Water Absorbing Agent Residual Monomer Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current water absorbing agents used in sanitary products face challenges in reducing residual monomer levels without compromising absorption properties or causing coloration and odor issues, due to variations in particle size distribution and segregation, leading to inconsistent product quality.
Innovation Solution
A water absorbing agent with a cross-linked structure, comprising particles of 300 to 850 μm and smaller particles, is developed, with a residual monomer index (RMI) not greater than 0.30, achieved through a production method involving surface crosslinking and a sulfur-containing reducing agent, ensuring low and consistent residual monomer levels across particle sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of radical polymerization initiator is increased to reduce residual monomer, then the amount of residual monomer is reduced, but the water absorbent resin becomes colored
Solution Approach 1:
The patent applies preliminary action by adding a radical polymerization initiator to the hydrogel polymer before drying to promote polymerization of residual monomer. This preliminary treatment reduces residual monomer content before the drying step, preventing both coloration and odor issues that would otherwise require more aggressive post-treatment methods
Solution Approach 2:
The patent changes the timing and conditions of initiator addition by introducing it at a specific stage (after polymerization but before drying) and controlling the drying conditions subsequently. This parameter optimization allows residual monomer to be converted without excessive initiator remaining to cause coloration, achieving a balance between monomer reduction and product quality
2Quantity of substance
If severe conditions are applied to reduce residual monomer to desired levels, then the amount of residual monomer is reduced, but physical properties such as absorption capacity are impaired due to polymer deterioration
Solution Approach 1:
The patent performs the monomer reduction action preliminarily by adding the initiator to the hydrogel polymer before drying. This timing allows residual monomer to be converted under controlled conditions without requiring severe post-treatment that would damage the polymer structure and absorption capacity
Solution Approach 2:
The patent optimizes parameters by controlling the amount of initiator added and the drying conditions subsequently. This balanced approach reduces residual monomer to desired levels while maintaining the polymer's physical properties and absorption functionality intact
3Quantity of substance
If reductive substance is added to reduce residual monomer, then the amount of residual monomer is reduced, but bad smell is emitted due to binding of reductive substance and impurities during heat treatment
Solution Approach 1:
The patent replaces the reductive substance approach with a preliminary action of adding radical polymerization initiator to the hydrogel polymer before drying. This alternative method achieves residual monomer reduction through polymerization rather than reduction, eliminating the source of bad smell that would otherwise be generated during heat treatment
Solution Approach 2:
The patent converts the potentially harmful effect of heat treatment with reductive substances (which causes bad smell) into a beneficial process by using radical polymerization initiator instead. The heat treatment step then serves to complete the polymerization reaction and remove water, achieving monomer reduction without the harmful side effects
4Ease of manufacture
If particle size distribution is not controlled, then production is simpler, but variance of residual monomer amount among absorbing articles increases
Solution Approach 1:
The patent controls the particle size distribution parameter by adjusting drying and pulverization conditions. This parameter control ensures uniform initiator distribution and consistent residual monomer reduction across particles of different sizes, reducing variance in residual monomer content among final absorbing articles while maintaining production feasibility
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 solution provides a water absorbing agent with low residual monomer levels, reduced variance in absorption capacity, and improved sanitary properties, preventing coloration and odor issues, while maintaining high absorption performance even under load.
Implementation Method 1
a reductive substance is added to a hydrogel polymer prior to or during drying
Implementation Method 2
cross-linked polymers of partially neutralized polyacrylic acid and the like have been known
Implementation Method 3
water absorbing properties, i.e., high absorption capacity without load and high absorption capacity under a load
Data Source
AI summary
An object of the present invention is to provide a water absorbing agent having a low amount of residual monomer, small variance of the amount of residual monomer among ranges of particle size distribution and favorable absorption properties, and being sanitary; an absorbing article; and a method for the production of a water absorbing agent. The water absorbing agent of the present invention has the amount of residual monomer of not higher than 500 ppm, and a residual monomer index of not greater than 0.30. The method for the production includes a first step of obtaining a hydrogel polymer by polymerizing an aqueous solution of a monomer including an unsaturated carboxylic acid and/or a salt thereof in the presence of a crosslinking agent; a second step of obtaining a water absorbent resin precursor which is in powder form and includes particles having a particle size of 300 to 850 μm and particles having a particle size of smaller than 300 μm as main components by drying said hydrogel polymer followed by pulverization and classification to adjust the particle size distribution, a third step of obtaining a water absorbent resin by heating a mixture of said water absorbent resin precursor and a surface crosslinking agent, which can form an ester bond around the surface of said water absorbent resin precursor, a fourth step of adding by spraying an aqueous solution that includes a sulfur-containing reducing agent to said water absorbent resin, and a fifth step of subjecting the mixture of the water absorbent resin and said aqueous solution to a heat treatment under an airflow of not lower than 40° C. but not higher than 120° C.