Method for producing pulp fiber raw material, and pulp fiber raw material as cellulose raw material

Abstract

To provide a method for producing a pulp fiber raw material suitable as a cellulose raw material.SOLUTION: A method for producing pulp fiber raw material as a cellulose raw material from pulp fiber to be treated includes an ozone treatment step S36 of supplying ozone-containing gas to a treatment tank that contains a treatment liquid containing a pulp fiber matter containing a pulp fiber to be treated, so that an ozone-treated pulp fiber is formed from the pulp fiber to be treated, and an alkaline treatment step S39 of treating the ozone-treated pulp fiber with an alkaline aqueous solution, so that a pulp fiber material containing a hemicellulose of less than 8.0 mass% is formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing pulp fiber raw material as a cellulosic raw material from pulp fibers to be treated, and to pulp fiber raw material as a cellulosic raw material derived from post-consumer hygiene products containing pulp fibers. [Background technology]

[0002] BACKGROUND ART Technologies for recycling used sanitary products such as disposable diapers are being investigated. For example, Patent Document 1 discloses a method for producing recycled pulp that can be reused mainly as sanitary products. Specifically, Patent Document 1 describes a method for producing recycled pulp that can be reused as sanitary products by recovering pulp fibers from used sanitary products containing pulp fibers and superabsorbent polymers, the method comprising the steps of: decomposing the used sanitary products into pulp fibers and other materials by applying physical force to the used sanitary products in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less; separating the pulp fibers from the mixture of pulp fibers and other materials produced in the decomposition step; and treating the separated pulp fibers with an ozone-containing aqueous solution having a pH of 2.5 or less.

[0003] In Patent Document 1, the reason for treating pulp fibers with an ozone-containing aqueous solution is that a significant amount of superabsorbent polymer remains in the separated pulp fibers, and the superabsorbent polymer is removed from the pulp fibers by oxidative decomposition and solubilization. Patent Document 1 discloses a method for treating pulp fibers with an ozone-containing aqueous solution, in which an ozone-containing aqueous solution is placed in a treatment tank and the separated pulp fibers are placed in the ozone-containing aqueous solution. In this method, it is preferable to moderately agitate the ozone-containing aqueous solution during treatment to create a water flow. Alternatively, ozone gas may be blown into the aqueous solution placed in a container, and the rising bubbles of ozone gas may generate a water flow in the ozone-containing aqueous solution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-881 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes the reuse of "recycled pulp fiber" as "pulp fiber" itself, but does not describe the use of recycled pulp fiber as a pulp fiber raw material.

[0006] Pulp fibers are often used in sanitary products, such as absorbents, and many of these pulp fibers are derived from coniferous trees. It is known that coniferous pulp fibers contain about 50 to 60% by mass of cellulose and about 10 to 25% by mass of hemicellulose. Hemicellulose is found in large amounts in plant cell walls. When pulp fibers are used as a cellulose raw material, for example, the hemicellulose present in the pulp fibers remains in the cellulose recovered from the pulp fibers and, ultimately, in cellulose-derived products, and the remaining hemicellulose may inhibit the function of the cellulose-derived products.

[0007] In the field of sanitary products, pulp fibers are used in absorbents, etc., and hemicellulose contained in pulp fibers is generally not removed from pulp fibers because (i) it is unlikely to interfere with the function of sanitary products (e.g., absorbency), (ii) it imparts elasticity to pulp fibers, and (iii) it contributes to the yield of pulp fibers produced. It would also be advantageous if cellulose-derived products could be produced not only from pulp fibers derived from hygiene products, but also from other pulp fibers to be treated, for example virgin pulp fibers. Therefore, an object of the present disclosure is to provide a method for producing a pulp fiber raw material suitable as a cellulose raw material. [Means for solving the problem]

[0008] The present inventors have discovered a method for producing a pulp fiber raw material as a cellulose raw material from pulp fibers to be treated, the method comprising an ozone treatment step in which ozone-treated pulp fibers are formed from the pulp fibers to be treated by supplying an ozone-containing gas to a treatment tank containing a treatment liquid containing a pulp fiber-containing material including the pulp fibers to be treated, and an alkali treatment step in which the ozone-treated pulp fibers are treated with an alkaline aqueous solution to form the pulp fiber raw material having a hemicellulose content of less than 8.0 mass%. [Effects of the Invention]

[0009] The method for producing a pulp fiber raw material of the present disclosure can produce a pulp fiber raw material that is suitable as a cellulose raw material. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flow chart illustrating an embodiment of a method of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of an apparatus for the ozone treatment step of FIG. 1. [Figure 3] FIG. 2 is a schematic diagram showing another example of the configuration of the device for the ozone treatment step in FIG. [Figure 4] 1. FIG. 4 is a schematic diagram showing still another example of the configuration of the apparatus for the ozone treatment step in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Specifically, the present disclosure relates to the following aspects: [Aspect 1] A method for producing a pulp fiber raw material as a cellulose raw material from pulp fibers to be treated, comprising: an ozone treatment step in which an ozone-containing gas is supplied to a treatment tank containing a treatment liquid containing a pulp fiber-containing material including pulp fibers to be treated, thereby forming ozone-treated pulp fibers from the pulp fibers to be treated; an alkali treatment step of treating the ozone-treated pulp fibers with an aqueous alkali solution to form the pulp fiber raw material having a hemicellulose content of less than 8.0% by mass; The above method, characterized in that it comprises:

[0012] In the above-described production method, a pulp fiber raw material having a predetermined hemicellulose content, that is, a pulp fiber raw material suitable as a cellulose raw material, can be produced from the pulp fibers to be treated.

[0013] [Aspect 2] 2. The method of claim 1, wherein the pulp fiber material has a lignin content of less than or equal to 0.10% by weight.

[0014] Pulp fibers are known to contain lignin in addition to cellulose. For example, softwood, which is often used in sanitary products, is known to contain 20 to 30% by mass of lignin. Furthermore, when pulp fibers are used, for example, as a cellulose raw material, the lignin present in the pulp fibers may remain in the cellulose recovered from the pulp fibers and ultimately in cellulose-derived products, and the remaining lignin may inhibit the function of the cellulose-derived products. In the above-described production method, a pulp fiber raw material having a predetermined lignin content, that is, a pulp fiber raw material suitable as a cellulose raw material, can be produced from the pulp fibers to be treated.

[0015] [Aspect 3] 3. The method of claim 1 or 2, wherein the pulp fiber material has a cellulose content of 94.0% by weight or greater.

[0016] In the above-described production method, a pulp fiber raw material having a predetermined cellulose content, that is, a pulp fiber raw material suitable as a cellulose raw material, can be produced from the pulp fibers to be treated.

[0017] [Aspect 4] Aspect 4. The method according to any one of Aspects 1 to 3, wherein in the ozone treatment step, the ozone-containing gas is supplied to the treatment tank so that the pulp fibers after the ozone treatment have a hemicellulose content of 10.0% by mass or less.

[0018] In the above-described production method, the ozone treatment step is performed so that the pulp fibers have a predetermined hemicellulose content after the ozone treatment, and therefore the hemicellulose content of the pulp fibers after the ozone treatment can be efficiently reduced in the subsequent alkali treatment step. Therefore, the above-described production method can easily produce a pulp fiber raw material having a predetermined hemicellulose content, i.e., a pulp fiber raw material suitable as a cellulose raw material, from the pulp fibers to be treated.

[0019] [Aspect 5] In the ozone treatment step, the ozone-containing gas is applied to the pulp fiber-containing material so that a CT value, which is a product of the ozone concentration in the ozone-containing gas and the treatment time, is 100 to 12,000. g / m 3 The method according to any one of aspects 1 to 4, wherein the ozone-treated pulp fibers are formed by contacting the pulp and the ozone-treated mixture for 1 minute.

[0020] In the ozone treatment step, the pulp fiber raw material is formed by contacting an ozone-containing gas with a pulp fiber-containing material under predetermined conditions. Therefore, the pulp fiber raw material having a predetermined hemicellulose content, i.e., a pulp fiber raw material suitable as a cellulose raw material, can be easily produced from the pulp fibers to be treated.

[0021] [Aspect 6] Aspect 6. The method according to any one of Aspects 1 to 5, wherein in the alkali treatment step, the aqueous alkaline solution has a normality of 3.0 N or less. In the above manufacturing method, since the alkaline aqueous solution in the alkaline treatment step has a predetermined normality, the pulp fibers, treatment tank, etc. are less likely to be damaged after ozone treatment, and waste liquid from the alkaline treatment step is easier to treat.

[0022] [Aspect 7] A method according to aspect 6, wherein in the alkali treatment step, the aqueous alkaline solution is added in an amount of 10 to 40 L per 1 kg of the dry mass of the ozone-treated pulp fibers. In the above manufacturing method, a predetermined amount of alkaline aqueous solution having a predetermined normality is added in the alkaline treatment step, which prevents damage to the pulp fibers, treatment tank, etc. after ozone treatment and makes it easier to dispose of the waste liquid from the alkaline treatment step.

[0023] [Aspect 8] The method according to any one of Aspects 1 to 7, wherein the pulp fiber raw material is a raw material for cellulose nanofibers, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding materials, or paper products.

[0024] In the above-described production method, the pulp fiber raw material is a raw material for a predetermined application (for cellulose nanofibers, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding materials, or paper processed products). Therefore, the above-described production method can produce a pulp fiber raw material that can be suitably used as a predetermined cellulose raw material.

[0025] [Aspect 9] Aspect 9. The method of any one of aspects 1 to 8, further comprising using the cellulose to form cellulose nanofibers, viscose rayon, a cellulose derivative, bioethanol, biobutanol, a molding material, or a paper product from the pulp fiber raw material.

[0026] The above-mentioned production method includes a step of using a specific cellulose, and can efficiently produce a specific cellulose-derived product (cellulose nanofiber, viscose rayon, cellulose derivative, bioethanol, biobutanol, molding material, or paper product).

[0027] [Aspect 10] A pulp fiber raw material as a cellulose raw material, The pulp fiber raw material has a hemicellulose content of less than 8.0% by mass. The pulp fiber raw material is characterized by:

[0028] The pulp fiber raw material has a predetermined hemicellulose content and is therefore suitable as a cellulose raw material.

[0029] [Aspect 11] A pulp fiber raw material as a cellulose raw material, The pulp fiber raw material has a cellulose content of 94.0% by mass or more. The pulp fiber raw material is characterized by:

[0030] The pulp fiber raw material has a predetermined cellulose content and is therefore suitable as a cellulose raw material.

[0031] [Aspect 12] 12. The pulp fiber material of claim 10 or 11, wherein the pulp fiber material has a lignin content of less than or equal to 0.10% by weight. The pulp fiber raw material has a predetermined lignin content and is therefore suitable as a cellulose raw material.

[0032] [Aspect 13] 13. The pulp fiber raw material according to any one of aspects 10 to 12, derived from a used sanitary product containing pulp fibers. The pulp fiber raw material is derived from used sanitary goods, which is preferable from the viewpoint of environmental protection.

[0033] [Aspect 14] The pulp fiber raw material according to any one of aspects 10 to 13, wherein the pulp fiber raw material is a raw material for cellulose nanofibers, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding materials, or paper products. The pulp fiber raw material is suitable as a cellulose raw material for certain applications.

[0034] [Aspect 15] A cellulose nanofiber, a viscose rayon, a cellulose derivative, bioethanol, biobutanol, a molding material, or a paper product, which is made from the pulp fiber raw material according to any one of aspects 10 to 14. The cellulose nanofiber, viscose rayon, cellulose derivative, molding material, or paper product has a high cellulose content. The bioethanol and biobutanol have a high ethanol and butanol content, respectively.

[0035] [Aspect 16] The method comprises the steps of: a preparation step of preparing the treatment tank having a pulp fiber-containing material supply port, a treatment liquid discharge port, and an ozone-containing gas supply port disposed below the treatment tank; a pulp fiber-containing material supply step of supplying the pulp fiber-containing material to the treatment tank through the pulp fiber-containing material supply port; an ozone-containing gas supply step of supplying the ozone-containing gas from the ozone-containing gas supply port to the processing liquid in the processing tank; the ozone treatment step of contacting the pulp fiber-containing material with the ozone-containing gas while allowing the ozone-containing gas to rise in the treatment tank, thereby forming the ozone-treated pulp fibers from the pulp fibers to be treated; a treatment liquid discharge step of discharging the treatment liquid containing the pulp fibers after the ozone treatment from the treatment liquid discharge port; 16. The method of any one of aspects 1 to 15, comprising:

[0036] Since hemicellulose has a lower specific gravity than cellulose, pulp fibers with a relatively low hemicellulose content (pulp fibers with a relatively high cellulose content) tend to have a relatively higher specific gravity than pulp fibers with a relatively high hemicellulose content (pulp fibers with a relatively low cellulose content). On the other hand, in the solution, the ozone-containing gas rises while consuming ozone, so the ozone-containing gas present at a lower position tends to have a higher ozone content (i.e., be fresher) than the ozone-containing gas present at an upper position.

[0037] The manufacturing method includes a predetermined preparation step, a pulp fiber-containing material supply step, an ozone-containing gas supply step, an ozone treatment step, and a treatment liquid discharge step. In the ozone treatment step, the pulp fiber-containing material is brought into contact with the ozone-containing gas while the ozone-containing gas is being raised.

