Digital vs. Offset Printing

Christian and Christine talk about digital and offset printing, and discuss some advantages and disadvantages of each. Also, Bob Stokes of Abbott Printing share information about the current printing industry and its future.

Category:

Howto & Style

Tags:

• Digital
• Offset
• Printing
• Abbott
• Treefrog Cinegraphix
• Christian Knightly
• Christine Cerniglia
• Printing Industry

[AlphagraphicsCom]

Good explanation - i like it.

[Matrix29bear]

An "O" shaped solvent droplet would penetrate the page surface slightly while wetting it, with a pigment droplet aimed dead-center, to the solvent "O", then as the solvent evaporates, it creates a micro-wicking suction effect around the pigment droplet (and limits droplet wicking spread in the process - think spilled coffee-cup stain ring). Of course, timing has to be precise or the benefit of this effect is lost if the solvent evaporates prior to pigment droplet impact.

[Matrix29bear]

Ideally you want to think of the ink spray channel much as you would the rifling on a standard gun or an paintball gun. If you can induce a slight spiral motion before the ink droplet leaves the channel, then droplet structure will remain intact longer prior to page impact. Ideally with print-interleaving techniques, you'd want a "O" droplet of solvent to hit the page a microsecond prior to the pigment droplet, so that as the solvent evaporates, it causes the pigment droplet to be sucked in.

[Matrix29bear]

Triangle inkjet nozzle drops can be made the same way as the "X" square dots with a slightly different similar design. Another consideration on inkjet micro-channels aside from pressure is the issue or adhesion surface-tension pressures in play on the sidewalls of the channels. Faster spraying of the dots means the dots will adhere to the channel walls and spray wider from rolling-motion surface tension. To prevent this, a small mask ring in the channel can break up the force of the rolling.

[Matrix29bear]

Otherwise variations on dot types for ink sprayer output can be created using modulation of the channel shapes (think cookie dough press design). The ink is pressurized prior to entering the sprayer channel, it will expand to regain pressure equalization as it exits. Square dots are possible by making the exit of the channel a rounded "X" shape with a straight up-down feed to the ends of the "X", and a 60 degree slope to the inner points of the "X". As pressure equalizes, it makes a square dot.

[Matrix29bear]

The better channel for the ink-wash I suppose would be a "Y" or inverted-"h" channel with a "L |" shape in place of my prior-suggests "+" shape for the air-blow ink-cleaning channel. The "L" being the ink-wash spray part of the channel with the "|" being the suction part of the channel. Although a "V" shape for the wash channels would allow dot placement modulation by varying the air blow/suction cycle pressures on either side of the air blow channels.

[Matrix29bear]

The ink-wash channel would not be in usage unless the jet sprayer nozzles are in cleaning mode. Otherwise the logical thing is to switch the dirty ink-wash suction channel and the ink-wash pressure spray channel to just air-spray mode. That way as the ink dots are sprayed onto the page, the ink is not encouraged to creep back into either cleaning channel and clog them up. Bonus is that the air spray can be ionized for superior electrostatic ink adhesion to the application surface.

[Matrix29bear]

With a "Y" or inverted-"h" sprayer the channel pressure is still problematic, but not so much that dot deformation occurs. Also the extended height of the channel allows an ink-washing spray to be channeled horizontally through the side of the bottom of the channel. This would allow longer printhead usage without ink-clogging issues. In this, think of a large "+" sign placed at the bottom of the "Y" leg with one side of the "+" feeding in ink-wash and the other side suctioning dirty wash.

[Matrix29bear]

One other thing to note, I figure that ROLAND has perfected their ink-sprayer heads, but the basic inject printheads could also use a redesign for superior print longevity. Most printheads use a "V" shaped feed-to-spray design, but that is inferior because as ink reaches the bottom of the "V" it is compressed and then sprays outward to equalize pressure creating large dot sizes and inducing later printhead clogging. A better design would be a "Y" shaped or an upside-down "h" sprayer.

[Matrix29bear]

With this technique you can have pressure-infused offset printing qualities for your paper output with the ROLAND vinyl-solvent printing process with the inexpensive properties of plateless printing with the ability to simultaneously duplex pages with two presser rollers. This also allows rapid cleanup with a simple automated routine between jobs with almost zero ink wastage. The direct-to-page MEMJET type sprayer array would allow short print runs with no slowdown for a cut sheet feed press.