Screen Printing White Ink
Whether you are new to the business, or have been printing for 20 years almost all screen printers encounter a white ink problem when printing. Sometimes the ink does not get great coverage, sometimes the ink is too thick and feels bulky, or too thin. The solution to this problem is not related to the press or the even the ink brand, although some brands are better then others. The problem lies within the process of which the white ink is being printed.
If you are coating a screen for white ink versus coating a screen for black ink, the process should be different. Black ink is a dark color and therefore does not need multiple hits, or a thick print. On the other hand, white ink is a light color and in order for light colors to look opaque on your shirts they would need to be printed and flashed multiple times. Normally you would print 1-2 hits of white, then flash the garments then print another 1-2 inks – but I have personally had to print-flash-print more than 2 times in my shop because I just wasn’t getting the right coverage. So I decided to do a little research and I found out I was emulsioning screens wrong all along. When making a screen that is being used for white ink, it is important to coat the screens from both side and let it dry. Once the screen is dry you will need to coat the screen once more on the outside (the side that touches the garments), this allows a thicker layer of emulsion on the outside. Once the screen is exposed (you will need to expose for a longer time), you can run your fingers across the outside and feel the opening of the stencil. This method allows for more ink to be laid onto the garment with each stroke, which allows for better coverage.
It’s important to always keep a sharp squeegee, but when printing white ink it is crucial that your squeegee is sharper than ever. I can’t tell you the number of times I’ve seen blotchy prints come out due to a dull squeegee. You will also have to hold the squeegee at a 80-90 degree angle to allow the corner of the rubber to push the ink through the open mesh. It is also recommended to stand above the squeegee, not behind it – this will reduce the back pains many printers complain about.
In order to get great coverage screen printing white ink, you must make sure the garment as well as the ink is flashed in between each print. This means that the ink gets to a state where it is not cured yet, but dry enough to allow another layer to be printed above. When one layer is printed over another dry later of white ink, the results are a bright white opaque layer of white ink.
Another important thing to look at when trying to get great coverage with white ink is the garment being printed. Sometimes the garments are made of heavyweight material and the ink seeps in much deeper into the fibers. Therefore more ink will need to be deposited in each print in order to get a vivd print. On the other hand, polyester garments requires less layers of ink. This is because the ink does not seep into the material as much.
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Check out Ryonet’s blog post on white ink.