[0038] In the above-mentioned production method, pulp fibers with a relatively low hemicellulose content (pulp fibers with a relatively high cellulose content) have a higher sedimentation tendency than pulp fibers with a relatively high hemicellulose content (pulp fibers with a relatively low cellulose content), and fresh ozone-containing gas comes into contact with the pulp fibers with a relatively low hemicellulose content, facilitating further decomposition of the hemicellulose contained therein. Therefore, the above-mentioned production method can produce a pulp fiber raw material that can be suitably used as a cellulose raw material.

[0039] In general, the higher the lignin content of pulp fibers, the lower their specific gravity tends to be. Therefore, in the above-described manufacturing method, pulp fibers with a relatively low lignin content have a relatively higher sedimentation tendency than pulp fibers with a relatively high lignin content, and therefore, fresher ozone-containing gas comes into contact with the pulp fibers with a relatively low lignin content, thereby further decomposing the lignin contained therein.

[0040] The ozone-containing gas supply port is located below the treatment tank, specifically within a range of preferably 30%, more preferably 20%, and even more preferably 10% of the height of the treatment tank from the bottom of the treatment tank. Furthermore, the pulp fiber-containing material supply port may be located below or above the ozone-containing gas supply port, and the treatment liquid discharge port may be located below or above the ozone-containing gas supply port.

[0041] The production method described in embodiment 16 includes both so-called continuous and batch production methods. Furthermore, "raising the ozone-containing gas" means that the ozone-containing gas rises as a whole, and includes the case where the ozone-containing gas rises vertically as a whole while being stirred horizontally when the treatment liquid in the treatment tank is being stirred.

[0042] [Aspect 17] the treatment liquid outlet is located below the pulp fiber-containing material supply port, In the ozone treatment step, the pulp fiber-containing material is brought into contact with the ozone-containing gas while being lowered. 17. The method of embodiment 16.

[0043] In the above-described manufacturing method, the descending pulp fiber-containing material is brought into contact with the ascending ozone-containing gas, which increases the frequency with which the pulp fiber-containing material comes into contact with the ozone-containing gas, narrowing the distribution of the hemicellulose content of the pulp fibers contained in the treatment liquid (pulp fibers after ozone treatment) (reducing variation). Furthermore, because fresh ozone-containing gas can come into contact with pulp fibers with a relatively low hemicellulose content, the hemicellulose content of the pulp fibers contained in the treatment liquid (pulp fibers after ozone treatment) tends to be low. Furthermore, because the treatment liquid outlet is located below the pulp fiber-containing material supply inlet, pulp fibers with a relatively low hemicellulose content (pulp fibers with a relatively high cellulose content) tend to be discharged from the treatment liquid outlet.

[0044] The manufacturing method described in embodiment 17 includes both so-called continuous and batch manufacturing methods. Furthermore, "descending the pulp fiber-containing material" means that at least a portion of the pulp fiber-containing material is descending, and includes, for example, the entire treatment liquid in the treatment tank when the entire treatment liquid is descending, and the descending portion of the pulp fiber-containing material when the treatment liquid in the treatment tank is undergoing vertical convection, etc.

[0045] [Aspect 18] the treatment liquid outlet is disposed above the pulp fiber-containing material supply port, In the ozone treatment step, the pulp fiber-containing material is brought into contact with the ozone-containing gas while the pulp fiber-containing material is being raised. 17. The method of embodiment 16.

[0046] In the above manufacturing method, the rising pulp fiber-containing material is brought into contact with the rising ozone-containing gas, so the time the pulp fiber-containing material is in contact with the ozone-containing gas is longer, making it easier to reduce the hemicellulose content in the pulp fibers.

[0047] The manufacturing method described in embodiment 18 includes both so-called continuous and batch manufacturing methods. Furthermore, "raising the pulp fiber-containing material" means that at least a portion of the pulp fiber-containing material is rising, and includes, for example, the entire treatment liquid in the treatment tank when the entire treatment liquid is rising, and the rising portion of the pulp fiber-containing material when the treatment liquid in the treatment tank is undergoing vertical convection, etc.

[0048] [Aspect 19] A method according to any one of aspects 16 to 18, wherein in the pulp fiber-containing material supply step, the pulp fiber-containing material is continuously supplied from the pulp fiber-containing material supply port to the treatment tank at a first flow rate, and in the treatment liquid discharge step, the treatment liquid is continuously discharged from the treatment liquid discharge port at a second flow rate.

[0049] In the above manufacturing method, in the pulp fiber-containing material supply step, the pulp fiber-containing material is continuously supplied from a pulp fiber-containing material supply port to a treatment tank at a first flow rate, and in the treatment liquid discharge step, the treatment liquid is continuously discharged from a treatment liquid discharge port at a second flow rate, thereby making the treatment time of the pulp fiber-containing material to be treated uniform and narrowing the distribution of the hemicellulose content of the pulp fiber raw material contained in the treatment liquid (reducing variation). Therefore, the above-mentioned production method can produce a pulp fiber raw material that can be suitably used as a cellulose raw material.

[0050] [Aspect 20] The pulp fiber-containing material comprises the pulp fibers to be treated derived from used sanitary products and a superabsorbent polymer; In the ozone treatment step, at least a portion of the superabsorbent polymer is dissolved in the treatment liquid. 20. The method according to any one of aspects 16 to 19.

[0051] In used sanitary products, in absorbents containing pulp fibers and superabsorbent polymers, (i) the superabsorbent polymers swell as they absorb liquids such as bodily fluids and entangle the pulp fibers, and (ii) the swollen superabsorbent polymers entangle the pulp fibers, causing gel blocking, and in many cases, multiple superabsorbent polymers and multiple pulp fibers form connected structures.

[0052] In the above-described manufacturing method, in the ozone treatment step, the pulp fiber-containing material is contacted with the ozone-containing gas while the ozone-containing gas is being raised. Among the free superabsorbent polymers, free pulp fibers, and connected structures, the free superabsorbent polymers and connected structures, which have relatively low buoyancy, tend to sink more easily than the free pulp fibers, which have relatively high buoyancy. Meanwhile, since the ozone-containing gas rises while consuming ozone and treating the pulp fiber-containing material, the ozone-containing gas at the lower position tends to have a higher ozone content (i.e., be fresher) than the ozone-containing gas at the upper position.

[0053] Therefore, in the above manufacturing method, the free superabsorbent polymer and the superabsorbent polymer in the connected structure, which have a relatively high sedimentation tendency, can be accurately oxidized and decomposed with fresher ozone-containing gas, thereby liberating the pulp fibers that made up the connected structure, and the free pulp fibers, which have a relatively low sedimentation tendency and take a relatively long time to reach the treatment liquid outlet, can be treated over a long period of time with the ozone-containing gas, thereby decomposing the hemicellulose contained in the free pulp fibers.

[0054] Furthermore, as mentioned above, pulp fibers with a relatively low hemicellulose content (pulp fibers with a relatively high cellulose content) have a higher sedimentation tendency than pulp fibers with a relatively high hemicellulose content (pulp fibers with a relatively low cellulose content), and in the above-mentioned manufacturing method, fresher ozone-containing gas comes into contact with pulp fibers with a relatively low hemicellulose content, thereby further decomposing the hemicellulose contained therein. Therefore, the above-mentioned production method can produce a pulp fiber raw material that can be suitably used as a cellulose raw material.

[0055] [Aspect 21] 21. The method of claim 20, wherein the treatment solution is acidic, weakly acidic, or neutral. In the above-mentioned production method, the treatment solution is acidic (specifically, pH greater than 0.0 and less than 3.0, preferably pH 2.5 or greater and less than 3.0), weakly acidic (specifically, pH 3.0 or greater and less than 6.0), or neutral (specifically, pH 6.0 or greater and less than 8.0, preferably pH 6.0 or greater and less than 7.0). Therefore, the superabsorbent polymer to be treated can be inactivated by the acid, or, if the superabsorbent polymer to be treated has already been inactivated, the superabsorbent polymer can be maintained in an inactivated state. This allows the ozone in the ozone-containing gas to remove the superabsorbent polymer that constitutes the connected structure, even when the superabsorbent polymer and pulp fibers form a connected structure, and the ozone in the ozone-containing gas acts on the pulp fibers that constitute the connected structure, thereby reducing the hemicellulose content of the pulp fibers. Therefore, the above-mentioned production method can produce a pulp fiber raw material that can be suitably used as a cellulose raw material.

[0056] [Aspect 22] 22. The method of claim 20 or 21, further comprising, prior to the pulp fiber-containing material providing step, inactivating the superabsorbent polymer with an acid.

[0057] Because the above manufacturing method further includes a predetermined inactivation step, even if the superabsorbent polymer and pulp fibers form a connected structure, the ozone in the ozone-containing gas can remove the superabsorbent polymer that makes up the connected structure immediately after the pulp fiber-containing material containing the superabsorbent polymer and pulp fibers derived from used sanitary products is supplied to the treatment tank, and the ozone in the ozone-containing gas can act on the pulp fibers that make up the connected structure, reducing the hemicellulose content of the pulp fibers. Therefore, the above-mentioned production method can produce a pulp fiber raw material that can be suitably used as a cellulose raw material.

[0058] [Aspect 23] 23. The method of claim 22, wherein the acid is an acid capable of forming a complex with a metal ion contained in feces.

[0059] In the above-described production method, the acid is capable of forming a complex with the metal ions contained in the excrement, so that the produced pulp fiber raw material is less likely to contain metal ions. Therefore, in the process of using the pulp fiber raw material from the pulp fiber raw material, the metal ions and their precipitates are less likely to damage the equipment used in the process of using the pulp fiber raw material and are less likely to inhibit the pulp fiber raw material from being pulverized.

[0060] Hereinafter, a method for producing a pulp fiber raw material from pulp fibers to be treated (hereinafter, sometimes simply referred to as a "method for producing a pulp fiber raw material") will be described. The pulp fibers to be treated are not particularly limited as long as they are pulp fibers, and examples thereof include unused pulp fibers (e.g., virgin pulp fibers) and used pulp fibers (e.g., pulp fibers derived from used sanitary products).

[0061] The above-mentioned used sanitary products are sanitary products that have been used by a user, and include sanitary products that have absorbed the user's liquid excrement, sanitary products that have been used but have not absorbed excrement, and sanitary products that have been discarded unused.

[0062] In this specification, the term "to be treated" in the term "pulp fiber to be treated" is a modifier used to distinguish between pulp fiber before treatment and pulp fiber raw material after treatment, and has no other meaning. Furthermore, in this specification, the "pulp fibers to be treated" refers to embodiments of used pulp fibers, particularly pulp fibers derived from used sanitary products, and in this context, the "pulp fibers to be treated" may be simply referred to as "pulp fibers."

[0063] An example of the configuration of a sanitary product will be described. The sanitary product includes, for example, a liquid-permeable sheet, a liquid-impermeable sheet, and an absorbent disposed between the liquid-permeable sheet and the liquid-impermeable sheet. Examples of sanitary products include disposable diapers, urine absorption pads, sanitary napkins, bed sheets, and pet sheets.

[0064] Examples of constituent members of the liquid-permeable sheet include nonwoven fabrics or films, and specific examples thereof include liquid-permeable nonwoven fabrics, synthetic resin films having liquid-permeable holes, composite sheets thereof, etc. Examples of constituent members of the liquid-impermeable sheet include nonwoven fabrics or films, and specific examples thereof include liquid-impermeable nonwoven fabrics, liquid-impermeable synthetic resin films, composite sheets thereof, etc.

[0065] Constituent components of the absorbent body include an absorbent core (e.g., pulp fibers and superabsorbent polymers) and a core wrap. There are no particular limitations on the pulp fibers as long as they can be used in sanitary products, and examples of such fibers include cellulosic fibers. Examples of cellulosic fibers include wood pulp (e.g., softwood pulp, hardwood pulp), crosslinked pulp, and non-wood pulp. There are no particular limitations on the superabsorbent polymer (SAP) as long as they can be used in sanitary products, and examples of such polymers include polyacrylates, polysulfonates, and maleic anhydrides.

[0066] One side and the other side of the absorbent body are bonded to a liquid-permeable sheet and a liquid-impermeable sheet, respectively, via an adhesive. In plan view, the portion (peripheral portion) of the liquid-permeable sheet that extends outward from the absorbent body so as to surround the absorbent body is bonded to the portion (peripheral portion) of the liquid-impermeable sheet that extends outward from the absorbent body so as to surround the absorbent body via an adhesive. Thus, the absorbent body is enclosed within the bonded body of the liquid-permeable sheet and the liquid-impermeable sheet. The adhesive is not particularly limited as long as it is usable for sanitary products and its bonding strength is reduced by softening or the like in hot water, as described below, and examples thereof include hot-melt adhesives. Examples of hot-melt adhesives include pressure-sensitive adhesives or heat-sensitive adhesives that are mainly based on rubbers such as styrene-ethylene-butadiene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or olefins such as polyethylene.

[0067] Fig. 1 is a flowchart showing a material separation method for separating used sanitary products into their constituent materials. This material separation method separates used sanitary products into film, nonwoven fabric, pulp fiber, and superabsorbent polymer. This material separation method includes a pretreatment step S11, a decomposition step S12, and a separation step S13. In the pretreatment step S11, the used sanitary product is swelled with water. In the decomposition step S12, the swollen used sanitary product is subjected to physical impact to decompose the used sanitary product into a film, nonwoven fabric, core wrap, etc., and an absorbent core (e.g., pulp fiber and superabsorbent polymer). In the separation step S13, the film, nonwoven fabric, pulp fiber, and superabsorbent polymer are separated.

