Alexey Arkhipov, Marcus Frank, Bühler Alzenau GmbH, Alzenau, Germany
Masking of glass substrates by printable media is already used in the architectural and automotive glass industries. Within this process, the desired area on the substrate that should be kept without the coating is covered with the masking material by a screen or digital printer, the applied mask is dried or cured by UV light, a PVD coating is applied, and the coated mask is removed either by water or a chemical solvent.
For the implementation of the mentioned steps within the in-line processing of large area glass substrates, several challenges have to be solved. First, printing technology should be suitable for the process cycle time, which in some cases can be below 30 seconds. At the same time, requirements on a high print resolution, a long uptime of equipment, and low operational costs should be fulfilled. Second, the selected masking material should be compatible with magnetron sputtering processes: on one hand, exposed plasma should not damage the mask pattern, and on the hand, the outgassing rate of applied mask should be low to minimize the impact on the sputtering process. Additionally, cost of the applied mask per square meter is a crucial factor driving the choice of the print technology, especially for large area applications. Third, washing off the mask after the sputtering process should not damage the applied film, whereas coated masking material should be completely removed from the glass surface. Residuals of coating and mask material remaining in tanks with used water or solvent must be filtered out to prevent their redeposition on the next substrates entering the washing area.
Successful solution of the mentioned challenges will allow to expand the range of applications for printable masking in a sputtering process. Masking technology can potentially replace the process of edge deletion on the glass, which is nowadays required for production of individual glass units for residential and commercial buildings. It can be effectively used for production of a bird protection glass which requires specific patterns nearly invisible for humans but well recognized by birds. Another field of application is the automotive industry: sunroofs and windshields of modern cars coated with low emission films always require uncoated areas, sometimes with specific pattern, to transmit various signals e.g. rain sensors, traffic sign recognition, etc. The application of printable masks enables an extremely accurate, high yield and cost-efficient high throughput production in the field of automotive products.
In this contribution different process optimization approaches of the large area masking technology are discussed, and first essential validation results of this in-line masking and coating technology are presented.