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Making touch devices with in-mould films

By David Eldridge
Posted 21 January 2013

PolyIC, a subsidiary of the hot stamping and coating group Leonhard Kurz Stiftung, has developed functional films that open the way for producing touch screen displays and controls using in-mould decoration (IMD) and in-mould labelling (IML) techniques.

The companies, based in Germany, have launched PolyTC transparent conductive films made from PET, which are produced roll-to-roll and can be used in established lamination processes as well as IMD/IML. The benefit of combining IMD and IML is that the functional film is back-moulded in the same injection moulding cycle as a decorative film.

In-mould production of touch units was shown for the first time in two demonstrations using Sumitomo (SHI) Demag and KraussMaffei machines at the Fakuma exhibition in Friedrichshafen, Germany, in October.

Kurz and PolyIC have received strong interest in the potential for producing touch units in a single injection moulding stage, said Martin Hahn, head of IMD sales management at Kurz. At Fakuma, he told European Plastics News the company had approximately 20 projects in development with customers.

Target markets include consumer electronics, automotive and household appliances. The first product made with PolyTC films in a combined IMD/IML process will enter commercial production at the end of 2013 or the start of 2014, he said.

PolyTC films already feature in a lamp made by German lighting company Occhio, but the films are used in a lamination process to give the lamp its touch functionality. Hahn said other items for the home are being developed, including a touch panel for climate controls.

Kurz and PolyIC are pursuing market development for PolyTC films in collaboration with a number of customers. “We are open to projects of 100,000 units per year, but also ones involving millions of units per year,” said Hahn.

The consumer electronics industry is actively searching for a substitute to the established multi-stage lamination process for producing touch units with expensive indium-tin oxide (ITO) materials. Hahn said ITO is not used in PolyTC films, which instead are made with more readily available materials, including silver, aluminium and copper.

Kurz is promoting a number of other advantages of PolyTC films. The circuits are printed on the film in a roll-to-roll process, which permits a large production capacity. The films are thin and flexible, giving design freedom and the potential for 3D applications. The supply line (or tail) is also integrated in the film.

Overall, the use of PolyTC films in combination with IMD/IML can improve manufacturing efficiency and reduce production costs for touch screens and controls, according to Kurz.

The decorative aspect of the process is also open to various design interpretations. Kurz makes IMD films in a wide variety of colours, patterns and structures, including bright metallic colours, with a variety of gloss levels, or with a sandblasted or brushed surface appearance. Wood, marble and carbon-look surfaces are also available from Kurz and can be used when decorating appliances with touch sensor panels.

Kurz and PolyIC are working with a number of injection moulding partners. At Fakuma, Stefan Genser, applications project manager at PolyIC, showed a demonstrator touch display with a 3.5-inch screen on the stand of Sumitomo (SHI) Demag. He said customers’ pilot projects had delivered very good results.

A non-functioning film was used for the demonstration, in which the touch screen was injection moulded using IMD and IML techniques on a 210-tonne Systec 210-430 machine. IMD was used in one half of the mould for the decorative metal-effect frame of the display and IML in the other half for the PolyTC film.

Markus Hausmann, senior engineer in technical sales at Sumitomo (SHI) Demag, explained the combined process. The IMD decorative film supplied by Kurz is placed in the mould half on the moving platen. This film is punched to the correct dimensions in the mould during the closing movement.

The PolyTC film for the back of the display is taken from a magazine by a six-axis robot and is placed in the non-moving mould half. The mould is closed and a grade of PMMA from Evonik is injected.

The one-cavity mould from HBW-Gubesch utilises variothermic mould temperature control which ensures that areas of the mould can be heated and cooled independently of the cycle. The temperature of the mould is controlled by technology from GWK.

Sumitomo (SHI) Demag says the active increase in mould wall temperature during the filling phase results in a better surface impression and reduces stresses in the moulded part. The subsequent intensive cooling phase helps keep the cycle time extension within reasonable limits.

Post-moulding, the film sprue is cut off using a laser, then the display is cleaned. Markus Hausmann said flakes from the decorative film lacquer sometimes remain and these are removed in the cleaning process. This involves cleaning with ionisation and brushing, followed by suction and filtering.

The final step is the application of a protective UV paint. The component is not transferred to a storage position until the paint has fully dried.

The total cycle time, including all production steps, is about 50 seconds.

Companies involved in the demonstration, in addition to ones already mentioned, were StŠubli (six-axis robot), SAR Elektronic (automation), Max Petek (clean room module), Kist Maschinenbau (finishing technology), Koch Technik (material conveyor and dryer), Moretto (temperature control unit) and MTF Technik (conveyor belt).

KraussMaffei and Roth Werk-zeugbau are also partners of Kurz. At Fakuma they demonstrated production of an automotive centre stack touch control using PolyTC films in a combined IMD/IML process similar to the one used for the touch screen display.

Roth, a mouldmaker based in Germany, demonstrated the process on its stand using a KraussMaffei CX 160-750 injection moulding machine. The housing for the controls is moulded in a grade of ABS from BASF with a 77g shot weight. The cycle time is 45s, similar to that in the Sumitomo (SHI) Demag demonstration.

The diverse potential for Poly-TC films was discussed by Wolfgang Mildner, managing director of PolyIC, during a presentation he made at the Plastics in Optical Applications conference in Brussels in October last year, which was organised by European Plastics News.

Mildner highlighted the possibility of using PolyTC in smartphone and tablet applications, but said non-touch applications are also achievable. He gave the example of films being used for heating purposes in car door mirrors.

He discussed a representative PolyTC film with a PET substrate of 50 µm thickness. However, other substrates and thicknesses are possible.

The adaptability of PolyIC’s process can be seen in other developments it is working on. Poly-ID is the name for its printed RFID technology which can be integrated into high volume products.

PolyLogo is similar to RFID but instead prints “smart objects” Ð predefined symbols which can be activated and then erased after they are taken out of the activation field in a short period of time. Mildner said applications could be in marketing materials, tickets, vouchers and toys.

The company is working on further developments for its technology, including printed photovoltaics and printed memory components.   


The Kurz Centrestack Touchkey
The Kurz Centrestack Touchkey


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