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PRECISION REEL TO REEL FILM FABRICATION SYSTEM ... critical components of large science .... Limited and Microsharp Innovations Limited, and.
MACHINE CONCEPTS AND DEVELOPMENTS IN CREATING A PRECISION REEL TO REEL FILM FABRICATION SYSTEM Paul Shore1,2,3, Paul Comley1, Paul Morantz1,2 John Allsop1,2 Nicholas Walker4, Shin Li5 1 Cranfield University Precision Engineering Institute, Bedfordshire, England 2 UPS2 - Loxham Precision, St Asaph, Denbighshire, Wales 3 National Physical Laboratory, Teddington, London, England 4 Ixscient limited, Uxbridge, London, England 5 Microsharp Innovations Limited, Oxford, England

INTRODUCTION The size of features to be incorporated within film based products such as flexible displays are decreasing. In order to cost effectively produce film based electronic products it will be necessary to precisely handle and manipulate large scale ( > 1 metre wide webs) films. Figure 1 indicates the present film production capability 2 in regards throughput in metres / second and the size of feature size in micrometres.

Cranfield R2R

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FIGURE 1. Film throughput (m /second) versus feature size (micrometers] with indication of the Cranfield R2R target specification range Furthermore the processing of the film substrates will include a number of processes of additive, subtractive and forming nature. These manufacturing processes will induce heat to the film, change its basic mechanical properties and consequently induce film substrate distortion. These “workpiece” issues are considered key to effective production of proposed and emerging products. This paper introduces some of the machine concepts and developments of a large scale

R2R research platform under construction at Cranfield which is funded by UK’s EPSRC Centre for Innovative Manufacturing in Ultra Precision. This R2R platform is in its construction and initial testing phases. An explanation of the key background, aims and objectives of this R2R system are provided along with an outline of the expected future research plan. BACKGROUND Since 1968 the Precision Engineering activity at Cranfield University has performed research, development and supply of ultra precision machines. Many machines that were created through this R&D were created to produce critical components of large science programmes. These machines have been widely reported in the literature [1,2]. Often the created machine tool technologies were subsequently incorporated into industrial production machines made at Cranfield. These production machines were key enabling machines of advanced production lines / manufacturing chains. The special purpose commercial machines were typically under tight industrial NDA’s. Today the commercial products of Cranfield spin out companies’ give evidence this ultra precision machine research contribution claim. In 2007 a consortium led by Cranfield University established the EPSRC Integrated Knowledge Centre in Ultra Precision and Structured Surfaces. This EPSRC Centre, with support of 2 Welsh Government created the UPS laboratory. This ultra precision production facility is situated in North Wales at the OpTIC Technium. It is operated through Cranfield and its spin out company Loxham Precision Limited. Over the 2 last 5 years UPS has been producing large

scale micro-structured drum moulds for production of high value passive optical films, fabric texturing systems and active electronic substrates. An example is shown in Figure 2. [3,4].

substrates. Consequently, the traditional ultra precision approaches of isolating major heat generation systems are not entirely possible. The Cranfield R2R research platform is specified to eventually incorporate a number of processes these include: Instrumented film control positioning Roll embossing – programmable curing Slot die deposition technology Ink jet printing - laser processing Multi film lamination

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FIGURE 2. UPS produced large scale microstructured drum roll (1.4m long by 0.4m diameter) In 2011, Cranfield University and the University of Cambridge, together with support of the National Physical Laboratory, secured funding for the EPSRC Centre for Innovative Manufacturing in Ultra Precision. A major task of this centre was identified as the realization of the R2R film processing research platform [5]. This research platform was targeted to provide three key demands: 1. To establish an effective R2R research platform to perform production research for a variety of future active film based products. 2. To provide a large scale 1.5 m wide film fabrication facility capable of producing high value passive films at high processing rates. 3. Establish an ultra-precision manufacturing supply chain that can better appreciate, and support, the needs of the emerging film based product researchers / developers. Many of which are based in the UK. CRANFIELD R2R RESEARCH PLATFORM The Cranfield R2R research platform incorporates a number of necessary processing technologies that lead to difficult, antagonistic, technologies for effective fine feature creation with high accuracy over large areas at high throughput. Rapid production of ultra precise fine featured films will require high temperature processes together with highly susceptible

FIGURE 3. Cranfield R2R schematic outline Development of the Cranfield R2R platform remains in progress [6]. Some of the key techniques and subsystem developments are summarised in this overview paper. Instrumented film control positioning In order to position and repeatedly reposition large scale films it requires an understanding of the dimensional state of the film. To accommodate these demands an initial instrumenting operation of films has been conceived. As an initialising process substrates are modified by introducing a group of fine feature measurement scales into the film. These grating features enable the film position, reposition and dimensional change to be measured during R2R processing. An example “multiple grating” embossing roll mounted on specially designed ultra precision hydrostatic bearing units is shown in Figure 4. This ability to induce fine gratings together with ultra precision positioning spindles offer submicrometre position measurement accuracy of films and a micrometer range positioning capability.

