Contents. 2 Flexographic Markets. 4 Traditional Printing Processes. 6 Flexographic Technology. 8 Flexographic Plates. 9 Plate Elongation & Distortion

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2 Look around you on store shelves, in your home and you re certain to see material that s been printed by flexography. Though often taken for granted, packaging is everywhere, and so, too, is flexography; it prints candy wrappers, shopping bags, corrugated boxes, milk cartons, gift wrap, wallpaper, and many other goods and packages. Printing on packaging is essential to businesses around the world. In fact, graphics on packages provide some of the most important advertising for the products themselves. Flexography s soft compressible plates, fast-drying inks, and its simple, efficient inking system make it possible for manufacturers to reproduce high-quality graphics on a wide variety of surfaces. Over the last decade, the use of the flexographic printing process has been growing approximately eight percent a year, a rate unparalleled by any other printing technology. Although some of this growth can be attributed to a greater need for packaging, flexography is increasingly used in markets traditionally served by gravure and offset lithography. Since advances in technology have significantly improved flexography s ability to print accurate type, color, and halftone images, manufacturers and print buyers are recognizing flexography as a high-quality, economical alternative to gravure and lithographic printing. This booklet describes the flexographic printing process from start to finish, including design, color, and prepress considerations. Understanding the requirements of flexography helps ensure that designs will look their best, and will aid in the communication between print buyers, in-house prepress departments, service bureaus, and printers.

3 2 Flexographic Markets 4 Traditional Printing Processes 6 Flexographic Technology Contents 8 Flexographic Plates 9 Plate Elongation & Distortion 10 Substrates 11 Color Capabilities 12 Trapping 13 Type 14 Color Management 15 Dot Gain 16 Halftones & Screening 18 Step-and-Repeat & Die-Cutting 19 Prepress Output 20 Proofing 21 Prepress Checklist & The Press Check 22 Glossary & Index The terms printed in red throughout this guide can also be found in the glossary. 1

4 2Flexographic Markets The use of flexography is growing in popularity in today s printing markets, where short run, low-cost, and high-quality are crucial to success. A look at the development of flexography reveals a printing technology and culture that has been willing and capable of change in response to the needs of the packaging industry. An evolutionary process of improvements in materials and equipment, rather than a single discovery, has led to flexography as it is known today. The first use of soft compressible plates can be traced back to the late 1880s, when letterpress printers needed to find a way to print kraft paper grocery bags and corrugated boxes. The materials were rough in texture, and did not respond well to the ink transfer pressure of hard letterpress plates. To solve the problem, printers began creating plates from rubber, rather than from wood or lead. This quickly became the dominant method for printing corrugated, and also grew steadily in the bag printing industry. In 1914, the Interstate Commerce Commission approved the corrugated box as a shipping container, a decision that began a new growth period for flexography. Clear Packaging In the early-to-mid 1920 s, flexographic printers responded quickly to the introduction of cellophane as a clear packaging material. White inks were developed, drying systems were improved for cellophane s non-absorbent surface, and press tension systems were refined to handle its caliper and weight. Approximately ten years later, polyethylene was introduced, and went on to become the most commonly used material for clear, flexible packaging. Market Categories The use of the flexographic process has continued to grow in all packaging markets, including those that have traditionally used gravure and lithographic methods. Corrugated By far the largest market for flexography, corrugated is printed on sheet-fed presses. Fast drying water-based inks, the soft, conforming plate, and light impression pressure make flexography well suited for printing corrugated boxes in large quantities. Flexible Packaging Most flexible packaging uses non-absorbent polymer film, including bread bags, snack food bags, candy wrappers, pouches, and textile wrap. Gift Wrap and Wallpaper A continuous repeat allows the printing of products such as wallpaper and gift wrap. Design rolls, which do not have a plate seam, are used to print a continuous background color. Folding Cartons Although folding cartons, including cereal, detergent, and cosmetic boxes, are printed by both the lithographic and gravure processes, flexography has recently increased its market share due to improved quality. Rigid Paper Boxes Rigid paper boxes, or pre-formed boxes are used for bakery products, shoes, and neckties. Envelopes Flexography is used to print many kinds of envelopes, including those for direct mail, sweepstakes, general mailing, and overnight delivery. The security printing on the inside of many envelopes is often applied by flexography.

5 Paper Grocery Bags The paper bag is the original flexographic product. In the late 1800 s flexography evolved from the need to apply graphics to plain brown grocery sacks. The evolution continues today. Plastic Carrier Bags Flexography can add advertising and graphics to plastic bags that are carried by customers in stores. Milk Cartons Approximately 90% of all milk cartons are printed using flexography. Newspapers In the United States alone there are between 35 and 40 newspapers using the flexographic printing process for the entire paper. Many newspapers use flexography to print the Sunday comics. Origins of the Name Originally, flexography was known as aniline printing, a name taken from the aniline dyes used as colorants for the ink. Aniline dyes, however, were considered toxic and eventually banned for use on food packaging. New inks were developed as replacements, but the name remained until 1951, when Franklin Moss, a leader in package printing, started a campaign to change it. He asked aniline printers and suppliers for suggestions, receiving over two hundred. Of those, three finalists were selected: permatone process, rotopake process, and flexography. After a vote, the process came to be known as flexography in In the United States, the Clean Air Act of 1980 began a development in flexography toward environmentally friendly printing using low-solvent and no-solvent inks. Today, flexography is often chosen because of the ability to print with clean water based or solventless ultraviolet inks. Today the process continues to adapt. As the technology is refined, quality continues to increase, making flexography the leader in packaging graphics applications. Tags and Labels The fast drying fluid inks used by flexographers allow inline die cutting immediately after printing. The quality of many flexographic labels is equal to or better than that offered by lithography or gravure. Pre-printed Linerboard Pre-printing linerboard allows high-quality graphics to be placed on corrugated containers. 3

6 Traditional Printing Processes The three most widely used printing processes in use today are offset lithography, gravure, and flexography. Printing presses for each method differ primarily in design of the image carrier or printing plate, the ink, and the ink delivery system to the printing plate. Offset Lithography Widely used in the publication industry, offset lithography presses print magazines, catalogs, and daily newspapers, as well as annual reports, advertising, and art reproduction. Offset lithography can also print paper-based packaging, such as cartons, labels, and bags. Offset Lithography Gravure Offset lithography is a planographic process, meaning that the printing plate holds both the image and non-image areas on one flat surface or plane. On most offset presses, image areas on the plate are chemically treated to attract the lithographic paste ink, while a fountain solution or ink repellent chemical treatment protects non-image areas from inking. From the plate, the image is first transferred to a blanket (hence the term offset), and then to the paper or other material, known as the substrate. To dry, most lithographic inks require a certain period of time or an application of heat. Flexography 4 Gravure The gravure method, sometimes known as roto-gravure, is used on a wide variety of substrates, including vinyl flooring, woodgrain desktops, and paneling. It is the second most often used process in Europe and the Far East, and the third in the United States. Gravure is used to print high-volume products such as packaging, magazines and the advertising inserts found in newspapers. In addition, offset versions of gravure presses are used to print labels or logos

