Production Process

Production Process Ananya PG GD 2013

Printing is a process for production of texts and images, typically with ink on paper using a printing press.

It is often carried out as a large scale and is essential part of publishing and transaction printing.

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CONVENTIONAL PRINTING

SCREEN

LETTERPRESS FLEXOGRAPHY

LITHOGRAPHY

GRAVURE

OFFSET DRY OFFSET

NON-IMPACT PRINTING

XEROGRAPHY IONOGRAPHY

MAGNETOGRAPHY LASER PRINTING

INKJET PRINTING

Classification of Printing Process - Conventional printing done with a master, transfers image by pressure, image area holds ink, non image area does not hold ink; sinlge plate or image can produce a number of productions on the press; letterpress, offset, gravure/intaglio, screen - Unconventional or non-impact printing no master or pressure, no separation between image area and non image area, non contact process; new image must be generated for each reproduction even if identical subject is being reproduced; digital, electrophotography, thermal imaging, xerography

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History of Printing Invention of paper - 105 A.D Woodblock printing - 200 A.D Movable type - 1040 Intaglio - 1430s Printing press - 1454 Lithography - 1796 Chromolithography - 1837 Rotary press - 1843 Flexography - 1873 Mimeograph - 1876 Hot metal typesetting - 1886 Offset press - 1903 Screen printing - 1907 Dye sublimation - 1957 Phototypesetting - 1960s Photocopier - 1960s Pad printing - 1960s Laser printing - 1969 Dot matrix printer - 1970s Thermal printer - 1970s Inkjet printer - 1976 3D printing - 1986 Stereolithography - 1986 Digital press - 1993 Frescography - 1998

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Major Printing Techniques Offset Lithography The basic principle of offset printingis that ink and water don’t mix. In modern presses, the image is transferred from the printing plate to a rubber blanket and then to the paper. Hence the name “offset.�When the printing plate is exposed, an ink receptive coating is activated at the image area. On the press, the plate is dampened, first by water rollers, then by ink rollers.

Ink adheres to the image area and water to the non-image area. As the cylinders rotate, the image is transferred to the blanket. Paper passes between the blanket cylinder and the image is transferred to the paper.

Letterpress Letterpress is often used for fine art prints, books and posters.

In the process, the image area is actually raised above the rest of the plate, so the image makes a physical impression on the paper.

Flexography Modern flexography is a versatile process that uses photoetched plates. The non-image areas on these plates are etched away, leaving only the printing surface that carries the ink directly to the substrate. Common applications for flexo include labels, tabs, corrugated boxes, cartons and newspapers.

Gravure Basically, gravure turns everything in the image into halftone dots. The plate cylinder consists of tiny cells, varying in depth and width, that hold the ink. As the press runs, a doctor blade scrapes excess ink off the surface of the plate, leaving ink only

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in cells. As the paper contacts the plate, the ink is transferred, reproducing type, rules, graphics, and photographs as composites of very fine dots. Gravure is used only in very long runs, usually for publications and packaging printing.

Screen Printing Screen printing is the most versatile form of print reproduction.

Although once thought of as being oriented to short production runs, modern high-speed technology allows for volume production where brilliant, accurate colors, and close tolerance are necessary. Ink is expressed through a stretched fabric mesh by a squeegee blade to reproduce the original image onto the substrate below. Screen printing is not limited to press size or the same of any substrate. A variety of materials such as paper, plastic, metal, fabric and glass can be screen printed.

Digital printing Digital printing is any printing process that uses a digital file to create an image using a non-impact imaging transfer method.

Common methods include ink jet and electrophotography.

Digital printing technology can be divided into two categories based on how the image is transfered to the substrate. These categories are direct to image carrier and direct to paper.

Direct to image carrier includes black and white and color electrophotography, while direct to paper includes Ink jet, dye sublimation, thermal direct transfer, electrostatic, and other printing methods that directly image the substrate. Both of these categories are classified as non-impact printing.

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Other Processes Electro Photography / Electrostat Printing / Xerography It was invented in 1937 by Chester Carlston and developed by Xerox Corporation. Artwork is placed face down and is illuminated by fluoroscent light which travels the length of the image. The reflected image is directed throught the lenses onto an electrically charged drum. This charge leaks away where light from the image falls on the drum. A resin based powder called toner, is attracted to the image areas. This pattern of toner is transferred to the sheet of paper where it is fixed (fused) by the heat. Laser copier works like combined scanners and image setters by scanning the image digitally and using a laser to write the image on to an electrostatic drum.

Collotype It is a screenless planographic process but is not used on a large scale in which the plates are coated with bichromated gelatin and exposed to continuous tone negatives and printed on lithographic presses with special dampening.

Thermography It produces a glossy, raised image by using infrared light. The image is first printed either by letterpress or lithography using an adhesive ink which is coated with a fusible resin containing pigment or a metallic powder. When passed under infrared light the resin pigment is fused to give a hard raised image.

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The Printing press Johannes Gutenberg's work on his printing press began in approximately 1436 when he partnered with Andreas Dritzehen and Andreas Heilman.

Platen press In the platen press, a flat surface bearing the paper is pressed against the flat, inked printing plate; the two surfaces come together and part with a jawlike motion. Most small hand presses are platen presses.

Rotary press The rotary printing press was invented by Richard March Hoe in 1843. It uses impressions curved around a cylinder to print on long continuous rolls of paper or other substrates. It is primarily used in high-speed, web-fed operations, in which the press takes paper from a roll.

Perfecting Press A printing press that allows the simultaneous printing on both sides of a sheet of paper in one pass through the press.

Sheet-fed Press In this kind of offset press the printing is carried out on single sheets of paper as they are fed to the press one at a time.

Web-fed Press In this kind of offset press the printing is carried out on a single, continuous sheet of paper fed from a large roll. The sheet is then cut into individual sheets of desired sizes.

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Offset printing Offset printing or web offset printing is a commonly used printing technique in which 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.

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

Advantages of offset printing compared to other printing methods include: - Consistent high image quality - Quick and easy production of printing plates.

- Longer printing plate life than on direct litho presses - Cheaper cost - possibility of adjusting the amount of ink on the fountain roller with screw keys for precise results Disadvantages of offset printing compared to other printing methods include: - Slightly inferior image quality compared to rotogravure or

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photogravure printing.

- Propensity for anodized aluminum printing plates to become sensitive (due to chemical oxidation) and print in non-image/ background areas when developed plates are not cared for properly.

- Time and cost associated with producing plates and printing press setup. As a result, very small quantity printing jobs may now use digital offset machines.

