Rediscovering Screen Printing for Glass Decoration

Key technical advances are being made in the field of industrial decoration on glass packaging, such as beer and soft drink bottles, using screen printing.

The development of digital printing to create a stable and repeatable process for commercial industrial digital printing machines has received much attention in the last few years. However, the quantum leaps made by screen printing technology in the same timeframe has been far less acknowledged.

This is not a comparison between digital and screen printing: both have their own right to exist. But we feel that the advancements in the field of screen printing deserve a closer look.

Screen printing has been rediscovered as a tool for producing premium decoration in the above-mentioned field. It has shown a growth rate which goes above and beyond the average.

These types of bottles are, with almost no exception, round, and have a volume between 200ml and 700ml. Since this is a very specific and clear definition/specification of the products, which are to be decorated, it is possible for a machine manufacturer to design a machine customised to this application.

Process

Before starting the design of a screen printing machine, it has to be decided which process to use: a ceramic or organic (UV/LED) process. In this case, it was an easy decision for various reasons. First of all, the use of UV/LED inks do not meet the criteria for adhesion during the filling process. Only ceramic thermoplastic inks offer the adhesion and strength again abrasion, which is required.

Secondly, although UV technology has matured and is safely curing at production speeds of 100ppm, it still is not possible to cure at much higher speeds, especially on a machine with continuous motion articles transport.This brings us to our next point. 

Production Speed

Whereas the average production speed on machines currently on the market is less than 150ppm, the next generation of machines offers double speed: 300ppm.

Why 300ppm?

300ppm has been identified as the most desirable printing speed, because on one hand, this is the speed at which in-line decoration becomes viable with the glass production, and on the other hand the proven infrastructure can be used or upgraded for integration of the new high speed printing machine.

By infrastructure I mean the existing screen making processes can be used, the same ink suppliers can offer modified versions of the standard inks and, if necessary, down flow equipment such as stackers can be upgraded to meet the higher speeds.

Machine Concepts

The choice between two common concepts, which is an indexing and a continuous motion type design, is not difficult to make. Machine speeds exceeding 100 cycles per minute typically prohibit the use of an indexing type machine because of the extremely high forces applied during acceleration and deceleration. This leaves us with a continuous motion process which safely allows article transportation at 300ppm and higher.

Features and Benefits:

Optical/camera registration. The lightweight glass bottles, which are produced to use less energy and less material, make it impossible to use mechanical type registration, which uses a lug/ramp on the base or on the side of the bottle. Touchless optical/camera systems are necessary to replace the old process. A long-awaited improvement, which goes along with the implementation of optical/camera systems, is the perfect color to color registration, which mechanical systems simply cannot offer.

Dual Squeegee: At speeds of 300ppm, the use of a dual squeegee is strongly advised. The reason is that with 2 squeegee heads per print station, the relative printing speed which is the rotational speed of the bottles relative to the squeegee during the printing process, is almost the same as the relative printing speed of 150ppm machines. Again, the advantages are that existing screen technology, existing squeegees, and existing set up procedures can be used. Also, there is no increase to wear and tear on the screens, which typically goes along with higher speeds.

Ink Pumps: The use of ink pumps, which is on standard speed machines with an output of max. 100ppm is very rare, becomes mandatory on a high-speed printer. Ink pumps are serving a dual purpose: of course, they are supplying the ink in the exact amount, which is needed to the printing station by programmable dosing. And secondly, they are holding the correct temperature by means of a controlled heating system in an insulated container. Depending on the print image, a consumption between 1kg and 4kg of thermoplastic ink is not uncommon.

Print Image Inspection: Another mandatory feature is the print image inspection system. Fortunately, the existing systems used on standard machines offered a good base for the development of a high-speed system. However, there are differences. In order to match the high speeds without scarifying inspection accuracy, the print image is looked at by the inspection system in 6 segments. These 60 degree segments are inspected individually and put together by software, allowing the operators to easily identify potential or actual quality problems. This greatly reduces the reject rates and increases customer satisfaction.

Summary

To position premium products in the highly competitive field of beer and soft drinks, brand owners have rediscovered screen printing for decoration, which consumers can easily identify as premium.

At the same time, glass manufacturers and decorators are forced to offer this kind of decoration at the lowest possible price. To make this possible and profitable, the glass manufacturers/decorators must use state of the art equipment.

As one of the leading manufactures of glass container decoration equipment, Koenig&Bauer Kammann offers equipment, which meet the criteria for implementing this process successfully.