7 Traditional Printing Processes Typical Uses Substrates Impression Pressure Plate Run- Length Press Width Repeat Length Press Speed (feet per minute) Offset Lithography Magazines, newspapers, advertising pieces, annual reports, cereal boxes, bags, tags & labels Coated & uncoated papers, newsprint, some polymer packaging films Moderate to heavy 300,000 to 400,000 maximum impressions Sheet-fed: to 60" Web: 11" to 60" Standard format with limited repeat length Product dependent: Magazines: 2,500 fpm Sheet fed: 12,000 impressions per hour Gravure Magazines & catalogs, Sunday supplements, candy wrappers, cereal boxes, snack food bags, vinyl flooring Coated & uncoated papers, newsprint, paperboard, foil, metallized paper, polyethylene vinyl, polypropylene, cellophane, polystyrene Heavy 6 to 7 million impressions average; longer with rechromed cylinder 2" to 144" Infinitely variable repeat length Product dependent: Magazines: 3,000 fpm Bread bags: fpm Vinyl flooring: 50 fpm Flexography Newspapers, phone directories, corrugated containers, bread bags, cereal boxes, milk cartons, gift wrap Coated & uncoated papers, newsprint, paperboard, corrugated board, foil, metallized paper, polyethylene vinyl, polypropylene, cellophane, polystyrene Light 1 to 2 million impressions average Narrow web: 6" to 24" Wide web: 24" to 90" 120" for corrugated presses Variable repeat length Product dependent: Toilet tissue: 3,000 fpm Bread bags: fpm Pressure sensitive labels: fpm on medicine capsules and the M on M&M candy. Gravure is an intaglio process, in which the image area is recessed below the level of the non-image areas. The image is etched or engraved in a cell format onto a copper plate or copper-plated cylinder. By varying the size and depth of each cell, a printer using a gravure press can vary tones. Often, after the copper is etched or engraved, the plate or cylinder is plated with chrome to add durability and increase its run-length. A fast drying ink fills the recessed cells, a thin metal strip called a doctor blade clears the non-image area of ink, and the image is transferred directly to the substrate under heavy pressure from a rubber covered impression cylinder. Flexography Because its soft compressible plate conforms to uneven surfaces, flexography is often used for printing on packaging materials, such as corrugated and paperboard. The fast-drying fluid inks used in flexography are ideal for such materials as polyethylene films, used for plastic grocery bags. Flexographic presses are often part of a manufacturing process, in which packaging is printed, folded, shaped, and die-cut. Ink Screen Ruling Minimum Printed Highlight Dot Dot Gain Paste ink Oil & soy based Heat set & non-heat set Wet trapping lpi Most common: lpi 3-5% Midtones: 20% Fast drying fluid ink Solvent & water-based Dry trapping lpi Most common: 150 lpi 3% Midtones: 23-26% Fast drying fluid ink Solvent & water-based UV curable Dry trapping lpi Most common: lpi 8-12% Midtones: 20-25% Flexography is characterized as a relief process. The image areas on the compressible plate are raised above the surrounding non-image areas. An ink metering cylinder called an anilox roll applies ink to the raised areas. The plate is then moved into light contact with the substrate to transfer the image. The minimal pressure during image transfer allows printing on material, such as corrugated board, that may be adversely affected by impression pressure. 5

8 6Flexographic Technology Flexographic printing units in use today consist of three basic types: the two roll unit, the two roll unit with a doctor blade, and the dual doctor ink chamber system. Two roll units are usually found on older flexographic presses, and on narrow web presses. Narrow web presses equipped for process colors often use the two roll unit with a doctor blade, and more modern wide web presses use the dual doctor ink chamber system. Each type of flexographic press uses an anilox roll. The surface of every anilox roll is engraved with a pattern of tiny cells, so small they can only be seen under magnification. The size and number of these cells determine how much ink will be delivered to the image areas of the plate, and ultimately to the substrate. An anilox roll is either copper engraved and then chrome-plated, or ceramic coated steel with a laser engraved cell surface. Anilox rolls are carefully selected for specific types of printing, substrates, and customer requirements. Often the flexographic printer will perform test runs to determine the ideal anilox for producing the desired ink distribution for halftones, spot color, and solids. The design of the flexographic printing unit enables press manufacturers to build presses in any one of three configurations: the stack press, the inline press (including corrugated presses), and the common impression cylinder press. Each configuration can be equipped with any of the basic printing units, depending upon the needs of the flexographic printer. Flexographic Ink Delivery System On a two-roll flexographic printing unit, the rubber covered fountain roll rotates in a fluid ink bath, dragging ink from the pan to cells of the anilox roll. The soft rubber fountain roll is held in tight contact with the anilox roll. As the anilox rotates past the nip point, the fountain roll wipes excess ink from non-cell areas. Once past the nip point, each cell is filled with ink, and a measured, repeatable amount of ink is available to the printing plate. The metered anilox roll is moved into light kiss contact with the image areas of the plate, and the plate cylinder is moved into kiss contact with the substrate to transfer the image. The steel impression cylinder supports the substrate. When a thin metal or polyethylene doctor blade is used with a two-roll unit, the nip point between the fountain and the anilox roll is opened to allow ink to flood the anilox and fill the cells. The doctor blade comes into contact with the anilox to clear excess ink from non-cell areas. With a dual doctor ink chamber, the fountain roll and inking pan can be eliminated; ink is delivered directly to the anilox through an enclosed chamber. Characteristics of Anilox Rolls Cell Per Inch (CPI) Cell Volume Cell Angle Application line art halftones at 65 lpi 4/c halftones at 133 lpi Two Roll with Doctor Blade Dual Doctor Ink Chamber System Range: 140 to 1200 CPI. As cell count increases, ink delivered to plate decreases. As line screen resolution increases, CPI should also increase. Range: 1.8 to 17 BCM (Billion Cubic Microns per square inch of cells). As CPI increases, cell volume decreases. Typical anilox cell angles are 30, 45, and 60. A 60 angle allows for more complete ink transfer, and is the preferred cell angle. The screen angle of the printing plate and the cell angle can combine to cause a moiré pattern, even with one color halftones. Moiré is avoided by angling separation screens. Substrate corrugated board corrugated board polyethylene bags Cells Per Inch Cell Volume BCM BCM BCM

9 Press Configurations Common Impression Cylinder (CIC) Press 4-8 color units Limited to one-sided printing Ideal press for hairline register at high speeds on stretchable films Longer make-ready times required because printing units are more difficult to access Stack Press 1-8 color units Some presses can print on both sides Traps should be no less than 1/64" for thin films Often used inline with other converting operations such as lamination, rotary and flatbed die cutting, and sideseal bag converting. Inline Press Up to 12 color units Can print two sides with the aid of a turn-bar Used for printing thick substrates such as paperboard Not recommended for printing thin packaging film Often used inline with other converting operations such as lamination, rotary and flatbed die cutting, and sideseal bag converting. Corrugated Press Same configuration as the inline press Sheet-fed; widths up to 120" Usually no more than 4 colors Limited to one-sided printing Less accurate registration capabilities Repeat Length Plate cylinders with different diameters can be mounted on many flexographic presses, allowing for variable repeat lengths. Printing a roll of packaging, such as gift wrap, uses a continuous repeat, where the same set of images is repeated many times on a continuous stream of substrate. To avoid the plate seam, images may require nesting, an arrangement that creates a staggered effect. Staggering images gives the appearance that the design is continuous, no matter where the substrate is cut. 7

10 Flexographic Plates Printing plates used on modern flexographic presses are produced in three different ways: molding rubber, exposing and processing photopolymer, and imaging with lasers. While molded rubber plates have been used since the 1930 s, photopolymer plates, introduced in the 1970 s, generally provide higher resolution and more accurate color registration. Direct-to-plate laser imaging, called ablating, is available for both materials. Selection of a particular type of plate depends on the press, the plate cylinder inventory, and the customer s requirements, such as resolution, registration, and cost. Plate Types Molded Rubber Molded rubber plates shrink when they are removed from the molding press. Plate films should be adjusted to compensate for shrinkage, which is typically 1.5%-2.0% in the direction of the rubber grain, and.5%-1% across it. Exact shrinkage amounts should be communicated between production artists and platemakers. Line screening is limited to 120 lpi. Registration can be more difficult than with photopolymer plates. Nesting is required for the appearance of continuous repeat. It is difficult to mold accurate rubber plates larger than 24" X 36". Larger designs must be placed on multiple plates for each color. Molded Rubber Molded rubber plates are created in a multistep process that involves exposing and etching a magnesium plate, making a mold, and then placing the image on the rubber plate using a molding press. Photopolymer Plates Line screening is at least 150 lpi and can be as high as 200 lpi. Nesting is required for the appearance of continuous repeat. Positioning and register devices on most modern flexographic presses are designed for one-piece photopolymer plates. Direct-to-plate laser imaging is available. Photopolymer Light-sensitive photopolymer is supplied in either solid sheets or in a thick liquid state. The image area of the plate is exposed through a film negative. Liquid photopolymer, about the consistency of honey, solidifies when exposed to ultraviolet light. After exposure, the nonimage area is removed by processing. 8 Laser Ablated Plates Some platemaking machines can transfer images directly from the computer to the plate, a process known as directto-plate that avoids the production of film. Some photopolymer plates can be directly imaged by lasers and then conventionally processed. A design roll is a cylinder covered with rubber or photopolymer and molded or imaged by a laser. Design rolls can provide a true continuous repeat with a continuous background color. Laser ablated plates must be nested to hide the plate seam for the appearance of continuous repeat. Laser Ablated Plates and Design Rolls Line screening is limited to 100 lpi for tone reproduction, but can be lpi for tints. Film is not required. Design rolls can provide a true continuous repeat with a continuous background color. Plates or design rolls imaged directly on the cylinder do not require compensation for plate elongation. Laser ablating is available for both rubber and photopolymer.

