Standardised digital printing processes for membrane switch graphic overlays

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Multi-faceted design, uniform technology: The certified digital printing process from Thieme, Mankiewicz and Folex is opening up new design options, such as the printing of colour gradients, for membrane switches manufacturers

Multi-faceted design, uniform technology

THIEME together with its industrial partners has developed a digital printing system for the printing of flexible membrane switch graphic overlays. This system is suitable for any desired graphic and print size while meeting the high demands on design, flexibility, and service life of these technically sophisticated products.

Membrane switches are encountered in many areas of daily life. They are particularly widespread in industrial and medical applications since, in contrast to typical PC keyboards, they resist dust, moisture, and chemicals. Membrane switches, adapted to each field of application, are available in numerous designs, sizes, and colors. The top membrane layer – referred to as the graphic overlay – is both a design element and it is also exposed to dynamic alternating loads due to keystrokes. The printing process is essential to insuring all of the overlay’s quality criteria are met and this is process very well implemented utilizing the screen printing process. In the future, graphic overlays will become increasingly produced using digital inkjet printing allowing even the smallest batch sizes to be efficiently reproduced, quick delivery times to be met, and the benefits of individualism to be exploited.

Many opportunities of creative design such as color gradients, integrated photorealistic motifs or other individualisations could previously be industrially produced only at great expense. Thanks to the new combined inkjet and screen printing process, which THIEME has developed and standardised together with its partners, the complete layer structure can now be individually and industrially reproduced.

The process includes a tested combination of special membranes, digital printing inks, screen printing inks, and at the heart of the system a specifically developed machine technology. This system enables optimal printing results as well as the durability to perform a million keystrokes and more without visible wear to the print layer.

Outstanding and durable printing results

The digital printing process opens up multi-faceted design options for sophisticated customer specific decors such as those using traditionally hard to print colour gradients. The graphic overlay is printed subsurface and the applied colour layer must therefore resist the stresses resulting from any subsequent embossing process without cracking. The stress caused by the compression of the raised keys every time they are touched cannot lead to premature wear. The graphic overlay is additionally back-printed with white and a barrier coat on a UV or solvent basis. These additional coats are applied in the screen printing process which enables high coating thickness and a good contact capacity for the adhesive layer which is ultimately used to bond the membranes in a laminating process.

"All of the components of our printing process are optimally matched to each other and were extensively tested", emphasises Harry Götz, Product Manager for digital printing systems at THIEME. Along with the testing of mechanical fatigue strength (keystroke test), embossing, and laminating tests were performed as well as tests of stresses caused by heat, cold, temperature change, damp heat, and UV exposure. All of the tests were performed in a certified laboratory. Visual tests also confirmed high colour fidelity and a very large colour space (FOGRA39). "We can therefore ensure our customers that they will achieve both visually and technically outstanding results with our printing process", sums up Götz. "Thanks to the defined quality of the membranes, printing inks, and the optimal adaptation of the process to the THIEME printing machine the customers can rely on consistently good results."

Uniform machine platform, free choice of formats

Since both digital and screen printing are used in the production of graphic overlays, it is highly advantageous that THIEME uses the same machine platform for both digital and screen printing processes. The material handling (e.g. movable printing table, positioning points, selectable vacuum zones) and additional equipment for printing optimisation (e.g. integration of cleaning and ionisation systems) are therefore identical for both printing processes which ensures an effective printing sequence.

The top-selling industrial machine THIEME 3020 with the printing format 750 x 1050 mm is used and available as either a screen printing station or a digital station. The THIEME 500 D with the printing format 600 x 400 mm is available as a less expensive alternative for the start-up digital inkjet production covering most of graphic overlay formats in 1-up production.

In addition to this, special customised formats can be realised on the THIEME machine platform. Optical alignment using a camera system in the screen printing and digital printing machines is also possible to allow prints to be automatically aligned with each other. Completely new design options are opening up for graphic overlay manufacturers.


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