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Screen printing cleans up
All too often screen printing is considered the poor performer of print technologies. This is often the case in graphics applications, particularly point of sale (POS), however, operating a culture of excellence could change the perception of this process. The aim has to be to delight the client with a product offering that exceeds their expectations.
Recent articles in this magazine, for example, have explored screen printing excellence in Austria using state of the art equipment and in Thailand working under extreme climatic conditions with more basic equipment. The common denominator in both cases was the involvement of the company owners and their insistence on continuous improvement.
It would be wonderful if time and money allowed perfection in every aspect of the screen printing process. This isn't always possible, but everyone should aim to excel where practical and achieve a product offering that exceeds customer expectations.
So what can screen printers offer customers to fulfil this aim? Start with the understanding that screen printing is a controllable, measurable and predictable printing process. Screen printing can be treated as an engineering technique. Unsound practices cause it to be unstable however, remove this flawed approach and you are left with a highly profitable image creation system.
Process flexibility
Virtually every other printing process needs inks specifically designed for that particular printing method. Screen printing, on the other hand, is ink friendly. Any material that can be dispersed in a fluid, with adjustable viscosity and particulate size that will pass through a mesh, can be screen printed, from concrete to melted chocolate.
The ability to print wet film thickness up to 300 microns, or 0.300 mm, is particularly attractive to graphics and POS printers. The resulting image is vibrant and can be used to produce special effects easily with an equally wide selection of substrates suitable for the process. If a substrate is wettable by the ink and the stencil can maintain contact with the substrate, it can be printed.
This flexibility is a compelling benefit for the client. Not only is there a huge range of printable substrates, but the working environment that the printed substrates will tolerate is much broader than with other processes. Screen printing enables the printer to satisfy customer needs at a reasonable price.
Despite the fact that wide format litho printing is faster and digital processes don't require stencils, the true cost of these printing methods often outweighs the benefits. How much work, for example, is required to pay for a multi-colour litho line and what is the true production rate of a £300,000 digital printer? Inks and servicing costs should also be factored into calculations.
A survey of the UK graphics market provided by PRISM confirmed the reality of these issues. One of the key responses was that for companies who use a combination of processes, screen printing was the most profitable. Some companies who set out as pure digital print producers found that it was necessary to install screen printing lines to cope with the work that was not suitable for digital print. These companies also combined print techniques on one job achieving results that gave them not only a unique selling point but also provided a profitable edge over the competition. Fespa's Sensations book demonstrates the successful marriage of screen printing with other techniques and is often used by print specifiers to demonstrate the special effects they require.
Digital adoption
Add to this the fact that the screen printing process hasn't stood still. It has adopted digital technology in many different areas to enhance performance.
Improved instrumentation is now available for every aspect of the process including: digital tensiometers for measuring stencil mesh tension; coating thickness gauges for checking emulsion over mesh (EoM); and moisture meters to ensure emulsion moisture content is a minimum level before exposure. Moisture content greater than four per cent will alter the required exposure level for the emulsion and if it is over six per cent the emulsion will not cure completely. An image is then created on the coated mesh by direct printing of either a wax or ink that is then exposed with a conventional exposure unit.
Computer to screen (CTS) exposure systems are also becoming increasingly popular. They use either the focussed UV that is directed by a digital mirror device (DMD) or guided laser. Both systems give good results and are ideal for profiling process colours to achieve optimum print results. The actual image on the stencil can then be checked electronically to ensure it has been developed correctly. Using process inks of controlled density and dot size, confirmed with a digital densitometer, provides the control that is necessary to give consistent results every time.
Printing machines have been transformed from ageing workhorses to servo controlled sophisticated print engines, linked to a range of different high efficiency dryers and curing systems. Substrate positioning uses optical sensors and on multi-colour lines registration is verified at every print station. Power consumption of modern units is often 50 per cent that of 10 year old equipment.
All these advances are built on the adoption of digital technology in its various forms. Digital workflows covering all the printing processes used in production adjust the images produced to provide a balanced result across a campaign. This allows print providers to utilise the advantages of all available processes without compromise.
Screen printing has a proven technological base with a two thousand year old history. Since its introduction, it has evolved into a highly developed imaging process, however there are still some people who consider it to be dirty, inconsistent, outdated and slow. Obviously they are not aware of today's technology developments and how the process fits into the current market. Those print providers who have the capability to work to high standards, gain the competitive advantage so it is worth remembering that screen printing is a very profitable process.
