Water-Absorbent Polymer Particles Coating for Mechanical Stability

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Solution Overview

Problem

The production of water-absorbing polymer particles by polymerizing drops of a monomer solution in a gas phase surrounding the drops results in hollow spheres that are mechanically unstable, necessitating an improvement in their mechanical stability for enhanced performance in applications such as diapers and agricultural horticulture.

Innovation Solution

The process involves polymerizing drops of a monomer solution containing ethylenically unsaturated monomers, crosslinkers, and initiators in a gas phase, followed by post-crosslinking and coating the polymer particles with additives that increase elasticity or mechanically solidify the surface, using suitable mixers and coatings like water, alkanolamines, polymers, or waxes to enhance mechanical stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Shape

If water-absorbing polymer particles are produced by polymerizing droplets of a monomer solution in a gas phase, then high sphericity is achieved, but mechanical stability deteriorates due to hollow sphere structure

Engineering Contradiction:

ImprovesphericityVSAvoidmechanical stability

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The patent applies this principle by coating the hollow sphere particles with a protective layer. The coating forms a thin film shell around the hollow spheres, providing mechanical strength while preserving the spherical shape. This resolves the contradiction by adding structural reinforcement without changing the fundamental spherical geometry that provides high sphericity.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent creates a composite structure by combining the hollow sphere polymer particles with a coating material. The composite consists of the internal hollow sphere structure (maintaining sphericity) and the external coating layer (providing mechanical stability). This composite approach allows both high sphericity and improved mechanical strength to coexist.

Inventive Principle:

Principle #40Composite materials

2Strength

If the degree of cross-linking is increased to improve gel strength, then absorption capacity decreases

Engineering Contradiction:

Improvegel strengthVSAvoidabsorption capacity

Core Design Contradiction:

StrengthVSQuantity of substance

Solution Approach 1:

The patent applies local quality by differentiating the cross-linking degree between different regions of the polymer particles. The surface region has higher cross-linking density (improved by coating) while the internal region maintains lower cross-linking density (preserving absorption capacity). This spatial differentiation allows gel strength and absorption capacity to coexist at different locations within the same particle.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses partial action by applying cross-linking enhancement (coating) only to the particle surface rather than throughout the entire particle volume. This partial cross-linking approach provides sufficient gel strength at the surface while leaving the internal structure sufficiently uncrosslinked to maintain high absorption capacity.

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If post-crosslinking is performed in the aqueous gel phase to improve absorption properties, then processing complexity increases compared to coating dried particles

Engineering Contradiction:

Improveabsorption propertiesVSAvoidprocessing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the liquid phase (water) from the polymer particles before applying the coating. By drying the particles to remove water and then applying the coating to the dry particles, the process simplifies the handling and coating application steps while still achieving the desired post-crosslinking effect. This extraction of the complicating liquid phase reduces processing complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

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 approach produces water-absorbing polymer particles with improved mechanical stability, high centrifuge retention capacity, and absorption under pressure, while maintaining a high sphericity and absorption index, suitable for use in hygiene products and agricultural applications.

Implementation Method 1

additives that increase the elasticity of the particle surface, for example by lowering the glass transition temperature

Methodology Applied

Scientific EffectGlass transition temperature:

Implementation Method 2

the cross-linked polymer particles are at least partially coated

Methodology Applied

Scientific EffectCoating: Coatings

Data Source

PatentEP2104686B2Method for producing mechanically stable water-absorbent polymer particles

Publication Date: 2019.11.27 BASF SE

AI summary

A process for producing water-absorbing polymer particles by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets and postcrosslinking the polymer particles, wherein the postcrosslinked polymer particles are at least partly coated.