"GRAVURE vs FLEXOGRAPHY"INTRODUCTION OF THE FLEXOGRAPHY & GRAVURE

Flexography is a type of printing process that uses a plate with a raised surface and fast

drying fluid inks to print directly onto the print material. The plates are made of rubber or

photopolymer and are attached to a drum on rotary printing equipment. Flexography

would be printed while the envelopes are being converted. On larger runs, this is a less

expensive process than lithography because it eliminates a separate printing process, but

the print quality will not be as good.

Flexography is a form of rotary web letterpress, combining features of both letterpress

and rotogravure printing, using relief plates comprised of flexible rubber or photopolymer

plates and fast drying, low viscosity solvent, water-based or UV curable inks fed from an

"anilox" or two roller inking system. The flexible (rubber or photopolymer) plates are

mounted onto the printing cylinder with double-faced adhesive. Plates are sometimes

backed with thin metal sheets and attached to the cylinder with fastening straps for close

register or ink alignment. This adds additional cost to the plate and requires more

makeready time, but when quality printing is critical this type of plate can make the

difference.

Flexography is related to the oldest printing process, letterpress, because both

flexography and letterpress print from a raised image. In its original form, letterpress

used individual metal characters called types and a mechanical press. The type was

combined to form words and sentences and tightly arranged on the flat surface of the

press. Then the raised areas were covered with ink. The message was formed when paper

was pressed against the flat metal type.

Flexography prints from a flexible printing plate that is wrapped around a rotating

cylinder. The plate is usually made of natural or synthetic rubber or a photosensitive

plastic material called photopolymer. It is usually attached to the plate cylinder with

double-sided sticky tape.

Gravure (Roto or Gravure for short) is a type of intaglio printing process; that is, it

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.

In the last quarter of the 19th century, the method of image photo transfer onto

carbon tissue covered with light-sensitive gelatin was discovered, and was the beginning

of rotogravure. In the 1930s–1960s, newspapers published relatively few photographs

and instead many newspapers published separate rotogravure sections in their Sunday

editions. These sections were devoted to photographs and identifying captions, not news

stories. Irving Berlin's song "Easter Parade" specifically refers to these sections in the

lines "the photographers will snap us, and you'll find that you're in the rotogravure". And

the song "Hooray for Hollywood" contains the line "…armed with photos from local

rotos" referring to young actresses hoping to make it in the movie industry.

In 1932 a George Gallup "Survey of Reader Interest in Various Sections of Sunday

Newspapers to Determine the Relative Value of Rotogravure as an Advertising Medium"

found that these special rotogravures were the most widely read sections of the paper and

that advertisements there were three times more likely to be seen by readers than in any

other section.

Flexography is one method of printing words and images onto foil, plastic film,

corrugated board, paper, paperboard, cellophane, or even fabric. In fact, since the

flexographic process can be used to print on such a wide variety of materials, it is often

the best graphic arts reproduction process for package printing.

Flexography is the major process used to print packaging materials. Flexography is used

to print corrugated containers, folding cartons, multiwall sacks, paper sacks, plastic bags,

milk and beverage cartons, disposable cups and containers, labels, adhesive tapes,

envelopes, newspapers, and wrappers (candy and food).

Flexographic presses are capable of producing good quality impressions on many

different substrates and is the least expensive and simplest of the printing processes used

for decorating and packaging printing. The use of flexographic printing presses is on the

rise.

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's major quality shortcoming is that all

images, including type and "solids," are actually printed as dots, and the screen pattern of

these dots is readily visible to the naked eye.

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 very expensive and best suited for high volume printing. Typical

uses include long-run magazines in excess of 1 million copies, mail order catalogs,

consumer packaging, Sunday newspaper ad inserts, wallpaper and laminates for furniture

where quality and consistency are desired. Another application area of gravure printing is

in the flexible-packaging sector. A wide range of substrates such as polyethylene,

polypropylene, polyester, BOPP, etc. can be printed in the gravure press. Gravure

printing is one of the common processes used in the converting industry.

Rotogravure presses for publication run at 45 feet (14 m) per second and more, with

paper reel widths of over 10 feet (3 m), enabling an eight-unit press to print about seven

million four-color pages per hour.

The vast majority of gravure presses print on rolls (also known as webs) of paper,

rather than sheets of paper. (Sheetfed gravure is a small, specialty market.) Rotary

gravure presses are the fastest and widest presses in operation, printing everything from

narrow labels to 12-foot-wide (3.66-meter-wide) rolls of vinyl flooring. For maximum

efficiency, gravure presses operate at high speeds producing large diameter, wide rolls.

These are then cut or slit down to the finished roll size on a slitting machine or slitter

rewinder. Additional operations may be in line with a gravure press, such as saddle

stitching facilities for magazine or brochure work.

Process Overview……….………………….2

In the typical flexo printing sequence, the substrate is fed into the pressfrom a roll. The image is printed as substrate is pulled through a series of stations, orprint units. Each print unit is printing a single color. As with Gravure and Lithographicprinting, the various tones and shading are achieved by overlaying the 4 basic shades ofink. These are magenta, cyan, yellow and black. Magenta being the red tones and cyanbeing the blue.The process of printing each color on a flexo press consists of a series of four rollers:· Ink Roller· Meter Roller· Plate Cylinder· Impression CylinderThe first roller transfers the ink from an ink pan to the meter roller or Anilox Roll, whichis the second roller. The Anilox roller meters the ink to a uniform thickness onto the plate

cylinder. The substrate then moves between the plate cylinder and the impressioncylinder, which is the fourth roller.The impression cylinder applies pressure to the plate cylinder, thereby transferring theimage onto the substrate. The web, which by now has been printed, is fed into theoverhead dryer so the ink is dry before it goes to the next print unit.After the substrate has been printed with all colors the web MAY be fed through anadditional overhead tunnel dryer to remove most of the residual solvents or water. Thefinished product is then rewound onto a roll or is fed through the cutter.The major unit operations in a flexographic printing operation are:· Image preparation· Platemaking· Printing· Finishing

