Printing Processes continued

Printmaking Processes

An original print is an image on paper or similar material made by one or more of the processes described here. Each medium has a special, identifiable quality, but because more than one impression of each image is possible, "original" does not mean "unique." Prints are multiple originals. The development of printmaking was connected to the development of movable type and the printing press in the fifteenth century, although woodblock printing had been done on textiles since ancient times. If you are interested in the history of printmaking, click on this link.

In contemporary printmaking, artists frequently number their prints. The total number of prints made of one image is an edition. The number may appear on the print with the individual print number as a fraction such as 5/25 meaning that this particular print is number 5 of 25 prints made.

Prints in color require two or more blocks, plates, screens or stones, one for each color, printed sequentially on top of each other to produce the final work of art. This process is called registration.

Prints can be classified according to the type of surface used to make them. Those with raised printing surfaces are known as relief prints; woodcuts are the most common type of relief print. When the printing surface is below the surface of the plate, the print technique is classified as intaglio. There are several important intaglio techniques. Planographic and stencil methods are also used, and print from a surface that is at the same level as the non-printing surface.

Relief Prints

Woodcuts are made by cutting into the broad face of a plank of wood, usually with a knife (the linocut is made the same way, except that linoleum is substituted for wood). In working the block, the artist cuts away areas not meant to print. These cut away areas appear in the finished print as the white parts of the design while the ink adheres to the raised parts. This link will take you to a Web site that contains an entire textbook on Woodblock printing by Hiroshi Yoshida Or also try this site which offers a set of past to recent examples of European relief printing.

Wood engravings are made by engraving a block of end-grain, extremely hard wood. The block, being naturally much harder, enables the artist to engrave (rather than cut) a much finer line than is possible on the softer plank surface used for woodcut. Albrect Durer (15th c.) used this technique in many of his works.

Intaglio

Intaglio printing involves the use of a metal plate. In printing, the ink settles in the sunken areas and the smooth surface of the plate is wiped clean. The plate, in contact with damp paper, is passed through a roller press under pressure. The paper is forced into the sunken areas to receive the ink. The plate can be incised by one of several methods:

·  Engraving The design is cut into the plate by driving furrows with a tool called a burin. The careful control required by the cutting method results in a rather stiff, controlled style of image, with shading accomplished through the use of parallel lines, or "hatching." The plate is printed in the manner described above. Hogarth (18th c.) is an artist who often created engravings.

·  Etching A metal plate is coated with a material called a ground. The artist then draws his design on the ground with a sharp needle, that cuts through the ground to the metal below. When the plate is put in an acid bath, these exposed areas will be etched (or eaten away). This produces the sunken line which will receive the ink. The artist etches on the plate those parts which will appear in the finished print as black or colored areas. Since the ground is soft, the artist is able to work more freely than is possible with engraving, displaying a freer, more relaxed quality of line. The length of time the plate is left in the acid bath will affect the darkness and character of the lines. Rembrandt (17th c.) did many etchings; scroll down in this link to select examples.

·  Drypoint In this technique, the sunken lines are produced directly by diamond-hard tools pulled across the plate. The depth of line is controlled by the artist's muscle and experience. The method of cutting produces a ridge along the incisions, called burr. This gives the dry-point line the characteristically soft, velvety appearance absent in the clean edged lines of an engraving or etching.

·  Aquatint A copper plate is protected by a powdered ground that is melted onto the surface of the plate. It is acid resistant, but covers incompletely, resulting in a grainy surface texture. The longer the plate is left in the acid bath, the darker and heavier the texture will become. It is usually combined with a standard etching ground that permits lines and clear white areas as well. The final effect is an image on a fine pebbled background (imparted by the porous ground). Aquatint is usually employed in combination with line etching when subtle value gradations are desired.

For additional information and examples of intaglio printing, try this link.

Planographic Prints: Lithograph

Lithograph is a planographic technique in which the artist draws directly on a flat stone or specially prepared metal plate (usually with a greasy crayon). The stone is dampened with water, then inked. The ink clings to the greasy crayon marks, but not to the dampened areas. When a piece of paper is pressed against the stone, the ink on the greasy parts is transferred to it. Toulouse-Lautrec and Picasso (left) are among the artists shown who used this technique. For additional information about lithographs, go to this site on litho technique .

