Developing Roll Surface Hardness Distribution for Toner Stress
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Solution Overview
Problem
Conventional conductive rolls used in electrophotographic devices experience increased toner stress in low-temperature and low-humidity environments, leading to defects in image formation due to increased hardness, toner friction, and degradation, which results in irregular images and foreign matter contamination.
Innovation Solution
A developing roll with a surface layer having a specific hardness distribution, measured by atomic force microscopy, and composed of a copolymer including (meth)acrylate units with silicone and fluorine-containing groups, which reduces toner stress and improves adhesion resistance by controlling the glass transition temperature and uneven distribution of the copolymer on the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional conductive rolls are used in low-temperature and low-humidity environment, then the roll maintains structural integrity, but the hardness of the roll increases and toner stress increases leading to image defects
Solution Approach 1:
The surface layer is designed with a specific hardness distribution where soft portions (hardness ≤45 MPa) constitute 80% or more of the surface area, while maintaining an average top peak hardness of 10-55 MPa. This local variation in hardness allows the roll to maintain structural integrity while reducing toner stress through the softer regions.
Solution Approach 2:
The invention changes the physical and chemical parameters of the surface layer by using a copolymer with specific glass transition temperature (Tg ≤10°C) and controlling the hardness distribution. The copolymer includes (meth)acrylate units with silicone groups, fluorine-containing groups, and units with Tg ≤10°C, creating a material that maintains appropriate hardness in low-temperature environments.
2Stability of the object's composition
If the hardness of the developing roll increases in low-temperature environment, then the roll maintains shape stability, but toner friction increases and external additives become short or buried
Solution Approach 1:
The surface layer contains soft portions with hardness of 45 MPa or below that cover 80% or more of the surface area, providing low-friction zones that prevent toner additive shortage and burying while maintaining overall shape stability through the controlled hardness distribution.
Solution Approach 2:
The surface layer is formed as a composite copolymer containing multiple types of (meth)acrylate units: silicone-containing units for flexibility, fluorine-containing units for low friction, and units with low glass transition temperature. This composite structure provides both shape stability and reduced toner friction.
3Reliability
If conventional conductive rolls are used as charging rolls, then the roll provides adequate charging function, but toner degradation occurs and foreign matter is mixed into collected toner
Solution Approach 1:
The charging roll surface layer uses a copolymer with glass transition temperature of 10°C or below, ensuring the material remains sufficiently soft and compliant in low-temperature environments to prevent toner degradation during the charging process while maintaining reliable charging function.
Solution Approach 2:
The surface layer's hardness distribution with soft portions (≤45 MPa) covering 80% or more of the surface provides gentle contact with toner particles during charging, preventing toner degradation and avoiding the generation of foreign matter while maintaining effective charging.
Data Source
AI summary
Provided is a developing roll (R) with which it is possible to suppress toner stress in a low-temperature and low-humidity environment. A developing roll (R) for an electrophotographic device has a surface layer (1). In a surface hardness histogram (10) of the surface layer (1) measured by using an atomic force microscope (AFM), the surface hardness (H) at the top peak (P) is in the range of 10-55 MPa, and the area ratio (S) of the histogram portion corresponding to a surface hardness of 45 MPa or below in relation to the entire histogram is 65% or above.