The Secondary Transfer Roller (STR) is one of the most important components in the image formation process of a Konica Minolta bizhub color photocopier. Although it is a relatively simple-looking roller, its function is critical: it transfers the complete full-color toner image from the Intermediate Transfer Belt (ITB) onto the paper.
If the Secondary Transfer Roller fails to apply the correct pressure or electrical bias, the machine may produce faded prints, color smearing, hollow text, poor image density, or incomplete image transfer.
For service technicians, understanding how the Secondary Transfer Roller works is essential for diagnosing many print-quality problems that are often mistakenly attributed to the drum, developer, or transfer belt.
What Is the Secondary Transfer Roller?
The Secondary Transfer Roller is a conductive rubber roller located directly beneath the Intermediate Transfer Belt.
During printing, the paper passes between:
- The Intermediate Transfer Belt (carrying the complete CMYK toner image)
- The Secondary Transfer Roller
The roller applies both:
- Mechanical pressure
- High-voltage electrical bias
Together, these forces pull the toner image from the transfer belt onto the paper.
Where It Fits in the Printing Process
The complete electrophotographic process is:
- Drum Charging
- Laser Exposure
- Toner Development
- Primary Transfer (Drums → Intermediate Transfer Belt)
- Secondary Transfer (Intermediate Transfer Belt → Paper)
- Fusing
- Cleaning
The Secondary Transfer Roller performs the fifth stage.
Without it, the toner image would remain on the Intermediate Transfer Belt instead of being transferred to the paper.
Main Components Involved
The secondary transfer system includes:
- Intermediate Transfer Belt (ITB)
- Secondary Transfer Roller
- Secondary Transfer High Voltage Power Supply (HVPS)
- Secondary Transfer Drive Mechanism
- Transfer Guides
- Registration Rollers
- Paper Transport Rollers
- Transfer Release Mechanism (model dependent)
Each component contributes to accurate toner transfer.
Step 1: The Image Is Built on the Intermediate Transfer Belt
Before secondary transfer begins, the machine has already completed the primary transfer process.
Each drum transfers its toner image onto the Intermediate Transfer Belt in sequence:
- Yellow
- Magenta
- Cyan
- Black
The belt now carries a complete full-color toner image.
At this stage, the toner is still held to the belt by electrostatic forces.
Step 2: Paper Arrives at the Transfer Nip
The registration rollers feed the paper with precise timing.
The leading edge of the paper must reach the transfer nip exactly when the toner image arrives.
Even a small timing error can result in:
- Image shift
- Uneven margins
- Color misregistration
Synchronization between the paper transport system and the Intermediate Transfer Belt is critical.
Step 3: The Secondary Transfer Roller Applies High Voltage
As the paper enters the transfer area, the High Voltage Power Supply applies a carefully controlled electrical bias to the Secondary Transfer Roller.
This creates a strong electric field across:
- Intermediate Transfer Belt
- Toner layer
- Paper
- Secondary Transfer Roller
The electric field attracts the charged toner particles away from the belt and onto the paper.
The polarity and voltage level are precisely controlled by the machine’s controller and adjusted according to paper type and environmental conditions.
Step 4: Mechanical Pressure Assists the Transfer
Electrical attraction alone is not enough.
The Secondary Transfer Roller presses the paper firmly against the Intermediate Transfer Belt, creating a narrow contact zone known as the transfer nip.
This pressure ensures:
- Uniform contact across the page
- Stable paper movement
- Consistent toner transfer
- Accurate image positioning
Both pressure and electrical bias must work together for reliable image transfer.
Step 5: Toner Moves to the Paper
As the paper passes through the transfer nip:
- The electrostatic force overcomes the attraction between the toner and the Intermediate Transfer Belt.
- Toner particles move onto the paper surface.
- The complete CMYK image is transferred in a single operation.
At this point, the toner is only loosely resting on the paper and can still be disturbed.
The image becomes permanent only after passing through the fusing unit.
Step 6: Residual Toner Remains on the Belt
No transfer process is 100% efficient.
A small amount of toner remains on the Intermediate Transfer Belt after the image has been transferred.
The Intermediate Transfer Belt Cleaning Unit removes this residual toner before the next print cycle.
If cleaning is ineffective, toner can accumulate on the belt and cause image defects on subsequent pages.
How the Machine Adjusts Secondary Transfer
Konica Minolta bizhub machines continuously optimize the secondary transfer process.
