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Are poly tags flame treated both sides?

I have always printed on poly with epoxy resin inks, and require my supplier to treat both sides of poly sheet. I am having a problem with one side of some sheets. How do I test for flame treat on both sides?

Rocco Esposito
screen printing, owner of shop - No. Branford, Connecticut, USA
2004

Many plastics and resin based coatings have a low surface energy, which means that liquids and inks will not wet out on that surface as their surface tension is higher than the surface energy of the substrate. Typically, flame treatment or corona discharge is used to treat the surface of the plastic so that inks will wet out. this is necessary for both layng down the ink and getting adhesion.

As the units of measuring surface tension and energy are very small, this is typically measured in units called Dynes. Polyethylene typically has a surface energy of around 32 Dynes Polypropylene is higher at around 34. To get adhesion, you will probably need a surface energy of 40 Dynes or more. Flame treatment involves passing the substrate momentarily through the blue part of a gas flame. If your sheet has been properly treated, you should be able to detect this by using a dyne pen.

A dyne pen is like a highlighter pen but is filled with a calibrated oil which has specific surface tension. If the surface energy is higher than the surface tension of the oil, the oil will stay wetted out on the surface, if not it will bead up. Dyne pens should be available from a printing supply house - particularly those supplying people such as web printers or UV cure inks. If you are only interested in a threshold you can get a 40 dyne pen as a go/no-go indicator. If you need to look at specifics you can get a set of pens from 32 - 44 Dynes. You will need to stripe them all and see which stripes bead up - the surface energy of the substrate will just below the lowest dyne rating stripe that does not bead up.

Merryck Leigh
Vacuum metallizing - Santa Ana, California, USA
2004

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There are several ways to determine the surface energy of a material. The most common methods are measuring contact angle and Dyne Testing. Dyne liquids are offered in a variety of forms and are formulated in several ways. If you want to comply with ASTM Standards, using Dyne solutions composed of Ethyl Cellosolve and Formimide would be the choice. These Solutions are available in pen form and liquid form. The liquids are usually available in a range of dyne levels from 30-70 Dynes in increments of 1, whereas the pens are usually available in levels from 32-60 Dynes, in increments of 2.

If you are only looking to determine the treated side of a polyethlyene, I would recommend a 38-40 Dyne Polytest Pen, which is very easy to read. However, if you are trying to determine the specific treat level for QC purposes, then I would recommend the dyne solutions, since they are more accurate. The dyne pens are a good production tool, if you are checking a specific dyne spec your supplier is required to achieve.

Jeff Opad
Jemmco, LLC - Mequon, WI
2004