May 31, 2017
Photonics guarantees top print quality
Whenever high-speed processes are used to print bottles, fabrics, tiles or floor coverings, photonics is not far away. It is both an enabler and a guarantee of quality.
Manufacturers of ceramics, furniture and textiles are increasingly relying on printing technology to color their products or adorn them with interesting motifs. Rotogravure printing processes are used to print laminate flooring, furniture materials and wall paneling by the square kilometer. Every second tile manufactured worldwide is printed using a digital inkjet process. Similarly, the use of print processes on glass bottles, crockery, flexible packaging, soccer balls, suitcases, motorcycle helmets and snowboards is also looking at steady growth.
Their advantage is their speed. The backbone of high-speed printing processes is drying technology in the infrared and ultraviolet wavelength range, since it ensures that the applied layers of color harden very quickly. Depending on the requirements, UV LEDs, UV lamps or infrared radiators are used. Interchangeable systems that work with both LEDs and conventional lamps improve flexibility.
Maximum precision on rough surfaces
Unlike straightforward printing on paper, mechanical engineers in industrial printing cannot rely on standardized formats or on uniform distances between printing heads and surfaces. In fact, producers of upmarket liquors or cosmetics contrive unusually shaped bottles, flacons and cans to set themselves apart from the competition. And tolerances for glass, ceramics, sports items or wooden materials are often in the millimeter range. Nevertheless, precision in the micrometer range remains in demand for clean printed images in multi-color printing. This is only possible with a combination of high-precision servo drives and efficient camera systems. The latter monitor the precise position of the surface and the print heads then trace the contours of the respective shapes while compensating for any dimensional deviations. The systems also monitor the color fidelity and quality of the printed image directly in the process.
Image processing specialists such as STEMMER IMAGING offer solutions that are specifically designed for high resolutions in the extremely fast processes. Line scan bars that combine sensors, optics and illumination in a single device are suitable for straightforward planar applications. Prism-based color line scan cameras are suitable for monitoring color fidelity. Shortwave infrared cameras detect disruptive moisture, and preprocessing by frame grabbers ensures that background computers can analyze the flood of images within milliseconds. Despite processing speeds, in part, of several hundred meters per minute and tens of thousands of containers per hour, these imaging technologies can reliably detect and reject misprints.
In the meantime, optical inspection is now commonplace especially in the high-speed processes used in the beverage industry. Where stretch blow molding processes shape up to 82,000 PET bottles per hour before they are labeled or printed and subsequently filled, high-speed cameras are indispensable. That’s because there’s more at stake than just clean printing and correctly positioned labels. In conjunction with LEDs, camera systems also detect foreign bodies or particles of dirt in bottles or cans. Other optical systems monitor distortions, cracks and splintering. In addition, before bottles are recycled, mass spectrometers first analyze any liquid remaining in them. With bottles and cans being increasingly printed directly, there will also be more demand for solutions that monitor whether printing ink has been completely removed prior to recycling. The industry is investing in bottle-to-bottle recycling. As the name implies, bottles are made into bottles that need to remain transparent even after several cycles. Even at this stage in the industrial printing process, it is photonics that guarantees the right quality and ensures that no waste is produced in the first place.