printing

printing, means of producing reproductions of written material or images in multiple copies. There are four traditional types of printing: relief printing (with which this article is mainly concerned), intaglio, lithography, and screen process printing. Relief printing encompasses type, stereotype, electrotype, and letterpress. Flexographic printing is a form of rotary letterpress printing using flexible rubber plates and rapid-drying inks.

For an account of type design, see type; typography. See also book; bookbinding.

Relief Printing

Early History

The story of the invention of printing and of its early days is told in the article type. In the 15th cent. the art spread, directly and indirectly, from Mainz to many parts of Europe. It was brought to England in 1476 by William Caxton; to the New World in 1539 by Juan Pablos, who set up his press in Mexico City.

Mechanization

The first papermaking machine producing a continuous roll of paper and capable of delivering sheets in specific sizes—the Fourdrinier machine—was installed in London in 1803. Steam power was successfully applied to the printing press in 1810 by Friedrich Koenig, a German. The invention did not improve the quality of the product but greatly increased the output of the machine. In Koenig's press, the type bed remained flat as in hand presses, but the paper was pressed on the type by a cylinder. The Adams power press was invented by an American, Isaac Adams, in 1827.

In 1846 and 1847, Richard March Hoe designed a rotary press in which stereotype plates were for the first time arranged in a true cylinder. In 1866 a press known later as the Walter press was patented in England; in this press the printing surfaces were not types but stereotype plates curved to form parts of cylinders. The invention of ways of making paper in sheets of any desired length, so that paper could be fed to cylinder presses from rolls, assisted in increasing the speed of printing. Machines for folding newspapers were incorporated with the power cylinder press.

Typesetting

Not until the late 19th cent. were typesetting machines invented. The Linotype machine, invented by Ottmar Mergenthaler in Baltimore in 1884, produced a metal slug corresponding to a single line of type as set by hand in printing. It was first put into operation at the New York Tribune in 1886. Operated from a keyboard like that of a typewriter, the machine assembled brass matrices into a line, cast the line, and distributed the matrices. The Intertype machine was substantially similar to the Linotype machine, and the matrices made by either machine could be used in the other.

The third principal typesetting machine is the Monotype, patented by Tolbert Lanston in 1887 and first produced commercially in 1897. The Monotype makes each character separately, assembling the characters as in hand composition, for which the Monotype characters can be used. Before electronic composition, monotype had an advantage in setting certain kinds of copy, e.g., mathematical and scientific material, where special symbols or other problems may be involved.

Intaglio

In intaglio printing, such as the etching and the steel engraving, the design to be printed is lower than the surface of the plate, which is wiped clean before each impression, leaving the incised design filled with ink, which the paper receives. In gravure intaglio printing, tone is produced by varying the thickness of the ink of the printing surface through depressions of varying depth; minute points constitute the clean surface that keeps the paper from being pressed into the depressions. In photogravure the gravure plate is made by a photographic process. Rotogravure is photogravure adapted for printing by a rotary or cylinder press.

Lithography

The third kind of printing, lithography, also known as planographic printing, was devised by Aloys Senefelder. Flat stones were the first lithographic plates and are still used, although a variety of thin metal, plastic, and paper plates are now also employed. A drawing is made on the plate with greasy ink or crayon, and water is then applied to the plate. When the plate is inked for printing, the greasy parts accept the ink and the wet parts do not. Preparing a printing surface so that ink will adhere only to parts of it is basic in all planographic printing.

Collotype, also called photogelatin, is a lithographic process that uses a gelatin-faced plate to achieve the tonal distribution obtained through screen dots in engraving. It is chiefly used in the reproduction of fine illustrations or of scientific subject matter requiring accuracy of detail.