Stencil prints: Silk Screen

Silk screen is a type of stencil. This technique first came into use in the early 20th century. The artist prepares a tightly stretched screen, usually of silk, and blocks out areas not to be printed by filling up the mesh of the screen with a varnish-like substance (or any number of other materials which would block up the pores of the fabric). Paper is placed under the screen and ink forced through the still-open mesh onto the paper. This technique is also widely used on textiles, including the ever-popular T-shirt. Robert Rauschenberg and Andy Warhol are examples of artists that used silkscreen.

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Original Graphic Arts Processes
Process	Relief	Intaglio	Planographic	Stencil
Common Name:	Woodcut, linocut, embossing	Engraving, drypoint, mezzotint, etching, aquatint	Lithograph	Serigraph (silkscreen)
What Area Prints:	Prints what is left of the original surface	Prints what is below the surface of the plate	Prints what is drawn on the surface	Prints open areas of the stencil
Type of Press:	Manual pressure or letter press	Etching press (clothes-wringer type)	Lith Press (sliding, scraping pressure)	Original Serigraphs are usually hand screened
Materials:	Wood or linoleum block or other film material	Copper, zinc, plastics, etc.	Limestone, zinc, aluminum plates, etc.	Silk, nylon, etc.
Basic Tools:	Knife, gouge, burin, etc.	Etching needles, burins, acids	Litho crayon, tusche, litho rubbing ink, etc.	Squeegee, screen, screen blocker (liquid, photosensitive block or film)

http://char.txa.cornell.edu/media/print/print.htm

Printing Methods Notes

http://www.kalamazoo.com.au/printing-help-center/printing-methods

Printing Methods

Welcome to the Printing Methods section of the Zoo Print School. This section serves to inform you of the multitude of different printing processes that may be employed to print your printed product.

The types of printing:

Digital Printing

Flexography

Letterpress Printing

Offset Printing

Rotogravure

Screen Printing

Digital Printing

Digital printing is the reproduction of digital images on physical surface, such as common or photographic paper, film, cloth, plastic, etc. It can be differentiated from litho printing in many ways, some of which are;

Every impression made onto the paper can be different, as opposed to making several hundred or thousand impressions of the same thing from one set of plates, as in traditional methods.

The Ink or Toner does not absorb into the paper, as does conventional Ink, but forms a layer on the surface.

It generally requires less waste in terms of chemicals used and paper wasted in set up.

Printing at home or in an office or engineering environment is subdivided into:

small format (up to ledger size paper sheets), as used in business offices and libraries

wide format (up to 3' or 914mm wide rolls of paper), as used in drafting and design establishments.

Some of the more common printing technologies are line printing — where pre-formed characters are applied to the paper by lines  daisy wheel — where pre-formed characters are applied individually

dot-matrix — which produces arbitrary patterns of dots with an array of printing studs

heat transfer — like early fax machines or modern receipt printers that apply heat to special paper, which turns black to form the printed image

blueprint — and related chemical technologies

inkjet — including bubble-jet — where ink is sprayed onto the paper to create the desired image

laser — where toner consisting primarily of polymer with pigment of the desired colours is melted and applied directly to the paper to create the desired image.

Vendors typically stress the total cost to operate the equipment, involving complex calculations that include all cost factors involved in the operation as well as the capital equipment costs, amortization, etc. For the most part, toner systems beat inkjet in the long run, whereas inkjets are less expensive in the initial purchase price.

Flexography

Flexography, often abbreviated to flexo, is a method of printing most commonly used for packaging.

 A flexo print is achieved by creating a mirrored master of the required image as a 3D relief 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 anilox roll. The print surface then rotates, contacting the print material which transfers the ink.

 Flexo is so named because it was originally used as a method of printing onto corrugated cardboard, which has a very uneven surface. It is required that the printing plate surface maintain contact with the cardboard, which it does by being flexible. Also, unprinted high points on the cardboard must not get printed by ink remnants not on the plate surface, which is achieved by ensuring a sufficient depth for the non-print areas of the plate.

 Originally flexo printing was very low quality. In the last 3 decades great advances have been made, including improvements to the plate material and the method of plate creation—usually photographic exposure followed by chemical etch, though also by direct laser engraving. Laser-etched anilox rolls also play a part in the improvement of print quality. Full colour picture printing now occurs, 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 flexo print.

Flexo has an advantage over lithography in that it can use a wider range of inks and is good at printing on a variety of different materials. Flexo inks, like those used in gravure and unlike those used in lithography generally have low viscosity. This enables faster drying and, as a result, faster production; that means low cost. Printing press speeds of 450 meters per minute are regular with modern technology high end printers, like Windmoeller und Hollscher or Schiavi type. The main printing process worldwide for flexible packaging are rotogravure, for very large runs, and flexo for large and medium runs.