Image preparation begins with camera-ready (mechanical) art/copy or electronicallyproduced art supplied by the customer. Images are captured for printing by camera,scanner or computer. Components of the image are manually assembled and positioned ina printing flat when a camera is used. This process is called stripping. When art/copy isscanned or digitally captured the image is assembled by the computer with specialsoftware. A simple proof (brown print) is prepared to check for position and accuracy.When color is involved, a color proof is submitted to the customer for approval.Flexographic Printing PressesThe five types of printing presses used for flexographic printing are the stack type,central impression cylinder (CIC), in-line, newspaper unit, and dedicated 4-, 5-, or 6-color unit commercial publication flexographic presses. All five types employ a platecylinder, a metering cylinder known as the anilox roll that applies ink to the plate, and anink pan. Some presses use a third roller as a fountain roller and, in some cases, a doctorblade for improved ink distribution.Flexographic Printing Press TypesStack TypeThe stack press is characterized by one or more stacks of printing stations arrangedvertically on either side of the press frame. Each stack has its own plate cylinder whichprints one color of a multicolor impression. All stations are driven from a common geartrain. Stack presses are easy to set up and can print both sides of the web in one pass.They can be integrated with winders, unwinders, cutters, creasers, and coating equipment.They are very popular for milk carton printing. A drawback of stack presses is their poorregistration; the image position on every printed sheet is not as consistent as in manyother printing processes.

Central impression cylinder (CIC)Central impression cylinder (CIC), like the common impression rotary letterpress, use asingle impression cylinder mounted in the press frame. Two to eight color printingstations surround the central impression cylinder. Each station consists of an ink pan,fountain roller, anilox roll, doctor blade, and plate cylinder. As the web enters the press itcomes into contact with the impression cylinder and remains in contact until it leaves thepress. The result is precise registration which allows CIC presses to produce very goodcolor impressions. CIC presses are used extensively for printing flexible films.

In LineIn Line flexo printing is similar to a unit type rotary press or the stacked press except theprinting stations are arranged in a horizontal line. They are all driven by a common lineshaft and may be coupled to folders, cutters, and other postpress equipment. Thesepresses are used for printing bags, corrugated board, folding boxes, and similar products.Newspaper Flexographic PressesA newspaper flexographic press consists of multiple printing units, each unit consistingof two printing stations arranged back-to-back in a common frame. The use of pairedstations allows both sides of the web to be printed in one pass. Multiple printing stationsare required to print the many pages that make up a typical newspaper. Single and doublecolor decks, stacked units, or 4-, 5-, or 6-color units are sometimes positioned abovethose units where the publisher wants to provide single or multiple spot color, spot colorfor both sides of the web, or process color, respectively (Buonicore).Commercial Publication Flexographic PressesCommercial publication flexographic presses are compact high-speed presses with wideweb capability that utilize dedicated 4-, 5-, or 6-color units. Typically, two four-colorunits are paired in one press to allow printing on both sides of the web. Publicationflexographic presses generally incorporate infrared dryers to ensure drying of thewaterborne ink after each side of the web is printed (Buonicore).Process Modification of GravureThe degree to which vegetable oils can replace petroleum oils in inks to reduce VOCsdepends on several things, including the type of press, the type of substrate, and the typeand color of the inks. Gravure presses generally use heatset inks, which are inks that areset by going through an oven or dryer. These inks generate the most VOCs because theytolerate only the smallest amount of vegetable oil content. The drying temperature neededto set vegetable oil inks will normally scorch the substrate and ruin the product.Vegetable inks dry slower than conventional inks - especially on coated papers.The absorbency of the substrate will determine the amount of vegetable oil content thatcan be used in the ink. Absorbent papers hold the ink in the substrate so less VOCs arereleased as compared to coated papers which normally need heat to dry the inks - thereby

releasing VOCs. Soy and vegetable based inks provide beneficial printing properties - butdry slower than petroleum based inks.Water-based inks, while environmentally friendly, pose their own special kinds ofconcerns in gravure printing. As a rule, water-based inks dry slower than solvent-basedinks resulting in initial obstacles when making a switch to water-based. They are moreabrasive and cause increased cylinder wear and they require somewhat differentengraving and etching processes. Water-based inks tend to have surface adhesion andlay-down problems that solvent-based inks do not have. Printing process adjustments areneeded to maintain the quality of finished product.Some of the more common solvents used in solvent-based gravure printing are toluene,xylene, methyl ethyl ketone (MEK), methyl isobutyl ketone, acetone, methylene chloride,isopropyl and normal-propyl alcohol. All pose risks that are inherent in a solvent-basedsystem. Alternative materials with less risk associated to their use should be considered.

-How does gravure work?Of the four traditional printing techniques of offset lithography, flexography, screen-printing and gravure, which are practised worldwide, gravure bears the greatestresemblance to photography. Gravure applies the ink in controlled doses from differentsizes of cell, which have been either chemically etched or electronic engraved into thesurface of the printing image carrier, a commonly copper coated cylinder. These cells canvary in their size, shape and depth depending on the way in which individual printinghouses work. They can have the same area and vary in depth, or both the area and thedepth can vary. The smaller the volume of the printing cells, the lighter the tone, which isreproduced by them. Concentrating on gravure means obtaining the highest picturequality and maintaining it over a long print run. Through fast, rationalised productionmethods costs can be kept, comparatively speaking, low. It is for this reason that gravureis ideal for the production of high circulation magazines, mail order catalogues,newspaper weekend colour supplements, and packaging and speciality products.Gravure production steps:-Reproduction

