EP-4741453-A1 - METHOD FOR PRODUCING SOLUBILIZED POLYMER-CONTAINING MATERIAL, AND METHOD FOR PRODUCING WATER-ABSORBENT RESIN USING SOLUBILIZED POLYMER-CONTAINING MATERIAL AS PORTION OF RAW MATERIAL

Abstract

Provided is a method for producing a solubilized polymer-containing material that makes it possible to efficiently decompose water-absorbent resins to efficiently produce the solubilized polymer-containing material, and provide a method for producing a water-absorbent resin in which a portion of the solubilized polymer-containing material is used as a raw material. The method for producing a solubilized polymer-containing material includes a heat treatment step of heat-treating a mixture (B) containing a water-absorbent resin (A), water, and a peroxide under conditions satisfying the following i) and ii), in which a mass average molecular weight (Mw) of a water-soluble content of a solubilized polymer-containing material (C) obtained in the heat treatment step is from 30000 to 1000000: i) a solid content concentration of the mixture (B) is 60 mass% or greater, and ii) a temperature of the heat treatment is 60°C or higher.

Inventors

• MATSUI, DAISUKE
• NOGI, KOZO
• FUJINO, SHIN-ICHI
• TORII, KAZUSHI
• ENOKIDA, Yusuke
• KOBAYASHI, NOBUHIRO
• ISHIZAKI, KUNIHIKO

Assignees

• Nippon Shokubai Co., Ltd.

Dates

Publication Date

20260513

Application Date

20240514

Claims (15)

1. A method for producing a solubilized polymer-containing material, the method comprising a heat treatment step of heat-treating a mixture (B) containing a water-absorbent resin (A), water, and a peroxide under conditions satisfying i) and ii) set forth below: i) a solid content concentration of the mixture (B) is 60 mass% or greater, and ii) a temperature of the heat treatment is 60°C or higher, wherein a mass average molecular weight (Mw) of a water-soluble content of a solubilized polymer-containing material (C) obtained in the heat treatment step is from 30000 to 1000000.
2. The production method according to claim 1, wherein in the heat treatment step, a dew point of a gas phase portion in a heat treatment device is 30°C or higher.
3. The production method according to claim 1, wherein in the heat treatment step, stirring is performed.
4. The production method according to claim 1, wherein the peroxide is a peroxide represented by General Formula (1) set forth below: R-O-OH (1) where in General Formula (1), R is a hydrogen atom or an aliphatic substituent.
5. The production method according to claim 1, wherein the peroxide is hydrogen peroxide.
6. The production method according to claim 1, wherein Mw/Mn of the water-soluble content of the solubilized polymer-containing material (C) is 6.0 or less.
7. The production method according to claim 1, wherein an amount of increase in the water-soluble content as calculated by Formula 1) set forth below is 5 mass% or greater: water − soluble content increase amount mass % = Extr . C − Extr . A where, Extr. A is an amount of a water-soluble content of the water-absorbent resin (A), and Extr. C is an amount of the water-soluble content of the solubilized polymer-containing material (C).
8. The production method according to claim 1, wherein a solid content concentration of the mixture (B) is 80 mass% or greater.
9. The production method according to claim 1, wherein in the heat treatment step, a temperature of the heat treatment is 105°C or higher.
10. The production method according to claim 1, wherein in the method for producing a solubilized polymer-containing material, a solubilized polymer is not generated by electromagnetic waves.
11. A method for producing a water-absorbent resin, the method comprising an addition step of adding the solubilized polymer-containing material (C) obtained by the production method described in any one of claims 1 to 10.
12. A solubilized polymer-containing material, which is a solubilized polymer-containing material (C) obtained by heat-treating a mixture (B) comprising a water-absorbent resin (A), water, and a peroxide, wherein a solid content concentration of the solubilized polymer-containing material (C) is 60 mass% or greater, and a mass average molecular weight (Mw) of a water-soluble content of the solubilized polymer-containing material (C) is from 30000 to 1000000.
13. The solubilized polymer-containing material according to claim 12, wherein Mw/Mn of the water-soluble content of the solubilized polymer-containing material (C) is 6.0 or less.
14. The solubilized polymer-containing material according to claim 12, wherein the solubilized polymer-containing material (C) is not obtained by use of electromagnetic waves.
15. The solubilized polymer-containing material according to claim 12, wherein a yellowness index (YI) value of the solubilized polymer-containing material (C) is 20 or less.