11 Plate Elongation As the soft plate wraps around the cylinder, it can elongate, stretching images, halftones, and text across the curve dimension. Without compensation for plate elongation, images will not print as designed. In the example, if no compensation is applied, the sun image is printed as an oval and the vertical lines on each side are lengthened. Spreading Distortion x 2(T) RL x 2(1.27") 18.8" Before plate mounting Plate After plate mounting Plate centerline Stretching = RL = 18.8"; repeat length of plate cylinder T = 1.27"; plate thickness with mounting tape Expected result Plate elongation occurs around the cylinder Printed piece without compensation for elongation Special flexographic software can compensate for plate elongation by adding distortion, using a basic formula, as shown in the following example. = " For every linear inch of plate used around the cylinder or curve direction, the images will increase at the rate of ". Design measures 12" in the curve direction. Calculate plate elongation: 12" x " = 5.09" 12" " The image is distorted to compensate for plate elongation. Film is output to " (12" 5.09") or 95.7% in the curve direction, and 100% in the non-curve direction. When designing images for flexographic printing, it is important to understand the effects of plate elongation. Because flexographic plates are made with soft material, they tend to stretch when mounted on the plate cylinder, sometimes distorting images and text. A circle, for example, may be stretched to look more like an oval. Fortunately, special flexographic software can compensate for plate elongation by slightly distorting images. Distortion is usually performed within the flexographic software application or at the RIP stage before the film is imaged. The amount of distortion depends on the thickness of the plate and the mounting tape used to fasten it, and on the circumference of the cylinder (the repeat length). In general, thicker plates and shorter repeat lengths increase the elongation. To be sure that images will be printed with the correct size and shape, the design should be output to film after plate thickness has been determined and the proper distortion factor has been applied. Improperly calculated distortion may also cause misregistration. Direct-to-plate imaging, which is becoming more widely available, avoids the need for distortion if the imaging is applied directly on a design roll, or on a plate already mounted on the cylinder. Because the image is applied to a curved surface, no stretching occurs. Plate Elongation & Distortion 12" 12" Final design prints correctly since plate elongation has been compensated for. 9

12 Substrates Flexography is ideal for printing packaging materials because the soft plates can transfer ink to many different kinds of substrates anything from corrugated board to candy wrappers. The quality of a printed product is determined not only by the type of plate, but also by the substrate itself. Different substrates allow varying degrees of ink absorption, gloss, brightness, and color definition. The chart on this page lists the characteristics of some common substrates. Substrate Characteristics Paper/ Paperboard kraft linerboard: corrugated, for boxes coated kraft: corrugated, for boxes solid bleached sulfate (SBS): folding cartons recycled paperboard: folding cartons coated paper: labels, gift wrap uncoated freesheet paper: paperback books Polymer Films polyethylene (PE): dry cleaner bags, bakery, textile bags polypropylene (PP): snack packages, candy wrappers, cookie packaging labels polyvinyl chloride: vinyl films, labels, wall coverings Multilayered/ Laminations metallized papers: gift wraps metallized film: snack food bags polyethylene coated solid bleached sulfate: milk cartons Color Dependent upon substrate material; substrate color will significantly influence ink. White, brown kraft, a variety of colored papers. Clear, white or colored. Determined by the top-most layer. Whiteness/Brightness The strength of white or color of a substrate. Increases with bleached & coated papers. Decreases with greater amounts of recycled fiber. Optical brighteners can be added. Determined by the opacity of white film. Clear films require the use of a white plate. Determined by the top most layer. Foil & metallized surfaces require the use of a white plate. Opacity Amount of light transmitted through the substrate. A lower opacity allows more light to pass through. Thin, lightweight papers have lower opacity & are more likely to have ink show through. Low for thin, lightweight papers, which are more likely to let ink show through on reverse side. Higher with multiple layers of material. Smoothness Smoother substrates allow higher lpi; rough, irregular surfaces require much lower lpi. Absorption Determines how ink dries and spreads. Low absorption produces drying at the surface, increasing color saturation and decreasing dot gain. Higher absorption increases dot gain. Newsprint, corrugated linerboard & paperboard are relatively rough; calendered & coated papers smoothest. Newsprint, corrugated linerboard & paperboard are very absorbent, calendered; coated papers are less absorbent & exhibit high ink hold-out. Smooth printing surfaces; ink adhesion is sometimes a problem. Non-absorbent, with no dot gain. Determined by the top-most layer. Usually low, but determined by the substrate used as a printing surface. Gloss Reflective quality of the substrate. Gloss can be increased with varnish or lamination and can be decreased with matte or low-gloss finishes. Calendered & coated papers are high gloss; corrugated linerboard, newsprint & paperboard are low gloss. High for most films, but films can be produced with a matte finish. Determined by the top-most layer. Caliper Thickness of a substrate, as measured by a micrometer. Range:.002" to.010"; paperboard.010". Thin papers more consistent in caliper; paperboard more inconsistent. Ranges from.00065" to.006". Thin films may stretch; inconsistency in caliper can cause misregistration and wrinkling. Increases as layers are added. Thin layers may be laminated together to obtain the required thickness. 10

13 Multicolor Options In flexography, opaque spot colors are printed in the order of lightest to darkest. Process color inks are made from transparent pigments and can be applied in any sequence. For transparent substrates, white ink is printed first to provide a background for colors. Because the appeal of packaging is significantly enhanced by color, flexographic presses commonly offer six and eight colors, and even as many as twelve for limited applications. Designers can choose from a number of different combinations, including multiple spot colors and HiFi printing, which is a method of increasing the color gamut by printing six or seven process colors. Color Capabilities Most flexographic inks consist of opaque or semi-opaque pigments. To ensure proper ink coverage, the spot colors are usually printed from lightest to darkest. Process color inks are made from transparent pigments and can be applied in any sequence. Transparent substrates, such as polypropylene, require a white backup plate provided by a choke plate, as a background for colors; otherwise, colors would appear flat and translucent. Reverse-Side Printing An exception to the rule of lightest to darkest printing occurs when a spot color or line art job calls for reverse-side printing, sometimes called back printing. Styrofoam products are often decorated by laminating a reverse-side printed film. Some snack food packaging is also done this way. Another technique used for applying ink to transparent substrates is reverse-side printing. The image is laterally reversed, and colors are printed instead from darkest to lightest; the packaging is then displayed from the non-ink side of the substrate. This provides a scratch proof surface to the ink layer, and a glossy finish. In some cases, a water-based ink is used for reverse-side printing lamination. Paper or styrofoam plates are often decorated by laminating a reverse-side printed film layer to the plate. White Plate In order to place colors on a transparent substrate, a solid white ink is printed first to create a reflective background that improves the color intensity. The colored inks are then printed on top of the white background. Corrugated containers have historically been only one color on brown kraft paper linerboard, but more designers are taking advantage of multiple spot and four-color process capabilities. In some cases, printing is done directly on a white or clay coated corrugated linerboard, avoiding the costly practice of applying labels to achieve high quality graphics. 11

