Date: Thu Oct 22 1998 - 09:28:06 CDT
This Ask PNEAC question was from:
New Jersey Institute of Technology
When printing on plastic with water based inks in either flexographic or
gravure printing, are there special additives added to the plastic resin
before blown film formation to make it easier to print with water based inks?
This question applies to polyethylene films, linear low density polyethylene
films, and oriented nylon films.
Some thoughts on this one. Indeed additives are added to the resin before
extrusion. Unfortunately, the additives needed to extrude and process the
plastic film want to impart good slip which implies low surface energy. Waxes
are added to do this. Of course, for printing, you want a higher surface
energy. So, it is a trade-off or competing problem to balance the opposite
requirements. That's why plastic film is treated inline before printing; to
raise the surface energy (dyne level).
Michael Mongi, NJIT
The following response to the question from Michael Mongi is provided by Fred
Many films require slip additives in order to be processed on converting or
packaging equipment. the clip enables the film to move smoothly and quickly
over roller, formers, etc. The slip level can be varied to facilitate water
inks. The higher the slip, the worse the adhesion; the lower the slip, the
less satisfactory the performance of the film on the equipment.
1. Where possible, use medium slip films. These should suffice for most
packaging and converting operations. High slip is used too frequently where
high slip is really not needed.
2. Some additives have been developed that are alleged to be friendlier for
use with water inks. A few plastics additives suppliers have announced slip
additives that are more receptive to water inks. How prevalent they are in
the market in questionable. Most extruders buy their resins with a slip
package already in place. Check with Ampacet, Witco, and other suppliers to
see what they are offering.
3. Check out new resins that are being designed for packaging films. While
the main concern has been physical properties, the absence of the slip
additives has proven to be an advantage for water ink adhesion and
performance. Two such films that I have worked with are Union Carbide Unipol
Easy Flow (blended with regular HPLDPE to get clarity and gloss) and DOW's
Elite metallocene resin. Check American Inkmaker for two issues with articles
on press trials with water inks and plastic films (November 1997 and an
earlier issue) both written by Fred Shapiro.
4. Some plastic films, (i.e. Blaxual Propelene), is coated. There are films in
the market which have water compatabile coatings. Check with Mobil.
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