Editing Screen printing (section)

== Method ==
[[File:Screen Stretch screen and squeegee and hinge clamps.jpg|thumb|upright|left|Screen printers use a silkscreen, a squeegee, and hinge clamps to screen print their designs.  The ink is forced through the mesh using the rubber squeegee, the hinge clamps keep the screen in place for easy registration.]]
[[File:Silketrykk.svg|thumb|A. Ink. B. Squeegee. C. Image. D. Photo-emulsion. E. Screen. F. Printed image]]
[[File:PrintLayers500px.gif|thumb|upright|Different samples of the printed image]]

A screen is made of a piece of mesh stretched over a frame. The mesh could be made of a [[synthetic polymer]], such as [[nylon]], and a finer and smaller aperture for the mesh would be utilized for a design that requires a higher and more delicate degree of detail. For the mesh to be effective, it must be mounted on a frame and it must be under tension. The frame which holds the mesh could be made of diverse materials, such as wood, metal, or aluminum, depending on the sophistication of the machine or the artisan procedure. The tension of the mesh may be checked by using a tensiometer; a common unit for the measurement of the tension of the mesh is [[Newton (unit)|Newton]] per [[centimeter]] (N/cm).

A stencil is formed by blocking off parts of the screen in the negative image of the design to be printed; that is, the open spaces are where the ink will appear on the substrate.
[[File:Washing out the unexposed portions of the stencil.jpg|thumb|228x228px|Process of washing out the uncured emulsion to have the positive of the design left on the screen]]
[[File:Maker Faire 2008 San Mateo 246.JPG|thumb|right|Screen with exposed image ready to be printed]]
Before printing occurs, the frame and screen must undergo the pre-press process, in which an emulsion is 'scooped' across the mesh. Once this emulsion has dried, it is selectively exposed to ultra-violet light, through a film printed with the required design. This hardens the emulsion in the exposed areas but leaves the unexposed parts soft. They are then washed away using a water spray, leaving behind a clean area in the mesh with the identical shape as the desired image, which will allow passage of ink. It is a positive process.

In fabric printing, the surface supporting the fabric to be printed (commonly referred to as a pallet) is coated with a wide 'pallet tape'. This serves to protect the 'pallet' from any unwanted ink leaking through the screen and potentially staining the 'pallet' or transferring unwanted ink onto the next substrate. The pallet tape is also used to protect the pallet from the usage of glue that keeps the substrate adhered and in place on the pallet. Over time the pallet tape will become covered with lint which it then can be removed, discarded, and replaced by new pallet tape.

Next, the screen and frame are lined with a tape to prevent ink from reaching the edge of the screen and the frame. The type of tape used in for this purpose often depends upon the ink that is to be printed onto the substrate. More aggressive tapes are generally used for UV and water-based inks due to the inks' lower viscosities and greater tendency to creep underneath tape.

The last process in the 'pre-press' is blocking out any unwanted 'pin-holes' in the emulsion. If these holes are left in the emulsion, the ink will continue through and leave unwanted marks. To block out these holes, materials such as tapes, speciality emulsions and 'block-out pens' may be used effectively.

{{ multiple image|align=left|
| image1   = ScreenPrinting500px.gif
| caption1 = How to screen print one image
| image2   = ScreenPrintingColors500px.gif
| caption2 = How to screen print with multiple layers using [[CMYK color model|CMYK]]
}}

The screen is placed atop a substrate. Ink is placed on top of the screen, and a floodbar is used to push the ink through the holes in the mesh. The operator begins with the fill bar at the rear of the screen and behind a reservoir of ink. The operator lifts the screen to prevent contact with the substrate and then using a slight amount of downward force pulls the fill bar to the front of the screen. This effectively fills the mesh openings with ink and moves the ink reservoir to the front of the screen. The operator then uses a [[squeegee]] (rubber blade) to move the mesh down to the substrate and pushes the squeegee to the rear of the screen. The ink that is in the mesh opening is pumped or squeezed by capillary action to the substrate in a controlled and prescribed amount, i.e. the wet ink deposit is proportional to the thickness of the mesh and or stencil. As the squeegee moves toward the rear of the screen the tension of the mesh pulls the mesh up away from the substrate (called snap-off) leaving the ink upon the substrate surface.

There are three common types of screen printing presses: flat-bed, cylinder, and rotary.<ref>{{cite web|url=http://www.screenprinting-technology.org/en/applications/screen-printing-variations/flatbed-cylinder-screen-printing.html|title=Flatbed cylinder screen printing|website=Screenprinting Technology|access-date=8 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180414011500/http://www.screenprinting-technology.org/en/applications/screen-printing-variations/flatbed-cylinder-screen-printing.html|archive-date=14 April 2018}}</ref> A development of screen printing with flat screens from 1963 was to wrap the screen around to form a tube, with the ink supply and squeegee inside the tube. The resulting roller rotates at the same speed as the web in a roll-to-roll machine.  The benefits are high output rates and long rolls of product.  This is the only way to make high-build fully patterned printing/coating as a continuous process, and has been widely used for manufacturing textured wallpapers.

Textile items printed with multi-coloured designs often use a wet on wet technique, or colours dried while on the press, while graphic items are allowed to dry between colours that are then printed with another screen and often in a different colour after the product is re-aligned on the press.

Most screens are ready for re-coating at this stage, but sometimes screens will have to undergo a further step in the reclaiming process called de-hazing. This additional step removes haze or "ghost images" left behind in the screen once the emulsion has been removed. Ghost images tend to faintly outline the open areas of previous stencils, hence the name. They are the result of ink residue trapped in the mesh, often in the knuckles of the mesh (the points where threads cross). A properly cleaned screen will not have any residual traces of the previous image apparent on its surface.