Edition 41 / March 2015

Gallus Screeny: Successful digital imaging

The world is becoming increasingly digital and label printing is no exception. Conventional processes such as flexographic, letterpress, offset and screen printing now face competition from digital technology. Although many labels are still printed using analogue processes, the printing formes they require can now be prepared better, faster and more efficiently if they are produced “digitally”. There are a range of digital imaging (computer to plate – CTP) systems available on the market that significantly simplify the production of conventional printing formes. But what exactly are the benefits of digital imaging systems and which is the right one for each particular label printer looking to produce printing formes digitally and cost-effectively?

No need for films and chemicals

One of the main advantages of digital imaging systems is that they do not depend on the availability of films and chemicals. Using films for printing formes requires both film material and a range of chemicals. The majority of presses, substrates and consumables in the printing industry are still used for commercial offset printing (sheet and reel). It is precisely in this area that CTP systems have now become the standard, and suppliers of classic computer to film (CTF) systems have lost their main market. This decrease in customer numbers makes it likely that suppliers of CTF systems will soon no longer be able to provide the necessary films and chemicals at cost-effective prices. Screen printing has become almost the only printing process where film is still required. This means it will soon no longer be possible to operate a filmsetter cost-effectively, as the raw material costs are also increasing. Digital imaging systems offer an ideal alternative.

Standardisation and automation for increased cost-effectiveness

Digital imaging systems have other advantages as well, as they enable prepress processes to be automated and standardised. Using computer to plate (CTP) systems involves significantly lower installation and material costs than indirect imaging with conventional computer to film (CFP) systems. CTP also eliminates complex manual processes, as these are completed by the machine. Once the machine parameters have been correctly set, all printing formes will be produced to these settings in the same quality. It is also easy to resolve any errors that occur while producing the formes.

Higher quality and improved process reliability

Direct plate imaging produces higher quality print results than are possible with film. For instance, the screen dot edges are sharper and smaller dots can be produced. This is because digital imaging systems use a laser whose light beam can be controlled more accurately. A further advantage of digital imaging systems is that they enable a contactless process that reduces mechanical effects on the printing plate such as imaging flaws, dust and scratches. The inconsistent print results caused by the use of different film thickness are also a thing of the past. The laser used in a digital imaging system ensures that quality remains consistent.

Technical structure of a digital imaging System

A digital imaging system involves a light source (laser) and a computer. The laser transfers data directly from the computer to the printing forme. For the transfer, the computer converts the print image into binary form and controls the laser as necessary. The printing forme has a reactive layer that is tuned to the laser’s wavelength. When the laser is beamed onto this layer, it is either burned away by the infrared (IR) rays or is imaged directly with the ultraviolet (UV) rays.

Computer to plate (CTP) digital screen printing with UV Radiation

Optimum wavelength for specific printing formes

In narrow-web label printing, the main analogue printing methods used are
flexographic, offset, letterpress and screen printing. These processes all require a printing forme. The print image is transferred to the photosensitive layer of the printing forme using a laser. Each type of photosensitive layer has a specific wavelength that it reacts to particularly well. The table below shows the optimum wavelength for each type of printing forme:

The table clearly shows that the optimum wavelength depends on the type of printing forme used. So the first question label printers should ask is: Which types of printing forme should they use for digital imaging? For label printers who want to use digital imaging for just one type of printing forme, choosing the right imaging system should be straightforward. However, the decision is more complicated for label printers who want to use digital imaging for several or all types of printing forme. They will either need to have several imaging systems with the optimum laser for each printing forme, or a single imaging system with multiple lasers so that the correct wavelength can be selected for each printing forme.

Workflow for a digital imaging System

Gallus Screeny system solution

Gallus Screeny is an extensive range of analogue and digital screen printing plates. Gallus has the perfect solution for all imaging systems on the market so that all label printers can use Gallus Screeny products successfully. As a result, label printers should ideally only need to use one imaging system to produce all printing formes (flexographic, offset, letterpress and screen printing plates). This saves initial investment costs, time outlay and money. The Gallus team is always happy to answer questions and advise on which imaging system will best suit your company. Please feel free to contact us at: screeny@gallus-group.com


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