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17 Jun 2002
At the expense of "older" laser technology, fibre lasers and ultraviolet diodes are breaking into the growing market for computer-to-plate printing. Michael Hatcher explains how printing systems are becoming smaller, faster and cheaper.
From Opto & Laser Europe May 2002
Printing is a huge and potentially very lucrative market for laser-system manufacturers. The leading exhibition - Drupa - attracted nearly half-a-million attendees when last held in 2000, dwarfing even the biggest optics events like the Optical Fiber Communication conference.
And laser systems have long been a fixture in the industry. Argon ion, Nd:YAG and HeNe sources have all featured in computer-to-plate (CTP) printing systems that improve productivity by removing the film-making stage of the process, while laser diodes are ubiquitous in desktop printing. Having first appeared on the scene in the mid-1980s, CTP started to make serious inroads after Drupa in 1995.
According to data from Heidelberg Prepress, although the total number of printing systems shipped
annually increased only slightly from 1997 to 2000, CTP systems' market share doubled. However, there are signs that this is
beginning to change, with two relatively new laser technologies leading the way: diode lasers, both in the violet and in the near-infrared,
and fibre lasers emitting in the 1 µm range. The emission wavelengths are a crucial part of this evolution, with a general trend
away from visible-range sources reflecting printers' desire to work with technology that is more daylight-friendly. On the
fibre-laser side, Hell Gravure Systems of Germany, a company with a history of innovative printing technology, is making serious
waves with its F2000 and C2000 photogravure systems. The F2000 flexographic printing system exploits an ytterbium-doped fibre
laser that emits at 1112 nm. It churns out a total of 60 W (7.5 W down each of eight channels). The F2000 is designed for heavy-duty
printing, primarily in packaging where print runs can reach millions. Using photogravure the fibre laser can also print on a variety of
materials, including plastic and glass. Whereas a YAG source would typically have a 60 µm depth of focus, the fibre laser's is
around 300 µm. This is a direct result of the beam quality, and Hell Gravure's Peter Ressel, R&D project manager for the F2000, says
that this is the fibre laser's key advantage over other coherent sources. The beam quality is almost diffraction-limited with an
M2 value of 1.1. The depth of focus is crucial in flexographic printing, in which a light source removes a layer of
photopolymer on the plate's surface. Slight variations in plate thickness mean that when it is exposed by a source with a shorter depth
of focus, this photopolymer layer is not always completely removed. With the fibre laser, however, the long focal depth ensures that all
the material is removed. Ressel adds that the other reasons for choosing a fibre laser were its compact design and long
lifetime. Coupled with the fact that no cooling water is needed, and with the absence of conventional optics for beam direction,
the fibre laser looks sure to be a popular choice. At the moment, Ressel says that the company is content to limit the F2000's use to a
few local European printers. Once any remaining teething problems have been worked out, the product will be launched in the US.
Early customers include Chemosvit, which is Slovakia's largest print shop. And Hell is not resting on its laurels - the F2000 can be
upgraded to accommodate more powerful lasers, and is equipped for digital direct engraving. Ressel points out that although the
system is expensive, the bulk of the cost is in the fibre itself and its 900 nm pump diodes both of which are expected to reduce in price
considerably in the near future. The cost of 405 nm violet-laser diodes should drop even faster, thanks to developments in
next-generation DVD standards and the likelihood of manufacturers to compete with Nichia. With signs that rival manufacturers such
as Sanyo and Cree are gearing up their own violet-laser-diode manufacturing, and the likely resolution of the ongoing patent disputes
between Shuji Nakamura and his previous employer, this looks to be more than likely. This should make violet-diode CTP more
competitive. Indeed, violet-diode-based systems are on the verge of making a big impact, according to Eskil Fjord Pedersen of Esko
Graphics. His company is the product of the recent merger between Purup-Eskofot of Denmark and Barco Graphics of Belgium, two
of Europe's biggest manufacturers of plate drivers. Pedersen says that with a number of manufacturers rolling out products at the
IPEX printing show held in Birmingham, UK, last month, violet diodes are starting to take over from all other visible-source CTP
systems. However, they are up against a tough competitor at the other end of the optical spectrum. "The next two years will see
thermal systems [i.e. those based on near-infrared semiconductor sources] and ultraviolet diodes in competition, although they will also
tend to serve different segments," said Pedersen. He thinks that violet-diode systems and their thermal counterparts are now "about
level" in terms of technological development and market potential. Pedersen sees newspaper and commercial printing as the big
markets for violet-diode CTP, along with the emerging small offset printing sector. For this last segment, though, the price of the
systems will have to drop markedly, and much of this will clearly depend on the cost of the laser diodes at the heart of the
systems. This means that the price of such plates is higher, and printers
are therefore reticent about investing in a new system if there is only one plate supplier. The solution is to use higher laser power, but
Pedersen says that violet diodes would have to hit 1-4 W for conventional plates to be compatible. This power level is clearly a
long way off, and unless some serious breakthroughs are made soon printers will have to make do with the more expensive
plates. To fill this niche, Esko used IPEX to launch Dicon, its newest CTP system. Dicon uses an ultraviolet lamp rather than a
violet laser, and consequently it emits far higher powers and is compatible with the conventional, cheaper ultraviolet
plates. Ultraviolet light from Dicon is guided down standard fibre onto the plates. Despite its attenuation of ultraviolet light, the
distance travelled is short enough that standard fibre can be used. Esko sees a big market opportunity for Dicon among commercial
and newspaper printers, 80% of whom still use the conventional plates. The company also has its own fibre-laser system, which
fits into its thermal-printing product range. Esko's laser is sourced from IPG Photonics. Pedersen says that while the performance of
the fibre-laser system is exceptional, with modulation speeds of up to 50 MHz, the price remains very high. The next two years
should see both violet-diode and thermal systems increasingly penetrating the smaller print shops. "Low-end CTP is just starting to
take off and we should see rapid growth. Violet [diode] systems will be the most important technology in this sector," concluded
Pedersen. Hell Gravure www.hell-gravure-systems.com Esko Graphics www.esko-graphics.com
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