Offset printing is a commonly used printing technique in which the injected image is transferred (or "offset") from the plate to the rubber blanket, then to the printing surface. When used in combination with lithographic processes, based on oil and water repulsion, the offset technique uses a planographic image in which the image to be printed obtains ink from the ink rollers, while the non-printed area attracts a water-based film (called a "solution" water fountain "), keeping the ink-free non-print area. The modern "web" process feeds large rolls of paper through large pressing machines in parts, usually for several meters, which are then printed continuously when paper is inserted.
The development of offset printing machines came in two versions: in 1875 by Robert Barclay of England to print on lead, and in 1904 by Ira Washington Rubel of the United States for printing on paper.
Video Offset printing
History
Lithography was originally made into an inexpensive method for reproducing artwork. This printing process is limited to use on flat and porous surfaces because the plates are produced from limestone. In fact, the word "lithograph" historically means "a picture of stone" or "stoned". Tin Cans are a popular packaging material in the 19th century, but transfer technology is required before lithographic processes can be used to print on tin.
The first rotary offset lithography printing machine was made in England and patented in 1875 by Robert Barclay. This development incorporates the mid-19th century transfer printing technology and the 1843 Richard March Hoe rotary printing machine - a press that uses metal cylinders instead of flat rocks. The offset cylinder is covered with a specially treated cardboard that transfers images printed from rock to metal surfaces. Then, the offset cylindrical cardboard cover is converted to rubber, which is still the most commonly used material.
When the 19th century closed and photography became popular, many lithographic companies went out of business. Photoengraving, a process that uses halftone technology as a substitute for illustrations, became a major aesthetic of the era. Many printers, including Ira Washington Rubel from New Jersey, use cheap lithographic processes to produce copies of photographs and books. The ruble was invented in 1901 - forgot to load the sheet - that when printing from rubber rollers instead of metal, the printed pages are clearer and sharper. After further refinement, the Potter Press printing company in New York produced the press in 1903. In 1907, the Rubel printing press had been used in San Francisco.
The Harris Automatic Press Company also made a similar press around the same time. Charles and Albert Harris mimicked their press "on a rotating press machine".
The newspaper publisher Staley T. McBrayer invented the Vanguard web printing press for printing newspapers, which he opened in 1954 in Fort Worth, Texas.
Maps Offset printing
Modern offset printing
One of the important functions in the printing process is the production of prepress. This stage ensures that all files are processed correctly in preparation for printing. This includes converting to the appropriate CMYK color model, completing the file, and creating plates for each job color that will run on the press.
Offset lithography is one of the most common ways to create printed materials. Some applications generally include: newspapers, magazines, brochures, stationery, and books. Compared to other printing methods, offset printing works best to produce high-quality prints economically in a way that requires minimal maintenance. Many modern offset pressures use computer-to-plate systems compared to older computer-to-film workflows, which are increasingly improving their quality.
The advantages of offset printing compared to other printing methods include:
- consistent high image quality. Offset printing produces sharp and clean images and typing is easier than, for example, letterpress printing; this is because the rubber blanket matches the texture of the printing surface;
- the production of fast and easy printing plates;
- the life of the print plate is longer than direct lit suppression because there is no direct contact between the plate and the print surface. Properly developed plates are used with optimized inks and fountain solutions can achieve a track length of over one million impressions; cost
- . Offset printing is the cheapest method to produce high-quality prints in commercial printing quantities;
- the ability to adjust the amount of ink on the fountain roller with the screw lock. Most commonly, a metal knife controls the amount of ink that is transferred from the ink trough to the fountain roll. By adjusting the screws, the operator changes 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 color density in the respective areas of the image. On older machines, one manually adjusts the screws, but on modern machines the screw lock is operated electronically by the printer that controls the engine, allowing far more precise results.
Offset print losses compared to other printing methods include:
- image quality is slightly lower than that of rotogravure or photogravure printing;
- the tendency for anodized aluminum printing plates to be sensitive (due to chemical oxidation) and to print in non-background areas when the developed plates are not properly maintained;
- the time and cost associated with plate-making and printing settings. As a result, very small quantity printing jobs can now use digital offset machines.