All colours in a printed image arise through a mixture of the basic colours yellow,magenta, and cyan, which are present in different intensities. In order to print colouredpictures, yellow, magenta, cyan and black printing inks have to be printed exactly inregister over each other. In order to do this, the amounts of the basic colours in theoriginal have to be separated. These colour separations are made today from originalsdigitised in scanners or supplied from digital cameras. Each of the basic colour portionsis presented in the form of higher or lower values, representing the amounts of ink neededin the subsequent printing operation. Any required colour corrections to these colourseparations, re-touching and the composition of complete pages including the text arealso carried out in prepress computer systems. The digital data is then supplied for the

engraving of printing formes. Alternatively, photographically produced positives,negatives, - so-called opalines or bromides, can be still used as the input for theengraving of the printing cylinder.-Cylinder preparation

Gravure cylinder preparation is based on either chemical etching or electronic engraving.For typical publication gravure, the engraving process is used. Traditionally, engravingtakes place in a copper surface for mechanical engraving. Most operations workcompletely digitally while some of the older type engraving equipment(HelioKlischographs) still uses synchronised scanning and engraving units. Mechanicalengraving uses tiny diamond stylines oscillating up to 9 000 times in one second. Onemechanical engraving machine can have a number of engraving heads, which worksimultaneously. Laser engraving reaches an engraving frequency of 70 000 cells persecond but is still limited to one engraving head. Both systems work with the utmostprecision and depending on the strength of the electronic signal, engrav cells in thecylinder surface, which are correspondingly of larger or smaller volume. During theprinting process these cells take up and then transfer onto the paper larger or smalleramounts of ink. In order to achieve the hardness necessary for the production printingoperation and the resilience to wear, the cylinders are finally plated with a thin chromiumlayer.-Printing and finishing

Depending on the product, different production methods are applied in gravurepressrooms. Publication gravure uses typical press designs of eight printing units (one percolour for each paper side) and one folder for the on-line production of a complete set offolded pages, so-called signatures. The latest presses run at speeds higher than 55 000cylinder revolutions per hour, printing up to 256 pages per revolution in full colour. Paperwebs up to 3,6 metres in width race at a speed of 15 metres per second through thepresses. The result is each hour 55 000 individual products are produced, which will beeither stitched and finished I a single operation or become parts of subsequent binderyproducts. Bindery finishing means collecting several signatures, a combination of insertsand covers, addressing, binding and trimming.Presses for packaging gravure printing have to fulfil different requirements, as the varietyof products require different substrates colours and finishing processes. Presses run atlower speeds to enable the processing of difficult materials and drying of special inks.Packaging presses can combine in-line finishing processes including laminating, cutting,creasing, embossing, etc.-Gravure ProcessGravure transfers ink from small wells or cells that are engraved into the surface of thecylinder. This is illustrated in the figure below. The cylinder rotates through a fountain ofink. The ink is wiped from the surface by a doctor blade. The cup-like shape of each cellholds the ink in place as the cylinder turns past the doctor blade.

The gravure engraver accomplishes the formation of nearly perfect cells or wells. Thegravure cell is characterized by 4 variables; depth, bottom, opening and bridge. The depthof the cell is measured from the bottom of the cell to the cylinder surface.The opening is described by shape and cross sectional area. The bridge is the surface ofthe cylinder between cells. The doctor blade rides along the cell bridges or ridges (alsocalled walls).

Preparation of Image Carrier ………….3Flexography is related to the oldest printing process, letterpress, because both

flexography and letterpress print from a raised image. In its original form, letterpress

used individual metal characters called types and a mechanical press. The type was

combined to form words and sentences and tightly arranged on the flat surface of the

press. Then the raised areas were covered with ink. The message was formed when paper

was pressed against the flat metal type.

Flexography prints from a flexible printing plate that is wrapped around a rotating

cylinder. The plate is usually made of natural or synthetic rubber or a photosensitive

plastic material called photopolymer. It is usually attached to the plate cylinder with

double-sided sticky tape.

Generally Flexography Plate are two type -

1. Rubber Plate

2. Photopolymer Plate

1. Rubber Flexography Plate Making Process - There are three basic steps in rubber

platemaking -

First an engraving from the negative is made by placing the negative over a light-

sensitized metal sheet and exposing it to intense light in a vacuum frame.

Then the metal sheet is etched with acid in an etching machine and becomes an engraved

pattern of the negative with the images areas high and the nonimage areas low.

The second step is making a mold from the engraving by pressing the metal engraving

against a heated matrix material that hardens in the molding press. Molding pressure is

generated by hydraulic power to the bottom table, or platen, as seen here, The top platen

stays stationary.

The third and final step, making the rubber plate from the matrix, is also accomplished

with the molding press. The relief image is formed on the rubber plate by pressing the

matrix against it under sufficient heat, time, and pressure, The plate is stripped from the

mold while still warm.

2. Photo-Polymer Flexography Plate Making Process -:

Unlike the rubber plate, which must have an engraving made from a

negative, the sheet photopolymer plate, shown here on the right, is made directly from the

negative by placing the negative over a sheet of light-sensitive photopolymer and

exposing it to ultraviolet light.

There are two type to make Photopolymer Flexography Plate are given bellow –

I. With Precast Photopolymer.II. With Liquid Photolymer.

With Precast Photopolymer :-Solar plates or Photopolymer Plate are made up of 3 layers:

A. A steel or plastic backing plate.

B. The light sensitive polymer layer that will form the impression. This is the layer that

hardens where it is exposed to UV light.

C. A cover film. This protects the plate and is removed before exposure..

In these steps are used to make this plate –1. Prepare your artwork on Overhead projection film.

2. Cut the Photopolymer plate.

3. Remove the cover film from the plate surface. These cover films could contain small

amounts of polymer residue and should be discarded.

