JP2020049398A - Processing method of used sanitary articles - Google Patents

Abstract

To provide a processing method of used sanitary articles for separation and recovery of constituting components (especially, pulp fiber ) to be reusable.SOLUTION: The processing method of used sanitary articles of the present invention is a processing method of used sanitary articles involving a pulp fiber and a water-absorbing resin characterized by including a step of treating the used sanitary articles with an alkaline treatment agent for solubilization of the water-absorbing resin involved therein.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for treating used sanitary articles. More specifically, the present invention relates to a treatment method for separating and recovering constituent components (particularly pulp fibers) from used sanitary articles in a reusable manner.

  With the aging, more people use adult disposable disposable diapers for nursing care. Also, worldwide, the number of people using disposable diapers for children is increasing. In recent years, the usage of disposable disposable diapers has been rapidly increasing. Sanitary articles such as these disposable disposable diapers are discarded after reuse because they are contaminated with dirt. Discarded used hygiene products are usually incinerated. However, with an increase in the amount of waste of used sanitary articles, attempts have been made to recycle used sanitary articles from the viewpoint of environmental protection. BACKGROUND ART In order to recycle used sanitary goods, components such as pulp fibers are separated and recovered from used sanitary goods.

  For example, Patent Literature 1 is a method for treating used sanitary articles, which includes at least a step of disintegrating the sanitary articles and dispersing the same in water, and a step of separating and collecting fibers and SAP contained in the sanitary articles, A treatment method is disclosed in which, in the step of disintegrating and dispersing the sanitary article in water, a polyvalent metal salt as a crosslinking agent and an acidic substance are added. Further, in Patent Document 1, in the step of separating and recovering the fiber and SAP contained in the sanitary article, treatment is performed using a screen or a cleaner to first recover the SAP component, and then to recover the fiber from the dispersion liquid containing the fiber. Recovery is disclosed.

  Patent Document 2 discloses a method for recovering pulp fibers from a used absorbent article containing pulp fibers and a superabsorbent polymer, the method comprising the steps of: Treating with an aqueous solution at a temperature of 80 ° C. or higher to inactivate the superabsorbent polymer, and separating the pulp fiber and the inactivated superabsorbent polymer from the used absorbent article after the treatment with the organic acid aqueous solution. A step of treating the mixture containing the separated pulp fiber and the inactivated superabsorbent polymer with an oxidizing agent (such as ozone) to decompose the inactivated superabsorbent polymer, reduce the molecular weight, and solubilize; Separating the pulp fibers from the mixture treated with the oxidizing agent.

  Patent Document 3 discloses a decomposition method characterized by contacting a decomposing agent containing a periodate as an oxidizing agent with a water-absorbing polymer to decompose the water-absorbing polymer.

  Patent Document 4 discloses a method for decomposing a water-absorbing polymer in a water-absorbing polymer or a water-absorbing material containing the same, wherein at least one alkali compound and a persulfate as an oxidizing agent are used for the water-absorbing polymer. There is disclosed a method for decomposing a water-absorbing polymer, which comprises adding a decomposing agent containing at least one compound and decomposing the water-absorbing polymer in the presence of water.

  Patent Literature 5 discloses that after crushing a used disposable diaper, the crushed used disposable diaper is put into a polymer dissolving tank in which a polymer decomposing agent is mixed with water and stirred, and water contained in the disposable diaper in the polymer dissolving tank is absorbed. Disclosed is a method for regenerating a used material of a used disposable diaper, which comprises decomposing a polymer into monomers and then separating and recovering a pulp component contained in the disposable diaper. As a polymer decomposer, for example, calcium chloride is described.

JP 2013-150976 A JP 2018-021283 A JP 2001-316519 A JP 2003-321574 A JP-A-2000-84533

  The water-absorbent resin is water-insoluble, and in the conventional method for treating used sanitary articles, the water-absorbent resin and the pulp fiber exist in an aggregated state. For this reason, it is difficult to completely remove the water-absorbent resin from the pulp fiber, and the water-absorbent resin remains in the pulp fiber after separation at a certain rate. The pulp fiber in which the water-absorbing resin remains at a certain ratio has a problem that it cannot be used for applications requiring high quality. Further, the method of oxidatively decomposing the water-absorbent resin has a problem that the oxidizing agent also acts on the hydroxyl group of the pulp fiber and oxidizes the hydroxyl group of the pulp fiber to a carboxyl group. The quality of the pulp fiber deteriorated by the oxidizing agent is reduced.

  Therefore, there is a need for a method of efficiently separating and recovering high-quality pulp fibers from used sanitary articles, which reduce the residual ratio of the water-absorbent resin and have little deterioration.

  Patent Literature 5 discloses calcium chloride as a decomposer for a water-absorbing polymer. However, calcium chloride is a dehydrating agent and cannot solubilize the water-absorbing polymer.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a processing method for separating and recovering constituent components, particularly pulp fibers, from used sanitary articles in a reusable manner.

  The method for treating a used sanitary article of the present invention that solves the above-mentioned problems is characterized in that a crushed used sanitary article containing pulp fibers and a water-absorbent resin, water, and an alkaline treating agent are mixed to mix the water-absorbent resin. And a step of separating the pulp fiber from a liquid containing the pulp fiber and the solubilized water-absorbent resin.