Printing process The most common kind of offset printing is derived from the photo offset process, which involves using light-sensitive chemicals and photographic techniques to transfer images and type from original materials to printing plates. In current use, original materials may be an actual photographic print and typeset text. However, it is more common — with the prevalence of computers and digital images — that the source material exists only as data in a digital publishing system.

In this process, ink is transferred from the ink duct to the paper in several steps - The ink duct roller delivers ink from the ink duct to the ink pyramid, also called the Ink Train.

- The ductor roller, sometimes called a vibrator roller due to its rapid back and forth motion, transfers ink from the duct roller to the first distribution roller. It is never in contact with both rollers at the same time.

- The distribution rollers evenly distribute the ink. The first distribution roller picks up the ink from driving rollers, and the last distribution rollers transfer the ink to the form rollers.

- The transfer rollers transfer ink between the ink-absorbing and ink-delivering driving rollers.

- Driving rollers roll against the distribution rollers and either absorb or deliver ink, depending on their placement.

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- Ink form rollers transfer ink from the last distribution rollers on to the printing plate.

- The printing plate transfers the ink to the offset cylinder (typically called the blanket cylinder) usually covered with a rubber “blanket.�

- The paper is then pressed against the blanket cylinder by the impression cylinder, transferring the ink onto the paper to form the printed image.

Plates Metal plates: Generally, the plates used in offset printing are thin, flexible, and usually larger than the paper size to be printed, and are usually made of aluminum, although sometimes they are made of multimetal, paper, or plastic.

Polyester plates: These are much cheaper and can be used in place of aluminum plates for smaller formats or medium quality jobs, as their dimensional stability is lower.

Computer-to-plate (CTP) / direct-to-plate (DTP) Computer-to-plate (CTP) is a newer technology that allows the imaging of metal or polyester plates without the use of film.

By eliminating the stripping, compositing, and traditional plate making processes, CTP altered the printing industry, which led to reduced prepress times, lower costs of labor, and improved print quality. Most CTP systems used thermal CTP as opposed to violet CTP, though both systems are effective, depending on the needs of the printing job.

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Rotogravure Rotogravure is a type of intaglio printing process, which involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a cylinder because, like offset printing and flexography, it uses a rotary printing press.

Once a staple of newspaper photo features, the rotogravure process is still used for commercial printing of magazines, postcards, and corrugated (cardboard) product packaging.

Components The first step of Gravure is to create the cylinder with the engraved images that need to be printed: the engraving process will create on the cylinder surface the cells that will contain the ink in order to transfer it to the paper. Since the amount of ink contained in the cells corresponds to different colour intensities on the paper, the dimensions of the cells must be carefully set: deeper cells will produce more intensive colours whereas less deep cells will produce less intensive ones. Gravure cylinders are usually made of steel and plated with copper and a light-sensitive coating. Previously machined to remove imperfections in the copper, most cylinders are now laser engraved. In the past, they were either engraved using a diamond stylus or chemically etched using ferric chloride, which creates pollution. If the cylinder was chemically etched, a resist (in the form of a negative image) was transferred to the cylinder before etching. The resist protects the nonimage areas of the cylinder from the etchant. After etching, the resist was stripped off. The operation is analogous to the manufacture of printed circuit boards. Following engraving, the cylinder is proofed and tested, reworked if necessary, and then chrome plated.

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A rotogravure printing press has one printing unit for each color, typically CMYK or cyan, magenta, yellow and key (printing terminology for black), but the number of units varies depending on what colors are required to produce the final image. There are five basic components in each color unit: an engraved cylinder (AKA "Gravure cylinder") whose circumference can differ according to the layout of the job; an ink fountain; a doctor blade; an impression roller; a dryer.

Process In direct image carriers such as gravure cylinders, the ink is applied directly to the cylinder and from the cylinder it is transferred to the substrate. 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 excess ink from the non-printing (non-recessed) areas and leaving in the cells the right amount of ink required: this tool is located quite close to the paper so that the ink left in the cells does not have enough time to dry.

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. The capillary action of the substrate and the pressure from impression rollers force the ink out of the cell cavity and transfer it to the substrate. 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.

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Features Because gravure is capable of transferring more ink to the paper than other printing processes, it 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 offset lithography. Gravure is an industrial printing process capable of consistent high quality printing. Since the Gravure printing process requires the creation of one cylinder for each colour of the final image, it is expensive for short runs and best suited for high volume printing. Another application area of gravure printing is in the flexible-packaging sector.

Advantages The rotogravure printing process is the most popular printing process used in flexible-packaging manufacturing, because of its ability to print on thin film such as polyester, OPP, nylon, and PE, which come in a wide range of thicknesses, commonly 10 to 30 micrometers.

Other appreciated features include: printing cylinders that can last through large-volume runs without the image degrading good quality image reproduction low per-unit costs running high volume production Disadvantages Shortcomings of the gravure printing process include: high start-up costs: hundreds of thousands of copies needed to make it profitable rasterized lines and texts use of chemicals in the ink.

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Letterpress printing Letterpress printing is a technique of relief printing using a printing press. A worker composes and locks movable type into the bed of a press, inks it, and presses paper against it to transfer the ink from the type. Letterpress printing was the normal form of printing text from its invention by Johannes Gutenberg in the mid-15th century until the 19th century and remained in wide use for books and other uses until the second half of the 20th century. Letterpress printing remained the primary way to print and distribute information until the twentieth century, when offset printing was developed, which largely supplanted its role in printing books and newspapers.

More recently, letterpress printing has seen a revival in an artisanal form.

Process The process of letterpress printing consists of several stages: composition, imposition and lock-up, and printing.

Composition Composition, or typesetting, is the stage where pieces of movable type are assembled to form the desired text. The person charged with composition is called a "compositor".

Traditionally, as in manual composition, it involves selecting the individual type letters from a type case, placing them in a composing stick, which holds several lines, then transferring those to a larger type galley. By this method the compositor gradually builds out the text of an individual page letter by letter. In mechanical typesetting, it may involve using a keyboard to select the type, or even cast the desired type on the spot, as in hot metal typesetting, which are then added to a galley designed for the product of that process.

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After a galley is assembled to fill a page-worth a type, the type is tied together into a single unit so that it may be transported without falling apart. From this bundle a galley proof is made, which is inspected by a proof-reader to make sure that the particular page is accurate.

Imposition A single-page form for printing the front page of the New Testament. The black frame surrounding it is the "chase", and the two objects each on the bottom and left side are the "quoins". Broadly, imposition or imposing is the process by which the tied assemblages of type are converted into a "form" ("forme") ready to use on the press. A person charged with imposition is a stoneman, doing their work on a large, flat imposition stone (though some later ones were also of iron).

