Once the Developing Unit has applied toner to the electrostatic latent image on the OPC (Organic Photoconductor) drum, the image is visible but still only loosely attached to the drum by electrostatic forces. To produce a printed page, the toner must be transferred from the drum to the paper.
In modern Konica Minolta bizhub color photocopiers, this transfer occurs in two separate stages:
- Primary Transfer – Toner moves from each OPC drum to the Intermediate Transfer Belt (ITB).
- Secondary Transfer – The complete color image moves from the Intermediate Transfer Belt to the paper.
Both stages rely on carefully controlled transfer charge, generated by the High Voltage Power Supply (HVPS). Instead of using mechanical pressure to remove the toner, the machine uses electrostatic attraction to move toner efficiently while maintaining excellent image quality.
For service technicians, understanding the transfer process is essential because transfer-related faults can cause light prints, missing colors, hollow characters, poor image density, color smearing, and transfer belt contamination.
What Is Transfer Charge?
Transfer charge is a high-voltage electrical bias applied to the transfer rollers.
Its purpose is to:
- Pull toner away from the OPC drum.
- Move toner to the Intermediate Transfer Belt.
- Transfer the complete image from the belt to the paper.
- Minimize residual toner left behind.
The transfer charge must be carefully controlled. If it is too low, toner remains on the drum or belt. If it is too high, image distortion, toner scatter, or excessive background contamination may occur.
Why Toner Needs Transfer Charge
After development, toner is held on the drum only by electrostatic attraction.
Without transfer charge:
- Toner would remain attached to the drum.
- No image would reach the paper.
- The cleaning system would remove all the toner as waste.
Transfer charge provides the stronger electrical attraction needed to move toner from one surface to another.
Components Involved
The transfer system includes:
- OPC Drum
- Primary Transfer Roller
- Intermediate Transfer Belt (ITB)
- Secondary Transfer Roller
- High Voltage Power Supply (HVPS)
- Belt Cleaning Unit
- Main Controller Board
Each component contributes to accurate toner transfer.
Stage 1: Toner on the OPC Drum
At this point in the imaging process:
- The Primary Charge Roller has charged the drum.
- The Laser Scanner Unit has written the latent image.
- The Developing Unit has applied toner.
The toner image is now completely visible on the drum surface.
However, it is still held only by electrostatic forces.
Stage 2: Primary Transfer
The first transfer stage moves toner from the OPC drum to the Intermediate Transfer Belt.
The Primary Transfer Roller is positioned behind the belt directly opposite the drum.
As the drum rotates against the belt:
- The High Voltage Power Supply applies transfer voltage to the Primary Transfer Roller.
- The roller creates a strong electrostatic field.
- The charged toner particles are attracted away from the drum.
- The toner transfers onto the Intermediate Transfer Belt.
Only the toner moves.
The drum itself never touches the belt directly.
Building the Full-Color Image
Color Konica Minolta bizhub machines contain four separate imaging stations:
- Yellow
- Magenta
- Cyan
- Black
Each imaging station performs primary transfer independently.
The Intermediate Transfer Belt receives the colors in sequence:
- Yellow
- Magenta
- Cyan
- Black
After the fourth transfer, the belt carries one complete full-color image.
Why Use an Intermediate Transfer Belt?
The Intermediate Transfer Belt offers several advantages:
- Improved color registration.
- Higher print quality.
- Better paper handling.
- More accurate color alignment.
- Reduced paper movement during image formation.
The belt acts as a temporary image carrier before the image reaches the paper.
Stage 3: Paper Arrival
While the Intermediate Transfer Belt carries the complete toner image, the paper transport system feeds a sheet of paper toward the Secondary Transfer Roller.
Precise timing is essential.
The leading edge of the paper must arrive exactly when the toner image reaches the secondary transfer point.
Stage 4: Secondary Transfer
The paper passes between:
- Intermediate Transfer Belt
- Secondary Transfer Roller
The High Voltage Power Supply applies a second transfer voltage to the Secondary Transfer Roller.
This creates a stronger electrostatic attraction than the bond between the toner and the Intermediate Transfer Belt.
The toner leaves the belt and transfers to the paper.
At this point:
- The paper carries the complete toner image.
- The toner remains unfused.
- The image can still be rubbed off until it passes through the fusing unit.
What Happens to Residual Toner?
No transfer process is 100% efficient.
Small amounts of toner remain on:
- OPC Drums
- Intermediate Transfer Belt
The cleaning system removes this toner.
