by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
FLEXO Magazine : June 2011
Technologies & Techniques blades are typically used with very abrasive inks or where you are running four-color process work every day with standard- ized setups. Other applications may include varnish or coat- ing applications and corrugated applications, where it could take hours to change a blade. All of the metal blades discussed can be used for doctoring applications as well as containment in dual blade flexograph- ic chambers. Metal blades can vary in thickness from 0.004 in. to 0.020 in. and even thicker in some cases. Typical blade thicknesses are either 0.006 in. or 0.008 in. with more demand- ing applications requiring the use of 0.010 in. or 0.012 in. thick blades. COMPOSITE BLADES Composite doctor blades are used on laser- engraved ceramic anilox rolls and provide longer life at high speeds when compared to carbon or stainless steel blades. Since they approach metal- lic blade performance with respect to fine screen metering, composite blades can be a good choice for most abrasive, high solids, and UV inks. How- ever, a composite blade will typically allow some surface ink to remain on the anilox roll, so use a metal blade if surface ink cannot be tolerated. Composite blades are reinforced with glass fibers which help them to avoid the plastic deformation issues that plague un-reinforced plastic blades dur- ing a pressrun. The composite material is also harder than plastic materials, so the working tip is less likely to be damaged by hard particles in the ink and they are not prone to embedment problems that can lead to anilox scoring. These blades do not get as sharp as metal blades when they wear, but they do still pose a cut hazard, so adequate safety training is required. Look for quality composite doctor blades made from cryogenic grade stock that is free of voids and inclusions which lower grade materials can contain. Common applications involve paper and board substrates and line work. Composite blades impregnated with graphite are typically used on larger ceramic anilox rolls. It is common to use them for higher end graphics in corrugated ap- plications. Composites can be used for doctor and containment blade applications and typical thick- nesses range from 0.014 in. to 0.035 in. PLASTIC BLADES Plastic doctor blades provide a lower coefficient of friction on ceramic anilox surfaces and long life. For doctoring applications, plastic blades have to be thicker than metal or composite blades to pro- vide the same rigidity. However, the thicker mate- rial will typically leave the most surface ink on the anilox roll of all blade material types and thereby provide less consistent print quality. Other issues with plastic blades that may hinder their use as a doctor blade include plastic deforma- tion, which can lead to dot gain; hard particle damage, and particle embedment or entrapment under a lifted tip (Figure 1). When used as doctor blades, plastics work best for line work with less than 400 count anilox screens that are printing abrasive or high solids, as well as water based inks on paper and board substrates. An area where plastic blades have been proven to be very useful for flexographic printing is on the containment side of a chambered inker. Thin, “floppy ” polyester, Mylar, and polyethylene blades have been successfully used as contain- ment blades. Plastic containment blades will prevent back doctoring and particle trapping between the blade and anilox www.flexography.org June 2011 FLeXO 67
Sustainable Spring 2011