SCREEN PRINTING ( Unit-4)

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. It is also known as silk screen, serigraphy, and serigraph printing.

There are various terms used for what is essentially the same technique. Traditionally the process was called screen printing or silkscreen printing because silk was used in the process. Currently, synthetic threads are commonly used in the screen printing process. 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.

Credit is generally given to the artist Andy Warhol for popularizing screen printing identified as serigraphy, in the United States. Warhol is particularly identified with his 1962 depiction of actress Marilyn Monroe screen printed in garish colors.

American entrepreneur, artist and inventor Michael Vasilantone would start to use, develop, and sell a rotary multicolor garment screen printing machine in 1960. Vasilantone would later file for patent on his invention in 1967 granted number 3,427,964 on February 18, 1969. The original rotary machine was manufactured to print logos and team information on bowling garments but soon directed to the new fad of printing on t-shirts. The Vasilantone patent was licensed by multiple manufacturers, the resulting production and boom in printed t-shirts made the rotary garment screen printing machine the most popular device for screen printing in the industry. Screen printing on garments currently accounts for over half of the screen printing activity in the United States.

In June 1986, Marc Tartaglia, Marc Tartaglia Jr. and Michael Tartaglia created a silk screening device which is defined in its US Patent Document as, "Multi-colored designs are applied on a plurality of textile fabric or sheet materials with a silk screen printer having seven platens arranged in two horizontal rows below a longitudinal heater which is movable across either row." This invention received the patent number 4,671,174 on June 9, 1987, however the patent no longer exists.

Graphic screen printing is widely used today to create many mass or large batch produced graphics, such as posters or display stands. Full color prints can be created by printing in CMYK (cyan, magenta, yellow and black. Screen printing is often preferred over other processes such as dye sublimation or inkjet printing because of its low cost and ability to print on many types of media.

Screen printing lends itself well to printing on canvas. Andy Warhol, Rob Ryan, Blex bolex, Arthur Okamura, Robert Rauschenberg, Harry Gottlieb, and many other artists have used screen printing as an expression of creativity and artistic vision.

HOW IT WORKS - 
A screen is made of a piece of porous, finely woven fabric called mesh stretched over a frame of aluminium or wood. Originally human hair was used, then silk was woven to make a screen mesh; currently most mesh is woven of man-made materials such as steel, nylon, and polyester. Areas of the screen are blocked off with a non-permeable material to form a stencil, which is a negative of the image to be printed; that is, the open spaces are where the ink will appear.

Before ink is applied to the screen, the screen and frame must go through a process referred to as 'pre-press'. In this process, an emulsion is 'scooped' across the mesh and the 'exposure unit' burns away the unnecessary emulsion leaving behind a clean area in the mesh with the identical shape as the desired image. The surface (commonly referred to as a pallet) that the substrate will be printed against is coated with a wide 'pallet tape'. This serves to protect the 'pallet' from any unwanted ink leaking through the substrate and potentially staining the 'pallet' or transferring unwanted ink onto the next substrate. Next, the screen and frame are lined with a tape. The type of tape used in for this purpose often depends upon the ink that is to be printed onto the substrate. 

With most plastisol inks and sometimes UV and water-based inks, Split Tape is recommended for its clean removability. However, if the user needs a more aggressive adhesive tape (often requiring cleaning adhesive residue), tapes such as Blue R-Tape and masking tape are recommended. These aggressive tapes are generally used for UV and water-based inks due to the inks' lower viscosities. 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, specialty emulsions and 'block-out pens' may be used effectively.

Types of screen printing
1. Flat bed- manual process, visiting card, greeting cards, letter pad, matrimonial cards etc.
2. Cylinder – sheet fed or web fed press with hot air dryers
3. Rotary- used for printing on garments

Speed- we can print 300 feet per minute or 4000 impression per hour. 1800 t-shirt printed in on hour.

Advantage
1. Cost effective printing
2. Can print any surface, flat or odd shaped.
3. Can use any color, transparent, glossy
4. Can use enamel paints, plastic colors, fluorescent or textile colors.

LIMITS
We cannot use halftone or process colors.  Amount of ink applied is far greater than letter press or offset press.


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