  That is, in the present invention, the pulp fiber and the water-absorbent resin are obtained by solubilizing the water-absorbent resin using a crushed product of a used sanitary article containing pulp fiber and a water-absorbent resin, and water and an alkaline treating agent. The gist lies in the fact that it is possible to easily separate them from each other. In general, the water-absorbing resin used for sanitary articles is a crosslinked polymer and has high water absorption, but is insoluble in water. In the present invention, as the crosslinked polymer, a crosslinked structure (crosslinked portion) having a bond hydrolyzed by an alkaline treating agent is used. When such a water-absorbent resin is treated with an alkaline treating agent, the bonds existing in the crosslinked structure are hydrolyzed and the water-absorbent resin is solubilized. According to the present invention, the pulp fiber can be easily separated from the solubilized water-absorbent resin by solubilizing the water-absorbent resin. Therefore, the residual ratio of the water-absorbent resin remaining in the recycled pulp fiber can be reduced, and the quality of the recycled pulp can be improved.

  FIG. 1 is an explanatory view schematically showing the state of a crosslinked polymer before and after treatment with an alkaline treating agent. The crosslinked polymer 100 is in a state before the treatment with the alkaline treating agent. The crosslinked polymer 100 has a three-dimensional network structure in which a polymer main chain 110 is crosslinked by a crosslink chain 120. Due to this three-dimensional network structure, the crosslinked polymer 100 absorbs body fluids and exhibits high water absorption, but is insoluble in water. In this crosslinked chain 120 (crosslinked structure), a bond 130 hydrolyzed by an alkaline treating agent is present. Then, when the crosslinked polymer 100 is treated with an alkaline treating agent, the crosslinked chain 120 of the crosslinked polymer 100 is cleaved from the polymer main chain 110 by hydrolysis to become a cleaved chain 120 '. As a result, the three-dimensional network structure of the crosslinked polymer 100 disappears, and the crosslinked polymer main chain 110 becomes a linear polymer 110 '. This linear polymer 110 'has water solubility. Therefore, when a crushed product of used sanitary goods is treated with an alkaline treating agent, the water-absorbing resin contained therein is solubilized.

  The solubilization step is preferably performed at a pH of 10 or more and a temperature of 40C to 100C. Further, it is preferable that the alkaline treating agent is at least one selected from alkali metal hydroxides and monoamine compounds.

  The water-absorbent resin is a cross-linked polymer containing acrylic acid as a main component, and at least a part of its carboxyl group is neutralized, and its cross-linked structure is hydrolyzed by the alkaline treating agent. Those having a bond that forms a bond are preferable, and those whose hydrolyzable bond is an ester bond are more preferable.

  ADVANTAGE OF THE INVENTION According to this invention, the residual rate of a water absorbent resin powder is reduced from used sanitary articles, and the processing method of separating and collect | recovering pulp fiber with little deterioration efficiently is provided.

The figure which shows the state of the crosslinked polymer before and behind the treatment by the alkaline treating agent. 4 is a flowchart of the method of the present invention. Explanatory drawing explaining an example of the crusher which crushes used sanitary goods. FIG. 3 is an explanatory diagram for explaining a solubilization step of the present invention. Explanatory drawing for explaining the film removing step of the present invention. FIG. 3 is an explanatory diagram illustrating an example of a separation mechanism used in the present invention. Explanatory drawing for explaining the separation step of the present invention. FIG. 3 is an explanatory diagram for explaining a pulp washing step of the present invention. FIG. 2 is an explanatory diagram for explaining a pulp molding step of the present invention. FIG. 2 is an explanatory diagram for explaining a pulp molding step of the present invention.

  The method for treating a used sanitary article according to the present invention is capable of solubilizing the water-absorbent resin by mixing a crushed used sanitary article containing pulp fiber and a water-absorbent resin, water, and an alkaline treating agent. A solubilizing step; and a step of separating the pulp fiber from a liquid containing the pulp fiber and the solubilized water-absorbent resin.

FIG. 2 is a flowchart illustrating the outline of the method for treating a used sanitary article of the present invention, the method for producing a recycled pulp according to the present invention, and the method for producing a recycled water absorbent resin according to the present invention.
In a more preferred embodiment, the method for treating used sanitary articles of the present invention comprises:
1) A solubilizing step A of mixing a crushed product of a used sanitary article containing pulp fiber and a water-absorbent resin, water and an alkaline treating agent to solubilize the water-absorbent resin,
2) a step of removing a film and a nonwoven fabric constituting the sanitary article from the mixture to obtain a liquid containing pulp fibers and a solubilized water-absorbent resin (film removal step B);
3) a step of separating pulp fibers from the liquid to obtain a liquid containing a solubilized water-absorbent resin (separation step C).

Further, the method for producing a recycled pulp of the present invention,
4) a step of washing the pulp fibers separated by the treatment method (pulp washing step D), and
5) forming a pulp fiber after washing (pulp forming step E).

The method for producing a recycled water-absorbent resin of the present invention,
6) a step of crosslinking the solubilized water-absorbent resin obtained by the treatment method with a polyvalent metal salt.

  The used sanitary articles to be treated according to the present invention are not particularly limited as long as they contain pulp fibers and a water-absorbent resin. For example, disposable paper diapers, incontinence pads, light incontinence pads, sanitary napkins, breast milk pads And an absorbent article such as a pet pad. Among these, the present invention can be suitably applied to disposable disposable diapers that use a large amount of pulp fibers.