Each printing technology has its own identification mark, as well as offset printing. In text reproduction, the edges are sharp and have clear borders. The paper around the ink point is usually not printed. The halftone point can be hexagonal although there are different filtration methods.
Process variation
Some variations of the printing process exist:
- Blanket-to-blanketÃ,
- A printing method in which there are two blanket cylinders per color in which a piece of paper is passed and printed on both sides. Pressing blanket-to-blanket is considered a finishing press because they print on both sides of the sheet at the same time. Because blanket-to-blanket press has two blanket cylinders per color, making it possible to print on both sides of the sheet, no cylinders of impressions. The opposite blanket cylinder acts as a cylinder of impressions to each other when print production occurs. This method is most widely used in offset presses designed for envelope printing. There are also two cylinders plates per color on the press;
- Blanket-to-steelÃ,
- A printing method similar to an offset sheet printing machine; except that the plate and cylinder pressure is quite precise. Actual squeeze between optimum blanket plate and cylinder at 0.005 ?; such as pressure or pressure between cylinder blanket and substrate. Pressing blanket-to-steel is considered a one-color emphasis. To print the reverse side, the web is reversed between the printing units by flipping the bar. This method can be used to print business forms, computer mail and direct mail ads,
- Printing of variables
- Printing process using detachable printing units, inserts, or tapes for two-sided single-sided printing and a second blanket;
- Keyless offsetÃ,
- The printing process based on the concept of using fresh ink for each revolution by removing the ink residue on the ink drum after each revolution. Perfect for printing newspapers;
- Print dry offset
- The printing process using metallic supported photopolymer support plates, similar to letterpress plates, but, unlike letterpress printing where ink is transferred directly from the plate to the substrate, in dry offset printing is transferred to the blanket rubber before it is transferred to the substrate. This method is used to print on rigid plastic bucket injection molds, tubs, cups, and flower pots.
Plates
Materials
Plates used in offset printing are thin, flexible, and usually larger than the size of paper to be printed. Two main ingredients used:
- Plates of metal, usually aluminum, although sometimes made of multimetal, paper, or plastic
- The polyester plate is much cheaper and can be used instead of aluminum plates for smaller formats or medium-quality work, because dimensional stability is lower.
Computer-to-plate
Computer-to-plate (CTP) is a new technology that replaces computer-to-film (CTF) technology, and allows the imaging of metal or polyester plates without the use of film. By eliminating traditional stripping, composting, and plate-making processes, CTP changed the printing industry, leading to reduced pre-arrangement time, lower labor costs, and improved print quality.
Most CTP systems use CTP or violet thermal technology. Both technologies have the same characteristics in terms of quality and resistance of plates (longer runs). But often purple CTP systems are cheaper than thermal ones, and thermal CTP systems do not need to be operated under yellow light.
Thermal CTP involves the use of a thermal laser to expose or remove the coating area when the plate is being imaged. It depends on whether the plate is negative, or works positively. 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 erode the material. The Violet CTP laser has a much lower wavelength, 405 nm-410Ã, nm. Violet CTP "based on emulsions that are set to visible light exposure".
Another process is a conventional computer-to-plate (CTCP) system in which conventional offset plates can be exposed, making it an economical choice.
Offset sheet-fed
The feeding sheet refers to a sheet of paper or individual rolls inserted into the press through a raised suction rod and drops each sheet into place. A lithograph ("litho" for short press) uses the lithography principle to apply ink to the printing plates, as described earlier. Sheet-fed litho is commonly used to print short-term magazines, brochures, mailings, and general printing (jobbing). In sheet-fed offsets, "printing is done on one sheet of paper because they are fed to one press at a time". The feeding sheet presses using mechanical registration to connect each sheet to each other to ensure that they are reproduced with the same image in the same position on each sheet that runs through the press.
Perfect press
The finishing press, also known as a duplex printing machine, is one that can print on both sides of the paper at the same time. Web and sheet-fed press offsets are similar in many of them can also print on both sides of the paper in one pass, making it easier and faster to duplex printing.
Offset Duplicator
Small offset lithographic emphasis used for quick reproduction, good quality of one-color and two-color copies in sizes up to 12? by 18?. Popular models are made by A. B. Dick Company, Multilith, and Chief and Davidson made by A.T.F.-Davidson. Offset duplicators are made for fast and fast printing jobs; printing up to 12,000 impressions per hour. They can print business forms, letterheads, labels, newsletters, postcards, envelopes, folders, reports, and sales literature.
