Core-Shell Toner with Solubility Parameter Gradient
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Solution Overview
Problem
Electrostatic charge image developing toners with low melting point binders and releasing agents tend to aggregate at high temperatures, causing image defects and fogging due to adhesion issues, and have poor fixability at low temperatures.
Innovation Solution
A toner with a core-shell structure where the shell layer has specific solubility parameter differences between its inner and outer layers, optimizing the compatibility and bonding between layers to enhance fixability and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a binder resin with a low melting point or glass transition point is used to achieve low temperature fixability, then fixability at low temperature is improved, but the toner tends to aggregate in high temperature storage
Solution Approach 1:
The toner is divided into core particles and a shell layer. The core contains the binder resin with low melting point for good fixability, while the shell layer with higher glass transition point prevents aggregation during high temperature storage, thus segmenting the conflicting requirements into different spatial zones
Solution Approach 2:
The invention uses a composite structure combining binder resin (for low temperature fixability) with shell layer material having different thermal properties (for high temperature stability). This composite approach allows the toner to exhibit both low temperature fixability and high temperature storage stability simultaneously
2Temperature
If a releasing agent with a low melting point is used to improve fixability, then fixability is enhanced, but adhesion of toner to development sleeve or photosensitive drum occurs causing image defect
Solution Approach 1:
The releasing agent is segregated into the core region of the toner particle, separated from the shell layer that contacts the development sleeve and photosensitive drum. This spatial segmentation allows the releasing agent to function at the fixation stage without causing unwanted adhesion during development
Solution Approach 2:
The shell layer acts as an intermediary barrier between the releasing agent in the core and the external components (development sleeve, photosensitive drum). This intermediary structure prevents direct contact between the releasing agent and these components, eliminating the harmful adhesion effect while preserving the releasing agent's function
3Reliability
If a shell layer with high glass transition point is added to prevent aggregation, then preservation stability is improved, but the complexity of toner structure increases
Solution Approach 1:
The toner is segmented into core and shell layers with distinct functional assignments. The core handles low temperature fixability while the shell provides high temperature stability, allowing each layer to be optimized independently for its specific function
Solution Approach 2:
Different regions of the toner particle are assigned different material properties: the core has low melting point binder resin for fixability, while the shell has higher glass transition point material for stability. This local differentiation of material quality allows simultaneous optimization of conflicting properties without requiring the entire structure to compromise
Data Source
AI summary
An electrostatic charge image developing toner includes a toner core including at least a binder resin and a shell layer configured to cover the toner core. The shell layer includes an inner layer and an outer layer. A difference obtained by subtracting a SP value of a material for the inner layer from a SP value of the binder resin, ΔSP1, is 0.3 or larger and 1.4 or lower. A difference obtained by subtracting a SP value of a material for the outer layer from the SP value of the material for the inner layer, ΔSP2, is 0.5 or larger and 1.6 or lower. The ΔSP1 is below the ΔSP2.