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Polygon scanner based ultra-short pulse laser processing in roll-to-roll manufacturing

Periodic Reporting for period 2 - PoLaRoll (Polygon scanner based ultra-short pulse laser processing in roll-to-roll manufacturing)

Reporting period: 2018-04-01 to 2020-01-31

The focus of PoLaRoll is on the continuous and digital production process for structuring a lacquer film on a stainless steel web and thereby substituting the need for a negative mask for imprinting the lacquer, which is making the current production process inflexible and expensive.
To achieve this ambitious goal, the development in PoLaRoll can be described through the following objectives:
• Objective 1: Development of a high performance laser source
The development of a high performance ultra-short pulsed laser source will focus on the improvement on the system’s pulse repetition rate and pulse energy, resulting in a pioneering overall optical power. This development will generate an industrial ultra-short pulsed laser source with never before presented specifications on industrial scale for high speed processing.
• Objective 2: Development of a high-speed polygon scanner
Besides the increased specification levels of the laser source, the polygon scanner will be further improved to cope with the new high processing speeds and the high pulse repetition rates achieved. Additionally to this goal, a further major effort will be addressed to ensure a high accuracy over the high-speed laser spot positioning based on the polygon scanning unit for the micro structuring process.
• Objective 3: Development of an in-line measurement for polygon scanner processing
To ensure a high precision for the material micro machining, two in-line measurement systems will be developed. On the one hand, the solution will address the direct measurement of the lacquer ablation results and therefore will show insufficient material treatment in real-time. On the other hand the solution will measure the resulting micro structures and perform an inline evaluation of its form and position. Based on both units, a control and adaptation of the process will be implemented. This allows an automatic adjustment of the process parameters and quality assurance.
• Objective 4: Laser based micro machining system with synchronization between laser source and multiple polygon scanners
The project will result in highly improved laser source and polygon scanning units with high speeds. Besides the synchronization of laser source and one polygon scanner this generates further high requirements on the overall system synchronization. In this context, the project PoLaRoll concentrates on the implementation of a highly innovative ultra-fast synchronization unit for at least two polygon scanners operated with one laser source, which will allow the full usage of all system specifications on real industrial context. This includes beam splitting and beam guiding to both sides of the web.
• Objective 5: Integration of laser based micro machining system for two-sided laser structuring into a roll-to-roll process
A further objective is the integration of the final laser micro structuring system including the enhanced ultra-short pulsed laser source and polygon based scanning unit as well as the in-line measurement systems in the roll-to-roll system. The design and composition of the system is modular, this fact offers a high adaptability and therefore the system is capable of being integrated in several roll-to-roll process chains. Here, concrete actions regarding process synchronization (roll-to-roll and laser processing unit) as well as data exchange and product information will be in focus, to warrant modular and robust system integration on industrial standard.
• Demonstrator: Structured stainless steel with sieve geometry for solar shading applications
The geometry of the demonstrator allows cutting the solar radiation and therefore reduces the energy used for cooling and ventilation. By changing the pitch between the etched holes on the front and the backside, different refractive properties can be achieved. Enabled through the individualized laser structuring process they can be placed on the same reel. Moreover, the laser processing allows a higher stitching quality compared to state of the art production since transitions caused by the masking process are completely eliminated. The development of a special dichromate free lacquer formulation will enable higher ablation rates with less energy per pulse.
"Within the project ""PoLaRoll"" the performed work was focused on the process investigations for the ablation of the lacquer, the lacquer development itself and the derivation of a conceptual design for the whole system and its components such as laser source, polygon scanner and in-line metrology. The main features of the PoLaRoll system are:
• Digital laser ablation using ultra-short pulse laser source
• Continuous production in a roll-to-roll environment
• Double sided processing with two polygon scanners
For the process investigations, a standard lacquer that was adapted for laser processing has been tested in order to derive a suitable pulse energy. For a full ablation, a pulse energy of 6 µJ, a spot size of 45 µm and a number of effective pulses of 30 was found at a low repetition rate laser setup. These results lead to the following key parameters of the concept:
• A 300 W ultra-short pulse laser source with a 100MHz seeder, a wavelength of 1030 nm and 25MHz pulse picking
• 2 polygon scanners achieving speeds up to 10,000 rpm each and enable 1000 lines per second on a 300 mm web width
• The achievable web speed is connected to the desired resolution. At 0.03 m/min a resolution of 10000dpi can be achieved

Furthermore, the development of a dichromate free lacquer for stainless steel etching was performed successfully.
A market analysis and the derivation of an exploitation strategy have shown that with the final PoLaRoll system a wide range of other applications can be addressed such as digital structuring of flexible printed circuit boards or selective surface treatment."
When looking along the value chain of laser manufacturing systems, the laser sources typically are the starting point and are integrated into downstream machines and processing systems. To position the next generation roll-to-roll manufacturing technology in the global market place, time to market is a key factor. The PoLaRoll results will help Europe to stay competitive on the international market of laser micro machining and roll-to-roll machinery solutions providing:
• Improved competiveness of laser-based manufacturing industry (equipment and suppliers) and the end-user industry
• Improved competiveness and strengthened Europe’s market position of laser-based manufacturing industry
• More efficient, more flexible and higher throughput of individualized laser-based production
Further impacts can be associated to PoLaRoll project:
• Environmental impacts: the partial replacement of environmental unfriendly chemicals on the etching process chain currently used on the foil perforation by laser based machining will lead towards a greener manufacturing. The partial replacement of unfriendly chemicals will generate environmental impacts on the reduction of this production as well as on the reduction of its waste management, which represents a direct economical aspect as well.
The PoLaRoll Logo
Illustration of the PoLaRoll process integrated into demonstrator application.