[0068] If a mixture of pulp fibers and superabsorbent polymers (pulp fiber-containing material) has been obtained in advance by some method, the pretreatment step S11, decomposition step S12, and separation step S13, which are steps prior to the method for producing pulp fibers after ozone treatment, are not required. Each step will be described below.

[0069] In the pretreatment step S11, multiple used sanitary products are left in the state they were in when collected from the outside, i.e., without being destroyed, cut, or otherwise broken, and if they are rolled or folded, left in that state, and without inactivating the superabsorbent polymer in the absorbent body, and are allowed to absorb water and swell. In this embodiment, the used sanitary products are allowed to absorb warm water and swell, or the water absorbed after absorbing and swelling water is heated to turn it into warm water. Warm water refers to water at a temperature higher than room temperature (20°C ± 15°C (5 to 35°C): JIS Z 8703).

[0070] Typically, the amount of liquid excrement actually absorbed by used sanitary products is much smaller than the maximum absorption capacity of the sanitary products (e.g., approximately 10 to 20% by mass of the maximum absorption capacity). In this embodiment, in the pretreatment step S11, used sanitary products are immersed in warm water to absorb water up to an amount close to the maximum absorption capacity of the used sanitary products (e.g., 80% by mass or more of the maximum absorption capacity). Alternatively, used sanitary products are immersed in room-temperature water to absorb water up to an amount close to the maximum absorption capacity of the used sanitary products, and then the entire used sanitary products are heated to the temperature of the warm water. This allows the used sanitary products to be highly expanded in warm or room-temperature water (hereinafter simply referred to as "warm water"). As a result, very high internal pressure is generated in the used sanitary products. The purpose of using warm water is mainly to weaken the adhesive strength of the adhesive, as described below.

[0071] Here, when a used sanitary product is initially rolled or folded with the liquid-impermeable sheet facing outward (with the liquid-permeable sheet hidden inside), it is immersed in warm water, whereby the absorbent body of the used sanitary product absorbs the warm water and expands. As a result, the internal pressure of the used sanitary product increases, and a force acts on the used sanitary product to open outward, causing the rolled or folded used sanitary product to open outward and become roughly flat. In other words, the used sanitary product can be laid out flat in the warm water. At this time, the absorbent body of the used sanitary product has absorbed a large amount of warm water and is so swelled that its surface, i.e., either the liquid-permeable sheet or the liquid-impermeable sheet enveloping the absorbent body, is in a state that could easily burst. In other words, the pretreatment step S11 can bring the used sanitary product to a state where either one of its surfaces is likely to tear or tear. Furthermore, if a used sanitary product is initially laid out flat, some part of the surface may easily burst if left in that state, which is not the case if the used sanitary product is broken or otherwise damaged.

[0072] Furthermore, when a used sanitary product is immersed in and / or absorbs warm water, the adhesive (e.g., hot melt adhesive) used to bond the components together can be softened by the heat of the warm water, thereby reducing the adhesive's bonding strength. For example, the adhesive bonding the peripheral edge of the liquid-permeable sheet to the peripheral edge of the liquid-impermeable sheet can be softened by the heat of the warm water, thereby reducing the adhesive's bonding strength. Furthermore, the adhesive bonding the liquid-permeable sheet to the absorbent and the adhesive bonding the liquid-impermeable sheet to the absorbent can be softened by the heat of the warm water, thereby reducing the adhesive's bonding strength.

[0073] In this way, in the pre-treatment step S11, the expansion of the absorbent body of the used sanitary product can cause some part of the surface of the used sanitary product to be in a state where it is about to burst and the adhesive strength is reduced. By putting the used sanitary product in this state, the used sanitary product can be reliably disassembled in the disassembly step described below.

[0074] The temperature of the hot water in the pretreatment step S11 is not particularly limited as long as it can soften the adhesive on the used sanitary products, but examples include 60°C or higher, and preferably 70°C or higher and 98°C or lower. By setting the hot water temperature to 70°C or higher, the heat of the hot water can further soften the adhesive that bonds the components, thereby further reducing the adhesive's bonding strength. By setting the hot water temperature to 98°C or lower, the hot water remains in a liquid state, allowing the used sanitary products to more reliably absorb the hot water. The expansion of the absorbent and the heat of the hot water can more reliably cause the surface of the used sanitary products to burst and the adhesive's bonding strength to be reduced. The temperature is measured either by measuring the temperature of the hot water in which the used sanitary products are immersed, or by measuring the temperature (with the tip of a temperature sensor inserted) 5 mm inside the surface of a used sanitary product that has absorbed water close to its maximum absorption capacity.

[0075] Furthermore, sterilization of the constituent materials is extremely important when reusing used sanitary products. Therefore, setting the temperature of the hot water to 70°C or higher is preferable because it can also sterilize (disinfect) the used sanitary products.

[0076] The treatment time in the pretreatment step S11, i.e., the time for which the used sanitary goods are immersed in warm water, is not particularly limited as long as it allows the absorbent body of the used sanitary goods to expand, but is, for example, 2 to 60 minutes, preferably 4 to 30 minutes. If the time is too short, the absorbent body will not expand sufficiently, and if it is too long, time will be wasted and treatment costs will unnecessarily increase.

[0077] The amount of hot water absorbed by the absorbent body in the pretreatment step S11 is not particularly limited as long as it can expand to the extent that the used sanitary goods can be decomposed in the decomposition step described below, but it can be, for example, 80% by mass or more of the maximum absorption capacity of the used sanitary goods, and preferably 90% by mass or more. This allows the used sanitary goods to be fully expanded with water. As a result, extremely high internal pressure can be generated in the absorbent body of the used sanitary goods.

[0078] However, the maximum absorption amount is measured by the following procedure. (1) Dry unused sanitary products in an atmosphere of 100°C or higher, and measure the mass of the sanitary products. (2) If the sanitary product contains elastic material (e.g., elastic parts around the legs, waist, etc.) that can form pockets that make it difficult for water to reach the absorbent body, the sanitary product can be flattened by making cuts in the elastic parts. (3) Immerse the sanitary product with the liquid-permeable sheet facing down in a water bath filled with sufficient tap water and leave it for 30 minutes. (4) After leaving it, the sanitary product is placed on a net with the liquid-permeable sheet facing downwards, and after draining for 20 minutes, the mass of the sanitary product is measured. The difference in mass before and after immersion in tap water is defined as the maximum absorption amount.

[0079] Next, in the decomposition process S12, physical impact is applied to the multiple used sanitary products that have been unfolded and swollen in the pretreatment process S11, and the multiple used sanitary products are decomposed into a film (liquid-impermeable sheet), a nonwoven fabric (liquid-permeable sheet), a core wrap, and an absorbent core (e.g., an absorbent body and a superabsorbent polymer).

[0080] The used sanitary products are flattened and unfolded in the pretreatment step S11, and some parts of their surface are prone to bursting due to expansion. In this embodiment, the adhesive strength is reduced, particularly due to the heat of the hot water. Therefore, in the disassembly step S12, physical impact is applied to the used sanitary products in this state, causing some parts of the surface, particularly the bonded part between the liquid-permeable sheet (nonwoven fabric) and the liquid-impermeable sheet (film), where the adhesive strength has been reduced, to burst. This allows the bonded part to be torn (peeled off). There are no particular limitations on the physical impact, but examples include hitting the used sanitary products against a surface made of a harder material than the used sanitary products, or pressing the used sanitary products from both sides while sandwiching and passing them between a pair of rolls arranged facing each other.

[0081] In this embodiment, the disassembly step S12 includes the steps of: placing multiple swollen used sanitary products into the bottom of a rotating drum with a horizontal rotation axis; and rotating the rotating drum around the rotation axis to lift the multiple used sanitary products to the top of the rotating drum and slam them against the bottom. This allows for stable, continuous, and easy physical impact on the multiple used sanitary products. An example of a rotating drum is the rotating drum of a horizontal washing machine. Therefore, the disassembly step S12 can be performed using an existing horizontal washing machine (e.g., ECO-22B, manufactured by Inamoto Seisakusho Co., Ltd.). The size of the rotating drum is not particularly limited as long as the above-mentioned impact can be realized, and examples of the inner diameter and depth include 50 to 150 cm and 30 to 120 cm. The rotation speed of the rotating drum is not particularly limited as long as the above-mentioned impact can be realized, and examples include 30 to 100 revolutions per minute.

[0082] Furthermore, the warm water absorbed into the used sanitary products keeps the temperature of the used sanitary products relatively high. However, from the viewpoint of preventing the temperature drop of the adhesive and maintaining the sterilization effect, the temperature of the atmosphere inside the rotating drum is preferably 70°C or higher, more preferably 75°C or higher. From the viewpoint of handling the used sanitary products, the temperature inside the rotating drum is preferably 98°C or lower, more preferably 90°C or lower. It is preferable that the amount of water in the rotating drum is as small as possible, and preferably so small that the used sanitary products do not fall below the water level at least at the bottom. If the used sanitary products fall below the water level, impacts on the used sanitary products will be absorbed by the water, making it difficult to apply the desired impact to the used sanitary products. The time for which the rotating drum is rotated is not particularly limited as long as it is possible to disassemble the liquid-permeable sheet, liquid-impermeable sheet, core wrap, etc. from the absorbent core, but is, for example, 2 to 40 minutes, preferably 4 to 20 minutes.

[0083] When a used sanitary product is subjected to a physical impact, the joint between the liquid-permeable sheet (nonwoven fabric) and the liquid-impermeable sheet (film) bursts and tears. At the same time, the internal pressure of the absorbent body causes the absorbent core (e.g., pulp fibers and superabsorbent polymer) inside the used sanitary product to eject (fly out) through the tear. This allows the used sanitary product to be more reliably decomposed into the liquid-permeable sheet (nonwoven fabric), liquid-impermeable sheet (film), core wrap, etc., and the absorbent core (e.g., a pulp fiber-containing material containing pulp fibers and superabsorbent polymer).

[0084] Next, in the separation step S13, the absorbent core (e.g., pulp fibers and superabsorbent polymer) is separated from the plurality of films (liquid-impermeable sheets), the plurality of nonwoven fabrics (liquid-permeable sheets), the core wrap, etc. However, the nonwoven fabrics may remain bonded to the films. The separation method is not particularly limited, but examples include a method using a sieve that allows the absorbent core to pass but not the liquid-permeable sheets, liquid-impermeable sheets, core wrap, etc.

[0085] In this embodiment, the separation step S13 may include an inactivation step S31 in which the superabsorbent polymer is inactivated with an aqueous solution containing an inactivating agent before separating the film, nonwoven fabric, core wrap, etc. from the absorbent core, and a first separation step S32 in which the film and nonwoven fabric are separated from a mixture containing pulp fibers, inactivated superabsorbent polymer, and wastewater discharged from the superabsorbent polymer due to inactivation.

[0086] In the inactivation step S31, before the first separation step S32, the liquid-permeable sheet (nonwoven fabric), the liquid-impermeable sheet (film), and the absorbent (pulp fibers and superabsorbent polymer) are immersed in an aqueous solution containing an inactivating agent capable of inactivating the superabsorbent polymer. This makes it possible to inactivate the superabsorbent polymer attached to the liquid-permeable sheet, the liquid-impermeable sheet, and the pulp fibers. This makes it possible to convert the superabsorbent polymer, which is in a high-viscosity state before inactivation, into a superabsorbent polymer in a low-viscosity state by dehydration through inactivation.

[0087] Here, the inactivating agent is not particularly limited, but examples thereof include acids (e.g., inorganic acids and organic acids), lime, calcium chloride, magnesium sulfate, magnesium chloride, aluminum sulfate, and aluminum chloride. The above-mentioned acids are preferred because they do not leave ash residue on the pulp fibers. When an acid is used as the inactivating agent, the pH is preferably 2.5 or less, and more preferably 1.3 to 2.4. If the pH is too high, the water absorption capacity of the superabsorbent polymer cannot be sufficiently reduced. Furthermore, the sterilizing ability may be reduced. If the pH is too low, there is a risk of corrosion of equipment, and a large amount of alkaline chemicals may be required for neutralization during wastewater treatment.

[0088] Examples of the inorganic acid include sulfuric acid, hydrochloric acid, and nitric acid, with sulfuric acid being preferred from the standpoint of not containing chlorine and cost. On the other hand, examples of the organic acid include citric acid, tartaric acid, glycolic acid, malic acid, succinic acid, acetic acid, and ascorbic acid, with acids capable of forming complexes with metal ions contained in excrement, such as hydroxycarbonate-based organic acids such as citric acid, tartaric acid, and gluconic acid, being particularly preferred. Examples of metal ions contained in excrement include calcium ions. This is because the chelating effect of acids capable of forming complexes with metal ions contained in excrement traps and removes metal ions in excrement. Furthermore, citric acid is expected to have a high stain removal effect due to its cleaning effect. Since the pH changes depending on the water temperature, the pH in this disclosure refers to the pH measured at an aqueous solution temperature of 20°C.