Photolithography, offset, litho-offset, and offset lithography are synonyms in commercial printing for the most widely used form of planographic printing, based on a modification of the lithographic press featuring a rubber-covered cylinder between the printing cylinder and the impression cylinder. The plate cylinder transfers the image to the rubber blanket cylinder, which in turn offsets it on the paper carried by the impression cylinder. Offset and other forms of planographic printing, through many technical refinements, make possible increased production speeds, improved quality in the reproduction of fine tones, and a substantial reduction in the number of impressions required to reproduce full-color copy.

Screen Process

The fourth traditional type of printing, screen process, includes silk screen and has special applications in the printing industry. Silk screen printing is a form of stencil printing, i.e., printing where the ink is applied to the back of the image carrier and pushed through porous or open areas. The image is on a piece of silk stretched on a frame and backed by a rubber squeegee containing ink. The nonprinting areas on the silk screen are blocked out, and the ink is pushed through the porous areas corresponding to the design; the process is widely used for posters and for printing on glass, plastics, and textured surfaces. Mimeographing is another commercial application of stencil printing.

Illustrations and Color Printing

In three kinds of printing—relief, intaglio, and planographic—illustrations are often produced by the halftone process, in which a plate is made by photographing through glass marked with a network of fine lines (see also photoengraving). A usual form of color printing is by the Ben Day, or Benday, process, invented by New York printer Benjamin Day, which utilizes celluloid sheets to achieve proper shading and color. Printing in colors is sometimes done, as excellently in Japan, by applying inks of different colors by hand to the printing surface, but usually a separate printing surface is used for each ink.

In full-color printing four standard colors are used—yellow, cyan (a hue between blue and green), magenta, and black—the first three being the complementary colors of blue, red, and green. Other colors are produced by printing one color over another, as green by printing cyan on yellow. Black is used to print the text accompanying the illustration, and it is often used as a fourth color in the illustration itself to add strength and detail.

Modern Innovations

In recent years the use of photographic processes has expanded greatly, and the development of electronic devices, as well as other technological advances, has introduced a new era in the evolution of printing. The development of typewriters and personal computers capable of delivering justified and proportionally spaced copy has made possible the production of camera-ready books and has met the demands for several special types of printing.

Perhaps the most revolutionary innovation has been the introduction of photocomposition machines for setting type by photographic means. Two of these are analogous in principle to the Monotype and Intertype casting machines and have been produced by the respective companies under the trademarks of Monophoto and Intertype Fotosetter. The Linofilm is a phototypesetting machine developed by the Linotype Corporation. The Photon machine, invented by the Frenchmen René Higonnet and Louis Moyroud, using an electric typewriter connected with a computer and a photographing unit, is noteworthy. Almost exclusively electronic, it can deliver justified type on film in a wide variety of styles at extraordinary speed.

Today photocomposition has been adopted in lithography, gravure, and letterpress printing, and its use, together with other electronic techniques, has revolutionized the printing industry (see optical sensing). In recent years some newspapers have started to use pagination systems, in which newspapers are electronically composed by computer, output to a negative, and a plate is made of the negative.

Many reproduction processes other than those cited above have also been developed. Xerography, or electrostatic printing, has been widely adopted for photocopying; it is also the basis of the laser printer, one type of computer printer. It is also an effective means of producing master plates for offset printing. One xerographic device is used for making full-size reprints of out-of-print books from microfilm. Other duplicating processes of commercial importance are the Multigraph, which operates on the letterpress principle; the Multilith, basically a small offset press; the Ditto, a duplicator using a special fluid to remove ink from the master plate and transfer it to the paper; and the well-known photostat process.

or relief printing or typographic printing

In commercial printing, process by which many copies are produced by repeated direct impression of an inked, raised surface against sheets or a continuous roll of paper. Letterpress is the oldest traditional printing technique, the only important one from the time of Johannes Gutenberg (circa 1450) until lithography (late 18th century) and especially offset printing (early 20th century). The ink-bearing surface for a page of text was originally assembled letter by letter and line by line. The Monotype and Linotype were the first keyboard-activated typesetting machines. Letterpress can produce high-quality work at high speed, but requires much time to prepare and adjust the press. For the sake of speed, newspapers are now printed by the offset process.