More specifically, imposition is the technique of arranging the various pages of type with respect to one another (this is its modern sense). Depending on page size and the sheet of paper used, several pages may be printed at once on a single sheet. After printing, these are cut and trimmed before folding or binding. In these steps, the imposition process ensures that the pages face the right direction and in the right order with the right margins. Low-height pieces of wood or metal furniture is added to make up the blank areas of a page. The printer uses a mallet to level the type and blocks to ensure the printing surface is flat.

Lock up Lock-up is the final step before printing. The printer removes the cords that hold the type together, and turns the quoins with a key or lever to "lock" the entire complex of type, blocks, furniture, and chase (frame) into place—creating what is called a form or forme. The printer takes the finished form to the

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printing press, and proofs it again for errors before starting the printing run.

Printing The working of the printing process depends on the type of press used, as well as any of its associated technologies (which varied by time period).

Hand presses generally required two people to operate them: one to ink the type, the other to work the press. Later mechanized jobbing presses require a single operator to feed and remove the paper, as the inking and pressing are done automatically.

The completed sheets are then taken to dry and for finishing, depending on the variety of printed matter being produced.

With newspapers, they are taken to a folding machine. Sheets for books are sent for bookbinding.

Flexography Flexography is a form of printing process which utilizes a flexible relief plate. It is essentially a modern version of letterpress which can be used for printing on almost any type of substrate, including plastic, metallic films, cellophane, and paper. It is widely used for printing on the non-porous substrates required for various types of food packaging. 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 like plastic, foil, acetate film, brown paper, and other materials used in packaging.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.

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Screen printing Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil to receive a desired image. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate.

A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink into the mesh openings for transfer by capillary action during the squeegee stroke. It is also known as silkscreen, serigraphy, and serigraph printing. One colour is printed at a time, so several screens can be used to produce a multicoloured image or design.

There are various terms used for what is essentially the same technique. Traditionally the process was called screen printing or silkscreen printing because silk was used in the process prior to the invention of polyester mesh. Currently, synthetic threads are commonly used in the screen printing process.

The most popular mesh in general use is made of polyester.

There are special-use mesh materials of nylon and stainless steel available to the screen printer. There are also different types of mesh size which will determine the outcome and look of the finished design on the material.

Printing technique A screen is made of a piece of mesh stretched over a frame.

A stencil is formed by blocking off parts of the screen in the negative image of the design to be printed; that is, the open spaces are where the ink will appear on the substrate.

Before printing occurs, the frame and screen must undergo the pre-press process, in which an emulsion is 'scooped' across the mesh and the 'exposure unit' burns away the

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unnecessary emulsion leaving behind a clean area in the mesh with the identical shape as the desired image. The surface (commonly referred to as a pallet) that the substrate will be printed against is coated with a wide 'pallet tape'. This serves to protect the 'pallet' from any unwanted ink leaking through the substrate and potentially staining the 'pallet' or transferring unwanted ink onto the next substrate. Next, the screen and frame are lined with a tape. The type of tape used in for this purpose often depends upon the ink that is to be printed onto the substrate. These aggressive tapes are generally used for UV and water-based inks due to the inks' lower viscosities. The last process in the 'pre-press' is blocking out any unwanted 'pinholes' in the emulsion. If these holes are left in the emulsion, the ink will continue through and leave unwanted marks. To block out these holes, materials such as tapes, specialty emulsions and 'block-out pens' may be used effectively.

The screen is placed atop a substrate. Ink is placed on top of the screen, and a floodbar is used to push the ink through the holes in the mesh. 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 proportional 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.

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Stenciling techniques A method of stenciling that has increased in popularity over the past years is the photo emulsion technique: The original image is created on a transparent overlay, and the image may be drawn or painted directly on the overlay, photocopied, or printed with a computer printer, but making so that the areas to be inked are not transparent. A black-andwhite positive may also be used (projected on to the screen).

However, unlike traditional plate-making, these screens are normally exposed by using film positives.

A screen must then be selected. There are several different mesh counts that can be used depending on the detail of the design being printed. Once a screen is selected, the screen must be coated with emulsion and put to dry in a dark room.

Once dry, it is then possible to burn/expose the print.

The overlay is placed over the screen, and then exposed with a light source containing ultraviolet light in the 350-420 nano meter spectrum.

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.

Another advantage of screen printing is that large quantities can be produced rapidly with new automatic presses, up to 1800 shirts in 1 hour.

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Identification of Major Printing Processes Letterpress - the edges of the text will show ink squash due to heavy pressure - due to heavy pressure at the back of the paper slight indentation will be seen - ink intensity is higher compared to offset printing due to direct transfer of ink Offset - the impression will be seen in both text and halftone - lines and text are sharp and have clear outlines - solid colors are evenly inked - better text production than gravure Gravure - the edges of the etxt will not be sharp and shows sawteeth effect at the edges. Even if text is rasterised, results in a lesser quality than offset printing - the reproduction of halftone dots is very precise because they are not pressed onto the paper as they are in offset printing. The image quality is therefore better than that achieved with offset printing Screen - due to heavy deposition of theink it shows slight raised impression - the ink intensity is also high and even - text is relatively blurry and low quality compared to text printed with the offset method

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Printing Process It can be divide into three - prepress, press and postpress Prepress It includes all steps which are carried out before the actual printing, the transferring of information onto paper or another substrate. Traditional press has three areas - Composition, i.e recording text, formatting text and pagination - Reproduction, i.e of pictures, graphics particularly color separations for multicolor printing - Assembly and Plate-making, i.e the assembly of text, picture and graphic elements into complete pages from pages to print sheets

Press It is the process of transferrin ink onto paper or another substrate via a printing plate

Postpress It includes all those steps which are carried out after priting on paper or another material has taken place.

Finishing processes are as diverse as the methods of producing printed products, whether they involove books, newspapers, folding boxes, or sets of labels.

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Graphic Art Reproduction It is the process of processing a duplicate of the originals based on photomechanical techniques. In photomechanical image processing, the master (film) is produced using optic devices to record the images (cameras, optics,filters) and process them (color filters, optical screens, special properties of the film material)

Types of Originals Line Art Images containing only black and white pixels. Also known as bi-level image. Sometimes used to describe drawings containing flat colors without tonal variations.

Continuous Tone A greyscale or color image format capable of illustrating continuously varying tonal ranges as opposed to line art.

