Screen printing
Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas 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 a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed. One colour is printed at a time, so several screens can be used to produce a multi-coloured image or design.
Not to be confused with Print Screen or screen painting.
Traditionally, silk was used in the process. Currently, synthetic threads are commonly used. The most popular mesh in general use is made of polyester. There are special-use mesh materials of nylon and stainless steel available to the screen-printer. There are also different types of mesh size which will determine the outcome and look of the finished design on the material.
The technique is used not only for garment printing but for printing on many other substances, including decals, clock and watch faces, balloons, and many other products. Advanced uses include laying down conductors and resistors in multi-layer circuits using thin ceramic layers as the substrate.
Screen printing is more versatile than traditional printing techniques. The surface does not have to be printed under pressure, unlike etching or lithography, and it does not have to be planar. Different inks can be used to work with a variety of materials, such as textiles, ceramics,[13] wood, paper, glass, metal, and plastic. As a result, screen printing is used in many different industries, including:
In screen printing on wafer-based solar photovoltaic (PV) cells, the mesh and buses of silver are printed on the front; furthermore, the buses of silver are printed on the back. Subsequently, aluminum paste is dispensed over the whole surface of the back for passivation and surface reflection. One of the parameters that can vary and can be controlled in screen printing is the thickness of the print. This makes it useful for some of the techniques of printing solar cells, electronics etc.
Solar wafers are becoming thinner and larger, so careful printing is required to maintain a lower breakage rate, though high throughput at the printing stage improves the throughput of the whole cell production line.
Automation[edit]
To print multiple copies of the screen design on garments in an efficient manner, amateur and professional printers usually use a screen printing press, which is a colloquial term as most screen printing machines are vastly different from offset printing presses. Many companies offer simple to sophisticated printing presses. These presses come in one of three types, manual (also referred to as handbench), semi-automatic, and fully automatic. Most printing companies will use one or more semi-automatic or fully automatic machines with manual machines for small runs and sampling.
Whilst manual screen printing can be done with carousels, handbenches (both of which are often referred to colloquially as presses) or even on to tables. Semi- and fully-automatic machines are broken into two main categories; flatbed printers[17] (poster, art printing or other flat substrates) and carousels and oval machines (garments and other apparel, amongst other textiles). Both which are fundamentally similar in terms of automation but differ in areas such as physical footprint and upgrade paths.[18]
These machines are much faster and use either pneumatic pressure generated by air compressors or use electric motors to draw the squeegees, rotate and raise or lower pallets removing much of the manual labour from the task and use UV for instant image curing - resulting in significant reductions in operator fatigue as well as more consistent results.[19]
Printed circuit boards (PCB)[edit]
In electronic design automation, the silk screen is part of the layer stack of the printed circuit board (PCB), and the top and bottom sides are described in individual Gerber files like any other layers (such as the copper and solder-stop layers).[20] Typical names for these service print overlays include tSilk/bSilk aka PLC/PLS[21][nb 1] or TSK/BSK (EAGLE), F.SilkS/B.SilkS (KiCad), PosiTop/PosiBot (TARGET), silkTop/silkBottom (Fritzing), SST/SSB (OrCAD), ST.PHO/SB.PHO (PADS), SEVS/SERS (WEdirekt)[22] or GTO/GBO (Gerber and many others[23]).