Feeder system
The feeding system is responsible for making sure the paper runs through the press correctly. This is where the substrate is loaded and then the system is set correctly to a specific specification of the substrate to the media.
Ink printing system
The Printing Unit consists of many different systems. Dampening systems are used to apply dampening solutions to plates with water rollers. The ink system uses rollers to deliver ink to the blanket plates and cylinders to be transferred to the substrate. The plate cylinder is where the plates containing all the imaging are fitted. Finally cylindrical blankets and impressions are used to transfer images to substrates that flow through the press.
Delivery system
The delivery system is the ultimate goal in the printing process while the paper goes through the press. Once the paper reaches the shipment, it is stacked in order for the ink to heal in a proper way. This is the step in which the sheets are checked to make sure they have the correct ink density and registration.
Slur
The production or impact of multiple images in printing is known as slur.
Web-feed balancing
Web-fed refers to the use of rolls (or "nets") of paper supplied to the printing press. Web offset printing is generally used to run more than five or ten thousand impressions. Common examples of web printing include newspapers, newspaper inserts or advertisements, magazines, direct mail, catalogs, and books. The Web-fed press is divided into two general classes: coldset (or non-heatset ) and heatset web offset presses, the difference is how the ink dries. The cold web offset printing dries through absorption into paper, while the heatset uses a heater or heater to heal or "set" the ink. Pressing the heatset can print on coated paper (slippery) or uncoated, while coldset emphasis is limited to uncoated paper, such as newspaper. Some cold web press presses can be fitted with a heat dryer, or ultraviolet lamp (for use with UV-curing inks), allowing newspaper press to print heatset and black color pages & amp; white pages coldset.
Pressing off the web offsets is useful in long-term printing jobs, usually running presses that exceed ten or twenty thousand impressions. Speed ​​is the decisive factor when considering the timing of completion for the production of the press; some web presses print at a speed of 3,000 feet (915 meters) per minute or faster. In addition to the benefits of speed and fast completion, some web compressions have the in-line ability to cut, punch, and fold.
Heatset web offset
This offset web printing subset uses dry ink by evaporation in a dryer normally positioned right after the printing unit; this is usually done on coated paper, where ink stays largely on the surface, and gives a high glossy contrasting print image after drying. Since the paper leaves the dryer too hot for folding and cutting which is usually a downstream procedure, a set of "cold rolls" positioned after the dryer lowers the paper temperature and adjusts the ink. The speed at which the ink dries is a function of dryer temperature and the length of time the paper is exposed to this temperature. This type of printing is typically used for magazines, catalogs, inserts, and other medium-to-high volume, medium to high quality production.
Coldset web correction
It is also part of web offset printing, usually used for low quality prints. This is typical of newspaper production. In this process, the ink dries due to absorption to the underlying paper. Common coldset configurations are often a set of vertically arranged print and peripheral units. Since newspapers are looking for new markets, which often imply higher quality (more gloss, more contrast), they can add tower heatsets (with dryers) or use UV (ultraviolet) based inks that "cure" on the surface with polymerization rather than by evaporation or absorption.
Feed-sheet vs. web-feed
Sheet-feeding offers several advantages. As each sheet is fed, a large number of sheet sizes and format sizes can be run through the same press. In addition, the waste sheet can be used to get ready (which is the testing process to ensure print quality is running). This allows lower cost preparation so that good paper is not wasted when setting up the press, for plates and ink. Waste sheets do bring some losses because there are often dust and offset powder particles that transfer to the blankets and plate cylinders, creating imperfections on the mold sheets. This method produces images of the highest quality.
Web-fed presses, on the other hand, are much faster than pressing the sheet-feeding, with speeds up to 80,000 cut-offs per hour (cut-off is a paper that has cut the scroll or web on the press; the length of each sheet is the same as the circumference of the cylinder). The speed of web feed suppression makes them ideal for big runs like newspapers, magazines, and comic books. However, web-feed emphasis has a fixed cut-off, unlike rotogravure or flexographic emphasis, which varies.
Ink
Print offset using ink which, compared to other printing methods, is very thick. The typical ink has a dynamic viscosity of 40-100 PaÃ, Â ° s.