  1) Solubilization step A in which a crushed product of a used sanitary article containing pulp fibers and a water absorbent resin, water and an alkaline treating agent are mixed to solubilize the water absorbent resin.

  The used sanitary article is preferably crushed by a crusher, for example, more preferably by a single-screw crusher or a twin-screw crusher. Specific examples of the crusher include a rotary press crusher manufactured by Miike Iron Works Co., Ltd., and a washing crusher manufactured by Nippon Seam Co., Ltd. The size of the crushed material is preferably about 50 mm to 100 mm square.

  FIG. 3 is an explanatory diagram for describing a mode of crushing used sanitary goods using the rotary press crusher 1. FIG. The used sanitary goods are put into the crushing chamber 5 through the inlet 3. The rotary press crusher 1 crushes the used sanitary goods put in the crushing chamber 5 by pressing the used sanitary goods against the rotor 11 having the rotary blade 15 with the horizontal pusher 7. The upper pusher 9 presses the used sanitary ware from above. The used sanitary article is crushed by the rotary blade 15 attached to the rotor 11 and the fixed blade 17 attached to the main body. After being crushed to a size that passes through the screen 13, the crushed material is discharged from the discharge port 19.

  By this crushing, a film, a nonwoven fabric, a pulp fiber, and the like constituting the used sanitary article are cut. The crushing physically breaks the main chain of the water-absorbent resin contained in the used sanitary article. As a result, it is possible to suppress an increase in the viscosity of a solution obtained by solubilizing the water-absorbing resin in the solubilizing step of the present invention described below.

  The water-absorbing resin contained in the used sanitary article is not particularly limited, but is formed of a crosslinked polymer having acrylic acid as a main component, and at least a part of its carboxyl group is neutralized. Can be mentioned.

  The content of the acrylic acid component constituting the crosslinked polymer is preferably 90% by mass or more, more preferably 95% by mass or more, preferably 99% by mass or less, and more preferably 97% by mass or less.

  The cation that neutralizes at least a part of the carboxyl group of the crosslinked polymer is not particularly limited, and examples thereof include alkali metal ions such as lithium, sodium, and potassium, and alkaline earth metal ions such as magnesium and calcium. be able to. Among these, it is preferable that at least a part of the carboxyl group of the crosslinked polymer is neutralized with sodium ions. In addition, the neutralization of the carboxyl group of the crosslinked polymer may be such that the carboxyl group of the crosslinked polymer obtained by polymerization may be neutralized, or the crosslinked polymer may be preliminarily neutralized using a monomer. May be formed.

The degree of neutralization of the carboxyl group of the crosslinked polymer is preferably at least 50 mol%, more preferably at least 55 mol%, even more preferably at least 60 mol%. The upper limit of the degree of neutralization is not particularly limited, and all of the carboxyl groups may be neutralized. The degree of neutralization is determined by the following equation.
Degree of neutralization (mol%) = 100 × “molar number of carboxyl groups neutralized in crosslinked polymer” / “total mole number of carboxyl groups in crosslinked polymer (including neutralized and unneutralized)”

  The crosslinked structure (crosslinked chain portion) of the crosslinked polymer preferably has a bond that is hydrolyzed by an alkaline treating agent. Examples of the bond hydrolyzed by the alkaline treating agent include an ester bond, an amide bond, and a urethane bond. In the present invention, it is preferable to use a used sanitary article containing a water-absorbing resin having an ester bond in a crosslinked structure (crosslinked chain portion).

As the crosslinked polymer, for example,
1) An unsaturated monomer composition containing acrylic acid and a crosslinking agent capable of reacting with the carboxyl group of the acrylic acid to form a hydrolyzable bond such as an ester bond or an amide bond is obtained by polymerization. What
2) reacting the surface of the polymer obtained by polymerizing the unsaturated monomer composition containing acrylic acid with a carboxyl group of acrylic acid to form a hydrolyzable bond such as an ester bond or an amide bond; What is obtained by surface treatment with the obtained crosslinking agent,
3) An unsaturated monomer composition containing acrylic acid and a crosslinking agent capable of reacting with a carboxyl group of the acrylic acid to form a hydrolyzable bond such as an ester bond or an amide bond, and is obtained by polymerization. Those obtained by further treating the surface of the obtained polymer with the above-mentioned crosslinking agent can be mentioned.

  Examples of the crosslinking agent capable of forming a hydrolyzable bond such as an ester bond, an amide bond, or a urethane bond by reacting with a carboxyl group of acrylic acid include, for example, polyhydric alcohol, polyglycidyl, polyamine, and polyhydric alcohol. Aziridine and polyvalent isocyanate can be exemplified. Examples of the polyvalent glycidyl compound include ethylene glycol diglycidyl ether and glycerin diglycidyl ether. Examples of the polyvalent amine compound include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine. Examples of the polyvalent aziridine compound include Chemitite PZ-33 {2,2-bishydroxymethylbutanol-tris (3- (1-aziridinyl) propinate)} and Chemitite HZ-22 {1,6-, manufactured by Nippon Shokubai Chemical Industry Co., Ltd. Hexamethylene diethylene urea} and Chemitite DZ-22 {diphenylmethane-bis-4, 4′-N, N′-diethylene urea}. Examples of the polyvalent isocyanate compound include 2,4-tolylene diisocyanate and hexamethylene diisocyanate. These crosslinking agents may be used alone or in combination of two or more.

