Water-Absorbent Resin Particles via Staged Crosslinking
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Solution Overview
Problem
Existing water-absorbent resin particles in absorbent articles require improved absorption performance, particularly in terms of physiological saline retention capacity, saline absorption capacity under a load of 4.14 kPa, and non-pressurization DW after 5 minutes, to reduce the amount of resin and hydrophilic fibers while maintaining article performance.
Innovation Solution
A method involving reversed phase suspension polymerization with two or more stages using an azo compound as a radical polymerization initiator, adjusting internal-crosslinking agents and surface-crosslinking steps to produce water-absorbent resin particles with enhanced absorption properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water-absorbent resin particles with high water retention capacity are used, then the amount of resin and hydrophilic fibers can be reduced, but other performance (permeation rate, re-wet, liquid leakage) may deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the neutralization degree of polyacrylic acid within 30-90% and controlling the particle size distribution (D10-D90 range of 1.4-2.6). These parameter optimizations enable the resin particles to achieve high water retention capacity while maintaining appropriate permeation rate, re-wet properties, and liquid leakage resistance, thus resolving the contradiction between improved feature and worsened feature
Solution Approach 2:
The patent creates a composite structure by combining polyacrylic acid with specific neutralization degree and controlled particle size distribution to form water-absorbent resin particles with optimized performance. The composite nature of the resin (partially neutralized polyacrylic acid with specific D10-D90 ratio) enables simultaneous achievement of high water retention and maintained article performance
2Quantity of substance
If the amount of water-absorbent resin particles is reduced, then cost and material usage improve, but absorption performance may deteriorate
Solution Approach 1:
By optimizing parameters including neutralization degree (30-90%) and particle size distribution (D10-D90 of 1.4-2.6), the patent achieves resin particles with superior water retention capacity, allowing reduction of resin quantity while maintaining absorption performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces resin particles with improved physiological saline retention capacity, absorption capacity under load, and non-pressurization DW, enabling reduced resin and fiber usage in absorbent articles without compromising performance.
Implementation Method 1
subjecting a water-soluble ethylenically unsaturated monomer to reversed phase suspension polymerization using a radical polymerization initiator, wherein an azo compound is used as the radical polymerization initiator
Implementation Method 2
crosslinked products of polymers of partially neutralized polyacrylic acid
Implementation Method 3
a surface-crosslinking step is included after the polymerization
Implementation Method 4
reversed phase suspension polymerization
Data Source
Figure 1~2
AI summary
There is provided a novel method for producing water-absorbent resin particles, the method being capable of producing water-absorbent resin particles having improved absorption performance (in particular, in terms of physiological saline retention capacity, physiological saline absorption capacity under a load of 4.14 kPa, and value of non-pressurization DW after 5 minutes). A method for producing water-absorbent resin particles by subjecting a water-soluble ethylenically unsaturated monomer to reversed phase suspension polymerization using a radical polymerization initiator, wherein the radical polymerization initiator comprises an azo compound as at least one radical polymerization initiator, wherein the reversed phase suspension polymerization comprises two or more stages of polymerization steps, wherein in a first-stage polymerization step, (a) an internal-crosslinking agent is used in an amount of 0.01 mmol or more and 0.11 mmol or less per mole of the water-soluble ethylenically unsaturated monomer used in first-stage polymerization, wherein in a second-stage polymerization step, (b) an internal-crosslinking agent is used in an amount of 0 mmol or more and 0.042 mmol or less per mole of the water-soluble ethylenically unsaturated monomer used in second-stage polymerization, and (c) the azo compound is used in an amount of 0.38 mmol or less per mole of the water-soluble ethylenically unsaturated monomer used in the second-stage polymerization, and wherein the method comprises a surface-crosslinking step after the second- or subsequent-stage polymerization step.