rshen:
The choice between PET and EVA is pretty much a toss up for low
temperature performance. I have summarized data on three films in a
chart below. (mostly charts do not show up very well in the answer box
but I have also uploaded the simple chart as a Excel file at:
http://www.lucidmatrix.com/uploads/092702petpetgeva.XLS
PET PETG EVA
Structure Crystalline Amorphous Amorphous
Specific Density 1.37 1.27 0.93
Water Absorption rate, % 0.15 0.13
0.07
Elongation, % 70 110 800
Tensile Strength (psi) 6600 4000
2000
Hardness R120 R110 R40
Utilization Temp F -4 to 212 -76 to 131 -40 to 140
Resistance to
Acid G G P
Alkalai G G G
Solvents G P P
Notes:
1.Since the Dupont patents on Polyester film ran out, you are likely
to find that the PET will be the cheapest film for you
application. The PETG is often used for thermoforming characteristics
if you are not using a wrapping film.
2.You will note that the low termperature performance of PETG and EVA
is quite similar. PET is particularly useful in high temperature
applications where it is actually approved for use as a class
B electrical insulation which requires continuous usage at 130 degrees
C. Of course, the key element here is having your vendor select the
grade which best fits your application since these films all come in
different grades.
3.EVA has excellent low temperature toughness as you would expect from
a film that stretches as much as EVA does. (800%)
4. Many convertors supply printed PET and EVA films.
Your question concentrated on cryogenic temperature suitability. As
you can see from the utlization temperature information, the PETG will
give you the lowest temperature performance.
Vendors:
PET: http://www.dupontteijinfilms.com
http://www.m-petfilm.com/mpf/eng/
PETG: http://www.sourceonepackagingllc.com/
http://www.packagingdigest.com/cgi-local/guide02_man_display?id=2047340
EVA: http://www.sunbeltplastics.com/site/content/index.asp
Be sure to note the higher specific gravity of the PET films. This
means they will yield more square inches per pound than the EVA film
approx 20% difference.
The following URL's may be useful in evaluating the materials for your
particular application:
http://www.mbhs.edu/classes/magnet/coursesandlife/RandE/matsci/2000-pd2/raff.html
http://www.dupontteijinfilms.com/datasheets/mylar/productinfo/properties/h37232-3.pdf
If there is any clarification of the information provided, please
don't hesitate to ask prior to rating the answer.
It was a pleasure researching this subject for you.
seedy
Search Strategy on Google: "EVA film" + properties
"PET film" + properties
"PETG film" + properties
"each film" +
manufacturers
I was already familiar with the various grades from my business
career. (now retired) |
Clarification of Answer by
seedy-ga
on
27 Sep 2002 14:58 PDT
rshen:
One more attempt at posting the chart in the answer box. It is perfect
on the upload site in the Excel file. This one will be the best I can
do on the posting to the answer box.
PET PETG EVA
Structure Crystalline Amorphous Amorphous
Specific Density 1.37 1.27 0.93
Water Absorption rate, % 0.15 0.13
0.07
Elongation, % 70 110 800
Tensile Strength (psi) 6600 4000
2000
Hardness R120 R110 R40
Utilization Temp F -4 to 212 -76 to 131 -40 to
140
Resistance to
Acid G G P
Alkalai G G G
Solvents G P P
seedy
|
Request for Answer Clarification by
rshen-ga
on
27 Sep 2002 15:19 PDT
I'm in awe and amazed by the researcher's speedy results. After
reading the researcher's table, minor clarifications are needed,
perhaps if I rephrase my question: instead of just saying
"Specifically, please show at what temperatures do the two substances
become breakable or brittle...I think for PET, at minus 70 degrees
Fahrenheit, it becomes brittle or breakable. I am looking for the
corresponding temperature for EVA."; I should have added the
following:
If one puts both PET and EVA materials inside a cooling chamber and
steadily reduces the temperature.
1) Around minus 76 degrees F, does PET become brittle and potentially
breakable by grinding?
2) How about EVA? Is that temperature around minus 40 degrees F?
3) And finally, what is the scientific term and industry jargon for
that temperature?
|
Clarification of Answer by
seedy-ga
on
27 Sep 2002 20:40 PDT
rchen:
Please excuse my lack of understanding of your needs. I had assumed
you were interested in the relative usefulness of PET and EVA for a
low temperature packaging application but now I see that you are more
interested in an absolute temperature where the plastics shatter and
can be ground. Thank you for clarifying this and I'll seek the
information to answer this clarification.
Let us look at your clarification questions:
1) Around minus 76 degrees F, does PET become brittle and potentially
breakable by grinding?
No. the -76 degree F temperature is where PET is still usable
2) How about EVA? Is that temperature around minus 40 degrees F?
No. Same reason as #1
3) And finally, what is the scientific term and industry jargon for
that temperature?
There are two definitions:
Brittle point or brittle temperature is:
Definition: Lowest temperature at which a material withstands an
impact test under standardized conditions.
Brittle temperaure is NOT the one where it shatters...
http://composite.about.com/library/glossary/b/bldef-b800.htm?terms=brittle+point
Cryogenic grinding temperaure is the effective temperature where the
material can be ground into various size particles with minimal
agglomeration of the resulting powder.
Definition: Thermoplastics are difficult to grind to small particle
sizes at ambient temperatures because they soften, adhere in lumpy
masses and clog screens. When chilled by dry ice, liquid carbon
dioxide or liquid nitrogen, the thermoplastics can be finely ground to
powders suitable for electrostatic spraying and other powder processes
http://composite.about.com/library/glossary/c/bldef-c1386.htm?terms=cryogenic+grinding+temperature
I now believe you want a cryogenic grinding temperature rather than
the brittle point. I will have to call the vendors on Monday morning,
which I will be glad to do, to see if this information is available
for some standard grades of PET and EVA. Additional information in
this area is available at:
http://www.fraunhofer.de/english/press/md/md2001/md02-2001e.pdf
|
Request for Answer Clarification by
rshen-ga
on
27 Sep 2002 23:45 PDT
Yes! Cryogenic grinding temperature is exactly what I was looking for.
Thank you for showing me what I was looking for. I hope to hear from
you on Monday.
|
Clarification of Answer by
seedy-ga
on
30 Sep 2002 09:26 PDT
rhen:
Speaking with Dupont Technical Service this morning, I found that PET
films are virtually industructible down to -250 degrees C. That is to
say, the biaxially oriented films (such as Mylar, Melinex etc) do lot
lose physically properties significantly as temperature is reduced.
These films can be ground easily at room temperature. The APET films
are slightly more "sticky" but also do not have a shatter point until
the film reaches very close to absolute zero. Shear strength, measured
at room temperature for Biax film is 15.0 kg/sqm while APET is
13.0kg/sqm. These films do not reach a brittle point (such as a metal
might reach).
I haven't been able to find anyone who was as knowledgeable about EVA
films. The general theory is that the EVA films will be stickier than
PET but the properties will not be affected by cryogenic temperatures
until you get very close to absolute zero.
Both the people I spoke with indicated that liquid nitrogen (-196
degrees C), or liquid oxygen (-183 degrees C) temperatures will not
affect the film properties significantly.
So...It appears that the properties of these films, crystalline in
form or amphorphous in form, will not be affected by cryogenic
temperatures.
seedy
|
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