Screen+Printing

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toc = = = = = = =**Introduction**=


 * Screen Printing** is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A roller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas.

Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface.

Arguably the most versatile of all printing processes screen printing is used to print on a wide variety of substrates such as paper, paperboard, plastics, glass, metals, fabrics, and many other materials. Common products of the screen printing industry include posters, labels, decals, signage, all types of textiles and even some electronic circuit boards. An advantage of screenprinting over other print processes is that the press can print on substrates of any shape, thickness and size.

=History=

Screen printing first appeared in a recognizable form in China during the Song Dynasty (960–1279 AD) Screen printing was largely introduced to Western Europe from Asia sometime in the late 18th century, but did not gain large acceptance or use in Europe until silk mesh was more available for trade from the east and a profitable outlet for the medium discovered. The first patent for screen printing in Europe, was held by Samuel Simon was in 1907. Originally his method was used as a popular method for printing the expensive wall paper, printed on linen, silk, and other fine fabrics, in style at the time.

Early in the 1910s, several printers experimenting with photo-reactive chemicals used the well-known actinic light activated cross linking or hardening traits of potassium, sodium or ammonium Chromate and dichromate chemicals with glues and gelatin compounds. Roy Beck, Charles Peter and Edward Owens studied and experimented with chromic acid salt sensitized emulsions for photo-reactive stencils. This trio of developers would prove to revolutionize the commercial screen printing industry by introducing photo-imaged stencils to the industry, though the acceptance of this method would take many years. Commercial screen printing now uses sensitizers far safer and less toxic than bichromates. Currently there are large selections of pre-sensitized and "user mixed" sensitized emulsion chemicals for creating photo-reactive stencils.

Joseph Ulano founded the industry chemical supplier Ulano and in 1928 created a method of applying a lacquer soluble stencil material to a removable base. This stencil material was cut into shapes, the print areas removed and the remaining material adhered to mesh to create a sharp edged screen stencil.

=Technique=

The first step in the screen printing process is to thinly coat the screen (a fine mesh, tightly stretched over a frame) with a light sensitive photo-emulsion. Then the screen is dried completely in a dark room. Once dry a photo positive is laid on the screen and it is exposed to light hardening the emulsion which is exposed, but leaving the portions protected by the positive soft.

The next step is to rinse the screen with water, washing away the soft portions of the emulsion but leaving the hardened surface in place. This process creates the stencil of the image to be printed. The screen is then taken to the press to be set up for printing and clamped in place to ensure that each image is exactly the same.

The screen is placed atop a substrate such as paper or fabric. Ink is placed on top of the screen, and a fill bar (also known as a floodbar) is used to fill the mesh openings with ink. 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. Additionally, the more colours used, the more stencils and screens needed, and a machine that is able to do so if being done automatically. Once complete the clothing must be run through a dryer or a curing unit to make it impervious to washing, drying and wear and tear.

=Ink Types=

There are many types of inks used in screen printing. Below is a list of some.


 * **Discharge inks** - used to print lighter colours onto dark background fabrics, they work by removing the dye in the garment – this means they leave a much softer texture. They are less graphic in nature than plastisol inks, and exact colours are difficult to control, but especially good for distressed prints and underbasing on dark garments that are to be printed with additional layers of plastisol.


 * **Expanding ink (puff)** - an additive to plastisol inks which raises the print off the garment, creating a 3D feel.


 * **Flocking** - consists of a glue printed onto the fabric and then foil or flock (or other special effect) material is applied for a mirror finish or a velvet touch.


 * **Glitter/Shimmermetallic** - flakes are suspended in the ink base to create this sparkle effect. Usually available in gold or silver but can be mixed to make most colours.Glossa clear base laid over previously printed inks to create a shiny finish.


 * **Metallic** - similar to glitter, but smaller particles suspended in the ink. A glue is printed onto the fabric, then nanoscale fibers applied on it.


 * **Mirrored silver** - a highly reflective, solvent based ink.


 * **Nylobonda** - special ink additive for printing onto technical or waterproof fabrics.


 * **Plastisol** - the most common ink used in commercial garment decoration. Good colour opacity onto dark garments and clear graphic detail with, as the name suggests, a more plasticized texture. This print can be made softer with special additives or heavier by adding extra layers of ink. Plastisol inks require heat (approx. 150°C (300°F) for many inks) to cure the print.


 * **PVC and Phthalate Free** - relatively new breed of ink and printing with the benefits of plastisol but without the two main toxic components. Has a soft texture.


 * **Suede Ink** - Suede is a milky coloured additive that is added to plastisol. With suede additive you can make any colour of plastisol have a suede feel. It is actually a puff blowing agent that does not bubble as much as regular puff ink. The directions vary from manufacturer to manufacturer, but generally up to 50% suede can be added to normal plastisol.


 * **Water-Based inks** - these penetrate the fabric more than the plastisol inks and create a much softer feel. Ideal for printing darker inks onto lighter coloured garments. Also useful for larger area prints where texture is important. Some inks require heat or an added catalyst to make the print permanent.

=Video=

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