14 Trapping Trapping is a technique of overlapping colors to avoid unsightly gaps created by misregistration. Small variations in the placement of color, called misregistration, can be caused by substrate handling and tension problems on the press, irregular plate elongation from one color to the next, inaccuracies in plate mounting, plate bounce, and limited register capabilities, especially with molded rubber plates. A test run, called a fingerprinting analysis, can determine the registration tolerances. When designing packaging for flexographic printing, it is best to avoid the requirement for tight registration, to design images with dominant colors printed on top of lighter ones, and to avoid trapping on gradations. Typically, a designer will build traps into the file if the design is simple, using options in publication or illustration software; more complicated designs require the help of service bureaus and special trapping software programs, such as Trapwise TM from Luminous Corporation or DK&A Island Trapper TM. Choking and Spreading Spread lighter color Choke lighter color Traps are created by spreading or choking graphic elements, depending on adjacent colors. When a lighter element appears against a darker background, the lighter color is spread into the darker color, slightly increasing the size of the graphic element. When a darker element appears against a lighter background, the knockout is choked by slightly filling it with the lighter color. Both methods create a small overlap of ink colors, called the trap width. This width depends on the thickness and size of type, the adjacent colors, and the registration capabilities of the press. Script, serif fonts, or small type can be spread or choked only small amounts before the shapes are compromised. In general, light and dark colors allow for greater trap widths than colors that are similar. Overprints and Traps Trap widths on narrow web presses should be set at a minimum of 0.005"; some presses require as much as 1/32" (0.031"), which is large compared to average traps of 0.002" " for offset lithography. A typical trap width for polyethylene printed on a wide web press is 1/72" (0.014"), though if an objectionable dark trap line is created, the width may need to be cut in half. Trapping for linerboard or corrugated cardboard may require a trap width of 1/64" to 1/8". Trap affecting colors Nailheads Printing inks on top of each other is called overprinting. In flexography, one ink can be printed on another only after the first has been completely dried or cured. For this reason, flexographic presses use dry trapping, where the printer must allow for drying. For substrates like clay-coated liner, or non-absorbent packaging such as polymer film, drying time can be a problem. Overprinting a second color when the first is not dry creates an unattractive blotchy effect (often called nailheads), especially on large solids. Excessive trapping can cause such problems and can slow down the printing process. 12

15 Type Weight In flexography, the soft plate compresses in the printing nip, causing the fluid ink to flow slightly outward from the image area. Thus the weight of type may appear to increase, and reverse type may fill-in. Over-impression Substrate Ink spreading Ink Deforming plate Pressure In flexography, printing consistently well-defined type is complicated by the soft plate, irregular substrate surface, and the fluid ink. Ink tends to spread outward, sometimes obscuring the definition of small point sizes or the fine detail of certain letter shapes. Reverse type, which uses the substrate or a background color to define the letter, tends to get filled in. Type Typographic Guidelines 4 point minimum positive san serif type for narrow web presses 6 point minimum positive san serif type for wide web presses 6 point minimum reverse type for narrow web presses 9 point minimum reverse type for wide web presses 8 point minimum positive serif type for wide web presses Kerning may cause squeezing across cylinder, avoid tight linespacing Kerning may cause squeezing across cylinder, avoid tight linespacing EDIENTS: FILTER AR, CORN SYRUP A AND LOWFAT CESSED WITH AL IN, NATURAL VA EDIENTS: FILTER AR, CORN SYRUP A AND LOWFAT CESSED WITH AL IN, NATURAL VA All positive text should be printed in a single color if possible PMS 407 All positive text should be printed in a single color if possible 6m 8.5y 27.5k Made in the U.S.A. 47c 94m 15y 5k 47c 94m 15y 5k Letterspacing and/or linespacing may increase slightly from plate elongation. Avoid placing fine type on the same color plate with line work and solid printing areas. Avoid reversing type out of two or more colors unless a dominant color outline is used. To help compensate for the typographic weight gain, it is possible to use the trapping techniques of spreading on positive type and choking on reverse type. Software programs, such as MacroMedia FreeHand TM and Adobe Illustrator TM, let the designer adjust the thickness of type. Some compensation can be done by choosing either a lighter or bolder face. For example, if medium positive type is desired, use a lighter weight face; if a medium reverse type is desired, specify a bold face. When possible, sans-serif fonts should be used. In general, larger point sizes produce more consistent type. Letterspacing must also be considered. Letters squeezed together for a denser appearance with offset lithography may merge together unacceptably in flexography. Ideal letterspacing keeps letters close enough together so that they lend support to each other while under the pressure of the printing nip, but separated enough to avoid merging. Specify type accurately to the service bureau or prepress department. 13

16 Color Management The wide variety of substrates, lack of standard ink hues, and unique dot gain characteristics all contribute to the difficulty of communicating and reproducing color by the flexographic process. Color Management Systems (CMS), such as Agfa s ColorTune 3.0 are software systems used to ensure color consistency among different input and output devices so that printed results match originals. The use of these systems aid in the color communication process by correlating colors on computer monitors and proofing devices with the actual or expected color results from the printing press. Because a color monitor can produce a much wider gamut of colors than the inks on a printing press, the designer needs to know the range of printable colors available on the computer. To find this range, a color specialist can run a CMS test on the flexographic printing press under controlled conditions, using the same ink, plates, mounting tape, and anilox rolls required for the actual production run. Since each substrate affects color in a different way, a new test needs to be run for each new type of material. The results of the test are entered into the CMS software, which sets up calibration tables and builds press profiles. Digital cameras, scanners, monitors, and proofing devices are all adjusted by the CMS, based on the colors printed by the individual press. Input devices such as cameras and scanners, and prepress output devices including monitors and proofing systems are adjusted according to the predicted outcome on press. Test Targets A B C D E High total ink amount to check density Shadows IT8.7/3 A B C D E F Saturated colors with no black CMYK density wedges to check dot gain Solid CMY patches Saturated colors with 20% black A B C D E F G H I J K L M N Neutral greys printed with CMY (and K in some cases) to check grey balance Color Management Systems build profiles by analyzing standard color data from test targets. The IT8 series of test targets can be used to calibrate prepress input devices (such as scanners), and output devices (such as proofing devices), monitors, and the press itself. The IT8 7/1, IT8 7/2, and the IT8 7/3 (shown above) test targets all contain the same standard color information, but each uses a different format. IT8 7/1 is a reflective color test target input to calibrate scanners for reflective art in a color management system. IT8 7/2 is a transparency of the same format as IT8 7/1, but used to calibrate scanners for reading transparencies, rather than reflective art. IT8 7/3 is a digital file of the same format used to calibrate imagesetters. To build a press profile, the imagesetter is calibrated and the IT8 7/3 file is output to film. Plates are made and mounted, and the IT8 7/3 is then printed under the actual production conditions. Printed samples are measured for density, dot gain, and colorimetric values, and the resulting data is entered into the color management system. CMS software then recalibrates monitors, digital proofing devices, and imagesetters to correlate the output at each of these devices with the expected output from the actual press run. There are several color measurement tools used by flexographers to measure printed samples. Used primarily in the press room, the reflection densitometer can only truly measure reflectance. It is used by the flexographer to measure solid ink density for process color printing. The colorimeter, important because it assigns numerical values to all colors in the gamut, measures hues printed as either spot colors or screen tint combinations of CYMK. The spectrophotometer is most useful for fingerprinting specific hues of CYMK and base colors used for ink mixing. 14