FIGURE 4. Grating inducing embossing roll mounted on high precision spindle units Hydrostatic bearing positioning units Fluid film bearing based positioning units are highly compact with low mass, low thermal capacity and with high diffusivity. They offer stiff sub – micrometre accuracy of axes of rotation which yields large drum roll run-out levels in the micrometre region. The bearing units are constructed from aluminium and employ diamond turnable coatings having low friction and resistant wear characteristics. The coating technology, derived from the Formula1 Motorsport sector was developed by Poeton Coatings of Gloucestershire, England.

FIGURE 6 FEA modeling of R2R bearing designs (G. Zhou MSc) [7] Roll embossing – programmable curing An air bearing “nip” roller control unit (design not yet disclosed) is employed to provide accurate thickness control between embossing and nip rollers. After embossing of the slot die applied acrylics (and variants) a low temperature curing unit is employed. To minimize necessary heat inducement during curing of applied acrylics a high specification 365nm LED UV curing source was developed. This unit offers intensity and region area control. This large scale UV unit was produced by UV Integration Limited, Oxfordshire, England, see Figure 5. This high specification light source offers up to 9w/cm2 over a programmable 1.41m by 0.046m light zone.

FIGURE 5 CAD images of the Aluminium based R2R hydrostatic bearing units Hydrostatic bearing design was supported through FEA modelling. This modeling work evaluated different pocket designs and the extent of component distortion at differing pressures and pocket designs. Component distortion was evaluated to ensure the aluminium based design performed with the relatively low Young’s modulus of the main spindle components.

FIGURE 7 UV Integration LED curing unit mounted under embossing roll The 14kW UV light source is cooled using a 3 stage 20kW capacity (~ 60 litres per minute) temperature control system developed by 3D Evolution of Bedfordshire, England. This large capacity cooling unit offers temperature control

of the UV cure system and other heat generating / absorbing systems of the R2R platform. Slot die deposition technology A slot die system is used to apply a range of fluids at 0.5 – 100 micrometre thickness range. Fluids ranging 50 – 3000 mPas viscosity can be applied at flow rates of 3 – 1000ml/minute. The system shown in Figure 6 was specified through film processing research performed by Ixscient Limited and Microsharp Innovations Limited, and manufactured by TSE/Troller of Switzerland.

research platform. The research platform has been created to provide a basis for experimental testing and optimizing of new precision production methods for the fabrication of ever finer features on a diverse range of films. The R2R platform has also been defined to provide a large scale passive film fabrication facility. Its ultra precision characteristics enable fine (sharp edged) micro-structured films to be produced. This passive film production process will employ ultra precision control of slot die, roll embossing and controlled UV curing processes. Creation of the Cranfield R2R research platform has encouraged development of a new manufacturing supply chain. In so doing, awareness of emergent film based products has evolved amongst leading precision engineering companies.

FIGURE 8 Slot die application system Control of the overall R2R research platform requires a comprehensive and integrated system. The UV curing system, motional control of the web, ink jet, laser and the thermal control of the main elements of the machine are incorporated within a single CNC system. Film positioning will be dealt with through a number of real and virtual axis within the control system.

FIGURE 9 Control units for, web motion, slot die, UV curing intensity, temperature, ink jet printing and laser processing. CONCLUSIONS This paper has briefly introduced progress in the design and development of a large scale R2R

REFERENCES [1] Shore P, Morantz P. Ultra Precision “enabling our future. Transcripts of the Royal Society, Phil. Trans. R. Soc. A. 2012 370 3993-4014 [2] Shore P, et al. Precision engineering of astronomy and gravity research. Journal of Manufacturing technology, CIRP Annals, 59/2/2010, 694-716 [3] Allsop J, Mateboer A, Shore P. Optimising efficiency in diamond turned Fresnel mould masters. SPIE, Volume 8065, 2011, 806509-11 [4] Shore P, et al. EPSRC Integrated Knowledge Centre in Ultra Precision and Structured final report, 9/9/2015 at http://www.ultraprecision.org/wpcontent/uploads/2013/12/IKC-reportA4FINAL-for-website.pdf [5] Shore P, Morantz P, O’Neill W. EPSRC Centre for Innovative Manufacturing in Ultra Precision Mid Term report, 9/9/2015 at http://www.ultraprecision.org/wpcontent/uploads/2014/06/EPSRC-Centrein-UP-Mid-Term-Report.pdf1 [6] Shore P, Morantz P, O’Neill W. EPSRC Centre for Innovative Manufacturing in Ultra rd Precision 3 year report, 9/9/2015 at http://www.ultraprecision.org/wpcontent/uploads/2014/06/EPSRC-Centrein-UP-Mid-Term-Report.pdf1 [7] Zhou G, Advanced bearing system for ultra precision plastic electronics production systems, Cranfield University MSc thesis 2014