Sheetfed+Lithography+Printing

**__Sheetfed Lithography Printing__**

**__WHAT IS SHEETFED LITHOGRAPHY PRINTING?__** Sheetfed lithography is a printing method in which images are placed on the desired substrate ( such as paper, previously cut to size) using plates, fountain solution and rollers. This is the most commonly used method for printing short-run products such as flyers, brochures, newspapers, manuals and posters.

**__THE HISTORY OF LITHOGRAPHY__** Lithography was invented by Alois Senefelder in 1798. Alois tried to produce his own copperplate engravings and since, making reverse images in copper wasn't an easy or cost effective process, Alois decided to practice his engravings on slabs of Bavarian limestone. The history of lithography happened in four major steps
 * The invention and early use of the process
 * The introduction of photography to the process
 * The addition of the offset press to the process
 * The revolution of the lithographic plate

Alois frequently made mistakes so he needed a liquid that could be used on the genuine copper plates to correct them. This "correction fluid" was in a liquid form that consisted of wax, soap, lampblack and rain water. These two materials, limestone and the correction fluid became the primary ingredients of Lithography. In 1817, he designed a press that featured automatic dampening and inking of the plate. He simply drew one picture on the stone which was then used to reproduce many copies of the identical picture onto paper. Because lithography was a very easy method to produce, this process became very popular throughout the world. For over a century and a half, lithography was a very small segment of the printing industry, used mainly by artists to produce their prints. However, during the very late 1800's and throughout the twentieth century, the advancements in technology turned lithography into the most popular form of printing in the USA. In 1875, Robert Barclay of England created the first lithography press that printed onto tin. Then in 1903, Ira Washington Rubel of Nutley, New Jersey, accidentally discovered that whenever a sheet of paper was not fed into the press, the stone printed the image onto the rubber-covered roller. Then once a sheet of paper was fed into the press, the sheet came out with an image on both sides. Rubel noticed that the image on the back of the sheet (that came off the rubber roller) was much clearer than the image that came off the stone. This discovery led to the creation of the first offset press to print onto paper.

There were still several disadvantages of that first offset press: The stones were difficult to store, heavy, and they couldn't be bent around the cylinder of the rotary press. This necessitated a change in medium: the metal plate. These offered more versatility with use, as they could be curved around a cylinder, were much lighter, and the metal was more readily available. Alphonse Luis Poitevin created the first coated metal plates using potassium bicromate and albumin, which was sensitive to light. Then, in the 1940's, the method of pre-coating plates was established. The disadvantage of these wast that the plates were paper based, so not feasible for long runs. In 1951, 3M discovered the first practical pre-coated aluminum plate. This was a new subtractive type, opposite of the previous additive process. A Japanese firm, Toray, discovered in the 1990's the first effective waterless lithographic plate, in which the non-image area repelled ink, while the image area attracted it. This process required that the ink rollers remained cold, otherwise the ink would stick to the non-image areas. **__PROCESS__** Water and ink are a very important part in the printing process. If the water and ink are not properly balanced, a variety of problems can affect the overall quality of the finished product such as scumming, catchup, trapping problems and ink density. Fountain solution is water based and the major component in the process that dampens the non-imaged area of the plate to stop the ink from lifting. This helps cool down the press and helps keep the ink stable so it can dry fast. Acid based solutions are most commonly used because of the superior protection of the printing plate, lower dot grains and adds to longer plate life. Water and ink are applied to the printing plate, which is mounted on a roller. The ink clings to the part of the plate that contains the design elements and the water is applied to the white space portion of the paper. Oil is mixed with the ink to make sure that the ink and water repel one another to ensure that there isn’t any smearing or blotchiness on the finished product. The plate cylinder transfers the image onto the offset cylinder, which then transfers the image onto the paper. If you are printing in colour, this process is repeated for each colour (black, cyan, magenta, yellow) before the printing process is complete. ** __USE__ ** media type="youtube" key="cGyKdvT1fV4" width="423" height="350" align="right" Today, there are two methods of offset printing: Sheetfed and [|Web-fed]. The difference between these two is at which point in the process the paper is cut. In webfed printing, it is printed on a continuous roll, but with sheetfed printing, it is cut into the proper sheet size before printing. According to the following chart, Offset Lithography printing lead the pack in distribution: Printing, Publishing, and Packaging ||
 * ~ Distribution by Process:
 * =  ||= 1995 ||= 2025* ||
 * = Offset Lithography ||= 47% ||= 30% ||
 * = Water-based ||= 46% ||= 20% ||
 * = Waterless ||= 1% ||= 10% ||
 * = Gravure ||= 20% ||= 20% ||
 * = Flexography ||= 18% ||= 20% ||
 * = Letterpress ||= 7% ||= 2% ||
 * = Screen & Other plate Systems ||= 3% ||= 2% ||
 * = Electronic, Ink Jet, etc. (non plate) ||= 5% ||= 26% ||
 * = *projections by Mike Bruno, an Industry consultant ||

**__ADVANTAGES__** The advantages compared to other printing methods include:
 * //Consistently High Quality Image// – the rubber blanket (rollers) conform to the printing surface producing clean and sharp images.
 * //Lack of Impressions// – other printing methods leave raised or indented impressions on the paper, rings of ink and serrated edges. Lithographic printing does not.
 * // Quick and easy production of printing plates. //
 * //Printing Plates Have a Longer Life Span// – this is due to the plates not having direct contact with the printing surface.
 * //Cost Effective// - when printing a large quantity of the same product.
 * //Speed// - quick and efficient due to printing on both sides of the printing surface simultaneously.
 * //Versatility// - doesn't just print on paper. Presses print on other surfaces such as cloth, leather, metal, plastic and wood.

**__DISADVANTAGES__** The disadvantages compared to other printing methods include: >  __**ADDITIONAL RESOURCES**__ [] []  [] __ http://www.pneac.org/printprocesses/lithography/ __
 * //Plates can Become Sensitive// – because of the chemical oxidation, the plates become rather sensitive.
 * //Time Constraints// – takes time to set-up the printing process (developing the plates).
 * //Expensive When Producing Small Jobs// - this is quite an expensive printing method when printing small quantities.
 * //Colour Variation// - this is due to the water/ink mixture.
 * //Paper can stretch due to dampening.//
 * //Environmental// - has the possibility to release air contaminants that will eventually enter the atmosphere.