[0089] The treatment temperature of the inactivation step S31, i.e., the temperature of the aqueous solution containing the inactivating agent, is not particularly limited as long as the inactivation reaction proceeds. The treatment temperature may be room temperature or higher, for example, 15 to 30°C. The treatment time of the inactivation step S31, i.e., the time for which the liquid-permeable sheet, the liquid-impermeable sheet, and the absorbent are immersed in the aqueous solution containing the inactivating agent, is not particularly limited as long as the superabsorbent polymer is inactivated and dehydrated, but is, for example, 2 to 60 minutes, preferably 5 to 30 minutes. The amount of the aqueous solution in the inactivation step S31, i.e., the amount of the aqueous solution containing the inactivating agent, is not particularly limited as long as the inactivation reaction proceeds. For example, the amount of the aqueous solution is preferably 300 to 3,000 parts by mass, more preferably 500 to 2,500 parts by mass, and even more preferably 1,000 to 2,000 parts by mass, per 100 parts by mass of the used sanitary goods.

[0090] In the first separation step S32, the liquid-permeable sheet (nonwoven fabric), the liquid-impermeable sheet (film), and the core wrap are separated from a mixture containing pulp fibers, the inactivated superabsorbent polymer, and wastewater discharged from the superabsorbent polymer by inactivation. Note that the wastewater is wastewater containing the water released from the superabsorbent polymer by dehydration with an aqueous solution containing an inactivating agent in the inactivation step S31, i.e., liquid derived from excrement and water derived from warm water.

[0091] In the first separation step S32, the method for separating the liquid-permeable sheet and liquid-impermeable sheet from the pulp fibers, superabsorbent polymer, and wastewater (pulp fiber-containing material) is not particularly limited. For example, the products (liquid-permeable sheet, liquid-impermeable sheet, pulp fibers, superabsorbent polymer, wastewater, etc.) generated in the inactivation step are discharged through a screen with a mesh size of 5 to 100 mm, preferably 10 to 60 mm. This allows the pulp fibers, superabsorbent polymer, and wastewater to be discharged, while the liquid-permeable sheet and liquid-impermeable sheet remain on the screen, allowing these products to be separated. Note that other large objects such as nonwoven fabrics and films may remain on the screen. In particular, because the superabsorbent polymer is in a highly viscous state before inactivation, it is not particularly easy to separate the superabsorbent polymer attached to the liquid-permeable sheet, liquid-impermeable sheet, and pulp fibers. However, after inactivation, the superabsorbent polymer becomes low in viscosity due to dehydration, and the superabsorbent polymer attached to the liquid-permeable sheet, the liquid-impermeable sheet, and the pulp fibers can be easily separated from the liquid-permeable sheet, the liquid-impermeable sheet, and the pulp fibers. Therefore, the components of the sanitary goods can be efficiently separated and recovered.

[0092] In this embodiment, the separation step S13 may further include a second separation step S33 of removing the adhesive at the joints between the film and other members using a solvent that dissolves the adhesive at the joints. In this embodiment, the adhesive at each joint between the film, nonwoven fabric, and absorbent body is removed using a solvent that dissolves the adhesive at each joint.

[0093] In the second separation step S33, the adhesive at the joint between the film (liquid-impermeable sheet) and other components (such as the nonwoven fabric of the liquid-permeable sheet, the liquid-permeable sheet, and the absorbent remaining on the surface of the liquid-impermeable sheet) is removed using a solvent. This allows the film and other components to be separated from each other while maintaining their original shapes, without tearing or the like. This makes it possible to efficiently recover components such as films for sanitary products. Furthermore, since the film can be separated from other components without leaving any adhesive on the film, the film can be reused as a high-purity resin. This prevents the adhesive from having a negative effect when the film is reused. The same applies to nonwoven fabrics as to films.

[0094] The solvent used in the second separation step S33 is not particularly limited as long as it can dissolve the adhesive, but examples include terpenes containing at least one of terpene hydrocarbons, terpene aldehydes, and terpene ketones. In this step, an aqueous solution containing terpenes is used, and the terpene concentration in the aqueous solution is, for example, 0.05% by mass or more and 2% by mass or less. It is preferably 0.075 to 1% by mass. If the terpene concentration is too low, it may not be possible to dissolve the adhesive at the bonded portion. If the terpene concentration is too high, costs may increase. Furthermore, terpenes not only dissolve adhesives such as hot-melt adhesives, but also have the effect of cleaning oil stains. Therefore, for example, if a component of a sanitary product, such as a liquid-impermeable sheet, is printed, terpenes can also decompose and remove the printing ink.

[0095] Examples of terpene hydrocarbons include myrcene, limonene, pinene, camphor, sapinene, phellandrene, para-cymene, ocimene, terpinene, carene, zingiberene, caryophyllene, bisabolene, and cedrene. Among these, limonene, pinene, terpinene, and carene are preferred. Examples of terpene aldehydes include citronellal, citral, cyclocitral, safranal, phellandral, perillaldehyde, geranial, and neral. Examples of terpene ketones include camphor and tsuyoshi. Among terpenes, terpene hydrocarbons are preferred, with limonene being particularly preferred. There are three types of limonene: d-limonene, l-limonene, and dipentene (dl-limonene), and all of these can be used preferably. Terpenes can be used alone or in combination of two or more.

[0096] The treatment temperature in the second separation step S33, i.e., the temperature of the aqueous solution containing a solvent, is not particularly limited, as long as the adhesive dissolves and the used sanitary goods are decomposed into their constituent parts. The treatment temperature may be room temperature or higher, for example, 15 to 30°C. The treatment time in the second separation step S33, i.e., the time for which the liquid-permeable sheet, the liquid-impermeable sheet, and the absorbent are immersed in the aqueous solution containing a solvent, is not particularly limited, as long as the adhesive dissolves and the used sanitary goods are decomposed into their constituent parts. The treatment time is, for example, 2 to 60 minutes, and preferably 5 to 30 minutes. The amount of the aqueous solution in the second separation step S33, i.e., the amount of the aqueous solution containing a solvent, is not particularly limited, as long as the adhesive dissolves and the used sanitary goods are decomposed into their constituent parts. The amount of the aqueous solution is, for example, preferably 300 to 3,000 parts by mass, and more preferably 500 to 2,500 parts by mass, per 100 parts by mass of the used sanitary goods. By the second separation step S33, the amount of adhesive remaining on the film, nonwoven fabric, absorbent body, etc. can be reduced to 1% by mass or less relative to the film, nonwoven fabric, absorbent body, etc.

[0097] In another preferred embodiment of the present invention, the second separation step S33 may be performed in conjunction with the inactivation step S31. That is, the adhesive attached to the liquid-permeable sheet, the liquid-impermeable sheet, and the pulp fibers may be dissolved while inactivating the superabsorbent polymer attached to the liquid-permeable sheet, the liquid-impermeable sheet, and the pulp fibers. In this case, the aqueous solution in which the liquid-permeable sheet, the liquid-impermeable sheet, the pulp fibers, and the superabsorbent polymer are immersed is an aqueous solution containing both an inactivating agent and a solvent. As a result, in the inactivation step S31, the liquid-impermeable sheet (film), the liquid-permeable sheet (nonwoven fabric), and the absorbent body (pulp fibers and superabsorbent polymer) can be substantially separated in the aqueous solution. Then, in the subsequent first separation step, the liquid-impermeable sheet (film), the liquid-permeable sheet (nonwoven fabric), and the absorbent body (pulp fibers and superabsorbent polymer) can be separated, and the second separation step S33 can be omitted. In this case, the liquid-impermeable sheet (film) and the liquid-permeable sheet (nonwoven fabric) are substantially separated by removing the adhesive.

[0098] In this embodiment, the separation step S13 may further include a first drying step S34 in which the film is dried in an atmosphere or with hot air at a temperature higher than room temperature to remove the solvent after the step of removing the adhesive from the bonded portions. In this embodiment, the nonwoven fabric is also dried in this step.

[0099] Sterilization is extremely important in the reuse of used sanitary products. In the first drying step S34, the separated film (liquid-impermeable sheet) and nonwoven fabric (liquid-permeable sheet) are dried in a high-temperature atmosphere or with hot air or the like. The drying temperature is, for example, 105 to 210°C, and preferably 110 to 190°C. The drying time varies depending on the drying temperature, but is, for example, 10 to 120 minutes, and preferably 15 to 100 minutes. This not only evaporates and removes the solvent remaining on the surfaces of the film and nonwoven fabric, but also sterilizes the film and nonwoven fabric with a high-temperature atmosphere or hot air or the like. This makes it possible to achieve the effect of sterilization (disinfection) while removing the solvent.

[0100] Meanwhile, in this embodiment, the separation step S13 may include a third separation step S35 in which pulp fibers are separated from the separated mixture. In the third separation step S35, the method for separating the pulp fibers from the separated mixture (including pulp fibers, superabsorbent polymer, and wastewater) is not particularly limited. For example, the separated mixture is discharged while passing through a screen with a mesh size of 0.1 to 4 mm, preferably 0.15 to 2 mm. This allows the superabsorbent polymer and wastewater to be discharged, while the pulp fibers (mainly the superabsorbent polymer remaining on the surface) remain on the screen, thereby separating the pulp fibers from the mixture. Although this pulp fiber contains many impurities, it can be reused in this state depending on the application. The separated pulp fibers have superabsorbent polymer attached to them, and the separated pulp fibers and the superabsorbent polymer attached to the pulp fibers are mixed with water in a predetermined ratio and proceed to the ozone treatment step S36 as a pulp fiber-containing material.

[0101] In this embodiment, the separation step S13 includes an ozone treatment step S36 in which the pulp fiber-containing material, which includes superabsorbent polymers, pulp fibers, their connected structures, and water, is treated with an aqueous solution containing ozone to reduce the molecular weight of the superabsorbent polymers attached to the pulp fibers, solubilize them, and remove them.

[0102] In used sanitary products, in absorbents containing pulp fibers and superabsorbent polymers, (i) as the superabsorbent polymer absorbs liquids such as bodily fluids, it swells and entangles the pulp fibers, and (ii) the swollen superabsorbent polymers entangle the pulp fibers, causing gel blocking, and in many cases, multiple superabsorbent polymers and multiple pulp fibers form connected structures. The pulp fiber-containing material includes not only free pulp fibers and free superabsorbent polymers, but also connected structures composed of multiple superabsorbent polymers and multiple pulp fibers.

[0103] In the ozone treatment step S36, the superabsorbent polymer contained in the pulp fiber-containing material (treatment liquid) is oxidatively decomposed by the ozone in the aqueous solution, and solubilized in the aqueous solution, thereby being removed. The state in which the superabsorbent polymer is oxidatively decomposed and solubilized in an aqueous solution refers to the state in which the superabsorbent polymer and the linked structure pass through a 2 mm screen. This allows impurities such as the superabsorbent polymer to be removed from the pulp fiber-containing material (treatment solution), producing high-purity pulp fibers. Furthermore, ozone treatment can perform secondary sterilization, bleaching, and deodorization of the pulp fibers.

[0104] 2 is a schematic diagram showing an example of the configuration of an apparatus 2 that performs the ozone treatment step S36. The apparatus 2 includes a pulp fiber-containing material storage unit 3 that stores a pulp fiber-containing material 51 containing water, the pulp fibers separated in the third separation step S35, and a superabsorbent polymer, and an ozone treatment unit 4 that oxidatively decomposes the superabsorbent polymer contained in the pulp fiber-containing material 51 and removes it from the pulp fibers.

[0105] The pulp fiber-containing material storage unit 3 includes a pulp fiber-containing material tank 12 and an agitator 13. The pulp fiber-containing material tank 12 stores the pulp fiber-containing material 51 supplied via piping 61. The agitator 13 agitates the pulp fiber-containing material 51 in the pulp fiber-containing material tank 12 so that the pulp fibers and the superabsorbent polymer in the pulp fiber-containing material 51 do not separate from the water and sink to the bottom of the pulp fiber-containing material 51.

[0106] On the other hand, the ozone treatment unit 4 includes a supply pump 21, a treatment tank 31, an ozone supply device 41, a delivery pump 22, and an ozone decomposition device 34. The treatment tank 31 contains an acidic aqueous solution as a treatment liquid 52. The treatment tank 31 is equipped with a pulp fiber-containing material supply port 32, a treatment liquid discharge port 33, and an ozone-containing gas supply port 43. The pulp fiber-containing material supply port 32 is located in the upper part of the treatment tank 31 and supplies the pulp fiber-containing material 51 to the treatment tank 31. The treatment liquid discharge port 33 is located in the lower part of the mixing tank 31 and discharges the treatment liquid 52. The ozone-containing gas supply port 43 is located in the lower part of the mixing tank 31, specifically, above the treatment liquid discharge port 33, and delivers an ozone-containing gas 53 into the treatment tank 31.

