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Subject: Re: problems with outgassing

Date: 07/16/03 at 4:37 PM
Posted by: Jim Williams
E-mail: jim.williams@polyonics.com
Message Posted:

In Reply to: problems with outgassing posted by juan martinez on 07/15/03 at 7:47 PM:

Outgassing of labels can be caused by several things. The surface you are applying the label to, the application temperature, the subsequent temperatures the label will be used in, and so on.

My first inclination is to see if there is trapped residual solvent in the adhesive used. Trapped solvent wants to escape, especially if the label is warmed up above the application temperature when the label was applied to the product surface. It is an awesome multiplier..out-gassing. For example for every 18 grams of water, it could totally outgas to 22.4 liters (about 5+gallons) of gas (water vapor). So the little bubbles you see MAY be caused by tenths of grams of trapped solvent…expanding hundreds of times in volume, causing the bubbles.

Exposure to sunlight may also cause outgassing, due to localized heating. Over time, exposure to the UV light from the sun can cause degradation which may also cause a lower level of outgassing. Surface contamination of the part may also contribute. And, if the label is applied while the part is cold, and then warmed up, trapped air may also expand dramatically, causing bubbles. This is true if the part is porous, trapping cold air inside. When the part is heated, the air expands.

I'll ask a couple of chemist friends to get their ideas as well.


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