Description

Technical Field The present invention relates to a method for producing a solubilized polymer-containing material and a method for producing a water-absorbent resin using the solubilized polymer-containing material as a portion of the raw material. Background Art Water-absorbent resins are widely used as water absorbents in absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads from the viewpoint of body fluid absorption. Absorbent articles are generally disposable, but in recent years, interest in recycling absorbent articles has increased due to an increase in environmental awareness. As a technique for recycling water-absorbent resins used in absorbent articles, a method has been developed in which a water-absorbent resin is decomposed and solubilized, and the solubilized polymer is then reused. Various techniques are known as methods for decomposing and solubilizing water-absorbent resins, such as a technique of solubilizing a water-absorbent resin by heat-treating a mixture of a water-absorbent resin and pulp in the presence of an oxidizing agent (Patent Document 1), a technique of solubilizing a water-absorbent resin using a reducing agent and a transition metal ion (Patent Document 2), and a technique of decomposing a water-absorbent resin by irradiating the water-absorbent resin with microwaves at 200°C in the presence of hydrogen peroxide (Patent Document 3). Moreover, as a method for using a solubilized polymer obtained by decomposing a water-absorbent resin, a technique of adding a solubilized polymer in a process of producing a water-absorbent resin is known (Patent Document 4). Citation List Patent Document Patent Document 1: Japanese Unexamined Patent Application Publication "JP H04-317785 A"Patent Document 2: Japanese Unexamined Patent Application Publication "JP 2019-131789 A"Patent Document 3: European Patent Application Publication No. EP 3783056 A1Patent Document 4: WO 2020/213298 Summary of Invention Technical Problem However, the above-mentioned techniques for producing a solubilized polymer are problematic in that all involve a solubilization treatment at a low solid content concentration, and the solid content of the obtained solubilized polymer is small relative to the total treatment amount, and thus production efficiency is low. In addition, since the obtained solubilized polymer also has a low solid content concentration (< 5 mass%), an aqueous solution containing the solubilized polymer is freeze-dried to increase the solid content concentration and then added to the production process for producing a water-absorbent resin. Therefore, another issue is that a large amount of energy is required for drying in order to reuse the solubilized polymer, and thus the existing techniques are extremely inefficient in terms of energy. Moreover, when a water-absorbent resin is excessively decomposed in the production of a solubilized polymer, the molecular weight of the solubilized polymer generally decreases. Therefore, when the solubilized polymer is to be reused as a part of the raw materials of a water-absorbent resin, and particularly when crosslinking is to be formed between the solubilized polymers or between the solubilized polymer and other molecules, an issue arises in that the crosslinking efficiency is deteriorated, and the process is not economical. Thus, a demand exists for a method for producing, with higher production efficiency, a solubilized polymer-containing material that contains a solubilized polymer having a high molecular weight. Hence, an object of one aspect of the present invention is to provide a method for producing a solubilized polymer-containing material that contains a high molecular weight solubilized polymer, the production method thereof allowing the efficient decomposition of a water-absorbent resin, and to provide an energy-efficient method for producing a water-absorbent resin, the method thereof using, as a portion of the raw materials, the solubilized polymer-containing material obtained by the production method and containing a solubilized polymer having a high molecular weight. Solution to Problem That is, in order to solve the issues described above, one aspect of the present invention includes the following configurations. [1] A method for producing a solubilized polymer-containing material, the method including a heat treatment step of heat-treating a mixture (B) containing a water-absorbent resin (A), water, and a peroxide under conditions satisfying i) and ii) set forth below: i) a solid content concentration of the mixture (B) is 60 mass% or greater, andii) a temperature of the heat treatment is 60°C or higher wherein a mass average molecular weight (Mw) of a water-soluble content of a solubilized polymer-containing material (C) obtained in the heat treatment step is from 30000 to 1000000.[2] The production method according to [1], wherein in the heat treatment step, a dew point of a gas phase portion in a heat t