[0107] Specifically, the supply pump 21 continuously supplies the pulp fiber-containing material 51 from the pulp fiber-containing material tank 12 through the pulp fiber-containing material supply port 32 into the treatment tank 31 at a first flow rate via the piping 62. The ozone supply device 41 supplies the ozone-containing gas 53 to the treatment tank 31. Examples of the ozone generator 42 of the ozone supply device 41 include the ozone water exposure tester ED-OWX-2 manufactured by Ecodesign Inc. and the ozone generator OS-25V manufactured by Mitsubishi Electric Corporation. The ozone-containing gas 53 is another type of gas containing ozone, such as ozone-containing oxygen gas. The ozone-containing gas supply port 43 is located at a lower portion (preferably the bottom) of the treatment tank 31 and sends the ozone-containing gas 53, which is supplied to the treatment tank 31 through the piping 65, into the treatment tank 31. The ozone-containing gas supply port 43 continuously supplies the ozone-containing gas 53 as a plurality of fine bubbles into the treatment liquid 52 (treatment tank 31) from the bottom to the top. The delivery pump 22 continuously discharges the treatment liquid 52 in the treatment tank 31 through a pipe 63 and from the treatment liquid outlet 33 to the outside of the treatment tank 31 at a second flow rate. The ozone decomposition device 34 receives the ozone-containing gas 53 accumulated in the upper part of the treatment tank 31 through a pipe 64, neutralizes the ozone, and releases it to the outside. Note that the treatment liquid 52 in the treatment tank 31 contains only the treatment liquid 52 before the start of the ozone treatment step S36, and becomes a mixture of the treatment liquid 52 and the pulp fiber-containing material 51 after the start. However, in this embodiment, the liquid in the treatment tank 31, including the mixture of the treatment liquid 52 and the pulp fiber-containing material 51, is referred to as the treatment liquid 52.

[0108] Next, a specific method for the ozone treatment step S36 will be described. The pulp fibers and superabsorbent polymer separated in the third separation step S35 are mixed with water to a preset concentration to form a pulp fiber-containing material 51. The concentration of the pulp fibers in the pulp fiber-containing material 51 is set to a preset concentration when the material is introduced into the treatment tank 31 and mixed with the treatment liquid 52. The pulp fiber-containing material 51 is supplied to the pulp fiber-containing material tank 12 via piping 61 and stored therein. Because the specific gravity of the pulp fibers and superabsorbent polymer is greater than 1, the pulp fiber-containing material 51 is stirred by a stirrer 13 in the pulp fiber-containing material tank 12 to prevent the pulp fibers and superabsorbent polymer from separating from the water.

[0109] The flow rate of the pulp fiber-containing material 51 in the pulp fiber-containing material tank 12 is controlled by the supply pump 21, and the pulp fiber-containing material 51 is continuously supplied at a first flow rate from the pulp fiber-containing material supply port 32 to the treatment tank 31 via the pipe 62. The treatment liquid 52 is an acidic aqueous solution, and has a specific gravity of approximately 1. Therefore, the pulp fibers and the superabsorbent polymer settle from the top to the bottom of the treatment liquid 52.

[0110] On the other hand, the ozone-containing gas 53 generated by the ozone generator 42 is supplied to the treatment tank 31 via the pipe 65 and is released in the form of fine bubbles (for example, microbubbles or nanobubbles) from the ozone-containing gas supply port 43 of the treatment tank 31 into the treatment liquid 52. That is, the ozone-containing gas 53 rises from the bottom to the top of the treatment liquid 52.

[0111] The pulp fibers and superabsorbent polymer moving downward, i.e., descending, and the ozone-containing gas 53 moving upward, i.e., ascending, collide with each other while moving in opposite directions within the treatment liquid 52. The ozone-containing gas 53 then adheres to the pulp fibers and superabsorbent polymer, as well as to the surfaces of the connected structure. The ozone in the ozone-containing gas 53 oxidatively decomposes the free superabsorbent polymer and dissolves it in the treatment liquid 52. As a result, the superabsorbent polymer on the pulp fibers is removed from the pulp fibers. The pulp fibers then descend to the bottom of the treatment tank 31, and the ozone-containing gas 53 escapes into the space above the treatment tank 31.

[0112] Among the free superabsorbent polymer, free pulp fibers, and connected structures, the free superabsorbent polymer, which has relatively low buoyancy, and the connected structure containing the superabsorbent polymer tend to sink more easily than the free pulp fibers, which have relatively high buoyancy. On the other hand, since the ozone-containing gas rises while consuming ozone and treating the superabsorbent polymer and pulp fibers, the ozone-containing gas at a lower position tends to have a higher ozone content (i.e., be fresher) than the ozone-containing gas at an upper position.

[0113] Therefore, the free superabsorbent polymer and the linked structure, which move downward relatively quickly, can be oxidatively decomposed by fresher ozone-containing gas to form free pulp fibers. On the other hand, the free pulp fibers move downward relatively slowly, so the ozone-containing gas can treat the free pulp fibers over time. Specifically, the ozone in the ozone-containing gas collides with the pulp fibers while facing them, thereby decomposing hemicellulose, lignin, and the like in the pulp fibers.

[0114] Thereafter, the treatment liquid 52 (containing pulp fibers after ozone treatment) at the bottom of the treatment tank 31 is continuously discharged at a second flow rate from the treatment liquid outlet 33 of the treatment tank 31 to the outside of the treatment tank 31 via piping 63 by flow rate control of the delivery pump 22. The ozone in the ozone-containing gas 53 accumulated in the upper part of the treatment tank 31 is detoxified by the ozone decomposition device 34 and released to the outside.

[0115] In this way, the pulp fiber-containing material 51 is continuously supplied into the treatment tank 31 from the top of the treatment tank 31 at a first flow rate, and the treatment liquid 52 is continuously discharged from the lower part (bottom) of the treatment tank 31 to the outside of the treatment tank 31 at a second flow rate. This makes it possible to forcibly generate a continuous and stable flow of fluid (including pulp fibers) from the top to the bottom within the treatment tank 31.

[0116] The treatment liquid 52 discharged from the treatment tank 31 contains ozone-treated pulp fibers from which the superabsorbent polymer, hemicellulose, lignin, etc. have been removed, and also contains low-molecular-weight organic matter produced by oxidative decomposition of the superabsorbent polymer. The ozone-treated pulp fibers are recovered in a process downstream of the delivery pump 22, for example, in the fourth separation process S37 described below.

[0117] In this method, a pulp fiber-containing material 51 containing at least pulp fibers and a superabsorbent polymer is continuously supplied at a first flow rate into a treatment tank 31 containing a treatment liquid 52 capable of dissolving the superabsorbent polymer, while a treatment liquid 52 containing post-ozone-treated pulp fibers from which the superabsorbent polymer has been removed and containing low-molecular-weight organic matter produced by oxidative decomposition of the superabsorbent polymer is continuously discharged at a second flow rate out of the treatment tank 31. This configuration makes it possible to forcibly generate a continuous and stable flow of fluid (including pulp fibers) from a pulp fiber-containing material supply port 32 that supplies the pulp fiber-containing material 51 in the treatment tank 31 toward a treatment liquid outlet 33 that discharges the treatment liquid 52. This fluid flow, i.e., a water flow, can treat (solubilize) the superabsorbent polymer and treat the pulp fibers, even when the treatment amounts of the pulp fibers and superabsorbent polymer are large.

[0118] Here, it is preferable that the first flow rate and the second flow rate are the same. By making the first flow rate and the second flow rate the same, the amount of the processing liquid 52 in the processing tank 31 can be kept constant, enabling stable, continuous processing. However, as long as the amount of the processing liquid 52 in the processing tank 31 can be kept substantially constant, i.e., the amount of the processing liquid 52 in the processing tank 31 does not increase or decrease significantly, the first flow rate and the second flow rate may fluctuate over time. In other words, the first flow rate and the second flow rate do not need to be completely the same all the time, but only need to be substantially the same on average over time. Here, "substantially the same" means that the difference between the first flow rate and the second flow rate is within 5% by mass. In this case, stable, continuous processing is also possible.

[0119] When ozone-containing gas 53 is supplied to treatment liquid 52, the ozone concentration in treatment liquid 52 is not particularly limited as long as it is a concentration that can oxidatively decompose the superabsorbent polymer, but may be, for example, 1 to 50 ppm by mass, preferably 2 to 40 ppm by mass, and more preferably 3 to 30 ppm by mass. If the ozone concentration in treatment liquid 52 is too low, the superabsorbent polymer may not be completely solubilized, and the superabsorbent polymer may remain in the pulp fibers. Conversely, if the ozone concentration in treatment liquid 52 is too high, the oxidizing power increases, which may damage the pulp fibers and may also pose safety issues. The ozone treatment temperature is not particularly limited as long as it is a temperature that can oxidatively decompose the superabsorbent polymer, but may be, for example, room temperature or higher.

[0120] The concentration of ozone in the treatment liquid 52 (aqueous solution) is measured by the following method. (1) 85 mL of the treatment liquid 52 in which ozone has been dissolved is placed in a 100 mL measuring cylinder containing about 0.15 g of potassium iodide and 5 mL of 10% citric acid solution, and the mixture is allowed to react. (2) After the reaction, the treated liquid 52 is transferred to a 200 mL Erlenmeyer flask, and the starch solution is added to the Erlenmeyer flask to color it purple. Then, the solution is titrated with 0.01 mol / L sodium thiosulfate while stirring until it becomes colorless, and the amount added, a (mL), is recorded. (3) Calculate the concentration of ozone in the aqueous solution using the following formula: The concentration of ozone in aqueous solution (ppm by mass) was calculated using the following formula: Ozone concentration in aqueous solution (ppm by mass) = a(mL) × 0.24 × 0.85(mL) It is calculated as follows.

[0121] The ozone concentration in the ozone-containing gas 53 is preferably 40 to 200 g / m 3 and more preferably 80 to 200 g / m 3 and more preferably 100 to 200 g / m 3If the ozone concentration in the ozone-containing gas 53 is too low, the superabsorbent polymer may not be completely solubilized, and some of the superabsorbent polymer may remain. If the concentration in the ozone-containing gas 53 is too high, it may damage the pulp fibers, reduce safety, and increase production costs. The ozone concentration in the ozone-containing gas 53 can be measured, for example, by an ultraviolet absorption ozone concentration meter (for example, Ozone Monitor OZM-5000G manufactured by Ecodesign Co., Ltd.).

[0122] The concentration of the pulp fiber-containing material (e.g., pulp fibers and superabsorbent polymer) in the treatment liquid 52 is not particularly limited as long as it is a concentration that allows the superabsorbent polymer to be oxidatively decomposed by the ozone in the treatment liquid 52, but may be, for example, 0.1 to 20% by mass, preferably 0.2 to 10% by mass, and more preferably 0.3 to 5% by mass. If the pulp fiber concentration is too high, the superabsorbent polymer may not be completely solubilized, and the superabsorbent polymer may remain in the pulp fibers. Conversely, if the pulp fiber concentration is too low, the oxidizing power increases, which may damage the pulp fibers and may also pose safety issues. The concentrations of the pulp fibers and superabsorbent polymer in the pulp fiber-containing material 51 are appropriately set based on the concentrations of the pulp fibers and superabsorbent polymer in the treatment liquid 52 and the amount of the treatment liquid 52.

[0123] When ozone is supplied to a treatment liquid 52 containing pulp fibers and a superabsorbent polymer, the treatment liquid 52 is preferably acidic (specifically, a pH greater than 0.0 and less than 3.0, preferably a pH greater than 2.5 and less than 3.0), weakly acidic (specifically, a pH greater than 3.0 and less than 6.0), or neutral (specifically, a pH greater than 6.0 and less than 8.0, preferably a pH greater than 6.0 and less than 7.0). More preferably, the pH of the treatment liquid 52 is greater than 0.0 and less than 7.0, and even more preferably 2.5 to 6.0. Treatment under an acidic condition suppresses ozone deactivation, improves the oxidative decomposition effect of the superabsorbent polymer by ozone, and enables the superabsorbent polymer to be oxidatively decomposed in a short period of time. To maintain the pH of the treatment liquid, the pH of the pulp fiber-containing material 51 may be adjusted to be the same as that of the treatment liquid 52 before being supplied to the treatment tank 31. Alternatively, the pH of the processing solution 52 may be monitored by a pH sensor, and when the pH fluctuates toward the neutral side, a predetermined acidic solution may be added to the processing solution 52 in an amount corresponding to the fluctuation range.

[0124] The amount of treatment liquid 52 (including pulp fiber-containing material 51) in treatment tank 31 is not particularly limited as long as it is an amount that can oxidatively decompose the superabsorbent polymer. However, it is preferable that the volume V (unit: L) of treatment liquid 52 in treatment tank 31 and the mass W (unit: kg) of pulp fiber satisfy 30≦V / W≦1000. More preferably, it is 50≦V / W≦400, and even more preferably, it is 100≦V / W≦200. If V / W is too small, the superabsorbent polymer may not be completely solubilized, and some superabsorbent polymer may remain. If V / W is too large, it may increase production costs. The volume V of treatment tank 31 is not particularly limited, but may be, for example, 50 to 80 L.

[0125] Flow rate of ozone-containing gas R O (unit: L / min) and the volume V (unit: L) of the treatment solution 52 in the treatment tank 31 are 0.01≦R O It is preferable that the relationship between R and V is satisfied. O / V≦1.0, and more preferably 0.06≦R O / V≦0.75.O If / V is too small, the superabsorbent polymer may not be completely solubilized, and the superabsorbent polymer may remain in the pulp fibers. O If the flow rate R of the ozone-containing gas is too high, it may cause damage to the pulp fibers, reduce safety, and increase production costs. O There are no particular limitations on the flow rate, but examples include 3 to 6 L / min.