 Also Known As:

 Flexographic printing

Flexo

Surface printing

Examples:

 Some typical applications for flexography are paper and plastic bags, milk cartons, disposable cups, and candy bar wrappers. Flexography printing may also be used for envelopes, labels, and newspapers.

Letterpress Printing

Letterpress printing is a term for printing text with movable type, in which the raised surface of the type is inked and then pressed against a smooth substance to obtain an image in reverse. In addition to the direct impression of inked movable type onto paper or another receptive surface, the term letterpress can also refer to the direct impression of inked media such as zinc "cuts" (plates) or linoleum blocks onto a receptive surface.

Early Chinese woodblock printing used characters or images carved in relief from before 750AD, and this form of printing was widespread throughout Eurasia as a means of printing patterns on textiles. Printing of images, first on cloth, then from about 1400 on paper was practised in Europe. In the 1400s, Johann Gutenberg (among others) is credited with the invention of movable type printing from individually-cast, reusable letters set together in a forme. This had previously been invented in Asia, but the two inventions were probably not connected. He also invented a wooden printing-press where the type surface was inked and paper laid carefully on top by hand, then slid under a padded surface and pressure applied from above by a large threaded screw. Later metal presses used a knuckle and lever arrangement instead of the screw, but the principle was the same.

With the advent of industrial mechanisation, the inking was carried out by rollers which would pass over the face of the type and move out of the way onto a separate ink-bed where they would pick up a fresh film of ink for the following sheet. Meanwhile a sheet of paper was slid against a hinged platen (see image) which was then rapidly pressed onto the type and swung back again to have the sheet removed and the next sheet inserted (during which operation the now freshly-inked rollers would run over the type again). In a fully-automated 20th century press, the paper was fed and removed by vacuum sucker grips.

Rotary presses were used for high-speed work. In the oscillating press, the forme slid under a drum around which each sheet of paper got wrapped for the impression, sliding back under the inking rollers while the paper was removed and a new sheet inserted. In a newspaper press, a papier-mâché mixture (flong) was used to make a mould of the entire forme of type, then dried and bent, and a curved metal plate cast against it. The plates were clipped to a rotating drum, and could thus print against a continuous reel of paper at the enormously high speeds required for overnight newspaper production.

As computerised typesetting and imaging replaced cast metal types, letterpress began to die out, as high-speed photographic imaging onto smooth flexible plates (lithography) became more economical. However, photopolymer plates and the invention of Ultra-Violet curing inks has helped keep rotary letterpress alive in areas like self-adhesive labels. There is also still a large amount of flexographic printing, a similar process, which uses rubber plates to print on curved or awkward surfaces, and a lesser amount of relief printing from huge wooden letters for lower-quality poster work.

 Also Known As:

Offset Letterpress

Relief Printing

Examples:

 Mostly replaced by offset printing and other processes, letterpress printing is still used for some newspapers, books, and limited edition prints. Letterpress printing may also be used for printing business cards, letterhead, posters, and some forms.

 Offset Printing

Offset printing is a widely 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 film of water, keeping the non-printing areas ink-free.

Advantages of offset printing include:

Consistent high image quality. Offset printing produces sharper and cleaner images and type 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.

 Also Known As:

 Lithographic

Offset

Planographic

Examples:

Offset lithography is the most commonly used commercial printing process for the bulk of desktop publishing on paper. Offset lithography is used on both sheet-fed and web offset presses.

Rotogravure Printing

Rotogravure is a type of intaglio printing process, in that it involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a copper cylinder because, like offset and flexography, it uses a rotary printing press. The vast majority of gravure presses print on reels of paper, rather than sheets of paper. (Sheetfed gravure is a small, specialty market.) Rotary gravure presses are the fastest and widest presses in operation, printing everything from narrow labels to 12-feet-wide rolls of vinyl flooring. Additional operations may be in-line with a gravure press, such as saddle stitching facilities for magazine/brochure work.

In 1932 a George Gallup "Survey of Reader Interest in Various Sections of Sunday Newspapers to Determine the Relative Value of Rotogravure as an Advertising Medium" found that rotogravures were the most widely read sections of the paper and that advertisements there were three times more likely to be seen by readers than in any other section. The rotogravure process is still used for commercial printing of magazines, postcards, and corrugated (cardboard) product packaging.

