Date 1/31/97

Attn: Dr. H. Jack, P.Eng.

From: Stan Vander Pol

Content: New "Tools" in Screen Printing

The original research topic that I planned on looking into was vinyl plastics and printing on vinyl. The information I found on vinyl plastics had little to do with breakthroughs in the plastics industry. I found more interesting information on screen printing and some of the new "tools" being used in the screen printing industry.

The same basic components of screen printing have changed very little over the years. The standard systems still use screens, squeegees, inks and a energy source to cure the ink. The new breakthroughs that I found deal with improvements in the curing of the ink, solutions to substrates problems, and improvements in automation.

The first breakthrough deals with a new computer-based system for on-line monitoring of UV lamps. This system was developed to isolate and identify current variables in UV curing that lead to products that do not meet quality control standards. This system uses a probe connected to a fiber optic cable which is then connected to a optical bench. The optical bench splits the incoming light "signal" into its various wavelength components. The wavelength information is then converted by 1,100 sensors into electoral signal voltages which is then monitored by the computer software. Using this system several tests were completed that pointed to why UV curing changes rapidly sometimes within a single run.

The system found out that every lamp during warm-up acted differently. The various wavelengths fluctuated in intensity in each lamp and some lamps reached 150 percent of their operating maximum before settling down. These similar fluctuations in the wavelengths were seen during production runs. The measurement of the total energy was taken during production and on some lamps showed no deviation. On these same lamps the actual output of the wavelengths were rising and falling with in the range.

The other test related to wavelength variation was in the life of the lamp. During this test certain wavelengths exhibited a linear decline in intensity while others showed oscillating declines, with peaks, valleys, and plateaus.

This technology could be incorporated into a program that would warn operators of when certain critical wavelengths of the UV lamps were low which could warrant containment of a run. This technology could also help in determining which wavelengths are damaging to substrates or essential for ink curing.

This next breakthrough deals with using certain type bulbs that emit longer wavelengths. The reason for using these bulbs is not to increase the curing of the ink but to reduce the amount of oxidization that occurs on the plastic substrate, specifically polycarbonate. The by-product from this reaction forms on the surface of the plastic and acts as contamination that blocks ink adhesion. The short-wavelength UV light is the primary responsibility for the oxidation on the plastic surface.

Again the printing of ink on plastic is not a new process, but the solutions are new to the problems that have been around for many years.

Changes in the automation of screen printing are also changing. Automated machines can now be purchased that are capable of printing 140 compact discs per minute. These machines come with quick change squeegee heads and floodbars that can be adjusted during print operations. The screen position in the print head is displayed on a digital readout for fast re-set when a certain job repeats. These machines also come with vision systems for inspecting for defects on the printed side and readside of the discs. The vision systems can also compare to make sure the correct label is being place on the correct disc.

Another system that has been developed is currently being used to improve changeover time. The system has been developed to reduce variation in the registration of the artwork films on the screens. This new system can locate the films to within a .001" tolerance. The system uses a back lit vacuum table with a motorized x/y/theta position controller. A camera is used to look at the image and then center the image in the proper location. It also punches the film with the registration holes located on the screen frame. This reduction in variation improves the quality of the product and reduces cost normally incurred during set-ups.

Many changes are happening in the screen printing industry that are making printing more repeatable, reliable, and cheaper. Some companies may not adapt to the changes or even be aware of what now can be done on old products. If such products present themselves to our company, it may be wise to use automation, new registration systems, and vision systems to produce a product cheaper and with better quality than what is currently being done. By combining these factors with informed people that can develop new breakthroughs may prove silk screen printing a profitable business. The best way to ensure success would be to pick a product that is currently not automated because this reduces the competition and allows the business to provide a niche in the industry.