[0126] The time that the pulp fiber-containing material remains in the treatment tank 31, i.e., the time that the pulp fiber-containing material is treated in the treatment liquid 52 (hereinafter also referred to as "tank treatment time"), varies depending on the purpose, such as decomposition of hemicellulose in the pulp fibers, decomposition of lignin, or oxidative decomposition of the superabsorbent polymer, and is not particularly limited. The tank treatment time may be shorter if the ozone concentration of the treatment liquid 52 is high, but longer if the ozone concentration of the treatment liquid 52 is low. The tank treatment time is, for example, 15 to 180 minutes, and preferably 30 to 60 minutes.

[0127] The ozone-containing gas and the pulp fiber-containing material are measured by the ozone concentration (mass p g / m 3 The contact can be performed based on the CT value, which is the product of the temperature (°C) of the water and the treatment time (minutes) in the tank. The CT value is preferably 100 g / m 3 minutes or more, preferably 1,000 g / m 3 minutes or more, preferably 2,000 g / m 3 minutes or more, even more preferably 4,000 g / m 3 minutes or more, even more preferably 5,000 g / m 3 minutes or more, and even more preferably 6,000 g / m 3 -minutes or more.

[0128] The CT value is preferably 12,000 g / m 3 minutes or less, preferably 11,000 g / m 3minutes or less, and preferably 10,000 minutes or less g / m 3 minutes or less, and even more preferably 9,000 g / m 3 minutes or less. If the CT value is too small, the degradation of hemicellulose, lignin, and superabsorbent polymers, especially hemicellulose, may be insufficient, whereas if the CT value is too large, it may lead to damage to pulp fibers, reduced safety, and increased production costs.

[0129] The method for measuring the ozone concentration in the ozone-containing gas in terms of the CT value is as described above. In addition, the in-tank treatment time in the CT value means the time (minutes) during which the ozone-containing gas is supplied in the case of a batch system, and means the value obtained by dividing the volume (L) of the treatment liquid in the treatment tank by the discharge amount per hour (L / min) in the case of a continuous system.

[0130] In the present disclosure, the pulp fibers after the ozone treatment preferably have a hemicellulose content of 10.0% by mass or less, more preferably 9.0% by mass or less, even more preferably 8.0% by mass or less, even more preferably 6.0% by mass or less, even more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less. This facilitates the formation of pulp fiber raw material in the subsequent alkali treatment step. The lower limit of the hemicellulose content is 0.0% by mass.

[0131] While the pulp fibers are present in the treatment tank 31, the ozone oxidatively decomposes the superabsorbent polymer into low-molecular-weight components, which then dissolve in the treatment liquid 52. The ozone also decomposes the hemicellulose in the pulp fibers, some of which dissolve in the treatment liquid 52. The ozone also decomposes the lignin in the pulp fibers, which then dissolves in the treatment liquid 52. The low-molecular-weight components of the superabsorbent polymer, decomposition products of hemicellulose, decomposition products of lignin, etc., dissolved in the treatment liquid 52 are discharged together with the treatment liquid 52. Furthermore, in this process, the sterilizing action of ozone primarily disinfects the used sanitary products. As described above, pulp fibers are formed after the ozone treatment.

[0132] The manufacturing method of the present disclosure includes the following steps. an ozone treatment step in which an ozone-treated pulp fiber is formed from the pulp fiber to be treated by supplying an ozone-containing gas to a treatment tank containing a treatment liquid containing a pulp fiber-containing material including the pulp fiber to be treated; an alkali treatment step in which the ozone-treated pulp fibers are treated with an aqueous alkali solution to form a pulp fiber raw material having a hemicellulose content of less than 8.0% by mass;

[0133] The ozone treatment step is not particularly limited as long as it involves supplying an ozone-containing gas to a treatment tank containing a treatment liquid containing a pulp fiber-containing material including the pulp fibers to be treated, thereby forming a predetermined ozone-treated pulp fiber from the pulp fibers, and can be carried out, for example, in a so-called batch or continuous manner.

[0134] When the pulp fibers to be treated are virgin pulp fibers, the pulp fiber-containing material can be virgin pulp fibers alone. When the pulp fibers to be treated are used pulp fibers, for example, pulp fibers derived from used sanitary goods, the pulp fiber-containing material contains at least pulp fibers and may be pulp fibers alone. The pulp fiber-containing material may also contain a superabsorbent polymer in addition to pulp fibers, and may also contain a connected structure in which multiple superabsorbent polymers and multiple pulp fibers are connected, materials constituting sanitary goods (e.g., core wrap, liquid-permeable sheet, liquid-impermeable sheet, etc.). The ozone-containing gas may be supplied into the processing solution in the processing tank, or may be supplied to the space above the processing solution in the processing tank. The alkaline treatment step will be described later.

[0135] The manufacturing method of the present disclosure may include the following steps: a preparation step, a pulp fiber-containing material supply step, an ozone-containing gas supply step, an ozone treatment step, and a treatment liquid discharge step. a preparation step of preparing the treatment tank having a pulp fiber-containing material supply port, a treatment liquid discharge port, and an ozone-containing gas supply port disposed below the treatment tank; a pulp fiber-containing material supply step of supplying the pulp fiber-containing material to the treatment tank through the pulp fiber-containing material supply port; an ozone-containing gas supply step of supplying the ozone-containing gas from the ozone-containing gas supply port to the processing liquid in the processing tank; the ozone treatment step in which the pulp fiber-containing material is brought into contact with the ozone-containing gas while the ozone-containing gas is being raised in the treatment tank, thereby forming the ozone-treated pulp fibers from the pulp fibers to be treated. a treated liquid discharge step of discharging the treated liquid containing the pulp fibers after the ozone treatment from the treated liquid discharge port;

[0136] The treatment liquid outlet may be positioned below the pulp fiber-containing material supply inlet, and in the ozone treatment step, the pulp fiber-containing material may be brought into contact with the ozone-containing gas while being lowered, and the treatment liquid outlet may be positioned above the pulp fiber-containing material supply inlet, and in the ozone treatment step, the pulp fiber-containing material may be brought into contact with the ozone-containing gas while being raised.

[0137] In one aspect of the present embodiment, the ozone treatment step S36 (continuous treatment step) includes a step of continuously supplying a pulp fiber-containing material 51 from the top of the treatment tank 31 while continuously discharging the treatment liquid 52 from the bottom of the treatment tank 31. The pulp fibers and superabsorbent polymer in the pulp fiber-containing material 51 have low buoyancy, and the pulp fibers, superabsorbent polymer, and connected structures naturally sink.

[0138] In one aspect of the present embodiment, the treatment liquid 52 capable of dissolving the superabsorbent polymer is an aqueous solution containing an ozone-containing gas that oxidatively decomposes the superabsorbent polymer to dissolve it. The ozone treatment step S36 (continuous treatment step) further includes a delivery step in which multiple bubbles of ozone-containing gas are continuously delivered from the bottom to the top of the treatment liquid 52. In this aspect of the method, the ozone-containing gas rises in the treatment liquid 52, while the pulp fibers and the superabsorbent polymer descend, i.e., a counterflow is formed. This increases the probability of contact between the pulp fibers and the superabsorbent polymer and the ozone-containing gas. Furthermore, the deeper the pulp fibers and the superabsorbent polymer sink, the higher the concentration of the ozone-containing gas they can come into contact with. Therefore, the superabsorbent polymer, hemicellulose, lignin, etc., which are not completely dissolved in the treatment liquid 52 by the ozone-containing gas contacted at a shallower portion of the treatment liquid 52, can be brought into contact with a high concentration of the ozone-containing gas at a deeper portion of the treatment liquid 52. This decomposes the superabsorbent polymer, hemicellulose, lignin, etc., and dissolves them in the treatment liquid 52, allowing them to be removed from the pulp fibers.

[0139] In one aspect of the present embodiment, the aforementioned delivery step includes a step of delivering the ozone-containing gas in the form of microbubbles or nanobubbles. Microbubbles are bubbles with a diameter of approximately 1 to 1,000 μm, preferably approximately 10 to 500 μm, and nanobubbles are bubbles with a diameter of approximately 100 to 1,000 nm, preferably approximately 100 to 500 nm. Microbubbles or nanobubbles are such minute bubbles, and have the properties of a large surface area per unit volume and a slow rising speed in the liquid. Therefore, in one aspect of the present method, such minute ozone-containing gas bubbles are delivered from the bottom to the top of the processing liquid 52 in the processing tank 31.

[0140] Because fine bubbles occupy a small area on the surface of the pulp fibers, more bubbles can come into contact with the surface of the pulp fibers. This allows the pulp fibers, superabsorbent polymer, and connected structures to be evenly wrapped with fine bubbles, further increasing the contact area between them and the ozone-containing gas. Furthermore, when the pulp fiber-containing material is allowed to descend in the ozone treatment step, the contact of more bubbles with the surface of the pulp fibers reduces the sedimentation tendency of the pulp fibers, superabsorbent polymer, and connected structures due to the buoyancy of the bubbles, thereby further increasing the contact time between them and the ozone-containing gas. This allows the superabsorbent polymer, hemicellulose, lignin, etc. to be decomposed, dissolved in the treatment liquid 52, and removed from the pulp fibers.

[0141] In one aspect of the present embodiment, treatment liquid 52 is an acidic aqueous solution, for example, an acidic aqueous solution with a pH of 2.5 or less. In this case, even if the superabsorbent polymer in pulp fiber-containing material 51 partially retains water absorption capacity, the superabsorbent polymer can be prevented from absorbing water and expanding. This allows the superabsorbent polymer to be dissolved in treatment liquid 52 in a short time, and the superabsorbent polymer can be removed more reliably. In particular, when treatment liquid 52 is an ozone-containing aqueous solution, the ozone in the ozone-containing aqueous solution is less likely to be deactivated, allowing the superabsorbent polymer to be oxidatively decomposed in a shorter time, thereby decomposing hemicellulose, lignin, and the like.

[0142] In another preferred embodiment, the configuration of the treatment tank 31 may be other than that shown in FIG. 2. FIG. 3 is a schematic diagram showing another example of the configuration of the ozone treatment device 2 of FIG. 1. The device 2 of FIG. 3 differs from the device 2 of FIG. 2 in that the piping 63 of the ozone treatment unit 4 has a continuous U-shaped pipe structure in which two U-shaped pipes are connected inversely and continuously to each other, and the delivery pump 22 is omitted. In this case, when the piping 63 is filled with the treatment liquid 52 and the liquid level of the treatment liquid 52 in the treatment tank 31 is higher than the liquid level of the liquid in the next step tank connected by the piping 63, the treatment liquid 52 is discharged into the next step tank through the piping 63 due to the siphon principle. Therefore, if the liquid level of the treatment liquid 52 in the treatment tank 31 and the liquid level of the liquid in the tank for the next process are initially set to the same level before the start of treatment, when the pulp fiber-containing material 51 is continuously supplied into the treatment tank 31 at the first flow rate upon the start of treatment, the treatment liquid 52 will be discharged into the tank for the next process through the piping 63 at the second flow rate = the first flow rate due to the siphon principle. However, the liquid level of the liquid in the tank for the next process is maintained at the same level as before the start of treatment even during treatment. In this case, the delivery pump 22 is not required, and control of the second flow rate of the delivery pump 22 is not necessary.

[0143] In this embodiment, the separation step S13 may further include a fourth separation step S37 for separating the ozone-treated pulp fibers from the treatment liquid 52 discharged from the treatment tank 31, and a second drying step S38 for drying the separated ozone-treated pulp fibers.

[0144] In the fourth separation step S37, the method for separating the ozone-treated pulp fibers from the treatment liquid 52 discharged from the treatment tank 31 is not particularly limited, but an example is a method in which the treatment liquid 52 containing the ozone-treated pulp fibers is passed through a screen mesh with an opening of 0.15 to 2 mm. When the treatment liquid 52 containing the ozone-treated pulp fibers is passed through a screen mesh with an opening of 0.15 to 2 mm, wastewater containing oxidized decomposition products of superabsorbent polymers, decomposition products of hemicellulose, decomposition products of lignin, etc. passes through the screen. Meanwhile, the ozone-treated pulp fibers remain on the screen.

[0145] In the subsequent second drying step S38, the separated ozone-treated pulp fibers are dried in a high-temperature atmosphere or with hot air, for example. The drying temperature is, for example, 105 to 210°C, and preferably 110 to 190°C. The drying time varies depending on the drying temperature, but is, for example, 10 to 120 minutes, and preferably 15 to 100 minutes. This evaporates and removes moisture remaining on the surface of the ozone-treated pulp fibers, allowing for the recovery of high-purity ozone-treated pulp fibers with an extremely low superabsorbent polymer content. The ozone-treated pulp fibers can also be sterilized (disinfected) in a high-temperature atmosphere or with hot air, for example. In addition, if the pulp fibers are not stored after the ozone treatment and the subsequent alkali treatment step S39 is carried out, the second drying step S38 can be omitted.

[0146] In the alkali treatment step S39, the ozone-treated pulp fibers are treated with an aqueous alkali solution to form a pulp fiber raw material having a hemicellulose content of less than 8.0% by mass. By subjecting the ozone-treated pulp fibers to the alkali treatment step, hemicellulose can be decomposed under milder conditions than conventionally known alkali treatment steps. Furthermore, by performing the alkali treatment step under milder conditions, it is expected that cellulose decomposition can be suppressed.

