Nehru Arts Ans Science College

NEHRU ARTS ANS SCIENCE COLLEGE

DEPARTMENT OF VISUAL COMMUNICATION

PRINTING TECHNOLOGY

INTAGLIO

It is a family of printmaking techniques in which the image is incised into a surface, known as the matrix or plate. Normally, copper or zinc plates are used as a surface, and the incisions are created by etching, engraving, drypoint, aquatint or mezzotint. Collographs may also be printed as intaglio plates. To print an intaglio plate, ink is applied to the surface and then rubbed with tarlatan cloth to remove most of the excess. The final smooth wipe is often done with newspaper or old public phone book pages, leaving ink only in the incisions. A damp piece of paper is placed on top and the plate and paper are run through a printing press that, through pressure, transfers the ink from the recesses of the plate to the paper.

Intaglio techniques are often combined on a plate. For example Rembrandt's prints are referred to as "etchings" for convenience, but very often they have engraving and drypoint work as well, and sometimes no actual etching at all.

Apart from intaglio, the other traditional families, or groups of printmaking techniques are:

• Relief prints, including woodcut, where the matrix is cut away to leave the image-making part on the original surface. The matrix is then just inked and printed; not wiped as described above.

• Planographic, including lithography, where the image rests on the surface of the matrix, which can therefore often be re-used.

• Other families have developed, especially in the twentieth century - see printmaking.

• Intaglio and relief, as well as pantographic printing processes, print a reversed image (a mirror-image of the matrix), which must be allowed for in the composition, especially if it includes text.

Printing press

For the invention and technology of movable type, see Movable type.

Printing press from 1811, photographed in Munich, Germany.

A printing press is a mechanical device for applying pressure to an inked surface resting upon a medium (such as paper or cloth), thereby transferring an image. The mechanical systems involved were probably first assembled in Germany by the goldsmithJohann Gutenberg around 1439,[1] based on existing screw-presses used to press cloth, grapes etc., and possibly to print woodcuts, which were printed in Europe before Gutenberg. Although both woodblock printing and movable type printing press technologies were already developed first in China, Korea in East Asia several hundred years earlier, Gutenberg was the first in WesternEurope to develop a printing press.

Printing methods based on Gutenberg's printing press spread rapidly throughout first Europe and then the rest of the world. It eventually replaced most versions of block printing, making it the most used format of modern movable type, until being superseded by the advent of offset printing

Lithography

(fromGreekλίθος - lithos, "stone" + γράφω - graphο, "to write") is a method for printing using a plate or stone with a completely smooth surface. By contrast, in intaglio printing plate is engraved, etched or stippled to make cavities to contain the printing ink, and in woodblock printing and letterpress ink is applied to the raised surfaces of letters or images. Lithography uses oil or fat and gum arabic to divide the smooth surface into hydrophobic regions which accept the ink, and hydrophilic regions which reject it and thus become the background. Invented by Bavarian author AloisSenefelder in 1796,[1][2] it can be used to print text or artwork onto paper or another suitable material. Most books, indeed all types of high-volume text, are now printed using offset lithography, the most common form of printing production. The word "lithography" also refers to photolithography, a microfabrication technique used to make integrated circuits and microelectromechanical systems, although those techniques have more in common with etching than with lithography.

The principle of lithography

Lithography stone and mirror-image print of a map of Munich.

Lithography uses chemical processes to create an image. For instance, the positive part of an image would be a hydrophobic chemical, while the negative image would be hydrophilic. Thus, when the plate is introduced to a compatible printing ink and water mixture, the ink will adhere to the positive image and the water will clean the negative image. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, Letterpress printing).

