The team of technical sales representatives at The Provident Group, collectively possessing better than 90 years in pressroom experience, does not hesitate in identifying a package printer’s five most pressing challenges related to doctor blades.
To Albert H. Jasper (Northeast US/Canada), Keith Wisnefske (Midwest/Northwest) and Sam Benson (Southeast/Southwest) it’s obvious. Evidence they offer supports their observations. Points emphasized go in a positive direction and speak to the fact that something can be done about every issue.
Of the answers offered and instructions issued, some require customized materials; others need minor manual adjustments; and still others speak to the simple mantra that preventive maintenance is a top priority.
Clearly, control is the order of the day. Dot and density gains be gone! Good, better and best solutions take hold!
White, opaque and metallic inks and coatings are quite the culprit, according to Jasper, Wisnefske and Benson. “These types of abrasive inks contain titanium dioxide and other harsh ingredients. As such, they have a massive appetite for carbon steel. They wear down basic blades in a few hours and create excess downtime and increased waste of substrate and ink.”
“What can we do to combat this issue?” the trio asks. Increasing blade thickness by 0.002-in. over your normal thickness helps, but the real answer here is turning to premium coated and treated doctor blades that are manufactured specifically to stand up to these abrasive inks and coatings.
They assure printers such moves will hold to promise. “Selecting blades manufactured to stand up to abrasive inks and coatings can extend their useful life by 3x to 10x normal!”
An example: Provident’s Super Coated and Nano treated blades are excellent options to provide total cost solutions in this kind of scenario.
“Excess pressure is one of the biggest issues in the pressroom,” the technical sales reps note. “This leads to reduced blade, seal and anilox roll life.” Their recommendation: “When setting blade pressure, the operator should adhere to the kiss impression method of setting printing plates. In other words, the less pressure the better.”
They continue, “This will not only lead to increase blade and end seal life, but also increase the life of your anilox roll—the heart of the printing press!” Advice rendered follows. “Rather than a manual setting or controlled by a pressure gauge, you want to set the pressure where you get a clean wipe—back off slightly till excess ink appears; then come in slowly, till you are wiping clean again. Less is more! (see Illustration 1)
Filters & Magnets
Jasper, Wisnefske and Benson indicated, “As the doctor blade wears down, shavings enter the ink stream. The use of filters and magnets is imperative to keep metal shavings out of your ink flow, thus preventing anilox scoring and damage.”
Stressing a point, they declared, “Preventative maintenance of the filters and magnets is a top priority. They need to be cleaned on a regular basis. Good housekeeping is key to things running smoothly. These inexpensive tools pay for themselves many times over. A large number of pressrooms leave money on the table because they have not committed to modest investment.”
Proper wipe and minimum contact pressure are primary concerns when navigating tip selection, the Provident Group maintained.
“When it comes to tip/profile selection for doctor blades the common choices are radius/rounded, beveled, stepped Lamella and elongated or wing Lamella,” the technical sales reps explained. “Radius is still very popular and the most forgiving, but it takes some time for radius tips to wear in and hone an edge; whereas blades, like wing Lamella, seat immediately and require less contact pressure to wipe the anilox.”
They reported that, “For today’s demanding process and expanded gamut printing with high-lpi anilox rolls, the patented wing Lamella blade is the perfect choice. This profile allows for a minimum contact with light pressure to meter the anilox clean. It helps keep a consistent dot longer and controls color better than a radius tip. You will not see the dot and density gain you would get normally.”
“Controlling viscosity and avoiding excess chamber pressure help curb back doctoring,” according to Jasper, Wisnefske and Benson. “Back doctoring occurs on central impression (CI) presses (typically)—on backside decks that rotate against the containment blade. Residue builds up, leaving excess ink on the anilox roller—leading to leaks and unsightly ink icicles.”
Pointing to the proper solution, they said, “The primary way to solve this problem is to go with a lighter, more flexible containment blade, 0.006-in. metal or 0.014-in. mylar. With the auto-wash systems on today’s modern presses, the thinner metal proves to be the best option, as mylar does not hold up as well to the wash cycle.”