Decomposition product of polyacrylic acid-based water-absorbent resin

Abstract

To provide a technique for regenerating a water-absorbent resin into a functional material that exhibits a function other than water absorption.SOLUTION: A decomposition product of a polyacrylic acid-based water-absorbent resin according to one embodiment of the present invention has a weight-average molecular weight of 100 or more and 1,000,000 or less and includes a structural unit derived from acrylic acid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a decomposition product of a polyacrylic acid-based water-absorbent resin and a method for producing the same. [Background technology]

[0002] Polyacrylic acid-based water-absorbent resins are used in a wide range of applications, including absorbent articles such as diapers and sanitary napkins, due to their ability to retain large amounts of water. On the other hand, from the perspectives of effective resource utilization and reduction of greenhouse gas emissions, technologies for recycling used water-absorbent resins have been investigated.

[0003] For example, Patent Document 1 describes a method for decomposing a water-absorbent resin with an acid and / or an alkali. Patent Document 2 describes a method for regenerating a used superabsorbent resin, which involves treating the superabsorbent resin with ozone water, reactivating the ozone-treated superabsorbent resin with an alkaline aqueous solution, adding hydrophilic particles to the reactivated superabsorbent resin, and then drying the resulting mixture. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-249711 [Patent Document 2] Japanese Patent Application Publication No. 2020-195994 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Documents 1 and 2 do not discuss any specific technology for regenerating a water-absorbent resin into a functional material having a function other than water absorption.

[0006] The present invention relates to a technique for regenerating a water-absorbent resin into a functional material having a function other than water absorption. [Means for solving the problem]

[0007] The decomposition product of the polyacrylic acid-based water-absorbing resin according to one embodiment of the present invention is The weight average molecular weight is 100 or more and 1,000,000 or less, It has structural units derived from acrylic acid.

[0008] A method for producing a decomposition product of a polyacrylic acid-based water-absorbing resin according to another embodiment of the present invention includes the steps of: The method includes a step of decomposing a polyacrylic acid-based water-absorbing resin to produce a decomposition product having a weight-average molecular weight of 100 or more and 1,000,000 or less and having a structural unit derived from acrylic acid. [Effects of the Invention]

[0009] According to the present invention, it is possible to regenerate a water-absorbent resin into a functional material having a function other than water absorption. [Brief explanation of the drawings]

[0010] [Figure 1] 1A and 1B are schematic diagrams for explaining the mechanism of thermal decomposition of a polyacrylic acid-based water-absorbent resin presumed in one embodiment of the present invention, in which (A) shows an example of a polyacrylic acid-based water-absorbent resin before decomposition, and (B) shows an example of a decomposition product of the polyacrylic acid-based water-absorbent resin. [Figure 2] 1 is a graph showing the measurement results of light transmittance at each wavelength when irradiated with light of 200 to 800 nm in an evaluation test of light absorption characteristics according to an example of the present invention, and is a graph showing the results of samples of Example 1 and Comparative Examples 1 to 3. [Figure 3] 3 is a graph showing the results of the samples of Examples 2 to 5 in a test similar to that of FIG. [Figure 4] 3 is a graph showing the results of the samples of Examples 6 to 9 in a test similar to that of FIG. [Figure 5] 3 is a graph showing the results of the samples of Examples 10 to 13 in a test similar to that of FIG. [Figure 6]3 is a graph showing the results of the samples of Examples 14 and 15 in a test similar to that of FIG. 2. [Figure 7] 3 is a graph showing the results of the samples of Examples 16 and 17 in a test similar to that of FIG. 2. [Figure 8] 1 is a graph showing the emission intensity at 400 nm when irradiated with varying excitation wavelengths (wavelength distribution 200 to 900 nm) in an evaluation test of the fluorescent properties of examples of the present invention, and is a graph showing the results of samples of Example 1 and Comparative Examples 1 to 3. [Figure 9] 9 is a graph showing the results of the samples of Examples 2 to 5 in a test similar to that of FIG. 8. [Figure 10] 9 is a graph showing the results of the samples of Examples 6 to 9 in a test similar to that of FIG. 8. [Figure 11] 9 is a graph showing the results of the samples of Examples 10 to 13 in a test similar to that of FIG. [Figure 12] 9 is a graph showing the results of the samples of Examples 14 and 15 in a test similar to that of FIG. 8. [Figure 13] 9 is a graph showing the results of the samples of Examples 16 and 17 in a test similar to that of FIG. 8. [Figure 14] 1 is a graph showing the distribution of spectral intensity (wavelength 200 to 900 nm) emitted when irradiated with ultraviolet light having a wavelength of 298 nm in an evaluation test of the fluorescent properties of an example of the present invention, and is a graph showing the results of samples of Example 1 and Comparative Examples 1 to 3. [Figure 15] 15 is a graph showing the results of the samples of Examples 2 to 5 in a test similar to that of FIG. [Figure 16] 15 is a graph showing the results of the samples of Examples 6 to 9 in a test similar to that of FIG. [Figure 17] 15 is a graph showing the results of the samples of Examples 10 to 13 in a test similar to that of FIG. [Figure 18] 15 is a graph showing the results of the samples of Examples 14 and 15 in a test similar to that of FIG. 14. [Figure 19]15 is a graph showing the results of the samples of Examples 16 and 17 in a test similar to that of FIG. 14. [Figure 20] FIG. 1 is a graph showing the relationship between the elapsed time and the average light transmittance when centrifugal force is applied to a suspension containing a sample and phthalocyanine under conditions of a temperature of 25°C and a rotation speed of 4,000 rpm in a dispersion stability evaluation test by a centrifugal sedimentation method according to an example of the present invention, and shows the results for the samples of Example 1 and Comparative Examples 1 to 3. [Figure 21] 21 is a graph showing the results of the samples of Examples 2 to 5 in a test similar to that of FIG. 20. [Figure 22] 21 is a graph showing the results of the samples of Examples 6 to 9 in a test similar to that of FIG. 20. [Figure 23] 21 is a graph showing the results of the samples of Examples 10 to 13 in a test similar to that of FIG. 20. [Figure 24] 21 is a graph showing the results of the samples of Examples 14 and 15 in a test similar to that of FIG. 20. [Figure 25] 21 is a graph showing the results of the samples of Examples 16 and 17 in a test similar to that of FIG. 20. [Figure 26] 1 is a graph showing the measurement results of light transmittance at each wavelength when light of 200 to 800 nm is irradiated onto the Japanese paper of Example 18 coated with the decomposition product of the polyacrylic acid-based water-absorbent resin of Example 1 of the present invention and the Japanese paper of Comparative Example 4 not coated with the decomposition product. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Decomposition products of polyacrylic acid-based water-absorbing resin> In the present invention, the decomposition product of the polyacrylic acid-based water-absorbing resin is a compound produced by decomposing the polyacrylic acid-based water-absorbing resin, has a weight-average molecular weight within a predetermined range, and contains structural units derived from acrylic acid. As will be described later, the decomposition product of the polyacrylic acid-based water-absorbing resin of the present invention can be used as a functional material such as a dispersant, an ultraviolet absorber, and a fluorescent agent.

