Electrostatic Toner Core-Shell Structure for Charge Stability

Solution Overview

Problem

Electrostatic-image developing toners with polyester resin binder experience decreased charge stability and fixed image strength in high-temperature, high-humidity environments due to high acid values and low melt viscosity.

Innovation Solution

Toner particles with a polyester resin binder having an acid value of 10 mg KOH/g to less than 15 mg KOH/g and a surface acid value between 0.3% to 1.7% of the resin's acid value, along with a melt viscosity of 1,800 Pa·s to 3,800 Pa·s at 100° C. or a glass transition temperature of 30° C. to 55° C., are developed to enhance charge stability and image strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If polyester resin with high acid value is used to improve adhesion and image strength, then fixed image strength improves, but charge stability deteriorates in high-temperature high-humidity environments

Engineering Contradiction:

Improvefixed image strengthVSAvoidcharge stability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention applies local quality by creating a core-shell structure where the resin particles have different acid values in different regions: the core maintains higher acid value (10-15 mg KOH/g) for adhesion, while the surface is modified to have lower acid value (0.05-0.2 mg KOH/g) for charge stability. This spatial differentiation resolves the contradiction between adhesion and charge stability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the acid value parameter across the resin particle structure. By controlling the acid value distribution (core: 10-15 mg KOH/g, surface: 0.05-0.2 mg KOH/g) and adjusting melt viscosity (1,800-3,800 Pa·s at 100°C), the invention optimizes both adhesion and charge stability simultaneously.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If polyester resin with low melt viscosity is used to improve transfer efficiency, then transfer efficiency improves, but fixed image strength deteriorates

Engineering Contradiction:

Improvetransfer efficiencyVSAvoidfixed image strength

Core Design Contradiction:

ProductivityVSStrength

Solution Approach 1:

The invention optimizes the melt viscosity parameter to a specific range (1,800-3,800 Pa·s at 100°C) that balances transfer efficiency and fixed image strength. This parameter optimization ensures sufficient fluidity for complete transfer while maintaining adequate strength for durable fixed images.

Inventive Principle:

Principle #35Parameter changes

3Strength

If resin particles with high surface acid value are used to improve adhesion, then adhesion improves, but charge stability deteriorates in high-temperature high-humidity environments

Engineering Contradiction:

ImproveadhesionVSAvoidcharge stability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention applies local quality by creating a core-shell structure where the resin particles have different acid values in different regions: the core maintains higher acid value (10-15 mg KOH/g) for adhesion, while the surface is modified to have lower acid value (0.05-0.2 mg KOH/g) for charge stability. This spatial differentiation resolves the contradiction between adhesion and charge stability.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS10670982B2Electrostatic-image developing toner, electrostatic image developer, and toner cartridge

Publication Date: 2020.06.02 FUJIFILM BUSINESS INNOVATION CORP

AI summary

An electrostatic-image developing toner contains toner particles containing a polyester resin having an acid value of from 10 mg KOH/g to less than 15 mg KOH/g. The toner particles have a surface with an acid value in a range from 0.3% to 1.7% of the acid value of the polyester resin. The toner particles have a melt viscosity of from 1,800 Pa·s to 3,800 Pa·s at 100° C.