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Differences Between CTP Laser Technologies
Apr 19, 2018

Differences Between CTP Laser Technologies

Platemaking technology has changed dramatically over the last 25 years. As the prepress segment of the printing industry has matured, so too have the technologies used to image plates. Thermal, Violet and to a lesser extent, UV lasers are currently the dominant technologies in plate imaging. Thermal platesetters are the most popular option among printers. While that is true, all three technologies have pros and cons that should be considered before deciding on a plate imaging system.

Thermal CtP Systems

Thermal platesetters offer users the highest quality output between the three competing technologies.
Thermal systems also have the largest section of plate options and a lower environmental impact compared to Violet or UV systems. Currently, only thermal systems can expose processless or chemistry-free plates. These plates eliminate the need for plate processing, which can greatly speed up plate production and lower costs. Unlike Violet or UV, thermal plates are not daylight-sensitive and don’t require a safe light. Thermal plates offer longer run lengths, but to achieve this, they must usually be baked. Unbaked plate run lengths can be anywhere from 100,000-500,000. When baked, thermal plates can exceed 1 million impressions. Processless thermal plates usually offer run lengths of 100,000 impressions.

Thermal is typically more expensive to buy and install. Thermal equipment is more complex than the competing technologies. Because of this, maintenance costs can be higher than with Violet or UV equipment. Plate imaging is also slower versus similarly priced Violet or UV devices.

Violet based CtP Systems

In general, violet based CtP equipment is less expensive to purchase than comparable thermal equipment. It is also faster, consume less energy and are less expensive to maintain. While violet platesetters can be less expensive to own and operate, there are many other factors to consider when buying a CtP. Violet technology provides lower acquisition and maintenance cost, and high throughput. Unfortunately, Violet does not offer the same range of plate choices and currently lack processless plate options. Violet plate run length varies among manufacturers, from 100,000 to 250,000. Like Thermal plates, Violet plates can also be baked to yield even longer run lengths but do not have the same longevity as Thermal plates. Thermal plates have another advantage over Violet in that they are not light sensitive and don’t require a safe light. Thermal plates can be handled in daylight conditions with no adverse effects. Violet plates are light sensitive and will require special handling under a yellow safelight. Risks of accidental exposure can be minimized with the addition of autoloaders which are available with many Violet systems. Violet users also have to make the choice between higher quality silver plates which have a significant environmental impact or photopolymer plates that do not contain silver but will require a special processor with a preheating capability.

One of the major concerns with Violet equipment is image quality. Although Thermal systems are capable of producing very high-quality screening, the quality that Violet is capable of producing will be more than expectable unless you need line screens well above 200 lpi. Plate imaging is generally faster with Violet systems compared to similar Thermal options. This is true because output speed is proportional to the resolution setting. The lower the resolution setting, the faster the machine will image.

Environmental concerns are also a consideration to keep in mind when comparing imaging technologies. Silver-based violet plates are the most harmful to the environment. Fortunately, that technology has become almost obsolete, having been replaced with photopolymer violet plates. Photopolymer violet plates do not have the same hazardous issues associated with silver based violet, but they do require chemical processing. Thermal plates are silver-free, but many still require chemical processing. You will, however, find that your chemistry cost may be a little more with violet. Violet chemistry usually gets dirtier than Thermal chemistry due to the coating on violet plates. This can cause problems with the processor which makes violet them more costly to maintain. This is, however, more of an issue with silver violet than with photopolymer. Processless thermal plates eliminate the need for chemicals altogether and provide the least environmental impact.

Maintenance cost should also be considered. Violet platesetters only have one laser diode to replace if it wears out. Violet lasers are not only less expensive to repair or replace but are also longer lived. Alternatively, Thermal platesetters can have either single or multiple diodes. While all lasers eventually fail, multi-diode platesetters may have diodes that are enclosed in a single head that cannot be replaced individually. Other thermal systems are more flexible and easier to repair. While some multi-diode thermal lasers can still operate at lower speeds with one or more failed diodes, the repair is more complex and expensive. Single laser Thermal systems typically offer a much higher resolution than what is possible with multi-diode thermal technology and is more expensive as a result. Additionally, Thermal equipment requires plate clamps to secure the plate during imaging. These clamps may need repair or replacement over time and are not usually found in Violet imaging systems.

UV CTCP Systems

CTCP systems image directly to conventional photosensitive plates. They were first developed to expose conventional plates for printers who wanted to move from film Imagesetters to CTP without moving to a new plate technology. Conventional plates are stable, mature, daylight safe and are cheaper to manufacture than double layered CTP plates. The chemistry in the processor is also relatively harmless, especially when compared to silver-violet plates. Unfortunately, CTCP systems were not able to achieve the quality, durability or throughput required for larger or medium-sized printers. This made them unattractive for smaller printers as well, since the difference in price between CTP plates and conventional plates did not compensate for the higher cost of the equipment. Because of this, most operations moved from film-based systems to CTP devices. As the market matured, most manufacturers couldn’t justify the R&D investment needed to increase CTCP throughput.

More recently, newer manufacturers from China and India have continued to develop and produce CTCP equipment. Newer CTCP platesetters are faster than earlier models and produce plates that are comparable in quality to Violet CTP. Most printers, however, quickly find that access to reliable sources for parts and service outweigh any saving offered by the lower plate cost.

There are pros and cons to consider with all three technologies. Thermal CTP offers users the highest quality output, longest run lengths, and widest variety of plate choices. Thermal is the only technology that currently offers processless plates. The downsides of thermal are higher acquisition and maintenance costs and slower speed compared to similarly priced violet systems. Violet systems are less expensive to own and operate, but can’t match the quality or ease of use when compared with thermal. Violet is also less environmentally friendly than thermal. UV CTCP systems offer the lowest plate cost and are easier to use than Violet, but lack in reliability and available support.