History

Lithography was initially created to be an inexpensive method of reproducing artwork. This printing process was limited to use on flat, porous surfaces because the printing plates were produced from limestone. In fact, the word "lithograph" historically means "an image from stone" or "printed from stone". Tin cans were popular packaging materials in the 19th century, but transfer technologies were required before the lithographic process could be used to print on the tin.

The first rotary offset lithographic printing press was created in England and patented in 1875 by Robert Barclay. This development combined mid-19th century transfer printing technologies and Richard March Hoe's 1843 rotary printing press—a press that used a metal cylinder instead of a flat stone. The offset cylinder was covered with specially treated cardboard that transferred the printed image from the stone to the surface of the metal. Later, the cardboard covering of the offset cylinder was changed to rubber, which is still the most commonly used material.

As the 19th century closed and photography became popular, many lithographic firms went out of business. Photoengraving, a process that used halftone technology instead of illustration, became the primary aesthetic of the era. Many printers, including Ira Washington Rubel of New Jersey, were using the low-cost lithograph process to produce copies of photographs and books. Rubel discovered in 1901—by forgetting to load a sheet—that printing from the rubber roller, instead of the metal, made the printed page clearer and sharper. After further refinement, the Potter Press printing Company in New York produced a press in 1903. By 1907 the Rubel offset press was in use in San Francisco.

The Harris Automatic Press Company also created a similar press around the same time. Charles and Albert Harris modeled their press "on a rotary letter press machine".

Newspaper publisher Staley T. McBrayer invented the Vanguard web offset press for newspaper printing, which he unveiled in 1954 in Fort Worth, Texas.

Modern offset printing

One of the important functions in the printing process is prepress production. This stage makes sure that all files are correctly processed in preparation for printing. This includes converting to the proper CMYK color model, finalizing the files, and creating plates for each color of the job to be run on the press.

Offset lithography is one of the most common ways of creating printed materials. A few of its common applications include: newspapers, magazines, brochures, stationery, and books. Compared to other printing methods, offset printing is best suited for economically producing large volumes of high quality prints in a manner that requires little maintenance. Many modern offset presses use computer-to-plate systems as opposed to the older computer-to-film work flows, which further increases their quality.

There are 2 types of offset printing: wet offset and waterless offset. Wet-offset lithography need to manage a complex mix of wetting fluids and ink. The water used in wet offset is added to several chemicals to make the wet solution suitable and efficent for the plate. The waterless offset, such as Codimag, are eco-friendly because it doesn't need to consume water. This is an advantage for all the processes; thanks to the absence of chemical balance the printing is stable, faster and has higher definition.

Advantages of offset printing compared to other printing methods include:

• consistent high image quality. Offset printing produces sharp and clean images and type more easily than, for example, letterpress printing; this is because the rubber blanket conforms to the texture of the printing surface;
• quick and easy production of printing plates;
  longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface. Properly developed plates used with optimized inks and
• fountain solution may achieve run lengths of more than a million impressions;
• cost. Offset printing is the cheapest method for producing high quality prints in commercial printing quantities;
• ability to adjust the amount of ink on the fountain roller with screw keys. Most commonly, a metal blade controls the amount of ink transferred from the ink trough to the fountain roller. By adjusting the screws, the operator alters the gap between the blade and the fountain roller, increasing or decreasing the amount of ink applied to the roller in certain areas. This consequently modifies the density of the colour in the respective area of the image. On older machines one adjusts the screws manually, but on modern machines the screw keys are operated electronically by the printer controlling the machine, enabling a much more precise result.

Disadvantages of offset printing compared to other printing methods include:

• slightly inferior image quality compared to rotogravure or photogravure printing;
• propensity for anodized aluminum printing plates to become sensitive (due to chemical oxidation) and print in non-image–background areas when developed plates are not cared for properly;
• time and cost associated with producing plates and printing press setup. As a result, very small quantity printing jobs may now use digital offset machines.
• Every printing technology has its own identifying marks, and offset printing is no exception. In text reproduction, the type edges are sharp and have clear outlines. The paper surrounding the ink dots is usually unprinted. The halftone dots can be hexagonal though there are different screening methods.

Process variations

Several variations of the printing process exist:

Blanket-to-blanket
A printing method in which both sides of a sheet of paper are printed simultaneously, with two blanket cylinders per colour; a sheet of paper is passed between them, with each cylinder printing on one side of it. Blanket-to-blanket presses are considered a perfecting press because they print on both sides of the sheet at the same time. There is no impression cylinder because the opposite blanket cylinders act as impression cylinders to each other during print production. This method is most used on offset presses designed for envelope printing. There are also two plate cylinders per colour on the press;

Blanket-to-steel
A printing method similar to a sheet offset press; except that the plate and cylinder pressures are quite precise. Actual squeeze between plate and blanket cylinder is optimal at 0.005″; as is the squeeze or pressure between the blanket cylinder and the substrate. Blanket-to-steel presses are considered one-color presses. In order to print the reverse side, the web is turned over between printing units by means of turning bars. The method can be used to print business forms, computer letters and direct mail advertising;

Variable-size printing
A printing process that uses removable printing units, inserts, or cassettes for one-sided and blanket-to-blanket two-sided printing;

Keyless offset
A printing process that is based on the concept of using fresh ink for each revolution by removing residual inks on the inking drum after each revolution. It is suitable for printing newspapers;

Dry offset printing
A printing process which uses a metal backed photopolymer relief plate, similar to a letterpress plate, but, unlike letterpress printing where the ink is transferred directly from the plate to the substrate, in dry offset printing the ink is transferred to a rubber blanket before being transferred to the substrate. This method is used for printing on injection moulded rigid plastic buckets, tubs, cups and flowerpots.

Plates

Materials
The plates used in offset printing are thin, flexible, and usually larger than the paper size to be printed. Two main materials are used:

• Metal plates, usually aluminum, although sometimes they are made of multimetal, paper, or plastic
• Polyester plates, which are much cheaper and can be used in place of aluminum plates for smaller formats or medium quality jobs, as their dimensional stability is lower.

Computer-to-plate
Computer-to-plate (CTP) is a newer technology which replaced computer-to-film (CTF) technology, and that allows the imaging of metal or polyester plates without the use of film. By eliminating the stripping, compositing, and traditional plate making processes, CTP altered the printing industry, which led to reduced prepress times, lower costs of labor, and improved print quality.

Most CTP systems use thermal CTP or violet technologies. Both technologies have the same characteristics in term of quality and plate durability (for longer runs). However, the violet CTP systems are often cheaper than thermal ones, and thermal CTP systems do not need to be operated under yellow light.

Thermal CTP involves the use of thermal lasers to expose or remove areas of coating while the plate is being imaged. This depends on whether the plate is negative, or positive working. These lasers are generally at a wavelength of 830 nm, but vary in their energy usage depending on whether they are used to expose or ablate material. Violet CTP lasers have a much shorter wavelength, 405 nm–410 nm. Violet CTP is "based on emulsion tuned to visible light exposure".

Another process is computer-to-conventional plate (CTCP) system in which conventional offset plates can be exposed, making it an economical option.

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Offset printing services

Print business card types:

• Laminate
• Simple
• Velvet
• Linen
• PVC
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Printing Types:

• Writing envelope and linen
• Writing tract and glass
• Shaped forms
• Office set
• Brochure
• envelope
• Catalog
• poster
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