[0012] In the present invention, the term "structural unit" is an expression that encompasses both a functional group that constitutes a compound and a structural unit that constitutes a polymer.

[0013] In the present invention, the polyacrylic acid-based water-absorbing resin capable of generating decomposition products (hereinafter also referred to as "water-absorbing resin") is a crosslinked polymer having structural units derived from acrylic acid. The crosslinked polymer referred to here means a three-dimensional network structure in which polymer chains, which are the main structure of the polymer, are linked within or between polymer chains, and does not have a weight-average molecular weight. The polyacrylic acid-based water-absorbing resin of the present invention is at least one type of water-absorbing resin, and may contain multiple water-absorbing resins.

[0014] The polymer having acrylic acid-derived structural units may be, for example, at least one selected from a homopolymer of acrylic acid, a copolymer of acrylic acid, and salts thereof. Examples of the homopolymer of acrylic acid and salts thereof include polyacrylic acid, polyacrylic acid / polyacrylate, and polyacrylate. Examples of the copolymer of acrylic acid include, but are not limited to, poly(vinyl alcohol / acrylate) copolymer and starch-acrylate graft copolymer.

[0015] Furthermore, the "salt" constituting the water absorbent resin includes at least one salt selected from, for example, alkali metal salts (sodium salts, potassium salts, lithium salts, etc.), alkaline earth metal salts (calcium salts, magnesium salts, barium salts, etc.), ammonium salts (quaternary ammonium salts, quaternary alkylammonium salts, etc.), etc. From the viewpoint of obtaining stable water absorption, the salt constituting the water absorbent resin preferably includes an alkali metal salt, more preferably includes a sodium salt.

[0016] Among these, the water-absorbent resin according to one embodiment of the present invention is preferably at least one selected from a crosslinked polyacrylate and a crosslinked polyacrylic acid / polyacrylate, and more preferably at least one selected from a crosslinked sodium polyacrylate and a crosslinked polyacrylic acid / sodium polyacrylate, from the viewpoint of supply stability, water absorbency, and the like.

[0017] In one embodiment of the present invention, the water-absorbent resin may be a water-absorbent resin derived from an absorbent article. In the present invention, an absorbent article refers to an article that contains a water-absorbent resin and is capable of absorbing moisture. Examples of absorbent articles include disposable diapers, sanitary napkins, urine absorption pads, panty liners, pet toilet sheets, drip sheets, moisture absorbents, deodorizers, etc. Note that a "drip sheet" refers to a water-absorbent sheet that absorbs excess moisture (body fluids, etc.) from food ingredients such as meat and fish. Furthermore, in the present invention, the absorbent article is preferably an absorbent hygiene product that absorbs body fluids such as urine and menstrual blood. Examples of absorbent hygiene products include disposable diapers, sanitary napkins, urine absorption pads, panty liners, etc.

[0018] In the present invention, the weight-average molecular weight of the decomposition product of the water-absorbent resin is 100 or more and 1,000,000 or less. A decomposition product having a weight-average molecular weight in this range may contain a structure related to functionality, such as an aromatic ring, while retaining structural units derived from acrylic acid. In one embodiment of the present invention, from the viewpoint of imparting functionality to the decomposition product, the weight-average molecular weight of the decomposition product of the water-absorbent resin is preferably 500 or more, more preferably 1,000 or more, more preferably 10,000 or more, and preferably 500,000 or less, more preferably 100,000 or less. The weight-average molecular weight of the decomposition product of the water-absorbent resin can be measured by size exclusion chromatography (SEC), as shown in the examples described later.

[0019] The decomposition product of the water-absorbent resin of the present invention has a structural unit derived from acrylic acid. The structural unit derived from acrylic acid may be an acryloyl group, which is a functional group having acrylic acid as a skeleton, but from the viewpoint of satisfying the above-mentioned condition of the weight-average molecular weight, it is preferable that the structural unit derived from acrylic acid is a repeating unit when the decomposition product is a polymer. The structure of the decomposition product is, for example, 1 H NMR and 13 It can be estimated by nuclear magnetic resonance spectroscopy such as C NMR.

[0020] In the decomposition product according to one embodiment of the present invention, the structural unit derived from acrylic acid may constitute a salt. The salt may be a salt derived from the water absorbent resin before decomposition, or may be a salt derived from a treating agent used in the decomposition treatment. Specific examples of the salt include at least one salt selected from the above-mentioned alkali metal salts (sodium salt, potassium salt, lithium salt, etc.), alkaline earth metal salts (calcium salt, magnesium salt, barium salt, etc.), ammonium salts (quaternary ammonium salt, quaternary alkylammonium salt, etc.). Among these, the salt constituting the structural unit derived from acrylic acid preferably contains an alkali metal salt, and more preferably contains a sodium salt.

[0021] In one embodiment of the present invention, the decomposition product of the water-absorbent resin preferably has a cyclic structure produced in the decomposition reaction of the polyacrylic acid-based water-absorbent resin. The decomposition product having a cyclic structure is, for example, at least one selected from a compound (including a polymer) having a functional group with the cyclic structure as a skeleton, and a polymer containing a cyclic structure in the polymer chain. Among these, the decomposition product having a cyclic structure is more preferably a polymer containing a cyclic structure in the polymer chain, which can be produced by a ring-closing reaction between functional groups of adjacent structural units of the water-absorbent resin, or an addition polymerization reaction to an unsaturated bond, as described below.

[0022] Furthermore, the cyclic structure preferably has an aromatic ring, such as a benzene ring, which is a cyclic hydrocarbon, or a heteroaromatic ring containing oxygen. It is believed that decomposition products having aromatic rings are produced during the decomposition process of a water-absorbent resin by a reaction involving ring closure, such as dehydration condensation or dehydrogenation, between carboxyl groups of adjacent structural units derived from acrylic acid. Chemical formula 1 shows an example of a cyclic structure that may be contained in the polymer chain of a decomposition product according to one embodiment of the present invention. The structural formula of Chemical formula 1 shows an example in which an aromatic ring (benzene ring) is contained between two structural units derived from acrylic acid. However, examples of the cyclic structure are not limited to this.

[0023] [ka]

[0024] In one embodiment of the present invention, in the case where a decomposition product of a water absorbent resin is a polymer having a constitutional unit derived from acrylic acid and a cyclic structure such as an aromatic ring, the ratio (mol %) of the cyclic structure when the constitutional unit derived from acrylic acid is taken as 100 mol %, from the viewpoint of exerting amphiphilicity, is preferably 0.01 mol % or more, more preferably 0.1 mol % or more, and is preferably 15 mol % or less, more preferably 7 mol % or less.

