Particulate Water Absorbing Agent Crosslinking Gradient
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Solution Overview
Problem
Current water absorbent resins in sanitary materials, such as diapers, face challenges in achieving optimal absorption capacity, liquid transportability, and re-wet properties due to limitations in gel strength and particle size distribution, leading to inefficiencies in liquid management.
Innovation Solution
A particulate water absorbing agent with a polyacrylic acid-based resin, characterized by a specific particle size distribution of 80% or more within 600 to 150 μm, a swelling rate of 32 to 45 g/g, and a minimal difference between first and second swelling times, ensuring high liquid transportability and preventing gel blocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of water absorbent resin is increased to reduce thickness, then the water absorption capacity is improved, but the liquid transportability deteriorates due to gel blocking phenomenon
Solution Approach 1:
The invention applies different crosslinking densities to different parts of the polymer structure - high crosslinking density at the particle surface for gel strength, and low crosslinking density in the interior for swelling capacity. This local differentiation allows simultaneous achievement of high water absorption and good liquid transportability.
Solution Approach 2:
The invention changes the crosslinking parameter by using a two-stage process: first forming a crosslinked gel structure, then selectively degrading surface crosslinks through controlled oxidation. This parameter transformation converts a high-crosslinked structure into a differentiated structure with surface-low and interior-high crosslinking density.
2Strength
If the degree of crosslinking is increased to improve gel strength, then the transportability is improved, but the swelling capacity and retention ability deteriorate
Solution Approach 1:
The invention creates a non-uniform crosslinking structure where the particle interior maintains high crosslinking density for gel strength while the surface has reduced crosslinking density. This local quality differentiation preserves swelling capacity at the surface while maintaining structural integrity through the crosslinked network.
Solution Approach 2:
The invention extracts or removes crosslinking bonds from the particle surface through controlled oxidation treatment. By selectively taking out crosslinks from the surface region while preserving them in the interior, the invention achieves the desired balance between gel strength and swelling capacity.
3Strength
If surface treatment is applied to increase gel strength, then the liquid-absorbing ability under pressure is improved, but the production complexity increases
Solution Approach 1:
The invention uses the water absorbent resin particles themselves to perform the surface treatment function. The particles undergo controlled oxidation that selectively modifies their own surface crosslinking structure, eliminating the need for separate surface treatment agents or complex multi-step surface modification processes.
Solution Approach 2:
The invention changes the chemical state of the crosslinking bonds through controlled oxidation, transforming the surface crosslinked structure into a less crosslinked state. This parameter change achieves the desired gel strength optimization while maintaining a relatively simple production process.
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 enhances the absorption capacity, maintains liquid transportability even after initial swelling, and reduces re-wet under pressure, providing improved performance in sanitary materials.
Implementation Method 1
A gel of a water absorbent resin swollen in an absorbent body serves a transportation function with use of a capillary phenomenon through gaps between gel particles.
Implementation Method 2
a water absorbent resin with higher gel strength has higher transportability, while a water absorbent resin with lower gel strength has lower transportability
Data Source
Figure 1
AI summary
A water absorbent resin (water absorbing agent) and method for producing it are provided which improve, in a water absorbent article (in particular, a diaper) including a water absorbent resin as a water absorbing agent, the absolute absorption amount (g), liquid absorbing times (in particular, liquid absorbing times at the second instance and later), re-wet (g), and diffusion distance (%) of the water absorbent article. A particulate water absorbing agent of the present invention has a CRC, a proportion of particles with sizes of 600 µm to 150 µm as defined through a standard-sieve classification, an SST, and the value of the difference between an FST and the SST each within a predetermined range.