JP-7856748-B2 - Method for producing water-absorbent resin powder

JP7856748B2JP 7856748 B2JP7856748 B2JP 7856748B2JP-7856748-B2

Inventors

野田敦裕
従野剛
足立芳史
佐藤舞
若林亮太
藤田佳佑
上田洵也
金子淳平

Assignees

株式会社日本触媒

Dates

Publication Date: 20260511
Application Date: 20230328
Priority Date: 20220330

Claims (13)

A polymerization step involves polymerizing an aqueous monomer solution to obtain a water-containing gel-like crosslinked polymer, After the polymerization step, the water-containing gel-like crosslinked polymer is pulverized using a gel pulverizer to obtain a particulate water-containing gel-like crosslinked polymer, It includes, The gel crushing apparatus comprises an inlet, an outlet, and a main body containing multiple rotating shafts, each of which has a crushing mechanism. In the gel pulverization step, the water-containing gel-like crosslinked polymer is continuously fed in from the inlet, and the particulate water-containing gel-like crosslinked polymer is continuously removed from the outlet. The polymerization rate of the water-containing gel-like crosslinked polymer introduced into the input port is 90% by mass or more. The gel pulverization coefficient is 0.020 J/g·sec or more and 3.0 J/g·sec or less. The mass-average particle size of the particulate water-containing gel-like crosslinked polymer discharged from the outlet is 500 μm or less, based on solid content. A method for producing a water-absorbing resin powder , wherein the water-containing gel-like crosslinked polymer is a crosslinked body mainly composed of poly(meth)acrylic acid (salt) .
The manufacturing method according to claim 1, wherein the average residence time of the water-containing gel-like crosslinked polymer in the gel pulverizing apparatus is 30 seconds or more and 1200 seconds or less.
The manufacturing method according to claim 1 or 2, wherein the hydrated gel-like crosslinked polymer obtained after the polymerization step is in the form of a sheet, and further comprises a shredding step of shredding the sheet-like hydrated gel-like crosslinked polymer before the gel pulverization step.
The manufacturing method according to claim 1 or 2, wherein the particulate water-containing gel-like crosslinked polymer contains a gel fluidizing agent.
The manufacturing method according to claim 4, wherein the gel fluidizing agent is added to the water-containing gel-like crosslinked polymer before and/or during the gel grinding step.
The manufacturing method according to claim 1 or 2, wherein the rotating shaft has a disk, and the ratio of the effective length L inside the main body to the maximum diameter D of the disk (or the diameter of the largest disk if multiple disks of different diameters are used), L/D, is 5 or more and 20 or less.
The manufacturing method according to claim 6, wherein, with respect to the major axis diameter X of the disk, the minor axis diameter Y satisfies 0.2 ≤ Y/X ≤ 0.6, and the thickness T of the disk satisfies 0.05 ≤ T/X ≤ 1.0.
The manufacturing method according to claim 1 or 2, wherein the porosity V of the gel grinding apparatus, calculated by the following formula, is 40% or more and 80% or less. V={(AB)/A}*100 (Here, A is the internal volume ( m³ ) of the main body portion excluding the portions corresponding to the inlet and outlet in the longitudinal direction, and B is the sum of the volumes ( m³ ) of the multiple rotating shafts and the crushing means located in the main body portion excluding the portions corresponding to the inlet and outlet in the longitudinal direction.)
The manufacturing method according to claim 1 or 2, wherein the arrangement of the grinding means in the gel grinding apparatus includes one or more locations where the phase difference between adjacent disks in the direction of travel from the input port to the discharge port is greater than 90° and less than 180°, resulting in a return phase.
The manufacturing method according to claim 1 or 2, wherein the solid content of the water-containing gel-like crosslinked polymer introduced into the input port is 25 to 75% by mass.
The manufacturing method according to claim 1 or 2, wherein the solid content of the particulate water-containing gel-like crosslinked polymer discharged from the outlet is 25 to 75% by mass.
The manufacturing method according to claim 1 or 2, wherein the introduced water-containing gel is continuously crushed by a crushing means on a rotating shaft from the input port to the discharge port.
The manufacturing method according to claim 1 or 2, further comprising a surface crosslinking step after the gel pulverization step.