[0025] Furthermore, in one embodiment of the present invention, the decomposition product preferably has an unsaturated bond between the acrylic acid-derived structural unit and the cyclic structure. It is more preferable that such an unsaturated bond is formed between a carbon adjacent to the cyclic structure and a carbon adjacent to the carbon adjacent to the unsaturated bond. The decomposition product having an unsaturated bond is, for example, at least one selected from a compound (including a polymer) having a functional group having an unsaturated bond and a polymer containing an unsaturated bond in the polymer chain. Among these, the decomposition product having an unsaturated bond is more preferably a polymer containing an unsaturated bond in the polymer chain, which can be produced by a cleavage reaction of adjacent structural units of a water-absorbent resin or an elimination reaction of functional groups of adjacent structural units of a water-absorbent resin. It is believed that the decomposition product has an unsaturated bond near the cyclic structure (for example, at a position that forms a π-conjugated system with the cyclic structure), and particularly, an unsaturated bond adjacent to the cyclic structure, thereby improving the ultraviolet light absorption characteristics.

[0026] The decomposition product of the present invention has the structure described above and can be used as a functional material having a function other than water absorption. For example, the decomposition product according to one embodiment of the present invention is preferably used as at least one functional material selected from a dispersant, an ultraviolet absorber, and a fluorescent agent, and more preferably used as a functional material having at least two of these functions.

[0027] For example, the decomposition product according to one embodiment of the present invention exhibits amphiphilicity due to the inclusion of a highly hydrophobic moiety, such as a cyclic structure, in addition to the highly hydrophilic moiety derived from acrylic acid. This property can be utilized as a dispersant. A dispersant is an agent that functions to uniformly and stably disperse fine particles in a liquid. Examples of materials that can contain the decomposition product of the present invention as a dispersant include, but are not limited to, paints, paper, detergents, cleaning aids, deodorizers and / or deodorants, electronic substrates, electronic components, batteries, rechargeable batteries, cement, concrete, asphalt, foundry sand, runners, cosmetics, etc.

[0028] Furthermore, the decomposition product according to one embodiment of the present invention may be used as an ultraviolet absorber having ultraviolet absorbing properties and / or a fluorescent agent that absorbs ultraviolet light and emits fluorescence. Such ultraviolet absorbing properties are believed to be due to the cyclic structure and unsaturated bonds in the vicinity thereof. The wavelength band in which the decomposition product absorbs light as an ultraviolet absorber and / or fluorescent agent is, for example, preferably 100 nm or more and 400 nm or less, and more preferably 315 nm or more and 400 nm or less, which corresponds to UV-A. Furthermore, the decomposition product may be used as a dispersant that functions as an ultraviolet absorber and / or fluorescent agent.

[0029] Materials that can contain the decomposition product of the present invention as an ultraviolet absorber are not particularly limited, but examples thereof include paints, paper, fibers, cosmetics, topical skin preparations, plastic products, etc. Materials that can contain the decomposition product of the present invention as a fluorescent agent are not particularly limited, but examples thereof include paints, paper, fibers, detergents, cleaning aids, etc.

[0030] As a specific example, the decomposition product according to one embodiment of the present invention may be contained in a paint containing at least one selected from pigments and dyes. The paint may be used in any application, including art supplies and printer inks. In the paint, the decomposition product may function as at least one functional material selected from a dispersant that disperses pigment particles in a medium such as a solvent, an ultraviolet absorber, and a fluorescent agent that emits fluorescence.

[0031] As another specific example, the decomposition product according to one embodiment of the present invention may be contained in paper, where the decomposition product can function as at least one papermaking agent selected from paints (dyes and / or pigments), pigment dispersants, fiber dispersants, ultraviolet absorbers, fluorescent agents, etc.

[0032] <Method for producing decomposition product of polyacrylic acid-based water-absorbent resin> A method for producing a decomposition product of a polyacrylic acid-based water-absorbent resin according to one embodiment of the present invention includes a step of decomposing a polyacrylic acid-based water-absorbent resin to produce a decomposition product having a weight-average molecular weight of 100 or more and 1,000,000 or less and having a constitutional unit derived from acrylic acid (hereinafter referred to as a "decomposition step").

[0033] From the viewpoint of efficiently carrying out the decomposition treatment, the water-absorbent resin to be treated in the decomposition step of the present invention is preferably present alone, but may be mixed with other components. For example, the water-absorbent resin may be contained in an absorbent article or the like. In this case, it is preferable to perform a pretreatment on the absorbent article or the like before the decomposition step to expose the water-absorbent resin from the absorbent article or the like. Specific examples of the pretreatment will be described later.

[0034] In one embodiment of the present invention, the decomposition of the polyacrylic acid-based water-absorbing resin may be carried out by any method capable of producing the above-mentioned decomposition products, and preferably includes at least one type of decomposition selected from the group consisting of thermal decomposition, decomposition with an acid, and decomposition with ozone.

[0035] Specifically, in the decomposition step according to one embodiment of the present invention, the polyacrylic acid-based water-absorbent resin is preferably thermally decomposed. Here, thermal decomposition refers to decomposing the molecules of the water-absorbent resin by dry heating. The thermal decomposition treatment according to this embodiment is preferably carried out under, for example, low-oxygen or oxygen-free conditions.

[0036] As a specific heating means in this embodiment, for example, a heating device that heats an open space or a closed space in which the water-absorbent resin can be stored can be used. From the viewpoint of efficiently heating the water-absorbent resin, it is preferable to use a heating device such as a heating furnace that heats a closed space. In this step, from the viewpoint of efficiently heating the water-absorbent resin, it is preferable to heat the water-absorbent resin while stirring it. The atmosphere during heating in this step can be appropriately selected from an air atmosphere or a low-oxygen atmosphere, etc., but from the viewpoint of controlling the decomposition of the water-absorbent resin molecules, a low-oxygen atmosphere is preferable. Note that a low-oxygen atmosphere refers to an atmosphere with an oxygen partial pressure of 10 kPa or less, preferably 8 kPa or less. Furthermore, even a low-oxygen atmosphere is more preferably an inert gas atmosphere or a water vapor atmosphere in which there is almost no oxygen. Examples of inert gases include nitrogen gas and argon gas.

[0037] The mechanism of thermal decomposition of a water-absorbent resin presumed in one embodiment of the present invention will be explained using the schematic diagrams of Figures 1(A) and (B). In these figures, the water-absorbent resin is a crosslinked polyacrylic acid / sodium polyacrylate, the linear structure is a polymer chain including a polymer main chain and a crosslinked chain, "COOH" is a carboxy group derived from acrylic acid, and "COONa" is a sodium salt of a carboxy group derived from acrylic acid.