  The water-absorbent resin contained in the used sanitary article is a cross-linked polymer containing acrylic acid as a main component, and the cross-linked structure (cross-linked chain portion) is composed of a carboxyl group of acrylic acid and a polyvalent glycidyl compound. Those having an ester bond formed by the crosslinking reaction of are preferred.

  The shape of the water-absorbent resin is not particularly limited, and examples thereof include powders such as irregularly crushed, scaly, pearl, and rice grain. Of these, amorphous crushed shapes are preferred.

  The pulp fibers to be separated and recovered according to the present invention are not particularly limited, and include, for example, cellulose fibers such as chemical pulp and dissolved pulp obtained from wood, and artificial cellulose fibers such as rayon and acetate. Examples of the raw material pulp for pulp fibers include non-wood pulp such as wood pulp such as softwood kraft pulp or hardwood kraft pulp, cotton pulp, and straw pulp.

  The alkaline treating agent used in the solubilization step of the present invention is a mixture of a crushed material, water, and an alkaline treating agent (hereinafter, sometimes referred to as an “aqueous treating solution”). It is not particularly limited as long as it decomposes the hydrolyzable bond of the crosslinked structure (crosslinked chain portion) of the contained water-absorbent resin. The alkaline treating agent is preferably water-soluble from the viewpoint of use in an aqueous treating solution. Further, the alkaline treating agent is a base, and it is preferable that the alkaline treating agent shows alkalinity in the aqueous treating solution. As the alkaline treating agent, for example, those having a pKa of 4 or more are preferable, those having a pKa of 4.2 or more are more preferable, and those having a pKa of 4.5 or more are still more preferable. In the case of a base, pKa is the pKa of the conjugate acid.

  Specific examples of the alkaline treating agent include an alkali metal compound, an alkaline earth metal compound, and an amine compound.

  Examples of the alkali metal compound include a hydroxide or a weak acid salt of an alkali metal. Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. Examples of the alkali metal weak acid salts include alkali metal carbonates such as lithium carbonate, sodium carbonate and potassium carbonate; alkali metal bicarbonates such as sodium bicarbonate and potassium bicarbonate; alkali metal acetates such as sodium acetate and potassium acetate; oxalic acid Alkali metal oxalates such as sodium and potassium oxalate; and alkali metal succinates such as sodium succinate.

  Examples of the water-soluble alkaline earth metal compound include alkaline earth metal hydroxides such as calcium hydroxide, strontium hydroxide, and barium hydroxide.

  Examples of the amine compound include ammonia and derivatives thereof; aliphatic amines; alicyclic amines; amines having a benzene ring; nitrogen-containing heterocyclic compounds such as pyrrolidine, piperidine, morpholine, pyrrole, pyrazole, imidazole, pyridine, and indole. And its derivatives.

  Examples of the derivative of ammonia include ammonium carbonate.

  Examples of the aliphatic amine include a monoamine, a diamine, and a polyamine. Examples of the monoamine include alkylamines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, dimethylamine, diethylamine, dipropylamine, methylethylamine, methylpropylamine, methylbutylamine, trimethylamine and triethylamine; monoethanolamine And aminoethanols such as diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine and dimethylethanolamine; and quaternary ammonium hydroxides (eg, tetramethylammonium hydroxide).

  Examples of the diamine include ethylene diamine, propylene diamine, tetramethylene diamine, and hexamethylene diamine. Examples of the polyamine include diethylene triamine, triethylene tetramine, tetraethylene pentamine, and the like.

  Examples of the alicyclic amine include cyclopentylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine and derivatives thereof.

  Examples of the amine having a benzene ring include an aromatic amine in which an amino group is directly bonded to a benzene ring, and a phenylalkylamine in which an amino group is bonded to a benzene ring via an alkylene group or the like. Can be. Specific examples of the aromatic amine include aniline, benzylaniline, methoxyaniline, diphenylamine, biphenylamine, and toluidine. Specific examples of phenylalkylamine include benzylamine and phenylethylamine.

  Examples of the pyridine derivative include pyridine, methylpyridine, ethylpyridine, phenylpyridine, benzylpyridine and the like.

  Further, the amino compound may be used as a ketimine in which the amino group is blocked with a ketone. Ketimine reacts with moisture to release the ketone of the blocking agent to regenerate an amino group. Examples of the ketone include, for example, acetone, ethyl methyl ketone, diethyl ketone, and the like.

  These alkaline treating agents may be used alone or in combination of two or more.

  In an aqueous solution, such as an alkaline earth metal compound, a diamine compound, and a polyamine compound, when an alkaline treating agent that generates a polyvalent cation is used, the solubilized water-absorbing resin is cross-linked again by the polyvalent cation. May be insolubilized. From the viewpoint of preventing the crosslinking of the water-absorbing resin by the polyvalent cation, the cation component generated in the aqueous solution of the alkaline treating agent is preferably a monovalent cation. From these points, the alkaline treating agent used in the present invention is particularly preferably an alkali metal hydroxide or a monoamine compound.