Originals not suited for Reproduction - stained, dust and scratches - faded color print - matt print - unsharp print Care of Originals - never write on the back of photographs - originals should be covered with tracing sheet - should not be handled with oily hand, avoid finger prints - don’t attach wire clip - don’t fold or roll a photograph

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Halftone Halftone is the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size, in shape or in spacing. Where continuous tone imagery contains an infinite range of colors or greys, the halftone process reduces visual reproductions to an image that is printed with only one color of ink, in dots of differing size. This reproduction relies on a basic optical illusion—that these tiny halftone dots are blended into smooth tones by the human eye. At a microscopic level, developed black-and-white photographic film also consists of only two colors, and not an infinite range of continuous tones. Just as color photography evolved with the addition of filters and film layers, color printing is made possible by repeating the halftone process for each subtractive color—most commonly using what is called the "CMYK color model". The semi-opaque property of ink allows halftone dots of different colors to create another optical effect—full-color imagery.

Traditional screening The most common method of creating screens—amplitude modulation—produces a regular grid of dots that vary in size. The other method of creating screens—frequency modulation—is used in a process also known as stochastic screening. Both modulation methods are named by analogy with the use of the terms in telecommunications.

Typical Halftone Resolutions Screen Printing 45–65 lpi Laser Printer (300dpi) 65 lpi Laser Printer (600dpi) 85–105 lpi Offset Press (newsprint paper) 85 lpi Offset Press (coated paper) 85–185 lpi

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The resolution of a halftone screen is measured in lines per inch (lpi). This is the number of lines of dots in one inch, measured parallel with the screen's angle. Known as the screen ruling, the resolution of a screen is written either with the suffix lpi or a hash mark; for example, "150 lpi" or "150#".

The higher the pixel resolution of a source file, the greater the detail that can be reproduced. However, such increase also requires a corresponding increase in screen ruling or the output will suffer from posterization. Therefore file resolution is matched to the output resolution.

Multiple screens and color halftoning When different screens are combined, a number of distracting visual effects can occur, including the edges being overly emphasized, as well as a moirĂŠ pattern. This problem can be reduced by rotating the screens in relation to each other.

This screen angle is another common measurement used in printing, measured in degrees clockwise from a line running to the left (9 o'clock is zero degrees).

Halftoning is also commonly used for printing color pictures.

The general idea is the same, by varying the density of the four secondary printing colors, cyan, magenta, yellow and black (abbreviation CMYK), any particular shade can be reproduced.

In this case there is an additional problem that can occur. In the simple case, one could create a halftone using the same techniques used for printing shades of grey, but in this case the different printing colors have to remain physically close to each other to fool the eye into thinking they are a single color.

To do this the industry has standardized on a set of known angles, which result in the dots forming into small circles or rosettes. The dots cannot easily be seen by the naked eye, but can be discerned through a microscope or a magnifying glass.

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Dot shapes Though round dots are the most common used, there are different dot types available, each of them having their own characteristics. They can be used simultaneously to avoid the moirĂŠ effect. Generally, the preferred dot shape is also dependent on the printing method or the printing plate.

Round dots: most common, suitable for light images, especially for skin tones. They meet at a tonal value of 70%.

Elliptical dots: appropriate for images with many objects.

Elliptical dots meet at the tonal values 40% (pointed ends) and 60% (long side), so there is a risk of a pattern.

Square dots: best for detailed images, not recommended for skin tones. The corners meet at a tonal value of 50%. The transition between the square dots can sometimes be visible to the human eye.

Digital halftoning Digital halftoning has been replacing photographic halftoning since the 1970s when "electronic dot generators" were developed for the film recorder units linked to color drum scanners made by companies such as Crosfield Electronics, Hell and Linotype-Paul. All halftoning uses a high frequency/ low frequency dichotomy. In photographic halftoning, the low frequency attribute is a local area of the output image designated a halftone cell. Each equal-sized cell relates to a corresponding area (size and location) of the continuous-tone input image. Within each cell, the high frequency attribute is a centered variable-sized halftone dot composed of ink or toner. The ratio of the inked area to the non-inked area of the output cell corresponds to the luminance or graylevel of the input cell. From a suitable distance, the human eye averages both the high frequency apparent gray level approximated by the ratio within the cell and the low frequency apparent

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changes in gray level between adjacent equally spaced cells and centered dots. Digital halftoning uses a raster image or bitmap within which each monochrome picture element or pixel may be on or off, ink or no ink. Consequently, to emulate the photographic halftone cell, the digital halftone cell must contain groups of monochrome pixels within the same-sized cell area. The fixed location and size of these monochrome pixels compromises the high frequency/low frequency dichotomy of the photographic halftone method. Clustered multi-pixel dots cannot "grow" incrementally but in jumps of one whole pixel. In addition, the placement of that pixel is slightly off-center. To minimize this compromise, the digital halftone monochrome pixels must be quite small, numbering from 600 to 2,540, or more, pixels per inch. However, digital image processing has also enabled more sophisticated dithering algorithms to decide which pixels to turn black or white, some of which yield better results than digital halftoning. Digital halftoning based on some modern image processing tools such as nonlinear diffusion and stochastic flipping has also been proposed recently.

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Color Theory Additive color is color created by mixing light of two or more different colors. Red, green, and blue are the additive primary colors normally used in additive color system. The combination of two of the standard three additive primary colors in equal proportions produces an additive secondary color—cyan, magenta or yellow. Computer monitors and televisions are the most common examples of additive color. The full gamut of color available in any additive color system is defined by all the possible combinations of all the possible luminosities of each primary color in that system.

In chromaticity space, the gamut is a plane convex polygon with corners at the primaries. For three primaries, it is a triangle. For example, in subtractive color systems green is a combination of yellow and blue; in additive color, red + green = yellow and no simple combination will yield green. Additive color is a result of the way the eye detects color, and is not a property of light.

A subtractive color model explains the mixing of a limited set of dyes, inks, paint pigments or natural colorants to create a wider range of colors, each the result of partially or completely subtracting (that is, absorbing) some wavelengths of light and not others. The color that a surface displays depends on which parts of the visible spectrum are not absorbed and therefore remain visible.

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Color printing Colour printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). Any natural scene or color photograph can be optically and physiologically dissected into three primary colors, red, green and blue, roughly equal amounts of which give rise to the perception of white, and different proportions of which give rise to the visual sensations of all other colors.

The additive combination of any two primary colors in roughly equal proportion gives rise to the perception of a secondary color.

Modern techniques While there are many techniques for reproducing images in color, specific graphic processes and industrial equipment are used for mass reproduction of color images on paper.

