How to Screen Print: Detail Process
Prepare your artwork - To print a shirt you of course have to have something TO print onto the shirt. Whether you create it, you copy it, or a customer brings it to you, screen printing all starts with artwork. When thinking about artwork keep in mind, garbage in = garbage out, so the better quality of artwork you start out with the better screen prints you are going to get on your t-shirt.
When you screen print a shirt you print one color at a time, so if you're artwork is multiple colors, you need a way to separate those colors so you can create different screens for your design.
Most screen printers use CorelDraw X5 or Photoshop as their artwork program in order to separate and cleanup the artwork for screen printing.
Print out your film positives - Once your artwork is created and separated, the next step is creating a film positive in order to burn your image into a silk screen. A film positive transparency is basically like an overhead transparency (remember those from back in the day), whatever you want to print on the t-shirt, you print out in black ink on the film positive.
There are many ways to make film positives whether it’s going to your local print shop, hand drawing your image, or purchasing a compatible printer for use at home. It's very important for your film positive to be as black a possible, we'll explain why in the next step...
Expose your image into a screen - Ok, you have the art, you printed your films, now it's time to make the screen. A screen printing frame consists of a wood or aluminum frame stretched with polyester mesh on it. The mesh holds the image onto the screen and lets ink pass through when you by pressing it with a squeegee.
The mesh holds the image by using a film or emulsion that is coated onto the mesh. Before you coat the mesh, it is cleaned with a special screen printing degreaser so that the emulsion sticks to it.
Emulsion is light sensitive, so when you coat the screen it is typically done in a darkroom that has special light safe yellow bulbs in it. After the screen is coated and dried, you get your film positive, align it to the screen, and expose it with a screen printing exposure unit or light for an allotted amount of time.
The screen hardens to light but the positive or black area of the film blocks the light from reaching the emulsion, this leaves that area of the emulsion unexposed or soft.
This is why it's so important to ensure you have a very black film, if your film is only partially black, it will let light in during the exposure process.
After the screen is exposed, simply rinse it with water, the soft part that was not exposed rinses out leaving that area of the mesh open so you can print ink through it! The exposure process is complete and you're almost ready to start screen printing shirts!
Set up your screen printing press - Alight, it's almost go time, but before you start printing you need to setup the screens on your screen printing press. A screen printing press consists of a base that holds you printing platen and a number of color arms (depending on how many colors your press is.) A manual press can be as small as a 1 color 1 station, or as large an 8 color 8 station.
Of course if you have more color arms you have the ability to print more colors at the shirt at one time, likewise if you have a higher amount of printing stations, you can print faster.
Right before you clamp your screens into your press you tape off the edges of your frame with screen tape which helps keep the screen and shirt clean during printing. If you are printing a multiple color job, you'll need to register the colors together in so that they match correctly when you print all of them at once on the shirt.
Using a press with joystick registration or micro registration is extremely helpful when printing fine detail multiple color jobs. Once you think your screens are in registration, you complete a test print typically on an old shirt or a printing test pellon to ensure everything lines up.
Take that and then print 40 shirts per hour on a small press or 100 shirts an hour on a larger screen printing press and you're making $120-$400 per hour! Not too bad for pushing ink huh!
There are a few things to keep in mind during the printing process. First is called flashing, if you are printing on dark garments where you have to use a white under base under color ink or if you have ink touching other ink, you'll need to flash dryer in order to cure/set the ink giving you the ability to print another color on top of your first layer.
Flashing only takes about 10-15 seconds, but it does slow the process down, typically shirts that need flashes are sold for more due to the increased production time. Once the shirt is printed it needs to cure in order for the ink to stay set into the garment.
Ink cures at 320 degrees through the entire ink film. To cure a shirt you can use an oven or heat gun (for the hobbyists), a flash dryer, or optimally a conveyor dryer.
It's important to ensure your ink is cured because if it is not cured thoroughly, it will wash out of the shirt. To help ensure your ink is cured you can use a laser temp gun to measure the temperature of the ink while it is being cured.
The shirts are printed and it's time to clean up - Many people think screen printing is a messy process, it's only super messy if you make it and don't clean up after yourself. Messy is as messy does right. Cleanup is pretty easy to do. First save as much ink as possible by using an ink cleanup card to scrape it out of the screen and back into your ink container.
Depending on the type of ink you use to print with you should use a screen printing screen wash to clean the ink out of your screen and to wipe down your press. If you are going to print more shirts in the future with the same design you can choose to save your screen for future use.
You can also use your screen again for a different design by using emulsion remover and a power sprayer to take the image off the screen so you can start the process over again!