In the latter quarter of the 19th centure, the method of image photo transfer onto carbon tissue covered with light-sensitive gelatin was discovered and was the beginning of rotogravure.

Gravure cylinders nowadays are typically engraved digitally by a diamond tipped or laser etching machine. On the gravure cylinder, the engraved image is composed of small recessed cells (or 'dots') that act as tiny wells. Their depth and size control the amount of ink that gets transferred to the substrate (paper or other material, such as plastic or foil) via a process of pressure, osmosis, and electrostatic pull. (A patented process called "Electrostatic Assist" is sometimes used to enhance ink transfer.)

A rotogravure printing press has one printing unit for each color, typically CMYK or cyan, magenta, yellow and key (printing terminology for black). The number of units vary depending on what colors are required to produce the final image. There are five basic components in each color unit: an engraved cylinder (whose circumference can change according to the layout of the job), an ink fountain, a doctor blade, an impression roller, and a dryer. While the press is in operation, the engraved cylinder is partially immersed in the ink fountain, filling the recessed cells. As the cylinder rotates, it draws ink out of the fountain with it. Acting as a squeegee, the doctor blade scrapes the cylinder before it makes contact with the paper, removing ink from the non-printing (non-recessed) areas. Next, the paper gets sandwiched between the impression roller and the gravure cylinder. This is where the ink gets transferred from the recessed cells to the paper. The purpose of the impression roller is to apply force, pressing the paper onto the gravure cylinder, ensuring even and maximum coverage of the ink. Then the paper goes through a dryer because it must be completely dry before going through the next color unit and absorbing another coat of ink.

Because gravure is capable of transferring more ink to the paper than other printing processes, gravure is noted for its remarkable density range (light to shadow) and hence is a process of choice for fine art and photography reproduction, though not typically as clean an image as that of sheet fed litho or web offset litho. Gravure is widely used for long-run magazine printing in excess of 1 million copies. Gravure's major quality shortcoming is that all images, including type and "solids," are actually printed as dots, and the screen pattern of these dots is readily visible to the naked eye. Examples of gravure work in the United States are typically long-run magazines, mail order catalogs, consumer packaging, and Sunday newspaper ad inserts.

Other application area of gravure printing is in the flexible packaging sector. A wide range of substrates such as Polyethylene, Polypropylene, Polyester, BOPP etc can be printed in the gravure press.

Also Known As:

Gravure

Examples:

Gravure printing is often used for high-volume printing of packaging, wallpaper, and giftwrap using fast-drying inks. Although less common, gravure printing may also be used for printing magazines, greeting cards, and high-volume advertising pieces.

Screen Printing

Screen printing is a printmaking technique that creates a sharp-edged image using a stencil. A screen print or serigraph is an image created using this technique.

A screen is made of a piece of porous, finely woven fabric (originally silk, but typically made of polyester or nylon since the 1940s) stretched over an aluminum frame. Areas of the screen are blocked off with a non-permeable material—a stencil—which is a positive of the image to be printed; that is, the open spaces are where the ink will appear.

The screen is placed on top of a piece of dry paper or fabric. Ink is placed on top of the screen, and a squeegee (rubber blade) is used to push the ink evenly into the screen openings and onto the substrate. The ink passes through the open spaces in the screen onto the paper or fabric below; the screen is lifted away and then the squeegee is pushed back across the screen, with the screen lifted, "flooding" the ink into the screen. The screen can be re-used after cleaning. If more than one color is being printed on the same surface, the ink is allowed to dry and then the process is repeated with another screen and different color of ink.

 While the public thinks of garments in conjunction with screen printing, the technique is used on tens of thousands of items, including birthday cake designs, decals, clock and watch faces, and many more products. The vast majority of silk-screen printings are monochromatic. 

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.

Also Known As:

 Silkscreening

Serigraphy

Examples:

Screen printing can be used to print images on T-shirts, hats, CDs, DVDs, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood.

Printing Notes

Printing Processes:

One source lists the following printing processes:

http://pirate.shu.edu/~mckenndo/Printing%20processes.htm

Letterpress (Relief) printing: the original ,mechanical Gutenberg printing process. Limited use today.

Flexography: a relief process used for special purposes such as packaging. Gravure (Intaglio) a more expensive process which produces higher quality color than Letterpress. Only specialized use today. Photo Offset Lithography: A chemical method of ink transferal and the primary major printing process today.

