Violet laser diodes — emitting in the 395–410 nm range — were not developed for the printing industry. They came from consumer electronics, where they were called “blue lasers” and used in optical disc drives. But their wavelength overlaps precisely with the absorption peak of conventional PS (presensitized) plate diazonaphthoquinone sensitizers at approximately 410 nm. That accidental match has been driving a quiet revolution in computer-to-plate technology for over two decades. Here is the technical timeline, the politics, and why 6W changes everything.
The Power Escalation: 5 mW to 6,000 mW
Agfa introduced the first violet-laser CTP system at Drupa 2000. The laser diode output was 5 mW — capable of exposing only high-speed silver-halide plates. The implication was clear even then: if the power could be scaled up, conventional offset plates could be imaged directly, eliminating the need for specialized (and expensive) digital plates.
The development trajectory over the following eight years was extraordinary:
| Year | Developer | Product | Power | Notes |
|---|---|---|---|---|
| 2000 | Agfa | First violet CTP | 5 mW | Silver-halide plates only |
| 2002 | Nichia + Sony | Joint development | — | First major electronics firm enters violet LD production |
| Jan 2007 | Photonic Products (UK) | 405 nm module | 25 mW | 3.5×2 mm, TTL modulation, elliptical beam |
| Mar 2007 | Nichia | High-power LD | 320 mW | Pulsed, >10,000 hrs at 80°C |
| Mar 2007 | UCSB (Nakamura team) | Non-polar LD | 405 nm | Low-threshold, non-polar GaN |
| May 2007 | Sharp | GH04020A4G | 20 mW peak | ¥10,000 (~$100), 10,000 hrs at 5 mW CW |
| Nov 2007 | Sony Shiraishi Semiconductor | Violet LD | 240 mW | 1.7 million units/month capacity |
| Sep 2008 | Mitsubishi Chemical | GaN substrate | — | Commercial GaN substrates for violet LDs |
| Oct 2008 | Sanyo | Violet LD | 450 mW | — |
| 2008 | Nichia | NUV101E | 6 W | 1,200× increase over 2000 baseline |
At 6 W output — a 1,200-fold increase from the original 5 mW — violet laser diodes were approaching the power density needed to expose conventional offset plates at speeds exceeding traditional vacuum frame exposure units.
The Wavelength Match Nobody Talked About
The technical case for violet-laser CTP on conventional plates was compelling from the start. PS plates use 2,1,5-diazonaphthoquinone sulfonyl chloride sensitizers with a spectral sensitivity range of 280–450 nm. The absorption maximum sits at approximately 410 nm — directly aligned with the 395–410 nm emission band of violet laser diodes. In physical chemistry terms, violet lasers and conventional PS plate sensitizers were nearly perfectly coupled.
So why didn’t CTP on conventional plates happen immediately? Two reasons. First, the initial 5 mW output was simply too weak to image a conventional plate at commercially viable speeds — the sensitivity difference between silver-halide digital plates and conventional PS plates was too large to bridge at milliwatt power levels. Second, and more significant: the global plate manufacturing oligopoly did not want it to happen.
The three dominant plate manufacturers — which at the time controlled over 90% of the international market — had invested heavily in thermal and violet digital plate R&D. Digital plates carried margins far higher than conventional PS plates, whose profitability had been steadily eroded by the expansion of Chinese manufacturing capacity. As Li Xianyong, general manager of Beijing Cron, put it: “Digital plates are widely considered the last piece of cake in offset platemaking.” When you can sell a premium digital plate, why would you enable a technology that lets customers use cheap conventional ones instead?
The author recounts interviewing senior executives from the major plate manufacturers on the subject of conventional-plate CTP. “Their universal reaction was to change the subject. They would not answer directly. Instead, they would tirelessly explain: ‘We can provide a complete solution. Our solution meets your needs. Accepting our solution is your best choice.'” This was not a technical objection. It was a business strategy.
China’s CTcP Opportunity
The politics of the plate market created a strategic opening for Chinese equipment and plate manufacturers. Unlike the global giants, Chinese plate producers had not sunk enormous R&D budgets into thermal and violet digital plate formulations. Their core competency remained conventional PS plate manufacturing. If they could improve coating uniformity and increase sensitizer speed by even modest increments — and combine those incremental improvements with 6 W violet laser diodes — they could leap directly to conventional-plate CTP without ever passing through the digital-plate intermediate step.
By 2008, only three companies worldwide were producing CTcP (Computer to Conventional Plate) equipment. Germany’s BasysPrint had historically used conventional UV lamps rather than laser diodes — an approach the author considered a technological dead end, though BasysPrint had begun integrating violet diodes into its next-generation systems. Switzerland’s Lüscher and China’s Cron both used violet laser diode arrays as their exposure source, a direction the author identified as the correct technological path for the industry.
For print shops, the CTcP value proposition was straightforward: avoid the escalating per-plate cost of proprietary digital plates while still gaining the workflow benefits of direct-to-plate imaging. The only barrier had been the upfront equipment cost. With Chinese CTcP manufacturers entering the market, that barrier was collapsing. At 6 W, platemaking speeds could rival — and potentially exceed — traditional vacuum frame exposure. “When the economics, quality, and speed all favor one technology,” the author wrote, “printers will not choose an inferior alternative for long.”
The article closes with a prescient observation from Zhan Wenqing, general manager of Wangchang, at All in Print China 2008: “One flower blooming alone does not make a spring. A hundred flowers blooming together fills the garden.” His advice to Cron and other Chinese manufacturers: open up the technology, encourage competitors, build an ecosystem. More players means faster adoption, and faster adoption means the technology becomes unstoppable.
References
- Wikipedia: Computer to Plate (CTP): Comprehensive overview of CTP technology, plate types, and the transition from film-based to direct-to-plate imaging.
- Wikipedia: Laser Diode: Technical explanation of semiconductor laser diode physics, including violet/blue GaN-based devices and power scaling.
- Wikipedia: Nichia Corporation: History of Nichia, inventor of the blue/violet GaN LED and laser diode, and its role in commercializing violet laser technology.
- Wikipedia: Shuji Nakamura: Profile of the Nobel laureate who invented the blue/violet GaN LED and laser diode — the foundational technology behind all violet CTP systems.
- Wikipedia: Photopolymer Plate: Description of photopolymer plate chemistry, spectral sensitivity, and comparison with silver-halide and thermal digital plates.