Core-Shell Absorbent Resin Particles for Fixation Without Absorbency Loss
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Solution Overview
Problem
Existing methods for fixing water-absorbing resin particles to fibrous base materials in absorbent articles, such as disposable diapers, face challenges with insufficient fixability and impairment of water absorption properties, particularly when using heat-weldable resins which require high amounts to achieve adequate fixation.
Innovation Solution
The development of core-shell type water-absorbing resin particles with a core layer composed of a water-absorbing resin and a shell layer made of a thermoplastic resin having a melting point of 50 to 180°C, specifically a polymer with a hydrophobic block comprising polyolefin, to enhance fixability without compromising water absorption performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat-weldable resin is used to fix water-absorbing resin particles to fibrous base material, then fixability is improved, but water absorption property is impaired
Solution Approach 1:
The water-absorbing resin particle is divided into a core region containing the water-absorbing resin and a shell region containing the thermoplastic resin. This segmentation allows the core to maintain water absorption capability while the shell provides fixation functionality, resolving the contradiction between fixability and water absorption property.
Solution Approach 2:
Different regions of the particle are assigned different functions: the core region is optimized for water absorption with hydrophilic polymers, while the shell region is optimized for fixation with thermoplastic resin. This local differentiation allows each region to excel at its specific function without compromising the other.
2Reliability
If amount of heat-weldable resin is increased to achieve adequate fixation, then fixability is improved, but water absorption capability is greatly impaired
Solution Approach 1:
By segmenting the particle into core and shell regions with distinct functions, the invention achieves adequate fixation with minimal thermoplastic resin content (0.1-10 parts by weight per 100 parts water-absorbing resin), preventing impairment of water absorption capability that would occur with higher amounts.
Solution Approach 2:
The particle is constructed as a composite material with water-absorbing resin in the core and thermoplastic resin in the shell. This composite structure combines the advantages of both materials: high water absorption from the hydrophilic core and effective fixation from the thermoplastic shell, achieving both goals without needing excessive amounts of either component.
3Volume of moving object
If pulp content in absorber is reduced to decrease thickness, then thickness is reduced, but fixation of water-absorbing resin particles becomes more difficult
Solution Approach 1:
The invention extracts the fixation function from the pulp matrix and transfers it to the particle level by coating each water-absorbing resin particle with thermoplastic resin. This allows fixation to occur through particle-to-fiber adhesion rather than relying on pulp content, enabling thin construction while maintaining fixation reliability.
Solution Approach 2:
The invention changes the fixation mechanism from bulk matrix embedding to surface-level thermoplastic bonding. By altering the fixation parameter from mechanical entanglement in pulp to thermal bonding of thermoplastic resin, the system achieves effective fixation even with minimal pulp content, enabling reduced thickness.
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 core-shell structure achieves excellent fixability and shape retention of water-absorbing resin particles on fibrous base materials while maintaining superior water absorption capabilities, even after swelling.
Implementation Method 1
a shell layer (Q) comprising a thermoplastic resin (B) having a melting point of 50 to 180°C
Implementation Method 2
a core layer (P) comprising a water-absorbing resin (A)... maintaining superior water absorption capabilities
Data Source
AI summary
Provided are the following: water-absorbing resin particles with which an absorber can be manufactured, the absorber enabling ample anchoring to be obtained without compromising on water absorbency; and an absorber obtained by anchoring together the water-absorbing resin particles and a fibrous base material. The present invention is: core-shell water-absorbing resin particles constituted of a core layer (P) containing a water-absorbing resin (A) and a shell layer (Q), the shell layer (Q) containing a thermoplastic resin (B) having a melting point of 50 to 180□, and the thermoplastic resin (B) being a polymer having a hydrophobic block comprising a polyolefin; an absorber obtained by anchoring the water-absorbing resin particles to a fibrous base material (F); and an absorbent article made using such absorber.