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FLEXO Magazine : June 2011
Technologies & Techniques require custom modification to incorporate specialized tips or coatings. Custom modification can raise the price of the doctor blade, but if a more costly blade eliminates problems that create unexpected downtime, the savings generated by uninterrupted runs will offset the price. Problems that may require a custom blade include the fol- lowing: • UV spitting. • Anilox score lines. • Abrasive inks and reduced blade life. • Corrosive inks. • Chatter marks. Recently, I was at a press trial where two major plate manu- facturers were going head to head in acquiring six figures’ worth of business from a converter. They used the same anilox rolls, ink and doctor blades. After running the press, one plate manufacturer’s print was much dirtier than the other’s . Changing the doctor blade specification to decrease the “ wear-in” factor improved that plate manufacturer ’s print so much that it became impossible to tell it apart from that of the competitor. BACK DOCTORING Does your press look like the one in Figure 2, page 55? This problem is commonly referred to as the back-doctoring phenomenon. It most often occurs on the back side of cen- tral impression presses. The good news is that a simple blade specification can eliminate or substantially minimize this problem. As you analyze the press, remember that the doctor blade cham- bers on the back side of the press are flip-flopped. The ink is metered from the top on decks 1 through 4, but from the bot- tom on decks 5 through 8. On a central impression 8-color or 10-color press, the front side decks (1 through 4 or 1 through 5) are not subject to back doctoring. Typically, the ink is pumped in on the top of the chamber and fills the chamber up to the top, where the containment blade is. The bottom blade (metering) transfers the ink to the plate, then to the substrate. The anilox roll turns clockwise, with the metering blade on the bottom. Once the ink passes to the plate, there is very little excess ink on top of the roll. Because the containment blade is on the top, there is no back doctoring or “icicle” problem. On the backside of the press (decks 5 through 8), the plate cylinder turns counter-clockwise while the anilox roll turns clockwise. Because the metering blade is on the top, some excess ink will rotate around to the containment blade once the ink is metered and transferred to the plate. If the contain- ment blade is too thick, it can cause the ink to back doctor and create ink “icicles,” as shown in Figure 3. These icicles dry up and hang down from the chamber, causing quite a www.luescher.com XPose! Flex and Multi DX The exposing solutions for best efficiency and flexibility Your advantages ● Manufacturing of a wide range of products for: offset-, letterpress-, flexo- and screen printing ● Direct UV imaging ● High flexibility of customized demands ● Highest quality and precision ● Simple and ergonomical handling XPose! Flex and Multi DX can give you the better competitive edge For more information visit: SAVEYOURTIMEANDMONEYWINONFLEXIBILITY Lüscher AG Maschinenbau | Bodenackerstrasse 7 | 5014 Gretzenbach | Switzerland | Phone +41 62 767 76 77 | Fax +41 62 767 76 76 | firstname.lastname@example.org | www.luescher.com www.flexography.org June 2011 FLeXO 57
Sustainable Spring 2011