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WEEK ONE SLIDES - GrC 329 Web Offset and Gravure Printing...

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Unformatted text preview: GrC 329 - Web Offset and Gravure Printing 9/16/2011 Web Offset and Gravure GrC 329 Kevin Cooper Cal Poly – Graphic Communication Department Introductions… Professor Students GrC Course Books Web printing technology Research Paper Information 1 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Winners! Cal Poly took 2011 Cal Poly took both undergraduate awards this year after taking first place in 2010. We have taken first, second, or both for at least the past six years. Every paper we’ve submitted came from 329 research projects. Basic definitions… • What's printed gravure in the class? Desks Web printing • Printing from a roll • Printing process • Method used to transfer image to substrate • Ex – Offset lithography • Web markets • Product groups that are often printed on web presses • Ex – catalogs. Big Ideas… Printing from roll is fast Used for large-volume publishing Printing from roll requires unique equipment and techniques. Tension control is critical in process 15,000 sheets per hour through a sheetfed press Fastest webpress = 3,000 feet per minute If you don't have proper tension: Tear, break, recoil, trouble maintaining color control and registration 2 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Success: Web Printing Only? WHAT DONNELLEY DOES BESIDES PRINT: -binding/finishing, direct marketing (increase response rates), language translation, design, reouching, premedia? Business of Print - California Employees Printing Firms Shipments $000’s Total Employees 1-4 3,236 836.8 7,728 5-9 1,206 934.2 8,428 10-19 790 1,310.7 10,879 20-49 554 2,240 16,712 50-99 237 2,869.3 18,184 100-249 128 3,442.4 18,833 250+ 49 4,652.7 23,273 Totals 6,200 16,286.1 2/3 of printers are smaller firms 104,037 Source: 2008 PIA/GATF Print Market Atlas California Print – Where $$’s Go Print Process Employees Shipments $000’s Digital 12,244 $1,721.7 Sheet-fed Offset 42,543 $6,447.3 Web Offset 20,819 10% of printing is digital $3,842.5 Other Printing/Trade 28,431 $4,274.6 Totals 104,037 $16,286.1 Source: 2008 PIA/GATF Print Market Atlas 3 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Advantages of Web printing: Web printing Presses feed a substrate through press in roll form delivers in a variety of forms (unlike sheetfied- sheet in sheet out...) Paper, film, label stock, paperboard, etc. Deliver various forms All major printing processes available in web configurations. Litho- takes a flat plate and wraps it around a cylinder, Web advantages (compared to sheetfed) Speed In-line finishing “Continuous image” products (Gravure) Cheaper substrates Lower basis weight substrates Press-sheet utilization Perfecting (offset). tuck into cylinder gap- causes a break in the plate- white strip where you wouldn't see images- gravure does continuous imaging WHY WEB PAPER IS CHEAPER THAN SHEETFED? -less processing going in, don't need to cut into sheets, web can print a lower basis weight Webpress= standard sizes- great paper utilization Litho- perfecting = both sides of paper at once (sheetfed does 1 at the time) -Can only use something that can roll with web Web disadvantages Substrate selection Single pass through press (unless using rewind) Makeready/changeover time Makeready waste Fixed cutoffs – size limitations (offset). -Can't rerun sheets unlike SF (to add more color, etc) -Can't go from job-job quickly, lots of setup/changeover -Bc they run faster, you waste faster (speed changes color, constantly fine tuning) -Fixed cutoff (exclusive to litho) cutoff cylinders are the same size as print cylinders 4 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Web Printing Processes Lithography, Gravure, Flexography Identification – Lithography Fundamental principle: ink and water don't mix -Print the water first -Viscosity- measuring the resistance to flow (litho ink is viscous (thick), gravure ink isn't) -Printing off a flat, smooth surface -almost always print on smooth substrates -Litho is more complex (have to deal w/ water AND ink) Identification - Flexo Printing from rasied surface 5 GrC 329 - Web Offset and Gravure Printing Identification - Gravure 9/16/2011 Printing from a recessed surface- INTAGLIO -Ink is very fluid -Simple (only use ink, unlike litho) and "elegant" process Offset Lithography principles Flat metal plate mounted on cylinder Viscous ink system Two fluid system - Ink and dampening Uses rubber blanket to “offset” image to substrate Quality is good but ink/water balance can be challenge Web offset growth - flat. Offset Lithography principles, cont. Typical web printing unit blanket-to-blanket Perfects in one unit Used in commercial, newspaper, publication. 