Go to any industry tradeshow or visit an actual screen-printing shop, and your eyes will naturally be drawn to the press, or presses there. This is true whether the shop in question employs a single manual press or is running multiple autos.FULL STORY
Screen Printing: Production
Top Tips to Improve T-Shirt Print Quality
One of the reasons I like working in this industry is that it has a great mixture of art and science. There is a craftsmanship feel to it that is palatable on the production floor.
During my time in management production — and even back when I was an art director — I’ve seen things that would commonly show up during the printing process that would need to be corrected on the press. Some of these are really simple and easy, while some are a little more complex.
Registration — There are a lot of factors you need to check if you are having registration issues. The problems could be as simple as the screens not being lined up correctly, or it could be something more elusive such as low-tension screens, an unleveled platen, an artwork problem, etc. A good press operator should be able to set up a job on press in about five minutes per screen, on average.
For this type of problem, start by ensuring you are registering the screens together using registration marks. I know some shops don’t use them, as they don’t want to tape them off, but that savings is quickly diminished if you are having difficulty getting the job set up as the screens won’t line up. At a minimum, these should be above and below the art, and large enough to be seen through the screen. Make sure your screen room blows these out completely and doesn’t block them out during the quality control/pinhole hunt step. These marks should line up exactly center with the platen. Dial them in one at a time.
Also, there are plenty of longstanding, on-press registration tricks you can use. Some printers will print the black or underbase screen on a junk shirt, platen or a clear tape-coated platen and quickly flash cure the print. They then will use this to register the other colors.
Using more advanced screen-preparation tools, such as a computer-to-screen (CTS) imaging system, Tri-Loc pin-registration systems or other devices will help reduce your registration time, as the screens will be imaged perfectly registered to each other as a set. You usually just need to use your micros to dial them in. If your platens are not perfectly centered on your press arms, you could have registration and off-center issues, so watch how you lock in your platens.
If you are having problems registering an image on screen, the best method for determining the cause of the problem is to review each screen individually. Only change one thing at a time. I’ve seen too many operators get frustrated after adjusting two or three screens at a time and then reviewing the result. If you do it that way, it’s like trying to hit a moving target, as there are too many variables. It’s actually quicker if you slow down and use your brain. Try it!
Color Matching — These days, most jobs have ink colors specified with a vast array of Pantone colors called out. Smaller shops may just offer a stock set of colors, but even they occasionally will be asked to match a particular PMS color. There is an ongoing debate for charging for a PMS match, as larger shops see it as simply a task that has to be accomplished and have built the infrastructure to handle it. Smaller shops with manual screen printing presses, however, aren’t set up for such requests and usually charge a fee. These smaller shops are the ones that usually have “a guy” that has a certain eye for mixing color and don’t see the need to change. To me, that’s foolish, as you want to make the task as easy as possible, and remove this step from a particular person and progress toward being a standardized function of your shop that can be trainable.
To build your ink room setup for quick and easy color matching, you only need a few tools, primarily a really good scale that measures to .01 and can be zeroed out. Get one that is stainless steel for easy cleaning.
Most ink companies have an ink system that allows you to build your Pantone color by using a base plus an assortment of pigments. To mix a color, simply type in a PMS number into a computer workstation in your ink room and the list of ingredients will appear. You enter the quantity of ink you want in the bucket and the system will tell you exactly how much of each ingredient to add by weight. Place an empty bucket on the scale and zero it out. Then, add the base per the requested weight and zero it out. Then, each required pigment is added, and the scale is zeroed out each time. Mix the ink when finished and it will exactly match the required PMS color in the volume of ink you need for the job. Average time to mix usually is about four minutes for a batch of one gallon or less.
Ink Coverage — Believe it or not, your ink coverage is mostly dependent on a combination of the mesh selected for the job and the thickness of the emulsion on the screen, rather than how much squeegee pressure you use. Using so much pressure that your squeegee bends like the letter “L” doesn’t add much more ink to the situation. It actually could start contributing to other problems.