The technique used to print full-color images, such as color photographs, is referred to as four-color-process or merely process printing. Four inks are used: three secondary colors plus black. These ink colors are cyan, magenta and yellow; abbreviated as CMYK. Cyan can be thought of as minus-red, magenta as minus-green, and yellow as minus-blue. These inks are semi-transparent or translucent. Where two such inks overlap on the paper due to sequential printing impressions, a primary color is perceived.

Two graphic techniques are required to prepare images for four-color printing. In the "pre-press" stage, original images are translated into forms that can be used on a printing press, through "color separation," and "screening" or "halftoning."

These steps make possible the creation of printing plates that can transfer color impressions to paper on printing presses based on the principles of lithography.

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An emerging method of full-color printing is six-color process printing (for example, Pantone's Hexachrome system) which adds orange and green to the traditional CMYK inks for a larger and more vibrant gamut, or color range. However, such alternate color systems still rely on color separation, halftoning and lithography to produce printed images.

Color printing can also involve as few as one color ink, or multiple color inks which are not the primary colors. Using a limited number of color inks, or specific color inks in addition to the primary colors, is referred to as "spot color" printing.

Generally, spot-color inks are specific formulations that are designed to print alone, rather than to blend with other inks on the paper to produce various hues and shades. The range of available spot color inks, much like paint, is nearly unlimited, and much more varied than the colors that can be produced by four-color-process printing. Spot-color inks range from subtle pastels to intense fluorescents to reflective metallics.

Color printing involves a series of steps, or transformations, to generate a quality color reproduction. The following sections focus on the steps used when reproducing a color image in CMYK printing, along with some historical perspective.

Factors to consider before starting a 4 color project - how is the product being printed, how many colors are being used?

- color and grade of paper stock being used - will the paper b coated or uncoated - which line screen will give the best result on that paper - will a service bureau or the printer output the film - will the printer be using film or going directly to the plate - how color can be proofed

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Color correcting images for press - quality of original image - quality of scanned image - ensuring proper contasr from light to dark - avoid light areas dropping out within the photograph - prevent the dark areas filling in (dot gain) which causes loss of detail and improper tonal range from light to dark - compensating for the printing process including the paper being utilised Calibration The process of returning a device to known color conditions, commonly done with devices that change color frequently such as monitors Color Separation A meaans of dividing a full color photograph into four separate components, corresponding to the four primary colors used in process color printing—cyan, magenta, yellow, and black.

Process color printing involves overprinting halftone dots of each of these four colors in varying densities, the various combinations producing the wide range of reproducible colors.

Consequently, a different printing plate needs to be made of each color and this, in turn, requires separate negatives or positives. (The term color separation refers to both the process and the products of that process.) The process of color separation can be accomplished photographically, electronically, or on the desktop.

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Desktop publishing Desktop publishing (abbreviated DTP) is the creation of documents using page layout skills on a personal computer.

When used skillfully, desktop publishing software can produce text and images with attractive layouts and typographic quality comparable to traditional typography and printing, so DTP is also the main reference for digital typography.Desktop publishing combines a personal computer and WYSIWYG page layout software to create publication documents on a computer for either large scale publishing or small scale local multifunction peripheral output and distribution. Desktop publishing methods provide more control over design, layout, and typography than word processing does. However, word processing software has evolved to include some, though by no means all, capabilities previously available only with professional printing or desktop publishing.

File Formats JPEG - Joint Photographic Experts Group. It has various file compression techniques. It is known as lossy format i.e while compressing file some data should be omitted from the file, in this format data is permanently omitted from the file, which results in poor quality output.

TIFF - Tag Image File Format. A popular lossless image file format supported by the majority of image-editing programs running on a variety of computer platforms.

EPS - Encapsulated Postscript. A standard format for drawing, image or complete page layout, allowing it to be palced in to other documents. EPS files normally include low resolution screen preview.

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Scanner A device used to analyze an original image and either generate color separations and/or digitize the image and store it in a computer for later manipulation and output. Essentially, a scanner records one row of the image at a time, and converts the original into an electronic matrix of pixels (or bit map).

Each pixel is recorded as some level of gray for each of the red, green, and blue components of an image, and the scanner then collates them back into the appropriate (or closely approximating the appropriate) color for each pixel.

An important distinction in prepress is drum scanner versus flatbed scanner. A drum scanner is a high-end machine that utilizes a highly sensitive photomultiplier tube to capture subtle variations in tone, and is capable of digitizing images at very high resolutions. Flatbed scanners are much less expensive, but their use of charge-coupled devices (CCDs) makes them less sensitive to subtle color variations.

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Planning and Design Things to keep in mind while palnning the project are - will the trim size of the finished sheet allow the best use of the signature sheet?

- make a dummy to make certain you have set up the correct amount of pages. Signatures consist of 4, 8 or 16 pages in most cases. The number of page smust be a multiple of 4. In your page layout program, set the page size to be the actual page size so that trim marks will be accurate.

- will the paper you have chosen run through the press? some lightweight and very heavy stocks may give you problems.

- how many ink units are on the press? if you are printing a job with 4 color process, three spot colors and varnish, the job will require an eight unit press - which paper and printing process will be used? you need to know this information so that you can set the correct halftone screen, image resolution (1.5-2 times the haftone screen) and dot gain for photographs.

- is the desktop publishing software in which the artwork was created, compatible with the software the printer uses? is the paltform and version number the same? are the fonts available or are they supplied (both printer and screen) and are they the correct type? are all linked images supplied?

- understand and use color management. Every device such as scanners, monitors and ink jet printers all use color differently. In order for the piece to end up printing like the designer intended, use a color management system - are your color settings correct for the printing process? if you have scanned images or other graphics they must be set for CMYK not RGB - what size of trap do you need? older presses may not be as accurate as newer presses and need a larger trap

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Imposition The positioning of pages on a press sheet in such a manner that when the sheet is folded into a signature and cut, the pages will be in the correct sequence. Imposition involves not just the correct positioning of pages on the same side of the sheet, but also the back printing, or the pages printed on the back of the sheet.

One side imposition The simplest form of imposition is one side imposition. In one side imposition, one priting plate is used to print on one side of the sheet as it passes through the printing press. This type of imposition is common in small, offset press operations Sheetwise imposition Two priting plates are used in sheet wise imposition. One printing plate is used to print on one side of a press sheet. A second plate containing different information is then made, the sheets are turned over, and the sheets are printed on the other side from the second plate. In half sheet work one printing plate is used to print both side of paper. Ater printing on one side of the paper, the paper is turned over to print on other side, feeding same gripper edge in to the machine. After printing paper is cut in half, giving two signatures from one plate.