17 Dot Gain in Flexography Impression Pressure Plate Durometer An instrument called a Shore A scale measures plate hardness, which is called durometer. The image on the left shows the scale measuring a soft plate; on the right it measures a harder plate. Inks Substrates Even though ink is transferred under relatively light pressure in the printing nip, the soft flexographic plate deforms slightly and compresses during image transfer. This causes ink to spread, increasing dot gain. Because harder plates do not compress as much as softer plates, they produce less dot gain. Softer plates, however, transfer solid images more completely. Dot gain can be minimized by using a thin (0.002"-0.005") capping layer surface with a higher durometer than the supporting plate material. Dot gain can also be reduced by mounting the plate with compressible tape or a blanket that absorbs pressure. A higher viscosity ink will not spread as quickly as one with lower viscosity. The spreading, or flow-out, of a low viscosity flexographic ink occurs as it is transferred to the substrate and before it dries, contributing to dot gain. By comparison, lithographic ink is a thicker, paste consistency, and is not prone to excessive flow-out. All printing processes are subject to the unavoidable occurrence known as dot gain. As dots are transferred from film to plate, they tend to grow in size during light exposure. When an ink dot is transferred from the plate to the substrate, it can increase in size once again as the ink spreads during absorption. A dot that began as 50% on film can grow to 51% on the plate, and eventually print on a flexographic press as a 65% or greater dot. The fluid ink and compressible plates used in flexography tend to increase dot gain, but it varies according to the type of press and the substrate. Smooth non-absorbent films and coated papers will have less dot gain than absorbent and irregular surfaces, such as uncoated papers, newsprint and corrugated liner board. Dot gain, however, is often consistent and predictable. Image or color separation software can adjust dots based on measurements supplied by the printer. Typically, the printer performs a fingerprinting analysis, which provides dot gain information to the color separator or desktop designer. The IT8 chart on page 14 shows an example of a test target used for a press fingerprint. By printing such a target under controlled conditions, dots can be adjusted in the color separation films. In addition, calibration packages built into raster image processors (RIPs), such as Agfa Calibrator, can also make adjustments. Dot Gain The printing surface or finish of a substrate also influences dot gain. When ink is applied to smooth non-absorbent films and coated papers it tends to spread very little, preserving the dot shape. With more absorbent and irregular printing surfaces, such as uncoated paper, newsprint, and corrugated liner board, the paper fibers act as a wick, absorbing the fluid ink and causing it to spread beyond the dot shape and pattern. 15

18 Halftones & Screening Throughout its history, flexography has been printing quality line art and spot colors on a wide variety of substrates. However, it is the recently improved capability of high-quality, economical four-color process printing that has given flexography an edge over other processes for packaging applications. The Halftone Dot In flexography, the shape of the halftone dot used to reproduce a continuous tone image can significantly affect the density of the image. Halftone dots can be generated in a number of shapes, including square, elliptical, octagonal, and both symmetrical and asymmetrical dots. At 50% coverage, for example, square dots produce a pattern resembling a checkerboard, with individual dots just beginning to join at their corners. When plates are created from film, dot gain increases the joining of the dots, which causes sudden jumps in density in the printed image, rather than a smooth, continuous transition. To minimize the density jumps, printers can use other kinds of dots that remain discreet and retain their shape, even at coverages of sixty and seventy percent. A round dot, or octagonal dot are often used. Though most design software can specify round dots, selection of dot shape should occur early in the process to avoid choosing a shape not available in the RIP, imagesetter, or platesetter. Conventional Screen Ruling Selection of proper screen ruling, which is critical to four-color process flexography, is often dictated by the type of substrate. Anilox cell count and screen ruling for separations should be correlated for best results. The cells of the anilox, which ink a halftone plate, should be large enough to produce appropriate Halftone Dot Shape Square dots at 50% Stochastic dots at 20% Symetrical round dots at 65% Asymetrical round dots at 75% Screen Tints and Gradations Offset lithography Flexography To minimize density jumps in halftones, round dots are preferred. Round dots do not touch until coverage is nearly 65% for the symmetrical round dots and 75% for asymmetrical dots. Dot gain is less at these higher coverages, and is more easily controlled or compensated for. Asymetrical round dots reversed at 80% Highlights Most photopolymer plates are capable of holding a 2% highlight dot. If plates aren t properly exposed, however, screen tints and highlight dots less than 3% tend to drop out. Because the small dots of highlight areas are subject to relatively large dot gain, it is important that any highlight limitations are discussed with the printer before separations are made. Although printers in offset lithography can print acceptable highlights using 5% film dots, flexographic printers may have to reduce a similarly bright highlight to 2%, taking into account the additions of dot gain. Gradations and Vignettes Flexographic dot gain on highlights makes it difficult to print a fade-to-white gradation without a harsh break at the highlight edge. When designing images for flexography, it is best to fade off the end of the design (rather than to white), or place a border at the highlight end of a vignette. 16

19 Line Screens and Cells Per Inch Screen Ruling (lpi) Cells Per Inch (cpi) Application 65 lpi cpi Corrugated 85 lpi cpi Newspaper 133 lpi cpi Flexible packaging The corrugated industry prints halftones screened at 45, 55, 65, or 85 lpi. Flexographic newspaper printers print halftones screened between 65 and 100 lpi. Flexible packaging on film substrates is commonly done at 120 to 150 lpi. color strength, but not so large that the halftone dots will dip into them like an inkwell. For conventional halftones, resolution is expressed as the number of lines of halftone dots per inch, also called screen ruling or lpi. Higher screen rulings produce higher resolution images because there are more dots per square inch used to reproduce detail. Compare the images in a newspaper (low screen ruling) to a picture in a monthly magazine (high screen ruling). Stochastic Screening Stochastic, or frequency modulated (FM) screening, can offer advantages over conventional halftone screening. Stochastic screening eliminates the possibility of moiré, and also allows the flexographic printer to use HiFi color, which involves the application of six or seven process colors. 150 lpi 800 cpi Labels Anilox Cell Angles and Halftone Screen Angles High quality label printers have the capability of printing 200 lpi images. Cells are engraved on an anilox roll at one of three angles: 30, 45, or 60. Dot size used for stochastic screening, however, is extremely small, comparable in size to the highlight dot of conventional screening. Since flexography is subject to significant dot gain, stochastic screening should only be used after the printer and color separator have performed press fingerprints to determine the ideal dot size and accurate compensation for dot gain. Offset halftone screen angle 7.5 from cell angle Anilox cell angle To avoid anilox moiré, film or plate screen angles should be at least 7.5 away from the anilox cell angle. Cyan, magenta, yellow, and black screen angles should also be set at least 15 apart from each other. The number of lines per inch on the plate should be no more than 25% of the cells per inch on the anilox. Ideally, the anilox should contain a minimum of 4 cells for every halftone dot. 17

20 Step-and-Repeat & Die-Cutting To save material costs and maximize productivity, the packaging industry uses a printing technique called step-and-repeat. Different images, such as labels, are arranged on the plate to fill its repeat length and use the entire width of the substrate when printing. Often, a technique called nesting will be required. Images are strategically staggered in an arrangement that maximizes the repeat length and avoids the plate seam. The plate ends are cut to accommodate the arrangement. Nesting can give the appearance of a continuous repeat, and is used for jobs where all the images are part of a single roll, such as gift wrap. Step-and-Repeat Die-Cutting Nesting images can maximize the plate area and avoid the plate seam for step-and-repeat printing. Layout and imposition software offer step-andrepeat options for specific repeat lengths and web widths. In addition to maximizing substrate area, staggering images can also avoid a problem called plate bounce. In flexography, images are on the raised areas of the plate, and can produce a bounce when coming into jarring contact with an anilox roll or impression cylinder. Bouncing can cause print areas to skip or misprint if the bounce is away from the impression, or areas of excess inking if the movement is toward the anilox roll. After printing, most substrates are cut, folded, scored, sealed, or glued, often inline. In order for packaging to be properly constructed, die-cutting requirements must be exactly specified for both the designer and the printer. A die-cut label or folding carton, for example, must have all graphical elements in the correct positions. Packaging engineers often use Computer Aided Design (CAD) systems to design folding cartons, corrugated containers, or rigid paper boxes; designers may also import the CAD layout to use as template for design. Bleeds To specify bleeds, the designer must know where the packaging will be cut, folded, and joined. In general, bleeds extend beyond fold and cut lines, but the precise amount of bleed depends on the press. Cut Areas When flexographic printers are connected to inline flatbed or rotary diecutting, the die must be held in register with the printed colors. Graphic elements should not be placed too close to cut areas. Glue & Seal Areas To ensure sealing, glue areas should be free of ink and varnish, especially those sealed by heat. Score Lines Die-cut folding cartons usually fold at score lines, where the designer should make sure that registration is precise. Plate Bounce Staggering images on the plate can help keep continuous contact between cylinders, minimizing plate bounce. Sometimes it is necessary to place nonprinting bearer bars on non-image areas to maintain contact. Varnish-Free Areas Areas that contain variable information, such as freshness dates and product coding, must be free of varnish. Windows Die-cut windows for folding cartons or labels should be clearly indicated, but may not be available on all die-cutting machines. Always check with the printer before including them in the design. Bar Coding To help keep bar codes precise for lasers, they should be printed parallel to the direction of the web, and must allow for dot gain. Die-Cut Templates Templates can be exported from CAD systems to illustration programs, providing the designer with a two dimensional layout of the job. 18

