The Basics of Flexible Packaging Printing
FlexographyRotogravure
Presented by:Warren E. DurlingAssociate Research FellowClorox Services Company / Glad Division
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Design to Substrate
Preproduction Design Creation
Substrate Management
Image Preparation Color Separation
Ink ManagementCylinder or
Plate Making
Converting
PrintingPrinting
Press Make Ready
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PRINTING INK, Form & Chemistry
Physical formLiquid – free flowingRelatively low viscosity
(closer to water than honey)30% to 60% solids and 100% solids UV/EB
ChemistrySolvent based – gravure, flexographicWater based – flexographic, (gravure)Radiation cured (UV/EB) – flexo, gravure
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Basic INK Formulation Examples
WATER65%
SOLUTIONRESIN 10%
EMULSIONRESIN 10%
SOLVENT65%
Primary RESIN 15%
SecondaryRESIN 5%
Reactive Diluents
Up to 30%
ACRYLATEMONOMER
ACRYLATEPREPOLYMER
55%
Water Solvent Radcure
80% ALCOHOL20% ACETATE
ADDITIVES 5%
ADDITIVES 5%ADDITIVES 5%
PIGMENT10%PIGMENT10%
PIGMENT20% - 25%
Dry InkDry Ink
Wet InkWet InkDry Ink
&Wet Ink
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Ink Blending / Color Matching
Typical Production Ink Blending:Color Base Systems:
High Solid, Concentrated Color Pigmentsused singly and as blendsspecific to the vehicle systemCMYK + many specific colors
Vehicle / Varnish Systems:Clear Backbone Resins
physical propertiesprocessabilityfilm strength
Additives & ModifiersScuff ResistancePlasticizers (improved flexibility)Coefficient of Friction (slippery or sticky)Aesthetic Appearance (matt vs. glossy)
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Cup Number Seconds Efflux Time Centistokes Range
1 40-60 10-36
2 20-60 19 to 156
3 12-60 64 to 596
4 10-60 79-784
5 10-60 161-1401
INK, Viscosity Measurement
ZAHN Cup conversions SHELL Cup
SECONDS (time) is the Operators press side, process measurementCENTISTOKE is the unit of reference in all viscosity cup measurements
POISE is the fundamental unit of viscosity defined as the resistance of a liquid to flow where gravity is not a factor. 100 CENTIPOISE = 1 POISE. Gravity is the driving force causing liquid in a viscosity cup to flow through the orifice so a high density material will flow from a cup in a shorter time than a low density material of the same viscosity.
STOKE is defined as the POISE divided by density. 100 CENTISTOKES = 1 STOKE.
ZAHN Cup
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PRESS SIDE Ink Management
1) PUMP & MOTOR
2) INK TANK
3) FILTER
4) PRINTING STATION
5) AUTOMATIC VISCOSITY CONTROL
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FLEXOGRAPHY Printing
Flexography: (often abbreviated to Flexo) A form of relief printing where ink is applied to a rubber or polymer plate on which the printing image is raised above the rest of the surface as a 3-D positive, mirrored relief.
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FLEXOGRAPHY – The Process
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FLEXOGRAPHY - Printing Plates
A photopolymer is a polymer that cures, or becomes solid, when exposed to light
(1) A photo negative image is used to expose (image wise), a photopolymerizable sheet to light
(2) The unexposed or unpolymerized areas of the plate are removed with solvent or water
(3) The resulting plate is dried, then detackify / harden by exposing it to specific frequencies of U.V. radiation
(1) A photo negative and acid wash process is used to engrave the image into a copper or magnesium positive image master plate
(2) The positive image master is used to produce a negative image plastic plate mold
(3) The printing plate is produced by molding raw rubber with the plastic mold then vulcanizing the resulting rubber sheet
Conventional rubber plates that rely upon a less precise molding process have become nearly obsolete except where lower quality is acceptable
Digital, direct to plate engraving is the latest innovation in flexo plate technology. A processed digital file controls a laser that directly burns away unwanted areas of the polymer printing plate. In the past, limited durability plate materials resulted in short plate life. Recent equipment and material developments are generating renewed interest.
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FLEXOGRAPHY - Anilox Rolls
The anilox roll is a steel or aluminum core cylinder with a ceramic surface that contains millions of very fine cells. They are specified by their "line screen", or the number of cells per linear inch ranging from below 250 to above 1500. Lower line screens are used to print a heavy layer of ink such as block lettering. The highest line screens produce fine detail for four-color process work such as reproducing photographs.
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FLEXOGRAPHY – Printing Presses
Stack Flexo Press Design
Historically, stack presses are lower cost compared to central impression presses and are used where lower quality printing is acceptable. However, recent advances in servo technology have resulted in quality improvements.
