Screen Printing Explained in 6 "Easy" Steps
1. Screen Prep
To achieve a good print on your substrate, your screen(s) need to be absolutely free of debris. Even a new screen could use a good degreasing. Just because a screen is brand new to you, doesn't mean it didn't sit in a warehouse somewhere and collect dust. It is good practice to degrease and rinse all screens before coating them with emulsion.
We like to use S Green Degreaser - Dehazer (All in One) for prep and reclaiming. S Green comes in gel form, so it sits nicely on the screen.
Use a scrub brush to apply the degreaser and let it sit for a few minutes before washing away with pressurized water. After ensuring the screen is completely clean let it air dry or pat it down with newspaper.
Probably the most important step in Screen Printing is artwork, bad artwork will never look good on a substrate. If it looks pixilated on your screen it will look even worse on your product. The best way to ensure you have a crisp design is to use vector art. If possible, convert your design into vector format. Of course, certain images will not be able to be converted, but if at all possible, USE VECTOR ART.
To get your artwork burned into your screen you need to first print it to a transparent film. We like to use 13" x 19" inkjet waterproof films. They give us the space we need and allow for halftones to be printed on them. If your artwork has halftones in it, you will not get results by printing to a laser velum. Laser printers cannot print halftones.
Depending on how you burn your screen you may want to mirror the image before printing. We burn our films straight to the print side of the screen without mirroring.
There are 2 sides to a screen: the print side and the squeegee side. These will be explained in the next step.
*It is very important to add registration marks and center lines to your work. Even if it is just one screen it only takes a second.
3. Screen Creation
After ensuring your screen is dry, the next step is to burn your image into it. Before you can burn your image, you must coat your screen with photo emulsion. There are many different types of emulsions on the market and it very important to research which type is best for you.
We mentioned that a screen has two sides to it: the print side and the squeegee side. The print side is the side that touches your substrate and the squeegee side is the side where the ink is held. When creating your screen, you want to make sure to coat both sides with emulsion. This helps to ensure your image doesn't wash out. Make sure not to overdo the coat though as the more emulsion you put on the screen the harder it will be to wash out. The more water pressure you use, the easier it is to blow out your image. We recommend one pass for each side. To get a beautiful even stroke on your screen use a scoop coater. Scoop coaters are made specifically for this process.
After you have a smooth coat on both sides of the screen leave it to dry. There are a lot of variables that can affect dry times, but we find 1-2 hours is usually good. If you aren't sure your screen is dry enough, touch a corner (away from where the image will be) and see if it is sticky. If it seems sticky let it dry more. You don't want your film to stick to your screen when burning as this can create problems when washing out.
The next step in creating a screen is to burn the image in. We like to tape our film to our light source, but you can tape the film to the screen as well. Make sure to clean the glass of your light source before taping your film to it.
Place the screen on your light source and expose it to light. Your time will vary depending on your light source and the type of emulsion you used. Make sure to follow recommended times or even purchase an emulsion exposure chart. You don't want to over or under expose your screen. This will cause problems when washing out.
With a perfectly exposed screen it is now time to wash the image out. Everything that light touched around your artwork will have hardened through exposure. Using LIGHT pressure, coat the squeegee side with water then turn the screen over. Still using LIGHT pressure, spray the squeegee side down and let the screen sit for 1-2 minutes. This gives the emulsion time to soak up the water and makes it easier to wash out. If you just keep spraying you could blow the image out. Lightly spray the screen until the image is visible in your screen.
Now that your image is burned into your screen it's time to let it dry.
If it is sunny outside USE THE SUN it helps to harden the emulsion and helps the screen dry really fast (just be careful of dirt) otherwise, use some fans to speed up the process.
Take time to inspect your screen after drying to inspect for particulates and make sure to wipe any out. The last thing you want is extras in your ink.
You took the time to add registration marks or at least center lines to your artwork right? Good job! Take your film and tape it to the platen of your press. We like to keep center lines drawn on ours to make the alignment easier.
Using masking tape (or something similar) block off all areas the emulsion didn't cover on your screen. Make sure to leave the registration marks uncovered. Once complete, load your screen into the registration gate of your screen press and lock it in place. Line up the registration marks in the screen to the registration marks on the film that is tapped to the platen. Once everything is aligned you are ready to print.
There are two different methods of printing through a screen: push and pull. When pushing a print you will flood the screen by pulling the ink and when pulling the print you will flood by pushing it. I prefer a push print (most of the time) so, this step will describe that process.
"Flashing" is the process of heating up ink until it dries, but is not "cured" all the way through.
"Curing" is the process of heating up the ink until it is completely dry. Plastisol needs an internal temperature of 300 - 330º F (143-166º C) to be fully cured
Whether you are using water based inks or plastisol, you want to stir the ink up to get it flowing. Some plastisol inks will need to have a reducer added to make them creamier. When you have reached a consistency that flows well and isn't hard to stir, apply it to the squeegee side of the screen. DO NOT over apply the ink. Plastisol especially, will go a long way when printing.
Before pushing ink onto your substrate, you want to ensure that there will be an even amount of ink on it. The way this is achieved is by flooding your screen. With your squeegee in hand, pull back on the ink until you have an even coat over your image. Then providing an equal amount of pressure and speed, push the ink through the screen onto your substrate. Always do a second pass WITHOUT FLOODING to ensure all of your ink has left the screen.
If you are satisfied with the way the print looks you can go ahead and flash/cure it otherwise, do another pass if you need it. Be careful not to overdo the print as you don't want a product that feels bad. If you have more than one color/ screen to print make sure to flash in between each print and cure the last one.
Your creation is complete!
Great job, but you're not done yet.
You still have to clean up your mess and reclaim your screens.
The first thing you want to do is cart off the unused ink from your screen and put it back into its container. Ink is expensive and there is no need to waste it. You also want to clean up immediately after the job has been printed to ensure particulates aren't put back in your ink. Make sure to get as much of the ink of the screen as possible as this helps the cleaning process.
Platisol is basically liquid plastic and it doesn't break down very easily. As long as you took the time to cart your ink off as much as possible you won't struggle with the reclaiming process. Make sure to remove all of the tape from your screen before spraying any chemicals on it.
There are a few different chemicals you can use to clean up plastisol, but the cheapest we have found is mineral spirits. It is easily found in stores and can be purchased in a pinch. Spray a rag (or junk shirt) with mineral spirits and wipe the squeegee side of the screen down until the excess amount of ink is gone. Do the same for the print side of the screen.
The next step is to remove the emulsion form the screen. There are basically two industry standards: spraying the screen with emulsion remover and using a dip tank. Using emulsion remover can require extra steps, so we like to use a dip tank. The chemicals we use in our dip tank also contain an ink degradent which helps with removing the image from the screen. We leave our screens in the dip tank for 15-30 minutes.
After the screens have sat long enough it is time to spray off the emulsion. The best way to remove all of the emulsion is to use a pressure washer. Even with a good dip tank, emulsion can tend to stick. Using high pressure make sure to remove all emulsion and any excess ink that may be present.
Scrub the screen with degreaser / dehazer and water. Make sure to coat both sides, working it in and scrubbing until you can't see the design in the screen. When you feel your screen is free of the image, let it sit for 15 minutes. Use high pressure to clean the screen thoroughly. If there is still an image left in the screen, repeat this process.
If not, leave the screen to dry.
*Sometimes screens may need several cleanings to get rid of the "ghost" image.
That's it, that's all it takes to make a shirt.
Just a few simple steps!