The gravure printing industry burns through over a million tons of organic solvents annually, releasing hundreds of thousands of tons of VOCs into the atmosphere. Water-based inks help, but can’t match solvent ink’s print quality — and their high-temperature drying creates problems for food, cosmetic, and pharma flexible packaging. A fundamentally different approach is needed.
Dongguan Wanhao has been developing one since 2006: a nitrogen-protected UV gravure press that eliminates VOC emissions entirely while delivering print quality that beats both conventional gravure and offset. The company holds multiple national invention patents for the technology.
How It Works
Conventional UV curing happens in normal atmosphere. Oxygen in the air scavenges the free radicals and ions that photoinitiators generate under UV light — a competing reaction that wastes energy and, worse, produces small-molecule organic volatiles as byproducts. Ink formulators compensate by overdosing photoinitiators and accept the VOC penalty as unavoidable.
Flood the curing chamber with nitrogen and the chemistry changes. With no oxygen present, every free radical and ion generated by the photoinitiator goes toward polymerizing the ink film. No oxidative side reactions. No VOC generation. The UV energy is fully utilized.
The consequences cascade through the entire system:
- Ink formulation gets simpler and cheaper. Manufacturers no longer need to compensate for oxygen inhibition. Photoinitiator loading drops. Raw material costs for UV ink come down significantly.
- Energy consumption collapses. N2-protected UV curing uses roughly 15% of the energy that conventional UV curing demands — because the photoinitiators are doing their job instead of fighting oxygen.
- Total cost reaches parity with solvent gravure. Lower ink cost plus dramatically lower energy cost offset the nitrogen supply expense.
Performance Data
Test prints run on cigarette packaging stock were sent to Shenzhen Jinjia Group for VOC residue analysis under China’s tobacco packaging standard YC/T207-2006 (Headspace Gas Chromatography method for volatile organic compounds in cigarette carton and case paper). Across three samples, VOC residue measured below 2% of the national standard limit — a level that conventional solvent gravure presses struggle to meet even with aggressive after-drying.
The print quality improvements are equally dramatic:
- Solid coverage: Better than conventional gravure — no solvent evaporation means the ink film stays full and dense through transfer.
- Dot reproduction: Better than offset — UV ink doesn’t lose solvent during transfer, so dots hold their shape and density. This eliminates gravure’s traditional weakness in fine-screen reproduction.
- Color consistency: No solvent evaporation during the run means ink concentration stays constant from first sheet to last.
Additional Advantages
Reduced startup waste. UV curing means a much shorter dryer path than conventional gravure. Each color station saves roughly 10 meters of substrate per startup — adding up to tens of thousands of yuan in annual material savings per color unit.
Higher speeds possible. The short curing path and room-temperature drying reduce demands on the registration system, enabling faster production.
Multi-process integration. The UV curing platform accommodates offset, flexo, screen, ice-crystal effect, foaming, embossing, and essentially all common printing and finishing processes on a single machine.
No heat damage. UV curing generates no substrate heating, eliminating the thermal distortion problems that plague water-based gravure on heat-sensitive flexible packaging films.
References
- Wikipedia: Rotogravure: Overview of gravure printing technology including solvent-based ink systems and VOC emission challenges in flexible packaging.
- Wikipedia: UV Curing: Fundamentals of ultraviolet curing chemistry including photoinitiator mechanisms, oxygen inhibition, and nitrogen-blanketed curing.
- Wikipedia: Volatile Organic Compounds (VOC): Definition, environmental impact, atmospheric chemistry, and regulatory framework for VOC emissions from industrial processes.
- ISO 12647-4:2014 — Gravure Process Control: International standard for tone value, registration, and production consistency in gravure printing relevant to quality benchmarking.
- EPA: VOC Emissions Standards: U.S. regulatory framework for volatile organic compound emissions from industrial sources including printing and coating operations.