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FLEXOGRAPHY – Printing Presses
Central Impression (CI)Flexo PressTraditional Open Architecture Gear Drive
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State of the Art Central Impression Flexo Press
FLEXOGRAPHY - Printing Presses
10 colorservo drivefully automated, automatic printing plate washingup to 1,900 feet per minute
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ROTOGRAVURE Printing
Rotogravure: (typically referred to as Gravure)An intaglio process (in-tal-yo means engraved or cut in) in which a negative image is etched into the surface of a copper printing cylinder as tiny cells or dots of various sizes and depths. The copper is chrome plated for durability. Ink is applied to the surface and a flexible metal blade called a doctor blade removes excess ink, leaving the surface clean, with ink only in the depressions.
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GRAVURE – The Process
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Acid Etching (Diffusion-Etching and Direct-Transfer) - Light sensitive gelatins or photopolymers on the coper surface are exposed through a film positive of the image, resulting in varying levels of acid resistance. The surface is exposed to acid, resulting in cells of the same size and cell wall thickness but varying depths.
Electromechanical Engraving - The original copy is scanned into a computer and digitized. The computer then controls a diamond stylus that cuts the cells into the surface of the gravure cylinder. Cell depth and cell area are varied simultanously by using a tapered engraving head.
GRAVURE - Cylinder Engraving
Laser Engraving - The method of choice to produce Flexo anilox rolls with some applications in gravure printing. An original is scanned into a computer, the various image densities are determined, then a laser etchs the cylinder. Highly reflective copper is a poor material choice so alternative special alloys, plastics and ceramics are used.
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GRAVURE - Cylinder Cell Structure
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GRAVURE - Electrostatic Discharge
Electrostatic Discharge (ESA) - A charge imballance is created between the printing cylinder holding the ink and the substrate. This results in an effect much like a maganet where the charged ink is attracted to the obsit charged substrate.Properly functioning ESA is escential to achieve high quality Gravure printing.
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Doctor Blade Design
Doctor Blade shape, construction material, tip honing, set angle and pressureare becoming more sciencitific and process controlable but there still remains a great deal of “ART” in the process.
Stainless SteelBlue SteelCeramicPlasticAlloys
Round TipSquare Tip
CombinationsStraight BeveledStepped Beveled
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GRAVURE - Printing Presses
Gravure PressTraditionalOpen Architecture
Solid line shaftManual print station change overLimited if any electronic process controlLower efficiency ovens
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GRAVURE - Printing Presses
Rapid Changeover Gravure PressState of the Art, High Speed
Fully automated print station, trolley change over systemOff-press trolleys washing unitElectronic line shaft, full PLC controlHigh efficiency compact dryersPrinting speed up to 1,300 feet per minute
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GRAVURE - Printing Presses
Automated Gravure Print Decks
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Flexo or Gravure - HOW TO TELL?
Rotogravure
Flexography
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Flexo or Gravure - HOW TO TELL?
Flexography
Rotogravure
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LINE Printing
Single colors are printed at varying densities
Individual colors do not overlap or combine to form new colors
The number of colors in a design is limited by press capability
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Flexo LINE - Reverse Print Film
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Flexo LINE - “Screened” Print
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Gravure LINE Printing - Surface Print
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Red, Green and Blue (RGB) are the primary colors of light as perceived by the human eye.
4 Color PROCESS Printing - CMYK
Printing utilizes a subtractive color process based on light reflecting from an object through pigments or dyes that absorb certain wavelengths, allowing others to be reflected. Unlike the additive system, which begins with black and adds color, the subtractive system begins with white and subtracts color.
When the three colors are together in a spectrum they create white and the absence of color altogether is black. This works great for digital images on computer and TV screens. Colors are created on monitors by adding light. RGB is an additive color system, which means that color is added to a black background.
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4 Color PROCESS Printing - CMYK
The base colors for process printing are CMYK and not RGB
CMYK are subtractive colors or secondary colors of red, blue and green
Blue + Green = Cyan (B+G = C)Red + Blue = Magenta (R+B = M)Red + Green = Yellow (R+G = Y)
And Black = K
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4 Color PROCESS Printing - CMYK
The image is separated into 4 different color valuesCyan / Magenta / Yellow / Black
A printing plate or cylinder is created for each process color using the individual separations
Individual colors are printed as dots at varying densities
Individual dots combine to form additional unique colors
In Packaging printing , 4 color process is typically combined with line colors to accurately represent
trademarks and logos and to maintain color consistency over large areas of solid colors.
The number of final colors in a design is nearly limitless
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Flexo PROCESS Printing
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Gravure PROCESS Printing
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Gravure PROCESS Printing
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GRAVURE vs. CI FLEXO
GRAVURE FLEXOPrinting Press Footprint larger smaller
Printing Press Cost much higher lower
Operating Costs (utilities and overhead) slightly higher lower
Maintenance slightly higher lower
Cylinder / Plate cost much higher lower
Impressions per Cylinder / Plate very high w/ rechrome lower
Make-Ready Time generally longer shorter
Water Base / Solvent Base solvent – water? both
Substrate Flexibility less more
Process Flexibility (coating & laminating) more less
Print Quality (detailed process printing) exceptional improving
Basic Printing Process Selection Guide
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PRESENTED BY
Warren E. DurlingAssociate Research FellowClorox Services [email protected]