  The alkaline treating agent can be used as a solid, an aqueous solution or the like. When used as a solid, for example, after adding an alkaline treating agent to the crushed product of used sanitary goods, adding water to these mixtures or dispersing the crushed product of used sanitary goods in water, An alkaline treating agent can be added to the dispersion. When used as an aqueous solution, for example, an alkaline treating agent is dissolved in water (including pure water and an aqueous solvent containing a water-soluble organic solvent such as alcohol and acetone) to prepare an aqueous solution having a predetermined concentration, This aqueous solution can be mixed with the crushed used sanitary article.

  The used amount of the alkaline treating agent is not particularly limited as long as it is an amount that hydrolyzes the water-absorbent resin contained in the used sanitary article, and from the viewpoint of facilitating the hydrolysis reaction, a crushed product of the used sanitary article It is preferable that the pH of the aqueous treatment liquid containing water, and the alkaline treatment agent be 10 or more. Preferably, the solubilization step is performed at a temperature of 40 ° C to 100 ° C.

  The pH of the aqueous treatment liquid in the solubilization step is preferably 10 or more, more preferably 10.5 or more, still more preferably 11 or more, and preferably 19 or less, more preferably 17 or less, More preferably, it is 14 or less. By setting the pH at the time of performing the solubilization step within the above range, the solubilization step can be performed efficiently.

  The solubilization step can be performed at normal pressure or under pressure.

  The temperature at which the solubilizing step is performed (the temperature of the aqueous treatment liquid when the solubilizing step is performed at normal pressure) is preferably 40 ° C. or higher, more preferably 45 ° C. or higher, and even more preferably 50 ° C. or higher. , 100 ° C. or lower, more preferably 90 ° C. or lower, still more preferably 80 ° C. or lower. By setting the temperature at which the solubilization step is performed within the above range, the solubilization step can be performed efficiently.

  The pressure when the solubilization step is performed under pressure is preferably 3 atm or less, more preferably 2.5 atm or less, further preferably 2 atm or less, preferably 1.1 atm or more, and preferably 1.3 atm or more. More preferably, the pressure is 1.5 atm or more. Further, the temperature of the aqueous treatment liquid at this time is preferably lower than 130 ° C, more preferably 125 ° C or lower, further preferably 120 ° C or lower, more preferably 10 ° C or higher, more preferably 20 ° C or higher, and further preferably 30 ° C or higher. preferable. By setting the temperature at which the solubilization step is performed within the above range, the solubilization step can be promoted.

  The time for performing the solubilization step may be appropriately adjusted depending on the reaction temperature, pH, and the treatment amount of the water-absorbent resin, but is usually preferably 1 minute or more, more preferably 3 minutes or more, and more preferably 5 minutes. The above is more preferably, within 240 hours, more preferably within 120 hours, even more preferably within 72 hours.

  When performing the solubilization step, the concentration of the alkaline treating agent in the aqueous treating solution may be appropriately adjusted according to the concentration of the water-absorbing resin in the aqueous treating solution, and is usually preferably 0.001 mol / L or more. , More preferably at least 0.01 mol / L, even more preferably at least 0.01 mol / L, preferably at most 50 mol / L, more preferably at most 40 mol / L, even more preferably at most 30 mol / L.

  In the solubilization step in the present invention, oxidizing agents such as ozone, periodate and persulfate are not used, so that pulp fibers with little deterioration can be obtained at low cost. Further, in the present invention, there is no need to previously dehydrate the water-absorbing resin with a dehydrating agent such as calcium chloride.

  As shown in FIG. 4, for example, the solubilization step A in the present invention includes a reaction tank 21 for adding and mixing a crushed shredded disposable diaper, an alkaline treating agent and water, An alkaline treating agent tank 23 for supplying the treating agent is provided. The used paper diaper crushed material cut by the crusher (rotary press crusher 1) is transported by, for example, a belt conveyor 25 and charged into the reaction tank 21.

  The reaction tank 21 is preferably provided with a jacket 27 and a stirring device 29 for stirring the mixture 28 so that the temperature can be adjusted. A pipe for transferring the mixture 28 after the solubilization step to the film removal step B and an on-off valve for opening and closing a flow path to the pipe are provided below the reaction tank 21.

  2) A step of removing a film and a nonwoven fabric constituting a sanitary article from the mixture to obtain a liquid containing pulp fibers and a solubilized water-absorbent resin (film removal step B).

  In the solubilization step A, the mixture (aqueous treatment liquid) obtained by mixing the crushed product of the used sanitary goods, water, and the alkaline treating agent contains the crushed material of the film and the nonwoven fabric constituting the sanitary goods. Exists. In the film removing step B, a crushed product of the film and the nonwoven fabric is removed from the mixture to obtain a liquid containing pulp fibers and a solubilized water-absorbing resin.

  In the film removing step B, for example, it is preferable to use a separation mechanism including a perforated plate having a plurality of holes, and more preferably to use a separation mechanism including a perforated plate having a plurality of holes having a diameter of 3 mm to 7 mm. Examples of the separation mechanism including a perforated plate provided with a plurality of holes having a diameter of about 3 mm to 7 mm include, for example, a pulper, a rotary drum type separator, a commercial laundry dehydrator, and the like. It is preferable to employ a pulper or a rotating drum type separator as the medium-scale equipment, and it is preferable to employ a commercial laundry dehydrator as the small-scale equipment.