Residual toner travels through:
- Cleaning blades
- Waste toner augers
- Waste toner transport system
Finally, it is collected in the waste toner bottle.
High Voltage Control
The High Voltage Power Supply continuously regulates:
- Primary transfer voltage
- Secondary transfer voltage
These voltages may be adjusted automatically according to:
- Paper type
- Paper thickness
- Temperature
- Humidity
- Toner characteristics
Automatic adjustment ensures stable transfer efficiency under varying operating conditions.
Automatic Image Quality Control
Several systems work together to optimize transfer performance.
Image Stabilization
Compensates for:
- Drum aging
- Belt wear
- Environmental conditions
- Toner characteristics
Color Registration Adjustment
Measures registration marks on the Intermediate Transfer Belt and adjusts the position of each color image.
Transfer Bias Control
The controller continuously adjusts transfer voltages to maintain proper toner transfer under different operating conditions.
Relationship to the Electrophotographic Process
Transfer charge is used during both transfer stages of the electrophotographic cycle.
The sequence is:
- Drum Cleaning
- Drum Discharge
- Drum Charging
- Laser Exposure
- Toner Development
- Primary Transfer (Drum → Intermediate Transfer Belt)
- Secondary Transfer (Intermediate Transfer Belt → Paper)
- Fusing
- Cleaning
These transfer stages move the toner image from the imaging components to the paper.
Common Transfer System Problems
| Symptom | Possible Cause |
|---|---|
| Light print | Low transfer voltage, worn transfer roller, or contaminated ITB |
| Missing one color | Failed Primary Transfer Roller or poor drum-to-belt transfer |
| Hollow characters | Weak Secondary Transfer charge |
| Toner remaining on drum | Low Primary Transfer voltage or worn transfer roller |
| Toner remaining on ITB | Weak Secondary Transfer voltage |
| Color smearing | Dirty Intermediate Transfer Belt or poor transfer efficiency |
| Color misregistration | ITB tracking problem or registration adjustment required |
| Background toner | Incorrect transfer bias or contaminated transfer components |
| Repeating defects | Damaged ITB surface or contaminated transfer roller |
Diagnostic Tips for Technicians
When investigating transfer-related image defects:
- Print full-color and single-color test pages.
- Determine whether the defect occurs before or after the fusing stage.
- Inspect the Intermediate Transfer Belt for scratches, contamination, or toner buildup.
- Examine the Primary and Secondary Transfer Rollers for wear, toner contamination, or damage.
- Verify High Voltage Power Supply outputs if transfer bias is suspected.
- Check belt tracking and drive mechanisms.
- Perform Color Registration Adjustment after replacing transfer components.
- Run Image Stabilization following replacement of the Intermediate Transfer Belt or transfer rollers, as recommended by the service manual.
Preventive Maintenance
To maintain reliable toner transfer:
- Clean transfer rollers according to the service manual.
- Avoid touching transfer roller surfaces with bare hands.
- Inspect the Intermediate Transfer Belt for wear during scheduled maintenance.
- Replace transfer rollers and the ITB at the recommended maintenance intervals.
- Use genuine Konica Minolta toner to reduce contamination and maintain transfer efficiency.
- Keep the interior of the machine free of excess toner and paper dust.
- Perform Image Stabilization and Color Registration Adjustment after servicing transfer components.
Why Understanding Transfer Charge Matters
The transfer stage is where the developed toner image leaves the imaging system and begins its journey to the printed page. Problems with transfer charge can mimic defects caused by the drum, developer unit, or fusing system. By understanding how the Primary and Secondary Transfer Rollers use electrostatic attraction to move toner from the drum to the Intermediate Transfer Belt and then to the paper, technicians can diagnose image-quality issues more accurately and avoid unnecessary replacement of expensive imaging components.
Conclusion
The transfer process in a Konica Minolta bizhub photocopier relies on precisely controlled electrostatic forces rather than mechanical pressure. During Primary Transfer, toner moves from each OPC drum to the Intermediate Transfer Belt, where the four color images are combined into a single full-color image. During Secondary Transfer, a second transfer charge pulls the complete image from the belt onto the paper. Working together with the High Voltage Power Supply, transfer rollers, Intermediate Transfer Belt, and automatic image-quality control systems, the transfer stage ensures efficient toner movement, accurate color registration, and consistent print quality. A thorough understanding of transfer charge enables service technicians to troubleshoot transfer-related faults effectively and maintain optimal performance throughout the life of the machine.