Tons of articles (even books) have been written about the term “emulsion over mesh” or EOM. The short-and-sweet lesson is that the emulsion you add to the screen creates a channel. When you flood your screen during the printing process, you are filling that channel with ink. If you have everything on press set up correctly, you need just enough squeegee pressure to sheer the ink through the channel and onto the T-shirt. You shouldn’t be driving the ink through the screen like a hammer and nail.
Want more ink on the shirt for an underbase screen? Try adding one more coat of emulsion to the screen (print side) during the preparation stage. Some shops even use capillary film for a thicker stencil for a “one-hit white.”
While the screen certainly plays an important role in your ink coverage, so does your squeegee choice. A softer squeegee will likely send more ink onto the shirt, while a harder squeegee won’t. When there are ink issues on press, one of the first questions I would ask is what type of squeegee the operator is using currently. Too much dot gain could be the result of using a softer squeegee.
Print Hand – “Hand” is the industry term for how the ink feels on the shirt after printing and curing. Many shops have moved to using water-based ink because it gives the final print that soft, retail hand that is very popular. Essentially, with each screen and color you are printing on a shirt, the thicker the ink deposit will be. Sometimes this is an issue, sometimes not. If want to achieve a softer hand on the print, here are some tips:
Use a higher mesh count for the screen. The higher the mesh, the less ink will be deposited onto the shirt. For underbase screens, try using a 156 instead of a 110. Screen selection isn’t automatic and is dependent upon the image being printed, as some mesh choices won’t be completely successful. The only way to learn is to experiment and see what works for you.
Try using a different ink base to increase the viscosity. Finesse base, Chino base — even adding some curable reducer to the ink you are using — will work. The idea here is to “thin” the ink down to improve how it flows onto the shirt substrate. Be careful though; inks are formulated to work a certain way on purpose. When you start introducing additives to the ink, you may change its properties and have some unintended consequences if you aren’t careful. Opacity and curing issues are the two most popular consequences, in most cases.
Roller squeegees also can help. This after-market type of device works great and we have them on all of our automatic screen printing presses at my shop. After you print your underbase and flash the shirt, use a roller squeegee in the cool-down station. This flattens the ink that has just been gelled by the flash unit and sets up the printed ink nicely for taking on more colors. You also can achieve this yourself by using an unexposed screen, a squeegee and some base. Set up the screen like normal with the squeegee. The base gives the squeegee something to move around and reduces friction. Underneath the screen, tape a big sheet of Teflon (like the kind you use for your heat press platen cover.) A roller works better, but this technique will work in a pinch.
Keeping Things Straight — Your print quality is sometimes only as good as your loader. Getting the shirt straight and in the correct position on the platen is a basic step in printing, and often overlooked until the client complains about crooked or off-center imprints. Let’s face it, loading a T-shirt press is a monotonous and robotic-like process, and it’s easy to lose focus and get distracted. Look at the following in your shop:
Speed. If your press operator misses boards as they rotate and has questionable image location results, it may be that the press speed is set too fast. Printing a bunch of misprints quickly is never better than running the press at a speed where quality counts. All too often in production, the emphasis is on how many impressions are printed during the shift. Start keeping a discrepancy log with misprints, quality control and other issues, and you’ll quickly see that these errors can add up fast. Slow down for better quality.
Ergonomics. Skilled press operators know exactly what they like in a work-station area. These can include a good, thick spongy mat under their feet, some music to print with and — most of all — a properly positioned cart or table full of shirts. As all press operators come in different shapes and sizes, let them adjust this to what they like. Shorter printers sometimes can’t handle the same mountain of shirts that a taller printer will churn through. Some printers like the shirt openings facing them; some like it the opposite way. There’s only one hard-and-fast rule: comfort counts. Good print quality for loading comes for being comfortable and relaxed in the process. Make sure there is room for your press operator to function and adjust along the way.
Mark Your Boards. Good press operators instinctively know where and how to load shirts to get the best print. However, they don’t stop there. For great results, mark your boards where the collar is to drop, where the center of the shirt will be or any other landmark that is a concern. Have a T-square, ruler, tape measure and some markers handy. If you are trying to line up a landmark on the shirt, such as a seam, top of the pocket or other item, a great trick is to use lasers. You can get lasers that will project dots or lines from any hardware store. These can be magnetically positioned onto the metal part of your press and the line will project down onto the board. Use two and form a cross for positioning pockets.
