CTP technology in offset printing

As CTP technology takes over once popular and visibly less expensive films, Som Nath Sapru charts the trajectory of the growth of CTP technology, and explains why CTP matters.

25 Jul 2017 | By Som Nath Sapru

From the early 1990s and beyond, the trend has been to produce printing plates directly from computer-generated page layout information, thus bypassing the film exposure stage entirely. This is called CTP (computer-to-plate) technology.

The CTP technology enhanced the quality of printing besides cutting down on several cumbersome steps and saving production time, labour and money. Just about three decades back, which were the initial days of computer-generated typesetting, galleys (long, single-column sheets of typeset material) arrived at the design studio having been either hand-set or mono or lino set by the typesetter/operator. A paste-up artist waxed the back of the galleys, then cut them apart and positioned the type on the paste-up key-sheets, along with opaque rectangular plastic patch windows as placeholders for the images.

At the offset print shop, the print supplier would then use a huge press camera to create negative images of the art sheets/boards and halftone negatives of the photographs on clear film. He would then strip these negatives together on a sheet of yellow plastic ‘goldenrod.’

Using a contact frame that held photographic plate material in close contact with the composite negatives, the printer would then burn a plate, using a bright light source to expose the plate emulsion through the negative. The printer then hung one plate per colour (C, M, Y, K, and any spot colours) on each of the press inking units, and the process of offset lithography could proceed.

Computer generated page layout software became available in the late 1980s and early 1990s, and it was possible to either produce composite positive images (type-set text and photos), which could be processed like the prior generation of paste-up boards, or composite negatives, which could be burned directly to printing plates.

The printing industry benefited with CTP technology in several areas. These include:

  • Computer to plate technology eliminates defects in the plates caused by scratches in the emulsion and dust on the film, as well as defects from variations in film exposure and processing.
  • In a CTP workflow, removing one generation of image reproduction (imaging plates directly from the digital information rather than producing film and then burning plates from the film) increases the sharpness of the type and image detail.
  • CTP eliminates the cost and management of film and its related processing chemistry, saving money and benefiting the environment.
  • Printing plates can be imaged more accurately, quickly, and consistently (from edge to edge across the plate): from approximately 60 to 300 plates per hour depending on the size and resolution of the plates. This is a huge productivity gain over film-based workflows. Printing plates can even be burned in an unattended mode, overnight.

CTP system has made production and quality of the jobs almost of international standard and economical as well. Undoubtedly, for the jobs with a huge print run it has proved economical besides it has improved production quality and cut down on the production time. It is a misnomer that small and medium size printers may not prefer the CTP system because of maintenance cost involved; in reality, they save almost on entire pre-press operation and steps involved in conventional system.

How printers can identify the core issues and select the system that best meets their needs – determining factor is if they are involved with newspaper publishing they should opt for violet CTP system as it will give them enhanced speed besides improvement of reproduction quality whereas for commercial printers which have short print-run jobs vis-à-vis newspapers should go for thermal CTP system.

Confirmed sources tell me that there are more than 2,000 CTP installations (comprising of both violet and thermal) all over India, inclusive of all metropolitan cities. These machines need up-gradations as and when there are changes in computer software and in applications reason being both the systems are computer based. In India, both the system are being used for more than one-and-a-half decade – initially Windows 5 was running the systems whereas majority of the systems are running with Windows 10.

At the initial stages, CTP system was tailored to give eight plates an hour whereas presently output of both the systems is more than 60 plates an hour. Plates used on CTP system have magnificent durability, good reproduction right up-to 400,000 print-run. I was told by an expert and a prominent printer, in whose veins ink runs, that he used a two-year old plate on a very prestigious job without any problem in reproduction quality.

Advantages of opting for the CTP technology are innumerable but to highlight few of them, they are: major gain in the saving of production real time; enhancement of reproduction quality; can store used plates at least for two years without any deficiency in reproduction quality; one can make changes right on plate without any hassle; plates once used can be used at least for next two runs without any quality loss.

Printers have gained in the consumption of plates, the reason being any PS plate used on CTP can be reused for at least next two print-runs.

Above all, one can save a lot of overhead expenses by utilising pre-press staff in other areas of new CTP technology which could prove as on the job orientation.

As opposed to newspapers and commercial printers, packaging printers have preferred to live with conventional pre-press process, the reason being that most of their print jobs are repeat jobs.

What I gathered in my prolonged discussions with small, medium and big printers that most of them all over the country have plans and are considering to upgrade their pre-press operation from film-based plate imaging to CTP due to increased demand of printed materials because of ever increasing literacy growth – besides increase in the wages of workers in all segments, which are part of pre-press operations.

