Surface-Crosslinked Polyacrylate Absorbents for Faster Uptake
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Solution Overview
Problem
Existing water-absorbing agents used in sanitary products face challenges such as gel blocking, reduced liquid diffusibility, and limited thinning due to high water-absorbing agent content, which affects fluid retention capacity and permeability, especially in varying urine concentrations, and require improved water absorbing speed and salt tolerance.
Innovation Solution
A method for producing a polyacrylic acid (salt)-based water-absorbing agent involves a surface crosslinking process with a mixture of water, a surface crosslinking agent, and a water-absorbing resin powder, treated under specific conditions to form a uniform, strong crosslinked layer, enhancing water absorbing speed, fluid retention capacity, and salt tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the water-absorbing agent content is increased to reduce product thickness, then the water absorption capacity is improved, but gel blocking occurs which reduces liquid diffusibility
Solution Approach 1:
The patent applies surface crosslinking treatment to create a crosslinked layer on the surface of the water-absorbing agent particles. This creates local quality differentiation where the surface has different properties (crosslinked structure) than the interior, allowing the surface to control liquid penetration while the interior maintains high absorption capacity. This resolves the gel blocking issue by preventing excessive gel formation at the particle surface while preserving bulk absorption ability.
Solution Approach 2:
The patent changes the crosslinking density parameter by controlling the surface crosslinking treatment conditions (temperature, time, crosslinking agent amount). By optimizing these parameters, the patent achieves a balance where the surface crosslinked layer is sufficiently dense to prevent gel blocking but not so dense as to hinder liquid penetration. The water-absorbing agent achieves FSR of 0.28 g/g/s or more and AAP of 20 g/g or more while maintaining liquid diffusibility.
2Quantity of substance
If the water-absorbing agent content is increased to reduce product thickness, then the water absorption capacity is improved, but liquid permeability is reduced
Solution Approach 1:
Surface crosslinking creates a differentiated structure where only the particle surface has crosslinked properties while the interior remains uncrosslinked or lightly crosslinked. This local quality change allows liquid to penetrate through the particle interior while the surface provides structural integrity and controlled absorption, maintaining high liquid permeability even with high water-absorbing agent content.
3Strength
If surface crosslinking is performed to improve fluid retention capacity, then water absorbing speed may be reduced due to denser crosslinked structure
Solution Approach 1:
The surface crosslinking treatment creates a crosslinked layer with controlled thickness and density on the particle surface. This local crosslinked structure provides mechanical strength and fluid retention capacity (AAP of 20 g/g or more) while the uncrosslinked interior maintains high water absorbing speed (FSR of 0.28 g/g/s or more). The key is that crosslinking is localized to the surface rather than throughout the entire particle.
Solution Approach 2:
The patent applies partial crosslinking rather than complete crosslinking of the water-absorbing agent particles. By crosslinking only the surface portion and leaving the interior largely uncrosslinked, the patent achieves sufficient fluid retention capacity while preserving the high water absorbing speed characteristic of uncrosslinked gels. This partial action approach optimizes both competing properties.
4Strength
If crosslinking density is increased to improve fluid retention capacity under load, then liquid diffusibility is reduced
Solution Approach 1:
The patent creates a gradient structure where crosslinking density is high at the particle surface and low or zero in the particle interior. This local quality differentiation allows the surface to provide high fluid retention capacity under load (AAP of 20 g/g or more) while the interior maintains high liquid diffusibility, enabling liquid to penetrate deep into the particle without encountering dense crosslinked barriers.
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 achieves a water-absorbing agent with high water absorbing speed, fluid retention capacity under load, high liquid permeability, and salt tolerance without reducing bulk specific gravity, suitable for thin sanitary products.
Implementation Method 1
a surface crosslinking process with a mixture of water, a surface crosslinking agent, and a water-absorbing resin powder, treated under specific conditions to form a uniform, strong crosslinked layer
Implementation Method 2
A water-absorbing agent that absorbs water turns to a soft gel-like water-absorbing agent
Data Source
Figure 1
AI summary
Provided is method for producing a polyacrylic acid (salt)-based water-absorbing agent. The method comprises heat treating a mixture containing water, a surface crosslinking agent and a water-absorbing resin powder, wherein the water-absorbing resin powder is heat treated for at least five minutes from a start of raising a temperature with a gas density of a specific surface crosslinking agent C2 compound and/or a specific surface crosslinking agent C3 compound being at least 0.01 g/L. The gas density is a weight of the surface crosslinking agent C2 compound or the surface crosslinking agent C3 compound that is contained per unit volume of a non-condensable gas. The method makes it possible to (i) uniformly form a strong crosslinked layer on a surface of a water-absorbing resin powder and (ii) obtain a water-absorbing agent which simultaneously achieves a high water absorbing speed, a high fluid retention capacity under load, high liquid permeability, and salt tolerance. Further, the polyacrylic acid (salt)-based water-absorbing agent produced by the method causes no reduction in fluid retention capacity and bulk specific gravity, and is preferably used in sanitary products such as disposable diapers, sanitary napkins, and incontinence pads.