It seems that one of the most common problems new screen printers run into is printing white ink. I’ve heard a lot of questions Silk road economic belt: Why do all my other colors print fine and white is so tough? Why is it that my white ink is so thick? Why can’t I get a smooth white ink? It’s always rough and seems to have texture to it. Is there anything I can do to thin my white ink to make it easier to print? Also comments like: “Our white ink is bad, it comes off after only a couple of washes.” “There’s something wrong with my press, it prints fine when I am printing on white shirts, but when I print on dark shirts the white ink is very blurry.”
Unfortunately, the answers to these quarries usually lie in the printer themselves. No, your white ink isn’t defecting, your press probably works fine, and you shouldn’t need to thin the ink. Yes, you probably need to change some variables and techniques during the printing process. The truth of the mater is, the answer is in the question all along.
So why does the screen printing process work fine for a while and then as soon as you start printing white ink, smash, a road block. The truth is, you may have been doing the wrong things the whole time, it just didn’t show up yet . It’s like swimming, sure you can dog paddle and flounder around the pool all day. However, when it comes to swimming a long distance, without the proper techniques you’ll work twice as hard and get half as far.
Printing on light garments is much easier than printing white on dark garments. On a light garment, not as much ink is required to achieve good coverage. Also many times you’re working with thinner inks. Ink varies in viscosity according to how much pigment it has in it. For instance, a black ink is almost always going to be printed on lighter colors, the pigments needed for the black to show up are considerably less then the pigments needed for a white ink to cover a dark garment. Thus, you’re black ink is much thinner and easier to work with. You can do almost every technique wrong when printing black ink on a white shirt, and there’s still a good chance that your final print will look pretty good. Since the ink is thinner, it passes through the screen mesh much easier, with less force, and clears the screen better. (For those unfamiliar with the term “clearing the screen,” this defines the point when all ink is cleared out of the screen mesh and properly transferred to the shirt.)
So basically when setting up a screen printing job that requires black ink on a white shirt, you can use the wrong screen mesh, have no off contact, and print with the completely wrong squeegee technique and still get an “OK” looking final print. However, if these same wrong techniques are tried when printing white ink, uh oh, game over! The unfortunate thing is, many printers start out this way and teach themselves completely wrong. In fact, this is how I learned. It’s not the end of the world though!
The first thing you’ll have to understand and come to terms with is the fact that white ink is probably going to be the thickest ink you’ll ever use. To achieve a bright white image on a black shirt, the ink has to be opaque which in turn means thicker. Sure you can find thinner white inks, or try to reduce the thicker ones, however you’re defeating the purpose and you’ll end up printing twice as much to try and achieve the same result. On the other hand, if you learn how to print correctly, then printing white is like taking a walk in the park.
Over the past several years, every ink manufacturer in the country has been on the hunt for the “best” white ink on the market. Yes, they’ve come a long way. In fact twenty or thirty years ago white on black looked more like a light tan or gray than white. Now with inks available like Triangle Phoenix White or International Coatings White, you can achieve maximum coverage with minimal passes. Still, white ink has to be loaded with pigment which means it will always have a high viscosity.
So what’s the trick? How can you print white ink like the
pros.? The answer usually lies in a few simple changes to your setup and
technique. Apply these changes and really, it’s not that hard.
Before we delve into techniques, let’s first discuss a little bit about pre press and setup.
To properly setup a job using white ink you first must
understand a little bit on how to select the proper mesh size. Because white is
thicker, you want to print through the lowest proper mesh size that applies to
that print. If you try and print white through a higher mesh screen which has
much smaller holes in it its going to make it much harder to push the ink through the screen. It’s also not going to allow as much ink through the screen as a lower mesh would.
Typically you want to print white through mesh sizes ranging from 110-156. Granted sometimes the image dictates a high mesh count. For instance, since a half tone or fine line drawing cannot hold on a lower mesh screen, you’ll have to use a high mesh frame and apply more passes to achieve a bright white. For the most part however, you’ll want to use the lower meshes so that a larger amount of ink is deposited on the shirt.
The second part of setup is to insure the screen is adjusted properly on the press. You want to be sure that you have a proper off contact of about 1/8-1/16 of an inch. Since white is a little thicker, you may want to go with a slightly higher off contact then normal, perhaps around 1/8 of an inch. Off contact is the height between the screen mesh and the substrate you are printing on.
Proper off contact also allows the ink to be cleared from the screen mesh easily by releasing the mesh upward directly after the print stroke leaving all the ink smoothly on the shirt. One thing that you also want to be sure to apply when printing white ink is an off contact tab. This is a small piece of material (ie. a penny, cardboard, paper, a piece of plastic) that is the height of your off contact. This tab is placed on the end of the screen frame where it hits the top of the neck platen and not the shirt. By using an off contact tab, you insure that your off contact will remain through the entire print stroke.
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