[0038] As shown in Figure 1(A), a water-absorbent resin has a three-dimensional network structure in which multiple main chains are cross-linked by cross-linking chains containing hydrogen bonds, ester bonds, and the like. When such a water-absorbent resin is heated within a certain temperature range, radicals are generated, which presumably cleave the molecules that form the three-dimensional network structure. During this process, relatively weak bonds such as hydrogen bonds and ester bonds are thermally unstable and therefore more likely to cleave. Furthermore, when the water-absorbent resin is a copolymer of multiple monomers, it is also possible that structural units derived from thermally unstable monomers are preferentially cleaved. Thus, in this step, by utilizing the thermally unstable sites of the water-absorbent resin, the three-dimensional network structure can be thermally decomposed while leaving the acrylic skeleton of the water-absorbent resin intact, producing a decomposition product as shown in Figure 1(B).

[0039] Furthermore, it is known that during the thermal decomposition of polyacrylic acid, the generated radicals cause reactions involving ring closure, such as dehydration condensation or dehydrogenation, between carboxy groups of adjacent structural units derived from acrylic acid, or reactions involving the generation of unsaturated bonds due to elimination reactions of carboxy groups derived from acrylic acid and ring closure due to addition polymerization to the unsaturated bonds. Therefore, as illustrated in Figure 1(B), it is presumed that decomposition products having a cyclic structure as represented by Chemical Formula 1 are generated. Note that Figure 1(B) shows an example in which a cyclic structure is formed at the intersection of the polymer main chain and the crosslinked chain, represented by a black circle, but the present invention is not limited thereto, and the cyclic structure may be formed within either the polymer main chain or the crosslinked chain.

[0040] The thermal decomposition temperature range in the heat treatment of the present embodiment, i.e., the temperature at which the water absorbent resin is heated, is not particularly limited as long as the decomposition product can be generated, but is preferably 300° C. or higher, more preferably 350° C. or higher, even more preferably 370° C. or higher, and preferably 500° C. or lower, more preferably 450° C. or lower, and even more preferably 430° C. or lower. Thereby, as shown in the examples described later, a decomposition product having a weight average molecular weight of 100 or higher and 1,000,000 or lower and having a constitutional unit derived from acrylic acid can be stably generated.

[0041] The heating temperature in the heat treatment of this embodiment may be varied within the range of the pyrolysis temperature zone or may be maintained approximately constant. The water-absorbent resin may be heated using a heating device preheated to a heating temperature within the temperature zone. Alternatively, the water-absorbent resin may be heated so that the maximum temperature reached falls within the temperature zone. The rate of temperature increase is preferably 0.001°C / min or more, more preferably 0.01°C / min or more, even more preferably 0.1°C / min or more, and even more preferably 1°C / min or more, and is preferably 20°C / min or less, more preferably 15°C / min or less, even more preferably 12°C / min or less, and even more preferably 10°C / min or less.

[0042] The time for which the thermal decomposition temperature range is maintained in the heat treatment of this embodiment can be changed as appropriate depending on the thermal decomposition temperature range, but is preferably 1 minute or more, more preferably 3 minutes or more, and preferably 120 minutes or less, more preferably 90 minutes or less.

[0043] In the present embodiment, by thermally decomposing a decomposition product of a water-absorbent resin, it is possible to generate a decomposition product having a weight-average molecular weight of 100 or more and 1,000,000 or less and having a constitutional unit derived from acrylic acid in a relatively short time. In addition, the thermal decomposition treatment has an advantage that it easily causes a ring-closing reaction and easily generates a decomposition product having functions such as a dispersant, an ultraviolet absorber, and / or a fluorescent agent.

[0044] Furthermore, pyrolysis treatment has the advantage that the decomposition treatment can be performed without producing waste liquid, which reduces the environmental impact and treatment costs. Furthermore, pyrolysis treatment has the advantage that the decomposition treatment can be performed using simple equipment and that the effort required for post-treatment, such as separation of the decomposition product from the treatment liquid, can be reduced.

[0045] In the decomposition step according to another embodiment, the water-absorbent resin may be brought into contact with a treatment liquid containing an acid. It is considered that radicals generated by a reaction with the acid act on unstable sites in the three-dimensional network structure of the water-absorbent resin, thereby promoting the decomposition of the water-absorbent resin.

[0046] Specifically, the acid contained in the treatment liquid is not particularly limited, but may be, for example, at least one selected from hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, phosphoric acid, acetic acid, ascorbic acid, etc., and particularly at least one selected from hydrochloric acid, sulfuric acid, ascorbic acid, and acetic acid. The treatment liquid may contain one or more acids. Furthermore, the treatment liquid is preferably an aqueous solution of an acid.

[0047] The concentration of the acid in the processing solution is not particularly limited as long as it is capable of producing the decomposition products described above, but is preferably 0.01% (w / v) or more, more preferably 1% (w / v) or more, and preferably 100% (w / v) or less, more preferably 20% (w / v) or less. The processing solution may also contain additives such as catalysts that promote the acid-induced decomposition reaction. For example, when the processing solution contains ascorbic acid, a trivalent iron compound (e.g., iron(III) chloride, iron(III) sulfate, ethylenediaminetetraacetic acid iron(III) sodium salt, etc.) may be added to the processing solution.

[0048] An example of the contact between the water-absorbent resin and the treatment agent is immersing the water-absorbent resin in a treatment liquid. In this case, for example, a tank containing the treatment liquid is prepared, and at least a part of the water-absorbent resin is immersed in the treatment liquid. The immersion time of the water-absorbent resin is not particularly limited as long as the decomposition product can be generated, but is preferably from 1 hour to 1 month. The water-absorbent resin may be stirred in the treatment liquid.

[0049] As another aspect of contacting the water-absorbent resin with the treatment liquid, for example, the treatment liquid may be poured into the water-absorbent resin to make the water-absorbent resin wet with the treatment liquid. Alternatively, the treatment liquid may be sprayed onto the water-absorbent resin to make the water-absorbent resin wet with the treatment liquid. Alternatively, a powdered acid agent may be added to the water-absorbent resin, and the water-absorbent resin may be made wet with the treatment liquid by pouring water, humidifying, or the like. Alternatively, the powdered acid agent may be added to a used water-absorbent resin in a wet state, or to a water-absorbent resin that has been further poured water, humidified, or the like to make the water-absorbent resin wet.

[0050] In another embodiment, in the decomposition step, the water-absorbent resin may be brought into contact with ozone. This allows the highly reactive ozone to promote the decomposition of the water-absorbent resin. The ozone may be in the form of ozone gas, or may be contained in treated water such as ozonated water and supplied.