Choosing a CTP system is quite tricky and involves quite an investment. Discussions with the suppliers of the system generate a debate as to which system would be economical and feasible as the suggestions offered to the concerned party have a choice of CTP system which begins with a discussion of imaging method, primarily thermal vs violet (visible) light. What may be surprising to many is that the imaging technology is the last point of discussion in the choice of a CTP system. The guiding factor is, in fact, the business impact the anticipated investment is intended to deliver to the printer.

Because the implementation of CTP can have positive impacts all the time on the printer’s entire business, it is important that a decision-maker consider objectives beyond the obvious one of eliminating film from the plate imaging process. A few examples might include reducing print manufacturing costs, improving output consistency, differentiating presswork offerings, increasing throughput, fostering closer customer relationships, attracting new classes of business. The decision about which technology to adopt should not begin with an assessment of the imaging technology, but rather with a thorough analysis of what the investment is intended to accomplish.

By definition, any type of CTP device will eliminate film. Printers interested solely in reducing redundancy in prepress would appear to have a wide range of CTP technologies to choose from and logically gravitate towards the offering with the lowest device cost. However, that decision only addresses the first criteria and misses the more important business value of reducing variation in the process. Plates that are repeatedly imaged accurately and consistently reduce costs, improve pressroom efficiency, and help meet customer expectations in the pressroom, thus increasing profitability. Process control and stability in plate imaging are the key value in moving to CTP; the one that unlocks all the potential benefits and the return on investment (ROI) for the printer. It is the reason why thermal imaging was quickly accepted and adopted by the print industry when it was originally introduced as an alternative to visible-light CTP imaging.

So why go CTP?

This simple, pragmatic, question is often neglected in the maelstrom of competing vendor claims. The reasons for printers to consider an investment in CTP are the same today as they have been since plates have been used in the production of presswork:

  • Eliminate manufacturing redundancy and the associated costs in time and materials, i.e. remove film from the plate production process.
  • Eliminate variation in the plate imaging process. Variation in plate imaging results in longer make-readies and increased time and material waste, compromised presswork-to-proof alignment, an inability to reliably run the finer screens increasingly demanded by today’s print buyers, inconsistent pressroom performance, and reworks.

Why is thermal more effective at eliminating plate imaging variation?  The answer is stability, accuracy, consistency, and repeatability. For a printer, the integrity of the image on plate directly impacts the integrity and profitability of the pressroom. Early CTP adopters realised that plate imaging accuracy, consistency, and repeatability were key requirements of an effective CTP investment. Thermal imaging earned strong support because it proved to be both stable and consistent, using high levels of power (measured in Watts) to image relatively low-sensitivity plates. The plate coatings respond to exposure by forming an image at a threshold temperature, in a process that is essentially binary: either the image is created or it is not. Over- and under-exposure are virtually nonexistent, and imaging is very consistent.

Comparatively, violet and other visible-light-sensitive technologies must be used in a light-safe environment, exposing photosensitive chemical coatings with tiny amounts of imaging power (measured in milli watts).

In this situation, even slight variations in power can cause over- or under-exposure of the plate. The quality of the imaged plate can also be affected by minor variation in plate manufacture, storage temperature, humidity, handling, and the development process. If the promise of CTP is to deliver consistency, by their very nature, visible-light CTP systems (including violet) exhibit greater potential for plate imaging variation.

Indeed, plates imaged using visible-light CTP can exhibit inconsistencies similar and even greater than those of a film-based workflow. The cost of that plate imaging inconsistency shows up in the printer’s most expensive asset—the pressroom—in the form of longer-than-necessary make-readies, difficulties aligning presswork to proof, and difficulties delivering consistent repeat jobs.

Versatility, flexibility, adaptability

While all available imaging technologies may do the job of exposing an image on plate, none can claim the flexibility and adaptability of thermal imaging. Thermal technology is used for imaging all three of the major press-based printing processes: offset, flexography, and gravure printing. With thermal plates, prepress operations can take place in daylight. Consistent thermal imaging also enables the reliable printing of finer halftone and FM screens, which are increasingly demanded by today’s critical print buyers.

In addition to imaging plates, thermal imaging can also be used to expose proofing media on the same device when there is a need to proof the actual halftone dots. Thermal also drives the vast majority of digital offset presses (including those from Heidelberg, Presstek, Komori, Manroland and KBA). It is also the enabling technology for true process-less platemaking, which removes yet another imaging variable from the process.