Signature imposition A large single sheet is frequently passed through a printing press and then foldedand trimmed to form a portion of a book or magazine. THis process is called signature imposition. four-, eight-, tweive-, sixteen-, twenty four- are common press runs.

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Ganging Grouping images, photographs, or other original art together.

Ganged imposition is done when the job to be printed is smaller than the press can handle or it is so much smaller than the standard press sheet size taht printing only that one would be an inefficient use of equipment.

Work-and-Turn In prepress and printing, an imposition or layout in which a printing plate containing both the front and back of a sheet are mounted on the press at the same time and print on a double-size sheet of paper. Thus, half the sheet is the top printing, while the other half of the sheet is the “back printing.�

When half the required number of sheets have been printed, the printed sheets are flipped over (keeping the same gripper edge) and run through again.

Work-and-Tumble In prepress and printing, an imposition or layout in which one plate contains all the images (pages) to be printed on both sides of a sheet. Once one side of a job has been printed, the pile of printed sheets is turned over, the edge of the sheet that was the gripper edge for the first side becoming the back edge for the second side. After printing, the sheet is cut in half, yielding two identical units.

The type of imposition used depends on several factors - the design of the printed piece - type and size of the press to be used - type of paper to be used during printing

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Gripper Margin - A space at the leading edge of a sheet of paper—usually three-eighths to one-half inch wide—in which, on a sheetfed press, printing cannot take place. This margin is reserved for use by the grippers, or the mechanisms that carry the sheet through the press.

Register Marks - Small designs, shapes, or other patterns (most commonly a circle or oval with a cross through it) placed in non-image areas of negatives, positives, color separations, and plates to ensure correct register—or alignment—of successive colors and/or images.

Fold Marks - In prepress, a set of marks added to a negative or flat—in the margins of a page—added as a guide for postpress folding.

Cropmarks - Lines drawn or printed on a photograph, overlay, or printed product to indicate the proper cropping of the image or print in question. Also spelled as two words, crop marks, and also known as trim marks.

Trapping - In prepress, the compensation for misregister of successive colors or images. Trapping and trapping techniques ensure that there are no unsightly gaps or overlaps of successively-printed colors or images.

Knockout/cutout - A space—or keyline—left in a document for the later insertion of some form of graphic image. Also known as a cutout. The term knockout is also used to refer to “white type” or, in other words, type which prints as a reverse, or, in fact, doesn’t really print at all, allowing the color of the page to show through a background in the shape of type.

Overprinting - Printing that is done on top of a previously printed area

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Types of Paper Matte Paper - Matte paper is best for everyday use. Matte paper is a kind of paper that has a white coating that allows the ink to dry quickly. Because the ink does dry so quickly on matte paper, it is unlikely to smear or become smudged with fingerprints.

Glossy Paper - Glossy paper is typically used for printing photos because the paper produces sharp, vibrant print due to its glossy finish. The glossy finish actually absorbs the ink to create beautiful pictures. However, it is easy to smudge the paper with fingerprints, so it is important to handle it gently until the freshly printed item has dried completely. Glossy paper can become stuck to pages that are against the printed side, so it is best to avoid using it in situations where it will be used that way, such as in scrapbooks. There is a specialized kind of glossy paper specifically designed for photo printing.

Photo Paper - Though glossy paper is primarily for photos and similar applications, photo paper is specifically designed just for photos. Photo paper has a glossy finish and it also allows the ink to dry quickly producing picturesque images.

Photo paper usually comes in several sizes and weights.

Bright White Paper - Bright white paper can be printed on both sides. In fact, it is designed for double use. With smooth, non-textured surfaces, it allows the user to print on both sides without affecting the quality of the print. Because of its brightness, it is designed to make black text as well as other colors stand out on the page.

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Resume Paper - When a buyer wants a document, resume, or important form to stand out in the stack, resume paper does the trick. Made heavier and more expensive looking than plain white paper, typically resume paper has a classy cream, ivory, or off-white appeal to it that tells employers and other professionals that the one who printed on this paper really means business.

Card Stock - Card stock is a very heavy and sturdy paper.

It can be used as printer paper as well as for everyday use.

Because of how heavy it is, card stock does not go through the printer as quickly as regular printer paper. Therefore cardstock is typically only used for scrapbooking, signage, and printing business cards or postcards.

Printer Paper Specific to Certain Printers - There are specific types of printer paper that are made specifically for certain kinds of printers. There is specialized paper for solid ink printers and printers that take rolled up paper, but the two of the best-known types of printer paper include the following: Inkjet Paper - Inkjet paper is specifically made for inkjet printers. For example, there is photo paper, glossy paper, business card paper, and greeting card paper made specifically to go through an inkjet printer.

Laser Paper - The laser printer also has its own set of paper called laser paper. Laser paper is generally used if printing checks, address labels, or mailing labels as there are specific settings on the laser printer to assist with printing this paper.

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Characteristics of Paper Coating There are various printer papers that are coated. Coated finished papers come in matte, dull, and smooth surfaces.

The smooth surfaces are called glossy and are designed for printing photos. There are many uncoated printer papers that have no smooth or waxy coating. They may have various surface textures like linen embedded in them. When choosing printer paper, it is important that the buyer know what project he or she will use the paper for to choose the right coating.

Brightness Printer paper comes in various colors and brightness levels.

The level of brightness of a particular type of paper is labeled on the package of paper. Typically brightness ranges from 80 to 100 with the higher number providing sharper images. The higher numbers also represent brighter paper. The contrast of the paper is a key element in the contrast with the toner or ink and the paper, and the whiter and brighter the paper is, the better a print will look.

Weight Printer paper can also come in various weights which are the result of the thickness of an individual piece of paper. The thickness is calculated in pounds and grams. One can find the weight of the paper on the package of paper. The weight of the paper indicates what the paper is intended to be used for.

The paper weight refers to the weight of a 500-sheet ream of 17 by 22 inch paper in which each of the sheets is equivalent to four of the letter size sheets. Therefore, if 500 sheets of paper weighs 20 pounds, then the paper actually weighs five

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pounds. The higher the paperweight is, the thicker the paper is. The thicker the paper is, the more durable it is; but the thicker it is, the slower it goes through the printer. Standard 20 pound paper is for every day, high-volume use while heavier paper is used for presentations and other areas where quality is important.

Opacity Another facet to consider when choosing printer paper is the opacity. The opacity simply means how much print will show through to the other side. Opacity is measured from 0 which means transparent to 100 which means completely opaque.

The opacity can be measured by how well the printer paper prevents light from passing through it. Standard paper at 20 pounds is more translucent while the heavier papers will be less likely to show print on the side that wasn’t printed on.

