What You Can't See

It’s what you can’t see that matters.

Screen room personnel often fall into a repetitive cycle in screen making. Handling screens becomes a constant work pattern where little thought is given to the condition of the emulsion, the screen room, the exposure process, or the condition of their equipment and the presses. They are constantly in a production 'pinch point' where a finite amount of screens can be processed through their area. Between sampling needs, production, and replacement screens for any that have broken down in production, they often aren't aware of anything but the need to line up the art and get another screen shot. They work at near capacity throughput for their system. Screens that are made in a hurry and rushed to production often look identical to any other screens. They are coated the same way, the exposure is the same time, the blockout and tape job are identical. One screen may last thousands of prints while one rushed to a press may breakdown in 300-500 prints. Same emulsion, same exposure time, same personnel yet some screens work well, some breakdown. The faster they go the more issues production has on press. So what is wrong with this picture? How can we change the process to make life easier for everyone in the shop, and with this process improve profits and company stability? 

The problem with the above scenario is this: the screen issues cannot be seen with the naked eye. It's what we don't see that causes most of the problems. So let’s look at areas that we find are often neglected in the screen room.

Coating: Coating the emulsion should not be done haphazardly. The thickness of the emulsion from the coating technique used along with mesh type, color of the mesh and more importantly the type of emulsion determines the exposure time. It amazes me how many shops I go into where this is simplified down to 2-3 exposure times for any mesh in the shop, no matter how the product is coated. Some mesh will be underexposed, some over, some exposures are plain lucky and just right with this method. The issue is the screen maker cannot see exactly how thick the coated and dry emulsion is without a tool like a Thickness Gauge. 

We often see workers coating too fast and not allowing the emulsion to flow through the mesh. His 110/TPI screens may vary from 0-7% emulsion over mesh to 25%+ emulsion over mesh in the center, and in almost all cases he will look at a chart for exposure times (if he is lucky to have one) and punch in the numbers. The 7-10% EOM screens shoot fine, The 0% can be over exposed but more importantly the 25% EOM screens will be underexposed. On press the 25% EOM screen will break down sooner on a discharge ink print and another screen will be rushed to press, often under exposed or under dried and break down even sooner. Nothing is predictable if only the naked eye is used to qualify the process; everything that needs control is invisible to the worker. Creating predictable results requires knowing what is happening in the areas you can’t see. Proper coating technique creates predictable exposure times. Coating slowly with a firm pressure allows the emulsion to flow through the mesh.