4. Place the OH transparency artwork on the plate and into the exposure frame, clamped

securely with bulldog clips. You are now ready to expose the plate, using the time

determined from the test strip exposure.

5. Wash out the plate in hand-warm water, gently scrubbing with a natural bristle brush, in a

circular motion. If you want a shallow depth wash out, like for Keum- boo, use a natural

sponge and keep checking your plate for depth. For a deep washout, keep brushing until

you can feel clean base material, any photopolymer left on the base will feel a bit

slippery. If you are using very thin lines it might be better to wash out leaving a little bit

of material on the base to reinforce the line. Thin lines have a tendency to lift off.

6. Wipe excess water off the plate with the natural sponge and dry the plate surface in front

of a fan heater set on medium, with the plate on its edge about 30cm (1') away from the

heater for about 5 minutes. The plate should feel totally dry with no stickiness.

7. Post expose the plate for the same amount of time you used for the initial exposure. This

will harden the plate all the way through. Brush a little vegetable oil over the whole plate,

this stops it from drying out and cracking. Store finished plates in a plastic bag, to

exclude moisture.

To use with metal clay: brush on vegetable oil, with very fine, or deep detail, a

smear of Badger Balm on the rolled out clay helps releasing the clay from the

plate.

For use with polymer clay: use corn flour (cornstarch) or just plain water.

With Liquid Photopolymer :-

Instead of using a precast sheet of photopolymer, liquid photopolymer

can be used to make a plate. The liquid photopolymer platemaking system uses a trough

of clean, slightly yellow photopolymer that flows like honey. Like the precast sheet plate,

the liquid plate is made in direct contact with the negative. A motorized carriage moves

over the negative depositing a layer of liquid along with a plastic backing sheet, Plate

thickness can be easily altered for specific jobs when using liquid photopolymer, while

precast sheets come in predetermined thicknesses.

On the left a negative is being placed over a precast sheet of photopolymer in an exposing

unit. But in both sheet and liquid photopolymer platemaking the photopolymer is exposed

through the negative by ultraviolet light, as shown on the right. The exposure causes the

polymer to harden in the image areas of the negative.

Next the exposed plate is put into a processor, which removes the unhardened polymer

from the nonimage areas, leaving the relief image areas. The plate then goes into a drying

unit for further hardening and drying.

In order to determine if the finished plate will print accurately once on press, the plate is

mounted on the printing cylinder with double-sided sticky back in a mounting and

proofing machine. Once attached to the plate cylinder, the plate is inked with a roller, and

then rolled against a piece of proofing paper that is attached to an impression cylinder.

The plate and proof are then inspected for precision. If approved, the plate is now ready

to be printed.

Gravure Cylinder PreparationThere are four basic means of engraving the image into a gravure cylinder:

Diffusion-Etch Process. Also called conventional gravure engraving, diffusion-etch is

the oldest method of gravure cylinder engraving. It uses two film positives, one of which

is a film positive of the image (solid areas, text, or continuous-tone, variable-density

image) the other being a special gravure screen, containing between 100:200 lines per

inch. The screen is used to "convert" the solid image into many tiny cells (similar to

making a halftone from a continuous-tone photograph, for example), which are small

squares oriented at a 45º angle to the direction of web travel through the press (diamonds,

basically). The positive image and the screen are placed on top of a carbon tissue, a

water-soluble paper covered with a light-sensitive gelatin resist, and consecutively

exposed to ultraviolet light. After exposure, the least exposed image areas are soft and

soluble, while the most highly exposed non-image areas are hard and insoluble, and those

mid-tone regions are slightly exposed and produce a slightly hard and insoluble emulsion.

The carbon tissue is then adhered to the surface of the gravure cylinder, and developed.

The cylinder with the developed resist is placed in an acid bath (commonly a ferric

chloride etchant), where the etchant eats through the resist and into the copper at varying

rates, depending on the hardness of the emulsion. In the highlight areas—those that have

received the most exposure—the etchant eats through very slowly, so that in a given

period of etching time the cells engraved into the copper are very shallow (and thus print

the lightest), while in the shadows and solids—areas that have received the least

exposure—the etchant eats through the resist and into the copper very quickly, so that the

engraved cells are deeper (and thus print the darkest). The mid-tone regions—which have

had varying degrees of exposure, spending on the density of the image—allow a

moderate amount of etchant through, producing cells that are not as ldeep as shadows and

not as shallow as highlights. Non-image areas possess the thickest portions of the

emulsion and thus allow the copper surface to remain unetched. The time required for the

completion of the etching process is about half an hour.

In the diffusion-etch process, all cells are the same size, and the thickness of the

membrane between cells—called the cell wall—remains constant. The amount of light

the resist received determines the depth of the cells; highlights and light areas produce

shallow cells (which don't hold much ink) while the shadows and darker areas produce

deeper cells (which hold more ink). A variation of this etching system is called a two-

positive system, which operates the same basic way, but the gravure screen is replaced by

a halftone screen made from continuous-tone illustration matter, while a standard gravure

screen is used for solids and text matter. The advantage of this system is that the halftone

screen allows the cells to vary in area, not just depth. This allows greater degrees of

sharpness and detail. Another variation is known as Hard Dot Engraving in which the

depth of each cell is the same, but the area of each cell varies, depending upon whether it

is a highlight or a solid.

