Positive vs Negative Working Plates: Where DNQ Chemistry Fits
Positive vs negative working plates explained — exposed area behaviour, developer chemistry, DNQ role. Conventional CtCP is positive; Orion Next is negative.
Plate coating buyers, pressroom managers, and prepress technicians use "positive" and "negative" to describe opposite imaging behaviours — but the terms describe what happens to the exposed coating, not the visual appearance of the plate. Mixing up positive and negative working modes produces plates with reversed images, background printing, or complete coating failure.
This guide defines both modes, explains where DNQ chemistry fits in each, and clarifies the central distinction in Orion's product line: conventional DNQ CtCP is positive-working; Orion Next developer-free CtCP is negative-working.
Defining positive and negative working
The plate setter RIP must match the plate working mode. A positive RIP setting on a negative-working plate — or the reverse — produces a wrong-reading image.
| Mode | Exposed coating behaviour | Unexposed coating behaviour | Image areas on plate |
|---|---|---|---|
| Positive-working | Removes in developer | Stays on plate | Coating remains in unexposed areas |
| Negative-working | Stays on plate | Removes in developer | Coating remains in exposed areas |
Positive-working plates and DNQ chemistry
Conventional UV CtCP (positive)
The majority of commercial UV CtCP plates are positive-working. The process:
- Coat anodised aluminium with DNQ-based diazo lacquer
- Self-cure under yellow safe light (minimum 24 hours)
- Expose on UV laser plate setter in positive mode — the laser images non-image (background) areas
- Develop in alkaline developer — exposed coating removes; unexposed areas retain the coating
On the finished plate, image areas (ink-receptive) carry the remaining coating. Non-image areas (water-receptive) are bare anodised aluminium where exposed coating was washed away.
DNQ chemistry in positive mode
In conventional positive UV CtCP, the DNQ-cresol ester coating (such as Orion Freedom Plus 1413) undergoes the Wolff rearrangement on UV exposure. The photochemical change makes exposed areas removable in alkaline developer. Unexposed areas retain the coating.
This is the same DNQ photochemistry used in positive photoresists — exposed areas become more soluble. The developer medium differs (alkaline solution for plates, TMAH for resists), but the photoswitch mechanism is the same.
Negative-working plates and DNQ chemistry
| Plate type | Photoactive chemistry | Working mode |
|---|---|---|
| Conventional UV CtCP | DNQ-cresol ester (diazo polymer) | Positive |
| Developer-free UV CtCP | Multi-polymer (Orion Next) | Negative |
Developer-free UV CtCP (negative)
Orion Next is negative-working. The process:
- Coat anodised aluminium with Orion Next multi-polymer solution (1.7–1.8 g/m²)
- Self-cure under yellow safe light (minimum 24 hours at 27–31 °C)
- Expose on UV laser plate setter in negative mode — laser hits image areas
- Develop in plain tap water — unexposed coating removes; exposed areas remain on the plate
Exposed areas stay on the plate and are ink-receptive. Unexposed areas wash away in water, exposing the hydrophilic anodised aluminium surface.
This is the opposite behaviour from conventional positive CtCP. The plate setter software must be set to negative mode. Using positive mode on Orion Next produces a reversed image.
Why Orion Next is negative-working
Developer-free coatings use a different polymer architecture than conventional DNQ-cresol ester lacquers. The multi-polymer Orion Next system crosslinks or hardens on UV exposure rather than converting to a soluble acid. Unexposed, uncrosslinked polymer removes in water.
The DNQ chemistry family is not the photoactive component in Orion Next (described as multi-polymer with photo-initiators). The working mode distinction is therefore:
Both image on UV laser plate setters at 360–375 nm. The chemistry and working mode differ.
Side-by-side comparison
| Parameter | Positive-working | Negative-working |
|---|---|---|
| Exposed areas | Removed in developer | Remain on plate |
| Unexposed areas | Remain on plate | Removed in developer |
| Plate setter mode | Positive | Negative |
| Typical developer | Alkaline (conventional CtCP) | Water (Orion Next) or alkaline |
| Orion product | Freedom Plus 1413 | Orion Next |
| Coat weight | 1.7–1.8 g/m² | 1.7–1.8 g/m² |
| Sensitivity | 365–405 nm | 360–375 nm |
Positive vs negative in photoresists (for context)
Electronic photoresists are almost exclusively positive-working with DNQ-novolak chemistry:
- Exposed resist dissolves in alkaline developer
- Unexposed resist stays on the wafer
- The wafer surface is etched or implanted where resist was removed
Photoresist positive mode is the same photochemical principle as conventional positive CtCP — DNQ photobleaching increases solubility in exposed areas. The substrate and developer differ; the mode does not.
See DNQ Novolak Resist Mechanism for the dissolution chemistry.
Common mistakes when switching modes
| Mistake | Consequence |
|---|---|
| Positive RIP setting on negative-working plate | Reversed (wrong-reading) image |
| Negative RIP setting on positive-working plate | Reversed image |
| Alkaline developer on Orion Next | Coating damage; plate failure |
| White-light exposure before development (either mode) | Background; non-image areas cure |
| Assuming all DNQ plates are positive-working | Wrong plate setter configuration for Orion Next |
Choosing the right mode for your pressroom
Stay with positive-working (conventional CtCP) if:
- Your plate setter, RIP, and processor are configured for positive mode
- Your coating line is qualified on DNQ-cresol ester lacquers
- Alkaline developer handling is acceptable in your operation
Evaluate negative-working (developer-free CtCP) if:
- You want to eliminate alkaline developer chemistry
- Your UV CtCP plate setter can switch to negative mode in software
- You are qualifying a new coating and can set the workflow from the start
The switch from conventional to developer-free is primarily a software setting on the plate setter (positive → negative mode) and a processor chemistry change (alkaline → water). Hardware does not change.
See Developer-Free vs Conventional CtCP for the full operational comparison.
Common questions.
What is the difference between positive and negative working plates?
On positive-working plates, exposed coating is removed in developer and unexposed coating stays. On negative-working plates, exposed coating stays on the plate and unexposed coating is removed. The plate setter RIP mode must match the plate working mode.
Is Orion Freedom Plus positive or negative working?
Orion Freedom Plus 1413 (conventional UV CtCP) is positive-working. Exposed diazo coating is removed in alkaline developer. Unexposed areas retain the coating for ink receptivity.
Is Orion Next positive or negative working?
Orion Next developer-free UV CtCP is negative-working. Exposed areas remain on the plate; unexposed coating removes in plain tap water. The plate setter must be set to negative mode.
Are all DNQ plates positive-working?
Conventional DNQ-cresol ester CtCP plates are positive-working. Developer-free multi-polymer systems such as Orion Next are negative-working. The working mode is set by formulation, not by the DNQ chemistry family alone.