Lithogrphy printing

ROTARY PRINTING PRESS

is a printing press in which the images to be printed are curved around a cylinder. Printing can be done on large number of substrates paper, cardboard, plastic. Substrates can be sheet feed or unwound on a continuous roll through the press to be printed and further modified if required (die cut, overprint varnish, embossing). Printing presses that use continuous rolls are sometimes referred to as "web presses". Rotary drum printing was invented by Richard March Hoe, and then slightly improved by William Bullock

Specific wallpaper printing machines, using mostly wooden printing cylinders

Today, there are three main types of rotary presses; offset commonly known as web offset, rotogravure, and flexo (short for flexography). While the three types use cylinders to print, they vary in their method.

Offset lithography uses a chemical process which an image is chemically applied to a plate (generally through exposure of photosensitive layers on the plate material). Lithography is based on the fact that water and oil do not mix, which enables the planographic process to work. In the context of a printing plate, a wettable surface (the non-image area) may also be termed hydrophilic and (the image area) a non-wettable surface hydrophobic.

Gravure is a process in which small cells or holes are etched into a copper cylinder which is filled with ink.

Flexography is a relief system in which a raised image is created on a typically polymer based plate.

In stamp collecting, rotary-press-printed stamps are sometimes a different size than stamps printed with a flat plate. This happens because the stamp images are further apart on a rotary press, which makes the individual stamps larger (typically 1/2 mm to 1 mm).

FLEXO GRAPHY

Flexography (often abbreviated to flexo) is a form of relief printing and is the method of printing most commonly used for packaging (labels, tape, bags, boxes, banners, etc.).

A flexographic print is made by creating a positive mirrored master of the required image as a 3Drelief in a rubber or polymer material. A measured amount of ink is deposited upon the surface of the printing plate (or printing cylinder) using an engraved anilox roll whose texture holds a specific amount of ink. The anilox roller is covered with small wells that enable it to transfer ink to the printing plate evenly and quickly. The print surface rotates, contacting the print material which transfers the ink. [1]

One method of plate development uses light-sensitive polymer. A film negative is placed over the plate, which is exposed to ultra-violet light. The polymer hardens where light passes through the film. The remaining polymer has the consistency of chewed gum. It is washed away in a tank of either water or solvent. Brushes scrub the plate to facilitate the "washout" process. This method is considered "old-fashioned," but is still widely used in smaller operations, and is still taught in most high school and college flexo programs.

Originally flexographic printing was basic in quality. Labels requiring high quality have generally been printed using the offset process until recently. In the last few years great advances have been made to the quality of flexographic printing presses.

The greatest advances in flexographic printing have been in the area of photopolymer printing plates, including improvements to the plate material and the method of plate creation, usually photographic exposure followed by chemical etching, though also by direct laser engraving.

Digital direct to plate systems have dominated the industry recently with their better resolution and the ability to print four color process (or more) as well as offset. Companies like Dupont, MacDermid, Kodak and Esko have pioneered the latest technologies with advances in FAST washout and the latest screening technology, even companies who make plates in house are going to trade shops to get these high quality plates.

Laser-etched anilox rolls also play a part in the improvement of print quality. Full color picture printing is now possible, and some of the finer presses available today, in combination with a skilled operator, allow quality that rivals the lithographic process. One ongoing improvement has been the increasing ability to reproduce highlight tonal values, thereby providing a workaround for the very high dot gain associated with flexographic printing.

Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials. Flexographic inks, like those used in gravure and unlike those used in lithography, generally have a low viscosity. This enables faster drying and, as a result, faster production, which results in lower costs.

Printing press speeds of up to 600 meters per minute (2000 feet per minute) are achieveable now with modern technology high-end printers, like Flexotecnica[1], which introduced the world's first 12-color central impression (CI) drum press at Drupa 2008. Other press formats, such as in-line and stack presses, are available from Tresu and other suppliers.

Process Overview

The major unit operations in a flexographic printing operation are:

* Image preparation:images are captured by the camera, transferred to a scanner or computer.A simple proof or brown print

is prepared to check position and accuracy.