Pinholes and Screen Problems — Why is it that most shops will staff their worst employees in the screen room when it is such a key part of the entire printing process? Granted, it is by far the grubbiest job in the building, but if you staff your screen room with great, process-minded people, you can eliminate a lot of on-press challenges involving screens.
A good number of issues stem from improperly cleaned screens, emulsion coating, exposure issues and failure to wash out the emulsion correctly. There are many variables that go into making a great screen, but one thing is certain: You can judge the craftsmanship of a screen printing shop by how its screen room is run. What emphasis is placed on standards and controlling variables? Top shops are very particular about their screens, and they go to great lengths to perfect the outcome by introducing more precision in this area.
If you are having challenges with your screens on the press, double back to the screen room and look for the cause of the issue. For example, pinholes can be the result of dust and smudges on the glass of the vacuum table. How often is that cleaned? By the way, one of the most overlooked benefits of going to a CTS system for imaging is the fact that you no longer need the vacuum step in exposing the screens, so the dust-on-the-glass problem is eliminated. Thus, so are the pinholes.
Artwork — Your art staff can help you control your print quality in many ways, too. It helps if they understand and comprehend the mechanical process of printing. Their knowledge and understanding of what happens on press will greatly influence the decisions they make in creating the art that will be printed later. They absolutely need to understand why you flash cure the ink on press…and more importantly, when you do it. Their knowledge of underbasing inks is crucial to your success. If you have a crack staff, they should be the ones determining mesh counts and recording their choices in your system so that your work order can be built with repeatable results. Start with standard choices, such as which mesh to use for an underbase screen, and build the knowledge from there.
As T-shirt printing is such a specialized industry, hiring an art staff with this knowledge can be difficult. Finding creative and talented people is easier, which is why so many shops have to “grow their own” and educate their art staff with on-the-job training. Get the art staff away from their computer screens and out into the shop. Have them hang around, take notes on their jobs, approve all their work…maybe even help a print crew set up and run a job or two. Creative people will make decisions on their work on an unconscious and gut level based on what they think will add to the work. If you combine that will the practical knowledge of what can be achieved on press, your print quality will be greatly increased and will lead to some outstanding work later.
Ink — Regardless of who makes the ink in your shop, it is manufactured to be handled and cured in a certain manner. Are you using yours correctly? How often are you checking to see if your dryer temperatures are correct so that you know you are curing your ink correctly? The most common ink failure is undercuring.
Different ink types have different dryer temperature needs. Are you adjusting accordingly? For example, one of the biggest problems these days is trying to control dye migration on performance fabrics. Shops will change over to use a performance ink, but fail to adjust their dryer temperatures. They may even flash the shirt one or two times during the print run, too. The dye migration still happens and they blame the ink for their white ink still turning pink on red shirts. It isn’t the ink, folks. Make sure you read and understand the specific instructions for the ink you are using in your shop.
Controlling variables is the key. At the end of the day, the standards you set in your shop will go a long way toward determining your printing production outcome. Minor details, such as the choices the art staff makes, the cleanliness of the screen room or the mesh selection, can go a long way to affect your print outcome. These may not be outwardly noticeable connections on your shop floor when you have a problem on press with a big deadline due. All of the big-picture challenges need to be addressed and corrected in a proactive manner.
Here’s where the leadership of your production staff should come into play. If they don’t address the situations, why should your print staff? Want to improve your print quality? Connect all the dots in the shop and see if you get better results.
Marshall Atkinson is the chief operating officer of Visual Impressions Inc., and Ink to the People, Milwaukee, Wis. A frequent contributor to Impressions, Marshall also lectures on sustainability at Imprinted Sportswear Shows (ISS) events and has participated in numerous industry webinar panel discussions. He is on the board of directors for the Sustainable Green Printing Partnership (SGP), and serves on the SGIA Leadership Committee. You can follow him on Twitter @atkinsontshirt or his blog, atkinsontshirt.com.
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