  In the separation mechanism provided with a perforated plate having a plurality of holes having a diameter of about 3 mm to 7 mm, the solubilized water-absorbent resin and the pulp fiber pass through the holes having a diameter of 3 mm to 7 mm, but the cut film and The nonwoven does not penetrate these holes. As a perforated plate provided with a plurality of holes having a diameter of about 3 mm to 7 mm, for example, a punching metal can be suitably used.

  As the pulper that can be suitably used as the separation mechanism, a known pulper can be used. For example, as shown in FIG. 5, the pulper 30 includes a storage tank 33 for storing a mixture 28 obtained by mixing a crushed product of used sanitary goods, water, and an alkaline treating agent, and a storage tank 33. And a rotor 39 rotatably provided on the top of the perforated plate 37. The storage tank 33 has a cylindrical shape, and a circular perforated plate 37 is provided at the center of the bottom.

  The perforated plate 37 is provided with a plurality of holes having a diameter of 3 mm to 7 mm. Below the perforated plate 37, there is provided an outlet 41 for the permeated material passing through the perforated plate 37. By rotating the rotor 39, the mixture 28 circulates in the storage tank. The solubilized water-absorbent resin and pulp fibers pass through the holes of the perforated plate 37 and are discharged from the discharge port 41.

  At the bottom of the storage tank 33, a discharge port 43 for discharging a cut material of the film and the nonwoven fabric is provided. The discharge port 43 for discharging the cut material of the film and the nonwoven fabric may be disposed outside the outer periphery of the circular perforated plate 37 provided at the center of the bottom and close to the outer wall of the storage tank 33. preferable. A gate valve (not shown) for opening and closing the outlet 43 is connected to the outlet 43.

  Examples of the rotary drum type separator that can be adopted as the separation mechanism include a used paper diaper separation device disclosed in FIGS. 2 to 6 of JP-A-2012-81433.

  Examples of the commercial washing and dewatering machine include a machine having a rotating drum provided with a plurality of holes. The film and the nonwoven fabric can be removed by throwing the mixture into a rotating drum and rotating the drum to perform dehydration. The solubilized water-absorbent resin and the pulp fiber pass through holes formed in the peripheral wall of the rotating drum due to centrifugal force, and are discharged as wastewater from the commercial washing and dewatering machine. On the other hand, the crushed material of the film and the nonwoven fabric cannot pass through the holes provided in the rotating drum and remains in the rotating drum. In addition, it is also a preferable embodiment to dry the crushed material of the film and the nonwoven fabric with a commercial washing and dewatering machine by using a material having a drying function.

3) a step of separating the pulp fiber from a liquid containing the pulp fiber and the solubilized water-absorbent resin (separation step C)

  In the treatment method of the present invention, pulp fibers as solids are separated by a solid-liquid separation means from the treatment liquid obtained in the film removing step to obtain a liquid containing a solubilized water-absorbing resin. The treatment liquid obtained in the film removal step includes a water-absorbent resin dissolved in the treatment liquid and pulp fibers of a solid content. Therefore, the liquid in which the water-absorbing resin is dissolved is obtained by separating the pulp fiber which is a solid content by the solid-liquid separating means.

  The solid-liquid separation means is not particularly limited, and includes, for example, known means such as filtration separation, centrifugation, sedimentation separation, a belt press, and a screw press. These solid-liquid separation means may be used alone or in combination of two or more.

  In the present invention, for example, a screw press can be suitably used as the solid-liquid separation means. For example, as shown in FIG. 6, the screw press 40 includes a cylindrical screen 43, a screw shaft 45 rotatably disposed inside the cylindrical screen 43, and an outside covering the outside of the cylindrical screen 43. And a cylinder 51. At one end of the cylindrical screen 43 is provided an inlet 42 into which a liquid containing pulp fibers and a solubilized water-absorbent resin is injected, and at the other end, a discharge port for discharging pulp fibers. An outlet 47 is provided. A screw blade 49 is wound around the surface of the screw shaft 45, and the pitch of the screw blade 49 becomes smaller as it goes from the inlet 42 to the outlet 47. The screw shaft 45 is rotatably supported by a support base 57 via a bearing 55. A sprocket 53 is provided at one end of the screw shaft 45, and is connected to a drive motor via a chain (not shown).

  The liquid containing the pulp fiber and the solubilized water-absorbent resin is introduced into the inside of the cylindrical screen 43 from the inlet 42. The volume of the space surrounded by the screw shaft, the screw blades, and the cylindrical screen gradually decreases from the inlet to the outlet. By rotating the screw shaft 45, the pulp fiber moves from the input port 42 to the discharge port 47 side. At this time, the pulp fiber is squeezed, and a liquid containing a water-absorbing resin solubilized from the pulp fiber is squeezed. The squeezed liquid containing the solubilized water-absorbent resin passes through the cylindrical screen 43 and is discharged to the outside of the cylindrical screen 43. The liquid containing the solubilized water-absorbent resin discharged to the outside of the cylindrical screen 43 is collected by the outer cylinder 51 and discharged from the discharge port 59. The pulp fiber from which the liquid containing the solubilized water-absorbent resin is squeezed moves to the outlet 47 and is discharged from the outlet 47.

