the mass ratio of pulp fibers to superabsorbent polymer in each component was calculated using the calculation method described above. The dried mass ratios of pulp fibers and superabsorbent polymer for each component were as follows. • Residual material in round basket container 6: Pulp fiber: 92%, Superabsorbent polymer: 8% • Dispensed into a plastic bucket. Pulp fiber: 14%, Superabsorbent polymer: 86%

[0070] (Example 3) Figure 4 shows a schematic diagram of the separation device used in Example 3. The separation device 9 shown in Figure 4 is installed with a mesh 11 fixed to a wooden frame 10 so that it is horizontal, and a collection container (not shown) is placed below it. The wooden frame 10 has inner dimensions of 34 cm and 22 cm, and the mesh 11 is made of stainless steel SUS304, with a wire diameter of 0.47 mm and a mesh opening of 2.1 mm. Figure 5 is a schematic diagram of the roller 12 used to apply pressure in Example 3. The roller 12 shown in Figure 5 has a cylindrical body 13 with a width of 21 cm and a diameter of 10 cm, and a stainless steel rod 14 that passes through the axis of the body 13. The body 13 is made of polyethylene and has a 5 mm thick polyurethane foam installed on its surface, and the stainless steel rod 14 has a diameter of 8 mm. Figure 6 shows the pressurizing member 15 with a handle used to apply pressure in Example 3, where (a) is a plan view and (b) is a left side view. The pressurized member with a handle 15 shown in Figure 6 has a dustpan-shaped body with a bottom surface 16a and sides 16b, 16c, and 16d made of a polyethylene terephthalate flat plate (width 21 cm at the tip, thickness 3 mm), and a wooden handle 17 is attached to the bottom surface 16a.

[0071] Approximately 500g of the aforementioned sample B (a mixture of pulp fiber aggregates and swollen superabsorbent polymer) was added to the mesh 11. A load of 2kg was applied to both ends of the stainless steel rod 14 of the roller 12 shown in Figure 5, for a total of 4kg. By moving the roller back and forth 10 times over the mesh, pressure was applied to the sample B on the mesh, causing the swollen superabsorbent polymer to pass through the mesh and fall into the collection container. After returning the pulp fiber aggregates attached to the roller 12 back onto the mesh 11, the pressurizing member with a handle 15 was moved back and forth 5 times over the mesh 11 to push the small amount of swollen superabsorbent polymer remaining on the mesh 11 to the bottom of the mesh 11. The wooden frame 10 was vibrated several times to dislodge the swollen superabsorbent polymer that had adhered to the back of the mesh.

[0072] When the water absorption characteristics in pure water were evaluated using the evaluation method described above with the components that passed through the mesh 11, a good water absorption characteristic of 290 g / g was observed.

[0073] Using the components remaining on the mesh 11 and the components that passed through the mesh, the mass ratio of pulp fibers to superabsorbent polymer in each component was calculated using the calculation method described above. The mass ratios of pulp fibers to superabsorbent polymer for each component were as follows. • Residue on screen 11: Pulp fibers: 99%, Superabsorbent polymer: 1% • Passes through mesh 11: Pulp fibers: 8%, Superabsorbent polymer: 92%

[0074] (Example 4) The procedure was the same as in Example 3, except that the mesh 11 fixed to the wooden frame 10 was changed to one with a wire diameter of 0.34 mm and a mesh opening of 1.3 mm.

[0075] When the water absorption characteristics in pure water were evaluated using the evaluation method described above with the components that passed through the mesh 11, a good water absorption characteristic of 290 g / g was observed.

[0076] Using the components remaining on the mesh 11 and the components that passed through the mesh 11, the mass ratio of pulp fibers to superabsorbent polymer in each component was calculated using the calculation method described above. The mass ratios of pulp fibers to superabsorbent polymer for each component were as follows. • Residual material on screen 11: Pulp fibers: >99%, Superabsorbent polymer: <1% • Passes through mesh 11: Pulp fibers: 5%, Superabsorbent polymer: 95% [Industrial applicability]

[0077] The separation method and manufacturing method of the present invention allow for the reuse of components of used absorbent articles such as disposable diapers as absorbent articles, and can also be effectively utilized in fields such as building materials and fuels, making them industrially useful. [Explanation of Symbols]

[0078] 1. Pulp fibers 2 Super absorbent resin 3. Pulp fiber aggregate 4 Separation member 5, 9 Separation device 6. Round basket container 7 pillars 8 motors 10 wooden frame 11 net 12 rollers 13 Main unit 14 stainless steel rods 15. Pressure component with handle 16a Bottom 16b, 16c, 16d side 17 Handle

Claims

1. This separation method involves passing a mixture containing pulp fibers and a superabsorbent polymer through a separation member having an opening, thereby separating it into a residual component containing aggregates of pulp fibers and a passing component containing the superabsorbent polymer. A separation method wherein the mixture supplied to the separation member is in a state in which the superabsorbent resin has swollen and the pulp fibers have formed aggregates.

2. The separation method according to claim 1, wherein the mixture contains 30 to 1,000 parts by mass of a liquid containing water with respect to 1 part by mass of a dry superabsorbent resin.

3. The separation method according to claim 1 or 2, wherein pressure or centrifugal force is applied when passing the mixture through the separation member.

4. A method for manufacturing recycled materials by separating and recovering at least a portion of the constituent materials from a used absorbent article composed of pulp fibers, superabsorbent polymers, and plastics, To prepare a mixture containing the pulp fibers and the superabsorbent resin, The mixture is passed through a separating member having an opening to separate it into a residual component containing the aggregate of pulp fibers and a pass-through component containing the superabsorbent resin. A method wherein the mixture supplied to the separating member is in a state in which the superabsorbent resin has swollen and the pulp fibers have formed aggregates.

5. The method according to claim 4, wherein the superabsorbent resin is swollen and the pulp fibers are dispersed in the liquid, the liquid is allowed to stand to settle, the superabsorbent resin and the pulp fibers are allowed to settle, the supernatant liquid is removed, and the mixture is prepared.

6. The method according to claim 4 or 5, wherein the recycled member is a superabsorbent resin, and the method includes obtaining a superabsorbent resin without deactivating it.

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