Hi fiends how are you. Today I am going to explain about what to do and what not to do during screen expose. Lots of our reader requested us on making more article on Screen exposing process. This is the very vital and only tough process in entire screen print technology. There have lots of factor work during screen expose. So today in this article we will mainly cover on those reason on which our expose badly affect.
During our expose process first we will take Screen quoting emulsion and sensitizer. Here in our case we have taken 50 ml (Sonakote Avilable In India Only) emulsion for one 12 by 15 inches screen and 5 ml of sensitizer. Here we mixing the sensitizer very slowly by a ice-cream stick. In this stage what point you need to take care?
First do not mix the emulsion vigorously. It may cause lots of bubble introduce in emulsion and latter that will create a circle spot in your screen.
Second you must have to maintain emulsion and sensitizer ratio. Here for 200 gm sonakote mix one packet of sensitizer. For the 50 gm you can able to calculate that. If you increase sensitizer proportion then your screen will be harder and if you reduce sensitizer proportion you’re your screen will soften and wash out your emulsion very easily.
Third you have to mix the emulsion at least for 15 minute otherwise your emulsion will not mix properly with sensitizer. Remember some time you can feel it become dissolved but maintain this 15 min time.
After mix the sensitizer keep that mixture in a dark place and cover it well from the light. After mixing the emulsion with sensitizer it’s become very photo sensitive for light. So keep it in dark place and keep that one for next 30 minutes.
After 30 minutes take it in a scoop coater and spread the emulsion above the screen. During coating maintain a single stoke movement. Do not stop your hand in between the screen. That will create an extra mark on screen and uneven. Remember you have to wipe out all excess emulsion from the screen and make the screen a thin layer. In this point if make your screen very thick it will take more exposing time and may create problem in fine graphics area.
After coating the screen keep horizontally the screen. Never make it vertical until its become dry. Here for faster process, we are using hair dryer at the 42 degree temperature to make it dry. During drying process keep your light as low as possible.
Next you have to put your transparent or semitransparent film on it and then expose it in light. The film you have to put in a develop side and have to keep pressure from the ink side. If any gape get place in between film and screen then your exposed impression on the screen will be blur. You have to maintain a proper exposing time for perfect exposure. This time is a very critical time, it vary on lots of factor so in your case you have to do little bit experiment by reducing or increasing it. Here in our case, in our exposing box its take exactly 3:50 to 4:00 minutes.
After expose now it’s the time to wash the screen. During wash time first you have to weigh the entire screen and wait for 3 to 4 minutes. Then you can start wash your screen from low pressure to high pressure. We always recommend that never give instant high pressure on screen. There have a chance of failure.