Cationic Silica Dispersion Gelation Prevention

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Solution Overview

Problem

Existing methods for producing cationically modified silica dispersions face challenges with gelation and insufficient cationic group introduction on silica particles, especially at high silica concentrations, which affects stability and purity.

Innovation Solution

Adding a silane coupling agent with a cationic group to a silica raw material with a negative zeta potential to react and introduce a sufficient amount of cationic groups onto the silica particles, preventing gelation and ensuring stability across a wide pH range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If basic aluminum chloride or basic aluminum salt is used to treat aqueous colloidal silica to improve stability under acidic conditions, then stability under acidic condition is improved, but content of metal impurities becomes large

Engineering Contradiction:

Improvestability under acidic conditionVSAvoidcontent of metal impurities

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The invention extracts and removes metal impurities from the colloidal silica system by using a cation exchange resin that selectively binds metal cations (Al³⁺, Fe³⁺, etc.) from the acidic colloidal silica solution, separating the harmful metal impurities from the desired colloidal silica particles

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces a cation exchange resin as an intermediary substance that mediates between the acidic colloidal silica and metal impurities, allowing the resin to capture metal cations while leaving the colloidal silica particles intact and stable

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If silane coupling agent is added to colloidal silica to prevent aggregation and gelation, then stability and purity are improved, but gelation may occur at the time of or after addition of silane coupling agent

Engineering Contradiction:

Improvestability of colloidal silicaVSAvoidgelation

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The invention performs preliminary removal of metal impurities using cation exchange resin before adding the silane coupling agent, creating a purified colloidal silica solution that is less prone to gelation during subsequent modification steps

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention changes the pH parameter of the colloidal silica solution to a specific range (pH 2-4) before adding the silane coupling agent, optimizing the conditions to prevent gelation while maintaining stability and enabling effective surface modification

Inventive Principle:

Principle #35Parameter changes

3Productivity

If silica concentration in the silica raw material is increased to improve productivity, then productivity is improved, but cationic modification reaction is insufficient and metal impurities increase

Engineering Contradiction:

Improvesilica concentrationVSAvoidcationic modification reaction

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The invention implements a continuous multi-step process where high-concentration colloidal silica undergoes sequential treatment: metal impurity removal by cation exchange resin, pH adjustment to optimal range, and gradual silane coupling agent addition, maintaining effective modification throughout the process

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The invention uses excess silane coupling agent relative to the silica surface area to ensure complete coverage and modification, compensating for the reduced reactivity at higher silica concentrations while the cation exchange resin prevents gelation from the excess agent

Inventive Principle:

Principle #16Partial or excessive action

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 allows for the production of cationically modified silica dispersions with improved stability and high purity, capable of stable dispersion over a wide pH range, including acidic conditions, without gelation issues.

Implementation Method 1

adding a silane coupling agent having a cationic group to a silica raw material in which a zeta potential shows a negative value, and causing the silica raw material to react with the silane coupling agent to obtain a cationically modified silica

Methodology Applied

Scientific EffectSilane coupling reaction: Chemical Bonding

Implementation Method 2

adding a silane coupling agent having a cationic group to a silica raw material in which a zeta potential shows a negative value

Methodology Applied

Scientific EffectElectrostatic repulsion: Ion Repulsion/Attraction

Data Source

PatentUS11167995B2Method for producing cationically modified silica and cationically modified silica dispersion

Publication Date: 2021.11.09 FUJIMI INCORPORATED

AI summary

Provided is a means capable of introducing a sufficient amount of a cationic group onto the surface of silica particles even in a case where a silica raw material having a high silica concentration is used while occurrence of gelation is suppressed at the time of or after addition of a silane coupling agent in production of a cationically modified silica dispersion including modifying raw silica using a silane coupling agent.Adding a silane coupling agent having a cationic group to a silica raw material in which a zeta potential shows a negative value, and causing the silica raw material to react with the silane coupling agent to obtain a cationically modified silica.