Prepress
Prepress (or make-ready) is the name given to the point in the screen printing process (and other printing processes) where the art and screen are given a final check, the stock or substrate is prepared and arranged for printing, the ink has been mixed and thinned, and the drying system and items needed during the print run are assembled close at hand and ready to use. It is important to carry out these prepress activities before the ink hits the screen, otherwise delays in printing will result, often stopping the print process or requiring cleaning of the screen.
ART & SCREEN CHECK
Using the film as a guide, a final inspection of the stencil should
be made. Pay special attention to pinholes, or lines caused by film
edges on the stencil, or any other imperfections in the stencil or
image. These should be touched up before the screen is put in the press.
Blockout and Touch-up
Touch-up or block-out is applied to the underside of the screen using a brush for spots, or a small flat spreader (old squeegee or sign vinyl applicators work great and clean easily) for larger areas. If touched up on the top-side of a screen, you risk wearing nicks or gouges in the squeegee rubber.
Commercial blockouts are available from most suppliers and are designed
for solvent based inks using water soluble stencil systems. When using
waterbase inks, direct emulsion can be used as blockout, but it must be
dried and re-exposed to harden it for printing. A lacquer blockout
works well for waterbase, and does not require curing, but does require
more aggressive removal during the reclaiming process.
Ensure that the screen is in good shape, with no serious rips or holes
that will let loose during the print run. If there is any doubt that a
stencil is suspect, or the image is flawed, re-shoot the screen. It
saves time, money, and frustration if the problem is fixed at this
point of the process.
Taping off screen gutters along the sides of the frame, or around
images, can be carried out at this time, or if it's easier, tape the
screen once it is in the press. Use thin packing tape, never paper or
masking tape. A good tape job makes production printing easier because
it controls where the ink goes, and makes clean-up a snap. On long
production runs, especially with waterbase, or when you know a stock
edge is going to wear on the screen, a line of tape on the underside
can protect the stencil from wearing thin from squeegee pressure along
an edge. Make sure the tape goes on flat with no creases or folds.
Stock Prep
Whatever the stock or substrate is, it needs to be prepared for printing. This includes cutting down in size from master sheet to press sheet size, or may mean removing wrapping or packaging, or cleaning dust or other residue from surfaces. The stock should be prearranged or stacked on a convenient table close to the press.