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Process for reproducing text and illustrations, traditionally by applying ink to paper under pressure, but today including various other methods. In modern commercial printing, three basic techniques are used. Letterpress printing relies on mechanical pressure to transfer a raised inked image to the surface to be printed. Gravure printing transfers ink from recessed cells of varying depths. In offset printing the printing and nonprinting areas of the plate differ not in height but in wettability.

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or offset lithography or litho-offset

In commercial printing, a widely used technique in which the inked image on a printing plate is imprinted on a rubber cylinder and then transferred (offset) to paper or other material. The rubber cylinder gives great flexibility, permitting printing on wood, cloth, metal, leather, and rough paper. In offset printing the matter to be printed is neither raised above the surface of the printing plate (as in letterpress printing) nor sunk below it (as in intaglio, or gravure, printing). Offset printing, a development of lithography, is based on the principle that water and grease do not mix, so that a greasy ink can be deposited on grease-treated printing areas of the plate, while nonprinting areas, which hold water, reject the ink. The offset plate is usually of zinc or aluminum or a combination of metals, with the surface treated to render it porous and then coated with a photosensitive material. Exposure to an image hardens the coating on printing areas; the coating on nonprinting areas is washed away, leaving wetted metal that will reject ink. Seealso xerography.

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Printing processes used for catalogs, magazines, newspaper supplements, cartons, floor and wall coverings, textiles, and plastics. The Bohemian Karel Klíchacek made photogravure a practical commercial process in 1878. An image is etched in the copper surface of the printing cylinder as pits or wells of different depths. In rotogravure printing, the cylinder rotates through a trough filled with fast-drying ink. A thin steel doctor blade removes the ink from the surface but not from the wells. The cylinder comes in contact with the paper, which draws the ink out of the wells. Because of the various depths of the wells, a full range of tonal values can be printed; in reproducing illustrations, gravure comes closest to simulating continuous-tone copy. In colour printing, a separate cylinder is prepared for each colour. Seealso letterpress printing; offset printing.

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Specialized printing technique using coloured inks and modified presses. Juxtaposition of colours is achieved by submitting each sheet to successive impressions by typeforms each of which prints only on areas designed to carry a single colour and inked only in that colour. Three colours of ink can reconstitute the visual effect of all the range of colours by combining them appropriately; if all three inks are applied to an area, it almost appears black. Standard colour printing, called four-colour printing, employs magenta, yellow, cyan (blue), and black inks.

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Screen printing is a printing technique that uses a woven mesh 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.

Taxonomy

There is considerable taxonomic, etymological and semantic confusion about this process, industry, and techniques known as Screen Printing, Screen-printing, Screen printing, silkscreen, and serigraph. Much of the current confusion is based on the popular traditional reference to the process of screen printing as silkscreen printing. Almost no professional businesses, artists, or trade organizations use references to silk because of the general abandonment of silk as a viable mesh material after the 1960s.

Encyclopedia references, dictionaries and trade publications also use an array of spellings for this process with the two most often encountered english spellings as, screen printing spelled as a single undivided word, and the more popular two word title of screen printing without hyphenation.

History

Screen-printing first appeared in a recognizable form in China during the Song Dynasty (960–1279 CE). Japan and other Asian countries adopted this method of printing and advanced the craft using it in conjunction with block printing and paints.

Screen-printing was introduced to Western Europe from Asia sometime in the late 1700s, but did not gain large acceptance or use in Europe until silk mesh was more available for trade from the east and a profitable outlet for the medium discovered.

Screen-printing was first patented in England by Samuel Simon in 1907. It was originally used as a popular method to print expensive wall paper, printed on linen, silk, and other fine fabrics. Western screen printers developed reclusive, defensive and exclusionary business policies intended to keep secret their workshops' knowledge and techniques.