What about the process-less plate making revolution?

The newspaper industry in India has taken a lead in reducing carbon footprint and adopt green printing solutions and have now opted for green CTP plates – newspapers industry has welcomed it and has found it most money-saving system. I am told that Lokmat has saved about 1.7 million litres of water and more than 13,000 litres of chemistry after having used TechNova’s Viogreen Plus plates – as these are low chemistry violet CTP plates specially developed for the newspaper industry. Viogreen plates can be imaged on any standard violet CTP platesetter. Fujifilm, Kodak and Sonora, besides TechNova have the distinction of providing green thermal and green violet plate technologies with total plateless technologies.

Anyone following the print industry understands the value being offered through ‘process-less’ printing plates, especially to smaller printers. Recently, some manufacturers have announced and started early production of violet ‘Chemistry Free’ plates. Gone are the days, when only thermal could deliver true non-process plates where no post-imaging treatment or washing equipment was required before putting the plates on press. This is because visible light plates (such as violet) are by definition sensitive to light, and cannot be handled in a normal pressroom environment unless the non-exposed coating is removed in a wash or processing unit first.

‘Chemistry Free’ is also a misnomer, because chemicals are still used in the washing of those plates after imaging — requiring proper chemical storage, handling, cleaning, and disposal procedures.

Printers who have invested in Kodak’s thermal CTP devices are, in most cases, able to switch to thermal non process plates whenever it makes economic sense for them to do so. The lower initial cost of violet devices makes them attractive in a price-conscious market, and violet CTP devices are heavily marketed to small printers. Those who invest in violet systems may pay a lower device price today but will not be able to totally eliminate the processing steps and associated maintenance, chemistry and disposal (including ‘wash out solution,’ which is chemistry) and running costs.

However, the device cost is only one of the factors to consider when deciding on a CTP solution. Making a wise business decision in an increasingly competitive market is challenging, and should not be based on device price alone. For printers considering CTP, a Total cost of ownership (TCO) calculation can clarify the true long-term costs and advantages of various options, and contribute to an informed purchase decision. When choosing a CTP system, business owners should consider the purchase in terms of these factors:

Initial Costs: Add the costs for the CTP device(s), the associated software and hardware, the space requirements and environmental preparation. This is only the starting point for a TCO analysis—ongoing costs and savings are far more important. In the initial costs, considerations should include:

  • CTP Device(s): How reliable is the device, and what is its proven track record? Will a redundant CTP device be required?
  • Workstations and software: What are the options to drive the CTP device? Is a workstation from the same supplier required, or can any workstation be used, together with a generic interface to drive the device?
  • Space and architectural costs: How large is the CTP system footprint? Does it require a clean, climate-controlled environment? Will a darkroom or other light-proof handling be required? Will it require processing equipment?
  • Installation costs including downtime costs: How long will operations be disrupted during installation?

Service Costs: For any printer, reliability is paramount. To minimise the risk of downtime, it is important to consider the requirements for service and ways to minimise unexpected costs.

Today big, medium and even small printers are investing in computer (CTP) systems that by pass film entirely. With the electronic imposition of complete flats, it makes sense to go a stage further and expose plates instead of film, eliminating several prepress production stages.

Imaging directly to plate also does away with the distortions introduced in film-based plate making. It is possible to resolve fine image detail more consistently, which is a special benefit with frequency-modulated screening where very small spots are being imaged.

Offset plates are quite thin. If the base material is flexible enough, they can be loaded in an imagesetter in roll form and exposed. Alternatively, dedicated plate exposure units commonly known as platesetter can be used for metal plates. These systems can incorporate automatic register punching.

Sometimes CTP loses out to conventional film-based platemaking due to the speed and low capital costs of conventional platemaking equipment. When duplicate plates or reprints are needed, a CTP system has to repeat the imaging process, while a conventional plate-making system has only to re-expose the film. Film is a convenient storage medium that is cheaper than archiving data on magnetic media. Proofing can also be a problem unless digital proofs are accepted as contact proofs.

The plate-setter receives the imposition instructions and exposes the digital information, masking the areas that are missing. The device then uses the register marks as a guide to position the films and expose them conventionally. Computer-to-plate technology eliminates the film output and stripping stages in the production workflow.

Alternatively, film or artwork can be scanned and converted into digital form. Very high resolution scanners are used to avoid image quality loss on line artwork, such as type with fine strokes and to avoid the need to de-screen halftones, which risks changing colour values. One type of scanner designed for this purpose converts the scanned data directly into postscript code, which can then be inserted into a postscript CTP workflow.

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