[0147] The conditions for the alkali treatment step are not particularly limited, as long as they can form a pulp fiber raw material having a hemicellulose content of less than 8.0% by mass. The alkali treatment step can be carried out by immersing the ozone-treated pulp fibers in an aqueous alkali solution having a normality of preferably 0.1 N or more, more preferably 0.2 N or more, and even more preferably 0.3 N or more. The alkali treatment step can be carried out by immersing the ozone-treated pulp fibers in an aqueous alkali solution having a normality of preferably 8.0 N or less, more preferably 6.0 N or less, even more preferably 5.0 N or less, even more preferably 4.0 N or less, and even more preferably 3.0 N or less.

[0148] By keeping the normality of the alkaline aqueous solution within the above range, damage to the pulp fibers, treatment equipment, etc. after ozone treatment is reduced, waste liquid from the alkaline treatment step can be easily disposed of, and the risk of carrying out the alkaline treatment step can be reduced. The normality of the alkaline aqueous solution includes a range lower than that used in conventional methods for forming cellulose nanofibers that do not use ozone treatment.

[0149] The amount of the alkaline aqueous solution is not particularly limited as long as it can form a pulp fiber raw material having a hemicellulose content of less than 8.0% by mass, and preferably 10 to 200 L, and more preferably 20 to 100 L, of the alkaline aqueous solution can be added per kg (dry mass) of pulp fiber after ozone treatment.

[0150] The temperature of the alkali treatment step is not particularly limited, and the alkali treatment step can be carried out, for example, at room temperature (25°C). The alkali treatment step can be carried out at a temperature of preferably 10°C or higher, more preferably 15°C or higher, and even more preferably 20°C or higher. The alkali treatment step can also be carried out at a temperature of preferably 80°C or lower, more preferably 60°C or lower, even more preferably 50°C or lower, and even more preferably 40°C or lower.

[0151] The time for the alkali treatment step is not particularly limited, and the alkali treatment step can be carried out for preferably 5 to 240 minutes, more preferably 10 to 120 minutes, and even more preferably 15 to 60 minutes.

[0152] For example, when a high temperature, e.g., 40°C or higher, is selected in the alkaline treatment step, the concentration of the alkaline aqueous solution can be selected to have a normality of, e.g., 0.3N to 4.5N, thereby decomposing hemicellulose in the pulp fibers after ozone treatment. In the alkali treatment step, the pulp fibers after the ozone treatment may be immersed in an aqueous alkali solution, and the pulp fibers after the ozone treatment may be stirred together with the aqueous alkali solution.

[0153] The alkaline aqueous solution can be prepared by dissolving an alkali that exhibits alkalinity when dissolved in water, such as a hydroxide or salt of an alkali metal or alkaline earth metal, in water. Examples of the alkali metal include lithium, sodium, and potassium, with sodium being preferred. Examples of the alkaline earth metal include magnesium, calcium, and barium. When the alkaline aqueous solution is an aqueous solution of sodium hydroxide, the concentration of the alkaline aqueous solution is, for example, 2 to 10% by mass.

[0154] In addition, in the alkaline treatment step S39, the second drying step S38 may be omitted and the undried (wet) recycled pulp fibers obtained in the fourth separation step S37 may be subjected to the alkaline treatment step S39, and the fourth separation step S37 and the second drying step S38 may be omitted and the treatment liquid 52 containing the recycled pulp fibers obtained in the ozone treatment step S36 may be subjected to the alkaline treatment step S39.

[0155] After the alkali treatment step, a washing step can be performed to wash away the alkali and hemicellulose decomposition product. After the washing step, a drying step can be performed. This drying step can be the same as the second drying step S38.

[0156] In the present disclosure, the pulp fiber raw material preferably has a cellulose content of 94.0% by mass or more, more preferably 95.0% by mass or more, even more preferably 96.0% by mass or more, and even more preferably 97.0% by mass or more. This allows the pulp fiber raw material to be suitably used as a cellulose raw material for cellulose-derived products. The upper limit of the cellulose content is 100.0% by mass.

[0157] In the present disclosure, the pulp fiber raw material preferably has a hemicellulose content of less than 8.0% by mass, more preferably less than 6.0% by mass, even more preferably less than 5.0% by mass, even more preferably less than 4.0% by mass, and even more preferably less than 3.0% by mass. This allows the pulp fiber raw material to be suitably used as a cellulose raw material for cellulose-derived products. The lower limit of the hemicellulose content is 0.0% by mass.

[0158] In the present disclosure, the pulp fiber raw material, and preferably the ozone-treated pulp fiber and pulp fiber raw material, preferably have a lignin content of 0.10% by mass or less, more preferably 0.08% by mass or less, and even more preferably 0.06% by mass or less. This allows the pulp fiber raw material to be suitably used as a cellulose raw material for cellulose-derived products. The lower limit of the lignin content is 0.00% by mass.

[0159] In the present disclosure, the pulp fibers after ozone treatment before forming the pulp fiber raw material preferably have a cellulose content of 87.0% by mass or more, more preferably 90.0% by mass or more, and even more preferably 93.0% by mass or more, which allows the pulp fiber raw material to be suitably used as a cellulose raw material for cellulose-derived products.

[0160] In the present disclosure, the cellulose content, hemicellulose content, and lignin content in pulp fiber raw materials, pulp fibers after ozone treatment, etc. can be measured according to known detergent analysis methods.

[0161] In the present disclosure, the pulp fiber raw material, and preferably the pulp fibers and pulp fiber raw material after ozone treatment, preferably have a beating rate reduction rate of 300 mL or more, more preferably 320 mL or more, even more preferably 340 mL or more, and even more preferably 360 mL or more, which makes the pulp fiber raw material more likely to fluff and facilitates the extraction of cellulose in a subsequent process using the pulp fiber raw material, such as a cellulose-using step for forming cellulose nanofibers, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding materials, or paper products.

[0162] In the production method of the present disclosure, the pulp fiber raw material, and preferably the pulp fibers and pulp fiber raw material after ozone treatment, preferably have a freeness reduction rate of 990 mL or less, more preferably 800 mL or less, even more preferably 700 mL or less, and even more preferably 600 mL or less, thereby suppressing damage to the pulp fiber raw material and the extracted cellulose. The above-mentioned rate of reduction in the beating degree is obtained by a low hemicellulose content, a low lignin content, etc. in the pulp fiber raw material or the pulp fiber after ozone treatment.

[0163] The above-mentioned freeness reduction rate is measured according to the following freeness reduction test. <Beating Degree Decrease Test> (1) Pulp fiber raw material or pulp fiber after ozone treatment is beaten for 1 hour or more, preferably 2 hours, according to JIS P 8221-1:1998 Pulp - Beating Method - Part 1: Beater Method. (2) After beating begins, samples are taken every 20 minutes and the beating degree (Canadian Standard freeness) of each sample is measured in accordance with JIS P 8121-2:2012, Pulp - Freeness Testing Method - Part 2: Canadian Standard Freeness Method. Note that the test may be stopped when the freeness of the sample falls below 100 mL. (3) Plot the time (h) on the horizontal axis and the degree of beating (mL) on the vertical axis, approximate it to a linear function using the least squares method, and use the absolute value of the slope as the rate of decrease in the degree of beating (mL / m). The higher the value of the beating degree reduction rate, the faster the beating degree decreases per unit time, meaning that the pulp fiber raw material or the pulp fibers after ozone treatment are more likely to be beaten (more likely to fluff).

[0164] In the present disclosure, the pulp fiber raw material preferably has a water contact angle of 20° or less, more preferably 15° or less, and even more preferably 10° or less. This allows the cellulose to be easily dispersed in an aqueous solution when extracted after drying and storage of the pulp fiber raw material. From the above perspective, the water contact angle of the pulp fiber raw material may be 0°.

[0165] The water contact angle of the pulp fiber material can be measured as follows. (1) In a constant temperature and humidity chamber with a temperature of 20±5°C and a humidity of 65±5% RH, an aluminum ring (outer diameter: 43 mm, inner diameter: 40 mm, height: 5 mm) and pulp fiber for saccharification that had been dried at 120°C for 60 minutes were prepared and left to stand for 24 hours. (2) 1.5 g of pulp fiber raw material is evenly packed into an aluminum ring, and the pulp fiber raw material, together with the aluminum ring, is compressed for 1 minute at a pressure of 3 MPa using a press with a smooth bottom to smooth the surface of the pulp fiber raw material. (3) The water contact angle of the compressed pulp fiber raw material is measured in accordance with JIS R 3257:1999, "Testing Methods for Wettability of Glass Substrate Surfaces," Section 6, Sessile Drop Method. An example of a contact angle measuring device is the CA-V Automatic Contact Angle Meter manufactured by Kyowa Interface Science Co., Ltd. The water contact angle is the value measured 200 ms after deionized water is dropped onto the surface. (4) The water contact angle is measured for 20 different samples, and the average value is used.

[0166] In the present disclosure, the pulp fiber raw material preferably has an ash content of 0.65% by mass or less, more preferably 0.50% by mass or less, even more preferably 0.30% by mass or less, and even more preferably 0.20% by mass or less, which makes it less likely that metal ions and their precipitates will damage equipment and inhibit the pulp fiber raw material from being pulverized when cellulose is extracted from the pulp fiber raw material. The ash content can be reduced, for example, by selecting an acid capable of forming a complex with metal ions contained in the excrement, particularly citric acid, as the inactivating agent in the inactivation step S31 in which the superabsorbent polymer is inactivated.

[0167] In this specification, ash content refers to the amount of inorganic or non-combustible residue remaining after organic matter has been incinerated, and ash percentage refers to the proportion (mass ratio) of ash contained in the material to be incinerated. The ash percentage is measured in accordance with "5. Ash Content Test Method" under "2. General Test Methods" in the Sanitary Treatment Product Materials Standards. Specifically, the ash percentage is measured as follows: (1) First, heat a platinum, quartz, or porcelain crucible to 500-550°C for 1 hour, then allow it to cool and accurately measure its mass. (2) Take 2 to 4 g of pulp fiber raw material that has been dried at 120°C for 60 minutes, place it in a crucible, accurately measure the mass, remove or shift the lid of the crucible if necessary, and heat it gently at first, gradually increase the temperature, and heat it at 500 to 550°C for at least 4 hours, until no carbonized material remains, and then ash it. (3) After cooling, accurately measure the mass. The residue is again incinerated until it reaches a constant weight, and after cooling, accurately measure the mass and use this as the ash content (% by mass).

[0168] In a preferred embodiment, the present method further includes an inactivation step S31, in which the mixture is treated with an aqueous solution capable of inactivating the water absorption performance of the superabsorbent polymer to inactivate the water absorption performance of the superabsorbent polymer in the mixture, prior to the ozone treatment step S36 (continuous treatment step), and a first separation step S32, in which the inactivated superabsorbent polymer and pulp fibers are separated from the aqueous solution, prior to the ozone treatment step S36 (continuous treatment step). Thus, in a preferred embodiment, the present method further includes an inactivation step S31, in which the water absorption performance of the superabsorbent polymer is suppressed with an aqueous solution capable of inactivating the water absorption performance of the superabsorbent polymer, so that the superabsorbent polymer can be more easily dissolved in the treatment liquid 52 in a short time in the subsequent ozone treatment step S36 (continuous treatment step).

[0169] In the present embodiment, as a preferred aspect, in the inactivation step S31, the aqueous solution capable of inactivating the water absorption performance of the superabsorbent polymer is an acidic aqueous solution, for example, an acidic aqueous solution with a pH of 2.5 or less. Thus, in the present method, as a preferred aspect, the aqueous solution capable of inactivating the water absorption performance of the superabsorbent polymer is an acidic aqueous solution, so that the superabsorbent polymer is more easily inactivated, thereby more reliably suppressing the water absorption performance of the superabsorbent polymer at the stage of the inactivation step S31. As a result, the superabsorbent polymer can be more easily dissolved in the treatment solution in a short time at the stage of the subsequent ozone treatment step S36 (continuous treatment step).

[0170] In another preferred embodiment, the treatment tank 31 may include at least a first treatment tank 31-1 and a second treatment tank 31-2 connected in series. FIG. 4 is a schematic diagram showing another example of the configuration of the apparatus 2 for the ozone treatment step of FIG. 1. The apparatus 2 of FIG. 4 differs from the apparatus 2 of FIG. 2 in that two ozone treatment units 4 are connected in series, in other words, the first treatment tank 31-1 and the second treatment tank 31-2 are connected in series. In this case, for example, the first treatment tank 31-1 is supplied with the pulp fiber-containing material 51 and discharges a first treated liquid (treatment liquid 52-1 from the first treatment tank 31-1), and the second treatment tank 31-2 is supplied with the first treated liquid and discharges a second treated liquid (treatment liquid 52-2 from the second treatment tank 31-2), thus treating the pulp fiber-containing material 51 in multiple stages. In this case, compared to when one large-capacity treatment tank 31 is provided, treatment is carried out with new treatment liquids 52-1 and 52-2 for each of the first and second treatment tanks 31-1 and 31-2. Therefore, for example, the superabsorbent polymer that was not completely dissolved in the first treatment tank (first-stage treatment tank) 31-1 can be easily dissolved in the second treatment tank (next-stage treatment tank) 31-2, and the superabsorbent polymer can be more reliably dissolved and removed from the fibers.

