Developing Roller Surface Roughness for Image Quality
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Solution Overview
Problem
Developing rollers in image forming apparatuses face issues with fog and stripe-like image defects due to the small particle size of developers, which increase contact points and lead to deterioration, resulting in non-uniform developer coating and charge reduction, especially in low-temperature and low-humidity environments.
Innovation Solution
A developing roller with an elastic layer and a surface layer containing resin and resin particles, where the surface roughness has a specific distortion degree and particle size distribution, reducing contact points and preventing developer accumulation to improve image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the particle diameter of the developer is made extremely small to improve granularity and character reproducibility, then image quality in terms of granularity and character reproducibility is improved, but the number of contacts/collisions of the developer with the developing roller and developer controlling member increases, causing developer deterioration and fusion on surfaces
Solution Approach 1:
The developing roller surface is designed with non-uniform roughness characteristics - specifically with valleys and peaks at controlled depths. This local variation in surface topology reduces the number of contact points between the developer particles and the roller surface, thereby reducing developer deterioration while maintaining the desired particle size for high image quality.
Solution Approach 2:
The developing roller surface is pre-formed with specific roughness characteristics (valleys and peaks) before the developer is applied. This preliminary surface preparation ensures that when small-particle developer is used, the contact points are already minimized, preventing developer fusion and deterioration before the developing process begins.
2Manufacturing precision
If a bias is applied on the developer controlling member (developing blade) to regulate the amount of developer on the developing roller, then uniformity of image and concentration of image density are improved, but the stress given to the developer increases, causing fusion of developer and external additive on the developing roller surface and developing blade
Solution Approach 1:
The developing roller surface features localized valleys and peaks that create specific contact zones. When bias is applied to the developing blade, the stress-induced developer fusion is minimized because the roughness structure distributes the contact stress across fewer, more controlled points, preventing widespread fog and stripe defects.
Solution Approach 2:
The surface roughness, which could be considered a defect, is actually utilized beneficially to reduce harmful effects. The valleys and peaks create a surface structure that, paradoxically, reduces developer fusion even under biased conditions, converting what might be seen as a surface imperfection into a protective feature against fog and stripe defects.
3Reliability
If the developing roller surface is made smooth to reduce contact points, then developer deterioration is reduced, but the charge imparting amount to the developer is reduced, causing fog in the electrophotographic image
Solution Approach 1:
Rather than making the entire surface smooth or uniformly rough, the developing roller has localized valleys and peaks with controlled depths. This local quality approach maintains charge imparting capability at the peaks while reducing contact-induced deterioration in the valleys, achieving both reliability and manufacturing precision.
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 solution effectively reduces fog and stripe defects in electrophotographic images by optimizing the surface roughness and particle distribution on the developing roller, enhancing image quality and stability during continuous printing.
Implementation Method 1
the surface layer has a convex portion attributable to the resin particles, and has a surface roughness in which a distortion degree Rsk of a roughness curve is 0.15 or more and 0.70 or less
Implementation Method 2
a uniform and high electrostatic property toward the developer
Data Source
AI summary
A developing roller having an elastic layer on the outer periphery of a mandrel and having a surface layer containing a resin and resin particles on its outer periphery, wherein the surface layer has a convex portion attributable to the resin particles, and has a surface of roughness in which a distortion degree Rsk of a roughness curve is 0.15 or more and 0.70 or less, wherein the resin particles have a peak P1 at a particle diameter d1 in a volume particle size distribution, and wherein “a”, “b”, “c”, d1, d2 and d3 satisfy a specific relationship, where, “a” denotes a volume fraction of the resin particle having the particle diameter d1 in the volume particle size distribution, and “b” and “c” denote volume fractions at particle diameters d2 and d3 respectively in the volume particle size distribution.