Often overlooked, the squeegee is integral to a successful print.
The act of screen printing utilizes three main components – the screen, the stencil and the squeegee. Of that trio, the squeegee is usually thought about the least in the typical screen-printing shop. It’s also often ranked below artwork, inks, stock and machinery in the pecking order of importance. Many times, it’s an afterthought, something with a funny name that hangs on the wall or sits inky in the sink, sharpened or replaced occasionally, never shown much love. In the big wide world, the dictionary definition of “squeegee” doesn’t even include the screen-printing version. (Yet somehow the “squeegee guy” who cleans your windshield at a traffic stop is.)
Well, the following information is for those guys and gals who aren’t stopping cars, because they are too busy printing. With their squeegees.
The Printer’s Buddy
Here is a more complete definition of the screen-printing squeegee: a flexible blade used to help deposit the ink or pastes through the stencil opening and mesh used in the screen-printing process. On manual presses, it is also used to flood the screen, in preparation for the next print. It is held within a holder which allows you to grip and print it; handheld holders are often made of wood while better-quality ones, particularly for automatic presses, are made of metal.
Although outwardly a very simple object, created specifically for the process of screen printing, the squeegee has evolved from metal to a hard piece of black rubber and into currently a variety of polyurethane “rubber.” These allow today’s screen printer to print better and faster on a mind-boggling array of materials and objects: From T-shirts to touchscreens, beer bottles to back-window defoggers, and everything in between.
This evolution continues today. Standard blades are made from a single piece of polyurethane. Its hardness is measured in various scales, the most common being “shore,” where the flexibility is measured in durometers (or “duro” for short). Squeegees often start at 65 duro, which are soft and supple, and run up to 90 duro, which is much harder and less flexible. For softer materials and inks that require a greater deposit (thin inks like waterbase, for example), opt for the lower duro. By contrast, harder materials (think glass or metal) as well as inks that require less desposit (thick opaque inks) should use a higher duro.
Manufacturers like Fimor, headquartered in Le Mans, France, have also introduced triple durometer blades, where a center core of 90 durometer has softer sides of 70. The hard center keeps the blade from flexing or bending under pressure, while allowing for a softer printing edge.
There are additional variations, such as the “Smiling Jack” and similar blades developed by Joe Clarke and his team at Clarke Product Renovation (CPR) in Naperville, IL. It features a channel cut into the side of the blade, some with an upward curvature at either end. The curves automatically compensate for the different resistance pressure experienced by the squeegee near the outer edges compared to the sweet spot in the center of a frame. And instead of setting the angle of a normal squeegee stroke at the holder – around 70 degrees – the blade is set almost perpendicular. The channel acts as a hinge and lets the blade flex itself to a proper print angle. They print much faster, with less pressure, and offer distinct printing benefits in high-volume applications.
A Clean Stroke
It may seem like a fairly simple operation, this squishing of the ink through the stencil opening. Unfortunately for printers, during printing, the squeegee is expected to perform a number of technically challenging actions, all in the time it takes to complete a print stroke. It’s a bit like asking a kid in kindergarten to solve a problem involving physics, outside forces, chemical reactions, fluid dynamics and a few other curveballs. All in a split second. No problem. Squeegees are consummate multitaskers. Here are the various factors which determine the effectiveness of a squeegee and its ability to print.
Sharp Edge: Squeegees print with the corner contact edge along the length of the blade. This wears down as you print. It must be sharp and free of nicks. Those streaks in your print? That blurred image from too much ink? Usually a dull squeegee. Grind, buff or shave it, and if that doesn’t work, replace it – you need a sharp edge to get a sharp print.
Angle: If you flop the squeegee over, you are printing with the side of the squeegee, not the corner edge. Flop it too much and you will blur the print. Stand it up too much, the edge can’t maintain contact and pressure – both of which are required to clear the screen and stencil of ink, sharply.
Pressure: How much is correct? The least amount it takes to make contact and transfer the ink through the mesh and stencil. Too much and you will bend the blade or wear the squeegee down prematurely. You can also rip the screen or distort the image with too much pressure.
Durometer: If a blade is too hard, it won’t flex and fill the texture of a surface. Experiment with durometer. In many cases, printers will use a different duro blade depending on the material being printed. If a blade is too soft, and too much pressure is used, then the squeegee won’t maintain contact with the corner edge and cause other problems already discussed.
Wear and Chemical Damage: The minute your blade takes its first breath, it is starting to grow old and hard. Once it gets mounted in a holder and begins its working life, every print stroke causes the edge to wear, and every ink bath and cleaning cycle ages the squeegee and makes it swell up and harden over time. Typically, squeegees are finished when they become hard and run out of height from too much sharpening, or develop a fatal nick.
So how to care for the squeegee? Various inks and cleaners attack the squeegee material in different ways, so many shops running automatics (where squeegees are printing thousands of impressions per day) will have a second set of blades and rotate them in and out of production in order to maintain sharpness and ensure the durometer is not changing too much. Along with choices in shore, blade manufacturers will provide a range of material formulations as well, with economic blades for hand printers, and tougher compounds for high-abrasion applications.
“Never use alcohol or solvents with alcohol to clean a blade!” Clarke adds. The alcohol attacks the material and causes it to degrade. Instead, Clarke advocates polishing with WD 40 and 400 emery cloth to extend the blade life and get the best performance from your squeegee. “Polish more, sharpen less,” he says. Other guidelines include minimizing pressure, wash immediately after use and sharpen only after resting. With volume users, Clarke advises to run an eight-hour production/clean cycle, followed by an eight-hour rest and sharpen, if required.
If all that seems like a lot of variables and problems, take heart. When you buy a new squeegee, you are paying for something that will potentially give you upward of 50,000 impressions over its lifetime with proper care. A good sharp squeegee, compared to the cost of all the other components that go into the price of each print stroke, is next to nothing. (Squeegees cost roughly $1.50 an inch and are often purchased in 12 foot lengths.) But an incorrect hardness or worn squeegee can immediately make the most expensive ink, stencil, mesh or machine useless, and ruin valuable stock and make artwork look terrible. Show your squeegee a little respect, and reap the rewards!
Andy MacDougall is a contributing writer for Wearables. He is a member of the Academy of Screen & Digital Printing Technology, author of Screenprinting Today: the Basics, and recently helped produce the book A History of Screenprinting. Contact him at www.squeegeeville.com.