* Platemaking:The photomechanical plate making method begins with making an engraving, which occurs when the metal plate

is exposed through a negative and processing the plate in an acid bath. The engraved plate is used to make a master which is molded

* Printing:

* Finishing:

This is accomplished by exposing a metal plate through a negative and processing the exposed plate in an acid bath. The metal engraved plate is used to make a master which is molded out of bakelite board. The engraving is placed in a mold press. The mold is produced by applying heat & pressure to the mold material (bakelite board), which can be either plastic or glass, against the engraving under controlled temperature and pressure. The bakelite board fills the engraving on the metal plate. When its cooled you end up with a master mold for the plastic or rubber compound that will be pressed into the mold under pressure and elevated temperature to produce the flexible printing plate with raised areas that will transfer the ink.

The second method of flexo plate making is relief plates. This utilizes a solid or liquid photopolymer. The sheet of photopolymer is exposed to light through a negative. The unexposed areas are then washed away with solvent or water wash. This is fast becoming the most common method of making plates.

Flexographic Printing Process Flow Diagram

Linotype machine

From Wikipedia, the free encyclopedia

The Linotype machine (pronounced "Line-O-Type" ['laɪnəˌtaɪp]) is a "line casting" machine used in printing. The machine revolutionized printing and especially newspaper publishing, making it possible for a relatively small number of operators to set type for many pages on a daily basis. Prior to its invention in 1884, no newspaper in the world had more than eight pages.

The Linotype machine operator enters text on a 90-characterkeyboard. The machine assembles "matrices", which are molds for the letter forms, into a line. The assembled line is then cast as a single piece, called a "slug", of type metal. The matrices are then returned to the type magazine from which they came. The name of the machine comes from the fact that it produces an entire line of metal type at once - hence a "line o' type". This allows much faster typesetting and composition than original hand composition in which operators place down one pre-cast metal letter, punctuation mark or space at a time.

HOT TYPE COMPOSITION

mono type

Lino type

OFF SET PRESS

Offset printing is a commonly used printing technique where the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film (called "fountain solution"), keeping the non-printing areas ink-free.

Ira Washington Rubel invented the first offset printing press in 1903.[1]

Offset printing advantages

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 letterpress printing 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 running in conjunction with optimized inks and fountain solution may exceed run lengths of a million impressions.
• The more you print, the less you pay per page, because most of the price goes into the preparation undergone before the first sheet of paper is printed and ready for distribution. Any additional paper print will only cost the client paper price (and ink), which is very minimal.

Offset printing disadvantages

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.

SCREEN-PRINTING

Screen printing 1. A printing technique that uses a wovenmesh to support an ink blocking stencil. The attached stencil forms open areas of mesh that transfer ink 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. 2. 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. Also known as Silk Screening or Serigraphy.

Printing technique

A screen is made of a piece of porous, finely woven fabric called mesh stretched over a frame of aluminum or wood. Originally human hair then silk was woven into screen mesh, currently most mesh is made 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.

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 equal 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.

There are three types of screenprinting presses. The 'flat-bed' (probably the most widely used), 'cylinder', and 'rotary'.[8]

Textile items are printed in multi-color designs using a wet on wet technique, while graphic items are allowed to dry between colors that are then printed with another screen and often in a different color.

The screen can be re-used after cleaning. However if the design is no longer needed, then the screen can be "reclaimed", that is cleared of all emulsion and used again. The reclaiming process involves removing the ink from the screen then spraying on stencil remover to remove all emulsion. Stencil removers come in the form of liquids, gels, or powders. The powdered types have to be mixed with water before use, and so can be considered to belong to the liquid category. After applying the stencil remover the emulsion must be washed out using a pressure washer.

Most screens are ready for recoating at this stage, but sometimes screens will have to undergo a further step in the reclaiming process called dehazing. This additional step removes haze or "ghost images" left behind in the screen once the emulsion has been removed. Ghost images tend to faintly outline the open areas of previous stencils, hence the name. They are the result of ink residue trapped in the mesh, often in the knuckles of the mesh, those points where threads overlap. [13]