Custom Screen Printing Services from Teca-Print USA
Screen printing is a printing process whereby ink is transferred to a substrate through a mesh, with the exception of places made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh apertures with ink, and then a reverse stroke causes the screen to briefly touch the substrate along a contact line. As the screen springs back after the blade has passed, the ink wets the substrate and is drawn out through the mesh. As each color is printed separately, multiple screens can be utilized to create a multi-colored image or design. There are various terms used for what is essentially the same technique.
Traditionally, the process was known as screen printing or silkscreen printing because of the use of silk. It's also known as serigraph printing or serigraphy. In the current screen-printing process, synthetic threads are utilized - with polyester mesh being the most popular in general use. There are special-use mesh materials of nylon and stainless steel available to the screen-printer, and also several mesh sizes that influence the outcome and appearance of the finished design on the material. TecaPrint uses screen printing in the application of graphics and text on objects, we do not print onto textiles.
How a Screen is made and how the process works
Mesh is stretched across a frame to make a screen. For a design that requires a higher and more delicate degree of detail, the mesh could be made of a synthetic polymer like nylon, with a finer and smaller mesh aperture. The mesh must be fixed on a frame and under tension in order to be effective. Depending on the sophistication of the machine or the artisan method, the frame that holds the mesh could be built of a variety of materials, such as wood or aluminum. A tensiometer can be used to examine the tension of the mesh, and a popular unit for measuring mesh tension is 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.
The frame and screen must go through a pre-press procedure in which an emulsion is ‘scooped’ across the mesh before printing. After the emulsion has dried, it is exposed to ultraviolet light selectively through a film with the required specification. The emulsion hardens in the exposed sections but remains soft in the rest. They are then wiped away with a water spray, leaving a clean patch in the mesh that is the same form as the desired image and allows ink to pass through.
In fabric printing, a wide ‘pallet tape’ is applied to the surface supporting the fabric to be printed (often referred to as a pallet). This protects the ‘pallet’ from any undesirable ink leaking through the screen and staining or transferring unwanted ink onto the next substrate.
The screen and frame are then taped together to prevent ink from reaching the screen’s and frame’s edges. The type of tape used for this purpose is frequently determined by the type of ink that will be printed on the substrate. Because UV and water-based inks have lower viscosities and a greater tendency to creep underneath tape, more aggressive tapes are typically utilized.
The final step in the ‘pre-press’ process is to eliminate any unwanted ‘pin-holes’ in the emulsion. If these holes in the emulsion are not filled, the ink will seep through and produce unwanted marks. Materials such as tapes, specialist emulsions, and ‘block-out pens’ can be used to successfully block out these holes.
The screen is placed on top of a substrate, and Ink is placed on top of the screen. Ink is then pushed through the holes in the mesh by a flood bar. 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 pulls the fill bar to the front of the screen using a small amount of downward force. 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 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.