Screen Printing: A very flexible process used extensively in specialty printing and advertising. (See Xerography: An electrostatic method of image transfer onto smooth paper. Ink Jet Printing: Printing by small jets propelling droplets of ink onto paper. (See "Ink Jet Printing", below

Engraving - think fine stationery

Thermography - raised printing, used in stationery. Reprographics - copying and duplicating

Digital printing: including direct to press and printing on demand. Possibly the printing processes of the future. Letterpress Printing The oldest method of printing used by Gutenberg. The image area is raised, usually in metal, and the non-image area is recessed.

The raised surface can be obtained by cutting away the white areas with hand tools (as in block printing or wood-engraving), by acid etching of metal (as in photoengraving), by light-hardening a photo-emulsion (photo-polymer plates), or by casting from a carved or punched matrix (as in metal type). There are other methods for creating the a raised surface, but most letterpress techniques tend to fall under the above categories.

Once a relief surface has been prepared it is put in the press. A roller (or sometimes a dauber) is used to place ink on the type or block, which is then pressed against paper. Multiple blocks are used to create images with more than one color.

From: http://work.colum.edu/~matma/letterpress/letterpress.html

The use of letterpresses is on the decline being replaced with faster and more efficient printing presses such as the offset lithographic press or the flexographic press. The amount of setup required to prepare the equipment to print a job is significant. For example, the image must be metal cast prior to print versus offset printing plates which are comparatively cheaper and require less time to make.

(From: http://www.pneac.org/printprocesses/letterpress/#Overview) (Back to Top)

Flexography: Frequently used for printing on plastic, foil, acetate film, brown paper, and other materials used in packaging, flexography uses flexible printing plates made of rubber or plastic. The inked plates with a slightly raised image are rotated on a cylinder which transfers the image to the substrate. Flexography uses fast-drying inks, is a high-speed print process, can print on many types of absorbent and non-absorbent materials, and can print continuous patterns (such as for giftwrap and wallpaper).

(From: http://desktoppub.about.com/cs/printing/g/flexography.htm) (Back to Top)

Gravure: With gravure printing an image is etched on the surface of a metal plate, the etched area is filled with ink, then the plate is rotated on a cylinder that transfers the image to the paper or other material. (From: http://desktoppub.about.com/cs/printing/g/gravure.htm)

In the various intaglio printing methods, the area of the image to be printed is recessed into the surface of the printing plate and the recessed areas are filled with ink. The incised image may be etched, engraved with chemicals or tools. The image to be printed is incised into the plates, the incisions filled with ink, and excess ink wiped from the plates. Heavy pressure is applied to transfer the ink from the plates to the paper, leaving the surface slightly raised and the back side slightly indented. (From:http://desktoppub.about.com/cs/printing/g/intaglio.htm)

Gravure printing is characteristically used for long run, high quality printing producing a sharp, fine image. The number of gravure printing plants in the U.S. is significantly lower than other printing processes. This is due, in part, to the cost of presses and components. While a lithographic press will cost in the range of $100,000 the cost of gravure press will be in the range of $1 million. Additionally a single gravure cylinder will cost around $5000 versus around $15 for a lithographic plate. Additionally, the gravure cylinder has a long service life and will yield a very large number of impressions without degradation. (Back to Top)

Thermography: Commonly known as poor man's engraving, thermography produces raised printing similiar in appearance to engraving but using a different process. In thermography, a special powder is added to the ink printed on the paper. The printed piece is heated and the powder and ink mixture dries to form a raised effect on the paper.

(From: http://desktoppub.about.com/cs/printing/g/thermography.htm) (Back to Top)Screen Printing

(Silk Screening)

Screen printing is arguably the most versatile of all printing processes. It can be used to print on a wide variety of substrates, including paper, paperboard, plastics, glass, metals, fabrics, and many other materials. including paper, plastics, glass, metals, nylon and cotton. Some common products from the screen printing industry include posters, labels, decals, signage, and all types of textiles and electronic circuit boards. The advantage of screenprinting over other print processes is that the press can print on substrates of any shape, thickness and size.

A significant characteristic of screen printing is that a greater thickness of the ink can be applied to the substrate than is possible with other printing techniques. This allows for some very interesting effects that are not possible using other printing methods. Because of the simplicity of the application process, a wider range of inks and dyes are available for use in screen printing than for use in any other printing process.

