Permeable Water-Absorbing Polymer Particles Coating

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Solution Overview

Problem

Current methods for producing permeable water-absorbing polymer particles face challenges in achieving high centrifuge retention capacity and permeability while minimizing the reduction in mechanical stability and unreacted monomer content.

Innovation Solution

The process involves polymerizing drops of a monomer solution containing ethylenically unsaturated acid group-bearing monomers, crosslinkers, initiators, and water in a gas phase, followed by coating with inorganic particulate substances or polyvalent cations as permeability improvers, which enhances permeability without requiring covalent surface crosslinking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If coating with permeability improvers is applied to enhance permeability, then liquid flow rate and permeability are improved, but mechanical stability may be reduced

Engineering Contradiction:

ImprovepermeabilityVSAvoidmechanical stability

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies inorganic particulate substances (such as silica, alumina, or metal oxides) as permeability improvers that form a porous coating structure on the polymer particles. This porous structure allows liquid to pass through while maintaining the mechanical integrity of the core polymer matrix, thus improving permeability without compromising mechanical stability.

Inventive Principle:

Principle #31Porous materials

Solution Approach 2:

The patent creates a composite structure by combining the water-absorbing polymer core with inorganic permeability improvers in the coating layer. This composite approach leverages the absorbency of the polymer and the permeability of the inorganic particles, achieving both functions simultaneously without sacrificing mechanical properties.

Inventive Principle:

Principle #40Composite materials

2Productivity

If spray polymerization is used to combine polymerization and drying steps, then productivity is improved, but control over particle size and monomer content becomes more difficult

Engineering Contradiction:

Improveproduction efficiencyVSAvoidparticle size control

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent implements feedback control mechanisms during spray polymerization by monitoring parameters such as droplet size, monomer conversion, and particle formation in real-time. This allows for dynamic adjustment of spray conditions, initiator concentration, and crosslinker amounts to maintain precise control over particle size and monomer content while maintaining high productivity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent optimizes multiple process parameters including spray droplet diameter, gas flow rate, temperature, and initiator concentration to achieve the desired particle size and monomer content. By carefully controlling these parameters, the process maintains precision despite the combined polymerization-drying approach.

Inventive Principle:

Principle #35Parameter changes

3Strength

If crosslinking is increased to improve mechanical stability, then strength is improved, but permeability and centrifuge retention capacity are reduced

Engineering Contradiction:

Improvemechanical stabilityVSAvoidpermeability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent applies different crosslinking densities to different regions of the polymer particle. The core region has higher crosslinking for mechanical stability, while the outer coating region has lower crosslinking to maintain permeability and centrifuge retention capacity. This spatial variation in crosslinking density allows simultaneous optimization of both properties.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The inorganic coating layer acts as a porous structure that maintains open pathways for liquid flow. This porous coating compensates for the reduced permeability that would result from high crosslinking in the polymer core, allowing the system to achieve both mechanical stability and permeability.

Inventive Principle:

Principle #31Porous materials

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

This method produces polymer particles with high centrifuge retention capacity, liquid transfer, and permeability, maintaining mechanical stability and reducing unreacted monomer content, thus improving the overall performance of water-absorbing polymers.

Implementation Method 1

polymerizing droplets of a monomer solution containing a) at least one ethylene-unsaturated, acid-group-bearing monomer, which may be at least partially neutralized, b) at least one crosslinker, c) at least one initiator

Methodology Applied

Scientific EffectPolymerization: Photopolymerisation

Implementation Method 2

the polymer particles obtained are coated with at least one permeability enhancer... wherein the permeability enhancer is an inorganic particulate substance, an inorganic colloidally dissolved substance and/or a multivalent cation

Methodology Applied

Scientific EffectAdsorption: Adsorption

Data Source

PatentEP2358769B1Method for producing permeable water-absorbing polymer particles through polymerization of drops of a monomer solution

Publication Date: 2022.01.05 BASF SE

AI summary

The invention relates to a method for producing water-absorbing polymer particles through polymerization of drops of a monomer solution in a surrounding gas phase, wherein the polymer particles are coated with a permeability improving agent.