21 The Prepress Process Following design, production, and ripping, a job may take different paths through the prepress output and platemaking stages. For conventional photopolymer or rubber plates, jobs are first processed through an imagesetter, creating film output, which is used for plate exposure and processing. Plates are then placed on a mounting machine where, in some cases, a plate proof is made. A platesetter device essentially follows the same flow with the exception that the film processing step is eliminated. With direct-to-plate (or cylinder), devices, shown below as laser ablation, both platemaking and processing steps are eliminated. After a design has been trapped, distorted to compensate for plate elongation, and electronically imposed (considering step-and-repeat requirements), the file is processed by the raster image processor (RIP) and output to film or plate. The RIP converts PostScript TM data into a series of bitmapped images. The laser output device records this visual information received from the RIP onto film or plate material. Larger, more complex files will take longer to process through the RIP than simple text files. Prepress Output Flexographic Imagesetting Requirements Accuracy To optimize registration, output devices should meet a minimum standard of 1 mil over multiple separations. Geometric and absolute accuracy capabilities are also important imagesetters considerations. Size The imagesetter format size should be large enough to make the most effective and economic use of film, given the particular application. Film All film for soft photopolymer plates should be output to matte emulsion film (minimum thickness: 0.004"; 0.007" is preferred). This helps avoid trapping air between the film and plate during exposure. Calibration Film dot percentages below 10% should not vary by more than 1%; areas over 10% should not vary by more than 3%. Uniformity Screen tints should be a uniform dot percentage, with no variation in size between individual dots. Dot Shape The imagesetter should be capable of outputting a hard round dot. Resolution Resolution should be between 1200 and 3600 dpi. For line art, solids and type, 1200 dpi is adequate; halftones require a minimum of 2400 dpi. Density Film density is an important factor; imagesetter exposure levels and film processing chemistry should provide DMax areas of

22 Proofing In flexography, proofing for halftone accuracy and color matching can be difficult and inexact. A digital or film-based proofing method used in offset lithography may not be suitable for different kinds of substrates, for matching spot colors, or for reproducing flexographic dot gain. Accurate proofing may require using two or more methods. Proofing for Flexography Soft Proof Digital Print Proof During preliminary design, proofing starts with a monitor, sometimes called a soft proof. A monitor can provide an overall view of the design, but RGB colors on a monitor will probably not match CMYK or spot colors printed on the substrate. Higher color fidelity is possible by calibrating the monitor and by using a color management system. Substrates Most proofing methods are limited to a small number of substrates. Because ink colors are affected by the absorption and color of the substrate, proofing to another material cannot provide accurate color matching. Flexographic printers often provide mock-up packages, using proofs from digital laser printers. Many high-end digital proofing methods meet industry color standards for prepress proofing systems. Inexpensive desktop color printers can also give an approximation of specified colors. When used with a color management system, digital printers can provide contract proofs. Most digital systems are based on CMYK toner applications, so spot colors may not be accurate. Spot Colors Since most film-based and digital proofing methods apply toner in CMYK colors, spot colors often cannot be accurately produced. If matching spot colors is critical to a job, some printers can provide a catalog of colors that they can consistently print on a variety of substrates. Catalogs may contain specially formulated colors, or use systems similar to Pantone or FocolTone TM. Sometimes it is possible to request samples. To ensure accurate matching, spot colors should also be evaluated by a color measurement instrument. Dot Gain Adjustments for flexographic dot gain are often not available in proofing systems designed to mimic the dot gain found in offset lithography. For this reason, halftone images and smaller type may not be accurately reproduced in the proof. However, once a characterized profile is established for a given press using a color management system, dot gain can be simulated by a digital proofing system. Film Proofs Plate Proof Press Proof Most film-based proofing systems are designed to compensate for dot gain occurring in offset lithography. To use these systems for flexography, two sets of film must be printed. The first set, which is used for platemaking, reduces dots to compensate for the actual flexographic dot gain during printing. The second set, used for proofing, increases the dots to simulate dot gain in the film proof. For many years, flexographic printers have used a plate proof created on a mounterproofer during plate mounting to verify plate register, quality, and content. Though expensive and not intended for customer approval, the plate proof today is mostly used on wide web presses. Plate proofs can be created for color matching, but they more commonly use ink hues that are not intended to match press colors. Color matching from a plate proof is very difficult due to the differences between proofing and press equipment. Printed on the press, a press proof is the most accurate method, but because it is also the most expensive, it is not common. 20

23 What to Look For During a Press Check Type Is the type sharp? Has the weight of the type changed? With a loupe, look for outline halos. Registration Are the colors in register? Make sure colors line up and check areas where inconsistent elongation may have caused misregistration. For a four-color process with traditional screening, color-to-color register should not vary by more than a single row of halftone dots. Density/Color Intensity Is the density of the color appropriate, especially in situations where screens and solids are printing from the same cylinder? Is the color strength consistent from side to side? Color Match Do spot colors match? Each color should be verified under 5000 Kelvin lighting conditions. When appropriate, use color measurement instruments to verify acceptable match. Ink Laydown Is the ink laydown consistent, without mottle? Are there pinholes or voids? Under a loupe, halftone dots should appear sharp, not slurred. Substrate Is the width, caliper, and type of substrate as specified? If the substrate is an opaque film, is the opacity appropriate? External Register Does the print line-up with the specified finishing operation, such as diecuts, sideseals, slots, scores, and glue areas? Request a mock-up container to check accuracy of external register. Ink and Impression Levels Look at the edges of solids for an outline halo, which is the result of excess ink or impression pressure. The press operator may be able to relieve some pressure; some plates may have spot color inaccuracies that require a plate remake or remount. Dot Gain Dot gain levels should be comparable to those achieved during fingerprint trial. UPC and Bar Coding Over-impression can change the width of bars and spaces, potentially making the bar code unreadable. Wind Direction Has the job been installed in the right direction on press? If the press is running roll-to-roll, is the print rewind in the proper direction? Before a flexographic job is printed, a number of factors need to be checked to ensure accuracy. Makeready on a flexographic press includes installation of the required plate cylinders and inks, setting levels for impression and ink pressure, register adjustment, and any setup for inline finishing, such as cutting, folding, or gluing. Pressure levels are particularly critical for accurate printing. Finally, after press adjustments are complete, the press operator checks colors for the job, running a sample at (or near) production speeds. Designers should also make sure to perform a press check for the first actual print run. These are some of the elements that should be verified prior to printing. Type Is the point size and font correct? Is the typography what was expected? Has plate elongation affected leading, letterspacing, or word spacing? Line Art Have all of the images elongated and reproduced accurately? Register Internal (color to color) and external (images to die-cut, sealing areas, perforations, etc.) If all colors have been accurately distorted, and the plates accurately mounted, the job should be in register. Traps Have plate mounting and plate elongation maintained accurate trap areas? Bar Coding Have the bar codes been positioned to allow proper open area surrounding the code for scanning? Has the bar code been positioned with the bars parallel or perpendicular to the web direction? When mounted perpendicular to the web direction, bar codes will be affected by plate elongation. Wind Direction Has the job been set-up to print in the right direction on press? Will the print direction match the packaging or labeling operation? Prepress Checklist & The Press Check 21

