I wanted to know how t-shirts were printed, so I checked out YouTube (an incredible resource for short “how to” films). I assumed that screen printing and heat transfers would be the major methods for printing on t-shirts, and the YouTube videos confirmed my expectations.
Screen Printing T-Shirts
A screen printing press looks a bit like an octopus. It has multiple arms, each supporting a single screen. Although one name for the process is “silkscreen,” the screens are now usually nylon or metal. Each screen prints one color on the t-shirt, and each color station includes a flat, ironing-board-like support for the shirt. You place the t-shirt around (as opposed to just on top of) this support as though you were “dressing” the support panel. This places only one layer of fabric on top of the support and therefore keeps the fabric absolutely flat once the screen has been lowered.
Once the screen is on top of the fabric, you can pour the thick ink mixture onto the screen and draw the rubber squeegie across the mesh, forcing the ink through the open areas of the screen (but not through the areas masked off by the design). Once this step is complete, the ink must dry. (Usually the solvent is flash dried with intense heat, although UV inks are now often used in screen printing, and these dry instantly upon exposure to ultraviolet light.)
To step back a bit in the screen printing process, the masks used to block out certain areas of the design while allowing ink to pass through other areas are prepared in the following way.
- You create the design on a computer using a raster art (bit-mapped) or vector art (line art) program, such as Photoshop or Illustrator. Alternatively, you can scan an image and save it in Photoshop. For this process, you need a positive (rather than negative) image.
- A light sensitive emulsion is slathered across the bottom of a screen stretched over a wood or metal frame.
- The art (laser printed in black toner on clear acetate) is placed on the glass of a lightbox. The stretched screen with the light-sensitive emulsion is placed over the art
- The intense light within the light box exposes the emulsion on the screen.
- The screen is then hosed down with water. The water washes away the liquid from the area that had been blocked by the artwork. The non-image areas of emulsion, which had been hardened through exposure to the light, do not wash wash away.
- Then the t-shirt can be printed, as noted above (one color per screen, consecutively, with each color in register with the others).
Benefits of Screen Printing T-Shirts
Screen printing ink is thick and saturated. You can print brilliant colors on fabric, and the t-shirts will withstand many washing cycles without the printed art showing any wear and tear.
T-Shirt Heat Transfers
Both laser printing and inkjet printing can be used to create artwork that can be fused to a t-shirt. Special transfer paper (designed for either inkjet printing or laser printing) is used in the process. The operator prints the graphics and type backwards (in a mirror image) so it will be “right-reading” once transferred to the t-shirt. Using heat and pressure (a hot iron against a t-shirt placed on a rigid surface) the operator can transfer the image from the carrier sheet to the fabric of the shirt.
Screen Printing vs. Heat Transfers
It has always been my experience that custom screen printing allows for thicker ink deposits with brighter colors, as well as more durable designs. That said, screen printing is not cost-effective for short print runs since preparation for a screen printing run takes a lot of time.
In addition, many t-shirt printers can only apply one or two colors to a t-shirt with custom screen printing. However, the more skilled screen printers can actually print 4-color process work (including halftone images). It’s just more tricky to produce this level of detail on fabric using the thicker screen printing inks, so the image will not be as precise as a sample of 4-color offset lithography on paper. In addition, some screen printers have the skill to print on darker colored fabrics while others prefer to only print on white t-shirts.
Heat transfers (laser or inkjet) are cheaper than screen printing for shorter runs since they do not require set-up time. It’s also easier to transfer highly detailed artwork to the t-shirt, since the transfer actually sits up on the surface of the shirt rather than seeping into the fibers of the fabric.
However, it has been my experience that heat transfers are not as durable as screen printed t-shirts, and the inks are not as brilliant as custom screen printing inks.
The Future: Direct to Garment Inkjet Printing
One final method is gaining traction as the technology improves. It is called “direct to garment printing.” The process omits the transfer sheet. Instead, inkjet or dye sublimation equipment prints the artwork directly into the fibers of the garment. This means the image is less likely to crack than a heat transfer image sitting on the top of the t-shirt fabric. And unlike screen printing, this digital process can be infinitely variable. You can print a different image on each t-shirt.
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on Monday, October 1st, 2012 at 3:27 pm and is filed under Screen Printing, T-Shirts.
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