Re: Stay Open Inks and Rub Resistance
John,
Most stay-open inks tend to exhibit poor to fair rub resistant rub / scuff properties on smooth uncoated, matte, dull, and satin coated substrates. This is mainly due to the nature of the ink component, anti-oxidant, that gives the ink the stay-open property. Therefore, in most cases it is recommended that the piece be varnished or coated on these substrates.
A stay-open ink printed on an uncoated sheet will take an excessive amount of time to dry / oxidize due to the porous nature of the stock. The ink tends to pool in the microscopic crevices and valley's of the paper, at which point the anti-oxidant in the inks performs its job of slowing the skinning of the heavier ink film located in these crevices.
Stay-open inks tend to have more petroleum based solvent, VOC's, in order to speed up the inks set time to allow for faster work and turn on press. Depending on the ink formulation and the vehicle system used to formulate the inks, this can cause the dried ink film to have a softer dried ink film resulting in increased rub and scratch problems in the bindery and shipping.
Ink companies, in most cases, use waxes as a component of the formulation to improve rub properties of an oxidized ink film however, this addition of wax will only reduce the rub slightly as the oxidized ink film is not as hard as a non-stay open ink. Also, increasing the wax over a certain percentage, 2-5% depending on wax type, will not have an effect on rub although it could cause piling on press. Another thing to consider when cutting these jobs on a gullitine cutter is to insure that the blade is sharp as a dulled blade will cause what is known as carbonizing.
It is highly recommended that when running on any of these problematic stocks, when no varnish or coating is applied, that you contact your ink company and have them recommend a suitable ink and allow sufficient time , 24-48 hours, before sending the job to the finishing department.
There is currently new green ink technologies available on the market for high solids 1-2% VOC inks that set extremely fast (30-minutes to bindery), exhibit excellent rub resistant properties, without any varnish or coating on these substrates. Superior Printing Inks has "Biolocity & Evolocity" both of these inks meet the ISO-2846 requirements for G7 compliance.
If you would like more technical or product recommendations please feel free to contact me.
Regards,
Bob Peterson
323-767-2173