Early in the 1910s, several printers experimenting with photo-reactive chemicals used the well-known actinic light activated cross linking or hardening traits of potassium, sodium or ammonium bichromate chemicals with glues and gelatin compounds. Roy Beck, Charles Peter and Edward Owens studied and experimented with chromic acid salt sensitized emulsions for photo-reactive stencils. This trio of developers would prove to revolutionize the commercial screen printing industry by introducing photo-imaged stencils to the industry, the acceptance of this method would take many years. Commercial screen printing now uses sensitizers far safer and less toxic than bichromates, currently there are large selections of pre-sensitized and "user mixed" sensitized emulsion chemicals for creating photo-reactive stencils.

Joseph Ulano founded the industry chemical supplier Ulano and in 1928 created a method of applying a lacquer soluble stencil material to a removable base. This stencil material was cut into shapes, the print areas removed and the remaining material adhered to mesh to create a sharp edged screen stencil.

Originally a profitable industrial technology, screen printing was eventually adopted by artists as an expressive and conveniently repeatable medium for duplication well before the 1900s. It is currently popular both in fine arts and in commercial printing, where it is commonly used to print images on T-shirts, hats, CDs, DVDs, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood.

A group of artist who later formed the National Serigraphic Society coined the word Serigraphy in the 1930s to differentiate the artistic application of screen printing from the industrial use of the process. "Serigraphy" is a combination word from the Latin word "Seri" (silk) and the Greek word "graphein" (to write or draw).

The Printer's National Environmental Assistance Center says "Screenprinting is arguably the most versatile of all printing processes." Since rudimentary screenprinting materials are so affordable and readily available, it has been used frequently in underground settings and subcultures, and the non-professional look of such DIY culture screenprints have become a significant cultural aesthetic seen on movie posters, record album covers, flyers, shirts, commercial fonts in advertising, and elsewhere.

History 1960's to present

Credit is generally given to the artist Andy Warhol for popularizing screen printing identified as serigraphy, in the United States. Warhol is particularly identified with his 1962 depiction of actress Marilyn Monroe screen printed in garish colors.

American entrepreneur, artist and inventor Michael Vasilantone would develop and patent a rotary multicolor garment screen printing machine in 1960. The original rotary machine was manufactured to print logos and team information on bowling garments but soon directed to the new fad of printing on t-shirts. The Vasilantone patent was soon licensed by multiple manufacturers, the resulting production and boom in printed t-shirts made the rotary garment screen printing machine the most popular device for screen printing in the industry. Screen printing on garments currently accounts for over half of the screen printing activity in the United States.

Graphic screenprinting 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). Screenprinting is often preferred over other processes such as dye sublimation or inkjet printing because of its low cost and ability to print on many types of media.

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 papyrus 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'.

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.

While the public thinks of garments in conjunction with screenprinting, the technique is used on tens of thousands of items, decals, clock and watch faces, and many more products. The technique has even been adapted for more advanced uses, such as laying down conductors and resistors in multi-layer circuits using thin ceramic layers as the substrate.

Stenciling techniques

There are several ways to create a stencil for screenprinting. An early method was to create it by hand in the desired shape, either by cutting the design from a non-porous material and attaching it to the bottom of the screen, or by painting a negative image directly on the screen with a filler material which became impermeable when it dried. For a more painterly technique, the artist would choose to paint the image with drawing fluid, wait for the image to dry, and then coat the entire screen with screen filler. After the filler had dried, water was used to spray out the screen, and only the areas that were painted by the drawing fluid would wash away, leaving a stencil around it. This process enabled the artist to incorporate their hand into the process, to stay true to their drawing.

A method that has increased in popularity over the past 70 years and is tremendously popular is the photo emulsion technique:

1. The original image is created on a transparent overlay such as acetate or tracing paper. The image may be drawn or painted directly on the overlay, photocopied, or printed with a laser printer, as long as the areas to be inked are opaque. A black-and-white negative may also be used (projected on to the screen). However, unlike traditional platemaking, these screens are normally exposed by using film positives.
2. The overlay is placed over the emulsion-coated screen, and then exposed with an ultraviolet light source in the 350-420 Nanometer spectrum. Other light sources do not work well. The UV light passes through the clear areas and create a polymerization (hardening) of the emulsion.
3. The screen is washed off thoroughly. The areas of emulsion that were not exposed to light dissolve and wash away, leaving a negative stencil of the image on the mesh.