Smoothness Smoothness can also be a factor when determining which paper to get. Laser printers for example use heat and toner to produce text and images, and therefore need a smooth paper to give good results, whereas many other printers use water based inks, and therefore, need textured paper to absorb the ink. The smoothness of the paper can be determined by whether or not the paper is coated as well as the material it is made out of.

Paper Size Size really does matter when choosing printer paper. There are several sizes that are used in printers today. It is important to know what size paper is used for what type of project. The following table is a breakdown of various paper sizes and when to use them.

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ISO Paper Sizes Standard sizes of international paper set by the International Standards Organization. ISO paper sizes all maintain a constant width-to-length ratio of 1:1.414. When a sheet is cut in half, both new sheets will still retain that size ratio.

A Series - In the metric system, series of standard paper sizes based on portions of a square meter. (A square meter is the area used to determine paper grammage, the metric equivalent of basis weight. Grammage is expressed as grams per square meter [g/m2].) In the A series, the length-to-width ratio is maintained from size to size, and the area varies from size to successive size by a factor of 2 or H. B Series - In the metric system, series of standard paper sizes based on portions of a square meter. The basic paper sizes are known as the A series, and the B series comprises intermediate paper sizes to the A series. The length-to-width ratio is maintained from size to size.

Traditional inch-based paper sizes Traditionally, a number of different sizes were defined for large sheets of paper, and paper sizes were defined by the sheet name and the number of times it had been folded. Thus a full sheet of “royal” paper was 25 × 20 inches, and “royal octavo” was this size folded three times, so as to make eight sheets, and was thus 10 by 6¼ inches. Imperial sizes were used in the United Kingdom and its territories. Traditional sizes for paper in the United Kingdom are Quarto (10 × 8), Foolscap (13 × 8), Imperial (9 × 7), Kings (8 × 6.5), Dukes (7 × 5.5)

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Binding Cutting and Trimming - Blank stock may need to be trimmed prior to printing in order to produce square, uniformly-sized press sheets (more properly called trimming), or printed sheets may need to be cut after printing, especially in case where signature pages need to be separated or multiple copies of the same image were printed on the same sheet. Most cutting and trimming is performed on a guillotine cutter, a manual or electronic device with a long, curved heavy knife.

Folding - A folder is an automated device which uses a variety of means to fold sheets of paper inserted into it. A right-angle fold involves making a fold in a sheet, rotating the sheet 90º and making a second fold. A parallel fold involves making two or more folds in a sheet which are oriented in the same direction. A common type of folder is known as a knife folder, also known as a right-angle folder. On a knife folder—which can have any number of folding stations depending on the ultimate number of folds which need to be made to a sheet—a sheet is carried by the feeder mechanism on a flat plane. It hits a gauge, is positioned by a side guide, and a moving metal blade, or knife, pushes down on the sheet at a right angle to its surface, pushing it down between two counter-revolving metal or rubber (or combination of both) rollers. The action of the knife and rollers creates and "cements" the fold. A second type of folder is called a buckle folder. A buckle folder uses diagonal rollers to position a sheet against side guides. Feed rollers push the sheet between two metal plates—collectively known as a fold plate—a preset stop in which causes the sheet to buckle. At this point, an additional set of rollers grasps the sheet and forms the first fold.

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Collating and Gathering - Before binding, cut, trimmed, and/ or folded sheets need to be placed in the correct sequence.

In the process of collating, individual sheets are organized into sets. In the process of gathering—which is a printing and binding operation—signatures are organized into sets, often using gathering machines comprising up to thirty individual pockets. Signatures are fed manually or automatically into these pockets, after which they are gathered together for binding.

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Types of Binding Perfect Binding - Perfect binding, also called adhesive binding, is a means of affixing pages to a cover or spine by means of glue; an adhesive material is applied to the edges of the book block, and a cover stock is attached on top of it. Common examples of perfect bound publications include paperback books, magazines, telephone books, etc. After gathering, a gluing device applies a film of adhesive (usually a hot-melt adhesive) to the edge of the pages commonly utilizing two applicator wheels. After application of the adhesive, a single-piece cover is applied, where nipping stations tightly press the cover over the book block. After binding, trimmers are used to cut the individual pages of the signatures apart at the top and/or bottom and remove excess paper. In perfect binding, trimming is done following the addition of the cover, as they are often designed to have flush covers, or covers which have edges that are trimmed flush with the interior pages.

Saddle-Stitching - Saddle-stitching essentially involves the use of wire staples to bind pages together. Saddle-stitching drives the staples through the center of the spine of folded sheets, and is commonly used for magazines, newsletters, and other such publications. A cursory glance at Newsweek, Time, Business Week, or other such magazines will provide an example of saddle-stitching. A less common variety of wire stitching is side stitching, in which staples are driven through the pages from the top of the cover down, usually oriented parallel to the bind margin. Side-stitching is most commonly used for reports, and had once been used for magazines.

Thread Sewing and Case Binding - In contrast to wire

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stitching, thread sewing involves stitching a book block together by means of thread or cord, often in conjunction with an adhesive. Thread sewing is used for hardcover books, encyclopedias, Bibles, etc. It should be pointed out that thread sewing is the means by which the pages are bound together, while case binding is the attaching of the book cover to the book clock. The most common means of thread sewing is called Smyth sewing, in which a thread is passed through the backfolds of the signatures comprising the book block, which secures the signatures to each other while still permitting the finished book to lie flat. There are essentially two means of thread sewing, saddle-sewing and side-sewing. In the former, the more popular of the two, thread is driven through the centerfold of each signature, and each signature is joined to the others. In the latter, the thread is driven through the top sheet down through the signatures and along the edge of the book parallel to the bind margin. In shorter books, a continuous lockstitch or standard sewing pattern is used. In both of these, the stitches are placed in the same position on each signature. The drawback to these stitches is that if there are many signatures, thread build-up can cause swelling of the book. Longer books use staggered or continuous staggered stitches, which move the position of the stitches from signature to signature, reducing thread build-up.

Mechanical Binding - Mechanical binding is the most basic form of binding, and includes such binding types as comb bindings, in which the teeth of a plastic "comb" are inserted into a series of slits drilled or punched into a stack of sheets, often used for reports and presentations; spiral binding, in which a continuous wire or plastic coil is threaded through holes drilled or punched into a stack of sheets, often used

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for notebooks; and loose-leaf binding, in which a set of holes (commonly three, but sometimes more or less) is drilled in a stack of sheets, allowing for insertion into standard or customized ring binders or post binders. The advantage of the latter is the easy removal and insertion of sheets. Loose-leaf binding is often used not only for notebooks but also for many types of prospecti, presentations, financial reports, instruction books, and other such uses that may require frequent updating.