24 Glossary & Index ablating: 8 To remove by cutting, erosion, evaporation, or vaporization. In flexography, laser ablating is used to image design rolls and plates. anilox: 5, 6, 17 An engraved metal or ceramic roll used to meter ink in the flexographic inking system. bearer bars: 18 Continuous strips of plate material usually placed on the outside of printing areas to minimize plate bounce and over-impression by taking up excess impression pressure during printing operations. blanket: 4 In offset printing, a rubber-surfaced fabric which is clamped around a cylinder, to which the image is transferred from the plate, and from which it is transferred to the paper. bleeds: 18 An image or color that extends to, and slightly beyond, the trimmed edge of a printed piece. calendered paper: 10 Paper that has been passed through a group of rolls to reduce thickness, increase density, and improve its surface smoothness and gloss. caliper: 10 Thickness of a substrate, usually measured in thousandths of an inch. cell angle: 6, 17 On an anilox roll, the measure of a line drawn through the center of a row of cells and a line drawn parallel to the shaft of the anilox. The angle at which cells are arranged on an anilox roll. cells per inch (CPI): 4, 17 On an anilox roll, the number of cells in a linear inch. cell volume: 6 A measure of the capacity to carry ink of a square inch of anilox roll. Cell volume may be calculated as theoretical volume, or measured by a technique of liquid volume measurement, or scientifically measured by a technique known as infratometry. choke: 12 A trapping technique of slightly reducing the size of a line, an image element, or a dot to create a trap. clay coated: 10 A high-quality paperboard having a surface coating of pigment or pigment like solids and appropriate binders. colorimeter: 14 Any of various instruments used to determine or specify colors. A colorimeter measures the spectral reflectance of a color, and computes numeric values for the hue, intensity, and purity. color management system (CMS): 14 A software system used to ensure color consistency among different input and output devices so that printed results match originals. common impression cylinder press (CIC): 6, 7 A printing press configuration that positions all color decks around a central impression cylinder. The CIC press configuration offers web support throughout the printing operations, and optimum registration capabilities. computer aided design (CAD): 18 Electronic equipment used by package design engineers to layout and design in three dimensions the structure of a package. continuous repeat: 7 The ability to print patterns or images on a web of substrate, void of any gaps in the printing. contract proof: 20 A proof supplied to a printer to document the color results expected on the press. converting operations: 7 In packaging, any process performed to manufacture a completed package from a raw material or an unfinished material. corrugated: 6, 7, 10 The combination of linerboard and corrugating medium as a fluted material. corrugated press: 2, 7 An inline sheet-fed press (usually a flexographic press) designed for printing sheets of corrugated. cut areas: 18 In die-cutting, a region of a package that will be cut-out as a window or as part of the package construction, or as a slot for a closure tab. cylinder: 5 In flexography, the term cylinder usually refers to the rollers on which plates are mounted (plate cylinders), and the impression roller (impression cylinder). design roll: 2, 8 A rubber covered cylinder often used as an image carrier by flexographic printers. Relief patterns and images are created by ablating the surrounding non-image area with laser light energy. die-cutting: 18 The process of using sharp steel rules to cut shapes for labels, boxes and containers, from printed sheets. Die-cutting can be done on either flat-bed or rotary presses. Rotary diecutting is usually done inline with printing. direct-to-plate: 8 The process of using digital information to laser image a printing plate or design roll, bypassing the film stage of production. distortion: 9 Intentional compensation for flexographic plate elongation. distortion factor: 9 A percentage number calculated by a plate elongation formula and applied to images prior to output of flexographic films. dot gain: 15, 16 An unavoidable increase in the size of halftone dots as they pass through the stages of platemaking and printing. Dot gain varies according to the characteristics of the press, ink, and substrate used. If dot gain is not accounted for during the creating of color separations and proofs, unexpected color shifts or loss of detail will occur on press. doctor blade: 4, 6 A thin blade of metal or polyethylene mounted parallel to and in contact with an anilox roll to meter excess ink from the non-cell areas. dry trapping: 12 The technique of printing multiple colors by drying each color immediately after it is applied and before the next ink is applied on or over it. Flexography and gravure print by dry trapping. See wet trapping dual doctor ink chamber: 4, 6 On a flexographic press, a cartridge designed to supply ink to the anilox roll in an enclosed area. Ink is pumped into and circulated through the cartridge which is positioned on the anilox roll. Two thin strips of metal or polyethylene (doctor blades) are in direct contact with the anilox roll. One of the blades contains the ink within the cartridge, the other blade contains and meters the ink from the non-cell areas of the anilox. When using a dual doctor ink chamber, the fountain roll can be eliminated. 22

25 durometer: 15 A measure of the hardness of rubber. The measuring instrument most widely used is a Shore A durometer gauge. fingerprint: 12, 14, 15 A method of testing characteristics of a printing press by use of a test plate. fluted material A paper substrate formed into rounded pleats and sandwiched between two paper linerboards. Fluting material adds structural strength to corrugated board. fountain roll: 6 In flexography, a rubber covered roll in the two roll flexographic inking system. The function of the fountain roll in a two roll system is to deliver and meter ink to the anilox roll. fountain solution: 4 In lithography, a solution of water, a natural or synthetic gum, and other chemicals used to dampen the plate and keep non-printing areas from accepting ink. freesheet paper: 10 Paper free of mechanical wood pulp. gradation: 14 A smooth transition between shades. gravure: 2, 4 An intaglio printing process that uses an engraved plate as a master image carrier. Gravure is used for printing packaging, speciality products, and publications. HiFi, high fidelity: 11, 17 A method of increasing the process color printing gamut by printing six, and sometimes seven, process colors. image carrier: 4 The physical component of a printing press responsible for transferring ink from the ink distribution system to the appropriate areas of a substrate. impression cylinder: 4, 6 The cylinder that provides web support during image transfer from plate to substrate. inline finishing: 7 Any converting operation done as a continuous process with a printing operation, including lamination, die-cutting, perforating, folding, and sealing. inline press: 6, 7 A multicolor press where the printing units are assembled on a common plane, or inline with one another. Also refers to any combination of printing and converting operation done simultaneously. intaglio: 4 A process in which the image is recessed below the non-image area, used in gravure and steel die engraving. kraft linerboard: 10 A type of paper made from chemically pulped wood fibers, and used as the top and bottom layers in a sheet of corrugated. kiss: 6 In flexographic printing, the lightest contact pressure necessary for complete image transfer to a substrate. laser ablation: 8 A process of imaging onto rubber or photopolymer design rolls or plates. Images are created by ablating the surrounding nonimage area with laser light energy. lithography: 2, 4 A method of printing from a plane surface (such as a smooth stone or metal plate) on which the image to be printed is ink-receptive and the nonprinting area ink repellent. lpi: 5,16, 17 (lines per inch) A measure of the frequency of a halftone screen, usually ranging from Originally, halftones were made by placing an etched glass plate over an image and exposing it to produce dots. Lpi refers to the frequency of the horizontal and vertical lines. metallized film, metallized paper: 10 Paper or film that has been coated with a microscopic film of metal. A metallized paper or film is produced by melting and vaporizing aluminum in a vacuum while passing a web of paper around a chilled roller and over the point of vaporization. Vaporized molecules collect on the cool web, giving the paper or film a metallic finish. moiré: 6, 17 A repetitive interference pattern caused by overlapping symmetrical grids of dots or lines having a differing pitch or angle. mounting tape: 9 A compressible, or a non-compressible substrate with adhesive applied to both sides, and used for affixing flexographic printing plates to plate cylinders. Mounting tapes are available in a variety of types and thicknesses. nailhead: 12 In flexographic printing, an ink drying problem usually caused by two or more colors printed on top of one another in a trapping situation, resulting in incomplete drying to the successive ink layers, and an ink pick-off area that resembles the head of a nail. narrow web: 6 The limit of narrow web flexography has been specified to be as narrow as 18" or as wide as 32" by various sources within the industry. There is presently no agreement on the exact cut-off width that differentiates wide web from narrow web. nesting: 7, 18 A technique of placing images between other images on a flexographic step-and-repeat layout. Nesting is done to minimize substrate waste, and/or to minimize flexographic plate bounce. nip: 6 Contact point between two rollers, usually a metal driven roller and undriven rubber covered roller. offset lithography: 4 Planographic print using an intermediate blanket cylinder to transfer an image from the lithographic plate to the substrate. over-impression: 13, 15 In a flexographic press set-up, excess pressure between the plate and the impression roll. paperboard: 10 There is some question as to the distinction between paper and paperboard. Paperboard is thicker, heavier in basis weight, and more rigid than paper. Most paper that is over 12 points (0.012") thick is considered paperboard, however, some thinner papers with a thickness of 10 points (0.010") are also considered to be paperboard. photopolymer: 8 Any of a variety of materials that undergo a chemical change when exposed to ultraviolet light. planographic: 4 A process for printing from a plane surface, both image and non-image are carried on a common plane as in lithography. plate elongation: 9 In flexographic printing, a physical lengthening of the flexographic image carrier around the cylinder or curve direction, that occurs during the plate mounting step. Glossary & Index 23

