In my classes and seminars, I talk to new screen printers all the time, many being in business a year or less. Some issues tend to repeat over and over again. Of course, there are more than five, but these are the most common, and fairly easy for the new screen printer to address.
Using the white underbase as a color in your image
It’s a big temptation to cut corners for time and money when you’re starting out. “What’s the harm?” is the thought here. By far the most common corner cut is when you’re printing on dark garments with a white underbase. The temptation is to use the white of the underbase as the white in the image as well.
An example would be an image of the American Flag on a black T-shirt. Many printers would count this as a three color design – red, white and blue. But to properly print this graphic, it needs to be a four-color print – white underbase, red, blue and highlight white to finish off the job.
Using the white underbase as part of the image requires you to lay down far too much ink to make the white bright enough for a final image. Then, the colors on top of this too-heavy underbase make the print even more thick. And, these overprint colors can become muddy because of the heavy base you are printing upon. You may have curing problems (cracking after washing) due to the excessive amount of ink as well.
Your underbase should be a minimal lay down of ink to give you an opaque base, but the thinnest final print you can achieve. Using a highlight white as the final color will give you a much more professional product.
Using a single mesh count for all jobs in your shop
There was a time when a supplier would tell you to buy a dozen 110 mesh screens and you can print anything. Unfortunately, there are still suppliers who tell new printers this. When I started printing (in 1979!!) this was common advice. But today we know better, or should at least.
Yet still I hear students in my classes and seminars tell me, “But my supplier said all I need is…”
There are many knowledgeable suppliers, but unfortunately there are also suppliers who have never pulled a squeegee and simply learned the business from overhearing other sales reps. The task is upon you, the printer, to be an educated buyer.
For my average spot color images, my basic mesh is a 156. I use 230 white and 305 color screens for simulated process. When I print puffs and plastisol transfers I use 87 mesh. Specialty inks… I use what the ink supplier recommends such as 196 for suedes, and 40 for glitter.
It doesn’t have to be complicated. Your ink manufacturer will recommend a mesh count for the types of ink they sell. Follow those recommendations and you’ll be much more successful. It is screen printing after all, so the screen is the critical component. I believe that getting the screen right – mesh and tension – is 90% of the job.
Do I have to have a dozen different mesh counts in my shop? The mesh variety you stock will depend on the markets you are selling. In most shops, you’ll see a variety of about five different mesh counts in their screen inventory.
Flashing between colors on a multicolor job
There’s usually one student in my classes who looks perplexed when we begin printing a four color job on Day 1. We’ll set up the job with each student participating, and then begin printing wet-on-wet. Up comes the hand.
“The guy who sold me my shop taught me to flash each color before printing the next.”
Flashing between colors is a band aid, for either mesh that is not stretched to the proper tension, poor quality films that overlap edges, or both. The greatest loss here is in production time. Flashing between colors can double, triple, quadruple the time it takes to print a job.
Get your screens right, and print your jobs wet-on-wet. The only time you should pull out your flash cure unit is when you print a white underbase.
Proper mesh tension is important
New printers struggle and struggle with release from the garment during the print stroke. By release, we’re referring to the screen coming away from the garment just after the squeegee passes, and not sticking to the garment until you lift the screen. In other words, printing off-contact the screen mesh should only touch the garment at the point where the squeegee comes in contact with the screen.
If your screen releases with a “pop” when you lift it, the screen mesh is likely too soft. This “pop” is caused by the ink on the shirt holding to the ink in the screen, until you forcibly separate it by lifting the screen. The result will be a rough finish on the shirt.
In the extreme, you will see white speckles in your image when you are printing an image over a white underbase. The white ink pulls upward when you lift your screen, and then is solidified in that position under flash. When you print the colors on top, the rough texture of the white underbase shows through as these white speckles in the image.
I’ve gotten this call 100 times, and 99 of those times the conversation starts with, “There’s something wrong with my ink.” It’s almost never the ink, no matter what the issue in your shop. And many of your shop issues will revolve around proper screen mesh, proper screen tension, proper preparation of your screen via degreasing and coating.
Improper curing that shows up after you deliver
Printers will call me up and say they have cracks in a printed image after it’s washed. I say, “It’s undercured.” They say, “It isn’t.” I say “It’s undercured.” They say… you know how this is going to end. If you see cracks in your finished image after a wash or two, it is nearly always a result of undercuring.
“But I pointed my temp gun at the image as it was coming out of the dryer and it said 325!”
That temperature is the surface of the ink film, but what about where the ink touches the garment? Plastisol ink cures when the entire ink film reaches about 320 degrees. The ENTIRE ink film, including where the ink is bonded to the fabric.
There are a variety of reasons why the ink didn’t cure all the way through, starting with a too thick lay down of ink. Another cause can be moisture in the garment due to humidity keeping your garment from reaching full curing temperature. That’s right, the ink AND the garment must reach full curing temperature. You need to test periodically.
Your temp gun is a good spot check, but for a real test, buy #5 Thermal Strips. Nearly every screen print supplier sells these. They come about 10 to a pack in perforated sheets. There is adhesive on the back to attach the strip to your garment.
Tear off one strip and put it on the front of the garment next to your image. Tear off the second strip and put it inside the shirt under the image. Both strips need to get to about 320 for the image to be fully cured. (The strip looks like a thermometer and will darken up to the highest temperature it reaches.)
Resolve these five errors in your own shop, and you’ll take a giant step from novice to the experienced screen printer.