The controller adjusts the transfer voltage based on:
- Paper thickness
- Paper type (Plain, Thick, Glossy, etc.)
- Humidity
- Temperature
- Toner characteristics
- Image coverage
For example:
- Thick paper generally requires a higher transfer voltage.
- Thin paper requires lower voltage to prevent image disturbance.
- High humidity may require voltage compensation because moisture affects electrical conductivity.
These adjustments help maintain consistent print quality under varying conditions.
Interaction with Other Components
The Secondary Transfer Roller does not work independently.
Its performance depends on several related systems.
Intermediate Transfer Belt
The belt must carry the toner image uniformly and maintain proper tension.
A worn or contaminated belt can reduce transfer efficiency.
Registration Rollers
The registration rollers control the timing of paper arrival.
Incorrect timing may cause:
- Image shift
- Misregistration
- Cropped images
High Voltage Power Supply
The High Voltage Power Supply generates the transfer bias.
If the voltage is incorrect or unstable, toner transfer will be incomplete.
Fusing Unit
After secondary transfer, the paper immediately enters the fusing unit.
If the fuser malfunctions, technicians may incorrectly suspect a transfer problem because unfused toner can resemble poor transfer.
Common Secondary Transfer Problems
| Symptom | Possible Cause |
|---|---|
| Light overall print | Worn Secondary Transfer Roller, low transfer voltage, or poor belt contact |
| Incomplete image transfer | Secondary Transfer Roller contamination, damaged belt, or HVPS fault |
| Color smearing | Dirty Secondary Transfer Roller, contaminated Intermediate Transfer Belt, or poor pressure |
| Hollow characters | Uneven transfer pressure or incorrect transfer voltage |
| Random white patches | Transfer roller contamination or paper transport instability |
| Toner remaining on the Intermediate Transfer Belt | Secondary Transfer Roller wear, incorrect bias, or transfer pressure problem |
| Repeating marks | Damaged Secondary Transfer Roller surface or contaminated Intermediate Transfer Belt |
| Image density variation | Uneven roller pressure, worn roller, or high-voltage instability |
Preventive Maintenance
Regular inspection of the Secondary Transfer Roller helps maintain consistent image quality.
Recommended maintenance includes:
- Inspect the roller surface for wear, cuts, or glazing.
- Remove toner buildup and paper dust using approved cleaning methods.
- Avoid touching the roller with bare hands, as skin oils can affect electrical conductivity.
- Verify that the roller moves freely and is correctly seated in its bearings.
- Check the transfer belt for contamination before replacing the roller.
- Inspect the High Voltage contacts for contamination or corrosion.
- Replace the Secondary Transfer Roller according to the machine’s preventive maintenance schedule or when print-quality symptoms indicate wear.
Diagnostic Tips for Technicians
When diagnosing transfer-related problems:
- Print an internal test page to eliminate scanner-related issues.
- Inspect the Intermediate Transfer Belt for residual toner after printing.
- Examine the Secondary Transfer Roller for contamination, wear, or physical damage.
- Check that the paper reaches the transfer area without skew or delay.
- Verify High Voltage Power Supply operation if transfer appears weak or inconsistent.
- Confirm that the registration rollers are correctly synchronizing paper movement.
- Inspect the fusing unit to ensure that transfer issues are not being confused with poor toner bonding.
Following these steps helps avoid unnecessary replacement of drums, developer units, or the Intermediate Transfer Belt.
Why Understanding the Secondary Transfer Roller Matters
Many image-quality defects occur after the toner image has already been formed correctly on the drums and Intermediate Transfer Belt. If technicians focus only on the imaging units, they may replace expensive components unnecessarily.
Understanding the role of the Secondary Transfer Roller allows technicians to distinguish between image formation faults and image transfer faults, leading to faster, more accurate repairs.
Conclusion
The Secondary Transfer Roller is responsible for moving the completed toner image from the Intermediate Transfer Belt onto the paper using a combination of controlled electrical bias and mechanical pressure. Working in precise synchronization with the registration system, High Voltage Power Supply, and Intermediate Transfer Belt, it ensures accurate image placement and consistent color density before the paper enters the fusing unit. A solid understanding of its operation enables technicians to diagnose transfer-related print defects efficiently, reduce unnecessary parts replacement, and maintain reliable print quality across Konica Minolta bizhub color multifunction printers.