Photographic screens can reproduce images with a high level of detail, and can be reused for tens of thousands of copies. The ease of producing transparent overlays from any black-and-white image makes this the most convenient method for artists who are not familiar with other printmaking techniques. Artists can obtain screens, frames, emulsion, and lights separately; there are also preassembled kits, which are especially popular for printing small items such as greeting cards.

Another advantage of screenprinting is that large quantities can be produced rapidly with new automatic presses (up to 1200 shirts in 1 hour). (The record is over 2000 shirts an hour.)

Screenprint methods

Plastisol: the most common plastisol based print used in garment decoration. Good color opacity onto dark garments and clear graphic detail with, as the name suggests, a more plasticized texture. This print can be made softer with special additives or heavier by adding extra layers of ink. Most plastisol inks require heat (approx. 300 degrees fahrenheit for many inks) to cure the print.Water-Based inks: these penetrate the fabric more than the plastisol inks and create a much softer feel. Ideal for printing darker inks onto lighter colored garments. Also useful for larger area prints where texture is important.PVC/ Phalate Free: relatively new breed of ink and printing with the benefits of plastisol but without the two main toxic components - soft feeling print.Discharge inks: used to print lighter colours onto dark background fabrics, they work by removing the dye in the garment – this means they leave a much softer texture. They are less graphic in nature than plastisol inks, and exact colours are difficult to control, but especially good for distressed and vintage prints.Foil: consists of a glue printed onto the fabric and then foil is applied for a mirror finish.Glitter/Shimmer: silver flakes are suspended in a plastisol ink to create this sparkle effect. Usually available in gold or silver but can be mixed to make most colours.Metallic: similar to glitter, but smaller particles suspended in the ink. A glue is printed onto the fabric then a nanoscale fibers applied on it. Expanding ink (puff): an additive to plastisol inks which raises the print off the garment, creating a 3D feel.Caviar beads: again a glue is printed in the shape of the design, to which small plastic beads are then applied – works well with solid block areas creating an interesting tactile surface.Four color process: artwork is created using dots (CMYK) which combine to create the full spectrum of colours needed for photographic prints – this means a large number of colors can be printed using only 4 screens, making the set-up costs viable. The inks are required to blend and are more translucent, meaning a compromise with vibrancy of color.Gloss: a clear base laid over plastisol inks to create a shiny finish.Nylobond: a special ink additive for printing onto technical or waterproof fabrics. Mirrored silver: Another solvent based ink but you can almost see your face in it.Suede Ink: Suede is another great ink that is easy to print and gives the image a textured leather, simulated suede look and feel. Suede is a milky colored additive (much like a plastisol base) that will work in a regular plastisol. It is actually a puff blowing agent that does not bubble as much as regular puff ink. With suede additive you can make any color of plastisol have a suede feel. The directions vary from manufacturer to manufacturer, but generally you can add up to 50% suede additive to your normal plastisol.Print Gocco: Print Gocco is a Japanese commercially-produced home screenprinting system. Masters are created with the use of flashbulbs to burn an image into the screen. Over one-third of Japanese households own a Print Gocco system.

Versatility

Screenprinting is more versatile than traditional printing techniques. The surface does not have to be printed under pressure, unlike etching or lithography, and it does not have to be planar. Screenprinting inks can be used to work with a variety of materials, such as textiles, ceramics, wood, paper, glass, metal, and plastic. As a result, screenprinting is used in many different industries, from clothing to product labels to circuit board printing.

External links

• http://www.fespa.com/ - The Federation of European Screen Printers Associations
• http://www.sgia.org/ SGIA - Specialty Graphic Imaging Association

Notes