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Finishing Embossing - Embossing is a process by which dies are used to stamp a relief image in a book cover or printed material.

Often, an ink or other substance is used to color or accent the relief image. Blind embossing, however, uses no decorative inks, keeping the stamped image "as is." A similar process, debossing, uses a die to stamp a sunken image on the substrate. In either embossing or debossing, the substrate passes beneath an embossing plate which carries the engraved die bearing the image. Directly beneath the substrate is a "counter" die, or a die which bears a relief image of the image engraved on the embossing die. When the substrate passes between these two dies and pressure is applied (forcing the two dies together), a relief image is produced on the substrate.

Foil Stamping - A process similar to embossing is foil stamping, in which a heated die presses against a roll of foil, contacting the substrate. This transfers the foil—in a pattern corresponding to the design on the die—to the substrate. In foil embossing, the embossing and foil stamping processes are performed simultaneously. Foil stamping replaced the earlier process of bronzing, in which a metallic powder was applied to the surface of a substrate.

Diecutting - The process of diecutting uses a different type of die, one which contains knives or creasing rules to cut a pattern into a substrate, or to cut the substrate into a particular pattern. The dies themselves are prepared and engraved for specific jobs out of a variety of materials and in a variety of ways.

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Coating - A variety of coatings can be applied to printed products, either for extra protection or for decorative purposes. (The two uses are not mutually exclusive, of course.) There are several classifications of coatings used in finishing operations: a primer is used to prepare a surface for ink reception or for the application of another type of coating. A lacquer is a combination protective/decorative coating applied to a printed piece. A barrier coating is a protective coating applied to printed packaging, designed to impart resistance to oxygen, water, or other chemicals.

Overprint varnish is a high-gloss coating which is added for decorative and protective purposes. Overprint varnish may be applied to the entire surface of a printed material, or to only select portions (in this case called spot varnish).

Coatings are classified according to the means by which they dry. Aqueous coatings are water-based, and dry upon exposure to air, thus requiring a long drying time. Ultraviolet and electron-beam coatings dry upon exposure to ultraviolet light and to beams of electrons, respectively, which cause polymerization of materials in the coating.

Laminating - Laminating differs from coating in that lamination involves the adhesive bonding of two separate materials or layers of material together. Often, laminating in the finishing sense refers to the sealing of a substrate between two layers of a plastic material.

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ELEMENTS OF INK Vehicle The ink vehicle is the fluid part of the ink that, as its name implies, transports the pigment onto the substrate. The type of vehicle to be used in a particular ink is dependent upon the type of drying system utilized. Inks that dry by absorption utilize non-drying oil vehicles. Inks that dry via oxidation and/ or polymerization require drying oil vehicles. Inks that dry via evaporation utilize low-boiling-point solvent-resin vehicles.

Inks that dry by precipitation require a water-soluble glycol vehicle in which are dissolved water-insoluble resins.

Pigment The pigment is the part of the ink that imparts gloss, color, texture, and other characteristics to the printed image.

Pigments can be black pigments (consisting primarily of various types of Carbon Black), white pigments (which are either opaque pigments or transparent pigments), and color pigments which can be produced from either mineral sources (the inorganic color pigments) or from organic derivatives of coal tar (the organic color pigments).

Additives Printing ink additives include driers, which speed up the drying of inks; bodying agents, which increase the viscosity of an ink; waxes such as microcrystalline, polyethylene, paraffin, beeswax, carnauba wax, and ozokerite are used to prevent such printing defects as ink setoff and blocking, and to increase the ink's scuff resistance. Antioxidants and antiskinning agents can be added to keep ink from oxidizing and setting while it is still on the press.

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TYPES OF PRINTING INKS Quick-Set Inks These types of inks utilize a resin-oil vehicle, consisting of a resin-oil-solvent mixture. The solvent drains very quickly into the substrate leaving the remainder behind to oxidize and polymerize on the surface.

Heatset inks These inks utilize a solvent-resin vehicle that dries primarily by evaporating the solvent from the vehicle, then re-cooling the remaining ink components. Heatset inks accomplish this by utilizing a solvent with a high boiling point, and the ink must then be dried in a special drying oven.

Moisture-Set Inks These inks utilize a glycol vehicle that dries primarily by precipitation. The pigment and a water-insoluble resin are dissolved in a water-soluble glycol. Upon contact with moisture, the glycol is dissolved, but the resin and pigment are not, and precipitate out of solution onto the surface of the paper.

Radiation-Curing Inks These inks utilize complex vehicles that harden and polymerize upon exposure to radiation, either ultraviolet light (as in UV curing ink), beams of electrons (as in EB curing ink), or infrared light (as in super quick-set infrared ink).

High-Gloss Inks These inks essentially are produced with an additional quantity of varnish, which allows them to dry with a highly glossy appearance. High-gloss inks are dependent upon the

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properties of the substrate to be truly effective; a high degree of ink holdout is necessary to keep the vehicle from draining into the paper before it can dry by oxidation.

Metallic Inks These inks are used for specialty applications and to produce a printed image with a metallic luster. The pigments used in these inks comprise flakes of metallic powders.

Magnetic Inks These inks were developed for use in banks and are used primarily for printing on MICR (Magnetic Ink Character Recognition) Check Paper and read with MICR equipment.

The pigments used in these inks have the ability to be magnetized after printing.

Fluorescent Inks These inks lack permanence, but make use of ultraviolet light to reflect back light in brilliant colors. Limited for many years solely to screen printing, recent innovations and formulations have produced fluorescent inks that can be printed in a variety of ways.

Scuff-Resistant Inks Inks that are able to withstand the wear and tear of shipping and handling are available in a variety of grades and formulations.

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Costing and Specifications - Define specifications Name of job Number of colors - (2/0 - 2 color on one side, 4/4 - 4 color on both sides) Finished size Quantity Paper Unfinished size No. of deliverables from one sheet Total quantity - (+100 for wastage) No. of reams - Total sheets/500 sheets per ream Cost of paper - No. of reams * weight of one ream (@ per kg) A - paper cost B - positive calculate area calculate cost - area * rate (@ per sq.cm.) * no. of colors C - plate making no. of colors = no. of plates cost - no. of plates * rate per plate D - printing no. of plates * quantity of prints * rate per plate or color (include ink, overhead, labour etc.)

E - cutting/finishing/folding Total cost - A+B+C+D+E+10% (printer’s margin)

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Guided by Tridha Gajjar, Bharat Suthar, Print Lab staff