Direct-Transfer Process

Also called the Single-Positive System, the direct transfer process is, like the

diffusion-etch process, a chemical etching process. The primary difference is in the

composition of the resist, which replaces the carbon tissue with high-contrast, high-

resolution photopolymer emulsions. The emulsion is applied (by a spray, ring coater, or

other means) directly to the copper-plated surface of the gravure cylinder itself. A single

screened positive is brought into contact with the emulsion on the cylinder and exposed

to ultraviolet light. As in the diffusion-etch process, the exposed (non-image) areas

become hard, while the unexposed (image) areas remain soft. A solvent is used to wash

away the unexposed resist, and the photopolymeric resist produces cells that print with

smoother edges than cells etched by electromechanical engraving. Etchant is applied, as

before, and engraves cells at a rate that varies according to the thickness of the resist. The

film positive is carried by clear mylar belts between the emulsion of the gravure cylinder

and a mercury-vapor lamp, which enables the engraver to expose the resist in a

circumferential fashion. The direct-transfer process is also quicker than the diffusion-etch

process, taking only about 4:10 minutes to etch a cylinder.

Despite the quickness and ease of the previous forms of chemical engraving, they have

been replaced for the most part by newer techniques, primarily by the electromechanical

process, while newer digital computer-to-laser systems are making inroads into the

gravure engraving process.

Electromechanical Engraving

Electromechanical engraving uses an electronically-controlled diamond-stylus to cut

the the cells into the surface of the gravure cylinder. The original copy is scanned into a

computer and digitized. Each scanned and digitized image is converted to halftone-like

dots, each having an electronic signal, ranging in intensity from 0:100%, depending upon

the darkness or lightness of the image. (For this reason, early-generation

electromechanical engraving devices couldn't scan in pre-screened images—such as

halftones—or it would create its own dots on top of the already-existing dots, producing

moiré patterns.) The image is then converted back into an analog signal which then drives

the engraving head , telling it how deep to carve the cell on the cylinder. (Cell depth and

cell area are varied simultanously by using a tapered engraving head.) The computer then

controls the engraving head, which moves across and around the cylinder, engraving cells

of varying depths. The thickness of the cell walls can also be varied; at 100% depth, the

diamond-shaped cells interlock with those of the rows on either side of it, with just a tiny

cell wall. At 10%, however, the cells are much reduced in size and there is a good deal of

space between them. With computerized engraving, the angle of the cells themselves can

be altered as well, by producing elongated or compressed diamond-shaped cells as

necessary. Electromechanical engraving devices take much longer than chemical

processes; on a 40-inch wide cylinder with a 30-inch circumference, there are over 25

million cells. At an average speed of 3,200 cells per second, it takes nearly 2H hours to

engrave a single cylinder.

Electromechanical engraving is also referred to as EME.

Laser-Cutting Process

The most recent development in gravure engraving is the use of computer-directed

lasers, which, like the electromechanical method, cut cells of varying depths and sizes.

The original is scanned into a computer, the various image densities are determined, and

lasers etch the cylinder. Due to the high light reflectance of copper, however, it is not

particularly useful for laser etching. Consequently, other materials such as special alloys

or plastics can be used to coat the cylinder. The real advantage of the laser processes is

the speed; at 30,000 cells per second, the 40-inch wide, 30-inch circumference cylinder

mentioned above would only take about 13 minutes.

Regardless of the system used (chemical engraving still has its adherents, but the

increasing tendency toward computer-generated originals is making direct computer-to-

cylinder processes more and more popular), after engraving the cylinder is electroplated

with a layer of chrome, to offer protection against the abrasive action of the doctor blade.

Direct Drive Technology …….........……..4 (Improving Flexo Printing Quality and

Throughput)

Geared Presses Gearless

Presses

Direct-Drive

Presses

Motor Servo Motor Direct-Drive

Rotary Motor

Precision Gears Gearboxes

Lubrication

System

Mounting

brackets for gear

motors

Oil Bath Shaft couplings

Filter

Pump

Sealed housing

Shaft

Bearing

Frame members

and supports

Mounting

hardware

Flexographic printing technology has become increasingly able to maintain print quality

and reduce startup time and waste. Most operators concern themselves with registration

and color accuracy and consistency—as they should. But many don’t realize the

importance that accurate synchronization of the anilox roller and plate cylinder used in

each print deck module plays on print quality. Traditionally, this has been accomplished

either by gearing the anilox roller and plate cylinder together and driving both with a

single AC induction motor or by using separate servo motors to drive each axis through

gearboxes. As press speed and printing quality requirements have increased, the

inevitable inaccuracies in the gearing system have become a limiting factor on press print

quality and speed.

Advancements make it possible to synchronize the anilox roller and plate cylinder to a

much higher level of precision without mechanical transmissions by using closed loop

control technology and driving both directly with independent, direct-drive rotary (DDR)

servo motors. The elimination of the mechanical transmission enables servo loop gain to

be increased, and therefore, bandwidth of the servo loop. Speed control and phasing

between the anilox and plate cylinder can now be closely controlled in the absence of the

gear backlash, thus providing for higher speeds and accuracies for improved print quality.

Throughput is also increased because the higher control loop gain enables faster machine

operation. This article will examine the trend toward DDR systems in flexo presses and

consider alternative implementation methods.

IMPORTANCE OF SYNCHRONIZING

In the flexo printing process, the anilox roller contacts the plate cylinder that carries the

plate with a dot pattern that forms the printed image. The dots on the plate act as suction

cups and lift the ink out off the anilox roller. Providing constant ink coverage is

obviously critical to printing quality and this depends on maintaining consistent motion

between the surfaces of the anilox roller and plate cylinder. Whenever the print cylinder

moves faster than the anilox roller, less ink is transferred to the print cylinder, resulting in

a light section in the printed piece. Whenever the anilox roller moves faster than the print

cylinder, more than the normal amount of ink is transferred, resulting in a dark section.

The traditional approach to synchronizing the anilox roller and plate cylinders is to use

a bull gear attached to the central impression drum to drive them both as shown in Figure

1. The problem with this approach is that backlash is inevitable in any mechanical

transmission system. Even when a geared system is tuned very tightly, within a short

period of time the gears will wear and backlash will begin to occur. Backlash causes the

roller and cylinder to rapidly accelerate and decelerate as the gear teeth bounce back and

forth against each other. The result sometimes is the appearance of alternating light and

dark horizontal lines on the printed product.