[0051] The ozone gas can be supplied using, for example, an ozone generator. The concentration of the supplied ozone gas is not particularly limited as long as it is capable of producing the decomposition products, but is preferably 10 g / m 2 More preferably, 20 g / m 2 or more, and preferably 100 g / m 2 Less than 80 g / m 2 The contact time is not particularly limited, but is preferably, for example, from 10 minutes to 3 hours.

[0052] The treated water containing ozone can be supplied, for example, using an ozone water generator. The concentration of ozone in the treated water is not particularly limited as long as it allows the production of the decomposition products, but is preferably 0.5 ppm (w / v) or more, more preferably 1 ppm (w / v) or more, and preferably 10 ppm (w / v) or less, more preferably 8 ppm (w / v) or less. The contact time is also not particularly limited, but is preferably, for example, 10 minutes to 3 hours.

[0053] As described above, according to the present invention, functional materials such as dispersants, ultraviolet absorbers, and / or fluorescent agents can be produced by decomposing a water-absorbent resin. This makes it possible to easily produce functional polymers that have been complicated or difficult to produce by polymerization reactions from monomers. Furthermore, by using a used water-absorbent resin, the resin material can be recycled, which contributes to reducing the environmental load.

[0054] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the gist of the present invention.

[0055] For example, the decomposition method in the decomposition step is not limited to the above-mentioned examples. For example, in the decomposition step, the water-absorbent resin may be brought into contact with a treatment liquid containing an alkali. Specifically, the alkali contained in the treatment liquid is not particularly limited, but examples thereof include sodium hydroxide, potassium hydroxide, ammonia, calcium hydroxide, etc. The alkali in the treatment liquid may be one type or multiple types. In addition, the treatment liquid is preferably an aqueous alkali solution. The concentration of the alkali in the treatment liquid is not particularly limited as long as it is possible to produce the decomposition product, but is preferably 0.01% (w / v) or more.

[0056] Alternatively, in the decomposition step, the water-absorbent resin may be contacted with an oxidizing agent other than ozone. Examples of such oxidizing agents include percarbonate, perborate, peracetic acid, hydrogen peroxide, hypochlorite, and chlorite. One or more oxidizing agents may be used. As a contact method, a treatment liquid containing an oxidizing agent may be contacted with the water-absorbent resin, or a gaseous oxidizing agent may be contacted with the water-absorbent resin. Furthermore, the oxidizing agent may be used in combination with other treatment agents such as acid, alkali, and ozone, within the scope that can ensure safety and the effects of the invention.

[0057] For example, a method for producing a decomposition product according to yet another embodiment of the present invention may include a step of preparing a water-absorbent resin before the decomposition step. When the water-absorbent resin is contained in the object to be treated, such as a used absorbent article, the step of preparing the water-absorbent resin preferably includes, for example, a treatment that exerts at least one of a physical action and a chemical action on the object to be treated.

[0058] The treatment that exerts a physical action on the object to be treated may be at least one treatment selected from, for example, stirring, crushing, cutting, vibration, drying, freezing, pressurization, decompression, irradiation with energy rays (laser, etc.), and squeezing. Such treatments can be performed using known devices that can perform each of the above treatments.

[0059] The treatment of exerting a chemical action on the object to be treated may include a treatment of separating each element of the absorbent article using, for example, an acid, an alkali, an oxidizing agent, a salt, etc. Furthermore, the treatment may include a treatment of dehydrating the water-absorbent resin using an aqueous solution or solid containing polyvalent metal ions, an acidic aqueous solution, electrolysis, etc.

[0060] Furthermore, the treatment that exerts a chemical action on the water-absorbent resin may include a heat treatment that modifies a thermoplastic resin other than the water-absorbent resin contained in the material to be treated, from the viewpoint of promoting separation of the water-absorbent resin without treatment of waste liquid, etc. In this case, the heating temperature is preferably below the thermal decomposition temperature range of the water-absorbent resin and equal to or higher than the glass transition point of the thermoplastic resin contained in the material to be treated. By modulating the thermoplastic resin other than the water-absorbent resin, it becomes easier to separate each element of the material to be treated, and the heating efficiency of the water-absorbent resin can be increased.

[0061] In addition, in this step, a treatment that exerts both a chemical action and a physical action on the object to be treated may be performed. One example of such a treatment is a treatment in which the object to be treated is heated while being stirred. This can further promote separation of the component containing the water-absorbent resin from the component containing other resins. Alternatively, a treatment that exerts a physical action may be performed while adding an additive such as an acid, an alkali, an oxidizing agent, or a salt to the object to be treated.

[0062] Furthermore, in this step, after the material to be treated is decomposed into each element, the elements not containing the water absorbent resin can also be removed by a separation treatment using a separator (a sieve, a classifier, a screen separator, a cyclone separator, a centrifugal separator, etc.) or a sedimentation treatment, etc. This makes it possible to increase the content ratio of the water absorbent resin in the material to be treated, and to further increase the treatment efficiency of the water absorbent resin. [Example]

[0063] <Test Example 1: Examination of molecular weight and chemical structure of degradation products> A water-absorbent resin (sodium polyacrylate crosslinked body) (manufactured by Sanyo Chemical Industries, Ltd.) was prepared. 5 g of the water-absorbent resin was placed in a tubular furnace and heated from room temperature to a predetermined maximum temperature in a nitrogen atmosphere. After being held at the predetermined maximum temperature for 5 minutes, it was cooled to room temperature. The cooled treated objects were designated Samples 1 to 5. The maximum temperature of Sample 1 was 350°C. The maximum temperature of Sample 2 was 375°C. The maximum temperature of Sample 3 was 400°C. The maximum temperature of Sample 4 was 425°C. The maximum temperature of Sample 5 was 450°C.

[0064] The weight-average molecular weight of each sample was measured by size exclusion chromatography (SEC) as follows. Each sample was dissolved in 1 mL of ion-exchanged water, then diluted with 9 mL of a solution of phosphate and lithium bromide dissolved in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. The solution was filtered through filter paper, and the filtrate was used for measurement. The dissolved solution was used as the eluent. A Tosoh Corporation "HLC-8320GPC" GPC system was used, and two Malvern Panalytical "SEC-MALS 20" and "OMNISEC Reveal" detectors were connected to the SEC system. Two Tosoh Corporation "TSK-GEL α-M, α2500" columns were used in conjunction. The column temperature was 45°C, and the eluent flow rate was 0.8 mL / min. Tosoh Corporation molecular weight standard polyacrylic acid was used for instrument calibration.

[0065] As a result, as shown in Table 1, the weight-average molecular weights of Samples 1 to 5 were within the range of 100 or more and 1,000,000 or less. It was also found that the weight-average molecular weight decreased as the maximum temperature reached increased. From these results, it was inferred that the water-absorbent resin was thermally decomposed by the heat treatment, and a decomposition product of the water-absorbent resin was generated.

