TPE responses

TPE responses

James Cobb

5/26/2004

Here are the responses to why my TPE bubbles.

 

 Thanks to all.

 

James Cobb C.O.

 

 

 

 

 

There is a couple of different factors involved in eliminating the bubbles.
First of all you should pre heat the TPE in a different oven (if at all
possible) on a temperature of about 100 to 150 degrees for about 1 to 1 1/2
hours. Then go straight into your infrared oven at 350 degrees. The reason
for this is TPE gathers moisture very easily and you have to preheat it to
cook it out.

 

My experience is mostly with polyethylene, but perhaps it is applicable to
your problem.

 

Bubbling is caused by expansion of the material as it is heated. Where it
can slide along the tray, it doesn't bubble. Where it sticks, a bubble forms
as material that can slide pushes into a blocked area - blocked, that is,
by the sticking boundary.

 

So the first solution to bubbling is to make the tray slippery. A
teflon-coated tray would be nice, and we use one, but even so, you need to
liberally spray with silicone.

 

Next, if you do get bubbles, you need to remove the plastic from the oven
about three minutes before it is done, lift each end carefully to break the
adhesion around the bubble and let the plastic back down to the surface of
the tray, then put the tray back in the oven. (We take this opportunity to
reverse the tray, although that is more for even heating than to counter a
bubble problem.)

 

 

The reason your TPE is bubbling is because this material is hygroscopic - it
absorbs moisture from the air. You should try to store this material in a
cool, dry place, preferably bagged. However, if it has been subjected to
high humidity (which can happen @ the distributors location and/or in
shipment, it can be predried before use by heating it for about 3 hours in a
150 degree oven. However, one solution if plausible in your lab, is to
store it on top of your oven so that the heat from the oven keeps it dried
out and ready for immediate use.

If you have other questions, please free to call me.

 

 

According to the plastic extruder we use, TPE is hydroscopic ( it absorbs
moisture). If you can't store it in a cool dry place then you might have to
dry it before actualy thermoforming with it. We have to dry our TPE for at
least 3 hours at 150 degrees. Thermoforming is done at 370 degrees. Hope
this info helps.

 

TPE needs to be dessicated like lexan, either keep it sealed in a bag, or
just buy fresh every time you need it. if you have to dessicate it you can
do it by putting it in the oven at 250 and raising the temp 10 or 20 degrees
every fifteen minutes until you get to 350. at that point you should be able
to form it or hold it at 350 just about forever with no bubbles.

 

Need to dry out the TPE -- it absorbs moisture from the environment fairly
rapidly -- this causes bubbles when heating/vac forming. Can dry it out
easily by placing in warm oven for a while (call plastic supplier for
procedure -- I forget details)

 

TPE has a tendency to absorb moisture out of the air, and is therefore
affected by humidity. We noticed no problem at all when draping in the
winter time (dry Canadian winter), but had troubles at other times of the
year when the humidity was greater, and when the TPE had been sitting out
for a long time. We contacted our supplier and they sent some info from the
manufacturer. It recommended 'drying' the TPE by placing in the oven for a
number of hours at temperature well below molding temperature. What happens
is that the moisture trapped in the TPE expands and tries to escape when the
plastic is heated, causing the dreaded orange peel bubbling. I am sorry,
I am not at my office right now, but if you want to email me on Tuesday (May

25th) I would be glad to email or fax back the information that we had
received.

 

TPE absorbs moisture from the air and when you heat it, the moisture turns
to steam and the bubbles result. There are two solutions:

                   1) Purchase your plastic from LIGON Bros. in Michigan.
they are an extruder and wrap their TPE in plastic to prevent the absorption
of moisture.

                   2) You can cut your sheet to size and place it in the
oven for about 20 minutes per side at a temp of 200-220 degrees.