“Gearless” printing presses (Figure 2) refer to those machines that eliminated gearing

together off all of the axes running from a single motor. Instead, each anilox, plate, and

impression cylinder has an independent servo applied. However, a gearbox is installed

between the load and the feedback device, which adds inaccuracies. The result is that

positioning accuracy in a “gearless” system typically is between +/- 1 arc minute and +/-

10 arc minutes. The acceleration and decelerations in a geared system are also limited by

the gear-train backlash. Increasing acceleration past the safe level will lead to instability

or gear damage. Some printing companies address these problems by frequently adjusting

the antibacklash control system on the press, sometimes as often as weekly. This can

result in a substantial amount of downtime without solving the underlying problem.

ELIMINATING THE MECHANICAL TRANSMISSION

Advancements in control and motor technology over the past decade now make it

possible for the motion of the anilox and plate cylinders to be electronically synchronized

by a closed loop control system to a much higher level of accuracy by eliminating the

mechanical transmission system and creating a totally directdrive configuration (Figure

3). The basic idea is that the anilox roller and plate cylinder are each driven

independently by separate, direct-drive servo motors.

A feedback device such as a high resolution sine encoder provides the servo motors with

far more accurate position and velocity information that the controller compares to its

programmed motion profile and based on this signal sends velocity command signals to

the amplifier that drives the servo motor. A motion profile defines the operation of each

servo motor in terms of time position and velocity. In practice, the anilox roller and plate

cylinder are synchronized in both speed and phase, ensuring that every point around the

surface of the anilox roller is synchronized with the plate cylinder. The latest generation

of servo motor controllers provides resolution feedback up to 27 bits, with 64-bit

positioning resolution, and 125msec position loops, 62.5msec velocity loops and

0.670msec current control loops. So DDR systems can deliver much greater accuracy

than the best mechanical transmission systems even immediately after adjustment of the

antibacklash control system. As a general rule, DDR systems offer accuracy of about +/-

25 arc seconds systemaccuracy, which can be up to 20 times higher accuracy than

conventional geared servo systems. The result is substantial improvements in print

quality.

IMPROVING THROUGHPUT

When the load is directly coupled, the settling time is no longer limited by the

transmission, so the servo loop gain can be increased. This provides the necessary servo

stiffness to achieve excellent speed regulation and phase control between the anilox,

plate, and central impression cylinders. Press speeds using direct-drive technology can be

increased in many applications because the accuracy of the mechanical transmission

system is often the limiting factor. Switching to direct-drive further improves press

throughput by reducing setup and maintenance time.

A typical flexo press servo system equipped with gearboxes requires periodic tuning

adjustments of the antibacklash control system to compensate for gear wear. DDR

systems, on the other hand, since they are directly coupled to the load, require no periodic

tuning. There is complete elimination of backlash and the need for antibacklash controls.

Years later, the tuning settings are typically the same as the day the machine was

installed. With a direct-drive press, the parts count on a typical Bill of Material (BOM) is

reduced by up to 10 parts per color print deck. This mechanical simplification translates

into faster assembly, less maintenance, and less overhead to purchase parts. Table 1

shows a comparison of a typical geared solution with a direct-drive system. When

considering a 10-color press, more than 100 parts can typically be removed from the

BOM. When the anilox roller and plate cylinder are driven by a single motor via a gear

system, it is difficult to separate the two axes for maintenance and exchange of printing

sleeves or plates. In a direct-drive configuration, the anilox, plate, and CI drum can be

moved independently of each other for easy maintenance, cleaning, and change of plate

blankets. This can also be viewed as a safety improvement since the rolls can be

controlled independently.

Finally, the direct-drive method also eliminates the need for alignment, lubrication and

eventual replacement of the mechanical transmission system.

SMALLER MOTORS

Since the direct-drive motor is directly connected to the machine, inertia-matching is not

required as it is on a conventional servo motor with gears. Stepper motors are typically

sized to match the load in order to have enough torque to overcome disturbances when

torque is low, which occurs as a result of nonlinearity caused by the torque roll-off or

resonance at certain frequencies. However, closed-loop servo motors with controlled

commutation are not prone to the same de-synchronization issues and torque losses. The

servo system also maintains a linear and predictable speed torque curve without the need

for special commutation sequences or anti-resonance control.

For these reasons, DDR motor size can be based on the peak torque required for

achieving the desired acceleration time specifications. With direct drives, inertia

mismatch of 250 to 1 is common and mismatch of 800 to 1 has been implemented. In

many flexo presses, the size of the motor is dictated by the inertial matching

requirements. The result is that a much smaller and more energy-efficient DDR motor

can be used in most applications.

Today, many machine specifications, even in the industrial environment, list the

maximum allowable audible noise levels.The audible noise level of a direct-drive system

can be as much as 20dB lower than a geared system, as transmission components

generate considerable noise levels. So, installing a direct-drive system can help achieve

the required audiblenoise specifications.

DDR ALTERNATIVES

Direct-drive rotary technology has developed in an evolutionary manner. The original

frameless direct-drive motors were designed into the machine architecture along with a

feedback device and became a fully integrated part of the machine. This approach has the

advantage of consuming the least amount of space. On the other hand, frameless motors

are relatively expensive to fully integrate as they typically require substantial changes to

the design of the underlying machine. Frameless motors are also more difficult to service

because they are embedded into the machine. While the initial development cost burden

is high, the benefits of higher performance, higher quality, and small space requirements

justify this technology in some applications.