[0066] [Table 1]

[0067] Next, the molecular structure of the compounds contained in each sample was determined using sodium polyacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (weight average molecular weight 225,000) as a standard substance. 1 Analysis by H NMR revealed that all samples contained structural units derived from polyacrylic acid (PAA). Samples 1 to 3 also contained aromatic rings and unsaturated bonds adjacent to the aromatic rings in addition to the structural units derived from PAA. Samples 4 and 5, which reached a maximum temperature of 425°C or higher, were insoluble in deuterated solvents, and therefore, 1 The molecular structure could not be analyzed by 1 H NMR.

[0068] Furthermore, for Samples 1 to 3, the content (mol %) of aromatic rings (also expressed as aromatic ring / PAA) was calculated assuming that the number of hydrogen atoms (H) contained in the aromatic rings was 3 and the PAA-derived structural unit was 100 mol %. Specifically, the molar amount of each was calculated from the integral value of the peak derived from PAA or the aromatic ring, and the ratio of the molar amount of aromatic rings to the molar amount of PAA was calculated. As a result, as shown in Table 1, it was found that the content of aromatic rings increased as the maximum temperature reached increased from 350°C to 400°C. From these results, it is considered that at 350 to 400°C, the ring-closing reaction proceeds along with the decomposition of the water-absorbent resin.

[0069] <Test Example 2: Examination of the functionality of degradation products> Next, samples of Examples 1 to 17, which are decomposition products of polyacrylic acid-based water-absorbing resins, have a weight-average molecular weight of 100 or more and 1,000,000 or less, and have structural units derived from acrylic acid, and samples of Comparative Examples 1 to 3, which do not satisfy the above conditions, were prepared, and their functionality was examined.

[0070] [Sample preparation] Example 1 A water-absorbent resin (sodium polyacrylate crosslinked body) (manufactured by Nippon Shokubai Co., Ltd.) (hereinafter referred to as "water-absorbent resin A") used in baby diapers was prepared. 3 kg of water-absorbent resin A was placed in a small kiln and heat-treated in a nitrogen atmosphere at 400°C (maximum temperature reached) for 5 minutes. This gave a sample of Example 1. The weight-average molecular weight was measured by SEC in the same manner as in Test Example 1, except that it was converted using molecular weight standard polystyrene. The measured weight-average molecular weight of the sample was 14,000. The polymer type and decomposition method of each sample are shown in Table 2. The weight-average molecular weight of each sample is shown in Table 3.

[0071] [Table 2]

[0072] [Table 3]

[0073] (Comparative Example 1) 1 g of a 20 wt % aqueous solution of sodium polyacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (weight average molecular weight 225,000) was prepared and mixed with 9 g of pure water to obtain a 2 wt % aqueous solution, which was used as the sample of Comparative Example 1. The weight average molecular weight was measured in the same manner as in Example 1.

[0074] (Comparative Example 2) Styrene-acrylic acid copolymer ("JONCRYL (registered trademark) 690" manufactured by BASF Japan Ltd.) (weight average molecular weight 12,800) was prepared, and 1 g of this copolymer was mixed with 50 g of 60% aqueous sodium hydroxide solution to neutralize it, and a 2 wt % aqueous solution was prepared as a sample of Comparative Example 2. The weight average molecular weight was measured in the same manner as in Example 1.

[0075] (Comparative Example 3) A water-absorbent resin (sodium polyacrylate crosslinked body) (manufactured by Sanyo Chemical Industries, Ltd.) (hereinafter referred to as "water-absorbent resin B") used in baby diapers was prepared. 1 g of water-absorbent resin B was immersed and stirred in 50 g of a 26 w / v % aqueous sodium chloride solution for 1 day, and then filtered through filter paper. The filtrate was used as a sample of Comparative Example 3.

[0076] Example 2 5 g of the water-absorbent resin B was placed in a small tubular furnace and heated at 375°C (maximum temperature) for 5 minutes in a nitrogen atmosphere. 1 g of the obtained sample was immersed and stirred in 50 g of pure water for 1 day, and filtered through filter paper to obtain a sample of Example 2 as a filtrate. The weight-average molecular weight of the sample of Example 2 measured using molecular weight standard polyacrylic acid in the same manner as in Test Example 1 was 32,000. Furthermore, the weight-average molecular weight of the sample measured using molecular weight standard polystyrene in the same manner as in Example 1 was 29,000.

[0077] Examples 3 and 4 Samples of Examples 3 and 4 were obtained by heat treatment in the same manner as in Example 2, except that the maximum temperatures reached in the heat treatment were changed to 400°C and 425°C, respectively. As in Example 2, the weight-average molecular weight of the sample of Example 3 measured using molecular weight standard polyacrylic acid and molecular weight standard polystyrene was 20,000. As in Example 2, the weight-average molecular weight of the sample of Example 4 measured using molecular weight standard polyacrylic acid was 1,200.

[0078] Example 5 A sample of Example 5 was obtained by heat treatment in the same manner as in Example 3, except that the atmosphere in the small tubular furnace was changed to a water vapor atmosphere. As in Example 2, the weight average molecular weight of the sample of Example 5 measured using molecular weight standard polystyrene was 17,000.

[0079] Example 6 The sample of Example 6 was obtained in the same manner as in Example 3, except that a water-absorbent resin (sodium polyacrylate crosslinked product) (manufactured by Nippon Shokubai Co., Ltd.) used in sanitary napkins (hereinafter referred to as "water-absorbent resin C") was used. As in Example 2, the weight-average molecular weight of the sample of Example 6 measured using molecular weight standard polystyrene was 16,000.

[0080] Example 7 A sample of Example 7 was obtained by heat treatment in the same manner as in Example 3, except that a water-absorbent resin (sodium polyacrylate crosslinked body) (manufactured by Nippon Shokubai Co., Ltd.) used in adult diapers (hereinafter referred to as "water-absorbent resin D") was used. As in Example 2, the weight-average molecular weight of the sample of Example 7 measured using molecular weight standard polystyrene was 17,000.

[0081] Example 8 A sample of Example 8 was obtained by heat treatment in the same manner as in Example 3, except that water absorbent resin A was used. As in Example 2, the weight average molecular weight of the sample of Example 8 measured using molecular weight standard polystyrene was 13,000.

[0082] Example 9 The water-absorbent resin A was immersed in a 2% aqueous calcium chloride solution to generate a precipitate, which was then collected. 5 g of the dried precipitate was placed in a small tubular furnace and heat-treated at 400°C (maximum temperature reached) for 5 minutes in a nitrogen atmosphere. 1 g of the obtained sample was placed in 50 g of a 2 w / v% aqueous citric acid solution and filtered with filter paper to obtain a sample of Example 9 as a filtrate. As in Example 2, the weight-average molecular weight of the sample of Example 9 measured using molecular weight standard polystyrene was 25,000.

