When printing from your computer to an ordinary printer, multiple heads spray the colors cyan, magenta, yellow and black in one pass of paper to create a multi-color image. When screen printing an image, each color has its own screen and the t-shirt or other garment makes a stop at each station on the press.
The actual “screen” is a frame stretched with mesh. Just as it sounds, “mesh” is a cris-cross pattern of thread. “Mesh count” refers to the number of threads per square inch - this is a similar concept to the dpi or lpi you refer to with an ink jet printer. Different meshes and mesh counts accomplish different things on press.
Discharge prints, especially those with fine detail, are among the hardest prints to sustain with high quality. They do have the ability to be very vibrant and hold great detail if the appropriate mesh is used. A particular mesh, known as S-Thread Mesh, allows ink to pass with ease through a greater open area than the standard T-Thread Mesh. The greater opening isn’t created by a lower mesh count (fewer threads per inch), but instead by using much finer and thinner thread.
Normally, in order to gain a good discharge color, the print should soak the shirt 50% of the way through the fabric so that the surface of the garment and the underlying weave is completely discharged. It’s important to note that different garments have different weights and weaves, which require specific mesh counts. The increased open area that S-Thread provides allows ink to soak the shirt, while the higher mesh count improves the detail of the screen printed design.
Using S-Thread with plastisol ink also has its advantages and will help to create a much-improved final screen printed design. As with discharge ink, prints will hold much more detail. However, a separate advantage when using plastisol ink on S-Thread is the outcome of a soft-hand print. The soft-hand print is the result of less squeegee pressure, since the ink is being laid on the surface of the t-shirt and not being driven into the fabric.
Get in contact with your decorating manufacturer to help determine which mesh-count is best and necessary for your custom screen printed design.