The fury of this revolution has deafened many to the continuing growth of screen printing onto roll-to-roll substrates: also known as web fed. Believe it or not, probably the largest screen printing company in the world (in terms of sales dependent on screen printing) is in Scotland, with the company using flat bed and web fed machines. For those unfortunate enough to have diabetes the instrument used to measure glucose blood/levels features a sensor comprising a small electronic circuit onto which is placed a spot of blood. Diabetes is a rapidly accelerating condition driven by our modern lifestyles. Seven per cent of the American population has it, with the UK rapidly catching up. Worldwide, 140 million people have diabetes. Not every one uses an electronic device to measure their blood condition but an increasing number does. That is an awful lot of biosensors that require screen printing. When volumes justify it, web fed screen printing is a highly cost effective solution.

Screen printing on a web is not a new process. For many years it has been used for label printing, combined with other printing processes and finishing operations to provide complex multifunctional labels. Web printing can use flatbed, cylindrical and rotational screen printing processes. The aim is the controlled placement of ink on a flexible substrate. The substrate's limiting factor is its flexibility, while print speed is limited by the ink's ability to dry sufficiently for the next operation.

The big advantage of web fed printing systems is their ability to integrate with other processes. This can be challenging because all the different techniques need to be balanced.

Web ink systems are as varied as conventional screen printing inks but machine suppliers' challenges can be much greater. UV curing ink simplifies matters because curing takes place quickly via a small curing unit. However, when considering an ink system dried and cured by radiant, conduction and/or hot air the degree of difficulty increases dramatically. A conventional screen printing line drying solvent-based ink systems requires a dryer several metres long. Then it is often necessary to stabilise the substrate by cooling it. The length would be prohibitive for a multi-station web fed screen printing line. Thus, the machine supplier must be ingenious regarding the drying process.

Substrates range from paper to polyester. They must be available on a roll and offer sufficient stability for accurate registration if required. Web tension is important to registration, as is stopping the web at the right point in the print cycle. Some systems run continuously with the web printed on the move. To do this, synchronisation of the print stoke/moving web is important. Some films are 100µm thick so handling delicate film is a science in itself.

One master of this science is Richard Rolt who runs Bishops Frome-based machine builder, Rolt. Richard has a busy production schedule, sadly all of it going to manufacturers overseas. If only the rest of UK manufacturing was so buoyant. That may be a dream but Richard has shown that determination and innovation will succeed. Rolt specialises in automated printing processes. Surprisingly, during recessions Rolt equipment becomes even more attractive with its competitive prices and imaginative solutions.

Normally, web or roll-to-roll screen printing is only viable for long runs. However, Rolt supplied a machine to a manufacturer who prints as few as twelve four-colour labels. The trick is to make stencil changes quick and easy. Normally, web width is 350mm, with 500mm the usual maximum.

Richard sells equipment worldwide, with a recent application involving textile transfers printed on paper and 70µm polyester. The key to this equipment is simple installation, operation and maintenance. Small, specialist companies cannot afford engineers dashing around the world explaining how to operate their machinery. Thermal transfers are difficult to produce due to multiple colours, adhesive, release layer and protective lacquer. Due to this variety of ink films, drying must be carefully controlled. The substrate must be stabilised throughout the process and, unless the company builds a hugely expensive 12-colour machine, the printer may have to feed printed substrate back through a four-colour line more than once. To do this, registration and handling must be perfect. Rolt uses flatbed print stations and indexes the substrate through the machine.

If space is an issue, Rolt's Snail Line offers an innovative solution. Here the dryer forms a square, with the take-off placed in the centre. This substantially reduced the line's length and height.

Werner Kammann offers a different approach to roll-to-roll printing with its KS61OS machine.

Each print station uses a cylindrical printing action  with a flat stencil. This means the web keeps moving. Brian Laming the UK's Kammann print specialist says the system enables close registration tolerances. He also emphasised the sophisticated drying techniques. The effect of these systems is that the machine can print the increasingly complex materials used in electroluminescent applications, RFID and other consumer electronics. The handling systems copes with substrates below 12µm. The K610S also supports offset litho and flexographic print stations.

Most of this technology is going to the Far East and other foreign shores, an indication of the destruction of UK and European manufacturing. We have engineers, ideas and development skills, yet equipment is driven towards cheap labour and low overheads. For those of us brought up in an era of home-based manufacturing, shipbuilding, a major UK electronics industry, textile production etc, the current decline is near criminal. Don't worry, we will soon be a low wage economy servicing historical theme parks, unless we get a grip and quickly.

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