TECHNICAL REPORT Computer-to-screen explained
Computer-to-screen, or CST as it is sometimes known, has the potential to drastically reduce the time and costs involved in making images on screens. The number of products on the market is growing too. SARA MCDONNELL looks at what’s out there and how it all works.
D
igital technology has had huge implications for film over the last twenty years or so. Digital cameras have rendered film cameras almost extinct – even the most ardent fans of film are at some point or another seduced by digitalʼs quick and easy transition from camera to screen and from screen to…well, almost any surface. In fact, many people donʼt even bother printing photos any more and just view them onscreen. A similar phenomenon has happened with moving images, where DVD and Blu-ray has replaced videos and d-cinemas beginning to overtake old fashioned celluloid.
The transition from film to digital has been more gradual in the screenprinting industry, however. Despite the recent emergence of direct to garment digital machines, there are still very many advantages – especially for those printing in high volumes – in sticking to screenprinting. And a lot of the screens used in this process are being made using film positives. However, there is another technological advance that is rivalling the use of film in producing screens for garment printing, and that is computer-to-screen systems. These machines cut out the need for using film positives in the creation of screens and instead image the screens directly. The creation of a film positive has, up until relatively recently, been a key stage in the screen printing process. Even digitally- produced images are usually outputted to film, via a specialist inkjet or laser printer, and used to block out the image on a screen when it is exposed to UV light, leaving that image on the screen after the rest of the photo-senstive emulsion has been exposed and washed out.
Time consuming
This process is, and continues to be, a very successful way to create screenprints. However, it is time consuming and can throw up a number of problems along the way. Catspit Productions, a US-based print shop which offers a huge amount of information for budding screenprinters on its website, points out just some of the pitfalls of producing screens from film positives. ʻIf your film is not opaque enough, you will have trouble making a good stencil,ʼ it notes. ʻFilms that lack the opacity to block the exposure source 100% and will end up semi curing the areas that you will need to wash out.ʼ Anyone whoʼs tried to wash out semi-cured emulsion will know the problems that semi-curing causes. There is also the danger of dust and dirt in the exposure unit and distorting the image youʼre trying to make.
The film positive part of the process is not without cost, either. Films are consumables that need replacing, along with printer cartridges and ink. Thereʼs also time involved in vacuuming the film to the screen before exposing it to ensure maximum image accuracy. All of these set-up processes take time and manpower.
Films take up space too, and for those working in locations where storage space is limited, the idea of being able to store your images on a computer rather than on easily damaged films is another attractive aspect of computer-to-screen systems.
The beauty of computer-to-screen systems is that they cut out this stage of the process altogether. Images are outputted to a machine which recreates them directly onto a screen – either by printing a UV-resistant image which is retained on the screen after exposing and washing out, or by directly and selectively exposing the screen before washing out. The latter has been made possible by German firm
CST (distributed in the UK by Natgraph). Using a digitally controlled mirror device (manufactured by Texas Instruments) CSTʼs DLE (Digital Light Engraver) system directly images and exposes screens – not only eliminating the need for film but also cutting out the exposure process.
Ultra violet light
An ultraviolet light is selectively shone at the screen instead of bathing the whole screen using a Digital Mirror Device (DMD). The device moves over the screen, exposing it with a high power UV light.
In this particular system, resolutions of 500-2,500dpi are possible, on screens of up to 4x12m in size. Up to 60 square metres per hour are possible, depending on the resolution. CST also produce a compact version for smaller budgets, where screens up to 1.5x1.5m in size with up to 2,540 dpi are possible.
“Films take up space too, and for those working in locations where storage space is limited, the idea of being able to store your images on a computer rather than on easily damaged films is another attractive aspect of computer-to-screen systems”
CST offers different versions: the DLE (digital light engraver), the DLE-Compact and DLE-ECO, all of which operate with a modern UV LED light. The company reports that in the last few years, it has delivered hundreds of inkjet and waxjet systems worldwide.
Other computer-to-screen systems use a UV-resistant substance to cover the parts of the screen that shouldnʼt let ink through, leaving the unprinted areas to be exposed and washed out.
Kiwo is one supplier of this type of system. Its I-Jet 2 is a machine specifically designed for garment decoration. Using a 256-nozzle piezo printhead, the Kiwo system can make its own 'T-shift' screens of up to 30”x38” (76x97cm) in size of up to 700dpi in resolution. The company also says that the I-Jet 2 can print a square foot (approximately 30x30cm) in a minute. The Spyder Direct-to-screen system from Exile Technologies (formerly OYO Instruments Europe) uses heated wax ink to place an image directly onto a coated screen. It offers a direct-
| 84 | January 2013
www.printwearandpromotion.co.uk
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