The next generation of DDR technology, sometimes referred to as full-frame systems,

integrates all of the components of a complete motor including the rotor, stator, bearings

and feedback device within a housing. The machine shaft slips through the bore in the

motor and attaches to the rotor. This approach substantially reduces development costs

since the motor no longer needs to be integrated with the printing press. The disadvantage

of this approach is that the motor’s and the machine’s bearings must be precisely aligned,

which is a complex and time-consuming task. The bearings in the motor and the load are

directly coupled in a linear fashion making it nearly impossible to align the system

components properly without causing premature bearing failure due to loading. The most

recent approach to DDR systems, the cartridge DDR servo motor, is fully housed and

ready for mounting to the machine. However it has no bearings and uses the host machine

to support the motor’s rotor. This approach makes it easy to use direct-drive technology

on machinery that already has bearings, particularly in applications such as printing

where rollers already use heavy-duty, precision bearings. The motor has a hole in the

middle which slips over the shaft of the anilox roller, plate cylinder, or central impression

roll and the motor housing bolts to the machine frame.

Installation typically takes less than five minutes. The motor slides over the shaft until a

motor pilot engages a machine pilot. The housing is secured with bolts. The motor rotor

is then secured to the machine roller shaft by means of a compression coupling tightened

to a specified torque. The rotor is now rigidly connected to the machine shaft. The

encoder alignment is pre-set so that no adjustments need to be made. Cables are

connected and the motor is ready to run.

A servo system equipped with a cartridge motor is expected to work for 10 years without

any maintenance. Although the initial system cost might be higher compared to a

conventional geared system, over a period of several years, eliminating the cost of repairs

and periodic maintenance makes the overall cost of purchasing and operating a cartridge

system lower. Even with the slightly higher initial cost, over a five-year period, cartridge

motors can reduce operating costs up to $10,000 per motion axis compared to

conventional geared servo systems.

It’s no secret why direct-drive technology is being increasingly used in new printing

press designs. For printers, the higher quality and throughput associated with DDR

systems translate into higher profitability. For manufacturers of printing presses, direct-

drive technology offers a substantial competitive advantage as well as easy integration

with current and new machine designs.

Flexo vsGravure……………………………..5

Rapid growth of flexo printing in packaging and suggested that gravure printing hadbeen out-marketed in North America by a very determined flexo community, which continues togain share. Gravure printing today has many technical advantages for the packaging market thatsometimes are overlooked. In addition there have been enough gravure improvements to warranta reassessment of some of the old paradigms of cost, setup time, and run length.TECHNICAL ASPECTS OF GRAVUREThis is a very simple process with only a single impression to be set, so there are few inherentvariables making for high quality print within the run and from run to run. Line and process canbe combined on a single deck with the possibility of running fewer total color stations on the job.

It is possible to carry very heavy ink films in gravure and maintain print resolution. With acommonly used solid cylinder, about 9 wet lb/ream can be delivered. This is about three timesthe flexo rate. If you compare the two ink delivery systems, there are two ink film splits in flexoand only one in gravure. The advantage of this is that gravure is capable of producing unmatchedwhite ink opacity, vivid metallics and fluorescents, and many other specialty effects andfunctional coatings not achievable in flexo. The gravure inking station allows use of very strongsolvent mixtures that often are high in acetate content, which, in turn, allows for morepossibilities in ink formulations. The high line resolution of gravure is a plus for small packageswhen ingredient labeling type is challenging for flexo.MANUFACTURING ASPECTS OF GRAVUREMany times comparisons are made between state-of-the-art flexo presses and old clunker gravureequipment. The current situation is that new flexo and gravure presses are about equivalent forfeatures, amenities, and also for cost. All of the advanced robotic controls and features for flexoare available for gravure, so the playing field is now level. This requires that the traditional chartfor gravure break-even analysis (see figure) be revisited. Opinions are numerous, but data is rare.One analysis1 available online makes a good case for gravure economics and is backed with data.The essence of the argument goes like this: The prepress cost of gravure should be spread overrepeat runs when the durability of the cylinder comes into effect and run length is less relevant.The cost of producing gravure cylinders is not proportional to the design complexity but is fixedand based on unit area of engraving. With flexo, the cost of plates increases with complexity ofdesign.Manufacturing improvements continue for gravure and include laser engraving of cylinders.Lightweight sleeves are available now and allow for easy handling, storage, and shipping.MARKETING OF GRAVUREThe Gravure Assn. of America and Packaging & Label Gravure Assn. Global are good forumsfor initiatives to promote gravure printing in packaging. If the history of flexo packaging growthis an example, it will take initiative and dedication from the supplier community to clearly defineand optimize the steps in the total gravure workflow and communicate this process with printbuyers.There are indications that gravure as a process is beginning to take this initiative. We should seesome interesting developments and an increased level of competition as these two processesbattle over their share of the market.

Benefits of gravure, unavailable with other methods

Due to the precise ability of the gravure cell to lay down a specific amount of ink, gravure is

able to print the widest variety of inks, UV, water based, solvent, metallics, flourescents - from

the lightest continuous vignette to heavy laydowns resembling screen printing

Flexographic and Gravure PrintingFlexography

Flexography, also known as aniline printing, is a form of relief printing; the image is slightly

raised, inked and then transferred directly to the subtrate. This printing method utilizes a flexible

plate, usually made from soft rubber or plastic and a quick-drying ink. This system can be well

suited for a wide variety of materials including acetate film, polyethylene, brown paper and

newsprint. It is a high-speed process used for extra large print runs.

Gravure/Rotogravure

Gravure is the opposite of flexography; the printing area is actually etched into the surface of a

plate or metal cylinder. The etched out sections are "filled" with ink, the excess ink in the non-

image area is removed with a thin stainless steel blade (doctor blade). The size and depth of the

etched out areas determine how much ink is deposited on the substrate. Web fed and high-speed

decorating systems are better known as rotogravure. This is a high-speed process used for large

print runs.