26 Glossary & Index plate bounce: 18 An erratic rotation of a printing press cylinder, such as a plate cylinder, that results in defective impressions. This is caused by the lead edge of image areas on a flexographic plate cylinder coming in contact with the anilox or impression roll. plate proofs: 20 A print made from the live production plates prior to going to press. Plate proofs are usually not appropriate for evaluating color results, but may be used as an in-house quality control proof before going to press. plate thickness: 9 A measure of the height of a flexographic plate from the back to the top of the image area, usually expressed in thousandths of an inch. resolution: 16, 17 The measure of fineness and detail in an image. The scale of resolution depends on the device being measured. Scans are measured in samples per inch (spi) or pixels per inch (ppi). Monitors are measured in ppi. Halftone screens can be measured in lines per inch (lpi). In all cases, the higher the resolution, the more detailed the image. reverse side printing: 11 Printing the underside of a clear substrate. Sometimes called back printing. run-length: 5 The size of a printing job, usually indicated by the number of impressions or footage required to complete the job. Also, the number of impressions that may be expected from a printing plate or a set of printing plates. trap, trapping: 12 In prepress, a technique which allows for variation in registration during the press run. On the desktop, this is done primarily by allowing an overlap between abutting colors. variable repeat length: 7 In printing, the capability of a printing press to print from various size plate cylinders or printing plates. vignettes: 16 An image in which the background fades gradually away until it blends into the unprinted substrate. wet-out: 10 The tendency of an ink to level-out as would a true liquid. On a substrate, an ink film should flow and level itself rather than beading. polyethylene films: 2, 5, 10 Thin clear substrates used as packaging materials, commonly known as plastic as in plastic bags. polymer films: 10 Any one of a number of different nonabsorbent, thin, clear, or colored substrates used as packaging materials, and commonly referred to as plastics. printing plate: 4 In flexography, a rubber or photopolymer material used as the image carrier to transfer ink from anilox to substrate. proof, proofing: 20 A prototype of a job to be printed that is made from plates, film or electronic data. Used for in-house quality control and/or for customer inspection and approval. raster image processor (RIP): 19 The computerized process that results in an electronic bitmap which indicates every spot position on a page in preparation for actual printout. reflection densitometer: 14 An apparatus for measuring the optical density, or light absorbing qualities, of an ink. relief: 5 In printing, a process that prints from raised image areas. solid bleached sulfate: 10 Paperboard made with sulfate pulp containing 100% bleached fibers. spectrophotometer: 14 An instrument used to determine the distribution of light energy reflected by a color or a printed ink. spot color: 11 Color printed with a custom ink, rather than with a process color combination. spread: 12 A prepress function that compensates for printing press misregistration. A spread is the slight size increase of the inserted image. stack press: 7 A multicolor printing press where all color units are built vertically or stacked. step-and-repeat: 18 In photomechanics, imagesetting, or plate exposure, the procedure of multiple exposures using the same image information by stepping it in position according to a predetermined layout. stochastic screening: 17 Also called frequency modulated or FM screening. An alternative to conventional screening that separates an image into very fine, randomly placed microdots, rather than a grid of geometrically aligned halftone cells. wet trapping: 12 The technique of printing multiple colors whereby each succeeding ink film remains open (not dry) as the next color is applied on or over it. white back-up plate: 11 A printing plate made for applying a solid white ink as a reflective base under all colored images on a clear substrate. wide web: 6 The lower limit of wide web flexo has been specified to be as narrow as 18" or as wide as 32" by various sources within the flexographic industry. There is presently no agreement on the exact cut-off width that differentiates wide web from narrow web. windows: 18 In packaging, an area of a package that will be cut out (or left clear on clear substrates) to expose the product held within the package. repeat length: 7 Printing length of a plate cylinder determined by one revolution of the plate cylinder gear. substrate: 4, 10 A material on which print or coating is applied, such as paper, polyethylene, or foil. 24

27 Other Educational and Reference Materials from Agfa An Introduction to Digital Color Prepress 1997 Edition A fundamental reference for anyone interested in PostScript color. Basic concepts are explained in a clear, objective and highly visual way. A useful and award-winning volume, with over 400,000 copies in print in eight languages. A Guide to Color Separation Digital Color Prepress - Volume Two This booklet provides a more advanced look at the topic of PostScript color. A special emphasis is placed on reproducing color pages in print, including the use of HiFi color and stochastic screening. Working With Prepress and Printing Suppliers Digital Color Prepress - Volume Three This booklet explains key elements in the relationship between document creators and their service providers. Contains time-saving tips to ensure successful transition of jobs from design to film output to final print. An Introduction to Digital Scanning Digital Color Prepress - Volume Four This booklet focuses specifically on many key aspects of scanning. Contains 40 pages of both basic and advanced information, presented objectively and graphically. An essential reference for scanner users with any level of expertise. An Introduction to Digital Photo Imaging This booklet looks at how computer technology is blending with and changing traditional photography, and the impact it has on photographers and imaging professionals. Explains how to evaluate digital cameras, scanners, input and output devices, and how to get started in this emerging field. An Introduction to Digital Color Printing A first-ever publication that provides an objective look at technology, applications, and processes. Learn how to save time and money and use digital printing to your best advantage. Includes a bound-in digitally printed insert for comparison with offset printing. A Guide to Digital Photography Theory and Basics This all-new guide is a must read for anyone working with or interested in digital photography. Offers clear, visual explanations on traditional photography basics as well as key concepts from the emerging digital realm. PostScript Process Color Guide 1996 Edition This 52-page oversized reference contains over 17,000 electronically created CMY and CMY+K process color combinations (on coated and uncoated stock), intended to help predict how colors on the screen will look in print. Also includes production tips, instructions for use, and special color viewing templates. Available in U.S. (SWOP) and a multilingual European standard version. The Agfa Guide to Digital Color Prepress Macintosh CD-ROM Edition The ultimate companion to the awardwinning Digital Color Prepress series. This CD-ROM contains over 630 Mb of interactive content, including 350 screens of detailed information, numerous animations, videos, voiceovers, glossary, timeline, build-a-page game, and more. For more information or to order, see contact listings on back cover.