Silver Powder Dispersibility via Chelating Agent Addition
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Solution Overview
Problem
Conventional silver powders for conductive pastes used in electronic components, such as multilayer capacitors and plasma display panels, suffer from particle coherency issues and phase separation, leading to poor dispersibility and non-uniform film thickness during screen printing.
Innovation Solution
A method involving the addition of a chelating agent, specifically compounds with an azole structure, dicarboxylic acids, or hydroxy carboxylic acids, to a silver powder slurry before or after reduction, to enhance dispersibility and prevent phase separation, resulting in a silver powder with improved tap density, particle size, and flowability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional reducing agents are used to deposit silver powder, then silver particles can be formed, but the particles violently cohere and have poor dispersibility
Solution Approach 1:
The patent introduces a complexing agent (such as ammonia, ethylenediamine, or EDTA) as an intermediary substance that coordinates with silver ions during the reduction process. This complexing agent acts as a mediator between the reducing agent and silver ions, controlling the reduction rate and preventing violent particle coherency. The complexing agent forms stable complexes with silver ions, enabling gradual reduction and producing silver particles with excellent dispersibility and narrow particle size distribution.
2Stability of the object's composition
If fatty acids or surface active agents are added as dispersing agents to improve dispersibility, then particle dispersibility improves, but phase separation occurs forming suspended matters
Solution Approach 1:
The patent fundamentally changes the chemical parameters of the dispersing system by replacing organic dispersing agents (fatty acids, surface active agents) with inorganic complexing agents. This parameter change transforms the dispersing mechanism from surface-active agent-based steric stabilization to complexation-based electrostatic and chemical stabilization. The complexing agents form stable water-soluble complexes with silver particles, preventing phase separation and maintaining paste homogeneity without causing suspended matters.
3Ease of manufacture
If conventional silver powder with poor dispersibility is used, then production is simpler, but the paste is not easily released from screen plate causing bubbles
Solution Approach 1:
The patent changes the surface chemical parameters of silver particles by using complexing agents during synthesis. This modifies the surface chemistry of the particles, making them more hydrophilic and less prone to agglomeration. The complexed silver particles exhibit improved flowability and release characteristics, allowing easy release from screen plates during printing without trapping bubbles, while maintaining production simplicity through a single-step synthesis process.
4Ease of manufacture
If alkali soluble polymer with carboxyl group is used in paste, then paste formulation is conventional, but bubbles are easily drawn into paste during screen printing
Solution Approach 1:
The patent changes the chemical composition parameters of the paste by replacing alkali-soluble polymers with carboxyl groups with complexing agents. This parameter change eliminates the high polarity and bubble-trapping characteristics of carboxyl-containing polymers. The complexing agents provide sufficient dispersion and rheological control without the harmful bubble-drawing effect, improving screen printing quality while maintaining conventional paste processing characteristics.
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 produces a silver powder with excellent dispersibility and uniform film thickness, preventing phase separation and ensuring consistent printing characteristics, suitable for forming fine lines and high-density conductive patterns in electronic components.
Implementation Method 1
adding a reducing agent to the silver oxide containing slurry or the aqueous silver complex salt containing solution to deposit a silver powder by reduction
Implementation Method 2
adding at least one chelating agent selected from compounds having an azole structure, dicarboxylic acids, hydroxy carboxylic acids and salts thereof
Data Source
AI summary
There is provided a method for producing a silver powder having excellent dispersibility and capable of forming a paste which do not form suspended matters by phase separation and which is printed on a substrate to form a film having a uniform thickness. In this method, an alkali or a complexing agent is added to an aqueous silver salt containing solution to form a silver oxide containing slurry or an aqueous silver complex salt containing solution. After or before silver particles are deposited by reduction by adding a reducing agent to the silver oxide containing slurry or aqueous silver complex salt containing solution while stirring it, at least one chelating agent selected from the group consisting of compounds having an azole structure, dicarboxylic acids, hydroxy carboxylic acids and salts thereof is added to a silver power containing slurry solution as a dispersing agent.