There are many types of pasta inks available for use in lithographic offset printing and each has its own advantages and disadvantages. These include heat-sets, cold-sets, and energy-curable (or EC), such as ultraviolet- (or UV-) curable, and electron beam- (or EB-) can be cured. Heat-set inks are the most common and "regulated" type by applying heat and then rapid cooling to catalyze the preservation process. They are used in magazines, catalogs, and inserts. The cold-set set is set only by absorption into non-coated stock and is generally used for newspapers and books but is also found in insert printing and is the most economical option. The energy-curable ink is a high-quality offset lithium ink and is set by the application of light energy. They require special equipment such as inter-station drying lights, and are usually the most expensive type of offset ink lito.
- Letterset ink is mainly used with offset presses that do not have a dampening system and use an imaging plate that has a raised image.
- waterless ink is heat resistant and is used to keep silicone-based plates from displaying toning in non-image areas. This ink is typically used on Immediate Imaging without water.
- Single Fluid Ink is a new ink that uses a process that allows lithographic slabs in the lithographic press without the use of a silencer system during the process.
Ink-water balance
The balance of ink and water is a very important part of offset printing. If ink and water are not properly balanced, the press operator may end up with many different problems affecting the quality of the finished product, such as emulsification (water that is too strong and mixing with ink). This leads to scumming, catchup, trapping, ink density problems and in extreme cases the ink does not dry well on paper; resulting in work being unfit for delivery to clients. With the right balance, the work will have the correct ink density and need a little further adjustment except the small ones. An example is when the press heats up during normal operation, thus evaporating water at a faster rate. In this case the machinist will gradually increase the water as the press heats up to compensate for the increased evaporation of the water. Printing engineers generally try to use as little water as possible to avoid these problems.
Solution fountain
The fountain solution is a water-based (or "aqueous") component in the lithographic process that moistens the non-image area of ​​the plate to keep the ink from depositing (and thus printing). Historically, acid-based fountain solutions are made with gum arabic, chromate or phosphate, and magnesium nitrate. Alcohol is added to the water to lower surface tension and helps cool the press slightly so that the ink stays so that it can be adjusted and dried quickly. While the solution of acid fountains has increased in recent decades, neutral and alkaline fountain solutions have also been developed. Both of these chemicals rely heavily on the emulsifying surfactants and phosphates and/or silicates to provide adequate cleansing and desensitization, respectively. Since about 2000, alkaline based fountain solutions have become less common due to the health hazards attached to high pH and inappropriate odors of the necessary microbiological additives.
The acid-based fountain solution is still the most common variety and produces the best quality results with superior protection from printing plates, lower dot gain, and longer plate life. Acid is also the most versatile; capable of running with any type of lithium offset ink. However, since these products require more active ingredients to run well than neutrals and bases, they are also the most expensive to produce. However, neutral and, to a lesser extent, alkaline is still an industry staple and will continue to be used for most newspapers and many low quality inserts. In recent years, alternatives have been developed that do not use fountain solutions at all (printing without water).
In industry
Offset lithography became the most popular form of commercial printing from the 1950s ("offset printing"). Substantial investment in greater emphasis required for offset lithography is required, and has an effect on the shape of the printing industry, leading to fewer, larger, printers. This change greatly increases the use of color printing, as it was much more expensive before. Subsequent improvements to plate, ink, and paper further enhance the superior production speed and endurance technology of the plate. Today, lithography is the main printing technology used in the US and most often as offset lithography, which is "responsible for more than half of all printing using platen".
See also
- Data printing variable
References
Further reading
- Hird, Kenneth F. (2000). Offset Litography Technology . Tinley Park, Illinois: Goodheart - Willcox. ISBN: 978-1-56637-621-1.
- Offset Print. EncyclopÃÆ'Â|dia Britannica . Retrieved 22 March 2004, from EncyclopÃÆ'Â|dia Britannica Premium Service.
External links
- Offset Web Printing Tour
- The American Printing Industry
- Heatset and Coldset Offset Printing- What's The Difference?
- How Offset Print Works - HowStuffWorks
- Offset Printing Truth: Read Before You Print - Print Blog
- Offset Printing Basics
Source of the article : Wikipedia
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