Description

This invention relates to a method for producing water-absorbent resin powder. Super absorbent polymers (SAP) are water-swellable, water-insoluble polymer gelling agents that are widely used in various fields, including absorbent products such as disposable diapers and sanitary napkins, water-retaining agents for agriculture and horticulture, and water-stopping agents for industry. While various monomers and hydrophilic polymers are used as raw materials for the above-mentioned superabsorbent polymers, polyacrylic acid (salt)-based superabsorbent polymers, which use acrylic acid and/or its salts as monomers, are the most widely produced industrially from the standpoint of water absorption performance. The above-mentioned superabsorbent polymers are required to have various functions (high physical properties) in line with the increasing performance of their primary application, disposable diapers. Specifically, in addition to basic physical properties such as water absorption ratio under no pressure and water absorption ratio under pressure, various other physical properties such as gel strength, water solubility, water content, water absorption rate, liquid permeability, particle size distribution, urine resistance, antibacterial properties, damage resistance, powder flowability, deodorizing properties, color resistance, low dust, and low residual monomers are required for superabsorbent polymers. In particular, for applications in hygiene products such as disposable diapers, further improvement in water absorption rate is desired as products become thinner. The above-mentioned commercial manufacturing method for powdered or particulate superabsorbent resin typically includes a polymerization step, a gel pulverization (fine granulation) step performed after or simultaneously with polymerization, a drying step of the finely granulated gel, a pulverization step of the dried product, a classification step of the pulverized product, a recovery step of the fine powder generated by pulverization and classification, and a surface crosslinking step of the classified superabsorbent resin powder. One method for producing superabsorbent polymers proposed to date involves using a polymerization apparatus with a pulverization mechanism to simultaneously perform the polymerization and gel pulverization steps. In this method, as the polymerization reaction of the liquid monomer progresses, the resulting water-containing gel is pulverized, and the finely granulated water-containing gel is discharged from the polymerization apparatus. Specific examples of this method, using batch-type kneaders and continuous-type kneaders, are shown in Patent Documents 1 to 3. However, the size of the gel particles obtained with these devices is only a few millimeters to a few centimeters, which is insufficient for the current situation where further improvements in water absorption rate are required, and additional gel grinding equipment was needed. Patent document 4 proposes a method of wet grinding using a batch-type kneader or a continuous-type kneader to a size smaller than the gel particles that will become the product particle size of the water-absorbent resin, but this is not practical because the size of the equipment becomes excessively large. Furthermore, in the polymerization process, the highly adhesive hydrated gel, which is undergoing monomer polymerization, is pulverized. This makes it easy for the hydrated gel to adhere to the internal components of the equipment. As the reaction progresses while the gel is attached, it solidifies, potentially causing damage to the components and requiring more time for cleaning during maintenance. Japanese Unexamined Patent Publication No. 57-34101Japanese Unexamined Patent Publication No. 60-55002International Publication No. 2001/038402 brochureJapanese Patent Application Publication No. 05-112654 In recent years, obtaining superabsorbent resins with superior water absorption rates has been particularly sought after. This requires grinding the water-containing gel to a smaller particle size than before during the gel grinding process. However, conventional kneader polymerization, which simultaneously performs the polymerization and gel grinding processes using a multi-axis kneader, has not been able to obtain water-containing gels with the desired particle size. Therefore, an object of the present invention is to provide a water-absorbing resin with excellent water absorption rate. Another object of the present invention is to reduce residual monomers. The inventors first discovered that, while conventionally a particulate water-containing polymer (hereinafter also referred to as "particulate water-containing gel") is obtained using an extruder (meat chopper) equipped with a porous plate (also called a die), particulate water-containing water-containing gel can be continuously obtained by performing gel pulverization using a multi-screw kneader (particularly a twin-screw kneader). Furth