Utilization of screenprinting presses has begun to increase because production rates have improved. This has been a result of the development of the automated and rotary screenprinting press, improved dryers, and U.V. curable ink. The major chemicals used include screen emulsions, inks, and solvents, surfactants, caustics and oxidizers used in screen reclamation. The inks used vary dramatically in their formulations (GATF 1992b).

Screen Printing Process Overview

Screen printing consists of three elements: the screen which is the image carrier; the squeegee; and ink. The screen printing process uses a porous mesh stretched tightly over a frame made of wood or metal. Proper tension is essential to accurate color registration. The mesh is made of porous fabric or stainless steel mesh. A stencil is produced on the screen either manually or photochemically. The stencil defines the image to be printed in other printing technologies this would be referred to as the image plate.

Screen printing ink is applied to the substrate by placing the screen over the material. Ink with a paint-like consistency is placed onto the top of the screen. Ink is then forced through the fine mesh openings using a squeegee that is drawn across the scree, applying pressure thereby forcing the ink through the open areas of the screen. Ink will pass through only in areas where no stencil is applied, thus forming an image on the printing substrate. The diameter of the threads and the thread count of the mesh will determine how much ink is deposited onto the substrates. (From: http://www.pneac.org/printprocesses/screen/) (Back to Top)

Xerography: Dry, electrostatic method of producing images, without the use of negatives or sensitized paper, invented in the USA by Chester Carlson in 1938 and applied in the Xerox photocopier. Also called electrophotography, method of dry photocopying in which the image is transferred by using the attractive forces of electric charges. A beam of light, usually from a laser, is made to strike the original material, e.g., a white page with black lettering. Light rays are reflected off the white areas onto a photosensitive plate over which electric charges have been spread. Charges are neutralized from the areas struck by the rays. Since no light rays are reflected from the lettering, charges are retained on the plate in areas corresponding to the lettered areas of the original. A plastic powder called toner is introduced that sticks to the charged areas. A sheet of paper is then passed between the plate and another charged object that draws the powder from the plate to the paper, forming an image of the original; the powder is fused to the paper with heat. The process has image resolution that is sufficient for printed or written materials, and certain pictorial materials are fairly well reproduced. As the image on the drum is a projected one rather than one made by contact printing, it is possible to produce a copy that is smaller or larger than the original. Variations of the xerographic process are used in such devices as computer laser printers and plain-paper facsimile machines.

(Mostly from: http://www.encyclopedia.com/html/x1/xerograp.asp)

laser printer a computer printer that produces high-resolution output by means of a process that is similar to photocopying . In place of reflected light from an image (as is used in xerography ), a laser printer uses data sent from a computer to turn a laser beam on and off rapidly as it scans a charged drum. The drum then attracts toner powder to the areas not exposed to the light. Finally, the toner is fused to paper over a belt by heated rollers. In a write-black printer the laser positively charges the printed areas to attract the toner, which gives better detail than a write-white printer. In a write-white printer, the beam negatively charges the areas not to be printed to repel the toner, which gives a denser image. Faster, quieter, and capable of producing more attractive results than standard printers, laser printers have become an important means of printing business documents since they became more generally available (1984) for personal computers .

(From: http://www.encyclopedia.com/html/l1/laser-pr.asp) (Back to Top)

Ink jet printing: A printer that propels droplets of ink directly onto the medium.  Today, almost all ink jet printers produce color.  Low-end ink jets use three ink colors (cyan, magenta and yellow), but produce a composite black that is often muddy.  Four-color ink jets (CMYK) use black ink for pure black printing.  Ink jet printers run the gamut from less than a hundred to a couple hundred dollars for home use to hundreds of thousands of dollars for commercial poster printers.

 The cost of ink cartridges for low-priced printers can make the less-expensive ink jet model more costly in the long run.  For example, if the black ink does not come in a separate cartridge, you have to replace the entire four-color unit when you run out of black.  Also, for resolution quality, examine text samples, not graphics.  Graphics always look better than text.  For color quality, be sure that samples from different models are printed on the same kind of paper.  Coated specialty papers, although costly, greatly improve the printed results, because they do not absorb the ink like regular copy paper.  Ink and paper costs are ongoing, which must be taken into consideration.

 Large wide-format ink jet printers are used to produce final output for commercial posters and banners.  Such printers can print on vinyl and textiles as well as paper, and their quality is extraordinary.  Wide-format printers have also replaced pen plotters that used to "draw" engineering and architectural renderings.

(From The Computer Desktop Encyclopedia) (Back to Top)

Printing

http://pirate.shu.edu/~mckenndo/Printing%20processes.htm



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