6 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Rotogravure principles Image is engraved in copper cylinder base Cylinder is chromed for strength Both solids and tones have engraved cells Cylinder “bathes” in fluid ink I Doctor blade “wipes” excess ink (non-image) Impression roller employs C “electrostatic assist” Growth - flat. Web handling principles Benefits of accurately controlling a roll through the printing sequence • • • • Registration Speed Wrinkles Safety 7 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Web handling Roll stand / splicer Web treatments Web tensioner Web break detector/severer Control web alignment Automatic register control Fold or other finishing. Image courtesy of Erhardt-Leimer Roll stands Hold & unwind substrate 2+ roll stands Expandable shaft Mechanical or pneumatic brake. Hydraulic lift Image courtesy of Martin Automatic 8 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Another Example of Web Feeding RRD Reel Stands Mounted Alongside & Behind Press Roll splicing Roll changes - manually or automatic? Automatic splicer Why? Print balance is interrupted during stops Best to splice w/o stopping Types of splicers: Flying Zero-speed. Flying splice High-speed applications or substrates incapable of zero speed apps 2nd roll brought up to press speed. 9 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Flying Splice (Not so) Flying Splice This One’s Better 10 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Zero-speed Paper “stored” in festoon Roll is momentarily stopped Festoon releases stored substrate Demo. Zero Speed Splicing Stand Web treatment Web cleaning Pre-conditioner De-curl Static neutralizer 11 GrC 329 - Web Offset and Gravure Printing Web tension Goal: consistent web tension front to back What factors impact tension? Where on the press is tension effected? Where is tension adjusted?. Mechanical drive principles Traditional drive shaft Drive shaft and gear system 9/16/2011 If you control the shaft, you control the roll- controlled by the brake and dancer. -pack the blankets- surface speed of roller is moving faster -No driveshaft that connects the entire press -Can infinitely adjust the speed for each individual unit -Don't need to worry about packing each blanket differently Shaftless - servo motors Individual motors at all drive points Better tension controlled. -the back of the press Infeed zone – major components Roll Stands Splicers Metering Rollers Dancer Roller Lateral Positioning Guides -Clues to know what kind of splicers: -festoons=zero speed -absence of festoons=flying -tape straight across the roll -Metering rollers=driven rollers (combo of steel and rubber coated rollers) 12 GrC 329 - Web Offset and Gravure Printing Web tension – infeed zone 9/16/2011 -dancer- loops around, some kind of connection to the brake -tension tranducer- no mechanical means to control Roll stand brake Controlled by “dancer” Infeed metering unit tension Pulls web from roll stands by driven metering rollers – controlled by dancer Tension transducer system Measures web tension – regulator outputs voltage to motor (no dancer). What kind of splicer? Tiny Dancer -flying -excelerator belts Typical tension for web materials Material Tension Foil .50 lb (per mil per inch of width) Polyethylene .12 lb Polypropylene .25 lb Vinyl .05 lb Sub 40 book 1.25 lb (per inch of width) Sub 100 book 4.00 lb (per inch of width). 13 GrC 329 - Web Offset and Gravure Printing 9/16/2011 -Roller same as the one on the apollo diddy Web break detector -pneumatic- blowing air on the web Designed to shut press down when web breaks Roller Photocell “Failsafe” Pneumatic May contain web severer. side-lay (web alignment)= web to folder- side to side Registration Print unit to print unit – across cylinder Print unit to print unit – around cylinder Web to folder – side to side Web to folder – cutoff lateral= print the print- across cylinder circumferential= print to print- around cylinder print-to-cut= web to folder- cutoff Registration Terminology: Lateral Circumferential Web alignment Side-lay (web alignment) Print-to-cut box tilt- Side-lay (web alignment) Move roll Box tilt Automated guide systems Side-lay sensor. 14 GrC 329 - Web Offset and Gravure Printing 9/16/2011 Register control Register controlled: Side-lay – unit 1(as dictated by folder) Lateral – unit 1 Circumferential – unit 1? Lateral – unit to unit control Circumferential – unit to unit Print to cut control compensator Automation: target – closedloop. Inline finishing 3 Ways to delivery Sheet Folder – signatures Rewind Remoistenable glue Perf/score Plows/prefolder Paster 15 ...
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