Screen Printing FAQ

Does Plastisol Ink Expire?

QUESTION: I’ve had this Plastisol inks sitting for a couple of years. How do I know if it’s still good?

ANSWER: Plastisol ink does not expire. You could have 20-year old ink that if mixed would likely print just fine. There is no water in plastisol to evaporate or solvent to flash off. It is a 100% solid product. You just have to mix the ink and off you go to the races. It may be a little thicker, but it will still print.

Screen Exposure Challenges

QUESTION: I’m having a hard time exposing my screens and getting enough detail. I think my film positive is good, but I’m not able to wash out enough detail from my screen.

ANSWER: This problem could be caused by too short of an exposure time, but usually you need to look at your film positive. When you hold your film positive up to the light, it should be totally black. Are your halftone dots the proper size? The rule of thumb is to take the mesh count and divided it by 5 to get your screen count. For example, if you want to print on a 110 mesh screen, divide 110 by 5. You should have a 22 line print halftone.

Can I reduce off contact with higher mesh tension?

QUESTION: We have been using the smaller Newman roller bar frames for awhile, and we have an air-powered stretching table. We often print 50-line halftones on 196 mesh. We tension between 26 and 28 newtons. We set the off contact on our automatic at around 1/16th inch. I’d like to know if we increase the screen tension, would we be able to run with less off contact to reduce registration and set-up time on the press.

ANSWER: Any time you increase mesh tension, you reduce the amount of off contact you need when using conventional screen mesh. At 26-28 newtons, your mesh is already high, but you might be able to go a little higher.

How many strokes should it take to create an opaque white on a dark shirt?

QUESTION: How many strokes of white should it take for the white ink to appear opaque on a dark T-shirt without feeling like sandpaper? We are thinning the white ink down with curable reducer, which allows us to get a nice smooth hand after printing, but it is taking three print passes to achieve this with a flash cure between each pass.

ANSWER: It should take two coats of ink. Apply the first layer, flash cure it and then apply another coat on top. If there are problems with a stippled surface, it’s possible that the ink is not being stirred up enough before use. A great way to ensure ink is properly mixed is to buy ink mixing blades that can be attached to a drill. This ensures that the ink is properly stirred and ready to use. Adding curable reducer is another way to thin down ink and detackify it. Also, always be aware of the room temperature as this has a dramatic effect on ink characteristics. The warmer the ink, the easier it flows. On a cold morning, it’s recommended to “warm up” your automatic press for 10 to 15 minutes before starting a job. This can prevent ink problems from the beginning.

Printing On Safety Vests

QUESTION: I have been asked to screen print on neon safety vests. It is a one-color (black) logo. What ink should I use? Do I add anything to the ink? What mesh count should I use for the screen?

ANSWER: Whenever you are trying to figure out what ink to use on a safety vest or anything else, the most important question is: What is it made out of? If the vest is made of polyester, you can use plastisol ink. If the vest is made of nylon, you may need to add a nylon catalyst to the ink to ensure it bonds with the material. If the vest is made out of some type of plastic, most likely you’ll need a solvent-based ink.

A mesh count similar to that for printing T-shirts, around a 160, is recommend. Find out what the vest is made of and then you call Regional Supply or an ink manufacturer to help you determine the best ink. Even once you’ve determined the best ink, do some test prints before full production. Neon-dyed garments are prone to scorching, so watch them go through the dryer to make sure you’ve got the right settings.

Preventing Ink from Bleeding Into Other Colors

QUESTION: When I print, the ink bleeds into the other colors. I started with a 110 mesh and then went to a 230 mesh to stop the bleeding. I’m using a water-based ink. With the 230 mesh, it helped with the bleed, but now I have to print two to three strokes to get the coverage, and by the third stroke I get bleeding again.

ANSWER: By applying multiple strokes, you are doing the same thing as when you used the 110 course mesh. So it really isn’t going to solve the issue. Make sure you get a good underbase down. The underbase gives you a printing surface that allows colors to pop, and give you a smoother printing surface. The underbase doesn’t have to be a good print it just has to block some of that fabric. Put other colors on top of the underbase with a 230 mesh. Course mesh such as 110 should never be used in a multicolor situation unless you are printing on athletic wear.

Avoiding Scorch Marks

QUESTION:. What causes scorch marks on shirts and how can you avoid it?

ANSWER: The simple answer is too much heat causes scorching. To eliminate scorching problems, you need a reliable dryer or flash cure with good temperature controls. Inks cure at relativity the same temperature, but depending on the color and thickness of the shirt, the temperature can vary. Also a white shirt cures at a slightly differently temperature than a black shirt due to the thickness of the ink deposit applied. In general, when curing ink it’s better to err on the hotter side than the cooler side, but a white shirt won’t always tolerate temperatures as high as a black shirt will take.

When you are curing, you have to take into consideration the amount of ink deposit and how hot you can go without overdoing it. In the case of a white T-shirt, 300 to 310 degrees F. is all that you are going to need if you are printing properly. That means you are not printing everything with 110 mesh. On a white T-shirt, if you are printing with 160, 180, or 200 monofilament mesh, you are going to have a fairly thin ink deposit, and it is going to cure beautifully at 290 degrees. So there’s not much of a chance you are going to scorch the shirt there. If you are printing an athletic print with a heavy ink deposit on a black shirt and using a 110, 86, 60, 30 monofilament mesh, the temperature will need to be in the 340 to 350 degree F. range because the ink is thicker and will take a higher temperature to get to the bottom of the ink deposit. Curing is a cumulative process. If you are printing on a very temperature-sensitive fabric like Spandex, you may need to lower the dryer temperature and run the garments through twice. Make sure the ink is reaching the right temperature to cure. You can’t do that by looking for smoke coming off the shirt. Use a probe to accurately test the ink temperature. In general, if you are running the dryer at 290 degrees, you will not scorch the garment.

Rubber Coated Vs. Uncoated Screen Printing Platens

QUESTION: What are the advantages of rubber top verses uncoated screen printing platens?

ANSWER: The reason rubber is added to aluminum platens is to soften the printing surface. This results in a better ink deposit. When a room temperature aluminum platen is used under a flash cure, initially it draws heat away from the shirt, which results in a longer flash time. However, an aluminum platen heats up after repeated use under a flash cure, and it retains that heat. It gets so hot, it may cure the ink in the screen, which you don’t want.

A rubber top helps dissipate the heat more rapidly eliminating this problem. A rubber-coated aluminum platen is more expensive and messier. No matter who you buy it from, the rubber doesn’t stay on the platen forever. Eventually it delaminates so you have to buy replacement rubber and glue it back on yourself. When reapplying it, you have to make sure it doesn’t get air bubbles. You can send your platens back to the manufacturer for resurfacing but that becomes expensive. Regional Supply offers both types: uncoated aluminum and rubber coated. It’s a personal preference. If you would like to buy the replacement rubber please contact Regional Supply.

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