CTP-flexo platemaking is all the rage. Its connotation of higher quality among print buyers ties in with a perceived added value through an all-digital workflow. Yet not one of the 2002 FTA Excellence Award winners was produced using CTP. All the plates were conventionally made using high-definition exposure.

Until recently, one supplier's point-light system has been the industry standard in the package-printing marketplace. Its quality rivals digital with significantly less upfront cost and waste. Now, however, a newer technology is available to push the analog-flexo platemaking envelope even further.

CTP claims several advantages. One is that digital files can be transferred anywhere, and dot structure can be "reproduced anywhere." Another is that CTP controls the angle of light, making for a much narrower shoulder angle and hence an improved dot.

While it's true that digital files can be sent anywhere, controls are unavailable to ensure the image is reproduced with integrity each time. When printing packaging for the same customer, one converter using Vendor A's CTP device may not produce plates exactly as another converter using Vendor B's CTP device. This represents no more control than film being sent from a single imagesetter to a number of converters.

CTP devices do control the angle of light, which is a benefit to flexo platemaking. This, in conjunction with oxygen, has a significant effect on the shoulder angle of dots. What if there was a less expensive way to control the angle of light and produce similar results without the need or expense of CTP?

This next generation of exposure systems controls the angle of light and hence creates industry-desired, steeper shoulder angles on dots that compete with CTP-flexo yet with a smaller upfront investment. The new eXact system is said to faithfully reproduce film to plate with predictable results.

Four major components make up the eXact system: a patent-pending mercury-plasma light source; a rectangular, concentrating reflector; a digital integrator; and automated flip-top operation. Flexo plates are exposed at least as fast as with bank-light exposure units with higher quality.

Mercury-plasma light sources emit the most 365-nm (UV) energy. This allows for shorter exposure times when the energy is properly harnessed. Point-light source exposure systems have been on the market for a few years; however, significant differences exist. The word "point" describes what happens to the dots. Because the light is relatively close to the plate, dots will point to the source. Also, the distance light travels in a point-light system from the source to the plate varies, thus lowering the energy on the outer edges.

Rather than a point-light system, eXact is more of a single light-source system using a rectangular, concentrating reflector to focus the UV light. eXact evenly distributes the light across the entire surface of the plate regardless of how large the plate is. There is no falloff or sweet spots on the plate.

The plasma-light source is liquid-cooled, benefiting all types of flexo plates. Ambient temperatures after a long exposure are reportedly only about 90 deg F.

The mercury-plasma light, in conjunction with the rectangular, concentrating reflector, accomplishes this even light distribution across the entire plate surface as well as eliminates any dot "pointing" due to direct energy radiation. The plasma source emits 360 deg of light. Inside the liquid-cooling jacket, one half of the light is blocked and reflected back to the concentrator combining with the other 180 deg of light to harness the full power of the source. This is done via a retro-reflector.

The light is then emitted into the main concentrating reflector area. This area is slightly larger than the total image area of the plate. The key to the even exposure is the shape of the reflector. In effect, the light source sits on top of a bowl-shaped (actually a rectangular parabola) reflector. Light is emitted out and down into the reflector where it is then reflected back to the plate as collimated focused light. The collimation eliminates dot pointing yet creates desired shoulders.

The light then has two legs as it travels from the plasma source to the plate. The first (A) is from the source to the reflector. The second (B) is from the reflector to the plate. Regardless of where the light is hitting the plate, A + B is always equal. Because light loses energy over distance, the equidistant light of eXact maintains the power being delivered to the plate.

The achievement of no falloff or even exposures is the first challenge. However, delivering straight collimated light builds "telephone-pole" dots with no shoulders. Because it is collimated light rather than diffused light, the angle can be controlled. eXact achieves this control through thousands of facets on the main reflector section. These facets are manufactured to yield "light "cones" between 0-26 deg. Light cannot stray outside of the 26-deg cone because light cannot bend outside of its reflected angles. This cone of light builds the desired flexo shoulders.

One of the benefits of a single light source is the ability to integrate the light. The exposure system's digital integrator measures units of UV rather than time because the power of light sources fluctuates over time. The integrator constantly measures light output and adjusts exposure time accordingly. The same number of UV-energy units is used to expose the plate. With photopolymer plates, time is almost irrelevant; it is the amount of UV transferred to the polymer that is important.

Integration insures a plate receives the right amount of UV because many converters reuse plates from previous jobs, but may need to make a change to one of the plates. If this is six months after the original plates were made, the likelihood of the old plates matching the new plates to produce a high-quality print job is low.

Because flexo printers seek to take market share away from offset and gravure, anything that enhances the final quality is paramount. Digital integration as implemented in eXact insures plate-to-plate consistency from job-to-job and month-to-month.

For an expanded version of this article, including close-up photos of plates made using various systems, go to: www.convertingmagazine.com

Marc Fioravanti is vp of sales and marketing for Cortron Corp., Minneapolis. He is a graduate of Princeton University and has been involved in graphic arts for nearly 20 years. He can be reached at 763/572-1555, email: marcf@cortron.com