The Basics of Flexible Packaging Printing Flexography Rotogravure

Transcription

1 The Basics of Flexible Packaging Printing Flexography Rotogravure Presented by: Warren E. Durling Associate Research Fellow Clorox Services Company / Glad Division

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3 Design to Substrate Ink Management Preproduction Design Creation Substrate Management Press Make Ready Image Preparation Color Separation Cylinder or Plate Making Printing Converting Slide 3

4 PRINTING INK, Form & Chemistry Physical form Liquid free flowing Relatively low viscosity (closer to water than honey) 30% to 60% solids and 100% solids UV/EB Chemistry Solvent based gravure, flexographic Water based flexographic, (gravure) Radiation cured (UV/EB) flexo, gravure Slide 4

5 Basic INK Formulation Examples Water Solvent Radcure Reactive Diluents Up to 30% WATER 65% SOLVENT 65% ACRYLATE MONOMER Wet Ink Wet Ink 80% ALCOHOL 20% ACETATE Dry Ink & Wet Ink ADDITIVES 5% Dry Ink ADDITIVES 5% SOLUTION RESIN 10% EMULSION RESIN 10% Dry Ink ADDITIVES 5% Primary RESIN 15% Secondary RESIN 5% ACRYLATE PREPOLYMER 55% PIGMENT 20% - 25% PIGMENT10% PIGMENT10% Slide 5

6 Ink Blending / Color Matching Typical Production Ink Blending: Color Base Systems: High Solid, Concentrated Color Pigments used singly and as blends specific to the vehicle system CMYK + many specific colors Vehicle / Varnish Systems: Clear Backbone Resins physical properties processability film strength Additives & Modifiers Scuff Resistance Plasticizers (improved flexibility) Coefficient of Friction (slippery or sticky) Aesthetic Appearance (matt vs. glossy) Slide 6

7 INK, Viscosity Measurement SECONDS (time) is the Operators press side, process measurement CENTISTOKE 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 ZAHN Cup conversions Cup Number Seconds Efflux Time Centistokes Range SHELL Cup to to Slide 7

8 PRESS SIDE Ink Management 1) PUMP & MOTOR 2) INK TANK 3) FILTER 4) PRINTING STATION 5) AUTOMATIC VISCOSITY CONTROL Slide 8

9 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. Slide 9

10 FLEXOGRAPHY The Process Slide 10

11 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 Conventional rubber plates that rely upon a less precise molding process have become nearly obsolete except where lower quality is acceptable (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 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. Slide 11

12 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 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. Slide 12

13 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. Slide 13

14 FLEXOGRAPHY Printing Presses Central Impression (CI) Flexo Press Traditional Open Architecture Gear Drive Slide 14

15 FLEXOGRAPHY - Printing Presses State of the Art Central Impression Flexo Press 10 color servo drive fully automated, automatic printing plate washing up to 1,900 feet per minute Slide 15

16 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. Slide 16

17 GRAVURE The Process Slide 17

18 GRAVURE - Cylinder Engraving 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. 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. Slide 18

19 GRAVURE - Cylinder Cell Structure Slide 19

20 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. Slide 20

21 Doctor Blade Design Doctor Blade shape, construction material, tip honing, set angle and pressure are becoming more sciencitific and process controlable but there still remains a great deal of ART in the process. Stainless Steel Blue Steel Ceramic Plastic Alloys Round Tip Square Tip Combinations Straight Beveled Stepped Beveled Slide 21

22 GRAVURE - Printing Presses Gravure Press Traditional Open Architecture Solid line shaft Manual print station change over Limited if any electronic process control Lower efficiency ovens Slide 22

23 GRAVURE - Printing Presses Rapid Changeover Gravure Press State of the Art, High Speed Fully automated print station, trolley change over system Off-press trolleys washing unit Electronic line shaft, full PLC control High efficiency compact dryers Printing speed up to 1,300 feet per minute Slide 23

24 GRAVURE - Printing Presses Automated Gravure Print Decks Slide 24

25 Flexo or Gravure - HOW TO TELL? Rotogravure Flexography Slide 25

26 Flexo or Gravure - HOW TO TELL? Flexography Rotogravure Slide 26

27 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 Slide 27

28 Flexo LINE - Reverse Print Film Slide 28

29 Flexo LINE - Screened Print Slide 29

30 Gravure LINE Printing - Surface Print Slide 30

31 4 Color PROCESS Printing - CMYK Red, Green and Blue (RGB) are the primary colors of light as perceived by the human eye. 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. 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. Slide 31

32 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 Slide 32

33 4 Color PROCESS Printing - CMYK The image is separated into 4 different color values Cyan / 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 Slide 33

34 Flexo PROCESS Printing Slide 34

35 Gravure PROCESS Printing Slide 35

36 Gravure PROCESS Printing Slide 36

37 GRAVURE vs. CI FLEXO Basic Printing Process Selection Guide GRAVURE FLEXO Printing 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 Slide 37

38 THANK YOU TO THE FOLLOWING COMPANIES FOR SUPPLYING CONTENT Slide 38

39 Slide 39

40 Thank you PRESENTED BY Warren E. Durling Associate Research Fellow Clorox Services Company Please remember to turn in your evaluation sheet... Slide 40