Advantages and Disadvantages

Flexography was the standard years ago but its place in the decorating market is not as profound

as it was. It is more suited to printing paper bags and plastic labels and films. It is a high speed

process using quick drying inks. Gravure, also a high speed process, produces high quality

images and is just the thing for large jobs. These two processes have their place in the industry

but have their limitations. Of course, the major drawback would be the set-up costs. Flexo is not

nearly as expensive as gravure but the cost for shorter runs would be far too expensive. Gravure

printing utilizes an etched cylinder. This printing cylinder can cost thousands of dollars. For a

gravure run to be cost effective, a run in the millions would be required. Si-Cal offers an

alternatve to these processes that may be just the process for your decorating project.

Computer to Gravure and Computer to Flexo

OFFSET PRINTING is the dominant form of printing for most types of products and for the

most common run lengths—in spite of offset’s well-known liabilities. For example, it requires

more craft knowledge and training on the pressman’s part than gravure or flexography; the press

itself is more complicated than presses for alternative printing technologies; and water-based

inks cannot be used.

But offset, with its flat-surface, light-sensitive plates, is the ideal companion to photographic

prepress processes. Producing flexo plates and gravure cylinders from film is fraught with time

and quality limitations. As long as film dominates prepress, offset will dominate printing.

Completely digital prepress changes the equation, however. With the advent of highly

automated, computer-controlled cylinder engraving and flexo plate making, most of the prepress

advantages of offset disappear (or are at least greatly reduced). Flexo printing can now begin to

compete in quality for many offset jobs, and gravure (which has always offered high-quality

colour reproduction) can begin to compete for shorter run lengths. Both technologies are likely to

take work away gradually from offset. At Drupa, there were a number of new developments that

emphasized this trend.

A Few Facts:

· Most of the large pressure sensitive label producers employ gravure as their premium process.

· Gravure was the first process to become all digital.

· Almost every gravure printer in Northeastern United States uses waterborne inks.

· While flexo and rotary letterpress pre-press costs have risen dramatically over the last decade,

gravure pre-press has seen only a modest increase.

In many situations, gravure printing does compete favourably with flexo production costs.

Flexography´s Strengths

• Less expensive process

• Versatility in substrates

• Flexibility due to exchangeability of parts of the print design

• Easy and simple plate making

• Good sharpness of bar codes, type and linework

• Best revolution-to-revolution registration even with thinnest

substrates due to CI presses.

Flexography´s Weaknesses

• Increasing cost due to growing quality demands in Anilox rollers,

printing inks, printing forms, tapes, etc.

• Limitations in Packaging Design

• Sporadic limitations in print quality due to:

– Squeezed ink

– Lack of coverage in solids

– High dot gain

– Insufficient uniformity of print production

Gravure´s Strengths

• Simple schematic of printing presses

• Any (odd) repeat length

• Typically very good print quality in images

Gravure´s Weaknesses

• plate making is demanding due to:

– treatment of metals

– handling of massive metal cylinders

– limitations in imaging systems, etc.

• Lack of flexibility due to long delivery times and missing

exchangeability of design elements

• Uniformity and repeatability quite demanding (larger impact of

substrate surface characteristics than in Flexo)

• Limited sharpness of type and linework

• Registration concerns with flexible substrates (revolution-torevolution)

Characteristic of Flexo & GravureFlexo Gravure

1- Solids and process may need to be

separated

Ability to print solids, type and

process on the same print station

2- Limitations in reverse and fine type work

(improvements due to C to P and DD

technology)

Ability to print fine type and line work

(further improved via laser technology)

down to 1 point text.

3- Can print up to 150 lpi Can print process work up to 250 lpi

4- Closed solids need correct

combination of plate, tape and ink

Can produce rich colors in solids and

achieves excellent brilliancy

5- Due to plate elasticity and to lerances,

reproducibility is largely dependent on

prepress conditions and operator skill.

Excellent reproducibility, largely

independent of operator skill

Market Share Interpretations………….6

• Flexo drastically outnumbers Gravure in North America and South America. Gravure

is the „underdog“, hence the aforementioned aggressive statements.

• In Asia, Gravure is almost unrivalled in its market share and standing. However, that

has been sponsored in the past by environmental legislation being less harsh than in EU

and the

Americas which enabled less expensive, but more hazardous plate making techniques

(etching) to be used.

• In Europe, Flexo enjoys the largest market share, but is being challenged by Gravure

constantly.

Relevance of printing and packaging

sector.......…………………………......................7

The printing and packaging industries in India have assumed growing significance

during the last decade. The printing industry is one of the biggest and fastest growing

industries in India. More than 1,20,000 printing presses are in operation all over the

country, with a capital investment of over Rs. 80,000 million. This industry provides

direct employment to over 6,00,000 people and indirect employment to another 2,00,000.

It is natural that along-side the growth of literacy, there is a commensurate rise in demand

for various inputs for the printing industry.

Packaging has become a dynamic and key area for manufacturers and trading

companies all over the country. The elements of aesthetics, hygiene and cost-

effectiveness on packaging receiving greater importance in commercial operations. The

exterior look and presentability of marketable goods leave a lasting impression on the

minds of consumers and in the context, packaging occupies centre-stage. New

packaging machines and technologies have been introduced in the country to meet the

challenges. Today, the Indian packaging industry is growing at a rate of 15 per cent per

annum.

Environmental Protection…….……….....…8

Gravure is an environmentally friendly printing process. Special care is

taken to ensure the application of the most ecological production methods for the

printing process, as well as for the production of materials. Currently, publication

gravure printers and suppliers are active in the following areas:

-Increasing use of papers with higher recycled fibre content

-Use of chlorine free bleached paper

-Use of highly effective solvent recovery installations

-Application of latest methods to save paper, ink and energy

-Further reduction of residual ink solvent content in publication gravure products

-Processing of gravure inks with even more environmental friendly formulations