  In the separation step C, for example, as shown in FIG. 7, a screw press 40 for separating pulp fibers from a treatment liquid containing pulp fibers and a solubilized water-absorbent resin, and discharging a liquid in which the water-absorbent resin is dissolved, And a pulp relay tank 62 for mixing and storing water in the pulp fibers separated by the screw press 40. The screw press 40 separates the pulp fiber which is a solid content from the treatment liquid, and discharges the liquid in which the water-absorbing resin is solubilized to the polymer relay tank 60. In the polymer relay tank 60, sodium hypochlorite is mixed with the liquid in which the water-absorbing resin is solubilized, and sterilized. The pulp fibers separated by the screw press 40 are transferred to a pulp relay tank 62.

  In the treatment method of the present invention, it is preferable to adjust the fluidity of a treatment liquid containing pulp fibers and a solubilized water-absorbent resin prior to the pulp fiber separation step. This is because the solubilization of the water-absorbing resin may increase the viscosity of the treatment liquid. As a method of adjusting the fluidity of the processing liquid, for example, a method of adjusting the concentration of the processing liquid, the processing liquid is processed by high-speed stirring and / or ultrasonic treatment, and the main chain of the water-absorbing resin contained in the processing liquid It is preferable to have a step of cutting Since the water-absorbent resin has a low molecular weight by the main chain cutting step, the viscosity of the treatment liquid containing pulp fibers and the solubilized water-absorbent resin decreases. Therefore, by providing this main chain cutting step, in the pulp fiber separation step, the pulp fiber separation operation becomes easy. As a result, it is possible to obtain a pulp fiber in which the residual ratio of the water absorbent resin is further reduced. The adjustment of the fluidity is preferably performed, for example, in a reaction tank.

  The high-speed stirring is a method of cutting the main chain of the water-absorbent resin by applying a mechanical shear force to the water-absorbent resin, and can be performed using a high-speed stirrer such as a homogenizer. The speed of the high-speed stirring is not particularly limited as long as it can cut the main chain of the water-absorbing resin, but is preferably 10 rpm or more, more preferably 20 rpm or more, and still more preferably 30 rpm or more from the viewpoint of cutting efficiency. is there. Further, from the viewpoint of the balance between cutting efficiency and energy consumption, the speed of high-speed stirring is preferably 30,000 rpm or less, more preferably 25,000 rpm or less, and further preferably 20,000 rpm or less.

  The ultrasonic treatment is a method of cutting the main chain of the water-absorbent resin by applying a shear force to the water-absorbent resin by ultrasonic vibration, and can be performed using an ultrasonic generator. The frequency of the ultrasonic treatment is not particularly limited as long as it can cut the main chain of the water-absorbent resin, but is preferably 20 Hz or more, more preferably 50 Hz or more, and still more preferably 100 Hz or more, from the viewpoint of cutting efficiency. It is. In addition, from the viewpoint of the balance between cutting efficiency and energy consumption, the frequency of the ultrasonic treatment is preferably 20 KHz or less, more preferably 15 KHz or less, and further preferably 10 KHz or less.

  The present invention includes a method for producing recycled pulp. The method for producing recycled pulp of the present invention includes 4) a step of washing pulp fibers separated by the treatment method of the present invention (pulp washing step D), and 5) a step of forming pulp fibers after washing (pulp molding). Step E).

  In the pulp washing process D, as shown in FIG. 8, a separation screen 64 for removing water by mixing water with the pulp-containing liquid in the pulp relay tank 62, and the large foreign matter was removed by the separation screen 64. The pulp-containing liquid is discharged from a first drum screen 66 (foreign matter removing device) for removing fine foreign matter by passing through a cylindrical screen having a vertical slit of 0.15 to 0.20 mm width, and discharged from a separation screen 64. A foreign matter collection tank 68 for storing water containing foreign matter, a pulp washing tank 70 for mixing and washing water with a pulp-containing liquid from which foreign matter has been removed by the first drum screen 66, and a pulp washing tank 70 for washing. A pulp relay tank 72 for storing the pulp-containing liquid until it is sent out, and a second drum screen for mixing water with the pulp-containing liquid in the pulp relay tank 72 to further remove fine foreign matter 4 (foreign matter removing device), a dehydrator 76 for dehydrating the pulp-containing liquid from which foreign matter has been removed by the second drum screen 74, and a pulp washing tank for storing water containing foreign matter discharged from the second drum screen 74 A circulating water tank 78 for supplying to 70 is provided. The second drum screen 74 has the same structure as the first drum screen 66.

  In the separation screen 64, a large film piece is removed as foreign matter from the pulp-containing liquid, and water containing the foreign matter is discharged to the foreign matter collection tank 68. The water containing the foreign matter stored in the foreign matter collection tank 68 is then subjected to a dehydration / drying process to collect a small film piece.

  As shown in FIG. 9, the pulp molding process E includes, as shown in FIG. 9, a pulp fiber dehydrated by the dehydrator 76 and a liquid preparation tank 80 for preparing one batch, and one batch prepared in the liquid preparation tank 80. Tank 82 for storing the pulp-containing liquid in the storage tank 82 until the pulp-containing liquid is sent out, a forming dryer 84 for pressurizing the pulp-containing liquid in the storage tank 82 to form a rectangular pulp sheet 85, followed by hot-pressure drying, and a forming dryer. An air-drying conveyor 86 for air-cooling the pulp sheet 85 formed in 84, an automatic binding machine 88 for stacking and bundling the pulp sheets 85 air-cooled by the air-drying conveyor 86, and storing water discharged from the forming and drying machine 84. A circulation tank 90 for returning the liquid to the liquid preparation tank 80 is provided.

