Computer to plate

This article is for those printers still debating the change from 'computer to film' to CTP.
Printers that have already made this change may wish to reconsider their business cases for CTP - to check that all the projected benefits have been achieved!

The computer-to-plate process uses a laser to expose the image directly onto the surface of the plate, without using the intermediate film common to imagesetting. This exposure can happen off the press, in a dedicated CTP system, or on a DI press - by directly imaging onto the plate in its 'run' position.

CTP systems make use of one of the following energy sources: green laser, violet diode, thermal laser head or red laser. (Note that some systems have interchangeable imaging heads). They can be used with internal-drums, external-drums, or in a flatbed configuration. They may have a single laser beam or multiple laser beams to image the plate. The are available for all plate formats, and various speeds, to suit all applications and all budgets. System prices, with a RIP range from around £40,000 to over £500,000 - according to size and method of loading and unloading the plates.

The energy source 'writes' the image to the plate by modifying the surface layers of the plate to capture the printing image. Then, commonly, a plate processor is used to develop the plate and gum it up ready for the press; however there are some processes (such as the ablative plates) that do not require a plate processor at all.

Much has been written about the technical merits of moving from computer-to-film (CTF) to CTP. On the face of it, such a move is a logical business step, yet, surprisingly, for some printing companies, especially in the B2 arena, only about 40% seem to have made the move so far. CTP as a technology is well proven and the arguments for not investing in it are diminishing as businesses try to further reduce the cost of getting to a plate stage.

Even some large web printers are still resisting the change to CTP. This is also unexpected, because where presses are operating 24 x 7 and accompanying pre-press shifts are also staffed - when in fact with CTP production, most, if not all of the plates could be made in a single shift with half the current staff. In a market sector where pricing is highly competitive, the reduced cost of CTP operations may provide an edge over competitors in winning significant business.

For printers with B1 size presses, around 60% are now running with CTP systems and in the B3 size printing companies, the take-up is much higher (probably due to the polyester plates more appropriate for the majority of their work).

Is this disparity caused by the technical options now available - thermal, violet, silver, or is it more to do with the consequential man-management issues that arise from the introduction of this technology into a printing company?

For most commercial printing applications, both the thermal and violet technologies give high quality results. Because the laser writes directly onto the plate, the image loss - that occurs through use of an intermediate film with imagesetting - is removed.

Increasingly, the CTP machines are moving towards a 'black box' production approach:

Load the machine with plate material out of the box.
The machine removes the interleaf papers between the plates and puts them in a bin;
Some systems punch the plates as part of the process. Others require pre-process or post-process punching operations.
The CTP system exposes the plate as part of a continuous operation and
It conveys the plate (sometimes via a bridge conveyor) into the processor. The plate eventually emerges after a minute or so developed and gummed;
It is then stacked by an automatic stacking unit, ready to go onto the press.

All of this process can be untouched by human hand. [Less expensive systems often require the operator to handle plates for loading and unloading operations].

The main problems to overcome in developing a CTP workflow usually occur upstream of the actual CTP device. There, the issues of pre-flight checking, file conversion, colour calibration, imposition, colour proofing and colour separation, must all be addressed to ensure that the signals sent to the CTP system will produce a predictable result. Correctly proofing the composite file on a colour calibrated printer, gives a perception of what the printed output is like - even though it may have been produced by an entirely different printing method (e.g. inkjet printed). The use of a proofing system with CTP is essential - to prevent the loss of expensive plates when things go wrong.

The main benefit of CTP is that the distribution of ink across the plate is known when the plate is made. For presses equipped with CIP3/CIP4 ink zone settings, making the link to the pre-press system allows ink ducts on the press to be set up automatically. Couple this with automatic, or semi-automatic plate loading on the press to achieve much reduced make-ready times (and costs) on the machines that attract the highest hourly rates.

If you are thinking about moving to CTP, try printing from a set of plates of each type in your environment and then decide for yourself on the most appropriate.

Thermal CTP

Thermal platesetters rely on laser-created heat to induce changes in the surface layers of the CTP plate material, or, in the case of ablative processes, to burn off the surface layer completely in the areas where the plate carries the image for printing.

The claimed benefits of the thermal process include:

Creation of very accurate and consistent dots that provide a sharp 'digital' cut off point between areas that carry ink and areas that do not;
Thermal plate processors can also process conventional plates;
They can operate in daylight conditions;
They can be sourced form a number of manufacturers;
They have tended to be the 'system of choice' by the early adopters in VLF (very large format) and B1 size printing companies, but less so for other sizes.

