UV Printing Guide

Technical Bulletin

UV PRINTING ON COROPLAST™ MATERIAL USING AUTOMATIC EQUIPMENT

The purpose of this bulletin is to provide insight on some of the issues that need to be addressed when performing four, five and six color UV printing utilizing full automatic equipment.

Some of the key factors to successful printing on Coroplast™ material are as follows:

1. A regular maintenance program that includes replacing UV bulbs on a regular basis. Cleaning all reflectors, air intake screens, exhaust fan blades, inspecting the shutter system for proper operation, etc. to ensure the heat exhaust system is operating properly.
2. Having an air make-up system that is large enough to supply plenty of air so the heat exhaust system will not be starved for air. This is very important.
3. The UV bulbs normally have three wattage settings: 150, 200, and 300 watts. The normal setting for Coroplast™ material would be 150 to 200 watts combined with a belt speed of 80 to l 00 feet per minute. It is never recommended to use the 300 watt setting.
4. How hot does the UV bulb get? The bulb approaches the melting temperature of glass. Care must be taken never to touch a UV bulb even when turned off. The oils in your fingerprint can cause a hot spot on the bulb and cause it to crack when it heats up. Also, periodically the bulb should be rotated 180 degrees to minimize sagging in the middle. This can lead to sheet failure as the bulb can get too close to the middle of the sheet especially on the larger UV machines.
5. An adhesion promoter should always be used when printing on Coroplast™ material. Check with your ink supplier for the proper adhesion promoter for the ink you are using.
6. A catalyst should be used for all outdoor UV printing applications. Without it the ink will become soft in a moist atmosphere and will be easy to scratch off. Check with your ink supplier for the proper catalyst.
7. Although Coroplast™ does not endorse any ink brand, many printers have achieved good results using Sericol and Nazdar brand inks.
8. For most UV ink applications, 380 to 390 mesh screen should work well. For metallic inks, a 330 to 350 mesh screen will probably be needed.
9. Metallic UV inks will be much more difficult to print successfully on Coroplast™ material due to several factors. In order for UV inks to get good adhesion to Coroplast™ material, the UV rays emitted from the UV bulb must penetrate through the ink to the Coroplast™ substrate and reflect back. The metal in the ink has a tendency to reflect the UV rays before they reach the substrate resulting in poor adhesion. Also, too much metallic material in the ink will result in the rays being blocked before reaching the substrate material due to the fact that the metal in the ink is not translucent and will not allow the rays to pass through. This also can cause excessive heat retention in the inks which can lead to Madeira collapse and failure. Lastly, if you must use a metallic in the ink, use a paste form metallic instead of a dry metallic. This will aid in getting better dispersion of the metallic when mixing resulting in less clumping of the material which will lead to adhesion and coverage problems.
10. Always pull the squeegee the direction of the flutes whenever possible. Pulling across the flutes on a multicolor automatic printing machine will dramatically increase the possibility of skin collapse between the flutes. This occurs because as the material is heated by the UV light it softens. If the squeegee is traveling with the flutes, it will be supported by all the flutes decreasing the likelihood of skin collapse.
11. Always set squeegee pressure as light as possible to avoid crushing the material.
12. Never stretch the screen too tight and allow plenty of clearance from the print area to the screen frame to ensure complete ink coverage. A good rule of thumb is a least 4 to 6 inches clearance on all sides. More on very large screens.
13. When using fully automatic multicolor printing machines it is very important that the bulb cooling system is in optimum operating condition. The exhaust duct work must be properly sized, there must be no air restrictions and all components of the machine must be working properly to keep the Coroplast™ material from overheating and failing during the multi printing process. Please remember, that unlike on a single station printer, the material does not have time to cool down before it is printed and run through the heated lights again and again.
14. Avoid handling the Coroplast™ sheet immediately after printing. It will be in a softened state due to the heat generated during the printing process. This can lead to skin collapse and failure of the sheet.
15. Your ink supplier and machine manufacturer should be your best sources of information if you encounter difficulties.
16. Take care in choosing the correct material when UV printing. Select a sheet with a thick enough skin to withstand the extreme heat generated during the automated UV printing process. Also avoid darker colors in the sheet or the ink when possible as they will have a tendency to retain heat and could lead to sheet failure.

In this process as in most processes, the real key to success is highly trained, competent production people well versed on all the different aspects of automated UV printing, a comprehensive maintenance program, support from top management and ink suppliers that understand the process and supply the correct ink products for each varied application.

This is intended to be used as a reference only and in no way does it reflect all the issues that need to be addressed when printing on Coroplast™ materials.