[0083] Example 10 5 g of water absorbent resin B was placed in a small tubular furnace and heat-treated at 350°C (maximum temperature reached) for 30 minutes in a nitrogen atmosphere. 1 g of the obtained sample was immersed and stirred in 50 g of pure water for one day, and filtered with filter paper to obtain a filtrate as a sample of Example 10. As in Example 2, the weight-average molecular weight of the sample of Example 10 measured using molecular weight standard polystyrene was 90,000.

[0084] Example 11 A sample of Example 11 was obtained by heat treatment in the same manner as in Example 10, except that the time of heat treatment at 350°C (maximum temperature reached) was changed to 60 minutes. As in Example 2, the weight average molecular weight of the sample of Example 11 measured using molecular weight standard polystyrene was 64,000.

[0085] Examples 12 and 13 Samples of Examples 12 and 13 were obtained by heat treatment in the same manner as in Example 10, except that the maximum temperature reached in the heat treatment was changed to 375°C and the heat treatment time at the maximum temperature was changed to 30 minutes and 60 minutes, respectively, as shown in Table 2. The weight average molecular weight of the sample of Example 12, measured using molecular weight standard polystyrene as in Example 2, was 29,000. The weight average molecular weight of the sample of Example 13, measured using molecular weight standard polystyrene as in Example 2, was 27,000.

[0086] Example 14 1 g of water absorbent resin B was immersed in 50 g of an aqueous solution of ascorbic acid with a concentration of 0.2 w / v % for 1 week, and filtered with filter paper to obtain a filtrate as a sample of Example 14. As in Example 2, the weight average molecular weight of the sample of Example 14 measured using molecular weight standard polystyrene was 167,000.

[0087] Example 15 A treatment liquid was prepared by mixing 0.02 w / v% ethylenediaminetetraacetic acid iron as a catalyst with 0.2 w / v% aqueous ascorbic acid solution. 1 g of water absorbent resin B was immersed in 50 g of this treatment liquid for 1 week, and filtered with filter paper to obtain a sample of Example 15 as a filtrate.

[0088] Example 16 5 g of water-absorbent resin B was added to ozone gas (ozone concentration: 50 g / m) generated by an ozone generator. 2 ) for 1 hour. 1 g of the obtained sample was immersed and stirred in 50 g of a 26 w / v % aqueous sodium chloride solution for 1 day, filtered through filter paper, and the filtrate was used to obtain the sample of Example 16. The weight-average molecular weight of the sample of Example 16, measured using molecular weight standard polystyrene in the same manner as in Example 2, was 14,000.

[0089] Example 17 5 g of water absorbent resin B was immersed for 1 hour in ozone water (ozone concentration: 6.1 ppm (w / v)) generated by an ozone water generator. 1 g of the obtained sample was immersed and stirred in 50 g of a 26 w / v % aqueous sodium chloride solution for 1 day, and filtered with filter paper to obtain a sample of Example 17 as a filtrate. As in Example 2, the weight average molecular weight of the sample of Example 17 measured using molecular weight standard polystyrene was 43,000.

[0090] [Evaluation of water solubility] All of the solid samples in Examples 1, 3 to 8, and 11 to 13 were made into 2 wt% aqueous solutions and filtered through filter paper, but no filtration residue remained on the filter paper. The aqueous solutions in Comparative Examples 1 and 2 were filtered through filter paper, but no filtration residue remained on the filter paper. In Examples 2, 9, 10, and 14 to 17, residue remained on the filter paper during the filtration process.

[0091] [Evaluation of absorption characteristics] All solid samples in Examples 1, 3 to 8, and 11 to 13 were prepared as 0.1 w / v% aqueous solutions. The solution samples in Comparative Examples 1 and 2 and Examples 2, 9, 10, 14, and 15 were diluted 20-fold to prepare solutions equivalent to 0.1 w / v%. Comparative Example 3 and Examples 16 and 17 were used as is. The solution to be measured was filled into a solution cell of an ultraviolet-visible spectrophotometer ("UV-2550," manufactured by Shimadzu Corporation). The comparison cell was filled with pure water. The measurement object of each sample was irradiated with light of 200 to 800 nm, and the light transmittance was measured. Graphs of the transmittance for each wavelength for each sample are shown in Figures 2 to 7.

[0092] 2, it was found that the sample of Example 1 has different light transmittance from the samples of Comparative Examples 1 to 3, and has low transmittance for light in the wavelength band of 280 to 315 nm corresponding to UV-B and light in the wavelength band of 315 to 400 nm corresponding to UV-A. This shows that the sample of Example 1 has different ultraviolet light absorption characteristics from those of Comparative Examples 1 and 2, and in particular, has significant absorbance of UV-A.

[0093] 3 to 7, it was found that the samples of Examples 2 to 20 also have ultraviolet light absorption characteristics different from those of Comparative Examples 1 and 2, and have higher UV-A absorption than Comparative Examples 1 to 3. Of these, it was found that the samples of Examples 4 and 13 have particularly high UV-A absorption.

[0094] [Evaluation of fluorescent properties] All solid samples in Examples 1, 3 to 8, and 11 to 13 were prepared as 0.05 w / v% aqueous solutions. The solution samples in Comparative Examples 1 and 2 and Examples 2, 9, 10, 14, and 15 were diluted 40-fold to a concentration equivalent to 0.05 w / v%. Comparative Example 3 and Examples 16 and 17 were used as is. The measurement target of each sample was filled into a cell of a spectrofluorometer (F-7000 model, manufactured by Hitachi, Ltd.). The emission intensity at 400 nm when each sample was irradiated with varying excitation wavelengths (wavelength distribution 200 to 900 nm) is shown in Figures 8 to 13. Furthermore, the measurement target of each sample was irradiated with 298 nm ultraviolet light, and the spectral intensity of the emitted fluorescence (wavelength 200 to 900 nm) was measured. The spectral intensity distribution of each sample when irradiated with 298 nm light is shown in Figures 14 to 19.

[0095] As shown in Fig. 8, it was found that, when irradiated with light having different excitation wavelengths, the sample of Example 1 emitted fluorescence with a higher intensity at 400 nm than the samples of Comparative Examples 1 to 3. Furthermore, the excitation wavelength distribution of the samples of Comparative Examples 1 to 3 mainly had one peak in the scattered light near 400 nm where the irradiated light was scattered, and no fluorescence was observed, whereas the excitation wavelength distribution of the sample of Example 1 had a peak near 330 to 340 nm in addition to the peak near 400 nm, and it was found that it had an excitation wavelength that excited fluorescence separate from the scattered light.