The increased energy of thermal imaging systems also enables a wide range of applications that visible and violet light cannot support *, such as digital half-tone proofing, waterless plates, flexographic plates and processless media. [* Source: Creo Product Bulletin]

Visible light CTP

Visible light platesetters use lasers that operate in the visible area of the spectrum to cause changes in the plate emulsion, for both photopolymer and silver halide CTP plates.

Some points about these plates include:

The latest CTP technology uses low-cost, long life, violet diodes (similar to those used in DVD and CD-ROM recorders), that result in lower maintenance and service costs;
There has been a good take-up of this technology with B2 size printers (possibly because there are more 'later converters' from imagesetting) for general purpose commercial printing applications;
Violet photopolymer plates can print in aggressive UV ink environments without baking; but they can also be baked for longer-run applications;
Violet CTP systems tend to have the better price/performance ratios;
Violet CTP plates need handling in bright yellow safe-light areas;
The silver halide plate technology was used to pioneer CTP. These plates give high-resolution results and can also be baked for longer runs;
For newspapers businesses that have a requirement for large numbers of plates in very short timescales, the high-speed visible light CTP systems (with plate coatings typically thousands of times more sensitive than for thermal plates) have enjoyed greater success than for thermal systems.

Processless CTP

The main driver behind this technology has been the elimination of the processor (often quite a significant Capex item) and the elimination of the cost of the chemistry to develop the plates and its disposal (at best, a messy procedure and a staff distraction).

If these plates are to gain wide acceptance, printers will want to see a combination of affordable prices and robust press performance. Since it is coming later in the CTP life cycle, many printers are already reaping the benefits of using CTP plate manufacture - by other processes - and the big business gains arising from re-engineering the workflow may already have taken place.

The Business drivers for CTP

Lean manufacturing principles are driving the costs out of making printing plates. The Japanese have taught us that you can continuously reduce the cost of a repetitive process by the application of automation - and a bit of ingenuity. The main idea is to try to remove as many processes, operations and manual interventions in a workflow as you can.

Formerly busy planning and platemaking rooms in printing companies, where films were ruled-up, imposed, had calibration strips added, spotted out, placed over plate material, then exposed to high-power UV lamps, are being replaced by the leaner processes in CTP systems. Originally, operations were subject to labour costs, with variable additional costs around overtime, holidays and sickness. Newer processes now take out many of the variables and make the product more predictable.

The development of software programmes to automatically impose pages to the size of the press plate, often take just one second in time. Suddenly, the manual effort of assembling pages has disappeared, as this operation moves forward onto workstations in pre-press departments. The result is faster, accurate register and control over this stage of the process, leading to dramatic improvements in make-ready time on the press. The deciding factor for many printers is now the number of plates/hour it needs to make to meet the increasing demands made by shorter print runs.

To test the validity of any investment decision, it helps to work through two essential comparative assessments:

Return on Investment [ROI] calculation to determine the time it will take for the system to pay for itself out of the material and time savings generated as a result of the change. It analyses current and future projections of the plates that will be needed and compares CTP material costs with current methods of platemaking. It also identifies the timesaving that will ensue in the pre-press and press make-ready stages.

The Total Cost of Ownership [TCO] over the period of the investment. It is this latter calculation that really matters. Some of the investment criteria could include:
The total likely usage of plates over, say, 3 years
Building & Services costs arising from the installation
Installation costs of the system, including: fingerprinting for each press,
Colour calibration of proofing devices;
Capex costs:

CTP system, RIP, Server, Raid, Networking, Back-up devices,
Processor, Plate stacker;

Uninterruptable Power Supplies;
New workstations, monitors, local and remote proofing systems;
New software, including firewall and anti-virus, imposition, trapping,

pre-flight checking, file conversion, back-up/archive, links to MIS;

Materials: Plates, chemistry, waste disposal
Staff costs:

CTP and revised workflow training,
Re-training for staff displaced by reduced requirement
Redundancy - if this is an outcome of the investment

Conclusions

There is a wide choice of CTP systems for printing businesses. Not all systems or technologies can suit all printers. The technologies all work well and have distinct production advantages over imagesetting systems. Companies still imagesetting are now working with cost and quality disadvantages when compared with their CTP competitors.

Considerable care needs to be taken in assessing both the technical and business parameters to assist in making informed decisions about the most appropriate investment for each company. Many of the issues about which system to buy will be affected by existing workflow solutions and the changes required, staffing considerations and relationships with existing suppliers.

However, investment in any CTP system should also be considered in terms of its real cost of ownership, impact on staff, changes to the bottom line of the business and its ability to assist the printer in meeting his client's expectations. A good question to ask potential suppliers is for how long do they expect their R & D programme to continue with the chosen system? Some comfort can be taken from the knowledge that they are still investing in your proposed purchase.