  As shown in FIG. 10, the forming and drying machine 84 has a stirrer 84b mounted at an upper position of an overflow tank 84a whose side wall on the transfer destination side is opened to a width of about 70 cm, and a mesh conveyor 84c is provided at a position ahead of the overflow tank 84a. It is installed, and a forming roller 84d is pivotally supported at the starting position of the mesh conveyor 84c. A press plate 84e is provided at the forward position of the forming roller 84d so as to be vertically movable, two sets of dewatering rollers 84f are pivotally supported at the forward position of the press plate 84e, and a water leakage receiver 84g is attached below the mesh conveyor 84c. I have. At the forward position of the dewatering roller 84f, a non-driven first roller conveyor 84h is installed inclined downward, and at the forward position of the first roller conveyor 84h, a press machine 84i is installed inclined downward, and the press machine is installed. A non-driven second roller conveyor 84j is installed at the forward position of 84i so as to be inclined downward. The press 84i is heated to about 250 ° C. The holding plate 84e operates so as to descend to a position in contact with the conveyor surface every time the conveyor surface of the mesh conveyor 84c advances by about 80 cm, and then immediately rise.

  The pulp fibers obtained according to the present invention have high quality and have few restrictions on reuse. Therefore, application to various fields can be expected. Reuse applications include, for example, sanitary articles, paper products, building materials, and the like.

  6) The present invention includes a method for producing a recycled water absorbent resin. The method for producing a recycled water-absorbent resin of the present invention preferably includes a step of recovering the water-absorbent resin (SAP) separated by the treatment method of the present invention. The method for collecting the water-absorbent resin is not particularly limited, but it is preferable that the water-absorbent resin dissolved in the aqueous liquid after separating the pulp fiber is treated with a polyvalent metal salt and collected as an aggregate. . By treating this water-soluble water-absorbent resin with a polyvalent metal salt, its carboxyl group is cross-linked by polyvalent metal ions of the polyvalent metal salt and aggregates. This aggregate (gel-like substance) can be easily separated from the treatment liquid by the above-described solid-liquid separation means.

  As the polyvalent metal salt, a divalent metal salt or a trivalent metal is suitably used. Examples of the divalent metal salt include calcium chloride, and examples of the trivalent metal salt include aluminum sulfate.

  Although the conditions of the dehydration treatment are not particularly limited, it is usually preferable to perform the dehydration treatment at 0 ° C to 100 ° C for 1 minute to 10 days. The amount of the polyvalent metal salt used may be appropriately adjusted according to the amount of the water-soluble polymer and the like.

  The separated and recovered water absorbent resin is preferably dried and reused as a recycled water absorbent resin, a soil conditioner, a solid fuel, or the like.

(Effect of the present invention)
It is confirmed that about 7 to 14% of the water absorbent resin remains in the recycled pulp according to the conventional method. In the recycled pulp obtained according to the present invention, the residual ratio of the water-absorbent resin cannot be confirmed, and thus the residual ratio is considered to be less than 1%.

  The treatment method of the present invention can be applied to used sanitary articles used to absorb bodily fluids discharged from the human body, particularly disposable disposable diapers, incontinence pads, light incontinence pads, sanitary napkins, breast milk pads, bed pads and the like. It can be suitably used for finished absorbent articles.

  100: crosslinked polymer not treated with an alkaline treating agent, 100 ′: solubilized polymer treated with an alkaline treating agent, 110: crosslinked polymer main chain, 110 ′: linear Polymer, 120: crosslinked chain, 120 ′: cleaved chain

Claims (9)

  A crushed product of used sanitary articles containing pulp fibers and a water-absorbent resin, water and an alkaline treating agent are mixed to solubilize the water-absorbent resin, and the pulp fibers are solubilized. Separating the pulp fiber from a liquid containing a water-absorbent resin.   The method for treating a used sanitary article according to claim 1, wherein the solubilizing step is performed at a pH of 10 or more and a temperature of 40C to 100C.   The method for treating used sanitary articles according to claim 1 or 2, wherein the alkaline treating agent is at least one selected from an alkali metal hydroxide and a monoamine compound.   The water-absorbent resin is made of a crosslinked polymer containing acrylic acid as a main component, and at least a part of its carboxyl group is neutralized, and its crosslinked structure is hydrolyzed by the alkaline treating agent. The method for treating a used sanitary article according to any one of claims 1 to 3, wherein the method has a bond.   The method for treating a used sanitary article according to claim 4, wherein the crosslinked structure of the water absorbent resin has an ester bond.   The method for treating used sanitary articles according to any one of claims 1 to 5, wherein the pulp fibers as solids are separated by a solid-liquid separation means.   7. The method according to claim 1, further comprising a step of treating the liquid containing the pulp fiber and the solubilized water-absorbent resin by high-speed stirring and / or ultrasonic treatment before the step of separating the pulp fiber. The method for treating used sanitary goods described in the above.   A method for producing recycled pulp, comprising: a step of washing pulp fibers separated by the treatment method according to any one of claims 1 to 7; and a step of molding the pulp fibers after the washing.   A method for producing a recycled water-absorbent resin, comprising a step of crosslinking a water-absorbent resin solubilized by the treatment method according to any one of claims 1 to 7 with a polyvalent metal salt.

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