[0096] 9 to 13, when irradiated with light having different excitation wavelengths, the excitation wavelength distributions of the samples of Examples 2 to 17 also had a peak at 350 nm or less in addition to the peak near 400 nm at an emission intensity of 400 nm, and thus had fluorescence emission properties compared to the non-fluorescent Comparative Examples 1 to 3. In particular, the excitation wavelength distributions of the samples of Examples 2 to 13 tended to emit fluorescence with higher intensity than Comparative Examples 1 to 3 at wavelengths of 250 to 350 nm.

[0097] 14, it was found that even when irradiated with light having a wavelength of 298 nm, the sample of Example 1 had a different spectral intensity distribution and emitted fluorescence from the samples of Comparative Examples 1 to 3. For example, the spectral intensity distributions of the samples of Comparative Examples 1 to 3 mainly had one peak in the scattered light near 298 nm, which is the scattering of the irradiated light, and did not emit fluorescence, whereas the spectral intensity distribution of the sample of Example 1 had a peak near 400 nm, which was not observed in the samples of Comparative Examples 1 to 3.

[0098] 15 to 19, when irradiated with light having a wavelength of 298 nm, the spectral intensity distributions of the samples of Examples 2 to 17 also had a peak in the 350 to 500 nm range, which was not observed in Comparative Examples 1 to 3. Furthermore, in particular, Examples 3, 5, 6, 7, and 8 had a high intensity peak in the wavelength range of 350 to 500 nm.

[0099] [Evaluation of dispersion stability] The dispersibility of each sample was evaluated using a centrifugal sedimentation dispersion stability evaluation device (LUMISizer, manufactured by MS Scientific Co., Ltd.). All solid samples in Examples 1, 3 to 8, and 11 to 13 were prepared as 2 w / v% aqueous solutions. The solution samples in Comparative Examples 1 to 3 and Examples 2, 9, 10, and 14 to 17 were used as is, with a water-absorbent resin concentration of 2 w / v%. Each sample was mixed with 2% by mass of phthalocyanine to prepare a sample-containing liquid suspension, which was then placed in the evaluation device. The relationship between the elapsed time and the average transmittance of light at a wavelength of 470 nm was analyzed when centrifugal force was applied to the sample-containing liquid at a temperature of 25°C and a rotation speed of 4,000 rpm. The results are shown in Figures 20 to 25. In this test, samples with higher dispersion stability were less likely to precipitate the phthalocyanine in the sample-containing liquid, resulting in lower average transmittance over time. Therefore, samples with lower average transmittance can be evaluated as having higher dispersion stability.

[0100] 20, it was found that the sample-containing liquid of Example 1 had a significantly lower average transmittance than the sample-containing liquids of Comparative Examples 1 and 3. Furthermore, the sample of Comparative Example 2 is sometimes used as a dispersant, and it was found that the sample-containing liquid of Example 1 had an average transmittance that was lower than or equivalent to that of the sample-containing liquid of Comparative Example 2. This shows that the sample of Example 1 has high dispersion stability and functions as a dispersant.

[0101] 21 to 24, it was found that the sample-containing liquids of Examples 2 to 15 also had average permeabilities that were lower than those of the sample-containing liquids of Comparative Examples 1 and 3, and lower than or equal to those of the sample-containing liquid of Comparative Example 2. These findings indicated that the samples of Examples 2 to 15 also function as dispersants. Furthermore, as shown in FIG. 25, the average permeabilities of the sample-containing liquids of Examples 16 and 17 were equal to those of the sample-containing liquids of Comparative Examples 1 and 3, and it could not be said that the dispersion stability of the samples of Examples 16 and 17 was high.

[0102] <Test Example 3: Examination of application examples of decomposition products> Next, the functionality of the paper containing the decomposition product of the polyacrylic acid-based water-absorbent resin of the present invention was evaluated.

[0103] [Sample preparation] Comparative Example 4 A commercially available Japanese paper was used as the sample of Comparative Example 4.

[0104] [Example 18] A solution prepared by preparing a 2 w / v % aqueous solution of the sample (decomposition product) of Example 1 was uniformly applied with a brush to the Japanese paper of Comparative Example 4. After application, the paper was dried to produce a sample of Example 18.

[0105] [Evaluation of absorption characteristics] The measurement object was placed in a film cell of an ultraviolet-visible spectrophotometer ("UV-2550", manufactured by Shimadzu Corporation) similar to that used in Test Example 2. The reference cell was left empty. The measurement object of each sample was irradiated with light of 200 to 800 nm, and the light transmittance was measured. A graph of the transmittance of each sample at each wavelength is shown in Figure 26.

[0106] 26, the Japanese paper sample of Example 18 had lower transmittance for all wavelengths of light between 200 and 800 nm, and particularly lower transmittance for ultraviolet light between 300 and 400 nm, compared to the Japanese paper sample of Comparative Example 4. This indicates that the Japanese paper sample of Example 18 has ultraviolet absorption properties.

Claims

1. A decomposition product of a polyacrylic acid-based water-absorbing resin, The weight average molecular weight is 100 or more and 1,000,000 or less, Contains structural units derived from acrylic acid Decomposition product of polyacrylic acid-based water-absorbing resin.

2. The polyacrylic acid-based water-absorbing resin is at least one selected from a crosslinked polyacrylate and a crosslinked polyacrylic acid / polyacrylate. A decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 1.

3. At least one functional material selected from the group consisting of a dispersant, an ultraviolet absorber, and a fluorescent agent is used. A decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 1.

4. Used as a dispersant A decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 1.

5. A paint containing the decomposition product of the polyacrylic acid-based water-absorbent resin according to any one of claims 1 to 4.

6. By decomposing a polyacrylic acid-based water-absorbing resin, a decomposition product having a weight-average molecular weight of 100 or more and 1,000,000 or less and having a structural unit derived from acrylic acid is generated. A method for producing a decomposition product of a polyacrylic acid-based water-absorbent resin.

7. In the decomposition of the polyacrylic acid-based water-absorbing resin, the polyacrylic acid-based water-absorbing resin is thermally decomposed. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 6.

8. The temperature at which the polyacrylic acid-based water-absorbing resin is thermally decomposed is 300° C. or higher and 500° C. or lower. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 7.

9. In the decomposition of the polyacrylic acid-based water-absorbing resin, the polyacrylic acid-based water-absorbing resin is brought into contact with a treatment liquid containing an acid. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 6.

10. In the decomposition of the polyacrylic acid-based water-absorbing resin, the polyacrylic acid-based water-absorbing resin is brought into contact with ozone. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 6.

11. The decomposition product is used as at least one functional material selected from a dispersant, an ultraviolet absorber, and a fluorescent agent. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 6.

12. The decomposition product is used as a dispersant. A method for producing a decomposition product of the polyacrylic acid-based water-absorbent resin according to claim 6.

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