[0171] In another preferred embodiment, the treatment tank 31 may include an ejector. For example, the ejector may include a drive fluid supply port, a mixed fluid discharge port connected to the treatment tank, and a suction fluid supply port therebetween, and while supplying the pulp fiber-containing material 51 to the drive fluid supply port of the ejector, ozone is supplied to the suction fluid supply port, and the mixed liquid formed by mixing the pulp fiber-containing material 51 and the ozone in the ejector is discharged from the mixed fluid discharge port into the treatment liquid in the treatment tank.

[0172] By supplying the pulp fiber-containing material 51 as a driving fluid and ozone as a suction fluid to the ejector and mixing them in the ejector, a mixed fluid in which the pulp fiber-containing material 51 and ozone are very well mixed can be efficiently formed. That is, a mixed fluid in which the pulp fiber-containing material 51 and ozone are in extremely intimate contact can be formed. Then, by discharging this mixed fluid into the treatment liquid in the treatment tank, the treatment liquid can be agitated. Furthermore, when the ozone is discharged into the treatment liquid, it is continuously discharged in the form of fine bubbles, allowing it to diffuse extremely widely within the treatment liquid. As a result, the reaction between the superabsorbent polymer and the gaseous substance can be very efficiently promoted not only in the pulp fiber-containing material 51 in the mixed fluid discharged from the ejector but also in the pulp fibers containing the superabsorbent polymer in the treatment liquid in the treatment tank.

[0173] In a preferred embodiment of the present invention, the material separation step S1 further includes a pretreatment step S11 in which the used sanitary product is kept in its original shape without breaking or otherwise being deactivated, and is highly swollen with water without inactivating the superabsorbent polymer. This generates extremely high internal pressure within the used sanitary product, causing some portion of its surface to burst. Then, in the disassembly step S12, a physical impact is applied to the used sanitary product in this state, causing some portion of its surface to tear and ejecting the internal absorbent core to the outside. This allows the used sanitary product to be disassembled into at least the film (liquid-impermeable sheet) and the absorbent core. Since the film generally maintains its original shape, it can be easily separated from the absorbent core in the subsequent separation step S13. This allows components such as the film to be separated from the other components while maintaining their original shape without breaking or otherwise being decomposed. Therefore, components such as the film of the sanitary product can be efficiently recovered.

[0174] In a preferred embodiment of the present invention, terpene is used to remove the adhesive, enabling the hot melt adhesive used to bond the components of sanitary products to be dissolved at room temperature. This allows the sanitary products to be easily and cleanly disassembled, allowing the pulp fibers and superabsorbent polymer to be separated from the sanitary products, and the nonwoven fabric and film to be separated while retaining their respective component forms. In other words, the pulp fibers, film, and nonwoven fabric can be easily recovered separately without crushing the sanitary products or undergoing complex separation processes. When limonene is used as a terpene, a secondary effect of limonene is its refreshing citrus odor, which can mask to some extent the odor originating from excrement, reducing the odor burden on workers and the odor impact on neighbors. Limonene is a monoterpene with a structure similar to styrene, and therefore can dissolve styrene-based hot melt adhesives commonly used in sanitary products. Because sanitary products can be washed at room temperature, energy costs can be reduced and odor generation and diffusion can be suppressed. Terpenes are highly effective at cleaning oil stains, and in addition to dissolving hot melt adhesives, they can also decompose and remove printing ink from films that have been printed, allowing the printed film to be recovered as a high-purity plastic material.

[0175] Furthermore, when an organic acid solution with a pH of 2.5 or less is used to inactivate the superabsorbent polymer, it is less likely to cause deterioration of the pulp fiber. Furthermore, when citric acid is used as the organic acid, the chelating effect and cleaning power of citric acid can be expected to remove dirt components derived from excrement. It can also be expected to have a disinfecting effect and a deodorizing effect against alkaline odors.

[0176] Furthermore, by oxidatively decomposing superabsorbent polymers with ozone, it is possible to prevent contamination of pulp fibers and a sudden increase in wastewater due to the absorption of water by the superabsorbent polymer. By adjusting the ozone concentration, it is possible to simultaneously perform the oxidative decomposition and sterilization of the superabsorbent polymer. Furthermore, since no chlorine-based chemicals are used when using ozone, it is possible to produce high-quality RPF from recovered plastic components that is less likely to damage combustion furnaces. Because no salts are used during the treatment process, no residue remains on the pulp fibers, making it possible to recover high-quality pulp fiber raw materials with low ash content.

[0177] In the cellulose using step, as shown in FIG. 1, the pulp fiber raw material is subjected to a cellulose using process to produce a cellulose-derived product.

[0178] The pulp fiber raw material produced by the production method of the present disclosure has a predetermined hemicellulose content and is therefore suitable as a cellulose raw material. The cellulose raw material is not particularly limited as long as it contains cellulose as a part of the raw material, and examples thereof include raw materials for various applications, such as cellulose nanofibers, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding materials, and processed paper products. The various applications will be described later.

[0179] The manufacturing method of the present disclosure can include a cellulose using step of utilizing cellulose from the pulp fiber raw material after the alkali treatment step. The cellulose using step is not particularly limited as long as it uses cellulose, and examples thereof include a cellulose nanofiber forming step of forming cellulose nanofibers, a viscose rayon forming step of forming viscose rayon, a cellulose derivative forming step of forming a cellulose derivative, a bioethanol forming step of forming bioethanol, a biobutanol forming step of forming biobutanol, a molding material forming step of forming a molding material, or a paper product forming step of forming a paper product.

[0180] The cellulose nanofiber formation step is not particularly limited and includes cellulose nanofiber formation methods known in the art, such as those described in JP 2010-235681 A and JP 2010-254726 A.

[0181] Regarding the cellulose-using step, the viscose rayon-forming step is not particularly limited and includes viscose rayon-forming methods known in the art (e.g., regenerated cellulose fiber-forming method, cellophane-forming method, cellulose sponge-forming method). Examples of the viscose rayon-forming method include the viscose method and the cuprammonium method. Examples of the viscose rayon include regenerated cellulose fiber, cellophane, and cellulose sponge.

[0182] Examples of the regenerated cellulose fibers include rayon fibers, such as viscose rayon fibers obtained from viscose, polynosic fibers, and modal fibers; cuprammonium rayon fibers (also called "cupra fibers") obtained from a cuprammonium salt solution of cellulose; and lyocell fibers and tencel fibers obtained by an organic solvent spinning method using an organic solvent, which is a mixed solution of an organic compound and water, without going through a cellulose derivative. Examples of the cellophane include cellophane tape and cellophane film.

[0183] Regarding the cellulose-using step, the cellulose derivative-forming step is not particularly limited and includes cellulose derivative-forming methods known in the art (e.g., methods for forming semi-synthetic cellulose fibers), such as those described in JP-A-10-251301. Examples of the cellulose derivatives include semi-synthetic cellulose fibers, such as acetate fibers, triacetate fibers, and diacetate fibers. Examples of the cellulose derivatives include carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0184] Regarding the cellulose use step, the bioethanol production step is not particularly limited and includes bioethanol production methods known in the art, such as those described in JP 2018-64514 A.

[0185] Regarding the cellulose-using step, the biobutanol-forming step is not particularly limited and includes biobutanol-forming methods known in the art, such as those described in JP 2015-517303 A.

[0186] Regarding the cellulose-using step, the molding material forming step is not particularly limited and includes molding material forming methods known in the art. Examples of the molding material include packaging cushioning materials, containers, and the like.

[0187] Regarding the cellulose use step, the paper product forming step is not particularly limited and includes any paper product forming method known in the art. Examples of the paper products include filter base paper and functional paper. [Example]

[0188] [Manufacturing Example 1] Recycled pulp fibers were produced from several types of used disposable diapers collected from nursing homes according to the method shown in Figures 1 and 2. The conditions related to the ozone treatment step S36 were as follows. (i) Pulp fiber content 51 Concentration: 1% by mass (concentration of pulp fiber and superabsorbent polymer) pH: 2.4 (ii) Treatment tank 31 ·Capacity: 60L Height: 2.6m Primary flow rate: 2L / min Secondary flow rate: 2L / min Processing time in the tank: 30 minutes V / W:100 ·R O / V:0.033 (iii) Ozone-containing gas Ozone concentration: 200g / m 3 Shape: nanobubbles

[0189] The inactivation step S31 was carried out using citric acid at pH 2.0, and the ozone treatment step S36 was carried out under the above-mentioned conditions. The obtained recycled pulp fiber was dried at 120°C for 60 minutes to obtain pulp fiber No. 1 after ozone treatment.

[0190] [Manufacturing Example 2] Pulp fiber No. 2 after ozone treatment was obtained in the same manner as in Production Example 1, except that the treatment time in the tank was changed to 15 minutes. [Comparative Manufacturing Example 1] The virgin pulp fiber of NBKP was treated with ozone and designated as pulp fiber No. 3.

[0191] After the ozone treatment, the cellulose content, hemicellulose content, and lignin content (mass%) of pulp fibers No. 1 to No. 3 were measured. The results are shown in Table 1.

[0192] [Table 1]

[0193] As shown in Table 1, the post-ozonation pulp fiber No. 1 of Production Example 1 had a cellulose content of 92.7% by mass, a hemicellulose content of 7.1% by mass, and a lignin content of less than 0.1% by mass. Therefore, the hemicellulose content can be further reduced by subjecting the post-ozonation pulp fiber No. 1 to a conventionally known alkali treatment process.

[0194] Furthermore, it is expected that by subjecting post-ozonation pulp fiber No. 1 to an alkali treatment process under milder conditions than those conventionally known, it will be possible to decompose hemicellulose while suppressing cellulose decomposition, thereby obtaining a pulp fiber raw material with a high cellulose yield and a high cellulose content (low hemicellulose content).

[0195] [Example 1] The ozone-treated pulp fiber No. 2 produced in Production Example 2 was subjected to an alkali treatment step.

[0196] Details of the alkali treatment step are as follows. (1) After the ozone treatment, the pulp fiber No. 2 is dried at 40°C for 1 hour and then crushed in a centrifugal crusher to form a measurement sample. (2) In a constant temperature room at 20°C, approximately 1.0 g of the sample and 25 mL of an aqueous sodium hydroxide (NaOH) solution with a normality specified in Table 2 are added to a container, and the sample is crushed in the container for 5 minutes. (3) After crushing, the sample is left to stand for 30 minutes.

[0197] (4) 25 mL of water at 20°C is added to the container, and the contents of the container are stirred for 1 minute. The water mentioned above is classified as type A3 in the "Water for use in testing water and wastewater" of JIS K0557:1998. (5) The contents of the container are filtered through a glass filter under suction to obtain the filtrate. (6) The filtrate is washed with water and then neutralized. (7) After neutralization, 40 mL of a 10% by mass aqueous solution of acetic acid is added to the filtered product, and the mixture is allowed to stand for 5 minutes. (8) The filtered residue after standing is washed with boiling water and then dried to form pulp fiber raw material No. 2. (9) The composition of pulp fiber raw material No. 2 is analyzed using a known detergent method. The normality of the aqueous sodium hydroxide solution and the results of the alkali treatment step are shown in Table 2. The composition with a NaOH concentration of 0.0N means the composition before the start of the alkali treatment step.

[0198] [Table 2]

[0199] It was confirmed that in the above alkali treatment step, pulp fiber raw material No. 2 with a low hemicellulose concentration can be produced not only at a high NaOH concentration (5.3 N) but also at a low NaOH concentration (0.5 N). When ozone-treated pulp fiber No. 3 (NBKP virgin pulp fiber) from Comparative Manufacturing Example 1 was subjected to the above-mentioned alkali treatment process, the hemicellulose concentration was not reduced easily at low NaOH concentrations (0.5N to 2.8N), and a high NaOH concentration (5.3N) was required to reduce the hemicellulose concentration. [Explanation of symbols]

[0200] 31 Treatment tank 32 Pulp fiber content supply port 33 Treatment liquid outlet 43 Ozone-containing gas supply port 51 Pulp fiber content 52 Processing liquid 53 Ozone-containing gases S36 Ozone treatment process

Claims

1. A pulp fiber raw material as a cellulose raw material, the pulp fiber raw material has a hemicellulose content of less than 8.0% by mass; derived from used hygiene products containing superabsorbent polymers and pulp fibers; The pulp fiber raw material characterized by:

2. A pulp fiber raw material as a cellulose raw material, 10. The pulp fiber material of claim 1, wherein the pulp fiber material has a cellulose content of 94.0% by weight or greater and a hemicellulose content of less than 6.0% by weight.

3. A pulp fiber raw material as described in claim 1 or 2, wherein the pulp fiber raw material has a lignin content of 0.10 mass% or less.

4. A pulp fiber raw material described in any one of claims 1 to 3, wherein the pulp fiber raw material is a raw material for cellulose nanofiber, viscose rayon, cellulose derivatives, bioethanol, biobutanol, molding material, or paper processed products.

5. A cellulose nanofiber, viscose rayon, a cellulose derivative, bioethanol, biobutanol, a molding material, or a paper product made from the pulp fiber raw material described in any one of claims 1 to 4.

6. A pulp fiber raw material described in any one of claims 1 to 5, wherein the pulp fiber raw material has an ash content of 0.65 mass% or less.

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